Showing papers on "Energy (signal processing) published in 1987"

Electron mean-free-path calculations using a model dielectric function

Abstract: The inelastic electron mean free path as a function of energy is calculated for Cu, Ag, Au, and Al. The calculations are based on a model dielectric function \ensuremath{\epsilon}(q,\ensuremath{\omega}), which is obtained from a modification of the statistical approximation. In this approach \ensuremath{\epsilon}(0,\ensuremath{\omega}) is determined by the experimentally measured optical dielectric function. Calculated mean free paths are compared to experimental data and to other theories.

Critical wave functions and a Cantor-set spectrum of a one-dimensional quasicrystal model

Abstract: The electronic properties of a tight-binding model which possesses two types of hopping matrix element (or on-site energy) arranged in a Fibonacci sequence are studied. The wave functions are either self-similar (fractal) or chaotic and show ``critical'' (or ``exotic'') behavior. Scaling analysis for the self-similar wave functions at the center of the band and also at the edge of the band is performed. The energy spectrum is a Cantor set with zero Lebesque measure. The density of states is singularly concentrated with an index ${\ensuremath{\alpha}}_{E}$ which takes a value in the range [${\ensuremath{\alpha}}_{E}^{\mathrm{min}}$,${\ensuremath{\alpha}}_{E}^{\mathrm{max}}$]. The fractal dimensions f(${\ensuremath{\alpha}}_{E}$) of these singularities in the Cantor set are calculated. This function f(${\ensuremath{\alpha}}_{E}$) represents the global scaling properties of the Cantor-set spectrum.

Two-dimensional antiferromagnetic quantum spin-fluid state in La2CuO

Abstract: Elastic, quasielastic, and inelastic neutron scattering measurements in ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ reveal novel two-dimensional antiferromagnetic behavior. At high temperatures the spins are ordered instantaneously over long distances two dimensionally but there is no measurable time-averaged staggered moment. The energy scale of the spin fluctuations is large, corresponding to an effective dispersion of \ensuremath{\gtrsim}0.4 eV A\r{}. The relevance to the high-temperature superconductivity in this class of materials is noted.

Associative recall of memory without errors

Abstract: A neural network which is capable of recalling without errors any set of linearly independent patterns is studied. The network is based on a Hamiltonian version of the model of Personnaz et al. The energy of a state of N (\ifmmode\pm\else\textpm\fi{}1) neurons is the square of the Euclidean distance\char22{}in phase space\char22{}between the state and the linear subspace spanned by the patterns. This energy corresponds to nonlocal updatings of the synapses in the learning mode. Results of the mean-field theory (MFT) of the system as well as computer simulations are presented. The stable and metastable states of the network are studied as a function of ``temperature'' T and \ensuremath{\alpha}=p/N, where p is the number of embedded patterns. The maximum capacity of the network is \ensuremath{\alpha}=1. For all \ensuremath{\alpha} (0\ensuremath{\le}\ensuremath{\alpha}l1) the embedded patterns are not only locally stable but are global minima of the energy. The patterns appear, as metastable states, below a temperature T=${T}_{M}$(\ensuremath{\alpha}). The temperature ${T}_{M}$(\ensuremath{\alpha}) decreases to zero as \ensuremath{\alpha}\ensuremath{\rightarrow}1. The spurious states of the network are studied in detail in the case of random uncorrelated patterns. At finite p, they are identical to the mixture states of Hopfield's model. At finite \ensuremath{\alpha}, a spin-glass phase exists as a metastable state. According to the replica symmetric MFT the spin-glass state becomes degenerate with the patterns at \ensuremath{\alpha}=${\ensuremath{\alpha}}_{g}$=1-2/\ensuremath{\pi} and disappears above it. Possible interpretations of this unusual result are discussed. The average radius of attraction R of the patterns has been determined by computer simulations, for sizes up to N=400. The value of R for 0l\ensuremath{\alpha}l1 depends on the details of the dynamics. Results for both parallel and serial dynamics are presented. In both cases R is unity (the largest distance in phase space by definition) at \ensuremath{\alpha}\ensuremath{\rightarrow}0 and decreases monotonically to zero as \ensuremath{\alpha}\ensuremath{\rightarrow}1. Contrary to the MFT, simulations have not revealed, so far, any singularity in the properties of the spurious states at an intermediate value of \ensuremath{\alpha}.

Trends of Total Reaction Cross-sections for Heavy-ion Collisions in the Intermediate Energy-range

Abstract: Direct measurements of total reaction cross sections (${\ensuremath{\sigma}}_{R}$) have been performed in the energy range of 10--300 MeV/nucleon for heavy ion collisions. A decrease of ${\ensuremath{\sigma}}_{R}$ with increasing energy was observed for a wide range of masses of the colliding systems. The data suggest that ${\ensuremath{\sigma}}_{R}$ reaches a minimum located around 300 MeV/nucleon independently of the projectile target combination. A dependence of ${\ensuremath{\sigma}}_{R}$ on mass asymmetry of the system is also demonstrated. Trends of ${\ensuremath{\sigma}}_{R}$ in this energy range are well reproduced by the predictions of a simple microscopic model based on individual nucleon-nucleon collisions. Our data have been employed in this framework to derive a new semi- empirical parametrization of ${\ensuremath{\sigma}}_{R}$. Most of the experimental results in the intermediate and high energy range have been reproduced by this parametrization using a single energy-dependent parameter.

Stochastic random network model in Ge and Si chalcogenide glasses.

Abstract: A stochastic random network model is proposed for the structure of ${\mathrm{Ge}}_{\mathrm{x}}$${\mathrm{S}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$, ${\mathrm{Ge}}_{\mathrm{x}}$${\mathrm{Se}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$, ${\mathrm{Si}}_{\mathrm{x}}$${\mathrm{S}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$, and ${\mathrm{Si}}_{\mathrm{x}}$${\mathrm{Se}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ (x\ensuremath{\le}0.33) glasses. This model is constructed to explain the existence of two types of microcrystalline states induced by photoirradiation above or below the threshold intensity. This model characterizes the glass structure by one parameter P which is related to the existing probability of the edge-sharing bonds between the tetrahedral ${\mathrm{MX}}_{4}$ molecules relative to the corner-sharing bonds. P depends only on the species of atoms forming the glass and not on x. In order to prove the validity of the present model, Raman scattering experiments were made and the x dependence of the intensity ratio of the ${A}_{1}^{c}$ companion peak to the ${A}_{1}$ peak, I(${A}_{1}^{c}$)/I(${A}_{1}$), was obtained. From the viewpoint of phonon localization, the ${A}_{1}$ mode is assigned to the breathing mode of ${\mathrm{MX}}_{4}$ molecules and the ${A}_{1}^{c}$ mode to the vibration of chalcogen atoms on the edge-sharing double bonds. The x dependence of the intensity ratio I(${A}_{1}^{c}$)/I(${A}_{1}$) calculated by the present model is in good agreement with the experimentally obtained ratio. The P obtained increases in order from ${\mathrm{Ge}}_{\mathrm{x}}$${\mathrm{S}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$, ${\mathrm{Ge}}_{\mathrm{x}}$${\mathrm{Se}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$, ${\mathrm{Si}}_{\mathrm{x}}$${\mathrm{Se}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ to ${\mathrm{Si}}_{\mathrm{x}}$${\mathrm{S}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ with the same order of tendency of getting edge-sharing bonds in the crystals. The value of P is independent of the method of making the amorphous but it can be changed by photoirradiation. P decreases with irradiation below the threshold intensity, but it increases with irradiation above the threshold. The local energy in the glass is lower in the corner-sharing bonds, but the total energy is lowest in the same structure as the crystal. The threshold irradiation intensity for Se glass is less than one-hundredth of that for ${\mathrm{GeSe}}_{2}$ glass.

Lidar studies of the nighttime sodium layer over Urbana, Illinois: 2. Gravity waves

Abstract: On 34 nights between December 1980 and May 1986, 171 monochromatic gravity waves were observed in the mesospheric Na layer at Urbana, Illinois, using a lidar system. The characteristics of the waves are compared with radar measurements of gravity wave activity and theoretical models of wave saturation and dissipation phenomena. The measured vertical wavelengths ({lambda}{sub z}) range from 2 km to 17 km, the observed periods (T{sub ob}) range from 25 min to 800 min and the horizontal wavelengths ({lambda}{sub x}) range from 20 km to almost 3,000 km. The most apparent seasonal characteristic of the waves is the absence in summer of periods greater than 200 min and horizontal wavelengths greater than 400 km. The wave kinetic enerrablgy distributions are approximately proportional to k{sub z}{sup {minus}3}, k{sub x}{sup {minus}15/14} and f{sup {minus}5/3}. Because the average amplitude growth length for the data is only 19 km and linear saturation theory predicts a k{sub z}{sup {minus}2} dependence for the kinetic energy distribution of saturated waves, the observed waves are not strongly damped and appear to be influenced more by dissipation rather than by saturation effects. Both {lambda}{sub z} and {lambda}{sub x} show a strong tendency to increase with T{sub ob}. Themore » measured power law relationships are approximately {lambda}{sub z} {proportional to} T{sub ob}{sup 5/9} and {lambda}{sub x} {proportional to} T{sub ob}{sup 14/9}. The wave induced mean flow acceleration ranges from 0 to {minus}200 m s{sup {minus}1} day{sup {minus}1} and the average value is {minus}27.2 m s{sup {minus}1} day{sup {minus}1}. The effective viscosity limiting wave amplitudes ranges from 0 to 140 m{sup 2}s{sup {minus}1} and the average value is 37 m{sup 2}s{sup {minus}1}.« less

Optical motion sensor

Abstract: An optical motion sensor comprises first and second light emitting diodes that emit complementary pulsed beams of infrared energy within a sensing region. A photodiode sums the energies to produce a proportional sensing signal. An amplifier AC coupled to the photodiode blocks the constant portion of the sensing signal and passes a time varying signal portion produced by motion of an object to a sampling circuit. The sampling circuit samples the sensing signal synchronous with emission of the first pulsed beam and converts the time varying signal to a proportional detection signal. An integrator coupled to the sampling circuit responds to a detection signal by modulating the intensity of the second pulsed beam to null the earlier time varying portion of the sensing signal. The motion sensor can be configured as a presence sensor by changing the time constant of the integrator. A slower time constant changes the rate at which the beam intensity is modulated and thus increases the duration of the detection signal.

Why is Tc of the oxide superconductors so low

Abstract: An analysis of the resistivity above ${\mathrm{T}}_{\mathrm{c}}$ in the oxide superconductors shows that the inelastic-scattering rate is several times kT. This inelastic scattering yields pair breaking which suppresses ${\mathrm{T}}_{\mathrm{c}}$ relative to the energy gap. The large energy scale in the problem suggests an electronic pairing mechanism, which we believe leads to d-wave pairing. The inelastic scattering has contributions from electron-phonon and from electron-electron scattering in a two-dimensional square lattice near half filling. In the latter case, the pair breaking can be reduced in a more three-dimensional structure.

Exact analytical model of the classical Weibel instability in a relativistic anisotropic plasma

Abstract: Detailed properties of the Weibel instability in a relativistic unmagnetized plasma are investigated for a particular choice of anisotropic distribution function F(${p}_{\ensuremath{\perp}}^{2}$,${p}_{z}$) that permits an exact analytical solution to the dispersion relation for arbitrary energy anisotropy. The particular equilibrium-distribution function considered in the present analysis assumes that all particles move on a surface with perpendicular momentum ${p}_{\ensuremath{\perp}}$=p${^}_{\ensuremath{\perp}}$=const and are uniformly distributed in parallel momentum from ${p}_{z}$=-p${^}_{z}$=const to ${p}_{z}$=+p${^}_{z}$=const. (Here, the propagation direction is the z direction.) The resulting dispersion relation is solved analytically, and detailed stability properties are determined for a wide range of energy anisotropy.

Low-temperature magnetic spectroscopy of a dilute magnetic semiconductor

Abstract: A newly developed integrated SQUID magnetic spectrometer yields direct high-resolution measurements of the optically induced magnetization in a 10 \ensuremath{\mu}m-diam sample of ${\mathrm{Cd}}_{0.8}$${\mathrm{Mn}}_{0.2}$Te. Both the magnitude and the picosecond dynamics of the magnetic response have been studied and are seen to be dramatically dependent on the energy and polarization of the optical excitation. The data show that the overall sample magnetization changes upon illumination, and that the perturbed spins equilibrate through spin-lattice relaxation.

Energy loss of MeV light ions specularly reflected from a SnTe(001) surface

Abstract: Energy losses of specularly reflected MeV protons and He ions from a clean (001) surface of SnTe single crystal are observed. The position-dependent stopping powers near the surface are derived from the observed results. The obtained stopping power is proportional to ${E}^{\mathrm{\ensuremath{-}}1/2}$ exp(-${\ensuremath{\beta}}_{3}$x/2${a}_{\mathrm{TF})}$, where E is the ion energy, ${a}_{\mathrm{TF}}$ is the Thomas-Fermi screening distance, ${\ensuremath{\beta}}_{3}$ is 0.3, and x is the distance from the surface. This result is similar to the observed position-dependent stopping power for planar channeled ions.

Desorption by electronically stimulated adsorbate rotation

Abstract: Time-of-flight laser resonance ionization is used to measure state-selective translational energies of neutral NO, CO, and metastable CO (${\mathrm{a}}^{3}$\ensuremath{\Pi}) desorbed from Pt(111) upon electron impact. A novel and dominant NO channel has a threshold of \ensuremath{\sim}6 eV and a peak translational energy of 0.05 eV. Lifetime calculations reveal a long-lived simple excitation (5${\mathrm{\ensuremath{\sigma}}}^{\mathrm{\ensuremath{-}}1}$). Dynamical calculations reproduce translational and rotational energy distributions and suggest that the excitation frees the hindered rotation of NO.

Quantum theory of post-collision interaction in inner-shell photoionization: Final-state interaction between two continuum electrons.

Abstract: In inner-shell photoionization followed by Auger decay, the Auger electron initially screens the ionic Coulomb field ``seen'' by the photoelectron. This screening phenomenon affects the post-collision interaction that shifts the Auger energy and distorts the line shape. The analytical Auger electron line-shape formula which we derived previously on the basis of asymptotic Coulomb wave functions is now modified to account for the screening effect. The ionic charge seen by the photoelectron is reinterpreted on the basis of asymptotic properties of the continuum wave function pertaining to two outgoing electrons. It is shown that this procedure is consistent with semiclassical models which account for the time required for the Auger electron to overtake the photoelectron. Our modified Coulomb line shapes are found to agree perfectly with the semiclassical line shapes for photon excess energies ${E}_{\mathrm{exc}\mathrm{\ensuremath{\gtrsim}}({\ensuremath{\Gamma}}_{i}{\ensuremath{\varepsilon}}_{A}{)}^{1/2}}$, where ${\ensuremath{\Gamma}}_{i}$ is the width of the initial hole state and ${\ensuremath{\varepsilon}}_{A}$, the Auger electron energy. Agreement between the present theory and recent synchrotron-radiation measurements consequently becomes excellent in this range of photon energies as well.

Many-body effects in a modulation-doped semiconductor quantum well.

Abstract: The electron areal concentration ${n}_{s}$ of a one-sided 130-\AA{}-thick GaAs-Ga(Al)As modulation-doped quantum well is continuously varied from 0 to 6.6\ifmmode\times\else\texttimes\fi{}${10}^{11}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ by use of a Schottky gate. This allows one to study the precise evolution of the luminescence and excitation spectra with increasing ${n}_{s}$. From a comparison between the measured peak positions and Hartree calculations of the energy levels, a measurement of the band-gap renormalization is obtained.

Electronic states of BaPb1-xBixO3 in the semiconducting phase investigated by optical measurements.

Abstract: The semiconducting ${\mathrm{BaPb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Bi}}_{\mathrm{x}}$${\mathrm{O}}_{3}$ (0.35lx\ensuremath{\le}1) is investigated in detail by optical measurements. The optical spectrum shows that ${\mathrm{BaPb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Bi}}_{\mathrm{x}}$${\mathrm{O}}_{3}$ has a clear optical gap over the whole semiconducting compositional range. It is clearly shown by resonant Raman scattering measurements that the origin of this gap is a charge-density wave (CDW) accompanied by the breathing-mode distortion. No apparent effect of Pb substitution can be observed in the reflectivity spectra for the sample with xg0.7. For x\ensuremath{\le}0.7, the CDW gap decreases with x and simultaneously the absorption tail extends into the gap. This spectral behavior can be well interpreted in terms of the recently proposed theoretical model with emphasis on a local CDW and/or a substantial energy difference between Pb and Bi sites arising from the strong electron-phonon interaction. Thus it can be concluded that the strong electron-phonon interaction plays an essential role in the semiconducting phase of this material as well as in the metallic phase.

Positron annihilation in the high-temperature superconductor YBa2Cu3O6+ delta.

Abstract: Positron-annihilation lifetime and Doppler broadening energy spectra have been measured in high-temperature superconductors $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+\ensuremath{\delta}}$ as a function of temperature between 10 and 293 K. The observed positron lifetime and Doppler boradening $S$ parameter show an onset increase near the superconducting critical temperature (${T}_{c}=90$ K). This variation does not exist in a similar nonsuperconducting sample that contains a saturated oxygen vacancy content. These results give evidence that the oxygen vacancy and electronic structure change play an important role for high-${T}_{c}$ superconductivity.

Observation of direct multiquantum vibrational excitation in gas-surface scattering: NH3 on Au(111).

Abstract: Vibrationally excited N${\mathrm{H}}_{3}$ molecules are observed in the scattering of N${\mathrm{H}}_{3}$ ($v=0$) from Au(111). We observe up to three quanta of vibrational excitation in the ${\ensuremath{ u}}_{2}$ "umbrella" vibrational mode of N${\mathrm{H}}_{3}$. The vibrational excitation probability scales linearly with the kinetic energy of the incident beam above a threshold energy corresponding to the quanta excited, and is independent of the surface temperature, ${T}_{s}$, over the range $300 \mathrm{K}\ensuremath{\le}{T}_{s}\ensuremath{\le}800 \mathrm{K}$. These results are discussed in terms of an electronically adiabatic collisional mechanism for vibrational excitation.

Γ-X mixing in GaAs/ Al x Ga 1 − x As and Al x Ga 1 − x As/AlAs superlattices

Abstract: A systematic study of the conduction bands of the (001) GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As and ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As/AlAs superlattices using a one-band Wannier orbital model is presented. The parameters in the Wannier orbital model are fitted to correctly describe the lowest conduction band of the bulk semiconductors over the entire Brillouin zone, including the correct effective masses. Using this model, we have examined the dependence of the superlattice conduction-band energy levels on layer thicknesses, alloy composition, and wave vectors, as well as external hydrostatic pressure. We have found that there can be substantial mixing between the \ensuremath{\Gamma}-valley states and the (001) X-valley states. The symmetry of the confined X-valley states is found to be critically dependent on whether the slabs with higher Al concentration contain an even or odd number of monolayers. As a result, the amount of \ensuremath{\Gamma}-X mixing is extremely sensitive to the layer thicknesses. An experimental procedure for observing this effect with use of high-quality samples of superlattices with ultrathin layers is proposed. Our calculations also show that the pressure coefficients associated with the \ensuremath{\Gamma}-like quantum-well states decrease with well width; the results are in good agreement with experimental data. In addition, mixing between states derived from the (100) and (010) X valleys is also reported.

Some Results and Conjectures in the Gradient Theory of Phase Transitions

Abstract: In the van der Waals-Cahn-Hilliard theory of phase transitions the energy depends not only on the density, but also on the density gradient, a dependence introduced to account for the interface between phases. Within this theory the stable density-distributions u(x) for a fluid confined to a container Ω are characterized by the variational problem: (Ph) minimize $$ {{\text{E}}_{\text{h}}}{\text{(u) = }}\int_{\Omega } \{ {\text{W(u(x)) + }}{{\text{h}}^2}{\left| {{\text{gradu(x)}}} \right|^2}\} {\text{dx}} $$ subject to the constraint $$ \int_{\Omega } {\text{u}} {\text{(x)dx = m}} $$ Here W(u) is the coarse-grain energy, assumed nonconvex, h is a constant which characterizes capillary effects, and m is the total fluid mass.

Dephasing time and one-dimensional localization of two-dimensional electrons in GaAs / Al x Ga 1 − x As heterostructures

Abstract: Low-field magnetoresistance measurements are made on the two-dimensional (2D) electron gas in $\mathrm{GaAs}/{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ heterostructures to study the size effects on weak localization and the phase-breaking rate ($\frac{1}{{\ensuremath{\tau}}_{\ensuremath{\varphi}}}$) as a function of sample width ($W$) and potential probe spacing ($L$). When $L$ and $W$ are larger than $\ensuremath{\pi}{l}_{\ensuremath{\varphi}}$ and $\ensuremath{\pi}{L}_{T}$, where ${l}_{\ensuremath{\varphi}}$ is the phase-breaking length and ${L}_{T}$ is the thermal diffusion length, $\frac{1}{{\ensuremath{\tau}}_{\ensuremath{\varphi}}}$, deduced from experiment using the 2D localization theory, has some agreement with the theoretical 2D phase-breaking rate due to electromagnetic fluctuations and disagrees with the energy relaxation rate. When $Wl\ensuremath{\pi}{l}_{\ensuremath{\varphi}}$ and $\ensuremath{\pi}{L}_{T}$, both the localization effect and the determined $\frac{1}{{\ensuremath{\tau}}_{\ensuremath{\varphi}}}$ are one dimensional. When $L$ is small and comparable to ${l}_{\ensuremath{\varphi}}$ a new dimensional crossover for localization is observed. In such small samples, we also observe the predicted conductance fluctuations of order $\frac{{e}^{2}}{h}$.

A single-point locating system

Abstract: A locating system employs a single-point device employ­ ing unique scanning patterns for generating peak signal data which can be used to calculate the position of a signal source (12,14) within a scanned region. One preferred embodiment utilizes a satellite (10) in high earth geosynchronous orbit and a simultaneous yaw and roll pattern to scan a substantial por­ tion of the earth's surface. The point source being located may be virtually any form of transmitter of radiant energy such as infrared, electromagnetic, light or acoustical energy. The scanning device may also be positioned in a low earth orbit satellite, an aircraft, a missile or a helicopter. The single-­ point device re-radiates the signal source transmission to a computer command center (16) which correlates single-point device scanning position data with received transmissions to accurately compute the location of the signal source (12, 14). Beacons (24) placed at precisely known locations may be used to interpret scan data. The computer triangulates peak signals of multiple roll orbits (74) generated during each yaw orbit (75) of the single-point device to determine the precise location of the source (76). The computer may also search a data base to identify the signal source and provide related information previously stored in the data base. The invention is particularly advantageous for locating stolen vehicles and for finding kidnapped persons. An alternative embodiment employs a peak-detecting ground-based receiver and a satellite or other single-point scanning device which generates and transmits a signal to the receiver indicating the satellite's precise current position in antenna yaw and roll. The ground-based receiver is equipped with a computer for calculating its own position by repeatedly correlating the time of peak signal detection and the yaw and roll data from the received satellite signal. Such an alternative embodiment would enable precise self-­ position determination without the use of a command center. The term "peak signal detection" also includes averag­ ing first and last signal acquisition, counting and averaging all signal acquisitions and all other techniques for determin­ ing the direction of maximum received signal strength.

Direct experimental determination of the crossover frequency between phonon and fracton regimes and its scaling behavior in superionic silver borate glasses.

Abstract: We determined the crossover frequency ${\mathrm{\ensuremath{\omega}}}_{\mathrm{co}}$ between phonon and fracton regimes from the study of the low-frequency inelastic light scattering in superionic borate glasses of the type (AgI${)}_{\mathit{x}}$(${\mathrm{Ag}}_{2}$O\ensuremath{\cdot}${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$${)}_{1\mathrm{\ensuremath{-}}\mathit{x}}$. The scaling of ${\mathrm{\ensuremath{\omega}}}_{\mathrm{co}}$ with the fractal characteristic length was studied by variation of the AgI concentration x. We thus obtained the diffusion coefficient scaling exponent theta and the spectral dimensionality d\ifmmode \tilde{}\else \~{}\fi{} which characterizes energy diffusion on a fractal.

Data processing apparatus with energy saving clocking device

Abstract: The energy consumption of a data processing apparatus, having a data processing element with an operating mode and a stop mode, in which latter mode RAM contents are saved but all other chip functions are inoperative, can be minimized by switching between the two modes and by adjusting the oscillator's frequency at the optimal value, depending among others, on the data processing apparatus' task.

Reaction (dpol,2He) at intermediate energies.

Abstract: We have succeeded in measuring at 0\ifmmode^\circ\else\textdegree\fi{} and small angles the energy spectra for the (d,2p${[\mathrm{}}^{1}$${S}_{0}$]) reaction (with the two protons in the singlet S state) at 650 MeV and 2 GeV. It is demonstrated that the reaction is a one-step process that can be used to study isospin-spin excitations. The \ensuremath{\Delta} excitation is very clearly observed. A shift down in energy of the \ensuremath{\Delta} peak from the proton to the $^{12}\mathrm{C}$ target is observed. The experiments are performed with a tensor polarized beam and the tensor analyzing power for the p(${d}_{\mathrm{pol}}$,${\mathrm{}}^{2}$He)n reaction at 2 GeV is given.

Neutrino mass from the beta spectrum in the decay of tritium.

Abstract: The data from the spectrum measurement of the tritium decay in a valine molecule carried out in a wide energy range (3.4 keV) with the Institute of Theoretical and Experimental Physics spectrometer are analyzed. The combined analysis of both these data and the data of the previous cycle gives the neutrino mass ${30.3}_{\ensuremath{-}8}^{+2}$ eV. The model-independent mass interval $17l{M}_{\ensuremath{ u}}l40$ eV is derived from the mass difference of the doublet $^{3}\mathrm{H}$-$^{3}\mathrm{He}$.

Time difference of arrival geolocation method, etc.

Abstract: A direction finding method and apparatus for a radio signal source, modulated by a digital information signal and existing in a heavy interference environment, is based on cyclic crosscorrelation. The direction finding technique exploits the second order periodicity of a transmitted signal having digital modulation, whereby the technique is immune to narrow-band interference. Radio frequency signals are received by two spaced antennas, and the signal of interest can be considered as a cyclostationary process. The signal time of arrival difference between the two antennas is determined using a cyclic crosscorrelation method. This is implemented by sending the electrical signals, developed by the antennas, through a variable delay device, then to a balanced mixer. The composite signal from the mixer is sent to a band-pass filter whose center frequency is equal to the baud rate of the signal of interest. The output energy of the filter is proportional to that portion of the cyclic crosscorrelation function where the cyclic frequency corresponds to the baud rate. With the use of a peak detector, which finds the peak values of the cyclic crosscorrelation function, the time difference of arrival between the two antennas is determined. This, in turn, determines a line of position to the radio source.

Observation of a soft surface-phonon mode in the reconstruction of clean W(100).

Abstract: He-atom-beam scattering has been used to investigate the reconstruction of the W(001) surface. At low surface temperatures ${T}_{s}$ a sharp $(\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2})R45\ifmmode^\circ\else\textdegree\fi{}$ diffraction pattern is observed. When ${T}_{s}$ is raised, the fractional-order beams broaden and shift towards the specular. At ${T}_{s}\ensuremath{\approx}450$ K the time-of-flight spectra reveal two different surface phonons along the $〈110〉$ direction, a normal Rayleigh mode and a strongly anomalous mode with a maximum at a wave vector $Q$ at one-half of the zone boundary ${Q}_{\mathrm{BZ}}$ and an energy approaching zero at $Q\ensuremath{\sim}0.8{Q}_{\mathrm{BZ}}$. This mode softens with decreasing temperature, identifying the structural transformation as a continuous displacive transition.

Temperature-dissipation measurements in a turbulent boundary layer

Abstract: The three components of the average temperature dissipation have been measured using a pair of parallel cold wires in an approximately self-preserving turbulent boundary layer. The mean square value of θ, x the temperature derivative in the longitudinal direction, is determined mainly by the use of Taylor's hypothesis, following direct verification of this hypothesis at a few locations in the flow. Mean square values of θ, y and θ, z , the temperature derivatives in directions normal to the flow, were estimated mainly from the curvature of spatial temperature autocorrelations. In the outer layer, the measurements indicate that $\overline{\theta^2}_{,z} > \overline{\theta^2}_{,y} > \overline{\theta^2}_{,x}$ , and the resulting distribution for dissipation leads to a good closure of the $\frac{1}{2}\overline{\theta^2}$ budget. In the near-wall region the measurements indicate that $\overline{\theta^2}_{,y} > \overline{\theta^2}_{,z} > \overline{\theta^2}_{,x}$ . The ratios $\overline{\theta^2}_{,y}/\overline{\theta^2}_{,x} $ and $\overline{\theta^2}_{,z}/\overline{\theta^2}_{,x}$ are as large as 13 and 7 respectively at y + = 12, underlining the strong anisotropy in this region. The behaviour of the turbulent diffusion, estimated by difference, provides reasonable support for the accuracy of the near-wall temperature-dissipation measurements. Using existing data of near-wall distributions of the turbulent energy and of its dissipation rate, the timescale for the turbulent-energy dissipation is found to be approximately equal to that for the temperature dissipation.

Energy-level correlation function and ac conductivity of a finite disordered system

Abstract: The space- and energy-difference- (\ensuremath{\omega}) dependent Wigner-type correlation function for the energy levels is studied for the Anderson disordered tight-binding model, including some of the effects of localization. For small metallic particles it is confirmed that these correlations, in the absence of spin and magnetic effects, are similar to those of the Gaussian orthogonal ensemble. This is in agreement with the conjecture made by Gor'kov and Eliashberg and the analytical results obtained by Efetov. The results are used to obtain the effective conductivity ${\ensuremath{\sigma}}_{\mathrm{eff}(\mathrm{\ensuremath{\omega}}}$), relevant for the absorption of low-frequency electromagnetic radiation, in all regimes, including the effects of localization and screening. It is found that in the orthogonal case, ${\ensuremath{\sigma}}_{\mathrm{eff}(\mathrm{\ensuremath{\omega}}}$) does not change at low \ensuremath{\omega} when level correlations become important. The conditions to observe changes in the absorption in this regime due to changes in the ensemble symmetry are formulated. In all cases except for the microscopic (critical) one, ${\ensuremath{\sigma}}_{\mathrm{eff}(\mathrm{\ensuremath{\omega}})\mathrm{\ensuremath{\propto}}{\ensuremath{\omega}}^{2}}$, and in the latter region, ${\ensuremath{\sigma}}_{\mathrm{eff}(\mathrm{\ensuremath{\omega}})\mathrm{\ensuremath{\propto}}{\ensuremath{\omega}}^{5/3}}$. For systems much larger than the localization length, the level correlations decay in space with a length \ensuremath{\xi} ln(${\ensuremath{\Delta}}_{\ensuremath{\xi}}$/\ensuremath{\omega}), as \ensuremath{\omega}\ensuremath{\rightarrow}0 (${\ensuremath{\Delta}}_{\ensuremath{\xi}}$ is the average spacing between levels within a localization volume). The connection with Mott's calculation of the ac conductivity in the insulating phase is made. It is shown that these ideas explain the ``level attraction'' found in one dimension by Gor'kov, Dorokhov, and Prigara. These considerations are generalized to the evaluation of the space-dependent level correlation function in an arbitrary dimension.