Well-defined Planes Research Articles

Ultrasound anatomy in the neonatal clubfoot.

Our objective was to assess clubfoot anatomy by US in newborn babies before and in the early phase of treatment. Reproducible US projections and measurements were carried out on 30 untreated clubfeet in 22 children, consecutively included in the study. The position of the navicular in relation to the head of the talus was visualised in all feet. The mean distance between the medial malleolus and the navicular was significantly shorter in the clubfeet than in normal feet. There was a tendency to medial displacement of the cuboid. Soft tissue thickness at the medial side of the foot was increased in all deformed feet. The measurements showed an acceptable intra- and inter-observer reliability for the different variables assessed ( r=0.71-0.96, Pearson's correlation coefficient). With US it is possible to obtain well-defined planes of investigation that give important information about the clubfoot deformity concerning the talo-crural, the talo-navicular and the calcaneo-cuboid joints. The method is simple enough to be used in everyday clinical practice and we recommend it as a guide during the non-operative treatment and for preoperative planning.

Slip Geometry and Plastic Anisotropy of Body-Centered Cubic Metals

The plastic anisotropy of bcc metals comprises the absence of well-defined slip planes, an orientation dependence of the uniaxial flow stress which seems to be in disagreement with Schmid's law of resolved shear stress, and an asymmetry between tension and compression. Recent theoretical and experimental work has shown that these phenomena are closely correlated to elementary slip on {211} planes in an intermediate temperature range. After a discussion of crystallographic peculiarities of 〈111〉 {211} slip, a kinematic model for microscopic cross-slip on triplets of slip planes is proposed which, in combination with the well-established model of thermally activated kink-pair formation, allows quantitative calculations of the plastic anisotropy.

Activation of the dienophilicity of indoles in normal electron demand [4 + 2] cycloadditions under high pressure.

[reaction: see Text] Activation by either high pressure or a combination of Lewis acid catalysis and high pressure allows indole derivatives to behave as dienophiles in [4 + 2] cycloaddition reactions under mild conditions. The biactivation mode has the highest impact on the stereoselectivity of the reaction. The cycloadducts resulting from these reactions are characterized by boat-shape conformations that bear well-defined orthogonal planes.

Small-angle neutron scattering investigation of deuteride (hydride) precipitation and decomposition in single-crystal Pd

Small-angle neutron scattering (SANS) measurements of deuteride formation and decomposition in single crystal Pd have been performed. The purpose of this work was to determine and compare the particle morphology during deuteride precipitation and reversion, with the overall goal of developing a model for the pressure hysteresis known to exist in the Pd-H system. Anisotropic Porod scattering at low Q was observed as the samples were driven well into the two-phase region from either solid solution (the α →α' transformation) or from 100% α' (the 'α →α reversion). This scattering is attributed to the formation of large, presumably semi-coherent or completely incoherent, tens-of-microns thick plates on well-defined habit planes. The orientation and dispersion of these larger plates was different for deuteride formation and decomposition: a very coarse dispersion on the {110}α habit plane developed during deuteride formation, while a much finer dispersion on the {100}α' habit plane occurred during deuteride reversion from the 100% deuteride phase. The latter orientation is consistent with the system selecting the habit plane orthogonal to the softest host direction to minimize the elastic accommodation energy of the precipitates. We suspect the {110}α' habit plane observed during deuteride formation is related to large over-pressure loading conditions. An isotropic SANS response from plates with thicknesses of 20 to 30 Å was also observed during deuteride formation and reversion. These plates are thought to act as (coherent) precursors to the large plate formation.

Efeito da adição simultânea de sementes e dopantes na microestrutura e propriedade dielétrica da cerâmica 0,93 PZN - 0,07 BT

O método de Pechini bem como o uso da adição simultânea de partículas sementes e solução dopante de BaTiO3 foram usados para preparar o Niobato de chumbo e zinco (PZN). Os pós calcinados a 800 ° C/2 h e 900 ° C/1 h, os quais apresentaram maior porcentagem de fase perovskita após a calcinação, foram compactados isostaticamente e sinterizados a 1100 ° C/1 h. A forma na qual os aditivos foram adicionados ao polímero (se como íons ou como sementes) influenciou no processo de sinterização, na microestrutura desenvolvida e na propriedade dielétrica da cerâmica. As cerâmicas contendo 80% dos aditivos na forma de sementes e 20% na forma de íons apresentaram em sua microestrutura grãos maiores e com faces cristalinas bem definidas. O maior tamanho médio de grão observado está em torno de 2 mi m. As amostras preparadas com 80% dos aditivos na forma de sementes e 20% na forma de íons apresentaram melhor propriedade dielétrica. O maior valor de constante dielétrica para esta composição está em torno de 9100.

Effect of elastic interaction on the formation of a complex multi-domain microstructural pattern during a coherent hexagonal to orthorhombic transformation

The effect of elastic interaction on the formation and dynamic evolution of multi-domain microstructures during a hexagonal to orthorhombic transformation in the absence and presence of an externally applied strain field is investigated numerically using the phase field model. In particular, three cases are considered, which include a single variant, two variants, and all three variants of the orthorhombic phase produced by the transformation. In each case, the morphology and spatial distribution of the orientation variants are characterized. It is shown that nucleation and growth of a single variant produces thin plates of the orthorhombic domains with definite habit planes. In the case of two variants, the domains developed at the initial stages are also platelets of well-defined habit planes, which is similar to the case of a single variant. However, the impingement and intersection of the platelets of different variants results in the formation of twin boundaries and “zig-zag” patterns. The overlap regions of the “zig-zag” cross sections remain untransformed which agrees very well with experimental observations. If all three variants are present, the hexagonal to orthorhombic transformation results in a number of unique multi-domain structures such as the star patterns, compound star patterns, fan patterns, etc., which have been frequently observed experimentally in systems undergoing hexagonal to orthorhombic or similar transformations. It is found that if the boundary of the system is constrained, e.g. a grain embedded in a polycrystalline material, the transformation can go to completion only when all three variants are present. In the presence of external strain field, the coupling between the applied strain field and the stress-free transformation strain associated with the domain formation leads to selective growth of variants.

Preparation of stair-step grooves by wet etching of AlAs/GaAs heterostructures and MOCVD growth of QWR

The possibility of preparing stair-step V- or U-grooves into a GaAs/AlAs heterostructure by isotropic and anisotropic wet chemical etching was studied. Several patterned structures with well-defined (100) planes of stairs were overgrown by MOCVD with the aim to realize quantum wires (QWRs) due to the selectivity of growth on these planes. This approach should allow for adjusting lateral and vertical dimensions independently as well as for a simple regulation of the density of QWRs. Samples were subsequently characterized by photoluminescence (PL), and it was supposed that the observed red shift could result from the presence of the QWRs.

Ultrasound measurements of the diameter of the fetal trachea, larynx and pharynx throughout gestation applicability to prenatal diagnosis of obstructive anomalies of the upper respiratory-digestive tract.

The purpose of the present study was to obtain normative data for the fetal upper respiratory tract by using high-resolution ultrasound techniques. Furthermore, we wanted to test the potential utility of the resulting normograms in diagnosing obstructive lesions of the trachea and oesophagus. Sonographic measurements of the diameters of the trachea, larynx and pharynx were obtained at well-defined planes from a prospective cross-sectional sample of 198 normal patients of known gestational age between 15 and 40 weeks' gestation. All measurements were performed during fetal apnea and in the absence of swallowing. The same measurements were also obtained from two cases with laryngeal atresia and three cases with oesophageal atresia, all of which were diagnosed prenatally. The data obtained were plotted on the constructed normograms. In normal fetuses approximately linear relationships existed between tracheal, laryngeal and pharyngeal diameter, on the one hand, and gestational age, on the other, with the measurements correlating significantly (p<0.0001) with gestational age. The linear regression coefficients (r2) for the tracheal, laryngeal and pharyngeal diameters were 0.66, 0.55 and 0.32, respectively. The 95 per cent prediction limits were also calculated. In fetuses with laryngeal atresia only the tracheal diameter was significantly higher as compared with that of normal fetuses. Data of the fetuses with oesophageal atresia showed that there were no changes in the upper airway anatomy. Our study provides normative data for the upper respiratory tract. In the prenatal diagnosis of obstructive neck anomalies the usefulness of the data would seem to be limited to those affecting the respiratory tract. Among the structures measured, only the trachea may prove to be of clinical significance.

Nanofabrication of model catalysts and simulations of their reaction kinetics

Nanofabrication of Pt particles on SiO2, with particle sizes and separations down to ∼20 nm, and more complex structures consisting of Pt particles deposited on top of CeO2 islands, have been made by electron beam lithography and lift-off techniques. Under catalytic reaction conditions (nonflammable mixture of H2+O2 in Ar at 1000 K, 1 atm) the originally deposited, disk-shaped, and polycrystalline particles, transform to three-dimensional crystalline particles. This restructuring is attributed to the surfactant role of oxygen (promoting Pt mobility), and the nonwetting of late transition metals on oxides. The exothermic H2+O2 reaction is a possible additional driving force. The catalytic kinetics on 3D crystalline particles with well-defined facet planes were explored by Monte Carlo simulations. The latter demonstrate that the catalytic kinetics on nm sized, crystalline particles may be absolutely unique and nonpredictable from single-crystal studies, primarily due to the diffusive mass transport between differently oriented facets on the particles.

Planar and cluster structure of icosahedral quasicrystals

Twofold-, threefold-, and fivefold-symmetry elements are observed in the near-surface region of the quasicrystal Al70Pd20Mn10 using a real-space imaging technique based on secondary-electron emission. The observed icosahedral point-group symmetry implies the presence of atomic clusters within the analyzed region of the solid. The same surface produces perfect low-energy electron diffraction patterns typical for well-defined crystallographic planes. We present a model which reconciles this dual structural nature of quasicrystals. Our model is constructed from an icosahedral seed followed by concentric symmetry-preserving “growth” to form the macroscopic solid.

The motion of multiple height ledges and disconnections in phase transformations

For phase transformations with well-defined terrace planes, interface motion can occur by the motion of ledges or disconnections (ledges with added dislocation character). Symmetry imposes restrictions on the nature of these defects and may lead to the need for multiple height ledges. The structure of the ledge riser can also be variable. These possibilities impose constraints that can influence the motion of the defects and hence affect the rate of phase transformation. Examples of these phenomena are presented for interfaces with differing degrees of lattice matching.

Listing's plane dependence on alternating fixation in a strabismus patient

Listing's law of the eye is one of the best studied findings in motor control, but its functional meaning is still incompletely understood and its status in neurological disorders and in strabismus is almost entirely unknown. We investigated the mechanisms underlying Listing's law and its possible clinical relevance. The dual magnetic search coil technique was used to record three-dimensional binocular eye movements in a stereoblind strabismic patient with good visual acuity in both eyes and capable of voluntarily alternating fixation. This technique yielded an accurate, objective and simultaneous measure of ocular misalignment in three dimensions and showed that the squint angle depended on which eye was fixating. Saccadic eye movement data throughout the oculomotor range were used to fit Listing's plane. Listing's primary position and the thickness of the plane for each eye were calculated for three different fixation conditions. For comparison, control measurements were taken from four normals. In the patient, no large deviations from normal values for the thickness of Listing's plane and the confidence limits of the Listing primary position were found. The most remarkable abnormality was that the orientation of Listing's plane depended on which eye was fixating. Both the change in ocular misalignment and the shift of Listing's primary positions observed when changing fixation are probably linked to accommodation-related vergence. Despite repeated surgery at early age, the patient had well-defined Listing planes for both eyes, but their alignment during left-eye fixation was abnormal. The obedience to Listing's law may reflect a strategy which minimizes muscular effort in each eye separately. The abnormal fixation-condition dependence is probably due to an aberrant coupling with vergence.

Stoichiometry effects on core structure and mobility in B2 NiAl

Abstract The effects of stoichiometry deviation on the core structure and motion of dislocations in B2 NiAl are studied. Vacancies and antisites are introduced into numerous positions in embedded atom simulation blocks containing [100](001) as well as [100](011) pure edge dislocations. The interaction of these point defects with the dislocation is quantified by calculating the change in total energy experienced by the simulated lattice. An off-stoichiometry Ni-rich alloy is generated by randomly substituting Ni atoms for Al atoms as well as simply deleting Al atoms from the perfect lattice structure. It was found that a 2% deviation from stoichiometry affects the shapes of dislocation cores in that they tend to lose their preference for the well-defined crystallographic planes seen in the stoichiometric alloy. Stoichiometry deviations also increase the non-planar spreading of the core as visualized using the strain invariant method. It was found that Al vacancies are strongly attracted to the dislocation core and produce much more significant changes in the core structure than antisites or Ni vacancies do. The Peierls stresses were found to increase significantly for the alloy when off-stoichiometry. The interaction of antisites with the dislocation core is not as strong, although the Peierls stress is still found to increase. The simulations suggest that an entirely different core structure may be stable for the off-stoichiometric alloys.

Atomistic modelling of stoichiometry effects on dislocation core structure in NiAl

Dislocation core structures in stoichiometric and non-stoichiometric NiAl have been analyzed. Atomistic computer simulation with embedded atom method potentials was used for the study of the configuration of the material in the vicinity of dislocation cores. The results were analyzed in terms of the stress tensor as a function of position, giving the detailed shape of the dislocation core. A non-stoichiometric Ni-rich alloy was generated by random substitution of Al atoms by Ni atoms in the perfect lattice structure. The results show that a 2% deviation from stoichiometry affects the shapes of the dislocation cores, in that they tend to lose their preference for the well-defined crystallographic planes seen in the stoichiometric alloy. Stoichiometry deviations also increase the non-planar spreading of the core. This increased non-planar spreading of the core in Ni-rich NiAl is in agreement with the experimental results of high resolution electron microscopy. In addition, it was found that Al vacancies are greatly attracted to the distribution core and produce more significant changes in the core structure. The Peierls stresses were found to increase significantly for the non-stoichiometric alloys. The interaction of antisites with the dislocation core is not as strong, although the Peierls stress is still found to increase.

Self-Organizing Growth of Nanometer Mesa Structures on Silicon (100) Substrates

Lateral patterning is a crucial technological step for the fabrication of complex nanostructures. It can be achieved either by etching or by a local deposition process. Most of the dry etching techniques for nanometer dimensions such as reactive ion etching (RIE) or focused ion beam (FIB) etching suffer from unintentional degradation such as crystal damage and contamination. In order to overcome these problems and to create well-defined and reproducible nanostructures we propose a self-organizing deposition process. It is based on local silicon molecular beam epitaxy (MBE) via ultrahigh-vacuum (UHV)-compatible shadow masks. By using this technique, well-defined tips and lines in the nanometer range have been fabricated. The shape of these mesa structures is basically determined by the physical growth mechanism. The sidewalls are well-defined crystallographic planes. This technique offers a convenient tool for the study of one- and zero-dimensional electronic systems.

The influence of chromium additions on order and ductility in Fe3Al intermetallic

It has previously been shown that the addition of Cr to the Fe 3 Al alloy can lead to improvements in ductility. Initial interpretations of this effect were based on changes in the fault energies and dislocation configurations, but recently the influence of environmental attack has been invoked. In the present study the role of Cr and other elemental additions on the state of order, dislocation dissociations and configurations, and on ductility has been examined under conditions where environmental attack should not be important. The addition of Cr is shown to have only a minor affect on ordering kinetics, fault energies and dislocation configurations. However, for the alloys generally considered, containing 28% Al, it is shown that the ordered state and microstructure depends sensitively on the precise composition and heat treatments given. In particular, small amounts of solute elements such as B can lead to the appearance of two-phase ordered-disordered microstructures over a wide temperature range, to the appearance of imperfect long range and short range order, and to major changes in the kinetics of ordering and disordering. The mechanical properties achieved are shown to depend critically on the extent and distribution of disorder (the long range order parameter, the extent of short range order, the presence and distribution of thick disordered domain walls) and this factor may explain much of the variability in properties reported between similar alloys. By way of example, the presence of short range order will confine dislocations to well-defined shear planes, concentrating shear and inducing early failure; disordered domain walls will dissociate superdislocations thereby spreading shear homogeneously; the ordered domains/disordered walls morphology will lead to particle-dispersion hardening

Non-associated plastic flow in single crystals

P lastic flow by shears on well-defined crystallographic planes is associated, most often, with the Schmid yield criterion which is expressed in terms of the resolved shear stress on those planes in the direction of the shears. In this case, for time-independent (low-temperature) flow, the yield function for each slip system is also the potential for the shear and. therefore, flow is said to be associated with that function (i.e. normality). Qin and Bassani (1992. J. Mech. Phys. Solids40, 813) propose a yield criterion to accommodate various non-Schmid behaviors. In this paper it is shown that this criterion leads to a nonassociated flow rule (i.e. non-normality). Time-independent constitutive relations are derived for single crystals undergoing non-associative plastic flow. The tension-compression asymmetry predicted for initial yield persists in strain hardening as well. Strain localization in the form of shear bands is investigated for both a single-slip and a symmetric double slip model. It is shown that non-Schmid effects increase the tendency for localization.

Measurement of intracardiac dimensions and structures in normal young adult subjects by transesophageal echocardiography

Transesophageal echocardiography (TEE) has proven to be an excellent diagnostic means of diagnosing different cardiac diseases. To distinguish between normal and pathologic findings, standardized measurements of well-defined cross-sectional planes are necessary. Therefore, the 2-dimensional echocardiography data of 2S healthy volunteers were obtained. In 13 men and 12 women, aged 19 to 30 years, recordings of the left ventricular shortaxis view, the 2- or 4-chamber view with the left and right atria, the long axes of the left and right ventricles, the mitral and tricuspid valve ring and the atrial septum were analyzed. Furthermore, the aortic valve plane and the ascending and descending aorta were also measured. All data are given as mean values ± 2 times the standard deviation. Enddiastolic and end-systolic left ventricular anteriorto-posterior diameter of the left ventricular short axis was 2.S ± 0.3 cm/cm 2 and 1.7 ± 0.3 cm/m 2, with the fractional shortening ranging from 27 to 42%. The end-systolic lateral diameter was 2.4 ± 0.5 cm/m 2 for the left atrium and 2.4 ± 0.4 cm/m 2 for the right atrium, and the end-systolic anteriorto-posterior diameter was LS ± 0.6 cm/m2 for the left atrium and 2.1 ± 0.6 cm/m 2 for the right atrium. End-diastolic diameters of 3.4 ± 0.6 cm/m 2 and 2.8 ± 0.4 cm/m 2 were obtained for the long axis of the left ventricle and for the right ventricle. Measurements ranged from LS to 2.2 cm/m2 for the end-diastolic diameter of the mitral ring and from 1.3 to 2.0 cm/m 2 for the tricuspid ring. The area of the aortic valve plane was 4.0 ± 1.2 cm 2/m 2 and those of the ascending and the descending aorta were 3.6 ± 1.0 cm 2/m 2 and 1.9 ± 0.8 cm 2/m 2. The values of the left ventricular axis, the pulmonary artery stem and right pulmonary artery in TEE corresponded very closely to those gained from transthoracic echocardlography. The normal values obtained in healthy young subjects should be taken into account in the diagnostic decision making in heart patients.

Geochemistry and sedimentology of a facies transition from limestone to iron-formation deposition in the early Proterozoic Transvaal Supergroup, South Africa

This study deals with the geochemistry and sedimentology of a facies transition from interbedded carbonate-shale to banded iron-formation in the Campbellrand carbonate sequence to the overlying Kuruman Iron Formation of the Transvaal Supergroup in South Africa which is approximately 2.3 Ga old. Four major lithologies are (1) limestone and dolomite, (2) shale and interbedded shale carbonate, (3) siderite-rich banded iron-formation, and (4) iron oxide-rich banded iron-formation. These rocks are unaltered and essentially unmetamorphosed with a maximum metamorphic-diagenetic overprint ranging in temperature from 110 degrees to 170 degrees C and with pressures of not more than 2 kbars.The oldest rocks are limestones and lesser dolomite with abundant cryptalgalaminae and intraclastic textures. Interbedded with the limestones and dolomites are carbonaceous shales, some of which are unusually ferruginous or pyrite rich. These carbonates and shales are overlain by meso- and microbanded siderite-chert iron-formation which grades upward into magnetite-, chert-, and carbonate-rich iron-formation.The averages for major and trace elements and rare earth element (REE) contents of the limestones, dolomites, and shales are distinct from those of the two types of iron-formation. The two most chemically diverse rock types are the shales (enriched in alkalis and most trace elements) and the two iron-formation types (siderite and magnetite rich) which are almost totally depleted in all elements except Si, Fe, Mg, and Ca (and CO 2 ). The high Al 2 O 3 contents of the shales (avg 9.55 wt %) correlate well with their high organic carbon contents (avg 3.91 wt %); the limestones and dolomites have average Al 2 O 3 and organic carbon contents of about 3.0 and 0.7 wt percent, respectively; the two iron-formation types have Al 2 O 3 average values of 0.099 wt percent (siderite rich) and 0.066 wt percent (magnetite rich) and corresponding averages for organic carbon of 0.080 wt percent (siderite rich) and 0.012 wt percent (magnetite rich). The REE are generally concentrated in the shales by a factor of about 10 over the iron-formations. The limestones and dolomites have intermediate values, and the iron-formations are most depleted. The iron-formation REE patterns (in a ratio with North American shale composite (NASC)) have pronounced positive Eu anomalies and slight negative Ce anomalies. Both of these anomalies are absent in the shales, but the limestones and dolomites show slight positive Eu anomalies.The siderite-rich iron-formations consist of chert-siderite-ankerite (or ferroan dolomite) with traces of pyrite and stilpnomelane. The siderite in these commonly microbanded assemblages is very fine grained along well-defined bedding planes. It is concluded, from petrographic study, that siderite is a primary precipitate. The ankerites and ferroan dolomites in these siderite-rich occurrences are commonly euhedral (rhombohedral), much coarser grained, and appear to be of later (diagenetic) origin. The magnetite-rich iron-formations consist of chert-magnetite-ankerite (or ferroan dolomite) + or - siderite + or - hematite + or - stilpnomelane + or - minnesotaite. In these oxide-rich iron-formations the ankerites (and ferroan dolomites) are similarly much coarser grained than the finely banded siderite. On the basis of the geochemical data and a reconstruction of the depositional basin for the carbonate-shale to iron-formation transition, we conclude that the limestone-dolomite-shale lithologies originated in a water column quite distinct from that in which the iron-formations were precipitated. We propose a model with a stratified water column in which the surface waters (during a regressive stage in the depositional basin) were the site of much organic carbon productivity and the locus of cryptalgal limestones and intraclastic limestone deposition; with at somewhat greater depth (below the chemocline) deposition of pyritic carbonaceous shale. Our model depicts the deeper waters (during a transgressive stage of the basin with the Kaapvaal craton more deeply submerged) as the site for iron-formation deposition; these deeper waters were depleted in organic carbon and enriched in dissolved ferrous iron relative to the shallower water mass, with continued availability of oxygen along the chemocline separating the two water masses. The ultimate source of the iron (and probably the SiO 2 ) in the iron-formations appears to be a very dilute hydrothermal input in the deep ocean waters, as concluded from mixing calculations of REE values for modern Atlantic Ocean water and hydrothermal solutions from the East Pacific Rise.

Stress control of seismicity patterns observed during hydraulic fracturing experiments at the Fenton Hill hot dry rock geothermal energy site, New Mexico

Abstract Seismicity accompanying hydraulic injections into granitic rock is often diffuse rather than falling along a single plane. This diffuse zone of seismicity cannot be attributed to systematic errors in locations of the events. A new scheme for determining orientations and locations of planes along which the microearthquakes occurred was recently developed. The basic assumption of the method, called the three-point method, is that many of the events fall along well-defined planes; these planes are often difficult to identify visually in the data because planes of many orientations are present. The method has been applied to four hydraulic fracturing experiments conducted at Fenton Hill as part of a hot dry rock geothermal energy project. While multiple planes are found for each experiment, one plane is common to all experiments. The ratio of shear to normal stress along planes of all orientations is calculated using a best estimate of the current stress state at Fenton Hill. The plane common to all experiments has the highest ratio of shear to normal stress acting along it, so it is the plane most likely to slip. The other planes found by the three-point method all have orientations with respect to current principal stresses that are favourable for slip to occur along pre-existing planes of weakness. These results are consistent with the assertion that the rock contains pre-existing joints which slip when the effective stress is reduced by the increased pore fluid pressure accompanying the hydraulic injection. Microearthquakes occur along those planes that are favourably aligned with respect to the current stress field.