6H Phase Research Articles

Genotoxic and cytotoxic effects of iron sulfate in cultured human lymphocytes treated in different phases of cell cycle

Iron (Fe) is a common chemical element that is essential for organisms as a co-factor in oxygen transport, but that in high amounts presents a significant risk of neurodegenerative disorders. The objective of this study was to evaluate the mutagenic potential of iron sulfate. The comet assay and chromosome aberration (CA) analysis were applied to determine the DNA-damaging and clastogenic effects of iron sulfate. Human lymphocytes were treated in the quiescent phase for the comet assay and proliferative phase during the G1, G1/S, S (pulses of 1 and 6h), and G2 phases of the cell cycle for CA analysis, with 1.25, 2.5 and 5μg/mL concentrations of FeSO4·7H2O. All tested concentrations were cytotoxic and reduced significantly the mitotic index (MI) in all phases of the cell cycle. They also induced CA in G1, G1/S and S (pulses of 1 and 6h) phases. Iron sulfate also induced polyploidy in cells treated during G1. In the comet assay, this metal did not induce significant DNA damage. Our results show that Fe causes alteration and inhibition of DNA synthesis only in proliferative cells, which explain the concomitant occurrence of mutagenicity and cytotoxicity, respectively, in the lymphocytes studied.

Structural and physical properties of the 6H BaRuO 3 polymorph synthesized under high pressure

The single-phase 6H BaRuO 3 with the hexagonal BaTiO 3 structure was synthesized at 5 GPa and 1000 °C. Rietveld refinement of the powder X-ray data for the 6H phase resulted in the lattice parameters to be a=5.7127(1) Å and c=14.0499(2) Å; the average Ru–O distance and direct Ru–Ru distance in the Ru 2O 9 dioctahedron being 1.992(6) and 2.5658(14) Å, respectively. The electrical resistivity of the 6H BaRuO 3 follows a relationship of ρ versus T 3/2 below 60.0 K, a signature deviation from the Fermi-liquid behavior. Both magnetic susceptibility and specific heat data indicate that the 6H BaRuO 3 is an exchange-enhanced Pauli paramagnet due to the electron correlation effect with large Wilson ratio R W and Stoner enhancement factor. The comprehensive evolution of transport and magnetic properties from 9R across 4H to 6H BaRuO 3 was discussed.

Rhombohedral (9R) and hexagonal (6H) perovskites in barium silicates under high pressure

Rhombohedral (9R) and hexagonal (6H) perovskites in BaSiO 3 were observed by using in-situ X-ray diffraction methods in high-pressure conditions. The 9R perovskite was found after successive laser heating at 27.9 GPa, and the 6H phase was identified at 48.5 GPa after laser annealing. No intermediate phase between the 9R and 6H phases was found in the pressure range between 27.9 and 48.5 GPa. These phases could not be recovered during decompression at room temperature and became amorphous at ambient pressure. The 9R and 6H structures are characterized by the periodicity of the stacking sequence of edge- and corner-sharing SiO 6 octahedra. In terms of the length of the O-O distance, the face-sharing SiO 6 octahedron in BaSiO 3 perovskite is the most distorted among oxide hexagonal perovskites.

Electrical Properties of AlN-SiC Ceramics

AlN-SiC ceramics with 0 to 75 mol% of AlN were fabricated through pressureless sintering of very fine AlN and SiC. Powder compacts with different amounts of AlN were fired at 2000°C for 1 h in Argon gas flow using an induction-heating furnace. The microstructure and phases present in the products were evaluated using SEM and XRD. The AlN-SiC ceramics had a porous structure with 30% porosity, and the grain size was increased with the addition of AlN. XRD analysis showed that 2H was a main phase in all samples, though 3C and 6H phases were found in 25 mol%AlN-75 mol%SiC ceramic. The electrical properties of the AlN-SiC ceramics were evaluated at various temperatures ranging from room temperature to 300°C. The electrical conductivity of the AlN-SiC ceramics depended on the amount of AlN and on the temperature. The 75 mol%AlN-SiC ceramic had higher electrical resistance, though the other samples were electrical conductors. The highest electrical conductivity was obtained with the 25 mol% AlN composition, which was 7 S/m at room temperature and 30 S/m at 300°C. The Seebeck coefficient for the AlN-SiC ceramics increased with rising temperatures. The AlN-SiC ceramics with 50 mol%AlN had the highest Seebeck coefficient of 220 2V/K at 300°C.

Raman Scattering Characterization of Polytype in Silicon Carbide Ceramics: Comparison with X‐ray Diffraction

Raman scattering measurements have been made on SiC ceramics prepared from two powdered by sintering at different temperatures. The Raman spectra of starting powders have also been measured. The volume contents of the 4H and 15R polytype phases relative to that of the 6H phase in the ceramics are inferred from the Raman intensity of folded modes of the acoustic branches and compared with those determined from X‐ray diffraction (XRD) analysis. A strong correlation is found between the results obtained from the two analyses. The 4H polytype contents estimated by Raman measurement for specimens prepared from one powder show a good agreement with those obtained by the XRD analysis. For the 15R polytype component there is a correlation between the contents inferred by the two techniques when the content is not very small. The results obtained by the two techniques demonstrate that the Raman spectroscopy as well as the XRD analysis is useful to study the natures and preparation conditions of SiC ceramics.

The Circadian System of Trypanosoma cruzi-Infected Mice

The effects of Chagas disease on the mammalian circadian system were studied in Trypanosoma cruzi-infected C57-Bl6J mice. Animals were inoculated with CAI or RA strains of T. cruzi or vehicle, parasitism confirmed by blood specimen visualization and locomotor activity rhythms analyzed by wheel-running recording. RA-strain infected mice exhibited significantly decreased amplitude of circadian rhythms, both under light–dark and constant dark conditions, probably due to motor deficiencies. CAI-treated animals showed normal locomotor activity rhythms. However, in these mice, reentrainment to a 6h phase shift of the LD cycle took significantly longer than controls, and application of 15min light pulses in DD produced smaller phase delays of the rhythms. All groups exhibited light-induced Fos expression in the suprachiasmatic nuclei. We conclude that the main effect of T. cruzi infection on the circadian system is an impairment of the motor output from the clock toward controlled rhythms, together with an effect on circadian visual sensitivity.

Effect of Sintering Atmosphere on Grain Shape and Grain Growth in Liquid‐Phase‐Sintered Silicon Carbide

We investigated the effects of the sintering atmosphere on the interface structure and grain‐growth behavior in 10‐vol%‐YAG‐added SiC. When α‐SiC was liquid‐phase‐sintered in an Ar atmosphere, the grain/matrix interface was faceted, and abnormal grain growth occurred, regardless of the presence of α‐seed grains. In contrast, when the same sample was sintered in N2, the grain interface was defaceted (rough), and no abnormal grain growth occurred, even with an addition of α‐seed grains. X‐ray diffraction analysis of this sample showed the formation of a 3C (β‐SiC) phase, together with a 6H (α‐SiC) phase. These results suggest that the nitrogen dissolved in the liquid matrix made the grain interface rough and induced normal grain growth by an α→β reverse phase transformation. Apparently, the growth behavior of SiC grains in a liquid matrix depends on the structure of the grain interface: abnormal growth for a faceted interface and normal growth for a rough interface.

CIRCADIAN CONTROL OF MIGRATORY RESTLESSNESS AND THE EFFECTS OF EXOGENOUS MELATONIN IN THE BRAMBLING, FRINGILLA MONTIFRINGILLA

Circadian pacemakers control both “daytime” activity and nocturnal restlessness of migratory birds, and the daily rhythm of melatonin release from the pineal has been suggested to be involved in the control of migratory activity. To study the phase relations between the two activity components during entrainment and when free running, locomotor activity of bramblings (Fringilla montifringilla) was recorded continuously under a 12:12 “cool light” to “warm light” cycle (CL:WL, ca. 5000 K and ca. 2500 K, respectively) or blue light to red light cycle (BL:RL, maxima at 440 and 650 nm, respectively) at different irradiance ratios. Migratory activity was expressed primarily during the WL or RL phase of the light cycles. Under free-running conditions, the circadian periods τ correlated with the phase relations between day and night (migratory) activity components during preceding entrainment. Bramblings with migratory activity had significantly longer τ at constant light intensity than the same individuals without migratory activity. Birds with migratory activity reentrained faster after a 6h phase shift of the CL:WL cycle than birds without migratory activity. When exogenous melatonin was given in the drinking water (200 μg/mL 1% ethanol or 0.86 mM) to bramblings exposed to 12:12 CL:WL cycles with constant irradiance, the amounts of activity, which were initially higher during the WL phase of the light cycle, were suppressed to similar low levels during both light phases. The systematic changes in the amounts of activity during melatonin treatment were not correlated with consistent changes in entrainment status. The data support the hypothesis that changes in the amplitude and level of the daily melatonin cycle are involved in regulating migratory restlessness, by either allowing or inhibiting nocturnal activity. (Chronobiology International, 17(4), 471–488, 2000)

Effect of annealing on mechanical properties of self-reinforced alpha-silicon carbide

Alpha-SIC powder containing 7.2 wt % Y3Al5O12 (YAG, yttrium aluminum garnet) and 4.8 wt % SiO2 as sintering aids were hot-pressed (SC0) at 1820°C for 1 h and subsequently annealed at 1920°C for 2 h (SC2), 4 h (SC4) and 8 h (SC8). When the annealing time was increased, the microstructure changed from equiaxed to elongated grains and resulted in self-reinforced microstructure consisted of large elongated grains and small equiaxed grains. Development of self-reinforced microstructure, consisted of mostly 6H phase, resulted in significant improvements in toughness. However, the improved toughness was offset by a significant reduction in strength as in the materials consisted of 4H originated from β-SiC. The fracture toughness and strength of the 8-h annealed materials were 5.5MPa · m1/2 and 490 MPa, respectively.

Timely Administration of Melatonin Accelerates Reentrainment to Phase-Shifted Light-Dark Cycles in the Field Mouse Mus Booduga

The effect of melatonin on the rate of reentrainment after a 6h phase delay and a 6h phase advance in the light-dark (LD) cycle was assayed in the nocturnal field mouse Mus booduga. After a phase delay of 6h in the LD cycle, a single dose of melatonin (1 mg/kg) was administered for three consecutive days at about CT4 (circadian time 4). After a phase advance of 6h in the LD cycle, melatonin was administered for three consecutive days at about CT22. Melatonin was found to accelerate reentrainment in both cases. Melatonin-treated animals took significantly fewer cycles to reentrain compared to vehicle-treated (50% dimethylsulfoxide [DMSO]) and nontreated control animals.

Solid-State Phase Transformation in Cubic Silicon Carbide

The thermal stability of single crystalline 3C-SiC was investigated at temperatures from 1800 to 2400°C in an Ar atmosphere, and a solid-state phase transformation from 3C-SiC to 6H-SiC was observed above 2150°C. Single crystals of 3C-SiC(100) grown on Si(100) were used as starting crystals after removing Si. Annealings were carried out with changing temperature, pressure and time. The change in the Si/C composition ratio of annealed samples was determined by Auger electron analysis. The polytypes of samples were examined by photoluminescence, Raman scattering, X-ray diffraction and reflection high-energy electron diffraction before and after annealing. The spatial distribution and depth profile of the phase-transformed 6H-SiC region in annealed samples were observed by means of Raman microscopy. The mechanism of 3C→6H phase transformation in SiC is discussed.

X‐ray investigation of the mechanisms of phase transformations in single crystals of ZnS, ZnxCd1−xS, and ZnxMn1−xS (II). Comparison of observed and calculated diffraction effects

AbstractThe experimentally observed intensity profiles recorded from ZnS, ZnxCd1−xS and ZnxMn1−xS crystals at different stages of the 2H‐3C and 2H‐6H transformations are compared with those computed theoretically from the three parameter model in the previous paper. It is found that the 2H‐3C and 2H‐6H transformations occur by the nonrandom nucleation of deformation faults. The probability of the growth of a nucleus is much greater than that of the creation of a fresh nucleus. At least two different fault probabilities have therefore to be employed in computing the diffraction effects in each case. The transformation behaviour of ZnxCd1−xS and ZnxMn1−xS crystals is strongly influenced by variations in stoichiometry (x). Large values of x (x > 0.95) favour the 2H‐3C transformation, whereas smaller values (x ≦ 0.94) favour the formation of the 6H phase. A comparison of the calculated and observed intensity distributions indicates that in some crystals the 2H‐3C and 2H‐6H transformations occur simultaneously in different regions of the same single crystal.

System BaIr 1− xFe xO 3− y

In the BaIr 1− x Fe x O 3− y system a mixed Ir-Fe phase with a hexagonal BaTiO 3 structure (6H; sequence, ( hcc) 2; space group, P6 3/ mmc) is present in air in addition to the pure iridium phase BaIrO 3 and the pure iron phase BaFeO 3− y . The 6H phase boundaries are in the range from x = 0.333 to x = 1.0. Within the 6H phase the specific resistance ρ increases with x. For x = 0.333, hardly any temperature dependence is observed for ρ. On the contrary the iron-rich members are typical semiconductors and show a strong increase in ρ with decreasing temperature.

X-Ray Diffraction from a Sic Crystal Undergoing the 3C–6H Solid State Transformation by Non-Random Microtwinning

Recent high resolution electron microscope studies of the 3C-6H transformation in SiC have shown that the transformation occurs by a process of non-random microtwinning. A theoretical model is developed for the transformation assuming that the twin faults occur preferentially at three layer spacings with a probability (β) which is greater than the probability (α) of their occurrence at larger separations. Then a corresponds to the probability of random nucleation of the 6H phase in the 3C matrix and β to the growth of the 6H nuclei. The probability of microtwinning at less than three-layer separations is assumed t o be negligible. On the basis of such a model the X-ray diffraction effects are predicted from a partially transformed crystal. The peak broadening and peak shifts of the 3C and 6H reflections are computed for various values of a and β. The proposed mechanism of transformation can be experimentally verified by recording the intensity profiles from electron diffraction patterns or by single crystal diffractometry of a partially transformed crystal.

Stacking faults and structural transformations in Zn xMn 1−xS single crystals grown from vapour

This paper reports an X-ray diffraction study of the stacking faults and solid state transformations observed in Zn x Mn 1− x S (0.9 < x < 1) single crystals grown from the vapour phase at 1100°C in the presence of H 2S. The crystals were found to contain 2H, 3C, 2H + 3C and polytypes as well as structures with considerable disorder due to random stacking faults. Needle shaped 2H crystals were annealed in vacuum in the temperature range from 300 to 1100°C to induce structural transformations. Nearly 75% of the crystals transformed to a disordered twinned 3C structure on annealing around 600°C. The rest of the crystals transformed first to a disordered 6H structure and then, on further annealing at higher temperatures, to the disordered twinned 3C structure. Most of the transformed 3C structures showed an intensity enhancement near the positions of the 6H reflections on X-ray diffraction photographs. All the 3C crystals transform back to a disordered 2H structure on annealing above 1050°C. To determine the nature of stacking faults involved in the 2H–6H transformation we have investigated the broadening of X-ray diffraction maxima along reciprocal lattice rows with H - K ≠ 3 n produced by crystals undergoing the transformation. The point intensity distribution along the 10. L reciprocal lattice row of several partially transformed crystals were recorded on a four circle single crystal diffractometer in steps of Δ L = 0.01. A study of the experimental profiles obtained by plotting the diffractometer record of intensity versus L in reciprocal space shows that the transformation occurs by the non-random insertion of deformation faults in the 2H structure. It is shown that the one-parameter model proposed by Pandey, Lele and Krishna [Proc. Roy. Soc. (London) A369 (1980) 451 is not applicable to 2H–6H solid state transformation in Zn x Mn 1− x S crystals. A two-parameter model involving different fault probabilities for the nucleation (α) and the growth (β) of the 6H phase in the 2H structure is suggested.

Forming and Sintering Behavior of B‐ and C‐Doped α and β‐SiC

The effects of forming pressure and sintering temperature on shrinkuge, density, and phase composition of α‐ and β‐SiC were determined. Alpha SiC developed the 4H phase at the expense of the 6H phase at &gt;2150°C. The beta form converted to the 6H phuse at &gt;2000°C, with intermediate development of the 15R and 4H phases

Electron microscopic study on new phases of BaMnO3ȡx formed by electron irradiation

New phases in the BaMnO3ȡx system were investigated by high resolution electron microscopy. A hexagonal cell with two atomic layers (2H, a = 0.57 nm, c = 0.48 nm) was found to have an oxygen-deficiency to some degree, though its X-ray powder pattern gave a single phase of a 2H crystal. Observed structure images showed that a 2H phase was transformed into a 10H (6L + 4L) phase under a low beam intensity and into a 6H (4L + 2L) phase under a very high beam intensity. A mechanism of phase transformation is proposed that oxygen-deficiency in face-sharing octahedra induces the displacement of the Mn ions which reduce the coordination number and the disruption of face-sharing octahedra.

Über das System BaFe 1− xRu xO 3− y

In the system BaFe 1− x Ru x O 3− y three phases, separated by immiscibility gaps, are present: an Fe-rich phase ( x = 0-0.75) with hexagonal BaTiO 3 structure (6H; sequence (hcc) 2), a Ru-rich phase ( x = 0.9) of hexagonal 4H type (sequence (hc) 2), and the pure Ru compound BaRuO 3 with rhombohedral 9R structure (sequence (hhc) 3). By vibrational spectroscopic investigations in the 6H phase a transition from n-type semiconduction (Fe-rich oxygen-deficient compounds) to good, metal-like conduction (Ru-rich compounds with complete oxygen lattice) can be detected. The 4H and 9R stacking polytypes are good, metal-like conductors.

On the deduction of silicon-carbide polytypes from screw dislocations

Mitchell has deduced the polytypic structures that would arise from theoretical screw dislocations in the 6H, 4H and 15R phases of silicon carbide, by the spiral-growth mechanism of Frank, and compared these with the structures actually observed. In doing so, he assumed that at the instant of the creation of a screw dislocation, the initial platelet consists of a completed number of unit cells and that the exposed ledge, irrespective of its own structure, can wind over itself in a close-packed manner, thereby repeating its own zig-zag sequence indefinitely during the subsequent spiral growth. It is shown that both these assumptions are not justified and that the use of Zhdanov symbols alone leads to incorrect results. The possible polytypic structures that can be derived from theoretical screw dislocations of different Burgers vectors are rededuced with corrected assumptions, by considering the different possible structures of the exposed ledge in terms of ABC layers and investigating the stacking of these layers during the subsequent spiral growth of the ledge. The results so obtained differ markedly from those of Mitchell. In particular a much larger number of structure series are shown to be actually possible. The results are compared with the polytypic structures reported so far.