The changes in the electronic structure of B2 FeAl alloy with a Fe antisite and absorbed hydrogen

The electronic structure and bonding in a B2 FeAl alloy with and without hydrogen interaction with a Fe antisite were computed using a density functional theoretical method. The hydrogen absorption turns out to be a favorable process. The hydrogen was found close to an octahedral site where one of its Al capped is replaced by a Fe antisite. The Fe–H distance is of 1.45 Å same as the Al–H distance.The density of states (DOS) curves show several peaks below the d metal band which is made up mostly of hydrogen based states (>50% H_1s) while the metal contribution in this region includes mainly s and p orbitals.An electron transfer of nearby 0.21e⁻ comes from the metal to the H. The overlap population values reveal metal–metal bond breaking, the intermetallic bond being the most affected. The H bond mainly with the Al atom and the reported Fe–H overlap population is much lower than that corresponding to FePd alloys and BCC Fe. The changes in the overlap population show the Fe–Al bond is weakened nearly 41.5% after H absorption, while the Fe–Fe bond is only weakened 34.5%. H also develops a stronger bond with the Al atoms. The main bond is developed with Al being twice stronger than Fe–H.     

A Spin-Shift Operator of the Multi-particle Ruijsenaars–Schneider Hamiltonian

We obtain a spin-shift operator for the multi-particle trigonometric Ruijsenaars–Schneider Hamiltonian. This result is a generalization of the argument in Phys. Lett. B 375 (1996), 89–97, where the integrability of the one-particle Ruijsenaars–Schneider system is shown by using the existence of a spin-shift operator.     

Ultra-fast dynamics of electron thermalization,cooling and transport effects in Ru(001)

Time-resolved two-photon photoelectron spectroscopy is used to study the dynamics of non-equilibrium electron and hole distributions at bare and D₂O-covered Ru(001) following optical excitation (55-fs, 800-nm pulses) with variable fluence (0.04–0.6 mJcm^-2). Within the first 0.5 ps we observe an ultra-fast transient of the excited-carrier population and energy density at the surface which is accompanied by pronounced deviations of the electron-energy distribution from a (thermalized) Fermi–Dirac distribution. Comparison of the transient energy density of the photoexcited electrons at the surface with predictions of the two-temperature model provides fair agreement up to 400 fs, but exhibits a systematically lower energy density at later times, where electrons and phonons are equilibrated. We propose that this reduced energy density at the surface originates from ultra-fast energy transport of non-thermal electrons into the bulk in competition to electron–phonon coupling at the surface. This is corroborated by extending the two-temperature model to account for non-thermal, photoexcited electrons, whereby quantitative agreement with experiment can only be achieved if ballistic transport and reduced electron–phonon coupling is incorporated for non-thermal electrons. Implications for surface femtochemistry are discussed. PACS 78.47.+p; 71.38.-k; 73.40.-c     

Theory of Dynamical Systems and the Relations Between Classical and Quantum Mechanics

We give a review of some works where it is shown that certain quantum-like features are exhibited by classical systems. Two kinds of problems are considered. The first one concerns the specific heat of crystals (the so called Fermi–Pasta–Ulam problem), where a glassy behavior is observed, and the energy distribution is found to be of Planck-like type. The second kind of problems concerns the self-interaction of a charged particle with the electromagnetic field, where an analog of the tunnel effect is proven to exist, and moreover some nonlocal effects are exhibited, leading to a natural hidden variable theory which violates Bell's inequalities.     

SiGe (Ge-dot) heterojunction phototransistors for efficient light detection at 1.3–1.55 μm

The aim of this work is to develop a Si/SiGe HBT-type phototransistor with several Ge dot layers incorporated in the collector, in order to obtain improved light detectivity at 1.3–1.55 μm. The MBE grown HBT detectors are of n–p–n type and based on a multilayer structure containing 10 Ge-dot layers (8 ML in each layer, separated by 60 nm Si spacer) in the base-collector junction. The transistors were processed for normal incidence or with waveguide geometry where the light is coupled through the edge of the sample. The measured breakdown voltage, BV_ceo, was about 6 V. Compared to a p–i–n reference photodiode with the same dot layer structure, photoconductivity measurements show that the responsivity is improved by a factor of 60 for normal incidence at 1.3 μm. When the light is coupled through the edge of the device, the detectivity is even further enhanced. The measured photo-responsivity is more than 100 and 5 mA/W at 1.3 and 1.55 μm, respectively.     

Non-ideal behavior of mixed micelles of cationic gemini surfactants with varying spacer length and anionic surfactants: A conductimetric study

Mixtures of cationic and anionic surfactants (catanionic mixtures) are often highly non-ideal, exhibiting strong synergism in their interfacial properties, manifested for instance in significant reduction of the mixture critical micelle concentration (cmc) and enhanced adsorption onto surfaces. The magnitude of such effects is of fundamental interest and has important application-related uses (e.g. in detergent formulation). In this work, the micellization process of mixtures of cationic gemini surfactants of the alkanediyl-α,ω-bis(alkyl dimethylammonium bromide) type, denoted by 12–n–12 (where n is the spacer length), with several common anionic surfactants has been investigated by electric conductivity. For the purpose of comparison, cationic–cationic mixtures, where dodecyltrimethylammonium bromide is the second cationic surfactant, have also been investigated. The cationic/anionic mixtures show relatively significant deviations from ideal behavior, depending on the structure of the gemini surfactant and the anionic surfactant. The interaction parameter β₁₂, within Rubingh's non-ideal model for mixed micelles, has been calculated for each mixture, as well as the mixed micelle composition as a function of mixture composition. The observed synergism in the different mixtures is interpreted in terms of the molecular structure of the surfactants and corresponding head–head and chain–chain interactions.     

The Contours of the Bands of the Structural Luminescence and Absorption Spectra of Solid Solutions and Crystals of Uranyl Compounds at Low Temperatures

Temperature evolution of the fine structure of the electronic spectra of uranyl nitrates and fluorides is considered. It is shown that for pure crystals at T = 4.2 K the contour is described by the Lorentz curve; for other cases a convolution of the type of the Voigt function is typical. Weak electron–phonon interaction leads to temperature broadening of spectra predominantly due to the Boltzmann change in the population of the initial electronic–vibrational states.     

Population densities and optical gain of VUV transitions of Cu II in Cu−He hollow cathode discharges

Population densities of excited Cu II-levels between 16 and 25 eV in Cu–He hollow cathode discharges were determined by emission spectroscopy. Population inversion was detected for several 6s-4p transitions. Investigation of the enhancement of Cu II vuv lines in He compared to Ne discharges showed that the excitation of the 6s levels by charge transfer is up to 100 times higher in He than in pure Ne discharges. Using the population densities and known transition probabilities, a single pass gain of 55% m^–1 at 780.8 nm and 1.2% m^–1 at 154.17 nm at a current density of 0.4 A cm^–2 was calculated.This paper is dedicated to Prof. Dr. H. Gobrecht on the occasion of his 75th birthday     

Decoherence and Bare Mass Induced by Nonconformal Metric Fluctuations

The effects, upon the Klein–Gordon field, of nonconformal stochastic metric fluctuations, are analyzed. It will be shown that these fluctuations allow us to consider an effective mass, i.e., the mass detected in a laboratory is not the parameter appearing in the Klein–Gordon equation, but a function of this parameter and of the fluctuations of the metric. In other words, in analogy to the case of a nonrelativistic electron in interaction with a quantized electromagnetic field, we may speak of a bare mass, where the observed mass shows a dependence upon the stochastic terms included in the metric. Afterwards, we prove, resorting to the influence functional, that the energy–momentum tensor of the Klein–Gordon field inherites this stochastic behavior, and that this feature provokes decoherence upon a particle immersed in the region where this tensor is present.     

intersubband pumping of an : InP symmetric double quantum well terahertz laser

The feasibility of intersubband optical excitation of a terahertz (1–10 THz) or far-infrared (30–300 ) emitter/laser by a laser diode is investigated by means of envelope function/effective mass approximation and subband carrier lifetime calculations. The material system is employed in order to supply the necessary conduction band offset and the basic design is that of a 6-level symmetric double quantum well. This can simultaneously satisfy the criteria of an 800 meV intersubband absorption and a far-infrared emission. It is shown that these device designs can satisfy a necessary criterion for population inversion at room temperature. A scheme for improving the population ratio based on a 9-level triple quantum well is discussed.     

HgSe:Fe quantum dots: growth and characterization

Mercury selenide and its ternary and quaternary modifications in the form Hg(A,B)Se with A, B magnetic ions, provide an interesting semiconductor family featuring different kinds of correlation effects. These effects manifest themselves already in three-dimensional, quasi-two-dimensional, and quasi-one-dimensional structures. We have succeeded now in fabricating HgSe:Fe quantum dots using three different growing procedures based on molecular beam epitaxy: (a) Stranski–Krastanov growth; (b) thermally activated surface reorganization; (c) pit filling. The special feature of the HgSe:Fe dots is the intrinsic population of the dot states by electrons, where a large amount of about 50–500 electrons form a many-electron system within a single dot. The formation of the dots was controlled in situ by RHEED. The morphology of the resulting structures was characterized by AFM. Subsequently, the electronic properties of the dots were investigated by megagauss magneto spectroscopy, indicating the presence of strong correlation effects as manifested in a 50% increase of the cyclotron mass in respect to that of structures with a higher dimensionality.     

Temperature dependence of the inelastic scattering in a GaAs/n-AlGaAs selectively doped heterojunction with InGaAs quantum dots

Inelastic scattering processes of two-dimensional electron gas (2DEG) have been investigated in a inverted GaAs/n-AlGaAs heterojunction with self-organized InGaAs quantum dots (QDs) embedded near the 2DEG channel where the electron population in the QDs is controllable by the gate voltage V_g. By analyzing magnetoresistance, the inelastic scattering time τ_ε have been evaluated as functions of V_g at 0.6, 0.8, 1.2, and 1.7 K. It is found that τ_ε increases with V_g below 0.8 K and decreases above 1.2 K, which suggests that the dominant scattering mechanisms below 0.8 K and above 1.2 K are different. To interpret this behavior, we have calculated the inelastic scattering time theoretically. It is found that the experimental data are well explained by a theoretical model where a 2D electron is considered to be inelastically scattered both by the other 2D electrons and by the trapped electrons in QDs. It is also found that the 2DEG–2DEG scattering is dominant at low temperature, while the 2DEG-QDs scattering becomes important as the temperature increases.     

Discrete Lagrangian Reduction,Discrete Euler–Poincaré Equations,and Semidirect Products

A discrete version of Lagrangian reduction is developed within the context of discrete time Lagrangian systems on G × G, where G is a Lie group. We consider the case when the Lagrange function is invariant with respect to the action of an isotropy subgroup of a fixed element in the representation space of G. Within this context, the reduction of the discrete Euler–Lagrange equations is shown to lead to the so-called discrete Euler–Poincaré equations. A constrained variational principle is derived. The Legendre transformation of the discrete Euler–Poincaré equations leads to discrete Hamiltonian (Lie–Poisson) systems on a dual space to a semiproduct Lie algebra.     

Periodic evolution of space chaos in the one-dimensional complex Ginzburg-Landau equation

Periodic evolution of the space chaos in a one-dimensional distributed system represented by the complex Ginzburg-Landau equation is studied. There exists a region of parameters where spatially chaotic distribution of the field varies periodically with time, and the boundaries of this region are determined. The regime of periodic space chaos was found to exist only for certain initial conditions. A system of ordinary differential equations that describes the space chaos is derived.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 1–2, pp. 37–43, January–February, 1995.     

Noncommutative Dynamics of Random Operators

We continue our program of unifying general relativity and quantum mechanics in terms of a noncommutative algebra А on a transformation groupoid Γ = E × G where E is the total space of a principal fibre bundle over spacetime, and G a suitable group acting on Γ . We show that every a ∊ А defines a random operator, and we study the dynamics of such operators. In the noncommutative regime, there is no usual time but, on the strength of the Tomita–Takesaki theorem, there exists a one-parameter group of automorphisms of the algebra А which can be used to define a state dependent dynamics; i.e., the pair (А, ϕ), where ϕ is a state on А, is a “dynamic object.” Only if certain additional conditions are satisfied, the Connes–Nikodym–Radon theorem can be applied and the dependence on ϕ disappears. In these cases, the usual unitary quantum mechanical evolution is recovered. We also notice that the same pair (А, ϕ) defines the so-called free probability calculus, as developed by Voiculescu and others, with the state ϕ playing the role of the noncommutative probability measure. This shows that in the noncommutative regime dynamics and probability are unified. This also explains probabilistic properties of the usual quantum mechanics.     

The influence of rotational states on the kinetic of vibrational levels of CO2. The method of rotational weight function

We study the influence of rotational states on the kinetics of vibrational levels of CO₂ using a numerical method. Spontaneous emission is considered to be the mechanism causing transitions between rotational-vibrational states. It is shown that results obtained in the generally assumed vibrational approximation can differ by factors of 5–10 from the results where rotational states are taken into account. We propose a method of rotational weight functions which takes into account rotational states in the calculation of the kinetics of vibrational levels. We also find numerical values of these weight functions and show that the results obtained differ from the exact ones by 1–3%.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 88–92, January, 1986.     

Photoluminescence asymmetry with quantum state preparation

We show that the number of photons in a strongly coupled exciton–photon system is asymmetric with the detuning of the modes when, in the spontaneous emission regime, the two modes are entangled. As changing the detuning is easy in semiconductor microcavities–where on the other hand the nature of the strong-coupling in terms of single-particle effects is not yet resolved–we propose this effect as a test of the quantum character of microcavity polaritons.     

Self-organization of aging in a population approaching the steady state

The nonequilibrium asymptotic dynamics of a model for aging in a population of individuals initially having a random distribution of survival rates is studied. The model drives itself toward a steady state, and the average age tends toward a well-defined value. An analytic derivation shows that the average age of the members of the population decays in a power law fashion with the leading term of ordert ^–1. Monte Carlo simulations agree with the analytic work, and show that thet ^–1 decay is universally observed even when somatic mutations are introduced into the population.     

Hartree–Fock versus quantum Monte Carlo study of persistent current in a one-dimensional ring with single scatterer

We calculate the persistent current of interacting spinless electrons in a one-dimensional ring containing a single δ barrier. We use the self-consistent Hartree–Fock method and the quantum Monte Carlo method which gives fully correlated solutions. Our Hartree–Fock method treats the non-local Fock term in a local approximation and also exactly (if the ring is not too large). Treating the Fock term exactly we attempt to support our previous Hartree–Fock result obtained in the local approximation, in particular the persistent current behaving like I∝L^-1-α, where L is the ring length and α>0 is the power depending only on the electron–electron interaction. Finally, we use the Hartree–Fock solutions as an input for our quantum Monte Carlo calculation. The Monte Carlo results exhibit only small quantitative differences from the Hartree–Fock results.     

A study of the mechanically milled h-BN-H system

Defective nanostructured h-BN, with different structural characteristics, can be prepared by mechanical milling under hydrogen and argon atmospheres. When h-BN was mechanically milled under a hydrogen atmosphere, hydrogen could be trapped by the B- and N-dangling bonds formed; the amount of which reached up to 2.6mass% after 80 h milling. The absorbed hydrogen can be released only as molecular hydrogen starting from about 570 K. As is clarified by a combination of TDS and IR measurements, the hydrogen detrapped from B–H and N–H bonds dominates the desorption at the lower and higher temperature ranges, respectively. After the nanostructured h-BN was heated to 1173 K, some of the hydrogen was still trapped by N–H bonds where, correspondingly, no recrystallization was detected. PACS 81.05.Tp; 61.46.+w; 81.20.Ev; 81.05.Zx