1,721,451 research outputs found
General O(D)-equivariant fuzzy hyperspheres via confining potentials and energy cutoffs
No full textWe summarize our recent construction [1–3] of new fuzzy hyperspheres SΛd of arbitrary dimension d ∈ N covariant under the full orthogonal group O(D), D = d+1. We impose a suitable energy cutoff on a quantum particle in RD subject to a confining potential well V(r) with a very sharp minimum on the sphere of radius r = 1; the cutoff and the depth of the well diverge with Λ ∈ N. Consequently, the commutators of the Cartesian coordinates xi are proportional to the angular momentum components Lij, as in Snyder’s noncommutative spaces. The xi generate the whole algebra of observables AΛ and thus the whole Hilbert space HΛ when applied to any state. HΛ carries a reducible representation of O(D) isomorphic to the space of harmonic homogeneous polynomials of degree Λ in the Cartesian coordinates of (commutative) RD+1; the latter carries an irreducible representation πΛ of O(D+1) ⊃ O(D). Moreover, AΛ is isomorphic to πΛ (Uso(D+1)). We identify the subspace CΛ ⊂ AΛ spanned by fuzzy spherical harmonics. We interpret {HΛ}Λ∈N, {CΛ}Λ∈N as fuzzy deformations of the space Hs ≡ L2(Sd) of square integrable functions and the space C(Sd) of continuous functions on Sd respectively, {AΛ}Λ∈N as fuzzy deformation of the associated algebra As of observables, because they resp. go to Hs,C(Sd), As as Λ diverges (with fixed ħ). With suitable ħ = ħ(Λ) Λ−→ →∞ 0, in the same limit AΛ goes to the (algebra of functions on the) Poisson manifold T∗Sd; more formally, {AΛ}Λ∈N yields a fuzzy quantization of a coadjoint orbit of O(D+1) that goes to the classical phase space T∗Sd. These models might be useful in quantum field theory, quantum gravity or condensed matter physics
Transition from Deflagration to Detonation Following Jet Ignition in Premixed H2-Air Mixtures
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Barriere verticali impermeabili e sistemi di drenaggio per il risanamento di un'area industriale inquinata
No full textTwisted submanifolds of Rn
No full textWe propose a general procedure to construct noncommutative deformations of an embedded submanifold M of Rn determined by a set of smooth equations fa(x) = 0. We use the framework of Drinfel’d twist deformation of differential geometry of Aschieri et al. (Class Quantum Gravity 23:1883, 2006); the commutative pointwise product is replaced by a (generally noncommutative) ⋆ -product determined by a Drinfel’d twist. The twists we employ are based on the Lie algebra Ξ t of vector fields that are tangent to all the submanifolds that are level sets of the fa (tangent infinitesimal diffeomorphisms); the twisted Cartan calculus is automatically equivariant under twisted Ξ t. We can consistently project a connection from the twisted Rn to the twisted M if the twist is based on a suitable Lie subalgebra e⊂ Ξ t. If we endow Rn with a metric, then twisting and projecting to the normal and tangent vector fields commute, and we can project the Levi–Civita connection consistently to the twisted M, provided the twist is based on the Lie subalgebra k⊂ e of the Killing vector fields of the metric; a twisted Gauss theorem follows, in particular. Twisted algebraic manifolds can be characterized in terms of generators and ⋆ -polynomial relations. We present in some detail twisted cylinders embedded in twisted Euclidean R3 and twisted hyperboloids embedded in twisted Minkowski R3 [these are twisted (anti-)de Sitter spaces dS2, AdS2]
Effects of vitamin E and C on placental oxidative stress: an in vitro evidence for the potential therapeutic or prophylactic treatment in PE.
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Dopamine in the ink defence system of Sepia officinalis: biosynthesis, vesicular compartmentation in mature ink gland cells, nitric oxide (NO)/cGMP-induced depletion and fate in secreted ink.
No full textThe biosynthesis, localization, and fate of catecholamines in the ink gland of the cuttlefish S. officinalis were investigated by combined biochem. and immunohistocytochem. methodologies. HPLC anal. of crude ink gland exts. indicated the presence of dopa (2.18 nmol/mg protein) and DA (dopamine, 0.06 nmol/mg protein), but no detectable noradrenaline or adrenaline. DA was shown to derive from L-tyrosine, according to expts. performed by incubating intact ink glands with [L-14C]tyrosine. The biosynthetic process involves a tyrosine hydroxylase and a dopa decarboxylase pathway and is independent of tyrosinase. The tyrosine hydroxylase activity was detected under conditions of tyrosinase suppression in the cytosolic fraction, but not in the melanosomal fraction, of ink gland exts., and the presence of the enzyme was confirmed by Western-blot anal. Dopa and DA were found to be released from the ink glands by processes controlled through the NMDA-nitric oxide-cGMP (where NMDA stands for N -methyl-D-aspartate) signaling pathway, as apparent from incubation expts. performed with [L-14C]tyrosine in the presence of NMDA, diethylamine NONOate (diethylamine diazeniumdiolate), a nitric oxide donor, 8-bromo-CGMP, or a guanylyl cyclase inhibitor. Immunohistochem. results coupled with electron microscopy indicated that DA was concd. in vesicles specifically localized in the mature melanin-producing cells of the ink gland proximal to the lumen and sepd. from the melanin-contg. melanosomes. NMDA receptor stimulation or exposure to an NO donor caused a marked loss of DA immunoreactivity in mature cells, consistent with a release process. In the lumen of the ink gland, where mature exhausted cells pour their contents, DA immunoreactivity was found to be assocd. with the melanin granules, due apparently to phys. adsorption. Overall, these results point to DA as a marker of cell maturation in Sepia ink gland subject to release by the NO/cGMP signaling pathway, and disclose apparently overlooked DA-melanin interactions in secreted ink of possible relevance to the defense mechanism
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