Simulations of Solid-on-Solid Models of Spreading of Viscous Droplets

We have studied the dynamics of spreading of viscous non-volatile fluids on surfaces by MC simulations of SOS models. We have concentrated on the complete wetting regime, with surface diffusion barriers neglected for simplicity. First, we have performed simulations for the standard SOS model. Formation of a single precursor layer, and a density profile with a spherical cap shaped center surrounded by Gaussian tails can be reproduced with this model. Dynamical layering (DL), however, only occurs with a very strongly attractive van der Waals type of substrate potential. To more realistically describe the spreading of viscous liquid droplets, we introduce a modified SOS model. In the new model, tendency for DL and the effect of the surface potential are in part embedded into the dynamics of the model. This allows a relatively simple description of the spreading under different conditions, with a temperature like parameter which strongly influences the droplet morphologies. Both rounded droplet shapes and DL can easily be reproduced with the model. Furthermore, the precursor width increases proportional to the square root of time, in accordance with experimental observations. PACS: 68.10.Gw, 05.70.Ln, 61.20.Ja.Comment: to appear in Physica A (1994), standard LaTex, 20 page

New Hope for the Working Poor: Effects After Eight Years for Families and Children

Implemented in 1994 in Milwaukee, New Hope provided full-time, low-wage workers with several benefits for three years: an earnings supplement, low-cost health insurance, and subsidized child care. A random assignment study shows positive effects for both adults and children, some of which persisted five years after the program ended

Consistency of pacing and metabolic responses during 2000-m rowing ergometry

PURPOSE: This study investigated the pacing strategy adopted and the consistency of performance and related physiological parameters across three 2000-m rowing-ergometer tests. METHODS: Fourteen male well-trained rowers took part in the study. Each participant performed three 2000-m rowing-ergometer tests interspersed by 3-7 d. Throughout the trials, respiratory exchange and heart rate were recorded and power output and stroke rate were analyzed over each 500 m of the test. At the completion of the trial, assessments of blood lactate and rating of perceived exertion were measured. RESULTS: Ergometer performance was unchanged across the 3 trials; however, pacing strategy changed from trial 1, which featured a higher starting power output and more progressive decrease in power, to trials 2 and 3, which were characterized by a more conservative start and an end spurt with increased power output during the final 500 m. Mean typical error (TE; %) across the three 2000-m trials was 2.4%, and variability was low to moderate for all assessed physiological variables (TE range = 1.4-5.1%) with the exception of peak lactate (TE = 11.5%). CONCLUSIONS: Performance and physiological responses during 2000-m rowing ergometry were found to be consistent over 3 trials. The variations observed in pacing strategy between trial 1 and trials 2 and 3 suggest that a habituation trial is required before an intervention study and that participants move from a positive to a reverse-J-shaped strategy, which may partly explain conflicting reports in the pacing strategy exhibited during 2000-m rowing-ergometer trials

The (In)Stability of Planetary Systems

We present results of numerical simulations which examine the dynamical stability of known planetary systems, a star with two or more planets. First we vary the initial conditions of each system based on observational data. We then determine regions of phase space which produce stable planetary configurations. For each system we perform 1000 ~1 million year integrations. We examine upsilon And, HD83443, GJ876, HD82943, 47UMa, HD168443, and the solar system (SS). We find that the resonant systems, 2 planets in a first order mean motion resonance, (HD82943 and GJ876) have very narrow zones of stability. The interacting systems, not in first order resonance, but able to perturb each other (upsilon And, 47UMa, and SS) have broad regions of stability. The separated systems, 2 planets beyond 10:1 resonance, (we only examine HD83443 and HD168443) are fully stable. Furthermore we find that the best fits to the interacting and resonant systems place them very close to unstable regions. The boundary in phase space between stability and instability depends strongly on the eccentricities, and (if applicable) the proximity of the system to perfect resonance. In addition to million year integrations, we also examined stability on ~100 million year timescales. For each system we ran ~10 long term simulations, and find that the Keplerian fits to these systems all contain configurations which may be regular on this timescale.Comment: 37 pages, 49 figures, 13 tables, submitted to Ap

Methodological Issues in Multistage Genome-Wide Association Studies

Because of the high cost of commercial genotyping chip technologies, many investigations have used a two-stage design for genome-wide association studies, using part of the sample for an initial discovery of ``promising'' SNPs at a less stringent significance level and the remainder in a joint analysis of just these SNPs using custom genotyping. Typical cost savings of about 50% are possible with this design to obtain comparable levels of overall type I error and power by using about half the sample for stage I and carrying about 0.1% of SNPs forward to the second stage, the optimal design depending primarily upon the ratio of costs per genotype for stages I and II. However, with the rapidly declining costs of the commercial panels, the generally low observed ORs of current studies, and many studies aiming to test multiple hypotheses and multiple endpoints, many investigators are abandoning the two-stage design in favor of simply genotyping all available subjects using a standard high-density panel. Concern is sometimes raised about the absence of a ``replication'' panel in this approach, as required by some high-profile journals, but it must be appreciated that the two-stage design is not a discovery/replication design but simply a more efficient design for discovery using a joint analysis of the data from both stages. Once a subset of highly-significant associations has been discovered, a truly independent ``exact replication'' study is needed in a similar population of the same promising SNPs using similar methods.Comment: Published in at http://dx.doi.org/10.1214/09-STS288 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

A Symplectic Integrator for Hill's Equations

Hill's equations are an approximation that is useful in a number of areas of astrophysics including planetary rings and planetesimal disks. We derive a symplectic method for integrating Hill's equations based on a generalized leapfrog. This method is implemented in the parallel N-body code, PKDGRAV and tested on some simple orbits. The method demonstrates a lack of secular changes in orbital elements, making it a very useful technique for integrating Hill's equations over many dynamical times. Furthermore, the method allows for efficient collision searching using linear extrapolation of particle positions.Comment: 15 pages, 2 figures; minor revisions; accepted for publication in the Astronomical Journa

The Gordon Growth Model: A Teaching Case

This case illustrates how the Gordon Growth Model is employed to estimate the value of a firm’s stock.  The model determines the value of stock based on dividends, growth rate, and the cost of capital. The Capital Asset Pricing Model (CAPM) is employed to calculate the cost of capital.  Both economic analysis and ratio analysis are used to examine the impact of external and internal factors on share worth.  The case discusses why the market share price may vary from an estimation of its worth. This case study can be used in an Introduction to Investments course, an Advanced Investments course, or a first level MBA graduate course

Problem-Based Learning in Mathematics

A teacher of mathematics has a great opportunity. If he fills his allotted time with drilling his students in routine operations, he kills their interest, hampers their intellectual development, and misuses his opportunity. But if he challenges the curiosity of his students by setting them problems proportionate to their knowledge and helps them to solve their problems with stimulating questions, he may give them a taste for, and some independent means of, independent thinking

Prognostically controlled comparison of dialysis and renal transplantation

Prognostically controlled comparison of dialysis and renal transplantation. Because the comparison of survival in patients with renal failure treated by dialysis and transplantation may be biased by pretreatment prognostic differences in the patients who receive these two therapies, we quantified the pretreatment prognosis of all 430 dialysis and transplant patients who began therapy for end-stage renal disease at two hospitals from 1970 to 1980. Five pretreatment factors had a statistically significant adverse effect on survival: age, duration of diabetes, left ventricular failure, myocardial infarction, and other serious comorbid illness. Dialysis patients had a worse pretreatment prognosis than transplant patients did. When we controlled for these pretreatment differences, the actuarial 5-year patient survivals were 80% for dialysis (D), 79% for cadaver transplantation (CT), and 91% for living donor transplantation (LDT), (P = 0.9 for CT vs. D, and P = 0.05 for LDT vs. D). This similarity in survival with dialysis and cadaver transplantation was quite different from the results obtained when pretreatment prognosis was not controlled; the uncontrolled 5-year patient survivals were 43% for D, 77% for CT, and 89% for LDT (P < 0.001 for CT vs. D, and P < 0.001 for LDT vs. D). Our data suggest that the major factor determining differences in survival with dialysis and renal transplantation is not the relative efficacy of the two treatments but the pretreatment prognostic status of the patients chosen to receive them.Une comparaison contrôlée de façon pronostique entre la dialyse et la transplantation rénale. Puisque la comparaison de la survie des malades en insuffisance rénale traités par dialyse ou par transplantation peut être biaisée par des différences pronostiques pré-thérapeutiques entre les malades qui reçoivent ces deux traitements, nous avons quantifié le pronostic pré-thérapeutique de l'ensemble des 430 malades dialysés et transplantés qui ont commencé le traitement de leur insuffisance rénale dans deux hôpitaux de 1970 à 1980. Cinq facteurs préthérapeutiques possédaient un effet adverse statistiquement significatif sur la survie: l'âge, la durée du diabète, une insuffisance ventriculaire gauche, un infarctus du myocarde, et une autre maladie sérieuse associée. Les dialysés avaient un pronostic pré-thérapeutique plus mauvais que les transplantés. Lorsque nous avons contrôlé ces différences pré-thérapeutiques, la survie actuarielle à 5 ans des malades était de 80% pour la dialyse (D), 79% pour la transplantation cadavérique (CT), et 91% pour la transplantation avec donneur vivant (LDT) (P = 0,9 pour CT contre D, et P = 0,05 pour LDT contre D). Cette similitude de survie en dialyse ou après transplantation cadavérique était très différente des résultats obtenus lorsque le pronostic pré-thérapeutique n'était pas contrôlé; les survies non contrôlées à 5 ans des malades étaient de 43% pour D, 77% pour CT, et 89% pour LDT (P < 0,001 pour CT contre D, et P < 0,001 pour LDT contre D). Nos données suggèrent que le facteur principal déterminant les différences de survie en dialyse ou après transplantation rénale n'est pas l'efficacité relative des deux traitements, mais l'état pronostique pré-thérapeutique des malades choisis pour les recevoir