1,249 research outputs found
Experimental analysis of perfobond shear connection between steel and lightweight concrete
This paper describes the experimental tests carried out at the University of Minho using
Perfobond connectors and lightweight concrete. The main objective of these tests is to describe the connection behaviour and to analyse and compare the contribution of the different elements to the slip measured between the steel profile and the concrete slab. In this way, it is possible to define the connection ductility. The test configuration follows some of the EC4 recommendations and repeats some dispositions referred to by Oguejiofor and Ferreira. The parameters under study are the concrete strength, the reinforcement disposition and the Perfobond rib existence and spacing of holes. An important comparison with the experimental results achieved by different authors using normal weight concrete may then be
established
Phase diagram of the mixed spin-2 and spin-5/2 Ising system with two different single-ion anisotropies
AbstractWe study the effect of two different single-ion anisotropies in the phase diagram and in the compensation temperature of mixed spin-2 and spin-5/2 Ising ferrimagnetic system. We employed the mean-field theory based on the Bogoliubov inequality for Gibbs free energy. We use the Landau expansion of free energy in the order parameter to describe the phase diagram. In the temperature versus single-ion anisotropy plane the phase diagram displays tricritical behavior. The critical and compensation temperatures increase with increasing values of the single-ion anisotropies
Mechanical Modelling of In-Plane Loaded Glass Panes
Glass panes are increasingly being used to the stabilization of one storey buildings by acting as shear walls and thus replacing conventional bracings. This is the case of glass pavilions and some timber or steel frames or facades. The behaviour of such structural systems mainly depends on the stiffness of the connections. This research focuses on the prediction of the in-plane structural behaviour of steel and timber frames with a single pane fixed by circumferentially glued joints or by point support connectors. Mechanical models have been implemented and validated. The results obtained clearly demonstrate that the models can be applicable for the purpose of the non-cracking pre-design of panes acting as a shear wall because theyare able to predict the in-plane stiffness and the force necessary to obtain a certain horizontal in-plane displacement at the top
An innovative framework for probabilistic-based structural assessment with an application to existing reinforced concrete structures
A novel framework for probabilistic-based structural assessment of existing structures, which combines model identification and reliability assessment procedures, considering in an objective way different sources of uncertainty, is presented in this paper. A short description of structural assessment applications, provided in literature, is initially given. Then, the developed model identification procedure, supported in a robust optimization algorithm, is presented. Special attention is given to both experimental and numerical errors, to be considered in this algorithm convergence criterion. An updated numerical model is obtained from this process. The reliability assessment procedure, which considers a probabilistic model for the structure in analysis, is then introduced, incorporating the results of the model identification procedure. The developed model is then updated, as new data is acquired, through a Bayesian inference algorithm, explicitly addressing statistical uncertainty. Finally, the developed framework is validated with a set of reinforced concrete beams, which were loaded up to failure in laboratory
Constraining scalar fields with stellar kinematics and collisional dark matter
The existence and detection of scalar fields could provide solutions to
long-standing puzzles about the nature of dark matter, the dark compact objects
at the centre of most galaxies, and other phenomena. Yet, self-interacting
scalar fields are very poorly constrained by astronomical observations, leading
to great uncertainties in estimates of the mass and the
self-interacting coupling constant of these fields. To counter this,
we have systematically employed available astronomical observations to develop
new constraints, considerably restricting this parameter space. In particular,
by exploiting precise observations of stellar dynamics at the centre of our
Galaxy and assuming that these dynamics can be explained by a single boson
star, we determine an upper limit for the boson star compactness and impose
significant limits on the values of the properties of possible scalar fields.
Requiring the scalar field particle to follow a collisional dark matter model
further narrows these constraints. Most importantly, we find that if a scalar
dark matter particle does exist, then it cannot account for both the
dark-matter halos and the existence of dark compact objects in galactic nucleiComment: 23 pages, 8 figures; accepted for publication by JCAP after minor
change
CARACTERÍSTICAS HIDROSSEDIMENTOLOGICA E AMBIENTAL DA BAÍA DA CARNE SECA NO RIO PARAGUAI EM CÁCERES, MATO GROSSO
O estudo foi desenvolvido no rio Paraguai, na baía da Carne Seca, com objetivo de avaliar a hidrodinâmica e sedimentologias. Realizou atividade de gabinete, trabalho de campo e análise de laboratório. A vazão no rio variou de 596,60 a 888,54 m3/s e na baía variou de 11,57 a 23,94 m3/s. Os dados granulométricos mostraram a predominância de areia fina e silte nos sedimentos de fundo
Point-contact Andreev-reflection spectroscopy in ReFeAsO_{1-x}F_x (Re = La, Sm): Possible evidence for two nodeless gaps
A deep understanding of the character of superconductivity in the recently
discovered Fe-based oxypnictides ReFeAsO1-xFx (Re = rare-earth) necessarily
requires the determination of the number of the gaps and their symmetry in k
space, which are fundamental ingredients of any model for the pairing mechanism
in these new superconductors. In the present paper, we show that point-contact
Andreev-reflection experiments performed on LaFeAsO1-xFx (La-1111) polycrystals
with Tc ~ 27 K and SmFeAsO0.8F0.2 (Sm-1111) ones with Tc ~ 53 K gave
differential conductance curves exhibiting two peaks at low bias and two
additional structures (peaks or shoulders) at higher bias, an experimental
situation quite similar to that observed by the same technique in pure and
doped MgB2. The single-band Blonder-Tinkham-Klapwijk model is totally unable to
properly fit the conductance curves, while the two-gap one accounts remarkably
well for the shape of the whole experimental dI/dV vs. V curves. These results
give direct evidence of two nodeless gaps in the superconducting state of
ReFeAsO1-xFx (Re = La, Sm): a small gap, Delta1, smaller than the BCS value
(2Delta1/kBTc ~ 2.2 - 3.2) and a much larger gap Delta2 which gives a ratio
2Delta2/kBTc ~ 6.5 - 9. In Sm-1111 both gaps close at the same temperature,
very similar to the bulk Tc, and follow a BCS-like behaviour, while in La-1111
the situation is more complex, the temperature dependence of the gaps showing
remarkable deviations from the BCS behaviour at T close to Tc. The normal-state
conductance reproducibly shows an unusual, but different, shape in La-1111 and
Sm-1111 with a depression or a hump at zero bias, respectively. These
structures survive up to T* ~ 140 K, close to the temperatures at which
structural and magnetic transitions occur in the parent, undoped compound.Comment: 10 pages, 7 color figures, Special Issue of Physica C on
Superconducting Pnictide
Crystal-field effects in Er 3 + - and Yb 3 + -doped hexagonal NaYF 4 nanoparticles
Since the up-conversion phenomenon in rare-earths (REs) doped NaYF4 is strongly affected by the crystal electric field (CF), determining the CF parameters, wave functions, and scheme of the energy levels of the RE J multiplets could be crucial to improve and tune the up-conversion efficiency. In this work, the temperature and magnetic field dependent magnetization of NaY1−x[Er(Yb)]xF4 hexagonal nanoparticles (NPs) is reported. The data were best fit using the appropriated CF Hamiltonian for the J=15/2(J=7/2) ground state multiplet of Er3+(Yb3+) ions. The B02, B04, B06, and B66 CF parameters were considered in the Hamiltonian for RE ions located at the hexagonal C3h point symmetry site of the NaYF4 host lattice. These results allowed us to predict an overall CF splitting of ∼214 (∼356 ) for Er3+(Yb3+) and the wave functions and their energy levels for the J=15/2 (J=7/2) ground state multiplet which are in good agreement with the low temperature electron spin resonance experiments. Besides, our measurements allowed us to calculate all the excited CF J multiplets that yield to a good estimation of the up-conversion light emission linewidth. The nonlinear optical light emission of the studied NaY1−x[Er(Yb)]xF4 hexagonal NPs was also compared with the most efficient up-conversion codoped NaY1−x−yErxY by F4 hexagonal NPs.Fil: García Flores, A. F.. Universidade Federal do ABC; BrasilFil: Matias, J.S.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Garcia, D. J.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Martínez, E. D.. Instituto de Física “Gleb Wataghin”, Unicamp; BrasilFil: Cornaglia de la Cruz, Pablo Sebastian. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Lesseux, G.G.. Instituto de Física “Gleb Wataghin”, Unicamp; BrasilFil: Ribeiro, R. A.. Universidade Federal do ABC; BrasilFil: Urbano, R. R.. Instituto de Física “Gleb Wataghin”, Unicamp; BrasilFil: Rettori, C.. Instituto de Física “Gleb Wataghin”, Unicamp; Brasil. Universidade Federal do ABC; Brasi
Discrete molecular dynamics simulations of peptide aggregation
We study the aggregation of peptides using the discrete molecular dynamics
simulations. At temperatures above the alpha-helix melting temperature of a
single peptide, the model peptides aggregate into a multi-layer parallel
beta-sheet structure. This structure has an inter-strand distance of 0.48 nm
and an inter-sheet distance of 1.0 nm, which agree with experimental
observations. In this model, the hydrogen bond interactions give rise to the
inter-strand spacing in beta-sheets, while the Go interactions among side
chains make beta-strands parallel to each other and allow beta-sheets to pack
into layers. The aggregates also contain free edges which may allow for further
aggregation of model peptides to form elongated fibrils.Comment: 15 pages, 8 figure
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