160 research outputs found
The long reach of DNA sequence heterogeneity in diffusive processes
Many biological processes involve one dimensional diffusion over a correlated
inhomogeneous energy landscape with a correlation length . Typical
examples are specific protein target location on DNA, nucleosome repositioning,
or DNA translocation through a nanopore, in all cases with 10
nm. We investigate such transport processes by the mean first passage time
(MFPT) formalism, and find diffusion times which exhibit strong sample to
sample fluctuations. For a a displacement , the average MFPT is diffusive,
while its standard deviation over the ensemble of energy profiles scales as
with a large prefactor. Fluctuations are thus dominant for
displacements smaller than a characteristic : typical values are
much less than the mean, and governed by an anomalous diffusion rule. Potential
biological consequences of such random walks, composed of rapid scans in the
vicinity of favorable energy valleys and occasional jumps to further valleys,
is discussed
Apex Exponents for Polymer--Probe Interactions
We consider self-avoiding polymers attached to the tip of an impenetrable
probe. The scaling exponents and , characterizing the
number of configurations for the attachment of the polymer by one end, or at
its midpoint, vary continuously with the tip's angle. These apex exponents are
calculated analytically by -expansion, and numerically by simulations
in three dimensions. We find that when the polymer can move through the
attachment point, it typically slides to one end; the apex exponents quantify
the entropic barrier to threading the eye of the probe
Subject–ventilator synchrony during neural versus pneumatically triggered non-invasive helmet ventilation
OBJECTIVE: Patient-ventilator synchrony during non-invasive pressure support ventilation with the helmet device is often compromised when conventional pneumatic triggering and cycling-off were used. A possible solution to this shortcoming is to replace the pneumatic triggering with neural triggering and cycling-off-using the diaphragm electrical activity (EA(di)). This signal is insensitive to leaks and to the compliance of the ventilator circuit. DESIGN: Randomized, single-blinded, experimental study. SETTING: University Hospital. PARTICIPANTS AND SUBJECTS: Seven healthy human volunteers. INTERVENTIONS: Pneumatic triggering and cycling-off were compared to neural triggering and cycling-off during NIV delivered with the helmet. MEASUREMENTS AND RESULTS: Triggering and cycling-off delays, wasted efforts, and breathing comfort were determined during restricted breathing efforts (<20% of voluntary maximum EA(di)) with various combinations of pressure support (PSV) (5, 10, 20 cm H(2)O) and respiratory rates (10, 20, 30 breath/min). During pneumatic triggering and cycling-off, the subject-ventilator synchrony was progressively more impaired with increasing respiratory rate and levels of PSV (p < 0.001). During neural triggering and cycling-off, effect of increasing respiratory rate and levels of PSV on subject-ventilator synchrony was minimal. Breathing comfort was higher during neural triggering than during pneumatic triggering (p < 0.001). CONCLUSIONS: The present study demonstrates in healthy subjects that subject-ventilator synchrony, trigger effort, and breathing comfort with a helmet interface are considerably less impaired during increasing levels of PSV and respiratory rates with neural triggering and cycling-off, compared to conventional pneumatic triggering and cycling-off
Identification of long-duration noise transients in LIGO and Virgo
The LIGO and Virgo detectors are sensitive to a variety of noise sources,
such as instrumental artifacts and environmental disturbances. The Stochastic
Transient Analysis Multi-detector Pipeline (STAMP) has been developed to search
for long-duration (t1s) gravitational-wave (GW) signals. This pipeline
can also be used to identify environmental noise transients. Here we present an
algorithm to determine when long-duration noise sources couple into the
interferometers, as well as identify what these noise sources are. We analyze
the cross-power between a GW strain channel and an environmental sensor, using
pattern recognition tools to identify statistically significant structure in
cross-power time-frequency maps. We identify interferometer noise from
airplanes, helicopters, thunderstorms and other sources. Examples from LIGO's
sixth science run, S6, and Virgo's third scientific run, VSR3, are presented.Comment: 10 pages, 7 figures, Gravitational-wave Physics & Astronomy Worksho
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