Efficient computation of the steady-state response of periodicnonlinear microwave circuits using a convolution-based sample-balancetechnique

The authors describe an efficient and robust approach to the computation of the steady-state response of periodic nonlinear microwave circuits. The problem of solving a set of differential equations is converted into that of solving a system of nonlinear algebraic equations using a technique called convolution-based sample balance. Although exact in all cases for which harmonic-balance techniques are exact, this technique does not require the use of discrete Fourier transforms, and calculating the Jacobian is straightforward. For the solution of the resulting system of nonlinear equations, an efficient and yet robust algorithm has been developed. In the examples given, savings in computational effort of over 85% are reported when this algorithm is compared with Newton's method     

A novel nucleation apparatus for regime separated granulation

A novel nucleation apparatus is presented for the production of narrow sized nuclei from various powder and binder liquid combinations. Mono-sized binder liquid droplets are produced by a specially designed mono-disperse droplet generator. The droplet generator is positioned above a conveyor belt, transporting a powder bed through the spray zone of the droplet generator. By nucleating powder on a conveyer belt, the nucleation mechanism is completely separated from all other granulation mechanisms due to the lack of relative motion between primary particles and/or formed nuclei. Nucleation tests were performed using chalcopyrite and limestone powders with water as the binder liquid. At all operating conditions, the formed nuclei were found to originate from multiplicities of drops that merged on the powder bed surface. Investigation of the dynamics of nuclei formation showed that powder-binder liquid combinations with fast penetration dynamics result in less variation in the number of droplets from which nuclei originate. Smaller and more narrowly distributed nuclei were also achieved by increasing powder speed through the spray zone.     

The effect of growth rate on anodically formed zirconium oxide films

Anodic oxide films have been grown on zirconium at constant current densities for a range of current densities extending over several orders of magnitude. Optical and scanning electron microscopy have shown structural differences for different current densities and the mechanical failure of the films has been studied by tensile testing after oxidation. As the current density was reduced, blistering and breaking of the oxide layer was found to increase and this has been associated with anomalies in the experimental voltage-time graphs. The relationship between electric field in the oxide and the current density has been investigated and values of the activation energies of diffusion have been estimated for both oxygen ions and zirconium ions. Possible mechanisms are discussed for the stress relaxation found to occur increasingly for current densities from 0·01 to 1 mAcm^?2.     

Physical Aging of Amorphous Fructose

ABSTRACT: Physical aging of amorphous anhydrous fructose at temperature 5 °C and at 22 °C was studied using differential scanning calorimetry (DSC). The dynamic glass transition temperature, T_g0 for unaged samples was 16 °C and 13.3 °C for heating rate of 10 °C/min and 1 °C/min, respectively. The fictive temperature, T_f0 for unaged samples calculated by Richardson and Savill method was 12 °C, which is close to the dynamic value obtained from the lower DSC heating rate. The fictive temperature T_f of the aged fructose glasses at temperatures both below and above the transition region was fitted well by a non-exponential decay function (Williams-Watts form). Aging above the transition region (22 °C) for 18 d increased both the dynamic glass transition temperature T_g and the fictive temperature T_f. However, aging below the transition region (5 °C) for 1 d increased the dynamic glass transition temperature T_g but decreased the fictive temperature T_f.     

Spray Drying of Skim Milk Mixed with Milk Permeate: Effect on Drying Behavior,Physicochemical Properties,and Storage Stability of Powder

The possibility of using milk permeate (MP) to lower the protein level of skim milk powder (SMP) in producing powders of 34% and lower protein is explored. Skim milk suspensions with various levels of MP were prepared by mixing SMP and MP powder (MPP) at the ratios of 1:0, 7:3, 3:7, and 0:1: from 34 to 5.3% protein. The suspensions were dried in a spray dryer with inlet and outlet temperatures of 180 and 80°C, respectively. Increasing permeate concentration in the mixture showed a greater tendency to stickiness manifested by lowered the cyclone recovery of the powder as more powder stuck on the wall of the dryer. Increasing permeate concentration in the resultant powder did not significantly affect the bulk density but led to a reduction in the particle size and also made the powder slight green and yellowish in color. It also found to lower the glass transition temperature (T_g ) of the skim milk powder (SMP) and induce crystallization of lactose at lower water activity (a_w  ≥ 0.328 for SMP:MPP of 3:7 and 0:1 compared to a_w  ≥ 0.0.432 for SMP:MPP of 1:0 and 3:7). Addition of MP in SMP lowered the T_g values of the resulting powders. The permeate fraction in spray-dried SMP/MPP mixtures found to lower the critical a_w and moisture content, suggesting the SMP mixed with MPP is more likely to become sticky than SMP alone (at 34% protein) when stored at a similar water activity and moisture content.     

Fourier Transform Infrared and Ion-Chromatographic Sulfate Analysis of Ambient Air Samples

Fourier transform infrared (FTIR) spectrometry has been evaluated as a method for determining the sulfate concentration of ambient aerosol particulate samples. Samples were collected on Teflon filters. The filters were analyzed for sulfate by both FTIR and ion chromatography (IC). There is good agreement between sulfate analysis by IC and analysis of the FTIR transmission spectra of the air filters during the first 5 1/2 days of the Carbonaceous Species Methods Intercomparison Study in which the ambient sulfate concentrations were above the 5.8 μg/cm² lower limit of detection of the FTIR technique. A method to improve the FTIR lower limit of detection is discussed. The difficulties incurred during background subtraction of the infrared spectra are described.     

Nonlinear circuit analysis of harmonic and intermodulationdistortions in laser diodes under microwave direct modulation

A microwave nonlinear circuit analysis technique which can account for all known steady-state responses has been developed and applied to the large-signal characterization of directly modulation laser diodes. An equivalent circuit derived from the rate equations is used to model the laser diode. The proposed technique is based on a harmonic balance algorithm which represents two-tone inputs by describing frequencies. Second-harmonic and third-order intermodulation distortion results for a single-mode GaAlAs diode have been compared with corresponding measured data to validate the method. Aperiodic responses are detected by means of bifurcation theory prior to the harmonic balance analysis and are simulated in the time domain. Simulated results are shown to agree well with published measurements, and indicate the capability of using this approach for the computer-aided design of microwave fiber-optic transmitters     

Radiation-induced degradation of ohmic contacts

Ohmic contacts can be severely degraded by the introduction of small amounts of radiation damage at the metal-semiconductor interface. This can lead to failure of GaAs transferred-electron devices; a safe limit for proton bombardment of ohmic contacts is proposed.     

Control of denitrification in a septage-treating artificial wetland: the dual role of particulate organic carbon

We examined the factors controlling organic carbon (C) cycling and its control of nitrogen (N) removal via denitrification in an aerated artificial wetland treating highly concentrated wastewater to nutrient-removal standards. Processing of organic material by the septage-treating wetland affected the biological reactivity (half-life, or t1/2) of organic C pools through microbial degradation and gravity fractionation of the influent septage. Primary sedimentation fractionated the initial septage material (t1/2 = 8.4d) into recalcitrant waste solids (t1/2 = 16.7d) and highly labile supernatant (t1/2 = 5.0d), allowing this reactive fraction to be further degraded during treatment in aerobic wetland tanks until a less labile material (t1/2 = 7.3d) remained. Organic C contributions from in situ fixation by nitrifying bacteria or algae in these tanks were small, about 1% of the C degradation rate. In the aerated tanks, denitrification was correlated with particulate organic C loading rates, although the average C required (0.35 mg C L(-1)h(-1)) to support denitrification was only 12% of the total C respiration rate (2.9 mg C L(-1)h(-1)). Additions of plant litter (2.5g C L(-1)) to the aerated tanks under normal operating conditions doubled denitrification rates to 0.58 mg N L(-1)h(-1), and reduced effluent nitrate levels by half, from 12.7 to 6.4 mg N L(-1). However, C degradation within the plant litter (0.15mg C L(-1)h(-1)) was sufficient to have accounted for only 35% of the additional denitrification. Evidence from laboratory and full-scale plant litter additions as well as process monitoring indicates that the stimulation of denitrification is due to the respiration-driven formation of anaerobic microsites within particulate organic C. In this aerated highly C-loaded septage-treating wetland, anaerobic microsite, rather than C substrate availability limits denitrification.