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Series

2001

All HMC Faculty Publications and Research

Articles 1 - 8 of 8

Full-Text Articles in Physics

Scroll Waves In The Presence Of Slowly Varying Anisotropy With Application To The Heart, S. Setayeshgar, Andrew J. Bernoff Dec 2001

Scroll Waves In The Presence Of Slowly Varying Anisotropy With Application To The Heart, S. Setayeshgar, Andrew J. Bernoff

All HMC Faculty Publications and Research

We consider the dynamics of scroll waves in the presence of rotating anisotropy, a model of the left ventricle of the heart in which the orientation of fibers in successive layers of tissue rotates. By choosing a coordinate system aligned with the fiber rotation and studying the phase dynamics of a straight but twisted scroll wave, we derive a Burgers’ equation with forcing associated with the fiber rotation rate. We present asymptotic solutions for scroll twist, verified by numerics, using a realistic fiber distribution profile. We make connection with earlier numerical and analytical work on scroll dynamics.

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Transformation Of Statistics In Fractional Quantum Hall Systems, John J. Quinn, Arkadiusz Wojs, Jennifer J. Quinn, Arthur T. Benjamin Oct 2001

Transformation Of Statistics In Fractional Quantum Hall Systems, John J. Quinn, Arkadiusz Wojs, Jennifer J. Quinn, Arthur T. Benjamin

All HMC Faculty Publications and Research

A Fermion to Boson transformation is accomplished by attaching to each Fermion a tube carrying a single quantum of flux oriented opposite to the applied magnetic field. When the mean field approximation is made in Haldane’s spherical geometry, the Fermion angular momentum lF is replaced by lB =lF − 1/2 (N −1). The set of allowed total angular momentum multiplets is identical in the two different pictures. The Fermion and Boson energy spectra in the presence of many body interactions are identical only if the pseudopotential V (interaction energy as a function of pair angular …

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Distinguishing Surface And Bulk Contributions To Third-Harmonic Generation In Silicon, Peter N. Saeta, Nathan A. Miller '01 Oct 2001

Distinguishing Surface And Bulk Contributions To Third-Harmonic Generation In Silicon, Peter N. Saeta, Nathan A. Miller '01

All HMC Faculty Publications and Research

We report measurements of third-harmonic generation from ultrathin crystalline silicon layers of gradually varying thickness. Both the angular and thickness dependence of the third-harmonic light generated in transmission at normal incidence are consistent with negligible surface contribution to third-harmonic generation in silicon, even under tight focusing. This work illustrates a method for distinguishing surface and bulk contributions to harmonic generation.

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Transcribing Spacetime Data Into Matrices, Vatche Sahakian Jun 2001

Transcribing Spacetime Data Into Matrices, Vatche Sahakian

All HMC Faculty Publications and Research

In certain supergravity backgrounds, D0 branes may polarize into higher dimensional Dp branes. We study this phenomenon in some generality from the perspective of a local inertial observer and explore polarization effects resulting from tidal-like forces. We find D2 brane droplets made of D0 branes at an extremum of the Born-Infeld action even in scenarios where the RR fields may be zero. These solutions lead us to a local formulation of the UV-IR correspondence. A holographic Planck scale bound on the number of D0 branes plays an important role in the analysis. We focus on the impact of higher order …

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On D0 Brane Polarization By Tidal Forces, Vatche Sahakian May 2001

On D0 Brane Polarization By Tidal Forces, Vatche Sahakian

All HMC Faculty Publications and Research

Gravitational tidal forces may induce polarization of D0-branes, in analogy to the same effects arising in the context of constant background gauge fields. Such phenomena can teach us about the correspondence between smooth curved spacetime and its underlying non-commutative structure. However, unlike polarization by gauge fields, the gravitational counterpart involves concerns regarding the classical stability of the corresponding polarized states. In this work, we study this issue with respect to the solutions presented in hepth0010237 and find that they are classically unstable. The instability however appears with intricate features with all but a few decay channels being lifted. Through a …

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Phase Modulation At 125 Khz In A Michelson Interferometer Using An Inexpensive Piezoelectric Stack Driven At Resonance, Barbara M. Hoeling, Andrew D. Fernandez, Richard C. Haskell, Daniel C. Petersen Mar 2001

Phase Modulation At 125 Khz In A Michelson Interferometer Using An Inexpensive Piezoelectric Stack Driven At Resonance, Barbara M. Hoeling, Andrew D. Fernandez, Richard C. Haskell, Daniel C. Petersen

All HMC Faculty Publications and Research

Fast phase modulation has been achieved in a Michelson interferometer by attaching a lightweight reference mirror to a piezoelectric stack and driving the stack at a resonance frequency of about 125 kHz. The electrical behavior of the piezo stack and the mechanical properties of the piezo-mirror arrangement are described. A displacement amplitude at resonance of about 350 nm was achieved using a standard function generator. Phase drift in the interferometer and piezo wobble were readily circumvented. This approach to phase modulation is less expensive by a factor of roughly 50 than one based on an electro-optic effect.

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Particle Size Determination: An Undergraduate Lab In Mie Scattering, I. Weiner '01, M. Rust '01, Thomas D. Donnelly Feb 2001

Particle Size Determination: An Undergraduate Lab In Mie Scattering, I. Weiner '01, M. Rust '01, Thomas D. Donnelly

All HMC Faculty Publications and Research

A technique for determining the size of microscopic spherical particles using light scattering is presented as an undergraduate physics lab. Scatterer size is determined from angular scattering distribution measurements of laser light scattered from a dilute suspension of latex spheres with diameters of 4.99±0.05 and 6.038±0.045 μm. Previous experiments of this type used approximate theoretical corrections and required the construction of specialized sample cells to minimize complicating effects. As a significant improvement to these, we generate angular scattering distributions from Mie theory and, using an accurate numerical procedure, correct these distributions for Snell’s law and foreshortening effects. Scatterer size …

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Transient Anomalous Diffusion In Poiseuille Flow, Marco Latini '01, Andrew J. Bernoff Jan 2001

Transient Anomalous Diffusion In Poiseuille Flow, Marco Latini '01, Andrew J. Bernoff

All HMC Faculty Publications and Research

We revisit the classical problem of dispersion of a point discharge of tracer in laminar pipe Poiseuille flow. For a discharge at the centre of the pipe we show that in the limit of small non-dimensional diffusion, D, tracer dispersion can be divided into three regimes. For small times (t [double less-than sign] D−1/3), diffusion dominates advection yielding a spherically symmetric Gaussian dispersion cloud. At large times (t [dbl greater-than sign] D−1), the flow is in the classical Taylor regime, for which the tracer is homogenized transversely across the pipe and diffuses with …

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