Temperature dependence of electron-spin relaxation in a single InAs quantum dot at zero applied magnetic field

The temperature-dependent electron spin relaxation of positively charged excitons in a single InAs quantum dot (QD) was measured by time-resolved photoluminescence spectroscopy at zero applied magnetic fields. The experimental results show that the electron-spin relaxation is clearly divided into two different temperature regimes: (i) T < 50 K, spin relaxation depends on the dynamical nuclear spin polarization (DNSP) and is approximately temperature-independent, as predicted by Merkulov et al. (ii) T > about 50 K, spin relaxation speeds up with increasing temperature. A model of two LO phonon scattering process coupled with hyperfine interaction is proposed to account for the accelerated electron spin relaxation at higher temperatures.Comment: 10 pages, 4 figure

Magnetic field processing to enhance critical current densities of MgB2 superconductors

Magnetic field of up to 12 T was applied during the sintering process of pure MgB2 and carbon nanotube (CNT) doped MgB2 wires. We have demonstrated that magnetic field processing results in grain refinement, homogeneity and significant enhancement in Jc(H) and Hirr. The Jc of pure MgB2 wire increased by up to a factor of 3 to 4 and CNT doped MgB2 by up to an order of magnitude in high field region respectively, compared to that of the non-field processed samples. Hirr for CNT doped sample reached 7.7 T at 20 K. Magnetic field processing reduces the resistivity in CNT doped MgB2, straightens the entangled CNT and improves the adherence between CNTs and MgB2 matrix. No crystalline alignment of MgB2 was observed. This method can be easily scalable for a continuous production and represents a new milestone in the development of MgB2 superconductors and related systems

Effects of various forms of lipopolysaccharide on the expression of inflammatory mediators and cardiac biomarkers in human cardiac fibroblasts and human coronary smooth muscle cells

Inflammation is an important event in the development of vascular diseases such as hypertension, atherosclerosis, and restenosis. The stimulation of lipopolysaccharide (LPS) from bacteria induces the release of critical proinflammatory cytokines that activate potent immune responses which may cause injury of cells in vivo and in vitro. Upon cardiac cell death caused by inflammation, the apoptotic cardiac cells express higher amount of cardiac markers. In this study, the effect of various LPS on human cardiac fibroblasts (HCFs) and human coronary smooth muscle cells (HCSMCs) were evaluated. Various forms of LPS were applied to HCFs and HCSMCs for 24, 48, 72 and 96 h. Proliferation rate of these cells was evaluated after stimulation. The levels of lactate dehydrogenase (LDH), N-terminal pro B-type natriuretic peptide (pro-BNP) and the MB isoenzyme of creatine kinase (CK-MB) were measured by an automation system. Cytokine levels in culture supernatants and extracted protein of cells were mixed and measured with IL-1β, IL-6 and IL-10 ELISA kits. Significant increase in the proliferation of two cardiac cells (P&lt;0.05) after incubation for 48 and 72 h was noted but not for 24 and 96 h (P&gt;0.05). Cardiac markers and inflammatory cytokines were significantly higher than control at 48 and 72 h (P&lt;0.05), which demonstrated that HCFs and HCMSCs were under inflammation leading to cell injury between 48 and 72 h. LPS is one of the factors giving rise to periodontal diseases, it is also involved in in vitro cardiac cell injury. Therefore, LPS may be used as a bio-marker to monitor local or systemic inflammation.Key words: Lipopolysaccharide, human cardiac fibroblasts, human coronary smooth muscle cell, inflammatory cytokines, cardiac bio-marker

Measurements of a fast nuclear spin dynamics in a single InAs quantum dot with positively charged exciton

By using highly time-resolved spectroscopy with an alternative {\sigma}+/{\sigma} - laser pulse modulation technique, we are able to measure the fast buildup and decay times of the dynamical nuclear spin polarization (DNSP) at 5 K for a single InAs quantum dot (QD) with positively charged exciton. It is shown that the nuclear dipole-dipole interaction can efficiently depolarize DNSP with a typical time constant of 500 {\mu}s in the absence of external magnetic field. By using an external field of 8 mT to suppress the nuclear dipolar interaction, the decay time turns to be mainly induced by interaction with unpaired electron and extends to about 5 ms. In addition, it is found that the time constant of hole-induced depolarization of nuclear spin is about 112 ms.Comment: 5 pages, 3 figure

Robust high-temperature magnetic pinning induced by proximity in YBa2Cu3O7-8/La0.67Sr0.33MnO3 hybrids

An elaborately designed bilayer consisting of superconducting YBa2Cu3O7-6 (YBCO) and ferromagnetic La0.67Sr0.33MnO3-6 (LSMO) was prepared on a single crystal LaAlO3 substrate by pulsed laser deposition (PLD), with a view to understanding the mechanism behind the influence of superconductor/ferromagnet proximity on the critical current density, Jc. The present bilayer system shows significant modifications in Jc, as evidenced by the suppressed decay of its temperature dependence, as well as the crossing behavior of the magnetic field dependence of Jc at high temperatures. This indicates that enhanced flux pinning emerges at high temperatures, and it is believed to arise from the special magnetic inhomogeneity, i.e., the ferromagnet/antiferromagnet clusters caused by phase separation due to the epitaxial stress between LSMO and the substrate

Carbon Storage and Sequestration Under Different Stocking Rates in a Eurasian Desert Steppe in China

The research on carbon source/sink of terrestrial ecosystem is an important part of global climate change. Under the sustainable grazing management, the carbon storage in grassland ecosystem will increase, which promotes the carbon sequestration in the grassland area. In order to understand the carbon sequestration in grazing system of desert steppe, a sheep grazing experiment for completely random block design was conducted in desert steppe. There were 4 stocking rates and 3 replications in this experiment. The effects of annual precipitation and stocking rate on the carbon sequestration of desert steppe were compared. The stocking rate treatments were as follows: no grazing, light grazing, moderate grazing, and heavy grazing. Plant composition, biomass, individual plant carbon, soil carbon, emission of soil and livestock, and carbon flux of ecosystem were measured. We discussed carbon storage and carbon sequestration based on the above indicators. The results showed that stocking rate has different effects on the aboveground net primary production, belowground net primary production, carbon storage of grassland ecosystem, net ecosystem exchange and soil respiration. We further analyzed the impact factors of different variables, understood the carbon sequestration and transition process from plant to soil in this steppe. Finally, we concluded that the optimal stocking rate in desert steppe according to the vegetation, balance of soil nutrients and livestock performance, provides the theoretical reference for the sustainable grassland management based on grassland carbon sequestration

Quantification of P-Glycoprotein in the Gastrointestinal Tract of Humans and Rodents: Methodology, Gut Region, Sex, and Species Matter

Intestinal efflux transporters affect the gastrointestinal processing of many drugs but further data on their intestinal expression levels are required. Relative mRNA expression and relative and absolute protein expression data of transporters are commonly measured by real-time polymerase chain reaction (RT-PCR), Western blot and mass spectrometry-based targeted proteomics techniques. All of these methods, however, have their own strengths and limitations, and therefore, validation for optimized quantification methods is needed. As such, the identification of the most appropriate technique is necessary to effectively translate preclinical findings to first-in-human trials. In this study, the mRNA expression and protein levels of the efflux transporter P-glycoprotein (P-gp) in jejunal and ileal epithelia of 30 male and female human subjects, and the duodenal, jejunal, ileal and colonic tissues in 48 Wistar rats were quantified using RT-PCR, Western blot and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A similar sex difference was observed in the expression of small intestinal P-gp in humans and Wistar rats where P-gp was higher in males than females with an increasing trend from the proximal to the distal parts in both species. A strong positive linear correlation was determined between the Western blot data and LC-MS/MS data in the small intestine of humans (R^{2} = 0.85). Conflicting results, however, were shown in rat small intestinal and colonic P-gp expression between the techniques (R^{2} = 0.29 and 0.05, respectively). In RT-PCR and Western blot, an internal reference protein is experimentally required; here, beta-actin was used which is innately variable along the intestinal tract. Quantification via LC-MS/MS can provide data on P-gp expression without the need for an internal reference protein and consequently, can give higher confidence on the expression levels of P-gp along the intestinal tract. Overall, these findings highlight similar trends between the species and suggest that the Wistar rat is an appropriate preclinical animal model to predict the oral drug absorption of P-gp substrates in the human small intestine

Peak effect in the critical current of type II superconductors with strong magnetic vortex pinning

We perform 2D Langevin simulations studying the peak effect (PE) of the critical current taking into account the temperature dependence of the competing forces. We observe and report that the PE results from the competition of vortex-vortex interactions and vortex-pin interactions which have different temperature dependencies. The simulations reveal that the PE can take place only for certain pinning strengths, densities of pinning centres, and driving forces, which is in good agreement with experiments. No apparent vortex order-disorder transition is observed across the PE regime. In addition, the PE is a dynamical phenomenon, and thermal fluctuations can speed up the process for the formation of the PE