Monte Carlo simulation of energy balance in a pure 3He migma of 4 MeV

The energy balance in a migma of self-colliding orbits of 4 MeV ³He is studied using a two-dimensional Monte Carlo simulation supplemented with results from a three-dimensional Monte Carlo simulation and a self-consistent calculation of diamagnetic effects. Electron drag is balanced against synchrotron radiation and bremsstrahlung and losses of hot electrons. Synchrotron radiation was assumed to be reflected and reabsorbed, but bremsstrahlung was not. Reabsorption was taken to be a function of position, but not of angle, which should be an underestimate. Electrons were treated relativistically. The results are presented as a function of density from just below to well into the diamagnetic regime. We find that diamagnetism can reduce synchroton radiation losses to manageable levels.     

Monte Carlo simulation of a transition radiation detector

This paper employs Monte Carlo simulations of the performance of a transition radiation detector (TRD). The program has been written for the TRD in the ZEUS spectrometer, which separates electrons from hadrons in the momentum range between 1 and 30 GeV/c. Both, total charge method and cluster counting method were simulated taking into account various experimental parameters. In particular, it was found that the cluster counting method relies on a quantitative understanding of the background originating from the production of δ-electrons by charged particles. The results of the Monte Carlo calculations are in agreement with experimental data obtained with prototypes within a systematic uncertainty of 20%. We applied our Monte Carlo program to studies in order to find an optimum layout for the TRD within available space in the ZEUS spectrometer. In this context, the performance of TRD layouts with different geometries and materials has been evaluated comprehensively. The geometry found by optimization promises an improvement on hadron suppression by a factor of about two for both methods compared with present results from test measurements. Applying algorithms for a detailed analysis of the energy and space distributions of the clusters in the TRD, hadrons in the momentum range from 1 to 30 GeV/c can be suppressed to a level of less than 2%. This method of cluster analysing improves the suppression of hadrons by a factor of about two compared to the total charge method.     

Monte Carlo simulation of a mammographic test phantom

A test phantom, including a wide range of mammographic tissue equivalent materials and test details, was imaged on a digital mammographic system. In order to quantify the effect of scatter on the contrast obtained for the test details, calculations of the scatter-to-primary ratio (S/P) have been made using a Monte Carlo simulation of the digital mammographic imaging chain, grid and test phantom. The results show that the S/P values corresponding to the imaging conditions used were in the range 0.084-0.126. Calculated and measured pixel values in different regions of the image were compared as a validation of the model and showed excellent agreement. The results indicate the potential of Monte Carlo methods in the image quality-patient dose process optimisation, especially in the assessment of imaging conditions not available on standard mammographic units.     

Monte Carlo simulation of the high energy cosmic muon background in a resonant gravitational wave antenna

We present the results of a Monte Carlo simulation for the energy loss distribution of high energy cosmic muons crossing a Weber-type gravitational wave (g.w.) antenna. The number of events per day of energy greater than an assigned value, generated in the antenna by the muons, is deduced.

The simulation shows that a rate of 60 events per week due to the cosmic background is expected in a sea-level g.w. detector with an energy sensitivity ten times greater than that of the present antennas. With the sensitivity of the resonant detectors approaching the quantum limit value the rate will increase to 5 × 10⁴ events per days. Therefore it seems unavoidable to carry on the experiment in an underground laboratory.     

Distributed Monte Carlo simulation of a dynamic expansion system

This paper presents a new approach to the implementation of the Monte Carlo (MC) method for the analysis of high vacuum metrological systems based on the principle of dynamic gas expansion. The main disadvantage of the Monte Carlo method, the very long time of computation, can be significantly reduced by using a distributed calculation schema. This paper describes the principles of the computation system and compares the computing times for some models of a chosen metrological system, performed using a network of Personal Computers.     

Monte Carlo simulation of a control for cathodic sputtering

Subject is a set-up for gas pressure and discharge power regulation of a cathodic sputtering plant. It comprises two film thickness monitors and a control unit. The film thickness monitors measure the deposition rate at target and substrate level. By means of a computer the control unit calculates a quotient from the monitor data and compares it with a set value. Any change in gas pressure or discharge power leads to a deviation of the quotient from the set value. The control unit eliminates the deviation by a regulation of gas pressure or discharge power. The Monte Carlo method makes it possible to calculate the pressure dependence of the set-sup. It was not possible to determine a relationship between discharge power and the output signal of the control unit by the used theoretical model.     

A potential energy scaling Monte Carlo simulation of thin film nucleation and growth

A Monte Carlo computer simulation employing a potential energy scaling technique has been used to model the initial stages of thin film growth. The model monitors variations in the interaction potential that occur as a result of the arrival or departure of adatoms or impurities at sites in a 20 x 20 array. Boltzmann-ordered statistics are used to simulate fluctuations in vibrational energy at each site in the array, and the resulting site energy is compared with threshold levels of possible atomic events. In addition to adsorption, desorption and surface migration of adatoms, the simulation considers adatom incorporation and diffusion of a substrate atom to the surface. The effect of lateral interaction of nearest, second-nearest and third-nearest neighbors is also considered. A series of computer experiments were conducted for the Ge-Fe(100) system to illustrate the behavior of the model and to show that the surface migration of monomers, the formation of multiatom clusters and the coalescence of growing clusters behave in an accurate physical manner. Further, the model was found to be especially useful in the study of growth around different types of surface defects.     

Monte Carlo simulation of tolerance synthesis equations

This paper presents results on ongoing research aimed at developing an integrated computer-aided tolerancing tool. Starting with explicit tolerance analysis equations used to model the relationship between a part's functional elements and an assembly's functional requirements, the reverse synthesis equations are obtained using a simple Jacobian inversion scheme. The explicit nature of the resulting equations lend themselves to conventional Monte Carlo simulation techniques to determine the percentage of rejects being produced given some statistical distributions of the tolerances appearing in these equations. An example is presented that will provide insight on the merits of the developed method.     

Monte Carlo simulation of model spin systems

In this paper, applications of the Monte Carlo technique to estimate the static and dynamic properties of model spin systems are discussed. Finite-size effects and choice of boundary conditions in simulating different types of real systems are outlined. Various applications of the Monte Carlo simulations to one-, two- and three-dimensional Ising models and Heisenberg models are dealt with in some detail. Recent applications of the Monte Carlo method to spin glass systems and to estimate renormalisation group critical exponents are reviewed. Communication No. 19 from the Solid State Structural Chemistry Unit.     

Monte Carlo simulation of low density flows

The necessity for adopting a kinetic-theoretical approach to obtain aerodynamic characteristics in low density flow past space vehicles is highlighted in this paper; it is shown how long-standing difficulties in theoretically handling such flows can be circumvented by adopting a Monte Carlo technique. The principles underlying the technique are briefly described, and are first illustrated by applying the technique to the evaluation of the drag of cylinders and cones in collisionless flow. The Markoff process underlying the Monte Carlo simulation of the full Boltzmann equation with collisions is then described in detail. Instead of the time-counter strategy of Bird, a theoretically sounder ‘Random Collision Number’ (RCN) strategy has been adopted in the present simulation. In this strategy the number of collisions in each time-step in the computation is a random number drawn from an appropriate distribution. Computer programs using this strategy have been developed for calculating aerodynamic characteristics like drag and heat transfer for a cone in the transition regime between free molecule and continuum flow. The results obtained from these programs show that both time-counter and RCN strategies require almost the same computer time.     

Monte Carlo simulation of electron heating in a one-dimensional GaAs-quantum conductor

The process of transport of one-dimensional electrons in a GaAs quantum conductor is investigated by the Monte Carlo method. It is shown that in addition to scattering by polar optical phonons, the heating of charge carriers is also appreciably affected, in the case of electric field intensities higher than 5.10⁵V/m, by ionized-impurity scattering and the transverse dimensions of the conductor.     

低能He+、Ar+、Xe+轰击SiC的蒙特卡诺模拟

应用蒙特卡诺程序SRIM对He 、Ar 、Xe 轰击SiC的微观过程进行了模拟.对不同能量(100～500eV)以及不同角度(0～85°)下He 、Ar 、Xe 轰击SiC引起的溅射率、溅射原子分布、溅射原子能量以及入射离子在SiC中的分布情况进行了分析比较.结果表明对于原子量较小的He 入射SiC所引起的溅射主要是由进入表面之下的背散射离子产生的碰撞级联造成的,溅射原子具有较高的能量;对于原子量较大的Ar 、Xe 入射所引起的溅射主要是由进入SiC内部的离子直接产生的碰撞级联产生,溅射原子的能量相对较低.随着离子入射角度的逐渐增加,SiC的溅射率逐渐增加,在70°左右达到溅射峰值,随着入射角度的继续增加,入射离子的背散射不能使碰撞级联充分扩大,反冲原子的生成效率急剧降低,导致溅射率开始急剧下降.     

Defining the surface binding energy in dynamic Monte Carlo simulation for reactive sputtering of compounds

In Monte Carlo simulations of reactive sputtering, it is commonly assumed that the surface binding energy (SBE) for the different phases in the target exhibits a linear behaviour in the transition between the metal mode and the compound mode. In this work we study how the transition between the two modes takes place, and more specifically attempt to experimentally identify how the SBE for the different phases behaves in the transition between the two modes. In essence, this is done by comparing XPS measurements of the aluminium 2p binding energy on samples comprising pure aluminium, stoichiometric aluminium nitride and aluminium oxide with the corresponding measurements on understoichiometric aluminium nitride samples. In this work, it is assumed that the binding energy of the core level is directly correlated to the SBE of the phase in question. That is to say, if the aluminium 2p binding energy in aluminium nitride exhibits a constant and discrete value independent of the nitrogen concentration, the SBE for the compound exhibits a constant and discrete value independent of the surface concentration of nitrogen. It was found by the XPS measurement that the aluminium 2p binding energy in aluminium nitride exhibits a constant and discrete value independent of the nitrogen concentration in the samples and it was, therefore, concluded that the SBE for the different phases exhibits constant and discrete values independent of the surface concentration of nitrogen. The discrete behaviour of the SBE was implemented in the TRIDYN program and the results from these simulations were compared with simulations in which it is assumed that the SBE of the different phases exhibits a linear behaviour in the transition between the metal mode and the compound mode.     

Temperature dependence of the Henry's law constant for hydrogen storage in NaA zeolites: a Monte Carlo simulation study

Grand canonical Monte Carlo simulations of hydrogen adsorption in zeolites NaA were carried out for a wide range of temperatures between 77 and 300 K and pressures up to 180 MPa. A potential model was used that comprised of three main interactions: van der Waals, coulombic and induced polarization by the electric field in the system. The computed average number of adsorbed molecules per unit cell was compared with available results and found to be in agreement in the regime of moderate to high pressures. The particle insertion method was used to calculate the Henry coefficient for this model and its dependence on temperature.     

Monte Carlo simulation approach for a modified FMECA in a power plant

This paper presents a new tool for failure mode and effect analysis developed for a new Integrated Gasification and Combined Cycle plant in an important Italian oil refinery. The methodology is based on the integration between a modified Failure Mode Effect and Criticality Analysis (FMECA) and a Monte Carlo simulation as a method for testing the weights assigned to the measure of the risk priority numbers (RPNs). The RPN proposed consists of a weighted sum of six parameters (safety, machine importance for the process, maintenance costs, failure frequency, downtime length, and operating conditions) multiplied by a seventh factor (the machine access difficulty). Adopting this tool and considering the budget constraints, the best maintenance policy has been selected for each plant facility (about 140 in total). Copyright © 2000 John Wiley & Sons, Ltd.     

磁性多层膜系统自旋重取向行为的Monte Carlo模拟

依据Heisenberg模型,利用Monte　Carlo方法模拟了磁性多层膜系统的自旋重取向行为,研究了各向异性、偶极相互作用以及外磁场对系统自旋取向的影响。通过模拟计算,获得了系统组态、磁分量等随偶极相互作用、外加磁场和温度的变化规律,重点研究了磁性多层膜系统在外磁场作用下的磁滞现象。     

SiC电子输运的蒙特卡罗模拟

采用了Monte Carlo方法研究了2H-、4H-和6H-SiC的电子输运特性.在模拟中,采用动量弛豫率近似的方法确定散射角,显著压缩散射次数,并用高效的新查表法确定自由飞行时间,相对于阶梯值的自散射方法,完全消除了自散射,大量节省cpu时间.     

Monte Carlo modelling of energy deposition in trabecular bone

This study includes the design and testing of a program that creates quadric-based geometric models of the trabecular region, designed specifically for use with the 2005 version of the Monte Carlo radiation transport code PENELOPE. Our model was tested, by comparison with published data, in two aspects: the distributions of path lengths throughout the geometry and absorbed fraction values from the monoenergetic emission of electrons from within our geometry. In both comparisons, our results show a close agreement with published methods.     

PVD薄膜生长的Monte Carlo模拟

蒙特卡罗(Monte Carlo,MC)和分子动力学是模拟薄膜生长的两种基本方法.本文结合各种PVD技术的工艺特点,介绍了薄膜生长的Monte Carlo模拟.详尽地总结了载能粒子沉积薄膜生长的Kinetic Monte Carlo模型和算法.最后指出建立精细的模型、算法并适当应用分子动力学是提高模拟可靠性的方法.