PHYSICS AND ENGINEERING.

Chair: T.M. Parchure, Waterways Experiment Station

THURSDAY MORNING

Chandeleur Room

9:00 HEXAPODS--MACHINE TOOLS WITH STAR TREK LOOKS

S. Kant Vajpayee, University of Southern Mississippi, Hattiesburg, MS 39406-5137

Technically a parallel kinematic link mechanism, the hexapod represents a revolutionary design concept since the dawn of machine tools. The idea originated with its application as an aircraft flight simulator. In this configuration two struts extend from each point of a triangular base to a triangular overhead platform where the simulator cockpit rides. Motor-driven ballscrews extend and retract the struts in response to controller commands. The transplantation of the idea to machine tool design had to wait until controllers could do the calculations fast enough. In the hexapods each command is a non-linear function of six sets of coordinates; even a simple X motion has to be translated into six coordinated leg lengths moving in real-time. The biggest benefit of hexapod is its higher volumetric accuracy--two to three times that of the conventional Cartesian structures. In the hexapod, the worst single element is the worst machine error. In contrast, classical machine tools stack up errors from all the elemen ts. The hexapod is five times more rigid and four times faster than a conventional machine tool. All these are expected to translate into higher productivity. Half-a-dozen companies currently manufacture hexapods.

9:15 SOCIAL ACCOUNTABILITY SA 8000--A NEW INTERNATIONAL STANDARD

S. Kant Vajpayee, University of Southern Mississippi, Hattiesburg, MS 39406-5137

The success of ISO 9000 and 14000 has propelled the world community to take the first step toward improvement of working conditions in factories throughout the world. As an embodiment of global community, the International Organization for Standardization created a new standard entitled SA 8000, where SA is an abbreviation for social accountability. SA 8000 aims to address and eventually eliminate unfair, inhumane labor practices. It targets poor factory conditions around the world. It has been written by a 25-member advisory board consisting of representatives from renowned organizations. SA 8000 requires that employers pay wages sufficient to meet workers' basic needs, provide a safe working environment, not employ child or forced labor, and limit work to 48 hours per week. Its implications to factories worldwide are quite unprecedented. For example, US companies may find that moving operations overseas no longer makes economic sense; goods imported into the US, produced by the sweat of child labor, will b ecome expensive. Companies are already being certified to SA 8000. It seems that this international inter-industry standard will dramatically accelerate the globalization process already in full swing.

9:30 PREVENTING SALINITY INTRUSION IN ESTUARIES AND NAVIGATION LOCKS

T.M. Parchure, US Army Engineer Waterways Experiment Station, Vicksburg, MS 39180

Intrusion of salt water from ocean in estuaries is a common natural occurrence driven by the differences in densities of salt and fresh water. The extent of salinity intrusion is predominantly a function of the magnitude of tidal range and quantity of fresh water flow. An increase in salinity intrusion may have profound adverse effects on the aquatic life forms and sedimentation patterns of the region. Increased salinity may also make water unfit for human consumption and industrial use. Structures such as barrages and navigation locks constructed on estuaries have to take into account the possibility of salt water intrusion and take preventive measures to arrest such intrusion. Several methods were considered for an engineering project to achieve this objective. These methods are described, which included options such as construction of a submerged sill on river bed, pneumatic curtains, hinged gates, holding ponds, and selective withdrawal. Selection of an effective method requires numerical or physical mod el study. Several estuaries require maintenance dredging in order to ensure adequate depth for navigation of vessels. Increased channel depth increases the extent of salinity intrusion. Assessment of the impact of channel deepening and preventive measures suggested through engineering studies are described.

9:45 EFFECT OF HEAVY SUBSTITUTION IN THE BENZENE RING ON THE RING-MODES OF BENZENE 1 PHENYLTHALLIUM DIFLUORIDE

Chandra M. Pathak [*] and B.P. Asthana, Alcorn State University, Alcorn State, MS 39096 and Banaras Hindu University, Varanasi 221005, India

The vibrational frequencies related to the ring modes in benzene remain fairly constant when one of the hydrogen atoms in the benzene ring is substituted with a single lighter atom or a lighter group of atoms. The present work describes the effect of replacing a single hydrogen atom in the benzene ring with a relatively heavier group [TIF.sub.2]. The studies included the investigation of the infrared spectra of Phenylthallium Difluoride in solid phase covering the spectral region 4000-20 [cm.sup.-1] and the normal coordinate analysis. The far-infrared spectra in the region 500-20 [cm.sup.-1] were recorded and investigated for the first time. The normal coordinate analysis was carried out, using the 'least square iterative technique' assuming a geometrical model with a [C.sub.2v] symmetry for the molecule and has supported the frequency assignment quite well. Twenty-eight symmetrized principal force constants and seven interaction force constants have been found to reproduce the observed frequencies. The aver age percentage error between the calculated and observed frequencies has been found to be 2.01% with the standard deviation not exceeding 6.63 [cm.sup.-1]. The standard deviation in the force constants was found to lie in the range 0.002-0.235 mdyne/A.

10:00 Break

10:15 CALIBRATION OF LASER-INDUCED BREAKDOWN SPECTROMETRY SPECTRA

Jagdish P. Singh, Fang-Yu Yueh, Chun Fu Su, Khurram Z. Moghal [*], and Robert L. Cook, Mississippi State University, Mississippi State, MS 39762

In the past years, we have reported the results of the laser-induced breakdown spectroscopy (LIBS) technique to the MAS annual meetings. The results included the identification of the metal elements in the vitrified glass samples, the concentration ratios of the elements, and the effect of the sample temperature on the spectral intensities and concentration ratios. Recently, an attempt was made to employ the technique for calibrating the elemental concentrations present man arbitrary sample. Five standard aluminum alloy samples with the known elemental concentrations were used in this study. In principle, at a certain sample temperature the intensity of a given line is linearly proportional to the elemental concentration. However, the matrix effects, excitation conditions, and other factors may significantly affect the measurement accuracy. Detailed results of the calibrations will be presented.

10:30 SOFTWARE DEVELOPMENT FOR 3-DIMENSIONAL DCO RATIO ANALYSIS

Russ Terry [1][*], Bent Herskind [2], Mats Bergstrom [3], Peter Varmette [1], and Wenchao Ma [1], [1] Mississippi State University, Mississippi State, MS 39762; (2.) Niels Bohr Institute, Copenhagen, Denmark; and (3.) Universitet zu Koln, Cologne, Germany

Directional Correlation of Oriented nuclei (DCO) ratio analysis is a very common and important approach used in finding the multipolarity of gamma ray transitions and subsequently to determine spin and parity of excited nuclear states. Traditionally DCO ratio analysis has been accomplished through the analysis of double coincidence data using an asymmetric two-dimensional coincidence matrix. This method often fails for weak transitions in a complex decay scheme or at high spin due to short-comings of 2-D coincidence measurements. The goal of this project is to develop software and techniques for performing DCO ratio analysis using an asymmetric 3-dimensional coincidence cube. The high-fold, high-statistics data available from large gamma ray detector arrays such as "Gammasphere" and "Euroball" compounded with the high speed and data storage capacity of modem computers have made it possible in recent years to generate and handle 3-dimensional data cubes. Since an asymmetric, as opposed to a symmetric, coincid ence cube cannot be folded, compression techniques must be implemented to increase manageability of the data. A 1024 x 1024 x 800 channel cube requiring only 0.5 GB was generated from a Gammasphere experiment at Argonne National Lab using the reaction of 76Ge + 96Zr. By using this double gating (3-D) approach, it is found that transitions are more easily and accurately resolved from spectra. A graphical interface was developed to increase ease and efficiency. The principle and technique will be demonstrated.

10:45 EXCITATION LEVELS IN VERY NEUTRON-DEFICIENT TE [111] ISOTOPE

W. Liu [1][*], Peter Varmette [1], W.C. Ma [1], Bent Herskind [2], G. Hagemann [2], G. Sletten [2], Mats Bergstrom [2], G. De Angelis [3], M. Cinausero [3], C. Fahlander [3], H. Jensen [3], D. Napoli [3], and P. Spolaore [3], (1.) Mississippi State University, Mississippi State, MS 39762; (2.) Niels Bohr Institute, Denmark; and (3.) INFN Laboratoria Nationale do Legnaro, Italy

In order to study the high spin states of very neutron deficient Xe, I, Te isotopes, an experiment was performed at Legnaro National Laboratory using the reaction of [[blank].sup.58] Ni + [[blank].sup.58]Ni. Beam energy of 275 MeV was chosen, which was higher than one would usually use, to bring into the compound system highest possible angular momentum. The symmetric reaction was calculated to be very "cold" thus reducing the fission cross section. The decay gamma rays, charged particles and recoiling nuclei were detected with the GASP spectrometer array (consisting of 40 Compton-suppressed Germanium detectors), the ISIS detector array (consisting of 39 Silicon telescopes), and the Recoil Mass Spectrometer. In the off-line analysis, gainmatched and Doppler corrected gamma rays were sorted into thirteen coincidence matrices with different mass and charged-particle (proton and alpha) gating conditions. Data analysis is in progress and results will be presented.

11:00 HI ABSORPTION TOWARDS PDS 456

C.H. Young [1][*], C.L. Brogan [2], and M. Yun [3], (1.) Mississippi State University, Mississippi State, MS 39762; (2.) University of Kentucky; and (3.) National Radio Astronomy Observatory 

PDS 456 is a nearby quasar that was discovered by the Pico dos Dias Survey in 1997. This object is of interest in the field of quasi-stellar object (QSO) formation because it is very bright in the optical regime (B=14.69), and it also has a high, inferred dust mass. We chose to observe this source in the hopes of detecting an HI absorption line towards the quasar. Confirmation of the presence of gas surrounding this quasar would suggest one of three possible scenarios: 1) the dust and gas form an acquiescent halo around the central engine of this object, 2) copious amount of mass is being ejected away from the quasar while the object is in a transition stage from dust-enshrouded to naked QSO, or 3) the central engine of the quasar is accreting large amounts of matter. We initially postulated that the second of these scenarios was the most likely for PDS 456 because of the bright infrared and optical characteristics. However, observations made with the Very Large Array on two separate occasions, instead, supp ort the third scenario. We intend to present the data and results of analysis. Also, implications of this discovery on the theories for QSO formation will be discussed. Finally, we will propose further investigations, which might include searching for emission lines or observing with the Very Long Baseline Array (VLBA).

11:15 Divisional Business Meeting and Awards Awards are made possible through the generosity of the Waterways Experiment Station, Vicksburg, MS

THURSDAY AFTERNOON

Chandeleur Room

1:30 UTILIZING A COMPUTATIONAL NUMERICAL MODEL TO STUDY THE PULTRUSION OF COMPOSITES

Corey L. Wallace [*] and Tyrus McCarty, University of Mississippi, University, MS 38677

The purpose of the project is to identify variables in the Pultrusion process and utilize these variables to enhance production quality. A mathematical model is utilized in the production design. This mathematical model dictates the computer program that performs the simulation of the process. The product of the process is a composite. A composite is a material derived from two or more materials. The desired result is to gain the best qualities from all of the components. The composite is formed on the macroscopic level and is made from unconventional materials, while alloys are made from metallic materials. The controllable variables are shape, viscosity of the initiates, the speed at which the material is fed through the Pultrusion machine and a combination of others. Testing is done through use of the PTI 804 commercial scale protruder. The University of Mississippi and one other American University are the only educational institutions with this scale; thus making this a unique experiment. Pultrusion is a method of manufacturing in which a composite is produced. The process follows a systematic method. Fibers of a material are pulled through a resin bath, then through a shaping system that also removes excess material. This section gives the material its uniform shape. The material is then heated and cured until ready. It is finally cut into the desired length. The composite is to take the desirable qualities from the materials. The research aspects of Pultrusion indicate that it is not as thoroughly tested as the other methods of forming composites. Other methods of forming a composite include compression molding, injection molding and extrusion. Pultrusion remains the target production method due to its cost-effectiveness. Through experimentation the shape of the material entry is altered. It is believed that the change in shape will increase pressure, alleviating voids in the material. The voids are pressure points of the material and cause failure of the offspring composite. The project experimentation i nvolves a 9-degree angle wedge shape. This information is calculated through computer programs and simulations. The resulting answers indicate that both an increase in viscosity and an increase in pull speed raise centerline pressure for the region of concern. The increase in pressure will alleviate voids providing stronger composites. The increase in quality will raise Pultrusion as the manufacturing method of choice.

1:45 A COMPARISON OF HORIZONTAL AND VERTICAL PENDULUM ARCHERY SIGHTS

John W. Lipscomb, Jr., University of Southern Mississippi, Hattiesburg, MS 39406

Archery accuracy requires estimating the target distance - a difficult task with 20% error in the field. If the archer is elevated, pendulum sights can adjust the aiming point to compensate for various ranges. One-inch horizontal and vertical pendulum sights are currently in use. The aiming point of a horizontal pendulum is at the same elevation as the pivot. It provides good trajectory correction, but it must be used from an elevated position. Shooting at targets on the same or a higher elevation is not possible because too much correction occurs. A vertical pendulum has the aiming point directly below the pivot point. For the same length, this pendulum cannot correct the aiming point as well as a horizontal pendulum but it can be sighted-in and used horizontally on the ground. For comparing the two pendulums, a 250-fps initial arrow velocity with [+ or -]1.5 inch maximum trajectory error was assumed. A spreadsheet program was used to model the arrow flight including arrow initial velocity and decay, elevat ion differences, and target distance. If both pendulums are sighted-in 15 feet over the target with [+ or -]1.5 inch maximum error, the maximum ranges of the horizontal and vertical pendulums are 85.1 and 75.6 feet respectively. This difference of 11.8% is acceptable because the vertical pendulum can be used on targets from 15 feet below to 15 feet above the archer with the similar accuracy.

2:00 DETECTOR TESTING FOR THE JEFFERSON LABORATORY [G.sup.0] EXPERIMENT

Sarah K. Phillips [1][*], Allison Lung [2], Bond Hutchinson [3], and David Larson [4], (1.) Mississippi State University, Mississippi State, MS 39762; (2.) Thomas Jefferson National Accelerator Facility, Newport News, VA 23606; (3.) Louisiana Tech, Ruston, LA 71272; and (4.) University of Maryland, College Park, MD 20742

The goal of the [G.sub.0] experiment (E91-017) is to measure parity-violating asymmetries over the range 0.1 [less than or equal to] [Q.sup.2] [less than or equal to] 1.0 Ge[V.sup.2] at both forward and backward angles. These measurements will be used to separate [[G.sup.S].sub.E] and [[G.sup.S].sub.M] form factors (the neutral weak E current analogs of the electric form factor [G.sub.E] and the magnetic form factor [G.sub.M]). Using these form factors, the u, d, and s quark contributions to the charge and current of the nucleon can be determined. The [G.sup.0] detector will be able to measure asymmetries at both forward and backward angles. It consists of a toroidal array of eight superconducting coils, designed to focus particles of the same momentum and scattering angle from the target to a single point. The detector will have sixteen scintillator pairs for each of the eight octants, which surround the beamline to cover phi of 360[degres] for maximum solid angle.

2:15 Break

2:30 POSITRON AND PION BACKGROUND CONTAMINATION TO THE MEASUREMENT OF THE RATIO OF THE ABSORPTION CROSS SECTION OF LONGITUDINALLY AND TRANSVERSELY POLARIZED VIRTUAL PHOTONS IN THE RESONANCE REGION

Kurt M. Spurlock [*] and James A. Dunne, Mississippi State University, Mississippi State, MS 39762

Inclusive electron scattering experiments consist of scattering a beam of electrons off a target and detecting the scattered electrons. Properly counting these scattered electrons is essential to the determination of the ratio of the absorption cross sections of longitudinally and transversely polarized virtual photons, a ratio known as R. An accurate measurement of R provides a more reliable model of electron-nucleon scattering. The results of the experiment are skewed, however, by the counting of unwanted electrons and misidentified electrons that traverse the spectrometer. A major source of this background comes from [[pi].sup.-] mesons, or pions, and electron-positron ([e.sup.-][e.sup.+] pair production from decaying, neutral pions ([[pi].sup.0]) The [[pi].sup.0] is created as the electron beam traverses the target and quickly decays into two photons. These photons, in a charge symmetric process (i.e., the oppositely charged particles are produced in a one-to-one ratio), convert to [e.sup.-][e.sup.+] pai rs in the target. The scope of this research consists of determining the background coming from mesons and charge symmetric processes for each kinematic setting.

2:45 SPACE-BASED IMAGES OF EARTH: A NEW ERA OF HIGH-RESOLUTION

Harold Dunsford [1], John Patrick Lestrade [1][*], and David Bandi [2], (1.) Mississippi State University, Mississippi State, MS 39762 and (2.) MapSAT, Starkville, MS 39759

Since the days of Sputnik, there has been a lot of interest in commercial applications of satellite images of the Earth. This interest has recently surged with the availability of 1-meter resolution data, an order of magnitude better than past resolutions. While our group is primarily involved in creating new mathematical algorithms designed to extract information from space-based imagery, we are also involved with joint corporate and government efforts to increase awareness of the new, potential benefits. In this paper, we present an overview of what data are available and we present ideas for interesting commercial applications.

3:00 FEASIBILITY STUDY OF A STEP BEAD AS OPPOSED TO A SQUARE BEAD IN GENERAL STAMPING OPERATIONS IN THE AUTOMOTIVE INDUSTRY

Josias Israel, Mississippi State University, Mississippi State, MS 39762

This study was purposed to analyze the usability and feasibility of the step bead, in the areas of raw material and tool operating cost. As opposed to the square bead, the step bead has been neglected in general stamping operations due to lack of knowledge of the applications of such tooling. Even though, intuitively, the cost savings are there, the actual use of the step bead has not yet been justified. Though the use of a draw bead tester machine, the aim of this experiment was to reproduce the results that the step bead would generate in actual production and compare them to the results gathered from the standard square bead. The process was then simulated using the same simulation package used to model actual stamping processes. The results from both the physical and simulated experiments proved too trivial an initial foundation for the justification of the step bead in actual production.

3:15 OCTUPOLE VIBRATIONS IN THE SD WELL OF 190 Hg

Hanan Amro [1][*], Robert V. F. Janssens [2] Greg Hackman [2], Susan Fischer [2], Irshad Ahmad [2], Mike Carpenter [2], Frank Moore [3], Ben Crowell [4], Teng Khoo [2], Torben Lauritsen [2], John Timar [5], amd Anna Wilson [5], (1.) Mississippi State University, Mississippi State, MS 39762; (2.) Argonne National Laboratory, Argonne, IL 60439; (3.) North Carolina State University, Raleigh, NC 27695; (4.) Fullerton Community College, Fullerton CA 92833; and (5.) University of Liverpool, Liverpool L69, United Kingdom

In an experiment that has been carried out using Gammasphere, the excited states in 190 Hg were populated with the reaction 160 Gd (34S, 4n) at a beam energy of 159 MeV with a thick target (1.17 mg/[cm.sup.2]) evaporated on a 13 mg/[cm.sup.2] Au backing. Three or higher-fold coincidence events were recorded. The triple-gated spectra corresponding to the 17 angular rings of Gammasphere were constructed individually. From gamma-ray centroids in each of the angle sorted spectra, the fractions of full Doppler shift F(tau) were extracted for transitions in the yrast and the first excited SD bands. Dipole transition rates have been established for the inter-band transitions, which connect those two SD bands. The measured B(El) strengths are of the same order as those reported for El inter-band transitions in nuclei with a substantial dipole moment arising from octupole collectivity. The intrinsic quadrupole moments, Q, were extracted for both SD bands and found to be essentially the same (dQ = 0.1 [+ or -] 1.9 eb) . Therefore, the present results show that there is no difference in deformation between the two SD bands. This, along with the measured B(El) strengths of the inter-band transitions, favors the interpretation of the excited SD band as a rotational band built on an octupole vibration. The comparison of the Q moment of the yrast SD band in 190 Hg with the moments of yrast SD bands in other Hg isotopes further strengthens the conclusion that the quadrupole deformation associated with SD minimum in the Hg isotopes is very stable and that Q values exhibit very little dependence an the nuclear mass or on the intrinsic structure of the SD bands being considered.

3:30 Divisional Poster Session

ELECTROCHEMICAL CELL DESIGN CONCEPTS FOR THE NEW MILLENNIUM

William C. Mahone [*], M. Ellison, O. James, and J. Brown, Mississippi Valley State University, Itta Bena, MS 38941

We have constructed a variety of electrochemical cells of different types designed to interface with alternative energy process cycles. These include zinc-air cells, aluminum copper cells and aluminum dry cells. We are using these prototype cells to study controlling processes. With these data and data from continuing studies we will optimize our design parameters and draw conclusions about the feasibility of their use.

HYDROGEN OXYGEN FUEL CELL DESIGN CONCEPTS

William C. Mahone [*] and T. Pierre, Mississippi Valley State University, Itta Bena, MS 38941

We have constructed a prototype hydrogen-oxygen fuel cell. The purpose of this cell is to allow us to study controlling processes, particularly porous electrode and salt bridge design. Fuel cells have high promise for the future because they are non-polluting, and highly efficient with the promise of providing low cost electricity. Also the hydrogen, which powers our fuel cell, is chemically generated on demand rather than stored hydrogen from k-bottles. Hydrogen handling is one of the major problems and costs associated with hydrogen-oxygen fuel cells.

REGIONAL SOLAR RADIATION PROFILE AND SOLAR POWER CONVERSION

William C. Mahone [*], A. Robinson, C. Flowers, and B. Adams, Mississippi Valley State University, Itta Bena, MS 38941

We have carried out a variety of measurements of the Sun's angle to earth observer view (Solar Angle). We have also carried out measurements of various aspects of the solar intensity profile at various times under various conditions. A third series of measurements allowed us to determine the power output of conventional solar panels at various time of the day under various conditions. With these data and data from continuing studies we draw conclusions about the feasibility of solar power systems in this area.

FRIDAY MORNING

Chandeleur Room

9:00 ARTIFICIAL SOFT AND HARD SURFACES AND THEIR APPLICATIONS IN ELECTRO-MAGNETICS: A REVIEW

Ji Wang [*] and Ahmed A. Kishk, University of Mississippi, University, MS 38677

A review on the understanding of the artificially soft and hard surfaces will be presented. Soft and hard surfaces are well known in acoustics. Such surfaces are naturally present for electromagnetic waves because of the polarization nature of the electromagnetic fields. However, these surfaces can be recognized by constructing anisotropic surfaces. These anisotropic surfaces can be developed by corrugated perfectly conducting surfaces or by dielectric coating of the conductor surface and loading the dielectric surface by conducting strips. The corrugated or strip loaded surfaces are hard when the waves propagate along the strips or the corrugation. They are soft when the waves propagate transversely to the strips or the corrugations direction. Using such surfaces one can control the boundary condition and use it to strengthen or weaken the waves propagating on the surface. The soft surfaces are used in the design of transversely corrugated horns to improve the polarization of the horn and reduce the sidelob e levels. These horns are normally used as feeds for reflector antennas. Hard surfaces are used to design polarization independent struts (that support feeds in front of the parabolic reflector) to reduce the forward scattering from the struts and consequently improve the radiation performance of the reflector. The surface integral equations are used to formulate these problems and solved using the method of moments. In some cases the approximate surface impedance is used with the corrugated surfaces and the asymptotic strip boundary condition is used with strip loaded surfaces. The results will show the improvement in the radiation characteristics of the antenna when these surfaces are used properly.

9:15 ANALYSIS OF CIRCULAR WAVEGUIDE WITH STRIPS LOADED WALLS USING ASYMPTOTIC BOUNDARY CONDITIONS

Michael Morgan [*] and Ahmed A. Kishk, University of Mississippi University, MS 38677

A circular waveguide with wall coated by uniform dielectric layer loads with conducting strips is analyzed using the approximate Asymptotic Strips Boundary Conditions (ASBC). The strips could be oriented along the waveguide axis or circurnferentially oriented in a periodic form to artificially create hard or soft surfaces, respectively. Such structures can be analyzed accurately by using the Floque's mode expansions, which is tedious. Here, the ASBC is used to simplify the solutions under the assumption that the strips period p is approaching zero. With this assumption, the tangential fields along the strips are zero electric field and continuous magnetic field and the tangential electric field in the transverse direction to the strips is continuous. At certain conditions the loaded strip surface can be electromagnetically soft or hard that makes the waves not propagating or propagating along the surface, respectively. The waveguide with such surfaces creates a uniform linear field distribution across its cross section, as we will show graphically. This makes it a good linearly polarized antenna with high gain and high sidelobe level for the hard surface and low sidelobe level for the soft surface. Here, our analysis provides the proper dimensions for the waveguide to achieve the soft and hard surfaces. It was found that the dielectric thick ness is a function of the waveguide radius and approaches a quarter wavelength as the waveguide radius increases.

9:30 INPUT INTERFACE FOR A FINITE DIFFERENCE TIME DOMAIN ELECTROMAGNETIC SIMULATION TOOL

Chris L. Riley [*], James D. Vernon, Atef Z. Elsherbeni, and Charles E. Smith, University of Mississippi, University, MS 38677

The finite difference time domain (FDTD) technique is widely used in the analysis of electromagnetic problems and in the design of antennas and microwave devices. The FDTD is a computation procedure that applies Maxwell's equations in time domain to the problem at hand. Commonly it requires a large number of time iterations and a significant amount of storage allocation for field components and material properties in the computational domain. These issues are under continuous investigation for adapting the method to current computer resources. A description of the geometry of the device under test for the computational engine is a very time consuming task, if programmed for every individual case. The optimal solution is to develop an interactive graphical input interface that creates and displays device details and transfers geometrical information to appropriate parameters for the FDTD computational engine. The purpose of this paper is to address this issue of creating an efficient interface. The interface should be simple to understand, and yet powerful to handle complex and composite structures. The development of such an interface is achieved by using the Microsoft Visual Basic, and the graphical library OpenGL. Examples of the simulated structures such as printed circuit board connectors and printed spiral and meander line antennas are considered.

9:45 ANALYSIS OF DIELECTRIC RESONATOR ANTENNAS MADE OF DIFFERENT DIELECTRIC MATERIALS

Xiao Zhang [*], Ahmed A. Kishk, and Allen W. Glisson, University of Mississippi, University, MS 38677

The dielectric resonator antenna (DRA) is a newly developed antenna made of high dielectric material placed above a conducting ground plane. Many different excitation mechanisms can be used for the antenna. In this work we use a coaxial probe penetrating through the ground plane and housed inside the dielectric material. DRA's have typically been made of a single very low loss ceramic material. However, resonators consisting of more than one dielectric material can be used to effectively create two resonators that are coupled to each other. With the proper excitation and selection of these resonators, the bandwidth of the DRA can be increased or the antenna can be designed for multi-frequency use. In this work two resonators are used with one resonator being stacked on top of the other above the ground plane. The DRA is then analyzed numerically using the method of moments after image theory is applied to the structure. The effect of different parameters on the antenna performance is investigated. It is foun d that the probe position and length have a significant effect on the input impedance of the antenna and on the bandwidth. Also, changing the arrangements of the two dielectric resonators has a significant effect on the antenna performance because of the change in the coupling factor between the two resonators and the excitation probe. Results will be presented to show the effect of these parameters on the antenna performance.

10:00 Break

10:15 PARAMETRIC STUDY OF THE DIELECTRIC RESONATOR ANTENNAS WITH CONICAL SHAPE

Yan Yin [*], Ahmed A. Kishk, and Allen W. Glisson, University of Mississippi, University, MS 38677

Dielectric resonator antennas are usually designed as circular discs of high dielectric material located on a perfectly conducting ground plane. In this study a dielectric resonator antenna of truncated conical shape is used to investigate the effect of this geometry on the dielectric resonator antenna performance as compared with the dielectric disc. The investigation is performed numerically using the method of moments for axisymmetric objects. With the aid of the image theory one can also analyze a halfcone dielectric resonator (split through its axis of symmetry) by converting it to a full axisymmetric cone. When the cone is placed with its axis of symmetry normal to the ground plane, either the [TM.sub.01] mode or the [HEM.sub.11] mode can be excited by locating a coaxial probe either on the cone axis or off the axis, respectively. The [TM.sub.01] mode produces a monopole type radiation pattern (end fire), while the HEM [11] mode produces a narrow slot type pattern (broadside). When the half cone is pla ced on the ground plane, the probe excitation is directed normal to both the ground plane and cone axis of symmetry. Different mode types will again be excited based on the probe location inside the dielectric. Thus, the radiation pattern type can be controlled by the probe position. The effect of the cone apex angle and the probe position on the input impedance is also investigated. It is found that the split structure provides wider bandwidth than the unsplit structure.

10:30 A NEW DEVICE FOR IMPOSING UNIFORM, CYCLIC STRAINS TO CELLS GROWING ON IMPLANT ALLOYS

Chad Winter [*] and Joel D. Bumgardner, Mississippi State University, Mississippi State, MS 39762

The objective of this study was to demonstrate an effective means for applying known, uniform, cyclic strain to cells growing on implant materials in vitro. The cell culture strain device was designed based on the application of the four-point bending principle. A medical-grade-2 Titanium plate was used as the cell substrate, and strain was applied at eight deflection levels at frequencies of 0.5-10 Hz for durations of 12-72 hours. Strain gauges recorded average maximum strain levels of 188 [+ or -] 6.5, 251 [+ or -] 8.3, 321 [+ or -] 10.4, 428 [+ or -] 11.8, 565 [+ or -] 9.5, 754 [+ or -] 14.1, 892 [+ or -] 5.8, and 1020 [+ or -] 9.3 [micro] strains. The device was tested with photo elastic film and viewed with a polarizer at the 8 different deflection levels. Human gingival fibroblasts (HGF) were seeded at l0 [5] cells/[cm.sup.2] on the plate in silicone-attached polystyrene wells. The strain device, with attached HGF cells, was tested in an amiable bioenvironment. Results from photo elastic coating indica ted a uniform strain field existed within the center region of the plate. Cells in the test plates stained viable and exhibited similar morphology to controls. Tests are being conducted to evaluate the responses of osteoblastic cells growing on implant surfaces at the different strain levels. The cell culture strain plate produced known, uniform, repeatable, and consistent cyclic strains to cells growing on the surfaces of implant materials.

10:45 A DIGITAL PHASE LOCK LOOP USING IN-PHASE AND QUADRATURE SIGNALS

Cheng Jia [*] and Paul M. Goggans, University of Mississippi, University, MS 38677

A new digital phase lock loop (DPLL) was developed to recover the time-varying ground surface velocity from the output of a laser Doppler vibrometer (LDV) used in landmine detection. The LDV output is frequency modulated by the velocity signal and the DPLL is used as a demodulator. The LDV output signal is band-pass limited and its center frequency is much greater than its bandwidth. To avoid the high sampling rate required to sample the band-pass limited signal, the LDV output is converted to base-band in-phase and quadrature signals before it is sampled and quantized. The software-based DPLL is implemented using floating-point arithmetic. As a result, a dynamic range comparable to an analog phase lock loop can be achieved. Unlike an analog phase lock loop, the DPLL uses a phase detector that is linear for phase differences between -180 degrees and +180 degrees. Consequently, the DPLL has an improved ability to achieve and maintain phase lock. This paper presents results obtained for both simulated and measured LDV output signals.

11:00 A DIGITAL SIGNAL PROCESSING IMPLEMENTATION OF THE TMS320C31 TO ANALYZE AND CATEGORIZE A SAMPLE OF COSMIC GAMMA-RAY BURSTS

Morgan Simpson and John Patrick Lestrade [*], Mississippi State University, Mississippi State, MS 39762

A Power Density Spectrum (PDS) analysis of Gamma Ray Burst (GRB) data has been implemented using the TMS320C31 digital signal processor. This relatively inexpensive, flexible chip is used in a wide range of applications. Implementation includes programming the TMS320C31 to receive and process the data. The analysis includes processing of data using PDS algorithms for 20 GRB's whose durations range from 10 seconds to over 200 seconds. A metric is chosen to sort the PDS of a given burst into different categories. The TMS320C31 outputs the PDS and the results of the categorization. This implementation of Digital Signal Processing hardware demonstrates the feasibility of utilizing DSP techniques for on-spacecraft analysis of gamma-ray burst data.