A novel approach for computing exact visual hull from silhouettes

Modeling from silhouettes is one of the main technologies for 3D reconstruction in computer vision. The existing methods are generally divided into two classes: volume-based approaches and surface-based approaches. The former are robust for complex objects but inaccurate, while the latter are accurate but time consuming and usually suffer from numerical instabilities. This paper proposes a novel method to compute exact visual hull by taking advantage of surface-based approaches while retaining the simplicity and robustness of volume-based approaches. To this aim, a line-based model is built for each cube on the edge of octree volume structure of object. Convex surface points of visual hull in line-based model are searched by the idea of surface-based approaches. Experiments with real data are conducted to test the efficiency and exactness of our method.     

重离子碰撞中的核温度

介绍了基于不同近似下的核温度的测量方法。不同测量方法给出的核温度不尽相同,这是因为它们使用的基本假设不一样。讨论了原子核系统的特殊性,这些特殊性使得核温度的提取特别困难。重点比较了动力学近似的几种温度计:使用经典Maxwell-Boltzmann 近似的,和使用量子Fermi-Dirac近似的。使用氦锂温度计对照考虑费米子属性后的斜率温度计和涨落温度计,发现考虑费米属性后提取的核温度更接近于热力学温度。仍需更多的工作,从核体系的孤立性、有限性和费米子属性等方面来研究核系统热力学温度的提取方法。Nuclear thermometers based on different approaches are reviewed. Due to the different basic assumptions of these methods, the nuclear temperatures extracted by different thermometer approaches are not consistent. Moreover,several problems which make the extraction of the nuclear temperatures even more difficult are discussed. The nuclear thermometers based on different kinetic approaches are compared. The nuclear temperatures extracted by methodsbased on quantum (Fermi-Dirac) kinetic approaches are compared to the double ratio temperatures THe; Li. Perspectives for future investigations of the thermal temperature are given.     

On unique predictions for single spin azimuthal asymmetry

Theoretically there are two approaches to predict single spin azimuthal asymmetries. One is to take transverse momenta of the partons into account by using transverse momentum dependent parton distributions, while another is to take asymmetries as twist-3 effects. The non-perturbative effects in these approaches are parameterized with different matrix elements, and predictions can be different. Recently, gauge invariant definitions of transverse momentum dependent parton distributions were derived. With these definitions it can be shown that there are relations between non-perturbative matrix elements in these two approaches. These relations may enable us to unify two approaches and to have unique predictions for single spin azimuthal asymmetries. In this letter we derive these relations by using time-reversal symmetry and show that even with these relations the single spin azimuthal asymmetry in a Drell-Yan process is predicted differently in different approaches.Received: 2 July 2004, Published online: 24 September 2004     

A comparison of different approaches to integrate flamelet tables with presumed-shape PDF in flamelet models for turbulent flames

Flamelet models for turbulent combustion modelling make use of presumed-shape probability density functions (PDFs) for integrating laminar flamelet solutions to obtain an integrated flamelet table that can readily be used for turbulent flame calculations. The existence of non-unique approaches for such an integration has rarely been investigated before. For the first time, this work studies systematically the non-uniqueness of the flamelet table integration approaches. A flamelet model called the flamelet/progress variable model is used in the study, although the issue exists generally in many other flamelet models. Two classes of table integration approaches are investigated, one preserving the laminar flamelet structures during integration and the other not. Three different table integration approaches are examined and compared in detail to provide a thorough understanding of the different approaches. A partially stirred reactor is used as a test case for examining the different approaches. A method based on the transported PDF method is also employed to provide a reference for the assessment of the different flamelet table integration approaches. It is found in general that the flamelet preserving integration approach yields a more reasonable joint PDF of the mixture fraction and the progress variable, and the prediction results are closer to the referenced transported PDF results.     

Ship recognition via its radiated sound: the fractal based approaches

Due to the complexity of its radiated sound, ship recognition is difficult. Fractal approaches are proposed in this study, including fractal Brownian motion based analysis, fractal dimension analysis, and wavelet analysis, to augment existing feature extraction methods that are based on spectrum analysis. Experimental results show that fractal approaches are effective. When used to augment two traditional features, line and average spectra, fractal approaches led to better classification results. This implies that fractal approaches can capture some information not detected by traditional approaches alone.     

消毒灭菌的电离辐射与电磁辐射等物理技术比较分析北大核心CSCD

消毒灭菌技术广泛应用于食品工业、医疗领域、水处理等方面。相对于传统化学和热效应的消毒灭菌方法,γ射线、X射线、电子束、微波、低温等离子体、紫外线、高压脉冲电场等物理手段具有不污染环境、消毒灭菌温度低、没有化学残留物等优点而日益受到重视。但这些物理技术手段各有不同,本文首先介绍了γ射线、X射线、电子束、微波、低温等离子体、紫外线、高压脉冲电场等消毒灭菌的技术原理,然后对比了各自优缺点和应用领域。每种方法都有优势和不足,应针对不同的消毒灭菌对象而选择不同的方式。最后,展望了消毒灭菌的发展方向,提出了消毒灭菌在家庭日常消毒、医疗垃圾处理、有人状态下的室内空气消毒等方面的迫切需求。     

Analysis of current-voltage characteristics of inhomogeneous Schottky diodes at low temperatures

Two approaches of Gaussian distribution of barrier heights in inhomogeneous Schottky diodes have been analyzed by comparing the results for consistency between the two. For this the current-voltage characteristics of inhomogeneous Schottky diodes have been generated by using analytically solved thermionic-emission diffusion equation incorporating Gaussian distribution of barrier heights and by direct numerical integration over a barrier height range. The differences in the results obtained in two approaches are discussed and it is shown that the two approaches yield current-voltage characteristics with slightly different features. The discrepancies in the results obtained in two approaches are attributed to the same series resistance assumed for all elementary barriers of the distribution. It is shown that assigning same series resistance to all barrier of the distribution in numerical integration approach causes current saturation at low bias and inhibits intersection of current-voltage curves from being observable which otherwise occurs in the curves obtained using analytical equation. The paper deals with these aspects in details.     

Numerical approaches to fractional calculus and fractional ordinary differential equation

Nowadays, fractional calculus are used to model various different phenomena in nature, but due to the non-local property of the fractional derivative, it still remains a lot of improvements in the present numerical approaches. In this paper, some new numerical approaches based on piecewise interpolation for fractional calculus, and some new improved approaches based on the Simpson method for the fractional differential equations are proposed. We use higher order piecewise interpolation polynomial to approximate the fractional integral and fractional derivatives, and use the Simpson method to design a higher order algorithm for the fractional differential equations. Error analyses and stability analyses are also given, and the numerical results show that these constructed numerical approaches are efficient.     

红外区Dyson-Schwinger方程的两种重整化方案的比较

在胶子和鬼传播子所满足的耦合的Dyson-Schwinger方程中, 采用裸胶子－鬼顶点, 利用两种重整化方案: 解析延拓方法和减除方法, 得到了胶子和鬼传播子的红外行为. 计算表明两种重整化方案在红外区对胶子和鬼传播子得到一致的结果.     

Non-Markovian random unitary qubit dynamics

We compare two approaches to non-Markovian quantum evolution: one based on the concept of divisible maps and the other one based on distinguishability of quantum states. The former concept is fully characterized in terms of local generator whereas it is in general not true for the latter one. A simple example of random unitary dynamics of a qubit shows the intricate difference between those approaches. Moreover, in this case both approaches are fully characterized in terms of local decoherence rates.     

极化中子照相磁场量化技术方案比较与分析

极化中子照相技术通过分析极化中子束的自旋相移对样品磁场进行成像,目前已发展出多种成像技术方案,其中能量选择法和自旋回波法极化中子成像技术从不同的原理出发,解决了极化中子照相中磁场量化的周期解问题,同时避免装置极化效率等参数的影响,可以实现较高的量化精度.本文对两种极化中子照相技术方案进行研究,通过对单色器能量分辨率和装置极化效率等关键参数的分析和模拟,确定在研究堆上开展相关实验的可行性,并初步明确其量化能力和适用范围.相关结果可为极化中子照相的实验数据处理技术研究及装置设计提供参考.     

Novel Light Source Integration Approaches for Silicon Photonics

Silicon does not emit light efficiently, therefore the integration of other light‐emitting materials is highly demanded for silicon photonic integrated circuits. A number of integration approaches have been extensively explored in the past decade. Here, the most recent progress in this field is reviewed, covering the integration approaches of III‐V‐to‐silicon bonding, transfer printing, epitaxial growth and the use of colloidal quantum dots. The basic approaches to create waveguide‐coupled on‐chip light sources for different application scenarios are discussed, both for silicon and silicon nitride based waveguides. A selection of recent representative device demonstrations is presented, including high speed DFB lasers, ultra‐dense comb lasers, short (850nm) and long (2.3μm) wavelength lasers, wide‐band LEDs, monolithic O‐band lasers and micro‐disk lasers operating in the visible. The challenges and opportunities of these approaches are discussed.     

Decay amplitudes and resonances

The structure of a type of decay amplitudes, which we considered recently and its connection to scattering amplitudes (of arbitrary arrangement channel cases), to conventional decay amplitudes, and to the energy distribution is worked out in detail. The meaning of unperturbed energies in usual approaches is clarified. Our considerations include the case of overlapping resonances. Sum rules for transition amplitudes, such as are of interest for neutral kaon decays, are rigorously derived. The exact interrelations between various approaches are shown.     

现阶段末制导红外成像跟踪系统性能提高的技术途径

提出现阶段提高末制导红外成像跟踪系统性能的几个主要技术途径：变帧频技术、非均匀性校正技术、识别与跟踪技术等．并探讨其实现方法。     

Comparison of subset-based local and FE-based global digital image correlation: Theoretical error analysis and validation

Subset-based local and finite-element-based (FE-based) global digital image correlation (DIC) approaches are the two primary image matching algorithms widely used for full-field displacement mapping. Very recently, the performances of these different DIC approaches have been experimentally investigated using numerical and real-world experimental tests. The results have shown that in typical cases, where the subset (element) size is no less than a few pixels and the local deformation within a subset (element) can be well approximated by the adopted shape functions, the subset-based local DIC outperforms FE-based global DIC approaches because the former provides slightly smaller root-mean-square errors and offers much higher computation efficiency. Here we investigate the theoretical origin and lay a solid theoretical basis for the previous comparison. We assume that systematic errors due to imperfect intensity interpolation and undermatched shape functions are negligibly small, and perform a theoretical analysis of the random errors or standard deviation (SD) errors in the displacements measured by two local DIC approaches (i.e., a subset-based local DIC and an element-based local DIC) and two FE-based global DIC approaches (i.e., Q4-DIC and Q8-DIC). The equations that govern the random errors in the displacements measured by these local and global DIC approaches are theoretically derived. The correctness of the theoretically predicted SD errors is validated through numerical translation tests under various noise levels. We demonstrate that the SD errors induced by the Q4-element-based local DIC, the global Q4-DIC and the global Q8-DIC are 4, 1.8–2.2 and 1.2–1.6 times greater, respectively, than that associated with the subset-based local DIC, which is consistent with our conclusions from previous work.     

Truncated Hamiltonian versus surface perturbation in nonlinear wave theories

Two fundamentally different theories on nonlinear surface waves are scrutinized. The first is a Stokes-like perturbation about a mean equilibrium level. The second is a perturbation about the surface itself by truncation of the Hamiltonian which relates two canonical variables: the velocity potential and the surface elevation. Both perturbation approaches are carefully generalized to include effects from both surface tension and fluid depth. It is found that either the velocity potential or the elevation can be equivalent in the approaches considered but not both variables simultaneously. The resonant condition determines which canonical variable will be equivalent. A clarification is also provided regarding past comparisons between these theories in terms of wave action equations. This study resolves a long-standing controversy as to whether these two approaches are equivalent.     

Gravity with propagating pseudoscalar torsion

The ECSK torsional theory of gravitation admits a new lagrangian term. The term introduces a propagating torsion potential in a manner which seems more motivated than other similar approaches. Also, unlike approaches involving similar new terms, no new physical constants need be introduced. The long-range effects of the new field are very small.     

Acoustic field analysis of detection and location of targets in layered media by time reversal-reverse time migration mixed method

Using the time reversal(TR)-reverse time migration(RTM) mixed method, the numerical analysis towards the acoustic field for detection and location of targets in layered media is performed. First the approaches and steps of the numerical analysis and simulation for acoustic field are proposed, then, the acoustic field distribution of single target and multiple targets are further computed by using the approaches of single emission-multiple receiving and multiple emission-multiple receiving. The numerical simulation results indicate that target detection and location can be well realized. By comparison, good results are obtained from the both two approaches, but large time-consuming is observed in way of multiple emission-multiple receiving, and so would be unacceptable. Additionally, the improved way is also proposed for multiple target detection.     

Recent Notable Approaches to Study Self-Assembly of Nanoparticles with X-Ray Scattering and Electron Microscopy

Self-assembly of nanoparticles (NPs) has evolved into a powerful tool for the synthesis of superstructures with tailored properties. The quality, diversity, and complexity of synthesized structures are continuously improving and fascinating new collective properties are demonstrated. At the same time, the rapid development of electron microscopy and synchrotron sources for X-rays has enabled new exciting experimental approaches to study structure and structure formation in the context of NP self-assembly. In this review, some recent studies and what can be learned from them are highlighted and discussed. It is started with a general introduction covering important concepts, experimental approaches, commonly obtained structures, the ideas of artificial atoms, and emerging properties are discussed. Recent experimental in situ and ex situ approaches with state-of-the-art electron microscopy and X-ray diffraction and scattering that helped to obtain a detailed picture of NP self-assembly processes and resulting structures are then presented.