3,938 research outputs found
Time Evolution of Entropy in Gravitational Collapse
We study the time evolution of the entropy of a collapsing spherical domain
wall, from the point of view of an asymptotic observer, by investigating the
entropy of the entire system (i.e. domain wall and radiation) and induced
radiation alone during the collapse. By taking the difference, we find the
entropy of the collapsing domain wall, since this is the object which will form
a black hole. We find that for large values of time (times larger than
), the entropy of the collapsing domain wall is a constant,
which is of the same order as the Bekenstein-Hawking entropy.Comment: 9 pages, 6 figure
Chemical signatures of the Anthropocene in the Clyde Estuary, UK: sediment hosted Pb, 207/206 Pb, Total Petroleum Hydrocarbons (TPH), Polyaromatic Hydrocarbon (PAH) and Polychlorinated Bipheny (PCB) pollution records
The sediment concentrations of total petroleum hydrocarbons (TPHs), polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), Pb and 207/206Pb isotope ratios were measured in seven cores from the middle Clyde estuary (Scotland, UK) with an aim of tracking the late Anthropocene. Concentrations of TPHs ranged from 34 to 4386 mg kg−1, total PAHs from 19 to 16 163 μg kg−1 and total PCBs between less than 4.3 to 1217 μg kg−1. Inventories, distributions and isomeric ratios of the organic pollutants were used to reconstruct pollutant histories. Pre-Industrial Revolution and modern non-polluted sediments were characterized by low TPH and PAH values as well as high relative abundance of biogenic-sourced phenanthrene and naphthalene. The increasing industrialization of the Clyde gave rise to elevated PAH concentrations and PAH isomeric ratios characteristic of both grass/wood/coal and petroleum and combustion (specifically petroleum combustion). Overall, PAHs had the longest history of any of the organic contaminants. Increasing TPH concentrations and a concomitant decline in PAHs mirrored the lessening of coal use and increasing reliance on petroleum fuels from about the 1950s. Thereafter, declining hydrocarbon pollution was followed by the onset (1950s), peak (1965–1977) and decline (post-1980s) in total PCB concentrations. Lead concentrations ranged from 6 to 631 mg kg−1, while 207/206Pb isotope ratios spanned 0.838–0.876, indicative of various proportions of ‘background’, British ore/coal and Broken Hill type petrol/industrial lead. A chronology was established using published Pb isotope data for aerosol-derived Pb and applied to the cores
Baryon Decuplet to Octet Electromagnetic Transitions in Quenched and Partially Quenched Chiral Perturbation Theory
We calculate baryon decuplet to octet electromagnetic transition form factors
in quenched and partially quenched chiral perturbation theory. We work in the
isospin limit of SU(3) flavor, up to next-to-leading order in the chiral
expansion, and to leading order in the heavy baryon expansion. Our results are
necessary for proper extrapolation of lattice calculations of these
transitions. We also derive expressions for the case of SU(2) flavor away from
the isospin limit.Comment: 16 pages, 3 figures, revtex
Hadronic Electromagnetic Properties at Finite Lattice Spacing
Electromagnetic properties of the octet mesons as well as the octet and
decuplet baryons are augmented in quenched and partially quenched chiral
perturbation theory to include O(a) corrections due to lattice discretization.
We present the results for the SU(3) flavor group in the isospin limit as well
as the results for SU(2) flavor with non-degenerate quarks. These corrections
will be useful for extrapolation of lattice calculations using Wilson valence
and sea quarks, as well as calculations using Wilson sea quarks and
Ginsparg-Wilson valence quarks.Comment: 19 pages, 0 figures, RevTeX
String order in spin liquid phases of spin ladders
Two-leg spin ladders have a rich phase diagram if rung, diagonal and
plaquette couplings are allowed for. Among the possible phases there are two
Haldane-type spin liquid phases without local order parameter, which differ,
however, in the topology of the short range valence bonds. We show that these
phases can be distinguished numerically by two different string order
parameters. We also point out that long range string- and dimer orders can
coexist
Quantum spin chains in a magnetic field
We demonstrate that the ``worm'' algorithm allows very effective and precise
quantum Monte Carlo (QMC) simulations of spin systems in a magnetic field, and
its auto-correlation time is rather insensitive to the value of H at low
temperature. Magnetization curves for the and chains are
presented and compared with existing Bethe ansatz and exact diagonalization
results. From the Green function analysis we deduce the magnon spectra in the
s=1 system, and directly establish the "relativistic" form E(p)=(\Delta ^2 +v^2
p^2)^{1/2} of the dispersion law.Comment: 6 pages, 8 figures; removed discussion of spin-2 case - will be
published later in a separate pape
Low-energy properties and magnetization plateaus in a 2-leg mixed spin ladder
Using the density matrix renormalization group technique we investigate the
low-energy properties and the magnetization plateau behavior in a 2-leg mixed
spin ladder consisting of a spin-1/2 chain coupled with a spin-1 chain. The
calculated results show that the system is in the same universality class as
the spin-3/2 chain when the interchain coupling is strongly ferromagnetic, but
the similarity between the two systems is less clear under other coupling
conditions. We have identified two types of magnetization plateau phases. The
calculation of the magnetization distribution on the spin-1/2 and the spin-1
chains on the ladder shows that one plateau phase is related to the partially
magnetized valence-bond-solid state, and the other plateau state contains
strongly coupled S=1 and s=1/2 spins on the rung.Comment: 6 pages with 8 eps figure
Hall effect in cobalt-doped TiO
We report Hall effect measurements on thin films of cobalt-doped
TiO. Films with low carrier concentrations (10 - 10)
yield a linear behavior in the Hall data while those having higher carrier
concentrations (10 - 10) display anomalous behavior near zero
field. In the entire range of carrier concentration, n-type conduction is
observed. The appearance of the anomalous behavior is accompanied by a possible
structural change from rutile TiO to Ti_[n}O Magneli phase(s)
Phase Transitions Between Topologically Distinct Gapped Phases in Isotropic Spin Ladders
We consider various two-leg ladder models exhibiting gapped phases. All of
these phases have short-ranged valence bond ground states, and they all exhibit
string order. However, we show that short-ranged valence bond ground states
divide into two topologically distinct classes, and as a consequence, there
exist two topologically distinct types of string order. Therefore, not all
gapped phases belong to the same universality class. We show that phase
transitions occur when we interpolate between models belonging to different
topological classes, and we study the nature of these transitions.Comment: 11 pages, 16 postscript figure
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