Large Number Of Grains Research Articles

Pollen anomaly - a clue to natural hybridity in Argemone (Papaveraceae)

Studies in the pollen morphology of Argemone mexicana (a diploid species, 2n=28), A. ochroleuca (a tetraploid, 2n=56), the wild populations of which growing side by side, and of a triploid (2n=42) observed in the population of A. ochroleuca, have been carried out using light and scanning electron microscope. Pollen grains in both the species are 3 (-4)-zonocolpate with reticulate exine surface, and are distinguishable only on the basis of pollen size, the tetraploid species having larger pollen grains. In the triploid plant, a large number of grains deviates from the normal 3-zonocolpate condition showing a number of apertural types, such as 1-aperturate-operculate, 2-colpate, 3-syncolpate, 4-zonocolpate and spiraperturate. Besides, planaperturate 3-colpate-trilobed grains also occur. The triploid is also characterised by 'minigrains' (size 13-19 μm), a feature not observed in A. mexicana and A. ochroleuca. Since these species are reported to be genetically close, the occurrence of the triploids (forming nearly 5% of the population of A. ochroleuca) indicates the possibility of a natural hybridization between A. ochroleuca and A. mexicana, which is well pronounced on its anomalous pollen features serving as marker for such a hybrid occurring in nature.

Airborne intensified charge‐coupled device observations of the 1998 Leonid shower

Abstract— We have used dual coaxial microchannel plate image‐intensified monochrome charge‐coupled device (CCD) detectors run at standard NTSC frame rates (30 frames per second, fps) to study the Leonid meteor shower on 1998 November 17 from an airborne platform at an altitude of ∼13 km. These observations were part of NASA's 1998 Leonid multi‐instrument aircraft campaign (MAC). The observing systems had fields of view (width) of 16.3° and 9.5°, and limiting stellar sensitivities of +8.3m and +8.9m. During 12 h of recording, 230 meteors were detected, of which 65 were Leonid meteors. Light curves are presented for 53 of these meteors. The magnitudes at peak brightness of the meteors investigated were generally in the range from +4.0m to +6.0m. The mass distribution indices for the two samples are 1.67 and 1.44, with the former being based on the wider field of view dataset. The light curves were skewed with the brightest point towards the beginning of the meteor trail. The F parameter for points one magnitude below maximum luminosity had a mean value of 0.47 for the wider field system and 0.37 for the more sensitive narrower field system. We provide leading and trailing edge light curve slopes for each meteor as another indication of light curve shape. There were few obvious flares on the light curves, indicating that in‐flight fragmentation into a large number of grains is not common. There is variability in light curve shape from meteor to meteor. The light curves are inconsistent with single, compact body meteor theory, and we interpret the data as indicative of a two‐component dustball model with metal or silicate grains bonded by a lower boiling point, possibly organic, substance. The variation in light curve shape may be indicative of differences in mass distribution of the constituent grains. We provide trail length vs. magnitude data. There is only a slight hint of a bend at +5m in the data, representing the difference between meteors that have broken into a cluster of grains prior to grain ablation, and those that continue to fragment during the grain ablation phase. Two specific meteors show interesting light curve features. One meteor is nebulous in appearance, with significant transverse width. The apparent light production region extends for 450 m from the center of the meteor path. Another meteor has several main fragments, and evidence of significant separated fragments. We offer several suggestions for improvements for the 1999 Leonid MAC light curve experiment.

Photothermal methods : application to diamond, aluminium nitride and zirconia

Photothermal methods have turned out to be a very interesting way to carry out the study of complex materials such as functional ceramics (polycrystalline diamond - aluminium nitride - zirconia) whose thermal properties have to be determined at different spatial scales if one wants to optimize their thermal behaviour. Results at microscopic scales (diffusivity at the scale of one single grain and thermal barriers at grain boundaries) and at macroscopic scales (averaged value of the diffusivity on a large number of grains and interfaces) are presented.

Linhagens diaplóides de trigo: produção de grãos, características agronômicas e tolerância à toxicidade de alumínio

Compararam-se 18 linhagens de trigo diaplóides obtidas via cultura de anteras de plantas híbridas, em geração F1, e os cultivares Al Res 102/84 e IAC-24, em quatro ensaios instalados em condições de irrigação por aspersão e de sequeiro. Analisaram-se a produção de grãos, outros componentes da produção, características agronômicas e resistência à ferrugem-da-folha. Estudou-se também a tolerância ao alumínio em soluções nutritivas, em condição de laboratório. A linhagem diaplóide 5, provinda do cruzamento IAS-63/ALDAN "S"//GLEN/3/IAC-24, de porte baixo, mostrou resistência ao acamamento e ao agente causal da ferrugem-da-folha e tolerância à toxicidade de alumínio, destacando-se, ainda, quanto à produção de grãos. A linhagem 6 identificou-se como fonte genética de maior número de grãos por espigueta, porte baixo, resistência ao acamamento e à ferrugem-da-folha, e a linhagem 8 apresentou espigas mais compridas e maior número de espiguetas por espiga. Todos os genótipos avaliados, com exceção do cultivar IAC-287 (controle sensível) exibiram elevada tolerância à toxicidade de alumínio.

Grain nitrogen concentration differences among three sorghum hybrids with similar grain yield

The differences in grain nitrogen (N) concentration among 3 sorghum (Sorghum bicolor (L.) Moench) hybrids with similar grain yield were examined under N-limiting conditions in relation to the availability of assimilate and N to grain. Several manipulation treatments [N fertiliser application, lower leaves shading, thinning (reduced plant population), whole canopy shading, canopy opening, spikelet removal] were imposed to alter the relative N and assimilate availability to grain under full irrigation supply. Grain N concentration increased by either increased grain N availability or yield reduction while maintaining N uptake. Grain N concentration, however, did not decrease in the treatments where relative abundance of N compared with assimilate was intended to be reduced. The minimum levels of grain N concentration differed from 0.95% (ATx623/RTx430) to 1.14% (DK55plus) in these treatments. Regardless of the extent of variation in assimilate and N supply to grain, the ranking of hybrids on grain N concentration was consistent across the manipulation treatments. For the 3 hybrids examined, higher grain N concentration was associated with higher N uptake during grain filling and, to a lesser extent, with higher N mobilisation. Hybrids with larger grain N accumulation had a larger number of grains. There was no tradeoff between grain N concentration and yield, suggesting that grain protein concentration can be improved without sacrificing yield potential.

Effect of grain orientation on deformation structure in cold-rolled polycrystalline aluminium

Pure (99.996%) polycrystalline aluminium (grain size about 300μm) has been cold-rolled to reductions in the range from 5 to 50% (εvm=0.06–0.80) and the deformation microstructure has been analysed by TEM in a large number of grains. The deformation microstructure is subdivided by dislocation boundaries having different characteristics depending on the orientation of the deformed grain. An analysis of the dislocation boundaries based on Frank's formula shows that the majority of the dislocations in the boundaries originate from active slip systems predicted by a Schmid factor analysis. Thereby a link is created between the microstructural evolution and the macroscopic plastic behaviour. The boundary parameters have also been used in a calculation of the dislocation density and the stored energy for grains of different orientations. These calculations together with measurements of the angular misorientation distribution shows that microstructural differences caused by differences in grain orientation are enhanced as the strain is increased.

Electrodeposition of Copper under Microgravity Conditions

Copper was electrodeposited from 0.9 M aqueous solution for 8 s during a free‐fall experiment in a drop shaft. A horizontally oriented quasi two‐dimensional electrolytic cell, in which a 200 μm thick electrolyte layer was sandwiched between two sheets of slide glass, fell in the shaft. Electrolysis was conducted at constant current densities from 0.05 to , and the potential difference between electrodes was simultaneously monitored. A common‐path microscopic interferometer was installed in the capsule. The time variation of interference fringe pattern, corresponding to the concentration profile due to the ionic mass‐transfer rate accompanied with copper electrodeposition, was measured in situ around the periphery of a 1 mm diam circular cathode. The morphology of copper electrodeposited under microgravity conditions was compared with that obtained in a ground level experiment. The development of diffusion layer thickness measured by the interferometer increased with the square root of time during the 8 s experiment. The transient diffusion model combined with the migration effect reasonably explained the development of diffusion layer thickness. Calculated surface concentrations corresponded with the measured time variation of potential difference between electrodes. Under the gravitational field, the radius of annual interference fringe pattern developed at a rate much faster than that under microgravity, beginning 1 or 3 s after initiation of electrodeposition. Natural convection was evident in the ground level experiment, even using such a shallow electrolyte layer. Under microgravity, lower index planes preferentially grew to form a smaller number of larger grains, even though electrodeposition was conducted at only for 8 s.

On the structure and composition of polycrystalline carbon nitride films synthesized by reactive rf magnetron sputtering

Polycrystalline β-C 3N 4 films have been deposited on single-crystal KCl(100) substrates using reactive rf magnetron sputtering. The films have been characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy. A large number of grains are found distributed in various regions of the film. The dimension of the largest grain is about 4 μm. The film is composed mainly of C and N with a small amount of O. XPS data show N-bonded to sp 3-hybridized C with some surface oxidation. The N/C ratio in the β-C 3N 4 region is deduced to be 1.23–1.27, close to an expected stoichiometric value of 1.33. The TED-measured interplanar spacings suggest that the crystalline grains are hexagonal with lattice parameters of a=6.30 Å and c=2.46 Å.

Kinetics of Grain Growth in a γ-Based TiAl Alloy

The strength and ductility of two-phase TiAl alloys are very dependent on microstructural size and morphologies and much research is being devoted to obtaining optimal properties. Recent research carried out on alloys produced by consolidation of powders of composition Ti-48Al-2Mn-2Nb-0.06C confirmed that very fine grain sizes are obtained by HIPping the atomized powders. This is due to the recrystallization of the initial cellular structures and the presence of the {alpha}{sub 2} phase at the boundaries between {gamma} grains that helps pinning them and slow down their growth. Such fine microstructures appear interesting to study the kinetics of grain growth as a larger number of grains can be measured thus providing good statistics for a proper analysis of the mechanisms involved in the process. The present study presents such analysis aiming at a better understanding of structure coarsening in {gamma}-based TiAl alloys.

Magnetic anisotropy produced by magma flow: theoretical model and experimental data from Ferrar dolerite sills (Antarctica)

SUMMARY Volcanic rocks forming sills, dykes or lava flows may display a magnetic anisotropy derived from the viscous flow during their emplacement. We model a sill as a steadystate flow of a Bingham fluid, driven by a pressure gradient in a horizontal conduit. The magma velocity as a function of depth is calculated from the motion and constitutive equations. Vorticity and strain rate are determined for a reference system moving with the fluid. The angular velocity and the orientation of an ellipsoidal magnetic grain immersed in the fluid are calculated as functions of time or strain. Magnetic susceptibility is then calculated for a large number of grains with a uniform distribution of initial orientations. It is shown that the magnetic lineation oscillates in the vertical plane through the magma flow direction, and that the magnetic foliation plane changes periodically from horizontal to vertical. The results are compared with the magnetic fabric of Ferrar dolerite sills (Victoria Land, East Antarctica) derived from low-field susceptibility measurements.

Estimation of heavy and opaque mineral contents of beach and offshore placers using rock magnetic techniques

Exploration for placer deposits involves heavy and opaque mineral data that are conventionally obtained using toxic and expensive chemicals and time-consuming and tedious microscopic counting of a large number of grains. In this investigation, we have used rock magnetic properties to obtain estimates of heavy and opaque mineral contents of placers from the SW coast of India. Magnetic susceptibility and other magnetic properties show strong correlations with heavy and opaque (r > 0.87 andr > 0.94; significant at the 1% level) mineral contents. As one or more types of magnetic minerals are invariably present in placers, magnetic properties may be used as a “proxy” for heavy and opaque mineral contents. This simple, rapid, inexpensive, and nondestructive method may be adopted by those involved in placer exploration to rapidly scan a large number of samples and delineate economically important pockets for more detailed investigations. This method saves considerable time and tedium. Using magnetic properties, rather than radioactivity, as a proxy for heavy and opaque mineral contents is more advantageous because one or more magnetic minerals are always present, but a radioactive mineral may not always be present in placers. An important limitation is that the ratio of magnetic to heavy/opaque mineral contents should not vary widely.

Avaliação de genótipos de trigo oriundos de cruzamento interespecífico e radiação gama no estado de São Paulo

Foram comparadas entre si e com dois controles vinte e três linhagens hexaplóides originárias de seleções realizadas em população submetida à radiação gama (27,5 krad), em geração F4, do cruzamento interespecífico entre BH-1146 (Triticum aestivum L.) e Anhinga "S" x Winged "S" (T. durum L.). Em nove ensaios em condições de irrigação e de sequeiro, analisou-se uma série de características agronômicas. Em laboratório efetuaram-se estudos da tolerância ao alumínio. As linhagens 11 e 19 de porte médio, com moderada resistência ao acamamento, tolerantes à toxicidade de alumínio destacaram-se quanto à produção de grãos. Sete linhagens apresentaram moderada resistência ao agente causai do oídio. Todos os genótipos foram suscetíveis aos agentes causais das manchas foliares. Alguns dos genótipos poderiam ser utilizados em programas de cruzamento como fontes genéticas para plantas de porte baixo, de espiga comprida, de grande numero de espiguetas por espiga, maior número de grãos por espiga, e maior número de grãos por espigueta e de grãos mais pesados. BH-1146 e sete das linhagens foram considerados os genótipos mais tolerantes à toxicidade de alumínio por por exibirem crescimento radicular após serem cultivados em soluções nutritivas contendo 10 mg/litro de Al+3.

Melhoramento do trigo: XXVIII. Novos genótipos obtidos por seleções em população segregante interespecífica submetida a irradiação gama

Compararam-se 23 linhagens provindas de seleções em população submetida à irradiação gama (27,5 krad), em geração F4, do cruzamento interespecífico entre 'BH-1146' (Triticum aestivum L.) e 'Anhinga' "S" x Winged "S" (Triticum durum L.) e os cultivares BH-1146 e Yavaros "S" (T. durum L.) em nove ensaios, denominados "Novas variedades III", instalados em condições de irrigação por aspersão e de sequeiro, analisando-se a produção de grãos, outros componentes da produção e resistência às doenças. Em condição de laboratório, estudou-se a tolerância ao alumínio em soluções nutritivas. As linhagens 11, 12, 13 e 14, de porte médio, com moderada resistência ao acamamento, com ciclo médio da emergência ao florescimento e tolerância à toxicidade de alumínio, destacaram-se quanto à produção de grãos, considerando-se a média dos nove experimentos. Yavaros "S" e as linhagens 8 e 12 apresentaram-se, ao mesmo tempo, imunes ao agente causal da ferrugem-da-folha e moderadamente resistentes ao agente causal de oídio. Todos os genótipos foram suscetíveis aos agentes causais de manchas foliares. As linhagens 3, 9 e 10 mostraram ser fontes genéticas de espiga comprida; a 12, de maior número de espiguetas por espiga; as linhagens 12, 13 e 14, de maior número de grãos por espiga; Yavaros "S", de maior número de grãos por espigueta, e 1, 2, 3, 4, 6, 7, 10, 15 e Yavaros "S", de grãos mais pesados. Todos os genótipos se mostraram tolerantes à toxicidade de Al3+, com exceção de Yavaros "S" e das linhagens 9 e 15, que exibiram elevada sensibilidade.

Grain impingement during solidification of cast iron

Simulations and experiments have been used to study the problem of grain impingement in cast iron. Calculation of the free surface in a volume which contains a large number of grains results in Avr...

Density of comet Shoemaker–Levy 9 deduced by modelling breakup of the parent 'rubble pile'

FOR a week beginning 16 July 1994, fragments of comet Shoemaker-Levy 9 will collide with Jupiter each day. Although the fragments are probably smaller than originally estimated1, the impacts may nevertheless have observable consequences that will provide valuable insight into the properties of comets and the dynamics of planetary atmospheres. Interpretation of these observations will depend sensitively on parameters such as the mass, density and overall structure of the fragments. To deduce some of these parameters, we have simulated the event that created the fragments—the passage of the parent comet through the tidal field of Jupiter in 1992. Modelling the comet as a strengthless aggregate consisting of a large number of grains, we find that the tidally disrupted body condenses rapidly into clumps, driven by their selfgravity. Formation of a fragment chain resembling Shoemaker-Levy 9 occurs for a narrow range of the simulated comet's bulk density, 0.3–0.7 g cm −3. A chain of ∼20 similar-sized fragments matching observations is obtained for a non-rotating parent comet of 1.5 km diameter and bulk density 0.5 g cm−3, suggesting that the clusters will each liberate ∼1027 erg on impact. A slightly larger initial density leads to significant mass variation among the clusters and the possibility of a few ∼1028-erg events.

A method for determination of volcanic glass concentrations in sedimentary sequences and its application to quaternary studies

AbstractA method for determination of volcanic glass concentration in sedimentary sequences is presented. This method consists of two steps: (1) systematic extraction of volcanic glass particles from samples taken at close intervals in a sedimentary section, and the determination of their concentration; (2) precise measurement of the refractive indices of the separated glass particles. A recently developed measuring system (RIMS 86) based on the thermal immersion method permits quick and accurate measurement of the refractive index of a large number of grains within samples. Based on these kinds of data, we typically recognize five types of concentration of volcanic glass shards in sedimentary sequences. The method proposed here enables the simultaneous determination of the refractive index of glass shards and the proportion of glass shards in a sample, which makes it possible to recognize certain ash‐fall‐horizons, even those undetectable through visual observation of a sedimentary column. © 1994 John Wiley & Sons, Inc.

Pituitary adenylate cyclase activating peptide (PACAP) mRNA in the rat neocortex

In agreement with previous studies, Northern blots revealed expression of pituitary adenylate cyclase-activating peptide (PACAP) mRNA in the rat cerebral cortex. In order to identify the cells expressing PACAP mRNA, semiquantitative in situ hybridization histochemistry was applied. A moderate concentration of PACAP mRNA transcripts was determined in the cingulate and frontal cortices, whereas lower concentrations were found in other cortical areas. In emulsion dipped sections, grains were detected over cell bodies in cortical layers II, III and IV. Grains were diffusely distributed over cells in the outer granular layer of the anterior cingulate and the retrosplenial areas. In the outer pyramidal cell layer a few neurons contained a large number of grains. These data show that PACAP mRNA is present in cells outside the hypothalamus and implies that PACAP could play a broader transmitter role in the CNS than earlier anticipated.

A two‐dimensional particle‐in‐cell model of a dusty plasma

Dusty plasmas are present in comets, in the ring systems of the outer planets, and in the interstellar medium. A two‐dimensional particle‐in‐cell (PIC) model of a dusty plasma is presented in this paper. The PIC code is best suited for modeling the plasma‐dust interaction for large grains, with diameters of the order of a centimeter. We have modeled the charging process for an individual dust grain and the associated potential pattern in the surrounding plasma. We have also considered the case of a large number of grains in a plasma, with intergrain separations of the order of the Debye length, and have shown that the plasma becomes depleted and the charge on a dust grain is reduced, as other workers in this field have predicted (cf. C. K. Goertz, 1989). We examine the electron and ion distribution functions in the vicinity of a charged grain and demonstrate that the ions near a grain have clearly been accelerated by the electrostatic potential.

Effect of ramp treatment on the cyclic response of coarse-grained copper

Recent studies on the effects of different variables, both intrinsic and extrinsic to the material itself, on the cyclic response of polycrystalline copper have been encouraging in the drive to understand the phenomenon of localized deformation during fatigue. In studying the effect of two intrinsic material parameters (grain size and annealing texture) on the cyclic response of f c c polycrystals, several sets of workers [1-3] have reported that the cyclic response of coarse-grained metal shows much more pronounced cyclic hardening and higher stresses, at low and intermediate strain amplitudes, than those for fine-grained metal. This behaviour is associated, in copper, with the strongly defined hard (1 1 1 ) ( 10 0) fibre texture, inherited in the coarsegrained material after annealing at relatively high temperatures [1]. Llanes et al. [1] also showed that in large-grained, strong-textured copper specimens, double and multiple slip related structures are already promoted in a relatively large number of grains (those oriented to favour multiple slip) at plastic strain amplitudes as low as 10 .4 . This early multiple slip activation homogenizes the deformation and seems to be the main factor contributing to the very strong cyclic hardening and the 10w levels of localization of deformation observed in the cyclic stress-strain curve (CSSC) of coarse-grained copper. In terms of the effect of extrinsic variables, Llanes and co-workers [4-6] observed enhancement of strain localization in small-grained copper in association with the use of ramp-loading both as loading mode and as mechanical pretreatment, in agreement with previous results [7-12]. From these studies it is now well established that ramp-loading promotes a gradual substructure evolution which leads to: a much more homogeneous substructure, from grain to grain; localization of slip in primary systems; and formation of persistent slip bands (PSBs). In the CSSC of small-grained copper, and in support of the results of Wang and Laird [7], Llanes and Laird [4] observed that ramp-treated copper polycrystals show, under subsequent conventional strain control testing, lower cyclic hardening rates, and therefore a greater tendency to localize deformation, than nontreated samples. However, the fact that Llanes and Laird [4] were unable to obtain the clear plateau behaviour observed by Wang and Laird [7] in the CSSC of ramp-treated small-grained copper suggests that the observation of a plateau in the CSSC of

Dry Matter Production, Yield, and Allocation of Carbon‐14 Assimilates by Wheat as Affected by Nitrogen Source and Salinity

AbstractWheat (Triticum aestivum L.) growth is affected by both salinity and the type of N fed to the plants. The objective of this research was to determine the effect of salinity applied at different stages of the life cycle of wheat plants supplied with either NH4 or NO3 on growth, yield, and translocation of photosynthates. Plants were grown in sand culture irrigated with nutrient solution until maturity. The nutrient solution contained 4 mM N, either as (NH4)2SO4 or Ca(NO3)2. Salinity (60 mM NaCl) was applied to the nutrient solution at 19, 70, and 92 d after sowing. Some of the plants received 14CO2 pulses 100 d after sowing, and 14C distribution in each plant part was determined 24 h later. Dry biomass production and grain yield were reduced when salinity was applied 19 d after sowing (beginning of the vegetative stage), whereas no effect of NaCl was observed when salinity was applied later. Ammonium‐fed plants always produced more tillers and spikes than NO3‐fed plants. Total grain yield was similar with plants growing in either N form. Nitrate‐treated plants produced fewer, but heavier, spikes due to a larger number of grains per spike than NH4‐fed plants. Ammonium‐fed plants showed a preferential allocation of 14C‐assimilates to young developing tillers. Nitrate‐fed plants, under similar conditions, allocated assimilates preferentially to grain. Salinity enhanced translocation of assimilates to the spikes when plants were grown with NO3.