Chouki Tibermacine
email: chouki.tibermacine@univ-ubs.fr

Régis Fleurquin
email: regis.fleurquin@univ-ubs.fr

Salah Sadou Valoria

On-Demand Quality-Oriented Assistance in Component-Based Software Evolution

Keywords:

During an architectural evolution of a component-based software, certain quality attributes may be weakened. This is due to the lack of an explicit definition of the links between these non-functional characteristics and the architectural decisions implementing them. In this paper, we present a solution that aims at assisting the software maintainer during an evolution activity on his demand. It requires the definition of a documentation during development, organized in the form of bindings between formal descriptions of architectural decisions and their targeted quality attributes. Through an assistance algorithm, the approach uses this documentation in order to notify the maintainer of the possible effects of architectural changes on quality requirements. We also present a prototype tool which automates our proposals. This tool and the overall approach has been experienced on a real-world software in order to validate them.

Introduction

An intrinsic characteristic of software, addressing a real world activity, is the need to evolve in order to satisfy new requirements. Maintenance is now, more than ever, an inescapable activity, the cost of which is ever increasing (between 80 % and 90 % of the software total cost [START_REF] Erlikh | Leveraging legacy system dollars for e-business[END_REF][START_REF] Seacord | Modernizing Legacy Systems: Software Technologies, Engineering Processes, and Business Practices[END_REF]). Among the maintenance activities, the checking of functional and non-functional non regression of a software, after its evolution, is one of the most expensive. It consists in checking the existence of the newly required service or property after modification, on the one hand, and in verifying that the other properties and/or services have not been altered on the other hand. This checking is done during the regression testing stage. When problems are found, a rework on the software architecture is required. This involves a sequence of iterations of the maintenance activities, which make undoubtedly its cost grow more and more.

In this paper, we present an approach which helps to reduce the number of these necessary iterations, in the context of component-based software. It consists of warning the software developer of the possible loss of some quality attributes during an architectural evolution, well before starting regression tests. Under the assumption that the architecture of an application is determined by quality requirements such as, maintainability, portability or availability [START_REF] Bass | Software Architecture in Practice[END_REF], we propose to formally document links between quality attributes and their realizing architectural decisions. Thus, we automate the checking of these quality properties after an architectural change has been made.

In the next section, we show, through a system architecture, how some quality requirements can be mapped into architectural decisions and how problems can rise when evolving this architecture. We present, in section 3, the principles of our approach which helps to resolve the problem pointed in the section before. The proposed solution is based on a documentation, which is introduced in section 4. An algorithm which uses this documentation and assists the maintenance activity is discussed and illustrated by an example in section 5. A prototype tool for evolution assistance, and the validation of the approach are then presented in section 6. Before concluding and presenting the perspectives, we discuss some related works in section 7.

Illustrative Example

Along this paper, we use a simple imaginary example which represents a Museum Access Control System (MACS) 1 . Figure 1 provides an overview of its architecture. The system receives as input the necessary data for user authentication (Authentication component). After identification, the data is sent to the access control component (AccessCtl). The latter consults an authorization database (the component AuthDataStore) to check if the user2 is authorized to enter the museum or not. Then, it adds other data elements (entrance hour, the visited gallery in the museum, etc.) to the received data flow and sends it to the Logging component. The component AdminService allows the administration of the database abstracted by the component AuthDataStore. The Logging component provides an interface for persistent local logging. This interface is used by the archiving data store component (ArchivDataStore) which provides an interface to a data retrieval service component (DataRetrievalService). This component implements an interface which allows local supervision of the museum and querying of logs. The two components AdminService and DataRetrievalService export their interfaces via the same component DataAdminRetrieval. After local archival storage, the data is transmitted (by the component ServerTrans) via the network to the central server of the organization responsible for the museum security for central archival storage.

Some Architectural Decisions and their Rationale

The architecture, described in Figure 1, was designed taking into account quality requirements defined in the NFRs (Non-Functional Requirements) specification. We present some of these requirements and their architectural mappings. 1. "The system should be easily maintained." (We mark this maintainability quality attribute QA1.) This is ensured by the layered pattern [START_REF] Shaw | Software Architecture: Perspectives on an Emerging Discipline[END_REF], which can be seen if we decompose the system's architecture vertically. (We mark this architectural decision AD1.) The sequence of these duplicates is organized as a pipeline [START_REF] Shaw | Software Architecture: Perspectives on an Emerging Discipline[END_REF]. (We mark this decision AD4.) In a pipeline each filter (component) has only one reference to the downstream component. This guarantees a certain level of maintainability (minimal coupling, QA1) required for such emergency solution. This pattern also guarantees a certain level of performance defined in the NFRs specification, but not detailed here. We mark this last quality attribute QA4.

The developers have introduced a data abstraction component (DataRetriv-alService), which abstracts details of the underlying databases. This architectural decision is marked AD5. Indeed, this traditional practice fulfills the first attribute (QA1).

Some Evolution Scenarios and their Consequences

Let us assume that the maintenance team receives two change requests that must be tackled urgently. As a consequence, changes are made without taking into account the associated design documentation. The first request imposes that henceforth some data should be directly transmitted to the central server.

That is, a part of information about service employees should be directly sent to the ServerTrans component after identification. This gives the system more (time and space) performance. Thus, the system maintainers decide to create a link between AccessCtl component and ServerTrans component; and between AccessCtlDup and ServerTrans components. (We mark this change ACG1.) In the last case, the AccessCtlDup component finds itself with two links. The first one with the LoggingDup component for the data flow that is not affected by the modification and the second one with the ServerTrans component for the data that is directly transmitted to the central server. This modification makes the system lose the benefits of the pipeline structure (breaks AD4). Therefore, the initial level of maintainability (QA1) of the system is now weakened. While the first change request has a non-functional goal, the second change is of functional nature. It asks to add a new component representing a notification service: DB UpdateNotification. This component notifies the client applications, subscribed to its services, when updates are done on the archiving database. This new component exports a publish/subscribe interface via the port that provides the interface DataManagement. It implements a publish ondemand interaction pattern and uses directly the component ArchivDataStore. This change (marked ACG2) makes the system lose the benefits of the façade pattern guaranteed by the component DataAdminRetrieval (AD2) and consequently weakens the availability quality attribute QA2.

The lack of knowledge during evolution about the reasons which have led the initial architects to make such decisions, may easily lead to break some architectural decisions and consequently affect the corresponding quality attributes. The two simple examples above illustrate how can we lose such properties. This is often noticed during regression testing. Thus, it is necessary to perform changes on the architecture another time, and to iterate, frequently, for many times. Several similar remarks have been noticed by our industrial partner when evolving one of its complex system (a cartographic converter from different binary files and spatial databases to SVG (Scalable Vector Graphics) format, for using them in a Geographic Information System -GIS-). We didn't present this system as an illustrative example in this paper for reasons of brevity and simplicity.

Principles of the Approach

Our approach aims at solving the problems quoted in the previous section. It consists in making explicit and formal the reasons behind architectural decisions. The choice of a formal language to specify this documentation guarantees not only the unambiguity of descriptions but also allows the automation of some operations, like the preservation of architectural choices throughout the development process of a component-based software [START_REF] Tibermacine | Preserving architectural choices throughout the component-based software development process[END_REF].

Based on the assumption that architectural decisions are determined by the quality information stated in the requirements specification, we propose to maintain the knowledge of the links binding quality attributes to architectural decisions. This knowledge is of great interest for maintainers on two accounts: -Preservation of Quality Attributes: it will be possible to warn the developer, at each architectural maintenance stage, of the potential deterioration of some quality attributes;

-Architecture Comprehension: it is easier to understand a specific architecture when we already know its motivations. Starting from the specification of a targeted evolution, it becomes possible to identify the related architectural artifacts.

In the remaining of this paper, we use some terms which we define as following:

Quality Attribute (QA): a quality characteristic targeted by one of the statements in the non-functional requirements specification; Architectural Decision (AD): a part of the software architecture that targets one or several QAs; Architectural Tactic (AT): a couple composed of an AD and a QA defining the link between one architectural decision and one quality attribute; Evolution Contract (EC): a set of ATs defined for a given software.

These definitions are illustrated in Figure 2. An architectural decision may have several related decisions, which are present in different ATs. For example, AD3 (replicated components) in section 2 has one related decision which is AD4 (pipeline). Indeed, if AD3 is removed from MACS architecture, AD4 will also disappear. As explained in section 4.2, an architectural decision is formalized as an architectural constraint. Each constraint is specified using an architectural predicate language, called ACL. This language has several profiles dedicated to existing architecture/component models, for example xAcme [START_REF]xAcme: Acme Extensions to xArch[END_REF] or CORBA Component Model [START_REF] Omg | Corba components, v3.0, adpoted specification[END_REF] (more details are given in section 4.2). A constraint targets an internal architectural element. Internal architectural elements are architectural abstractions present in the metamodel of the used architecture or component description language (e.g. a component, a connector or an interface). An architectural change is applied on one or many internal architectural elements. It can affect or generate one or several architectural decisions. A QA corresponds to an ISO/IEC 9126 [START_REF]Software engineering -product quality -part 1: Quality model[END_REF] characteristic or sub-characteristic (e.g. maintainability, portability or usability). Each QA has a degree of criticality (inspired from Kazman's QA scores and Clements's QA priorities [START_REF] Clements | Evaluating Software Architectures, Methods and Case Studies[END_REF]). The value of this degree, specified by developers, stipulate the importance of this quality attribute in the architecture. It takes values between 1 and 100. The sum of values of all these degrees should be at most 100. Starting from non-functional requirements (NFRs), we may extract one or several QAs. Each one is attached to several external architectural elements. These elements represent the common externally visible architectural concepts present in existing component models (component, interface and operation). These external architectural elements are a subset of internal architectural elements.

Capturing Architecture Decisions and their Rationale in Contracts

Based on the structure presented above, to document an architecture, we need a language for defining evolution contracts and a tool set to edit and interpret this documentation.

Evolution Contract Organization

In order to specify textually ECs, we use an XML representation which conforms to the structure presented in Figure 2. The following listing illustrates an example of such specification.

<evolution-contract id = "000001"> <architecture-tactic id = "000100"> <description> This tactic ensures the Portability quality requirement by using a Facade Design Pattern </description> <quality-attribute id = "001000" name = "Portability" characteristic = "Portability"> <description>

The software system should be portable over different environments. It can serve different applications for museum supervision or access control data administration </description> </quality-attribute> <architecture-decision id = "010000"> <description> Facade design pattern </description> <formalization profile = "Fractal"> <!--Here we edit the ACL constraint--> </formalization> </architecture-decision> </architecture-tactic> </evolution-contract>

This simple example illustrates a simple EC composed of only one of the ATs presented in section 2. This AT concerns the façade design pattern AD associated to the portability QA. The formalization element of this EC contains the formal definition of the AD which is described in the next section.

AD Definition Language

In order to formalize architectural decisions, we proposed a predicate language called ACL (Architectural Constraint Language). This language is based on a slightly modified version of UML's Object Constraint Language [START_REF]OMG. Uml 2.0 ocl final adopted specification[END_REF], called CCL (Core Constraint Language), and on a set of MOF metamodels. Each metamodel represents the architectural abstractions used at a given stage in the component-based development process. A couple formed by CCL and a given metamodel represents an ACL profile. Each profile can be used at a stage in the development process. We defined ACL profiles for xAcme, UML 2 [START_REF]OMG. Uml 2.0 superstructure final adopted specification[END_REF], CORBA components, Enterprise JavaBeans [START_REF]Enterprise javabeans(tm) specification[END_REF] and many others. CCL navigates in the architecture's metamodel in order to define constraints on its elements.

Instead of presenting the grammar of ACL, we preferred to illustrate it through the description of two AD examples from section 2.1. We describe this ADs using the standard profile of ACL, which is composed of CCL and of a generic architecture metamodel called ArchMM [START_REF] Tibermacine | Preserving architectural choices throughout the component-based software development process[END_REF]. This metamodel is used as an intermediate representation when transforming ACL constraints from one profile to another.

The listing below describes the constraint enforcing the façade architectural pattern in the component MACS. This constraint states that the DataManagement provided interface of MACS component must be bound internally to one and only one interface. The latter corresponds to the provided interface of DataAdminRetrieval component.

The following constraint concerns the replicated components stated by AD3. This constraint uses two operations from ArchMM. The first one (getIntern-alComponent()) returns the subcomponent attached to a given port of a composite component. The second operation (getPaths(c1:Component,c2:Component)) returns an ordered set of all the paths between the components given as parameters. The returned paths are also represented by ordered sets of components. A returned path excludes the parameter components. The constraint states that it must exist two distinct paths between the component attached to UserAuthentication port and the component attached to CentralServerArchiving port.

The two-level expression nature of ACL guarantees the homogeneity of constraints defined in different stages of the development process. Indeed, only metamodels change from one stage to another; the core constraint language remains the same. This has been of great interest when we performed transformations of constraints from one stage to another in order to automatically preserve architectural decisions [START_REF] Tibermacine | Simplifying transformations of architectural constraints[END_REF].

Using Contracts in Evolution Assistance

In the proposed approach, an AT is perceived as a constraint which has to be checked for validity during each evolution. An evolution contract may be seen as a contract, because it documents the rights and the duties of two parties: the developer of the previous version of the architecture who guarantees the quality attributes and the developer of the new version who should respect the evolution contract established by the former. The evolution contract is elaborated during the development of the first version of the architecture. ATs appear in each development stage where a motivated AD is made. Thus, the evolution contract is built gradually and enriched as the project evolves. ATs can even be inherited from a Software Quality Plan and thus, can emerge even before starting the software development. Thereafter, this evolution contract can be modified in respect of the rules below:

-Rule 1: "a consistent system is a system where each QA is involved in at least one AT ". This condition ensures that, at the end of the maintenance process, there is no dangling QA (i.e. with no associated ADs). The breach of this condition implies de facto the obligation to modify the non-functional specification; -Rule 2: "we should not prohibit an evolution stage. We simply notify, at the demand by the developer of a change validation, the attempt of breaking one or more ADs and we specify the affected QAs stated in the evolution contract". It is of the developer's responsibility, fully aware of the consequences, to maintain or not the modification. If this modification is maintained, the corresponding ATs are discarded. Indeed, The substitution of an architectural decision by another may be done without affecting the targeted quality attributes. Moreover, we can be brought to invalidate, temporally, a decision to perform a specific modification; -Rule 3: "we can add new ATs to the evolution contract". Thus, during an evolution, new architectural decisions can complete, improve or replace old ones.

The previous rules are illustrated by the simple architectural maintenance scenario in Figure 3. Consider the previous example presented in section 2. The evolution contract associated to the MACS component, which contain 6 ATs, is illustrated in the bottom part of the figure. Note that for reasons of simplicity we organized the evolution contract by factorizing QAs. Architectural changes are represented at the top of the figure. The minus symbol stipulates that the corresponding AD has been affected, and the plus symbol shows that the AD is preserved or enhanced. Forward arrows mean that the architectural maintainer decides to validate her/his change, however backward arrows mean she/he does not maintain her/his decision. At the middle of the figure, we illustrate the evolution of the assistance system, the different warnings that it triggers and the validation or not of the different intermediate evolution contracts.

Assistance System Side AD1 AD5 AD4 AD2 AD3 AD1 AD5 AD1 AD5 AD1 AD5 QA1 QA2 QA3 QA4 QA1 QA2 QA3 QA4 QA1 QA2 QA3 QA4 QA1 QA2 QA3 QA4 QA1 QA2 QA3 QA4 Side Developer ACG1 ACG2 ACG3 ACG4 AD4 - AD4 - AD4 - AD4 - AD4 State AD4 AD4 AD4 AD4 AD4 AD2 AD3 AD1 AD5 AD6 + AD2 - AD2 - AD2 - AD3 - AD3 - AD3 AD3 AD6 AD3 EC QA1 QA4 AD2 QA2 AD4 QA1 AD4 AD4 QA1 AD2 QA2 AD3 QA3 AD4 QA4 QA1 AD2 QA2 AD3 QA3 AD4 QA4 AD6 QA2

Fig. 3. Assisting the evolution activity with evolution contract

Let us suppose that a software maintainer applies ACG1, which was presented in section 2, to MACS architecture (second column of figure 3). As stated in that section, this change affects AD4. The assistance algorithm checks the ACL constraint present in MACS's EC which is associated to this decision, and consequently warn the maintainer that AD4 is altered and that QA1 and QA4 are also possibly affected. Knowing that ACG1 enhances QA4 -AT6(QA4,AD4) not affected-, the maintainer decides to validate his change. The EC is considered valid, while there is no QA without associated ADs (see the second table in the bottom of the figure).After that, the maintainer decides to apply ACG2, which was also presented in section 2. He is thus notified that AD2 and its associated QA, namely QA2, are potentially affected. He decides to continue, but the EC is in this case not valid, as soon as there is one QA (QA2) without associated AD (see the third table in the bottom of the figure). Later, the maintainer tries to apply ACG3. This change consists in removing the LoggingDup component. Concretely, the system maintainer discovered that data in this com-ponent is not consistent with data in the ArchivDataStore component. He is immediately notified that ACG3 alter AD3 (replicated components) and consequently QA3 (availability property) will be eventually affected. In addition, this AD has one related decision, namely AD4 which represents the pipeline pattern. The assistance system, by scanning the EC, warns the maintainer that AD4 and QA1 (Maintainability) and QA4 (Performance) are also affected. This time, the maintainer does not keep his changes and undoes the changes made on the architecture. Note that, the EC is still invalid. Finally, the maintainer decides to make a new architectural change (ACG4). It consists in removing the hierarchical connector between the newly added notification sub-component (DB UpdateNotification) and MACS's DataManagement port, and adding a new connector between the former and the component DataAdminRetrieval. The motivation behind adding this new AD, marked AD6, is to re-ensure the portability quality characteristic and thus reintroduce QA2 in the EC. In this case, all QAs have corresponding ADs. The contract is thus considered valid.

Evolution Assistance Prototype Tool & Validation

In order to validate our approach we developed a prototype tool, called AURES (ArchitURe Evolution aSsistant), which allows the edition, the validation and the evaluation of ECs. In addition, it assists the software developer during an evolution operation. We experienced our approach with our industrial partner on real-world software system they developed the last year. We present in the following subsections the prototype tool, its structure and how it operates. After that, we introduce how we validated our approach.

AURES Architecture

This tool is organized as in Figure 4 and is composed of the following elements: architecture evolver is warned that some ADs are altered and that consequently the associated QAs are affected. EC Evaluator: To evaluate an EC, this component uses a temporary pivot model and the ArchMM metamodel. The pivot model is a direct instance of ArchMM, produced by the Description Transformer subcomponent, from a given architecture description. This subcomponent executes a set of XSL scripts to make XML transformations of architecture descriptions. For the moment, the prototype presented in this paper supports architectures described in the Fractal ADL [START_REF] Bruneton | An open component model and its support in java[END_REF] and in xAcme. However, the pivot model makes the tool easily extensible. The EC Evaluator is composed of an ACL Compiler which extends the OCL Compiler [START_REF] Loecher | A Metamodel-Based OCL-Compiler for UML and MOF[END_REF] and which requires the AD part of the EC. It also contains an ACL Interpreter, which evaluates ACL boolean expressions. Note that, this component is used by two other components: the EC Validator and the Evolution Assistant. When it is invoked by the first one, only constraints involving one version of the architecture are evaluated. However, if it is requested by the second one, all constraints are evaluated. The latest architecture description is checked out with the EC and transformed to the pivot model to be evaluated.

Example of Use

Let us consider one of the evolution scenarios presented in section 2.2. This concerns the addition of a component representing a notification service. Once this new architecture description introduced to the Evolution Assistant component, the latter checks out the EC corresponding to MACS from the component Version Handler and then displays a warning report. This report notifies the architecture evolver that the Façade pattern does not hold anymore and that the portability property has been affected. The architecture evolver should either modify his new architecture description, or the EC and consequently the NFRs specification.

Validation of the Approach

We experienced our approach on Alkanet, a GIS developed by our industrial partner. The project cost has been estimated at 2500 men-hours and its maintenance cost at 1400 men-hours. Starting from maintenance logs, we took the software components that have been the most affected by the maintenance. These components perform the conversion of different types of data format to SVG.

A team composed of developers, who know the initial NFRs specification, has documented these components (their initial version) by the necessary evolution contracts. After that, starting from this documented version of the components, another group of developers, equivalent to that who has performed the maintenance initially, has performed the same set of evolution scenarios as in logs.

They use AURES for validating changes on the components after applying each scenario. We noticed that the maintenance cost has been reduced by 35 %. Indeed, we passed from 600 men-hours estimated for the maintenance of the converter components to 390 men-hours. It is true that the chosen components are the most complex. For components of less complexity, the gain would be undoubtedly less. But, the most complex components have the highest maintenance costs (Lehman's 2nd law of system evolution [START_REF] Lehman | Software evolution in the age of component-based software engineering[END_REF]). This allowed us to extrapolate this result on the whole application without a lot of errors. According to the developers' declarations, evolution contracts helped them to better understand the architecture of the software to evolve. Furthermore, automatic checking of architectural constraints has been of great benefit.

Related Work

Capturing and documenting design rationale is a research challenge, with an increased interest in the software engineering community [START_REF] Tang | A survey of the use and documentation of architecture design rationale[END_REF]. Within the context of software architecture, Tyree and Akerman in [START_REF] Tyree | Architecture decisions: Demystifying architecture[END_REF] discussed the importance of documenting architecture decisions and making them first-class entities in architecture description. They present a template to describe them at a high-level of abstraction during development. Their paper focuses on the methodological aspect of describing these templates and not on how they can be used when evolving an architecture as in our approach. In the architecture evolution field, Lindvall et al. presented a survey on techniques employed in diagnosing or researching degeneration in software architectures and treating it [START_REF] Hochstein | Combating architectural degenration: A survey[END_REF]. Architecture degeneration is seen as the deviation of the actual architecture from the planned one. Many of the technologies presented in this paper focus on recognition of architecture styles and design patterns, and their extraction from code. This helps to identify deviations by comparing architectures and their properties before and after an evolution. The authors also discuss visualization techniques of architectural changes to understand software evolution and thus deduce degenerated portions in the evolved architecture. For treating this degeneration, the authors present a survey of existing refactoring techniques. Our approach allows the degeneration identification by checking formal documents (evolution contracts) on architecture descriptions before and after evolution. It alerts software evolvers about degenerated components in the architecture and the consequences of this degeneration on quality requirements. It then assists them by using quality information to treat this degeneration.

As in software architecture evaluation methods like ATAM or SAAM [START_REF] Clements | Evaluating Software Architectures, Methods and Case Studies[END_REF], our approach forces the architect to create architecture documentation. However, while these evaluation methods are applied during design to detect if a given architectural decision is risky or not according to quality requirements; in our approach, we assume that a posteriori all decisions are non-risky and we care about their preservation during evolution. Our approach can be seen as a complementary technique to these methods and is used downstream. In this manner, we may use an evaluation method only during analysis/design stage and avoid its use after each evolution.

In the literature, non-functional properties (which include quality attributes) has been supported on the software development through two approaches. The first one is process-oriented, while the second is product-centric. In the first approach, methods for software development driven by NFRs are proposed. They support NFR refinement to obtain a software product which complies to the initial NFRs [START_REF] Mylopoulos | Representing and using nonfunctional requirements: A process-oriented approach[END_REF][START_REF] Cysneiros | Nonfunctional requirements: From elicitation to conceptual models[END_REF]. In the second approach, the non-functional information is embedded within the software product. It is the case in our approach, where evolution contracts, which embed statements of NFRs, are associated to architectural descriptions. In [START_REF] Franch | Supporting software maintenance with non-functional information[END_REF], Franch and Botella propose to formalize non-functional requirement specifications. The statements of these specifications are encapsulated in modules, which are associated to a component definition and to its implementations. They propose also an algorithm, which allows the selection of the best implementation for a given component definition. This selection method can be used when a new implementation is proposed to ensure that the best one is used. The authors mean by "best", the implementation that better fits to its non-functional requirements. In our work, we focus on the architectural (structural) aspect of components, while they consider the abstract data type view of components. In addition, in our case, the maintenance is performed on architectural descriptions or component configurations while changes in their approach are made at a fine-grained implementation level.

Conclusion & Future Work

In early 1990's, Perry and Wolf presented a model for software architectures. This model represents software architectures in the form of three basic abstractions: Elements, Form and Rationale [START_REF] Perry | Foundations for the study of software architecture[END_REF]. Elements are architectural entities responsible for processing and storing data or encapsulating interactions. Form consists of properties -constraints on the choice of elements-and relationships -constraints on the topology of the elements-. The Rationale captures the motivation for the choice of an architectural style, the choice of elements and the form. While the description of the two first aspects have received a lot of attention by the software architecture community [START_REF] Medvidovic | A classification and comparison framework for software architecture description languages[END_REF], there has been a little effort devoted to the last aspect. In this paper, we presented evolution contracts, as a contribution to the description of the last element in Perry's model. This evolution contract leads to make explicit and checkable architectural decisions (Elements and Form in Perry's model). Thus, it is possible to assist architectural evolution activity and prevent the loss of quality attributes (Rationale in Perry's model). It is, as we think best, a good practice for documenting software architectures and design rationale, and thus facilitating software comprehension in maintenance activities.

On the conceptual level, we plan studying: i) reusability, substitution and extension of ECs, and ii) quality quantification by associating metrics to QAs. This helps to better assist the maintenance activity. On the tool level, we project to stabilize the prototype before integrating it in a CASE tool. This would guide, in a continuous way, the system maintainer. We are also studying the feasibility of integrating the tool in a Configuration Management System. We limit our study to CMS dedicated to software architectures, like Mae [START_REF] Roshandel | Mae -a system model and environment for managing architectural evolution[END_REF]. Thus we take advantage from the enhanced control version capabilities of these systems.

Fig. 1 .

 1 Fig. 1. A Simplified architecture of a Museum Access Control System

Fig. 2 .

 2 Fig. 2. Structure of Contracts

  context MACS:CompositeComponent inv: let boundToDataManagement:Bag=MACS.port.interface ->select(i:Interface|i.kind = 'Provided' and i.name = 'DataManagement').port.binding in ((boundToDataManagement->size() = 1) and (boundToDataManagement.interface ->select(i:Interface|i.kind = 'Provided').port.component.name ->includes('DataAdminRetrieval')))

  context MACS:CompositeComponent inv: let startingPort:Port=MACS.port->select(p:Port| i.name='UserAuthentication') in let startingComponent:Component=startingPort.getInternalComponent() in let endingPort:Port=MACS.port->select(p:Port| i.name='CentralServerArchiving') in let endingComponent:Component=endingPort.getInternalComponent() in let paths:OrderedSet=MACS.configuration .getPaths(startingComponent,endingComponent) in paths.size() = 2 and paths->first()->excludesAll(paths->last())

EC Editor:Fig. 4 .

 4 Fig. 4. A prototype tool for ECs edition and interpretation, and for evolution assistance

  AccessCtlDup authorizes the access only to service employees. Logs remain in the state of the component LoggingDup and are not persistent in the ArchivDataStore component. Then, the data is transmitted to the central server.

[START_REF] Bruneton | An open component model and its support in java[END_REF]

. "The software system should be portable over different environments. It can serve different applications for museum supervision or access control data administration." (This portability property is marked QA2.) To reach this portability level, a façade component -with analogy to façade objects

[START_REF] Gamma | Design Patterns: Elements of Reusable Object-Oriented Sofware[END_REF]

was designed as front to MACS's internals. In Figure

1

, this is performed by the component DataAdminRetrieval. All communications from client applications to access MACS's data management services transit by this component. (We mark this architectural decision AD2.) 3. "The access control functionality should be more available for service employees." (We mark this availability property QA3) In the bottom of Figure

1

, the sequence of components AccessCtl and Logging is duplicated. This redundancy scheme (marked AD3) is a mean to make the system fault tolerant and thus fulfills the availability requirement. If one of the two components (AccessCtl or Logging) fails, the sequence below (AccessCtlDup and LoggingDup) takes over the process. In this degraded mode of the system functioning, the component

This software system is not a real-world component-based one. We just defined a few years ago within a development project a formal specification of it. We think that it is simple to present and to use as an illustrative example.

Users of the museum are visitors, exhibition organizing committee members, museum administrative and service employees


Jean-François Ponge
email: jean-francois.ponge@wanadoo.fr

Ipsa Bandyopadhyaya

Valérie Marchetti

Interaction between humus form and herbicide toxicity to Collembola (Hexapoda)

Keywords: Herbicides, Humus, Collembola, Communities, Isoproturon

Laboratory experiments were conducted using intact collembolan communities, exposed to Madit D®, a phenylurea herbicide (active ingredient isoproturon). Effects two distinct humus types, an acid Dysmoder and a neutral Eumull. Within two weeks, no effect of the herbicide was displayed by the Eumull population, while the Dysmoder population was stimulated. When animals were able to escape from the herbicide through a perforated wall separating two compartments filled with natural soil, the behaviour of collembolan communities exhibited interactive (non-additive) effects of humus type and herbicide application. The combination of an acid soil (supposedly providing greater tolerance to organic pollutants) with a neutral soil increased biodiversity of Collembola, but caused the disappearance of some acido-sensitive species, pointing to complex relationships between pesticides, soils and soil organisms. Parallel experiments with single species demonstrated that at the recommended dose Madit D® may cause avoidance effects, but no toxicity.

Introduction

Numerous studies have assessed the impact of herbicides on soil fauna, but contradictory results have been obtained, depending on animal groups studied, chemical nature of the herbicide and additives, soil type and rate of application [START_REF] Rapoport | Herbicides and the soil fauna[END_REF][START_REF] Edwards | Effects of pesticide residues on soil invertebrates and plants[END_REF][START_REF] Edwards | The influence of agricultural practice on soil micro-arthropod populations[END_REF][START_REF] Curry | The effects of different methods of new sward establishment and the effects of the herbicides paraquat and dalapon on the soil fauna[END_REF][START_REF] Van Der Drift | Pesticides and soil fauna[END_REF][START_REF] Fratello | Effects of atrazine on soil microarthropods in experimental maize fields[END_REF][START_REF] Mallow | Effects of different management practices on Collembola and Acarina in corn production systems. II. The effects of moldboard plowing and atrazine[END_REF][START_REF] Prasse | Indications of structural changes in the communities of microarthropods of the soil in an agro-ecosystem after applying herbicides[END_REF][START_REF] Chalupský | The influence of Zeazin 50 on Enchytraeidae (Oligochaeta) in an apple orchard soil[END_REF][START_REF] Krogh | Perturbation of the soil microarthropod community with the pesticides benomyl and isofenphos[END_REF]. Before standardized laboratory tests were developed some authors claimed that there was no direct effect of herbicides on soil animals and that most increases or decreases of populations were indirect effects, mostly caused by vegetation changes [START_REF] Curry | The effects of different methods of new sward establishment and the effects of the herbicides paraquat and dalapon on the soil fauna[END_REF][START_REF] Edwards | Pesticides and the soil fauna[END_REF][START_REF] Chalupský | The influence of Zeazin 50 on Enchytraeidae (Oligochaeta) in an apple orchard soil[END_REF]. Nevertheless, under standardized conditions without interference from vegetation, herbicides differ strongly in toxic as well as stimulatory effects when applied at field doses [START_REF] Eijsackers | Side effects of the herbicide 2,4,5-T affecting mobility and mortality of the springtail Onychiurus quadriocellatus Gisin (Collembola)[END_REF][START_REF] Subagja | The side effects of the herbicides atrazine and paraquat upon Folsomia candida and Tullbergia granulata (Insecta, Collembola)[END_REF][START_REF] Eijsackers | Litter fragmentation by isopods as affected by herbicide application[END_REF][START_REF] Van Gestel | Comparison of sublethal and lethal criteria for nine different chemicals in standardized toxicity tests using the earthworm Eisenia andrei[END_REF].

Despite fruitful efforts to standardize methods [START_REF] Riepert | Development of laboratory methods for testing effects of chemicals and pesticides on Collembola and earthworms[END_REF][START_REF] Crouau | The use of Folsomia candida (Collembola, Isotomidae) for the bioassay of xenobiotic substances and soil pollutants[END_REF] some uncertainty is inherent in the representativeness of ecotoxicological studies for field conditions, given what we know about avoidance and dispersion behaviour of Collembola [START_REF] Ulber | Einfluss von Zuckerrüben-Herbiziden auf Mortalität und Verhalten von Onychiurus fimatus Gisin (Collembola, Onychiuridae)[END_REF][START_REF] Duelli | Population movements of arthropods between natural and cultivated areas[END_REF][START_REF] Mebes | A method for estimating the significance of surface dispersal for population fluctuations of Collembola in arable land[END_REF]Alvarez et al., 2000). Acute toxicity levels given by standardized indices such as LOEC or EC 50 [START_REF] Reinecke | A review of ecotoxicological test methods using earthworms[END_REF][START_REF] Forbes | Ecotoxicology in theory and practice[END_REF][START_REF] Riepert | Development of laboratory methods for testing effects of chemicals and pesticides on Collembola and earthworms[END_REF][START_REF] Crouau | The use of Folsomia candida (Collembola, Isotomidae) for the bioassay of xenobiotic substances and soil pollutants[END_REF]) may be irrelevant for risk assessment if field animals are killed by moving to untreated but unfavourable micro-sites at doses far below recommended levels. The reversibility of local changes in habitat use, induced by pesticides, can also be questioned, given the large variation in recovery processes from one species to another (Alvarez et al., 2000). Given what we know about the behaviour of whole animal communities compared to single species facing experimental stresses, and strong interactions between animal species [START_REF] Haukka | Growth and survival of Eisenia fetida (Sav.) (Oligochaeta: Lumbricidae) in relation to temperature, moisture and presence of Enchytraeus albidus (Henle) (Enchytraeidae)[END_REF][START_REF] Hågvar | Reactions to soil acidification in microarthropods: is competition a key factor?[END_REF][START_REF] Ponge | Interaction between soil fauna and their environment[END_REF][START_REF] Salmon | Distribution of Heteromurus nitidus (Hexapoda, Collembola) according to soil acidity: interactions with earthworms and predator pressure[END_REF], community-level effects must be suspected, which are not taken into account in standardized tests using mass cultures of single species [START_REF] Van Gestel | Comparison of sublethal and lethal criteria for nine different chemicals in standardized toxicity tests using the earthworm Eisenia andrei[END_REF]. Thus there is a need for field-and laboratory-based tests using communities [START_REF] Frampton | The potential of Collembola as indicators of pesticide usage: evidence and methods from the UK arable ecosystem[END_REF][START_REF] Urzelai | Biotic indices based on soil nematode communities for assessing soil quality in terrestrial ecosystems[END_REF][START_REF] Cortet | Impact de produits phytopharmaceutiques sur les microarthropodes du sol en culture de maïs irrigué: approche fonctionnelle par la méthode des sacs de litière[END_REF] if we want to become more realistic in ecological risk assessment [START_REF] Van Straalen | Ecological approaches in soil ecotoxicology[END_REF][START_REF] Van Straalen | Ecotoxicological risk assessment of soil fauna recovery from pesticide application[END_REF][START_REF] Suter | Ecological risk assessment for contaminated sites[END_REF].

From our knowledge of the biochemical properties of soils at varying levels of acidity and organic matter content [START_REF] Coulson | Polyphenols in plant, humus, and soil. I. Polyphenols of leaves, litter, and superficial humus from mull and mor sites[END_REF][START_REF] Davies | Polyphenols in plant, humus, and soil. IV. Factors leading to increase in biosynthesis of polyphenol in leaves and their relationship to mull and mor formation[END_REF][START_REF] Lindqvist | The interaction between a humic acid and a charge-transfer acceptor molecule[END_REF][START_REF] Petersen | Comparison of the biological effects of humic materials under acidified conditions[END_REF][START_REF] White | Monoterpenes: their effects on ecosystem nutrient cycling[END_REF], it may be hypothesized that organisms living in acid organic soils are more tolerant of phenolic and terpenic compounds than organisms living in neutral organo-mineral soils [START_REF] Hågvar | Collembola in Norwegian coniferous forest soils. III. Relations to soil chemistry[END_REF][START_REF] Poinsot-Balaguer | Effects of tannin compounds on two species of Collembola[END_REF][START_REF] Ponge | Biocenoses of Collembola in atlantic temperate grass-woodland ecosystems[END_REF][START_REF] Loranger | Does soil acidity explain altitudinal sequences in collembolan communities?[END_REF]. Thus, the effects of pesticides on non-target organisms can be expected to vary according to soil features, in particular acidity, organic matter, clay and water content, not only because of the impact of these factors on the fate of organic compounds [START_REF] Mortland | Clay-organic complexes as adsorbents for phenol and chorophenols[END_REF][START_REF] Müller-Wegener | Electron donor acceptor complexes between organic nitrogen heterocycles and humic acid[END_REF][START_REF] Laszlo | Chemical reactions on clays[END_REF][START_REF] Stehouwer | Characteristics of earthworm burrow lining affecting atrazine sorption[END_REF]Akhouri et al., 1997), but also because of different tolerance levels of different soil biocenoses. The latter point has remained unstudied until now. Springtails (Class Collembola, Phylum Arthropoda) were chosen, due to their abundance and diversity in most soils [START_REF] Petersen | A comparative analysis of soil fauna populations and their role in decomposition processes[END_REF][START_REF] Ponge | Soil fauna and site assessment in beech stands of the Belgian Ardennes[END_REF][START_REF] Hopkin | Biology of the springtails (Insecta: Collembola)[END_REF] and marked shifts in species composition caused by changes in acidity [START_REF] Hågvar | Collembola in Norwegian coniferous forest soils. III. Relations to soil chemistry[END_REF][START_REF] Ponge | Biocenoses of Collembola in atlantic temperate grass-woodland ecosystems[END_REF][START_REF] Chagnon | Relationships between soil chemistry, microbial biomass and the collembolan fauna of southern Québec sugar maple stands[END_REF][START_REF] Loranger | Does soil acidity explain altitudinal sequences in collembolan communities?[END_REF].

In addition to laboratory bio-assays in semi-natural conditions, using two undisturbed acid and neutral soils, attraction or avoidance of a herbicide by Collembola was assessed on impregnated filter paper, using two different species coming from the same soils.

Materials and methods

Laboratory tests using complete communities

Experiments were performed on natural soils, with undisturbed animal communities, to which a herbicide (Madit D®, with isoproturon as the active molecule) was applied at doses and in the same way as in conventional agriculture. In order to test simultaneously the effects of herbicide application and of acid humus inoculation, two different soils, the hemorganic A horizon from a neutral (pH 7.5) Eumull and the holorganic O horizon from an acid (pH 4.3) Dysmoder [START_REF] Brêthes | Classification of forest humus forms: a French proposal[END_REF], were put together in two-compartmented boxes, with or without the addition of herbicide to one or both compartments. Other experiments used the same soil in both compartments, with and without herbicide.

The neutral hemorganic Eumull was considered to be a reference for agricultural soils, harbouring more complete faunal communities due to organic matter input and the absence of pesticide use and deep ploughing (Ponge, 2000b). Previous studies had shown that agricultural soils and forest soils did not differ fundamentally when soil-dwelling communities were considered [START_REF] Ponge | Biocenoses of Collembola in atlantic temperate grass-woodland ecosystems[END_REF]. The acid organic Dysmoder was used as a possible source for the introduction of more tolerant strains of soil animals in agricultural soils.

Boxes made of moulded polystyrene (175 x 115 x 65 mm LxWxH) were used for these experiments. A 2 mm thick wall made of polymethylmethacrylate was perforated (400 holes, 2 mm diameter each) then inserted in the central part of each box, dividing it into two connected compartments 650 mL each. Small arthropods (including springtails) and worms (nematodes, enchytraeids, small epigeic earthworms) were expected to cross the wall easily, following preliminary experiments using defaunated soil (data not shown). There was no contact between the soils present in the two compartments. Thus only animals and gases could move between compartments.

OF (fragmented) and OH (humified) organic horizons of a Dysmoder humus profile (10 cm deep) were collected in a mixed forest stand (Senart forest, 20 km southwest of Paris), made of sessile oak (Quercus petraea (Mattus.) Liebl. and Scots pine (Pinus sylvestris L.), then gently homogenized by hand in a plastic sheet before being added to the appropriate compartments. Stones, large roots and large pieces of wood were removed during the homogenizing process. The same method was used for collecting the A (organo-mineral) horizon of a calcic Eumull profile in a hornbeam stand (Carpinus betulus L.) in the park adjacent to the laboratory (close to the Senart forest). Compartments were filled with humus, leaving only the top 1cm free of soil, thus each compartment held ca. 500 mL of soil.

The herbicide Madit D® comprised 50% (w/v) isoproturon. It was applied at a rate of 3

L. ha -1
, which is the rate prescribed for the current control of annual grasses and broad-leaved weeds. For that purpose each compartment receiving the herbicide (1 square decimeter) was sprayed with 1.5 mL of a diluted solution containing 3 µL of the herbicide. Thus 1.5 mg of isoproturon was applied to each compartment, corresponding to a nominal concentration of 5.6 mg.kg -1 dry weight for the Eumull and 23 mg.kg -1 dry weight for the Dysmoder. Boxes were then closed and randomly placed in a dark chamber at constant temperature (15°C) for two weeks.

The At the end of the experiment, the twin boxes were thoroughly voided and the soil samples corresponding to the 100 compartments were separately extracted in Berlese funnels.

Soil samples (500 mL) were gently spread on a large size wire net (5 mm mesh size, 20 cm diameter), in order to avoid possible barrier effects of surface-applied pesticides during extraction [START_REF] Krogh | Perturbation of the soil microarthropod community with the pesticides benomyl and isofenphos[END_REF]. During the 10-d extraction the soil was gently heated by 25 W bulb lamps in order to avoid too rapid desiccation. Animals collected under the desiccating soil were preserved in 95% ethyl alcohol before being sorted under a dissecting microscope. Collembola were mounted in chloral-lactophenol (25 ml lactic acid, 50 g chloral hydrate, 25 ml phenol) and identified to species under a phase contrast microscope at x400 magnification. [START_REF] Gisin | Collembolenfauna Europas[END_REF] was used as a reference book but several more recent identification keys and diagnoses were used additionally, including [START_REF] Zimdars | Synopses on palaearctic Collembola[END_REF], [START_REF] Jordana | Fauna Iberica. VIII. Collembola Poduromorpha[END_REF], [START_REF] Fjellberg | The Collembola of Fennoscandia and Denmark. I. Poduromorpha[END_REF] and [START_REF] Bretfeld | Synopses on palaearctic Collembola[END_REF].

The basic data consisted of animal densities and number of species per compartment.

An additional index was calculated as the ratio between the number of species and the number of individuals. It was referred to as the relative richness. Comparisons between treatments were done at the species level or at the community level, using Kruskal-Wallis tests for comparisons of means when replicates of compared treatments were independent (not in the same boxes) or

Friedman tests for paired comparisons when two compartments within the same box were compared [START_REF] Sokal | Biometry. The principles and practice of statistics in biological research[END_REF]. When the two compartments received the same treatment, values were averaged for each box and used for comparisons with other treatments. Given that extraction efficiency could vary from one humus type to another [START_REF] Macfadyen | Animal ecology. Aims and methods[END_REF], comparisons between Eumull and Dysmoder should be made with care. Thus most conclusions were based on comparisons between treatments applied to the same humus type. Despite the (apparent) factorial design of the experiment, data could not be analysed by multi-way ANOVA, since i) humus types were too different in their chemical and biological properties to expect additive effects of humus type and herbicide, ii) compartments within a box were not independent from each other.

Laboratory tests using single species

Two collembolan species, Heteromurus nitidus (Entomobryidae), living in the Eumull, and Folsomia manolachei (Isotomidae), living in the Dysmoder, were previously reared on an artificial substrate used for standardized tests [START_REF] Riepert | Development of laboratory methods for testing effects of chemicals and pesticides on Collembola and earthworms[END_REF], made of a mixture of 10% sphagnum peat, 20% kaolinite and 70% fine quartz sand. The pH of the artificial substrate was brought to 6.2 by adding 0.45% calcium carbonate. The substrate was moistened to 50% of water holding capacity by adding deionized water. Cattle dung powder was given as additional food when necessary. Cultures were kept in the dark at 15°C. Before each experimental run, animals were conditioned for 20 min to light (artificial light) and temperature (20°C) used in the experiment. Animals were individually introduced into 8 cm diameter Petri dishes, on the bottom which was partially covered by two half-disks of 7 cm diameter Whatman filter paper at a distance of 0.5 cm from each other. One half-disk was impregnated with deionized water and used as a control, the other was impregnated with the test solution at varying concentration.

Fifteen Petri dishes (replicates) were placed under a Sharp® fluorescent illuminator normally used for scanning documents, each with an animal placed in the space between two half-disks at the beginning of the trial. Since subterranean springtails such as H. nitidus are highly sensitive to light [START_REF] Salmon | Responses to light in a soil-dwelling springtail[END_REF], control experiments were done with water on both half-disks in order to verify the absence of light gradients under the illuminator. One hour after the introduction of test animals, their position on one or the other half-disk was checked in each Petri dish. Data were total numbers of animals either on water or on test solution. The significance of attractive or repulsive effects of test solutions was assessed by a sign-test, based on binomial distribution [START_REF] Rohlf | Statistical tables[END_REF]. Animals used for an experimental run were kept for further experiments with at least 48 h interval between two successive runs with the same animal. In the meantime animals were kept on uncontaminated artificial substrate with food added.

Results

Untreated collembolan communities

Thirty-nine species were identified in the material extracted at the end of the experiment (Table 1). Ten were common to both soils (ubiquitous species), nine were found in the neutral Eumull (pH 7.5) only (Eumull species), 16 in the acid Dysmoder (pH 4.3) only (Dysmoder species), and six could not be attributed unambiguously to one or other humus type, since they were found only in boxes with the two different soils (dubious species). Based on our extraction results, five times as many animals and twice as many species were present in the acid than in the neutral soil (Table 2, Fig. 1). Thus the relative richness of the Eumull was higher than that of the Dysmoder. Abundance and number of ubiquitous species were higher in the Dysmoder than in the Eumull. Among the common species (species present in more than 10 compartments) ubiquitous relative to humus type, all but one either did not express significant differences in their densities between humus types or were more abundant in the Dysmoder, the exception being Dicyrtoma fusca which was more abundant in the Eumull (Table 2). Parisotoma notabilis, although classified as ubiquitous, was nearly absent in the Eumull although it was the second most abundant species in the Dysmoder, after Isotomiella minor, which dominated both communities.

Collembolan communities with herbicide and the same humus in both compartments

Laboratory effects of Madit D® on collembolan communities can be assessed by comparing between untreated experimental boxes with those in which the herbicide was added to both compartments (Table 2, Fig. 1). There were no significant effects of the herbicide on the abundance as well as the species richness of collembolan communities, whatever the humus type, but two species, namely Megalothorax minimus and Sphaeridia pumilis, reacted positively to the addition of the herbicide in the Dysmoder. Both species were found exclusively in herbicide-treated boxes.

Possible avoidance or attraction effects could be tested when the herbicide was applied to only one compartment. No such effect was detected in Eumull (Table 3), but a small although significant effect was perceived in Dysmoder (Table 4). In Dysmoder, Friesea truncata decreased in abundance in the treated compartment (DH/D) compared to the control (D/D), while its abundance in the untreated compartment (D/DH) was not different from the control.

The case of the ubiquitous species Sphaeridia pumilis was somewhat different, since it was absent in the control (D/D), but present in both treated (DH/D) and untreated (D/DH) compartments (Table 4). This resulted in an increase by one in the number of ubiquitous species, as well as in the relative richness index.

Interaction between humus type and herbicide in Eumull communities

The combination of Dysmoder with Eumull caused an increase in the relative richness of the collembolan Eumull community (Table 5). This increase was due to the addition of Dysmoder species to the Eumull population (Fig. 1). This addition was counterbalanced by a strong decrease in the abundance and number of Eumull species, from 5.5 and 2.5, respectively, to only one individual (and thus one species) per compartment. The net result was a decrease in the total abundance and an increase in the total number of species of Collembola per compartment. The relative richness index increased accordingly. At the species level (Table 5), Isotomurus palustris, an Eumull species, was negatively affected by the presence of Dysmoder, its population collapsing to less than one individual per compartment. The observed decrease in the total abundance of Collembola was mainly due to a collapse in the population of Isotomurus palustris, the second most abundant species of the Eumull after Isotomiella minor.

The decrease in the number of Eumull species was due, not only to the collapse of the Isotomurus palustris population, but also to the disappearance of several other less abundant Eumull species, among them Heteromurus nitidus (data not shown).

The observed collapse in Eumull species (both in abundance and number) under the influence of the presence of Dysmoder was less pronounced when the herbicide was added, regardless of the compartment chosen for this addition (Table 5, Fig. 1). Nevertheless the abundance of Isotomurus palustris remained always at a very low level, compared to Eumull alone (with or without herbicide, see Table 2). An increase of the number of ubiquitous species was observed in Eumull when it was combined with Dysmoder plus herbicide. As already mentioned Dysmoder species appeared, too, in Eumull when this was combined with Dysmoder, irrespective of the application of the herbicide.

Interaction between humus type and herbicide in Dysmoder communities

An increase in the total number of species was observed in Dysmoder combined with Eumull, compared to Dysmoder alone (Table 6, Fig. 1). At the species level, the only effect of the presence of Eumull was a strong decrease in the abundance of Neanura muscorum, a Dysmoder species (Table 1).

The herbicide interacted with the humus type by increasing the number of ubiquitous species in Dysmoder combined with Eumull when the application occurred in both compartments (Fig. 1, Table 6). The abundance of Dysmoder species in Dysmoder combined with Eumull decreased by 50% when the herbicide was applied to the Dysmoder compartment.

At the species level, the abovementioned decrease in the abundance of Neanura muscorum when Dysmoder was combined with Eumull disappeared in the presence of herbicide, whatever the compartment chosen for the application (Table 6). Sphaeridia pumilis, which was absent from Dysmoder in the absence of Eumull (Table 6) or of herbicide (Table 2), was present when the acid humus was combined with Eumull, and the abundance of this species increased in the presence of herbicide, whatever the compartment chosen for its application. Another stimulatory effect of the herbicide was observed also on Lepidocyrtus lignorum, the population of which doubled when the herbicide was applied to both compartments.

Laboratory assays on single species

Experiments with Heteromurus nitidus, a typical Eumull species [START_REF] Ponge | Biocenoses of Collembola in atlantic temperate grass-woodland ecosystems[END_REF][START_REF] Salmon | Distribution of Heteromurus nitidus (Hexapoda, Collembola) according to soil acidity: interactions with earthworms and predator pressure[END_REF], showed it to be indifferent to the presence of isoproturon until a concentration of 0.5 mg.L -1 was reached (Fig. 2). Above this threshold, the animals avoided the herbicide, but the departure from indifference was significant only above 5 mg.L -1

. The other species, Folsomia manolachei, coming from Dysmoder soil, exhibited a weak (insignificant) attraction to the herbicide at concentrations below 0.05 mg.L -1

, then the response abruptly turned to avoidance, which became significant above 0.5 mg.L -1

.

At the beginning of the experiment with complete collembolan communities, the concentration of isoproturon in the soil solution varied from 2.7 mg.L -1 for Eumull to 4.4 mg.L -1

for Dysmoder, as ascertained from the amount of herbicide applied at the beginning of the experiment and the amount of water present in the soil. Compared to filter paper experiments this corresponded to a concentration where Heteromurus nitidus shifted from indifference to avoidance (Fig. 1) and to a range of concentration where Folsomia manolachei clearly avoided the herbicide.

Discussion

The two-week laboratory experiment on complete collembolan communities did not reveal effects of the application of isoproturon on the Eumull population. On the contrary, in several treatments the Dysmoder population showed an increase in the abundance of two species, the Symphypleone Sphaeridia pumilis and the Neelipleone Megalothorax minimus.

Both were totally absent from the untreated soil; thus the herbicide can be suspected of favouring egg hatching, for instance by terminating diapause, or by decreasing egg predation.

Although no clear-cut explanation can be found, it should be noted that Sphaeridia pumilis is known for its temporary disappearance, eggs being the only resting stage during unfavourable seasons (Blancquaert et al., 1982). A higher predation pressure can be suspected in Dysmoder compared to Eumull [START_REF] Salmon | Distribution of Heteromurus nitidus (Hexapoda, Collembola) according to soil acidity: interactions with earthworms and predator pressure[END_REF], which could explain why such effects were not shown in Eumull. Thus direct as well as indirect effects of the herbicide could explain the observed phenomenon, although literature data cannot support either one or the other hypothesis.

Avoidance effects were revealed by choice experiments on filter paper, at the same concentration as that employed for the community experiment with natural soils. Such a phenomenon was only poorly revealed in soil when animals were allowed to cross a perforated wall to reach a compartment without herbicide. Among the more abundant species only the predator Friesea truncata was suspected of having escaped from the herbicide-treated Dysmoder compartment. This species decreased in density in the treated Dysmoder soil when combined with Eumull, but in this case no corresponding increase was observed in the Eumull counterpart, pointing to the ability of the Dysmoder population of F. truncata to cross the perforated wall to escape from the herbicide-treated compartment, but its inability to survive in Eumull.

Most marked effects were displayed by the Eumull community when Dysmoder was present in the neighbouring compartment. A strong depressive effect was observed on the epigeic species Isotomurus palustris, although it was not affected at all by the herbicide. At first sight this could be due to attraction to Dysmoder as well as to toxicity. Attraction to the Dysmoder compartment can be ruled out since only a few individuals of this Eumull species were found in Dysmoder when adjacent to Eumull, thus no compensatory increase occurred in the Dysmoder. Since Isotomurus palustris normally lives aboveground [START_REF] Ponge | Biocenoses of Collembola in atlantic temperate grass-woodland ecosystems[END_REF], we can suspect that it did not withstand the Dysmoder smell in our experimental boxes, where volatile compounds (fungal odours, terpenes) probably abound. It has been demonstrated that the odour of the micromycete Trichoderma was avoided by the collembolan Onychiurus sinensis [START_REF] Sadaka-Laulan | Feeding preferences of the collembolan Onychiurus sinensis for fungi colonizing holm oak litter (Quercus rotundifolia Lam.)[END_REF], and that some compounds isolated from fungal odours could be repellent to Collembola, too (Bengtsson et al., 1991), but no toxic effect mediated by olfactory compounds has been demonstrated so far. Despite weak effects of the herbicide alone, the combination of herbicide and humus treatments exhibited non-additive effects. The disappearance of toxic effects of Dysmoder upon herbicide application could result from an inactivation of the toxic components of the Dysmoder smell (if any) by isoproturon or adjuvant compounds. In the absence of any knowledge on the formulation of Madit D®, this information being not given by the producer, no clear hypotheses can be drawn. If we take into account the rapid transformation of isoproturon in the soil [START_REF] Verschueren | Handbook of environmental data on organic chemicals[END_REF], mainly resulting from demethylation, hydrolysis and hydroxylation of the phenylurea moiety within a few weeks, a number of different chemicals, each with its own sorptive properties, may have appeared within the two weeks of our experiment. When

Reverse effects of

Dysmoder was combined with Eumull, Dysmoder species were not eliminated by the herbicide, which otherwise would have resulted in a decrease in their number. Nevertheless, we observed a decrease in the abundance of species commonly but exclusively living in acid soils, such as the epigeic Lipothrix lubbocki and the endogeic Proisotoma minima [START_REF] Ponge | Biocenoses of Collembola in atlantic temperate grass-woodland ecosystems[END_REF]Ponge, 2000a), in addition to the already mentioned depressive effect on the ubiquitous Friesea truncata. Since L. lubbocki and P. minima were never retrieved in the adjacent Eumull compartment, it appears that either i) they were directly or indirectly affected by the herbicide without being able to escape it or ii) they escape Dysmoder compartments but were killed in Eumull compartments. Such an effect was not displayed by the application of herbicide to Dysmoder in the absence of Eumull, which could give support to the second hypothesis.

Methods used in the present study allow the measurement of subtle effects of herbicides on motile non-target organisms, such as soil microarthropods, in particular when toxicity, attraction and avoidance are combined. Doses at which the herbicide was applied are well below the thresholds given for the toxicity of isoproturon. For instance, nitrification is not inhibited below 300 mg.L -1 [START_REF] Verschueren | Handbook of environmental data on organic chemicals[END_REF], nominal data per unit of soil not given), which is not far from the concentration of the undiluted herbicide (500 mg.L -1

). Despite low concentration of the herbicide, perturbations of soil animal communities were displayed, especially when two distinct humus types were put together in the same boxes, pointing on non-additive effects of humus type and herbicide application. At the low doses used for our experiment on collembolan communities, avoidance rather than toxic effects can be suspected, supported by experimental results with single species, but toxic effects of one humus type upon the other, as well as detoxifying effects of the herbicide were registered, too, pointing to complex relationships between pesticides and soils when living organisms are involved [START_REF] Torstensson | Degradation studies[END_REF]. We conclude that further experiments are necessary before the inoculation of organisms living in acid soils, suggested as a trade-off for the negative impact of pesticides on biodiversity [START_REF] Forbes | Ecotoxicology in theory and practice[END_REF], could be applied successfully to agricultural soils.

Acknowledgements

The authors are greatly indebted to Benoit Cambon (Monsanto-France), Philippe Viaux (ITCF) and Eric Thybaud (INERIS) for financial support and fruitful exchange of ideas.

Akhouri, N.M., Kladivko, E.J., Turco, R.F., 1997. Sorption and degradation of atrazine in middens formed by Lumbricus terrestris. Soil Biol. Biochem. 29, 663-666.

Alvarez, T., Frampton, G.K., Goulson, D., 2000. The role of hedgerows in the recolonisation of arable fields by epigeal Collembola. Pedobiologia 44, 516-526.

Bengtsson, G., Hedlund, K., Rundgren, S., 1991. Selective odor perception in the soil Collembola Onychiurus armatus. J. Chem. Ecol. 17, 2113-2125.

Blancquaert, J.P., Mertens, J., Coessens, R., 1982. Annual cycle of populations of Sphaeridia pumilis (Collembola). Rev. Ecol. Biol. Sol 19, 605-611. The slash sign separates the considered compartment (left) and the adjacent compartment (right). When both compartments were given the same treatment, corresponding data were pooled, otherwise they were considered as distinct treatments. Significant differences between treatments (P<0.

Figure captions

  Eumull upon the Dysmoder community were quite different. No toxic effect of Eumull was observed, except a decrease in the abundance of the neanurid Neanura muscorum. Colonization of the Eumull compartment by animals coming from the Dysmoder was demonstrated. In the Dysmoder compartment, the population was stimulated to a great extent, probably above numbers actually found at the end of the experiment if Dysmoder animals found in the Eumull compartment (colonizing individuals) are added.

Fig. 1 .

 1 Fig. 1. Species richness of Collembola in the adjacent compartments of experimental twin boxes. E = Eumull soil. EH = Eumull soil treated with isoproturon. D = Dysmoder soil. DH = Dysmoder soil treated with isoproturon. Bars indicate standar errors (five replicates).

Fig. 2 .

 2 Fig. 2. Results of choice experiments with Heteromurus nitidus (Eumull population) and Folsomia manolachei (Dysmoder population), showing the number of animals found on impregnated filter paper after one hour (15 replicates with one individual each) plotted as a function of the concentration of the herbicide (logarithmic scale). Arrows (E for Eumull and D for Dysmoder) indicate the concentration of the soil solutions in experiments with complete collembolan communities. Horizontal lines indicate absence of choice (7.5 individuals on each side) and its confidence interval at the 95% threshold level.

  Fig. 1 2

Table 2 .

 2 Results of treatments in which both 550 mL compartments of experimental boxes received or not the herbicide. Data are numbers of animals per compartment, averaged over five replicates, with standard errors. Significant differences among treatments (P<0.05) are indicated by different letters

			Eumull	Eumull+Herbicide Dysmoder	Dysmoder+Herbicide
		Dicyrtoma fusca	1.9±0.7a	2.3±0.3a	0b	0.1±0.1b
		Folsomia manolachei	0.6±0.3	0.3±0.1	0	0
		Friesea truncata	1.5±0.3b	1.3±0.3b	14.6±0.9a	18.4±3.4a
		Heteromurus major	0b	0b	1.7±0.7a	3.2±0.5a
		Isotomiella minor	10.7±1.6b	9.9±1.3b	46.8±6.3a	56.7±10.0a
		Isotomurus palustris	3.7±1.6a	4.5±2.2a	0b	0b
		Lepidocyrtus lanuginosus	0b	0.1±0.1b	7.0±1.0a	3.9±1.3a
		Lepidocyrtus lignorum	0b	0.2±0.2b	2.8±0.6a	3.3±1.1a
		Lipothrix lubbock i	0b	0b	2.8±0.4a	2.7±0.3a
		Megalothorax minimus	0b	0b	0b	0.9±0.2a
		Mesaphorura leitzaensis	0	0.1±0.1	0.1±0.1	0.7±0.3
		Micranurida pygmaea	0	0	0.2±0.2	0.4±0.2
		Neanura muscorum	0b	0b	3.3±1.0a	3.4±2.4ab
		Orchesella cincta	0.1±0.1	0	0.6±0.4	0
		Paratullbergia callipygos	0	0	0.2±0.1	0.9±0.4
		Parisotoma notabilis	0.2±0.2b	0.2±0.2b	16.7±0.9a	14.4±2.6a
		Proisotoma minima	0b	0b	7.9±1.6a	8.7±1.9a
		Sphaeridia pumilis	0b	0.1±0.1b	0b	3.4±1.9a
		Stenaphorura denisi	0.4±0.2	0.3±0.2	0	0
		Tomocerus minor	0b	0b	1.2±0.3a	1.3±0.4a
		Total abundance	19.9±2.2b	19.9±3.8b	106.3±7.5a	122.8±13.0a
		Total number of species	5.0±0.6b	4.9±0.6b	10.3±0.3a	11.7±0.7a
		Relative richness	0.27±0.08a	0.28±0.03a	0.10±0.01b	0.10±0.01b
		Abundance of Eumull species	5.5±1.9a	5.5±2.5a	0b	0b
		Number of Eumull species	2.5±0.4a	1.7±0.2a	0b	0b
		Abundance of ubiquitous species 14.4±1.8b	14.3±1.8b	88.7±6.3a	100.9±12.7a
		Number of ubiquitous species	2.5±0.3b	3.1±0.4b	5.5±0.3a	5.9±0.4a
		Abundance of Dysmoder species 0b	0b	17.6±1.7a	21.9±4.1a
	1	Number of Dysmoder species	0b	0b	4.8±0.4a	5.8±0.3a
	2

Table 3 .

 3 Experiments with Eumull in the two compartments of experimental boxes. Data are numbers of animals per compartment averaged over five replicates, with standard errors. The slash sign separates the considered compartment (left) and the adjacent compartment (right). When both compartments were given the same treatment, corresponding data were pooled, otherwise they were considered as distinct treatments.

	Differences between treatments are not significant (P>0.05)

Table 4 .

 4 Experiments with Dysmoder in the two compartments of experimental boxes. Data are numbers of animals per compartment averaged over five replicates, with standard errors. The slash sign separates the considered compartment (left) and the adjacent compartment (right). When both compartments were given the same treatment, corresponding data were pooled, otherwise they were considered as distinct treatments. Significant differences between treatments (P<0.05) are indicated by

	different letters

Table 5 .

 5 Experiments with Eumull communities adjacent to Dysmoder. Data are means of five replicates with standard errors. The slash sign separates the considered compartment (left) and the adjacent compartment (right). When both compartments were given the same treatment, corresponding data were pooled, otherwise they were considered as distinct treatments. Significant differences between treatments (P<0.05) are indicated by different letters Dysmoder/Dysmoder Dysmoder/Eumull Dysmoder/Eumull+Herbicide Dysmoder+Herbicide/Eumull+Herbicide Dysmoder+Herbicide/Eumull

	Dicyrtoma fusca	0	0	0.4±0.4	0	0.2±0.2
	Folsomia manolachei	0	0	0.2±0.2	0.2±0.2	0
	Friesea truncata	14.6±0.9a	15.0±4.8ab	14.8±3.6ab	16.4±4.8ab	8.4±1.9b
	Heteromurus major	1.7±0.7	2.2±0.9	3.8±0.7	3.6±0.7	2.2±0.4
	Isotomiella minor	46.8±6.3	63.8±12.8	45.6±12.3	54.8±9.3	67.8±8.0
	Isotomurus palustris	0	0.2±0.2	1.0±1.0	0.2±0.2	0
	Lepidocyrtus lanuginosus	7.0±1.0	4.8±0.7	7.8±3.0	6.6±1.3	5.2±1.7
	Lepidocyrtus lignorum	2.8±0.6b	2.6±0.4b	3.6±0.8ab	5.0±0.5a	3.6±0.9ab
	Lipothrix lubbocki	2.8±0.4a	2.8±1.0ab	3.6±0.9a	2.4±0.7ab	1.4±0.4b
	Megalothorax minimus	0	0	0.2±0.2	0.2±0.2	0.8±0.4
	Mesaphorura leitzaensis	0.1±0.1	0.6±0.6	0.2±0.2	0.4±0.2	0.8±0.4
	Micranurida pygmaea	0.2±0.2	0.2±0.2	0.6±0.2	0.4±0.2	0.2±0.2
	Neanura muscorum	3.3±1.0a	0.6±0.2b	4.6±3.1a	3.0±1.4ab	1.0±0.3ab
	Orchesella cincta	0.6±0.4	0.4±0.2	0.8±0.8	1.0±0.4	0.2±0.2
	Paratullbergia callipygos	0.2±0.1	1.2±0.6	0.6±0.4	0.8±0.4	0.6±0.2
	Parisotoma notabilis	16.7±0.9	19.6±4.3	16.0±3.4	18.8±1.8	18.4±4.1
	Proisotoma minima	7.9±1.6a	7.4±1.5ab	9.8±3.6a	7.4±1.4a	2.4±0.7b
	Sphaeridia pumilis	0.0±0.0c	1.2±0.6bc	5.2±2.3ab	4.8±1.2a	3.4±1.0ab
	Stenaphorura denisi	0	0	0	0	0
	Tomocerus minor	1.2±0.3	1.2±0.6	0.4±0.4	1.2±0.4	1.0±0.4
	Total abundance	106.3±7.5	127.8±18.1	121.0±29.5	127.6±13.7	118.0±14.7
	Total number of species	10.3±0.3b	12.2±0.4a	13.8±1.1a	13.8±0.7a	13.0±0.8a
	Relative richness	0.10±0.01	0.10±0.01	0.13±0.02	0.11±0.01	0.11±0.01
	Abundance of Eumull species	0	0.2±0.2	1.6±1.1	0.4±0.2	0.2±0.2
	Number of Eumull species	0	0.2±0.2	0.8±0.4	0.4±0.2	0.2±0.2
	Abundance of ubiquitous species 88.7±6.3	108.0±17.6	94.4±22.7	107.8±12.7	108.0±14.0
	Number of ubiquitous species	5.5±0.3c	6.2±0.2bc	6.6±0.4ab	7.0±0.0a	7.0±0.3ab
	Abundance of Dysmoder species 17.6±1.7a	19.6±1.2ab	24.2±6.9a	19.2±2.3a	9.6±1.7b
	Number of Dysmoder species	4.8±0.4	5.8±0.2	5.8±0.7	6.2±0.7	5.6±0.8

Table 6 .

 6 Experiments with Dysmoder communities adjacent to Eumull. Data are means of five replicates with standard errors.


Prof. Dr Sanjay Mathur
email: sanjay.mathur@uni-koeln.de

Christian Cavelius

Hao Shen

CoGa 2 O 4 Nanoparticles and Films Using a Single Molecular Source †

Keywords:

nanoparticles showed as expected an antiferromagentic behaviour.

Introduction

Nano-sized metal oxides in particle and film forms are gaining significant attention due to size-dependent novel mechanical, electrical, optical and magnetic properties, [1][2][3][4][5][6][7][8] which can be tuned by controlling the grain size. [9][10][START_REF]Nanoparticles and Nanostructured Films[END_REF] For example, magnetic phases like Fe 3 O 4 become superparamagnetic when the particle size is less than the critical size of Weiss domains. [START_REF] Wiedenmannn | [END_REF] Due to the pre-existent metal-ligand connectivity in the metal-organic compounds, they are been increasingly used as "molecular seeds" to grow nanoscopic materials. [START_REF] Mathur | Encyclopedia of Nanoscience and Nanotechnology[END_REF][14][15] This concept is especially attractive for materials where several phases of similar chemical composition coexist in a narrow temperature range. Although molecule-to-material transformation processes are not well-studied, the compelitive edge of molecule-based synthesis is sufficient by homogeneous chemical compositions and more importantly the ability to synthesize metastable phases. Among transition metal ternary oxides, metal gallates are promising materials for optical [16][17][18] and catalytic applications. 19 2+ and Ga 3+ ions in an ethylene glycol solutions. 23 After the slow evaporation of glycol (< 100 o C), the resinous mass obtained was calcined and heattreated at 1000 o C (6 h).

CVD

A cold-wall horizontal low-pressure CVD reactor was used in this experiment. The substrate (Si) was placed on a graphite susceptor and heated (450-650 o C) inductively using a radio frequency generator. Optical pyrometer and a thermocouple were used to monitor the substrate temperature with accurary ± 1 o C. The precursor reservoir was maintained at the required temperature (105-140 o C) for an adequate flux. The precursor flux was regulated from the feedback of the pressure measurement in the reactor during the CVD process. The thermolysis products and unreacted precursor were removed through the pumping. A

CoCl 2 + 2/n [NaGa(O t Bu) 4 ] n → → → → [CoGa 2 (O t Bu) 8 ] + 2 NaCl ↓ ↓ ↓ ↓ (1)
quadrupole mass spectrometer was connected to the quartz tube to provide an on-line analysis of the decomposed fragments of the precursor.

Characterization

For studying the decomposition pathway of the precursor, the xerogel was placed in a

Results and discussion

Synthesis and Processings

The hetero-bimetallic precursor, [CoGa 2 (OBu t ) 8 ], was obtained by a salt-elimination reaction between anhydrous cobalt chloride and sodium tetra-alkoxogallate as reported by Singh and Mehrotra. 19 The crystals of [CoGa 2 (OBu t ) 8 ] were found to be unsuitable for single crystal X-ray diffraction analysis. The product crystallized from a concentrated toluene solution produced crystals of poor quality, most of them were twinned and degraded catastrophically during the X-ray diffraction analysis (several crystals were examined). .

C H 3 CH 3 CH 3 C H 3 CH 3 CH 3 C H 3 CH 3 CH 3 C H 3 Ga Co O O O O Ga CH 3 CH 3 C H 3 CH 3 CH 3 CH 3 CH 3 C H 3 CH 3 C H 3 C H 3 C H 3 C H 3 CH 3
Thermal, Phase, Microstructure Analyses TG-DTA profiles of [CoGa 2 (O t Bu) 8 ] in dry synthetic air (Fig. 1a) showed three distinct steps: (i) in range 20 to 200 °C, evaporation of volatile components takes place, which is indicated by a strong endothermic peak observed at 180 °C and associated with nearly 52 % weight loss. (ii) The strong exothermic peaks at 313, 384 and 432 °C correspond to oxidative expulsion (combustion) of organic ligands. The exothermic peak at 480 °C suggests the incipient crystallization of spinel phase with no significant weight loss observed afterward.

The observed gradual weight gain at higher temperature (480 -1200 o C) is possibly due to the uptake of oxygen from the surrounding, which indicates either micro-phase separation (Ga 2 O 3 and CoO x ), which would increase the metal:oxygen ratio (0.75 for spinel) or formation of non-stoichiometric oxides. The appearance of this feature at rather high temperature indicates that additional oxygen contributing towards weight gain is not originating from the source molecule as the precursor decomposition is already completed below 480 °C and the rest oxygen is eliminated as volatile byproducts. This aspect was not further investigated in this study.

The IR spectra of heat-treated (400 -1000 °C) CoGa 2 O 4 powders (Fig. 1b) exhibit the characteristic spectral pattern expected for CoGa 2 O 4 consisting of two well-defined groups of sharp peaks in the range 300-800 cm -1 , which is conform with the reported data. 14 The peaks are more resolved for samples heat-treated at higher temperatures probably due to enhanced The phase composition of spinel powders calcined at 400 and 600 °C revealed poor crystallinity, however the major peaks at 36 and 63 o (Fig. 2) could be assigned to CoGa 2 O 4 phase (PDF [11-0698]). At 800 o C and above, the FWHM of the XRD peaks become narrower indicating the grain growth in the samples (Fig. 2a). Figure 2b synthesized by molecular and glycolate approaches, transmission electron microscopy (Fig. 3) was performed in both the cases. The sample obtained from glycolate synthesis (Fig. 3a) revealed strong agglomeration of particles with diameter ranges lying in tens to several hundreds of nanometers. The particles obtained from gycolate route show irregular form composed of amorphous and crystalline parts which were evident in HR-TEM image (Fig. 3c). The TEM image (Fig. 3b) of the alkoxide-derived sample (calcined at 1000 o C) showed regularly dispersed crystallites of nearly uniform size (~ 100 nm). The distinct lattice fringes observed in HRTEM image (Fig. 3d) confirmed the high crystallinity and phase purity of CoGa 2 O 4 nanoparticles.

In-plane and cross-sectional SEM images of CVD film deposited on Si substrates (Fig. 4a) at 550 o C typically showed the compact coating with granular morphology, which can be attributed either to the lattice mismatch between film and substrate to competitive 2D (films) and 3D (islands) growth mechanisms due to different interfacial/surface energies. The crosssectional SEM image of CoGa 2 O 4 film revealed a dense film of homogeneous thickness (Fig. 4a). An EDX line-scan confirmed a homogeneous atomic ratio (Co:Ga ~ 1:2) across the film.

The homogeneity of the surface morphology was conformed by AFM analysis which showed the film to be smooth (R a ~ 50 nm) with no cracks or inhomogeneous growth (Fig. 4b).

Optical and Magnetic Properties

The UV-Vis spectra (Fig. 5) of sol-gel derived CoGa 2 O 4 powders show the characteristic features of Co 2+ ions present in the tetrahedral and/or octahedral configurations.

A triple band (tetrahedral: 4 A 2 (F) → 4 T 1 (P); octahedral: 4 T 1 (F) → 4 T 1 (P)) located at 500-800 nm can be attributed to a John-Teller distortion of the Co 2+ in the crystal field. [START_REF] Griffith | The Theory of Transition-Metal Ions[END_REF][START_REF] Stangar | [END_REF][27] The color of CoGa 2 O 4 powders changed from dark-green (400 -500 o C) to grass green (600 -800 o C) and finally to blue (1000 -1200 o C). The peaks I, II and III located at 560, 600 and 650 nm, can be considered as the spectral distribution of green, yellow orange and red colors, respectively. The peaks I and II reveal an increase in intensity with respect to peak III upon increasing the calcined temperature. Peaks II and III shift to low wavelength whereas the peak I is fixed. Previous investigation 15 on ZnAl 2 O 4 has shown that it has a partially inverse structure at low crystallization temperature, which was confimed by the co-existence of 4-and 6-fold coordinated Al centers by 27Al solid state NMR analysis. 15 The degree of inversion is reduced upon heat-treatment at high temperatures, which result in the thermodynamically controlled migration of Al ions from tetrahedral into octahedral sites. This is evident in the gradual decrease of the NMR peaks corresponding to AlO 4 units. 15 The evoluation of inverse/normal conversion of CoGa 2 O 4 can be reflected in the change of Co 2+ triple band (Fig. 5). The triple band of CoGa 2 O 4 calcined at lower temperatures (400 -600 o C) can be considered as the summation of contribution from inverse and normal spinel phases.

Since the Co 2+ ion is the only magnetic ion in the CoGa 2 O 4 compound which can be distributed in tetrahedral (A) and octahedral (B) sites, the magnetization is composed of A-A, B-B and A-B magnetic interactions among Co 2+ ions. D. Fiorani et al. 28 have reported that the polycrystalline CoGa 2 O 4 revealed an antiferromagnetic order with T N ~ 10 K.

TOC CoGa 2 O 4

 24 Nanoparticles and Films Using a Single Molecular Source Sanjay Mathur, Christian Cavelius and Hao Shen Mixed-metal tert-butoxide, [CoGa 2 (O t Bu) 8 ], was used in chemical vapor deposition (CVD) and sol-gel processes to obtain monophasic cobalt gallate (CoGa 2 O 4 ) in film and nanoparticulate forms. The results demonstrate that the heteronuclear precursor effectively transforms at relatively low temperature (CVD: < 500 o C; Sol-Gel: < 700 o C) into nanosized CoGa 2 O 4 , without showing any micro-phase separation into individual metal oxides commonly observed in spinel produced from a mixture of individual metal sources.

  tert-butoxide, [CoGa 2 (O t Bu) 8 ], was employed in the chemical vapor deposition (CVD) and sol-gel processes to obtain thin films and nanoparticles of spinel CoGa 2 O 4 phase, respectively. The appropriate Co:Ga ratio and intact vaporisation (115-120 o C / 10 -2 Torr) of the molecular source produced crystalline deposits of CoGa 2 O 4 at relatively low temperatures (~ 500 o C). A clean transformation of the heterometal precursor in spinel oxide of definite composition was supported by TG/DTA analysis that showed no weight loss above 470 o C. The SEM images of CoGa 2 O 4 films showed homogeneous morphology and dense microstructure constituted by nanometric grains (<d>, ~ 35 nm). Hydrolytic decomposition of the precursor produced gels that upon heat-treatment (400 -1200 o C) formed nanoscaled spinel. For comparison, CoGa 2 O 4 was also prepared by complexing Co 2+ and Ga 3+ ions with glycolate ligands, significant agglomeration effect, broader size dispersion and amorphous domains were observed indicating that low-temperature synthesis of monophasic materials following conventional chemical approaches is hampered by thermodynamic impediments. The UV-Vis spectra of CoGa 2 O 4 particles exhibit characteristic peaks corresponding to 4 A 2 (F) → 4 T 1 (P) transition in the divalent cobalt cation. The magnetization data of the CoGa 2 O 4

  crystallinity. When compared to powder samples, the CVD deposit (at 550 o C) reveals a shift to large wave number (~ 140 cm -1 ) indicating the probable presence of stress within the thin film form. Further, the broad band centred at 3400 cm -1 can be ascribed to stretches of metalbound hydroxy groups. The bands corresponding to C-H, C-C and C-O vibrations of the residual alkoxy groups are observed in the regions of lower wave numbers. The absence of peaks characteristic of C-H fragements despite lower deposition temperature (550 o C) indicates an effective ligand-stripping in the gas phase decomposition of [CoGa 2 (O t Bu) 8 ].

  shows XRD-patterns of CoGa 2 O 4 films deposited at different substrate temperatures (450 -650 o C); the film deposited at 450 o C is amorphous whereas crystalline CoGa 2 O 4 phase is already obtained at 550 and 650 o C. To evaluate the particle size and chemical homogeneity in CoGa 2 O 4 phases

  Scheme 2. Controllable transformation from molecule to materials.

Fig. 1 .

 1 Fig. 1. (a) TG/DTA curves of [CoGa 2 (O t Bu) 8 ] precursor obtained under synthetic air flow (75 sccm) and 10 o C/min ramping rate. (b) FT-IR spectra of CoGa 2 O 4 samples derived from solgel (400, 600, 800 and 1000 o C) and CVD (550 o C) processes.

Fig. 2 .

 2 Fig. 2. XRD patterns of (a) sol-gel derived CoGa 2 O 4 samples calcined at 400, 600, 800 and 1000 o C and (b) CoGa 2 O 4 films deposited at 450, 550 and 650 °C.

Fig. 3 .

 3 Fig. 3. TEM images of CoGa 2 O 4 nanopowders (1000 o C) obtained from (a) glycolate and (c) alkoxide routes. The corresponding HR-EM images are shown in (b) and (d).

Fig. 4 .

 4 Fig. 4. (a) In-plane and cross-sectional SEM and (b) AFM images of CoGa 2 O 4 film deposited at 550 o C.

Fig. 5 .

 5 Fig. 5. UV-VIS spectra of sol-gel derived CoGa 2 O 4 samples calcined at 400, 500, 600, 800 and 1200 o C.

Fig. 6 .

 6 Fig. 6. Room-temperature M-H curve of CoGa 2 O 4 sample calcined at 1000 o C.

  TGA/DTA crucible, and heated upto 1200 °C, with a ramping rate of 10 o C/min. The FT-IR spectra of CoGa 2 O 4 powders were recorded in a KBr matrix on a Biorad-165 Fourier Transform spectrometer whereas the spectrum of CoGa 2 O 4 film was recorded in reflection mode. XRD data of CoGa 2 O 4 powders were collected with a STOE diffractometer (STADIP) operating with a CuK α radiation. XRD patterns of CoGa 2 O 4 films were recorded on an

Siemens D-500 diffractometer with small incident angle (~ 1°). XRD data were used to calculate the average sizes of CoGa 2 O 4 nanoparticles using Scherrer's formula. Particle morphology and elemental distribution in xerogel and calcined powders were recorded using a scanning electron microscope JSM-6400F (JEOL) coupled with an Energy Dispersive X-ray (EDX) facility. TEM analyses were performed by drawing an amorphous carbon coated copper grid through sonicated dispersions (Pr i OH) of the samples derived from alkoxide and glycolate routes. The film surface topology and average roughness were analyzed with a Topometrix TMX2000 Explorer atomic force microscope (AFM) using a Si 3 N 4 standard tip (radius, 20 nm). The UV-Vis spectra of CoGa 2 O 4 powders were recorded with the help of an integrating sphere by Cary 5E UV-Vis spectrometer. Magnetic measurements on nanopowder samples were accomplished using a commercial SQUID magnetometer at room temperature and applied fields up to 20 kOe.

  The powder X-ray diffraction studies were prevented by extremely hygroscopic nature of the crystals, which made sample preparation (filling the powdered samples in glass capillary) difficult as the product upon pulverization formed a wax-like mass. Elemental analysis in [CoGa 2 (O t Bu) 8 ] was performed gravimetrically: (MW: 789 Da): Co 7.38 (found: 7.18); Ga 17.49 (found: 17.88), which provided Co:Ga ratio of 0.96: 2.04 and supported the proposed chemical formula. The proposed chemical composition (Scheme 1) for the title compound was supported by the elemental analyses as well as the structural data available for similar transition metal aluminates [MAl 2 (OBu t ) 8 ] (M II = Co, Ni, Cu, Fe, Zn) 14,15 and recently reported [NiGa 2 (O t Bu) 8 ].24 The thermal fragmentation of the precursor during CVD

	experiment was examined by on-line mass spectroscopy, whereby major products were
	identified to be H 2 O + , C 2 H 4 + , C 3 H 6 + and C 4 H 8 + whose distributions in the gas phase were
	found to be temperature dependent. 24
	Scheme 1. Proposed molecular structure of [CoGa 2 (O t Bu) 8 ]

Acknowledgement

Thanks are due to the German Science Foundation (DFG), Federal Ministry of Education and Research (BMBF) and University of Cologne for supporting this work.

Wiley-VCH ZAAC