Total angular momentum and reaction plane in collisions of high-energy particles

The reaction plane is an efficient tool for studying nucleus-nucleus collisions and other particle interactions. In order to determine it in those cases, use is made of model (hydrodynamic) concepts of the relationship between the impact parameter and collective flows of particles. It is shown that there is a direct possibility for reconstructing, in a model-independent way, the orientation of the plane in which particle collisions in reactions occur. The idea of the method is based on the relationship between experimentally measured quantities and the total angular momentum of the system of particles involved in the collision process. The concept of the reaction plane is defined for the case of multiparticle-production processes; it is shown that a normal to it is aligned with the total angular momentum. This circumstance ultimately leads to the interplay of particle azimuthal angles. This effect is interpreted in the literature as a manifestation of a collective production of particle flows in nuclear collisions.     

Three-dimensional particle imaging by wavefront sensing

We present two methods for three-dimensional particle metrology from a single two-dimensional view. The techniques are based on wavefront sensing where the three-dimensional location of a particle is encoded into a single image plane. The first technique is based on multiplanar imaging, and the second produces three-dimensional location information via anamorphic distortion of the recorded images. Preliminary results show that an uncertainty of 8 microm in depth can be obtained for low-particle density over a thin plane, and an uncertainty of 30 microm for higher particle density over a 10 mm deep volume.     

The Use of Azimuthal Intensity Variations in Diffraction Patterns for Particle Shape Characterization

Forward light scattering is a well established technique for measuring particle size distributions. The light intensity fluctuations which can be observed in the diffraction plane of the instrument can be used to stabilize the inversion process [1]. Particle shape information is also present in these fluctuations. It is shown that an azimuthal-type of detector can be used to extract this information from the statistical correlations of the detector signals.     

The kinetic boundary layer for the Fokker-Planck equation with absorbing boundary

The Fokker-Planck equation for the distribution of position and velocity of a Brownian particle is a particularly simple linear transport equation. Its normal solutions and an apparently complete set of stationary boundary layer solutions can be determined explicitly. By a numerical algorithm we select linear combinations of them that approximately fulfill the boundary condition for a completely absorbing plane wall, and that approach a linearly increasing position space density far from the wall. Various aspects of these approximate solutions are discussed. In particular we find that the extrapolated asymptotic density reaches zero at a distance x_M beyond the wall. We find x_M=1.46 in units of the velocity persistence length of the Brownian particle. This study was motivated by certain problems in the theory of diffusion-controlled reactions, and the results might be used to test approximate theories employed in that field.     

Laser-driven collisions of electron bunches

A novel scheme allowing for relativistic collisions of laser-accelerated electrons is introduced. Two spatially separated electron bunches are driven in opposite directions by two counterpropagating laser pulses until they reach the point of collision which lies within the laser fields. This method can be employed to accelerate electrons to the maximum kinetic energy which can be transferred to charged particles by plane propagating laser fields. Due to the symmetric setup, the center of momentum is at rest with respect to the laser propagation direction such that virtually the whole kinetic energy is available for particle reactions.     

光学微操纵过程的轴平面显微成像技术

光学俘获技术利用光与物质相互作用产生的光势阱效应来实现对微粒的操控,已经成功应用于生物医学、材料科学等交叉领域.在对微粒进行三维俘获时,传统的宽场光学显微技术只能观测到某一平面内微粒的横向运动,对微粒沿轴向运动的观测受到很大限制.本文将轴平面显微成像技术引入光学微粒操控研究中,利用45?倾斜的反射镜把微粒的轴向运动信息转换到横向平面进行观测,与传统宽场显微成像技术相结合,实现了对二氧化硅小球俘获过程横向和轴向运动的同步观测.该成像方法无需扫描和数据重构,具有实时快速等优点,在新型光束光镊、厚样品三维观测和成像等领域具有潜在的应用价值.     

Exclusion principle and nuclear reaction mechanism

Effects of the Exclusion Principle in specific reference to direct reactions are studied in detail by formulating a simple one-dimensional model in the two channel approximation. The fact that a target wavefunction can be described by different systems of cluster wavefunctions on account of the indistinguishability of nucleons is exploited to bring out the connections between the various aspects of the reaction mechanism and the forward and the backward reaction amplitudes. The coupled integro-differential equations of the model are solved by a matrix method, and an iteration method respectively for low and high energies of the incident particle in the entrance channel. The exact solution of the coupled integro-differential equations takes into account the Exclusion Principle and the effects of rescattering and target recoil. The result shows that the direct reactions are long distance or “surface” phenomena. An evidence is presented that this is a consequence of the Exclusion Principle. The exact result is compared with various approximate results. The latter include the cases; 1. antisymmetrization is completely neglected; 2. antisymmetrization is performed on the target wavefunctions only; 3. plane wave Born approximation; 4. distorted wave Born approximation. The result obtained by target antisymmetrization coincides with the exact result only for high energies of the incident particle. The practical use of this result obtained by use of the two equivalent clusterwavefunctions which describe the target wavefunction is discussed in connection with heavy particle stripping.     

Calculating the soot particle size distribution function in turbulent diffusion flames using a sectional method

Soot formation in a turbulent jet diffusion flame is modeled using an unsteady flamelet approach in post-process. In the present work, we apply a detailed kinetic soot model with a sectional method, and study the evolution of the particle size distribution. Detailed information on the evolution of the soot particle size distribution function is acquired. It is found that the particle size distribution function is bimodal throughout the flame. The transition from the small to large particle size distributions is strongly influenced by surface growth and oxidation reactions. We find that large particles are most likely to be emitted from the flame.     

The correlations of identical pions in multibody production

The identical quanta correlations give an information on the spatial and time structure of the production reactions. Their dependence on the multiplicity and average particle energy is estimated and compared with available data.     

Factorized knowledge from factorized polarization experiments

A general analysis is presented which yields a simple and economical picture of the information obtained about the reaction amplitudes from an incomplete set of polarization experiments. Spinwise inclusive (“spin-clusive”) reactions can thus furnish “spinclusive” information about the amplitudes. The analysis is used to derive a method to determine the spin of a particle in a reaction without ever measuring anything about that particle.     

Green's electron function in a quantized plane wave field

It is shown that the Green's function of an electron that interacts with a quantized plane wave can be expressed in terms of the corresponding Green's function of a scalar particle. By using the known expression for the Green's function of a scalar particle, an integral representation is found with respect to the intrinsic time for the Green's electron function in a quantized plane wave of arbitrary form.     

A “Hybrid Plane” with spin-orbit interaction

In this paper, we attempt to reconstruct one of the last and incomplete projects of Volodya Geyler. We study the motion of a quantum particle in the plane to which a halfline lead is attached, assuming that the particle has spin ½ and the plane component of the Hamiltonian contains a spin-orbit interaction, of Rashba or Dresselhaus type. We construct a class of admissible Hamiltonians and derive an explicit expression for the Green function, which is applied to scattering in a system of this kind.     

High-intensity lasers as radiation sources

In the last decade or so, an evolution in experimental relativistic laser-plasma physics has led to highly sophisticated lasers which are now capable of generating ultra-short pulses and can be focused to intensities in excess of 10²¹ W cm^-2. The laser interaction with solid or gas targets can generate collimated beams of highly energetic electrons, protons and ions. These high-intensity laser systems, therefore, turn out to be versatile and powerful sources of radiation and high-energy particles, without recourse to large-scale facilities such as nuclear reactors or particle accelerators. The potential to induce various kinds of nuclear reactions with laser-induced radiation fields has been demonstrated at several laboratories in recent years. The present paper lays out a comprehensive overview of nuclear reactions induced by high-intensity laser matter interactions. Mechanisms for electron, proton and ion acceleration, in addition to secondary bremsstrahlung, positron and neutron production, are addressed, with a focus on the types of nuclear reactions that are possible and potential applications. Discussion of the extrapolation of these processes and applications to the next generation of table-top lasers under construction is also presented.     

Quantum mechanics on noncommutative plane and sphere from constrained systems

It is shown that quantum mechanics on noncommutative (NC) spaces can be obtained by canonical quantization of some underlying constrained systems. Noncommutative geometry arises after taking into account the second class constraints presented in the models. It leads, in particular, to a possibility of quantization in terms of the initial NC variables. For a two-dimensional plane we present two Lagrangian actions, one of which admits addition of an arbitrary potential. Quantization leads to quantum mechanics with ordinary product replaced by the Moyal product. For a three-dimensional case we present Lagrangian formulations for a particle on NC sphere as well as for a particle on commutative sphere with a magnetic monopole at the center, the latter is shown to be equivalent to the model of usual rotor. There are several natural possibilities to choose physical variables, which lead either to commutative or to NC brackets for space variables. In the NC representation all information on the space variable dynamics is encoded in the NC geometry. Potential of special form can be added, which leads to an example of quantum mechanics on the NC sphere.     

Calculation of the eddy current in a small conducting spherical particle

The eddy current in a small conducting spherical particle located in the field of a plane electromagnetic wave is calculated. The frequencies under study are bounded above by frequencies of the near IR region. The calculation is performed within the kinetic approach for a comparatively small particle (～10 nm) in which the skin effect can be neglected; the ratio of the particle size to the electron mean free path is assumed to be arbitrary. The reflection of the charge carriers from the sample boundary is assumed to be purely diffuse. The effect of temperature on the current density in the particle is studied.     

Fragmentation processes in nuclear reactions

Fragmentation processes in nuclear collisions are reviewed. The main emphasis is put on light ion breakup at nonrelativistic energies. The post- and prior-form DWBA theories are discussed. The post-form DWBA, appropriate for the “spectator breakup” describes elastic as well as inelastic breakup modes. This theory can also account for the stripping to unbound states. The theoretical models are compared to typical experimental results to illustrate the various possible mechanisms. It is discussed, how breakup reactions can be used to study high-lying single particle strength in the continuum; how they can yield information about momentum distributions of fragments in the nucleus.     

基于相对论平均场理论对超重核冷熔合反应截面的研究

在形变约束的相对论平均场理论框架下计算了合成Z=102—118元素的(可能)冷熔合反应中复合核及蒸发一或两个中子剩余核的位能曲面,得到了复合核和剩余核平衡点和鞍点的性质、静态裂变垒高度和冷熔合反应的最佳入射能;利用壳修正和对修正方法计算了平衡点和鞍点的壳修正能、对修正能和微观能.利用由此得到的壳结构信息,用简单的熔合蒸发唯象模型计算了相应反应的冷熔合截面.结果发现,TM1参数提供的结构性质给出了与实验接近的反应截面.     

Note on relativistic coulomb wave functions

Some results on the wave functions of a Dirac particle in a point charge Coulomb field are presented. Angular momentum and parity eigenfunctions are tabulated and used to construct solutions representing asymptotically a plane wave plus incoming or outgoing spherical waves. The solutions forr → 0 are exhibited in a form closely similar to the corresponding free particle spinors and are used to construct generalizations of the Casimir projection operators for positive or negative energy particles. The various wave functions presented are useful in calculations such as nuclear beta decay in which it is necessary to take into account final (or initial) state Coulomb interactions. Because of the similarity of the wave functions to those of a free particle, calculations including rigorously all Coulomb corrections for such processes as allowed beta decay can be performed with little more effort than is involved in a calculation using only plane waves.     

The effect of potassium bromide and sodium carbonate on coal char combustion reactivity

The addition of halogens, particularly iodine, to the gas during coal char oxidation has been used in previous studies to quench gas-phase chemistry, thereby allowing one to separate the effects of homogeneous and heterogeneous reactions. Halogen addition suppresses the gas-phase radicals to near-equilibrium levels. A similar effect can be expected from other compounds with high efficiency as fire suppressants, such as alkali metals. The effectiveness of the use of additives in distinguishing homogeneous and heterogeneous reactions during char oxidation relies on the assumption that radicals are suppressed while heterogeneous reactions occurring on the char surface are not affected. The present work tests this assumption for potassium bromide (KBr) and sodium carbonate (Na₂CO₃) reacting with a pulverized eastern bituminous coal char during oxidation. An increase in CO and a slight reduction in particle temperature were observed with the addition of KBr, consistent with known effects of halogens on gas-phase chemistry. An increase in particle size was also observed with the KBr addition. This observation and the results of model calculations suggest that there is significant incorporation of liquid KBr on the char surface under the conditions examined. With Na₂CO₃ addition, the particle temperature did not change, the particle size showed a slight decrease, and CO production increased. Although the mechanisms for Na interaction with radicals at combustion conditions are not well established, char oxidation modeling suggests that a decrease in OH concentration in the particle boundary layer is the cause for the observed increase in CO production. It is concluded that Na₂CO₃ has clear advantages over KBr for inhibiting gas-phase chemistry without affecting char oxidation for the conditions investigated here.     

Particle digital in-line holography with spherical wave recording

In this paper, we propose a method of digital in-line holography of particle. A diverging spherical beam is used for illumination in recording hologram, the complex amplitude distribution generated by particle field at a single plane located in the Fresnel diffraction region is recorded by CCD, and a plane beam for reconstructing hologram, then, the magnified image can be obtained by numerical reconstruction in computer. This procedure can be interpreted by Fourier optical theory and the theoretical analysis have been done in detail, the experimental results, the air freshener being subject, are also given.