1,742 research outputs found
Conjugacy in VLF Emissions
VLF emissions observed simultaneously in opposite magnetic hemispheres of the earth often show marked similarities. The correlation is best when the receivers are close to the opposite ends of a magnetic line of force. Echoing emissions show the same travel times as associated whistlers, indicating that they travel over the same discrete paths. Conjugacy in VLF emissions is observed most commonly with periodic and quasi-periodic emissions which appear most frequently in the 1 to 10 kc/s range. Polar chorus, in the range 500 cps to 1000 cps, and auroral hiss, appearing above 4 kc/s, are less likely to be observed simultaneously at conjugate points. "Periodic" emissions appear alternately in opposite hemispheres and may or may not show dispersion. Their similarity in strength and spectral shape as observed at conjugate points indicates that they are produced by a mechanism that is equally effective in both directions. It has been suggested that the transverse resonance instability operating with trapped electrons at the top of the path may account for periodic emissions. Quasi-periodic (QP) emissions (also called long-period pulsations) on the other hand appear approximately in-phase at conjugate points, suggesting modulation of the emission process by an external agency, such as hydromagnetic waves. In some cases, QP emissions are found to consist of two bands of periodic emissions that interact in such a way as to account for the observed modulation of intensity and spectral shape. Conjugate VLF emission phenomena show promise of providing new data on energetic particle streams and on the properties of the ambient propagation medium
Experiments A17 /OGO 1/ and B17 /OGO 3/ Final report, 16 Feb. 1962 - 30 Jun. 1968
VLF experiments flown on OGO 1 /A17/ and OGO 3 /B17/ including orbits and attitudes of both satellite
Modelling nitrogen dynamics at Lochnagar, N.E. Scotland.
International audienceControls on nitrate leaching from upland moorland catchments are not yet fully understood and yet, despite agreements on emission reductions, increased surface water nitrate concentrations may affect significantly the acidity status of these waters in the future. At Lochnagar, an upland moorland catchment in N.E. Scotland, 12 years of surface water chemistry observations have identified a steady increase in nitrate concentration despite no measured change in inorganic nitrogen deposition. The MAGIC model has been applied to simulate a "best case" situation assuming nitrate in surface water represents "hydrological" contributions (direct run-off) and a ?worst case' assuming a nitrogen saturation mechanism in the catchment soil. Only the ?saturation' model is capable of matching the 12 years of observation for nitrate but both model structures match the pH and acid neutralising capacity record. Future predictions to 2040, in response to the agreed emission reductions under the Gothenburg Protocol, are markedly different. The worst case predicts continued surface water acidification whilst the best case predicts a steady recovery. Keywords: nitrogen saturation, modelling, Lochnagar, Gothenburg Protoco
Quantum healing of classical singularities in power-law spacetimes
We study a broad class of spacetimes whose metric coefficients reduce to
powers of a radius r in the limit of small r. Among these four-parameter
"power-law" metrics we identify those parameters for which the spacetimes have
classical singularities as r approaches 0. We show that a large set of such
classically singular spacetimes is nevertheless nonsingular quantum
mechanically, in that the Hamiltonian operator is essentially self-adjoint, so
that the evolution of quantum wave packets lacks the ambiguity associated with
scattering off singularities. Using these metrics, the broadest class yet
studied to compare classical with quantum singularities, we explore the
physical reasons why some that are singular classically are "healed" quantum
mechanically, while others are not. We show that most (but not all) of the
remaining quantum-mechanically singular spacetimes can be excluded if either
the weak energy condition or the dominant energy condition is invoked, and we
briefly discuss the effect of this work on the strong cosmic censorship
hypothesis.Comment: 14 pages, 1 figure; extensive revision
Experiments C02 /OGO 2/ and D02 /OGO 4/ Final report, 2 Nov. 1962 - 31 Jul. 1969
VLF data from OGO 2 and OGO 4 on propagation, wave-particle interactions, and noise in ionosphere and magnetospher
Quantum singularity of Levi-Civita spacetimes
Quantum singularities in general relativistic spacetimes are determined by
the behavior of quantum test particles. A static spacetime is quantum
mechanically singular if the spatial portion of the wave operator is not
essentially self-adjoint. Here Weyl's limit point-limit circle criterion is
used to determine whether a wave operator is essentially self-adjoint. This
test is then applied to scalar wave packets in Levi-Civita spacetimes to help
elucidate the physical properties of the spacetimes in terms of their metric
parameters
Classical and quantum properties of a 2-sphere singularity
Recently Boehmer and Lobo have shown that a metric due to Florides, which has
been used as an interior Schwarzschild solution, can be extended to reveal a
classical singularity that has the form of a two-sphere. Here the singularity
is shown to be a scalar curvature singularity that is both timelike and
gravitationally weak. It is also shown to be a quantum singularity because the
Klein-Gordon operator associated with quantum mechanical particles approaching
the singularity is not essentially self-adjoint.Comment: 10 pages, 1 figure, minor corrections, final versio
Recovery from acidification of lochs in Galloway, south-west Scotland, UK: 1979-1998
International audienceThe Galloway region of south-west Scotland has historically been subject to long-term deposition of acidic precipitation which has resulted in acidification of soils and surface waters and subsequent damage to aquatic ecology. Since the end of the 1970s, however, acidic deposition has decreased substantially. The general pattern is for a rapid decline in non-marine sulphate in rainwater over the period 1978-1988 followed by stable concentrations to the mid-1990s. Concentrations of nitrate and ammonium in deposition have remained constant between 1980 and 1998. Seven water quality surveys of 48 lochs in the Galloway region have been conducted between 1979 and 1998. During the first 10 years, from 1979, there was a major decline in regional sulphate concentrations in the lochs, which was expected to have produced a decline in base cations and an increase in the acid neutralising capacity. But sea-salt levels (as indicated by chloride concentrations) were approximately 25% higher in 1988 than in 1979 and thus short-term acidification due to sea-salts offset much of the long-term recovery trend expected in the lochs. During the next 10 years, however, the chloride concentrations returned to 1979 levels and the lochs showed large increases in acid neutralising capacity despite little change in sulphate concentrations. From the observed decline in sulphate deposition and concentrations of sulphate in the lochs, it appears that approximately 75% of the possible improvement in acid neutralising capacity has already occurred over the 20-year period (1979-1998). The role of acid deposition as a driving factor for change in water chemistry in the Galloway lochs is confounded by concurrent changes in other driving variables, most notably, factors related to episodic and year-to-year variations in climate. In addition to inputs of sea-salts, climate probably also influences other chemical signals such as peaks in regional nitrate concentrations and the sharp increase in dissolved organic carbon during the 1990s. Keywords: acidification, recovery, Galloway, sulphur, nitroge
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