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Comment My Dad's 30 year old radio glowed in the dark (Score 2) 674

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...

Comment Re:Stoll's "Cuckoo's Egg" has some great anecdotes (Score 5, Informative) 90

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.


Comment Don't grumble, Volunteer ! (Score 2) 414

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


China's Nine-Day Traffic Jam Tops 62 Miles 198

A traffic jam on the Beijing-Tibet expressway has now entered its ninth day and has grown to over 62 miles in length. This mother-of-all delays has even spawned its own micro-economy of local merchants selling water and food at inflated prices to stranded drivers. Can you imagine how infuriating it must be to see someone leave their blinker on for 9 days?

First Halophile Potatoes Harvested 117

Razgorov Prikazka writes "A Dutch-based company from Groningen is trying to create a potato race that is able to survive in a saline environment. The first test-batch was just harvested (English translation of Dutch original) on the island Texel and seem to be in good shape. The company states that rising sea-levels will create a demand for halophile crops. I do wonder if one still has to put salt on ones potatoes when they are grown in salt water."

Comment Wonderful man in person (Score 4, Interesting) 96

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.


Comment SawStop for table saws (Score 1) 132

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.

Details at

Comment Hard to debug floating point when it goes wrong! (Score 4, Interesting) 359

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:

Comment Resolution of the human eye: about 570 Megapixels (Score 4, Interesting) 952

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:

Comment 15 years later (Score 5, Informative) 259

I agree with many of the Slashdot posters who've commented on my article of 15 years ago. There's a great deal to munch on - plenty of hilarious mistakes as well as several ideas still worth thinking about.

That 1995 article grew from my questioning attitude. When I hear nearly unanimous commentary without any critical dialog, I become skeptical. Perhaps too skeptical, as that article shows.

At the time, I saw my role as encouraging questions about then-common predictions. As a way of introducing dialog through debate, if not deliberation.

Clearly, I'm no futurist, able to extrapolate across decades. If anyone, I suspect that school teachers are the most in touch with future generations.

Now? Oh, I try to stay away from predictions; two teenagers gleefully keep me informed of my daily mistakes. I teach physics, speak at meetings, and write the occasional article for Scientific American. I make Klein Bottles ... and, yes, I sell them online, in obvious contradiction to that 1995 article.

Best wishes to all,
-Cliff (in Oakland California, on a Monday afternoon without sunspots)

Comment Dimensional Weight (Score 2, Informative) 940

Most air freight shippers use dimensional weight to charge extra on high volume/low mass items. Charging by weight alone won't recover the costs of shipping lightweight items. For example, a pound of popped popcorn will cost more to ship than a pound of popcorn kernels.

Typically, a shipper assumes that typical freight has a nominal density of about 0.2 gm/cm^3 ... packages with a lower density than this will be charged more.

Of course, humans have a density of about 1gm/cm^3, so we wouldn't be charged extra, should we decide to be shipped airfreight.

Comment 2.5 percent of Klein Bottle purchasers now use AOL (Score 1) 1049

For the past 12 years, I've been making & selling Klein Bottles. A quick analysis of online order email addresses (no, I don't spam!) shows the decline in AOL domain for people ordering onesided manifolds:

    1997 13% (about)
    1998 15% (about)
    1999 16% (about)
    2000 14.8%
    2001 13.4%
    2002 12.2%
    2003 10.0%
    2004 4.8%
    2005 4.4%
    2006 4.7%
    2007 3.9%
    2008 3.5%
    2009 2.5%

    Cheers, -Cliff

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The most delightful day after the one on which you buy a cottage in the country is the one on which you resell it. -- J. Brecheux