ISU - Multigrid for computing propagators

The Iteratively Smoothing Unigrid algorithm (ISU), a new multigrid method for computing propagators in Lattice Gauge Theory, is explained. The main idea is to compute good (i.e.\ smooth) interpolation operators in an iterative way. This method shows {\em no critical slowing down} for the 2-dimensional Laplace equation in an SU(2) gauge field. First results for the Dirac-operator are also shown.Comment: 3 pages, latex, no figures, Contribution to Lattice 94, uses espcrc2.sty and fleqn.sty as required for lattice proceeding

An Investigation of the Chip Segmentation Process Using Finite Elements

A finite element model of a two-dimensional orthogonal metal cutting process is used to simulate the formation of segmented chips. The deformation of the chip during segmentation is studied and the distribution of deformation energy in chip and shear band is analyzed. It is shown that the plastic deformation both in the shear band and the segment contribute significantly to the cutting force. A variation of the thermal conductivity strongly affects the segmentation and indicates that segmentation is energetically favorable

Mitigating the Goldilocks effect: the effects of different substrate models on track formation potential

In ichnology, the Goldilocks effect describes a scenario in which a substrate must be ‘just right’ in order for tracks to form—too soft, the animal will be unable to traverse the area, and too firm, the substrate will not deform. Any given substrate can therefore only preserve a range of tracks from those animals which exert an underfoot pressure at approximately the yield strength of the sediment. However, rarely are substrates vertically homogeneous for any great depth, varying either due to heterogeneity across sediment layers, or from mechanical behaviour such as strain hardening. Here, we explore the specificity of the Goldilocks effect in a number of virtual substrates simulated using finite- element analysis. We find that the inclusion of strain hardening into the model increases the potential range of trackmaker sizes somewhat, compared with a simple elastic–perfectly plastic model. The simulation of a vertically heterogeneous, strain hardening substrate showed a much larger range of potential trackmakers than strain hardening alone. We therefore show that the Goldilocks effect is lessened to varying degrees by the inclusion of more realistic soil parameters, though there still remains an upper and lower limit to the size of trackmaker able to traverse the area while leaving footprints

Another Look at Neural Multigrid

We present a new multigrid method called neural multigrid which is based on joining multigrid ideas with concepts from neural nets. The main idea is to use the Greenbaum criterion as a cost functional for the neural net. The algorithm is able to learn efficient interpolation operators in the case of the ordered Laplace equation with only a very small critical slowing down and with a surprisingly small amount of work comparable to that of a Conjugate Gradient solver. In the case of the two-dimensional Laplace equation with SU(2) gauge fields at beta=0 the learning exhibits critical slowing down with an exponent of about z = 0.4. The algorithm is able to find quite good interpolation operators in this case as well. Thereby it is proven that a practical true multigrid algorithm exists even for a gauge theory. An improved algorithm using dynamical blocks that will hopefully overcome the critical slowing down completely is sketched.Comment: 13 pages, 3 ps figures, uses IJMPC styl

Старение аккумуляторов как часть системы проектирования парков городских аккумуляторных электрических автобусов

The lifetime of traction battery systems is an essential feature of the economy of battery electric urban bus fleets. This paper presents a model for the analysis and prediction of the lifetime of urban electric bus batteries. The parameterization of the model is based on laboratory measurements. The empirical ageing model is an integral part of a three-stage battery model, which in turn is an important component of the methodology for the overall system design, evaluation and optimisation of battery electric urban bus fleets. In an equidistant closed simulation loop, the electrical and thermal loads of the traction battery are determined, which are then used in the ageing model to calculate the SOH (state of health) of the battery. The closed simulation loop also considers the effects of a constantly changing SOH on the driving dynamics of the vehicles. The model for lifetime analysis and prognosis is presented in the paper, placed in the context of the overall system design and demonstrated by means of a practice-oriented example. The results show that the optimal system design depends, among other things, on whether an ageing simulation was used. Taking battery aging into account, system costs in the example presented can be reduced by up to 17 %.Срок службы систем тяговых аккумуляторов играет существенную роль в вопросе экономии для парка электрических городских автобусов. В статье представлена модель для анализа и прогнозирования срока службы аккумуляторных батарей электрических городских автобусов. Параметризация модели основана на лабораторных измерениях. Эмпирическая модель старения – неотъемлемая часть трехступенчатой модели аккумуляторов, которая, в свою очередь, является важным компонентом методологии для общего проектирования системы, оценки и оптимизации парка аккумуляторных электрических городских автобусов. В эквидистантном замкнутом контуре моделирования определяются электрические и тепловые нагрузки тягового аккумулятора, используемые в модели старения для расчета SOH (состояния работоспособности) аккумулятора. Замкнутый цикл моделирования также учитывает влияние постоянно меняющегося SOH на динамику вождения транспортных средств. Предлагаемая модель используется в контексте общего проектирования системы; показан пример практического применения. Согласно результатам исследования, оптимальное проектирование системы зависит, помимо прочего, от того, используется или нет моделирование процесса старения. Принимая во внимание старение аккумулятора, системные затраты в рассматриваемом примере могут быть уменьшены до 17 %

Dynamical scaling of the quantum Hall plateau transition

Using different experimental techniques we examine the dynamical scaling of the quantum Hall plateau transition in a frequency range f = 0.1-55 GHz. We present a scheme that allows for a simultaneous scaling analysis of these experiments and all other data in literature. We observe a universal scaling function with an exponent kappa = 0.5 +/- 0.1, yielding a dynamical exponent z = 0.9 +/- 0.2.Comment: v2: Length shortened to fulfil Journal criteri

Bowling Together: Scientific Collaboration Networks of Demographers at European Population Conferences

Studies of collaborative networks of demographers are relatively scarce. Similar studies in other social sciences provide insight into scholarly trends of both the fields and characteristics of their successful scientists. Exploiting a unique database of metadata for papers presented at six European Population Conferences, this report explores factors explaining research collaboration among demographers. We find that (1) collaboration among demographers has increased over the past 10 years, however, among co-authored papers, collaboration across institutions remains relatively unchanged over the period, (2) papers based on core demographic subfields such as fertility, mortality, migration and data and methods are more likely to involve multiple authors and (3) multiple author teams that are all female are less likely to co-author with colleagues in different institutions. Potential explanations for these results are discussed alongside comparisons with similar studies of collaboration networks in other related social sciences