965 research outputs found
Collisionless galaxy simulations
Three-dimensional fully self-consistent computer models were used to determine the evolution of galaxies consisting of 100 000 simulation stars. Comparison of two-dimensional simulations with three-dimensional simulations showed only a very slight stabilizing effect due to the additional degree of freedom. The addition of a fully self-consistent, nonrotating, exponential core/halo component resulted in considerable stabilization. A second series of computer experiments was performed to determine the collapse and relaxation of initially spherical, uniform density and uniform velocity dispersion stellar systems. The evolution of the system was followed for various amounts of angular momentum in solid body rotation. For initally low values of the angular momentum satisfying the Ostriker-Peebles stability criterion, the systems quickly relax to an axisymmetric shape and resemble elliptical galaxies in appearance. For larger values of the initial angular momentum bars develop and the systems undergo a much more drastic evolution
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Why training is not improving the police response to sexual violence against women: a glimpse into the 'black box' of police training
Innovative and timely, this collection of essays holds broad appeal to academics and practitioners, as well as students of criminology, criminal justice and law, and all those with an interest in feminism, justice, and inequality
The validity of clinical diagnoses of dementia in a group of consecutively autopsied memory clinic patients
Background: Epidemiological studies show that up to 10 % of individuals aged 65 years and older suffer from dementia, most commonly from dementia of the Alzheimer Type (DAT) [1]. Clinicopathological studies are critical to our understanding of this disease and improving the accuracy of clinical diagnoses.Objectives: Our objectives were to examine the validity of clinical diagnoses of DAT, to determine the prevalence of different forms of dementia in this sample, and to investigate the relationship between age at death and polymorbidity.Subjects and method: Clinical data were available from 221 patients who had been examined at the Basel Memory Clinic between 1986 and 1996. From this population, 34 % (75 patients) were autopsied in the Department of Pathology, University Hospital Basel, and neuropathological examinations were additionally performed on 62 (83 %) of these patients. Clinical and neuropathological data were retrospectively compared.Results: 67.8 % of the neuropathologically examined patients received a definitive diagnosis of AD (Alzheimer's disease), vascular dementia (VaD) or mixed dementia (AD and VaD). AD alone or with other histopathological hallmarks of dementia was the most prevalent neuropathological diagnosis (63 %). VaD was deemed the only cause of dementia in only 4.8 % of patients. The sensitivity for DAT was 75.9 %, the specificity 60.6 %. Increasing age was associated with an increasing number of clinical and neuropathological diagnoses.Conclusion: The sensitivity and specificity of the clinical diagnoses of DAT found in our study are similar to previous reports (2-5). Older patients had more etiologies of their dementia than younger patients. This study reaffirms the need for internationally accepted criteria for clinical and neuropathological diagnoses, as well as further clinical-neuropathological investigations to further refine the clinical diagnostic proces
Policing by consent: understanding the dynamics of police power and legitimacy
This is the first of the country-specific European Social Survey topline results reports. Focusing on UK data from the Round 5 module entitled âtrust in justice,' we link peopleâs perceptions of police legitimacy to their compliance with the law and their willingness to cooperate with the police and criminal courts. We also extend the existing literature by addressing wider forms of trust and peopleâs attachment to order and security. Framing the findings in the context of a long and rich history of policing by consent, we show the value of the European Social Survey in shaping public policy, practice and debate
Exploring Alternatives to the Traditional Conference Format: Introduction to the Special Issue on Composing Conferences
Pneumomediastinum in the neonatal and paediatric intensive care unit
The incidence, aetiology and pathophysiology of pneumomediastinum (PM), an uncommon and potentially serious disease in neonates and children, were evaluated. A retrospective chart review of all patients diagnosed with PM who were hospitalised in the intensive care unit of the University Childrenâs Hospital ZĂźrich, Switzerland, from 2000 to 2006, was preformed. We analysed the incidence, severity and causes of PM and investigated the possible differences between neonatal and non-neonatal cases. Seven children and nine neonates were identified with PM. All patients had a good outcome. Six cases of PM in the group of children older than 4Â weeks were deemed to be caused by trauma, infection and sports, whereas one case was idiopathic. All nine neonatal cases presented with symptoms of respiratory distress. We were able to attribute four cases of neonatal PM to pulmonary infection, immature lungs and ventilatory support. Five neonatal cases remained unexplained after careful review of the hospital records. In conclusion, PM in children and neonates has a good prognosis. Mostly, it is associated with extrapulmonary air at other sites. It is diagnosed by chest X-ray alone. We identified mechanical events leading to the airway rupture in most children >4Â weeks of life, whereas we were unable to identify a cause in half of the neonates studied (idiopathic PM)
Ab initio simulations of liquid systems: Concentration dependence of the electric conductivity of NaSn alloys
Liquid NaSn alloys in five different compositions (20, 40, 50, 57 and 80%
sodium) are studied using density functional calculations combined with
molecular dynamics(Car-Parrinello method). The frequency-dependent electric
conductivities for the systems are calculated by means of the Kubo-Greenwood
formula.
The extrapolated DC conductivities are in good agreement with the
experimental data and reproduce the strong variation with the concentration.
The maximum of conductivity is obtained, in agreement with experiment, near the
equimolar composition.
The strong variation of conductivity, ranging from almost semiconducting up
to metallic behaviour, can be understood by an analysis of the
densities-of-states.Comment: LaTex 6 pages and 2 figures, to appear in J.Phys. Cond. Ma
Surrogate regression modelling for fast seismogram generation and detection of microseismic events in heterogeneous velocity models
This is the author accepted manuscript. The final version is available from Oxford University Press (OUP) via the DOI in this record.Given a 3D heterogeneous velocity model with a few million voxels, fast generation of accurate seismic responses at specified receiver positions from known microseismic event locations is a well-known challenge in geophysics, since it typically involves numerical solution of the computationally expensive elastic wave equation. Thousands of such forward simulations are often a routine requirement for parameter estimation of microseimsic events via a suitable source inversion process. Parameter estimation based on forward modelling is often advantageous over a direct regression-based inversion approach when there are unknown number of parameters to be estimated and the seismic data has complicated noise characteristics which may not always allow a stable and unique solution in a direct inversion process. In this paper, starting from Graphics Processing Unit (GPU) based synthetic simulations of a few thousand forward seismic shots due to microseismic events via pseudo-spectral solution of elastic wave equation, we develop a step-by-step process to generate a surrogate regression modelling framework, using machine learning techniques that can produce accurate seismograms at specified receiver locations. The trained surrogate models can then be used as a high-speed meta-model/emulator or proxy for the original full elastic wave propagator to generate seismic responses for other microseismic event locations also. The accuracies of the surrogate models have been evaluated using two independent sets of training and testing Latin hypercube (LH) quasi-random samples, drawn from a heterogeneous marine velocity model. The predicted seismograms have been used thereafter to calculate batch likelihood functions, with specified noise characteristics. Finally, the trained models on 23 receivers placed at the sea-bed in a marine velocity model are used to determine the maximum likelihood estimate (MLE) of the event locations which can in future be used in a Bayesian analysis for microseismic event detection.This work has been supported by the Shell Projects and Technology. The Wilkes high performance GPU computing service at the University of Cambridge has been used in this work
Continuous stellar mass-loss in N-body models of galaxies
We present an N-body computer code - aimed at studies of galactic dynamics -
with a CPU-efficient algorithm for a continuous (i.e. time-dependent) stellar
mass-loss. First, we summarize available data on stellar mass-loss and derive
the long-term (20 Gyr) dependence of mass-loss rate of a coeval stellar
population. We then implement it, through a simple parametric form, into a
particle-mesh code with stellar and gaseous particles. We perform several tests
of the algorithm reliability and show an illustrative application: a 2D
simulation of a disk galaxy, starting as purely stellar but evolving as
two-component due to gradual mass-loss from initial stars and due to star
formation. In a subsequent paper we will use the code to study what changes are
induced in galactic disks by the continuous gas recycling compared to the
instantaneous recycling approximation, especially the changes in star formation
rate and radial inflow of matter.Comment: accepted for publication in Astronomy & Astrophysics (13 pages, 11
postscript figures
Structural insights into Legionella RidL-Vps29 retromer subunit interaction reveal displacement of the regulator TBC1D5
Legionella pneumophila can cause Legionnairesâ disease and replicates intracellularly in a distinct Legionella-containing vacuole (LCV). LCV formation is a complex process that involves a plethora of type IV-secreted effector proteins. The effector RidL binds the Vps29 retromer subunit, blocks retrograde vesicle trafficking, and promotes intracellular bacterial replication. Here, we reveal that the 29-kDa N-terminal domain of RidL (RidL2â281) adopts a âfoot-likeâ fold comprising a protruding β-hairpin at its âheelâ. The deletion of the β-hairpin, the exchange to Glu of Ile170 in the β-hairpin, or Leu152 in Vps29 abolishes the interaction in eukaryotic cells and in vitro. RidL2â281 or RidL displace the Rab7 GTPase-activating protein (GAP) TBC1D5 from the retromer and LCVs, respectively, and TBC1D5 promotes the intracellular growth of L. pneumophila. Thus, the hydrophobic β-hairpin of RidL is critical for binding of the L. pneumophila effector to the Vps29 retromer subunit and displacement of the regulator TBC1D5
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