化学试题难度影响因素的实证研究

依据高考化学试题的特点,厘清影响试题难度主要因素的要素特征,并据此编制相应的变式题进行抽样测试。统计分析数据表明各因素在试题中的不同表现形式对试题难度有着显著性影响。以“信息呈现方式”这一影响因素为例,分析并研究了同一因素的不同表现形式对试题相对难度变化的影响,为后续试题难度的建模研究奠定了基础。     

Chiral Extrapolation of Lattice Data of Λ_b→Λ_c Form Factors

An extrapolation to the physical limit for the lattice data of Λ_b →Λ_c form factors computed in the nonphysical region is made in this work through a class of fitting functions proposed by us with nonlinear dependence on m2/π derived in the chiral perturbative theory(ChPT) and the heavy quark effective theory(HQET) framework. Then the results are applied to calculate the differential and integrated Λ_b →Λ_c semileptonic decay rates. Meanwhile, a comparison between our results and those obtained through the extrapolation functions with naive linear dependenceon m2/π is made.It is shown that the difference between the extrapolated central values of these two cases is about 5%.The total uncertainties(depending on the momentum transfer q~2) in the linear case are about 5% ～10%(caused by the uncertainties of lattice data) and those in the nonlinear case are about 10% ～ 20%(caused by the uncertainties of both lattice data and input parameters in Ch PT and HQET). More accurate lattice data and parameters in ChPT and HQET are needed to reduce the uncertainties of the extrapolated results.     

Stay-eat or run-away: Two alternative escape behaviors

Pursuit-and-evasion behavior in groups of animals is a phenomenon that can be easily observed in nature. Immediate flight upon detection is a common but not exclusive response for prey with both stay-eat behavior and run-away behavior occur during the predation process. It remains unclear why these two contrasting survival tactics appear, what the triggering conditions are and what internal mechanisms are at play. Here we investigate the effect of energy level on the behavior of prey during predation. We find that (1) the optimal escape speed of prey is context-dependent rather than the fastest always producing the best chance of survival. (2) The stay-eat or run-away decision depends mainly on the maximum speed and the energy dissipation ratio of prey to predator. (3) Stay-eat behavior is more effective when the prey have a higher escape speed and a higher energy dissipation rate, where aggregation can induce this stay-eat behavior. The reported findings are not only of relevance when considering survival tactics in nature, but such an understanding is useful in the design of swarm robotic systems where energy conservation and task optimization could be incorporated into any escape and hunting strategies.     

脉动热管实验研究

建立了铜管脉动热管实验台,进行了实验研究.分析了在水冷的条件下,充液率、工质、倾斜角等因素对脉动热管传热性能的影响,结果发现,热阻随着充液率的增加而增大;选用蒸馏水、无水乙醇以及丙酮为工质时,在相同条件下,丙酮热阻最低;不同倾斜角的实验中垂直底加热时脉动热管热阻最低.     

Baryon structure from Lattice QCD

We present recent lattice results on the baryon spectrum, nucleon electromagnetic and axial form factors, nucleon to △ transition form factors as well as the △ electromagnetic form factors. The masses of the low lying baryons and the nucleon form factors are calculated using two degenerate flavors of twisted mass fermions down to pion mass of about 270 MeV. We compare to the results of other collaborations. The nucleon to △ transition and △ form factors are calculated in a hybrid scheme, which uses staggered sea quarks and domain wall valence quarks. The dominant magnetic dipole nucleon to △ transition form factor is also evaluated using dynamical domain wall fermions. The momentum frame are extracted using the form factors transverse density distributions of the △ in the infinite determined from lattice QCD.     

中国近1000年旱涝的持续性特征研究

应用中国近531年旱涝指数和近1041年干湿指数,定义干旱(湿润)等级,滑动计算原指数序列各干旱(湿润)等级的出现次数,发现各等级出现的次数与其窗口长度之间均遵循指数分布P_i(x)=Ae^-γx.结合指数分布的数理意义,定义指数特征值γ的倒数λ为描述旱(涝)持续性的尺度因子并对华北和江淮流域旱(涝)发生的持续性特征进行研究.结果表明：旱尺度因子的空间分布表现为由北向南呈带状式波动分布,我国北方地区干旱的持续性相对长江流域要长一些,由北向南三个区的旱尺度因子的均值分别为187,162,182.旱涝指数序列中旱或偏旱(涝或偏涝)相对集中的时段对旱(涝)持续性影响较显著,12世纪末期、13世纪早期、17世纪早期和20世纪末期华北和江淮流域发生时间上同步、空间上尺度较大的极端干旱事件的概率较高,这也从侧面验证了旱涝指数序列中群发现象的存在;华北地区1260—1280年(对应的气候背景为中世纪暖期的末期)的旱涝指数对旱尺度因子的影响较1980—2000年(对应的气候背景为20世纪全球增暖)的情况更显著;1260—1280年这一时段旱或偏旱年数较1980—2000年也要多一些.因此,在气候较暖的时期可能易发生强度大、范围广的同步干旱事件,而近30年的中国北方干旱化可能是自然变率起主导作用下人为变率和自然变率共同作用的结果. 关键词： 旱(涝)尺度因子 持续性 群发性 指数分布     

Total Atomic Scattering Factors of 1s^23s ^2S States for Lithium Isoelectronic Sequence

Total atomic scattering factors for the 1s^23s ^2S stages for the lithium isoelectronic sequence from Z = 3 - 10 are calculated by using the full core plus correlation wave function. The influence of electron correlation on total atomic scattering factors is considered sufficiently in our calculation. For the 1s^2 3s ^2S states of the lithium isoelectronic sequence, the general functional behaviour of total atomic scattering factors is analyzed together for each state of the isoelectronic sequence.     

结构偏心对开放式同轴谐振腔性能的影响

 采用CST微波工作室软件,数值模拟了内外导体轴线偏心对开放式同轴谐振腔的影响。结果表明：不管是内外导体的轴线发生平行偏心,还是倾斜偏心,都引起开放式同轴谐振腔的谐振频率、品质因数和场振幅实质性下降;其中,倾斜偏心产生的影响比平行偏心更为严重。     

Interaction of the single-particle and collective degrees of freedom in non-magic nuclei: The role of phonon tadpole terms

A method of consistent treatment of phonon contributions to the self-energy and gap terms in non-magic nuclei is developed in so-called g ² approximation, where g is the creation amplitude of a low-lying phonon. The method simultaneously takes into account both usual non-local and local phonon tadpole terms. Relations that allow the tadpoles to be calculated without introduction of new parameters are derived. As an application of the method, the effect of the phonon tadpoles on the single-particle strength distribution, single-particle energies and gap values is considered. Hypothesis of the surface nature of pairing correlations is discussed in the light of the tadpole effect.