Summer 2000 -- Vol. 17, No. 1

NEW FACULTY

Squire Booker
assistant professor of biochemistry and molecular biology

Squire Booker is an enzymologist whose research focuses on unraveling the reaction mechanisms employed by various enzymes using S-adenosyl-L-methionine (SAMe) as a cofactor. In most known reactions involving SAMe, the enzyme acts as a methylating agent to add a methyl group to a wide variety of biological molecules. However, Booker's research focuses on the details of the mechanisms for other classes of chemical reactions in which SAMe acts as a cofactor. In one reaction, the cofactor is used to insert sulfur into octanoic acid to make lipoic acid, a compound that is integral to energy production in the cell and that is believed to be a free-radical scavenger, providing resistance to some types of cell damage.

The goal of Booker's research is to put all the components of the reaction together to make the reaction work outside the living cell in order to better understand the molecular workings of the cell. Another novel reaction under study that involves SAMe is the biosynthesis of fatty acids containing cyclopropane groups, produced by adding a methylene group to a carbon-carbon double bond. Since certain types of bacteria, including Mycobacterium tuberculosis, are known to contain this modification, undertanding the details of the process may be useful in developing novel antibacterial agents.

Booker was attracted to Penn State by the opportunities for teaching as well as for research. "I enjoy working with graduate and undergraduate students," he says. "I want to share with them my fascination with the vast number and variety of molecular transformations that constitute life." Booker earned a bachelor-of-arts degree in chemistry from the Austin College in Sherman, Texas, in 1987 and a doctorate in chemistry from the Massachusetts Institute of Technology in 1994. Following postdoctoral research at Rene Descartes University in Paris and at the University of Wisconsin, he joined the Penn State faculty in fall 1999.

Dmitry Dolgopyat, assistant professor of mathematics

Dmitry Dolgopyat studies the mathematics of dynamical systems and how complex systems change over time.  The behavior of systems can be seen as either regular, such as the motion of planets, or chaotic, such as the motion of a hurricane, and Dolgopyat explains that most complex systems can be viewed as a composite of multiple pieces, some regular and some chaotic.  His mathematical models interpret data based on the effects of a small change in the initial conditions by studying changes within this composite structure.  The object of Dolgopyat's research is to define techniques for choosing analytical methods to analyze these systems by determining which parameters are most important for defining the motion.  "Chaotic systems are normally studied by computer models, but you still need to define which questions are meaningful and which are not," he says.  "No matter how much computer power you have and how precise your data, you cannot predict the weather fifty years from now in detail.  In this case, it is better to use a general theoretical extrapolation."  By using statistical approximations to chaotic behavior, Dolgopyat is working toward defining common elements and building models that can effectively predict behavior in systems from various disciplines, such as physics, meteorology, and geology.

Dolgopyat earned his bachelor's degree in mathematics at Moscow State University in Russia in 1994 and his doctorate in mathematics at Princeton University in 1997.  He did postdoctoral research at the University of California at Berkeley before joining the Penn State faculty as an assistant professor of mathematics in the fall semester of 1999.

Alexander Dranishnikov, professor of mathematics

Alexander Dranishnikov is a topologist who is known for his work on cohomological dimension theory.  In the late 1980s, he solved several long-standing problems in topology, including the Alexandroff problem concerning the equivalence between two approaches to the definition of dimension, geometric and algebraic--the cohomological and the covering dimension. The Alexandroff problem was first stated in the 1920s, sparking intensive investigation by mathematicians including Alexandroff, Hopf, and Pontryagin, who were only partially successful, although their efforts helped define much of modern algebraic topology.  After most mathematicians had declared the problem unsolvable, Dranishnikov proved that, based on a unique application of a mathematical tool called K-theory, the cell-like mapping problem from a different area of topology is exactly equivalent to the Alexandroff problem.  For solving the Alexandroff problem, he received the prize for the best research in mathematics in the Soviet Union in 1989.  His current research is connected with the Novikov higher-signature conjecture, and he is basing his approach to this problem on dimension theory.  He has discovered that the Novikov conjecture, from a completely different area of topology, resembles the Alexandroff problem.  "The Novikov conjecture is almost exactly the Alexandroff problem considered from macroscopic point of view," he says.  Much of Dranishnikov's research now focuses on defining the similarity between topological properties on a small scale and on an infinitely large scale.  "I work on the problems both by looking for a proof and by looking for a counter example," he says.  "The tension between the two leads to interesting conclusions.  If you examine the evidence each way, interesting problems sift through that can lead to an answer.  It's like a jury deciding guilt or innocence based on the evidence."

Dranishnikov earned a doctorate in mathematics at Moscow State University in 1983 and a doctor-of-science degree in mathematics at the Steklov Mathematical Institute in 1987.  He was appointed assistant professor of mathematics at Kolmogorov College in Moscow in 1984 and was promoted to associate professor in 1984 and to professor in 1991.  He simultaneously held a position as scientific collaborator at the Steklov Mathematical Institute from 1985 to 1992.  He was a visiting professor of mathematics at Cornell University from 1992 to 1994, was appointed associate professor of mathematics at the University of Miami in 1994, and became professor of mathematics at the University of Florida in 1995.  He joined the Penn State faculty as a professor of mathematics in the fall of 1999.

Among his honors, Dranishnikov received a prize for his significant contribution to mathematical research from the Moscow Mathematical Society in 1985, a research prize from the USSR Academy of Science in 1989, and the R. H. Bing Award from the Mathematical Association of America in 1990.

Peter Eklund, professor of physics

Peter Eklund is a materials physicist whose interests concern the synthesis and characterization of new materials, particularly materials with practical importance.  "I like to pick topics that are relevant as applied technology as well as fundamental science," he says.  "It is a lot more interesting when you actually make something."  Using the results of optical, spectroscopic, and electrical transport measurements, Eklund builds microscopic models of the structure of new materials to explain their physical properties.  From these models, he looks for patterns that help in the design of materials with desired characteristics.  Much of his work has involved carbon materials, such as fullerenes and carbon nanotubes--topics on which he has co-authored two comprehensive books.  His current carbon-materials research involves the use of carbon nanofibers as a storage medium for gases.  A second research focus is developing materials for thermoelectric refrigeration.  This cooling technique uses no moving parts; instead, it uses the flow of electrons though two different types of electrical conductors to transfer heat energy.  Eklund is developing the unique conductors needed to apply this technology, with the goal of making it a viable alternative to current refrigeration technologies.

Eklund earned a bachelor's degree in physics from the University of California at Berkeley in 1967 and a doctorate at Purdue University in 1974.  After doing postdoctoral research at the Massachusetts Institute of Technology, he became an assistant professor of physics at the University of Kentucky in 1977 and was promoted to associate professor in 1981.  He was professor of physics there from 1986 to 1999 and was the associate director of the university's Center for Applied Energy Research from 1991 to 1998.  He has served as visiting professor at several universities in Japan.  Eklund is also the  president of CarboLex, Inc., a company that manufactures carbon nanotubes.  He joined the Penn State faculty in fall 1999 as professor of physics.

David Hunter, assistant professor of statistics

David Hunter is a computational statistician whose research involves finding ways to optimize the analysis of complex and incomplete data sets.  His methods develop ways to approximate solutions to a problem when an exact solution is not possible.  Although computers have increased the ability to analyze data, existing numerical methods are not applicable to every problem.  The purpose of Hunter's research is to develop the theories that lead to novel methods of solving complex problems using computation.  Some analyses are so difficult that they cannot be solved even with powerful computers using existing techniques.  "Improved computational ability is the combination of greater speed and a better algorithm," he explains.  "Statistical research is not just analyzing data sets, but learning how to analyze data sets.  Researchers in other fields often bring us data sets and ask if there is a statistical way to analyze it.  Frequently, the answer is ënot yet.' "  Once a new analysis method is defined for a specific problem, Hunter develops the general application of the method, allowing its use for different types of problems.  One major interest of his research is optimization of quantile regressions, which focus on ranges of values, as opposed to mean regression, which focuses on the average.  These techniques are used in problems involving complex information and are frequently used in economic analyses.

Hunter earned his bachelor's degree in mathematics at Princeton University in 1992 and his doctorate in statistics at the University of Michigan in 1999.  He joined the Penn State faculty in the fall of 1999.

Joseph Kiesecker, assistant professor of biology

Joseph Kiesecker is an ecologist who studies disease and parasites in plant and animal communities.  His main research interests are the factors responsible for disease outbreaks and how disease can contribute to the decline of threatened species.  He focuses on how disease is spread, how parasites are transferred between different species, and the effects of environmental change on parasite hosts and vectors.  Most of Kiesecker's research involves amphibians, including the impacts of exotic-species introduction, climate change, and increased ultraviolet exposure on the health of amphibian communities.

He says, "I focus on amphibians because I think they are fascinating animals but also because you can do things with them that are impossible to do with other invertebrates, like building artificial pond communities where the researcher can have greater environmental control."

One research project currently under way examines the effect of changes on wetlands by land development.  Frequently, large intermittent wetlands are replaced by smaller, permanent wetlands along with increased flow of nutrients into the ecosystem, which can lead to shifts in the ecological balance of the wetlands, for instance an increase in snail populations, which are vectors for the spread of parasitic trematode infections, he explains.

Kiesecker says he hopes that a better understanding of these changes will help in management of disease transmission, not only in amphibians but in other populations, including humans.  He also is interested in learning how species reduce the risk of infection by changing their behavior.

Normal epidemiological models are based on the number of infected individuals and the random interaction between infected and susceptible individuals.

New research, conducted by Kiesecker, suggests that, in some cases, susceptible individuals avoid infected individuals, reducing the chance of disease spread.  These results may revise our understanding of the dynamics of infection and may ultimately lead to a fundamental shift in the conception of host-pathogen interactions.

Kiesecker earned bachelor's and master's degrees in biology at the University of Northern Colorado in 1989 and 1991 and a doctorate in zoology from Oregon State University in 1997.  Following postdoctoral research at Yale University, he joined the Penn State faculty in the fall of 1999.

Jouni Kuha, assistant professor of statistics

Jouni Kuha's research involves the selection of the appropriate statistical model for a particular problem.  Kuha's work on model comparisons considers, for example, the index of dissimilarity of categorical data as well as the role of simplicity of models in the selection criteria.  Statistical-model selection requires particular care as data sets become larger and more complex, Kuha explains.  "Standard techniques, such as significance tests, might then misinterpret even very small variations as important lack of fit and require changing the model," he says.  "Instead, we can use other techniques that try to avoid this problem, also using such partially nonstatistical considerations as the balance between the model's fit and its complexity."

His second area of interest is analyzing data in samples that have inherent measurement error in some variable, such as self-reported information about behavior.  In order to minimize the effect of measurement error or missing data, Kuha is developing modified methods of modeling and estimation based on additional data samples or realistic assumptions about the inherent errors.  He says the specific methods must take into account the type of model being employed as well as the nature of the error.

He is particularly interested in defining the correction models for problems involving more than one type of inaccurate measurement or a combination of measurement error and missing data.

Kuha earned his master's degree in statistics at the University of Helsinki in Finland in 1992 and his doctorate in social statistics at the University of Southampton in the United Kingdom in 1996.

After his postdoctoral research at Oxford University in England, he joined the Penn State faculty in the fall of 1999.

Mark Levi, professor of mathematics

Mark Levi uses mathematical methods to predict and to explain the complex motion of various dynamical systems, such as satellites, asteroids, electric circuits, and fluids.  Many mechanical problems are geometrical in nature, although in a higher-dimensional space--the so-called phase space--than the usual three-dimensional physical space.  Some fascinating phenomena, such as the stable levitation of charged particles in an oscillating electric field, are much better explained when translated into an equivalent geometrical setting, says Levi, who uses the concepts of geometry and analysis to understand these physical problems.  The analysis of this hidden "geometrical world" gives new insight into concrete problems--an insight that is not accessible by direct experimental or numerical inspection.  Some remarkable changes in patterns that develop in apparently stable systems, such as a satellite or asteroid that is spinning, can become transparent by his approach, Levi explains.  This combined approach allowed Levi to predict a new phenomenon in the motion of a chain of interconnected pendula--a system that imitates the current in superconducting crystals.  This new observation was later rediscovered by experimentalists.  "I use mathematics as a tool to explain how things work," he says.  "In the classroom, I also like using the mechanics of objects in motion to demonstrate mathematical principles to my students with physical examples."

Levi earned his bachelor's degree in mathematics at the Latvian State University at Riga in 1973 and his doctorate in mathematics at the Courant Institute of New York University in 1978.  He has taught mathematics at a number of universities in the United States and Europe, most recently as professor of mathematics at Rensselar Polytechnic Institute from 1993 to 1998, before joining the Penn State faculty as a professor of mathematics in the fall semester of 1998.

Robert Vaughan, professor of mathematics

Robert Vaughan is a number theorist whose research concerns the properties of whole numbers.  One of his primary interests is the distribution of prime numbers and the implications of the Riemann hypothesis and its natural generalizations.  Another research interest is Waring's problem, which in its original form, as stated by Waring in the third quarter of the seventeenth century, says that "every positive whole number can be expressed as a sum of at most nine cubes, as a sum of at most nineteen fourth powers, and so on," Vaughan says.  "The numbers, nine, nineteen, and so on, are determined by some peculiar properties of relatively small numbers and this form of the problem was almost completely solved by the combined efforts of many mathematicians in the first half of the twentieth century," he says.  Vaughan's investigations are centered on the much-more-difficult modern version of the problem, in which "one asks for the minimum number of cubes that suffice to represent every sufficiently large whole number, and similarly for fourth powers, and so on.  It is believed that every large number can be written as a sum of at most four cubes, as a sum of at most sixteen fourth powers, as a sum of at most six fifth powers, and so on," Vaughan says.  He adds that this version of the problem is still largely unresolved, but all the best known bounds have been contributed by Vaughan and his collaborators.  His investigations also focus on the relationship that may exist between the Riemann hypothesis and Waring's problems and its generalizations.  "Waring's problem itself is not fundamental," he says, "but the techniques developed in connection with it often apply to a diverse array of questions relating to the underlying structure of the mathematics of whole numbers."

Vaughan earned his bachelor's degree in mathematics in 1966 and his doctorate in mathematics in 1970, both at University College in London.  After postdoctoral research at Nottingham University and Sheffield University, he became a lecturer in mathematics at Imperial College in London in 1972, reader in pure mathematics at Imperial College in 1976, and professor of pure mathematics at Imperial College in 1980.  He served as head of the pure-mathematics section at Imperial College from 1988 to 1990.  He has been a visiting professor at universities and institutes in Australia, England, Sweden, and the United States--most recently at the University of Michigan.  Vaughan joined the Penn State faculty as a professor of mathematics in the spring semester of 1999.

Among his honors, he was awarded the Junior Berwick Prize by the London Mathematical Society in 1979, was elected a Fellow of the British Royal Society in 1990, received a doctoral degree at London University in 1990, and was an Engineering and Physical Sciences (EPSRC) Senior Fellow from 1991 to 1996.
 

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