3,633 research outputs found
THEORETICAL AND EXPERIMENTAL STUDY OF THE INTERIOR BALLISTICS OF A RIFLE 7.62
This study aims to examine theoretically and experimentally the interior ballistics of a rifle 7.62. Three theoretical methods are employed: the Vallier-Heydenreich, which is based on empirical data tables; the lumped parameters that is represented by a differential-algebraic system of equations, describing the propellant combustion, the thermodynamics of the gas inside the gun and the projectile dynamics; and the commercial software PRODAS. The theoretical solutions furnish the pressure, the projectile velocity and the projectile position inside the gun, the maximum pressure,the muzzle velocity and the total time of the interior ballistics. The experiments measure the pressure along of the time and the projectile velocity at seven meters ahead of the barrel. The proposed lumped parameter model indicates alternatives to model the energy lost and the resistance pressure functions. The theoretical solutions are compared with experiments. A thermodynamics analysis of the energy conversion in the gun is provided. The results are analyzed and the relevance of each method is highlighted
Analysis of the dynamics of a spacecraft in the vicinity of an asteroid binary system with equal masses
In this work, we performed a dynamical analysis of a spacecraft around a
nearly equal-mass binary near-Earth asteroid with application to the asteroid
2017 YE5, which is also a possible dormant Jupiter-family comet. Thus, we
investigated the motion of a particle around this binary system using the
circular restricted three-body problem. We calculated the locations of the
Lagrangian points of the system and their Jacobi constant. Through numerical
simulations, using the Poincar\'e Surface of Sections, it was possible to find
several prograde and retrograde periodic orbits around each binary system's
primary, some exhibiting significantly-sized higher-order behavior. We also
calculated the stability of these orbits. After finding the periodic orbits, we
investigated the influence of solar radiation pressure on these orbits. For
this analysis, we considered that the area-to-mass ratio equals 0.01 and 0.1.
We also performed a spacecraft lifetime analysis considering the physical and
orbital characteristics of the 2017YE5 system and investigated the behavior of
a spacecraft in the vicinity of this system. We analyzed direct and retrograde
orbits for different values of Jacobi's constant. This study investigated
orbits that survive for at least six months, not colliding or escaping the
system during that time. We also analyze the initial conditions that cause the
spacecraft to collide with or , or escape from the system. In this
work, we take into account the gravitational forces of the binary asteroid
system and the solar radiation pressure (SRP). Finally, we calculated optimal
bi-impulsive orbital maneuvers between the collinear Lagrangian points. We
found a family of possible orbital transfers considering times of flight
between 0.1 and 1 day
Effect of non-abrupt doping and interfacial profiles on the carrier sheet density in one-side modulation-doped GaN/AlGaN quantum wells
Contribution from Tree Legumes to Mixed Grass-Legume Pastures
Legumes and associated microorganisms may fix N from atmosphere and benefit grass on mixed grass-legume pastures. Nitrogen may be transferred by different mechanisms, including direct transfer of N compounds by roots, decomposition of nodules, roots, litter from legume (Nair 1993), and through animal excreta after legume intake by cattle. Silvopastoral systems including tree legumes may become a viable option in tropical regions, considering the increasing prices of N fertilizers compared to farm products such as beef and milk.
This experiment evaluated legume contribution on mixed grass-legume pastures in the coastal region of Pernambuco State, Brazil
Accelerating Cold Dark Matter Cosmology ()
A new kind of accelerating flat model with no dark energy that is fully
dominated by cold dark matter (CDM) is investigated. The number of CDM
particles is not conserved and the present accelerating stage is a consequence
of the negative pressure describing the irreversible process of gravitational
particle creation. A related work involving accelerating CDM cosmology has been
discussed before the SNe observations [Lima, Abramo & Germano, Phys. Rev. D53,
4287 (1996)]. However, in order to have a transition from a decelerating to an
accelerating regime at low redshifts, the matter creation rate proposed here
includes a constant term of the order of the Hubble parameter. In this case,
does not need to be small in order to solve the age problem and the
transition happens even if the matter creation is negligible during the
radiation and part of the matter dominated phase. Therefore, instead of the
vacuum dominance at redshifts of the order of a few, the present accelerating
stage in this sort of Einstein-de Sitter CDM cosmology is a consequence of the
gravitational particle creation process. As an extra bonus, in the present
scenario does not exist the coincidence problem that plagues models with
dominance of dark energy. The model is able to harmonize a CDM picture with the
present age of the universe, the latest measurements of the Hubble parameter
and the Supernovae observations.Comment: 9 pages, 6 figures, typos corrected, references added, discussion in
Appendix B extende
THERMODYNAMIC PROPERTIES OF --FLUIDS AND THE QUANTUM VACCUM
The thermodynamic behaviour of a relativistic perfect simple fluid obeying
the equation of state , where is a
constant, has been investigated. Particular cases include: vacuum(,
), a randomly oriented distribution of cosmic strings (, ), blackbody radiation (, ) and stiff matter (, ). Fluids with become
hotter when they expand adiabatically (). By assuming
that such fluids may be regarded as a kind of generalized radiation, the
general Planck's type form of the spectrum is deduced. As a limiting case, a
new Lorentz invariant spectrum of the vacuum which is compatible with the
equation of state and other thermodynamic constraints is proposed. Some
possible consequences to the early universe physics are also discussed.Comment: 20 pages, uses LATE
Effects of the aqueous extract of hyptis pectinata on liver regeneration after 70% partial hepatectomy preliminar results
O uso de plantas medicinais tem aumentado bastante na população mundial. O objetivo desta pesquisa é avaliar os efeitos do extrato aquoso das folhas da Hyptis pectinata, popularmente conhecida como "sambacaitá" ou "canudinho", sobre a regeneração hepática após hepatectomia parcial de 70%. Foram utilizados 24 ratos, divididos em 4 grupos: grupo OS, em que se realizou operação simulada e aplicação oral de água destilada por 4 dias; grupo OSD200, também submetido à laparotomia com manipulação do fígado e aplicação de 200 mg de extrato/Kg de animal durante o mesmo período; grupo HP, hepatectomizado a 70% após 4 dias de aplicação por via oral de água destilada; e grupo HPD200, hepatectomizado a 70% após 4 dias de administração de 200 mg extrato/Kg de animal. Foram dosadas fosfatase alcalina, bilirrubina total e as aminotransferases e estudou-se o estado III da função mitocondrial. O grupo OSD200, quando comparado ao OS, apresentou redução significativa da fosfatase alcalina. O grupo HPD200, em comparação ao HP, teve redução estatisticamente significativa no nível da AST e do estado III da função mitocondrial. _________________________________________________________________________________________ ABSTRACT: The use of medicinal plants has strongly increased by the world population. The objetive of this study is to assess the effects of the aqueous extract of Hyptis pectinata leaves, popularly known as "sambacaitá" or "canudinho", on liver regeneration after 70% partial hepatectomy. Twenty four rats were divided into 4 groups: group OS, submitted to sham operation and oral administration of distilled water during 4 days; group OSD200, also submitted to sham operation and ingestion of 200 mg of extract/Kg of animal for the same period of time; group HP, which underwent 70% hepatectomy after 4 days of distilled water administration; and group HPD200, which underwent 70% hepatectomy after 4 days of oral administration of 200 mg of extract/Kg of animal. Alkaline phosphatase, total bilirubin and the serum level of aminotransferases were measured and state III of mitochondrial respiratory activity was assessed. Group OSD200, when compared to OS, presented significant decrease of alcaline fosfatase. Group HPD200, when compared to HP, showed statistically significant decrease of AST level and state III respiratory process
Avaliação do Ensino de Empreendedorismo entre Estudantes Universitários por meio do Perfil Empreendedor
Entrepreneurship is a socioeconomic phenomenon that has been valued for its influence on the growth and
development of regional and national economies. The main promoter of this phenomenon are entrepreneurs,
subjects endowed with multiple features that make up their profiles. They are dynamic and results oriented,
benefitting from the fruits of their own personal efforts. Entrepreneurial education is highlighted as one of the most
efficient ways to promote an entrepreneurial culture and train new entrepreneurs. However, some difficulty has
been observed in assessing the effectiveness of teaching and learning this subject. The objective of this study was
to analyze, by means of multivariate techniques, an instrument whose function is to measure the learning of
Entrepreneurship, verifying the change in entrepreneur profiles of 407 college students participating or not in an
entrepreneurial training process. The results showed that students who participated in Entrepreneurship
educational training activities showed significant changes in their entrepreneurial profiles. The main contributions
showed growth in the Self-realization, Planner, Innovative and Risks Assumed dimensions
Incised valley paleoenvironments interpreted by seismic stratigraphic approach in Patos Lagoon, Southern Brazil
<div><p>ABSTRACT: The Rio Grande do Sul (RS) coastal plain area (33,000 km 2 ) had its physiography modified several times through the Quaternary, responding to allogenic and autogenic forcings. The Patos Lagoon covers a significant area of RS coastal plain (10,000 km 2 ), where incised valleys were identified in previous works. About 1,000 km of high resolution (3.5 kHz) seismic profiles, radiocarbon datings, Standard Penetration Test (SPT) and gravity cores were analyzed to interpret the paleoenvironmental evolution as preserved in incised valley infills. Seismic facies were recognized by seismic parameters. The sediment cores were used to ground-truth the seismic interpretations and help in the paleoenvironmental identification. Key surfaces were established to detail the stratigraphical framework, and seismic facies were grouped into four seismic units, which one classified in respective system tracts within three depositional sequences. The oldest preserved deposits are predominantly fluvial and estuarine facies, representing the falling stage and lowstand system tracts. The Holocene transgressive records are dominated by muddy material, mainly represented by estuarine facies with local variations. The transgression culminated in Late Holocene deposits of Patos Lagoon, representing the highstand system tract. The depositional pattern of the vertical succession was controlled by eustatic variations, while the autogenic forcing (paleogeography and sediment supply) modulated the local facies variation.</p></div
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