184 research outputs found
Signals of primordial phase transitions on CMB maps
The analysis of the CMB anisotropies is a rich source of cosmological
informations. In our study, we simulated the signals produced by the relics of
a first order phase transition occured during an inflationary epoch in the
early Universe. These relics are bubbles of true vacuum that leave a
characteristic non-Gaussian imprint on the CMB. We use different statistical
estimators in order to evaluate this non-Gaussianity. We obtain some limits on
the allowed values of the bubble parameters comparing our results with the
experimental data.
We also predict the possibility to detect this signal with the next high
resolution experiments.Comment: 2 pages, submitted to Proceedings of 9th Marcel Grossmann meetin
Extension of soil thermal conductivity models to frozen meats with low and high fat content
Thermal conductivity models of frozen soils were analyzed and compared with similar models developed for frozen foods. In
total, eight thermal conductivity models and 54 model versions were tested against experimental data of 13 meat products in the
temperature range from 0 toK40 8C. The model by deVries, with waterCice (wi) as the continuous phase, showed overall the
best predictions. The use of wi leads generally to improved predictions in comparison to ice; water as the continuous phase is
beneficial only to deVries model, mostly from K1 to K20 8C; fat is advantageous only to meats with high fat content. The
results of this work suggest that the more sophisticated way of estimating the thermal conductivity for a disperse phase in the
deVries model might be more appropriate than the use of basic multi-phase models (geometric mean, parallel, and series).
Overall, relatively small differences in predictions were observed between the best model versions by deVries, Levy,
Mascheroni, Maxwell or Gori as applied to frozen meats with low content of fat. These differences could also be generated by
uncertainty in meat composition, temperature dependence of thermal conductivity of ice, measurement errors, and limitation of
predictive models
Deployment of solar sails by joule effect: thermal analysis and experimental results
Space vehicles may be propelled by solar sails exploiting the radiation pressure coming from the sun and applied on their surfaces. This work deals with the adoption of Nickel-Titanium Shape Memory Alloy (SMA) elements in the sail deployment mechanism activated by the Joule Effect, i.e., using the same SMA elements as a resistance within suitable designed electrical circuits. Mathematical models were analyzed for the thermal analysis by implementing algorithms for the evaluation of the temperature trend depending on the design parameters. Several solar sail prototypes were built up and tested with different number, size, and arrangement of the SMA elements, as well as the type of the selected electrical circuit. The main parameters were discussed in the tested configurations and advantages discussed as well
Heat Conduction and Microconvection in Nanofluids: Comparison between Theoretical Models and Experimental Results
A nanofluid is a suspension consisting of a uniform distribution of nanoparticles in a base
fluid, generally a liquid. Nanofluid can be used as a working fluid in heat exchangers to dissipate heat
in the automotive, solar, aviation, aerospace industries. There are numerous physical phenomena
that affect heat conduction in nanofluids: clusters, the formation of adsorbate nanolayers, scattering
of phonons at the solid–liquid interface, Brownian motion of the base fluid and thermophoresis in
the nanofluids. The predominance of one physical phenomenon over another depends on various
parameters, such as temperature, size and volume fraction of the nanoparticles. Therefore, it is very
difficult to develop a theoretical model for estimating the effective thermal conductivity of nanofluids
that considers all these phenomena and is accurate for each value of the influencing parameters.
The aim of this study is to promote a way to find the conditions (temperature, volume fraction)
under which certain phenomena prevail over others in order to obtain a quantitative tool for the
selection of the theoretical model to be used. For this purpose, two sets (SET-I, SET-II) of experimental
data were analyzed; one was obtained from the literature, and the other was obtained through
experimental tests. Different theoretical models, each considering some physical phenomena and
neglecting others, were used to explain the experimental results. The results of the paper show that
clusters, the formation of the adsorbate nanolayer and the scattering of phonons at the solid–liquid
interface are the main phenomena to be considered when ϕ = 1 ÷ 3%. Instead, at a temperature of 50
◦C and in the volume fraction range (0.04–0.22%), microconvection prevails over other phenomen
Modeling and Measuring Thermodynamic and Transport Thermophysical Properties: A Review
The present review describes the up-to-date state of the evaluation of thermophysical prop erties (TP) of materials with three different procedures: modeling (also including inverse problems), measurements and analytical methods (e.g., through computing from other properties). Methods to measure specific heat and thermal conductivity are described in detail. Thermal diffusivity and
thermal effusivity are a combination of the previously cited properties, but also for these proper ties, specific measurement and calculation methods are reported. Experiments can be carried out in steady-state, transient, and pulse regimes. For modeling, special focus is given to the inverse methods and parameter estimation procedures, because through them it is possible to evaluate the thermophysical property, assuring the best practices and supplying the measurement uncertainty. It
is also cited when the most common data processing algorithms are used, e.g., the Gauss–Newton and Levenberg–Marquardt least squares minimization algorithms, and how it is possible to retrieve values of TP from other data. Optimization criteria for designing the experiments are also mentione
Quinstant Dark Energy Predictions for Structure Formation
We explore the predictions of a class of dark energy models, quinstant dark
energy, concerning the structure formation in the Universe, both in the linear
and non-linear regimes. Quinstant dark energy is considered to be formed by
quintessence and a negative cosmological constant. We conclude that these
models give good predictions for structure formation in the linear regime, but
fail to do so in the non-linear one, for redshifts larger than one.Comment: 9 pages, 14 figures, "Accepted for publication in Astrophysics &
Space Science
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Spinal autophagy is differently modulated in distinct mouse models of neuropathic pain
BACKGROUND
Autophagy is a homeostatic degradative process essential for basal turnover of long-lived proteins and organelles as well as for removal of dysfunctional cellular components. Dysregulation of the autophagic machinery has been recently associated to several conditions including neurodegenerative diseases and cancer, but only very few studies have investigated its role in pain processing.
RESULTS
We previously described autophagy impairment at the spinal cord in the experimental model of neuropathic pain induced by spinal nerve ligation (SNL). In this study, we characterized the main autophagic markers in two other common experimental models of neuropathic pain, the chronic constriction injury (CCI) and the spared nerve injury (SNI). The different modulation of LC3-I, Beclin 1 and p62 suggested that autophagy is differentially affected in the spinal dorsal horn depending on the type of peripheral injury. Confocal analysis of p62 distribution in the spinal dorsal horn indicated its presence mainly in NeuN-positive cell bodies and occasionally in glial processes, thus suggesting a predominant expression in the neuronal compartment. Finally, we investigated the consequences of autophagy impairment on pain behaviour by using the autophagy blocker cloroquine. Intrathecal chloroquine injection in naïve mice induced spinal accumulation of LC3 and p62 paralleled by significant mechanical hypersensitivity thus confirming the block in autophagosome clearance and suggesting the participation of the autophagic process in spinal mechanisms of pain processing. Altogether, our data indicate that spinal autophagy is differentially altered in different experimental pain models of neuropathic pain and that this process may be relevant for pain control
Dissipative Future Universe without Big Rip
The present study deals with dissipative future universe without big rip in
context of Eckart formalism. The generalized chaplygin gas, characterized by
equation of state , has been considered as
a model for dark energy due to its dark-energy-like evolution at late time. It
is demonstrated that, if the cosmic dark energy behaves like a fluid with
equation of state ; , as well as chaplygin gas
simultaneously then the big rip problem does not arises and the scale factor is
found to be regular for all time.Comment: 6 pages, 2 figures, To appear in Int. J. Theor. Phy
Spherical collapse model in dark energy cosmologies
We study the spherical collapse model for several dark energy scenarios using
the fully nonlinear differential equation for the evolution of the density
contrast within homogeneous spherical overdensities derived from Newtonian
hydrodynamics. While mathematically equivalent to the more common approach
based on the differential equation for the radius of the perturbation, this
approach has substantial conceptual as well as numerical advantages. Among the
most important are that no singularities at early times appear, which avoids
numerical problems in particular in applications to cosmologies with dynamical
and early dark energy, and that the assumption of time-reversal symmetry can
easily be dropped where it is not strictly satisfied. We use this approach to
derive the two parameters characterising the spherical-collapse model, i.e.~the
linear density threshold for collapse and the virial
overdensity , for a broad variety of dark-energy models and
to reconsider these parameters in cosmologies with early dark energy. We find
that, independently of the model under investigation, and
are always very close to the values obtained for the
standard CDM model, arguing that the abundance of and the mean density
within non-linear structures are quite insensitive to the differences between
dark-energy cosmologies. Regarding early dark energy, we thus arrive at a
different conclusion than some earlier papers, including one from our group,
and we explain why.Comment: 11 pages, 7 figures, accepted for publications on MNRA
Constraining the dark energy dynamics with the cosmic microwave background bispectrum
We consider the influence of the dark energy dynamics at the onset of cosmic
acceleration on the Cosmic Microwave Background (CMB) bispectrum, through the
weak lensing effect induced by structure formation. We study the line of sight
behavior of the contribution to the bispectrum signal at a given angular
multipole : we show that it is non-zero in a narrow interval centered at a
redshift satisfying the relation , where the
wavenumber corresponds to the scale entering the non-linear phase, and is
the cosmological comoving distance. The relevant redshift interval is in the
range 0.1\lsim z\lsim 2 for multipoles 1000\gsim\ell\gsim 100; the signal
amplitude, reflecting the perturbation dynamics, is a function of the
cosmological expansion rate at those epochs, probing the dark energy equation
of state redshift dependence independently on its present value. We provide a
worked example by considering tracking inverse power law and SUGRA Quintessence
scenarios, having sensibly different redshift dynamics and respecting all the
present observational constraints. For scenarios having the same present
equation of state, we find that the effect described above induces a projection
feature which makes the bispectra shifted by several tens of multipoles, about
10 times more than the corresponding effect on the ordinary CMB angular power
spectrum.Comment: 15 pages, 7 figures, matching version accepted by Physical Review D,
one figure improve
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