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Articles 1 - 30 of 39
Full-Text Articles in Physical Sciences and Mathematics
Geometrical Folding Transitions Of The Triangular Lattice In The Face-Centred Cubic Lattice, Mark Bowick, Oliver Golinelli, Emmanuel Guitter, S. Mori
Geometrical Folding Transitions Of The Triangular Lattice In The Face-Centred Cubic Lattice, Mark Bowick, Oliver Golinelli, Emmanuel Guitter, S. Mori
Physics - All Scholarship
We study the folding of the regular two-dimensional triangular lattice embedded in the regular three-dimensional Face-Centred Cubic lattice, a discrete model for the crumpling of membranes. Possible folds are complete planar folds, folds with the angle of a regular tetrahedron (71 degrees) or with that of a regular octahedron (109 degrees). We study this model in the presence of a negative bending rigidity K, which favours the folding process. We use both a cluster variation method (CVM) approximation and a transfer matrix approach. The system is shown to undergo two separate geometrical transitions with increasing |K|: a first discontinuous transition …
Laboratory Synthesis Of Molecular Hydrogen On Surfaces Of Astrophysical Interest, Gianfranco Vidali, V Pirronello, Chi Liu, Liyong Shen
Laboratory Synthesis Of Molecular Hydrogen On Surfaces Of Astrophysical Interest, Gianfranco Vidali, V Pirronello, Chi Liu, Liyong Shen
Physics - All Scholarship
We report on the first results of experiments to measure the recombination rate of hydrogen on surfaces of astrophysical interest. Our measurements give lower values for the recombination efficiency (sticking probability S x probability of recombination upon H-H encounter \gamma) than model-based estimates. We propose that our results can be reconciled with average estimates of the recombination rate (1/2 n(H) n(g) v(H)A S \gamma) from astronomical observations, if the actual surface of an average grain is rougher, and its area bigger, than the one considered in models.
Discrete Folding, Mark Bowick, Philippe Di Francesco, Oliver Golinelli, Emmanuel Guitter
Discrete Folding, Mark Bowick, Philippe Di Francesco, Oliver Golinelli, Emmanuel Guitter
Physics - All Scholarship
Models of folding of a triangular lattice embedded in a discrete space are studied as simple models of the crumpling transition of fixed-connectivity membranes. Both the case of planar folding and three-dimensional folding on a face-centered-cubic lattice are treated. The 3d-folding problem corresponds to a 96-vertex model and exhibits a first-order folding transition from a crumpled phase to a completely flat phase as the bending rigidity increases.
Comment On ``Confirmation Of The Sigma Meson'', Joseph Schechter, Masayasu Harada, Francesco Sannino
Comment On ``Confirmation Of The Sigma Meson'', Joseph Schechter, Masayasu Harada, Francesco Sannino
Physics - All Scholarship
We comment on the recent paper by N.A. Tornqvist and M. Roos published in Phys. Rev. Lett. 76, 1575 (1996).
Ground-State Roughness Of The Disordered Substrate And Flux Line In D=2, Alan Middleton, Chen Zeng, Y. Shapir
Ground-State Roughness Of The Disordered Substrate And Flux Line In D=2, Alan Middleton, Chen Zeng, Y. Shapir
Physics - All Scholarship
We apply optimization algorithms to the problem of finding ground states for crystalline surfaces and flux lines arrays in presence of disorder. The algorithms provide ground states in polynomial time, which provides for a more precise study of the interface widths than from Monte Carlo simulations at finite temperature. Using $d=2$ systems up to size $420^2$, with a minimum of $2 \times 10^3$ realizations at each size, we find very strong evidence for a $\ln^2(L)$ super-rough state at low temperatures.
Suppressing Curvature Fluctuations In Dynamical Triangulations, Simon Catterall, Mark Bowick, G. Thorleifssona
Suppressing Curvature Fluctuations In Dynamical Triangulations, Simon Catterall, Mark Bowick, G. Thorleifssona
Physics - All Scholarship
We study numerically the dynamical triangulation formulation of two-dimensional quantum gravity using a restricted class of triangulation, so-called minimal triangulations, in which only vertices of coordination number 5, 6, and 7 are allowed. A real-space RG analysis shows that for pure gravity (central charge c = 0) this restriction does not affect the critical behavior of the model. Furthermore, we show that the critical behavior of an Ising model coupled to minimal dynamical triangulations (c = 1/2) is still governed by the KPZ-exponents.
Blocking Of Dynamical Triangulations With Matter, Simon Catterall, E. Gregory, G. Thorleifsson
Blocking Of Dynamical Triangulations With Matter, Simon Catterall, E. Gregory, G. Thorleifsson
Physics - All Scholarship
We use the recently proposed node decimation algorithm for blocking dynamical geometries to investigate a class of models, with central charge greater than unity, coupled to 2D gravity. We demonstrate that the blocking preserves the fractal structure of the surfaces.
The Flat Phase Of Fixed-Connectivity Membranes, Simon Catterall, Mark Bowick, Marco Falcioni, G. Thorleifsson, Konstantinos N. Anagnostopoulos
The Flat Phase Of Fixed-Connectivity Membranes, Simon Catterall, Mark Bowick, Marco Falcioni, G. Thorleifsson, Konstantinos N. Anagnostopoulos
Physics - All Scholarship
The statistical mechanics of flexible two-dimensional surfaces (membranes) appears in a wide variety of physical settings. In this talk we discuss the simplest case of fixed-connectivity surfaces. We first review the current theoretical understanding of the remarkable flat phase of such membranes. We then summarize the results of a recent large scale Monte Carlo simulation of the simplest conceivable discrete realization of this system \cite{BCFTA}. We verify the existence of long-range order, determine the associated critical exponents of the flat phase and compare the results to the predictions of various theoretical models.
Simplicial Gravity In Dimension Greater Than Two, Simon Catterall, G. Thorleifsson, John B. Kogut, R. Renken
Simplicial Gravity In Dimension Greater Than Two, Simon Catterall, G. Thorleifsson, John B. Kogut, R. Renken
Physics - All Scholarship
We consider two issues in the DT model of quantum gravity. First, it is shown that the triangulation space for D>3 is dominated by triangulations containing a single singular (D-3)-simplex composed of vertices with divergent dual volumes. Second we study the ergodicity of current simulation algorithms. Results from runs conducted close to the phase transition of the four-dimensional theory are shown. We see no strong indications of ergodicity br eaking in the simulation and our data support recent claims that the transition is most probably first order. Furthermore, we show that the critical properties of the system are determined …
Comment On "Moving Glass Phase Of Driven Lattices", Leon Balents, M. Cristina Marchetti, Leo Radzihovsky
Comment On "Moving Glass Phase Of Driven Lattices", Leon Balents, M. Cristina Marchetti, Leo Radzihovsky
Physics - All Scholarship
We consider a periodic lattice rapidly driven through a quenched random potential as a model of a moving Abrikosov lattice. In addition to the transverse phonon displacements u_y, we consider the displacements u_x along the direction of motion, which were assumed to be small in earlier treatments. We show that these displacements are in fact divergent even on large length scales and therefore lead to a breakdown of the elastic model along the direction of motion. We propose that the resulting phase is a moving "smectic" with translational order that is quasi-long-range transverse and liquid-like parallel to the direction of …
Hidden Structure In A Lagrangian For Hyperfine Splitting Of The Heavy Baryons, Joseph Schechter, Masayasu Harada, Asif Qamar, Francesco Sannino, Herbert Weigel
Hidden Structure In A Lagrangian For Hyperfine Splitting Of The Heavy Baryons, Joseph Schechter, Masayasu Harada, Asif Qamar, Francesco Sannino, Herbert Weigel
Physics - All Scholarship
We investigate the hyperfine splitting of the heavy baryons in the bound-state approach. We start with an ordinary relativistic Lagrangian which has been extensively used to discuss finite mass corrections to the heavy limit predictions. It turns out that the dominant contribution arises from terms which do not manifestly break the heavy spin symmetry. The actual heavy spin violating terms are uncovered by carefully performing a 1/M expansion of this Lagrangian.
Efficient Heuristic Search Algorithms For Soft-Decision Decoding Of Linear Block Codes, Ching-Cheng Shih, C. R. Wulff, Carlos R.P. Hartmann, Chilukuri K. Mohan
Efficient Heuristic Search Algorithms For Soft-Decision Decoding Of Linear Block Codes, Ching-Cheng Shih, C. R. Wulff, Carlos R.P. Hartmann, Chilukuri K. Mohan
Electrical Engineering and Computer Science - Technical Reports
This paper deals with maximum-likelihood soft-decision decoding as well as suboptimal soft-decision decoding of linear block codes. In this paper we present a novel and efficient hybrid decoding algorithm for (n, k) linear block codes. This algorithm consists of three new decoding algorithms: M A*, H*, and Directed Search. It hybridizes these three algorithms to take advantage of their strengths and make the decoding more efficient. The first algorithm, M A*, is a modified Algorithm A* that conducts a heuristic search through a code tree of the transmitted code when the decoding problem is transformed into a problem of graph-search …
Cleavage Of Dna By The Insulin-Mimetic Compound, Nh4[Vo(O2)2(Phen)], Catharina Hiort, Jerry Goodisman, James C. Dabrowiak
Cleavage Of Dna By The Insulin-Mimetic Compound, Nh4[Vo(O2)2(Phen)], Catharina Hiort, Jerry Goodisman, James C. Dabrowiak
Chemistry - All Scholarship
The kinetics and mechanism of cleavage of DNA by the insulin-mimetic peroxo-vanadate NH4[VO(O2)2(phen)], pV, are described. In the presence of low energy UV radiation or biologically common reducing agents, pV decomposes into the monomer, dimer, and tetramer of vanadate and an uncharacterized compound of V4+ as shown by 51V NMR, ESR, and absorption spectra. The rate of photodecomposition of pV is reduced in the presence of calf thymus DNA, indicating that a decomposition product of the peroxo-vanadate, that is important in the destruction pathway of the complex, is interacting with DNA. This species, probably a short-lived complex of V4+, may …
The Flat Phase Of Crystalline Membranes, Simon Catterall, Mark Bowick, Konstantinos N. Anagnostopoulos
The Flat Phase Of Crystalline Membranes, Simon Catterall, Mark Bowick, Konstantinos N. Anagnostopoulos
Physics - All Scholarship
We present the results of a high-statistics Monte Carlo simulation of a phantom crystalline (fixed-connectivity) membrane with free boundary. We verify the existence of a flat phase by examining lattices of size up to 128^2. The Hamiltonian of the model is the sum of a simple spring pair potential, with no hard-core repulsion, and bending energy. The only free parameter is the the bending rigidity \kappa. In-plane elastic constants are not explicitly introduced. We obtain the remarkable result that this simple model dynamically generates the elastic constants required to stabilise the flat phase. We present measurements of the size (Flory) …
The Flat Phase Of Crystalline Membranes, Mark Bowick, Simon Catterall, Marco Falcioni, Gudmar Thorleifsson, Konstantinos N. Anagnostopoulos
The Flat Phase Of Crystalline Membranes, Mark Bowick, Simon Catterall, Marco Falcioni, Gudmar Thorleifsson, Konstantinos N. Anagnostopoulos
Physics - All Scholarship
We present the results of a high-statistics Monte Carlo simulation of a phantom crystalline (fixed-connectivity) membrane with free boundary. We verify the existence of a flat phase by examining lattices of size up to $128^2$. The Hamiltonian of the model is the sum of a simple spring pair potential, with no hard-core repulsion, and bending energy. The only free parameter is the the bending rigidity $\kappa$. In-plane elastic constants are not explicitly introduced. We obtain the remarkable result that this simple model dynamically generates the elastic constants required to stabilise the flat phase. We present measurements of the size (Flory) …
Vortex Dynamics And Defects In Simulated Flux Flow, Alan Middleton, Michael Chance Faleski, M. C. Marchetti
Vortex Dynamics And Defects In Simulated Flux Flow, Alan Middleton, Michael Chance Faleski, M. C. Marchetti
Physics - All Scholarship
We present the results of molecular dynamic simulations of a two-dimensional vortex array driven by a uniform current through random pinning centers at zero temperature. We identify two types of flow of the driven array near the depinning threshold. For weak disorder the flux array contains few dislocation and moves via correlated displacements of patches of vortices in a {\it crinkle} motion. As the disorder strength increases, we observe a crossover to a spatially inhomogeneous regime of {\it plastic} flow, with a very defective vortex array and a channel-like structure of the flowing regions. The two regimes are characterized by …
Scaling Behavior In Soliton Models, Joseph Schechter, Masayasu Harada, F. Sannino, H. Weigel
Scaling Behavior In Soliton Models, Joseph Schechter, Masayasu Harada, F. Sannino, H. Weigel
Physics - All Scholarship
In the framework of chiral soliton models we study the behavior of static nucleon properties under rescaling of the parameters describing the effective meson theory. In particular we investigate the question of whether the Brown--Rho scaling laws are general features of such models. When going beyond the simple Skyrme model we find that restrictive constraints need to be imposed on the mesonic parameters in order to maintain these scaling laws. Furthermore, in the case when vector mesons are included in the model it turns out that the isoscalar form factor no longer scales according to these laws. Finally we note …
Probabilistic Analysis Of The Median Rule: Asymptotics And Applications, Anil Ravindran Menon, Kishan Mehrotra, Chilukuri K. Mohan, Sanjay Ranka
Probabilistic Analysis Of The Median Rule: Asymptotics And Applications, Anil Ravindran Menon, Kishan Mehrotra, Chilukuri K. Mohan, Sanjay Ranka
Electrical Engineering and Computer Science - Technical Reports
The solution of integer optimization problems by relaxation methods consists of three parts. First, the discrete problem is converted into a continuous optimization problem, which is generally more tractable. Second, the relaxed problem is solved efficiently, yielding a optimal solution in the continuous space. Finally, an assignment procedure is used to map this solution to a "suitable" discrete solution. One heuristic - we call it the relaxation heuristic - that often guides the choice and design of assignment algorithms is: "given a continuous optimal solution, the corresponding integer optimal solution is likely to be nearby" (with respect to some well …
A Library-Based Approach To Task Parallelism In A Data-Parallel Language, Ian Foster, David R. Kohr, Rakesh Krishnaiyer, Alok Choudhary
A Library-Based Approach To Task Parallelism In A Data-Parallel Language, Ian Foster, David R. Kohr, Rakesh Krishnaiyer, Alok Choudhary
College of Engineering and Computer Science - Former Departments, Centers, Institutes and Projects
The data-parallel language High Performance Fortran (HPF) does not allow efficient expression of mixed task/data-parallel computations or the coupling of separately compiled data-parallel modules. In this paper, we show how these common parallel program structures can be represented, with only minor extensions to the HPF model, by using a coordination library based on the Message Passing Interface (MPI). This library allows data-parallel tasks to exchange distributed data structures using calls to simple communication functions. We present microbenchmark results that characterize the performance of this library and that quantify the impact of optimizations that allow reuse of communication schedules in common …
Array Decompositions For Nonuniform Computational Environments, Maher Kaddoura, Sanjay Ranka, Albert Wang
Array Decompositions For Nonuniform Computational Environments, Maher Kaddoura, Sanjay Ranka, Albert Wang
College of Engineering and Computer Science - Former Departments, Centers, Institutes and Projects
Two-dimensional arrays are useful in a large variety of scientific and engineering applications. Parallelization of these applications requires the decomposition of array elements among different machines. Several data-decomposition techniques have been studied in the literature for machines with uniform computational power. In this paper we develop new methods for decomposing arrays into a cluster of machines with nonuniform computational power. Simulation results show that our methods provide superior decomposition over naive schemes.
Hierarchical Growing Cell Structures, Vanco Burzevski, Chilukuri K. Mohan
Hierarchical Growing Cell Structures, Vanco Burzevski, Chilukuri K. Mohan
College of Engineering and Computer Science - Former Departments, Centers, Institutes and Projects
We propose a hierarchical self-organizing neural network ("HiGS") with adaptive architecture and simple topological organization. This network combines features of Fritzke's Growing Cell Structures and traditional hierarchical clustering algorithms. The height and width of the tree structure depend on the user-specified level of error desired, and the weights in upper layers of the network do not change in later phases of the learning algorithm. Parameters such as node deletion rate are adaptively modified by the learning algorithm.
A Unified Tiling Approach For Out-Of-Core Computations, Rajesh Bordawekar, Alok Choudhary, J. Ramanujam, Mahmut Kandemir
A Unified Tiling Approach For Out-Of-Core Computations, Rajesh Bordawekar, Alok Choudhary, J. Ramanujam, Mahmut Kandemir
College of Engineering and Computer Science - Former Departments, Centers, Institutes and Projects
This paper describes a framework by which an out-of-core stencil program written in a data-parallel language can be translated into node programs in a distributed-memory message-passing machine with explicit I/O and communication. We focus on a technique called Data Space Tiling to group data elements into slabs that can fit into memories of processors. Methods to choose legal tile shapes under several constraints and deadlock-free scheduling of tiles are investigated. Our approach is unified in the sense that it can be applied to both FORALL loops and the loops that involve flow-dependences.
Shape Recognition Using Genetic Algorithms, Ender Ozcan, Chilukuri K. Mohan
Shape Recognition Using Genetic Algorithms, Ender Ozcan, Chilukuri K. Mohan
College of Engineering and Computer Science - Former Departments, Centers, Institutes and Projects
Shape recognition is a challenging task when shapes overlap, forming noisy, occluded, partial shapes. This paper uses a genetic algorithm for matching input shapes with model shapes described in terms of features such as line segments and angles (extracted using traditional algorithms). The quality of matching is gauged using a measure derived from attributed shape grammars [12, 13]. Preliminary results, using shapes with about 30 features each, are extremely encouraging.
Characterization Of A Class Of Sigmoid Functions With Applications To Neural Networks, Anil Ravindran Menon, Kishan Mehrotra, Chilukuri K. Mohan, Sanjay Ranka
Characterization Of A Class Of Sigmoid Functions With Applications To Neural Networks, Anil Ravindran Menon, Kishan Mehrotra, Chilukuri K. Mohan, Sanjay Ranka
College of Engineering and Computer Science - Former Departments, Centers, Institutes and Projects
Sigmoid functions, whose graphs are “S-shaped” curves, appear in a great variety of contexts, such as the transfer functions in many neural networks. Their ubiquity is no accident; these curves are among the simplest non-linear curves, striking a graceful balance between linear and non-linear behavior. .. This paper undertakes a study of two classes of sigmoids: the simple sigmoids, defined to be odd, asymptotically bounded, completely monotone functions in one variable, and the Hyperbolic sigmoids, a proper subset of simple sigmoids and a natural generalization of the hyperbolic tangent. The class of hyperbolic sigmoids includes a surprising number of well …
Unsupervised Algorithms For Learning Emergent Spatio-Temporal Correlations, Chaitanya Tumuluri
Unsupervised Algorithms For Learning Emergent Spatio-Temporal Correlations, Chaitanya Tumuluri
Electrical Engineering and Computer Science - Technical Reports
Many applications require the extraction of spatiotemporal correlations among dynamically emergent features of non-stationary distributions. In such applications it is not possible to obtain an a priori analytical characterization of the emergent distribution. This paper extends the Growing Cell Structures (GCS) network and presents two novel (GIST and GEST) networks, which combine unsupervised feature-extraction and Hebbian learning, for tracking such emergent correlations. The networks were successfully tested on the challenging Data Mapping problem, using an execution driven simulation of their implementation in hardware. The results of the simulations show the successful use of the GIST and GEST networks for extracting …
A Review Of Commercial And Research Cluster Management Software, Mark Baker, Geoffrey C. Fox, Hon W. Yau
A Review Of Commercial And Research Cluster Management Software, Mark Baker, Geoffrey C. Fox, Hon W. Yau
Northeast Parallel Architecture Center
In the past decade there has been a dramatic shift from mainframe or ‘host-centric’ computing to a distributed ‘client-server’ approach. In the next few years this trend is likely to continue with further shifts towards ‘network-centric’ computing becoming apparent. All these trends were set in motion by the invention of the mass-reproducible microprocessor by Ted Hoff of Intel some twenty-odd years ago. The present generation of RISC microprocessors are now more than a match for mainframes in terms of cost and performance. The long-foreseen day when collections of RISC microprocessors assembled together as a parallel computer could outperform the vector …
Tests Of Random Number Generators Using Ising Model Simulations, Paul D. Coddington
Tests Of Random Number Generators Using Ising Model Simulations, Paul D. Coddington
Northeast Parallel Architecture Center
Large-scale Monte Carlo simulations require high-quality random number generators to ensure correct results. The contrapositive of this statement is also true – the quality of random number generators can be tested by using them in large-scale Monte Carlo simulations. We have tested many commonly used random number generators with high precision Monte Carlo simulations of the 2-d Ising model using the Metropolis, Swendsen-Wang, and Wolff algorithms. This work is being extended to the testing of random number generators for parallel computers. The results of these tests are presented, along with recommendations for random number generators for high-performance computers, particularly for …
An Application Perspective On High-Performance Computing And Communications, Geoffrey C. Fox
An Application Perspective On High-Performance Computing And Communications, Geoffrey C. Fox
Northeast Parallel Architecture Center
We review possible and probable industrial applications of HPCC focusing on the software and hardware issues. Thirty-three separate categories are illustrated by detailed descriptions of five areas -- computational chemistry; Monte Carlo methods from physics to economics; manufacturing; and computational fluid dynamics; command and control; or crisis management; and multimedia services to client computers and settop boxes. The hardware varies from tightly-coupled parallel supercomputers to heterogeneous distributed systems. The software models span HPF and data parallelism, to distributed information systems and object/data flow parallelism on the Web. We find that in each case, it is reasonably clear that "HPCC works …
Snap, Crackle, Webwindows!, Geoffrey C. Fox, Wojtek Furmanski
Snap, Crackle, Webwindows!, Geoffrey C. Fox, Wojtek Furmanski
Northeast Parallel Architecture Center
We elaborate the SNAP---Scalable (ATM) Network and (PC) Platforms---view of computing in the year 2000. The World Wide Web will continue its rapid evolution, and in the future, applications will not be written for Windows NT/95 or UNIX, but rather for WebWindows with interfaces defined by the standards of Web servers and clients. This universal environment will support WebTop productivity tools, such as WebWord, WebLotus123, and WebNotes built in modular dynamic fashion, and undermining the business model for large software companies. We define a layered WebWindows software architecture in which applications are built on top of multi-use services. We discuss …
The Distributed Array Descriptor For A Pcrc Hpf Compiler Version 2.0 Sccs-770d, Bryan Carpenter, James Cowie, Donald Leskiw, Xiaoming Li
The Distributed Array Descriptor For A Pcrc Hpf Compiler Version 2.0 Sccs-770d, Bryan Carpenter, James Cowie, Donald Leskiw, Xiaoming Li
Northeast Parallel Architecture Center
We describe a distributed array descriptor that can be used by a runtime supporting HPFlike compilers. This descriptor captures all five types of alignment and BLOCK and CYCLIC distribution as defined in HPF specification. In essence, this descriptor does not distinguish whole array and array sections. Prior to this version, we had versions 1.0, 1.1, and 1.2. This version is not only an update of previous versions, but more importantly it also directly reflects our current practice in an HPF compilation effort.