4,082 research outputs found
Development of a Combined Quanity and Quality Model for Optimal Groundwater Management
Presented is a procedure for incorporating solute transport as linear constraints within computer models for optimizing regional groundwater extraction strategies. The MODCON modelling procedure uses linear goal programming, embedded linearized equations for flow and solute transport and a MOC simulation model. Assumed is 2D flow and solute transport and a dispersed conservative contaminant. The MODCON procedure develops steady groundwater extraction strategies that will satisfy future groundwater quality constraints while simultaneously causing future piezometric heads to be as close to current heads as possible. The procedure is applied to a 160 square mile area in southeastern Arkansas
Gravitational radiation from pulsar glitches
The nonaxisymmetric Ekman flow excited inside a neutron star following a
rotational glitch is calculated analytically including stratification and
compressibility. For the largest glitches, the gravitational wave strain
produced by the hydrodynamic mass quadrupole moment approaches the sensitivity
range of advanced long-baseline interferometers. It is shown that the
viscosity, compressibility, and orientation of the star can be inferred in
principle from the width and amplitude ratios of the Fourier peaks (at the spin
frequency and its first harmonic) observed in the gravitational wave spectrum
in the plus and cross polarizations. These transport coefficients constrain the
equation of state of bulk nuclear matter, because they depend sensitively on
the degree of superfluidity.Comment: 28 page
Recommended from our members
Association of C2, a derivative of the radial artery pressure waveform, with new onset of type 2 diabetes mellitus: the MESA study.
BackgroundAlthough microvascular dysfunction is known to result from diabetes, it might also lead to diabetes. Lower values of C2, a derivative of the radial artery pressure waveform, indicate microvascular dysfunction and predict hypertension and cardiovascular disease (CVD). We studied the association of C2 with incident diabetes in subjects free of overt CVD.MethodsAmong multi-ethnic participants (n = 5214), aged 45-84 years with no diabetes, C2 was derived from the radial artery pressure waveform. Incident diabetes (N = 651) was diagnosed as new fasting glucose ≥ 126 mg/dL or antidiabetic medicine over ~ 10 years. The relative incidence density (RID) for incident diabetes per standard deviation (SD) of C2 was studied during ~ 10 years follow-up using four levels of adjustment.ResultsMean C2 at baseline was 4.58 ± 2.85 mL/mmHg × 100. The RID for incident diabetes per SD of C2 was 0.90 (95% CI 0.82-0.99, P = 0.03). After adjustment for demographics plus body size, the corresponding RID was 0.81 (95% CI 0.73-0.89, P < 0.0001); body mass index (BMI) was the dominant covariate here. After adjustment for demographics plus cardiovascular risk factors, the RID was 0.98 (95% CI 0.89, 1.07, P = 0.63). After adjustment for all the parameters in the previous models, the RID was 0.87 (95% CI 0.78, 0.96, P = 0.006).ConclusionsIn a multi-ethnic sample free of overt CVD and diabetes at baseline, C2 predicted incident diabetes after adjustment for demographics, BMI and CVD risk factors. Differences in arterial blood pressure wave morphology may indicate a long-term risk trajectory for diabetes, independently of body size and the classical risk factors
Superfluid spherical Couette flow
We solve numerically for the first time the two-fluid,
Hall--Vinen--Bekarevich--Khalatnikov (HVBK) equations for a He-II-like
superfluid contained in a differentially rotating, spherical shell,
generalizing previous simulations of viscous spherical Couette flow (SCF) and
superfluid Taylor--Couette flow. In axisymmetric superfluid SCF, the number of
meridional circulation cells multiplies as \Rey increases, and their shapes
become more complex, especially in the superfluid component, with multiple
secondary cells arising for \Rey > 10^3. The torque exerted by the normal
component is approximately three times greater in a superfluid with anisotropic
Hall--Vinen (HV) mutual friction than in a classical viscous fluid or a
superfluid with isotropic Gorter-Mellink (GM) mutual friction. HV mutual
friction also tends to "pinch" meridional circulation cells more than GM mutual
friction. The boundary condition on the superfluid component, whether no slip
or perfect slip, does not affect the large-scale structure of the flow
appreciably, but it does alter the cores of the circulation cells, especially
at lower \Rey. As \Rey increases, and after initial transients die away,
the mutual friction force dominates the vortex tension, and the streamlines of
the superfluid and normal fluid components increasingly resemble each other. In
nonaxisymmetric superfluid SCF, three-dimensional vortex structures are
classified according to topological invariants.Comment: Accepted for publication in the Journal of Fluid Mechanic
Virtually Interactive Large-scale Model for Arkansas: User\u27s Guide (VILMA)
This user’s guide supports the use of VILMA (Virtually Interactive Large-scale Model for Arkansas). This document presents the basic concepts in Chapter I. Chapter II discusses the execution steps that the user follows during a VILMA session. Chapter III provides a detailed illustration of example data files. Chapter IV presents two example VILMA sessions. Finally, Chapter V elaborates on additional concepts. The Appendices consist of relevant program listings, instructions, and example files. In this user’s guide, the word interactive means the user enters his responses to the prompts that appear on a computer terminal while he is logged on to his CMS (Conversational Monitor System) account
Superfluid turbulence and pulsar glitch statistics
Experimental evidence is reviewed for the existence of superfluid turbulence
in a differentially rotating, spherical shell at high Reynolds numbers
(\Rey\gsim 10^3), such as the outer core of a neutron star. It is shown that
torque variability increases with \Rey, suggesting that glitch activity in
radio pulsars may be a function of \Rey as well. The \Rey distribution of
the 67 glitching radio pulsars with characteristic ages {\rm
yr} is constructed from radio timing data and cooling curves and compared with
the \Rey distribution of all 348 known pulsars with {\rm
yr}. The two distributions are different, with a Kolmogorov-Smirnov probability
. The conclusion holds for (modified) Urca and
nonstandard cooling, and for Newtonian and superfluid viscosities
Analytical and numerical study of the non-linear noisy voter model on complex networks
We study the noisy voter model using a specific non-linear dependence of the
rates that takes into account collective interaction between individuals. The
resulting model is solved exactly under the all-to-all coupling configuration
and approximately in some random networks environments. In the all-to-all setup
we find that the non-linear interactions induce "bona fide" phase transitions
that, contrary to the linear version of the model, survive in the thermodynamic
limit. The main effect of the complex network is to shift the transition lines
and modify the finite-size dependence, a modification that can be captured with
the introduction of an effective system size that decreases with the degree
heterogeneity of the network. While a non-trivial finite-size dependence of the
moments of the probability distribution is derived from our treatment,
mean-field exponents are nevertheless obtained in the thermodynamic limit.
These theoretical predictions are well confirmed by numerical simulations of
the stochastic process
Stochastic pair approximation treatment of the noisy voter model
We present a full stochastic description of the pair approximation scheme to
study binary-state dynamics on heterogeneous networks. Within this general
approach, we obtain a set of equations for the dynamical correlations,
fluctuations and finite-size effects, as well as for the temporal evolution of
all relevant variables. We test this scheme for a prototypical model of opinion
dynamics known as the noisy voter model that has a finite-size critical point.
Using a closure approach based on a system size expansion around a stochastic
dynamical attractor we obtain very accurate results, as compared with numerical
simulations, for stationary and time dependent quantities whether below, within
or above the critical region. We also show that finite-size effects in complex
networks cannot be captured, as often suggested, by merely replacing the actual
system size by an effective network dependent size $N_{{\rm eff}}
- …