2,250 research outputs found
Lost Relatives of the Gumbel Trick
The Gumbel trick is a method to sample from a discrete probability distribution, or to estimate its normalizing partition function. The method re- lies on repeatedly applying a random perturbation to the distribution in a particular way, each time solving for the most likely configuration. We derive an entire family of related methods, of which the Gumbel trick is one member, and show that the new methods have superior properties in several settings with minimal additional computational cost. In particular, for the Gumbel trick to yield computational benefits for discrete graphical models, Gumbel perturbations on all configurations are typically replaced with so- called low-rank perturbations. We show how a subfamily of our new methods adapts to this set- ting, proving new upper and lower bounds on the log partition function and deriving a family of sequential samplers for the Gibbs distribution. Finally, we balance the discussion by showing how the simpler analytical form of the Gumbel trick enables additional theoretical results.Alan Turing Institute under EPSRC grant EP/N510129/1, and by the Leverhulme Trust via the CFI
The weak field limit of quantum matter back-reacting on classical spacetime
Consistent coupling of quantum and classical degrees of freedom exists so long as there is both diffusion of the classical degrees of freedom and decoherence of the quantum system. In this paper, we derive the Newtonian limit of such classical-quantum (CQ) theories of gravity. Our results are obtained both via the gauge fixing of the recently proposed path integral theory of CQ general relativity and via the CQ master equation approach. In each case, we find the same weak field dynamics. We find that the New-tonian potential diffuses by an amount lower bounded by the decoherence rate into mass eigenstates. We also present our results as an unraveled system of stochastic differential equations for the trajectory of the hybrid classical-quantum state and provide a series of kernels for constructing figures of merit, which can be used to rule out part of the parameter space of classical-quantum theories of gravity by experimentally testing it via the decoherence-diffusion trade-off. We compare and contrast the weak field limit to previous models of classical Newtonian gravity coupled to quantum systems. Here, we find that the Newtonian potential and quantum state change in lock-step, with the flow of time being stochastic
Singlet Ground State and Magnetization Plateaus in BaMnO
Magnetic susceptibility and the magnetization process have been measured in
\green polycrystal. In this compound, the magnetic manganese ion exists as
Mn in a tetrahedral environment, and thus the magnetic interaction can
be described by an S=1 Heisenberg model. The ground state was found to be a
spin singlet with an excitation gap K. Magnetization
plateaus were observed at zero and at half of the saturation magnetization.
These results indicate that the present system can be represented by a coupled
antiferromagnetic dimer model.Comment: 4 pages, 4 figures, jpsj styl
Coherent photonuclear reactions for isotope transmutation
Coherent photonuclear isotope transmutation (CPIT) produces exclusively
radioactive isotopes (RIs) by coherent photonuclear reactions via E1 giant
resonances. Photons to be used are medium energy photons produced by laser
photons backscattered off GeV electrons. The cross sections are as large as 0.2
- 0.6 b, being independent of individual nuclides. A large fraction of photons
is effectively used for the photonuclear reactions, while the scattered GeV
electrons remain in the storage ring to be re-used. CPIT with medium energy
photons provides specific/desired RIs with the high rate and the high density
for nuclear science, molecular biology and for nuclear medicines.Comment: 8 pages, 2 figure
Percolation limited magnetic order in Eu1-xCaxB6
Abstract.: We report the results of measurements of the low-temperature specific heat Cp(T) and the ac susceptibility χac(T) in low applied magnetic fields for a series of samples of Eu1-xCaxB6. The anomalies in Cp(T), together with the results for χac(T) and M(H), confirm the onset of phase transitions to long range magnetic order for x < 0.7 and provide evidence that for x ≥ 0.7, the Eu moments, which are captured in large magnetic clusters with magnetic moments of the order of 260 μB, adopt a spin-glass type ground state. The data set allows to establish the low-temperature [ T,x] phase diagram of this alloy serie
Constraining dark energy with Sunyaev-Zel'dovich cluster surveys
We discuss the prospects of constraining the properties of a dark energy
component, with particular reference to a time varying equation of state, using
future cluster surveys selected by their Sunyaev-Zel'dovich effect. We compute
the number of clusters expected for a given set of cosmological parameters and
propogate the errors expected from a variety of surveys. In the short term they
will constrain dark energy in conjunction with future observations of type Ia
supernovae, but may in time do so in their own right.Comment: 5 pages, 3 figures, 1 table, version accepted for publication in PR
Seeing the smart city on Twitter: Colour and the affective territories of becoming smart
This paper pays attention to the immense and febrile field of digital image files which picture the smart city as they circulate on the social media platform Twitter. The paper considers tweeted images as an affective field in which flow and colour are especially generative. This luminescent field is territorialised into different, emergent forms of becoming ‘smart’. The paper identifies these territorialisations in two ways: firstly, by using the data visualisation software ImagePlot to create a visualisation of 9030 tweeted images related to smart cities; and secondly, by responding to the affective pushes of the image files thus visualised. It identifies two colours and three ways of affectively becoming smart: participating in smart, learning about smart, and anticipating smart, which are enacted with different distributions of mostly orange and blue images. The paper thus argues that debates about the power relations embedded in the smart city should consider the particular affective enactment of being smart that happens via social media. More generally, the paper concludes that geographers must pay more attention to the diverse and productive vitalities of social media platforms in urban life and that this will require experiment with methods that are responsive to specific digital qualities
Evolution of density perturbations in double exponential quintessence models
In this work we investigate the evolution of matter density perturbations for
quintessence models with a self-interaction potential that is a combination of
exponentials. One of the models is based on the Einstein theory of gravity,
while the other is based on the Brans-Dicke scalar tensor theory. We constrain
the parameter space of the models using the determinations for the growth rate
of perturbations derived from data of the 2-degree Field Galaxy Redshift
Survey.Comment: 5 pages, 3 eps figure
3D characterization of CdSe nanoparticles attached to carbon nanotubes
The crystallographic structure of CdSe nanoparticles attached to carbon
nanotubes has been elucidated by means of high resolution transmission electron
microscopy and high angle annular dark field scanning transmission electron
microscopy tomography. CdSe rod-like nanoparticles, grown in solution together
with carbon nanotubes, undergo a morphological transformation and become
attached to the carbon surface. Electron tomography reveals that the
nanoparticles are hexagonal-based with the (001) planes epitaxially matched to
the outer graphene layer.Comment: 7 pages, 8 figure
Dupilumab reduces absenteeism in patients with moderate to severe atopic dermatitis: Pooled results from the LIBERTY AD SOLO clinical trials
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