734 research outputs found
Resolving the wave-vector in negative refractive media: The sign of
We address the general issue of resolving the wave-vector in complex
electromagnetic media including negative refractive media. This requires us to
make a physical choice for the sign of a square-root imposed merely by
conditions of causality. By considering the analytic behaviour of the
wave-vector in the complex plane, it is shown that there are a total of eight
physically distinct cases in the four quadrants of two Riemann sheets.Comment: 3 pages, 2 figures, RevTe
One- and two-proton transfer reactions with vibrational Nuclei
We extend a semiclassical model of transfer reactions to the case in which
one of the collision partners is a vibrational nucleus. The model is applied to
one- and two-proton stripping reactions in the 37Cl + 98Mo system, for which a
rapid transition from normal to anomalous slope in the two proton transfer
reaction at energies around the Coulomb barrier is experimentally observed.
This behavior is satisfactorily reproduced by the present extension of the
model.Comment: LaTeX, 10 pages, 1 figure (PostScript
Produtos de hidratação em argamassas geopoliméricas à base de argila da Tunísia para reparação de estruturas de concreto
A reparação de estruturas degradadas de concreto representa uma oportunidade para a indústria da construção
mas também um desafio para a comunidade científica. O desenvolvimento de novas argamassas de reparação
constitui por isso uma importante área de investigação. Os geopolímeros são ligantes inovadores alternativos
ao cimento Portland pelo que as argamassas à base destes materiais, geopolíméricas, apresentam algumas
potencialidades no campo da reparação das estruturas de concreto.
O presente artigo apresenta resultados de uma investigação sobre o desenvolvimento de argamassas
geopoliméricas à base de uma argila da Tunísia sujeita a tratamento térmico. É incluída uma análise da argila
e também dos produtos de hidratação da argamassa os quais apresentam fases geopoliméricas típicas
H-dibaryons and Primordial Nucleosynthesis
The apparent discrepancy between abundances of light nuclides predicted by
the standard Big-Bang and observational data is explained, by assuming the
presence of metastable H dibaryons at the nucleosynthesis era. These dibaryons
could be formed out of a small fraction of strange quarks at the moment of the
confinement transition. For a primordial deuterium abundance of the order of 3
10^{-5}, the measured differences in the 4He abundances requires a relative
abundance of H dibaryons of the order of n_H/n_B = 0.07, decaying in a
timescale of the order of 10^5 s.Comment: Latex, 5 pages, to appear in PR
Directional detection as a strategy to discover Galactic Dark Matter
Directional detection of Galactic Dark Matter is a promising search strategy
for discriminating genuine WIMP events from background ones. Technical progress
on gaseous detectors and read-outs has permitted the design and construction of
competitive experiments. However, to take full advantage of this powerful
detection method, one need to be able to extract information from an observed
recoil map to identify a WIMP signal. We present a comprehensive formalism,
using a map-based likelihood method allowing to recover the main incoming
direction of the signal and its significance, thus proving its galactic origin.
This is a blind analysis intended to be used on any directional data.
Constraints are deduced in the () plane and systematic
studies are presented in order to show that, using this analysis tool,
unambiguous dark matter detection can be achieved on a large range of exposures
and background levels.Comment: 20 pages, 5 figures Final version to appear in Phys. Lett.
Deciphering The Preservation Of Fossil Insects: A Case Study From The Crato Member, Early Cretaceous Of Brazil
Exceptionally well-preserved three-dimensional insects with fine details and even labile tissues are ubiquitous in the Crato Member Konservat Lagerstätte (northeastern Brazil). Here we investigate the preservational pathways which yielded such specimens. We employed high resolution techniques (EDXRF, SR-SXS, SEM, EDS, micro Raman, and PIXE) to understand their fossilisation on mineralogical and geochemical grounds. Pseudomorphs of framboidal pyrite, the dominant fossil microfabric, display size variation when comparing cuticle with inner areas or soft tissues, which we interpret as the result of the balance between ion diffusion rates and nucleation rates of pyrite through the originally decaying carcasses. Furthermore, the mineral fabrics are associated with structures that can be the remains of extracellular polymeric substances (EPS). Geochemical data also point to a concentration of Fe, Zn, and Cu in the fossils in comparison to the embedding rock. Therefore, we consider that biofilms of sulphate reducing bacteria (SRB) had a central role in insect decay and mineralisation. Therefore, we shed light on exceptional preservation of fossils by pyritisation in a Cretaceous limestone lacustrine palaeoenvironment. © 2016 Osés et al.20161
Granular discharge and clogging for tilted hoppers
We measure the flux of spherical glass beads through a hole as a systematic
function of both tilt angle and hole diameter, for two different size beads.
The discharge increases with hole diameter in accord with the Beverloo relation
for both horizontal and vertical holes, but in the latter case with a larger
small-hole cutoff. For large holes the flux decreases linearly in cosine of the
tilt angle, vanishing smoothly somewhat below the angle of repose. For small
holes it vanishes abruptly at a smaller angle. The conditions for zero flux are
discussed in the context of a {\it clogging phase diagram} of flow state vs
tilt angle and ratio of hole to grain size
- …