Multiple fire interactions: A further investigation by burning rate data of square fire arrays

This paper presents the first effort to explore the spatial distributions of the burning rates in group fires consisting of a large number of fire points, by analyzing burn-out time data from experimental square fire arrays ranging from 3 × 3 to 15 × 15. A new concept termed fire layer is introduced and defined to characterize the spatial locations of fire points by which the complex spatial variations of burning rates, under different conditions, are analyzed and physically interpreted. Analysis shows that the fire layer burning rates vary from outer to inner in definite nonlinear modes. This indicates that the two fire interaction effects, heat feedback enhancement and air supply restriction, involve distinct spatial fluctuations in fire arrays. The spatial fluctuations of the two interaction effects are significantly affected by the two major parameters, fire spacing and fire array size. Definite spatial regions and parameter ranges for the spatial fluctuations and high competitions of the two interaction effects are clearly distinguished. It is demonstrated that the average burning rates of all fire layers involve consistent variations versus fire spacing or fire array size, especially with high comparability to the entire fire array. It is found that by varying fire spacing, the average burning rates for all fire layers vary linearly versus the fire area ratio, within the same ranges as the entire fire array, while there exist different fluctuation modes of fire layer burning rates with respect to fire array size. Furthermore, analysis shows that the burning rates of all fire layers will be significantly affected by fire merging when it occurs. Finally, a new approach is presented to simulate fire propagation among discrete fuel sources, by which the positive effect of the surrounding new fire points on the burning rates of the original ones is definitely indicated.     

An improved radio frequency heavy ion source

Abstract

An improved r.f. heavy ion source, which can operate with gases, liquids and solids is described. The operating temperature of the ion source may reach 1000°C. It can therefore, generate ion beams of a considerable number of elements. including metallic ions. At present, ion beams of S⁺, Al⁺, As⁺. Zn⁺, Mg⁺, Cd⁺, Ag⁺, Sm⁺, Te⁺, Se⁺, Sn⁺, In⁺, Hg⁺, etc. have been extracted. The extracted total beam current ranges from several hundred microamperes to the order of milliampere. The useful fraction of ion in the total beam is 70–90%. Life span of the source ranges from 40 hours to more than 100 hours. The emittance of the source is 3 × 10^?6 cm rad. Structure and operating characteristics of this ion source are discussed.     

High-power,high-quality ZGP OPO pumped by a Tm,Ho:GdVO<Subscript>4</Subscript> laser

We report a ZGP OPO system capable of producing >6 W at a signal wavelength of 3.80 μm and an idler wavelength of 4.45 μm. The pumping source is the Tm,Ho:GdVO₄ laser operated at 2.049 μm with an M ² of 1.07. The ZGP OPO generated a total combined output power of 6.1 W at signal wavelength and idler wavelength under pumping power of 18.3 W, and an M ² of 1.7 for OPO output was obtained.     

In vivo label-free photoacoustic microscopy of cell nuclei by excitation of DNA and RNA

Imaging of cell nuclei plays a critical role in cancer diagnosis and prognosis. To image noninvasively cell nuclei in vivo without staining, we developed UV photoacoustic microscopy (UV-PAM), in which 266 nm wavelength UV light excites unlabeled DNA and RNA in cell nuclei to produce photoacoustic waves. We applied UV-PAM to ex vivo imaging of cell nuclei in a mouse lip and a mouse small intestine and to in vivo imaging of the cell nuclei in the mouse skin. The UV-PAM images of unstained cell nuclei match the optical micrographs of the histologically stained cell nuclei. Given intrinsic optical contrast and high spatial resolution, in vivo label-free UV-PAM has potential for unique biological and clinical application.     

高温、高压、高应变速率动态过程晶体塑性有限元理论模型及其应用

对于高温、高压、高应变速率加载条件下的材料冲击变形行为,动态晶体塑性模型能够直接反映晶体中塑性滑移的各向异性及其对温度、压力和微观组织结构的依赖性,因而广泛应用于材料的动态冲击力学响应、微观结构演化以及动态损伤破坏的模拟。本文综述了高压冲击下动态晶体塑性有限元的理论模型,主要包括变形运动学、包含状态方程的超弹性本构模型和晶体塑性本构模型,涉及位错滑移、相变、孪生等塑性变形机制,以及层裂、绝热剪切带等动态破坏方式。     

AlGaN/GaN高电子迁移率器件外部边缘电容的物理模型

AlGaN/GaN HEMT外部边缘电容Cofd是由栅极垂直侧壁与二维电子气水平壁之间的电场构成的等效电容.本文基于保角映射法对Cofd进行物理建模,考虑沟道长度调制效应,研究外部偏置、阈值电压漂移和温度变化对Cofd的影响:随着漏源偏压从零开始增加,Cofd先保持不变再开始衰减,其衰减速率随栅源偏压的增加而减缓;AlGaN势垒层中施主杂质浓度的减小和Al组分的减小都可引起阈值电压的正向漂移,正向阈值漂移会加强沟道长度调制效应对Cofd的影响,导致Cofd呈线性衰减.在大漏极偏压工作情况下,Cofd对器件工作温度的变化更加敏感.     

Aerial Video Trackers Review

Target tracking technology that is based on aerial videos is widely used in many fields; however, this technology has challenges, such as image jitter, target blur, high data dimensionality, and large changes in the target scale. In this paper, the research status of aerial video tracking and the characteristics, background complexity and tracking diversity of aerial video targets are summarized. Based on the findings, the key technologies that are related to tracking are elaborated according to the target type, number of targets and applicable scene system. The tracking algorithms are classified according to the type of target, and the target tracking algorithms that are based on deep learning are classified according to the network structure. Commonly used aerial photography datasets are described, and the accuracies of commonly used target tracking methods are evaluated in an aerial photography dataset, namely, UAV123, and a long-video dataset, namely, UAV20L. Potential problems are discussed, and possible future research directions and corresponding development trends in this field are analyzed and summarized.     

Monte Carlo simulations on magnetic behavior of a spin-chain system in triangular lattice doped with antiferromagnetic bonds

A three-dimensional Ising-like model doped with anti-ferromagnetic (AFM) bonds is proposed to investigate the magnetic properties of a doped triangular spin-chain system by using a Monte-Carlo simulation. The simulated results indicate that a steplike magnetization behavior is very sensitive to the concentration of AFM bonds. A low concentration of AFM bonds can suppress the stepwise behavior considerably, in accordance with doping experiments on Ca₃Co₂O₆. The analysis of spin snapshots demonstrates that the AFM bond doping not only breaks the ferromagnetic ordered linear spin chains along the hexagonal c-axis but also has a great influence upon the spin configuration in the ab-plane.      

聚酰亚胺薄膜表面粗糙度的影响因素

 采用热蒸发气相沉积聚合方法（VDP）制备了聚酰亚胺(PI)薄膜,研究了设备、衬底温度、升温过程和单体配比因素对PI薄膜表面形貌的影响。利用干涉显微镜和扫描电镜对薄膜表面形貌进行了分析;利用原子力显微镜测定了薄膜表面粗糙度。结果表明：设定蒸发源-衬底距离为74 cm时可成连续膜;蒸发源采用一段升温和多段升温时,膜表面均方根粗糙度分别为291.23 nm和61.99 nm;采用细筛网可防止原料的喷溅;均苯四甲酸二酐和4,4′-二氨基二苯醚（PMDA和ODA）单体沉积速率比值为0.9∶1时,膜表面均方根粗糙度值可减小至3.30 nm;沉积衬底温度保持30 ℃左右时,膜表面均方根粗糙度为4.01 nm, 随温度的上升,膜表面质量会逐渐变差。