131 research outputs found
Faraday Rotation, Band Splitting, and One-Way Propagation of Plasmon Waves on a Nanoparticle Chain
We calculate the dispersion relations of plasmonic waves propagating along a
chain of semiconducting or metallic nanoparticles in the presence of both a
static magnetic field and a liquid crystalline host. The dispersion
relations are obtained using the quasistatic approximation and a dipole-dipole
approximation to treat the interaction between surface plasmons on different
nanoparticles. For a plasmons propagating along a particle chain in a nematic
liquid crystalline host with both and the director parallel to the
chain, we find a small, but finite, Faraday rotation angle. For
perpendicular to the chain, but director still parallel to the chain, the field
couples the longitudinal and one of the two transverse plasmonic branches. This
coupling is shown to split the two branches at the zero field crossing by an
amount proportional to . In a cholesteric liquid crystal host and an
applied magnetic field parallel to the chain, the dispersion relations for
left- and right-moving waves are found to be different. For some frequencies,
the plasmonic wave propagates only in one of the two directions.Comment: 6 pages, 4 figures. arXiv admin note: substantial text overlap with
arXiv:1502.0496
Calculation of the Anisotropic Coefficients of Thermal Expansion: A First-Principles Approach
Predictions of the anisotropic coefficients of thermal expansion are needed
to not only compare to experimental measurement, but also as input for
macroscopic modeling of devices which operate over a large temperature range.
While most current methods are limited to isotropic systems within the
quasiharmonic approximation, our method uses first-principles calculations and
includes anharmonic effects to determine the temperature-dependent properties
of materials. These include the lattice parameters, anisotropic coefficients of
thermal expansion, isothermal bulk modulus, and specific heat at constant
pressure. Our method has been tested on two compounds (Cu and AlN) and predicts
thermal properties which compare favorably to experimental measurement over a
wide temperature range.Comment: 8 pages, 9 figures, 1 tabl
Vibrational and dielectric properties of monolayer transition metal dichalcogenides
First-principles studies of two-dimensional transition metal dichalcogenides
have contributed considerably to the understanding of their dielectric,
optical, elastic, and vibrational properties. The majority of works to date
focus on a single material or physical property. Here we use a single
first-principles methodology on the whole family of systems, to investigate in
depth the relationships between different physical properties, the underlying
symmetry and the composition of these materials, and observe trends. We compare
to bulk counterparts to show strong interlayer effects in triclinic compounds.
Previously unobserved relationships between these monolayer compounds become
apparent. These trends can then be exploited by the materials science,
nanoscience, and chemistry communities to better design devices and
heterostructures for specific functionalities.Comment: 4 figures, 11 page
Vibrational and dielectric properties of the bulk transition metal dichalcogenides
Interest in the bulk transition metal dichalcogenides for their electronic,
photovoltaic, and optical properties has grown and led to their use in many
technological applications. We present a systematic investigation of their
interlinked vibrational and dielectric properties, using density functional
theory and density functional perturbation theory, studying the effects of the
spin-orbit interaction and of the long-range e- e correlation as part
of our investigation. This study confirms that the spin-orbit interaction plays
a small role in these physical properties, while the direct contribution of
dispersion corrections is of crucial importance in the description of the
interatomic force constants. Here, our analysis of the structural and
vibrational properties, including the Raman spectra, compare well to
experimental measurement. Three materials with different point groups are
showcased and data trends on the full set of fifteen existing hexagonal,
trigonal, and triclinic materials are demonstrated. This overall picture will
enable the modeling of devices composed of these materials for novel
applications.Comment: 11 pages, 6 figure
Electron-Beam Manipulation of Silicon Dopants in Graphene
The direct manipulation of individual atoms in materials using scanning probe
microscopy has been a seminal achievement of nanotechnology. Recent advances in
imaging resolution and sample stability have made scanning transmission
electron microscopy a promising alternative for single-atom manipulation of
covalently bound materials. Pioneering experiments using an atomically focused
electron beam have demonstrated the directed movement of silicon atoms over a
handful of sites within the graphene lattice. Here, we achieve a much greater
degree of control, allowing us to precisely move silicon impurities along an
extended path, circulating a single hexagon, or back and forth between the two
graphene sublattices. Even with manual operation, our manipulation rate is
already comparable to the state-of-the-art in any atomically precise technique.
We further explore the influence of electron energy on the manipulation rate,
supported by improved theoretical modeling taking into account the vibrations
of atoms near the impurities, and implement feedback to detect manipulation
events in real time. In addition to atomic-level engineering of its structure
and properties, graphene also provides an excellent platform for refining the
accuracy of quantitative models and for the development of automated
manipulation.Comment: 5 figures, 4 supporting figure
The simplest amino‐borane H2B=NH2 trapped on a rhodium dimer : pre‐catalysts for amine–borane dehydropolymerization
Funding: The EPSRC (A.S.W. and S.A.M., EP/M024210/1; N.A.B., DTP Studentship), the Rhodes Trust (A.K.), G. M. Adams (G. P. C. analysis).The μ‐amino–borane complexes [Rh2(LR)2(μ‐H)(μ‐H2B=NHR′)][BArF4] (LR=R2P(CH2)3PR2; R=Ph, iPr; R′=H, Me) form by addition of H3B⋅NMeR′H2 to [Rh(LR)(η6‐C6H5F)][BArF4]. DFT calculations demonstrate that the amino–borane interacts with the Rh centers through strong Rh‐H and Rh‐B interactions. Mechanistic investigations show that these dimers can form by a boronium‐mediated route, and are pre‐catalysts for amine‐borane dehydropolymerization, suggesting a possible role for bimetallic motifs in catalysisPublisher PDFPeer reviewe
Modelling chemistry in the nocturnal boundary layer above tropical rainforest and a generalised effective nocturnal ozone deposition velocity for sub-ppbv NOx conditions
Measurements of atmospheric composition have been made over a remote rainforest landscape. A box model has previously been demonstrated to model the observed daytime chemistry well. However the box model is unable to explain the nocturnal measurements of relatively high [NO] and [O3], but relatively low observed [NO2]. It is shown that a one-dimensional (1-D) column model with simple O3 -NOx chemistry and a simple representation of vertical transport is able to explain the observed nocturnal concentrations and predict the likely vertical profiles of these species in the nocturnal boundary layer (NBL). Concentrations of tracers carried over from the end of the night can affect the atmospheric chemistry of the following day. To ascertain the anomaly introduced by using the box model to represent the NBL, vertically-averaged NBL concentrations at the end of the night are compared between the 1-D model and the box model. It is found that, under low to medium [NOx] conditions (NOx <1 ppbv), a simple parametrisation can be used to modify the box model deposition velocity of ozone, in order to achieve good agreement between the box and 1-D models for these end-of-night concentrations of NOx and O3. This parametrisation would could also be used in global climate-chemistry models with limited vertical resolution near the surface. Box-model results for the following day differ significantly if this effective nocturnal deposition velocity for ozone is implemented; for instance, there is a 9% increase in the following day’s peak ozone concentration. However under medium to high [NOx] conditions (NOx > 1 ppbv), the effect on the chemistry due to the vertical distribution of the species means no box model can adequately represent chemistry in the NBL without modifying reaction rate constants
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Dose response of the 16p11.2 distal copy number variant on intracranial volume and basal ganglia.
Carriers of large recurrent copy number variants (CNVs) have a higher risk of developing neurodevelopmental disorders. The 16p11.2 distal CNV predisposes carriers to e.g., autism spectrum disorder and schizophrenia. We compared subcortical brain volumes of 12 16p11.2 distal deletion and 12 duplication carriers to 6882 non-carriers from the large-scale brain Magnetic Resonance Imaging collaboration, ENIGMA-CNV. After stringent CNV calling procedures, and standardized FreeSurfer image analysis, we found negative dose-response associations with copy number on intracranial volume and on regional caudate, pallidum and putamen volumes (β = -0.71 to -1.37; P < 0.0005). In an independent sample, consistent results were obtained, with significant effects in the pallidum (β = -0.95, P = 0.0042). The two data sets combined showed significant negative dose-response for the accumbens, caudate, pallidum, putamen and ICV (P = 0.0032, 8.9 × 10-6, 1.7 × 10-9, 3.5 × 10-12 and 1.0 × 10-4, respectively). Full scale IQ was lower in both deletion and duplication carriers compared to non-carriers. This is the first brain MRI study of the impact of the 16p11.2 distal CNV, and we demonstrate a specific effect on subcortical brain structures, suggesting a neuropathological pattern underlying the neurodevelopmental syndromes
Adalimumab vs placebo as add-on to Standard Therapy for autoimmune Uveitis: Tolerability, Effectiveness and cost-effectiveness-a protocol for a randomised controlled trial (ASTUTE trial).
IntroductionAdalimumab is an effective treatment for autoimmune non-infectious uveitis (ANIU), but it is currently only funded for a minority of patients with ANIU in the UK as it is restricted by the National Institute for Health and Care Excellence guidance. Ophthalmologists believe that adalimumab may be effective in a wider range of patients. The Adalimumab vs placebo as add-on to Standard Therapy for autoimmune Uveitis: Tolerability, Effectiveness and cost-effectiveness (ASTUTE) trial will recruit patients with ANIU who do and do not meet funding criteria and will evaluate the effectiveness and cost-effectiveness of adalimumab versus placebo as an add-on therapy to standard care.Methods and analysisThe ASTUTE trial is a multicentre, parallel-group, placebo-controlled, pragmatic randomised controlled trial with a 16-week treatment run-in (TRI). At the end of the TRI, only responders will be randomised (1:1) to 40 mg adalimumab or placebo (both are the study investigational medicinal product) self-administered fortnightly by subcutaneous injection. The target sample size is 174 randomised participants. The primary outcome is time to treatment failure (TF), a composite of signs indicative of active ANIU. Secondary outcomes include individual TF components, retinal morphology, adverse events, health-related quality of life, patient-reported side effects and visual function, best-corrected visual acuity, employment status and resource use. In the event of TF, open-label drug treatment will be restarted as per TRI for 16 weeks, and if a participant responds again, allocation will be switched without unmasking and treatment with investigational medicinal product restarted.Ethics and disseminationThe trial received Research Ethics Committee (REC) approval from South Central - Oxford B REC in June 2020. The findings will be presented at international meetings, by peer-reviewed publications and through patient organisations and newsletters to patients, where available.Trial registrationISRCTN31474800. Registered 14 April 2020
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