576 research outputs found
The energy partitioning of non-thermal particles in a plasma: or the Coulomb logarithm revisited
The charged particle stopping power in a highly ionized and weakly to
moderately coupled plasma has been calculated to leading and next-to-leading
order by Brown, Preston, and Singleton (BPS). After reviewing the main ideas
behind this calculation, we use a Fokker-Planck equation derived by BPS to
compute the electron-ion energy partitioning of a charged particle traversing a
plasma. The motivation for this application is ignition for inertial
confinement fusion -- more energy delivered to the ions means a better chance
of ignition, and conversely. It is therefore important to calculate the
fractional energy loss to electrons and ions as accurately as possible, as this
could have implications for the Laser Megajoule (LMJ) facility in France and
the National Ignition Facility (NIF) in the United States. The traditional
method by which one calculates the electron-ion energy splitting of a charged
particle traversing a plasma involves integrating the stopping power dE/dx.
However, as the charged particle slows down and becomes thermalized into the
background plasma, this method of calculating the electron-ion energy splitting
breaks down. As a result, the method suffers a systematic error of order T/E0,
where T is the plasma temperature and E0 is the initial energy of the charged
particle. In the case of DT fusion, for example, this can lead to uncertainties
as high as 10% or so. The formalism presented here is designed to account for
the thermalization process, and in contrast, it provides results that are
near-exact.Comment: 10 pages, 3 figures, invited talk at the 35th European Physical
Society meeting on plasma physic
The quantized Hall conductance of a single atomic wire: A proposal based on synthetic dimensions
We propose a method by which the quantization of the Hall conductance can be
directly measured in the transport of a one-dimensional atomic gas. Our
approach builds on two main ingredients: (1) a constriction optical potential,
which generates a mesoscopic channel connected to two reservoirs, and (2) a
time-periodic modulation of the channel, specifically designed to generate
motion along an additional synthetic dimension. This fictitious dimension is
spanned by the harmonic-oscillator modes associated with the tightly-confined
channel, and hence, the corresponding "lattice sites" are intimately related to
the energy of the system. We analyze the quantum transport properties of this
hybrid two-dimensional system, highlighting the appealing features offered by
the synthetic dimension. In particular, we demonstrate how the energetic nature
of the synthetic dimension, combined with the quasi-energy spectrum of the
periodically-driven channel, allows for the direct and unambiguous observation
of the quantized Hall effect in a two-reservoir geometry. Our work illustrates
how topological properties of matter can be accessed in a minimal
one-dimensional setup, with direct and practical experimental consequences.
Absorption imaging of a quasi 2D gas: a multiple scattering analysis
Absorption imaging with quasi-resonant laser light is a commonly used
technique to probe ultra-cold atomic gases in various geometries. Here we
investigate some non-trivial aspects of this method when it is applied to in
situ diagnosis of a quasi two-dimensional gas. Using Monte Carlo simulations we
study the modification of the absorption cross-section of a photon when it
undergoes multiple scattering in the gas. We determine the variations of the
optical density with various parameters, such as the detuning of the light from
the atomic resonance and the thickness of the gas. We compare our results to
the known three-dimensional result (Beer-Lambert law) and outline the specific
features of the two-dimensional case.Comment: 22 pages, 5 figure
Genomic determinants of Furin cleavage in diverse European SARS-related bat coronaviruses
The furin cleavage site (FCS) in SARS-CoV-2 is unique within the Severe acute respiratory syndrome–related coronavirus (SrC) species. We re-assessed diverse SrC from European horseshoe bats and analyzed the spike-encoding genomic region harboring the FCS in SARS-CoV-2. We reveal molecular features in SrC such as purine richness and RNA secondary structures that resemble those required for FCS acquisition in avian influenza viruses. We discuss the potential acquisition of FCS through molecular mechanisms such as nucleotide substitution, insertion, or recombination, and show that a single nucleotide exchange in two European bat-associated SrC may suffice to enable furin cleavage. Furthermore, we show that FCS occurrence is variable in bat- and rodent-borne counterparts of human coronaviruses. Our results suggest that furin cleavage sites can be acquired in SrC via conserved molecular mechanisms known in other reservoir-bound RNA viruses and thus support a natural origin of SARS-CoV-2
Spin transport in a one-dimensional quantum wire
We analyze the spin transport through a finite-size one-dimensional
interacting wire connected to noninteracting leads. By combining
renormalization-group arguments with other analytic considerations such as the
memory function technique and instanton tunneling, we find the temperature
dependence of the spin conductance in different parameter regimes in terms of
interactions and the wire length. The temperature dependence is found to be
nonmonotonic. In particular, the system approaches perfect spin conductance at
zero temperature for both attractive and repulsive interactions, in contrast
with the static spin conductivity. We discuss the connection of our results to
recent experiments with ultracold atoms and compare the theoretical prediction
to experimental data in the parameter regime where temperature is the largest
energy scale.Comment: 16 pages, 10 figure
The structure and function of complex networks
Inspired by empirical studies of networked systems such as the Internet,
social networks, and biological networks, researchers have in recent years
developed a variety of techniques and models to help us understand or predict
the behavior of these systems. Here we review developments in this field,
including such concepts as the small-world effect, degree distributions,
clustering, network correlations, random graph models, models of network growth
and preferential attachment, and dynamical processes taking place on networks.Comment: Review article, 58 pages, 16 figures, 3 tables, 429 references,
published in SIAM Review (2003
Simulations of Aerodynamic Damping for MEMS Resonators
Aerodynamic damping for MEMS resonators is studied based on the numerical solution of Boltzmann-ESBGK equation. A compact model is then developed based on numerical simulations for a wide range of Knudsen numbers. The damping predictions are compared with both Reynold equation based models and several sets of experimental data. It has been found that the structural damping is dominant at low pressures (high Knudsen numbers). For cases with small length-to-width ratios and large vibration amplitudes, the threedimensionality effects must be taken into account. Finally, an uncertainty quantification approach based on the probability transformation method has been applied to assess the influence of pressure and geometric uncertainties. The output probability density functions (PDF) of the damping ratio has been studied for various input PDF of beam geometry and ambient pressure
Real‐world treatment patterns and outcomes using terlipressin in 203 patients with the hepatorenal syndrome
Background: Hepatorenal syndrome and acute kidney injury are common complications of decompensated cirrhosis, and terlipressin is recommended as first‐line vasoconstrictor therapy. However, data on its use outside of clinical trials are lacking. /
Aims: To assess practice patterns and outcomes around vasoconstrictor use for hepatorenal syndrome in UK hospitals. /
Methods: This was a multicentre chart review study. Data were extracted from medical records of patients diagnosed with hepatorenal syndrome and treated by vasoconstrictor drugs between January 2013 and December 2017 at 26 hospitals in the United Kingdom. The primary outcome was improvement of kidney function, defined as complete response (serum creatinine improved to ≤1.5 mg/dL), partial response (serum creatinine reduction of ≥20% but >1.5 mg/dL) and overall response (complete or partial response). Other outcomes included need for dialysis, mortality, liver transplantation and adverse events. /
Results: Of the 225 patients included in the analysis, 203 (90%) were treated with terlipressin (median duration, 6 days; range: 2‐24 days). Mean (±standard deviation) serum creatinine at vasopressor initiation was 3.25 ± 1.64 mg/dL. Terlipressin overall response rate was 73%. Overall response was higher in patients with mild acute kidney injury (baseline serum creatinine <2.25 mg/dL), compared to those with moderate (serum creatinine ≥2.25 mg/dL and <3.5 mg/dL) or severe (serum creatinine ≥3.5 mg/dL). Ninety‐day survival was 86% for all patients (93% for overall responders vs 66% for treatment nonresponders, P < 0.0001). /
Conclusion: Terlipressin is the most commonly prescribed vasoconstrictor for patients with hepatorenal syndrome in the United Kingdom. Treatment with terlipressin in patients with less severe acute kidney injury (serum creatinine <2.25 mg/dL) was associated with higher treatment responses, and 90‐day survival
Pre-activated antiviral innate immunity in the upper airways controls early SARS-CoV-2 infection in children
Children have reduced severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection rates and a substantially lower risk for developing severe coronavirus disease 2019 compared with adults. However, the molecular mechanisms underlying protection in younger age groups remain unknown. Here we characterize the single-cell transcriptional landscape in the upper airways of SARS-CoV-2-negative (n = 18) and age-matched SARS-CoV-2-positive (n = 24) children and corresponding samples from adults (n = 44), covering an age range of 4 weeks to 77 years. Children displayed higher basal expression of relevant pattern recognition receptors such as MDA5 (IFIH1) and RIG-I (DDX58) in upper airway epithelial cells, macrophages and dendritic cells, resulting in stronger innate antiviral responses upon SARS-CoV-2 infection than in adults. We further detected distinct immune cell subpopulations including KLRC1 (NKG2A)+ cytotoxic T cells and a CD8+ T cell population with a memory phenotype occurring predominantly in children. Our study provides evidence that the airway immune cells of children are primed for virus sensing, resulting in a stronger early innate antiviral response to SARS-CoV-2 infection than in adults
- …