Results 1 - 10 of 5115
Results 1 - 10 of 5115. Search took: 0.035 seconds
|Sort by: date | relevance|
[en] Microstructural changes in nanocrystalline materials are driven by their high grain boundary density and greater mobility at elevated temperatures. For instance, segregation, precipitation, and grain growth become active as the temperature increases. The potential of nanometallic multilayers as a route to synthesize nanostructures is explored examining the microstructural evolution of Hf-Ti nanometallic multilayers through differential scanning calorimetry and characterization at different temperatures. Thermodynamic and kinetic calculations were performed to understand the observed transitions. This study presents a guide to microstructural changes in nanometallic multilayers which can be used to develop new nanocrystalline systems.
[en] Friction stir welding is essentially a solid state joining process and this method is being used for joining variety of metals and alloys including Al alloys, Mg alloys and steels. This joining process eliminates several welding defects such as hot cracking and porosity in the welding zone. It is well reported that the there is a large variation in the grain size and microhardness in the friction stir welded zone and these parameters adversely affect the mechanical properties of the welded joint. The objective of the present work is to determine the nature of microstructure, microtexture and variation of composition in the welding direction. The paper presents details of microstructural changes at various regions in the weld zone
[en] Mineral grains and grain aggregates in meteorites carry potential information on the conditions in the environment where they formed. To avoid model-dependent interpretations it is necessary to develop experimental criteria that uniquely reflect the environmental parameters of interest. These parameters include the various temperatures of the source medium and the temperature of grains at growth all of which are observed to be highly differentiated in the space medium in accordance with the radiation laws. (orig./WL)
[en] Large bulk Y-Ba-Cu-O superconductors, 62 mm in diameter and 12 mm in thickness, have been fabricated by a cold seeding method in which four seeds are placed on top of the precursor at room temperature prior to melt processing. The advantage of a cold seeding technique is that the desired seeding location can be arranged at room temperature. However, due to the reaction of the seed with the precursor at high temperatures, controlled single-grain growth has been difficult. In the present study, we carefully investigated the influence of the processing parameters such as the maximum heating temperature, the dwelling time at this temperature, the temperature to start slow cooling and the slow cooling rate on the grain growth behavior. Through the optimization of these processing parameters, we have succeeded in growing large bulk Y-Ba-Cu-O with four large grains. The sample with 1 wt% CeO2 addition showed almost the same field trapping ability as a single-domain sample.
[en] The orientation distribution of the ''C''-axes with respect to the columnar, or growth, axes of columnar grains in large beryllium castings has been measured by an optical technique. The distribution is nearly random, with a small tendency for the ''C''-axes to be perpendicular to the growth axis. The distribution of angles between the ''C''-axes of adjacent grains is nonrandom; small angle boundaries are favored and there is some indication of the existence of growth twins
[en] The comparison of sintering behavior and mechanical properties of ultra-fine WC-10wt.%Co and WC-10wt.%Fe hard materials produced by High-Frequency Induction Heated Sintering (HFIHS) was accomplished using ultra fine powder of WC and binders(Co, Fe). The advantage of this process allows very quick densification to near theoretical density and prohibition of grain growth in nano-structured materials. Highly dense WC-10Co and WC-10Fe with a relative density of up to 99% could be obtained with simultaneous application of 60 MPa pressure and induced current within 1 minute without significant change in grain size. The hardness and fracture toughness of the dense WC-10Co and WC-10Fe composites produced by HFIHS were investigated
[en] We present observations in eight wavebands from 1.25 to 24 μm of four dense cores: L204C-2, L1152, L1155C-2, and L1228. Our goals are to study the young stellar object (YSO) population of these cores and to measure the mid-infrared extinction law. With our combined near-infrared and Spitzer photometry, we classify each source in the cores as, among other things, background stars, galaxies, or embedded YSOs. L1152 contains three YSOs and L1228 has seven, but neither L204C-2 nor L1155C-2 appear to contain any YSOs. We estimate an upper limit of 7 x 10-5 to 5 x 10-4 Lsun for any undiscovered YSOs in our cores. We also compute the line-of-sight extinction law toward each background star. These measurements are averaged spatially, to create χ2 maps of the changes in the mid-infrared extinction law throughout our cores, and also in different ranges of extinction. From the χ2 maps, we identify two small regions in L1152 and L1228 where the outflows in those cores appear to be destroying the larger dust grains, thus altering the extinction law in those regions. On average, however, our extinction law is relatively flat from 3.6 to 24 μm for all ranges of extinction and in all four cores. From 3.6 to 8 μm, this law is consistent with a dust model that includes larger dust grains than the diffuse interstellar medium, which suggests grain growth has occurred in our cores. At 24 μm, our extinction law is two to four times higher than predicted by dust models. However, it is similar to other empirical measurements.
[en] Silicon (Si) has been considered a beneficial element for plant growth. We have assessed the effects of Si application on rice (Oryza sativa L.) growth and its grain yield at field level. For this, we performed two experiments. In experiment 1, we applied Si of three different concentrations (liquid Si-10, 25 and 36%) to the seedbed of rice before transplantation into paddy field. The results of this experiment showed that Si application to rice seedbeds did not affected the rice plant height and shoot fresh weight but its application significantly increased the pushing resistance of rice plants from 12.2-16.7% as compared with water applied control plants. The lodging index of Si treated rice plants significantly decreased (13.7% on LS-25) as compared with control. Similarly, Si treated plants had significantly higher yield. Upon Si treatment (LS-36), the grain yield per 10 acre and panicles per plant were 15.1% and 6. 3% higher than the water treated control plants respectively. The best concentration (LS-36%) revealed in the first experiment was foliar applied at 10 days before heading stage, initial tilling stage and panicle initiation stage to the rice leaves and we observed that shoot biomass was not significantly different between control and Si treated plants. However, significantly higher pushing resistance (10.5%-13.8%) and plant height (12.2%-16.7%) were observed while lower lodging index (7.6-7.8%) was recorded for Si treated plants as compared to control plants. Similarly, Si application increased the number of panicles per plant as well as the grain yield per 10 acre as compared to control. In conclusion, the Si application can significantly regulate plant growth and yield if applied at proper time with feasible concentration. (author)
[en] This paper will review recent advancements in our understanding of protoplanetary disks, the region where we expect planets to form. We include a discussion of transition disks and their relevance for our understanding of planet formation. We summarize observational evidence for grain growth and alteration, and discuss the challenges to understanding planetesimal formation