77 research outputs found
Growth of Thin Oxidation-Resistive Crystalline Si Nanostructures on Graphene
We report the growth of Si nanostructures, either as thin films or
nanoparticles, on graphene substrates. The Si nanostructures are shown to be
single crystalline, air stable and oxidation resistive, as indicated by the
observation of a single crystalline Si Raman mode at around 520 cm-1, a STM
image of an ordered surface structure under ambient condition, and a Schottky
junction with graphite. Ultra-thin silicon regions exhibit silicene-like
behavior, including a Raman mode at around 550 cm-1, a triangular lattice
structure in STM that has distinctly different lattice spacing from that of
either graphene or thicker Si, and metallic conductivity of up to 500 times
higher than that of graphite. This work suggests a bottom-up approach to
forming a Si nanostructure array on a large scale patterned graphene substrate
for fabricating nanoscale Si electronic devices
Valley vortex states and degeneracy lifting via photonic higher-band excitation
We demonstrate valley-dependent vortex generation in a photonic graphene.
Without breaking the inversion symmetry, excitation of two equivalent valleys
leads to formation of an optical vortex upon Bragg-reflection to the third
valley, with its chirality determined by the valley degree of freedom.
Vortex-antivortex pairs with valley-dependent topological charge flipping are
also observed and corroborated by numerical simulations. Furthermore, we
develop a three-band effective Hamiltonian model to describe the dynamics of
the coupled valleys, and find that the commonly used two-band model is not
sufficient to explain the observed vortex degeneracy lifting. Such
valley-polarized vortex states arise from high-band excitation without
inversion symmetry breaking or synthetic-field-induced gap opening. Our results
from a photonic setting may provide insight for the study of valley contrasting
and Berry-phase mediated topological phenomena in other systems
Longitudinal Association between Selenium Levels and Hypertension in a Rural Elderly Chinese Cohort
Objectives
Results from previous studies have been inconsistent on the association between selenium and hypertension, and very few studies on this subject have focused on the elderly population. The purpose of this study is to examine the relationship between selenium level and hypertension in a rural elderly Chinese cohort.
Design
A longitudinal study was implemented and data were analyzed using logistic regression models and Cox proportional hazards regression model adjusting for potential confounders. The associations between selenium level and prevalent hypertension at baseline and between selenium and incident hypertension were examined.
Setting
Community-based setting in four rural areas in China.
Subjects
A total of 2000 elderly aged 65 years and over (mean 71.9±5.6 years) participated in this study.
Measurements
Nail selenium levels were measured in all subjects at baseline. Blood pressure measures and self-reported hypertension history were collected at baseline, 2.5 years and 7 years later. Hypertension was defined as systolic blood pressure 140 mmHg or higher, diastolic blood pressure 90 mmHg or higher, or reported use of anti-hypertensive medication.
Results
The rate of baseline hypertension was 63.50% in this cohort and the mean nail selenium level is 0.413±0.183”g/g. Multi-covariate adjusted cross-sectional analyses indicated that higher selenium level was associated with higher blood pressure measures at baseline and higher rates of hypertension. For the 635 participants with normal blood pressure at baseline, 360 had developed hypertension during follow-up. The incidence rate for hypertension was 45.83%, 52.27%, 62.50%, 70.48%, and 62.79% from the first selenium quintile to the fifth quintile respectively. Comparing to the lowest quintile group, the hazard ratios were 1.41 (95%CI: 1.03 to1.94), 1.93 (95%CI: 1.40 to 2.67), 2.35 (95%CI: 1.69 to 3.26) and 1.94 (95%CI: 1.36 to 22.77) for the second selenium quintile to the fifth quintile respectively.
Conclusions
Our findings suggest that high selenium may play a harmful role in the development of hypertension. Future studies are needed to confirm our findings and to elucidate a plausible biological mechanism
The relationship between cholesterol and cognitive function is homocysteine-dependent
Introduction
Previous studies have identified hyperlipidemia as a potential risk factor for dementia and Alzheimerâs disease. However, studies on cholesterol measured in late-life and cognitive function have been inconsistent. Few studies have explored nonlinear relationships or considered interactions with other biomarker measures.
Methods
A cross-sectional sample of 1,889 participants from four rural counties in the Peopleâs Republic of China was included in this analysis. Serum total cholesterol, high-density lipoprotein, triglycerides, and homocysteine levels were measured in fasting blood samples. A composite cognitive score was derived based on nine standardized cognitive test scores. Analysis of covariance models were used to investigate the association between biomarker measures and the composite cognitive scores.
Results
There was a significant interaction between the homocysteine quartile group and the cholesterol quartile group on cognitive scores (P=0.0478). In participants with normal homocysteine levels, an inverse U-shaped relationship between total cholesterol level and cognitive score was found, indicating that both low and high cholesterol levels were associated with lower cognitive scores. In participants with high homocysteine levels, no significant association between cholesterol and cognition was found.
Conclusion
The relationship between cholesterol levels and cognitive function depends upon homocysteine levels, suggesting an interactive role between cholesterol and homocysteine on cognitive function in the elderly population. Additional research is required to confirm our findings in other populations, and to explore potential mechanisms underlying the lipidâhomocysteine interaction
Two ultraviolet radiation datasets that cover China
Ultraviolet (UV) radiation has significant effects on ecosystems, environments, and human health, as well as atmospheric processes and climate change. Two ultraviolet radiation datasets are described in this paper. One contains hourly observations of UV radiation measured at 40 Chinese Ecosystem Research Network stations from 2005 to 2015. CUV3 broadband radiometers were used to observe the UV radiation, with an accuracy of 5%, which meets the World Meteorology Organization's measurement standards. The extremum method was used to control the quality of the measured datasets. The other dataset contains daily cumulative UV radiation estimates that were calculated using an all-sky estimation model combined with a hybrid model. The reconstructed daily UV radiation data span from 1961 to 2014. The mean absolute bias error and root-mean-square error are smaller than 30% at most stations, and most of the mean bias error values are negative, which indicates underestimation of the UV radiation intensity. These datasets can improve our basic knowledge of the spatial and temporal variations in UV radiation. Additionally, these datasets can be used in studies of potential ozone formation and atmospheric oxidation, as well as simulations of ecological processes
From classic medicinal chemistry to stateâofâtheâart interdisciplinary medicine: Recent advances in proteolysisâtargeting chimeras technology
Abstract Proteolysisâtargeting chimeras (PROTACs) is a targeted protein degradation (TPD) technique effected by hijacking the ubiquitinâproteasome system (UPS) of the cells. A PROTAC molecule specifically binds to its protein of interest (POI) and recruits an E3 ligase to assemble a ternary complex. The POI was subsequently ubiquitinated, followed by being degraded by proteasomes. After 20Â years of development, PROTAC technology has made a significant progress, and quite some candidates have entered clinical trials. Along with the excitement of realizing that PROTAC technology can develop therapeutics toward those traditionally believed âundruggableâ targets; there are still unmet demands in PROTAC design, screening, and intracellular availability. PROTAC technology is rapidly advancing from employing traditional medicinal chemistry methodologies to integrating stateâofâtheâart chemical biology technologies, becoming a typical example of interdisciplinary medicine. This review summarizes the progress made in PROTAC technology in recent years, including expanding new targets, developing dualâtarget PROTACs, rational design and screening strategies, regulatory activation, targeted delivery, and developing biological macromoleculeâcontained PROTACs
Valley Vortex States and Degeneracy Lifting via Photonic Higher-Band Excitation
We demonstrate valley-dependent vortex generation in photonic graphene. Without breaking inversion symmetry, the excitation of two valleys leads to the formation of an optical vortex upon Bragg reflection to the third equivalent valley, with its chirality determined by the valley degree of freedom. Vortex-antivortex pairs with valley-dependent topological charge flipping are also observed and corroborated by numerical simulations. Furthermore, we develop a three-band effective Hamiltonian model to describe the dynamics of the coupled valleys and find that the commonly used two-band model is not sufficient to explain the observed vortex degeneracy lifting. Such valley-polarized vortex states arise from high-band excitation without a synthetic-field-induced gap opening. Our results from a photonic setting may provide insight for the study of valley contrasting and Berry-phase-mediated topological phenomena in other systems. © 2019 American Physical Societ
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