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.

Femtosecond laser damage threshold and nonlinear characterization in bulk transparent SiC materials

Abstract: Semi-insulating and conducting SiC crystalline transparent substrates were studied after being processed by femtosecond (fs) laser radiation (780 nm at 160 fs). Z-scan and damage threshold experiments were performed on both SiC bulk materials to determine each sample's nonlinear and threshold parameters. "Damage" in this text refers to an index of refraction modification as observed visually under an optical microscope. In addition, a study was performed to understand the damage threshold as a function of numerical aperture. Presented here for the first time, to the best of our knowledge, are the damage threshold, nonlinear index of refraction, and nonlinear absorption measured values.

A Study of Fatigue Damage in Composites by Nondestructive Testing Techniques

Abstract: The methodology and experimental results of damage mechanism studies in graphite/epoxy composites using a modified X-ray nondestructive testing technique and continuous acoustic emission monitoring (AEM) method are presented. Fracture specimens were fabricated from Narmco 5208/T300 and Narmco 5208/ Modmor II graphite/epoxy composites with different ply orientations chosen to exhibit fiber failure and linear and nonlinear matrix failures. The specimens with center slits were subjected to tensile ramp loading, constant-amplitude cyclic loading, and an air combat fighter randomized flight-by-flight spectrum loading. During tensile ramp loading, the specimens were monitored by an X-ray "movie" to observe the damage initiation and growth in the areas around the slit tips. An opaque additive was injected in the slit opening to enhance the damage indications. For specimens undergoing cyclic loading and fatigue spectrum loading, periodic X-ray records were made for damage growth monitoring. Continuous AEM was conducted on specimens undergoing tensile ramp loading. The actual fatigue damage initiation and growth within the composite laminates can be observed by the periodic X-ray records of the specimens. These observations were correlated with the AEM results. Three parameters measurable by the AEM system-accumulated counts, amplitude distribution, and frequency spectrum-characterized fatigue damage initiation and growth in different fiber directions. Damage redistribution mechanisms in the fatigue specimens can be observed from the damage growth study.

Large capacitance in the nanosecond-scale transient response of quantum point contacts

Abstract: The transient electrical response of split-gate quantum point contacts (QPCs) is investigated using ultrashort voltage pulses with rise times as small as 2ns. Our measurements reveal a large (∼1nF) parallel capacitance under conditions where the QPC is formed. The capacitance is independent of the QPC gate geometry, and the amplitude and rise time of the applied transient pulse. Some speculations on the source of this capacitance are offered.