331,557 research outputs found
Informality and the Development and Demolition of Urban Villages in the Chinese Peri-urban Area
The fate of Chinese urban villages (chengzhongcun) has recently attracted both research and policy attention. Two important unaddressed questions are: what are the sources of informality in otherwise orderly Chinese cities; and, will village redevelopment policy eliminate informality in the Chinese city? Reflecting on the long-established study of informal settlements and recent research on informality, it is argued that the informality in China has been created by the dual urban-rural land market and land management system and by an underprovision of migrant housing. The redevelopment of chengzhongcun is an attempt to eliminate this informality and to create more governable spaces through formal land development; but since it fails to tackle the root demand for unregulated living and working space, village redevelopment only leads to the replication of informality in more remote rural villages, in other urban neighbourhoods and, to some extent, in the redeveloped neighbourhoods. © 2012 Urban Studies Journal Limited
A mesoscale finite element simulation of intermittent plastic flow of micropillar compression under hybrid loading mode
The plastic deformation of the micropillar proceeds as a series of strain bursts, showing an intermittent plastic flow. In this work, we present a stochastic finite element method in crystal plasticity to describe the intermittent characteristic of crystal deformation under the hybrid loading mode (HLM). The microscopic boundary conditions(MBCs) using the HLM are studied and they are demonstrated to be different in various deformation periods such as loading stage, burst slip and holding stage, which occur alternatively as the plastic flow proceeds. In order to determine the MBCs, we use the Monte Carlo (MC) stochastic model to predict the amplitude of the burst displacement and then incorporate such model into our established continuum framework accounting for the characteristics of the strain burst. By implementing this continuum model into the finite element analysis, we predict the plastic flow of single crystal nickel micropillars that deform under uniaxial compression along the [2 6 9] crystalline direction. The simulation results indicate clearly visible strain bursts in the course of plastic deformation, producing a stair-case like stress-strain behavior that agrees well with experimental observations. The computational results reveal that the intermittent flow in the micrometer-scale is intensified due to the increasing amplitude of the strain burst, as well as the occurrence of successive strain bursts rather than the discrete strain bursts, with decreasing of the specimen size. In addition, the micropillar displacement in the context of burst activity predicted from our simulations is similar to the experimental observations. We demonstrate that our simulation method could provide further insights into the intermittent plastic flow characteristics such as burst time duration, micropillar velocity; plus, it is feasible to apply this method to investigate the plastic flow behaviors under complex loading conditions
N K Pi molecular state with I=1 and J(Pi)=3/2-
The structure of the molecule-like state of with spin-parity
and isospin I=1 is studied within the chiral SU(3) quark
model. First we calculate the , , and phase shifts in the
framework of the resonating group method (RGM), and a qualitative agreement
with the experimental data is obtained. Then we perform a rough estimation for
the energy of , and the effect of the mixing to
the configuration is also considered. The
calculated energy is very close to the threshold of the system. A
detailed investigation is worth doing in the further study.Comment: 11 pages, 3 figures; accepted for publication in Phys. Rev.
Renormalization of transition matrix elements of particle number operators due to strong electron correlation
Renormalization of non-magnetic and magnetic impurities due to electron
double occupancy prohibition is derived analytically by an improved Gutzwiller
approximation. Non-magnetic impurities are effectively weakened by the same
renormalization factor as that for the hopping amplitude, whereas magnetic
impurities are strengthened by the square root of the spin-exchange
renormalization factor, in contrast to results by the conventional Gutzwiller
approximation. We demonstrate it by showing that transition matrix elements of
number operators between assumed excited states and between an assumed ground
state and excited states are renormalized differently than diagonal matrix
elements. Deviation from such simple renormalization with a factor is also
discussed. In addition, as related calculation, we correct an error in
treatment of renormalization of charge interaction in the literature. Namely,
terms from the second order of the transition matrix elements are strongly
suppressed. Since all these results do not depend on the signs of impurity
potential or charge interaction parameter, they are valid both in attractive
and repulsive cases.Comment: 12 page
Hot and crispy : CRISPR-Cas systems in the hyperthermophile Sulfolobus solfataricus
The CRISPR (clustered regularly interspaced short palindromic repeats) and Cas (CRISPR-associated) genes are widely spread in bacteria and archaea, representing an intracellular defence system against invading viruses and plasmids. In the system, fragments from foreign DNA are captured and integrated into the host genome at the CRISPR locus. The locus is transcribed and the resulting RNAs are processed by Cas6 into small crRNAs (CRISPR RNAs) that guide a variety of effector complexes to degrade the invading genetic elements. Many bacteria and archaea have one major type of effector complex. However, Sulfolobus solfataricus strain P2 has six CRISPR loci with two families of repeats, four cas6 genes and three different types of effector complex. These features make S. solfataricus an important model for studying CRISPR-Cas systems. In the present article, we review our current understanding of crRNA biogenesis and its effector complexes, subtype I-A and subtype III-B, in S. solfataricus. We also discuss the differences in terms of mechanisms between the subtype III-B systems in S. solfataricus and Pyrococcus furiosus.PostprintPeer reviewe
Quantile clocks
Quantile clocks are defined as convolutions of subordinators , with
quantile functions of positive random variables. We show that quantile clocks
can be chosen to be strictly increasing and continuous and discuss their
practical modeling advantages as business activity times in models for asset
prices. We show that the marginal distributions of a quantile clock, at each
fixed time, equate with the marginal distribution of a single subordinator.
Moreover, we show that there are many quantile clocks where one can specify
, such that their marginal distributions have a desired law in the class of
generalized -self decomposable distributions, and in particular the class of
self-decomposable distributions. The development of these results involves
elements of distribution theory for specific classes of infinitely divisible
random variables and also decompositions of a gamma subordinator, that is of
independent interest. As applications, we construct many price models that have
continuous trajectories, exhibit volatility clustering and have marginal
distributions that are equivalent to those of quite general exponential
L\'{e}vy price models. In particular, we provide explicit details for
continuous processes whose marginals equate with the popular VG, CGMY and NIG
price models. We also show how to perfectly sample the marginal distributions
of more general classes of convoluted subordinators when is in a sub-class
of generalized gamma convolutions, which is relevant for pricing of European
style options.Comment: Published in at http://dx.doi.org/10.1214/10-AAP752 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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