Error estimation in the histogram Monte Carlo method

We examine the sources of error in the histogram reweighting method for Monte Carlo data analysis. We demonstrate that, in addition to the standard statistical error which has been studied elsewhere, there are two other sources of error, one arising through correlations in the reweighted samples, and one arising from the finite range of energies sampled by a simulation of finite length. We demonstrate that while the former correction is usually negligible by comparison with statistical fluctuations, the latter may not be, and give criteria for judging the range of validity of histogram extrapolations based on the size of this latter correction.Comment: 7 pages including 3 postscript figures, typeset in LaTeX using the RevTeX macro packag

Possible applications of soaring technology to drag reduction in powered general aviation aircraft

A brief examination of the performance figures achieved by modern soaring machines and a little reflection on the often huge disparity in L/D values between sailplanes and GA aircraft indicates that careful attention to lessons learned in sailplane design and manufacture hold realistic promise for substantial gains in the aerodynamic efficiency of several GA types

Some implications of sampling choices on comparisons between satellite and model aerosol optical depth fields

The comparison of satellite and model aerosol optical depth (AOD) fields provides useful information on the strengths and weaknesses of both. However, the sampling of satellite and models is very different and some subjective decisions about data selection and aggregation must be made in order to perform such comparisons. This work examines some implications of these decisions, using GlobAerosol AOD retrievals at 550 nm from Advanced Along-Track Scanning Radiometer (AATSR) measurements, and aerosol fields from the GEOS-Chem chemistry transport model. It is recommended to sample the model only where the satellite flies over on a particular day; neglecting this can cause regional differences in model AOD of up to 0.1 on monthly and annual timescales. The comparison is observed to depend strongly upon thresholds for sparsity of satellite retrievals in the model grid cells. Requiring at least 25% coverage of the model grid cell by satellite data decreases the observed difference between the two by approximately half over land. The impact over ocean is smaller. In both model and satellite datasets, there is an anticorrelation between the proportion <i>p</i> of a model grid cell covered by satellite retrievals and the AOD. This is attributed to small <i>p</i> typically occuring due to high cloud cover and lower AODs being found in large clear-sky regions. Daily median AATSR AODs were found to be closer to GEOS-Chem AODs than daily means (with the root mean squared difference being approximately 0.05 smaller). This is due to the decreased sensitivity of medians to outliers such as cloud-contaminated retrievals, or aerosol point sources not included in the model

GRBs and the thermalization process of electron-positron plasmas

We discuss the temporal evolution of the pair plasma created in Gamma-Ray Burst sources. A particular attention is paid to the relaxation of the plasma into thermal equilibrium. We also discuss the connection between the dynamics of expansion and the spatial geometry of the plasma. The role of the baryonic loading parameter is emphasized.Comment: 4 pages, 3 figures, in the Proceedings of the "Gamma Ray Bursts 2007" meeting, November 5-9, 2007, Santa Fe, New Mexico, US

Dispersal of meiofauna in a turbulent tidal creek

Traditionally meiofauna have been viewed as strictly infaunal organisms adapted for life between sediment grains. Recent evidence has shown that marine meiofauna also occur in the water column. A set of field experiments investigated processes controlling the abundance of meiofauna in the water column. The transport of meiofauna in a tidal creek was identified to be primarily a passive process resulting from mechanical removal due to current scour. Drifting meiofauna included interstitial, burrowing, and epibenthic species. Copepods, foraminiferans, and juvenile bivalves were suspended in greatest numbers relative to their sediment abundances. Suspension of meiofauna was greatest for species residing in the upper sediment layers and/or occasionally crawling about on the sediment surface. Suspended meiofauna and sediment were well-mixed within the water column, suggesting that behavioral control over water column dispersal was limited once the animals were in the water. Suspension of meiofauna was not a function of winds, time of day, lunar cycle (neap vs. spring tides), or the abundance of meiofauna in the sediment. The abundance of meiofauna in the water was determined primarily by the magnitude of the friction velocity (u.). The emerging concept is that in habitats where water currents are strong enough to lead to sediment scour, meiofauna dispersal is a two-step process with erosion rather than active water column entry (modified by behavior patterns for some species) and subsequent mixing and transport as passive particles

Developmental design, fabrication, and test of acoustic suppressors for fans of high bypass turbofan engines

An analysis procedure was developed for design of acoustically treated nacelles for high bypass turbofan engines. The plan was applied to the conceptual design of a nacelle for the quiet engine typical of a 707/DC-8 airplane installation. The resultant design was modified to a test nacelle design for the NASA Lewis quiet fan. The acoustic design goal was a 10 db reduction in effective perceived fan noise levels during takoff and approach. Detailed nacelle designs were subsequently developed for both the quiet engine and the quiet fan. The acoustic design goal for each nacelle was 15 db reductions in perceived fan noise levels from the inlet and fan duct. Acoustically treated nacelles were fabricated for the quiet engine and quiet fan for testing. Performance of selected inlet and fan duct lining configurations was experimentally evaluated in a flow duct. Results of the tests show that the linings perform as designed