2,758 research outputs found
Force-Velocity Relations of a Two-State Crossbridge Model for Molecular Motors
We discuss the force-velocity relations obtained in a two-state crossbridge
model for molecular motors. They can be calculated analytically in two limiting
cases: for a large number and for one pair of motors. The effect of the
strain-dependent detachment rate on the motor characteristics is studied. It
can lead to linear, myosin-like, kinesin-like and anomalous curves. In
particular, we specify the conditions under which oscillatory behavior may be
found.Comment: 5 pages, 4 figures, REVTeX; thoroughly revised version; also
available at http://www.physik.tu-muenchen.de/~frey
Traffic jams induced by rare switching events in two-lane transport
We investigate a model for driven exclusion processes where internal states are assigned to the particles. The latter account for diverse situations, ranging from spin states in spintronics to parallel lanes in intracellular or vehicular traffic. Introducing a coupling between the internal states by allowing particles to switch from one to another induces an intriguing polarization phenomenon. In a mesoscopic scaling, a rich stationary regime for the density profiles is discovered, with localized domain walls in the density profile of one of the internal states being feasible. We derive the shape of the density profiles as well as resulting phase diagrams analytically by a mean-field approximation and a continuum limit. Continuous as well as discontinuous lines of phase transition emerge, their intersections induce multi-critical behaviour
Critical dynamics of ballistic and Brownian particles in a heterogeneous environment
The dynamic properties of a classical tracer particle in a random, disordered
medium are investigated close to the localization transition. For Lorentz
models obeying Newtonian and diffusive motion at the microscale, we have
performed large-scale computer simulations, demonstrating that universality
holds at long times in the immediate vicinity of the transition. The scaling
function describing the crossover from anomalous transport to diffusive motion
is found to vary extremely slowly and spans at least 5 decades in time. To
extract the scaling function, one has to allow for the leading universal
corrections to scaling. Our findings suggest that apparent power laws with
varying exponents generically occur and dominate experimentally accessible time
windows as soon as the heterogeneities cover a decade in length scale. We
extract the divergent length scales, quantify the spatial heterogeneities in
terms of the non-Gaussian parameter, and corroborate our results by a thorough
finite-size analysis.Comment: 14 page
Pair distribution function and structure factor of spherical particles
The availability of neutron spallation-source instruments that provide total
scattering powder diffraction has led to an increased application of real-space
structure analysis using the pair distribution function. Currently, the
analytical treatment of finite size effects within pair distribution refinement
procedures is limited. To that end, an envelope function is derived which
transforms the pair distribution function of an infinite solid into that of a
spherical particle with the same crystal structure. Distributions of particle
sizes are then considered, and the associated envelope function is used to
predict the particle size distribution of an experimental sample of gold
nanoparticles from its pair distribution function alone. Finally, complementing
the wealth of existing diffraction analysis, the peak broadening for the
structure factor of spherical particles, expressed as a convolution derived
from the envelope functions, is calculated exactly for all particle size
distributions considered, and peak maxima, offsets, and asymmetries are
discussed.Comment: 7 pages, 6 figure
NCLB technology and a rural school: A case study
The requirements of the No Child Left Behind Act of 2001 (NCLB) have presented special challenges and opportunities for rural schools (Reeves, 2003). Researchers have suggested that one way rural schools may be able to overcome these challenges is through an increase in the level of technology integration in their school (Collins &
Dewees, 2001). This case study reports on one school’s attempt to use grant resources funded through NCLB to integrate specific instructional technologies to facilitate increased student achievement. Through interviews and observations, the roles, attitudes, and difficulties of teachers and administrators in implementing a technology initiative in a rural middle school were observed, examined and discussed. Emerging themes included issues related to teacher
ownership of the technology, teacher feelings of power and participation, differing goals of teachers and
administrators, technical difficulties, school wide support, and changes in school culture
NCLB Technology and a Rural School: A Case Study
The requirements of the No Child Left Behind Act of 2001 (NCLB) have presented special challenges and opportunities for rural schools (Reeves, 2003). Researchers have suggested that one way rural schools may be able to overcome these challenges is through an increase in the level of technology integration in their school (Collins & Dewees, 2001). This case study reports on one school’s attempt to use grant resources funded through NCLB to integrate specific instructional technologies to facilitate increased student achievement. Through interviews and observations, the roles, attitudes, and difficulties of teachers and administrators in implementing a technology initiative in a rural middle school were observed, examined and discussed. Emerging themes included issues related to teacher ownership of the technology, teacher feelings of power and participation, differing goals of teachers and administrators, technical difficulties, school wide support, and changes in school culture
Renewal processes and fluctuation analysis of molecular motor stepping
We model the dynamics of a processive or rotary molecular motor using a
renewal processes, in line with the work initiated by Svoboda, Mitra and Block.
We apply a functional technique to compute different types of multiple-time
correlation functions of the renewal process, which have applications to
bead-assay experiments performed both with processive molecular motors, such as
myosin V and kinesin, and rotary motors, such as F1-ATPase
Critically ill COVID-19 patients with neutralizing autoantibodies against type I interferons have increased risk of herpesvirus disease
Autoantibodies neutralizing the antiviral action of type I interferons (IFNs) have been associated with predisposition to severe Coronavirus Disease 2019 (COVID-19). Here, we screened for such autoantibodies in 103 critically ill COVID-19 patients in a tertiary intensive care unit (ICU) in Switzerland. Eleven patients (10.7%), but no healthy donors, had neutralizing anti-IFNα or anti-IFNα/anti-IFNω IgG in plasma/serum, but anti-IFN IgM or IgA was rare. One patient had non-neutralizing anti-IFNα IgG. Strikingly, all patients with plasma anti-IFNα IgG also had anti-IFNα IgG in tracheobronchial secretions, identifying these autoantibodies at anatomical sites relevant for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection. Longitudinal analyses revealed patient heterogeneity in terms of increasing, decreasing, or stable anti-IFN IgG levels throughout the length of hospitalization. Notably, presence of anti-IFN autoantibodies in this critically ill COVID-19 cohort appeared to predict herpesvirus disease (caused by herpes simplex viruses types 1 and 2 (HSV-1/-2) and/or cytomegalovirus (CMV)), which has been linked to worse clinical outcomes. Indeed, all 7 tested COVID-19 patients with anti-IFN IgG in our cohort (100%) suffered from one or more herpesviruses, and analysis revealed that these patients were more likely to experience CMV than COVID-19 patients without anti-IFN autoantibodies, even when adjusting for age, gender, and systemic steroid treatment (odds ratio (OR) 7.28, 95% confidence interval (CI) 1.14 to 46.31, p = 0.036). As the IFN system deficiency caused by neutralizing anti-IFN autoantibodies likely directly and indirectly exacerbates the likelihood of latent herpesvirus reactivations in critically ill patients, early diagnosis of anti-IFN IgG could be rapidly used to inform risk-group stratification and treatment options.
Trial Registration: ClinicalTrials.gov Identifier: NCT04410263
Nominal or Real? The Impact of Regional Price Levels on Satisfaction with Life
According to economic theory, real income, i.e., nominal income adjusted for purchasing power, should be the relevant source of life satisfaction. Previous work, however, has only studied the impact of inflation adjusted nominal income and not taken into account regional differences in purchasing power. Therefore, we use a novel data set to study how regional price levels affect satisfaction with life. The data set comprises about 7 million data points that are used to construct a price level for each of the 428 administrative districts in Germany. We estimate pooled OLS and ordered probit models that include a comprehensive set of individual level, time-varying and time-invariant control variables as well as control variables that capture district heterogeneity other than the price level. Our results show that higher price levels significantly reduce life satisfaction. Furthermore, we find that a higher price level tends to induce a larger loss in life satisfaction than a corresponding decrease in nominal income. A formal test of neutrality of money, however, does not reject neutrality of money. Our results provide an argument in favor of regional indexation of government transfer payments such as social welfare benefits
An X-ray jet discovered by Chandra in the z=4.3 radio-selected quasar GB 1508+5714
We report the Chandra discovery of an X-ray jet associated with the redshift
4.3 radio-loud quasar GB 1508+5714. The jet X-ray emission peaks ~2 arcsec to
the South-West of the quasar core. We present archival HST WFPC2 data of the
quasar field which shows no optical emission at the location of the X-ray jet.
We discuss possible emission mechanisms and give constraints to the magnetic
field and energy densities for synchrotron radiation or for Compton scattering
of the Cosmic Microwave Background radiation as the jet X-ray emission process.Comment: 5 pages, 4 figures, submitted to ApJ. Letters on Aug.13, accepted for
publication in ApJ Letters on Oct.
- …