3,137 research outputs found
Simple colorimetric method determines uranium in tissue
Simple colorimetric micromethod determines concentrations of uranium in tissue. The method involves dry ashing organic extraction, and colorimetric determination of uranyl ferrocyanide. This uranium determination technique could be used in agricultural research, tracer studies, testing of food products, or medical research
<investigation of radar echoes from the moon planets, using methods and data from earth radar-return studies< semiannual status report, 1 nov. 1964 - 30 apr. 1965
Differential reflectivity for estimating surface properties of reflecting body - radar signal reflectio
Investigation of radar echoes from the moon and planets, using methods and data from earth radar-return studies Semiannual status report, 1 May - 31 Oct. 1965
Monostatic reflection from statistically rough sphere, electromagnetic properties of smooth sphere from bistatic power measurement, and acoustic differential reflectivity developmen
Group B streptococcal infection and activation of human astrocytes.
BACKGROUND:Streptococcus agalactiae (Group B Streptococcus, GBS) is the leading cause of life-threatening meningitis in human newborns in industrialized countries. Meningitis results from neonatal infection that occurs when GBS leaves the bloodstream (bacteremia), crosses the blood-brain barrier (BBB), and enters the central nervous system (CNS), where the bacteria contact the meninges. Although GBS is known to invade the BBB, subsequent interaction with astrocytes that physically associate with brain endothelium has not been well studied. METHODOLOGY/PRINCIPAL FINDINGS:We hypothesize that human astrocytes play a unique role in GBS infection and contribute to the development of meningitis. To address this, we used a well- characterized human fetal astrocyte cell line, SVG-A, and examined GBS infection in vitro. We observed that all GBS strains of representative clinically dominant serotypes (Ia, Ib, III, and V) were able to adhere to and invade astrocytes. Cellular invasion was dependent on host actin cytoskeleton rearrangements, and was specific to GBS as Streptococcus gordonii failed to enter astrocytes. Analysis of isogenic mutant GBS strains deficient in various cell surface organelles showed that anchored LTA, serine-rich repeat protein (Srr1) and fibronectin binding (SfbA) proteins all contribute to host cell internalization. Wild-type GBS also displayed an ability to persist and survive within an intracellular compartment for at least 12 h following invasion. Moreover, GBS infection resulted in increased astrocyte transcription of interleukin (IL)-1β, IL-6 and VEGF. CONCLUSIONS/SIGNIFICANCE:This study has further characterized the interaction of GBS with human astrocytes, and has identified the importance of specific virulence factors in these interactions. Understanding the role of astrocytes during GBS infection will provide important information regarding BBB disruption and the development of neonatal meningitis
A new form of the Kerr solution
A new form of the Kerr solution is presented. The solution involves a time
coordinate which represents the local proper time for free-falling observers on
a set of simple trajectories. Many physical phenomena are particularly clear
when related to this time coordinate. The chosen coordinates also ensure that
the solution is well behaved at the horizon. The solution is well suited to the
tetrad formalism and a convenient null tetrad is presented. The Dirac
Hamiltonian in a Kerr background is also given and, for one choice of tetrad,
it takes on a simple, Hermitian form.Comment: 8 pages, LaTeX, no figures. Corrected and improved version. To appear
in Phys. Rev.
4D, N = 1 Supersymmetry Genomics (I)
Presented in this paper the nature of the supersymmetrical representation
theory behind 4D, N = 1 theories, as described by component fields, is
investigated using the tools of Adinkras and Garden Algebras. A survey of
familiar matter multiplets using these techniques reveals they are described by
two fundamental valise Adinkras that are given the names of the cis-Valise
(c-V) and the trans-Valise (t-V). A conjecture is made that all off-shell 4D, N
= 1 component descriptions of supermultiplets are associated with two integers
- the numbers of c-V and t-V Adinkras that occur in the representation.Comment: 53 pages, 19 figures, Report-II of SSTPRS 2008 Added another chapter
for clarificatio
Quadratic Lagrangians and Topology in Gauge Theory Gravity
We consider topological contributions to the action integral in a gauge
theory formulation of gravity. Two topological invariants are found and are
shown to arise from the scalar and pseudoscalar parts of a single integral.
Neither of these action integrals contribute to the classical field equations.
An identity is found for the invariants that is valid for non-symmetric Riemann
tensors, generalizing the usual GR expression for the topological invariants.
The link with Yang-Mills instantons in Euclidean gravity is also explored. Ten
independent quadratic terms are constructed from the Riemann tensor, and the
topological invariants reduce these to eight possible independent terms for a
quadratic Lagrangian. The resulting field equations for the parity
non-violating terms are presented. Our derivations of these results are
considerably simpler that those found in the literature
Fermion absorption cross section of a Schwarzschild black hole
We study the absorption of massive spin-half particles by a small
Schwarzschild black hole by numerically solving the single-particle Dirac
equation in Painleve-Gullstrand coordinates. We calculate the absorption cross
section for a range of gravitational couplings Mm/m_P^2 and incident particle
energies E. At high couplings, where the Schwarzschild radius R_S is much
greater than the wavelength lambda, we find that the cross section approaches
the classical result for a point particle. At intermediate couplings we find
oscillations around the classical limit whose precise form depends on the
particle mass. These oscillations give quantum violations of the equivalence
principle. At high energies the cross section converges on the geometric-optics
value of 27 \pi R_S^2/4, and at low energies we find agreement with an
approximation derived by Unruh. When the hole is much smaller than the particle
wavelength we confirm that the minimum possible cross section approaches \pi
R_S^2/2.Comment: 11 pages, 3 figure
New Techniques for Analysing Axisymmetric Gravitational Systems. 1. Vacuum Fields
A new framework for analysing the gravitational fields in a stationary,
axisymmetric configuration is introduced. The method is used to construct a
complete set of field equations for the vacuum region outside a rotating
source. These equations are under-determined. Restricting the Weyl tensor to
type D produces a set of equations which can be solved, and a range of new
techniques are introduced to simplify the problem. Imposing the further
condition that the solution is asymptotically flat yields the Kerr solution
uniquely. The implications of this result for the no-hair theorem are
discussed. The techniques developed here have many other applications, which
are described in the conclusions.Comment: 30 pages, no figure
Analyze This! A Cosmological Constraint Package for CMBEASY
We introduce a Markov Chain Monte Carlo simulation and data analysis package
that extends the CMBEASY software. We have taken special care in implementing
an adaptive step algorithm for the Markov Chain Monte Carlo in order to improve
convergence. Data analysis routines are provided which allow to test models of
the Universe against measurements of the cosmic microwave background,
supernovae Ia and large scale structure. We present constraints on cosmological
parameters derived from these measurements for a CDM cosmology and
discuss the impact of the different observational data sets on the parameters.
The package is publicly available as part of the CMBEASY software at
www.cmbeasy.org.Comment: Published version, JCAP style, 16 pages, 7 figures. The software is
available at http://www.cmbeasy.or
- …