30,582 research outputs found
Noncommutative Effects in the Black Hole Evaporation in Two Dimensions
We discuss some possible implications of a two-dimensional toy model for
black hole evaporation in noncommutative field theory. While the
noncommutativity we consider does not affect gravity, it can play an important
role in the dynamics of massless and Hermitian scalar fields in the event
horizon of a Schwarzschild black hole. We find that noncommutativity will
affect the flux of outgoing particles and the nature of its UV/IR divergences.
Moreover, we show that the noncommutative interaction does not affect Leahy's
and Unruh's interpretation of thermal ingoing and outgoing fluxes in the black
hole evaporation process. Thus, the noncommutative interaction still destroys
the thermal nature of fluxes. In the process, some nonlocal implications of the
noncommutativity are discussed.Comment: 33+1 pages, 3 eps figures, typos corrected, references added, figure
3 corrected, modifications in sections 4 and 6, version published in Phys.
Rev.
Heisenberg-limited eavesdropping on the continuous-variable quantum cryptographic protocol with no basis switching is impossible
The Gaussian quantum key distribution protocol based on coherent states and
heterodyne detection [Phys. Rev. Lett. 93, 170504 (2004)] has the advantage
that no active random basis switching is needed on the receiver's side. Its
security is, however, not very satisfyingly understood today because the bounds
on the secret key rate that have been derived from Heisenberg relations are not
attained by any known scheme. Here, we address the problem of the optimal
Gaussian individual attack against this protocol, and derive tight upper bounds
on the information accessible to an eavesdropper. The optical scheme achieving
this bound is also exhibited, which concludes the security analysis of this
protocol.Comment: 10 pages, 6 figure
Predicción de la frescura del aceite de oliva virgen extra durante el almacenamiento mediante espectroscopía de fluorescencia
Virgin olive oil quality relates to flavor and unique health benefits. Some of these properties are
at the most desirable level when the oil is just extracted, since it is not a product that improves with age. On the
contrary, the concentrations of many compounds change during its shelf-life. These changes reveal the aging of
the oil but do not necessarily mean decay in sensory properties, so in some cases an aged oil from healthy olives
may be better qualified than a fresh one from olives affected by fermentation. The aim of this work is to analyze
different methodologies proposed for assessing the quality of virgin olive oil with implications in freshness and
aging of the oil, and to highlight the possibilities of rapid spectrofluorimetric techniques for assessing oil freshness by checking the evolution of pigments during storage. The observed change in the selected spectral features
and mathematical modelling over time was compared with the accepted model for predicting the amount of
pyropheophytin a, which is based on isokinetic studies. The best regression was obtained for 655 nm (adjustedR2
= 0.91) wavelength, which matches the distinctive band of pigments. The two mathematical models described
in this study highlight the usefulness of pigments in the prediction of the shelf-life of extra virgin olive oil.La calidad del aceite de oliva virgen está relacionada con su flavor y sus beneficios
únicos para la salud. Algunas de estas propiedades se encuentran en el nivel más deseable cuando el aceite está
recién extraído, ya que no es un producto que mejore con el tiempo. Por el contrario, las concentraciones de
muchos compuestos cambian a lo largo de la vida útil. Estos cambios revelan el envejecimiento del aceite, pero
no implican necesariamente la alteración de las propiedades sensoriales, por lo que en algunos casos un aceite
envejecido procedente de aceitunas sanas puede presentar mejor calidad que uno fresco procedente de aceitunas
afectadas por procesos de fermentación. El objetivo de este trabajo es estudiar diferentes metodologías propuestas para evaluar la calidad del aceite de oliva virgen con implicaciones en la frescura y el envejecimiento del
aceite, destacando las posibilidades de las rápidas técnicas espectrofluorométricas para evaluar la frescura del
aceite verificando la evolución de los pigmentos durante el almacenamiento. El cambio observado en las características espectrales seleccionadas y su modelado matemático a lo largo del tiempo se comparó con el modelo
aceptado para predecir la cantidad de pirofeofitina a, que se basa en estudios isocinéticos. Los dos modelos
matemáticos descritos en este estudio pusieron de manifiesto la utilidad de los pigmentos en la predicción de la
vida útil del aceite de oliva virgen extra. La mejor regresión se obtuvo para 655 nm (R2
-ajustado = 0,91), longitud de onda que coincide con la banda distintiva de pigmentos.Secretaría de Estado de Investigación, Desarrollo e Innovación de España-AGL2015-69320-
Predicción de la frescura del aceite de oliva virgen extra durante el almacenamiento mediante espectroscopía de fluorescencia
Virgin olive oil quality relates to flavor and unique health benefits. Some of these properties are
at the most desirable level when the oil is just extracted, since it is not a product that improves with age. On the
contrary, the concentrations of many compounds change during its shelf-life. These changes reveal the aging of
the oil but do not necessarily mean decay in sensory properties, so in some cases an aged oil from healthy olives
may be better qualified than a fresh one from olives affected by fermentation. The aim of this work is to analyze
different methodologies proposed for assessing the quality of virgin olive oil with implications in freshness and
aging of the oil, and to highlight the possibilities of rapid spectrofluorimetric techniques for assessing oil freshness by checking the evolution of pigments during storage. The observed change in the selected spectral features
and mathematical modelling over time was compared with the accepted model for predicting the amount of
pyropheophytin a, which is based on isokinetic studies. The best regression was obtained for 655 nm (adjustedR2
= 0.91) wavelength, which matches the distinctive band of pigments. The two mathematical models described
in this study highlight the usefulness of pigments in the prediction of the shelf-life of extra virgin olive oil.La calidad del aceite de oliva virgen está relacionada con su flavor y sus beneficios
únicos para la salud. Algunas de estas propiedades se encuentran en el nivel más deseable cuando el aceite está
recién extraído, ya que no es un producto que mejore con el tiempo. Por el contrario, las concentraciones de
muchos compuestos cambian a lo largo de la vida útil. Estos cambios revelan el envejecimiento del aceite, pero
no implican necesariamente la alteración de las propiedades sensoriales, por lo que en algunos casos un aceite
envejecido procedente de aceitunas sanas puede presentar mejor calidad que uno fresco procedente de aceitunas
afectadas por procesos de fermentación. El objetivo de este trabajo es estudiar diferentes metodologías propuestas para evaluar la calidad del aceite de oliva virgen con implicaciones en la frescura y el envejecimiento del
aceite, destacando las posibilidades de las rápidas técnicas espectrofluorométricas para evaluar la frescura del
aceite verificando la evolución de los pigmentos durante el almacenamiento. El cambio observado en las características espectrales seleccionadas y su modelado matemático a lo largo del tiempo se comparó con el modelo
aceptado para predecir la cantidad de pirofeofitina a, que se basa en estudios isocinéticos. Los dos modelos
matemáticos descritos en este estudio pusieron de manifiesto la utilidad de los pigmentos en la predicción de la
vida útil del aceite de oliva virgen extra. La mejor regresión se obtuvo para 655 nm (R2
-ajustado = 0,91), longitud de onda que coincide con la banda distintiva de pigmentos.Secretaría de Estado de Investigación, Desarrollo e Innovación de España-AGL2015-69320-
On the low-field Hall coefficient of graphite
We have measured the temperature and magnetic field dependence of the Hall
coefficient () in three, several micrometer long multigraphene
samples of thickness between to ~nm in the temperature range
0.1 to 200~K and up to 0.2~T field. The temperature dependence of the
longitudinal resistance of two of the samples indicates the contribution from
embedded interfaces running parallel to the graphene layers. At low enough
temperatures and fields is positive in all samples, showing a
crossover to negative values at high enough fields and/or temperatures in
samples with interfaces contribution. The overall results are compatible with
the reported superconducting behavior of embedded interfaces in the graphite
structure and indicate that the negative low magnetic field Hall coefficient is
not intrinsic of the ideal graphite structure.Comment: 10 pages with 7 figures, to be published in AIP Advances (2014
Demixing in a single-peak distributed polydisperse mixture of hard spheres
An analytic derivation of the spinodal of a polydisperse mixture is
presented. It holds for fluids whose excess free energy can be accurately
described by a function of a few moments of the size distribution. It is shown
that one such mixture of hard spheres in the Percus-Yevick approximation never
demixes, despite its size distribution. In the
Boublik-Mansoori-Carnahan-Starling-Leland approximation, though, it demixes for
a sufficiently wide log-normal size distribution. The importance of this result
is twofold: first, this distribution is unimodal, and yet it phase separates;
and second, log-normal size distributions appear in many experimental contexts.
The same phenomenon is shown to occur for the fluid of parallel hard cubes.Comment: 4 pages, 2 figures, needs revtex, multicol, epsfig and amstex style
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