8,741 research outputs found
CAD and creativity: does the computer really help?
We are frequently told by its exponents that computeraided design (CAD) liberates designers and gives them new ways of envisioning their work, but is this really true? CAD in architecture is examined to see to what extent it has enhanced creativity in design. This is partly
done by applying a test of creativity advanced by contemporary architect Herman Hertzberger. In this analysis, CAD is found somewhat wanting,
and some suggestions are made as to why this might be so
Measuring Omega_0 with higher-order Quasar-Galaxy Correlations induced by Weak Lensing
Via the magnification bias, gravitational lensing by large-scale structures
causes angular cross-correlations between distant quasars and foreground
galaxies on angular scales of arc minutes and above. We investigate the
three-point cross-correlation between quasars and galaxy pairs measurable via
the second moment of the galaxy counts around quasars and show that it reaches
the level of a few per cent on angular scales near one arc minute. Combining
two- and three-point correlations, a skewness parameter can be defined which is
shown to be virtually independent on the shape and normalisation of the
dark-matter power spectrum. If the galaxy bias is linear and deterministic, the
skewness depends on the cosmic matter density parameter Omega_0 only;
otherwise, it can be used to probe the linearity and stochasticity of the bias.
We finally estimate the signal-to-noise ratio of a skewness determination and
find that around twenty thousand distant quasars e.g. from the Sloan Digital
Sky Survey should suffice for a direct measurement of Omega_0.Comment: 11 pages, 6 figures, submitted to Astronomy and Astrophysic
Cosmological Information from Quasar-Galaxy Correlations induced by Weak Lensing
The magnification bias of large-scale structures, combined with galaxy
biasing, leads to a cross-correlation of distant quasars with foreground
galaxies on angular scales of the order of arc minutes and larger. The
amplitude and angular shape of the cross-correlation function w_QG contain
information on cosmological parameters and the galaxy bias factor. While the
existence of this cross-correlation has firmly been established, existing data
did not allow an accurate measurement of w_QG yet, but wide area surveys like
the Sloan Digital Sky Survey now provide an ideal database for measuring it.
However, w_QG depends on several cosmological parameters and the galaxy bias
factor. We study in detail the sensitivity of w_QG to these parameters and
develop a strategy for using the data. We show that the parameter space can be
reduced to the bias factor b, Omega_0 and sigma_8, and compute the accuracy
with which these parameters can be deduced from SDSS data. Under reasonable
assumptions, it should be possible to reach relative accuracies of the order of
5%-15% for b, Omega_0, and sigma_8. This method is complementary to other
weak-lensing analyses based on cosmic shear.Comment: 11 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Optical Integral in the Cuprates and the Question of Sum Rule Violation
Much attention has been given to a possible violation of the optical sum rule
in the cuprates, and the connection this might have to kinetic energy lowering.
The optical integral is composed of a cut-off independent term (whose
temperature dependence is a measure of the sum rule violation), plus a cut-off
dependent term that accounts for the extension of the Drude peak beyond the
upper bound of the integral. We find that the temperature dependence of the
optical integral in the normal state of the cuprates can be accounted for
solely by the latter term, implying that the dominant contribution to the
observed sum rule `violation' in the normal state is due to the finite cut-off.
This cut-off dependent term is well modeled by a theory of electrons
interacting with a broad spectrum of bosons.Comment: some clarifications and minor additions are offered in the final
(published) versio
Calculation of Effective Coulomb Interaction for , , and
In this paper, the Slater integrals for a screened Coulomb interaction of the
the Yukawa form are calculated and by fitting the Thomas-Fermi wavevector, good
agreement is obtained with experiment for the multiplet spectra of
and ions. Moreover, a predicted multiplet spectrum for the heavy
fermion superconductor is shown with a calculated Coulomb U of 1.6 eV.
These effective Coulomb interactions, which are quite simple to calculate,
should be useful inputs to further many-body calculations in correlated
electron metals.Comment: 8 pages, revtex, 3 uuencoded postscript figure
Best Practices and Innovations for Managing Codeine Misuse and Dependence.
PURPOSE: Promoting and ensuring safe use of codeine containing medicines remains a public health issue given the rise in reporting of misuse and dependence particularly in countries where available over-the-counter (OTC). The aim of this unique study was to identify best practices in management of opioid abuse and dependence, particularly codeine, and innovations to meet challenges surrounding safe and compliant use, patient awareness-raising, reducing health harms and enhancing successful treatment of dependence. METHODS: A mixed methods approach using three data points was used that included : (1) analysis of data from existing scoping reviews to identify potential areas for innovation (2) interviews with key national stakeholders from public health, pharmaceutical, regulatory, primary care and addiction practice in three distinct regulatory regimes (Ireland, United Kingdom and South Africa); and (3) a circular email request for information on potential innovations to members of the European Medicine's Agency European Network of Centres for Pharmacoepidemiology and Pharmacovigilance (ENCEPP). Data from these three sources were analysed to identify best practices and opportunities for innovation. RESULTS: Best practices and potential innovations were identified under the nine headings: (1) manufacture; (2) product information and public education; (3) responsible prescribing; (4) monitoring and surveillance; (5) dispensing, screening and brief interventions in community pharmacies; (6) safety in the workplace and on the road; (7) internet supply of codeine and online support; (8) treatment of codeine dependence; and (9) learning resources and training for health professionals. CONCLUSIONS: Challenges ensuring availability of codeine containing medicines for legitimate therapeutic use, while minimising misuse, dependence and related health harms warrant consideration of new innovations. Most promising innovative potential lies across the products' retail lifecycle from manufacture to prescriber and community pharmacy practitioner.This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page
Extended polarized semiclassical model for quantum-dot cavity QED and its application to single-photon sources
We present a simple extension of the semi-classical model for a two-level
system in a cavity, in order to incorporate multiple polarized transitions,
such as those appearing in neutral and charged quantum dots (QDs), and two
nondegenerate linearly polarized cavity modes. We verify the model by exact
quantum master equation calculations, and experimentally using a neutral QD in
a polarization non-degenerate micro-cavity, in both cases we observe excellent
agreement. Finally, the usefulness of this approach is demonstrated by
optimizing a single-photon source based on polarization postselection, where we
find an increase in the brightness for optimal polarization conditions as
predicted by the model.Comment: 8 pages, for simple code see https://doi.org/10.5281/zenodo.347666
BYPASS1: synthesis of the mobile root-derived signal requires active root growth and arrests early leaf development
<p>Abstract</p> <p>Background</p> <p>The Arabidopsis <it>bypass1 </it>(<it>bps1</it>) mutant root produces a biologically active mobile compound that induces shoot growth arrest. However it is unknown whether the root retains the capacity to synthesize the mobile compound, or if only shoots of young seedlings are sensitive. It is also unknown how this compound induces arrest of shoot growth. This study investigated both of these questions using genetic, inhibitor, reporter gene, and morphological approaches.</p> <p>Results</p> <p>Production of the <it>bps1 </it>root-synthesized mobile compound was found to require active root growth. Inhibition of postembryonic root growth, by depleting glutathione either genetically or chemically, allowed seedlings to escape shoot arrest. However, the treatments were not completely effective, as the first leaf pair remained radialized, but elongated. This result indicated that the embryonic root transiently synthesized a small amount of the mobile substance. In addition, providing glutathione later in vegetative development caused shoot growth arrest to be reinstated, revealing that these late-arising roots were still capable of producing the mobile substance, and that the older vegetative leaves were still responsive.</p> <p>To gain insight into how leaf development responds to the mobile signal, leaf development was followed morphologically and using the CYCB1,1::GUS marker for G2/M phase cells. We found that arrest of leaf growth is a fully penetrant phenotype, and a dramatic decrease in G2/M phase cells was coincident with arrest. Analyses of stress phenotypes found that late in development, <it>bps1 </it>cotyledons produced necrotic lesions, however neither hydrogen peroxide nor superoxide were abundant as leaves underwent arrest.</p> <p>Conclusions</p> <p><it>bps1 </it>roots appear to require active growth in order to produce the mobile <it>bps1 </it>signal, but the potential for this compound's synthesis is present both early and late during vegetative development. This prolonged capacity to synthesize and respond to the mobile compound is consistent with a possible role for the mobile compound in linking shoot growth to subterranean conditions. The specific growth-related responses in the shoot indicated that the mobile substance prevents full activation of cell division in leaves, although whether cell division is a direct response remains to be determined.</p
A quantum phase transition from triangular to stripe charge order in NbSe
The competition between proximate electronic phases produces a complex
phenomenology in strongly correlated systems. In particular, fluctuations
associated with periodic charge or spin modulations, known as density waves,
may lead to exotic superconductivity in several correlated materials. However,
density waves have been difficult to isolate in the presence of chemical
disorder, and the suspected causal link between competing density wave orders
and high temperature superconductivity is not understood. Here we use scanning
tunneling microscopy to image a previously unknown unidirectional (stripe)
charge density wave (CDW) smoothly interfacing with the familiar
tri-directional (triangular) CDW on the surface of the stoichiometric
superconductor NbSe. Our low temperature measurements rule out thermal
fluctuations, and point to local strain as the tuning parameter for this
quantum phase transition. We use this discovery to resolve two longstanding
debates about the anomalous spectroscopic gap and the role of Fermi surface
nesting in the CDW phase of NbSe. Our results highlight the importance of
local strain in governing phase transitions and competing phenomena, and
suggest a new direction of inquiry for resolving similarly longstanding debates
in cuprate superconductors and other strongly correlated materials.Comment: PNAS in pres
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