Schlieren Structures Research Articles

Physically based simulation of focusing schlieren imaging for a hypersonic boundary layer flow.

Focusing schlieren systems are more advantageous than conventional schlieren systems in providing a schlieren image with certain spatial discrimination along the light path. The present work employed a hybrid of the optical-transfer matrix and ray-tracing method to faithfully replicate complete physical imaging processes throughout a focusing schlieren optic system. A direct numerical simulation of a hypersonic boundary layer flow was employed to synthesize focusing schlieren images. The influence of various configuration parameters on the properties of focusing schlieren image such as local schlieren structure, brightness, sensitivity, and depth of field were systematically explored. In addition, an approximation method was proposed as a simplified means to facilitate the simulation of a focusing schlieren image.

Investigation of flow characteristics in a twin-surface dielectric barrier discharge reactor by Schlieren imaging

Dielectric barrier discharges are an emerging technology for the plasma-catalytic removal of volatile organic compounds and other gas purification challenges such as the removal of O2 traces from H2. Packed-bed reactors are mainly used for these applications, but surface dielectric barrier discharges (SDBDs) typically printed on thin dielectric plates are promising alternatives for the treatment of large volumetric flow rates due to their low flow resistance causing a low pressure drop. Especially for SDBDs the flow conditions are crucial, because the active plasma filled volume covering the mentioned plates with a typical thickness of 0.1 mm is small in comparison to the overall reactor volume with a typical distance of some tens of millimeters to the reactor wall. In this study, the flow conditions of a twin-SDBD were investigated by Schlieren imaging applied in converting O2 traces in H2 containing gas mixtures to H2O and compared to fluid dynamics simulations. Schlieren imaging was used to visualize local gradients of the refractive index inside the SDBD reaction chamber, while gas composition, dissipated power, or flow rate were varied. Without a plasma discharge, laminar flow dominates, resulting in a conversion below 10% over a Pt-coated electrode configuration in the reaction of O2 traces with H2. With the plasma discharge, full conversion was achieved for the same reaction without catalyst, although the plasma is also confined to the surface of the electrode configuration. Schlieren structures covering the complete cross section of the reaction chamber were observed, showing that strong radial mass transport is induced by the plasma. The shape and extent of the Schlieren structures is ascribed to a superimposition of gas flow, thermal expansion from the plasma volume, thermal buoyancy as well as an electrohydrodynamic force between the electrodes and the grounded reactor walls. Fluid dynamics simulations show vortex formation above and below the electrode, created by the electrohydrodynamic force further implying extensive mass transport by the plasma, which is visualized in addition by carbonaceous deposits on the reactor lid. This emerging deposition pattern during toluene decomposition closely corresponds to the electrode geometry. It is proposed that the reaction proceeds only in the active plasma volume and that reactive species transported to the bulk gas phase only have a minor contribution. Thus, the degree of conversion of the SDBD reactor is not only determined by the chemical reactivity in the plasma volume, but also by its plasma-induced mass transport resulting in efficient gas mixing. These findings reveal new possibilities to improve SDBD reactors for gas purification applications based on their favorable flow conditions.

Liquid Crystalline Behaviors of Single-Walled Carbon Nanotubes in an Aqueous Sodium Cholate Dispersion.

Controlling the alignment of single-walled carbon nanotubes (SWCNTs) on the macroscopic scale is critical for practical applications because SWCNTs are extremely anisotropic materials. One efficient technique is to create an effective SWCNT dispersion, which shows a liquid crystal (LC) phase. A strong acid treatment can realize SWCNT liquid crystalline dispersions. However, strong acids pose a substantial safety risk, which renders the process unfit for mass production. Herein, an isolated SWCNT dispersion displaying an LC behavior is prepared using sodium cholate without an acid treatment, and its phase transition behaviors are systematically investigated across the isotropic to biphasic to nematic phases. As the SWCNT concentration increases, the dispersion undergoes an isotropic-to-nematic phase transition in which the spindle-shaped LC droplets, or the so-called tactoids, and the Schlieren textures can be observed in the intermediate biphasic state and the nematic phase, respectively. The arrangements of SWCNTs in the tactoids and the Schlieren structures are directly investigated by polarized optical microscopy. The clear LC behaviors of the CNT dispersion suggest that the CNT orientations can be controlled by the normal surfactant-assisted method, which is a crucial advantage for the liquid-phase processing of CNT fibers and films.

Deformation characteristics of the high-grade metamorphic and anatectic rocks in the Daqingshan Paleoproterozoic orogenic belt, Inner Mongolia: A case study from the Shijiaqu-Xuehaigou area

The high-grade granulite-phase metamorphic and anatectic rocks are widespread in the Daqingshan area, which is an archetypical of the Early Paleoproterozoic Orogenic Belt (POB) in the North China Carton (NCC), providing an ideal object to delineate the rheology of partially molten lower crust. The multiple approaches of SEM-EBSD fabric analysis, electron probe microanalyses (EPMA) and LA-ICP-MS zircon U-Pb geochronology have been carried out on the metamorphic and anatectic rocks from the Shijiaqu-Xuehaigou area in the Daqingshan. The results of zircon U-Pb dating show that the anatexis process in the POB took place more or less prior to ca. 1920 Ma, subsequently, the main plastic deformation event occurred at ca. 1915–1870 Ma. The macro- and microscopic structures suggest that the Xuehaigou and Shijiaqu areas show the characteristics of the diatexite and metatexite zones, respectively. In the diatexite zone, appearance of abundant melts tends to form schollen and schlieren structures in the high-grade metamorphic and anatectic rocks. The deformation mechanism of plagioclase is mainly represented by diffusion creep and particle flow. In contrast, in the metatexite zone, the deformation pattern is represented by stromatic structure with light-colored bands paralleling to the main gneissosity, and the deformation mechanism of plagioclase is characterized by dislocation creep. Besides, the deformation mechanism of amphibole in the lower crustal rocks from both zones is mostly dominated by dislocation creep. Significantly, the presence of melts in the high-grade metamorphic and anatectic rocks probably weaken their strength, and may have aided to form the sub-horizontal channel, contributing significantly to the subsequent exhumation of the lower crustal rocks in the orogenic belt.

Analysis of light emission and Schlieren from short gap high voltage streamers representing lightning impulses

Light emissions and Schlieren structures were simultaneously observed from streamers produced by tens of kilovolts 1.2/50 μs impulses, representing the high voltage component of lightning, applied across a 4 cm air gap between a variety of electrode geometries and a ground plane in an unconfined environment. The results demonstrated that the light emissions and Schlieren structures coincide along the same streamer filaments but on different timescales; the light existing only during the microsecond timeframe impulse whereas the Schlieren continued to develop into the millisecond timeframe, moving towards the centre of the air gap whilst diffusing into the surrounding air within 100 ms. If an electrical breakdown did occur, the Schlieren structures outside the arc remained visible. Streamer formation theory for high voltage impulses is subsequently refined to include the observed Schlieren mechanism.

Multiple Projection Laser Microscopy in the Ulbricht Integrating Sphere (MPLM-UIS) using lens-less microscopes with CCD and CMOS (active-pixel) sensors, including angle sensitive ones.

Microscopy with an integrating sphere (also known as the photometric Ulbricht sphere) is rarely used in histological and cytological practice due to the difficulties in manufacturing the integrating chamber with the technological holes for the sample placing, as well as the high cost of the modern commercially available Ulbricht spheres. The additional difficulties appear at the ultrastructural / submicroscopic level, especially when using near-field optical microscopy (SNOM) techniques determining the size of the integrating sphere. The required correspondence between the radius of the integrating sphere and the size of the specific sample / sample stage results in a physical and technical contradiction, which in principle can be overcome only if a number of conditions are met. The first and obvious one is the equal dimensions of the transmission window of the sample stage and the sample itself. The final condition is obtaining a wide-field image at the stationary position of the stage, since its displacement inside the integrating sphere will lead to the changes in the light-shadow (schlieren) structure of the registrogram. The same is true for the movement of the coordinate stage or a slide / sample itself, but for the sample in vivo / in situ perturbations of the optical field of the isotropic-integrating sphere can be used as an analytical signal. In a general case, when all the above planes and sections are located at the stationary position at the center of the Ulbricht sphere, the only possible solution is to use CCD / CMOS sensors with a simple printed circuit board, which act as an analytical chip with a function of a lensless projection microscope instead of the reduced conventional optical microscope.

Analysis of shock metamorphic processes in the Zagami meteorite

The study of shock-metamorphic features of the Zagami meteorite revealed pseudotachylite-like melt veins with inhomogeneous chemistry and schlieren structure of silica-glass and alkali feldspar melt glass. The feldspar occurs as diaplectic glass in the interstitial area indicating short-time (few seconds) quenching of shock pressure during the impact event, with post-shock annealing. At several locations, apatite needles were identified, which are formed by fluids (cold water with dissolved ions) after the crystallization of cumulate magmatic minerals. Phosphates also could form in impact melts due to circulation of fluids after the impact event. The other signature for the high shock temperature is the presence of Ca–Ti-rich pyroxenes and titanomagnetite, which indicate temperature above 1,200 °C. The formation of silica-rich melt in interstitial area has two scenarios: (a) fractional melting of the Martian crust or (b) formation by pseudotachylite-like impact melting. According to textural observations (schlieren pattern), we propose an impact origin of the large amount of silica-rich melt in this meteorite. Pseudotachylite-like textures were mentioned earlier in terrestrial impact craters; however, we first propose them to form in a Martian meteorite based on their similarity of texture with terrestrial pseudotachylites.

New insights on petrography and geochemistry of impactites from the Lonar crater, India

AbstractThe Lonar impact crater, India, is one of the few known terrestrial impact craters excavated in continental basaltic target rocks (Deccan Traps, ~65 Ma). The impactites reported from the crater to date mainly include centimeter‐ to decimeter‐sized impact‐melt bombs, and aerodynamically shaped millimeter‐ and submillimeter‐sized impact spherules. They occur in situ within the ejecta around the crater rim and show schlieren structure. In contrast, non–in situ glassy objects, loosely strewn around the crater lake and in the ejecta around the crater rim do not show any schlieren structure. These non–in situ fragments appear to be similar to ancient bricks from the Daityasudan temple in the Lonar village. Synthesis of existing and new major and trace element data on the Lonar impact spherules show that (1) the target Lonar basalts incorporated into the spherules had undergone minimal preimpact alteration. Also, the paleosol layer as preserved between the top‐most target basalt flow and the ejecta blanket, even after the impact, was not a source component for the Lonar impactites, (2) the Archean basement below the Deccan traps were unlikely to have contributed material to the impactite parental melts, and (3) the impactor asteroid components (Cr, Co, Ni) were concentrated only within the submillimeter‐sized spherules. Two component mixing calculations using major oxides and Cr, Co, and Ni suggest that the Lonar impactor was a EH‐type chondrite with the submillimeter‐sized spherules containing ~6 wt% impactor components.

Energy transfer mechanism of supersonic jet noise through rectangular nozzles

A series of experiments were conducted with nozzle pressure ratios (NPRs) from 2.2 to 8.0 to explore energy transfer mechanisms of under-expanded supersonic jet noise through rectangular nozzles. The results from these experiments resulted in the discovery of a fundamental-frequency-moving phenomenon. The fundamental frequencies were extracted from sound pressure signals for different nozzles, and then by switching modes, energy flows and flow fields' Schlieren structures were compared and analyzed. As a result, two key structural parameters, cross section area and aspect ratio (AR) of the exit, were found to have a contributing effect in jet noise. Single screech tone and the turbulent mixing noise switched, dominated and then disappeared when jet pressure was varied. Besides that, the AR has a more significant effect on the screech tone than another parameter according to the analysis results. Specifically, for AR4 nozzle with cross-section area 20 by 5 mm2, an interesting phenomenon was noticed. As jet pressure decreased after the switching of modes energy moved from the high-frequency tone screech to the low-frequency turbulent noise, and finally gathered in a lower-frequency region, the so called fundamental-frequency-moving phenomenon. Explanations for this fundamental-frequency-moving phenomenon were given based on Powell's acoustic feedback theory and Tam's weakest link theory, as well as analysis on spectra by Schlieren photos.

Experimental study on screech tone mode switching of supersonic jet flowing through rectangular nozzles

An experiment was carried out to analyse and compare the screech tone characteristics and schlieren structures of an under-expanded jet flowing through four rectangular nozzles, aspect ratios of which are different (having the same height but different widths), with the jet pressure ranging from 0.2 to 0.8 MPa. Results indicate that there exist two different screech tone modes in the noise generated by supersonic jet flowing through the rectangular nozzles with different aspect ratios, and a mode switching can be found by altering the jet pressure. Mode switching is a phenomenon that different mode dominates or disappears according to the change of jet pressure. The switching time of fundamental frequencies in the screech tone modes and the width of the domination interval would be shortened as the aspect ratio decreases. The jet flow pressure drop interval of one mode, whose aspect ratio is 2, is extremely small. This phenomenon has never been mentioned in the literature. When the aspect ratio of the rectangular nozzle is 4, there exists an interruption and skip on the fundamental frequency-jet pressure curve within the jet flow domination interval for jet pressure at 0.49 MPa. As the pressure reduces, the axes of the schlieren figures begin to shake, and the structure stability of the flow field with different aspect ratio varies with the jet pressure. When the jet pressure is within the range of 0.45 to 0.70 MPa, the density in the first shock-cell decreases as the aspect ratio reduces. Meanwhile, axial pulsation and disorder of the flow field behind the second shock-cell appear. When the jet pressure is under 0.45 MPa, the flow field structure of the shock wave becomes more stable as the aspect ratio increases. In this pressure region, the periodical shock-cell structure is weaker than those above 0.45 MPa. Analyzing the screech frequency spectrum and the schlieren figures, we can find that the second and third shock-cells also have feedback and enhancement for the sound pressure of the screech frequency.

Contrasting Aerodynamic Morphology and Geochemistry of Impact Spherules from Lonar Crater, India: Some Insights into Their Cooling History

The ~50 or 570 ka old Lonar crater, India, was excavated in the Deccan Trap flood basalt of Cretaceous age by the impact of a chondritic asteroid. The impact-spherules known from within the ejecta around this crater are of three types namely aerodynamically shaped sub-mm and mm size spherules, and a sub-mm sized variety of spherule, described as mantled lapilli, having a core consisting of ash-sized grains, shocked basalt and solidified melts surrounded by a rim of ash-sized materials. Although, information is now available on the bulk composition of the sub-mm sized spherules (Misra et al. in Meteorit Planet Sci 7:1001–1018, 2009), almost no idea exists on the latter two varieties. Here, we presented the microprobe data on major oxides and a few trace elements (e.g. Cr, Ni, Cu, Zn) of mm-sized impact spherules in unravelling their petrogenetic evolution. The mm-sized spherules are characterised by homogeneous glassy interior with vesicular margin in contrast to an overall smooth and glassy-texture of the sub-mm sized spherules. Undigested micro-xenocrysts of mainly plagioclase, magnetite and rare clinopyroxene of the target basalt are present only at the marginal parts of the mm-sized spherules. The minor relative enrichment of SiO2 (~3.5 wt% in average) and absence of schlieren structure in these spherules suggest relatively high viscosity of the parent melt droplets of these spherules in comparison to their sub-mm sized counterpart. Chemically homogeneous mm-sized spherule and impact-melt bomb share similar bulk chemical and trace element compositions and show no enrichment in impactor components. The general depletion of Na2O within all the Lonar impactites was resulted due to impact-induced volatilisation effect, and it indicates the solidification temperature of the Lonar impactites close to 1,100 °C. The systematic geochemical variation within the mm-sized spherules (Mg# ~0.38–0.43) could be attributed to various level of mixing between plagioclase-dominated impact melts and ultrafine pyroxene and/or titanomagnetite produced from the target basalt due to impact. Predominance of schlieren and impactor components (mainly Cr, Ni), and nearly absence of vesicles in the sub-mm sized spherules plausibly suggest that these quenched liquid droplets could have produced from the impactor-rich, hotter (~1,100 °C or more) central part of the plume, whereas the morpho-chemistry of the mm-sized spherules induces their formation from the relatively cool outer part of the same impact plume.

Mineral chemistry of banded migmatites from Hafafit and Feiran areas, Egypt

The migmatitic rocks exposed in Hafafit and Feiran areas exhibit some migmatitic structures as the banded, agmatic, boudinage and schlieren structures. The dominant type of these structures is the stromatic migmatites. Electron microprobe analyses of plagioclases, biotites and amphiboles from Hafafit and Feiran areas, in the Eastern Desert and Sinai, Egypt, are carried out and the metamorphic conditions are discussed. The present study revealed marked differences in the composition of plagioclases, biotites and amphiboles from Hafafit and Feiran localities. The obtained data indicated that plagioclases of the Feiran migmatites are of andesine and oligoclase composition, and display anorthite content from An20 to An38; whereas the Hafafit migmatites show a wider range of plagioclases from An10 to An60, and therefore plagioclases have labradorite, andesine and oligoclase composition. This may be due to the slow rate of the crystallisation processes. The analyses indicated that biotites of the studied areas are of metamorphic origin showing significant variation in Fe–Mg. It is worth mentioning that biotites from Hafafit migmatites have Mg–biotite composition while that of Feiram migmatites have Fe–biotite composition. High Mg and low Fe contents in biotite suggest higher crystallisation temperature. The composition of amphiboles in Hafafit migmatites is ferro-tschermakitic hornblende, while amphiboles from Feiram migmatites are magnesio-hornblende. High Ti content in the hornblende of Feiran migmatites suggests that they were formed at slightly higher temperatures and lower pressure than the Hafafit migmatites (i.e. Feiram migmatites and Hafafit migmatites were formed at granulite and amphibolite facies, respectively). Discrimination diagrams show that the muscovite is of secondary origin. Moreover, the present study confirmed that these migmatites are mainly formed by metamorphic differentiation via partial melting.

Tube-like schlieren structures in the Fürstenstein Intrusive Complex (Bavarian Forest, Germany): Evidence for melt segregation and magma flow at intraplutonic contacts

Tube-like schlieren structures occur at the boundary between two units of the Fürstenstein Intrusive Complex, the Tittling and the Saldenburg granites. We have analysed the magnetic fabrics, petrographic variation and geochemistry of key examples of these structures in order to test the hypothesis that they originated as granitic microdiapirs. The rims of the schlieren structures have high magnetic susceptibility compared to their interiors and surrounding granite due to the enrichment of biotite ± opaques. The low anisotropy that characterizes the AMS fabric is probably caused by magmatic flow. Hypersolidus microfabrics support this interpretation. Magnetic fabric orientation within the schlieren structures differs significantly from the NE–SW-trending magnetic foliation generally observed within the hosting Tittling granite. A steeply plunging magnetic lineation and a NNE–SSW girdle distribution of the magnetic foliation poles within the schlieren structures are consistent with the conical geometry of the schlieren structures evolved during the rise of the magma. Based on geochemistry, granite in the schlieren structures is interpreted to be differentiated melt expelled from the Tittling granite mush that formed after early crystallization of plagioclase. We suggest that the schlieren structures are pockets of residual melt of the Tittling granite that were mobilized buoyantly due to a thermal input from the neighbouring Saldenburg granite. The mafic rims of the schlieren structures formed as a result of early crystallization and subsequent accumulation due of the Bagnold effect. The results of the magnetic and geochemical investigations allow us to interpret the schlieren structures as diapiric in nature and consequently as “within-chamber diapirs” (sensu Weinberg et al., 2001).

Geochemical identification of impactor for Lonar crater, India

Abstract— The only well‐known terrestrial analogue of impact craters in basaltic crusts of the rocky planets is the Lonar crater, India. For the first time, evidence of the impactor that formed the crater has been identified within the impact spherules, which are ?0.3 to 1 mm in size and of different aerodynamic shapes including spheres, teardrops, cylinders, dumbbells and spindles. They were found in ejecta on the rim of the crater. The spherules have high magnetic susceptibility (from 0.31 to 0.02 SI‐mass) and natural remanent magnetization (NRM) intensity. Both NRM and saturation isothermal remanent magnetization (SIRM) intensity are ?2 Am2/Kg. Demagnetization response by the NRM suggests a complicated history of remanence acquisition. The spherules show schlieren structure described by chains of tiny dendritic and octahedral‐shaped magnetite crystals indicating their quenching from liquid droplets. Microprobe analyses show that, relative to the target basalt compositions, the spherules have relatively high average Fe2O3 (by ?1.5 wt%), MgO (?1 wt%), Mn (?200 ppm), Cr (?200 ppm), Co (?50 ppm), Ni (?1000 ppm) and Zn (?70 ppm), and low Na2O (?1 wt%) and P2O5 (?0.2 wt%). Very high Ni contents, up to 14 times the average content of Lonar basalt, require the presence of a meteoritic component in these spherules. We interpret the high Ni, Cr, and Co abundances in these spherules to indicate that the impactor of the Lonar crater was a chondrite, which is present in abundances of 12 to 20 percent by weight in these impact spherules. Relatively high Zn yet low Na2O and P2O5 contents of these spherules indicate exchange of volatiles between the quenching spherule droplets and the impact plume.

Global Significance of a Sub-Moho Boundary Layer (SMBL) Deduced from High-Resolution Seismic Observations

We infer the fine structure of a sub-Moho boundary layer (SMBL) at the top of the lithospheric mantle from high-resolution seismic observations of Peaceful Nuclear Explosions (PNE) on superlong-range profiles in Russia. Densely recorded seismograms permit recognition of previously unknown features of teleseismic propagation of the well known Pn and Sn phases, such as a band of incoherent, scattered, high-frequency seismic energy, developing consistently from station to station, apparent velocities of sub-Moho material, and high-frequency energy to distances of more than 3000 km with a coda band, incoherent at 10 km spacing and yet consistently observed to the end of the profiles. Estimates of the other key elements of the SMBL were obtained by finite difference calculations of wave propagation in elastic 2D models from a systematic grid search through parameter space. The SMBL consists of randomly distributed, mild velocity fluctuations of 2% or schlieren of high aspect ratios (≥40) with long horizontal extent (~20 km) and therefore as thin as 0.5 km only; SMBL thickness is 60-100 km. It is suggested that the SMBL is of global significance as the physical base of the platewide observed high-frequency phases Pn and Sn. It is shown that wave propagation in the SMBL waveguide is insensitive to the background velocity distribution on which its schlieren are superimposed. This explains why the Pn and Sn phases traverse geological provinces of various age, heat flow, crustal thickness, and tectonic regimes. Their propagation appears to be independent of age, temperature, pressure, and stress. Dynamic stretching of mantle material during subduction or flow, possibly combined with chemical differentiation have to be considered as scale-forming processes in the upper mantle. However, it is difficult to distinguish with the present sets of Pn/Sn array data whether (and also where) the boundary layer is a frozen-in feature of paleo-processes or whether it is a response to an on-going processes; nevertheless, the derived quantitative estimates of the SMBL properties provide important constraints for any hypothesis on scale-forming processes. Models to be tested by future numerical and field experiments are, for example, repeated subduction-convection stretching of oceanic lithosphere (marble-cake model) and schlieren formation at mid-ocean ridges. It is also proposed that the modeling of the observed blocking of Sn and Pn propagation at active plate margins offers a new tool to study the depth range of tectonics below the crust-mantle boundary. Finally, the deduced schlieren structure of the SMBL closes an important scale gap of three to four orders of magnitude between structural dimensions studied in petrological analysis of mantle samples (xenoliths or outcrop of oceanic lithosphere) and those imaged in classical seismological studies of the lithosphere.

The influences of composition-sand temperature-dependent rheology in thermal-chemical convection on entrainment of the D″-layer

The entrainment dynamics in the D″-layer are influenced by multitudinous factors, such as thermal and compositional buoyancy, and temperature- and composition-dependent viscosity. Here, we are focusing on the effect of compositionally dependent viscosity on the mixing dynamics of the D″-layer, arising from the less viscous but denser D″-material. The marker method, with one million markers, is used for portraying the fine scale features of the compositional components, D″-layer and lower-mantle. The D″-layer has a higher density but a lower viscosity than the ambient lower-mantle, as suggested by melting point systematics. Results from a two-dimensional finite-difference numerical model including the extended Boussinesq approximation with dissipation number Di=0.3, show that a D″-layer, less viscous than the ambient mantle by 1.5 orders of magnitude, cannot efficiently mix with the lower-mantle, even though the buoyancy parameter is as low as R ρ =0.6. However, very small-scale schlieren structures of D″-layer material are entrained into the lower-mantle. These small-scale lower-mantle heterogeneities have been imaged with one-dimensional wavelets in order to delineate quantitatively the multiscale features. They may offer an explanation for small-scale seismic heterogeneity inferred by seismic scattering in the lower-mantle.

Deformed A-type granites in northern Malawi, east-central Africa: pre- or syntectonic?

Metamorphosed and deformed A-type granites ranging in age from 1087 to 1119 Ma occur in strike-slip and reverse-slip shear zones of the Ubendian and Irumide belts of northern Malawi. Peak metamorphic conditions in the granites and their wallrocks reached about 12–13 kbar and 680–740°C. Microstructures reveal that the granites experienced a seemingly progressive deformation from magmatic to solid state. Magmatic deformation is manifested by the coexistence of aligned magmatic potassium feldspar, plagioclase, amphibole, biotite and ilmenite with undeformed quartz and schlieren structures. High-temperature solid-state deformation is characterized by widespread grain-boundary migration, dynamic recrystallization and myrmekitic potassium feldspar replacement. The tectonic foliation is generally subparallel to the magmatic foliation in the granites and also subparallel to the borders of the plutons and to the foliation in the wallrock. Kinematic indicators in both granite and wallrock reveal sinistral movement in the Ubendian-belt shear zones and top-to-the-ESE thrusting in the Irumide-belt shear zones. The overall parallelism of magmatic and tectonic foliations would suggest syntectonic emplacement of the granites with respect to a c. 1100 Ma Irumide orogeny. However, similar deformation patterns of granite-related dykes and some Pan-African pegmatites and geochronologic work suggests that the first deformation of the granites, their related dykes and some of the pegmatites occurred during the Pan-African orogeny. This study implies that a purely structural approach to distinguish syn- and pretectonic granites is rendered difficult when post-emplacement deformation occurred under high-grade metamorphic conditions. Strongly heterogeneous deformation with a pronounced degree of coaxial flattening in the granites allows magmatic structures to be preserved in low-strain zones and to be passively rotated into parallelism with penetrative deformation structures. Our work also implies that there was no Irumide orogen in northern Malawi.

Photoconductive property in the lyotropic liquid crystalline cell composed of hole transport molecules pendant poly(glutamate)

Hole transport molecules pendant polypeptide was synthesized in order to investigate the photoconductive property in the lyotoropic liquid crystalline polypeptide. By the application of an electric field to the liquid crystalline cell, the schlieren structure indicating the nematic structure was observed in the cell by using a polarized optical micrograph. Relatively high drift mobility of ca. 10 −3 (cm 2/V·s) and photoconductivity were obtained in the nematic liquid crystalline cell. Consequently, we conclude that highly ordered intra and interchain structure is effective for the photoconductive and charge carrier transport properties.

Geochemistry and origin of tektites from the Penglei area, Hainan province, southern China

Ten tektites from the Penglei area in Hainan province were analyzed for the abundances of major elements, 31 trace elements, and the RbSr isotopic composition. These tektites can be divided into two compositional categories, which are distinguished by high (> 80 wt %) and low (<76 wt %) SiO 2 contents. Tektite TK-1 (high SiO 2) shows a vesicular massive body and has lower refractive index, density, major and trace elements. Its chemical composition closely resembles the average composition of Muong Nong-type indochinites. The others with low SiO 2 either pitted or grooved surfaces, with schlieren structures on some surfaces, and splash-form have similar chemical compositions to those of indochinites. From the chemical composition, it is suggested that the tektites within the Indochina and the Hainan subfields are derived from similar parental material and are similar to the post-Archean upper crustal rocks. In addition, the tektites from Hainan (Hainanites) have large positive ϵ Sr(0) ratios, indicating that the parent material for these tektites resembles old terrestrial sedimentary rocks. From the Sr isotopic data, it is interpreted that the hainanites do not originate from continental material recently derived from the mantle or recent young sediments such as soil or loess. Based on RbSr isotopic data, it has been suggested by Blum et al. Geochim. Cosmochim. Acta 56, 483–492, 1992 that the depositional age of sedimentary target materials is close to 170 Ma (Jurassic). Mixing calculations for various amounts and combinations of target rocks indicate that the best fit for sample TK-1 tektite is a mixture of 2% shale, 38% sandstone, 50% greywacke and 10% quartzite, and the other splash-form tektite is a mixture of 41% shale, 2% sandstone, 20% greywacke and 37% quartzite.

Stars, stripes and shells in monolayers: simulation of the molecular arrangement in Schlieren structures

Recent publications have reported on shell, star and stripe textures in monolayer films of long-chain fatty acids and esters at the air-water interface, observed with polarized fluorescence and Brewster angle microscopy (BAM). The difference in the brightness of the domains is related to a difference of the azimuthal tilt of the hydrocarbon chains of the molecules. We present model calculations concerning the various textures, observed by BAM using the 4 × 4 matrix algorithm of Berreman, J. Opt. Soc. Am., 62 (1972) 502–510. The calculations show that all observed textures are of splay type, with an azimuthal orientation directed to the inside of the shell or stripe in the case of a fatty acid and to the outside in the case of stars in methyl ester monolayers.