Renormalization group study of intervalley scattering and valley splitting in a two-valley system

Renormalization group equations are derived for the case when both valley splitting and intervalley scattering are present in a two-valley system. A third scaling parameter is shown to be relevant when the two bands are split but otherwise distinct. The existence of this parameter changes the quantitative behavior at finite temperatures, but the qualitative conclusions of the two-parameter theory are shown to be unaffected for realistic choice of parameters

Magnetoconductivity in the presence of Bychkov-Rashba spin-orbit interaction

A closed-form analytic formula for the magnetoconductivity in the diffusive regime is derived in the presence of Bychkov-Rashba spin-orbit interaction in two dimensions. It is shown that at low fields B << B_{so}, where B_{so} is the characteristic field associated with spin precession, D'yakonov-Perel' mechanism leads to spin relaxation, while for B >> B_{so} spin relaxation is suppressed and the resulting spin precession contributes a Berry phase-like spin phase to the magnetoconductivity. The relative simplicity of the formula greatly facilitates data fitting, allowing for the strength of the spin-orbit coupling to be easily extracted

Test of scaling theory in two dimensions in the presence of valley splitting and intervalley scattering in Si-MOSFETs

We show that once the effects of valley splitting and intervalley scattering are incorporated, renormalization group theory consistently describes the metallic phase in silicon metal-oxide-semiconductor field-effect transistors down to the lowest accessible temperatures

Renormalization group study of a two-valley system with spin-splitting

Renormalization group equations in a two-valley system with valley-splitting and intervalley scattering are derived in the presence of spin-splitting induced by a parallel magnetic field. The relevant amplitudes in different regimes set by the relative strengths of the spin and valley splittings and the intervalley scattering rate are identified. The range of applicability of the standard formula for the magnetoconductance is discussed

Dilute electron gas near the metal-insulator transition in two dimensions

In recent years systematic experimental studies of the temperature dependence of the resistivity in a variety of dilute, ultra clean two dimensional electron/hole systems have revived the fundamental question of localization or, alternatively, the existence of a metal-insulator transition in the presence of strong electron-electron interactions in two dimensions. We argue that under the extreme conditions of ultra clean systems not only is the electron-electron interaction very strong but the role of other system specific properties are also enhanced. In particular, we emphasize the role of valleys in determining the transport properties of the dilute electron gas in silicon inversion layers (Si-MOSFETs). It is shown that for a high quality sample the temperature behavior of the resistivity in the region close to the critical region of the metal-insulator transition is well described by a renormalization group analysis of the interplay of interaction and disorder if the electron band is assumed to have two distinct valleys. The decrease in the resistivity up to five times has been captured in the correct temperature interval by this analysis, without involving any adjustable parameters. The considerable variance in the data obtained from different Si-MOSFET samples is attributed to the sample dependent scattering rate across the two valleys, presenting thereby with a possible explanation for the absence of universal behavior in Si-MOSFET samples of different quality

Unusual Crystallite Growth and Modification of Ferromagnetism Due to Aging in Pure and Doped Zno Nanoparticles

We report the unusual growth of pure and Fe-doped ZnO nanoparticles prepared by forced hydrolysis and the weakening of ferromagnetism due to aging in ambient conditions. More than four dozen nanoparticle samples in the size range of 4–20 nm were studied over 1 to 4 years. The as-prepared samples had significant changes in their crystallite sizes and magnetization as they aged in ambient conditions. Detailed studies using x ray diffraction and transmission electron microscopy (TEM) demonstrated that the crystallite size increased by as much as 1.4 times. Lattice parameters and strain also showed interesting changes. Magnetometry studies of Zn1−xFexO with x = 0–0.2 showed ferromagnetism at room temperature; however, keeping the samples in ambient conditions for one year resulted in modifications in the crystallite size and magnetization. For the Zn0.95Fe0.05O sample, the size changed from 7.9 nm to 9.0 nm, while the magnetization decreased from 1×10–3emu/g (memu/g) to 0.2 memu/g. Both magnetic and structural changes due to aging varied with the environment in which they were stored, indicating that these changes are related to the aging conditions

Interaction effects on magnetooscillations in a two-dimensional electron gas

Motivated by recent experiments, we study the interaction corrections to the damping of magnetooscillations in a two-dimensional electron gas (2DEG). We identify leading contributions to the interaction-induced damping which are induced by corrections to the effective mass and quantum scattering time. The damping factor is calculated for Coulomb and short-range interaction in the whole range of temperatures, from the ballistic to the diffusive regime. It is shown that the dominant effect is that of the renormalization of the effective electron mass due to the interplay of the interaction and impurity scattering. The results are relevant to the analysis of experiments on magnetooscillations (in particular, for extracting the value of the effective mass) and are expected to be useful for understanding the physics of a high-mobility 2DEG near the apparent metal-insulator transition.Comment: 24 pages; subsection adde

Comparative metal oxide nanoparticle toxicity using embryonic zebrafish

AbstractEngineered metal oxide nanoparticles (MO NPs) are finding increasing utility in the medical field as anticancer agents. Before validation of in vivo anticancer efficacy can occur, a better understanding of whole-animal toxicity is required. We compared the toxicity of seven widely used semiconductor MO NPs made from zinc oxide (ZnO), titanium dioxide, cerium dioxide and tin dioxide prepared in pure water and in synthetic seawater using a five-day embryonic zebrafish assay. We hypothesized that the toxicity of these engineered MO NPs would depend on physicochemical properties. Significant agglomeration of MO NPs in aqueous solutions is common making it challenging to associate NP characteristics such as size and charge with toxicity. However, data from our agglomerated MO NPs suggests that the elemental composition and dissolution potential are major drivers of toxicity. Only ZnO caused significant adverse effects of all MO particles tested, and only when prepared in pure water (point estimate median lethal concentration=3.5–9.1mg/L). This toxicity was life stage dependent. The 24h toxicity increased greatly (∼22.7 fold) when zebrafish exposures started at the larval life stage compared to the 24h toxicity following embryonic exposure. Investigation into whether dissolution could account for ZnO toxicity revealed high levels of zinc ion (40–89% of total sample) were generated. Exposure to zinc ion equivalents revealed dissolved Zn2+ may be a major contributor to ZnO toxicity

Prescription pattern of NSAIDS and the prevalence of NSAID-induced gastrointestinal risk factors of orthopaedic patients

Background: Nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most commonly used medications in the world. NSAID-induced adverse reactions involve upper gastrointestinal (GI) tract complications, which can be life-threatening. Objectives: The study was conducted to explore the current prescription pattern of non-steroidal anti-inflammatory drugs (NSAIDs) and the prevalence of NSAID-induced gastrointestinal(GI) risk factors of orthopedic adult inpatient.Materials and methods: A prospective observational NSAIDs induced GI risk related study was conducted over a period of 6 months by clinical pharmacist. Study cohort included 105 orthopaedic inpatients who are taking or will be taking NSAIDs for more than a week. A self-administered questionnaire was completed by each patient. A simplified risk scoring scale (the Standardized Calculator of Risk for Events; SCORE) was used to measure patients‟ risk for GI complications. The pattern of NSAIDs prescription was identified from medical recordings.Results: The study groups were stratified into four risk groups according to GI SCORE tool, 27.6% of the patients belonged to high risk or very high risk groups for GI complications. Analysis of prescription pattern revealed that 11.4% of the patients aged over 65 yr, 19% with co morbid disease were prescribed with COX-2 selective inhibitor. Conclusion: In this study assessment of prescription pattern and GI risk factors for NSAIDs were evaluated and in conclusion, physician‟s considerate prescription of NSAIDs with well-understanding of each patient‟s GI risk factors is strongly encouraged to prevent serious GI complication