A practical approach to achieve strong coherent synchrotron emissions (CSE) in relativistic laser-plasma interaction is proposed, where a plane target with its electron density satisfying the self-similar parameter S similar or equal to n(e0)/a(0)n(c) = 1 is obliquely irradiated by a P-polarized laser pulse. In this case, electrons at the target surface are periodically dragged out into the vacuum by the laser field component perpendicular to the target surface, resulting in the formation of a series of dense electron bunches propagating along the target surface. Intense CSE is generated by these electron bunches under acceleration by the laser field component parallel to the target surface. Two-dimensional particle-in-cell simulations show that an intense attosecond light pulse at intensity 9.1 x 10(20) W/cm(2) (electric field strength similar to 41% as that of the drive laser) can be obtained through such CSE. In the high-order harmonics with 15 omega(0) < omega(n) < 500 omega(0) (omega(0) is the laser frequency), the power spectrum of the emission scales as I(n) similar to n(-1.8) and the conversion efficiency from laser to emission reaches similar to 10(-2). Published by AIP Publishing.
It is shown that relativistic many-body Hamiltonians and wave functions can beexpressed systematically with Tracy-Singh products for partitioned matrices. The latter gives rise to the usual notion for a relativistic $N$-electron wave function: A column vector composed of $2^N$ blocks, each of which consists of $2^N$ components formed by the Kronecker products of $N$ one-electron 2-spinors. Yet, the noncommutativity of the Tracy-Singh product dictates that the chosen serial ordering of electronic coordinates cannot be altered when antisymmetrizing a Tracy-Singh product of 4-spinors. It is further shown that such algebraic representation uncovers readily the internal symmetries of the relativistic Hamiltonians and wave functions, which are crucial for deriving the electron-electron coalescence conditions.
A compact laser plasma accelerator that is a novel accelerator based on the interaction of ultra-intense laser and plasmas is being built now at Peking University. According to the results of experiments and numerical simulations, a beam line combining the advantages of quadrupole and analyzing magnets is designed to deliver proton beams with energy ranging from 1 to 44 MeV, energy spread within +/- 5% and 10(6-8) protons per pulse. It turns out that the existence of space charge force of protons can be ignored for the increase of transverse and longitudinal envelopes even in the case of 109 protons in one pulse. To cope with the challenge to obtain a uniform distribution of protons at the final experiment target in laser acceleration, we manipulate the envelope beam waist in the.. direction to a proper position and obtain a relatively good distribution uniformity of protons with an energy spread of 0-+/- 5%.
Bibliometric analysis was applied to identify global patterns and trends in the research of biogenic volatile organic compounds (BVOCs), which are important to atmospheric ozone formation and secondary organic aerosol formation. Yearly publications, mainstream subject categories and journals, leading countries and institutions, research emphases and trends were identified. Number of publications and times of citation were used as indicators to evaluate publication performances. A summary of the most frequently used keywords obtained from author keywords and KeyWords Plus provided clues for research emphases in different periods. A network of keywords was drawn to visualize the cross-relationship of keywords. Results indicated that annual output of the related scientific papers increased notably during 1991–2014. Atmospheric Sciences, Environmental Sciences & Ecology, Environmental Sciences & Engineering, and Chemistry were the main subject categories. Journal of Geophysical Research-Atmospheres was the most competitive journal in productivity and academic impact. The USA and the National Center for Atmospheric Research (NCAR) were, respectively, the leading country and leading institution in BVOC research. “Emissions,” “isoprene,” and “model” were the leading research emphases in BVOC field in terms of word frequencies and centrality driven from the network structure. The three leading research hotspots cross-fields, emissions-isoprene, emissions-model, and isoprene-model showed substantial growth in scientific outputs during the study period. These trends were evidenced by the evolution of research contents in various studies.
Terahertz applications urgently require high performance and room temperature terahertz sources. The gyrotron based on the principle of electron cyclotron maser is able to generate watt-to-megawatt level terahertz radiation, and becomes an exceptional role in the frontiers of energy, security and biomedicine. However, in normal conditions, a terahertz gyrotron could generate terahertz radiation with high efficiency on a single frequency or with low efficiency in a relatively narrow tuning band. Here a frequency tuning scheme for the terahertz gyrotron utilizing sequentially switching among several whispering-gallery modes is proposed to reach high performance with broadband, coherence and high power simultaneously. Such mode-switching gyrotron has the potential of generating broadband radiation with 100-GHz-level bandwidth. Even wider bandwidth is limited by the frequency-dependent effective electrical length of the cavity. Preliminary investigation applies a pre-bunched circuit to the single-mode wide-band tuning. Then, more broadband sweeping is produced by mode switching in great-range magnetic tuning. The effect of mode competition, as well as critical engineering techniques on frequency tuning is discussed to confirm the feasibility for the case close to reality. This multi-mode-switching scheme could make gyrotron a promising device towards bridging the so-called terahertz gap.
This paper investigates whether children’s political success contributes to social stratification and health inequality among older adults. Using China Health and Retirement Longitudinal Study (CHARLS) data, we investigate whether having a cadre (i.e., politically employed) child substantially increases overall cognitive functioning among older adults. We find that the beneficial effect of having a cadre child on cognitive functioning is equivalent to a 1.5-year increase in education, even after controlling for other variables related to general intelligence. This positive effect is more salient among parents of higher-ranking cadre children, and more salient in less-marketized regions. The results of a Sobel test suggest that about one-fifth of the effect can be explained by the channel of increased social interaction.
Proton-transfer-reaction mass spectrometry (PTR-MS) allows the detection of a large number of trace gases in air through proton-transfer reaction with H3O+ reagent ions and detection by a mass spectrometer. Measurement sensitivities can be experimentally determined using calibration gases or calculated using the rate constant for the proton-transfer reaction, but rate constants have only been measured for a subset of compounds. Numerous theoretical approaches that describe the ion-molecule collision processes have shown how to accurately calculate capture collision rate constants between an ion and neutral molecules using the polarizability and permanent dipole moment of the molecule. Here we show that polarizability, dipole moment, and resulting capture rate constants for proton-transfer reactions of H3O+ with various different volatile organic compounds (VOCs) can be obtained using the molecular mass, elemental composition, and functionality of VOCs. The polarizabilities of a class of VOCs possessing a specific number of electronegative atoms were linearly correlated with their molecular mass. The dipole moments in a series of VOCs, in which VOCs contain a specific functional group and arbitrary residual hydrocarbon parts, can be approximated as a constant value. The capture rate constants calculated using polarizability and dipole moment, as estimated from molecular mass, elemental composition, and functional group, agreed within 10% with measured values for most VOCs. Those capture rate constants were applied to the calculation of the sensitivities of VOCs detected by our PTR-MS, taking into account the ion transmission efficiency and the degree of fragmentation of protonated VOCs observed in that instrument as well as chemical properties of the VOCs. The resulting calculated sensitivities agreed within 20-50% of those measured by PTR-MS, but several notable exceptions exist. This result shows that the neutral concentration of a VOC detected as a protonated molecule in PTR-MS can be approximated using only molecular mass, elemental composition, and functionality of the VOC. The present study is useful for all PTR-MS instruments regardless of the type of mass analyzer; however, the identification of elemental composition by high mass resolution instrumentation is important. (C) 2017 Elsevier B.V. All rights reserved.
Objective To understand the relationships between CDH13 (T-cadherin) genetic polymorphisms, adiponectin levels and ischemic stroke, and possible interactions between CDH13 polymorphisms and other risk factors. Methods We recruited 342 Chinese ischemic stroke sib pairs. We genotyped rs4783244 and rs7193788 on CDH13 using time-of-flight mass spectrometry genotyping technology and measured total and high-molecular weight (HMW) adiponectin levels. We investigated associations between SNPs and ischemic stroke, and interactions between SNPs and other risk factors using multi-level mixed-effects regression model. Results In individuals without ischemic stroke, CDH13 rs4783244 was associated with total adiponectin levels (per T: Coef = -0.257, P = 0.001). CDH13 rs7193788 was associated with total adiponectin levels (per A: Coef = -0.221, P = 0.001) and HMW adiponectin levels (per A: Coef = -0.163, P = 0.003). rs7193788 was significantly associated with ischemic stroke (GA/AA vs. GG: OR = 1.55, 95% CI: 1.07 to 2.24, P = 0.020) after Bonferroni correction (alpha = 0.025). There was an interaction between rs7193788 and diabetes (P = 0.036). Compared to diabetes-free individuals with rs7193788 GG genotype, diabetes patients with rs7193788 GA/AA genotypes had higher risks for ischemic stroke (OR = 2.64, 95% CI: 1.58-4.40, P < 0.001). Conclusion CDH13 genetic polymorphisms are associated with adiponectin levels and ischemic stroke. An interaction is found between CDH13 SNP and diabetes for ischemic stroke.
Cell-associated ARGs in wastewater treatment plants (WWTPs) has been concerned, however, cell-free ARGs in WWTPs was rarely studied. In this study, the abundances of four representative ARGs, sulII, tetC, blaPSE‑1,and ermB, in a large municipal WWTP were investigated in both cell-associated and cell-free fractions. Cell-associated ARGs was the dominant ARGs fraction in the raw wastewater. After biological treatment, sludge settling, membrane filtration, and disinfection, cell-associated ARGs were substantially reduced, though the ratios of ARG/16S rRNA gene were increased with disinfection. Cell-free ARGs persisted in the WWTP with a removal of 0.36 log to 2.68 logs, which was much lower than the removal of cell-associated ARGs (3.21 logs to 4.14 logs). Therefore, the abundance ratio of cell-free ARGs to cell-associated ARGs increased from 0.04−1.59% to 2.00−1895.08% along the treatment processes. After 25-day-storage, cell-free ARGs in both biological effluent and disinfection effluent increased by 0.14 log to 1.99 logs and 0.12 log to 1.77 logs respectively, reflecting the persistence and low decay rate of cell-free ARGs in the discharge water. Therefore, cell-free ARGs might be a kind of important but previously neglected pollutant from WWTPs, which added potential risks to the effluent receiving environments.
The leakage of low and intermediate level radioactive wastes from cementitious barriers at disposal sites can pose long-term environmental threats. In this study, cementitious materials were modified with hematite nanoparticles at 1.0%, 3.0%, and 5.0% by mass to enhance uranium immobilization for the first time. After curing the specimens for 28 days, leaching experiments were carried out at 90 °C up to 28 days. The leached uranium and sodium ions in solutions were quantified, and the effects of hematite nanoparticles on the physicochemical and mechanical properties of cementitious materials were studied. The experimental results revealed that the addition of 1.0%, 3.0% and 5.0% hematite nanoparticles all significantly reduced uranium leaching, which is partially due to uranium adsorption onto hematite nanoparticles. Interestingly, the slowest uranium leaching was found in the specimens with 1.0% hematite nanoparticles. The leaching results were complemented by isothermal calorimetry measurements, mercury intrusion porosimetry, chemical analysis, and compression tests, which showed that hematite nanoparticles increased the cement hydration rate and degree, affected cementitious material pore structure development, decreased leachability, and increased compressive strength. These effects were found to be the strongest in specimens containing 1.0% hematite nanoparticles. This study provides new insights into the modification of cementitious materials with hematite nanoparticles for enhanced cement hydration and uranium immobilization. It suggests an economical strategy for the long-term disposal of low and intermediate level radioactive wastes.