Improvements of cloud particle sizing with a 2D-Grey probe

The potential of the 2D-Grey optical array probe (OAP) (with 10-μm resolution) to determine cloud microphysical properties is studied. Systematic test measurements with a spinning glass disk with sample spots of various sizes between 50 and 500 μm in diameter were conducted. These measurements show that the particle image diameter increases considerably if the particle crosses the illuminating laser beam at increasing distance from the object plane. Eventually, shadow images of the smaller spots lose even their circular image shape and appear fragmented. A method is proposed to improve the estimation of the nominal particle size of droplets from the recorded image by exploiting the four available shadow (grey) levels. Laboratory tests show that spherical particles from 50 to 500 μm in diameter can be properly sized with an rms uncertainty of less than 6. After discussion of the concept of depth of field in OAPs, a definition for the 2D-Grey probe is presented that is consistent with the standard definition for the 2D-C probe. The authors' measurements show the depth of field of the 2D-Grey probe to be three times larger than the value conventionally assumed for the 2D-C probe for which similar corrections have been recently discussed in the literature. Finally, the impact of these findings on particle size distribution for in situ measurements is discussed

Activation Energy of Metastable Amorphous Ge2Sb2Te5 from Room Temperature to Melt

Resistivity of metastable amorphous Ge2Sb2Te5 (GST) measured at device level show an exponential decline with temperature matching with the steady-state thin-film resistivity measured at 858 K (melting temperature). This suggests that the free carrier activation mechanisms form a continuum in a large temperature scale (300 K - 858 K) and the metastable amorphous phase can be treated as a super-cooled liquid. The effective activation energy calculated using the resistivity versus temperature data follow a parabolic behavior, with a room temperature value of 333 meV, peaking to ~377 meV at ~465 K and reaching zero at ~930 K, using a reference activation energy of 111 meV (3kBT/2) at melt. Amorphous GST is expected to behave as a p-type semiconductor at Tmelt ~ 858 K and transitions from the semiconducting-liquid phase to the metallic-liquid phase at ~ 930 K at equilibrium. The simultaneous Seebeck (S) and resistivity versus temperature measurements of amorphous-fcc mixed-phase GST thin-films show linear S-T trends that meet S = 0 at 0 K, consistent with degenerate semiconductors, and the dS/dT and room temperature activation energy show a linear correlation. The single-crystal fcc is calculated to have dS/dT = 0.153 {\mu}V/K for an activation energy of zero and a Fermi level 0.16 eV below the valance band edge.Comment: 5 pages, 5 figure

Sea surface freshwater flux estimates from GECCO, HOAPS and NCEP

Surface net freshwater flux fields, estimated from the GECCO ocean state estimation effort over the 50 yr period 1951-2001, are compared to purely satellite-based HOAPS freshwater flux estimates and to the NCEP atmospheric re-analysis net surface freshwater flux fields to assess the quality of all flux products and to improve our understanding of the time-mean surface freshwater flux distribution as well as its temporal variability. Surface flux fields are adjusted by the GECCO state estimation procedure together with initial temperature and salinity conditions so that the model simulation becomes consistent with ocean observations. The entirely independent HOAPS net surface freshwater flux fields result from the difference between SSM/I based precipitation estimates and fields of evaporation resulting from a bulk aerodynamic approach using SSM/I data and the Pathfinder SST. All three products agree well on a global scale. However, overall GECCO seems to have moved away from the NCEP/NCAR first guess surface fluxes and is often closer to the HOAPS data set. This holds for the time mean as well as for the seasonal cycle

Structured matrices, continued fractions, and root localization of polynomials

We give a detailed account of various connections between several classes of objects: Hankel, Hurwitz, Toeplitz, Vandermonde and other structured matrices, Stietjes and Jacobi-type continued fractions, Cauchy indices, moment problems, total positivity, and root localization of univariate polynomials. Along with a survey of many classical facts, we provide a number of new results.Comment: 79 pages; new material added to the Introductio

Evaluation of HOAPS-3 ocean surface freshwater flux components

Today, latent heat flux and precipitation over the global ocean surface can be determined from microwave satellite data as a basis for estimating the related fields of the ocean surface freshwater flux. The Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data (HOAPS) is the only generally available satellite-based dataset with consistently derived global fields of both evaporation and precipitation and hence of freshwater flux for the period 1987–2005. This paper presents a comparison of the evaporation E, precipitation P, and the resulting freshwater flux E − P in HOAPS with recently available reference datasets from reanalysis and other satellite observation projects as well as in situ ship measurements. In addition, the humidity and wind speed input parameters for the evaporation are examined to identify sources for differences between the datasets. Results show that the general climatological patterns are reproduced by all datasets. Global mean time series often agree within about 10% of the individual products, while locally larger deviations may be found for all parameters. HOAPS often agrees better with the other satellite-derived datasets than with the in situ or the reanalysis data. The agreement usually improves in regions of good in situ sampling statistics. The biggest deviations of the evaporation parameter result from differences in the near-surface humidity estimates. The precipitation datasets exhibit large differences in highly variable regimes with the largest absolute differences in the ITCZ and the largest relative biases in the extratropical storm-track regions. The resulting freshwater flux estimates exhibit distinct differences in terms of global averages as well as regional biases. In comparison with long-term mean global river runoff data, the ocean surface freshwater balance is not closed by any of the compared fields. The datasets exhibit a positive bias in E − P of 0.2–0.5 mm day−1, which is on the order of 10% of the evaporation and precipitation estimates

Suppression of thermoelectric Thomson effect in silicon microwires under large electrical bias and implications for phase-change memory devices

We have observed how thermoelectric effects that result in asymmetric melting of silicon wires are suppressed for increasing electric current density (J). The experimental results are investigated using numerical modeling of the self-heating process, which elucidates the relative contributions of the asymmetric thermoelectric Thomson heat (∼J) and symmetric Joule heating (∼J2) that lead to symmetric heating for higher current levels. These results are applied in modeling of the self-heating process in phase-change memory devices. While, phase-change memory devices show a clearly preferred operation polarity due to thermoelectric effects, nearly symmetric operation can be achieved with higher amplitude and shorter current pulses, which can lead to design of improved polarity-invariant memory circuitry. © 2014 AIP Publishing LLC

Multispectral plasmonic structures using native aluminum oxide and aluminum

We report the use of native aluminum oxide to fabricate periodic metal-insulator-metal resonators with simultaneous resonances in the visible and IR wavelengths. The cavity size is in the order of λ3/25000 in the NIR. © 2017 OSA

All-aluminum hierarchical plasmonic surfaces in the infrared

All-Aluminum metal-insulator-metal resonator structures withmultiple metal-insulator stacks showing resonances in the mid-infrared(MIR) are fabricated. Ultrathin native Al2O3 is used as the insulator layersenabling simple fabrication of the resonator structures. The structures withtwo oxide layers exhibit two distinct resonances in the MIR. Simulation ofthese structures shows confinement of magnetic field to the thicker bottomoxide at the shorter wavelength resonance and to the thinner top oxide at theother resonance. Simulations of higher order hierarchical structures with 3 and 4 oxide layers show multispectral response with precise control of theoxide thicknesses. The studied structures show great potential for IRapplications that require durability and multispectral characteristics. © 2016 Optical Society of America