26,888 research outputs found
Cosmological scenarios from multiquintessence
In this work we derive and analyse cosmological scenarios coming from
multi-component scalar field models. We consider a direct sum of a sine-Gordon
with a Z2 model, and also a combination of those with a BNRT model. Moreover,
we work with a modified version of the BNRT model, which breaks the Z2 x Z2
symmetry of the original BNRT potential, coupled with the sine-Gordon and with
the standard Z2 models. We show that our approach can be straightforwardly
elevated to fields. All the computations are made analytically and some
parameters restriction is put forward in order to get in touch with complete
and realistic cosmological scenarios
Constraining non-minimally coupled tachyon fields by Noether symmetry
A model for a spatially flat homogeneous and isotropic Universe whose
gravitational sources are a pressureless matter field and a tachyon field
non-minimally coupled to the gravitational field is analyzed. Noether symmetry
is used to find the expressions for the potential density and for the coupling
function, and it is shown that both must be exponential functions of the
tachyon field. Two cosmological solutions are investigated: (i) for the early
Universe whose only source of the gravitational field is a non-minimally
coupled tachyon field which behaves as an inflaton and leads to an exponential
accelerated expansion and (ii) for the late Universe whose gravitational
sources are a pressureless matter field and a non-minimally coupled tachyon
field which plays the role of dark energy and is the responsible of the
decelerated-accelerated transition period.Comment: 11 pages, 5 figures. Version accepted for publication in Classical
and Quantum Gravit
Prolonging disuse in aged mice amplifies cortical but not trabecular bones’ response to mechanical loading
Objective: Short-term neurectomy-induced disuse (SN) has been shown to restore load responses in aged mice. We examined whether this restoration was further enhanced in both cortical and trabecular bone by simply extending the SN. Methods: Following load: strain calibration, tibiae in female C57BL/J6 mice at 8, 14 and 20 weeks and 18 months (n=8/group) were loaded and bone changes measured. Effects of long-term SN examined in twenty-six 18 months-old mice, neurectomised for 5 or 100 days with/without subsequent loading. Cortical and trabecular responses were measured histomorphometrically or by micro-computed tomography. Results: Loading increased new cortical bone formation, elevating cross-sectional area in 8, 14 and 20 week-old (p <0.05), but not 18 month-old aged mice. Histomorphometry showed that short-term SN reinstated load-responses in aged mice, with significant 33% and 117% increases in bone accrual at 47% and 37%, but not 27% of tibia length. Cortical responses to loading was heightened and widespread, now evident at all locations, following prolonged SN (108, 167 and 98% at 47, 37 and 27% of tibial length, respectively). In contrast, loading failed to modify trabecular bone mass or architecture. Conclusions: Mechanoadaptation become deficient with ageing and prolonging disuse amplifies this response in cortical but not trabecular bone
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