10,080 research outputs found
Comparative Enumeration Gene Expression
This paper is about differential gene expression measured by transcript counting methods such as SAGE or MPSS. It introduces two significance tests for detection of differential expressed tags: frequentist and Bayesian. Under the frequentist view, it is proposed a test that computes the critical level as a function of each tag total frequency. Under the Bayesian view the Full Bayesian Significance Test is used considering the logistic normal distribution. The two proposed significance levels, the frequentist and the Bayesian, are compared for a data set with four libraries. The linking function between them is a Beta distribution function with mean 0.39 and standard deviation 0.30
Positive Ricci curvature through Cheeger deformation
Let be a Riemannian manifold with an isometric -action. If a
principal orbit has finite fundamental group and , Searle--Wilhelm proved that admits a new metric of positive
Ricci curvature. is obtained after a conformal change followed by a
Cheeger deformation. The question remained on whether it is sufficient to
consider only the Cheeger deformation to attain positive Ricci curvature on the
new metric . Here we approach this question by giving necessary and
sufficient conditions on the -action. In particular, we construct an
infinite family of manifolds satisfying the hypothesis of Searle--Wilhelm that
do not develop positive Ricci curvature after Cheeger deformation. Further
exploring the theory, we give a alternative proofs for Lawson--Yau result on
positive scalar curvature under non-abelian symmetry, among others.Comment: 26 pages. Exposition reviewed. Applications include
Scattering of Dirac and Majorana Fermions off Domain Walls
We investigate the interaction of fermions having both Dirac and left-handed
and right-handed Majorana mass terms with vacuum domain walls. By solving the
equations of motion in thin-wall approximation, we calculate the reflection and
transmission coefficients for the scattering of fermions off walls.Comment: 6 pages, 1 figure, some typos corrected, one reference added, major
revisions, title changed, version accepted for publication in Phys. Rev.
Long wavelength structural anomalies in jammed systems
The structural properties of static, jammed packings of monodisperse spheres
in the vicinity of the jamming transition are investigated using large-scale
computer simulations. At small wavenumber , we argue that the anomalous
behavior in the static structure factor, , is consequential of an
excess of low-frequency, collective excitations seen in the vibrational
spectrum. This anomalous feature becomes more pronounced closest to the jamming
transition, such that at the transition point. We introduce an
appropriate dispersion relation that accounts for these phenomena that leads us
to relate these structural features to characteristic length scales associated
with the low-frequency vibrational modes of these systems. When the particles
are frictional, this anomalous behavior is suppressed providing yet more
evidence that jamming transitions of frictional spheres lie at lower packing
fractions that that for frictionless spheres. These results suggest that the
mechanical properties of jammed and glassy media may therefore be inferred from
measurements of both the static and dynamical structure factors.Comment: 8 pages, 6 figure captions. Completely revised version to appear in
Phys. Rev.
Vanishing conductivity of quantum solitons in polyacetylene
Quantum solitons or polarons are supposed to play a crucial role in the
electric conductivity of polyacetylene, in the intermediate doping regime. We
present an exact fully quantized calculation of the quantum soliton
conductivity in polyacetylene and show that it vanishes exactly. This is
obtained by applying a general method of soliton quantization, based on
order-disorder duality, to a Z(2)-symmetric complex extension of the TLM
dimerization effective field theory. We show that, in this theory,
polyacetylene solitons are sine-Gordon solitons in the phase of the complex
field.Comment: To appear in J. Phys. A: Math. Theor., 15 page
Modular Implementation of a Hybrid DSMC-NS Algorithm for Hypersonic Non-Equilibrium Flows
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76683/1/AIAA-2007-613-871.pd
Hybrid Particle-Continuum Simulations of Hypersonic Flow Over a Hollow-Cylinder-Flare Geometry
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77198/1/AIAA-36681-416.pd
Hybrid Particle-Continuum Simulations of Low Knudsen Number Hypersonic Flows
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76429/1/AIAA-2007-3892-932.pd
Daytime turbulent exchange between the Amazon forest and the atmosphere
Detailed observations of turbulence just above and below the crown of the Amazon rain forest during the wet season are presented. The forest canopy is shown to remove high frequency turbulent fluctuations while passing lower frequencies. Filter characteristics of turbulent transfer into the Amazon rain forest canopy are quantified. Simple empirical relations that relate observed turbulent heat fluxes to horizontal wind variance are presented. Changes in the amount of turbulent coupling between the forest and the boundary layer associated with deep convective clouds are presented both as statistical averages and as a series of case studies. These convective processes during the rainy season are shown to alter the diurnal course of turbulent fluxes. In wake of giant coastal systems, no significant heat or moisture fluxes occur for up to a day after the event. Radar data is used to demonstrate that even small raining clouds are capable of evacuating the canopy of substances normally trapped by persistent static stability near the forest floor. Recovery from these events can take more than an hour, even during mid-day. In spite of the ubiquitous presence of clouds and frequent rain during this season, the average horizontal wind speed spectrum is well described by dry CBL similarity hypotheses originally found to apply in flat terrain
- …