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Articles 301 - 330 of 333
Full-Text Articles in Physical Sciences and Mathematics
Surface Conductance Of A Copper Wire In A Fluid At High Pressure, Daniel L. Decker
Surface Conductance Of A Copper Wire In A Fluid At High Pressure, Daniel L. Decker
Faculty Publications
The three-dimensional flow of heat in a wire carrying a current and immersed in a liquid is solved in detail. Using this exact result the surface conductance of copper in petroleum ether has been measured as a function of pressure to 40 kbars. The measured surface conductance for copper in a fluid is very small, justifying approximations which yield results that are in agreement with a simplified one-dimensional heat-flow problem. Surprisingly, even at 40 kbars pressure a very large fraction of the joule heating within a wire with a length-to-diameter ratio of ~100 is dissipated through the ends of the …
Superconductivity At 155 K, David D. Allred, S. R. Ovshinsky, R. T. Young, G. Demaggio, G. A. Van Der Leeden
Superconductivity At 155 K, David D. Allred, S. R. Ovshinsky, R. T. Young, G. Demaggio, G. A. Van Der Leeden
Faculty Publications
Transition to a superconducting zero-resistance state at 155 K is observed for the first time in bulk material. A new five-element compound has been synthesized with nominal composition Y1Ba2Cu3F2Oy. Fluorine plays a critical role in achieving this effect. X-ray diffraction and electron microprobe analysis indicate that the samples are multiphasic. Evidence is presented that the samples contain superconducting phases with onset temperatures considerably above 155 K. Magnetic measurements suggest a flux-trapping effect below 260 K, and diamagnetic deviations from Curie-Weiss behavior in the range from 250 K≤T≤100 K indicate that Meissner effect in a small superconducting volume fraction.
Some Aspects Of The Isogroup Of The Self-Dual Yang-Mills System, C. J. Papachristou, B. Kent Harrison
Some Aspects Of The Isogroup Of The Self-Dual Yang-Mills System, C. J. Papachristou, B. Kent Harrison
Faculty Publications
A generalized isovector formalism is used to derive the isovectors and isogroup of the self-dual Yang-Mills (SDYM) equation in the so-called J formulation. In particular, the infinitesimal "hidden symmetry'' transformation, a linear system, and a well-known Backlund transformation of the SDYM equation are derived in the process. Thus symmetry and integrability aspects of the SDYM system appear in natural relationship to each other within the framework of the isovector approach.
Anneal Induced Changes In Amorphous Semiconductor Multilayers, David D. Allred, Jesus González-Hernández, O. V. Nguyen
Anneal Induced Changes In Amorphous Semiconductor Multilayers, David D. Allred, Jesus González-Hernández, O. V. Nguyen
Faculty Publications
We have prepared, heat treated and characterized various amorphous semiconductor periodic multilayers and ultrathin films. These were prepared by several vapor deposition techniques at substrate temperatures ranging from 25°C to 300°C and possessed periodicities from 22 to 400Å. Films were subjected to isochronal thermal treatments at progressively higher temperatures. Two effects were observed: enhanced diffusion and retarded crystallization. Interdiffusion, at rates which are many orders of magnitude higher than those anticipated from crystalline data, was observed in a-Si/a-Ge multilayers. Crystallization of germanium, the more readily crystallized member of the couple, is retarded; the extent depends on the thickness of the …
Equilibrium Properties Of Short Field-Reversed Configurations, Ross L. Spencer, M. Tuszewski
Equilibrium Properties Of Short Field-Reversed Configurations, Ross L. Spencer, M. Tuszewski
Faculty Publications
Some features of short field-reversed configuration (FRC) equilibria relevant to transport and stability are studied numerically and analytically. It is shown that magnetic field curvature effects significantly increase the FRC magnetization for plasma elongations epsilon is less than or equal to 4.
Considerations Of Temperature Stability In A Cylindrical Plasma, S. Neil Rasband, Yao-Hui Xu
Considerations Of Temperature Stability In A Cylindrical Plasma, S. Neil Rasband, Yao-Hui Xu
Faculty Publications
A variational formulation is used to consider thermal equilibrium and stability for a cylindrical plasma modeled by dissipative magnetohydrodynamics. The parameter dependence of equilibrium solutions and their stability is followed using homotopy techniques. Solution branches and their connections are studied in relation to the applied fields.
A Generalized Molien Function For Field Theoretical Hamiltonians, Jeffrey W. Felix, Dorian M. Hatch
A Generalized Molien Function For Field Theoretical Hamiltonians, Jeffrey W. Felix, Dorian M. Hatch
Faculty Publications
A generating function, or Molien function, the coefficients of which give the number of independent polynomial invariants in G, has been useful in the Landau and renormalization group theories of phase transitions. Here a generalized Molien function for a field theoretical Hamiltonian (with short-range interactions) of the most general form invariant in a group G is derived. This form is useful for more general renormalization group calculations. Its Taylor series is calculated to low order for the FGamma-2 representation of the space group R[3 bar]c and also for the l=1 (faithful) representation of SO(3).
Example Of A Group Action Determined Phase Transition, Jeffrey W. Felix, Dorian M. Hatch
Example Of A Group Action Determined Phase Transition, Jeffrey W. Felix, Dorian M. Hatch
Faculty Publications
The principles of the group action approach to structural phase transitions are outlined. It is assumed that all properties of the transition are determined by the action of a single physically irreducible represention of the space group of the more symmetric phase. We determine the isotropy groups using the image space of the representation. The free energy minima are determined to fourth order and to all orders using the results of Gufan and then compared. This theory is applied to Calcite (Roverline3c) to determine all possible continuous commensurate phase transitions.
Isotropy Group Description Of A Phase Transition In Nano3, W. Scott Stornetta, Dorian M. Hatch
Isotropy Group Description Of A Phase Transition In Nano3, W. Scott Stornetta, Dorian M. Hatch
Faculty Publications
Predictions of the possible post-transition symmetries of an R 3c zone center continuous phase transition are made using recent extensions of the Landau theory. The Landau theory is summarized and direct group theoretical methods are applied to the R 3c phase. General techniques for solving systems of nonlinear polynomial equations are reviewed and these techniques are applied to the minimization of the free energy F for the aforementioned possible symmetries. The results of the direct methods and the minimization procedures are shown to be compatible. It is shown that the transition to R 3c in NaNO3 is consistent with the …
Unification Of Ernst-Equation Backlund Transformations Using A Modified Wahlquist-Estabrook Technique; Wahlquist-Estabrook, B. Kent Harrison
Unification Of Ernst-Equation Backlund Transformations Using A Modified Wahlquist-Estabrook Technique; Wahlquist-Estabrook, B. Kent Harrison
Faculty Publications
The three known Backlund transformations for the Ernst equation are derived using a modification of the Wahlquist-Estabrook prolongation procedure. The modification requires that the equation to be studied be cast into a set of differential forms and their exterior derivatives, such that all coefficients are constant (a "CC ideal''). Analysis of the resulting equations produces 16 solutions composed of the three basic transformations combined with identity and other essentially trivial transformations. The group structure of the transformations is discussed. A Backlund transformation (already known) for the Ernst-Maxwell equations can be found by the same method. Promising generalizations are mentioned.
Landau Free Energy Form At The F Point Of The Roverline3 Structure, Dorian M. Hatch, Daniel L. Decker
Landau Free Energy Form At The F Point Of The Roverline3 Structure, Dorian M. Hatch, Daniel L. Decker
Faculty Publications
A free energy form compatible with the F point of the trigonal D63d(Roverline3c) symmetry is constructed. It is a function of the order parameter, elastic strain, and the stress. The resulting free energy exhibits a close formalistic analogy to the stressed cubic perovskite structures and their associated multicriticality.
Chemical Vapor Deposited Molybdenum Films For Use In Photothermal Conversion, David D. Allred, G. E. Carver, B. O. Seraphin
Chemical Vapor Deposited Molybdenum Films For Use In Photothermal Conversion, David D. Allred, G. E. Carver, B. O. Seraphin
Faculty Publications
High infrared reflectance, coupled with higher solar absorptance, is required for efficient photothermal conversion. Converters can be fabricated by depositing an absorber on a highly reflecting metal. The absorber functions in the visible, yet becomes transparent in the near infrared, allowing the metal to suppress the thermal emittance. Economic considerations demand the use of thin films, rather than bulk materials. The thin film reflector must be capable of withstanding high temperatures of operation. Compatibility of the reflector with the substrate below, and the absorber above, is required for long-time service. Highly reflective silver films suffer reflectance losses by agglomeration, and …
Chemical Vapor Deposited Amorphous Silicon For Use In Photothermal Conversion, David D. Allred, D. C. Booth, M. Janai, G. Weiser, B. O. Seraphin
Chemical Vapor Deposited Amorphous Silicon For Use In Photothermal Conversion, David D. Allred, D. C. Booth, M. Janai, G. Weiser, B. O. Seraphin
Faculty Publications
Efficient photothermal conversion requires surfaces of high solar absorptance and low thermal emittance. This can be accomplished by the tandem action of a good infrared reflector overlaid by a film of sufficient solar absorptance that is transparent in the infrared. Crystalline silicon is a suitable candidate for the absorber layer. Its indirect band gap, however, results in a shallow absorption edge that extends to far into the visible. In contrast, the absorption edge of amorphous silicon is steeper and located farther into the infrared, resulting in a larger solar absorptance. We report on the fabrication of amorphous silicon absorbers by …
The Use Of Nuclear Reactions And Sims For Quantitative Depth Profiling Of Hydrogen In Amorphous Silicon, David D. Allred, G. J. Clark, C. W. White, B. R. Appleton, C. W. Magee, D. E. Carlson
The Use Of Nuclear Reactions And Sims For Quantitative Depth Profiling Of Hydrogen In Amorphous Silicon, David D. Allred, G. J. Clark, C. W. White, B. R. Appleton, C. W. Magee, D. E. Carlson
Faculty Publications
Depth profiles for hydrogen in amorphous silicon have been determined by the use of resonant nuclear reactions [1H(15N,αγ)12C and 1H(19F,αγ)16O] and by secondary ion mass spectroscopy (SIMS). Independent calibration procedures were used for the two techniques. Measurements were made on the same amorphous silicon film to provide a direct comparison of the two hydrogen analysis techniques. The hydrogen concentration in the bulk of the film was determined to be about 9 at % H. The SIMS results agree with the resonant nuclear reaction results to within 10%, which demonstrates that quantitative hydrogen depth profiles can be obtained by SIMS analysis …
Computer Model Of A Fast Toroidal Plasma Compression, With Application To The Topolotron, H. Mark Nelson, Keith H. Brown, Charles A. Hart
Computer Model Of A Fast Toroidal Plasma Compression, With Application To The Topolotron, H. Mark Nelson, Keith H. Brown, Charles A. Hart
Faculty Publications
The method is developed for a comuputer sequence which models a fast toroidal theta or screw pinch for a highly conducting axially symmetric plasma. The computer sequence takes into account the self-inductances of the plasma and the external conductors which drive the compression as well as the mutual inductance which electromagnetically couples the two. The computer sequence is divided into three phases: a snowplow compression phase, an adiabatic compression phase, and a crowbarred circuit phase. The computer sequence is applied to a topolotron and an example is given of a magnetohydrodynamic equilibrium geometry for which the plasma surface possesses an …
Behavior Of A Manganin Coil At Elevated Temperatures And Pressures, Jonathan D. Weiss, Daniel L. Decker, H. B. Vanfleet
Behavior Of A Manganin Coil At Elevated Temperatures And Pressures, Jonathan D. Weiss, Daniel L. Decker, H. B. Vanfleet
Faculty Publications
We have determined the temperature dependence in the first-order pressure coefficient of a manganin coil to be dBetaB/dT= (4.2±0.8) ×10^-7 (kbar degrees C)^-1 in the equation R (T,P) =R (T,0)(1+BetaP+GammaP2), where R (T,P) is the coil resistance at temperature T and pressure P. The measurements were performed by simultaneously measuring the coil resistance and temperature at the transitions of mercury and bismuth, which were observed by differential thermal analysis.
X-Ray Diffraction Studies On Liquids At Very High Pressures Along The Melting Curve. I. Methods And Techniques, Keith H. Brown, J. Dean Barnett
X-Ray Diffraction Studies On Liquids At Very High Pressures Along The Melting Curve. I. Methods And Techniques, Keith H. Brown, J. Dean Barnett
Faculty Publications
A technique using the tetrahedral anvil high-pressure x-ray system has been developed to extract coherent x-ray intensity patterns of liquids near melting from measured scattering curves in the presence of high-background counts. Radial distribution functions for liquids along the melting curve to pressures of at least 50 kbar can be obtained. At each pressure scattering curves are recorded for the liquid and solid on opposite sides of the melting curve and a subtraction is made to eliminate background and incoherent scattering. Theoretical estimates of the thermal diffuse scattering from the solid are added to the appropriately corrected difference patterns to …
X-Ray Diffraction Studies On Liquids At Very High Pressures Along The Melting Curve Ii. Sodium, Keith H. Brown, J. Dean Barnett
X-Ray Diffraction Studies On Liquids At Very High Pressures Along The Melting Curve Ii. Sodium, Keith H. Brown, J. Dean Barnett
Faculty Publications
Coherent x-ray diffraction patterns for liquid Na have been extracted from measured patterns at 0.5, 7.5, 17, and 43 kbar along the melting curve. The experimentally determined liquid structure factor and resulting radial distribution function are given at each pressure. The position of the principal x-ray intensity peak is reproducible to within 0.5% and shows shifts of the order of 12%. The resulting nearest neighbor distance in the radial distribution function also shifts 12% but is reproducible only to approximately 2%. The distribution functions obtained at points along the melting curve suggest a simple dimensional compression or scaling; however, a …
Β-Delayed Proton Decay Of 9c, David D. Allred, John E. Esterl, J. C. Hardy, R. G. Sextro, Joseph Cerny
Β-Delayed Proton Decay Of 9c, David D. Allred, John E. Esterl, J. C. Hardy, R. G. Sextro, Joseph Cerny
Faculty Publications
The delayed-proton spectrum following the β decay of 9C (t1/2=126.5±1.0 msec) was found to consist primarily of a continuum extending from 13 to 1.5 MeV, the latter being the lowest energy observed. In addition to the previously observed peaks at 9.28 and 12.30 MeV (C.M.), possible peaks between 3 and 7 MeV have been tentatively identified.
High-Pressure Equation Of State For Nacl, Kcl, And Cscl, Daniel L. Decker
High-Pressure Equation Of State For Nacl, Kcl, And Cscl, Daniel L. Decker
Faculty Publications
A calculation of the equation of state for NaCl from a Mie-Grüneisen equation was repeated using more accurate values of the zero-pressure compressibility. It was also extended to KCl and CsCl. An analysis of this approach to pressure calibration indicates that it will yield pressures with about the same accuracy as can be presently achieved by experimental measurements above 25 kbar, and thus furnishes a temporary practical pressure scale.
Lamb-Mössbauer Factor Of Sodium Ferrocyanide, Daniel L. Decker, L. E. Lortz
Lamb-Mössbauer Factor Of Sodium Ferrocyanide, Daniel L. Decker, L. E. Lortz
Faculty Publications
Using a set of commercially prepared sodium ferrocyanide absorbers enriched to 91.2% Fe57 the Lamb-Mössbauer factor was measured to be 0.28±0.03. The thickness of Fe57 for these absorbers was measured using x-ray absorption techniques and was found to be considerably smaller than that advertised by the manufacturer even after correcting for the size of the ferrocyanide particles in the absorbers.
Rayleigh Hysteresis Shape: Its Relationship To Displacement Distance Of A Single Domain Wall In 50% Ni–Fe, R. C. Woodbury, M. R. Hunt
Rayleigh Hysteresis Shape: Its Relationship To Displacement Distance Of A Single Domain Wall In 50% Ni–Fe, R. C. Woodbury, M. R. Hunt
Faculty Publications
The need to measure the displacement distance of domain walls from equilibrium for very weak alternating fields (H ≪ coercive force) in bulk magnetic material has prompted a study of the possible use of the opening of the Rayleigh hysteresis loop to indicate the amount of wall displacement. This paper contains (1) a review of the theoretical relationship between hysteresis shape and the displacement distance of a domain wall, based upon defect-energy models of Rodbell and Bean, and Baldwin; and (2) an experimental approach which provides a measure of the wall displacements versus hysteresis shape for 50% Ni–Fe tape. Discrepancies …
Proposed Thermodynamic Pressure Scale For An Absolute High-Pressure Calibration, Daniel L. Decker, J. Dean Barnett
Proposed Thermodynamic Pressure Scale For An Absolute High-Pressure Calibration, Daniel L. Decker, J. Dean Barnett
Faculty Publications
The field of high pressure has developed rapidly over the past few years to a point where relatively sophisticated experiments are being attempted. In many experiments it is no longer sufficient to qualitatively estimate the pressure or to base conclusions on experimental results tied to an empirical pressure parameter. One desires to accurately know the pressure dependence of physical quantities related to a true thermodynamic scale.
New Solutions Of The Einstein-Maxwell Equations From Old, B. Kent Harrison
New Solutions Of The Einstein-Maxwell Equations From Old, B. Kent Harrison
Faculty Publications
Methods are discussed with which one may derive theorems which allow one to generate new solutions of the Einstein-Maxwell equations from old ones. The old solutions used to generate new ones must admit at least one nonnull Killing vector and may be required to satisfy other conditions, depending on the theorem derived. Examples of derivable theorems are shown; these theorems are used in turn to show how generation of new solutions is accomplished. Examples of the latter are shown, such as generation of Brill or electrified NUT space from the Schwarzschild solution, generation of a new twisted Melvin universe from …
A Method For Measuring Magnetization To High Pressures, C. R. Johansen, Mark H. Nelson, J. H. Gardner
A Method For Measuring Magnetization To High Pressures, C. R. Johansen, Mark H. Nelson, J. H. Gardner
Faculty Publications
A partially successful attempt has been made to measure the magnetic moment per unit volume of ferromagnetic materials as a function of pressure to the 100-kbar region. The apparatus, an early version of which has been described previously, consists basically of two opposed Bridgman flat anvils of alumina. One anvil also acts as a dielectric-filled microwave resonant cavity for an x-band spectrometer, allowing electron spin resonance studies to be made to high pressure. The sample to be studied is placed in contact with the anvil-cavity and covered with a pressure-transmitting medium which in turn is encircled by a flat pyrophyllite …
Very High Pressure Effects Upon The Epr Spectrum Of Ruby, H. Mark Nelson, D. B. Larson, J. H. Gardner
Very High Pressure Effects Upon The Epr Spectrum Of Ruby, H. Mark Nelson, D. B. Larson, J. H. Gardner
Faculty Publications
The variation in the electron paramagnetic resonance (EPR) spectrum of ruby as a function of pressure has been observed to beyond 70 kbar for a magnetic field orientation parallel to the crystalline c axis. The data can be interpreted in terms of the usual spin Hamiltonian, where the spectroscopic splitting factor g|| has the same value as at ambient pressures, but where the zero-field splitting deltaincreases in a linear fashion from 0.38 to 0.43 cm. The experimental apparatus has been described previously, although important improvements in the pressure seal and in the pressure calibration have been made and are described …
Equation Of State Of Sodium Chloride, Daniel L. Decker
Equation Of State Of Sodium Chloride, Daniel L. Decker
Faculty Publications
Because of many requests, I wish to publish the following numerical table of results for the equation of state of NaCl as calculated in an earlier paper1 along with a few comments on various proposed equations for NaCl. Table I gives the pressure in kilobars at the corresponding values of t.a/ao and temperature in the appropriate row and column. The parameter t.a/ao is the fractional compression of the lattice parameter where the standard value ao is the appropriate lattice parameter at zero pressure and 25°C. The increments between the values given in the table were chosen such that one can …
Model Of Electron Correlation In Solids, Everett G. Larson, Walter R. Thorson
Model Of Electron Correlation In Solids, Everett G. Larson, Walter R. Thorson
Faculty Publications
The usual Hartree-Fock model (energy-band theory) does not always give an adequate description of electronic structure in a solid, because it ignores the effects of electron correlation. It was shown first by Wigner that such a situation always develops in an electron ''gas'' at sufficiently low density; a solid structure described by ''resonance'' of Heitler-London pair bonds between electrons localized on neighboring atoms is then a good model of the system.The transition from a Bloch-type state to such a highly correlated state as a function of electron density (lattice parameter) is a problem of considerable interest for the theory of …
Pressure Calibration To 100 Kbar Based On The Compression Of Nacl, R. N. Jeffrey, J. Dean Barnett, H. B. Vanfleet, H. Tracy Hall
Pressure Calibration To 100 Kbar Based On The Compression Of Nacl, R. N. Jeffrey, J. Dean Barnett, H. B. Vanfleet, H. Tracy Hall
Faculty Publications
An independent determination has been made of the transformation pressures assigned to the high-pressure transformations in Ba and Bi which are generally used for calibration points. The metals were imbedded in NaCl, and the transitions were detected by the resistance change of the metal while the NaCl lattice parameter was simultaneously measured by x-ray diffraction. The NaCl compression values determined at the fixed points were related to pressure by reference to the semiempirical compression curve of Decker. The Ba I-II and Bi III-V transformations at room temperature were assigned thermodynamic equilibrium values of 53.3 ±1.2 kbar and 73.8 ±1.3 kbar, …
X-Ray Diffraction Studies On Tin To 100 Kilobars, J. Dean Barnett, Vern E. Bean, H. Tracy Hall
X-Ray Diffraction Studies On Tin To 100 Kilobars, J. Dean Barnett, Vern E. Bean, H. Tracy Hall
Faculty Publications
The high-pressure equilibrium phase diagram of tin is investigated, and the crystal structure of Sn II at 98 kbar and 25degrees C is shown to be body-centered tetragonal with a=3.70 Angstroms, c=3.37 Angstroms, c/a=0.91, and with two atoms per unit cell. The linear compressibility of white tin is given at 25degrees C up to the high-pressure transformation at 92 kbar, and the latent heat of the transformation is measured as 225 cal/g-atom.