Fine Substructure Research Articles

Experimental Study of Ternary Pd-Si-C Phase Equilibria and Pd/SiC Interface Reactions

The phase diagram of Pd-Si-C was investigated by experimental methods (XRD, SEM/EDX) and approximate thermodynamic calculations. Based on these results several isothermal sections between 700 and 1000°C are developed. Bulk diffusion couples between Pd and monocrystalline SiC were studied in the same temperature range, 700 to 900°C. A comparison of reaction behaviour between monocrystalline 6H-SiC and ceramic HIP-SiC with Pd is given. The formation of periodic bands consisting of Pd 2 Si + C and Pd 2 Si is clearly observed in the Pd/6H-SiC diffusion zone. These periodic bands are obscured in the Pd/HIP-SiC diffusion couples. In addition, a fine periodic substructure in the two-phase layer (Pd 2 Si + C) is detected. Furthermore, at least a modest joining pressure may be required to produce the reaction zone and the periodic bands. The sequence of reaction layers as observed in the diffusion couples, SiC/C+Pd 2 Si/Pd 2 Si/-/C+Pd 2 Si/Pd 2 Si/Pd 3 Si/Pd, could be related to the isothermal section at 800°C. At 850 °C a liquid phase is formed in the diffusion zone. Interpretations pertaining to the observed diffusion paths are discussed based on the ternary solid state equilibria.

Hetero-amorphous Fe-Co-B-C soft magnetic thin films with uniaxial magnetic anisotropy and large magnetostriction

Hetero-amorphous (Fe/sub 0.75/Co/sub 0.25/)/sub 1-x/(B/sub 1-y/C/sub y/)/sub x/ films have been obtained by RF magnetron sputtering. Magnetic properties strongly depended on the hetero-amorphous substructure of the films. The film with a fine substructure less than 10 nm in mean diameter exhibited low coercive force of 40 A/m along the hard axis, large spontaneous magnetization of 1.6 T, and in-plane anisotropy field of 1.2 kA/m induced by field-annealing although the film had a large magnetostriction constant of 39/spl times/10/sup -6/.

Optical Imaging of Cytosolic Calcium, Electrophysiology, and Ultrastructure in Pyramidal Neurons of Organotypic Slice Cultures from Rat Hippocampus

Organotypic slice cultures from rat hippocampal cortex grown in an interface between culture medium and a CO2-enriched atmosphere maintained much of the morphological connectivity characteristic of the hippocampus in situ and thinned out considerably, facilitating optical measurements of fluorescent dyes sensitive to Ca2+ in individual neurons. Pyramidal neurons of the CA3 region presented morphological features of differentiated cells, including complex dendritic arborization and large numbers of dendritic spines. The fine cytoskeletal substructure at the postsynaptic density, below the plasma membrane, and within the core of the head and neck of dendritic spines in rapidly frozen slice cultures presents the characteristic morphology previously described for Purkinje cell dendritic spines in acutely dissected cerebellar cortex slices after rapid freezing. CA3 neurons responded to intracellular current injection with a train of action potentials, spike frequency adaptation, and a slow afterhyperpolarization. These spike trains caused rapid increases in dendritic [Ca2+]i that decayed to resting levels after termination of the current pulse. Dendritic spines were clearly observed in proximal dendrites of CA3 neurons in live preparations. [Ca2+]i transients in these dendritic spines closely followed the changes observed in the main dendritic shaft. Orthodromic synaptic stimulation from the dentate hilus generated long-lasting synaptic potentials accompanied by large [Ca2+]i transient in CA3 pyramidal neurons. The [Ca2+]i response was first observed in the proximal dendrites, after which the soma exhibited a [Ca2+]i increase, returning to resting levels within 10 s after the synaptic stimulus. Slice cultures thus provide a favorable opportunity to investigate [Ca2+]i responses in individual neurons maintained in an organotypic synaptic environment, taking advantage of high-resolution optical techniques.

L-H interface improvement for ultra-high-efficiency Si solar cells

Several phenomena normally considered separately are taken into account simultaneously to model a new solar-cell structure. A planar substructure inserted in the cell emitter is provided at its faces with two L-H interfaces which modify recombination mechanisms inside the accumulation layers. The theoretical modelization and one-dimensional numerical simulation show its yield to be 35%–40%. In practice, fabrication would necessitate uniting recent technological advances in the same fine substructure to ensure: (i) absorption of low-energy photons; (ii) optical confinement of the infrared light; and (iii) formation of the L-H interfaces at its edges.

ラット顎下腺排せつ管の結さつ解除後の再生

The ducts of rat submandibular glands were ligated for 4 weeks, and the location of peroxidase activity in the glands was examined for 24 weeks.One week after release, the pattern of peroxidase activity was identical to that immediately after the release of the 4-week duct ligation.At 2 weeks some cells revealed peroxidase activity in the cisterna of the rough endoplasmic reticulum and in the nuclear envelope. Those cells contained no secretory granules.At 4 weeks the cisterna of the rough endoplasmic reticulum, the nuclear envelope, and the secretory granules showed high peroxidase activity.Granulated cells with high peroxidase activity were increasingly numerous after 8 weeks and 16 weeks. A fine filamentous substructure was found in some granules with peroxidase activity.At 24 weeks cells containing granules with high peroxidase activity were scarce, and most of the acini consisted of cells similar to those in the control specimens.

Microstructural development in AlSiC composites made by resistance sintering of mechanically alloyed powders

Abstract SiC particles were found to be distributed homogeneously in the aluminum matrix by the mechanical alloying (MA) process. It was observed that the aluminum matrix of the MA powders consists mainly of fine subgrains with a wide range of misorientations. In addition, a band structure consisting of lamellae of elongated subgrains was observed. The substructure of the aluminum matrix of MA powders indicates that the average temperature in the MA process in quite low, i.e. near room temperature. It was found that the fine substructure of MA powders can be maintained after resistance sintering. The high strength of the resistance-sintered AlSiC composites may be attributed to the fine subgrain structure in the aluminum matrix and the high dislocation densities which exist owing to the presence of a worked structure arising from the MA process, and are generated by the thermal mismatch between aluminum and SiC particulates.

Adhesive properties conferred by the plasminogen activator of Yersinia pestis.

A genomic library of Yersinia pestis EV76c created in a cosmid vector was screened for clones capable of binding type IV collagen. An unexpectedly high number of such clones was observed. One recombinant plasmid was selected for further study, and the locus controlling collagen binding was mapped by subcloning, transposon mutagenesis and exonuclease digestion. The outer-membrane protein profiles of transposon insertion mutants were correlated with phenotype to implicate a 36 kDa polypeptide in type IV collagen binding. Fine substructure restriction mapping and limited DNA sequence analysis showed the cloned locus to be identical to the locus (pla) for the plasminogen activator, previously characterized genetically and biochemically. The pla locus is resident on a 9.5 kb plasmid in wild-type Y. pestis strains. Curing of this plasmid resulted in negligible reduction in collagen-binding capacity, implying the existence of a chromosomally located determinant for collagen binding. The affinity of the plasminogen activator for collagen was relatively weak. When the cloned pla locus was introduced into E. coli, it conferred upon the cell the ability to bind to cells from a number of cell lines. Binding to glycolipids separated by thin-layer chromatography demonstrated that the receptor was a member of the globo-series of glycolipids. Since it has been reported that mutation of pla dramatically reduces virulence, we propose that this hitherto undescribed function of the gene product could contribute to the biological activities necessary for full virulence.

Surface crystallization in melt-spun metallic glasses

A series of hypoeutectic FeSiB metallic glasses produced by single-roller melt spinning were found to have substantial wheel-side surface crystallization. These crystals were shown to be associated with areas on the ribbon surface which were in good contact with the wheel rather than in the depressions formed by gas entrainment during casting, as has been previously suggested for similar effects in other alloys. Transmission electron microscopy revealed that the crystals have a fine cellular substructure with the intercellular spaces freezing as glass and that the structure becomes progressively finer during growth.

Interstellar Scattering Towards Cyg X-3

MERLIN observations at 0.408 GHz of the December 1985 outburst of Cyg X-3 have enabled us to characterise the angular broadening, caused by interstellar scattering, very accurately. The scattering along the line of sight towards Cyg X-3 is exceeded by only two other lines of sight through the Galaxy: towards the Galactic centre (see e.g. Lo et al. 1985. Nature, 315, 124) and towards NGC 6334 (Rodriguez et al. 1982. Astrophys. J., 225, 103); as a result quite short baselines are needed to study the scattering disk at 73 cm wavelength (0.408 GHz). The projected MERLIN baselines for our observations cover the range from a few km (on which the source was unresolved and had a correlated flux density ∼3.6 Jy) to ∼130 km (on which the source was totally resolved i.e. a correlated flux density <0.030 Jy). The basic result from these observations is that over this range of baselines the scattering appears to be purely diffractive in character. The scattering disk is, to quite a good approximation, a circular gaussian and shows no evidence of fine scale substructure. Model fitting to the visibility amplitudes, assuming circular symmetry, yields θ0.408GHz = 2.85±0.05 arcsec (FWHM).

The substructure of quasicrystalline Al‐Mn alloy observed by TEM

SUMMARYThe morphology of the icosahedral phase in Al86Mn14 alloy has been observed as flower‐like and of granular shape by TEM. These two kinds of morphologies may be regarded as the different sections of a three‐dimensional flower‐like grain. Inside these grains, a fine substructure of a few nm in size has been found. A dendritic morphology with a diffraction pattern showing five‐fold symmetry have also been observed in the Al86Mn14 alloy. On the basis of these observations, a model based on nucleation, growth and aggregation has been proposed to explain the formation process of the quasicrystalline state.

Differentiation of nuclear structure during the sexual cycle in Tetrahymena thermophila: I. Development and transcriptional activity of macronuclear anlagen

During the postzygotic period of the sexual cycle (conjugation) in the ciliated protozoan Tetrahymena, transcriptionally active somatic macronuclei develop from descendants of the germinal micronuclei, which are mostly transcriptionally inactive. This nuclear differentiation process is accompanied by the amplification of ribosomal genes, genome polyploidization, and reorganization. In this context, the developmental sequence of macronuclear anlagen represents an interesting system for the study of finestructural aspects of nuclear differentiation in combination with an analysis of the onset and location of transcriptional activity. From our data, the differentiation of the fine structure of macronuclear anlagen can be divided into three distinct stages. During the first stage, the anlagen appear very electron lucent and exhibit a loose, fine fibrillar substructure (achromatic stage). 3H-Uridine incorporation was low, and the autoradiographic label was evenly distributed over the nuclear areas. During the second stage, specific nuclear regions showing arrays of small, condensed flocculent patches could be seen. In such areas, primary nucleolar structures are obviously formed; these structures initially only consist of fibrillar components and show very little or no transcriptional activity. During the last stage of differentiation, the macronuclear anlagen attain a fine structure similar to that exhibited by macronuclei in starved vegetative cells. The fibrillogranular substructure becomes more dense, and typical heterochromatic chromatin bodies appear. The multiple extrachromosomal nucleoli are exclusively located at the periphery of the nuclei and organized as either single units or nucleolar aggregates containing a cortex of granular components. The autoradiographic label was dense and clearly concentrated over the nucleoli. The combined fine-structural and autoradiographic data indicates that, during the first stage of macronuclear differentiation, only nonribosomal RNA transcription occurs and that there is a lag phase between the first appearance of nucleolar structures and the expression of the amplified ribosomal genes.

Metallurgical reaction and deposit fusion boundary microstructure under a stationary plasma arc

Alloy element loss, decarburization in melted region and microstructural change of a deposit fusion boundary under a stationary plasma arc have been investigated by a first-order kinetic and interfacial microstructure. The cylindrical specimens of iron-based alloys, Fe-C, Ni-C, and Co-C alloys were locally melted by a plasma arc using argon plasma gas and Ar+H2 shielding gas, and the rates of alloy element loss and decarburization in the melted region were measured. Moreover, the fusion boundaries experienced when nickel, iron, Ni-Fe filler metals were deposited on iron, Fe-C, nickel and cobalt base metals, were evaluated metallographically. The initial rate of alloy element loss decreases as follows: Fe-Al>Fe-Mn>Fe-Cr>SGI-Mg>Fe-Ni. The loss reaction mechanism is metallic evaporation and the rate seems to be limited by transport in the gas boundary layer. The magnitude of decarburization is as follows: Ni-C>Fe-C> Co-C. The decarburization rate in Fe-C alloy is assumed to be governed by a process involving mass transfer in the gas phase and the molten metal. However, at low carbon concentrations, the rate appears to be limited by transfer in liquid metal. Fusion boundary deposited with nickel filler metal on iron is regular, but with carbon added to iron, an infiltration of deposit metal into adjacent base metal occurs. The fusion boundary with iron deposited on nickel is irregular where thin Ni-Fe solid solution is formed. In a deposited fusion boundary of cobalt with iron, nickel, and Ni-Fe filler metals, FeCo compound formation occurs, with cobalt dissolving into the nickel deposit metal resulting in a tongue-like structure produced by nickel penetration and a fine columnar substructure formation produced by Ni-Fe diffusion.

Effect of Warm-Rolling Spheroidization on the Mechanical Properties of 0.9% Carbon Steel

Thermomechanical treatments for steels involve deformation produced during or before an allotropic change in the microstructure. The treatments are often associated with an increase in the mechanical properties. It was found that improvement in mechanical properties was produced by the formation of a microstructure which consisted of spheroidal cementite in a ferritic matrix containing a very fine subgrain substructure. The experimental method is delineated with respect to the spheroidization process in the 823–973 K range. The mechanical properties of steel spheroidized at these temperatures have been correlated with the microstructure. It was verified that the flow stress and the ultimate tensile stress were significantly enhanced when the rolling temperature was decreased in the temperature range of 823–973 K. The greatest ductility obtained in the material was about 6 % and the ductility decreased with decreasing rolling temperature. The findings of this study indicated that for a constant carbide volume fraction, the flow stress and ductility were controlled by the interparticle spacing of spheroidized cementite.

Composition and ultrastructure of calcium phosphate-citrate complexes in bovine milk systems

The present studies show that the colloidal calcium phosphate of cow's milk has a (Ca + Mg)/P i ratio of 1.67 (± 0.10; n = 22) and contains citrate, Mg and Zn at molar ratios to Ca averaging 0.05, 0.03 and 0.003, respectively. The composition of the natural colloidal phosphate of milk is similar to the precipitates formed by neutralization of ultrafiltrates obtained from acidified milks, and to that of the calcium phosphate-enriched fraction produced by extensive enzymic hydrolysis of the casein micelles in milk. Examination by electron microscopy of these artificial preparations of milk calcium phosphate revealed in both a very fine and uniform substructure which consisted of granules having an average, true diameter of approx. 2.5 nm. The size and shape of these tiny granules closely resemble the morphologies reported for the colloidal phosphate particles in native casein micelles, as well as for the subunits of amorphous calcium phosphate observed during calcification in other biological systems such as mitochondria and bone.

The Red Neuronal Pigment in the Nervous System of the Mussel, Mytilus Edulis: Localization and Its Effect on Lateral Ciliary Activity with Spectral and Analytical Changes

The purpose of this study was to localize the red neuronal pigment in Mytilus edulis and examine its role in the control of lateral ciliary activity in the gill. The visceral ganglia (Vg) in the central nervous system show an over al red pigmentation. Most red pigments examined in squash preps and cryostat sec tions were localized in the neuronal cell bodies and proximal axon regions. Unstained cryostat sections showed highly localized patches of this pigment scattered throughout the cells in the form of dense granular masses about 5-7 um in diameter, with the individual granules ranging from 0.6-1.3 um in diame ter. Tissue stained with Gomori's method for Fe showed bright blue granular masses of about the same size and structure as previously seen in unstained cryostat sections.Thick section microanalysis (Fig.l) confirmed both the localization and presence of Fe in the nerve cell. These nerve cells of the Vg share with other pigmented photosensitive cells the common cytostructural feature of localization of absorbing molecules in intracellular organelles where they are tightly ordered in fine substructures.

Stigma and flagellar swelling in relation to light and carotenoids in Euglena gracilis var. bacillaris

Wild-type Euglena gracilis var. bacillaris, W3BUL (a mutant having lower amounts and a different mix of carotenoids), and W10BSmL (in which colored carotenoids are undetectable) were grown in light and darkness and were serially sectioned to ascertain the form and relations of stigma and flagellar swelling by electron microscopy. The length and width of the flagellar swelling in all organisms in light and darkness was the same within experimental error, and this structure showed the characteristic fine reticulate substructure in all cases. The stigma is absent or is reduced to a few tiny vesicles in W10 and show less staining in W3 compared with wild type. In dark-grown resting wild type and W3 the stigma is rather amorphous and only becomes a group of spheres after prolonged exposure to light. Three-dimensional reconstructions of the reservoir region showing the relations of organelles including the stigma and flagellar swelling have been made. Comparing wild-type B and its mutants, the presence of a normal flagellar swelling is not correlated with the ability to form colored carotenoids. This conclusion is supported by experiments with (4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H) pyridazinone) (SAN 9789) a specific inhibitor of carotenoid biosynthesis in Euglena at the phytoene stage. Growing cells of dark-grown wild type or W3 treated with SAN show a very great reduction in the stigma, but the flagellar swelling is unaffected. We conclude that ability to form stigma material does correlate with the ability to make colored carotenoids but light is required to organize this material into the individual spheres characteristic of the normal stigma.

Three ultrastructural markers on pachytene bivalents of human spermatocytes

The occurrence and morphology of three ultrastructural markers on meiotic chromosomes are described on the basis of three dimensional reconstructions of 29 early pachytene and 28 mid-late pachytene nuclei: 1) A condensed granular structure surrounded by a larger body of uncondensed chromatin is situated near the telomere of the short arm of bivalent 1. 2) A globoid structure with a fine granular substructure is present in the middle of the short arm of bivalent 6.3) A body of coarse granules is situated near the middle of the long arm of one of the two longest D group bivalents.

Crystallization of an amorphous Cu-Zr alloy

A Cu-40 at. % Zr alloy was splat cooled into a non-crystalline structure. The crystallization behavior of this alloy was studied by calorimetry, transmission electron microscopy, and hardness testing. Calorimetric studies indicated that crystallization of the initial non-crystalline material occurred by a single exothermic reaction. The heat release was 1260 cal/mole and occurred at 480°C. Evidence for a glass transition at approx. 450°C was also found. Samples previously isothermally annealed below the crystallization temperature exhibited two exothermic reactions when studied calorimetrically. The additional second peak increased in size and shifted to temperatures higher than the first peak with increased annealing. Transmission electron microscopy indicated that crystallization occurred by a nucleation and growth mechanism during isothermal annealing. The crystallites were found to have a fine substructure with a subgrain size of approx. 300–500 A. The crystallization product was single phase. Calorimetry results, direct observations from transmission electron microscopy, and changes in the electron diffraction pattern of annealed samples led to the conclusion that the initial non-crystalline matrix transforms to a second non-crystalline structure which, in turn, transforms to the crystalline phase. Hardness measurements were performed to follow the crystallization process. Results indicated that hardness monitors the transformation of the initial non-crystalline structure with high sensitivity.

A NEW ELECTRON MICROSCOPIC HISTO-CYTOCHEMICAL STAINING METHOD -DEMONSTRATION OF GLYCOGEN PARTICLES-

For electron microscopic demonstration of glycogen particles in tissue sections, a new histochemical staining method is introduced as a substitute for stains such as periodic acid thiosemicarbazide silver proteinate. It is based on the fact that glycogen particles can be demonstrated with alkaline bismuth (A·Bi) solution alone and without periodic acid pretreatment.A. The staining mechanism involves a direct reaction where vic-glycol groups in glycogen compounds are oxidized into carboxyl groups and bismuth is reduced. The latter combines with the carboxyl groups to effect increased electron opacity of glycogen particles under electron microscopic observations.B. The glycogen particles can be observed even if periodic acid treatment is added on condition that the treatment be stopped within 10-15min. But glycogen particles disappear when the treatment lasts more than 30min. The treatment is not necessary even in theory because the A·Bi stainable vic-glycol groups are gradually decreased in proportion to the duration of the treatment.C. The technique is adapted to the observation under high magnification of the mode of α-D-glucopyranose arrangement in glycogen compounds because the bismuth deposit has a high electron opacity due to the high atomic number of bismuth and is positioned only in the vic-glycol group of the glycogen compound.D. The staining technique is remarkably simple as staining needs to be carried out only once, in contrast with previous methods.This A·Bi staining technique permits excellent high contrast observation of glycogen particles in the cytoplasm of liver cells and myocardial muscle cells which could be seen to consist of fine granular substructures.

Comparative X-Ray Diffraction and Electron Microscopic Study of the Transformation-Induced Substructures in the Iron-Nickel Martensites and Their Influence on the Martensite Properties

Transformation-induced fine substructures in iron-nickel martensites have been studied by x-ray diffraction and electron microscopy. The dislocation density, microstrains, and twinning increased while the dislocation cell size (particle size) decreased, with increasing nickel contents. The effect of the substructures on the hardness and yield strength of the martensites has been discussed. The anisotropic particle-size values obtained from x-ray analysis are shown to be due to faulting and/or twinning. From the compound fault probability (1.5α + β) obtained through Warren-Averbach analysis and the β values obtained from measured peak asymmetry, the stacking-fault probability α values have been derived and the stacking fault energy γ of the bcc iron-nickel alloys have been calculated. By extrapolation of the stacking-fault energy-composition curve a γ value of 50 ± 10 erg/cm2 has been estimated for pure iron.