Physical Sciences and Mathematics Commons^™

Measuring The Speed Of Sound Of Quintessence, Christian Armendariz-Picon, Joel K. Erickson, R. R. Caldwell, Paul J. Steinhardt, V. Mukhanov

Physics - All Scholarship

Quintessence, a time-varying energy component that may account for the accelerated expansion of the universe, can be characterized by its equation of state and sound speed. In this paper, we show that if the quintessence density is at least one percent of the critical density at the surface of last scattering the cosmic microwave background anisotropy can distinguish between models whose sound speed is near the speed of light versus near zero, which could be useful in distinguishing competing candidates for dark energy.

Testing A Fourier Accelerated Hybrid Monte Carlo Algorithm, Simon Catterall, Sergey Karamov

Physics - All Scholarship

We describe a Fourier Accelerated Hybrid Monte Carlo algorithm suitable for dynamical fermion simulations of non-gauge models. We test the algorithm in supersymmetric quantum mechanics viewed as a one-dimensional Euclidean lattice field theory. We find dramatic reductions in the autocorrelation time of the algorithm in comparison to standard HMC.

Introduction To Effective Lagrangians For Qcd, Joseph Schechter

Physics - All Scholarship

A brief introduction to the effective Lagrangian treatment of QCD (in the sense of using fields representing physical particles rather than quarks and gluons) will be given. The historical evolution of the subject will be discussed. Some background material related to a recent model for Gamma Ray Bursters will be given. Finally, some recent work on low energy strong interactions will be mentioned.

Anomaly Induced Qcd Potential And Quark Decoupling, Joseph Schechter, Stephen D.H. Hsu, Francesco Sannino

Physics - All Scholarship

We explore the anomaly induced effective QCD meson potential in the framework of the effective Lagrangian approach. We suggest a decoupling procedure, when a flavored quark becomes massive, which mimics the one employed by Seiberg for supersymmetric gauge theories. It is seen that, after decoupling, the QCD potential naturally converts to the one with one less flavor. We study the N_c and N_f dependence of the \eta^{\prime} mass.

The Formation Of Vortex Loops (Strings) In Continuous Phase Transitions, Mark Bowick, Angelo Cacciuto, Alex Travesset

Physics - All Scholarship

The formation of vortex loops (global cosmic strings) in an O(2) linear sigma model in three spatial dimensions is analyzed numerically. For over-damped Langevin dynamics we find that defect production is suppressed by an interaction between correlated domains that reduces the effective spatial variation of the phase of the order field. The degree of suppression is sensitive to the quench rate. A detailed description of the numerical methods used to analyze the model is also reported.

Complementary Ansatz For The Neutrino Mass Matrix, Joseph Schechter, Deirdre Black, Amir H. Fariborz, Salah Nasri

Physics - All Scholarship

We propose a simple Ansatz for the three generation neutrino mass matrix M_\nu which is motivated from an SO(10) grand unified theory. The Ansatz can be combined with information from neutrino oscillation experiments and bounds on neutrinoless double beta decay to determine the neutrino masses themselves and to reconstruct, with some assumptions, the matrix M_\nu.

Investigating The Light Scalar Mesons, Joseph Schechter, D. Black, Amir H. Fariborz, Salah Moussa, S. Nasri

Physics - All Scholarship

We first briefly review a treatment of the scalars in meson meson scattering based on a non-linear chiral Lagrangian, with unitarity implemented by a "local" modification of the scalar propagators. It is shown that the main results are confirmed by a treatment in the SU(3) linear sigma model in which unitarity is implemented "globally". Some remarks are made on the speculative subject of the scalars' quark structure.

A Two-Dimensional Lattice Model With Exact Supersymmetry, Simon Catterall, S. Karamov

Physics - All Scholarship

Starting from a simple discrete model which exhibits a supersymmetric invariance we construct a local, interacting, two-dimensional Euclidean lattice theory which also admits an exact supersymmetry. This model is shown to correspond to the Wess-Zumino model with extended N=2 supersymmetry in the continuum. We have performed dynamical fermion simulations to check the spectrum and supersymmetric Ward identities and find good agreement with theory.

Universal Negative Poisson Ratio Of Self Avoiding Fixed Connectivity Membranes, Mark Bowick, Angelo Cacciuto, G. Thorleifsson, A. Travesset

Physics - All Scholarship

We determine the Poisson ratio of self-avoiding fixed-connectivity membranes, modeled as impenetrable plaquettes, to be sigma=-0.37(6), in statistical agreement with the Poisson ratio of phantom fixed-connectivity membranes sigma=-0.32(4). Together with the equality of critical exponents, this result implies a unique universality class for fixed-connectivity membranes. Our findings thus establish that physical fixed-connectivity membranes provide a wide class of auxetic (negative Poisson ratio) materials with significant potential applications in materials science.

The Three-Dimensional Random Field Ising Magnet: Interfaces, Scaling, And The Nature Of States, Alan Middleton, Daniel S. Fisher

Physics - All Scholarship

The nature of the zero temperature ordering transition in the 3D Gaussian random field Ising magnet is studied numerically, aided by scaling analyses. In the ferromagnetic phase the scaling of the roughness of the domain walls, $w\sim L^\zeta$, is consistent with the theoretical prediction $\zeta = 2/3$. As the randomness is increased through the transition, the probability distribution of the interfacial tension of domain walls scales as for a single second order transition. At the critical point, the fractal dimensions of domain walls and the fractal dimension of the outer surface of spin clusters are investigated: there are at least …

Doubly Perturbed S_3 Neutrinos And The S_{13} Mixing Parameter, Joseph Schechter, Renata Jora, M. Naeem Shahid

Physics - All Scholarship

We further study a predictive model for the masses and mixing matrix of three Majorana neutrinos. At zeroth order the model yielded degenerate neutrinos and a generalized ``tribimaximal" mixing matrix. At first order the mass splitting was incorporated and the tribimaximal mixing matrix emerged with very small corrections but with a zero value for the parameter $s_{13}$. In the present paper a different, assumed weaker, perturbation is included which gives a non zero value for $s_{13}$ and further corrections to other quantities. These corrections are worked out and their consequences discussed under the simplifying assumption that the conventional CP violation …

Remark On Pion Scattering Lengths, Joseph Schechter, Deirdre Black, Nae Woong Park

Physics - All Scholarship

First it is shown that the tree amplitude for pion pion scattering in the minimal linear sigma model has an exact expression which is proportional to a geometric series in the quantity (s-$m_\pi^2$)/($m_B^2-m_\pi^2$), where $m_B$ is the sigma mass which appears in the Lagrangian and is the only a priori unknown parameter in the model. This induces an infinite series for every predicted scattering length in which each term corresponds to a given order in the chiral perturbation theory counting. It is noted that, perhaps surprisingly, the pattern, though not the exact values, of chiral perturbation theory predictions for both …

The Ising Model On A Dynamically Triangulated Disk With A Boundary Magnetic Field, Simon Catterall, Scott V. Mcguire, Mark Bowick, Simeon Warner

Physics - All Scholarship

We use Monte Carlo simulations to study a dynamically triangulated disk with Ising spins on the vertices and a boundary magnetic field. For the case of zero magnetic field we show that the model possesses three phases. For one of these the boundary length grows linearly with disk area, while the other two phases are characterized by a boundary whose size is on the order of the cut-off. A line of continuous magnetic transitions separates the two small boundary phases. We determine the critical exponents of the continuous magnetic phase transition and relate them to predictions from continuum 2-d quantum …

Observations On Lemon Cells, Jerry Goodisman

Chemistry - All Scholarship

In many general chemistry texts (1), the electrochemistry chapter is introduced with a picture of a “lemon cell”, leads of Zn and Cu piercing a lemon (or sometimes a grapefruit). A voltmeter connected across them shows a potential of about 1 V. (It has been shown how several fruits connected in series can be used to run a calculator [2].) The texts then discuss oxidation–reduction, half-cells, and the rest of what we teach freshmen about electrochemistry, and the lemon is never mentioned again.

It would appear to be questionable scientific pedagogy to present something, even something …

The Geometrical Structure Of 2d Bond-Orientational Order, Mark Bowick, Alex Travesset

Physics - All Scholarship

We study the formulation of bond-orientational order in an arbitrary two dimensional geometry. We find that bond-orientational order is properly formulated within the framework of differential geometry with torsion. The torsion reflects the intrinsic frustration for two-dimensional crystals with arbitrary geometry. Within a Debye-Huckel approximation, torsion may be identified as the density of dislocations. Changes in the geometry of the system cause a reorganization of the torsion density that preserves bond-orientational order. As a byproduct, we are able to derive several identities involving the topology, defect density and geometric invariants such as Gaussian curvature. The formalism is used to derive …

Universality Classes Of Self-Avoiding Fixed-Connectivity Membranes, Mark Bowick, Angelo Cacciuto, Gudmar Thorleifsson, Alex Travesset

Physics - All Scholarship

We present an analysis of extensive large-scale Monte Carlo simulations of self-avoiding fixed-connectivity membranes for sizes (number of faces) ranging from 512 to 17672 (triangular) plaquettes. Self-avoidance is implemented via impenetrable plaquettes. We simulate the impenetrable plaquette model in both three and four bulk dimensions. In both cases we find the membrane to be flat for all temperatures: the size exponent in three dimensions is nu=0.95(5) (Hausdorff dimension d_H=2.1(1)). The single flat phase appears, furthermore, to be equivalent to the large bending rigidity phase of non-self-avoiding fixed-connectivity membranes - the roughness exponent in three dimensions is xi=0.63(4). This suggests that …

Examining The Reflective Outcomes Of Asynchronous Computer-Mediated Communication On Inservice Teacher Development, Mark Hawkes, Alexander Romiszowski

Instructional Design, Development and Evaluation - All Scholarship

This study explored the professional development experiences of 28 practicing teachers in 10 Chicago suburban schools involved in a two-year technology supported Problem-Based Learning curriculum development effort. Asynchronous computer-mediated communications (CMC) were featured as teacher communication tools of the project. The computer-mediated discourse produced by the teachers was compared with the discourse produced by teachers in face-to-face meetings. Research methods including discourse analysis and archival data analysis were applied to determine the nature of the teacher discourse and its reflective content. The results show that while the computer-mediated teacher dialogue was less interactive, it was significantly more reflective (t=4.14, p=.001) …

Privacy-Preserving Cooperative Statistical Analysis, Wenliang Du, Mikhail J. Atallah

Electrical Engineering and Computer Science - All Scholarship

The growth of the Internet opens up tremendous opportunities for cooperative computation, where the answer depends on the private inputs of separate entities. Sometimes these computations may occur between mutually untrusted entities. The problem is trivial if the context allows the conduct of these computations by a trusted entity that would know the inputs from all the participants; however if the context disallows this then the techniques of secure multi-party computation become very relevant and can provide useful solutions. Statistic analysis is a widely used computation in real life, but the known methods usually require one to know the whole …

Secure Multi-Party Computation Problems And Their Applications: A Review And Open Problems, Wenliang Du, Mikhail J. Atallah

Electrical Engineering and Computer Science - All Scholarship

The growth of the Internet has triggered tremendous opportunities for cooperative computation, where people are jointly conducting computation tasks based on the private inputs they each supplies. These computations could occur between mutually untrusted parties, or even between competitors. For example, customers might send to a remote database queries that contain private information; two competing financial organizations might jointly invest in a project that must satisfy both organizations' private and valuable constraints, and so on. Today, to conduct such computations, one entity must usually know the inputs from all the participants; however if nobody can be trusted enough to know …

Inter-Domain Lsp Setup Using Bandwidth Management Points, Ibrahim Taner Okumus, Junseok Hwang, Haci Ali Mantar, Steve J. Chapin

Electrical Engineering and Computer Science - All Scholarship

Bandwidth Management Points (BMP) are a necessity to manage the intra and inter-domain resources in the Internet. In this paper we propose a way to setup inter-domain Label Switched Path (LSP) with the help of a BMP in a MultiProtocol Label Switching (MPLS) over DiffServ network. We use extended Simple Inter-domain Bandwidth Broker Signalling Protocol (SIBBS) to distribute the labels inter-domain. We also use a BMP to interact with the MPLS to setup the intra-domain LSP and to provision the intra-domain traffic. With the help of a BMP, we show how end-to-end Quality of Service (QoS) can be achieved.

Interdomain Resource Reservation Via Third-Party Agent, Haci Ali Mantar, Junseok Hwang, Ibrahim Taner Okumus, Steve J. Chapin

Electrical Engineering and Computer Science - All Scholarship

This paper describes interdomain resource reservation through a third-party agent called a Bandwidth Management Point (BMP). The BMP of each domain is responsible for admission control, dynamic bandwidth provisioning, DSCP assignment, policy control, etc. We also propose that each domain be free to choose its own intradomain resource reservation protocol.This model solves two significant problems of today's Internet: interdomain dynamic resource provisioning, and scalability of the backbone. The BMP makes bulk reservations with each possible destination domain on behalf of hosts in its domain, and end hosts can join or leave the reservation without being involved with communication protocol between …

Parallel Suffix Sorting, Natsuhiko Futamura, Srinivas Aluru, Stefan Kurtz

Electrical Engineering and Computer Science - All Scholarship

We present a parallel algorithm for lexicographically sorting the suffixes of a string. Suffix sorting has applications in string processing, data compression and computational biology. The ordered list of suffixes of a string stored in an array is known as Suffix Array, an important data structure in string processing and computational biology. Our focus is on deriving a practical implementation that works well for typical inputs rather than achieving the best possible asymptotic running-time for artificial, worst-case inputs. We experimentally evaluated our algorithm on an IBM SP-2 using genomes of several organisms. Our experiments show that the algorithm delivers good, …

Jobqueue: A Computational Grid-Wide Queuing System, Dimitros Katramatos, Marty Humphrey, Andrew Grimshaw, Steve Chapin

Electrical Engineering and Computer Science - All Scholarship

In a Computational Grid, it is not easy to maintain grid-wide control over the number of executing jobs, as well as a global view of the status of submitting jobs, due to the heterogeneity in resource type, availability, and access policies. This paper describes the design and implementation of JobQueue, which is a Computational Grid-wide queuing system, or metaqueuing system, implemented in Legion. JobQueue is unique because of its ability to span multiple administrative domains. It can also be reconfigured dynamically along a number of dimensions and in the general case does not require special privileges to create, facilitating new …

Time-Domain Electric-Field Integral Equation With Central Finite Difference, Baek Ho Jung, Tapan Kumar Sarkar

Electrical Engineering and Computer Science - All Scholarship

In this paper, we present a new formulation using the time-domain electric-field integral equation (TD-EFIE) to obtain a transient scattering response from arbitrarily shaped conducting bodies. The time derivative of the magnetic vector potential is approximated with a central finite difference, and the scalar potential is time averaged by dividing it into two terms. This approach with an implicit method using central-difference results in accurate and stable transient scattering responses from conducting objects. Detailed mathematical steps are included, and several numerical results are presented.

Some New Approaches To Formulate And Estimate Friction-Bernoulli Jump Diffusion And Friction-Garch, Chihwa Kao

Center for Policy Research

In this paper we propose a friction model with a Beroulli jump diffusion and a friction with GARCH to examine the exchange rates movements in Taiwan. The proposed model resolves the estimation problem associated with the stepwise movements of observed exchange rates. The specification maintains the desirable economic properties associated with movements in exchange rate returns and is empirically tractable. The AIC apparently favors the model based on Friction-GARCH model.

Asymptotic Inference In Censored Regression Models Revisited, Chihwa Kao

Center for Policy Research

This paper establishes that regressors in the models with censored dependent variables need not be bounded for the standard asymptotic results to apply. Thus, regressors that grow monotonically with the observation index may be acceptable. It also purports to provide an upper bound on the rate at which regressors may grow.