1,173 research outputs found
Dynamics with matrices possessing kronecker product structure
In this paper we present an application of Alternating Direction Implicit (ADI) algorithm for solution of non-stationary PDE-s using isogeometric finite element method. We show that ADI algorithm has a linear computational cost at every time step. We illustrate this approach by solving two example non-stationary three-dimensional problems using explicit Euler and Newmark time-stepping scheme: heat equation and linear elasticity equations for a cube. The stability of the simulation is controlled by monitoring the energy of the solution
Time-stepping beyond CFL: a locally one-dimensional scheme for acoustic wave propagation
In this abstract, we present a case study in the application of a time-stepping method, unconstrained by the CFL condition, for computational acoustic wave propagation in the context of full waveform inversion. The numerical scheme is a locally one-dimensional (LOD) variant of alternating dimension implicit (ADI) method. The LOD method has a maximum time step that is restricted only by the Nyquist sampling rate. The advantage over traditional explicit time-stepping methods occurs in the presence of high contrast media, low frequencies, and steep, narrow perfectly matched layers (PML). The main technical point of the note, from a numerical analysis perspective, is that the LOD scheme is adapted to the presence of a PML. A complexity study is presented and an application to full waveform inversion is shown.National Science Foundation (U.S.); Alfred P. Sloan Foundatio
Comparison of Wide and Compact Fourth Order Formulations of the Navier-Stokes Equations
In this study the numerical performances of wide and compact fourth order
formulation of the steady 2-D incompressible Navier-Stokes equations will be
investigated and compared with each other. The benchmark driven cavity flow
problem will be solved using both wide and compact fourth order formulations
and the numerical performances of both formulations will be presented and also
the advantages and disadvantages of both formulations will be discussed
Numerical Performance of Compact Fourth Order Formulation of the Navier-Stokes Equations
In this study the numerical performance of the fourth order compact
formulation of the steady 2-D incompressible Navier-Stokes equations introduced
by Erturk et al. (Int. J. Numer. Methods Fluids, 50, 421-436) will be
presented. The benchmark driven cavity flow problem will be solved using the
introduced compact fourth order formulation of the Navier-Stokes equations with
two different line iterative semi-implicit methods for both second and fourth
order spatial accuracy. The extra CPU work needed for increasing the spatial
accuracy from second order (O(x2)) to fourth order (O(x4)) formulation will be
presented
Treatment of Subclinical Hypothyroidism or Hypothyroxinemia in Pregnancy
Subclinical thyroid disease during pregnancy may be associated with adverse outcomes, including a lower-than-normal IQ in offspring. It is unknown whether levothyroxine treatment of women who are identified as having subclinical hypothyroidism or hypothyroxinemia during pregnancy improves cognitive function in their children
Critical number of atoms for attractive Bose-Einstein condensates with cylindrically symmetrical traps
We calculated, within the Gross-Pitaevskii formalism, the critical number of
atoms for Bose-Einstein condensates with two-body attractive interactions in
cylindrical traps with different frequency ratios. In particular, by using the
trap geometries considered by the JILA group [Phys. Rev. Lett. 86, 4211
(2001)], we show that the theoretical maximum critical numbers are given
approximately by . Our results also show that, by
exchanging the frequencies and , the geometry with
favors the condensation of larger number of particles.
We also simulate the time evolution of the condensate when changing the ground
state from to using a 200ms ramp. A conjecture on higher order
nonlinear effects is also added in our analysis with an experimental proposal
to determine its signal and strength.Comment: (4 pages, 2 figures) To appear in Physical Review
Mathematical Modelling of Transient Thermography and Defect Sizing
The principle employed to obtain an image of a sub-surface defect by transient thermography is deceptively simple. A surface is heated by powerful flash lamps and subsequent thermal transients are recorded by an infrared camera. Defects cause perturbations in heat flow which are revealed by the camera. Whilst there is now a considerable body of practical experience of the application of the technique, there is rather less precise quantitative information about the image formation process that could lead to reliable defect sizing. In earlier papers [1,2] one of the authors considered circular air gap defects by treating them as buried uniformly heated disks. The thermal edge-effect occurring at the tip of a perfect crack-like defect was dealt with analytically by adapting the well established Wiener-Hopf [3] solution for the scattering of light or sound from the edge of a semi-infinite half-plane. The problem was solved in the frequency-domain, i.e. to obtain a thermal wave solution, and then a time-domain solution was obtained by a suitable transformation. The analysis showed an edge-effect amounting to a decay in temperature contrast over a distance of about a thermal diffusion length from the edge of the crack. A crucial feature of the edge-effect was the decay of thermal contrast to zero at the crack tip. This, and the edge-effect as a whole, is caused by the flow of heat around the crack tip from the hot upper surface of the crack to the cold under surface. The symmetry of this process ensures that there is no net flux increase for material in front of the crack tip
Prescription and Other Medication Use in Pregnancy
OBJECTIVE:
To characterize prescription and other medication use in a geographically and ethnically diverse cohort of women in their first pregnancy.
METHODS:
In a prospective, longitudinal cohort study of nulliparous women followed through pregnancy from the first trimester, medication use was chronicled longitudinally throughout pregnancy. Structured questions and aids were used to capture all medications taken as well as reasons they were taken. Total counts of all medications taken including number in each category and class were captured. Additionally, reasons the medications were taken were recorded. Trends in medications taken across pregnancy and in the first trimester were determined.
RESULTS:
Of the 9,546 study participants, 9,272 (97.1%) women took at least one medication during pregnancy with 9,139 (95.7%) taking a medication in the first trimester. Polypharmacy, defined as taking at least five medications, occurred in 2,915 (30.5%) women. Excluding vitamins, supplements, and vaccines, 73.4% of women took a medication during pregnancy with 55.1% taking one in the first trimester. The categories of drugs taken in pregnancy and in the first trimester include the following: gastrointestinal or antiemetic agents (34.3%, 19.5%), antibiotics (25.5%, 12.6%), and analgesics (23.7%, 15.6%, which includes 3.6%; 1.4% taking an opioid pain medication).
CONCLUSION:
In this geographically and ethnically diverse cohort of nulliparous pregnant women, medication use was nearly universal and polypharmacy was common
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