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December 29, 2009

五庄观的土地道:“这果子遇金而落,遇木而枯,遇水而化,遇火而焦,遇土而入。”

遇金而落。凡是重金砸的项目,必然衰落。

遇木而枯。你若给它桎梏,它就枯竭了。

遇水而化。参见这里。我不多说,去看高露洁广告先。

遇火而焦。网上火的东西,最后都是灰头土脸。

遇土而入。也不多说,今年我写的最火的一篇,居然就应在这个土字上。

December 23, 2009

休假在家,无聊之余忽然想起了小时候听父母讲的“良民证”。于是跑去用google百度了一把良民证的图片。却发现一个问题:大多数网络上面良民证图片的日期,居然都是民国的纪元。这和我小时候听来的故事不太一样。印象里,良民证是日本侵略军在中国占领区用来控制的一种手段,是中国人痛恨的东西。我又仔细看了看,保留下来的那些良民证,似乎都是江苏那边的,或许当时敌占区也还用民国的纪元。后来又发现同时有日本和民国两种纪元共存的良民证,看来当时的确是两者并用的。

看图片,良民证一般是纸的或者布的,制作很粗糙。小时候听故事,经常有游击队员伪造良民证,混进城里的故事。我的父辈里面,也有几位干过这种事情的,可见当时漏洞还是很多的。其实即使在高科技的今天,漏洞也不少。比如入境美国,边境检察官咋咋呼呼的让每个外国人来按指纹。我排在队里就暗自好笑:真要是有重金支持的恐怖分子,哪个会这么老实的排队让你取指纹?早就从机场某个漏洞溜走了;或者从墨西哥边境钻进去了。在这里老老实实排队的,都是良民。

嗯,听起来好像我回到高中时代了,要写议论文。

还是看到郑昀的理性声音少吗? 这句话说的太好了:“因为理性的声音传不开。它们太严谨了”。有个很著名的笑话:爸爸对女儿说:今天冷,穿牛仔裤!不能穿裙子!女儿说:凭什么?你让我穿我就穿?而妈妈的处理方法就不一样。妈妈会问:乖,今天你要穿牛仔裤,还是穿紧身裤?女儿:嗯…牛仔裤!

无论在哪里,要想传播,就要了解传播的对象能接受什么,不能接受什么。国内很多知识分子悲愤的大喊“月亮不懂我的心”。那是,您对着月亮喊,不被当成狼人抓到动物园,已经不错了,就别指望被人理解了。

上次我们创业小组活动,Robert给我们说起王建硕提出的“农民营销”的概念。其实道理是一样的,就是要针对受众,采取合适的传播形式。

另:月光博客的这篇有趣的人民网微博客很好玩,script注入,加上全能的IE,还有tomcat错误助阵,给我140个字符,能撬动的,绝对不仅仅是几个对话框这么简单的东西。

December 22, 2009

是王建硕提出的。他用英文写的,我用英文和他探讨了一下,觉得还是很有意思的一个题目。我这里用中文总结一下,免得忘记了。

有一个数据库的表T,表里面有多个列Ci,每个列的值域是实数。在这个表上可以定义查询。一个查询Q是一个表达式树,这个表达式树的非叶子结点,都是布尔表达式;而叶子结点,都是比较表达式。比较表达式的意思,就是一个列的名字Ci,一个比较运算符(<,<=,>,>=,<>)这些,然后一个实数值。

一个查询的例子:NOT (AND ((C1>5), OR ((C2<6),(C3<>9))))

问题是:给出两个这样的查询Q1和Q2,如何确定Q1的结果是否是Q2结果的子集?

这个的确是一个比较难的题目,因为比较的是两个查询,而不是两个结果集合。建硕也指出,这里最麻烦的,是那些比较表达式,因为它们是多个列上面的比较。

我给出了一个解法,是这样的:

  1. 对比较表达式进行改造,变为值域。比如:C1>=3变为:C1:[3,+∞);C2<>9变为:C2:(-∞,9) OR C2:(9,+∞)
  2. 对布尔表达式进行计算,最终的目的,是把表达式树变成一组item的OR的运算;而每个item,是一组factor之间的AND运算;每个factor,是一个值域。每个item里面,一个列名Ci最多只能出现一次。
  3. 对于每一个item,找出里面没有出现的列名Ci,增加相应的值域Ci(-∞,+∞)。
  4. 剩下的事情就简单了。对于Q2里面所有的item,看Q1里面是否存在一个item可以把它覆盖。如果是,那么Q2的结果,一定是Q1的子集。

这个是代数的解法,对应的几何映射,就是一个N维空间,其中N是表T的列的数目。每个列,都是空间里面的一维。每个item,都是空间里面的一个区域。每个查询,就是空间里面的一组这样的区域。表格T里面的任何一个可能的列,都是空间里面的一个点。查询的结果,就是落在这组空间里面的点的集合。

那么计算Q2是否是Q1的子集,就是计算Q2定义的空间区域集合,是否能被Q1定义的空间区域集合所容纳。

December 17, 2009

早上看到论坛里面朋友说:facebook修改了用户隐私协议:

缺省公开用户的所有信息

用户必须登录修改回原来的设定,否则在网上就是赤身裸体。

MSNBC的报道用了这样的标题:

Check your Facebook privacy settings. Now!

检查你的非死不可隐私设定。现在就去!

今早又收到以前系主任给大家的信,这次是说,美国女生的Mac在以色列遭到枪击。国内三大门户的记者们,你们稿子的标题我都替你们想好了:“妙龄美国女生在以遭到枪击,笔记本殒命”,你们拿去用吧,我不收版权,给我一个link就可以了。

这个女生叫Lily Sussman,21岁的妙龄,在从埃及进入以色列的时候,被以色列边境警察询问了两小时,把她的行李搜了个遍,连肥皂都打开看,强制她脱去多余的衣物(抢眼吧?),还问她很多不合适的问题。比如:你有男友吗?他是阿拉伯人,埃及人还是巴勒斯坦人?你为什么住在埃及不住以色列?

最令人发指的是,以色列边境警察最后声称,Lily的苹果笔记本是“安全威胁”,向Lily的笔记本开了三枪。所以这个事情,或许也可以叫做:以色列三枪拍案惊奇。

新闻链接在这里,Lily的blog在这里

最后,系里的一个老师看了照片以后指出:警察的三枪,都没有击中硬盘。

December 15, 2009

好久没去看老白的博客,这次去看,发现老白在担心女儿的学习和将来。同样作为一个有女儿的爹,同样作为一个企图周游世界的家伙,我对老白的担心有共鸣,这里说说我家关于蒙氏的一家之言。一家之言的意思,就是片面的,偏激的,不正确的,需要纠正的,我和我老婆这一家大人的看法。

蒙氏这个东西,据说是从美国兴起的,坊间传闻,google的创始人之一就是从小受的蒙氏教育,从而培养了独立的探索和创新精神,此事待考。不过我们没有给女儿选择随便踩一脚就能踩到的蒙氏学校,原因很简单:觉得不合适。

我们女儿遗传了我们两个书虫的特点:害羞,沉静,凡事不争,随遇而安。而我们参观的蒙氏学校,老师是放手让学生去玩,说的不好听一点,就是不管,你无聊的坐在那里,哪怕是因为对陌生环境的恐惧,而不敢对老师提出要求,老师也是一样当成是“儿童的天性”,俩字:不管。

相反,对于小孩子偶尔的调皮,比如在地上跳一下,甚至走路快了一些,老师就立刻予以制止,这个时候,天性?天性是谁啊?

所以我们没有选蒙氏学校,事实上,蒙氏的定义相当的宽泛,我曾经在论坛上面见过很多人说起不同的蒙氏,以至于有人打错了字,把蒙氏打成“蒙事”,这个事情,如有雷同,纯熟巧合。

昨天写了电波和列车,引来Song的专业评论。看来我这里虽然偏僻,但是还是有不少专业人士在看,这样好,我也不靠口水和美女去争取流量,有高质量的读者才重要。

那我今天再写一个物理量让人迷惑的事情:芯片的速度。

通常在通俗读物里面,芯片之所以快,都是因为它们是用电信号来计算的,这个电信号其实不准确:到底这个信号是不是电磁波的速度呢?比如:一个计算的结果,从芯片的一级流水线传递到下一级,是不是用光速传播的呢?

当然你可以说,这个速度不是每秒30万公里,因为芯片的导线是铝或者铜,不是真空,所以没有那么快。事实上,信号在芯片里面传播的速度,比电磁波的速度要小很多很多,否则intel的那群芯片设计师们,也不要努力缩小线宽了,把线路弄短是正经。

说到这里,再提一个问题:为什么线宽越小,芯片的速度越快呢?

答案是:在芯片里面,信号的传递速度,是受限于导线的充电速度的。当电流从一根导线的一段传递到另外一段的时候,这根导线实际上相当于一个电容,而高电平则是对电容充电,低电平则是放电,当充电/放电的过程结束的时候,导线两端的电压一致,信号就传递过去了。电容越大,充电和放电的时间越长,信号就传递的越慢。

导线的电容,正比于导线的面积,所以导线越短,线宽越窄,电容就越小,信号速度就越快。

December 14, 2009

上次说到,手机在通过基站覆盖区域的时候,基站之间要进行手机的交接,如果基站之间交接不好,就不能保证手机的通讯畅通,会发生掉线现象。

可是,现在的基站处理速度,应该是可以应付高速公路上面汽车的速度的。高速列车的速度,也不比汽车的速度快很多。那么,为什么会发生高速列车上面,手机经常掉线的事情呢?

一个原因,是基站的密度。新建的高速铁路,会有部分通过人烟稀少地区,那篇报道里面也提到,会经过隧道。隧道造价不菲,通常都是在高山峻岭里才不得不造,这种地方,基站的密度自然就比较小了。另外高山和隧道对信号的阻隔,也是一个因素。高速公路,特别是已经建好的高速公路周围,往往已经有很多基站,信号的覆盖就不再是问题。

还有一个原因,我相信也是不可忽略的,就是手机的密度。按照一般的安全驾驶规范,前后车距应该是4秒,也就是说,一个单向4车道的高速,每秒会有一辆车通过一个检查点。假设这个检查点,正好就是基站A和基站B交接手机的边界,并且每辆车里面有一个手机,那么每秒要交接一个手机,双向就是两个手机。

当然实际操作要远比这个复杂,因为交接不是瞬间完成的,所以交接不是在一个点完成,而是在一段路完成。不过我们这里就是估算一下比例。

假定火车速度和汽车一样快,都是200公里每小时,那么一秒通过检查点的火车长度,就是55.6米。和谐号的总长213.9米,共8节车厢,那么一秒就有两节车厢通过检查点。每个车厢座位大概是72人,如果满员的时候,在每个人都有至少一个手机的中国,一秒种通过检查点的,就是144个手机。

December 13, 2009

某次看交友网站,发现女生的照片都喜欢打个’V',问朋友为啥?朋友说:

那哪是V,那个是2,是说,当二奶也可以。

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