Physics tip sheet #34 - April 1, 2003

Patients with sickle cell disease have mutant hemoglobin proteins that form long, stiff fibers inside red blood cells. Now, researchers propose a mathematical model to explain the persistent stability of these deadly fibers. The theory suggests that an inherent "twistiness" in the strands that make up the fibers could be the key to their durability and possibly to new treatments.

Physical Review Focus: http://focus.aps.org/story/v11/st12
Journal article: http://link.aps.org/abstract/PRL/v90/e128103

2) How treatments affect cancer growth
S. C. Ferreira Jr., M. L. Martinsy, M. J. Vilela
Physical Review E (to appear)

Chemotherapeutic strategies use quite different means to prevent cancer growth. Cytotoxic treatments directly kill cancer cells (and take some healthy cells with them). Antimitotic treatments do not kill cancer cells but stop the cell cycle at specific checkpoints. This paper looks at the differences these strategies have on the structure of cancerous growths by using computer models. For cytotoxic strategies, tumors can be completely eradicated, cease their growth or grow continuously, depending on the frequency and efficiency of individual treatments. However mitotic strategies cause a distinct change in the patterns of tumor growth. The types of changes seen are similar to when bacterial colonies exposed to non-lethal concentrations of antibiotics exhibit drastic changes in their growth patterns. Seeing as this behavior has not yet been seen in laboratory, the authors suggest that these observing these structural transitions may give important information about treatment efficacy. The authors are currently conducting some of those laboratory studies.

Journal article: Available to journalists on request

3) How does the Sun shine?
J. N. Bahcall, M. C. Gonzalez-Garcia, C. Pena-Garay
Physical Review Letters (to appear)

The sun generates energy through nuclear fusion but there is more than one way for this to occur. The standard solar model says that 98.5% of the energy comes from p-p chains (reactions of very light elements) and 1.5% comes from the CNO cycle (carbon atoms causing nitrogen and oxygen atoms to enter fusion reactions). However, until now, there has been no real demonstration about how much energy comes from which source, just the assumptions of a model. In fact, experiments allowed for the CNO cycle to generate anywhere up to 99.95% of the energy! New analysis of neutrino data from a range of experiments has allowed physicists to constrain the contribution of the CNO cycle from the 99.95% previous bound all the way down to 7.3%. To bring this limit down further will require direct measurements of neutrinos generated in the CNO cycle.

Physics News Update: http://www.aip.org/enews/physnews/2003/split/629-2.html
Journal article: Available to journalists on request

4) Electron searchlights from single molecules
Th. Weber, et al.
Physical Review Letters (to appear)

When electrons are knocked out of atoms, they usual fly off in many different directions. However, a process explored at the Lawrence Berkeley National Laboratory's Advanced Light Source shows how a single molecule (CO - carbon monoxide) can cause electrons to be emitted in a very well defined direction. The procedure works by essentially pulling the bottom electron from the pile in a carbon atom using an x-ray pulse. All the other electrons fall down to fill the gap and the energy released knocks another electron out. This electron is emitted along the line from the carbon atom toward the oxygen atom, creating the electron "searchlight". This process, called Auger emission has been known of since 1925 but this is the first observation of the strong focusing effect from a free molecule.

Journal article: Available to journalists on request