Unconventional Uses of Cantilevers for Chemical Sensing in Gas and Liquid Environments

Microcantilevers used as (bio)chemical sensors are usually coated with a chemically sensitive layer. The coated devices operate either in a static bending regime or in a dynamic flexural mode. While the coated devices operate generally well in both the static and dynamic mode, they do suffer from certain shortcomings depending on the medium of operation and the application, including lack of selectivity and of reversibility of the sensitive coating and a reduced quality factor due to the surrounding medium. In particular, the performance of microcantilevers excited in their standard out-of-plane dynamic mode drastically decreases in viscous liquid media. Moreover, the responses of coated cantilevers operating in the static bending mode are often difficult to interpret. To resolve those performance issues, unconventional uses of microcantilever are reviewed in this paper, which consist of the use of the dynamic mode without sensitive coating, the use of in-plane (flexural and longitudinal) vibration modes in liquid media, and fully accounting for the viscoelastic effects of the coatings in the static mode of operation. The advantages and drawbacks of these unconventional uses of microcantilevers for chemical sensing in gas and liquid environments are discussed

Study of Viscoelastic Effect on the Frequency Shift of Microcantilever Chemical Sensors (proceedings)

Microcantilevers coated with a chemically sensitive layer are increasingly being used in chemical detection systems. The sensitive coating, often a polymer, absorbs specific molecules, which can be detected by monitoring the shift in the mechanical resonant frequency. Usually, the frequency shift resulting from molecular absorption is interpreted as a mass loading effect. However, mass loading is not the only effect that has an impact on the frequency shift; the viscoelastic properties of the sensitive coating are also affected by the sorption process. Sorption-induced modulus changes are typically difficult to characterize. However, it is known that the sorption of analyte molecules in a polymer coating results in the plasticization of the coating. In most cases, the polymer becomes more rubbery with increasing concentration of analyte molecules, i.e., the coating becomes softer with increasing loss modulus while the storage modulus decreases. Using a new analytical model developed for the resonant frequency expression of a hybrid microcantilever (elastic base and viscoelastic layer), the effects of the modification of the storage and loss moduli of the sensitive layer on the resonant frequency are examined. The main conclusion of this analytical study is that, even if the sensitive coating moduli are small compared to the base cantilever\u27s Young\u27s modulus, the effect of the change in the viscoelastic coating properties could contribute significantly to the overall frequency shift (8-23% in the simulations depending on the coating thickness, with even higher contributions for other sets of problem parameters)

Effect of Viscoelasticity on Quality Factor of Microcantilever Chemical Sensors: Optimal Coating Thickness for Minimum Limit of Detection

Microcantilevers with polymer coatings hold great promise as resonant chemical sensors. It is known that the coated cantilever sensitivity increases with coating thickness; however, the drawback of increasing the coating thickness is the increase of the frequency noise and thus the deterioration of the sensor\u27s limit of detection. In this paper, an analytical expression for the viscoelastic losses in the coating, hence the quality factor is established and is used to explain the observed increase of the frequency noise with the polymer thickness. This result is then used to demonstrate that an optimum coating thickness exists that minimise the limit of detectio

The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III

The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with new instrumentation and new surveys focused on Galactic structure and chemical evolution, measurements of the baryon oscillation feature in the clustering of galaxies and the quasar Ly alpha forest, and a radial velocity search for planets around ~8000 stars. This paper describes the first data release of SDSS-III (and the eighth counting from the beginning of the SDSS). The release includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap, bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a third of the Celestial Sphere. All the imaging data have been reprocessed with an improved sky-subtraction algorithm and a final, self-consistent photometric recalibration and flat-field determination. This release also includes all data from the second phase of the Sloan Extension for Galactic Understanding and Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars at both high and low Galactic latitudes. All the more than half a million stellar spectra obtained with the SDSS spectrograph have been reprocessed through an improved stellar parameters pipeline, which has better determination of metallicity for high metallicity stars.Comment: Astrophysical Journal Supplements, in press (minor updates from submitted version

Rab27a and Rab27b control different steps of the exosome secretion pathway

Exosomes are secreted membrane vesicles that share structural and biochemical characteristics with intraluminal vesicles of multivesicular endosomes (MVEs). Exosomes could be involved in intercellular communication and in the pathogenesis of infectious and degenerative diseases. The molecular mechanisms of exosome biogenesis and secretion are, however, poorly understood. Using an RNA interference (RNAi) screen, we identified five Rab GTPases that promote exosome secretion in HeLa cells. Among these, Rab27a and Rab27b were found to function in MVE docking at the plasma membrane. The size of MVEs was strongly increased by Rab27a silencing, whereas MVEs were redistributed towards the perinuclear region upon Rab27b silencing. Thus, the two Rab27 isoforms have different roles in the exosomal pathway. In addition, silencing two known Rab27 effectors, Slp4 (also known as SYTL4, synaptotagmin-like 4) and Slac2b (also known as EXPH5, exophilin 5), inhibited exosome secretion and phenocopied silencing of Rab27a and Rab27b, respectively. Our results therefore strengthen the link between MVEs and exosomes, and introduce ways of manipulating exosome secretion in vivo

Travail social et champ sociojudiciaire : vers une contribution renouvelée?

Le travail social a traditionnellement été très actif dans le champ sociojudiciaire. Or, depuis les années 80, on constate que cette profession y est moins exercée. L’objectif de cet article est de débusquer les raisons qui ont provoqué cet exode et de mettre en exergue les principaux défis et enjeux contemporains reliés à la pratique du travail sociojudiciaire. Cette analyse critique permettra ensuite d’explorer le contexte actuel favorisant une contribution renouvelée de la discipline à ce champ de pratique.Social work and criminal justice domain have always been traditionally related. But since the beginning of 1980’s, there are less socials workers working in this field. This article aim to uncover the reasons that are related to this abandon and to explore the difficulties that social workers encounters today in this field. This socio historical analysis serves as a basis to explore the new opportunities that would make it possible for the social work discipline to reaffirm a strong presence in this field

Chapitre 7. « Maman, as-tu bientôt fini tes devoirs ? »

Entreprendre un doctorat est probablement la décision la plus égocentrique que l’on puisse prendre sur le plan intellectuel. Il s’agit en effet d’une quête que l’on parcourt seul et souvent uniquement pour soi (c’est-à-dire pour se prouver qu’on est capable, pour trouver une réponse à la question qui nous préoccupe depuis des années, pour pouvoir faire le métier qui nous fait rêver). Pendant de longues années, cette expédition scientifique nous habite, jusqu’à définir qui nous sommes. Comment..

Le désistement assisté ? Les interventions des agents de probation telles que perçues par des sursitaires qui se sont désistés du crime

Un nombre grandissant d’études sur le désistement ont permis de déterminer le ou les processus qui conduisent à l’abandon de la « carrière criminelle ». On reconnaît généralement que ces processus peuvent être facilités (ou contrecarrés) par l’agent de probation chargé du suivi du désisteur. Or, il y a encore peu d’études ayant porté sur le rôle des agents de probation dans le processus de désistement du crime et, généralement, celles qui existent sont centrées sur l’étape de désistement primaire (arrêt des comportements criminels). Cet article illustre le point de vue de 22 désisteurs secondaires (changement identitaire) sur les interventions facilitantes (ou non) offertes par leurs agents de probation lors de leur emprisonnement avec sursis. Les résultats indiquent que la perception de ces interventions varie selon le type de processus de désistement du crime emprunté par les sursitaires.The growing amount of research on desistance makes it possible to determine which processes are effective in leading individuals to abandon a criminal career. It is generally recognized that probation officers can assist (or undermine) this process, but there are still only a few studies that look specifically at the role of probation officers in desistance. Existing studies generally draw on the experiences of primarily (criminal behavior only) desisters. This article highlights the views of 22 secondary (criminal identity) desisters on interventions by probation officers that helped or hindered their process of desistance during a conditional sentence in the province of Quebec in Canada. The results indicate that their perceptions of these interventions varied accordingly to the type of desistance process provided.Numerosos estudios sobre el desistimiento han permitido determinar el o los procesos que conducen a renunciar a la « carrera criminal ». Se reconoce generalmente que esos procesos pueden ser facilitados (o entorpecidos) por el agente de libertad condicional a cargo del desistiente. Ahora bien, aún son escasos los estudios que se han ocupado del rol de los agentes de libertad condicional en el proceso de desistimiento del crimen y, generalmente, aquellos que existen se enfocan en la etapa de desistimiento primario (cese de los comportamientos criminales). Este artículo ilustra el punto de vista de 22 disidentes secundarios (cambio de identidad) sobre las intervenciones facilitadoras (o no) que ofrecen sus agentes de libertad condicional durante sus encarcelamientos con remisión condicional. Los resultados indican que la percepción de esas intervenciones varía de acuerdo al tipo de proceso de desistimiento del crimen empleado