s=355GeV附近的R值测量

利用北京谱仪(BES)在s=3.55GeV附近获取的总积分亮度约为5pb^－1的实验数据,测量了e⁺e^－湮没强子产生截面与μ子对产生截面的比值(即R值).其测量误差比其它实验组已发表的此能区的测量误差减小约50%.     

e+e－湮没中的胶子碎裂

本文假定e⁺e^－湮没时产生的胶子的强子化,胶子首先劈裂成一对等效的夸克、反夸克对.夸克之间的色相互作用,碎裂成末态强子.由此计算的e⁺e^－→3jet事例中的带电粒子多重数,胶子与夸克jet中多重数比率,以及e⁺e^－三胶子事例中的重子比率,都与实验结果一致.解释了e⁺e^－→3jet末态粒子的角分布.     

北京正负电子对撞机上QCD的精确检验

广义的Crewther关系式可以把正负电子湮没过程中强子产生的分支比R=σ(e⁺e^－→强子)/σ(e⁺e^－→μ⁺μ^－),同轻子核子深度非弹性散射中的Bjorken求和规则和Gross-UewellynSmith求和规则联系起来,提供一个没有标度和重整化方案任意性的有关量子色动力学(QCD)物理量的基本关系式.强子产生分支比R可以在升级后的北京正负电子对撞机或τ–粲工厂上进行精确的测量,从而提供对QCD的精确检验.     

400GeV/c pp碰撞两粒子关联的角度依赖性

利用400GeV/c pp碰撞多重产生的实验数据计算了粒子-粒子关联(PPC)及其不对称性(PPCA)的角度依赖性.结果与L3的e⁺e^－数据有明显的差别,但与NA22强子碰撞的实验数据符合得很好;领头粒子对强子碰撞的PPCA分布有很大影响.通过计算两粒子方位角差的分布观察到了方位角关联.     

随机组合模型中夸克动量分数的随机抽样问题

本文简要介绍了e⁺e^－湮没成强子喷注的物理图象,引入了随机夸克组合模型中夸克动量分数的分布,重点从数学上严格推导了这一分布的抽样方法.     

北京谱仪R值测量中的初态辐射修正

从R值测量实验的角度讨论了e⁺e^－碰撞通过单光子湮没产生强子截面的辐射修正,分析了3种典型的计算方案.在BEPC/BES上运行的2—5GeV能区,不同方案给出的辐射修正因子理论值(1+δ)的差别大约是1%—2%,而每一方案计算中由于各种不确定因素带来的有效辐射修正因子(1+δobs)的总误差约为2%—3%.     

北京谱仪Ⅱ中性径迹测量误差的确定

选取辐射Bhabha样本,研究了北京谱仪Ⅱ(BESⅡ)桶部簇射计数器(BSC)对中性径迹的沉积能量和空间位置的测量,定出了实际数据的测量误差.并利用Monte Carlo产生的e⁺e^－→γγ事例定出MC数据的能量及位置测量误差.结果已用于BESⅡ运动学拟合,能改善物理分析结果.     

弦张量与奇异粒子产生

用一种参数化的形式研究了弦上具有硬胶子纽结所导致的有效弦张量的增长.在此种形式下强子一强子碰撞中有效弦张量随碰撞能量的增加而增加是来自碰撞中微喷注的产生.这种机制既能解释强子一强子碰撞奇异夸克压低因子随碰撞能量之增而增的行为,又能解释e⁺e^－湮没中该因子与能量近似无关的现象.     

τ轻子Michel参数测量中的电子识别方法

北京谱仪(BES)合作组通过τ→eνν衰变的电子能谱测定Michel参数,本文利用BES在质心系能量4,03GeV处获取的e⁺e^－对撞数据,通过BES给出的带电粒子dE/dx、β、E/p测定值及其适当组合,实现了电子的有效识别.     

部分子末态的色分离联接对e+e－反应中强子产额及其动量谱的影响

用JETSET事例产生器对e⁺e^－→qq+ng→hadrons反应中,末态部分子(qq+ng)以色分离的联接方式进行强子化时,各种强子产额及π⁺,K^±,p/p的动量谱进行了计算;与传统的色中性流联接方式强子化结果进行比较.结果表明:由T权重确定的色分离单态和色中性流这两种完全不同的色联接方式强子化得到的强子产额及π⁺,K^±,p/p的动量谱,与实验符合的程度相同,有些更好.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.