229 research outputs found
K-essential Phantom Energy: Doomsday around the Corner? Revisited
We generalize some of those results reported by Gonz\'{a}lez-D\'{i}az by
further tuning the parameter () which is closely related to the
canonical kinetic term in -essence formalism. The scale factor could
be negative and decreasing within a specific range of (, : the equation-of-state parameter) during the initial
evolutional period.Comment: 1 Figure, 6 page
Auger-induced charge migration
Novel perspectives of controlling molecular systems have recently arisen from the possibility of generating attosecond pulses in the ultraviolet regime and tailoring electron dynamics in its natural time scale. The cornerstone mechanism is the so-called charge migration, he production of a coherent charge transfer with subfemtosecond oscillations across a molecule. Typically, charge migration is induced by the ionization of valence molecular orbitals. However, recent technological developments allow the generation of attosecond pulses in the x-ray regime. In this case, the absorption of photons creates core-hole states. In light elements, core-hole states mainly decay by Auger processes that, driven by electron correlations, involve valence orbitals. We theoretically demonstrate in a fluoroacetylene molecule a double-hole charge migration triggered by attosecond core-electron photoionization, followed by Auger electron relaxations. This opens a new route for inducing with x rays charge transfer processes in the subfemtosecond time scaleThis project has received funding from the European Union’s Horizon 2020 research and innovation programme under Marie Sklodowska-Curie Grant Agreement No. 702565, from Comunidad de Madrid through the TALENTO program with Reference No. 2017-T1/IND-5432, and from the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences through Argonne National
Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge support from Junta de Castilla y León (Project No. SA046U16) and MINECO (Grant No. FIS2016-
75652-P). C.H.-G. acknowledges support from a 2017 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundatio
EP-1450: Analysis of delivered dose differences due to MLC errors using dynamic MLC log files
Regularity of maximal functions on Hardy–Sobolev spaces
We prove that maximal operators of convolution type associated to smooth kernels are bounded in the homogeneous Hardy–Sobolev spaces H1,p(Rd) when p > d/(d + 1). This range of exponents is sharp. As a by-product of the proof, we obtain similar results for the local Hardy–Sobolev spaces h1,p(Rd) in the same range of exponents
Campo tensional en el entorno de una fisura. Determinación de KI y KII usando técnicas fotoelásticas
Trabajo reproducido y difundido en el repositorio idUS con permiso de la Asociación Española de Ingeniería Mecánica (AEIM)Tras introducir la forma general del campo de tensiones en
un borde de grieta se hace una exposición detallada de los
métodos para medir K I y K II, resaltando sus ventajas e
inconvenientes. Por su generalldad, se ha implementado un
método que desarrolla en serie las funciones de tensión. La
introducción de las medidas fotoelásticas (que pueden ser de
campo lejano) conduce a un sistema sobredetermlnado no
lineal de ecuaclones, que es resuelto por un métooo de
Neewton-Raphson y mínimos cuadrados. Sobre una
aplicación experimental se comentan las caracterlstlcas de
este métodoFirst of all, the general form of the crack-tip stress
field is introduced. Then, a detailed review of K I-K II methods
is pressented, showing thelr features. A stress-functions
series expansion method has been implemented, due to its
generality. Experimental far-fleld isochromatic polnts are
used to fit the series expanslon coefflclents and the
overdeterminlstlc non-linear equation system is solved with
a Newton-Rapshon least-squares method. Finally the
features of thls method are dlscussed uslng an experimental
applicatio
A new view of k-essence
K-essence models, relying on scalar fields with non-canonical kinetic terms,
have been proposed as an alternative to quintessence in explaining the observed
acceleration of the Universe. We consider the use of field redefinitions to
cast k-essence in a more familiar form. While k-essence models cannot in
general be rewritten in the form of quintessence models, we show that in
certain dynamical regimes an equivalence can be made, which in particular can
shed light on the tracking behaviour of k-essence. In several cases, k-essence
cannot be observationally distinguished from quintessence using the homogeneous
evolution, though there may be small effects on the perturbation spectrum. We
make a detailed analysis of two k-essence models from the literature and
comment on the nature of the fine tuning arising in the models.Comment: 7 pages RevTeX4 file with four figures incorporate
Use of Heat Transfer Enhancement Techniques in the Design of Heat Exchangers
Heat transfer enhancement refers to application of basic concepts of heat transfer processes to improve the rate of heat removal or deposition on a surface. In the flow of a clean fluid through the tube of a heat exchanger, the boundary layer theorem establishes that a laminar sublayer exists where the fluid velocity is minimal. Heat transfer through this stagnant layer is mainly dominated by thermal conduction, becoming the major resistance to heat transfer. From an engineering point of view, heat transfer can be enhanced if this stagnant layer is partially removed or eliminated. In single-phase heat transfer processes, three options are available to increase the heat transfer rate. One of them is the choice of smaller free flow sectional area for increased fluid velocity bringing about a reduction of the thickness of the laminar sublayer. A second option is the engineering of new surfaces which cause increased local turbulence, and the third option consists in the use of mechanical inserts that promote local turbulence. The application of these alternatives is limited by the pressure drop. This chapter describes the concept of heat transfer enhancement and the ways it is applied to the development of new heat exchanger technology
Dark matter to dark energy transition in k-essence cosmologies
We implement the transition from dark matter to dark energy in k-essence
cosmologies for a very large set of kinetic functions , in a way alternative
to recent proposals which use generalized Chaplygin gas and transient models.
Here we require that the pressure admits a power-law expansion around some
value of the kinetic energy where the pressure vanishes. In addition, for
suitable values of the parameters of the model, the speed of sound of the dark
matter will be low. We first present the discussion in fairly general terms,
and later consider for illustration two examples.Comment: 5 pages, revte
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