3,992 research outputs found
Numerical analysis of the stability of the Electrohydrodynamic (EHD) electroconvection between two plates
The time evolution of the problem of Electrohydrodynamic (EHD)
convection in a liquid between two plates is analysed numerically. The equations are
nondimensionalized using the ion drift velocity and the viscous time scales. Following
the non-dimensionalisation of the respective model, two different techniques have been
used to describe the charge evolution, namely the Finite-Element Flux-Corrected
Transport Method and the Particle-In-Cell technique. The results obtained with the
two schemes, apart from showing good agreement, have revealed the appearance of a
two-roll structure not described in previous works. This is investigated in detail for
both strong and weak injection.Ministerio de ciencia y tecnología FQM-42
Determination of the Chiral Couplings L_10 and C_87 from Semileptonic Tau Decays
Using recent precise hadronic tau-decay data on the V-A spectral function,
and general properties of QCD such as analyticity, the operator product
expansion and chiral perturbation theory, we get accurate values for the QCD
chiral order parameters L_10^r(M_rho) and C_87^r(M_rho). These two low-energy
constants appear at order p^4 and p^6, respectively, in the chiral perturbation
theory expansion of the V-A correlator. At order p^4 we obtain L_10^r(M_rho) =
-(5.22\pm 0.06)10^{-3}. Including in the analysis the two-loop (order p^6)
contributions, we get L_10^r(M_rho) = -(4.06\pm 0.39)10^{-3} and C_87^r(M_rho)
= (4.89\pm 0.19)10^{-3}GeV^{-2}. In the SU(2) chiral effective theory, the
corresponding low-energy coupling takes the value \overline l_5 = 13.30 \pm
0.11 at order p^4, and \overline l_5 = 12.24 \pm 0.21 at order p^6.Comment: 17 pages, 3 figures, v2: Added reference, published versio
Selection of AGN candidates in the GOODS-South Field through SPITZER/MIPS 24 m variability
We present a study of galaxies showing mid-infrared variability in data taken
in the deepest Spitzer/MIPS 24 m surveys in the GOODS-South field. We
divide the dataset in epochs and subepochs to study the long-term
(months-years) and the short-term (days) variability. We use a
-statistics method to select AGN candidates with a probability
1% that the observed variability is due to statistical errors alone. We find 39
(1.7% of the parent sample) sources that show long-term variability and 55
(2.2% of the parent sample) showing short-term variability. That is, 0.03
sources arcmin for both, long-term and short-term variable
sources. After removing the expected number of false positives inherent to the
method, the estimated percentages are 1.0% and 1.4% of the parent sample for
the long-term and short-term respectively. We compare our candidates with AGN
selected in the X-ray and radio bands, and AGN candidates selected by their IR
emission. Approximately, 50% of the MIPS 24 m variable sources would be
identified as AGN with these other methods. Therefore, MIPS 24 m
variability is a new method to identify AGN candidates, possibly dust obscured
and low luminosity AGN, that might be missed by other methods. However, the
contribution of the MIPS 24 m variable identified AGN to the general AGN
population is small ( 13%) in GOODS-South.Comment: Accepted for publication in MNRA
Anisotropy of Mechanical Properties of Pinctada margaritifera Mollusk Shell
The research was co-financed by the European Union from the resources of the European
Social Fund (Project No.WND-POWR.03.02.00-00-I043/16), the DAAD program. A.C. acknowledges project
CGL2017-85118-P of the Spanish Ministerio de Ciencia e Innovaciónfor funding.The mechanical properties such as compressive strength and nanohardness were
investigated for Pinctada margaritifera mollusk shells. The compressive strength was evaluated through
a uniaxial static compression test performed along the load directions parallel and perpendicular to the
shell axis, respectively, while the hardness and Young modulus were measured using nanoindentation.
In order to observe the crack propagation, for the first time for such material, the in-situ X-ray
microscopy (nano-XCT) imaging (together with 3D reconstruction based on the acquired images)
during the indentation tests was performed. The results were compared with these obtained during
the micro-indentation test done with the help of conventional Vickers indenter and subsequent
scanning electron microscopy observations. The results revealed that the cracks formed during the
indentation start to propagate in the calcite prism until they reach a ductile organic matrix where
most of them are stopped. The obtained results confirm a strong anisotropy of both crack propagation
and the mechanical strength caused by the formation of the prismatic structure in the outer layer of
P. margaritifera shell.The research was co-financed by the European Union from resources of the European Social Fund
(Project No.WND-POWR.03.02.00-00-I043/16)
Ribs of Pinna nobilis shell induce unexpected microstructural changes that provide unique mechanical properties
The authors thank Mr Łukasz Niedzielski from Keyence International
for the possibility of performing microstructural analysis using a VHX-
7000 digital microscope. Thanks to Damian Sapijaszka who collected
the P. nobilis specimen for scientific research. The work was supported
by the Polish National Agency for Academic Exchange (grant PPI/APM/
2018/1/00049/U/001) and the National Science Center (grant UMO-
2018/29/B/ST8/02200). MS was supported by the European Union
from the resources of the European Social Fund (Project No.WNDPOWR.
03.02.00-00-I043/16). AGC was funded by project CGL2017-
85118-P of the Spanish Ministerio de Ciencia e Innovaci´on. Jos´e Rafael
García March (Universidad Cat´olica de Valencia, Spain) provided the
images of Pinna nobilis of Fig. A1.The reinforcement function of shell ribs depends not only on their vaulted morphology but also on their
microstructure. They are part of the outer layer which, in the case of the Pinna nobilis bivalve, is built from almost
monocrystalline calcitic prisms, always oriented perpendicular to the growth surfaces. Originally, prisms and
their c-axes follow the radii of rib curvature, becoming oblique to the shell thickness direction. Later, prisms bend
to reach the nacre layer perpendicularly, but their c-axes retain the initial orientation. Calcite grains form
nonrandom boundaries. Most often, three twin disorientations arise, with two of them observed for the first time.
Nano-indentation and impact tests demonstrate that the oblique orientation of c-axes significantly improves the
hardness and fracture toughness of prisms. Moreover, compression tests reveal that the rib area achieves a unique
strength of 700 MPa. The detection of the specific microstructure formed to toughen the shell is novel.Polish National Agency for Academic Exchange (grant PPI/APM/
2018/1/00049/U/001)National Science Center (grant UMO-
2018/29/B/ST8/02200)European Social Fund (Project No.WNDPOWR.
03.02.00-00-I043/16)CGL2017-
85118-P of the Spanish Ministerio de Ciencia e Innovaci´o
The unique fibrilar to platy nanoand microstructure of twinned rotaliid foraminiferal shell calcite
Open Access funding enabled and organized by Projekt DEALGerman Research
Council (Grant No. GR9/1234 SCHM/930/11-2)
Diseño de un proyecto de investigación básico
Nos proponemos que los estudiantes entren en contacto con las actividades de investigación y que, de manera autónoma, aunque guiados por el profesor, encuentren la respuesta a una pregunta mediante el desarrollo del método científico, haciendo uso también de unos procedimientos básicos para la elaboración de un proyecto de investigación.We propose that the students come in contact with the activities of research and that, in an autonomous manner, while guided by the professor, to find the answer to a question through the development of the scientific method, by using a few basic procedures for the preparation of a research project
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