Observations about the universe, life, Lausanne and me

Tuesday, March 31, 2009

Sudden Flash of Inspiration

Yes, sudden inspiration happens, even to me. Last Friday for example, I was sitting on the office, picking my nose with dedication, when it suddenly came to me: "Why not a low-pass?"

You see, I have had this problem with triggering. I want to measure the voltage between electrodes in the instant of breakdown - just when the plasma forms. This instant is reasonably short (breakdown happens in the order of nanoseconds if you are an electron, and microseconds for ions), so I need to tell my oscilloscope when to measure with some other method than pressing a button. This is commonly known as triggering, and I have been using the light from the discharge as a trigger. An optic fibre picks up the light, a photomultiplier converts it into an electric signal, and when this signal surpasses a certain level the oscilloscope measures the voltage for a couple of microseconds.

Unfortunately the light emitted by the plasma can be very faint. If I boost it to a sufficient level to trigger, the noise generated by the pesky cosmic radiation hitting my photomultiplier fools the oscilloscope into triggering at the wrong time, resulting in something like this:

The voltage is the friendly pink trace, and yellow represents the light (the lower it is the more light, because the PM has an inverted op-amp somewhere). As you can see, the scope triggered on a big spike - but if it were a real breakdown, then the light-trace would stay at a lower level afterwards as the plasma continues to burn.

So, why not a low-pass? A low-pass filter is an electronic circuit that only lets low frequencies pass - in its simplest form (which I used) it is implemented by an RC circuit.

I used  an 1 Ohm resistance and a capacitor with 82 nanofarad. That gives the filter a cut-off frequency of around 2 MHz, or a rise-time of 550 nanoseconds. And the result?

Smoooth. (The little metal box on the lower left is the filter).

Of course, the filter does distort the signal a bit, but since I only use it for triggering, it does not matter. But to be sure, I overlaid the two signals to compare:

Th unfiltered light signal is in orange. It is a bit faster, but the difference is not big. If I ever want to use the signal itself, I'll whip up a Butterworth or Chebyshev filter with a steeper cut-off, but for now I am shiny.

I should have thought of that weeks ago though - a large part of my Master's Thesis was constructing band-stop filters for langmuir probes! Only I thought myself into a box trying to use the oscilloscopes smart-trigger functions to avoid the noise...

Monday, March 30, 2009

New Desktop Wallpaper

without furter ado, my new desktopwallpaper:

via Martian Chronicles.

The ISS, backlit, in case you didn't recognise it. Really, really awesome. The photo was taken by the space shuttle Discovery after separation on the 25th of March this year. Original source here.

Friday, March 27, 2009


Eothen: Traces of Travel in the East by Alexander William Kinglake.

It was his Nigeness that  mentioned it on his blog recently. Eothen is an excellent insight not only into the Ottoman empire of the Victorian age, but also into the mind of an English gentleman, braveing the rigours of  travel, observing with a keen and faintly condescending eye, the people and customs that he encounters.Yet, he seems to be aware of the absurdity of this self-assumed superiority, so his remarks are also laced with irony:

But presently there issued from the postern a group of human beings - beings with immortal souls, and possibly some reasoning faculties; but to me the grand point was this, that they had real, substantial, and incontrovertible turbans. 
 From time to time Kinglake can also brutally honest with himself. See what he has to say when his companion falls ill:

I have a notion that tenderness and pity are affections occasioned in some measure by living within doors; certainly, at the time I speak of, the open-air life which I have been leading, or the wayfaring hardships of the journey, had so strangely blunted me, that I felt intolerant of illness, and looked down upon my companion as if the poor fellow in falling ill had betrayed a want of spirit. I entertained too a most absurd idea — an idea that his illness was partly affected. You see that I have made a confession: this I hope — that I may always hereafter look charitably upon the hard, savage acts of peasants, and the cruelties of a “brutal” soldiery. God knows that I strived to melt myself into common charity, and to put on a gentleness which I could not feel, but this attempt did not cheat the keenness of the sufferer; he could not have felt the less deserted because that I was with him. 

Kingslake doesn't loose himself into tedious linear descriptions of his route, daily routine or details. He just gives you the highlights, the amusing or interesting events - which incidentally makes this an ideal book to read in short bursts during your commute or in the bathroom.

Read it online here or here or download it from project Gutenberg.

Wednesday, March 25, 2009

Obsolete Hardware

or: "How to waste an afternoon".

Today I saw a funny thing during an experiment on the 'scope. Naturally, I wanted to file a copy of the  mesurement for future reference. Previously, this wouldn't have been a problem, because I was using a very modern oscilloscope, which even had a USB interface and a network plug (And - of course -  a sticker saying "This is a scientific instrument, do NOT use it to browse the internet). I had to downgrade to an older Waverunner LT 344, because my student wanted to control it via the PC, and programming the GPIB bus is much easier than figuring out this new-fangled TCP/IP thing.

The older  oscilloscope is actually much nicer to use - it does not use a stupid touchscreen (which will misread the position of your finger on principle), and it does not run MS Windows. That means that when you switch it on it is on - no waiting for five minutes for the stupid thing to boot. Of course, the trigger is not as sophisticated, it is a bit slower, etc., etc., but I am not using microwaves anyway.

But, the 'scope can only safe it's traces to 3.5'' floppies. So I scrounged one up (this is a lab, we have all kinds of 'obsolete' storage media floating around - 3.5'' floppies, 5 1/2'' floppies, zip disks, minidisks, you name it, we have it. Somewhere.), inserted it - and the scope complained about 'bad format'. Naturally. Next, I tried the following solution:

Veterans of the DOS area will recognise the pink tape as an attempt to make a HD (High Density, 1.44 MB) floppy behave like a DD (Double Density, 720 KB) floppy. Back in the eighties I used to do it the other way 'round: Drill a hole into an old DD floppy and hey presto!, you can store twice as much on it. Doesn't do much for your data retention rate of course, but it will hold up long enough to get a copy of that hot new AMIGA game. Now I tape up the hole to fool my oscilloscope. Which is almost as much fun.

Anyway, next you have to format your disk, and there I ran into the next problem: Windows XP does not do 720K anymore.
 "You want me to do what?"

Not a problem, I thought. I'll just head over to the command line, and use the old FORMAT A: /F:720.
Nope.Windows XP does not do 720K anymore.

Thankfully, I have no photographic documentation for what followed, but yes, I did do the "Angry Monkey" dance.

Never one to be put  off easily by those infernal, modern devices that govern our daily lives, I searched the internet for an answer, and lo and behold, the oracle answered with the cryptic statement: FORMAT A: /T:80 /N:9. Now which genius in the developement team of Microsoft came up with the glorious idea of taking out the 720K option? I can see the reason for leaving it out of the GUI - you don't want to confuse users needlessly. But the command line? Who thought: "I know, let's take out all the old backwards compatibility for floppy disks, only not completely. This way, we can frustrate savy users, but still have happy floppy-formating fêtes in the evening!"

Anyway, the internet was right as always, so I headed down to the lab with my new DD disk. The oscilloscope took one quick look at it and smugly replied 'bad format'.

One quick "Angry Monkey" dance later, I sighed and went to dig up the documentation (Always the last thing to do for any self-respecting scientist). Turns out that the stupid thing can read HD floppies - only the floppy drive seems to be broken.

So finally I did what I should have done in the first place: I snapped a quick photo of the screen with my iPhone. Yay high-tech!

Tuesday, March 24, 2009

Role Playing Games

On Saturday I was at my very first game convention, the Orc'idee. I hadn't played RPGs for a loong time, so it was real fun to roll the dice again.

Unfortunately I did not snap any photos, since I still have no small camera, and didn't want to shlepp around my SLR. But here are a few random thoughts:

*) Gaming in French is hard. Half of the time I did not know what was going on, and after the game I was exhausted from concentrating (Yes I know. Me? Concentrating? Take it on faith.)

*) Legend of the Five Rings is an interesting game, and could be very much fun to play, but: It concentrates on diplomacy, intrigue and etiquette, not something that is easy to do in a foreign language. Also, it is set in a setting similarish to the medieval japan. I actually know a bit about that time, because I once wrote big paper in school about feudalism in japan. But... I and everybody else here in Europe knows more about the courts and customs of medieval Europe, obviously. I think playing in a setting here would be more fun, since it is easier to concentrate on the intrigue if you don't have to wrack your brain constantly for basic rules of etiquette. Just saying.

*) 10-sided dice are the underprivileged cousins of the role-playing dice family. Everybody else is a platonic solid, and they never, ever let the poor ten-siders forget that.

*) This being my first Convention: Gamer stereotypes? So true. Male-female ration 9-to-1 or worse. Obesity still en vogue. Bad social skills? Don't know - I hardly ever talk to strangers ;)

Monday, March 23, 2009

Excessive Force

Sometimes, when you pump down your reactor, you don't get the base pressure you think you are entitled to. Now, this is either and indication of your overblown, consumerist expectations that will be the downfall of us all, or you have a leak somewhere.  Since all know that consumerism is all that keeps the failed, capitalist system limping along (at least until you are ready to take over the world), you ignore possibility #1 and go with the leak-theory.
The first thing to do is tightening all the nuts on the seals - maybe one of the seals has not settled squarely in its groove?
The second thing to do is to notice that maybe you shouldn't have tightened the nuts too much, especially those holding  your big glas window in place. Yes, those that shows those fascinating cracks in the glass underneath the clamps. Insert a short episode of argueing with yourself about the relative merits of thinking things over versus the frantic-monkey approach and your general level of intelligence (or rather, the lack thereof).

Third, replace the now broken window with a new one. Notice that you reach your normal base pressure without trouble. Speculate loudly about the base, base nature of your reactor that delights in mocking you. Remember that you used alcohol to clean the surfaces of your reactor in the morning. Muse a bit of the effect of evaporating alcohol on your base pressure. Recognise that ther was no spoon, and certainly no leak. Complain to anybody in the vincinity about how somebody switched your morning dose of caffeine with a double-dose of stupid.

Lastly, notice that everybody in the lab is looking at you with an expression that is a mixture of pity and the expression normally reserved for the clinically insane. Try to salvage the situation (pity is unacceptable!) by cackling loudly, and announcing that your plan for world domination via glas breakage has commenced, with this very window in your hand!

Monday, March 16, 2009

Anti theft device

Try to steal my car now, filthy thieves!

Yes, the stupid battery died again. Car punishes me if I don't drive regularily.

Tuesday, March 10, 2009

The New Annotated Dracula

While waiting for my new iPhone to arrive (what, you expect me to have a life without my favourite electronic toy?), I pass the time by reading Leslie S. Klinger's "New Annotated Dracula". And when it says annotated, it means annotated: for every page of the original, there are two to three pages of annotation, describing the end of the 19th century, expounding on places mentioned by Stoker, etc.

Klinger does something I was first leery of, but which really pays off: He pretends, that Dracula was real, and that he forced Stoker to change parts of the story to protect his identity. This plot device allows Klinger to go on meandering asides over the nature of vampires, the real location of Draculas castle, etc. without compromising the information you get about the times and Stokers writing process (here, it is pretended that he assembled 'Dracula' from Harker's notes).

"The New Annotated Dracula" is not a book you devour in one sitting, and I wouldn't recommend it to readers new to Bram Stoker's Dracula. But it is an excellent book if you are interested in the times, something to peruse for half an hour or so at a time. Also, it is amazingly satisfying to read a big, heavy hardcover book again. I do have one serious complaint about it, though: the publisher really should have included on of those built-in string bookmarks. All my other "serious" hardcovers are making fun of it over it's lack.

Wednesday, March 4, 2009

Moral Dilemma

Imagine you are accused of a crime, but can't remember anything. Do you try to defend yourself? Are you feeling guilty? Would it feel unfair to you if you were convicted?

I am not speaking about me, thankfully, but about the German prime minister of Thuringia, Dieter Althaus. On the first of January he collided with Mrs. C. on the ski slopes of the Riesneralm in Styria, Austria. He wore a helmet and (barely) survived, she did not and didn't. According to eye-witnesses it was his fault - he disregarded warning signs and went around a barrier there to prevent exactly this type of accident.

But here is the twist: He doesn't remember anything of the incident. This is fairly common after severe injuries, particularily when suffering head trauma, so there is no reason to doubt Mr. Althaus - especially since he was in a coma  for two days.

Yesterday the trial took place - Mr. Althaus was accused of involuntary manslaughter. And he did a very honourable thing: Since he doens't remember anything, he didn't even show up for the trial, but rather admitted his guilt and accepted any punishment the court would agree on a priori. Because of this, the court session was very short - it took only one hour, and Mr. Althaus was fined 33 300 Euro and 5000 Euro compensation to Mrs. C's widower.

There is some grumbling in the juridical profession in Austria about the speed of the trial, but what is there to deliberate? The only thing they had to do was to decide on the punishment, everything else was clear.

I'll tip my hat to Mr. Althaus comportment, it can't be easy to admit guilt to something you can't remember doing, butit was the right thing to do.  That's the kind of behaviour I'd like to see in all politicians, standing up to their mistakes.

Tuesday, March 3, 2009

Die die die

Look, I admire your courage. I would hesitate to steal something from a guy who is celebrating his anniversary with his entire martial arts club. Of course, you did wait until I forgot my backpack, and grabbed the camera and iPhone that I stupidly had left in the top pocket (where I normally never leave them, because of scumbags like you), but still - you couldn't know that nobody was going to catch you in flagranti. And, as I am sure you know, every martial artist is secretly itching to know how applicable all that stuff he has learned over the years is in a real fight. But you took heart, made the plunge, and got away with your loot. Lucky you! Have fun with my iPhone - I certainly did, it was one of the best toys I have ever owned. The Casio Exilim is also a sweet little camera, even though the image stabilisation system was broken.

A word of caution though: You might want to return to the scene of the crime, for an eventual repeat performance. Who knows what else there is to grab? Resist this temptation, because if one of us Võ-Sinh (i.e. practicians of Võ Vietnam) sees you, retribution will be swift in coming, violent and prolonged.