Physics and Astronomy Comps, 2006-2007


The comprehensive exercise ("comps") in our department involves choosing a physics or astrophysics topic that is not covered in depth in the classes in the department; assembling, reading, and understanding a set of sources related to that topic; writing a 10-page paper explaining the relevant physics at a level that is understandable by a junior major; and presenting a 15-minute talk on the topic.

The comps coordinator this year is Eric Jensen (SC 123).  Please talk with Eric about any questions you have about the overall process (deadlines, expectations, etc.).  Once you have chosen a topic, you will be assigned a faculty advisor for your comps, and you will work with that person regarding the content and presentation of your comps paper and talk.

The goals of Physics/Astronomy comps

In the Swarthmore Physics and Astronomy department, we strive to help our students develop the ability to learn independently from primary and secondary sources (i.e. journal articles and textbooks); to synthesize what they have learned from across the curriculum; and to present clearly what they have learned, both orally and in writing. Many of these are skills you use each week in seminars, and more broadly, they are some of the central skills of science. As you move on from Swarthmore, you will find that these skills will help you to contribute in a wide variety of fields and settings.

Thus, the comps are designed to give you a chance to demonstrate these skills, using a topic of your choice. You should choose a topic that you find interesting, so that you will enjoy researching it further, and so that you will be able to present it in an interesting and engaging manner to the rest of the department.

The schedule for this year:


(1) Receive potential topics. December 8, 2006
(2) Choose your topic and let Eric know; you will then be assigned a faculty advisor. ~ December 15, 2006
(3)
  • Read associated paper(s).
  • Trace back/forward and read necessary references.
  • Work with your advisor when needed.
  • Write a 10-page paper understandable by a junior Physics/Astrophysics/Astronomy major.
  • Turn in complete paper to your advisor.
 February 23, 2007 (end of 5th week)
(4) Your advisor returns your paper with comments. March 9, 2007 (before spring break)
(5) Revise your paper based on your advisor's comments; turn in final version to Eric Jensen. March 30, 2007
(6) Working with your advisor, prepare slides for a 15 minute talk.  
(7) Give talk; turn in slides after talk. April 9–20, 2007 


Students taking comps this year:

Possible Topics

Below are some topics suggested by faculty members.  Each topic is linked to one or more articles that you can use to start your exploration of that topic.  You will certainly want to go beyond the articles listed there in order to get a more complete and up-to-date view of each topic, but these will give you a place to start.  If you would like to choose a topic that is not on this list, please talk to Eric Jensen; depending on availability of a faculty member to help advise you, we may or may not be able to accommodate requests for a given topic.

Astrophysical Evidence for the Existence of Black Holes

Recent observations show that black holes are present in the center of almost every galaxy, including our own.

You might start with A. Celotti, J.C. Miller and D.W. Sciama, Classical and Quantum Gravity 16 (1999) A3-A21, and The Supermassive Black Hole at the Galactic Center,  Fulvio Melia, Heino Falcke, Annual Review of Astronomy and Astrophysics, Volume 39, Page 309-352, Sep 2001.

There are also several Nature papers on increasingly-better constraints on the mass and properties of the black hole at the center of the Milky Way.

Electronic Structure of Quantum Dots

Try this article.

Phase and Angle Variables in Quantum Mechanics

Try this article.

Soft Matter

Soft matter is something "softer" than a crystal and "harder" than a liquid. Examples include gels, colloidal suspensions, liquid crystals, polymers, and emulsions, just to name a few. What exactly does it mean to be "soft"? What are some of the properties unique to soft matter?

Here's an article to get you started, a Nobel Prize lecture by P. G. de Gennes.

The (Astro)Physics of Brown Dwarfs

Recent years have brought a wealth of observational data on these "failed stars", objects that are not massive enough to sustain core hydrogen fusion.  Some recent reviews that would provide a starting point:

As this is a fast-moving field, you would also want to find more recent observational and theoretical papers.

Formation and properties of silica nanowires

Formation and properties of silica nanowires

Atomic-level view of melting by femtosecond electron diffraction

Atomic-level view of melting by femtosecond electron diffraction

Monte Carlo Methods in Statistical Physics

Here is an on-line textbook, which, although brief, contains all the main topics. Start with this, and then narrow down to a particular subtopic, e.g.

etc, etc. and write a comps paper in that specialized area.

Generation of Ultrafast Light Pulses

Describe the methods and physics behind the generation of ultrafast pulses in a mode-locked Titanium Sapphire laser, control of linear dispersion via prism and grating based compressors/expanders, and amplification using regenerative gain. As a starting point, here is an article by Backus et al. on generation, amplification and manipulation of intense, ultrafast light pulses .

Particle Accelerators Using Light (Wakefield accelerators)

Intense light focused into a plasma generates a propagating electric pulse called the wakefield. The electric field amplitude can be thousands of times larger than the fields used in conventional particle accelerators. The primary limitation of a laser driven wakefield is the length of acceleration. The most recent advances have reached acceleration length of a few millimeters.

You can start with some most recent work by Geddes et al. on wakefield accelerators.

Detection of Fluorescence from Single Molecules

A combination of optical, physical, and measurement techniques allow for the isolation/detection of a single molecule's fluorescent light. Present either a review of different techniques or detail of a particular technique.

Here's a recent review article.

Quantum Cryptography

Present the standard BB84 protocol that uses both classical communication (telephone) and quantum communication (entangled photons or electrons) to attain perfect security (in principle, 100% confidence that nobody is eavesdropping).

For general background, see the review article by Gisin et al. Real physical systems have been implemented (see article by Aspelmeyer et al.).

Universality, Scaling, and Renormalization in Critical Phenomena

Universality, Scaling, and Renormalization in Critical Phenomena

Smectic Liquid Crystals: Physics in Two Dimensions

If you make a membrane one molecule thick out of a smectic liquid crystal, the molecules are more or less prevented from moving in the direction perpendicular to the membrane. The motion of molecules in the other two directions is relatively unaffected, so you have an example of a two-dimensional system. How does physics change for a collection of molecules when the number of dimensions goes from three to two?

Structure and fluctuations of smectic membranes, de Jeu et al., Rev. Modern Physics, 75:181, 2003.

The Tricritical Point

The fact that many substances possess critical points, where the transition between the liquid and gas phases terminates, is well known. As the critical point is approached, the latent heat of the transition decreases, reaching zero at the critical point. Since the phase transition disappears, the two phases must possess the same symmetry. For that reason the liquid and gas phases are sometimes collectively called the fluid phase. What is not well known is that a similar phenomenon can occur when the two phases have different symmetries. The latent heat of the transition decreases to zero, but then the transition continues with no latent heat. Such a transition is sometimes called a "continuous" or "second order" transition, as opposed to a "discontinuous" or "first order" transition when latent heat is present. The point at which the transition changes from being discontinuous to continuous is called a tricritical point. Perhaps the most interesting way to study such a phenomenon is through a theoretical analysis. This is made even more attractive by the ease at which the physical behavior can be calculated and displayed using simple programs such as Matlab and IDL.

Laser Cooling and Trapping

The Cosmological Constant

Recent observations have shown that roughly 70% of the energy in the universe is in some form of "dark energy"; a leading candidate for what form this energy takes is the cosmological constant. Explain how this constant enters the equations of general relativity, and the state of current observational measurements of its value. A good observational overview is "The Case for an Accelerating Universe from Supernovae" by Adam Riess, in Publ. of the Astr. Soc. of the Pacific, vol. 112, p. 1284. There are also brand-new observational results of supernovae up to z ~ 2; search astro-ph for a recent paper by Riess et al.

For a theoretical overview try "Dark Energy and the Preposterous Universe" by S. Carroll, (2001).

The Cosmic Microwave Background Radiation and Cosmology

Recent observations of the Cosmic Microwave Background are giving unprecedented amounts of information about the conditions in the early universe and the large-scale geometry of spacetime; some of these discoveries were the source of this year's Nobel Prize in physics. The latest work involves statistical analysis of the angular scale of anisotropies, determined primarily by the WMAP satellite.

You might start with "Theoretical Overview of Cosmic Microwave Background
Anisotropy" (http://arxiv.org/abs/astro-ph/0305591) or "WMAP First Year
Results" (http://arxiv.org/abs/astro-ph/0306132), both by E. Wright. (You can also have a look at the third-year results, which aren't grossly different but which have better significance levels.)

A relatively recent review article is "Cosmic Microwave Background Anisotropies" by Hu and Dodelson, ARAA, 40, 121, (2002)