1,021 research outputs found
Random walks in random Dirichlet environment are transient in dimension
We consider random walks in random Dirichlet environment (RWDE) which is a
special type of random walks in random environment where the exit probabilities
at each site are i.i.d. Dirichlet random variables. On , RWDE are
parameterized by a -uplet of positive reals. We prove that for all values
of the parameters, RWDE are transient in dimension . We also prove that
the Green function has some finite moments and we characterize the finite
moments. Our result is more general and applies for example to finitely
generated symmetric transient Cayley graphs. In terms of reinforced random
walks it implies that directed edge reinforced random walks are transient for
.Comment: New version published at PTRF with an analytic proof of lemma
Comparison between measured and predicted turbulence frequency spectra in ITG and TEM regimes
The observation of distinct peaks in tokamak core reflectometry measurements
- named quasi-coherent-modes (QCMs) - are identified as a signature of
Trapped-Electron-Mode (TEM) turbulence [H. Arnichand et al. 2016 Plasma Phys.
Control. Fusion 58 014037]. This phenomenon is investigated with detailed
linear and nonlinear gyrokinetic simulations using the \gene code. A Tore-Supra
density scan is studied, which traverses through a Linear (LOC) to Saturated
(SOC) Ohmic Confinement transition. The LOC and SOC phases are both simulated
separately. In the LOC phase, where QCMs are observed, TEMs are robustly
predicted unstable in linear studies. In the later SOC phase, where QCMs are no
longer observed, ITG modes are identified. In nonlinear simulations, in the ITG
(SOC) phase, a broadband spectrum is seen. In the TEM (LOC) phase, a clear
emergence of a peak at the TEM frequencies is seen. This is due to reduced
nonlinear frequency broadening of the underlying linear modes in the TEM regime
compared with the ITG regime. A synthetic diagnostic of the nonlinearly
simulated frequency spectra reproduces the features observed in the
reflectometry measurements. These results support the identification of core
QCMs as an experimental marker for TEM turbulenc
High platelet content can increase storage lesion rates following Intercept pathogen inactivation primarily in platelet concentrates prepared by apheresis
Background: Pathogen inactivation methods for platelet concentrates are increasingly being used in blood banks worldwide. In vitro studies have demonstrated its effects on storage lesion, but little routine quality control data on blood banking outcomes have been reported.
Materials and Methods: Swirling of distributed products was monitored before and after implementation of Intercept pathogen inactivation. Metabolic parameters pH, glucose and lactic acid were determined in a random cohort of expired pathogen-inactivated products. Storage lesion indicators in apheresis concentrates with premature low swirling were compared to concentrates with normal swirling.
Results: During validation for implementing Intercept pathogen inactivation, pH and glucose levels decreased faster in apheresis platelet concentrates with high platelet content than with low platelet content or than in pathogen-inactivated pooled buffy coat-derived products. In routine products, glucose exhaustion was more often found in apheresis compared to buffy coat-derived platelet concentrates despite 3-7% more plasma carryover in the former. Annual incidence of premature low swirling increased significantly by 50% following implementation of pathogen inactivation implementation for apheresis but not for pooled buffy coat platelet concentrates. In addition, apheresis concentrates with premature low swirling had a significantly higher median platelet count (50 x 10(11)) than unaffected products (35 x 10(11)).
Conclusion: The risk of increased storage lesion rates following Intercept pathogen inactivation is higher for apheresis than for buffy coat-derived platelet concentrates, especially when platelet contents are higher than 50 x 10(11)
Discriminating the trapped electron modes contribution in density fluctuation spectra
Quasi-coherent (QC) modes have been reported for more than 10 years in reflectometry
fluctuations spectra in the core region of fusion plasmas. They have characteristics in-between
coherent and broadband fluctuations as they oscillate at a marked frequency but have a wide
spectrum. This work presents further evidences of the link recently established between QC
modes and the trapped electron modes (TEM) instabilities (Arnichand et al 2014 Nucl. Fusion
54 123017). In electron cyclotron resonance heated discharges of Tore Supra, an enhancement
of QC modes amplitude is observed in a region where TEM cause impurity transport and
turbulence. In JET Ohmic plasmas, QC modes disappear during density ramp-up and current
ramp-down. This is reminiscent of Tore Supra and TEXTOR observations during transitions
from the linear Ohmic confinement (LOC) to the saturated Ohmic confinement (SOC)
regimes. Evidencing TEM activity then becomes experimentally possible via analysis of
fluctuation spectra.EURATOM 63305
On non-zero space average density perturbation effects in tokamak plasma reflectometer signals
12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)The effects of the non-zero average density perturbation on phase and amplitude measured by reflectometry are presented. The non-zero average density perturbation on the phase variation can be seen as an index effect as soon as the shape of the density perturbation does not introduce spectral effects. Amplitude modulation in time follows generally the properties of the cut-off layer seen as a mirror but some specific situations produce a time modulation two times higher than the input time variation of the density perturbation as observed in Tore Supra. The introduction of secondary cut-off can exhibit this effect as shown in 2D simulations
Study of cathodic reactions in defects of thermal spray aluminium coatings on steel in artificial seawater
Electrochemical and surface characterization techniques were used to study the corrosion protection provided by Thermal Spray Aluminium (TSA) coatings on carbon steel substrates with and without defects in artificial seawater. Results showed that the presence of defects accelerates the formation of a protective corrosion product layer on the TSA coating. Voltammetry and Electrochemical Impedance Spectroscopy (EIS) revealed that both calcareous deposits and aluminium corrosion products hindered diffusion of dissolved O2. Analysis of corrosion products by SEM-EDX, ÎĽ-Raman spectroscopy and XRD revealed Al oxides/hydroxides and hydrotalcite on top of TSA coating and a bilayer of calcareous deposits on the defect area
- …