23,201 research outputs found
The space of generically \'etale families
We construct a space and a rank , generically etale family of
closed subspaces in a separated ambient space . The constructed pair
satisfies a universal property of generically etale families of closed
subspaces in . This universal property is derived directly from the
construction and does in particular not use the Hilbert scheme. The constructed
space is by its universal property canonically identified with a closed
subspace of the Hilbert scheme.Comment: 28 pages; replaced with ;
simplified some proof
Self-consistent theory of many-body localisation in a quantum spin chain with long-range interactions
Many-body localisation is studied in a disordered quantum spin-1/2 chain with
long-ranged power-law interactions, and distinct power-law exponents for
interactions between longitudinal and transverse spin components. Using a
self-consistent mean-field theory centring on the local propagator in Fock
space and its associated self-energy, a localisation phase diagram is obtained
as a function of the power-law exponents and the disorder strength of the
random fields acting on longitudinal spin-components. Analytical results are
corroborated using the well-studied and complementary numerical diagnostics of
level statistics, entanglement entropy, and participation entropy, obtained via
exact diagonalisation. We find that increasing the range of interactions
between transverse spin components hinders localisation and enhances the
critical disorder strength. In marked contrast, increasing the interaction
range between longitudinal spin components is found to enhance localisation and
lower the critical disorder.Comment: 30 pages, 4 figure
Real Exchange Rate Misalignment: Prelude to Crisis?
A model of the long run equilibrium real exchange rate based upon macroeconomic fundamentals is employed to calculate real exchange rate misalignments for Poland and Russia during the 1990s using the Beveridge and Nelson (1981) decomposition of macrofundamentals into transitory and permanent components. Short run movements of the real exchange rate are estimated with ARIMA and GARCH error correction specifications. The different nominal exchange rate regimes of the two countries generate different levels of misalignment and different responses to exogenous shocks. The average misalignment in Russia is substantially greater than that in Poland, indicating incipient pressures to devalue the ruble immediately preceding the August 1998 crisis. The half life of an exogenous shock is found to be much shorter for Poland than for Russia in the pre-crisis period. Dynamic forecasts indicate that the movements of the real exchange rate in the post-crisis period are significantly different from those in the pre-crisis period. Thus, the currency crisis in Russia could not be anticipated with the movements of the real exchange rate estimated with the macroeconomic fundamentals.http://deepblue.lib.umich.edu/bitstream/2027.42/40183/3/wp797.pd
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