873 research outputs found
Qualitative and Quantitative Detection of Chlamydophila pneumoniae DNA in Cerebrospinal Fluid from Multiple Sclerosis Patients and Controls
A standardized molecular test for the detection of Chlamydophila pneumoniae DNA in cerebrospinal fluid (CSF) would assist the further assessment of the association of C. pneumoniae with multiple sclerosis (MS). We developed and validated a qualitative colorimetric microtiter plate-based PCR assay (PCR-EIA) and a real-time quantitative PCR assay (TaqMan) for detection of C. pneumoniae DNA in CSF specimens from MS patients and controls. Compared to a touchdown nested-PCR assay, the sensitivity, specificity, and concordance of the PCR-EIA assay were 88.5%, 93.2%, and 90.5%, respectively, on a total of 137 CSF specimens. PCR-EIA presented a significantly higher sensitivity in MS patients (p = 0.008) and a higher specificity in other neurological diseases (p = 0.018). Test reproducibility of the PCR-EIA assay was statistically related to the volumes of extract DNA included in the test (p = 0.033); a high volume, which was equivalent to 100 µl of CSF per reaction, yielded a concordance of 96.8% between two medical technologists running the test at different times. The TaqMan quantitative PCR assay detected 26 of 63 (41.3%) of positive CSF specimens that tested positive by both PCR-EIA and nested-PCR qualitative assays. None of the CSF specimens that were negative by the two qualitative PCR methods were detected by the TaqMan quantitative PCR. The PCR-EIA assay detected a minimum of 25 copies/ml C. pneumoniae DNA in plasmid-spiked CSF, which was at least 10 times more sensitive than TaqMan. These data indicated that the PCR-EIA assay possessed a sensitivity that was equal to the nested-PCR procedures for the detection of C. pneumoniae DNA in CSF. The TaqMan system may not be sensitive enough for diagnostic purposes due to the low C. pneumoniae copies existing in the majority of CSF specimens from MS patients
Axial Vector Current Matrix Elements and QCD Sum Rules
The matrix element of the isoscalar axial vector current,
, between nucleon
states is computed using the external field QCD sum rule method. The external
field induced correlator, , is calculated
from the spectrum of the isoscalar axial vector meson states. Since it is
difficult to ascertain, from QCD sum rule for hyperons, the accuracy of
validity of flavour SU(3) symmetry in hyperon decays when strange quark mass is
taken into account, we rely on the empirical validity of Cabbibo theory to
dertermine the matrix element between
nucleon states. Combining with our calculation of and the well known nucleon -decay
constant allows us to determine
occuring in the Bjorken sum rule. The result is in reasonable agreement with
experiment. We also discuss the role of the anomaly in maintaining flavour
symmetry and validity of OZI rule.Comment: 8 pages, 4 figures, revtex
Spin splitting and Kondo effect in quantum dots coupled to noncollinear ferromagnetic leads
We study the Kondo effect in a quantum dot coupled to two noncollinear
ferromagnetic leads. First, we study the spin splitting
of an energy level
in the quantum dot by tunnel couplings to the ferromagnetic leads, using the
Poor man's scaling method. The spin splitting takes place in an intermediate
direction between magnetic moments in the two leads. , where is the spin
polarization in the leads, is the angle between the magnetic moments,
and is an asymmetric factor of tunnel barriers (). Hence the spin
splitting is always maximal in the parallel alignment of two ferromagnets
() and minimal in the antiparallel alignment (). Second,
we calculate the Kondo temperature . The scaling calculation
yields an analytical expression of as a function of
and , , when .
is a decreasing function with respect to
. When is
relevant, we evaluate using the
slave-boson mean-field theory. The Kondo resonance is split into two by finite
, which results in the spin accumulation in the quantum dot and
suppression of the Kondo effect.Comment: 11 pages, 8 figures, revised versio
Modeling and Representation of Geometric Tolerances Information in Integrated Measurement Processes
Modeling and representation of geometric tolerances information across an enterprise is viable due to the advances in Internet technologies and increasing integration requirements from industry. In Integrated Measurement Processes (IMP), geometric tolerances data model must support different models from several well-defined standards: including ASME Y14.5M-1994, STEP, DMIS, and others. In this paper, we propose a layered conformance level geometric tolerances representation model. This model uses the widely applied ASME Y14.5M-1994 as its foundation layer by abstracting most information from this standard. The additional geometric tolerances information defined by DMIS and STEP is incorporated into this model to form corresponding conformance layers that support IMP. Thus, different application domains in an enterprise can use this data model to exchange product information. This model is further transformed with XML Schema that can be used to generate XML instance file to satisfy geometric tolerances representation requirements in IMP
Thermoelectric phenomena in a quantum dot asymmetrically coupled to external leads
We study thermoelectric phenomena in a system consisting of strongly
correlated quantum dot coupled to external leads in the Kondo regime. We
calculate linear and nonlinear electrical and thermal conductance and
thermopower of the quantum dot and discuss the role of asymmetry in the
couplings to external electrodes. In the linear regime electrical and thermal
conductances are modified, while thermopower remains unchanged. In the
nonlinear regime the Kondo resonance in differential conductance develops at
non-zero source-drain voltage, which has important consequences on
thermoelectric properties of the system and the thermopower starts to depend on
the asymmetry. We also discuss Wiedemann-Franz relation, thermoelectric figure
of merit and validity of the Mott formula for thermopower.Comment: 6 pages, 7 figure
Evolutionary Algorithm for the Placement of Fluid Power Valves on a Valve Stand
The choice of placement of fluid power valves on a valve stand and routing by pipes has an impact on operational costs. Choosing the right placement that provides optimum routing configuration or determining the optimum routing for a chosen placement are both computationally hard problems. An evolutionary algorithm (EA), to minimize operational costs while optimizing placement and routing of valves, is developed here. The best practices in the industry are abstracted and implemented in the EA. In this paper, the algorithm and its performance for examples with varying complexities are presented. Our results meet or exceed experienced designers’ solutions
Evolutionary Algorithm for the Placement of Fluid Power Valves on a Valve Stand
The choice of placement of fluid power valves on a valve stand and routing by pipes has an impact on operational costs. Choosing the right placement that provides optimum routing configuration or determining the optimum routing for a chosen placement are both computationally hard problems. An evolutionary algorithm (EA), to minimize operational costs while optimizing placement and routing of valves, is developed here. The best practices in the industry are abstracted and implemented in the EA. In this paper, the algorithm and its performance for examples with varying complexities are presented. Our results meet or exceed experienced designers’ solutions
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