4,435 research outputs found
Negative reflection of elastic guided waves in chaotic and random scattering media
The propagation of waves in complex media can be harnessed either by taming
the incident wave-field impinging on the medium or by forcing waves along
desired paths through its careful design. These two alternative strategies have
given rise to fascinating concepts such as time reversal or negative
refraction. Here, we show how these two processes are intimately linked through
the negative reflection phenomenon. A negative reflecting mirror converts a
wave of positive phase velocity into its negative counterpart and vice versa.
In this article, we experimentally demonstrate this phenomenon with elastic
waves in a 2D billiard and in a disordered plate by means of laser
interferometry. Despite the complexity of such configurations, the negatively
reflected wave field focuses back towards the initial source location, thereby
mimicking a phase conjugation operation while being a fully passive process.
The super-focusing capability of negative reflection is also highlighted in a
monochromatic regime. The negative reflection phenomenon is not restricted to
guided elastic waves since it can occur in zero-gap systems such as photonic
crystals, chiral metamaterials or graphene. Negative reflection can thus become
a tool of choice for the control of waves in all fields of wave physics.Comment: 9 pages, 6 figure
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Distinct cytokine profiles across trajectories of self-perceived cognitive impairment among early-stage breast cancer survivors.
The aim of the current study is to identify distinct cytokine profiles in relation to self-perceived cognitive trajectories. In our study cohort (n = 128), early-stage breast cancer patients were categorized into no impairment reported, acute, delayed, persistent and intermittent cognitive decline respectively. Pro-inflammatory cytokines were elevated compared to baseline; with TNF-α implicated in the acute cognitive trajectory while IL-6 and IL-8 were involved in the persistent cognitive trajectory. Our findings help to further our understanding of cytokine profiles implicated in cancer-related cognitive impairment (CRCI) and support the use of cytokine levels as biomarkers of cognitive decline over time
Mobile Money as an Engine of Financial Inclusion and Lynchpin of Financial Integrity
Few people would dispute that mobile money can be an engine of financial inclusion and has the potential to reach millions of customers, including those at the bottom of the socio-economic pyramid. Fewer though would characterize mobile money as the lynchpin of financial integrity. But financial inclusion and financial integrity have at least three tangential points to mobile money: (1) mobile money will help reduce dependency on cash, which is the common enemy of both financial inclusion and financial integrity, (2) mobile money generates data which is instrumental to the health and growth of both financial inclusion and financial integrity, and (3) mobile money accelerates the development of accounts, which are the backbone of financial inclusion and financial integrity. In any case, if mobile money is to deliver on its promises for both financial inclusion and financial integrity, three regulatory barriers need to be removed
PASTIS: Bayesian extrasolar planet validation. I. General framework, models, and performance
A large fraction of the smallest transiting planet candidates discovered by
the Kepler and CoRoT space missions cannot be confirmed by a dynamical
measurement of the mass using currently available observing facilities. To
establish their planetary nature, the concept of planet validation has been
advanced. This technique compares the probability of the planetary hypothesis
against that of all reasonably conceivable alternative false-positive (FP)
hypotheses. The candidate is considered as validated if the posterior
probability of the planetary hypothesis is sufficiently larger than the sum of
the probabilities of all FP scenarios. In this paper, we present PASTIS, the
Planet Analysis and Small Transit Investigation Software, a tool designed to
perform a rigorous model comparison of the hypotheses involved in the problem
of planet validation, and to fully exploit the information available in the
candidate light curves. PASTIS self-consistently models the transit light
curves and follow-up observations. Its object-oriented structure offers a large
flexibility for defining the scenarios to be compared. The performance is
explored using artificial transit light curves of planets and FPs with a
realistic error distribution obtained from a Kepler light curve. We find that
data support for the correct hypothesis is strong only when the signal is high
enough (transit signal-to-noise ratio above 50 for the planet case) and remains
inconclusive otherwise. PLATO shall provide transits with high enough
signal-to-noise ratio, but to establish the true nature of the vast majority of
Kepler and CoRoT transit candidates additional data or strong reliance on
hypotheses priors is needed.Comment: Accepted for publication in MNRAS; 23 pages, 11 figure
Closure of huge tubular patent ductus arteriosus using amplatzer vascular plug II or IV in premature infants and small children under 6kg
Beyond Average Return in Markov Decision Processes
What are the functionals of the reward that can be computed and optimized
exactly in Markov Decision Processes? In the finite-horizon, undiscounted
setting, Dynamic Programming (DP) can only handle these operations efficiently
for certain classes of statistics. We summarize the characterization of these
classes for policy evaluation, and give a new answer for the planning problem.
Interestingly, we prove that only generalized means can be optimized exactly,
even in the more general framework of Distributional Reinforcement Learning
(DistRL).DistRL permits, however, to evaluate other functionals approximately.
We provide error bounds on the resulting estimators, and discuss the potential
of this approach as well as its limitations.These results contribute to
advancing the theory of Markov Decision Processes by examining overall
characteristics of the return, and particularly risk-conscious strategies.Comment: Neurips 2023, Dec 2023, New Orleans, United State
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