1,427 research outputs found
Who Shrunk China? Puzzles in the Measurement of Real GDP
The latest World Bank estimates of real GDP per capita for China are significantly lower than previous ones. We review possible sources of this puzzle and conclude that it reflects a combination of factors, including substitution bias in consumption, reliance on urban prices which we estimate are higher than rural ones, and the use of an expenditure-weighted rather than an output-weighted measure of GDP. Taking all these together, we estimate that real per-capita GDP in China was 50% higher relative to the U.S. in 2005 than the World Bank estimates.
Percolation in random environment
We consider bond percolation on the square lattice with perfectly correlated
random probabilities. According to scaling considerations, mapping to a random
walk problem and the results of Monte Carlo simulations the critical behavior
of the system with varying degree of disorder is governed by new, random fixed
points with anisotropic scaling properties. For weaker disorder both the
magnetization and the anisotropy exponents are non-universal, whereas for
strong enough disorder the system scales into an {\it infinite randomness fixed
point} in which the critical exponents are exactly known.Comment: 8 pages, 7 figure
Determination of Heavy Metals in Hoplobatrachus occipitalis (Crowned Bullfrogs) and Water from Some Reservoirs in Kadawa Irrigation Project Kano, Nigeria
This study was carried out to evaluate the concentrations of heavy metals (Cd, Cu, Mn, Pb, and Zn) in water and crowned bullfrog (Hoplobatrachus occipitalis) organs/parts (muscle, liver, leg, lung and trunk) from Kadawa irrigation project, Kano State, Nigeria. Atomic Absorption Spectroscopy was carried out using Atomic Absorption Spectrometer (AAS) Buck Scientific VGP-210 model (2008). The mean concentration of heavy metals in water samples were 0.11 mg/L, 0.18 mg/L, 0.26 mg/L, and 3.65 mg/L for Cu, Mn, Pb and Zn respectively. The sequence of metal accumulation in all the organs was Zn > Pb > Mn > Cu. The highest concentration of Zn (77.38 mg/kg), Pb (1.81 mg/kg) and Mn (0.68 mg/kg) were found in the lung while Cu (0.07 mg/kg) was deposited more in the liver. Cadmium was notdetected in all the samples analysed. Zinc and lead were the most accumulated metals in all the organs/parts with the range of 77.38 mg/kg - 18.10 mg/kg and 1.81 mg/kg - 0.13 mg/kg respectively. The highest accumulation of metals was found in the lung and liver. The organ/parts accumulation pattern was: lung > liver > trunk > muscle > leg for Zn, Pb and Mn, while liver > lung > trunk > muscle > leg was for Cu. Lung and liver have the highest bioaccumulation of heavy metals while the leg and muscle bioaccumulated the least heavy metals. Hence the water, liver and lung of H. occipitallis are unsafe for consumption, and therefore posed a threat to public health. Farmers should be trained on proper usage of agrochemical.Keywords: Heavy Metals, Crowned Bullfrog, Hoplobatrachus occipitalis, Kadawa, Bioaccumulatio
Griffiths Effects in Random Heisenberg Antiferromagnetic S=1 Chains
I consider the effects of enforced dimerization on random Heisenberg
antiferromagnetic S=1 chains. I argue for the existence of novel Griffiths
phases characterized by {\em two independent dynamical exponents} that vary
continuously in these phases; one of the exponents controls the density of
spin-1/2 degrees of freedom in the low-energy effective Hamiltonian, while the
other controls the corresponding density of spin-1 degrees of freedom.
Moreover, in one of these Griffiths phases, the system has very different low
temperature behavior in two different parts of the phase which are separated
from each other by a sharply defined crossover line; on one side of this
crossover line, the system `looks' like a S=1 chain at low energies, while on
the other side, it is best thought of as a chain. A strong-disorder RG
analysis makes it possible to analytically obtain detailed information about
the low temperature behavior of physical observables such as the susceptibility
and the specific heat, as well as identify an experimentally accessible
signature of this novel crossover.Comment: 16 pages, two-column PRB format; 5 figure
Superradiant and Aharonov-Bohm effect for the quantum ring exciton
The Aharonov-Bohm and superradiant effect on the redaitive decay rate of an
exciton in a quantum ring is studied. With the increasing of ring radius, the
exciton decay rate is enhanced by superradiance, while the amplitude of AB
oscillation is decreased. The competition between these two effects is shown
explicitly and may be observable in time-resolved exeriments.Comment: 4 pages, 2 figures, to appear in Solid State Communications (2004
Spin Reduction Transition in Spin-3/2 Random Heisenberg Chains
Random spin-3/2 antiferromagnetic Heisenberg chains are investigated using an
asymptotically exact renormalization group. Randomness is found to induce a
quantum phase transition between two random-singlet phases. In the strong
randomness phase the effective spins at low energies are S_eff=3/2, while in
the weak randomness phase the effective spins are S_eff=1/2. Separating them is
a quantum critical point near which there is a non-trivial mixture of S=1/2,
S=1, and S=3/2 effective spins at low temperatures.Comment: 4 pages, 3 figures. Typos correcte
Spin-3/2 random quantum antiferromagnetic chains
We use a modified perturbative renormalization group approach to study the
random quantum antiferromagnetic spin-3/2 chain. We find that in the case of
rectangular distributions there is a quantum Griffiths phase and we obtain the
dynamical critical exponent as a function of disorder. Only in the case of
extreme disorder, characterized by a power law distribution of exchange
couplings, we find evidence that a random singlet phase could be reached. We
discuss the differences between our results and those obtained by other
approaches.Comment: 4 page
B_c meson rare decays in the light-cone quark model
We investigate the rare decays
and in the framework of the
light-cone quark model (LCQM). The transition form factors are calculated in
the space-like region and then analytically continued to the time-like region
via exponential parametrization. The branching ratios and longitudinal lepton
polarization asymmetries (LPAs) for the two decays are given and compared with
each other. The results are helpful to investigating the structure of
meson and to testing the unitarity of CKM quark mixing matrix. All these
results can be tested in the future experiments at the LHC.Comment: 9 pages, 11 figures, version accepted for publication in EPJ
Smeared phase transition in a three-dimensional Ising model with planar defects: Monte-Carlo simulations
We present results of large-scale Monte Carlo simulations for a
three-dimensional Ising model with short range interactions and planar defects,
i.e., disorder perfectly correlated in two dimensions. We show that the phase
transition in this system is smeared, i.e., there is no single critical
temperature, but different parts of the system order at different temperatures.
This is caused by effects similar to but stronger than Griffiths phenomena. In
an infinite-size sample there is an exponentially small but finite probability
to find an arbitrary large region devoid of impurities. Such a rare region can
develop true long-range order while the bulk system is still in the disordered
phase. We compute the thermodynamic magnetization and its finite-size effects,
the local magnetization, and the probability distribution of the ordering
temperatures for different samples. Our Monte-Carlo results are in good
agreement with a recent theory based on extremal statistics.Comment: 9 pages, 6 eps figures, final version as publishe
Gapless Spin-Fluid Ground State in a Random Quantum Heisenberg Magnet
We examine the spin- quantum Heisenberg magnet with Gaussian-random,
infinite-range exchange interactions. The quantum-disordered phase is accessed
by generalizing to symmetry and studying the large limit. For large
the ground state is a spin-glass, while quantum fluctuations produce a
spin-fluid state for small . The spin-fluid phase is found to be generically
gapless - the average, zero temperature, local dynamic spin-susceptibility
obeys \bar{\chi} (\omega ) \sim \log(1/|\omega|) + i (\pi/2) \mbox{sgn}
(\omega) at low frequencies. This form is identical to the phenomenological
`marginal' spectrum proposed by Varma {\em et. al.\/} for the doped cuprates.Comment: 13 pages, REVTEX, 2 figures available by request from
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