36,786 research outputs found
Non-ergodic states induced by impurity levels in quantum spin chains
The semi-infinite XY spin chain with an impurity at the boundary has been
chosen as a prototype of interacting many-body systems to test for non-ergodic
behavior. The model is exactly solvable in analytic way in the thermodynamic
limit, where energy eigenstates and the spectrum are obtained in closed form.
In addition of a continuous band, localized states may split off from the
continuum, for some values of the impurity parameters. In the next step, after
the preparation of an arbitrary non-equilibrium state, we observe the time
evolution of the site magnetization. Relaxation properties are described by the
long-time behavior, which is estimated using the stationary phase method.
Absence of localized states defines an ergodic region in parameter space, where
the system relaxes to a homogeneous magnetization. Out of this region, impurity
levels split from the band, and localization phenomena may lead to
non-ergodicity.Comment: 10 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:1703.0344
Optimal investment under behavioural criteria -- a dual approach
We consider a discrete-time, generically incomplete market model and a
behavioural investor with power-like utility and distortion functions. The
existence of optimal strategies in this setting has been shown in a previous
paper under certain conditions on the parameters of these power functions.
In the present paper we prove the existence of optimal strategies under a
different set of conditions on the parameters, identical to the ones which were
shown to be necessary and sufficient in the Black-Scholes model.
Although there exists no natural dual problem for optimisation under
behavioural criteria (due to the lack of concavity), we will rely on techniques
based on the usual duality between attainable contingent claims and equivalent
martingale measures.Comment: Forthcoming in Banach Center Publications. Some errors have been
corrected, in particular in Assumption 2.3
Equation of state of hard oblate ellipsoids by replica exchange Monte Carlo
We implemented the replica exchange Monte Carlo technique to produce the
equation of state of hard 1:5 aspect-ratio oblate ellipsoids for a wide density
range. For this purpose, we considered the analytical approximation of the
overlap distance given by Bern and Pechukas and the exact numerical solution
given by Perram and Wertheim. For both cases we capture the expected
isotropic-nematic transition at low densities and a nematic-crystal transition
at larger densities. For the exact case, these transitions occur at the volume
fraction 0.341, and in the interval , respectively.Comment: 4 pages, 2 figure
The impacts of the milk pricing policy in Zimbabwe
Analyses the effects of government price policies on the production and consumption of milk in Zimbabwe. Gives an overview of the Dairy Marketing Board which is responsible for the collection and distribution of commercial milk products at prices set by the government. Discusses the implications of changes in the milk producer price for the opportunity costs of land and animal draught power in the communal areas. Describes the trends in the consumption of dairy products and aggregate demand relationships for whole milk and milk products
Beef supply price response estimation and implications for policy analysis: The Zimbabwe case
Illustrates the role of supply price elasticities in policy making and analysis, and discusses the experience with respect to the sensitiveness of beef supply price elasticities estimated for commercial farms in Zimbabwe and the corresponding policy implication
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