29,520 research outputs found
Runoff modelling in glacierized Central Asian catchments for present-day and future climate
A conceptual precipitation–runoff model was applied in five glacierized catchments in Central Asia. The model, which was first developed and applied in the Alps, works on a daily time step and yields good results in the more continental climate of the Tien Shan mountains for present-day climate conditions. Runoff scenarios for different climates (doubling of CO2) and glacierization conditions predict an increased flood risk as a first stage and a more complex picture after a complete glacier loss: a higher discharge during spring due to an earlier and more intense snowmelt is followed by a water deficiency in hot and dry summer periods. This unfavourable seasonal redistribution of the water supply has dramatic consequences for the Central Asian lowlands, which depend to a high degree on the glacier melt water for irrigation and already nowadays suffer from water shortages
The leading-twist pion and kaon distribution amplitudes from the QCD instanton vacuum
We investigate the leading-twist light-cone distribution amplitudes for the
pion and kaon, based on the nonlocal chiral quark model from the instanton
vacuum. Effects of explicit flavor SU(3)-symmetry breaking are taken into
account. The Gegenbauer moments are computed, analyzed and compared with those
of other models. The one-loop QCD evolution of the moments is briefly
discussed. The transverse momentum distributions are also discussed for the
pion and kaon light-cone wave functions.Comment: 17 pages, 12 figures. Accepted for publication in Physical Review
Modeling the Void H I Column Density Spectrum
The equivalent width distribution function (EWDF) of \hone absorbers specific
to the void environment has been recently derived (Manning 2002), revealing a
large line density of clouds (dN/dz ~500 per unit z for Log (N_HI)> 12.4). I
show that the void absorbers cannot be diffuse (or so-called filamentary)
clouds, expanding with the Hubble flow, as suggested by N-body/hydro
simulations. Absorbers are here modeled as the baryonic remnants of
sub-galactic perturbations that have expanded away from their dark halos in
response to reionization at z ~ 6.5. A 1-D Lagrangian hydro/gravity code is
used to follow the dynamic evolution and ionization structure of the baryonic
clouds for a range of halo circular velocities. The simulation products at z=0
can be combined according to various models of the halo velocity distribution
function to form a column density spectrum that can be compared with the
observed. I find that such clouds may explain the observed EWDF if the halo
velocity distribution function is as steep as that advanced by Klypin (1999),
and the halo mass distribution is closer to isothermal than to NFW.Comment: 21 pages, 15 figures. Paper in press; ApJ 591, n
Gluon production on two centers and the effective action approach
Application of the effective action formalism is studied for processes in
which the reggeons may split. It is shown that the gluon production on two
centers is described by the contribution of the
Reggeon-to-two-Reggeons-plus-Particle vertex supplemented by certain singular
contributions from the double gluon exchange. The rules for longitudinal
integrations are established from the comparison to perturbative QCD amplitude.
Convenient expressions for application to the inclusive gluon production are
derived.Comment: 15 pages, 7 figures; some misprints corrected; submitted to
Eur.Phys.Jour.
Rescattering and finite formation time effects in electro-disintegration of the deuteron in the cumulative region
The role of rescattering due to the final state interaction (FSI) and the
influence of the finite formation time (FFT) on the inclusive and
exclusive electro-disintegration of the deuteron are studied in the
cumulative kinematical region and moderate values of the 4-momentum
transfer (GeV/c). The spins are averaged out. It is found
that in the inclusive process the relative magnitude of rescattering steadily
grows with and that at it has the same order as the plane wave
impulse approximation (PWIA) contribution, with the finite formation time
effects decreasing the rescattering contribution by %. In the
exclusive process, with increasing momentum transfer, FFT substantially reduces
the effects from FSI, although the latter are still appreciable in the region
of momentum transfer investigated.Comment: 5 pages, 5 EPS figures. Presented by M. A. Braun at the Fourth
International Conference on Hadronic Physics, Trieste (Italy), ICTP May
12-16, 2003. To appear in EPJ
Cumulative structure function in terms of nucleonic wave function of the nucleus
The structure function of the nucleus in the cumulative region is
studied in terms of nucleon degrees of freedom. At high the resulting
expressions are presented as a sum of contributions from few-nucleon
correlations. Two-nucleon correlations are studied in some detail. Spin
variables are averaged out. In the region the structure functions are
calculated for the relativistic interaction proposed by F.Gross {\it et al}.
They are found to fall with faster than the exponential. For Carbon at
, where the method is not rigorously applicable, they turn out to be
rougly twice larger than the experimental data.Comment: text and 2 figures in LaTex, 7 figures in P
Towards the theory of coherent hard dijet production on hadrons and nuclei
We carry out a detailed calculation of the cross section of pion diffraction
dissociation into two jets with large transverse momenta, originating from a
hard gluon exchange between the pion constituents. Both the quark and the gluon
contribution are considered and in the latter case we present calculations both
in covariant and in axial gauges. We find that the standard collinear
factorization does not hold in this reaction. The structure of non-factorizable
contributions is discussed and the results are compared with the experimental
data. Our conclusion is that the existing theoretical uncertainties do not
allow, for the time being, for a quantitative extraction of the pion
distribution amplitude.Comment: 45 pages, latex, 17 figures, final version to appear in Nuclear
Physics
Modelling of hydrological response to climate change in glacierized Central Asian catchments
The arid lowlands of Central Asia are highly dependent on the water supplied by the Tien Shan mountains. Snow and ice storage make large contributions to current runoff, particularly in summer. Two runoff models with different temporal resolutions, HBV-ETH and OEZ, were applied in three glaciated catchments of the Tien Shan mountains. Scenario runs were produced for a climate change caused by the doubling of atmospheric CO2 as predicted by the GISS global circulation model and assuming a 50% reduction of glaciation extent, as well as a complete loss of glaciation. Agreement of the results was best for runs based on 50% glaciation loss, where both models predict an increase in spring and summer runoff compared to current levels. Scenarios for complete loss of glaciation predict an increase in spring runoff levels, followed by lower runoff levels for July and August. Model predictions differ concerning the degree of reduction of late summer runoff. These scenarios are sensitive to model simulation of basin precipitation, as well as to reduction of glaciation extent
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