Multidomain switching in the ferroelectric nanodots

Controlling the polarization switching in the ferroelectric nanocrystals, nanowires and nanodots has an inherent specificity related to the emergence of depolarization field that is associated with the spontaneous polarization. This field splits the finite-size ferroelectric sample into polarization domains. Here, based on 3D numerical simulations, we study the formation of 180$^{\circ }$ polarization domains in a nanoplatelet, made of uniaxial ferroelectric material, and show that in addition to the polarized monodomain state, the multidomain structures, notably of stripe and cylindrical shapes, can arise and compete during the switching process. The multibit switching protocol between these configurations may be realized by temperature and field variations

Transceivers and Spectrum Usage Minimization in Few-Mode Optical Networks

Metro-Area networks are likely to create the right conditions for the deployment of few-mode transmission (FMT) due to limited metro distances and rapidly increasing metro traffic. To address the new network design problems arising with the adoption of FMT, integer linear programming (ILP) formulations have already been developed to optimally assign modulation formats, baud rates, and transmission modes to lightpaths, but these formulations lack scalability, especially when they incorporate accurate constraints to capture inter-modal coupling. In this paper, we propose a heuristic approach for the routing, modulation format, baud rate and spectrum allocation in FMT networks with arbitrary topology, accounting for inter-modal coupling and for distance-Adaptive reaches of few-mode (specifically, up to five modes) signals generated by either full multi-in multi-out (MIMO) or low-complexity MIMO transceivers and for two different switching scenarios (i.e., spatial full-joint and fractional-joint switching). In our illustrative numerical analysis, we first confirm the quasi-optimality of our heuristic by comparing it to the optimal ILP solutions, and then we use our heuristic to identify which switching scenario and FMT transceiver technology minimize spectrum occupation and transceiver costs, depending on the relative costs of transceiver equipment and dark fiber leasing

Further studies on the use of molecular probes to grapevine closterovirus A

Two cloned cDNA probes to genomic RNA of grapevine closterovirus A (GVA) were utilized successfully for the detection of viral sequences in infected herbaceous hosts (Nicotiana benthamiana) and grapevines. One of the probes (pGA112) was complementary to the central part of the viral genome and gave light false positive signals with healthy grapevine extracts, whereas the other (pGA240), which is presumably colinear with the 3' terminus, was virus-specific and hybridized only with infected sample extracts. The two probes recognized smaller than genome RNAs in electrophoresed N. benthamiana extracts and hybridized differentially with the bands, thus suggesting that these represent subgenomic RNAs. Probe pGA240 may be used for GVA detection, but the preparation of samples for hybridization needs further improvement for routine testing.Weitere Untersuchungen über die Verwendung von Molekülsonden beim Grapevine-Closterovirus AZwei klonierte cDNA-Sonden für genomische RNA des Grapevine-Closterovirus A (GVA} wurden mit Erfolg zum Nachweis von Virussequenzen in infizierten krautigen Wirtspflanzen (Nicotiana benthamiana) und Reben benützt. Die eine Sonde (pGA112} war komplementär zum zentralen Teil des Virusgenoms und lieferte schwache falsch-positive Nachweisreaktionen mit Extrakten aus gesunden Reben; die andere Sonde (pGA240}, die vermutlich kolinear mit dem 3'-Terminus ist, war dagegen virusspezifisch und hybridisierte nur mit Extrakten aus infizierten Proben. In elektrophoretisch aufgetrennten N. benthamiana-Extrakten "erkannten" die beiden Sonden RNAs von weniger als Genomgröße; sie hybridisierten differenziert mit den Banden, so daß diese subgenomische RNAs darstellen könnten. Die Sonde pGA240 kann für den GVA-Nachweis verwendet werden; für Routinetests muß die Vorbereitung der Proben für die Hybridisierung noch verbessert werden

M-theory and Seven-Dimensional Inhomogeneous Sasaki-Einstein Manifolds

Seven-dimensional inhomogeneous Sasaki-Einstein manifolds $Y^{p,k}(KE_4)$ present a challenging example of AdS/CFT correspondence. At present, their field theory duals for $KE_4=\mathbb{CP}^2$ base are proposed only within a restricted range $3p/2\le k \le 2p$ as ${\cal N}=2$ quiver Chern-Simons-matter theories with $SU(N)\times SU(N)\times SU(N)$ gauge group, nine bifundamental chiral multiplets interacting through a cubic superpotential. To further elucidate this correspondence, we use particle approximation both at classical and quantum level. We setup a concrete AdS/CFT mapping of conserved quantities using geodesic motions, and turn to solutions of scalar Laplace equation in $Y^{p,k}$. The eigenmodes also provide an interesting subset of Kaluza-Klein spectrum for $D=11$ supergravity in ${\rm AdS}_4\times Y^{p,k}$, and are dual to protected operators written in terms of matter multiplets in the dual conformal field theory.Comment: v2 refs added. 19 pages 1 figur

Beta, Dipole and Noncommutative Deformations of M-theory Backgrounds with One or More Parameters

We construct new M-theory solutions starting from those that contain 5 U(1) isometries. We do this by reducing along one of the 5-torus directions, then T-dualizing via the action of an O(4,4) matrix and lifting back to 11-dimensions. The particular T-duality transformation is a sequence of O(2,2) transformations embedded in O(4,4), where the action of each O(2,2) gives a Lunin-Maldacena deformation in 10-dimensions. We find general formulas for the metric and 4-form field of single and multiparameter deformed solutions, when the 4-form of the initial 11-dimensional background has at most one leg along the 5-torus. All the deformation terms in the new solutions are given in terms of subdeterminants of a 5x5 matrix, which represents the metric on the 5-torus. We apply these results to several M-theory backgrounds of the type AdS_r x X^{11-r}. By appropriate choices of the T-duality and reduction directions we obtain analogues of beta, dipole and noncommutative deformations. We also provide formulas for backgrounds with only 3 or 4 U(1) isometries and study a case, for which our assumption for the 4-form field is violated.Comment: v2:minor corrections, v3:small improvements, v4:conclusions expanded, to appear in Class. Quant. Gra

Virus-like particles and ultrastructural modifications in the phloem of leafroll-affected grapevines

Ultrastructural studies were carried out on thin-sectioned phloem and mesophyll tissues of 42 grapevine accessions with leafroll symptoms, coming from 12 different countries (Italy, Portugal, Spain, France, Yugoslavia, Hungary, Soviet Union, Bulgaria, Greece, Cyprus, Malta and Nigeria). A total of 47 specimens were observed with the electron microscope. About half (48 %) the samples examined contained isometric virus-like particles in one or more phloem elements (sieve tubes, companion and parenchyma cells), whereas only 15 % of the samples contained filamentous virus-like particles in the same type of cells. None of these viruses could be transmitted by sap inoculation. Ultrastructural features of major importance were double-membraned vesiculated bodies possibly representing profoundly modified cell organelles (mitochondria and/or plastids) and bundles of tubular structures 40-45 nm or 60-100 nm in diameter, the !arger of which exhibited a central core seemingly made up of one or more filaments of tubular P-protein. The present results are discussed in the light of the findings reported in the literature on leafroll-infected grapevine tissues.Virusartige Partikeln und Veränderungen der Ultrastruktur im Phloem blattrollkranker RebenBei 42 Rebenstämmen mit Blattrollsymptomen wurde die Ultrastruktur des Blattphloems und Mesophylls untersucht. Die Reben stammten aus 12 verschiedenen Ländern (Italien, Portugal, Spanien, Frankreich, Jugoslawien, Ungarn, Sowjetunion, Bulgarien, Griechenland, Cypern, Malta und Nigeria). Insgesamt wurden 47 Exemplare elektronenmikroskopisch untersucht. Etwa die Hälfte der Proben (48 %) enthielt isometrische virusartige Partikeln in einem oder mehreren Phloemelementen (Siebröhren, Geleit- und Parenchymzellen); bei 15 % der Proben waren in denselben Zelltypen filamentöse virusartige Partikeln enthalten. Eine Saftübertragung der Viren war in keinem Falle möglich. Wichtige ultrastrukturelle Bildungen waren doppelwandige vesiculäre Körper, die möglicherweise stark abgewandelte Zellorganellen (Mitochondrien und/oder Plastiden) darstellen, sowie Bündel tubulärer Strukturen vom Durchmesser 40-45 nm oder 60-100 nm; die größeren Tubuli zeigten einen zentralen Kern, der anscheinend von einem oder mehreren Filamenten tubulären P-Proteins gebildet wurde. Die vorliegenden Ergebnisse werden im Zusammenhang mit den Literaturbefunden über blattrollinfiziertes Rebengewebe diskutiert

Resolution à la Kronheimer of C3/ Γ singularities and the Monge–Ampère equation for Ricci-flat Kähler metrics in view of D3-brane solutions of supergravity

In this paper, we analyze the relevance of the generalized Kronheimer construction for the gauge/gravity correspondence. We begin with the general structure of D3-brane solutions of type IIB supergravity on smooth manifolds YΓ that are supposed to be the crepant resolution of quotient singularities C3/ Γ with Γ a finite subgroup of SU(3). We emphasize that nontrivial 3-form fluxes require the existence of imaginary self-dual harmonic forms ω2 , 1. Although excluded in the classical Kronheimer construction, they may be reintroduced by means of mass deformations. Next we concentrate on the other essential item for the D3-brane construction, namely, the existence of a Ricci-flat metric on YΓ. We study the issue of Ricci-flat Kähler metrics on such resolutions YΓ, with particular attention to the case Γ = Z4. We advance the conjecture that on the exceptional divisor of YΓ the Kronheimer Kähler metric and the Ricci-flat one, that is locally flat at infinity, coincide. The conjecture is shown to be true in the case of the Ricci-flat metric on tot KWP[112] that we construct, i.e., the total space of the canonical bundle of the weighted projective space WP[112] , which is a partial resolution of C3/ Z4. For the full resolution, we have YZ4=totKF2, where F2 is the second Hirzebruch surface. We try to extend the proof of the conjecture to this case using the one-parameter Kähler metric on F2 produced by the Kronheimer construction as initial datum in a Monge–Ampère (MA) equation. We exhibit three formulations of this MA equation, one in terms of the Kähler potential, the other two in terms of the symplectic potential but with two different choices of the variables. In both cases, one can establish a series solution in powers of the variable along the fibers of the canonical bundle. The main property of the MA equation is that it does not impose any condition on the initial geometry of the exceptional divisor, rather it uniquely determines all the subsequent terms as local functionals of this initial datum. Although a formal proof is still missing, numerical and analytical results support the conjecture. As a by-product of our investigation, we have identified some new properties of this type of MA equations that we believe to be so far unknown

Supersymmetric AdS_5 solutions of M-theory

We analyse the most general supersymmetric solutions of D=11 supergravity consisting of a warped product of five-dimensional anti-de-Sitter space with a six-dimensional Riemannian space M_6, with four-form flux on M_6. We show that M_6 is partly specified by a one-parameter family of four-dimensional Kahler metrics. We find a large family of new explicit regular solutions where M_6 is a compact, complex manifold which is topologically a two-sphere bundle over a four-dimensional base, where the latter is either (i) Kahler-Einstein with positive curvature, or (ii) a product of two constant-curvature Riemann surfaces. After dimensional reduction and T-duality, some solutions in the second class are related to a new family of Sasaki-Einstein spaces which includes T^{1,1}/Z_2. Our general analysis also covers warped products of five-dimensional Minkowski space with a six-dimensional Riemannian space.Comment: 40 pages. v2: minor changes, eqs. (2.22) and (D.12) correcte

A Note on Einstein Sasaki Metrics in D \ge 7

In this paper, we obtain new non-singular Einstein-Sasaki spaces in dimensions D\ge 7. The local construction involves taking a circle bundle over a (D-1)-dimensional Einstein-Kahler metric that is itself constructed as a complex line bundle over a product of Einstein-Kahler spaces. In general the resulting Einstein-Sasaki spaces are singular, but if parameters in the local solutions satisfy appropriate rationality conditions, the metrics extend smoothly onto complete and non-singular compact manifolds.Comment: Latex, 13 page