Analysis of an experimental technique for determining Van der Polparameters of a transistor oscillator

The Van der Pol (VDP) model of a transistor oscillator describes the behaviour of the oscillator with three parameters. When operating in steady state, only two parameters can be determined by spectrum analysis, these being the oscillation frequency and amplitude of oscillation. In this paper, a technique for measuring the other VDP parameter is examined. In this approach, a periodically modulated voltage is added to the bias of the oscillator to perturb the operational state. A theoretical derivation shows that the power spectrum of the perturbed oscillator contains additional information for determination of the other VDP parameter. A simple analytical perturbation formula predicts the oscillator's response to the ramped bias. Our experimental results agree with the analytical perturbation solution and therefore, this allows one to read off the other VDP parameter from the experimental data. The VDP model allows one to predict the behaviour of coupled transistor oscillators more accurately and simply than does the traditional large-signal model of the transistor. This VDP model will simplify oscillator array design since the number of parameters needed to describe each oscillator is reduced from that which would be required using a large-signal circuit model     

Remote Laboratories for Optical Circuits

This paper presents a remote laboratory implementation for an optical circuits course. The process from design and implementation towards assessment and continuous improvement phase is outlined. The design of the experiments involved the research on remote access technology and the investigation of best practices for an experimental setup. The first pilot implementations were used to determine the possible shortfalls during an ldquoIntroduction to an Optical Communicationsrdquo course in fall 2004 at the University of Colorado, Boulder, and an ldquoOptical Circuitsrdquo course in fall 2005 at the University of Houston, Houston, TX. After improvements, two experiments were pilot tested during spring 2006 at the University of Houston. Assessment of learning outcomes and teaching methods were performed. The remote access methods, in addition to the delivery of the class and lectures, are presented in the paper. Delivery of a class with remote laboratories and videotaped lectures are also outlined under future directions of this project.     

Testing the smoking behavior of fire-retarded materials

The authors investigated the smoke generating behavior of a fire-retardant-treated urethane polymer using a newly designed test chamber and test method, which they believe provides more meaningful information than the currently used smoke tests.     

Voltage calibration of the direct electrooptic sampling technique

A detailed study of various voltage calibration factors or the direct electrooptic sampling technique is presented. In reflection mode optical probing, the circuit substrate forms an etalon for the optical probe beam. Analytical expressions for the calibration factors due to etalon effects and decaying surface potentials are derived. on the length of the sampling pulse relative to the substrate transit time, the etalon will affect either the voltage calibration factor or the system bandwidth: For pulses that are long compared to the transient time, interference at the surface results in a probe wavelength dependent storage time effect. The resulting electrooptic signal shows a resonant behavior as a function of wavelength or substrate thickness. For pulses that are short compared to the substrate transit time, multiple reflections reduce the effective system bandwidth to a bandwidth less than that given by the single transit time or the sampling pulse width. Experimental verification of the theoretical results is presented. Various deembedding procedures for implementing the voltage calibration are discussed     

Backscatter readout from serial microbending sensors

Backscattering measurements performed on test fibers perturbed by several serially placed microbending sensors reveal the surprising result that the loss induced in a given sensor is nearly independent of the losses induced in the other sensors. A simple theoretical model is constructed to predict the conditions under which this desirable phenomenon can occur.     

Effects of nutritional characteristics of Streptococcus agalactiae on inhibition of growth by lactoperoxidase-thiocyanate-hydrogen peroxide in chemically defined culture medium

Five cultures of Streptococcus agalactiae have an absolute requirement for L-cystine to grow in a chemically defined medium. The L-cystine could be replaced with cysteine, glutathione, or the disulfide form of glutathione. Dithiothreitol could not substitute for the sulfur-containing amino acids of glutathione; hence, the growth requirement appears to be truly nutritional. Growth was maximum with 4 to 5 mug of L-cystine per ml. If the concentration of L-cystine was no greater than 4 to 5 mug/ml, complete growth inhibition could be obtained by the addition of lactoperoxidase, thiocyanate, and H2O2. The growth inhibition, however, was nullified by additions of L-cystine 10-fold or more in excess of the concentration needed for maximum growth. During the aerobic degradation of glucose by cell suspensions, H2O2 accumulation could be shown with cultures 317 and 11-13, the only cultures the growth of which was inhibited without addition of exogenous H2O2. All of the cultures had varying degrees of peroxidase activity. The balance between H2O2 generation and peroxidase activity of the culture evidently determined whether growth could be inhibited with lactoperoxidase and thiocyanate without H2O2 addition. The growth yeilds per 0.5 mol of the disulfide forms (cystine and oxidized glutathione) were 1.5 and 1.9 times greater than that per 1 mol of the sulfhydryl forms (cysteine and glutathione).     

Effects of noise on transients of injection locked semiconductorlasers

Semiconductor laser injection locking transients are analyzed. By adiabatically eliminating the carrier dynamics, a single nonlinear stochastic differential equation is obtained for the relative phase between the master and slave lasors. The corresponding Fokker-Planck equation is used to study the steady-state locked conditions as well as phase transients of the locking process. Noise causes the steady-state relative phase between the master and the slave lasers to be a random variable with a standard deviation of approximately a few degrees for typical injection levels. The standard deviation can be reduced by using a phase detector with a limited bandwidth. The mean locking time in the presence of noise is slightly less than the deterministic prediction. Noise also causes the locked lasers to have a finite probability to momentarily unlock     

Experimentally verifiable modeling of coplanar waveguidediscontinuities

A general technique for obtaining the frequency dependent scattering parameters of open waveguiding structures is discussed. The first step of the analysis is an iterative solution for the charge distribution on the electrodes which, in our case, uses the “straight line” solution, the one first derived by Maxwell, as the starting value. A calibrated optical sampling technique allows for direct verification of the validity of the quasi-static charge distribution for structures in which the dielectric layers are also electrooptic. (Common waveguiding dielectrics such as GaAs and InP are sufficiently electrooptic to yield more than sufficient signal-to-noise ratios for accurate verification.) In cases where the quasi-static solution is valid, it is shown that the full dynamics of the propagation problem can be recovered from an equivalent nonuniform transmission line, the parameters of which can be determined from the phase velocity and impedance distribution defined by the static charge distribution. Here, we present analysis of planar discontinuities in coplanar waveguides (CPW), but the method can be modified and applied to include active devices, as well as three-dimensional discontinuities, such as airbridges. The method is based on an iterative solution of the quasi-static charge distribution using successive over relaxation and the dynamics are introduced via the Riccati equation. Additional measurements performed on the “in-house” fabricated passive circuits using an HP8510 network analyzer verify the accuracy of the dynamical part of the method     

Fabrication and characterization of a third-order nonlinear organic-polymer composite glass waveguide: a self-phase modulator

Composite organic-polymer glass optical waveguides in which coupling to the nonlinear organic-polymer layers was achieved by excitement of the underlying ion-exchanged glass waveguide and coupling of the light to the organic-polymer layer were fabricated and measured. A picosecond pulsed color center laser (λ = 1.5 μm) was used to measure the third-order optical susceptibility χ((3))(-w; w, -w, w) in an organic-dye-polymer composite glass waveguide with a Mach-Zehnder interferometer. For a squaryliumdye-doped poly(methyl methacrylate)-styrene-acrylonitrile matrix polymer layer, a composite χ((3)) of roughly 90, in units of (χLiNbO)(3)((3)), was measured.     

Physiological characteristics of Streptococcus dysgalactiae and Streptococcus uberis and the effect of the lactoperoxidase complex on their growth in a chemically-defined medium and milk

Aerobic or anaerobic degradation of glucose by Streptococcus dysgalactiae and Streptococcus uberis yielded products qualitatively similar to those observed previously for Streptococcus agalactiae. There were, however, quantitative differences. Though acetoin was formed during aerobic growth of Streptococcus uberis, there was none with Streptococcus dysgalactiae. Differences between Streptococcus dysgalactiae and Streptococcus uberis in their aerobic metabolism of glucose was in lower oxygen consumption (.5 mol/mol of glucose), greater conversion of glucose to lactic acid, and lower molar growth yields with Streptococcus uberis. Cell suspensions of Streptococcus uberis had strong peroxidase activity, and no hydrogen peroxide accumulated during the respiration on glucose. With Streptococcus dysgalactiae, there was more oxygen consumed during growth (1.5 mol/mol of glucose used), greater conversion of glucose to acetic and formic acids and carbon dioxide, and a cell yield of about 6 g of dry cells more per mole of glucose than with Streptococcus uberis. This increase in molar growth yield with Streptococcus dysgalactiae over Streptococcus uberis could be nearly all accounted for by differences in the amount of substrate level adenosine triphosphate generated. Cell suspensions oxidizing glucose accumulated hydrogen peroxide and showed no peroxidase activity. Streptococcus dysgalactiae showed the same growth relationships in three milk media as Streptococcus agalactiae, although growth and acid formation values were much lower. Growth inhibition by the lactoperoxidase complex was reversed with cystine. Acid formation by Streptococcus uberis was decreased by the lactoperoxidase complex and increased by the addition of cystine; however, neither appeared to affect the growth of the organism.