2,807 research outputs found
Local inverse scattering at fixed energy in spherically symmetric asymptotically hyperbolic manifolds
In this paper, we adapt the well-known \emph{local} uniqueness results of
Borg-Marchenko type in the inverse problems for one dimensional Schr{\"o}dinger
equation to prove \emph{local} uniqueness results in the setting of inverse
\emph{metric} problems. More specifically, we consider a class of spherically
symmetric manifolds having two asymptotically hyperbolic ends and study the
scattering properties of massless Dirac waves evolving on such manifolds. Using
the spherical symmetry of the model, the stationary scattering is encoded by a
countable family of one-dimensional Dirac equations. This allows us to define
the corresponding transmission coefficients and reflection
coefficients and of a Dirac wave having a fixed
energy and angular momentum . For instance, the reflection
coefficients correspond to the scattering experiment in which a
wave is sent from the \emph{left} end in the remote past and measured in the
same left end in the future. The main result of this paper is an inverse
uniqueness result local in nature. Namely, we prove that for a fixed , the knowledge of the reflection coefficients (resp.
) - up to a precise error term of the form with
B\textgreater{}0 - determines the manifold in a neighbourhood of the left
(resp. right) end, the size of this neighbourhood depending on the magnitude
of the error term. The crucial ingredients in the proof of this result are
the Complex Angular Momentum method as well as some useful uniqueness results
for Laplace transforms.Comment: 24 page
How to Discount Deep Reinforcement Learning: Towards New Dynamic Strategies
Using deep neural nets as function approximator for reinforcement learning
tasks have recently been shown to be very powerful for solving problems
approaching real-world complexity. Using these results as a benchmark, we
discuss the role that the discount factor may play in the quality of the
learning process of a deep Q-network (DQN). When the discount factor
progressively increases up to its final value, we empirically show that it is
possible to significantly reduce the number of learning steps. When used in
conjunction with a varying learning rate, we empirically show that it
outperforms original DQN on several experiments. We relate this phenomenon with
the instabilities of neural networks when they are used in an approximate
Dynamic Programming setting. We also describe the possibility to fall within a
local optimum during the learning process, thus connecting our discussion with
the exploration/exploitation dilemma.Comment: NIPS 2015 Deep Reinforcement Learning Worksho
On Genocide, Economic Reasons vs. Ethnic Passion
The traditional vision of genocide is exogenous. In this framework, ethnies have a real sense. The economic approach of conflicts has expressed slight differences in the relation between ethnies and conflicts. However it does not reject this explanation. Here we propose an alternative approach, an endogenous vision of genocide. Genocide appears in society where social capital plays a major role in solidarities. But social capital is a weak asset in the individual portfolio. Economic and social shocks may have impacts on the assets structure and may produce conflicts such as genocide. In this new framework, policy makers may have to adopt prudential rules.Conflicts, Ethnocide, Genocide, Policies implications, Social capital
Fast Selection of Spectral Variables with B-Spline Compression
The large number of spectral variables in most data sets encountered in
spectral chemometrics often renders the prediction of a dependent variable
uneasy. The number of variables hopefully can be reduced, by using either
projection techniques or selection methods; the latter allow for the
interpretation of the selected variables. Since the optimal approach of testing
all possible subsets of variables with the prediction model is intractable, an
incremental selection approach using a nonparametric statistics is a good
option, as it avoids the computationally intensive use of the model itself. It
has two drawbacks however: the number of groups of variables to test is still
huge, and colinearities can make the results unstable. To overcome these
limitations, this paper presents a method to select groups of spectral
variables. It consists in a forward-backward procedure applied to the
coefficients of a B-Spline representation of the spectra. The criterion used in
the forward-backward procedure is the mutual information, allowing to find
nonlinear dependencies between variables, on the contrary of the generally used
correlation. The spline representation is used to get interpretability of the
results, as groups of consecutive spectral variables will be selected. The
experiments conducted on NIR spectra from fescue grass and diesel fuels show
that the method provides clearly identified groups of selected variables,
making interpretation easy, while keeping a low computational load. The
prediction performances obtained using the selected coefficients are higher
than those obtained by the same method applied directly to the original
variables and similar to those obtained using traditional models, although
using significantly less spectral variables
Superconducting quantum node for entanglement and storage of microwave radiation
Superconducting circuits and microwave signals are good candidates to realize
quantum networks, which are the backbone of quantum computers. We have realized
a quantum node based on a 3D microwave superconducting cavity parametrically
coupled to a transmission line by a Josephson ring modulator. We first
demonstrate the time-controlled capture, storage and retrieval of an optimally
shaped propagating microwave field, with an efficiency as high as 80%. We then
demonstrate a second essential ability, which is the timed-controlled
generation of an entangled state distributed between the node and a microwave
channel.Comment: 6 pages, 4 figures. Supplementary information can be downloaded as
the ancillary file her
A novel approach for determining fatigue resistances of different muscle groups in static cases
In ergonomics and biomechanics, muscle fatigue models based on maximum
endurance time (MET) models are often used to integrate fatigue effect into
ergonomic and biomechanical application. However, due to the empirical
principle of those MET models, the disadvantages of this method are: 1) the MET
models cannot reveal the muscle physiology background very well; 2) there is no
general formation for those MET models to predict MET. In this paper, a
theoretical MET model is extended from a simple muscle fatigue model with
consideration of the external load and maximum voluntary contraction in passive
static exertion cases. The universal availability of the extended MET model is
analyzed in comparison to 24 existing empirical MET models. Using mathematical
regression method, 21 of the 24 MET models have intraclass correlations over
0.9, which means the extended MET model could replace the existing MET models
in a general and computationally efficient way. In addition, an important
parameter, fatigability (or fatigue resistance) of different muscle groups,
could be calculated via the mathematical regression approach. Its mean value
and its standard deviation are useful for predicting MET values of a given
population during static operations. The possible reasons influencing the
fatigue resistance were classified and discussed, and it is still a very
challenging work to find out the quantitative relationship between the fatigue
resistance and the influencing factors
Does Holbrook’s Nostalgia Index measure nostalgia proneness?
This research highlights the conceptual limitations of Holbrook’s Nostalgia Index: it conflates the cause (nostalgia) with the consequence (preference); it does not consider nostalgia as an emotion; and it opposes the past to the present and future. Hence, Holbrook’s Nostalgia Index measures belief in decline, not nostalgia proneness
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