General Dynamics

About: General Dynamics is a company organization based out in Fairfax, Virginia, United States. It is known for research contribution in the topics: Signal & Propellant. The organization has 5722 authors who have published 5819 publications receiving 85768 citations. The organization is also known as: GD & General Dynamics Corporation.

Interband electron-electron scattering and transport phenomena in semiconductors

Abstract: The effect of interband electron-electron scattering (electron-hole scattering, light hole-heavy hole scattering, etc.) on the electrical transport phenomena is studied with a variational method obtained by a generalization of Kohler's variation principle to a multiband conductor. To this end we make the following assumptions: (1) The electronic structure is given by parabolic conduction and valence bands, separated from each other by $\ensuremath{\Delta}E\ensuremath{\gg}{k}_{B}T$; the valence band may be twofold degenerate; (2) The average occupation numbers of electronic eigenstates are given by Fermi-Dirac statistics; (3) The dynamical interaction between charge carriers is described by a shielded Coulomb potential.Assuming nondegenerate semiconductors, we consider acoustical and optical phonon scattering and ion scattering, besides electron-electron scattering. Quantitative results are obtained for the electrical conductivity, the heat conductivity, and the Seebeck coefficient, including the ambipolar effect. The results can easily be applied to cases of physical interest; we discuss here hole-hole scattering and mobility of $p$ germanium, intercarrier scattering and mobility of intrinsic germanium, transient conductivity of charge carriers in germanium produced by short pulses of high-energy electrons, intercarrier scattering and its influence on the heat conductivity, and the Wiedemann-Franz ratio of intrinsic semiconductors.

Mean light intensity—a useful concept in correlating growth rates of dense cultures of microalgae

Abstract: An analysis of the distribution of light within some culture vessels developed at General Dynamics/Electric Boat is presented The concept of a mean effective light intensity, Ē, is introduced and procedures are developed for computing Ē for any culture vessel geometry and incident light intensity distribution A correlation is performed indicating the significance of Ēin assessing the growth rate of dense, continuous cultures of microalagae

Electronic engine control

Abstract: An electronic controller for an internal combustion engine provides a ratio control signal corresponding to a respective air/fuel ratio, and responds to an air flow signal, a fuel flow signal and the ratio control signal to control fuel flow as to make the ratio of air flow to fuel flow substantially equal to said respective air/fuel ratio. The ratio control signal is developed from a base run ratio control signal as modified in response to various parameters such as engine temperature, manifold pressure, idle, manifold vacuum, fuel temperature, wide open throttle, engine speed, and start. The controller also provides a speed-up circuit for promptly responding to change in air flow and dynamic braking for the fuel metering pump. The pump speed circuit includes a range extender. The controller further provides a timing advance control signal in response to air/fuel ratio and various engine parameters such as engine speed, manifold pressure, throttle position, engine temperature, air temperature, air/fuel ratio, and start.

Optimization-Based Dynamic Sensor Management for Distributed Multitarget Tracking

Abstract: In this paper, the general problem of dynamic assignment of sensors to local fusion centers (LFCs) in a distributed tracking framework is considered. With technological advances, a large number of sensors can be deployed for multitarget tracking purposes. However, due to physical limitations such as frequency, power, bandwidth, and fusion center capacity, only a limited number of them can be used by each LFC. The transmission power of future sensors is anticipated to be software controllable within certain lower and upper limits. Thus, the frequency reusability and the sensor reachability can be improved by controlling transmission powers. Then, the problem is to select the sensor subsets that should be used by each LFC and to find their transmission frequencies and powers in order to maximize the tracking accuracies and minimize the total power consumption. The frequency channel limitation and the advantage of variable transmitting power have not been discussed in the literature. In this paper, the optimal formulation for the aforementioned sensor management problem is provided based on the posterior Cramer-Rao lower bound. Finding the optimal solution to the aforementioned NP-hard multiobjective mixed-integer optimization problem in real time is difficult in large-scale scenarios. An algorithm is presented to find a suboptimal solution in real time by decomposing the original problem into subproblems, which are easier to solve, without using simplistic clustering algorithms that are typically used. Simulation results illustrating the performance of sensor array manager are also presented.

Characterization of fatigue crack growth behavior in LENS fabricated Ti-6Al-4V using high-energy synchrotron x-ray microtomography

Abstract: Laser Engineered Net Shaping (LENS) is an additive manufacturing technique that belongs to the ASTM standardized directed energy deposition category. To date, very limited work has been conducted towards understanding the fatigue crack growth behavior of LENS fabricated materials, which hinders the widespread adoption of this technology for high-integrity structural applications. In this study, the propagation of a 20 μm initial crack in LENS fabricated Ti-6Al-4V was captured in-situ, using high-energy synchrotron x-ray microtomography. Fatigue crack growth (FCG) data were then determined from 2D and 3D tomography reconstructions, as well as from fracture surface striation measurements using SEM. The generated data were compared to those obtained from conventional FCG tests that used compliance and direct current potential drop (DCPD) techniques to measure long and small crack growth. The observed agreement demonstrates that x-ray microtomography and fractographic analysis using SEM can be successfully combined to study the propagation behavior of fatigue cracks.