The optically pumped hydrazine FIR laser: Assignments and new laser lines

Strong far-infrared (FIR) lasing action has been observed in hydrazine optically pumped with isotopic CO2lasers and the N2O laser. The wavelengths of 13 new laser lines have been determined. The results of a recent infrared-microwave double resonance study of hydrazine have been used to assign the transitions involved in the production of five of these new lines and nine of the previously observed laser lines.     

A kairomone forTrichogramma nubilale (Hymenoptera: Trichogrammatidae) isolation,identification, and synthesis

A kairomone that effects host-seeking behavior inTrichogramma nubilale Ertle and Davis, an egg parasitoid of the European corn borer,Ostrinia nubilalis (Hübner), was isolated from moth scales of the European corn borer. The kairomone was identified as a mixture of 11,15-, 13,17-, and 15,19-dimethylnonatriacontanes. The three dimethylnonatriacontanes were synthesized, and bioassays showed that the 13,17 isomer was the most active in terms of klinokinetic and retention effects. The 11,15 isomer and the 15,19 isomer had some effect on klinokinesis, but they failed to effect retention of the wasps. The 13,17-dimethylnonatriacontane is considered to be the most important component of the kairomone.Paper No. 16684 Scientific Journal Series, Minnesota Agricultural Experiment Station, University of Minnesota, St. Paul, Minnesota 55108.     

A generalist herbivore in a specialist mode Metabolic,sequestrative, and defensive consequences

Adults of a generalist herbivore, the lubber grasshopper,Romalea guttata, can be converted to functional specialists by feeding them exclusively on catnip,Nepeta cataria. No obvious adverse effects on adult development resulted from this enforced monophagy. Notwithstanding the fact thatR. guttata has had no coevolutionary relationship with this Eurasian mint, it readily sequesters compounds that are identical to or derived from the terpenoid lactones that are characteristic ofN. cataria. R. guttata appears to both biomagnify minor allelochemicals and to sequester metabolites of theNepeta terpenes in its paired defensive glands. The levels of autogenously produced phenolics are not affected by feeding onN. cataria and the defensive secretions of catnip-fed grasshoppers are more repellent to ants than those of wild-fed acridids. Metabolites of theN. cataria monoterpenes are sequestered in the defensive glands when catnip is added to the natural diet ofR. guttata. The ability of a generalist,R. guttata, to facilely bioaccumulate a potpourri of foreign allelochemicals when feeding in a specialist mode is analyzed in terms of its biochemical, physiological, and functional significance. Sequestration is examined as a response to the enteric effronteries represented by the phytochemicals that can be characteristic of the overload in a monophagous diet.     

Ultralow oil-water IFTs using neutralized oxidized hydrocarbons as surfactants

Surfactants that may be suitable for application in enhanced oil recovery have been produced from C₂₂ and C₂₆ paraffinic and naphthenic petroleum fractions by a two-step process. The hydrocarbon feed stocks were first oxidized in the vapor-phase, followed by neutralization of the oxidized products with aqueous alkali. As a result, dilute solutions of organic acid salts were produced that achieved ultralow (<10⁻² dyne/cm) interfacial tensions against a synthetic oil. Surfactant solutions that exhibited the lowest interfacial tensions (IFTs) were prepared from neutralizations that used low concentrations of sodium hydroxide rather than sodium silicate, sodium tripolyphosphate, or sodium carbonate. Neutralizations that used sodium silicate or sodium carbonate resulted in surfactant solutions having IFT profiles that were less sensitive to the electrolyte concentration. When sodium hydroxide was combined with either sodium silicate or sodium tripolyphosphate in the neutralizations, solutions having intermediate IFT properties were produced. The amount of alkali used in the neutralizations was observed to affect the IFT properties of the resultant surfactant solution. The electrolyte concentration at which the minimum IFT occurred was inversely related to the pH of the surfactant solution. For surfactant solutions of common pH prepared from different concentrations of oxidized product, the minimum IFTs all occurred at the same concentration of electrolyte. Surfactant solutions remained interfacially active even in the presence of significant concentrations of calcium chloride. One pore volume of a solution containing only about 1% of active surfactant recovered 42.0% of the residual oil in a tertiary core-flood experiment.     

Enhanced Frequency-Domain Frost Algorithm Using Conjugate Gradient Techniques for Speech Enhancement

In this paper, the frequency-domain Frost algorithm is enhanced by using conjugate gradient techniques for speech enhancement. Unlike the non-adaptive approach of computing the optimum minimum variance distortionless response （MVDR） solution with the correlation matrix inversion, the Frost algorithm implementing the stochastic constrained least mean square （LMS） algorithm can adaptively converge to the MVDR solution in mean-square sense, but with a very slow convergence rate. In this paper, we propose a frequency-domain constrained conjugate gradient （FDCCG） algorithm to speed up the convergence. The devised FDCCG algorithm avoids the matrix inversion and exhibits fast convergence. The speech enhancement experiments for the target speech signal corrupted by two and five interfering speech signals are demonstrated by using a four-channel acoustic-vector-sensor （AVS） micro-phone array and show the superior performance.     

DC and large-signal time-dependent electron transport in heterostructure devices: an investigation of the heterostructure barrier varactor

The DC and large-signal time-dependent electron transport properties of Heterostructure Barrier Varactors (HBVs) are investigated using a physical model which combines drift-diffusion current transport through the heterostructure bulk with thermionic and thermionic-field emission currents imposed at the abrupt heterointerfaces in a fully self-consistent manner. A fast and accurate hydrodynamic device simulator for generic unipolar InGaAs-InAlAs on InP, InGaAs-InP on InP, and GaAs-InGaAs-AlGaAs on GaAs HBVs has been developed based on this model. The experimentally observed current-voltage and capacitance-voltage characteristics of GaAs-AlGaAs and GaAs-InGaAs-AlGaAs HBVs are compared with the simulated results over a wide range of DC bias. Large-signal time-dependent simulations at a pump frequency of 100 GHz confirm the odd-harmonic operation of these devices and indicate that multiple barrier HBVs should provide efficient frequency multiplication, especially in high order frequency multipliers, broadband frequency triplers, and quasi-optical tripler arrays.<>     

The properties of MOVPE grown 1.3 μm DFB MQW lasers infilled with semi-insulating InP fabricated on semi-insulating substrates

The use of optoelectronic integrated circuits (OEICs) is now emerging as a practical technology for a variety of applications, particularly in advanced telecommunications. OEICs consist of a range of devices such as lasers, waveguides, modulators, amplifiers, transistors, detectors, etc. fabricated on the same substrate. When a semi-insulating substrate is used, these devices can be electrically isolated by channel etching, resulting in a low capacitance structure with reduced electrical interference between the subcomponents. One of the devices which is particularly advantageous for this type of integration scheme is the distributed feedback (DFB) laser. The laser can be made to function more efficiently by minimizing the current flowing outside the active region. This can be achieved by surrounding the active region with semi-insulating iron doped InP. This work describes for the first time, the MOVPE growth, fabrication, and device characterization of 1.3 um buried heterostructure DFB MQW lasers, which combine the advantages of using both a semi-insulating substrate and a semi-insulating infill region in the same device structure. The potential advantage of this design scheme is improved OEIC performance as a result of, reduced capacitance and electrical crosstalk, enhanced laser output power, higher speed, increased efficiency, wider operating temperature and reduced threshold current. The laser active region consists of 8 x 140 Å quantum wells of GalnAsP (λ = 1.3 μm) and 110 Åbarriers of GalnAsP (λ= 1.07 μm). Single mode 1.3 urn devices of length 250 μm operating at room temperature produced threshold currents of 8 mA, efficiencies of up to 25%, output powers of 18 mW at 80 mA (pulsed), and a frequency response greater than 12GHz. The parasitic capacitance was estimated to be less than 3 pF.     

Crystallographic orientation dependence of the growth rate for GaAs low pressure organometallic vapor phase epitaxy

The complete crystallographic orientation dependence of the growth rate for GaAs low pressure organometallic vapor phase epitaxy (LPOMVPE) is determined using a previously described semi-empirical model. A set of LPOMVPE growth rate polar diagrams is presented for reactor temperatures near 550°C as well as near 700°C. Also, the variation of the growth rate polar diagrams as a function of process variables is given. The experimental data utilized in the semiempirical model was attained using a typical horizontal reactor LPOMVPE system and typical LPOMVPE process parameters.     

Efficient representation of object shape for silhouetteintersection

A new shape representation-the radial intersection set (RIS)-is presented. The RIS is an object-centred model in which 2-D and 3-D boundaries are represented via their intersection with radial lines from some specific origin. The RIS representation allows efficient 3-D reconstruction using silhouette intersection from an arbitrary number of 2-D perspective views. The relationship between the visual hull (Laurentini, 1994) of the 3-D object and the silhouettes it may generate is defined as a set intersection operator. This operator allows the direct generation of 3-D RIS models from silhouettes. The RIS method is shown to compare favourably, in terms of both speed and storage, with existing octree techniques. Examples of images rendered from RIS models are presented. These show high visual fidelity     

Oxygen Deficiency and Hydrogen Turn ZnO Red

The effect of hydrogen on ZnO while annealing at 1370 K under oxygen-poor conditions with excess Zn vapor or Ti metal is studied. ZnO turns red only when hydrogen is present in a complex with oxygen vacancies. A practical method is described to remove hydrogen from ZnO in a sealed ampoule and to bind it to Ti metal. Hydrogen coupled to an oxygen vacancy is the simplest defect to explain the observations. The coloration is reversible at 1370 K by adding or removing hydrogen, consistent with an activation energy >1.5 eV. In red ZnO Hall data show a shallow donor level around 45 meV.