Generation and detection of nano ultrasound waves with a multiple strained layer structure

2008 ◽  
Vol 40 (8) ◽  
pp. 577-586 ◽  
Author(s):  
Bahareh Kaviani ◽  
Ali Sadr ◽  
Adib Abrishamifar
1995 ◽  
Vol 66 (15) ◽  
pp. 1957-1959 ◽  
Author(s):  
I. J. Fritz ◽  
J. F. Klem ◽  
J. E. Schirber ◽  
J. A. Olsen ◽  
W. A. Bonner

Author(s):  
Kazumichi Ogura ◽  
Michael M. Kersker

Backscattered electron (BE) images of GaAs/AlGaAs super lattice structures were observed with an ultra high resolution (UHR) SEM JSM-890 with an ultra high sensitivity BE detector. Three different types of super lattice structures of GaAs/AlGaAs were examined. Each GaAs/AlGaAs wafer was cleaved by a razor after it was heated for approximately 1 minute and its crosssectional plane was observed.First, a multi-layer structure of GaAs (100nm)/AlGaAs (lOOnm) where A1 content was successively changed from 0.4 to 0.03 was observed. Figures 1 (a) and (b) are BE images taken at an accelerating voltage of 15kV with an electron beam current of 20pA. Figure 1 (c) is a sketch of this multi-layer structure corresponding to the BE images. The various layers are clearly observed. The differences in A1 content between A1 0.35 Ga 0.65 As, A1 0.4 Ga 0.6 As, and A1 0.31 Ga 0.69 As were clearly observed in the contrast of the BE image.


Author(s):  
C. W. Allen ◽  
D. L. Kuruzar

The rare earth/transition element intermetallics R2T17 are essentially topologically close packed phases for which layer structure models have already been presented. Many of these compounds are known to undergo allotropic transformation of the type at elevated temperatures. It is not unexpected that shear transformation mechanisms are involved in view of the layering character of the structures. The transformations are evidently quite sluggish, illustrated in furnace cooled Dy2Co17 by the fact that only rarely has the low temperature rhombohedral form been seen. The more usual structures observed so far in furnace cooled alloys include 4H and 6H in Dy2Co17 (Figs. 1 and 2) . In any event it is quite clear that the general microstructure is very complicated as a consequence of the allotropy, illustrated in Fig. 3. Numerous planar defects in the layer plane orientation are evident as are non-layer plane defects inherited from a high temperature structure.


Author(s):  
F. M. Ross ◽  
R. Hull ◽  
D. Bahnck ◽  
J. C. Bean ◽  
L. J. Peticolas ◽  
...  

We describe an investigation of the electrical properties of interfacial dislocations in strained layer heterostructures. We have been measuring both the structural and electrical characteristics of strained layer p-n junction diodes simultaneously in a transmission electron microscope, enabling us to correlate changes in the electrical characteristics of a device with the formation of dislocations.The presence of dislocations within an electronic device is known to degrade the device performance. This degradation is of increasing significance in the design and processing of novel strained layer devices which may require layer thicknesses above the critical thickness (hc), where it is energetically favourable for the layers to relax by the formation of misfit dislocations at the strained interfaces. In order to quantify how device performance is affected when relaxation occurs we have therefore been investigating the electrical properties of dislocations at the p-n junction in Si/GeSi diodes.


Author(s):  
Hamish L. Fraser

The topic of strain and lattice parameter measurements using CBED is discussed by reference to several examples. In this paper, only one of these examples is referenced because of the limitation of length. In this technique, scattering in the higher order Laue zones is used to determine local lattice parameters. Work (e.g. 1) has concentrated on a model strained-layer superlattice, namely Si/Gex-Si1-x. In bulk samples, the strain is expected to be tetragonal in nature with the unique axis parallel to [100], the growth direction. When CBED patterns are recorded from the alloy epi-layers, the symmetries exhibited by the patterns are not tetragonal, but are in fact distorted from this to lower symmetries. The spatial variation of the distortion close to a strained-layer interface has been assessed. This is most readily noted by consideration of Fig. 1(a-c), which show enlargements of CBED patterns for various locations and compositions of Ge. Thus, Fig. 1(a) was obtained with the electron beam positioned in the center of a 5Ge epilayer and the distortion is consistent with an orthorhombic distortion. When the beam is situated at about 150 nm from the interface, the same part of the CBED pattern is shown in Fig. 1(b); clearly, the symmetry exhibited by the mirror planes in Fig. 1 is broken. Finally, when the electron beam is positioned in the center of a 10Ge epilayer, the CBED pattern yields the result shown in Fig. 1(c). In this case, the break in the mirror symmetry is independent of distance form the heterointerface, as might be expected from the increase in the mismatch between 5 and 10%Ge, i.e. 0.2 to 0.4%, respectively. From computer simulation, Fig.2, the apparent monocline distortion corresponding to the 5Ge epilayer is quantified as a100 = 0.5443 nm, a010 = 0.5429 nm and a001 = 0.5440 nm (all ± 0.0001 nm), and α = β = 90°, γ = 89.96 ± 0.02°. These local symmetry changes are most likely due to surface relaxation phenomena.


1987 ◽  
Vol 48 (C5) ◽  
pp. C5-321-C5-327 ◽  
Author(s):  
H. BRUGGER ◽  
G. ABSTREITER

Author(s):  
А. Г. Гребеников ◽  
И. В. Малков ◽  
В. А. Урбанович ◽  
Н. И. Москаленко ◽  
Д. С. Колодийчик

The analysis of the design and technological features of the tail boom (ТB) of a helicopter made of polymer composite materials (PCM) is carried out.Three structural and technological concepts are distinguished - semi-monocoque (reinforced metal structure), monocoque (three-layer structure) and mesh-type structure. The high weight and economic efficiency of mesh structures is shown, which allows them to be used in aerospace engineering. The physicomechanical characteristics of the network structures are estimated and their uniqueness is shown. The use of mesh structures can reduce the weight of the product by a factor of two or more.The stress-strain state (SSS) of the proposed tail boom design is determined. The analysis of methods for calculating the characteristics of the total SSS of conical mesh shells is carried out. The design of the tail boom is presented, the design diagram of the tail boom of the transport category rotorcraft is developed. A finite element model was created using the Siemens NX 7.5 system. The calculation of the stress-strain state (SSS) of the HC of the helicopter was carried out on the basis of the developed structural scheme using the Advanced Simulation module of the Siemens NX 7.5 system. The main zones of probable fatigue failure of tail booms are determined. Finite Element Analysis (FEA) provides a theoretical basis for design decisions.Shown is the effect of the type of technological process selected for the production of the tail boom on the strength of the HB structure. The stability of the characteristics of the PCM tail boom largely depends on the extent to which its design is suitable for the use of mechanized and automated production processes.A method for the manufacture of a helicopter tail boom from PCM by the automated winding method is proposed. A variant of computer modeling of the tail boom of a mesh structure made of PCM is shown.The automated winding technology can be recommended for implementation in the design of the composite tail boom of the Mi-2 and Mi-8 helicopters.


2016 ◽  
Vol 2 (4) ◽  
Author(s):  
Marco Antônio Guimarães Da Silva

O primeiro registro de algia vertebral (AV) na historia, relatado pelo Dr. Inhotep,  ocorreu em um trabalhador que construía uma pirâmide em Sakara, no antigo Egito, em 2748 AC (Hagberg, 1993). Desde então, as AV integram-se, ao longo dos séculos, à historia da Medicina através de inúmeras contribuições literárias e científicas: Hipócrates (460-377, AC), Galenus (130-200), Vesalius (1555), Cotugno (1764), Valleix (1847), Lasegue (1864), Bernhardt (1895), Lindsetd (1920), Lortat, Jacob y Sobareanu (1904), Petrén (1908), Dejerine (1914), Sicard (1918), Heuman (1920), Danforth y Wilson (1925), Putti (1927), Ghormley (1933), Pette y Becker (1938). Atualmente, as algias vertebrais podem ser consideradas como um desastre médico, pois assumiram um perfil de distribuição verdadeiramente epidêmico e, a despeito de sua antiguidade, ainda são, sob ponto de vista etiológico,  um grande mistério.Os nossos conhecimentos atuais na área de anatomo-fisiologia nos permitem observar que a série de vértebras dos discos intervertebrais, dos músculos e dos tendões, dos ligamentos, dos vasos e dos vários tipos de nervos, acabam por formar o conjunto de estruturas que compõem as nossas costas. Todas estas estruturas suportam o nosso peso, protegem o nosso sistema nervoso e nos permitem, ainda, conviver, paradoxalmente, com um sistema biomecânico que evita a telescopagem e nos possibilita uma locomoção eficiente. Nobre e importante função desempenham as nossas costas, ao nos oferecer tantas coisas, desde que, segundo a teoria evolucionista, adotamos a postura bípede. Mas e nós, o que fazemos por elas? As preservamos de cargas compressivas intra discais que, via de regra, extrapolam os limites máximos permitidos? Adotamos hábitos posturais que permitem o equilíbrio entre os segmentos corporais e solicitam harmonicamente o sistema músculo articular? Trabalhamos em um local que nos poupe das agressões ambientais? Controlamos nossas emoções e sentimentos o suficiente para não somatizarmos em nossas costas quaisquer evidências de nossos transtornos psicológicos? Conseguimos viver, sem  aborrecimentos,  em uma sociedade que  longe de ser justa e igualitária, ainda permite que os cinismos e as hipocrisias se associem a  providenciais  omissões para indultar  gente mais esperta e sabida do que nós?Ao prefaciar o livro “The Back pain revolution”, de Gordon Waddell, (Churchill Livinstone ed., 1998),  Red Phillips parece definir muito claramente o que realmente temos feito pelas nossas costas, quando afirma:  “We have stretched our backs. We have twisted and curled our backs. We have cooked our backs. We have frozen our backs. We have stimuled our backs with electric currents of various sorts, and with ultrasound waves, infrared waves, magnetic waves and X-rays waves. We have rubbed our backs with liniments, spirits, gels, perfumes and poultices”. Na verdade, somos obrigados a tratar o sintoma e não a doença.È bem possível que neste novo século os avanços na área da psico-neuro-endocrinologia, da fisiologia e genética da dor, possam finalmente descobrir o que realmente causa a dor nas costas. Até lá, devemos aceitar o desafio de combater e prevenir esse velho mal que, como o vampiro do romance de Bran Stoker, resiste a todos os ataques e insiste em ser imortal. A diferença entre os casos de mortos retornando para aterrorizar, atacar e matar durante a noite, tão bem descritos no século XII pelo historiador inglês William de Newburgh, e a dor nas costas está no fato de que esta não seleciona como vítima apenas lindas jovens e tampouco restringe seus ataques a períodos noturnos. Ainda no campo das analogias, podemos afirmar, na atualidade, que, se o relacionamento entre vampiro e vítima estava cheio de conotações psico-sexuais, a relação  dor nas costas/ paciente interage sob ação de fortes componentes psico-sociogênicos. Não há, portanto, como negligenciar, seja qual for a nossa conduta terapêutica para a dor nas costas, o modelo proposto por Waddel (1992), que considera o paciente como resultado de uma série de conjunções fortemente influenciadas pelo seu entorno social, cultural e psicológico.De qualquer forma, ainda que essa dor nas costas possa, às vezes, ser minimizada por condutas médicas ou atenuada por protocolos fisioterapêuticos, o seu equacionamento total ainda está longe de tornar-se uma realidade, enquanto a sua verdadeira etiologia permanecer desconhecida. 


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