8,202 research outputs found
Generating functionals, consistency, and uniqueness in the integral equation theory of liquids
We discuss and illustrate through numerical examples the relations between
generating functionals, thermodynamic consistency (in particular the
virial-free energy one), and uniqueness of the solution, in the integral
equation theory of liquids. We propose a new approach for deriving closures
automatically satisfying such characteristics. Results from a first exploration
of this program are presented and discussed.Comment: 27 pages, 5 figure
Advanced radar absorbing ceramic-based materials for multifunctional applications in space environment
In this review, some results of the experimental activity carried out by the authors on advanced composite materials for space applications are reported. Composites are widely employed in the aerospace industry thanks to their lightweight and advanced thermo-mechanical and electrical properties. A critical issue to tackle using engineered materials for space activities is providing two or more specific functionalities by means of single items/components. In this scenario, carbon-based composites are believed to be ideal candidates for the forthcoming development of aerospace research and space missions, since a widespread variety of multi-functional structures are allowed by employing these materials. The research results described here suggest that hybrid ceramic/polymeric structures could be employed as spacecraft-specific subsystems in order to ensure extreme temperature withstanding and electromagnetic shielding behavior simultaneously. The morphological and thermo-mechanical analysis of carbon/carbon (C/C) three-dimensional (3D) shell prototypes is reported; then, the microwave characterization of multilayered carbon-filled micro-/nano-composite panels is described. Finally, the possibility of combining the C/C bulk with a carbon-reinforced skin in a synergic arrangement is discussed, with the aid of numerical and experimental analyses
Thermal neutron captures on and He
We report on a study of the and n\,^3He radiative captures at thermal
neutron energies, using wave functions obtained from either chiral or
conventional two- and three-nucleon realistic potentials with the
hyperspherical harmonics method, and electromagnetic currents derived in chiral
effective field theory up to one loop. The predicted and n\,^3He cross
sections are in good agreement with data, but exhibit a significant dependence
on the input Hamiltonian. A comparison is also made between these and new
results for the and n\,^3He cross sections obtained in the conventional
framework for both potentials and currents.Comment: 4 pages, 4 eps figures; references added; corrections to text and
abstract as suggested by referee adde
Import substitution and implicit taxation of agriculture in Brazil.
The industrialization that Brazil experienced prior to World War II was not induced by the government It had its origin in the relative profitability of the agricultura1 and industrial sectors, which favored a shift in resources to the indup trial sector. During the period from the end of World War II until the early sixties, a deliberate import-substitution policy was pursued. The factors that gave rise to that policy were the diff iculty that the country encountered in foreign trade during. the Depression and the two world wars, the influente of the Prebish thesis, and the dominance of two sector models (Rannis & Fei 1961 and Jorgenson 1969) as the basis for development policies
Local chiral interactions and magnetic structure of few-nucleon systems
The magnetic form factors of H, H, and He, deuteron
photodisintegration cross sections at low energies, and deuteron threshold
electrodisintegration cross sections at backward angles in a wide range of
momentum transfers, are calculated with the chiral two-nucleon (and
three-nucleon) interactions including intermediate states that have
recently been constructed in configuration space. The =3 wave
functions are obtained from hyperspherical-harmonics solutions of the
Schr\"odinger equation. The electromagnetic current includes one- and two-body
terms, the latter induced by one- and two-pion exchange (OPE and TPE,
respectively) mechanisms and contact interactions. The contributions associated
with intermediate states are only retained at the OPE level, and are
neglected in TPE loop (tree-level) corrections to two-body (three-body) current
operators. Expressions for these currents are derived and regularized in
configuration space for consistency with the interactions. The low-energy
constants that enter the contact few-nucleon systems. The predicted form
factors and deuteron electrodisintegration cross section are in excellent
agreement with experiment for momentum transfers up to 2--3 fm. However,
the experimental values for the deuteron photodisintegration cross section are
consistently underestimated by theory, unless use is made of the Siegert form
of the electric dipole transition operator. A complete analysis of the results
is provided, including the clarification of the origin of the aforementioned
discrepancy.Comment: 24 pages, 13 figure
Finite-size effects and collective vibrations in the inner crust of neutron stars
We study the linear response of the inner crust of neutron stars within the
Random Phase Approximation, employing a Skyrme-type interaction as effective
interaction. We adopt the Wigner-Seitz approximation, and consider a single
unit cell of the Coulomb lattice which constitutes the inner crust, with a
nucleus at its center, surrounded by a sea of free neutrons. With the use of an
appropriate operator, it is possible to analyze in detail the properties of the
vibrations of the surface of the nucleus and their interaction with the modes
of the sea of free neutrons, and to investigate the role of shell effects and
of resonant states
Reforming the brazilian agricultural research system.
bitstream/item/158310/1/Reforming-the-brazilian.pd
Dynamic phase coexistence in glass-forming liquids
One of the most controversial hypotheses for explaining the heterogeneous
dynamics of glasses postulates the temporary coexistence of two phases
characterized by a high and by a low diffusivity. In this scenario, two phases
with different diffusivities coexist for a time of the order of the relaxation
time and mix afterwards. Unfortunately, it is difficult to measure the
single-particle diffusivities to test this hypothesis. Indeed, although the
non-Gaussian shape of the van-Hove distribution suggests the transient
existence of a diffusivity distribution, it is not possible to infer from this
quantity whether two or more dynamical phases coexist. Here we provide the
first direct observation of the dynamical coexistence of two phases with
different diffusivities, by showing that in the deeply supercooled regime the
distribution of the single-particle diffusivities acquires a transient bimodal
shape. We relate this distribution to the heterogeneity of the dynamics and to
the breakdown of the Stokes-Einstein relation, and we show that the coexistence
of two dynamical phases occurs up to a timescale growing faster than the
relaxation time on cooling, for some of the considered models. Our work offers
a basis for rationalizing the dynamics of supercooled liquids and for relating
their structural and dynamical properties.Comment: 12 pages, 7 figure
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