标签: magic

Welcome to this week's Freaky Friday blog, in which we pause for a while to take a deep breath (hold it... hold it... now exhale), slow down, relax, and start winding down in preparation for the weekend. As part of this exercise, I've gathered a few choice diversions for your delectation and delight. This week's humble offerings are as follows: No. 1: I must admit that I do like to see magic tricks. On the one hand, I really enjoy the smaller sleight-of-hand tricks that are performed right under one's nose. On the other hand, I also delight in the larger, more spectacular offerings that leave you gasping out loud and thinking "How on Earth did they do that?" ( Click here to see an amazing magic trick.) No. 2: Is it true that my circle of friends is somewhat eclectic? The reason I ask is that a few minutes ago, Bruce, the guy who owns the building in which I have my office, approached me in the kitchen and said, "You certainly do have some strange guests." When I inquired as to why Bruce had this impression, he replied "Well, look at the guy with the goats in the back of his truck who was parked outside the front door of the building yesterday." Of course, I responded by saying "How did you know he was my guest?" To which Bruce replied (speaking slowly as though he was talking to an idiot): "Because. He. Had. Goats. In. The. Back. Of. His. Truck." Hmmm, I guess he has a point. The reason this just popped into my mind is that my chum, Arthur Smith, is one of the world's foremost authorities on cosmic rays. Having said this, Arthur currently spends the bulk of his time farming, beekeeping, and making bars of soap. Arthur also keeps me informed of the latest developments in astrophysics, including, for example, a way to teach children all about the phases of the moon using Oreo Cookies ( Click here to learn more.) No. 3: Speaking of Arthur, he recently sent me another interesting snippet about the possibility of embedding tiny LEDs in special contact lenses and using them to make augmented vision a reality—think Google Glass on steroids! ( Click here to see more.) No. 4: Are you familiar with the equation (bN)(S/N)Z = bSZ? You should be, because it could spell your doom. Suffice it to say that if you wish to survive a Zombie Apocalypse (see also my blog Zombie stories for people with brains ), then you need to understand the implications of (bN)(S/N)Z = bSZ. ( Click here to discover more.) No. 5: As you may recall, I recently ordered a 3D Printer (I cannot wait for this little beauty to arrive). So you can only imagine my surprise to hear about a guy who uses 80,000 honey bees to "print" the most amazing 3D sculptures. ( Click here to "bee" impressed.) No. 6: Speaking of bees (gosh, I'm smooth), scientists used to say it was impossible for a bee to fly. Of course, many people were of the opinion that airplanes would never fly. Then they said that human-powered airplanes weren't possible. Of course each of these "impossibles" has eventually proved to be possible. The final bastion of this class of impossible was the helicopter. Many pundits have claimed that it's simply not possible to create a helicopter powered only by human strength. Need I say "Boing!" ( Click here to see the impossible made possible.) No. 7: Finally, speaking of human flight (I just can't stop myself), this reminds me of the classic YouTube video: Jeb Corliss "Grinding The Crack," which is augmented by an absolutely perfect soundtrack. If you haven't already seen this, it will completely blow you away (no pun intended). Even if you have already seen it, it's always worth another look. ( Click here to have your socks blown off!) If you know of any interesting sites you'd care to share, please leave comments below.  

Do you know the American illusionists and entertainers Penn and Teller who are, perhaps, best described as "Eccentric magicians with a psychotic twist" ? Penn is the big tall one who talks a lot, while Teller is the small weedy-looking one who never says a word. Well, it seems they hosted a TV show in the UK called "Penn Teller: Fool Us" (I'd never heard of this before). This was a magic competition show, which challenged magicians to perform in front of Penn and Teller. If they could fool thy dynamic duo, they would win a five-star trip to Las Vegas to perform as the opening act in Penn and Teller's world famous show at the Rio Hotel and Casino. I'm not sure how this came about, but I ran across a video on YouTube (where else) billed as "Easily the funniest magic trick I've ever seen!" So, of course, I had to take a look. This features a guy called "Piff the Magic Dragon." The way he comports himself is really very funny. I love the part where he talks about his brother... In fact there are a number of Piff videos on YouTube – here's another featuring little bunny rabbits . If you have any favourite "magic trick" videos on YouTube, please share them with us here.  

CRC 校验：从原理到实现（二）   1、 收发端CRC校验的可选机制   CRC 校验是为了保证信息在发送端和接收端之间传输的完整性，所以除了在收发两端都要实现 CRC 计算之外，还需要确定一些具体的机制，主要的几种机制分类列举如下：   表 1-1 收发端 CRC 校验的六种机制   机制 发送端 接收端 初始寄存器值 校验序列 初始寄存器值 校验范围 正确判定 1 0 不操作 0 明文 结果 = 校验序列？ 2 0 不操作 0 明文 + 序列 结果 =0 ？ 3 0 逐位取反 0 明文 + 序列 结果 =Magic Num ？ 4 全 1 不操作 全 1 明文 结果 = 校验序列？ 5 全 1 不操作 全 1 明文 + 序列 结果 =0 ？ 6 全 1 逐位取反 全 1 明文 + 序列 结果 =Magic Num ？   初始寄存器。初始寄存器的值为 0 ，符合一般的 CRC 校验原理，也便于在 MATLAB 中计算。但是容易出现“前导 0 ”问题，即在明文序列之前插入或者删除 0 序列，这是由于 0 与 0 异为 0 。因此，将初始寄存器值设为全 1 可以避免“前导 0 ”的出现。发送端和接收端的初始寄存器值须保持一致以保证两端校验正确。   接收端的校验范围。可以选择明文或者明文 + 序列，若传输完整无误，明文的 CRC 计算结果等于收到的校验序列，明文 + 序列的计算结果归 0 。两者相比，后者实现流程简单。   Magic Num 。明文 + 序列的计算结果归 0 并不定能严格证明信息传输完整无误，无法检测“拖尾 0 ”问题，即在序列之后插入或者删除 0 序列，同样是由于 0 与 0 异为 0 。所以引入了 Magic Num 的机制，在发送端需要对校验序列逐位取反添加在明文序列之后发送，在接收端对明文 + 序列做校验，若结果等于 Magic Num 则说明信息传输完整无误。 Magic Num 是与生成多项式对应的序列，计算过程如下：   一般情况下，在接收端对明文 + 序列做计算，结果为 0 说明传输完整无误： ，其中 M 是明文序列， R 是校验序列， G 是生成多项式。   用 /R 表示 R 对 1 取反，我们得到： 因此，由接收端计算出的无差错的传输的校验和应该是： ，这就是 Magic Number 。   Magic Num的校验方法在网络传输的设计中比较常见，在 802.3 的 IP 核和 802.11 标准的附录框图中对 CRC32 校验的设计都采用了初始寄存器全 1 和 Magic Num 的方式 。   参考资料：   http://blog.sina.com.cn/s/blog_62d9edac01015lsd.html http://blog.csdn.net/highyyy/article/details/6208227   http://www.eefocus.com/Galois/blog/10-02/184555_16c21.html   http://wenku.baidu.com/view/a5b7d38002d276a200292e80