251 research outputs found
Comparison of unitary transforms
We analyze the problem of comparing unitary transformations. The task is to
decide, with minimal resources and maximal reliability, whether two given
unitary transformations are identical or different. It is possible to make such
comparisons without obtaining any information about the individual
transformations. Different comparison strategies are presented and compared
with respect to their efficiency. With an interferometric setup, it is possible
to compare two unitary transforms using only one test particle. Another
strategy makes use of a two-particle singlet state. This strategy is more
efficient than using a non-entangled two-particle test state, thus
demonstrating the benefit of entanglement. Generalisations to higher
dimensional transforms and to more than two transformations are made.Comment: 11 pages, 4 figures, revtex4, submitted to J. Phys.
Human Performance Models of Pilot Behavior
Five modeling teams from industry and academia were chosen by the NASA Aviation Safety and Security Program to develop human performance models (HPM) of pilots performing taxi operations and runway instrument approaches with and without advanced displays. One representative from each team will serve as a panelist to discuss their team s model architecture, augmentations and advancements to HPMs, and aviation-safety related lessons learned. Panelists will discuss how modeling results are influenced by a model s architecture and structure, the role of the external environment, specific modeling advances and future directions and challenges for human performance modeling in aviation
Understanding concurrent earcons: applying auditory scene analysis principles to concurrent earcon recognition
Two investigations into the identification of concurrently presented, structured sounds, called earcons were carried out. One of the experiments investigated how varying the number of concurrently presented earcons affected their identification. It was found that varying the number had a significant effect on the proportion of earcons identified. Reducing the number of concurrently presented earcons lead to a general increase in the proportion of presented earcons successfully identified. The second experiment investigated how modifying the earcons and their presentation, using techniques influenced by auditory scene analysis, affected earcon identification. It was found that both modifying the earcons such that each was presented with a unique timbre, and altering their presentation such that there was a 300 ms onset-to-onset time delay between each earcon were found to significantly increase identification. Guidelines were drawn from this work to assist future interface designers when incorporating concurrently presented earcons
Experimental Implementation of the Deutsch-Jozsa Algorithm for Three-Qubit Functions using Pure Coherent Molecular Superpositions
The Deutsch-Jozsa algorithm is experimentally demonstrated for three-qubit
functions using pure coherent superpositions of Li rovibrational
eigenstates. The function's character, either constant or balanced, is
evaluated by first imprinting the function, using a phase-shaped femtosecond
pulse, on a coherent superposition of the molecular states, and then projecting
the superposition onto an ionic final state, using a second femtosecond pulse
at a specific time delay
Field Theory And Second Renormalization Group For Multifractals In Percolation
The field-theory for multifractals in percolation is reformulated in such a
way that multifractal exponents clearly appear as eigenvalues of a second
renormalization group. The first renormalization group describes geometrical
properties of percolation clusters, while the second-one describes electrical
properties, including noise cumulants. In this context, multifractal exponents
are associated with symmetry-breaking fields in replica space. This provides an
explanation for their observability. It is suggested that multifractal
exponents are ''dominant'' instead of ''relevant'' since there exists an
arbitrary scale factor which can change their sign from positive to negative
without changing the Physics of the problem.Comment: RevTex, 10 page
Predicting the Impact of Climate Change on Threatened Species in UK Waters
Global climate change is affecting the distribution of marine species and is thought to represent a threat to biodiversity. Previous studies project expansion of species range for some species and local extinction elsewhere under climate change. Such range shifts raise concern for species whose long-term persistence is already threatened by other human disturbances such as fishing. However, few studies have attempted to assess the effects of future climate change on threatened vertebrate marine species using a multi-model approach. There has also been a recent surge of interest in climate change impacts on protected areas. This study applies three species distribution models and two sets of climate model projections to explore the potential impacts of climate change on marine species by 2050. A set of species in the North Sea, including seven threatened and ten major commercial species were used as a case study. Changes in habitat suitability in selected candidate protected areas around the UK under future climatic scenarios were assessed for these species. Moreover, change in the degree of overlap between commercial and threatened species ranges was calculated as a proxy of the potential threat posed by overfishing through bycatch. The ensemble projections suggest northward shifts in species at an average rate of 27 km per decade, resulting in small average changes in range overlap between threatened and commercially exploited species. Furthermore, the adverse consequences of climate change on the habitat suitability of protected areas were projected to be small. Although the models show large variation in the predicted consequences of climate change, the multi-model approach helps identify the potential risk of increased exposure to human stressors of critically endangered species such as common skate (Dipturus batis) and angelshark (Squatina squatina)
Six new candidate ultracompact X-ray binaries
Ultracompact X-ray binaries (UCXBs) appear able to sustain accretion onto the
compact accretor at rates lower than in wider X-ray binaries. This may be
understood by the smaller accretion disks in UCXBs: a lower X-ray luminosity
suffices to keep a disk completely ionized through irradiation and, thus, keep
the viscosity at a sufficiently high level to allow effective transport of
matter to the compact object. We employ this distinguishing factor on data from
RXTE and BeppoSAX to identify six new candidate UCXBs, thus increasing the
population by one quarter. The candidates are drawn from the population of
persistently accreting and type-I X-ray bursting low-mass X-ray binaries. The
X-ray bursts establish the low-mass X-ray binary nature and provide a handle on
the accretion rate. We find that the low accretion rates are supported by the
long burst recurrence times and the hard X-ray spectra of the persistent
emission as derived from the 2nd INTEGRAL catalog of soft gamma-ray sources. We
discuss the peculiar light curves of some new UCXB candidates.Comment: Section 2 corrected and improved thanks to comments by J.-P. Lasota.
Accepted for publication in Astronomy and Astrophysic
Vaginal progesterone prophylaxis for preterm birth (the OPPTIMUM study): a multicentre, randomised, double-blind trial
Efficacy and Mechanism Evaluation (EME) Programme, a Medical Research Council (MRC) and National
Institute for Health Research (NIHR) partnership. The EME Programme is funded by the MRC and NIHR, with
contributions from the Chief Scientist Office in Scotland and National Institute for Social Care and Research in Wales
Emergent global patterns of ecosystem structure and function from a mechanistic general ecosystem model
Anthropogenic activities are causing widespread degradation of ecosystems worldwide, threatening the ecosystem services upon which all human life depends. Improved understanding of this degradation is urgently needed to improve avoidance and mitigation measures. One tool to assist these efforts is predictive models of ecosystem structure and function that are mechanistic: based on fundamental ecological principles. Here we present the first mechanistic General Ecosystem Model (GEM) of ecosystem structure and function that is both global and applies in all terrestrial and marine environments. Functional forms and parameter values were derived from the theoretical and empirical literature where possible. Simulations of the fate of all organisms with body masses between 10 µg and 150,000 kg (a range of 14 orders of magnitude) across the globe led to emergent properties at individual (e.g., growth rate), community (e.g., biomass turnover rates), ecosystem (e.g., trophic pyramids), and macroecological scales (e.g., global patterns of trophic structure) that are in general agreement with current data and theory. These properties emerged from our encoding of the biology of, and interactions among, individual organisms without any direct constraints on the properties themselves. Our results indicate that ecologists have gathered sufficient information to begin to build realistic, global, and mechanistic models of ecosystems, capable of predicting a diverse range of ecosystem properties and their response to human pressures
- …