Raman imaging and electronic properties of graphene

Graphite is a well-studied material with known electronic and optical properties. Graphene, on the other hand, which is just one layer of carbon atoms arranged in a hexagonal lattice, has been studied theoretically for quite some time but has only recently become accessible for experiments. Here we demonstrate how single- and multi-layer graphene can be unambiguously identified using Raman scattering. Furthermore, we use a scanning Raman set-up to image few-layer graphene flakes of various heights. In transport experiments we measure weak localization and conductance fluctuations in a graphene flake of about 7 monolayer thickness. We obtain a phase-coherence length of about 2 $\mu$m at a temperature of 2 K. Furthermore we investigate the conductivity through single-layer graphene flakes and the tuning of electron and hole densities via a back gate

Raman Topography and Strain Uniformity of Large-Area Epitaxial Graphene

We report results from two-dimensional Raman spectroscopy studies of large-area epitaxial graphene grown on SiC. Our work reveals unexpectedly large variation in Raman peak position across the sample resulting from inhomogeneity in the strain of the graphene film, which we show to be correlated with physical topography by coupling Raman spectroscopy with atomic force microscopy. We report that essentially strain free graphene is possible even for epitaxial graphene.Comment: 10 pages, 3 figure

LISA L3 gravity wave observatory: Non-linear modelling and possible DFAC methods

Recently, we witnessed the revolutionary discovery of gravitational waves (GW) by a ground-based laser interferometric observatory: a potentially game-changing observation tool in astronomy. Hence, the opportunity of setting up a space-based GW observatory, including their low-frequency spectrum not accessible from the ground, is gaining more and more support. In this framework, the Laser Interferometer Space Antenna (LISA) mission has been already selected, within the European Space Agency selection of the L3 launch opportunity. Consequently, LISA might be the first space mission scanning the sky to retrieve both polarisations of the GWs simultaneously, and to measure their source parameters in a bandwidth spanning from 10-4 to 10-1 Hz. The latest LISA mission concept, nominally lasting 4 years in Science Mode, encompasses three identical satellites, in an Earth-trailing heliocentric orbit about 50 Mkm from the Earth. What is more, the three satellites will be placed in a triangular constellation, whose three arms, averagely long 2.5 Mkm, are endowed with six optical links for laser interferometry. Laser interferometry aims to measure, with high accuracy, the distance variations among the free-flying test masses hosted in the three spacecrafts. To this purpose, each spacecraft is drag-free controlled, in order to follow its own two test masses, along each of its two interferometric axes. In this paper, we first review the general aspects of the LISA mission, including those successfully tested in the LISA Pathfinder experiment. Then, an overall non-linear model is proposed to describe the LISA constellation dynamics. Possible methodologies for the LISA Drag-Free Attitude Control System (DFACS) are finally discussed

role of winter host plants in vineyard colonization and phenology of zygina rhamni hemiptera cicadellidae typhlocybinae

Abstract Zygina rhamni Ferrari (Hemiptera: Cicadellidae: Typhlocybinae) is a mesophyll-feeding leafhopper that infests grapevine, Vitis vinifera L. This leafhopper's overwintering strategy and the dynamics of its vineyard colonization, relative to the distance between the grapevines and the winter host plants and different grapevine vegetative densities, are described herein. This species shows a facultative heteroecious life cycle. In autumn, it migrates from vineyards to bramble, Rubus gr. fruticosus, and rose, Rosa chinensis Jacquin. On these host plants, females lay eggs that start to hatch at the end of March. Adults that developed on bramble colonize grapevines beginning in May; the leaf fall of rose, which takes place during the first half of April, probably causes the death of unhatched eggs and nymphs. We found that overwintering females can move back to vineyards and lay eggs until early June. The dynamics of vineyard colonization by the leafhopper involved initial concentration in areas close t..

Genetic differentiation among host-associated Alebra leafhoppers (Hemiptera: Cicadellidae)

The limited importance ascribed to sympatric speciation pro cesses via host race formation is partially due to the few cases of host races that have been reported among host populations. This work sheds light on the taxonomy of Alebra leafhoppers and examines the possible existence of host races among host-associated populations. The species of this genus show varying degrees of host association with deciduous trees and shrubs and, frequently, host popu lations of uncertain taxonomic status coexist and occasion ally become pests. Allozyme electrophoresis of 21 Greek populations including sympatric, local and geographically distant samples collected on 13 different plant species, show that they represent at least five species: A. albostriella Falle´n, A. viridis (Rey) (sensu Gillham), A. wahlbergi Bo Keywords: host races; leafhoppers; sympatric speciation; sibling species; allozymes; Alebra Introduction Sympatric speciation is a controversial subject in evol utionary biology (see Mayr, 1963; Futuyma and Mayer, 1980; Paterson, 1981; Via, 2001). One of the reasons for this controversy is that sympatric speciation seems to be an extremely rare phenomenon occurring only in very few groups of taxa, represented chiefly by phytophagous insects (Tauber and Tauber, 1977; Menken, 1981; Wood, 1993; Emelianov et al, 1995; Via, 1999; Finchak et al, 2000; Craig et al, 2001). The limited number of reported cases among organisms with sexual reproduction can be at least partially attributed to the fact that taxa undergoing sympatric speciation events must fulfill very restrictive biological and ecological requirements. Most sympatric speciation models demand that there is intraspecific genetic variation in traits that differentially affect the fitness of individuals that colonise new habitats or hosts (Dieckman and Doebeli, 1999; Hawthorne and Via, 2001 but see Higashi et al, 1999 and Takimoto et al, 2000). They assume that selection acting on these traits can prevent genetic exchange between populations (Bush, 1975; Tauber and Tauber, 1977; Diehl and Bush, 1989). In phytophagous insects, this means that host pref erences must be genetically determined and mating should occur on the host (Bush, 1975; Diehl and Bush, Correspondence: D Aguin-Pombo, Department of Biology, University of Madeira, Campus Universitario da Penteada, 9000 Funchal, Madeira, Portugal. E-mail: aguin uma.pt Received 12 December 2000; accepted 13 December 2001 heman and two new species. Of these, one is associated to Quercus frainetto and other is specific to Crataegus spp. Significant genetic differences among sympatric and local host populations were found only in A. albostriella, between populations on Turkey oak, beech and common alder. It is suggested that the last two of these host populations may represent different host races. The results show that both the host plant and geographical distance affect the patterns of differentiation in the genus. The formation of some spec ies seems to have been the result of allopatric speciation events while, for others, their origin can be equally explained either by sympatric or allopatric speciation.info:eu-repo/semantics/publishedVersio

Quantifying defects in graphene via Raman spectroscopy at different excitation energies.

We present a Raman study of Ar(+)-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities, for a given defect density, strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an interdefect distance ∼3 nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity

seasonal abundance of the nearctic gall midge obolodiplosis robiniae in italy and the impact of its antagonist platygaster robiniae on pest populations

The Nearctic gall midge Obolodiplosis robiniae (Haldeman, 1847) (Diptera Cecidomyiidae) infesting black locusts, Robinia pseudoacacia L. (Fabaceae), was detected in Asia in 2002 and in Europe (first in Italy) in 2003. Its distribution in Europe has expanded dramatically, probably favored by extensive distribution of its host plant along the main routes. The results of a 3-yr study on the seasonal abundance of O. robiniae in northern Italy are reported here. O. robiniae can develop three to four generations per year by exploiting plants of different ages and vigor. Overwintering takes place as diapausing larvae and adults emerge in spring. Two generations are completed on mature plants where populations decline in summer. Two additional generations can develop on root suckers from midsummer onward. Pest population densities reach their highest levels in late spring. Gall midge larvae were attacked by various predators, but parasitism by the platygastrid Platygaster robiniae Buhl & Duso was particularly significant. The impact of parasitism by P. robiniae is indicated as a key factor in reducing O. robiniae population densities

Phytoplasma transmission: Insect rearing and infection protocols

Phytoplasmas are obligate pathogens and thus they can be studied only in association with their plants or insect hosts. In this chapter, we present protocols for rearing some phytoplasma insect vectors, to obtain infected insects and plants under controlled environmental conditions. We focus on Euscelidius variegatus and Macrosteles quadripunctulatus that can infect Arabidopsis thaliana, and Hyalesthes obsoletus and Scaphoideus titanus, that can infect grapevine

Cold winter temperatures condition the egg-hatching dynamics of a grape disease vector

The leafhopper Scaphoideus titanus is the vector of a major phytoplasma grapevine disease, Flavescence dorée. The vector’s distribution is in Eastern and Northern Europe, and its population dynamics varies as a function of vineyard latitude. We tested the hypothesis that hatching dynamics are cued by cold temperatures observed in winter. We exposed eggs from a natural population to simulated “cold” and “mild” winters and varied the exposure time at 5 °C from 0 to 63 days. We show that temperature cooling mainly affected the onset of hatching and is negatively correlated to the cold time exposure. The majority of hatchings occurred more quickly in cold rather than in mild winter simulated conditions, but there was no significant difference between the duration of hatching of eggs whatever the cold time exposure. In agreement with the Northern American origin of the vector, the diapause termination and thus the timing regulation of egg hatching require cold winters

Raman spectroscopy as a versatile tool for studying the properties of graphene.

Raman spectroscopy is an integral part of graphene research. It is used to determine the number and orientation of layers, the quality and types of edge, and the effects of perturbations, such as electric and magnetic fields, strain, doping, disorder and functional groups. This, in turn, provides insight into all sp(2)-bonded carbon allotropes, because graphene is their fundamental building block. Here we review the state of the art, future directions and open questions in Raman spectroscopy of graphene. We describe essential physical processes whose importance has only recently been recognized, such as the various types of resonance at play, and the role of quantum interference. We update all basic concepts and notations, and propose a terminology that is able to describe any result in literature. We finally highlight the potential of Raman spectroscopy for layered materials other than graphene