Transmission electron microscopy of a transformation toughened white cast iron

Transmission electron microscopy has been used to study the microstructure of an experimental white cast iran, in which a combination of modified alloy composition and unconventional heat treatment has resulted in a fracture toughness of 40 MPa m(-1/2). Microstructural features of the alloy that contribute to the toughness improvement and hence distinguish it from conventional white irons have been investigated. In the as-cast condition the dendrites are fully austenitic and the eutectic consists of M7C3 carbides and martensite. During heat treatment at 1130 degrees C the austenite is partially destabilized by precipitation of chromium-rich M7C3 carbides. This results in a dendritic microconstituent consisting of bulk retained austenite and secondary carbides which are sheathed with martensite. The martensite sheaths, which contain interlath films of retained austenite, are irregular in shape with some laths extending into the bulk retained austenite. Emphasis has been placed on the morphology, distribution, and stability of the retained austenite and its transformation products in the dendrites. The implications of these findings on the transformation toughening mechanism in this alloy are discussed.

Effectiveness of iron repletion in the diet for the optic nerve development of anaemic rats

Purpose To compare the process of myelination in the developing optic nerve (ON) of anaemic rats with the subsequent recovery after being fed an iron-recovery diet. Methods In this study, the morphometrical parameters in the ON were assessed by electron microscopy in Wistar rats that were on an iron-deficient diet for 32 days or for 21 days followed by 10 days on an iron-recovery diet. Qualitative and quantitative analyses were performed using representative electron ultramicrographs. Data were analysed by one-way analysis of variance (ANOVA). When differences were detected, comparisons were made using Tukey`s post hoc test (P<0.05 was considered to be significant). Results Qualitative analysis of the ONs in anaemic and recovered animals showed a higher rate of deformed axons and increased lamellar separation in the myelin sheath when compared with the respective control group. The ON of the anaemic group showed a reduced mean density of myelinated fibres when compared with the control group. The fibre area ratio, axon area ratio, and myelin area ratio of large axons/small axons in the ONs of the control group showed the highest values for the myelin areas, axon areas, and total fibre areas. The control group showed a significantly higher myelin sheath thickness when compared with the anaemic and recovered groups. Conclusions Our data indicate that iron is necessary for maintenance of the ON cell structure, and that morphological damage from iron deficiency is not easily reverted by iron repletion. Eye (2010) 24, 901-908; doi:10.1038/eye.2009.205; published online 14 August 2009

Integrable extended hubbard models with boundary Kondo impurities

Three kinds of integrable Kondo impurity additions to one-dimensional q-deformed extended Hubbard models are studied by means of the boundary Z(2)-graded quantum inverse scattering method. The boundary K matrices depending on the local magnetic moments of the impurities are presented as nontrivial realisations of the reflection equation algebras in an impurity Hilbert space. The models are solved by using the algebraic Bethe ansatz method, and the Bethe ansatz equations are obtained.

A sensitive vorticity gauge using rotated porphyroblasts, and its application to rocks adjacent to the Alpine Fault, New Zealand

Variable aspect ratio porphyroblasts deformed in non-coaxial flow. and internally containing rotated relicts of an external foliation, can be used to characterise plane strain flow regimes. The distribution obtained by plotting the orientation of the long axis of such grains, classified by aspect ratio, against the orientation of the internal foliation is potentially a sensitive gauge of both the bulk shear strain (as previously suggested) and kinematic vorticity number. We illustrate the method using rotated biotite porphyroblasts in the Alpine Schist: a sequence of mid-crustal rocks that have been ramped to the surface along the Alpine Fault. a major transpressional plate boundary. Results indicate that, at distances greater than or equal to similar to1 km from the fault, the rocks have undergone a combination of irrotational fattening and dextral-oblique, normal-sense shear, with a bulk shear strain of similar to0.6 and kinematic vorticity number of similar to0.2. The vorticity analysis is compatible with estimates of strongly oblate bulk strain of similar to 75% maximum shortening. Dextral-reverse transpressional flow characterises higher strain S-tectonite mylonite within similar to1 km of the Alpine Fault. These relationships provide insight into the kinematics of flow and distribution of strain in the hangingwall of the Alpine Fault and place constraints on numerical mechanical models for the exhumation of these mid-crustal rocks. (C) 2001 Elsevier Science Ltd. All rights reserved.

The effect of heat treatment on the toughness, hardness and microstructure of low carbon white cast irons

The effect of destabilisation and subcritical heat treatment on the impact toughness, hardness, and the amount and mechanical stability of retained austenite in a low carbon white cast iron have been investigated. The experimental results show that the impact energy constantly increases when the destabilisation temperature is raised from 950 degreesC to 1200 degreesC. Although the hardness decreases, the heat-treated hardness is still greater than the as-cast state. After destabilisation treatment at 1130 degreesC, tempering at 200 to 250 degreesC for 3 hours leads to the highest impact toughness, and secondary hardening was observed when tempering over 400 degreesC. The amount of retained austenite increased with the increase in the destabilisation temperature, and the treatment significantly improves the mechanical stability of the retained austenite compared with the as-cast state. Tempering below 400 degreesC does not affect the amount of retained austenite and its mechanical stability. But the amount of retained austenite is dramatically reduced when tempered above 400 degreesC. The relationship between the mechanical properties and the microstructure changes was discussed. (C) 2001 Kluwer Academic Publishers.

Relationship between stress-induced martensitic transformation and impact toughness in low carbon austenitic steels

The effect of test temperature, which controls the stability of austenite, on the impact toughness of a low carbon Fe-Ni-Mn-C austenitic steel and 304 stainless steel, has been investigated. Under impact conditions, stress-induced martensitic transformation occurred, in a region near the fracture surface, at test temperatures below 80degreesC for the Fe-Ni-Mn-C steel and below -25degreesC for 304 stainless steel. The former shows significant transformation toughening and the highest impact toughness was obtained at 10degreesC, which corresponds to the maximum amount of martensite formed by stress-induced transformation above the Ms temperature. The stress-induced martensitic transformation contributes negatively to the impact toughness in the 304 stainless steel. Increasing the amount of stress-induced transformation to martensite, lowered the impact toughness. The experimental results can be well explained by the Antolovich theory through the analysis of metallography and fractography. The different effect of stress-induced transformation on the impact toughness in Fe-Ni-Mn-C steel and 304 stainless steel has been further understood by applying the crystallographic model for stress-induced martensitic transformation to these two steels. (C) 2002 Kluwer Academic Publishers.

Kinematics of oblique collision and ramping inferred from microstructures and strain in middle crustal rocks, central Southern Alps, New Zealand

The hanging wall of the Alpine Fault near Franz Josef Glacier has been exhumed during the past similar to2-3 m.y. providing a sample of the ductilely deformed middle crust of a modem obliquely convergent orogen. Presently exposed rocks of the Pacific Plate are inferred to have undergone several phases of ductile deformation as they moved westward above a mid-crustal detachment. Initially they were transpressed across the outboard part of the orogen, resulting in oblate fabrics with a down-dip stretch. Later, they encountered the Alpine Fault, experiencing an oblique-slip backshearing on vertical planes. This escalator-like deformation tilted and thinned the incoming crust onto that crustal-scale oblique ramp. This style of hanging wall deformation may affect only the most rapidly uplifting, central part of the Southern Alps because of the low flexural rigidity of the crust in that region and its displacement over a relatively sharp ramp-angle at depth. A 3D transpressive flow affected mylonites locally near the fault, but their shear direction remained parallel to plate motion, ruling out ductile 'extrusion' as an important process in this orogen. Outside the mylonite zone, late Cenozoic shortening is inferred to be modest (30-40%), as measured from deformation of younger biotite grains. Oblique collision is dominated by translation on the Alpine Fault, and rocks migrate rapidly through the deforming zone, preventing the accumulation of large finite strains. Transpression may play a minor role in oblique collision. (C) 2001 Elsevier Science Ltd. All rights reserved.

Expression of anterior Hox genes during larval development of the gastropod Haliotis asinina

We report the spatial expression patterns of five anterior Hox genes during larval development of the gastropod mollusc Haliotis asinina, an unsegmented spiralian lophotrochozoan. Molecular alignments and phylogenetic analysis indicate that these genes are homologues of Drosophila HOM-C genes labial, proboscipedia, zen, Deformed, and Sex combs reduced, the abalone genes are named Has-Hox1, -Hox2, -Hox3, -Hox4, and -Hox5. Has-Hox transcripts are first detected in the free-swimming trochophore larval stage- and restricted to the posttrochal ectoderm. Has-Hox2, -Hox3, and -Hox4 are expressed in bilaterally symmetrical and overlapping patterns in presumptive neuroectodermal cells on the ventral side of the trochophore. Has-Hox1 expression is restricted to a ring of cells on the dorsoposterior surface, corresponding to the outer mantle edge where new larval shell is being synthesized. There appears to be little change in the expression domains of these Has-Hox genes in pre- and posttorsional veliger larvae, with expression maintained in ectodermal and neuroectodermal tissues. Has-Hox2, -Hox3, -Hox4, and-Hox5 appear to be expressed in a colinear manner in the ganglia and connectives in the twisted nervous system. This pattern is not evident in older larvae. Has-Hox1 and-Hox4 are expressed in the margin of the mantle in the posttorsional veliger, suggesting that Hox genes play a role in gastropod shell formation.

Microstructural evolution of the Serido Belt, NE-Brazil: the effect of two tectonic events on development of c-axis preferred orientation in quartz

The polyphase evolution of the Serido Belt (NE-Brazil) includes D, crust formation at 2.3-2.1 Ga, D-2 thrust tectonics at 1.9 Ga and crustal reworking by D-3 strike-slip shear zones at 600 Ma. Microstructural investigations within mylonites associated with D-2 and D-3 events were used to constrain the tectono-thermal evolution of the belt. D-2 shear zones commenced at deeper crustal levels and high amphibolite facies conditions (600-650 degreesC) through grain boundary migration, subgrain rotation and operation of quartz Q-prism slip. Continued shearing and exhumation of the terrain forced the re-equilibration of high-T fabrics and the switching of slip systems from (c)-prism to positive and negative (a)-rhombs. During D-3, enhancement of ductility by dissipation of heat that came from syn-D-3 granites developed wide belts of amphibolite facies mylonites. Continued shearing, uplift and cooling of the region induced D-3 shear zones to act in ductile-brittle regimes, marked by fracturing and development of thinner belts of greenschist facies mylonites. During this event, switching from (a)-prism to a basal slip indicates a thermal path from 600 to 350 degreesC. Therefore, microstructures and quartz c-axis fabrics in polydeformed rocks from the Serido Belt preserve the record of two major events, which includes contrasting deformation mechanisms and thermal paths. (C) 2003 Elsevier Ltd. All rights reserved.

Numerical study of hydrogenic effective mass theory for an impurity P donor in Si in the presence of an electric field and interfaces

In this paper we examine the effects of varying several experimental parameters in the Kane quantum computer architecture: A-gate voltage, the qubit depth below the silicon oxide barrier, and the back gate depth to explore how these variables affect the electron density of the donor electron. In particular, we calculate the resonance frequency of the donor nuclei as a function of these parameters. To do this we calculated the donor electron wave function variationally using an effective-mass Hamiltonian approach, using a basis of deformed hydrogenic orbitals. This approach was then extended to include the electric-field Hamiltonian and the silicon host geometry. We found that the phosphorous donor electron wave function was very sensitive to all the experimental variables studied in our work, and thus to optimize the operation of these devices it is necessary to control all parameters varied in this paper.

Estudo da corrosão e inibição dos aços carbono AISI 1010, inoxidável AISI 316 e duplex UNS S31803 em meio de solução de íons cloreto

O comportamento da corrosão e inibição à corrosão dos aços carbono AISI 1010, inox AISI 316 e duplex UNS S31803 foi estudado em meio de solução de íons cloreto à 3,0% (m/v), na ausência e presença do benzimidazol e imidazol como inibidores. A caracterização química e morfológica dos aços foi realizada por meio das técnicas de espectrometria de emissão ótica, difração de raios X (DRX), microscopia ótica, microscopia eletrônica de varredura (MEV) e energia dispersiva de raios X (EDX). As análises eletroquímicas foram realizadas através das técnicas de polarização potenciodinâmica e espectroscopia de impedância eletroquímica. As análises de DRX e de metalografia mostraram as fases presentes em cada aço, sendo o aço AISI 1010 composto pela fase ferrita, o aço AISI 316 pelas fases de FeNi e Cr e o aço UNS S31803 pelas fases austenita e ferrita. Além disso, a metalografia e as análises de MEV e EDX permitiram identificar regiões e certos elementos presentes nos aços que propiciam à ocorrência da corrosão, tais como inclusões. Os inibidores foram testados em diferentes concentrações (25 ppm, 50 ppm, 100 ppm, 500 ppm e 1000 ppm) para os três aços, através das curvas de polarização e impedância eletroquímica, e verificou-se que para todas as concentrações houve aumento da resistência à corrosão dos aços. Pelas curvas de polarização verificou-se que o benzimidazol proporcionou aos aços AISI 1010, AISI 316 e UNS S31803, eficiências de inibição de cerca de 51%, 71% e 75%, respectivamente. Enquanto que o imidazol apresentou eficiência de cerca de 73%, 95% e 86%, respectivamente. Os resultados de impedância eletroquímica mostraram que as eficiências de inibição do benzimidazol foram de aproximadamente 52%, 73% e 71%, respectivamente, para os aços AISI 1010, AISI 316 e UNS S31803. E por sua vez, o imidazol apresentou eficiências de aproximadamente 96% para os aços AISI 1010 e AISI 316 e 85% para o aço UNS S31803. O teste de perda de massa mostrou que para o aço AISI 1010 tanto o benzimidazol quanto e o imidazol inibiram a corrosão, sendo que reduziram a corrosão em cerca de 17% e 24%, respectivamente. Nas análises das curvas de polarização em estudos com a água do mar observou-se que os inibidores foram menos eficientes do que em meio de solução de cloreto. O benzimidazol obteve eficiências de cerca de 14%, 50% e 33%, respectivamente, para os aços AISI 1010, AISI 316 e UNS S31803. Enquanto que o imidazol apresentou eficiências de aproximadamente 21%, 59% e 34%, respectivamente. Em todas as análises eletroquímicas e análise de perda de massa, o imidazol se mostrou o melhor inibidor para os aços estudados.

Perfis de tensão residual do aço duplex UNS S32304 submetido a diferentes processos de soldagem TIG e condições de tratamento térmico

Visando a aplicação do aço UNS S32304 em embalados para transporte de material radioativo, amostras soldadas por processo TIG, com diferentes gases de proteção, foram submetidas a tratamentos térmicos nas temperaturas de 475°C, 600°C e 750°C por 8 horas, seguidas de resfriamento ao ar, a fim de analisar o efeito de temperaturas críticas no perfil de tensões residuais e microestrutura. A difratometria de raios X foi utilizada para determinação das tensões residuais, em diferentes condições (amostras como recebidas e apenas tratadas termicamente) e o perfil de tensões residuais total das amostras soldadas é apresentado para cada fase (austenita e ferrita). As tensões residuais das fases foram determinadas pela técnica sen2ψ, utilizando um difratômetro com fonte de radiação CuKα (<λ

Análise numérica de freqüência natural de materiais compósitos híbridos com memória de forma

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2007.

Response of a multi-domain continental margin to compression: Study from seismic reflection-refraction and numerical modelling in the Tagus Abyssal Plain

The effects of the Miocene through Present compression in the Tagus Abyssal Plain are mapped using the most up to date available to scientific community multi-channel seismic reflection and refraction data. Correlation of the rift basin fault pattern with the deep crustal structure is presented along seismic line IAM-5. Four structural domains were recognized. In the oceanic realm mild deformation concentrates in Domain I adjacent to the Tore-Madeira Rise. Domain 2 is characterized by the absence of shortening structures, except near the ocean-continent transition (OCT), implying that Miocene deformation did not propagate into the Abyssal Plain, In Domain 3 we distinguish three sub-domains: Sub-domain 3A which coincides with the OCT, Sub-domain 3B which is a highly deformed adjacent continental segment, and Sub-domain 3C. The Miocene tectonic inversion is mainly accommodated in Domain 3 by oceanwards directed thrusting at the ocean-continent transition and continentwards on the continental slope. Domain 4 corresponds to the non-rifted continental margin where only minor extensional and shortening deformation structures are observed. Finite element numerical models address the response of the various domains to the Miocene compression, emphasizing the long-wavelength differential vertical movements and the role of possible rheologic contrasts. The concentration of the Miocene deformation in the transitional zone (TC), which is the addition of Sub-domain 3A and part of 3B, is a result of two main factors: (1) focusing of compression in an already stressed region due to plate curvature and sediment loading; and (2) theological weakening. We estimate that the frictional strength in the TC is reduced in 30% relative to the surrounding regions. A model of compressive deformation propagation by means of horizontal impingement of the middle continental crust rift wedge and horizontal shearing on serpentinized mantle in the oceanic realm is presented. This model is consistent with both the geological interpretation of seismic data and the results of numerical modelling.

Hexanuclear and undecanuclear iron(III) carboxylates as catalyst precursors for cyclohexane oxidation

Two multinuclear complexes [Fe-6(mu(3)-O)(2)(mu(4)-O-2)L-10(OAc)(2)(H2O)(2)]center dot 2.625Et(2)O center dot 2.375H(2)O (1) and [(Fe11Cl)-Cl-III-(mu(4)-O)(3)(mu(3)-O)(5)L-16(dmf)(2.5)(H2O)(0.5)]center dot Et2O center dot 1.25dmf center dot 3.8H(2)O (2), where HL = 3,4,5-trimethoxybenzoic acid and dmf = dimethylformamide, have been prepared from trinuclear iron(III) carboxylates via their structural rearrangement in dimethylformamide or diethyl ether-dimethylformamide 9:1, respectively, and slow vapor diffusion of diethyl ether into the reaction mixture. Both compounds have been characterized by X-ray diffraction, optical, Mossbauer spectroscopy, and magnetic measurements. Complex 1 possesses a hexanuclear ferric peroxido-dioxido {Fe-6(O-2)(O)(2)}(12+) core unit, which adopts a recliner conformation, while complex 2 contains an unprecedented {Fe11O8Cl}(16+) core, in which 9 ferric ions are six-coordinate and the remaining two are five-coordinate. Another structural feature of note of the undecanuclear core is the presence of a deformed cubane entity {Fe-4(mu(3)-O)(mu(4)-O)(3)}(4+). Both complexes act as catalyst precursors for the oxidation of cyclohexane to cyclohexanol and cyclohexanone with aqueous H2O2, in the presence of pyrazinecarboxylic acid. Remarkable TONs and TOFs (the latter mainly for 1) with concomitant quite good yields have been achieved under mild conditions. Moreover, 1 exhibits remarkably high activity in an exceptionally short reaction time (45 min), being unprecedented for any metal catalyzed alkane oxidation by H2O2. The catalytic reactions proceed via Fenton type chemistry.