Liquid-liquid transition in supercooled silicon determined by first-principles simulation

First principles molecular dynamics simulations reveal a liquid-liquid phase transition in supercooled elemental silicon. Two phases coexist below $T_c\approx 1232K$. The low density phase is nearly tetra-coordinated, with a pseudogap at the Fermi surface, while the high density phase is more highly coordinated and metallic in nature. The transition is observed through the formation of van der Waals loops in pressure-volume isotherms below $T_c$.Comment: 9 pages 4 figure

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Effect of Radius on Load/Strain Distribution between Ulna and Radius: Experimental and Numberical Analyses

Computational Infrastructure and Informatics Poster SessionIt has been hypothesized that osteocytes are stimulated by local strain distribution within the bone subjected to mechanical loadings. This collaborative research project between bone biologists and mechanical engineers is attempting to identify local strain fields around osteocytes that can account for their behavior in response to loading. Using CT images we have built and conducted an extensive finite element study of the mouse forearm. Our model incorporates many components of forearm anatomy not previously included in these models such as the radius and marrow cavities. The results of the current research will shed light on how bone perceives mechanical load and the pathway whereby a physical load is transduced into a biochemical signal that eventually results in new bone formation. The study will help in developing new treatments for bone diseases such as osteoporosis

Spiral order by disorder and lattice nematic order in a frustrated Heisenberg antiferromagnet on the honeycomb lattice

Motivated by recent experiments on Bi$_3$Mn$_4$O$_{12}$(NO$_3$), we study a frustrated $J_1$-$J_2$ Heisenberg model on the two dimensional (2D) honeycomb lattice. The classical $J_1$-$J_2$ Heisenberg model on the two dimensional (2D) honeycomb lattice has N\'eel order for $J_2 J_1/6$, it exhibits a one-parameter family of degenerate incommensurate spin spiral ground states where the spiral wave vector can point in any direction. Spin wave fluctuations at leading order lift this accidental degeneracy in favor of specific wave vectors, leading to spiral order by disorder. For spin $S=1/2$, quantum fluctuations are, however, likely to be strong enough to melt the spiral order parameter over a wide range of $J_2/J_1$. Over a part of this range, we argue that the resulting state is a valence bond solid (VBS) with staggered dimer order - this VBS is a nematic which breaks lattice rotational symmetry. Our arguments are supported by comparing the spin wave energy with the energy of the dimer solid obtained using a bond operator formalism. Turning to the effect of thermal fluctuations on the spiral ordered state, any nonzero temperature destroys the magnetic order, but the discrete rotational symmetry of the lattice remains broken resulting in a thermal analogue of the nematic VBS. We present arguments, supported by classical Monte Carlo simulations, that this nematic transforms into the high temperature symmetric paramagnet via a thermal phase transition which is in the universality class of the classical 3-state Potts (clock) model in 2D. We discuss the possible relevance of our results for honeycomb magnets, such as Bi$_3$M$_4$O$_{12}$(NO$_3$) (with M=Mn,V,Cr), and bilayer triangular lattice magnets.Comment: Slightly revise

Structure and evolution of the cold dome off northeastern Taiwan : a numerical study

Author Posting. © The Oceanography Society, 2013. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 26, no. 1 (2013): 66–79, doi:10.5670/oceanog.2013.06.Numerous observational and modeling studies of ocean circulation surrounding Taiwan have reported occurrences of cold water and doming of isotherms (called the cold dome) that result in the formation of coastal upwelling on the northeastern Taiwan shelf. We use a high-resolution (1/24°) ocean model based on the Massachusetts Institute of Technology general circulation model to study the evolution of this distinct shelf-slope circulation phenomenon. We performed a number of model simulations spanning a five-year period (2004–2008) using realistic atmospheric forcing and initial and open boundary conditions. The model solutions were compared with satellite measurements of sea surface height (SSH), sea surface temperature (SST), and historical temperature and salinity observations. The model showed a realistically shaped cold dome with a diameter of ~ 100 km and temperature of ~ 3°C below the ambient shelf waters at 50 m depth. The occurrences of simulated cold dome events appeared to be connected with the seasonal variability of the Kuroshio Current. The model simulations showed more upwelling events during spring and summer when the core of the Kuroshio tends to migrate away from the east coast of Taiwan, compared to fall and winter when the core of the Kuroshio is generally found closer to the east coast of Taiwan. The model also reproduced weak cyclonic circulation associated with the upwelling off northeastern Taiwan. We analyzed the spatio-temporal variability of the cold dome using the model solution as a proxy and designed a "cold dome index" based on the temperature at 50 m depth averaged over a 0.5° × 0.5° box centered at 25.5°N, 122°E. The cold dome index correlates with temperature at 50 m depth in a larger region, suggesting the spatial extent of the cold dome phenomenon. The index had correlation maxima of 0.78 and 0.40 for simulated SSH and SST, respectively, in and around the cold dome box region, and we hypothesize that it is a useful indicator of upwelling off northeastern Taiwan. In addition, both correlation and composite analysis between the temperature at 50 m depth and the East Taiwan Channel transport showed no cold dome events during low-transport events (often in winter) and more frequent cold dome events during high-transport events (often in summer). The simulated cold dome events had time scales of about two weeks, and their centers aligned roughly along a northeastward line starting from the northeastern tip of Taiwan.This work was supported by Office of Naval Research grant N00014-08- 1-0587

Perancangan Case Tools untuk Diagram Use Case, Activity, dan Class untuk Permodelan Uml Berbasis Web Menggunakan HTML5 dan PHP

This study is intended to generate an application tools (CASE tools) that allows a software developer to create a modeling system design using Unified Modeling Language (UML), especially in making use case, activity or class diagrams more quickly and easily. The tools developed will also facilitate developers in doing UML modeling by accessing the network through a web-based internet application. With the web-based applications, the users require only a browser and an internet connection to use this application. This application also helps developers to understand of how to make UML diagrams correctly and good. In this research traditional methods Scrum model is used. Scrum method is Agile methods that is a process to cultivate software easily and can be developed in accordance with the development of information technology. Scrum is using empirical methods or in other words every stage in it involves inspection and adaptation

Poisson approximations for the Ising model

A $d$-dimensional Ising model on a lattice torus is considered. As the size $n$ of the lattice tends to infinity, a Poisson approximation is given for the distribution of the number of copies in the lattice of any given local configuration, provided the magnetic field $a=a(n)$ tends to $-\infty$ and the pair potential $b$ remains fixed. Using the Stein-Chen method, a bound is given for the total variation error in the ferromagnetic case.Comment: 25 pages, 1 figur

Towards Verifying Nonlinear Integer Arithmetic

We eliminate a key roadblock to efficient verification of nonlinear integer arithmetic using CDCL SAT solvers, by showing how to construct short resolution proofs for many properties of the most widely used multiplier circuits. Such short proofs were conjectured not to exist. More precisely, we give n^{O(1)} size regular resolution proofs for arbitrary degree 2 identities on array, diagonal, and Booth multipliers and quasipolynomial- n^{O(\log n)} size proofs for these identities on Wallace tree multipliers.Comment: Expanded and simplified with improved result

Bit-Vector Model Counting using Statistical Estimation

Approximate model counting for bit-vector SMT formulas (generalizing \#SAT) has many applications such as probabilistic inference and quantitative information-flow security, but it is computationally difficult. Adding random parity constraints (XOR streamlining) and then checking satisfiability is an effective approximation technique, but it requires a prior hypothesis about the model count to produce useful results. We propose an approach inspired by statistical estimation to continually refine a probabilistic estimate of the model count for a formula, so that each XOR-streamlined query yields as much information as possible. We implement this approach, with an approximate probability model, as a wrapper around an off-the-shelf SMT solver or SAT solver. Experimental results show that the implementation is faster than the most similar previous approaches which used simpler refinement strategies. The technique also lets us model count formulas over floating-point constraints, which we demonstrate with an application to a vulnerability in differential privacy mechanisms