66,213 research outputs found
Facies Patterns and Conodont Biogeography in Arctic Alaska and the Canadian Arctic Islands: Evidence against Juxtaposition of These Areas during Early Paleozoic Time
Symmetry Analysis of Multiferroic Co_3TeO_6
A phenomenological explanation of the magnetoelectric behavior of Co_3TeO_6
is developed. We explain the second harmonic generation data and the magnetic
field induced spontaneous polarization in the magnetically ordered phase below
20K.Comment: Phys rev B Rapids, to appea
Extreme 18O-enrichment in majorite constrains a crustal origin of transition zone diamonds
The fate of subducted oceanic lithosphere and its role in the planet-scale geochemical cycle is a key problem in solid Earth studies. Asthenospheric and transition zone minerals included in diamond have been interpreted as representing subducted oceanic crust based on inclusion REE patterns and strong 13C depletion of their host diamond (δ13C as low as -23 ‰). This view/explanation, however, has been challenged by alternative interpretations that variable carbon isotopic compositions either result from high temperature fractionation involving carbides, or reflect primordial, unhomogenised mantle reservoirs. Here, we present the first oxygen isotope analyses of inclusions in such ultradeep diamonds – majoritic garnets in diamond from Jagersfontein (South Africa). The oxygen isotope compositions provide unambiguous evidence for derivation of the inclusions from subducted crustal materials. The δ18OVSMOW values of the majorites range from +8.6 ‰ to +10.0 ‰, well outside that of ambient mantle (+5.5 ±0.4 ‰) and indicate that the protoliths were very heavily weathered at relatively low temperatures. When this information is combined with the broadly eclogitic composition of the majoritic garnets, a derivation from subducted sea-floor basalts is implied. Based on the association between the heavy oxygen and light carbon, the light carbon isotope composition cannot relate to deep mantle processes and is also ultimately derived from the crust
Current fluctuations in stochastic systems with long-range memory
We propose a method to calculate the large deviations of current fluctuations
in a class of stochastic particle systems with history-dependent rates.
Long-range temporal correlations are seen to alter the speed of the large
deviation function in analogy with long-range spatial correlations in
equilibrium systems. We give some illuminating examples and discuss the
applicability of the Gallavotti-Cohen fluctuation theorem.Comment: 10 pages, 1 figure. v2: Minor alterations. v3: Very minor alterations
for consistency with published version appearing at
http://stacks.iop.org/1751-8121/42/34200
Towards a Microscopic Model of Magnetoelectric Interactions in Ni3V2O8
We develop a microscopic magnetoelectric coupling in NiVO (NVO)
which gives rise to the trilinear phenomenological coupling used previously to
explain the phase transition in which magnetic and ferroelectric order
parameters appear simultaneously. Using combined neutron scattering
measurements and first-principles calculations of the phonons in NVO, we
determine eleven phonons which can induce the observed spontaneous
polarization. Among these eleven phonons, we find that a few of them can
actually induce a significant dipole moment. Using the calculated atomic
charges, we find that the required distortion to induce the observed dipole
moment is very small (~0.001 \AA) and therefore it would be very difficult to
observe the distortion by neutron-powder diffraction. Finally, we identify the
derivatives of the exchange tensor with respect to atomic displacements which
are needed for a microscopic model of a spin-phonon coupling in NVO and which
we hope will be obtained from a fundamental quantum calculation such as LDA+U.
We also analyze two toy models to illustrate that the Dzyaloskinskii-Moriya
interaction is very important for coexisting of magnetic and ferroelectric
order but it is not the only mechanism when the local site symmetry of the
system is low enough.Comment: 20 pages, 10 figure
Competition Between Exchange and Anisotropy in a Pyrochlore Ferromagnet
The Ising-like spin ice model, with a macroscopically degenerate ground
state, has been shown to be approximated by several real materials. Here we
investigate a model related to spin ice, in which the Ising spins are replaced
by classical Heisenberg spins. These populate a cubic pyrochlore lattice and
are coupled to nearest neighbours by a ferromagnetic exchange term J and to the
local axes by a single-ion anisotropy term D. The near neighbour spin
ice model corresponds to the case D/J infinite. For finite D/J we find that the
macroscopic degeneracy of spin ice is broken and the ground state is
magnetically ordered into a four-sublattice structure. The transition to this
state is first-order for D/J > 5 and second-order for D/J < 5 with the two
regions separated by a tricritical point. We investigate the magnetic phase
diagram with an applied field along [1,0,0] and show that it can be considered
analogous to that of a ferroelectric.Comment: 7 pages, 4 figure
Young\u27s modulus of [111] germanium nanowires
This paper reports a diameter-independent Young’s modulus of 91.9 ± 8.2 GPa for [111] Germaniumnanowires (Ge NWs). When the surface oxide layer is accounted for using a core-shell NW approximation, the YM of the Ge core approaches a near theoretical value of 147.6 ± 23.4 GPa. The ultimate strength of a NW device was measured at 10.9 GPa, which represents a very high experimental-to-theoretical strength ratio of ∼75%. With increasing interest in this material system as a high-capacity lithium-ion battery anode, the presented data provide inputs that are essential in predicting its lithiation-induced stress fields and fracture behavior
Visual scanning behavior and pilot workload
An experimental paradigm and a set of results which demonstrate a relationship between the level of performance on a skilled man-machine control task, the skill of the operator, the level of mental difficulty induced by an additional task imposed on the basic control task, and visual scanning performance. During a constant, simulated piloting task, visual scanning of instruments was found to vary as a function of the level of difficulty of a verbal mental loading task. The average dwell time of each fixation on the pilot's primary instrument increased as a function of the estimated skill level of the pilots, with novices being affected by the loading task much more than the experts. The results suggest that visual scanning of instruments in a controlled task may be an indicator of both workload and skill
Field behavior of an Ising model with aperiodic interactions
We derive exact renormalization-group recursion relations for an Ising model,
in the presence of external fields, with ferromagnetic nearest-neighbor
interactions on Migdal-Kadanoff hierarchical lattices. We consider layered
distributions of aperiodic exchange interactions, according to a class of
two-letter substitutional sequences. For irrelevant geometric fluctuations, the
recursion relations in parameter space display a nontrivial uniform fixed point
of hyperbolic character that governs the universal critical behavior. For
relevant fluctuations, in agreement with previous work, this fixed point
becomes fully unstable, and there appears a two-cycle attractor associated with
a new critical universality class.Comment: 9 pages, 1 figure (included). Accepted for publication in Int. J.
Mod. Phys.
Estimating the value of service exports by destination from different parts of Great Britain: 2015
This is the first time we are publishing service export figures by country of destination for countries, regions and industries in Great Britain; our analysis includes around 45% of total service exports and excludes finance, travel and transport because of data limitations. London dominated the absolute value of service exports to the EU, contributing 42% of the total EU exports (around £15.6 billion) in 2015. The EU market was more significant for service exports from the North East and West Midlands compared with London and the North West. In the North East, half of total service exports went to the EU, whereas this figure is only one-quarter for the North West.
Real estate, professional, scientific and technical industries were the largest exporters of services, followed by information and communication industries, then services connected to manufacturing, generating 35%, 29% and 15% of the total service exports respectively. Of all Great Britain service exports in 2015, 10% went to the Commonwealth (around £9.8 billion), and London generated almost half of those exports (around £4.6 billion). Of Asian markets, Japan was the single largest destination for service exports from London and the East (receiving about £0.8 billion and £0.2 billion respectively), while the single largest Asian destination from Yorkshire and The Humber, Wales and the South West was Saudi Arabia
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