8,826 research outputs found
Quantitative Phase Field Model of Alloy Solidification
We present a detailed derivation and thin interface analysis of a phase-field
model that can accurately simulate microstructural pattern formation for
low-speed directional solidification of a dilute binary alloy. This advance
with respect to previous phase-field models is achieved by the addition of a
phenomenological "antitrapping" solute current in the mass conservation
relation [A. Karma, Phys. Rev. Lett 87, 115701 (2001)]. This antitrapping
current counterbalances the physical, albeit artificially large, solute
trapping effect generated when a mesoscopic interface thickness is used to
simulate the interface evolution on experimental length and time scales.
Furthermore, it provides additional freedom in the model to suppress other
spurious effects that scale with this thickness when the diffusivity is unequal
in solid and liquid [R. F. Almgren, SIAM J. Appl. Math 59, 2086 (1999)], which
include surface diffusion and a curvature correction to the Stefan condition.
This freedom can also be exploited to make the kinetic undercooling of the
interface arbitrarily small even for mesoscopic values of both the interface
thickness and the phase-field relaxation time, as for the solidification of
pure melts [A. Karma and W.-J. Rappel, Phys. Rev. E 53, R3017 (1996)]. The
performance of the model is demonstrated by calculating accurately for the
first time within a phase-field approach the Mullins-Sekerka stability spectrum
of a planar interface and nonlinear cellular shapes for realistic alloy
parameters and growth conditions.Comment: 51 pages RevTeX, 5 figures; expanded introduction and discussion; one
table and one reference added; various small correction
Women’s Experiences with Prenatal Care: A Mixed-Methods Study Exploring the Influence of the Social Determinants of Health
Background & Purpose: Racial and ethnic disparities pervade birth outcomes in the United States and the state of Connecticut. While Connecticut’s infant mortality rate is less than the national average, rates for the state’s Black/African American and Hispanic/Latino communities exceed it. This study explored how prenatal care in Connecticut may be enhanced to address these disparities.
Methods: In spring 2013, seven focus groups and two semi-structured interviews were conducted (n=47). Participants also self-administered brief surveys. Recruited by local service providers, participants were 18 or older, pregnant and/or in the first year post-partum at the time. Most self-identified as non-white.
Results: Even when care was perceived as strong quality, participants perceived a lack of patient-centeredness. Participants knew the importance of prenatal care and actively prioritized it even when experiencing challenges accessing healthcare services or barriers to broader conditions needed to be healthy. Participants also reported experiencing discrimination in healthcare.
Conclusions & Implications: The women esteemed providers’ clinical advice, but felt unheard in their prenatal care experiences and faced structural challenges which may be addressed by changing institutional policies and procedures
Vector chiral order in frustrated spin chains
By means of a numerical analysis using a non-Abelian symmetry realization of
the density matrix renormalization group, we study the behavior of vector
chirality correlations in isotropic frustrated chains of spin S=1 and S=1/2,
subject to a strong external magnetic field. It is shown that the field induces
a phase with spontaneously broken chiral symmetry, in line with earlier
theoretical predictions. We present results on the field dependence of the
order parameter and the critical exponents.Comment: 8 pages, 9 figure
A Carleman type estimate for the Mindlin-Timoshenko plate model
This thesis focuses on results concerning providing a Carleman type estimate for the Mindlin-Timoshenko plate equations. The main approach is to provide an estimate for each of the three equations in the model then present these estimates in totality as a singular Carleman estimate for the entire model. The initial equation in the model is a simple two dimensional hyperbolic partial differential equation known as the wave equation. Prior research has been done for this type of equation and will be applied to provide the Carleman estimate for the first equation in the model. The estimate for the second and third equations will be derived by first establishing a point-wise inequality for the principal part of the equation multiplied by an exponential weight. After establishing a suitable pseudo-convex function for the exponential weight factor, specifications will be applied to the established point-wise estimates which will lead to the Carleman type estimates and their corresponding integral inequalities
Death in the Medical Social System: An Analysis of Deviance
A thesis presented to the faculty of the School of Social Sciences at Morehead State University in partial fulfillment of the requirements for the Degree of Master of Arts in Sociology by Christine A. Larson-Kurz in December of 1977
Transparent conducting films in the Zn-Sn-O tie line
Coatings were obtained on borosilicate glass and fused silica substrates with thicknesses of up to 230 nm from solutions with compositions along the Zn-Sn-O tie line. The preparation of the sols was accomplished by combinatorial chemistry with a robotic sample processor using different Zn-II, Sn-II and Sn-IV salts and alkoxides, as well as salts of different doping agents ( e. g. Sb-V, Ta-V, In-III) dissolved in various solvents and additives. The films were made by spin- coating followed by a thermal treatment in air, inert or reducing atmosphere at temperatures up to 1000°C. Except for a few cases, mixed crystalline phases of ZnO, SnO2 and ZnSnO3 or Zn2SnO4 are usually observed within the range 0.4 < [Zn]/([ Zn] + [ Sn]) < 0.75. Pure Zn2SnO4 and ZnSnO3 coatings exhibit good optical properties with a haze < 0.2% and a transmission in the visible range > 85%. In contrast to literature, results obtained for similar coatings by sputtering and pulsed laser deposition, all the sol - gel coatings showed a high resistivity of rho > 3 Ωcm even after a forming gas treatment and/ or doping
Light-by-light-type corrections to the muon anomalous magnetic moment at four-loop order
The numerically dominant QED contributions to the anomalous magnetic moment
of the muon stem from Feynman diagrams with internal electron loops. We
consider such corrections and present a calculation of the four-loop
light-by-light-type corrections where the external photon couples to a closed
electron or muon loop. We perform an asymptotic expansion in the ratio of
electron and muon mass and reduce the resulting integrals to master integrals
which we evaluate using analytical and numerical methods. We confirm the
results present in the literature which are based on different computational
methods.Comment: 16 page
Feedback control of unstable cellular solidification fronts
We present a numerical and experimental study of feedback control of unstable
cellular patterns in directional solidification (DS). The sample, a dilute
binary alloy, solidifies in a 2D geometry under a control scheme which applies
local heating close to the cell tips which protrude ahead of the other. For the
experiments, we use a real-time image processing algorithm to track cell tips,
coupled with a movable laser spot array device, to heat locally. We show,
numerically and experimentally, that spacings well below the threshold for a
period-doubling instability can be stabilized. As predicted by the numerical
calculations, cellular arrays become stable, and the spacing becomes uniform
through feedback control which is maintained with minimal heating.Comment: 4 pages, 4 figures, 1 tabl
Intraframe Sequential Picture Coding
This Paper Generalizes Time-Discrete Autoregressive Source Coding Results of Rate-Distortion Theory to Two Dimensions. a 2-D Discrete Autoregressive Source is Defined and Shown to Produce a 2-D Wide-Sense Markovian Field. the Rate Distortion Function of the Source is Then Obtained under Assumption of Gaussian Field Statistics and a Squared Error Fidelity Criterion. a Procedure for Generating an Ensemble of 2-D Codewords Whose Statistics Satisfy the Variational Equations for R(D) is Given. These 2-D Codewords Are, by Space-Time Mappings, 1-D Tree Codes, and It is Noted that a Tree Coding Theorem of Jelinek, Berger, Davis and Hellman Applies. the Problem of Instrumenting Nearly Optimum 2-D Sequential Encoding is Discussed Briefly. the Paper Stresses Potential Application to Image Coder Design. Copyright © 1977 by the Institute of Electrical and Electronics Engineers, Inc
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