A combined magnetic field stabilization system for improving the stability of 40Ca^(+) optical clock

Future applications of portable40Ca^(+)optical clocks require reliable magnetic field stabilization to improve frequency stability, which can be achieved by implementing an active and passive magnetic field noise suppression system. On the one hand, we have optimized the magnetic shielding performance of the portable optical clock by reducing its apertures and optimizing its geometry;on the other hand, we have introduced an active magnetic field noise suppression system to further suppress the magnetic field noise experienced by the ions. These efforts reduced the ambient magnetic field noise by about 10000 times, significantly reduced the linewidth of the clock transition spectrum, improved the stability of the portable40Ca+optical clock, and created the conditions for using portable optical clocks in non-laboratory magnetic field environments. This active magnetic field suppression scheme has the advantages of simple installation and wide applicability.

A cryogenic radio-frequency ion trap for a 40Ca^(+) optical clock

A liquid-nitrogen cryogenic40Ca^(+)optical clock is presented that is designed to greatly reduce the blackbody radiation(BBR) shift. The ion trap, the electrodes and the in-vacuum BBR shield are installed under the liquid-nitrogen container,keeping the ions in a cryogenic environment at liquid-nitrogen temperature. Compared with the first design in our previous work, many improvements have been made to increase the performance. The liquid-nitrogen maintenance time has been increased by about three times by increasing the volume of the liquid-nitrogen container;the trap position recovery time after refilling the liquid-nitrogen container has been decreased more than three times by using a better fixation scheme in the liquid-nitrogen container;and the magnetic field noise felt by the ions has been decreased more than three times by a better design of the magnetic shielding system. These optimizations make the scheme for reducing the BBR shift uncertainty of liquid-nitrogen-cooled optical clocks more mature and stable, and develop a stable lock with a narrower linewidth spectrum,which would be very beneficial for further reducing the overall systematic uncertainty of optical clocks.

Relationship of Old World Pseudoxenodon and New World Dipsadinae,with Comments on Underestimation of Species Diversity of Chinese Pseudoxenodon

Assessment of the relationship between Pseudoxenodon and Dipsadinae has been hampered by lack of adequate samples. In this paper, we conducted phylogenetic analyses using two mitochondrial genes （12S and 16S rRNA） and one nuclear gene （c-mos） from thirteen specimens representing two species of Pseudoxenodon, together with 84 sequences of caenophidians and an outgroup sequence of Boa constrictor. Our study suggests that the Southeast Asian genus, Pseudoxenodon forms a robust genetic subclade within South American xenodontines, indicating that at least one lineage within this genus entered or returned to the Old World （OW） from the New World （NW） across the Beringian Land Bridge during the early Tertiary and the warm mid-Miocene. It also reveals the high intraspecific genomic variation within the populations of Pseudoxenodon macrops, indicating that species diversity of Pseudoxenodon in China is likely underestimated.

Progress on the^40Ca^+ion optical clock

Progress of the ^40Ca^+ion optical clock based on the 4^2S1/2-3d ^2D5/2 electric quadrupole transition is reported.By setting the drive frequency to the“magic”frequencyΩ0,the frequency uncertainty caused by the scalar Stark shift and second-order Doppler shift induced by micromotion is reduced to the 10^-19 level.By precisely measuring the differential static scalar polarizability∆α0,the uncertainty due to the blackbody radiation(BBR)shift(coefficient)is reduced to the 10^-19 level.With the help of a second-order integrating servo algorithm,the uncertainty due to the servo error is reduced to the 10^-18 level.The total fractional uncertainty of the ^40Ca^+ion optical clock is then improved to 2.2×10^-17,whereas this value is mainly restricted by the uncertainty of the BBR shift due to temperature fluctuations.The state preparation is introduced together with improvements in the pulse sequence,and furthermore,a better signal to noise ratio(SNR)and less dead time are achieved.The clock stability of a single clock is improved to 4.8×10^-15√τ(in seconds).

Self-assembly of Blended PS-b-P2VP Block Copolymers

Directed Self-Assembly(DSA)of block copolymers(BCPs)is a promising technique for sub-10 nm nanofabrication,which is highly compatible with conventional lithography.DSA relies on the microphase separation of block copolymers to form nanostructures of different morphologies.The pitch size of the obtained nanostructure depends largely on the intrinsic properties of BCPs and is usually fixed when BCPs are produced.One effective way of tuning the pitch size of BCPs is by blending BCPs of different molecular weight.In this paper,we have demonstrated the pitch tuning capability by blending the triblock poly(2-vinyl pyridine-bpolystyrene-b-poly 2-vinyl)pyridine(P2VP-b-PS-b-P2VP)with another triblock P2VP-b-PS-b-P2VP or diblock copolymer(PS-b-P2VP)at various volume ratios by solvent annealing.The nanopatterns of blended BCPs after sequential infiltration synthesis(SIS)and plasma etching process,were characterized by scanning electron microscopy.It’s observed that the blended BCPs can form highly ordered lamellar nanostructures of different pitch sizes at different blending ratios.The method of blending BCPs of varying molecular weights greatly extends the functionality of existing BCPs,with the capability of fine-tuning nanopatterning pitch at nanometer resolution.

辊压机框架结构的加固

辊压机的结构框架,承担着辊压机总体设备的重量,同时承担着运行过程中的动载荷。特别是对于生产工艺状态不稳定的情况下,辊压机在运行过程中整体振动大,造成框架固定螺栓断裂、框架定位销串动,液压系统管路泄露等问题,严重影响设备可靠性。针对存在此情况的辊压机,通过设计制作一套结构组件、对框架结构进行加固升级优化,通过较少的费用投入,达到辊压机的整体平稳运行,减少设备故障率,提高运转率。

Evaluating Optimal Treatment for Melanoma:A Network Meta-Analysis

Background It is necessary to determine the optimal treatment for melanoma as the incidence of melanoma is increasing every year.In this study,we conducted a metaanalysis to compare the effectiveness of available treatments for melanoma.Methods The index keywords“melanoma”and“treatment”were used to search the PubMed,Cochrane Library,Web of Science,and Embase databases,and the articles were limited to randomized controlled trials.The search was filtered for articles published until February 2020,and articles were independently extracted by two reviewers.Network metaanalysis(Stata®14.0 software network package,StataCorp LLC,TX,USA)was used to compare the effectiveness of the mentioned treatments of melanoma.Results A total of 616 articles were screened of which 6 were selected for meta-analysis,involving 5 treatment measures and 2047 patients(those who were not followed up on were excluded).The treatment strategies reported for melanoma included tumor necrosis factor(L19-TNFα)and interleukin-2(L19IL2)in combination with dacarbazine(L19IL2+DTIC),DTIC,programmed cell death-1 plus cytotoxic T cell antigen-4(PD-1+CTLA-4),PD-1,and CTLA-4.Conclusion Among L19IL2+DTIC,DTIC,PD-1+CTLA-4,PD-1,and CTLA-4,CTLA-4 is found to be the best treatment method for melanoma.Our study findings provide a reference for the clinical treatment of melanoma and can clarify the direction for setting up controlled clinical trials.

Mapk7 deletion in chondrocytes causes vertebral defects by reducing MEF2C/PTEN/AKT signaling

Mutation of the MAPK7 gene was related to human scoliosis.Mapk7 regulated the development of limb bones and skulls in mice.However,the role of MAPK7 in vertebral development is still unclear.In this study,we constructed Col2a1-cre;Mapk7 f/f transgenic mouse model to delete Mapk7 in cartilage,which displayed kyphosis and osteopenia.Mechanistically,Mapk7 loss decreased MEF2C expression and thus activated PTEN to oppose PI3K/AKT signaling in vertebral growth plate chondrocytes,which impaired chondrocyte hypertrophy and attenuated vertebral ossification.In vivo,systemic pharmacological activation of AKT rescued impaired chondrocyte hypertrophy and alleviated mouse vertebral defects caused by Mapk7 deficiency.Our study firstly clarified the mechanism by which MAPK7 was involved in vertebral development,which might contribute to understanding the pathology of spinal deformity and provide a basis for the treatment of developmental disorders of the spine.

Parametric study on controllable growth of SrZrS_(3)thin films with good conductivity for photodetectors

SrZrS_(3)is a promising chalcogenide perovskite with unique advantages including high abundance of consisting elements,high chemical stability,strong light absorption above its direct band gap,excellent carrier transport ability.While unfortunately,due to the lack of breakthroughs in its thin film synthesis technique,its optoelectronic properties are not fully investigated,not to mention the device applications.In this work,large-area and uniform SrZrS_(3)thin film(5 cm×5 cm)was prepared by facile sputtering method,followed by a post-annealing treatment at a high temperature of 1000℃for 2–12 h under CS_(2)atmosphere.All SrZrS_(3)samples prepared adopt distorted orthorhombic structure with pnma space group and have high crystallinity.In addition,the band gap of SrZrS_(3)thin film is measured to be 2.29 eV,higher than that of the powder form(2.06 eV).Importantly,the light absorption coefficient of SrZrS_(3)thin film reaches over 105 cm^(−1),the carrier mobility is as high as 106 cm^(2)/(V∙s).The above advantages allow us to use the SrZrS_(3)thin film as photoactive layer for photodetector applications.Finally,a symmetrically structured photoconductive detector was fabricated,performing a high responsivity of 8 A/W(405 nm light excitation).These inspiring results promise the glorious application potential of SrZrS_(3)thin film in photodetectors,solar cells,other optoelectronic devices.

Demonstration of epitaxial growth of strain-relaxed GaN films on graphene/SiC substrates for long wavelength light-emitting diodes

Strain modulation is crucial for heteroepitaxy such as GaN on foreign substrates.Here,the epitaxy of strain-relaxed GaN films on graphene/SiC substrates by metal-organic chemical vapor deposition is demonstrated.Graphene was directly prepared on SiC substrates by thermal decomposition.Its pre-treatment with nitrogen-plasma can introduce C–N dangling bonds,which provides nucleation sites for subsequent epitaxial growth.The scanning transmission electron microscopy measurements confirm that part of graphene surface was etched by nitrogen-plasma.We study the growth behavior on different areas of graphene surface after pre-treatment,and propose a growth model to explain the epitaxial growth mechanism of GaN films on graphene.Significantly,graphene is found to be effective to reduce the biaxial stress in GaN films and the strain relaxation improves indium-atom incorporation in InGaN/GaN multiple quantum wells(MQWs)active region,which results in the obvious red-shift of light-emitting wavelength of InGaN/GaN MQWs.This work opens up a new way for the fabrication of GaN-based long wavelength light-emitting diodes.

NEW DESIGN AND ANALYSIS OF FINITE DIFFERENCE DOMAIN DECOMPOSITION ALGORITHM FOR THE TWO-DIMENSIONAL HEAT EQUATION

It is presented in this paper that the new design and its analysis of finite difference domaindecomposition algorithms for the two-dimensional heat equation,and the numerical results have shownthe stability and accuracy of the algorithms,where Saul'yev asymmetric schemes have been used atthe interface points.The Algorithm Ⅱ in this paper has further extended those developed by Dawsonand the others,Zhang and Shen.

Difference graphs of a class of alternating block Crank-Nicolson methods

By using the concept of multigraphs, the difference graphs of a class of alternating block Crank-Nicolson methods are defined and described, which extends the results on difference graphs of parallel computing for the finite difference method.