123 research outputs found
Study of the spring and autumn daemon-flux maxima at the Baksan Neutrino Observatory
Detection of daemons in low-background conditions in September 2005 and March
2006 has provided evidence for the expected to occur at that times maxima in
the flux of daemons with V ~ 10-15 km s-1, which hit the Earth from near-Earth,
almost circular heliocentric orbits. The ability of some FEU-167-1 PM tubes
with a thicker inner Al coating to detect directly daemon passage through them
has also been demonstrated, an effect increasing ~100-fold the detector
efficiency. As a result, the daemon flux recorded at the maxima was increased
from ~10-9 to ~10-7 cm-2 s-1. The intensity and direction of the flux during
maxima depend on the time of day and latitude of observations (therefore,
synchronous measurements in the Northern and Southern Earth's hemispheres are
desirable). All the experimental results obtained either support the
conclusions following from the daemon paradigm or find a simple interpretation
within it.Comment: 15 pages, including 8 figures and 3 table
Bioinformatic identification of novel putative photoreceptor specific cis-elements
<p>Abstract</p> <p>Background</p> <p>Cell specific gene expression is largely regulated by different combinations of transcription factors that bind <it>cis</it>-elements in the upstream promoter sequence. However, experimental detection of <it>cis</it>-elements is difficult, expensive, and time-consuming. This provides a motivation for developing bioinformatic methods to identify <it>cis</it>-elements that could prioritize future experimental studies. Here, we use motif discovery algorithms to predict transcription factor binding sites involved in regulating the differences between murine rod and cone photoreceptor populations.</p> <p>Results</p> <p>To identify highly conserved motifs enriched in promoters that drive expression in either rod or cone photoreceptors, we assembled a set of murine rod-specific, cone-specific, and non-photoreceptor background promoter sequences. These sets were used as input to a newly devised motif discovery algorithm called Iterative Alignment/Modular Motif Selection (IAMMS). Using IAMMS, we predicted 34 motifs that may contribute to rod-specific (19 motifs) or cone-specific (15 motifs) expression patterns. Of these, 16 rod- and 12 cone-specific motifs were found in clusters near the transcription start site. New findings include the observation that cone promoters tend to contain TATA boxes, while rod promoters tend to be TATA-less (exempting <it>Rho </it>and <it>Cnga1</it>). Additionally, we identify putative sites for IL-6 effectors (in rods) and RXR family members (in cones) that can explain experimental data showing changes to cell-fate by activating these signaling pathways during rod/cone development. Two of the predicted motifs (NRE and ROP2) have been confirmed experimentally to be involved in cell-specific expression patterns. We provide a full database of predictions as additional data that may contain further valuable information. IAMMS predictions are compared with existing motif discovery algorithms, DME and BioProspector. We find that over 60% of IAMMS predictions are confirmed by at least one other motif discovery algorithm.</p> <p>Conclusion</p> <p>We predict novel, putative <it>cis-</it>elements enriched in the promoter of rod-specific or cone-specific genes. These are candidate binding sites for transcription factors involved in maintaining functional differences between rod and cone photoreceptor populations.</p
Fiber Organization has Little Effect on Electrical Activation Patterns during Focal Arrhythmias in the Left Atrium
Over the past two decades there has been a steady trend towards the
development of realistic models of cardiac conduction with increasing levels of
detail. However, making models more realistic complicates their personalization
and use in clinical practice due to limited availability of tissue and cellular
scale data. One such limitation is obtaining information about myocardial fiber
organization in the clinical setting. In this study, we investigated a chimeric
model of the left atrium utilizing clinically derived patient-specific atrial
geometry and a realistic, yet foreign for a given patient fiber organization.
We discovered that even significant variability of fiber organization had a
relatively small effect on the spatio-temporal activation pattern during
regular pacing. For a given pacing site, the activation maps were very similar
across all fiber organizations tested
Theory of Spike Spiral Waves in a Reaction-Diffusion System
We discovered a new type of spiral wave solutions in reaction-diffusion
systems --- spike spiral wave, which significantly differs from spiral waves
observed in FitzHugh-Nagumo-type models. We present an asymptotic theory of
these waves in Gray-Scott model. We derive the kinematic relations describing
the shape of this spiral and find the dependence of its main parameters on the
control parameters. The theory does not rely on the specific features of
Gray-Scott model and thus is expected to be applicable to a broad range of
reaction-diffusion systems.Comment: 4 pages (REVTeX), 2 figures (postscript), submitted to Phys. Rev.
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Kinematic reduction of reaction-diffusion fronts with multiplicative noise: Derivation of stochastic sharp-interface equations
We study the dynamics of generic reaction-diffusion fronts, including pulses
and chemical waves, in the presence of multiplicative noise. We discuss the
connection between the reaction-diffusion Langevin-like field equations and the
kinematic (eikonal) description in terms of a stochastic moving-boundary or
sharp-interface approximation. We find that the effective noise is additive and
we relate its strength to the noise parameters in the original field equations,
to first order in noise strength, but including a partial resummation to all
orders which captures the singular dependence on the microscopic cutoff
associated to the spatial correlation of the noise. This dependence is
essential for a quantitative and qualitative understanding of fluctuating
fronts, affecting both scaling properties and nonuniversal quantities. Our
results predict phenomena such as the shift of the transition point between the
pushed and pulled regimes of front propagation, in terms of the noise
parameters, and the corresponding transition to a non-KPZ universality class.
We assess the quantitative validity of the results in several examples
including equilibrium fluctuations, kinetic roughening, and the noise-induced
pushed-pulled transition, which is predicted and observed for the first time.
The analytical predictions are successfully tested against rigorous results and
show excellent agreement with numerical simulations of reaction-diffusion field
equations with multiplicative noise.Comment: 17 pages, 6 figure
SphinX soft X-ray spectrophotometer: Science objectives, design and performance
The goals and construction details of a new design Polish-led X-ray spectrophotometer are described. The instrument is aimed to observe emission from entire solar corona and is placed as a separate block within the Russian TESIS X- and EUV complex aboard the CORONAS-PHOTON solar orbiting observatory. SphinX uses silicon PIN diode detectors for high time resolution measurements of the solar spectra in the range 0.8–15 keV. Its spectral resolution allows for discerning more than hundred separate energy bands in this range. The instrument dynamic range extends two orders of magnitude below and above these representative for GOES. The relative and absolute accuracy of spectral measurements is expected to be better than few percent, as follows from extensive ground laboratory calibrations
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