oscillation

摘要： We present an oscillation-based method to measure absolute adsorption,or total gas,contained in porous rocks without and with excess adsorption.Experiments conducted with a macroporous Berea sandstone sample in nitrogen where excess adsorption is negligible show that absolute adsorption can be obtained after the added mass of co-accelerated gas outside the sample is subtracted.In experiments conducted in propane with a crushed Niobrara shale sample with micro-and mesopores,absolute adsorption included significant excess adsorption.After subtracting both the added mass outside the sample and the gas that would be in the sample assuming no excess adsorption existed,estimated excess adsorption of propane is in good agreement with that projected based on capillary condensation of propane in the volume of mesopores.

摘要： The behavior of multiple modes before and during minor disruption with the external resonant magnetic perturbations(RMPs)has been studied on a J-TEXT tokamak.The main component of RMPs is m/n=2/1,where m and n are the numbers of the poloidal and toroidal modes,respectively.During the mode-locking caused by RMPs,it is found that before a minor or a major disruption(if there is no minor disruption),strong oscillations in both electron temperature and density occur if the edge safety factor q_(a)>3.The analysis shows that the oscillations are caused by the m/n=3/1 mode.In addition,using the ECE,Mirnov coils and 2D electron cyclotron emission imaging diagnostic systems,it is found that a thermal collapse occurs on the inner side of the 2/1magnetic island during the minor disruption,and before the collapse,a 3/2 island increases,after the collapse,the 3/2 island may disappear.Moreover,the study also shows that these 3/1,2/1 and 3/2modes play roles in the thermal collapse of disruptions.

摘要： In this paper, we study the oscillatory theory for two classes of fractional neutral differential equations. By using fractional calculus and the Laplace transform, we obtain several new sufficient conditions for the oscillation of all solutions of this equation. Our results improve and extend some known results in the literature. Furthermore, some examples are provided to show the effectiveness and feasibility of the main results.

摘要： 基于再分析资料揭示了2019年2—3月中国南方持续性降水事件的成因及其与Madden-Julian Oscillation(MJO)的关系。此次持续性降水事件可以分为两个阶段:第一阶段降水覆盖了整个南方地区,第二阶段降水主要出现在华南地区,且降水强度比第一阶段更强。大尺度环流分析表明,此次降水事件中,中国南方和西太平洋的位势高度异常呈现出西低东高的形势,有利于南方地区出现偏南气流和水汽辐合。在第一阶段,整个南方地区都出现明显的水汽辐合和上升运动;而第二阶段,仅在华南地区出现显著的水汽辐合和上升运动。水汽收支诊断分析发现两个阶段中的水汽通量散度异常主要是经向水汽辐合所导致,它对水汽通量散度的贡献率达到70%以上。通过对比分析降水和MJO活动演变,发现降水的变化与MJO位相和振幅的演变有着紧密的联系。当MJO振幅明显增强(减弱)时,南方地区的降水异常显著增加(减少)。经向水汽辐合的尺度分析表明,低频尺度(大于90 d)和季节内尺度(30~90 d)的水汽和环流的相互作用对经向水汽辐合起到决定性作用,尤其是季节内经向风对大于90 d低频水汽的辐合。因此,热带地区MJO的活动可通过调节季节内经向风对低频水汽的输送,从而对此次南方地区的持续性降水事件产生重要影响。

摘要： Antiferromagnets have been attracting tremendous interest in the spintronics community due to their intrinsic appealing properties,such as zero stray field and ultrafast spin dynamics.Recently,the electrical manipulation of bulk properties of antiferromagnets has been widely studied,but exploring the use of antiferromagnetic(AFM)interfacial properties to investigate some key issues in spintronic devices is urgently desired.In this study,the magnetic and spin transport properties mediated by interlayer exchange coupling(IEC)are examined through spin-orbit torque(SOT)-induced tunability of interfacial spins in heavy-metal/like-synthetic antiferromagnet/antiferromagnet heterostructure devices.We found that the exchange bias and coercivity and the critical current density for SOT switching can be modulated by IEC,associating with the oscillation of SOTinduced interfacial spins reorientation at zero field,which can be well understood with the modified Ruderman-Kittel-KasuyaYosida model.Our finding opens a new route for understanding and using the AFM interfacial spins in spintronics.

摘要： The Shubnikov-de Haas(Sd H)oscillation,as evidenced by the oscillating resistivity as a function of magnetic field at sufficiently low temperature,is not uncommon in metals,semimetals and narrow gap semiconductors at their conducting state.The origin of Sd H oscillation is associated with Landau quantization,at which the cyclotron orbits of electrons are quantized.In other words,electrons can only occupy discrete energy levels,which are called the Landau levels.As the magnetic field increases,the split,quantized Landau levels move across the Fermi level and hence the material’s transport properties start to oscillate periodically.

摘要： It is of high interest to study laminar flow with mass and heat transfer phenomena that occur in a viscoelastic fluid taken over a vertical plate due to its importance in many technological processes and its increased industrial applications.Because of its wide range of applications,this study aims at evaluating the solutions corresponding to Casson fluids’oscillating flow using fractional-derivatives.As it has a combined mass-heat transfer effect,we considered the fluid flow upon an oscillatory infinite vertical-plate.Furthermore,we used two new fractional approaches of fractional derivatives,named AB(Atangana–Baleanu)and CF(Caputo–Fabrizio),on dimensionless governing equations and then we compared their results.The Laplace transformation technique is used to get the most accurate solutions of oscillating motion of any generalized Casson fluid because of the Cosine oscillation passed over the infinite vertical-plate.We obtained and analyzed the distribution of concentration,expressions for the velocity-field and the temperature graphically,using various parameters of interest.We also analyzed the Nusselt number and the skin friction due to their important engineering usage.

摘要： The influence of low-frequency sonolysis on the kinetics bimolecular liquid-phase reactions was studied with due regard for the association (dimers and trimers) of starting reagents. The mathematical modeling of chemical reactions that were described by nonlinear differential equations is performed. The steady states, the singular points characteristics, the nature of concentration oscillations in the reaction system are described. With increasing frequency and amplitude of low-frequency sonic waves (up to some critical value), we observed the cessation of the reaction. This observation offers an additional tool for controlling reaction rate by the external action of low-frequency vibrations. The conclusions of the work are obtained under certain assumptions. The exact determination of the critical conditions for changes in dynamics is beyond the scope of the problem.

摘要： In this study, an underexpanded radial jet issuing from a small gap between two circular tubes facing each other is investigated numerically. Radial jet is formed, for example, downstream of high-pressure valves in piping system and of poppet valves in engines, and causes many industrial problems such as the noise generation and the fatigue failure of structure. In this study, the jet issuing from a small gap between two tubes with same diameter is numerically simulated. The flow field is assumed to be axisymmetric against the central axis of tubes and to be symmetric against the intermediate plane between the exits of two tubes. The axisymmetric Euler equations are solved using symmetric TVD (Total Variation Diminishing) scheme. The effects of nozzle pressure ratio and of diameter of circular tubes on the structure and the behavior of jets are examined. Typical cell structure of underexpanded jet appears in radial jet and the length of cell becomes smaller in downstream region because the jet spreads radially like a disc. The length and width of first cell are larger with higher nozzle pressure ratio. Many vortices are generated one after another near the jet boundary and move downstream, which cause the oscillation of jet. Outside of jet, two types of density waves are observed. One of them propagates toward the nozzle (toward the upstream region) and the other propagates in opposite direction. Focusing on the pressure change caused by the former waves, which is related to well-known screech, dominant frequency obtained by FFT analysis was found to become lower with higher pressure ratio and smaller diameter of tube.

摘要： We consider the oscillation of a class fractional differential equation with Robin and Dirichlet boundary conditions. By generalized Riccati transformation technique and the differential inequality method, oscillation criteria for a class of nonlinear fractional differential equation are obtained.