5,409 research outputs found
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Indirect long-term global radiative cooling from NOx emissions
Anthropogenic emissions of shortâlived, chemically reactive gases, such as NO x and CO, are known to influence climate by altering the chemistry of the global troposphere and thereby the abundance of the greenhouse gases O3, CH4 and the HFCs. This study uses the characteristics of the natural modes of the tropospheric chemical system to decompose the greenhouse effect of NO x and CO emissions into (i) shortâlived modes involving predominantly tropospheric O3 and (ii) the longâlived mode involving a global coupled CH4âCOâO3 perturbation. Combining these two classes of greenhouse perturbationsâlarge, shortâlived, regional O3 increases and smaller, longâlived, global decreases in CH4 and O3âwe find that most types of anthropogenic NO x emissions lead to a negative radiative forcing and an overall cooling of the earth
Crossover Time in Relative Fluctuations Characterizes the Longest Relaxation Time of Entangled Polymers
In entangled polymer systems, there are several characteristic time scales,
such as the entanglement time and the disengagement time. In molecular
simulations, the longest relaxation time (the disengagement time) can be
determined by the mean square displacement (MSD) of a segment or by the shear
relaxation modulus. Here, we propose the relative fluctuation analysis method,
which is originally developed for characterizing large fluctuations, to
determine the longest relaxation time from the center of mass trajectories of
polymer chains (the time-averaged MSDs). Applying the method to simulation data
of entangled polymers (by the slip-spring model and the simple reptation
model), we provide a clear evidence that the longest relaxation time is
estimated as the crossover time in the relative fluctuations.Comment: 17 pages, 9 figures, to appear in J. Chem. Phy
Tokyo Axion Helioscope
A new search result of the Tokyo axion helioscope is presented. The axion
helioscope consists of a dedicated cryogen-free 4T superconducting magnet with
an effective length of 2.3 m and PIN photodiodes as x-ray detectors. Solar
axions, if exist, would be converted into X-ray photons through the inverse
Primakoff process in the magnetic field. Conversion is coherently enhanced even
for massive axions by filling the conversion region with helium gas. The
present third phase measurement sets a new limit of
g_{a\gamma\gamma}<(5.6--13.4)\times10^{-10} GeV^{-1} for the axion mass of
0.84<m_a<1.0 eV at 95% confidence level.Comment: 4th Patras Workshop on Axions, WIMPs and WISP
Generalized Arcsine Law and Stable Law in an Infinite Measure Dynamical System
Limit theorems for the time average of some observation functions in an
infinite measure dynamical system are studied. It is known that intermittent
phenomena, such as the Rayleigh-Benard convection and Belousov-Zhabotinsky
reaction, are described by infinite measure dynamical systems.We show that the
time average of the observation function which is not the function,
whose average with respect to the invariant measure is finite, converges to
the generalized arcsine distribution. This result leads to the novel view that
the correlation function is intrinsically random and does not decay. Moreover,
it is also numerically shown that the time average of the observation function
converges to the stable distribution when the observation function has the
infinite mean.Comment: 8 pages, 8 figure
Observation of strong electron dephasing in disordered CuGeAu thin films
We report the observation of strong electron dephasing in a series of
disordered CuGeAu thin films. A very short electron dephasing
time possessing very weak temperature dependence around 6 K, followed by an
upturn with further decrease in temperature below 4 K, is found. The upturn is
progressively more pronounced in more disordered samples. Moreover, a ln
dependent, but high-magnetic-field-insensitive, resistance rise persisting from
above 10 K down to 30 mK is observed in the films. These results suggest a
nonmagnetic dephasing process which is stronger than any known mechanism and
may originate from the coupling of conduction electrons to dynamic defects.Comment: to appear in Phys. Rev. Let
A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer
International audienceA new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit description of oxidative degradation of up to C3-hydrocarbons (CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in forming halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from a reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. The reaction between Br atoms and C2H2 is shown to be unimportant for determining the degree of bromine activation in the remote MBL. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL
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Chemical transport model ozone simulations for spring 2001 over the western Pacific:comparisons with TRACE-P lidar, ozonesondes, and Total Ozone Mapping Spectrometer columns
Two closely related chemical transport models (CTMs) employing the same high-resolution meteorological data (similar to180 km x similar to180 km x similar to600 m) from the European Centre for Medium-Range Weather Forecasts are used to simulate the ozone total column and tropospheric distribution over the western Pacific region that was explored by the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) measurement campaign in February-April 2001. We make extensive comparisons with ozone measurements from the lidar instrument on the NASA DC-8, with ozonesondes taken during the period around the Pacific Rim, and with TOMS total column ozone. These demonstrate that within the uncertainties of the meteorological data and the constraints of model resolution, the two CTMs (FRSGC/UCI and Oslo CTM2) can simulate the observed tropospheric ozone and do particularly well when realistic stratospheric ozone photochemistry is included. The greatest differences between the models and observations occur in the polluted boundary layer, where problems related to the simplified chemical mechanism and inadequate horizontal resolution are likely to have caused the net overestimation of about 10 ppb mole fraction. In the upper troposphere, the large variability driven by stratospheric intrusions makes agreement very sensitive to the timing of meteorological features
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