2,012 research outputs found
Black holes and information theory
During the past three decades investigators have unveiled a number of deep
connections between physical information and black holes whose consequences for
ordinary systems go beyond what has been deduced purely from the axioms of
information theory. After a self-contained introduction to black hole
thermodynamics, we review from its vantage point topics such as the information
conundrum that emerges from the ability of incipient black holes to radiate,
the various entropy bounds for non-black hole systems (holographic bound,
universal entropy bound, etc) which are most easily derived from black hole
thermodynamics, Bousso's covariant entropy bound, the holographic principle of
particle physics, and the subject of channel capacity of quantum communication
channels.Comment: RevTeX, 12 pages, 5 figures. To appear in Contemporary Physic
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Latitudinal distribution of reactive nitrogen in the free troposphere over the Pacific Ocean in late winter/early spring
The late winter/early spring (February/March, 1994) measurements of Pacific Exploratory Mission-West (PEM-W) B have been analyzed to show latitudinal distributions (45°N to 10°S) of the mixing ratios of reactive nitrogen species (NO, peroxyacetylnitrate (PAN), HNO3, and NOy), ozone, and chemical tracers (CO, NMHCs, acetone, and C2Cl4) with a focus on the upper troposphere. Mixing ratios of all species are relatively low in the warm tropical and subtropical air south of the polar jetstream (≈28°N) but increase sharply with latitude in the cold polar air north of the jetstream. Noteworthy is the continuous increase in reservoir species (PAN and HNO3) and the simultaneous decrease in NOx toward the northern midlatitudes. The Harvard global three-dimensional model of tropospheric chemistry has been used to compare these observations with predictions. In the upper troposphere the magnitude and distribution of measured NOy and PAN as a function of latitude is well represented by this model, while NOx (measured NO + model calculated NO2) is underpredicted, especially in the tropics. Unlike several previous studies, where model-predicted HNO3 exceeded observations by as much as a factor of 10, the present data/model comparison is improved to within a factor of 2. The predicted upper tropospheric HNO3 is generally below or near measured values, and there is little need to invoke particle reactions as a means of removing or recycling HNO3. Comparison between measured NOy and the sum of its three main constituents (PAN + NOx + HNO3) on average show a small mean shortfall (<15%). This shortfall could be attributed to the presence of known but unmeasured species (e.g., peroxynitric acid and alkyl nitrates) as well as to instrument errors. Copyright 1998 by the American Geophysical Union
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ATMOSPHERIC CHEMISTRY IN THE ARCTIC AND SUB-ARCTIC - INFLUENCE OF NATURAL FIRES, INDUSTRIAL EMISSIONS, AND STRATOSPHERIC INPUTS
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On the origin of tropospheric ozone and NOx over the tropical South Pacific
The budgets of ozone and nitrogen oxides (NOx = NO + NO2) in the tropical South Pacific troposphere are analyzed by photochemical point modeling of aircraft observations at 0-12 km altitude from the Pacific Exploratory Mission-Tropics A campaign flown in September-October 1996. The model reproduces the observed NO2/NO concentration ratio to within 30% and has similar success in simulating observed concentrations of peroxides (H2O2, CH3OOH), lending confidence in its use to investigate ozone chemistry. It is found that chemical production of ozone balances only half of chemical loss in the tropospheric column over the tropical South Pacific. The net loss is 1.8 x 1011 molecules cm-2 s-1. The missing source of ozone is matched by westerly transport of continental pollution into the region. Independent analysis of the regional ozone budget with a global three-dimensional model corroborates the results from the point model and reveals the importance of biomass burning emissions in South America and Africa for the ozone budget over the tropical South Pacific. In this model, biomass burning increases average ozone concentrations by 7-8 ppbv throughout the troposphere. The NOx responsible for ozone production within the South Pacific troposphere below 4 km can be largely explained by decomposition of peroxyacetylnitrate (PAN) transported into the region with biomass burning pollution at higher altitudes. Copyright 1999 by the American Geophysical Union
The controversy in the process: potential scattering or resonance ?
The reaction shows a broad peak at 1.5
GeV in the channel which has no counterpart in the
channel. This "resonance" is considered as a candidate for a
state in the "s-channel". We show, however, that it can also
be explained by potential scattering of via the -
exchange in the "t-channel".Comment: 12 pages, latex, 3 postscript figures, to appear in Zeitschrift fur
Physi
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