Oklahoma State Physics Department

Seminars and Colloquia, July through December, 1997

• This Week's schedule.
• Earlier Semesters.
• Typical Week's schedule.
• August 18-22, 1997's schedule.
• August 25-29, 1997's schedule.
• September 1-5, 1997's schedule.
• September 8-12, 1997's schedule.
• September 15-19, 1997's schedule.
• September 22-26, 1997's schedule.
• September 29-October 3, 1997's schedule.
• October 6-10, 1997's schedule.
• October 13-17, 1997's schedule.
• October 20-24, 1997's schedule.
• October 27-31, 1997's schedule.
• November 3-7, 1997's schedule.
• November 10-14, 1997's schedule.
• November 17-21, 1997's schedule.
• November 24-28, 1997's schedule.
• December 1-5, 1997's schedule.
• December 8-12, 1997's schedule.
• December 15-19, 1997's schedule.

Seminars and Colloquia, Typical Week:

Center of Laser and Photonics Research Seminar:

Physics Colloquium:

Oklahoma High Energy Physics Seminar on Talk-Back Television:

Oklahoma State Physics Department

Seminars and Colloquia, August 18-22, 1997

No Seminars

Oklahoma State Physics Department

Seminars and Colloquia, August 25-29, 1997

No Seminars: First Week of Classes

Oklahoma State Physics Department

Seminars and Colloquia, September 1-5, 1997

No Seminars

Oklahoma State Physics Department

Seminars and Colloquia, September 8-12, 1997

Oklahoma High Energy Physics Seminar on Talk-Back Television:

Note:

Please note new location and time.

Oklahoma State Physics Department

Seminars and Colloquia, September 15-19, 1997

Physics Colloquium:

Abstract:

Advanced ceramics and glasses are difficult to finish due to their hardness and brittleness. Diamond abrasive is invariably used in the production of components of the highest quality in terms of form, finish, accuracy, and surface integrity. While optical, mechanical, and electronic applications of advanced ceramic glasses, and semiconducting materials may require a high degree of surface finish (roughness in the angstrom range), the depth and nature of the subsurface damage that may have been generated on these materials during manufacture may be equally important for it can also limit the performance of the components. For economic manufacture and for improved reliability of brittle materials, an understanding of the mechanisms of material removal in fine abrasive processes as well as the nature of the damage imparted during various finishing processes are essential prerequisites. This way, the process can be improved and surface and sub-surface damage can be minimized if not altogether removed. This presentation focusses on fine abrasive processes with emphasis on material removal in brittle workmaterials.

Note:

The traditional student-speaker chat will begin in Physical Sciences Room 147 at 3:30 p.m. All students are welcome! Refreshments will be served.

Oklahoma State Physics Department

Seminars and Colloquia, September 22-26, 1997

Oklahoma High Energy Physics Seminar on Talk-Back Television:

Note:

Please note new location and time.

Oklahoma State Physics Department

Seminars and Colloquia, September 29-October 3, 1997

Joint Center for Laser and Photonics Research Seminar &

Center for Sensors and Sensor Technologies Seminar:

Abstract:

There is a widespread and growing interest in the development of devices that incorporate redox heme-containing proteins as part of a catalytic or sensing scheme. The common idea behind this approach has been to take advantage of the rich chemistry exhibited by the heme enzymes. It is important to appreciate, however, that the chemical properties of the heme prosthetic group in natural systems is tuned via interactions with the polypeptide and results in reduction potentials that span two volts and in a wide range of chemical functions. For this reason, a detailed understanding of how the structure of the polypeptide affects the function of the heme prosthetic group will prove invaluable in our ability to utilize these enzymes or engineered derivatives in sensing and/or bioremediation. Our approach to this problem has been the following: a) Develop electrochemical methodology aimed at initiating the redox activity of these enzymes at a surface-modified electrode surface. b) Engineer proteins with predictable redox potentials and high activity for their subsequent use in sensing or in bioremediation.

Electrochemical communication between electrodes and proteins is dependent on the hydrophilicity of the electrode surface as well as on the electrostatic recognition between protein and electrode. To achieve these ends we have been studying the applicability of electrodes whose surfaces have been modified with either thiolate monolayers, or with films prepared frpm poly-electrolytes or lipids. These modified electrodes have been used to study the electrochemical and catalytic properties of the heme-containing cytochrome b₅ and several of its site-directed mutants, which were designed to probe our current understanding of structure-function relationships.

Note:

Coffee & cookies will be served prior to the seminar.

Joint Physics, Biochemistry and Molecular Biology Colloquium:

Abstract:

It is well known that the native conformation of a protein is determined entirely by the various interatomic interactions dictated by the amino acid sequence in a given environment. The determination of the secondary and tertiary structures by the primary sequence has been called "the second coding probblem" (X), and is one of the most pressing problems in modern biology. Efforts to fold a protein from a random structure corresponding to its sequence have met with little success, to date. Using a well-defined set of high-resolution protein structures, we have derived statistical potentials, in the form of distance probability density functions, which describe the interatomic interaction of native proteins. When applied to highly randomized and noisy structures of proteins distinct from the basic set, native-like structures were obtained to very high precision. The examples tested included proteins of all sizes (up to 461 amino acids long), topologies (alpha, beta, and alpha-beta classes). The potentials appear to define the protein energy landscape in a smooth manner and are sensitive enough to recognize subtle distortions from a native packing structure. They therefore also provide a powerful tool for refinement of X-ray derived structures at any degree of initial precision.

Note:

Note different time and location. Refreshments at 3:45.

Oklahoma State Physics Department

Seminars and Colloquia, October 6-10, 1997

Physics Colloquium:

Abstract:

We propose a size effect which leads to negative magnetoresistance (NMR) in non-magnetic granular materials in which the hopping between two nearest neighbor clusters is the main transport mechanism. We show that the hopping resistance decreases with magnetic field at low temperature near the percolation treshold. This is originated from the level shifting (crossing) in a cluster. At high temperature, the magnetoresistance is positive. We also show that the magnetoresistance changes from negative to positive as the separations between the nearest neighbor clusters increase. based on the results, we propose a novel type of giant magnetoresistance (GMR) in a non-magnetic granular material.

Note:

The traditional student-speaker chat will begin in Physical Sciences Room 147 at 3:30 p.m. All students are welcome! Refreshments will be served.

Oklahoma State Physics Department

Seminars and Colloquia, October 13-17, 1997

Oklahoma High Energy Physics Seminar on Talk-Back Television:

Note:

Please note new location and time.

Oklahoma State Physics Department

Seminars and Colloquia, October 20-24, 1997

Fall Break

Oklahoma State Physics Department

Seminars and Colloquia, October 27-31, 1997

Center for Laser and Photonics Research Seminar:

Abstract:

Shipboard radars for detecting and tracking sea-skimmed targets will illuminate the sea surface at small grazing angles, leading to sea clutter that can mask the desired target returns. This small-grazing-angle clutter usually includes short bursts of strong, rapidly fluctuating returns known as "sea spikes". The echoes of the sea spikes are similar to those of the actual targets. Full understanding of the scattering mechanisms include edge diffraction, direct scattering from spray and foam, and multipath scattering from breaking plumes.

The scattering from a breaking-wave surface profile has been examined using a numerical technique that combines the geometrical theory of diffraction with the moment method. This hybrid approach overcomes the limitations of other more standard finite-conductivity sea-water surfaces. Comparison of the calculated scattering with the experimental measurements of the scattering from a metal model of a breaking wave confirms the validity of the numerical approach. Additional calculations of the scattering degrees of breaking show that the backscatter level is closely associated with the size of the breaking-wave plume. The features of the calculated scattering are consistent with predictions of the multipath scattering model of sea-spike generation.

Note:

Coffee & cookies will be served prior to the seminar.

Oklahoma High Energy Physics Seminar on Talk-Back Television:

Note:

Please note new location and time.

Oklahoma State Physics Department

Seminars and Colloquia, November 3-7, 1997

Physics Colloquium:

Abstract:

The formation of patterns in extended non-equilibrium systems provides fertile ground for new developments in nonlinear physics, situated midway between chaos and turbulence. The rotating spiral wave is a striking, commonly observed stable structure in reaction-diffusion systems, among which the Belousov-Zhabotinsky chemical reaction is a classical example. For a given set of reaction parameters, the spiral obtains a unique, well defined pitch and period. I will present results from a series of experiments at the Institut Nonlineaire de Nice, France, which focus on the selection of the steady state and its instabilities. We vary different chemical concentrations in an open spatial reactor, which provides steady chemical conditions. The spiral pitch p_s and period T_s follow the scaling p_s~T_s^1/2, and both have a power law dependence on a single control parameter. The dispersion relation of the medium conforms to the same scaling, which we derive from the underlying chemical equations, and speculate on the existence of an extremum principle. The instabilities of the spiral lead to different forms of spatiotemporal disorder, including "defect-mediated turbulence".

Note:

The traditional student-speaker chat will begin in Physical Sciences Room 147 at 3:30 p.m. All students are welcome! Refreshments will be served.

Special Colloquium:

Abstract:

The use of high dose, single fraction stereotactic radiosurgery is an established procedure for treating small well-defined intracranial tumors (usually < or = 40 mm). Linac-based radiosurgery is widely available for the treatment of AVM, acoustic neuromas, recurrent primary CNS tumors and brain metastases. The current treatment plan for each patient depends on delivering a circularly collimated x-ray beam while rotating about the target volume. The target volume center is always aligned with the Linac isocenter. Consequently, the target voulme is caught in a cross fire of collimated x-ray beams which deliver a lethal dose to the target and limiting dose to the surrounding normal tissues. Brain lesions are not typically spherical shaped. If a non-spherical lesion is treated with a single isocenter technique, normal tissue within the circular field is irradiated to the maximum dose. Current alternatives for these tumors are to be irradiated by two more isocenters which doubles the treatment time and the dose in the volume of overlap. Both of these techniques are undesirable because the absorbed dose to normal brain outside the target volume is increased. Therefore, clearly brain toxicity and other complications can be minimized by conforming the irradiated volume with the target volume and by maintaining the uniformity of the dose distribution inside the target.

A computer controlled miniature multileaf collimator (MMCL) had been developed for use in conformal stereotactic radiosurgery (CSRS) by the University of Texas, M.D. Anderson Cancer Center. Conformal SRS will improve the dose delivery in approximately 40-70% of the SRS patients without compromising the critical structures in near proximity. The extension of CSRS or conformal stereotactic radiotherapy could be used for management of skull base malignancies, nasopharyngeal carcinoma, and prostate tumor. The steps to implement CSRS procedures include the availability of (1) the computer-controlled MMLC, (2) non-invasive sterotactic frame, (3) 3-D treatment planning software (including inverse planning), and (4) treatment portal verification. The MMLC approach to the conformal SRS/radiotherapy could enhance the local tumor control without compromising normal tissue complication risk.

Note:

Note different time and location.

Oklahoma State Physics Department

Seminars and Colloquia, November 10-14, 1997

Physics Colloquium:

Abstract:

An overview on diode laser linewidth and the techniques of its reduction will be presented with particular attention to the method of external optical feedback. New experiments on locking of the diode laser frequency to the high Q whispering gallery mode of a silica microsphere will be given.

Note:

The traditional student-speaker chat will begin in Physical Sciences Room 147 at 3:30 p.m. All students are welcome! Refreshments will be served.

Special Colloquium:

Note:

Contact D. Bandy, x7488 for further information.

Oklahoma State Physics Department

Seminars and Colloquia, November 17-21, 1997

Oklahoma High Energy Physics Seminar on Talk-Back Television:

Note:

Please note new location and time.

Oklahoma State Physics Department

Seminars and Colloquia, November 24-28, 1997

Center for Laser and Photonics Research Seminar:

Abstract:

The ultraprecision finishing of semiconductor materials continues to receive attention because of the critical need to provide surfaces with both extreme control of surface roughness and flatness as well as minimized damage of subsurface crystalline structure. Interest in assessing subsurface damage is motivated by the limitations which lattice disorder pose on device performance, and the fact that the extent of subsurface damage may provide a critical complement to surface finish in assessing machining performance. The objective of the present work is to examine the extent and distribution of subsurface damage in ultraprecision machined semiconductors by the use of ion channeling. Single crystal (0001) oriented CdS was single point diamond turned over a range of depths of cut from 0.1-10 micrometers, and subsurface lattice disorder was examined for regions cut parallel to, and 30 degrees off, a preferred cleavage plane. The energy spectrum of 2 MeV ⁴He+ ions backscattered from the crystal surface was used to obtain depth profiles of lattice disorder.

Note:

Coffee & cookies will be served prior to the seminar.

Thanksgiving

Oklahoma State Physics Department

Seminars and Colloquia, December 1-5, 1997

Joint Center for Laser and Photonics Research Seminar &

Center for Sensors and Sensor Technologies Seminar:

Abstract:

This presentation will cover current clinical uses for both FDA-approved and prototype devices. Safety requirements for medical applications will be emphasized. Current research projects involving collaborations with OSU and OU faculty will be reviewed. Finally, the potential for biomedical research involving OSU faculty in the Center for Laser and Photonics Research, the Center for Sensors and Sensor Technologies, and the College of Veterinary Medicine Surgical Laser Laboratory will be discussed.

Note:

Coffee & cookies will be served prior to the seminar.

Center for Laser and Photonics Research Seminar:

Abstract:

Atomic Force Microscopy (AFM) has been used for the determination of piezoelectric properties of Lead Zirconate Titanate (PZT) films in the morphotropic phase boundary composition. An AFM tip was used, in the contact mode, as a top electrode to apply a voltage to polarize the film and to apply an oscillating field to obtain piezoelectric coefficients and piezoelectric loops from the inverse piezoelectric effect induced on the film. The piezoelectric coefficient in nanoregions was measured as a function of stress by changing the applied force with the AFM tip. The piezoelectric coefficient was found to decrease monotonically ad the stress as increased. It was additionally found that as the stress was decreased to its initial value, the effective piezoelectric coefficient approximately followed the same trace on increasing the stress. These results suggested that non 180^o domains did not contribute to the measured piezoelectric coefficient for the sterss levels applied and that the mobility of ferroelastic domain walls is very low for these PZT films.

Note:

Coffee & cookies will be served prior to the seminar.

Oklahoma State Physics Department

Seminars and Colloquia, December 8-12, 1997

Prefinals Week

Oklahoma State Physics Department

Seminars and Colloquia, December 15-19, 1997

Finals Week

Last Updated: 14 August, 1998.

This page was prepared by Helen Au-Yang and Jacques H.H. Perk.