8,189 research outputs found
On Koopman-von Neumann Waves II
In this paper we continue the study, started in [1], of the operatorial
formulation of classical mechanics given by Koopman and von Neumann (KvN) in
the Thirties. In particular we show that the introduction of the KvN Hilbert
space of complex and square integrable "wave functions" requires an enlargement
of the set of the observables of ordinary classical mechanics. The possible
role and the meaning of these extra observables is briefly indicated in this
work. We also analyze the similarities and differences between non selective
measurements and two-slit experiments in classical and quantum mechanics.Comment: 18+1 pages, 1 figure, misprints fixe
Quantum error correction with degenerate codes for correlated noise
We introduce a quantum packing bound on the minimal resources required by
nondegenerate error correction codes for any kind of noise. We prove that
degenerate codes can outperform nondegenerate ones in the presence of
correlated noise, by exhibiting examples where the quantum packing bound is
violated.Comment: 5 pages, published versio
Wavevector Selective Metasurfaces and Tunnel Vision Filters
Metasurfaces offer unprecedented flexibility in the design and control of
light propagation, replacing bulk optical components and exhibiting exotic
optical effects. One of the basic properties of the metasurfaces, which renders
them as frequency selective surfaces, is the ability to transmit or reflect
radiation within a narrow spectral band that can be engineered on demand. Here
we introduce and demonstrate experimentally in the THz domain the concept of
wavevector selective surfaces -- metasurfaces transparent only within a narrow
range of light propagation directions operating effectively as tunnel vision
filters. Practical implementations of the new concept include applications in
wavefront manipulation, observational instruments, vision and free-space
communication in light-scattering environments, as well as passive camouflage
The peculiar Na-O anticorrelation of the bulge globular cluster NGC 6440
Context. Galactic Globular Clusters (GCs) are essential tools to understand
the earliest epoch of the Milky Way, since they are among the oldest objects in
the Universe and can be used to trace its formation and evolution. Current
studies using high resolution spectroscopy for many stars in each of a large
sample of GCs allow us to develop a detailed observational picture about their
formation and their relation with the Galaxy. However, it is necessary to
complete this picture by including GCs that belong to all major Galactic
components, including the Bulge. Aims. Our aim is to perform a detailed
chemical analyses of the bulge GC NGC 6440 in order to determine if this object
has Multiple Populations (MPs) and investigate its relation with the Bulge of
the Milky Way and with the other Galactic GCs, especially those associated with
the Bulge, which are largely poorly studied. Methods. We determined the stellar
parameters and the chemical abundances of light elements (Na, Al), iron-peak
elements (Fe, Sc, Mn, Co, Ni), -elements (O, Mg, Si, Ca, Ti) and heavy
elements (Ba, Eu) in seven red giant members of NGC 6440 using high resolution
spectroscopy from FLAMES@UVES. Results. We found a mean iron content of
[Fe/H]=-0.500.03 dex in agreement with other studies. We found no internal
iron spread. On the other hand, Na and Al show a significant intrinsic spread,
but the cluster has no significant O-Na anticorrelation nor exhibits a Mg-Al
anticorrelation. The -elements show good agreement with the Bulge field
star trend, although they are at the high alpha end and are also higher than
those of other GCs of comparable metallicity. The heavy elements are dominated
by the r-process, indicating a strong contribution by SNeII. The chemical
analysis suggests an origin similar to that of the Bulge field stars.Comment: 12 pages, 13 figures, Accepted for publication in A&
Milage aprender+ uma app para aprender matemática usando smartphones e tablets
O baixo desempenho dos estudantes na aprendizagem da matemática constitui problema que em alguns paĂses se tem vindo a acentuar nos Ăşltimos anos. De acordo com um estudo realizado pelo Departamento de Educação dos EUA, em 2010, as aulas em regime de blended-learning, ou b-learning, apresentam melhores resultados do que as tradicionais aulas presenciais. Por outro lado, observa-se um nĂşmero crescente de estudantes que usa smartphones e tablets nas escolas, cuja popularidade pode ser aproveitada para estimular a sua utilização em atividades educacionais para melhorar a aprendizagem.
Nesta comunicação apresenta-se uma nova aplicação para dispositivos mĂłveis, smartphones e tablets, app MILAGE, atravĂ©s da qual o aluno pode aceder a conteĂşdos pedagĂłgicos, dentro e fora da sala de aula. De modo a estimular e apoiar a realização das várias atividades propostas, a interface incorpora caracterĂsticas de gamificação e recursos multimĂ©dia.info:eu-repo/semantics/publishedVersio
Optimal estimation of quantum observables
We consider the problem of estimating the ensemble average of an observable
on an ensemble of equally prepared identical quantum systems. We show that,
among all kinds of measurements performed jointly on the copies, the optimal
unbiased estimation is achieved by the usual procedure that consists in
performing independent measurements of the observable on each system and
averaging the measurement outcomes.Comment: Submitted to J. Math Phy
Vanishing of the upper critical field in Bi_2Sr_2CaCu_2O_{8+\delta} from Landau-Ott scaling
We apply Landau-Ott scaling to the reversible magnetization data of
BiSrCaCuO published by Y. Wang et al. [\emph{Phys.
Rev. Lett. \textbf{95} 247002 (2005)}] and find that the extrapolation of the
Landau-Ott upper critical field line vanishes at a critical temperature
parameter, T^*_c, a few degrees above the zero resistivity critical
temperature, T_c. Only isothermal curves below and near to T_c were used to
determine this transition temperature. This temperature is associated to the
disappearance of the mixed state instead of a complete suppression of
superconductivity in the sample.Comment: 3 figure
The Beta coefficient of an unlisted bank
The problem that we set ourselves in this work is related to the determination of capital return invested in an unlisted bank,
particularly, in a credit cooperative bank. The model that we use is the Capital Asset Pricing Model (CAPM) equation, with its
various difficulties in applying it to a category of unlisted activities. The biggest obstacle in using CAPM is given by the Beta
determination representing the systematic risk of the units under examination. Therefore, to determine this risk coefficient, we
assumed a first step in which we consider a similar sector sample, consists of a portfolio of listed banks, from which we obtain a
Business Risk Index (BRI), that we use to go back to unlisted bank Beta under consideration. In a second case, it is thought of a
target market constituted by the whole unlisted banks sample of the same sector under analysis, then relating the returns of
individual observed banks with average returns provided by this market, we obtain the Regression Beta. A third step, provides
the Business Risk Index determination of the sector, in this case obtained from the unlisted banks market, and then to reach to our
banks Beta under observation. Comparing the results obtained from this analysis allows us to suggest a quite satisfying line for
determining the Beta of an unlisted bank and consequently for its expected return estimation
Extremal covariant measurements
We characterize the extremal points of the convex set of quantum measurements
that are covariant under a finite-dimensional projective representation of a
compact group, with action of the group on the measurement probability space
which is generally non-transitive. In this case the POVM density is made of
multiple orbits of positive operators, and, in the case of extremal
measurements, we provide a bound for the number of orbits and for the rank of
POVM elements. Two relevant applications are considered, concerning state
discrimination with mutually unbiased bases and the maximization of the mutual
information.Comment: 11 pages, no figure
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