Dislocation slip and twinning in Ni-based L12 type alloys

We report theoretical results on dislocation slip and twinning in Ni₃ (Al, Ti, Ta, Hf) compositions with L1₂ crystal structures utilizing first-principles simulations. The lattice parameters of Ni₃Al, Ni₃Al_0.75Ta_0.25, Ni₃Al_0.5Ta_0.5, Ni₃Ta, Ni₃Ti and Ni₃Al_0.75Hf_0.25 are calculated, and the crystal structures with lower structural energies are determined. We established the Generalized Stacking Fault Energy (GSFE) and Generalized Planar Fault Energy (GPFE), and calculated stacking fault energies APB (anti-phase boundary) and CSF (complex stacking fault) matched other calculations and experiments. Based on the extended Peierls–Nabarro model for slip and the proposed twin nucleation model, we predict slip and twinning stress and the results show a general agreement with available experimental data. The results show that in the studied intermetallic alloys, twinning stress is lower than slip stress; Ta and Hf ternary addition are substantial to increase flow stress in Ni₃Al. The models proposed in the paper provide quantitative understanding and guidelines for selecting optimal precipitate chemistry and composition to obtain higher mechanical strength in Shape Memory Alloys.     

An intelligence-based route choice model for pedestrian flow in a transportation station

This study proposes a method that uses an artificial neural network (ANN) to mimic human decision-making about route choice in a crowded transportation station. Although ANN models have been developed rapidly and widely adopted in various fields in the last three decades, their application to predict human decision-making in pedestrian flows is limited, because the video clip technology used to collect pedestrian movement data in crowded conditions is still primitive. Data collection must be carried out manually or semi-manually, which requires extensive resources and is time consuming. This study adopts a semi-manual approach to extract data from video clips to capture the route choice behaviour of travellers, and then applies an ANN to mimic such decision-making. A prediction accuracy of 86% (ANN model with ensemble approach) is achieved, which demonstrates the feasibility of applying the ANN approach to decision-making in pedestrian flows.     

Performance of the bearing reinforcement earth wall as a retaining structure in the Mae Moh mine,Thailand

In this research, a Bearing Reinforcement Earth (BRE) wall with a residual clay stone backfill was successfully implemented as an alternative truck ramp support for an on-site crusher plant in the Mae Moh mine, Thailand. The performance of the BRE wall during and after the end of construction as well as during the service state was evaluated in terms of, settlement, bearing stress, lateral movement, lateral earth pressure and tension force in the reinforcements. Bearing reinforcement is a cost-effective inextensible earth reinforcement, which is composed of a longitudinal member and transverse members. The maximum settlement at the end of construction (20 days) was about 5 mm. The installation of the truck ramp (10 days after the end of construction) resulted in an immediate settlement of about 2 mm. The final settlement due to the backfill, truck ramp and truck load after 270 days was found to be uniform due to the contribution of bearing reinforcement and was approximately 25 mm. The bearing stress which was uniformly distributed was found to increase rapidly with construction time, which was in agreement with the relatively uniform settlements. The lateral wall movement at the front and lateral sides at the end of construction was very small with the maximum movement (at the top of the wall) found to be less than 10 mm. As such, the ratio of lateral movement to height (δ/H) was found to be approximately 0.12%, which was lower than the allowable value of 0.4%. With this low δ/H and the insignificant change in the measured settlement and lateral movement during service, the BRE wall was considered to have a very high stability. The coefficients of lateral earth pressure, K and depth relationship were proposed based on the analysis of measured maximum tensile force in the reinforcements. The maximum tension plane of the BRE wall could be represented by the coherent gravity hypothesis. Using the proposed K and maximum tension plane, the internal stability of the BRE wall was furthermore examined. A proposed method of designing the BRE wall with claystone backfill was also proposed.     

充填采煤液压支架充填特性理论研究及工程实践

固体充填采煤液压支架既具有传统支架掩护采煤所需要的基本功能,又具有掩护充填所需要的特殊功能,是实现采充一体化的关键设备。针对其掩护充填的特殊功能,提出充填特性的概念,并分别从支护强度、后顶梁支护强度、运动特性、夯实力、夯实离顶距以及地质条件适应性6方面具体阐述了充填特性的基本内涵。架型结构、地质条件、充填工艺是影响充填特性的主要因素,其中架型结构直接决定充填支架的充填特性;煤层厚度、煤层顶底板、煤层倾角、煤层埋深等地质条件影响充填特性的发挥;充填工艺则通过改变离顶距及夯实力大小、改善对不同地质条件的适应性3方面影响充填性能的保障。具体工程实践中则通过工作面布置优化、结构设计优化、充填工艺优化、实时在线监测等措施保障充填性能的发挥。济三矿ZZC10000/20/40型六柱正四连杆充填采煤液压支架的工程应用验证了本文的研究成果。     

Reorientation patterns in central-place foraging: internal clocks and klinokinesis

We study central-place foraging patterns of Aphaenogaster senilis ants at a population level by video framing individual ant trajectories in a circular arena with a nest connected to its centre. The ants naturally leave and enter the nest and forage generating non-trivial movement patterns around the nest. Our data analysis indicated that the trajectories observed can be classified into two strategies: the risk-averse strategy, which involves wandering around the nest without departing far from it and the risk-prone strategy, which involves long exploration paths with periodic returns to the central region, nearby the nest. We found that both risk-prone and risk-averse strategies exhibit qualitatively the same reorientation patterns, with the time between consecutive reorientations covering a wide range of scales, and fitting a stretched exponential function. Nevertheless, differences in the temporal scales and the time variability of such reorientation events differ, together with other aspects of motion, such as average speed and turns. Our results give experimental evidence that the internal mechanisms driving reorientations in ants tend to favour frequently long relocations, as theory predicts for efficient exploration in patchy landscapes, but ants engaged in central-place foraging can modulate such behaviour to control distances from the nest. Previous works on the species support the idea that risk-prone and risk-averse strategies may reflect actual differences between individuals age and experience; these factors (age and experience) should be then relevant in modulating the internal reorientation clocks. To support the validity of our findings, we develop a random-walk model combining stretched exponential reorientation clocks with klinokinesis that fits the time length and the travelled distance distributions of the observed trajectories.     

From daily movements to population distributions: weather affects competitive ability in a guild of soaring birds

The ability of many animals to access and exploit food is dependent on the ability to move. In the case of scavenging birds, which use soaring flight to locate and exploit ephemeral resources, the cost and speed of movement vary with meteorological factors. These factors are likely to modify the nature of interspecific interactions, as well as individual movement capacity, although the former are less well understood. We used aeronautical models to examine how soaring performance varies with weather within a guild of scavenging birds and the consequences this has for access to a common resource. Birds could be divided broadly into those with low wing loading that are more competitive in conditions with weak updraughts and low winds (black vultures and caracaras), and those with high wing loading that are well adapted for soaring in strong updraughts and moderate to high winds (Andean condors). Spatial trends in meteorological factors seem to confine scavengers with high wing loading to the mountains where they out-compete other birds; a trend that is borne out in worldwide distributions of the largest species. However, model predictions and carcass observations suggest that the competitive ability of these and other birds varies with meteorological conditions in areas where distributions overlap. This challenges the view that scavenging guilds are structured by fixed patterns of dominance and suggests that competitive ability varies across spatial and temporal scales, which may ultimately be a mechanism promoting diversity among aerial scavengers.     

A computational algorithm for catalysts experiencing concentration‐dependent deactivation

Abstract

A computational algorithm is proposed for catalyst pellets or reactors experiencing concentration‐dependent deactivation. In the integration of the deactivation equation in each time interval, the concentration of poison, reactant or/and product is considered to be a constant. The value of concentration is recalculated from the mass balance equation before integrating the deactivation equation. By such an approach, the number of equations is reduced; thus a two‐dimensional problem can be converted to a single‐dimensional one.     

眼睛运动模型的设计

现阶段，生物模式识别系统主要有两种实现方案，且这些方案的实现都与眼睛的运动有关，因此这里利用细胞神经网络（CNN），基于欧氏距离的质心（COG）搜索算法以及距离权重选择模型（RSDW）的思想建立了一个眼睛运动模型。该模型输出的眼睛运动轨迹图特性与实际仪器测试的眼睛运动轨迹图特性具有较好的一致性，同时该模型能直接作为生物模式识别系统中信息获取模块的重要组成部分。     

Analysis of cracked layers under transient temperature field

The uncoupled thermoelasticity problem of a homogenous isotropic layer containing a line of temperature discontinuity and a Volterra edge dislocation is solved. The analysis is performed for discontinuity lines with two different directions of parallel and perpendicular to the layer boundary. The solutions for heat flux and stress fields exhibit the familiar Cauchy type singularity. These results are utilized to derive integral equations for the intensity of heat flux and densities of dislocation in a layer weakened by interacting cracks which are parallel and/or perpendicular to the layer boundary. The numerical solution of integral equations is performed and stress intensity factors for cracks are obtained.