Nanooxidation of <Emphasis Type="Italic">n</Emphasis>-In<Subscript>0.53</Subscript>Ga<Subscript>0.47</Subscript>As with an atomic force microscope

It is shown that the features formed when an InGaAs layer lattice-matched with the InP substrate is modified by an atomic force microscope are of the oxide nature. Various models of InGaAs nanooxidation by an atomic force microscope are considered. The conventional Cabrera-Mott model refined by introducing the space charge into the oxide is taken as the basic model of nanooxidation by an atomic force microscope.     

Electric-field-induced magnetization reversal in a ferromagnet-multiferroic heterostructure

A reversal of magnetization requiring only the application of an electric field can lead to low-power spintronic devices by eliminating conventional magnetic switching methods. Here we show a nonvolatile, room temperature magnetization reversal determined by an electric field in a ferromagnet-multiferroic system. The effect is reversible and mediated by an interfacial magnetic coupling dictated by the multiferroic. Such electric-field control of a magnetoelectric device demonstrates an avenue for next-generation, low-energy consumption spintronics.     

Employment of the scattering amplitude in solving the diffraction problems for waves in a halfspace

The problem on the diffraction of an acoustic wave by a finite-size scatterer (inclusion) located in a halfspace is considered. The method of solving this problem is based on the use of the scattering amplitude of the inclusion. A formula analogous to the Green formula is presented. It allows one to determine the scattering amplitude of the inclusion for an arbitrary incident wave (determined by the directional pattern of the source of primary waves) from the scattering amplitude corresponding to plane incident waves. The algorithm is presented for solving the problem on the operation of an acoustically opaque radiator in a halfspace whose boundary is characterized by an arbitrary reflection coefficient. As an example, the problem is solved on the generation of low-frequency oscillations by a sphere with an acoustically soft boundary near an acoustically hard or soft boundary of the halfspace.     

Scattering of waves by an aperture in an impedance screen

The transmission and diffraction of waves by an aperture in an impedance screen is investigated. The Senior's solution of the scattering problem of waves by an impedance half-plane is transformed into a physical optics type integral. The obtained method is applied to the transmission problem of waves by a slit in an impedance screen. The results are compared with the aperture problem in black and conducting screens numerically.     

The dynamics of exchange rate time series and the chaos game

This work presents a novel method of reconstructing some relevant characteristics of exchange rate time series by the superposition of two components: a mostly deterministic one, the chaos game as expressed by the Yuan/USD exchange rate and a purely stochastic one, Gaussian white noise. We analyzed 20 economic systems with the average Index of Economic Freedom above 50. The considered characteristics (the Lempel-Ziv complexity index, the slimness of the distribution and the Iterated Function Systems clumpiness test) are well reproduced by the reconstruction process. Additional confirmation is obtained by an analysis of the exchange rate of the Romanian national currency as an example of an application of the method to a transition economy, and by an analysis of the time series of the Euro-zone as an example of an application to a multinational system using a shorter time series.     

Discrete dislocation simulation of nanoindentation: the influence of obstacles and a limited number of dislocation sources

Nanoindentation is simulated on the computer by means of a 2D discrete dislocation model under the conditions of a constrained geometry. First, an indentation test near a grain boundary is investigated by the arrangement of only one boundary and second, an indentation test into the center of the surface of a small grain (lamella) is mimicked by the arrangement of two boundaries. The effect of a limited number of dislocation sources is studied by the simulations of an indentation test in a plastically deformable film on an ideal elastic substrate and by such tests on an ideal elastic film on a plastically deformable substrate. The discrete nature of plasticity is shown to have a significant influence on the mechanical material behavior in all our investigations.     

Electromagnetic radiation from a polarization sheet located at an interface between two media

We derive concise expressions for the intensity of radiation emitted by an oscillating polarization sheet located at an interface between two media. The expressions find application in a number of experimental situations involving scattering or secondharmonic generation at an interface. As an application we discuss the angular dependence of p-polarized second-harmonic light emitted by a layer of adsorbed molecules stimulated by s-polarized incident radiation.     

On the van Cittert-Zernike theorem

The van Cittert-Zernike theorem states that the spatial coherence over a space illuminated by an incoherent extended source is described by the Fourier transform of the intensity distribution over the source. The theorem is usually used in a restricted case of the spatial coherence in a plane parallel to the source plane and illuminated by an incoherent extended source of uniform intensity distribution. In this paper we re-examine the van Cittert-Zernike theorem by reviewing it in an original formulation and extend the theorem to the spatial coherence at any two points of a light field illuminated by an incoherent extended source having a non-uniform intensity distribution.     

Smoothing of an atomically rough vicinal surface – STM observation and MC simulation

Smoothing of an atomically rough vicinal surface of SrTiO₃ is studied by scanning tunneling microscope (STM) observation and by Monte Carlo (MC) simulation. A complex step pattern that resembles a two-dimensional phase separation pattern is observed on the surface. Analysis of the step pattern during annealing obtained by the STM in comparison with the MC simulation reveals an asymmetry of the relaxation pattern between islands and holes. The asymmetry is attributed to the difference of the mobility of an adatom and an atomic hole, and the asymmetry is enhanced by the step edge diffusion barrier. Values of an effective bond energy and an effective diffusion barrier as well as the surface diffusion coefficient are deduced from the relaxation pattern.     

Control of a Bose–Einstein condensate on a chip by external optical and magnetic potentials

In this paper we explore the possibilities of control of a Bose–Einstein condensate on an atom chip by the use of potentials generated by photonic and magnetic components. We show that the fields produced by both types of components can be modelled by a generic exponential potential and derive analytic expressions that allow for an easy assessment of their impact on a trapped condensate. Using dynamical numerical simulations we study the transport of the condensate between the control structures on a chip. We study in detail different regimes of the condensate behaviour in an evanescent light potential generated by a photonic structure in the vicinity of the condensate and in magnetic potentials generated by a wire or a coil. The calculations are based on the reported parameters of atom chip setups and available photonic and magnetic components. Finally, the model is verified by an experiment with a condensate on an atom chip and a coil.     

Self-healing properties of asymmetric Bessel beams

Recent studies have shown that an asymmetric Bessel beam, similar to a conventional non-diverging Bessel beam; recovers their original intensity profile after encountering an obstruction. Here, we investigate the ability of an asymmetric Bessel beam to recover their original intensity profile when it is perturbed by an obstruction, and additionally drastically perturbed by a pattern of light generated by an annular obstruction. We believe that their intriguing properties have not been fully studied. A better understanding of their properties can help to make use of them appropriately in a variety of potential applications. Our investigations reveal that the dynamics of the reconstruction is affected by the asymmetry degree of the beam.     

Optical Packet Routing Performance of an Optical Packet Switch Digital/ Analog-Conversion-Type With an Optical Header Processor (Wavelength Label Switch)

We demonstrate the routing operation of optical packets by an optical packet switch consisting of an optical digital-to-analog conversion-type header processor, a wavelength converter using an electrically-tunable laser, and an arrayed-waveguide grating router. A packet transfer by two -bit optical header was achieved for the first time.     

Atomic condensate in an optical trap formed by a cavity mode

It has been shown that an optical trap for an atomic condensate formed by a mode of a ring cavity possesses specific properties. These properties are not featured by a trap formed by free beams and arise owing to quantum correlations (entanglement) between the localized atoms and the optical mode. In particular, there is an effect similar to an optomechanical phenomenon known as an “optical spring” (S. Martellucci et al., Bose–Einstein Condensates and Atom Lasers (Kluwer, Dordrecht, 2002)) and manifested by the emergence of an effective correction to the interaction between the localized atoms. The magnitude and sign of this correction can be controlled by varying the frequency of the source forming the trap.     

Transformation of an Atomic Alignment into an Orientation in a Discharge

It is shown that an atomic state aligned by optical pumping with linearly polarized laser light, is partly transformed into an oriented state by the action of an electric field (Stark effect) or by collisional interaction with electrons. The outcome of the experiment suggests that the influence of the electrons prevails.     

A comparison measurement of nonlinear ultrasonic waves in tubes by a microphone and by an optical interferometric probe

This paper deals with the analysis of ultrasonic fields inside waveguides generated by ultrasonic waves of high amplitude. These waves behave nonlinearly, so it is not possible to use standard linear equations to describe their behaviour. Therefore, we started with an experimental determination of the acoustic pressure of air in glass tubes. We chose two methods of measurement--by a microphone and by an optical interferometric probe. The conventional method by a microphone creates numerous problems, which can be avoided by using an optical method, a heterodyne laser interferometer.     

Axial super-resolution by mirror-reflected stimulated emission depletion microscopy

In stimulated emission depletion (STED) microscopy, the lateral resolution is in the range of tens of nanometers depending on the sample and the instrument. The axial resolution, however, is in standard systems limited by diffraction to about 500 nm. We present an approach to three-dimensional diffraction-unlimited resolution by observing the sample at two optical angles. The system is realized by using an atomic force microscope (AFM) chip as a microreflector to deflect the STED beams near the region-of-interest (ROI), thus allowing observations at an angle ∠. Consequently, the superior lateral resolution can be utilized to resolve details in the axial direction of the main optical axis of the microscope. Here, fluorescent nanoparticles 90 nm apart and biological structures 80 nm apart along axial direction were distinguished by utilizing an off-the-shelf, commercial STED microscope, coupled with an AFM and an AFM chip micro-reflector.     

Invisible defects in complex crystals

We show that invisible localized defects, i.e. defects that cannot be detected by an outside observer, can be realized in a crystal with an engineered imaginary potential at the defect site. The invisible defects are synthesized by means of supersymmetric (Darboux) transformations of an ordinary crystal using band-edge wavefunctions to construct the superpotential. The complex crystal has an entire real-valued energy spectrum and Bragg scattering is not influenced by the defects. An example of complex crystal synthesis is presented for the Mathieu potential.     

Cooling trapped atoms in optical resonators

We derive an equation for the cooling dynamics of the quantum motion of an atom trapped by an external potential inside an optical resonator. This equation has broad validity and allows us to identify novel regimes where the motion can be efficiently cooled to the potential ground state. Our result shows that the motion is critically affected by quantum correlations induced by the mechanical coupling with the resonator, which may lead to selective suppression of certain transitions for the appropriate parameters regimes, thereby increasing the cooling efficiency.     

Republication of: The physical reality of some normal spaces of Bianchi

This is an English translation of the first of two papers by Tullio Levi-Civita, first published in 1917 and 1919. The papers are remarkable as being among the earliest in which exact solutions of Einstein’s equations were derived. Of the two solutions presented, the first (republished as this Golden Oldie) is better known today as the Bertotti-Robinson solution, and the second one (republished as an accompanying Golden Oldie) is the gravitational field of an infinite cylinder. The papers have been selected by the Editors of General Relativity and Gravitation for republication in the Golden Oldies series of the journal. This republication is accompanied by an editorial note written by Malcolm MacCallum, and by a brief biography of the author, compiled from internet sources by Andrzej Krasiński.     

Dynamics of an ion flow in an electron layer

We study the acceleration of an ion flow in the electron layer formed by an electron flow moving in a transverse electric field and confined by the intrinsic magnetic field. The possibility of extraction of heavy ions with velocities lower than the ion sound velocity from the plasma, and the feasibility of their further acceleration by an external field is demonstrated.