449 research outputs found
Electrical properties of epoxies and film resistors
The reliability of hybrid microcircuits has been enhanced in recent years by the use of organic adhesives as a replacement for solder and eutectics. The epoxies have been the most effective and widely used material for this application. Methods for measuring the electrical and mechanical properties of epoxies are developed. Data are given for selected conductive adhesives at high and low frequencies. The temperature coefficients of resistance of thick film resistors are presented
Transport and percolation in a low-density high-mobility two-dimensional hole system
We present a study of the temperature and density dependence of the
resistivity of an extremely high quality two-dimensional hole system grown on
the (100) surface of GaAs. For high densities in the metallic regime (p\agt 4
\times 10^{9} cm), the nonmonotonic temperature dependence ( mK) of the resistivity is consistent with temperature dependent
screening of residual impurities. At a fixed temperature of = 50 mK, the
conductivity vs. density data indicates an inhomogeneity driven
percolation-type transition to an insulating state at a critical density of
cm.Comment: accepted for publication in PR
Acoustic phonon scattering in a low density, high mobility AlGaN/GaN field effect transistor
We report on the temperature dependence of the mobility, , of the
two-dimensional electron gas in a variable density AlGaN/GaN field effect
transistor, with carrier densities ranging from 0.4 cm to
3.0 cm and a peak mobility of 80,000 cm/Vs. Between
20 K and 50 K we observe a linear dependence T
indicating that acoustic phonon scattering dominates the temperature dependence
of the mobility, with being a monotonically increasing function of
decreasing 2D electron density. This behavior is contrary to predictions of
scattering in a degenerate electron gas, but consistent with calculations which
account for thermal broadening and the temperature dependence of the electron
screening. Our data imply a deformation potential D = 12-15 eV.Comment: 3 pages, 2 figures, RevTeX. Submitted to Appl Phys Let
Quelle rĂ©gulation pour lâarrĂȘt dâun protocole de recherche clinique de thĂ©rapie gĂ©nique somatique ? Ătat des lieux auprĂšs des cliniciens-chercheurs europĂ©ens
Depuis 2002, le dĂ©bat sur les risques associĂ©s Ă la thĂ©rapie gĂ©nique est initiĂ© suite Ă lâannonce
que deux enfants inclus dans un essai thérapeutique impliquant une thérapie génique ont
développé des effets indésirables important. En Janvier 2005, le débat sur les risques reprit suite
Ă lâinterruption du protocole sur les enfants bulle du Pr Fischer Ă lâhĂŽpital Necker de Paris. Nous
avons donc étudié le processus impliqué ainsi que la réflexion éthique associée aux décisions
dâarrĂȘt de protocole de recherche. Notre travail a Ă©tĂ© menĂ© par une Ă©quipe pluridisciplinaire
combinant chercheurs en santé, généticiens et éthiciens. Nous avons étudié la participation des
chercheurs, des patients, des institutions officielles, des comitĂ©s dâĂ©thique ainsi que des
associations de patients dans le processus de dĂ©cision dâinterruption dâun protocole de recherche.Nous avons Ă©galement analysĂ© les critĂšres jugĂ©s les plus pertinents dans lâarrĂȘt dâun protocole
de recherche. Enfin nous avons analysé le point de vue des personnes directement impliquées
dans la thĂ©rapie gĂ©nique au moyen dâun questionnaire. Toutes les personnes contactĂ©es ont
présenté un poster de recherche au congrÚs de la Société Européenne de Thérapie Génique. 62
personnes dâautant dâĂ©quipes de recherche diffĂ©rentes, de 17 pays, sur les 350 contactĂ©s ont
rĂ©pondu. Selon eux, la dĂ©cision dâarrĂȘt dâun protocole de recherche doit ĂȘtre prise suite Ă une
consultation des chercheurs, des patients, du ministĂšre de tutelle, dâune agence nationale de
rĂ©gulation ou dâun comitĂ© dâĂ©thique ; la lĂ©gitimitĂ© Ă©tant accordĂ©e Ă des dĂ©cisions prises en
commun par les chercheurs, les patients et les comitĂ©s dâĂ©thique. Les incidents sĂ©rieux et de façon
plus surprenante, les incidents moins graves sont jugés comme étant des critÚres suffisants pour
interrompre un essai. Nous avons fini par analyser les conséquences éthiques, telles que balance
bĂ©nĂ©fice/risque, processus de rĂ©gulation ou responsabilitĂ©, de ces critĂšres sur lâarrĂȘt dâun protocole
de recherche.In 2002, the debate on the risks of gene therapy was initiated following the annoucement that two
children included in a clinical trial developed serious adverse effects. In January 2005, the debate
was reignited following the interruption of the âbubble kids protocolâ at the HĂŽpital Necker in Paris.
We have thus investigated the ethical stakes involved in decisions to stop protocols. This work was
carried out by a multidisciplinary team combining ethics researchers and geneticists. We studied
the specific participation of researchers, patients, official institution, ethics committees and patient
associations in the processes that can lead to an interruption of trial.We also analysed the criterion
judged most relevant for halting a trial. Finally, we analyzed the perspective of the actors implicated
directly in the provision of gene therapy, by means of a questionnaire. All the individuals contacted
had presented a scientific poster at the European Society of Gene Therapy. 62 out of 350 persons,
from 17 countries, responded to our questionnaire. According to these respondants, decisions to stop
a trial should be taken after consultation with researchers, patients, the ministry, national agencies
or ethics committees. Legitimacy was accorded to joint decision-making by researchers, patients and
committees. Serious incidents, and surprisingly less serious incidents, clearly emerge as criterion for
stopping a trial. We conclude by analyzing the ethical consequences, such as risk/benefit ratios,
regulatory processes and responsibility, associated with these criterions and decisions to stop a trial
Large Bychkov-Rashba spin-orbit coupling in high-mobility GaN/AlGaN heterostructures
We present low temperature magnetoconductivity measurements of a
density-tunable and high mobility two-dimensional electron gas confined in the
wide bandgap GaN/AlGaN system. We observed pronounced anti-localization minima
in the low-field conductivity, indicating the presence of strong spin-orbit
coupling. Density dependent measurements of magnetoconductivity indicate that
the coupling is mainly due to the Bychkov-Rashba mechanism. In addition, we
have derived a closed-form expression for the magnetoconductivity, allowing us
to extract reliable transport parameters for our devices. The Rashba spin-orbit
coupling constant is 6 10eVm, while the
conduction band spin-orbit splitting energy amounts to
0.3meV at n=1m.Comment: Accepted for publication in PR
Quantum theory of dissipation of a harmonic oscillator coupled to a nonequilibrium bath; Wigner-Weisskopf decay and physical spectra
We extend the quantum theory of dissipation in the context of
system-reservoir model, where the reservoir in question is kept in a
nonequilibrium condition. Based on a systematic separation of time scales
involved in the dynamics, appropriate generalizations of the
fluctuation-dissipation and Einstein's relations have been pointed out. We show
that the Wigner-Weisskopf decay of the system mode results in a rate constant
which depending on the relaxation of nonequilibrium bath is dynamically
modified. We also calculate the time-dependent spectra of a cavity mode with a
suitable gain when the cavity is kept in contact with a nonequilibrium bath.Comment: Plain Latex, 28 pages, 2 PS figure
Longer fixation duration while viewing face images
The spatio-temporal properties of saccadic eye movements can be influenced by the cognitive demand and the characteristics of the observed scene. Probably due to its crucial role in social communication, it is argued that face perception may involve different cognitive processes compared with non-face object or scene perception. In this study, we investigated whether and how face and natural scene images can influence the patterns of visuomotor activity. We recorded monkeysâ saccadic eye movements as they freely viewed monkey face and natural scene images. The face and natural scene images attracted similar number of fixations, but viewing of faces was accompanied by longer fixations compared with natural scenes. These longer fixations were dependent on the context of facial features. The duration of fixations directed at facial contours decreased when the face images were scrambled, and increased at the later stage of normal face viewing. The results suggest that face and natural scene images can generate different patterns of visuomotor activity. The extra fixation duration on faces may be correlated with the detailed analysis of facial features
Pseudomonas aeruginosa Expresses a Functional Human Natriuretic Peptide Receptor Ortholog: Involvement in Biofilm Formation
This is the final version of the article. Available from the publisher via the DOI in this record.Considerable evidence exists that bacteria detect eukaryotic communication molecules and modify their virulence accordingly. In previous studies, it has been demonstrated that the increasingly antibiotic-resistant pathogen Pseudomonas aeruginosa can detect the human hormones brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) at micromolar concentrations. In response, the bacterium modifies its behavior to adapt to the host physiology, increasing its overall virulence. The possibility of identifying the bacterial sensor for these hormones and interfering with this sensing mechanism offers an exciting opportunity to directly affect the infection process. Here, we show that BNP and CNP strongly decrease P. aeruginosa biofilm formation. Isatin, an antagonist of human natriuretic peptide receptors (NPR), prevents this effect. Furthermore, the human NPR-C receptor agonist cANF(4-23) mimics the effects of natriuretic peptides on P. aeruginosa, while sANP, the NPR-A receptor agonist, appears to be weakly active. We show in silico that NPR-C, a preferential CNP receptor, and the P. aeruginosa protein AmiC have similar three-dimensional (3D) structures and that both CNP and isatin bind to AmiC. We demonstrate that CNP acts as an AmiC agonist, enhancing the expression of the ami operon in P. aeruginosa. Binding of CNP and NPR-C agonists to AmiC was confirmed by microscale thermophoresis. Finally, using an amiC mutant strain, we demonstrated that AmiC is essential for CNP effects on biofilm formation. In conclusion, the AmiC bacterial sensor possesses structural and pharmacological profiles similar to those of the human NPR-C receptor and appears to be a bacterial receptor for human hormones that enables P. aeruginosa to modulate biofilm expression. IMPORTANCE: The bacterium Pseudomonas aeruginosa is a highly dangerous opportunist pathogen for immunocompromised hosts, especially cystic fibrosis patients. The sites of P. aeruginosa infection are varied, with predominance in the human lung, in which bacteria are in contact with host molecular messengers such as hormones. The C-type natriuretic peptide (CNP), a hormone produced by lung cells, has been described as a bacterial virulence enhancer. In this study, we showed that the CNP hormone counteracts P. aeruginosa biofilm formation and we identified the bacterial protein AmiC as the sensor involved in the CNP effects. We showed that AmiC could bind specifically CNP. These results show for the first time that a human hormone could be sensed by bacteria through a specific protein, which is an ortholog of the human receptor NPR-C. The bacterium would be able to modify its lifestyle by favoring virulence factor production while reducing biofilm formation.We thank Magalie Barreau and Olivier Maillot for technical assistance.
We thank Christine Farmer for linguistic insight for the manuscript.
T. Rosay is a recipient of a doctoral fellowship from the French Ministry
of Research (MRE). This work was supported by grants from the
CommunautĂ© dâAgglomĂ©ration dâEvreux, the Conseil GĂ©nĂ©ral de lâEure,
European Union (FEDER no. 31970), the French Association âVaincre la
Mucoviscidoseâ and the InterReg IVA PeReNE project
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