摘要:

We have constructed an exact and stable algorithm for few‐electron systems, with which we have determined the energies of an excited state of the He atom and of the ground state of the Li atom. Significant features of the new method include the following: There are equal populations of random walkers that carry positive and negative weights. The positions of walkers are selected from a distribution that couples all walkers using a Green’s function with a known form. The correct importance functions that take into account the global interactions of the populations are different for positive and negative walkers. This symmetry breaking is an essential element for long‐term stability. A novel transformation of the potential energy facilitates the exact evaluation of the energyE.

ISSN:0094-243X    

DOI:10.1063/1.42615

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The calculation of photoionization cross sections of atoms is discussed in the framework of many‐body perturbation theory. The use of appropriate coupled equations allows the summation to infinite order of certain classes of diagrams and can account for resonance structure in the cross sections. The calculations are carried out using complete sets of single‐particle states with discretization of the continuum. Examples are given for the process of photoionization with excitation for helium and argon atoms. The cross section of atomic tungsten is calculated as an example of a complex, open shell atom. As an example of an alternative method, an extensive R‐matrix calculation for the 1s photoionization cross section of beryllium is presented.

ISSN:0094-243X    

DOI:10.1063/1.42617

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The rapid growth in the power of large‐scale computers has had a resolutionary effect on the study of charged‐particle accelerators that is similar to the impact of smaller computers on everyday life. Before an accelerator is built, it is now the absolute rule to simulate every component and subsystem by computer to establish modes of operation and tolerances. We will bypass the important and fruitful areas of control and operation and consider only application to design and diagnostic interpretation. Applications of computers can be divided into separate categories including: ▪ component design, ▪ system design, ▪ stability studies, ▪ cost optimization, and ▪ operating condition simulation.For the purposes of this report, we will choose a few examples taken from the above categories to illustrate the methods and we will discuss the significance of the work to the project, and also briefly discuss the accelerator project itself. The examples that will be discussed are: (1) the tracking analysis done for the main ring of the Superconducting Supercollider, which contributed to the analysis which ultimately resulted in changing the dipole coil diameter to 5 cm from the earlier design for a 4‐cm coil‐diameter dipole magnet; (2) the design of accelerator structures for electron‐positron linear colliders and circular colliding beam systems (B‐factories); (3) simulation of the wake fields from multibunch electron beams for linear colliders; and (4) particle‐in‐cell simulation of space‐charge dominated beams for an experimental linear induction accelerator for Heavy Ion Fusion.

ISSN:0094-243X    

DOI:10.1063/1.42618

出版商:AIP    

年代:1992

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.42619

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We introduce a dynamical model for the description of hadron‐hadron collisions at relativistic energies. The model is based on classical Nambu‐Goto¯ strings. The string motion is performed in unrestricted four‐dimensional space‐time. The string endpoints are interpreted as partons which carry energy and momentum. We studye+e−,e−p, andp−pcollisions at various center‐of‐mass energies. The three basic features of our model are as follows. An ensemble of strings with different endpoint dynamics is used to approximately reproduce the valence quark structure functions. We introduce an adiabatic hadronization mechanism for string breakup viaqq¯ pair production. The interaction between strings is formulated in terms of a quark‐quark scattering amplitude and exchange. This model will be used to describe relativistic heavy‐ion collisions in future work.

ISSN:0094-243X    

DOI:10.1063/1.42620

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Recent numerical work on strongly correlated electronic models using the Lanczos approach is reviewed. In particular, static and dynamical properties of the Hubbard andt–Jmodels are presented attempting to make a connection with experiments. We conclude that numerical methods like the Lanczos technique are providing useful information in the study of these models.

ISSN:0094-243X    

DOI:10.1063/1.42621

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The scattering of waves in classical physics and quantum scattering theory have many dissimilarities, but also many things in common. Many of the modern developments in classical wave theory have their origin in quantum scattering despite the later development of quantum physics. Although each field has diverged from the other over time, there are many analogies between the two disciplines and much in one area may enhance the other. In this work an outline is given of some aspects of the classical scattering theory of waves which have some relation with quantum theory. In addition, some numerical techniques are presented that may be of use in both areas.

ISSN:0094-243X    

DOI:10.1063/1.42622

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We review briefly the R‐matrix approach to atomic collisions. We then discuss its application to the electron impact excitation of Si3+and Zn+, and to the excitation‐autoionization of Ca+, and discuss the results in comparison with experiment.

ISSN:0094-243X    

DOI:10.1063/1.42624

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We discuss preliminary calculations of impact‐parameter‐dependent probabilities and cross sections for muon‐pair production with capture of the negative muon into theK‐shell of the target caused by the time‐dependent electromagnetic fields generated in peripheral relativistic heavy‐ion collisions. Our approach is nonperturbative in that we calculate probabilities by solving the time‐dependent Dirac equation on a three‐dimensional Cartesian lattice using the basis‐spline collocation method. Use of the axial gauge for the electromagnetic potentials produces an interaction easier to implement on the lattice than the Lorentz gauge.

ISSN:0094-243X    

DOI:10.1063/1.42600

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We present a QCD based relativistic kinetic model for high energy nuclear collisions, which is inspired by the parton picture of hadronic interactions. The nuclear dynamics is traced back to the microscopic level of quark and gluon interactions in the framework of perturbative QCD. The time evolution of the nuclear system is described in real time by a relativistic transport equation for the parton distributions that is solved by the Monte Carlo method.

ISSN:0094-243X    

DOI:10.1063/1.42601

出版商:AIP    

年代:1992

数据来源: AIP