Dan's Data letters #181
Publication date: January 2007.Last modified 03-Dec-2011.
Death ray
Seeing as you're apparently into flashlights, [dr evil]laser beams[/dr evil] and similar devices, I thought you'd like to see this fire-lighting flashlight.
Maybe you could shed some light on how this could work - whether its legitimate, or indeed even possible..
A A
Answer:
Sure, it's possible. 140 watts, a large slice of it heat rather than light, focussed to a pretty small spot? That'll
light paper with no trouble at all.
One can, of course, easily light paper with a magnifying glass and sunlight. If you've got insolation of 500 watts per square metre, and your magnifying glass is (for simplicity) a square ten centimetres on a side, it'll have an area of only 0.01 square metres and be collecting only five watts. And yet you can coax a flame out of newspaper with a glass that small without much trouble.
(All kids who've spent their youth correctly know that it's best to draw a converging spiral with the focussed dot, on a darkly printed part of the paper.)
Now, a filament globe in a Mag-sized reflector won't have the accuracy of focus of even a cheap flat plastic Fresnel magnifier. But to collect 140 watts from 500W/m^2 sunlight would take a magnifier fifty-three centimetres (almost 21 inches) square. You'd be pretty freakin' surprised if that large a magnifier didn't smoke any paper you pointed it at long before you got the focus down to the finest dot possible.
Of course, the down side of putting a 100W-plus lamp in a flashlight is that your battery life will be quite miserable. If you're lugging around 12 D rechargeables then you might get an hour of run time, but sucking almost ten amps out of the AAs that're all that'll fit in a Mag body when you need that many cells will probably give significantly less than the sticker capacity. I'd be very pleased with anything above a ten-minute run time.
The usual lamps used in hyper-bright flashlights these days, by the way (this is a bit out of date now, but conveys the general idea), are high-intensity discharge (HID) lamps like those used for car headlights. It took a while to develop HIDs that didn't need a lengthy warm-up period, which is obviously unacceptable for automotive applications.
They're much more efficient than incandescent, achieving lumens-per-watt figures up there with fluorescent, so you get a lot more light for your power input. A big part of the reason for this better efficiency is that they don't emit tons of useless heat. But that also means that they're no good for lighting your campfire.
Since it also means that they're less likely to unexpectedly set your tent on fire, though, most people count this as a feature, not a bug.
Computing comfort
I'm buying a new PC monitor soon and don't know if it will be a CRT or LCD. I don't have a hate for CRTs or an absolute love for LCDs (IMHO they have too many unsolved problems, and they still cost more than CRT's), but I read a lot (things like your excellent site, complete books, online magazines, etc) on the PC monitor and I heard in a lot of forums that "the radiation CRTs emit kill your vision/eyes", "my ophthalmologist told me that I lost vision and have to use prescription glasses from using CRTs for so much time" and "CRTs leave you almost blind". So what's your knowledge about this? Do CRTs really kill your vision?
I will be using my future monitor to use programs like GIMP/Photoshop Inkscape/Illustrator and Blender, so I need it to have somewhat faithful colors. I'll also use it to watch movies and occasionally to play games, so I don't want it to show any ghosting at all (I've seen it on some monitors/TVs and I can tell you I HATE IT). So I guess a cheap LCD won't cover all the things I want from a monitor. And I have a small budget!
I'm 25 and in the last three years I have lost more vision than I would like to. I'm not sure if it was from using CRTs or because of my flawed DNA, and people in general don't seem to really know about this issue, and they always suppose that CRTs are guilty and LCDs are ultra cool just because are a newer technology than CRT.
I'd like a monitor with DVI and VGA connectors, 'cause I've heard for years that you get better quality with DVI.
Also, which mouses (:D) are the best in the ergonomics department and ok in the others? Can you recommend one? Very very occasionally I suffer from what I think is a slight form of carpal tunnel syndrome.
I was thinking something like the A4 "X7 Game Mouse" - that variable sensitivity sure is useful when you edit images in Photoshop. Or maybe this not so cheap copy of the Logitech MX5XX?
And I could sure use some recommendation on a good chair for use when I use the computer a looong time, one also with good ergonomics, and a reasonable price please. Do you know any?
Thank you for your excellent site, I'm close to reading all of your site, it's one of the few sites that deserve reading it entirely, I like your sincerity and your marketing-hate :D very much.
Mariano
Answer:
The notion that CRTs endanger your eyes in some special way is complete rubbish.
It's possible that staring at a CRT with a relatively low refresh rate will give you eyestrain faster than an LCD monitor would. To suggest that this will do you any sort of permanent damage, though, is nonsense.
(See also: Magic computer glasses.)
As far as your vision loss goes, I'd bet on lousy DNA long before monitor choice.
Regarding colour quality, modern LCDs are more than good enough for most "colour critical work". If you're considering a full calibrated monitor setup, one of those arrangements with a big black shield around the screen and a monitor that costs ten times as much as a consumer model, then LCD is still not quite there yet. Most people who say that they need a CRT for the super-important colour critical stuff they do, though, are wrong.
The difference between DVI and "VGA", by the way, can be surprisingly hard to pick. But DVI is standard equipment for modern video cards and LCDs, so you might as well use it if you get an LCD screen.
There's not much money to be saved any more by going for a CRT, especially now that large consumer CRTs aren't even stocked by a lot of retailers. If you can find something like a Samsung SyncMaster 1100p Plus (21 inch CRT, 20 inch viewable) for considerably less than you'd pay for a similar-sized LCD, I recommend you buy it. You'll probably have a hard time even finding someone who wants to sell you one these days, though.
(Second-hand monitors on eBay remain a viable option for cheapskates, but you obviously don't want to pay for long distance shipping for a big CRT...)
I have no firm recommendations as far as mouses, mice or meese go. People's opinions differ. I've used IntelliMouse Explorer 3.0s for years because I like the shape, but other people prefer other models.
Setting up your desk and chair properly are the important things. Most people who have ergonomic problems have them because of where and how they sit and reach, not because of the computer hardware they use.
In the cheap chair recommendation department, I have none. Take a checklist from one of those URLs with you to your local office furnishings place and see what they've got. You can get nine tenths of the important features of the fancy Aeron and Steelcase chairs in a much cheaper no-name unit, but those no-name chairs vary from country to country, since they're often locally manufactured.
The Car They Won't Make
I drive a fair amount (anywhere from 150km to 600km per day - life in Canada has its drawbacks), and, as such, I've got a keen interest in saving on gas. The current crop of hybrids, however, don't really suit my needs - longer range, almost exclusively highway driving (at a rate of anywhere from 110km/hr to 130km/hr).
My ideal vehicle would, essentially, be an electric-only drive car, with a very small gasoline/diesel/whatever engine, running not to drive the vehicle at all, but rather only to recharge the batteries to give the vehicle a longer range (and I'd plug it in during the evening hours to replenish the batteries).
(Equally, I'd prefer the transmission to be aligned to favour high-speed-low-RPM operation, versus guts at low speed - but that's a side item, I suppose).
I know that there is significant work going on in support of plug-in hybrid vehicles (PHEVs), but it doesn't seem to be headed towards the application I've described above. Why not? Is there a fundamental truth about poor efficiency in recharging batteries that I'm not aware of?
Thanks for reading, and again - I really enjoy the site.
Dave
Answer:
I don't know why nobody's making such a car, but I think it's because there really isn't that much real fuel-price pressure driving customers toward them yet.
The hybrids we've already got are enough to soak up the greenies who want to feel environmentally sound, modern small diesels take care of everyone else who really cares about fuel economy, and that's about it.
That said, you may already have heard about Chevrolet's Volt concept car, which is pretty much exactly what you're talking about, at least as far as the drivetrain goes. God alone knows when such a thing might actually make it to market, though.
A modular car would probably suit you quite well, too, but those are even further away from production.
They must never know about my Donkey high score
If I disassemble a crashed and hopeless hard drive and apply a magnet directly to the disk platter and rub it really fast, will that erase all the sensitive data? How strong a magnet would I need? Could I lose a finger?
Stac
Answer:
If your magnet has the same or better surface field strength (in
Gauss) as the drive platter has
coercivity (in
Oersteds),
then yes, you could erase the drive with it.
Since drive platters these days have coercivity in the few-thousand-Oersted range, though, this isn't likely to actually be possible with any normal permanent magnet. Rare earth magnets are often quoted as having some ridiculous Gauss figure, but the surface magnetic strength is likely to be well below 2000G, and that may well not be enough.
Hard drive bulk erasers use electromagnets, and work on still-assembled drives. They turn the drives into paperweights, though, since they erase the servo tracks on the platters along with the data. There's no way to re-write the servo tracks, and those tracks are essential if the heads are to be able to tell where they are.
Of course, if you've got the platter in your hand and you're rubbing something on it, the data is pretty much screwed anyway. Only a data recovery expert is likely to be able to even reassemble the drive so that it works again.
If you want to prevent even that, then sandpaper will do the trick rapidly, as will acid, a hatchet, firearms, et cetera. Many corporations and government agencies go to remarkable lengths to prevent attackers with lots of time, knowledge and resources from recovering any data at all from scrapped hard drives. But even if you're trying to cover up your involvement in international terrorism or something, just taking the platters out and throwing them in the garbage is likely to be more than good enough.
Or it could be aliens
As guru of all obscure things technical, and debunker of a thousand urban myths, I thought that you might be interested in this one.
Earlier this week, we had a power cut. The power went off for about six to eight hours or so, overnight, and came on again sometime during the day. When it came back on, the digital clocks in things like my bedside clock radio, the cooker and microwave were all, of course, reset. So, they were set correctly again. Today, I noticed that they were all about five to ten minutes fast (not my PC clock, or my wristwatch, or my pocket computer's clock: just the manually-set, mains-powered digital clocks). It cannot have been an error in setting them, since a different person set the microwave and oven clock as set the clock in my bedroom, and I set the one in my bedroom from my wristwatch, which is still accurate.
My father once told me that the timekeeping of mains-powered quartz clocks is linked to the frequency of the electrical power supply, and that, due to power drain, the frequency sags in the day, and, in order to make up for the slowness that that will give to clocks, it's boosted during the night. Could this have anything to do with the weird clocks thing - would that suggest that the frequency has been way out of range on our electricity supply recently?
James
Answer:
Quartz clocks, by definition, ignore the mains frequency,
but mains-powered clocks in general certainly do use it. As you say, the mains frequency is deliberately kept reliable
over the long term; if the generating company turns the generators slower under heavier load, or whatever, then they
run them faster later, and vice versa. This, indeed, is done solely to keep all of those clocks close to accurate.
(Mains-frequency clocks also, of course, go haywire if the mains frequency changes permanently. That's only likely to happen in the modern world if you plug them into odd-frequencied generator power or take them to an area with a different mains frequency. Such clocks will run from a step-down or step-up converter if you move them to a country with a different mains voltage, but if the frequency is different, they'll only be of ornamental value.)
I wouldn't be surprised if the constant-frequency rule has been relaxed somewhat now (given the proliferation of quartz clocks, which are immune to supply variations, not to mention the general turpitude of the electricity industry in many countries), or if the power companies just don't care when there's been a long power cut for a large area and all mains-frequency clocks can therefore be expected to be badly wrong anyway. It may be unavoidable - if the long power cut was the result of a generation failure and some generator out there is now straining to supply power to a larger area, it may have to turn at a non-standard speed to do so.
But I also wouldn't be surprised if a surprising number of digital timekeepers that you'd reasonably assume to be quartz, in this day and age, are actually old-style electrical clocks. That could easily give rise to the symptoms you've seen.
Standalone mains-powered clocks have been obsolete for a long time now, of course. If you want a close-enough-for-government-work wall clock in this day and age, you just buy a battery-powered quartz clock for $3, and change the single AA battery once a year or whatever. This was not an option in the olden days of bakelite and miniskirts, when quartz clocks were very expensive (or completely unavailable - Seiko introduced the first commercial quartz wall clock only in 1968), and wind-up models weren't nearly as accurate as mains-locked versions.
(The excellent series "The Secret Life of Machines" has a whole episode devoted to the quartz watch, by the way. You can download the whole series, legally, for free!)
Perhaps You've Noticed You're Changing
From: "Pete Bright"
To: dan@dansdata.com
Subject: Link Request
Date: Wed, 10 Jan 2007 15:51:11 -0800Hi,
I was wondering if it was possible to add our website www.feminax.co.uk to your links page. The website gives comprehensive advice to women, young adults and mums alike about period pains, which I feel will be of great relevance to your audience. It also hosts the very popular Period predictor which can predict your period up to 12months in advance, as well as many other things that can help relieve period pains.
If you require anymore information please don't hesitate to contact me
Thank you in advance
Pete Bright
Webaddiction
PO Box 992
Cheltenham
GL50 9FQ+44 (0)1242 582033
pete.bright@webaddiction.co.uk
www.webaddiction.co.uk
Answer:
Your guess, gentle reader, is as good as mine regarding why Pete decided I needed to be sent this message.
Perhaps Pete's spamming software was triggered by the acronym for the old Precise Mousing Surface.
Perhaps Pete is mildly deranged.
Life is mystery.
