Physical Sciences and Mathematics Commons^™

Isotropization In Brane Gas Cosmology, Scott Watson, Robert H. Brandenberger

Physics - All Scholarship

Brane Gas Cosmology (BGC) is an approach to unifying string theory and cosmology in which matter is described by a gas of strings and branes in a dilaton gravity background. The Universe is assumed to start out with all spatial dimensions compact and small. It has previously been shown that in this context, in the approximation of neglecting inhomogeneities and anisotropies, there is a dynamical mechanism which allows only three spatial dimensions to become large. However, previous studies do not lead to any conclusions concerning the isotropy or anisotropy of these three large spatial dimensions. Here, we generalize the equations …

Stripes From (Noncommutative) Stars, Simon Catterall, J. Ambjorn

Physics - All Scholarship

We show that lattice regularization of noncommutative field theories can be used to study non-perturbative vacuum phases. Specifically we provide evidence for the existence of a striped phase in two-dimensional noncommutative scalar field theory

Hysteresis In Driven Disordered Systems: From Plastic Depinning To Magnets, M. Cristina Marchetti, Karin A. Dahmen

Physics - All Scholarship

We study the dynamics of a viscoelastic medium driven through quenched disorder by expanding about mean field theory in $6-\epsilon$ dimensions. The model exhibits a critical point separating a region where the dynamics is hysteretic with a macroscopic jump between strongly pinned and weakly pinned states, from a region where the sliding state is unique and no jump occurs. The disappearance of the jump at the critical point is described by universal exponents. As suggested in \onlinecite{MMP00}, the model appears to be in the same universality class as the zero-temperature random field Ising model of hysteresis in magnets.

Precision Measurement Of Energy And Position Resolutions Of The Btev Electromagnetic Calorimeter Prototype, Raymond Mountain, K. Khroustalev, V.A. Batarin, T. Brennan

Physics - All Scholarship

The energy dependence of the energy and position resolutions of the electromagnetic calorimeter prototype made of lead tungstate crystals produced in Bogoroditsk (Russia) and Shanghai (China) is presented. These measurementswere carried out at the Protvino accelerator using a 1 to 45 GeV electron beam. The crystals were coupled to photomultiplier tubes. The dependence of energy and position resolutions on different factors as well as the measured electromagnetic shower lateral profile are presented.

Effects Of Light Scalar Mesons In Η\To 3Π Decay, Joseph Schechter, Abdou Abdel-Rehim, Deirdre Black, Amir H. Fariborz

Physics - All Scholarship

We study the role of a possible nonet of light scalar mesons in the still interesting \eta \to 3\pi decay process, with the primary motivation of learning more about the scalars themselves. The framework is a conventional non-linear chiral Lagrangian of pseudoscalars and vectors, extended to include the scalars. The parameters involving the scalars were previously obtained to fit the s-wave \pi\pi and \piK scatterings in the region up to about 1 GeV as well as the strong decay \eta' \to \eta \pi\pi. At first, one might expect a large enhancement from diagrams including a light \sigma(560). However there is …

Crystalline Order On A Sphere And The Generalized Thomson Problem, Mark Bowick, Angelo Cacciuto, David R. Nelson, A. Travesset

Physics - All Scholarship

We attack generalized Thomson problems with a continuum formalism which exploits a universal long range interaction between defects depending on the Young modulus of the underlying lattice. Our predictions for the ground state energy agree with simulations of long range power law interactions of the form 1/r^{gamma} (0 < gamma < 2) to four significant digits. The regime of grain boundaries is studied in the context of tilted crystalline order and the generality of our approach is illustrated with new results for square tilings on the sphere.

Intersection Multiplicities Over Gorenstein Rings, Claudia M. Miller, Anurag K. Singh

Mathematics - All Scholarship

We construct a complex of free-modules over a Gorenstein ring R of dimension five, for which the Euler characteristic and Dutta multiplicity are different. This complex is the resolution of an R-module of finite length and finite projective dimension. As a consequence, the ring R has a nonzero Todd class tau_3(R) and a bounded free complex whose local Chern character does not vanish on this class.
In the course of our work, we construct a module N of finite length and finite projective dimension over the hypersurface A=K[u,v,w,x,y,z]/(ux+vy+wz), such that the Serre intersection multiplicity of the modules N and A/(u,v,w)A …

Development Of A Hybrid Photo-Diode And Its Front-End Electronics For The Btev Experiment, Raymond Mountain

Physics - All Scholarship

This paper describes the development of a 163-channel Hybrid Photo-Diode (HPD) to be used in the RICH Detector for the BTEV Experiment. This is a joint development project with DEP, Netherlands. It also reports on the development of associated front-end readout electronics based on the va_btev ASIC, undertaken with IDEAS, Norway. Results from bench tests of the first prototypes are presented.

Construction, Pattern Recognition And Performance Of The Cleo Iii Lif-Tea Rich Detector, Raymond Mountain, R. Ayad, Konstantin Vladimirovich Bukin, A. Efimov

Physics - All Scholarship

We briefly describe the design, construction and performance of the LiF-Tea RICH detector built to identify charged particles in the CLEO III experiment. Excellent pion/kaon separation is demonstrated.

Scaling, Domains, And States In The Four-Dimensional Random Field Ising Magnet, Alan Middleton

Physics - All Scholarship

The four dimensional Gaussian random field Ising magnet is investigated numerically at zero temperature, using samples up to size $64^4$, to test scaling theories and to investigate the nature of domain walls and the thermodynamic limit. As the magnetization exponent $\beta$ is more easily distinguishable from zero in four dimensions than in three dimensions, these results provide a useful test of conventional scaling theories. Results are presented for the critical behavior of the heat capacity, magnetization, and stiffness. The fractal dimensions of the domain walls at criticality are estimated. A notable difference from three dimensions is the structure of the …

Predictions And Observations In Theories With Varying Couplings, Christian Armendariz-Picon

Physics - All Scholarship

We consider a toy universe containing conventional matter and an additional real scalar field, and discuss how the requirements of gauge and diffeomorphism invariance essentially single out a particular set of theories which might describe such a world at low energies. In these theories, fermion masses and g-factors, as well as the electromagnetic coupling turn to be scalar field dependent; fermion charges and the gravitational coupling might be assumed to be constant. We then proceed to study the impact of a time variation of the scalar field on measurements of atomic spectra at high redshifts. Light propagation is not affected …

Footprinting, Circular Dichroism And Uv Melting Studies On Neomycin B Binding To The Packaging Region Of Human Immunodeficiency Virus Type-1 Rna, Mark P. Mcpike, Julie M. Sullivan, Jerry Goodisman, James C. Dabrowiak

Chemistry - All Scholarship

We have studied the binding of neomycin to a 171mer RNA (Ψ-RNA) from the packaging region of the LAI strain of human immunodeficiency virus type-1, HIV-1 (LAI). The RNase I footprinting studies reveal that the primary binding site for the drug is in stem-loop 1, which contains the dimer initiation site of HIV-1. Loading this site with neomycin causes a structural change in the RNA, allowing nucleotides in the neighboring stem-loop 2 to participate in the drug site. Drug binding to secondary sites induces structural changes in other stem-loops of the RNA. Footprinting plots, showing cutting at a site as …

Local Rings Of Countable Cohen-Macaulay Type, Craig Huneke, Graham J. Leuschke

Mathematics - All Scholarship

We prove (the excellent case of) Schreyer's conjecture that a local ring with countable Cohen-Macaulay type has at most a one-dimensional singular locus. Furthermore we prove that the localization of a Cohen-Macaulay local ring of countable CM type is again of countable CM type.

Footprinting And Circular Dichroism Studies On Paromomycin Binding To The Packaging Region Of Human Immunodeficiency Virus Type-1, Mark P. Mcpike, Jerry Goodisman, James C. Dabrowiak

Chemistry - All Scholarship

We have studied the interaction of the aminoglycoside drug, paromomycin, with a 171-mer from the packaging region of HIV-1 (ψ-RNA), using quantitative footprinting and circular dichroism spectroscopy. The footprinting autoradiographic data were obtained by cutting end-labeled RNA with RNase I or RNase T1 in the presence of varying paromomycin concentrations. Scanning the autoradiograms produced footprinting plots showing cleavage intensities for specific sites on the ψ-RNA as functions of drug concentration. Footprinting plots showing binding were analyzed using a two-state model to give apparent binding constants for specific sites of the ψ-RNA. These plots show that the highest-affinity paromomycin binding site …

Exact Lattice Supersymmetry: The Two-Dimensional N=2 Wess-Zumino Model, Simon Catterall, Sergey Karamov

Physics - All Scholarship

We study the two-dimensional Wess-Zumino model with extended N=2 supersymmetry on the lattice. The lattice prescription we choose has the merit of preserving {\it exactly} a single supersymmetric invariance at finite lattice spacing a. Furthermore, we construct three other transformations of the lattice fields under which the variation of the lattice action vanishes to O(ga^2) where g is a typical interaction coupling. These four transformations correspond to the two Majorana supercharges of the continuum theory. We also derive lattice Ward identities corresponding to these exact and approximate symmetries. We use dynamical fermion simulations to check the equality of the massgaps …

Vector Meson Dominance Model For Radiative Decays Involving Light Scalar Mesons, Joseph Schechter, Deirdre Black, Masayasu Harada

Physics - All Scholarship

We study a vector dominance model which predicts a fairly large number of currently interesting decay amplitudes of the types S -> \gamma \gamma, V -> S \gamma and S -> V \gamma, where S and V denote scalar and vector mesons, in terms of three parameters. As an application, the model makes it easy to study in detail a recent proposal to boost the ratio Gamma(phi -> f_0 gamma) / Gamma(phi -> a_0 gamma) by including the isospin violating a_0 - f_0 mixing. However we find that this effect is actually small in our model.

Clash Of Symmetries On The Brane, Aharon Davidson, B. F. Toner, R. R. Volkas, K. C. Wali

Physics - All Scholarship

If our 3 + 1-dimensional universe is a brane or domain wall embedded in a higher dimensional space, then a phenomenon we term the “clash of symmetries” provides a new method of breaking some continuous symmetries. A global

Gcts ⊗ Gdiscrete symmetry is spontaneously broken to Hcts ⊗ Hdiscrete, where the continuous subgroup Hcts can be embedded in several different ways in the parent group Gcts, and Hdiscrete < Gdiscrete. A certain class of topological domain wall solutions connect two vacua that are invariant under differently embedded Hcts subgroups. There is then enhanced symmetry breakdown to the intersection of these two subgroups on the domain wall.This is the “clash”. In the brane limit, we obtain a configuration with Hcts symmetries in the bulk but the smaller intersection symmetry on the brane itself. We illustrate this idea using a permutation symmetric three-Higgstriplet toy model exploiting the distinct I−, U− and V − spin U(2) subgroups of U(3). The three disconnected portions of the vacuum manifold can be treated symmetrically through the construction of a three-fold planar domain wall junction configuration, with our universe at the nexus. A possible con-

Determining The Locus For Photocarrier Recombination In Dye-Sensitized Solar Cells, Kai Zhu, Eric A. Schiff, N. G. Park, J. Van De Lagemaat, A. J. Frank

Physics - All Scholarship

We present intensity-modulated photocurrent and infrared transmittance measurements on dye-sensitized solar cells based on a mesoporous titania (TiO2) matrix immersed in an iodine-based electrolyte. Under short-circuit conditions, we show that an elementary analysis accurately relates the two measurements. Under open-circuit conditions, infrared transmittance, and photovoltage measurements yield information on the characteristic depth at which electrons recombine with ions (the ‘‘locus of recombination’’). For one particular series of samples recombination occurred near the substrate supporting the titania film, as opposed to homogeneously throughout the film.

Infrared Charge-Modulation Spectroscopy Of Defects In Phosphorus Doped Amorphous Silicon, Kai Zhu, Eric A. Schiff, G. Ganguly

Physics - All Scholarship

We present infrared charge-modulation absorption spectra on phosphorus-doped amorphous silicon (a-Si:H:P) with doping levels between 0.17% - 5%. At higher doping levels (1% - 5%) we find a sharp spectral line near 0.75 eV with a width of 0.1 eV. We attribute this line to the internal optical transitions of a complex incorporating four fold coordinated phosphorus and a dangling bond. This line is barely detectable in samples with lower doping levels (below 1%). In these samples a much broader line dominates the spectrum that we attribute to uncomplexed dopants. The relative strength of the two spectral features is in …

Thermionic Emission Model For Interface Effects On The Open-Circuit Voltage Of Amorphous Silicon Based Solar Cells, Eric A. Schiff

Physics - All Scholarship

We present computer modeling for effects of the p/i interface upon the open-circuit voltage VOC in amorphous silicon based pin solar cells. We show that the modeling is consistent with measurements on the intensitydependence for the interface effect, and we present an interpretation for the modeling based on thermionic emission of electrons over the electrostatic barrier at the p/i interface. We present additional modeling of the relation of VOC with the intrinsic layer bandgap EG. The experimental correlation for optimized cells is VOC = (EG/e)-0.79. The correlation is simply explained if VOC in these cells is determined by the intrinsic …

Photocarrier Drift Mobility Measurements And Electron Localization In Nanoporous Silicon, P. N. Rao, Eric A. Schiff, L. Tsybeskov, P. Fauchet

Physics - All Scholarship

We report photocarrier time-of-flight measurements in diode structures made of highly porous crystalline silicon. The corresponding electron and hole drift mobilities are very small ð<104 cm2=V sÞ compared to homogeneous crystalline silicon. The mobilities are dispersive (i.e., having a power-law decay with time or length-scale), but are only weakly temperature-dependent. The dispersion parameter lies in the range 0.55–0.65 for both electrons and holes. We conclude that the drift mobilities are limited by the nanoporous geometry, and not by disorder-induced localized states acting as traps. This conclusion is surprising in the context of luminescence models based on radiative recombination of localized excitons.

From Computational Science To Internetics: Integration Of Science With Computer Science, Geoffrey C. Fox

Northeast Parallel Architecture Center

We describe how our world dominated by Science and Scientists has been changed revolutionized by technologies moving with Internet time. Computers have always been well-used tools but in the beginning only the science counted and little credit or significance was attached to any computing activities associated with scientific research. Some 20 years ago, this started to change and the area of computational science gathered support with the NSF Supercomputer centers playing a critical role. However this vision has stalled over the last 5 years with information technology increasing in importance. The Holy Grail of computational science-- scalable parallel computing-- is …

Building Decision Tree Classifier On Private Data, Wenliang Du, Zhijun Zhan

Electrical Engineering and Computer Science - All Scholarship

This paper studies how to build a decision tree classifier under the following scenario: a database is vertically partitioned into two pieces, with one piece owned by Alice and the other piece owned by Bob. Alice and Bob want to build a decision tree classifier based on such a database, but due to the privacy constraints, neither of them wants to disclose their private pieces to the other party or to any third party. We present a protocol that allows Alice and Bob to conduct such a classifier building without having to compromise their privacy. Our protocol uses an untrusted …

A Practical Approach To Solve Secure Multi-Party Computation Problems, Wenliang Du, Zhijun Zhan

Electrical Engineering and Computer Science - All Scholarship

Secure Multi-party Computation (SMC) problems deal with the following situation: Two (or many) parties want to jointly perform a computation. Each party needs to contribute its private input to this computation, but no party should disclose its private inputs to the other parties, or to any third party. With the proliferation of the Internet, SMC problems becomes more and more important. So far no practical solution has emerged, largely because SMC studies have been focusing on zero information disclosure, an ideal security model that is expensive to achieve. Aiming at developing practical solutions to SMC problems, we propose a new …

Distributed And Multiprocessor Scheduling, Steven J. Chapin, Jon B, Weissman

Electrical Engineering and Computer Science - All Scholarship

This chapter discusses CPU scheduling in parallel and distributed systems. CPU scheduling is part of a broader class of resource allocation problems, and is probably the most carefully studied such problem. The main motivation for multiprocessor scheduling is the desire for increased speed in the execution of a workload. Parts of the workload, called tasks, can be spread across several processors and thus be executed more quickly than on a single processor. In this chapter, we will examine techniques for providing this facility. The scheduling problem for multiprocessor systems can be generally stated as \How can we execute a set …

Integration Of Naradabrokering And Audio/Video Conferencing As A Web Service, Hasan Bulut, Geoffrey C. Fox, Shrideep Pallickara, Ahmet Uyar, Wenjun Wu

Electrical Engineering and Computer Science - All Scholarship

Audio/Video Conferencing Systems need communication channels between their clients in order to transport RTP packets from one client to another. In this paper we investigate audio/video conferencing as a Web Service and the deployment of publish/subscribe systems in the context of audio/video conferencing systems. In this paper we use our research system NaradaBrokering, which supports both peer-to-peer and publish/subscribe paradigms, as a test bed to investigate these ideas. We also present results from our research system.

A Survey Of Various Frequency Domain Integral Equations For The Analysis Of Scattering From Three-Dimensional Dielectric Objects, Baek Ho Jung, T. K. Sarkar, Y.-S. Chung

Electrical Engineering and Computer Science - All Scholarship

In this paper, we present four different formulations for the analysis of electromagnetic scattering from arbitrarily shaped three-dimensional (3-D) homogeneous dielectric body in the frequency domain. The four integral equations treated here are the electric field integral equation (EFIE), the magnetic field integral equation (MFIE), the combined field integral equation (CFIE), and the PMCHW (Poggio, Miller, Chang, Harrington, and Wu) formulation. For the CFIE case, we propose eight separate formulations with different combinations of expansion and testing functions that result in sixteen different formulations of CFIE. One of the objectives of this paper is to illustrate that not all CFIE …

Interoperable Web Services For Computational Portals, Marlon Pierce, Geoffrey C. Fox, Choonhan Youn, Steve Mock, Kurt Mueller

Electrical Engineering and Computer Science - All Scholarship

Computational web portals are designed to simplify access to diverse sets of high performance computing resources, typically through an interface to computational Grid tools. An important shortcoming of these portals is their lack of interoperable and reusable services. This paper presents an overview of research efforts undertaken by our group to build interoperating portal services around a Web Services model. We present a comprehensive view of an interoperable portal architecture, beginning with core portal services that can be used to build Application Web Services, which in turn may be aggregated and managed through portlet containers.

Buffer Overflow And Format String Overflow Vulnerabilities, Kyung-Suk Lhee, Steve J. Chapin

Electrical Engineering and Computer Science - All Scholarship

This article surveys representative techniques of exploiting buffer overflow and format string overflow vulnerabilities and their currently available defensive measures. We also describe our buffer overflow detection technique that range checks the referenced buffers at run time. We augment executable files with type information of automatic buffers (local variables and parameters of functions) and static buffers (global variables in the data/bss section), and maintain the sizes of allocated heap buffers in order to detect an actual occurrence of buffer overflow. We describe a simple implementation with which we currently protect vulnerable copy functions in the C library.

Perspectives On The Evolution Of Simulation, Richard E. Nance, Robert G. Sargent

Electrical Engineering and Computer Science - All Scholarship

Simulation is introduced in terms of its different forms and uses, but the focus on discrete event modeling for systems analysis is dominant as it has been during the evolution of the technique within operations research and the management sciences. This evolutionary trace of over almost fifty years notes the importance of bidirectional influences with computer science, probability and statistics, and mathematics. No area within the scope of operations research and the management sciences has been affected more by advances in computing technology than simulation. This assertion is affirmed in the review of progress in those technical areas that collectively …