Top PDF Momentum of the Pure Radiation Field

Momentum of the Pure Radiation Field

Momentum of the Pure Radiation Field

In the original and current presentation of Quantum Electro- dynamics, the Poynting vector forms a basis for the quant- ized momentum of the pure radiation field [1, 2]. Thereby Maxwell’s equations with a vanishing electric field diverg- ence in the vacuum state are used to determine the electro- magnetic field strengths and their potentials which, in their turn, are expressed by sets of quantized plane waves.

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Mapping of the radiation field of a mammography  equipment using molybdenum and rhodium filters

Mapping of the radiation field of a mammography equipment using molybdenum and rhodium filters

The use of X rays for diagnostic radiology is very common and important to Medicine, including mammographic diagnosis focusing decreasing of the doses applied to the patients and preserving high quality of the diagnostic image. A quality control program of the irradiation systems it is very necessary. The Instruments Calibration Laboratory (LCI) of IPEN perform calibration in dosemeters used in radiation dosimetry (in diagnostic radiology) for many years. The objective of that paper is determining the point of greatest intensity of the beam issued by the mammograph equipment. Exposures were made with filters Rhodium and Molybdenum. That mapping is important before applied a routine quality control program of the mammograph equipment and the calibration of instruments in the diagnosis.
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Liquid Crystal Bow-Tie Microstrip antenna for Wireless Communication Applications

Liquid Crystal Bow-Tie Microstrip antenna for Wireless Communication Applications

In this paper we presented the design and analysis of Bow-Tie antenna on liquid crystal substrate, which is suitable for the Bluetooth/WLAN-2.4/WiBree/ZigBee applications. The Omni-directional radiation patterns along with moderate gain make the proposed antenna suitable for above mentioned applications. Details of the antenna design and simulated results Return loss, Input impedance, Radiation Patterns, E-Field, H-Field and Current Distributions, VSWR are presented and discussed. The proposed antenna is simulated at 2.4 GHz using Ansoft HFSS-11.
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Esc. Anna Nery  vol.15 número1

Esc. Anna Nery vol.15 número1

The referrals contained in the document prepared by the division of the field of nursing express the political momentum to advance science, technology and innovation in our country which has a bearing on the evolution of the field of nursing, its mission and the challenges it faces: to promote and consolidate the scientific, technological and innovative nursing knowledge, through the development of human resources of excellence in all academic levels - masters, professional masters, doctorate and post-doctoral internships. With the purpose of promoting a society that offers a better quality of life, promotes health and the full exercise of citizenship, diversity and free debate of ideas must be respected. Our perspectives can be promising if we stand firm in our commitment to create and enforce policies that achieve excellence in the formation of postgraduate programs for the nurses of Brazil.
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On a one-equation turbulent model with feedbacks

On a one-equation turbulent model with feedbacks

Abstract A one-equation turbulent model is derived in this work on the basis of the approach used for the k-epsilon model. The novelty of the model consists in the consideration of a general feedback forces field in the momentum equation and a rather general turbulent dissipation function in the equation for the turbulent kinetic energy. For the steady-state associated boundary value problem, we prove the uniqueness of weak solutions under monotonous conditions on the feedbacks and smallness conditions on the solutions to the problem. We also discuss the existence of weak solutions and issues related with the higher integrability of the solutions gradients.
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Covariance properties and regularization of conserved currents in tetrad gravity

Covariance properties and regularization of conserved currents in tetrad gravity

Accordingly, we derive the explicit transformation laws of the canonical current and of the related field momentum under finite general linear and local Lorentz transformations.. Althoug[r]

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Braz. J. Phys.  vol.40 número1

Braz. J. Phys. vol.40 número1

In this work, we first explicitly verify the equivalence be- tween GR and TEGR. More specifically, we consider the so- lution for an isotropic and homogeneous universe described by the FLRW metric in Cartesian coordinates. The main rea- son for using these coordinates is for subsequent comparison of our work with other literature results. We find an identical equation to the cosmological equation of Friedmann. We also verify the consistency of the tensorial expressions of the total energy-momentum and angular momentum from the Hamil- tonian formalism of the TEGR. For this, we apply the Hamil- tonian formulation implemented by Maluf [21][29] to find the total energy-momentum (gravitational field plus matter) and gravitational angular momentum values in the FLRW uni- verse. It is shown that all these quantities vanish for flat and spherical geometries.
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Braz. J. Phys.  vol.34 número4A

Braz. J. Phys. vol.34 número4A

Analogue models of general relativity have recently been considered with great interest by the scientific commu- nity. They connect branches of physics as different as gravitation, condensed matter physics, electrodynamics, acoustics, and quantum field theory. One of the main expectations about such models lies on the possibility of testing in laboratory some aspects of quantum field theory in curved spacetimes. For instance, it seems to be possible to probe the existence of Hawking radiation by means of analogue models in the context of certain condensed matter systems. We briefly report the present day status of this topic of research. Some specific models are considered, particularly those presenting analogue event horizons as solutions. The issue of thermal emission (analogue Hawking radiation) is also discussed.
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Energy and momentum for the electromagnetic field described by three outstanding electrodynamics

Energy and momentum for the electromagnetic field described by three outstanding electrodynamics

We may now present a simple algorithm for computing the symmetric energy–momentum tensor from the field equation. Multiply the equation for the field in hand by a suitable derivative of this field so that the resulting expres- sion contains only one free spacetime index and then rewrite it as a four-derivative. Of course, this algorithm is nothing but an ‘‘operational’’ summary of the main points we have just discussed. As such, its main role is to work as a mne- monic device for the reader.
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Development of object simulator for radiation field of dental x-rays

Development of object simulator for radiation field of dental x-rays

Another document was published IAEA by the International Code of Practice for Dosimetry in Radiodiagnosis in 2007 [2]. Besides the IAEA has the International Commission on Radiological Protection (ICRP) founded in 1928, is considered the benchmark for many countries for the development of guidelines for radiological protection [3].

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STUDIES CONCERNING THE EFFECT OF GAMMA RADIATION AND MAGNETIC FIELD EXPOSURE ON GLADIOLUS

STUDIES CONCERNING THE EFFECT OF GAMMA RADIATION AND MAGNETIC FIELD EXPOSURE ON GLADIOLUS

In our investigation we have tested the effect of gamma irradiation and magnetic field exposure of gladiolus corms and cormels of the cultivars: Her Majesty, Applause and Speranţa. The corms and cormels were irradiated for 72 hrs with 137 Cs gamma source on cylindrical exposure geometry. At medium dose of 1 Gy has been accumulated for each corm and cormel. For each variety we used 10 corms and 30 cormels in five variants:

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Braz. J. Phys.  vol.36 número4A

Braz. J. Phys. vol.36 número4A

We start this paper with a historical survey of the Casimir effect, showing that its origin is related to ex- periments on colloidal chemistry. We present two methods of computing Casimir forces, namely: the global method introduced by Casimir, based on the idea of zero-point energy of the quantum electromagnetic field, and a local one, which requires the computation of the energy-momentum stress tensor of the corresponding field. As explicit examples, we calculate the (standard) Casimir forces between two parallel and perfectly conducting plates and discuss the more involved problem of a scalar field submitted to Robin boundary conditions at two parallel plates. A few comments are made about recent experiments that undoubtedly confirm the existence of this effect. Finally, we briefly discuss a few topics which are either elaborations of the Casimir effect or topics that are related in some way to this effect as, for example, the influence of a magnetic field on the Casimir effect of charged fields, magnetic properties of a confined vacuum and radiation reaction forces on non-relativistic moving boundaries.
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Noise and Fano-Factor Control in AC-Driven Aharonov-Casher Ring

Noise and Fano-Factor Control in AC-Driven Aharonov-Casher Ring

The spin dependent current and Fano factor of Aharonov-Casher semiconducting ring is investigated under the effect of microwave, infrared, ultraviolet radiation and magnetic field. Both the average current and the transport noise (Fano factor) characteristics are expressed in terms of the tunneling probability for the respective scattering channels. For spin transport induced by microwave and infrared radiation, a random oscillatory behavior of the Fano factor is observed. These oscillations are due to constructive and destructive spin interference effects. While for the case of ultraviolet radiation, the Fano factor becomes constant. This is due to that the oscillations has been washed out by phase averaging (i.e. ensemble dephasing) over the spin transport channels. The present investigation is very important for quantum computing and information processing.
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Momentum transfer at the high-latitude magnetopause and boundary layers

Momentum transfer at the high-latitude magnetopause and boundary layers

Abstract. How and where momentum is transferred from the solar wind to the magnetosphere and ionosphere is one of the key problems of space physics. Much of this transfer oc- curs through direct reconnection on the dayside, particularly when the IMF is southward. However, momentum transfer also occurs at higher latitudes via Alfv´en waves on old open field lines, even for southward IMF. This momentum is trans- ferred to the ionosphere via field-aligned currents (FACs), and the flow channel associated with these FACs produces a Hall current which causes magnetic variations at high lat- itude (the Svalgaard-Mansurov effect). We show examples where such momentum transfer is observed with multiple spacecraft and ground-based instruments.
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Influence of supply voltage frequency of induction coil on inoculation efficiency of pure aluminium structure

Influence of supply voltage frequency of induction coil on inoculation efficiency of pure aluminium structure

In paper is presented problem concerning inoculation of pure aluminium structure, which is realized mainly by intensification of liquid metal movement in mould. In aim of realization of forced movement during the crystallization of liquid metal was used rotate electromagnetic field, which is generated by induction coil fed with frequency of supply voltage from 25 to 100Hz. Effect of structure refinement obtained by influence of electromagnetic field was compared with refinement obtained by use of traditional inoculation, which consists in introducing of additions in form of titanium and boron to metal bath.
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Energy and angular momentum of the gravitational field in the teleparallel geometry

Energy and angular momentum of the gravitational field in the teleparallel geometry

Teleparallel theories of gravity have been considered a long time ago in connection with attempts to define the en- ergy of the gravitational field @1#. By studying the properties of solutions of Einstein’s equations that describe the gravita- tional field of isolated material systems, it is concluded that a consistent expression for the energy density of the gravita- tional field would be given in terms of second order deriva- tives of the metric tensor. It is known that there exists no covariant, nontrivial expression constructed out of the metric tensor, both in three and in four dimensions, that contains such derivatives. However, covariant expressions that con- tain second order derivatives of tetrad fields are feasible. Thus it is legitimate to conjecture that the difficulties regard- ing the problem of defining the gravitational energy- momentum is related to the geometrical description of the gravitational field, rather than being an intrinsic drawback of the theory @2#.
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A Method To Find The Area Of Sector Without The Usage Of Angle Made By The Chord

A Method To Find The Area Of Sector Without The Usage Of Angle Made By The Chord

As we know that to find the area of sector the angle made by the chord (that is chord which divides the circle) is required. But in the below method we find the ratio of the segments of the circle. Thus by relating the area of segment to the area of sector the area of sector could be found. The ratio of area of segments is related to tangents that are drawn through diameter on either side.

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Assessment Of Some Acceleration Schemes In The Solution Of Systems Of Linear Equations.

Assessment Of Some Acceleration Schemes In The Solution Of Systems Of Linear Equations.

Richardson with SOR, Chebyshev with Gauss-Seidel and Chebyshev with SOR. The iterative schemes were applied to Banded system, Tridiagonal systems and SPD system with varying dimensions. The Krylov subspace methods: GMRES, QMR, MINRES and BiCGSTAB converged to an approximate solutions less than or equal to the dimension of the coefficient matrix for each identified systems of linear equations. Again, Chebyshev and Richardson acceleration methods were the fastest convergence methods in terms of number of iterations. Again, Residual smoothing and the accelerated gradient schemes should be used for large and sparse systems of linear equations. The acceleration processes were very efficient when solving large and sparse systems of linear equation and therefore useful especially for systems resulting from the solution of partial differential equations.
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The analysis of solidification process of ferritic-austenitic cast steel

The analysis of solidification process of ferritic-austenitic cast steel

The possibility of increasing the hardness of the copper- containing alloy by ageing has made it reasonable to choose cast steels with copper addition for castings working under corrosive-erosive conditions, such as elements of pump casing, impellers, connector pipes, guide vanes, etc [3]. But the quantity of defected castings (due to hot cracking) and the difficulty with the copper-containing scrap management at piece production have resulted in the fact that Polish power industry still uses imported elements [4].
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Evaluating the influence of selected parameters on sensitivity of a numerical model of solidification

Evaluating the influence of selected parameters on sensitivity of a numerical model of solidification

The presented results from a series of analyses indicate lack of dependence of certain sensitivity analysis parameters. In case of increasing the parameter r (the number the matrix B* is generated) obtaining identical results despite increasing r, may be explained as converging of the results to a certain fixed value. It should be noticed that increase of the number r causes increase of the number of required computer simulations. Therefore it is significant to obtain credible results for the smallest r number possible.
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