1,344 research outputs found

    On the dimension of subspaces with bounded Schmidt rank

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    We consider the question of how large a subspace of a given bipartite quantum system can be when the subspace contains only highly entangled states. This is motivated in part by results of Hayden et al., which show that in large d x d--dimensional systems there exist random subspaces of dimension almost d^2, all of whose states have entropy of entanglement at least log d - O(1). It is also related to results due to Parthasarathy on the dimension of completely entangled subspaces, which have connections with the construction of unextendible product bases. Here we take as entanglement measure the Schmidt rank, and determine, for every pair of local dimensions dA and dB, and every r, the largest dimension of a subspace consisting only of entangled states of Schmidt rank r or larger. This exact answer is a significant improvement on the best bounds that can be obtained using random subspace techniques. We also determine the converse: the largest dimension of a subspace with an upper bound on the Schmidt rank. Finally, we discuss the question of subspaces containing only states with Schmidt equal to r.Comment: 4 pages, REVTeX4 forma

    Modelling the role of groundwater hydro-refugia in East African hominin evolution and dispersal.

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    Water is a fundamental resource, yet its spatiotemporal availability in East Africa is poorly understood. This is the area where most hominin first occurrences are located, and consequently the potential role of water in hominin evolution and dispersal remains unresolved. Here, we show that hundreds of springs currently distributed across East Africa could function as persistent groundwater hydro-refugia through orbital-scale climate cycles. Groundwater buffers climate variability according to spatially variable groundwater response times determined by geology and topography. Using an agent-based model, grounded on the present day landscape, we show that groundwater availability would have been critical to supporting isolated networks of hydro-refugia during dry periods when potable surface water was scarce. This may have facilitated unexpected variations in isolation and dispersal of hominin populations in the past. Our results therefore provide a new environmental framework in which to understand how patterns of taxonomic diversity in hominins may have developed

    Band anticrossing in GaNxSb1–x

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    Fourier transform infrared absorption measurements are presented from the dilute nitride semiconductor GaNSb with nitrogen incorporations between 0.2% and 1.0%. The divergence of transitions from the valence band to E– and E+ can be seen with increasing nitrogen incorporation, consistent with theoretical predictions. The GaNSb band structure has been modeled using a five-band k·p Hamiltonian and a band anticrossing fitting has been obtained using a nitrogen level of 0.78 eV above the valence band maximum and a coupling parameter of 2.6 eV

    Band gap reduction in GaNSb alloys due to the anion mismatch

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    The structural and optoelectronic properties in GaNxSb1–x alloys (0<=x<0.02) grown by molecular-beam epitaxy on both GaSb substrates and AlSb buffer layers on GaAs substrates are investigated. High-resolution x-ray diffraction (XRD) and reciprocal space mapping indicate that the GaNxSb1–x epilayers are of high crystalline quality and the alloy composition is found to be independent of substrate, for identical growth conditions. The band gap of the GaNSb alloys is found to decrease with increasing nitrogen content from absorption spectroscopy. Strain-induced band-gap shifts, Moss-Burstein effects, and band renormalization were ruled out by XRD and Hall measurements. The band-gap reduction is solely due to the substitution of dilute amounts of highly electronegative nitrogen for antimony, and is greater than observed in GaNAs with the same N content

    Senior Sway: Using a Mobile Application to Measure Fall Risk

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    Background and Purpose: The Senior Sway mobile application uses the iPhone/iPad gyroscope to assess postural sway and motion reaction time. Impairment in postural sway and motion reaction time have the potential to increase risk for future falls. Senior Sway thereby has the potential to provide a quick, easy to use, objective measure for predicting falls in older adults. The purpose of this study was to evaluate the feasibility of the Senior Sway mobile application and its associations with fall risk in community-dwelling older adults. Methods: Adults older than 62 years were recruited from senior centers and community events. Descriptive and bivariate statistics were used to examine feasibility on the basis of enrollment, time required, satisfaction with application, and association with fall risk. Results and Discussion: Fifty-seven adults were recruited. Use of the Senior Sway mobile application was feasible. Ninety-one percent said that they liked the application and reported length of time of assessment was “just right.” The average Senior Sway score was 64.0 (range: 47.8-84.0), which was signifi cantly associated with the 30-second sit-to-stand test. In addition, the motor reaction time score was associated with the Timed Up and Go. Conclusions: Senior Sway is a promising application to improve identifi cation of adults at risk for falls and need for rehabilitation but warrants further research

    On the distinguishability of random quantum states

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    We develop two analytic lower bounds on the probability of success p of identifying a state picked from a known ensemble of pure states: a bound based on the pairwise inner products of the states, and a bound based on the eigenvalues of their Gram matrix. We use the latter to lower bound the asymptotic distinguishability of ensembles of n random quantum states in d dimensions, where n/d approaches a constant. In particular, for almost all ensembles of n states in n dimensions, p>0.72. An application to distinguishing Boolean functions (the "oracle identification problem") in quantum computation is given.Comment: 20 pages, 2 figures; v2 fixes typos and an error in an appendi

    Novel B(Ar')2(Ar'') hetero-tri(aryl)boranes: a systematic study of Lewis acidity

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    A series of homo- and hetero-tri(aryl)boranes incorporating pentafluorophenyl, 3,5-bis(trifluoromethyl)phenyl, and pentachlorophenyl groups, four of which are novel species, have been studied as the acidic component of frustrated Lewis pairs for the heterolytic cleavage of H2. Under mild conditions eight of these will cleave H2; the rate of cleavage depending on both the electrophilicity of the borane and the steric bulk around the boron atom. Electrochemical studies allow comparisons of the electrophilicity with spectroscopic measurements of Lewis acidity for different series of boranes. Discrepancies in the correlation between these two types of measurements, combined with structural characterisation of each borane, reveal that the twist of the aryl rings with respect to the boron-centred trigonal plane is significant from both a steric and electronic perspective, and is an important consideration in the design of tri(aryl)boranes as Lewis acids

    What ‘children’ experience and ‘adults’ may overlook: phenomenological approaches to media practice, education and research

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    This paper argues that each utterance of media should be seen as in dialogue with each other utterance, and that children, being the phenomenological hub to their lived media experience, should be recognised as engaging with media holistically. Argument draws upon two recent qualitative studies with children between six and eleven years of age. These studies, although separate, shared certain phenomenology orientated conceptual underpinnings and arrived at relatable findings. Notably that participating children tended to address media in a platform agnostic manner and offered little sense that they saw the media platform itself as being of overriding significance to their holistic media engagement. Ultimately, if children’s lived media engagement is dialogic and holistic, then focusing on only one discreet media utterance (like television for example) can be said to become deeply problematic to those within children’s media practice, education and research
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