883 research outputs found
Certainty relations between local and nonlocal observables
We demonstrate that for an arbitrary number of identical particles, each
defined on a Hilbert-space of arbitrary dimension, there exists a whole ladder
of relations of complementarity between local, and every conceivable kind of
joint (or nonlocal) measurements. E.g., the more accurate we can know (by a
measurement) some joint property of three qubits (projecting the state onto a
tripartite entangled state), the less accurate some other property, local to
the three qubits, become. We also show that the corresponding complementarity
relations are particularly tight for particles defined on prime dimensional
Hilbert spaces.Comment: 4 pages, no figure
Two-photon imaging and quantum holography
It has been claimed that ``the use of entangled photons in an imaging system
can exhibit effects that cannot be mimicked by any other two-photon source,
whatever strength of the correlations between the two photons'' [A. F.
Abouraddy, B. E. A. Saleh, A. V. Sergienko, and M. C. Teich, Phys. Rev. Lett.
87, 123602 (2001)]. While we believe that the cited statement is true, we show
that the method proposed in that paper, with ``bucket detection'' of one of the
photons, will give identical results for entangled states as for appropriately
prepared classically correlated states.Comment: 4 pages, 2 figures, REVTe
Charge Localization and Ordering in AMnO Hollandite Group Oxides: Impact of Density Functional Theory Approaches
The phases of AMnO hollandite group oxides emerge from the
competition between ionic interactions, Jahn-Teller effects, charge ordering,
and magnetic interactions. Their balanced treatment with feasible computational
approaches can be challenging for commonly used approximations in Density
Functional Theory. Three examples (A = Ag, Li and K) are studied with a
sequence of different approximate exchange-correlation functionals. Starting
from a generalized gradient approximation (GGA), an extension to include van
der Waals interactions and a recently proposed meta-GGA are considered. Then
local Coulomb interactions for the Mn electrons are more explicitly
considered with the DFT+ approach. Finally selected results from a hybrid
functional approach provide a reference. Results for the binding energy of the
A species in the parent oxide highlight the role of van der Waals interactions.
Relatively accurate results for insertion energies can be achieved with a low
and a high approach. In the low case, the materials are described
as band metals with a high symmetry, tetragonal crystal structure. In the high
case, the electrons donated by A result in formation of local Mn
centers and corresponding Jahn-Teller distortions characterized by a local
order parameter. The resulting degree of monoclinic distortion depends on
charge ordering and magnetic interactions in the phase formed. The reference
hybrid functional results show charge localization and ordering. Comparison to
low temperature experiments of related compounds suggests that charge
localization is the physically correct result for the hollandite group oxides
studied here. . . .Comment: 16 pages, 8 figure
Properties of antithrombin-thrombin complex formed in the presence and in the absence of heparin
Experimental study of the delayed threshold phenomenon in a semiconductor laser
An experimental study of the delayed threshold phenomenon in a Vertical
Extended Cavity Semiconductor Emitting Laser is carried out. Under modulation
of the pump power, the laser intensity exhibits a hysteresis behavior in the
vicinity of the threshold. The temporal width of this hysteresis is measured as
a function of the modulation frequency, and is proved to follow the predicted
scaling law. A model based on the rate equations is derived and used to analyze
the experimental observations. A frequency variation of the laser around the
delayed threshold and induced by the phase-amplitude coupling is predicted and
estimated
Entangled-State Lithography: Tailoring any Pattern with a Single State
We demonstrate a systematic approach to Heisenberg-limited lithographic image
formation using four-mode reciprocal binominal states. By controlling the
exposure pattern with a simple bank of birefringent plates, any pixel pattern
on a grid, occupying a square with the side half a
wavelength long, can be generated from a -photon state.Comment: 4 pages, 4 figure
Polariton Dispersion Law in Periodic Bragg and Near-Bragg Multiple Quantum Well Structures
The structure of polariton spectrum is analyzed for periodic multiple quantum
well structures with periods at or close to Bragg resonance condition at the
wavelength of the exciton resonance. The results obtained used to discuss
recent reflection and luminescent experiments by M. H\"{u}bner et al [Phys.
Rev. Lett. {\bf 83}, 2841 (1999)] carried out with long multiple quantum well
structures. It is argued that the discussion of quantum well structures with
large number of wells is more appropriate in terms of normal modes of infinite
periodic structures rather then in terms of super- and sub- radiant modes.Comment: replaced with a new version, an error in one of the equations is
correcte
Cystatins as calpain inhibitors: Engineered chicken cystatin- and stefin B-kininogen domain 2 hybrids support a cystatin-like mode of interaction with the catalytic subunit of μ-calpain
Within the cystatin superfamily, only kininogen domain 2 (KD2) is able to inhibit μ- and m-calpain. In an attempt to elucidate the structural requirements of cystatins for calpain inhibition, we constructed recombinant hybrids of human stefin B (an intracellular family 1 cystatin) with KD2 and Delta L110 deletion mutants of chicken cystatin-KD2 hybrids. Substitution of the N-terminal contact region of stefin B by the corresponding KD2 sequence resulted in a calpain inhibitor of K-i = 188 nM. Deletion of L110, which forms a beta -bulge in family 1 and 2 cystatins but is lacking in KD2, improved inhibition of mu -calpain 4- to 8-fold. All engineered cystatins were temporary inhibitors of calpain due to slow substrate-like cleavage of a single peptide bond corresponding to Gly9-Ala10 in chicken cystatin. Biomolecular interaction analysis revealed that, unlike calpastatin, the cystatin-type inhibitors do not bind to the calmodulin-like domain of the small subunit of calpain, and their interaction with the mu -calpain heterodimer is completely prevented by a synthetic peptide comprising subdomain B of calpastatin domain 1. Based on these results we propose that (i) cystatin-type calpain inhibitors interact with the active site of the catalytic domain of calpain in a similar cystatin-like mode as with papain and (ii) the potential for calpain inhibition is due to specific subsites within the papain-binding regions of the general cystatin fold
Many-Body Effects on Tunneling of Electrons in Magnetic-Field-Induced Quasi One-Dimensional Electron Systems in Semiconductor Nanowhiskers
Effects of the electron-electron interaction on tunneling in a semiconductor
nanowhisker are studied in a magnetic quantum limit. We consider the system
with which bulk and edge states coexist. In bulk states, the temperature
dependence of the transmission probability is qualitatively similar to that of
a one-dimensional electron system. We investigate contributions of edge states
on transmission probability in bulk states. Those contributions can be
neglected within our approximation which takes into account only most divergent
terms at low temperatures.Comment: 9 pages, 6 figure
Pricing Options in Incomplete Equity Markets via the Instantaneous Sharpe Ratio
We use a continuous version of the standard deviation premium principle for
pricing in incomplete equity markets by assuming that the investor issuing an
unhedgeable derivative security requires compensation for this risk in the form
of a pre-specified instantaneous Sharpe ratio. First, we apply our method to
price options on non-traded assets for which there is a traded asset that is
correlated to the non-traded asset. Our main contribution to this particular
problem is to show that our seller/buyer prices are the upper/lower good deal
bounds of Cochrane and Sa\'{a}-Requejo (2000) and of Bj\"{o}rk and Slinko
(2006) and to determine the analytical properties of these prices. Second, we
apply our method to price options in the presence of stochastic volatility. Our
main contribution to this problem is to show that the instantaneous Sharpe
ratio, an integral ingredient in our methodology, is the negative of the market
price of volatility risk, as defined in Fouque, Papanicolaou, and Sircar
(2000).Comment: Keywords: Pricing derivative securities, incomplete markets, Sharpe
ratio, correlated assets, stochastic volatility, non-linear partial
differential equations, good deal bound
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