370 research outputs found
Pressure and temperature driven phase transitions in HgTe quantum wells
We present theoretical investigations of pressure and temperature driven
phase transitions in HgTe quantum wells grown on CdTe buffer. Using the 8-band
\textbf{kp} Hamiltonian we calculate evolution of energy band structure
at different quantum well width with hydrostatic pressure up to 20 kBar and
temperature ranging up 300 K. In particular, we show that in addition to
temperature, tuning of hydrostatic pressure allows to drive transitions between
semimetal, band insulator and topological insulator phases. Our realistic band
structure calculations reveal that the band inversion under hydrostatic
pressure and temperature may be accompanied by non-local overlapping between
conduction and valence bands. The pressure and temperature phase diagrams are
presented.Comment: 9 pages, 8 figures + Supplemental material (5 pages
High intensity study of THz detectors based on field effect transistors
Terahertz power dependence of the photoresponse of field effect transistors,
operating at frequencies from 0.1 to 3 THz for incident radiation power density
up to 100 kW/cm^2 was studied for Si metal-oxide-semiconductor field-effect
transistors and InGaAs high electron mobility transistors. The photoresponse
increased linearly with increasing radiation power up to kW/cm^2 range. The
saturation of the photoresponse was observed for all investigated field effect
transistors for intensities above several kW/cm^2. The observed signal
saturation is explained by drain photocurrent saturation similar to saturation
in direct currents output characteristics. The theoretical model of terahertz
field effect transistor photoresponse at high intensity was developed. The
model explains quantitatively experimental data both in linear and nonlinear
(saturation) range. Our results show that dynamic range of field effect
transistors is very high and can extend over more than six orderd of magnitudes
of power densities (from 0.5 mW/cm^2 to 5 kW/cm^2)
Correlation of liver stiffness and histological features in healthy persons and in patients with occult hepatitis B, chronic active hepatitis B, or hepatitis B cirrhosis
OBJECTIVES: Liver stiffness measurement using transient elastography has become a popular tool to assess liver fibrosis. The aim of this study was to determine liver stiffness values and histological features in healthy subjects and in patients with chronic hepatitis B (CHB).METHODS: A total of 157 people were included (28 healthy subjects and 18 patients with occult hepatitis B infection, 102 with active CHB, and 9 with end-stage hepatitis B cirrhosis). Histology and liver stiffness measurements were obtained from all patients.RESULTS: The median liver stiffness in healthy subjects and in occult hepatitis B, active hepatitis B, and end-stage cirrhosis patients was 4.6, 4.2, 8.7, and 33.8 kPa, respectively. In healthy subjects and in patients with occult hepatitis B infection, none had significant fibrosis on histology, and all had liver stiffness 7.2 kPa. In patients with active CHB, 32 (31%) had liver stiffness 11.0 kPa, but only four (12%) had cirrhosis on histology. Using liver stiffness to predict cirrhosis in this group had a sensitivity of 100%, a specificity of 69%, a positive predictive value of 10%, and a negative predictive value of 100%. All nine patients with end-stage liver cirrhosis had liver stiffness 11.0 kPa. The overall area under the ROC curve (AUROC) for diagnosing cirrhosis using a cutoff of 11.3 kPa was 0.89.CONCLUSIONS: Liver stiffness measurement has an overall good diagnostic accuracy with excellent negative predictive value. However, in active CHB with elevated alanine aminotransferase (ALT) levels, the positive predictive value for diagnosing cirrhosis is poor, and further studies are needed to optimize the use of transient elastography in this important group. © 2010 by the American College of Gastroenterology.postprin
Temperature-driven single-valley Dirac fermions in HgTe quantum wells
We report on temperature-dependent magnetospectroscopy of two HgTe/CdHgTe
quantum wells below and above the critical well thickness . Our results,
obtained in magnetic fields up to 16 T and temperature range from 2 K to 150 K,
clearly indicate a change of the band-gap energy with temperature. The quantum
well wider than evidences a temperature-driven transition from
topological insulator to semiconductor phases. At the critical temperature of
90 K, the merging of inter- and intra-band transitions in weak magnetic fields
clearly specifies the formation of gapless state, revealing the appearance of
single-valley massless Dirac fermions with velocity of
ms. For both quantum wells, the energies extracted from
experimental data are in good agreement with calculations on the basis of the
8-band Kane Hamiltonian with temperature-dependent parameters.Comment: 5 pages, 3 figures and Supplemental Materials (4 pages
Ketone body 3-hydroxybutyrate as a biomarker of aggression
Human aggression is a complex behaviour, the biological underpinnings of which remain poorly known. To gain insights into aggression biology, we studied relationships with aggression of 11 low-molecular-weight metabolites (amino acids, ketone bodies), processed using H-1 nuclear magnetic resonance spectroscopy. We used a discovery sample of young adults and an independent adult replication sample. We studied 725 young adults from a population-based Finnish twin cohort born 1983-1987, with aggression levels rated in adolescence (ages 12, 14, 17) by multiple raters and blood plasma samples at age 22. Linear regression models specified metabolites as the response variable and aggression ratings as predictor variables, and included several potential confounders. All metabolites showed low correlations with aggression, with only one-3-hydroxybutyrate, a ketone body produced during fasting-showing significant (negative) associations with aggression. Effect sizes for different raters were generally similar in magnitude, while teacher-rated (age 12) and self-rated (age 14) aggression were both significant predictors of 3-hydroxybutyrate in multi-rater models. In an independent replication sample of 960 adults from the Netherlands Twin Register, higher aggression (self-rated) was also related to lower levels of 3-hydroxybutyrate. These exploratory epidemiologic results warrant further studies on the role of ketone metabolism in aggression.Peer reviewe
Best Practices for Teaching Chemistry Disciplines to Graduates Majoring in Pharmacy During the COVID-19 Restrictions: A Systematic Review
The purpose of the study was to identify the - interventions that can be adopted for teaching chemistry disciplines to the graduates majoring in Pharmacy (Mpharm) in Ukraine. The study employed a systematic review methodology and a qualitative approach to synthesising the sources. The triangular assessment method was used to rate the short-listed instructional interventions for feasibility, transferability, and duplicability in the settings of teaching chemistry disciplines to pharmacy graduates in Ukraine. The review found seven eligible publications for the analysis. It was identified that the shortlisted instructional models were technology-mediated and positively affected students’ skills and occupational knowledge. Three out of seven instructional models used chatbots and AI to automate the process of management of students learning activity which suggested that automation of the process of educational content delivery was becoming an emerging trend in instructional design. Having performed the triangular assessment method (TAM) analysis, three instructional models were given preference in terms of their use in medical education settings in Ukraine. These models were as follows: a) PhET simulations-based model, b) the model based on automated delivery of the course using the Smart Sender platform and c) the model based on automation of the Moodle-driven e-course using Dialogflow chatbot
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