Showing papers on "Energy (signal processing) published in 1977"

New method for the calculation of atomic phase shifts: Application to extended x-ray absorption fine structure (EXAFS) in molecules and crystals

Abstract: The scattering of electrons of kinetic energy up to 1000 eV by an atom is of special interest in the understanding of extended x-ray absorption fine-structure (EXAFS) spectra. An important physical feature is the reduction of the exchange and correlation potential as the kinetic energy of the electron increases. This is taken into account by replacing the atom by an electron gas with spatially varying density and calculating the self-energy using the plasmon pole approximation. This results in a set of complex phase shifts which is then applied to the EXAFS problem. Comparison is made with phase shifts extracted from experimental EXAFS spectra and excellent agreement is obtained. Direct comparison of the theoretical and experimental spectra again shows excellent agreement in both the amplitude and the phase. We also analyze the EXAFS spectra by a Fourier-transform technique which first removes the amplitude and phase shift using the calculated result. The importance of a proper choice of zero of energy ${E}_{0}$ is emphasized. We choose ${E}_{0}$ by the requirement that the imaginary part and the absolute value of the Fourier transform should peak at the same distance, thus assuring that the absolute phase is given correctly. Using this procedure the nearest-neighbor distances in ${\mathrm{Br}}_{2}$, Ge${\mathrm{Cl}}_{4}$, and crystalline germanium are determined. In all cases the results are within 0.01 \AA{} of the known distances. Several shells in germanium are also determined, with accuracy of better than 1%. Application of our method to crystalline copper indicates that the outer shells are more seriously affected by multiple-scattering problems and our procedure permits us to discard peaks that are spurious or unreliable. The present determination of the nearest-neighbor distance in copper is found to be in error by 0.014 \AA{}. Results of the application of this method to the determination of the bond lengths of a variety of compounds are summarized.

Neutron scattering study of the charge-density wave transitions in 2 H − Ta Se 2 and 2 H − Nb Se 2

Abstract: We have used the triple-axis neutron-scattering technique to study $2H\ensuremath{-}\mathrm{Ta}{\mathrm{Se}}_{2}$ and $2H\ensuremath{-}\mathrm{Nb}{\mathrm{Se}}_{2}$ which undergo charge-density wave transitions at ${T}_{0}=122.3$ K and ${T}_{0}=33.5$ K, respectively. The transitions in both compounds appear to be second-order and involve atomic displacements of ${\ensuremath{\Sigma}}_{1}$ symmetry. At inception, the superlattices in both compounds have nearly identical incommensurate wave vectors with magnitude ${q}_{\ensuremath{\delta}}=\frac{1}{3(1\ensuremath{-}\ensuremath{\delta}){a}^{*}}$, with $\ensuremath{\delta}\ensuremath{\sim}0.02$. The Nb${\mathrm{Se}}_{2}$ superlattice remains incommensurate to 5 K but Ta${\mathrm{Se}}_{2}$ undergoes a first-order lock-in transition where $\ensuremath{\delta}\ensuremath{\rightarrow}0$ at 90 K. The temperature dependence of the superlattice wave vector $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$ in the incommensurate phase and the lock-in transition are discussed using a free energy involving third-order "umklapp" terms and a secondary order parameter. The secondary lattice distortion which is predicted in this model is observed experimentally. Most phonon branches having energies less than 10 meV with propagation vectors in the [$\ensuremath{\zeta}00$] and [$00\ensuremath{\zeta}$] directions have been measured at 300 K. Strong anomalies are found in the ${\ensuremath{\Sigma}}_{1}[\ensuremath{\zeta}00]$ phonon branches in both materials near the wave vector ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}}_{c}=(\frac{1}{3},0,0)$ characteristic of the low-temperature superlattices. Substantial softening of this phonon is observed as the transition is approached. In addition, the spectral profile exhibits a central peak which is not measurably inelastic.

Energy Bands in Ferromagnetic Iron

Abstract: Results of a self-consistent tight-binding calculation of the band structure of body-centered-cubic iron are reported. The basis set consisted of atomic wave functions for the $1s$, $2s$, $3s$, $4s$, $2p$, $3p$, and $4p$ states, expressed as linear combinations of Gaussian-type orbitals (GTO), and five individual GTO for each $3d$ state. The Coulomb part of the crystal potential in the first iteration was constructed from a superposition of overlapping neutral-atom charge densities; the atoms being in the $3{d}^{7}4{s}^{1}$ configuration. Exchange potentials for both spins were calculated utilizing the $X\ensuremath{\alpha}$ method. Self-consistent band structures were obtained for different values of the exchange parameter $\ensuremath{\alpha}$. Best results appear to be obtained for $\ensuremath{\alpha}=0.64$. In this case, 140 points in $\frac{1}{48}$ of the Brillouin zone (BZ) were used to determine the charge density. The resulting self-consistent potentials were then utilized to compute energy levels at 819 regularly spaced points in $\frac{1}{48}$ of the BZ. The results thus obtained are discussed and compared with other reported band-structure results for the same metal. The Fermi surface is analyzed in detail. The density of states has been computed. Magnetic and x-ray form factors are presented. The results are found to be in reasonably good agreement with experiment.

Multiple-trapping model of anomalous transit-time dispersion in a − S e

Abstract: A generalized model of multiple trapping from a band of extended or localized states is used to study timedependent charge transport in amorphous solids. The model differs from a conventional multiple-trapping model by including a distribution of trap release rates for a constant trap energy. An extensive analysis of transient photocurrent experiments on $a\ensuremath{-}\mathrm{S}\mathrm{e}$ is carried out to determine the transport parameters for this case. It is found that a small number of parameters can be used to analyze the experimental results over a wide range of temperature and sample thickness. The results of the analysis are interpreted in terms of trapcontrolled hopping, which is a special case of the generalized multiple-trapping model. The asymptotic value of the theoretical photocurrent transient is obtained for the multiple-trapping model, and the results of Scher and Montroll are recovered for the case of extreme or anomalous dispersion, which occurs for $a\ensuremath{-}\mathrm{S}\mathrm{e}$ at low temperature ($T\ensuremath{\simeq}140$ K). The density of trapping sites is estimated, and the difficulties associated with considering a continuous distribution of trap release rates are discussed. It is concluded that the generalized multiple-trapping model, defined by simple first-order rate equations, is capable of describing detailed shapes of photocurrent transients, including dispersive and nondispersive charge transport.

Compact and accurate integral-transform wave functions. I. The 1 S 1 state of the helium-like ions from H − through Mg 1 0 +

Abstract: Accurate and compact integral-transform wave functions are constructed for the $1^{1}S$ state of the helium-like ions from ${\mathrm{H}}^{\ensuremath{-}}$ through ${\mathrm{Mg}}^{10+}$. The variational ansatz is of the form $\ensuremath{\Psi}({r}_{1}, {r}_{2}, {r}_{12})={(4\ensuremath{\pi})}^{\ensuremath{-}1}{\ensuremath{\Sigma}}_{k=1}^{N}{c}_{k}(1+{P}_{12})\mathrm{exp}(\ensuremath{-}{\ensuremath{\alpha}}_{k}{r}_{1}\ensuremath{-}{\ensuremath{\beta}}_{k}{r}_{2}\ensuremath{-}{\ensuremath{\gamma}}_{k}{r}_{12})$ where the ${c}_{k}$ are found by solving the secular equation and the exponents ${\ensuremath{\alpha}}_{k}$, ${\ensuremath{\beta}}_{k}$, and ${\ensuremath{\gamma}}_{k}$ are chosen to be the abscissas of Monte Carlo and number-theoretic quadrature formulas for a variationally optimized parallelotope in $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\beta}\ensuremath{-}\ensuremath{\gamma}$ space. A 66-term function of this type for the helium atom yields an energy of -2.903 724363 a.u. as compared with the 1078-term function of Pekeris which yields an energy of -2.903 724376 a.u. In order to test the accuracy of the wave functions a number of properties including $〈{r}^{n}〉$ and $〈{r}_{12}^{n}〉$ with $n=\ensuremath{-}2, \ensuremath{-}1, 1, \dots{}, 4$, $〈{\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}}}_{1}\ifmmode\cdot\else\textperiodcentered\fi{}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}}}_{2}〉$, $〈{cos\ensuremath{\theta}}_{12}〉$, $〈\ensuremath{\delta}({\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}}}_{1})〉$, and $〈\ensuremath{\delta}({\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}}}_{12})〉$ are computed and compared with the best available results. The electric dipole polarizability is computed from a simple formula due to Thorhallsson, Fisk, and Fraga. Comments on the limiting accuracy of this formula are made. Electron-nuclear and electron-electron cusp condition tests are made for the functions. Detailed convergence studies are presented for ${\mathrm{H}}^{\ensuremath{-}}$ and He in the form of a sequence of functions with increasing $N$. The functions are found to be rather accurate and more compact than any other functions available in the literature with the exception of those containing logarithmic terms. Possible refinements to the basis set used are discussed.

Tidal Dissipation in the Oceans: Astronomical, Geophysical and Oceanographic Consequences

Abstract: The most precise way of estimating the dissipation of tidal energy in the oceans is by evaluating the rate at which work is done by the tidal forces and this quantity is completely described by the fundamental harmonic in the ocean tide expansion that has the same degree and order as the forcing function. The contribution of all other harmonics to the work integral must vanish. These harmonics have been estimated for the principal M$\_{2}$ tide using several available numerical models and despite the often significant difference in the detail of the models, in the treatment of the boundary conditions and in the way dissipating forces are introduced, the results for the rate at which energy is dissipated are in good agreement. Equivalent phase lags, representing the global ocean-solid Earth response to the tidal forces and the rates of energy dissipation have been computed for other tidal frequencies, including the atmospheric tide, by using available tide models, age of tide observations and equilibrium theory. Orbits of close Earth satellites are periodically perturbed by the combined solid Earth and ocean tide and the delay of these perturbations compared with the tide potential defines the same terms as enter into the tidal dissipation problem. They provide, therefore, an independent estimate of dissipation. The results agree with the tide calculations and with the astronomical estimates. The satellite results are independent of dissipation in the Moon and a comparison of astronomical, satellite and tidal estimates of dissipation permits a separation of energy sinks in the solid Earth, the Moon and in the oceans. A precise separation is not yet possible since dissipation in the oceans dominates the other two sinks: dissipation occurs almost exclusively in the oceans and neither the solid Earth nor the Moon are important energy sinks. Lower limits to the Q of the solid Earth can be estimated by comparing the satellite results with the ocean calculations and by comparing the astronomical results with the latter. They result in Q > 120. The lunar acceleration [Note: See the image of page 546 for this formatted text], the Earth's tidal acceleration $\ddot{\theta}\_{\text{T}}$ and the total rate of energy dissipation $\dot{E}$ estimated by the three methods give [Note: See the image of page 546 for this formatted text] $ \matrix\format\l\kern.8em&\c\kern.8em&\c\kern.8em&\c \\ & \dot{n} & \theta \_{\text{T}} & \dot{E} \\ & 10^{-23}\,\text{s}^{-2}\quad ^{\prime \prime}\text{cy}^{-2} & \overline{10^{-22}\,\text{s}^{-2}} & \overline{10^{19}\,\text{erg s}^{-1}} \\ \text{astronomical based estimate} & -1.36\quad -28\pm 3 & -7.2\pm 0.7 & 4.1\pm 0.4 \\ \text{satellite based estimate} & -1.03\quad -24\pm 5 & -6.4\pm 1.5 & 3.6\pm 0.8 \\ \text{numerical tide model} & -1.49\quad -30\pm 3 & -7.5\pm 0.8 & 4.5\pm 0.5 \endmatrix $ The mean value for $\ddot{\theta}\_{\text{T}}$ corresponds to an increase in the length of day of 2.7 ms cy$^{-1}$. The non-tidal acceleration of the Earth is (1.8 $\pm $ 1.0) 10$^{-22}$ s$^{-2}$, resulting in a decrease in the length of day of 0.7 $\pm $ 0.4 ms cy$^{-1}$ and is barely significant. This quantity remains the most unsatisfactory of the accelerations. The nature of the dissipating mechanism remains unclear but whatever it is it must also control the phase of the second degree harmonic in the ocean expansion. It is this harmonic that permits the transfer of angular momentum from the Earth to the Moon but the energy dissipation occurs at frequencies at the other end of the tide's spatial spectrum. The efficacity of the break-up of the second degree term into the higher modes governs the amount of energy that is eventually dissipated. It appears that the break-up is controlled by global ocean characteristics such as the ocean-continent geometry and sea floor topography. Friction in a few shallow seas does not appear to be as important as previously thought: New estimates for dissipation in the Bering Sea being almost an order of magnitude smaller than earlier estimates. If bottom friction is important then it must be more uniformly distributed over the world's continental shelves. Likewise, if turbulence provides an important dissipation mechanism it must be fairly uniformly distributed along, for example, coastlines or along continental margins. Such a global distribution of the dissipation makes it improbable that there has been a change in the rate of dissipation during the last few millennium as there is no evidence of changes in ocean volume, or ocean geometry or sea level beyond a few metres. It also suggests that the time scale problem can be resolved if past ocean-continent geometries led to a less efficient breakdown of the second degree harmonic into higher degree harmonics.

Spin relaxation of photoelectrons in p -type gallium arsenide

Abstract: We have measured by optical-pumping methods the spin-relaxation time ${T}_{1}$ of photocreated conduction electrons in $p$-type GaAs (${N}_{A}=4\ifmmode\times\else\texttimes\fi{}{10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) as a function of temperature. To analyze our results we present a detailed discussion of the possible relaxation mechanisms in $p$-type semiconductors. The electronic spin relaxation may originate from: (i) the splitting of the conduction band, (ii) the spin-orbit interaction, (iii) the hyperfine interaction with nuclei of the host crystal, and (iv) the exchange interaction between electrons and holes. The spin-relaxation time is given in each case as a function of experimentally attainable parameters and permits one to obtain a numerical result for all usual III-V compounds. It is established that in doped $p$-type GaAs the exchange interaction with the holes is the dominant relaxation mechanism at low temperatures, the other mechanisms being too weak by several orders of magnitude. For higher temperatures ($T\ensuremath{\ge}100$ \ifmmode^\circ\else\textdegree\fi{}K), the relaxation due to the ${k}^{3}$ splitting of the conduction band may become predominant for ${N}_{A}\ensuremath{\lesssim}{10}^{+7}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. The theory is compared with experimental data available in the literature and with our experiments. From our measurements we obtain in GaAs the value of the exchange splitting of $1s$ exciton ${\ensuremath{\Delta}}_{x.1s}\ensuremath{\simeq}0.1$ meV. We also show that the observed spin depolarization at high kinetic energy (200-300 meV) can be explained by the splitting of the conduction band, taking into account the energy relaxation by optical-phonon scattering.

Coupled-cluster expansion applied to the electron gas: Inclusion of ring and exchange effects

Abstract: The coupled-cluster expansion (or the Coester-K\"ummel-\ifmmode \check{C}\else \v{C}\fi{}i\ifmmode \check{z}\else \v{z}\fi{}ek method) is applied to the correlation problem in the uniform electron gas Coupled nonlinear integral equations are developed for ring summations and the analytic structure of the expansion coefficients is examined To facilitate the solution of the equations a technique is introduced to reduce the dimensionality of the problem Numerical solution of the equations enable the evaluation of both ring and exchange effects The direct random-phase-approximation (RPA) energy agrees with other work to the accuracy of the calculation The screened exchange energy is evaluated for the first time and contributes about 30% of the RPA energy The resulting correlation energy compares favorably with recent calculations using a dielectric formulation over the range of metallic electron densities

Fermion-field nontopological solitons. II. Models for hadrons

Abstract: We examine the possibility, and its consequences, that in a relativistic local field theory, consisting of color quarks $q$, scalar gluon $\ensuremath{\sigma}$, color gauge field ${V}_{\ensuremath{\mu}}$, and color Higgs field $\ensuremath{\varphi}$, the mass of the soliton solution may be much lower than any mass of the plane-wave solutions; i.e., the quark mass ${m}_{q}$, the gluon mass ${m}_{\ensuremath{\sigma}}$, etc. There appears a rather clean separation between the physics of these low-mass solitons and that of the high-energy excitations, in the range of ${m}_{q}$ and ${m}_{\ensuremath{\sigma}}$, provided that the parameters $\ensuremath{\xi}\ensuremath{\equiv}{(\frac{\ensuremath{\mu}}{{m}_{q}})}^{2}$ and $\ensuremath{\eta}\ensuremath{\equiv}\frac{\ensuremath{\mu}}{{m}_{\ensuremath{\sigma}}}$ are both \ensuremath{\ll}1, where $\ensuremath{\mu}$ is an overall low-energy scale appropriate for the solitions [but the ratio $\frac{\ensuremath{\eta}}{\ensuremath{\xi}}$ is assumed to be $O(1)$, though otherwise arbitrary]. Under very general assumptions, we show that, independently of the number of parameters in the original Lagrangian, the mathematical problem of finding the quasiclassical soliton solutions reduces, through scaling, to that of a simple set of two coupled first-order differential equations, neither of which contains any explicit free parameters. The general properties and the numerical solutions of this reduced set of differential equations are given. The resulting solitons exhibit physical characteristics very similar to those of a "gas bubble" immersed in a "medium": there is a constant surface tension and a constant pressure exerted by the medium on the gas; in addition, there are the "thermodynamical" energy of the gas and the related gas pressure, which are determined by the solutions of the reduced equations. Both a SLAC-type bag and the Creutz-Soh version of the MIT bag may appear, but only as special limiting cases. These soliton solutions are applied to the physical hadrons; their static properties are calculated and, within a 10-15% accuracy, agree with observations.

Infrared lattice vibrations and dielectric dispersion in α-Fe 2 O 3

Abstract: The infrared reflection spectra of $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ were measured in the energy range 30-1000 ${\mathrm{cm}}^{\ensuremath{-}1}$; two optical-phonon modes were observed for extraordinary ray; four optical-phonon modes were observed for ordinary ray. The optical constants were calculated by Kramers-Kronig analysis, and were also analyzed by the classical-oscillator model. From these dielectric constants, the longitudinal and transverse optical-phonon frequencies were estimated. The Born and Szigeti effective charges were calculated and the ionicities among $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$, $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$, and $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ were studied. It is verified also that the generalized Lyddane-Sachs-Teller equation apply very well to $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$.

Statistical mechanics of dense ionized matter. VII. Equation of state and phase separation of ionic mixtures in a uniform background

Abstract: By solving the hypernetted chain (HNC) equation for the pair distribution functions, and by Monte Carlo simulations, we have calculated the equation of state and the pair structure of dense binary mixtures of classical point ions in a rigid, uniform background of opposite charge. All of our results indicate that the excess internal and free energies of mixing are negligible compared to the energies of the mixture or the pure phases, for ionic-charge ratios $\frac{{Z}_{2}}{{Z}_{1}}=2 \mathrm{and} 3$, in the strong coupling (high density or low temperature) regime. This feature allows us to write down a simple equation of state for such mixtures, which is used to determine the phase diagram of pressure-ionized H-He and H-Li mixtures in a rigid background of degenerate electrons. We then treat the polarization of the electron gas by the ionic-charge distribution by perturbation theory and include quantum corrections to the free energy of the ions. Both effects do not drastically modify the phase diagrams. The applicability of our results in astrophysical situations is discussed.

Identification of the defect state associated with a gallium vacancy in GaAs and Al x Ga 1 − x As

Abstract: Arguments based on new data as well as an analysis of the literature are given to show that the so-called $E3$ radiation-damage defect state in GaAs and ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ is most likely a gallium vacancy. It is first shown that on the basis of chemical trends one should expect vacancies in GaAs to be stable at room temperature. It is then argued that most of the defects observed in room-temperature 1-MeV electron-irradiated GaAs are likely to be simply native defects rather than clusters or impurity complexes. Data on the orientation dependence of the defect production rate are given which show that the defects which recover at 500 K in GaAs are all due to Ga atom displacements. Finally, data are presented on the energy-level shifts of seven deep levels, including the $E3$ level, in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ as a function of Al mole fraction. These data show that the $E3$ level is anomalous and remains fixed relative to the valence band whereas all other levels shift in energy to maintain their same relative position in the gap. This anomalous behavior is interpreted on the basis of theories of surface dangling bonds and vacancy states to be evidence that the $E3$ level is a gallium vacancy.

Molecular cluster studies of binary alloys: LiAl

Abstract: The electronic structure of the ordered Zintl ($B32$) phase of LiAl has been studied in a molecular-cluster model within the framework of the Hartree-Fock-Slater theory. ${\mathrm{Li}}_{5}$${\mathrm{Al}}_{4}$ and ${\mathrm{Al}}_{5}$${\mathrm{Li}}_{4}$ clusters were embedded in a potential field representative of the alloy environment; energy levels and wave functions were obtained by self-consistent iteration. Density-of-states and charge-density results are used to interpret NMR and electrical-conductivity studies. The case of a single Li vacancy was also treated, and discussed in the light of positronannihilation data.

Theory of the ionization of the hydrogen atom by an external electrostatic field

Abstract: The theory of the field ionization of the hydrogen atom is developed analytically. The leading term of an asymptotic expansion for the ionization rate---the reciprocal lifetime---is derived. In the weak-field limit, the formula for the ionization rate reduces to $\frac{1}{\ensuremath{\tau}}={n}^{\ensuremath{-}3}{[{n}_{2}!({n}_{2}+|m|)!]}^{\ensuremath{-}1} {(n\frac{^{3}F}{4})}^{\ensuremath{-}2{n}_{2}\ensuremath{-}{|m|}_{\ensuremath{-}1}}\ifmmode\times\else\texttimes\fi{}\mathrm{exp}[3({n}_{1}\ensuremath{-}{n}_{2})\frac{\ensuremath{-}2}{(3n^{3}F)}]$, where $n$, $m$, and ${n}_{1}$ and ${n}_{2}$ are the usual principal, magnetic, and parabolic quantum numbers, respectively, and $F$ is the field strength in atomic units. For the ground state, this formula agrees with that of Landau and Lifshitz. For all ${m}^{2}=1$ states, the formula agrees asymptotically for large ${n}_{2}$ with that of Lanczos after correction of the latter for an error. It is in disagreement with the result of Oppenheimer and with the low-field result of Rice and Good. Significantly better agreement with numerical calculations of Alexander, of Hehenberger, McIntosh, and Br\"andas, of Damburg and Kolosov, and of Bailey, Hiskes, and Riviere is obtained with a formula for not quite such small $F$, $\frac{1}{\ensuremath{\tau}}={(\ensuremath{-}2\mathrm{Re}E)}^{\frac{3}{2}}{[{n}_{2}!({n}_{2}+|m|)!]}^{\ensuremath{-}1}{f}^{\ensuremath{-}B}\mathrm{exp}[\ensuremath{-}\frac{1}{(6f)}]$, where $E$ is the perturbed energy, where $f=\frac{[{(\ensuremath{-}2E)}^{\ensuremath{-}\frac{3}{2}}F]}{4}$, and where $\frac{B}{2}={\ensuremath{\beta}}_{2,{n}_{2}}$ is the usual perturbed separation constant [${\ensuremath{\beta}}_{2}\ensuremath{\rightarrow}\frac{{n}_{2}+|m|}{2}+\frac{1}{2}$, as $F\ensuremath{\rightarrow}0$].

Optical properties of the chalcopyrite semiconductors ZnGeP/sub 2/, ZnGeAs/sub 2/, CuGaS/sub 2/, CuAlS/sub 2/, CuInSe/sub 2/, and AgInSe/sub 2/

Abstract: The reflectivities at 80 K of the chalcopyrite semiconductors CuGa${\mathrm{S}}_{2}$, CuAl${\mathrm{S}}_{2}$, CuIn${\mathrm{Se}}_{2}$, AgIn${\mathrm{Se}}_{2}$, ZnGe${\mathrm{P}}_{2}$, and ZnGe${\mathrm{As}}_{2}$ were measured in the energy range from 2 to 26 eV using sychrotron radiation. Occupied and unoccupied electronic states are described with the aid of the sharp reflectivity features from $d$ levels and of the electronic spectrum from an ESCA spectrometer.

Stochastic climate models, part 3. Application to zonally averaged energy models

Abstract: A stochastic Budyko-Sellers model is considered in which, in contrast to the usual statistical dynamical climate models, the nonaveraged weather fluctuations are retained as internal random forcing terms. Consequently, the climate variables are no longer deterministic but are stochastic variables, which can be characterized by their variance spectra. The calculated variance spectra of the yearly and zonally averaged surface temperature of the earth are consistent with observations both in the qualitative structure of the spectrum and the order of magnitude of the energy levels. DOI: 10.1111/j.2153-3490.1977.tb00749.x

Electronic structure of Si O 2 , Si x Ge 1 − x O 2 , and Ge O 2 from photoemission spectroscopy

Abstract: The valence-band structure of the mixed silicate ${\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$ was investigated for a range of compositions by x-ray and uv photoemission spectroscopy Structure in the valence band, which is derived from the oxygen nonbonding orbitals and from the Si-O bonding orbital, is seen to move continuously in initial energy in going from Si${\mathrm{O}}_{2}$ to Ge${\mathrm{O}}_{2}$ The width of the nonbonding bands at the top of the valence band decreases from about 33 eV in Si${\mathrm{O}}_{2}$ to 20 eV in Ge${\mathrm{O}}_{2}$ in which separate peaks are no longer resolved The decrease in width of the nonbonding bands is correlated with an increase in the average oxygen-oxygen separation from 262 to 285 \AA{} The results indicate that the width of the nonbonding bands is largely due to oxygen wave-function overlap The valence bands measured by photoemission from the mixed oxide are not a superposition of Si${\mathrm{O}}_{2}$ and Ge${\mathrm{O}}_{2}$ valence bands On the other hand, band-gap excitations, as determined by energy-loss satellites on the photoemission spectra, were found to be a superposition of those for Si${\mathrm{O}}_{2}$ and Ge${\mathrm{O}}_{2}$, indicating local conduction-band states centered about the Ge and Si sites

Angular-resolved uv photoemission and the band structure of GeS

Abstract: Angular-resolved photoelectron spectra (ARPES) are presented for GeS using 21-eV excitation energy. From the measurements that cover a wide range of angles along the two principal directions in the basal plane of the orthorhombic layered compound GeS $E$ vs ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}}_{\ensuremath{\parallel}}$ curves were constructed. The band structure of GeS was calculated utilizing the empirical pseudopotential method. The $E$ vs ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}}_{\ensuremath{\parallel}}$ curves can almost completely be understood in terms of this band structure under the assumption that only peaks in the one-dimensional density of states along ${k}_{\ensuremath{\perp}}$ contribute significantly to the ARPES spectrum.

Apparatus for extracting energy from movement of water

Abstract: This invention relates to apparatus for converting into useful energy movements imparted thereto by movement of water, preferably sea waves and/or sea currents, the apparatus comprising two or more interconnected members of which at least one is buoyant and which in use of the apparatus are movable relative to each other due to vertical motions of the water, at least one of said members being provided with or connected to means which in use of the apparatus is responsive to horizontal motions of the water, and means for converting the relative movements of said interconnected members and operation of the means responsive to horizontal motions of the water into useful energy, such as electricity.

Energy and structure of the ground state of liquid He4

Abstract: We present the results of a calculation of the energy- and liquid-structure function of the ground state of liquid $^{4}\mathrm{He}$ in the density range 0.0180-0.0257 ${\mathrm{\AA{}}}^{\ensuremath{-}3}$, using both the Lennard-Jones 6-12 potential and the second Morse-dipole-dipole potential of Bruch and McGee. The method is to determine the optimum Jastrow trial wave function by multiple iteration of the paired-phonon analysis, and then calculate the contributions of three-body factors in the wave function. Tables of values are given at several densities for the radial distribution function, Jastrow function, and liquid-structure function. We also present a variational formulation of the paired phonon analysis and numerical examples of its convergence and self-consistency.

Two-photon production processes at high energy. III

Abstract: We discuss the production of pairs of heavy leptons and pairs of heavy spinless mesons in ${e}^{+}{e}^{\ensuremath{-}}$ colliding beams. The two-photon production cross section of these particles is large in the energy region covered by the new machines at DESY and SLAC, and competes favorably with the one-photon production cross section. Leptonic decays of the new particles are incorporated in the analysis. We present both total cross sections and distributions in several important variables. Backgrounds from the regular two photon reaction ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ are also discussed.

Infrared studies of the energy gap and electron-phonon interaction in potassium-tetracyanoquinodimethane (K-TCNQ)

Abstract: The polarized reflectance at room temperature of potassium-tetracyanoquinodimethane (K-TCNQ) has been measured. Analysis using the Kramers-Kronig transforms gives the response functions (dielectric function and conductivity) between 300 and 23 000 ${\mathrm{cm}}^{\ensuremath{-}1}$. Attempts have been made to fit these functions with Lorentzian oscillators and it has been found that at least two such oscillators were required to give a satisfactory fit to the electronic transitions above 4000 ${\mathrm{cm}}^{\ensuremath{-}1}$: a strong, sharp peak corresponding to interband transitions and a weaker, broader absorption at higher energy from an intramolecular excitation. The oscillator-strength sum rule indicates that the energy gap is much larger than that inferred from magnetic resonance measurements and supports the view that Coulomb correlations are important in K-TCNQ. The molecular stretching modes are found to be stronger for the infrared electric field along the chain axis than perpendicular to it. As shown by recent calculations, this effect arises from electron\char22{}optical-phonon coupling effects. From the infrared data, we estimate the dimensionless electron\char22{}optical-phonon coupling constant to be ${\ensuremath{\lambda}}_{\mathrm{opt}}\ensuremath{\sim}0.1$.

Stress tensor of cosmic and laboratory type-II superconductors

Abstract: It has recently been pointed out by P. B. Jones that for $B\ensuremath{\ll}{H}_{\mathrm{cl}}$ the anisotropic part of the stress tensor associated with the flux lines in a type-II superconductor could be considerably larger than $\frac{{B}^{2}}{4\ensuremath{\pi}}$, and that consequently the magnetic distortions of a neutron star could be appreciably larger than previously supposed. We calculate the stress tensor of a type-II superconductor using a thermodynamic approach, and find that the magnitude of the anisotropic term is just $\frac{\mathrm{BH}}{4\ensuremath{\pi}}$, which agrees in order of magnitude, but not in detail, with Jones's result. The stress tensor derived here is then compared with that found by Josephson. We find additional terms arising from the strain dependence of the magnetic free energy.