204 research outputs found
A one-parameter family of interpolating kernels for Smoothed Particle Hydrodynamics studies
A set of interpolating functions of the type f(v)={(sin[v pi/2])/(v pi/2)}^n
is analyzed in the context of the smoothed-particle hydrodynamics (SPH)
technique. The behaviour of these kernels for several values of the parameter n
has been studied either analytically as well as numerically in connection with
several tests carried out in two dimensions. The main advantage of this kernel
relies in its flexibility because for n=3 it is similar to the standard widely
used cubic-spline, whereas for n>3 the interpolating function becomes more
centrally condensed, being well suited to track discontinuities such as shock
fronts and thermal waves.Comment: 36 pages, 12 figures (low-resolution), published in J.C.
High temperature combustion: Approaching equilibrium using nuclear networks
A method for integrating the chemical equations associated with nuclear
combustion at high temperature is presented and extensively checked. Following
the idea of E. M\"uller, the feedback between nuclear rates and temperature was
taken into account by simultaneously computing molar fraction changes and
temperature response in the same matrix. The resulting algorithm is very stable
and efficient at calculating nuclear combustion in explosive scenarios,
especially in those situations where the reacting material manages to climb to
the nuclear statistical equilibrium regime. The numerical scheme may be useful
not only for those who carry out hydrodynamical simulations of explosive
events, but also as a tool to investigate the properties of a nuclear system
approaching equilibrium through a variety of thermodynamical trajectories.Comment: 31 pages, 11 figures, accepted for publication in the ApJ
Axisymmetric smoothed particle hydrodynamics with self-gravity
The axisymmetric form of the hydrodynamic equations within the smoothed
particle hydrodynamics (SPH) formalism is presented and checked using idealized
scenarios taken from astrophysics (free fall collapse, implosion and further
pulsation of a sun-like star), gas dynamics (wall heating problem, collision of
two streams of gas) and inertial confinement fusion (ICF, -ablative implosion
of a small capsule-). New material concerning the standard SPH formalism is
given. That includes the numerical handling of those mass points which move
close to the singularity axis, more accurate expressions for the artificial
viscosity and the heat conduction term and an easy way to incorporate
self-gravity in the simulations. The algorithm developed to compute gravity
does not rely in any sort of grid, leading to a numerical scheme totally
compatible with the lagrangian nature of the SPH equations.Comment: 17 pages, 10 figures, 1 Table. Accepted for publication in MNRA
Constraining deflagration models of Type Ia supernovae through intermediate-mass elements
The physical structure of a nuclear flame is a basic ingredient of the theory
of Type Ia supernovae (SNIa). Assuming an exponential density reduction with
several characteristic times we have followed the evolution of a planar nuclear
flame in an expanding background from an initial density 6.6 10^7 g/cm3 down to
2 10^6 g/cm3. The total amount of synthesized intermediate-mass elements (IME),
from silicon to calcium, was monitored during the calculation. We have made use
of the computed mass fractions, X_IME, of these elements to give an estimation
of the total amount of IME synthesized during the deflagration of a massive
white dwarf. Using X_IME and adopting the usual hypothesis that turbulence
decouples the effective burning velocity from the laminar flame speed, so that
the relevant flame speed is actually the turbulent speed on the integral
length-scale, we have built a simple geometrical approach to model the region
where IME are thought to be produced. It turns out that a healthy production of
IME involves the combination of not too short expansion times, t_c > 0.2 s, and
high turbulent intensities. According to our results it could be difficult to
produce much more than 0.2 solar masses of intermediate-mass elements within
the deflagrative paradigma. The calculations also suggest that the mass of IME
scales with the mass of Fe-peak elements, making it difficult to conciliate
energetic explosions with low ejected nickel masses, as in the well observed
SN1991bg or in SN1998de. Thus a large production of Si-peak elements,
especially in combination with a low or a moderate production of iron, could be
better addressed by either the delayed detonation route in standard
Chandrasekhar-mass models or, perhaps, by the off-center helium detonation in
the sub Chandrasekhar-mass scenario.Comment: 9 pages, 5 figures, 2 table
Gravitational waves as tracers of nuclear equation of state
The signal of neutron star (NS) mergers has the imprint of the EOS of dense nuclear matter, which is still not well known. A set of gravitational waves (GW) signals have been calculated from 3D hydrodynamical simulations of NS-NS mergers using the Smoothed Particle Hydrodynamics technique (SPH) with different EOS. By analyzing the morphology and time evolution of the signal we want to be able to discriminate among the variety of proposed EOS after a successful GW detection has been done
Enose lab made with vacuum sampling: quantitative applications
A lab-made electronic nose (Enose) with vacuum sampling and a sensor array, comprising
nine metal oxide semiconductor Figaro gas sensors, was tested for the quantitative analysis of
vapor–liquid equilibrium, described by Henry’s law, of aqueous solutions of organic compounds:
three alcohols (i.e., methanol, ethanol, and propanol) or three chemical compounds with different
functional groups (i.e., acetaldehyde, ethanol, and ethyl acetate). These solutions followed a fractional
factorial design to guarantee orthogonal concentrations. Acceptable predictive ridge regression
models were obtained for training, with RSEs lower than 7.9, R2 values greater than 0.95, slopes
varying between 0.84 and 1.00, and intercept values close to the theoretical value of zero. Similar
results were obtained for the test data set: RSEs lower than 8.0, R2 values greater than 0.96, slopes
varying between 0.72 and 1.10, and some intercepts equal to the theoretical value of zero. In addition,
the total mass of the organic compounds of each aqueous solution could be predicted, pointing
out that the sensors measured mainly the global contents of the vapor phases. The satisfactory
quantitative results allowed to conclude that the Enose could be a useful tool for the analysis of
volatiles from aqueous solutions containing organic compounds for which Henry’s law is applicable.The authors are grateful to the Foundation for Science and Technology (FCT,
Portugal) and FED-ER under Programme PT2020 for financial support by national funds FCT/MCTES
to CIMO (UID/AGR/00690/2019) and SusTEC (LA/P/0007/2020)info:eu-repo/semantics/publishedVersio
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