1,186 research outputs found
Decoherence, fluctuations and Wigner function in neutron optics
We analyze the coherence properties of neutron wave packets, after they have
interacted with a phase shifter undergoing different kinds of statistical
fluctuations. We give a quantitative (and operational) definition of
decoherence and compare it to the standard deviation of the distribution of the
phase shifts. We find that in some cases the neutron ensemble is more coherent,
even though it has interacted with a wider (i.e. more disordered) distribution
of shifts. This feature is independent of the particular definition of
decoherence: this is shown by proposing and discussing an alternative
definition, based on the Wigner function, that displays a similar behavior. We
briefly discuss the notion of entropy of the shifts and find that, in general,
it does not correspond to that of decoherence of the neutron.Comment: 18 pages, 7 figure
Dark Matter in split extended supersymmetry
We consider the split extended (N=2) supersymmetry scenario recently proposed
by Antoniadis et al. [hep-ph/0507192] as a realistic low energy framework
arising from intersecting brane models. While all scalar superpartners and
charged gauginos are naturally at a heavy scale, the model low energy spectrum
contains a Higgsino-like chargino and a neutralino sector made out of two
Higgsino and two Bino states. We show that the lightest neutralino is a viable
dark matter candidate, finding regions in the parameter space where its thermal
relic abundance matches the latest determination of the density of matter in
the
Universe by WMAP. We also discuss dark matter detection strategies within
this model: we point out that current data on cosmic-ray antimatter already
place significant constraints on the model, while direct detection is the most
promising technique for the future. Analogies and differences with respect to
the standard split
SUSY scenario based on the MSSM are illustrated.Comment: 14 pages, references added, typos corrected, matches with the
published versio
Trigonometry of 'complex Hermitian' type homogeneous symmetric spaces
This paper contains a thorough study of the trigonometry of the homogeneous
symmetric spaces in the Cayley-Klein-Dickson family of spaces of 'complex
Hermitian' type and rank-one. The complex Hermitian elliptic CP^N and
hyperbolic CH^N spaces, their analogues with indefinite Hermitian metric and
some non-compact symmetric spaces associated to SL(N+1,R) are the generic
members in this family. The method encapsulates trigonometry for this whole
family of spaces into a single "basic trigonometric group equation", and has
'universality' and '(self)-duality' as its distinctive traits. All previously
known results on the trigonometry of CP^N and CH^N follow as particular cases
of our general equations. The physical Quantum Space of States of any quantum
system belongs, as the complex Hermitian space member, to this parametrised
family; hence its trigonometry appears as a rather particular case of the
equations we obtain.Comment: 46 pages, LaTe
Instability of hyper-compact Kerr-like objects
Viable alternatives to astrophysical black holes include hyper-compact
objects without horizon, such as gravastars, boson stars, wormholes and
superspinars. The authors have recently shown that typical rapidly-spinning
gravastars and boson stars develop a strong instability. That analysis is
extended in this paper to a wide class of horizonless objects with approximate
Kerr-like geometry. A detailed investigation of wormholes and superspinars is
presented, using plausible models and mirror boundary conditions at the
surface. Like gravastars and boson stars, these objects are unstable with very
short instability timescales. This result strengthens previous conclusions that
observed hyper-compact astrophysical objects with large rotation are likely to
be black holes.Comment: 15 pages, 3 figures. To be published in CQ
Polarity in GaN and ZnO: Theory, measurement, growth, and devices
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Rev. 3, 041303 (2016) and may be found at https://doi.org/10.1063/1.4963919.The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade
Total costs and benefits of biomass in selected regions of the European Union
The paper describes results of the BioCosts project in which a comprehensive analysis of the economic and environmental performance of the energy use of biomass was carried out for selected existing facilities throughout the European Union. It is demonstrated that the appropriately organized use of biofuels has significant environmental advantages compared to the use of fossil fuels. Mitigation of global warming is the largest single incentive to use biofuels. However, only a few technologies are economically competitive under prevailing conditions, while others lead to up to 100% higher energy production costs than fossil fuels. Employment effects of using biofuels are small but positive.http://www.sciencedirect.com/science/article/B6V2S-41JM99D-4/1/514a3253589af4590f84544e2966bcb
Flavor Phenomenology in General 5D Warped Spaces
We have considered a general 5D warped model with SM fields propagating in
the bulk and computed explicit expressions for oblique and non-oblique
electroweak observables as well as for flavor and CP violating effective
four-fermion operators. We have compared the resulting lower bounds on the
Kaluza-Klein (KK) scale in the RS model and a recently proposed model with a
metric modified towards the IR brane, which is consistent with oblique
parameters without the need for a custodial symmetry. We have randomly
generated 40,000 sets of O(1) 5D Yukawa couplings and made a fit of the quark
masses and CKM matrix elements in both models. This method allows to identify
the percentage of points consistent with a given KK mass, which in turn
provides us with a measure for the required fine-tuning. Comparison with
current experimental data on Rb, FCNC and CP violating operators exhibits an
improved behavior of our model with respect to the RS model. In particular,
allowing 10% fine-tuning the combined results point towards upper bounds on the
KK gauge boson masses around 3.3 TeV in our model as compared with 13 TeV in
the RS model. One reason for this improvement is that fermions in our model are
shifted, with respect to fermions in the RS model, towards the UV brane thus
decreasing the strength of the modifications of electroweak observables.Comment: 28 pages, 7 figures, 4 table
Investigación en Progreso: Ingeniería de Software en el Desarrollo de Aplicaciones Sensibles al Contexto
Las aplicaciones han ido evolucionando independientemente de cuál sea su dominio de aplicación, actualmente nos encontramos con aplicaciones que pueden brindar servicios de acuerdo a la ubicación, tiempo y perfil del usuario. Este tipo de aplicaciones que brindan estos servicios se las conoce como Aplicaciones Sensibles al Contexto (CA – Context Aware), en este tipo de aplicaciones predominan los dispositivos móviles y el perfil del usuario. La evolución varía en función de la forma de uso de la computadora, es decir que se brinden servicios a pedido del usuario o que se brinden servicios de manera automática. Para acompañar la evolución de este tipo de aplicaciones, la Ingeniería de Software ha focalizado sus esfuerzos en aspectos relacionados a separar la aplicación de todo lo concerniente a la captación, interpretación, control y supervisión de la información contextual. Es decir que desde el punto de vista del diseño, se separe la conducta sensible al contexto de la conducta propia de la aplicación con el propósito de que ambos tipos de aplicaciones pueden evolucionar en forma independiente además de reducir el tiempo de desarrollo en este tipo de sistemas. Este proyecto presenta una sub línea, la cual orientará sus aportes, en la consolidación de un framework de gestión contextual de dos o tres variables de contexto como por ejemplo: la ubicación, considerando la construcción de la documentación relevante que lo respalde como así también su fase de experimentación con una aplicación que permitirá a los usuarios de la comunidad universitaria UM hacer uso de los servicios ofrecidos por la misma. La segunda sub línea, se vincula al Área de la Ingeniería de Requisitos, pretendiendo obtener un modelo para la especificación de requisitos de software para sistemas sensibles al contexto
Monopelopia caraguata (Chironomidae: Tanypodinae: Pentaneurini) and Phytotelmatocladius delarosai (Chironomidae: Orthocladiinae) : Two Phytotelmatous Chironomids Distributed from Florida to Argentina
Fil: Siri, Augusto. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología Dr. Raúl A. Ringuelet; ArgentinaFil: Donato, Mariano. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Laboratorio de Sistemática y Biología Evolutiva; Argentin
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