Geometric transformations on the hexagonal grid

The hexagonal grid has long been known to be superior to the more traditional rectangular grid system in many aspects in image processing and machine vision related fields. However, systematic developments of the mathematical backgrounds for the hexagonal grid are conspicuously lacking. The purpose of this paper is to study geometric transformations on the hexagonal grid. Formulations of the transformation matrices are carried out in a symmetrical hexagonal coordinate frame. A trio of new trigonometric functions are defined in this paper to facilitate the rotation transformations. A fast algorithm for rounding an arbitrary point to the nearest hexagonal grid point is also presented.     

Indexing the aperture 3 hexagonal discrete global grid

Over the past decade there has been interest in the computer representation of global data based on multi-resolution subdivisions of regular polyhedra. A simple and efficient indexing of the cells of such a subdivision, called A3-coordinates, is introduced. These can be used to encode the 4 · 3ⁿ + 2 cells at the nth level of resolution of the octahedral aperture 3 hexagonal discrete global grid using n + 3 digits, each digit from the set {−1, 0, 1}.     

Efficient backward selection ofk-space samples in MRI on a hexagonal grid

Certain types of magnetic resonance imaging (MRI) such as magnetic resonance spectroscopic imaging and three-dimensional (3D) MRI require a great deal of time to acquire the image data. The acquisition time can be reduced if the image has a limited region of support, such as when imaging the brain or a cross section of the chest. Hexagonal sampling of the spatial frequency-domain (k-space) yields a 13.4% sampling density reduction compared to rectangular sampling of thek-space for images with a circular region of support (ROS) without incurring spatial aliasing in the reconstructed image. However, certain nonuniform sampling patterns are more efficient than hexagonal sampling for the same ROS. Sequential backward selection (SBS) has been used in previous work to optimize a nonuniform set ofk-space samples selected from a rectangular grid. To reduce the selection time, we present SBS of samples from a hexagonal grid. A Smith normal decomposition is used to transform the nonrectangular 2D discrete Fourier transform to a standard rectangular 2D fast Fourier transform so that the spatial-domain samples are represented directly on a rectangular grid without interpolation. The hexagonal grid allows the SBS algorithm to begin with a smaller set of candidate samples so that fewer samples have to be eliminated. Simulation results show that a significantly reduced selection time can be achieved with the proposed method in comparison with SBS on a rectangular grid.This work was supported by a Biomedical Engineering Research Grant from the Whitaker Foundation.     

A generalized methodology for the gridding of microarray images with rectangular or hexagonal grid

Microarrays provide a simple way to measure the level of hybridization of known probes of interest with one or more samples under different conditions. The rapid development of microarray technology requires the implementation of smart and flexible algorithms to deal either with the great amount of data or with the variations of the used hardware. In this paper, a generalized methodology for spot addressing and gridding of microarray images is presented. The methodology can cope with both rectangular and hexagonal grids, which are used for the probes placement onto the substrate. Initially, the methodology identifies the structure of the image, and an efficient spot-by-spot approach has been developed for the detection of all spots in the image. The evaluation of the methodology was performed using both rectangular and hexagonal structured images, merged in a single dataset. The methodology results in high accuracy in the spots detection, ranging from 92.8 to 99.8 % depending on the dataset used.     

Getting a grip on the grid

When accidents occur in the systems that comprise an interconnected electric power grid, these accidents must be regarded as the symptom of inadequate grid design and management. As such, there is an urgent need for cross-regional reforms so that the best available technology is promptly put to use, without lengthy delays arising from the legislative or regulatory process. The reform process needs to recognize that all interconnected systems will experience major blackouts if operated outside intended design limits. Ultimately, end users must accept the price for reliability or the consequence of unavailability.     

Studies on grid emission

This paper is concerned only with the study of primary grid emission of various types of grid materials resulting from the evaporation products of L, impregnated, oxide-coated, and thoriated tungsten cathodes. The factors contributing to grid emission are analyzed. A detailed discussion of the performance of titanium, which exhibits excellent grid emission inhibiting properties, is included. In our investigation a planar triode construction was used, the grids of which consisted of a two-terminal loop of 0.010 inch diameter wire. In the assembly and processing utmost precautions were taken to insure minimum contamination of the various elements. The methods of assembly and processing are fully described in the paper. These tubes were tested using pulsed and dc techniques, and a discussion of the testing methods is included. The work function of a tungsten grid exposed to the evaporation products of the L, impregnated, and oxide-coated cathodes varies from 1.2 to 2.0 ev, the final value depending upon the past history of the cathodes, namely, the nature of the surface of the grid and the temperature and length of exposure to the cathodes.     

关于网格中间件的研究

网格中间件是网格关键技术之一。研究的目的是为用户提供具有同一编程接口的虚拟机器,支持复杂应用问题的求解和广域网上各类资源的共享。美国、英国都很重视这方面的研究,NMI中间件计划、Internet2中间件计划都取得了很大进展。设计网格中间件要具备资源动态监测、屏蔽节点异构、优化资源选择和协同计算等功能。网格中间件包括资源监测组件、计算服务组件、网格安全组件、容错服务组件、信息服务组件和应用调度组件。成功的网格中间件典型范例说明,它可以更好地支持系统为用户提供高品质的服务以满足需求。     

网格关键技术论析

信息技术的下一个浪潮高峰是万维网(World Wide Web)升级为网格(Grid)。了解、认识。进而应用网格技术意义重大。网格的关键技术主要有网格硬件、网格操作系统、网格应用层面、网格计算以及其他一些关键技术。     

Visualizing the electric grid

In the new world of competition, power traders, grid managers, public service boards, and the public itself all need to take in what's happening at a glance. Visualization software enables viewers to interpret the data more rapidly and more accurately than ever before. This kind of software will become still more useful, even indispensable, as electricity grids are integrated over ever-larger areas, as transmission and generation become competitive markets, and as transactions grow in number and complexity. Concepts like power flow, loop flow, and reactive power, which once mattered only to the engineers directly involved in grid operations, now must be made intuitive. This is because they must be communicated to public service commissions and the consumer-voters to whom such boards are answerable. In short, whether the client/user is a power marketer, a grid operator or manager, a public authority, or a member of the public, power system visualization tools can aid their comprehension by lifting the truly significant above background noise. Such tools can expedite decision-making for congestion management, power trading, market organization, and investment planning for the long term     

Empire off the grid

Dean Kamen, arguably the world's most famous living inventor, is in his favorite place. It's the basement of the main house on his private island, a pristine concrete bunker outfitted with a command station that can monitor and control all aspects of the production and consumption of electric power on the island. The island, off the coast of Connecticut, is called North Dumpling Island, but Kamen, who invented the Segway and is something of an eccentric, calls it the Dumplonian Empire. He, of course, is Lord Dumpling.     

光伏并网发电问题研究

介绍了光伏并网发电的类型,分析了光伏并网发电对电网的影响,针对光伏并网发电的收益问题,提出了电网负荷预测模型。根据所提出的预测模型可以对光伏并网发电出力提供指导,以提高电网发电的效益。最后,以辽宁地区数据为例,绘制出了电网负荷与温度之间变化关系的拟合曲线。     

网格计算中的安全问题探讨

介绍了网格计算环境的特点、安全需求及其安全问题研究现状，对网格计算中的安全标准、安全认证、公有与私有资源的安全利用、应用安全、恶意攻击的检测与防范等安全问题进行了分析和讨论，提出了在研究和解决网格计算的安全问题时，一方面可以借鉴传统网络的安全策略和技术并加以改进，另一方面要充分考虑网格计算环境的特殊性，研究和构建“特殊．的安全策略和技术”。     

基于智能电网的EAM测距改进研究

随着国内智能电网的快速发展,无线传感器网络中的节点位置的难题成了急需改进的一个难点。文中采用自适应的方法完成了EAM测距设计,然后分析了EAM测距实现障碍物误差降低的特点,在对EAM测距MATLAB平台上的仿真表明相对于普通的测量方法,EAM的测距方法可以提高测距精度在25%左右,这一研究对于智能电网的发展具有一定的理论和实际意义。     

网格信息服务初探

信息服务是网格系统提供给各类用户以满足需求的主要功能。由于信息资源的需求者与提供者分布在不同地域或不同节点上，二者是非透明状态下的，不均衡的“多对多”关系，因此，需要网格信息服务。数据网格和信息网格是网格信息服务的基础；SOA的优势在于其高度的可复用性、灵活性、可靠性和更好的可扩展性；Web服务描述了一种基于标准技术的新型分布式计算范例，并提供应用程序的接口WSDL。在Web协议的支持下，就可以为信息获取、信息提供、信息管理等提供基本操作，实现网格信息服务的功能。     

虚拟现实视觉体验对事件相关电位影响的研究

虚拟现实技术具有广阔应用前景,但它对大脑信息处理及认知影响尚不清楚。本文结合头皮脑电,设计了平面和虚拟现实两种模式的视觉任务,对比分析虚拟现实对事件相关电位（ERP）的影响,探索沉浸式视觉体验过程中大脑的认知加工过程。参考电极的选择是研究事件相关电位的关键,为获得更客观的脑电信息,本文首先使用参考电极标准化技术将记录的脑电信号的参考近似转换为理想的零点,经过必要的预处理,再采用叠加平均的方法从中提取ERP。结果发现,与平面模式相比,在虚拟现实模式下ERP成分中没有出现显著的P300成分,这可能与大脑产生疲劳感相关;虚拟现实模式下N100成分的潜伏期提前、幅值增大,反映了虚拟现实环境更容易引起注意,并使人产生沉浸感。      

六角形阵列相干信号二维DOA估计

提出了一种基于扩展重构相关矩阵去相干的二维DOA估计算法。针对六角形阵列的结构特点,首先对各个阵元的接收数据求其共轭矩阵来扩展阵列,扩展后的阵列分为3个六角形子阵列,以此为基础,求得各子阵列的自相关矩阵及互相关矩阵来扩展重构相关矩阵,从而实现解相干的目的,最后利用二维MUSIC算法进行DOA估计。该算法在不减少阵列有效孔径的前提下,增加了可估计相干源数目,并且能够得到较好的估计性能。最后,通过计算机仿真证实了该算法的有效性。      

Square to hexagonal lattices conversion

In order to build up hexagonal digital pictures from square ones, each point of the hexagonal lattice is given the value of its nearest neighbour in a superimposed square lattice. This simple rule has the advantage to transform a binary set into a binary set and a grey-tone function into a grey-tone function. In case of convolution, it gives almost identical results. For the increasing transformations, the results are satisfying as soon as the square digital set contains neither grain nor pore reduced to one isolated point, i.e. if the euclidian set corresponding to it is open-closed by a disk of radius a, the step of the square grid. If this set is also open-closed by a disk of radius 2a, then the rule of conversion also preserves the homotopy. At last, the three Minkowski's functionals are estimated with a good precision. These properties are also valid for the class of grey-tone functions.     

Research on the piezoelectric response of cubic and hexagonal boron nitride films

Boron nitride (BN) films for high-frequency surface acoustic wave (SAW) devices are deposited on Ti/Al/Si(111) wafers by radio frequency (RF) magnetron sputtering. The structure of BN films is investigated by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) spectra, and the surface morphology and piezoelectric properties of BN films are characterized by atomic force microscopy (AFM). The results show that when the flow ratio of nitrogen and argon is 2:18, the cubic BN (c-BN) film is deposited with high purity and c-axis orientation, and when the flow ratio of nitrogen and argon is 4:20, the hexagonal BN (h-BN) film is deposited with high c-axis orientation. Both particles are uniform and compact, and the roughnesses are 1.5 nm and 2.29 nm, respectively. The h-BN films have better piezoelectric response and distribu- tion than the c-BN films.     

Sub-band coding of hexagonal images

According to the circle-packing theorem, the packing efficiency of a hexagonal lattice is higher than an equivalent square tessellation. Consequently, in several contexts, hexagonally sampled images compared to their Cartesian counterparts are better at preserving information content. In this paper, novel mapping techniques alongside the wavelet compression scheme are presented for hexagonal images. Specifically, we introduce two tree-based coding schemes, referred to as SBHex (spirally-mapped branch-coding for hexagonal images) and BBHex (breadth-first block-coding for hexagonal images). Both of these coding schemes respect the geometry of the hexagonal lattice and yield better compression results. Our empirical results show that the proposed algorithms for hexagonal images produce better reconstruction quality at low bits per pixel representations compared to the tree-based coding counterparts for the Cartesian grid.     

六边形开口谐振器的太赫兹特性

电磁超材料通常是由一些在介质基底表面上周期分布的亚波长谐振器组成的。它的特性在很大程度上取决于基底的性质和谐振器的结构细节。由于开口环谐振器(SRRs)可实现多种功能,因此在超材料中应用广泛。通过设计一种二维六边形SRRs阵列,利用时域有限差分方法(FDTD)研究了单元开口形式、单元周期和介质基底性质对其传输特性的影响。研究结果表明,开口形式可使超材料在1~2.5 THz处产生谐振响应,且介质基底的性质对该谐振特性的影响权重较大。