269 research outputs found
Thermionic charge transport in CMOS nano-transistors
We report on DC and microwave electrical transport measurements in
silicon-on-insulator CMOS nano-transistors at low and room temperature. At low
source-drain voltage, the DC current and RF response show signs of conductance
quantization. We attribute this to Coulomb blockade resulting from barriers
formed at the spacer-gate interfaces. We show that at high bias transport
occurs thermionically over the highest barrier: Transconductance traces
obtained from microwave scattering-parameter measurements at liquid helium and
room temperature is accurately fitted by a thermionic model. From the fits we
deduce the ratio of gate capacitance and quantum capacitance, as well as the
electron temperature
Size scaling of the addition spectra in silicon quantum dots
We investigate small artificial quantum dots obtained by geometrically
controlled resistive confinement in low mobility silicon-on-insulator
nanowires. Addition spectra were recorded at low temperature for various dot
areas fixed by lithography. We compare the standard deviation of the addition
spectra with theory in the high electron concentration regime. We find that the
standard deviation scales as the inverse area of the dot and its absolute value
is comparable to the energy spacing of the one particle spectrum.Comment: 4 pages, 5 figure
Extraction and physicochemical characterization of chitin from Cicadaorni sloughs of the south-eastern French Mediterranean basin
Chitin is a structural polysaccharide of the cell walls of fungi and exoskeletons of insects
and crustaceans. In this study, chitin was extracted, for the first time in our knowledge, from the
Cicada orni sloughs of the south-eastern French Mediterranean basin by treatment with 1 M HCl for
demineralization, 1 M NaOH for deproteinization, and 1% NaClO for decolorization. The different
steps of extraction were investigated by Fourier Transform Infrared Spectroscopy (FTIR), X-ray
Diffraction (XRD), Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM).
Results demonstrated that the extraction process was efficiently performed and that Cicada orni
sloughs of the south-eastern French Mediterranean basin have a high content of chitin (42.8%) in
the α-form with a high degree of acetylation of 96% ± 3.4%. These results make Cicada orni of the
south-eastern French Mediterranean basin a new and promising source of chitin. Furthermore, we
showed that each step of the extraction present specific characteristics (for example FTIR and XRD
spectra and, consequently, distinct absorbance peaks and values of crystallinity as well as defined
values of maximum degradation temperatures identifiable by TGA analysis) that could be used
to verify the effectiveness of the treatments, and could be favorably compared with other natural
chitin sources.publishe
Development of novel chitosan / guar gum inks for extrusion-based 3D bioprinting: process, printability and properties
The major limitation of 3D bioprinting is the availability of inks. In order to develop new ink formulations, both their rheological behavior to obtain the best printability and the target bio-printed objects conformities must be studied. In this paper, for the first time in our knowledge, the preparation and the characterization of novel ink formulations based on two natural biocompatible polysaccharides, chitosan (CH) and guar gum (GG), are presented. Five ink formulations containing different proportions of CH and GG were prepared and characterized in terms of rheological properties and solvent evaporation. Their printability was assessed (by varying the nozzle diameter, pressure and speed) using an extrusion-based 3D bioprinting process performed directly in air at 37 °C. Results showed that the incorporation of GG improved both the printability of the pure chitosan ink by increasing the viscosity of the solution and the shape fidelity by accelerating the solvent evaporation. We showed that the ink containing 15% (w/w) of GG and 85% (w/w) of CH had the best printability. This formulation was therefore used for the preparation of membranes that were characterized by infrared spectroscopy (FTIR) and X-Ray Diffraction (XRD) before and after gelation as well as for their mechanical properties (Young modulus, strength and strain at break). The optimal process printing parameters were determined to be: 27 G micronozzle, extrusion pressure below 2 bars and robot head speed between 20 and 25 mm/s. This novel ink formulation is a guideline for developing 2D scaffolds (such as auto-supported membranes) or 3D scaffolds for biomedical applications.publishe
Energy dependent counting statistics in diffusive superconducting tunnel junctions
We present an investigation of the energy dependence of the full charge
counting statistics in diffusive
normal-insulating-normal-insulating-superconducting junctions. It is found that
the current in general is transported via a correlated transfer of pairs of
electrons. Only in the case of strongly asymmetric tunnel barriers or energies
much larger than the Thouless energy is the pair transfer uncorrelated. The
second cumulant, the noise, is found to depend strongly on the applied voltage
and temperature. For a junction resistance dominated by the tunnel barrier to
the normal reservoir, the differential shot noise shows a double peak feature
at voltages of the order of the Thouless energy, a signature of an ensemble
averaged electron-hole resonance.Comment: 8 pages, 5 figure
Semiclassical theory of shot noise in disordered SN contacts
We present a semiclassical theory of shot noise in diffusive superconductor -
normal metal contacts. At subgap voltages, we reproduce the doubling of shot
noise with respect to conventional normal-metal contacts, which is interpreted
in terms of an energy balance of electrons. Above the gap, the voltage
dependence of the noise crosses over to the standard one with a
voltage-independent excess noise. The semiclassical description of noise leads
to correlations between currents at different electrodes of multiterminal SN
contacts which are always of fermionic type, i.e. negative. Using a quantum
extension of the Boltzmann - Langevin method, we reproduce the peculiarity of
noise at the Josephson frequency and obtain an analytical frequency dependence
of noise at above-gap voltages.Comment: 4 pages RevTeX, 1 eps figur
Nonlinear shot noise in mesoscopic diffusive normal-superconducting systems
We study differential shot noise in mesoscopic diffusive
normal-superconducting (NS) heterostructures at finite voltages where nonlinear
effects due to the superconducting proximity effect arise. A numerical
scattering-matrix approach is adopted. Through an NS contact, we observe that
the shot noise shows a reentrant dependence on voltage due to the
superconducting proximity effect but the differential Fano factor stays
approximately constant. Furthermore, we consider differential shot noise in the
structures where an insulating barrier is formed between normal and
superconducting regions and calculate the differential Fano factor as a
function of barrier height.Comment: 4 pages, 6 figure
J Vis Exp
Macrophages are key-cells in the initiation, the development and the regulation of the inflammatory response to bacterial infection. Macrophages are intensively and increasingly recruited in septic joints from the early phases of infection and the infiltration is supposed to regress once efficient removal of the pathogens is obtained. The ability to identify in vivo macrophage activity in an infected joint can therefore provide two main applications: early detection of acute synovitis and monitoring of therapy. In vivo noninvasive detection of macrophages can be performed with magnetic resonance imaging using iron nanoparticles such as ultrasmall superparamagnetic iron oxide (USPIO). After intravascular or intraarticular administration, USPIO are specifically phagocytized by activated macrophages, and, due to their magnetic properties, induce signal changes in tissues presenting macrophage infiltration. A quantitative evaluation of the infiltrate is feasible, as the area with signal loss (number of dark pixels) observed on gradient echo MR images after particles injection is correlated with the amount of iron within the tissue and therefore reflects the number of USPIO-loaded cells. We present here a protocol to perform macrophage imaging using USPIO-enhanced MR imaging in an animal model of septic arthritis, allowing an initial and longitudinal in vivo noninvasive evaluation of macrophages infiltration and an assessment of therapy action
Shot Noise through a Quantum Dot in the Kondo Regime
The shot noise in the current through a quantum dot is calculated as a
function of voltage from the high-voltage, Coulomb blockaded regime to the
low-voltage, Kondo regime. Using several complementary approaches, it is shown
that the zero-frequency shot noise (scaled by the voltage) exhibits a
non-monotonic dependence on voltage, with a peak around the Kondo temperature.
Beyond giving a good estimate of the Kondo temperature, it is shown that the
shot noise yields additional information on the effects of electronic
correlations on the local density of states in the Kondo regime, unaccessible
in traditional transport measurements.Comment: 4 pages, 1 figur
Current noise in long diffusive SNS junctions in the incoherent MAR regime
Spectral density of current fluctuations at zero frequency is calculated for
a long diffusive SNS junction with low-resistive interfaces. At low
temperature, T << Delta, the subgap shot noise approaches linear voltage
dependence, S=(2/ 3R)(eV + 2Delta), which is the sum of the shot noise of the
normal conductor and voltage independent excess noise. This result can also be
interpreted as the 1/3-suppressed Poisson noise for the effective charge q =
e(1+2Delta/eV) transferred by incoherent multiple Andreev reflections (MAR). At
higher temperatures, anomalies of the current noise develop at the gap
subharmonics, eV = 2Delta/n. The crossover to the hot electron regime from the
MAR regime is analyzed in the limit of small applied voltages.Comment: improved version, to be published in Phys. Rev.
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