Generation of High-Energy Photons with Large Orbital Angular Momentum by Compton Backscattering

Usually, photons are described by plane waves with a definite 4-momentum. In addition to plane-wave photons, "twisted photons" have recently entered the field of modern laser optics; these are coherent superpositions of plane waves with a defined projection hbar*m of the orbital angular momentum onto the propagation axis, where m is integer. In this paper, we show that it is possible to produce high-energy twisted photons by Compton backscattering of twisted laser photons off ultra-relativistic electrons. Such photons may be of interest for experiments related to the excitation and disintegration of atoms and nuclei, and for studying the photo-effect and pair production off nuclei in previously unexplored experimental regimes.Comment: 4 pages; RevTe

Stabilization and control system power sensitivity study

Stabilization and control system sensitivity to power-off failure rate studied by simulated missions using block power switchin

Hydrogen atom in phase space. The Kirkwood-Rihaczek representation

We present a phase-space representation of the hydrogen atom using the Kirkwood-Rikaczek distribution function. This distribution allows us to obtain analytical results, which is quite unique because an exact analytical form of the Wigner functions corresponding to the atom states is not known. We show how the Kirkwood-Rihaczek distribution reflects properties of the hydrogen atom wave functions in position and momentum representations.Comment: 5 pages (and 5 figures

Competition between Diffusion and Fragmentation: An Important Evolutionary Process of Nature

We investigate systems of nature where the common physical processes diffusion and fragmentation compete. We derive a rate equation for the size distribution of fragments. The equation leads to a third order differential equation which we solve exactly in terms of Bessel functions. The stationary state is a universal Bessel distribution described by one parameter, which fits perfectly experimental data from two very different system of nature, namely, the distribution of ice crystal sizes from the Greenland ice sheet and the length distribution of alpha-helices in proteins.Comment: 4 pages, 3 figures, (minor changes

Quasi-chemical Theories of Associated Liquids

It is shown how traditional development of theories of fluids based upon the concept of physical clustering can be adapted to an alternative local clustering definition. The alternative definition can preserve a detailed valence description of the interactions between a solution species and its near-neighbors, i.e., cooperativity and saturation of coordination for strong association. These clusters remain finite even for condensed phases. The simplest theory to which these developments lead is analogous to quasi-chemical theories of cooperative phenomena. The present quasi-chemical theories require additional consideration of packing issues because they don't impose lattice discretizations on the continuous problem. These quasi-chemical theories do not require pair decomposable interaction potential energy models. Since calculations may be required only for moderately sized clusters, we suggest that these quasi-chemical theories could be implemented with computational tools of current electronic structure theory. This can avoid an intermediate step of approximate force field generation.Comment: 20 pages, no figures replacement: minor typographical corrections, four references added, in press Molec. Physics 199

Dirac-harmonic maps from index theory

We prove existence results for Dirac-harmonic maps using index theoretical tools. They are mainly interesting if the source manifold has dimension 1 or 2 modulo 8. Our solutions are uncoupled in the sense that the underlying map between the source and target manifolds is a harmonic map.Comment: 26 pages, no figur

Plasma instability and amplification of electromagnetic waves in low-dimensional electron systems

A general electrodynamic theory of a grating coupled two dimensional electron system (2DES) is developed. The 2DES is treated quantum mechanically, the grating is considered as a periodic system of thin metal strips or as an array of quantum wires, and the interaction of collective (plasma) excitations in the system with electromagnetic field is treated within the classical electrodynamics. It is assumed that a dc current flows in the 2DES. We consider a propagation of an electromagnetic wave through the structure, and obtain analytic dependencies of the transmission, reflection, absorption and emission coefficients on the frequency of light, drift velocity of 2D electrons, and other physical and geometrical parameters of the system. If the drift velocity of 2D electrons exceeds a threshold value, a current-driven plasma instability is developed in the system, and an incident far infrared radiation is amplified. We show that in the structure with a quantum wire grating the threshold velocity of the amplification can be essentially reduced, as compared to the commonly employed metal grating, down to experimentally achievable values. Physically this is due to a considerable enhancement of the grating coupler efficiency because of the resonant interaction of plasma modes in the 2DES and in the grating. We show that tunable far infrared emitters, amplifiers and generators can thus be created at realistic parameters of modern semiconductor heterostructures.Comment: 28 pages, 15 figures, submitted to Phys. Rev.

Psychotherapy Dropout: Using the Adolescent Psychotherapy Q-Set to Explore the Early In-Session Process of Short-Term Psychodynamic Psychotherapy

Research suggests that short-term psychodynamic psychotherapy (STPP) is an effective treatment for depression in adolescence, yet treatment dropout is a major concern and what leads to dropout is poorly understood. Whilst studies have begun to explore the role of patient and therapist variables, there is a dearth of research on the actual therapy process and investigation of the interaction between patient and therapist. This study aims to address this paucity through the utilisation of the Adolescent Psychotherapy Q-set (APQ) to examine the early treatment period. The sample includes 69 adolescents aged 16–18 years with major depressive disorder receiving STPP as part of the First Experimental Study of Transference Work–in Teenagers (FEST-IT) trial. Of these, 21 were identified as dropouts and were compared to completers on pre-treatment patient characteristics, symptomatology, functioning, and working alliance. APQ ratings available for an early session from 16 of these drop out cases were analysed to explore the patient-therapist interaction structure. Results from the Q-factor analysis revealed three distinct interaction structures that explained 54.3% of the total variance. The first described a process of mutual trust and collaboration, the second was characterised by patient resistance and emotional detachment, the third by a mismatch and incongruence between therapist and adolescent. Comparison between the three revealed interesting differences which taken together provide further evidence that the reasons why adolescents drop out of therapy vary and are multidimensional in nature

Effect of formic acid in drinking water on the incidence of Salmonella in growing-finishing pigs

The effect of formic acid in drinking water on the incidence of salmonella in growing-finishing pigs was tested in two herds. where there for a long period had been problems with salmonella in the pig production. The pigs were tested from approximately 30 kg live weight until slaughter. There were a total of 20 blocks in herd 1 and 12 blocks in herd 2 and a total of 710 pigs in group I (control) and 7 I 2 pigs in group 2 (I per mille formic acid in the drinking water). The primary registration parameter was a serological test for salmonella antibodies. Before slaughter blood samples from 6 pigs in each pen were collected for analysis. The secondary registration parameter was average daily gain and lean meat percentage. The conclusion of this study was that there was no clear effect of adding 1 per mille formic acid to the drinking water on the incidence of salmonella. neither was there a growth promoting effect