144 research outputs found
Common reasoning in games: a Lewisian analysis of common knowledge of rationality
The game-theoretic assumption of âcommon knowledge of rationalityâ leads to paradoxes when rationality is represented in a Bayesian framework as cautious expected utility maximisation with independent beliefs (ICEU). We diagnose and resolve these paradoxes by presenting a new class of formal models of playersâ reasoning, inspired by David Lewisâs account of common knowledge, in which the analogue of common knowledge is derivability in common reason. We show that such models can consistently incorporate any of a wide range of standards of decision-theoretic practical rationality. We investigate the implications arising when the standard of decision-theoretic rationality so assumed is ICEU.Common reasoning; common knowledge; common knowledge of rationality; David Lewis; Bayesian models of games
Swelling of phospholipid floating bilayers: the effect of chain length
The equilibrium distance between two lipid bilayers stable in bulk water and
in proximity of a substrate was investigated. Samples consisted of a
homogeneous lipid bilayer, floating near an identical bilayer deposited on the
hydrophilic surface of a silicon single crystal. Lipids were saturated di-acyl
phosphocholines, with the number of carbon atoms per chain, n, varying from 16
to 20. The average and r.m.s. positions of the floating bilayer were determined
by means of neutron specular reflectivity. Samples were prepared at room
temperature (i.e. with the lipids in the gel phase) and measurements performed
at various temperatures so that the whole region of transition from gel to
fluid phase was explored. Data have been interpreted in terms of competition
between the interbilayer potential and membrane fluctuations and used to
estimate the bending rigidity of the bilayer
Common reasoning in games: a Lewisian analysis of common knowledge of rationality
Abstract: We present a new class of models of playersâ reasoning in non-cooperative games, inspired by David Lewisâs account of common knowledge. We argue that the models in this class formalise common knowledge of rationality in a way that is distinctive, in virtue of modelling steps of reasoning; and attractive, in virtue of being able to represent coherently common knowledge of any consistent standard of individual decision-theoretic rationality. We contrast our approach with that of Robert Aumann (1987), arguing that the former avoids and diagnoses certain paradoxes to which the latter may give rise when extended in particular ways
Unconventional superconductivity in the nickel-chalcogenide superconductor, TlNiSe
We present the results of a study of the vortex lattice (VL) of the nickel
chalcogenide superconductor TlNi2Se2, using small angle neutron scattering.
This superconductor has the same crystal symmetry as the iron arsenide
materials. Previous work points to it being a two-gap superconductor, with an
unknown pairing mechanism. No structural transitions in the vortex lattice are
seen in the phase diagram, arguing against d-wave gap symmetry. Empirical fits
of the temperature-dependence of the form factor and penetration depth rule out
a simple s-wave model, supporting the presence of nodes in the gap function.
The variation of the VL opening angle with field is consistent with earlier
reports of of multiple gaps
Oriented Three-Dimensional Magnetic Biskyrmion in MnNiGa Bulk Crystals
A biskyrmion consists of two bound, topologically stable skyrmion spin
textures. These coffee-bean-shaped objects have been observed in real-space in
thin plates using Lorentz transmission electron microscopy (LTEM). From LTEM
imaging alone, it is not clear whether biskyrmions are surface-confined
objects, or, analogously to skyrmions in non-centrosymmetric helimagnets,
three-dimensional tube-like structures in bulk sample. Here, we investigate the
biskyrmion form factor in single- and polycrystalline MnNiGa samples using
small angle neutron scattering (SANS). We find that biskyrmions are not
long-range ordered, not even in single-crystals. Surprisingly all of the
disordered biskyrmions have their in-plane symmetry axis aligned along certain
directions, governed by the magnetocrystalline anisotropy. This anisotropic
nature of biskyrmions may be further exploited to encode information
Multiple low-temperature skyrmionic states in a bulk chiral magnet
Magnetic skyrmions are topologically protected nanoscale spin textures with particle-like properties. In bulk cubic helimagnets, they appear under applied magnetic fields and condense spontaneously into a lattice in a narrow region of the phase diagram just below the magnetic ordering temperature, the so-called A-phase. Theory, however, predicts skyrmions to be locally stable in a wide range of magnetic fields and temperatures. Our neutron diffraction measurements reveal the formation of skyrmion states in large areas of the magnetic phase diagram, from the lowest temperatures up to the A-phase. We show that nascent and disappearing spiral states near critical lines catalyze topological charge changing processes, leading to the formation and destruction of skyrmionic states at low temperatures, which are thermodynamically stable or metastable depending on the orientation and strength of the magnetic field. Skyrmions are surprisingly resilient to high magnetic fields: the memory of skyrmion lattice states persists in the field polarized state, even when the skyrmion lattice signal has disappeared. These findings highlight the paramount role of magnetic anisotropies in stabilizing skyrmionic states and open up new routes for manipulating these quasi-particles towards energy-efficient spintronics applications
Gravimetric and density profiling using the combination of surface acoustic waves and neutron reflectivity
A new approach is described herein, where neutron reflectivity measurements that probe changes in the density profile of thin films as they absorb material from the gas phase have been combined with a Love wave based gravimetric assay that measures the mass of absorbed material. This combination of techniques not only determines the spatial distribution of absorbed molecules, but also reveals the amount of void space within the thin film (a quantity that can be difficult to assess using neutron reflectivity measurements alone). The uptake of organic solvent vapours into spun cast films of polystyrene has been used as a model system with a view to this method having the potential for extension to the study of other systems. These could include, for example, humidity sensors, hydrogel swelling, biomolecule adsorption or transformations of electroactive and chemically reactive thin films. This is the first ever demonstration of combined neutron reflectivity and Love wave-based gravimetry and the experimental caveats, limitations and scope of the method are explored and discussed in detail
Towards generalized data reduction on a time-of-flight neutron reflectometer
The calculation of neutron reflectivity from raw time-of-flight data including instrumental corrections and an improved resolution calculation is presented. The theoretical calculations are compared with experimental data measured on the vertical sample plane reflectometer D17 and the horizontal sample plane reflectometer FIGARO at the Institut LaueâLangevin (ILL), Grenoble, France. This article comprises the mathematical body of the time-of-flight reflectivity data-reduction software COSMOS which is used on D17 and FIGARO.</jats:p
α-Synuclein fibril and synaptic vesicle interactions lead to vesicle destruction and increased lipid-associated fibril uptake into iPSC-derived neurons
Monomeric alpha-synuclein (aSyn) is a well characterised protein that importantly binds to lipids. aSyn monomers assemble into amyloid fibrils which are localised to lipids and organelles in insoluble structures found in Parkinsonâs disease patientâs brains. Previous work to address pathological aSyn-lipid interactions has focused on using synthetic lipid membranes, which lack the complexity of physiological lipid membranes. Here, we use physiological membranes in the form of synaptic vesicles (SV) isolated from rodent brain to demonstrate that lipid-associated aSyn fibrils are more easily taken up into iPSC-derived cortical i3Neurons. Lipid-associated aSyn fibril characterisation reveals that SV lipids are an integrated part of the fibrils and while their fibril morphology differs from aSyn fibrils alone, the core fibril structure remains the same, suggesting the lipids lead to the increase in fibril uptake. Furthermore, SV enhance the aggregation rate of aSyn, yet increasing the SV:aSyn ratio causes a reduction in aggregation propensity. We finally show that aSyn fibrils disintegrate SV, whereas aSyn monomers cause clustering of SV using small angle neutron scattering and high-resolution imaging. Disease burden on neurons may be impacted by an increased uptake of lipid-associated aSyn which could enhance stress and pathology, which in turn may have fatal consequences for neurons
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