967 research outputs found
Photo-assisted shot noise in Coulomb interacting systems
We consider the fluctuations of the electrical current (shot noise) in the
presence of a voltage time-modulation. For a non-interacting metal, it is known
that the derivative of the photo-assisted noise has a staircase behavior. In
the presence of Coulomb interactions, we show that the photo-assisted noise
presents a more complex profile, in particular for the two following systems:
1) a two-dimensional electron gas in the fractional quantum Hall regime for
which we have obtained evenly spaced singularities in the noise derivative,
with a spacing related to the filling factor and, 2) a carbon nanotube for
which a smoothed staircase in the noise derivative is obtained.Comment: Proceedings of the 6th Rencontres du Vietnam, Hanoi (2006
Groupoids and Wreath Products of Musical Transformations: a Categorical Approach from poly-Klumpenhouwer Networks
Transformational music theory, pioneered by the work of Lewin, shifts the
music-theoretical and analytical focus from the "object-oriented" musical
content to an operational musical process, in which transformations between
musical elements are emphasized. In the original framework of Lewin, the set of
transformations often form a group, with a corresponding group action on a
given set of musical objects. Klumpenhouwer networks have been introduced based
on this framework: they are informally labelled graphs, the labels of the
vertices being pitch classes, and the labels of the arrows being
transformations that maps the corresponding pitch classes. Klumpenhouwer
networks have been recently formalized and generalized in a categorical
setting, called poly-Klumpenhouwer networks. This work proposes a new
groupoid-based approach to transformational music theory, in which
transformations of PK-nets are considered rather than ordinary sets of musical
objects. We show how groupoids of musical transformations can be constructed,
and an application of their use in post-tonal music analysis with Berg's Four
pieces for clarinet and piano, Op. 5/2. In a second part, we show how groupoids
are linked to wreath products (which feature prominently in transformational
music analysis) through the notion of groupoid bisectionsComment: 16 pages, 9 figures; comments welcom
Coherent control of photocurrent in a strongly scattering photoelectrochemical system
A fundamental issue that limits the efficiency of many photoelectrochemical
systems is that the photon absorption length is typically much longer than the
electron diffusion length. Various photon management schemes have been
developed to enhance light absorption; one simple approach is to use randomly
scattering media to enable broadband and wide-angle enhancement. However, such
systems are often opaque, making it difficult to probe photo-induced processes.
Here we use wave interference effects to modify the spatial distribution of
light inside a highly-scattering dye-sensitized solar cell to control photon
absorption in a space-dependent manner. By shaping the incident wavefront of a
laser beam, we enhance or suppress photocurrent by increasing or decreasing
light concentration on the front side of the mesoporous photoanode where the
collection efficiency of photoelectrons is maximal. Enhanced light absorption
is achieved by reducing reflection through the open boundary of the photoanode
via destructive interference, leading to a factor of two increase in
photocurrent. This approach opens the door to probing and manipulating
photoelectrochemical processes in specific regions inside nominally opaque
media.Comment: 21 pages, 4 figures, in submission. The first two authors contributed
equally to this paper, and should be regarded as co-first author
Reproductibilité intra-juge et inter-juge de la mesure goniométrique de flexion dorsale de cheville des patients hémiparétiques
Optimal Concentration of Light in Turbid Materials
In turbid materials it is impossible to concentrate light into a focus with
conventional optics. Recently it has been shown that the intensity on a dyed
probe inside a turbid material can be enhanced by spatially shaping the wave
front of light before it enters a turbid medium. Here we show that this
enhancement is due to concentration of light energy to a spot much smaller than
a wavelength. We focus light on a dyed probe sphere that is hidden under an
opaque layer. The light is optimally concentrated to a focus which does not
exceed the smallest focal area physically possible by more than 68%. A
comparison between the intensity enhancements of both the emission and
excitation light supports the conclusion of optimal light concentration.Comment: We corrected an ambiguous description of the focus size in our
abstract and text pointed out by an anonymous refere
Case report: Abdominal transcutaneous exposure of the distal tip of a ventriculo-peritoneal shunt for post-traumatic hydrocephalus
The Schr\"odinger operator on an infinite wedge with a tangent magnetic field
We study a model Schr\"odinger operator with constant magnetic field on an
infinite wedge with Neumann boundary condition. The magnetic field is assumed
to be tangent to a face. We compare the bottom of the spectrum to the model
spectral quantities coming from the regular case. We are particularly motivated
by the influence of the magnetic field and the opening angle of the wedge on
the spectrum of the model operator and we exhibit cases where the bottom of the
spectrum is smaller than in the regular case. Numerical computations enlighten
the theoretical approach
- …