Analysis of lower-boundary climate factors contributing to the summer heatwave frequency over eastern Europe using a machine-learning model

本文使用LightGBM机器学习模型模拟了欧洲东部夏季热浪频率的变化,并分析了多个底边界层气候因子的贡献.所选取的气候因子包括前期冬季,前期春季以及同期夏季的下垫面海温,土壤湿度,积雪以及海冰.分析结果说明LightGBM模型能够较好的模拟出欧洲东部夏季热浪频率的变化,其中海温因子对模拟的贡献最大.进一步的分析研究显示,使用前期冬季的气候因子进行的模拟可以获得最佳模拟结果,意味着前期冬季的下垫面气候因子可能对夏季欧洲东部热浪频率变化的预报能起到关键作用.

中国造物观的现代转型与当代构建

中国在西方刺激下的现代转型经历了器物、制度、文化三个层次,"器物"之变常常被理解为学习西方现代"科学",实际上与科学、制度、文化都有关的"造物"之变值得研究。晚清"西器东输"打破了我国器物造型结构的自然演化,国人以图强救亡为目的,以"中体西用"认知指导新的造物观建立。自此长达百年的造物观"破"与"立",实质是我国由西化到现代化想象的实现过程,酝酿和缔造了本国物品信仰及生活状态,终将从民生驱动、国家形象、社会意识三个层面逐步构建出新时期的中国化造物观念。

Variational Assimilation of Satellite Cloud Water/Ice Path and Microphysics Scheme Sensitivity to the Assimilation of a Rainfall Case

Hydrometeor variables （cloud water and cloud ice mixing ratios） are added into the WRF three-dimensional variational assimilation system as additional control variables to directly analyze hydrometeors by assimilating cloud observations. In addition, the background error covariance matrix of hydrometeors is modeled through a control variable transform, and its characteristics discussed in detail. A suite of experiments using four microphysics schemes （LIN, SBU-YLIN, WDM6 and WSM6） are performed with and without assimilating satellite cloud liquid/ice water path. We find analysis of hydrometeors with cloud assimilation to be significantly improved, and the increment and distribution of hydrometeors are consistent with the characteristics of background error covariance. Diagnostic results suggest that the forecast with cloud assimilation represents a significant improvement, especially the ability to forecast precipitation in the first seven hours. It is also found that the largest improvement occurs in the experiment using the WDM6 scheme, since the assimilated cloud information can sustain for longer in this scheme. The least improvement, meanwhile, appears in the experiment using the SBU-YLIN scheme.

High-Performance Aqueous Zinc–Manganese Battery with Reversible Mn^(2+)/Mn^(4+) Double Redox Achieved by Carbon Coated MnO_x Nanoparticles

There is an urgent need for low-cost,high-energy-density,environmentally friendly energy storage devices to fulfill the rapidly increasing need for electrical energy storage.Multi-electron redox is considerably crucial for the development of high-energy-density cathodes.Here we present highperformance aqueous zinc-manganese batteries with reversible Mn2+/Mn4+ double redox.The active Mn4+is generated in situ from the Mn2+-containing MnOx nanoparticles and electrolyte.Benefitting from the low crystallinity of the birnessite-type MnO2 as well as the electrolyte with Mn2+additive,the MnOX cathode achieves an ultrahigh energy density with a peak of845.1 Wh kg-1 and an ultralong lifespan of 1500 cycles.The combination of electrochemical measurements and material characterization reveals the reversible Mn2+/Mn4+double redox(birnessite-type MnO2? monoclinic MnOOH and spinel ZnMn2O4 H?Mn2+ions).The reversible Mn2+/Mn4+double redox electrode reaction mechanism offers new opportunities for the design of low-cost,high-energy-density cathodes for advanced rechargeable aqueous batteries.

The Fabrication of Silver/Poly(Methyl Methacrylate) Nanocomposite with Size-Controlled In-Situ Synthesis Method

The Ag/poly(methyl methacrylate)(PM-MA)nanocomposite materials have been intensive-ly studied owing to its superior mechanical,opticaland electrical properties.In this paper,Monodispersed silver nanoparticles with controllable sizehave been successfully in situ synthesized in

From Euler disk to phonon bottleneck effect: Excited state physics

The Euler disk,known since 1765,1 describes a solid disk that rotates on a smooth,firm surface,similar to a coin spun by a finger on a table,before its energy dissipates and it falls on the table.2 It represents a typical nonequilibrium excited state in classical physics.The most striking characteristic of an Euler disk is that it exhibits a sharply enhanced sound frequency when approaching the critical time,tc,after which the disk instantly ceases rotation and precession.At the excited-state-to-ground-state transition,its frequency abruptly changes from infinite to zero.This quasi-divergent and suddenly disappearing behavior is intriguing,revealing that this is a shared physical property in the microscopic quantum regime.

Natural selection maintains the transcribed LTR retrotransposons in Nosema bombycis

Eight intact LTR retrotransposons （Nbr1-Nbr8） have been previously characterized from the genome of Nosema bombycis, a eu- karyotic parasite with a compact and reduced genome. Here we describe six novel transcribed Nbr elements （Nbr9-Nbr14） identified through either cDNA library or RT-PCR. Like previously determined ones, all of them belong to the Ty3/Gypsy superfamily. Retrotransposon diversity and incomplete domains with insertions （Nbr12）, deletions （Nbrll） and in-frame stop codons in coding regions （Nbr9） were detected, suggesting that both defective and loss events of LTR retrotransposon have happened in N. bornbycis genome. Analysis of selection showed that strong purifying selection acts on all elements except Nbr11. This implies that selective pressure keeps both these Nbrs and their functions in genome. Interestingly, Nbrll is under positive selection and some positively selected codons were identified, indicating that new functionality might have evolved in the Nbrll retrotransposon. Unlike other transposable elements, Nbrll has integrated into a conserved syntenic block and probably resulted in the inversion of both flanking regions. This demonstrates that transposable element is an important factor for the reshuffling and evolution of their host genomes, and may be maintained under natural selection.

Experimental and numerical investigations into flow features in an intake duct for the waterjet propulsion under mooring conditions

The waterjet propulsion is widely applied in the marine vessels over 30 knots,and the intake duct is considered as an essential component that strongly relates to the propulsion performance.This paper sheds light on the flow features inside an intake duct under mooring conditions by using the particle image velocimetry(PIV)technique with three-dimensional(3D)numerical simulations.The hydraulic loss gradually increase as the flow-rate increases.According to analyses via the Bernoulli equation,the hydraulic loss is composed of the frictional head loss(h_(f)~V^(1.75))and the local head loss(h_(j)~V^(2.0)).A recirculation region is observed near the duct lower wall with a high-velocity flow near the upper wall,and subsequently a shear flow presents in the horizontal straight pipe with an obvious velocity gradient.Three-dimensional simulations demonstrate that the vortex pair is very strong in the recirculation region and then it gradually decreases as the fluid flows downstream.With the flow-rate increasing,the non-uniformity at the duct outlet firstly increases to a peak and then slightly decreases,while the perpendicularity at the duct outlet dramatically decreases to a minimum and then increases.This work not only reveals some physics of the waterjet propulsion under mooring conditions,but also promotes its efficient operation.

Thermoelectric performance enhancement of(BiS)1.2(TiS2)2 misfit layer sulfide by chromium doping

A misfit layer sulfide(BiS)_(1.2)(TiS_(2))_(2) with a natural superlattice structure has been shown to be a promising thermoelectric material,but its high carrier concentration should be reduced so as to further optimize the thermoelectric performance.However,ordinary acceptor doping has not succeeded because of the non-parabolic band structure.In this paper,we have successfully doped chromium ions into the Ti sites,which can maintain or even enhance the high effective mass of electrons so as to effectively improve ZT value.X-ray diffraction analysis,coupled with X-ray photoelectron spectroscopy,shows that chromium has been substituted into titanium sites in TiS2 layers and confirms its ionic state.The chromium doping has successfully reduced the carrier concentration with the subsequent reduction of electrical conductivity.Unlike other acceptor dopants(alkaline earth metals),chromium also enhances Seebeck coefficient and the effective mass,which can possibly be attributed to the formation of additional resonant states near Fermi level.Though the power factor does not improve,the significant reduction in the electronic part of the thermal conductivity leads to a measurable improvement in ZT.

A high-efficiency charge pump in BCD process for implantable medical devices

This paper presents a high-efficiency charge pump circuit composed of cascaded cross-coupled voltage doublers implemented in an isolated bipolar-CMOS-DMOS（BCD） technology for implantable medical devices.Taking advantage of the transistor structures in the isolated BCD process, the leakage currents caused by the parasitic PNP transistors in the cross-coupled PMOS serial switches are eliminated by simply connecting the inside substrate terminal to the isolation terminal of each PMOS transistor. The simple circuit structure leads to small parasitic capacitance in the voltage doubler, which in turn ensures high efficiency of the overall charge pump. The proposed charge pump with 5 cascaded voltage doublers is fabricated in a 0.35-μm isolated BCD process. Measurement results with 2-V power supply, 1-MHz driving clock frequency and 40-μA current load show that an efficiency of 72.6% is achieved, and the output voltage can be pumped to about 11.5 V at zero load current. The chip area of the charge pump is 1.6 × 0.35 mm^2.