Uellue's Blog

Currency backed by gold?

In these economically volatile times with the 2009 financial crisis and the European debt crisis, some people argue that a gold-based currency would be desirable because gold is a "real value", as opposed to pieces of paper with elaborate imprints on them or numbers in a database. But how is gold a value more real than paper money or bank accounts? As such, a piece of gold seems rather useless to me. It can serve as paperweight, blunt weapon or door stopper. I admit that you can make pretty, shiny things out of it, but, lets say, martensitic stainless steel in the shape of a knife is more useful in the daily life. Should we have a currency backed by martensitic stainless steel?

The value of gold, just like paper money, is based on the fact that other people want to have it and that they are willing to trade their work force or posessions for it. The demand for it has always been higher than the production capacity, and mining gold is an expensive and slow process in itself. It is therefore quite suitable as a currency in a primitive society: It's supply is self-limiting and keeps the value of gold at a more or less constant level that is related to it's mining cost. A rising gold price makes gold mining more profitable and increases supply, while a falling gold price discourages mining.

But on the long run and in a growing global economy, a gold-based currency could be fatal for the following reasons:

There is a good reason for which gold was abandoned as a currency or base of a currency. Gold is not a real value. Real values are the house that you live in, the food that you eat, the tools that you use, the things that you know, and most importantly, the people who you love and who love you. All these don't make a good currency, but definitely a good investment.

Alice Schwarzer remix


HOWTO: Epson Perfection V200 Photo with Linux

[Update] I don't own this scanner anymore for quite some time, so I don't know if things still work the same way. Please also have a look at the comments below, because they contain some hints on how to fix problems. If you have an addition to make: Please leave a comment![/Update]

This howto describes the steps necessary to use the Epson Perfection V200 Photo scanner with Debian Testing (lenny) as of October 2007. The used kernel versions are 2.6.18 and 2.6.22. Other Epson scanners should work in a similar way, see list of supported devices. The scanner is perfectly supported, 8 bit and 16 bit color depth as well as the transparency unit work. This howto will probably also work with Ubuntu, but that's not tested.

Needed Debian packages

Download and install drivers

The drivers are available on the Japanese vendor's site. Choose your scanner and your distribution, fill out the small questionnaire and submit the form. You are directed to a download page. There get the RPM packages for "gcc 3.4 or later".

Now you need to convert the packages to the .deb format in order to install them:
sudo alien --scripts iscan-2.8.0-1.c2.i386.rpm
iscan_2.8.0-2_i386.deb generated
sudo alien --scripts iscan-plugin-gt-f670-2.0.0-1.c2.i386.rpm
iscan-plugin-gt-f670_2.0.0-2_i386.deb generated

To install the generated .deb packages we use dpkg:
sudo dpkg -i iscan_2.8.0-2_i386.deb
sudo dpkg -i iscan-plugin-gt-f670_2.0.0-2_i386.deb

Test the installation

Now plug in and switch on the scanner. lsusb must show the scanner.
uellue@yggdrasil:~$ lsusb
Bus 005 Device 002: ID 04b8:012e Seiko Epson Corp.

With sane-find-scanner you can check whether Sane finds the device. With scanimage -L you can find out if the driver is properly installed. For now only root has access to the scanner.

uellue@yggdrasil:~$ sudo sane-find-scanner
  # sane-find-scanner will now attempt to detect your scanner. If the
  # result is different from what you expected, first make sure your
  # scanner is powered up and properly connected to your computer.
found USB scanner (vendor=0x04b8 [EPSON], product=0x012e [EPSON Scanner]) at libusb:005:002
  # Your USB scanner was (probably) detected. It may or may not be supported by
  # SANE. Try scanimage -L and read the backend's manpage.
uellue@yggdrasil:~$ sudo scanimage -L
device `epkowa:libusb:005:002' is a Epson Perfection V200 flatbed scanner

To allow ordinary users to access the scanner, they must be member of the scanner group. You also need to restart the udev daemon.

uellue@yggdrasil:~$ sudo adduser uellue scanner
Adding user `uellue' to group `scanner' ...
Adding user uellue to group scanner
uellue@yggdrasil:~$ sudo /etc/init.d/udev restart
Stopping the hotplug events dispatcher: udevd.
Starting the hotplug events dispatcher: udevd

After logging out and logging in again to make the altered group membership effective scanimage -L should show the scanner for all members of the group scanner. Now you can use the device for example with xscanimage or xsane.

US nuclear bomb test site

A place with hundreds of craters from nuclear bomb tests of various strength: 37.177 -116.0462. The coordinates point to a large crater which was created by the test explosion Sedan (Video) in 1962. If you open these coordinates in Google Earth and activate the layer "Google Earth Community" you can inform yourself about the names and strengths of the various test explosions.

In the so-called "Operation Plowshare" the US gouvernment wanted to explore possible applications of nuclear explosive devices for mining and large excavations. The until then not so well-known "side effects" of nuclear explosions doomed those plans and finally led to the Partial Test Ban Treaty.

Numpy makes your python math 10x faster

As an exercise in parallel number crunching with python and numpy, I wrote a program for the computer language benchmark game. It is more than 10x faster than the python runner-up without numpy and plays already in the league of compiled languages. The speedup comes solely from the high-level vector math functions of numpy.

As a remark: The program was disqualified from the competition but is shown anyway. I don't exactly understand why. Well, I also don't really feel like asking the admin Isaac Gouy, as he seems to be a bit tense about the subject.


It is almost too obvious to state that computers have become ubiquitous today: Almost every electronic component contains one or many freely programmable microprocessor(s) and some memory, which makes it a universal computer. We just don't make too much use of this universality because we don't change the programs of these devices. That is even true for "real" computers, like laptops, smartphones and desktop computers: We use an e-mail program for writing e-mail, browse the web with a web browser, manipulate images with image maipulation programs and so on. But only a minority of users actually create new programs, because making good programs is quite difficult and the majority of people want to do the same things with their computer so that they can just use the same programs.

As long as people stick to routine tasks, they will get along just fine like that. But the fun in science is outside the routine: Do things or look at things in a way that nobody did before. And if anybody wants to use computers for that, he will soon reach the limits of existing programs. Now there are two ways to proceed: Either do things manually, like pushing buttons, taking readings, doing calculations, or write a program that can do that. Writing the program is definitely more difficult at first, because the thing one wants to do needs to be described rigorously in some sort of programming language.

There's a positive correlation between the complexity of the problem and the complexity of the program that solves it: A simple program might be a formula in a spreadsheet software that takes the values of some other cells as input, and a complex program can maybe reach millions of lines of code to control the interactions between many devices or do involved calculations with enormous data sets.

There is also another correlation: The more general a tool is, the more skill it requires to master it, but it also allows to solve more complex problems. The limitations are often not really like a hard wall, but more a soft transition: Specialized tools like spreadsheet software may be easy to use for some simple numerical calculations, but if the data sets grow larger, the program will at some point be too slow; if the data is too complex or in a wrong format, it may need to be converted manually; available extensions or software libraries may only include functionality for specific use cases. A universal programming language however is more difficult to use for trivial tasks, but complex functionality is easier to implement. Many "evolved" software packages do in fact contain a scripting engine for that reason.

The conclusion may sound trivial: You can solve more complex problems if you master more general and complex tools, and the most general way of using a computer is programming it with a programming language like C++ or Python: It allows you to combine a huge amount of existing code in the form of libraries for any purpose and empowers you, in principle, to solve any probem that can be solved with a computer program.

As a scientist, being able to program is most useful: One can implement automated measurement procedures without any complexity limits that need only a minimum of user interaction, meaning that the program works while one sleeps at night or does other useful things, one can evaluate and present data in new and complex ways and one can work on new or more efficient computer simulations.

Therefore: Go learn a programming language! You will be able to do things that you can't even imagine without it now.

Two-column float gets stuck with revtex

When preparing a manuscript with revtex (documentclass[aip,apl,amsmath,amssymb,reprint]{revtex4-1}), I ran into a problem: A two-column float with the figure* environment got stuck and ended up at the end of the document. The solution was trivial: Remove all placing hints for the float, instead of \begin{figure*}[h] use just \begin{figure*}!

iBook surgery

On friday my beloved iBook didn't wake up when I opened it. Instead the hard disk made sounds like rtrtrt...rtrtrt...rtrtrt...rtrtrt... Powercycling didn't help, so I decided to replace the harddisk. This sounds easier than it is, because you have to disassemble an iBook to get to the harddrive buried deep inside the "guts". And iBooks are not made for easy disassembly!

I had some experience with opening an iBook before, and I still remembered how it took a load off my mind when this little cutie booted again.

Anticipating the worst I checked the prices for the new Apple MacBook. Well, if I failed to repair my iBook I had to pay roughly 1400 € for a new one. Certainly too much for my taste!

Atelco in Raisdorf only had a 60 GB notebook drive, so I bought it although it meant downgrading from my 80 GB drive. To make a backup of the old drive I also bought an USB 2.0 to IDE and SATA adapter.

Following this excellent guide I went to the next hardware store and bought a Torx T8 and a Philips #0 screwdriver. At home we have tons and tons of different screwdrivers, but most small ones are ultra-cheap crap. I mean, why do people produce, sell and even buy this stuff? They usually "screw up" on their first or second screw...

These are the tools I used: The iBook with disassembly tools

The hardest part is to remove the plastic shell, because you have to release a few notches and you might easily break something. I used the wooden tools you can see on the picture above for that; it worked quite well. On the next picture you can see the almost disassembled iBook:The disassembled iBook

Fortunately I managed to back up the data on the broken hard disk (although there is almost nothing important on it), but the drive is really broken, it paused during backup again and again, making the rtrtrt...rtrtrt noises. The new one works smoothely, I already installed OS X again and decided not to use the backup except of a few precious files like the browser's bookmarks. I had too much old stuff on the iBook anyway. Now I hope that the next time my iBook gets broken I have significantly more money so I can buy such a nice dual-core MacBook or MacBook Pro...

Why is the air in airplanes so dry?

If you ever traveled a long distance by plane, you may have noticed that the air is extremely dry: The eyes start burning, the skin is dry and you get thirsty. But why is the air not moistened so that the passengers are more comfortable?

There are actually two reasons. First, the air at the altitudes where the plane is flying is extremely cold (say, -60 °C and below) and consequently dry. It contains practically no water. This air is compressed by the turbines and used as cabin air. Any water in the air would come from people breathing or would have to be added. Such a "moisturizing" system costs money, takes up space and has weight, so an airline would have to think if the added cost is worth it.

Second, airplanes are usually made of high-strength aluminum alloys that can corrode in contact with water. They also have a lot of electrical cables running all over. And they fly at high altitude where it is very, very cold. So at least some parts of the hull are cold, too. This means that moisture from the air inside the plane could condense to liquid water on cold parts and cause trouble. Dry cabin air can reliably prevent that: If the dew point (resp. frost point in that case) of the cabin air is below the freezing point of water, there can be no liquid water condensing. Only frost can form, i.e. water vapor turns directly into ice, which does not cause corrosion problems. And a frost point of roughly 0 °C corresponds to a relative humidity of 25 % at 20 °C. If the humidity in the cabin is desired to be above 25 %, one would have to take special measures: Corrosion-resistant materials or a completely sealed vapor barrier on top of the cabin's thermal insulation. Such a barrier would prevent the moisture from reaching colder parts. But it would make the insulation more complex and add weight...

Large-Scale Patterning of Gold Nanopillars in a Porous Anodic Alumina Template by Replicating Gold Structures on a Titanium Barrier

Just wanted to link the article that came out as a result of my Diplom thesis:

Weber, Dieter; Mourzina, Yulia; Brüggemann, Dorothea; Offenhäusser, Andreas:
Large-Scale Patterning of Gold Nanopillars in a Porous Anodic Alumina Template by Replicating Gold Structures on a Titanium Barrier

Gold nanopillars are grown in patterns inside a porous anodic alumina template. On selected positions, defined by a gold "seed" pattern, gold is electroplated into the pores, while a barrier layer underneath the porous template blocks the deposition on the rest of the surface. Large-scale arrays of free-standing nanopillar islands are obtained after selective etching of the alumina template.