Biofuels: network analysis of the literature reveals key environmental and economic unknowns

Despite rapid growth in biofuel production worldwide, it is uncertain whether decision-makers possess sufficient information to fully evaluate the impacts of the industry and avoid unintended consequences. Doing so requires rigorous peer-reviewed data and analyses across the entire range of direct and indirect effects. To assess the coverage of scientific research, we analyzed over 1600 peer-reviewed articles published between 2000 and 2009 that addressed 23 biofuels-related topics within four thematic areas: environment and human well-being, economics, technology, and geography. Greenhouse gases, fuel production, and feedstock production were well-represented in the literature, while trade, biodiversity, and human health were not. Gaps were especially striking across topics in the Southern Hemisphere, where the greatest potential socio-economic benefits, as well as environmental damages, may co-occur. There was strong asymmetry in the connectedness of research topics; greenhouse gases articles were twice as often connected to other topics as biodiversity articles. This could undermine the ability of scientific and economic analyses to adequately evaluate impacts and avoid significant unintended consequences. At the least, our review suggests caution in this developing industry and the need to pursue more interdisciplinary research to assess complex trade-offs and feedbacks inherent to an industry with wide-reaching potential impacts.     

Determination of the threshold for instability in four-wave mixingmediated by Brillouin scattering

The threshold for instability in Brillouin-enhanced four-wave mixing has been experimentally determined as a function of both the phase mismatch and the ratio of the pump beam intensities and is shown to agree with theoretical modeling. The effective input noise intensity for four-wave mixing in the unstable regime is compared to the noise in a stimulated Brillouin scattering amplifier and is found to be higher by a factor of three in the forward direction. Competition between two input signals has been investigated, and it is shown that the signal which arrives first dominates the interaction in the unstable regime     

A simple scheme for unity power-factor rectification for highfrequency AC buses

A simple scheme is proposed for offline unity power factor rectification for high-frequency AC buses (20 kHz). A bandpass filter of the series-resonant type, centered at the line frequency, is inserted between the line and the full-wave rectified load. The Q=Z ₀/R_L formed by the load and the characteristic impedance of the tank circuit determines the power factor, the boundary between continuous and discontinuous conduction modes, the peak stresses, and the transient response of the rectifier. It is shown that for Q>2/π the rectifier operates in continuous conduction mode and the output voltage is independent of the load. Also, it is shown that for Q>2 the line current is nearly sinusoidal with less than 5% third-harmonic distortion and the power factor is essentially unity. An increase in Q causes an increase in the peak voltages of the tank circuit and a slower transient response of the rectifier circuit. The DC, small-signal, and transient analyses of the rectifier circuit are carried out, and the results are in good agreement with simulation and experimental results     

Microstructural development in complex nickel-aluminum bronzes

The development of microstructure in complex nickel-aluminum bronzes of nominal composition Cu-10 wt pet Al-5 wt pct Ni-5 wt pct Fe, during continuous cooling from temperatures approaching the solidus, has been investigated using optical and electron microscopic techniques. At high temperatures the alloy consists of bccβ phase, and as the temperature is lowered the fcc copper-rich α phase is precipitated with a Widmanstätten morphology. As the temperature continues to decrease, Fe₃Al precipitates form in theβ phase and this is followed by the formation of Fe₃Al precipitates in the a phase. On further cooling theβ phase decomposes eutectoidally into ga+ NiAl; the eutectoid reaction initiates at thea/β interface and grows into theβ regions. Under normal cooling conditions the decomposition ofβ into α+ NiAl does not reach completion and the remnantβ phase transforms to martensite.     

Anterior approach for CT-guided biopsy of skull base and parapharyngeal space lesions

At our institution we use an anterior approach to biopsy of the parapharyngeal space or skull base lesions because it provides more direct access than the traditional lateral approach through the mandibular notch. The anterior approach follows a course lateral to the alveolar ridge of the maxilla and lateral pterygoid plate, and inferior to the zygomatic process of the maxilla. Biopsy was performed on 15 patients with either a skull base or a parapharyngeal space mass, none of which could be palpated externally or through the oral cavity by the ear, nose, and throat surgeon. In 12 patients the needle biopsy correlated with the surgical pathology. Three needle biopsies were nondiagnostic.     

Small-signal modeling of average current-mode control

A recently proposed average current-mode control method is analyzed. A complete small-signal model for the control scheme is developed. The model is accurate up to half the switching frequency. This control scheme is suitable for applications where the average inductor current needs to be controlled, as in power factor correction circuits and battery charger dischargers. The subharmonic oscillation, commonly found in peak current-mode control, also exists in this method. This subharmonic oscillation can be eliminated by properly choosing the proper gain of the compensation network in the current loop. Model predictions are confirmed experimentally     

Hot electron energy relaxation via acoustic phonon emission in GaAs/Al0.24Ga0.76As single and multiple quantum wells

The energy relaxation associated with acoustic phonons has been investigated in a series of modulation doped GaAs/AlGaAs single and multiple quantum wells grown by molecular beam epitaxy, using the hot electron Shubnikov — de Haas effect. The power loss is shown to be proportional to (T_e² − T_L²) for electron temperatures 2.2K < T_e < 8K and proportional to (T_e³ − T_L³) for 8K < T_e < 20K. The energy loss rates due to acoustic phonon scattering via both deformation potential coupling and piezoelectric coupling have been calculated. The total energy loss rate as a function of electron temperature is compared with the experimental results. Good agreement is obtained for 2.2K < T_e < 8K. Above 8K the energy loss rate is seen to rise above the predicted values, indicating the onset of an extra energy relaxation mechanism. The application of a high electric field (E = 3kV/cm) at low lattice temperatures is shown to induce persistent parallel conduction and a subsequent reduction of the low field well mobility.     

Comparisons of JOULE 1 rocket thermospheric wind observations in high latitudes with GITM simulations

The JOULE sounding rocket 1 experiment was carried out at Poker Flat Research Range in Alaska around 1200 UT on March 27th, 2003 with two instrumented rockets and one chemical tracer rocket. From the released trimethyl aluminum (TMA) trails, neutral wind measurements showed a wind peak at 120 km altitude and a jet structure around it, which were superposed by a vertically propagating wave. Running global ionosphere thermosphere model (GITM) with a stretched grid structure, sub-degree resolution around the JOULE rocket position was applied. Data-model comparison shows that the GITM simulation reproduced the large neutral wind at 120 km altitude. The simulation also shows a strong vertical wind shear below 120 km, which is generally consistent with observation but with a smaller gradient. The primary discrepancies were the wave features below 115 km and the wind gradient above 120 km altitude, which indicates that the wave forcing besides the ion-drag force plays an important role to the neutral dynamics in the lower thermosphere. The comparison between simulations using different high-latitude drivers was also conducted to emphasize the significance of the electrodynamics to the neutral wind. Using assimilative mapping of ionospheric electrodynamics (AMIE) procedure as the high latitude driver produced more accurate neutral wind patterns than using Weimer empirical model.     

Cavitation behaviour in fine grain 3Y-TZP during tensile and compressive superplastic flow

Studies of cavitation in Y-TZP during superplastic flow have been made for both tensile and compressive deformation conditions. It was observed that the morphologies of cavities near the fracture faces of tensile specimens varied markedly with testing conditions and in most cases differed from those near the gauge heads. Two quite different forms of cavitation behaviour were observed leading to high and low strains to failure, respectively. For optimum conditions of superplastic flow, of high temperature/low strain rate (low stress), when large elongations were observed, cavities were either spherical or elongated parallel to the tensile axis. Those near the fracture face interlinked in a plastic (necking) mode to give transverse cavities and subsequent failure. At high strain rate/low temperature (high stress), transverse intergranular cracking played a dominant role in failure at low elongations. For intermediate conditions of temperature/strain rate, elongated cavities developed parallel to the tensile axis, but near the fracture face these usually interlinked by transverse cracking. These conditions were associated with intermediate elongations to failure. For the assessment of cavity growth mechanisms, artificial pores were introduced into fine grain Y-TZP specimens and changes in their shape and size during tensile or compressive deformation were investigated. Results show that the change of pore volume, in the superplastic regime, is controlled by plastic deformation of the matrix and can be described by the relationship of dR/d = ;R, where is the true strain, the cavity growth rate parameter and R is the radius of the pore.     

Cavitation during the superplastic deformation of an α/β brass

Cavitation during superplastic tensile flow has been studied in an/ brass using metallography and precision density measurements. Cavities nucleated primarily at triple points and were sometimes associated with small second phase particles. The level of cavitation increased as strain, strain rate and grain size were increased and as the temperature was decreased. The influence of these variables can be interpreted in terms of their effects on cavity nucleation and/or cavity growth rates.