Seismic Inference using Genetic Algorithms     

Travis S. Metcalfe 《Astrophysics and Space Science》2003,284(1):141-151

A flood of reliable seismic data will soon arrive. The migration to largertelescopes on the ground may free up 4-m class instruments for multi-sitecampaigns, and several forthcoming satellite missions promise to yieldnearly uninterrupted long-term coverage of many pulsating stars. We willthen face the challenge of determining the fundamental properties of thesestars from the data, by trying to match them with the output of ourcomputer models. The traditional approach to this task is to make informedguesses for each of the model parameters, and then adjust them iterativelyuntil an adequate match is found. The trouble is: how do we know that oursolution is unique, or that some other combination of parameters will notdo even better? Computers are now sufficiently powerful and inexpensivethat we can produce large grids of models and simply compare all ofthem to the observations. The question then becomes: what range ofparameters do we want to consider, and how many models do we want tocalculate? This can minimize the subjective nature of the process, but itmay not be the most efficient approach and it may give us a false sense ofsecurity that the final result is correct, when it is really justoptimal. I discuss these issues in the context of recent advances inthe asteroseismological analysis of white dwarf stars.  相似文献   

The Citation Impact of Digital Preprint Archives for Solar Physics Papers   总被引：1，自引：0，他引：1  

Travis S. Metcalfe 《Solar physics》2006,239(1-2):549-553

Papers that are posted to a digital preprint archive are typically cited twice as often as papers that are not posted. This has been demonstrated for papers published in a wide variety of journals, and in many different subfields of astronomy. Most astronomers now use the arXiv.org server (astro-ph) to distribute preprints, but the solar physics community has an independent archive hosted at Montana State University. For several samples of solar physics papers published in 2003, I quantify the boost in citation rates for preprints posted to each of these servers. I show that papers on the MSU archive typically have citation rates 1.7 times higher than the average of similar papers that are not posted as preprints, while those posted to astro-ph get 2.6 times the average. A comparable boost is found for papers published in conference proceedings, suggesting that the higher citation rates are not the result of self-selection of above-average papers. Editors’ Note: This paper lies outside the normal purview of Solar Physics papers, however the editors feel that the content is of sufficient importance for all Solar Physics authors and readers to merit its publication.  相似文献   

Mantle circulation models with variational data assimilation: inferring past mantle flow and structure from plate motion histories and seismic tomography   总被引：3，自引：0，他引：3  

Hans-Peter Bunge  C. R. Hagelberg  B. J. Travis 《Geophysical Journal International》2003,152(2):280-301

  相似文献   

Macrobenthic infaunal communities associated with deep‐sea hydrocarbon seeps in the northern Gulf of Mexico          下载免费PDF全文

Travis W. Washburn  Amanda W. J. Demopoulos  Paul A. Montagna 《Marine Ecology》2018,39(3)

There are thousands of seeps in the deep ocean worldwide; however, many questions remain about their contributions to global biodiversity and the surrounding deep‐sea environment. In addition to being globally distributed, seeps provide several benefits to humans such as unique habitats, organisms with novel genes, and carbon regulation. The purpose of this study is to determine whether there are unique seep macrobenthic assemblages, by comparing seep and nonseep environments, different seep habitats, and seeps at different depths and locations. Infaunal community composition, diversity, and abundance were examined between seep and nonseep background environments and among three seep habitats (i.e., microbial mats, tubeworms, and soft‐bottom seeps). Abundances were higher at seep sites compared to background areas. Abundance and diversity also differed among microbial mat, tubeworm, and soft‐bottom seep habitats. Although seeps contained different macrobenthic assemblages than nonseep areas, infaunal communities were also generally unique for each seep. Variability was 75% greater within communities near seeps compared to communities in background areas. Thus, high variability in community structure characterized seep communities rather than specific taxa. The lack of similarity among seep sites supports the idea that there are no specific infauna that can be used as indicators of seepage throughout the northern Gulf of Mexico, at least at higher taxonomic levels.  相似文献   

Some Biases in Sampling Multilevel Piezometers for Volatile Organics     

J. F. Barker  G. C Patrick  L. Lemon  G. M. Travis 《Ground Water Monitoring & Remediation》1987,7(2):48-54

Multilevel piezometers are cost-effective monitoring devices for determining the three-dimensional distribution of solutes in ground water. Construction includes flexible tubing (plastic or Teflon®). Their sampling is subject to a number of'potential biases, particularly: (1) losses of volatile organic solutes via volatilization, (2) sorption onto the flexible tubing of the piezometers, (3) leaching of organics from this tubing, and (4) collection of unrepresentative samples due to inadequate piezometer flushing. It is shown that these biases are minimal or are easily controlled in most situations.
Another source of bias has been recognized. Organic solutes present in ground water above the screened level can penetrate the flexible plastic or Teflon tubing and contaminate the sampled water being drawn through this tubing. Laboratory tests and field results indicate this transmission causes low organic contaminant concentrations to be erroneously attributed to ground water which is free of such contaminants. The transmitted organics apparently desorb from the plastic tubing during flushing of even 40 piezometer volumes.
Recognition of this transmission problem provides for a better interpretation of existing organic contaminant distribution data. Caution is advised when considering the use of these monitoring devices in organic solute contaminant studies.  相似文献   

Methodological recommendations for ungulate mortality analyses in paleoanthropology     

Henry T. Bunn  Travis Rayne Pickering 《Quaternary Research》2010,74(3):388-394

Age profiling of fossil faunal samples relies on the correlation of animal tooth-wear patterns with life history stages, but the criteria used to infer these stages are not necessarily valid. Here we redefine some commonly used prey age classes, such as “juvenile,” “prime-age adult,” and “old adult,” based on the variable characteristics of tooth wear that we have observed in different ungulate size classes, and argue that prey vulnerability to predation is not so clearly predicted by the simplified age classes in widespread use by zooarchaeologists. We recommend instead classifying the youngest animal remains as either young juvenile or subadult juvenile, and adult remains as early prime, late prime or old, and provide specific criteria of dental eruption and occlusal wear for making these determinations. We argue this refined age profiling system, when used in combination with other types of zooarchaeological and taphonomic data, can provide accurate inferences of faunal accumulation processes.  相似文献   

Bovid mortality profiles in paleoecological context falsify hypotheses of endurance running–hunting and passive scavenging by early Pleistocene hominins     

Henry T. Bunn  Travis Rayne Pickering   《Quaternary Research》2010,74(3):395-404

The world’s first archaeological traces from 2.6 million years ago (Ma) at Gona, in Ethiopia, include sharp-edged cutting tools and cut-marked animal bones, which indicate consumption of skeletal muscle by early hominin butchers. From that point, evidence of hominin meat-eating becomes increasingly more common throughout the Pleistocene archaeological record. Thus, the substantive debate about hominin meat-eating now centers on mode(s) of carcass resource acquisition. Two prominent hypotheses suggest, alternatively, (1) that early Homo hunted ungulate prey by running them to physiological failure and then dispatching them, or (2) that early Homo was relegated to passively scavenging carcass residues abandoned by carnivore predators. Various paleontologically testable predictions can be formulated for both hypotheses. Here we test four predictions concerning age-frequency distributions for bovids that contributed carcass remains to the 1.8 Ma. old FLK 22 Zinjanthropus (FLK Zinj, Olduvai Gorge, Tanzania) fauna, which zooarchaeological and taphonomic data indicate was formed predominantly by early Homo. In all but one case, the bovid mortality data from FLK Zinj violate test predictions of the endurance running-hunting and passive scavenging hypotheses. When combined with other taphonomic data, these results falsify both hypotheses, and lead to the hypothesis that early Homo operated successfully as an ambush predator.  相似文献   

Sensitivity of the regional climate model RegCM4.2 to planetary boundary layer parameterisation     

Ivan Güttler  Čedo Branković  Travis A. O’Brien  Erika Coppola  Branko Grisogono  Filippo Giorgi 《Climate Dynamics》2014,43(7-8):1753-1772

This study investigates the performance of two planetary boundary layer (PBL) parameterisations in the regional climate model RegCM4.2 with specific focus on the recently implemented prognostic turbulent kinetic energy parameterisation scheme: the University of Washington (UW) scheme. When compared with the default Holtslag scheme, the UW scheme, in the 10-year experiments over the European domain, shows a substantial cooling. It reduces winter warm bias over the north-eastern Europe by 2 °C and reduces summer warm bias over central Europe by 3 °C. A part of the detected cooling is ascribed to a general reduction in lower tropospheric eddy heat diffusivity with the UW scheme. While differences in temperature tendency due to PBL schemes are mostly localized to the lower troposphere, the schemes show a much higher diversity in how vertical turbulent mixing of the water vapour mixing ratio is governed. Differences in the water vapour mixing ratio tendency due to the PBL scheme are present almost throughout the troposphere. However, they alone cannot explain the overall water vapour mixing ratio profiles, suggesting strong interaction between the PBL and other model parameterisations. An additional 18-member ensemble with the UW scheme is made, where two formulations of the master turbulent length scale in unstable conditions are tested and unconstrained parameters associated with (a) the evaporative enhancement of the cloud-top entrainment and (b) the formulation of the master turbulent length scale in stable conditions are systematically perturbed. These experiments suggest that the master turbulent length scale in the UW scheme could be further refined in the current implementation in the RegCM model. It was also found that the UW scheme is less sensitive to the variations of the other two selected unconstrained parameters, supporting the choice of these parameters in the default formulation of the UW scheme.  相似文献   

A benchmark comparison of numerical methods for infinite Prandtl number thermal convection in two-dimensional Cartesian geometry     

B. J. Travis  C. Anderson  J. Baumgardner  C. W. Gable  B. H. Hager  R. J. O'Connell 《地球物理与天体物理流体动力学》2013,107(3-4):137-160

Abstract

A comparison is made between seven different numerical methods for calculating two-dimensional thermal convection in an infinite Prandtl number fluid. Among the seven methods are finite difference and finite element techniques that have been used to model thermal convection in the Earth's mantle. We evaluate the performance of each method using a suite of four benchmark problems, ranging from steady-state convection to intrinsically time-dependent convection with recurring thermal boundary layer instabilities. These results can be used to determine the accuracy of other computational methods, and to assist in the development of new ones.  相似文献   

Mapping of Io's thermal radiation by the Galileo photopolarimeter-radiometer (PPR) instrument   总被引：1，自引：0，他引：1  

J.A. Rathbun  J.R. Spencer  T.Z. Martin  L.D. Travis 《Icarus》2004,169(1):127-139

Between 1999 and 2002, the Galileo spacecraft made 6 close flybys of Io during which many observations of Io's thermal radiation were made with the photopolarimeter-radiometer (PPR). While the NIMS instrument could measure thermal emission from hot spots with T>200 K, PPR was the only Galileo instrument capable of mapping the lower temperatures of older, cooling lava flows, and the passive background. We tabulate all data taken by PPR of Io during these flybys and describe some scientific highlights revealed by the data. The data include almost complete coverage of Io at better than 250 km resolution, with extensive regional coverage at higher resolutions. We found a modest poleward drop in nighttime background temperatures and evidence of thermal inertia variations across the surface. Comparison of high spatial resolution temperature measurements with observed daytime SO₂ gas pressures on Io provides evidence for local cold trapping of SO₂ frost on scales smaller than the 60 km resolution of the PPR data. We also calculated the power output from several hot spots and estimated total global heat flow to be about 2.0-2.6 W m⁻². The low-latitude diurnal temperature variations for the regions between obvious hot spots are well matched by a laterally-inhomogeneous thermal model with less than 1 W m⁻² endogenic heat flow.  相似文献