943 research outputs found
A hierarchy of models related to nanoflows and surface diffusion
In last years a great interest was brought to molecular transport problems at
nanoscales, such as surface diffusion or molecular flows in nano or
sub-nano-channels. In a series of papers V. D. Borman, S. Y. Krylov, A. V.
Prosyanov and J. J. M. Beenakker proposed to use kinetic theory in order to
analyze the mechanisms that determine mobility of molecules in nanoscale
channels. This approach proved to be remarkably useful to give new insight on
these issues, such as density dependence of the diffusion coefficient. In this
paper we revisit these works to derive the kinetic and diffusion models
introduced by V. D. Borman, S. Y. Krylov, A. V. Prosyanov and J. J. M.
Beenakker by using classical tools of kinetic theory such as scaling and
systematic asymptotic analysis. Some results are extended to less restrictive
hypothesis
Determination of the Properties of Composite Materials Thanks to Digital Image Correlation Measurements
AbstractDesigning composite structures for civil aircrafts necessitates a better understanding of the damage and failure mechanisms occurring in these components through experimental test campaigns and associated numerical simulations. These experimental tests have been performed at Onera using different classical measurement techniques (LVDT sensor, strain gaugesâŠ) and digital image correlation (DIC). The additional information provided by DIC allows (i) to validate the boundary conditions of the tests, (ii) to cross-check the measurements with other techniques, (iii) to improve the understanding of the physical mechanisms and (iv) to validate the predictions of the finite element simulations
Electrically Driven Light Emission from Individual CdSe Nanowires
We report electroluminescence (EL) measurements carried out on three-terminal
devices incorporating individual n-type CdSe nanowires. Simultaneous optical
and electrical measurements reveal that EL occurs near the contact between the
nanowire and a positively biased electrode or drain. The surface potential
profile, obtained by using Kelvin probe microscopy, shows an abrupt potential
drop near the position of the EL spot, while the band profile obtained from
scanning photocurrent microscopy indicates the existence of an n-type Schottky
barrier at the interface. These observations indicate that light emission
occurs through a hole leakage or an inelastic scattering induced by the rapid
potential drop at the nanowire-electrode interface.Comment: 12 pages, 4 figure
Improvement Of Cavity Performance By Electro-polishing In The 1.3ghz Nb Superconducting Cavities
Radioelectric Field Features of Extensive Air Showers Observed with CODALEMA
Based on a new approach to the detection of radio transients associated with
extensive air showers induced by ultra high energy cosmic rays, the
experimental apparatus CODALEMA is in operation, measuring about 1 event per
day corresponding to an energy threshold ~ 5. 10^16 eV. Its performance makes
possible for the first time the study of radio-signal features on an
event-by-event basis. The sampling of the magnitude of the electric field along
a 600 meters axis is analyzed. It shows that the electric field lateral spread
is around 250 m (FWHM). The possibility to determine with radio both arrival
directions and shower core positions is discussed.Comment: Accepted for publication in Astroparticle Physic
Quantification of lentiviral vector copy numbers in individual hematopoietic colony-forming cells shows vector dose-dependent effects on the frequency and level of transduction
Lentiviral vectors are effective tools for gene transfer and integrate variable numbers of proviral DNA copies in variable proportions of cells. The levels of transduction of a cellular population may therefore depend upon experimental parameters affecting the frequency and/or the distribution of vector integration events in this population. Such analysis would require measuring vector copy numbers (VCN) in individual cells. To evaluate the transduction of hematopoietic progenitor cells at the single-cell level, we measured VCN in individual colony-forming cell (CFC) units, using an adapted quantitative PCR (Q-PCR) method. The feasibility, reproducibility and sensitivity of this approach were tested with characterized cell lines carrying known numbers of vector integration. The method was validated by correlating data in CFC with gene expression or with calculated values, and was found to slightly underestimate VCN. In spite of this, such Q-PCR on CFC was useful to compare transduction levels with different infection protocols and different vectors. Increasing the vector concentration and re-iterating the infection were two different strategies that improved transduction by increasing the frequency of transduced progenitor cells. Repeated infection also augmented the number of integrated copies and the magnitude of this effect seemed to depend on the vector preparation. Thus, the distribution of VCN in hematopoietic colonies may depend upon experimental conditions including features of vectors. This should be carefully evaluated in the context of ex vivo hematopoietic gene therapy studies
An active dipole for cosmic ray radiodetection with CODALEMA
A paraĂźtre dans NIM AInternational audienceThe CODALEMA experiment detects the electromagnetic pulses radiated during the development of Extensive Air Showers (EAS). Since 2005, in addition to spiral log-periodic antennas, ultra broad bandwidth active dipoles have been designed to detect the full electric pulse shape of these signals. A few performances of these new detectors are presented
Biosafety Studies of a Clinically Applicable Lentiviral Vector for the Gene Therapy of Artemis-SCID
Genetic deficiency of the nuclease DCLRE1C/Artemis causes radiosensitive severe combined immunodeficiency (RS-SCID) with lack of peripheral T and B cells and increased sensitivity to ionizing radiations. Gene therapy based on transplanting autologous gene-modified hematopoietic stem cells could significantly improve the health of patients with RS-SCID by correcting their immune system. A lentiviral vector expressing physiological levels of human ARTEMIS mRNA from an EF1a promoter without post-transcriptional regulation was developed as a safe clinically applicable candidate for RS-SCID gene therapy. The vector was purified in GMP-comparable conditions and was not toxic in vitro or in vivo. Long-term engraftment of vector-transduced hematopoietic cells was achieved in irradiated Artemis-deficient mice following primary and secondary transplantation (6 months each). Vector-treated mice displayed T and B lymphopoiesis and polyclonal T cells, had structured lymphoid tissues, and produced immunoglobulins. Benign signs of inflammation were noted following secondary transplants, likely a feature of the model. There was no evidence of transgene toxicity and no induction of hematopoietic malignancy. In vitro, the vector had low genotoxic potential on murine hematopoietic progenitor cells using an immortalization assay. Altogether, these preclinical data show safety and efficacy, and support further development of the vector for the gene therapy of RS-SCID
Radio emission of extensive air shower at CODALEMA: Polarization of the radio emission along the v*B vector
Cosmic rays extensive air showers (EAS) are associated with transient radio
emission, which could provide an efficient new detection method of high energy
cosmic rays, combining a calorimetric measurement with a high duty cycle. The
CODALEMA experiment, installed at the Radio Observatory in Nancay, France, is
investigating this phenomenon in the 10^17 eV region. One challenging point is
the understanding of the radio emission mechanism. A first observation
indicating a linear relation between the electric field produced and the cross
product of the shower axis with the geomagnetic field direction has been
presented (B. Revenu, this conference). We will present here other strong
evidences for this linear relationship, and some hints on its physical origin.Comment: Contribution to the 31st International Cosmic Ray Conference, Lodz,
Poland, July 2009. 4 pages, 8 figures. v2: Typo fixed, arxiv references adde
Gut Bacterial Communities in the Giant Land Snail Achatina fulica and Their Modification by Sugarcane-Based Diet
The invasive land snail Achatina fulica is one of the most damaging agricultural pests worldwide representing a potentially serious threat to natural ecosystems and human health. This species is known to carry parasites and harbors a dense and metabolically active microbial community; however, little is known about its diversity and composition. Here, we assessed for the first time the complexity of bacterial communities occurring in the digestive tracts of field-collected snails (FC) by using culture-independent molecular analysis. Crop and intestinal bacteria in FC were then compared to those from groups of snails that were reared in the laboratory (RL) on a sugarcane-based diet. Most of the sequences recovered were novel and related to those reported for herbivorous gut. Changes in the relative abundance of Bacteroidetes and Firmicutes were observed when the snails were fed a high-sugar diet, suggesting that the snail gut microbiota can influence the energy balance equation. Furthermore, this study represents a first step in gaining a better understanding of land snail gut microbiota and shows that this is a complex holobiont system containing diverse, abundant and active microbial communities
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