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05/17/2006
Weighing Small - Scanning Large
Last week, I wrote about Michael Brown at Caltech and his
discoveries of objects rivaling or exceeding the size of the planet
(or non-planet) Pluto. Another Michael at Caltech pursues a
smaller objective. Michael Roukes hopes some day to measure
an object weighing about one yoctogram! You say, “What the
devil is a yoctogram?” That’s what I said when I saw the term in
an article by Robert Service in the May 5 issue of Science. A
yoctogram is 0.000000000000000000000001 gram (10 to the
minus 24th grams). A hydrogen atom weighs 1.66 yoctograms.
Roukes and co-workers, in the April 4 issue of Nano Letters,
report the world’s most sensitive mechanical scale. They have
weighed something as light as 7 zeptograms. (A zeptogram is a
thousand yoctograms or 0.000000000000000000001 grams.)
How do they do it? Consider a string in an instrument such as a
guitar or violin. Pluck the string and it vibrates at a specific
frequency or pitch. The thicker the string, the lower the pitch.
Shorten the string by placing a finger on it and the frequency
goes up, a higher pitch. The frequency depends on the weight of
the part of the string that’s vibrating.
During a concert, the string may shed or pick up bits of dust.
The change in weight should affect the frequency. However, the
dust weighs so little compared to the weight of the string that you
don’t detect any significant change in pitch. But suppose you
make a super thin, super short string and place it in a vacuum
chamber. Now pluck the string. If the string is of a nano size, it
will vibrate at a very high frequency you can’t hear, nearly
microwave frequency. While it’s vibrating, squirt in a spray of
relatively heavy xenon atoms or nitrogen molecules. If you keep
your string cold, some of the atoms or molecules sit down on the
string. For our miniscule string, the extra weight lowers the
frequency enough that the change is detected by your sensitive
frequency-measuring apparatus.
This is essentially what Roukes and his colleagues did. By
measuring how much the frequency changes, they can calculate
the extra weight. Their limit of detection of 7 zeptograms is
equivalent to being able to detect about 30 xenon atoms. This is
also about the mass of a typical protein molecule. The “strings”
in their experiments were tiny rods of silicon carbide a micron
long and a hundred or so nanometers in width. (I just measured a
hair on my arm as between 30 and 50 microns. A micron is
1,000 nanometers.) They “plucked” the silicon carbide rods
electronically by placing them in a magnetic field and passing
current through them. The sideways force in the magnetic field
simulated the plucking.
Roukes and Kamil Ekinci, a former postdoc and now a professor
at Boston University, and their colleagues are working to get
smaller slivers and to improve the sensitivity of their frequency
measuring apparatus. They are optimistic that they will be able
to weigh that individual hydrogen atom. They also foresee the
possibility that in the future assemblies of these tiny vibrating
tuning forks will be used to weigh and determine the presence of
various proteins in applications such as identifying proteins
associated with cancers or other maladies.
There’s another type of effort going on at nearby Stanford
University that sort of falls between the Caltech projects of the
very large and the very small. This effort involves taking
something very large and condensing it into something very
small. In the May 14 New York Times Magazine section, the
feature article “Scan This Book” by Kevin Kelly is a provocative
treatment of the projects currently underway to create a “library
of libraries”. This utopian library would involve scanning all the
world’s books and incorporating them into a digital library that
could be housed on a relatively small number of disks, perhaps
even in the iPod of the future. The ultimate library would, of
course, contain not only all the books but also all the TV
programs and movies and all the songs ever recorded plus all the
art ever painted, as well as all the Web pages ever published.
According to the Times article, in the course of human history
there have been “published” over 32 million books, 25 million
songs, half a million movies, 3 million TV shows, videos and
short films, half a million images and a hundred billion public
Web pages. Let’s just worry about the books. I visualized the
scanning operation as being a painful process requiring a person
to turn each page, flatten it on the scanner and push the button.
Wrong. Stanford University is scanning its collection of some 8
million books utilizing a robotic scanner made by a Swiss
company, 4DigitalBooks.
Go to the company’s Web site (4DigitalBooks.com) and you can
watch pages being turned. The machine turns pages at a rate of
1,500 to 3,000 pages an hour without the need for a human
attendant, except to place and remove the books! The robot is
also delicate enough to handle older rare books and can handle
both hard and soft cover books. It’s only costing Stanford $30 a
book, according to the Times article.
China is also scanning. A Beijing company called Superstar has
already scanned all the books from 900 universities in China;
well over a million different titles. In China, the cost is only $10
a book. Do you smell outsourcing? You bet. In 2004, Prof. Raj
Reddy of Carnegie Mellon University gathered 30,000 books
from the Carnegie Mellon and Carnegie libraries and shipped
them off to China. Carnegie Mellon’s “Million Book Project” is
a multinational effort involving universities and institutions from
China, India and the U.SA. The goal is to finish scanning a
million books by 2007. As of last November, over 600,000
books had been scanned, according to Carnegie Mellon’s Million
Book Web site.
When the Million Book Project is finished the million books will
take 50 petabytes of disk space. (I had to look up petabyte – it’s
a quadrillion (10 to the 15th) bytes.) A double-sided DVD can
store 17 gigabytes. I figure it would take 3 million DVDs to
store the million books. I’m skeptical that the ultimate library
will ever fit into an iPod but I could be wrong.
To make the ultimate library worthwhile, you want to be able to
search the library for various titles or topics, just as you can do
now on the Internet. To do this, the scanned pages in the library
can’t just be photographs of the pages. The letters and words
have to be identified as what they are. An “a” must be
recognized as an a, etc. Enter the problem of Optical Character
Recognition. The scanning software has to recognize the letters
and words as such. In older books especially, the images might
be poor and 100% accuracy is impossible.
Of the over 600,000 books scanned in the Million Book Project,
only about 135,000 were in English. The rest were in Chinese,
“Indian”, French, and other languages. India has over a hundred
spoken languages and 17 different scripts. The number of
characters the scanning software must recognize is in the
hundreds. Not only that, but in a couple of Indian languages the
characters in a word are connected by a line that makes
separation of the characters very difficult. It’s a huge task!
A parting thought. When that ultimate library gets shrunk down
to the size of a few disks, NASA clearly must send a spacecraft
containing copies of these disks out into space beyond our solar
system. Zillions of years from now, some unsuspecting creature
from another universe may find the disks and be able to read this
column and watch reruns of Seinfeld. I’d love to see his or her
or it’s reaction!
Allen F. Bortrum
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