850 research outputs found
AN EXPLICIT EXPRESSION FOR k-NEGATIONS
Abstract We give a new proof for the existence and the uniqueness of k-negations. With the aid of a generalised dyadic representation system is possible to give an explicit expression for k-negations and it is possible to showing that there exists a set of measure 1 where knegations have derivatives with zero values
Unstable and stable regimes of polariton condensation
Modulational instabilities play a key role in a wide range of nonlinear
optical phenomena, leading e.g. to the formation of spatial and temporal
solitons, rogue waves and chaotic dynamics. Here we experimentally demonstrate
the existence of a modulational instability in condensates of cavity
polaritons, arising from the strong coupling of cavity photons with quantum
well excitons. For this purpose we investigate the spatiotemporal coherence
properties of polariton condensates in GaAs-based microcavities under
continuous-wave pumping. The chaotic behavior of the instability results in a
strongly reduced spatial and temporal coherence and a significantly
inhomogeneous density. Additionally we show how the instability can be tamed by
introducing a periodic potential so that condensation occurs into negative mass
states, leading to largely improved coherence and homogeneity. These results
pave the way to the exploration of long-range order in dissipative quantum
fluids of light within a controlled platform.Comment: 7 pages, 5 figure
Un proyecto escultórico: la tortuga
En enero de 2003, los escultores Pablo de Arriba del Amo y José de las Casas Gómez presentaron la idea de una posible creación escultórica a la Junta municipal de Villaverde Alto.
Este proyecto fue aprobado; por tanto, contó con la financiación necesaria para llevarlo a
cabo, posteriormente fue instalado en la localización final propuesta, que era en la plaza
Ágata de ese mismo distrito. En este artículo se van a desarrollar pormenorizadamente
todos los pasos que se siguieron en el proceso de creación de este monumento, el cual por
su envergadura era especialmente complejo. Desde la elección del tema, los materiales y los
procesos hasta el desarrollo y estudio de la cimentación, todo ello será explicado para dar
cuenta de un proyecto de máximo interés no sólo para los propios escultores, sino que, para
el público general, la aproximación a este procedimiento puede hacer valorar el universo de la
escultura mucho más. Hay que tener en consideración que ambos escultores se inventaron un
procedimiento escultórico mediante la aplicación de sus conocimientos en una configuración
novedosa, tanto por el procedimiento como por el método de aplicación de los materiales.
Durante las páginas que siguen se verán y comprenderán las dificultades que tuvieron que
afrontar no sólo a nivel técnico, sino a nivel conceptual para hilvanar todos los aspectos del
proyecto, viéndose, así mismo, los ámbitos en los que este proyecto concreto es singular.In January 2003, the sculptors Pablo de Arriba del Amo and José de las Casas Gómez,
presented the idea of a possible sculptural creation to the Municipal Board of Villaverde
Alto, this project was approved, therefore, it had the necessary financing to carry it out. It
was later installed in the proposed final location, which was in Plaza Ágata in that same
district. In this article, all the steps that were followed in the process of creating this monument, which was especially complex due to its size, will be developed in detail. From the
choice of theme, materials and processes to the development and study of the foundation,
all of this will be explained to account for a project of maximum interest not only for the
sculptors themselves, but also for the general public. The approach to this procedure can
make the universe of sculpture much more appreciated. It must be taken into account,
that both sculptors invented a sculptural procedure by applying their knowledge in a novel
configuration, both in terms of the procedure and the method of applying the materials.
During the following pages you will see and understand the difficulties they had to face
not only at a technical level but also at a conceptual level to put together all the aspects of
the project, seeing, likewise, the areas in which this specific project is unique
How large are the level sets of the Takagi function?
Let T be Takagi's continuous but nowhere-differentiable function. This paper
considers the size of the level sets of T both from a probabilistic point of
view and from the perspective of Baire category. We first give more elementary
proofs of three recently published results. The first, due to Z. Buczolich,
states that almost all level sets (with respect to Lebesgue measure on the
range of T) are finite. The second, due to J. Lagarias and Z. Maddock, states
that the average number of points in a level set is infinite. The third result,
also due to Lagarias and Maddock, states that the average number of local level
sets contained in a level set is 3/2. In the second part of the paper it is
shown that, in contrast to the above results, the set of ordinates y with
uncountably infinite level sets is residual, and a fairly explicit description
of this set is given. The paper also gives a negative answer to a question of
Lagarias and Maddock by showing that most level sets (in the sense of Baire
category) contain infinitely many local level sets, and that a continuum of
level sets even contain uncountably many local level sets. Finally, several of
the main results are extended to a version of T with arbitrary signs in the
summands.Comment: Added a new Section 5 with generalization of the main results; some
new and corrected proofs of the old material; 29 pages, 3 figure
Sculpting oscillators with light within a nonlinear quantum fluid
Seeing macroscopic quantum states directly remains an elusive goal. Particles
with boson symmetry can condense into such quantum fluids producing rich
physical phenomena as well as proven potential for interferometric devices
[1-10]. However direct imaging of such quantum states is only fleetingly
possible in high-vacuum ultracold atomic condensates, and not in
superconductors. Recent condensation of solid state polariton quasiparticles,
built from mixing semiconductor excitons with microcavity photons, offers
monolithic devices capable of supporting room temperature quantum states
[11-14] that exhibit superfluid behaviour [15,16]. Here we use microcavities on
a semiconductor chip supporting two-dimensional polariton condensates to
directly visualise the formation of a spontaneously oscillating quantum fluid.
This system is created on the fly by injecting polaritons at two or more
spatially-separated pump spots. Although oscillating at tuneable THz-scale
frequencies, a simple optical microscope can be used to directly image their
stable archetypal quantum oscillator wavefunctions in real space. The
self-repulsion of polaritons provides a solid state quasiparticle that is so
nonlinear as to modify its own potential. Interference in time and space
reveals the condensate wavepackets arise from non-equilibrium solitons. Control
of such polariton condensate wavepackets demonstrates great potential for
integrated semiconductor-based condensate devices.Comment: accepted in Nature Physic
A Continuum Robot and Control Interface for Surgical Assist in Fetoscopic Interventions
Twin-twin transfusion syndrome requires interventional treatment using a fetoscopically introduced laser to sever the shared blood supply between the fetuses. This is a delicate procedure relying on small instrumentation with limited articulation to guide the laser tip and a narrow field of view to visualize all relevant vascular connections. In this letter, we report on a mechatronic design for a comanipulated instrument that combines concentric tube actuation to a larger manipulator constrained by a remote centre of motion. A stereoscopic camera is mounted at the distal tip and used for imaging. Our mechanism provides enhanced dexterity and stability of the imaging device. We demonstrate that the imaging system can be used for computing geometry and enhancing the view at the operating site. Results using electromagnetic sensors for verification and comparison to visual odometry from the distal sensor show that our system is promising and can be developed further for multiple clinical needs in fetoscopic procedures
Level Sets of the Takagi Function: Local Level Sets
The Takagi function \tau : [0, 1] \to [0, 1] is a continuous
non-differentiable function constructed by Takagi in 1903. The level sets L(y)
= {x : \tau(x) = y} of the Takagi function \tau(x) are studied by introducing a
notion of local level set into which level sets are partitioned. Local level
sets are simple to analyze, reducing questions to understanding the relation of
level sets to local level sets, which is more complicated. It is known that for
a "generic" full Lebesgue measure set of ordinates y, the level sets are finite
sets. Here it is shown for a "generic" full Lebesgue measure set of abscissas
x, the level set L(\tau(x)) is uncountable. An interesting singular monotone
function is constructed, associated to local level sets, and is used to show
the expected number of local level sets at a random level y is exactly 3/2.Comment: 32 pages, 2 figures, 1 table. Latest version has updated equation
numbering. The final publication will soon be available at springerlink.co
Analysis of the radiative decays among the charmonium states
In this article, we study the radiative decays among the charmonium states
with the heavy quark effective theory, and make predictions for the ratios
among the radiative decay widths of an special multiplet to another multiplet.
The predictions can be confronted with the experimental data in the future and
put additional constraints in identifying the , , charmonium-like
mesons.Comment: 12 pages, revised revisio
Regional circulation patterns of Mediterranean Outflow Water near the Iberian and African continental slopes
The Mediterranean Outflow Water (MOW) is a dense water
mass originated in the Strait of Gibraltar. Downstream of the Gulf of Cádiz,
the MOW forms a reservoir region west of the Iberian continental slopes at a
buoyant depth of approximately 1000 m. This region plays a key role as the
main centre where the MOW is mixed and distributed into the North Atlantic.
The seafloor in this area is characterized by the presence of a complex
bathymetry with three abyssal plains separated by mountain chains. Although
the topographic features do not reach the surface, they influence ocean
flows at intermediate and deep ocean layers, conditioning the distribution
and circulation of MOW.
The Copernicus Marine Environmental Monitoring Service (CMEMS) Iberian–Biscay–Ireland (IBI) ocean reanalysis is used to provide a detailed view of the
circulation and mixing processes of MOW near the Iberian and African
continental slopes. This work emphasizes the relevance of the complex
bathymetric features defining the circulation processes of MOW in this
region. The high resolution of the IBI reanalysis allows us to make a
description of the mesoscale features forced by the topography. The
temperature, salinity, velocity, transport, and vorticity fields are
analysed to understand the circulation patterns of MOW. The high-resolution
circulation patterns reveal that Horseshoe Basin and the continental
slope near Cape Ghir (a.k.a. Cap Rhir or Cabo de Aguer) are key areas controlling the mixing processes of MOW
with the surrounding water masses, mainly North Atlantic Central Water (NACW)
and Antarctic Intermediate Water (AAIW). The water mass
variability is also analysed by means of composite analysis. Results
indicate the existence of a variability in the MOW tongue which retracts and
expands westwards in opposition to the movement of the underlying North
Atlantic Deep Water.</p
All -optical control of the quantum flow of a polariton condensate
Although photons in vacuum are massless particles that do not appreciably interact with each other, significant interactions appear in suitable nonlinear media, leading to hydrodynamic behaviours typical of quantum fluids(1-6). Here, we show the generation and manipulation of vortex-antivortex pairs in a coherent gas of strongly dressed photons (polaritons) flowing against an artificial potential barrier created and controlled by a light beam in a semiconductor microcavity. The optical control of the polariton flow allows us to reveal new quantum hydrodynamical phenomenologies such as the formation of vortex pairs upstream from the optical barrier, a case of ultra-short time excitation of the quantum flow, and the generation of vortices with counterflow trajectories. Additionally, we demonstrate how to permanently trap and store quantum vortices hydrodynamically generated in the wake of a defect. These observations are supported by time-dependent simulations based on the non-equilibrium Gross-Pitaevskii equation(7)
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