7,630 research outputs found
Temporal recompression through a scattering medium via a broadband transmission matrix
The transmission matrix is a unique tool to control light through a
scattering medium. A monochromatic transmission matrix does not allow temporal
control of broadband light. Conversely, measuring multiple transmission
matrices with spectral resolution allows fine temporal control when a pulse is
temporally broadened upon multiple scattering, but requires very long
measurement time. Here, we show that a single linear operator, measured for a
broadband pulse with a co-propagating reference, naturally allows for spatial
focusing, and interestingly generates a two-fold temporal recompression at the
focus, compared with the natural temporal broadening. This is particularly
relevant for non-linear imaging techniques in biological tissues.Comment: 4 pages, 3 figure
Enhanced nonlinear imaging through scattering media using transmission matrix based wavefront shaping
Despite the tremendous progresses in wavefront control through or inside
complex scattering media, several limitations prevent reaching practical
feasibility for nonlinear imaging in biological tissues. While the optimization
of nonlinear signals might suffer from low signal to noise conditions and from
possible artifacts at large penetration depths, it has nevertheless been
largely used in the multiple scattering regime since it provides a guide star
mechanism as well as an intrinsic compensation for spatiotemporal distortions.
Here, we demonstrate the benefit of Transmission Matrix (TM) based approaches
under broadband illumination conditions, to perform nonlinear imaging. Using
ultrashort pulse illumination with spectral bandwidth comparable but still
lower than the spectral width of the scattering medium, we show strong
nonlinear enhancements of several orders of magnitude, through thicknesses of a
few transport mean free paths, which corresponds to millimeters in biological
tissues. Linear TM refocusing is moreover compatible with fast scanning
nonlinear imaging and potentially with acoustic based methods, which paves the
way for nonlinear microscopy deep inside scattering media
Revisiting Complex Moments For 2D Shape Representation and Image Normalization
When comparing 2D shapes, a key issue is their normalization. Translation and
scale are easily taken care of by removing the mean and normalizing the energy.
However, defining and computing the orientation of a 2D shape is not so simple.
In fact, although for elongated shapes the principal axis can be used to define
one of two possible orientations, there is no such tool for general shapes. As
we show in the paper, previous approaches fail to compute the orientation of
even noiseless observations of simple shapes. We address this problem. In the
paper, we show how to uniquely define the orientation of an arbitrary 2D shape,
in terms of what we call its Principal Moments. We show that a small subset of
these moments suffice to represent the underlying 2D shape and propose a new
method to efficiently compute the shape orientation: Principal Moment Analysis.
Finally, we discuss how this method can further be applied to normalize
grey-level images. Besides the theoretical proof of correctness, we describe
experiments demonstrating robustness to noise and illustrating the method with
real images.Comment: 69 pages, 20 figure
Universal quantum criticality at the Mott-Anderson transition
We present a large N solution of a microscopic model describing the
Mott-Anderson transition on a finite-coordination Bethe lattice. Our results
demonstrate that strong spatial fluctuations, due to Anderson localization
effects, dramatically modify the quantum critical behavior near disordered Mott
transitions. The leading critical behavior of quasiparticle wavefunctions is
shown to assume a universal form in the full range from weak to strong
disorder, in contrast to disorder-driven non-Fermi liquid ("electronic
Griffiths phase") behavior, which is found only in the strongly correlated
regime.Comment: 4 pages + references, 4 figures; v2: minor changes, accepted for
publication in Phys. Rev. Let
NeXSPheRIO results on elliptic flow at RHIC and connection with thermalization
Elliptic flow at RHIC is computed event-by-event with NeXSPheRIO. Reasonable
agreement with experimental results on is obtained. Various effects
are studied as well: reconstruction of impact parameter direction, freeze out
temperature, equation of state (with or without crossover), emission mecanism.Comment: Contribution to the Proceedings of the Quark-Gluon Plasma
Thermalization workshop. Content slightly increase
Chaotic and deterministic switching in a two-person game
We study robust long-term complex behaviour in the Rock-Scissors-Paper game with two players, played using reinforcement learning. The complex behaviour is connected to the existence of a heteroclinic network for the dynamics. This network is made of three heteroclinic cycles consisting of nine equilibria and the trajectories connecting them. We provide analytical proof both for the existence of chaotic switching near the heteroclinic network and for the relative asymptotic stability of at least one cycle in the network, leading to behaviour ranging from almost deterministic actions to chaotic-like dynamics. Our results are obtained by making use of the symmetry of the original problem, a new approach in the context of learning.learning process, dynamics, switching, chaos
A paisagem vegetal e o uso do território ao longo do tempo
A estabilidade macroclimática é uma ilusão transmitida pela nossa curta
esperança de vida. À escala geológica, desde tempos geológicos muito remotos
(cf. Briggs 1995), nos terrenos que hoje constituem o território português, o clima
oscilou entre os frios glaciares e os calores tropicais, passando pelos macroclimas
de tipo temperado e mediterrânico (Suc 1984). No início da época Miocénica
(23,8-5,3 Ma BP*) grande parte da Península Ibérica estava submetida a um
macrobioclima de tipo tropical, com chuvas bem distribuídas ao longo do ano
e, à excepção das montanhas, com uma estação fria amena e sem geadas.
Cobriam a Península Ibérica amplas florestas tropicais e subtropicais, entre as
quais sobressaíam pela sua abundância as florestas laurifólias (laurissilva), i.e.
florestas dominadas por espécies de folhas grandes, largas, por norma inteiras
(não recortadas), persistentes, sem pêlos, rijas, lisas e brilhantes. A partir do
Miocénico Médio a flora e a vegetação ibéricas foram profundamente marcadas
por uma sucessão de convulsões geológicas e macroclimáticas, em particular
pelas alterações climáticas que culminaram na transição do macrobioclima tropical
para o mediterrânico no Pliocénico e pelos numerosos ciclos glaciar-interglaciar
plistocénicos
A paisagem vegetal e o uso do território ao longo do tempo
A estabilidade macroclimática é uma ilusão transmitida pela nossa curta
esperança de vida. À escala geológica, desde tempos geológicos muito remotos
(cf. Briggs 1995), nos terrenos que hoje constituem o território português, o clima
oscilou entre os frios glaciares e os calores tropicais, passando pelos macroclimas
de tipo temperado e mediterrânico (Suc 1984). No início da época Miocénica
(23,8-5,3 Ma BP*) grande parte da Península Ibérica estava submetida a um
macrobioclima de tipo tropical, com chuvas bem distribuídas ao longo do ano
e, à excepção das montanhas, com uma estação fria amena e sem geadas.
Cobriam a Península Ibérica amplas florestas tropicais e subtropicais, entre as
quais sobressaíam pela sua abundância as florestas laurifólias (laurissilva), i.e.
florestas dominadas por espécies de folhas grandes, largas, por norma inteiras
(não recortadas), persistentes, sem pêlos, rijas, lisas e brilhantes. A partir do
Miocénico Médio a flora e a vegetação ibéricas foram profundamente marcadas
por uma sucessão de convulsões geológicas e macroclimáticas, em particular
pelas alterações climáticas que culminaram na transição do macrobioclima tropical
para o mediterrânico no Pliocénico e pelos numerosos ciclos glaciar-interglaciar
plistocénicos
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