10,008 research outputs found
Seasonal changes in microbial dissolved organic sulfur transformations in coastal waters
The marine trace gas dimethylsulfide (DMS) is the single most important biogenic source of atmospheric sulfur, accounting for up to 80% of global biogenic sulfur emissions. Approximately 300 million tons of DMS are produced annually, but the majority is degraded by microbes in seawater. The DMS precursor dimethylsulfoniopropionate (DMSP) and oxidation product dimethylsulphoxide (DMSO) are also important organic sulfur reservoirs. However, the marine sinks of dissolved DMSO remain unknown. We used a novel combination of stable and radiotracers to determine seasonal changes in multiple dissolved organic sulfur transformation rates to ascertain whether microbial uptake of dissolved DMSO was a significant loss pathway. Surface concentrations of DMS ranged from 0.5 to 17.0 nM with biological consumption rates between 2.4 and 40.8 nM·dâ1. DMS produced from the reduction of DMSO was not a significant process. Surface concentrations of total DMSO ranged from 2.3 to 102 nM with biological consumption of dissolved DMSO between 2.9 and 111 nM·dâ1. Comparisons between 14C2-DMSO assimilation and dissimilation rates suggest that the majority of dissolved DMSO was respired (>94%). Radiotracer microbial consumption rates suggest that dissimilation of dissolved DMSO to CO2 can be a significant loss pathway in coastal waters, illustrating the significance of bacteria in controlling organic sulfur seawater concentrations
Random Matrix Theory, Chiral Perturbation Theory, and Lattice Data
Recently, the chiral logarithms predicted by quenched chiral perturbation
theory have been extracted from lattice calculations of hadron masses. We argue
that the deviations of lattice results from random matrix theory starting
around the so-called Thouless energy can be understood in terms of chiral
perturbation theory as well. Comparison of lattice data with chiral
perturbation theory formulae allows us to compute the pion decay constant. We
present results from a calculation for quenched SU(2) with Kogut-Susskind
fermions at \beta=2.0 and 2.2.Comment: LaTeX, 12 pages, 7 .eps figure
Beyond the Thouless energy
The distribution and the correlations of the small eigenvalues of the Dirac
operator are described by random matrix theory (RMT) up to the Thouless energy
, where is the physical volume. For somewhat larger
energies, the same quantities can be described by chiral perturbation theory
(chPT). For most quantities there is an intermediate energy regime, roughly
, where the results of RMT and chPT agree with each other. We
test these predictions by constructing the connected and disconnected scalar
susceptibilities from Dirac spectra obtained in quenched SU(2) and SU(3)
simulations with staggered fermions for a variety of lattice sizes and coupling
constants. In deriving the predictions of chPT, it is important to take into
account only those symmetries which are exactly realized on the lattice.Comment: LATTICE99(Theoretical Developments), 3 pages, 3 figures, typo in Ref.
[10] correcte
Random Matrix Theory and Chiral Logarithms
Recently, the contributions of chiral logarithms predicted by quenched chiral
perturbation theory have been extracted from lattice calculations of hadron
masses. We argue that a detailed comparison of random matrix theory and lattice
calculations allows for a precise determination of such corrections. We
estimate the relative size of the m*log(m), m, and m^2 corrections to the
chiral condensate for quenched SU(2).Comment: LaTeX (elsart.cls), 9 pages, 6 .eps figures, added reference, altered
discussion of Eq.(9
Time-dependent density-functional theory for ultrafast interband excitations
We formulate a time-dependent density functional theory (TDDFT) in terms of
the density matrix to study ultrafast phenomena in semiconductor structures. A
system of equations for the density matrix components, which is equivalent to
the time-dependent Kohn-Sham equation, is derived. From this we obtain a TDDFT
version of the semiconductor Bloch equations, where the electronic many-body
effects are taken into account in principle exactly. As an example, we study
the optical response of a three-dimensional two-band insulator to an external
short-time pulsed laser field. We show that the optical absorption spectrum
acquires excitonic features when the exchange-correlation potential contains a
Coulomb singularity. A qualitative comparison of the TDDFT optical
absorption spectra with the corresponding results obtained within the
Hartree-Fock approximation is made
Correlator of Topological Charge Densities in Instanton Model in QCD
The QCD sum rule for the correlator of topological charge densities and
related to it longitudinal part of the correlator of singlet axial currents is
considered in the framework of instanton model. The coupling constant of
eta'-meson with the singlet axial current is determined. Its value appears to
be in a good coincidence with the value determined recently from the connection
of the part of proton spin, carried by u,d,s quarks, with the derivative of QCD
topological susceptibility. From the same sum rule eta-eta' mixing angle is
found in the framework of two mixing angles model. Its value is close to that
found in the chiral effective theory. The correlator of topological charge
densities at large momenta is calculated.Comment: 14 pages, 2 figure
Effective one-body approach to general relativistic two-body dynamics
We map the general relativistic two-body problem onto that of a test particle
moving in an effective external metric. This effective-one-body approach
defines, in a non-perturbative manner, the late dynamical evolution of a
coalescing binary system of compact objects. The transition from the adiabatic
inspiral, driven by gravitational radiation damping, to an unstable plunge,
induced by strong spacetime curvature, is predicted to occur for orbits more
tightly bound than the innermost stable circular orbit in a Schwarzschild
metric of mass M = m1 + m2. The binding energy, angular momentum and orbital
frequency of the innermost stable circular orbit for the time-symmetric
two-body problem are determined as a function of the mass ratio.Comment: 52 pages, RevTex, epsfig, 8 figure
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