Using airborne laser scanning to monitor tree migration in the boreal-alpine transition zone

The boreal tree line is expected to advance upwards into the mountains and northwards into the tundra due to global warming. The major objective of this study was to find out if it is possible to use high-resolution airborne laser scanner data to detect very small trees — the pioneers that are pushing the tree line up into the mountains and out onto the tundra. The study was conducted in a sub-alpine/alpine environment in southeast Norway. A total of 342 small trees of Norway spruce, Scots pine, and downy birch with tree heights ranging from 0.11 to 5.20 m were precisely georeferenced and measured in field. Laser data were collected with a pulse density of 7.7 m^− 2. Three different terrain models were used to process the airborne laser point cloud in order to assess the effects of different pre-processing parameters on small tree detection. Greater than 91% of all trees > 1 m tall registered positive laser height values regardless of terrain model. For smaller trees (< 1 m), positive height values were found in 5-73% of the cases, depending on the terrain model considered. For this group of trees, the highest rate of trees with positive height values was found for spruce. The more smoothed the terrain model was, the larger the portion of the trees that had positive laser height values. The accuracy of tree height derived from the laser data indicated a systematic underestimation of true tree height by 0.40 to 1.01 m. The standard deviation for the differences between laser-derived and field-measured tree heights was 0.11-0.73 m. Commission errors, i.e., the detection of terrain objects — rocks, hummocks — as trees, increased significantly as terrain smoothing increased. Thus, if no classification of objects into classes like small trees and terrain objects is possible, many non-tree objects with a positive height value cannot be separated from those actually being trees. In a monitoring context, i.e., repeated measurements over time, we argue that most other objects like terrain structures, rocks, and hummocks will remain stable over time while the trees will change as they grow and new trees are established. Thus, this study indicates that, given a high laser pulse density and a certain density of newly established trees, it would be possible to detect a sufficient portion of newly established trees over a 10 years period to claim that tree migration is taking place.     

Parametric 3D modeling of young women's lower bodies based on shape classification

Three-dimensional (3D) human body modeling is an important research direction in the field of clothing virtual design. On the basis of 3D human body scanning, this paper studied a method to build a 3D parametric lower body model according to body classification. The research includes three main parts. (1) Anthropometry and body shape classification. We randomly selected 333 young women ages 18–25 years old in Northeast China as the experimental sample. Then we divided the lower body shape into three categories using principal component analysis and K-means clustering. (2) Determination of feature cross sections and points, and reconstruction of feature curves. According to the average values of each body type, we obtained the mean reference body by Euclidean distance method. We determined feature cross sections and points, and extracted the 3D coordinates of the feature points of the mean reference body to reconstruct the feature curves. (3) The surface lofting and establishment of parametric 3D lower body model. According to the shape characteristics of the lower body, we constructed the guiding lines for the crotch and lower limbs, and established parametric lower body models for three body types.Relevance to industry3D human modeling is an important part of garment industry digitization. This research provides an effective way to construct a parametric 3D lower body model. The method offers a reference for the parametric virtual human modeling and virtual fitting of trousers.     

计算机网络安全扫描技术研究

随着互联网技术的发展,网络安全问题日益突出。作为一种主动防御手段,网络安全扫描技术在保护网络安全方面发挥着越来越大的作用。本文主要对主机探测,端口扫描,操作系统探测以及漏洞扫描等四种主要的网络安全扫描技术做了研究。     

Differential equations for a dynamic thermal conductivity experiment

The mathematical model that describes a dynamic thermal conductivity experiment is reconsidered by taking into account the role of thermal expansion. Two differential equations are presented that take into account the various physical phenomena occurring in a long thin rod directly heated by a current pulse. One of the two equations keeps variables space and time completely separate and is particularly useful for computer simulations.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

Isochoric specific heat of sulfur hexafluoride at the critical point: Laboratory results and outline of a spacelab experiment for the d1-mission in 1985

The specific heat at constant volume c_v shows a weak singularity at the critical point. Renormalization group techniques have been applied, predicting a universal critical behavior which has to be experimentally confirmed for different systems. In this paper an experiment is presented to measure the specific heat of SF₆ along the critical isochore (_c=0.737 g·cm^–3), applying a continuous heating method. The results cover a temperature span of –1.5×10^–2< <1.70×10^–2 [=(T–T _c)/T _c] and were strongly affected by gravity effects that emerge in the sample of 1-mm hydrostatic height near the critical point. Using regression analysis, data were fitted with functions of the form c _v/R=A × ¦¦^– + B for the one-phase state and c _v/R=A × ¦¦^– + B for the twophase state. Within their error bounds the critical values (==0.098, A/A=1.83) represent the measurements for the temperature span 3.5×10^{–5< ¦¦<2.0×10 –3}, in good agreement with theoretical predictions. In order to exclude density profiles in the specimen, which are unavoidable in terrestrial experiments due to the high compressibility of fluids at the critical point and the gravity force, a space-qualified scanning ratio calorimeter has been constructed, which will permit long-term c_v measurements under microgravity (-g) conditions. The experiment will be part of the German Spacelab mission in October 1985. The significant features of the apparatus are briefly sketched.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Changes in seebeck coefficient of Pt and Pt 10% Rh after use to 1700°C in High-purity polycrystalline alumina

A technique is presented that enables the effects of temperature on the Seebeck coefficient to be assessed for individual wires. The technique, involving a high-resolution thermoelectric scanning rig and a nonuniform conditioning furnace of known temperature profile, was applied to 0.5-mm-diameter wires of Pt and Pt 10% Rh. Changes were observed in Seebeck coefficient when these wires were used in high-purity twin-bore insulation for up to 200 h at temperatures over the range 500 to 1700°C. Contamination from the insulation was found to be transmitted by a vaporization process, having an activation energy of 3 eV. This caused changes of up to 0.14 V · °C^–1 in Pt and 0.01 V · °C^–1 in Pt 10% Rh. Rhodium transfer to the pure Pt wire changed its Seebeck coefficient by up to 5 V · °C^–1. The consequences of both processes for thermocouple pyrometry are presented.     

X射线透射成像技术原位追踪混凝土吸水过程

为了表征二维混凝土的传输过程,制备厚度为1 mm的混凝土薄片. 采用X射线透射成像（TXR）技术,联合扫描电镜、背散射和能谱分析技术（SEM/BSE/EDS）原位追踪水在2维混凝土薄片中的毛细自吸过程. 测试不同质量分数CsCl溶液对X射线透射图像的增强效果. 结果表明,CsCl能够提高吸水过程中混凝土薄片的TXR图像对比度,使得水在混凝土中的渗流路径更清晰、可辨. 水泥浆体在吸收CsCl后,扫描电子背散射图像的对比度显著增强. 不同位置铯原子的EDS能谱结果验证了TXR技术确定吸水前锋位置的准确性.     

高铝高炉渣系的熔化特性

 为了掌握高Al₂O₃条件下(w(Al₂O₃)为15%以上)高炉渣系的熔化特性,利用差式扫描量热仪分析了不同w(MgO)/w(Al₂O₃)、碱度(R)以及w(Al₂O₃)对高铝高炉渣的熔化温度及熔化热的影响。试验结果表明,炉渣熔化开始温度为1 248～1 291 ℃、熔化结束温度为1 432～1 485 ℃、熔化热为137～211 J/g;当w(Al₂O₃)=15%、高w(MgO)/w(Al₂O₃)时,发生了共晶逆反应,导致高炉炉渣熔化开始温度逐渐降低,但由于高炉炉渣的液相线温度基本未变,所以炉渣熔化结束温度基本未发生改变;w(Al₂O₃)为20%时,随着w(MgO)/w(Al₂O₃)的增加,炉渣中易生成熔点较高的镁铝尖晶石,导致高炉炉渣熔化开始温度逐渐增大,与此同时,炉渣液相线温度逐渐降低,导致炉渣熔化结束温度逐渐降低;随着碱度R的增加,高炉炉渣中生成了具有高熔点的化合物、炉渣的液相线温度升高,使得高炉炉渣的熔化开始温度逐渐增加、炉渣熔化结束温度逐渐升高;随着w(Al₂O₃)的增加,发生了共晶逆反应,故炉渣的熔化开始温度逐渐降低,而随着w(Al₂O₃)的增加,炉渣中键能较大的Al—O键增多,需要在更高温度下才能实现炉渣的最终熔化,即熔化结束温度逐渐增加;随着w(MgO)/w(Al₂O₃)、R以及w(Al₂O₃)的增加,炉渣熔化热逐渐增多。分析认为,随着R的增加,炉渣中有高熔点化合物的生成,熔化热增加;随着炉渣中w(Al₂O₃)的增加,炉渣中Al—O键增多,解聚破坏熔渣结构消耗的热量增多;而随着w(MgO)/w(Al₂O₃)增加,高熔点化合物的生成或熔化开始温度降低,造成熔化热增加。     

扫描速度对硼铸铁气缸套表面钨极氩弧硬化效果的影响

研究了钨极氩弧扫描速度对硼铸铁表面硬化效果的影响规律。结果表明：扫描速度增加,硬化层宽度、深度减小,而硬度提高,裂纹率增大；硬化层硬度沿层深的分布是从表及里由高而低,在过渡区下降缓慢；沿层宽的分布是层中心最高,向两侧逐渐降低,直至硼铸铁基体达到最低值；在保证不出现裂纹的条件下,硬化层表面的最高硬度值可达61．4HRC,硬化层最高显微硬度值可达1156．4HV0．1；硼铸铁材料采用氩弧热源淬火时,淬硬层与基体之间过渡区明显,硬化区组织为莱氏体,过渡区为马氏体、残余奥氏体和少量石墨。