|
Physics@VCU Links:
               
| |
Research Interests
Dr. Marilyn F. Bishop
Theoretical Condensed Matter Physics, Theoretical Biophysics
In the area of condensed matter physics, the two major thrusts have been (1)
theoretical studies of charge density waves and spin density waves in simple
metals and (2) the theory of superconductivity. The importance of understanding
the properties of simple metals extends well beyond the explaination of a few
phenomena. Different theoretical treatments of electron-electron interactions of
exchange and correlation in an electron gas will lead to different ground states,
and the choice of the ground state one uses can lead to various predictions of
optical and transport properties of a simple metal. This implies that the simple
metals, especially the alkali metals, are a testing ground for theories of electron
gas interactions. Comparison of theory with a large number of experiments shows
that the correct ground state of simple metals must be that of a charge density wave.
Until one can explain the properties of the alkali metals, the predictions for more
complicated systems will also be in question. In fact, the understanding of the
electronic interactions in superconductors must rely on some of the same principles
as found in simple metals.
The work on simple metals has included a theory of the residual resistivity anisotropy
determined in potassium by induced torque measurements, a theory of electron-phason
scattering and an explaination of the low temperature resistivity of potassium below 1.3 K,
including variability from sample to sample, localization effects in thin potassium wire,
effects of charge density waves on the x-ray band spectra of alkali metals, and the calculation
of the Bloch-Grüneisen functions by the use of series expansions. Current and future
work include Hartree-Fock calculations of spin density waves in one and three dimensional
systems, including the study of spiral and canted spiral spin density wave states. In the study
of superconductivity, my work has involved a study of the phonon-mediated electron-electron
interaction, which is integral to the BCS theory of superconductivity and is important in the
theory of bipolaronic superconductors, and a theory of the proximity-induced superconducting
transition temperature.
The research in biophysics involves the theoretical study of the kinetics of polymerization,
light scattering, and optical properties of biological polymers. Kinetic theories, which include
the nucleation and growth of polymers, have been applied to sickle hemoglobin, actin, and
collagen. Actin, a fibrous tissue in muscle and an important component in the structure of
cells, undergoes a polymerization that is complicated by the hydrolysis of ATP to ADP during
the polymerization process. Sickle hemoglobin, which is a mutation of normal hemoglobin but
transports oxygen as does normal hemoglobin, polymerizes only when deoxygenated, which
occurs when delivering oxygen in the capillaries. Polymerization proceeds through a double
nucleation process in which nuclei form from a solution of hemoglobin molecules (monomers)
and once polymers are formed, nuclei are formed on the surfaces of existing polymers. The
work on light scattering and optical properties of polymers focusses on sickle hemoglobin but
could equally apply to any system in which the polymers are rigid straight fibers. These include
actin, tubulin, intermediate filaments, myosin, collagen, crystallin, fibrin, and amyloid. Most
formulations of light scattering from particles assume that those particles are dilute, i.e. well
separated compared with the wavelength of light. This work is developing a theoretical
formulation whose validity will range from the dilute to dense concentrations of polymers.
This is especially important in the study of the sickle hemoglobin because the most physiologically
significant regime ranges from intermediate to high concentration. In sickle hemoglobin, polymers
are known to form in spherulitic arrays known as domains. Recent studies involve calculations
of the expected light scattering from these domains as compared to scattering form individual
polymers, in order to determine the processes involved in the growth and alignment of polymers
in the formation of domains.
Marilyn F. Bishop and Frank A. Ferrone, "Kinetics of Nucleation-Controlled Polymerization",
Biophys. J. 46, 631-644 (1984).
Marilyn F. Bishop, "Calculations of Scattered Light from Rigid Polymers by Shifrin and Rayleigh-
Debye Approximations", Biophys. J. 56, 911-925 (1989).
Mary Eileen Farrell, Marilyn F. Bishop, "Theory of the Proximity-Induced Superconducting
Transition Temperature", Phys. Rev. B 40, 10786-10795 (1989).
Mary Eileen Farrell, Marilyn F. Bishop, N. Kumar, and W.E. Lawrence, "Theory of the Effects
of the Destruction of Localization by Inelastic Scattering in the Resistivity of Pure Thin Potassium
Wires", Phys. Rev. B 42, 3260-3270 (1990).
Department Faculty
 Physics Homepage.
|
