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University of Massachusetts Amherst

1996

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Articles 61 - 77 of 77

Full-Text Articles in Physical Sciences and Mathematics

The Dynamics Of The Galatic Bar, Martin D. Weinberg Jan 1996

The Dynamics Of The Galatic Bar, Martin D. Weinberg

Astronomy Department Faculty Publication Series

No abstract provided.

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The Global Rate And Efficiency Of Star Formation In Spiral Galaxies As A Function Of Morphology And Environment, Judith S. Young, Lori Allen, Jeffrey D.P. Kenney, Amy Lesser, Brooks Rownd Jan 1996

The Global Rate And Efficiency Of Star Formation In Spiral Galaxies As A Function Of Morphology And Environment, Judith S. Young, Lori Allen, Jeffrey D.P. Kenney, Amy Lesser, Brooks Rownd

Astronomy Department Faculty Publication Series

CCD images of Hα and R-band emission in 120 spiral galaxies were obtained using the now-retired No. 1-0.9 m telescope of Kitt Peak National Observatory. These images were used to derive the distribution and total flux of continuum-subtracted Hα line emission, and therefore the Hα surface brightnesses and high mass star formation rates in these galaxies. We find a small but significant variation in the mean Hα surface brightness for spiral galaxies along the Hubble sequence; the Sd-Ir galaxies exhibit a mean Hα surface brightness 1.4 times higher than the Sbc-Scd galaxies, and 2-3 times higher than the Sa-Sb galaxies. …

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Indexing Handwriting Using Word Matching, R. Manmatha Jan 1996

Indexing Handwriting Using Word Matching, R. Manmatha

Computer Science Department Faculty Publication Series

There are many historical manuscripts written in a single hand which it would be useful to index. Examples include theW. B. DuBois collection at theUniversity ofMassachusetts and the early Presidential libraries at the Library of Congress. The standard technique for indexing documents is to scan them in, convert them to machine readable form (ASCII) using Optical Character Recognition (OCR) and then index them using a text retrieval engine. However, OCR does not work well on handwriting. Here an alternative scheme is proposed for indexing such texts. Each page of the document is segmented into words. The images of the words …

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Systematics Of Soft Final-State Interactions In B Decays, Jf Donoghue, Eugene Golowich, Aa Petrov, Jm Soares Jan 1996

Systematics Of Soft Final-State Interactions In B Decays, Jf Donoghue, Eugene Golowich, Aa Petrov, Jm Soares

Physics Department Faculty Publication Series

By using very general and well established features of soft strong interactions we show, contrary to conventional expectations, that (i) soft final-state interactions (FSI) do not disappear for large mB, (ii) inelastic rescattering is expected to be the main source of soft FSI phases, and (iii) FSI which interchange charge and/or flavors are suppressed by a power of mB, but are quite likely to be significant at mB≃5GeV. We briefly discuss the influence of these interactions on tests of CP violation and on theoretical calculations of weak decays.

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Improving The Accuracy Of Petri Net-Based Analysis Of Concurrent Programs, A. T. Chamillard, Lori A. Clarke Jan 1996

Improving The Accuracy Of Petri Net-Based Analysis Of Concurrent Programs, A. T. Chamillard, Lori A. Clarke

Computer Science Department Faculty Publication Series

Spurious results are an inherent problem of most static analysis methods. These methods, in an effort to produce conservative results, overestimate the executable behavior of a program. Infeasible paths and imprecise alias resolution are the two causes of such inaccuracies. In this paper we present an approach for improving the accuracy of Petri net-based analysis of concurrent programs by including additional program state information in the Petri net. We present empirical results that demonstrate the improvements in accuracy and, in some cases, the reduction in the search space that result from applying this approach to concurrent Ada programs.

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Tracking Object Motion Across Aspect Changes For Augmented Reality, S. Ravela Jan 1996

Tracking Object Motion Across Aspect Changes For Augmented Reality, S. Ravela

Computer Science Department Faculty Publication Series

A model registration system capable of tracking an object through distinct aspects in real-time is presented. The system integrates tracking, pose determination, and aspect graph indexing. The tracking combines steerable filters with normalized cross-correlation, compensates for rotation in 2D and is adaptive. Robust statistical methods are used in the pose estimation to detect and remove mismatches. The aspect graph is used to determine when features will disappear or become difficult to track an dto predict when and where new features will become trackable. The overall system is stable and is amenable to real-time performance.

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Learning Situation-Specific Coordination In Generalized Partial Global Planning, M. V. Nagendra Prasad, Victor R. Lesser Jan 1996

Learning Situation-Specific Coordination In Generalized Partial Global Planning, M. V. Nagendra Prasad, Victor R. Lesser

Computer Science Department Faculty Publication Series

No abstract provided.

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Theory Of Weak Hypernuclear Decay, Jf Dubach, Gb Feldman, Br Holstein, L Delatorre Jan 1996

Theory Of Weak Hypernuclear Decay, Jf Dubach, Gb Feldman, Br Holstein, L Delatorre

Physics Department Faculty Publication Series

The weak nomesonic decay ofΛ-hypernuclei is studied in the context of a one-meson-exchange model. Predictions are made for the decay rate, thep/nstimulation ratio and the asymmetry in polarized hypernuclear decay.

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Final State Interactions In The Decay Of Heavy Quarks, John Donoghue Jan 1996

Final State Interactions In The Decay Of Heavy Quarks, John Donoghue

Physics Department Faculty Publication Series

I discuss some recent results on the systematic behavior of final state rescattering which makes use of the limit of a heavy B meson. The results suggest that soft final state interactions do not disappear in the large $m_B$ limit. Soft and hard final state phases can both contribute to CP violating asymmetries in B decay. The way that the soft phases occur is interesting theoretically and suggests the violation of local quark-hadron duality.

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Virtual Compton Scattering And Generalized Polarizabilities Of The Nucleon In Heavy Baryon Chiral Perturbation Theory, Thomas Hemmert, Br Holstein, Et. Al Jan 1996

Virtual Compton Scattering And Generalized Polarizabilities Of The Nucleon In Heavy Baryon Chiral Perturbation Theory, Thomas Hemmert, Br Holstein, Et. Al

Physics Department Faculty Publication Series

The spin-independent part of the virtual Compton scattering (VCS) amplitude from the nucleon is calculated within the framework of heavy baryon chiral perturbation theory (HBChPT). The calculation is performed to third order in external momenta according to chiral power counting. The relation of the tree-level amplitudes to what is expected from the low-energy theorem is discussed. We relate the one-loop results to the structure coefficients of a low-energy expansion for the model-dependent part of the VCS amplitude recently defined by Fearing and Scherer. Finally we discuss the connection of our results with the generalized polarizabilities of the nucleon defined by …

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Improving The Convergence Of Su(3) Baryon Chiral Perturbation Theory, John Donoghue, Barry Holstein Jan 1996

Improving The Convergence Of Su(3) Baryon Chiral Perturbation Theory, John Donoghue, Barry Holstein

Physics Department Faculty Publication Series

Baryon chiral perturbation theory as conventionally applied using dimensional regularization has a well-known problem with the convergence of the SU(3) chiral expansion. One can reformulate the theory equally rigorously using a momentum-space cutoff and we show that the convergence is thereby greatly improved for reasonable values of the cutoff. In effect, this is accomplished because the cutoff formalism removes the spurious physics of propagation at distance scales much smaller than the baryon size.

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Exact Quantum Monte Carlo Process For The Statistics Of Discrete Systems, Nikolai Prokof'ev, Boris Svistunov, I Tupitsyn Jan 1996

Exact Quantum Monte Carlo Process For The Statistics Of Discrete Systems, Nikolai Prokof'ev, Boris Svistunov, I Tupitsyn

Physics Department Faculty Publication Series

We propose an exact Monte Carlo approach for the statistics of discrete quantum systems that does not employ the standard partition of the imaginary time into a mesh and does not contain small parameters. The method operates with discrete objects — kinks, describing virtual transitions at different moments in time. The global statistics of the kinks is reproduced by exact local procedures, the main one being based on the known solution for an asymmetric two-level system.

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Execution Performance Issues In Full-Text Information Retrieval, Eric W. Brown Jan 1996

Execution Performance Issues In Full-Text Information Retrieval, Eric W. Brown

Computer Science Department Faculty Publication Series

The task of an information retrieval system is to identify documents that will satisfy a user’s information need. Effective fulfillment of this task has long been an active area of research, leading to sophisticated retrieval models for representing information content in documents and queries and measuring similarity between the two. The maturity and proven effectiveness of these systems has resulted in demand for increased capacity, performance, scalability, and functionality, especially as information retrieval is integrated into more traditional database management environments. In this dissertation we explore a number of functionality and performance issues in information retrieval. First, we consider creation …

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Packet Loss Correlation In The Mbone Multicast Network, Maya Yajnik, Jim Kurose, Don Towsley Jan 1996

Packet Loss Correlation In The Mbone Multicast Network, Maya Yajnik, Jim Kurose, Don Towsley

Computer Science Department Faculty Publication Series

The recent success ofmulticast applications such as Internet teleconferencing illustrates the tremendous potential of applications built upon wide-area multicast communication services. A critical issue for such multicast applications and the higher layer protocols required to support them is the manner in which packet losses occur within the multicast network. In this paper we present and analyze packet loss data collected on multicast-capable hosts at 17 geographically distinct locations in Europe and the US and connected via the MBone. We experimentally and quantitatively examine the spatial and temporal correlation in packet loss among participants in a multicast session. Our results show …

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Knowledge-Directed Vision: Control, Learning, And Integration, Bruce A. Draper, Allen R. Hanson, Edward M. Riseman Jan 1996

Knowledge-Directed Vision: Control, Learning, And Integration, Bruce A. Draper, Allen R. Hanson, Edward M. Riseman

Computer Science Department Faculty Publication Series

The knowledge-directed approach to image interpretation, popular in the 1980's, sought to identify objects in unconstrained two-dimensional images and to determine the threedimensional relationships between these objects and the camera by applying large amounts of object- and domain-specific knowledge to the interpretation problem. Among the primary issues faced by these systems were variations among instances of an object class and differences in how object classes were defined in terms of shape, color, function, texture, size, and/or substructures. This paper argues that knowledge-directed vision systems typically failed for two reasons. The first is that the low- and mid-level vision procedures that …

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Nonperturbative Methods In Kaon Physics (Aside From The Lattice), John Donoghue Jan 1996

Nonperturbative Methods In Kaon Physics (Aside From The Lattice), John Donoghue

Physics Department Faculty Publication Series

I discuss the progress in the use of analytic techniques for low energy QCD, in particular as applied to kaon physics. These methods are becoming increasingly powerful and we have gained a good deal of control over the difficult hadronic interactions. There are continuing developments, and I speculate on the ways that these techniques may become yet more sophisticated in the future.

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Is B→Xsγ Equal To B→Sγ? Spectator Contributions To Rare Inclusive B Decays, John Donoghue, Alexey A. Petrov Jan 1996

Is B→Xsγ Equal To B→Sγ? Spectator Contributions To Rare Inclusive B Decays, John Donoghue, Alexey A. Petrov

Physics Department Faculty Publication Series

In B→Xsγ, there are perturbative QCD corrections at order αs not only to the single quark line process b→sγ but also coming from a set of diagrams where the weak interaction vertex involves a gluon which interacts with the spectator quark in the B hadron. We discuss the impact of the full set of these diagrams. These can influence the decay rate and also the line shape of the photon spectrum as they favor a softer photon energy than does the pure spectator decay b→sγ. A subset of these diagrams generates differences in the decay rates for charged and neutral …

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