313 research outputs found
A proposed baroclinic wave test case for deep‐ and shallow‐atmosphere dynamical cores
Idealised studies of key dynamical features of the atmosphere provide insight into the behaviour of atmospheric models. A very important, well understood, aspect of midlatitude dynamics is baroclinic instability. This can be idealised by perturbing a vertically sheared basic state in geostrophic and hydrostatic balance. An unstable wave mode then results with exponential growth (due to linear dynamics) in time until, eventually, nonlinear effects dominate and the wave breaks. A new, unified, idealised baroclinic instability test case is proposed. This improves on previous ones in three ways. First, it is suitable for both deep‐ and shallow‐atmosphere models. Second, the constant surface pressure and zero surface geopotential of the basic state makes it particularly well‐suited for models employing a pressure‐ or height‐based vertical coordinate. Third, the wave triggering mechanism selectively perturbs the rotational component of the flow; this, together with a vertical tapering, significantly improves dynamic balance.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108108/1/qj2241.pd
Violation of the `Zero-Force Theorem' in the time-dependent Krieger-Li-Iafrate approximation
We demonstrate that the time-dependent Krieger-Li-Iafrate approximation in
combination with the exchange-only functional violates the `Zero-Force
Theorem'. By analyzing the time-dependent dipole moment of Na5 and Na9+, we
furthermore show that this can lead to an unphysical self-excitation of the
system depending on the system properties and the excitation strength.
Analytical aspects, especially the connection between the `Zero-Force Theorem'
and the `Generalized-Translation Invariance' of the potential, are discussed.Comment: 5 pages, 4 figure
Single \pi^- production in np collisions for excess energies up to 90 MeV
The quasifree reaction np\to pp\pim was studied in a kinematically complete
experiment by bombarding a liquid hydrogen target with a deuteron beam of
momentum 1.85 GeV/c and analyzing the data along the lines of the spectator
model. In addition to the three charged ejectiles the spectator proton was also
detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was
identified by its momentum and flight direction thus yielding access to the
Fermi motion of the bound neutron and to the effective neutron 4-momentum
vector which differed from event to event. A range of almost 90
MeV excess energy above threshold was covered. Energy dependent angular
distributions, invariant mass spectra as well as fully covered Dalitz plots
were deduced. Sizeable FSI effects were found as were contributions of
and partial waves. The behavior of the elementary cross section
close to threshold is discussed in view of new cross section
data. In comparison with existing literature data the results provide a
sensitive test of the spectator model.Comment: 21 pages, 9 figures, 4 tables, submitted to EPJ
Systematic study of the pp -> pp omega reaction
A systematic study of the production of omega-mesons in
proton-proton-collisions was carried out in a kinematically complete experiment
at three excess energies(epsilon= 92, 128, 173MeV). Both protons were detected
using the large-acceptance COSY-TOF spectrometer at an external beam line at
the Cooler Synchrotron COSY at Forschungszentrum J\"ulich. The total cross
section, angular distributions of both omega-mesons and protons were measured
and presented in various reference frames such as the overall CMS, helicity and
Jackson frame. In addition, the orientation of the omega-spin and invariant
mass spectra were determined. We observe omega-production to take place
dominantly in Ss and Sp final states at epsilon = 92, 128 MeV and,
additionally, in Sd at epsilon= 173 MeV. No obvious indication of resonant
omega-production via N^*-resonances was found, as proton angular distributions
are almost isotropic and invariant mass spectra are compatible with phase space
distributions. A dominant role of ^3P_1 and ^1S_0 initial partial waves for
omega-production was concluded from the orientation of the decay plane of the
omega-meson. Although the Jackson angle distributions in the omega-p-Jackson
frame are anisotropic we argue that this is not an indication of a resonance
but rather a kinematical effect reflecting the anisotropy of the omega angular
distribution. The helicity angle distribution in the omega-p-helicity frame
shows an anisotropy which probably reflects effects of the omega angular
momenta in the final state; this observable may be, in addition to the
orientation of the omega decay plane, the most sensitive one to judge the
validity of theoretical descriptions of the production process.Comment: 17 pages, 16 figures, accepted for publication in EPJ
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Contrasting responses of Atlantic and Pacific tropical cyclone activity to Atlantic Multidecadal Variability
This research assesses the influences of Atlantic Multidecadal Variability (AMV) on global tropical cyclones (TCs) using two large ensembles of idealized global climate model simulations with opposite signs of AMV forcings superimposed (i.e., AMV+ and AMV–). We first detect TCs and then compare TC activity by basin in the two AMV experiments. We find contrasting responses of Atlantic and Pacific TC frequency to the AMV anomalies. Compared to AMV–, AMV+ significantly increases TC frequency in the North Atlantic, including those making landfalls. The increase is explained by warmer sea surface temperature, higher relative humidity, increased relative vorticity, and weaker vertical wind shear under AMV+. By contrast, AMV+ decreases TC occurrence over the western North Pacific and South Pacific, which is tied to stronger vertical wind shear and lower relative humidity. The opposite responses of TC activity to AMV+ are attributed to strengthened Walker Circulation between the Atlantic and Pacific
Rough titanium alloys regulate osteoblast production of angiogenic factors
Multiple biomaterials are clinically available to spine surgeons for performing interbody fusion. Poly-ether-ether-ketone (PEEK) is used frequently for lumbar spine interbody fusion, but alternative materials are also used, including titanium (Ti) alloys. Previously, we showed that osteoblasts exhibit a more differentiated phenotype when grown on machined or grit-blasted titanium aluminum vanadium (Ti6Al4V) alloys with micron-scale roughened surfaces than when grown on smoother Ti6Al4V surfaces or on tissue culture polystyrene (TCPS). We hypothesized that osteoblasts cultured on rough Ti alloy substrates would present a more mature osteoblast phenotype than cells cultured on PEEK, suggesting that textured Ti6Al4V implants may provide a more osteogenic surface for interbody fusion devices. PURPOSE: The aim of the present study was to compare osteoblast response to smooth Ti6Al4V (sTiAlV) and roughened Ti6Al4V (rTiAlV) with their response to PEEK with respect to differentiation and production of factors associated with osteogenesis. STUDY DESIGN: This in vitro study compared the phenotype of human MG63 osteoblast-like cells cultured on PEEK, sTiAlV, or rTiAlV surfaces and their production of bone morphogenetic proteins (BMPs). METHODS: Surface properties of PEEK, sTiAlV, and rTiAlV discs were determined. Human MG63 cells were grown on TCPS and the discs. Confluent cultures were harvested, and cell number, alkaline phosphatase–specific activity, and osteocalcin were measured as indicators of osteoblast maturation. Expression of messenger RNA (mRNA) for BMP2 and BMP4 was measuredMultiple biomaterials are clinically available to spine surgeons for performing interbody fusion. Poly-ether-ether-ketone (PEEK) is used frequently for lumbar spine interbody fusion, but alternative materials are also used, including titanium (Ti) alloys. Previously, we showed that osteoblasts exhibit a more differentiated phenotype when grown on machined or grit-blasted titanium aluminum vanadium (Ti6Al4V) alloys with micron-scale roughened surfaces than when grown on smoother Ti6Al4V surfaces or on tissue culture polystyrene (TCPS). We hypothesized that osteoblasts cultured on rough Ti alloy substrates would present a more mature osteoblast phenotype than cells cultured on PEEK, suggesting that textured Ti6Al4V implants may provide a more osteogenic surface for interbody fusion devices. PURPOSE: The aim of the present study was to compare osteoblast response to smooth Ti6Al4V (sTiAlV) and roughened Ti6Al4V (rTiAlV) with their response to PEEK with respect to differentiation and production of factors associated with osteogenesis. STUDY DESIGN: This in vitro study compared the phenotype of human MG63 osteoblast-like cells cultured on PEEK, sTiAlV, or rTiAlV surfaces and their production of bone morphogenetic proteins (BMPs). METHODS: Surface properties of PEEK, sTiAlV, and rTiAlV discs were determined. Human MG63 cells were grown on TCPS and the discs. Confluent cultures were harvested, and cell number, alkaline phosphatase–specific activity, and osteocalcin were measured as indicators of osteoblast maturation. Expression of messenger RNA (mRNA) for BMP2 and BMP4 was measure
Improved study of a possible Theta+ production in the pp -> p K0 sigma+ reaction with the COSY-TOF spectrometer
The pp -> p K0 Sigma+ reaction was investigated with the TOF spectrometer at
COSY at 3.059 GeV/c incident beam momentum. The main objective was to clarify
whether or not a narrow exotic S = +1 resnance, the Theta+ pentaquark, is
populated at 1.53 GeV/c2 in the K0 p subsystem with a data sample of much
higher statistical significance compared to the previously reported data in
this channel. An analysis of these data does not confirm the existence of the
Theta+ pentaquark. This is expressed as an upper limit for the cross section
sigma (pp -> p K0 Sigma+) < 0.15 microbarn at the 95 percent confidence level.Comment: 11 pages, 5 figure
Psychopathy among prisoners in England and Wales
Most research into psychopathy among prisoners is based on selected samples. It remains unclear whether prevalences are lower among European populations. This study aimed to measure the prevalence of psychopathy, and the distribution and correlates of psychopathic traits in a representative national sample of prisoners. Psychopathy was measured using the revised Psychopathy Checklist (PCL-R) in a second stage, cross-sectional survey of prisoners in England and Wales in 1997 (n = 496). Poisson regression analysis was carried out to examine independent associations between correlates and PCL-R total and factor scores. The prevalence of categorically diagnosed psychopathy at a cut off of 30 was 7.7% (95%CI 5.2–10.9) in men and 1.9% (95%CI 0.2–6.9) in women. Psychopathic traits were less prevalent among women. They were correlated with younger age, repeated imprisonment, detention in higher security, disciplinary infractions, antisocial, narcissistic, histrionic, and schizoid personality disorders, and substance misuse, but not neurotic disorders or schizophrenia. The study concluded that psychopathy and psychopathic traits are prevalent among male prisoners in England and Wales but lower than in most previous studies using selected samples. However, most correlates with psychopathic traits were similar to other studies. Psychopathy identifies the extreme of a spectrum of social and behavioral problems among prisoners
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