Distinct Preferred Orientation Research Articles

An Investigation into the Microstructures and Mechanical Properties of a TIG Welding Joint in Ti-4Al-2V Titanium Alloy

The Ti-4Al-2V (wt. %) titanium alloy has garnered widespread applications across diverse fields due to its exceptional strength-to-weight ratio, high toughness, specific strength, and corrosion resistance. The welding of Ti-4Al-2V titanium alloy components is often necessary in manufacturing processes, where the reliability of a welded joint critically influences the overall service life of these components. Consequently, a comprehensive understanding of the welded joint’s microstructure and mechanical properties is imperative. In this study, Ti-4Al-2V titanium alloy was welded using multi-layer and multi-pass TIG welding techniques, and a detailed examination was conducted to analyze the microstructure and grain morphology of each microzone of the welded joint. The results revealed the presence of an initial α phase and a secondary lamellar α phase in the heat affected zone (HAZ). Meanwhile, the fusion zone (FZ) primarily comprised a coarse secondary α phase and a small amount of an acicular martensitic α’ phase. Both the recrystallization zone and the superheated zone exhibited a distinct preferred orientation, with grains smaller than 10 μm accounting for 65.9% and 55.1%, respectively. To assess the mechanical properties of the various microzones and the typical microstructure within the welded joint, nanoindentation tests were performed. The results indicated that the recrystallization zone possessed a higher nanohardness (3.753 GPa) than the incomplete recrystallization zone (3.563 GPa) and the superheated zone (3.48 GPa). Among all the microzones, the FZ exhibited the lowest average nanohardness (3.058 GPa). Notably, the basket-weave microstructure demonstrated the highest average nanohardness, reaching 3.93 GPa. This was followed by the fine-grain microstructure, which possessed a slightly lower nanohardness. The Widmanstätten microstructure, on the other hand, exhibited the lowest nanohardness among the three microstructures within the HAZ. Therefore, the basket-weave microstructure stands out as the most desirable microstructure to achieve in the welded joint. In summary, this study provides a comprehensive characterization and analysis of the microstructure and properties of Ti-4Al-2V titanium alloy TIG welds, aiming to contribute to the optimization of the TIG welding process for Ti-4Al-2V titanium alloy.

Effect of Chloride Incorporation on the Intermediate Phase and Film Morphology of Methylammonium Lead Halide Perovskites.

The influence of chloride integration on perovskite film deposition, encompassing both the structures of intermediate phases and the properties of the final films, was explored. Our methodology involved the fabrication of perovskite intermediate-phase films with varying concentrations of methylammonium chloride (MACl). Subsequently, we conducted an analysis employing X-ray diffraction and Rietveld refinement, incorporating the March-Dollase correction, to gain insights into how chloride-induced intermediate phases impact film morphology. Remarkably, a distinct preferred orientation was observed in the (020) lattice plane perpendicular to the substrate surface, and this orientation was found to be directly correlated to the MACl concentration. This distinctive arrangement of chloride-induced intermediate-phase complexes facilitated controlled crystallization, leading to highly oriented crystals and an improved film morphology. As a consequence, perovskite solar cell devices incorporating chloride-containing methylammonium lead iodide achieved a power conversion efficiency exceeding 20%. These findings suggest a crucial link between the preferred orientation observed in the final chlorine-derived perovskite films and the intermediate-phase structure formed during the initial stages of perovskite formation. These results suggest a profound impact of intermediate phase compositions and crystal structures on perovskite formation, emphasizing the importance of a comprehensive understanding of these factors to enable precise control over ideal structures and the subsequent transformation into high-quality perovskite films.

Effect of machining processes on the quenching and tempering surface layer of ultra-high strength steel

The initial characteristics of the surface layer following the quenching and tempering treatment of ultra-high-strength steel play a significant role in determining the subsequent precision machining. This study focus on investigating the influence of machining processes on the quenching and tempering surface layer. The machining processes affect both the oxidation of the quenching and tempering treatment and the development of a distinct preferred grain orientation. Gradual diminishment of surface abrasions leads to the transformation of the needle-like oxidation pattern into a layered oxidation structure. The preferred orientation of the grains prevents the grains from shear sliding, thereby enhancing the Taylor effect. Formation mechanisms of the microhardness and residual stress of the quenching and tempering surface layer induced by machining processes were also discussed and completely revealed. The microhardness is mainly attributed to the dynamic Hall-Petch effect, while plastic strain, dislocation energy storage, and phase transformation contribute to the residual stress changes.

The anisotropy of geomaterial granite

Abstract. Granites appear to be isotropic, which qualifies them as suitable crystalline host rocks for nuclear waste repository sites. However, despite their optical appearance, granites show a primary structural anisotropy (Bouchez, 1997) that evolved during emplacement and crystallization of the melt. The major processes involved are magmatic flow and oriented crystal growth (Müller et al., 2011). Hypothetically, it is expected that different tectonic environments, i.e. different orientations of the stress tensor, cause significant differences in the primary anisotropy, which is expressed by the crystallographic preferred orientation (CPO) of the rock-forming minerals. It is likely that primary anisotropic petrophysical properties control the orientation of post-magmatic structural features like extensional fractures and thus shape potential fluid pathways. We present the first results of a systematic study of felsic plutonites, i.e. the GAME project (Gefüge, Textur- und Anisotropie-Messungen von potenziell für die Endlagerung geeigneten Graniten zur Charakterisierung möglicher Fluidwegsamkeiten). The samples of syn-Variscan felsic plutons from two sites (Erzgebirge and Fichtelgebirge) represent different tectonic settings during intrusion: extension and compression. Furthermore, they depict different stages of fractionation of the peraluminous granite suites. The CPOs were analysed using the neutron time-of-flight (ToF) texture diffractometer SKAT (Keppler et al., 2014; Ullemeyer et al., 1998) and EBSD (electron backscatter diffraction). Using scanning electron microscope (SEM) automated mineral liberation analysis (Schulz et al., 2020), modal mineral compositions are quantified. This enables us to model primary or “intrinsic” petrophysical properties for these granites based on the elastic stiffness tensor of the individual rock-forming minerals (Mainprice et al., 2011). Main- and trace-element geochemical data (ICP-AES and ICP-MS) allow for a characterization of the different magmatic settings of the samples. All granites show distinct preferred orientations of rock-forming minerals. The quartz textures, for example, exhibit similar CPOs, with point maxima of the positive rhombs in combination with small circles to crossed-girdle c-axis distributions. However, the orientation with respect to the geographic reference system strongly varies. We will discuss the CPOs in relation to the stress tensor orientation during emplacement of the felsic plutons and compare the primary anisotropy with the post-magmatic fracture patterns of the particular granites.

Laser powder bed fusion of 316L stainless steel with 2 wt.% nanosized SiO2 additives: Powder processing and consolidation

Gas atomized 316L stainless steel powder was processed with 2 wt.% of nanosized SiO2 in a planetary ball milling (BM) system to produce feedstock material for laser powder bed fusion (L-PBF). X-ray diffraction (XRD) of powders revealed the development of micro-strains over increasing milling durations and the strain-induced ferrite formation. BM was limited in duration to preserve the austenitic phase and morphological characteristics analyzed by electron microscopy. In turn, 316L-2wt.% SiO2 feedstock powder was consolidated by L-PBF with varied process parameters and scanning strategies, that demonstrated a maximum density of 7.84 g/cm3 and relatively stable microhardness values close to 220 HV. A distinct (110) preferred orientation was observed in XRD pole figures of austenite for deeper melt pools over the building direction, whereas in-plane alignment reflected variations in scanning strategy. Furthermore, electron backscatter diffraction revealed columnar grains accompanied by the suspected depletion of SiO2, while electrochemical behavior displayed consistent characteristics.

A facile one-step gel process for precipitation of multifractal NaCl crystals and morphology evolution from sodium silicate gel

• Crystallization of NaCl in colloidal-salt system by a one-step gelation process. • Varying the pretreatment and gel conditions synthesizes DLA and dendrite patterns. • XRD analysis explains the dendrite pattern with distinct preferred orientation. • <110> and <111> directions determine the three- and four-fold symmetry dendrites. • Higher gelation degree contributes to precipitate regular fractal dendrite. In the colloidal-salt system of sodium silicate and sodium chloride, three-fold and four-fold symmetric dendrites and diffusion-limited aggregation (DLA) of sodium chloride crystals have been synthesized by a simple one-step gelation process without changing the solution composition. The morphology variation is realized by changing the sol pretreatment and gelation process’s heating mode. And the gelation degree of sodium silicate and the anisotropy of crystal growth is the morphology formation mechanism. Four-fold symmetric dendrites are related to preferential growth in the <110> direction, while three-fold symmetric dendrites are due to preferential orientation changes from <111> to <100> and then to <111>. EDS composition analysis showed that the high gelling degree is more accessible to precipitate regular fractal dendrites with preferred orientation.

Thermal Stability of PS-PVD YSZ Coatings with Typical Dense Layered and Columnar Structures

Yttria-stabilized zirconia (YSZ) coatings with typical pyramid columnar and dense layered structure were prepared by plasma spray-physical vapor deposition (PS-PVD). The evolution behavior of microstructure and crystallography of the coatings before and after thermal aging treatment were observed by electron backscatter diffraction (EBSD) and field emission scanning electron microscopy (FE-SEM). Results showed that the as-deposited coatings exhibited many types of structures and were mainly composed of a nonequilibrium tetragonal (t’-ZrO2) phase. With the prolonging of thermal exposure time, the initial nonequilibrium tetragonal phase of YSZ coatings gradually transformed into a monoclinic (m-ZrO2) phase. During the process of stationary deposition, at a proper spraying distance, each column exhibited a certain preferred orientation, but the ceramic topcoat did not exhibit distinct preferred orientation statistically.

In situ evidence of earthquakes near the crust mantle boundary initiated by mantle CO2 fluxing and reaction-driven strain softening

This study aims to understand the process behind the worldwide connection between deep crustal/upper mantle earthquakes and CO2 emissions along faults in rift zones. We do this by studying CO2-induced mineral reactions that facilitate strain localization in peridotites from an ancient rift zone in the Seiland Igneous Province (SIP), North Norway.Strain localization in association with hydration processes is well documented in all types of tectonic settings and has major implications for rheological behavior in active plate margin processes. The implications of CO2-bearing fluids are less studied, though experiments have shown how CO2 can influence the flow laws of olivine by imposing a brittle and more localized type of deformation.This study documents narrow shear zones observed within ultramafic rocks from the Seiland Igneous Province (SIP) comprising large volumes (>20,000 km3) of mafic, ultramafic, silicic and alkaline melts that were emplaced into the lower continental crust (25–30 km) between 570 and 560 Ma under an extensional regime. The extensional shear zones are mm cm-scale and contain extremely fine-grained material with a distinct shape preferred orientation (SPO), but weak to absent crystallographic preferred orientation. The shear zones offset dykes across numerous micro-faults that are documented in areas close to a major fault zone cutting through the area. Within the shear zones, olivine and clinopyroxene react to form orthopyroxene and dolomite at approximately 11 kb and 850°C according to the reaction:2 Olivine + Clinopyroxene + 2 CO2 = Dolomite + 2 OrthopyroxeneThis reaction formed coronas of orthopyroxene and dolomite between olivine and clinopyroxene in the shear zones. In addition, large olivine grains proximal to the shear zones show a microfabric with subgrain walls decorated by rounded grains of dolomite and more irregular and elongated grains of orthopyroxene. Clinopyroxene grains are separated from the enstatite and dolomite by at least hundreds of microns, suggesting material transport within the shear zone. The shear zones thus provide a unique insight into the interplay between CO2-metasomatism and reaction accommodated strain softening. Carbonation-driven cracking and mineral reaction also serves to reduce grain size, making grain boundary sliding an efficient process, further enhancing the rheological contrast between the shear zone and the host rock. The sudden decrease in rock strength could lead to rapid deformation and triggered pseudotachylite formation during earthquake events in the near proximity of the micro-shear zones. Our observations match the relations between CO2 emissions and earthquakes observed in present rift environments such as the East African rift and in New Zealand, and underline the importance of active shear zones as fluid conduits in the lower crust and upper mantle.

Measuring spatio-temporal dynamics of impervious surface in Guangzhou, China, from 1988 to 2015, using time-series Landsat imagery

This study evaluated the spatio-temporal change characteristics of urban development at different scales with time-series impervious surface fractions. Landsat-5 Thematic Mapper (TM) and Landsat-8 Operational Land Imager (OLI) images were used to extract impervious surface fractions using a modified linear spectral mixture analysis method in Guangzhou from 1988 to 2015. The results indicated that the impervious surface area has substantially increased, from 70.3 km2 in 1988 to 580.5 km2 in 2015. In 2015, the impervious surfaces were distributed almost throughout the whole region of the study area, except in the forest region. Next, impervious surface weighted mean centre (ISWMC) and the standard deviational ellipse (SDE) methods were used to systematically analyse the principle orientation, direction, spatio-temporal expansion trends, and the distribution differences of impervious surfaces at the whole and local region scales from 1988 to 2015. The spatio-temporal dynamics of ISWMC exhibited different expansion directions and intensities of impervious surfaces at the whole and local region scales. On a whole region scale, the principle expansion direction of impervious surfaces was northward. However, the expansion trend of impervious surfaces in the different districts was significantly different from other trends at the local region scale. The parameters of SDE were used to investigate the orientation and the clustering or dispersion degree of impervious surface at different scales. The results from SDE analysis indicated that the impervious surfaces exhibited uncertainty in the expansion direction at the whole region scale; in contrast, they had a distinct preferred orientation and expansion direction at the local region scale. The analysis revealed that urban expansion exhibited different change characteristics in various directions at the local region scale. In summary, the results at the local region scale can better reflect the change trajectory of spatio-temporal dynamics of urban development and its fine spatial structure than at the whole region scale.

Electron Backscatter Diffraction Analysis of the Microstructure Fineness in Pure Copper Under Torsional Deformation

Torsional deformation is regarded a promising deformation procedure to prepare the gradient structural materials. Pure copper was subjected to large plastic strains in torsion. Electron backscatter diffraction analysis was used to explore the microstructure evolution. The observations demonstrate that both high-angle grain boundaries and misorientation increase with strain. The grains finer and more homogeneous. In addition, the microstructure within the shear band demonstrates a distinct preferred orientation. The crystal direction is parallel to the shear direction, and the crystal {111} inclines to the plane shear surface. A torsion-induced bar specimen includes a {011} brass texture, {011} Gaussian texture, and stronger {112} copper texture.

Grain size reduction due to fracturing and subsequent grain-size-sensitive creep in a lower crustal shear zone in the presence of a CO2-bearing fluid

To understand rheological weakening in the lower continental crust, we studied mylonites in the Paleoproterozoic Eidsfjord anorthosite, northern Norway. The zones of anorthositic mylonites range from a few millimeters to several meters thick, and include ultramylonites and protomylonites. They contain syn-kinematic metamorphic minerals, including Cl-bearing amphibole and scapolite. Thermodynamic analysis reveals that syn-deformational hydration reactions occurred at ∼600 °C and ∼700 MPa under CO2-bearing conditions. The protomylonites contain many fragmented plagioclase porphyroclasts. The fractures in porphyroclasts are filled with fine-grained plagioclase, suggesting that fracturing is a common mechanism of grain size reduction. The anorthite contents of fine-grained polygonal matrix plagioclase are different from those of porphyroclastic plagioclase, suggesting that the matrix grains nucleated and grew during syn-kinematic metamorphism. Plagioclase aggregates in the matrices of mylonites do not exhibit a distinct crystallographic preferred orientation, which implies that the dominant deformation mechanism was grain-size-sensitive creep. Consequently, in the lower crustal anorthositic mylonites, grain size reduction occurred via fracturing, rather than through dynamic recrystallization, leading to grain-size-sensitive creep. The syn-kinematic recrystallization of minor phases at plagioclase grain boundaries may suppress the growth of plagioclase and contribute to the development of grain-size-sensitive creep.

Strain localization in brittle–ductile shear zones: fluid-abundant vs. fluid-limited conditions (an example from Wyangala area, Australia)

Abstract. This study focuses on physiochemical processes occurring in a brittle–ductile shear zone at both fluid-present and fluid-limited conditions. In the studied shear zone (Wyangala, SE Australia), a coarse-grained two-feldspar–quartz–biotite granite is transformed into a medium-grained orthogneiss at the shear zone margins and a fine-grained quartz–muscovite phyllonite in the central parts. The orthogneiss displays cataclasis of feldspar and crystal-plastic deformation of quartz. Quartz accommodates most of the deformation and is extensively recrystallized, showing distinct crystallographic preferred orientation (CPO). Feldspar-to-muscovite, biotite-to-muscovite and albitization reactions occur locally at porphyroclasts' fracture surfaces and margins. However, the bulk rock composition shows very little change in respect to the wall rock composition. In contrast, in the shear zone centre quartz occurs as large, weakly deformed porphyroclasts in sizes similar to that in the wall rock, suggesting that it has undergone little deformation. Feldspars and biotite are almost completely reacted to muscovite, which is arranged in a fine-grained interconnected matrix. Muscovite-rich layers contain significant amounts of fine-grained intermixed quartz with random CPO. These domains are interpreted to have accommodated most of the strain. Bulk rock chemistry data show a significant increase in SiO2 and depletion in NaO content compared to the wall rock composition. We suggest that the high- and low-strain microstructures in the shear zone represent markedly different scenarios and cannot be interpreted as a simple sequential development with respect to strain. Instead, we propose that the microstructural and mineralogical changes in the shear zone centre arise from a local metasomatic alteration around a brittle precursor. When the weaker fine-grained microstructure is established, the further flow is controlled by transient porosity created at (i) grain boundaries in fine-grained areas deforming by grain boundary sliding (GBS) and (ii) transient dilatancy sites at porphyroclast–matrix boundaries. Here a growth of secondary quartz occurs from incoming fluid, resulting in significant changes in bulk composition and eventually rheological hardening due to the precipitation-related increase in the mode and grain size of quartz. In contrast, within the shear zone margins the amount of fluid influx and associated reactions is limited; here deformation mainly proceeds by dynamic recrystallization of the igneous quartz grains. The studied shear zone exemplifies the role of syn-deformational fluids and fluid-induced reactions on the dominance of deformation processes and subsequent contrasting rheological behaviour at micron to metre scale.

Growth of biomimetic films – influences of polymer topography and phase structure

The current work explains the influence of the polymer substrate on the topography formation of nano-wrinkled thin titanium films. Similar to the biomimetic antetype of human skin, this wrinkling phenomenon increases the elastic deformability of hard materials under tensile loading by flattening the wrinkled waves before high tensile stresses occur. Low energetic plasma deposition in direct current magnetron sputtering leads to smoother films with equiaxed domed wrinkle topography without a distinct preferred orientation on polymers (polyethylene terephthalate, polycarbonate, thermoplastic polyurethane). These domes are at least one order of magnitude larger than the commonly found topography on stiff silicon and correlates to the size of crystalline spherulites and segments in the applied semi- and pseudo-crystalline polymers. High energetic plasma deposition in pulsed laser deposition results in denser films with stretching of wrinkles. Higher intrinsic stresses require for relaxation deformation of deeper regions of the polymer below the surface. Because the width of these sinusoidal wrinkles is quite similar to sputtered films and the preferred stretching orientation correlates to the main direction of the polymer chains, the change in the wrinkle shape can only be explained by stress relaxation due to mechanical anisotropy by extrusion-based manufacturing.

Membrane-Dependent Modulation of the mTOR Activator Rheb: NMR Observations of a GTPase Tethered to a Lipid-Bilayer Nanodisc

Like most Ras superfamily proteins, the GTPase domain of Ras homologue enriched in brain (Rheb) is tethered to cellular membranes through a prenylated cysteine in a flexible C-terminal region; however, little is known about how Rheb or other GTPases interact with the membrane or how this environment may affect their GTPase functions. We used NMR methods to characterize Rheb tethered to nanodiscs, monodisperse protein-encapsulated lipid bilayers with a diameter of 10 nm. Membrane conjugation markedly reduced the rate of intrinsic nucleotide exchange, while GTP hydrolysis was unchanged. NMR measurements revealed that the GTPase domain interacts transiently with the surface of the bilayer in two distinct preferred orientations, which are determined by the bound nucleotide. We propose models of membrane-dependent signal regulation by Rheb that shed light on previously unexplained in vivo properties of this GTPase. The study presented provides a general approach for direct experimental investigation of membrane-dependent properties of other Ras-superfamily GTPases.

Growth of vanadium dioxide thin films on Pt metal film and the electrically-driven metal–insulator transition characteristics of them

High-quality VO2 thin films are deposited on the metal platinum (Pt) electrode buffered by silicon dioxide (SiO2) using radio frequency magnetron sputtering. The effect of the thickness of SiO2 on the the crystal structure, morphology and metal-insulator transition (MIT) performance of the films are discussed. Results show that SiO2 buffer layer with a thickness of 0.2 μm can effectively eliminate huge stress between the VO2 film and the metal film; and the VO2 thin film with the distinct MIT are deposited. When the buffer layer reaches more than 0.7 μm, the VO2 film has a distinct (011) preferred orientation, the smooth surface and compact nanostructure, and the resistance change reaches more than three orders of magnitude. At the same time, Pt-SiO2/VO2-Au sandwiched structure is achieved to test the current versus voltage curves, in which can be seen several distinct steps of current caused by the voltage perpendicular to the plane of a VO2 film. The result confirms the electrically-driven metal-insulator transition. Due to the high-quality VO2 and the flexible device structure, the VO2/Pt-SiO2 can be widely used for large-scale integrated electronic control devices.

Elastic stiffness of single-crystalline FeSe measured by picosecond ultrasonics

We report investigations on the elasticity of superconducting FeSe using picosecond ultrasonic technique. The tetragonal (001) FeSe thin film, deposited on a processed SrTiO3 substrate by the pulsed laser deposition, exhibits distinct c-axis preferred orientation and single-crystalline features as a result of the x-ray diffraction. The high-quality crystallinity thus enables quantitative examinations of anisotropic stiffness coefficients (C33) of FeSe, correlating to the interatomic interaction in the simplest iron-based superconductor. Our experiment indicates a room-temperature C33 of 40.9 ± 0.4 GPa and material stiffening of 4.3% at low temperatures, which can be explained by the weakening of anharmonic phonon–phonon interactions.

L1 FePt nanoparticles with distinct perpendicular magnetic anisotropy prepared on Au buffer layers by a micellar method

FePt nanoparticles were self-assembled on a MgO (001) substrate by a micellar method. We introduced an Au buffer layer to control the lattice orientation and the magnetic alignment of FePt nanoparticles. A distinct c-axis preferred orientation of the FePt nanoparticles was achieved during the thermal annealing treatment. The driving force of lattice reorientation is considered to be the result of the stress caused by the lattice misfit between Au and FePt. The degree of c-axis orientation is significantly enhanced with increasing Au thickness, which is attributed to the decrease of the in-plane lattice and the improved crystal quality of the Au layer. Perpendicular magnetic anisotropy was observed for the FePt samples with the Au buffer layer. The out-of-plane coercivity and remanence ratio are 3.1 kOe and 0.8, respectively, which far exceed the in-plane values.

Amphibole and lower crustal seismic properties

Measurements of seismic anisotropy frequently offer insights of the deformation kinematics in-situ within the Earth. In the continental crust, seismic anisotropy is commonly ascribed to regionally aligned lattice preferred orientation (LPO) of mica crystals. However, determinations of composition suggest that the deep continental crust contains rather little mica. In this contribution, the role of amphibole, a far more plausible constituent, especially for deep continental crust of basic composition, is assessed. A field analogue approach is adopted, where the LPO are measured, correlated with the strain state of the rocks, and used to calculate the seismic properties. The seismic properties may be up-scaled through the specimen using the modal proportions of the constituent mineral phases. To examine the role of composition in controlling the intensity of seismic anisotropy, seismic properties are computed using an array of modal compositions (so-called ‘rock recipes’). The case history comes from the Central Block of the Lewisian of NW Scotland, where a regional basic dyke swarm (the Scourie dykes) is locally deformed within amphibolite facies shear zones, conditions that are representative of the deep crust. Shear strain (γ) profiles across a 100 m wide shear zone, using deflected banding in the host gneisses, yield values of 0<γ<15 or greater. A Scourie dyke deflected into the shear zone exhibits hornblende with distinct preferred dimensional orientations representative of such strains. In contrast, plagioclase (and quartz) clots are almost totally insensitive to deformation (due to grain-size sensitive creep deformation) and yield approximately constant apparent strains of γ=1–2. Hornblende–plagioclase–quartz LPOs, combined in their modal proportions and modulated by their individual single-crystal elastic properties, define the seismic properties of the shear zone. Rock recipe modelling demonstrates that it is the hornblende that dominates the seismic response and that plagioclase and quartz serve simply to dilute the intensity of anisotropy. The values calculated indicate significant (up to ~13%) seismic anisotropy for strongly sheared amphibolites. Thus amphibole, aligned through deformation, is likely be a major contributor to the seismic anisotropy of the deep continental crust.

Electrostatic Contributions to Indole−Lipid Interactions

The role of electrostatic forces in indole-lipid interactions was studied by (1)H and (2)H NMR in ether- and ester-linked phospholipid bilayers with incorporated indole. Indole-ring-current-induced (1)H NMR chemical shifts of lipid resonances in bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, 1,2-dioleoyl-sn-glycero-3-phosphocholine, 1,2-di-O-octadecenyl-sn-glycero-3-phosphocholine, and 1,2-di-O-octadecenyl-sn-glycero-3-phosphomethanol show a bimodal indole distribution, with indole residing at the upper hydrocarbon chain/glycerol region of the lipid and near the choline group, when present. (2)H NMR of indole-d(7)-incorporated lipid bilayers reveals that the former site is occupied by about two-thirds of the indole, which adopts a distinct preferred orientation with respect to the bilayer normal. The results suggest that the upper hydrocarbon chain/glycerol location is dictated by many factors, including interactions with the electric charges and dipoles, van der Waals interactions, entropic contributions, and hydrogen bonding. Indole diffusion rates are higher in lipids with ester bonds and lower in choline-containing lipids, suggesting that interactions between indole and carbonyl groups are of minor importance for lipid-indole association and that cation-pi interactions with choline drive the second indole location. Nuclear Overhauser effect spectroscopy cross-relaxation rates suggest a 30-ns lifetime for indole-lipid associations. These results may have important implications for sidedness and structural transitions in tryptophan-rich membrane proteins.

Direct observation and measurement of fiber architecture in short fiber-polymer composite foam through micro-CT imaging

A non-destructive X-ray imaging technique was used to determine internal structure in a polymer foam reinforced with short fibers. The technique, known as micro-CT (for computerized tomography), was used to measure the fiber length distribution (FLD) and fiber orientation distribution (FOD), two parameters that are critical to the behavior of short-fiber-reinforced composites. Phenolic foam reinforced with short glass fibers was used as an exemplar to demonstrate the potential of this technique, exploiting the large difference in density between the two components. Direct 2D and 3D images were generated in which individual fibers were clearly resolved, along with portions of the foam structure. The images were analyzed using computer software to obtain quantitative FLD and FOD data. A distinct preferred orientation of fibers was revealed that was attributed to shear flow during foam expansion. For quantitative analysis of microstructure in short fiber composites, the micro-CT technique affords numerous advantages over the conventional approach of parallel dissection followed by image analysis of polished surfaces, and may be useful for determining FLD and FOD in polymer composites with dense matrices.