467 research outputs found
Some extremal functions in Fourier analysis, III
We obtain the best approximation in , by entire functions of
exponential type, for a class of even functions that includes
, where , and , where . We also give periodic versions of these results where the
approximating functions are trigonometric polynomials of bounded degree.Comment: 26 pages. Submitte
Suhtumine teksti autorisse keelevigade pÔhjal
http://www.ester.ee/record=b5144942*es
Similar patterns of leaf temperatures and thermal acclimation to warming in temperate and tropical tree canopies
As the global climate warms, a key question is how increased leaf temperatures will affect tree physiology and the coupling between leaf and air temperatures in forests. To explore the impact of increasing temperatures on plant performance in open air, we warmed leaves in the canopy of two mature evergreen forests, a temperate Eucalyptus woodland and a tropical rainforest. The leaf heaters consistently maintained leaves at a target of 4 °C above ambient leaf temperatures. Ambient leaf temperatures (Tleaf) were mostly coupled to air temperatures (Tair), but at times, leaves could be 8â10 °C warmer than ambient air temperatures, especially in full sun. At both sites, Tleaf was warmer at higher air temperatures (Tair > 25 °C), but was cooler at lower Tair, contrary to the âleaf homeothermy hypothesisâ. Warmed leaves showed significantly lower stomatal conductance (â0.05 mol mâ2 sâ1 or â43% across species) and net photosynthesis (â3.91 ÎŒmol mâ2 sâ1 or â39%), with similar rates in leaf respiration rates at a common temperature (no acclimation). Increased canopy leaf temperatures due to future warming could reduce carbon assimilation via reduced photosynthesis in these forests, potentially weakening the land carbon sink in tropical and temperate forests
Testing the Meson Cloud Model in Inclusive Meson Production
We have applied the Meson Cloud Model to calculate inclusive momentum spectra
of pions and kaons produced in high energy proton-proton and proton-nucleus
collisions. For the first time these data are used to constrain the cloud
cut-off parameters. We show that it is possible to obtain a reasonable
description of data, especially the large () part of the
spectrum and at the same time describe (partially) the E866 data on and . We also discuss the relative strength of the
and vertices. We find out that the corresponding cut-off
parameters should be both soft and should not differ by more than 200 MeV from
each other. An additional source (other than the meson cloud) of sea antiquark
asymmetry, seems to be necessary to completely explain the data. A first
extension of the MCM to proton nucleus collisions is discussed.Comment: 14 pages, Latex, 6 ps figures. Submitted to Phys. Rev.
Systematics of Leading Particle Production
Using a QCD inspired model developed by our group for particle production,
the Interacting Gluon Model (IGM), we have made a systematic analysis of all
available data on leading particle spectra. These data include diffractive
collisions and photoproduction at HERA. With a small number of parameters
(essentially only the non-perturbative gluon-gluon cross section and the
fraction of diffractive events) good agreement with data is found. We show that
the difference between pion and proton leading spectra is due to their
different gluon distributions. We predict a universality in the diffractive
leading particle spectra in the large momentum region, which turns out to be
independent of the incident energy and of the projectile type.Comment: 13 pages, Latex, 4 ps figures. To appear in Phys. Rev.
Quantum-mechanical model for particles carrying electric charge and magnetic flux in two dimensions
We propose a simple quantum mechanical equation for particles in two
dimensions, each particle carrying electric charge and magnetic flux. Such
particles appear in (2+1)-dimensional Chern-Simons field theories as charged
vortex soliton solutions, where the ratio of charge to flux is a constant
independent of the specific solution. As an approximation, the charge-flux
interaction is described here by the Aharonov-Bohm potential, and the
charge-charge interaction by the Coulomb one. The equation for two particles,
one with charge and flux () and the other with () where
is a pure number is studied in detail. The bound state problem is solved
exactly for arbitrary and when . The scattering problem is
exactly solved in parabolic coordinates in special cases when takes integers or half integers. In both cases the cross sections obtained
are rather different from that for pure Coulomb scattering.Comment: 12 pages, REVTeX, no figur
Mean first-passage time of surface-mediated diffusion in spherical domains
We present an exact calculation of the mean first-passage time to a target on
the surface of a 2D or 3D spherical domain, for a molecule alternating phases
of surface diffusion on the domain boundary and phases of bulk diffusion. The
presented approach is based on an integral equation which can be solved
analytically. Numerically validated approximation schemes, which provide more
tractable expressions of the mean first-passage time are also proposed. In the
framework of this minimal model of surface-mediated reactions, we show
analytically that the mean reaction time can be minimized as a function of the
desorption rate from the surface.Comment: to appear in J. Stat. Phy
Evidence of Final-State Suppression of High-p_T Hadrons in Au + Au Collisions Using d + Au Measurements at RHIC
Transverse momentum spectra of charged hadrons with 6 GeV/c have
been measured near mid-rapidity (0.2 1.4) by the PHOBOS experiment
at RHIC in Au + Au and d + Au collisions at . The spectra for different collision centralities are compared to collisions at the same energy. The resulting nuclear modification
factor for central Au + Au collisions shows evidence of strong suppression of
charged hadrons in the high- region ( GeV/c). In contrast, the d +
Au nuclear modification factor exhibits no suppression of the high-
yields. These measurements suggest a large energy loss of the high-
particles in the highly interacting medium created in the central Au + Au
collisions. The lack of suppression in d + Au collisions suggests that it is
unlikely that initial state effects can explain the suppression in the central
Au + Au collisions.Comment: 3 pages, 4 figures, International Europhysics Conference on High
Energy Physics EPS (July 17th-23rd 2003) in Aachen, German
Muon production in extensive air showers and its relation to hadronic interactions
In this work, the relation between muon production in extensive air showers
and features of hadronic multiparticle production at low energies is studied.
Using CORSIKA, we determine typical energies and phase space regions of
secondary particles which are important for muon production in extensive air
showers and confront the results with existing fixed target measurements.
Furthermore possibilities to measure relevant quantities of hadron production
in existing and planned accelerator experiments are discussed.Comment: To appear in the proceedings of international conference on
interconnection between high energy physics and astroparticle physics "From
Colliders to Cosmic Rays" (C2CR 2005), Prague, Czech Republic, 7-13 September
200
Modelling J/psi production and absorption in a microscopic nonequilibrium approach
Charmonium production and absorption in heavy ion collisions is studied with
the Ultrarelativisitic Quantum Molecular Dynamics model. We compare the
scenario of universal and time independent color-octet dissociation cross
sections with one of distinct color-singlet J/psi, psi' and chi_c states,
evolving from small, color transparent configurations to their asymptotic
sizes. The measured J/psi production cross sections in pA and AB collisions at
SPS energies are consistent with both - purely hadronic - scenarios. The
predicted rapidity dependence of J/psi suppression can be used to discriminate
between the two experimentally. The importance of interactions with secondary
hadrons and the applicability of thermal reaction kinetics to J/psi absorption
are investigated. We discuss the effect of nuclear stopping and the role of
leading hadrons. The dependence of the psi' to J/psi ratio on the model
assumptions and the possible influence of refeeding processes is also studied.Comment: 35 pages, 16 figure
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