Open Access. Powered by Scholars. Published by Universities.®

Physics Commons™

Open Access. Powered by Scholars. Published by Universities.®

2002

All Physics Faculty Publications

Articles 1 - 14 of 14

Full-Text Articles in Physics

Poiseuille Advection Of Chemical Reaction Fronts: Eikonal Approximation, R. S. Spangler, Boyd F. Edwards, J. Chem Dec 2002

Poiseuille Advection Of Chemical Reaction Fronts: Eikonal Approximation, R. S. Spangler, Boyd F. Edwards, J. Chem

All Physics Faculty Publications

An eikonal equation including fluid advection is derived from the cubic reaction-diffusion-advection equation, and is used to investigate the speeds and shapes of chemical reaction fronts subject to Poiseuille flow between parallel plates. Although the eikonal equation is usually regarded as valid when the front thickness is small compared to the radius of curvature of the front and to the size of the system, it is also found to be valid when the reaction front is thick with respect to the gap width. This new regime of applicability of the eikonal equation is consistent with its derivation, which requires only …

Go to article

Statistical Characteristics Ofsprite Halo Events Using Coincident Photometric And Imaging Data, R. Miyasato, Michael J. Taylor, H. Fukunishi, Y. Takahashi, H. Nielsen Nov 2002

Statistical Characteristics Ofsprite Halo Events Using Coincident Photometric And Imaging Data, R. Miyasato, Michael J. Taylor, H. Fukunishi, Y. Takahashi, H. Nielsen

All Physics Faculty Publications

Sprite halos are brief, diffuse flashes, which occur at the top of a sprite and precede the development of streamer structures at lower altitudes. We have investigated the characteristics of sprite halos in detail using coincident photometric and imaging data obtained during the Sprites'96 and '99 campaign in Colorado and Wyoming, USA. It is found that the average altitude of the centroid of the halo emission and the mean horizontal diameter of the halo events are ∼80 and ∼86 km, respectively, while the average speed of the descending motion of the sprite halos was ∼4.3 × 107 m/s. It …

Go to article

Influence Of Terrain On Scaling Laws For River Networks, D. A. Vasquez, D. H. Smith, Boyd F. Edwards Nov 2002

Influence Of Terrain On Scaling Laws For River Networks, D. A. Vasquez, D. H. Smith, Boyd F. Edwards

All Physics Faculty Publications

The upper Cheat River network departs from scaling laws describing a large number of river networks in North America. This departure is traced to its corrugated terrain. The more typical random terrain of the lower Cheat River network obeys the standard scaling laws. We modify the random network model of Scheidegger to include the effects of topography, reproducing the behavior observed in the Cheat River basin.

Go to article

Femtosecond Pump-Probe Reflectivity Study Of Silicon Carrier Dynamics, A. J. Sabbah, D. Mark Riffe Oct 2002

Femtosecond Pump-Probe Reflectivity Study Of Silicon Carrier Dynamics, A. J. Sabbah, D. Mark Riffe

All Physics Faculty Publications

We have studied the ultrafast optical response of native-oxide terminated Si(001) with pump-probe reflectivity using 800 nm, 28 fs pulses at an excitation density of (5.5±0.3)×1018cm-3. Time-dependent reflectivity changes comprise third-order-response coherent-transient variations arising from anisotropic state filling and linear-response variations arising from excited free carriers, state filling, and lattice heating. A time constant of 32±5fs associated with momentum relaxation is extracted from the coherent-transient variations. The state-filling and free-carrier responses are sensitive to carrier temperature, allowing an electron-phonon energy relaxation time of 260±30fs to be measured. The recovery of the reflectivity signal back towards its …

Go to article

Poiseuille Advection Of Chemical Reaction Fronts, Boyd F. Edwards Aug 2002

Poiseuille Advection Of Chemical Reaction Fronts, Boyd F. Edwards

All Physics Faculty Publications

Poiseuille flow between parallel plates alters the shapes and velocities of chemical reaction fronts. In the narrow-gap limit, the cubic reaction-diffusion-advection equation predicts a front-velocity correction equal to the gap-averaged fluid velocity ϵ. In the singular wide-gap limit, the correction equals the midgap fluid velocity 3ϵ/2 when the flow is in the direction of propagation of the reaction front, and equals zero for adverse flow of any amplitude for which the front has a midgap cusp. Stationary fronts are possible only for adverse flow and finite gaps. Experiments are suggested.

Go to article

Visual And Lidar Observations Ofnoctilucent Clouds Above Logan, Utah, At 41.7°N, Vincent B. Wickwar, Michael J. Taylor, Joshua P. Herron, B. A. Martineau Apr 2002

Visual And Lidar Observations Ofnoctilucent Clouds Above Logan, Utah, At 41.7°N, Vincent B. Wickwar, Michael J. Taylor, Joshua P. Herron, B. A. Martineau

All Physics Faculty Publications

Noctilucent clouds (NLCs) were observed from a midlatitude site (Logan, Utah) on the evenings of 22 and 23 June 1999 mountain daylight time. On both nights the clouds were seen for approximately an hour by experienced observers, and they were photographed. The NLC was also observed on the second evening for approximately an hour in the zenith with the Rayleigh-scatter lidar at the Atmospheric Lidar Observatory, which is operated by the Center for Atmospheric and Space Sciences on the campus of Utah State University. These observations enabled several of the properties of the cloud to be determined. They were within …

Go to article

River Meandering Dynamics, Boyd F. Edwards, D. H. Smith Mar 2002

River Meandering Dynamics, Boyd F. Edwards, D. H. Smith

All Physics Faculty Publications

The Ikeda, Parker, and Sawai river meandering model is reexamined using a physical approach employing an explicit equation of motion. For periodic river shapes as seen from above, a cross-stream surface elevation gradient creates a velocity shear that is responsible for the decay of small-wavelength meander bends, whereas secondary currents in the plane perpendicular to the downstream direction are responsible for the growth of large-wavelength bends. A decay length D=H/2Cf involving the river depth H and the friction coefficient Cf sets the scale for meandering, giving the downstream distance required for the fluid velocity profile to recover from …

Go to article

Quantum Dynamics Of The Polarized Gowdy T3 Model, Charles G. Torre Jan 2002

Quantum Dynamics Of The Polarized Gowdy T3 Model, Charles G. Torre

All Physics Faculty Publications

The polarized Gowdy T3 vacuum spacetimes are characterized, modulo gauge, by a “point particle” degree of freedom and a function φ that satisfies a linear field equation and a nonlinear constraint. The quantum Gowdy model has been defined by using a representation for φ on a Fock space F. Using this quantum model, it has recently been shown that the dynamical evolution determined by the linear field equation for φ is not unitarily implemented on F. In this paper, (1) we derive the classical and quantum model using the “covariant phase space” formalism, (2) we show that time evolution is …

Go to article

Temperature Dependence Of Silicon Carrier Effective Masses With Application To Femtosecondreflectivity Measurements, D. Mark Riffe Jan 2002

Temperature Dependence Of Silicon Carrier Effective Masses With Application To Femtosecondreflectivity Measurements, D. Mark Riffe

All Physics Faculty Publications

The conductivity effective masses of electrons and holes in Si are calculated for carrier temperatures from 1 to 3000 K. The temperature dependence of the electron mass is calculated by use of a phenomenological model of conduction-band nonparabolicity that has been fitted to experimental measurements of the dependence of the electron conductivity effective mass on carrier concentration. The hole mass is investigated by tight-binding calculations of the valence bands, which have been adjusted to match experimental values of the valence-band curvature parameters at the top of the valence band. The calculations are in excellent agreement with femtosecond-laser reflectivity measurements of …

Go to article

The Principle Of Symmetric Criticality In General Relativity, Mark E. Fels, Charles G. Torre Jan 2002

The Principle Of Symmetric Criticality In General Relativity, Mark E. Fels, Charles G. Torre

All Physics Faculty Publications

We consider a version of Palais' principle of symmetric criticality (PSC) that is applicable to the Lie symmetry reduction of Lagrangian field theories. Given a group action on a space of fields, PSC asserts that for any group-invariant Lagrangian, the equations obtained by restriction of Euler–Lagrange equations to group-invariant fields are equivalent to the Euler–Lagrange equations of a canonically defined, symmetry-reduced Lagrangian. We investigate the validity of PSC for local gravitational theories built from a metric and show that there are two independent conditions which must be satisfied for PSC to be valid. One of these conditions, obtained previously in …

Go to article

Relative Solar And Auroral Contribution To The Polar F Region: Implications For National Space Weather Program, Michael David, Jan Josef Sojka, Robert W. Schunk, R. Heelis Jan 2002

Relative Solar And Auroral Contribution To The Polar F Region: Implications For National Space Weather Program, Michael David, Jan Josef Sojka, Robert W. Schunk, R. Heelis

All Physics Faculty Publications

When plasma in the polar cap F region becomes highly structured, patches, irregularities, and scintillations of HF signals may be observed. The topic of this paper is not the mechanism for structuring or distributing the plasma but rather the source of the plasma. By understanding the plasma source we gain insight into the specification and forecasting of ionospheric structures and irregularities as required for space weather applications. The two major sources of polar cap F region plasma are the solar EUV radiation and the auroral precipitation. The region over which solar EUV production occurs is readily modeled. In contrast, the …

Go to article

The Lisa Optimal Sensitivity, Thomas A. Prince, Massimo Tinto, Shane L. Larson, J. W. Armstrong Jan 2002

The Lisa Optimal Sensitivity, Thomas A. Prince, Massimo Tinto, Shane L. Larson, J. W. Armstrong

All Physics Faculty Publications

The multiple Doppler readouts available on the Laser Interferometer Space Antenna (LISA) permit simultaneous formation of several interferometric observables. All these observables are independent of laser frequency fluctuations and have different couplings to gravitational waves and to the various LISA instrumental noises. Within the functional space of interferometric combinations LISA will be able to synthesize, we have identified a triplet of interferometric combinations that show optimally combined sensitivity. As an application of the method, we computed the sensitivity improvement for sinusoidal sources in the nominal, equal-arm LISA configuration. In the part of the Fourier band where the period of the …

Go to article

Unequal Arm Space-Borne Gravitational Wave Detectors, Shane L. Larson, Ronald W. Hellings, William A. Hiscock Jan 2002

Unequal Arm Space-Borne Gravitational Wave Detectors, Shane L. Larson, Ronald W. Hellings, William A. Hiscock

All Physics Faculty Publications

Unlike ground-based interferometric gravitational wave detectors, large space-based systems will not be rigid structures. When the end stations of the laser interferometer are freely flying spacecraft, the armlengths will change due to variations in the spacecraft positions along their orbital trajectories, so the precise equality of the arms that is required in a laboratory interferometer to cancel laser phase noise is not possible. However, using a method discovered by Tinto and Armstrong, a signal can be constructed in which laser phase noise exactly cancels out, even in an unequal arm interferometer. We examine the case where the ratio of the …

Go to article

Calculation Of Spectral Degradation Due To Contaminant Films On Infrared And Optical Sensors, L. Gamble, John R. Dennison, B. Wood, J. Herrick, J. S. Dyer Jan 2002

Calculation Of Spectral Degradation Due To Contaminant Films On Infrared And Optical Sensors, L. Gamble, John R. Dennison, B. Wood, J. Herrick, J. S. Dyer

All Physics Faculty Publications

Molecular surface contaminants can cause degradation of optical systems, especially if the contaminants exhibit strong absorption bands in the region of interest. Different strategies for estimation of spectral degradation responses due to uniform films for various types of systems are reviewed. One tool for calculating the effects of contaminant film thickness on signal degradation in the mid IR region is the simulation program CALCRT. The CALCRT database will be reviewed to correlate spectral n and k values associated with specific classes of organic functional groups. Various schemes are also investigated to estimate the spectral degradation in the UV-Vis region. Experimental …

Go to article