10,480 research outputs found
Full sky harmonic analysis hints at large UHECR deflections
The full-sky multipole coefficients of the ultra-high energy cosmic ray
(UHECR) flux have been measured for the first time by the Pierre Auger and
Telescope Array collaborations using a joint data set with E > 10 EeV. We
calculate these harmonic coefficients in the model where UHECR are protons and
sources trace the local matter distribution, and compare our results with
observations. We find that the expected power for low multipoles (dipole and
quadrupole, in particular) is sytematically higher than in the data: the
observed flux is too isotropic. We then investigate to which degree our
predictions are influenced by UHECR deflections in the regular Galactic
magnetic field (GMF). It turns out that the UHECR power spectrum coefficients
are quite insensitive to the effects of the GMF, so it is unlikely
that the discordance can be reconciled by tuning the GMF model. On the
contrary, a sizeable fraction of uniformly distributed flux (representing for
instance an admixture of heavy nuclei with considerably larger deflections) can
bring simulations and observations to an accord.Comment: 8 pages, 4 figures and one table, JETPL style -- v2 as published in
JETP
Simulated testing of an adaptive multimedia information retrieval system
The Semantic Gap is considered to be a bottleneck in image and video retrieval. One way to increase the communication between user and system is to take advantage of the user's action with a system, e.g. to infer the relevance or otherwise of a video shot viewed by the user. In this paper we introduce a novel video retrieval system and propose a model of implicit information for interpreting the user's actions with the interface. The assumptions on which this model was created are then analysed in an experiment using simulated users based on relevance judgements to compare results of explicit and implicit retrieval cycles. Our model seems to enhance retrieval results. Results are presented and discussed in the final section
Nonlinear effects of phonon fluctuations on transport through nanoscale junctions
We analyze the effect of electron-phonon coupling on the full counting
statistics of a molecular junction beyond the lowest order perturbation theory.
Our approach allows to take into account analytically the feedback between the
non-equilibrium phonon and electronic distributions in the quantum regime. We
show that even for junctions with high transmission and relatively weak
electron-phonon coupling this feedback gives rise to increasingly higher
nonlinearities in the voltage dependence of the cumulants of the transmitted
charges distribution.Comment: 4 pages, 3 figure
Local Observables in a Landscape of Infrared Gauge Modes
Cosmological local observables are at best statistically determined by the
fundamental theory describing inflation. When the scalar inflaton is coupled
uniformly to a collection of subdominant massless gauge vectors, rotational
invariance is obeyed locally. However, the statistical isotropy of fluctuations
is spontaneously broken by gauge modes whose wavelength exceed our causal
horizon. This leads to a landscape picture where primordial correlators depend
on the position of the observer. We compute the stochastic corrections to the
curvature power spectrum, show the existence of a new local observable (the
shape of the quadrupole), and constrain the theory using Planck limits.Comment: 5 pages, 3 figures, v2: minor updates, matches version published in
Physics Letters
Brane Cosmology and KK Gravitinos
The cosmology of KK gravitinos in models with extra dimensions is considered.
The main result is that the production of such KK modes is not compatible with
an epoch of non--standard expansion after inflation. This is so because the BBN
constraint on the zero mode forces the reduced five dimensional Planck mass
down to values much smaller than the usual four dimensional one, but this
in turn implies many KK states available for a given temperature. Once these
states are taken into account one finds that there is no for which the
produced KK gravitinos satisfy BBN and overclosure constraints. This conclusion
holds for both flat and warped models in which only gravity propagates in the
full spacetime.Comment: 19 pages, references added, IoP styl
Natural extension of the Generalised Uncertainty Principle
We discuss a gedanken experiment for the simultaneous measurement of the
position and momentum of a particle in de Sitter spacetime. We propose an
extension of the so-called generalized uncertainty principle (GUP) which
implies the existence of a minimum observable momentum. The new GUP is directly
connected to the nonzero cosmological constant, which becomes a necessary
ingredient for a more complete picture of the quantum spacetime.Comment: 4 pages, 1 figure, v2 with added references, revised and extended as
published in CQ
Dynamics of a trapped Fermi gas in the BCS phase
We derive semiclassical transport equations for a trapped atomic Fermi gas in
the BCS phase at temperatures between zero and the superfluid transition
temperature. These equations interpolate between the two well-known limiting
cases of superfluid hydrodynamics at zero temperature and the Vlasov equation
at the critical one. The linearized version of these equations, valid for small
deviations from equilibrium, is worked out and applied to two simple examples
where analytical solutions can be found: a sound wave in a uniform medium and
the quadrupole excitation in a spherical harmonic trap. In spite of some
simplifying approximations, the main qualitative results of quantum mechanical
calculations are reproduced, which are the different frequencies of the
quadrupole mode at zero and the critical temperature and strong Landau damping
at intermediate temperatures. In addition we suggest a numerical method for
solving the semiclassical equations without further approximations.Comment: 15 pages, 4 figures; v2: discussion and references adde
Glasgow University at TRECVID 2006
In the first part of this paper we describe our experiments in the automatic and interactive search tasks of TRECVID 2006. We submitted five fully automatic runs, including a text baseline, two runs based on visual features, and two runs that combine textual and visual features in a graph model. For the interactive search, we have implemented a new video search interface with relevance feedback facilities, based on both textual and visual features.
The second part is concerned with our approach to the high-level feature extraction task, based on textual information extracted from speech recogniser and machine translation outputs. They were aligned with shots and associated with high-level feature references. A list of significant words was created for each feature, and it was in turn utilised for identification of a feature during the evaluation
Přesnost měření v senzorových systémech s optovláknovými Braggovými mřížkami
Práce se zabývá aplikací optovláknových Braggových mřížek (FBG) v senzorice a nalyzuje faktory, které ovlivňují přesnost vyhodnocování snímaných veličin. Zaměřili jsme pozornost na spektrální měření posunu maxima reflexivity snímací mřížky, které má potenciál dosažení nejvyšších přesností měření. V práci analyzujeme skenovací způsob vyhodnocení spektra a jeho změn jako nejvhodnější metodu pro průmyslové aplikace, která poskytuje širokou volbu přijatelného kompromisu mezi rychlostí vyčítání hodnot spektrálních změn a přesností měření. Veličina, která zásadně ovlivňuje přesnost měření, je šum superponovaný v přijímači na časový signál odezvy reflexivity měřící mřížky ozařované periodicky přelaďovaným úzkopásmovým optickým zdrojem. Práce analyzuje vliv tohoto šumu na měření a zkoumá parametry skenovacího optického zdroje a vlastnosti měřící mřížky z pohledu dosažitelné přesnosti měření. Pro hodnocení vhodnosti mřížky a parametrů skenování k přesnému měření zavádíme parametr šumová šířka spektra mřížky a šumová šířka skenování spektra mřížky. V práci sou naznačeny souvislosti technologických kroků výrobního procesu mřížky s odrazivostí mřížky kritickou pro minimalizaci měřících chyb. Význam šířky spektra měřící mřížky na přesnost měření vedl ke zkoumání možností apodizace mřížek, tedy vytváření mřížkových struktur s podélně proměnným profilem amplitudy změn indexu lomu.. Analýza apodizačních profilů a technické možnosti přípravy mřížek s apodizací nás přivedly k řešení čistě apodizovaných mřížkových struktur, které je realizovatelné technikou vícenásobné příčné expozice vlákna interferenčním polem fázové mřížky ozářené výkonným UV laserem. Je představen design mřížky s potenciálem významnéhu zvýšení přesnosti detekce posunu spektra
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