浅谈速写的有关概念及其重要性

结合教学实践经验,重点澄清当代艺术教学中对速写概念的一些模糊理解,探讨它的定义与范畴,简介其在人类艺术文化领域等方面发挥的重要作用。     

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.     

A calibration method for the energy-integrating function in photovoltaic system monitoring

Solar radiation has an irregularly varying factor due to a basic day and night cycle and climatic conditions. For such conditions a data sampling interval is important to ensure the accuracy of energy monitoring in a photovoltaic system. While treating a system monitoring equipment as a black box. the author has developed the method of calibrating an energy-integrating function. At first for various input waveforms, the relationship between sampling intervals and quasi-integration outputs have been examined by trapezoidal rule. In the numerical simulation the phases of the sampling clock also are considered Then it is concluded that a sampling interval can be inspected through outside observation only by using a rectangular single pulse. By applying the pulse to the energy-integrating process, two kinds of integrated outputs can be obtained for different sampling phases. The calculated difference between both outputs can uniquely give the sampling interval being inspected. Conditions to ensure measuring accuracy are discussed and the validity of this method has been demonstrated experimentally. Practical calibrating procedures also are proposed for the integrating function of PV system monitoring.     

集成电路测试系统中波形数字化仪的校准研究

文章介绍了波形数字化仪的原理、结构、工作方式及特点,并针对其校准技术进行了深入的研究。通过多功能校准源、示波器及测试系统数字模块实现波形数字化仪模块的精确校准,解决了波形数字化仪模块的校准问题。校准结果表明,该校准装置及校准方法能够满足集成电路测试系统任意波形发生器的校准要求。     

GemstoneFire: adaptive dispersive ray tracing of polyhedrons

Synthesizing realistic images of gemstones requires techniques beyond the scope of normal ray tracing. The fire of such highly refractive objects is what makes gemstones attractive, and also imposes very high computational overhead to perform time consuming dispersive ray tracing. Gemstones are usually cut in polyhdrons as for example, a brillant cut. After a detailed analysis of the nature of dispersive ray tracing of polyhedral objects, we propose here a new method of using three simple rays adaptively to model the ray spreading caused by dispersive refraction. It is shown that the proposed method reduces the computational complexity to an order close to that of normal ray tracing.     

Accurate Receptor-Ligand Binding Free Energies from Fast QM Conformational Chemical Space Sampling

Small molecule receptor-binding is dominated by weak, non-covalent interactions such as van-der-Waals hydrogen bonding or electrostatics. Calculating these non-covalent ligand-receptor interactions is a challenge to computational means in terms of accuracy and efficacy since the ligand may bind in a number of thermally accessible conformations. The conformational rotamer ensemble sampling tool (CREST) uses an iterative scheme to efficiently sample the conformational space and calculates energies using the semi-empirical ‘Geometry, Frequency, Noncovalent, eXtended Tight Binding’ (GFN2-xTB) method. This combined approach is applied to blind predictions of the modes and free energies of binding for a set of 10 drug molecule ligands to the cucurbit[n]urils CB[8] receptor from the recent ‘Statistical Assessment of the Modeling of Proteins and Ligands’ (SAMPL) challenge including morphine, hydromorphine, cocaine, fentanyl, and ketamine. For each system, the conformational space was sufficiently sampled for the free ligand and the ligand-receptor complexes using the quantum chemical Hamiltonian. A multitude of structures makes up the final conformer-rotamer ensemble, for which then free energies of binding are calculated. For those large and complex molecules, the results are in good agreement with experimental values with a mean error of 3 kcal/mol. The GFN2-xTB energies of binding are validated by advanced density functional theory calculations and found to be in good agreement. The efficacy of the automated QM sampling workflow allows the extension towards other complex molecular interaction scenarios.     

一种联合采样的神经网络光场

相比传统的光场绘制技术,神经网络光场(NeRF)方法可使用神经网络拟合场景的光线采样,将隐式编码输入图片的光场,合成新视图. 针对NeRF方法训练时间长,绘制视图慢的问题,提出了一种基于联合采样的NeRF方法,通过使粗糙网络和细腻网络共享均匀采样结果的方法,减少了不必要的光线采样,从而加快了网络训练和视图合成的速度. 实验结果表明,在取得近似视图合成质量的情况下,与NeRF方法相比,所提方法的训练时间减少了20%,视图合成的效率提高了25%.     

交流电量的实时检测技术及实现

针对电力参数的实时高精度检测难题，介绍了一种用于交流电量(电压、电流、有功功率、功率因数、频率等)的采用双速率同步交流采样算法的实时自动检测技术。该系统基于16位单片机，以交流电量为检测对象，通过对工频的跟踪检测和双速率同步交流采样算法，提高系统的检测精度。文中阐述了该技术的原理、硬件实现和软件设计。经过实践证明，该技术在电力系统的智能检测中有很大的应用前景。     

点扩展函数与采样频率及量化精度对图像边缘的影响分析

文章在建立理想边缘成像模型的基础上,分析研究了一般成像系统的点扩展函数与空间采样频率的关系及对图像边缘定位精度的影响,给出了边缘定位误差.同时,还分析研究了量化精度对图像边缘的移位影响,给出了移位误差.最后,给出了本文的分析研究在零件视觉精密检测的应用情况.     

Multivehicle coverage control for a nonstationary spatiotemporal field

This paper presents a multivehicle sampling algorithm to generate trajectories for nonuniform coverage of a nonstationary spatiotemporal field characterized by spatial and temporal decorrelation scales that vary in space and time, respectively. The sampling algorithm described in this paper uses a nonlinear coordinate transformation that renders the field locally stationary so that existing multivehicle control algorithms can be used to provide uniform coverage. When transformed back to the original coordinates, the sampling trajectories are concentrated in regions of short spatial and temporal decorrelation scales. For fields with coupled spatial statistics, i.e., the spatial decorrelation scales are functions of both spatial dimensions, the coordinate transformation is implemented numerically, whereas for decoupled spatial statistics, the transformation is expressed analytically. We show that the analytical transformation results in vehicle motion that preserves the vehicle sampling speed (which is a measure of vehicle speed scaled by the ratio of the spatial and temporal decorrelation scales), in the original domain; the sampling speed determines the minimum number of vehicles needed to cover a spatiotemporal domain. Theoretical results are illustrated by numerical simulations.