On air temperature fluctuations immediately above a glacier surface

Developing remote sensing techniques for measuring meteorological parameters in surface layers of snow field

Atmospheric muon background in the ANTARES detector

An evaluation of the background due to atmospheric muons in the ANTARES high energy neutrino telescope is presented. Two different codes for atmospheric shower simulation have been used. Results from comparisons between these codes at sea level and detector level are presented. The first results on the capability of ANTARES to reject this class of background are given.Comment: 4 pages, 4 figures, To appear in Proceedings of the 29th International Cosmic Ray Conference (ICRC 2005), Pune, India, 3 - 10 Aug 200

Technological change and productivity growth in the air transport industry

The progress of the civil air transport industry in the United States was examined in the light of a proposal of Enos who, after examining the growth of the petroleum industry, divided that phenomenon into two phases, the alpha and the beta; that is, the invention, first development and production, and the improvement phase. The civil air transport industry developed along similar lines with the technological progress coming in waves; each wave encompassing several new technological advances while retaining the best of the old ones. At the same time the productivity of the transport aircraft as expressed by the product of the aircraft velocity and the passenger capacity increased sufficiently to allow the direct operating cost in cents per passenger mile to continually decrease with each successive aircraft development

High-Resolution Crystal Truncation Rod Scattering: Application to Ultrathin Layers and Buried Interfaces

In crystalline materials, the presence of surfaces or interfaces gives rise to crystal truncation rods (CTRs) in their X‐ray diffraction patterns. While structural properties related to the bulk of a crystal are contained in the intensity and position of Bragg peaks in X‐ray diffraction, CTRs carry detailed information about the atomic structure at the interface. Developments in synchrotron X‐ray sources, instrumentation, and analysis procedures have made CTR measurements into extremely powerful tools to study atomic reconstructions and relaxations occurring in a wide variety of interfacial systems, with relevance to chemical and electronic functionalities. In this review, an overview of the use of CTRs in the study of atomic structure at interfaces is provided. The basic theory, measurement, and analysis of CTRs are covered and applications from the literature are highlighted. Illustrative examples include studies of complex oxide thin films and multilayers

Compressive and Noncompressive Power Spectral Density Estimation from Periodic Nonuniform Samples

This paper presents a novel power spectral density estimation technique for band-limited, wide-sense stationary signals from sub-Nyquist sampled data. The technique employs multi-coset sampling and incorporates the advantages of compressed sensing (CS) when the power spectrum is sparse, but applies to sparse and nonsparse power spectra alike. The estimates are consistent piecewise constant approximations whose resolutions (width of the piecewise constant segments) are controlled by the periodicity of the multi-coset sampling. We show that compressive estimates exhibit better tradeoffs among the estimator's resolution, system complexity, and average sampling rate compared to their noncompressive counterparts. For suitable sampling patterns, noncompressive estimates are obtained as least squares solutions. Because of the non-negativity of power spectra, compressive estimates can be computed by seeking non-negative least squares solutions (provided appropriate sampling patterns exist) instead of using standard CS recovery algorithms. This flexibility suggests a reduction in computational overhead for systems estimating both sparse and nonsparse power spectra because one algorithm can be used to compute both compressive and noncompressive estimates.Comment: 26 pages, single spaced, 9 figure

Observations of ozone production in a dissipating tropical convective cell during TC4

From 13 July–9 August 2007, 25 ozonesondes were launched from Las Tablas, Panama as part of the Tropical Composition, Cloud, and Climate Coupling (TC4) mission. On 5 August, a strong convective cell formed in the Gulf of Panama. World Wide Lightning Location Network (WWLLN) data indicated 563 flashes (09:00–17:00 UTC) in the Gulf. NO2 data from the Ozone Monitoring Instrument (OMI) show enhancements, suggesting lightning production of NOx. At 15:05 UTC, an ozonesonde ascended into the southern edge of the now dissipating convective cell as it moved west across the Azuero Peninsula. The balloon oscillated from 2.5–5.1 km five times (15:12–17:00 UTC), providing a unique examination of ozone (O3) photochemistry on the edge of a convective cell. Ozone increased at a rate of 1.6–4.6 ppbv/hr between the first and last ascent, resulting cell wide in an increase of (2.1–2.5)×106 moles of O3. This estimate agrees to within a factor of two of our estimates of photochemical lightning O3 production from the WWLLN flashes, from the radar-inferred lightning flash data, and from the OMI NO2 data (1.2, 1.0, and 1.7×106 moles, respectively), though all estimates have large uncertainties. Examination of DC-8 in situ and lidar O3 data gathered around the Gulf that day suggests 70–97% of the O3 change occurred in 2.5–5.1 km layer. A photochemical box model initialized with nearby TC4 aircraft trace gas data suggests these O3 production rates are possible with our present understanding of photochemistry

Ground-runup tests of acoustically treated inlets and fan ducts

Ground performance tests on noise intensity of turbofan engine ducts modified by acoustic lining

Relativistic Winds from Compact Gamma-Ray Sources: II. Pair Loading and Radiative Acceleration in Gamma-ray Bursts

We consider the effects of rapid pair creation by an intense pulse of gamma-rays propagating ahead of a relativistic shock. Side-scattered photons colliding with the main gamma-ray beam amplify the density of scattering charges. The acceleration rate of the pair-loaded medium is calculated, and its limiting bulk Lorentz factor related to the spectrum and compactness of the photon source. One obtains, as a result, a definite prediction for the relative inertia in baryons and pairs. The deceleration of a relativistic shock in the moving medium, and the resulting synchrotron emissivity, are compared with existing calculations for a static medium. The radiative efficiency is increased dramatically by pair loading. When the initial ambient density exceeds a critical value, the scattering depth traversed by the main gamma-ray pulse rises above unity, and the pulse is broadened. These considerations place significant constraints on burst progenitors: a pre-burst mass loss rate exceeding 10^{-5} M_\odot per year is difficult to reconcile with individual pulses narrower than 10 s, unless the radiative efficiency is low. An anisotropic gamma-ray flux (on an angular scale \Gamma^{-1} or larger) drives a large velocity shear that greatly increases the energy in the seed magnetic field forward of the propagating shock.Comment: 19 pp., LaTeX (aaspp4.sty), revised 12/23/99, Ap. J. in press; summary section added and several minor improvements in presentatio