自然元素在建筑设计中的创意与表达——石材

石材,在建筑发展的历史上一直扮演着重要角色,不但为人类提供遮风避雨的场所,还以其多变的魅力活跃在当今建筑文化的舞台上.建筑师通过各种充满创意的设计表达手法,赋予建筑更多的品质和意义.从石材在建筑上应用的起源入手,分析石材在景观和建筑设计中的表现手法,并结合大量的实例总结了石材的创意设计方法.     

辅助任务增强的中文跨域NL2SQL算法

自然语言到结构化查询语言(natural language to structured query language,NL2SQL)任务旨在将自然语言询问转化为数据库可执行的结构化查询语言(structured query language,SQL) 语句。本文提出了一种辅助任务增强的中文跨域 NL2SQL 算法,其核心思想是通过在解码阶段添加辅助任务以结合原始模型来进行多任务训练,提升模型的准确率。辅助任务的设计是通过将数据库模式建模成图,预测自然语言询问与数据库模式图中的节点的依赖关系,显式地建模自然语言询问和数据库模式之间的依赖关系。针对特定的自然语言询问,通过辅助任务的提升,模型能够更好地识别数据库模式中哪些表/列对预测目标 SQL 更有效。在中文 NL2SQL 数据集 DuSQL 上的实验结果表明,添加辅助任务后的算法相对于原始模型取得了更好的效果,能够更好地处理跨域 NL2SQL 任务。     

Natural convection effects on TNT solidification inside a shaped charge mold

High Explosive Anti-Tank (HEAT) warheads and ammunitions are frequently produced by explosive casting inside an axis-symmetric mold with an inverted conical geometry in the basis. In order to prevent manufacturing defects, the solidification process must be controlled. In this study, a dimensionless solidification model has been proposed to investigate the heat transfer considering the natural convection inside the liquid explosive and the numerical simulations were performed by using COMSOL Multiphysics and Modeling Software, employing trinitrotoluene (TNT) thermophysical properties. The effect of three different boundary conditions on the top of the mold have been evaluated: convection, adiabatic and isothermal. It has been observed that solidification process was faster for convection case and slower for isothermal case, while an intermediary total solidification time value was found for adiabatic case. Moreover, liquid explosive was completely surrounded by solid explosive during the solidification process for convection case and also for adiabatic case through the end of the process. Otherwise, it was not observed for isothermal case. The natural convection effects promoted a vortex inside the liquid explosive, accelerating the heat transfer process. It has been concluded that isothermal mold top boundary condition should be preferred to prevent manufacturing defects, avoiding high thermal stress.     

大气对流层气压公式推导的新方法及对国际气压方程的修正

论证了对流层气体分子平均质量的变化相对于温度的变化可以忽略,并利用对流层大气温度随海拔高度变化的规律,研究其压强随高度的变化规律,明确了其参数的意义.同时,在海拔超过10000 m时,国际气压方程出现了越来越明显的误差,提出了合理的修正方法,并发现其温度变化远小于近地面的情况.     

运动场馆火灾烟气蔓延规律数值模拟研究

运动场馆规模大、人员密集、功能复杂、用电负荷大、配电线路多、火灾荷载大,一旦发生火灾可能导致群死群伤恶性事故的发生。研究运动场馆火灾情况下烟气变化规律,能够更好的指导消防安全设计。以某运动场馆为例,应用火灾模拟软件对其火灾情况下烟气蔓延过程进行数值模拟研究,分析了常见自然排烟方式对烟气层的高度、温度、氧气浓度、一氧化碳浓度变化的影响,从而为运动场馆防排烟设计提供依据。     

Natural resource degradation and conflict in the East African pastoral drylands

Based on a literature review, this article examines the dynamics in pastoral systems, natural resource conservation and conflict in the drylands of East Africa. It argues that, in the context of East Africa, pastoralism and biodiversity conservation in general are distinct forms of land use that are complementary rather than competitive. The present state of natural resource degradation in the drylands is explained in terms of factors related to ecological and demographic pressures, land use conflicts and inefficient land administration policies. When the customary pastoral institutions of land administration and resource management are threatened, the problem of degradation is further exacerbated and violent conflicts occur among multiple resource users, including pastoralists, farmers and the state. The article recommends the revitalisation, empowerment and recognition of pastoral institutions in a way that ensures effective synergy between the formal and customary structures of resource governance.     

卫星整流罩结构动力特性与分离运动分析

针对复合材料蜂窝夹芯板壳组成的卫星整流罩,用有限元法建立了该罩的结构动力学数值模型,编制了相应的有限元分析软件包,计算了全罩、半罩在不同边界条件下的自由振动频率和模态,并分析了抛罩时半罩的分离轨迹和气动力作用下爆炸螺栓的承载情况。     

轮式越野车动力学建模及行驶动力学特性仿真

为准确评估某型6×6轮式越野车行驶动力学性能,建立了该越野车的整车多刚体动力学模型,分析了模型的振动固有特性和频率响应特性,并进行了特定工况下的行驶动力学特性仿真,计算了悬架动行程均方根值和车轮动载荷均方根值,分析了悬架与限位块的碰撞概率和车轮跳离地面的概率。结果表明:该动态工况下越野车的悬架设计工作空间满足使用要求,但行驶安全性能较差。     

蒙特卡洛剖分投影法的爆震弹破片平均比动能评估

为了评估爆震弹封装壳体破片致死、致伤半径,并削弱其平均比动能,基于蒙特卡洛剖分投影法建立破片平均比动能计算模型。通过LS-DYNA及自编程联合仿真方法对爆震弹自然破片、半预制破片比动能计算模型进行仿真求解,获得了全破片全时域的质量分布、初始速度、垂直靶分布、平均比动能阈值及安全半径等指标。结果表明:在相同装药参数下,半预制破片相比于自然破片,质量分布、初始速度阈值更低且更集中;在小于等于2.5 m范围内半预制破片平均比动能阈值比自然破片更低,大于2.5 m后半预制破片平均比动能阈值比自然破片更高。相比于自然破片,采用半预制破片可显著减小爆震弹破片的致死半径,但并不能明显增大其安全半径。     

自然场景车标数据集的构建及其应用

车标作为车辆身份的关键特征之一,在车辆的监控与辨识中发挥着重要作用。由于自然场景复杂多变,对其中的车标进行准确识别仍具有很大的挑战性。目前公开数据库很少且存在诸多局限,导致研究缺乏可信度和实用性。本文建立了一个面向自然场景的全新数据集,包含多种采集环境下的10 324幅、67类车辆图像。基于此数据集开展应用研究,提出一个目标检测与深度学习相结合的车标识别方法,包括车标区域定位和车标种类预测两大步骤。实验表明,该方法对复杂背景有较强的适应性,在涉及30种车标的分类任务中达到89.0%的总体识别率。