United States Air Force Academy

Abstract A new method for obtaining optimized parameters for semiempirical methods has been developed and applied to the modified neglect of diatomic overlap (MNDO) method. The method uses derivatives of calculated values for properties with respect to adjustable parameters to obtain the optimized values of parameters. The large increase in speed is a result of using a simple series expression for calculated values of properties rather than employing full semiempirical calculations. With this optimization procedure, the rate‐determining step for parameterizing elements changes from the mechanics of parameterization to the assembling of experimental reference data.

Abstract MNDO/AM1‐type parameters for twelve elements have been optimized using a newly developed method for optimizing parameters for semiempirical methods. With the new method, MNDO‐PM3, the average difference between the predicted heats of formation and experimental values for 657 compounds is 7.8 kcal/mol, and for 106 hypervalent compounds, 13.6 kcal/mol. For MNDO the equivalent differences are 13.9 and 75.8 kcal/mol, while those for AM1, in which MNDO parameters are used for aluminum, phosphorus, and sulfur, are 12.7 and 83.1 kcal/mol, respectively. Average errors for ionization potentials, bond angles, and dipole moments are intermediate between those for MNDO and AM1, while errors in bond lengths are slightly reduced.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation R. L. Bagley, P. J. Torvik; A Theoretical Basis for the Application of Fractional Calculus to Viscoelasticity. J. Rheol. 1 June 1983; 27 (3): 201–210. https://doi.org/10.1122/1.549724 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentThe Society of RheologyJournal of Rheology Search Advanced Search |Citation Search

Ionic liquids, defined here as salts with melting temperatures below 100 °C, evolved from traditional high temperature molten salts. Some materials we would now recognize as ionic liquids were observed as far back as the mid 19th century. The quest for useful molten salts with lower melting temperatures led to inorganic chloroaluminates, to organic chloroaluminates, then to the water and air stable salts now being developed for green chemistry applications.

The next great leap for jet propulsion will be to power-sustained, efficient flight through the atmosphere. Hypersonic Airbreathing Propulsion presents the first comprehensive, unified introduction to all elements of the scramjet engine that will make this feat possible. The text emphasizes fundamental principles, guiding concepts, analytical derivations, and numerical examples having clear, useful, insightful results.

The term plasma actuator has now been a part of the fluid dynamics flow-control vernacular for more than a decade. A particular type of plasma actuator that has gained wide use is based on a single–dielectric barrier discharge (SDBD) mechanism that has desirable features for use in air at atmospheric pressures. For these actuators, the mechanism of flow control is through a generated body-force vector field that couples with the momentum in the external flow. The body force can be derived from first principles, and the effect of plasma actuators can be easily incorporated into flow solvers so that their placement and operation can be optimized. They have been used in a wide range of internal and external flow applications. Although initially considered useful only at low speeds, plasma actuators are effective in a number of applications at high subsonic, transonic, and supersonic Mach numbers, owing largely to more optimized actuator designs that were developed through better understanding and modeling of the actuator physics. New applications continue to appear through a growing number of programs in the United States, Germany, France, England, the Netherlands, Russia, Australia, Japan, and China. This review provides an overview of the physics and modeling of SDBD plasma actuators. It highlights some of the capabilities of plasma actuators through examples from experiments and simulations.

Generalized constitutive relationships for viscoelastic materials are suggested in which the customary time derivatives of integer order are replaced by derivatives of fractional order. To this point, the justification for such models has resided in the fact that they are effective in describing the behavior of real materials. In this work, the fractional derivative is shown to arise naturally in the description of certain motions of a Newtonian fluid. We claim this provides some justification for the use of ad hoc relationships which include the fractional derivative. An application of such a constitutive relationship to the prediction of the transient response of a frequency-dependent material is included.

Fractional calculus is used to construct stress-strain relationships for viscoelastic materials. These relationships are used in the finite element analysis of viscoelastically damped structures and closed-form solutions to the equations of motion are found. The attractive feature of this approach is that very few empirical parameters are required to model the viscoelastic material and calculate the response of the structure for general loading conditions.

Large arrays are difficult to thin in order to obtain low sidelobes. Traditional statistical methods of aperiodic array synthesis fall far short of optimum configurations. Traditional optimization methods are not well suited for optimizing a large number of parameters or discrete parameters. This paper presents how to optimally thin an array using genetic algorithms. The genetic algorithm determines which elements are turned off in a periodic array to yield the lowest maximum relative sidelobe level. Simulation results for 200 element linear arrays and 200 element planar arrays are shown. The arrays are thinned to obtain sidelobe levels of less than -20 dB. The linear arrays are also optimized over both scan angle and bandwidth.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In today's tightly connected global economy, traditional management practices that rely on “steady‐state” conditions are challenged by chaotic external pressures and turbulent change. Just in the last few years, the world has experienced a string of catastrophic events, including a global economic meltdown, a volcanic eruption in Iceland, an oil spill in the Gulf of Mexico, a disastrous tsunami and power blackout in Japan, and political upheavals in Africa and the Middle East. Managing the risk of an uncertain future is a challenge that requires resilience— the ability to survive, adapt, and grow in the face of turbulent change. This research develops a measurement tool titled the Supply Chain Resilience Assessment and Management (SCRAM™). Data gathered from seven global manufacturing and service firms are used to validate SCRAM™, using qualitative methodology with 1,369 empirical items from focus groups reviewing 14 recent disruptions. Critical linkages are uncovered between the inherent vulnerability factors and controllable capability factors. Through mixed‐method triangulation, this research identified 311 specific linkages that can be used to guide a resilience improvement process. Pilot testing suggests a correlation between increased resilience and improved supply chain performance.

This meta‐analysis finds that parents report lower marital satisfaction compared with nonparents ( d =−.19, r =−.10). There is also a significant negative correlation between marital satisfaction and number of children ( d =−.13, r =−.06). The difference in marital satisfaction is most pronounced among mothers of infants (38% of mothers of infants have high marital satisfaction, compared with 62% of childless women). For men, the effect remains similar across ages of children. The effect of parenthood on marital satisfaction is more negative among high socioeconomic groups, younger birth cohorts, and in more recent years. The data suggest that marital satisfaction decreases after the birth of a child due to role conflicts and restriction of freedom.

Abstract A finite‐field method for the calculation of polarizabilities and hyperpolarizabilities is developed based on both an energy expansion and a dipole moment expansion. This procedure is implemented in the MOPAC semiempirical program. Values and components of the dipole moment (μ), polarizability (α), first hyperpolarizability (β), and second hyperpolarizability (γ) are calculated as an extension of the usual MOPAC run. Applications to benzene and substituted benzenes are shown as test cases utilizing both MNDO and AM1 Hamiltonians.

The North American Power Systems Interconnection Committee recommends that each control area set its frequency bias equal to the so-called area frequency response characteristic (AFRC). The authors question seriously the basis for this practice and prove by the methods of optimum control that better response and wider stability margins can be obtained by lower bias settings.

This article is a tutorial on using genetic algorithms to optimize antenna and scattering patterns. Genetic algorithms are "global" numerical-optimization methods, patterned after the natural processes of genetic recombination and evolution. The algorithms encode each parameter into binary sequences, called a gene, and a set of genes is a chromosome. These chromosomes undergo natural selection, mating, and mutation, to arrive at the final optimal solution. After providing a detailed explanation of how a genetic algorithm works, and a listing of a MATLAB code, the article presents three examples. These examples demonstrate how to optimize antenna patterns and backscattering radar-cross-section patterns. Finally, additional details about algorithm design are given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper records the development of a state variable model of the megawatt-frequency control problem of multiarea electric energy systems. The model is in a mathematical form necessary for application of theorems of modem optimal control theory.

In Brief Background: Effective combat trauma management strategies depend upon an understanding of the epidemiology of death on the battlefield. Methods: A panel of military medical experts reviewed photographs and autopsy and treatment records for all Special Operations Forces (SOF) who died between October 2001 and November 2004 (n = 82). Fatal wounds were classified as nonsurvivable or potentially survivable. Training and equipment available at the time of injury were taken into consideration. A structured analysis was conducted to identify equipment, training, or research requirements for improved future outcomes. Results: Five (6%) of 82 casualties had died in an aircraft crash, and their bodies were lost at sea; autopsies had been performed on all other 77 soldiers. Nineteen deaths, including the deaths at sea were noncombat; all others were combat related. Deaths were caused by explosions (43%), gunshot wounds (28%), aircraft accidents (23%), and blunt trauma (6%). Seventy of 82 deaths (85%) were classified as nonsurvivable; 12 deaths (15%) were classified as potentially survivable. Of those with potentially survivable injuries, 16 causes of death were identified: 8 (50%) truncal hemorrhage, 3 (19%) compressible hemorrhage, 2 (13%) hemorrhage amenable to tourniquet, and 1 (6%) each from tension pneumothorax, airway obstruction, and sepsis. The population with nonsurvivable injuries was more severely injured than the population with potentially survivable injuries. Structured analysis identified improved methods of truncal hemorrhage control as a principal research requirement. Conclusions: The majority of deaths on the modern battlefield are nonsurvivable. Improved methods of intravenous or intracavitary, noncompressible hemostasis combined with rapid evacuation to surgery may increase survival. Effective combat trauma management strategies depend on an understanding of the epidemiology of death on the battlefield. A review of photographs and autopsy and treatment records of 82 combat deaths classified the majority as nonsurvivable. Twelve (15%) deaths identified as potentially survivable led us to conclude that improved methods of intravenous or intracavitary, noncompressible hemostasis, and rapid evacuation may increase survival.

Two experiments, one conducted with American college students and one with Israeli pilots and their instructors, explored the predictive power of reputation-based assessments versus the stated "name of the game" (Wall Street Game vs. Community Game) in determining players' responses in an N-move Prisoner's Dilemma. The results of these studies showed that the relevant labeling manipulations exerted far greater impact on the players' choice to cooperate versus defect--both in the first round and overall--than anticipated by the individuals who had predicted their behavior. Reputation-based prediction, by contrast, failed to discriminate cooperators from defectors. A supplementary questionnaire study showed the generality of the relevant short-coming in naïve psychology. The implications of these findings, and the potential contribution of the present methodology to the classic pedagogical strategy of the demonstration experiment, are discussed.

Abstract Using a recently developed procedure for optimizing parameters for semiempirical methods, 1 PM3 has been extended to a total of 28 elements. Average Δ H f errors for the newly parameterized elements are Be: 8.6, Mg: 8.4, Zn: 5.8, Ga: 14.9, Ge: 11.4, As: 8.5, Se: 11.1, Cd: 2.6, In: 11.3, Sn: 9.0, Sb: 13.7, Te: 11.3, Hg: 6.8, Tl: 6.5, Pb: 7.4, and Bi: 10.9 kcal/mol. For some elements the paucity of data has resulted in a method, which, while highly accurate, is likely to be only poorly predictive.

We present simultaneous optical, electrical, and thrust measurements of an aerodynamic plasma actuator. These measurements indicate that the plasma actuator is a form of the dielectric barrier discharge, whose behavior is governed primarily by the buildup of charge on the dielectric-encapsulated electrode. Our measurements reveal the temporal and macroscale spatial structure of the plasma. Correlating the morphology of the plasma and the electrical characteristics of the discharge to the actuator performance as measured by the thrust produced indicates a direct coupling between the interelectrode electric field (strongly modified by the presence of the plasma) and the charges in the plasma. Our measurements discount bulk heating or asymmetries in the structure of the discharge as mechanisms for the production of bulk motion of the surrounding neutral air, although such asymmetries clearly exist and impact the effectiveness of the actuator.

The single dielectric barrier discharge plasma, a plasma sustainable at atmospheric pressure, has shown considerable promise as a flow control device operating at modest (tens of watts) power levels. Measurements are presented of the development of the plasma during the course of the discharge cycle, and the relevance of these measurements to the modeling of the actuator's electrical properties is discussed. Experimental evidence is presented strongly pointing to the electric field enhancement near the leading edge of the actuator as a dominant factor determining the effectiveness of momentum coupling into the surrounding air