5,183 research outputs found
Preservation of Web Resources: The JISC PoWR Project
This paper describes the work of the JISC-funded PoWR (Preservation Of Web Resources) project which is developing a handbook on best practices and advice aimed at UK higher and further educational institutions for the preservation of Web sites and Web resources.
The paper summarises the challenges institutions face in preserving Web resources, describes the workshops organized by the project in order to identify the challenges and identify appropriate best practices, and outlines areas in which further work is required
Affine maps of density matrices
For quantum systems described by finite matrices, linear and affine maps of
matrices are shown to provide equivalent descriptions of evolution of density
matrices for a subsystem caused by unitary Hamiltonian evolution in a larger
system; an affine map can be replaced by a linear map, and a linear map can be
replaced by an affine map. There may be significant advantage in using an
affine map. The linear map is generally not completely positive, but the linear
part of an equivalent affine map can be chosen to be completely positive and
related in the simplest possible way to the unitary Hamiltonian evolution in
the larger system.Comment: 4 pages, title changed, sentence added, reference update
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Florality: A Mouthpiece for the Oppressed and the Power of Words in Margaret Atwood's Speculative Fiction
Maps for Lorentz transformations of spin
Lorentz transformations of spin density matrices for a particle with positive
mass and spin 1/2 are described by maps of the kind used in open quantum
dynamics. They show how the Lorentz transformations of the spin depend on the
momentum. Since the spin and momentum generally are entangled, the maps
generally are not completely positive and act in limited domains. States with
two momentum values are considered, so the maps are for the spin qubit
entangled with the qubit made from the two momentum values, and results from
the open quantum dynamics of two coupled qubits can be applied. Inverse maps
are used to show that every Lorentz transformation completely removes the spin
polarization, and so completely removes the information, from a number of spin
density matrices. The size of the spin polarization that is removed is
calculated for particular cases.Comment: 7 Pages, 3 Figure
Medicines prescribed for asthma, discontinuation and perinatal outcomes, including breastfeeding: A population cohort analysis
ObjectivesTo explore associations between exposures to medicines prescribed for asthma and their discontinuation in pregnancy and preterm birth [MethodsDesign. A population-based cohort study. Setting. The Secure Anonymised Information Linkage [SAIL] databank in Wales, linking maternal primary care data with infant outcomes. Population. 107,573, 105,331, and 38,725 infants born 2000-2010 with information on premature birth, SGA and breastfeeding respectively, after exclusions. Exposures. maternal prescriptions for asthma medicines or their discontinuation in pregnancy. Methods. Odds ratios for adverse pregnancy outcomes were calculated for the exposed versus the unexposed population, adjusted for smoking, parity, age and socio-economic status.ResultsPrescriptions for asthma, whether continued or discontinued during pregnancy, were associated with birth atConclusionsPrescription of asthma medicines before or during pregnancy was associated with higher prevalence of adverse perinatal outcomes, particularly if prescriptions were discontinued during pregnancy. Women discontinuing medicines during pregnancy could be identified from prescription records. The impact of targeting close monitoring and breastfeeding support warrants exploration
Undoing a weak quantum measurement of a solid-state qubit
We propose an experiment which demonstrates the undoing of a weak continuous
measurement of a solid-state qubit, so that any unknown initial state is fully
restored. The undoing procedure has only a finite probability of success
because of the non-unitary nature of quantum measurement, though it is
accompanied by a clear experimental indication of whether or not the undoing
has been successful. The probability of success decreases with increasing
strength of the measurement, reaching zero for a traditional projective
measurement. Measurement undoing (``quantum un-demolition'') may be interpreted
as a kind of a quantum eraser, in which the information obtained from the first
measurement is erased by the second measurement, which is an essential part of
the undoing procedure. The experiment can be realized using quantum dot
(charge) or superconducting (phase) qubits.Comment: 5 page
Loss of quantum coherence in a system coupled to a zero-temperature environment
We discuss the influence of a zero-temperature environment on a coherent
quantum system. First, we calculate the reduced density operator of the system
in the framework of the well-known, exactly solvable model of an oscillator
coupled to a bath of harmonic oscillators. Then, we propose the sketch of an
Aharonov--Bohm-like interferometer showing, through interference measurements,
the decrease of the coherence length of the system due to the interaction with
the environment, even in the zero temperature limit
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