Bi-criteria assembly line balancing by considering flexible operation times

This paper addresses a novel approach to deal with Flexible task Time Assembly Line Balancing Problem (FTALBP). In this regard, machines are considered in which operation time of each task can be between lower and upper bounds. These machines can compress the processing time of tasks, but this action may lead to higher cost due to cumulative wear, erosion, fatigue and so on. This cost is described in terms of task time via a linear function. Hence, a bi-criteria nonlinear integer programming model is developed which comprises two inconsistent objective functions: minimizing the cycle time and minimizing the machine total costs. In order to sustain these objectives concurrently, this paper applies the LP-metric method to make a combined dimensionless objective. Moreover, a genetic algorithm (GA) is presented to solve this NP-hard problem and design of experiments (DOE) method is hired to tune various parameters of our proposed algorithm. The computational results demonstrate the effectiveness of implemented procedures.     

Optimizing departure times in vehicle routes

Most solution methods for the vehicle routing problem with time windows (VRPTW) develop routes from the earliest feasible departure time. In practice, however, temporary traffic congestion make such solutions non-optimal with respect to minimizing the total duty time. Furthermore, the VRPTW does not account for driving hours regulations, which restrict the available travel time for truck drivers. To deal with these problems, we consider the vehicle departure time optimization (VDO) problem as a post-processing of a VRPTW. We propose an ILP formulation that minimizes the total duty time. The results of a case study indicate that duty time reductions of 15% can be achieved. Furthermore, computational experiments on VRPTW benchmarks indicate that ignoring traffic congestion or driving hours regulations leads to practically infeasible solutions. Therefore, new vehicle routing methods should be developed that account for these common restrictions. We propose an integrated approach based on classical insertion heuristics.     

考虑机器调整次数和产品质量的卷烟批量计划和柔性流水车间调度集成问题

针对卷烟企业生产中的批量计划和柔性流水车间调度集成问题,构建了整数规划模型,目标函数由卷烟生产时间、生产线调整次数、卷烟质量、库存成本四部分组成。鉴于该问题的NP-hard性,设计遗传算法进行求解,通过合理设计遗传算子,避免不可行解出现。应用某卷烟企业数据得到优化排产结果,与该企业之前依照经验排产方案进行对比,发现优化排程结果在减少品牌转换次数,提高生产的连续性方面具有明显优势。该算法已作为某卷烟企业排产人员的排产参考,应用于排产决策中,取得了良好的效果,对卷烟企业制定排产计划具有一定的实际指导意义。     

Ergodic theorems for queuing systems with dependent inter-arrival times

We study a G/GI/1 single-server queuing model with i.i.d. service times that are independent of a stationary process of inter-arrival times. We show that the distribution of the waiting time converges to a stationary law as time tends to infinity provided that inter-arrival times satisfy a Gärtner-Ellis type condition. A convergence rate is given and a law of large numbers established. These results provide tools for the statistical analysis of such systems, transcending the standard case with independent inter-arrival times.     

一种低原子序数元素EDX RF的多次导-样条小波解析方法研究

能量色散X射线荧光（EDXRF）光谱分析待测元素的信息主要反映在能谱的特征峰峰位以及特征峰净峰面积中。对于特征峰的准确检测是EDXRF光谱分析的关键。特征X射线之间的能量在低原子序数元素中相差很小,在实际测量过程中由其他一些因素干扰会导致EDXRF光谱中特征峰产生严重重叠,以EDXRF光谱中低序列元素的重叠峰作为研究对象,提出一种四次导数结合三样条小波变换处理低序列元素重叠峰的新方法。通过数学模型模拟重叠峰检测了该方法的可行性,并仿真了实测X荧光光谱数据进行检测得到良好的效果,通过使用了CIT-3000SY X 荧光元素录井仪实测T铅黄铜数据和混合轻元素数据荧光光谱作为验证。首先,介绍导数法以及三样条小波法分解重叠的原理。导数法阶数越高信号越畸形但可以有效提高重峰分离度,而三样条小波变换对低分离度重峰处理较为无力但能有效的保持峰型。通过Tsallis峰信号模拟重叠峰,模拟出3个峰信号,第1个峰和第2个峰的分离度R=0.33,第2个峰和第3个峰的分离度R=0.67,导数处理后信号任仍具有一部分重叠,但是导数处理后不仅保留了信号的峰位值,且出现了分离度变大的现象,而三样条小波对低分离度重叠峰的分解较为无力,但是对于分离度较大的重叠峰具有较好的效果,信号通过四次导增加分离度再进行三样条小波变换,通过调节样条小波分解层次的次数,然后对分解出的高频信号采取适当的系数进行放大,最后进行信号重构。实验实现了对模拟信号的分解。验证了此方法针对重叠峰分解具有可行性。实验采用分解4层的三样条小波变换以及放大6倍的高频信号。然后,处理仿真K元素的重叠光谱,实现了重叠峰的分解,通过仿真实验表明新方法能准确的识别峰位,结果表明只有1%之内的误差,证明了新方法对X荧光光谱重叠峰分解的适用性。最后用此方法对CIT-3000SY X荧光元素录井仪实测T铅黄铜元素数据以及混合轻元素数据X荧光光谱进行处理,实现了对重叠峰的分解,且分解后的峰位误差控制在1%之内,具有较高的准确率。实验结果证明：四次导数结合三样条小波变换能有效分离重叠峰,并且在处理X荧光光谱的重叠峰分解上具有实用性。     

Body Temperature Mapping by Magnetic Resonance Imaging

Abstract

There are numerous clinical situations, such as hyperthermia cancer therapy, under which body temperature has to be accurately evaluated. Magnetic Resonance Imaging presently offers the best set of non-invasive methods for body temperature mapping, including diffusion imaging, relaxation time measurement, magnetization transfer contrast and chemical shift spectroscopic imaging. The basic NMR parameters involved in each are first analyzed. The role of temperature in their physical variation is then presented and finally the different practical MRI methods are briefly discussed. In the present slate of available technology and for basic physical reasons, the T 1 method appears the best compromise at low and medium magnetic field in a limited temperature range. Chemical shift could be theoretically more promising but strictly depends from the homogeneity and stability of the magnet and will be available only at high or very high field.

     

Competition between associative and dissociative adsorption of 1,2-dihalogenated benzenes on Si(1 0 0)2 × 1: Formation of dihalocyclohexadiene, halophenyl and phenylene adstructures

The room temperature (RT) adsorption of 1,2-difluorobenzene (1,2-DFB), 1,2-dichlorobenzene (1,2-DCB) and 1,2-dibromobenzene (1,2-DBB) on Si(1 0 0)2 × 1 have been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Both XPS and TPD data show that the relative degree of dissociative to associative adsorption of the dihalogenated benzene (DXB) appears to increase with decreasing electronegativity of the halogen atom (X). In particular, the C 1s intensity ratios for the C-H and C-Si components to the C-X component are found to be 2, 3 and 9.6 for 1,2-DFB, 1,2-DCB and 1,2-DBB, respectively. These results indicate that 1,2-DFB, like benzene, exclusively adsorbs molecularly as a difluorocyclohexadiene adspecies on Si(1 0 0)2 × 1 while 1,2-DBB adsorbs predominantly with double debromination to form 1,2-phenylene. The majority of 1,2-DCB (75%) is found to adsorb molecularly, with the rest (25%) undergone single or double dechlorination to form chlorophenyl and phenylene, respectively. All three DXB molecules appear to have similar coverage as benzene. The two molecular desorption features for 1,2-DFB and 1,2-DCE are observed with desorption maxima at 460 K and 540 K similar to those found for benzene, which suggests that the dihalocyclohexadiene adstructures involve similar bonding through the benzene ring. In accord with the XPS data, no molecular desorption feature is observed for 1,2-DBB on the 2 × 1 surface. Further decomposition of the resulting phenylene adstructures is evident from the desorption fragment, C₂H₂, found at 610 K and 740 K. Recombinative desorption of HCl and HBr above 880 K are also found for 1,2-DCB and 1,2-DBB, respectively. The observed differences between associative and dissociative adsorption for the three DXB adsorbates could be attributed not only to the large difference in the C-X bond strength but also to the relative contributions from inductively withdrawing and resonantly donating electrons exerted by the halogen (X) atoms to the benzene ring.     

Sojourn and waiting times in a single-server system with state-dependent mean service rate

A birth-death queueing system with asingle server, first-come first-served discipline, Poisson arrivals and state-dependent mean service rate is considered. The problem of determining the equilibrium densities of the sojourn and waiting times is formulated, in general. The particular case in which the mean service rate has one of two values, depending on whether or not the number of customers in the system exceeds a prescribed threshold, is then investigated. A generating function is derived for the Laplace transforms of the densities of the sojourn and waiting times, leading to explicit expressions for these quantities. Explicit expressions for the second moments of the sojourn and waiting times are also obtained.     

Quantitative cerebral magnetic resonance imaging during ACTH treatment of multiple sclerosis

Serial MR scans were performed with the 2DFT imaging method and the filtered backprojection imaging method on 12 patients with multiple sclerosis in acute phase, 4 in a relapsing/remitting form, and 8 in a progressive form, before, during and after ACTH treatment. Both T₁ and T_2mono relaxation times, obtained by fitting transverse magnetization decay curves with a monoexponential function within the apparently normal white matter and the areas of increased signal, were measured. With the backprojection method it was possible to fit the transverse magnetization decay curve with a biexponential function and obtain T_2long and T_2short relaxation times. The T_2mono and T₁ relaxation times of the apparently normal white matter were significantly different from those obtained for volunteers, but no significant differences were found before, during, or after treatment. The transverse magnetization decay curves of the areas of increased signal were better fitted by a biexponential function. No significant changes in these relaxation times were observed after ACTH treatment. These results argue against an anti-oedematous action of ACTH and may suggest that it has an immunosuppressant effect.     

Killing time

Theoretical consequences of the gravitational origin of inertial reaction forces, that is, Mach's principle, are explored. It is argued that Mach's principle leads to the conclusion that time, as we normally treat it in our common experience and physical theory, is not a part of fundamental reality; the past and future have a real, objective existence, as is already suggested by both special and general relativity theory. A laboratory scale experiment whereby Mach's principle, and thus radical timeless ness, can be established is mentioned.