Kategorie: Articles

Jets in QCD

What are jets? What does QCD mean?

The intuitive picture of a jet is a collimated spray of particles which is created by the collision of two particles in a high energy physics experiment. (There can be more than one jet.) Quantum chromodynamics (QCD) is the physical theory behind them. It states that a certain class of particles, hadrons, are built of quarks and gluons. If a quark or gluon is scattered, a jet is created. A quark or gluon has never been observed as a free elementary particle and QCD states that this is not possible. Instead after a scattering new particles are created very rapidly that can be observed. Regarded as a jet they have the momentum of the scattered quark or gluon. The exact definition of a jet is not trivial and there are sophisticated algorithms to find them.

Why are jets interesting to physicists?

With their aid conclusions can be made on the fundamental process without having to measure a free quark or gluon.

Falling Films

In process engineering a falling film is a thin liquid film which flows down an inclined plate by the action of gravity. Falling films are employed in various fields, like the food industry, the pharmaceutical industry or in power plants. They have the advantage of a good heat transfer and a small hold up. Furthermore, they have a large surface for the exchange between gas and liquid (like in gas scrubbing).

A falling film flowing down a vertical wall is always hydrodynamically unstable. However, if the Reynolds number is very small, the waves may not be seen.

In the EU project EasyMED I simulated evaporating seawater falling films. Turbulence wires were employed to improve the heat transfer.

Tritone Blues

This is a blues which sounds a bit off-key, but where I stay within the harmonies. It has been performed for several times. Here you can listen to a recording I made at home with a guitarist and a bass trombone player. I played the soprano saxophone. Bass and drums came from Band in a Box, i.e. from the computer.

Where does the name come from? The tritone is a dissonant interval consisting of three whole steps. For improvisation you should play the third and the seventh. However, between the major third and the minor seventh, there is the tritone. Take, as an example, the chord C7. The third is E and the seventh Bb. There are mainly dominant seventh chords in the blues. Thus I could compose a blues with many tritones.

You can find the lead sheets here:

TritoneBlues_C   TritoneBlues_Bb   TritoneBlues_Eb

 

The Plug Calorimeter

I am going to summarise my diploma thesis in plain words. It was a simulation of the ZEUS detector. ZEUS was the name of a collaboration which ran an experiment at the storage ring HERA in Hamburg, Germany. There, electrons and protons of high energy were brought to collision. Around the interaction point was the ZEUS detector covering almost the whole solid angle with the exception of the openings for the beam pipes. The idea for the plug calorimeter was to make the opening in the proton direction smaller. Thus the acceptance of the detector was enlarged. A calorimeter is an energy measuring device. The additional calorimeter was kind of a plug.

My first step was to implement several versions into the ZEUS detector simulation program MOZART. Then I simulated a test beam, i.e. I used a beam of particles of a single type with uniform energy. Finally, I tested with two kinds of electron proton scattering events. It could be demonstrated that these two types of scattering events can be much more easily separated in an analysis with the aid of a plug calorimeter.

A plug calorimeter was eventually built und installed. Finishing this article I want to mention a publication:

Bamberger et al., The ZEUS Forward Plug Calorimeter with Lead-Scintillator Plates and WLS Fiber Readout, Nucl. Instr. Meth. A450 (2000) 235-252 ( http://arxiv.org/abs/hep-ex/9912045 )

 

Japanese Bossa

This piece was performed during the Xmas Session 2015 at Jazz Institute Darmstadt by the Jürgen Wuchner Workshop Band.

You find the lead sheets here:

JapaneseBossa_C   JapaneseBossa_Bb   JapaneseBossa_Eb

I would like to add some remarks on the harmonic background. The melody consists of a Japanese pentatonic. This can be built by a major pentatonic where the major third is substituted by a minor third and the second note becomes the root. I give an example:

D major pentatonic: D E F# A B

Major third is substituted by minor third: D E F A B

Second note becomes root: E F A B D

When I harmonised the melody, I did not do the last step. To stay within the example, I kept D as the root.

 

Current Leads

Current leads are a cryo-electrical component of the circuit of a superconducting magnet, a pair for each electrical circuit. One end, the warm terminal, has ambient temperature, about 300 K (Kelvin). The other end, the cold terminal, has the temperature of liquid helium, approximately 4 K.

If the cross-section of the conductor is too large, a lot of heat comes from the warm to the cold terminal. On the other hand, if the cross-section is too small, the electrical current will cause a significant heating and the current leads may burn through. The designer has to find a compromise.

There are current leads which are only cooled at the cold terminal. This is the conduction cooled type. The vapour cooled current leads guide the helium vapour all along the whole length from the cold to the warm terminal. Sometimes the temperature is fixed in between with liquid nitrogen (77 K) by the employment of a thermal anchor.

Computational Fluid Dynamics

In CFD a computer solves the discretized equations on a numerical grid which should be fine enough in order not to neglect important features of the flow in between. Beside of the real experiment and pure theory it has established itself as the third column of fluid dynamics. In contrast to the real experiment, the numerical experiment offers much more data. Pure theory has the disadvantage that it can only provide solutions of few simple problems. It shall not be concealed that by far not all situations of interest can be simulated accurately. For example, in most cases turbulent flows have to be modelled which involves simplifications.

A mocking interpretation of CFD is Colors For Dollars, since the visualisation is very colourful and the software in most cases expensive. Alas, this is only the opinion of the mockers! 🙂