A quasi-time-dependent radiative transfer model of OH104.9+2.4

We investigate the pulsation-phase dependent properties of the circumstellar dust shell (CDS) of the OH/IR star OH104.9+2.4 based on radiative transfer modeling (RTM) using the code DUSTY. Our previous study concerning simultaneous modeling of the spectral energy distribution (SED) and near-infrared (NIR) visibilities (Riechers et al. 2004) has now been extended by means of a more detailed analysis of the pulsation-phase dependence of the model parameters of OH104.9+2.4. In order to investigate the temporal variation in the spatial structure of the CDS, additional NIR speckle interferometric observations in the K' band were carried out with the 6 m telescope of the Special Astrophysical Observatory (SAO). At a wavelength of 2.12 micron the diffraction-limited resolution of 74 mas was attained. Several key parameters of our previous best-fitting model had to be adjusted in order to be consistent with the newly extended amount of observational data. It was found that a simple rescaling of the bolometric flux F_bol is not sufficient to take the variability of the source into account, as the change in optical depth over a full pulsation cycle is rather high. On the other hand, the impact of a change in effective temperature T_eff on SED and visibility is rather small. However, observations, as well as models for other AGB stars, show the necessity of including a variation of T_eff with pulsation phase in the radiative transfer models. Therefore, our new best-fitting model accounts for these changes.Comment: 7 pages, including 5 postscript figures and 3 tables. Published in Astronomy and Astrophysics. (v1: accepted version; v2: published version, minor grammatical changes

Interplay between carrier and impurity concentrations in annealed Ga1−x_{1-x}Mnx_{x}As intrinsic anomalous Hall Effect

Investigating the scaling behavior of annealed Ga$_{1-x}$Mn$_{x}$As anomalous Hall coefficients, we note a universal crossover regime where the scaling behavior changes from quadratic to linear, attributed to the anomalous Hall Effect intrinsic and extrinsic origins, respectively. Furthermore, measured anomalous Hall conductivities when properly scaled by carrier concentration remain constant, equal to theoretically predicated values, spanning nearly a decade in conductivity as well as over 100 K in T$_{C}$. Both the qualitative and quantitative agreement confirms the validity of new equations of motion including the Berry phase contributions as well as tunablility of the intrinsic anomalous Hall Effect.Comment: 4 pages, 5 figure

Phase boundary between ripple and hut in the initial roughening stage in heteroepitaxy

A regularly undulating surface topography has been observed during growth of heteroepitaxial layers such as Si1-xGex/Si-2 and InxGa1-xAs/GaAs5. We present a modified evolution mechanism of this ripple structure, which consists of initial roughening and evolving stages. A theoretical relationship is derived through energy minimization, which indicates that the ratio of the amplitude to the square of the period of the ripple structure is constant in the evolving stage. Also derived is a criterion for determining the phase boundary between the ripple and hut phases in the Stranski-Krastanov growth

Composition dependence of activation energy in solid phase epitaxial growth of Si1-xGex alloys

A theoretical model called the ''multibody model'' is developed for the composition dependence of the activation energy. The model that is based on the diffusion required of the recrystallization for the solid phase epitaxy does not involve any adjustable parameters and is shown to represent experimental data satisfactorily. For the Si1-xGex alloys that are of diamond structure, the most logical choice is the ''five-body model'' involving five atoms. The model is equally applicable to any other binary alloy

Ge composition in Si1-xGex films grown from SiH2Cl2/GeH4 precursors

A simple model for the Ge composition in Si1-xGex films grown from SiH2Cl2/GeH4 precursors is developed on the basis of adsorption and desorption kinetics for the intermediate temperature range (600 degrees C < T < 900 degrees C). For this system, the solid phase composition of Ge, x, is related to the gas phase composition ratio of the two source gases, G, by x(2)/(1-x) = constantxG, which contrasts with the conventional relationship, x/(1-x) = constantxG, that is known for SiH4/GeH4 chemical vapor deposition. The proportionality constant depends not only on temperature but also on pressure. The model compares well with the experimental data in the literature

Putative spin liquid in the triangle-based iridate Ba3_3IrTi2_2O9_9

We report on thermodynamic, magnetization, and muon spin relaxation measurements of the strong spin-orbit coupled iridate Ba$_3$IrTi$_2$O$_9$, which constitutes a new frustration motif made up a mixture of edge- and corner-sharing triangles. In spite of strong antiferromagnetic exchange interaction of the order of 100~K, we find no hint for long-range magnetic order down to 23 mK. The magnetic specific heat data unveil the $T$-linear and -squared dependences at low temperatures below 1~K. At the respective temperatures, the zero-field muon spin relaxation features a persistent spin dynamics, indicative of unconventional low-energy excitations. A comparison to the $4d$ isostructural compound Ba$_3$RuTi$_2$O$_9$ suggests that a concerted interplay of compass-like magnetic interactions and frustrated geometry promotes a dynamically fluctuating state in a triangle-based iridate.Comment: Physical Review B accepte