2,733 research outputs found
Surface-Enhanced Plasmon Splitting in a Liquid-Crystal-Coated Gold Nanoparticle
We show that, when a gold nanoparticle is coated by a thin layer of nematic
liquid crystal, the deformation produced by the nanoparticle surface can
enhance the splitting of the nanoparticle surface plasmon. We consider three
plausible liquid crystal director configurations in zero electric field: boojum
pair (north-south pole configuration), baseball (tetrahedral), and homogeneous.
From a calculation using the Discrete Dipole Approximation, we find that the
surface plasmon splitting is largest for the boojum pair, intermediate for the
homogeneous, and smallest for the baseball configuration. The boojum pair
results are in good agreement with experiment. We conclude that the
nanoparticle surface has a strong effect on the director orientation, but,
surprisingly, that this deformation can actually enhance the surface plasmon
splitting.Comment: 5 pages, 3 figures To be published in PR
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Correlated analytical studies of organic material from the Tagish Lake carbonaceous chondrite
We report on correlated studies of organic material using SIMS, FIB-SEM, and TEM
Quantum Monte Carlo study of a magnetic-field-driven 2D superconductor-insulator transition
We numerically study the superconductor-insulator phase transition in a model
disordered 2D superconductor as a function of applied magnetic field. The
calculation involves quantum Monte Carlo calculations of the (2+1)D XY model in
the presence of both disorder and magnetic field. The XY coupling is assumed to
have the form -J\cos(\theta_i-\theta_j-A_{ij}), where A_{ij} has a mean of zero
and a standard deviation \Delta A_{ij}. In a real system, such a model would be
approximately realized by a 2D array of small Josephson-coupled grains with
slight spatial disorder and a uniform applied magnetic field. The different
values \Delta A_{ij} then corresponds to an applied field such that the average
number of flux quanta per plaquette has various integer values N: larger N
corresponds to larger \Delta A_{ij}. For any value of \Delta A_{ij}, there
appears to be a critical coupling constant K_c(\Delta
A_{ij})=\sqrt{[J/(2U)]_c}, where U is the charging energy, above which the
system is a Mott insulator; there is also a corresponding critical conductivity
\sigma^*(\Delta A_{ij}) at the transition. For \Delta A_{ij}=\infty, the order
parameter of the transition is a renormalized coupling constant g. Using a
numerical technique appropriate for disordered systems, we show that the
transition at this value of \Delta A_{ij} takes place from an insulating (I)
phase to a Bose glass (BG) phase, and that the dynamical critical exponent
characterizing this transition is z \sim 1.3. By contrast, z=1 for this model
at \Delta A_{ij}=0. We suggest that the superconductor to insulator transition
is actually of this I to BG class at all nonzero \Delta A_{ij}'s, and we
support this interpretation by both numerical evidence and an analytical
argument based on the Harris criterion.Comment: 17 pages, 23 figures, accepted for publication in Phys. Rev.
There are many barriers to species’ migrations
Temperature-change trajectories are being used to identify the geographic barriers and thermal ‘cul-de-sacs’ that will limit the ability of many species to track climate change by migrating. We argue that there are many other potential barriers to species’ migrations. These include stable ecotones, discordant shifts in climatic variables, human land use, and species’ limited dispersal abilities. To illustrate our argument, for each 0.5° latitude/longitude grid cell of the Earth’s land surface, we mapped and tallied the number of cells for which future (2060–2080) climate represents an analog of the focal cell’s current climate. We compared results when only considering temperature with those for which both temperature and total annual precipitation were considered in concert. We also compared results when accounting for only geographic barriers (no cross-continental migration) with those involving both geographic and potential ecological barriers (no cross-biome migration). As expected, the number of future climate analogs available to each pixel decreased markedly with each added layer of complexity (e.g. the proportion of the Earth’s land surface without any available future climate analogs increased from 3% to more than 36% with the inclusion of precipitation and ecological boundaries). While including additional variables can increase model complexity and uncertainty, we must strive to incorporate the factors that we know will limit species’ ranges and migrations if we hope to predict the effects of climate change at a high-enough degree of accuracy to guide management decisions
Determination of Interface Atomic Structure and Its Impact on Spin Transport Using Z-Contrast Microscopy and Density-Functional Theory
We combine Z-contrast scanning transmission electron microscopy with
density-functional-theory calculations to determine the atomic structure of the
Fe/AlGaAs interface in spin-polarized light-emitting diodes. A 44% increase in
spin-injection efficiency occurs after a low-temperature anneal, which produces
an ordered, coherent interface consisting of a single atomic plane of
alternating Fe and As atoms. First-principles transport calculations indicate
that the increase in spin-injection efficiency is due to the abruptness and
coherency of the annealed interface.Comment: 16 pages (including cover), 4 figure
Anolis Newsletter VII
Newsletter for the 7th Anolis Symposium, Fairchild Tropical Botanic Gardens, Miami, Florida, 17-18 March 2018.
It had been nearly a decade since the previous Anolis symposium was held in Cambridge, MA, at the Museum for Comparative Zoology, Harvard. A reunion of anole biologists en masse was long past due and it was decided that this symposium would be slightly different – we were going to hold it somewhere with anoles! And so, on the weekend of 17-18th March, 2018, nearly 70 anole biologists traveled to sunny south Florida to attend the 7th Anolis Symposium held at the beautiful Fairchild Tropical Botanic Gardens in Miami. In the grounds of the botanical gardens, attendees were presented with a diverse community of six (!) species of anole, both native and non-native, representing four distinct ecomorphs
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Correlated analyses of D- and 15N-rich carbon grains from CR2 chondrite EET 92042
Extract from introduction: Insoluble organic matter (IOM) and matrix from primitive carbonaceous chondrites carry isotope enrichments (?D?20000', ?15N?3200�) that are comparable to those in interplanetary dust particles [1, this work]. Hence, primitive organics that formed in the protosolar cloud (PSC) – or maybe in the cold outer regions of the protoplanetary disk – survived accretion and planetary processing on the asteroids, the parent bodies of the chondrites
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Correlated Microscale Isotope and Scanning Transmission X-Ray Analyses of Isotopically Anomalous Organic Matter from the CR2 Chondrite EET 92042
We discuss correlated examinations of organic matter from the CR2 chondrite EET 92042, using SIMS, STXM and other methods. We found a large, isotopically highly anomalous region of probable presolar origin that is C- and 13C-poor and 15N-rich
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Secondary ion mass spectrometry and x-ray absorption near-edge structure spectroscopy of isotopically anomalous organic matter from CR1 chondrites GRO 95577
We located interstellar organics from a CR1 chondrite with NanoSIMS and analyzed FIB-extracted sections with XANES. D-rich material appears not associated with a functional group, whereas 15N-rich matter shows some affinity to nitrile functionality
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