27,958 research outputs found
Modelling plasticity of unsaturated soils in a thermodynamically consistent framework
Constitutive equations of unsaturated soils are often derived in a
thermodynamically consistent framework through the use a unique 'effective'
interstitial pressure. This later is naturally chosen as the space averaged
interstitial pressure. However, experimental observations have revealed that
two stress state variables were needed to describe the stress-strain-strength
behaviour of unsaturated soils. The thermodynamics analysis presented here
shows that the most general approach to the behaviour of unsaturated soils
actually requires three stress state variables: the suction, which is required
to describe the retention properties of the soil and two effective stresses,
which are required to describe the soil deformation at water saturation held
constant. Actually, it is shown that a simple assumption related to internal
deformation leads to the need of a unique effective stress to formulate the
stress-strain constitutive equation describing the soil deformation. An
elastoplastic framework is then presented and it is finally shown that the
Barcelona Basic Model, a commonly accepted model for unsaturated soils, as well
as all models deriving from it, appear as special extreme cases of the
thermodynamic framework proposed here
Maintenance engineering management of a LNG plant critical system: a case study of gas turbine dry gas seal
Conformal and gauge invariant spin-2 field equations
Using an approach based on the Casimir operators of the de Sitter group, the
conformal invariant equations for a fundamental spin-2 field are obtained, and
their consistency discussed. It is shown that, only when the spin-2 field is
interpreted as a 1-form assuming values in the Lie algebra of the translation
group, rather than a symmetric second-rank tensor, the field equation is both
conformal and gauge invariant.Comment: 12 pages, no figures; accepted for publication in Gravitation &
Cosmolog
Chemical analysis of giant stars in the young open cluster NGC 3114
Context: Open clusters are very useful targets for examining possible trends
in galactocentric distance and age, especially when young and old open clusters
are compared. Aims: We carried out a detailed spectroscopic analysis to derive
the chemical composition of seven red giants in the young open cluster NGC
3114. Abundances of C, N, O, Li, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce,
and Nd were obtained, as well as the carbon isotopic ratio. Methods: The
atmospheric parameters of the studied stars and their chemical abundances were
determined using high-resolution optical spectroscopy. We employed the
local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral
analysis code MOOG. The abundances of the light elements were derived using the
spectral synthesis technique. Results: We found that NGC 3114 has a mean
metallicity of [Fe/H] = -0.01+/-0.03. The isochrone fit yielded a turn-off mass
of 4.2 Msun. The [N/C] ratio is in good agreement with the models predicted by
first dredge-up. We found that two stars, HD 87479 and HD 304864, have high
rotational velocities of 15.0 km/s and 11.0 km/s; HD 87526 is a halo star and
is not a member of NGC 3114. Conclusions: The carbon and nitrogen abundance in
NGC 3114 agree with the field and cluster giants. The oxygen abundance in NGC
3114 is lower compared to the field giants. The [O/Fe] ratio is similar to the
giants in young clusters. We detected sodium enrichment in the analyzed cluster
giants. As far as the other elements are concerned, their [X/Fe] ratios follow
the same trend seen in giants with the same metallicity.Comment: 17 pages, 9 figures, 10 tables; accepted for publication in A&
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