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And that which makes their Fame ring louder,
With much adoe they shew’d the King
To make glasse Buttons turn to powder,
If off the[m] their tayles you doe but wring.
How this was donne by soe small Force
Did cost the Colledg a Month’s discourse

(Ballad of Gresham College)

It was Prince Rupert of the Rhine who brought tadpole-shaped droplets of glass with a long, thin tail to Britain in 1660 as a gift to King Charles. These droplets have extreme hardness. They could withstand a blow from a hammer on the bulbous end without breaking, while they disintegrate explosively if the tail end is even slightly damaged. It can be said to be a kind of tempered glass.

Watch this video!


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The Dark Fiber

fiber_opticIt won’t scare you away. It’s just an optical fiber. It is not a special one, too.

When companies run fiber optic cable, they run two or three times the amount of fiber they require for future sake. These spare, unused strands are called dark fiber, simply because there is no light passing through them.

Telecommunication companies often leases out these extra strands to other companies.

The fact that the diameter of these strands is very small might scares you. A commonly used single-mode fiber strand core has 8.3 microns in diameter. (Micron is a non-SI name for micrometer. One micron equals to one micrometer, that is 0.000001 meter). The core of multi-mode fiber is typically 50 or 62.5 microns. They are smaller than a human hair. The coating layer usually has 250 microns in diameter. They are all the way to one-ten thousandth of a centimeter.

Dual fiber-optic cable

The tiny diameter of fiber strands makes them extremely dangerous. When stripped of their coating layer, the strands can easily penetrate the skin. The shards can be carried by blood vessels to the other parts of the body, even the brain! This could wreak serious havoc. They can pierce the eyeball too, and possibly getting trapped inside.

That might be the dark side of the fiber.

So, use your safety glasses and special shard-disposal containers when connecting or splicing fibers.

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Signals and Systems for Free

I am trying Windows Live Writer to write this post. Hope it’ll work just fine.

One of books I fond of during my study is Signal and Systems, 3rd edition by Prof. Chi-Tsong Chen. This book is a lot of thinner than everyone expects compare to other books of the same subject less than half of two other books available in my department’s library. But it is still a focused and concise text of CT and DT signals and systems.

signal system

Today, I found this information in the author’s website:

After teaching and writing for over forty years, I am on the verge of retirement and have decided to give the book [Signals and Systems: A fresh look] away as a gift to the students in my class and any other interested readers. It can be downloaded as a pdf file of size 4.6MB. If you find the book useful, please spread the word.

Well, I simply recommend this book to be downloaded. Solution manual is available too.

Oh, almost forget! I also like the author’s sympathy:

Students taking a course on signals and systems usually take three or four other courses at the same time. They may also have many distractions: part-time jobs, relationships, or the Internet. They simply do not have the time to really ponder a topic. Thus, I fully sympathize with their lack of understanding. (p. 12, or p. xviii at 3rd ed.)

It is what most instructors forget about 😀

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