基于激光扫描技术的三维模型重建

通过分析三维激光扫描系统获取的点云数据,得到了利用点云数据构建三维模型的技术、方法和流程。介绍了利用地面三维激光扫描仪获取点云数据的过程以及结合RiSCAN PRO软件和Geomagic Studio软件进行建模的方法。对原始测量的点云数据进行处理(去除噪声,平滑,对多站点数据做拼接配准,提取目标建筑物等)得到正确和完整的目标建筑物的表面信息,然后构建三角网建立它的三维表面模型,最后通过所拍的照片进行纹理映射得到真实的三维模型。实验结果表明,利用上述方法可以有效地处理三维激光扫描获取的点云数据,实现对建筑物快速三维可视化建模。     

TEE EFFECT OF EXTENDED THIN FILM EVAPORATION DURING TEE CONSTANT DRYING RATE PERIOD

The extended thin film evaporation is analyzed during the constant drying rate period. The extended thin film is defined as the liquid film which the disjoining pressure dominates the fluid flow field and works as the driving force of replenishing the evaporating liquid. The results of the analysis show that the extended thin film evaporation can compensate the reduction of evaporation rate due to the increase of dry spots and keep the evaporation rate nearly constant. Experimental data in the literature are in good agreement with the results of this work. This implies that the extended thin film evaporation may be an important part of the mechanism for drying.     

The influences of technological conditions and Au cluster islands on morphology of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires grown by VLS method on GaAs substrate

The synthesis of semiconductor nanowires is more and more interested to the applications for building blocks of the innovative nano-sized devices and circuits, but the research and fabrication of these nanowires are also holding a number of difficulties and challenges. Among many different kinds of semiconductor nanowires, Ga₂O₃ is increasingly grown for many promising applications in nano-device production, namely nanowire LED and Laser. So far there are many synthesizing methods of semiconductor nanowires, among them the vapor–liquid–solid (VLS) method is simple, cheap and popular. However, when we use the VLS method for nanowire growth, various technological problems exist. This paper aims at investigating some influences of the growth technological conditions and Au metal catalyst on the morphology of Ga₂O₃ nanowire grown by VLS on GaAs substrate. The main considering factors include the different growing temperatures and times, the effects of Au diffusion, Au droplets formation, Au cluster islands formation, and gas volume of the growing tube/ampoule at the 10⁻¹ torr low air pressure. The obtained experimental results regarding the structural properties of nanowires under these effects investigated by scanning electron microscopy, field emission scanning electron microscopy, high angle annular dark field and bright field, scanning transmission electron microscopy, energy-dispersive X-ray techniques, and focus ion beam are presented and discussed.     

Weakly Binding Molecules-Based Fast Charging Li-Ion Batteries

Fast charging of Li-ion batteries (LIBs) beyond standard 0.3 C (charged in 3.3 h) are desperately pursued but hindered by sluggish desolvation kinetics of ethylene carbonate-based traditional electrolyte, and Li-plating and dendrites growth at graphite anode and fire hazard. Herein, a new class of weakly binding all linear molecules-based nonflammable electrolyte (WNLE) is reported, comprising 1 m LiPF₆ in ethyl methyl carbonate and 2,2,2-trifluoroethyl acetate with additives for 10–20 times faster charging LIBs than traditional ones. The critical benefits of WNLE are 44% lower viscosity, 62% higher Li⁺ diffusion coefficient, 20% higher Li⁺ transference number, and 17% lower desolvation energy, which promotes diffusion kinetics and desolvation kinetics of Li⁺ in the vicinity of graphite anode enabling dendrites-free LIB, along with nonflammability. Under 3 C (charged in 20 min), WNLE-based industrial 800 mAh graphite//LiNi_0.8Mn_0.1Co_0.1O₂ (high active mass 13 mg cm⁻²) Li-ion pouch battery achieves outstanding 700 cycles, delivering 82% capacity retention and high Coulombic efficiencies ≈100%. Robust solid electrolyte interphase layers formed at the anode and cathode mitigate interfacial failures, making fast charge to 7 C and longer cycle-life. This new class of electrolyte formulation is a promising solution and a new opportunity to realize safe and long operation of fast-charging LIBs for practical applications.     

The thermal diffusivity and conductivity of transformation-toughened solid solutions of alumina and chromia

The thermal diffusivity of a series of solid solutions of alumina and chromia transformation toughened with a dispersed phase of unstabilized zirconia was measured by means of the laser-flash method from room temperature to 1400° C. It was found, in general, that the thermal diffusivity could be decreased significantly by the combined effects of solid solution alloying, microcracking and by the presence of the low conductivity dispersed phase of zirconia. The decrease in thermal diffusivity by microcracking was found to be present in the solid solution with low chromia content which underwent extensive grain growth. The effectiveness of solid solution formation and microcracking on thermal diffusivity was found to be greatest at the lower and intermediate ranges of temperature. The decrease in the thermal diffusivity due to the zirconia inclusions was found to be effective over the total temperature range. A numerical example is presented for the thermal conductivity calculated from the thermal diffusivity multiplied by the volumetric heat capacity.     

On the effects of a spacecraft subcarrier unbalanced modulator

This paper presents mathematical models with associated analysis of the deleterious effects which a spacecraft's subcarrier unbalanced modulator has on the performance of a phase-modulated residual carrier communications link. The undesired spectral components produced by the phase and amplitude imbalances in the subcarrier modulator can cause (1) potential interference to the carrier tracking and (2) degradation in the telemetry bit signal-to-noise ratio (SNR). A suitable model for the unbalanced modulator is developed and the threshold levels of undesired components that fall into the carrier tracking loop are determined. The distribution of the carrier phase error caused by the additive White Gaussian noise (AWGN) and undesired component at the residual RF carrier is derived for the limiting cases. Further, this paper analyses the telemetry bit signal-to-noise ratio degradations due to undesirable spectral components as well as the carrier tracking phase error induced by phase and amplitude imbalances. Numerical results which indicate the sensitivity of the carrier tracking loop and the telemetry symbol-error rate (SER) to various parameters of the models are also provided as a tool in the design of the subcarrier balanced modulator.     

The effects of substrate bias,substrate temperature,and pulse frequency on the microstructures of chromium nitride coatings deposited by pulsed direct current reactive magnetron sputtering

Recently, great attention has been devoted to the pulsed direct current (DC) reactive magnetron sputtering technique, due to its ability to reduce arcing and target poisoning, and its capability of producing insulating thin films. In this study, chromium nitride (CrN) coatings were deposited by the bipolar symmetric pulsed DC magnetron reactive sputtering process at different pulse frequency, substrate bias voltage, and the substrate temperature. It was observed that the texture of CrN changed from (111) to (200) as substrate temperature increased to 300°C as deposited at 2 kHz without substrate bias. With increasing pulsing bias and pulse frequency of target, predominated (200) orientation of CrN film was shown due to the ion bombardment/channeling effect to preferentially sputter those unaligned planes. For the CrN coatings deposited with pulsed biasing, the grain size decreased with increasing pulse frequency and substrate bias, whereas the surface roughness showed a reverse trend. The deposition rate of the CrN films decreased with increasing pulse frequency. It was concluded that the pulse frequency, substrate bias, and substrate temperature played important role in the texture, microstructure, and surface roughness of the CrN coatings deposited by the pulsed DC magnetron sputtering process.     

An availability model for MIN-based multiprocessors

System decomposition is a novel technique for modeling the dependability of complex systems without constructing a single-level Markov Chain (MC). This is demonstrated in this paper for the availability computation of a class of multiprocessors that uses 4×4 switching elements for the multistage interconnection network (MIN). The availability model is known as task-based availability, where a system is considered operational as long as the task requirements are satisfied. The authors develop two simple MC's for the processors and memories and solve them using a software package, called HARP. The probabilities of i processing elements (PE's) and j memory modules (MM's) working at any time t, denoted as Pi(t) and Pj(t), are obtained from their corresponding MC's. The effect of the MIN is captured in the model by finding the number of switches required for the connection of i PE's and j MM's. A third MC is then developed for the switches to find the probability that the MIN provides the required (i×j) connection. Multiplying this term with Pi(t) and Pj(t), the probability of an (i×j) working group is obtained. The methodology is generalized to model arbitrary as well as larger size systems. Transient and steady state availabilities are computed for a variety of MIN configurations and the results are validated through simulation