Top PDF Gap Waves in Piezoelectric layered Medium

Gap Waves in Piezoelectric layered Medium

Gap Waves in Piezoelectric layered Medium

In the present paper the conditions of existence of shear electroelastic gap waves in piezoelectric- vacuum-dielectric layered system are found. It is shown that in the discontact layered system the gap electroelastic waves can be propagated. It is considered the limiting case when the thickness of vacuuming layer tends to zero. It is proved that the statement of the problem is true when there is no acoustic contact between piezoelectric and dielectric grounded media.

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POROELASTIC MODELING IN STRATIFIED MEDIA ACROSS ALL FREQUENCIES

POROELASTIC MODELING IN STRATIFIED MEDIA ACROSS ALL FREQUENCIES

ABSTRACT. There is considered a layered heterogeneous poroelastic isotropic medium with physical parameters characterized by piecewise constant functions of the depth only. We derive a mathematical algorithm for calculating reflected/transmitted poroelastic waves across all temporal frequencies. To define the frequency effect we use the dynamic permeability expression proposed by Johnson, Koplik and Dashen; in the time domain, this coefficient introduces order 1/2 shifted fractional time derivative involving a convolution product. The algorithm proposed is based on the formalism introduced by Ursin. The algorithm is tested numerically in a 1D-case. The numerical experiments confirm the effectiveness of the proposed algorithm in identifying the main wave events in both low frequency and high frequency regimes in the reservoir and laboratory scales.
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The Ultrasound Propagation Analysis through Two Mediums in Case of High Energy Piezoelectric Transducer

The Ultrasound Propagation Analysis through Two Mediums in Case of High Energy Piezoelectric Transducer

The case of the transmission/concentrator elements [2], when the ultrasound waves pass through one medium (usual alloy aluminum or titan) and the case of ultrasound piezoelectric transducer [3], when the ultrasound waves pass through two mediums (usual alloy aluminum # piezoelectric element).

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Influence	of	Stress	on	Propagation	of	Shear	Wave	in	Piezoelectric‐ Piezoelectric PE‐PE Composite	Layered	Structure

Influence of Stress on Propagation of Shear Wave in Piezoelectric‐ Piezoelectric PE‐PE Composite Layered Structure

Shear waves SH propagation in piezoelectric composite under the influence of initial stress is investigated analytically and numerically. The dispersion equation of shear waves propagation in direction normal to the layering is obtained in presence of initial stress. Numer‐ ical solutions were obtained for evaluating the effect of stress on dimensionless frequency and phase velocity. The effect of stress on stop band is discussed in this study. It can be concluded from the results that initial stress has significant effect on propagation charac‐ teristics of shear waves. The variation of initial stress has small effect on the phase velocity of shear waves. This study provides insight for development of piezoelectric composite structure under the influence of initial stress.
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Spin waves in periodic layered ferromagnetic structure when exchange effect is considered

Spin waves in periodic layered ferromagnetic structure when exchange effect is considered

20. Danoyan Z.N, Atoyan L.H., Danoyan N.Z. Shear horizontal electro-magneto-elastic surface waves in a layered piezoelectric structure in the presence of an electric or ЦКРnОЭТМ ЬМrООn. ,,TopТМКХ ProЛХОЦЬ oП ConЭТnuuЦ MОМСКnТМЬ’’. TСО proМООНТnРЬ oП international Conference, 4-8 October 2010, Dilijan, Armenia, pp. 266-271.

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Lat. Am. j. solids struct.  vol.10 número6

Lat. Am. j. solids struct. vol.10 número6

The paper is devoted to develop a new scheme to calculate imped- ance matrices for axial-symmetric foundations embedded in half- space medium. The half-space medium can be approximated by increasing thickness of one layer stratum on rigid bedrock due to the effect of material damping. However, as thickness increases, the numerical problem will arise. This problem is caused by the numerical contamination by some negligible reflection waves from rigid bedrock. In reality, the effect of these reflection waves on impedance is getting small as the thickness of the one layer stra- tum increases. Therefore, the scheme will employ the solutions for one layer stratum with suppressing these reflection waves to gen- erate the impedance for the case of half-space. The numerical results by the presented scheme are compared with the results by other scheme in order to show that the new numerical scheme is effective and the solutions in layered medium can be extended to obtain the results for the cases of layered half-space medium. Some numerical results of torsional, vertical, horizontal, coupling and rocking impedances with different embedded depths will be presented and comments on the numerical scheme will be given.
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Electric Gap Control in a Semiconductor

Electric Gap Control in a Semiconductor

The experimental study of graphene triggered a grow- ing attention to its electronic properties,[14] because the honeycomb lattice defines a band structure [19] with two nodal points in the Brillouin zone which determines a relativistic Dirac-type electronic dynamics [18] (creat- ing links with certain theories of particle physics). These properties are responsible for unusual phenomena, such as the fractional Hall effect,[13, 20, 7, 16] which al- lows the possibility for magnetic catalysis of an excitonic gap,[6, 5, 10, 9, 8, 11] ferromagnetism and superconduc- tivity. [12]

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Avaliação do processamento auditivo e da linguagem em pacientes com neurofibromatose tipo 1

Avaliação do processamento auditivo e da linguagem em pacientes com neurofibromatose tipo 1

Introduction: High prevalence of learning disabilities resulting in poor academic performance has already been described in Neurofibromatosis type 1. Learning process depends on the ability to listen, understand and separate the relevant parts of speech from background noise, regardless of the physical environment. It is known that much of the language is learned by hearing which is considered a functional system responsible for receiving sound information and convert them into specific transduction signals along the nerve fibers to the cortex. When there is a weak performance in one or more auditory abilities, it is much more difficult to learn without special assistance, even with normal intelligence, motivation and health. Objectives: Verify the neurological processing of the auditory information and its possible association with language and learning disabilities in patients with NF1. Methods: Descriptive-comparative study with 25 patients with NF1 (14 female and 11 male) and 22 controls (15 female and 7 male) aged 10 to 34 years. We analyzed the performance in auditory behavioral tests: sound localization (SL), sequential verbal memory (SVM), sequential non-verbal memory (SNVM), frequency patterns (FP), duration patterns (DP), Gap in Noise (GIN), speech in noise (SN), synthetic sentence identification with ipsilateral competing message (SSI – ICM) and contralateral competing message (SSI – CCM), dichotic digits (DD), staggered spondaic word (SSW) and dichotic nonverbal (DNV), in addition to analyze the results in the School Performance Test (TDE), phonologic and syntactic awareness. The statistical tools used were: t-Test, Mann- Whitney test, Fisher’s Exact test and the Pearson correlations. Probability values <0.05 were considered statistically significant. Results: Differences between NF1 and control groups were found in the tests: SVM, SNVM, FP, DP, GIN, SN RE and LE, SSI ICM, DD RE and LE, SSW RE and LE, SSI CCM in the LE ratios speech/noise -40 dB, DNV attention to RE and in the phonologic awareness. Positive correlations were observed between the dichotic tests and the school performance subtests. The PF and PD showed positive correlation with the phonologic awareness test. Conclusion: Patients with NF1 displayed auditory processing disorders associated to language and learning disabilities.
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Piezoelectric biosensors for molecular analysis in biomedical applications

Piezoelectric biosensors for molecular analysis in biomedical applications

A quantidade de proteína imobilizada pode ser determinada se a relação de Sauerbrey for válida. Como referido anteriormente a frequência de ressonância é afectada por efeitos viscoelásticos tanto do meio líquido como do filme adsor- vido [9]. A análise por espectroscopia de impedância permite quantificar essas in- terferências, sendo possível aplicar correcções à frequência de ressonância de modo a obter a massa real adsorvida. A imobilização de GST–scFv4BL levou ao aumento de resistência com dependência da concentração de anticorpo (fig. 3.3(b)). Este resultado está de acordo com o anteriormente obtido em sensores de 5 MHz [10], su- gerindo que o filme proteico apresenta um carácter viscoelástico e que a frequência de ressonância foi sobrestimada. A figura 3.3(a) apresenta os valores de varia- ção de frequência de ressonância obtidos com oscilador e os valores de frequência corrigidos (eq. 1.22) tendo em conta a variação de resistência para cada concentra- ção (fig. 3.3(b)). A viscoelasticidade do filme influenciou a resposta do oscilador com aumentos da variação de frequência na ordem dos 20 − 30%, o que significa que para a concentração de 100 µg/mL de anticorpo a massa real adsorvida é 30% menor. Assim, é possível estimar a massa a equação de Sauerbrey à frequência corrigida o valor de massa de anticorpo imobilizado foi de 1.3 µg/cm 2 . Este valor
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BRS Pampeira: new irrigated rice cultivar with high yield potential

BRS Pampeira: new irrigated rice cultivar with high yield potential

The cultivar BRS Pampeira is recommended for sowing in six rice-producing regions of the RS state, the west frontier being the preferred region, where it showed greater adaptability to the favorable environment. In registration with the Ministry of Agriculture, Livestock and Supply (MAPA), the cultivar was also recommended to the states of Goiás and Mato Grosso do Sul (midwest region); Tocantins, Pará and Roraima (north region); Maranhão, Piauí, Ceará, Rio Grande do Norte, Paraíba, Pernambuco, Alagoas and Sergipe (northeast region).

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Non-linear dynamo waves in an incompressible medium when the turbulence dissipative coefficients depend on temperature

Non-linear dynamo waves in an incompressible medium when the turbulence dissipative coefficients depend on temperature

Lp0/Lt"0 then Dep0Dip0/¸. In accordance with Eq. 11 we obtain: ¸"10 6 RQ. When (ep0)"0 and Lp0/Ltip0/tx, then txi105t0(t0"year 22). In these conditions we can suggest that p0 depends weakly on time and position. In this case we can use p0 as a constant in the equations for perturbed quantities.

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CHIRAL WAVES IN GRAPHENE TUNNELING

CHIRAL WAVES IN GRAPHENE TUNNELING

From a crystallographic point of view, the graphene is a triangular Bravais lattice with a diamond-shaped unit tile consisting of two sites so one gets the honeycomb structure. The electronic propagation in such a perfect crystal is described by Bloch waves (a generalization to lattices of the ordinary plane waves in free space). The corresponding Bloch wave vector k spans the so-called Brillouin zone and the way the energy of these Bloch waves depends on k is encoded in the band structure. The very unique feature of the graphene band structure is that the two lowest-energy bands, known as the valence and the conduction band touch at two isolated points located at the corners of the Brillouin zone. In the immediate vicinity of these degeneracy points, known as the Dirac points, the band structure is a cone. In natural graphene samples, there is exactly one electron per site, and thus, at zero temperature, all levels in the valence band are filled (a situation known as half-filling). As a result, the energy of the last occupied level precisely slices the band structure at the Dirac points. The low-energy excitations of this system are then described by the massless two-dimensional Weyl-Dirac equation and their energy dispersion relation   v k F is that of
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Comput. Appl. Math.  vol.30 número2

Comput. Appl. Math. vol.30 número2

These days, oil companies are interested in the process of thermodiffusion for more efficient extraction of oil from oil deposits. The spontaneous movement of the particles from high concentration region to the low concentration region is defined as diffusion and it occurs in response to a concentration gradient expressed as the change in the concentration due to change in position. The thermodiffusion in elastic solids is due to coupling of fields of temperature, mass diffusion and that of strain in addition to heat and mass exchange with environment.

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Building a thinner gap in a Gas Gap Heat Switch

Building a thinner gap in a Gas Gap Heat Switch

In such type of switch, the ON state is obtained by introducing a gas between two copper blocks separated by a very narrow gap — typically 100-200 microns — to obtain a good conductance through the gas. Despite the rather low thermal conductivity of a gas, the narrower the gap the best the conductance. The OFF state is obtained by removing the gas, for instance by using a small cryopump. Heating or cooling the cryopump allows toggling between the ON and the OFF conduction states of the switch, achieved in the absence of any moving parts. The two copper blocks are held apart by a thin stainless steel tube (typically 100-200 m thick) to avoid short-circuiting the blocks as well as to enclose the working gas.
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Antenna Design for Underwater Applications

Antenna Design for Underwater Applications

wireless communication known as an electric current method. The writers gave an overview of studies that had been conducted in the undersea communication and detection and through experimental analysis were able to conclude that propagation range in the medium at this frequency can be expanded, only if the current output is increased, without increasing the power output [76]. The experiment was carried out in the Mystic Lakes in Massachusetts, the relative permittivity and conductivity of the lake are 81 and 0.06 S/m respectively. The measured electric field patterns at a distance of 50 m below the surface of the water from the transmitting antenna are quite directional. These were compared with the computed field patterns and their results are similar, with which the conclusion is drawn that traveling wave antenna can be appropriately used for subsurface communication in the lake and also that at 144 MHz bands, and that water behaves like a dielectric medium at this frequency. In [77], Davis et al presented results of research and experimental validation on SQUIDS antennas operating at ELF bands to demonstrate the feasibility of using the antenna in an underwater environment as well as overcoming the sub-problems associated with its performance. Each of these problems was typically analyzed through measurements and the conclusion as presented by the team shows that SQUIDs antenna is potentially capable to be used as an extremely sensitive ELF RF receiving element on a mobile platform. In addition, the antenna has the ability to operate at a depth of 100 m below the water surface and can also deal with anticipated buoy motions through motion-processing method. In the same year, J. R. Wait presented propagation of ELF electromagnetic waves for Surface ELF Antenna For Addressing REmotely-deployed Receivers (SEAFARER), research in this band had actually been a fertile field of investigation for many years. The project came to address some grays area of Project Sanguine that was fraught with some controversies. In principle the two projects are very alike as the frequency of operation for antennas for this project is the same as that of Project Sanguine. Only that in the latter project power requirements were better estimated, but the US Navy was not able to explain the influence of either project on physical and biological environments. Also, this project has striking similarities and fascinating developments with an early investigation by Nicola Tesla [78].
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Complete Band Gaps in Nano-Piezoelectric Phononic Crystals

Complete Band Gaps in Nano-Piezoelectric Phononic Crystals

We study the band structure of elastic waves propagating in a nano-piezoelectric phononic crystal consisting of a polymeric matrix reinforced by BaTiO 3 inclusions in square, rectangular, triangular, honeycomb and Kagomé lattices. We also investigate the influence of inclusion cross section geometry - circular, hollow circular, square and rotated square with a 45º angle of rotation with respect to x and y axes. Plane wave expansion method is used to solve the governing equations of motion of a piezoelectric solid based on classical elasticity theory, ignoring nanoscopic size effects, considering two-dimensional periodicity and wave propagation in the xy plane. Complete band gaps between XY and Z modes are observed for all inclusions and the best performance is for circular inclusion in a triangular lattice. Piezoelectricity influences significantly the band gaps for hollow circular inclusion in lower frequencies. We suggest that nano-piezoelectric phononic crystals are feasible for elastic vibration management in GHz.
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Spherical linear waves in de Sitter spacetime

Spherical linear waves in de Sitter spacetime

We apply Christodoulou’s framework, developed to study the Einstein-scalar field equations in spherical symmetry, to the linear wave equation in de Sitter spacetime, as a first step towards the Einstein-scalar field equations with positive cosmological constant. We obtain an integro-differential evolution equation which we solve by taking initial data on a null cone. As a corollary we obtain elementary derivations of expected properties of linear waves in de Sitter spacetime: boundedness in terms of (characteristic) initial data, and a Price law establishing uniform exponential decay, in Bondi time, to a constant.
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Lat. Am. j. solids struct.  vol.11 número7

Lat. Am. j. solids struct. vol.11 número7

These phenomena have been investigated for the simple isotropic semi-space as well as the complicated systems of multilayered anisotropic media. A detailed review in this respect is given by Nayfeh (1995). Qi (1994) investigated the influence of viscous fluid loading on the propagation of leaky Rayleigh waves in the presence of heat conduction effects. Wu and Zhu (1995) suggested an alternative approach to the treatment of Qi (1994). They presented solutions for the dispersion relations of leaky Rayleigh waves in the absence of heat conduction effects. Zhu and Wu (1995) used this technique to study Lamb waves in submerged and fluid coated plates. Nayfeh and Nagy (1997) formulated the exact characteristic equations for leaky waves propagating along the inter- faces of systems which involve isotropic elastic solids loaded with viscous fluids, including half- spaces and finite thickness fluid layers.
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