Physics Commons^™

Paschen's Law For A Hollow Cathode Discharge, H. Eichhorn, K. H. Schoenbach, T. Tessnow

Bioelectrics Publications

An expression for the breakdown voltage of a one‐dimensional hollow cathode discharge has been derived. The breakdown condition which corresponds to Paschen’s law contains, in addition to the first Townsend coefficient, and the secondary electron emission coefficient two parameters which characterize the reflecting action of the electric field and the lifetime of the electrons in the discharge. The breakdown voltage for a hollow cathode discharge in helium was calculated and compared to that of a glow discharge operating under similar conditions.

Gravitational Observables And Local Symmetries, Charles G. Torre

All Physics Faculty Publications

Using a recent classification of local symmetries of the vacuum Einstein equations, it is shown that there can be no observables for the vacuum gravitational field (in a closed universe) built as spatial integrals of local functions of Cauchy data and their derivatives.

Symmetries Of The Einstein Equations, Charles G. Torre, Ian M. Anderson

All Physics Faculty Publications

We classify all generalized symmetries of the vacuum Einstein equations in four spacetime dimensions. They consist of constant scalings of the metric, and of the infinitesimal action of generalized spacetime diffeomorphisms. Our results rule out a large class of possible ‘‘observables’’ for the gravitational field, and suggest that the vacuum Einstein equations are not integrable.

A First-Principle Derivation Of The High Latitude Total Electron Content Distribution, D. J. Crain, Jan Josef Sojka, Robert W. Schunk, P. H. Doherty, J. A. Klobucher

All Physics Faculty Publications

Calculation of the high-latitude distribution of the vertical total electron content (TEC) is possible using a three-dimensional, time-dependent ionospheric model. Global and local comparisons may be made with observations of TEC. We compare the local diurnal variation of TEC calculated by the model with observations of TEC at Goose Bay, Labrador and Hamilton, Massachusetts. Data from the period of March 1–11, 1989, and monthly averaged data for solar maximum and solar minimum periods are examined. We extend the model to predict diurnal variations of TEC in the polar cap and compare these results with the observed TEC at Thule, Greenland, …

Modeling Polar Cap F-Region Patches Using Time Varying Convection, Jan Josef Sojka, M. D. Bowline, Robert W. Schunk, D. T. Decker, Cesar E. Valladares, R. Sheehand, D. N. Anders, R. A. Heelis

All Physics Faculty Publications

Creation of polar cap F‐region patches are simulated for the first time using two independent physical models of the high latitude ionosphere. The patch formation is achieved by temporally varying the magnetospheric electric field (ionospheric convection) input to the models. The imposed convection variations are comparable to changes in the convection that result from changes in the B_y IMF component for southward interplanetary magnetic field (IMF). Solar maximum‐winter simulations show that simple changes in the convection pattern lead to significant changes in the polar cap plasma structuring. Specifically, in winter, as enhanced dayside plasma convects into the polar …

A Time-Dependent Model Of Polar Cap Arcs, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain

All Physics Faculty Publications

A two-dimensional time-dependent model of polar cap arcs has been developed. The electrodynamics of the polar cap arcs are treated self-consistently in the frame of the coupled magnetosphere-ionosphere system. The focus of this paper is to introduce the physics and mathematical formulation of the model and describe the features of the spatial structure and temporal evolution of the polar cap arcs. The modeling results indicate that the time constant for the formation of the polar cap arcs is around 10 min. It is found that an initial single-arc precipitation pattern associated with a polar cap arc tends to split into …

Influence Of Horizontal Inhomogeneity In The Ionosphere On The Reflection Of Alfvén Waves, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain

All Physics Faculty Publications

A study of the reflection of Alfvén waves at a horizontally inhomogeneous ionosphere has been carried out. In this study, the Alfvén speed above the ionosphere is assumed to be uniform and the ionosphere is treated as a height‐integrated conducting slab. Analytical and numerical results indicate that the horizontal nonuniformity of the ionospheric conductivity can lead to a rotation of the reflected wave fields and cause field‐aligned currents that originate in the ionosphere. A strong conductivity nonuniformity in the direction perpendicular to the incident wave field, large Hall to Pedersen conductivity ratios, and low conductivity values lead to a large …

Hydrodynamic Theory Of Multicomponent Diffusion And Thermal Diffusion In Multitemperature Gas Mixtures, John D. Ramshaw

Physics Faculty Publications and Presentations

A phenomenological theory is developed for multicomponent diffusion, including thermal diffusion, in gas mixtures in which the components may have different temperatures. The theory is based on the hydrodynamic approach of Maxwell and Stefan, as extended and elaborated by Furry [1] and Williams [2]. The present development further extends these earlier treatments to multiple temperatures and multicomponent thermal diffusion. The resulting diffusion fluxes obey generalized Stefan-Maxwell relations which include the effects of ordinary, forced, pressure, and thermal diffusion. When thermal diffusion is neglected, these relations have the same form as the usual single-temperature ones, except that mole fractions are replaced …

Resonant Vibrations Of The Irish Folk Harp, Patrick Healy

Other Resources

An analysis of the resonant vibration of an O’Meachair cedar and mahogany Irish folk harp is reported. A report is also made of a small number of measurements carried out on an O’Meachair spruce and maple Irish folk harp. The structure and operation of the harp is described.

The theory of small vibrations of plates and wooden boards is set out.

The system devised to measure input admittance at driving points on the harp body over a frequency range O-2 kHz is described. Tests of its linearity and out of its frequency flatness are reported.

Resonant vibrations of an isolated …

²H (D,Γ) ⁴He Polarization Observables At 20, 30, And 50 Mev, R. M. Whitton, H. R. Weller, E. Hayward, W. R. Dodge, S. E. Kuhn

Physics Faculty Publications

Tensor and vector analyzing powers for the ²H (d,γ) ⁴He reaction have been obtained as a function of angle at E_d(lab) = 20, 30, and 50 MeV. Differential cross sections were extracted at 30 and 50 MeV. Data for A_yy(θ) and A_y(θ) were obtained at all three energies, while T₂₀(θ) was also measured at E_d(lab) = 50 MeV. A direct capture calculation was performed and compared to the data. This calculation assumes point deuterons and that the reaction proceeds primarily via E2 radiation in this energy region. A value of …

The Equivalence Theorem And Global Anomalies, Jf Donoghue, J Tandean

Physics Department Faculty Publication Series

In the presence of some forms of global anomalies, the equivalence theorem, which relates the interactions of longitudinal gauge bosons to those of the Goldstone bosons, is not always valid. This can occur when the Goldstone sector gauge an anomaly which is cancelled in the gauge currents by the effects of a different sector of the theory. The example of the standard model without Higgs particles is used to illustrate this phenomena.

Induced Mach Wave-Flame Interactions In Laminar Supersonic Fuel Jets, F. Q. Hu, T. L. Jackson, D. G. Lasseigne, C. E. Grosch

Mathematics & Statistics Faculty Publications

A model problem is proposed to investigate the steady response of a reacting, compressible laminar jet to Mach waves generated by wavy walls in a channel of finite width. The model consists of a two-dimensional jet of fuel emerging into a stream of oxidizer which are allowed to mix and react in the presence of the Mach waves. The governing equations are taken to be the steady parabolized Navier-Stokes equations which are solved numerically. The kinetics is assumed to be a one-step, irreversible reaction of the Arrhenius type. Two important questions on the Mach wave-flame interactions are discussed: (i) how …

A Numerical Study Of Wave Propagation In A Confined Mixing Layer By Eigenfunction Expansions, Fang Q. Hu

Mathematics & Statistics Faculty Publications

It is well known that the growth rate of instability waves of a two-dimensional free shear layer is reduced greatly at supersonic convective Mach numbers. In previous works, it has been shown that new wave modes exist when the shear layers are bounded by a channel due to the coupling effect between the acoustic wave modes and the motion of the mixing layer. The present work studies the simultaneous propagation of multiple stability waves using numerical simulation. It is shown here that the coexistence of two wave modes in the flow field can lead to an oscillatory growth of disturbance …

Generation Of Surface Shape From Variable-Resolution Video Moire Contours, Joel H. Blatt, Scott C. Cahall, Bernard Gilbert, Jeffrey A. Hooker, Gary L. Wallace

Aerospace, Physics, and Space Science Faculty Publications

Several methods for generation of three dimensional surface shapes from variable resolution video moire contours are described. In a classical moire system, a physical grating is projected on a target and also used to view the target. The moire contours are generated in the plane of the viewing grating. An unambiguous surface shape can then be computed by processing a set of moire images where the grating, target, or both are moved. By using an interferometer to generate and project variable pitch gratings and video technology to generate the moire contours, a 3-D surface can be scanned at different resolutions …

Variable-Resolution Video Moire Error Map System For Inspection Of Continuously Manufactured Objects, Joel H. Blatt, Scott C. Cahall, Jeffery A. Hooker

Aerospace, Physics, and Space Science Faculty Publications

Moire techniques can be a powerful tool to determine deviation of a manufactured shape from a desired shape. In a traditional moire system, distorted gratings on an object are viewed through an undistorted grating. The moire contours that result represent equal depth contours over the entire viewed surface. By generating the moire patterns in video, it is possible to view the distorted gratings on a test object through a set of gratings that has been distorted by a similar but perfect object. The output is then a set of moire contours that corresponds to the differences between the two surfaces. …

Real-Time Generation Of Intersection Of Surfaces For Welding By Video Moire, Scott Christian Cahall, Jeffery A. Hooker, Joel H. Blatt

Aerospace, Physics, and Space Science Faculty Publications

A common problem in fabrication and welding of complex structures is that there is no simple way to determine where to cut one part so that it will fit another part unless both parts designed and built on a CAD/CAM system. Particularly in prototype or retrofit work, cutting and fitting parts for welding is more of an art than a science. We have developed a unique video moire system that generates the intersection contour in near real time with the contour superimposed on a video image of the part, allowing the cut line to be marked while following the contour …

The Light-Ion Pulsed Power Induction Accelerator For The Laboratory Microfusion Facility (Lmf), Ronald E. Olson, J. Boyes, M. G. Mazarakis, D. L. Smith, L. F. Bennett, T. R. Lockner, J. W. Poukey

Physics Faculty Research & Creative Works

In order to initiate ignition and substantial energy yield from an inertial confinement fusion target (ICF), a light-ion pulse of ~700 TW peak power and 15-20 ns duration is required. The preconceptual design presented provides this power. The HERMES-III technology of linear inductive voltage addition in a self-magnetically insulated transmission line (MITL) is utilized to generate the 25-36 MV peak voltage needed for lithium ion beams. The 15-20 MA ion current is achieved by utilizing many accelerating modules in parallel. The lithium ion beams are produced in two-stage extraction diodes. To provide the two separate voltage pulses required by the …

The Lmf Triaxial Mitl Voltage Adder System, Ronald E. Olson, M. G. Mazarakis, D. L. Smith, L. F. Bennett, T. R. Lockner, J. W. Poukey

Physics Faculty Research & Creative Works

No abstract provided.

Hysteresis And Anchoring Energy In Ferroelectric Liquid Crystals, Yuri Panarin

Articles

The frequency dispersion of the coercive force of Ferroelectric Liquid Crystals (FLC) cells has been detected and examined in the range of infralow (lower than 0.1 Hz) frequencies. To clarify the low-frequency dispersion, the model has been suggested, based on the arrangement of free charges and well describing the experimental curves. The method for determination of the energy of FLC anchoring at the surface, developed on the basis of the static hysteresis loop, has been proposed. The dependence of bistability and the anchoring energy upon the orientant layer thickness has experimentally been investigated.

Sign Correlations And The Mechanism For Parity Violation, Vladimir Gudkov

Faculty Publications

The problem of possible sign correlations of P-odd effects due to parity mixing on the compound nuclear stage is discussed. For an unambiguous test of the conventional model of parity violation on the compound nuclear stage, it is not enough only to measure the sign correlation of P-odd effects on some resonances, but it is necessary also to know the neutron decay amplitudes for each resonance.