深水压电换能器电声性能的研究

本文通过电换能器的等效机电图,根据压电陶瓷材料的有关参数随压力的变化关系,研究了深水压电换能器在深水高静压力下的电声性能。     

Near-focus high-sensitivity wavefront sensing

A new method of wavefront sensing that uses a pair of equally defocused images to derive the wavefront aberrations is presented. Unlike in conventional curvature-sensing systems, the sensor works in a near-focus regime where the transport of intensity equation is not valid, and, unlike in phase-diversity methods, a non-iterative algorithm is used to infer the wavefront aberrations. The sensor designs outlined only require a small number of detector pixels: two designs with five and nine pixels per plane are analysed, and the nine-element sensor (NES) is shown to have a competitive measurement sensitivity compared with existing low-order astronomical wavefront sensors. The NES is thus well suited to applications such as adaptive optics for the individual telescopes in an optical interferometer array.     

Spatial localization of closeness and betweenness measures: a self-contradictory but useful form of network analysis

Closeness and betweenness are forms of spatial network analysis grounded in a long-standing tradition of measuring accessibility and flow potential. More recently, these measures have been enhanced by the concept of spatial localization, producing effective models for the prediction of pedestrian and vehicle driver behaviour.

A contradiction arises where the distance metric used to define locality does not match the distance metric used to define shortest paths for closeness and betweenness. A typical case is the use of angular shortest paths within a Euclidean buffer as a pedestrian flow model. Such a model assumes that people make a mode choice based on distance, but a route choice based on least angular change – even when this results in an excessively long ‘problem route’, which conflicts with their criterion for mode choice.

This study examines the prevalence of problem routes and the magnitude of their effect on some pedestrian and vehicle models. We show that while in a weighted analysis, pathological cases could invalidate an entire model, in the models presented the effect of this contradiction is minor. We do this by comparing model predictions to real flow data, using four strategies for handling problem routes: ignore, discard, reroute and strict locality. Strict locality is justified on the grounds of bounded rationality. We find all strategies to give broadly similar results, although the reroute and strict strategies give marginally better simulation accuracy. We also present a discussion of the characteristics of each strategy, and findings on computational efficiency.

We conclude that it is prudent in any computation of localized closeness and betweenness to consider the impact of problem routes; however, they do not necessarily invalidate these forms of analysis, which remain useful.     

Reexamination of the Relationship between Tropical Cyclone Size and Intensity over the Western North Pacific

This study reexamines the correlation between the size and intensity of tropical cyclones (TCs) over the western North Pacific from the perspective of individual TCs, rather than the previous large-sample framework mixing up all TC records. Statistics show that the positive size-intensity correlation based on individual TCs is relatively high. However, this correlation is obscured by mixing large samples. The weakened correlation based on all TC records is primarily due to the diversity in the size change relative to the same intensity change among TCs, which can be quantitatively measured by the linear regression coefficient (RC) of size against intensity. To further explore the factors that cause the variability in RCs that weakens the size-intensity correlation when considering all TC records, the TCs from 2001 to 2020 are classified into two groups according to their RC magnitudes, within which the high-RC TCs have a larger size expansion than the low-RC TCs given the same intensity change. Two key mechanisms responsible for the RC differences are proposed. First, the high-RC TCs are generally located at higher latitudes than the low-RC TCs, resulting in higher planetary vorticity and thus higher planetary angular momentum import at low levels. Second, the high-RC TCs are susceptible to stronger environmental vertical wind shear, leading to more prolific outer convection than the low-RC TCs. The positive feedback between outer diabatic heating and boundary layer inflow favors the inward import of absolute angular momentum in the outer region, thereby contributing to a larger size expansion in the high-RC TCs.     

Hopes and expectations with GREGOR

This contribution to the series of GREGOR inauguration articles addresses the history of the GREGOR telescope. It was obvious since a long time that the study of the atmospheric dynamics on the Sun needs telescopes with a large aperture. So the first plans to replace the 40 years old Gregory‐Coudé Telescope, with its 45 cm primary mirror, by a large, 1.5‐meter telescope date back to 1997. After a positive review of the project by the Deutsche Forschungsgemeinschaft in 2000, the large financial support started in 2000. Unfortunately, the new technology of the Cesic mirrors was not yet ripe to produce the large primary mirror with this light‐weight material. So, the project was much delayed. After recollecting for the reader several dates, I also go through some properties of GREGOR. I recall the aims of the project and discuss difficulties and ways to realise the intentions (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A retrospective of the GREGOR solar telescope in scientific literature

In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post‐focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer‐reviewed journals and conference proceedings also provides the “historical” context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

机械式自动垂钻工具偏重机构角位置测量方法研究

机械式自动垂直钻具在实际应用过程中,偏重机构由于自身的惯性以及外部环境的影响,会出现不能稳定在井眼低边的情况,导致纠斜精度降低。为研究偏重机构在钻进过程中角位置的变化规律,本文提出了基于绝对式磁编码器的一种非接触式的角位置测量方法,构建了测量数据采集界面并进行了实验室验证及可靠性分析。该方法可有效地实现偏重机构变化角度的测量,测量误差不超过3°。非接触式的角位置测量方法能够监测角位移且其误差在工程允许的误差范围内,可以为后续的机械式垂直钻井系统的研发实验和改进优化提供可靠的数据。     

基于改进的角度偏差法的采空区点云数据精简

在保证采空区几何特征不变的前提下,有必要对点云数据进行精简,提高三维建模及其应用的效率。介绍了点云数据精简算法的评价体系,探讨了空区探测系统扫测采空区的点云数据特点;在对比最小距离法、平均距离法、角度偏差法、弦高偏差法等采空区点云数据精简方法的基础上,提出了保留采空区几何特征更为有效的点云数据精简方法——改进的角度偏差法。通过对比精简前后的扫描线周长、面积及标准差等指标,认为该方法不但保持了扫描线的细节,而且使精简后扫描线上的点分布较均匀,为后续三维建模及应用打下良好基础。     

Blind Deconvolution of Astronomical Images with a Constraint on Bandwidth Determined by the Parameters of the Optical System

Atmospheric turbulence severely restricts the spatial resolution of astronomical images obtained by a large ground-based telescope. In order to reduce effectively this effect, we propose a method of blind deconvolution, with a bandwidth constraint determined by the parameters of the telescope's optical system based on the principle of maximum likelihood estimation, in which the convolution error function is minimized by using the conjugate gradient algorithm. A relation between the parameters of the telescope optical system and the image's frequency-domain bandwidth is established, and the speed of convergence of the algorithm is improved by using the positivity constraint on the variables and the limited-bandwidth constraint on the point spread function. To avoid the effective Fourier frequencies exceed the cut-off frequency, it is required that each single image element (e.g., the pixel in the CCD imaging) in the sampling focal plane should be smaller than one fourth of the diameter of the diffraction spot. In the algorithm, no object-centered constraint was used, so the proposed method is suitable for the image restoration of a whole field of objects. By the computer simulation and by the restoration of an actually-observed image of α Piscium, the effectiveness of the proposed method is demonstrated.     

内核地球自转动力学理论的研究进展--Ⅲ液核自转动力学方程

本文是序列文章的第三篇,其内容包括：基于连续介质力学的基本理论,给出了液体外核（FOC）两种形式的角动量方程,对作用在FOC上外力矩进行了详细研究,同时对液核作用在固体内核（SIC）上的压力产生的压力矩进行了讨论,在O(ms)的量级上给出了它们的表达式.本文改正了文献〔1〕在推导过程中的某些错误（例如：（B18）、（B28）、（B29）、（B30）、（B35a）和（B35b）式）.本文是对文献〔1〕有关理论的扩展和改进,对进一步研究内核地球自转的动力学理论是非常重要的.