Electron-phonon interactions in transition metals

The tight-binding method is used to calculate 〈I²〉, the Fermi surface average of the squared electron-phonon coupling constant for 4d b.c.c.—transition metals and alloys. When nonorthogonality effects are properly included, our results for 〈I²〉 agree very well with empirical values. Moreover, the variation of 〈I²〉 can be understood in simple physical terms.     

A comparison of electron-phonon interaction in metallic hydrogen and free electron like metals

The electron-phonon interaction 〈I)²〉 for metallic hydrogen is calculated directly from McMillan's expression and compared with the result recently obtained by Papaconstantopoulos and Klein using the Gaspari-Gyorffy theory. Comparison is also made with 〈I)²〉 for Na.     

Effects of cross-correlation between the real and imaginary parts of the quantum noise in a two-mode saturation laser system

A two-mode saturation laser model with cross-correlation between the real and imaginary parts of the quantum noise is considered. The laser intensity Langevin equation and corresponding Fokker-Planck equation are derived by the phase-locking method. The effects of the cross-correlation strength λ between the real and imaginary parts of quantum noise and the cavity decay constant K on the steady-state intensity distribution Q(I₁,I₂), the mean light intensity 〈I〉, the normalization autocorrelation λ₁₁(0) and cross correlation λ₁₂(0) are studied by numerical calculation. The results show that as λ increases the Qs(I₁,I₂) show two extrema, and λ almost does not affect the 〈I〉, λ₁₁(0) and λ₁₂(0) when the laser system is operated far above threshold. Nevertheless, when the laser system is operated at and below threshold, λ makes the curves of Qs(I₁,I₂) have the higher peak and drop faster. Furthermore, it enhances the deviation of λ₁₁(0) and λ₁₂(0) and lessens the mean light intensity 〈I〉 when the laser system is operated at and below threshold.     

Mass asymmetry dependence of angular distribution in237Np(α29 and 44 MeV,f): single particle effect

Angular distributions of fission products have been measured as a function of mass asymmetry in the odd-Z ²³⁷Np(α_{29 and 44 MeV},f) system using a recoil-catcher technique and off-line gamma spectrometry. Higher angular anisotropies were observed for the asymmetric mode products compared to the symmetric mode products at both energies. Average anisotropies for individual modes are lower than those for neighbouring even-even fissioning nucleus²⁴²Pu due to odd-nucleon spin effect. Present data have been analysed according to the transition state model assuming two modes of fission with characteristic saddle-shapes, barriers and multichance fission probabilities. It is seen that angular distributions for the symmetric and asymmetric modes are decided at and well past the corresponding saddle points respectively. Odd-nucleon spin contribution (〈k ²〉) to the tilting mode variance have been deduced. For (²⁴¹)Am fission, 〈k ²〉 values for the asymmetric and symmetric modes are ≤ 14 and > 14 ?² respectively. The 〈k ²〉 value averaged over several nuclei from preactinide (²⁰¹Ti) to actinide (²⁴⁸Cf) is 11.5 ± 4.2 ?². Average 〈k ²〉 value is in close agreement with the theoretical estimate.     

Dynamical properties of a dissipative discontinuous map: A scaling investigation

The effects of dissipation on the scaling properties of nonlinear discontinuous maps are investigated by analyzing the behavior of the average squared action 〈I²〉$〈I^2〉$ as a function of the n-th iteration of the map as well as the parameters K and γ  , controlling nonlinearity and dissipation, respectively. We concentrate our efforts to study the case where the nonlinearity is large; i.e., K?1$K?1$. In this regime and for large initial action _I0?K$I_0?K$, we prove that dissipation produces an exponential decay for the average action 〈I〉$〈I〉$. Also, for _I0≅0$I_0\cong 0$, we describe the behavior of 〈I²〉$〈I^2〉$ using a scaling function and analytically obtain critical exponents which are used to overlap different curves of 〈I²〉$〈I^2〉$ onto a universal plot. We complete our study with the analysis of the scaling properties of the deviation around the average action ω.     

Changes in nuclear mean square charge radii of stable Krypton isotopes

The isotope shifts of stable even Kr isotopes (A=78 throughA=86) in the optical transitions at 432 nm and 557 nm were measured by means of polarization laser spectroscopy. The observed shifts are consistent with earlier results for other transitions. From the isotope shifts the changes in the nuclear mean square charge radiiδ〈r ²〉 were inferred using preliminary muonic isotope shift data. Starting from⁷⁸Kr, a monotonic decrease of 〈r ²〉 with increasing mass number is found throughout theg _9/2 neutron shell. The effect onδ〈r ²〉 of nuclear deformations as well as possible contributions due to changes in the skin thickness of the nuclear charge distribution are discussed.     

Nuclear moments and optical isotope shifts of108m Ag and110m Ag

The hyperfine structure of the resonance lines of^108m Ag and^110m Ag has been investigated by means of optical interference spectroscopy. The metastable isotopes were produced by neutron irradiation in a reactor. From the measureda- andb-values we derive the value for the nuclear magnetic dipole moment of^108mAgμ _I (108m)=3.577 (20)μ _n and the values for the electric quadrupole momentsQ _I (108m)=1.52(8) bQ _I (110m)=1.65(10) b (without Sternheimer correction). The measured isotope shifts allow the determination of the changes in the mean square charge radii of the nuclei involved:δ 〈r ²〉(108m-107)=0.022(3)fm² δ 〈r ²〉(110m-109)=0.029(2)fm². The isotope positions show odd-even staggering comparable with those of neighbouring isotonic nuclides.     

Averaged local field intensities in composite films

The photophysical properties of molecules adsorbed in composite films (e.g. surface island films) depend on the local electromagnetic field within the film. The ratio between the average field intensity 〈|E|²〉 in the film and the intensity |E_I|² associated with the incident field is a measure of the electromagnetic contribution to the surface influence on molecular photophysical phenomena. This ratio depends on the film composition and morphology, on the dielectric properties of the pure components making the film and on the frequency, direction and polarization of the incident radiation. Calculations of this ratio as a function of these parameters for several models of composite films are presented. Image interactions and retardation effects as well as radiative damping and finite size contributions to the dielectric response of the films are taken into account. In addition, an estimate of the field inhomogeneity within the film is obtained by calculating also the ratio 〈|E|²〉_shell/|E_I|² associated with the field in thin shells surrounding the dielectric particles which constitute the film.     

Isotope shifts in the atomic spectrum of xenon and nuclear deformation effects

Optical isotope shifts of four lines in the atomic spectrum of xenon have been measured using enriched samples of all stable xenon isotopes. The spectrograms were recorded with the aid of a pressure-scanned Fabry-Pérot interferometer and analysed by digital data techniques. The measured isotope shifts are shown to be self-consistent by means of a King plot. An estimate of the specific mass effect is given and the changesδ 〈r ²〉 of the mean square radius of the nuclear charge distribution are extracted from the measured shifts. These changesδ 〈r ²〉 are discussed in terms of the nuclear deformation parameterβ ². The results for the deformation of the stable even xenon isotopes are shown to be in good agreement with the systematic of deformation found for the neighbouring elements from Coulomb excitation experiments.     

Resonant paramagnetic enhancement of the thermal and zero-point Nyquist noise

The interaction between a very thin macroscopic solenoid, and a single magnetic particle precessing in a external magnetic field B₀, is described by taking into account the thermal and the zero-point fluctuations of stochastic electrodynamics. The inductor belongs to a RLC circuit without batteries and the random motion of the magnetic dipole generates in the solenoid a fluctuating current I_dip(t), and a fluctuating voltage ε_dip(t), with spectral distribution quite different from the Nyquist noise. We show that the mean square value 〈I_dip²〉 presents an enormous variation when the frequency of precession approaches the frequency of the circuit, but it is still much smaller than the Nyquist current in the circuit. However, we also show that 〈I_dip²〉 can reach measurable values if the inductor is interacting with a macroscopic sample of magnetic particles (atoms or nuclei) which are close enough to its coils.     

Structure of crystallized layers by laser annealing of 〈100〉 and 〈111〉 self-implanted silicon samples

Channeling effect techniques with a 2.0 MeV He⁺ Rutherford backscattering and transmission electron microscopy were used to characterize the crystallized layers after Q-switched ruby laser irradiation of 4000 Å thick amorphous layer on 〈100〉 and 〈111〉 underlined crystal substrates. At a laser energy density of 2.5 J/cm² the crystal layer on the 〈111〉 specimen contains a large density of stacking-faults, that on 〈100〉 specimen contains a very small amount of screw dislocation lines. High quality single-crystal layers have been obtained after irradiation at 3.5 J/cm². From a comparison with the growth rate and defect structure observed in thermally annealed implanted-amorphous layers, we propose that crystal growth by 50 ns pulse laser annealing occurs by melting the amorphous layer.     

Exactly Complete Solutions of the Pseudoharmonic Potential in N-Dimensions

We present analytically the exact solutions of the Schrödinger equation in the N-dimensional spaces for the pseudoharmonic oscillator potential by means of the ansatz method. The energy eigenvalues of the bound states are easily calculated from this eigenfunction ansatz. The normalized wavefunctions are also obtained. A realization of the ladder operators for the wavefunctions is studied and we deduced that these operators satisfy the commutation relations of the generators of the dynamical group SU(1,1). Some expectation values for 〈r ^?2〉, 〈r ²〉, 〈T〉, 〈V〉, 〈H〉, 〈p ²〉 and the virial theorem for the pseudoharmonic oscillator potential in an arbitrary number of dimensions are obtained by means of the Hellmann–Feynman theorems. Each solution obtained is dimensions and parameters dependent.     

Electromagnetic moments and nuclear charge radii for neutron-deficient Tb isotopes and the deformation jump nearZ=64,N=90

Optical isotope shifts and hyperfine structures of the^{147–153,155,157,159} Tb isotopes have been measured by the resonance ionization spectroscopy method. Nuclear moments and changes in nuclear charge radiiΔ 〈r ²〉 have been deduced. The “jump” inΔ 〈r ²〉 atN=88–90 has been revealed. It is compared with the relevant data for nuclei with other proton numbers.     

Ultrasonic attenuation in aluminium

Second- and third-order elastic-constant data have been used to determine the Grüneisen mode, 〈γ〉, average-square Grüneisen constant, 〈γ²〉 and nonlinearity constant D, for Aluminium. The attenuation suffered by longitudinal ultrasonic wave propagating in 〈100〉 and 〈110〉 directions and shear wave polarized along 〈100〉 and 〈1$\text{1}$0〉 directions, due to phonon viscosity and thermoelastic phenomena have been evaluated from two different values of TOEM at 289°K and comparison with observed experimental results has been made also.     

Observations of MeV ions emitted from a laser produced plasma

Fast-ion emission from tungsten plasmas has been studied with neodymium laser intensities from 5x10¹² to 2x10¹⁵ W/cm². Ion energies into the MeV region have been observed. The variation of ion energy (E_I) with laser intensity (I) was found to be of the form E_I∞I^0.65.     

Exact Results for Conditional Means of a Passive Scalar in Certain Statistically Homogeneous Flows

For a passive scalar T(r, t) randomly advected by a statistically homogeneous flow, the probability density function (pdf) of its fluctuation can in general be expressed in terms of two conditional means: 〈?² T|T〉 and 〈|?T|²|T〉. We find that in some special cases, either one of the two conditional means can be obtained explicitly from the equation of motion. In the cases when there is no external source and that the normalized fluctuation reaches a steady state or when a steady state results from a negative damping, 〈?² T|T〉=?(〈|?T|²〉/〈T ²〉)T. The linearity of the conditional mean in these cases follows directly from the fact that the advection equation of a passive scalar is linear. On the other hand, when the scalar is supported by a homogeneous white-in-time external source, 〈|?T|²|T〉=〈|?T|²〉.     

Classical Motion in Force Fields with Short Range Correlations

We study the long time motion of fast particles moving through time-dependent random force fields with correlations that decay rapidly in space, but not necessarily in time. The time dependence of the averaged kinetic energy 〈p ²(t)〉/2 and mean-squared displacement 〈q ²(t)〉 is shown to exhibit a large degree of universality; it depends only on whether the force is, or is not, a gradient vector field. When it is, 〈p ²(t)〉～t ^2/5 independently of the details of the potential and of the space dimension. The stochastically accelerated particle motion is then superballistic in one dimension, with 〈q ²(t)〉～t ^12/5, and ballistic in higher dimensions, with 〈q ²(t)〉～t ². These predictions are supported by numerical results in one and two dimensions. For force fields not obtained from a potential field, the power laws are different: 〈p ²(t)〉～t ^2/3 and 〈q ²(t)〉～t ^8/3 in all dimensions d≥1.     

Franck-Condon factors and R-centroids for the BΣ → AΠ band system of CN

Franck-Condon factors and R-centroids for the transition from the B²Σ electronic state of CN to the A²Π state have been calculated. The validity of the Morse potential energy function for this system has been studied by using the calculated values of α_e. Also, the ratios 〈rⁿ〉/〈rⁿ⁻¹〉 have been obtained to check the applicabili ty of the R-centroid approximation.     

Threshold behavior of multiple photon dissociation of SF6

Multiple photon dissociation of SF₆ by a short pulse of a CO₂ laser has been investigated by simultaneous measurements of the average number of photons absorbed per molecule 〈n〉 and chemiluminescence intensities which result from the dissociated F atoms. A criterion for the dissociation threshold which is independent of laser wavelength is found to be 〈n〉 = 16 ± 3 photons per molecule. A thermal distribution of the excited molecules is shown to be inconsistent with the behavior just above threshold.     

Structure and phase composition of thin a-C:H films modified by Ag and Ti

The structure and phase composition of thin a-C:H and a-C:H〈M〉 films (M = Ag, Ti, or Ag + Ti) have been studied by Raman and X-ray photoelectron spectroscopy. The a-C:H〈M〉 films were prepared by ion-plasma magnetron sputtering of a combined target of graphite and metal in an Ar–CH₄ gas mixture. The Raman spectra of these films indicate that their structure is amorphous. The a-C:H〈Ag + Ti〉 films have a more graphitized structure in comparison with pure a-C:H films and films containing only one metal. It is established that carbon in the a-C:H〈Ag + Ti〉 films is in the sp ², sp ³, and C=O states, which are characteristic of the a-C:H, a-C:H〈Ag〉, and a-C:H〈Ti〉 films. In addition, there are also ether (–C–O–C–) or epoxy (?C?O–) carbon groups in the a-C:H〈Ag + Ti〉 films. It has been revealed that silver atoms in the a-C:H〈Ag〉 and a-C:H〈Ag + Ti〉 films form no chemical bonds with carbon, oxygen, and titanium. Titanium in the a-C:H〈Ti〉 and a-C:H〈Ag + Ti〉 films exists in the form of titanium IV oxide (TiO₂).