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University of Massachusetts Amherst

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1999

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Articles 1 - 30 of 59

Full-Text Articles in Physical Sciences and Mathematics

17th International Herman F. Mark Symposium: Polypropylene - A Material Of The Future, Otto Vogl, Helga Roder Dec 1999

17th International Herman F. Mark Symposium: Polypropylene - A Material Of The Future, Otto Vogl, Helga Roder

Emeritus Faculty Author Gallery

No abstract provided.


12. Pierre Sigwalt, Otto Vogl Dec 1999

12. Pierre Sigwalt, Otto Vogl

Emeritus Faculty Author Gallery

No abstract provided.


13. Josef Schurz, Otto Vogl Nov 1999

13. Josef Schurz, Otto Vogl

Emeritus Faculty Author Gallery

No abstract provided.


14. Paolo Galli, Otto Vogl, Anna Maria Marcon-Galli Oct 1999

14. Paolo Galli, Otto Vogl, Anna Maria Marcon-Galli

Emeritus Faculty Author Gallery

No abstract provided.


15. Clement Henry Bamford, Otto Vogl, Daphne Stephen-Bamford Sep 1999

15. Clement Henry Bamford, Otto Vogl, Daphne Stephen-Bamford

Emeritus Faculty Author Gallery

No abstract provided.


The Impact Of Multicast Layering On Network Fairness, Jim Kurose Sep 1999

The Impact Of Multicast Layering On Network Fairness, Jim Kurose

Computer Science Department Faculty Publication Series

Many definitions of fairness for multicast networks assume that sessions are single-rate, requiring that each multicast session trans- mits data to all of its receivers at the same rate. These defini- tions do not account for multi-rate approaches, such as layering, that permit receiving rates within a session to be chosen indepen- dently. We identify four desirable fairness properties for multicast networks, derived from properties that hold within the max-min fair allocations of unicast networks. We extend the definition of multicast max-min fairness to networks that contain multi-rate sessions, and show that all four fairness properties hold in a multi- …


Perturbations Of Spherical Stellar Systems During Fly-By Encounters, E. Vesperini, Martin D. Weinberg Aug 1999

Perturbations Of Spherical Stellar Systems During Fly-By Encounters, E. Vesperini, Martin D. Weinberg

Astronomy Department Faculty Publication Series

We study the internal response of a galaxy to an unbound encounter and present a survey of orbital parameters covering typical encounters in different galactic environments. Overall, we conclude that relatively weak encounters by low-mass interloping galaxies can cause observable distortions in the primaries. The resulting asymmetries may persist long after the interloper is evident. We focus our attention on the production of structure in dark halos and in cluster ellipticals. Any distortion produced in a dark halo can distort the embedded stellar disk, possibly leading to the formation of lopsided and warped disks. We show that distant encounters with …


16. Eli M. Pearce, Otto Vogl, Judith Pearce Aug 1999

16. Eli M. Pearce, Otto Vogl, Judith Pearce

Emeritus Faculty Author Gallery

No abstract provided.


17. Hermann Klare, Otto Vogl, Burkart Philipp Jul 1999

17. Hermann Klare, Otto Vogl, Burkart Philipp

Emeritus Faculty Author Gallery

No abstract provided.


18. Dieter Freitag, Otto Vogl, Karina Rigby Jun 1999

18. Dieter Freitag, Otto Vogl, Karina Rigby

Emeritus Faculty Author Gallery

No abstract provided.


19. Makoto Okawara, Otto Vogl, Teiji Tsuruta, Seiichi Nakahama May 1999

19. Makoto Okawara, Otto Vogl, Teiji Tsuruta, Seiichi Nakahama

Emeritus Faculty Author Gallery

No abstract provided.


Bounded Depth Arithmetic Circuits: Counting And Closure, Eric Allender Apr 1999

Bounded Depth Arithmetic Circuits: Counting And Closure, Eric Allender

Computer Science Department Faculty Publication Series

Constant-depth arithmetic circuits have been defined and studied in [AAD97,ABL98]; these circuits yield the function classes #AC0 and GapAC0. These function classes in turn provide new characterizations of the computational power of threshold circuits, and provide a link between the circuit classes AC0 (where many lower bounds are known) and TC0 (where essentially no lower bounds are known). In this paper, we resolve several questions regarding the closure properties of #AC0 and GapAC0 and characterize #AC0 in terms of counting paths in a family of bounded-width graphs.


20. Hiroshi Inagaki, Otto Vogl, Takeshi Fukuda, Masaki Tsuji Apr 1999

20. Hiroshi Inagaki, Otto Vogl, Takeshi Fukuda, Masaki Tsuji

Emeritus Faculty Author Gallery

No abstract provided.


21. Teiji Tsuruta, Otto Vogl Mar 1999

21. Teiji Tsuruta, Otto Vogl

Emeritus Faculty Author Gallery

No abstract provided.


Determination Of Calcium, Magnesium And Strontium In Soils By Flow Injection Flame Atomic Absorption Spectrometry, Z Arslan, Jf Tyson Jan 1999

Determination Of Calcium, Magnesium And Strontium In Soils By Flow Injection Flame Atomic Absorption Spectrometry, Z Arslan, Jf Tyson

Chemistry Department Faculty Publication Series

No abstract provided.


High-Performance, Flow-Based, Sample Pre-Treatment And Introduction Procedures For Analytical Atomic Spectrometry, Jf Tyson Jan 1999

High-Performance, Flow-Based, Sample Pre-Treatment And Introduction Procedures For Analytical Atomic Spectrometry, Jf Tyson

Chemistry Department Faculty Publication Series

No abstract provided.


A Note On A Symplectic Structure On The Space Of G-Monopoles, M Finkelberg, A Kuznetsov, N Markarian, I Mirkovic Jan 1999

A Note On A Symplectic Structure On The Space Of G-Monopoles, M Finkelberg, A Kuznetsov, N Markarian, I Mirkovic

Mathematics and Statistics Department Faculty Publication Series

Let G be a semisimple complex Lie group with a Borel subgroup B. Let X=G/B be the flag manifold of G. Let C=\PP1 ' ¥Unknown control sequence '\PP' be the projective line. Let a Î H2(\bX,\Bbb Z)Unknown control sequence '\bX'. The moduli space of G-monopoles of topological charge f is naturally identified with the space \CMb(\bX,a)Unknown control sequence '\CM' of based maps from (C,X) to (X,B) of degree f. The moduli space of G-monopoles carries a natural hyperkähler structure, and hence a holomorphic symplectic structure. It was explicitly computed by R. Bielawski in …


Hyperon Physics—A Personal Overview, Br Holstein Jan 1999

Hyperon Physics—A Personal Overview, Br Holstein

Physics Department Faculty Publication Series

A range of issues in the field of hyperon physics is presented, together with an assessment of where important challenges remain.


Overlapping Branes In M-Theory, Jerome Gauntlett, David Kastor, Jennie Traschen Jan 1999

Overlapping Branes In M-Theory, Jerome Gauntlett, David Kastor, Jennie Traschen

Physics Department Faculty Publication Series

We construct new supersymmetric solutions of D = 11 supergravity describing n orthogonally “overlapping” membranes and fivebranes for n = 2,…,8. Overlapping branes arise after separating intersecting branes in a direction transverse to all of the branes. The solutions, which generalize known intersecting brane solutions, preserve at least 2−n of the supersymmetry. Each pairwise overlap involves a membrane overlapping a membrane in a 0-brane, a fivebrane overlapping a fivebrane in a 3-brane or a membrane overlapping a fivebrane in a string. After reducing n overlapping membranes to obtain n overlapping D-2-branes in D = 10, T-duality generates new overlapping D-brane …


Electric Dipole Moment Of A Bps Monopole, David Kastor, Euy Na Jan 1999

Electric Dipole Moment Of A Bps Monopole, David Kastor, Euy Na

Physics Department Faculty Publication Series

Monopole “superpartner” solutions are constructed by acting with finite, broken supersymmetry transformations on a bosonic N=2 BPS monopole. The terms beyond first order in this construction represent the back reaction of the fermionic zero-mode state on the other fields. Because of the quantum nature of the fermionic zero modes, the superpartner solution is necessarily operator valued. We extract the electric dipole moment operator and show that it is proportional to the fermion zero-mode angular momentum operator with a gyroelectric ratio g=2. The magnetic quadrupole operator is shown to vanish identically on all states. We comment on the usefulness of the …


Infrared Behavior Of Graviton-Graviton Scattering, Jf Donoghue, T Torma Jan 1999

Infrared Behavior Of Graviton-Graviton Scattering, Jf Donoghue, T Torma

Physics Department Faculty Publication Series

The quantum effective theory of general relativity, independent of the eventual full theory at high energy, expresses graviton-graviton scattering at one loop order O 􀀀 E4 with only one parameter, Newton’s constant. Dunbar and Norridge have calculated the one loop amplitude using string based techniques. We complete the calculation by showing that the 1 d−4 divergence which remains in their result comes from the infrared sector and that the cross section is finite and model independent when the usual bremsstrahlung diagrams are included.


Resonances In Weak Nonleptonic Omega(-) Decay, B Borasoy, Br Holstein Jan 1999

Resonances In Weak Nonleptonic Omega(-) Decay, B Borasoy, Br Holstein

Physics Department Faculty Publication Series

We examine the importance of JP=1/2+,1/2- resonances for weak nonleptonic Ω- decays within the framework of chiral perturbation theory. The spin-1/2 resonances are included into an effective theory and the tree contributions to the Ω- decays are calculated. We find significant contributions to the decay amplitudes and satisfactory agreement with experiment. This confirms and extends previous results wherein such spin-1/2 resonances were included in nonleptonic and radiative-nonleptonic hyperon decays.


Role Of Resonances In Nonleptonic Hyperon Decays, B Borasoy, Br Holstein Jan 1999

Role Of Resonances In Nonleptonic Hyperon Decays, B Borasoy, Br Holstein

Physics Department Faculty Publication Series

We examine the importance of resonances for the nonleptonic hyperon decays in the framework of chiral perturbation theory. Lower lying resonances are included in the effective theory. Integrating out the heavy degrees of freedom in the resonance saturation scheme generates higher order counterterms in the effective Lagrangian, providing an estimate of the pertinent coupling constants. A fit to the eight independent decay amplitudes that are not related by isospin symmetry is performed and reasonable agreement for both s and p waves is achieved.


Non-Leptonic Hyperon Decays In Chiral Perturbation Theory, B Borasoy, Br Holstein Jan 1999

Non-Leptonic Hyperon Decays In Chiral Perturbation Theory, B Borasoy, Br Holstein

Physics Department Faculty Publication Series

The non-leptonic hyperon decays are analyzed up to one-loop order including all counterterms in the framework of heavy baryon chiral perturbation theory. We use the exchange of the spin- decuplet resonances as an indication of which low-energy constants contribute significantly to these investigated processes. We choose four independent decay amplitudes that are not related by isospin relations in order to perform a fit for the pertinent low-energy constants and find a satisfactory fit both for s- and p-waves. The chiral corrections to the lowest order forms for the s-waves are moderate whereas there are significant modifications of the p-wave amplitudes.


An Adaptive Algorithm For N-Body Field Expansions, Md Weinberg Jan 1999

An Adaptive Algorithm For N-Body Field Expansions, Md Weinberg

Astronomy Department Faculty Publication Series

An expansion of a density field or particle distribution in basis functions that solve the Poisson equation both provides an easily parallelized N-body force algorithm and simplifies perturbation theories. The expansion converges quickly and provides the highest computational advantage if the lowest order potential-density pair in the basis looks like the unperturbed galaxy or stellar system. Unfortunately, there are only a handful of such bases in the literature that limit this advantage. This paper presents an algorithm for deriving these bases to match a wide variety of galaxy models. The method is based on efficient numerical solution of the Sturm-Liouville …


Closing In On Omega(M): The Amplitude Of Mass Fluctuations From Galaxy Clusters And The Ly Alpha Forest, Dh Weinberg, Rac Croft, L Hernquist, N Katz, M Pettini Jan 1999

Closing In On Omega(M): The Amplitude Of Mass Fluctuations From Galaxy Clusters And The Ly Alpha Forest, Dh Weinberg, Rac Croft, L Hernquist, N Katz, M Pettini

Astronomy Department Faculty Publication Series

We estimate the present-day value of the matter density parameter ΩM by combining constraints from the galaxy cluster mass function with Croft et al.'s recent measurement of the mass power spectrum, P(k), from Lyα forest data. The key assumption of the method is that cosmic structure formed by gravitational instability from Gaussian primordial fluctuations. For a specified value of ΩM, matching the observed cluster mass function then fixes the value of σ8, the rms amplitude of mass fluctuations in 8 h-1 Mpc spheres, and it thus determines the normalization of P …


Properties Of Galaxy Clusters: Mass And Correlation Functions, F Governato, A Babul, T Quinn, P Tozzi, Cm Baugh, N Katz, G Lake Jan 1999

Properties Of Galaxy Clusters: Mass And Correlation Functions, F Governato, A Babul, T Quinn, P Tozzi, Cm Baugh, N Katz, G Lake

Astronomy Department Faculty Publication Series

We analyse parallel N-body simulations of three cold dark matter (CDM) universes to study the abundance and clustering of galaxy clusters. The simulation boxes are 500 h−1 Mpc on a side and cover a volume comparable to that of the forthcoming Sloan Digital Sky Survey. The use of a treecode algorithm and 47 million particles allows us at the same time to achieve high mass and force resolution. We are thus able to make robust measurements of cluster properties with good number statistics up to a redshift larger than unity. We extract haloes using two independent, public domain …


The Clustering Of High-Redshift Galaxies In The Cold Dark Matter Scenario, N Katz, L Hernquist, Dh Weinberg Jan 1999

The Clustering Of High-Redshift Galaxies In The Cold Dark Matter Scenario, N Katz, L Hernquist, Dh Weinberg

Astronomy Department Faculty Publication Series

We investigate the clustering of high-redshift galaxies in five variants of the cold dark matter (CDM) scenario, using hydrodynamic cosmological simulations that resolve the formation of systems with circular velocities vc ≥ 100 km s-1 (Ω = 1) or vc ≥ 70 km s-1 (Ω = 0.4). Although the five models differ in their cosmological parameters and in the shapes and amplitudes of their mass power spectra, they predict remarkably similar galaxy clustering at z = 2, 3, and 4. The galaxy correlation functions show almost no evolution over this redshift range, even though the mass …


The Power Spectrum Of Mass Fluctuations Measured From The Ly Alpha Forest At Redshift Z=2.5, Rac Croft, Dh Weinberg, M Pettini, L Hernquist, N Katz Jan 1999

The Power Spectrum Of Mass Fluctuations Measured From The Ly Alpha Forest At Redshift Z=2.5, Rac Croft, Dh Weinberg, M Pettini, L Hernquist, N Katz

Astronomy Department Faculty Publication Series

We measure the linear power spectrum of mass-density fluctuations at redshift z = 2.5 from the Lyα forest absorption in a sample of 19 QSO spectra, using the method introduced by Croft et al. The P(k) measurement covers the range 2π/k ~ 450-2350 km s-1 (2-12 comoving h-1 Mpc for Ω = 1), limited on the upper end by uncertainty in fitting the unabsorbed QSO continuum and on the lower end by finite spectral resolution (0.8-2.3 Å FWHM) and by nonlinear dynamical effects. We examine a number of possible sources of systematic error and …


The Nature Of Lyman Break Galaxies In Cosmological Hydrodynamic Simulations, R Dave, J Gardner, L Hernquist, N Katz, D Weinberg Jan 1999

The Nature Of Lyman Break Galaxies In Cosmological Hydrodynamic Simulations, R Dave, J Gardner, L Hernquist, N Katz, D Weinberg

Astronomy Department Faculty Publication Series

What type of objects are being detected as $z\sim 3$ "Lyman break galaxies"? Are they predominantly the most massive galaxies at that epoch, or are many of them smaller galaxies undergoing a short-lived burst of merger-induced star formation? We attempt to address this question using high-resolution cosmological hydrodynamic simulations including star formation and feedback. Our $\Lambda$CDM simulation, together with Bruzual-Charlot population synthesis models, reproduces the observed number density and luminosity function of Lyman break galaxies when dust is incorporated. The inclusion of dust is crucial for this agreement. In our simulation, these galaxies are predominantly the most massive objects at …