3,442 research outputs found
Estimating the Value of Medal Success at the 2010 Winter Olympic Games
We estimate Canadiansâ willingness to pay (WTP) for success by Team Canada in the 2010 Winter Olympics. The Canadian government subsidized elite athletes in the run up to the 2010 Games through the Own the Podium program, which was designed to increase Canadaâs medal count. WTP estimates from a contingent valuation method (CVM) study using data from nationally representative surveys before and after the Games suggest that Own the Podium generated intangible benefits of between 3 and 5 times its cost. The aggregate value of the intangible benefits generated by the program was between 3.4 billion. Key Words: Olympic Games, contingent valuation method, willingness to pay
Atomistic Study of Irradiation-Induced Plastic and Lattice Strain in Tungsten
We demonstrate a practical way to perform decomposition of the elasto-plastic
deformation directly from atomistic simulation snapshots. Through molecular
dynamics simulations on a large single crystal, we elucidate the intricate
process of converting plastic strain, atomic strain, and rigid rotation during
irradiation. Our study highlights how prismatic dislocation loops act as
initiators of plastic strain effects in heavily irradiated metals, resulting in
experimentally measurable alterations in lattice strain. We show the onset of
plastic strain starts to emerge at high dose, leading to the spontaneous
emergence of dislocation creep and irradiation-induced lattice swelling. This
phenomenon arises from the agglomeration of dislocation loops into a
dislocation network. Furthermore, our numerical framework enables us to
categorize the plastic transformation into two distinct types: pure slip events
and slip events accompanied by lattice swelling. The latter type is
particularly responsible for the observed divergence in interstitial and
vacancy counts, and also impacts the behavior of dislocations, potentially
activating non-conventional slip systems
Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials
Knowledge of mechanical and physical property evolution due to irradiation
damage is essential for the development of future fission and fusion reactors.
Ion-irradiation provides an excellent proxy for studying irradiation damage,
allowing high damage doses without sample activation. Limited
ion-penetration-depth means that only few-micron-thick damaged layers are
produced. Substantial effort has been devoted to probing the mechanical
properties of these thin implanted layers. Yet, whilst key to reactor design,
their thermal transport properties remain largely unexplored due to a lack of
suitable measurement techniques. Here we demonstrate non-contact thermal
diffusivity measurements in ion-implanted tungsten for nuclear fusion armour.
Alloying with transmutation elements and the interaction of retained gas with
implantation-induced defects both lead to dramatic reductions in thermal
diffusivity. These changes are well captured by our modelling approaches. Our
observations have important implications for the design of future fusion power
plants.Comment: 15 pages, 3 figure
Top-down, decoupled control of constitutive parameters in electromagnetic metamaterials with dielectric resonators of internal anisotropy
A meta-atom platform providing decoupled tuning for the constitutive wave parameters remains as a challenging problem, since the proposition of Pendry. Here we propose an electromagnetic meta-atom design of internal anisotropy (Δ_rââ âΔ_Ξ), as a pathway for decoupling of the effective- permittivity Δ_(eff) and permeability ÎŒ_(eff). Deriving effective parameters for anisotropic meta-atom from the first principles, and then subsequent inverse-solving the obtained decoupled solution for a target set of Δ_(eff) and ÎŒ_(eff), we also achieve an analytic, top-down determination for the internal structure of a meta-atom. To realize the anisotropy from isotropic materials, a particle of spatial permittivity modulation in r or Ξ direction is proposed. As an application example, a matched zero index dielectric meta-atom is demonstrated, to enable the super-funneling of a 50λ-wide flux through a sub-λ slit; unharnessing the flux collection limit dictated by the λ-zone
Estimate for thermal diffusivity in highly irradiated tungsten using molecular dynamics simulation
The changing thermal conductivity of an irradiated material is among the principal design considerations for any nuclear reactor, but at present few models are capable of predicting these changes starting from an arbitrary atomistic model. Here we present a simple model for computing the thermal diffusivity of tungsten, based on the conductivity of the perfect crystal and resistivity per Frenkel pair, and dividing a simulation into perfect and athermal regions statistically. This is applied to highly irradiated microstructures simulated with molecular dynamics. A comparison to experiments shows that simulations closely track observed thermal diffusivity over a range of doses from the dilute limit of a few Frenkel pairs to the high-dose saturation limit at three displacements per atom (dpa).Peer reviewe
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Malaria parasite translocon structure and mechanism of effector export.
The putative Plasmodium translocon of exported proteins (PTEX) is essential for transport of malarial effector proteins across a parasite-encasing vacuolar membrane into host erythrocytes, but the mechanism of this process remains unknown. Here we show that PTEX is a bona fide translocon by determining structures of the PTEX core complex at near-atomic resolution using cryo-electron microscopy. We isolated the endogenous PTEX core complex containing EXP2, PTEX150 and HSP101 from Plasmodium falciparum in the 'engaged' and 'resetting' states of endogenous cargo translocation using epitope tags inserted using the CRISPR-Cas9 system. In the structures, EXP2 and PTEX150 interdigitate to form a static, funnel-shaped pseudo-seven-fold-symmetric protein-conducting channel spanning the vacuolar membrane. The spiral-shaped AAA+ HSP101 hexamer is tethered above this funnel, and undergoes pronounced compaction that allows three of six tyrosine-bearing pore loops lining the HSP101 channel to dissociate from the cargo, resetting the translocon for the next threading cycle. Our work reveals the mechanism of P. falciparum effector export, and will inform structure-based design of drugs targeting this unique translocon
Dynamic communities in multichannel data: An application to the foreign exchange market during the 2007--2008 credit crisis
We study the cluster dynamics of multichannel (multivariate) time series by
representing their correlations as time-dependent networks and investigating
the evolution of network communities. We employ a node-centric approach that
allows us to track the effects of the community evolution on the functional
roles of individual nodes without having to track entire communities. As an
example, we consider a foreign exchange market network in which each node
represents an exchange rate and each edge represents a time-dependent
correlation between the rates. We study the period 2005-2008, which includes
the recent credit and liquidity crisis. Using dynamical community detection, we
find that exchange rates that are strongly attached to their community are
persistently grouped with the same set of rates, whereas exchange rates that
are important for the transfer of information tend to be positioned on the
edges of communities. Our analysis successfully uncovers major trading changes
that occurred in the market during the credit crisis.Comment: 8 pages, 6 figures, accepted for publication in Chao
A multi-scale model for stresses, strains and swelling of reactor components under irradiation
Predicting strains, stresses and swelling in nuclear power plant components exposed to irradiation directly from the observed or computed defect and dislocation microstructure is a fundamental problem of fusion power plant design that has so far eluded a practical solution. We develop a model, free from parameters not accessible to direct evaluation or observation, that is able to provide estimates for irradiation-induced stresses and strains on a macroscopic scale, using information about the distribution of radiation defects produced by high-energy neutrons in the microstructure of materials. The model exploits the fact that elasticity equations involve no characteristic spatial scale, and hence admit a mathematical treatment that is an extension to that developed for the evaluation of elastic fields of defects on the nanoscale. In the analysis given below we use, as input, the radiation defect structure data derived from ab initio density functional calculations and large-scale molecular dynamics simulations of high-energy collision cascades. We show that strains, stresses and swelling can be evaluated using either integral equations, where the source function is given by the density of relaxation volumes of defects, or they can be computed from heterogeneous partial differential equations for the components of the stress tensor, where the density of body forces is proportional to the gradient of the density of relaxation volumes of defects. We perform a case study where strains and stresses are evaluated analytically and exactly, and develop a general finite element method implementation of the method, applicable to a broad range of predictive simulations of strains and stresses induced by irradiation in materials and components of any geometry in fission or fusion nuclear power plants.Peer reviewe
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