Nuclear quantum effects in water exchange around lithium and fluoride ions

We employ classical and ring polymer molecular dynamics simulations to study the effect of nuclear quantum fluctuations on the structure and the water exchange dynamics of aqueous solutions of lithium and fluoride ions. While we obtain reasonably good agreement with experimental data for solutions of lithium by augmenting the Coulombic interactions between the ion and the water molecules with a standard Lennard-Jones ion-oxygen potential, the same is not true for solutions of fluoride, for which we find that a potential with a softer repulsive wall gives much better agreement. A small degree of destabilization of the first hydration shell is found in quantum simulations of both ions when compared with classical simulations, with the shell becoming less sharply defined and the mean residence time of the water molecules in the shell decreasing. In line with these modest differences, we find that the mechanisms of the exchange processes are unaffected by quantization, so a classical description of these reactions gives qualitatively correct and quantitatively reasonable results. We also find that the quantum effects in solutions of lithium are larger than in solutions of fluoride. This is partly due to the stronger interaction of lithium with water molecules, partly due to the lighter mass of lithium, and partly due to competing quantum effects in the hydration of fluoride, which are absent in the hydration of lithium.Comment: 12 pages, 8 figure

Deriving star formation histories: Inverting HR diagrams through a variational calculus maximum likelihood method

We introduce a new method for solving maximum likelihood problems through variational calculus, and apply it to the case of recovering an unknown star formation history, $SFR(t)$, from a resulting HR diagram. This approach allows a totally non-parametric solution which has the advantage of requiring no initial assumptions on the $SFR(t)$. As a full maximum likelihood statistical model is used, we take advantage of all the information available in the HR diagram, rather than concentrating on particular features such as turn off points or luminosity functions. We test the method using a series of synthetic HR diagrams produced from known $SFR(t)$, and find it to be quite successful under noise conditions comparable to those present in current observations. At this point we restrict the analysis to situations where the metallicity of the system is known, as is the case with the resolved populations of the dwarf spheroidal companions to the Milky Way or the solar neighbourhood Hipparcos data. We also include tests to quantify the way uncertainties in the assumed metallicity, binary fraction and IMF affect our inferences.Comment: 16 pages including 12 figures. Accepted for publication in MNRAS, appendix adde

Non-parametric star formation histories for 5 dwarf spheroidal galaxies of the local group

We use recent HST colour-magnitude diagrams of the resolved stellar populations of a sample of local dSph galaxies (Carina, LeoI, LeoII, Ursa Minor and Draco) to infer the star formation histories of these systems, $SFR(t)$. Applying a new variational calculus maximum likelihood method which includes a full Bayesian analysis and allows a non-parametric estimate of the function one is solving for, we infer the star formation histories of the systems studied. This method has the advantage of yielding an objective answer, as one need not assume {\it a priori} the form of the function one is trying to recover. The results are checked independently using Saha's $W$ statistic. The total luminosities of the systems are used to normalize the results into physical units and derive SN type II rates. We derive the luminosity weighted mean star formation history of this sample of galaxies.Comment: 14 pages including 7 figures. Accepted to MNRA

Solar neutrinos and the MSW effect for three-neutrino mixing

Researchers considered three-neutrino Mikheyev-Smirnov-Wolfenstein (MSW) mixing, assuming m sub 3 is much greater than m sub 2 is greater than m sub 1 as expected from theoretical consideration if neutrinos have mass. They calculated the corresponding mixing parameter space allowed by the Cl-37 and Kamiokande 2 experiments. They also calculated the expected depletion for the Ga-71 experiment. They explored a range of theoretical uncertainty due to possible astrophysical effects by varying the B-8 neutrino flux and redoing the MSW mixing calculation

Nonlinear Schr\"odinger Equation for Superconductors

Using the Hartree-Fock-Bogoliubov factorization of the density matrix and the Born-Oppenheimer approximation we show that the motion of the condensate satisfies a nonlinear Schr\"odinger equation in the zero temperature limit. The Galilean invariance of the equation is explicitly manifested. {}From this equation some general properties of a superconductor, such as Josephson effects, the Magnus force, and the Bogoliubov-Anderson mode can be obtained readily.Comment: Latex, 12 page

Modelling and stability of FAST TCP

We introduce a discrete-time model of FAST TCP that fully captures the effect of self-clocking and compare it with the traditional continuous-time model. While the continuous-time model predicts instability for homogeneous sources sharing a single link when feedback delay is large, experiments suggest otherwise. Using the discrete-time model, we prove that FAST TCP is locally asymptotically stable in general networks when all sources have a common round-trip feedback delay, no matter how large the delay is. We also prove global stability for a single bottleneck link in the absence of feedback delay. The techniques developed here are new and applicable to other protocols

Building capacity for policy analysis

This paper attempts to examine the concept and scope of policy analysis and to distill the lessons of experience in building the capacity for policy analysis in a number of developing countries over the past three decades. It concludes that strategies for developing indigenous capabilities for policy analysis will vary from country to country. In countries where non-government clientele and sources of support are limited but government is interested, the initial focus should be on strengthening government capability. Countries where there is demand for policy analysis in both the government and private sector may be ripe for arm's length centers for policy analysis. If such centers are not appropriate, private sector associations could help set up policy analysis units. In countries where the private sector is weak, academic institutions with close links to government may help create some local capability.Poverty Assessment,ICT Policy and Strategies,Geographical Information Systems,Inequality,Achieving Shared Growth

Job Stability in the United States

Two key attributes of a job are its wage and its duration. Much has been made of changes in the wage distribution in the 1980s, but little attention has been given to job durations since Hall (1982). We fill this void by examining the temporal evolution of job retention rates in U.S. labor markets, using data assembled from the sequence of Current Population Survey job tenure supplements. In contrast to the distribution of wages, which clearly changed in the 1980s, we find that job retention rates have remained stable.