Surface segregation and the Al problem in GaAs quantum wells

Low-defect two-dimensional electron systems (2DESs) are essential for studies of fragile many-body interactions that only emerge in nearly-ideal systems. As a result, numerous efforts have been made to improve the quality of modulation-doped Al$_x$Ga$_{1-x}$As/GaAs quantum wells (QWs), with an emphasis on purifying the source material of the QW itself or achieving better vacuum in the deposition chamber. However, this approach overlooks another crucial component that comprises such QWs, the Al$_x$Ga$_{1-x}$As barrier. Here we show that having a clean Al source and hence a clean barrier is instrumental to obtain a high-quality GaAs 2DES in a QW. We observe that the mobility of the 2DES in GaAs QWs declines as the thickness or Al content of the Al$_x$Ga$_{1-x}$As barrier beneath the QW is increased, which we attribute to the surface segregation of Oxygen atoms that originate from the Al source. This conjecture is supported by the improved mobility in the GaAs QWs as the Al cell is cleaned out by baking

Consumer Acceptance of Genetically Modified Foods in South Korea: Factor and Cluster Analysis

This study extends biotechnology discourse to cover South Korea in the Asian sub-continent showing a marked difference in perceptions between traditional and GM foods. Factor analysis suggests South Koreans may treat foods that are locally produced and those with no artificial flavors or colorings preferentially to GM foods. Additionally, South Koreans have concerns about perceived risks related to biotechnology, and, given a choice, they may pay more to avoid GM foods. Cluster analysis results yielded four consumer segments: (a) ardent supporters of the attribute of “naturalness†in foods, (b) those apprehensive about biotechnology, (c) the food adventurous, and (d) information seekers about biotechnology.consumer perceptions, factor and cluster analysis, food attributes, genetic modification, Consumer/Household Economics, Food Consumption/Nutrition/Food Safety,

Hysteresis and the dynamic phase transition in thin ferromagnetic films

Hysteresis and the non-equilibrium dynamic phase transition in thin magnetic films subject to an oscillatory external field have been studied by Monte Carlo simulation. The model under investigation is a classical Heisenberg spin system with a bilinear exchange anisotropy in a planar thin film geometry with competing surface fields. The film exhibits a non-equilibrium phase transition between dynamically ordered and dynamically disordered phases characterized by a critical temperature Tcd, whose location of is determined by the amplitude H0 and frequency w of the applied oscillatory field. In the presence of competing surface fields the critical temperature of the ferromagnetic-paramagnetic transition for the film is suppressed from the bulk system value, Tc, to the interface localization-delocalization temperature Tci. The simulations show that in general Tcd < Tci for the model film. The profile of the time-dependent layer magnetization across the film shows that the dynamically ordered and dynamically disordered phases coexist within the film for T < Tcd. In the presence of competing surface fields, the dynamically ordered phase is localized at one surface of the film.Comment: PDF file, 21 pages including 8 figure pages; added references,typos added; to be published in PR

CONSUMER ACCEPTANCE OF GENETICALLY MODIFIED FOODS IN KOREA: FACTOR AND CLUSTER ANALYSIS

The study applies multivariate statistical and econometric tools to estimate the importance of the various factors driving Korean consumer acceptance of GM food products. The evidence thus far on biotechnology is decidedly mixed: public perceptions of food biotechnology are characterized by ongoing tension between opposing forces. The South Korean perceptions about food in general and ranges from excitement about the promise of environmental and economic benefits from GM products to fear and distrust of the technology for unknown risks. This highlights the importance of credibility of private and public institutions responsible for certifying the safety of GM foods and implementing necessary regulatory controls on GM processes and products. In between, many people are undecided, trying to learn more about the issues and reach a definitive position. Encouraging though is that some people are eager to try new foods. Koreans strongly favors food naturalness, familiarity, and access just as the west countries. Results suggest that the South Korean Consumer priorities with respect to various biotechnology and general food issues are related to their socioeconomic and value attributes. This implies that, at least in the near term, there will be considerable divergence within the society in terms of acceptance of food biotechnology. The finding that large segments of the Korean society are either not fully informed or interested in learning more about biotechnology calls for a public education program. A program that may play a constructive role in not only informing consumers but help them in arriving at a socially optimal collective decisions on the wisdom and desirability of food biotechnology.Research and Development/Tech Change/Emerging Technologies,

PUBLIC APPROVAL OF PLANT AND ANIMAL BIOTECHNOLOGY IN KOREA: AN ORDERED PROBIT ANALYSIS

This study analyzes predictors of Korean public acceptance of the use of biotechnology to create genetically modified food products. Results indicate that the consumers with above average knowledge of specific outcomes of genetic modification were more likely than those with inaccurate or no knowledge to approve use of plant or animal genetic modification for the creation of new food products. Young South Koreans consumers (ages 20 to 29 years old) were more likely than old consumers (ages 50 to 59) to approve use of biotechnology to create both plant and animal based foods. Further, those Koreans in favor of GM labeling were less likely to approve the use of biotechnology for the creation of food products. The results also suggest that public trust and confidence on various institutions associated with biotechnology is critical for the future of the technology. There was some evidence of differential biotechnology approval among consumers of different residential areas, income levels and political affiliation. Thus, those in cities, those with incomes above 40 million Won, and of liberal political affiliation were found to be more approving of animal biotechnology.Research and Development/Tech Change/Emerging Technologies,

Determination of Letrozole in Tablet Formulations by Reversed Phase High Performance Liquid Chromatography

Purpose: To develop a simple, rapid, accurate and cost-effective reversed phase high performance liquid chromatography (RP-HPLC) method for letrozole in bulk and in tablets. Methods: Development of a method for the determination of letrozole, an anti-cancer drug, by RPHPLC was undertaken using a new mobile phase of acetonitrile:water (50:50, v/v). The eluent was monitored at 265 nm. Results: The optimized conditions developed showed a linear response from 160 to 240 &mu;g/mL, with a correlation coefficient (R2) of 0.999. The limit of detection (LOD) and limit of quantification ( LOQ) were 136 and 160 &mu;g/mL, respectively. The assay values for the two branded letrozole tablets tested were 99.2 and 100.2 %, respectively with % relative standard deviation (RSD) of 0.781 and 0.568, respectively. The bench top stability data of the drug in the mobile phase indicate that the drug was stable in the mobile phase for 24 h. Recovery data were good. Placebo study for specificity and interference of common excipients showed that the method was specific and free from interfering substances. Conclusion: Therefore, the fully validated method developed was sensitive enough to carry out routine analysis of letrozole in tablet formulations with regard to its run time, simplicity of sample preparation and accuracy.Key words: Letrozole, Assay, HPLC, Validation, Tablet formulation

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

Exchange anisotropy and the dynamic phase transition in thin ferromagnetic Heisenberg films

Monte Carlo simulations have been performed to investigate the dependence of the dynamic phase behavior on the bilinear exchange anisotropy of a classical Heisenberg spin system. The system under consideration is a planar thin ferromagnetic film with competing surface fields subject to a pulsed oscillatory external field. The results show that the films exhibit a single discontinuous dynamic phase transition (DPT) as a function of the anisotropy of the bilinear exchange interaction in the Hamiltonian. Furthermore there is no evidence of stochastic resonance (SR) associated with the DPT. These results are in marked contrast to the continuous DPT observed in the same system as a function of temperature and applied field strength for a fixed bilinear exchange anisotropy.Comment: 11 pages including 3 figure pages; submitted to PR