Typical Grains Research Articles

Numerical simulation of the pulsing air separation field based on CFD

The flow field of pulsing air separation is normally in an unsteady turbulence state. With the application of the basic principles of multiphase turbulent flows, we established the dynamical computational model, which shows a remarkable variation of the unstable pulsing air flow field. CFD (computational fluid dynamics) was used to conduct the numerical simulation of the actual geometric model of the classifier. The inside velocity of the flowing fields was analyzed later. The simulation results indicate that the designed structure of the active pulsing air classifier provided a favorable environment for the separation of the particles with different physical characters by density. We shot the movement behaviors of the typical tracer grains in the active pulsing flow field using a high speed dynamic camera. The displacement and velocity curves of the particles in the continuous impulse periods were then analyzed. The experimental results indicate that the effective separation by density of the particles with the same settling velocity and different ranges of the density and particle size can be achieved in the active pulsing airflow field. The experimental results provide an agreement with the simulation results.

Effect of crystallographic orientation on instability behavior of planar interface in directional solidification

The instability process of planar interface in directional solidification with respect to the crystallographic orientation is studied using a transparent model alloysuccinonitrile-acetone. Three typical crystal grains which have preferred dendrite, tilted dendrite and seaweed patterns at rapid pulling velocity respectively are chosen in our experiment. The experimental results show that the preferred dendrite grain has the shortest incubation time and the smallest initial perturbation wavelength of planar interface instability, the tilted dendrite grain has the largest ones and the seaweed grain has median ones. These results accord qualitatively with previous analytical results and phase-field simulation results. It is also found that the interfacial non-steady-state evolution behaviors of the preferred dendrite grain and the tilted dendrite grain are significantly different from that of the seaweed grain, suggesting that the non-steady-state evolution behavior of planar interface instability is closely related to the crystallographic orientation.

VERY LARGE TELESCOPE/NACO POLARIMETRIC DIFFERENTIAL IMAGING OF HD100546—DISK STRUCTURE AND DUST GRAIN PROPERTIES BETWEEN 10 AND 140 AU

We present polarimetric differential imaging (PDI) data of the circumstellar disk around the Herbig Ae/Be star HD100546 obtained with VLT/NACO. We resolve the disk in polarized light in the H and Ks filter between ~0.1-1.4" (i.e., ~10-140 AU). The innermost disk regions are directly imaged for the first time and the mean apparent disk inclination and position angle are derived. The surface brightness along the disk major axis drops off roughly with S(r) ~ r^-3 but has a maximum around 0.15" suggesting a marginal detection of the main disk inner rim at ~15 AU. We find a significant brightness asymmetry along the disk minor axis in both filters with the far side of the disk appearing brighter than the near side. This enhanced backward scattering and a low total polarization degree of the scattered disk flux of 14%(+19%/-8%) suggests that the dust grains on the disk surface are larger than typical ISM grains. Empirical scattering functions reveal the backward scattering peak at the largest scattering angles and a second maximum for the smallest scattering angles. This indicates a second dust grain population preferably forward scattering and smaller in size. It shows that, relatively, in the inner disk regions (40-50 AU) a higher fraction of larger grains is found compared to the outer disk regions (100-110 AU). Finally, our images reveal distinct substructures between 25-35 AU physical separation from the star and we discuss the possible origin for the two features in the context of ongoing planet formation.

U and Th zonation in apatite observed by laser ablation ICPMS, and implications for the (U–Th)/He system

A laser-ablation inductively-coupled plasma mass spectrometry technique was developed to measure U, Th, and Ce zonation in polished sections of apatite for assessing the consequences of parent zonation for (U–Th)/He thermochronometry. The technique produces concentration maps with an averaging length-scale of ∼20 μm, comparable to the α-stopping distance, and a precision of ∼5% down to few ppm concentration levels. A model was developed to transform the measured concentration distribution into a simplified representation for use in spherical-geometry He production–diffusion models. To illustrate these methods, 30 sections of apatite from a single granite (GC863) were mapped. Every analyzed apatite from GC863 is zoned, with most grains having variable thickness rims and terminations that are enriched in U and Th by about a factor of three over the grain cores. Parent zonation has three independent effects on (U–Th)/He He ages: it influences the α ejection correction, the 4He concentration profile which governs diffusive loss, and, via radiation damage trap accumulation, spatial variability of diffusivity within the crystal. If the observed zonation is typical of the apatite population in GC863, use of the standard homogenous α ejection correction would cause He ages to be on average 3% too young, and with a large amount of grain-to-grain variability (9% too young in the most rim-enriched case to 6% too old in a core-enriched case). Independent of the ejection correction, the concentration profile modifies the effective closure temperature of the apatites by placing more (or less) 4He near the grain edge. The parent zonation in GC863 apatites causes closure temperatures to range from four degrees lower (rim-enriched case) to two degrees higher (core-enriched case) than applies in the homogenous case. Alpha ejection and concentration profile effects on He age are additive and of the same sense. In the case of typical grains in GC863 cooled between 1 and 10 °C/Ma, the two effects are roughly equal in magnitude. The effects of intracrystalline variations in radiation damage trap accumulation become apparent at slow cooling rates (1 °C/Ma). For example, in rim-enriched GC863 grains cooled at 1 °C/Ma, preferential accumulation of radiation damage traps near the grain rim almost compensates for the higher loss rate expected of 4He also located preferentially near the rim. Under some circumstances strong rim-enrichment may actually increase the effective closure temperature of an apatite. Zonation at the level observed in GC863 modifies the 4He/ 3He spectra substantially from that expected from a uniform distribution. Measured 4He/ 3He spectra are strikingly similar to predictions based on the mapped eU distributions of the very same crystals, supporting the overall validity of the analytical and interpretive approach presented here. The magnitude and style of U, Th zonation documented in GC863 is one possible source of frequently observed over-dispersion of apatite (U–Th)/He ages as well as anomalous 4He/ 3He spectra.

High-efficiency grinding of cold-work die steel with ultrafine-crystalline cBN abrasive grains

This paper presents the grinding characteristics of newly developed ultrafine-crystalline cBN (UcBN) abrasive grains in high-efficiency grinding of cold-work die steel. This new UcBN grain possesses an ultrafine crystal structure composed of sub-micron sized primary crystal grains. The fracture strength of the UcBN grain is about 3.7 times higher than that of conventional monocrystalline cBN grain. The grinding ratio in grinding with the UcBN grain is eight to 11 times higher than those in grinding with conventional typical monocrystalline and polycrystalline cBN grains.

Ferroelectric Na0.5Bi0.5TiO3 Additives on the Microwave Dielectric Properties of Ba4.2(Sm0.9,Bi0.1)9.2Ti18O54 Ceramics

In this paper, ferroelectric Na 0.5 Bi 0.5 TiO 3 (NBT, in short) was used as additives to improve the permittivities of Ba 4.2 (Sm 0.9 ,Bi 0.1 ) 9.2 Ti 18 O 54 (BSBT, in short) solid solutions. X-ray diffraction (XRD) analysis did not reveal any second phases or modification of the BSBT crystal structure. Field emission scanning electron microscopy (FE-SEM) analysis showed typical columnar grains became more rod-like with the increasing amounts of NBT addition. Electron probe microanalyzer (EPMA) results revealed a change of second phases from BaTi 4 O 9 to Ba-Sm-Bi-Ti-O solid solutions with a very long needle shape. The addition of NBT (≤10 wt. %) increased the relative permittivities remarkably while the Qf values decreased. The TCf values increased slightly with the increasing additions of NBT and the sintering temperatures. BSBT doped with 5 wt.% NBT additives exhibited excellent dielectric properties with ϵ r = 90.1, Qf = 5450 GHz and TCf = 0.2 ppm/°C when sintered at 1320°C for 2 hours.

NanoSIMS analysis and Auger electron spectroscopy of silicate and oxide stardust from the carbonaceous chondrite Acfer 094

We have detected 138 presolar silicate, 20 presolar oxide and three presolar complex grains within the carbonaceous chondrite Acfer 094 by NanoSIMS oxygen isotope mapping. These grains were further investigated by scanning electron microscopy (SEM) and Auger electron spectroscopy for morphological and chemical details and their distribution within the meteorite matrix. The three complex grains consist of Al-rich oxides (grossite and hibonite) attached to non-stoichiometric Si-rich silicates. Refractory Al-rich oxides therefore serve as seed nuclei for silicates to condense onto, which is proposed by condensation theory and astronomical observations. However, in the majority of presolar silicates we did not find any indications for large subgrains. Most of the grains (80%) belong to O isotope Group I ( 17O-enriched) and come from 1 to 2.5 M ⊙ asymptotic giant branch (AGB) stars of close-to-solar or slightly lower-than-solar metallicity. About 60% of these grains are irregular in shape; ∼40% display elliptical morphologies together with smooth, platy surfaces. Three grains with large 17O enrichments ( 17O/ 16O > 3 × 10 −3) have highly irregular shapes and are very small (<250 nm); these grains may have formed in binary star systems or around higher mass ( ∼ 3 M ⊙ ) AGB stars. About 10% of the presolar silicates in this study can be assigned to the O isotope Group IV, which most likely originate from type II supernovae (SNeII). These grains are also generally smaller than 300 nm and are often irregular in shape (88%), consistent with the SNII origin scenario. The presolar grains are generally evenly distributed within the matrix on an mm scale, although in one case a statistically significant clustering of five grains in one 10 × 10 μm 2 sized field is observed. This could be an important hint that the distribution of presolar material in the parental molecular cloud was heterogeneous on a very fine scale. The matrix-normalized abundance of silicate stardust in Acfer 094 is 163 ± 14 ppm, which is among the highest abundance of O-rich stardust in primitive meteorites. Oxide stardust comprises 26 ± 6 ppm of the matrix. Auger Nanoprobe measurements of 69 presolar silicates and oxides (30 on a quantitative, 39 on a qualitative basis) indicate that most of the grains are Fe-rich (Mg/(Mg + Fe) of 0.82 and lower), which is either due to non-equilibrium condensation, secondary alteration, or both. (Mg + Fe)/Si ratios of the silicates are mostly non-stoichiometric and scatter around pyroxene-like rather than olivine-like compositions, which is consistent with recent Auger and transmission electron microscopy observations and astrophysical predictions. Mg-rich grains (Mg/(Mg + Fe) > 0.5) more likely exhibit elliptical, smooth surfaces (14 out of 18 grains), which is an indication that these grains have not been strongly altered since their circumstellar condensation. We identified only one grain similar to the “glass with embedded metal and sulfides” (GEMS) with a statistically significant sulfur content (>2–3 at.%). It remains unclear why the typical high-sulfur GEMS grains are only found in interplanetary dust particles, but have not yet been unequivocally identified in primitive meteorites.

Sterigmatocystin presence in typical Latvian grains

Ninety five samples of different Latvian grains (wheat, buckwheat, barley, oats and rye) from the year 2006 and 120 samples from the year 2007 were analyzed for Aspergillus ssp. mycotoxin–sterigmatocystin (STC) content. 13.7% of the analyzed 2006 year samples were positive for STC with the concentration levels ranging from <0.7 to 83μg/kg and 35% of the analyzed 2007 year samples were positive for STC with the concentration levels ranging from <1 to 47μg/kg. A previously developed sensitive LC – Electrospray Positive Ionization – MS/MS method was applied for the analysis of STC in grains. Method includes sample extraction with acetonitrile/water solution, solid phase extraction (SPE) on Strata X SPE column, separation on reversed phase C18 column and STC detection by LC–MS/MS.

Microstructure and properties of bulk Ta 2AlC ceramic synthesized by an in situ reaction/hot pressing method

Dense bulk Ta 2AlC ceramic was synthesized by an in situ reaction/hot pressing method using Ta, Al, and C as initial materials. The average grain size of Ta 2AlC is 15 μm in length and 3 μm in width. The physical and mechanical properties were investigated. Ta 2AlC is a good electrical and thermal conductor. The flexural strength and fracture toughness of Ta 2AlC were measured to be 360 MPa and 7.7 MPa m 1/2, respectively. The typical layered grains contribute to the damage tolerance of this ceramic. After indentation up to 200 N at the tensile surface of the beam specimens, no obvious decrease of the residual flexural strength was observed. Even at above 1200 °C, Ta 2AlC still retains a high Young's modulus and shows excellent thermal shock resistance, which renders it a promising high-temperature structural material.

Microstructure and dielectric properties control of Ba4(Nd0.7Sm0.3)9.33Ti18O54 microwave ceramics

Abstract Microwave ceramics of Ba4(Nd0.7Sm0.3)9.33Ti18O54 with 0–3 wt% Ag additions were synthesized by a citrate sol–gel method. The BaO–B2O3–SiO2 glass was also added into the sol–gel derived BNST ceramic powders as sintering aids. The undoped, Ag- and BaBS-doped samples can be sintered at 1250 °C, 1150 °C and 1000 °C, respectively. The microstructure and dielectric properties were then controlled by doping Ag or BaBS glass. Near isoaxial grains with about 250 nm and typical columnar grains were obtained for the silver-doped and BaBS-doped samples, respectively. For the

Valence of titanium and vanadium in pyroxene in refractory inclusion interiors and rims

The clinopyroxene in coarse-grained refractory inclusions contains significant amounts of Ti and V, two elements that are multivalent over the range of temperatures and oxygen fugacities under which the inclusions formed. The Ti 3+/Ti 4+ ratios and the valence of V of these pyroxenes are valuable recorders of nebular conditions. The former can be calculated stoichiometrically from electron probe analyses, but only for relatively Ti-rich grains (i.e., >∼4 wt% TiO 2 tot ). For Ti-poor pyroxene, and for measurement of V valence, another technique is needed. We have, for the first time, applied K-edge X-ray absorption near edge structure (XANES) spectroscopy to the measurement of Ti and V valence in meteoritic clinopyroxene in refractory inclusions. Use of MicroXANES, a microbeam technique with high (μm-scale) spatial resolution, allowed measurement of Ti and V valence along traverses across (a) Ti-, V-rich “spikes” in pyroxene in Type B1 inclusions; (b) typical grains in a Type B2 inclusion; and (c) the pyroxene layer of the Wark–Lovering rim sequence on the outsides of two inclusions. Measurements of Ti 3+/(Ti 3+ + Ti 4+), or Ti 3+/Ti tot, by XANES agree with values calculated from electron probe analyses to within ∼0.1, or ∼2 σ. The results show that Ti 3+/Ti tot increases sharply at the spikes, from 0.46 ± 0.03 to 0.86 ± 0.06, but the V valence, or V 2+/(V 2+ + V 3+), does not change, with V 2+ ≈ V 3+. We found that pyroxene in both Types B1 and B2 inclusions has Ti 3+/Ti tot and V 2+/V tot ratios between 0.4 and 0.7, except for the spikes. These values indicate, to first order, formation at similar, highly reducing oxygen fugacities that are consistent with a solar gas. The pyroxene in the rim on an Allende fluffy Type A coarse-grained refractory inclusion, TS24, has an average Ti 3+/Ti tot of 0.51 ± 0.08 and an average V 2+/V tot of 0.61 ± 0.06, determined by XANES. These values are within the range of those of pyroxene in the interiors of inclusions, indicating that the rims also formed under highly reducing conditions. Measurements of Ti 3+/Ti tot of pyroxene in the rim of a Leoville compact Type A inclusion, 144A, by both XANES and electron probe give a wide range of results. Of our 72 XANES analyses of this rim, 66% have Ti 3+/Ti tot of 0.40–0.71, and the remaining analyses range from 0 to 0.38. In data from Simon et al. [Simon J. I., Young E. D., Russell S. S., Tonui E. K., Dyl K. A., and Manning C. E. (2005) A short timescale for changing oxygen fugacity in the solar nebula revealed by high-resolution 26Al– 26Mg dating of CAI rims. Earth Planet. Sci. Lett. 238, 272–283.] for this sample, 7 electron probe analyses yield calculated Ti 3+/Ti tot values that are positive and 15 do not. In the probe analyses that have no calculated Ti 3+, Ca contents are anticorrelated and Al contents directly correlated with the total cations per 6 oxygens, and the data fall along trends calculated for addition of 1–7% spinel to pyroxene. It appears likely that electron probe analyses of pure pyroxene spots have Ti 3+/Ti tot values that are typical of refractory inclusions, in agreement with the majority of the XANES results. The average of the XANES data for 144A, 0.41 ± 0.14, is within error of that for TS24. The rim of 144A probably formed under reducing conditions like those expected for a solar gas, and was later heterogeneously altered, resulting in an uneven distribution of secondary, FeO-, Ti-bearing alteration products in the rim, and accounting for the measurements with low Ti 3+/Ti tot values.

On the natural polymorphism of pollen grains of Acer tataricum L.

To study natural polymorphism, pollen grains should be collected from ecologically clean sites. Taking the ecological conditions at the end of the 19th century and at the beginning of the 20th century as more favorable than the modern state, herbarium material (LE) was examined. In addition to typical (normally developed) pollen grains, we found two more morphological types within the range of natural polymorphism of pollen grains of Acer tataricum L. that were produced at the end of the 19th century and at the beginning of the 20th century.

Characterization of facing-target reactive sputtered polycrystalline Fe3O4 films

Polycrystalline half-metallic Fe3O4 films fabricated by facing-target reactive sputtering were investigated systemically. Structural results reveal that typical Fe3O4 grains were well isolated by grain boundaries and grew with columnar structure. The room-temperature magnetization of Fe3O4 films at 50kOe field is much lower than that of bulk Fe3O4 (471emu∕cm3), due to the presence of strong antiferromagnetic coupling within grain boundary and the amorphous bottom and top layers. The insaturation magnetization and loop shift in high field region at low temperature also stem from the strong antiferromagnetic coupling. The resistivity increases with the decreasing temperature and is consistent with fluctuation-induced tunneling mechanism in a wide temperature ranging from 50to300K. The negative magnetoresistances up to −9.7% at 150K and −6.4% at 300K under 90kOe magnetic field perpendicular to the film plane were observed and discussed.

Shock and thermal history of Martian meteorite Allan Hills 84001 from transmission electron microscopy

Abstract— Microstructures in the Allan Hills 84001 meteorite were studied using optical and electron microscopy, putting emphasis on shock effects, which are widespread. Some orthopyroxene exhibits only (100) slip, but more typical grains suffered extensive slip, microfracturing, and frequently contain (100) clino‐inversion lamellae. In fracture zones, shock deformation of orthopyroxene has produced all three effects in profusion, together with intergranular pockets of orthopyroxene glass and intragranular glass lamellae, which were apparently created by shearing on low index planes, usually (100) or {110}. Both types of plane are loci that pseudo‐planar fractures tend to follow. Thus, the glass lamellae, which have not been observed in other meteorites, probably formed by frictional heating during the sliding of microscale corrugated surfaces, one over another, leading to local melting. We infer that the orthopyroxene glass and the fracture zones both formed from shear stresses created by strong shock. Ubiquitous undeformed micrometer and submicrometer euhedral chromites in orthopyroxene and plagioclase glasses and carbonate probably crystallized after shock heating and fracture zone formation. Nanocrystals of eskolaite (Cr2O3) coating silica glass grains are probably also a result of shock‐induced thermal decomposition of chromite. Iron sulfides (pyrite and pyrrhotite were identified) tended to be associated with plagioclase glass. A carbonate disk showing no evidence for shock deformation had a substructure of elongated, slightly misoriented subcells in the exterior; interior regions had more eqiaxed subcells. Both microstructures probably formed during growth, but the conditions are undetermined. Chemical composition varied on a micron scale, but the rim of the disk was more ferroan; oxide precipitates and voids were widely distributed as in fracture‐filling carbonates. If the fracture zones and opx glass are the result of strong shock, as we deduce, it is very unlikely that pores could have filled by carbonate long after the fracture zones formed. We infer that the carbonate, like the phosphate, olivine, pyrrhotite, eskolaite, and many euhedral, submicrometer chromites, crystallized during the final stages of the impact that created the fracture zones and glasses with compositions of plagioclase, silica, and orthopyroxene.

Ｒ‐Ａｌ２Ｏ３基板上ＥｕＢａ２Ｃｕ３Ｏ７‐δ薄膜の超伝導特性及び結晶成長に対する厚膜ＣｅＯ２バッファ層の表面性状の影響

A buffer layer is indispensable for preventing chemical reactions between high-temperature superconducting thin films and R-Al2O3. CeO2 is a promising buffer layer. However, when a CeO2 buffer layer with a thickness of more than 50 nm is sputter-deposited onto a R-Al2O3 substrate, grains with facets grow and a high-quality EuBa2Cu3O7-δ (EBCO) thin film do not grow on the buffer layer. In order to fabricate a flat and facet-free CeO2 buffer layer and a high-quality EuBa2Cu3O7-δ (EBCO) thin film, we examined the effects of off-center distance (Doff) and substrate temperature (Ts) of the CeO2 buffer layer on the properties of CeO2 buffer layers and EBCO thin films. Doff was defined by the distance from the on-center position to the off-center position. The deposition rate (Rd) was controlled by Doff. A 300-nm-thick CeO2 buffer layer and a 150-nm-thick EBCO thin film were prepared by RF and DC magnetron sputtering, respectively. The surface morphology of CeO2 buffer layer was dependent on Ts and Doff. At Ts = 650°C and Doff = 30 mm, minute grains grew. When Doff was increased to 50 mm, grains with (111) facet planes grew. The surface roughness (Rz) of the CeO2 buffer layer rapidly increased as Doff was increased. The orientation of the EBCO thin film was dependent on the Doff of the buffer layer. At Doff = 0 ∼ 30 mm, only (00l) peaks of an EBCO thin film were observed in X-ray diffraction patterns. Typical rectangular grains were observed on the surface of the thin film. At Doff values over 40 mm, (110) or (103) peaks, in addition to (00l) peaks, were observed. At Doff = 30 mm, the EBCO thin film exhibited a critical temperature (Tce) of approximately 89 K and a critical current density (Jc) of approximately 3.6 MA/cm2.

A discrete particle model and numerical modeling of the failure modes of granular materials

PurposeTo present a discrete particle model for granular materials.Design/methodology/approachStarting with kinematical analysis of relative movements of two typical circular grains with different radii in contact, both the relative rolling and the relative sliding motion measurements at contact, including translational and angular velocities (displacements) are defined. Both the rolling and sliding friction tangential forces, and the rolling friction resistance moment, which are constitutively related to corresponding relative motion measurements defined, are formulated and integrated into the framework of dynamic model of the discrete element method.FindingsNumerical results demonstrate that the importance of rolling friction resistance, including both rolling friction tangential force and rolling friction resistance moment, in correct simulations of physical behavior in particulate systems; and the capability of the proposed model in simulating the different types of failure modes, such as the landslide (shear bands), the compression cracking and the mud avalanching, in granular materials.Research limitations/implicationsEach grain in the particulate system under consideration is assumed to be rigid and circular. Do not account for the effects of plastic deformation at the contact points.Practical implicationsTo model the failure phenomena of granular materials in geo‐mechanics and geo‐technical engineering problems; and to be a component model in a combined discrete‐continuum macroscopic approach or a two‐scale discrete‐continuum micro‐ macro‐scopic approach to granular media.Originality/valueThis paper develops a new discrete particle model to describe granular media in several branches of engineering such as soil mechanics, power technologies or sintering processes.

Directional Crystallizing Si Films with a Fundamental Continuous Wave Yttrium Aluminum Garnet Laser (Zone Melting for Film)

To form large-grained polycrystalline-silicon (poly-Si) films on glass substrates, we propose a new lateral crystallization method, zone melting for film, which uses a high-power fundamental continuous wave yttrium aluminum garnet (CW-YAG) laser and an absorption layer. The laser's infrared light is changed into thermal energy at the absorption layer and heats the amorphous Si (a-Si) film. Next, the Si film is zone-melted and solidified in one direction with a scanning laser beam. By this method, columnar structured Si films were successfully formed with scanning velocities from 400 to 1000 mm/s. Very large typical grains of 1 or 2 µm by few hundreds of µm were obtained on both glass and quartz substrates, and the long axes of the grains were almost parallel to the laser scanning direction. Textures were also observed in these columnar structured Si films. Recombination carrier lifetimes of these films were several times longer than those of conventional low-temperature-processed poly-Si films.

Perspective of Nanomaterials Production, by Cyclic Extrusion Compression Method of Exerting Unconventional, Large Plastic Deformations

Aluminium and copper monocrystals and also AlMg5 and AlCu4Zr alloys have been deformed by the cyclic extrusion compression method (CEC) in the range of true strains φ = 0.4 -14. It has been found, that about 50% of the volume fraction of aluminium alloys samples, deformed to the true strain φ = 14, shows features of nanostructure. This kind of microstructure consists of nanograins with the average dimension of about 150 - 200 nm, having large misorientations. The investigations indicate that mutually crossing of microbands is the main mechanism of formation of nanograins. In the areas of mutually crossing microbands, the nanograins, which have been formed, are showing large misorientation angles. In aluminium and copper monocrystals, also about 50% of the investigated subgrains, showed large misorientation, however their size was much larger than the typical nanograin size. In aluminium monocrystals it showed dimension of about 600 nm. In copper monocrystals subgrains had average dimension of about 200 nm and were more closed to the typical nanosize grains in the polycrystals. The aluminium alloys, deformed to the true strain of about 14 revealed very high level of microhardness (about 100 μHV), comparable with the level of properties, characteristic for nanomaterials produced by other methods. The level of microhardness of copper monocrystals, after a true strain of 14 by the CEC method, was comparable to the microhardness of copper obtained by the condensation - evaporation method. The obtained results indicate, that using the CEC method, it is possible to produce bulk nanomaterials, especially from the aluminium alloys, which reveal the unconventional large level of mechanical properties.

Pollen dimorphism in Ephedra L. (Ephedraceae)

The pollen of three Ephedra taxa, Ephedra torreyana, E. trifurca and E. funerea⇔ E. torreyana, showed a marked pollen dimorphism when examined using scanning electron microscopy. Typical pollen grains in all of these taxa have straight ridges, but the variant forms exhibit a highly folded ectexine. In addition, previously used characters such as the presence or absence of bifurcating valley structure do not appear to be uniform, even within a single microsporangium, suggesting that their value to taxonomic study should be reassessed.

Laser beam induced currents in polycrystalline silicon thin films prepared by interference laser crystallization

Polycrystalline silicon layers are prepared by interference laser crystallization (ILC) in the superlateral growth regime. To characterize their microscopic photoelectrical properties, light beam induced current (LBIC) is used, employing a focused laser beam for local generation of photocarriers in the layers with spatial resolution of ≈0.4 μm. The results are correlated with surface morphology obtained by atomic force microscopy. In the single pulse ILC, the temperature profiles are optimized by changing the proportion of interfering beam intensities. The typical grains are of triangular shape, with a length of 1.5 μm and width &amp;lt;0.5 μm. The photocurrent response is dominated by variations in the sample thickness. In the multiple pulse ILC, thin films with grains of quadratic shape and of size exceeding 5 μm are obtained by shifting the sample through an interference pattern, thus taking advantage of lateral epitaxial regrowth. Here, by use of a lock–in, LBIC can detect position and local electronic properties of individual grain boundaries. Grain boundaries are clearly identified by 180° shifts of the photocurrent phase close to maxima of photocurrent amplitude. The photocurrent is attributed to local fields at grain boundaries. These fields extend about 1.4 μm into the grains. The barrier height at the boundary is about 110 mV.