Increase In Grain Density Research Articles

Hydrogen retention and affecting factors in rolled tungsten: Thermal desorption spectra and molecular dynamics simulations

Hydrogen isotope retention of tungsten in nuclear fusion reactors is one of the hot research issues all along. In this paper, tungsten samples in different rolled surfaces were polished by mechanical processing, subsequently subjected to D2+ irradiation and thermal desorption. To better understand the experimental observations, this study also performed molecular dynamics (MD) simulation and investigated the effects of temperature, grain number, grain boundary density, and crystal orientation on hydrogen retention. It is found that the grain number and grain boundary density of rolled tungsten increase successively in RD/TD, RD/ND, and TD/ND surfaces. The RD/ND surface exhibits the best hydrogen radiation resistance, whereas the TD/ND surface is unsatisfactory. MD simulations further indicate that hydrogen retention is more obvious with the increase of grain density in tungsten, and hydrogen atoms are more easily enriched at the grain boundaries. With the increase in temperature, the retention of hydrogen atoms in monocrystalline/polycrystalline tungsten decreases significantly. The average implantation depth of H atoms is deepest along the <111> and <112> crystalline directions, which reveals that hydrogen retention is dependent on the crystal orientations. The good agreement between the experimental data and simulation results reveals that grain boundaries play an important role in hydrogen retention.

Generation of ultra high-power thermal plasma jet and its application to crystallization of amorphous silicon films

We have successfully generated ultra high-power thermal plasma jet (Super TPJ: s-TPJ) by increasing the Ar gas supply pressure to 0.4 MPa and the flow rate to 18 L/min. DC arc discharge was stably performed under a supply power of 4.6 kW. The peak power density of s-TPJ reached 64.1 kW/cm2 and enabled us to melt and recrystallize amorphous silicon (a-Si) films on quartz substrates with a scanning speed as high as 8000 mm/s. Under ultra high-speed scanning faster than 3000 mm/s, we observed granular crystal growth (GCG) competing with conventional high-speed lateral crystallization (HSLC). When further high speed scanning was performed, we observed a significant increase in grain density, which suggests spontaneous nucleation in undercooled molten Si as the origin of GCG. When we crystallized an isolated pattern of 6 × 6 µm2 under GCG conditions, single crystalline growth was successfully achieved.

An alternative method to determine the steady state nucleation rate in thermally annealed HWCVD a-Si:H films

A determination of the steady state nucleation rate r n in thermally annealed a-Si:H has typically been performed using TEM, where the increase in grain density with isothermal sample anneal time can be directly observed for samples with small crystalline volume fractions. Using the classical model of crystallite nucleation and grain growth, this paper presents an alternative technique for determining r n using in situ XRD measurements of the crystallization time and EBSD measurements of the final grain size, the latter in fully annealed samples. HWCVD a-Si:H samples containing different as-grown film H contents C H have been examined by both techniques, and the agreement between these techniques is excellent. R n is seen to decrease with increasing as-grown film C H. Differences in the values of r n are suggested as being due to variations in the transition rate per atom at the amorphous/crystalline interface.

Titanium as an endogenous grain-refining nucleus

Several studies have confirmed the applicability of the inverse growth restriction theory for predicting grain size in titanium alloy systems. However, until now, no work has identified nuclei particles that could be used to refine the β-grain size of titanium alloys during solidification. This work investigated whether titanium powder can be used to nucleate β-grains during solidification. A novel technique was used to introduce titanium powder to a series of titanium alloys, which results in significant grain refinement with an order of magnitude increase in grain density. Electron back-scattered diffraction (EBSD) was used to prove that titanium substrates can epitaxially nucleate titanium during solidification, and although a number of other potential mechanisms were investigated, it was concluded that the titanium particles heterogeneously nucleate β-grains.

Identification and characterization of the erect-pose panicle gene EP conferring high grain yield in rice (Oryza sativa L.)

The breeding of japonica varieties with erect-pose panicle (EP) has recently progressed in the northern part of China, because these varieties exhibit a far higher grain yield than the varieties with normal-pose panicle (NP). A genetic analysis using the F(2) population from the cross between Liaojing5, the first japonica EP variety in China, and the Japanese japonica NP variety Toyonishiki revealed that EP is governed by a single dominant gene EP. Based on previous studies, map-based cloning of EP locus was conducted using Liaojing5, Toyonishiki, their F(2) population, and a pair of near-isogenic lines for EP locus (ZF14 and WF14) derived from the cross between the two varieties; consequently, the STS marker H90 was found to completely cosegregate with panicle pose. The H90 is located in the coding sequence AK101247 in the database, and the AK101247 of Liaojing5 has a 12 bp sequence in exon 5 replaced with a 637 bp sequence of its wild type allele. It was therefore considered that the AK101247 encodes the protein of the wild type allele at EP locus, and that the sequence substitution in exon 5 of Liaojing5 is crucial for expression of the EP phenotype. The effects of EP gene on agronomic traits were investigated using two pairs of near-isogenic lines (ZF6 vs. WF6 and ZF14 vs. WF14) derived from the cross between the two varieties. Experimental results showed that EP gene markedly enhanced grain yield, chiefly by increasing number of secondary branches and number of grains on the secondary branch. EP gene also produced a remarkable increase in grain density.

Progesterone neuroprotection in spinal cord trauma involves up-regulation of brain-derived neurotrophic factor in motoneurons

Progesterone (PROG) provides neuroprotection to the injured central and peripheral nervous system. These effects may be due to regulation of myelin synthesis in glial cells and also to direct actions on neuronal function. Both types of cells express classical intracellular PROG receptors (PR), while neurons additionally express the PROG membrane-binding site called 25-Dx. In motoneurons from rats with spinal cord injury (SCI), PROG restores to normal the deficient levels of choline acetyl-transferase and of α3 subunit Na,K-ATPase mRNA, while levels of the growth associated protein GAP-43 mRNA are further stimulated. Recent studies suggest that neurotrophins are possible mediators of hormone action, and in agreement with this assumption, PROG treatment of rats with SCI increases the expression of brain-derived neurotrophic factor (BDNF) at both the mRNA and protein levels in ventral horn motoneurons. In situ hybridization (ISH) has shown that SCI reduces BDNF mRNA levels by 50% in spinal motoneurons, while PROG administration to injured rats (4 mg/kg/day during 3 days, s.c.) elicits a three-fold increase in grain density. In addition to enhancement of mRNA levels, PROG increases BDNF immunoreactivity in perikaryon and cell processes of motoneurons of the lesioned spinal cord, and also prevents the lesion-induced chromatolytic degeneration of spinal cord motoneurons as determined by Nissl staining. Our findings strongly indicate that motoneurons of the spinal cord are targets of PROG, as confirmed by the expression of PR and the regulation of molecular parameters. PROG enhancement of endogenous neuronal BDNF could provide a trophic environment within the lesioned spinal cord and might be part of the PROG activated-pathways to provide neuroprotection. Thus, PROG treatment constitutes a new approach to sustain neuronal function after injury.

Progesterone up-regulates neuronal brain-derived neurotrophic factor expression in the injured spinal cord

Progesterone (PROG) provides neuroprotection to the injured central and peripheral nervous system. These effects may be due to regulation of myelin synthesis in glial cells and also to direct actions on neuronal function. Recent studies point to neurotrophins as possible mediators of hormone action. Here, we show that the expression of brain-derived neurotrophic factor (BDNF) at both the mRNA and protein levels was increased by PROG treatment in ventral horn motoneurons from rats with spinal cord injury (SCI). Semiquantitative in situ hybridization revealed that SCI reduced BDNF mRNA levels by 50% in spinal motoneurons (control: 53.5±7.5 grains/mm 2 vs. SCI: 27.5±1.2, P<0.05), while PROG administration to injured rats (4 mg/kg/day during 3 days, s.c.) elicited a three-fold increase in grain density (SCI+PROG: 77.8±8.3 grains/mm 2, P<0.001 vs. SCI). In addition, PROG enhanced BDNF immunoreactivity in motoneurons of the lesioned spinal cord. Analysis of the frequency distribution of immunoreactive densities (χ 2: 812.73, P<0.0001) showed that 70% of SCI+PROG motoneurons scored as dark stained whereas only 6% of neurons in the SCI group belonged to this density score category ( P<0.001). PROG also prevented the lesion-induced chromatolytic degeneration of spinal cord motoneurons as determined by Nissl staining. In the normal intact spinal cord, PROG significantly increased BDNF inmunoreactivity in ventral horn neurons, without changes in mRNA levels. Our findings suggest that PROG enhancement of endogenous neuronal BDNF could provide a trophic environment within the lesioned spinal cord and might be part of the PROG activated-pathways to provide neuroprotection.

Numerical modeling of columnar to equiaxed transition with consideration of molten steel flow

The numerical model of columnar to equiaxed transition (CET) was constructed with consideration of molten steel flow. Solid shell growth was analyzed by using macroscopic heat flow model in addition to heat transfer due to the fluid flow at the solidification front, which was calculated by fluid flow model. At the same time, the dendrite tip temperature and the growth of equiaxed crystal in the undercooled liquid region was estimated and the CET position was diagnosed. By the application of electromagnetic stirrer (EMS), the superheat in the pool diminished and undercooled region was enlarged by heat transfer due to fluid flow at the solidification front. In addition, the ratio of equiaxed zone increased with the increase of grain density by EMS. Therefore, it has been estimated that solidification structure change by application of EMS was caused by superimposition of these two effects. Moreover the size of equiaxed crystal estimated by this model could show good agreements with experimental ones.

Angiogenesis during follicular development in the primate and its inhibition by treatment with truncated Flt-1-Fc (vascular endothelial growth factor Trap(A40)).

The aims of this study were to 1) quantify changes in angiogenesis during follicular growth in a primate model; 2) investigate the molecular regulation using in situ hybridization of vascular endothelial growth factor (VEGF), its receptor, Flt-1, the angiopoietins (Ang-1 and Ang-2), and their receptor, Tie-2; 3) elucidate the role of VEGF in follicular angiogenesis by blocking its action by treatment with a soluble truncated form of the Flt-1 receptor, (VEGF Trap(A40)). Changes in angiogenesis were quantified using bromodeoxyuridine to obtain a proliferation index, and CD31 immunocytochemistry to visualize endothelial cell area. Percentage of proliferating endothelial cells was calculated by double labeling for bromodeoxyuridine and CD31. Vascularization was first observed in follicles containing four granulosa cell layers. A significant increase in proliferation in the thecal layer was observed from the early to late secondary stage, and dual staining showed that 25% of proliferating cells were of endothelial cell origin. VEGF messenger RNA (mRNA) was expressed in granulosa cells with an increase of grain density from late secondary to tertiary follicles. Ang-1 was weakly expressed in the theca of tertiary follicles. Ang-2 mRNA was not detected in any follicles. The mRNA for the Flt-1 and Tie-2 receptors was localized in endothelial cells of the theca. Unexpectedly, Tie-2 mRNA was also found in granulosa cells of early follicular stages and its translation was confirmed by immunocytochemistry. VEGF trap treatment for 3 days resulted in an 87% decrease of proliferation in the theca of secondary and tertiary follicles, a reduction in endothelial cell area and a marked decline in Flt-1 mRNA expression. Granulosa cell proliferation also decreased. These results show that onset and establishment of the follicle vasculature takes place early during follicular development. The ability of VEGF trap treatment to severely restrict follicular angiogenesis establishes that VEGF is the major regulator of this process in the primate ovary.

Nerve Growth Factor Derived from Terminals Selectively Increases the Ratio of p75 to trkA NGF Receptors on Mature Sympathetic Neurons

Exposure of neuronal terminals to target-derived NGF has been hypothesized to regulate cell body responses at a distance. To test this hypothesis and, more specifically, to determine whether NGF distally regulates the synthesis of its two characterized receptors, we developed the following paradigm. Sympathetic neurons of the superior cervical ganglion (SCG) that project either to the eye or to the ear were labeled, in adult animals, with the retrograde tracers Fast Blue and Fluoro-Gold, respectively. NGF was then injected daily into the anterior chamber of one eye, exposing the terminals of the ipsilateral eye neurons to increased NGF. To control for systemic and/or localized injury effects, cytochrome C or PBS were injected into the contralateral eye of the same animals. In situ hybridization and image analysis were then used to determine neuronal levels of p75 NGF receptor, trkA, and Tα1 α-tubulin mRNAs, with the latter providing a correlative measure of neuronal sprouting. Morphological measurements revealed that exogenous, terminally-derived NGF increased the mean cross-sectional area of eye neurons by 37%. Grain counts for p75 NGF receptor mRNA increased from 2- to 6-fold in the NGF-treated neurons, and grain densities, which accounted for neuronal hypertrophy, also increased significantly. In contrast, grain counts for trkA mRNA were not significantly increased by this treatment, while Tα1 α-tubulin mRNA levels increased only 1.5- to 2-fold. No increase in grain density was detected for either of these mRNAs. The NGF-induced increased in p75 NGF receptor mRNA levels was accompanied by terminal sprouting and by an increase in the density of p75 NGF receptors on terminal neurites, as indicated by IgG-192 immunostaining of the NGF-treated iris. These data therefore suggest that, in addition to promoting local sprouting, increased target-derived NGF increases the levels of p75 NGF receptor relative to trkA on terminal neurites, by differentially regulating receptor synthesis. Such a direct regulatory feedback loop may well play an integral role in precisely modulating neuronal responses as a function of the amount of available trophic support and/or target tissue.

Cerebellar benzodiazepine receptors: cellular localization and consequences of neurological mutations in mice

The distribution of cerebellar [ 3H]flunitrazepam binding sites was studied autoradiographically in Purkinje cell degeneration ( pcd/pcd), weaver ( wv/wv), staggerer ( sg/sg) and reeler ( rl/rl) mutant mice. In the normal 78-day-old C57BL/6J mouse cerebellum, the highest concentration of [ 3H]flunitrazepam binding sites was observed over the molecular layer. Intermediate grain density was present over the Purkinje cell layer and intermediate to high density over the deep cerebellar nuclei. Low labeling was observed over the granule cell layer. Negligible concentrations of binding sites were seen in the white matter. In 45–49-day-old Purkinje cell degeneration mutants, where essentially all Purkinje cells have disappeared by day 45, there was a small decrease in grain density over the cerebellar cortex. Concomitantly, a substantial increase in grain density was observed over the deep cerebellar nuclei of the pcd/pcd mutants when compared to littermate controls. A significant increase in [ 3H]flunitrazepam labeling was observed over the cerebellar cortex of 81–86-day-old wv/wv mutants; this was most pronounced in the vermis where the granule cell loss was greatest. Over the hemispheres, where fewer granule cells degenerate, a lower density of binding sites was seen. Grain density over the wv/wv deep cerebellar nuclei was comparable to that of littermates. Substantially lower [ 3H]flunitrazepam labeling was detected over the cerebellar cortex of 25–27-day-old sg/sg mutants in which the number of granule. Purkinje and Golgi cells is greatly reduced; the labeling over the deep nuclei, however, was significantly increased. In 27–29-day-old rl/rl mutant cerebella, where all classes of cells are malpositioned, labeling density over all areas of the cerebellar cortex, including the Purkinje cell masses. was increased. Our autoradiographic data suggest that a proportion of cerebellar cortical benzodiazepine receptors are associated with Purkinje cells; we propose that the remainder of the receptors are localized on Golgi cells, while granule cells are devoid of receptors. In the deep cerebellar nuclei, the observed increase in benzodiazepine receptors in the pcd/pcd and sg/sg mutants may be a manifestation of denervation supersensitivity subsequent to the loss of innervation by Purkinje cell axon terminals. The finding of a high receptor density in the Purkinje cell masses of the rl/rl mutant, where Purkinje cells are devoid of afferent basket cell input, suggests that benzodiazepine receptors are expressed and maintained in the absence of a full complement of GABAergic afferents.

Processes of Selective Grain Transport and the Formation of Placers on Beaches

Placers are found on many beaches of the Oregon coast. In the beach that is the focus of this study, the principal placer minerals are ilmenite (22.0%), epidote (20.0%), garnet (18.7%), augite (15.5%), hypersthene (8.1%), hornblende (5.8%) and zircon (2.0%), the "ilmenite" fraction actually being partly chromite. A series of beach-face sand samples was obtained along a profile when sand was being eroded from the upper beach and transported to offshore bars, since the processes of grain-selective sorting leading to placer formation were probably most active at such a time. The landward-most sample contained 96% heavy minerals, being part of the placer. This concentration systematically decreased offshore to a 6% heavy-mineral content in the seaward-most sample (54 m offshore). Determinations of individual heavy mineral concentrations revealed that, although they all tended to become concentrated within the placer with light quartz and feldspar dominating the offshore transport, the sorting processes were most effective in concentrating the ilmenite (concentration factor = 1403) and least efficient in concentrating the hornblende (factor = 5). All of the minerals form a pattern of increasing efficiency of concentration within the placer with an increase in grain density and decrease in mean grain size. Thus the sorting processes are most effective in concentrating the ilmenite, which is both the densest and finest-grained of the minerals present in the beach, least efficient for the hornblende, which has the lowest density and is the coarsest of the heavy minerals. Measurements of grain settling velocities indicate that this parameter cannot account for the observed selective grain sorting. Instead, evaluations of the selective entrainment and transport rates of the mineral grains yield trends which exactly parallel their observed concentration factors within the placer, indicating the probable dominance of these grain-sorting processes in placer formation. Shear sorting of the light and heavy minerals may also be an important process, but its role could not be determined in the present study.

Changes of the protein metabolism in rat spinal motoneurons and perineuronal glial cells induced by anticipation stress and the administration of diazepam. A cytospectrophotometric and autoradiographic study

In rats, subjected repeatedly to anticipation stress, an increase of the size of spinal motoneurons (parallel with an increase of their total protein content) was observed. No similar changes occurred in perineuronal glial cells. A single administration of diazepam prevented the stress-induced changes in motoneurons, but concomitantly increased the volume and protein content of glial cell nuclei. Quantitative autoradiography did not reveal a significant increase of grain density over the neurons of stressed animals which had been injected with 4,5-[ 3H]leucine. After a single administration of diazepam to the stressed animals, however, the grain density over neuronal perikarya as well as over neuronal nuclei increased markedly. Analysis of the precursor pools and estimation of specific activities of proteins in brain, liver, testes and thymus indicated that (i) diazepam-induced changes in the size of the pool of radioactive precursors are the main factor which causes the increase of grain density, observed in autoradiograms. and (ii) diazepam decreases the utilization of labelled leucine for the synthesis of proteins in brain and liver. The experiments suggest that the repeated exposure to stress is associated with changes in the macro-molecular metabolism and size of single motor nerve cells. The activation of perineuronal glial cells is suggested to one mode of action of diazepam, but whether this contributes to its effect on behaviour is unknown.

Protein synthesis in regenerating motor neurons in the cockroach

Protein synthesis was studied in the thoracic ganglia of the cockroach. All the motor neurons leaving the metathoracic ganglion were axotomized by cutting the nerve roots. In vivo experiments demonstrated that within two days of the operation those ganglia with cut nerve roots had an increased [ 3H]leucine incorporation into protein resulting from an increased uptake and labeling of the leucine pool. These effects were non-specific responses to the damage and trauma produced by the operation. In vitro labeling experiments failed to demonstrate any change in incorporation or uptake of [ 3H]leucine up to 16 days after the operation. Autoradiographic experiments w were done on ganglia in which only nerve root 5 on one side was cut. Grain densities and cytoplasmic areas were measured for the ipsilateral, axotomized, identified, fast motor neuron, D f and the homologous, contralateral, intact cell of the same ganglion. The first statistically significant increase in grain density in the axotomized D f was observed 12 days after the operation. This may be compared with the 13 day lag period after the operation before the nerves start growing from the proximal stump. The significance of this relatively long lag period before the increased [ 3H]-leucine incorporation and the start of nerve growth is discussed in terms of the ability of regenerating neurons to specifically reinnervate the cells to which they were originally c connected.

The sites of iodide concentration in the oviduct and the uterus of the rat.

SUMMARY Previous studies have shown that under the influence of progesterone the concentrations of radioiodide in the uterus and oviduct of the rat are maintained at levels higher than that in the plasma. In the present experiments the uterus and oviducts from rats killed 2 h after the injection of Na125I were autoradiographed by a technique which permits the localization of diffusible radioactive material. In intact non-pregnant rats and ovariectomized rats not injected with progesterone, uniformly low grain densities were observed over sections of oviduct and uterus with the exception of the epithelium and lumen of the oviduct where some increase in grain density was observed. In intact and ovariectomized rats treated with progesterone and in rats killed on Day 3 or 4 of pregnancy, grain densities over the epithelium and lumen of the oviduct were very high but the fimbria of the oviduct were consistently unlabelled. The stroma underlying the oviduct epithelium was also labelled. In the uteri of these animals the principal site of concentration of radioiodide was the luminal epithelium, but for technical reasons it was not possible to exclude the stroma immediately adjacent to the luminal epithelium as a less active site of concentration of iodide. No other site in the uterus concentrated radioiodide. The luminal epithelium occupies less than 3% of the volume of the uterus in ovariectomized rats: if this tissue is taken as the sole site of iodide concentration in the uterus, the levels reached in these cells must be at least a hundred times that of the plasma when the overall uterus: plasma concentration ratio for radioiodide is 4 or more.

An Unusual Electron Shower

Figure 1 depicts an event observed in a 600 � glass-backed Ilford G5 emulsion. The shower occurred at point 0 as indicated by a sudden increase in grain density of the incident track. For the first 150 � from 0 the grain density of all secondary tracks (which are not separated) is 46 �4 grains per 50 (�, approximately 3�5 times the plateau value (13�0 grains/50 �). 200 � from 0 five tracks are resolved and the sum of their grain densities is 64 � 2 grains/50 �, approximately five times plateau. These values suggest that one track originated some 150?200 � from 0, although the possibility that it originated at 0 is not entirely excluded.

Variation of Grain Density with Temperature of Exposure in Nuclear Emulsions

Ilford C-2 unloaded and C-2 boron loaded plates, subjected to temperature changes varying from −66°C to +66°C, were bombarded with 10-Mev neutrons. The recoil protons showed that the temperature change had caused an increase in grain density which varied as much as ⅓ from −66°C to +25°C. Although the C-2 boron loaded plates showed a greater initial grain density than the unloaded plates, the ⅓ increase was preserved.