A temperature and emissivity separation algorithm for AdvancedSpaceborne Thermal Emission and Reflection Radiometer (ASTER)images

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) scanner on NASA's Earth Observing System (EOS)-AM1 satellite (launch scheduled for 1998) will collect five bands of thermal infrared (TIR) data with a noise equivalent temperature difference (NEΔT) of ⩽0.3 K to estimate surface temperatures and emissivity spectra, especially over land, where emissivities are not known in advance. Temperature/emissivity separation (TES) is difficult because there are five measurements but six unknowns. Various approaches have been used to constrain the extra degree of freedom. ASTER's TES algorithm hybridizes three established algorithms, first estimating the normalized emissivities and then calculating emissivity band ratios. An empirical relationship predicts the minimum emissivity from the spectral contrast of the ratioed values, permitting recovery of the emissivity spectrum. TES uses an iterative approach to remove reflected sky irradiance. Based on numerical simulation, TES should be able to recover temperatures within about ±1.5 K and emissivities within about ±0.015. Validation using airborne simulator images taken over playas and ponds in central Nevada demonstrates that, with proper atmospheric compensation, it is possible to meet the theoretical expectations. The main sources of uncertainty in the output temperature and emissivity images are the empirical relationship between emissivity values and spectral contrast, compensation for reflected sky irradiance, and ASTER's precision, calibration, and atmospheric compensation     

Phenomenological modeling of the response of a dense colloidal suspension under dynamic squeezing flow

The split Hopkinson pressure bar experimental technique is used to evaluate the squeezing flow response of a concentrated, discontinuously thickening colloidal suspension of spherical silica particles loaded at high stresses/strain rates. These results provide insight into the transitional behavior of these materials, as well as the post-transitional response under compressive loading. A method of analyzing the strain and strain rate dependent behavior is presented to identify modes of material response (viscous, elastic, etc.). Experimental results are presented as stress–strain–strain rate plots and a surface fitting approach is used to develop a phenomenological model describing the overall response. From this model, it is possible to identify regions of elastic and viscous behavior using a gradient analysis approach. It was found that, after an initial period of viscous deformation, the suspension behaves like a viscoelastic material – this regime corresponds well with transition in which large clusters of particles percolate. This is followed by a third, viscous regime in which the material undergoes viscous deformation. At the highest stresses, a plateau region of plastic deformation has been identified. This approach and the conditions under which it may be applied are described in detail in the paper.     

Solvable base change and Rankin-Selberg convolutions

Let π and π′ be unitary automorphic cuspidal representations of GL_n(A_E) and GL_m(A_F), and let E and F be solvable Galois extensions of Q of degrees ? and ?′, respectively. Using the fact that the automorphic induction and base change maps exist for E and F, and assuming an invariance condition under the actions of the Galois groups, we attach to the pair(π, π′) a Rankin-Selberg L-function L(s, π×E,Fπ′) for which we prove a prime number theorem. This gives a method for comparing two representations that could be defined over completely different extensions, and the main results give a measure of how many cuspidal components the two representations π and π′ have in common when automorphically induced down to the rational numbers. The proof uses the structure of the Galois group of the composite extension EF and the character groups attached to the fields via class field theory. The second main theorem also gives an indication of when the base change of π up to the composite extension EF remains cuspidal.     

Measured backscatter from conductive thin films deposited onfibrous substrates

The functional dependence of the electromagnetic backscatter by thin, straight, dielectric fibers with metallic coatings was measured as a function of coating thickness and conductivity at a wavelength of 0.86 cm (35 GHz). Cu and Ni coatings were applied to fibrous glass substrates (having a nominal diameter of 5.50 μm) using an evaporative process. The thicknesses of the thin films were directly measured by scanning electron microscopy (SEM) and ranged from 0.02 to 0.70 μm. Measurements were conducted using single fibers. Measured quantities agreed well with calculations based on previously developed theory     

The role of cleaning conditions and epitaxial layer structure on reliability of Sc2O3 and MgO passivation on AlGaN/GaN HEMTS

The effect of layer structure (GaN versus AlGaN cap) and cleaning procedure prior to Sc₂O₃ or MgO deposition at 100 °C were examined for their effects on the long-term bias-stress stability of AlGaN/GaN high electron mobility transistors (HEMTs). Surface cleaning by itself was not sufficient to prevent current collapse in the devices. The forward and reverse gate leakage currents were decreased under most conditions upon deposition of the oxide passivation layers. After ≈13 h of bias-stressing, the MgO-passivated HEMTs retain 90% their initial drain–source current. The Sc₂O₃-passivated devices retained 80% recovery of the current under the same conditions.     

Accurate non-invasive determination of pKa of surface functionalised ion exchange monoliths using capacitively coupled contactless conductivity detection

The use of on-column capacitively coupled contactless conductivity detection for the accurate non-invasive visualisation of the pH dependence of covalently bound boronic acid groups within a monolithic polymeric capillary column is demonstrated.     

Simulating prescribed particle densities in the grand canonical ensemble using iterative algorithms

We present two efficient iterative Monte Carlo algorithms in the grand canonical ensemble with which the chemical potentials corresponding to prescribed (targeted) partial densities can be determined. The first algorithm works by always using the targeted densities in the kT log(rho(i)) (ideal gas) terms and updating the excess chemical potentials from the previous iteration. The second algorithm extrapolates the chemical potentials in the next iteration from the results of the previous iteration using a first order series expansion of the densities. The coefficients of the series, the derivatives of the densities with respect to the chemical potentials, are obtained from the simulations by fluctuation formulas. The convergence of this procedure is shown for the examples of a homogeneous Lennard-Jones mixture and a NaCl-CaCl(2) electrolyte mixture in the primitive model. The methods are quite robust under the conditions investigated. The first algorithm is less sensitive to initial conditions.