9,871 research outputs found
From the Desktop to the Cloud: Leveraging Hybrid Storage Architectures in Your Repository
4th International Conference on Open RepositoriesThis presentation was part of the session : Conference PresentationsDate: 2009-05-19 01:00 PM – 02:30 PMRepositories collect and manage data holdings using a storage device. Mainly this has been a local file system, but recently attempts have been made at using open storage products and cloud storage solutions, such as Sun's Honeycomb and Amazon S3 respectively. Each of these solutions has their own pros and cons but There are advantages in adopting a hybrid model for repository storage, combining the relative strengths of each one in a policy-determined model. In this paper we present an implementation of a repository storage layer which can dynamically handle and manage a hybrid storage systemJoint Information Systems Committee (JISC
Information geometry of density matrices and state estimation
Given a pure state vector |x> and a density matrix rho, the function
p(x|rho)= defines a probability density on the space of pure states
parameterised by density matrices. The associated Fisher-Rao information
measure is used to define a unitary invariant Riemannian metric on the space of
density matrices. An alternative derivation of the metric, based on square-root
density matrices and trace norms, is provided. This is applied to the problem
of quantum-state estimation. In the simplest case of unitary parameter
estimation, new higher-order corrections to the uncertainty relations,
applicable to general mixed states, are derived.Comment: published versio
Statistical Geometry in Quantum Mechanics
A statistical model M is a family of probability distributions, characterised
by a set of continuous parameters known as the parameter space. This possesses
natural geometrical properties induced by the embedding of the family of
probability distributions into the Hilbert space H. By consideration of the
square-root density function we can regard M as a submanifold of the unit
sphere in H. Therefore, H embodies the `state space' of the probability
distributions, and the geometry of M can be described in terms of the embedding
of in H. The geometry in question is characterised by a natural Riemannian
metric (the Fisher-Rao metric), thus allowing us to formulate the principles of
classical statistical inference in a natural geometric setting. In particular,
we focus attention on the variance lower bounds for statistical estimation, and
establish generalisations of the classical Cramer-Rao and Bhattacharyya
inequalities. The statistical model M is then specialised to the case of a
submanifold of the state space of a quantum mechanical system. This is pursued
by introducing a compatible complex structure on the underlying real Hilbert
space, which allows the operations of ordinary quantum mechanics to be
reinterpreted in the language of real Hilbert space geometry. The application
of generalised variance bounds in the case of quantum statistical estimation
leads to a set of higher order corrections to the Heisenberg uncertainty
relations for canonically conjugate observables.Comment: 32 pages, LaTex file, Extended version to include quantum measurement
theor
Two-body scattering in a trap and a special periodic phenomenon sensitive to the interaction
Two-body scattering of neutral particles in a trap is studied theoretically.
The control of the initial state is realized by using optical traps. The
collisions inside the trap occur repeatedly; thereby the effect of interaction
can be accumulated. Two periodic phenomena with a shorter and a much longer
period, respectively, are found. The latter is sensitive to the interaction.
Instead of measuring the differential cross section as usually does, the
measurement of the longer period and the details of the periodic behavior might
be a valid source of information on weak interactions among neutral particles.Comment: 5 pages, 5 figure
Comment on "Typicality for Generalized Microcanonical Ensemble"
The validity of the so-called "typicality" argument for a generalised
microcanonical ensemble proposed recently is examined.Comment: Version to appear in PR
Photoproduction of K^+ Mesons in Hydrogen
The photoproduction of K^+ mesons in hydrogen has been measured with the purpose of extending the previous CalTech measurements to smaller angles, and obtaining better absolute values for the cross sections. The technique of Donoho and Walker, using a magnetic spectrometer and a time-of-flight measurement to detect the K^+ mesons, was modified so as to achieve a better discrimination against pions and scattered protons. The results obtained are in fairly good agreement with the more extensive measurements made at Cornell by a somewhat different method
Metric approach to quantum constraints
A new framework for deriving equations of motion for constrained quantum
systems is introduced, and a procedure for its implementation is outlined. In
special cases the framework reduces to a quantum analogue of the Dirac theory
of constrains in classical mechanics. Explicit examples involving spin-1/2
particles are worked out in detail: in one example our approach coincides with
a quantum version of the Dirac formalism, while the other example illustrates
how a situation that cannot be treated by Dirac's approach can nevertheless be
dealt with in the present scheme.Comment: 13 pages, 1 figur
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