Breadboard linear array scan imager using LSI solid-state technology

The performance of large scale integration photodiode arrays in a linear array scan (pushbroom) breadboard was evaluated for application to multispectral remote sensing of the earth's resources. The technical approach, implementation, and test results of the program are described. Several self scanned linear array visible photodetector focal plane arrays were fabricated and evaluated in an optical bench configuration. A 1728-detector array operating in four bands (0.5 - 1.1 micrometer) was evaluated for noise, spectral response, dynamic range, crosstalk, MTF, noise equivalent irradiance, linearity, and image quality. Other results include image artifact data, temporal characteristics, radiometric accuracy, calibration experience, chip alignment, and array fabrication experience. Special studies and experimentation were included in long array fabrication and real-time image processing for low-cost ground stations, including the use of computer image processing. High quality images were produced and all objectives of the program were attained

Coupling nonpolar and polar solvation free energies in implicit solvent models

Recent studies on the solvation of atomistic and nanoscale solutes indicate that a strong coupling exists between the hydrophobic, dispersion, and electrostatic contributions to the solvation free energy, a facet not considered in current implicit solvent models. We suggest a theoretical formalism which accounts for coupling by minimizing the Gibbs free energy of the solvent with respect to a solvent volume exclusion function. The resulting differential equation is similar to the Laplace-Young equation for the geometrical description of capillary interfaces, but is extended to microscopic scales by explicitly considering curvature corrections as well as dispersion and electrostatic contributions. Unlike existing implicit solvent approaches, the solvent accessible surface is an output of our model. The presented formalism is illustrated on spherically or cylindrically symmetrical systems of neutral or charged solutes on different length scales. The results are in agreement with computer simulations and, most importantly, demonstrate that our method captures the strong sensitivity of solvent expulsion and dewetting to the particular form of the solvent-solute interactions.Comment: accpted in J. Chem. Phy

Oxidation of Zr-2.5 Nb Nuclear Reactor Pressure Tubes A New Model

The corrosion and associated deuterium (D) uptake of Zr alloy nuclear reactor pressure tubes have been studied for over 40 years. Zircaloy tubes exhibit rapid D ingress after a period of in-reactor exposure, and have been replaced with tubes fabricated from the more resistant Zr-2.5 wt % Nb alloy. Recently, however, a small percentage of Zr-2.5 Nb tubes have been found to contain high D contents. There is currently no clear understanding of the mechanism for this increased D uptake, and concern exists that an increasing number of high-D tubes will develop with time. A new model for Zr-2.5 Nb corrosion is presented in this paper. The rate of corrosion is shown to be dependent on the rate of transformation of the protective inner oxide layer (closer to the metal) to a porous outer layer. The mechanism of this transformation is not known and should be the subject of future investigations. It is assumed in the model that zirconia chemically dissolves into the solution at the pore bottom. The rate of this dissolution reaction depends on the local pH, which increases if there is a buildup of deuteroxyl ions generated in the cathodic part of the Zr corrosion reaction. A mathematical description of this model, containing several parameters with unknown values, is presented. Assigning certain values to these parameters results in predictions of oxide formation (and thus D buildup) that correspond well with observations.Support of this work by the Atomic Energy Control Board under AECB project no. 2.349.1 is gratefully acknowledged

Massive spinor fields in flat spacetimes with non-trivial topology

The vacuum expectation value of the stress-energy tensor is calculated for spin $1\over 2$ massive fields in several multiply connected flat spacetimes. We examine the physical effects of topology on manifolds such as $R^3 \times S^1$, $R^2\times T^2$, $R^1 \times T^3$, the Mobius strip and the Klein bottle. We find that the spinor vacuum stress tensor has the opposite sign to, and twice the magnitude of, the scalar tensor in orientable manifolds. Extending the above considerations to the case of Misner spacetime, we calculate the vacuum expectation value of spinor stress-energy tensor in this space and discuss its implications for the chronology protection conjecture.Comment: 18 pages, Some of the equations in section VI as well as typographical errors corrected, 5 figures, Revtex

"Marginal pinching" in soap films

We discuss the behaviour of a thin soap film facing a frame element: the pressure in the Plateau border around the frame is lower than the film pressure, and the film thins out over a certain distance lambda(t), due to the formation of a well-localized pinched region of thickness h(t) and extension w(t). We construct a hydrodynamic theory for this thinning process, assuming a constant surface tension: Marangoni effects are probably important only at late stages, where instabilitites set in. We find lambda(t) ~ t^{1/4}, and for the pinch dimensions h(t) ~ t^{-1/2}$ and w(t) ~ t^{-1/4}. These results may play a useful role for the discussion of later instabilitites leading to a global film thinning and drainage, as first discussed by K. Mysels under the name ``marginal regeneration''.Comment: 7 pages, 2 figure

Connections and dynamical trajectories in generalised Newton-Cartan gravity I. An intrinsic view

The "metric" structure of nonrelativistic spacetimes consists of a one-form (the absolute clock) whose kernel is endowed with a positive-definite metric. Contrarily to the relativistic case, the metric structure and the torsion do not determine a unique Galilean (i.e. compatible) connection. This subtlety is intimately related to the fact that the timelike part of the torsion is proportional to the exterior derivative of the absolute clock. When the latter is not closed, torsionfreeness and metric-compatibility are thus mutually exclusive. We will explore generalisations of Galilean connections along the two corresponding alternative roads in a series of papers. In the present one, we focus on compatible connections and investigate the equivalence problem (i.e. the search for the necessary data allowing to uniquely determine connections) in the torsionfree and torsional cases. More precisely, we characterise the affine structure of the spaces of such connections and display the associated model vector spaces. In contrast with the relativistic case, the metric structure does not single out a privileged origin for the space of metric-compatible connections. In our construction, the role of the Levi-Civita connection is played by a whole class of privileged origins, the so-called torsional Newton-Cartan (TNC) geometries recently investigated in the literature. Finally, we discuss a generalisation of Newtonian connections to the torsional case.Comment: 79 pages, 7 figures; v2: added material on affine structure of connection space, former Section 4 postponed to 3rd paper of the serie

Stress-Induced Angular Momentum Quenching in MgO: Fe\u3csup\u3e2+\u3c/sup\u3e as Observed by Mössbauer Spectroscopy

Under the influence of a suitable uniaxial stress, the quenching of the electronic angular momentum of the low-lying threefold degenerate Γ5g level of Fe2+ in cubic MgO has been observed by Mössbauer spectroscopy. The result is consistent with Ham\u27s model for the appearance of a quadrupole doublet at low temperatures. A value for the strain coefficient of Fe2+ in MgO has been obtained: G11=585 cm-1

Taylor dispersion of gyrotactic swimming micro-organisms in a linear flow

The theory of generalized Taylor dispersion for suspensions of Brownian particles is developed to study the dispersion of gyrotactic swimming micro-organisms in a linear shear flow. Such creatures are bottom-heavy and experience a gravitational torque which acts to right them when they are tipped away from the vertical. They also suffer a net viscous torque in the presence of a local vorticity field. The orientation of the cells is intrinsically random but the balance of the two torques results in a bias toward a preferred swimming direction. The micro-organisms are sufficiently large that Brownian motion is negligible but their random swimming across streamlines results in a mean velocity together with diffusion. As an example, we consider the case of vertical shear flow and calculate the diffusion coefficients for a suspension of the alga <i>Chlamydomonas nivalis</i>. This rational derivation is compared with earlier approximations for the diffusivity

International capital mobility in an era of globalisation: adding a political dimension to the 'Feldstein–Horioka Puzzle'

The debate about the scope of feasible policy-making in an era of globalisation continues to be set within the context of an assumption that national capital markets are now perfectly integrated at the international level. However, the empirical evidence on international capital mobility contradicts such an assumption. As a consequence, a significant puzzle remains. Why is it, in a world in which the observed pattern of capital flows is indicative of a far from globalised reality, that public policy continues to be constructed in line with more extreme variants of the globalisation hypothesis? I attempt to solve this puzzle by arguing that ideas about global capital market integration have an independent causal impact on political outcomes which extends beyond that which can be attributed to the extent of their actual integration

Hodge Dual for Soldered Bundles

In order to account for all possible contractions allowed by the presence of the solder form, a generalized Hodge dual is defined for the case of soldered bundles. Although for curvature the generalized dual coincides with the usual one, for torsion it gives a completely new dual definition. Starting from the standard form of a gauge lagrangian for the translation group, the generalized Hodge dual yields precisely the lagrangian of the teleparallel equivalent of general relativity, and consequently also the Einstein-Hilbert lagrangian of general relativity.Comment: 8 pages, no figures. Accepted for publication in Journal of Physics