The size and albedo of the Kuiper-belt object (20000) Varuna

Observations over the last decade have revealed the existence of a large number of bodies orbiting the Sun beyond Neptune. Known as the Kuiper-belt objects (KBOs), they are believed to be formed in the outer reaches of the protoplanetary disk around the young Sun, and have been little altered since then. They are probably the source of short-period comets. The KBOs are, however, difficult objects to study because of their distance from earth, so even basic physical properties such as their sizes and albedos remain unknown. Previous size estimates came from assuming an albedo with the canonical value being 0.04. Here we report simultaneous measurements of the thermal emission and reflected optical light of the bright KBO (20000) Varuna, which allow us to determine independently both the size and the albedo. Varuna has an equivalent circular diameter of D = 900+129-145 km and a red geometric albedo of pR = 0.070+0.030-0.017. Its surface is darker than Pluto's, suggesting that it is largely devoid of fresh ice, but brighter than previously assumed for KBOs.     

The formation of Kuiper-belt binaries through exchange reactions

Recent observations have revealed that an unexpectedly high fraction--a few per cent--of the trans-Neptunian objects (TNOs) that inhabit the Kuiper belt are binaries. The components have roughly equal masses, with very eccentric orbits that are wider than a hundred times the radius of the primary. Standard theories of binary asteroid formation tend to produce close binaries with circular orbits, so two models have been proposed to explain the unique characteristics of the TNOs. Both models, however, require extreme assumptions regarding the size distribution of the TNOs. Here we report a mechanism that is capable of producing binary TNOs with the observed properties during the early stages of their formation and growth. The only required assumption is that the TNOs were initially formed through gravitational instabilities in the protoplanetary dust disk. The basis of the mechanism is an exchange reaction in which a binary whose primary component is much more massive than the secondary interacts with a third body, whose mass is comparable to that of the primary. The low-mass secondary component is ejected and replaced by the third body in a wide but eccentric orbit.     

基于物体坐标系的三维图形数据表示

鉴于世界坐标系定义的空间往往远大于被描绘物体的几何尺寸、导致了数据冗余、分辨率低。提出用物体坐标系表示三维图形，使存储空间减小，分辨率提高，并可提高运算速度。     

结合局部二元图特征的运动目标阴影抑制方法

针对基于局部二元图纹理的阴影区分算法不能有效抑制暗阴影边缘的问题,提出了一个结合图像边缘信息的改进方案.当进行阴影抑制时,对不在边缘上的像素直接通过比较前景像素及其相应背景像素的局部二元图纹理值进行区分;否则,以待判定的像素为中心,设定一个滑窗,对滑窗内相同位置的前景像素与背景像素的局部二元图纹理值进行比较,统计滑窗内纹理值相同的像素对的数量.若该数量大于一定的阈值,则判定中心像素为背景像素,否则为目标像素.实验结果表明:改进方案能适应阴影的明暗程度变化,消除仅使用局部二元图时存在的伪阴影边缘,所增加的计算量与阴影区域的大小成比例.     

需求变化的多阶段库存控制动态规划算法研究

多阶段库存管理是供应链研究的重要课题,其中独立需求的订购策略问题,在需求率不是恒定、计划执行过程中各阶段需求不再变化的情况下,动态规划方法（WW算法）效率较高。给定费用参数（物资单价、一次订货费用、单位库存保管费用）,订购计划执行到阶段i（1〈f〈m）时需要调整阶段m的需求,而其它阶段的需求不变,订购策略如何调整,使得库存总费用最低;文中研究了此类独立需求多阶段订购策略问题,并改进了WW算法。     

分布式对象通信的实现

分布式系统是多计算机系统,在不同计算机上的运行进程如何通信是关键问题.本文介绍了一种高效的分布式对象通信的模型,即远程方法调用,并利用一个简单的例子说明其实现方法.     

WEB元素的对象表达

文章阐述了面向领域的构件化的Web站点辅助开发方法中需要解决的首要问题,即Web元素的对象表达,使Web元素不再表现为文本代码而是表现为具有方法和属性的对象,用户无须熟悉HTML标记,只要通过对对象属性的设置,可以方便地完成网页编辑功能.     

二元关系性质的组合性

讨论了二元关系五种性质的组合存在性问题,证明了二元关系5种性质的所有组合模式中有14种是不可能出现的,并对其余组合模式的存在性进行了实例说明。     

一个对象-关系型DBMS的数据存储组织策略

提出了一个对象关系DBMS的数据存储组织策略，给出了其底层存储的具体实现，其中包括类，对象的存储方案。给出并分析比较了类层次的3种存储策略，确定了将每个类映射成一张表（包含该类继承的属性）作为本系统实现的策略。论述了大对象等的分散存储策略。结果表明，本 系统在增强对象处理能力的同时，能满足对数据的快速高效检索。     

PowerBuilder 6.0共享对象的应用

介绍了在分布式应用中如何使用PowerBuilder提供的共享对象实现数据共享．     

多粒度面向对象概念格的构造

目的研究多粒度面向对象概念格的构造。方法在单粒度面向对象概念格外延集上作并运算,得到多粒度面向对象概念的外延集,再运用下近似粒算子,得到多粒度面向对象概念的内涵集,进而构造多粒度面向对象概念格。结果给出了由单粒度面向对象概念格构造多粒度面向对象概念格的方法。结论多粒度面向对象概念格的提出进一步完善了概念格理论。     

面向对象系统分析中的对象识别技术

结合面向对象和结构化系统分析的思想,对面向对象软件开发中的对象识别方法进行了研究     

离散二进制粒子群算法分析

粒子群算法（Particle Swarm Optimization,PSO）主要用优化计算实值的连续性问题,而离散二进制粒子群算法（Binary Particle Swarm Optimization,BPSO）则用来优化离散空间问题,它扩展了PSO算法的应用,现已广泛应用到各种离散优化问题计算中,但目前对BPSO算法...     

立体二叉树在排序中的应用

提出了立体二叉树的数据结构,对立体二叉树的基本概念进行了讨论;对满立体二叉树结构的结点分布与结点编码之和问题进行了研究并给出了有关的公式;最后探讨了立体二叉树在排序中的应用,提出立体堆的排序方法,并对它的算法实现进行设计与分析,得出了立体堆排序方法在最坏情况下的时间复杂性,从而减少了堆排序方法的时间复杂性的常数因子．     

The trans-neptunian object UB313 is larger than Pluto

The most distant known object in the Solar System, 2003 UB313 (97 au from the Sun), was recently discovered near its aphelion. Its high eccentricity and inclination to the ecliptic plane, along with its perihelion near the orbit of Neptune, identify it as a member of the 'scattered disk'. This disk of bodies probably originates in the Kuiper belt objects, which orbit near the ecliptic plane in circular orbits between 30 and 50 au, and may include Pluto as a member. The optical brightness of 2003 UB313, if adjusted to Pluto's distance, is greater than that of Pluto, which suggested that it might be larger than Pluto. The actual size, however, could not be determined from the optical measurements because the surface reflectivity (albedo) was unknown. Here we report observations of the thermal emission of 2003 UB313 at a wavelength of 1.2 mm, which in combination with the measured optical brightness leads to a diameter of 3,000 +/- 300 +/- 100 km. Here the first error reflects measurement uncertainties, while the second derives from the unknown object orientation. This makes 2003 UB313 the largest known trans-neptunian object, even larger than Pluto (2,300 km). The albedo is 0.60 +/- 0.10 +/- 0.05, which is strikingly similar to that of Pluto, suggesting that the methane seen in the optical spectrum causes a highly reflective icy surface.     

旋转体体积公式及其推论

传统的旋转体体积求法是通过对坐标的积分求得，借助数学和物理的方法推导出一个脱离坐标系的旋转体体积公式，利用这个公式，用悬线法测出均匀转面的重心，就可求出旋转体体积，并在生活和生产中得到广泛的应用．     

二元与三元等价关系的联系

二元关系是最基本的关系。本文给出三元等价关系的定义,讨论三元等价关系的分类性质,以及三元等价关系与二元等价关系之间的联系。     

萘-脂肪酸二元体系液相线

用目视变温法研究了萘－月桂酸，萘－肉豆蔻酸，萘－棕榈酸二元系的固液平衡，三个二元系均为低共熔型，低共熔点分别为：35度，77．1％（wt)月桂酸，44度，73．9％（wt)肉豆蔻酸，52度 ，67．9％（wt)棕榈酸。     

The binary progenitor of Tycho Brahe's 1572 supernova

The brightness of type Ia supernovae, and their homogeneity as a class, makes them powerful tools in cosmology, yet little is known about the progenitor systems of these explosions. They are thought to arise when a white dwarf accretes matter from a companion star, is compressed and undergoes a thermonuclear explosion. Unless the companion star is another white dwarf (in which case it should be destroyed by the mass-transfer process itself), it should survive and show distinguishing properties. Tycho's supernova is one of only two type Ia supernovae observed in our Galaxy, and so provides an opportunity to address observationally the identification of the surviving companion. Here we report a survey of the central region of its remnant, around the position of the explosion, which excludes red giants as the mass donor of the exploding white dwarf. We found a type G0-G2 star, similar to our Sun in surface temperature and luminosity (but lower surface gravity), moving at more than three times the mean velocity of the stars at that distance, which appears to be the surviving companion of the supernova.     

基于单成分被测物体的射束硬化校正算法

经典的CT重建算法基于X射线源为单色源的假设,而实际上由于工业CT机或医用CT机的X射线是多色的,通常只能得到多色投影数据。若直接用多色投影数据来重建图像,就会出现射束硬化伪迹,这种硬化伪迹如果不校正就会影响医学诊断和工业检测的结果。本文通过对计算机断层成像中射束硬化产生的原因分析,给出了基于单成分被测物体的射束硬化校正算法,并对算法进行了数值模拟。