501 research outputs found
Concepts for radically increasing the numerical convergence rate of the Euler equations
Integral equation and finite difference methods have been developed for solving transonic flow problems using linearized forms of the transonic small disturbance and Euler equations. A key element is the use of a strained coordinate system in which the shock remains fixed. Additional criteria are developed to determine the free parameters in the coordinate straining; these free parameters are functions of the shock location. An integral equation analysis showed that the shock is located by ensuring that no expansion shocks exist in the solution. The expansion shock appears as oscillations in the solution near the sonic line, and the correct shock location is determined by removing these oscillations. A second objective was to study the ability of the Euler equation to model separated flow
Blip glitches in Advanced LIGO data
Blip glitches are short noise transients present in data from ground-based
gravitational-wave observatories. These glitches resemble the
gravitational-wave signature of massive binary black hole mergers. Hence, the
sensitivity of transient gravitational-wave searches to such high-mass systems
and other potential short duration sources is degraded by the presence of blip
glitches. The origin and rate of occurrence of this type of glitch have been
largely unknown. In this paper we explore the population of blip glitches in
Advanced LIGO during its first and second observing runs. On average, we find
that Advanced LIGO data contains approximately two blip glitches per hour of
data. We identify four subsets of blip glitches correlated with detector
auxiliary or environmental sensor channels, however the physical causes of the
majority of blips remain unclear
Inhibitors of SARS-CoV entry--identification using an internally-controlled dual envelope pseudovirion assay.
Severe acute respiratory syndrome-associated coronavirus (SARS-CoV) emerged as the causal agent of an endemic atypical pneumonia, infecting thousands of people worldwide. Although a number of promising potential vaccines and therapeutic agents for SARS-CoV have been described, no effective antiviral drug against SARS-CoV is currently available. The intricate, sequential nature of the viral entry process provides multiple valid targets for drug development. Here, we describe a rapid and safe cell-based high-throughput screening system, dual envelope pseudovirion (DEP) assay, for specifically screening inhibitors of viral entry. The assay system employs a novel dual envelope strategy, using lentiviral pseudovirions as targets whose entry is driven by the SARS-CoV Spike glycoprotein. A second, unrelated viral envelope is used as an internal control to reduce the number of false positives. As an example of the power of this assay a class of inhibitors is reported with the potential to inhibit SARS-CoV at two steps of the replication cycle, viral entry and particle assembly. This assay system can be easily adapted to screen entry inhibitors against other viruses with the careful selection of matching partner virus envelopes
Mycobacterium tuberculosis MycP1 Protease Plays a Dual Role in Regulation of ESX-1 Secretion and Virulence
SummaryMycobacterium tuberculosis uses the ESX-1 secretion system to deliver virulence proteins during infection of host cells. Here we report a mechanism of posttranscriptional control of ESX-1 mediated by MycP1, a M. tuberculosis serine protease. We show that MycP1 is required for ESX-1 secretion but that, unexpectedly, genetic inactivation of MycP1 protease activity increases secretion of ESX-1 substrates. We demonstrate that EspB, an ESX-1 substrate required for secretion, is a target of MycP1 in vitro and in vivo. During macrophage infection, an inactive MycP1 protease mutant causes hyperactivation of ESX-1-stimulated innate signaling pathways. MycP1 is required for growth in mice during acute infection, while loss of its protease activity leads to attenuated virulence during chronic infection. As the key ESX-1 substrates ESAT-6 and CFP-10 are highly immunogenic, fine-tuning of their secretion by MycP1 may balance virulence and immune detection and be essential for successful maintenance of long-term M. tuberculosis infection
Strings with Negative Stiffness and Hyperfine Structure
We propose a new string model by adding a higher-order gradient term to the
rigid string, so that the stiffness can be positive or negative without loosing
stability. In the large-D approximation, the model has three phases, one of
which with a new type of generalized "antiferromagnetic" orientational
correlations. We find an infrared-stable fixed point describing world-sheets
with vanishing tension and Hausdorff dimension D_H=2. Crumpling is prevented by
the new term which suppresses configurations with rapidly changing extrinsic
curvature.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper also at http://www.physik.fu-berlin.de/~kleinert/kleiner_re27
Phase structure of intrinsic curvature models on dynamically triangulated disk with fixed boundary length
A first-order phase transition is found in two types of intrinsic curvature
models defined on dynamically triangulated surfaces of disk topology. The
intrinsic curvature energy is included in the Hamiltonian. The smooth phase is
separated from a non-smooth phase by the transition. The crumpled phase, which
is different from the non-smooth phase, also appears at sufficiently small
curvature coefficient . The phase structure of the model on the disk is
identical to that of the spherical surface model, which was investigated by us
and reported previously. Thus, we found that the phase structure of the fluid
surface model with intrinsic curvature is independent of whether the surface is
closed or open.Comment: 9 pages with 10 figure
A systematic review of biomarkers for disease progression in Parkinson's disease
Peer reviewedPublisher PD
Fluctuations of elastic interfaces in fluids: Theory and simulation
We study the dynamics of elastic interfaces-membranes-immersed in thermally
excited fluids. The work contains three components: the development of a
numerical method, a purely theoretical approach, and numerical simulation. In
developing a numerical method, we first discuss the dynamical coupling between
the interface and the surrounding fluids. An argument is then presented that
generalizes the single-relaxation time lattice-Boltzmann method for the
simulation of hydrodynamic interfaces to include the elastic properties of the
boundary. The implementation of the new method is outlined and it is tested by
simulating the static behavior of spherical bubbles and the dynamics of bending
waves. By means of the fluctuation-dissipation theorem we recover analytically
the equilibrium frequency power spectrum of thermally fluctuating membranes and
the correlation function of the excitations. Also, the non-equilibrium scaling
properties of the membrane roughening are deduced, leading us to formulate a
scaling law describing the interface growth, W^2(L,T)=L^3 g[t/L^(5/2)], where
W, L and T are the width of the interface, the linear size of the system and
the temperature respectively, and g is a scaling function. Finally, the
phenomenology of thermally fluctuating membranes is simulated and the frequency
power spectrum is recovered, confirming the decay of the correlation function
of the fluctuations. As a further numerical study of fluctuating elastic
interfaces, the non-equilibrium regime is reproduced by initializing the system
as an interface immersed in thermally pre-excited fluids.Comment: 15 pages, 11 figure
Observations of Energetic-particle Population Enhancements along Intermittent Structures near the Sun from the Parker Solar Probe
Observations at 1 au have confirmed that enhancements in measured energetic-particle (EP) fluxes are statistically associated with "rough" magnetic fields, i.e., fields with atypically large spatial derivatives or increments, as measured by the Partial Variance of Increments (PVI) method. One way to interpret this observation is as an association of the EPs with trapping or channeling within magnetic flux tubes, possibly near their boundaries. However, it remains unclear whether this association is a transport or local effect; i.e., the particles might have been energized at a distant location, perhaps by shocks or reconnection, or they might experience local energization or re-acceleration. The Parker Solar Probe (PSP), even in its first two orbits, offers a unique opportunity to study this statistical correlation closer to the corona. As a first step, we analyze the separate correlation properties of the EPs measured by the Integrated Science Investigation of the Sun (ISâIS) instruments during the first solar encounter. The distribution of time intervals between a specific type of event, i.e., the waiting time, can indicate the nature of the underlying process. We find that the ISâIS observations show a power-law distribution of waiting times, indicating a correlated (non-Poisson) distribution. Analysis of low-energy (~15 â 200 keV/nuc) ISâIS data suggests that the results are consistent with the 1 au studies, although we find hints of some unexpected behavior. A more complete understanding of these statistical distributions will provide valuable insights into the origin and propagation of solar EPs, a picture that should become clear with future PSP orbits
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