3,788 research outputs found
Computerized Construction of a Seasonal Flow-Duration Table
Various graphical methods have been developed to handle the statistical data gathered for hydrological studies. Those most familiar are probably the hydrograph, the mass curve, and the flow-duration curve. The first two graphical techniques have been in use for numerous years and as a result, are described in many textbooks. The first published writings dealing with the flow-duration curve are believed to have been released in about 1878. However, the general use of the flow-duration curve started around the year 1915, but as late as 1934 it was felt that many of the fundamental principles of the flow-duration curve were not fully understood by many engineers. Flow-duration curves and tables are statistical devices which show the probability of occurrence of different flows. In actuality, the flow-duration curve or table gives the percentage of time a certain flow is equaled or exceeded. A further discussion on the definition, construction, and uses of the flow-duration table and curve will be presented later in this paper. A series of studies on the seasonal flow characteristics of various river basins in eastern South Dakota have been conducted at South Dakota State University. During the course of these studies of the seasonal variations in stream flow, conducted by Rakness and Chen. It was considered useful to construct the flow-duration curves for the streams being studied. It was shown by Rakness that an annual flow-duration curve or table will not depict the seasonal variations of a stream. That is to say, while a given flow may be equaled or exceeded 50% of the time, the annual flow-duration curve does not indicate when the flow is available. For example, the time when the flow is available is extremely important in the case of irrigation, water supply, fish life propagation, pollution control, or for any other usage where the demand is seasonal. As a result of these studies and the apparent utility of the seasonal flow-duration table, it became apparent that a computer program capable of constructing the seasonal flow-duration table directly from the given records would be an important tool for hydrological studies. This awareness of the need for a computer program to construct the seasonal flow-duration table resulted in the study described in this paper
Spectral Models of Convection-Dominated Accretion Flows
For small values of the dimensionless viscosity parameter, namely
, the dynamics of non-radiating accretion flows is
dominated by convection; convection strongly suppresses the accretion of matter
onto the central object and transports a luminosity from small to large radii in the flow. A fraction of this convective
luminosity is likely to be radiated at large radii via thermal bremsstrahlung
emission. We show that this leads to a correlation between the frequency of
maximal bremsstrahlung emission and the luminosity of the source, . Accreting black holes with X-ray luminosities are expected to
have hard X-ray spectra, with photon indices , and sources with
are expected to have soft spectra, with
. This is testable with {\it Chandra} and {\it XMM}.Comment: final version accepted by ApJ; significant modifications from
previous versio
Decline of nucleotide excision repair capacity in aging Caenorhabditis elegans
Repair of UVC-induced DNA damage in Caenorhabditis elegans is similar kinetically and genetically to repair in humans, and it slows significantly in aging C. elegans
Towards the glueball spectrum from unquenched lattice QCD
We use a variational technique to study heavy glueballs on gauge
configurations generated with 2+1 flavours of ASQTAD improved staggered
fermions. The variational technique includes glueball scattering states. The
measurements were made using 2150 configurations at 0.092 fm with a pion mass
of 360 MeV. We report masses for 10 glueball states. We discuss the prospects
for unquenched lattice QCD calculations of the oddballs.Comment: 19 pages, 4 tables and 8 figures. One figure added. Now matches the
published versio
Using Markov chain Monte Carlo methods for estimating parameters with gravitational radiation data
We present a Bayesian approach to the problem of determining parameters for
coalescing binary systems observed with laser interferometric detectors. By
applying a Markov Chain Monte Carlo (MCMC) algorithm, specifically the Gibbs
sampler, we demonstrate the potential that MCMC techniques may hold for the
computation of posterior distributions of parameters of the binary system that
created the gravity radiation signal. We describe the use of the Gibbs sampler
method, and present examples whereby signals are detected and analyzed from
within noisy data.Comment: 21 pages, 10 figure
Singular Isothermal Disks: II. Nonaxisymmetric Bifurcations and Equilibria
We review the difficulties of the classical fission and fragmentation
hypotheses for the formation of binary and multiple stars. A crucial missing
ingredient in previous theoretical studies is the inclusion of dynamically
important levels of magnetic fields. As a minimal model for a candidate
presursor to the formation of binary and multiple stars, we therefore formulate
and solve the problem of the equilibria of isopedically magnetized, singular
isothermal disks, without the assumption of axial symmetry. Considerable
analytical progress can be made if we restrict our attention to models that are
scale-free, i.e., that have surface densities that vary inversely with distance
from the rotation axis of the system. In agreement with earlier analysis by
Syer and Tremaine, we find that lopsided (M=1) configurations exist at any
dimensionless rotation rate, including zero. Multiple-lobed (M = 2, 3, 4, ...)
configurations bifurcate from an underlying axisymmetric sequence at
progressively higher dimensionless rates of rotation, but such nonaxisymmetric
sequences always terminate in shockwaves before they have a chance to fission
into M=2, 3, 4, ... separate bodies. On the basis of our experience in this
paper, and the preceding Paper I, we advance the hypothesis that binary and
multiple star-formation from smooth (i.e., not highly turbulent) starting
states that are supercritical but in unstable mechanical balance requires the
rapid (i.e., dynamical) loss of magnetic flux at some stage of the ensuing
gravitational collapse.Comment: 49 pages, 11 figures, LaTeX, needs aaspp4.sty. The Astrophysical
Journal, in pres
Myocardial ischemia in the absence of epicardial coronary artery disease in Friedreich's ataxia
We present the first in vivo detection of microvascular abnormality in a patient with Friedreich's ataxia (FA) without epicardial coronary artery disease using cardiac magnetic resonance (CMR). The patient had exertional chest pain and dyspnea prompting referral for cardiac evaluation. These symptoms were reproduced during intravenous adenosine infusion, and simultaneous first-pass perfusion imaging showed a significant subendocardial defect; both symptoms and perfusion deficit were absent at rest. Epicardial coronaries were free of disease by invasive angiography; together, these findings support the notion of impaired myocardial perfusion reserve in FA
Coherent Bayesian inference on compact binary inspirals using a network of interferometric gravitational wave detectors
Presented in this paper is a Markov chain Monte Carlo (MCMC) routine for
conducting coherent parameter estimation for interferometric gravitational wave
observations of an inspiral of binary compact objects using data from multiple
detectors. The MCMC technique uses data from several interferometers and infers
all nine of the parameters (ignoring spin) associated with the binary system,
including the distance to the source, the masses, and the location on the sky.
The Metropolis-algorithm utilises advanced MCMC techniques, such as importance
resampling and parallel tempering. The data is compared with time-domain
inspiral templates that are 2.5 post-Newtonian (PN) in phase and 2.0 PN in
amplitude. Our routine could be implemented as part of an inspiral detection
pipeline for a world wide network of detectors. Examples are given for
simulated signals and data as seen by the LIGO and Virgo detectors operating at
their design sensitivity.Comment: 10 pages, 4 figure
New paradoxical games based on Brownian ratchets
Based on Brownian ratchets, a counter-intuitive phenomenon has recently
emerged -- namely, that two losing games can yield, when combined, a
paradoxical tendency to win. A restriction of this phenomenon is that the rules
depend on the current capital of the player. Here we present new games where
all the rules depend only on the history of the game and not on the capital.
This new history-dependent structure significantly increases the parameter
space for which the effect operates.Comment: 4 pages, 3 eps figures, revte
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