Research

Cosmology is the study of the origin and evolution of the universe. Professor Aparna Venkatesan's scientific background lies primarily in theoretical cosmology, including studies of the first stars and quasars, the microwave background, dark matter, and gravitational lensing. She has also worked in high-energy astrophysics (gamma-ray bursts and cosmic rays) as well as extensive data analysis in planetary astronomy. Her current interests include studies of the first stars and their properties; constraining the duration of first-generation star formation through semi-analytic and numerical methods; the evolution of cosmic star formation and related observational signatures, such as the reionization and the metal enrichment of the high-redshift universe; models for the cosmological transport of metals; feedback from the first stars and supernovae on the cosmic microwave background and on the physics and chemistry of early halos and the intergalactic medium; and predictions for detecting the first objects through the next generation of instruments and satellites.

Electric Perception in Biological Systems

Physics and Biology enjoy an ever-expanding overlap where the collaboration is certainly greater than the sum of its parts. And the collaboration is not new — Crick of Watson and Crick (see DNA) was a physicist. At USF, we investigate the physical principles that contribute to the electric sense in biological systems. Sharks, for instance, can detect minute fluctuations of electric fields in the sea, and this is not well-understood. On one front, we collect an extracellular gel from the electrically sensitive organs, and we measure various thermal and electromagnetic properties of the gel as a form of soft condensed matter. On another front, we mathematically model how a sea creature could use hundreds of these organs in concert to "see" an electrical landscape underwater.

Computational Neuroscience is an interdisciplinary field of research that tries to understand how the brain works. It ranges from the study of the individual ion channels in neuron membranes, to the modeling of brain functions. As physicists, we use analytical techniques and computational approaches to formulate biophysical models of neurons, synaptic transmissions, and network circuits. Computer simulations and mathematical analysis are combined to study the resulting nonlinear dynamical systems. We study how different conductances contribute to the electrical characteristics of a neuron, how neurons interact to produce functioning neural circuits and how large populations of neurons represent, store and process information. Current areas of interest at the USF Physics Department are modulation of neural networks, dynamical properties of neural networks and their relation to memory and vision, and methods for encoding and processing information in neuronal spike trains.

The currently accepted fundamental frameworks dealing with space, time, and the particles and interactions of nature are ultimately based on quantum physics and relativity. By playing with these fundamental concepts, physicists discover, define, and redefine the fundamental laws of nature. At the frontiers of this line of research, physicists are trying to understand the behavior of particles and fields at high energies and in strong gravitational fields. The fundamental frameworks used for these investigations are: quantum field theory, which combines quantum mechanics and special relativity (essential for the description of elementary particles, the ultimate building blocks); and general relativity, which merges space, time, and gravitation in its simplest geometric form (Einstein's gravitational theory, essential for strong gravitational fields and cosmology). One of the most perplexing problems in contemporary theoretical physics is finding the correct description of gravitation at the quantum level: quantum gravity, by properly combining and modifying these two dissimilar frameworks. Natural laboratories to explore these notions are provided by black holes and the Big Bang.

Computation is an integral part of modern science, and the ability to exploit effectively the power offered by modern computers is therefore essential to a working physicist. In general, phenomena under study are represented by computer models, which implies no actual analytical solution of equations. These so called simulations are particularly important and relevant in complex systems, where the analytical approach may break down. In addition, a simulation allows for "pseudo-experiment" in which one can ask the system under study questions that would be impractical or impossible to ask experimentally.

While no substitute for good analytical and/or experimental work, the computational approach does complement the other two traditional approaches to Physics, namely Theoretical and Experimental.

Condensed Matter Physics seeks to understand the physical properties of solid materials exposed to all sorts of environments. For example, some condensed matter physicists explore how different materials conduct heat, conduct electricity, or react to an applied magnetic field. Here at USF, we subject ceramic materials to a wide range of temperatures (in many cases cryogenic), magnetic fields, and electric currents. When cooled well below room temperature, some solid materials display an infinite electrical conductivity. Some of these so-called superconductors exhibit magnetic behavior as complex as it is fascinating. The high-temperature superconductors, first discovered in 1987, are some of the most perplexing of all superconductors. In the department's cryogenic laboratory, we probe the magnetic response of high-temperature superconductors.

In recent years, a "standard model" of the universe has been well established but fundamental questions about the nature of Dark Energy — that which causes the expansion of the Universe to accelerate! — remain unanswered. Along with collaborators in the Supernova Cosmology Project (SCP) and the Nearby Supernova Factory (SNfactory) led by Saul Perlmutter and Greg Aldering, respectively, at the Lawrence Berkeley National Laboratory, Prof. Huang is working on the following projects and would like to engage undergraduate students as researchers in finding solutions to cutting edge problems of observational cosmology.

Most recently Prof. Huang has been working on nearby SNe Ia that are in the Hubble flow. Careful analysis of the spectra of low-redshift SNe can contribute significantly to reducing statistical and systematic uncertainties on the cosmological parameters. An important source of uncertainty is the effect of dimming (or "extinction") and reddening of a distant SN by intervening dust. Using spectra obtained by the SNfactory, he and his collaborators made significant progress toward understanding the dust properties in the host galaxy of a highly "reddened" SN. They hope to publish their results soon and extend our analysis to other SNe affected by dust.

Tom Böttger studies optical, dynamical, and magnetic properties of solids, specifically optical materials doped with rare earth ions. This work is centered on understanding the fundamental material physics at the microscopic scale but also geared towards the development of optical materials for optical signal processing, optical memories, quantum computing, and laser frequency stabilization. Prof. Böttger has been specifically interested in Erbium doped materials as they enable optical devices operating at the fiber telecommunication wavelength. This work is carried out using a variety of linear and nonlinear optical methods, such as stimulated photon echoes, spectral hole burning, time-resolved spectroscopy and more conventional methods such as optical absorption spectroscopy. Prof. Böttger is also interested in laser development and has worked on the technique of frequency stabilizing external cavity diode lasers to the narrow frequency references found in rare-earth-doped materials. By locking the laser frequency to an ultra-narrow spectral hole, experiments have reached the limits of precision in the optical spectroscopy of solids.