1,289 research outputs found
Universal quantum computation with the Orbital Angular Momentum of a single photon
We prove that a single photon with quantum data encoded in its orbital
angular momentum can be manipulated with simple optical elements to provide any
desired quantum computation. We will show how to build any quantum unitary
operator using beamsplitters, phase shifters, holograms and an extraction gate
based on quantum interrogation. The advantages and challenges of these approach
are then discussed, in particular the problem of the readout of the results.Comment: First version. Comments welcom
Delayed commutation in quantum computer networks
In the same way that classical computer networks connect and enhance the
capabilities of classical computers, quantum networks can combine the
advantages of quantum information and communications. We propose a
non-classical network element, a delayed commutation switch, that can solve the
problem of switching time in packet switching networks. With the help of some
local ancillary qubits and superdense codes we can route the information after
part of it has left the network node.Comment: 4 pages. 4 figures. Preliminar versio
Using social networks sites in the purchasing decision process
The rise of Web 2.0 tools and mobile devices means that the image of the traditional consumer has to be replaced with an active, permanently connected, consumer who uses the Internet to find information about brands and to share opinions and shopping experiences with other consumers – a consumer who can be classified as a prosumer (producer + consumer). In this context it is important for marketers to know how consumers use social networks within their purchasing decision process. The present work describes an online survey of more than 500 Facebook users in Spain and Portugal, aimed at identifying which aspects most influence their intention to use this social network in their purchasing decisions. A structural equation model was constructed based on the Technology Acceptance Model (TAM), in which the intended use of Facebook in purchasing decisions depends on two variables: perceived usefulness and perceived ease of use, with attitude being a mediating variable. The background variables considered were aptitude, network externalities, perceived privacy protection, and social influence. The results show that the intended use of Facebook in purchasing decisions is influenced by its perceived usefulness, by social influence, and by the attitude to Facebook. In contrast, the perceived ease of use does not have such direct influence
Fungiform Papillae of the Pig and the Wild Boar Analyzed by Scanning Electron Microscopy
Fungiform papillae of wild boar and pig were studied by scanning electron microscopy (SEM). Four regions were defined on the tongue: rostral, medial and caudal thirds and lateral sides. Morphologically the fungiform papillae correspond with their denomination. Rostral and lateral tongue regions presented the largest average number of fungiform papillae. Taste pores opened onto the upper surface of the papillae and were easily identifiable by SEM. The total number of fungiform taste pores from both animals was the highest reported in the literature. The lateral papillae of wild boar and pig contained the largest average number of pores per papilla. This region must be important in taste sensitivity. Lateral and rostral papillae from both animals can provide a source of taste buds for study since each fungiform papilla presents numerous taste buds and these papillae are very abundant
Charging Interacting Rotating Black Holes in Heterotic String Theory
We present a formulation of the stationary bosonic string sector of the whole
toroidally compactified effective field theory of the heterotic string as a
double Ernst system which, in the framework of General Relativity describes, in
particular, a pair of interacting spinning black holes; however, in the
framework of low--energy string theory the double Ernst system can be
particularly interpreted as the rotating field configuration of two interacting
sources of black hole type coupled to dilaton and Kalb--Ramond fields. We
clarify the rotating character of the --component of the
antisymmetric tensor field of Kalb--Ramond and discuss on its possible torsion
nature. We also recall the fact that the double Ernst system possesses a
discrete symmetry which is used to relate physically different string vacua.
Therefore we apply the normalized Harrison transformation (a charging symmetry
which acts on the target space of the low--energy heterotic string theory
preserving the asymptotics of the transformed fields and endowing them with
multiple electromagnetic charges) on a generic solution of the double Ernst
system and compute the generated field configurations for the 4D effective
field theory of the heterotic string. This transformation generates the
vector field content of the whole low--energy heterotic string
spectrum and gives rise to a pair of interacting rotating black holes endowed
with dilaton, Kalb--Ramond and multiple electromagnetic fields where the charge
vectors are orthogonal to each other.Comment: 15 pages in latex, revised versio
A Tolman-Bondi-Lemaitre Cell-Model for the Universe and Gravitational Collapse
A piecewise Tolman-Bondi-Lemaitre (TBL) cell-model for the universe
incorporating local collapsing and expanding inhomogeneities is presented here.
The cell-model is made up of TBL underdense and overdense spherical regions
surrounded by an intermediate region of TBL shells embedded in an expanding
universe. The cell-model generalizes the Friedmann as well as Einstein-Straus
swiss-cheese models and presents a number of advantages over other models, and
in particular the time evolution of the cosmological inhomogeneities is now
incorporated within the scheme. Important problem of gravitational collapse of
a massive dust cloud, such as a cluster of galaxies or even a massive star, in
such a cosmological background is examined. It is shown that the collapsing
local inhomogeneities in an expanding universe could result in either a black
hole, or a naked singularity, depending on the nature of the set of initial
data which consists of the matter distribution and the velocities of the
collapsing shells in the cloud at the initial epoch from which the collapse
commences.Comment: 14 pages, 3 figure
On the Meaning of the Principle of General Covariance
We present a definite formulation of the Principle of General Covariance
(GCP) as a Principle of General Relativity with physical content and thus
susceptible of verification or contradiction. To that end it is useful to
introduce a kind of coordinates, that we call quasi-Minkowskian coordinates
(QMC), as an empirical extension of the Minkowskian coordinates employed by the
inertial observers in flat space-time to general observers in the curved
situations in presence of gravitation. The QMC are operationally defined by
some of the operational protocols through which the inertial observers
determine their Minkowskian coordinates and may be mathematically characterized
in a neighbourhood of the world-line of the corresponding observer. It is taken
care of the fact that the set of all the operational protocols which are
equivalent to measure a quantity in flat space-time split into inequivalent
subsets of operational prescriptions under the presence of a gravitational
field or when the observer is not inertial. We deal with the Hole Argument by
resorting to de idea of the QMC and show how it is the metric field that
supplies the physical meaning of coordinates and individuates point-events in
regions of space-time where no other fields exist. Because of that the GCP has
also value as a guiding principle supporting Einstein's appreciation of its
heuristic worth in his reply to Kretschmann in 1918
Establishment and Effects on Soil and Pasture of Diverse Arrangements of \u3ci\u3eAcacia decurrens\u3c/i\u3e, \u3ci\u3eAcacia melanoxylon\u3c/i\u3e and \u3ci\u3eAlnus acuminata\u3c/i\u3e as Silvopasture Systems in the High Tropic in Colombia
Bacterias endofitas: un nuevo campo de investigación para el desarrollo del sector agropecuario
The endophytic bacteria living within the tissues of the plants at least during part of their life cycle without causing any damage to the host, establish a symbiotic relationship where both benefit. The endophytic bacteria play a wide variety of roles as promoters of plant growth, biological control on a variety of pathogens, improve process efficiency of phytoremediation of toxic compound in the rhizosphere. These microorganisms are inexhaustible sources of over 20.000 biologically active compounds, which have a direct bearing on the performance and survival of host plants. The endophytic bacteria are reported to produce a number of metabolites such as antibiotics, secondary metabolites including some antitumor compounds and anti-inflammatory agents.Las bacterias endófitas habitan dentro de los tejidos de las plantas al menos durante una parte de su ciclo de vida sin causar daño alguno al hospedero, establecen asociación simbiótica y producen grandes beneficios para las plantas. Las bacterias endófitas cumplen una gran diversidad de funciones como promotoras de crecimiento vegetal, control biológico sobre una diversidad de fitopatógenos, mejoran la eficiencia de los procesos de fitoremediación de compuesto tóxicos en la rizósfera. Estos microorganismo son fuentes inagotable de más de 20.000 compuestos biológicamente activos, los cuales influyen de manera directa en el rendimiento y supervivencia de las plantas hospederas. Las bacterias endófitas son reportadas por producir un número de metabolitos como antibióticos, metabolitos secundarios incluyendo algunos compuestos antitumorales, agentes antiinflamatorios
Bacterias endófitas: una alternativa biologica para el control de burkholderia glumae en el cultivo del arroz en colombia.
Research common in microbial ecology have been directed toward the plantmicrobe interactions from the point of view of symbiotic and pathogenic. Endophytic bacteria reside in plant tissues mainly in intercellular, rarely in intracellular spaces and inside vascular tissues without causing symptoms of disease. The penetration in the plant can by stomates, wounds, areas of emergence by lateral roots, being that these bacteria can produce hydrolytic enzymes able to degrade the cell wall of vegetables. Recent molecular studies on endophytic diversity bacteria have revealed a large richness of species, endophytes promote plants growth and yield, suppress pathogens, may help to remove contaminants, solubilize phosphate and contribute assimilation biological nitrogen to plant.Las investigaciones más comunes en ecología microbiana, han sido orientadas a las interacciones microbio-planta desde el punto de vista simbiótico y de patogénico. Las bacterias endófitas colonizan el interior de los tejidos de las plantas, principalmente espacios intercelulares, raramente en espacios intracelulares y dentro de tejidos vasculares sin causar síntomas de enfermedad en la planta. La penetración en la planta puede ocurrir por estomas, heridas, áreas de emergencia de raíces laterales, siendo que estas bacterias pueden producir enzimas hidrolíticas capaces de degradar la pared celular de los vegetales. Estudios moleculares reciente sobre diversidad de bacterias endófitas han revelado una alta riqueza de filotipos, que promueven el crecimiento de las planta, suprimen fitopatógenos, ayudan a remover contaminantes, solubilizan fosfato y contribuyen a la asimilación biológica de nitrógeno
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