9,301 research outputs found
A remote sensing evaluation of potential for sinkhole occurrence
The relationship between lowering of the water table and sinkhole development in Pierson and in Hillsborough County, Florida was investigated. The locations of recently developed (1973) collapses were examined with respect to lineaments or fracture traces that are expressed in the terrain and visible in aerial photography and satellite imagery. It was anticipated that these relationships would provide the basis for establishment of criteria for mapping those land areas that have the greatest potential for sinkhole development. A very good correlation was found between mapped lineament intersections and known location of sinkhole occurrences for both study areas. This indicates that lineament and fracture trace mapping may be very useful in locating zones with the greatest potential for sinkhole development. It is further shown that this information is quite beneficial in land use planning applications
Importance Tempering
Simulated tempering (ST) is an established Markov chain Monte Carlo (MCMC)
method for sampling from a multimodal density . Typically, ST
involves introducing an auxiliary variable taking values in a finite subset
of and indexing a set of tempered distributions, say . In this case, small values of encourage better
mixing, but samples from are only obtained when the joint chain for
reaches . However, the entire chain can be used to estimate
expectations under of functions of interest, provided that importance
sampling (IS) weights are calculated. Unfortunately this method, which we call
importance tempering (IT), can disappoint. This is partly because the most
immediately obvious implementation is na\"ive and can lead to high variance
estimators. We derive a new optimal method for combining multiple IS estimators
and prove that the resulting estimator has a highly desirable property related
to the notion of effective sample size. We briefly report on the success of the
optimal combination in two modelling scenarios requiring reversible-jump MCMC,
where the na\"ive approach fails.Comment: 16 pages, 2 tables, significantly shortened from version 4 in
response to referee comments, to appear in Statistics and Computin
Basic hydrogeologic and remote sensing data for selection of sanitary landfill sites
Solid waste disposal were studied in Volusia County to protect the water supply in the area. Highlands in this County are of limited areal extent and, most significantly, the sand hills and ridges are in areas where recharge of the Floridan aquifer occurs. This study proves that well drained soils meeting the current State requirements are of limited areal extent. These areas should not be utilized as sanitary landfill sites! Rather, it is recommended that the Tomoka Farm Road site into the adjacent wetlands be extended. The County site on Rima Ridge recommended by Greenleaf-Telesca as the primary waste burial site in the County should be re-evaluated because of potential danger to the Daytona Beach water supply
Hydraulics and geology related to beach restoration in Lee County, Florida
The erosion problem on Captiva Island is discussed. It is due to a deficit in the sand budget of the littoral drift system; a system with losses due to attrition of the particles and mass losses into the lagoons, to offshore, and to lateral transport. The effect that reopening Blind Pass would have, and the placement of sediment retaining structures in the surf zone at the northern and southern limits of the Captiva beach system, wave examined. A geological approach was used to study the origin and dynamic changes that have occurred. Through hydraulic modeling, changes that will occur by reopening and stabilizing Blind Pass are predicted. It is concluded that if the island is to be stabilized, beach nourishment with proper amounts and particle size is a necessity and that jetties adequate to restrict lateral and offshore losses are essential. It is shown that the reopening of Blind Pass would have minimal effects on the passes to the north and south, and would improve the environmental conditions in the sound with no adverse effects on the beach system
Global Cosmological Parameters Determined Using Classical Double Radio Galaxies
A sample of 20 powerful extended radio galaxies with redshifts between zero
and two were used to determine constraints on global cosmological parameters.
Data for six radio sources were obtained from the VLA archive, analyzed, and
combined with the sample of 14 radio galaxies used previously by Guerra & Daly
to determine cosmological parameters. The results are consistent with our
previous results, and indicate that the current value of the mean mass density
of the universe is significantly less than the critical value. A universe with
of unity is ruled out at 99.0% confidence, and the best fitting
values of in matter are and
assuming zero space curvature and zero cosmological
constant, respectively. Note that identical results obtain when the low
redshift bin, which includes Cygnus A, is excluded; these results are
independent of whether the radio source Cygnus A is included. The method does
not rely on a zero-redshift normalization.
The radio properties of each source are also used to determine the density of
the gas in the vicinity of the source, and the beam power of the source. The
six new radio sources have physical characteristics similar to those found for
the original 14 sources. The density of the gas around these radio sources is
typical of gas in present day clusters of galaxies. The beam powers are
typically about .Comment: 39 pages includes 21 figures, accepted to Ap
Magnetic states of linear defects in graphene monolayers: effects of strain and interaction
The combined effects of defect-defect interaction and of uniaxial or biaxial
strains of up to 10\% on the development of magnetic states on the
defect-core-localized quasi-one-dimensional electronic states generated by the
so-called 558 linear extended defect in graphene monolayers are investigated by
means of {\it ab initio} calculations. Results are analyzed on the basis of the
heuristics of the Stoner criterion. We find that conditions for the emergence
of magnetic states on the 558 defect can be tuned by uniaxial tensile parallel
strains (along the defect direction) at both limits of isolated and interacting
558 defects. Parallel strains are shown to lead to two cooperative effects that
favor the emergence of itinerant magnetism: enhancement of the DOS of the
resonant defect states in the region of the Fermi level and tuning of the Fermi
level to the maximum of the related DOS peak. A perpendicular strain is
likewise shown to enhance the DOS of the defect states, but it also effects a
detunig of the Fermi level that shifts away from the maximum of the DOS of the
defect states, which inhibts the emergence of magnetic states. As a result,
under biaxial strains the stabilization of a magnetic state depends on the
relative magnitudes of the two components of strain.Comment: 9 pages 8 figure
New data and the hard pomeron
New structure-function data are in excellent agreement with the existence of
a hard pomeron, with intercept about 1.4. It gives a very economical
description of the data. Having fixed 2 parameters from the data for the
real-photon cross section , we need just 5 further
parameters to fit the data for with . The available
data range from to 35 GeV. With guesses consistent with
dimensional counting for the dependences of our three separate terms, the
fit extends well to larger and to GeV. With no additional
parameters, it gives a good description of data for the charm structure
function from to 130 GeV. The two pomerons also give
a good description of both the and the dependence of .Comment: 11 pages, plain tex, with 10 figures embedded using epsf. (Spurious
figure removed.
Signature of the Simplicial Supermetric
We investigate the signature of the Lund-Regge metric on spaces of simplicial
three-geometries which are important in some formulations of quantum gravity.
Tetrahedra can be joined together to make a three-dimensional piecewise linear
manifold. A metric on this manifold is specified by assigning a flat metric to
the interior of the tetrahedra and values to their squared edge-lengths. The
subset of the space of squared edge-lengths obeying triangle and analogous
inequalities is simplicial configuration space. We derive the Lund-Regge metric
on simplicial configuration space and show how it provides the shortest
distance between simplicial three-geometries among all choices of gauge inside
the simplices for defining this metric (Regge gauge freedom). We show
analytically that there is always at least one physical timelike direction in
simplicial configuration space and provide a lower bound on the number of
spacelike directions. We show that in the neighborhood of points in this space
corresponding to flat metrics there are spacelike directions corresponding to
gauge freedom in assigning the edge-lengths. We evaluate the signature
numerically for the simplicial configuration spaces based on some simple
triangulations of the three-sphere (S^3) and three-torus (T^3). For the surface
of a four-simplex triangulation of S^3 we find one timelike direction and all
the rest spacelike over all of the simplicial configuration space. For the
triangulation of T^3 around flat space we find degeneracies in the simplicial
supermetric as well as a few gauge modes corresponding to a positive
eigenvalue. Moreover, we have determined that some of the negative eigenvalues
are physical, i.e. the corresponding eigenvectors are not generators of
diffeomorphisms. We compare our results with the known properties of continuum
superspace.Comment: 24 pages, RevTeX, 4 eps Figures. Submitted to Classical Quantum
Gravit
THE DRINKING PATTERNS OF AMERICAN AND POLISH UNIVERSITY STUDENTS: A CROSS-NATIONAL STUDY
This is the post-print version of an article published in Drug and Alcohol Dependence located at http://www.journals.elsevier.com/drug-and-alcohol-dependence/. No DOI is listed for this article.Other research PUBLICATIONS and PAPERS on university students drinking, drug use and health concerns and behaviors can be found at: https://scholarworks.iu.edu/dspace/handle/2022/17130/browse?type=title; https://scholarworks.iu.edu/dspace/handle/2022/17127/browse?type=title and https://scholarworks.iu.edu/dspace/handle/2022/17124/browse?type=title. Further information about the questionnaire, calculations, and the original data base used can be found in the following item records within IUScholarworks repository. Details about the reliability and validity of the SAQ are found at: http://hdl.handle.net/2022/17337; http://hdl.handle.net/2022/17154; http://hdl.handle.net/2022/17181. The classic 1975 copy of the SAQ is found at http://hdl.handle.net/2022/17153. ALL QUESTIONNAIRES developed by Engs are found in the repository at: https://scholarworks.iu.edu/dspace/handle/2022/17141/browse?type=dateissuedA study of 3375 American and 1408 Polish university students was accomplished to test the hypotheses that cultural differences influence drinking patterns and beverage preferences between countries. Using the same questionnaire in both samples, the results revealed that significantly (p < .001) more drinks per week were consumed by both Polish male (24.9) and female (15.2) students compared to American male (15.0) and female (7.6) students. Significantly (p < .001) more wine was consumed by Polish (8.7) compared to the American (0.8) students. American female students consumed more beer than Polish female students. There was no difference between beer and spirits consumption between American and Polish males and Polish students in latter school years consumed more alcohol compared to students in the first years of school. It was concluded that the samples of students in this study reflected their cultures in terms of drinking patterns and beverage preference
- …