Exact and semiclassical approach to a class of singular integral operators arising in fluid mechanics and quantum field theory

A class of singular integral operators, encompassing two physically relevant cases arising in perturbative QCD and in classical fluid dynamics, is presented and analyzed. It is shown that three special values of the parameters allow for an exact eigenfunction expansion; these can be associated to Riemannian symmetric spaces of rank one with positive, negative or vanishing curvature. For all other cases an accurate semiclassical approximation is derived, based on the identification of the operators with a peculiar Schroedinger-like operator.Comment: 12 pages, 1 figure, amslatex, bibtex (added missing label eq.11

Root Senescence in Red Clover (\u3cem\u3eTrifolium Pratense\u3c/em\u3e L.)

Legume root systems form a mosaic of living, ageing and dead roots and nodules. The balance between these stages alters during plant development. Stressful events (drought, temperature change, reduced carbon supply, etc.) disturb the balance (Butler et al., 1959). Effects of root and nodule death on soil structure, composition and leaching and on plant persistency are understood poorly. Plants with differing senescence patterns are useful tools to study these effects. Molecular studies of root senescence need detailed knowledge of the process and timing of root senescence and death. Biochemical and histochemical markers of senescence were used to generate preliminary results of the effects of reduced carbon input, temporary (by defoliation, D) or permanent (by defoliation and shading, DS) on red clover shoot survival and root death

Reinterpreting aircraft measurements in anisotropic scaling turbulence

Due to both systematic and turbulent induced vertical fluctuations, the interpretation of atmospheric aircraft measurements requires a theory of turbulence. Until now virtually all the relevant theories have been isotropic or "quasi isotropic" in the sense that their exponents are the same in all directions. However almost all the available data on the vertical structure shows that it is scaling but with exponents different from the horizontal: the turbulence is scaling but anisotropic. In this paper, we show how such turbulence can lead to spurious breaks in the scaling and to the spurious appearance of the vertical scaling exponent at large horizontal lags. <br></br> We demonstrate this using 16 legs of Gulfstream 4 aircraft near the top of the troposphere following isobars each between 500 and 3200 km in length. First we show that over wide ranges of scale, the horizontal spectra of the aircraft altitude are nearly <i>k</i><sup>-5/3</sup>. In addition, we show that the altitude and pressure fluctuations along these fractal trajectories have a high degree of coherence with the measured wind (especially with its longitudinal component). There is also a strong phase relation between the altitude, pressure and wind fluctuations; for scales less than ≈40 km (on average) the wind fluctuations lead the pressure and altitude, whereas for larger scales, the pressure fluctuations leads the wind. At the same transition scale, there is a break in the wind spectrum which we argue is caused by the aircraft starting to accurately follow isobars at the larger scales. In comparison, the temperature and humidity have low coherencies and phases and there are no apparent scale breaks, reinforcing the hypothesis that it is the aircraft trajectory that is causally linked to the scale breaks in the wind measurements. <br></br> Using spectra and structure functions for the wind, we then estimate their exponents (β, <i>H</i>) at small (5/3, 1/3) and large scales (2.4, 0.73). The latter being very close to those estimated by drop sondes (2.4, 0.75) in the vertical direction. In addition, for each leg we estimate the energy flux, the sphero-scale and the critical transition scale. The latter varies quite widely from scales of kilometers to greater than several hundred kilometers. The overall conclusion is that up to the critical scale, the aircraft follows a fractal trajectory which may increase the intermittency of the measurements, but doesn't strongly affect the scaling exponents whereas for scales larger than the critical scale, the aircraft follows isobars whose exponents are different from those along isoheights (and equal to the vertical exponent perpendicular to the isoheights). We bolster this interpretation by considering the absolute slopes (|Δ<i>z</i>/Δ<i>x</i>|) of the aircraft as a function of lag Δ<i>x</i> and of scale invariant lag Δ<i>x</i>/Δ<i>z<sup>1/H<sub>z</sub></sup></i>. <br></br> We then revisit four earlier aircraft campaigns including GASP and MOZAIC showing that they all have nearly identical transitions and can thus be easily explained by the proposed combination of altitude/wind in an anisotropic but scaling turbulence. Finally, we argue that this reinterpretation in terms of wide range anisotropic scaling is compatible with atmospheric phenomenology including convection

Haloe Antarctic observations in the spring of 1991

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95167/1/grl6630.pd

Inserting Components into Geometries Constructed onto a Non-Standard Substrate for Electronics Packaging

Additive manufacturing (AM) has matured from its initial concept as a prototyping technique to an industrial manufacturing process. Consequently, AM processes must meet relevant standards for an increasing number of applications. Here, we investigate inserting components into geometries constructed onto a silicon nitride substrate, using stereolithography (SLA), for the purpose of electronics packaging. Compared to conventional processes, SLA avoids high temperatures and stresses while permitting much greater flexibility to arrange components in three dimensions. This facilitates an increased feature density and the construction of packages for use in complex spaces. A characteristic of interest to this application, is the SLA material-substrate interaction and the resulting quality of adhesion. The adhesion mechanism between SLA and silicon nitride is investigated and substantially enhanced by a pre-treatment process. A process for then inserting large and complex geometries and components into the SLA build process is identified and compliance of the product with relevant standards is reviewed.Mechanical Engineerin

Small scale structure and mixing at the edge of the Antarctic vortex

Small scale correlations and patterns in the chemical tracers measured from the NASA ER-2 aircraft in the 1987 AAOE campaign can be used to investigate the structure of the edge of the polar vortex and the chemically perturbed region within it. Examples of several types of transport processes can be found in the data. Since ClO and O3 have similar vertical gradients and opposite horizontal gradients near the chemically perturbed region, the correlation between ClO and O3 can be used to study the extent of horizontal transport at the edge of the chemically perturbed region. Horizontal transport dominates the correlation for a latitude band up to 4 degrees on each side of the boundary. This implies a transition zone containing a substantial fraction of the mass of the total polar vortex. Similar horizontal transport can be seen in other tracers as well. It has not been possible to distinguish reversible transport from irreversible mixing. One manifestation of the horizontal transport is that the edge of the chemically perturbed region is often layered rather than a vertical curtain. This can be seen from the frequent reversed vertical gradients of NO2, caused by air with high NO2 overlapping layers with lower mixing ratios. Water and NO2 are positively correlated within the chemically perturbed region. This is the opposite sign to the correlation in the unperturbed stratosphere. The extent of the positive correlation is too great to be attributed solely to horizontal mixing. Instead, it is hypothesized that dehydration and descent are closely connected on a small scale, possibly due to radiative cooling of the clouds that also cause ice to fall to lower altitudes

Root Senescence in Red Clover (\u3cem\u3eTrifolium Pratense\u3c/em\u3e L.)

Legume root systems form a mosaic of living, ageing and dead roots and nodules. The balance between these stages alters during plant development. Stressful events (drought, temperature change, reduced carbon supply, etc.) disturb the balance (Butler et al., 1959). Effects of root and nodule death on soil structure, composition and leaching and on plant persistency are understood poorly. Plants with differing senescence patterns are useful tools to study these effects. Molecular studies of root senescence need detailed knowledge of the process and timing of root senescence and death. Biochemical and histochemical markers of senescence were used to generate preliminary results of the effects of reduced carbon input, temporary (by defoliation, D) or permanent (by defoliation and shading, DS) on red clover shoot survival and root death

Robo-Soar: An Integration of External Interaction, Planning, and Learning using Soar

This chapter reports progress in extending the Soar architecture to tasks that involve interaction with external environments. The tasks are performed using a Puma arm and a camera in a system called Robo-Soar. The tasks require the integration of a variety of capabilities including problem solving with incomplete knowledge, reactivity, planning, guidance from external advice, and learning to improve the efficiency and correctness of problem solving. All of these capabilities are achieved without the addition of special purpose modules or subsystems to Soar

Learning in Tele-autonomous Systems using Soar

Robo-Soar is a high-level robot arm control system implemented in Soar. Robo-Soar learns to perform simple block manipulation tasks using advice from a human. Following learning, the system is able to perform similar tasks without external guidance. Robo-Soar corrects its knowledge by accepting advice about relevance of features in its domain, using a unique integration of analytic and empirical learning techniques

Diffusion mechanism of Zn in InP and GaP from first principles

The diffusion mechanism of Zn in GaP and InP has been investigated using first-principles computational methods. It is found that the kickout mechanism is the favored diffusion process under all doping conditions for InP, and under all except n-type conditions for GaP. In n-type GaP the dissociative mechanism is probable. In both p-type GaP and InP, the diffusing species is found to be Zni+2. The activation energy for the kickout process is 2.49 eV in GaP and 1.60 eV in InP, and therefore unintentional diffusion of Zn should be a larger concern in InP than in GaP. The dependence of the activation energy both on the doping conditions of the material and on the stoichiometry is explained, and found to be in qualitative agreement with the experimentally observed dependencies. The calculated activation energies agree reasonably with experimental data, assuming that the region from which Zn diffuses is p type. Explanations are also found as to why Zn tends to accumulate at pn junctions in InP and to why a relatively low fraction of Zn is found on substitutional sites in InP