Nitric oxide and nitrous oxide production and cycling during dissimulatory nitrite reduction by Pseudomonas perfectomarina

The denitrifier Pseudomonas perfectomarina reduced nitrite under conditions of kinetic competition between cells and gas sparging for extracellular dissolved nitric and nitrous oxides, NOaq and N2Oaq, in a chemically defined marine medium. Time courses of nitrite reduction and NOg and N2Og removal were integrated to give NOg , and N2Og yields. At high sparging rates, the NOg yield was >50% of nitrite-N reduced, and the yield of NOg + N2Og was ~75%. Hence interrupted denitrification yields NOaq and N2Oaq as major products. The yields varied with sparging rates in agreement with a quantitative model of denitrification (Betlach, M. P., and Tiedje, J. M. (1981) Appl. Environ. Microbiol. 42, 1074-1084) that applies simplified Michaelis-Menten kinetics to NO2 > NOaq > N2Oaq > N2. The fit gave an estimate of the maximum scavengeable NOaq yield of 73 ± 8% of nitrite-N. Thus a minor path independent of NOaq is also required. The fit of the model to data at lower sparging rates, where normal denitrification products predominate, implies that the extracellular NOaq pool yield is independent of gas sparging rate. Thus in P. perfectomarina NOaq and N2Oaq are intermediates, or facilely equilibrate with true intermediates, during complete denitrification. The recovery of most nitrite-N as NO and/or N20 under perturbed conditions is not an artifact of irreversible product removal, but an attribute of denitrification in this species, and most probably it is characteristic of denitrification in other species as well

Transport property analysis method for thermoelectric materials: material quality factor and the effective mass model

Thermoelectric semiconducting materials are often evaluated by their figure-of-merit, zT. However, by using zT as the metric for showing improvements, it is not immediately clear whether the improvement is from an enhancement of the inherent material property or from optimization of the carrier concentration. Here, we review the quality factor approach which allows one to separate these two contributions even without Hall measurements. We introduce practical methods that can be used without numerical integration. We discuss the underlying effective mass model behind this method and show how it can be further advanced to study complex band structures using the Seebeck effective mass. We thereby dispel the common misconception that the usefulness of effective band models is limited to single parabolic band materials.Comment: 5 pages, 3 figure

Coulomb entangler and entanglement testing network for waveguide qubits

We present a small network for the testing of the entanglement of two ballistic electron waveguide qubits. The network produces different output conditional on the presence or absence of entanglement. The structure of the network allows for the determination of successful entanglement operations through the measurement of the output of a single qubit. We also present a simple model of a dynamic coulomb-like interaction and use it to describe some characteristics of a proposed scheme for the entanglement of qubits in ballistic electron waveguides.Comment: 12 pages of text plus 7 figures: total 19 page

Vehicle for civil helicopter ride quality research

A research aircraft for investigating the factors involved in civil helicopter operations was developed for NASA Langley Research Center. The aircraft is a reconfigured 17000 kg (36000 lb) military transport helicopter. The basic aircraft was reconfigured with advanced acoustic treatment, air-conditioning, and a 16-seat airline cabin. During the spring of 1975, the aircraft was flight tested to measure interior environment characteristics - noise and vibration - and was flown on 60 subjective flight missions with over 600 different subjects. Data flights established noise levels somewhat higher than expected, with a pure tone at 1400 Hz and vertical vibration levels between 0.07g and 0.17g. The noise and vibration levels were documented during subjective flight evaluations as being the primary source of discomfort. The aircraft will be utilized to document in detail the impact of various noise and vibration levels on passenger comfort during typical short-haul missions

Evaluation of true interlamellar spacing from microstructural observations

A method for evaluating true interlamellar spacing from micrographs is proposed for a multidomained lamellar structure. The microstructure of these materials is assumed to be composed of many domains with the lamellae aligned roughly parallel to each other within each domain and with the domains themselves randomly oriented relative to one another. An explicit expression for the distribution of apparent interlamellar spacing is derived assuming that the distribution of the true interlamellar spacing is Gaussian. The average interlamellar spacing is close to the peak interlamellar spacing observed in the distribution. The theoretical distributions are compared with experimental ones obtained by analyzing micrographs of PbTe–Sb2Te3 lamellar composites

Zone Leveling Crystal Growth of Thermoelectric PbTe Alloys with Sb_(2)Te_3 Widmanstätten Precipitates

Unidirectional solidification of PbTe-rich alloys in the pseudobinary PbTe-Sb_(2)Te_3 system using the zone leveling technique enables the production of large regions of homogeneous solid solutions for the formation of precipitate nanocomposites as compared with Bridgman solidification. (PbTe)_(0.940)(Sb_(2)Te_3)_(0.060) and (PbTe)_(0.952)(Sb_(2)Te_3)_(0.048) alloys were successfully grown using (PbTe)_(0.4)(Sb_(2)Te_3)_(0.6) and (PbTe)_(0.461)(Sb_(2)Te_3)_(0.539) as seed alloys, respectively, with 1 mm h^(–1) withdrawal velocity. In the unidirectionally solidified regions of both alloys, Widmanstatten precipitates are formed due to the decrease in solubility of Sb_(2)Te_3 in PbTe. To determine the compositions of the seed alloys for the zone leveling experiments, the solute distribution in solidification in the PbTe-richer part of the pseudobinary PbTe-Sb_(2)Te_3 system has been examined from the concentration profiles in the samples unidirectionally solidified by the Bridgman method

Phonon engineering through crystal chemistry

Mitigation of the global energy crisis requires tailoring the thermal conductivity of materials. Low thermal conductivity is critical in a broad range of energy conversion technologies, including thermoelectrics and thermal barrier coatings. Here, we review the chemical trends and explore the origins of low thermal conductivity in crystalline materials. A unifying feature in the latest materials is the incorporation of structural complexity to decrease the phonon velocity and increase scattering. With this understanding, strategies for combining these mechanisms can be formulated for designing new materials with exceptionally low thermal conductivity

Rapid consolidation of powdered materials by induction hot pressing

A rapid hot press system in which the heat is supplied by RF induction to rapidly consolidate thermoelectric materials is described. Use of RF induction heating enables rapid heating and consolidation of powdered materials over a wide temperature range. Such rapid consolidation in nanomaterials is typically performed by spark plasma sintering (SPS) which can be much more expensive. Details of the system design, instrumentation, and performance using a thermoelectric material as an example are reported. The Seebeck coefficient, electrical resistivity, and thermal diffusivity of thermoelectric PbTe material pressed at an optimized temperature and time in this system are shown to agree with material consolidated under typical consolidation parameters