3,486 research outputs found
Of gene expression and cell division time: a mathematical framework for advanced differential gene expression and data analysis
Estimating fold changes of average mRNA and protein molecule counts per cell is the most common way to perform differential expression analysis. However, these gene expression data may be affected by cell division, an often-neglected phenomenon. Here, we develop a quantitative framework that links population-based mRNA and protein measurements to rates of gene expression in single cells undergoing cell division. The equations we derive are easy-to-use and widely robust against biological variability. They integrate multiple "omics" data into a coherent, quantitative description of single-cell gene expression and improve analysis when comparing systems or states with different cell division times. We explore these ideas in the context of resting versus activated B cells. Analyzing differences in protein synthesis rates enables to account for differences in cell division times. We demonstrate that this improves the resolution and hit rate of differential gene expression analysis when compared to analyzing population protein abundances alone
Patterns of convection in rotating spherical shells
Patterns of convection in internally heated, self-gravitating rotating
spherical fluid shells are investigated through numerical simulations. While
turbulent states are of primary interest in planetary and stellar applications
the present paper emphasizes more regular dynamical features at Rayleigh
numbers not far above threshold which are similar to those which might be
observed in laboratory or space experiments. Amplitude vacillations and spatial
modulations of convection columns are common features at moderate and large
Prandtl numbers. In the low Prandtl number regime equatorially attached
convection evolves differently with increasing Rayleigh number and exhibits an
early transition into a chaotic state. Relationships of the dynamical features
to coherent structures in fully turbulent convection states are emphasized
Presence of asthma risk factors and environmental exposures related to upper respiratory infection-triggered wheezing in middle school-age children.
Viral respiratory infections and exposure to environmental constituents such as tobacco smoke are known or suspected to trigger wheezing/asthma exacerbations in children. However, few population-based data exist that examine the relationship between wheezing triggered by viral respiratory infections and environmental exposures. In this investigation we used population-based data to evaluate differences in exposures between symptomatic middle school-age children who did and did not report wheezing triggered by viral respiratory infections. As part of the North Carolina School Asthma Survey (NCSAS), a 66-question data instrument was used to collect information from children enrolled in North Carolina public middle schools during the 1999-2000 school year. Associations between exposures and upper respiratory infection-triggered wheezing (URI-TW) among symptomatic children were examined using adjusted prevalence odds ratios (PORs). Video methods developed for the International Study of Asthma and Allergies in Childhood were used to assess wheezing. Among the 33,534 NCSAS symptomatic participants, positive associations were observed between most exposures and URI-TW. Reported presence of all allergy variables (PORs ranging from 2.11 to 2.45) was more strongly associated with URI-TW than either smoking or other exposures. Presence of URI-TW was higher at increasing levels of tobacco smoke exposure, but no apparent dose-response effect was observed for other indoor air pollutants. URI-TW in middle school children is most associated with reported allergen sensitivity, relative to other asthma risk factors and environmental exposures. Data from this investigation may be useful in developing assessment, screening, and targeting strategies to improve asthma and wheezing management in children
Continuum-type stability balloon in oscillated granular layers
The stability of convection rolls in a fluid heated from below is limited by
secondary instabilities, including the skew-varicose and crossroll
instabilities. We observe a stability boundary defined by the same
instabilities in stripe patterns in a vertically oscillated granular layer.
Molecular dynamics simulations show that the mechanism of the skew-varicose
instability in granular patterns is similar to that in convection. These
results suggest that pattern formation in granular media can be described by
continuum models analogous to those used in fluid systems.Comment: 4 pages, 6 ps figs, submitted to PR
Intermittent magnetic field excitation by a turbulent flow of liquid sodium
The magnetic field measured in the Madison Dynamo Experiment shows
intermittent periods of growth when an axial magnetic field is applied. The
geometry of the intermittent field is consistent with the fastest growing
magnetic eigenmode predicted by kinematic dynamo theory using a laminar model
of the mean flow. Though the eigenmodes of the mean flow are decaying, it is
postulated that turbulent fluctuations of the velocity field change the flow
geometry such that the eigenmode growth rate is temporarily positive.
Therefore, it is expected that a characteristic of the onset of a turbulent
dynamo is magnetic intermittency.Comment: 5 pages, 7 figure
Hysteresis phenomenon in turbulent convection
Coherent large-scale circulations of turbulent thermal convection in air have
been studied experimentally in a rectangular box heated from below and cooled
from above using Particle Image Velocimetry. The hysteresis phenomenon in
turbulent convection was found by varying the temperature difference between
the bottom and the top walls of the chamber (the Rayleigh number was changed
within the range of ). The hysteresis loop comprises the one-cell
and two-cells flow patterns while the aspect ratio is kept constant (). We found that the change of the sign of the degree of the anisotropy of
turbulence was accompanied by the change of the flow pattern. The developed
theory of coherent structures in turbulent convection (Elperin et al. 2002;
2005) is in agreement with the experimental observations. The observed coherent
structures are superimposed on a small-scale turbulent convection. The
redistribution of the turbulent heat flux plays a crucial role in the formation
of coherent large-scale circulations in turbulent convection.Comment: 10 pages, 9 figures, REVTEX4, Experiments in Fluids, 2006, in pres
Autonomous on-board data processing and instrument calibration software for the SO/PHI
The extension of on-board data processing capabilities is an attractive
option to reduce telemetry for scientific instruments on deep space missions.
The challenges that this presents, however, require a comprehensive software
system, which operates on the limited resources a data processing unit in space
allows. We implemented such a system for the Polarimetric and Helioseismic
Imager (PHI) on-board the Solar Orbiter (SO) spacecraft. It ensures autonomous
operation to handle long command-response times, easy changing of the processes
after new lessons have been learned and meticulous book-keeping of all
operations to ensure scientific accuracy. This contribution presents the
requirements and main aspects of the software implementation, followed by an
example of a task implemented in the software frame, and results from running
it on SO/PHI. The presented example shows that the different parts of the
software framework work well together, and that the system processes data as we
expect. The flexibility of the framework makes it possible to use it as a
baseline for future applications with similar needs and limitations as SO/PHI.Comment: Conference: SPIE Astronomical Telescopes + Instrumentatio, Software
and Cyberinfrastructure for Astronomy
Convection in nanofluids with a particle-concentration-dependent thermal conductivity
Thermal convection in nanofluids is investigated by means of a continuum
model for binary-fluid mixtures, with a thermal conductivity depending on the
local concentration of colloidal particles. The applied temperature difference
between the upper and the lower boundary leads via the Soret effect to a
variation of the colloid concentration and therefore to a spatially varying
heat conductivity. An increasing difference between the heat conductivity of
the mixture near the colder and the warmer boundary results in a shift of the
onset of convection to higher values of the Rayleigh number for positive values
of the separation ratio psi>0 and to smaller values in the range psi<0. Beyond
some critical difference of the thermal conductivity between the two
boundaries, we find an oscillatory onset of convection not only for psi<0, but
also within a finite range of psi>0. This range can be extended by increasing
the difference in the thermal conductivity and it is bounded by two
codimension-2 bifurcations.Comment: 13 pages, 11 figures; submitted to Physical Review
Wave function mapping in graphene quantum dots with soft confinement
Using low-temperature scanning tunneling spectroscopy, we map the local
density of states (LDOS) of graphene quantum dots supported on Ir(111). Due to
a band gap in the projected Ir band structure around the graphene K point, the
electronic properties of the QDs are dominantly graphene-like. Indeed, we
compare the results favorably with tight binding calculations on the honeycomb
lattice based on parameters derived from density functional theory. We find
that the interaction with the substrate near the edge of the island gradually
opens a gap in the Dirac cone, which implies soft-wall confinement.
Interestingly, this confinement results in highly symmetric wave functions.
Further influences of the substrate are given by the known moir{\'e} potential
and a 10% penetration of an Ir surface resonanceComment: 7 pages, 11 figures, DFT calculations directly showing the origin of
soft confinment, correct identification of the state penetrating from Ir(111)
into graphen
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