Abstract: The Spread Spectrum Image Steganography (SSIS) of the present invention is a data hiding/secret communication steganographic system which uses digital imagery as a cover signal. SSIS provides the ability to hide a significant quantity of information bits within digital images while avoiding detection by an observer. The message is recovered with low error probability due the use of error control coding. SSIS payload is, at a minimum, an order of magnitude greater than of existing watermarking methods. Furthermore, the original image is not needed to extract the hidden information. The proposed recipient need only possess a key in order to reveal the secret message. The very existence of the hidden information is virtually undetectable by human or computer analysis. Finally, SSIS provides resiliency to transmission noise, like that found in a wireless environment and low levels of compression.

Abstract: A high electron mobility transistor photodetector includes an undoped GaAs buffer, a p-type GaAs layer positioned above the undoped GaAs buffer that is between 0.5 to 1 &mgr;m in thickness, an undoped low temperature GaAs layer positioned above the p-type GaAs layer, an undoped GaAs layer positioned above the low temperature GaAs layer, a layer of undoped InGaAs positioned above the undoped GaAs layer, a layer of undoped AlGaAs positioned above the layer of InGaAs, an n+ AlGaAs charge-suppling layer positioned above the layer of undoped AlGaAs, an n+ GaAs contact layer positioned above the n+ AlGaAs charge-supplying layer, and source and drain ohmic contacts positioned above the n+ GaAs contact layer. A negative bias voltage is applied to the p-type GaAs layer to sweep the holes from the photo-absorptive layer which greatly increases the speed and responsiveness of the device.

Abstract: A method for fluorescence probing of particles flowing in a fluid includes defining a trigger volume in the fluid by intersecting a plurality of substantially orthogonally aimed trigger laser beams, each of a different wavelength, detecting light scattered from the vicinity of the trigger volume by a plurality of particle detectors each sensitive to a wavelength corresponding to the wavelength of a trigger laser beam, probing the particles with a pulsed laser triggered by the particle detectors, collecting fluorescence emitted from the particle in a detection volume and focusing it in a detection region, detecting the fluorescence focused in the detection region. The invention also includes devices for carrying out the foregoing method.

Abstract: A GaN epilayaer grown on a lattice mismatched saphire substrate is subjected to rapid thermal processing in order the reduce the defect density especially in the proximate the top (device) surface of the GaN epilayer.

Abstract: A pressure sensor includes two birefringent media, one of which is exposed o pressure to undergo pressure-variable birefringence. Polarized light passes through the birefringent media to be modulated in accordance with the pressure and is then made incident on a photodetector to detect the modulation. The use of two birefringent media provides temperature compensation.

Abstract: A transducer in communication with fluid in a pad held in close contact against a sound or movement source monitors acoustic signals transferred into the fluid. The signal pattern is monitored aurally and/or compared to predetermined reference patterns, and optional control and stimulation means can be activated in response to the comparison results. The sensed acoustic signal can be transmitted to a remote receiver or processed locally. Typically, the acoustic signal is representative of the heartbeat or breathing of a living organism. The monitoring system may be applied to diverse situations including SIDS, apnea, home baby monitoring, medical transport devices, blood pressure cuffs, seats, combat casualty care and hand-held devices.