866 research outputs found
Efficient oxide phosphors for light upconversion; green emission from Yb3+ and Ho3+ co-doped Ln(2)BaZnO(5) (Ln = Y, Gd)
This is the author's accepted version of the article. The final published article can be found here: http://dx.doi.org/10.1039/C0JM01652
The persistence of a chlorophyll spectral biosignature from Martian evaporite and spring analogues under Mars-like conditions
Spring and evaporite deposits are considered two of the most promising environments for past habitability on Mars and preservation of biosignatures. Manitoba, Canada hosts the East German Creek (EGC) hypersaline spring complex, and the post impact evaporite gypsum beds of the Lake St. Martin (LSM) impact. The EGC complex has microbial mats, sediments, algae and biofabrics, while endolithic communities are ubiquitous in the LSM gypsum beds. These communities are spectrally detectable based largely on the presence of a chlorophyll absorption band at 670 nm; however, the robustness of this feature under Martian surface conditions was unclear. Biological and biology-bearing samples from EGC and LSM were exposed to conditions similar to the surface of present day Mars (high UV flux, 100 mbar, anoxic, CO_2 rich) for up to 44 days, and preservation of the 670 nm chlorophyll feature and chlorophyll red-edge was observed. A decrease in band depth of the 670 nm band ranging from ∼16 to 80% resulted, with correlations seen in the degree of preservation and the spatial proximity of samples to the spring mound and mineral shielding effects. The spectra were deconvolved to Mars Exploration Rover (MER) Pancam and Mars Science Laboratory (MSL) Mastcam science filter bandpasses to investigate the detectability of the 670 nm feature and to compare with common mineral features. The red-edge and 670 nm feature associated with chlorophyll can be distinguished from the spectra of minerals with features below ∼1000 nm, such as hematite and jarosite. However, distinguishing goethite from samples with the chlorophyll feature is more problematic, and quantitative interpretation using band depth data makes little distinction between iron oxyhydroxides and the 670 nm chlorophyll feature. The chlorophyll spectral feature is observable in both Pancam and Mastcam, and we propose that of the proposed EXOMARS Pancam filters, the PHYLL filter is best suited for its detection
Noncommutative Geometry Framework and The Feynman's Proof of Maxwell Equations
The main focus of the present work is to study the Feynman's proof of the
Maxwell equations using the NC geometry framework. To accomplish this task, we
consider two kinds of noncommutativity formulations going along the same lines
as Feynman's approach. This allows us to go beyond the standard case and
discover non-trivial results. In fact, while the first formulation gives rise
to the static Maxwell equations, the second formulation is based on the
following assumption
The results extracted from the second formulation are more significant since
they are associated to a non trivial -extension of the Bianchi-set of
Maxwell equations. We find and where
, , and are local functions depending on
the NC -parameter. The novelty of this proof in the NC space is
revealed notably at the level of the corrections brought to the previous
Maxwell equations. These corrections correspond essentially to the possibility
of existence of magnetic charges sources that we can associate to the magnetic
monopole since is not vanishing in general.Comment: LaTeX file, 16 page
Pseudo-Riemannian manifolds with recurrent spinor fields
The existence of a recurrent spinor field on a pseudo-Riemannian spin
manifold is closely related to the existence of a parallel
1-dimensional complex subbundle of the spinor bundle of . We
characterize the following simply connected pseudo-Riemannian manifolds
admitting such subbundles in terms of their holonomy algebras: Riemannian
manifolds; Lorentzian manifolds; pseudo-Riemannian manifolds with irreducible
holonomy algebras; pseudo-Riemannian manifolds of neutral signature admitting
two complementary parallel isotropic distributions.Comment: 13 pages, the final versio
Counteracting Green Alder Shrub Expansion by Low-Input Grazing
In the past decades, the decline of traditional agriculture has caused an abandonment of marginal pastures in many mountain areas of Europe. In the Swiss Alps, green alder (Alnus viridis) is the most abundant successional shrub. A survey of 24 pasture-shrub gradients showed that the encroachment by green alder, in contrast to other shrubs, is associated with a substantial decline in plant species richness. The understorey of alder is primarily populated by very few, broad-leaved herbaceous species benefitting from the atmospheric nitrogen fixed by actinomycetes in symbiosis with green alder. However, the understory vegetation also provides an underestimated forage, rich in protein and comparable in productivity and digestibility to nearby open pastures. A two-year grazing experiment with cattle (Dexter), sheep (local Engadine sheep) and mixed-breed goats in the Eastern Swiss Alps demonstrated that robust breeds were able to exploit these resources as they readily penetrated the thickets. The Engadine sheep and the goats consumed green alder bark and thus actively counteracted shrub encroachment. Dexter cattle did not forage on alder bark but on leaves and opened the thickets by their movement through them. Since goats preferred other woody species to green alder and depleted them before the alder, they may impair the regeneration of late-successional forest. Dexter heifers and Engadine lambs performed equally well on pastures with high shrub cover and on open pastures in terms of average daily weight gain, carcass and meat quality. This was facilitated by the comparatively low productivity of these breeds. In this way, low-input grazing systems utilizing adapted breeds, especially sheep, can add to conservation goals and sustain a viable meat production in marginal areas
Berry effect in acoustical polarization transport in phononic crystals
We derive the semiclassical equations of motion of a transverse acoustical
wave packet propagating in a phononic crystal subject to slowly varying
perturbations. The formalism gives rise to Berry effect terms in the equations
of motion, manifested as the Rytov polarization rotation law and the
polarization-dependent Hall effect. We show that the formalism is also
applicable to the case of non-periodic inhomogeneous media, yielding explicit
expressions for the Berry effect terms.Comment: To appear in JETP Let
New Einstein-Sasaki and Einstein Spaces from Kerr-de Sitter
In this paper, which is an elaboration of our results in hep-th/0504225, we
construct new Einstein-Sasaki spaces L^{p,q,r_1,...,r_{n-1}} in all odd
dimensions D=2n+1\ge 5. They arise by taking certain BPS limits of the
Euclideanised Kerr-de Sitter metrics. This yields local Einstein-Sasaki metrics
of cohomogeneity n, with toric U(1)^{n+1} principal orbits, and n real
non-trivial parameters. By studying the structure of the degenerate orbits we
show that for appropriate choices of the parameters, characterised by the (n+1)
coprime integers (p,q,r_1,...,r_{n-1}), the local metrics extend smoothly onto
complete and non-singular compact Einstein-Sasaki manifolds
L^{p,q,r_1,...,r_{n-1}}. We also construct new complete and non-singular
compact Einstein spaces \Lambda^{p,q,r_1,...,r_n} in D=2n+1 that are not
Sasakian, by choosing parameters appropriately in the Euclideanised Kerr-de
Sitter metrics when no BPS limit is taken.Comment: latex, 26 page
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