L Maxit

C Yang

L Cheng

J.-L Guyader

Modeling of micro-perforated panels in a complex vibro-acoustic environment using Patch Transfer Function approach

Keywords: numbers: 43, 50, Gf; 43, 55, Ev

The micro-perforated panel (MPP) with a backing cavity is a well known efficient device for noise absorption. This device has been thoroughly studied in the experimental conditions of an acoustic tube (Kundt tube), in which the MPP is excited by a normal incident plane wave in one dimension. In an industrial situation, the efficiency of MPP may be influenced by the vibro-acoustic behaviour of the surrounding systems as well as excitation. To deal with this problem, a vibroacoustic formulation based on the Patch Transfer Functions (PTF) approach is proposed to model the behaviour of micro-perforated structure in a complex vibro-acoustic environment. PTF is a substructuring approach which allows assembling different vibroacoustic subsystems through coupled surfaces. Upon casting micro-perforations and the flexibility of the MPP under transfer function framework, the proposed PTF formulation provides explicit representation of the coupling between subsystems and facilitates explanation of physical phenomenon. As an illustration example, application to a MPP with a backing cavity located in an infinite baffle is demonstrated. The proposed PTF formulation is finally validated through comparison with experimental measurements available in the literature.

Introduction

Since the pioneer work by Maa [START_REF] Maa | Theory and design of microperforated-panel sound-absorbing construction[END_REF], micro-perforated panels (MPP) have been extensively used to design various sound absorption devices. The basic configuration is the one in which an air gap/cavity is placed at the back of the MPP, which creates a Helmholtz sound absorption effect, resulting in effective sound absorption. This basic configuration has been thoroughly studied both theoretically and experimentally using an acoustic tube (Kundt tube) in order to quantify its absorption coefficient. In such situation, the system has one single dimension and the MPP is excited by a normal incident plane wave. The prevailing motivation behind these efforts is the assumption that, the acoustic property of the MPP is assumed to locally reactive. Upon obtaining the surface acoustic impedance or the sound absorption coefficient of the MPP, it will be treated as conventional sound absorption materials.

Meanwhile, in the pursuit of a more efficient sound absorption, effort has also been made to use MPP in forming more complex system which deviates more or less from the basic configuration mentioned above. Such devices, taking various forms, can loosely be refereed as Micro-Perforated Structure (MPS). Double layer [START_REF] Zhang | The theoretical and application study on a double layer microperforated sound absorption structure[END_REF] or multiple layer absorbers [START_REF] Lee | Estimation of the absorption performance of multiple layer perforated panel systems by transfer matrix method[END_REF] using MPPs are typical examples. The insertion of additional micro-perforated panel increases the acoustic resistance of the absorber and extends the effective absorption band toward lower frequency. The performance of the device, however, is limited by the coupling between the MPP and the backing cavity. By transforming the conventional rectangular cavity to an irregular shaped cavity [START_REF] Wang | Sound absorption of a micro-perforated panel backed by an irregular-shaped cavity[END_REF], the coupling can be modified and manipulated due to the distortion of the acoustic mode by tilting cavity walls. The change of the cavity geometry promotes more acoustic modes into the coupling and thereby improves the sound absorption performance at selected frequency bands.

The trend of using MPP in more complex system or in the real industrial setting brings about one critical issue to be addressed. In fact, most of the existing works focused on investigating the property of the MPP device itself, usually validated in a Kundt tube. When placed in a practical environment, however, experimental methods usually become the only option [START_REF] Kang | Feasibility of applying microperforated absorbers in acoustic window system[END_REF] & [START_REF] Droltleff | Attractive room acoustics design for multi-purpose halls[END_REF]. More importantly, the efficiency of the MPP is shown to be influenced by the vibro-acoustic behaviour of the surrounding systems as well as excitations, which may be significantly different from the Kundt tube setting. Therefore, the increasing complexity of the system calls for efficient tools to predict the performance of the MPP in a complex vibroacoustic environment. Versatility, efficiency and flexibilities are among the top of the list of major attributes required for such simulation tools, which unfortunately are still lacking in the literature.

This paper attempts to propose a method based on the Patch Transfer Function (PTF) approach for modeling the MPP behaviour in a practical acoustic environment. To illustrate the idea, a general complex vibro-acoustic environment of the MPP is schematically represented in Fig. 1(a). Subject to acoustic or mechanical excitations, the whole system is composed of acoustic cavities, semi-infinite acoustic domain, absorbing materials, and flexible panels which are coupled through surfaces. PTF [START_REF] Ouisse | Patch Transfer Functions : a Tool to Couple Linear Acoustic Problems[END_REF] is a substructuring approach which allows assembling different vibro-acoustic subsystems through coupled surfaces. In the present case, the global system is divided into different sub-systems as shown on figure 1 (b).

Each coupling surface connecting a pair of subsystem is further divided into elementary areas called patches. The transfer functions, called Patch Transfer Functions (PTFs), of each uncoupled subsystem patch are calculated to form a database. For a mechanical structure, the PTFs are defined as the ratio of the mean velocity over the mean force on a patch, equivalent to patch structural mobilities. For an acoustic domain, the PTFs are defined as the ratio of the mean pressure over the mean velocity on a patch, which are the patch acoustic impedances.

Using the superposition principle for linear systems and the continuity relation among different subsystems, the PTF approach allows calculating the response of a global system from the PTFs of uncoupled subsystems by inverting a square symmetric matrix whose dimension corresponds to the number of patches.

The PTFs can be calculated using different methods depending on the subsystem considered. For cavities or flexible structures, these PTFs can be obtained from modal expansions for academic cases or from Finite Element simulation for complex cases. For semi-infinite acoustic domains, Rayleigh integral may be used for a plane boundary or Boundary Element Method (BEM) for a more complex geometry. The sound absorption material may be directly taken into account by its surface impedance. These calculations have been developed and validated for different applications [START_REF] Ouisse | Patch Transfer Functions : a Tool to Couple Linear Acoustic Problems[END_REF][START_REF] Maxit | Airborne noise prediction using patch acoustic impedance[END_REF][START_REF] Chazot | Prediction of transmission loss of double panels with a patch-mobility method[END_REF]. It should be noted that, calculations of PTFs are performed beforehand for each subsystem separately. As a result, parallel computation is possible. Moreover, when FEM is used, the size of the numerical models of each subsystem is considerably smaller than that of the global model. In a typical design problem, re-calculations of PTFs are required only for those subsystems or components with modifications, endowing the method the flexibility and efficiency in dealing with complex system, conducive to conducting system optimization. This allows a deep analysis on the coupling between the MPP and the backing cavity and a quantification of their effects on the sound absorption. It is shown that a MPP with the backing cavity does not behave like a locally reactive material, especially at resonances of the backing cavity. Finally, the proposed model is validated through comparisons with experimental results given in the literature [START_REF] Fenech | The use of microperforated plates to attenuate cavity resonances[END_REF].

In

Principle of PTF approach

Let us consider the basic vibro-acoustic problem presented in Fig. 2 corresponding to a thin elastic structure coupled on both side with an acoustic domain. The acoustic domain may either be closed or semi-infinite. The PTF approach is briefly recalled here based on this basic system for the sake of clarity, bearing in mind that the methodology can be extended to more complex linear systems.

Assuming harmonic excitations at an angular frequency ω, we are interested in the steady response of the system, such omitting the time dependence in the notation. Along the surface Sc occupied by the thin structure, the whole system is partitioned into three subsystems: an elastic structure and the two acoustic domains at each side. The coupling surface Sc is then

divided into N elementary surfaces   N i S i , 1 ,  
, called patches. The size of the patches should be less than the half wavelength (i.e. /2) corresponding to the highest frequency of interest, either acoustic or structural, whichever is less [START_REF] Ouisse | Patch Transfer Functions : a Tool to Couple Linear Acoustic Problems[END_REF][START_REF] Chazot | Prediction of transmission loss of double panels with a patch-mobility method[END_REF].

The Patch Transfer Functions (PTFs) are defined for each subsystem, with all quantities being defined with respect to the unit normal vector n  to the coupling surface Sc . For the structure, a constant normal force s i f is prescribed on patch i, whereas no force is prescribed on the other patches. The PTFs between the two patches, s ij Y , is defined as the ratio between the mean normal velocity on patch j and the normal force

s i f : s i s j s ij f u Y  , (1)
where

s j
u is the space-averaged normal velocity on the patch , i.e.

dS u S u j S s j j s j     1 , (2)
The afore-defined PTFs are equivalent to structural motilities of the structure.

For each acoustic domain  ( = [START_REF] Maa | Theory and design of microperforated-panel sound-absorbing construction[END_REF][START_REF] Zhang | The theoretical and application study on a double layer microperforated sound absorption structure[END_REF]), a constant normal velocity

 i u is imposed on patch i
with a null normal velocity on the other patches. The PTFs between excited patch i and receiving patch j,  ij Z , is defined as:

   i j ij u f Z  , (3)
where  j f is the resulted force from the acoustic pressure p  on the patch j when patch i vibrates with

 i u : dS p f j S j      , (4)
The PTFs such defined correspond to the conventional acoustic impedance.

For the above definitions, the bar in the notation indicates the mean velocities or the sum of the pressure on the patches (i.e. Eqs. [START_REF] Zhang | The theoretical and application study on a double layer microperforated sound absorption structure[END_REF][START_REF] Wang | Sound absorption of a micro-perforated panel backed by an irregular-shaped cavity[END_REF]). To alleviate the notations, these bars are suppressed in the following.

The coupling between the structure and the acoustic domains is performed in two steps:

-The first step consists in using the linearity properties of the system to express the relationship between the patch velocities and the patch forces for each subsystem. Indeed, the patch velocity of the structure can be expressed as a sum of the velocity due to the mechanical force acting on the structure before coupling s i u ~and the velocities resulted from the forces exerted on each patch:

  N i f Y u u N j s j s ij s i s i ,..., 1 , ~1       (5)
Similarly, the force on a patch is equal to the sum of the force corresponding to the acoustic source with a rigid surface,

 i f ~,
and the forces generated by the patch vibrations:

    N j j ij i i u Z f f 1 1 1 1 1 ~  N i ,..., 1 ,       N j j ij i i u Z f f 1 2 2 2 2 ~  N i ,..., 1 ,   (6)
-the second step consists in writing the continuity conditions at each connecting patch, namely the force equilibrium and the equality of normal velocities:

  N i u u u s i i i ,..., 1 , 2 1     12 s i i i f f f    N i ,..., 1 ,   (7)
where it was assumed that the normal vector is from the acoustic domain 1 toward 2.

Introducing (5), ( 6) into [START_REF] Ouisse | Patch Transfer Functions : a Tool to Couple Linear Acoustic Problems[END_REF] yields

      N i u Z Z Y f f Y u u N j N k k jk jk s ij N j j j s ij s i i ,..., 1 , ~1 1 1 2 1 1 2 1 1                    (8)
This system of linear equations with 1 i u as unknowns may be written in the matrix form:

    1 1 2 1 2 1 u u Y f f Y Z Z u s s s      (9)
Equation ( 9) is a full system, with its size being equal to the number of patches. Upon resolving this system,

    1 1 1 2 1 2 u I Y Z Z u Y f f s s s           ( 10
)
where I is the NN  identity matrix .

All other physical quantities, such as acoustic pressure in each domain can be calculated in a post-processing phase.

The PTF approach allows calculating the response of a global system from the PTFs of uncoupled subsystems by inverting a square symmetrical matrix whose dimension corresponds to the number of patches. The PTFs can be calculated by different methods depending on the subsystem considered. These calculations are performed beforehand for each subsystem separately. When FEM is used, the size of the numerical models of each subsystem is considerably smaller than that of the global model. Moreover, the use of incompatible meshes at the subsystem interface is possible, since the problem of compatibility is solved by patch averaging.

PTF equations for the micro-perforated structure subsystem

Assuming the structure separating the two acoustic domains in Fig. 2 takes the form of a micro-perforated structure, corresponding PTF equations will be developed in the following sections.

Modeling of micro-perforated structure

Considering a MPP element shown in Fig. 3, the sound pressure difference between the two sides of MPP, given by [START_REF] Maa | Potential of microperforated panel absorber[END_REF][START_REF] Takahaski | Flexural vibration of perforated plates and porous elastic materials under acoustic loading[END_REF]:

                                        t d K c t i t d K K d c t Z 85 . 0 32 1 1 . 32 2 32 1 32 5 . 0 2 0 5 . 0 2 2 0 0 0    (11)
where  is the angular frequency; t the thickness of the structure; d the orifice diameter;  the coefficient of viscosity and,  

4 0 d K 
. The real part is the resistive term which corresponds to the viscous force whereas the imaginary part is the reactance term corresponding to the inertial force.

Assume that the MPP is flexible and let s u be its normal velocity. The viscous force depends on the relative velocity of the air in the hole and the structure, s u u  0 and the inertial force depends only on the air velocity. Thus, one can write [START_REF] Takahaski | Flexural vibration of perforated plates and porous elastic materials under acoustic loading[END_REF][START_REF] Lee | Sound absorption of a finite flexible micro-perforated panel backed by an air cavity[END_REF]:

       2 1 0 0 0 0 0 0 1 Im Re p p c u Z i u u Z s      (12)
As the orifice diameter of the hole is much smaller than the acoustic and flexural wavelengths of interests, the mean velocity of the surrounding air particle in the vicinity of the MPP, 1 u , can be approximated from the relation:

  0 1 1 u u u s      (13)
1 u allows expressing the velocity continuity conditions of the MPP with the adjacent acoustic domains. On the contrary, 0 u will not be directly used and can be substituted from Eq. ( 12):

    s u Z Z p p Z c u 0 0 2 1 0 0 0 0 Re 1     . ( 14
)
Using the above expression in Eq. ( 13) gives

      2 1 0 0 0 0 0 1 Re 1 p p Z c u Z Z u s                . ( 15
)
This relation can be rewritten in a compact form as

  2 1 1 p p u u s      , (16) where:
-

    0 0 Re 1 Z Z      
is a non-dimensional parameter which may be called the MPP transmissibility, which represents the contribution of the structure vibrations to the surrounding acoustic particle vibrations.

-

0 0 0 Z c     is a parameter having [m.s -1 .Pa -1
] as dimension and may be called the equivalent mobility of the perforation.

Equation ( 16) clearly demonstrates the underlying relationship among the acoustic velocity of the surrounding medium, the pressure difference across the MPP and the vibration of the structure. The resultant velocity in the vicinity of the MPP is a combination of partial transmission of the structural vibration and the air motion of the micro-perforation. The development of the PTF equation for a MPP subsystem in the next section is based on this relation.

PTF developments

Direct formulation

For a MPP patch, whilst Eqs (5-6) relating the patch pressures and the patch velocities remain valid, the continuity conditions at connecting patches need to be modified. Indeed, by a space averaging on the patch i of Eq. ( 16), one has:

  2 1 2 1 i i s i i i p p u u u         N i ,..., 1 ,   . ( 17
)
Meanwhile, the pressure difference

2 1 i i p p  acting on the   i S   1
surface of the MPP generates a force,

s i f , at the patch i:    i i i s i S p p f      1 2 1   N i ,..., 1 ,   (18)
As

i i i S p f    
, these two relations can be rewritten as:

    N i S f f u u u i i i i i s i i i ,..., 1 , with , 2 1 2 1             . (19)        1 2 1 i i s i f f f   N i ,..., 1 ,   , (20)
The above expressions describe the continuity conditions in the presence of a microperforated structure.

Introducing the linear decompositions Eqs. [START_REF] Kang | Feasibility of applying microperforated absorbers in acoustic window system[END_REF][START_REF] Droltleff | Attractive room acoustics design for multi-purpose halls[END_REF] in Eqs.(19-20), the patch velocity of the fluid domain 1 can be written as:

                                     N j N k k jk jk s ij ij i N j j j s ij ij i s i i u Z Z Y f f Y u u 1 1 1 2 1 1 2 1 1 1 1 ~      N i ,..., 1 ,   (21)
where ij  is the Kronecker symbol. The above system may be condensed into a matrix form:

          1 1 2 1 2 1 uu Ψ 1 Y f f Ψ 1 Y Z Z u s s s              , (22)
which admits solution in the following form:

          1 1 1 2 1 2 uI Ψ 1 Y Z Z u Ψ 1 Y f f s s s                   (23)
Note Ψ is a diagonal matrix. In a post-processing phase, the pressure inside the acoustic domains and the velocity on the MPP can be calculated.. Equation (23) seems to differ significantly from Eq. [START_REF] Fenech | The use of microperforated plates to attenuate cavity resonances[END_REF]. However, if we introduce an equivalent PTFs, Y eq and equivalent free patch velocities, u eq such that:

  Y Ψ 1 Y eq s     
, and,

uu eq s  , (24)
one can rewrite Eq. ( 23) as:

    1 1 1 2 1 2 u I Y Z Z u Y f f eq eq eq           . ( 25
)
This expression takes the same form as Eq. ( 10) except that the PTFs and patch free velocities are replaced by their equivalent expressions for the MPP case.

In the case of a rigid MPP (i.e.

Y0 s  and u0 s  ), Eq. ( 23) becomes:

    1 1 1 2 1 2 uI Ψ Z Z Ψ f f        (26)
and the equivalent PTFs and patch free velocity of the MPP are: Y Ψ eq  , and, u0 eq  . (

Then, the equivalent PTFs are equal to the MPP mobility for the input terms (i.e.

 

Y , 1,...,

eq ii i iN    
) and are null for the cross terms (i.e Y 0, eq ij ij  ). In this case, the MPP can be considered as a locally reactive structure characterised by the mobilities Ψ . On the contrary, as can be shown later, a MPP with a backing cavity cannot be considered as a locally reactive device, as opposed to the common assumption made for porous absorbing materials.

Equivalent PTFs for a cavity-backed MPP

A typical micro-perforated panel absorber takes the form of a MPP fitted in front of a backing wall or a cavity. The air gap/volume behind the MPP provides an acoustic-stiffness [START_REF] Wang | Sound absorption of a micro-perforated panel backed by an irregular-shaped cavity[END_REF] which leads to resonance-type absorption with the perforation. This cavity-backed MPP finds its use in various system configurations and therefore deserves a particular treatment. In order to facilitate the modeling of the overall system, a cavity-backed MPP can be regarded as a standalone subsystem. Once the acoustic property is known in terms of PTFs over its surface, it can be integrated into the conventional PTF framework [START_REF] Ouisse | Patch Transfer Functions : a Tool to Couple Linear Acoustic Problems[END_REF], such providing an alternative to the direct formulation presented in Section 3.2.1. Meanwhile, this will allow a significant simplification and the down-sizing of the number of the sub-system to be handled in a complex system.

To this end, the equivalent PTF of a cavity-backed MPP is defined, to be obtained according to the calculation scheme established hereafter. Consider a typical MPP backed by an acoustic cavity. The outer surface Sc of the cavity-backed MPP is divided into N patches. By imposing a unit normal velocity on patch i, the resulted force on patch j needs to be calculated using the PTFs of the cavity and the MPP.

The same matrix notation as in the previous section is used and a Ξ vector is defined as:

  N k    1 Ξ       otherwise. , 0 , for , 1 i k k (28)
The resulted forces on the patches are contained in the f 1 vector and the imposed velocity condition writes:

1 u Ξ  (29)
The continuity relations Eq (19) and Eq. (20) become: 2 u Ξ  , and, (30)

  12 u Ψ f f Ξ s     (31)
As the MPP and the cavity are not directly excited, Eqs.(5-6) become u Y f

s s s  (32) 2 2 2 f Z u  (33) Combining Eqs.(30-33) yields      12 Ψ 1 Y f Z Ξ Ξ s       (34)
The resulting forces 1 f on the patches due to a unit velocity imposed on patch i write  

1 12 f Ψ I 1 Y Z Ξ s             (35)
This gives the equivalent PTF between patch i and patch j,  

  1 eq 2 Z Ψ I 1 Y Z s          (36)
These equivalent PTFs may be used in the classical PTF approach to represent the behaviour of the MPP with a backing cavity. In such case, the standard continuity relations Eqs [START_REF] Ouisse | Patch Transfer Functions : a Tool to Couple Linear Acoustic Problems[END_REF] should be used to assemble the equivalent PTFs with the PTFs of the connected subsystem.

Eq. ( 36) also gives indications on the behaviour of the system and in particular, on whether the system has a localised reaction. With a rigid MPP, the equivalent PTFs become:

eq 1 2 Z ΨZ   ( 37
)
where 1 Ψ  is a diagonal matrix. The system is locally reactive if the first term dominates (i.e.

eq 1 Z Ψ  
). Otherwise, the system is not locally reactive when eq Z is full due to the cavity effect characterized by Z 2 . Examples will be given in the next section for further elaborate this point.

An illustration of application

The general framework of a MPP coupled to a complex environment is now established by using the PTF approach. In this section, the proposed method is applied to a basic case which differs from the conventional case of a micro-perforated panel in an acoustic tube. The purpose is to show the potential of the present approach, instead of detailed treatment of the configuration itself.

A cavity-backed micro-perforated panel inserted in a rigid baffle

Let us consider a MPP backed by rectangular cavity. The surface of the MPP is flush with a rigid baffle of infinite size. Excited by an incident plane wave

      z k x k j e p   cos sin 0 0 0  impinging
on the MPP at an angle of incidence  , the MPP radiates sound towards both the cavity and the semi-infinite acoustic domain. For an easier interpretation of the results, the MPP is supposed to be rigid, bearing in mind that this assumption is not a limitation of the approach as the structure vibration has already been incorporated into the PTF model. Previous investigations demonstrated that the panel vibration mainly affects the absorption performance at the structural resonances [START_REF] Lee | Sound absorption of a finite flexible micro-perforated panel backed by an air cavity[END_REF]. The size of the panel is 0.5m x 0.5m whereas the depth of the cavity is 0.3m. The panel thickness, t and the orifice diameter, d are both 0.2mm. The perforation ratio  is 1%. The acoustic medium involved is air (

29 . 1 0   kg/m 3 , 340 0  c m/s).
The first 24 modes of the rigid-walled cavity are tabulated in Table 1.

PTF calculation procedure

The PTF approach presented in this paper is used for estimating the acoustic pressure in the semi-infinite medium and the absorption coefficient of the MPP with the backing cavity. We are interested in the response of this system in a frequency range up to 2000 Hz. The system is decomposed into three PTF subsystems: the MPP, the backing cavity and the infinite acoustic medium. We are typically in the situation described in section 3 with an excitation in the domain 1 which is semi-infinite. The coupling surface between the three PTF subsystems is divided in 81 patches ( 81 9x9   N

) ensuring a patch size less than half the acoustic wavelength at 2000 Hz (in accordance with the patch size criterion 2 /  defined in [START_REF] Ouisse | Patch Transfer Functions : a Tool to Couple Linear Acoustic Problems[END_REF]). The PTFs of the cavity are calculated using a modal expansion method as detailed in Appendix A (A.1). Acoustic modes of the rigid-walled cavity having a natural frequency below 4000 Hz are used to ensure the convergence of the calculation. For the semi-infinite domain, the PTFs are estimated by using the Rayleigh integral as described in appendix A.2. It is relevant to note that they are independent of the incident wave and of the characteristics of the MPP.

As the MPP is impinged by an incident plane wave propagating in the semi-infinite medium, the patch blocked forces of the acoustic domain 1,

1 ~i f are:      i S inc i dS M p f 2 ~1   N i ,..., 1 ,   (38)
where

        z k x k j inc e p M p   cos sin 0 0 0  
, and the patch blocked forces of the fluid domain 2 (i.e. cavity), 2 ~i f are:

0 ~2  i f   N i ,..., 1 ,   (39)
For a normal incident wave, 0   , one has:

i i S p f   0 1 2 ~ and 0 ~2  i f   N i ,..., 1 ,   (40)
Using these patch blocked forces and the PTFs of the cavity and the semi-infinite medium, one can calculate the patch velocities,

1 i u ,   N i ,..., 1  
from Eq. ( 23) when the MPP is coupled with the backing cavity on one side and the semi-infinite medium on the other side.

The acoustic power absorbed by the cavity-backed MPP, abs  can then be derived from:

  i N i i i abs S u p     1 * 1 1 2 1 ( 41
)
where the asterisk denotes the complex conjugate. The patch pressures, 1 i p can be calculated from:

             N j j ij i i i u Z p S p 1 1 1 1 1 1 (42)
The absorption coefficient abs  is defined as the ratio of the absorption power over the incident power through the MPP surface:

inc abs abs     , (43)
where inc  is the acoustic power injected on the MPP surface by the incident plane wave propagating freely in the acoustic medium:

     N i i inc S c p 1 0 0 2 0 2 1  . ( 44
)
A patch absorption coefficient can be defined for each patch (i.e. local absorption coefficient)

as the ratio of the absorption power by the incident power through the patch surface:

  * 1 1 2 0 0 0 , i i i abs v p p c      N i ,..., 1 ,   . ( 45
)
These coefficients indicate the distribution of the absorption through the MPP surface. In the case where all patches are identical,

   N i i abs abs N 1 , 1     N i ,..., 1 ,   . ( 46
)

Analysis of results

Normal incident wave

The results show in this section concern an incident plane wave, normal to the MPP surface and having unit amplitude ( 1 0  p Pa). As can be seen from section 2, although the oblique incident wave excitation is not a limitation of the current model, we stick to the normal incident case so that results can be compared with literature.

Absorption coefficient

The sound absorption coefficient is calculated using the PTF formulation described in section 4.2. Numerical results are compared with the results of the equivalent electric circuit method in Fig. 4. Note the electric circuit method considers an infinite MPP with an air gap of the same depth in one dimensional case. With a limited panel size, the three dimensional system considered in the present PTF scheme differs significantly from the classical one dimensional case. Figure 4 shows that the two methods give similar results in the high frequency range whereas significant differences occur at low frequencies. At some frequencies, PTF results

give a sound absorption coefficient greater than one for our system. This behaviour can be explained by the fact that the present system is three dimensional one, in which the "edge effect" [START_REF] Sabine | What is measured in sound absorption measurements[END_REF][START_REF] Pellam | Sound Diffraction and absorption by a strip of absorbing material[END_REF][START_REF] Cook | Absorption of Sound by Patches of Absorbent Materials[END_REF][START_REF] Pellam | The absorption of Sound by Small Areas of Absorbing Material[END_REF][START_REF] Daniel | On the dependence of absorption coefficients upon the area of the absorbent material[END_REF] occurs. In the low frequency range, the diffraction phenomenon in the vicinity of the edge of the MPP results in an increase of the energy absorption coming from the neighbourhood of the edges. This can be better seen by investigating the acoustic intensity in the neighbourhood of the MPP. The calculation of the acoustic intensity in the framework of the PTF is described in Appendix B. The acoustic intensity maps are then plotted for three selected frequencies corresponding to the local maxima (of Fig. 4) in figure 5. One can clearly observe that at 150 Hz, corresponding to the maximum absorption, the energy entry into the MPP comes not only from the front of the MPP due to the acoustic incidence, but also from the side way of the MPP (due to the diffraction effect). As the definition of the absorption coefficient only considers the acoustic power of the incident wave over a surface corresponding to the MPP surface (see Eq. 43), the acoustic power diffracted from the side of the MPP is not taken into account. This results in an underestimation of the actual power impinging on the panel and an absorption coefficient greater than one in the low frequency range. For higher frequencies, Fig. 5 shows the absorbed power predominately comes from the front and the effect of the diffraction becomes more and more negligible when frequency increases. This can also be reflected in Fig. 4 in which the corresponding sound absorption coefficient is lower than one.

Based on this understanding, one can surmise that the size of the MPP with respect to the acoustic wave length should play an important role in this phenomenon. This was indeed shown in the past by different authors considering classical absorbing material of finite sizes [START_REF] Pellam | Sound Diffraction and absorption by a strip of absorbing material[END_REF][START_REF] Cook | Absorption of Sound by Patches of Absorbent Materials[END_REF][START_REF] Pellam | The absorption of Sound by Small Areas of Absorbing Material[END_REF][START_REF] Daniel | On the dependence of absorption coefficients upon the area of the absorbent material[END_REF]. They showed that the absorption coefficient of a patch of absorbent material depends on the size of the patch relative to the wavelength. In general, the absorption coefficient increases when the size of the patch material decreases. Same phenomenon has been observed in the present MPP case, in agreement with the previous studies [START_REF] Pellam | Sound Diffraction and absorption by a strip of absorbing material[END_REF][START_REF] Cook | Absorption of Sound by Patches of Absorbent Materials[END_REF][START_REF] Pellam | The absorption of Sound by Small Areas of Absorbing Material[END_REF][START_REF] Daniel | On the dependence of absorption coefficients upon the area of the absorbent material[END_REF]. It should be noted however that these studies considered porous or fibrous absorbing materials which present rather poor absorption at low frequencies. On the contrary, depending on its design, cavitybacked MPP provides efficient sound absorption even at relatively low frequencies, where the acoustic wavelength is large. By the same token, the size effect is also reinforced in the case of a MPP.

By increasing the MPP size to 2m x 2m, we approach more closely to the infinite panel scenario which the equivalent circuit method can model. Results obtained form the current PTF approach is superposed to the two existing curves in Fig. 4. It can be seen that using a larger panel, the present PTF approach gives similar result as the equivalent circuit method does, such demonstrating the validity of the approach.

The spatial distribution of the energy absorption by the MPP at the same frequencies can be revealed using the patch absorption coefficients defined by Eq. ( 45), shown in Fig. 6. At 150

Hz, the absorption is rather uniformly distributed which may be explained by the large wavelength (2.26m) at this frequency. At 707 Hz, corresponding to the second peak in the absorption coefficient curve, the patch absorption coefficients are significantly greater on the boundaries of the MPP than the centre, reaching maximum around the corners. This result can be expected given that the diffraction phenomenon occurs at the boundary and the acoustic wavelength is of the same order of magnitude as the panel size. For an even higher frequency at 1267, one observes variations of the patch absorption coefficients with some values greater than one whereas the (global) absorption coefficients remain lower than one. The diffraction phenomenon in this 3D system and the size of the acoustic wavelength (i.e. 0.27m) may explain this distribution.

Equivalent Patch Transfer Functions

The proposed PTF formulation provides explicit representation of the coupling between subsystems and facilitates explanation of physical phenomenon. This feature is explored using the current system of cavity-backed MPP in terms of the equivalent PTFs defined in Section

3.3.2.
The equivalent PTFs are calculated and depicted in Fig. 7 for three different frequencies.

Figure 7(a) shows that at 150 Hz, the equivalent PTF matrix, eq Z (Eq. ( 37)) is a diagonal- dominant matrix and Z 2 in Eq. ( 37) is negligible comparing with Ψ -1 . This shows that the system is rather local reactive at this frequency. This gives,

I Z eq    S , ( 47
)
where S  is the surface of the patches. At this frequency, the equivalent PTFs depend only on the equivalent mobility of the perforation  and the surface of the patches, indicating the strong dominance of the MPP. On the contrary, for the two other frequencies corresponding to the first two modes of the hard-walled cavity, the equivalent PTF matrices are full matrices as shown in Fig. 7(b-c), which indicates the system has not a localised reaction. In this case, the behaviour of the cavity-backed MMP is dominated by the cavity. The equivalent PTFs vary in function of the modal variation on the coupling surface. As an extreme example, from the third modes (0,0,1) at 567 Hz, the PTFs are quasi-constant as shown in Fig. 7(c) due to the uniform spatial shape of this mode on the coupling surface. Slight variations at the diagonal terms are due to the term  S in Eq. ( 37).

It is pertinent to mention that  S is the impedance of the perforation and becomes the impedance of the MPP when the vibration of the latter is neglected. The comparison between this impedance term and the impedance of the cavity provides very useful physical insight in the way the MMP is coupled to the cavity. This is done in Fig. 8, in which the impedance of the MPP, 

S

, is compared to that of the cavity ii Z for one particular patch [START_REF] Lee | Estimation of the absorption performance of multiple layer perforated panel systems by transfer matrix method[END_REF][START_REF] Wang | Sound absorption of a micro-perforated panel backed by an irregular-shaped cavity[END_REF]. It can be seen that,  S are generally larger than ii Z , except for frequencies close to the natural frequencies of the cavity. Provided these modes are excited, the equivalent PTFs correspond to the cavity impedance at their resonance frequencies. In that case, the effect of the MPP becomes negligible compared to the cavity resonance. One such example is the mode (0,0,1) at 567 Hz. As the acoustic damping inside the cavity is small ( ) 0001 . 0   , the absorption coefficient is quasi null at this frequency, as shown in Fig. 4. Similar observations can be made at 1133 Hz and 1700 Hz which correspond to the natural frequencies of modes (0,0,2) and (0,0,3), respectively. It should be mentioned that quite a few acoustic modes cannot be excited due to the nature of the normal incident wave, which are reflected in the sound absorption curve.

In conclusion, the equivalent PTFs of the cavity-backed MPP allows representing the MPP coupled with the backing cavity as a single PTF subsystem. This subsystem cannot be considered as a locally reactive material in general.

EXPERIMENTAL VALIDATIONS

The proposed PTF approach is used to investigate the acoustic field inside a rectangular cavity used in Fenech et al. [START_REF] Fenech | The use of microperforated plates to attenuate cavity resonances[END_REF]. Results obtained from the present approach are compared with the experimental data reported in that paper. This comparison allows further validation of the proposed approach in a vibro-acoustic environment. The rectangular air cavity of dimension 2m x 1.2m x 0.2m was made of 22-mm fiberboard panels screwed and glued together. As shown in Fig. 9. a loudspeaker with a diameter of 9 cm was mounted on one of the vertical side panels to provide a white noise excitation to the cavity. The sound pressure was measured at various locations for three configurations: (a) the empty cavity; (b), a MPP installed at the middle of the cavity at x=1m; (c), a MPP installed near the cavity wall at d =0.25m (Fig. 9). In Fenech et al.

[10], the reverberation time of the empty cavity was found to be roughly 0.5 s in most of the frequency range of interest. This allows to estimate an overall damping loss factor from 2.2 r fT

 

where f is the frequency and r T the reverberation time. The aluminium MPP was 1-mm-thick and supplied by the Swedish manufacturer Sontech under the trade name Acustimet. Due to the manufacturing process, the punched perforations were found to produce holes with sharp edges that protrude out of the surface of the plate. Therefore, instead of using Maa's theory [START_REF] Maa | Potential of microperforated panel absorber[END_REF], the flow impedance 0 Z was experimentally measured using an impedance tube and used in their model [START_REF] Fenech | The use of microperforated plates to attenuate cavity resonances[END_REF]. The vibration of the MPP was supposed to be negligible, i.e.

    2 0, , 1, s ij Y i j N    in the present formulation.
When the MPP is placed inside the cavity, the system is divided into three subsystems: the MPP, and the two rectangular sub-cavities as shown on Fig. 10. The rectangular coupling surface is divided in 5 patches to ensure the convergence of the solution up to 500 Hz, according to the /2 criterion. The PTFs of the sub-cavities are calculated from the modal method using rigid-walled modes of the sub-cavities below 1000 Hz (Appendix A.1). This calculation is the most time consuming part, even though it requires only few seconds in the case. These PTFs are also used for calculating the response of the empty cavity in the PTF approach. In this case, the system has only two subsystems, namely the two sub-cavities, connected by a virtual surface between them at the middle of the cavity. Of course, it is straightforward to use modes of the entire cavity in a modal expansion scheme for estimating the response of the empty cavity. The goal of treating the system by PTF approach is to highlight the efficiency of the method through comparisons with experimental measurement.

Comparisons between the present PTF and experimental results obtained by Fenech et al. are made in Fig. 11 in terms of sound pressure level at the measurement point. For the empty cavity, Fig. 11 (a) shows a satisfactory agreement between these two sets of results, despite some noticeable differences in the resonance frequencies as well as the peak values. The discrepancy in frequencies may be due to the cavity boundary used in experiment, which does not totally comply with theoretical model. Indeed, the first nonzero natural frequency of the cavity was predicted at 88 Hz by the present PTF approach, as opposed to 93 Hz measured experimentally and 86 Hz calculated from analytical solutions under the assumption of rigid walls. It is remarkable that, although this frequency does not correspond to any of the natural frequencies of the sub-cavities, it was correctly predicted using PTF approach.

With the MPP placed at the middle of the cavity, similar comparisons are plotted in Fig. 11 (b). Again, the agreement between the PTF results and the experimental results is globally good. Compared with Fig. 11(a), the effect of the MPP can be observed: some resonance frequencies of the empty cavity are altered by the presence of the MPP on one hand, and reduction of some resonance peaks due to the sound absorption of the MPP on the other hand.

An attenuation of as much as 25 dB for some modes (i.e. (1,0), (3,0), (3,1)) noticed in the experiment of Fenech et. al.) are well reproduced by our simulations. It is noteworthy that due to the location of the MPP, some modes are practically not affected by the presence of the MPP.

As the last example, Fig. 12 compares the PTF result with that obtained by Fenech' calculation based on the complex mode evaluation of the modified cavity, along with the experimentally measured sound pressure level when the MPP was placed toward a wall of the cavity d =0.25m. Despite some differences, the agreement between the experiment and the simulation is generally satisfactory, bearing in mind that the sound pressure level is sensitive to the location of the measurement point. Similar agreement was also observed for other figures presented in [START_REF] Fenech | The use of microperforated plates to attenuate cavity resonances[END_REF] (not shown here). The two calculation models give very similar results albeit more apparent discrepancies occur at higher frequencies. Differences and uncertainties in the modeling (i.e. damping model, modal convergence) and the data (i.e. damping value, flow impedance value) may explain these differences.

In conclusion, these comparisons demonstrate the validity of the present P TF formulation in dealing with systems of various configurations.

Conclusions

A vibroacoustic formulation based on the Patch Transfer Functions (PTF) approach is proposed to model micro-perforated structures in a complex vibro-acoustic environment. The PTFs of the micro-perforated structure is first formulated. Its coupling with surrounding acoustic domains is then cast into transfer function paradigm through velocity continuity and force equilibrium over connecting patches. This leads to two different formulations, namely direct formulation and equivalent PTFs for cavity-backed micro-perforated structure, both providing explicit representation of the coupling between subsystems and facilitating physical explanations.

By virtue of its substructuring nature, the PTF approach proposed in this paper is an efficient tool to deal with micro-perforated structure in a complex vibro-acoustic environment. Calculations of PTFs are performed beforehand for each subsystem separately.

As a result, parallel computation is possible. In a typical design problem, re-calculations of PTFs are required only for those subsystems or components with modifications, endowing the method the flexibility and efficiency in dealing with complex system, conducive to conducting system optimization.

As an illustration example, application to a MPP with a backing cavity located in an infinite baffle is demonstrated. The proposed PTF formulation is finally validated through comparison with experimental measurements available in the literature.

As a final note, it is relevant to mention that the PTF approach has been applied to several basic systems in this paper. It can be extended to more practical cases with complex geometries. In this case, the patch transfer functions of each subsystem may be calculated by numerical methods like Finite Element Method or Boundary Element Method. The size of the numerical models of each subsystem is considerably smaller than that of the global model.

expressed, for all test regular functions p on c  , as follows:

           c i c S pdS j pdV p c dV p p        2 0 0 2 0 1 . (A.1)
Eigenfunctions qrs  and eigenfrequencies qrs  are available for a rigid-walled parallelepiped cavity of dimension Lx×Ly×Lz:

2 2 2 0                           z y x qrs L x s L x r L x q c     , (A.2)                            z y x qrs L z s L y r L x q z y x     cos cos cos , , , (A.3)
The modal generalised mass qrs  is defined by: where i a is the radius of the equivalent circular patch:

       
 i i S a   . (A.12)
The PTF of patch i is then: .13) For the PTF between patch i and patch j (

  i a jk ii S e c Z i     0 1 0 0  . ( A
j i  ),
     K k k M Q jk i M M Q e K S j p k 1 0 0 2   . (A.14)
where k Q is the center point of the k th elementary surface.

Thus, the PTF between patch i and patch j can be evaluated by: .15) and the patch PTF between the patch i and the receiving point M  inside the semi-infinite acoustic medium by: is the acoustic velocity in the  direction at point M  .

            K k K k k k Q Q jk j i ij Q Q e K K S S j Z k k 1 1 0 0 2   , ( A
        K k k M Q jk i M i M Q e K S j Z k 1 0 0 2   . (A.16)         x k j M e z k p p   sin 0 0 1 0 cos cos 2 ~  . (B.
The particle velocity can be related to the pressure gradient using Euler's equation:

         1 0 1 , M M p j u . (B.5)
The pressure gradient can be calculated from Eq. (A.14) when a unit normal velocity is prescribed on patch i: This leads to:

                         K k k M Q jk k M Q jk k k i M M Q e M Q e jk M Q M Q K S j p k k
                      K k k M Q jk k M Q jk k k i M M Q e M Q e jk M Q M Q K S T

  this paper, a new formulation for calculating the PTFs of MPP is first proposed. In a first step, the equations of motion of the MPP are expressed on each patch of the coupling surface. The patch flexural velocity of the MPP and the patch acoustic velocity of the surrounding acoustic medium are then linked to the difference of the patch pressures on both sides of the MPP. Two approaches are then proposed: The first one consists in resolving directly the global problem using the MPP relation as a coupling condition with other subsystems. In this formulation, acoustic and mechanical PTFs of each individual subsystem intervene directly in the global equations. Upon casting micro-perforations and the flexibility of the MPP under PTF framework, the proposed PTF formulation provides explicit representation of the coupling between subsystems and facilitates explanation of physical phenomenon. The second approach consists in first calculating the equivalent Patch Transfer Functions of a MPP with a backing cavity, which can be further coupled with the PTFs of other fluid domains in a second step. This second formulation is then explored to illustrate the application of the proposed model to a cavity-backed MPP absorber with an infinite baffle.



  generates the vibration of air mass u 0 at each single hole. As the orifice diameter of the hole is much smaller than the acoustic wavelength of interests, it is appropriate to assume that the air particle velocity is distributed uniformly within the area of each hole. Let 0 Z denote the complex acoustic impedance of the hole normalized by the , where ρ0 is the air density and 0 c the speed of sound. 0 Z is

7 )A. 2 .

 72 r, s) denotes the mode numberThe pressure may be expended on this modal basis as: qrs  are the modal amplitudes to be determined.Introducing this modal expansion in the variational formulation and usingDissipation in the fluid medium can be taken into account by introducing a modal damping factor, c  . This is done by adding an imaginary term in the denominator. Then, the PTF between excited patch i and receiving patch j, ij Z is: between the excited patch i and the receiving point M inside the cavity is: PTFs for a semi-infinite acoustic domain.One considers a semi-infinite acoustic domain where a unit normal velocity is prescribed on the patch i and where the other patches are supposed to be rigid. The pressure at point M inside or at the boundary of the acoustic domain is given by the Rayleigh integral equation: wavenumber. Note that the integrand is singular (tends to infinity) as QM tends to zero. This problem which intervenes in the calculation of the PTF of patch i, ii Z must be overcome by the use of cylindrical coordinates by considering a circular patch having the same surface as the original one. In this case, the calculation of Cauchy's principal value of the integral gives:

3 )

 3 In order to calculate the acoustic velocities at point M  with the same process, one should introduce a supplementary patch transfer function between patch i and point M  , velocity in the  direction at point M  when a normal velocity,

  acoustic intensity at point M  in the direction  can be obtained by introducing Eq. (B.2) and (B.8) in the relation (B.1).

Figure 1 .Figure 2 .

 12 FIGURES

Figure 3 .Figure 4 .Figure 5 .Figure 6 .Figure 7 .Figure 8 .

 345678 Figure 3. Description of pressure and velocity variables for the MPP.

Figure 9 .

 9 Figure 9. Rectangular cavity used in the experiments by Fenech et al. [10].

Figure 10 .Figure 11 .

 1011 Figure 10. PTF substructuring and patch definition.

Figure 12 .

 12 Figure 12. Comparison of PTF results with the pressures measured and calculated by Fenech et al. for a MPP at d=0.25m. Solid line: PTF results; Dash line, Fenech' measurement; Grey line: Fenech' prediction;

TABLETable 1 .

 1 Natural frequencies of the rectangular cavity with rigid boundaries.

Appendix A. calculations of PTFs

, the variational formulation of the problem can be

Appendix B. Acoustic intensity calculation in a semi-infinite space

The acoustic intensity at point M  in the direction  (

is the acoustic velocity in the  direction at point M  and the asterisk denotes the complex conjugate.

The pressure at point M  can be calculated from the patch velocities,

where the blocked pressure at point M  due to the incident wave is:


domain: info shs info.info-dl

text:
Andreas Witt

Clarin-D And

CLARIN-D AND CLARIN-ERIC

-In CLARIN, the Center-oriented infrastructure offers options to include parts of the infrastructure budget of the host institutions to contribute to the shared funding -Technical development may be distributed over several partners

-•

  ERIC: European Research Infrastructure Consortium -The Members of an ERIC are countries • Governance -General Assembly (representatives from the ministries of the member countries) -ScientiKic Advisory Board -Board of Directors -Several committees www.clarin-d.netV Which ways of funding are feasible for research infrastructures and how can international cooperation contribute to sustainability?

-Organizational (from governance to community builing) -Technical


text:
Universität Leipzig

DIE DIGITAL HUMANITIES ALS FÄCHERÜBERGREIFENDES FORSCHUNGSPARADIGMA

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members from: ermany ustria (39) witzerland ( 17) uxembourg (3) rance (2) S (2) elgium (1) orway ( 1) taly ( 1) aiwan (1) members from: ermany ustria (39) witzerland ( 17) uxembourg (3) rance (2) S ( 2) elgium ( 1) orway ( 1) taly ( 1) aiwan (1) hUp://geobrowser.de.dariah.eu/?csv1=hUps://geobrowser.de.dariah.eu/storage/469752&currentStatus=mapChanged=Contemporary+map+2014

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Working groups: hUp://dig-hum.de/dhd-ags Academic disciplines: ? 27.04.17

Evelyn Gius: Remarks from the Community's PerspecOve 5 members from: ermany ustria (39) witzerland ( 17) uxembourg (3) rance (2) S ( 2) elgium ( 1) orway ( 1) taly ( 1 AddiOonal specialised services such as:

• access to data resources (via metadata and full text) • tools for the analysis and the visualisaOon of 'humanOes' data rtance of generic services, as: comprehensive authenOcaOon and thorizaOon infrastructure, ovision of permanent idenOfiers, and ovision of database infrastructures.

Digital Humani<es and Digital Research Infrastructure Crucial aspect for sustainability:

• Projects need to know about the infrastructures, and • be willing to use them (because the infrastructures do meet the projects' requirements).

→ Sustainability = conFnuous exploitaFon by the community 27.04.17 Evelyn Gius: Remarks from the Community's PerspecOve

  \b\S*?[N,n]achhalt\S*\b" reg=" "\b\S*?[s,S]ustain\S*\b" • occurences of sustainability related words: .17 Evelyn Gius: Remarks from the Community's PerspecOve Sustainability reg = "\b\S*?[N,n]achhalt\S*\b" reg=" "\b\S*?[s,S]ustain\S*\b"• occurences of sustainability related words: .17 Evelyn Gius: Remarks from the Community's PerspecOveSustainability and Infrastructure at DHd conferences

2. 4

 4 Die Digital HumaniFes und die virtuellen InfrastrukturenVirtuelle Infrastrukturen ermöglichen die gemeinsame Nutzung generischer Dienste und bieten eine grundlegende Basis für Werkzeuge. Solche Infrastrukturen sollten vorhandene Anforderungen erfüllen, Werkzeuge sollten kompa1bel zu ihnen entwickelt werden. Mit der zunehmenden Komplexität der Algorithmen, der zunehmenden Größe der untersuchten Datenbestände und dem die Zusammenarbeit stärker betonenden ArbeitssOl, wird eine leistungsstarke technische Infrastruktur für die Digital HumaniOes immer wichOger. Deshalb entwickeln sich gegenwärOg virtuelle Forschungsinfrastrukturen, wie sie für die Naturwissenschalen schon lange üblich waren, auch in den Geisteswissenschalen. Ziel hierbei ist es, alle einschlägigen projekt-übergreifenden Anforderungen, die Digital HumaniOes-Projekte haben, zu erfüllen. Abhängig von der örtlichen Lage und organisatorischen EinbeUung eines Projekts können solche Anforderungen schon in der reinen Zurverfügungstellung von virtuellen Servern und Speicherplatz bestehen. In jedem Fall können Projekte aber profiOeren von generischen Diensten, wie der EinbeUung von Anwendungen in eine übergreifende AuthenOfizierungs-und Autorisierungsinfrastruktur, der Bezugsmöglichkeit von permanenten IdenOfikatoren für Daten und der Bereitstellung von Datenbank-Infrastrukturen. Neben inhaltsneutralen Diensten, können virtuelle Forschungsinfrastrukturen für die Geisteswissenschalen aber auch fachbezogene projektübergreifende Dienste anbieten, wie zum Beispiel den über Metadaten und Volltext erfolgenden Zugriff auf Datensammlungen oder die Bereitstellung von Visualisierungs-und Analysewerkzeugen für häufig in den Geisteswissenschalen verwendete Datentypen, etwa computerlinguisOsche Verfahren für Sprachdaten oder Darstellungswerkzeuge für Zeit-und Raum-bezogene Daten. KriOsch dabei ist, dass Projekte solche Infrastrukturen kennen und auch bereit sind sie zu verwenden -weil Infrastrukturen ihre Anforderungen auch wirklich erfüllen. Schließlich sind virtuelle Forschungsinfrastrukturen nur sinnvoll, wenn ihr nachhalOger Betrieb gesichert ist.Digital Humani<es and Digital Research Infrastructure 2.4 Die Digital HumaniFes und die virtuellen Infrastrukturen Virtuelle Infrastrukturen ermöglichen die gemeinsame Nutzung generischer Dienste und bieten eine grundlegende Basis für Werkzeuge. Solche Infrastrukturen sollten vorhandene Anforderungen erfüllen, Werkzeuge sollten kompa1bel zu ihnen entwickelt werden. Mit der zunehmenden Komplexität der Algorithmen, der zunehmenden Größe der untersuchten Datenbestände und dem die Zusammenarbeit stärker betonenden ArbeitssOl, wird eine leistungsstarke technische Infrastruktur für die Digital HumaniOes immer wichOger. Deshalb entwickeln sich gegenwärOg virtuelle Forschungsinfrastrukturen, wie sie für die Naturwissenschalen schon lange üblich waren, auch in den Geisteswissenschalen. Ziel hierbei ist es, alle einschlägigen projekt-übergreifenden Anforderungen, die Digital HumaniOes-Projekte haben, zu erfüllen. Abhängig von der örtlichen Lage und organisatorischen EinbeUung eines Projekts können solche Anforderungen schon in der reinen Zurverfügungstellung von virtuellen Servern und Speicherplatz bestehen. In jedem Fall können Projekte aber profiOeren von generischen Diensten, wie der EinbeUung von Anwendungen in eine übergreifende AuthenOfizierungs-und Autorisierungsinfrastruktur, der Bezugsmöglichkeit von permanenten IdenOfikatoren für Daten und der Bereitstellung von Datenbank-Infrastrukturen. Neben inhaltsneutralen Diensten, können virtuelle Forschungsinfrastrukturen für die Geisteswissenschalen aber auch fachbezogene projektübergreifende Dienste anbieten, wie zum Beispiel den über Metadaten und Volltext erfolgenden Zugriff auf Datensammlungen oder die Bereitstellung von Visualisierungs-und Analysewerkzeugen für häufig in den Geisteswissenschalen verwendete Datentypen, etwa computerlinguisOsche Verfahren für Sprachdaten oder Darstellungswerkzeuge für Zeit-und Raum-bezogene Daten. KriOsch dabei ist, dass Projekte solche Infrastrukturen kennen und auch bereit sind sie zu verwenden -weil Infrastrukturen ihre Anforderungen auch wirklich erfüllen. Schließlich sind virtuelle Forschungsinfrastrukturen nur sinnvoll, wenn ihr nachhalOger Betrieb gesichert ist. rtance of generic services, as: comprehensive authenOcaOon and thorizaOon infrastructure, ovision of permanent idenOfiers, and ovision of database infrastructures. 27.04.17 Evelyn Gius: Remarks from the Community's PerspecOve Digital Humani<es and Digital Research Infrastructure 27.04.17 Evelyn Gius: Remarks from the Community's PerspecOve 15 2.4 Die Digital HumaniFes und die virtuellen Infrastrukturen Virtuelle Infrastrukturen ermöglichen die gemeinsame Nutzung generischer Dienste und bieten eine grundlegende Basis für Werkzeuge. Solche Infrastrukturen sollten vorhandene Anforderungen erfüllen, Werkzeuge sollten kompa1bel zu ihnen entwickelt werden. Mit der zunehmenden Komplexität der Algorithmen, der zunehmenden Größe der untersuchten Datenbestände und dem die Zusammenarbeit stärker betonenden ArbeitssOl, wird eine leistungsstarke technische Infrastruktur für die Digital HumaniOes immer wichOger. Deshalb entwickeln sich gegenwärOg virtuelle Forschungsinfrastrukturen, wie sie für die Naturwissenschalen schon lange üblich waren, auch in den Geisteswissenschalen. Ziel hierbei ist es, alle einschlägigen projekt-übergreifenden Anforderungen, die Digital HumaniOes-Projekte haben, zu erfüllen. Abhängig von der örtlichen Lage und organisatorischen EinbeUung eines Projekts können solche Anforderungen schon in der reinen Zurverfügungstellung von virtuellen Servern und Speicherplatz bestehen. In jedem Fall können Projekte aber profiOeren von generischen Diensten, wie der EinbeUung von Anwendungen in eine übergreifende AuthenOfizierungs-und Autorisierungsinfrastruktur, der Bezugsmöglichkeit von permanenten IdenOfikatoren für Daten und der Bereitstellung von Datenbank-Infrastrukturen. Neben inhaltsneutralen Diensten, können virtuelle Forschungsinfrastrukturen für die Geisteswissenschalen aber auch fachbezogene projektübergreifende Dienste anbieten, wie zum Beispiel den über Metadaten und Volltext erfolgenden Zugriff auf Datensammlungen oder die Bereitstellung von Visualisierungs-und Analysewerkzeugen für häufig in den Geisteswissenschalen verwendete Datentypen, etwa computerlinguisOsche Verfahren für Sprachdaten oder Darstellungswerkzeuge für Zeit-und Raum-bezogene Daten. KriOsch dabei ist, dass Projekte solche Infrastrukturen kennen und auch bereit sind sie zu verwenden -weil Infrastrukturen ihre Anforderungen auch wirklich erfüllen. Schließlich sind virtuelle Forschungsinfrastrukturen nur sinnvoll, wenn ihr nachhalOger Betrieb gesichert ist.

2. 4

 4 Die Digital HumaniFes und die virtuellen InfrastrukturenVirtuelle Infrastrukturen ermöglichen die gemeinsame Nutzung generischer Dienste und bieten eine grundlegende Basis für Werkzeuge. Solche Infrastrukturen sollten vorhandene Anforderungen erfüllen, Werkzeuge sollten kompa1bel zu ihnen entwickelt werden. Mit der zunehmenden Komplexität der Algorithmen, der zunehmenden Größe der untersuchten Datenbestände und dem die Zusammenarbeit stärker betonenden ArbeitssOl, wird eine leistungsstarke technische Infrastruktur für die Digital HumaniOes immer wichOger. Deshalb entwickeln sich gegenwärOg virtuelle Forschungsinfrastrukturen, wie sie für die Naturwissenschalen schon lange üblich waren, auch in den Geisteswissenschalen. Ziel hierbei ist es, alle einschlägigen projekt-übergreifenden Anforderungen, die Digital HumaniOes-Projekte haben, zu erfüllen. Abhängig von der örtlichen Lage und organisatorischen EinbeUung eines Projekts können solche Anforderungen schon in der reinen Zurverfügungstellung von virtuellen Servern und Speicherplatz bestehen. In jedem Fall können Projekte aber profiOeren von generischen Diensten, wie der EinbeUung von Anwendungen in eine übergreifende AuthenOfizierungs-und Autorisierungsinfrastruktur, der Bezugsmöglichkeit von permanenten IdenOfikatoren für Daten und der Bereitstellung von Datenbank-Infrastrukturen. Neben inhaltsneutralen Diensten, können virtuelle Forschungsinfrastrukturen für die Geisteswissenschalen aber auch fachbezogene projektübergreifende Dienste anbieten, wie zum Beispiel den über Metadaten und Volltext erfolgenden Zugriff auf Datensammlungen oder die Bereitstellung von Visualisierungs-und Analysewerkzeugen für häufig in den Geisteswissenschalen verwendete Datentypen, etwa computerlinguisOsche Verfahren für Sprachdaten oder Darstellungswerkzeuge für Zeit-und Raum-bezogene Daten. KriOsch dabei ist, dass Projekte solche Infrastrukturen kennen und auch bereit sind sie zu verwenden -weil Infrastrukturen ihre Anforderungen auch wirklich erfüllen. Schließlich sind virtuelle Forschungsinfrastrukturen nur sinnvoll, wenn ihr nachhalOger Betrieb gesichert ist.

sustainable infrastructure data tool repository DARIAH CLARIN all tags infrastructure, data, tools, repositories occurrences of tags

	Digital Humani<es and Research Infrastructures
		sustainable	infrastructure	data	tool		repository	DARIAH	CLARIN	all tags	infrastructure,	data, tools,	repositories	CollocaOons of "sustainable"-tags digitale 38 digitalen 37 Daten 22 Infrastruktur 8 Forschungssolware 8 Open 7 (occurrences >=6)
	occurrences of tags												Solware	20	NachhalOgkeit	7
	DHd 2015 Graz DHd 2015 Graz	25 25	64 1.163 64 1.163	321 321	63 63	68 68	17 17	1.721 1.721	1.611 1.611	Forschungsdaten 20	DokumentaOon	7
	DHd 2016 Leipzig DHd 2017 Bern DHd 2016 Leipzig DHd 2017 Bern al HumaniOes	61 365 61 365	209 1.613 146 1.361 209 1.613 146 1.361	397 295 397 295	110 108 92 96 110 108 92 96	111 13 111 13	2.609 2.368 2.609 2.368	2.329 1.894 2.329 1.894	Entwicklung Digitale	19 18	Thema Sinne	6 6
	total average per contribu1on* DHd 2015 Graz total DHd 2015 Graz contribu1on* average per theses	451 0,32 0,83 15,10 4,17 0,82 0,88 0,22 22,35 20,92 419 4.137 1.013 265 272 141 6.698 5.834 451 419 4.137 1.013 265 272 141 6.698 5.834 0,32 0,83 15,10 4,17 0,82 0,88 0,22 22,35 20,92	Kultur technischer digitaler HumaniOes Digital	10 10 13 17 16	Grundlage langfrisOge Projekt Ressourcen Projekten	6 6 6 6 6
	DHd 2016 Leipzig DHd 2016 Leipzig	0,39 1,32 10,21 2,51 0,70 0,68 0,70 16,51 14,74 0,39 1,32 10,21 2,51 0,70 0,68 0,70 16,51 14,74	technische	9	geisteswissenschallicher 6
	DHd 2017 Bern DHd 2017 Bern	4,01 1,60 14,96 3,24 1,01 1,05 0,14 26,02 20,81 4,01 1,60 14,96 3,24 1,01 1,05 0,14 26,02 20,81	Sicherung	9	Forschung	6
	average 2015-2017 average 2015-2017	1,38 1,29 12,69 3,11 0,81 0,83 0,43 20,55 17,90 1,38 1,29 12,69 3,11 0,81 0,83 0,43 20,55 17,90	Nutzung	9	Beitrag	6
				no. of no. of			no. of no. of	no. of no. of			words/ words/	aUendants/ aUendants/
	Some more numbers: Some more numbers:	DHd 2015 Graz DHd 2016 Leipzig DHd 2015 Graz DHd 2016 Leipzig	contribuOons* 77 158 contribuOons* 77 158	aUendants 365 479 aUendants 365 479	words in BoA 141.747 213.776 words in BoA 141.747 213.776		contribuOon 1.841 1.353 contribuOon 1.841 1.353	contribuOon 4,7 3,0 contribuOon 4,7 3,0
		DHd 2017 Bern DHd 2017 Bern	91 91			398 398	136.915 136.915			1.505 1.505	4,4 4,4
		total total		326 326			1.233 1.233	492.938 492.938	average average	1.566 1.566	4,0 4,0
		*: all workshops, keynotes, papers, panels, and posters.
	27.04.17 27.04.17				Evelyn Gius: Remarks from the Community's PerspecOve Evelyn Gius: Remarks from the Community's PerspecOve	9 10

*: all workshops, keynotes, papers, panels, and posters. /dig-hum.de/ n-digital-niOes-2020) 27.04.17 Evelyn Gius: Remarks from the Community's PerspecOve Digital Humani<es and Tradi<onal Research Infrastructures al HumaniOes theses /dig-hum.de/ n-digital-niOes-2020) 27.04.17 Evelyn Gius: Remarks from the Community's PerspecOve 12 Libraries, Archives and Museums as enablers for the applicaOon and development of digital methods 27.04.17 Evelyn Gius: Remarks from the Community's PerspecOve 13 Digital Humani<es and Digital Research Infrastructure

from the Community's PerspecOve hUp://geobrowser.de.dariah.eu/?csv1=hUps://geobrowser.de.dariah.eu/storage/469752&currentStatus=mapChanged=Contemporary+map+2014 DHd members

• sustainability of digital research infrastructure

• is not only achieved for the community, • it also is achieved and maintained by the community that uses it,

• by means of using it.

27.04.17

Evelyn Gius: Remarks from the Community's PerspecOve Sustainability of research infrastructures?

• sustainability of digital research infrastructure

• is not only achieved for the community,

• it also is achieved and maintained by the community that uses it,

• by means of using it.

• possible involvement of DHd?

• complemenOng the experOse of DARIAH/CLARIN with the community perspecOve? • DHd conferences as (even bigger) pool for issues, new themes, potenOal users, etc.?

27.04.17 Evelyn Gius: Remarks from the Community's PerspecOve


Gurpreet Dhillon
email: gdhillon@vcu.edu

Tiago Oliveira
email: toliveira@isegi.unl.pt

Santa Susarapu
email: susarapusr@vcu.edu

Mário Caldeira
email: caldeira@iseg.utl.pt

When Convenience Trumps Security. Defining Objectives for Security and Usability of Systems

Keywords: security values, usability values, value focused-thinking, qualitative methods, instrument development, quantitative methods

Security and usability of systems continues to be an important topic for managers and academics alike. In this paper we propose two instruments for assessing security and usability of systems. These instruments were developed in two phases. In Phase 1, using the value-focused thinking approach and interviews with 35 experts, we identified 16 clusters of means and 8 clusters of fundamental objectives. In phase 2 drawing on a sample of 201 users we administered a survey to purify, ensure reliability, and unidimensionality of the two instruments. This resulted in 15 means objectives, organized into four categories (minimize system interruptions and licensing restrictions, maximize information retrieval, maximize system aesthetics, and maximize data quality) and 12 fundamental objectives grouped into four categories (maximize standardization and integration, maximize ease of use, maximize system capability, and enhance system related communication). Collectively the objectives offer a useful basis for assessing the extent to which security and usability has been achieved in systems.

Introduction

Consider a situation where Alice has to set up her friend's new computer. Alice sets up a limited user account, changes the file permissions for the entire user class, thus allowing write and modify access for all non system partitions. Alice goes a step further and installs a freeware SuRun so that in case her friend called her again, she could run certain programs without necessarily asking for administrative rights. Alice also installed Returnil, a software suite that allows automatic recovery in case of problems. All in all, Alice considered this to be a rather secure and a usable arrangement. Alice's friend however encountered significant problems with the set up. Following a system update, SIW (System Information for Windows) kept popping up warning windows and later hung up. With little computing knowledge Alice's friend tried uninstalling the virtual machine. With some luck she was able to delete the folder, which stopped the conflict messages from popping up. However in the process she probably left her computer open for several vulnerabilities.

So, where does one draw a line between security and usability? Alice thought that she was probably doing a pretty good job, but by imposing her own values in configuring a system, she ended up creating several vulnerabilities without even realizing that they existed. Within organizations it is common to see such problem occur and the solution perhaps resides in addressing user expectation and inferring authorizations based on designations [START_REF] Yee | Aligning security and usability[END_REF]. While the literature has made several calls for balancing security and usability, these have not been adequately heeded to (e.g. see [START_REF] Dewitt | Aligning usability and security: a usability study of Polaris[END_REF][START_REF] Frøkjaer | Measuring usability: are effectiveness, efficiency, and satisfaction really correlated[END_REF]). In majority of the cases where security and usability has been considered, it's been an afterthought at best with developers design systems and later realizing that security and usability considerations had not been adequately addressed. Such development duality typically results in a haphazard system development (see [START_REF] Baskerville | Information systems security design methods: implications for information systems development[END_REF][START_REF] Dhillon | Managing information system security[END_REF]). A definition of a common set of security and usability objectives would to a large extent elevate the development duality problem by presenting objectives that must be achieved. Such objectives would also help in providing a strategic direction for secure and usable systems development.

In this paper, following Keeney [START_REF] Keeney | Value-focused thinking[END_REF], Dhillon and Torkzadeh [START_REF] Dhillon | Value-focused assessment of information system security in organizations[END_REF], and Torkzadeh and Dhillon [START_REF] Torkzadeh | Measuring factors that influence the success of Internet commerce[END_REF], we use value-focused thinking to define security and usability objectives. The study was undertaken in two phases. Phase 1 involved a qualitative definition of value-based objectives. Phase 2 helped in developing a parsimonious set of security and usability objectives. The two phases and a final set of objectives are discussed in the rest of the paper.

Value Focused Security and Usability Objectives

As stated earlier, methodologically this research is based on Keeney's [START_REF] Keeney | Value-focused thinking[END_REF] 'value focused thinking' approach. Keeney suggests that most decision-making methods are based on alternative thinking practices where choices are made only from a limited list of available alternatives. The alternative based approach is constrained by the limits imposed by decision-makers in the process of identifying constraints and subsequently alternatives. As a consequence, individuals tend to forget what they really want to achieve. Since achieving an objective is the primary reason for being involved in any decision situation, Keeney contends that one should remain focused on the bottom-line objectives, which makes decisions meaningful and of value, instead of making choices among current alternatives. Value focused thinking is proposed as a method by Keeney, to address the most fundamental question -what do we want to do and why. Research conducted by Keeney (e.g. see [START_REF] Keeney | Value-focused thinking[END_REF][START_REF] Keeney | The value of Internet commerce to the customer[END_REF]), has attempted to expose underlying values in a wide array of decision contexts. The inherent argument is that the value thinking process can help researchers and managers alike to be proactive and hence create more alternatives instead of being limited by available choices.

Value focused thinking consists of two main steps in eliciting and framing values: (1) conduct interviews and construct a list of what they want in the decision context, (2) convert these statements into a common format of objectives (an object and a preference). In terms of modeling the means and fundamental objectives, a network hierarchy can also be put together. In the context of our research, this two-step method is applied in order to assess values attached by users, to IS Security and Usability. Thirty-five end-users of IS/IT services were contacted from employees of five large businesses in the US. The businesses represented the following industries -IT consulting, Hotel and Casino, Banking, Education and Training. The interviews formed the basis for eliciting the values.

Construct a list of what users want. The best way to find out what users value most is to ask them. Also, it is better to ask as many users as possible because different users may have different values and they may express them differently. However a difficulty lies in the latency of these values. In many cases users' values are hidden under the surface. Keeney recommends several stimulation techniques to surface these latent values. We chose a combination of two techniques to identify the latent values. The first method used was a wish list. Each interviewee was asked to express what their needs were in terms of security and usability of systems they used within their organizations. The second method, which augments the simple wish list method, was the probing technique. In order to expand the wish list and whenever subjects are having problem articulating what they want, interviewer posed several probing questions prepared beforehand. The list of probing questions included: "If you did not have any constraints, what would your objectives be?" "What needs to be changed from the status quo?" "How do you evaluate security and usability of systems?" "What do you expect in terms of security and usability?" "How do they tell if security and usability of systems is good or bad?" Besides asking the interviewees to generate a wish list, we also asked them to generate a list of problems and shortcomings in security and usability of systems they used. The basic idea behind asking problems and shortcomings was to generate objectives by articulating their concerns. The thirty-five interviews generated three hundred and thirty seven wishes/problems/concerns.

Convert statements into objectives. These statements are converted to objectives, using a verb (direction of change) plus an object (target of change) format. Some statements on the list are compound sentences, which produce more than one objective, and some statements were being repeated by several users. For example, one user wishes "to be educated in moving between different applications and wants help when he gets lost." Two objectives can actually be derived from this wish: (1) ease of navigation through the application and (2) enhance system training quality. To eliminate these ambiguities and redundancies, two researchers reviewed each item on the list independently. This review and refinement produced one hundred and thirty objectives in a common form of a verb plus an object.

In ensuring security and usability, users wanted to achieve these one hundred and thirty objectives. However, these objectives are not adequately articulating values yet, and also include duplication. The objectives were then categorized in order to surface the meanings, and the values attached to cluster the objectives. The categorization resulted in twenty-four clusters of objectives.

As a next step of framing values out of objectives, twenty-four objectives were classified into two categories: means objectives and fundamental objectives. The criterion of classification is whether an objective is an intermediate one, i.e. is it a means to achieve another objective or is it a final and a fundamental one in terms of security and usability. As a result, eight fundamental objectives were identified. The means objectives, a total of sixteen, are presented in Table 1 and fundamental objectives in Table 2. The tables do not show all the individual objectives. These are available from the authors on request. Maximize system capability e.g.: Enhance application features Maximize ease of use e.g.: Ensure ease of navigation through application Maximize system integration e.g.: Ensure functionality is designed into system Maximize standardization of system features e.g.: Enhance customizable interfaces Maximize user requirements elicitation e.g.: Ensure system functionality meets requirements Quantitatively Derived Parsimonious Set of Security and Usability Objectives

Method

In Phase 1, 150 items that influence information systems (IS) usability were developed. These items were based on the total set of 130 objectives identified in phase 1. The additional 20 items were added to ensure that all objectives were well represented in the survey instrument. These items were grouped into two categories of means and fundamental objectives. The means objectives contain 91 questions (items) grouped in 16 clusters (constructs). The fundamental objectives present 59 items grouped in 8 constructs. The large number of items found in both objective sets may have led to redundancy, but it helped content validity, since we were drawing on a large universe of possible items [START_REF] Boudreau | Validation in information systems research: A state-of-the-art assessment[END_REF].

Based on items found in Phase 1, we developed a questionnaire. A five-point Likert-type scale was used, with a range from one (strongly disagree) to five (strongly agree). The respondents were asked to express agreement with 150 questions pertaining to the following context statement -"In order to respond to the questions below, think of any system that you may be using or are familiar with. What would your ideal state be in terms of achieving your objectives?" The survey was administered to graduate and undergraduate students in a European University. We obtained a sample of 201 (30.3% male, 69.7% female) respondents. The respondent rate was 66.3%. The respondents were mature students with work experience in a variety of professions, such as, banking, sales, healthcare, information systems, engineering, education among others areas. The age of the participants ranged from 18 and 50. All participants had experience with security and usability of IS, thus being qualified to answer this survey.

The analysis of the data was undertaken with several goals: purification, reliability, and unidimensionality. The following three steps were used in the elimination process:

1. We eliminated the items if their corrected item-total correlation (the correlation of each item with the sum of the other items in its category) was less than 0.5, because, according to Churchill [START_REF] Churchill | Paradigm for Developing Better Measures of Marketing Constructs[END_REF], all items that belong to the same domain of the concept (construct) should be highly inter-correlated. 2. We eliminated the items if the reliability of the remaining items was at least 0.9. Cronbach's α was computed to see if additional items could be eliminated without substantially lowering reliability. 3. A factor analysis was undertaken with the remaining items for each group to eliminate items that were not factorially pure [START_REF] Weiss | Factor analysis and counseling research[END_REF]. This means that we eliminated items that had a loading greater than 0.3 on more than one factor. The purification of the items was done before the factor analysis, to produce less dimensions and not to confound the interpretation of the factor analysis [START_REF] Churchill | Paradigm for Developing Better Measures of Marketing Constructs[END_REF]. This methodology provides brevity and simplicity of the factor structure.

Data

Means Objectives. We performed the item procedure, described before, to purify the means objectives category. First, corrected item-total correlation of less than 0.5 suggests the elimination of 29 items. Second, the reliability analysis does not eliminate any item. Finally, the factor analysis suggests an elimination of 47 more items.

After the elimination process, 15 items of the means objectives category were obtained. In Table 3, we present the results of the factor analysis using varimax rotation for the retained items. Bartlett's test of sphericity was 1278.4 (p < 0.001). This means that the data contains enough common variance to perform a factor analysis. Kaiser-Meyer-Olkin (KMO) measures the adequacy of the sample; KMO is 0.88 (KMO ≥ 0.80 is good [START_REF] Sharma | Applied Multivariate Techniques[END_REF]), which reveals that the matrix of correlation is adequate for the factor analysis. The results of the factor analysis revealed four factors with eigenvalues greater than one. These factors explain 67.5% of the variance contained in the data. The four factors found were easily interpreted, they are: minimize system interruptions and licensing restrictions (five items), maximize information retrieval (four items), maximize system esthetics (three items), and maximize data quality (three items). The range of loadings is respectively: 0.55-0.73, 0.62-0.74, 0.59-0.81, and 0.56-0.74. All the factors have a loading greater than 0.5. This indicates that our analysis employs a well-explained factor structure.

The range of corrected item-total correlation varies between 0.55 to 0.69 for minimize system interruptions and licensing restrictions, 0.65 to 0.74 for maximize information retrieval, 0.60 to 0.66 for maximize system esthetics, and 0.53 to 0.61 for maximize data quality.

The reliability for each construct was: 0.84 for minimize system interruptions and licensing restrictions, 0.86 for maximize information retrieval, 0.80 for maximize system esthetics, and 0.75 for maximize data quality. The overall reliability for the 15 item scale was 0.88. This reveals that reliability exceeds the suggested cutoff value of 0.70 [START_REF] Nunnally | Psychometric Theory[END_REF].

Fundamental Objectives. To purify the fundamental objectives category we used the same item purification procedure. The first criteria was to eliminate items below 0.5, it allowed us to eliminate 17 of the 59 items obtained in Phase 1. The second criteria, reliability analysis, did not eliminate any items. Finally, the factor analysis suggested the elimination of 30 more items.

Subsequent to the elimination process, the fundamental objectives scale included 12 items. First, Bartlett's test of sphericity was 1292.3 (p < 0.001). These factors explain 76.5% of the variance contained in the data. The KMO is 0.82 (KMO ≥ 0.80 is good [START_REF] Sharma | Applied Multivariate Techniques[END_REF]), which reveals that the matrix of correlation is adequate for factor analysis. This reveals that the data contains enough common variance to perform the factor analysis. Four factors with eigenvalues greater than one is obtained (Table 4), and the interpretation of each factor was not difficult, i.e.: maximize standardization, integration and user requirements (4 items), maximize ease of use (3 items), maximize system capability (3 items), and enhance system related communications (2 items). The ranges for factor loading were, respectively, 0.61-0.86, 0.56-0.85, 0.62-0.75, and 0.87-0.87. All the factors have a loading greater than 0.5. This indicates that our analysis employs a well-explained factor structure.

The range of corrected item-total correlation for each item varies between: 0.61 to 0.78 for maximize standardization, integration and user requirements, 0.59 to 0.74 for maximize ease of use, 0.61 to 0.72 for maximize system capability, and 0.81 to 0.81 for enhance system related communications. The reliability scores were 0.87, 0.83, 0.82, and 0.89 respectively for each construct. The overall reliability for the 18 item scale was 0.88. The reliability exceeds the suggested cutoff value of 0.70 [START_REF] Nunnally | Psychometric Theory[END_REF]. In short, the results obtained in Phase 2 present good reliability and validity measures for both instruments developed (means objectives: 4-factor with 15 items; fundamental objectives: 4-factor with 12 items).

Discussion

The findings from our research present an interesting mix of security and usability objectives that any software developer would find useful. The fundamental objectives identified include: maximize standardization and integration, maximize ease of use, maximize system capability, enhance system related communication. Typically system developers tend to focus on one or the other set of objectives. For instance past research has typically suggested that perceived ease of use effects perceived usefulness and hence behavioral intention to use [START_REF] Venkatesh | Determinants of perceived ease of use: Integrating control, intrinsic motivation, and emotion into the technology acceptance model[END_REF]. However the measures are not entirely useful to a typical system developer (viz. constructs such as perceptions of internal control, computer anxiety, playfulness etc). From a security and usability perspective perhaps ease of system navigation and the general perception of easy to use seem more logical.

Another important aspect as always, is related to system related communications. In the literature various proposals have been made. These have ranged from development of hybrid managers [START_REF] Earls | Hybrid managers -what do we know about them?[END_REF] who can help bridge the gap between technical system developers and actual users to the development of intrinsic competencies for harnessing technology [START_REF] Dhillon | Organizational competence for harnessing IT: A case study[END_REF]. While all these assertions may present significant theoretical opportunities, typically in organizations we are still to see adequate management of interactions between users and the technical staff. Inability to deal with such relationships results in systems getting abused or not properly used. And thus pose significant security challenges.

The importance of standardization and integration in security and usability cannot be underestimated. A casual review of various security and usability standards itself suggests a plethora of options. In the usability community although ISO standards such as ISO 9241 1995 exist, there is lack of consensus with respect to the conformance methods. Dzida [START_REF] Dzida | International usability standards[END_REF] notes, "If a product is claimed to meet a standard, the procedure used in testing the product against the requirements should be specified to guarantee reproducibility of results. Some standards prescribe a certain test method, some recommend a method, and some inform the reader that the procedure used in testing is a matter of negotiation between the parties involved". In information security, while ISO 27799 exists, there are equally other competing standards (viz. SSE-CMM among others). Perhaps one of the reason for the inadequacy of existing standards and an existence of a large set is because of a lack of core objectives that need to be achieved in managing security and usability. More often than not the standards seem to be "cobbled" together to fit a purpose. Our research has identified four rather interesting standardization requirements -standardization of features, functional standardization, interoperability and automated internal controls. As a case in point simply consider academic university websites across institutions. Perhaps some functional and feature standardization would come in handy as would access and availability of information. Failure to do so not only makes it difficult to navigate systems but; opens up institutions to several vulnerabilities (e.g. see website breaches at Utkal University India, St Louis University USA among others).

Our research has found that fundamental objectives for security and usability can be achieved if there is a corresponding appreciation of the means to achieve the fundamental objectives. Means objectives identified in this study include: minimize system interruptions and licensing restrictions, maximize information retrieval, maximize system aesthetics, maximize data quality.

In our study we found that the higher licensing costs and poor quality of systems and data results in bypassing legal software and many of the controls. This can have serious consequences on the integrity of systems. As a consequence, virus and malware problems are also known to creep in. Grabosky and Smith [START_REF] Grabosky | Telecommunication fraud in the digital age: The convergence of technologies[END_REF] has argued that proper guardianship helps in preventing such vulnerabilities. Guardians are also known to facilitate usability of system. Retrieval of information from systems has also been a well-researched topic area and sits at the cusp of security and usability dimensions. Griffith and Jakobsson [START_REF] Griffith | Messin' with Texas deriving mother's maiden names using public records[END_REF] for example note that mother's maiden name, a usual means to retrieve data from financial institutions, can actually be deduced with great accuracy from public records. Some progress has however been made by adding personal knowledge questions for information retrieval, but more so for fallback authentication. From a security and usability perspective enough thought has not gone into the strategic aspects of information retrieval and their relationship to security and usability. Our research indicates it to be an important objective for consideration.

Another important aspect, as identified in our study, pertains to data quality. In the literature poor data quality has been known to have two implications. First, the security of an enterprise gets compromised (see Redman [START_REF] Redman | The impact of poor data quality on the typical enterprise[END_REF]). This is because security is directly linked to the accuracy of data. Second, usability of the system gets questioned. If the system and the data therein is not useful [START_REF] Arts | Defining and improving data quality in medical registries: A literature review, case study, and generic framework[END_REF], is out of context, there is typically a loss of ownership. This results in significant security problems.

Theoretical and practical contributions. The major theoretical contribution of the security and usability objectives presented in this paper is their intertwined nature. Typically security and usability have been treated as separate constructs. At best researchers have pondered about security implications of low usability systems or the implications of highly secure systems on lack of usability (see [START_REF] Yee | Aligning security and usability[END_REF][START_REF] Dewitt | Aligning usability and security: a usability study of Polaris[END_REF][START_REF] Redman | The impact of poor data quality on the typical enterprise[END_REF][START_REF] Arts | Defining and improving data quality in medical registries: A literature review, case study, and generic framework[END_REF]). While both the contentions are worthy of investigation, they fall short of providing a strategic direction for secure and usable system development. We believe that our research provides a theoretical framework for addressing security and usability. The major tenants of our theoretical contribution are:

• Well-grounded security and usability objectives that are based on the values of individuals. Value based objectives are considered much better for strategic planning relative to the alternative based objectives (see [START_REF] Leon | Value-focused thinking versus alternative-focused thinking: Effects on generation of objectives[END_REF]). • Our value proposition combines security and usability. While in the literature calls for aligning the two have been made [START_REF] Dewitt | Aligning usability and security: a usability study of Polaris[END_REF], there has been practically no follow up research. By combining the two constructs we have in many ways presented a well-aligned set of security and usability objectives.

At a practical level, research presented in this paper offers requirement objectives that system developers should use to design security and usability into the systems. Typically security has been considered as an afterthought in the design process [START_REF] Dhillon | Value-focused assessment of information system security in organizations[END_REF]. And usability has been addressed in an iterative manner. While system developers seem to develop their own processes in addressing security and usability concerns, a structured framework is however a preferred approach. We believe that the guidance provided by the security and usability objectives described in this paper forms a solid, theoretically grounded, empirically derived basis for the range of development tasks.

Conclusion

This paper examines the combination of security and usability of systems in two phases. In Phase 1, we developed value-focused security and usability objectives. A qualitative approach revealed 150 objectives, 91 means objectives and 59 fundamental objectives, grouped respectively into 16 and 8 means and fundamental objectives. A quantitative approach was developed in Phase 2, with the aim of purification, reliability and unidimensionality, from which a parsimonious set of security and usability objectives were derived. 15 means objectives were obtained, grouped in four constructs, which are: minimize system interruptions and licensing restrictions, maximize information retrieval, maximize system aesthetics, and maximize data quality. In terms of fundamental objectives, 12 fundamental objectives were obtained, grouped in four constructs, respectively: maximize standardization and integration, maximize ease of use, maximize system capability, and enhance system related communication. We believe that this paper offers a good basis for better understanding of security and usability objectives. Finally, with further research the instruments presented in this paper could be further validated.

Table 1 .

 1 Means objectives

	Means Objectives (16 clusters, 91 items)
	Clarify & improve system documentation	Maximize system access
	e.g.: Ensure easy access to system	e.g.: Define role-based external access
	documentation
	Improve system search capability	Maximize system efficiency
	e.g.: Ensure semantic based search features	e.g.: Ensure process fairness
	Maximize data quality	Maximize system esthetics
	e.g.: Enhance data integrity

e.g.: Enhance visualization of system security Maximize database and system access e.g.: Ensure web access to the system Maximize system integrity e.g.: Maximize system adaptability Maximize disaster recovery e.g.: Ensure data availability Maximize system maintainability e.g.: Ensure hardware robustness Maximize productivity e.g.: Ensure automated password retrieval Maximize system reliability e.g.: Maximize process execution accuracy Maximize security & privacy e.g.: Decrease restrictiveness of system Maximize task efficiency e.g.: Maximize automation of manual tasks Maximize self-efficacy in training e.g.: Enhance system training quality Minimize system interruptions e.g.: Minimize system down-time

Table 2 .

 2 Fundamental objectives

	Fundamental Objective (8 clusters, 59 items)
	Enhance system related communications	Maximize system administration
	e.g.: Ensure exception reports go to	functionality
	management	e.g.: Enhance connectivity at affordable price
	Improve data organization
	e.g.: Ensure data archival functionality

Table 3 .

 3 Factor analysis of means objectives in Phase 2 (n=201)

					Corrected
	F1	F2	F3	F4	Item-Total
					Correlation

Table 4 .

 4 Factor analysis of fundamental objectives in Phase 2 (n=201)

					Corrected
	F1	F2	F3	F4	Item-Total
					Correlation