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Search Results: 1 - 10 of 690616 matches for " C. A. F.;Santos "
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The electrostatic field of a point charge and an electrical dipole in the presence of a conducting sphere
F C Santos,A C Tort
Physics , 2004, DOI: 10.1088/0143-0807/25/6/018
Abstract: We evaluate the electrostatic potential and the electrostatic field created by a point charge and an arbitrarly oriented electrical dipole placed near a grounded perfectly conducting sphere. Induced surface charge distributions as well as electrostatic energy, force and torque associated with this configuartion are fully discussed. Possible variants of the problem are also discussed.
Confined Maxwell Field and Temperature Inversion Symmetry
A. C. Tort,F. C. Santos
Physics , 2000, DOI: 10.1016/S0370-2693(00)00498-6
Abstract: We evaluate the Casimir vacuum energy at finite temperature associated with the Maxwell field confined by a perfectly conducting rectangular cavity and show that an extended version of the temperature inversion symmetry is present in this system.
The Casimir energy of a massive fermion field revisited
F. C. Santos,A. C. Tort
Physics , 2002,
Abstract: We introduce a general, simple and effective method of evaluating the zero point energy of a quantum field under the influence of arbitrary boundary conditions imposed on the field on flat surfaces perpendicular to a chosen spatial direction. As an example we apply the method to the Casimir effect associated with a massive fermion field on which MIT bag model type of boundary conditions are imposed.
Duality Transformations and temperature inversion symmetry
F C Santos,A C Tort
Physics , 2001,
Abstract: We argue that the temperature inversion symmetry present in the original Casimir setup and also in other Casimir systems for which symmetrical boundary conditions are imposed is not related to the duality transformations that in the context defined in Ref. [1] are transformations relating spatial extension and temperature, and pressure and energy density. We provide an example of a Casimir system for which in principle there is no temperature inversion symmetry but nevertheless these duality transformations can be found.
The first steps in vision in the classroom
Santos, A.C.F;
Revista Brasileira de Ensino de Física , 2010, DOI: 10.1590/S1806-11172010000200003
Abstract: we examine, using the particle-in-the-box model, the transient absorption measurements of the cis-trans isomerization by the visual pigment rhodopsin present in the retina [r.w. schoenlein et al., science 254, 412 (1991)], which contains the retinene group, a conjugated system, which is formed by single and double carbon-carbon atoms, and works as a light antenna in the process of photon absorption. the present approach is directly applicable to the classroom in undergraduate chemistry and physics major courses.
A note on spherical f--tilings by right triangles
C. P. Avelino and A. F. Santos
ACTA MATHEMATICA UNIVERSITATIS COMENIANAE , 2012,
Abstract: In this paper we present some spherical f-tilings by two (distinct) right triangles. We classify the group of symmetries of the presented tilings and the transitivity classes of isohedrality are also determined.
A note on spherical f-tilings by right triangles
C. P. Avelino,A. F. Santos
ACTA MATHEMATICA UNIVERSITATIS COMENIANAE , 2012,
Abstract: In this paper we present some spherical f-tilings by two (distinct) right triangles.We classify the group of symmetries of the presented tilings and the transitivity classes of isohedrality are also determined.
Evaluation of subsurface contact stresses in railroad wheels using an elastic half-space model
Santos, F. de C.;Santos Jr, A. A. dos;Bruni, F.;Santos, L. T.;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2004, DOI: 10.1590/S1678-58782004000400007
Abstract: railroad wheels fail in two main modes: rolling surface defects like spalling, shelling and wear, and internal defects including cracks propagating after a change takes place in the original stress pattern. although the effects of the latter are almost always catastrophic, the former is more usual. the onset of rolling surface defects depends on the strength of the surface and the applied loads. the strength is related to surface hardness and can be determined through experimental evaluation under controlled conditions. evaluating the loads is one of the challenges for contact researchers. this paper presents the evaluation of the stress field inside elastic rolling bodies with an elliptic area of contact. this kind of model can be applied to wheel-rail contact phenomena. typical high freight transportation loads are used in conjunction with regular recommended wheel and rail sizes. the results have shown that shear stress reaches the maximum magnitude below the surface of contact, and this explains the presence of shelling defects in service. they have also shown that a new model including plasticity is required, because the range of the stresses reached surpasses, by far, the elastic limit
Lack of Relationship between Testicular Echotexture and Seminal Characteristics in Adult Texel Rams  [PDF]
Mariana A. G. Urt, Edwin W. B. Bakarji, Fábio J. C. Faria, Elisvania F. Santos, Deiler S. Costa
Agricultural Sciences (AS) , 2018, DOI: 10.4236/as.2018.98065
Abstract: The objective of this study was to determine the minimum representative area to evaluate testicular echotexture parenchyma and to identify the correlations between the intensity of pixels of the testicular parenchyma and the fibrosis score with the physical and morphological characteristics of the ejaculate of Texel rams. The study used 88 Texel rams, aged between 10 and 12 months, and reared in a semi-extensive system. The animals underwent breeding soundness evaluation (BSE) and ultrasound of the testicles. The images were transferred to a computer where they were defined in areas of 400, 1600, 3600, and 6400 mm2, after which the average intensity of the pixels of each image of the testicular regions was evaluated. A testicular fibrosis score was assigned in order to quantify the frequency of fibrotic lesions. In relation to the intensity of pixels of the predetermined regions, only the area of 400 mm2 presented a difference (P < 0.05), with the area of 1600 mm2 being the smallest area that best represented the testicular parenchyma. There were no correlations between the intensity of pixels of the testicular parenchyma and the fibrosis score with the physical and morphological characteristics of the ejaculate of the rams.
A note on the Lorentz force, magnetic charges and the Casimir effect
C. Farina,F. C. Santos,A. C. Tort
Physics , 2003,
Abstract: We show that in order to account for the repulsive Casimir effect in the parallel plate geometry in terms of the quantum version of the Lorentz force, virtual surface densities of magnetic charges and currents must be introduced. The quantum version of the Lorentz force expressed in terms of the correlators of the electric and magnetic fields for planar geometries yields then correctly the Casimir pressure.
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