160 research outputs found
A study on interlaminar behavior of carbon/epoxy laminated curved beams by use of acoustic emission
The interlaminar tensile strength of carbon/epoxy laminated curved beams with variable thickness and through-the-thickness tufted reinforcement is studied experimentally by means of a four-point-bending test in accordance with ASTM D6415. These tests are monitored by the acoustic emission (AE) technique in order to gain deeper knowledge of the delamination onset and post-failure behavior. The results show that AE technique has proven to perform well when identifying delamination onset and its evolution after failure. In addition to this, AE has demonstrated to be an appropriate tool to assess the manufacturing quality of the carbon/epoxy laminated curved-beam, once the right pattern has previously been established
G_2 Perfect-Fluid Cosmologies with a proper conformal Killing vector
We study the Einstein field equations for spacetimes admitting a maximal
two-dimensional abelian group of isometries acting orthogonally transitively on
spacelike surfaces and, in addition, with at least one conformal Killing
vector. The three-dimensional conformal group is restricted to the case when
the two-dimensional abelian isometry subalgebra is an ideal and it is also
assumed to act on non-null hypersurfaces (both, spacelike and timelike cases
are studied). We consider both, diagonal and non-diagonal metrics and find all
the perfect-fluid solutions under these assumptions (except those already
known). We find four families of solutions, each one containing arbitrary
parameters for which no differential equations remain to be integrated. We
write the line-elements in a simplified form and perform a detailed study for
each of these solutions, giving the kinematical quantities of the fluid
velocity vector, the energy-density and pressure, values of the parameters for
which the energy conditions are fulfilled everywhere, the Petrov type, the
singularities in the spacetimes and the Friedmann-Lemaitre-Robertson-Walker
metrics contained in each family.Comment: Latex, no figure
Micro-computed tomography and histology to explore internal morphology in decapod larvae
Traditionally, the internal morphology of crustacean larvae has been studied using destructive
techniques such as dissection and microscopy. The present study combines advances in microcomputed
tomography (micro-CT) and histology to study the internal morphology of decapod larvae,
using the common spider crab (Maja brachydactyla Balss, 1922) as a model and resolving the individual
limitations of these techniques. The synergy of micro-CT and histology allows the organs to be easily
identified, revealing simultaneously the gross morphology (shape, size, and location) and histological
organization (tissue arrangement and cell identification). Micro-CT shows mainly the exoskeleton,
musculature, digestive and nervous systems, and secondarily the circulatory and respiratory systems,
while histology distinguishes several cell types and confirms the organ identity. Micro-CT resolves a
discrepancy in the literature regarding the nervous system of crab larvae. The major changes occur in
the metamorphosis to the megalopa stage, specifically the formation of the gastric mill, the shortening
of the abdominal nerve cord, the curving of the abdomen beneath the cephalothorax, and the
development of functional pereiopods, pleopods, and lamellate gills. The combination of micro-CT and
histology provides better results than either one alone.Financial support was provided by the Spanish Ministry of Economy and Competitiveness through the INIA
project (grant number RTA2011-00004-00-00) to G.G. and a pre-doctoral fellowship to D.C. (FPI-INIA)
Discrimination between magnetic shear and toroidal electric field effects in TJ-II plasmas
The response of TJ-II plasmas to an induced toroidal electric field, Eǿ , was studied in past experiments with the aid of Ohmic inducted current. It was found that positive induced plasma current, Ip, degrades the confinement while negative Ip improves it. Candidates to provide a physical explanation are Eǿ itself and the plasma current via magnetic shear modification. A movable mirror in an electron Cyclotron Heating line of TJ-II permits varying the refraction index of the heating wave, N||, thus allowing for non inductive electron cyclotron current drive (ECCD) up to Ip ≈ ±1 kA. Comparing discharges without and with ECCD (changing shear but not Eǿ ) but sharing the same transformer action (changing both shear and Eǿ ), magnetic shear and electric field effects can be discriminated in time. It has been found that plasma response with ECCD is delayed respect to the transformer switch-on time, clearly pointing to shear effects. Effects related to Eǿ alone, if they exist, are weaker
Zonal flows and long-distance correlations during the formation of the edge shear layer in the TJ-II stellarator
A theoretical interpretation is given for the observed long-distance
correlations in potential fluctuations in TJ-II. The value of the correlation
increases above the critical point of the transition for the emergence of the
plasma edge shear flow layer. Mean (i.e. surface averaged, zero-frequency)
sheared flows cannot account for the experimental results. A model consisting
of four envelope equations for the fluctuation level, the mean flow shear, the
zonal flow amplitude shear, and the averaged pressure gradient is proposed. It
is shown that the presence of zonal flows is essential to reproduce the main
features of the experimental observations.Comment: 19 pages, 7 figure
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