In‐line Bragg magnifier based on V‐shaped germanium crystals

In this work an X‐ray imaging system based on a recently developed in‐line two‐dimensional Bragg magnifier composed of two monolithic V‐shaped crystals made of dislocation‐free germanium is presented. The channel‐cut crystals were used in one‐dimensional and in two‐dimensional (crossed) configurations in imaging applications and allowed measurement of phase‐contrast radiograms both in the edge‐enhanced and in the holographic regimes. The measurement of the phase gradient in two orthogonal directions is demonstrated. The effective pixel size attained was 0.17 µm in the one‐dimensional configuration and 0.5 µm in the two‐dimensional setting, offering a twofold improvement in spatial resolution over devices based on silicon. These results show the potential for applying Bragg magnifiers to imaging soft matter at high resolution with reduced dose owing to the higher efficiency of Ge compared with Si.     

Hydrodynamic simulation of electron transport in n-type Hg<Subscript>0.8</Subscript>Cd<Subscript>0.2</Subscript>Te

A hydrodynamic approach based on concentration, velocity and energy conservation equations is developed and used for the simulation of the electron transport in bulk HgCdTe. Both transient and steady-state regimes are simulated using input parameters calculated with a Monte Carlo simulator. The model is validated through a comparison in excellent agreement with Monte Carlo results.     

Atmospheric teleconnections and flow regimes under future climate projections

This paper presents an analysis of the low-frequency variability of the midtropospheric atmospheric flow of the Northern Hemisphere during winter in terms of teleconnection patterns and atmospheric flow regimes. Teleconnection patterns have been determined by two different methods, correlation analysis and empirical orthogonal function analysis. Flow regimes have been determined by analysing the structure of a spherical probability density function in a low-dimensional state space spanned by the three leading empirical orthogonal functions. To assess the ability of state-of-the-art coupled atmosphere-ocean general circulation models (AOGCMs), multi-model simulations for present day conditions, performed for the 4th assessment report of the Intergovernmental Panel on Climate Change have been analysed. The comparison with observations reveals, that state-of-the-art AOGCMs are able to describe the low-frequency variability in terms of teleconnections and flow regimes realistically. The analyses of simulations for future climate scenarios reveal changes in the strengths of the centers of action. Concerning climate regimes, two new regimes appear and additionally, slight changes were found in the structure of some regimes.     

III. Electron-impact dissociative ionization of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

The dynamics of cold atoms in conservative optical lattices obviously depends on the geometry of the lattice. But very similar lattices may lead to deeply different dynamics. In a 2D optical lattice with a square mesh, it is expected that the coupling between the degrees of freedom leads to chaotic motions. However, in some conditions, chaos remains marginal. The aim of this paper is to understand the dynamical mechanisms inhibiting the appearance of chaos in such a case. As the quantum dynamics of a system is defined as a function of its classical dynamics – e.g. quantum chaos is defined as the quantum regime of a system whose classical dynamics is chaotic – we focus here on the dynamical regimes of classical atoms inside a well. We show that when chaos is inhibited, the motions in the two directions of space are frequency locked in most of the phase space, for most of the parameters of the lattice and atoms. This synchronization, not as strict as that of a dissipative system, is nevertheless a mechanism powerful enough to explain that chaos cannot appear in such conditions.     

Morphology of Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript>x</Subscript>Se epitaxial film surfaces after plasma treatment

The morphology of surfaces of Pb _1−x Eu _x Se epitaxial films on CaF ₂ /Si(111) substrates in the initial state and after treatment by high-density inductive Ar plasma in different regimes is investigated by the methods of atomic force microscopy. It is demonstrated that threading dislocations serve as cores for the formation of large bulges during sputtering of a semiconductor material. The influence of treatment regimes on the geometrical parameters of large bulges and characteristics of the surrounding nanorelief is revealed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 90–93, November, 2007.     

Energy transfer in weakly coupled nonlinear oscillator chains: Transition from a wandering breather to nonlinear self-trapping

We present analytical and numerical studies of phase-coherent dynamics of intrinsically localized excitations (breathers) in a system of two weakly coupled nonlinear oscillator chains. We show that there are two qualitatively different dynamical regimes of the coupled breathers, either immovable or slowly moving: the periodic wandering of the low-amplitude breather between the chains, and the one-chain-localization of the high-amplitude breather. These two modes of coupled breathers can be mapped exactly onto two solutions of a pendulum equation, detached by a separatrix mode. We also show that these two regimes of the coupled breathers are similar, and are described by a similar pair of equations, to the two regimes in the nonlinear tunneling dynamics of two weakly coupled Bose-Einstein condensates. On the basis of this analogy, we predict a new tunneling mode of two weakly coupled Bose-Einstein condensates in which their relative phase oscillates around π/2 modulo π.     

One-dimensional caricature of phase transition

In the limit as the volume grows and the temperature vanishes, it is shown that the one-dimensional nearest neighbor ferromagnetic Ising model presents a sharp transition between two different regimes. Fluctuations are studied in one of these regimes and also in the critical case.     

Optical characterization of methanol adsorption on the bare and oxygen precovered Cu(1 1 0) surface

We have studied the adsorption and reaction of methanol on the bare and oxygen precovered Cu(1 1 0) surface at 200 K using reflectance difference spectroscopy (RDS). On the bare and fully oxygen covered surface, the sticking coefficient is close to zero. In contrast, on the partially oxygen covered surface, a sticking coefficient close to unity is obtained. This observation suggests a high mobility of methanol on both bare and oxygen covered Cu(1 1 0) and of methoxy on Cu(1 1 0). Two reaction regimes, an oxygen supply limited and an adsorption site limited regime are identified. The transition between these two regimes occurs for an oxygen coverage of about 0.2.     

Relaxation of stretched DNA in slitlike confinement

We experimentally observe two separate time scales governing the entropic recoil in the linear force-extension regime of single double-stranded DNA in slit confinement. We demonstrate the existence of two distinct relaxation regimes at different extensions during relaxation. Contrary to bulk measurements, the true longest relaxation time may only be probed very close to equilibrium. A simple model of the relaxation mechanism leads to a scaling analysis that correctly predicts the extension at the crossover between the two regimes.     

Influence of Al-concentration on the current density in GaAs/Al<Subscript><Emphasis Type="Italic">c</Emphasis></Subscript>Ga<Subscript>1-</Subscript><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript>As generalized Thue-Morse superlattices

The influence of Al concentration on the current density in GaAs-Al _c Ga_{1- c} As heterostructure is studied for two different classes of the Generalized Thue-Morse superlattice (GTS): (i) width-barrier GTS and (ii) height-barrier GTS. The occurrence of resonances in the transmission is found to be highly dependent on the Al concentration as well as on the degree of quasi-periodicity of the system. Interesting features are noted for the current density profile with the increase in the Al content for the width-barrier case. The use of the height-barrier GTS with small Al content could be suggested to achieve the negative differential conducting regimes at comparatively low applied bias. The effects of the applied field as well as of the quasi-periodicity on the carrier localization are also studied.     

Magnetic Field Line Random Walk in Two‐dimensional Turbulence: Markovian Diffusion versus Superdiffusion

In the present article previous work is complemented by investigating analytically the field line random walk in partially turbulent magnetic fields. By using the well‐established model of two‐dimensional turbulence with a general spectrum at large scales, we compute the field line diffusion coefficient for all length scales. This work will also clarify some confusion about the superdiffusive and diffusive regimes discovered earlier (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Two regimes of two-beam coupling in cubic < ![IGNORE[3m crystals

We show that in crystals of symmetry 3m (lacking optical activity) two regimes are possible for two-wave mixing in the longitudinal geometry: one regime is similar to ordinary two-wave mixing where energy exchange is always in the same direction whereas the other one is oscillatory with energy transfer in both directions. Received: 27 November 1998 / Revised version: 18 February 1999 / Published online: 12 April 1999     

Magnetism and optical properties of nanocrystalline Cu<Subscript>2</Subscript>O and TiO<Subscript>2</Subscript> powders

The optical spectra of Cu₂O and TiO₂ nanopowders have been studied, which contain information about structural defects and are of interest in the search for optimum regimes providing the synthesis of ferromagnetic nanocrystals with Curie temperatures above room temperature.     

Study of the Nonlinear Dynamics of a Traveling-Wave-Tube Oscillator with Delayed Feedback

We present the results of numerical simulations of the nonlinear dynamics of a traveling-wave-tube (TWT) oscillator with delayed feedback. Basic properties of stationary single-frequency oscillation regimes are considered, and the onset of self-modulation is studied in detail. Various route-to-chaos scenarios corresponding to successively increasing values of the beam current are simulated numerically. It is shown that the basic scenario is a quasi-periodic route to chaos, while the beam deceleration in strongly nonlinear regimes causes transitions via intermittency to regimes based on modes with higher frequencies. Competition between these two scenarios leads to a complex picture of regular and chaotic self-modulation regimes in the parameter space. Such a behavior is typical of distributed electron–wave self-excited oscillators with delayed feedback.     

Sensitivity of wave field evolution and manifold stability in chaotic systems

The sensitivity of a wave field's evolution to small perturbations is of fundamental interest. For chaotic systems, there are two distinct regimes of either exponential or Gaussian overlap decay in time. We develop a semiclassical approach for understanding both regimes and give a simple expression for the crossover time between the regimes. The wave field's evolution is considerably more stable than the exponential instability of chaotic trajectories seems to suggest. The resolution of this paradox lies in the collective behavior of the appropriate set of trajectories. Results are given for the standard map.     

Kondo impurities in nanoscopic and mesoscopic systems

We present results for Kondo impurities in nanoscopic systems. Using Wilson's numerical renormalization group we analyze two different situations: an isolated system with a discrete spectrum of well-defined energy levels and a fixed number of electrons and a nanoscopic system weakly coupled to a macroscopic reservoir. In the latter case, new regimes not observed in macroscopic homogeneous systems are induced by the confinement of conduction electrons. These new confinement-induced regimes are very different depending on whether the Fermi energy is at resonance or between two quasi-bound states.     

Spatiotemporal antiphase dynamics in coupled extended optical media

Experimental evidence of spatiotemporal antiphase dynamics is given for an extended system made of two liquid crystal slices that are optically coupled by two equal amplitude counterpropagating pumping beams. Theory and experiments carried out in a transverse one-dimensional configuration show that roll patterns are generated in each slice. These rolls are spatially in-phase or antiphase for a focusing or a defocusing nonlinearity type, respectively. These in-phase or antiphase dynamics remain robust even for complex spatiotemporal regimes such as dislocation regimes.     

Effects of nonlocal electron kinetics and transition from αto γ regime in an RF capacitive discharge in nitrogen

The electron kinetics and regime of operation of asymmetrically coupled RF (27-MHz) nitrogen discharges in two vessels with different interelectrode gaps over the range of 0.20-0.35 torr gas pressure are studied in terms of the electron energy distribution function (EEDF). The latter is measured by means of a computer-controlled data acquisition system, a Langmuir probe with cross-modulation second derivative technique applied. The experiments are performed with an axial resolution along the RF electric field and accompanied with a measurement of electrical discharge characteristics. The effects of local and nonlocal plasma response are considered. The transition between α and γ discharge regimes is registered by measuring the EEDF and its moments' changes with the increase of the RF discharge current density     

Study of “forbidden” atomic transitions on D2 line using Rb nano-cell placed in external magnetic field

In this paper the treatment of a three-level atom which is confined in a Fabry-Perot optical cavity with a nonlinear mirror is investigated. Despite the nonlinear effects we show that this system operates in two different regimes. In one regime the system shows conventional laser properties which is approximated by a semiclassical laser theory and in the other one the system displays new quantum properties which is approximated by an effective two-level atom. For validity of the behavior of the system in two different regimes computer simulations are implemented.