317 research outputs found
A supersonic crowdion in mica: Ultradiscrete kinks with energy between K recoil and transmission sputtering
In this chapter we analyze in detail the behaviour and properties of the
kinks found in an one dimensional model for the close packed rows of potassium
ions in mica muscovite. The model includes realistic potentials obtained from
the physics of the problem, ion bombardment experiments and molecular dynamics
fitted to experiments. These kinks are supersonic and have an unique velocity
and energy. They are ultradiscrete involving the translation of an interstitial
ion, which is the reason they are called 'crowdions'. Their energy is below the
most probable source of energy, the decay of the K isotope and above the
energy needed to eject an atom from the mineral, a phenomenon that has been
observed experimentallyComment: 28 pages, 15 figure
Dispersive, superfluid-like shock waves in nonlinear optics
In most classical fluids, shock waves are strongly dissipative, their energy
being quickly lost through viscous damping. But in systems such as cold
plasmas, superfluids, and Bose-Einstein condensates, where viscosity is
negligible or non-existent, a fundamentally different type of shock wave can
emerge whose behaviour is dominated by dispersion rather than dissipation.
Dispersive shock waves are difficult to study experimentally, and analytical
solutions to the equations that govern them have only been found in one
dimension (1D). By exploiting a well-known, but little appreciated,
correspondence between the behaviour of superfluids and nonlinear optical
materials, we demonstrate an all-optical experimental platform for studying the
dynamics of dispersive shock waves. This enables us to observe the propagation
and nonlinear response of dispersive shock waves, including the interaction of
colliding shock waves, in 1D and 2D. Our system offers a versatile and more
accessible means for exploring superfluid-like and related dispersive
phenomena.Comment: 21 pages, 6 figures Revised abstrac
Amazonian chemical weathering rate derived from stony meteorite finds at Meridiani Planum on Mars
© The Author(s) 2016.Spacecraft exploring Mars such as the Mars Exploration Rovers Spirit and Opportunity, as well as the Mars Science Laboratory or Curiosity rover, have accumulated evidence for wet and habitable conditions on early Mars more than 3 billion years ago. Current conditions, by contrast, are cold, extremely arid and seemingly inhospitable. To evaluate exactly how dry today's environment is, it is important to understand the ongoing current weathering processes. Here we present chemical weathering rates determined for Mars. We use the oxidation of iron in stony meteorites investigated by the Mars Exploration Rover Opportunity at Meridiani Planum. Their maximum exposure age is constrained by the formation of Victoria crater and their minimum age by erosion of the meteorites. The chemical weathering rates thus derived are ~1 to 4 orders of magnitude slower than that of similar meteorites found in Antarctica where the slowest rates are observed on Earth
Observation of bright polariton solitons in a semiconductor microcavity
Microcavity polaritons are composite half-light half-matter quasi-particles,
which have recently been demonstrated to exhibit rich physical properties, such
as non-equilibrium Bose-Einstein condensation, parametric scattering and
superfluidity. At the same time, polaritons have some important advantages over
photons for information processing applications, since their excitonic
component leads to weaker diffraction and stronger inter-particle interactions,
implying, respectively, tighter localization and lower powers for nonlinear
functionality. Here we present the first experimental observations of bright
polariton solitons in a strongly coupled semiconductor microcavity. The
polariton solitons are shown to be non-diffracting high density wavepackets,
that are strongly localised in real space with a corresponding broad spectrum
in momentum space. Unlike solitons known in other matter-wave systems such as
Bose condensed ultracold atomic gases, they are non-equilibrium and rely on a
balance between losses and external pumping. Microcavity polariton solitons are
excited on picosecond timescales, and thus have significant benefits for
ultrafast switching and transfer of information over their light only
counterparts, semiconductor cavity lasers (VCSELs), which have only nanosecond
response time
The deuteron: structure and form factors
A brief review of the history of the discovery of the deuteron in provided.
The current status of both experiment and theory for the elastic electron
scattering is then presented.Comment: 80 pages, 33 figures, submited to Advances in Nuclear Physic
All-optical routing and switching for three-dimensional photonic circuitry
The ability to efficiently transmit and rapidly process huge amounts of data has become almost indispensable to our daily lives. It turned out that all-optical networks provide a very promising platform to deal with this task. Within such networks opto-optical switches, where light is directed by light, are a crucial building block for an effective operation. In this article, we present an experimental analysis of the routing and switching behaviour of light in two-dimensional evanescently coupled waveguide arrays of Y- and T-junction geometries directly inscribed into fused silica using ultrashort laser pulses. These systems have the fundamental advantage of supporting three-dimensional network topologies, thereby breaking the limitations on complexity associated with planar structures while maintaining a high dirigibility of the light. Our results show how such arrays can be used to control the flow of optical signals within integrated photonic circuits
Going Coastal: Shared Evolutionary History between Coastal British Columbia and Southeast Alaska Wolves (Canis lupus)
Many coastal species occupying the temperate rainforests of the Pacific Northwest in North America comprise endemic populations genetically and ecologically distinct from interior continental conspecifics. Morphological variation previously identified among wolf populations resulted in recognition of multiple subspecies of wolves in the Pacific Northwest. Recently, separate genetic studies have identified diverged populations of wolves in coastal British Columbia and coastal Southeast Alaska, providing support for hypotheses of distinct coastal subspecies. These two regions are geographically and ecologically contiguous, however, there is no comprehensive analysis across all wolf populations in this coastal rainforest.By combining mitochondrial DNA datasets from throughout the Pacific Northwest, we examined the genetic relationship between coastal British Columbia and Southeast Alaska wolf populations and compared them with adjacent continental populations. Phylogenetic analysis indicates complete overlap in the genetic diversity of coastal British Columbia and Southeast Alaska wolves, but these populations are distinct from interior continental wolves. Analyses of molecular variation support the separation of all coastal wolves in a group divergent from continental populations, as predicted based on hypothesized subspecies designations. Two novel haplotypes also were uncovered in a newly assayed continental population of interior Alaska wolves.We found evidence that coastal wolves endemic to these temperate rainforests are diverged from neighbouring, interior continental wolves; a finding that necessitates new international strategies associated with the management of this species
Strain-induced pseudomagnetic field and Landau levels in photonic structures
Magnetic effects at optical frequencies are notoriously weak. This is
evidenced by the fact that the magnetic permeability of nearly all materials is
unity in the optical frequency range, and that magneto-optical devices (such as
Faraday isolators) must be large in order to allow for a sufficiently strong
effect. In graphene, however, it has been shown that inhomogeneous strains can
induce 'pseudomagnetic fields' that behave very similarly to real fields. Here,
we show experimentally and theoretically that, by properly structuring a
dielectric lattice, it is possible to induce a pseudomagnetic field at optical
frequencies in a photonic lattice, where the propagation dynamics is equivalent
to the evolution of an electronic wavepacket in graphene. To our knowledge,
this is the first realization of a pseudomagnetic field in optics. The induced
field gives rise to multiple photonic Landau levels (singularities in the
density of states) separated by band gaps. We show experimentally and
numerically that the gaps between these Landau levels give rise to transverse
confinement of the optical modes. The use of strain allows for the exploration
of magnetic effects in a non-resonant way that would be otherwise inaccessible
in optics. Employing inhomogeneous strain to induce pseudomagnetism suggests
the possibility that aperiodic photonic crystal structures can achieve greater
field-enhancement and slow-light effects than periodic structures via the high
density-of-states at Landau levels. Generalizing these concepts to other
systems beyond optics, for example with matter waves in optical potentials,
offers new intriguing physics that is fundamentally different from that in
purely periodic structures.Comment: 24 pages including supplementary information section, 4 figure
Ecomorph or Endangered Coral? DNA and Microstructure Reveal Hawaiian Species Complexes: Montipora dilatata/flabellata/turgescens & M. patula/verrilli
M. dilatata, M. flabellata, and M. patula and 80 other scleractinian corals were petitioned to be listed under the US Endangered Species Act (ESA), which would have major conservation implications. One of the difficulties with this evaluation is that reproductive boundaries between morphologically defined coral species are often permeable, and morphology can be wildly variable. We examined genetic and morphological variation in Hawaiian Montipora with a suite of molecular markers (mitochondrial: COI, CR, Cyt-B, 16S, ATP6; nuclear: ATPsβ, ITS) and microscopic skeletal measurements. Mitochondrial markers and the ITS region revealed four distinct clades: I) M. patula/M. verrilli, II) M. cf. incrassata, III) M. capitata, IV) M. dilatata/M. flabellata/M. cf. turgescens. These clades are likely to occur outside of Hawai'i according to mitochondrial control region haplotypes from previous studies. The ATPsβ intron data showed a pattern often interpreted as resulting from hybridization and introgression; however, incomplete lineage sorting may be more likely since the multicopy nuclear ITS region was consistent with the mitochondrial data. Furthermore, principal components analysis (PCA) of skeletal microstructure was concordant with the mitochondrial clades, while nominal taxa overlapped. The size and shape of verrucae or papillae contributed most to identifying groups, while colony-level morphology was highly variable. It is not yet clear if these species complexes represent population-level variation or incipient speciation (CA<1MYA), two alternatives that have very different conservation implications. This study highlights the difficulty in understanding the scale of genetic and morphological variation that corresponds to species as opposed to population-level variation, information that is essential for conservation and for understanding coral biodiversity
Genetic Structure of the Polymorphic Metrosideros (Myrtaceae) Complex in the Hawaiian Islands Using Nuclear Microsatellite Data
Five species of Metrosideros (Myrtaceae) are recognized in the Hawaiian Islands, including the widespread M. polymorpha, and are characterized by a multitude of distinctive, yet overlapping, habit, ecological, and morphological forms. It remains unclear, despite several previous studies, whether the morphological variation within Hawaiian Metrosideros is due to hybridization, genetic polymorphism, phenotypic plasticity, or some combination of these processes. The Hawaiian Metrosideros complex has become a model system to study ecology and evolution; however this is the first study to use microsatellite data for addressing inter-island patterns of variation from across the Hawaiian Islands.Ten nuclear microsatellite loci were genotyped from 143 individuals of Metrosideros. We took advantage of the bi-parental inheritance and rapid mutation rate of these data to examine the validity of the current taxonomy and to investigate whether Metrosideros plants from the same island are more genetically similar than plants that are morphologically similar. The Bayesian algorithm of the program structure was used to define genetic groups within Hawaiian Metrosideros and the closely related taxon M. collina from the Marquesas and Austral Islands. Several standard and nested AMOVAs were conducted to test whether the genetic diversity is structured geographically or taxonomically.The results suggest that Hawaiian Metrosideros have dynamic gene flow, with genetic and morphological diversity structured not simply by geography or taxonomy, but as a result of parallel evolution on islands following rampant island-island dispersal, in addition to ancient chloroplast capture. Results also suggest that the current taxonomy requires major revisions in order to reflect the genetic structure revealed in the microsatellite data
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