Monte Carlo Simulations of Quantum Spin Systems in the Valence Bond Basis

We discuss a projector Monte Carlo method for quantum spin models formulated in the valence bond basis, using the S=1/2 Heisenberg antiferromagnet as an example. Its singlet ground state can be projected out of an arbitrary basis state as the trial state, but a more rapid convergence can be obtained using a good variational state. As an alternative to first carrying out a time consuming variational Monte Carlo calculation, we show that a very good trial state can be generated in an iterative fashion in the course of the simulation itself. We also show how the properties of the valence bond basis enable calculations of quantities that are difficult to obtain with the standard basis of Sz eigenstates. In particular, we discuss quantities involving finite-momentum states in the triplet sector, such as the dispersion relation and the spectral weight of the lowest triplet.Comment: 15 pages, 7 figures, for the proceedings of "Computer Simulation Studies in Condensed Matter Physics XX

Global Implications of U.S. Biofuels Policies in an Integrated Partial and General Equilibrium Framework

With the increasing research interests in biofuels, global implications of biofuels production have been generally examined either in a partial equilibrium (PE) or general equilibrium (GE) frameworks. Though both of these approaches have unique strengths, they also suffer from many limitations due to complexity of addressing all the relevant aspects of biofuels. In this paper we have exploited the strengths of both PE and GE approaches for analyzing the economic and environmental implications of the U.S. policies on corn-ethanol and biodiesel production. In this study, we utilize the Forest and Agricultural Sector Optimization Model (FASOMGHG: Adams et al. 1996, 2005; Beach et al. 2009), a non-linear programming, PE model for the United States. We also use the GTAP-BIO model (Birur et al. 2008), a multi-region, multi-sector CGE model for global-scale assessment of biofuels policies. Following Britz and Hertel (2009), we link the GTAP-BIO model through a static, quadratic restricted revenue function obtained from perturbing crop prices from the FASOMGHG model. With this linkage we implement the U.S. Corn ethanol and biodiesel scenarios in the GTAP-BIO model and obtain the FASOMGHG-consistent, global land use changes. The resulting crop price changes from the GE model are fed back into the FASOMGHG model to obtain the disaggregated impacts in the U.S.Biofuels, Indirect land use change, Land use emissions, Partial Equilibrium, Computable General Equilibrium, Land Economics/Use, Resource /Energy Economics and Policy,

Hardiness in the apple as correlated with structure and composition

The breeding of hardy apples is naturally such a long time proposition that it would be a distinct advantage if by microscopic examination of the wood, by mechanical tests, or by other observations the hardiness of a tree could be determined while it was still in the nursery, The following is a summary of the facts brought out in the investigation of Hardiness in the Apple as Correlated with Structure and Composition. 1. The cutting, compression and penetration tests seemed to indicate some correlation between hardiness and hardness, but exceptions were found. 2, Twigs from northern sections, except the forms of Metlus rivularis, Red June and Patten, were no harder than twigs from Iowa and further south. 3, Specific gravity tests of dry wood showing density corresponded very closely with the mechanical tests showing hardness, indicating that the two tests are fairly accurate means to the same end. 4. Variat ions in the specific gravity of twigs of the same variety from different sources were noted, as was also the case in the mechanical tests. Twigs of the same variety from the same source gave pretty uniform results. 5. The specific gravity of twigs varies, to some extent depending upon what part of the twig is used. The tenderer varieties, which mature a little later in the summer, gave the greatest specific gravity a short distance back of the tip; earlier maturing varieties increased in specific gravity in proportion to the distance from the tip. As the tests were made in July this difference is in all probability due to the difference in the maturing of the twigs used. 6. The maturity of the wood at the time cold weather sets in undoubtedly has a most important bearing upon the ability of the tree to withstand cold. 7. By noting the formation of terminal buds and the time of leaf fall a pretty accurate idea of maturity can be secured, except in case of a few varieties. 8. The hardier varieties on the average had a slightly lower moisture content than the more tender varieties. 9. The difference in water content can be explained partly at least by the fact that the more tender sorts evaporate water more readily than do the hardy varieties. Freezing tends to dry the twig out, and after a period of very cold weather the twigs of the hardy varieties are generally found to contain the most moisture. 10. The rate of evaporation is due in part to small differences in thickness and structure of bark, including differences in the number of cutinized layers. 11. Most of the hardy varieties contained a large amount of starch stored in the pith and medullary rays. The Malus ioensis, however, proved to be an exception in this regard. 12. Large, thick petals are correlated with hardiness, although the converse of this is not always true. 13. The results of the freezing experiments show that within the limits observed a sudden drop in temperature is more injurious than the actual degree of cold. 14. While all twigs not previously dried were injured to some extent when held in a temperature of -10 degrees F. for 20 minutes, the injury was less in the hardier varieties, thus showing their ability better to withstand such a sudden drop in temperature. 15. While in the various lines of comparison which were made there were found many indications of morphological differences between hardy and tender varieties, yet from the practical view point as yet it is impossible to name anyone test by which the degree of constitutional hardiness of a seedling apple may be foretold. Among the various tests for hardiness, that of the length of season required by the tree to mature the season\u27s growth is of first importance. Perhaps by taking careful notes on a number of trees of any particular variety for two or three years or more, noting their time of starting and cessation of growth, their ability to produce a good root system from the cion, their water content, the resistance of their twigs to sudden zero temperatures, and their rate of evaporation, a pretty accurate idea of the ability of the tree to withstand, ,cold might be obtained. If in addition the variety has hard wood, a good amount of stored starch and large petals these would be further indications of hardiness, although from this study it appears that these points are of less importance than those first named

A water-vapor electrolysis cell with phosphoric acid electrolyte

Feasibility of phosphoric acid water vapor electrolysis cell for spacecraft cabin air conditioning syste

Conductance through Quantum Dots Studied by Finite Temperature DMRG

With the Finite temperature Density Matrix Renormalization Group method (FT-DMRG), we depeloped a method to calculate thermo-dynamical quantities and the conductance of a quantum dot system. Conductance is written by the local density of states on the dot. The density of states is calculated with the numerical analytic continuation from the thermal Green's function which is obtained directly from the FT-DMRG. Typical Kondo behaviors in the quantum dot system are observed conveniently by comparing the conductance with the magnetic and charge susceptibilities: Coulomb oscillation peaks and the unitarity limit. We discuss advantage of this method compared with others.Comment: 14 pages, 13 fiure

Enhanced magnetic moment and conductive behavior in NiFe2O4 spinel ultrathin films

Bulk NiFe2O4 is an insulating ferrimagnet. Here, we report on the epitaxial growth of spinel NiFe2O4 ultrathin films onto SrTiO3 single-crystals. We will show that - under appropriate growth conditions - epitaxial stabilization leads to the formation of a spinel phase with magnetic and electrical properties that radically differ from those of the bulk material : an enhanced magnetic moment (Ms) - about 250% larger - and a metallic character. A systematic study of the thickness dependence of Ms allows to conclude that its enhanced value is due to an anomalous distribution of the Fe and Ni cations among the A and B sites of the spinel structure resulting from the off-equilibrium growth conditions and to interface effects. The relevance of these findings for spinel- and, more generally, oxide-based heterostructures is discussed. We will argue that this novel material could be an alternative ferromagetic-metallic electrode in magnetic tunnel junctions.Comment: accepted for publication in Phys. Rev.

Online change detection for energy-efficient mobilec crowdsensing

Mobile crowdsensing is power hungry since it requires continuously and simultaneously sensing, processing and uploading fused data from various sensor types including motion sensors and environment sensors. Realizing that being able to pinpoint change points of contexts enables energy-efficient mobile crowdsensing, we modify histogram-based techniques to efficiently detect changes, which has less computational complexity and performs better than the conventional techniques. To evaluate our proposed technique, we conducted experiments on real audio databases comprising 200 sound tracks. We also compare our change detection with multivariate normal distribution and one-class support vector machine. The results show that our proposed technique is more practical for mobile crowdsensing. For example, we show that it is possible to save 80% resource compared to standard continuous sensing while remaining detection sensitivity above 95%. This work enables energy-efficient mobile crowdsensing applications by adapting to contexts

New solid state lasers from the ultraviolet to the mid-infrared

The authors discuss three new laser materials that offer improved access to the ultraviolet, near infrared and mid-infrared spectral regions. In order for each of these materials to have been identified, a particular hurdle needed to be overcome with respect to the fundamental laser physics impacting the material. In the case of the 280-320nm Ce:LiSAF laser, the main issue is the need to reduce the loss associated with excited state absorption, while for 1047nm Yb:S-FAP it is the ground state absorption at the laser wavelength that must be minimized. Cr:ZnSe has been down-selected from a number of potential candidates which could lase in the 2200-3000nm region, in order to mitigate the detrimental impact of nonradiative decay. In all three cases the authors discuss how appropriate consideration of fundamental concerns has led to the identification and understanding of the new laser system