324 research outputs found
Gravitational sliding of the Mt. Etna massif along a sloping basement
Geological field evidence and laboratory modelling indicate that volcanoes constructed on slopes slide downhill. If this happens on an active volcano, then the movement will distort deformation data and thus potentially compromise interpretation. Our recent GPS measurements demonstrate that the entire edifice of Mt. Etna is sliding to the ESE, the overall direction of slope of its complex, rough sedimentary basement. We report methods of discriminating the sliding vector from other deformation processes and of measuring its velocity, which averaged 14 mm year−1 during four intervals between 2001 and 2012. Though sliding of one sector of a volcano due to flank instability is widespread and well-known, this is the first time basement sliding of an entire active volcano has been directly observed. This is important because the geological record shows that such sliding volcanoes are prone to devastating sector collapse on the downslope side, and whole volcano migration should be taken into account when assessing future collapse hazard. It is also important in eruption forecasting, as the sliding vector needs to be allowed for when interpreting deformation events that take place above the sliding basement within the superstructure of the active volcano, as might occur with dyke intrusion or inflation/deflation episodes
Negative Thermal Expansion Coefficient of Graphene Measured by Raman Spectroscopy
The thermal expansion coefficient (TEC) of single-layer graphene is estimated
with temperature-dependent Raman spectroscopy in the temperature range between
200 and 400 K. It is found to be strongly dependent on temperature but remains
negative in the whole temperature range, with a room temperature value of
-8.0x10^{-6} K^{-1}. The strain caused by the TEC mismatch between graphene and
the substrate plays a crucial role in determining the physical properties of
graphene, and hence its effect must be accounted for in the interpretation of
experimental data taken at cryogenic or elevated temperatures.Comment: 17 pagese, 3 figures, and supporting information (4 pages, 3
figures); Nano Letters, 201
Infrared nanoscopy of Dirac plasmons at the graphene-SiO2 interface
We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac
fermions in graphene. This is achieved by confining mid-IR radiation at the
apex of a nanoscale tip: an approach yielding two orders of magnitude increase
in the value of in-plane component of incident wavevector q compared to free
space propagation. At these high wavevectors, the Dirac plasmon is found to
dramatically enhance the near-field interaction with mid-IR surface phonons of
SiO2 substrate. Our data augmented by detailed modeling establish graphene as a
new medium supporting plasmonic effects that can be controlled by gate voltage.Comment: 12 pages, 4 figure
Graphene plasmonics: A platform for strong light-matter interaction
Graphene plasmons provide a suitable alternative to noble-metal plasmons
because they exhibit much larger confinement and relatively long propagation
distances, with the advantage of being highly tunable via electrostatic gating.
We report strong light- matter interaction assisted by graphene plasmons, and
in particular, we predict unprecedented high decay rates of quantum emitters in
the proximity of a carbon sheet, large vacuum Rabi splitting and Purcell
factors, and extinction cross sections exceeding the geometrical area in
graphene ribbons and nanometer-sized disks. Our results provide the basis for
the emerging and potentially far-reaching field of graphene plasmonics,
offering an ideal platform for cavity quantum electrodynamics and supporting
the possibility of single-molecule, single-plasmon devices.Comment: 39 pages, 15 figure
Optical Excitations and Field Enhancement in Short Graphene Nanoribbons
The optical excitations of elongated graphene nanoflakes of finite length are
investigated theoretically through quantum chemistry semi-empirical approaches.
The spectra and the resulting dipole fields are analyzed, accounting in full
atomistic details for quantum confinement effects, which are crucial in the
nanoscale regime. We find that the optical spectra of these nanostructures are
dominated at low energy by excitations with strong intensity, comprised of
characteristic coherent combinations of a few single-particle transitions with
comparable weight. They give rise to stationary collective oscillations of the
photoexcited carrier density extending throughout the flake, and to a strong
dipole and field enhancement. This behavior is robust with respect to width and
length variations, thus ensuring tunability in a large frequency range. The
implications for nanoantennas and other nanoplasmonic applications are
discussed for realistic geometries
Artificial graphene as a tunable Dirac material
Artificial honeycomb lattices offer a tunable platform to study massless
Dirac quasiparticles and their topological and correlated phases. Here we
review recent progress in the design and fabrication of such synthetic
structures focusing on nanopatterning of two-dimensional electron gases in
semiconductors, molecule-by-molecule assembly by scanning probe methods, and
optical trapping of ultracold atoms in crystals of light. We also discuss
photonic crystals with Dirac cone dispersion and topologically protected edge
states. We emphasize how the interplay between single-particle band structure
engineering and cooperative effects leads to spectacular manifestations in
tunneling and optical spectroscopies.Comment: Review article, 14 pages, 5 figures, 112 Reference
Depression and sickness behavior are Janus-faced responses to shared inflammatory pathways
It is of considerable translational importance whether depression is a form or a consequence of sickness behavior. Sickness behavior is a behavioral complex induced by infections and immune trauma and mediated by pro-inflammatory cytokines. It is an adaptive response that enhances recovery by conserving energy to combat acute inflammation. There are considerable phenomenological similarities between sickness behavior and depression, for example, behavioral inhibition, anorexia and weight loss, and melancholic (anhedonia), physio-somatic (fatigue, hyperalgesia, malaise), anxiety and neurocognitive symptoms. In clinical depression, however, a transition occurs to sensitization of immuno-inflammatory pathways, progressive damage by oxidative and nitrosative stress to lipids, proteins, and DNA, and autoimmune responses directed against self-epitopes. The latter mechanisms are the substrate of a neuroprogressive process, whereby multiple depressive episodes cause neural tissue damage and consequent functional and cognitive sequelae. Thus, shared immuno-inflammatory pathways underpin the physiology of sickness behavior and the pathophysiology of clinical depression explaining their partially overlapping phenomenology. Inflammation may provoke a Janus-faced response with a good, acute side, generating protective inflammation through sickness behavior and a bad, chronic side, for example, clinical depression, a lifelong disorder with positive feedback loops between (neuro)inflammation and (neuro)degenerative processes following less well defined triggers
Application of Graphene within Optoelectronic Devices and Transistors
Scientists are always yearning for new and exciting ways to unlock graphene's
true potential. However, recent reports suggest this two-dimensional material
may harbor some unique properties, making it a viable candidate for use in
optoelectronic and semiconducting devices. Whereas on one hand, graphene is
highly transparent due to its atomic thickness, the material does exhibit a
strong interaction with photons. This has clear advantages over existing
materials used in photonic devices such as Indium-based compounds. Moreover,
the material can be used to 'trap' light and alter the incident wavelength,
forming the basis of the plasmonic devices. We also highlight upon graphene's
nonlinear optical response to an applied electric field, and the phenomenon of
saturable absorption. Within the context of logical devices, graphene has no
discernible band-gap. Therefore, generating one will be of utmost importance.
Amongst many others, some existing methods to open this band-gap include
chemical doping, deformation of the honeycomb structure, or the use of carbon
nanotubes (CNTs). We shall also discuss various designs of transistors,
including those which incorporate CNTs, and others which exploit the idea of
quantum tunneling. A key advantage of the CNT transistor is that ballistic
transport occurs throughout the CNT channel, with short channel effects being
minimized. We shall also discuss recent developments of the graphene tunneling
transistor, with emphasis being placed upon its operational mechanism. Finally,
we provide perspective for incorporating graphene within high frequency
devices, which do not require a pre-defined band-gap.Comment: Due to be published in "Current Topics in Applied Spectroscopy and
the Science of Nanomaterials" - Springer (Fall 2014). (17 pages, 19 figures
Torpor on Demand: Heterothermy in the Non-Lemur Primate Galago moholi
Hibernation and daily torpor are energy- and water-saving adaptations employed to survive unfavourable periods mostly in temperate and arctic environments, but also in tropical and arid climates. Heterothermy has been found in a number of mammalian orders, but within the primates so far it seems to be restricted to one family of Malagasy lemurs. As currently there is no evidence of heterothermy of a primate outside of Madagascar, the aim of our study was to investigate whether small primates from mainland Africa are indeed always homeothermic despite pronounced seasonal changes in weather and food availability., which inhabits a highly seasonal habitat with a hot wet-season and a cold dry-season with lower food abundance, was investigated to determine whether it is capable of heterothermy. We measured skin temperature of free-ranging individuals throughout the cool dry season using temperature-sensitive collars as well as metabolic rate in captured individuals. Torpor was employed by 15% of 20 animals. Only one of these animals displayed heterothermy in response to natural availability of food and water, whereas the other animals became torpid without access to food and water. are physiologically capable of employing torpor. However they do not use it as a routine behaviour, but only under adverse conditions. This reluctance is presumably a result of conflicting selective pressures for energy savings versus other ecological and evolutionary forces, such as reproduction or territory defence. Our results support the view that heterothermy in primates evolved before the division of African and Malagasy Strepsirhini, with the possible implication that more primate species than previously thought might still have the potential to call upon this possibility, if the situation necessitates it
Graphene based widely-tunable and singly-polarized pulse generation with random fiber lasers
Pulse generation often requires a stabilized cavity and its corresponding mode structure for initial phase-locking. Contrastingly, modeless cavity-free random lasers provide new possibilities for high quantum efficiency lasing that could potentially be widely tunable spectrally and temporally. Pulse generation in random lasers, however, has remained elusive since the discovery of modeless gain lasing. Here we report coherent pulse generation with modeless random lasers based on the unique polarization selectivity and broadband saturable absorption of monolayer graphene. Simultaneous temporal compression of cavity-free pulses are observed with such a polarization modulation, along with a broadly-tunable pulsewidth across two orders of magnitude down to 900 ps, a broadly-tunable repetition rate across three orders of magnitude up to 3 MHz, and a singly-polarized pulse train at 41 dB extinction ratio, about an order of magnitude larger than conventional pulsed fiber lasers. Moreover, our graphene-based pulse formation also demonstrates robust pulse-to-pulse stability and widewavelength operation due to the cavity-less feature. Such a graphene-based architecture not only provides a tunable pulsed random laser for fiber-optic sensing, speckle-free imaging, and laser-material processing, but also a new way for the non-random CW fiber lasers to generate widely tunable and singly-polarized pulses
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