File system metadata virtualization

The advance of computing systems has brought new ways to use and access the stored data that push the architecture of traditional file systems to its limits, making them inadequate to handle the new needs. Current challenges affect both the performance of high-end computing systems and its usability from the applications perspective. On one side, high-performance computing equipment is rapidly developing into large-scale aggregations of computing elements in the form of clusters, grids or clouds. On the other side, there is a widening range of scientific and commercial applications that seek to exploit these new computing facilities. The requirements of such applications are also heterogeneous, leading to dissimilar patterns of use of the underlying file systems. Data centres have tried to compensate this situation by providing several file systems to fulfil distinct requirements. Typically, the different file systems are mounted on different branches of a directory tree, and the preferred use of each branch is publicised to users. A similar approach is being used in personal computing devices. Typically, in a personal computer, there is a visible and clear distinction between the portion of the file system name space dedicated to local storage, the part corresponding to remote file systems and, recently, the areas linked to cloud services as, for example, directories to keep data synchronized across devices, to be shared with other users, or to be remotely backed-up. In practice, this approach compromises the usability of the file systems and the possibility of exploiting all the potential benefits. We consider that this burden can be alleviated by determining applicable features on a per-file basis, and not associating them to the location in a static, rigid name space. Moreover, usability would be further increased by providing multiple dynamic name spaces that could be adapted to specific application needs. This thesis contributes to this goal by proposing a mechanism to decouple the user view of the storage from its underlying structure. The mechanism consists in the virtualization of file system metadata (including both the name space and the object attributes) and the interposition of a sensible layer to take decisions on where and how the files should be stored in order to benefit from the underlying file system features, without incurring on usability or performance penalties due to inadequate usage. This technique allows to present multiple, simultaneous virtual views of the name space and the file system object attributes that can be adapted to specific application needs without altering the underlying storage configuration. The first contribution of the thesis introduces the design of a metadata virtualization framework that makes possible the above-mentioned decoupling; the second contribution consists in a method to improve file system performance in large-scale systems by using such metadata virtualization framework; finally, the third contribution consists in a technique to improve the usability of cloud-based storage systems in personal computing devices.Postprint (published version

Non-Invasive Determination of Breslow Index

Breslow index is defined as maximal thickness of cutaneous malignant melanoma measured in several slides from the top of the granular cell layer to the deepest point of invasion. Prognosis, prediction of sentinel lymph node status as well as excision margins are based on Breslow index determination. Non-invasive Breslow index determination would allow one-time procedure for melanoma clinical management which would be of utmost medical interest for several reasons: unimpaired sentinel lymph node status, low morbidity, pain and stress associated to surgical excision margins. However, as explained throughout the current chapter, such a determination requires melanoma diagnosis prior to Breslow determination. As a result, all techniques reported in this chapter (based on ultrasounds, optical waves or both), not only demonstrate their ability to determine Breslow thickness but also their ability to increase diagnosis accuracy. Ultrasonography and dermoscopy are currently evaluated in clinical environments. Diffuse reflectance spectroscopy, has been tested on tissue phantoms. Infrared microimaging and photoacoustic microscopy have shown preliminary results on fixed and paraffin-embedded tissues without staining and on xenografted tumours on mice respectively. Finally, optical coherence tomography and confocal microscopy may have a clinical interest in the management of very thin melanomas but require further studies to show their potential interest

“The damned behaviorist” versus French phenomenologists: Pierre Naville and the French indigenization of Watson's behaviorism.

What do we know about the history of John Broadus Watson’s behaviorism outside of its American context of production? In this article, using the French example, we propose a study of some of the actors and debates that structured this history. Strangely enough, it was not a “classic” experimental psychologist, but Pierre Naville (1904–1993), a former surrealist, Marxist philosopher, and sociologist, who can be identified as the initial promoter of Watson’s ideas in France. However, despite Naville’s unwavering commitment to behaviorism, his weak position in the French intellectual community, combined with his idiosyncratic view of Watson’s work, led him to embody, as he once described himself, the figure of “the damned behaviorist.” Indeed, when Naville was unsuccessfully trying to introduce behaviorism into France, alternative theories defended by philosophers such as Jean-Paul Sartre and Maurice Merleau-Ponty explicitly condemned Watson’s theory and met with rapid and major success. Both existentialism and phenomenology were more in line than behaviorism with what could be called the “French national narrative” of the immediate postwar. After the humiliation of the occupation by the Nazis, the French audience was especially critical of any deterministic view of behavior that could be seen as a justification for collaboration. By contrast, Sartre’s ideas about absolute freedom and Merleau-Ponty’s attempt to preserve subjectivity were far more acceptable at the time

Using file system virtualization to avoid metadata bottlenecks

Abstract—Parallel file systems are very sensitive to adverse conditions, and the lack of synergy between such file systems and some of the applications running on them has a negative impact on the overall system performance. Our observations indicate that the increased pressure on metadata management is one of the relevant causes of performance drops. This paper proposes a virtualization layer above the native file system that, transparently to the user, reorganizes the underlying directory tree, mitigating bottlenecks by taking advantage of the native file system optimizations and limiting the effects of potentially harmful application behavior. We developed COFS (COmposite File System) as a proof-of-concept virtual layer to evaluate the feasibility of the proposal.Peer ReviewedPostprint (published version

A parametric study on the emissions from an HCCI alternative combustion engine resulting from the auto-ignition of primary reference fuels

The homogeneous charge compression ignition is an alternative combustion technology that can reduce automobile pollution, provided that the exhaust emission can be controlled. A parametric study can be useful in order to gain more understanding in the emission reduction possibilities via this new combustion technology. For this purpose, the inlet temperature, the equivalence ratio and the compression ratio are changed, respectively, from 30 to 70 degrees C, 0.28 to 0.41 and 6 to 14. Also the diluting, thermal and chemical effects of exhaust gas recirculation were studied. The emission of CO, CO2, O-2 and hydrocarbons has been measured using primary reference fuels. It appears that an increase in the inlet temperature, the EGR temperature, the equivalence ratio and the compression ratio results into a decrease of the emissions of CO and the hydrocarbons of up to 75%. The emission of CO2 increased, however, by 50%. The chemical parameters showed more complicated effects, resulting into a decrease or increase of the emissions, depending on whether the overall reactivity increased or not. If the reactivity increased, generally, the emissions of CO and hydrocarbons increased, while that of CO2 increased. The increase of CO2 emissions could be compensated by altering the compression ratio and the EGR parameters, making it possible to control the emission of the HCCI engine. (c) 2008 Elsevier Ltd. All rights reserved

On the role of chirality in structure-odor relationships

The influence of chirality on odors was studied on 16 enantiomeric pairs according to the dispersion/hydrogen bonding theory of receptor-odorant interaction. Comparisons of molecular structures were made by superimposition of optimized conformations, using the Alchemy II package. The quality of fit was assessed using the RMS parameter included in Alchemy II and a new index for hydrogen bonding: the angle between H-bonds in the two molecules. In the case of camphoraceous odorants where an interaction model was already known superimposition according to the model led to correct predictions of the high similarity of odors observed in enantiomeric pairs. For several urinous odorants comparisons were made using d-androstenone as a reference compound for the urinous odor. Correct predictions were obtained for l-androstenone, both enantiomers of androsta-4, 16-dienone, and (+)-2-methyl-4-(5,5,6-exo-trimethy1-2-exonorbornyl)-cyclobexane. The (−) enantiomer of the latter compound was correctly predicted only if it was assumed that its weak intensity is due to a partial interaction with the hydrophobic zone of the receptor. For ambergris odorants which have a complex odor (−)-Ambrox was selected as the reference compound. The odors of (+)-Ambrox and enantiomers of four other compounds (ambergris or woody) were correctly predicted by superimposition. For nootkatone and three derivatives which have a grapefruit note for one enantiomer and a woody note for the other no models or reference compounds were available. The superimpositions were made between grapefruit enantiomers, on the one hand, and woody enantiomers on the other hand. Woody and grapefruit characters were correctly predicted in all cases. The limits of this approach based on molecular modelling are discusse