Jean-Loup Bertaux
email: jean-loup.bertaux@latmos.ipsl.fr

Rosine Lallement

From Diffuse Interstellar Bands to comets: the organic connection

. We suggest that the comet organic molecules are the same organic molecules that produce, in the Interstellar Medium (ISM), diffuse absorption features imprinted on stellar spectra (DIBs, Diffuse Interstellar Bands). The large molecules forming the DIBs are not yet identified, except for fullerene C 60 + , but are thought to constitute "… the largest reservoir of organic material in the Universe" ([7], Snow, 2014).

Introduction

The COSIMA instrument on board Rosetta collected dust grains escaping from the nucleus of 67P. Their composition was analyzed with a SIMS-TOF technique. They all show C + , CH + , CH 2 + , CH 3 + , which are fragments of much larger unidentified organic molecules ( [6], Fray et al., 2015). We propose that they are the same large molecules producing the DIB absorptions in the ISM that agglomerate together in a condensing interstellar cloud which became eventually our solar system ([3], [START_REF] Bertaux | Diffuse Interstellar Bands carriers and cometary organic material[END_REF]. Therefore, there is no need to invoke a massive fabrication of organics during the solar system. They were conserved from ISM during the formation of the solid comet nucleus, within the scenario established by [4] Davidsson et al. (2016) based on many arguments collected by Rosetta: a hierarchical scenario of gentle accretion of small interstellar grains to the final size of the nucleus. We back up our suggestion from both qualitative and quantitative arguments.

The ratio organic/mineral

A statistical analysis of the Equivalent Width (EW) of all known DIBs absorptions was performed. Assigning to all DIBs an oscillator strength equal to C 60 + and an average number of 60 C atoms per DIB carrier molecule, it is computed that at least 30% of ISM carbon is locked into a DIB carrier. It implies that in the ISM, the ratio organic/mineral is at least R ISM =0.32, to be compared to R C = 0.8±0.1 for the comet [START_REF] Bardyn | Carbon-rich dust in comet 67P/Churyumov-Gerasimenko measured by COSIMA/Rosetta[END_REF]. For the ISM, R ISM =0.32 is a lower limit, since only those organic molecules which absorb are accounted for.

DIB carriers decrease within dense clouds

On the other hand, the sounding of some interstellar nebulae show that, when the Line-of-sight approaches the centre, the DIBs depths are levelling off while the dust extinction is still increasing, suggesting an accretion process for the DIB molecules. These organic molecules would agglomerate to form interstellar grains that will end up in the proto-solar nebula, then in comet nuclei. As an example of such an accretion process in the ISM, the EW of an infra-red DIB has been compared to the dust extinction in the Barnard 68 nebula [START_REF] Elyajouri | The 15 273 Å diffuse interstellar band in the dark cloud Barnard 68[END_REF]. On fig. 1 is represented the distribution of dust extinction (taken from [1]) which increases toward the center of the nebula. The dust extinction and corresponding H columns may be plotted as a function of distance to center (not shown here). They then may be inverted by an onion-peeling method to yield the local density distribution function of [H] as a function of distance to center (in arcsec, figure 2). The same method was applied to the EW of the IR band at 1527.3 nm, to derive a local volume density of this particular DIB carrier associated to this IR DIB.

Figure 1: Target positions on the Barnard 68 extinction map from [1]. Solid contours correspond to 2 magnitude steps from extinction AV = 4 to 30 mag. The dashed line represents AV = 1:2 mag (taken form [START_REF] Elyajouri | The 15 273 Å diffuse interstellar band in the dark cloud Barnard 68[END_REF]).

While the local densities of both H atoms and DIB carriers are increasing toward the center of the nebula (figure 2), the increase of DIB carriers is much slower than the H atoms, as displayed by their ratio n(H)/n(DIB) which decreases toward center (blue curve of figure 2). This fact may be interpreted by an accretion process of DIB carriers molecules, either aggregating between themselves or accreting onto dust grains. Once these molecules are accreted, they can no longer absorb as they were when free-floating in space before accretion. Once formed, these grains (which could contain also minerals) would constitute the major fraction of the proto solar system from which condensed comet nuclei.

Conclusions.

It is often stated that early bombardment of comet nuclei on Earth could have facilitated the emergence of life on this planet by bringing organic material. Comet 67/P contains 3.5 billion tons of organic matter. Since the presence of DIBs is ubiquitous in our Galaxy, and in other galaxies, it is likely that organic material has been brought to all habitable exo-planets. How many of them have developed life, and intelligent life, are two other questions that would deserve large research investments, since they are related to the layman question: "Are we alone in the Universe ?" Our proposed scenario of DIB connection with comets implies that a comet return-sample mission would not need to be much cooled to keep the double interest for comets and for Interstellar Medium studies, since the solid organic phase of the comet is not very volatile.

  axis unit) DIB carriers (arb. unit) n(DIB)/n(H) ratio

Figure 2 :

 2 Figure 2: Volume density of DIB carrier n(DIB) based on the simplified inversion of EWs (left scale). Also shown is the inverted volume density n(H) based on AV data. The n(DIB) has been artificially scaled in such a way the two curves cross for the external layer at 96 arcsec. The ratio between the DIB carrier and H volume densities is also shown (right scale): it decreases toward center (taken from [5]).


Mireille Louys
email: mireille.louys@unistra.fr

François Bonnarel

Daniel Durand

Anais Egner

Implementation Feedback of the IVOA Provenance Data Model

The IVOA Provenance Data model defines entities, agents and activities as container classes to describe the provenance of datasets, with the executed tasks and responsibilities attached to agents. It also provides a set of classes to describe the activities type and their configuration template, as well as the configuration applied effectively during the execution of a task. Here we highlight lessons learned in the implementation of the CDS ProvHiPS service distributing provenance metadata for the HST HiPS data collections, and for the HST archive original images used to produce the HiPS tiles. ProvHiPS is based on the ProvTAP protocol, the emerging TAP standard for distributing provenance metadata. ProvTAP queries may rapidly become very complex. Various graph representation strategies, including ad hoc solutions, triplestore and SQL CTE have been considered and are discussed shortly.

Introduction: IVOA provenance data model and provenance of CDS HiPS

Datasets used in astronomy are generally the results of a flow of observation and processing steps. Information on this process is generally called "provenance" of the dataset and is stored in various formats and logical organizations. This makes in general the provenance information difficult to compare and use interoperably among different data collections. That's the main reason why IVOA developed an astronomy-oriented provenance data model during the last years. This formalization not only allows traceability of products but also acknowledgment and contact information, quality and reliability assessment and discovery of datasets by provenance details. At the time of writing the Provenance data model specification is an IVOA proposed recommendation [START_REF] Servillat | IVOA Provenance Data model[END_REF]. HiPS (Fernique et al. 2015) defines a new way of organizing image, cube and catalogue data in an all sky and hierarchical way based on HEALPix tessellation of the sky. HiPS datasets are generated from image data collections or catalogues which have their own history. The ProvHiPS service developed at CDS aims at providing provenance information for HiPS stored at CDS back to original raw data when available.

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Louys et al.

HiPS datasets for HST image collections

HiPS are made of hierarchies of tiles containing pixelized information at a given HEAL-Pix order. In the case of image HiPS datasets each tile is generated from a small subset of the original image collection intersecting with the tile. The HiPS format stores internally the progenitor information for each tile in the HiPS tree. The CDS data center publishes HiPS at various wavelengths for the HST image collections. They have been produced from HST drizzled images in collaboration with CADC astronomer Daniel Durand. HST data collections are stored and retrievable from the CADC HST archive through IVOA DAL services. The drizzled images have their own history: they are produced from sets of calibrated images closely related on the sky by a specific type of co-addition called "drizzling".

A rich tree of related data is then potentially available. We have browsed HiPS tiles metadata and FITS headers of the HST images to extract features relevant in terms of the IVOA Provenance data model to trace historical information and map it into the ProvTAP tables. This resulted in a database containing ten of thousands of entities and activities. Dozen of descriptions of the various kinds of entities have also been produced as well as ten of thousands of configuration parameters for the drizzling and HiPS generation activities.

ProvHiPS implementation

In order to make such information available we implemented a ProvTAP1 service called ProvHiPS. ProvTAP specification is currently an IVOA working draft describing how to map the provenance data model in a TAP service. The heart of it is the Prov-TAP TAP SCHEMA definition providing the list of tables and columns required for storing the provenance metadata information and mapping respectively the classes and attributes of the model. Tables and columns come with datatype, unit, ucd, and utypes consistent with the model. By default a ProvTAP service is queriable via the ADQL language defined in IVOA and provides results in VOTable format.

The CDS ProvHiPS service implements a database containing the provenance information sketched out in the workflow scenario presented in Fig 1 .  Fig. 2 shows a 13-joins query tracing the provenance of a single HiPS V HST tile around the target NGC104. The query response is presented in Fig. 3 as displayed with the TAPHandle application [START_REF] Michel | Astronomical Data Analysis Software and Systems[END_REF]. Some drizzled and calibrated images are visualized in Aladin via SAMP messaging as well.

Fig. 4 shows the activity description associated with one of the previous calibration activity. This Activity description provides interoperable typing of the calibration activities as well as a link to the software documentation.

More sophisticated user scenarios may include retrieving "siblings" of a given dataset entity using various depths or selecting datasets sharing the same creator agent or generated with similar parameters. The number of joins needed to traverse the provenance graph may increase tremendously. That's the reason why we experimented various ways of representing and querying graphs on top of relational databases. Former tests with a triplestore architecture has shown promising results [START_REF] Louys | Astronomical Data Analysis Software and Systems[END_REF]. As published in [START_REF] Oberto | ADASS XXIX[END_REF] and proposed by M.Nullmeier2 , graphical or Common Table Expressions (CTE) techniques to navigate through graph connections on top of the RDBMS are new solutions to consider. We plan to add such layers on top of our service to improve user-friendliness.

Conclusion

Despite the query" issue, the ProvTAP implementation of ProvHiPS demonstrates it is feasible to map information stored in FITS headers of homogeneous image collections or HiPS metadata into the IVOA PROV DM profile. The scalability of the database allows coping with very large data collections. Retrieval of multiple steps pipelines is easy as long as the appropriate ADQL queries are provided.

Figure 1 .

 1 Figure 1.The historical path from raw HST images to their projected tiles in the HiPS HST representation.

Figure 2 .

 2 Figure 2. Deep query from tile back to original raw image.

Figure 3 .

 3 Figure 3.Query response as shown in the TapHandle application. Access links to images at each step allow to understand the sequence of activities and how they transform data.

Figure 4 .

 4 Figure 4. Metadata for an instance Activity for image calibration and its corresponding ActivityDescription instance.

https://wiki.ivoa.net/internal/IVOA/ObservationProvenanceDataModel/ProvTAP.pdf

https://www.asterics2020.eu/dokuwiki/lib/exe/fetch.php?media=open:wp4: nullmeier_tf5_prov_custom_adql.pdf

Acknowledgments. We thank the CDS intership program for supporting A. Egner. This work has been partly supported by the ESCAPE project (the European Science Cluster of Astronomy and Particle Physics ESFRI Research Infrastructures) funded by the EU Horizon 2020 research and innovation program under the Grant Agreement n.824064, and also the ASTERICS project under Grant Agreement n.653477.


Olivier Piccin
email: olivier.piccin@insa-strasbourg.fr

Pierre Renaud

Laurent Barb
email: barbe@eavr.u-strasbg.fr

Bernard Bayle

Benjamin Maurin

Michel De Mathelin

A ROBOTIZED NEEDLE INSERTION DEVICE FOR PERCUTANEOUS PROCEDURES

In this paper, a new robotized needle insertion device is proposed for computer-assisted percutaneous therapy. The insertion device is integrated in a robotic system dedicated to gesture guidance in a Computed Tomography (CT) scan. The presented design fulfills the stringent requirements of such a medical application: compatibility with a CT-scan and haptic control by the practitioner are ensured as well as safety and sterilization. The novel design of the insertion device is first presented, outlining its main properties, before introducing preliminary experimental results.

INTRODUCTION

Computed Tomography (CT) is an imaging technique which is now widely used for medical diagnosis as well as interventions. Minimally invasive percutaneous procedures performed with a CT-scan for chest or abdomen treatments [START_REF] Gangi | Tomodensimétrie Interventionnelle[END_REF] reduce the trauma for the patient while ensuring the accuracy of the surgeon's gesture. In such treatment however, the radiologist is exposed to harmful X-rays during needle insertion. X-rays intensity is even more harmful when CT fluoroscopy-guided intervention is achieved to improve gesture accuracy. A robotic system designed to position and introduce the needle at a safer distance can therefore be an adequate solution to improve percutaneous procedures.

CT-guided surgery systems have already been proposed. The RCM+PAKY system [START_REF] Stoianovici | A modular surgical robotic system for image guided percutaneous procedures[END_REF][START_REF] Navab | Visual servoing for automatic and uncalibrated needle placement for percutaneous procedures[END_REF][START_REF] Cleary | Image-guided robotic delivery system for precise placement of therapeutic agents[END_REF] has been efficiently used in the operating room. Clinical experiments [START_REF] Lavallee | Computer Integrated Surgery[END_REF][START_REF] Hong | A motion adaptable needle placement instrument based on tumor specific ultrasonic image segmentation[END_REF] have also been achieved in other medical fields to validate computer-aided surgery by needle insertion. In these systems, image-guided positioning was resorted to in spite of two noticeable downsides. First, the surgeon receives no haptic feedback, when his/her gesture needs to take the insertion force into account and adapt accordingly. Second, the effects of chest motion due to patient breathing have not been considered at any time, although their importance is crucial for chest or abdomen applications.

To solve these problems, we are currently developing a robotized CT-guided needle insertion system with haptic feedback [START_REF] Maurin | A new robotic system for CT-guided percutaneous procedures with haptic feedback[END_REF]: a needle positioning robot which is compatible with the CT-scan has been developed [START_REF] Maurin | A parallel 5 dof positioner for semi-spherical workspaces[END_REF] and can be fastened to the patient so as to compensate for chest motion due to patient breathing. The needle positioning robot is based on a 5-DOF parallel structure to set the position and orientation of the needle. A stereotactic system allows to locate the target of the treatment in reference with the robot using only one CT-scan image [START_REF] Maurin | Pose reconstruction with an uncalibrated computed tomography imaging device[END_REF]. The stiffness of the structure is improved thanks to its parallel architecture, and compactness is optimized so that a standard CT-scan can be used for the intervention.

As far as we know, very few papers have been published about the design of a robotized needle insertion device to control the penetration of the needle. Friction-based insertion devices have been proposed in [START_REF] Hong | A motion adaptable needle placement instrument based on tumor specific ultrasonic image segmentation[END_REF][START_REF] Stoianovici | A novel mechanical transmission applied to percutaneous renal access[END_REF]. They are mostly interesting because of the large stroke of the needle: since its displacement is obtained by a continuous rotation movement, the system compactness is ensured. Friction also mechanically allows to limit the insertion force, since those devices provide the surgeon with no haptic feedback. On the contrary, in the case of our robotic 1

Copyright c 2005 by ASME system the needle displacement and the interaction forces have to be evaluated to give the surgeon the needle tip position as well as the insertion effort. In this paper, a new robotized needle insertion device is proposed to fulfill the requirements of remote force-controlled needle insertion. The design constraints which have to be complied with include compactness, as the device has to be CT-scan compatible, and preservation of a safe and sterile environment owing to the medical context involved.

In the next section, the overall structure of the needle positioning robot is briefly reviewed. The design of the proposed needle insertion device shall then be presented, outlining its kinematic properties and its thorough adequacy with medical requirements. In the last section, the current development of the prototype shall be described and a first validation of the proposed architecture will be demonstrated through preliminary experimental results. Conclusions on further developments of the insertion device and the overall robotized system will finally be drawn.

THE ROBOTIZED PERCUTANEOUS THERAPY SCE-NARIO

In this section, the overall structure of the needle positioning robot is briefly recalled, with the associated intervention procedure. It outlines the design requirements of the needle insertion device. Further details may be found in [START_REF] Maurin | A new robotic system for CT-guided percutaneous procedures with haptic feedback[END_REF][START_REF] Maurin | A parallel 5 dof positioner for semi-spherical workspaces[END_REF].

The Robotic Positioning Device

The needle positioning robot called CT-Bot is a parallel mechanism attached to the abdomen of the patient with special straps. Its volume is less than 200 × 200 × 250 mm 3 . It weighs less than 2.5 kg which is suitable for most patients. This mechanism features the five degrees of freedom required to position the needle and orient the line supporting its axis. Figures 1 and2 show the CAD model of the CT-Bot and a constructed prototype.

The structure is composed of one 6-bar linkage and a 4-bar linkage joined together by the end-effector. Due to the choice of the legs geometry, the forward and inverse kinematic models can be computed analytically.

The positioning of the end-effector is obtained using ultrasonic motors. The high holding torque of these motors fits particularly the safety requirements in this medical application: the needle positioning robot remains motionless in case of accidental power failure.

The Robotized Percutaneous Procedure

Once a percutaneous therapy is decided by the practitioner, the procedure is composed of three main steps:

1 -Registration of the Robot with Respect to the Patient. The robot registration in the CT-scan is performed using a specifically developed marker linked to the base of the robot. From one CT-scan image of this marker, the robot base position and orientation can be computed [START_REF] Maurin | Pose reconstruction with an uncalibrated computed tomography imaging device[END_REF]. It is necessary to notice that, due to the limited thickness of the CT-scan image slices, the needle tip is not always visible. In particular, the needle tip is very likely to be invisible in the slice of the target (e.g. a tumor). It is therefore necessary to estimate the needle tip position with respect to the CT-scan images using the needle insertion device. positioned for the insertion procedure. The positioning is performed using a collision avoidance algorithm so that the device configuration is always valid.

-Force-Controlled Needle Insertion Using Haptic

Feedback. When the robot end-effector position and orientation are obtained, the needle insertion can be performed. The practitioner uses the visual feedback of the CT-scan image to estimate the required displacement and the haptic feedback to get information on the nature of the tissues. The self-rotation of the needle may also be needed to orient the bevel of the needle.

The needles have dimensions which vary from 100 to 180 mm in length and 0.5 to 2.4 mm in diameter. The available space to carry out insertion is limited by the size of the ring of the scanner and the corpulence of the patient. The minimal available volume corresponds to a 200 mm radius half-sphere centered on the entry point of the needle on the patient's skin. A main constraint of the insertion device is therefore its compactness.

To summarize, in this robotized percutaneous therapy scenario, the needle insertion device has to provide:

1. two degrees-of-freedom, the needle insertion displacement and its self-rotation, 2. the insertion force measurement to provide the practitioner with a force feedback, 3. an insertion principle compatible with the small available volume in the CT-scan, and which allows us also to locate the needle tip with respect to the robot end-effector, 4. safety and sterilization properties.

DESIGN OF THE INSERTION DEVICE

In this section, the main elements of the insertion device are presented to outline its integration on the existing needle positioning robot. The device design is then detailed, before introducing the needle kinematics, the insertion force measurement principle and the device compatibility with medical requirements.

Global Overview

The main components of the needle insertion device are presented on Figure 3 with the platform of the needle positioning robot (item 1 on the figure). The device is composed of three parts: the interface supporting the sensors for needle insertion force measurement (item 2), the driving mechanism including the actuators for all the needle displacements (item 3) and the needle insertion mechanism that performs both grasp and displacements of the needle (item 4).

Design presentation

Grasping of the Needle. The grasping of the needle is carried out using two specifically-designed miniature chucks allowing the insertion device to grasp needles with various diameters. Each chuck is composed of a body, three jaws, a spur gear and an indexing ring (Figure 4). The rotation of the gear with respect to the body generates a radial displacement of the jaws and consequently the grasp or release of the needle.

Insertion Mechanism Design. The insertion mechanism is composed of a casing and a mobile carriage in translation with respect to the casing (Figure 5). A chuck C 1 is mounted on the casing while the other C 2 is linked to the carriage. This latter is displaced by means of the shaft 1 thanks to a nut. The tightening/release of the chucks C 1 and C 2 is obtained by the rotation of the shafts 2 and 3. For each chuck, a pawl system controls the rotation of the indexing ring so that the chuck self-rotation is blocked during a needle release. On the opposite, the chuck and the needle can turn simultaneously during a needle tightening if the applied torque is beyond a threshold defined by the pawl system design.

The two chucks are locked in position using two stems (Figure 5). These stems are pushed in release position by two com-pression springs so that a rotation of the shaft 4 induces the extraction of the chucks.

Driving Mechanism Design. The driving mechanism is composed of two piezoelectric ultrasonic motors M 1 and M 2 (Figure 6). The shaft 1 is actuated by the motor M 1 for carriage translation. The motor M 2 drives simultaneously in rotation the shafts 2 and 3 with opposite directions, thanks to a special gear arrangement. The rotation of only one actuator operates therefore the simultaneous tightening of one chuck (for example C 1 connected to shaft 3) and the loosening of the other (C 2 connected to shaft 2).

A spring-pulled locking blade is maintained armed by a controlled holding electromagnet. In case of power failure, the holding effort vanishes and the locking blade swivels of a fraction of turn. In this way, it drives the shaft 4 in rotation which itself causes the release of the stems 1 and 2.

Device Kinematics

Needle Translation. To perform the large needed needle translation in the limited available volume, the translational movement is split into a sum of elementary translations. These elementary displacements are obtained using translation of the carriage and alternate tightening of the chucks (figure 7).

Initially, the carriage is in its upper position and the chuck C 2 is tightened on the needle. The needle guidance is ensured by having the jaws of the lower chuck C 1 in loose contact with the needle (figure 7-a).

The insertion movement cycle is then divided into four steps:

1. The carriage is translated to its lower position (Figure 7-b). 2. The chuck C 2 is loosened while C 1 is tightened on the needle (Figure 7-c). 3. The carriage is translated back while the needle position remains constant due to its grasp with the chuck C 1 (Figure 7d). 4. The chuck C 2 on the carriage tightens whereas the lower prehensor C 1 releases the needle (Figure 7-e).

This cycle is iterated until the needle tip is at the desired position. For needle extraction, the movement is similar except that the carriage stands initially in its lower position.

Needle Rotation. As previously presented, the pawl systems installed on the chucks limit the tightening torque applied to the needle. Beyond a given torque threshold, the tightened chuck can rotate with the needle providing in this manner a security against overloading.

It should therefore be noted that the single motor M 2 not only performs the needle tightening/release but then also allows the practitioner to rotate the needle about its axis. As a result, the proposed system features a needle self-rotation capability useful for the surgeon to modify the orientation of the bevel without an additional actuator.

Insertion Force Measurement

The interface (Figure 3) is connected to the platform of the needle positioning robot by three 1-DOF bidirectional force sensors symmetrically placed on a circle of radius r drawn around the needle axis (Figure 8). These sensors located at points (A 1 , A 2 , A 3 ) are miniature tension/compression load cells. Vector #» z indicates the needle axis which is different from the direction of the gravity vector #» z 0 (not represented on Figure 8). The entry point B on the patient's skin is located at a distance d from the plane (A 1 , A 2 , A 3 ). We call N the system composed of the needle insertion mechanism, the needle and the three force sensors.

The external actions on N are the force and torque exerted by the skin S on the needle, the action of gravity and the action of the robot platform on the force sensors. Each sensor enables to measure the z-component f i of the action of the robot platform at point A i . After deriving the conditions for system N equilibrium, the z-component of the effort # » F S →N exerted by the skin on the needle can be computed from the force measurements f 1 , f 2 and f 3 :

# » F S →N • #» z = Mg #» z 0 • #» z -f 1 -f 2 -f 3
where M and -g #» z 0 denote the mass of the insertion mechanism attached to the platform of the robot and the gravity acceleration vector. The platform orientation remains constant during the insertion so that Mg #» z 0 • #» z is a measurement offset easily identified before the needle penetration.

The special arrangement of the 1-axis bidirectional sensors enables us also to calculate two components of the torque exerted by the skin on the needle, expressed in O:

#» T O,S →N • #» x = Mg # » OG × #» z 0 • #» x - r 2 f 2 - r √ 3 2 f 3 #» T O,S →N • #» y = Mg # » OG × #» z 0 • #» y + r f 1 - r √ 3 2 f 2 - r 2 f 3
where G denotes the center of mass of the insertion mechanism and the × symbol stands for the vector product. These informations on the torque applied to the needle can be useful for control purposes to detect lateral flexure under needle insertion loading.

Medical Requirements

With the proposed design, the robotized insertion device exhibits several safety properties. First, the grasping of the needle and its displacement are completely decoupled from a kinematic point-of-view and operated by non-backdrivable transmissions. The control of the system is hence simplified and the needle tip position is not influenced by the interaction with the environment. Furthermore, the use of ultrasonic motors enhances safety in the event of a power failure since the configuration of the needle driver remains unchanged. Finally, the chucks linked to the needle can be extracted at any time during the needle insertion or extraction, thanks to the holding electromagnet located on the driving mechanism. The robotic system can therefore be disengaged in a few seconds if it is necessary for medical reasons.

Concerning the sterility requirement, it should be noted that the proposed needle insertion device has two main parts. The active part of the system comprising the force sensors and the driving mechanism is attached to the platform of the positioning robot. The robot and the active part of the needle insertion device can be wrapped in a sterile bag whereas the passive part corresponding to the needle insertion mechanism can be easily detached and sterilized. The chucks constructed out of polycarbonate can also be sterilized and used as disposable units.

CURRENT DEVELOPMENT AND PRELIMINARY EX-PERIMENTS

In this section we present the current state of development of the needle insertion device. A first prototype has been produced to achieve some preliminary experiments concerning the CT-scan compatibility and the tightening capability of the chucks.

Current Development

The first release of a prototype was constructed to validate the presented design. Most of the parts were obtained using a rapid prototyping system except the threaded shaft 1 that was machined with conventional means (Figure 9). In the same way, since the chucks physical properties needed to be close to the final-product ones a mold was constructed using rapid tooling to produce polycarbonate chucks (Figure 10). Due to their small size, mechanisms such as the pawl systems and the quick needle release feature are still in development.

Needle Tightening Capability

Initially we expected to perform insertion forces up to 20 N [START_REF] Maurin | A new robotic system for CT-guided percutaneous procedures with haptic feedback[END_REF]. However, previous experiments [START_REF] Maurin | In vivo study of forces during needle insertions[END_REF] showed that this constraint for the robotized insertion device was somewhat overestimated. Experiments have been achieved to validate the currently developed prototype behavior, and especially the absence of nee- dle sliding in the chucks.

The experimental set-up is composed of the insertion device, a needle, an ATI Nano-17 6-axis force sensor, a PC for data acquisition, a spring-pulled cart sliding on two columns and a 6-DOF robot FANUC LR-200i (Figure 11). The needle and the insertion device are linked to the robot, and displaced at a constant speed of 1 mm/s.

Thanks to the spring-pulled cart, the position control of the The deviation between the two curves is quite certainly due to the flexure of the needles, which does not influence the experimental results. This first evaluation of the needle tightening capability of the insertion device tends to validate the proposed design.

CT-Scan Compatibility

Some experiments have been conducted at the University Hospitals of Strasbourg to perform trials on a phantom.

CONCLUSION

In this paper, a new needle insertion device has been proposed. This device is included in a robotic system dedicated to gesture guidance in percutaneous procedures.

A grasp/release scheme has been proposed to accommodate various size of needles and to allow force sensors integration for haptic feedback. The specific kinematics ensures the device compactness required for a use in a CT-scan without introducing redundant actuation since two motors control the two required DOF. With the proposed design, the needle displacements are controlled in a safe way and quite high insertion forces are possible. The system architecture facilitates its sterilization and the quick disengagement of the robotic system if required for medical reasons.

The first release of a prototype has been issued and tested during preliminary experiments. Further evaluations will be performed on a bench and in a CT-scan to validate the design. The development of the robotic system will then include the design of a specific haptic interface to interact with the surgeon.

Figure 1 .

 1 Figure 1. CT-BOT CAD MODEL.

Figure 2 .

 2 Figure 2. CT-BOT PROTOTYPE.

Figure 3 .

 3 Figure 3. EXPLODED VIEW OF THE NEEDLE INSERTION DEVICE.

Figure 4 .

 4 Figure 4. EXPLODED VIEW OF A CHUCK.

Figure 5 .

 5 Figure 5. INSERTION MECHANISM.

Figure 6 .

 6 Figure 6. DRIVING MECHANISM.

Figure 7 .

 7 Figure 7. INSERTION CYCLE.

Figure 8 .

 8 Figure 8. SCHEMATIC REPRESENTATION OF FORCE SENSORS LO-CATION.

Figure 9 .

 9 Figure 9. FABRICATED PROTOTYPE OF THE INSERTION DEVICE.

Figure 10 .

 10 Figure 10. FABRICATED PROTOTYPE OF A CHUCK.

Figure 11 .Figure 12 .

 1112 Figure 11. EXPERIMENTAL SETUP FOR NEEDLE INSERTION EF-FORT CAPABILITY.

Figure 13

 13 Figure 13. CT-SCAN IMAGE OF THE ROBOTIC SYSTEM.

-Displacement of the Needle Positioning Robot. From the previous registration, the robot end-effector can be

Copyright c 2005 by ASME

ACKNOWLEDGMENT

The authors wish to thank the Alsace Region and the CNRS-ROBEA program for the financial support of this research work.


Mireille Louys
email: mireille.louys@unistra.fr

Katharina Lutz

Yelena Stein

Anais Egner

François Bonnarel

Radio Astronomy visibility data discovery and access using IVOA standards

Enhancing interoperable data access to radio data has become a science priority within the International Virtual Observatory Alliance (IVOA). This lead to the foundation of the IVOA Radio astronomy Interest Group. Several radio astronomers and project scientists enrolled in various projects (NRAO, ASKAP, LOFAR, JIVE, ALMA, SKA, INAF, NenuFAR, etc.) have joined. Together they are paving the way to a better integration of their services in the virtual observatory (VO) infrastructure and propose extension of IVOA standards to help achieving this goal.

) and to establish cross-walks between the ObsCore and the existing Measurement Set (MS) metadata profile for data discovery of radio visibility data (VD).

In order to account for the difference in granularity between radio VD datasets and science-ready datasets of the VO, the approach splits a MS data file into a list of datasets served by an ObsTAP service, thus enabling coarse grain discovery in the multi-wavelength context. Radio specific metadata such as number of antennae, frequency ranges, uv plane coverage plots, frequency-phase and frequency-amplitude plots, primary and synthesized beams are also provided either by adding column metadata or by using the DataLink technique. Future evolution of this approach and lessons learnt are discussed.

Goal

Radio astronomical archives for large facilities (e. g. VLA, LOFAR, EVN, ATCA, ...) used to store mostly raw or calibrated visibility data. However, the situation is changing and some projects (e. g. ALMA, ASKAP, MeerKAT...), distribute science-ready data 1 like cubes. This approach is also planned for the SKA, the future Square Kilometer Array project. Up to now raw visibility data are mostly accessed through project-specific web interfaces. Scientists can reduce the data with adjusted tools and customized configuration parameters. In the future, this workflow will evolve towards the use of next generation science platforms like e. g. ESAP proposed within the ESCAPE1 project where reduction codes will run close to the data. The tremendous increase of observations provided by many large projects in the radio frequency domain is interesting beyond the radio astronomical community. Multi-messenger and multi-wavelength observations analysis is essential nowadays to explore and validate more advanced models of astrophysical processes involving complex interactions.

Many radio observatory archives already provide reduced data via VO-enabled services (e.g., CADC, CASDA, ATCA,...). These services include e.g. ObsTAP, HiPS servers, DataLink (Dowler et al. 2015) and SODA [START_REF] Bonnarel | IVOA Server-side Operations for Data Access Version 1.0[END_REF], for instance for science-ready radio cubes. In this study, we show how to adapt ObsTAP to serve as a VO interface for discovering and accessing especially visibility data from radio astronomy facilities.

Metadata extraction from visibility-dedicated Measurement Set to ObsCore metadata profile

The MS format (van Diepen 2015) for radio visibility observations contains multiple exposures pointed on various sky regions which are stored in Fields. Within each Field, the signal can be observed across several spectral windows and with various polarisation settings. The MS format wraps them together in one container. The CASA [START_REF] Emonts | The casa software for radio astronomy: status update from adass[END_REF]) listobs command displays a summary of the main metadata keywords of the observation. In addition various plots and maps can be produced to interpret the information content such as uv plane coverage maps, amplitude/phase plots or amplitude/uv distance, etc. In the ObsCore approach however, multi-wavelength search requires feature separation in order to express how data are spanned on the spatial, spectral, temporal and observable axis. Hence, data stored in a MS file must be represented as a collection of coverage-homogeneous subsets that ObsCore can describe. We have set-up a split procedure for this. We consider one ObsCore dataset to be a subset of contiguous or overlapping SpectralWindows of same ChannelWidth for a given Field. Scans pointed towards the same Field are grouped together and gather all related time stamps for this dataset. This procedure has been trained on various test data stemming from ATCA, LOFAR, VLA, JIVE radio visibilities archives. Fig . 1 illustrates the partition of an MS dataset as a collection of ObsCore member datasets. Following the split procedure, an individual ObsCore dataset corresponds to one identified Field observed on one specific frequency interval, gathering contiguous channels. Such data set can be characterised using existing ObsCore keywords. The data-product_type is set to 'visibility'. The spatial features s_ra, s_dec, can be mapped to the reference sky position of one Field, s_resolution can be estimated from the longest baseline in the MS, and s_fov from the antennae diameter. Note that s_fov is dependent on the frequency. If the observations covers a large frequency range, one individual value for s_fov will only be a first approximation. The spectral coverage in radio observations refers to frequency and multiple of Hz as units. We propose to add f_min and f_max for the frequency interval in kHz. We would still keep the converted spectral band in em_min and em_max in m as defined in ObsCore to allow multi-wavelength queries, and support interoperability between different ObsTAP services. In this case, the ObsCore convention allows to set em_unit=kHz and em_ucd=em.freq, for instance, in order to explicitly declare the usage of frequencies for the spectral information within the dataset. The spectral resolution power em_respower, defined similarly in both wavelength and frequency also allows querying in both spectral quantities.

The VD values are complex Fourier coefficients stored in the uv plane; the observable axis of ObsCore can then represent it using o_ucd=stat.Fourier. Time features t_min, t_max, t_resolution can directly be taken from the scan table within listobs output. t_exptime is the sum of integration times on one Field and independent of the spectral coverage.

In radio astronomy the potential scientific interest for a dataset depends on the uv plane coverage, sensitivity, signal-to-noise ratio, etc. The quality measures cannot be directly translated to one value, but instead are based on additional interpretation maps and instrument-dependent simulations. Software like CASA, for instance, allow to extract such maps and files from a MS dataset.

We have considered delivering these maps via a Datalink capability added to an ObsTAP service, as shown in Fig. 2. in order to provide access to : 1) the listobs metadata summary file; 2) the MS file; 3) explanatory plots for the uv plane coverage, antennae positions, amplitude/phase graphs, etc.

A radio extension table for the ObsTAP standard is under study with LOFAR AS-TRON and JIVE collaborators, to gather specific radio properties of these datasets: -s_maxscale : the largest angular scale captured in the observation (LAS) -n_vis : the nb of visibilities covered within the individual dataset uv plane coverage filling factor uv plane coverage ellipse approximation or beam estimate (b_max, b_min, b_angle)

Conclusion

This work demonstrates how to build a VO front-end for discovery of radio visibility data, based on an ObsTAP service enriched with radio specific metadata selected here from the MS metadata profile. The extension of the ObsTAP TAP_SCHEMA with an extra radio specific table is proposed for final discussion in the IVOA pages of the IVOA Radio Interest Group and will be consolidated using a wider set of radio datasets from various projects and data formats.

The effective partitioning of the data contained in the MS file into a set of data chunks corresponding to an individual ObsCore dataset is not required. This implies a duplication of the data volume which is undesirable for such amount of data. On the contrary, these data chunks can be generated on the fly by a customized extraction process that recombines or splits data chunks from the discovered MS datasets with the state-of-the-art tools appropriate to each particular radio archive. This approach would allow on the one hand full command of instrument/project specific processing to happen on the radio experts/ archives side and would, on the other hand, still facilitate multi-wavelength and multi-messenger data discovery for the astronomical community at large.

Figure 1 .

 1 Figure 1. The SPLIT procedure represents a MS dataset as a collection of members datasets whose coverage in spatial and spectral features in ObsCore is compact.

Figure 2 .

 2 Figure 2. ObsTAP query response with DataLink options to associated explanatory files. In blue the uv plane coverage for a MS observation of NGC 104.

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Acknowledgments. For the support of ESCAPE (European Science Cluster of Astronomy and Particle Physics ESFRI Research Infrastructures) funded by the EU Horizon 2020 research and innovation program (Grant Agreement n.824064).