Differential susceptibility to noise of mixed Turing and Hopf modes in a photosensitive chemical medium

We report on experiments with the photosensitive chlorine dioxide-iodine-malonic acid reaction (CDIMA) when forced with a random (spatiotemporally) distributed illumination. Acting on a mixed mode consisting of oscillating spots, close enough to the Hopf and Turing codimension-two bifurcation, we observe attenuation of oscillations while the spatial pattern is preserved. Numerical simulations confirm and extend these results. All together these observations point out to a larger vulnerability of the Hopf with respect to the Turing mode when facing noise of intermediate intensity and small correlation parameters.Peer ReviewedPostprint (published version

Invariance Violation Extends the Cosmic Ray Horizon ?

We postulate in the present paper that the energy-momentum relation is modified for very high energy particles to violate Lorentz invariance and the speed of photon is changed from the light velocity c. The violation effect is amplified, in a sensitive way to detection, through the modified kinematical constraints on the conservation of energy and momentum, in the absorption process of gamma-rays colliding against photons of longer wavelengths and converting into an electron-positron pair. For gamma-rays of energies higher than 10 TeV, the minimum energy of the soft photons for the reaction and then the absorption mean free path of gamma-rays are altered by orders of magnitude from the ones conventionally estimated. Consideration is similarly applied to high energy cosmic ray protons. The consequences may require the standard assumptions on the maximum distance that very high energy radiation can travel from to be revised.Comment: 14 pages, 1 figure, to be published in Ap J Letter

Selective epitaxial growth of graphene on SiC

We present an innovative method of selective epitaxial growth of few layers graphene (FLG) on a pre-patterned SiC substrate. The methods involves, successively, the sputtering of a thin AlN layer on top of a mono-crystalline SiC substrate and, then, patterning it with e-beam lithography (EBL) and wet etching. The sublimation of few atomic layers of Si from the SiC substrate occurs only through the selectively etched AlN layer. The presence of the Raman G-band at ~1582 cm-1 in the AlN-free areas is used to validate the concept, it gives absolute evidence of the selective FLG growth.Comment: comments: 3 pages, reference 3 replace

Inspecting absorption in the spectra of extra-galactic gamma-ray sources for insight into Lorentz invariance violation

We examine what the absorbed spectra of extra-galactic TeV gamma-ray sources, such as blazars, would look like in the presence of Lorentz invariance violation (LIV). Pair-production with the extra-galactic background light modifies the observed spectra of such sources, and we show that a violation of Lorentz invariance would generically have a dramatic effect on this absorption feature. Inspecting this effect, an experimental task likely practical in the near future, can provide unique insight on the possibility of LIV.Comment: Published in Phys. Rev.

Determinación ponderal de fibras en una mezcla y relación entre diametro y densidad aparente de la lana

Se hace un estudio crítico de los métodos corrientemente empleados en análisis de mezclas de fibras por microscopía, haciendo notar la imposibilidad de poder obtener resultados relativamente exactos al analizar mezclas en las que algunos de sus componentes son fibras celulósicas o proteicas, debido a que en los cálculos intervienen datos como el diámetro y la densidad de las mismas. El primero es determinado sin tener en cuenta que la fibra presenta poros sensibles dando lugar a un volumen aparente que al ser mayor que el volumen real (volumen de masa fibrilar sin huecos), hace que tenga que considerarse una densidad aparente, necesariamente menor que la real. El trabajo se orientó en el sentido de hallar un método factible de poder determinar la densidad aparente de cada fibra, con objeto de utilizarla en las fórmulas y método de análisis por contaje ya establecidos. Se determinó la densidad aparente de la lana en sus distintos tipos, encontrándose una correlación entre el diámetro y la densidad aparente, de la cual se deduce la ecuación analítica que liga estas dos variablesPeer Reviewe

Testing the Special Relativity Theory with Neutrino interactions

A recent measurement of neutrino velocity by the OPERA experiment and prediction of energy loss of superluminal neutrino via the pair creation process $\nu\to \nu e^+e^-$ stimulated a search of isolated $e^+e^-$ pairs in detectors with good tracking capability traversed by a large flux of high energy neutrino like NOMAD. NOMAD has already searched for similar topologies. These results can be reinterpreted to provide stringent limits on special relativity violating parameters separately for each $\nu$ species.Comment: 3 pages, 3 figures, 1 table Accepted by EPL (Europhysics Letters

Influence of Si substitution on the reactivity of a-tricalcium phosphate

Silicon substituted calcium phosphates have been widely studied over the last ten years due to their enhanced osteogenic properties. Notwithstanding, the role of silicon on a-TCP reactivity is not clear yet. Therefore, the aim of this work was to evaluate the reactivity and the properties of Si-a-TCP in comparison to a-TCP. Precursor powders have similar properties regarding purity, particle size distribution and specific surface area, which allowed a better comparison of the Si effects on their reactivity and cements properties. Both Si-a-TCP and a-TCP hydrolyzed to a calcium-deficient hydroxyapatite when mixed with water but their conversion rates were different. Si-a-TCP exhibited a slower setting rate than a-TCP, i.e. kSSA for Si-TCP (0.021 g·m- 2·h- 1) was almost four times lower than for a-TCP (0.072 g·m- 2·h- 1). On the other hand, the compressive strength of the CPC resulting from fully reacted Si-a-TCP was significantly higher (12.80 ± 0.38 MPa) than that of a-TCP (11.44 ± 0.54 MPa), due to the smaller size of the entangled precipitated apatite crystals.Preprin

Early stage formation of graphene on the C-face of 6H-SiC

An investigation of the early stage formation of graphene on the C-face of 6H-SiC is presented. We show that the sublimation of few atomic layers of Si out of the SiC substrate is not homogeneous. In good agreement with the results of theoretical calculations it starts from defective sites, mainly dislocations that define nearly circular flakes, which have a pyramidal, volcano-like, shape with a center chimney where the original defect was located. At higher temperatures, complete conversion occurs but, again, it is not homogeneous. Within the sample surface the intensity of the Raman G and 2D bands, evidences non-homogeneous thickness.Comment: 12 pages, 3 figure

GRBs Neutrinos as a Tool to Explore Quantum Gravity induced Lorentz Violation

Lorentz Invariance Violation (LIV) arises in various quantum-gravity theories. As the typical energy for quantum gravity is the Planck mass, $M_{pl}$, LIV will, most likely, be manifested at very high energies that are not accessible on Earth in the foreseeable future. One has to turn to astronomical observations. Time of flight measurement from different astronomical sources set current limits on the energy scale of possible LIV to $> 0.01 M_{pl}$ (for n=1 models) and $> 10^{-9} M_{pl}$ (for n=2). According to current models Gamma-Ray Bursts (GRBs) are accompanied by bursts of high energy (\gsim 100TeV) neutrinos. At this energy range the background level of currently constructed neutrino detectors is so low that a detection of a single neutrino from the direction of a GRB months or even years after the burst would imply an association of the neutrino with the burst and will establish a measurement of a time of flight delay. Such time of flight measurements provide the best way to observe (or set limits) on LIV. Detection of a single GRB neutrino would open a new window on LIV and would improve current limits by many orders of magnitude