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.

Knowledge-based hierarchical region-of-interest detection

Abstract: Detecting regions of interest (ROIs) in a complex image is a critical step in many image processing applications. In this paper, we present a new algorithm that addresses several challenges in ROI detection. The novelty of our algorithm includes: (i) every ROI contains one and only one object; (ii) the detected ROIs can have irregular shapes as opposed to the rectangular shapes that are typical of other algorithms; (iii) the algorithm is applicable to images that contain connected objects, or when the objects are broken into pieces; (iv) the algorithm is not sensitive to contrast levels in the image, and is robust to noise. These characteristics make the proposed algorithm applicable to low-resolution, real-world imagery without costly post-processing. The proposed algorithm is shown to provide outstanding performance with low-quality imagery, and is shown to be fast and robust.

nsPEF-induced PIP2 depletion, PLC activity and actin cytoskeletal cortex remodeling are responsible for post-exposure cellular swelling and blebbing.

Abstract: Cell swelling and blebbing has been commonly observed following nanosecond pulsed electric field (nsPEF) exposure. The hypothesized origin of these effects is nanoporation of the plasma membrane (PM) followed by transmembrane diffusion of extracellular fluid and disassembly of cortical actin structures. This investigation will provide evidence that shows passive movement of fluid into the cell through nanopores and increase of intracellular osmotic pressure are not solely responsible for this observed phenomena. We demonstrate that phosphatidylinositol-4,5-bisphosphate (PIP2) depletion and hydrolysis are critical steps in the chain reaction leading to cellular blebbing and swelling. PIP2 is heavily involved in osmoregulation by modulation of ion channels and also serves as an intracellular membrane anchor to cortical actin and phospholipase C (PLC). Given the rather critical role that PIP2 depletion appears to play in the response of cells to nsPEF exposure, it remains unclear how its downstream effects and, specifically, ion channel regulation may contribute to cellular swelling, blebbing, and unknown mechanisms of the lasting "permeabilization" of the PM.

Navigation system and method for determining the position of an ocean mining ship

Abstract: A system for determining the position of a ship in relation to predetermined positions on the ocean floor is disclosed. A plurality of first acoustic addressable transponders and a plurality of second acoustic addressable transponders are respectively located at first and second sets of predetermined positions on the ocean floor. Each of the acoustic transponders transmits an acoustic ranging response and identification signal in response to receipt of an acoustic ranging interrogation signal. First and second buoy communications systems are located on first and second buoys respectively moored to the ocean floor in the vicinity of the first and second pluralities of acoustic transponders. Each buoy communication system includes an acoustic communications devices for transmitting an acoustic ranging interrogation signal to the respective acoustic transponders in its vicinity and for receiving acoustic ranging response and identification signals from such acoustic transponders in response thereto; a buoy RF communications device for transmitting RF signals containing information representative of the respective propagation delays between transmission of the acoustic ranging interrogation signal and receipt of the acoustic ranging response and identification signals from the acoustic transponders; and a buoy RF addressable transponder for transmitting an RF buoy ranging response and identification signal in response to receipt of an RF ranging interrogation signal. A ship communications system located on the ship transmits the RF ranging interrogation signals and receives the RF buoy ranging response and identification signals in response thereto. The ship communications system also transmits command signals. The first and second buoy communications systems each respond to the command signal by transmitting the acoustic interrogation signals to the acoustic transponders. The ship communications system receives the RF signals containing the acoustic propagation delay information. A data processing system processes the received RF signals in relation to the transmitted RF ranging interrogation signals to determine the position of the ship in relation to the first and second sets of predetermined positions on the ocean floor.

Effect of shaft rotation on the incompressible flow in a labyrinth seal

Abstract: A computational/experimental study was conducted concerning the incompressible flow in a labyrinth seal at low leakage rates over a wide range of seal rotation rates. The predictions were obtained using a finite-difference code that utilized a higher order differencing scheme (QUICK) to reduce the effects of false diffusion. Measured inlet boundary conditions for the axial and swirl velocity components as well as turbulence kinetic energy were employed. This yielded fair agreement between velocity predictions and hot-film anemometer measurements. The effects of seal rotation rate on the overall pressure drop are presented in terms of a loss coefficient. It was determined that when the rotation rate is increased beyond a certain point, a second recirculation zone (SRZ) forms inside the seal cavity. This dramatically alters the flowfield in the cavity and results in a substantial increase in the pressure drop across it. A flow map is presented indicating the approximate rotation rate required to produce this phenomenon at a given leakage rate. Unfortunately, for most practical applications, the SRZ will not form until an extremely high shaft speed is reached.