Search

The first rhodium(i)-catalyzed asymmetric S–H insertion of α-diazoarylacetates with tert-butyl mercaptan using chiral diene as the ligand has been developed.

Additional file 1:Figure S1. HPLC analysis of icariside I and baohuoside I hydrolysis by SPRHA2 and PBGL; Figure S2. HPLC analysis of epimedin A, B, and C hydrolysis by SPRHA2 and PBGL; Figure S3. HPLC analysis of the time course of epimedin C hydrolysis by SPRHA2; Figure S4. Time course of hydrolysis of whole-cell hydrolysis of icariin; Figure S5. SDS-PAGE analysis of pET-pbgl-sprha2 and pET-sprha2-pbgl in E. coli. Table S1. NMR data for standard icaritin and icaritin produced

We present a lattice QCD study of the neutrinoless double beta decay involving light sterile neutrinos. The calculation is performed at physical pion mass using five gauge ensembles generated with 2+1-flavor domain wall fermions. We obtain the low-energy constants gLRππ(mν) with the neutrino mass mν from 0 to 3 GeV. The lattice results are reasonably consistent with the previous interpolation method with a ∼20% deviation at small mν. We provide an explanation on the discrepancy at vanishing neutrino mass. At large mν, a good consistency between our results and the previous lattice determination of g4ππ(μ) is found at μ=mν=3 GeV.

BACKGROUND In recent years, neoadjuvant chemotherapy (NAC) has been increasingly used in patients with resectable colorectal liver metastases. However, the efficacy and safety of NAC in the treatment of resectable colorectal liver metastases (CRLM) are still controversial. AIM To assess the efficacy and application value of NAC in patients with resectable CRLM. METHODS We searched PubMed, Embase, Web of Science, and the Cochrane Library from inception to December 2020 to collect clinical studies comparing NAC with non-NAC. Data processing and statistical analyses were performed using Stata V.15.0 and Review Manager 5.0 software. RESULTS In total, 32 studies involving 11236 patients were included in this analysis. We divided the patients into two groups, the NAC group (that received neoadjuvant chemotherapy) and the non-NAC group (that received no neoadjuvant chemotherapy). The meta-analysis outcome showed a statistically significant difference in the 5-year overall survival and 5-year disease-free survival between the two groups. The hazard ratio (HR) and 95% confidence interval (CI) were HR = 0.49, 95%CI: 0.39-0.61, P = 0.000 and HR = 0.48 95%CI: 0.36-0.63, P = 0.000. The duration of surgery in the NAC group was longer than that of the non-NAC group [standardized mean difference (SMD) = 0.41, 95%CI: 0.01-0.82, P = 0.044)]. The meta-analysis showed that the number of liver metastases in the NAC group was significantly higher than that in the non-NAC group (SMD = 0.73, 95%CI: 0.02-1.43, P = 0.043). The lymph node metastasis in the NAC group was significantly higher than that in the non-NAC group (SMD = 1.24, 95%CI: 1.07-1.43, P = 0.004). CONCLUSION We found that NAC could improve the long-term prognosis of patients with resectable CRLM. At the same time, the NAC group did not increase the risk of any adverse event compared to the non-NAC group.

Objective To investigate the distribution of inhaled allergens and analyze the related risk factors among allergic rhinitis (AR) patients in Zhangjiakou area. Methods Serum specific IgE antibody of inhaled allergens was detected in 532 suspected AR patients in the Department of Otolaryngology, Head and Neck Surgery of the First Affiliated Hospital of Hebei North University form April 2019 to August 2020. A total of 245 family members of outpatient and inpatient patients (except family members of respiratory department, dermatology department and otolaryngology department) in the same period were selected as the control group. AR questionnaire survey was conducted in the AR patients and control group, and the survey results were statistically analyzed. Results Of the 532 patients with suspected allergic rhinitis, 388 (72.9%) were positive for at least one allergen. The top three positivity rates of inhalation allergens were mugwort (89.9%), common ragweed (44.1%) and cat epithelium (21.4%) among the AR patients. In the single allergen positive patients, the mudwort has a much higher positive detection rate (86.0%). The positive degree of allergens was mainly distributed in class 2, class 3 and class 6 of mugwort, in class 1 of house dust and house dust mite, and in class 2 of other allergens. There were statistically significant differences in the allergen positive rate of AR patients in different months, regions and ages (P1), regular physical exercise was an effective protective factor for AR (OR

We develop a methodology for the computation of the K→ℓνℓℓ′+ℓ′− decay width using lattice QCD and present an exploratory study here. We use a scalar function method to account for the momentum dependence of the decay amplitude and adopt the infinite-volume reconstruction method to reduce the systematic errors such as the temporal truncation effects and the finite-volume effects. We then perform a four-body phase-space integral to obtain the decay width. The only remaining technical problem is the possible power-law finite-volume effects associated with the process of K→ππℓνℓ→ℓνℓℓ′+ℓ′−, where the intermediate state involves multiple hadrons. In this work, we use a gauge ensemble of a twisted-mass fermion with a pion mass mπ=352 MeV and a nearly physical kaon mass. At this kinematics, the ππ in the intermediate state cannot be on shell simultaneously, as 2mπ>mK, and the finite-volume effects associated with the ππ state are exponentially suppressed. Using the developed methods mentioned above, we calculate the branching ratios for four channels of K→ℓνℓℓ′+ℓ′−, and obtain the results comparable to the experimental measurements and ChPT predictions. Our work demonstrates the capability of lattice QCD to improve the Standard Model prediction in the K→ℓνℓℓ′+ℓ′− decay width.

A method for the highly enantioselective Rh-catalyzed dehydrated arylation of unprotected hemiaminals has been developed, and provided a series of chiral benzosultams bearing trifluoromethylated quaternary stereocenters in high yields with excellent enantioselectivities (up to 99% ee). The synthetic utility was further demonstrated by the facile enantioselective construction of a HIV-1 inhibitor molecule.

Biological diversity plays an important role in the stability of ecosystems. The Mu Us Desert (MUD), located in Northern China, is an aeolian desert. Although it has been governed by a series of ecological restoration programs, the MUD still has limited biological diversity.

The microstructures and mechanical properties of TiAl alloys are directly linked to micro-segregation which cannot be avoided during solidification. So a thorough understanding of the micro-segregation should be a great help to further enhance the mechanical properties of the cast products. Theoretical analysis and experiments have been used to predict the micro-segregation, but it is very difficult to observe and determine the dendritic segregation in the micro region. Phase-field method has been employed for the simulation of dendritic growth. However, due to the complicated quasi-sub regular solution model for Ti-45Al(at.%) alloy, the classic phase-field models have difficulty to deal with the free energy. In this work, a phase-field model by linking thermodynamic calculation was used to simulate solidification dendritic segregation of Ti-45Al alloy for Liquid→Liquid+β(Ti). The free energies of solid phase and liquid phase for Ti-45Al alloy were calculated by Thermo-Calc and then coupled with the phase-field equations. The simulation results show the dendritic morphology and Al content variations between liquid and growing solid phase for Ti-45Al alloy. With the growth of the β(Ti), dendritic segregation is formed in the liquid and solid phases due to the solute partitioning and rejection into the liquid. As a result, the dendrite arms are depleted of Al element, while the inter-dendrites are enriched. The dendritic tip growth velocity decreases with the progress of solidification, whereas the segregation ratio increases.

Neutrinoless double beta decay, if detected, would prove that neutrinos are Majorana fermions and provide the direct evidence for lepton number violation. If such decay exists in nature, then π−π−→ee and π−→π+ee (or equivalently π−e+→π+e−) are the two simplest processes accessible via first-principle lattice QCD calculations. In this work, we calculate the long-distance contributions to the π−→π+ee transition amplitude using four ensembles at the physical pion mass with various volumes and lattice spacings. We adopt the infinite-volume reconstruction method [1] to control the finite-volume effects arising from the (almost) massless neutrino. Providing the lattice QCD inputs for chiral perturbation theory, we obtain the low energy constant gνππ(mρ)=−10.89(28)stat(74)sys, which is close to gνππ(mρ)=−11.96(31)stat determined from the crossed-channel π−π−→ee decay [2].

We present an exploratory lattice QCD calculation of the neutrinoless double beta decay $\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\rightarrow}ee$. Under the mechanism of light-neutrino exchange, the decay amplitude involves significant long-distance contributions. The calculation reported here, with pion masses ${m}_{\ensuremath{\pi}}=420$ and 140 MeV, demonstrates that the decay amplitude can be computed from first principles using lattice methods. At unphysical and physical pion masses, we obtain that amplitudes are 24% and 9% smaller than the predication from leading order chiral perturbation theory. Our findings provide the lattice QCD inputs and constraints for effective field theory. A follow-on calculation with fully controlled systematic errors will be possible with adequate computational resources.

Wind resource assessment has important economic and ecological implications. Many developing countries in arid and semiarid areas are caught in a dilemma between the development of wind energy and the threat of sandy desertification. Sand-driving winds are momentous for both generating wind energy and aeolian research. The estimation for the probability of sand-driving winds has been rarely studied. The ability of the two-parameter Weibull distribution to estimate high wind velocities is questioned and parameters appear to have no practical significance. Drift potential (DP) is a way of evaluating potential sand transport volume by sand-driving winds, but the relationship between DP and the wind energy of sand-driving winds has been rarely studied. In this paper, a function was constructed from the expressions of DP and the two-parameter Weibull probability distribution to improve the estimation of sand-driving winds. This is simple and applicable to arid and semiarid areas worldwide. The mean wind velocity and the mean wind power density at a height of 10 m around the Badain Jaran Sand Sea in China, are in the range between 2.64 and 4.79 m·s−1, and 27.61–165.61 W·m−2, respectively. The mean wind power density of sand-driving winds accounted for half or more of the total mean wind power density. The relationship among DP, the wind power density of sand-driving winds and the probability of sand-driving winds, was proved theoretically. Gentle winds and strong winds are distinguished by the drift wind velocity at which potential sand transport activities (potential lost wind power density) reach their maximum. The scale parameter dominates the mean and median wind velocity, and represents the effect of convection. The shape parameter characterizes the atmospheric stability. These results provide a basis for the wind energy development, improve the understanding of aeolian activities, and have implications for sand control engineering.

Some of the surface on Earth, Mars, Venus, and Titan is covered by ripples, dunes, and other features formed by sand-driving winds. Many developing countries in arid and semiarid areas are caught in a dilemma between the threat of sandy desertification and the development of wind energy. The estimation for the probability of sand-driving winds has been rarely studied. The ability of two-parameter Weibull probability distribution to estimate sand-driving winds is questioned. Sand transport rate is used only for the evaluation of short-term aeolian activities. Drift potential (DP) is an accessible way of evaluating potential sand transport volume by sand-driving winds. However, the relationship among annual sand transport volume, DP and wind energy has been rarely studied. Sand-driving winds can be divided into gentle winds and strong winds, but it is hard to distinguish them and to quantify their effects on aeolian geomorphology. A function was constructed from expressions of sand transport rate and the two-parameter Weibull probability distribution to improve the estimation of sand-driving winds. On this basis, annual sand transport volume was accurately evaluated by sand-driving winds. This is applicable to arid and semiarid areas worldwide. The relationship among annual sand transport volume, DP and wind energy was analyzed from the perspective of dimensional analysis. Gentle winds and strong winds are distinguished by transport wind velocity at which aeolian activities on a sandy underlying surface reach the erosion–deposition balance, and which corresponds to annual maximum sand transport rate. On a sandy underlying surface strong winds control deposition, while gentle winds dominate wind erosion. The transport wind velocity is nearly constant, weakly related to the probability distribution of sand-driving winds. These results provide a basis for an improved understanding of aeolian activities as an important planetary surface process, sand control engineering, and wind energy development.

We present an exploratory lattice QCD calculation of the neutrinoless double beta decay ππ→ee. Under the mechanism of light-neutrino exchange, the decay amplitude involves significant long-distance contributions. The calculation reported here, with pion masses m_{π}=420 and 140 MeV, demonstrates that the decay amplitude can be computed from first principles using lattice methods. At unphysical and physical pion masses, we obtain that amplitudes are 24% and 9% smaller than the predication from leading order chiral perturbation theory. Our findings provide the lattice QCD inputs and constraints for effective field theory. A follow-on calculation with fully controlled systematic errors will be possible with adequate computational resources.

As an emerging two-dimensional (2D) material, monolayer molybdenum disulfide films show excellent electrical and optical properties and have aroused great interest due to their potential applications in electronics and optoelectronics. In this paper, we review our works about molybdenum disulfide films in the past few years. Chemical vapor deposition (CVD) is a convenient and low-cost method to synthesize 2D materials. By oxygen-assisted CVD, the wafer-scale highly-oriented monolayer molybdenum disulfide films and large single-crystal monolayer molybdenum disulfide on various substrates have been prepared epitaxially. Preparation of high-quality monolayer molybdenum disulfide films is the key to measure its intrinsic properties and realize its large-scale applications. Besides the preparation of high-quality materials, the optimizing of transfer technique and fabrication technique are of equal importance for improving the properties of electronic and optoelectronic devices. Water-assisted lossless transfer, patterned peeling, structural change and local phase transition of monolayer molybdenum disulfide films pave the way for preparing and optimizing the functionalized devices. For example, water-assisted transfer and patterned peeling provide methods of preparing molybdenum disulfide samples with clean surfaces and interfaces. Phase transition in the contact area of field-effect transistor reduces the contact resistance effectively, which improves the electrical performance. In addition, the heterojunctions of molybdenum disulfide and other 2D materials show novel electrical and optical properties. As for the functional devices, ultrashort-channel field-effect transistors, integrated flexible thin film transistors, and humidity sensor array have been realized with monolayer molybdenum disulfide films. A grain boundary widening technique is developed to fabricate graphene electrodes for ultrashort-channel monolayer molybdenum disulfide transistors. Field-effect transistors with channel lengths scaling down to 4 nm can be realized reliably and exhibit superior performances, such as the nearly Ohmic contacts and excellent immunity to short channel effects. Furthermore, monolayer molybdenum disulfide films show excellent electrical properties in the measurement of integrated flexible thin film transistors. Under a uniaxial stain of 1%, the performance of the device shows no obvious change, revealing not only the high quality of CVD-grown molybdenum disulfide films, but also the stabilities of these flexible thin film transistor devices. Molybdenum disulfide humidity sensor array for noncontact sensation also shows high sensitivity and stability. Mobility and on/off ratio of the devices in the array decrease linearly with the relative humidity increasing, leading to a high sensitivity of more than 104. The study of monolayer molybdenum disulfide films is universal and instructive for other 2D transition metal dichalcogenides.

In the field of the application of modern HF communication, much more attention is paid to the technology of HF OFDM modulation-demodulation. HF channel is the frequency and time selective fading channel. To reliably receive information, HF receiver must estimate real-time channel parameters to equalize. A performance comparing with the channel parameters estimate methods based on the first-order linear interpolation, Gaussian interpolation, Cubic interpolation and DFT interpolation is analyzed. Simulation results show that a better performance will gain when using DFT interpolation channel estimate method in HF OFDM system.