6,376 research outputs found
“Canada’s Roll of Honour”: Controversy over Casualty Notification and Publication During the Second World War
During the Second World War, the Canadian Army’s announcement of casualties to next–of–kin and the press often caused controversy. Even though the army tried to notify the family and public as quickly as possible, it could not always do so. Unofficial communications with the family, procedural failures, and more frequently press and censorship errors, cause occasional mistakes in casualty reporting. Moreover, the interests of Canada’s allies often prevented the timely publication of casualty names and figures, as in the aftermath of the Dieppe Raid, Sicily campaign and Normandy landings. These delays were often for alleged security reasons, sometimes with questionable justification. This led to widespread, albeit inaccurate, suspicion of political manipulation of this process by the Canadian Army and federal government
Field-assisted doublon manipulation in the Hubbard model. A quantum doublon ratchet
For the fermionic Hubbard model at strong coupling, we demonstrate that
directional transport of localized doublons (repulsively bound pairs of two
particles occupying the same site of the crystal lattice) can be achieved by
applying an unbiased ac field of time-asymmetric (sawtooth-like) shape. The
mechanism involves a transition to intermediate states of virtually zero double
occupation which are reached by splitting the doublon by fields of the order of
the Hubbard interaction. The process is discussed on the basis of numerically
exact calculations for small clusters, and we apply it to more complex states
to manipulate the charge order pattern of one-dimensional systems.Comment: 6 pages, 6 figure
Second-order Shape Optimization for Geometric Inverse Problems in Vision
We develop a method for optimization in shape spaces, i.e., sets of surfaces
modulo re-parametrization. Unlike previously proposed gradient flows, we
achieve superlinear convergence rates through a subtle approximation of the
shape Hessian, which is generally hard to compute and suffers from a series of
degeneracies. Our analysis highlights the role of mean curvature motion in
comparison with first-order schemes: instead of surface area, our approach
penalizes deformation, either by its Dirichlet energy or total variation.
Latter regularizer sparks the development of an alternating direction method of
multipliers on triangular meshes. Therein, a conjugate-gradients solver enables
us to bypass formation of the Gaussian normal equations appearing in the course
of the overall optimization. We combine all of the aforementioned ideas in a
versatile geometric variation-regularized Levenberg-Marquardt-type method
applicable to a variety of shape functionals, depending on intrinsic properties
of the surface such as normal field and curvature as well as its embedding into
space. Promising experimental results are reported
Auxiliary Hamiltonian representation of the nonequilibrium Dyson equation
The nonequilibrium Dyson (or Kadanoff-Baym) equation, which is an equation of
motion with long-range memory kernel for real-time Green functions, underlies
many numerical approaches based on the Keldysh formalism. In this paper we map
the problem of solving the Dyson equation in real-time onto a noninteracting
auxiliary Hamiltonian with additional bath degrees of freedom. The solution of
the auxiliary model does not require the evaluation of a memory kernel and can
thus be implemented in a very memory efficient way. The mapping is derived for
a self-energy which is local in space and is thus directly applicable within
nonequilibrium dynamical mean-field theory (DMFT). We apply the method to study
the interaction quench in the Hubbard model for an optical lattice with a
narrow confinement, using inhomogeneous DMFT in combination with second-order
weak-coupling perturbation theory. We find that, although the quench excites
pronounced density oscillations, signatures of the two-stage relaxation similar
to the homogeneous system can be observed by looking at the time-dependent
occupations of natural orbitals.Comment: 14 pages, 11 figure
A Primer on Causality in Data Science
Many questions in Data Science are fundamentally causal in that our objective
is to learn the effect of some exposure, randomized or not, on an outcome
interest. Even studies that are seemingly non-causal, such as those with the
goal of prediction or prevalence estimation, have causal elements, including
differential censoring or measurement. As a result, we, as Data Scientists,
need to consider the underlying causal mechanisms that gave rise to the data,
rather than simply the pattern or association observed in those data. In this
work, we review the 'Causal Roadmap' of Petersen and van der Laan (2014) to
provide an introduction to some key concepts in causal inference. Similar to
other causal frameworks, the steps of the Roadmap include clearly stating the
scientific question, defining of the causal model, translating the scientific
question into a causal parameter, assessing the assumptions needed to express
the causal parameter as a statistical estimand, implementation of statistical
estimators including parametric and semi-parametric methods, and interpretation
of our findings. We believe that using such a framework in Data Science will
help to ensure that our statistical analyses are guided by the scientific
question driving our research, while avoiding over-interpreting our results. We
focus on the effect of an exposure occurring at a single time point and
highlight the use of targeted maximum likelihood estimation (TMLE) with Super
Learner.Comment: 26 pages (with references); 4 figure
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