Stark ladders as tunable far-infrared emitters

A superlattice of GaAs/Ga(1 – x)Al(x)As quantum wells forms a Stark ladder under the influence of a perpendicular electric field. A two level incoherent emitter system, formed by radiative intersubband transitions between adjacent wells, is investigated as a tunable far-infrared radiation source. Intersubband transition rates are calculated at 4, 77, and 300 K for applied fields from 0 to 40 kV cm(–1). It is shown that the quantum efficiency of the radiative emission reaches a maximum at low temperatures for a field of 32 kV cm(–1). Under these conditions the emission wavelength is 38 µm with an estimated power output of 1.1 mW. © 1998 American Institute of Physics

Assessment of the environmental toxicity and carcinogenicity of tungsten-based shot.

The toxicity of elemental tungsten released from discharged shot was assessed against previous studies that established a 1% toxic threshold for soil organisms. Extremely heavy theoretical shot loadings of 69,000 shot/ha were used to generate estimated environmental concentrations (EEC) for two brands of tungsten-based shot containing 51% and 95% tungsten. The corresponding tungsten EEC values were 6.5–13.5 mg W/kg soil, far below the 1% toxic threshold. The same shot loading in water produced tungsten EEC values of 2.1–4.4 mg W/L, levels that are not toxic under experimental conditions. Pure tungsten has not been shown to exhibit carcinogenic properties when ingested or embedded in animal tissues, but nickel, with which it is often alloyed, has known carcinogenicity. Given the large number of waterfowl that carry shot embedded in their body, it is advisable to screen lead shot substitutes for their carcinogenic potential through intra-muscular implantation

Flight Respiration and Energetics

We Use a Comparative Approach to Examine Some of the Physiological Traits that Make Flight Possible. Comparisons of Related Fliers and Runners Suggest that Fliers Generally Have Higher Aerobic Metabolic Capacities Than Runners But that the Difference is Highly Dependent on the Taxa Studied. the High Metabolic Rates of Fliers Relative to Runners, Especially in Insects, Are Correlated with High Locomotory Muscle Cycle Frequencies and Low Efficiencies of Conversion of Metabolic Power to Mechanical Power. We Examine Some Factors that Produce Variation in Flight Respiration and Energetics. Air Temperature Strongly Affects the Flight Metabolic Rote of Some Insects and Birds. Flight Speed Interacts with Flier Mass, So that Small Fliers Tend to Exhibit a J-Shaped Power Curve and Larger Fliers a U-Shaped Power Curve. as Body Size Increases, Mass-Specific Aerobic Flight Metabolism Decreases in Most Studies, But Mass-Specific Power Output is Constant or Increases, Leading to an Increase in Efficiency with Size. Intraspecific Studies Have Revealed Specific Genetically based Effects on Flight Metabolism and Power Output and Multiple Ecological Correlates of Flight Capabilities

Allometry of Kinematics and Energetics in Carpenter Bees (Xylocopa Varipuncta) Hovering in Variable-Density Gases

We Assessed the Energetic and Aerodynamic Limits of Hovering Flight in the Carpenter Bee Xylocopa Varipuncta. using Normoxic, Variable-Density Mixtures of O2, N2 and He, We Were Able to Elicit Maximal Hovering Performance and Aerodynamic Failure in the Majority of Bees Sampled. Bees Were Not Isometric Regarding Thorax Mass and Wing Area, Both of Which Were Disproportionately Lower in Heavier Individuals. the Minimal Gas Density Necessary for Hovering (MGD) Increased with Body Mass and Decreased with Relative Thoracic Muscle Mass. Only the Four Bees in Our Sample with the Highest Body Mass-Specific Thorax Masses Were Able to Hover in Pure Heliox. Wingbeat Frequency and Stroke Amplitude during Maximal Hovering Were Significantly Greater Than in Normodense Hovering, Increased Significantly with Body Mass during Normodense Hovering But Were Mass Independent during Maximal Hovering. Reserve Capacity for Wingbeat Frequency and Stroke Amplitude Decreased Significantly with Increasing Body Mass, Although Reserve Capacity in Stroke Amplitude (10-30%) Exceeded that of Wingbeat Frequency (0-8%). Stroke Plane Angle during Normodense Hovering Was Significantly Greater Than during Maximal Hovering, Whereas Body Angle Was Significantly Greater during Maximal Hovering Than during Normodense Hovering. Power Production during Normodense Hovering Was Significantly Less Than during Maximal Hovering. Metabolic Rates Were Significantly Greater during Maximal Hovering Than during Normodense Hovering and Were Inversely Related to Body Mass during Maximal and Normodense Hovering. Metabolic Reserve Capacity Averaged 34% and Was Independent of Body Mass. Muscle Efficiencies Were Slightly Higher during Normodense Hovering. the Allometry of Power Production, Power Reserve Capacity and Muscle Efficiency Were Dependent on the Assumed Coefficient of Drag (CD), with Significant Allometries Most Often at Lower Values of CD. Larger Bees Operate Near the Envelope of Maximal Performance Even in Normodense Hovering Due to Smaller Body Mass-Specific Flight Muscles and Limited Reserve Capacities for Kinematics and Power Production

Propagation of sausage soliton in the solar lower atmosphere observed by Hinode/SOT

Acoustic waves and pulses propagating from the solar photosphere upwards may quickly develop into shocks due to the rapid decrease of atmospheric density. However, if they propagate along a magnetic flux tube, then the nonlinear steepening may be balanced by tube dispersion effects. This may result in the formation of sausage soliton. The aim of this letter is to report an observational evidence of sausage soliton in the solar chromosphere. Time series of Ca II H line obtained at the solar limb with the Solar Optical Telescope (SOT) on the board of Hinode is analysed. Observations show an intensity blob, which propagates from 500 km to 1700 km above the solar surface with the mean apparent speed of 35 km s$^{-1}$. The speed is much higher than expected local sound speed, therefore the blob can not be a simple pressure pulse. The blob speed, length to width ratio and relative intensity correspond to slow sausage soliton propagating along a magnetic tube. The blob width is increased with height corresponding to the magnetic tube expansion in the stratified atmosphere. Propagation of the intensity blob can be the first observational evidence of slow sausage soliton in the solar atmosphere.Comment: 5 pages, 4 figures, accepted in MNRA

A high spatial resolution synchrotron Mössbauer study of the Tazewell IIICD and Esquel pallasite meteorites.

Metallic phases in the Tazewell IIICD iron and Esquel pallasite meteorites were examined using 57Fe synchrotron Mössbauer spectroscopy. Spatial resolution of ~10-20 μm was achieved, together with high throughput, enabling individual spectra to be recorded in less than 1 h. Spectra were recorded every 5-10 μm, allowing phase fractions and hyperfine parameters to be traced along transects of key microstructural features. The main focus of the study was the transitional region between kamacite and plessite, known as the "cloudy zone." Results confirm the presence of tetrataenite and antitaenite in the cloudy zone as its only components. However, both phases were also found in plessite, indicating that antitaenite is not restricted exclusively to the cloudy zone, as previously thought. The confirmation of paramagnetic antitaenite as the matrix phase of the cloudy zone contrasts with recent observations of a ferromagnetic matrix phase using X-ray photoemission electron spectroscopy. Possible explanations for the different results seen using these techniques are proposed.The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007 - 2013) / ERC Grant Agreement No. 320750

SU(3) family symmetry and neutrino bi-tri-maximal mixing

The observed large mixing angles in the lepton sector may be the first signal for the presence of a non-Abelian family symmetry. However, to obtain the significant differences between the mixing of the neutrino and charged fermion sectors, the vacuum expectation values involved in the breaking of such a symmetry in the two sectors must be misaligned. We investigate how this can be achieved in models with an SU(3) family symmetry consistent with an underlying GUT. We show that such misalignment can be achieved naturally via the see-saw mechanism. We construct a specific example in which the vacuum (mis)alignment is guaranteed by additional symmetries. This model generates a fermion mass structure consistent with all quark and lepton masses and mixing angles. Neutrino mixing is close to bi-tri-maximal mixing.Comment: References added; typos correcte

Micromagnetic simulations of first-order reversal curve (FORC) diagrams of framboidal greigite

Greigite is a sensitive environmental indicator and occurs commonly in nature as magnetostatically interacting framboids. Until now only the magnetic response of isolated non-interacting greigite particles have been modelled micromagnetically. We present here hysteresis and first-order reversal curve (FORC) simulations for framboidal greigite (Fe3S4), and compare results to those for isolated particles of a similar size. We demonstrate that these magnetostatic interactions alter significantly the framboid FORC response compared to isolated particles, which makes the magnetic response similar to that of much larger (multidomain) grains. We also demonstrate that framboidal signals plot in different regions of a FORC diagram, which facilitates differentiation between framboidal and isolated grain signals. Given that large greigite crystals are rarely observed in microscopy studies of natural samples, we suggest that identification of multidomain-like FORC signals in samples known to contain abundant greigite could be interpreted as evidence for framboidal greigite

Slow magnetoacoustic waves in coronal loops : EIT and TRACE

On May 13, 1998 the EIT (Extreme ultraviolet Imaging Telescope) on board of SoHO (Solar and Heliospheric Observatory) and TRACE (Transition Region And Coronal Explorer) instruments produced simultaneous high cadence image sequences of the same active region (AR 8218). TRACE achieved a 25 s cadence in the FeIX (171 Å) bandpass while EIT achieved a 15 s cadence (operating in "shutterless mode", SoHO JOP 80) in the FeXII (195 Å) bandpass. These high cadence observations in two complementary wavelengths have revealed the existence of weak transient disturbances in an extended coronal loop system. These propagating disturbances (PDs) seem to be a common phenomenon in this part of the active region. The disturbances originate from small scale brightenings at the footpoints of the loops and propagate along the loops. The projected propagation speeds roughly vary between 65 and 150 km s-1 for both instruments which is close to and below the expected sound speed in the coronal loops. The measured slow magnetoacoustic propagation speeds seem to suggest that the transients are sound (or slow) wave disturbances. This work differs from previous studies in the sense that it is based on a multi-wavelength observation of an entire loop bundle at high cadence by two EUV imagers. The observation of sound waves along the same path shows that they propagate along the same loop, suggesting that loops contain sharp temperature gradients and consist of either concentric shells or thin loop threads, at different temperatures