由58Fe 和209Bi 熔合后的相关衰变过程得到的109号元素的证据

本文报导了合成109号元素的实验。用能量为4.95,5.05和5.15MeV/u 的~(58)Fe 束轰击~(209)Bi 靶,研究了全熔合产物衰变模式的特性。总辐照剂量为7×10~(17)粒子。所用的实验方法是:用静电场速度过滤器在飞行过程中分离向前方向成峰的反应产物,经过飞行时间装置后注入到位置灵敏固态探测器中,测量其动能,估算出质量、入射的时间和位置。以所有的出射粒子的能量和时间来记录很有限的反应产物发生级联α粒子和(或)自发裂变的继发衰变。在5.15 MeV/u 时的一个特别的衰变过程是:在5ms 和22ms 先分别发射两个α粒子,最后,在13s 后发生自发裂变。第一个α粒子的动能为11.10±0.04MeV。对各种可能的解释进行了详细的分析,例如纯属偶然的信号相关,转移反应产物的衰变和从能量上看允许的余核蒸发等。最后表明质量数为266的109号元素的同位素、即全熔合后的单中子蒸发道、从统计的观点看是最好的指定。本文同时也讨论了合成新元素的前景。     

现代物理教学和多媒体技术

物理教学中,怎样把物理概念、规律传授给学生,并通过生动、活泼的课内外教学使学生领略物理世界的奇景异致,激起学习物理学的兴趣,是物理教师反复思考的问题．以往的教学手段主要是老师通过演示实验、模型,配合简单的作图进行讲授．近年来随着计算机技术的飞速发展,教师利用多媒体信息显示的多样性、过程的交互性、信息的存储性、网络化、智能化等进行教学,取得更佳的教学效果．     

多重表征——建构主义物理教学的新思路

编者按:本文引用了心理学界长期使用的"结构良好领域的知识和结构不良领域的知识"的知识分类观点,实际上就科学知识而言,心理学的那种分类和解释并不很恰当,可以"通过复制与同化而获取"的知识,不能说是结构良好的,只能说是简单的确定的,"概念比较复杂,理解一个概念要涉及灵活性和变化性"的知识是多元的,开放的知识,不应该冠以"不良结构"的帽子,这一点也许正是心理学与自然科学,中、西方文化存在的差异的反映;但是我们认为对上述概念作科学的理解后,本文关于物理教学所讨论的问题仍然是有价值的.     

9-cell TESLA超导加速腔研制中Dumb-Bells的测量与调整

为了保证9-cell超导加速腔在场的平滑度、TM010的频率以及加速器的总长度达到TESLA国际标准,必须确保每个Dumb-Bell在以上各方面达到标准要求.由于冲压、机加工以及电子束焊接等过程会引起形变,因此,必须在完成iris和加强筋的电子束焊接之后对Dumb-Bells进行微波和机械测量,并根据测量的结果对其腔形和长度等作必要的调整.北京大学已经建立了一套完整的测量和调整Dumb-Bells的装置,本文深入研究了Dumb-Bells的测量与调整的方法.     

家用空调风冷冷凝器的数值分析

对单排管的家用空调风冷冷凝器进行了CFD的数值模拟,并搭建了冷凝器的实验系统对3D模型的CFD模拟进行验证.比较结果表明;两者存在一个小偏差(<9%),但是两者的趋势完全一致.CFD计算可以得到一些实验无法得到的内部流动信息,有助于我们更好地理解冷凝器的机理.本文在实验的范围以外进行了"数值实验",冷凝器的其它结构不变,翅片的间距存在一个最优值,同样管间距也存在一个最优值,为设计新的冷凝器提供了合理、可靠的方向.     

光存储技术的原理、应用和发展方向

造纸术的发明使人们可以方便的记录信息,同时也使我国数千年的历史和众多优秀的传统文化得到了较为完整的保存.随着社会的不断进步、科技的高速发展,尤其是计算机和网络技术日新月异的发展,各种信息以不可阻挡的力量涌入人们的生活,人们几乎每天都要处理和存储大量的信息,用纸张来记录信息已远不能满足人们的需求,这就需要一种更为有效的信息存储技术来存储信息,而光存储技术是信存储技术中最有效的方法.本文对光存储技术的原理、应用和发展前景做一简要介绍.     

PAMELA合作组的测量数据挑战宇宙射线理论

欧洲PAMELA合作组的科学家声称,PAMELA合作组所获得的测量数据对宇宙射线在宇宙中如何加速的理论提出了挑战.根据他们的说法,通过宇宙的质子和氦核的能谱不仅彼此不同,而且不符合宇宙射线理论中用于描述这些粒子的能谱(通量与能量之间的关系)的简单幂律.这种不一致可能意味着物理学家不得不寻找对宇宙射线加速的新的解释.     

降低了对称程度的狭义相对论

作为爱因斯坦狭义相对论基础的两个假设是:相对性原理和光速不变原理.相对性原理说的是不论对于一个固定不动的观测者,还是对于一个匀速运动的观测者,各种物理现象的规律应该是相同的 光速不变原理认为不论光源如何运动,光速总是恒定的.欲使这两个假设成立,时-空必须具有一定的对称性.将以上这些合并考虑便形成了与旋转及速度之变化有关的所谓Lorentz对称群(以下简称"L对称"):如果在你进行一项物理实验时,实验室上下倒置了或开始以不同的速度移动,但由于L对称,自然界的基本规律是不会改变的.     

高能粒子辐照二氧化硅玻璃E''色心形成机理研究

考虑高能粒子辐照二氧化硅玻璃形成E'色心的情况.建立了E'色心形成的动力学模型,得到了E'色心浓度与辐照剂量的关系式.结果表明,在高能粒子辐照情况下,E'色心的形成包括两个过程,即色心的创造过程和色心的激活过程.色心的创造过程主要由二氧化硅网格中疲劳键的断裂形成或网格中氧移位形成,E'色心浓度随剂量的变化呈线性增长.色心的激活过程主要由二氧化硅玻璃中固有点缺陷形成,E'色心浓度随剂量的变化呈饱和趋势.理论结果和实验结果符合很好,说明建立的模型是有效的.     

物理教学中的科学猜想与直觉思维

直觉思维是在早已获得的经验、知识的基础上,凭思维的"感觉"直观地把握事物本质和规律的心理过程 是对客观现象的详细内容或所遇问题没有经过充分逻辑推理和系统论证而作出的一种迅速而"径直"猜度的认识活动.比如,当学生遇到难题百思不得其解时,有时却忽然灵机一动,豁然开朗,从而导致认识活动的飞跃和突破,这种思维活动便属直觉思维,也叫灵感思维、顿悟思维.当然,直觉的猜想和假说需要逻辑的论证和事实的检验.在创造性的思维活动中,逻辑思维和直觉思维是相互补充、相互渗透的,但直觉思维具有独特的作用.正如爱因斯坦所说,在科学研究和创造发明中"真正可贵的因素是直觉".     

Pb-Mg-Al合金腐蚀机理的电子理论研究

为了了解Pb-Mg-Al合金腐蚀的物理本质, 本文采用基于第一性原理的赝势平面波方法系统地计算了Pb-Mg-Al合金中各物相的结合能、费米能级和局域态密度等电子结构参数, 分析了合金的电化学腐蚀机理. 计算结果表明：Pb-Mg-Al合金中各主要组成物相稳定性大小关系为 Mg₁₇Al₁₂>Mg₂Pb>Mg;Mg,Mg₂Pb和Mg₁₇Al₁₂的费米能级存在E_f(Mg)>E_f(Mg₂Pb)>E_f(Mg₁₇Al₁₂)的关系, 说明Mg最容易失去电子, Mg₂Pb次之, Mg₁₇Al₁₂最难;局域态密度表明, 在同样的外界条件下, 体系中Mg相和Mg₂Pb相对于Mg₁₇Al₁₂均处于不稳定的状态, 容易失去电子, 即容易发生腐蚀. Pb-Mg-Al合金体系中不同物相的费米能级差构成了电化学腐蚀的电动势, 导致电子从费米能级高的Mg相和Mg₂Pb相流向费米能级低的Mg₁₇Al₁₂相, 使Pb-Mg-Al合金发生腐蚀.     

Extreme compression behaviour of equations of state

The extreme compression (P→∞) behaviour of various equations of state with K′_∞>0 yields (P/K)_∞=1/K′_∞, an algebraic identity found by Stacey. Here P is the pressure, K the bulk modulus, K^′=dK/dP, and K′_∞, the value of K^′ at P→∞. We use this result to demonstrate further that there exists an algebraic identity also between the higher pressure derivatives of bulk modulus which is satisfied at extreme compression by different types of equations of state such as the Birch–Murnaghan equation, Poirier–Tarantola logarithmic equation, generalized Rydberg equation, Keane's equation and the Stacey reciprocal K-primed equation. The identity has been used to find a relationship between λ_∞, the third-order Grüneisen parameter at P→∞, and pressure derivatives of bulk modulus with the help of the free-volume formulation without assuming any specific form of equation of state.     

Effect of ultrasound on the kinetics of anti-solvent crystallization of sucrose

The effect of ultrasound on the kinetics of anti-solvent crystallization of sucrose was studied. The influence of temperature, stirring rate, supersaturation and ultrasonic power on the anti-solvent crystallization of sucrose was investigated. The relationship between infrared spectral characteristic band of sucrose and supersaturation was determined with an online reaction analyzer. The crystal size distribution of sucrose was detected by a laser particle-size analyzer. Ultrasound accelerated the crystallization process, and had no impact on the crystal shape. Abegg, Stevens and Larson model was fitted to the experimental data, and the results were the following: At 298.15 K, the average size of crystals was 133.8 μm and nucleation rate was 4.87 × 10⁹ m⁻³·s⁻¹ without ultrasound. In an ultrasonic field, the average size was 80.5 μm, and nucleation rate was 1.18 × 10¹¹ m⁻³·s⁻¹. Ultrasound significantly reduced the average size of crystals and improved the nucleation rate. It was observed that the crystal size decreased with the increase of stirring rate in silent environment. When the stirring rate increased from 250 to 400 rpm, the average size decreased from 173.0 to 132.9 μm. However, the stirring rate had no significant impact on the crystal size in the ultrasonic field. In addition, the activation energy of anti-solvent crystallization of sucrose was decreased, and the kinetic constant of nucleation rate was increased due to the effect of ultrasound. In the ultrasonic field, the activation energy was reduced from 20422.5 to 790.5 J·mol⁻¹, and the kinetic constant was increased from 9.76 × 10² to 8.38 × 10⁸.     

Mechanisms of broadening of emission lines of a laser-induced plasma generated on the surface of rigid targets

This article reports the results of an experimental investigation of the basic mechanisms that cause the broadening of emission lines of a laser-induced plasma generated on the surface of rigid targets in a gaseous atmosphere. The contribution of Stark and resonance mechanisms of emission-line broadening for the resonance doublet Al I 3s²3p²P_3/2,1/2-3s²4s²S_1/2 and triplet Mg I 3s3p³P _0,1,2 ⁰ -3s4s³S₁ is discussed. The concentrations of neutral Al atoms in the laser-induced plasma are evaluated by the magnitude of resonance line broadening. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 234–237, March–April, 2000.     

Studies of the phosphorescence of polycrystalline hafnia

Persistent phosphorescence induced by ultraviolet light in polycrystalline HfO₂ and enhancement of the phosphorescence by sintering are investigated. The phosphorescence afterglow emission is in the 1.8-3.2 eV spectral range, with a peak at 2.53 eV. The afterglow intensity is significantly increased by sintering in either inert atmosphere or air. The afterglow light sum measured at room temperature for samples sintered at 1500 °C is more than an order of magnitude higher than that before sintering. In the temperature range −50 to 200 °C, three thermoluminescence (TL) peaks are observed near −10, 30, and 100 °C. The relative contribution of the low-temperature TL peak to the total TL intensity decreases after sintering, and this effect is more pronounced upon sintering in inert atmosphere. Conversely, the contribution of the TL peak near 100 °C increases after sintering. The enhancement of the afterglow by sintering is associated with the observed increase in the intensity of TL peaks at and above room temperature and attributed to an increase in the number of deep charge traps. The room-temperature afterglow time decay has a form consistent with the second-order mechanism, ∝(t₀+t)⁻ⁿ, and the best-fit values of both fitting parameters t₀ and n tend to increase with the sintering temperature.     

Influence of packing on the vibrations of homogeneous bundles of C60 peapods

The non-resonant Raman spectra of homogeneous bundles of C₆₀ peapods (C₆₀ inserted in single-walled carbon nanotubes) are calculated in the framework of spectral moment method, together with a bond-polarizability model. The evolutions of the low wavenumber range of the Raman spectrum of homogeneous bundles of C₆₀ peapods as a function of the nanotube diameter and the size of bundles are discussed. The effect of the C₆₀ filling factor is investigated in detail. The results are compared to experimental Raman data measured on various samples of C₆₀ peapods.     

Measurement of the g-Factor of the 27− High-Spin Isomer State of 152Dy

The g-factor of the 27⁻ isomer state of ¹⁵²Dy has been measured using the Time-Integral Perturbed Angular Distribution (TIPAD) method. The high-spin states of ¹⁵²Dy have been populated by ¹⁴¹Pr(¹⁶O,p4n)¹⁵²Dy reaction at E = 115 MeV from the AVF cyclotron at CYRIC. The paramagnetic correction factor of Dy ions in Pr has been determined to be 4.2(5) by the Time-Differential Perturbed Angular Distribution (TDPAD) measurement of the 21⁻ state of ¹⁵²Dy. As a result, the g-factor of the 27⁻ isomer state of ¹⁵²Dy has been obtained to be +0.09(5). This shows the smaller value than the expected one of +0.39 deduced from a fully aligned configuration of π(h _11/2 ²) ⊗ ν(f _7/2 ² h _9/2 i _13/2).     

Simulation of the contours of spectral lines of closed-ARC radiation

Simulated contours of self-reversed lines of Tl at 535 nm (7²S_1/2−6²P_3/2) and 378 nm (7²S_1/2-6²P_1/2) in alternating-current closed-arc radiation in mercury vapor with an addition of Tll were compared with experimental contours. It is shown that while a single self-reversed contour has many different sets of model parameters that ensure coincidence of experimental and calculated profiles, in the case of operation with a large data file of contours that correspond to different directions of observation along chords perpendicular to the discharge axis, and with different lines that have a common level, such a set of parameters becomes virtually unique. Instantaneous spatial distributions of Hg and Tl atoms in the ground state and of Tl atoms in the 6²P_3/2 state are determined and the parameters of the van der Waals broadening of the 7²S_1/2 level are found. It is shown that a considerable “red” shift of absorption contours in the outer layers of the discharge is observed. The results obtained contradict the presumed existence of local thermodynamic equilibrium in the given discharge. Reported at the Conference “Plasma Physics and Plasma Technologies,” Minsk, September 15–19, 1997 Petrozavodsk State University, 33, Lenin Ave, Petrozavodsk, 185640, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 761–768, September–October, 1998.     

Thickness dependence of elastic modulus of polycarbonate interphase

The oligomer of bis-phenol A (oligo-PC) with M _w = 1300 and bis-phenol A polycar-bonate (PC) with M _w = 20 000 were deposited onto E-glass surface using SiCl₄ as the grafting and cross-linking agent. Thickness of the deposited layers was varied from 30 to 10⁶ nm and the layers were investigated as prepared and after thermal annealing at 245°C for 10 min in the air. Vibrational piezoelectric resonator technique and the speed of Rayleigh wave measurement were used to determine elastic moduli of the ultra thin layers deposited on flat E-glass substrate as a function of their thickness. In all cases, increase of the Young modulus of the interphase, E _i, with decreasing layer thickness, t _i, was observed. At a given thickness, the E _i of PC layer was significantly lower than that for the oligo-PC layer. Thermal annealing of the deposited PC layer resulted in a significant increase of its E _i compared to the as received layer. No significant change was observed for oligo-PC interphases. Increase of the shear strength of the interface, τ _a, with reducing interphase thickness, t _i, was observed. The observed increase of E _i with the decreasing t _i was ascribed to the reduction of the molecular mobility of chains near solid surface compared to their mobility in the bulk. Most probably, the observed increase of E _i after thermal annealing of PC was caused by rearrangement of both segment density distribution in individual PC coils near the solid surface and cooperative rearrangements of multiple PC chains. Since the oligomers attached to the surface attained presumably more regular extended conformations with lower conformation entropy compared to the PC random coils, the effect of thermal annealing was negligible. In agreement with theoretical predictions, increase of E _i at the same extent of interfacial interactions resulted in the observed increase of the τ _a measured using the single embedded fiber test.