An overview of fast convergent ordered-subsets reconstruction methods for emission tomography based on the incremental EM algorithm

Statistical reconstruction has become popular in emission computed tomography but suffers slow convergence (to the MAP or ML solution). Methods proposed to address this problem include the fast but non-convergent OSEM and the convergent RAMLA [1] for the ML case, and the convergent BSREM [2], relaxed OS-SPS and modified BSREM [3] for the MAP case. The convergent algorithms required a user-determined relaxation schedule. We proposed fast convergent OS reconstruction algorithms for both ML and MAP cases, called COSEM (Complete-data OSEM), which avoid the use of a relaxation schedule while maintaining convergence. COSEM is a form of incremental EM algorithm. Here, we provide a derivation of our COSEM algorithms and demonstrate COSEM using simulations. At early iterations, COSEM-ML is typically slower than RAMLA, and COSEM-MAP is typically slower than optimized BSREM while remaining much faster than conventional MAP-EM. We discuss how COSEM may be modified to overcome these limitations.     

个人电脑防杀电脑病毒三大注意

使用计算机免不了时常受到各种病毒的骚扰,而且随着网络应用的不断深入,这种骚扰也越来越多。在和计算机病毒的对抗中,专业人士发现了一些规律,我们在这儿将这些规律总结归纳,暂且叫做“三大注意”供大家参考,希望能为您对付病毒有所帮助。     

架起语音互通的桥梁

现在即时聊天工具的互通问题一直没有很好解决,给我们日常交流带来不少障碍。虽然MSN和Yahoo Messenger已经实现了互通,但也仅限于文字交流,还无法实现语音聊天互通。不过现在有一家Gtalk to VOIP公司推出了语音"回拨服务",可以在MSN、Yahoo Messenger和Gtalk等即时聊天工具间实现语音互通,轻松解决不同聊天工具间的语音交流问题,相当实用。     

Geomicrobiological redox cycling of the transuranic element neptunium

Microbial processes can affect the environmental behavior of redox sensitive radionuclides, and understanding these reactions is essential for the safe management of radioactive wastes. Neptunium, an alpha-emitting transuranic element, is of particular importance because of its long half-life, high radiotoxicity, and relatively high solubility as Np(V)O(2)(+) under oxic conditions. Here, we describe experiments to explore the biogeochemistry of Np where Np(V) was added to oxic sediment microcosms with indigenous microorganisms and anaerobically incubated. Enhanced Np removal to sediments occurred during microbially mediated metal reduction, and X-ray absorption spectroscopy showed this was due to reduction to poorly soluble Np(IV) on solids. In subsequent reoxidation experiments, sediment-associated Np(IV) was somewhat resistant to oxidative remobilization. These results demonstrate the influence of microbial processes on Np solubility and highlight the critical importance of radionuclide biogeochemistry in nuclear legacy management.     

只聊QQ非诚勿扰

用QQ聊天交流非常方便。但它也有闹心的时候：安装时捆绑的各种附加功能对某些人并不实用．而且聊天窗口还会夹杂广告,这对于仅仅想用它聊天交流的人就多余了,既然不能忍,就只有自己动手将这些烦恼“拒之门外”。本文以最新版的QQ 2009 beta2为例来说明,同样适用于QQ 2008的版本。     

电脑上过把DJ瘾

听惯了的老歌,如果改变一下它的节拍,一曲抒情歌曲没准就会变成澎湃激昂的摇滚乐,在现实生活中可以玩这种音乐魔法的人我们称之为DJ。虽然DJ那昂贵的调音台可不是每个人都有机会触碰的,     

用“剩余物资”造本本散热桌

经过一次装修．家中或多或少都会剩下一些装修材料。它们虽然形同鸡肋,但直接扔掉未免太过可惜。既然是一名Geek,那么就应该利用这些“剩余物质”敲打出一点东西来。比如下面介绍的本本散热桌。虽然看外观它也许不如许多成品本本桌,但除了成本低廉之外,它还拥有出色的散热性能哟!既然能够自己做,那么何必费力去电脑城看着JS（奸商）的脸色杀价呢？下面,我们就把本本散热桌的诞生史和盘托出。     

非诚勿扰 QQ空间关注问题

如果你的QQ好友比较多,那么在你的QQ空间个人中心里就会充斥着大量的好友动态信息。对于自己真正想关注的好友动态信息却被淹没在无关的动态更新信息流中了,查找起来反倒非常麻烦,     

让卡巴斯基不再卡

卡巴斯基是很多朋友都在使用的反病毒软件,但是它比较耗费系统资源也是不争的事实,由于它要实时监控而常驻内存,因此无论是打开网页还是运行程序都比较“卡”,尤其是一些电脑配置不高的朋友感觉尤为明显,那么有什么办法让其不影响操作的效率呢？其实我们完全可以简单配置一下,让卡巴不再“卡”,     

机票酒店提前网上淘出来

公司要安排到外地出差,或者到外地旅游,最重要的就是解决“行”和“住”的问题。“兵马未动,粮草先行”,因此提前订好机票和预定好酒店就是很有必要的,酒店自不必说,但是如何买到最便宜的机票呢？尽管现在各大航空公司的打折机票满天飞,不少网站也大打折扣机票的旗号,但是这类网站值得信赖吗？这里不作定论,其实不妨到“淘宝网”去逛逛吧,会有意想不到的收获哦!