基于虚拟样机技术的折叠翼厢式车液压开启系统的仿真研究

折叠翼厢式车是一种新式厢式车,给货物的装卸带来了极大的方便。本文介绍了这种厢式车的基本原理,并运用 UG建立了三维实体模型,然后导入机械动力学仿真软件ADAMS中,建立起液压与机械一体化虚拟样机模型,并进行了动 力学仿真,预见了设计方案的可行性,为物理样机的试制提供了参考。     

High-Tc superconductivity and electronic band structure

We review the main results of the van Hove scenario applied to superconducting cuprates. It is based on the assumption that in these materials, the Fermi level lies near a singularity in the density of states (DOS). This hypothesis has recently been confirmed experimentally. We show that this model explains many properties of the high-T _c superconductors. We show that an anaogous model with a peak in the DOS may also be applied to the superconducting doped fullerenes. A general feature of the model is a very short coherence length.     

采煤机搬运车整车静态分析

对采煤机搬运车进行了三维建模;将动态仿真所得到的载荷加载在采煤机搬运车上,应用Unigraphics进行整车静态分析,得出分析结果。     

墙的嬗变（下）

本文以墙这种基本建筑元素为线索．回顾了密斯两种基本空间类型——流动空间和均一（或通用）空间产生、转化、交错、融合的复杂历史。这种过程跨越密斯的整个建筑生涯,反映了密斯对待建筑的基本思考和选择．也给今天留下了启示。     

创造历史：密斯·凡·德·罗和纽约现代艺术博物馆

1947年由菲利普·约翰逊（Philip Johnson）策划,在纽约现代艺术博物馆（MoMA）举办了著名的题为《密斯·凡·德·罗》的个人作品展。布展设计是密斯本人,而约翰逊则编辑出版了关于这个展览的书籍。本文作者将约翰逊的出版书籍和由密斯本人设计的展览进行了详尽的比较和分析,展示了两者之间的不同之处。约翰逊对于密斯作品的诠释是叙事-历史性的,他认为密斯在欧洲的作品是他在美国的作品的前奏。他强调了密斯早期欧洲作品的＂传统＂风格和后期美国作品的普适化、国际化风格之间的区别和发展过程。而本文作者则从密斯对展览作品的选择和陈设,归纳出了密斯本人对待自己作品是批判性的,不受时间限制的,只注重作品本身的品质和它们所反映的思想。而约翰逊认为密斯后期作品是完全抽象化和普适化的理论也是不完全正确的,因为无论从解读密斯的作品到他本人的一些陈述,都证实了他对一个作品相关的景观、历史和文脉的重视。密斯给我们带来的遗产也存在于这些思考之中。     

上下吐根哈特

阅读密斯建筑作品的平面图,常常会产生“单层密斯”或“标准层密斯”的印象。然而建于1930年的吐根哈特住宅却是一个显著的例外。本文以吐根哈特住宅为切入点,通过对它的两个差异很大的上下层平面的分析和研究,试图揭示密斯对于建筑上、下层关系处理的变化过程。这种分析也展示了密斯在其早期建筑思想走向成熟的过程中,对于“空间”、“功能”、“地形”等建筑基本问题理解的演化。它们同时显示了吐根哈特住宅作为密斯建筑生涯中“承上启下”关节点的历史地位。     

Direct Growth of Germanene at Interfaces between Van der Waals Materials and Ag(111)

Germanene, a 2D honeycomb germanium crystal, is grown at graphene/Ag(111) and hexagonal boron nitride (h-BN)/Ag(111) interfaces by segregating germanium atoms. A simple annealing process in N₂ or H₂/Ar at ambient pressure leads to the formation of germanene, indicating that an ultrahigh-vacuum condition is not necessary. The grown germanene is stable in air and uniform over the entire area covered with a van der Waals (vdW) material. As an important finding, it is necessary to use a vdW material as a cap layer for the present germanene growth method since the use of an Al₂O₃ cap layer results in no germanene formation. The present study also proves that Raman spectroscopy in air is a powerful tool for characterizing germanene at the interfaces, which is concluded by multiple analyses including first-principles density functional theory calculations. The direct growth of h-BN-capped germanene on Ag(111), which is demonstrated in the present study, is considered to be a promising technique for the fabrication of future germanene-based electronic devices.     

Dielectric Properties of Ultrathin CaF2 Ionic Crystals

Mechanically exfoliated 2D hexagonal boron nitride (h-BN) is currently the preferred dielectric material to interact with graphene and 2D transition metal dichalcogenides in nanoelectronic devices, as they form a clean van der Waals interface. However, h-BN has a low dielectric constant (≈3.9), which in ultrascaled devices results in high leakage current and premature dielectric breakdown. Furthermore, the synthesis of h-BN using scalable methods, such as chemical vapor deposition, requires very high temperatures (>900 °C) , and the resulting h-BN stacks contain abundant few-atoms-wide amorphous regions that decrease its homogeneity and dielectric strength. Here it is shown that ultrathin calcium fluoride (CaF₂) ionic crystals could be an excellent solution to mitigate these problems. By applying >3000 ramped voltage stresses and several current maps at different locations of the samples via conductive atomic force microscopy, it is statistically demonstrated that ultrathin CaF₂ shows much better dielectric performance (i.e., homogeneity, leakage current, and dielectric strength) than SiO₂, TiO₂, and h-BN. The main reason behind this behavior is that the cubic crystalline structure of CaF₂ is continuous and free of defects over large regions, which prevents the formation of electrically weak spots.     

Layered Antiferromagnetism Induces Large Negative Magnetoresistance in the van der Waals Semiconductor CrSBr

The recent discovery of magnetism within the family of exfoliatable van der Waals (vdW) compounds has attracted considerable interest in these materials for both fundamental research and technological applications. However, current vdW magnets are limited by their extreme sensitivity to air, low ordering temperatures, and poor charge transport properties. Here the magnetic and electronic properties of CrSBr are reported, an air-stable vdW antiferromagnetic semiconductor that readily cleaves perpendicular to the stacking axis. Below its Néel temperature, T_N = 132 ± 1 K, CrSBr adopts an A-type antiferromagnetic structure with each individual layer ferromagnetically ordered internally and the layers coupled antiferromagnetically along the stacking direction. Scanning tunneling spectroscopy and photoluminescence (PL) reveal that the electronic gap is Δ_E = 1.5 ± 0.2 eV with a corresponding PL peak centered at 1.25 ± 0.07 eV. Using magnetotransport measurements, strong coupling between magnetic order and transport properties in CrSBr is demonstrated, leading to a large negative magnetoresistance response that is unique among vdW materials. These findings establish CrSBr as a promising material platform for increasing the applicability of vdW magnets to the field of spin-based electronics.     

A New Opportunity for 2D van der Waals Heterostructures: Making Steep-Slope Transistors

The use of a foreign metallic cold source (CS) has recently been proposed as a promising approach toward the steep-slope field-effect-transistor (FET). In addition to the selection of source material with desired density of states–energy relation (D(E)), engineering the source:channel interface for gate-tunable channel-barrier is crucial to CS-FETs. However, conventional metal:semiconductor (MS) interfaces generally suffer from strong Fermi-level pinning due to the inevitable chemical disorder and defect-induced gap states, precluding the gate tunability of the barriers. By comprehensive materials and device modeling at the atomic scale, it is reported that 2D van der Waals (vdW) MS interfaces, with their atomic sharpness and cleanness, can be considered as general ingredients for CS-FETs. As test cases, InSe-based n-type FETs are studied. It is found that graphene can be spontaneously p-type doped along with slightly opened bandgap around the Dirac-point by interfacing with InSe, resulting in superexponentially decaying hot carrier density with increasing n-type channel-barrier. Moreover, the D(E) relations suggest that 2D transition-metal dichalcogenides and 2D transition-metal carbides are a rich library of CS materials. Graphene, Cd₃C₂, T-VTe₂, H-VTe₂, and H-TaTe₂ CSs lead to subthreshold swing below 60 mV dec⁻¹. This work broadens the application potentials of 2D vdW MS heterostructures and serves as a springboard for more studies on low-power electronics based on 2D materials.