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Articles 2461 - 2490 of 2865

Full-Text Articles in Physical Sciences and Mathematics

Remote Ergonomic Research In Space: Spacelab Findings And A Proposal, Stewart I. Donaldson, Harvey Wichman Jan 1996

Remote Ergonomic Research In Space: Spacelab Findings And A Proposal, Stewart I. Donaldson, Harvey Wichman

CGU Faculty Publications and Research

This paper discusses ergonomics research using remotely situated video camerasin spacecraft. Two prototype studies of crewmembers working in the micro-G environments aboard the first two flights of Spacelab are described. Various aspects of crew restraint, stabilization, manipulation of controls, and mobilization were observed, operationally defined, and quantified by observing videotaped scenes of Spacelab crewmembers. In the first study, four performance behaviors were quantified to provide estimates of their frequency of occurrence and variation over the course of each of the flights. The behaviors and their mean percent of observed times were: Hand-Hold 32.2%, Foot Restraint 35.3%, Translation 9.4%, and Struggle …

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An Nmr Investigation Of The Effect Of Hydrogen Bonding On The Rates Of Rotation About The C-N Bonds In Urea And Thiourea, Karl A. Haushalter, Janice Lau, John D. Roberts Jan 1996

An Nmr Investigation Of The Effect Of Hydrogen Bonding On The Rates Of Rotation About The C-N Bonds In Urea And Thiourea, Karl A. Haushalter, Janice Lau, John D. Roberts

All HMC Faculty Publications and Research

The interaction between urea and tetrabutylammonium acetate was investigated in dimethylformamide/ dimethyl sulfoxide solutions using ¹H and 15^N NMR. The chemical-shift behavior of the urea protons is consistent with a urea-acetate hydrogen-bonded complex involving both carboxylate oxygens and the urea hydrogens trans to the carbonyl oxygen with K_assoc = 120 ± 10. Line shape analysis of the temperature-dependent ¹H NMR spectra show that ∆G^‡ for rotation about the C-N bond of urea changes only slightly from 11.0 ± 0.1 to 11.2 ± 0.1 kcal/mol on 1:1 molar addition of tetrabutylammonium acetate to a dilute solution of urea. A parallel investigation …

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Syllogism Solving Under Time Pressure, Gondy Leroy, Koen Lamberts Jan 1996

Syllogism Solving Under Time Pressure, Gondy Leroy, Koen Lamberts

CGU Faculty Publications and Research

No abstract provided.

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Meyer Jerison, 1922-1995, Leonard Gillman, Melvin Henriksen Jan 1996

Meyer Jerison, 1922-1995, Leonard Gillman, Melvin Henriksen

All HMC Faculty Publications and Research

Memories and biography of mathematician Meyer Jerison (b. November 28, 1922 - d. March 19, 1995).

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Complex Dynamics And Multistability In A Damped Harmonic Oscillator With Delayed Negative Feedback, Sue Ann Campbell, Jacques Bélair, Toru Ohira, John Milton Dec 1995

Complex Dynamics And Multistability In A Damped Harmonic Oscillator With Delayed Negative Feedback, Sue Ann Campbell, Jacques Bélair, Toru Ohira, John Milton

WM Keck Science Faculty Papers

A center manifold reduction and numerical calculations are used to demonstrate the presence of limit cycles, two-tori, and multistability in the damped harmonic oscillator with delayed negative feedback. This model is the prototype of a mechanical system operating with delayed feedback. Complex dynamics are thus seen to arise in very plausible and commonly occurring mechanical and neuromechanical feedback systems.

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Effect Of Disorder On Synchronization In Prototype 2-Dimensional Josephson Arrays, Adam S. Landsberg, Yuri Braiman, Kurt Wiesenfeld Dec 1995

Effect Of Disorder On Synchronization In Prototype 2-Dimensional Josephson Arrays, Adam S. Landsberg, Yuri Braiman, Kurt Wiesenfeld

WM Keck Science Faculty Papers

We study the effects of quenched disorder on the dynamics of two-dimensional arrays of overdamped Josephson junctions. Disorder in both the junction critical currents and resistances is considered. Analytical results for small arrays are used to identify a physical mechanism which promotes frequency locking across each row of the array, and to show that no such locking mechanism exists between rows. The intrarow locking mechanism is surprisingly strong, so that a row can tolerate large amounts of disorder before frequency locking is destroyed.

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Tilings In Art And Science, James E, Hall Oct 1995

Tilings In Art And Science, James E, Hall

Humanistic Mathematics Network Journal

No abstract provided.

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Mathematics As An Aesthetic Discipline, J. D. Phillips Oct 1995

Mathematics As An Aesthetic Discipline, J. D. Phillips

Humanistic Mathematics Network Journal

No abstract provided.

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"Modern Mathematics" At Sonoma State University, C. E. Falbo Oct 1995

"Modern Mathematics" At Sonoma State University, C. E. Falbo

Humanistic Mathematics Network Journal

No abstract provided.

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Letter Division, Paul J. Tobias Oct 1995

Letter Division, Paul J. Tobias

Humanistic Mathematics Network Journal

No abstract provided.

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Book Review: Introductory Algebra: A Just In Time Approach, By Alice Kaseberg, Gayle Smith Oct 1995

Book Review: Introductory Algebra: A Just In Time Approach, By Alice Kaseberg, Gayle Smith

Humanistic Mathematics Network Journal

No abstract provided.

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Haiku, Frances Rosamond Oct 1995

Haiku, Frances Rosamond

Humanistic Mathematics Network Journal

No abstract provided.

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Attitudes Of Students To Independent Learning, S. Kenneth Houston Oct 1995

Attitudes Of Students To Independent Learning, S. Kenneth Houston

Humanistic Mathematics Network Journal

No abstract provided.

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From The Editor, Alvin White Oct 1995

From The Editor, Alvin White

Humanistic Mathematics Network Journal

No abstract provided.

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The Questionable Probability Theory Behind The Strange Story Of The Bell Curve's Bell Curve, Miriam Lipschütz-Yevick Oct 1995

The Questionable Probability Theory Behind The Strange Story Of The Bell Curve's Bell Curve, Miriam Lipschütz-Yevick

Humanistic Mathematics Network Journal

No abstract provided.

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Voices From The Reform Movement, Allyn Jackson Oct 1995

Voices From The Reform Movement, Allyn Jackson

Humanistic Mathematics Network Journal

No abstract provided.

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Mathematizing, Lee Goldstein Oct 1995

Mathematizing, Lee Goldstein

Humanistic Mathematics Network Journal

No abstract provided.

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A University Mathematician's View Of What's Wrong With University Mathematics Education, Reuben Hersh Oct 1995

A University Mathematician's View Of What's Wrong With University Mathematics Education, Reuben Hersh

Humanistic Mathematics Network Journal

No abstract provided.

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The Most Humanistic Mathematician: Florentin Smarandache, Joanne S. Growney Oct 1995

The Most Humanistic Mathematician: Florentin Smarandache, Joanne S. Growney

Humanistic Mathematics Network Journal

No abstract provided.

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Poem In Arithmetic Space, Larry Seagull Oct 1995

Poem In Arithmetic Space, Larry Seagull

Humanistic Mathematics Network Journal

No abstract provided.

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Strong X-Ray Emission From High-Temperature Plasmas Produced By Intense Irradiation Of Clusters, T. Ditmire, Thomas D. Donnelly, R. W. Falcone, M. D. Perry Oct 1995

Strong X-Ray Emission From High-Temperature Plasmas Produced By Intense Irradiation Of Clusters, T. Ditmire, Thomas D. Donnelly, R. W. Falcone, M. D. Perry

All HMC Faculty Publications and Research

The interaction of an intense laser pulse with large (∼100Å) clusters present in pulsed gas jets is shown to produce novel plasmas with electron temperatures far in excess of that predicted by above-threshold ionization theory. The enhanced absorption of the laser light by the dense clusters results in the production of high ion charge states via collisional ionization resulting in strong x-ray emission from the hot plasma.

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Disorder And Synchronization In A Josephson Junction Plaquette, Adam S. Landsberg, Yuri Braiman, Kurt Wiesenfeld Sep 1995

Disorder And Synchronization In A Josephson Junction Plaquette, Adam S. Landsberg, Yuri Braiman, Kurt Wiesenfeld

WM Keck Science Faculty Papers

We describe the effects of disorder on the coherence properties of a 2 x 2 array of Josephson junctions (a "plaquette"). The disorder is introduced through variations in the junction characteristics. We show that the array will remain one-to-one frequency locked despite large amounts of the disorder, and determine analytically the maximum disorder that can be tolerated before a transition to a desynchronized state occurs. Connections with larger N x M arrays are also drawn.

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Branches Of Radial Solutions For Semipositone Problems, Alfonso Castro, Sudhasree Gadam, Ratnasingham Shivaji Jul 1995

Branches Of Radial Solutions For Semipositone Problems, Alfonso Castro, Sudhasree Gadam, Ratnasingham Shivaji

All HMC Faculty Publications and Research

We consider the radially symmetric solutions to the equation −Δu(x) = λƒ(u(x)) for x ∈ Ω, u(x) = 0 for x ∈ ∂Ω, where Ω denotes the unit ball in RN (N > 1), centered at the origin and λ > 0. Here ƒ: R→R is assumed to be semipositone (ƒ(0) < 0), monotonically increasing, superlinear with subcritical growth on [0, ∞). We establish the structure of radial solution branches for the above problem. We also prove that if ƒ is convex and ƒ(t)/(tƒ'(t)−ƒ(t)) is a nondecreasing function then for each λ > 0 there exists at most one positive solution u such that (λ, u) belongs to the unbounded branch of positive solutions. Further when ƒ(t) = tp − k, k > 0 and 1 < p < (N + 2)/(N − 2), we prove that the set of positive solutions is connected. Our results are motivated by and extend the developments in [4].

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A High-Bandwidth Frequency-Domain Photon Migration Instrument For Clinical Use, Steen J. Madsen, Eric R. Anderson, Richard C. Haskell, Bruce J. Tromberg May 1995

A High-Bandwidth Frequency-Domain Photon Migration Instrument For Clinical Use, Steen J. Madsen, Eric R. Anderson, Richard C. Haskell, Bruce J. Tromberg

All HMC Faculty Publications and Research

We have developed a high-bandwidth frequency-domain photon migration (FDPM) instrument which is capable of noninvasively determining the optical properties of biological tissues in near-real-time. This portable, inexpensive, diode-based instrument is unique in the sense that we employ direct diode laser modulation and avalanche photodiode detection. Diffusion models were used to extract the optical properties (absorption and transport scattering coefficients)of tissue-simulating solutions.from the 300 kHz to I GHz photon density wave data.

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Distortion And Evolution Of A Localized Vortex In An Irrotational Flow, Joseph F. Lingevitch, Andrew J. Bernoff May 1995

Distortion And Evolution Of A Localized Vortex In An Irrotational Flow, Joseph F. Lingevitch, Andrew J. Bernoff

All HMC Faculty Publications and Research

This paper examines the interaction of an axisymmetric vortex monopole, such as a Lamb vortex, with a background irrotational flow. At leading order, the monopole is advected with the background flow velocity at the center of vorticity. However, inhomogeneities of the flow will cause the monopole to distort. It is shown that a shear‐diffusion mechanism, familiar from the study of mixing of passive scalars, plays an important role in the evolution of the vorticity distribution. Through this mechanism, nonaxisymmetric vorticity perturbations which do not shift the center of vorticity are homogenized along streamlines on a Re1/3 time scale, much faster …

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Visible Luminescence From Single Crystal‐Silicon Quantum Wells, Peter N. Saeta, A. C. Gallagher May 1995

Visible Luminescence From Single Crystal‐Silicon Quantum Wells, Peter N. Saeta, A. C. Gallagher

All HMC Faculty Publications and Research

Single crystal‐silicon quantum wells with SiO2 barriers have been grown from SIMOX silicon‐on‐insulator substrates. Photoluminescence in the red and near‐infrared is observed for average well width <8 >nm, with peak signal for 2‐nm average width. The luminescence spectrum is independent of well width for SiO2 barriers, but shifts 0.3 eV to higher energy upon removal of the upper oxide layer with HF. Both results suggest the importance of radiation from surface states.

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Descartes And Problem-Solving, Judith V. Grabiner Apr 1995

Descartes And Problem-Solving, Judith V. Grabiner

Pitzer Faculty Publications and Research

What can Descartes' Geometry teach us about problem solving?

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Dynamics Of Optical-Field-Ionized Plasmas For X-Ray Lasers, Thomas D. Donnelly, R. W. Lee, R. W. Falcone Apr 1995

Dynamics Of Optical-Field-Ionized Plasmas For X-Ray Lasers, Thomas D. Donnelly, R. W. Lee, R. W. Falcone

All HMC Faculty Publications and Research

The success of recombination-pumped x-ray laser schemes is determined by the kinetics of ions in plasmas with relatively dense, cold-electron distributions. We examine how laser gain in such systems is affected by a multipeaked electron distribution generated by sequential ionization of atoms using high-intensity, ultrashort-pulse lasers. We also investigate the role of heating processes that modify electron energy distributions during the recombination and the accompanying collisional cascade. We find that conditions for the success of these schemes are critically modified by the inclusion of these effects.

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Sensible Rules For Remembering Duals -- The S-O-B Method, Arthur T. Benjamin Mar 1995

Sensible Rules For Remembering Duals -- The S-O-B Method, Arthur T. Benjamin

All HMC Faculty Publications and Research

We present a natural motivation and simple mnemonic for creating the dual LP of any linear programing problem.

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Phase Velocity Limit Of High-Frequency Photon Density Waves, Richard C. Haskell, Lars O. Svaasand, Steen J. Madsen, Fabio E. Rojas, Ti-Chen C. Feng, Bruce J. Tromberg Feb 1995

Phase Velocity Limit Of High-Frequency Photon Density Waves, Richard C. Haskell, Lars O. Svaasand, Steen J. Madsen, Fabio E. Rojas, Ti-Chen C. Feng, Bruce J. Tromberg

All HMC Faculty Publications and Research

In frequency-domain photonmigration (FDPM), two factors make high modulation frequencies desirable. First, with frequencies as high as a few GHz, the phase lag versus frequency plot has sufficient curvature to yield both the scattering and absorption coefficients of the tissue under examination. Second, because of increased attenuation, highfrequency photon density waves probe smaller volumes, an asset in small volume in vivo or in vitro studies. This trend toward higher modulation frequencies has led us to reexamine the derivation of the standard diffusion equation (SDE)from the Boltzman transport equation. We find that a second-order time-derivative term, ordinarily neglected in the derivation, …

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