28,839 research outputs found
Vacuum Polarization on the Schwarzschild Metric with a Cosmic String
We consider the problem of the renormalization of the vacuum polarization in
a symmetry space-time with axial but not spherical symmetry, Schwarzschild
space-time threaded by an infinite straight cosmic string. Unlike previous
calculations, our framework to compute the renormalized vacuum polarization
does not rely on special properties of Legendre functions, but rather has been
developed in a way that we expect to be applicable to Kerr space-time
Precise determination of the lattice spacing in full lattice QCD
We compare three different methods to determine the lattice spacing in
lattice QCD and give results from calculations on the MILC ensembles of
configurations that include the effect of , and sea quarks. It is
useful, for ensemble to ensemble comparison, to express the results as giving a
physical value for , a parameter from the heavy quark potential. Combining
the three methods gives a value for in the continuum limit of
0.3133(23)(3) fm. Using the MILC values for , this corresponds to a
value for the parameter of 0.4661(38) fm. We also discuss how to use the
for determining the lattice spacing and tuning the -quark mass
accurately, by giving values for (0.6858(40) GeV) and
(0.1815(10) GeV).Comment: 15 page
Pollution in the open oceans: 2009-2013
This review of pollution in the open oceans updates a report on this topic prepared by GESAMP five years previously (Reports and Studies No. 79, GESAMP, 2009). The latter report, the first from GESAMP focusing specifically on the oceans beyond the 200 m depth contour, was prepared for purposes of the Assessment of Assessments, the preparatory phase of a regular process for assessing the state of the marine environment, led jointly by the United Nations Environment Programme (UNEP) and the Intergovernmental Oceanographic Commission (UNESCO-IOC)
Structural perfection of Hg1−xCdxTe Grown by THM
The defect structure of single crystals of Hg1-xCdxTe grown by the travelling heater method (THM) has been investigated using X-ray double crystal topography and a chemical etching technique. The structural perfection is found to depend on the ratio of growth and solidus temperature Tg/Ts
Criteria for dynamically stable decoherence-free subspaces and incoherently generated coherences
We present a detailed analysis of decoherence free subspaces and develop a
rigorous theory that provides necessary and sufficient conditions for
dynamically stable decoherence free subspaces. This allows us to identify a
special class of decoherence free states which rely on incoherent generation of
coherences. We provide examples of physical systems that support such states.
Our approach employs Markovian master equations and applies primarily to
finite-dimensional quantum systems
Catching on to concatenation : evidence for prepollination intrasexual selection in plants
[from introduction] Darwin (1871) proposed the mechanism of sexual selection to explain the extreme traits, secondary sex characters, seen primarily in male animals for either display or competition. These elaborate traits for attracting members of the opposite sex or competing for access to mates, inter- and intra-sexual selection, respectively, would increase the mating success of individuals but may reduce individual survival. Sexual selection has traditionally been associated with motile, dioecious animals that have well-developed sensory abilities and has long been viewed as absent as a mode of selection in plants (Grant, 1995). However, since the 1980s, several workers have argued that sexual selection is applicable to plants and should be considered as a factor in floral evolution (Skogsmyr & Lankinen, 2002). Opponents such as Grant (1995) point to incompatibility with Darwin’s usage, hermaphroditism, the absence of obvious secondary sex characters and the apparent absence of female choice in plants (Skogsmyr & Lankinen, 2002; Moore & Pannell, 2011). Proponents, however, argue that historical definitions should be expanded to explain modern evidence and that sexual selection can, in principle, occur in hermaphrodites and hence play a role in the evolution of floral traits. The latter view is supported by a recent study by Cocucci et al. (this issue of New Phytologist, pp. 280–286) which demonstrates intra-sexual selection in plants via direct male–male competition between the pollinaria of milkweeds for optimal attachment sites on pollinators to ensure subsequent pollinium deposition. This is the first example of male–male competition resulting in secondary sex characters in hermaphrodite plants, highlighting the possibility of overlooked mechanisms of sexual selection in plants
Eigenvector Approximation Leading to Exponential Speedup of Quantum Eigenvalue Calculation
We present an efficient method for preparing the initial state required by
the eigenvalue approximation quantum algorithm of Abrams and Lloyd. Our method
can be applied when solving continuous Hermitian eigenproblems, e.g., the
Schroedinger equation, on a discrete grid. We start with a classically obtained
eigenvector for a problem discretized on a coarse grid, and we efficiently
construct, quantum mechanically, an approximation of the same eigenvector on a
fine grid. We use this approximation as the initial state for the eigenvalue
estimation algorithm, and show the relationship between its success probability
and the size of the coarse grid.Comment: 4 page
Mimics and magnets : The importance of color and ecological facilitation in floral deception
Plants that lack floral rewards can attract pollinators if they share attractive floral signals with rewarding plants. These deceptive plants should benefit from flowering in close proximity to such rewarding plants, because pollinators are locally conditioned on floral signals of the rewarding plants (mimic effect) and because pollinators are more abundant close to rewarding plants (magnet effect). We tested these ideas using the non-rewarding South African plant Eulophia zeyheriana (Orchidaceae) as a study system. Field observations revealed that E. zeyheriana is pollinated solely by solitary bees belonging to a single species of Lipotriches (Halictidae) that appears to be closely associated with the flowers of Wahlenbergia cuspidata (Campanulaceae), a rewarding plant with which the orchid is often sympatric. The pale blue color of the flowers of E. zeyheriana differs strongly from flowers of its congeners, but is very similar to that of flowers of W. cuspidata. Analysis of spectral reflectance patterns using a bee vision model showed that bees are unlikely to be able to distinguish the two species in terms of flower color. A UV-absorbing sunscreen was applied to the flowers of the orchid in order to alter their color, and this resulted in a significant decline in pollinator visits, thus indicating the importance of flower color for attraction of Lipotriches bees. Pollination success in the orchid was strongly affected by proximity to patches of W. cuspidata. This was evident from one of two surveys of natural populations of the orchid, as well as experiments in which we translocated inflorescences of the orchid either into patches of W. cuspidata or 40 m outside such patches. Flower color and location of E. zeyheriana plants relative to rewarding magnet patches are therefore key components of the exploitation by this orchid of the relationship between W. cuspidata and Lipotriches bee pollinators
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