7 Matching Results

Results open in a new window/tab.

How an antenna launches its input power into radiation: thepattern of the Poynting vector at and near an antenna (open access)

How an antenna launches its input power into radiation: thepattern of the Poynting vector at and near an antenna

In this paper I first address the question of whether theseat of the power radiated by an antenna made of conducting members isdistributed over the "arms" of the antenna according to $ - \bf J \cdotE$, where $\bf J$ is the specified current density and $\bf E$ is theelectric field produced by that source. Poynting's theorem permits only aglobal identification of the total input power, usually from a localizedgenerator, with the total power radiated to infinity, not a localcorrespondence of $- \bf J \cdot E\ d^3x $ with some specific radiatedpower, $r^2 \bf S \cdot \hat r\ d\Omega $. I then describe a modelantenna consisting of two perfectly conducting hemispheres of radius\emph a separated by a small equatorial gap across which occurs thedriving oscillatory electric field. The fields and surface current aredetermined by solution of the boundary value problem. In contrast to thefirst approach (not a boundary value problem), the tangential electricfield vanishes on the metallic surface. There is no radial Poyntingvector at the surface. Numerical examples are shown to illustrate how theenergy flows from the input region of the gap and is guided near theantenna by its "arms" until it is launched at larger \emph r/a into theradiation pattern …
Date: May 18, 2005
Creator: Jackson, J.D.
System: The UNT Digital Library
3-Center-4-Electron Bonding in [(silox)2Mo=NtBu]2(μ-Hg) Controls Reactivity while Frontier Orbitals Permit a Dimolybdenum π-Bond Energy Estimate (open access)

3-Center-4-Electron Bonding in [(silox)2Mo=NtBu]2(μ-Hg) Controls Reactivity while Frontier Orbitals Permit a Dimolybdenum π-Bond Energy Estimate

Article describing research on 3-center-4-electron bonding in [(silox)2Mo=NtBu]2(mu-Hg).
Date: May 18, 2005
Creator: Rosenfeld, Devon C.; Wolczanski, Peter T.; Barakat, Khaldoon A.; Buda, Corneliu & Cundari, Thomas R., 1964-
System: The UNT Digital Library
Modeling Initiation in Exploding Bridgewire Detonators (open access)

Modeling Initiation in Exploding Bridgewire Detonators

One- and two-dimensional models of initiation in detonators are being developed for the purpose of evaluating the performance of aged and modified detonator designs. The models focus on accurate description of the initiator, whether it be an EBW (exploding bridgewire) that directly initiates a high explosive powder or an EBF (exploding bridgefoil) that sends an inert flyer into a dense HE pellet. The explosion of the initiator is simulated using detailed MHD equations of state as opposed to specific action-based phenomenological descriptions. The HE is modeled using the best available JWL equations of state. Results to date have been promising, however, work is still in progress.
Date: May 18, 2005
Creator: Hrousis, C A
System: The UNT Digital Library
Measurement of the dispersion of thermal ion-acoustic fluctuations in high-temperature laser plasmas using multiple wavelength Thomson-scattering (open access)

Measurement of the dispersion of thermal ion-acoustic fluctuations in high-temperature laser plasmas using multiple wavelength Thomson-scattering

The dispersion of ion-acoustic fluctuations has been measured using a novel technique that employed multiple color Thomson scattering to measure the frequency spectrum for two separate thermal ion-acoustic fluctuations with significantly different wave vectors. The plasma fluctuations are shown to become dispersive with increasing electron temperature. They demonstrate that this technique allows a time resolved local measurement of electron density and temperature in inertial confinement fusion plasmas.
Date: May 18, 2005
Creator: Froula, D H; Davis, P; Divol, L; Ross, J S; Meezan, N; Price, D et al.
System: The UNT Digital Library
Role of Double-Porosity Dual-Permeability Models for Multi-Resonance Geomechanical Systems (open access)

Role of Double-Porosity Dual-Permeability Models for Multi-Resonance Geomechanical Systems

It is known that Biot's equations of poroelasticity (Biot 1956; 1962) follow from a scale-up of the microscale equations of elasticity coupled to the Navier-Stokes equations for fluid flow (Burridge and Keller, 1981). Laboratory measurements by Plona (1980) have shown that Biot's equations indeed hold for simple systems (Berryman, 1980), but heterogeneous systems can have quite different behavior (Berryman, 1988). So the question arises whether there is one level--or perhaps many levels--of scale-up needed to arrive at equations valid for the reservoir scale? And if so, do these equations take the form of Biot's equations or some other form? We will discuss these issues and show that the double-porosity dual-permeability equations (Berryman and Wang, 1995; Berryman and Pride, 2002; Pride and Berryman, 2003a,b; Pride et al., 2004) play a special role in the scale-up to equations describing multi-resonance reservoir behavior, for fluid pumping and geomechanics, as well as seismic wave propagation. The reason for the special significance of double-porosity models is that a multi-resonance system can never be adequately modeled using a single resonance model, but can often be modeled with reasonable accuracy using a two-resonance model. Although ideally one would prefer to model multi-resonance systems using the correct numbers, …
Date: May 18, 2005
Creator: Berger, E. L.
System: The UNT Digital Library
Liner Compression of a MAGO / Inverse-Pinch Configuration (open access)

Liner Compression of a MAGO / Inverse-Pinch Configuration

In the ''metal liner'' approach to Magnetized Target Fusion (MTF), a preheated magnetized plasma target is compressed to thermonuclear temperature and high density by externally driving the implosion of a flux conserving metal enclosure, or liner, which contains the plasma target. As in inertial confinement fusion, the principle fusion fuel heating mechanism is pdV work by the imploding enclosure, called a pusher in ICF. One possible MTF target, the hard-core diffuse z pinch, has been studied in MAGO experiments at VNIIEF, and is one possible target being considered for experiments on the Atlas pulsed power facility. Numerical MHD simulations show two intriguing and helpful features of the diffuse z pinch with respect to compressional heating. First, in two-dimensional simulations the m=0 interchange modes, arising from an unstable pressure profile, result in turbulent motions and self-organization into a stable pressure profile. The turbulence also gives rise to convective thermal transport, but the level of turbulence saturates at a finite level, and simulations show substantial heating during liner compression despite the turbulence. The second helpful feature is that pressure profile evolution during compression tends towards improved stability rather than instability when analyzed according to the Kadomtsev criteria. A liner experiment is planned …
Date: May 18, 2005
Creator: Siemon, R. E.; Atchison, W. L.; Awe, T.; Bauer, B. S.; Buyko, A. M.; Chernyshev, V. K. et al.
System: The UNT Digital Library
First Data on Lake Level Changes in Northeastern Siberia during the Postglacial Time (open access)

First Data on Lake Level Changes in Northeastern Siberia during the Postglacial Time

Moraines of the Tyellakh Group [1] (QIII{sub 2-4}) preserved in river valleys of the northeastern Kolyma River basin indicate development of cirque-valley glaciers originating in the Kilgan Mountains located at the northeastern periphery of the Kolyma Ridge that separates drainage basins of the Sea of Okhotsk and Kolyma River. Moraines host lakes with a length of up to 1-5 km and a relatively small width depending on the valley bottom dimension. The study of lacustrine sediments, their bed-by-bed palynological analysis, and radiocarbon dating provided the first information on lake levels during the final glacial stage of the Late Pleistocene, as well as the Pleistocene-Holocene boundary and Holocene, for the upper reaches of the Kolyma River.
Date: May 18, 2005
Creator: Shilo, N. A.; Anderson, P. M.; Brown, T. A.; Lozhkin, A. V.; Pakhomov, A. Y. & Solomatkina, T. B.
System: The UNT Digital Library