2,136 research outputs found
The Use of Artificial Neural Networks in Prediction of Congenital CMV Outcome from Sequence Data
A large number of CMV strains has been reported to circulate in the human population, and the biological significance of these strains is currently an active area of research. The analysis of complex genetic information may be limited using conventional phylogenetic techniques
Local Percolation Probabilities for a Natural Sandstone
Local percolation probabilities are used to characterize the connectivity in
porous and heterogeneous media. Together with local porosity distributions they
allow to predict transport properties \cite{hil91d}. While local porosity
distributions are readily obtained, measurements of the local percolation
probabilities are more difficult and have not been attempted previously. First
measurements of three dimensional local porosity distributions and percolation
probabilities from a pore space reconstruction for a natural sandstone show
that theoretical expectations and experimental results are consistent.Comment: 9 pages, see also http://www.ica1.uni-stuttgart.de , Physica
The 8Li Calibration Source for the Sudbury Neutrino Obervatory
A calibration source employing 8Li (t_1/2 = 0.838s) has been developed for
use with the Sudbury Neutrino Observatory (SNO). This source creates a spectrum
of beta particles with an energy range similar to that of the SNO 8B solar
neutrino signal. The source is used to test the SNO detector's energy response,
position reconstruction and data reduction algorithms. The 8Li isotope is
created using a deuterium-tritium neutron generator in conjunction with a 11B
target, and is carried to a decay chamber using a gas/aerosol transport system.
The decay chamber detects prompt alpha particles by gas scintillation in
coincidence with the beta particles which exit through a thin stainless steel
wall. A description is given of the production, transport, and tagging
techniques along with a discussion of the performance and application of the
source.Comment: 11 pages plus 9 figures, Sumbitted to Nuclear Instruments and Methods
Novel Technique for Ultra-sensitive Determination of Trace Elements in Organic Scintillators
A technique based on neutron activation has been developed for an extremely
high sensitivity analysis of trace elements in organic materials. Organic
materials are sealed in plastic or high purity quartz and irradiated at the
HFIR and MITR. The most volatile materials such as liquid scintillator (LS) are
first preconcentrated by clean vacuum evaporation. Activities of interest are
separated from side activities by acid digestion and ion exchange. The
technique has been applied to study the liquid scintillator used in the KamLAND
neutrino experiment. Detection limits of <2.4X10**-15 g 40K/g LS, <5.5X10**-15
g Th/g LS, and <8X10**-15 g U/g LS have been achieved.Comment: 16 pages, 3 figures, accepted for publication in Nuclear Instruments
and Methods
Magnetic moments of W 5d in Ca2CrWO6 and Sr2CrWO6 double perovskites
We have investigated the magnetic moment of the W ion in the ferrimagnetic
double perovskites Sr2CrWO6 and Ca2CrWO6 by X-ray magnetic circular dichroism
(XMCD) at the W L(2,3) edges. In both compounds a finite negative spin and
positive orbital magnetic moment was detected. The experimental results are in
good agreement with band-structure calculations for (Sr/Ca)2CrWO6 using the
full-potential linear muffin-tin orbital method. It is remarkable, that the
magnetic ordering temperature, TC, is correlated with the magnetic moment at
the 'non-magnetic' W atom.Comment: accepted for publicatio
Rescaling Relations between Two- and Three-dimensional Local Porosity Distributions for Natural and Artificial Porous Media
Local porosity distributions for a three-dimensional porous medium and local
porosity distributions for a two-dimensional plane-section through the medium
are generally different. However, for homogeneous and isotropic media having
finite correlation-lengths, a good degree of correspondence between the two
sets of local porosity distributions can be obtained by rescaling lengths, and
the mapping associating corresponding distributions can be found from
two-dimensional observations alone. The agreement between associated
distributions is good as long as the linear extent of the measurement cells
involved is somewhat larger than the correlation length, and it improves as the
linear extent increases. A simple application of the central limit theorem
shows that there must be a correspondence in the limit of very large
measurement cells, because the distributions from both sets approach normal
distributions. A normal distribution has two independent parameters: the mean
and the variance. If the sample is large enough, LPDs from both sets will have
the same mean. Therefore corresponding distributions are found by matching
variances of two- and three-dimensional local porosity distributions. The
variance can be independently determined from correlation functions. Equating
variances leads to a scaling relation for lengths in this limit. Three
particular systems are examined in order to show that this scaling behavior
persists at smaller length-scales.Comment: 15 PostScript figures, LaTeX, To be published in Physica
Local Entropy Characterization of Correlated Random Microstructures
A rigorous connection is established between the local porosity entropy
introduced by Boger et al. (Physica A 187, 55 (1992)) and the configurational
entropy of Andraud et al. (Physica A 207, 208 (1994)). These entropies were
introduced as morphological descriptors derived from local volume fluctuations
in arbitrary correlated microstructures occuring in porous media, composites or
other heterogeneous systems. It is found that the entropy lengths at which the
entropies assume an extremum become identical for high enough resolution of the
underlying configurations. Several examples of porous and heterogeneous media
are given which demonstrate the usefulness and importance of this morphological
local entropy concept.Comment: 15 pages. please contact [email protected] and have a look
at http://www.ica1.uni-stuttgart.de/ . To appear in Physica
Chaotic flow and efficient mixing in a micro-channel with a polymer solution
Microscopic flows are almost universally linear, laminar and stationary
because Reynolds number, , is usually very small. That impedes mixing in
micro-fluidic devices, which sometimes limits their performance. Here we show
that truly chaotic flow can be generated in a smooth micro-channel of a uniform
width at arbitrarily low , if a small amount of flexible polymers is added
to the working liquid. The chaotic flow regime is characterized by randomly
fluctuating three-dimensional velocity field and significant growth of the flow
resistance. Although the size of the polymer molecules extended in the flow may
become comparable with the micro-channel width, the flow behavior is fully
compatible with that in a table-top channel in the regime of elastic
turbulence. The chaotic flow leads to quite efficient mixing, which is almost
diffusion independent. For macromolecules, mixing time in this microscopic flow
can be three to four orders of magnitude shorter than due to molecular
diffusion.Comment: 8 pages,7 figure
Study of Photon Dominated Regions in Cepheus B
Aim: The aim of the paper is to understand the emission from the photon
dominated regions in Cepheus B, estimate the column densities of neutral carbon
in bulk of the gas in Cepheus B and to derive constraints on the factors which
determine the abundance of neutral carbon relative to CO. Methods: This paper
presents 15'x15' fully sampled maps of CI at 492 GHz and 12CO 4-3 observed with
KOSMA at 1' resolution. The new observations have been combined with the FCRAO
12CO 1-0, IRAM-30m 13CO 2-1 and C18O 1-0 data, and far-infrared continuum data
from HIRES/IRAS. The KOSMA-tau spherical PDR model has been used to understand
the CI and CO emission from the PDRs in Cepheus B and to explain the observed
variation of the relative abundances of both C^0 and CO. Results: The emission
from the PDR associated with Cepheus B is primarily at V_LSR between -14 and
-11 km s^-1. We estimate about 23% of the observed CII emission from the
molecular hotspot is due to the ionized gas in the HII region. Over bulk of the
material the C^0 column density does not change significantly, (2.0+-1.4)x10^17
cm^-2, although the CO column density changes by an order of magnitude. The
observed \cbyco abundance ratio varies between 0.06 and 4 in Cepheus B. We find
an anti-correlation of the observed C/CO abundance ratio with the observed
hydrogen column density, which holds even when all previous observations
providing C/CO ratios are included. Here we show that this observed variation
of C/CO abundance with total column density can be explained only by clumpy
PDRs consisting of an ensemble of clumps. At high H2 column densities high mass
clumps, which exhibit low C/CO abundance, dominate, while at low column
densities, low mass clumps with high C/CO abundance dominate.Comment: 12 pages, 10 figures, Accepted for publication in A&
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