Showing papers by "Georgia Institute of Technology published in 1981"

Rigorous coupled-wave analysis of planar-grating diffraction

Abstract: A rigorous coupled-wave approach is used to analyze diffraction by general planar gratings bounded by two different media. The grating fringes may have any orientation (slanted or unslanted) with respect to the grating surfaces. The analysis is based on a state-variables representation and results in a unifying, easily computer-implementable matrix formulation of the general planar-grating diffraction problem. Accurate diffraction characteristics are presented for the first time to the authors’ knowledge for general slanted gratings. This present rigorous formulation is compared with rigorous modal theory, approximate two-wave modal theory, approximate multiwave coupled-wave theory, and approximate two-wave coupled-wave theory. Typical errors in the diffraction characteristics introduced by these various approximate theories are evaluated for transmission, slanted, and reflection gratings. Inclusion of higher-order waves in a theory is important for obtaining accurate predictions when forward-diffracted orders are dominant (transmission-grating behavior). Conversely, when backward-diffracted orders dominate (reflection-grating behavior), second derivatives of the field amplitudes and boundary diffraction need to be included to produce accurate results.

Constrained iterative restoration algorithms

Abstract: This paper describes a rather broad class of iterative signal restoration techniques which can be applied to remove the effects of many different types of distortions. These techniques also allow for the incorporation of prior knowledge of the signal in terms of the specification of a constraint operator. Conditions for convergence of the iteration under various combinations of distortions and constraints are explored. Particular attention is given to the use of iterative restoration techniques for constrained deconvolution, when the distortion band-limits the signal and spectral extrapolation must be performed. It is shown that by predistorting the signal (and later removing this predistortion) it is possible to achieve spectral extrapolation, to broaden the class of signals for which these algorithms achieve convergence, and to improve their performance in the presence of broad-band noise.

Solid state characterization of the structure of chitosan films

Abstract: Films of chitosan, prepared by different fabrication processes, were examined at several structural levels, from the molecular to the macroscopic. This revealed the presence of polymorphic crystal forms, which varied with film treatment. Similarly, morphological structures varying from spherulites to rods were formed, depending on film processing conditions. The effect of structure on the mechanical properties, as well as the orientability of the films, were also investigated.

A Scale to Measure Self-Concepts, Person Concepts, and Product Concepts:

Abstract: The author describes the construction of a scale to measure self-concepts, person concepts, and product concepts. Multivariate analysis and multidimensional scaling procedures are employed to devel...

Antennas in Matter: Fundamentals, Theory, and Applications

Abstract: The volume provides an introduction to antennas and probes embedded within or near material bodies such as the earth, the ocean, or a living organism. After a fundamental analysis of insulated and bare antennas, an advanced treatment of antennas in various media is presented, including a detailed study of the electromagnetic equations in homogeneous isotropic media, the complete theory of the bare dipole in a general medium, and a rigorous analysis of the insulated antenna as well as bare and insulated loop antennas. Finally, experimental models and measuring techniques related to antennas and probes in a general dissipative or dielectric medium are examined.

Kinetics of the reactions of hydroxyl radical with benzene and toluene

Abstract: Absolute rate constants for the reactions of the hydroxyl radical with benzene and toluene were measured within the temperature and pressure ranges 213 less than or equal to T less than or equal to 1150 K and 20 less than or equal to P less than or equal to 200 torr by using He, Ar, and SF/sub 6/ as diluent gases. To help elucidate the variations in reaction mechanism with temperature, we also studied OH reactions with deuterated benzene (C/sub 6/D/sub 6/) and with selectively deuterated toluenes (C/sub 6/H/sub 5/CD/sub 3/, C/sub 6/D/sub 5/CD/sub 3/, and C/sub 6/D/sub 5/CH/sub 3/). Three major reaction channels were characterized kinetically. At T less than or equal to 298 K, electrophilic addition of the OH radical to the aromatic ring is the dominant reactive pathway in all systems studied. At temperatures above 500 K, rapid decomposition of the thermalized adduct back to reactants diminishes the importance of the addition channel and leads to bimolecular reaction rate-constant values significantly lower than those measured near room temperature. At elevated temperatures, the ring hydrogen abstraction (for benzene) and side-chain hydrogen abstraction (for toluene) pathways are shown to be predominant. The measured bimolecular rate constants increase monotonically withmore » increases in temperature above 500 K, and kinetic separation of the two hydrogen abstraction modes for toluene is achieved.« less

Lunar seismology : the internal structure of the moon.

Abstract: The direct P and S wave arrival times are the primary data set that can be measured on the seismograms of natural lunar seismic events. Polarization filtering techniques allow the enhancement of secondary body wave arrivals and record curves to identify the secondary phases and deduce structural information. Finally, shear wave amplitude vs. distance curves yield information on the location and magnitude of seismic velocity gradients in the interior. The results of these analyses show that the moon appears to have a two-layer crust at all four seismic stations: a 20 km upper crust that seems to be constant at all sites and a lower crust that is 40 km thick at stations 12 and 14 (mare), 55 + or - 10 km at station 16 (highland), and tentatively either 40 km or 70 km at station 15. The lower mantle extends from 480 km to at least 1100 km depth which is the maximum depth of penetration of all but a few seismic waves used as data. No definitive evidence for or against a lunar core exists.

Set partitioning based heuristics for interactive routing

Abstract: The set partitioning model is used as the basis for an interactive approach for solving a broad class of routing problems. A pricing mechanism is developed which can be used with a variety of methods in generating improving solutions. A version of the approach for delivery problems has been implemented via a colorgraphics display. The human aided optimization procedure was tested on the standard 50-point, 75-point, and 100-point test problems of Eilon, Watson-Gandy, and Christofides [6]. In the case of the first two test problems, the procedure was able to generate the best known solutions. In the 100-point problem, a better solution was generated than the current best known solution.

Acousto-optic signal processing: Convolution and correlation

Abstract: The use of acousto-optic devices in real-time signal convolution and correlation has increased dramatically during the past decade because of improvements in device characteristics and implementation techniques. Depending on the application, processing can be implemented via spatial or temporal integration. Two-dimensional signal processing (including image processing) is possile, in spite of the inherent one-dimensional nature of the acousto-optic device as a spatial light modulator.

Group properties of utt=[F(u)ux]x

Abstract: The group properties and the associated Lie algebra are developed for the subject quasilinear wave equation, for arbitrary f[fϵC2(R), f > 0, f ≠ 0]. From the resulting information sets of explicit invariant solutions are constructed for wave propagation in gases and for the transonic equation.

Rates of fixation by lightning of carbon and nitrogen in possible primitive atmospheres.

Abstract: A thermochemical-hydrodynamic model of the production of trace species by electrical discharges has been used to estimate the rates of fixation of C and N by lightning in the primitive atmosphere. Calculations for various possible mixtures of CH4, CO2, CO, N2, H2, and H2O reveal that the prime species produced were probably HCN and NO and that the key parameter determining the rates of fixation was the ratio of C atoms to O atoms in the atmosphere. Atmospheres with C more abundant than O have large HCN fixation rates, in excess of 10 to the 17th molecules/J, but small NO yields. However, when O is more abundant than C, the NO fixation rate approaches 10 to the 17th molecules/J while the HCN yield is small. The implications for the evolution of life are discussed.

Analysis of Sales Call Effectiveness

Abstract: The sales response of an established ethical drug to sales calls by one Belgian pharmaceutical manufacturer is measured. A key feature is the systematic variation in the sales call elasticity over ...

The effects of realistic previews: a study and discussion of the literature

Abstract: The effects of realistic job previews (RJPs) were studied with a sample of 842 candidates for telephone service representative. Two types of preview, a film and job visit, were used. Results showed no significant differences between RJP candidates and control candidates with respect to job acceptance, met expectations, job commitment and turnover. Because the findings were at variance with the conclusions of previous RJP research the data from previous studies were reexamined. Based on pooled data from eleven studies the average effect of RJPs on turnover rate was estimated as six percentage points overall. Neither the type of media used nor the length of time turnover is studied appears to interact with RJP effectiveness. RJPs appear to be more effective with more complex jobs, however. Explanations of RJP effects on turnover have not been consistently supported. Though data are limited, self-selection, met expectations and coping ability do not appear to be impacted by RJPs. There is some evidence that RJPs result in more positive job related attitudes, but the explanation for this is not clear. Difficulties in interpreting job preview research are noted, including insufficient statistical power, differences in organizational roles and the lack of a clear operational definition of realism.

Myopic Solutions of Markov Decision Processes and Stochastic Games

Abstract: Sufficient conditions are presented for a Markov decision process to have a myopic optimum and for a stochastic game to possess a myopic equilibrium point. An optimum or an equilibrium point is said to be "myopic" if it can be deduced from an optimum or an equilibrium point of a static optimization problem or a static [Nash] game. The principal conditions are a each single period reward is the sum of terms due to the current state and action, b each transition probability depends on the action taken but not on the state from which the transition occurs, and c an appropriate static optimum or equilibrium point is ad infinitum repeatable. These conditions are satisfied by several dynamic oligopoly models and numerous Markov decision processes.

New Approaches to Alloy Development in the Al-Li System

Abstract: This paper describes the approach and results of recent work in our laboratories on identifying and solving the ductility problems which have plagued Al-Li alloys. In addition, specific property goals for developing new Al-Li alloys have been established. These include a) a 30% increase in modulus:density ratio, compared to 7075-T76, without significant loss in other properties, and b) a 20% increase in modulus:density ratio and a 20% increase in strength:density ratio compared to 7075-T76, without significant loss in other properties. Two approaches are being pursued, one using conventional ingot metallurgy (I/M) and the other using rapid solidification of fine particulate plus powder metallurgy (P/M) consolidation. The rapid solidification approach is designed to reduce or eliminate segregation effects, reduce the grain size, extend solid solubility of additional elements, and refine the dispersoid particle size. In some cases, we have made a comparison of the structure and properties of similar alloys fabricated by the two methods.

Mapping the active sites of bovine thrombin, factor IXa, factor Xa, factor XIa, factor XIIa, plasma kallikrein, and trypsin with amino acid and peptide thioesters: development of new sensitive substrates.

Abstract: The subsite specificities of bovine factor IXa, factor Xa, factor XIa, factor XIIa, thrombin, plasma kallikrein, and trypsin were mapped with amino acid, dipeptide, and longer peptide thioester substrates. Each substrate contained a P1 Arg residue. The P1' residues included thiol residues which are analogues of valine, leucine, and isoleucine, respectively, and the P2 residue included 12 representative amino acid residues. Longer substrates with the sequence at the antithrombin III reactive site and at the zymogen activation site of various coagulation factors were also studied. The enzymatic hydrolysis of the thioesters was measured in the presence of 4,4'-dithiodipyridine which provides a very sensitive assay for the free thiol. The thioesters were excellent substrates for the coagulation factors studied, and the kcat/Km values for the best thioester substrates were higher than those previously reported for most of these enzymes. Thrombin and plasma kallikrein were the most active of the coagulation factors toward the thioester substrates. The best substrate for thrombin was Z-Gly-Arg-SCH2C6H5, although substrates containing proline in the P2 position were also quite effective. Some of the better substrates for plasma kallikrein had a P2 Phe or Trp residue. Factor IXa was the least reactive of the coagulation factors and hydrolyzed only four of the dipeptide thioesters. Substrates with bulky hydrophobic groups such as Phe or Trp in the P2 position were the most reactive with factor IXa. Factor Xa hydrolyzed all the thioester substrates tested, the most reactive being Z-Gly-Arg-SCH2C6H5. This is consistent with the fact that glycine and arginine are present in the P2 and P1 positions, respectively, of the factor Xa sensitive bonds in prothrombin which is the physiological substrate for factor Xa. Bovine factor XIa showed the least amount of specificity of the various coagulation factors and was quite reactive toward all of the thioester substrates. The most sensitive substrate for this enzyme was also Z-Gly-Arg-SCH2C6H5. Factor XIIa preferred the dipeptide with a P2 Phe, although the simpler thioester Z-Arg-SCH2CH(CH3)2 was more reactive. Trypsin hydrolyzed all of the thioester substrates at a high rate and showed little substrate specificity. With all enzymes studied, extension of the thioester substrate beyond P2 or the P1' thiol leaving group did not lead to an improvement in hydrolysis. Due to their high kcat/Km values and the ease of detecting the thiol leaving group, thioester substrates should be extremely useful for future studies of coagulation proteases.

The effect of copper content and heat treatment on the stress corrosion characteristics of Ai-6Zn-2Mg-X Cu alloys

Abstract: The effect of copper and aging on the stress corrosion characteristics of Al-6 pct Zn-2 pct Mg-(0.01-2.1) pct Cu alloys in 3.5 pct NaCl was studied with other variables remaining constant. In the peak-strength condition the crack velocity in the stress-independent region decreased by two orders of magnitude when copper was increased from 0.01 to 2.1 pct. In the stress-dependent region crack velocity decreased only for copper contents higher than 1 pct. Overaging further reduced the plateau crack velocity in all the alloys studied. The results are interpreted on the basis of the effects of copper and aging on the deformation mechanism and electrochemical activity of the phases.

Memoryless stabilization of linear delay-differential systems

Abstract: Sufficient conditions for memoryless feedback stabilization of linear time-invariant delay-differential systems are derived for both constant and time-dependent delays.

Seismic energy release of the moon

Abstract: Lunar seismicity is investigated by calculating various source parameters for a number of shallow and deep-focus moonquakes. The seismic moment, seismic energy release, annual seismic energy release, stress drop, and body-wave magnitude are determined for the largest shallow moonquakes and for large deep-focus events. It is found that the shallow events dominate the lunar seismic energy release, that tidal dissipation may account for the energy release by the deep-focus events, and that the stress drops for the deep-focus events are comparable to or smaller than the calculated tidal stresses. A comparison of the results with terrestrial data indicates that the seismic characteristics of a planet are controlled more by tectonic style and state than by the relative magnitude of the driving forces.