Brad Antanaitis' research focuses on the structure and function of metal-bearing proteins and enzymes isolated from sources as diverse as photosynthetic bacteria, leguminous plants and pregnant sows. These proteins participate in a wide variety of fundamental life processes including photosynthetic electron transport, iron and oxygen transport, and enzymatic catalysis. Since all of the proteins contain one or more metal atoms, they are amenable to study by an arsenal of magnetic resonance and spectroscopic techniques, studies frequently supplemented with biochemical data obtained through isoelectric focusing or enzymatic assay. Where applicable, the dynamical aspects of a biopolymer's behavior are also probed by measuring electron transfer rates, or the rates at which small molecules "hop" on and off their larger biomolecular cousins. Ultimately these results may be used to develop low molecular weight analogs that mimic the protein's function. Synthetic analogs, which closely resemble the protein's active site, also aid in the elucidation of the protein's structure.
Much of this research has been carried out off-campus, primarily at the Albert Einstein College of Medicine and at Princeton and Cornell Universities. However, the acquisition (jointly with the Dept. of Chemistry) of a 300 MHz pulsed Fourier-transform nuclear magnetic resonance (NMR) spectrometer, housed in the Hugel Science Center, and the establishment of a biophysical laboratory in the basement of Hugel Science Center now makes it possible to conduct a greater proportion of the research on campus.
Student candidates with a variety of interests and backgrounds are welcome to participate in this work for honors or independent research. Several students have already successfully completed independent research projects involving the following types of work: isolation of an iron protein from uterine flushings of pseudopregnant gilts, biochemical manipulation of protein samples prior to their physicochemical characterization, characterization of protein active sites by magnetic resonance (EPR and NMR) techniques, and development of theoretical models to account for the electronic and magnetic properties of spin-coupled binuclear iron centers. Nickolay Neshkov '96 worked with Brad in summer 1993.
Andy Dougherty's area of research is the experimental study of interfacial instabilities and pattern formation in condensed matter systems. He is especially concerned with interfaces that are not in equilibrium, such a crystal growing from solution. Many materials grow in complex dendritic shapes, similar to snowflakes in appearance, and Andy studies the interplay between the microscopic physics and the macroscopic shapes. He is also interested in the extent to which concepts that are useful in describing equilibrium systems may be applied to non-equilibrium systems.
The experiments are performed on an ordinary microscope, and images are recorded on a high-resolution video cassette recorder. The data are then analyzed with computer-based digital image processing techniques. All work is carried out in the Hugel Science Center, and student participation is welcome in all aspects of the research.
Another of Andy's interests is pattern formation in fluid mechanics, such as in the motion of a fluid through a porous medium. Here again, simple microscopic physics leads to complex macroscopic shapes, but the process is not completely understood.
Andy's work has been supported by grants from the Research Corporation and from NSF. Previous student assistants are co-authors on several publications.
Prior to coming to Lafayette College in 1990, Andy has been supported by a grant from the National Science Foundation and has had Haverford student co-authors on several papers.
Andy's home page is here.
Lyle Hoffman's research is in the field of radioastronomy and cosmology. He travels to Arecibo Observatory, the 305m radio telescope in Puerto Rico, during the summers and January intersessions, taking a student assistant each time. He also makes use of the Very Large Array in New Mexico. The data acquired at these observatories allow him to investigate the internal structure and dynamics of individual dwarf and spiral galaxies; the motions of these galaxies about the Local Supercluster of galaxies; and the effects of the galaxies' environment on their gas content and evolution.
Lyle uses the Sun workstation in his office heavily, both for detailed analysis of the data he brings back from Arecibo and the Very Large Array and for numerical simulations of galaxy groups, clusters and superclusters. The N-body integration package (to solve Newton's laws for a large number, N, of point masses interacting by gravity) on the campus machines has been used to study mass segregation in groups (~30 members) and clusters (~300 or more members) of galaxies, and to simulate fields of several galaxy groups to develop procedures for identifying groups in observed catalogs of galaxies.
Lyle's work is supported by a grant from the National Science Foundation, and he maintains collaborations with astronomers at Cornell University, the University of Minnesota, the Infrared Processing and Analysis Center, and the University of Pittsburgh along with those at Arecibo. In the recent past, he has supervised student research and honors theses in numerical simulation of galaxy groups, in analysis of neutral hydrogen data for dwarf galaxies, and in the acoustics of the human vocal tract. Students have been named as coauthors on several recent publications of Arecibo data. Rene Fromhold-Treu '97 worked with Lyle during the past academic year and summer 1994 on various projects.
Lyle's home page is here.
David Hogenboom's research interests lie in the field of experimental studies of liquids and plastic solids at high pressures. He has developed a sensitive method to study the change in density when samples melt or freeze at high pressures and to measure the compressibility of the liquid and solid phases. Most recently this method has been applied to the compressibility of ammonia-water and magnesium sulfate-water solutions, which are believed to be major components of the icy moons of the outer planets as well as some asteroids and meteorites. These laboratory data are needed to develop models for the composition and internal structure of these moons and will help explain some of the surface features observed by the Voyager spacecraft -- why, for example, large cracks, rifts and other surface features appear on the surfaces of some moons and not others. In the past, David has also studied the viscosity of liquids as a function of temperature and pressures up to 4000 times atmospheric. He has also used pulsed nuclear magnetic resonance to measure the self-diffusion coefficient of liquids at high pressures.
David's planetary science research is currently supported by a NASA research grant. Earlier grants from the Research Corporation were helpful in acquiring the high pressure apparatus and associated instrumentation. Student researchers have been involved in all stages of his work and expecially with the task of enabling microcomputer control of the instruments. Previous student assistants were coauthors of abstracts of talks at recent Lunar and Planetary Science conferences in Houston. Mark Buyyounouski '95 was his research assistant in summer 1994, and Yashovardhan Pandey '97 worked with him during the academic year 1994-95.
David's home page is here.
Andrew Kortyna's research focuses on the physics of atomic and molecular collisions. Andy uses lasers, as well as atomic and molecular beam techniques, to study these collisions at very low kinetic energies. Such low-energy collisions are interesting because they provide sensitive tests of quantum mechanical scattering theory. Currently, his main research efforts are divided between two distinct projects: electron-molecule scattering at threshold energies, and cold collisions between electronically excited atoms.
One project is in collaboration with the Atomic and Molecular Scattering Group at NASA's Jet Propulsion Laboratory. Under investigation is the interaction between free-electrons and molecules at energies very near attachment threshold. We have constructed a novel laser-based photoelectron source with ultrahigh energy resolution: a tunable vacuum-ultraviolet laser intersects a molecular beam containing a mixture of xenon atoms and the target molecule. The laser ionizes the xenon atoms, producing photoelect rons that are free to collide with nearby target molecules. This apparatus can easily produce electrons whose de Broglie wavelengths are an order of magnitude larger than the dimensions of a typical target molecule. At these energies, fully quantum mechan ical scattering can be observed and quantum mechanical predictions can be tested.
The second project, currently being set up in Lafayette College's new Hugel Science Center, has the goal of studying orientation, alignment, and velocity effects in associative ionization collisions of electronically excited atoms at very low temperatures. Associative ionization occurs when two free atoms collide to simultaneously form a molecular bond and eject an electron. This process for producing a molecular ion is energetically allowed when the internal excitations of the two free atoms are in excess of the ionization energy of the associated molecule. Associative ionization is of interest because it is a simple example of chemical bond formation, because it can be a common process in low temperature plasmas (important for understanding plasma etching techniques used in the manufacturing of integrated circuits), and because associative ionization cross sections at low temperatures have proven difficult to calculate.
Experimentally, associative ionization will be studied in a single effusive beam of potassium atoms. Intrabeam collisions arise from the effusive beam's inherent thermal velocity distribution. External-cavity diode lasers, built on-campus, are employed to prepare the initial excited states of potassium. The collision velocity is precisely controlled by using the diode lasers' very narrow linewidths to Doppler-tune the laser frequencies into resonance with selective components of the atomic beam's velocity distribution. This method will be used to study collisions at velocities associated with temperatures below 1K.
Andy's home page is here.
Tony Novaco's area of research is the theory of condensed matter (the liquid and solid phases of materials), and includes computer simulations of these condensed phases. Of particular interest to Tony are those states which are associated with monolayer films of atoms of one type adsorbed on the surface of a crystal of another type. A related problem of some interest is the reconstruction of surfaces. These systems are predominantly two-dimensional (rather than three-dimensional) and so show rather interesting and uncommon phenomena. The problems of interest are those which examine the structure of the phases of these systems and the nature of the phase transitions.
Incommensurate solids, those which possess some aperiodic structure which does not reflect the fundamental periodicity of the parent crystal structure, pose another very interesting class of problems. Since the natural periodicity of the monolayer is usually different from that of the surface on which it lies, monolayer systems often form incommensurate structures due to the competing forces of the intra-monolayer interactions and the interactions of the monolayer with the surface. Sometimes the periodicity of the parent crystal can be partially recovered, and this leads to the so-called commensurate phases. Another part of Tony's research program is the study of the structure of both the commensurate and incommensurate phases and of the phase transitions between them.
One of the more interesting problems in condensed matter physics is that of the melting of a solid in two dimensions. The main question is whether the melting occurs through a discontinuous transition as it does in bulk (three-dimensional) systems, or whether this melting occurs via a continuous transition, very different from bulk systems. Tony is approaching this problem through computer simulations.
Tony's work has been funded by research grants from the National Science Foundation, and he maintains contact with experimental groups at Brookhaven National Laboratory, Exxon Corporate Research Center, and the University of Washington at Seattle to foster the kind of interaction between theory and experiment needed for a healthy research program. Students have been involved with Tony's research on a number of occasions in the past, and he has supervised recent honors theses on computer simulations of monolayer melting, adsorption of quantum solids, and deterministic chaos. Jo Heem Loh '95 worked as a student research assistant with Tony during the academic year 1994-95.
Tony's home page is here.
Michael Stark is principally interested in the study of the compact objects that are the final stages in the lives of stars much more massive than our Sun. These objects include black holes and neutron stars. The study of these stars is complicated by the fact that they have no internal source of heat so they do not emit radiation in the same way as most visible stars. In fact, when these objects are isolated, they often emit very little detectable radiation of any kind. Fortunately, many of these objects exist in binary systems with more typical stars and can be studied through their interaction with their binary companion.
The radiation produced in neutron star and black hole binary systems is very bright at X-ray energies. Since X-rays do not penetrate the Earth's atmosphere, Michael observes these systems using X-ray astronomy satellites operates by NASA, the European Space Agency and the Japanese Institute for Space and Astronautical Science. These observations are sometimes complemented by simultaneous observations with ground-based telescopes.
Michael uses precise timing of changes in brightness of the X-ray emission of these sources to study their rotation and their orbital motion about their binary companion. He also studies the changes in the hot gas in the space surrounding the compact objects. He is currently interested in Cygnus X-3, an X-ray emitting binary system in the constellation Cygnus, and GRO J1744-28, the Bursting Pulsar, a unique source located near the center of the Milky Way. Michael collaborates in these studies and in the study of other transient X-ray sources with scientists at NASA's Goddard Space Flight Center and the Middle East Technical University in Ankara, Turkey.
Michael's graduate work involved the analysis of data from an Extensive Air-shower Array in the high desert of New Mexico. This experiment and others like it use the Earth's atmosphere as a detector for the highest energy radiation in the Universe. The source of this radiation is not completely understood but some of it comes from the compact object sources Michael still studies.
Michael's home page is here.