Random pulse generator

An exemplary embodiment of the present invention provides a source of random width and random spaced rectangular voltage pulses whose mean or average frequency of operation is controllable within prescribed limits of about 10 hertz to 1 megahertz. A pair of thin-film metal resistors are used to provide a differential white noise voltage pulse source. Pulse shaping and amplification circuitry provide relatively short duration pulses of constant amplitude which are applied to anti-bounce logic circuitry to prevent ringing effects. The pulse outputs from the anti-bounce circuits are then used to control two one-shot multivibrators whose output comprises the random length and random spaced rectangular pulses. Means are provided for monitoring, calibrating and evaluating the relative randomness of the generator

Pulse stretcher for narrow pulses

Pulse stretching circuit can linearly stretch pulses as narrow as 50 nanoseconds and block incoming pulses following accepted input pulse until processing has been completed. It also removes baseline distortion by being completely direct coupled and provides monitor output which measures true number of input events that exceed predetermined threshold

Chirped arrays of diode lasers for supermode control

We propose nonuniform structures of phase-locked diode lasers, which make it possible to discriminate efficiently against all the higher order array supermodes (lateral modes). In these nonuniform arrays, the effective mode index in each channel varies across the array. Consequently, the envelopes of the various supermodes, including the highest order one, differ significantly from each other. Thus, by proper tailoring of the gain distribution across the array, one can conveniently select the fundamental supermode. Such fundamental supermode oscillation is essential in order to obtain single lobe, diffraction limited beams and minimal spectral spread from phase-locked laser arrays

Coupling mechanism of gain-guided integrated semiconductor laser arrays

It is shown that a gain-guided laser array couples via propagating fields rather than the evanescent mode coupling typically responsible for directional coupling in passive (directional couplers) and active (laser array) devices. We show that these phase-locked modes exhibit an interference pattern, in the junction plane, which arises from the curvature of the phase fronts of optical fields of the interacting lasers. The experimental results are interpreted with the aid of a simple theoretical model, and the effect of the observed mode pattern on the coupling of gain-guided lasers is discussed

Control of mutual phase locking of monolithically integrated semiconductor lasers

The mutual coherence of two coupled semiconductor lasers is investigated experimentally. It is demonstrated that by varying the gain in the overlap region, the degree of phase coherence can be continuously controlled. The quantitative characterization of the degree of phase coherence by fringe visibility is demonstrated

Transcriptional Control of the Opp Operon in Clostridium Difficile

As a serious expense for both the hospital and the patient, nosocomial infections create a burden on the health care industry that is not easily overcome. Among the infections commonly contracted in the hospital environment, those associated with the Clostridium difficile bacterium account for millions of cases each year. Largely due to the nature of C. difficile infection as a response to the disruption of the normal flora of the colon caused by antibiotic activity, no completely effective treatment for this condition has been identified. It is this problem that forms the foundation for research devoted to the development of a control mechanism for the expression of the oligopeptide permease (opp) genes, which are important metabolic structural genes in the C. difficile genome. In the work reported here, a genetic construct with the ability to monitor the activity of the dual promoter known to control the expression of the opp genes was created. When this construct was used in combination with a highly expressed gene for an opp regulatory protein, we found that gene expression associated with the oppDF promoter was enhanced significantly, while oppAB expression was greatly inhibited. This pattern was observed using fructose, glucose, mannitol, and pep tides as growth substrates, with the degree of induction and repression varying with the nature of the substrate. Future applications of the pUA442 construct may make it possible to determine the specific conditions that prevent the formation of structures of metabolism in C. difficile on the most basic transcriptional level, and ultimately allow for the regulation of one of the nosocomial infections that so greatly contributes to the problems of the health care industry

Single contact tailored gain phased array of semiconductor lasers

We demonstrate a single contact tailored gain-guided array in which the gain profile across the array is made strongly asymmetric by varying the width of the contact stripes. A proton isolated array of six (GaAl)As lasers with 5-µm separations and widths varying linearly between 3 and 8 µm had a single lobed far field 2° wide, close to the diffraction limit for a single supermode. Fabrication of this device is simple, and suited to large-scale processing techniques. We also show that in such an asymmetric gain-guided array the fundamental mode is favored over higher order modes, and that higher order modes can have single lobed far-field patterns differing only slightly from that of the fundamental