3,890 research outputs found
Self-diffusion of Rod-like Viruses Through Smectic Layer
We report the direct visualization at the scale of single particles of mass
transport between smectic layers, also called permeation, in a suspension of
rod-like viruses. Self-diffusion takes place preferentially in the direction
normal to the smectic layers, and occurs by quasi-quantized steps of one rod
length. The diffusion rate corresponds with the rate calculated from the
diffusion in the nematic state with a lamellar periodic ordering potential that
is obtained experimentally.Comment: latex, 4 pages, 4 figures, accepted in Phys. Rev. Let
Separability of calcium slow waves and functional connectivity during wake, sleep, and anesthesia
Consistency Conditions for Orientifolds and D-Manifolds
We study superstrings with orientifold projections and with generalized open
string boundary conditions (D-branes). We find two types of consistency
condition, one related to the algebra of Chan-Paton factors and the other to
cancellation of divergences. One consequence is that the Dirichlet 5-branes of
the Type I theory carry a symplectic gauge group, as required by string
duality. As another application we study the Type I theory on a
orbifold, finding a family of consistent theories with various unitary and
symplectic subgroups of . We argue that the orbifold
with spin connection embedded in gauge connection corresponds to an interacting
conformal field theory in the Type I theory.Comment: Reference added. 27 pages LaTeX, 2 epsf figures. To appear in
Phys.Rev.D (15Jly96
The Luminosity of SN 1999by in NGC 2841 and the Nature of `Peculiar' Type Ia Supernovae
We present UBVRIJHK photometry and optical spectroscopy of the so-called
'peculiar' Type Ia supernova 1999by in NGC 2841. The observations began one
week before visual maximum light which is well-defined by daily observations.
The light curves and spectra are similar to those of the prototypical
subluminous event SN 1991bg. We find that maximum light in B occurred on 1999
May 10.3 UT (JD 2,451,308.8 +/- 0.3) with B=13.66 +/- 0.02 mag and a color of
B_max-V_max=0.51 +/- 0.03 mag. The late-time color implies minimal dust
extinction from the host galaxy. Our photometry, when combined with the recent
Cepheid distance to NGC 2841 (Macri et al. 2001), gives a peak absolute
magnitude of M_B=-17.15 +/- 0.23 mag, making SN 1999by one of the least
luminous Type Ia events ever observed. We estimate a decline rate parameter of
dm15(B)=1.90 mag, versus 1.93 for SN 1991bg, where 1.10 is typical for
so-called 'normal' events. We compare SN 1999by with other subluminous events
and find that the B_max-V_max color correlates strongly with the decline rate
and may be a more sensitive indicator of luminosity than the fading rate for
these objects. We find a good correlation between luminosity and the depth of
the spectral feature at 580 nm, which had been attributed solely to Si II. We
show that in cooler photospheres the 580 nm feature is dominated by Ti II,
which provides a simple physical explanation for the correlation. Using only
subluminous Type Ia supernovae we derive a Hubble parameter of H_0=75 +12 -11
km/s Mpc, consistent with values found from brighter events.Comment: 36 preprint pages including 18 figures. Near-IR photometry of the SN
has been added to the paper. Scheduled to appear in ApJ vol. 613 (September
2004). High-resolution version available from
http://www.nd.edu/~pgarnavi/sn99by/sn99by.p
Application of the FUN3D Unstructured-Grid Navier-Stokes Solver to the 4th AIAA Drag Prediction Workshop Cases
FUN3D Navier-Stokes solutions were computed for the 4th AIAA Drag Prediction Workshop grid convergence study, downwash study, and Reynolds number study on a set of node-based mixed-element grids. All of the baseline tetrahedral grids were generated with the VGRID (developmental) advancing-layer and advancing-front grid generation software package following the gridding guidelines developed for the workshop. With maximum grid sizes exceeding 100 million nodes, the grid convergence study was particularly challenging for the node-based unstructured grid generators and flow solvers. At the time of the workshop, the super-fine grid with 105 million nodes and 600 million elements was the largest grid known to have been generated using VGRID. FUN3D Version 11.0 has a completely new pre- and post-processing paradigm that has been incorporated directly into the solver and functions entirely in a parallel, distributed memory environment. This feature allowed for practical pre-processing and solution times on the largest unstructured-grid size requested for the workshop. For the constant-lift grid convergence case, the convergence of total drag is approximately second-order on the finest three grids. The variation in total drag between the finest two grids is only 2 counts. At the finest grid levels, only small variations in wing and tail pressure distributions are seen with grid refinement. Similarly, a small wing side-of-body separation also shows little variation at the finest grid levels. Overall, the FUN3D results compare well with the structured-grid code CFL3D. The FUN3D downwash study and Reynolds number study results compare well with the range of results shown in the workshop presentations
Interference effects in two-photon ATI by multiple orders high harmonics with random or locked phases
We numerically study 2-photon processes using a set of harmonics from a
Ti:Sapphire laser and in particular interference effects in the Above Threshold
Ionization spectra. We compare the situation where the harmonic phases are
assumed locked to the case where they have a random distribution. Suggestions
for possible experiments, using realistic parameters are discussed.Comment: 11 pages, 13 figures, LaTe
Cellular infiltration in traumatic brain injury
Abstract: Traumatic brain injury leads to cellular damage which in turn results in the rapid release of damage-associated molecular patterns (DAMPs) that prompt resident cells to release cytokines and chemokines. These in turn rapidly recruit neutrophils, which assist in limiting the spread of injury and removing cellular debris. Microglia continuously survey the CNS (central nervous system) compartment and identify structural abnormalities in neurons contributing to the response. After some days, when neutrophil numbers start to decline, activated microglia and astrocytes assemble at the injury site—segregating injured tissue from healthy tissue and facilitating restorative processes. Monocytes infiltrate the injury site to produce chemokines that recruit astrocytes which successively extend their processes towards monocytes during the recovery phase. In this fashion, monocytes infiltration serves to help repair the injured brain. Neurons and astrocytes also moderate brain inflammation via downregulation of cytotoxic inflammation. Depending on the severity of the brain injury, T and B cells can also be recruited to the brain pathology sites at later time points
Expression profiling of human renal carcinomas with functional taxonomic analysis
BACKGROUND: Molecular characterization has contributed to the understanding of the inception, progression, treatment and prognosis of cancer. Nucleic acid array-based technologies extend molecular characterization of tumors to thousands of gene products. To effectively discriminate between tumor sub-types, reliable laboratory techniques and analytic methods are required. RESULTS: We derived mRNA expression profiles from 21 human tissue samples (eight normal kidneys and 13 kidney tumors) and two pooled samples using the Affymetrix GeneChip platform. A panel of ten clustering algorithms combined with four data pre-processing methods identified a consensus cluster dendrogram in 18 of 40 analyses and of these 16 used a logarithmic transformation. Within the consensus dendrogram the expression profiles of the samples grouped according to tissue type; clear cell and chromophobe carcinomas displayed distinctly different gene expression patterns. By using a rigorous statistical selection based method we identified 355 genes that showed significant (p < 0.001) gene expression changes in clear cell renal carcinomas compared to normal kidney. These genes were classified with a tool to conceptualize expression patterns called "Functional Taxonomy". Each tumor type had a distinct "signature," with a high number of genes in the categories of Metabolism, Signal Transduction, and Cellular and Matrix Organization and Adhesion. CONCLUSIONS: Affymetrix GeneChip profiling differentiated clear cell and chromophobe carcinomas from one another and from normal kidney cortex. Clustering methods that used logarithmic transformation of data sets produced dendrograms consistent with the sample biology. Functional taxonomy provided a practical approach to the interpretation of gene expression data
Density functional theory and Kohn-Sham scheme for self-bound systems
We demonstrate how the separation of the total energy of a self-bound system
into a functional of the internal one-body Fermionic density and a function of
an arbitrary wave vector describing the center-of-mass kinetic energy can be
used to set-up an "internal" Kohn-Sham scheme.Comment: 6 pages. To be published in Phys. Rev.
An algebraic/numerical formalism for one-loop multi-leg amplitudes
We present a formalism for the calculation of multi-particle one-loop
amplitudes, valid for an arbitrary number N of external legs, and for massive
as well as massless particles. A new method for the tensor reduction is
suggested which naturally isolates infrared divergences by construction. We
prove that for N>4, higher dimensional integrals can be avoided. We derive many
useful relations which allow for algebraic simplifications of one-loop
amplitudes. We introduce a form factor representation of tensor integrals which
contains no inverse Gram determinants by choosing a convenient set of basis
integrals. For the evaluation of these basis integrals we propose two methods:
An evaluation based on the analytical representation, which is fast and
accurate away from exceptional kinematical configurations, and a robust
numerical one, based on multi-dimensional contour deformation. The formalism
can be implemented straightforwardly into a computer program to calculate
next-to-leading order corrections to multi-particle processes in a largely
automated way.Comment: 71 pages, 7 figures, formulas for rank 6 pentagons added in Appendix
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