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Identifying a mystery MAC address

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Maybe you won't have to hit "Refresh" this time,
even in Chrome

I've been struggling with the problem that some browsers, including Chrome and Firefox 5.0, don't necessarily load the latest version of this web page when you go to it. You might think I haven't written a new entry when I actually have.

Putting appropriate META tags in the HTML code didn't seem to affect this (although it worked with Internet Explorer 8 and 9 and Firefox 3).

Well, it turns out that this blog is hosted under Microsoft IIS 6.0, and in this situation, you can and should tell IIS that you want "immediate expiration," which means to put Cache-control: no-cache in the header of the HTTP messages (not the HTML code, but the lines of data that precede it).

I got my ISP to do this for me, and now I think everything's fine.

I think it was Rob Caskey who put me on the trail of this. Thanks, Rob!

Another hiatus: We have a lot going on, and you'll read all about it in the first week of August! Until then, I'll be away from the Daily Notebook for a while.


Happy anniversary, Melody!


So many standards to choose from

"The nice thing about standards," said my old friend Bob Stearns, "is that we have so many of them to choose from."

I recently came across a particularly amusing situation about the way air pressure is measured. In studies of human respiration, pressure is measured in centimeters of water (cm H2O), because of traditional instruments that involved making the air move a column of water up or down.

Well, since the density of water is 1 gram per cubic centimeter, you might think this unit would work out to something neat in the Metric System. It almost does. Consider these numbers:

1.000 atmosphere = 1013.25 millibars = 1033.23 cm H2O

Why couldn't it have been 1.000, 1000, 1000? The situation is messy, but the key idea is that people have tried to make "normal atmospheric pressure" come out to 1 or 1000, and the pressure of the atmosphere varies. Also, it's a handy coincidence that the normal pressure of the air will raise a column of water 10 meters — if it's a slightly stormy day.


A disquisition on fluorescent light fixtures

If you have overhead fluorescent light fixtures, and they don't have a crinkly surface like this one, you're missing something important.

The untrained person — including me, a few years ago — tends to prefer a "cloud" or "puff" fixture with a plain matte white surface. That's a mistake.

In fact, the way they're displayed at Lowe's or Home Depot facilitates the mistake. You look straight at the fixtures as they're displayed on a wall or tilted panel. In that position, the good ones look as if they produce too much glare, and the glare-prone ones aren't recognizable.

The prismatic (crinkly) surface in the picture is what you always see in offices and institutions. It looks official or institutional, so it's not what we initially chose for our home office — but it works better. I am now in the process of correcting my mistake.

Plain matte white plastic absorbs a surprising amount of light (maybe 50%). The rest, it sends in directions that are not optimal. Much of the light goes sideways, into your eye. The rest goes on the objects nearest the light fixture.

The prismatic surface transmits nearly 100% of the light, more of it at a 45-degree angle than straight down, so that it reaches the corners of the room evenly. And very little light goes sideways, into your eyes. A prismatic fixture on the ceiling doesn't look as bright as a "white cloud" fixture, even though it's putting out more light.

The one we are installing is a Crescent 4-bulb fixture with only the outer two bulbs installed, for evenness. We've put two of these in my long workroom, replacing bedroom-style incandescent fixtures, and we're about to put one in Melody's studio, replacing a "litepuff" style fluorescent that was actually considerably more expensive, though less efficacious.

Identifying mystery MAC addresses

Yesterday I read about a heinous crime perpetrated by someone who hacked into his neighbors' wireless network in order to harass them.

I should add that this was a rare crime, but there are other Wi-Fi hazards. If you have any kind of network security (password, WEP, etc.) at all, you almost certainly won't get hacked. But if your Wi-Fi network is unsecured, it will certainly be used by strangers who may be up to no good. If nothing else, they will violate copyrights or send spam and get their behavior traced to your address.

So although my network is relatively secure, I decided to ask my Linksys router for a list of DHCP clients (computers to which it had assigned addresses). These are not necessarily all the devices connected by Wi-Fi, because some have fixed addresses, but it's the most likely way to spot an interloper.

And there did seem to be an interloper. After about a dozen (!) computers with known names (even Caligula, which is Sharon's Asus Eee), I saw this:

What on earth is an NP-K0A123006681? Fortunately, I was able to look up its MAC address, 00:0D:4B:81:02:91, at http://coffer.com/mac_find/.

It's our Roku box, for watching Internet TV.


Color business cards

Full-color business cards are cheaper than ever. I recommend OvernightPrints, whose cards come in amusing little bubble packs of 25, so that if you order 500, you get twenty packs. I don't recommend Vistaprint, whose ordering process had me running the gauntlet of optional features and "free" magazine subscriptions until I gave up on it.

Either way, you follow their instructions and upload a 300-dpi TIFF file with nothing too close to the edges. OvernightPrints held the margins much more precisely than they had promised to.

Strange tax law repealed

One of our oddest tax laws has been repealed without ever taking effect.

The law would have required small businesses to file Form 1099 every time they spent more than $600 buying supplies or services from any vendor. That would have been a huge paperwork burden. I would have had to send out dozens of Form 1099s every year.

Form 1099 has been around for a while. It's used when a business makes a payment to an individual (not a corporation) for work, and that individual is not its employee, so no taxes are being withheld. Magazines and publishers file Form 1099 to tell the IRS they've paid me royalties.

Someone had the wacky idea that by burdening us with lots more Form 1099s, the government would be able to collect some taxes it was otherwise missing out on (with no change in the actual tax rates). Fortunately, everybody saw that this was a bad idea.


Farewell to Borders


Word has just come that the entire Borders bookstore chain is closing down. Back in 1995, I think it was, I came across a Borders bookstore in Atlanta, in the Peachtree-Dunwoody area of Atlanta, and I was excited — even though not attached to a university, it had Cambridge and Springer mathematics books.

Soon they opened up a store in the Gwinnett Place area, and we regularly went there as a family. It closed in 2004, but a new Borders, a bit smaller, had already opened up in Athens. [The newspaper tells me it opened in November 2000.] We regularly shopped there, and also at their large store in Buckhead (Atlanta).

In recent years, the local store stopped selling music (CDs) and generally scaled down. It's much less academic than it used to be (no Loeb Classical Library, for instance). But it's still a decent bookstore. Until now.

We still have Barnes and Noble — at least for the moment.


What I said yesterday...

Word from Capitol Hill is that a lot of people are saying what I said yesterday, and Congress is getting the message. Threats of a default have become less intense.

On to a more mundane matter. Did you have to press Refresh (the circular arrow) in order to see this or any other recent update to this Notebook? If so, please tell me what browser you are using.

As your credit card bills arrive this month, check the due date, and if it's less than about 18 days from the day the bill reaches you, the biller may be violating the law. I caught one of them at it today.

The law requires that the bill be sent out at least 21 days before the payment is due. Most bills are bulk-mailed without postmarks, so there is no proof of the actual mailing date. The date on the bill is, of course, irrelevant — it's the day they printed it, not the day they mailed it. Allowing 3 days for first class mail, you should have 18 days to pay every bill. If you don't, you should complain.


Incompetent Congress, or worse

By even threatening to default on government payments, Congress is already damaging the U.S. economy. An actual default would do terrible damage and undermine our national prosperity for decades to come. We are not in an emergency here, just a management mess of our own making. Creating an artificial emergency does no good.

I realize that when I say "incompetent Congress" I may be repeating myself. But deliberately damaging the economy for political purposes is worse than incompetence — it is malfeasance and might justify impeachment, or certainly recall.

Personally, I think defaulting would be illegal under the 14th Amendment, and accordingly, the debt ceiling has no real force (it is just a statement of intent). And I'm strongly in favor of cutting government spending and raising revenues. But let's not ruin the whole economy while doing it.

Speaking of revenues... Many people who call themselves "conservatives" don't want to conserve anything except their favorite tax loopholes. Giving someone a tax break is exactly equivalent to paying them money — economists call it a tax expenditure — but that is where the most wasteful government spending occurs, because some "conservatives" will say, "you're just letting them keep their own money" (instead of paying their fair share), and the tax breaks don't get the kind of scrutiny that actual payments would.

The most popular tax loophole right now is the low income tax rate on long-term capital gains. Is there any real reason at all why income from an investment should be taxed at a lower rate if you've held the investment six months than if you haven't? No, but lots of moderately-rich Americans use this to shelter much of their income. As I understand it, this tax break was instituted as a clumsy way to compensate for inflation in the 1970s. We haven't had that kind of inflation for decades. But if you want to know why the rich don't pay income tax at the rates corresponding to their income, that's the main reason.

Economist Greg Mankiw sensibly recommends that for now, we keep our tax rates the same but fill the loopholes. That would raise revenue appreciably.


You are not a gadget

One of my first blog entries was titled Against cybernetic totalism and was written in response to (and agreement with) an essay by Jaron Lanier. Since then, Mr. Lanier has kept writing. His latest book is titled You are Not a Gadget. I haven't read all of it yet, but here are some observations of my own along similar lines:

The Internet is pressuring people to package all information in just a few simple ways. If something can't be Googled, it's not an idea. Quick information retrieval is substituting for deep thought.

A few computer geeks in the early days of microcomputing were too glamorous, and even their limitations have been glamorized. That's why the Net community is still so very naïve about ethics, economics, and the fair allocation of costs. Everything "wants to be free" because the glamorous leaders are (or used to be) young students supported by their parents.

Anonymous commenting has led to anti-intellectualism and bullying. There's a reason this Notebook doesn't have a "comment" button, and there's a reason I sometimes "unfriend" people for heckling me on Facebook. And look at the dreck that appears on the web pages of newspapers that allow anonymous comments. No sooner does a crime occur than people start heckling the victim. This is uncivilized. It is not freedom of thought or freedom of expression.

As I said some time back, defending my choice not to allow anonymous comments here, some ideas cannot ever be expressed in a hostile environment. They require subtle elaboration and pondering, not quick responses to detractors.

Advice for freshman computer programming students

A graduate student friend of mine is about to teach the University of Georgia's CSCI 1301 (introduction to programming) for the first time. I shared with him the following advice for the students (especially freshmen):

(1) We do not teach by repetition. In high school, all courses take about four times as long as they need to, and there's plenty of "review" and just plain repetition all the time. Not in college. You're supposed to learn things as they go by; there won't be much review. If you really like repetition, you can take the course again, I suppose.

(2) There is no busy-work. All the unnecessary parts have already been left out. We don't have time to waste, and we aren't here to waste your time. If you find you need lots of extra practice with something, give yourself an extra assignment!

(3) This is a hard subject, and we can't make it easier. If you want your computer programs to work, you have to learn the material. Yes, it's hard, which is why it's worthwhile. Don't ask us to give you an inadequate course just to make it easier.

(4) You are not here to "think like the computer." You are here to learn how the computer thinks. If you become at one with the computer, you become useless; we already have the computer! Always cultivate the ability to describe your computer programs in English (not just the programming language) and to compare them to computer programs in other programming languages.


It's gone!

My very first date with Melody was lunch at a pizza buffet called Pizza Inn in April or May of 1976. In the mid-1980s, I used to go to the same buffet with Harold Pritchett and the late Bob Stearns to talk about cutting-edge computer technology. And then, in the late 1980s, the building became a strip joint named Chelsea's. Melody and I used to jeer (inside the car, of course) every time we rode by.

This morning I was at the electrical supply shop next door and noticed that Chelsea's is no more. The building (1051 Baxter Street) is vacant and for sale. The electricians are happy because their customers no longer think they are parking at a strip joint.

Maybe the next owner will turn it back into a restaurant. More likely, like so many Baxter Street buildings from the 1970s, it will be torn down.

I'm sure I have some readers who will want to defend the strip joint. To them I say: Stop thinking about how liberal and tolerant you are, and start thinking about what strip joints do to people, both their employees and their customers.


My Orthodox daughter

Last Sunday, Cathy was received into the Orthodox Church in a beautiful chrismation (anointing) ceremony. Her fiancé, Nathaniel Barrett, is Orthodox and in the picture you see the interior of the church in which the wedding will take place.

The Orthodox Church is a loose federation of self-goverining churches in places like Greece, Russia, and Syria that trace their origins to Jesus and to the churches founded by the Apostles in ancient times. Note that Orthodoxy is not as close to Roman Catholicism as you may think; the Orthodox did not go along with most of the medieval doctrinal developments against which the Protestants eventually rebelled. (And it has nothing to do with Orthodox Jews; same word, different context!)

If you've read C. S. Lewis's Mere Christianity, you've already been taught a good bit of Orthodox theology. Although the setting and traditions may seem exotic, the faith is familiar, and Biblical. We congratulate Cathy on this step and wish her God's blessing.

Hiatus explained

I've just returned from a week in Lexington, Kentucky, where, along with doing many other things, I attended the International Conference on Logic Programming (ICLP 2011) and gave this presentation, which is based on this newly published paper.

The conference is about logic programming — that is, programming computers to reason logically about information, rather than just to execute a laundry-list of operations, and most logic programming is done in the Prolog programming language.

Too much Fourth of July

Back home in Georgia, the Fourth of July may have a 30-minute parade and, if you're lucky, a firework show later in a different location. So we were quite unprepared for the way Lexington celebrated it — and I think Lexington made some serious tactical mistakes.

There were more fireworks in Lexington than in the entire state of Georgia — perhaps twenty good-sized shows. As we drove around, we often could see four or five of them at once.

But the real problem is why we were driving around. From 3 p.m. to 11 p.m. the major downtown streets were closed and we couldn't get to the Hilton Hotel, which is where we were staying. Apparently, through some kind of tactical foul-up, the city closed more streets than they said they were going to, and they blocked access to the hotel on all sides. The hotel's management was quite angry — essentially they were put out of business for much of a day, with arriving guests stuck at the airport and unable to get in.

I'm angry, too. This is 2011 and Lexington is a city of 300,000. This is not 1930 and Lexington is not a little town that can shut everything down because nobody has anything else to do anyway. Holidays are not as absolute as they may once have been. Plenty of businesses, including hotels and banks, have some essential operations on everyone else's "day off."

I think, fundamentally, there is an issue of freedom here. You don't have the right to make everybody do something just because most people supposedly want to do it. (Click here and scroll to the section on deontological ethics.) In this case, Lexington celebrated Independence Day, at huge hidden cost, by taking away people's freedom, including mine.

Cascading failure of a freeway

And we also participated in another man-made disaster, though not so deliberately man-made. The trip up to Lexington was expeditious, from Athens, Georgia, westward to Atlanta and then northward along Interstate 75. Not so the trip back.

We headed back yesterday (July 9), and by the time we got halfway through Tennessee we had been in six major traffic jams (each bringing us to a standstill) and had averaged less than 40 miles per hour in a 70-mph zone. Infrastructure (gas stations, rest rooms, etc.) was overcrowded and failing.

What was going on? We heard about a chemical spill on the road in northern Tennessee and road work in southern Tennessee, but that doesn't explain it all. My theory is that it was a cascading failure — each traffic jam was causing crashes which caused more traffic jams. We were nearly rear-ended by numerous vehicles — either trucks with overheated brakes or people asleep at the wheel — that just didn't slow down when we had to stop ahead of them.

In Loudon, Tennessee, we bailed out and came home through the mountains, via Vonore, Madisonville, Ducktown, and into Georgia on the Canton Highway, then eastward to Dawsonville and Gainesville. Tennessee 168 near Tellico Springs is very scenic, but I'm glad I don't normally have to go this way!

Will this fix a battery?

I haven't tried this, but the oddest thing I learned at the conference is that a failing NiMH battery can be fixed by dropping it onto the table from a height of six inches, then charging it.

We know that batteries often fail because small conductive crystals grow inside them, causing the charge to leak off. I've removed these crystals by briefly charging with very high current; this burns out the crystals but may also blow a fuse in modern laptop battery packs. So I'm going to try the dropping trick. Does anybody know more about it?


Cameras you can focus after you take the picture

By now you've heard about newly invented digital cameras that let you adjust the focus after you take the picture soon to be marketed by Lytro. How on earth do they do that?

It's called light field photography, plenoptic photography, or, sometimes, "4-D photography" because you're recording four dimensions for each pixel — two dimensions of position and two more dimensions to indicate which way the ray of light was traveling when it hit the sensor. Maybe "5-D" because you can also reconstruct distance.

I don't have time to draw diagrams, but here's the key idea, as best I understand it.

Where an ordinary sensor would have one pixel, a 4-D sensor has a small square array of pixels, with a microlens in front of it. I'll call the smaller pixels "subpixels."

If the camera lens is focused perfectly on the plane of the microlens, then the light from a point on the subject will go right through the middle of the microlens and hit all the subpixels.

If the camera lens is slightly out of focus, then the light from a specific point on the subject does not hit all the subpixels in one set. Part of it goes to specific subpixels in neighboring sets.

Afterward, the computer can figure out what went where, and reassemble the picture as it would have looked if the camera lens had been focused differently. It can also extract some 3-D (true distance) information, since, essentially, each pixel is now a whole eye.

The down side, as I see it? You need all those subpixels — a Stanford prototype used 175 subpixels per real pixel, and their 16-megapixel sensor produced only a tenth of a megapixel of ultimate image resolution. There is no word yet on how many pixels Lytro will give us.

Short notes and a hiatus

Politico-economic oddity of the day: The federal debt limit might be unconstitutional (or rather might have force only as Congress's statement of its own intent, not an actual restriction on the government). We'll see how this plays out.

Illumination: My upstairs workroom, about 12 by 25 feet, originally had 3-bulb bedroom-style incandescent light fixtures. Over the years I replaced the bulbs with brighter compact fluorescents and hung the covers a little lower to try to spread out the light more evenly.

Yesterday I moved into the 20th Century. You've seen fluorescent light fixtures with an alligator-skin texture in the clear plastic? That's called a "prismatic" texture, and it really works as a way of getting light all over the room. The edges of the cover have a different, straight-line prismatic structure in order to throw more light onto the ceiling.

We see these in office buildings all the time. Now I have some at home, and they're bright. I have four-bulb fixtures but will probably take out half of the bulbs. A four-bulb fixture is a good way to hold two bulbs relatively far apart, for more even illumination.

Hiatus: I'm not kidding about the date on this entry. The Notebook is going to go on hiatus for a few days while I'm doing other things. I'll see you again at mid-month!

If what you are looking for is not here, please look at previous months.