75 research outputs found
Knots in Charged Polymers
The interplay of topological constraints and Coulomb interactions in static
and dynamic properties of charged polymers is investigated by numerical
simulations and scaling arguments. In the absence of screening, the long-range
interaction localizes irreducible topological constraints into tight molecular
knots, while composite constraints are factored and separated. Even when the
forces are screened, tight knots may survive as local (or even global)
equilibria, as long as the overall rigidity of the polymer is dominated by the
Coulomb interactions. As entanglements involving tight knots are not easy to
eliminate, their presence greatly influences the relaxation times of the
system. In particular, we find that tight knots in open polymers are removed by
diffusion along the chain, rather than by opening up. The knot diffusion
coefficient actually decreases with its charge density, and for highly charged
polymers the knot's position appears frozen.Comment: Revtex4, 9 pages, 9 eps figure
All-particle cosmic ray energy spectrum measured with 26 IceTop stations
We report on a measurement of the cosmic ray energy spectrum with the IceTop
air shower array, the surface component of the IceCube Neutrino Observatory at
the South Pole. The data used in this analysis were taken between June and
October, 2007, with 26 surface stations operational at that time, corresponding
to about one third of the final array. The fiducial area used in this analysis
was 0.122 km^2. The analysis investigated the energy spectrum from 1 to 100 PeV
measured for three different zenith angle ranges between 0{\deg} and 46{\deg}.
Because of the isotropy of cosmic rays in this energy range the spectra from
all zenith angle intervals have to agree. The cosmic-ray energy spectrum was
determined under different assumptions on the primary mass composition. Good
agreement of spectra in the three zenith angle ranges was found for the
assumption of pure proton and a simple two-component model. For zenith angles
{\theta} < 30{\deg}, where the mass dependence is smallest, the knee in the
cosmic ray energy spectrum was observed between 3.5 and 4.32 PeV, depending on
composition assumption. Spectral indices above the knee range from -3.08 to
-3.11 depending on primary mass composition assumption. Moreover, an indication
of a flattening of the spectrum above 22 PeV were observed.Comment: 38 pages, 17 figure
An improved method for measuring muon energy using the truncated mean of dE/dx
The measurement of muon energy is critical for many analyses in large
Cherenkov detectors, particularly those that involve separating
extraterrestrial neutrinos from the atmospheric neutrino background. Muon
energy has traditionally been determined by measuring the specific energy loss
(dE/dx) along the muon's path and relating the dE/dx to the muon energy.
Because high-energy muons (E_mu > 1 TeV) lose energy randomly, the spread in
dE/dx values is quite large, leading to a typical energy resolution of 0.29 in
log10(E_mu) for a muon observed over a 1 km path length in the IceCube
detector. In this paper, we present an improved method that uses a truncated
mean and other techniques to determine the muon energy. The muon track is
divided into separate segments with individual dE/dx values. The elimination of
segments with the highest dE/dx results in an overall dE/dx that is more
closely correlated to the muon energy. This method results in an energy
resolution of 0.22 in log10(E_mu), which gives a 26% improvement. This
technique is applicable to any large water or ice detector and potentially to
large scintillator or liquid argon detectors.Comment: 12 pages, 16 figure
Modified Chaplygin Gas as a Unified Dark Matter and Dark Energy Model and Cosmic Constraints
A modified Chaplygin gas model (MCG),
,
as a unified dark matter model and dark energy model is constrained by using
current available cosmic observational data points which include type Ia
supernovae, baryon acoustic oscillation and the seventh year full WMAP data
points. As a contrast to the consideration in the literatures, we {\it do not}
separate the MCG into two components, i.e. dark mater and dark energy
component, but we take it as a whole energy component-a unified dark sector. By
using Markov Chain Monte Carlo method, a tight constraint is obtained: , and .}Comment: 6 pages, 3 figure
Scalability considerations for multivariate graph visualization
Real-world, multivariate datasets are frequently too large to show in their entirety on a visual display. Still, there are many techniques we can employ to show useful partial views-sufficient to support incremental exploration of large graph datasets. In this chapter, we first explore the cognitive and architectural limitations which restrict the amount of visual bandwidth available to multivariate graph visualization approaches. These limitations afford several design approaches, which we systematically explore. Finally, we survey systems and studies that exhibit these design strategies to mitigate these perceptual and architectural limitations
Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries
Background
Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres.
Methods
This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries.
Results
In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia.
Conclusion
This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries
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An assessment of worldwide supercomputer usage
This report provides a comparative study of advanced supercomputing usage in Japan and the United States as of Spring 1994. It is based on the findings of a group of US scientists whose careers have centered on programming, evaluating, and designing high-performance supercomputers for over ten years. The report is a follow-on to an assessment of supercomputing technology in Europe and Japan that was published in 1993. Whereas the previous study focused on supercomputer manufacturing capabilities, the primary focus of the current work was to compare where and how supercomputers are used. Research for this report was conducted through both literature studies and field research in Japan
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A benchmark of the SCS-40 computer: A mini supercomputer compatible with the Cray X-MP/24
An accurate benchmark of the SCS-40 mini supercomputer manufactured by Scientific Computer Systems Corporation has been carried out. A new, revised set of standard ANSI77 Fortran benchmark codes were run on the SCS-40 in a dedicated environment, using Version 1.13 of the CFT compiler. The results are compared with those obtained on one processor of a CRAY X-MP/24 computer using the Cray Research Inc. version of the same compiler. The results suggest that for a typical Los Alamos National Laboratory computational workload, the SCS-40 is equivalent to one-quarter to one-third of a single processor of the CRAY X-MP/24. 15 refs., 5 tabs
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