417 research outputs found
Submicrosecond comparisons of time standards via the Navigation Technology Satellites (NTS)
An interim demonstration was performed of the time transfer capability of the NAVSTAR GPS system using a single NTS satellite. Measurements of time difference (pseudo-range) are made from the NTS tracking network and at the participating observatories. The NTS network measurements are used to compute the NTS orbit trajectory. The central NTS tracking station has a time link to the Naval Observatory UTC (USNO,MC1) master clock. Measurements are used with the NTS receiver at the remote observatory, the time transfer value UTC (USNO,MC1)-UTC (REMOTE, VIA NTS) is calculated. Intercomparisons were computed using predicted values of satellite clock offset and ephemeus
Accuracy of the "traffic light" clinical decision rule for serious bacterial infections in young children with fever: A retrospective cohort study
Objectives To determine the accuracy of a clinical decision rule (the traffic light system developed by the National Institute for Health and Clinical Excellence (NICE)) for detecting three common serious bacterial infections (urinary tract infection, pneumonia, and bacteraemia) in young febrile children. Design Retrospective analysis of data from a two year prospective cohort study Setting A paediatric emergency department. Participants 15 781 cases of children under 5 years of age presenting with a febrile illness. Main outcome measures Clinical features were used to categorise each febrile episodes as low, intermediate, or high probability of serious bacterial infection (green, amber, and red zones of the traffic light system); these results were checked (using standard radiological and microbiological tests) for each of the infections of interest and for any serious bacterial infection. Results After combination of the intermediate and high risk categories, the NICE traffic light system had a test sensitivity of 85.8% (95% confidence interval 83.6% to 87.7%) and specificity of 28.5% (27.8% to 29.3%) for the detection of any serious bacterial infection. Of the 1140 cases of serious bacterial infection, 157 (13.8%) were test negative (in the green zone), and, of these, 108 (68.8%) were urinary tract infections. Adding urine analysis (leucocyte esterase or nitrite positive), reported in 3653 (23.1%) episodes, to the traffic light system improved the test performance: sensitivity 92.1% (89.3% to 94.1%), specificity 22.3% (20.9% to 23.8%), and relative positive likelihood ratio 1.10 (1.06 to 1.14). Conclusion The NICE traffic light system failed to identify a substantial proportion of serious bacterial infections, particularly urinary tract infections. The addition of urine analysis significantly improved test sensitivity, making the traffic light system a more useful triage tool for the detection of serious bacterial infections in young febrile children
Finite-size scaling of the error threshold transition in finite population
The error threshold transition in a stochastic (i.e. finite population)
version of the quasispecies model of molecular evolution is studied using
finite-size scaling. For the single-sharp-peak replication landscape, the
deterministic model exhibits a first-order transition at , where is the probability of exact replication of a molecule of length , and is the selective advantage of the master string. For
sufficiently large population size, , we show that in the critical region
the characteristic time for the vanishing of the master strings from the
population is described very well by the scaling assumption \tau = N^{1/2} f_a
\left [ \left (Q - Q_c) N^{1/2} \right ] , where is an -dependent
scaling function.Comment: 8 pages, 3 ps figures. submitted to J. Phys.
Profitable and Sustainable Grazing Systems for Livestock Producers with Saline Land in Southern Australia
Dryland salinity affects over 2.5 M ha in Australia, mostly in southern states and is expanding at 3-5% per year (NLWRA, 2001). The prognosis is for considerable expansion of the area affected by salinity and waterlogging (1217 M ha at equilibrium), because groundwater levels continue to rise and only small-scale land management programmes have been implemented. In addition, many waterways are increasingly saline, especially in the Murray Darling Basin and in Western Australia (WA). Sustainable Grazing on Saline Land (SGSL) addresses the need to make productive use of saline land and water resources. Its research component operates at 12 sites across WA, South Australia (SA), Victoria and New South Wales (NSW) and consists of coordinated activities that have regional relevance and contribute nationally. The programme seeks to develop and demonstrate profitable and sustainable grazing systems on saline land that have positive environmental and social impacts. Whilst there are different priority research issues at each site, data collection is governed by common measurement protocols for salt and water movement, biodiversity, and pasture and animal performance in order to make comparisons and data sharing across sites practical
Error threshold in finite populations
A simple analytical framework to study the molecular quasispecies evolution
of finite populations is proposed, in which the population is assumed to be a
random combination of the constiyuent molecules in each generation,i.e.,
linkage disequilibrium at the population level is neglected. In particular, for
the single-sharp-peak replication landscape we investigate the dependence of
the error threshold on the population size and find that the replication
accuracy at threshold increases linearly with the reciprocal of the population
size for sufficiently large populations. Furthermore, in the deterministic
limit our formulation yields the exact steady-state of the quasispecies model,
indicating then the population composition is a random combination of the
molecules.Comment: 14 pages and 4 figure
Profitable and Sustainable Grazing Systems for Livestock Producers with Saline Land in Southern Australia
Dryland salinity affects over 2.5 M ha in Australia, mostly in southern states and is expanding at 3-5% per year (NLWRA, 2001). The prognosis is for considerable expansion of the area affected by salinity and waterlogging (12–17 M ha at equilibrium), because groundwater levels continue to rise and only small-scale land management programmes have been implemented. In addition, many waterways are increasingly saline, especially in the Murray Darling Basin and in Western Australia (WA). Sustainable Grazing on Saline Land (SGSL) addresses the need to make productive use of saline land and water resources. Its research component operates at 12 sites across WA, South Australia (SA), Victoria and New South Wales (NSW) and consists of coordinated activities that have regional relevance and contribute nationally. The programme seeks to develop and demonstrate profitable and sustainable grazing systems on saline land that have positive environmental and social impacts. Whilst there are different priority research issues at each site, data collection is governed by common measurement protocols for salt and water movement, biodiversity, and pasture and animal performance in order to make comparisons and data sharing across sites practical
Anderson Localization, Non-linearity and Stable Genetic Diversity
In many models of genotypic evolution, the vector of genotype populations
satisfies a system of linear ordinary differential equations. This system of
equations models a competition between differential replication rates (fitness)
and mutation. Mutation operates as a generalized diffusion process on genotype
space. In the large time asymptotics, the replication term tends to produce a
single dominant quasispecies, unless the mutation rate is too high, in which
case the populations of different genotypes becomes de-localized. We introduce
a more macroscopic picture of genotypic evolution wherein a random replication
term in the linear model displays features analogous to Anderson localization.
When coupled with non-linearities that limit the population of any given
genotype, we obtain a model whose large time asymptotics display stable
genotypic diversityComment: 25 pages, 8 Figure
Distribution of graph-distances in Boltzmann ensembles of RNA secondary structures
Large RNA molecules often carry multiple functional domains whose spatial
arrangement is an important determinant of their function. Pre-mRNA splicing,
furthermore, relies on the spatial proximity of the splice junctions that can
be separated by very long introns. Similar effects appear in the processing of
RNA virus genomes. Albeit a crude measure, the distribution of spatial
distances in thermodynamic equilibrium therefore provides useful information on
the overall shape of the molecule can provide insights into the interplay of
its functional domains. Spatial distance can be approximated by the
graph-distance in RNA secondary structure. We show here that the equilibrium
distribution of graph-distances between arbitrary nucleotides can be computed
in polynomial time by means of dynamic programming. A naive implementation
would yield recursions with a very high time complexity of O(n^11). Although we
were able to reduce this to O(n^6) for many practical applications a further
reduction seems difficult. We conclude, therefore, that sampling approaches,
which are much easier to implement, are also theoretically favorable for most
real-life applications, in particular since these primarily concern long-range
interactions in very large RNA molecules.Comment: Peer-reviewed and presented as part of the 13th Workshop on
Algorithms in Bioinformatics (WABI2013
Helicon Plasma Injector and Ion Cyclotron Acceleration Development in the VASIMR Experiment
In the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) radio frequency (rf) waves both produce the plasma and then accelerate the ions. The plasma production is done by action of helicon waves. These waves are circular polarized waves in the direction of the electron gyromotion. The ion acceleration is performed by ion cyclotron resonant frequency (ICRF) acceleration. The Advanced Space Propulsion Laboratory (ASPL) is actively developing efficient helicon plasma production and ICRF acceleration. The VASIMR experimental device at the ASPL is called VX-10. It is configured to demonstrate the plasma production and acceleration at the 10kW level to support a space flight demonstration design. The VX-10 consists of three electromagnets integrated into a vacuum chamber that produce magnetic fields up to 0.5 Tesla. Magnetic field shaping is achieved by independent magnet current control and placement of the magnets. We have generated both helium and hydrogen high density (>10(exp 18) cu m) discharges with the helicon source. ICRF experiments are underway. This paper describes the VX-10 device, presents recent results and discusses future plans
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