top Satellite Swarm Spots North Pole Drift
This is important work, which compliments terrestial geomagnetic measurements and space based observations.
The earth's magnetic field results from a planetary dynamo. Magnetic field lines get frozen into the electrically conductive fluid core. Then, differential motions in the fluid causes the magnetic field to get twisted up -- it's no longer is the simple dipole (like those bar magnets that you played with as a kid). Instead, the earth's magnetic field develops high order moments (sorta like bumps and dips). These shapes evolve as the conductive core moves. Eventually, the magnetic field gets so tangled up, that it unravels. At that time, the earth's field reverses. These magnetic field reversals show up in the geologic record
... every 10,000 to 100,000 years, there's a flipover.
Measurements like the ESA Swarm satellite give us a handle on the evoloution of the Earth's magnetic field, as well as showing how that field interacts with the magnetic and particle environment of the solar wind.
(disclaimer - most of what I just posted is from a terrific graduate class that I took at the Lunar & Planetary Labs way back in 1979, and when I worked with Charles Sonett, who studied the solar wind. Likely, much of this is way out of date!)
top Whom Must You Trust?
I saw a short section of the German version of that Nova show
... apparently I speak fluent German in the that version!
Mit den besten Wünschen,
top Whom Must You Trust?
And my thanks back to you, oh Anonymous Coward: The 15 cents in royalties from your purchase of m'book is now helping my kids attend college. Uh, it'll last about 1.3 minutes.
You say that you're managing firewalls - all sorts of possibilities! I had the honor of working with Van Jacobson at LBL when he first researched TCP/IP traffic jams and compression. I was amazed at how much could be done by looking at traffic and thinking about the interaction of traffic, buffers, routers, and network congestion. Wonderful stuff - what looks like a boring problem may be an opportunity for research.
With that in mind, here's my encouragement to you: Go and sharpen your tcpdump & wireshark tools. Figure out what's really happening to those packets. Who knows what you'll uncover?
top Whom Must You Trust?
Now it's your turn: Go forth and make our networked community friendlier, stronger, more trustworthy, and more useful.
PS: Of course, you raise a fascinating, self-referential question. How can you tell if this posting is from the real Cliff Stoll? I know it's me - and it's easy to prove in person, but difficult online. For the best proof, well, stop by for coffee. Way more fun than posting online.
top Whom Must You Trust?
It's been a quarter century since I chased down those hackers. Hard to think back that far: 2400 baud modems were rarities, BSD Unix was uncommon, and almost nobody had a pocket pager. As an astronomy postdoc (not a grad student), I ran a few Unix boxes at Lawrence Berkeley Labs. When the accounting system crashed, my reaction was curiosity: How come this isn't working? It's an attitude you get from physics -- when you don't understand something, it's a chance to do research. And oh, where it led...
Today, of course, everything's changed: Almost nobody has a pocket pager, 2400 baud modems are a rarity, and Berkeley Unix is, uh, uncommon. What started out as a weirdness hiding in our etc/passwd file has become a multi-billion dollar business. So many stories to tell
I've since tiptoed away from computer security; I now make Klein bottles and work alongside some amazing programmers at Newfield Wireless in Berkeley. Much fun debugging code and occasionally uncorking stories from when Unix was young.
Warm cheers to m'slashdot friends,
top Billion Year Storage Media
Excellent thesis and a most delightful dedication!
A few salient points from this thesis, for the Slashdot crowd:
- Accumulation: knowing what to keep and what to toss
- Distribution: where/how to keep copies
- Digital stewardship: maintaining objects isn't enough ... you must properly catalog things
- Long term access means more than just saving bits ... they must be properly rendered
Convolved on this are problems with copyright, fair use, payment for archives, orphaned collections...
Then there's the cost of creating and maintaining a long term digital repository.
Librarians have done a terrific job with our printed archives. Who will become our digital librarians?
top TSA Reminds You Not To Travel With Hand Grenades
Some 25 years ago, I was on booktour for Cuckoo's Egg. I visited Iowa City and spoke at Prairie Lights bookstore -- delightful people and a wonderful place! A haven for writers, readers, and hackers.
After my talk, I passed along a Klein bottle to an Iowa computer hacker who was fooling with unix. In turn, he gave me a
Corn Grenade . I tossed it in my backpack, headed for my next stop, and next evening went to Ames Municipal Airport.
This was in pre-TSA days, but there was certainly airport security: the security guy at the Ames airport discovered the corn grenade in my carry on. Happily, he recognized what it was - a cool, brass, art sculpture which was completely inert. By that time into booktour, I was pretty inert. We chatted for a few minutes, and I took the commuter plane to Chicago.
I'd forgotten about my 3 pound brass friend when the plane landed at O'Hare. But the Chicago X-ray scanner found it, and all sorts of alarms went off. Natch, I was taken aside, given the third degree. Seems that corn grenades aren't recognized in the distant lands of northern Illinois. I had to explain all about corn grenades (and my book, and klein bottles...) Missed my flight, slept overnight in O'Hare, and wound up shipping the heavy lil' guy by UPS ground. Today, that brass ear of corn smiles at me from across my dining room, reminding me when I got hacked by a computer jock in Iowa City...
top With an Eye Toward Disaster, NYC Debuts Solar Charging Stations
Solar powered chargers in the aftermath of a hurricane?
It'll be days after a hurricane before there's a clear day. Solar panels work poorly on cloudy days ... those on my roof generate about 5 to 30 percent compared to full sunlight.
top India To Send World's Last Telegram
My first job was delivering telegrams (by bicycle) in downtown Buffalo during the 1960's.
My Western Union office had its hours posted on the door: "We Never Close". The building's been torn down, so, in a sense, the message turned out to be true.
Question: what'll happen to the American Telephone and Telegraph Corporation?
Here in Berkeley, one of the main drags is Telegraph Avenue and a cell-phone store is named "Telegraph Wireless"
top Ask Slashdot: How Important Is Advanced Math In a CS Degree?
I work in computing; a meter away is a mathematician.
He knows real math: group theory, complex analysis, Lie algebras, topology, and, yes, differential equations. To him, math isn't about numbers
... it's about rigor, elegance, and beauty.
No surprise that his code is rigorous, elegant, and beautiful. When he showed me how to use Cheetah to build templates in Python, he explained things with an clarity and parsimony. In his world, clumsy coding is as bad as a clunky math; a clear mathematical proof is as fascinating as a tightly written function.
This man is the go-to guy for the 100 person business. Soft spoken and never argumentative, his advice and opinions carry weight. I'm honored to work alongside him; not a week goes by that I don't learn from him.
top Bennett's Whimsi-Geek Gift Guide For 2012
Yes, I am sending out Klein bottles, in plenty of time for Christmas. And, yes, my website also carries copies of my book.
-Cliff about a year and a half ago
top Why Your Dad's 30-Year-Old Stereo Sounds Better Than Yours
Sure - I remember my Dad's 30 year old radio, a
Philco model 60 from 1936. Those thirty years were the the golden age of radio I caught just the tail end in the late1950's.
His cathedral radio glowed in the dark, thanks to 5 vacuum tubes and an incandescent dial lamp. Took a minute to warm up (boot?) thanks to the 6 volt filaments and sagging line voltage (the thing drew 60 watts just idling). Superhetrodyne tuning of the AM broadcast band gave it a response from perhaps 50 to 2000 Hz, give or take 10 db. Stereo? Naw it didn't even have FM (though you could tune in shortwave broadcasts from Moscow)
Fidelity? Well, the Lone Ranger theme came boomed in just fine, as did Jack Benny, Elvis, Carl Perkins, Jerry Lee Lewis, Buddy Holly, Ritchie Valens, and the Big Bopper. Nothing like staying up late to tune the latest releases from WKBW, CKLW, or WABCs Cousin Brucie. Or joining the Night People to catch Jean Shepherd on WOR after midnight.
I've heard plenty of music since then, on vinyl, cassette, 8-track, CD's and mp3 -- great stuff! But I miss the excitement of stalking the elusive Rock and Roll station...
top Early UNIX Contributor Robert Morris Dead at 78
Whoops = replace Robert H. Morris for Robert T. Morris. My mistake...
top Early UNIX Contributor Robert Morris Dead at 78
Yes, I met and worked with Robert T. Morris in the late 1980's.
During 1986 and 1987, I had tracked a computer intruder from our systems in Berkeley California, through a complex trail, into Hannover, Germany. Using a honeypot, we were able to show the involvement of the E. German Stassi and a rather mysterious Bulgarian connection. I testified at the intruders' trial in Germany.
As the investigation wound up, I visited the National Computer Security Center (a part of the NSA), and met Robert T. Morris. Of course, I'd known him from his Unix/Bell Labs days. With a cigarette in his hand, we talked extensively about password security and the need to go beyond simple encryption of the Unix etc/passwd file. (At this time, salts & rainbow files were in the experimental stage). He was convinced that encryption was needed for many more processes than just logging into a system.
Later, Bob Morris encouraged me to write up my experiences in a paper, "Stalking the Wily Hacker", which was published in the April 1988 CACM.
Robert T. Morris was one of the computer pioneers who foresaw the troubles of unsecured computers and networks. He recognized that it wasn't possible to simply isolate a computer from the network -- that a computer's power was multiplied when connected to others. And his work in applying cryptographic protection to data foreshadowed much of today's efforts in computer security.
All of us owe Robert T. Morris a debt: our systems and networks work better and more securely because of his work.
May he rest in peace.
top Sputnik Moment Or No, Science Fairs Are Lagging
Two mornings each week, I volunteer to teach physics to local 12 & 13 year old kids.
They're homeschooled kids; we meet at one of their homes for 4 hours a week. I'm teaching the science class that I wish I'd received when I was in 8th grade.
3 months of Newtonian physics, then a month on wave mechanics (made a glass wave tank!), we're now finishing thermodynamics and will soon start E&M. Heavy on experiments: bicycle wheel gyroscope, conservation of momentum when throwing a football while standing on a skateboard, entropy & heat of crystallization using Sodium Acetate. We use the physics apparatus that I've collected over the years
... some professional equipment and a lot of homebrew demos. An oscilloscope that cost $25 at a yardsale.
This past Tuesday, we measured the distance to the sun by comparing the warmth of sunlight on the kids hands to the warmth from a 100 watt incandescent lamp. By adjusting the distance from hand to lamp, they found the distance from the light where it was "just about as warm as sunlight". Then they looked up the solar luminosity and used the inverse square law to deteremine the astronomical unit. Got it to with 30 percent of the canonical value. (of course, Slashdot people will see the circular reasoning here, but letting the kids figure that out is part of the fun).
No tests - it's immediately apparent when someone doesn't get something, and when to take a different approach. Occasional homework (always an experiment: for instance, determine the vertical distance (in meters) from the sidewalk outside your house to your bed. Knowing your mass in Kg and the gravitational constant, find the amount of work it takes to walk into your house and go to bed. Notice that there's no "right" answer to this question, and it's unlikely that two kids will get the same answer)
Parents often bring muffins & goodies; the kids are curious, enthusiastic, and motivated. Best part: I take home a broad smile
... it's the high point of my week.
A friend of mine - a PhD chemical engineer - volunteers at the San Francisco Exploratorium. Another friend works as a docent at a nearby bird sanctuary.
All of us are busy, yet each of has something to contribute. Mix your interests with enthusiasm, toss in some creativity, then get out there and volunteer. You'll never know how much fun it'll be!
-Cliff on a sunny Saturday morning in Oakland, California
top Science Luminary Martin Gardner Dead at 95
After he saw one of my first Klein Bottles, Martin Gardner encouraged me to make them for recreational mathematics enthusiasts. "Even if the Klein Bottles don't work out, you'll have fun meeting these folks"
And so began my zero-volume business.
In high school, I followed his instructions to make hexaflexagons and fooled with Knights tours on chess boards. Much later, I was honored to correspond and meet him.
In person, he was just as curious, creative, and encouraging as you would expect from his writing.
Along with others here, I will miss Martin Gardner - his Scientific American articles, his wide ranging books, and his warm support. He leaves a wide wake behind him.
top Taylor Momsen Did Not Write This Slashdot Headline
I graduated high school in 1968. Used to mow the grass of a neighbor -- a crotchety old woman who was apparently the niece of Herman Hollerith.
And yes, she used to shoo the kids off her lawn...
top Robot With Knives Used In Robotics Injury Study
To prevent injury from rotary table saws, a company called SawStop makes a finger-detecting rotary saw. If your finger gets into the blade, the saw instantly stops.
It detects finger or flesh by electrical conduction, it mechanically and electrically stops the rotation of the saw blade - so quickly that your finger is not injured.
The finger detection is impressive - if a hot dog is pushed into the fast rotating blade, the blade stops with less than a millimeter of cut into the hotdog.
This is not simple proximity detection or optical sensing. I think that the sawstop system detects contact of the sawblade with a human through capacitance. Much like a high-gain, high input impedimenta audio amplifier will create a loud hum if you touch the input.
I can imagine future robotics also using similar electrical detection of humans.
top What Every Programmer Should Know About Floating-Point Arithmetic
Over at Evans Hall at UC/Berkeley, stroll down the 8th floor hallway. On the wall, you'll find an envelope filled with flyers titled, "Why is Floating-Point Computation so Hard to Debug whe it Goes Wrong?"
It's Prof. Kahan's challenge to the passerby - figure out what's wrong with a trivial program. His program is just 8 lines long, has no adds, subtracts, or divisions. There's no cancellation or giant intermediate results.
But Kahan's malignant code computes the absolute value of a number incorrectly on almost every computer with less than 39 significant digits.
Between seminars, I picked up a copy, and had a fascinating time working through his example. (Hint: Watch for radioactive roundoff errors near singularities!)
Moral: When things go wrong with floating point computation, it's surprisingly difficult to figure out what happened. And assigning error-bars and roundoff estimates is really challenging!
Try it yourself at:
top HDTV Has Ruined the LCD Market
Making many assumptions, the human eye has about 500 to 600 megapixels of resolution.
But determining visual acuity is nontrivial. Lots of physics, physiology, and neuroscience enter into it.
Visual acuity depends on a number of physical limitations set by the optics of the lens of the eye as well as the sampling on the retina.
For example, the point spread function of the lens roughly matches the sampling of the retinal mosaic (well, within a factor of 3 or so). A nicely evolved system!
Our eyes' acuity are influenced by
- Refractive error (out of focus lens, often correctable by glasses or contacts)
- Size of the pupil (physical optics tells us that a wide open iris will reduce diffraction)
- Illumination (brighter scenes give more photons, and our neuroprocessing can do more
- Time of exposure to the field
- Area of the retina exposed
- State of adaption of the eye (night [scotopic] vs day [photopic] vision.
- Eye motion & object motion in scene
For a good review of visual acuity, see: