Science with radioactive beams: The alchemist's dream

Nuclear science is being transformed by a new capacity to create beams of radioactive nuclei. Until now all of our knowledge of nuclear physics and the applications which flow from it has been derived from studies of radioactive decay and nuclear reactions induced by beams of the 283 stable or long-lived nuclear species we can find on Earth. Here we describe first how beams of radioactive nuclei can be created. The present status of nuclear physics is then reviewed before potential applications to nuclear physics, nuclear astrophysics, materials science, bio-medical, and environmental studies are described.     

第一类永动机幻梦的破灭

介绍了13~18世纪物理学史和科技史上曾名噪一时的第一类永动机的设计方案的破灭.第一类永动机幻梦破灭的历史引起了人们的反思与启示,有力地促进了19世纪中叶能量转化和守恒定律的确立.     

Subdiffusion-limited A+A reactions

We consider the coagulation dynamics A+A-->A and A+A <==> A and the annihilation dynamics A+A-->0 for particles moving subdiffusively in one dimension. This scenario combines the "anomalous kinetics" and "anomalous diffusion" problems, each of which leads to interesting dynamics separately and to even more interesting dynamics in combination. Our analysis is based on the fractional diffusion equation.     

色度学实验研究

本文通过实验验证了颜色相加、相减的规律及任意复色光与汞灯的色坐标、色调、色饱和度的测量及三原色滤色片的透过滤测定等各项实验内容。并对复色光的研究分别用精确算法与粗略算法进行了分析研究。     

矩形波导与圆柱波导或圆柱谐振腔间的小孔耦合

本文讨论了三种不同系统的小孔耦合的近似解法:矩形波导与圆柱波导的同轴耦合,矩形波导中的TE₁₀型波与圆柱谐振腔中的TM₁₂₀型波间的耦合和矩形波导中的TE₁₀型波与圆柱波导中的TM_mn型波间的耦合。通过这几个问题的解法,我们希望读者可以看到处理复杂微波元件问题时所需的从物理概念出发的灵活应用已有方法的必要性。这里提供的几个公式有着广泛的应用范围而是在现有文献中探讨得不够的。这里介绍的方法可以应用到其他新的微波网络问题中去。     

煤粒均相着火规律的研究

煤粒均相着火规律的研究张军，傅维标（清华大学工程力学系北京１０００８４）关键词均相着火，简化模型，预报１前言煤粉颗粒既能发生均相着火，又能发生非均相着火山。对非均相着火，许多学者进行了研究，取得了很多有价值的成果。均相着火由于比较复杂，一直发展缓慢。...     

一个自由界面的磁面方程一维的模型解

近来文献[1]证明:对于准均匀的或趋肤的电流分布,自由界面的磁面方程,化为似线性椭圆型方程后,可以用一简单迭代法求出最大解,并且指出,这一方程或者只有平庸解,或者会有三个以上的解(包括平庸解)。但现有的计算方法,对寻找除最大解以外的其他解还不太有效。但是找出第三个解,并且研究这些解的性质,将是十分重要的。因为特别是对有快磁压缩的环形装置,如带状装置上,原则上不能排除等离子体会平衡在不同的位型上。这样就出现下面的问题:不同的平衡位型中,哪一个才是最稳定的?为此目的,在进行数值计算的同时,我们解析地研究了如下的一维模型。     

一个三体问题的解法

应用两次广义坐标变换，将彼此间由弹性力作用的三体问题的拉格朗日函数简化为两个独立的谐振子的拉格朗日函数之和，在理论上提供了解决此三体问题的方法。     

裂纹与夹杂物的互作用

本文求解了一个圆形夹杂物对裂纹尖端应力场的影响,计算了反平面切变问题经典的应力场和应力强度因数,进而求得了非局域应力场,得到非奇异的裂纹尖端应力的解析表达式,讨论了解的应用。 关键词：     

LowpT phenomena in A+A and p+A collisions at mid-rapidity

CERN experiment NA44 measures pion and kaon distributions atpT=0–320 MeV/c at midrapidity in p+A and A+A collisions at 450 and 200A GeV/c, respectively. Pion production from p+Pb and A+A is slightly enhanced at lowpT relative to p+Be, but less than observed at target rapidity. The lowpT behavior can be understood in the context of the RQMD model as arising from baryonic resonance decays.     

DYNAMIC RESPONSE OF A BEAM WITH A CRACK SUBJECT TO A MOVING MASS

An iterative modal analysis approach is developed to determine the effect of transverse cracks on the dynamic behavior of simply supported undamped Bernoulli-Euler beams subject to a moving mass. The presence of crack results in higher deflections and alters the beam response patterns. In particular, the largest deflection in the beam for a given speed takes longer to build up, and a discontinuity appears in the slope of the beam deflected shape at the crack location. Crack effects become more noticeable as crack depth increases. The effect of the inertia force due to the moving mass is, in general, qualitatively similar and additive to the effect of the crack. The exact effect of crack and mass depends on the speed, time, crack size, crack location, and the moving mass level. Other approximate methods, namely a stationary mass model and a single iteration technique, are also evaluated. The stationary mass approach is useful for light moving masses (<20% of beam mass) and cracks at mid-span. For other cases, the errors can be unacceptably large. The results of the single-iteration approximation are quite close to the iterative modal analysis approach, which indicates that this approximate solution is an excellent tool for the analysis of the moving mass problem.     

宽沟道SI-GaAs衬底上适于光发射机的BH激光器

目前,光发射机中的激光器有采用MOCVD和MBE方法生长的多量子阱激光器,用LPE法生长的BH激光器。我们根据现有的实验条件,为了制作单片集成的光发射机,在沟道SI-GaAs衬底上采用两次液相外延生长BH激光器,实现了表面平面化。在800℃一次外延生长四层。第一层n⁺-GaAs缓冲层,第二层N-GaAlAs下限制层,第三层非掺杂构GaAs有源层,第四层为P-GaAlAs上限制层。采用适当的腐蚀条件刻蚀出有源区最窄的燕尾形隐埋条。在二次外延中,我们仅装一槽GaAlAs源液,在晶片上仅停留一次便生长出两个掩埋层,且层间界面与有源区自对准。上层为N-GaAlAs,载流子浓度为10¹⁶cm^-3,下层为高阻伴随生长层。由于高阻伴随层的存在对电流产生了有有效的侧向限制作用,因此避免了通常的SiO₂膜沉积等一系列工艺,提高了成品率,减化了工艺程序。利用n型掩埋层和隐埋条区P型上限制层之间铝组分及载流子类型、浓度的差异,虽然做一种宽接触电极,但由于隐埋条区上有良好的欧姆接触,而在掩埋层上为非良欧姆接触,所以起到了一定的电流外限制作用。n型电极是从n⁺-GaAs层引出的。 这种沟道SI-GaAs衬底正装GaAlAs/GaAs BH激光器室温连续工作阈值电流为55mA,P-I曲线在100℃仍有良好的线性关系。     

A WAVE MODEL FOR A PNEUMATIC TYRE BELT

A one-dimensional wave equation of an infinite flattened tyre belt is generated. The belt vibration is controlled by bending, tension, shear and the sidewall stiffness. The dispersion relations for two waves in the belt are calculated and used to find both the input impedance and attenuation on a tyre belt of infinite extent. Tension and the sidewall controls the deformation and stiffness below 100Hz. Waves propagate around the belt above this frequency. The wave speeds due to bending and shear were predicted and measured. The model presented here should be valid for the prediction of tyre response above about 400 Hz when for a car tyre the modal behaviour is observed to cease. In this high-frequency region, the tyre at the input appears to be of infinite extent.     

A study of molybdenum radiation from alcator A

Radiation emitted by molybdenum impurity ions in the Alcator A tokamak has been investigated. A grazing incidence monochromator photometrically calibrated against synchrotron radiation was used to determine absolute brightnesses of emission lines and the role of molybdenum radiative losses in the plasma discharge power balance. At line average electron densities of 3 × 10¹⁴ cm^?3, molybdenum radiation from the central (0–3 cm) region was equal to ～17% of the local ohmic heating power, implying radiation from molybdenum ions does not dominate the power loss from the central part of the plasma. The temporal behavior of molybdenum ions injected by the laser blow off technique at $\text{n}{}_{\mathrm{e}}\text{= 3 × 10}{}^{14}\text{cm}{}^{\mathrm{?3}}$ indicated that the molybdenum ion confinement time was finite in conflict with neoclassical theory. At lower densities (1–2 × 10¹⁴ cm^?3) the radiation from intrinsic molybdenum increased faster than the electron density during the discharge, indicating a buildup of molybdenum ions in the plasma.     

借助集团展开的超辐射热力学

N原子-单模辐射场相互作用系统当作相互作用准玻色子-光子系统并处理作巨正则系综.系统热力学势的明显表达式应用集团展开得到，某些热力学量按通常的热力学公式导出.数值计算和图示表明了这个超辐射系统的热力学行为，在超辐射态临界线上和其他地方出现的奇异性揭示了在此合作系统中存在第二类相变换. 关键词：     

Low p T phenomena in A+A and p+A collisions at mid-rapidity

CERN experiment NA44 measures pion and kaon distributions at p _T = 0–320 MeV/c at midrapidity in p+A and A+A collisions at 450 and 200A GeV/c, respectively. Pion production from p+Pb and A+A is slightly enhanced at low p _T relative to p+Be, but less than observed at target rapidity. The low p _T behavior can be understood in the context of the RQMD model as arising from baryonic resonance decays.     

双酚A和双酚A二缩水甘油醚振动谱的理论和实验比较分析

利用基于密度泛函理论的第一性原理计算,本文研究双酚A(BPA)和双酚A二缩水甘油醚(EDGEBA)分子的结构和振动性质,分析了两种分子红外活性和拉曼活性特征振动的频率和对称性。计算结果表明,BPA分子的拉曼散射峰基本归属于对位取代苯的骨架振动,500~1600cm-1红外强度较强;对于DGEBA分子环氧基团指纹区的特征振动频率为860,930,1123,1260cm-1,其红外光谱强度较大,可用于DGEBA类树脂固化反应过程监控;1260cm1附近的振动模,其拉曼散射强度较高,可成为拉曼光谱研究固化反应过程的特征振动。而1160cm-1附近的振动属于芳香环的特征振动,强度基本不变。     

A new sonic emulsifying system: A preliminary report

Acoustic emulsification techniques are not so widely exploited as other emulsification methods such as propeller stirrers, peddlers and colloid mills of different kinds. Liquid borne acoustic generators cannot produce the same size of dispersed particles as those produced by ultrasonic emulsifiers using velocity transformers. A combination of the liquid borne acoustic generator with ‘static mixer modules’ may help to overcome this drawback. The combination of these two systems in one unit may also be used for the gentle mixing of explosive materials and to improve heat-transfer.