Science.gov

Sample records for abrasive grain size

  1. Investigating selective transport and abrasion on an alluvial fan using quantitative grain size and shape analysis

    NASA Astrophysics Data System (ADS)

    Litwin, K. L.; Jerolmack, D. J.

    2011-12-01

    Selective sorting and abrasion are the two major fluvial processes that are attributed to the downstream fining of sediments in rivers and alluvial fans. Selective transport is the process by which smaller grains are preferentially transported downstream while larger grains are deposited closer to the source. Abrasion is defined by the production of fine sediments and sand that occurs by saltation of gravel, where particle-to-particle collisions supply the energy required to break apart grains. We hypothesize that abrasion results in the gradual fining of large grains and the production of fine sands and silts, while sorting accounts for the differences in transport of these two grain-size fractions produced from abrasion, thereby creating the abrupt gravel-sand transition observed in many channel systems. In this research, we explore both selective transport and abrasion processes on the Dog Canyon alluvial fan near Alamogordo, New Mexico. We complete an extensive grain size analysis down the main channel of the fan employing an image-based technique that utilizes an autocorrelation process. We also characterize changes in grain shape using standard shape parameters, as well as Fourier analysis, which allows the study of contributions of grain roughness on a variety of length scales. Sorting appears to dominate the upper portion of the fan; the grain-size distribution narrows moving downstream until reaching a point of equal mobility, at which point sorting ceases. Abrasion exerts a subtle but persistent effect on grains during transport down the fan. Shape analysis reveals that particles become more rounded by the removal of small-scale textural features, a process that is expected to only modestly influence grain size of gravel, but should produce significant quantities of sand. This study provides a better understanding of the importance of grain abrasion and sorting on the downstream fining of channel grains in an alluvial fan, as well as an improved knowledge

  2. The grain-size distribution of pyroclasts: Primary fragmentation, conduit sorting or abrasion?

    NASA Astrophysics Data System (ADS)

    Kueppers, U.; Schauroth, J.; Taddeucci, J.

    2013-12-01

    Explosive volcanic eruptions expel a mixture of pyroclasts and lithics. Pyroclasts, fragments of the juvenile magma, record the state of the magma at fragmentation in terms of porosity and crystallinity. The grain size distribution of pyroclasts is generally considered to be a direct consequence of the conditions at magma fragmentation that is mainly driven by gas overpressure in bubbles, high shear rates, contact with external water or a combination of these factors. Stress exerted by any of these processes will lead to brittle fragmentation by overcoming the magma's relaxation timescale. As a consequence, most pyroclasts exhibit angular shapes. Upon magma fragmentation, the gas pyroclast mixture is accelerated upwards and eventually ejected from the vent. The total grain size distribution deposited is a function of fragmentation conditions and transport related sorting. Porous pyroclasts are very susceptible to abrasion by particle-particle or particle-conduit wall interaction. Accordingly, pyroclastic fall deposits with angular clasts should proof a low particle abrasion upon contact to other surfaces. In an attempt to constrain the degree of particle interaction during conduit flow, monomodal batches of washed pyroclasts have been accelerated upwards by rapid decompression and subsequently investigated for their grain size distribution. In our set-up, we used a vertical cylindrical tube without surface roughness as conduit. We varied grain size (0.125-0.25; 0.5-1; 1-2 mm), porosity (0; 10; 30 %), gas-particle ratio (10 and 40%), conduit length (10 and 28 cm) and conduit diameter (2.5 and 6 cm). All ejected particles were collected after settling at the base of a 3.3 m high tank and sieved at one sieve size below starting size (half-Φ). Grain size reduction showed a positive correlation with starting grain size, porosity and overpressure at the vent. Although milling in a volcanic conduit may take place, porous pyroclasts are very likely to be a primary product

  3. Microwave sintering of sol-gel derived abrasive grain

    DOEpatents

    Plovnick, Ross; Celikkaya, Ahmet; Blake, Rodger D.

    1997-01-01

    A method is provided for making microwave-sintered, free flowing alpha alumina-based ceramic abrasive grain, under conditions effective to couple microwaves with calcined alpha alumina-based abrasive gain precursor and sinter it at a temperature of at least about 1150.degree. C.

  4. What Controls Ooid Grain Size?

    NASA Astrophysics Data System (ADS)

    Trower, L.; Lamb, M. P.; Fischer, W. W.

    2015-12-01

    Ooids are subspherical chemical sand grains composed of concentric layers of CaCO₃ surrounding a central nucleus. These grains represent a common mode of carbonate sedimentation, making them potentially powerful proxies for paleoenvironmental conditions, provided a mechanistic understanding of the physical, chemical, and perhaps biological conditions necessary for their formation. At a basic level, growth of an ooid reflects that precipitation has outpaced abrasion over the ooid's lifetime. We can describe change in ooid size over time (net growth rate) mechanistically as the sum of a growth rate (the rate of carbonate precipitation on the ooid surface) and an abrasion rate (the rate of removal of material through grain-grain and grain-bed collisions). Previous studies have addressed the growth rate, investigating the extent to which microbial activity affects and/or controls carbonate precipitation on ooid surfaces, and the net growth rate, using stepwise acid digestion and radiocarbon dating to determine the ages of cortical layers. We focused on the abrasion rate and designed an experimental study to measure abrasion rates of ooids as a function of grain size and sediment transport stage. Preliminary experiments with medium-sand-sized ooids at a Rouse number of ~1.2 yielded an abrasion rate of 0.04 g/hr (or ~40 ng/ooid/hr), which is four orders of magnitude greater than the fastest net growth rates reported in the recent high resolution ooid cortex radiocarbon dating study by Beaupre et al. (2015). This result requires that either: 1) ooids are essentially not moving and therefore not being abraded or 2) precipitation rates are also much more rapid than the net growth rates estimated by incremental radiocarbon dating. The former constraint is inconsistent with field observations that most marine ooids occur in high energy shoal environments, both in modern examples and in the rock record. Precipitation rates must therefore also be relatively rapid compared

  5. Forecasting of operational indicators of grinding tools with the controlled form and orientation of abrasive grains

    NASA Astrophysics Data System (ADS)

    Korotkov, V. A.; Minkin, E. M.

    2015-09-01

    The interconnection of the abrasive grain front angle parameter with the form, orientation and wear out parameters is investigated. The form of the abrasive grains was estimated by means of form coefficient which represents the relation of diameters of the spheres described around contours of grains, to diameters of the spheres entered in them. The spatial orientation angle of the abrasive grains was defined between main (i.e. the biggest) axis of the grains and the cutting plane. It is established that, depending on an orientation angle at increase in a form coefficient of the abrasive grains can be either an increase or a decrease in the values of their front angles. In most cases, with an increase in a form coefficient of the oriented grinding grains (at orientation angles Θ=10°÷125°) the growth of their front angles is fixed. At tangential orientation of grains (Θ=0°) and at the close directions of orientation (Θ=135°÷80°) the return picture is observed. Also established that the longer the abrasive grain wears along the main axis and located in the tool body, the larger is its front angle. Besides that, the front angles of the abrasive grains reach the maximum positive values at orientation angles Θ=22.5°÷45°.Dependence of tension in grains during the work with parameters of their form, orientation and depth of embedment in the bundle is investigated. It was found that for all orientation angles of grains their tension significantly increases with an increase in their form coefficient. Besides that it is confirmed that the deeper the grain is in the bundle, the lower the tension is there. Also found that tension is minimal when the grains are tangential orientated. Further on increase the option of the grains in the direction of action of the cutting force follows. Such option of orientation is the most rational both from the point of view of minimization of tension, and for ensuring rational sizes of front angles of the abrasive grains. The

  6. Development of a High Performance Vitrified Grinding Wheel using Ultrafine-Crystalline cBN Abrasive Grains

    NASA Astrophysics Data System (ADS)

    Ichida, Yoshio; Fujimoto, Masakazu; Inoue, Yuichiro; Matsui, Keisuke

    This paper describes the development of a high-performance vitrified bonded cBN grinding wheel using a new type of ultrafine-crystalline cBN (cBN-U) abrasive grain. Surface plunge grinding experiments using a vitrified wheel made of the cBN-U grains with a mesh size of #80/100 were carried out, and the wheel’s grinding performance was compared with those of cBN vitrified wheels made of representative conventional monocrystalline and polycrystalline cBN abrasive grains. This new cBN-U abrasive grain was found to possess a higher fracture strength than these conventional cBN grains. Therefore, the cBN-U wheel exhibits a higher grinding ratio and longer grinding wheel life than conventional cBN wheels.

  7. Sliding and Abrasive Wear Behavior of WC-CoCr Coatings with Different Carbide Sizes

    NASA Astrophysics Data System (ADS)

    Thakur, Lalit; Arora, Navneet

    2013-02-01

    This study examines the sliding and abrasive wear behaviors of high-velocity oxy-fuel (HVOF)-sprayed WC-CoCr coatings with different WC grain sizes. The HVOF coating deposition was assisted by in-flight particle temperature and velocity measurement system. The powder feedstocks and their corresponding coatings were characterized by means of XRD and Field Emission Scanning Electron Microscope analysis. Hardness, porosity, and indentation fracture toughness of these coatings were calculated and compared with each other. Sliding wear resistance of these coatings was calculated using pin-on-disk tribometer (ASTM G99-90). The two-body abrasion was quantified by sliding the samples over silicon carbide (SiC) abrasive paper bonded to a rotating flat disk of auto-polisher. The mechanism of materials' removal in both the sliding and abrasive wears was studied and discussed on microstructural investigations. It was observed that fine grain WC-CoCr cermet coating exhibits higher sliding and abrasive wear resistances as compared with conventional cermet coating.

  8. Grain decoration in aluminum oxynitride (ALON) from polishing on bound abrasive laps

    NASA Astrophysics Data System (ADS)

    Gregg, Leslie L.; Marino, Anne E.; Hayes, Jennifer C.; Jacobs, Stephen D.

    2004-01-01

    Aluminum oxynitride (ALON) is a polycrystalline material that has proven difficult to polish due to its grain structure. Bound abrasives are an effective means for polishing ALON, and work is being done with them to obtain good surfaces, with reasonable removal rates. Laps consisting of abrasives bound in epoxy matrices were created for polishing ALON. The effects of varying abrasive type, abrasive concentration, lap shape, coolant and load were studied. Metrology procedures were developed to monitor different aspects of the grain structure and numerically evaluate grain boundary decoration. Strategies were developed to polish ALON at acceptable rates with reasonably good surface quality. Work is directed toward finding optimal bound abrasive lap formulations that can be fabricated into ring and/or contour tools for testing on CNC machining platforms.

  9. Grain decoration in aluminum oxynitride (ALON) from polishing on bound abrasive laps

    NASA Astrophysics Data System (ADS)

    Marino, Anne E.; Hayes, Jennifer; Gregg, Leslie L.; Jacobs, Stephen D.

    2003-05-01

    Aluminum oxynitride (ALON) is a material with desirable qualities for a variety of applications that has proven difficult to polish because of its grain structure. Bound abrasives may prove to be an effective means of polishing it, and work is being done with them to obtain good surfaces on ALON, with reasonable removal rates. Laps consisting of abrasives bound in epoxy matrices have been created for polishing ALON. The effects of varying abrasive type, abrasive concentration, lap shape, coolant and load are being studied. Metrology procedures are being developed to monitor different aspects of the grain structure and numerically evaluate its decoration. Strategies have been developed to polish ALON at acceptable rates with reasonably good surface quality. Work is directed toward finding optimal bound abrasive lap formulations that can be fabricated into ring and/or contour tools for testing on CNC machining platforms.

  10. Grain Size and Morphological Variability

    NASA Astrophysics Data System (ADS)

    Macmahan, J.; Gallagher, E.; Reniers, A.; Thornton, E.

    2008-12-01

    Grain size on natural beaches has traditionally been assumed to be uniform and modeling efforts assume a single mean grain size for an entire beach environment. Many recent studies contradict this assumption and suggest that sediment grain size on a beach is not homogeneous and that variations in sediment size and supply are important in sediment transport and morphodynamics at all scales. Unfortunately, measuring grain size is difficult, tedious and time consuming. Therefore, in spite of the evidence pointing to the importance of grain size in sediment transport and morphodynamics, many previous studies have been based on only a few field samples. Rubin (2004) introduced a technique for measuring surface grain size in situ in rivers and deeper coastal waters, using a digital camera and auto-correlation of digital images. Using this technique, information about the surface grain size distribution can be obtained quickly and inexpensively. Following Rubin (2004), we have developed a mobile digital imaging system (DIS) for surveying grain size on beaches. The DIS was used during two experiments: RCEX, a rip current experiment in Monterey, CA in April 2007 and Truc Vert '08, a multi-institutional, international experiment, on the Atlantic coast of France in March 2008. Preliminary results suggest that grain size varies spatially with the morphology of beach features and temporally with changes in tide level, wave energy, and morphodynamics. These data are being used to examine the relationship between morphological, sedimentological and hydrodynamic variability.

  11. Effect of abrasive grit size on wear of manganese-zinc ferrite under three-body abrasion

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa

    1987-01-01

    Wear experiments were conducted using replication electron microscopy and reflection electron diffraction to study abrasion and deformed layers produced in single-crystal Mn-Zn ferrites under three-body abrasion. The abrasion mechanism of Mn-Zn ferrite changes drastically with the size of abrasive grits. With 15-micron (1000-mesh) SiC grits, abrasion of Mn-Zn ferrite is due principally to brittle fracture; while with 4- and 2-micron (4000- and 6000-mesh) SiC grits, abrasion is due to plastic deformation and fracture. Both microcracking and plastic flow produce polycrystalline states on the wear surfaces of single-crystal Mn-Zn ferrites. Coefficient of wear, total thickness of the deformed layers, and surface roughness of the wear surfaces increase markedly with an increase in abrasive grit size. The total thicknesses of the deformed layers are 3 microns for the ferrite abraded by 15-micron SiC, 0.9 microns for the ferrite abraded by 4-micron SiC, and 0.8 microns for the ferrite abraded by 1-micron SiC.

  12. Friability and crushing strength of micrometer-size diamond abrasives used in microgrinding of optical glass

    NASA Astrophysics Data System (ADS)

    Zhou, Yiyang; Takahashi, Toshio; Quesnel, David J.; Funkenbusch, Paul D.

    1996-04-01

    In abrasive grinding, the properties of the abrasives and their response to impact loading play a significant role in determining the results achievable. For micrometer-size diamond abrasives used for bound-abrasive microgrinding of optical glass, friability testing is used to estimate the related particle properties. Friability and crushing strength of diamond abrasives are estimated based on the data from comminution of sample powders on a commercial SPEX mixer/mill. Different diamond abrasives as well as a CBN abrasive are tested. Evolution of powder size and size distribution with comminution time is characterized with a HORIBA laser scattering analyzer. Correlation is established for the impact stress and the probability of fracture during comminution. This study demonstrates how to combine the ease of data acquisition found in a conventional friability test with the capability of predicting specific mechanical properties normally found only by crushing individual abrasive particles.

  13. Grain Size and Morphological Variability

    NASA Astrophysics Data System (ADS)

    Gallagher, E. L.; Reniers, A. J.; Macmahan, J. H.; Thornton, E. B.

    2009-12-01

    Grain size on natural beaches has traditionally been assumed to be uniform and modeling efforts assume a single mean grain size for an entire beach environment. Many recent studies contradict this assumption and suggest that sediment grain size on a beach is not homogeneous and that variations in sediment size and supply are important in sediment transport and morphodynamics at all scales. Unfortunately, measuring grain size is tedious and time consuming. Therefore, in spite of the evidence pointing to the importance of grain size in sediment transport and morphodynamics, many previous studies have been based on only a few field samples. Rubin (2004) introduced a technique for measuring surface grain size in situ in rivers and deeper coastal waters, using a digital camera and auto-correlation of digital images. Using this technique, information about the surface grain size distribution can be obtained quickly and inexpensively. Following Rubin (2004), we have developed a mobile digital imaging system (DIS) for surveying grain size on beaches. The DIS was used during three experiments: RCEX and REX, both rip current experiments in Monterey, CA (April 2007 and April 2009) and Truc Vert ’08, a multi-institutional, international experiment, on the Atlantic coast of France in March 2008. In 2007 and 2008 spatial surveys of surface grain size were completed every few days over large (~500x500m) intertidal areas. The 2009 experiment focused on twice-daily sampling of two cross shore lines to examine temporal grain size variability of the intertidal beach. Preliminary results suggest that grain size varies spatially with the morphology of beach features (eg, rip channels and shoals) and temporally with changes in tide level, wave energy, and morphodynamics. These data are being used to examine the relationship between morphological, sedimentological and hydrodynamic variability.

  14. EFFECT OF GRAIN SIZE ON DYNAMIC SCRATCH RESPONSE IN ALUMINA

    SciTech Connect

    Wang, Hong; Wereszczak, Andrew A; Lance, Michael J

    2006-01-01

    The machining and wear of ceramics and ceramic components are obviously influenced by abrasive damage. One parameter that can affect the abrasion process is the grain size of the ceramic material. To investigate this, single-grit pendulum scratch testing was used to investigate the dynamic scratch response in three 99.9% aluminas that each had a tight size distribution about mean grain sizes of 2, 15, or 25 m, respectively. The scratch speeds generated had an order of magnitude of ~ 1 m/s and the maximum scratch depths were several tens of micrometers. Tangential and normal scratch forces were monitored during each test and interpreted in conjunction with postmortem SEM and profilometry results. It was observed that both plastic deformation and brittle fracture participated in the scratching process and the relative activity of each was dependent on depth of penetration. At a specific depth of penetration, the material removal of alumina prevailingly relies on the generation and interaction of oblique radial and lateral cracks. Chip formation is greatly enhanced when the created cracks interact and that interaction itself depends on grain size. Larger grain size gives rise to larger lateral cracks, more severe fracture at the groove's bottom, and larger amplitude of scratch force oscillation. Lastly, the cutting pressure and the scratch hardness of alumina exhibit sensitivity to both grain size and the groove depth.

  15. Lunar soils grain size catalog

    NASA Technical Reports Server (NTRS)

    Graf, John C.

    1993-01-01

    This catalog compiles every available grain size distribution for Apollo surface soils, trench samples, cores, and Luna 24 soils. Original laboratory data are tabled, and cumulative weight distribution curves and histograms are plotted. Standard statistical parameters are calculated using the method of moments. Photos and location comments describe the sample environment and geological setting. This catalog can help researchers describe the geotechnical conditions and site variability of the lunar surface essential to the design of a lunar base.

  16. A light-scattering study of Al2O3 abrasives of various grit sizes

    NASA Astrophysics Data System (ADS)

    Heinson, Yuli W.; Chakrabarti, Amitabha; Sorensen, Christopher M.

    2016-09-01

    We report light scattering phase function measurements for irregularly shaped Al2O3 abrasive powders of various grit sizes. Q-space analysis is applied to the angular scattering to reveal a forward scattering regime, Guinier regime, power law regime with quantifiable exponents, and an enhanced backscattering regime. The exponents of the power laws for Al2O3 abrasives decrease with increasing internal coupling parameter ρ ‧ , which is in agreement with previous observations for other irregular particles. Unlike other dust particles previously studied showing single power laws under Q-space analysis, the largest three abrasives, for which ρ ‧ ≳ 100 , showed a kink in the power law, which is possibly due to the higher degree of symmetry for the abrasives than for all the particles studied previously. Direct comparison of the 1200, 1000, and 800 grit abrasive scattering to scattering by corresponding spheres shows that the scatterings approximately coincide at the spherical particle qR ≃ ρ ‧ crossover point. Furthermore, the scattering at the maximum qR = 2 kR by the irregularly shaped abrasives is close to the geometric centers of the glories of the spheres.

  17. Grain size control of rhenium strip

    NASA Technical Reports Server (NTRS)

    Schuster, Gary B.

    1991-01-01

    Ensuring the desired grain size in the pure Re strip employed by the SP-100 space nuclear reactor design entails the establishment of an initial grain size in the as-received strip and the avoidance of excessive grain growth during subsequent fabrication. Pure Re tapered tensile specimens have been fabricated and tested in order to quantify the effects of grain-boundary migration. Grain size could be rendered fine and uniform by means of a rolling procedure that uses rather large reductions between short intermediate anneals. The critical strain regime varies inversely with annealing temperature.

  18. Abrasive wear: The efects of fibres size on oil palm empty fruit bunch polyester composite

    NASA Astrophysics Data System (ADS)

    Kasolang, S.; Kalam, A.; Ahmad, M. A.; Rahman, N. A.; Suhadah, W. N.

    2012-06-01

    This paper presents an experimental investigation carried out to determine the effect of palm oil empty fruit bunch (OPEFB) fibre size in dry sliding testing of polyester composite. These composite samples were produced by mixing raw OPEFB fibre with resin. The samples were prepared at different sizes of fibre (100, 125, 180 and 250μm). Abrasion Resistance Tester (TR-600) was used to carried out abrasive wear tests in dry sliding conditions. These tests were performed at room temperature for two different loads (10 and 30N) and at a constant sliding velocity of 1.4m/s. The specific wear rates of OPEFB polyester composites were obtained. The morphology of composite surface before and after tests was also examined using 3D microscope imaging. Preliminary work on thermal distribution at the abrasive wheel point was also conducted for selected samples.

  19. Physical abrasion of mafic minerals and basalt grains: Application to martian aeolian deposits

    NASA Astrophysics Data System (ADS)

    Cornwall, C.; Bandfield, J. L.; Titus, T. N.; Schreiber, B. C.; Montgomery, D. R.

    2015-08-01

    Sediment maturity, or the mineralogical and physical characterization of sedimentary deposits, has been used to identify sediment sources, transport medium and distance, weathering processes, and paleoenvironments on Earth. Mature terrestrial sands are dominated by quartz, which is abundant in source lithologies on Earth and is physically and chemically stable under a wide range of conditions. Immature sands, such as those rich in feldspars or mafic minerals, are composed of grains that are easily physically weathered and highly susceptible to chemical weathering. On Mars, which is predominately mafic in composition, terrestrial standards of sediment maturity are not applicable. In addition, the martian climate today is cold and dry and sediments are likely to be heavily influenced by physical weathering rather than chemical weathering. Due to these large differences in weathering processes and composition, martian sediments require an alternate maturity index. This paper reports the results of abrasion tests conducted on a variety of mafic materials and results suggest that mature martian sediments may be composed of well sorted, well rounded, spherical polycrystalline materials, such as basalt. Volcanic glass is also likely to persist in a mechanical weathering environment while more fragile and chemically altered products are likely to be winnowed away. A modified sediment maturity index is proposed that can be used in future studies to constrain sediment source, paleoclimate, mechanisms for sediment production, and surface evolution. This maturity index may also provide insights into erosional and sediment transport systems and preservation processes of layered deposits.

  20. Estimating snow grain size using AVIRIS data

    NASA Technical Reports Server (NTRS)

    Nolin, Anne W.; Dozier, Jeff

    1993-01-01

    Estimates of snow grain size for the near-surface snow layer were calculated for the Tioga Pass region and Mammoth Mountain in the Sierra Nevada, California, using an inversion technique and data collected by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). The Tioga Pass and Mammoth Mountain single-band AVIRIS radiance images were atmospherically corrected to obtain surface reflectance. A discrete-ordinate model was used to calculate directional reflectance as a function of snowpack grain size for a wide range of snow grain radii. The resulting radius vs. reflectance curves were each fit using a nonlinear least squares technique which provided a means of transforming surface reflectance in each AVIRIS image to optically equivalent grain size on a per-pixel basis. The model results and grain size estimates derived from the AVIRIS data show that, for solar incidence angles between 0 and 30, the technique provides good estimates of grain size. This work provides the first quantitative estimates for grain size using data acquired from an airborne remote sensing instrument and is an important step in improving our ability to retrieve snow physical properties independent of field measurements.

  1. The size distribution of interstellar grains

    NASA Technical Reports Server (NTRS)

    Witt, Adolf N.

    1987-01-01

    Three major areas involving interstellar grains were investigated. First, studies were performed of scattering in reflection nebulae with the goal of deriving scattering characteristics of dust grains such as the albedo and the phase function asymmetry throughout the visible and the ultraviolet. Secondly, studies were performed of the wavelength dependence of interstellar extinction designed to demonstrate the wide range of grain size distributions naturally occurring in individual clouds in different parts of the galaxy. And thirdly, studies were also performed of the ultraviolet powered emission of dust grains in the 0.5 to 1.0 micron wavelength range in reflection nebulae. Findings considered of major importance are highlighted.

  2. Interstellar chemical differentiation across grain sizes

    NASA Astrophysics Data System (ADS)

    Ge, J. X.; He, J. H.; Li, Aigen

    2016-07-01

    In this work, we investigate the effects of ion accretion and size-dependent dust temperatures on the abundances of both gas-phase and grain-surface species. While past work has assumed a constant areal density for icy species, we show that this assumption is invalid and the chemical differentiation over grain sizes is significant. We use a gas-grain chemical code to demonstrate this numerically for two typical interstellar conditions: a dark cloud (DC) and a cold neutral medium (CNM). It is shown that, although the grain-size distribution variation (but with the total grain surface area unchanged) has little effect on the gas-phase abundances, it can alter the abundances of some surface species by up to ∼2-4 orders of magnitude. The areal densities of ice species are larger on smaller grains in the DC model as a consequence of ion accretion. However, the surface areal density evolution tracks are more complex in the CNM model due to the combined effects of ion accretion and dust temperature variation. The surface areal density differences between the smallest ( ∼ 0.01 μm) and the biggest ( ∼ 0.2 μm) grains can reach ∼1 and ∼5 orders of magnitude in the DC and CNM models, respectively.

  3. BHQ revisited (1) - Looking at grain size

    NASA Astrophysics Data System (ADS)

    Heilbronner, Renée; Kilian, Rüdiger; Tullis, Jan

    2016-04-01

    Black Hills Quartzite (BHQ) has been used extensively in experimental rock deformation for numerous studies. Coaxial and general shear experiments have been carried out, for example, to define the dislocation creep regimes of quartz (Hirth & Tullis, 1992), to determine the effect of annealing (Heilbronner & Tullis, 2002) or to study the development of texture and microstructure with strain (Heilbronner & Tullis, 2006). BHQ was also used to determine the widely used quartz piezometer by Stipp & Tullis (2003). Among the microstructure analyses that were performed in those original papers, grain size was usually determined using CIP misorientation images. However, the CIP method (= computer-integrated polarization microscopy, details in Heilbronner and Barrett, 2014) is only capable of detecting the c-axis orientation of optically uniaxial materials and hence is only capable of detecting grain boundaries between grains that differ in c-axis orientation. One of the puzzling results we found (Heilbronner & Tullis, 2006) was that the recrystallized grain size seemed to depend on the crystallographic preferred orientation of the domain. In other words the grain size did not only depend on the flow stress but also on the orientation of the c-axis w/r to the shear direction. At the time, no EBSD analysis (electron back scatter diffraction) was carried out and hence the full crystallographic orientation was not known. In principle it is therefore possible that we missed some grain boundaries (between grains with parallel c-axes) and miscalculated our grain sizes. In the context of recent shear experiments on quartz gouge at the brittle-viscous transition (see Richter et al., this conference), where EBSD is used to measure the recrystallized grain size, we wanted to re-measure the CIP grain sizes of our 2006 samples (deformed in regime 1, 2 and 3 of dislocation) in exactly the same way. In two companion posters we use EBSD orientation imaging to repeat, refine and expand the

  4. Grain size segregation in debris discs

    NASA Astrophysics Data System (ADS)

    Thebault, P.; Kral, Q.; Augereau, J.-C.

    2014-01-01

    Context. In most debris discs, dust grain dynamics is strongly affected by stellar radiation pressure. Because this mechanism is size-dependent, we expect dust grains to be spatially segregated according to their sizes. However, because of the complex interplay between radiation pressure, grain processing by collisions, and dynamical perturbations, this spatial segregation of the particle size distribution (PSD) has proven difficult to investigate and quantify with numerical models. Aims: We propose to thoroughly investigate this problem by using a new-generation code that can handle some of the complex coupling between dynamical and collisional effects. We intend to explore how PSDs behave in both unperturbed discs at rest and in discs pertubed by planetary objects. Methods: We used the DyCoSS code to investigate the coupled effect of collisions, radiation pressure, and dynamical perturbations in systems that have reached a steady-state. We considered two setups: a narrow ring perturbed by an exterior planet, and an extended disc into which a planet is embedded. For both setups we considered an additional unperturbed case without a planet. We also investigated the effect of possible spatial size segregation on disc images at different wavelengths. Results: We find that PSDs are always spatially segregated. The only case for which the PSD follows a standard dn ∝ s-3.5ds law is for an unperturbed narrow ring, but only within the parent-body ring itself. For all other configurations, the size distributions can strongly depart from such power laws and have steep spatial gradients. As an example, the geometrical cross-section of the disc is very rarely dominated by the smallest grains on bound orbits, as it is expected to be in standard PSDs in sq with q ≤ -3. Although the exact profiles and spatial variations of PSDs are a complex function of the set-up that is considered, we are still able to derive some reliable results that will be useful for image or SED

  5. Paleowattmeters: A scaling relation for dynamically recrystallized grain size

    NASA Astrophysics Data System (ADS)

    Austin, Nicholas J.; Evans, Brian

    2007-04-01

    During dislocation creep, mineral grains often evolve to a stable size, dictated by the deformation conditions. We suggest that grain-size evolution during deformation is determined by the rate of mechanical work. Provided that other elements of microstructure have achieved steady state and that the dissipation rate is roughly constant, then changes in internal energy will be proportional to changes in grain-boundary area. If normal grain-growth and dynamic grain-size reduction occur simultaneously, then the steady-state grain size is determined by the balance of those rates. A scaling model using these assumptions and published grain-growth and mechanical relations matches stress grain-size relations for quartz and olivine rocks with no fitting. For marbles, the model also explains scatter not rationalized by assuming that recrystallized grain size is a function of stress alone. When extrapolated to conditions typical for natural mylonites, the model is consistent with field constraints on stresses and strain rates.

  6. Abrasion by aeolian particles: Earth and Mars

    NASA Technical Reports Server (NTRS)

    Greeley, R.; Marshall, J. R.; White, B. R.; Pollack, J. B.; Marshall, J.; Krinsley, D.

    1984-01-01

    Estimation of the rate of aeolian abrasion of rocks on Mars requires knowledge of: (1) particle flux, (2) susceptibilities to abrasion of various rocks, and (3) wind frequencies on Mars. Fluxes and susceptibilities for a wide range of conditions were obtained in the laboratory and combined with wind data from the Viking meteorology experiment. Assuming an abundant supply of sand-sized particles, estimated rates range up to 2.1 x 10 to the minus 2 power cm of abrasion per year in the vicinity of Viking Lander 1. This rate is orders of magnitude too great to be in agreement with the inferred age of the surface based on models of impact crater flux. The discrepancy in the estimated rate of abrasion and the presumed old age of the surface cannot be explained easily by changes in climate or exhumation of ancient surfaces. The primary reason is thought to be related to the agents of abrasion. At least some sand-sized (approx. 100 micrometers) grains appear to be present, as inferred from both lander and orbiter observations. High rates of abrasion occur for all experimental cases involving sands of quartz, basalt, or ash. However, previous studies have shown that sand is quickly comminuted to silt- and clay-sized grains in the martian aeolian regime. Experiments also show that these fine grains are electrostatically charged and bond together as sand-sized aggregates. Laboratory simulations of wind abrasion involving aggregates show that at impact velocities capable of destroying sand, aggregates from a protective veneer on the target surface and can give rise to extremely low abrasion rates.

  7. Simulation of grain size effects in nanocrystalline shape memory alloys

    NASA Astrophysics Data System (ADS)

    Ahluwalia, Rajeev; Quek, Siu Sin; Wu, David T.

    2015-06-01

    Recently, it has been demonstrated that martensitic transformation in nanocrystalline shape memory alloys can be suppressed for small grain sizes. Motivated by these results, we study the grain size dependence of martensitic transformations and stress-strain response of nanocrystalline shape memory alloys within the framework of the Ginzburg-Landau (GL) theory. A GL model for a square to rectangle transformation in polycrystals is extended to account for grain boundary effects. We propose that an inhibition of the transformation in grain boundary regions can occur, if the grain boundary energy of the martensite is higher than that of the austenite phase. We show that this inhibition of transformation in grain boundary regions has a strong influence on domain patterns inside grains. Although the transformation is inhibited only at the grain boundaries, it leads to a suppression of the transformation even inside the grains as grain size is decreased. In fact, below a critical grain size, the transformation can be completely suppressed. We explain these results in terms of the extra strain gradient cost associated with grain boundaries, when the transformation is inhibited at grain boundaries. On the other hand, no significant size effects are observed when transformation is not inhibited at grain boundaries. We also study the grain size dependence of the stress strain curve. It is found that when the transformation is inhibited at grain boundaries, a significant reduction in the hysteresis associated with stress-strain curves during the loading-unloading cycles is observed. The hysteresis for this situation reduces even further as the grain size is reduced, which is consistent with recent experiments. The simulations also demonstrate that the mechanical behavior is influenced by inter-granular interactions and the local microstructural neighbourhood of a grain has a stronger influence than the orientation of the grain itself.

  8. A continuum theory of grain size evolution and damage

    NASA Astrophysics Data System (ADS)

    Ricard, Y.; Bercovici, D.

    2009-01-01

    Lithospheric shear localization, as occurs in the formation of tectonic plate boundaries, is often associated with diminished grain size (e.g., mylonites). Grain size reduction is typically attributed to dynamic recrystallization; however, theoretical models of shear localization arising from this hypothesis are problematic because (1) they require the simultaneous action of two creep mechanisms (diffusion and dislocation creep) that occur in different deformation regimes (i.e., in grain size stress space) and (2) the grain growth ("healing") laws employed by these models are derived from normal grain growth or coarsening theory, which are valid in the absence of deformation, although the shear localization setting itself requires deformation. Here we present a new first principles grained-continuum theory, which accounts for both coarsening and damage-induced grain size reduction in a monomineralic assemblage undergoing irrecoverable deformation. Damage per se is the generic process for generation of microcracks, defects, dislocations (including recrystallization), subgrains, nuclei, and cataclastic breakdown of grains. The theory contains coupled macroscopic continuum mechanical and grain-scale statistical components. The continuum level of the theory considers standard mass, momentum, and energy conservation, as well as entropy production, on a statistically averaged grained continuum. The grain-scale element of the theory describes both the evolution of the grain size distribution and mechanisms for both continuous grain growth and discontinuous grain fracture and coalescence. The continuous and discontinuous processes of grain size variation are prescribed by nonequilibrium thermodynamics (in particular, the treatment of entropy production provides the phenomenological laws for grain growth and reduction); grain size evolution thus incorporates the free energy differences between grains, including both grain boundary surface energy (which controls coarsening

  9. Grain size dependence of silicon solar cell parameters

    NASA Technical Reports Server (NTRS)

    Koliwad, K. M.; Daud, T.

    1980-01-01

    Measurements of the non-uniform diffusion length of the minority carriers near grain boundaries in polycrystalline silicon have been used to develop an analytical model for the calculation of solar cell output as a function of grain size. Experimental results are presented which verify the theoretical analysis. Variation of open circuit voltage and fill factor with grain size is discussed.

  10. Carpel size, grain filling, and morphology determine individual grain weight in wheat.

    PubMed

    Xie, Quan; Mayes, Sean; Sparkes, Debbie L

    2015-11-01

    Individual grain weight is a major yield component in wheat. To provide a comprehensive understanding of grain weight determination, the carpel size at anthesis, grain dry matter accumulation, grain water uptake and loss, grain morphological expansion, and final grain weight at different positions within spikelets were investigated in a recombinant inbred line mapping population of bread wheat (Triticum aestivum L.)×spelt (Triticum spelta L.). Carpel size, grain dry matter and water accumulation, and grain dimensions interacted strongly with each other. Furthermore, larger carpels, a faster grain filling rate, earlier and longer grain filling, more grain water, faster grain water absorption and loss rates, and larger grain dimensions were associated with higher grain weight. Frequent quantitative trait locus (QTL) coincidences between these traits were observed, particularly those on chromosomes 2A, 3B, 4A, 5A, 5DL, and 7B, each of which harboured 16-49 QTLs associated with >12 traits. Analysis of the allelic effects of coincident QTLs confirmed their physiological relationships, indicating that the complex but orderly grain filling processes result mainly from pleiotropy or the tight linkages of functionally related genes. After grain filling, distal grains within spikelets were smaller than basal grains, primarily due to later grain filling and a slower initial grain filling rate, followed by synchronous maturation among different grains. Distal grain weight was improved by increased assimilate availability from anthesis. These findings provide deeper insight into grain weight determination in wheat, and the high level of QTL coincidences allows simultaneous improvement of multiple grain filling traits in breeding.

  11. Carpel size, grain filling, and morphology determine individual grain weight in wheat

    PubMed Central

    Xie, Quan; Mayes, Sean; Sparkes, Debbie L.

    2015-01-01

    Individual grain weight is a major yield component in wheat. To provide a comprehensive understanding of grain weight determination, the carpel size at anthesis, grain dry matter accumulation, grain water uptake and loss, grain morphological expansion, and final grain weight at different positions within spikelets were investigated in a recombinant inbred line mapping population of bread wheat (Triticum aestivum L.)×spelt (Triticum spelta L.). Carpel size, grain dry matter and water accumulation, and grain dimensions interacted strongly with each other. Furthermore, larger carpels, a faster grain filling rate, earlier and longer grain filling, more grain water, faster grain water absorption and loss rates, and larger grain dimensions were associated with higher grain weight. Frequent quantitative trait locus (QTL) coincidences between these traits were observed, particularly those on chromosomes 2A, 3B, 4A, 5A, 5DL, and 7B, each of which harboured 16−49 QTLs associated with >12 traits. Analysis of the allelic effects of coincident QTLs confirmed their physiological relationships, indicating that the complex but orderly grain filling processes result mainly from pleiotropy or the tight linkages of functionally related genes. After grain filling, distal grains within spikelets were smaller than basal grains, primarily due to later grain filling and a slower initial grain filling rate, followed by synchronous maturation among different grains. Distal grain weight was improved by increased assimilate availability from anthesis. These findings provide deeper insight into grain weight determination in wheat, and the high level of QTL coincidences allows simultaneous improvement of multiple grain filling traits in breeding. PMID:26246614

  12. Physical abrasion of mafic minerals and basalt grains: application to Martian aeolian deposits

    USGS Publications Warehouse

    Cornwall, Carin; Bandfield, Joshua L.; Titus, Timothy N.; Schreiber, B. C.; Montgomery, D.R.

    2015-01-01

    Sediment maturity, or the mineralogical and physical characterization of sediment deposits, has been used to locate sediment source, transport medium and distance, weathering processes, and paleoenvironments on Earth. Mature terrestrial sands are dominated by quartz, which is abundant in source lithologies on Earth and is physically and chemically stable under a wide range of conditions. Immature sands, such as those rich in feldspars or mafic minerals, are composed of grains that are easily physically weathered and highly susceptible to chemical weathering. On Mars, which is predominately mafic in composition, terrestrial standards of sediment maturity are not applicable. In addition, the martian climate today is cold, dry and sediments are likely to be heavily influenced by physical weathering rather than chemical weathering. Due to these large differences in weathering processes and composition, martian sediments require an alternate maturity index. Abrason tests have been conducted on a variety of mafic materials and results suggest that mature martian sediments may be composed of well sorted, well rounded, spherical basalt grains. In addition, any volcanic glass present is likely to persist in a mechanical weathering environment while chemically altered products are likely to be winnowed away. A modified sediment maturity index is proposed that can be used in future studies to constrain sediment source, paleoclimate, mechanisms for sediment production, and surface evolution. This maturity index may also provide details about erosional and sediment transport systems and preservation processes of layered deposits.

  13. Grain size evolution and convection regimes of the terrestrial planets

    NASA Astrophysics Data System (ADS)

    Rozel, A.; Golabek, G. J.; Boutonnet, E.

    2011-12-01

    A new model of grain size evolution has recently been proposed in Rozel et al. 2010. This new approach stipulates that the grain size dynamics is governed by two additive and simultaneous processes: grain growth and dynamic recrystallization. We use the usual normal grain growth laws for the growth part. For dynamic recrystallization, reducing the mean grain size increases the total area of grain boundaries. Grain boundaries carry some surface tension, so some energy is required to decrease the mean grain size. We consider that this energy is available during mechanical work. It is usually considered to produce some heat via viscous dissipation. A partitioning parameter f is then required to know what amount of energy is dissipated and what part is converted in surface tension. This study gives a new calibration of the partitioning parameter on major Earth materials involved in the dynamic of the terrestrial planets. Our calibration is in adequation with the published piezometric relations available in the literature (equilibrium grain size versus shear stress). We test this new model of grain size evolution in a set of numerical computations of the dynamics of the Earth using stagYY. We show that the grain size evolution has a major effect on the convection regimes of terrestrial planets.

  14. Effect of Grain Size and Grain Orientation on the Raman Spectra of Minerals

    NASA Technical Reports Server (NTRS)

    Sharma, S. K.; Chio, C. H.; Deb, P.; Lucey, P. G.; Domergue-Schmidt, N.; Horton, K. A.

    2000-01-01

    We have examined effects of grain size and grain orientation on the Raman spectra of quartz and olivine to evaluate the effect of these parameters on in situ and remote analysis of planetary surface rocks.

  15. Air Abrasion

    MedlinePlus

    ... delivered directly to your desktop! more... What Is Air Abrasion? Article Chapters What Is Air Abrasion? What Happens? The Pros and Cons Will I Feel Anything? Is Air Abrasion for Everyone? print full article print this ...

  16. Unfolding grain size effects in barium titanate ferroelectric ceramics.

    PubMed

    Tan, Yongqiang; Zhang, Jialiang; Wu, Yanqing; Wang, Chunlei; Koval, Vladimir; Shi, Baogui; Ye, Haitao; McKinnon, Ruth; Viola, Giuseppe; Yan, Haixue

    2015-01-01

    Grain size effects on the physical properties of polycrystalline ferroelectrics have been extensively studied for decades; however there are still major controversies regarding the dependence of the piezoelectric and ferroelectric properties on the grain size. Dense BaTiO3 ceramics with different grain sizes were fabricated by either conventional sintering or spark plasma sintering using micro- and nano-sized powders. The results show that the grain size effect on the dielectric permittivity is nearly independent of the sintering method and starting powder used. A peak in the permittivity is observed in all the ceramics with a grain size near 1 μm and can be attributed to a maximum domain wall density and mobility. The piezoelectric coefficient d33 and remnant polarization Pr show diverse grain size effects depending on the particle size of the starting powder and sintering temperature. This suggests that besides domain wall density, other factors such as back fields and point defects, which influence the domain wall mobility, could be responsible for the different grain size dependence observed in the dielectric and piezoelectric/ferroelectric properties. In cases where point defects are not the dominant contributor, the piezoelectric constant d33 and the remnant polarization Pr increase with increasing grain size. PMID:25951408

  17. Unfolding grain size effects in barium titanate ferroelectric ceramics

    PubMed Central

    Tan, Yongqiang; Zhang, Jialiang; Wu, Yanqing; Wang, Chunlei; Koval, Vladimir; Shi, Baogui; Ye, Haitao; McKinnon, Ruth; Viola, Giuseppe; Yan, Haixue

    2015-01-01

    Grain size effects on the physical properties of polycrystalline ferroelectrics have been extensively studied for decades; however there are still major controversies regarding the dependence of the piezoelectric and ferroelectric properties on the grain size. Dense BaTiO3 ceramics with different grain sizes were fabricated by either conventional sintering or spark plasma sintering using micro- and nano-sized powders. The results show that the grain size effect on the dielectric permittivity is nearly independent of the sintering method and starting powder used. A peak in the permittivity is observed in all the ceramics with a grain size near 1 μm and can be attributed to a maximum domain wall density and mobility. The piezoelectric coefficient d33 and remnant polarization Pr show diverse grain size effects depending on the particle size of the starting powder and sintering temperature. This suggests that besides domain wall density, other factors such as back fields and point defects, which influence the domain wall mobility, could be responsible for the different grain size dependence observed in the dielectric and piezoelectric/ferroelectric properties. In cases where point defects are not the dominant contributor, the piezoelectric constant d33 and the remnant polarization Pr increase with increasing grain size. PMID:25951408

  18. Magnetoresistance of polycrystalline gadolinium with varying grain size

    SciTech Connect

    Chakravorty, Manotosh Raychaudhuri, A. K.

    2015-01-21

    In this paper, we report a study of evolution of low field magnetoresistance (MR) of Gadolinium as the grain size in the sample is changed from few microns (∼4 μm) to the nanoscopic regime (∼35 nm). The low field MR has a clear effect on varying grain size. In large grain sample (few μm), the magnetic domains are controlled by local anisotropy field determined mainly by the magnetocrystalline anisotropy. The low field MR clearly reflects the temperature dependence of the magnetocrystalline anisotropy. For decreasing gain size, the contribution of spin disorder at the grain boundary increases and enhances the local anisotropy field.

  19. Mechanics, kinematics and geometry of pebble abrasion from binary collisions

    NASA Astrophysics Data System (ADS)

    Miller, K. L.; Jerolmack, D. J.

    2014-12-01

    As sediment is transported downstream as bedload, it collides with the bed causing sharp edges to chip and wear away, rounding the rock through the process of abrasion. Previous work has linked abrasion to downstream fining and rounding of grains, however, there has been little attempt to understand the underlying kinematics of abrasion. Furthermore, most studies neglect the fine particle produced during the abrasion process, as the initial grain gets smaller and rounder. In this research, we preform well-controlled laboratory experiments to determine the functional dependence between impact energy and mass lost from abrasion. We use a double-pendulum "Newton's Cradle" set-up to examine the abrasion between two grains and with a high-speed camera, we can quantify the impact energies during collision. Results from experiments verify that mass loss is proportional to kinetic energy. We define a material parameter that incorporates material density, Young's modulus, and tensile stress and show that this parameter is directly related to the proportionality between mass loss and energy. We identify an initial region of the mass loss curves in which abrasion is independent of energy and material properties; results suggest this region is determined by shape. We show that grain size distributions of daughter products are universal and independent of material; they follow a Weibull distribution, which is expected distribution from brittle fracture theory. Finally, scanning electron microscope (SEM) images show a thin damage zone near the surface, suggesting that collision energy is attenuated over some small skin depth. Overall, we find that pebble abrasion by collision can be characterized by two universal scaling relations - the mass loss versus energy curves and the size distribution of daughter products. Results will be useful for estimating expected abrasion rates in the field, and additionally demonstrate that low-energy collisions produce large quantities of sand

  20. Strategic Regulation of Grain Size in Memory Reporting over Time

    ERIC Educational Resources Information Center

    Goldsmith, M.; Koriat, A.; Pansky, A.

    2005-01-01

    As time passes, people often remember the gist of an event though they cannot remember its details. Can rememberers exploit this difference by strategically regulating the ''grain size'' of their answers over time, to avoid reporting wrong information? A metacognitive model of the control of grain size in memory reporting was examined in two…

  1. Preparation of monodisperse polystyrene/silica core-shell nano-composite abrasive with controllable size and its chemical mechanical polishing performance on copper

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Wang, Haibo; Zhang, Zefang; Qin, Fei; Liu, Weili; Song, Zhitang

    2011-11-01

    Monodisperse silica-coated polystyrene (PS) nano-composite abrasives with controllable size were prepared via a two-step process. Monodisperse positively charged PS colloids were synthesized via polymerization of styrene by using a cationic initiator. In the subsequent coating process, silica formed shell on the surfaces of core PS particles via the ammonia-catalyzed hydrolysis and condensation of tetraethoxysilane. Neither centrifugation/water wash/redispersion cycle process nor surface modification or addition surfactant was needed in the whole process. The morphology of the abrasives was characterized by scanning electron microscope. Transmission electron microscope and energy dispersive X-ray analysis results indicated that silica layer was successfully coated onto the surfaces of PS particles. Composite abrasive has a core-shell structure and smooth surface. The chemical mechanical polishing performances of the composite abrasive and conventional colloidal silica abrasive on blanket copper wafers were investigated. The root mean square roughness decreases from 4.27 nm to 0.56 nm using composite abrasive. The PS/SiO2 core-shell composite abrasives exhibited little higher material removal rate than silica abrasives.

  2. The influence of grain size on the mechanical properties ofsteel

    SciTech Connect

    Morris Jr., J.W.

    2001-05-01

    Many of the important mechanical properties of steel, including yield strength and hardness, the ductile-brittle transition temperature and susceptibility to environmental embrittlement can be improved by refining the grain size. The improvement can often be quantified in a constitutive relation that is an appropriate variant on the familiar Hall-Petch relation: the quantitative improvement in properties varies with d{sup -1/2}, where d is the grain size. Nonetheless, there is considerable uncertainty regarding the detailed mechanism of the grain size effect, and appropriate definition of ''grain size''. Each particular mechanism of strengthening and fracture suggests its own appropriate definition of the ''effective grain size'', and how it may be best controlled.

  3. Orientation influence on grain size-effects in ultrafine-grained magnesium

    SciTech Connect

    Fan, Haidong; Aubry, Sylvie; Arsenlis, A.; El-Awady, Jaafar

    2014-11-08

    The mechanical behavior of ultrafine-grained magnesium was studied by discrete dislocation dynamics (DDD) simulations. Our results show basal slip yields a strong size effect, while prismatic and pyramidal slips produce a weak one. We developed a new size-strength model that considers dislocation transmission across grain boundaries. Good agreement between this model, current DDD simulations and previous experiments is observed. These results reveal that the grain size effect depends on 3 factors: Peierls stress, dislocation source strength and grain boundary strength.

  4. Influence of grain size on the grinding response of alumina

    SciTech Connect

    Xu, H.H.K.; Wei, L.; Jahanmir, S.

    1996-05-01

    The effect of grain size on the grinding response, i.e., grinding forces, surface roughness, and grinding-induced subsurface damage, is investigated in a series of alumina ceramics with the average grain size ranging from 3 to 35 {micro}m. The grinding forces are measured as a function of depth of cut in surface grinding. It is found that the grinding forces decrease as the grain size is increased from 3 to 9 {micro}m. But at larger grain sizes, the grinding forces are independent of the grain size. Subsurface damage in grinding is observed using a bonded-interface sectioning technique. The subsurface damage is found to consist of intragrain twin/slip bands and intergranular microcracks. The density of grinding-induced subsurface microcracks increases with the grain size. In addition to using optical microscopy on the sections of the ground specimens, a nondestructive thermal wave measurement technique is used directly on the ground surfaces for the detection of grinding-induced subsurface microcracks. The grain size dependence of the microcrack density estimated from the thermal images is found to agree with the results obtained using the bonded-interface technique.

  5. Grain size-sensitive creep in ice II

    USGS Publications Warehouse

    Kubo, T.; Durham, W.B.; Stern, L.A.; Kirby, S.H.

    2006-01-01

    Rheological experiments on fine-grained water ice II at low strain rates reveal a creep mechanism that dominates at conditions of low stress. Using cryogenic scanning electron microscopy, we observed that a change in stress exponent from 5 to 2.5 correlates strongly with a decrease in grain size from about 40 to 6 micrometers. The grain size-sensitive creep of ice II demonstrated here plausibly dominates plastic strain at the low-stress conditions in the interior of medium- to large-sized icy moons of the outer solar system.

  6. Grain size-sensitive creep in ice II.

    PubMed

    Kubo, Tomoaki; Durham, William B; Stern, Laura A; Kirby, Stephen H

    2006-03-01

    Rheological experiments on fine-grained water ice II at low strain rates reveal a creep mechanism that dominates at conditions of low stress. Using cryogenic scanning electron microscopy, we observed that a change in stress exponent from 5 to 2.5 correlates strongly with a decrease in grain size from about 40 to 6 micrometers. The grain size-sensitive creep of ice II demonstrated here plausibly dominates plastic strain at the low-stress conditions in the interior of medium- to large-sized icy moons of the outer solar system. PMID:16513977

  7. Grain size-sensitive creep in ice II.

    PubMed

    Kubo, Tomoaki; Durham, William B; Stern, Laura A; Kirby, Stephen H

    2006-03-01

    Rheological experiments on fine-grained water ice II at low strain rates reveal a creep mechanism that dominates at conditions of low stress. Using cryogenic scanning electron microscopy, we observed that a change in stress exponent from 5 to 2.5 correlates strongly with a decrease in grain size from about 40 to 6 micrometers. The grain size-sensitive creep of ice II demonstrated here plausibly dominates plastic strain at the low-stress conditions in the interior of medium- to large-sized icy moons of the outer solar system.

  8. The influence of aluminum grain size on alumina nanoporous structure

    SciTech Connect

    Feil, A. F.; Costa, M. V. da; Amaral, L.; Teixeira, S. R.; Migowski, P.; Dupont, J.; Machado, G.; Peripolli, S. B.

    2010-01-15

    An approach to control the interpore distances and nanopore diameters of 150-nm-thick thin aluminum films is reported here. The Al thin films were grown by sputtering on p-type silicon substrate and anodized with a conventional anodization process in a phosphoric acid solution. It was found that interpore distance and pore diameter are related to the aluminum grain size and can be controlled by annealing. The grain contours limit the sizes of alumina cells. This mechanism is valid for grain sizes supporting only one alumina cell and consequently only one pore.

  9. The Effects of Grain Size and Texture on Dynamic Abnormal Grain Growth in Mo

    NASA Astrophysics Data System (ADS)

    Noell, Philip J.; Taleff, Eric M.

    2016-10-01

    This is the first report of abnormal grain morphologies specific to a Mo sheet material produced from a commercial-purity arc-melted ingot. Abnormal grains initiated and grew during plastic deformation of this material at temperatures of 1793 K and 1813 K (1520 °C and 1540 °C). This abnormal grain growth during high-temperature plastic deformation is termed dynamic abnormal grain growth, DAGG. DAGG in this material readily consumes nearly all grains near the sheet center while leaving many grains near the sheet surface unconsumed. Crystallographic texture, grain size, and other microstructural features are characterized. After recrystallization, a significant through-thickness variation in crystallographic texture exists in this material but does not appear to directly influence DAGG propagation. Instead, dynamic normal grain growth, which may be influenced by texture, preferentially occurs near the sheet surface prior to DAGG. The large grains thus produced near the sheet surface inhibit the subsequent growth of the abnormal grains produced by DAGG, which preferentially consume the finer grains near the sheet center. This produces abnormal grains that span the sheet center but leave unconsumed polycrystalline microstructure near the sheet surface. Abnormal grains are preferentially oriented with the < 110rangle approximately along the tensile axis. These results provide additional new evidence that boundary curvature is the primary driving force for DAGG in Mo.

  10. The Effects of Grain Size and Texture on Dynamic Abnormal Grain Growth in Mo

    NASA Astrophysics Data System (ADS)

    Noell, Philip J.; Taleff, Eric M.

    2016-07-01

    This is the first report of abnormal grain morphologies specific to a Mo sheet material produced from a commercial-purity arc-melted ingot. Abnormal grains initiated and grew during plastic deformation of this material at temperatures of 1793 K and 1813 K (1520 °C and 1540 °C). This abnormal grain growth during high-temperature plastic deformation is termed dynamic abnormal grain growth, DAGG. DAGG in this material readily consumes nearly all grains near the sheet center while leaving many grains near the sheet surface unconsumed. Crystallographic texture, grain size, and other microstructural features are characterized. After recrystallization, a significant through-thickness variation in crystallographic texture exists in this material but does not appear to directly influence DAGG propagation. Instead, dynamic normal grain growth, which may be influenced by texture, preferentially occurs near the sheet surface prior to DAGG. The large grains thus produced near the sheet surface inhibit the subsequent growth of the abnormal grains produced by DAGG, which preferentially consume the finer grains near the sheet center. This produces abnormal grains that span the sheet center but leave unconsumed polycrystalline microstructure near the sheet surface. Abnormal grains are preferentially oriented with the < 110rangle approximately along the tensile axis. These results provide additional new evidence that boundary curvature is the primary driving force for DAGG in Mo.

  11. Impact of grain size on the convection of terrestrial planets

    NASA Astrophysics Data System (ADS)

    Rozel, A.

    2012-10-01

    This article presents a set of simulations of mantle convection, using a new model of grain size-dependent rheology. In the present paper, it is shown that this rheology behaves in many ways as a visco-plastic rheology. I use a model of grain size evolution which has been calibrated on experimental data in a previous paper. In this physical model, the grain size is directly related to the stress state, following a temperature-dependent piezometric law. The rheology used here allows both diffusion and dislocation creep, depending on the grain size. At low stress, the grain size is high and forces the rheology to be dislocation dominated. For sufficiently high stresses, the equilibrium regime reached by the grains is located in the diffusion creep. In this case, the viscosity is linked to a stress-dependent grain size, which actually makes the rheology more non-Newtonian than it is in dislocation creep. This experimentally calibrated model allowed me to perform a set of numerical experiments of convection in which the rheology may be diffusion or dislocation creep dominated, depending on the state of the stress tensor. Then, The stress exponent varies from 3 to 5 because of grain size, which has a large impact on the temperature dependence of the viscosity. The present paper shows the impact of this new model on the convection regimes of terrestrial planets. In particular, for a wide range of parameters, I observe the episodic regime which is thought to govern the dynamics of Venus. This process of episodic resurfacing was obtained in previous simulations using visco-plastic rheologies is a tight range of parameters. I obtain it here without using an ad hoc plasticity law, only using a viscous rheology based on laboratory measurements. In these simulations, I show that the cooling rate of the terrestrial planets may be largely modified by the consideration of a grain size-dependent rheology.

  12. A Rare Allele of GS2 Enhances Grain Size and Grain Yield in Rice.

    PubMed

    Hu, Jiang; Wang, Yuexing; Fang, Yunxia; Zeng, Longjun; Xu, Jie; Yu, Haiping; Shi, Zhenyuan; Pan, Jiangjie; Zhang, Dong; Kang, Shujing; Zhu, Li; Dong, Guojun; Guo, Longbiao; Zeng, Dali; Zhang, Guangheng; Xie, Lihong; Xiong, Guosheng; Li, Jiayang; Qian, Qian

    2015-10-01

    Grain size determines grain weight and affects grain quality. Several major quantitative trait loci (QTLs) regulating grain size have been cloned; however, our understanding of the underlying mechanism that regulates the size of rice grains remains fragmentary. Here, we report the cloning and characterization of a dominant QTL, grain size on chromosome 2 (GS2), which encodes Growth-Regulating Factor 4 (OsGRF4), a transcriptional regulator. GS2 localizes to the nucleus and may act as a transcription activator. A rare mutation of GS2 affecting the binding site of a microRNA, OsmiR396c, causes elevated expression of GS2/OsGRF4. The increase in GS2 expression leads to larger cells and increased numbers of cells, which thus enhances grain weight and yield. The introduction of this rare allele of GS2/OsGRF4 into rice cultivars could significantly enhance grain weight and increase grain yield, with possible applications in breeding high-yield rice varieties.

  13. Radiation Pressure on Fluffy Submicron-sized Grains

    NASA Astrophysics Data System (ADS)

    Silsbee, Kedron; Draine, Bruce T.

    2016-02-01

    We investigate the claim that the ratio β of radiation pressure force to gravitational force on a dust grain in our solar system can substantially exceed unity for some grain sizes, provided that grain porosity is high enough. For model grains consisting of random aggregates of silicate spherules, we find that the maximum value of β is almost independent of grain porosity, but for small (\\lt 0.3 μ {{m}}) grains, β actually decreases with increasing porosity. We also investigate the effect of metallic iron and amorphous carbon inclusions in the dust grains and find that while these inclusions do increase the radiation pressure cross-section, β remains below unity for grains with 3 pg of silicate material. These results affect the interpretation of the grain trajectories estimated from the Stardust mission, which were modeled assuming β values exceeding one. We find that radiation pressure effects are not large enough for particles Orion and Hylabrook captured by Stardust to be of interstellar origin given their reported impact velocities. We also consider the effects of solar radiation on transverse velocities and grain spin, and show that radiation pressure introduces both transverse velocities and equatorial spin velocities of several hundred meters per second for incoming interstellar grains at 2 au. These transverse velocities are not important for modeling trajectories, but such spin rates may result in centrifugal disruption of aggregates.

  14. Grain-size considerations for optoelectronic multistage interconnection networks.

    PubMed

    Krishnamoorthy, A V; Marchand, P J; Kiamilev, F E; Esener, S C

    1992-09-10

    This paper investigates, at the system level, the performance-cost trade-off between optical and electronic interconnects in an optoelectronic interconnection network. The specific system considered is a packet-switched, free-space optoelectronic shuffle-exchange multistage interconnection network (MIN). System bandwidth is used as the performance measure, while system area, system power, and system volume constitute the cost measures. A detailed design and analysis of a two-dimensional (2-D) optoelectronic shuffle-exchange routing network with variable grain size K is presented. The architecture permits the conventional 2 x 2 switches or grains to be generalized to larger K x K grain sizes by replacing optical interconnects with electronic wires without affecting the functionality of the system. Thus the system consists of log(k) N optoelectronic stages interconnected with free-space K-shuffles. When K = N, the MIN consists of a single electronic stage with optical input-output. The system design use an effi ient 2-D VLSI layout and a single diffractive optical element between stages to provide the 2-D K-shuffle interconnection. Results indicate that there is an optimum range of grain sizes that provides the best performance per cost. For the specific VLSI/GaAs multiple quantum well technology and system architecture considered, grain sizes larger than 256 x 256 result in a reduced performance, while grain sizes smaller than 16 x 16 have a high cost. For a network with 4096 channels, the useful range of grain sizes corresponds to approximately 250-400 electronic transistors per optical input-output channel. The effect of varying certain technology parameters such as the number of hologram phase levels, the modulator driving voltage, the minimum detectable power, and VLSI minimum feature size on the optimum grain-size system is studied. For instance, results show that using four phase levels for the interconnection hologram is a good compromise for the cost

  15. Grain size reduction by electromagnetic stirring inside gold alloys

    NASA Astrophysics Data System (ADS)

    Ernst, R.; Mangelinck-Noël, N.; Hamburger, J.; Garnier, C.; Ramoni, P.

    2005-06-01

    The final properties of cast materials depend greatly on the solidification process undergone by the material. In this paper, we study gold alloys dedicated to the watch industry and jewellery in the framework of a research collaboration with the Metalor Company. The aim is to improve the concentration homogeneity of the ingots by controlling the solidification step. It can be achieved by reducing segregations by a decrease in the grain size. For this purpose, we set up a multiphase electromagnetic stirring of the melt to favour the growth of finer grains and improve the homogeneity of the composition. We first design an electromagnetic stirrer by numerical simulation. The stirrer is then implemented on a model experiment. Eventually, the alloys are characterised by metallography and etching to evidence the grain structure. As expected, we obtain a substantial reduction of the grain size although, some work remains to be done to attain the final goal of even finer grains.

  16. Grain size distribution of the matrix in the Allende chondrite

    NASA Astrophysics Data System (ADS)

    Toriumi, M.

    1989-03-01

    Results are presented from analytical TEM, high-resolution TEM, and SEM studies of the Allende chondrite, showing that the matrix consists of very fine-grained Fe-rich olivine, Ca-poor and Fe-rich clinopyroxene, Fe-rich spinel, and Ni-bearing troilite. Slightly sintered and non-sintered very fine-grained aggregates are observed. The results suggest that the coarse-grained olivine aggregates experienced a heating event, whereas the ultrafine-grained aggregates did not. The size and frequency distributions of matrix grains are measured. The frequency distribution displays a long-term tail with power law and a log-normal pattern with a peak at 5 nm in the range from 1 to 10 nm. This suggests that the fine-grained matrix was probably formed at conditions far from equilibrium in the protosolar cloud.

  17. On the maximum grain size entrained by photoevaporative winds

    NASA Astrophysics Data System (ADS)

    Hutchison, Mark A.; Laibe, Guillaume; Maddison, Sarah T.

    2016-09-01

    We model the behaviour of dust grains entrained by photoevaporation-driven winds from protoplanetary discs assuming a non-rotating, plane-parallel disc. We obtain an analytic expression for the maximum entrainable grain size in extreme-UV radiation-driven winds, which we demonstrate to be proportional to the mass loss rate of the disc. When compared with our hydrodynamic simulations, the model reproduces almost all of the wind properties for the gas and dust. In typical turbulent discs, the entrained grain sizes in the wind are smaller than the theoretical maximum everywhere but the inner disc due to dust settling.

  18. Activation of Big Grain1 significantly improves grain size by regulating auxin transport in rice.

    PubMed

    Liu, Linchuan; Tong, Hongning; Xiao, Yunhua; Che, Ronghui; Xu, Fan; Hu, Bin; Liang, Chengzhen; Chu, Jinfang; Li, Jiayang; Chu, Chengcai

    2015-09-01

    Grain size is one of the key factors determining grain yield. However, it remains largely unknown how grain size is regulated by developmental signals. Here, we report the identification and characterization of a dominant mutant big grain1 (Bg1-D) that shows an extra-large grain phenotype from our rice T-DNA insertion population. Overexpression of BG1 leads to significantly increased grain size, and the severe lines exhibit obviously perturbed gravitropism. In addition, the mutant has increased sensitivities to both auxin and N-1-naphthylphthalamic acid, an auxin transport inhibitor, whereas knockdown of BG1 results in decreased sensitivities and smaller grains. Moreover, BG1 is specifically induced by auxin treatment, preferentially expresses in the vascular tissue of culms and young panicles, and encodes a novel membrane-localized protein, strongly suggesting its role in regulating auxin transport. Consistent with this finding, the mutant has increased auxin basipetal transport and altered auxin distribution, whereas the knockdown plants have decreased auxin transport. Manipulation of BG1 in both rice and Arabidopsis can enhance plant biomass, seed weight, and yield. Taking these data together, we identify a novel positive regulator of auxin response and transport in a crop plant and demonstrate its role in regulating grain size, thus illuminating a new strategy to improve plant productivity. PMID:26283354

  19. Activation of Big Grain1 significantly improves grain size by regulating auxin transport in rice.

    PubMed

    Liu, Linchuan; Tong, Hongning; Xiao, Yunhua; Che, Ronghui; Xu, Fan; Hu, Bin; Liang, Chengzhen; Chu, Jinfang; Li, Jiayang; Chu, Chengcai

    2015-09-01

    Grain size is one of the key factors determining grain yield. However, it remains largely unknown how grain size is regulated by developmental signals. Here, we report the identification and characterization of a dominant mutant big grain1 (Bg1-D) that shows an extra-large grain phenotype from our rice T-DNA insertion population. Overexpression of BG1 leads to significantly increased grain size, and the severe lines exhibit obviously perturbed gravitropism. In addition, the mutant has increased sensitivities to both auxin and N-1-naphthylphthalamic acid, an auxin transport inhibitor, whereas knockdown of BG1 results in decreased sensitivities and smaller grains. Moreover, BG1 is specifically induced by auxin treatment, preferentially expresses in the vascular tissue of culms and young panicles, and encodes a novel membrane-localized protein, strongly suggesting its role in regulating auxin transport. Consistent with this finding, the mutant has increased auxin basipetal transport and altered auxin distribution, whereas the knockdown plants have decreased auxin transport. Manipulation of BG1 in both rice and Arabidopsis can enhance plant biomass, seed weight, and yield. Taking these data together, we identify a novel positive regulator of auxin response and transport in a crop plant and demonstrate its role in regulating grain size, thus illuminating a new strategy to improve plant productivity.

  20. Activation of Big Grain1 significantly improves grain size by regulating auxin transport in rice

    PubMed Central

    Liu, Linchuan; Tong, Hongning; Xiao, Yunhua; Che, Ronghui; Xu, Fan; Hu, Bin; Liang, Chengzhen; Chu, Jinfang; Li, Jiayang; Chu, Chengcai

    2015-01-01

    Grain size is one of the key factors determining grain yield. However, it remains largely unknown how grain size is regulated by developmental signals. Here, we report the identification and characterization of a dominant mutant big grain1 (Bg1-D) that shows an extra-large grain phenotype from our rice T-DNA insertion population. Overexpression of BG1 leads to significantly increased grain size, and the severe lines exhibit obviously perturbed gravitropism. In addition, the mutant has increased sensitivities to both auxin and N-1-naphthylphthalamic acid, an auxin transport inhibitor, whereas knockdown of BG1 results in decreased sensitivities and smaller grains. Moreover, BG1 is specifically induced by auxin treatment, preferentially expresses in the vascular tissue of culms and young panicles, and encodes a novel membrane-localized protein, strongly suggesting its role in regulating auxin transport. Consistent with this finding, the mutant has increased auxin basipetal transport and altered auxin distribution, whereas the knockdown plants have decreased auxin transport. Manipulation of BG1 in both rice and Arabidopsis can enhance plant biomass, seed weight, and yield. Taking these data together, we identify a novel positive regulator of auxin response and transport in a crop plant and demonstrate its role in regulating grain size, thus illuminating a new strategy to improve plant productivity. PMID:26283354

  1. Grain size evolution and fractionation trends in an experimental regolith

    NASA Technical Reports Server (NTRS)

    Horz, F.; Cintala, M. J.; See, T. H.; Cardenas, F.; Thompson, T. D.

    1984-01-01

    The communication of blocky planetary surfaces into fine-grained regoliths was simulated by impacting a fragmental gabbro target 200 times with stainless steel projectiles. It is found that the comminution efficiency of the surfaces changes with time, being highest in the early stages of regolith formation and decreasing gradually. The relationship between mean grain size and cumulative energy is not linear. Individual, fine-grained regolith components can be generated very early from relatively large progenitor fragments without going through intermediate-size fractions. Impact comminution is capable of producing fractionated fines as postulated by Papike et al. (1982). The role of grain-size selective, lateral transport to explain the fractionated nature of lunar regolith fines may have been overestimated in the past.

  2. Morphological Variability and Grain Size From Digital Images

    NASA Astrophysics Data System (ADS)

    Gallagher, E. L.; Macmahan, J.; Russell, P.; Masselink, G.

    2006-12-01

    In the past, hydrodynamic and morphologic coastal modelers have assumed that the sand layer on the beach is thick, well-sorted (uniform in grain size) and relatively smooth. Many recent studies contradict this assumption and suggest that sediments on a beach are not homogeneous and that variations in sediment size and supply are important in sediment transport and morphodynamics at all scales. Unfortunately, traditional techniques for measuring grain size are difficult, tedious and time consuming. Therefore, in spite of the evidence pointing to the importance of grain size and its variability in sediment transport and morphodynamics, most of the studies are based on relatively few field samples. In May 2006, a new digital imaging system for measuring grain size quickly and efficiently was used during a field experiment that took place at Truc Vert on the west coast of France. The field site is a high-energy, macro-tidal beach characterized by beach cusps, crescentic bars and a rip channel system. The digital imaging system was used to conduct daily surveys of sand size, alongside simultaneous surveys of beach morphology and traditional sand sampling. Preliminary results are promising and suggest that the imaging system is ideal for sampling large areas for detailed spatial grain size information. The data will be examined for morphological and sedimentological variability associated with the complex morphology at Truc Vert.

  3. Grain size assisted formation of pseudotachylites: A numerical study

    NASA Astrophysics Data System (ADS)

    Thielmann, Marcel; Rozel, Antoine; Kaus, Boris; Ricard, Yanick

    2014-05-01

    The processes resulting in the formation of lithospheric-scale shear zones are still poorly understood. Among others, shear heating and grain size reduction have been proposed to be viable weakening mechanisms to localize deformation and form lithospheric-scale shear zones. The interplay between both mechanisms is particularly interesting, as both compete for a part of the deformational work. High temperatures favor grain growth, therefore one would expect larger grain sizes in shear zones that have been formed by shear heating. However, larger temperatures increase strain rates, thus also the amount of deformational work, which in turn would favor grain size reduction. Here we investigate the interplay between both mechanisms using numerical models of a viscoelastic slab deforming in simple shear, employing a viscous rheology composed of dislocation and diffusion creep. Grain size evolution is governed by a recently developed physics-based evolution law. We develop scaling laws for the peak stress and the dominating deformation mechanisms depending on various material parameters and boundary conditions. We find that grain size reduction alone does not localize deformation in simple shear. In conjunction with shear heating however, a localized shear zone is formed due to thermal runaway. During this process, grain size is significantly reduced. Depending on grain growth parameters, a mylonitic shear zone is formed in which deformation is permanently localized and which deforms in diffusion creep. Additionally, the stress required to initiate thermal runaway is reduced compare to cases with shear heating alone, thus facilitating the formation of a narrow localized shear zone in the ductile regime. These results have several implications ranging and from simultaneous pseudotachylite and mylonite formation at depths below the seismogenic depth to subduction initiation.

  4. The Strength-Grain Size Relationship in Ultrafine-Grained Metals

    NASA Astrophysics Data System (ADS)

    Balasubramanian, N.; Langdon, Terence G.

    2016-04-01

    Metals processed by severe plastic deformation (SPD) techniques, such as equal-channel angular pressing (ECAP) and high-pressure torsion (HPT), generally have submicrometer grain sizes. Consequently, they exhibit high strength as expected on the basis of the Hall-Petch (H-P) relationship. Examples of this behavior are discussed using experimental data for Ti, Al, and Ni. These materials typically have grain sizes greater than ~50 nm where softening is not expected. An increase in strength is usually accompanied by a decrease in ductility. However, both high strength and high ductility may be achieved simultaneously by imposing high strain to obtain ultrafine-grain sizes and high fractions of high-angle grain boundaries. This facilitates grain boundary sliding, and an example is presented for a cast Al-7 pct Si alloy processed by HPT. In some materials, SPD may result in a weakening even with a very fine grain size, and this is due to microstructural changes during processing. Examples are presented for an Al-7034 alloy processed by ECAP and a Zn-22 pct Al alloy processed by HPT. In some SPD-processed materials, it is possible that grain boundary segregation and other features are present leading to higher strengths than predicted by the H-P relationship.

  5. Novel ultrafine grain size processing of soft magnetic materials.

    SciTech Connect

    Michael, Joseph Richard; Robino, Charles Victor

    2009-01-01

    High performance soft magnetic alloys are used in solenoids in a wide variety of applications. These designs are currently being driven to provide more margin, reliability, and functionality through component size reductions; thereby providing greater power to drive ratio margins as well as decreases in volume and power requirements. In an effort to produce soft magnetic materials with improved properties, we have conducted an initial examination of one potential route for producing ultrafine grain sizes in the 49Fe-49Co-2V alloy. The approach was based on a known method for the production of very fine grain sizes in steels, and consisted of repeated, rapid phase transformation cycling through the ferrite to austenite transformation temperature range. The results of this initial attempt to produce highly refined grain sizes in 49Fe-49Co-2V were successful in that appreciable reductions in grain size were realized. The as-received grain size was 15 {micro}m with a standard deviation of 9.5 {micro}m. For the temperature cycling conditions examined, grain refinement appears to saturate after approximately ten cycles at a grain size of 6 {micro}m with standard deviation of 4 {micro}m. The process also reduces the range of grain sizes present in these samples as the largest grain noted in the as received and treated conditions were 64 and 26 {micro}m, respectively. The results were, however, complicated by the formation of an unexpected secondary ferritic constituent and considerable effort was directed at characterizing this phase. The analysis indicates that the phase is a V-rich ferrite, known as {alpha}{sub 2}, that forms due to an imbalance in the partitioning of vanadium during the heating and cooling portions of the thermal cycle. Considerable but unsuccessful effort was also directed at understanding the conditions under which this phase forms, since it is conceivable that this phase restricts the degree to which the grains can be refined. Due to this difficulty

  6. Grain-size Distribution of Apollo 11 Soil 10084

    NASA Technical Reports Server (NTRS)

    Basu, A.; Wentworth, S. J.; McKay, D. S.

    2000-01-01

    Results of a new grain size analysis of 0.99 g of the submillimeter fraction of the soil 10084, using the JSC methodology, are: 4.28 phi =(51 micrometers) and 2.23 phi (=213 micrometers). A significant fraction (14.2%) of the soil is less than 10 micrometers in size.

  7. Digital grain-size analysis based on autocorrelation algorithm

    NASA Astrophysics Data System (ADS)

    Cheng, Zhixuan; Liu, Haijiang

    2015-08-01

    Grain size is one of the most important parameters in geology and coastal engineering. However, all traditional methods are time consuming, laborious, and expensive. In this study, the autocorrelation technique, which was first expounded by Rubin (2004), was extended to estimate the size of well-sorted sediments and the grain-size distribution of mixed-size sediments. Long and intermediate axes of well-sorted sediments ranging from 1 to 20 mm obtained from applying the autocorrelation method are compared with the corresponding results measured using a vernier caliper. Using the autocorrelation technique, the sediment mean size was calculated and was found to compare better with point counts than sieving. Regarding the mixed-size sediment, a nonlinear programming method, which is different from the conventional 'least-squares with non-negativity' method, the kernel density method, and the maximum entropy method, was used to obtain the representative grain sizes and associated sediment inherent parameters, such as mean diameter, median diameter, sorting, skewness, and kurtosis. Image pre-processing was used in the present analysis to enhance the contrast of the recorded image, and a conversion method applied to take into account the difference between the two-dimensional digital image method and the three-dimensional sieving method. Using the modified fitting points and the improved Gaussian function fitting method, the cumulative grain-size distribution curve and the probability density curve of the mixed-size sediments were obtained. The enhanced autocorrelation technique that was developed from the traditional 'look-up-catalogue' approach provided a more accurate estimation of the grain-size distribution, as well as the relevant physical parameters of the mixed-size sediment.

  8. On Suspended matter grain size in Baltic sea

    NASA Astrophysics Data System (ADS)

    Bubnova, Ekaterina; Sivkov, Vadim; Zubarevich, Victor

    2016-04-01

    Suspended matter grain size data were gathered during the 25th research vessel "Akademik Mstislav Keldysh" cruise (1991, September-October). Initial quantitative data were obtained with a use of the Coulter counter and subsequently modified into volume concentrations (mm3/l) for size intervals. More than 80 samples from 15 stations were analyzed (depth range 0-355 m). The main goal of research was to illustrate the spatial variability of suspended matter concentration and dispersion in Baltic Sea. The mutual feature of suspended matter grain size distribution is the logical rise of particle number along with descending of particle's size. Vertical variability of grain size distribution was defined by Baltic Sea hydrological structure, including upper mixed layer - from the surface to the thermocline - with 35 m thick, cold intermediate layer - from the thermocline to the halocline- and bottom layer, which lied under the halocline. Upper layer showed a rise in total suspended matter concentration (up to 0.6 mm3/l), while cold intermediate level consisted of far more clear water (up to 0.1 mm3/l). Such a difference is caused by the thermocline boarding role. Meanwhile, deep bottom water experienced surges in suspended matter concentration owing to the nepheloid layer presence and "liquid bottom" effect. Coastal waters appeared to have the highest amount of particles (up to 5.0 mm3/l). Suspended matter grain size distribution in the upper mixed layer revealed a peak of concentration at 7 μ, which can be due to autumn plankton bloom. Another feature in suspended matter grain size distribution appeared at the deep layer below halocline, where both O2 and H2S were observed and red/ox barrier is. The simultaneous presence of Fe and Mn (in solutions below red/ox barrier) and O2 leads to precipitation of oxyhydrates Fe and Mn and grain size distribution graph peaking at 4.5 μ.

  9. Photovoltaic Performance of Perovskite Solar Cells with Different Grain Sizes.

    PubMed

    Kim, Hyung Do; Ohkita, Hideo; Benten, Hiroaki; Ito, Shinzaburo

    2016-02-01

    Perovskite solar cells exhibit improved photovoltaic parameters with increasing perovskite grain size. The larger photocurrent is due to the enhanced absorption efficiency for thicker perovskite layers. The larger open-circuit voltage (VOC ) is ascribed to the reduced trap-assisted recombination for the larger grains. As a result, the power conversion efficiency exceeds 19% at best. Further improvement in VOC would be possible if the trap density were reduced.

  10. Physics-Based Reactive Burn Model: Grain Size Effects

    NASA Astrophysics Data System (ADS)

    Lu, X.; Hamate, Y.; Horie, Y.

    2007-12-01

    We have been developing a physics-based reactive burn (PBRB) model, which was formulated based on the concept of a statistical hot spot cell. In the model, essential thermomechanics and physiochemical features are explicitly modeled. In this paper, we have extended the statistical hot spot model to explicitly describe the ignition and growth of hot spots. In particular, grain size effects are explicitly delineated through introduction of grain size-dependent, thickness of the hot-region, energy deposition criterion, and specific surface area. Besides the linear relationships between the run distance to detonation and the critical diameter with respect to the reciprocal specific surface area of heterogeneous explosives (HE), which is based on the original model and discussed in a parallel paper of this meeting, parametric studies have shown that the extended PBRB model can predict a non-monotonic variation of shock sensitivity with grain size, as observed by Moulard et al.

  11. Universal scaling relations for pebble abrasion

    NASA Astrophysics Data System (ADS)

    Litwin, K. L.; Jerolmack, D. J.

    2012-12-01

    The process of abrasion of gravel in bed load transport results from particle-to-particle collisions, where the energy involved is sufficient to cause chipping and spallation but not fragmentation of parent grains. The removed rock material is not infinitesimal; daughter products as large as coarse sand can be produced. Although previous work has shown that lithology, grain shape, and energy of collision are contributing factors that control abrasion rates of river-bed material, little is known regarding the relationship between these factors and diminution rates. Here we explicitly isolate and investigate how these three factors influence rates of abrasion and the size distribution of daughter products, with laboratory experiments. The apparatus is a double pendulum (Newton's cradle) that produces well-controlled binary collisions. A high-speed camera precisely measures collision energy, while mass of parent rocks. and the size and shape distributions of daughter products, are measured periodically. We examined abrasion of initially square-cut 'rocks' as they underwent successive collisions in the binary collision apparatus. We have examined mass loss rate for varied lithologies, and observe a similar power-law relationship between impact energy and mass abraded. When normalized by sensible material properties, mass loss curves for all materials collapse onto a single curve, suggesting that the underlying mechanics of abrasion for different materials are the same. The relationship does not display the linear trend expected from pure energetics, and we suggest that this is a shape effect as protruding - and hence easily eroded - corners are worn away. Analysis of daughter-product particle size distributions for different lithology fragments - including natural rocks and also bricks - show the same functional form. Surprisingly, it is the power-law relation expected for brittle materials undergoing fragmentation. This suggests that brittle fracture theory also

  12. Effects of grain size evolution on mantle dynamics

    NASA Astrophysics Data System (ADS)

    Schulz, Falko; Tosi, Nicola; Plesa, Ana-Catalina; Breuer, Doris

    2016-04-01

    The rheology of planetary mantle materials is strongly dependent on temperature, pressure, strain-rate, and grain size. In particular, the rheology of olivine, the most abundant mineral of the Earth's upper mantle, has been extensively studied in the laboratory (e.g., Karato and Wu, 1993; Hirth and Kohlstedt, 2003). Two main mechanisms control olivine's deformation: dislocation and diffusion creep. While the former implies a power-law dependence of the viscosity on the strain-rate that leads to a non-Newtonian behaviour, the latter is sensitively dependent on the grain size. The dynamics of planetary interiors is locally controlled by the deformation mechanism that delivers the lowest viscosity. Models of the dynamics and evolution of planetary mantles should thus be capable to self-consistently distinguish which of the two mechanisms dominates at given conditions of temperature, pressure, strain-rate and grain size. As the grain size can affect the viscosity associated with diffusion creep by several orders of magnitude, it can strongly influence the dominant deformation mechanism. The vast majority of numerical, global-scale models of mantle convection, however, are based on the use of a linear diffusion-creep rheology with constant grain-size. Nevertheless, in recent studies, a new equation has been proposed to properly model the time-dependent evolution of the grain size (Austin and Evens, 2007; Rozel et al., 2010). We implemented this equation in our mantle convection code Gaia (Hüttig et al., 2013). In the framework of simple models of stagnant lid convection, we compared simulations based on the fully time-dependent equation of grain-size evolution with simulations based on its steady-state version. In addition, we tested a number of different parameters in order to identify those that affects the grain size to the first order and, in turn, control the conditions at which mantle deformation is dominated by diffusion or dislocation creep. References Austin

  13. Influence of mineral fraction on the rheological properties of forsterite + enstatite during grain-size-sensitive creep: 1. Grain size and grain growth laws

    NASA Astrophysics Data System (ADS)

    Tasaka, Miki; Hiraga, Takehiko

    2013-08-01

    conducted grain growth and creep experiments on forsterite (Fo) plus enstatite (En) aggregates at 1 atmosphere pressure and temperatures of 1260 - 1360°C, with variable volumetric fractions of the two minerals, forsterite and enstatite (Fo1.00 to Fo0.03 En0.97). The grain size ratios of forsterite and enstatite in annealed (reference) and deformed samples follow the Zener relationship of dI/dII = β/fIIz, where d is the grain size, and the subscripts I and II indicate the primary and secondary phases, respectively. When fEn < 0.5, I is forsterite, II is enstatite, then β = 0.67, and z = 0.52; for samples where fEn > 0.5, I is enstatite, II is forsterite, then β = 0.73, and z = 0.53. Grain growth in reference samples conforms to the relationship ds4 - d04 = kt, where ds is the grain size under static conditions, d0 is the initial grain size, k is the grain growth coefficient, and t is time. The observed growth coefficient for the primary phase (kI) becomes smaller with increasing fII, which is consistent with the theoretical prediction. Overall, our results are consistent with previously proposed grain growth models for static conditions that use mineral physical parameters such as diffusivity (DiGB) and interfacial energy (γ). We discuss grain size variations in the mantle, with compositions ranging from dunite to pyroxenite, and we go on to present a method that predicts the grain sizes of different mantle lithologies, provided that the diffusivity and interfacial energy of the constituent minerals are known.

  14. Solidification of Suspended Sediments with Two Characteristic Grain Sizes

    NASA Astrophysics Data System (ADS)

    Zarski, G.; Borja, R. I.

    2010-12-01

    We use mixture theory to formulate the problem of solidification of sediments with two characteristic grain sizes in a suspension. The formulation involves a mixture of larger grains in a thick fluid, where the thick fluid is a mixture of smaller particles in a host fluid. This mixture within a mixture description resembles a double porosity representation in unsaturated soil mechanics. Two independent variables of interest include the volume fraction of the larger grains relative to the total volume of the mixture, and the volume fraction of the smaller grains relative to the volume of the thick fluid. The two volume fractions are coupled by a constitutive law based on the Richardson-Zaki equation. The governing partial differential equations describing the settling velocities of the two solid groups are solved simultaneously in space and time using the finite element method.

  15. Promise and Pitfalls of Using Grain Size Analysis to Identify Glacial Sediments in Alpine Lake Cores.

    NASA Astrophysics Data System (ADS)

    Clark, D. H.

    2011-12-01

    Lakes fed by glacier outwash should have a clastic particle-size record distinct from non-glacial lakes in the same area, but do they? The unique turquoise color of alpine glacial lakes reflects the flux of suspended clastic glacial rock flour to those lakes; conversely, lakes not fed by outwash are generally clear with sediments dominated by organics or slope-wash from nearby hillslopes. This contrast in sediment types and sources should produce a distinct and measureable different in grain sizes between the two settings. Results from a variety of lakes suggest the actual situation is often more subtle and complex. I compare grain size results to other proxies to assess the value of grain size analysis for paleoglacier studies. Over the past 10 years, my colleagues and I have collected and analyzed sediment cores from a wide variety of lakes below small alpine glaciers in an attempt to constrain the timing and magnitude of alpine glaciation in those basins. The basic concept is that these lakes act as continuous catchments for any rock flour produced upstream by glacier abrasion; as a glacier grows, the flux of rock flour to the lake will also increase. If the glacier disappears entirely, rock flour deposition will also cease in short order. We have focused our research in basins with simple sedimentologic settings: mostly small, high-altitude, stripped granitic or metamorphic cirques in which the cirque glaciers are the primary source of clastic sediments. In most cases, the lakes are fed by meltwater from a modern glacier, but were ice free during the earlier Holocene. In such cases, the lake cores should record formation of and changes in activity of the glacier upstream. We used a Malvern Mastersizer 2000 laser particle size analyzer for our grain size analyses, as well as recording magnetic susceptibility, color, and organics for the same cores. The results indicate that although lakes often experience increases in silt and clay-size (<0.63 mm) clastic

  16. Transitional grain-size-sensitive flow of milky quartz aggregates

    NASA Astrophysics Data System (ADS)

    Fukuda, J. I.; Holyoke, C. W., III; Kronenberg, A. K.

    2014-12-01

    Fine-grained (~15 μm) milky quartz aggregates exhibit reversible flow strengths in triaxial compression experiments conducted at T = 800-900oC, Pc = 1.5 GPa when strain rates are sequentially decreased (typically from 10-3.5 to 10-4.5 and 10-5.5 s-1), and then returned to the original rate (10-3.5 s-1), while samples that experience grain growth at 1000oC (to 35 μm) over the same sequence of strain rates exhibit an irreversible increase in strength. Polycrystalline quartz aggregates have been synthesized from natural milky quartz powders (ground to 5 μm) by HIP methods at T = 1000oC, Pc = 1.5 GPa and t = 24 hours, resulting in dense, fine-grained aggregates of uniform water content of ~4000 ppm (H/106Si), as indicated by a broad OH absorption band at 3400 cm-1. In experiments performed at 800o and 900oC, grain sizes of the samples are essentially constant over the duration of each experiment, though grain shapes change significantly, and undulatory extinction and deformation lamellae indicate that much of the sample shortening (to 50%) is accomplished, over the four strain-rate steps, by dislocation creep. Differential stresses measured at T = 800oC decrease from 160 to 30 MPa as strain rate is reduced from 10-4.6 to 10-5.5 s-1, and a stress of 140 MPa is measured when strain rate is returned to 10-4.5 s-1. Samples deformed at 1000o and 1100oC experience normal grain growth, with grain boundary energy-driven grain-coarsening textures superposed by undulatory extinction and deformation lamellae. Differential stresses measured at 1000oC and strain rates of 10-3.6, 10-4.6, and 10-5.5 s-1 are 185, 80, and 80 MPa, respectively, while an increased flow stress of 260 MPa is measured (following ~28 hours of prior high temperature deformation and grain growth) when strain rate is returned to 10-3.6 s-1. While all samples exhibit lattice preferred orientations, the stress exponent n inferred for the fine-grained 800oC sample is 1.5 and the stress exponent of the coarse-grained

  17. Detecting sedimentary cycles using autocorrelation of grain size.

    PubMed

    Xiao, Shangbin; Li, Rui; Chen, Muhong

    2013-01-01

    Detection of sedimentary cycles is difficult in fine-grained or homogenous sediments but is a prerequisite for the interpretation of depositional environments. Here we use a new autocorrelation analysis to detect cycles in a homogenous sediment core, E602, from the northern shelf of the South China Sea. Autocorrelation coefficients were calculated for different mean grain sizes at various depths. The results show that sediments derived from rapid depositional events have a better autocorrelation. Analysis of two other cores confirms this result. Cores composed of sediments deposited quickly under stable and/or gradually changing hydrodynamic conditions, have higher autocorrelation coefficients, whereas, those composed of sediments deposited during calm periods have relatively low autocorrelation coefficients. It shows that abrupt changes in autocorrelation coefficients usually indicate the existence of a boundary between adjacent sedimentary cycles, with each cycle beginning with a high positive autocorrelation coefficient of grain size and ending with a low negative one.

  18. Spatial analysis of grain size in Santa Monica Bay.

    PubMed

    Leecaster, Molly

    2003-01-01

    Maps are useful scientific tools for presenting environmental information, but the statistical techniques necessary to prepare scientifically rigorous maps have primarily focused on terrestrial habitats. This study compares three popular techniques (triangulation, kriging, and co-kriging) to map sediment grain size in Santa Monica Bay, California. Two grain size data sets, one collected in 1994 (79 sites) and one collected in 1997 and 1998 (149 sites) were used for model development. A bathymetric data set collected in 1997 was used as a model covariate. A third grain size data set (40 sites) collected in 1996 from independent sites was used for model evaluation. Predictions were compared to validation data by average difference, prediction mean square error (PMSE), and a goodness-of-prediction measure, G. The average difference between prediction and truth was similar for all methods, but the PMSE for triangulation was more than twice that for kriging or co-kriging, which were similar. The G measure also shows triangulation to be a far worse predictor than kriging and co-kriging. Small-scale differences were observed between kriging and co-kriging at steep depth contours, where co-kriging predicted values commensurate with the expected depth-defined grain size.

  19. Permeability & Grain Size Distribution of Wenchuan Earthquake Fault Rocks

    NASA Astrophysics Data System (ADS)

    Yang, X.; Chen, J.; Ma, S.

    2010-12-01

    Permeability and grain size distribution of fault rocks from two outcrops of Wenchuan earthquake fault zone were measured. The results show that the permeability (at 40MPa) varies obviously across the fault zone, from 10-13 m2 -10-15 m2 for fractured and shattered breccias, ~ 10-17 m2 for crushed breccias to 10-18 m2 - <10-19 m2 for fresh gouges and country rocks. Particle sizes dominate the permeability of the fault rocks. The more the percentage of fine particles is, the lower the permeability is. Due to the impermeable gouges and permeable fractured breccias, seismic fault zone is characterized by anisotropy for fluid flowing. Fluids cycle along fault zone easily if breccias are not cemented. Two methods, sieve weighting and laser analyzer, were combined to analyze the grain size distribution of the fault rocks. The measurements indicate that the slope of log(N) ~ log(d) changes at a critical diameter dc with 1 - 2 mm, which corresponds to grinding limit of rocks and may represent a change from grinding process to attrition one. The fractal dimension (D), calculated based on the grains with size larger than dc, of gouges is higher than 3.0 with the fresh gouges having the highest value (≥ 3.4), of crushed breccias ranges from 2.56 to 2.99, and of fractured and shattered breccias has the lowest value, about 2.63 in average. However, the fractal dimension matching smaller grains (> 2 mm) becomes much lower, ranging from 1.7 to 2.2. It is expected that the estimation of surface fracture energy associated with faulting is less than that we thought if the grain size distribution is considered.

  20. Enhanced Sucrose Loading Improves Rice Yield by Increasing Grain Size.

    PubMed

    Wang, Liang; Lu, Qingtao; Wen, Xiaogang; Lu, Congming

    2015-12-01

    Yield in cereals is a function of grain number and size. Sucrose (Suc), the main carbohydrate product of photosynthesis in higher plants, is transported long distances from source leaves to sink organs such as seeds and roots. Here, we report that transgenic rice plants (Oryza sativa) expressing the Arabidopsis (Arabidopsis thaliana) phloem-specific Suc transporter (AtSUC2), which loads Suc into the phloem under control of the phloem protein2 promoter (pPP2), showed an increase in grain yield of up to 16% relative to wild-type plants in field trials. Compared with wild-type plants, pPP2::AtSUC2 plants had larger spikelet hulls and larger and heavier grains. Grain filling was accelerated in the transgenic plants, and more photoassimilate was transported from the leaves to the grain. In addition, microarray analyses revealed that carbohydrate, amino acid, and lipid metabolism was enhanced in the leaves and grain of pPP2::AtSUC2 plants. Thus, enhancing Suc loading represents a promising strategy to improve rice yield to feed the global population.

  1. High-strength transparent spinel with fine, unimodal grain size

    NASA Astrophysics Data System (ADS)

    Sweeney, S. M.; Brun, M. K.; Yosenick, T. J.; Kebbede, A.; Manoharan, M.

    2009-05-01

    Spinel (MgAl2O4) is a good candidate material for transparent armor and IR window applications. Traditionally, transparent spinel has suffered from poor strength and difficult polishing owing to its large, bimodal grain structure. Starting from a spinel nanopowder, spinel ceramics with a grain size of less than 2 microns have been made with better than 80% in-line transmittance at 632 nm wavelength for 3/8" thick samples. A ring-on-ring test has been used to measure biaxial flexural strength on samples machined to 0.8 mm thickness. The average strength was found to exceed 480 MPa.

  2. Spatial and Temporal Snow Grain Size Variability across Northwestern Greenland

    NASA Astrophysics Data System (ADS)

    Courville, Z.; Polashenski, C. M.; Domine, F.

    2015-12-01

    The albedo of snow-covered surfaces is influenced by several factors including the presence of water; the inclusion of impurities, in particular black carbon and dust; and snow grain size and shape. The SAGE project (Sunlight Absorption across the Greenland ice sheet Experiment) aims at determining the impact of these interdependent factors. The SAGE project consisted of two overland traverses in 2013 and 2014 between Summit Station in the center of the ice sheet and Thule Air Base, on the northwest coast. This route crosses over several facies of the ice sheet representing different accumulation and melt regimes. The SAGE field objectives included detailed shallow pit studies of snow grain size, stratigraphy, and chemistry. In addition to snow pit data from the SAGE traverses that can be used to examine spatial variations, snow grain size and chemistry data from seasonal campaigns at Summit Station are used to examine temporal variations. Here, we present snow grain and chemistry seasonal and spatial results, and compare the relative effects to available ground-based albedo and meteorological data from co-located weather stations and hand-held spectro-radiometer measurements.

  3. Grain-size Distributions from Deconvolved Broadband Magnetic Susceptibility

    NASA Astrophysics Data System (ADS)

    Fukuma, K.

    2014-12-01

    A magnetic susceptibility meter with several-decade frequency band has recently made it possible to obtain superparamagnetic grain-size distributions only by room-temperature measurement. A rigorous deconvolution scheme of frequency dependence of susceptibility is already available. I have made some corrections on the deconvolution scheme and present its applications to broadband susceptibility data on loess and volcanic rocks. Deconvolution of frequency dependence of susceptibility was originally developed by Shchervakov and Fabian [2005]. Suppose an ensemble of grains distributed for two independent variables of volume (grain-size) and energy barrier. Applying alternating magnetic field with varying frequency results in differentiating grains by energy barrier - not directly by volume. Since the response function for frequency is known, deconvolution of frequency dependence of susceptibility provide a rigorous solution for the second moment of volume on the volume-energy barrier distribution. Based on a common assumption of a linear relation between volume and energy barrier, we can obtain analytical volume or grain-size distributions of superparamagnetic grains. A ZH broadband susceptibility meter comprises of two separated devices for lower (SM-100, 65 - 16kHz) and higher (SM-105, 16k - 512kHz) frequency ranges. At every frequency susceptibility calibration was conducted using three kinds of paramagnetic rare earth oxides [Fukuma and Torii, 2011]. Almost all samples exhibited seemingly linear dependences of in-phase susceptibility on logarithmic frequency. This indicates that the measured data do not suffer serious noise, and that the second moment of volume is relatively constant against energy barrier. Nonetheless, third-order polynomial fittings revealed slight deflections from the quasi-linear susceptibility - logarithmic frequency relations. Deconvolving the polynomials showed that such slight defections come from peaks or troughs in varying second moment

  4. Lunar Surface Imaging Polarimetry: I. Roughness and Grain Size

    NASA Astrophysics Data System (ADS)

    Dollfus, Audouin

    1998-11-01

    Imaging polarimetry characterizes the physical nature of the lunar surface by the median size of the grains and by the roughness of the surface. A video-polarimeter was designed at Observatoire de Paris to produce at the telescope images of planetary surfaces in intensity, degree of linear polarization, flux of polarized light, and other relevant photo-polarimetric images. With these images, the median grain sizeMdand mean roughness slope angle θ have been derived and mapped over characteristic lunar features. The method is explained. Terrains of anomalous surface textures have been discovered. The Imbrian and Eratosthenian mare surfaces, worked by the long term accumulation of impacts and by space exposure, produce a “mature” morphology characterized byMd= 47 μm and θ = 10°, irrespective of the composition of the material. Ejecta blankets around craters of Copernican age or younger show smoother surfaces and larger grains. Pyroclastic deposits have the same roughness, θ = 10°, but consist of grains too small to have been produced by mechanical impact comminution. Very specific terrain types have been discovered along the cliff of Rupes Recta and the crater Birt, which indicate clean rocks depleted of dust. These anomalies may result from seismic action when an impact formed the recent nearby crater Thebit A.

  5. Using equal-channel angular pressing for refining grain size

    NASA Astrophysics Data System (ADS)

    Langdon, Terence G.; Furukawa, Minoru; Nemoto, Minoru; Horita, Zenji

    2000-04-01

    Equal-channel angular pressing is an effective tool for attaining ultrafine grain sizes in bulk materials. An important advantage of this technique over conventional metalworking processes, such as extrusion and rolling, is that very high strains may be attained without any concomitant change in the cross-sectional dimensions of the sample. The microstructures introduced by equalchannel angular pressing critically depend on a number of experimental factors, including the nature of the slip systems introduced during the pressing operation and the total strain imposed on the sample. These factors are illustrated by reference to experiments conducted on pure aluminum; results are also included to demonstrate the influence of alloying additions and especially the remarkably small grain sizes that may be achieved in materials having low rates of recovery.

  6. Evolution of 2D Potts Model Grain Microstructures from an Initial Hillert Size Distribution

    SciTech Connect

    Battaile, C.C.; Holm E.A.

    1998-10-19

    Grain growth experiments and simulations exhibit self-similar grain size distributions quite different from that derived via a mean field approach by Hillert [ 1]. To test whether this discrepancy is due to insufficient anneal times, two different two-dimensional grain structures with realistic topologies and Hillert grain size distributions are generated and subjected to grain growth via the Monte Carlo Potts Model (MCPM). In both cases, the observed self-similar grain size distributions deviate from the initial Hillert form and conform instead to that observed in MCPM grain growth simulations that start from a random microstructure. This suggests that the Hillert grain size distribution is not an attractor.

  7. Grain-size-sensitive creep and its relationship to grain-size-insensitive attenuation in ice-I

    NASA Astrophysics Data System (ADS)

    Caswell, T. E.; Cooper, R. F.; Goldsby, D. L.

    2014-12-01

    Tidal dissipation in the ice shell of, e.g., Europa, occurs in the context of a periodic strain amplitude ɛa ~10-5 imposed upon a material with a deformation-effected microstructure related to tectonic activity. Tidal flexing "samples" this microstructure; the microstructure's anelastic (attenuation, Q-1) response effects dissipation. Experiments combining steady-state creep of polycrystalline ice-I with superposed sinusoidal loading demonstrated an attenuation response that is (a) an order of magnitude more attenuating than predicted by the Maxwell Solid model, (b) similar in form to the Andrade Solid model, which at high-temperature and/or low-frequency conditions is approximated by a power law, (c) modestly non-linear (i.e., Q-1 is a function of the periodic strain amplitude) and (d) insensitive to grain size [1]. The grain-size insensitivity is profound, as steady-state creep of the specimens occurred by the geologically relevant mechanism of grain boundary sliding accommodated by basal dislocation glide (GBS)—a grain-size-sensitive rheology [2]. Here GBS involves emission, motion and interaction of lattice dislocations, and dislocation structures (e.g., subgrain boundaries and secondary grain boundary dislocations) are part of the microstructure sampled by the periodic stress. Transient creep responses sample the aspects of creep microstructure that effect attenuation. In our experiments, polycrystalline ice-I specimens are crept to steady state in the GBS regime (σ = 0.5-5.0 MPa, T = 243K, d = 30-150µm) and subjected to instantaneous drops in differential stress: initial strain-rate recovery is related to the creep microstructure of the previous, higher stress. Our results map-out in stress-strain rate space a "hardness" curve consistent with dislocation microstructure self-similarity - a requirement for grain size-insensitive attenuation. Cryogenic electron backscatter diffraction (EBSD) characterizes the associated microstructure. We have not observed

  8. Grain Size Hardening Effects in Mg-Gd Solid Solutions

    NASA Astrophysics Data System (ADS)

    Nagarajan, Devarajan; Cáceres, Carlos H.; Griffiths, John R.

    2016-11-01

    Pure Mg and alloys with 0.4, 1.3, and 3.8 at. pct Gd were cast with grain sizes between 700 and 35 µm and tested in tension and compression after solid solution heat treatment and quenching. The grain structure of the castings was random, that is, there was no preferred orientation, unlike the situation in extrusions and forgings usually reported in the literature. The results are compared to earlier work on Mg-Zn alloys. A tension-compression asymmetry in which the yield strength in compression is less than in tension was observed in pure Mg but was reversed for the concentrated alloys. The Hall-Petch stress intensity factor, k, first increased then decreased with the amount of Gd in solution. It is noted that defining the friction stress by extrapolating the data to infinite grain size should be treated with caution in Mg and its alloys: nevertheless, a rationale involving solid solution softening/hardening and twinning is offered for the observed values of the friction stress. The reversion of the tension-compression asymmetry is explained by the operation of { {10bar{1}1} } (contraction) twinning in the concentrated alloys in place of { {10bar{1}2} } (extension) twinning in pure Mg and the dilute alloys. It is argued that the activation of { {10bar{1}1} } twinning in the more concentrated alloys accounts for their lower k-value.

  9. Grain Size Hardening Effects in Mg-Gd Solid Solutions

    NASA Astrophysics Data System (ADS)

    Nagarajan, Devarajan; Cáceres, Carlos H.; Griffiths, John R.

    2016-08-01

    Pure Mg and alloys with 0.4, 1.3, and 3.8 at. pct Gd were cast with grain sizes between 700 and 35 µm and tested in tension and compression after solid solution heat treatment and quenching. The grain structure of the castings was random, that is, there was no preferred orientation, unlike the situation in extrusions and forgings usually reported in the literature. The results are compared to earlier work on Mg-Zn alloys. A tension-compression asymmetry in which the yield strength in compression is less than in tension was observed in pure Mg but was reversed for the concentrated alloys. The Hall-Petch stress intensity factor, k, first increased then decreased with the amount of Gd in solution. It is noted that defining the friction stress by extrapolating the data to infinite grain size should be treated with caution in Mg and its alloys: nevertheless, a rationale involving solid solution softening/hardening and twinning is offered for the observed values of the friction stress. The reversion of the tension-compression asymmetry is explained by the operation of {10bar{1}1} (contraction) twinning in the concentrated alloys in place of {10bar{1}2} (extension) twinning in pure Mg and the dilute alloys. It is argued that the activation of {10bar{1}1} twinning in the more concentrated alloys accounts for their lower k-value.

  10. EVOLUTION OF SIZE DISTRIBUTION OF ICY GRAINS BY SUBLIMATION AND CONDENSATION

    SciTech Connect

    Kuroiwa, Takuto; Sirono, Sin-iti

    2011-09-20

    In the outer part of a protoplanetary disk, dust grains consist of silicate core covered by an ice mantle. A temporal heating event in the disk results in sublimation of the ice mantle. After the end of the heating event, as the temperature decreases, H{sub 2}O molecules recondense on the surface of the dust grain. Ultimately, the dust grain is covered by an ice mantle. Because the equilibrium vapor pressure on the grain surface decreases with the grain size, a large grain grows faster than a small grain. As a result, the size of an icy dust grain changes as a result of the heating event. The change in size also affects the mechanical properties of the dust aggregates formed by the icy grains. In this paper, we investigated the evolution of the size distribution of icy dust grains during sublimation and condensation. We found that the size evolution of icy grains can be divided into two stages. In the first stage, the icy grains grow through condensation of H{sub 2}O molecules. In the second stage, the size of grains changes further as H{sub 2}O molecules are transferred between icy grains while the surrounding gas condenses. The size distribution of the icy dust grains becomes bimodal, with a small number of relatively large grains and many small grains without an icy mantle. Possible effects of the size change on the evolution of icy dust aggregates are discussed.

  11. Grain size distribution and microstructures of experimentally sheared granitoid gouge at coseismic slip rates - criteria to distinguish seismic and aseismic faults?

    NASA Astrophysics Data System (ADS)

    Stunitz, H.; Keulen, N.; Hirose, T.; Heilbronner, R.

    2009-04-01

    In order to assess whether seismic and aseismic fault rocks can be distinguished on the basis of their microstructure, the grain size distribution and the microstructures from high velocity friction experiments are compared with those of slow deformation experiments of Keulen et al (2007, 2008) for the same material (Verzasca granitoid). The mechanical behavior of granitoid gouge in fast velocity friction experiments at slip rates of 0.65 and 1.28 m/s and normal stresses of 0.4-0.9 MPa characterizes the slip weakening in a typical exponential friction coefficient vs displacement relationship. The grain size distributions yield similar D-values (slope of frequency versus log grain size curve ≈ 2.2 - 2.3) as those of slow deformation experiments (D = 2.0 - 2.3) for grain sizes larger than 1 μm. These values are independent of the total displacement above a gamma value of about γ ≈ 20. The D-values are also independent of the displacement rates in the range of ≈1 µm/s to ≈1.3 m/s and do not vary in the normal stress range between 0.5 MPa and 500 MPa. Grain shapes evolve towards more rounded and less serrated grains with increasing displacement. The progressive grain shape evolution while the grain size distribution remains constant suggests that the wear at clast boundaries produces a range of grain sizes by instant crushing rather than by gradual comminution and abrasion. The results of the study demonstrate that most cataclastic and gouge fault zones may have resulted from seismic deformation but the distinction of seismic and aseismic deformation cannot be made on the basis of grain size distribution.

  12. The effects of grain size composition on the efficiency of fine-grained coal separation

    SciTech Connect

    Blahova, O.; Rezek, K.; Novacek, J.

    1994-12-31

    One factor that favorably affects the economics of exploitation and preparation of coal is reducing the loss of coal matter in the tailings from washeries. Thus, it is necessary to modify existing technologies for the preparation of coking coal. This study of the effects of grain size composition for run-of-mine coal on the efficiency of coal separation, as well as on the quality of the products, was performed on the following equipment used for fine-grained coal separation: fine coal jigs (0.5 to 10/15 mm); jigs (0.5 to 40 mm); heavy medium cyclones (0.5 to 10 mm); slurry hydrocyclones (0.0 to 0.5 mm); HIRST hydrocyclones (0.0 to 0.5 mm); and spiral concentrators (0.0 to 3.0 mm). The results of the study lead to the following conclusions. (1) It is impossible to attain efficient separation in a wide range of fine grain sizes processed simultaneously in a single piece of equipment. (2) Among the equipment available for separation, one type can be found with the highest efficiency for a given grain size of fine coal. (3) The newly introduced spiral concentrators have attained such an efficiency of separation and are so economical that they could be included with advantage between the jigs and the lotion process. This would favorably affect the output and the efficiency of separation of all the equipment involved in the process. (4) All measures to be taken in the flow sheet of coal preparation plants and designed to increase the efficiency of separation should be documented with data that show the expected economic benefits of any change for both the mine and the preparation plant.

  13. Grain size control and superplasticity in 6013-type aluminum alloys

    NASA Astrophysics Data System (ADS)

    Troeger, Lillianne Plaster Whitelock

    Aluminum alloys have been the material of choice for aircraft construction since the 1930's. Currently, the automotive industry is also showing an increasing interest in aluminum alloys as structural materials. 6xxx aluminum alloys possess a combination of strength and formability which makes them attractive to both industries. In addition, 6xxx alloys are highly weldable, corrosion resistant, and low in cost as compared with the 2xxx and 7xxx aluminum alloys. Superplastic forming (SPF) is a manufacturing process which exploits the phenomenon of superplasticity in which gas pressure is used to form complex-shaped parts in a single forming operation. This reduces part counts and the need for fasteners and connectors, resulting in reduced product weight. Reduced product/vehicle weight improves fuel economy. Most alloys must be specially processed for superplasticity. Much research effort has been directed at the development of thermomechanical processes for the grain refinement of aluminum alloys by static or dynamic recrystallization. to induce superplasticity. While large numbers of studies have been conducted on 2xxx, 5xxx, 7xxx, and 8xxx aluminum alloys, very few studies have been focused on the grain refinement of 6xxx aluminum alloys for superplasticity. The current research describes a new thermomechanical process for application to 6xxx aluminum alloys for grain refinement and superplasticity. The process is shown to successfully refine and induce superplasticity in an Al-Mg-Si-Cu alloy which falls within the compositional limits of both 6013 and 6111. The grain refinement is by particle-stimulated nucleation of recrystallization. The microstructural evolution during the thermomechanical processing is characterized in terms of precipitate size, shape, distribution and composition; texture; recrystallization; and grain size, shape, and thermal stability. The new process produces a statically-stable, weakly-textured, equiaxed grain structure with an average

  14. The grain size distribution and the detection of abnormal grain growth of austenite in an eutectoid steel containing niobium

    SciTech Connect

    Bruno, J.C. . Dept. de Engenharia Mecanica e de Materiais); Rios, P.R. . Dept. de Ciencia dos Materiais e Metalurgia)

    1995-02-15

    The abnormal grain growth of austenite was studied in a commercial steel of composition (wt%): 0.70 C, 1.36 Mn, 0.72 Si, 0.015 P, 0.027 S and 0.03 Nb. Specimens were thermocycled at various conditions and then grain size distribution determined. The grain size distribution shape did not change during normal grain growth but this distribution widened and flattened during the abnormal grain growth. The initial smaller mean size of carbonitrides and/or the highest homogeneity of niobium carbonitride size distribution of the samples submitted to thermal cycles, in comparison with the normalized samples, increased the abnormal grain growth temperature from 1,373 K to 1,473 K.

  15. Mapping Snow Grain Size over Greenland from MODIS

    NASA Technical Reports Server (NTRS)

    Lyapustin, Alexei; Tedesco, Marco; Wang, Yujie; Kokhanovsky, Alexander

    2008-01-01

    This paper presents a new automatic algorithm to derive optical snow grain size (SGS) at 1 km resolution using Moderate Resolution Imaging Spectroradiometer (MODIS) measurements. Differently from previous approaches, snow grains are not assumed to be spherical but a fractal approach is used to account for their irregular shape. The retrieval is conceptually based on an analytical asymptotic radiative transfer model which predicts spectral bidirectional snow reflectance as a function of the grain size and ice absorption. The analytical form of solution leads to an explicit and fast retrieval algorithm. The time series analysis of derived SGS shows a good sensitivity to snow metamorphism, including melting and snow precipitation events. Preprocessing is performed by a Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm, which includes gridding MODIS data to 1 km resolution, water vapor retrieval, cloud masking and an atmospheric correction. MAIAC cloud mask (CM) is a new algorithm based on a time series of gridded MODIS measurements and an image-based rather than pixel-based processing. Extensive processing of MODIS TERRA data over Greenland shows a robust performance of CM algorithm in discrimination of clouds over bright snow and ice. As part of the validation analysis, SGS derived from MODIS over selected sites in 2004 was compared to the microwave brightness temperature measurements of SSM\\I radiometer, which is sensitive to the amount of liquid water in the snowpack. The comparison showed a good qualitative agreement, with both datasets detecting two main periods of snowmelt. Additionally, MODIS SGS was compared with predictions of the snow model CROCUS driven by measurements of the automatic whether stations of the Greenland Climate Network. We found that CROCUS grain size is on average a factor of two larger than MODIS-derived SGS. Overall, the agreement between CROCUS and MODIS results was satisfactory, in particular before and during the

  16. Quantifying Sediment Transport Determined From Grain-Size Distributions

    NASA Astrophysics Data System (ADS)

    de Almeida, R. A.; Möller, O. O.; Lentini, C. A.; Campos, E. J.

    2005-05-01

    A technique derived from McLaren & Bowles (1985) has been applied to investigate sediment dynamics in the Patos Lagoon estuary (Brazil). Qualitative sediment transport in the access channel of the estuary was inferred from changes in statistical properties describing grain-size distributions. Assuming the influence of a single transport function, the spatial gradient of particle mean size, sorting and skewness was used to determine the transport direction along the channel. A long-average net sediment deposition rate in the area was estimated using digitalized historical nautical charts. This deposition rate was used to quantify the sediment transport inside the estuary, through a simple application of Green's Theorem. Results show a net seaward transport in the deep channel of approximately 50 m3 day-1, accompanied by a net inward transport in the shallower channel margin of similar intensity. The estimated net sediment transport was validated against a numerical model output, with good agreement in terms of direction and intensity.

  17. Formation of asteroids from mm-cm sized grains

    NASA Astrophysics Data System (ADS)

    Carrera, D.; Johansen, A.; Davies, M. B.

    2014-03-01

    Context. Asteroids and comets are intricately connected to life in the universe. Asteroids are the building blocks of terrestrial planets; water-rich asteroids and comets are likely to be the primary source of water for Earth's oceans and other volatiles (Morbidelli et al. 2000; Hartogh et al. 2011); and they may play role in mass extinctions. Yet, the formation of these objects is poorly understood. There is mounting evidence that the traditional picture of the formation of asteroids must be revised. The size distribution of asteroids is hard to reconcile with a traditional bottomup formation scenario. Instead, asteroids may form top-down, with large 100 - 1000 km sized objects forming first by the gravitational collapse of dense clumps of small particles. Experiments and simulations suggest that dust grains cannot grow to sizes larger than mm-cm in protoplanetary disks (Zsom et al. 2010). Also, primitive meteorites from the asteroid belt contain a large mass fraction in chondrules of sizes from 0.1 mm to a few mm. Hence, it is desirable to find a model for asteroid formation from mm-sized particles. Aims. In this work, we model the dynamics of mm-cm sized grains in dust-enriched inner regions of protoplanetary disks. We model the dust-gas interaction to determine whether dust grains of this size can form dense, self-gravitating clouds that can collapse to form asteroids. Methods. We perform shearing box simulations of the inner disk using the Pencil Code (Brandenburg & Dobler 2002). The simulations start with a Solar-type solids-to-gas ratio of 0.01 and we gradually increase the particle concentration. In a real protoplanetary disk, solid particles are expected to migrate from the outer regions and concentrate in the inner disk. Results. Our simulations show that mm-sized particles can form very dense clumps, driven by a run-away convergence in the radial-drift flow of these particles - this dynamic is known as the streaming instability (Youdin & Goodman 2005

  18. High Resolution Aquifer Characterization - Busting the Grain Size Myth

    NASA Astrophysics Data System (ADS)

    Vienken, T.; Dietrich, P.

    2014-12-01

    While major advancements have been made in the field of aquifer characterization, field method development and application for reliable model parametrization and improving system understanding are in many cases yet under-developed. One key parameter for the description of groundwater flow and transport is hydraulic conductivity (K). In every day practice, K is often estimated based on literature values or ex-situ laboratory measurements. The calculation of K based on grain size distribution data is a very prominent example of a well-established but unsuitable method for the characterization of heterogeneous sedimentary deposits. Even though concerns about the suitability of this method for detailed aquifer characterization have been raised in several publications, this approach is still widely used by both, scientists and practitioners - mainly due to its simplicity. Hence, a vast number of different empirical and semi-empirical formulas already exist and even more adapted formulas are proposed, although reliable alternatives are available. With this contribution we want to raise awareness about the intrinsic limitations of using grain size data for the determination of K and show direct push-based alternatives for reliable and efficient high resolution aquifer characterization.

  19. Analysis of Abrasive Blasting of DOP-26 Iridium Alloy

    SciTech Connect

    Ohriner, Evan Keith; Zhang, Wei; Ulrich, George B

    2012-01-01

    The effects of abrasive blasting on the surface geometry and microstructure of DOP-26 iridium alloy (Ir-0.3% W-0.006% Th 0.005% Al) have been investigated. Abrasive blasting has been used to control emissivity of components operating at elevated temperature. The effects of abrasive blasting conditions on surface morphology were investigated both experimentally and by numerical modeling. The simplified model, based on finite element analysis of a single angular particle impacting on Ir alloy disk, calculates the surface deformation and residual strain distribution. The experimental results and modeling results both indicate that the surface geometry is not sensitive to the abrasive blast process conditions of nozzle pressure and standoff distance considered in this study. On the other hand, the modeling results suggest that the angularity of the abrasive particle has an important role in determining surface geometry, which in turn, affects the emissivity. Abrasive blasting causes localized surface strains and localized recrystallization, but it does not affect grain size following extended exposure at elevated temperature. The dependence of emissivity of the DOP-26 alloy on mean surface slope follows a similar trend to that reported for pure iridium.

  20. Grain Size of Recall Practice for Lengthy Text Material: Fragile and Mysterious Effects on Memory

    ERIC Educational Resources Information Center

    Wissman, Kathryn T.; Rawson, Katherine A.

    2015-01-01

    The current research evaluated the extent to which the grain size of recall practice for lengthy text material affects recall during practice and subsequent memory. The "grain size hypothesis" states that a smaller vs. larger grain size will increase retrieval success during practice that in turn will enhance subsequent memory for…

  1. Grain size analysis of the Bright Materials on 4 Vesta

    NASA Astrophysics Data System (ADS)

    Zambon, F.; De Sanctis, M.; Capaccioni, F.; Ammannito, E.; Li, J.; Longobardo, A.; Mittlefehldt, D. W.; Palomba, E.; Pieters, C. M.; Schröder, S.; Tosi, F.; Hiesinger, H.; Blewett, D. T.; Russell, C. T.; Raymond, C. A.; Capria, M.; Fonte, S.; Carraro, F.; Frigeri, A.; Magni, G.

    2012-12-01

    The Dawn spectrometer, VIR-MS (Visible and InfraRed Mapping Spectrometer), has provided data for almost all of Vesta's surface in the wavelength interval between 0.25 μm and 5 μm [1]. The VIR spectra are similar to the spectra of howardite-eucrite-diogenite (HED) meteorites and are characterized by the presence of two strong absorption bands at 0.9 μm and 1.9 μm, associated with iron-bearing pyroxenes [2]. Vesta's surface presents a large number of Bright Materials (BM) deposits distributed mostly in the equatorial region. BM have different spectral characteristics than do other regions. Band depths for the bright areas are deeper than the surroundings, while the BM visible reflectance is higher than the Vesta's average. In the infrared channel, bright areas are associated with low thermal emission regions [3]. The bright deposits are of several types and are classified according to their characteristics. On Vesta we can recognize: Crater Wall/Scarp Material, Radial Material, Slope Material, Patchy Material, Spot Material and Diffuse Plains Material [4]. These deposits differ from each other for instance for the albedo, in particular, Crater Walls have an albedo level 40% higher than the others, while Spot Materials are 20% brighter than the rest of the surface [5]. Band depth and albedo are affected by various parameters including the grain size; in particular the albedo increases with decreasing particle size [6]. Therefore, deposits with different albedo or band depth may correspond to different grain sizes. During the High Altitude Mapping Orbit (HAMO) and High Altitude Mapping Orbit 2 (HAMO2) mission phases, VIR acquired data that allow us to map the BM at a spatial resolution of ~180 m/pixel. Analysis of the spectral features of HED meteorites at different grain sizes and comparison with the VIR spectra provides more information about the nature of the bright deposits and their physical properties. The authors acknowledge the support of the Dawn Science

  2. The coupled effect of grain size and solute on work hardening of Cu-Ni alloys

    NASA Astrophysics Data System (ADS)

    Shadkam, A.; Sinclair, C. W.

    2015-12-01

    A modified grain size-dependent model developed to capture the combined effects of solute and grain size on the work hardening behaviour of fine-grained Cu-Ni alloys is provided. This work builds on a recent model that attributes the grain size-dependent work hardening of fine-grained Cu to backstresses. In the case of Cu-Ni alloys, unlike commercially pure Cu, a grain size-dependent separation between the Kocks-Mecking curves develops, this being explained here based on an extra contribution from geometrically necessary dislocations in the solid solution alloy. This is corroborated by strain-rate sensitivity experiments.

  3. Awns reduce grain number to increase grain size and harvestable yield in irrigated and rainfed spring wheat

    PubMed Central

    Rebetzke, G. J.; Bonnett, D. G.; Reynolds, M. P.

    2016-01-01

    Genotypic variation in ear morphology is linked to differences in photosynthetic potential to influence grain yield in winter cereals. Awns contribute to photosynthesis, particularly under water-limited conditions when canopy assimilation is restricted. We assessed performance of up to 45 backcross-derived, awned–awnletted NILs representing four diverse genetic backgrounds in 25 irrigated or rainfed, and droughted environments in Australia and Mexico. Mean environment grain yields were wide-ranging (1.38–7.93 t ha−1) with vegetative and maturity biomass, plant height, anthesis date, spike number, and harvest index all similar (P >0.05) for awned and awnletted NILs. Overall, grain yields of awned–awnletted sister-NILs were equivalent, irrespective of yield potential and genetic background. Awnletted wheats produced significantly more grains per unit area (+4%) and per spike (+5%) reflecting more fertile spikelets and grains in tertiary florets. Increases in grain number were compensated for by significant reductions in grain size (–5%) and increased frequency (+0.8%) of small, shrivelled grains (‘screenings’) to reduce seed-lot quality of awnletted NILs. Post-anthesis canopies of awnletted NILs were marginally warmer over all environments (+0.27 °C) but were not different and were sometimes cooler than awned NILs at cooler air temperatures. Awns develop early and represented up to 40% of total spikelet biomass prior to ear emergence. We hypothesize that the allocation of assimilate to large and rapidly developing awns decreases spikelet number and floret fertility to reduce grain number, particularly in distal florets. Individual grain size is increased to reduce screenings and to increase test weight and milling quality, particularly in droughted environments. Despite the average reduction in grain size, awnless lines could be identified that combined higher grain yield with larger grain size, increased grain protein concentration, and reduced

  4. LUNAR DUST GRAIN CHARGING BY ELECTRON IMPACT: DEPENDENCE OF THE SURFACE POTENTIAL ON THE GRAIN SIZE

    SciTech Connect

    Nemecek, Z.; Pavlu, J.; Safrankova, J.; Beranek, M.; Richterova, I.; Vaverka, J.; Mann, I.

    2011-09-01

    The secondary electron emission is believed to play an important role for the dust charging at and close to the lunar surface. However, our knowledge of emission properties of the dust results from model calculations and rather rare laboratory investigations. The present paper reports laboratory measurements of the surface potential on Lunar Highlands Type regolith simulants with sizes between 0.3 and 3 {mu}m in an electron beam with energy below 700 eV. This investigation is focused on a low-energy part, i.e., {<=}100 eV. We found that the equilibrium surface potential of this simulant does not depend on the grain size in our ranges of grain dimensions and the beam energies, however, it is a function of the primary electron beam energy. The measurements are confirmed by the results of the simulation model of the secondary emission from the spherical samples. Finally, we compare our results with those obtained in laboratory experiments as well as those inferred from in situ observations.

  5. A phenomenological numerical approach for investigating grain size evolution in ductiley deforming rocks

    NASA Astrophysics Data System (ADS)

    Cross, Andrew J.; Ellis, Susan; Prior, David J.

    2015-07-01

    The sizes of recrystallised grains in exhumed ductile shear zones are often used to infer conditions of deformation (i.e. stress, strain rate and temperature). Here we present a simple numerical method of calculating the dynamic evolution of grain size during ductile deformation. Our phenomenological method is based on the fact that the dynamic competition between grain growth and recrystallisation will drive grains towards a steady-state size. At each time increment, grain growth and reduction contributions are calculated, with magnitudes which depend on the difference between the current grain size and a desired steady-state grain size. In our models we use a recrystallised grain size piezometer to calculate the steady-state grain size for a given stress. Our numerical routine is incorporated into the SULEC finite element package, allowing us to explore spatial and temporal changes in grain size. As a test, we compare model results to measured grain sizes in quartz layers thinned and recrystallised around rigid garnet porphyroclasts under simple shear dominated deformation in the Alpine Fault Zone of New Zealand. Numerical models are able to replicate observed grain size variations, with boundary conditions consistent with those constrained for the central Alpine Fault Zone.

  6. Wheel Abrasion Experiment Conducted on Mars

    NASA Technical Reports Server (NTRS)

    Ferguson, Dale C.

    1998-01-01

    that the Martian dust has a size somewhat smaller than 40 microns in diameter. The WAE experiment has detected electrostatic charging in the Martian environment for the first time; however, under conditions when the wheel is relatively clean of Martian dust, flight data now indicate that abrasion has also been detected. Crude limits so far place the hardness of the Martian dust at harder than aluminum but softer than nickel, and place the grain size at somewhat smaller than 40 microns.

  7. A simple autocorrelation algorithm for determining grain size from digital images of sediment

    USGS Publications Warehouse

    Rubin, D.M.

    2004-01-01

    Autocorrelation between pixels in digital images of sediment can be used to measure average grain size of sediment on the bed, grain-size distribution of bed sediment, and vertical profiles in grain size in a cross-sectional image through a bed. The technique is less sensitive than traditional laboratory analyses to tails of a grain-size distribution, but it offers substantial other advantages: it is 100 times as fast; it is ideal for sampling surficial sediment (the part that interacts with a flow); it can determine vertical profiles in grain size on a scale finer than can be sampled physically; and it can be used in the field to provide almost real-time grain-size analysis. The technique can be applied to digital images obtained using any source with sufficient resolution, including digital cameras, digital video, or underwater digital microscopes (for real-time grain-size mapping of the bed). ?? 2004, SEPM (Society for Sedimentary Geology).

  8. Composite grain size sensitive and grain size insensitive creep of bischofite, carnallite and mixed bischofite-carnallite-halite salt rock

    NASA Astrophysics Data System (ADS)

    Muhammad, Nawaz; de Bresser, Hans; Peach, Colin; Spiers, Chris

    2016-04-01

    Deformation experiments have been conducted on rock samples of the valuable magnesium and potassium salts bischofite and carnallite, and on mixed bischofite-carnallite-halite rocks. The samples have been machined from a natural core from the northern part of the Netherlands. Main aim was to produce constitutive flow laws that can be applied at the in situ conditions that hold in the undissolved wall rock of caverns resulting from solution mining. The experiments were triaxial compression tests carried out at true in situ conditions of 70° C temperature and 40 MPa confining pressure. A typical experiment consisted of a few steps at constant strain rate, in the range 10-5 to 10-8 s-1, interrupted by periods of stress relaxation. During the constant strain rate part of the test, the sample was deformed until a steady (or near steady) state of stress was reached. This usually required about 2-4% of shortening. Then the piston was arrested and the stress on the sample was allowed to relax until the diminishing force on the sample reached the limits of the load cell resolution, usually at a strain rate in the order of 10-9 s-1. The duration of each relaxation step was a few days. Carnallite was found to be 4-5 times stronger than bischofite. The bischofite-carnallite-halite mixtures, at their turn, were stronger than carnallite, and hence substantially stronger than pure bischofite. For bischofite as well as carnallite, we observed that during stress relaxation, the stress exponent nof a conventional power law changed from ˜5 at strain rate 10-5 s-1 to ˜1 at 10-9 s-1. The absolute strength of both materials remained higher if relaxation started at a higher stress, i.e. at a faster strain rate. We interpret this as indicating a difference in microstructure at the initiation of the relaxation, notably a smaller grain size related to dynamical recrystallization during the constant strain rate step. The data thus suggest that there is a gradual change in deformation

  9. Wind abrasion on Mars

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald

    1991-01-01

    Aeolian activity was predicted for Mars from earth based observations of changing surface patterns that were interpreted as dust storms. Mariner 9 images showed conclusive evidence for aeolian processes in the form of active dust storms and various aeolian landforms including dunes and yardangs. Windspeeds to initiate particle movement are an order of magnitude higher on Mars than on Earth because of the low atmospheric density on Mars. In order to determine rates of abrasion by wind blown particles, knowledge of three factors is required: (1) particle parameters such as numbers and velocities of windblown grains as functions of windspeeds at various heights above the surface; (2) the susceptibility to abrasion of various rocks and minerals; and (3) wind frequencies and speeds. For estimates appropriate to Mars, data for the first two parameters can be determined through lab and wind tunnel tests; data for the last two factors are available directly from the Viking Lander meteorology experiments for the two landing sites.

  10. Dressing of diamond grinding wheels by abrasive water jet for freeform optical surface grinding

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Yao, Peng; Li, Chengwu; Huang, Chuanzhen; Wang, Jun; Zhu, Hongtao; Liu, Zengwen

    2014-08-01

    During the ultra-precision grinding of a large aperture mirror made of RB-SiC, the grinding wheel becomes dull rapidly, which will lead to an increase of grinding force and a decrease of grinding ratio. In this paper, diamond grinding sticks were dressed with micro SiC abrasive water jet and water jet. Through single factorial experiments, the influence of jet pressure on the dressing performance was investigated. To analyze and evaluate the effect of dressing quantitatively, the 3D roughness and the wheel topography were measured and compared with laser scanning confocal microscope before and after dressing. The experimental results show that the abrasive grains are well protruded from binder and the distribution of the abrasive grains becomes uniform after dressing by abrasive water jet when the dressing parameters are properly selected. The dressing performance of abrasive water jet is much better than water jet. For dressing ultra-fine grit size wheels, the abrasive size of the jet should be smaller than the wheel grit size to achieve a better result. The jet pressure is an obvious influence factor of the surface topography.

  11. Ceramic-bonded abrasive grinding tools

    DOEpatents

    Holcombe, C.E. Jr.; Gorin, A.H.; Seals, R.D.

    1994-11-22

    Abrasive grains such as boron carbide, silicon carbide, alumina, diamond, cubic boron nitride, and mullite are combined with a cement primarily comprised of zinc oxide and a reactive liquid setting agent and solidified into abrasive grinding tools. Such grinding tools are particularly suitable for grinding and polishing stone, such as marble and granite.

  12. Ceramic-bonded abrasive grinding tools

    SciTech Connect

    Holcombe, Jr., Cressie E.; Gorin, Andrew H.; Seals, Roland D.

    1994-01-01

    Abrasive grains such as boron carbide, silicon carbide, alumina, diamond, cubic boron nitride, and mullite are combined with a cement primarily comprised of zinc oxide and a reactive liquid setting agent and solidified into abrasive grinding tools. Such grinding tools are particularly suitable for grinding and polishing stone, such as marble and granite.

  13. Grain size effects on dielectric properties of barium strontium titanate composite ceramics

    SciTech Connect

    Zhang, Qiwei; Zhai, Jiwei; Shen, Bo; Zhang, Haijun; Yao, Xi

    2013-03-15

    Graphical abstract: The tunability (T) and quality factor (Q) were found to be strongly dependent on the grain sizes. With increasing the grain size, the tunability significantly decreased. In contrary, the quality factor (Q) at microwave frequencies increased with increasing grain size. A moderate tunability while maintaining a high Q value is still realizable for composite ceramics when grain sizes were controlled to a suitable region A (from 6.5 to 15.0 μm). Highlights: ► The tunability (T) and quality factor (Q) were found to be strongly dependent on the grain sizes. ► With increasing the grain size, the tunability significantly decreased, while the quality factor Q at microwave frequencies increased. ► A moderate tunability while maintaining a high Q value is realizable for composites with grain sizes from about 6.5 to 15.0 μm. - Abstract: Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3}–Mg{sub 2}TiO{sub 4} composite ceramics with different grain sizes were prepared by three sintering methods. The dielectric constant dependences of temperature and frequency showed an increased degree of diffuseness of the Curie peaks as the grain sizes decreased. The tunability (T) and quality factor (Q) were found to be strongly dependent on the grain sizes. The tunability significantly decreased with increasing the grain size. In contrary, the quality factor (Q) at microwave frequencies increased with increasing grain size. A moderate tunability while maintaining a high Q value is still realizable for composite ceramics with grain sizes from about 6.5 to 15.0 μm.

  14. Migration Reversals in Grain-size Transitions to Shoreline

    NASA Astrophysics Data System (ADS)

    Baumanis, C.; Kim, W.

    2015-12-01

    The migration of the lithofacies boundary recorded in the sedimentary record is key to interpreting changes in depositional environments. Change in grain size in the stratigraphic record is one of the most recognizable physical lithological features. Advance and retreat of the lithofacies boundary (gravel-sand transition) is attributed to external control variation, e.g., climate variation, sea-level change, and tectonic subsidence. While most models focus on predicting the response of the fluviodeltaic shoreline to these forcings, none have thoroughly incorporated the migration of grain-size transitions (GST) that coevolve within the fluviodeltaic system. We present a delta evolution model that treats the shoreline and GST as moving boundaries to provide quantitative understanding of the dynamic interaction between the external boundary (shoreline) and the internal lithofacies boundaries (GSTs) under relative sea-level rise. We tested a range of relative sea-level rise rates in the model. The shoreline and GST gradually reduced their progradation rates and eventually retreated landward as the fluviodeltaic topset and foreset elongated. However, their timings of retreats were different, resulting in a counterintuitive case for a quicker retreat of GST while the shoreline still continued to advance. A series of scaled flume experiments with a sand and crushed walnut sediment mixture captured the same behaviors of these two moving boundaries. We found that GST experienced higher relative sea-level rise rates that scale with the downstream river slope and the shoreline progradation rate, which caused earlier GST retreat timing in comparison to the shoreline. Time series data from the experiments show higher natural variability in migration rate of GST compared to that of the shoreline. Therefore, final recorded stratigraphy displayed a GST trajectory as a shazam line that shows zigzag fluctuations. This study investigates autogenic processes acting on the

  15. Potts model simulation of grain size distributions during final stage sintering

    SciTech Connect

    Zeng, P.; Tikare, V.

    1998-09-01

    The Potts Monte Carlo model was used to simulate microstructural evolution and characterize grain size distribution during the final stages of sintering. Simultaneous grain growth, pore migration and pore shrinkage were simulated in a system with an initial porosity of 10% with varying ratios of grain boundary mobility to pore shrinkage rates. This investigation shows that the presence of pores changes the grain size distribution and the topological characteristics due to pinning of grains by pores. As pores shrink away, their pinning effect decreases. Once pore shrinkage is complete, normal grain growth is achieved.

  16. SMALL GRAIN 1, which encodes a mitogen-activated protein kinase kinase 4, influences grain size in rice.

    PubMed

    Duan, Penggen; Rao, Yuchun; Zeng, Dali; Yang, Yaolong; Xu, Ran; Zhang, Baolan; Dong, Guojun; Qian, Qian; Li, Yunhai

    2014-02-01

    Although grain size is one of the most important components of grain yield, little information is known about the mechanisms that determine final grain size in crops. Here we characterize rice small grain1 (smg1) mutants, which exhibit small and light grains, dense and erect panicles and comparatively slightly shorter plants. The short grain and panicle phenotypes of smg1 mutants are caused by a defect in cell proliferation. The smg1 mutations were identified, using a map-based cloning approach, in mitogen-activated protein kinase kinase 4 (OsMKK4). Relatively higher expression of OsMKK4/SMG1 was detected in younger organs than in older ones, consistent with its role in cell proliferation. Green fluorescent protein (GFP)-OsMKK4/SMG1 fusion proteins appear to be distributed ubiquitously in plant cells. Further results revealed that OsMKK4 influenced brassinosteroid (BR) responses and the expression of BR-related genes. Thus, our findings have identified OsMKK4 as a factor for grain size, and suggest a possible link between the MAPK pathways and BRs in grain growth.

  17. The grain size of auditory mismatch response in speech perception

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Kuhl, Patricia; Imada, Toshiaki; Imada, Toshiaki; Kotani, Makoto

    2005-09-01

    This phonetic study examined neural encoding of within-and cross- category information as a function of language experience. Behavioral and magnetoencephalography (MEG) measures for synthetic /ba-wa/ and /ra-la/ stimuli were obtained from ten American and ten Japanese subjects. The MEG experiments employed the oddball paradigm in two conditions. One condition used single exemplars to represent the phonetic categories, and the other introduced within-category variations for both the standard and deviant stimuli. Behavioral results showed three major findings: (a) a robust phonetic boundary effect was observed only in the native listeners; (b) all listeners were able to detect within-category differences on an acoustic basis; and (c) both within- and cross- category discriminations were strongly influenced by language experience. Consistent with behavioral findings, American listeners had larger mismatch field (MMF) responses for /ra-la/ in both conditions but not for /ba-wa/ in either. Moreover, American listeners showed a significant MMF reduction in encoding within-category variations for /ba-wa/ but not for /ra-la/, and Japanese listeners had MMF reductions for both. These results strongly suggest that the grain size of auditory mismatch response is determined not only by experience-dependent phonetic knowledge, but also by the specific characteristics of speech stimuli. [Work supported by NIH.

  18. Relationship among fatigue strength, mean grain size and compressive strength of a rock

    NASA Astrophysics Data System (ADS)

    Singh, S. K.

    1988-10-01

    Fatigue tests carried on three sets of samples having different mean grain sizes revealed that fatigue strength is a function of mean grain size of the rock. Samples having smaller grain size show higher value of fatigue strength. Graywacke samples from Flagstaff formation having mean grain sizes of 1.79 mm, 1.35 mm and 0.93 mm showed fatigue strengths of 87%, 88.25% and 89.1% respectively. Since the mean uniaxial compressive strength also varied with varying grain size, i. e. higher mean strength value for samples having finer grain size; the fatigue strength of a rock also shows a converse relation with mean uniaxial compressive strength.

  19. Grain size and doping effect on structure and electromechanical properties of polycrystalline silicon for MEMS applications

    NASA Astrophysics Data System (ADS)

    Ageev, O. A.; Gusev, E. Yu; Jityaeva, J. Y.; Ilina, M. V.; Bykov, Al V.

    2016-08-01

    Grain size effect on microhardness and Young modulus of polysilicon layers was obtained by nanoindentation experiments: 14.1-16.3 GPa and 240-300 GPa, respectively, for the particle-diameter of 117-430 nm. The range of grain size correlated to mechanical properties exceed theoretical values was defined. The doping effect was considered. The grain size range of PECVD polysilicon with aspects of hardening and suitable conductivity is presented with the objective to formation of micro- and nanomechanical devices.

  20. Material grain size characterization method based on energy attenuation coefficient spectrum and support vector regression.

    PubMed

    Li, Min; Zhou, Tong; Song, Yanan

    2016-07-01

    A grain size characterization method based on energy attenuation coefficient spectrum and support vector regression (SVR) is proposed. First, the spectra of the first and second back-wall echoes are cut into several frequency bands to calculate the energy attenuation coefficient spectrum. Second, the frequency band that is sensitive to grain size variation is determined. Finally, a statistical model between the energy attenuation coefficient in the sensitive frequency band and average grain size is established through SVR. Experimental verification is conducted on austenitic stainless steel. The average relative error of the predicted grain size is 5.65%, which is better than that of conventional methods.

  1. Impact of Volume Fraction and Size of Reinforcement Particles on the Grain Size in Metal-Matrix Micro and Nanocomposites

    NASA Astrophysics Data System (ADS)

    Ferguson, J. B.; Lopez, Hugo F.; Rohatgi, Pradeep K.; Cho, Kyu; Kim, Chang-Soo

    2014-08-01

    In metal-matrix micro and nanocomposites (MMCs and MMNCs), the presence and interactions of various strengthening mechanisms are not well understood, but grain boundary strengthening is considered as one of the primary means of improving the yield strength of composites. Owing to the importance of grain size on mechanical properties, it is necessary to be able to describe how incorporation of nanoparticles (NPs) in both powder metallurgy (PM) and solidification processing (SP) affects this critical property. In the present work, we provide a basis for an empirical equation that relates particle fraction and particle size to MMNC grain size for both PM and SP synthesis methods. The model suggests that NPs retard grain coarsening in PM MMNCs and also seems to describe the effect of reinforcement concentration on grain size in SP MMCs and MMNCs.

  2. Grain size dependent mechanical properties of nanocrystalline diamond films grown by hot-filament CVD

    SciTech Connect

    Wiora, M; Bruehne, K; Floeter, A; Gluche, P; Willey, T M; Kucheyev, S O; Van Buuren, A W; Hamza, A V; Biener, J; Fecht, H

    2008-08-01

    Nanocrystalline diamond (NCD) films with a thickness of {approx}6 {micro}m and with average grain sizes ranging from 60 to 9 nm were deposited on silicon wafers using a hot-filament chemical vapor deposition (HFCVD) process. These samples were then characterized with the goal to identify correlations between grain size, chemical composition and mechanical properties. The characterization reveals that our films are phase pure and exhibit a relatively smooth surface morphology. The levels of sp{sup 2}-bonded carbon and hydrogen impurities are low, and showed a systematic variation with the grain size. The hydrogen content increases with decreasing grain size, whereas the sp{sup 2} carbon content decreases with decreasing grain size. The material is weaker than single crystalline diamond, and both stiffness and hardness decrease with decreasing grain size. These trends suggest gradual changes of the nature of the grain boundaries, from graphitic in the case of the 60 nm grain size material to hydrogen terminated sp{sup 3} carbon for the 9 nm grain size material. The films exhibit low levels of internal stress and freestanding structures with a length of several centimeters could be fabricated without noticeable bending.

  3. Grain-size dynamics beneath mid-ocean ridges: Implications for permeability and melt extraction

    PubMed Central

    Turner, Andrew J; Katz, Richard F; Behn, Mark D

    2015-01-01

    Grain size is an important control on mantle viscosity and permeability, but is difficult or impossible to measure in situ. We construct a two-dimensional, single phase model for the steady state mean grain size beneath a mid-ocean ridge. The mantle rheology is modeled as a composite of diffusion creep, dislocation creep, dislocation accommodated grain boundary sliding, and a plastic stress limiter. The mean grain size is calculated by the paleowattmeter relationship of Austin and Evans (2007). We investigate the sensitivity of our model to global variations in grain growth exponent, potential temperature, spreading-rate, and mantle hydration. We interpret the mean grain-size field in terms of its permeability to melt transport. The permeability structure due to mean grain size may be approximated as a high permeability region beneath a low permeability region. The transition between high and low permeability regions occurs across a boundary that is steeply inclined toward the ridge axis. We hypothesize that such a permeability structure generated from the variability of the mean grain size may focus melt toward the ridge axis, analogous to Sparks and Parmentier (1991)-type focusing. This focusing may, in turn, constrain the region where significant melt fractions are observed by seismic or magnetotelluric surveys. This interpretation of melt focusing via the grain-size permeability structure is consistent with MT observation of the asthenosphere beneath the East Pacific Rise. Key Points: The grain-size field beneath MORs can vary over orders of magnitude The grain-size field affects the rheology and permeability of the asthenosphere The grain-size field may focus melt toward the ridge axis PMID:26693211

  4. GS6, a member of the GRAS gene family, negatively regulates grain size in rice.

    PubMed

    Sun, Lianjun; Li, Xiaojiao; Fu, Yongcai; Zhu, Zuofeng; Tan, Lubin; Liu, Fengxia; Sun, Xianyou; Sun, Xuewen; Sun, Chuanqing

    2013-10-01

    Grain size is an important yield-related trait in rice. Intensive artificial selection for grain size during domestication is evidenced by the larger grains of most of today's cultivars compared with their wild relatives. However, the molecular genetic control of rice grain size is still not well characterized. Here, we report the identification and cloning of Grain Size 6 (GS6), which plays an important role in reducing grain size in rice. A premature stop at the +348 position in the coding sequence (CDS) of GS6 increased grain width and weight significantly. Alignment of the CDS regions of GS6 in 90 rice materials revealed three GS6 alleles. Most japonica varieties (95%) harbor the Type I haplotype, and 62.9% of indica varieties harbor the Type II haplotype. Association analysis revealed that the Type I haplotype tends to increase the width and weight of grains more than either of the Type II or Type III haplotypes. Further investigation of genetic diversity and the evolutionary mechanisms of GS6 showed that the GS6 gene was strongly selected in japonica cultivars. In addition, a "ggc" repeat region identified in the region that encodes the GRAS domain of GS6 played an important historic role in the domestication of grain size in rice. Knowledge of the function of GS6 might aid efforts to elucidate the molecular mechanisms that control grain development and evolution in rice plants, and could facilitate the genetic improvement of rice yield. PMID:23650998

  5. Significant effect of grain size distribution on compaction rates in granular aggregates

    NASA Astrophysics Data System (ADS)

    Niemeijer, André; Elsworth, Derek; Marone, Chris

    2009-07-01

    We investigate the role of pressure solution in deformation of upper- to mid-crustal rocks using aggregates of halite as a room temperature analog for fluid-assisted deformation processes in the Earth's crust. Experiments evaluate the effects of initial grain size distribution on macroscopic pressure solution rate of the aggregate and compare the results to theoretical models for pressure solution. We find that the grain size exponent deviates significantly from the theoretical value of 3 for diffusion-controlled pressure solution. Models typically assume mono-dispersed spherical particles in pseudo-regular packing. We infer that the discrepancy between experimentally determined grain size exponents and the theoretical values are a result of deviation of experimental (and natural) samples from regular packs of mono-dispersed spherical particles. Moreover, we find that compaction rates can vary by up to one order of magnitude as a function of the width of the grain size distribution for a given mean grain size. Wider size distributions allow for higher initial compaction rates, increasing the macroscopic compaction rate with respect to more narrow grain size distributions. Grain sizes in rocks, fault gouges, and hydrocarbon reservoirs are typically log-normal or power law distributed and therefore pressure solution rates may significantly exceed theoretical predictions. Spatiotemporal variations in pressure solution rates due to variations in grain size may cause the formation of low porosity zones, which could potentially focus deformation in these zones and produce pockets of high pore pressures, promoting nucleation of frictional instability and earthquake rupture.

  6. HIGH SPATIAL RESOLUTION SURVEY OF GRAIN SIZE INFORMATION ON RIVER BED BY IMAGE PROCESSING

    NASA Astrophysics Data System (ADS)

    Ohashi, Keisuke; Ihara, Kazuki; Yasuda, Shingo

    We tried a method of grain sizing by image processing which is available to survey and analyze in short time. The high-efficiency method actualizes high spatial resolution information of grain size distribution. Thus, the information has a vailability to express a situation of stream flow better than traditional grain sizing methods. For this reason, we paid attention to 50 m reservoir area upper from the check dam in mountainous region and surveyed the grain distribution at 26 sites and river channel landform. The grain sizing by image processing provided the appropriate result qualitatively. Moreover we estimated the critical diameter of moving from hydraulic information simultaneously. A qualitative appropriate result is showed less than 50 mm error as a result, however, quantitative response is not found between the critical diameter of moving and the grain size distribution surveyed. Meanwhile,the different grain sizing methods that are image processing and traditional sieving are used to cover the bilateral weak point. Thereby, a peak of grain existence probability is found in the threshold diameter between image processing and sieving. This result indicates that it is necessary to change the threshold diameter much larger than the limit of image processing grain sizing.

  7. Characterizing the Large (cm-size) Grains Around Comet 103P/Hartley 2

    NASA Astrophysics Data System (ADS)

    Sunshine, Jessica M.; Feaga, Lori M.; Farnham, Tony; Protopapa, Silvia; Kelley, Michael S.; Engle, Anna

    2016-10-01

    During the flyby of comet 103P/Hartley 2, two populations of bright grains were identified in the coma. Small, 1 µm-sized, water ice-rich grains were observed near the small end of the nucleus that were dragged from the interior by CO2 gas emissions. At closest approach a population of larger grains was clearly seen in visible images off the large lobe. The estimated brightness of the isolated grains suggests that they are likely cm-sized particles and likely water ice-rich. Both sets of grains were simultaneously observed in visible images, at two different resolutions, and by Deep Impact infrared spectrometer. However, because of the difficulty in finding isolated grains in the infrared slit, the population of larger grains has not previously been characterized. Doing so allows us to determine both the reflected and thermal properties of the grains, which when compared to visible images can be used to constrain the size of the grains. Their spectral properties can also be used to definitively detect water ice as has been assumed from visible albedos. In addition, the infrared spectra can be used estimate the relative abundance and particle sizes of ice and non-ice components. The velocity and dynamics of these larger grains can also be characterized. These data will be compared with those of the population of smaller grains emanated directly from the nucleus.Funding from NASA'S Discovery Data Analysis Program (NNX16AJ93G) is greatfully acknowledged.

  8. Grain size softening effect in Al62.5Cu25Fe12.5 nanoquasicrystals

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, N. K.; Ali, F.; Scudino, S.; Samadi Khoshkhoo, M.; Stoica, M.; Srivastava, V. C.; Uhlenwinkel, V.; Vaughan, G.; Suryanarayana, C.; Eckert, J.

    2013-11-01

    Inverse Hall-Petch (IHP) behavior in nano-quasicrystalline Al62.5Cu25Fe12.5 is reported. Powders with varying grain sizes were produced by mechanical milling of spray-formed quasicrystals. The hardness of the milled powders increased with decreasing grain size down to about 40 nm and decreased with further refinement, demonstrating the IHP behavior. This critical grain size was found to be larger compared to other metallic nanocrystalline alloys. This IHP behaviour has been attributed to the structural complexity in quasicrystals and to thermally activated shearing events of atoms at the grain boundaries.

  9. Relative importance of grain boundaries and size effects in thermal conductivity of nanocrystalline materials.

    PubMed

    Dong, Huicong; Wen, Bin; Melnik, Roderick

    2014-11-13

    A theoretical model for describing effective thermal conductivity (ETC) of nanocrystalline materials has been proposed, so that the ETC can be easily obtained from its grain size, single crystal thermal conductivity, single crystal phonon mean free path (PMFP), and the Kaptiza thermal resistance. In addition, the relative importance between grain boundaries (GBs) and size effects on the ETC of nanocrystalline diamond at 300 K has been studied. It has been demonstrated that with increasing grain size, both GBs and size effects become weaker, while size effects become stronger on thermal conductivity than GBs effects.

  10. Eyewitness Recall: Regulation of Grain Size and the Role of Confidence

    ERIC Educational Resources Information Center

    Weber, Nathan; Brewer, Neil

    2008-01-01

    Eyewitness testimony plays a critical role in Western legal systems. Three experiments extended M. Goldsmith, A. Koriat, and A. Weinberg-Eliezer's (2002) framework of the regulation of grain size (precision vs. coarseness) of memory reports to eyewitness memory. In 2 experiments, the grain size of responses had a large impact on memory accuracy.…

  11. Grain size effect on magnetic and dielectric properties of hexagonal YbMnO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Han, Tai-Chun; Hsu, Hsin-Kai; Chu, Yih-Tsyr; Hu, Yu-Min

    2015-05-01

    We have synthesized a series of YbMnO3 nanoparticles with different grain sizes (25-450 nm) and study the effect of grain size on their structural, magnetic, and dielectric properties. The YbMnO3 nanoparticles crystallized in hexagonal perovskite-type structure. It shows that magnetic and dielectric properties are strongly dependent on the grain size. The magnetic characterization indicates that with increasing grain size, the antiferromagnetic (AFM) transition temperature increases from 70 to 86 K. A corresponding shift in the peak-positions of dielectric anomaly and AFM transition temperature is observed, indicating a strong correlation between the magnetic ordering and the electric polarization. As evidenced by the variation in the ab-plane lattice parameters and Mn-O bond lengths, the AFM interactions and dielectric anomalies of YbMnO3 can be effectively modulated by varying grain size.

  12. Tungsten Carbide Grain Size Computation for WC-Co Dissimilar Welds

    NASA Astrophysics Data System (ADS)

    Zhou, Dongran; Cui, Haichao; Xu, Peiquan; Lu, Fenggui

    2016-06-01

    A "two-step" image processing method based on electron backscatter diffraction in scanning electron microscopy was used to compute the tungsten carbide (WC) grain size distribution for tungsten inert gas (TIG) welds and laser welds. Twenty-four images were collected on randomly set fields per sample located at the top, middle, and bottom of a cross-sectional micrograph. Each field contained 500 to 1500 WC grains. The images were recognized through clustering-based image segmentation and WC grain growth recognition. According to the WC grain size computation and experiments, a simple WC-WC interaction model was developed to explain the WC dissolution, grain growth, and aggregation in welded joints. The WC-WC interaction and blunt corners were characterized using scanning and transmission electron microscopy. The WC grain size distribution and the effects of heat input E on grain size distribution for the laser samples were discussed. The results indicate that (1) the grain size distribution follows a Gaussian distribution. Grain sizes at the top of the weld were larger than those near the middle and weld root because of power attenuation. (2) Significant WC grain growth occurred during welding as observed in the as-welded micrographs. The average grain size was 11.47 μm in the TIG samples, which was much larger than that in base metal 1 (BM1 2.13 μm). The grain size distribution curves for the TIG samples revealed a broad particle size distribution without fine grains. The average grain size (1.59 μm) in laser samples was larger than that in base metal 2 (BM2 1.01 μm). (3) WC-WC interaction exhibited complex plane, edge, and blunt corner characteristics during grain growth. A WC ( { 1 {bar{{1}}}00} ) to WC ( {0 1 1 {bar{{0}}}} ) edge disappeared and became a blunt plane WC ( { 10 1 {bar{{0}}}} ) , several grains with two- or three-sided planes and edges disappeared into a multi-edge, and a WC-WC merged.

  13. Genetic Dissection of Grain Size and Grain Number Trade-Offs in CIMMYT Wheat Germplasm

    PubMed Central

    Griffiths, Simon; Wingen, Luzie; Pietragalla, Julian; Garcia, Guillermo; Hasan, Ahmed; Miralles, Daniel; Calderini, Daniel F.; Ankleshwaria, Jignaben Bipinchandra; Waite, Michelle Leverington; Simmonds, James; Snape, John; Reynolds, Matthew

    2015-01-01

    Grain weight (GW) and number per unit area of land (GN) are the primary components of grain yield in wheat. In segregating populations both yield components often show a negative correlation among themselves. Here we use a recombinant doubled haploid population of 105 individuals developed from the CIMMYT varieties Weebill and Bacanora to understand the relative contribution of these components to grain yield and their interaction with each other. Weebill was chosen for its high GW and Bacanora for high GN. The population was phenotyped in Mexico, Argentina, Chile and the UK. Two loci influencing grain yield were indicated on 1B and 7B after QTL analysis. Weebill contributed the increasing alleles. The 1B effect, which is probably caused by to the 1BL.1RS rye introgression in Bacanora, was a result of increased GN, whereas, the 7B QTL controls GW. We concluded that increased in GW from Weebill 7B allele is not accompanied by a significant reduction in grain number. The extent of the GW and GN trade-off is reduced. This makes this locus an attractive target for marker assisted selection to develop high yielding bold grain varieties like Weebill. AMMI analysis was used to show that the 7B Weebill allele appears to contribute to yield stability. PMID:25775191

  14. The effects of grain size and grain boundary characteristics on the thermal conductivity of nanocrystalline diamond

    NASA Astrophysics Data System (ADS)

    Spiteri, David; Anaya, Julian; Kuball, Martin

    2016-02-01

    Molecular dynamics simulation was used to study the effects of each grain dimension and of grain boundary characteristics on the inter-grain thermal boundary resistance (TBR) and intragrain thermal conductivity of nanocrystalline diamond. The effect of the grain boundaries perpendicular to the heat flow was studied using a multiple slab configuration, which greatly reduced the artifacts associated with the heat source/sink. The TBR between the slabs was found to be more sensitive to the atomic arrangement at the boundary than to the tilt angle between the slabs. When the atomic arrangement at the interface was altered from the minimum energy configuration, the TBR increased by a factor of three, suggesting that a sub-optimal interface quality between the grains could play a large role in reducing the thermal conductivity of nanocrystalline diamond. The thermal conductivity between the boundaries was found to be similar to the bulk value, even when the boundaries were only 25 nm apart. The effect of grain boundaries parallel to the heat flow was found to have a large dependence on the microstructural details. Parallel boundaries which were 2 nm apart reduced the thermal conductivity of defect-free diamond by between one third and a factor of ten.

  15. Grain Size as a Control for Melt Focusing Beneath Mid-Ocean Ridges

    NASA Astrophysics Data System (ADS)

    Turner, A.; Katz, R. F.; Behn, M. D.

    2015-12-01

    Grain size is a fundamental control on both the rheology and permeability of the mantle. These properties, in turn, affect the transport of melt beneath mid-ocean ridges. Previous models of grain size beneath ridges have considered only the single-phase problem of dynamic recrystallisation and the resultant pattern of grain-size variation [1,2]. These models have not coupled the spatially variable grain-size field to two-phase (partially molten) mechanics to investigate the implications of spatially variable grain size on melt transport. Here, we present new results from numerical models that investigate the consequences of this coupling. In our two-dimensional, two-phase model the grain-size is coupled to both the permeability and rheology. The rheology is strain-rate and grain-size dependent. For simplicity, however, the grain-size field is not computed dynamically — rather, it is imposed from a single-phase, steady-state model [1] that is based on the "wattmeter" theory [3]. Our calculations predicts that a spatially variable grain size field can promote focusing of melt towards the ridge axis. This focusing is distinct from the commonly discussed, sub-lithospheric decompaction channel [4]. Furthermore, our model predicts that the shape of the partially molten region is sensitive to rheological parameters associated with grain size. The comparison of this shape with observations [5] may help to constrain the rheology of the upper mantle beneath mid-ocean ridges. References: [1] Turner et al., Geochem. Geophys. Geosyst., 16, 925-946, 2015. [2] Behn et al., EPSL, 282, 178-189, 2009. [3] Austin and Evans, Geology, 35:343-346, 2007. [4] Sparks and Parmentier, EPSL, 105, 368-377, 1991. [5] Key et al., Nature, 495, 499-502, 2013.

  16. Grain Size Dependence of Uniform Elongation in Single-Phase FCC/BCC Metals

    NASA Astrophysics Data System (ADS)

    Liu, Haiting; Shen, Yao; Ma, Jiawei; Zheng, Pengfei; Zhang, Lei

    2016-07-01

    We studied the dependence of uniform elongation on grain size in the range of submicron to millimeter for single-phase FCC/BCC metals by reviewing recent experimental results and applying crystal plasticity finite element method simulation. In the order of increasing grain size, uniform elongation can be divided into three stages, namely low elongation stage, nearly constant elongation stage, and decreased elongation with large scatters stage. Low elongation stage features a dramatic increase near the critical grain size at the end of the stage, which is primarily attributed to the emergence of dislocation cell size transition from ultrafine to mid-size grain. Other factors can be neglected due to their negligible influence on overall variation trend. In nearly constant elongation stage, uniform elongation remains unchanged at a high level in general. As grain size keeps growing, uniform elongation starts decreasing and becomes scattered upon a certain grain size, indicating the initiation of decreased elongation with large scatters stage. It is shown that the increase is not linear or smooth but rather sharp at the end of low elongation stage, leading to a wider range in nearly constant elongation stage. The grain size dependence of uniform elongation can serve as a guiding principle for designing small uniaxial tensile specimens for mechanical testing, where size effect matters in most cases.

  17. Grain Size Dependence of Uniform Elongation in Single-Phase FCC/BCC Metals

    NASA Astrophysics Data System (ADS)

    Liu, Haiting; Shen, Yao; Ma, Jiawei; Zheng, Pengfei; Zhang, Lei

    2016-09-01

    We studied the dependence of uniform elongation on grain size in the range of submicron to millimeter for single-phase FCC/BCC metals by reviewing recent experimental results and applying crystal plasticity finite element method simulation. In the order of increasing grain size, uniform elongation can be divided into three stages, namely low elongation stage, nearly constant elongation stage, and decreased elongation with large scatters stage. Low elongation stage features a dramatic increase near the critical grain size at the end of the stage, which is primarily attributed to the emergence of dislocation cell size transition from ultrafine to mid-size grain. Other factors can be neglected due to their negligible influence on overall variation trend. In nearly constant elongation stage, uniform elongation remains unchanged at a high level in general. As grain size keeps growing, uniform elongation starts decreasing and becomes scattered upon a certain grain size, indicating the initiation of decreased elongation with large scatters stage. It is shown that the increase is not linear or smooth but rather sharp at the end of low elongation stage, leading to a wider range in nearly constant elongation stage. The grain size dependence of uniform elongation can serve as a guiding principle for designing small uniaxial tensile specimens for mechanical testing, where size effect matters in most cases.

  18. Evolutionary models of the Earth with a grain size-dependent rheology: diffusion versus dislocation creep

    NASA Astrophysics Data System (ADS)

    Rozel, Antoine; Golabek, Gregor; Thielmann, Marcel; Schierjott, Jana; Tackley, Paul

    2016-04-01

    We present a set of 2D numerical simulations of mantle convection considering grain size evolution and a composite visco-plastic rheology including diffusion and dislocation creep. A 1D parameterization allows us to anticipate the stress conditions for the present-day temperature profile in a convection cell. We are therefore able to obtain self-consistent 2D convecion models together with non-equilibrium grain size for present-day conditions, controlling the partitioning between diffusion and dislocation creep. However, the internal temperature of the mantle is thought to have significantly evolved throughout the history of the Earth. Using a higher internal temperature is usually believed to decrease both viscosity and internal stresses. In our case, a high temperature potentially increases the grain size, which tends to increase the viscosity: the temperature and grain size-dependence of the viscosity are in competition. We study the evolution of the diffusion-dislocation partitioning throughout the history of the Earth. We report the evolution of grain size and stress over time in our simulations. Several complex processes are included in our models. Grain size evolution is a sum of grain growth and dynamic recrystallization. All our simulations consider thermochemical convection in a compressible mantle with melting producting basaltic crust and depleted mantle. Close to the surface, melting produces basaltic material which is erupted or intruded at the base of the crust. Phase transitions reset the grain size to a low value, which influences the whole dynamics of the mantle.

  19. Porosity and grain size dependence of the longitudinal wave velocity of water-saturated beach sand

    NASA Astrophysics Data System (ADS)

    Kimura, Masao; Noguchi, Masahiro

    2003-04-01

    The longitudinal wave velocity of water-saturated sand is dependent on the porosity. The data which show the relationship between the velocity and the porosity are dispersed [E. L. Hamilton and R. T. Bachman, J. Acoust. Soc. Am. 72, 1891-1904 (1982)]. It seems that this dispersion is due to the grain size, the standard deviation of the grain size, and the grain shape. In this study, to investigate the dispersion, the longitudinal wave velocities, the porosities, and the grain sizes of many kinds of water-saturated beach sands are measured. The relationships between the velocity, the porosity, and the grain size are obtained. From these results, it is seen that the velocity of the water-saturated beach sand with the same porosity varies with the grain size. That is, the velocity of the water-saturated beach sand with the same porosity increases, as the grain size increases. It is considered that the frame bulk modulus of the water-saturated beach sand with the same porosity varies with the grain size.

  20. The effects of surface finish and grain size on the strength of sintered silicon carbide

    NASA Technical Reports Server (NTRS)

    You, Y. H.; Kim, Y. W.; Lee, J. G.; Kim, C. H.

    1985-01-01

    The effects of surface treatment and microstructure, especially abnormal grain growth, on the strength of sintered SiC were studied. The surfaces of sintered SiC were treated with 400, 800 and 1200 grit diamond wheels. Grain growth was induced by increasing the sintering times at 2050 C. The beta to alpha transformation occurred during the sintering of beta-phase starting materials and was often accompanied by abnormal grain growth. The overall strength distributions were established using Weibull statistics. The strength of the sintered SiC is limited by extrinsic surface flaws in normal-sintered specimens. The finer the surface finish and grain size, the higher the strength. But the strength of abnormal sintering specimens is limited by the abnormally grown large tabular grains. The Weibull modulus increases with decreasing grain size and decreasing grit size for grinding.

  1. Can grain size sensitive creep lubricate faults during earthquake propagation?

    NASA Astrophysics Data System (ADS)

    De Paola, N.; Holdsworth, R.; Viti, C.; Collettini, C.; Bullock, R. J.; Faoro, I.

    2014-12-01

    In the shallow portion of crustal fault zones, fracturing and cataclasis are thought to be the dominant processes during earthquake propagation. In the lower crust/upper mantle, viscous flow is inferred to facilitate aseismic creep along shear zones. Recent studies show that slip zones (SZs), in natural and experimental carbonate seismic faults, are made of nanograins with a polygonal texture, a microstructure consistent with deformation by grain boundary sliding (GBS) mechanisms. Friction experiments performed on calcite fine-grained gouges, at speed v = 1 ms-1, normal stress sn = 18 MPa, displacements d = 0.009-1.46 m, and room temperature and humidity, show a four stage-evolution of the fault strength: SI) attainment of initial value, f = 0.67; SII) increase up to peak value f = 0.82; SIII) sudden decrease to low steady-state value, f = 0.18; and SIV) sudden increase to final value, f = 0.44, during sample deceleration. Samples recovered at the end of each displacement-controlled experiments (Stages I-IV) show the following microstructures evolution of the SZ material, which is: SI) poorly consolidated, and made of fine-grained (1 < D < 5 microns), angular clasts formed by brittle fracturing and cataclasis; SII) cohesive, and made of larger clasts of calcite (D ≈ 1 microns), exhibiting a high density of free dislocations and hosting subgrains (D ≤ 200 nm), dispersed within calcite nanograins. SIII) made of nanograin aggregates exhibiting polygonal grain boundaries, and 120° triple junctions between equiaxial grains. The grains display no preferred elongation, no crystal preferred orientation and low free dislocation densities, possibly due to high temperature (> 900 C) GBS creep deformation. Our microstructural observations suggest that GBS mechanisms can operate in geological materials deformed at high strain rates along frictionally heated seismogenic slip surfaces. The observed microstructures in experimental slip zones are strikingly similar to those

  2. Investigating feedback mechanisms between stress and grain-size: preliminary findings from finite-element modelling

    NASA Astrophysics Data System (ADS)

    Cross, A. J.; Prior, D. J.; Ellis, S. M.

    2012-12-01

    It is widely accepted that changes in stress and grain size can induce a switch between grain-size insensitive (GSI) and sensitive (GSS) creep mechanisms. Under steady-state conditions, grains evolve to an equilibrium size in the boundary region between GSS and GSI, described by the paleopiezometer for a given material. Under these conditions, significant rheological weakening is not expected, as grain size reduction processes are balanced by grain growth processes. However, it has been shown that the stress field surrounding faults varies through the seismic cycle, with both rapid loading and unloading of stress possible in the co- and post-seismic stages. We propose that these changes in stress in the region of the brittle-ductile transition zone may be sufficient to force a deviation from the GSI-GSS boundary and thereby cause a change in grain size and creep mechanism prior to system re-equilibration. Here we present preliminary findings from numerical modelling of stress and grain size changes in response to loading of mechanical inhomogeneities. Our results are attained using a grain-size evolution (GSE) subroutine incorporated into the SULEC finite-element code developed by Susan Ellis and Susanne Buiter, which utilises an iterative approach of solving for spatial and temporal changes in differential stress, grain size and active creep mechanism. Preliminary models demonstrate that stress changes in response to the opening of a fracture in a flowing medium can be significant enough to cause a switch from GSI to GSS creep. These results are significant in the context of understanding spatial variations and feedback between stress, grain size and deformation mechanisms through the seismic cycle.

  3. Environmental monitoring of Columbia River sediments: Grain-size distribution and contaminant association

    SciTech Connect

    Blanton, M.L.; Gardiner, W.W.; Dirkes, R.L.

    1995-04-01

    Based on the results of this study and literature review, the following conclusions can be made: Sediment grain size and TOC (total organic carbon) influence contaminant fate and transport (in general, sediments with higher TOC content and finer grain-size distribution can have higher contaminant burdens than sediments from a given river section that have less TOC and greater amounts of coarse-grained sediments). Physiochemical sediment characteristics are highly variable among monitoring sites along the Columbia River. Sediment grain characterization and TOC analysis should be included in interpretations of sediment-monitoring data.

  4. An Informatics Based Approach to Reduce the Grain Size of Cast Hadfield Steel

    NASA Astrophysics Data System (ADS)

    Dey, Swati; Pathak, Shankha; Sheoran, Sumit; Kela, Damodar H.; Datta, Shubhabrata

    2016-04-01

    Materials Informatics concept using computational intelligence based approaches are employed to bring out the significant alloying additions to achieve grain refinement in cast Hadfield steel. Castings of Hadfield steels used for railway crossings, requires fine grained austenitic structure. Maintaining proper grain size of this component is very crucial in order to achieve the desired properties and service life. This work studies the important variables affecting the grain size of such steels which includes the compositional and processing variables. The computational findings and prior knowledge is used to design the alloy, which is subjected to a few trials to validate the findings.

  5. Influence of Grain Size on Electrically Assisted Tensile Behavior of Ti-6Al-4V Alloy

    NASA Astrophysics Data System (ADS)

    Li, Xifeng; Ji, Boyu; Zhou, Qiang; Chen, Jun; Gao, Peng

    2016-10-01

    The effect of grain size and current density on deformation behavior during electrically assisted tension of Ti-6Al-4V alloy was investigated. The microstructural variations under different conditions were observed by optical microscope, SEM and TEM. The dislocation density was quantified by x-ray diffraction technique. The decrease in grain size could increase the elongation growth and stress reduction during electrically assisted tension. Fine grain size specimens can reach higher temperature than coarse grain specimens. With increasing current density, wider and deeper dimples on the fracture surfaces were observed, and less dislocation density and pileups were found in comparison with room-temperature tension without current. The dislocation density has a 62.1% reduction at 10.48 A/mm2 compared with room-temperature tension for 9.2 μm grain size specimens.

  6. Grain size dependence of elastic anomalies accompanying the α β phase transition in polycrystalline quartz

    NASA Astrophysics Data System (ADS)

    McKnight, Ruth E. A.; Moxon, T.; Buckley, A.; Taylor, P. A.; Darling, T. W.; Carpenter, M. A.

    2008-02-01

    The effects of grain size on the elastic properties of quartz through the α-β phase transition have been investigated by resonant ultrasound spectroscopy. It is found that there are three regimes, dependent on grain size, within which elastic properties show different evolutions with temperature. In the large grain size regime, as represented by a quartzite sample with ~100-300 µm grains, microcracking is believed to occur in the vicinity of the transition point, allowing grains to pull apart. In the intermediate grain size regime, as represented by novaculite (1-5 µm grain size) and Ethiebeaton agate (~120 nm grain size), bulk and shear moduli through the transition follow closely the values expected from averages of single crystal data. The novaculite sample, however, has a transition temperature ~7 °C higher than that of single crystal quartz. This is assumed to be due to the development of internal pressure arising from anisotropic thermal expansion. In the small grain size region, agates from Mexico (~65 nm) and Brazil (~50 nm) show significant reductions in the amount of softening of the bulk modulus as the transition point is approached from below. This is consistent with a tendency for the transition to become more second order in character. The apparent changes towards second order character do not match quantitative predictions for samples with homogeneous strain across elastically clamped nanocrystals, however. Some of the elastic variations are also due to the presence of moganite in these samples. True 'nanobehaviour' for quartz in ceramic samples thus appears to be restricted to grain sizes of less than ~50 nm.

  7. Charging of Individual Micron-Size Interstellar/Planetary Dust Grains by Secondary Electron Emissions

    NASA Technical Reports Server (NTRS)

    Tankosic, D.; Abbas, M. M.

    2012-01-01

    Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with UV/X-ray radiation, as well as by electron/ion impact. Knowledge of physical and optical properties of individual dust grains is required for understanding of the physical and dynamical processes in space environments and the role of dust in formation of stellar and planetary systems. In this paper, we discuss experimental results on dust charging by electron impact, where low energy electrons are scattered or stick to the dust grains, thereby charging the dust grains negatively, and at sufficiently high energies the incident electrons penetrate the grain leading to excitation and emission of electrons referred to as secondary electron emission (SEE). Currently, very limited experimental data are available for charging of individual micron-size dust grains, particularly by low energy electron impact. Available theoretical models based on the Sternglass equation (Sternglass, 1954) are applicable for neutral, planar, and bulk surfaces only. However, charging properties of individual micron-size dust grains are expected to be different from the values measured on bulk materials. Our recent experimental results on individual, positively charged, micron-size lunar dust grains levitated in an electrodynamic balance facility (at NASA-MSFC) indicate that the SEE by electron impact is a complex process. The electron impact may lead to charging or discharging of dust grains depending upon the grain size, surface potential, electron energy, electron flux, grain composition, and configuration (e.g. Abbas et al, 2010). Here we discuss the complex nature of SEE charging properties of individual micron-size lunar dust grains and silica microspheres.

  8. Grain size evolution in the mantle and its effect on geodynamics, seismic velocities and attenuation

    NASA Astrophysics Data System (ADS)

    Dannberg, Juliane; Eilon, Zach; Gassmoeller, Rene; Moulik, Pritwiraj; Myhill, Robert; Faul, Ulrich; Asimow, Paul

    2015-04-01

    Dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity and a limited treatment of variations associated with changes in mineral assemblage. These simplifications greatly reduce computational requirements but preclude effects such as shear localisation and transient changes in rheology associated with phase transitions, which have the potential to fundamentally change flow patterns in the mantle. Here we use the finite-element code ASPECT (Bangerth et al., 2013) to model grain size evolution and the interplay between grain size, stress and strain rate in the convecting mantle. We include the simultaneous and competing effects of dynamic recrystallisation resulting from work done by dislocation creep, grain growth in multiphase assemblages and recrystallisation at phase transitions. Grain size variations also affect seismic properties of mantle materials. We use several published formulations to relate intrinsic variables (P, T, and grain size) from our numerical models to seismic velocity (Vs) and attenuation (Q). Our calculations use thermodynamically self-consistent anharmonic elastic moduli determined for the mineral assemblages in the mantle using HeFESTo (Stixrude and Lithgow-Bertelloni, 2013). We investigate the effect of realistically heterogeneous grain sizes by computing body wave travel times, ray paths, and attenuation (t*) at different frequencies. We highlight the frequency-dependent sensitivity of seismic waves to grain size, which is important when interpreting Vs and Q observations in terms of mineral assemblage and temperature. Our models show that rapid metamorphic reactions in mantle upwellings and downwellings lead to high lateral viscosity contrasts, as a result of gradual grain size evolution. Positive feedback between grain size reduction and viscosity reduction results in shear localisation. As a result, the edges of thermal plumes have smaller grain sizes and lower

  9. Estimating wind speed from spatial grain size sorting in ripples on Earth and Mars

    NASA Astrophysics Data System (ADS)

    Jerolmack, D. J.

    2007-12-01

    The landscape initially seen by the Mars Exploration Rover Opportunity at Meridiani Planum is dominated by aeolian (wind-blown) ripples with concentrated surface lags of hematitic spherules and fragments. These ripples exhibit profound spatial grain size sorting, with well-sorted coarse-grained crests and poorly sorted, generally finer-grained troughs - they were the most common bed form encountered by Opportunity in its traverse from Eagle Crater to Endurance Crater. Similar bed features have been sporadically studied in the terrestrial literature, but not in detail. We measured wind speed and sediment flux profiles in White Sands National Monument, New Mexico, during conditions under which such coarse-grained ripples were forming. Data show that these bed features formed by the different transport modes of coarse- and fine-grain fractions in an initially bi-modal sediment distribution. Fine grains were transported via saltation, while coarse grains moved only by creep due to ballistic impacts of finer grains, as originally envisioned by Bagnold. We use this observation to place tight constraints on formative wind conditions of coarse-grained ripples on Mars: wind speed must have exceeded the threshold for saltation of fine grains, but was less than the saltation threshold for coarse grains. Estimated wind speeds are only moderately greater than those associated with modern dust storms. When combined with the observation of sand grains on Opportunity's solar panel following a dust storm, results indicate that modern winds may occasionally be strong enough to cause significant sediment transport on the Martian surface.

  10. Effect of carbonitride precipitates on the abrasive wear behaviour of hardfacing alloy

    NASA Astrophysics Data System (ADS)

    Yang, Ke; Yu, Shengfu; Li, Yingbin; Li, Chenglin

    2008-06-01

    Hardfacing alloy of martensitic stainless steel expect higher abradability to be achieved through the addition of nitrogen being provided by the fine scale precipitation of complex carbonitride particles. Niobium and titanium as the most effective carbonitride alloying elements were added in the Fe-Cr13-Mn-N hardfacing alloy to get carbonitride precipitates. Carbonitride was systematically studied by optical microscopy, scanning electronic microscopy and energy spectrum analysis. Abrasive wear resistance of hardfacing alloy in as-welded and heat-treated conditions was tested by using the belt abrasion test apparatus where the samples slide against the abrasive belt. It is found that carbonitride particles in the hardfacing alloy are complex of Cr, Ti and Nb distributing on the grain boundary or matrix of the hardfacing alloy with different number and size in as-welded and heat-treated conditions. A large number of carbonitrides can be precipitated with very fine size (nanoscale) after heat treatment. As a result, the homogeneous distribution of very fine carbonitride particles can significantly improve the grain-abrasion wear-resisting property of the hardfacing alloy, and the mass loss is plastic deformation with minimum depth of grooving by abrasive particles and fine delamination.

  11. The relation of stream sediment surface area, grain size and composition to trace element chemistry

    USGS Publications Warehouse

    Horowitz, A.J.; Elrick, K.A.

    1987-01-01

    Intensive studies of 17 geographically and hydrologically diverse stream bed sediments provide information on the relation between grain size, surface area, and operationally defined geochemical phases (e.g. Mn oxides, amorphous Fe oxides) to trace element concentrations. Of the size fractions investigated ( 125 ??m), each of the various phases contribute to overall sample surface area. For material having mean grain sizes in the very fine sand range and finer (<125 ??m), the same phases act as surface-area inhibitors by cementing fine grains together to form aggregates. This increases the mean grain size of the sample and reduces the surface area. The presence of these aggregates may explain why the <63 ??m or <125 ??m size fractions are more important to sediment-trace element levels and surface area than other finer fractions. ?? 1987.

  12. A study of the charged ice grains in the Enceladus plume with a composite size distribution

    NASA Astrophysics Data System (ADS)

    Dong, Y.; Hill, T. W.

    2013-12-01

    We study the negatively charged ice grains in the Enceladus plume ranging from nanometer to micrometer in size based on Cassini's multiple instrument observations. We have constructed a composite size distribution by combining the CAPS nanograin size distributions (Hill et al., 2012 JGR) and the CDA dust power-law size distribution (Kempf et al., 2008 Icarus). We also study the charging of the ice grains using RPWS-LP data (Morooka et al., 2011 JGR). E3 and E5 CDA data are not available, but RPWS detected impacts of micron sized dust grains with the same power law size distribution (Ye et al., 2012 AGU meeting). Our size distribution formula is fitted with E3 and E5 CAPS and RPWS data, and constrained with the total dust charge density inferred from the RPWS-LP cold plasma data. The fitting with E17 and E18 CAPS nanograin data (Tokar et al., 2012 AGU meeting) and RPWS dust data (Ye et al., 2013 MAPS workshop) will also be discussed. Based on the charge per grain and the size distribution, the densities, source rate, motion, and currents of the ice grains can be calculated. Our size distribution implies that the grains ~2-20 nm dominate in both charge density and number density. But the mass density is very sensitive to the larger grains. We discuss the mass densities and source rates with different size distribution parameters, and compare with the water vapor plume. We study the trajectories of the charged ice grains in both Enceladus and Saturn frames, and calculate the dust currents from their motion. We find that the total dust pickup current at Enceladus is ≥10^5 A. We will also discuss the ion and dust current systems and resulting magnetic perturbations near the moon.

  13. The effect of abrasive blasting on the strength of a joint between dental porcelain and metal base.

    PubMed

    Pietnicki, Krzysztof; Wołowiec, Emilia; Klimek, Leszek

    2014-01-01

    This paper presents the effect of selected parameters of abrasive blasting on the strength of a joint between dental porcelain and metal base. Experiments were conducted for different grain sizes of abrasive material and different blasting angles, with a constant blasting pressure. InLine dental porcelain was fused on samples of cobalt-chromium alloy following abrasive blasting; they were subsequently subjected to shearing forces on a testing machine. The fractures were observed under an electron scanning microscope in order to determine the character and course of fracturing. Strength tests showed that the grain size of abrasive material was a parameter with the greatest effect on the strength. The best effects were achieved for samples subjected to abrasive blasting with material with grain size of 110 μm. No statistically significant differences were found for the strength of samples worked at different angles. The results of the fractographic examinations have shown that in all the samples, fracturing occurred mainly along the porcelain-metal boundary, with few cases of fracturing through porcelain.

  14. Millimeter-sized grains in the protostellar envelopes: Where do they come from?

    NASA Astrophysics Data System (ADS)

    Wong, Yi Hang Valerie; Hirashita, Hiroyuki; Li, Zhi-Yun

    2016-08-01

    Grain growth during star formation affects the physical and chemical processes in the evolution of star-forming clouds. We investigate the origin of the millimeter (mm)-sized grains recently observed in Class I protostellar envelopes. We use the coagulation model developed in our previous paper and find that a hydrogen number density of as high as 1010 cm-3, instead of the typical density 105 cm-3, is necessary for the formation of mm-sized grains. Thus, we test a hypothesis that such large grains are transported to the envelope from the inner, denser parts, finding that gas drag by outflow efficiently "launches" the large grains as long as the central object has not grown to ≳0.1 M⊙. By investigating the shattering effect on the mm-sized grains, we ensure that the large grains are not significantly fragmented after being injected in the envelope. We conclude that the mm-sized grains observed in the protostellar envelopes are not formed in the envelopes but formed in the inner parts of the star-forming regions and transported to the envelopes before a significant mass growth of the central object, and that they survive in the envelopes.

  15. Size Distribution and Rate of Dust Generated During Grain Elevator Handling

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dust generated during grain handling is an air pollutant that produces safety and health hazards. This study was conducted to characterize the particle size distribution (PSD) of dust generated during handling of wheat and shelled corn in the research elevator of the USDA Grain Marketing and Product...

  16. Transport, retention, and size perturbation of graphene oxide in saturated porous media: Effects of input concentration and grain size

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Accurately predicting the fate and transport of graphene oxide (GO) in porous media is critical to assess its environmental impact. In this work, sand column experiments were conducted to determine the effect of input concentration and grain size on transport, retention, and size perturbation of GO ...

  17. Cobble cam: Grain-size measurements of sand to boulder from digital photographs and autocorrelation analyses

    USGS Publications Warehouse

    Warrick, J.A.; Rubin, D.M.; Ruggiero, P.; Harney, J.N.; Draut, A.E.; Buscombe, D.

    2009-01-01

    A new application of the autocorrelation grain size analysis technique for mixed to coarse sediment settings has been investigated. Photographs of sand- to boulder-sized sediment along the Elwha River delta beach were taken from approximately 1??2 m above the ground surface, and detailed grain size measurements were made from 32 of these sites for calibration and validation. Digital photographs were found to provide accurate estimates of the long and intermediate axes of the surface sediment (r2 > 0??98), but poor estimates of the short axes (r2 = 0??68), suggesting that these short axes were naturally oriented in the vertical dimension. The autocorrelation method was successfully applied resulting in total irreducible error of 14% over a range of mean grain sizes of 1 to 200 mm. Compared with reported edge and object-detection results, it is noted that the autocorrelation method presented here has lower error and can be applied to a much broader range of mean grain sizes without altering the physical set-up of the camera (~200-fold versus ~6-fold). The approach is considerably less sensitive to lighting conditions than object-detection methods, although autocorrelation estimates do improve when measures are taken to shade sediments from direct sunlight. The effects of wet and dry conditions are also evaluated and discussed. The technique provides an estimate of grain size sorting from the easily calculated autocorrelation standard error, which is correlated with the graphical standard deviation at an r2 of 0??69. The technique is transferable to other sites when calibrated with linear corrections based on photo-based measurements, as shown by excellent grain-size analysis results (r2 = 0??97, irreducible error = 16%) from samples from the mixed grain size beaches of Kachemak Bay, Alaska. Thus, a method has been developed to measure mean grain size and sorting properties of coarse sediments. ?? 2009 John Wiley & Sons, Ltd.

  18. Modeling grain size variations of aeolian gypsum deposits at White Sands, New Mexico, using AVIRIS imagery

    USGS Publications Warehouse

    Ghrefat, H.A.; Goodell, P.C.; Hubbard, B.E.; Langford, R.P.; Aldouri, R.E.

    2007-01-01

    Visible and Near-Infrared (VNIR) through Short Wavelength Infrared (SWIR) (0.4-2.5????m) AVIRIS data, along with laboratory spectral measurements and analyses of field samples, were used to characterize grain size variations in aeolian gypsum deposits across barchan-transverse, parabolic, and barchan dunes at White Sands, New Mexico, USA. All field samples contained a mineralogy of ?????100% gypsum. In order to document grain size variations at White Sands, surficial gypsum samples were collected along three Transects parallel to the prevailing downwind direction. Grain size analyses were carried out on the samples by sieving them into seven size fractions ranging from 45 to 621????m, which were subjected to spectral measurements. Absorption band depths of the size fractions were determined after applying an automated continuum-removal procedure to each spectrum. Then, the relationship between absorption band depth and gypsum size fraction was established using a linear regression. Three software processing steps were carried out to measure the grain size variations of gypsum in the Dune Area using AVIRIS data. AVIRIS mapping results, field work and laboratory analysis all show that the interdune areas have lower absorption band depth values and consist of finer grained gypsum deposits. In contrast, the dune crest areas have higher absorption band depth values and consist of coarser grained gypsum deposits. Based on laboratory estimates, a representative barchan-transverse dune (Transect 1) has a mean grain size of 1.16 ??{symbol} (449????m). The error bar results show that the error ranges from - 50 to + 50????m. Mean grain size for a representative parabolic dune (Transect 2) is 1.51 ??{symbol} (352????m), and 1.52 ??{symbol} (347????m) for a representative barchan dune (Transect 3). T-test results confirm that there are differences in the grain size distributions between barchan and parabolic dunes and between interdune and dune crest areas. The t-test results

  19. Using the 10-Be Grain Size Dependency in Alluvial Sediments to Investigate Hillslope and Channel Processes

    NASA Astrophysics Data System (ADS)

    Belmont, P.; Pazzaglia, F. J.; Gosse, J.

    2006-12-01

    The method for estimating basin-wide erosion rates from in situ produced 10-Be in alluvial sediments has matured over the past decade; nevertheless, several applications have not been fully explored. Foremost among these is identifying hillslope weathering and erosion processes through a study of the cosmogenic inventories of specific grain-size fractions of alluvial sediment. We applied a nested sampling strategy to two (6-12 km 2) basins on the Olympic Peninsula, western Washington State, to investigate how cosmogenic nuclides are sequestered across different alluvial grain sizes. Alluvium was sampled near the mouth and headwaters of each basin. The 10-Be concentration in river-borne quartz was measured for two grain-size fractions, medium-sized sand (0.25 - 0.50 mm) and an amalgamation of 80+ cobbles (22.6 - 90 mm). Extensive granulometry was conducted at each site and several different methods were used to qualify weathering intensity of channel boulders, which differs substantially for the two basins. We observed different concentrations of 10-Be in all eight grain size fractions. At both headwater sites the cobbles consistently exhibit 25% lower 10-Be concentrations, compared to sand. In contrast, the cobbles in the downstream sites differed with one basin exhibiting 22% higher 10-Be concentration compared to sand and the other site exhibiting 55% lower 10-Be concentration in the cobbles, compared to sand. A GIS was used to extract basin morphological metrics including basin hypsometry, hillslope gradient and channel gradient. Concentrations of 10-Be at the headwater sites are best explained by shielding of the coarser grain size fraction and its delivery to the channel by deep-seated landslide processes. The contrasting grain-size dependency at the two downstream sites requires a more complex interplay between hillslope and channel processes including cobble weathering and grain size reduction during fluvial transport. Although preliminary, these results

  20. Snow grain size and albedo in Dronning Maud Land, Antarctica: measurements and modeling

    NASA Astrophysics Data System (ADS)

    Pirazzini, Roberta; Räisänen, Petri; Vihma, Timo; Johansson, Milla; Tastula, Esa-Matti

    2014-05-01

    Snow grain macro-photos collected near the Finnish Antarctic Station Aboa during summer 2009-2010 were analyzed, and the link between snow grain metamorphism and surface albedo was investigated. Snow grain macro-photos were taken twice a day for a one-month period from four snowpack layers (at the surface and at the depths of 5, 10, and 20 cm). A cave inside the snowpack was used as a cold and dark "laboratory". The dataset also includes vertical profiles of snow temperature and density (twice a day), surface broadband albedo, surface spectral reflectance during clear and overcast days, and ancillary meteorological data. With such an extensive and complete dataset, we studied the snow grain metric that best represents the grain scattering properties at various wavelengths, establishing a direct relationship between measured grain dimensions and optically-equivalent grain size. For this purpose, we analyzed the 2D macro-photos with an image processing software (based on Matlab) that allows the determination of the size distribution of many dimensional quantities. A statistical approach was applied to estimate the representativeness error in the snow grain observations. The distributions of the obtained grain size metrics and the snow density profiles were utilized in the radiative transfer model DISORT to simulate the surface spectral albedo. The comparison of the model results with the observed spectral albedo allowed the identification of the snow grain dimensions that best explain the albedo at each wavelength. The impact of the snow grain shape in the model simulations was addressed utilizing spherical and droxtal grain representations.

  1. The effect of grain size on deformation and failure of copper under dynamic loading

    SciTech Connect

    Lassila, D.H.; LeBlanc, M.M.; Magness, F.H.

    1994-02-01

    In this work, we show experimentally, and using computer modeling that the effect of grain size manifested as an effect on constitutive behavior can have an appreciable effect on the deformation stability of copper deformed in tension under both quasi-static and dynamic loading: an increase in grain size results in greater extents of deformation. In a work previously published by Gourdin and Lassila, the effect of grain size was incorporated into the Mechanical Threshold Stress (MTS) material model applied to OFE copper. Dynamic tensile tests were modeled using a 3-D computer code in which the MTS material model was incorporated. The computer code model accurately predicted the occurrence and growth of necking during dynamic deformation as a function of grain size.

  2. Strain Rate Effect on the Mechanical Behaviour of Sandstones with Different Grain Sizes

    NASA Astrophysics Data System (ADS)

    Wasantha, P. L. P.; Ranjith, P. G.; Zhao, J.; Shao, S. S.; Permata, G.

    2015-09-01

    Sandstone specimens with different grain sizes were tested under uniaxial compression at a range of strain rates to investigate the coupled influence of strain rate and grain size on the mechanical behaviour of sandstone. Average grain sizes of sandstones were 105.4 µm (fine grained, FG), 228 µm (medium grained, MG) and 321 µm (coarse grained, CG), and the considered strain rates were 10-6, 10-5, 10-4 and 10-3 S-1. We used an optical deformation and strain measuring system for all the tests to determine the deformation characteristics of specimens during loading. The peak strength was observed to increase non-linearly with an increasing gradient against logarithmic strain rate for FG sandstone, while the trend was a linear increase for MG sandstone and unsystematic for CG sandstone. The relationships of elastic modulus versus logarithmic strain rate for the three types of sandstones showed similar trends as for the peak strength. This observation suggests that the FG sandstones are more responsive to strain rate compared to coarser-grained sandstones and this was attributed to the differences in micro-crack development patterns of sandstones with different grain sizes. A surprising behaviour was observed for CG sandstone, which displayed an increase of strength at the slowest strain rate, reversing the general decreasing trend of strength with decreasing strain rate. Stress redistribution associated with grain fracturing was proposed as a possible mechanism to explain this counter-intuitive behaviour. Finally, the results of this paper suggest that the size of constituent grains is a critical parameter that needs to be incorporated in considerations of the mechanical behaviour of sandstones under different strain rates.

  3. Objective Delineation of River Bed Surface Patches from High-Resolution Spatial Grain Size Data

    NASA Astrophysics Data System (ADS)

    Nelson, P. A.; Bellugi, D.; Dietrich, W. E.

    2010-12-01

    Gravel-bed rivers commonly display distinct sorting patterns on their beds. Visually, this heterogeneity often appears to form an organization of distinct textural patches or facies. The local bed surface grain size, and therefore bed surface patchiness, exerts considerable influence on local bed mobility, bedload transport rates, hydrodynamic roughness, and benthic microhabitats. Despite the ecological and morphodynamic importance of bed surface patchiness, we lack accurate and objective methods to delineate bed patches. However, recent advances in photographic measurement of bed surface grain size distributions are capable of providing data at a spatial resolution high enough to allow us an opportunity to answer the question: what is a patch? Here, we explore a variety of techniques that can be applied to high-resolution spatial grain size data to automatically generate maps of grain size patches. We apply a state-of-the-art image processing and machine learning procedure to a photographic survey of the bed surface of a near-field scale flume to extract grain size data and to generate a spatial grid of bed surface grain size distributions. The flume bed was composed of gravel 2-45 mm in diameter and it featured clearly identifiable sorting features. Using this dataset, we investigate several possible methods of patch delineation. The grid of grain size distributions can be represented by a graph of nodes (grain size distributions) connected by edges whose weight is a function of the similarity between two nodes. Spectral graph theory is then used to optimally cut the edges in order to produce a spatial structure of patches that minimizes the association between patches and maximizes the association of nodes within a patch. In a different approach, agglomerative clustering of spatially adjacent grain size distributions is used to produce a hierarchical dendrogram that can be thresholded to partition the bed into patches. We also explore using the k-means algorithm

  4. Grain size and shape evolution of experimentally deformed sediments: the role of slip rate

    NASA Astrophysics Data System (ADS)

    Balsamo, Fabrizio; Storti, Fabrizio; De Paola, Nicola

    2016-04-01

    Sediment deformation within fault zones occurs with a broad spectrum of mechanisms which, in turn, depend on intrinsic material properties (porosity, grain size and shape, etc.) and external factors (burial depth, fluid pressure, stress configuration, etc.). Fieldworks and laboratory measurements conducted in the last years in sediments faulted at shallow depth showed that cataclasis and grain size reduction can occur very close to the Earth surface (<1-2 km), and that fault displacement is one of the parameters controlling the amount of grain size, shape, and microtextural modifications in fault cores. In this contribution, we present a new set of microstructural observations combined with grain size and shape distribution data obtained from quart-feldspatic loose sediments (mean grain diameter 0.2 mm) experimentally deformed at different slip rates from subseismic (0.01 mm/s, 0.1 mm/s, 1 mm/s, 1 cm/s, and 10 cm/s) to coseismic slip rates (1 m/s). The experiments were originally performed at sigma n=14 MPa, with the same amount of slip (1.3 m), to constrain the frictional properties of such sediments at shallow confining pressures (<1 km). After the experiments, the granular materials deformed in the 0.1-1 mm-thick slip zones were prepared for both grain size distribution analyses and microstructural and textural analyses in thin sections. Grain size distribution analyses were obtained with a Malvern Mastersizer 3000 particle size laser-diffraction analyser, whereas grain shape data (angularity) were obtained by using image analysis technique on selected SEM-photomicrographs. Microstructural observations were performed at different scales with a standard optical microscope and with a SEM. Results indicate that mean grain diameter progressively decreases with increasing slip rates up to ~20-30 m, and that granulometric curves systematically modify as well, shifting toward finer grain sizes. Obtained fractal dimensions (D) indicate that D increases from ~2.3 up

  5. Influence of Mineral Fraction on the Rheological Properties of Forsterite + Enstatite during Grain Size Sensitive Creep

    NASA Astrophysics Data System (ADS)

    Tasaka, M.; Hiraga, T.

    2014-12-01

    Since the majority of crustal and mantle rocks are polymineralic, it is important to consider the effects of secondary mineral phases on their rheological properties. To examine these effects, we have conducted grain growth and deformation experiments on samples composed of different volumetric fractions of forsterite (Fo) and enstatite (En) at 1 atmosphere and temperatures from 1260 to 1360°C. The results of our grain growth experiments indicate that the grain size ratios of Fo and En in annealed (reference) and deformed samples follow a Zener relationship with dI/dII = b/fIIz, where dI/dII is the grain size of the primary or secondary phase, b and z are the Zener parameters relating grain boundary energies and location of secondary phase, and fII is the volume fraction of the associated phase. Grain growth in the reference samples conforms to the relationship ds 4-d04 = kt, where ds is the grain size under static conditions, d0 is the initial grain size, k is the grain growth coefficient, and t is time. The growth coefficient of Fo decrease with increasing En volume fraction (fEn), and is consistent with theoretical predictions of Ardell's grain growth model that incorporates physical parameters such as diffusivity and interfacial energy of the mineral phases. The results of our deformation experiments at constant temperature and strain rate indicate that the flow stress decreases with increasing fEn, for samples with 0 < fEn < 0.5, and increases with increasing fEn, for samples with 0.5 < fEn < 1. The values of the pre-exponential term, stress and grain size exponents, and activation energy in the constitutive equation for a wide range of fEn were determined. The majority of samples exhibited diffusion accommodated grain boundary sliding creep (i.e., stress exponent = 1). The viscosity measured for all samples is fit well by a model that takes into account (1) grain size calculated from grain growth laws established in our experiments and (2) the flow laws for

  6. Autonomous bed-sediment imaging-systems for revealing temporal variability of grain size

    USGS Publications Warehouse

    Buscombe, Daniel; Rubin, David M.; Lacy, Jessica R.; Storlazzi, Curt D.; Hatcher, Gerald; Chezar, Henry; Wyland, Robert; Sherwood, Christopher R.

    2014-01-01

    We describe a remotely operated video microscope system, designed to provide high-resolution images of seabed sediments. Two versions were developed, which differ in how they raise the camera from the seabed. The first used hydraulics and the second used the energy associated with wave orbital motion. Images were analyzed using automated frequency-domain methods, which following a rigorous partially supervised quality control procedure, yielded estimates to within 20% of the true size as determined by on-screen manual measurements of grains. Long-term grain-size variability at a sandy inner shelf site offshore of Santa Cruz, California, USA, was investigated using the hydraulic system. Eighteen months of high frequency (min to h), high-resolution (μm) images were collected, and grain size distributions compiled. The data constitutes the longest known high-frequency record of seabed-grain size at this sample frequency, at any location. Short-term grain-size variability of sand in an energetic surf zone at Praa Sands, Cornwall, UK was investigated using the ‘wave-powered’ system. The data are the first high-frequency record of grain size at a single location of a highly mobile and evolving bed in a natural surf zone. Using this technology, it is now possible to measure bed-sediment-grain size at a time-scale comparable with flow conditions. Results suggest models of sediment transport at sandy, wave-dominated, nearshore locations should allow for substantial changes in grain-size distribution over time-scales as short as a few hours.

  7. The influence of grain size, grain color, and suspended-sediment concentration on light attenuation: Why fine-grained terrestrial sediment is bad for coral reef ecosystems

    NASA Astrophysics Data System (ADS)

    Storlazzi, Curt D.; Norris, Ben K.; Rosenberger, Kurt J.

    2015-09-01

    Sediment has been shown to be a major stressor to coral reefs globally. Although many researchers have tested the impact of sedimentation on coral reef ecosystems in both the laboratory and the field and some have measured the impact of suspended sediment on the photosynthetic response of corals, there has yet to be a detailed investigation on how properties of the sediment itself can affect light availability for photosynthesis. We show that finer-grained and darker-colored sediment at higher suspended-sediment concentrations attenuates photosynthetically active radiation (PAR) significantly more than coarser, lighter-colored sediment at lower concentrations and provide PAR attenuation coefficients for various grain sizes, colors, and suspended-sediment concentrations that are needed for biophysical modeling. Because finer-grained sediment particles settle more slowly and are more susceptible to resuspension, they remain in the water column longer, thus causing greater net impact by reducing light essential for photosynthesis over a greater duration. This indicates that coral reef monitoring studies investigating sediment impacts should concentrate on measuring fine-grained lateritic and volcanic soils, as opposed to coarser-grained siliceous and carbonate sediment. Similarly, coastal restoration efforts and engineering solutions addressing long-term coral reef ecosystem health should focus on preferentially retaining those fine-grained soils rather than coarse silt and sand particles.

  8. The influence of grain size, grain color, and suspended-sediment concentration on light attenuation: why fine-grained terrestrial sediment is bad for coral reef ecosystems

    USGS Publications Warehouse

    Storlazzi, Curt; Norris, Benjamin; Rosenberger, Kurt

    2015-01-01

    Sediment has been shown to be a major stressor to coral reefs globally. Although many researchers have tested the impact of sedimentation on coral reef ecosystems in both the laboratory and the field and some have measured the impact of suspended sediment on the photosynthetic response of corals, there has yet to be a detailed investigation on how properties of the sediment itself can affect light availability for photosynthesis. We show that finer-grained and darker-colored sediment at higher suspended-sediment concentrations attenuates photosynthetically active radiation (PAR) significantly more than coarser, lighter-colored sediment at lower concentrations and provide PAR attenuation coefficients for various grain sizes, colors, and suspended-sediment concentrations that are needed for biophysical modeling. Because finer-grained sediment particles settle more slowly and are more susceptible to resuspension, they remain in the water column longer, thus causing greater net impact by reducing light essential for photosynthesis over a greater duration. This indicates that coral reef monitoring studies investigating sediment impacts should concentrate on measuring fine-grained lateritic and volcanic soils, as opposed to coarser-grained siliceous and carbonate sediment. Similarly, coastal restoration efforts and engineering solutions addressing long-term coral reef ecosystem health should focus on preferentially retaining those fine-grained soils rather than coarse silt and sand particles.

  9. Nano-scale machining of polycrystalline coppers - effects of grain size and machining parameters

    PubMed Central

    2013-01-01

    In this study, a comprehensive investigation on nano-scale machining of polycrystalline copper structures is carried out by molecular dynamics (MD) simulation. Simulation cases are constructed to study the impacts of grain size, as well as various machining parameters. Six polycrystalline copper structures are produced, which have the corresponding equivalent grain sizes of 5.32, 6.70, 8.44, 13.40, 14.75, and 16.88 nm, respectively. Three levels of depth of cut, machining speed, and tool rake angle are also considered. The results show that greater cutting forces are required in nano-scale polycrystalline machining with the increase of depth of cut, machining speed, and the use of the negative tool rake angles. The distributions of equivalent stress are consistent with the cutting force trends. Moreover, it is discovered that in the grain size range of 5.32 to 14.75 nm, the cutting forces and equivalent stress increase with the increase of grain size for the nano-structured copper, while the trends reserve after the grain size becomes even higher. This discovery confirms the existence of both the regular Hall–Petch relation and the inverse Hall–Petch relation in polycrystalline machining, and the existence of a threshold grain size allows one of the two relations to become dominant. The dislocation-grain boundary interaction shows that the resistance of the grain boundary to dislocation movement is the fundamental mechanism of the Hall–Petch relation, while grain boundary diffusion and movement is the reason of the inverse Hall–Petch relation. PMID:24267785

  10. Nano-scale machining of polycrystalline coppers - effects of grain size and machining parameters.

    PubMed

    Shi, Jing; Wang, Yachao; Yang, Xiaoping

    2013-11-22

    In this study, a comprehensive investigation on nano-scale machining of polycrystalline copper structures is carried out by molecular dynamics (MD) simulation. Simulation cases are constructed to study the impacts of grain size, as well as various machining parameters. Six polycrystalline copper structures are produced, which have the corresponding equivalent grain sizes of 5.32, 6.70, 8.44, 13.40, 14.75, and 16.88 nm, respectively. Three levels of depth of cut, machining speed, and tool rake angle are also considered. The results show that greater cutting forces are required in nano-scale polycrystalline machining with the increase of depth of cut, machining speed, and the use of the negative tool rake angles. The distributions of equivalent stress are consistent with the cutting force trends. Moreover, it is discovered that in the grain size range of 5.32 to 14.75 nm, the cutting forces and equivalent stress increase with the increase of grain size for the nano-structured copper, while the trends reserve after the grain size becomes even higher. This discovery confirms the existence of both the regular Hall-Petch relation and the inverse Hall-Petch relation in polycrystalline machining, and the existence of a threshold grain size allows one of the two relations to become dominant. The dislocation-grain boundary interaction shows that the resistance of the grain boundary to dislocation movement is the fundamental mechanism of the Hall-Petch relation, while grain boundary diffusion and movement is the reason of the inverse Hall-Petch relation.

  11. Fatigue Resistance of the Grain Size Transition Zone in a Dual Microstructure Superalloy Disk

    NASA Technical Reports Server (NTRS)

    Gabb, T. P.; Kantzos, P. T.; Telesman, J.; Gayda, J.; Sudbrack, C. K.; Palsa, B. S.

    2010-01-01

    Mechanical property requirements vary with location in nickel-based superalloy disks. To maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored microstructures. In this study, a specialized heat treatment method was applied to produce varying grain microstructures from the bore to the rim portions of a powder metallurgy processed nickel-based superalloy disk. The bore of the contoured disk consisted of fine grains to maximize strength and fatigue resistance at lower temperatures. The rim microstructure of the disk consisted of coarse grains for maximum resistance to creep and dwell crack growth at high temperatures up to 704 C. However, the fatigue resistance of the grain size transition zone was unclear, and needed to be evaluated. This zone was located as a band in the disk web between the bore and rim. Specimens were extracted parallel and transverse to the transition zone, and multiple fatigue tests were performed at 427 and 704 C. Mean fatigue lives were lower at 427 C than for 704 C. Specimen failures often initiated at relatively large grains, which failed on crystallographic facets. Grain size distributions were characterized in the specimens, and related to the grains initiating failures as well as location within the transition zone. Fatigue life decreased with increasing maximum grain size. Correspondingly, mean fatigue resistance of the transition zone was slightly higher than that of the rim, but lower than that of the bore. The scatter in limited tests of replicates was comparable for all transition zone locations examined.

  12. Grain size of recall practice for lengthy text material: fragile and mysterious effects on memory.

    PubMed

    Wissman, Kathryn T; Rawson, Katherine A

    2015-03-01

    The current research evaluated the extent to which the grain size of recall practice for lengthy text material affects recall during practice and subsequent memory. The grain size hypothesis states that a smaller vs. larger grain size will increase retrieval success during practice that in turn will enhance subsequent memory for lengthy text material. Participants were prompted to recall directly after studying each section (section recall) or after all sections had been studied (whole-text recall) during practice, and then all participants completed a final test after a delay. Results across 7 experiments (including 587 participants and 1,394 recall protocols) partially disconfirmed the predictions of the grain size hypothesis: Although the smaller grain size produced sizable recall advantages during practice as expected (ds from 1.02 to 1.87 across experiments), the advantage was substantially or completely attenuated across a delay. Experiments 2-7 falsified several plausible methodological and theoretical explanations for the fragility of the effect, indicating that it was not due to particular text materials, retrieval from working memory during practice, the length of the retention interval, the spacing between study and practice recall, a disproportionate increase in recall of unimportant details, or a deficit in integration of ideas across text sections. In sum, results conclusively establish an initially sizable but mysteriously fragile effect of grain size, for which an explanation remains elusive.

  13. Metamorphic reactions, grain size reduction and deformation of mafic lower crustal rocks

    NASA Astrophysics Data System (ADS)

    Degli Alessandrini, Giulia; Menegon, Luca; Beltrando, Marco; Dijkstra, Arjan; Anderson, Mark

    2016-04-01

    This study investigates grain-scale deformation mechanisms associated with strain localization in the mafic continental lower crust, with particular focus on the role of syn-kinematic metamorphic reactions and their product - symplectites - in promoting grain size reduction and phase mixing. The investigated shear zone is hosted in the Finero mafic-ultramafic complex in the Italian Southern Alps. Shearing occurred at T ≥ 650° C and P ≥ 0.4-0.6 GPa. The shear zone reworks both mafic and ultramafic lithologies and displays anastomosing patterns of (ultra)mylonitic high strain zones wrapping less foliated, weakly deformed low strain domains. Field and microstructural observations indicate that different compositional layers of the shear zone responded differently to deformation, resulting in strain partitioning. Four distinct microstructural domains have been identified: (1) an ultramylonitic domain characterized by an amph + pl matrix (grain size < 30μm) with large amphibole porphyroclasts (grain size between 200μm and 5000μm) and rare garnets; (2) a domain rich in garnet porphyroclasts embedded in a matrix of monomineralic plagioclase displaying a core and mantle structure (average grain size 45μm) (3) a metagabbroic domain with porphyroclasts of clinopyroxene, orthopyroxene and garnets (200μm average grain size) wrapped by monomineralic ribbons of recrystallized plagioclase and (4) a garnet-free ultramylonitic domain composed of an intermixed amph + cpx + opx + pl matrix (6μm average grain size). In these domains, each porphyroclastic mineral responds differently to deformation: amphibole readily breaks down to symplectitic intergrowths of amph + pl or opx + pl. Garnet undergoes fracturing (in domain 2) or reacts to give symplectites of pl + opx (in domain 3). Plagioclase dynamically recrystallizes in mono-phase aggregates, whereas clinopyroxene undergoes fracturing and orthopyroxene undergoes plastic deformation. The behaviour of the different phases

  14. The Importance of Grain Size to Mantle Dynamics and Seismological Observations: A Multidisciplinary Approach

    NASA Astrophysics Data System (ADS)

    Gassmöller, Rene; Dannberg, Juliane; Eilon, Zach; Moulik, Pritwiraj; Myhill, Robert; Faul, Ulrich

    2016-04-01

    Dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity and a limited treatment of variations associated with changes in mineral assemblage. These simplifications greatly reduce computational requirements but preclude effects such as shear localisation and transient changes in rheology associated with phase transitions, which have the potential to fundamentally change flow patterns in the mantle. Here we use the finite-element code ASPECT [Bangerth et al., 2013] to model grain size evolution and the interplay between grain size, stress and strain rate in the convecting mantle. We include the simultaneous and competing effects of dynamic recrystallisation resulting from work done by dislocation creep, grain growth in multiphase assemblages and recrystallisation at phase transitions. Grain size variations also affect seismic properties of mantle materials. We apply published formalisms [Jackson & Faul, 2010; McCarthy et al., 2011; Takei et al., 2014] to relate intrinsic variables (P, T, and grain size) from our numerical models to seismic velocity (Vs) and attenuation (Q). We investigate these formalisms for consistency with seismic observations at conditions beyond the range of the experiments upon which they are based; this requires constraining the range of pre-factors and activation volumes relevant for the lower mantle. Our calculations use thermodynamically self-consistent anharmonic elastic moduli determined for the mineral assemblages in the mantle using HeFESTo [Stixrude and Lithgow-Bertelloni, 2013]. We investigate the effect of realistically heterogeneous grain sizes by computing synthetic seismological data; these highlight the frequency-dependent sensitivity of seismic waves to grain size, which is important when interpreting Vs and Q observations in terms of mineral assemblage and temperature. Our models show that grain size evolution can lead to lateral viscosity variations of six

  15. Multiscale architectured materials with composition and grain size gradients manufactured using high-pressure torsion

    PubMed Central

    Kang, Ji Yun; Kim, Jung Gi; Park, Hyo Wook; Kim, Hyoung Seop

    2016-01-01

    The concept of multiscale architectured materials is established using composition and grain size gradients. Composition-gradient nanostructured materials are produced from coarse grained interstitial free steels via carburization and high-pressure torsion. Quantitative analyses of the dislocation density using X-ray diffraction and microstructural studies clearly demonstrate the gradients of the dislocation density and grain size. The mechanical properties of the gradient materials are compared with homogeneous nanostructured carbon steel without a composition gradient in an effort to investigate the gradient effect. Based on the above observations, the potential of multiscale architecturing to open a new material property is discussed. PMID:27229160

  16. Multiscale architectured materials with composition and grain size gradients manufactured using high-pressure torsion.

    PubMed

    Kang, Ji Yun; Kim, Jung Gi; Park, Hyo Wook; Kim, Hyoung Seop

    2016-05-27

    The concept of multiscale architectured materials is established using composition and grain size gradients. Composition-gradient nanostructured materials are produced from coarse grained interstitial free steels via carburization and high-pressure torsion. Quantitative analyses of the dislocation density using X-ray diffraction and microstructural studies clearly demonstrate the gradients of the dislocation density and grain size. The mechanical properties of the gradient materials are compared with homogeneous nanostructured carbon steel without a composition gradient in an effort to investigate the gradient effect. Based on the above observations, the potential of multiscale architecturing to open a new material property is discussed.

  17. Small angle neutron scattering from nanometer grain sized materials

    SciTech Connect

    Epperson, J.E.; Siegel, R.W.

    1991-11-01

    Small angie neutron scattering has been utilized, along with a number of complementary characterization methods suitable to the nanometer size scale, to investigate the structures of cluster-assembled nanophase materials. Results of these investigations are described and problems and opportunities in using small angle scattering for elucidating nanostructures are discussed.

  18. Trajectories and energy transfer of saltating particles onto rock surfaces : application to abrasion and ventifact formation on Earth and Mars

    NASA Technical Reports Server (NTRS)

    Bridges, Nathan T.; Phoreman, James; White, Bruce R.; Greeley, Ronald; Eddlemon, Eric E.; Wilson, Gregory R.; Meyer, Christine J.

    2005-01-01

    The interaction between saltating sand grains and rock surfaces is assessed to gauge relative abrasion potential as a function of rock shape, wind speed, grain size, and planetary environment. Many kinetic energy height profiles for impacts exhibit a distinctive increase, or kink, a few centimeters above the surface, consistent with previous field, wind tunnel, and theoretical investigations. The height of the kink observed in natural and wind tunnel settings is greater than predictions by a factor of 2 or more, probably because of enhanced bouncing off hard ground surfaces. Rebounded grains increase the effective flux and relative kinetic energy for intermediate slope angles. Whether abrasion occurs, as opposed to simple grain impact with little or no mass lost from the rock, depends on whether the grain kinetic energy (EG) exceeds a critical value (EC), as well as the flux of grains with energies above EC. The magnitude of abrasion and the shape change of the rock over time depends on this flux and the value of EG > EC. Considering the potential range of particle sizes and wind speeds, the predicted kinetic energies of saltating sand hitting rocks overlap on Earth and Mars. However, when limited to the most likely grain sizes and threshold conditions, our results agree with previous work and show that kinetic energies are about an order of magnitude greater on Mars.

  19. Grain size evolution in the mantle and its effect on geodynamics and seismic observables

    NASA Astrophysics Data System (ADS)

    Myhill, R.; Dannberg, J.; Eilon, Z.; Gassmoeller, R.; Moulik, P.; Faul, U.; Asimow, P. D.

    2014-12-01

    Dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity and a limited treatment of variations associated with changes in mineral assemblage. These simplifications greatly reduce computational requirements but preclude effects such as shear localisation and transient changes in rheology associated with phase transitions, which have the potential to fundamentally change flow patterns in the mantle. Here we use the finite-element code ASPECT (Bangerth et al., 2013) to model grain size evolution and the interplay between grain size, stress and strain rate in the convecting mantle. We include the simultaneous and competing effects of dynamic recrystallisation resulting from work done by dislocation creep, grain growth and recrystallisation at phase transitions. Further expressions account for slow growth in multiphase assemblages resulting from pinning. Grain size variations also affect seismic properties of mantle materials. We use several formulations from the literature to relate intrinsic variables (P, T, and grain size) from our numerical models to seismic velocity (Vs) and attenuation (Q). Our calculations use thermodynamically self-consistent anharmonic elastic moduli determined for the mineral assemblages in the mantle using HeFESTo (Stixrude and Lithgow-Bertelloni, 2013). We investigate the effect of realistically heterogeneous grain sizes by computing seismic observables such as body wave travel times, ray paths, and attenuation (t*) as well as mode eigenfrequencies and quality factors at different frequencies. We highlight the frequency-dependent sensitivity of seismic waves to grain size, which is important when interpreting Vs and Q observations in terms of mineral assemblage and temperature. This work is based on a project started at the CIDER 2014 summer program. References: Bangerth, W. et al., 2014, ASPECT: Advanced Solver for Problems in Earth's ConvecTion. Computational

  20. Compaction creep of sands due to time-dependent grain failure: Effects of chemical environment, applied stress, and grain size

    NASA Astrophysics Data System (ADS)

    Brzesowsky, R. H.; Hangx, S. J. T.; Brantut, N.; Spiers, C. J.

    2014-10-01

    Time-dependent brittle creep plays a role in controlling compaction of sands and sandstones under upper crustal conditions, influencing phenomena such as production-induced reservoir compaction, surface subsidence, and induced seismicity. Brittle creep also plays a role in determining the mechanical behavior of gouge-rich faults. We performed uniaxial creep experiments on sand to investigate the effects of chemical environment (dry versus solution flooded), grain size (d = 196-378 µm), and applied effective stress (σa up to 30 MPa), at room temperature conditions favoring grain-scale brittle processes. Creep measurements were complemented with acoustic emission (AE) detection and microstructural analysis to characterize the main creep mechanism. Wet samples showed much higher creep strains than dry-tested samples. AE event counts showed a direct relation between grain failure and creep strain, with higher AE rates occurring in the wet samples. Therefore, we inferred that time-dependent deformation was dominated by subcritical crack growth, resulting in grain failure accompanied by intergranular sliding rearrangements, and that crack growth in the presence of chemically active fluids was controlled by stress corrosion. The sensitivity of the compaction rate of the sands to d and σa can be expressed as ɛ˙∝diσaj where i ≈ 6 and j ≈ 21 under dry conditions and i ≈ 9 and j ≈ 15 under wet conditions. Our results were compared to a simple model based on Hertzian contact theory, linear elastic fracture mechanics, and subcritical crack growth. This model showed agreement between the observed stress and grain size sensitivities of creep, within a factor of 2.

  1. The magnetized sheath of a dusty plasma with grains size distribution

    SciTech Connect

    Ou, Jing Gan, Chunyun; Lin, Binbin; Yang, Jinhong

    2015-05-15

    The structure of a plasma sheath in the presence of dust grains size distribution (DGSD) is investigated in the multi-fluid framework. It is shown that effect of the dust grains with different sizes on the sheath structure is a collective behavior. The spatial distributions of electric potential, the electron and ion densities and velocities, and the dust grains surface potential are strongly affected by DGSD. The dynamics of dust grains with different sizes in the sheath depend on not only DGSD but also their radius. By comparison of the sheath structure, it is found that under the same expected value of DGSD condition, the sheath length is longer in the case of lognormal distribution than that in the case of uniform distribution. In two cases of normal and lognormal distributions, the sheath length is almost equal for the small variance of DGSD, and then the difference of sheath length increases gradually with increase in the variance.

  2. Deformation mechanisms and grain size evolution in the Bohemian granulites - a computational study

    NASA Astrophysics Data System (ADS)

    Maierova, Petra; Lexa, Ondrej; Jeřábek, Petr; Franěk, Jan; Schulmann, Karel

    2015-04-01

    A dominant deformation mechanism in crustal rocks (e.g., dislocation and diffusion creep, grain boundary sliding, solution-precipitation) depends on many parameters such as temperature, major minerals, differential stress, strain rate and grain size. An exemplary sequence of deformation mechanisms was identified in the largest felsic granulite massifs in the southern Moldanubian domain (Bohemian Massif, central European Variscides). These massifs were interpreted to result from collision-related forced diapiric ascent of lower crust and its subsequent lateral spreading at mid-crustal levels. Three types of microstructures were distinguished. The oldest relict microstructure (S1) with large grains (>1000 μm) of feldspar deformed probably by dislocation creep at peak HT eclogite facies conditions. Subsequently at HP granulite-facies conditions, chemically- and deformation- induced recrystallization of feldspar porphyroclasts led to development of a fine-grained microstructure (S2, ~50 μm grain size) indicating deformation via diffusion creep, probably assisted by melt-enhanced grain-boundary sliding. This microstructure was associated with flow in the lower crust and/or its diapiric ascent. The latest microstructure (S3, ~100 μm grain size) is related to the final lateral spreading of retrograde granulites, and shows deformation by dislocation creep at amphibolite-facies conditions. The S2-S3 switch and coarsening was interpreted to be related with a significant decrease in strain rate. From this microstructural sequence it appears that it is the grain size that is critically linked with specific mechanical behavior of these rocks. Thus in this study, we focused on the interplay between grain size and deformation with the aim to numerically simulate and reinterpret the observed microstructural sequence. We tested several different mathematical descriptions of the grain size evolution, each of which gave qualitatively different results. We selected the two most

  3. Influence of the grain size on deleterious phase precipitation in superduplex stainless steel UNS S32750

    SciTech Connect

    Pardal, J.M.

    2009-03-15

    In the present work, the effect of grain size on deleterious phase precipitation in a superduplex stainless steel was investigated. The materials studied were heat treated isothermally at 800 deg. C, 850 deg. C and 900 deg. C for times up to 120 min. Hardness tests, light optical microscopy, scanning electron microscopy and X-ray diffraction were carried out to detect sigma and other harmful precipitate phases. The ferritic and austenitic grain sizes in the solution treated condition of the two steels analyzed were measured by electron backscattered diffraction (EBSD). Cyclic polarization corrosion tests were performed to evaluate the effect of grain size on the corrosion resistance. The results presented show that the precipitation of deleterious phases such as {chi}, {sigma} and {gamma}{sub 2}, which can occur during welding and forming operations, is retarded by grain growth.

  4. Underwater microscope for measuring spatial and temporal changes in bed-sediment grain size

    USGS Publications Warehouse

    Rubin, David M.; Chezar, Henry; Harney, Jodi N.; Topping, David J.; Melis, Theodore S.; Sherwood, Christopher R.

    2007-01-01

    For more than a century, studies of sedimentology and sediment transport have measured bed-sediment grain size by collecting samples and transporting them back to the laboratory for grain-size analysis. This process is slow and expensive. Moreover, most sampling systems are not selective enough to sample only the surficial grains that interact with the flow; samples typically include sediment from at least a few centimeters beneath the bed surface. New hardware and software are available for in situ measurement of grain size. The new technology permits rapid measurement of surficial bed sediment. Here we describe several systems we have deployed by boat, by hand, and by tripod in rivers, oceans, and on beaches.

  5. Underwater Microscope for Measuring Spatial and Temporal Changes in Bed-Sediment Grain Size

    USGS Publications Warehouse

    Rubin, David M.; Chezar, Henry; Harney, Jodi N.; Topping, David J.; Melis, Theodore S.; Sherwood, Christopher R.

    2006-01-01

    For more than a century, studies of sedimentology and sediment transport have measured bed-sediment grain size by collecting samples and transporting them back to the lab for grain-size analysis. This process is slow and expensive. Moreover, most sampling systems are not selective enough to sample only the surficial grains that interact with the flow; samples typically include sediment from at least a few centimeters beneath the bed surface. New hardware and software are available for in-situ measurement of grain size. The new technology permits rapid measurement of surficial bed sediment. Here we describe several systems we have deployed by boat, by hand, and by tripod in rivers, oceans, and on beaches.

  6. The double effect of grain size on the work hardening behavior of polycrystalline copper

    SciTech Connect

    Gracio, J.J. . Dept. de Engenharia Mecanica)

    1994-08-15

    Following the approach by Ashby, one can consider that strain compatibility between adjacent grains of a polycrystal generates geometrical dislocations. These dislocations participated in the strengthening mechanism in conjunction with statistically stored dislocations which are related to the single-crystal behavior. The dislocations of either species are indistinguishable and, as a whole, they may contribute to cell formation. The dislocation structure formed in a polycrystal is then a function of the major or minor intergranular accommodation complexity. At intermediate strain values the accommodation is distributed over the cells leading to a linear relationship between the tensile stress and the inverse of the cell size, whatever the grain size of the tested samples. The aim of the present work is to check that the presence of statistical and geometrical dislocations in the grains, as well as the fact that at the very early stage of plastic deformation the mean free path of dislocations is of the order of the grain size, leads to a double effect of the grain size on the work hardening behavior of polycrystalline copper. Moreover, careful analysis of the mechanical behavior of polycrystalline copper, including the microstructural aspects of plastic deformation, is performed, allowing the understanding of the relationship between the work hardening ratio and the grain size.

  7. The influence of stress history on the grain size and microstructure of experimentally deformed quartzite

    NASA Astrophysics Data System (ADS)

    Kidder, Steven; Hirth, Greg; Avouac, Jean-Philippe; Behr, Whitney

    2016-02-01

    Deformation of middle crustal shear zones likely varies with time as a result of the stress build-up and release associated with earthquakes and post-seismic deformation, but the processes involved and their microstructural signature in the rock record are poorly understood. We conducted a series of experiments on quartzite at 900 °C to characterize microstructures associated with changes in stress and strain rate, and to investigate the feasibility of carrying out grain size piezometry in natural rocks that experienced analogous changes. Differential stress (referred to simply as "stress") was varied in two-stage experiments by changing strain rate and by stopping the motor and allowing stress to relax. The two-stage samples preserve a microstructural record that can be interpreted quantitatively in terms of stress history. The microstructure associated with a stress increase is a bimodal distribution of recrystallized grain sizes. The smaller grains associated with the second deformation stage accurately record the stress of the second stage, and the surviving coarse grains remain similar in size to those formed during the earlier stage. The transient microstructure associated with stress decrease is a "partial foam" texture containing a larger concentration of stable 120° triple junctions than occur in samples deformed at a relatively constant strain rate. Our results indicate that microstructures preserved in rocks that experienced relatively simple, two-stage deformation histories can be used to quantitatively assess stress histories. Grain growth rates during deformation are similar to rates observed in previous isostatic growth experiments, supporting theoretical approaches to recrystallized grain size, such as the wattmeter theory (Austin and Evans, 2007), that incorporate static growth rates. From an analysis of the experimental data for quartz recrystallized grain size, we find: 1) Recrystallized grain size quickly reaches a value consistent with

  8. Effects of grain size on the quasi-static mechanical properties of ultrafine-grained and nanocrystalline tantalum

    NASA Astrophysics Data System (ADS)

    Ligda, Jonathan Paul

    The increase in strength due to the Hall-Petch effect, reduced strain hardening capacity, a reduced ductility, and changes in deformation mechanisms are all effects of reducing grain size (d) into the ultrafine-grained (UFG, 100 < d < 1000 nm) and nanocrystalline (NC, d<100 nm) state. However, most of the studies on the mechanical behavior of UFG/NC metals have been on face-centered cubic (FCC) metals. Of the few reports on UFG/NC body-centered cubic (BCC) metals, the interest is related to their increase in strength and reduced strain rate sensitivity. This combination increases their propensity to deform via adiabatic shear bands (ASBs) at high strain rates, which is a desired response for materials being considered as a possible replacement for depleted uranium in kinetic energy penetrators. However, an ideal replacement material must also plastically deform in tension under quasi-static rates to survive initial launch conditions. This raises the question: if the material forms ASBs at dynamic rates, will it also form shear bands at quasi-static isothermal rates? As well as, is there a specific grain size for a material that will plastically deform in tension at quasi-static rates but form adiabatic shear bands at dynamic rates? Using high pressure torsion, a polycrystalline bulk tantalum disk was refined into the UFG/NC regime. Using microscale mechanical testing techniques, such as nanoindentation, microcompression, and microtension, it is possible to isolate locations with a homogeneous grain size within the disk. Pillars are compressed using a nanoindenter with a flat punch tip, while "dog-bone" specimens were pulled in tension using a custom built in-situ tension stage within a scanning electron microscope (SEM). The observed mechanical behavior is related to the microstructure by using transmission electron microscopy (TEM) on the as-processed material and tested specimens. Synchrotron X-ray based texture analysis was also conducted on the disk to

  9. Winds of M-type AGB stars driven by micron-sized grains

    NASA Astrophysics Data System (ADS)

    Höfner, S.

    2008-11-01

    Context: In view of the recent problem regarding the dynamical modelling of winds of M-type AGB stars (insufficient radiation pressure on silicate grains), some of the basic assumptions of these models need to be re-evaluated critically. Aims: Accepting the conclusion that non-grey effects will force silicate grains to be virtually Fe-free, the viability of driving winds with micron-sized Fe-free silicates, instead of small particles, is examined. Methods: Using both simple estimates and detailed dynamical atmosphere and wind models, it is demonstrated that radiation pressure on Fe-free silicate grains is sufficient to drive outflows if the restriction to the small particle limit is relaxed, and prevailing thermodynamic conditions allow grains to grow to sizes in the micrometer range. Results: The predicted wind properties, such as mass loss rates and outflow velocities, are in good agreement with observations of M-type AGB stars. Due to a self-regulating feedback between dust condensation and wind acceleration, grain growth naturally comes to a halt at particle diameters of about 1~μm. Conclusions: The most efficient grain sizes to drive winds are in a rather narrow interval around 1~μm. These values are set by the wavelength range corresponding to the flux maximum in typical AGB stars, and are very similar to interstellar grains.

  10. Anomalous polarization switching related to grain size in Pb(Zr,Ti)O3 polycrystalline films

    NASA Astrophysics Data System (ADS)

    Guo, Huifen; Cheng, Gang; Yong, Yongliang; Li, Liben

    2016-04-01

    Pb(Zr,Ti)O3 films of various grain size were prepared by the sol-gel technique. X-ray diffraction results show that these films are of single tetragonal phase with no evidence of preferential orientation. Anomalous polarization switching (APS) was induced in the films with average grain size ~150 nm by using the tip of a scanning force microscope. After scanning an area by the tip with constant poling parameter, the polarization of some grains orient opposite to the applied electric field irrespective of applied field polarity, exhibiting APS; while the rest switch in a normal way. The ratio of the APS grains to the total number decreases with the decrease of average grain size. Pulse poling experiments reveal that APS is likely to be related to the intrinsic characteristic of grains. Control experiments of poling (during and after) exclude backswitching after the removal of the external field due to the charge injection effect or the built-in field; both of which are possible reasons for APS. It is suggested that coupling between the temporary stress created in grains during field-induced normal switching and the applied field probably plays a key role in APS.

  11. Species sensitivity distributions for suspended clays, sediment burial, and grain size change in the marine environment.

    PubMed

    Smit, Mathijs G D; Holthaus, Karlijn I E; Trannum, Hilde C; Neff, Jerry M; Kjeilen-Eilertsen, Grete; Jak, Robbert G; Singsaas, Ivar; Huijbregts, Mark A J; Hendriks, A Jan

    2008-04-01

    Assessment of the environmental risk of discharges, containing both chemicals and suspended solids (e.g., drilling discharges to the marine environment), requires an evaluation of the effects of both toxic and nontoxic pollutants. To date, a structured evaluation scheme that can be used for prognostic risk assessments for nontoxic stress is lacking. In the present study we challenge this lack of information by the development of marine species sensitivity distributions (SSDs) for three nontoxic stressors: suspended clays, burial by sediment, and change in sediment grain size. Through a literature study, effect levels were obtained for suspended clays, as well as for burial of biota. Information on the species preference range for median grain size was used to assess the sensitivity of marine species to changes in grain size. The 50% hazardous concentrations (HC50) for suspended barite and bentonite based on 50% effect concentrations (EC50s) were 3,010 and 1,830 mg/L, respectively. For burial the 50% hazardous level (HL50) was 5.4 cm. For change in median grain size, two SSDs were constructed; one for reducing and one for increasing the median grain size. The HL50 for reducing the median grain size was 17.8 mum. For increasing the median grain size this value was 305 mum. The SSDs have been constructed by using information related to offshore oil- and gas-related activities. Nevertheless, the results of the present study may have broader implications. The hypothesis of the present study is that the SSD methodology developed for the evaluation of toxic stress can also be applied to evaluate nontoxic stressors, facilitating the incorporation of nontoxic stressors in prognostic risk assessment tools.

  12. Species sensitivity distributions for suspended clays, sediment burial, and grain size change in the marine environment.

    PubMed

    Smit, Mathijs G D; Holthaus, Karlijn I E; Trannum, Hilde C; Neff, Jerry M; Kjeilen-Eilertsen, Grete; Jak, Robbert G; Singsaas, Ivar; Huijbregts, Mark A J; Hendriks, A Jan

    2008-04-01

    Assessment of the environmental risk of discharges, containing both chemicals and suspended solids (e.g., drilling discharges to the marine environment), requires an evaluation of the effects of both toxic and nontoxic pollutants. To date, a structured evaluation scheme that can be used for prognostic risk assessments for nontoxic stress is lacking. In the present study we challenge this lack of information by the development of marine species sensitivity distributions (SSDs) for three nontoxic stressors: suspended clays, burial by sediment, and change in sediment grain size. Through a literature study, effect levels were obtained for suspended clays, as well as for burial of biota. Information on the species preference range for median grain size was used to assess the sensitivity of marine species to changes in grain size. The 50% hazardous concentrations (HC50) for suspended barite and bentonite based on 50% effect concentrations (EC50s) were 3,010 and 1,830 mg/L, respectively. For burial the 50% hazardous level (HL50) was 5.4 cm. For change in median grain size, two SSDs were constructed; one for reducing and one for increasing the median grain size. The HL50 for reducing the median grain size was 17.8 mum. For increasing the median grain size this value was 305 mum. The SSDs have been constructed by using information related to offshore oil- and gas-related activities. Nevertheless, the results of the present study may have broader implications. The hypothesis of the present study is that the SSD methodology developed for the evaluation of toxic stress can also be applied to evaluate nontoxic stressors, facilitating the incorporation of nontoxic stressors in prognostic risk assessment tools. PMID:18333685

  13. Grain Size Distribution and Geochemical Analysis of Terrigenous Minerals Transported to the Modern Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Hovan, S. A.; Ziegler, C.; Rea, D. K.; Murray, R. W.

    2001-05-01

    We examined core-top sediments recovered from 85 locations throughout the central and southern Atlantic Ocean to gain insight into possible source regions and transport modes and pathways of terrigenous minerals transported to the deep sea floor. Bulk sediments were treated with a sequential series of chemical leaches to remove biogenic and authigenic components and isolate the terrigenous mineral material. Once segregated, terrigenous sediment was analyzed for detailed grain size, mineralogical, and geochemical variability. From these data, we can infer several broadly-defined source regions and modes of transport for terrigenous grains carried to the deep Atlantic Ocean. In the central deep Atlantic, terrigenous grains are characterized by relatively fine-grained material (2 to 3 μ m), moderately to well-sorted (4-5 μ m std. dev.) and moderately low ratios of Al, Fe and Mn relative to Ti. Sites approaching the continental margins have grain size distributions with a slightly coarser mean and are more poorly sorted. South of about 20° S, terrigenous sediment display much coarser mean grain sizes (3-6 μ m), broader distributions (generally 8-10 μ m std. dev.) and slightly elevated elemental ratios relative to Ti. Grain size data from the southwestern sector of the Atlantic are coarser than the southeastern sector. These data broadly define several different regional transport modes. Terrigenous input to the tropical and subtropical Atlantic beyond about 2000 km away from the continental margin is likely dominated by eolian transport processes in the deeper basins along the flanks of the mid ocean ridges with material supplied from the arid Sahar-Sahel regions of northern Africa. At sites closer to the continental margin, turbidites and hemipelagic processes appear to be the main mechanisms that transport terrigenous material to the seafloor. In the southern Atlantic, grain size distribution data, geochemical patterns, and clay mineralogy (Petschick et al, 1996

  14. Fatigue Failure Modes of the Grain Size Transition Zone in a Dual Microstructure Disk

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Kantzos, Pete T.; Palsa, Bonnie; Telesman, Jack; Gayda, John; Sudbrack, Chantal K.

    2012-01-01

    Mechanical property requirements vary with location in nickel-based superalloy disks. In order to maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored grain microstructures. In this study, fatigue failure modes of a grain size transition zone in a dual microstructure disk were evaluated. A specialized heat treatment method was applied to produce varying grain microstructure in the bore to rim portions of a powder metallurgy processed nickel-based superalloy disk. The transition in grain size was concentrated in a zone of the disk web, between the bore and rim. Specimens were extracted parallel and transversely across this transition zone, and multiple fatigue tests were performed at 427 C and 704 C. Grain size distributions were characterized in the specimens, and related to operative failure initiation modes. Mean fatigue life decreased with increasing maximum grain size, going out through the transition zone. The scatter in limited tests of replicates was comparable for failures of uniform gage specimens in all transition zone locations examined.

  15. Model for evolution of grain size in the rim region of high burnup UO2 fuel

    NASA Astrophysics Data System (ADS)

    Xiao, Hongxing; Long, Chongsheng; Chen, Hongsheng

    2016-04-01

    The restructuring process of the high burnup structure (HBS) formation in UO2 fuel results in sub-micron size grains that accelerate the fission gas swelling, which will raise some concern over the safety of extended the nuclear fuel operation life in the reactor. A mechanistic and engineering model for evolution of grain size in the rim region of high burnup UO2 fuel based on the experimental observations of the HBS in the literature is presented. The model takes into account dislocations evolution under irradiation and the grain subdivision occur successively at increasing local burnup. It is assumed that the original driving force for subdivision of grain in the HBS of UO2 fuel is the production and accumulation of dislocation loops during irradiation. The dislocation loops can also be annealed through thermal diffusion when the temperature is high enough. The capability of this model is validated by the comparison with the experimental data of temperature threshold of subdivision, dislocation density and sub-grain size as a function of local burnup. It is shown that the calculated results of the dislocation density and subdivided grain size as a function of local burnup are in good agreement with the experimental results.

  16. Correlating grain size to radiation damage tolerance of tungsten materials exposed to relevant fusion conditions

    NASA Astrophysics Data System (ADS)

    Gonderman, Sean

    Tungsten remains a leading candidate for plasma facing component (PFC) in future fusion devices. This is in large part due to its strong thermal and mechanical properties. The ITER project has already chosen to use an all tungsten divertor. Despite having a high melting temperature and low erosion rate, tungsten faces a large variety of issues when subject to fusion like conditions. These include embrittlement, melting, and extreme morphology change (growth of fuzz nanostructure). The work presented here investigates mechanisms that drive surface morphology change in tungsten materials exposed to fusion relevant plasmas. Specifically, tungsten materials of different grain sizes are studied to elucidate the impact of grain boundaries on irradiation damage. Exposure of ultrafine (< 500 nm) and nanocrystalline (< 100 nm) grain materials are exposed to high flux helium plasmas at the Dutch Institute for Fundamental Energy Research (DIFFER) in the Netherlands. These samples are then compared to large grain (1-5 microns) tungsten materials exposed to similar conditions at DIFFER or tungsten samples from other published studies. After exposing the ultrafine grain materials to a variety of helium plasmas to different fluences between 1 x 1023 - 1 x 1027 ions-m-2, temperatures between 600-1500 °C, and ion energies between 25-70 eV, it is observed that ultrafine grained tungsten samples develop fuzz at an order of magnitude larger fluence when compared to large grained tungsten. These observations suggest that grain boundaries play a role in dictating damage accumulation and damage rate caused by ion bombardment of tungsten surfaces. These experiments are complemented by In-situ TEM analysis during 8 keV Helium irradiation of ultrafine tungsten samples to see damage propagation in different sized grains in real time. The in-situ TEM work was completed in a JEOL JEM-2000FX TEM at the Microscope and Ion Accelerator for Materials Investigation (MIAMI) facility at the

  17. Grain Size and Parameter Recovery with TIMSS and the General Diagnostic Model

    ERIC Educational Resources Information Center

    Skaggs, Gary; Wilkins, Jesse L. M.; Hein, Serge F.

    2016-01-01

    The purpose of this study was to explore the degree of grain size of the attributes and the sample sizes that can support accurate parameter recovery with the General Diagnostic Model (GDM) for a large-scale international assessment. In this resampling study, bootstrap samples were obtained from the 2003 Grade 8 TIMSS in Mathematics at varying…

  18. Phosphorus removal from slow-cooled steelmaking slags: Grain size determination and liberation studies

    SciTech Connect

    Fregeau-Wu, E.; Iwasaki, I.

    1995-07-01

    The major obstacle in recycling steelmaking slags to the blast furnace is their phosphorus content. Removal of the phosphorus, which is primarily associated with the silicate and phosphate phases, would allow for greater recycle of these slags for their iron, manganese, and lime contents. Calculations show that separation of the silicates from the oxide phases would remove nearly 90% of the phosphorus from the slag. The variable grain size of the as-received slag made liberation by fine grinding difficult. Therefore, slow-cooling experiments were undertaken to improve the grain size distribution. The grain size distributions were determined using in-situ image analysis. The samples were ground to their apparent liberation size and high gradient magnetic separation was used to separate the magnetic oxides from the nonmagnetic silicates and phosphates. Liberation analysis and modeling was performed on selected separation products for discussion of benefication characteristics.

  19. Effect of time and temperature on grain size of V and V-Cr-Ti alloys

    SciTech Connect

    Natesan, K.; Rink, D.L.

    1996-10-01

    Grain growth studies were conducted to evaluate the effect of time and temperature on the grain size of pure V, V-4 wt.%Cr-4 wt.%Ti, and V-5 wt.%Cr-5 wt.%Ti alloys. The temperatures used in the study were 500, 650, 800, and 1000{degrees}C, and exposure times ranged between 100 and {approx}5000 h. All three materials exhibited negligible grain growth at 500, 650, and 800{degrees}C, even after {approx}5000 h. At 1000{degrees}C, pure V showed substantial grain growth after only 100 h, and V-4Cr-4Ti showed growth after 2000 h, while V-5Cr-5Ti showed no grain growth after exposure for up to 2000 h.

  20. Wear characterization of abrasive waterjet nozzles and nozzle materials

    NASA Astrophysics Data System (ADS)

    Nanduri, Madhusarathi

    Parameters that influence nozzle wear in the abrasive water jet (AWJ) environment were identified and classified into nozzle geometric, AWJ system, and nozzle material categories. Regular and accelerated wear test procedures were developed to study nozzle wear under actual and simulated conditions, respectively. Long term tests, using garnet abrasive, were conducted to validate the accelerated test procedure. In addition to exit diameter growth, two new measures of wear, nozzle weight loss and nozzle bore profiles were shown to be invaluable in characterizing and explaining the phenomena of nozzle wear. By conducting nozzle wear tests, the effects of nozzle geometric, and AWJ system parameters on nozzle wear were systematically investigated. An empirical model was developed for nozzle weight loss rate. To understand the response of nozzle materials under varying AWJ system conditions, erosion tests were conducted on samples of typical nozzle materials. The effect of factors such as jet impingement angle, abrasive type, abrasive size, abrasive flow rate, water pressure, traverse speed, and target material was evaluated. Scanning electron microscopy was performed on eroded samples as well as worn nozzles to understand the wear mechanisms. The dominant wear mechanism observed was grain pullout. Erosion models were reviewed and along the lines of classical erosion theories a semi-empirical model, suitable for erosion of nozzle materials under AWJ impact, was developed. The erosion data correlated very well with the developed model. Finally, the cutting efficiency of AWJ nozzles was investigated in conjunction with nozzle wear. The cutting efficiency of a nozzle deteriorates as it wears. There is a direct correlation between nozzle wear and cutting efficiency. The operating conditions that produce the most efficient jets also cause the most wear in the nozzle.

  1. Grain-size distribution and morphology of metal in E-chondrites

    NASA Astrophysics Data System (ADS)

    Easton, A. J.

    1983-03-01

    The size distribution and morphology of metal grains have been examined in 11 sections of types I and II E-chondrites. The changes in the grain-size distribution and morphology of metal grains correspond with the petrologic types and define a series that reflects increase in thermal metamorphism in the following order: type I, Kota Kota-Indarch-South Oman-St. Mark's; and type II, Jajh deh Kot Lalu-Atlanta-Daniel's Kuil-Hvittis-Pillistfer-Khairpur-Blithfield. Concentrations of metal grains adjacent to the perimeters of chondrules are observable throughout the sequence and delineate relic chondritic structure in six of the seven type II E-chondrites; relic structures are absent from Blithfield.

  2. Grain size control and phase transformations in nanocrystalline ZrO(2)-Al(2)O(3)

    NASA Astrophysics Data System (ADS)

    Smyser, Bridget Maureen

    1998-12-01

    An effort has been made to develop nanocrystalline ZrOsb2-Alsb2Osb3 powders that exhibit grain size and phase stability during one thermal cycle from room temperature to 1100-1200sp°C for potential use as thermal barrier coating materials. For this use, the tetragonal phase of ZrOsb2 must be maintained. Tetragonal ZrOsb2 can be prevented from transforming to the monoclinic form by maintaining the grain size below a critical value. Alsb2Osb3 was intended to provide this grain size control due to its immiscibility with ZrOsb2. Several sol-gel and precipitation methods of producing the powders were compared, along with two different forms of high energy mixing. The powders were subsequently calcined and heat treated in order to assess their ability to maintain the desired phase distribution during thermal cycling. The powders were characterized by x-ray diffraction and transmission electron microscopy. The method producing the greatest fraction of tetragonal ZrOsb2 with the least amount of added Alsb2Osb3 was that in which a commercial colloidal solution of ZrOsb2 was mixed with an aluminum nitrate solution. The critical grain size of ZrOsb2 in this system was 30 nm. The grain size was controlled not by a pinning mechanism as is often seen in conventional, high Alsb2Osb3,\\ Alsb2Osb3-ZrOsb2 ceramics, but instead by mutual constraint of surrounding grains aided by sluggish grain boundary diffusion. The grain growth kinetics in all the phases tended to be slower than in micron sized materials, and a range of grain growth exponents from n = 1 to n = 30 were determined for the various phases. Transformation kinetics in ZrOsb2 followed classic Avrami behavior. Alsb2Osb3 phase transformation kinetics were not specifically determined, however, gamma-Alsb2Osb3 was identified at temperatures well beyond its usual stability, which is possibly a grain size effect.

  3. Grain-size-independent plastic flow at ultrahigh pressures and strain rates.

    PubMed

    Park, H-S; Rudd, R E; Cavallo, R M; Barton, N R; Arsenlis, A; Belof, J L; Blobaum, K J M; El-dasher, B S; Florando, J N; Huntington, C M; Maddox, B R; May, M J; Plechaty, C; Prisbrey, S T; Remington, B A; Wallace, R J; Wehrenberg, C E; Wilson, M J; Comley, A J; Giraldez, E; Nikroo, A; Farrell, M; Randall, G; Gray, G T

    2015-02-13

    A basic tenet of material science is that the flow stress of a metal increases as its grain size decreases, an effect described by the Hall-Petch relation. This relation is used extensively in material design to optimize the hardness, durability, survivability, and ductility of structural metals. This Letter reports experimental results in a new regime of high pressures and strain rates that challenge this basic tenet of mechanical metallurgy. We report measurements of the plastic flow of the model body-centered-cubic metal tantalum made under conditions of high pressure (>100  GPa) and strain rate (∼10(7)  s(-1)) achieved by using the Omega laser. Under these unique plastic deformation ("flow") conditions, the effect of grain size is found to be negligible for grain sizes >0.25  μm sizes. A multiscale model of the plastic flow suggests that pressure and strain rate hardening dominate over the grain-size effects. Theoretical estimates, based on grain compatibility and geometrically necessary dislocations, corroborate this conclusion. PMID:25723227

  4. The grain size gap and abrupt gravel-sand transitions in rivers due to suspension fallout

    NASA Astrophysics Data System (ADS)

    Lamb, Michael P.; Venditti, Jeremy G.

    2016-04-01

    Median grain sizes on riverbeds range from boulders in uplands to silt in lowlands; however, rivers with ~1-5 mm diameter bed sediment are rare. This grain size gap also marks an abrupt transition between gravel- and sand-bedded reaches that is unlike any other part of the fluvial network. Abrupt gravel-sand transitions have been attributed to rapid breakdown or rapid transport of fine gravel, or a bimodal sediment supply, but supporting evidence is lacking. Here we demonstrate that rivers dramatically lose the ability to transport sand as wash load where bed shear velocity drops below ~0.1 m/s, forcing an abrupt transition in bed-material grain size. Using thresholds for wash load and initial motion, we show that the gap emerges only for median bed-material grain sizes of ~1-5 mm due to Reynolds number dependencies in suspension transport. The grain size gap, therefore, is sensitive to material properties and gravity, with coarser gaps predicted on Mars and Titan.

  5. Effects of the sintering conditions of dental zirconia ceramics on the grain size and translucency

    PubMed Central

    Kim, Mi-Jin; Kim, Ji-Hwan; Kim, Hae-Young

    2013-01-01

    PURPOSE This study aimed to identify the effects of the sintering conditions of dental zirconia on the grain size and translucency. MATERIALS AND METHODS Ten specimens of each of two commercial brands of zirconia (Lava and KaVo) were made and sintered under five different conditions. Microwave sintering (MS) and conventional sintering (CS) methods were used to fabricate zirconia specimens. The dwelling time was 20 minutes for MS and 20 minutes, 2, 10, and 40 hours for CS. The density and the grain size of the sintered zirconia blocks were measured. Total transmission measurements were taken using a spectrophotometer. Two-way analysis of variance model was used for the analysis and performed at a type-one error rate of 0.05. RESULTS There was no significant difference in density between brands and sintering conditions. The mean grain size increased according to sintering conditions as follows: MS-20 min, CS-20 min, CS-2 hr, CS-10 hr, and CS-40 hr for both brands. The mean grain size ranged from 347-1,512 nm for Lava and 373-1,481 nm for KaVo. The mean light transmittance values of Lava and KaVo were 28.39-34.48% and 28.09-30.50%, respectively. CONCLUSION Different sintering conditions resulted in differences in grain size and light transmittance. To obtain more translucent dental zirconia restorations, shorter sintering times should be considered. PMID:23755342

  6. Effect of grain size on deformation stability of copper under quasi- static and dynamic tensile loading

    SciTech Connect

    Lassila, D.H.; Gourdin, W.H.

    1991-10-31

    The effects of grain size on the deformation stability of copper deformed in tension under quasi-static and dynamic conditions have been studied experimentally and analytically. Oxygen Free Electronic (OFE) copper samples with grain sizes of 15 {mu} and 120 {mu}m were tested. Results of the tests indicated that an increase in grain size resulted in greater extents of elongation prior to deformation instability and eventual failure under both quasi-static and dynamic loading. We have applied the deformation stability condition of Considere to both a simple power law modified to include a Hall-Petch grain size dependence and the more descriptive mechanical threshold stress (MTS) model. Calculations of the stress-strain behavior in uniaxial tension and the instability strain under quasi-static loading are compared with experiment. Both models predict an increase in the instability strain with increasing grain size, but the power law, included as a heuristic, yields a poor overall fit to both the stress-strain and the instability strains. Under dynamic loading comparison of the experimental results with analytical predictions were difficult due to inherent inaccuracy in the dynamic stress-strain data.

  7. An evaluation of different measures of dynamically recrystallized grain size for paleopiezometry or paleowattometry studies

    NASA Astrophysics Data System (ADS)

    Lopez-Sanchez, M. A.; Llana-Fúnez, S.

    2015-05-01

    Paleopiezometry and paleowattometry studies are essential to validate models of lithospheric deformation and therefore increasingly common in structural geology. These studies require a single measure of dynamically recrystallized grain size in natural mylonites to estimate the magnitude of differential paleostress (or the rate of mechanical work). This contribution tests the various measures of grain size used in the literature and proposes the frequency peak of a grain size distribution as the most robust estimator for paleopiezometry or paleowattometry studies. The novelty of the approach resides in the use of the Gaussian kernel density estimator as an alternative to the classical histograms, which improves reproducibility. A free, open-source, easy-to-handle script named GrainSizeTools ( http://www.TEOS-10.org) was developed with the aim of facilitating the adoption of this measure of grain size in paleopiezometry or paleowattometry studies. The major advantage of the script over other programs is that by using the Gaussian kernel density estimator and by avoiding manual steps in the estimation of the frequency peak, the reproducibility of results is improved.

  8. Grain-size-independent plastic flow at ultrahigh pressures and strain rates.

    PubMed

    Park, H-S; Rudd, R E; Cavallo, R M; Barton, N R; Arsenlis, A; Belof, J L; Blobaum, K J M; El-dasher, B S; Florando, J N; Huntington, C M; Maddox, B R; May, M J; Plechaty, C; Prisbrey, S T; Remington, B A; Wallace, R J; Wehrenberg, C E; Wilson, M J; Comley, A J; Giraldez, E; Nikroo, A; Farrell, M; Randall, G; Gray, G T

    2015-02-13

    A basic tenet of material science is that the flow stress of a metal increases as its grain size decreases, an effect described by the Hall-Petch relation. This relation is used extensively in material design to optimize the hardness, durability, survivability, and ductility of structural metals. This Letter reports experimental results in a new regime of high pressures and strain rates that challenge this basic tenet of mechanical metallurgy. We report measurements of the plastic flow of the model body-centered-cubic metal tantalum made under conditions of high pressure (>100  GPa) and strain rate (∼10(7)  s(-1)) achieved by using the Omega laser. Under these unique plastic deformation ("flow") conditions, the effect of grain size is found to be negligible for grain sizes >0.25  μm sizes. A multiscale model of the plastic flow suggests that pressure and strain rate hardening dominate over the grain-size effects. Theoretical estimates, based on grain compatibility and geometrically necessary dislocations, corroborate this conclusion.

  9. The influence of grain size on the ductility of micro-scale stainless steel stent struts.

    PubMed

    Murphy, B P; Cuddy, H; Harewood, F J; Connolley, T; McHugh, P E

    2006-01-01

    Vascular stents are used to restore blood flow in stenotic arteries, and at present the implantation of a stent is the preferred revascularisation method for treating coronary artery disease, as the introduction of drug eluting stents (DESs) has lead to a significant improvement in the clinical outcome of coronary stenting. However the mechanical limits of stents are being tested when they are deployed in severe cases. In this study we aimed to show (by a combination of experimental tests and crystal plasticity finite element models) that the ductility of stainless steel stent struts can be increased by optimising the grain structure within micro-scale stainless steel stent struts. The results of the study show that within the specimen size range 55 to 190 microm ductility was not dependent on the size of the stent strut when the grain size maximised. For values of the ratio of cross sectional area to characteristic grain length less than 1,000, ductility was at a minimum irrespective of specimen size. However, when the ratio of cross sectional area to characteristic grain length becomes greater than 1,000 an improvement in ductility occurs, reaching a plateau when the ratio approaches a value characteristic of bulk material properties. In conclusion the ductility of micro-scale stainless steel stent struts is sensitive to microstructure and can be improved by reducing the grain size.

  10. Grain size bias in cosmogenic nuclide studies of stream sediment in steep terrain

    NASA Astrophysics Data System (ADS)

    Lukens, Claire E.; Riebe, Clifford S.; Sklar, Leonard S.; Shuster, David L.

    2016-05-01

    Cosmogenic nuclides in stream sediment are widely used to quantify catchment-average erosion rates. A key assumption is that sampled sediment is representative of erosion from the entire catchment. Here we show that the common practice of collecting a narrow range of sizes—typically sand—may not yield a representative sample when the grain size distribution of sediment produced on slopes is spatially variable. A grain size bias arises when some parts of the catchment produce sand more readily than others. To identify catchments that are prone to this bias, we used a forward model of sediment mixing and erosion to explore the effects of catchment relief and area across a range of altitudinal gradients in sediment size and erosion rate. We found that the bias increases with increasing relief, because higher-relief catchments have a larger fraction of high elevations that are underrepresented in the sampled sand when grain size increases with altitude. The bias also increases with catchment area, because sediment size reduction during transport causes an underrepresentation of more distal, higher elevations within the catchment. Our analysis indicates that grain size bias may be significant at many sites where cosmogenic nuclides have been used to quantify catchment-average erosion rates. We discuss how to quantify and account for the bias using cosmogenic nuclides and detrital thermochronometry in multiple sediment sizes.

  11. Statistical considerations for grain-size analyses of tills

    USGS Publications Warehouse

    Jacobs, A.M.

    1971-01-01

    Relative percentages of sand, silt, and clay from samples of the same till unit are not identical because of different lithologies in the source areas, sorting in transport, random variation, and experimental error. Random variation and experimental error can be isolated from the other two as follows. For each particle-size class of each till unit, a standard population is determined by using a normally distributed, representative group of data. New measurements are compared with the standard population and, if they compare satisfactorily, the experimental error is not significant and random variation is within the expected range for the population. The outcome of the comparison depends on numerical criteria derived from a graphical method rather than on a more commonly used one-way analysis of variance with two treatments. If the number of samples and the standard deviation of the standard population are substituted in a t-test equation, a family of hyperbolas is generated, each of which corresponds to a specific number of subsamples taken from each new sample. The axes of the graphs of the hyperbolas are the standard deviation of new measurements (horizontal axis) and the difference between the means of the new measurements and the standard population (vertical axis). The area between the two branches of each hyperbola corresponds to a satisfactory comparison between the new measurements and the standard population. Measurements from a new sample can be tested by plotting their standard deviation vs. difference in means on axes containing a hyperbola corresponding to the specific number of subsamples used. If the point lies between the branches of the hyperbola, the measurements are considered reliable. But if the point lies outside this region, the measurements are repeated. Because the critical segment of the hyperbola is approximately a straight line parallel to the horizontal axis, the test is simplified to a comparison between the means of the standard

  12. Effect of Grain Size Distribution on Processing Maps for Isothermal Compression of Inconel 718 Superalloy

    NASA Astrophysics Data System (ADS)

    Wang, Jianguo; Liu, Dong; Hu, Yang; Yang, Yanhui; Zhu, Xinglin

    2016-02-01

    Cylindrical specimens of Inconel 718 alloys with three types of grain size distribution were used in the compression tests and processing maps were developed in 940-1040 °C and 0.001-10 s-1. The equiaxed fine grain is more effective on the dynamic softening behavior. For partial recrystallized microstructure, the peak efficiency of power dissipation occurs at the strain rate of 0.001 s-1, and the temperature range of 1000-1020 °C. In order to obtain homogeneous microstructure with fine grains, the partial recrystallized microstructure should be deformed at the low temperature and slow strain rates. The area fraction of instability domains decreases with strain increasing. The peak efficiency of power dissipation increases with average grain size decreasing. The efficiency of power dissipation will be stimulated by the precipitation of δ phase at slow strain rate of 0.001-0.01 s-1, and the initial deformed substructure at the strain rate of 0.1-1 s-1. Equiaxed fine grain is the optimum state for forging process and dynamic recrystallization. The grain size distribution has slight influence on the microstructure evolution at high temperatures.

  13. A new database sub-system for grain-size analysis

    NASA Astrophysics Data System (ADS)

    Suckow, Axel

    2013-04-01

    Detailed grain-size analyses of large depth profiles for palaeoclimate studies create large amounts of data. For instance (Novothny et al., 2011) presented a depth profile of grain-size analyses with 2 cm resolution and a total depth of more than 15 m, where each sample was measured with 5 repetitions on a Beckman Coulter LS13320 with 116 channels. This adds up to a total of more than four million numbers. Such amounts of data are not easily post-processed by spreadsheets or standard software; also MS Access databases would face serious performance problems. The poster describes a database sub-system dedicated to grain-size analyses. It expands the LabData database and laboratory management system published by Suckow and Dumke (2001). This compatibility with a very flexible database system provides ease to import the grain-size data, as well as the overall infrastructure of also storing geographic context and the ability to organize content like comprising several samples into one set or project. It also allows easy export and direct plot generation of final data in MS Excel. The sub-system allows automated import of raw data from the Beckman Coulter LS13320 Laser Diffraction Particle Size Analyzer. During post processing MS Excel is used as a data display, but no number crunching is implemented in Excel. Raw grain size spectra can be exported and controlled as Number- Surface- and Volume-fractions, while single spectra can be locked for further post-processing. From the spectra the usual statistical values (i.e. mean, median) can be computed as well as fractions larger than a grain size, smaller than a grain size, fractions between any two grain sizes or any ratio of such values. These deduced values can be easily exported into Excel for one or more depth profiles. However, such a reprocessing for large amounts of data also allows new display possibilities: normally depth profiles of grain-size data are displayed only with summarized parameters like the clay

  14. Composition and grain size effects on the structural and mechanical properties of CuZr nanoglasses

    SciTech Connect

    Adibi, Sara; Branicio, Paulo S. Zhang, Yong-Wei; Joshi, Shailendra P.

    2014-07-28

    Nanoglasses (NGs), metallic glasses (MGs) with a nanoscale grain structure, have the potential to considerably increase the ductility of traditional MGs while retaining their outstanding mechanical properties. We investigated the effects of composition on the structural and mechanical properties of CuZr NG films with grain sizes between 3 to 15 nm using molecular dynamics simulations. Results indicate a transition from localized shear banding to homogeneous superplastic flow with decreasing grain size, although the critical average grain size depends on composition: 5 nm for Cu{sub 36}Zr{sub 64} and 3 nm for Cu{sub 64}Zr{sub 36}. The flow stress of the superplastic NG at different compositions follows the trend of the yield stress of the parent MG, i.e., Cu{sub 36}Zr{sub 64} yield/flow stress: 2.54 GPa/1.29 GPa and Cu{sub 64}Zr{sub 36} yield/flow stress: 3.57 GPa /1.58 GPa. Structural analysis indicates that the differences in mechanical behavior as a function of composition are rooted at the distinct statistics of prominent atomic Voronoi polyhedra. The mechanical behavior of NGs is also affected by the grain boundary thickness and the fraction of atoms at interfaces for a given average grain size. The results suggest that the composition dependence of the mechanical behavior of NGs follows that of their parent MGs, e.g., a stronger MG will generate a stronger NG, while the intrinsic tendency for homogeneous deformation occurring at small grain size is not affected by composition.

  15. Measuring Snow Grain Size with the Near-Infrared Emitting Reflectance Dome (NERD)

    NASA Astrophysics Data System (ADS)

    Schneider, A. M.; Flanner, M.

    2014-12-01

    Because of its high visible albedo, snow plays a large role in Earth's surface energy balance. This role is a subject of intense study, but due to the wide range of snow albedo, variations in the characteristics of snow grains can introduce radiative feedbacks in a snow pack. Snow grain size, for example, is one property which directly affects a snow pack's absorption spectrum. Previous studies model and observe this spectrum, but potential feedbacks induced by these variations are largely unknown. Here, we implement a simple and inexpensive technique to measure snow grain size in an instrument we call the Near-infrared Emitting Reflectance Dome (NERD). A small black styrene dome (~17cm diameter), fitted with two narrowband light-emitting diodes (LEDs) centered around 1300nm and 1550nm and three near-infrared reverse-biased photodiodes, is placed over the snow surface enabling a multi-spectral measurement of the hemispheric directional reflectance factor (HDRF). We illuminate the snow at each wavelength, measure directional reflectance, and infer grain size from the difference in HDRFs measured on the same snow crystals at fixed viewing angles. We validate measurements from the NERD using two different reflectance standards, materials designed to be near perfect Lambertian reflectors, having known, constant reflectances (~99% and ~55%) across a wide range of wavelengths. Using a 3D Monte Carlo model simulating photon pathways through a pack of spherical snow grains, we calculate the difference in HDRFs at 1300nm and 1550nm to predict the calibration curve for a wide range of grain sizes. This theoretically derived curve gives a relationship between effective radius and the difference in HDRFs and allows us to approximate grain sizes using the NERD in just a few seconds. Further calibration requires knowledge of truth values attainable using a previously validated instrument or measurements from an inter-comparison workshop.

  16. Preparation and Characterization of Grain Size Controlled LaB6 Polycrystalline Cathode Material

    NASA Astrophysics Data System (ADS)

    Bao, Li-Hong; Zhang, Jiu-Xing; Zhou, Shen-Lin; Wei, Yong-Feng

    2010-10-01

    The grain size controlled bulk Lanthanum hexaboride (LaBe) cathode material was prepared by using the spark plasma sintering method in an oxygen free system. The starting precursor nanopowders with average grain size of 50 nm were prepared by high-energy ball milling. The nanopowder was fully densified at 1300° C, which is about 350° C lower than the sintering temperature of the coarse powders. The thermionic emission current density was measured to be 42.0 A/cm2, which is much higher than 24.2 A/cm2 of coarse powders and Vickers hardness to be 1860 kg/mm2, which is also higher than 1700 kg/mm2 of coarse one. These results indicate that refining the powder grain size to nano level was beneficial for reducing the sintering temperature and promoting the thermionic emission and mechanic properties.

  17. An automated and universal method for measuring mean grain size from a digital image of sediment

    USGS Publications Warehouse

    Buscombe, Daniel D.; Rubin, David M.; Warrick, Jonathan A.

    2010-01-01

    Existing methods for estimating mean grain size of sediment in an image require either complicated sequences of image processing (filtering, edge detection, segmentation, etc.) or statistical procedures involving calibration. We present a new approach which uses Fourier methods to calculate grain size directly from the image without requiring calibration. Based on analysis of over 450 images, we found the accuracy to be within approximately 16% across the full range from silt to pebbles. Accuracy is comparable to, or better than, existing digital methods. The new method, in conjunction with recent advances in technology for taking appropriate images of sediment in a range of natural environments, promises to revolutionize the logistics and speed at which grain-size data may be obtained from the field.

  18. Retrieval of Surface Snow Grain Size and Melt Water from AVIRIS Spectra

    NASA Technical Reports Server (NTRS)

    Green Robert O.; Dozier, Jeff

    1996-01-01

    The Earth's energy balance and hydrology are affected by the distribution and characteristics of snow cover on the surface. Snow grain size and snow melt influence surface albedo and hydrology. A model of snow reflectance that depends on both grain size and surface melt water was developed to derive these parameters from remote spectral measurements. This reflectance model is based on a discrete ordinate radiative transfer approach that uses Mie calculations of snow optical properties, which are based on the complex refractive index of ice and water. This snow model was linked to an atmospheric radiative transfer code and a nonlinear least squares fitting algorithm. The resulting combined algorithm was applied to an AVIRIS snow data set acquired over Mammoth Mountain, California. Maps of grain size and surface snow melt were generated that are consistent with the expected ranges and distributions for conditions at the site.

  19. NANOCRYSTALLINE GROWTH AND GRAIN-SIZE EFFECTS IN AU-CU ELECTRODEPOSITS

    SciTech Connect

    Jankowski, A F; Saw, C K; Harper, J F; Vallier, R F; Ferreira, J L; Hayes, J P

    2005-02-25

    The processing-structure-property relationship is investigated for electrodeposited foils of the gold-copper alloy system. A model is presented that relates the deposition process parameters to the nanocrystalline grain size. An activation energy of 1.52 eV {center_dot} atom{sup -1} for growth is determined for a long pulse (>10 msec) mode, and is 0.16 eV {center_dot} atom{sup -1} for short pulses (<5 msec). The affect of nanocrystalline grain size on the mechanical properties is assessed using indentation measurements. A Hall-Petch type variation of the Vickers microhardness with nanocrystalline grain size (>6 nm) is observed for Au-Cu samples with 1-12 wt.% Cu as tested in cross-section. The hardness increases three-fold from a rule-of-mixtures value <1 GPa to a maximum of 2.9 GPa.

  20. Scattering and Absorption Properties of Polydisperse Wavelength-sized Particles Covered with Much Smaller Grains

    NASA Technical Reports Server (NTRS)

    Dlugach, Jana M.; Mishchenko, Michael I.; Mackowski, Daniel W.

    2012-01-01

    Using the results of direct, numerically exact computer solutions of the Maxwell equations, we analyze scattering and absorption characteristics of polydisperse compound particles in the form of wavelength-sized spheres covered with a large number of much smaller spherical grains.The results pertain to the complex refractive indices1.55 + i0.0003,1.55 + i0.3, and 3 + i0.1. We show that the optical effects of dusting wavelength-sized hosts by microscopic grains can vary depending on the number and size of the grains as well as on the complex refractive index. Our computations also demonstrate the high efficiency of the new superposition T-matrix code developed for use on distributed memory computer clusters.

  1. The effect of grain size on aluminum anodes for Al-air batteries in alkaline electrolytes

    NASA Astrophysics Data System (ADS)

    Fan, Liang; Lu, Huimin

    2015-06-01

    Aluminum is an ideal material for metallic fuel cells. In this research, different grain sizes of aluminum anodes are prepared by equal channel angular pressing (ECAP) at room temperature. Microstructure of the anodes is examined by electron backscatter diffraction (EBSD) in scanning electron microscope (SEM). Hydrogen corrosion rates of the Al anodes in 4 mol L-1 NaOH are determined by hydrogen collection method. The electrochemical properties of the aluminum anodes are investigated in the same electrolyte using electrochemical impedance spectroscopy (EIS) and polarization curves. Battery performance is also tested by constant current discharge at different current densities. Results confirm that the electrochemical properties of the aluminum anodes are related to grain size. Finer grain size anode restrains hydrogen evolution, improves electrochemical activity and increases anodic utilization rate. The proposed method is shown to effectively improve the performance of Al-air batteries.

  2. Spectral Profiler Probe for In Situ Snow Grain Size and Composition Stratigraphy

    NASA Technical Reports Server (NTRS)

    Berisford, Daniel F.; Molotch, Noah P.; Painter, Thomas

    2012-01-01

    An ultimate goal of the climate change, snow science, and hydrology communities is to measure snow water equivalent (SWE) from satellite measurements. Seasonal SWE is highly sensitive to climate change and provides fresh water for much of the world population. Snowmelt from mountainous regions represents the dominant water source for 60 million people in the United States and over one billion people globally. Determination of snow grain sizes comprising mountain snowpack is critical for predicting snow meltwater runoff, understanding physical properties and radiation balance, and providing necessary input for interpreting satellite measurements. Both microwave emission and radar backscatter from the snow are dominated by the snow grain size stratigraphy. As a result, retrieval algorithms for measuring snow water equivalents from orbiting satellites is largely hindered by inadequate knowledge of grain size.

  3. Effects of grain size, hardness, and stress on the magnetic hysteresis loops of ferromagnetic steels

    NASA Astrophysics Data System (ADS)

    Kwun, H.; Burkhardt, G. L.

    1987-02-01

    Effects of grain size, hardness, and stress on the magnetic hysteresis loops of AISI 410 stainless steel and SAE 4340 steel specimens were investigated experimentally. It was observed that both hardness and stress significantly influenced the hysteresis loops, while the grain size had a minimal effect. For each material, the mechanically harder specimen was more difficult to magnetize. Upon application of uniaxial stress, the magnetic induction increased under tension and decreased under compression, with the sides of the hysteresis loops becoming inclined more toward the vertical axis under tension and the horizontal axis under compression. For each material, the effects of stress on the hysteresis loops were greater for the mechanically softer specimen and exhibited an inverse relationship to the hardness. The effects of stress were not dependent on grain size.

  4. Computational characterizations on the grain-size-dependent properties of polycrystalline nanomaterials

    NASA Astrophysics Data System (ADS)

    Hyun, Sangil; Park, Youngho; Kim, Hyo-tae

    2015-12-01

    The microstructures of real nanomaterials can be quite complex with variety of grain sizes aligned in different crystal orientations and structural defects possibly created in a fabrication process. Material properties of these polycrystalline materials are generally known strongly dependent on the nanoscale morphology. First principle calculations based on the density functional theory need to be employed in these atomic characterizations; however, it may not be suitable for the polycrystalline nanomaterials for which large number of atoms is required in the simulation model. Instead, a mesoscale computer simulation scheme is employed to investigate these morphology-dependent mechanical properties of polycrystalline materials. We demonstrated the Voronoi construction of various polycrystalline atomic models such as two-dimensional graphene and three-dimensional silicon carbide. General behavior of the mechanical characteristics of the bulk nanostructured silicon carbide (SiC) was addressed, particularly the contribution of grain sizes. From this study, the optimal grain size was determined near 10 nm under tensile and compressive deformations.

  5. Microstructure of TRISO Coated Particles from the AGR-1 Experiment I: SiC Grain Size and Grain Boundary Character

    SciTech Connect

    Rita Kirchhofer; John D, Hunn; Paul A. Demkowicz; James I. Cole; Brian P. Gorman

    2013-01-01

    Pre-irradiation SiC microstructures in TRISO coated fuel particles from the AGR-1 experiment were quantitatively characterized using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). From EBSD it was determined that only the cubic polymorph of as-deposited SiC was present and the SiC had a high fraction of CSL S3 grain boundaries. Additionally, the local area misorientation (LAM), which is a qualitative measurement of strain in the SiC lattice, was mapped for each fuel variant. The morphology of the SiC / IPyC interfaces were characterized by TEM following site-specific focused ion beam (FIB) specimen preparation. It was determined that the SiC layer had a heavily faulted microstructure typical of CVD deposited SiC and that the average grain diameter increased from the SiC/IPyC interface for all the fuel variants, except V3 that showed a constant grain size across the layer.

  6. Influence of grain size on ultrasonic spectral parameters in AISI type 316 stainless steel

    SciTech Connect

    Kumar, A.; Jayakumar, T.; Palanichamy, P.; Raj, B.

    1999-01-08

    The grain size of a material is an important engineering parameter which influences the mechanical properties such as fatigue, creep, yield strength, impact transition temperature, etc. The reliability of the ultrasonic methods for grain size measurement, particularly amplitude based measurements are highly dependent upon the couplant condition. Therefore, application of these methods may be difficult for some practical applications, where uniform couplant condition can not be maintained. Therefore, it would be useful if a simplified method is developed, which could be used on-line and is free from the above mentioned limitations of the other methods. The shift in the spectral peak frequency has been used for microstructural characterization in carbon steel and for evaluation of structural variations induced by tensile deformation in SUS304 stainless steel. The spectral peak frequency in SUS304 steel was found to increase with increase in the tensile elongation. This was attributed to formation and growth of martensite structures due to tensile deformation resulting in smaller crystalline grains, thus reducing the attenuation due to ultrasonic scattering. The peak frequency has also been found to shift with the change in the grain size in Inconel 600 and copper. In the present study, the shift in the spectral peak frequency and the change in full width at half maximum (FWHM) of the autopower spectrum are correlated with the grain size in AISI type 316 austenitic stainless steel, a widely used structural material in nuclear, chemical, fertilizer and many other industries.

  7. Effects of grain size on high temperature creep of fine grained, solution and dispersion hardened V -1.6Y -8W -0.8TiC

    NASA Astrophysics Data System (ADS)

    Furuno, T.; Kurishita, H.; Nagasaka, T.; Nishimura, A.; Muroga, T.; Sakamoto, T.; Kobayashi, S.; Nakai, K.; Matsuo, S.; Arakawa, H.

    2011-10-01

    Creep resistance is the major concern of vanadium and its alloys for fusion reactor structural applications. In order to elucidate the effects of grain size on the creep behavior of solution and dispersion strengthened vanadium alloys, V-1.6Y-8W-0.8TiC specimens with fine grain sizes from 0.58 to 1.45 μm were prepared by mechanical alloying and HIP without any plastic working and tested at 1073 K and 250 MPa in vacuum. It is shown that the creep resistance of V-1.6Y-8W-0.8TiC depends strongly on grain size and increases with increasing grain size: The creep life for the grain size of 1.45 μm is almost one order longer than that of 0.58 μm, and about two orders longer than that of V-4Cr-4Ti (NIFS-Heat 2) although the grain size of V-4Cr-4Ti is as large as 17.8 μm. The observed creep behavior is discussed in terms of grain size effects on dislocation glide and grain boundary sliding.

  8. A universal approximation to grain size from images of non-cohesive sediment

    USGS Publications Warehouse

    Buscombe, D.; Rubin, D.M.; Warrick, J.A.

    2010-01-01

    The two-dimensional spectral decomposition of an image of sediment provides a direct statistical estimate, grid-by-number style, of the mean of all intermediate axes of all single particles within the image. We develop and test this new method which, unlike existing techniques, requires neither image processing algorithms for detection and measurement of individual grains, nor calibration. The only information required of the operator is the spatial resolution of the image. The method is tested with images of bed sediment from nine different sedimentary environments (five beaches, three rivers, and one continental shelf), across the range 0.1 mm to 150 mm, taken in air and underwater. Each population was photographed using a different camera and lighting conditions. We term it a “universal approximation” because it has produced accurate estimates for all populations we have tested it with, without calibration. We use three approaches (theory, computational experiments, and physical experiments) to both understand and explore the sensitivities and limits of this new method. Based on 443 samples, the root-mean-squared (RMS) error between size estimates from the new method and known mean grain size (obtained from point counts on the image) was found to be ±≈16%, with a 95% probability of estimates within ±31% of the true mean grain size (measured in a linear scale). The RMS error reduces to ≈11%, with a 95% probability of estimates within ±20% of the true mean grain size if point counts from a few images are used to correct bias for a specific population of sediment images. It thus appears it is transferable between sedimentary populations with different grain size, but factors such as particle shape and packing may introduce bias which may need to be calibrated for. For the first time, an attempt has been made to mathematically relate the spatial distribution of pixel intensity within the image of sediment to the grain size.

  9. Wind tunnel calibration of the USGS dust deposition sampler: Sampling efficiency and grain size correction

    NASA Astrophysics Data System (ADS)

    Goossens, Dirk

    2010-11-01

    Wind tunnel experiments were conducted with the USGS (United States Geological Survey) dust deposition sampler to test its efficiency for dust deposition and its capacity to collect representative samples for grain size analysis. Efficiency for dust deposition was ascertained relative to a water surface, which was considered the best alternative for simulating a perfectly absorbent surface. Capacity to collect representative samples for grain size analysis was ascertained by comparing the grain size distribution of the collected dust to that of the original dust. Three versions were tested: an empty sampler, a sampler filled with glass marbles, and a sampler filled with water. Efficiencies and capacity to collect representative samples were ascertained for five wind velocities (range: 1-5 m s -1) and seven grain size classes (range: 10-80 μm). All samplers showed a rapid drop in collection efficiency with increasing wind speed. Efficiencies are low, in the order of 10% or less for most common wind speeds over the continents. Efficiency also drops as the particles become coarser. Adding glass marbles to the sampler increases its efficiency, protects the settled dust from resuspension, and minimizes outsplash during rainfall. The sediment collected by the sampler is finer than the original dust. The bias in the grain size is more expressed in fine particle fractions than in coarse particle fractions. The performance of the USGS sampler is rather low when compared to other dust deposition samplers, but a procedure is provided that allows calculation of the original grain size distribution and dust deposition quantities.

  10. Application of composite flow laws to grain size distributions derived from polar ice cores

    NASA Astrophysics Data System (ADS)

    Binder, Tobias; de Bresser, Hans; Jansen, Daniela; Weikusat, Ilka; Garbe, Christoph; Kipfstuhl, Sepp

    2014-05-01

    Apart from evaluating the crystallographic orientation, focus of microstructural analysis of natural ice during the last decades has been to create depth-profiles of mean grain size. Several ice flow models incorporated mean grain size as a variable. Although such a mean value may coincide well with the size of a large proportion of the grains, smaller/larger grains are effectively ignored. These smaller/larger grains, however, may affect the ice flow modeling. Variability in grain size is observed on centimeter, meter and kilometer scale along deep polar ice cores. Composite flow laws allow considering the effect of this variability on rheology, by weighing the contribution of grain-size-sensitive (GSS, diffusion/grain boundary sliding) and grain-size-insensitive (GSI, dislocation) creep mechanisms taking the full grain size distribution into account [1]. Extraction of hundreds of grain size distributions for different depths along an ice core has become relatively easy by automatic image processing techniques [2]. The shallow ice approximation is widely adopted in ice sheet modeling and approaches the full-Stokes solution for small ratios of vertical to horizontal characteristic dimensions. In this approximation shear stress in the vertical plain dominates the strain. This assumption is not applicable at ice divides or dome structures, where most deep ice core drilling sites are located. Within the upper two thirds of the ice column longitudinal stresses are not negligible and ice deformation is dominated by vertical strain. The Dansgaard-Johnsen model [3] predicts a dominating, constant vertical strain rate for the upper two thirds of the ice sheet, whereas in the lower ice column vertical shear becomes the main driver for ice deformation. We derived vertical strain rates from the upper NEEM ice core (North-West Greenland) and compared them to classical estimates of strain rates at the NEEM site. Assuming intervals of constant accumulation rates, we found a

  11. Eyewitness recall: Regulation of grain size and the role of confidence.

    PubMed

    Weber, Nathan; Brewer, Neil

    2008-03-01

    Eyewitness testimony plays a critical role in Western legal systems. Three experiments extended M. Goldsmith, A. Koriat, and A. Weinberg-Eliezer's (2002) framework of the regulation of grain size (precision vs. coarseness) of memory reports to eyewitness memory. In 2 experiments, the grain size of responses had a large impact on memory accuracy. Further, participants achieved a compromise between the accuracy and informativeness of their testimony by volunteering precise answers only when likely to be correct. The level of detail reported was strongly, positively related to confidence in the accuracy of the response. This highlights the importance of considering the level of detail, not just the accuracy, of eyewitness testimony. PMID:18377166

  12. Effect of grain size on the high temperature properties of B2 aluminides

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel

    1987-01-01

    Measurements of the slow plastic flow behavior of cobalt, iron and nickel B2 crystal structure aluminides were conducted on materials fabricated by metallurical techniques. Due to this processing, the aluminides invariably had small equiaxed grains, ranging in size from about 3 to 60 microns in diameter. Grain size was dependent on the extrusion temperature used for powder consolidation, and it proved to be remarkably stable at elevated temperatures. Mechanical properties of all three aluminides were determined via constant velocity compression testing in air between 1000 and 1400 K at strain rates ranging from approx. 10 to the minus 3 power to 10 to the minus 7 power s (-1).

  13. Effect of grain size of polycrystalline diamond on its heat spreading properties

    NASA Astrophysics Data System (ADS)

    Simon, Roland B.; Anaya, Julian; Faili, Firooz; Balmer, Richard; Williams, Gruffudd T.; Twitchen, Daniel J.; Kuball, Martin

    2016-06-01

    The exceptionally high thermal conductivity of polycrystalline diamond (>2000 W m-1 K-1) makes it a very attractive material for optimizing the thermal management of high-power devices. In this paper, the thermal conductivity of a diamond sample capturing grain size evolution from nucleation towards the growth surface is studied using an optimized 3ω technique. The thermal conductivity is found to decrease with decreasing grain size, which is in good agreement with theory. These results clearly reveal the minimum film thickness and polishing thickness from nucleation needed to achieve single-crystal diamond performance, and thus enable production of an optimal polycrystalline diamond for heat-spreading applications.

  14. Grain size dependency in clumped isotope ratios in high temperature calcites

    NASA Astrophysics Data System (ADS)

    Banerjee, Y.; Ghosh, P.; Misra, S.

    2013-12-01

    Here we have extended the application of clumped isotope thermometry for understanding the geospeedometers using calcite produced at high temperature and pressure. Static recrystallization experiments were conducted on cylindrical discs of AR grade carbonate with three different grain sizes (40μm, 200μm and 400μm) at constant pressure (170×5 MPa) and two different temperatures (6000×10°C and 8000×10°C) for 24 hours. The rate of temperature ramps for heating and cooling were set at 20°C/min and 60°C/min, respectively, mimicking a laboratory scale metamorphic condition of sudden burial and exhumation. The carbonate rocks, with prominent calcite mineral composition were prepared in a cylindrical capsule and were investigated for grain size distribution using Mastersizer, a laser technology to measure grain size. We identified three categories of crystals with grain size varying between 40μm, 200μm and 400μm. 15mg carbonate powder drilled from the periphery of the cylindrical discs were analysed for Clumped isotope ratio (Ghosh et al., 2006). Calcite formation experiment allowed re-crystallization of original powder produced at ambient temperature by subjecting the experimental setup to the temperatures of 800 and 600°C (Pressure was maintained constant at 170×5 MPa). We found broadly three different grain size fractions measured using in-situ laser probe. The present experiments were performed in dry environment unlike the wet high pressure experiment presented in the Passey and Henkes (2012). The present experimental value for Δ 47 was translated into absolute temperature using thermometry equation proposed by Ghosh et al., (2006). We observed a strong relationship of clumped isotopic composition with grain sizes of carbonates, which was rather inconsistent with the earlier presumption (Passey and Henkes 2012). The clumped temperature value was found matching with the true temperature in cases where grain size attained 400 micron, while finer fraction

  15. Effect of grain size on the melting point of confined thin aluminum films

    SciTech Connect

    Wejrzanowski, Tomasz; Lewandowska, Malgorzata; Sikorski, Krzysztof; Kurzydlowski, Krzysztof J.

    2014-10-28

    The melting of aluminum thin film was studied by a molecular dynamics (MD) simulation technique. The effect of the grain size and type of confinement was investigated for aluminum film with a constant thickness of 4 nm. The results show that coherent intercrystalline interface suppress the transition of solid aluminum into liquid, while free-surface gives melting point depression. The mechanism of melting of polycrystalline aluminum thin film was investigated. It was found that melting starts at grain boundaries and propagates to grain interiors. The melting point was calculated from the Lindemann index criterion, taking into account only atoms near to grain boundaries. This made it possible to extend melting point calculations to bigger grains, which require a long time (in the MD scale) to be fully molten. The results show that 4 nm thick film of aluminum melts at a temperature lower than the melting point of bulk aluminum (933 K) only when the grain size is reduced to 6 nm.

  16. Preferential cataclastic grain size reduction of feldspar in deformation bands in poorly consolidated arkosic sands

    PubMed Central

    Exner, Ulrike; Tschegg, Cornelius

    2012-01-01

    This study presents microstructural as well as bulk and mineral chemical investigations of deformation bands in uncemented, friable arkosic sands of Miocene age (Vienna Basin, Austria). Our microstructural study indicates grain size reduction by grain flaking in deformation bands with small offsets (0.5–8 cm), and dominant intragranular fracturing and cataclasis of altered feldspar grains at larger displacements (up to 60 cm). Relative to quartz, the sericitized feldspar grains are preferably fractured and abraded, which additionally leads to an enrichment of mainly phyllosilicates by mechanical expulsion from feldspar. Both cataclasis of quartz and feldspar grains and enrichment of phyllosilicates result in grain size reduction within the deformation bands. The measured reduction in porosity of up to 20% is in some cases associated with a permeability reduction, reflected in the retention of iron-oxide rich fluids along deformation bands. These deformation bands formed at very shallow burial depths in unconsolidated sediments indicate that fault sealing may occur in the absence of chemical alteration of the deformation bands and lead to a compartmentalization of a groundwater or hydrocarbon reservoir. PMID:26523078

  17. Preferential cataclastic grain size reduction of feldspar in deformation bands in poorly consolidated arkosic sands

    NASA Astrophysics Data System (ADS)

    Exner, Ulrike; Tschegg, Cornelius

    2012-10-01

    This study presents microstructural as well as bulk and mineral chemical investigations of deformation bands in uncemented, friable arkosic sands of Miocene age (Vienna Basin, Austria). Our microstructural study indicates grain size reduction by grain flaking in deformation bands with small offsets (0.5-8 cm), and dominant intragranular fracturing and cataclasis of altered feldspar grains at larger displacements (up to 60 cm). Relative to quartz, the sericitized feldspar grains are preferably fractured and abraded, which additionally leads to an enrichment of mainly phyllosilicates by mechanical expulsion from feldspar. Both cataclasis of quartz and feldspar grains and enrichment of phyllosilicates result in grain size reduction within the deformation bands. The measured reduction in porosity of up to 20% is in some cases associated with a permeability reduction, reflected in the retention of iron-oxide rich fluids along deformation bands. These deformation bands formed at very shallow burial depths in unconsolidated sediments indicate that fault sealing may occur in the absence of chemical alteration of the deformation bands and lead to a compartmentalization of a groundwater or hydrocarbon reservoir.

  18. Laboratory Experiments on Rotation of Micron Size Cosmic Dust Grains with Radiation

    NASA Technical Reports Server (NTRS)

    Abbas, M. M.; Craven, P. D.; Spann, J. F.; Tankosic, D.; LeClair, A.; Gallagher, D. L.; West, E.; Weingartner, J.; Witherow, W. K.

    2004-01-01

    The processes and mechanisms involved in the rotation and alignment of interstellar dust grains have been of great interest in astrophysics ever since the surprising discovery of the polarization of starlight more than half a century ago. Numerous theories, detailed mathematical models and numerical studies of grain rotation and alignment along the Galactic magnetic field have been presented in the literature. In particular, the subject of grain rotation and alignment by radiative torques has been shown to be of particular interest in recent years. However, despite many investigations, a satisfactory theoretical understanding of the processes involved in grain rotation and alignment has not been achieved. As there appears to be no experimental data available on this subject, we have carried out some unique experiments to illuminate the processes involved in rotation of dust grains in the interstellar medium. In this paper we present the results of some preliminary laboratory experiments on the rotation of individual micron/submicron size nonspherical dust grains levitated in an electrodynamic balance evacuated to pressures of approx. 10(exp -3) to 10(exp -5) torr. The particles are illuminated by laser light at 5320 A, and the grain rotation rates are obtained by analyzing the low frequency (approx. 0-100 kHz) signal of the scattered light detected by a photodiode detector. The rotation rates are compared with simple theoretical models to retrieve some basic rotational parameters. The results are examined in the light of the current theories of alignment.

  19. Relationship between ferromagnetic properties and grain size of Inconel alloy 600

    NASA Astrophysics Data System (ADS)

    Kikuchi, H.; Takahashi, H.; Yanagiwara, H.; Murakami, T.

    2015-05-01

    Inconel alloy 600 is widely used in steam generator tubings where sensitization due to chromium depletion occurs at grain boundaries and the sensitization induces tubing failures. Though the alloy usually exhibits paramagnetic properties, it shows ferromagnetic properties along grain boundaries when chromium depletion occurs. This means that magnetic nondestructive evaluation of sensitization is possible. Therefore, as a fundamental study to develop magnetic nondestructive evaluation technique for sensitization, the relationship between ferromagnetic properties and grain size in Inconel 600 was investigated using isothermal heat treatment. The grain was controlled using solution annealing, and then, specimens were heat treated at 873, 923, and 973 K within 400 h. The saturation magnetization increases as heat treatment time increases and eventually peaks. The peak time depends on the heat treatment temperature. The coercivity increases during the initial heat treatment stage, and decreases as the duration of heat treatment increases. The maximum saturation magnetization decreases as the grain diameter increases and is inversely proportional to the grain diameter squared, which is consistent with the fact that the ferromagnetic phase only formed along grain boundaries.

  20. Optimal reproduction in salmon spawning substrates linked to grain size and fish length

    NASA Astrophysics Data System (ADS)

    Riebe, Clifford S.; Sklar, Leonard S.; Overstreet, Brandon T.; Wooster, John K.

    2014-02-01

    Millions of dollars are spent annually on revitalizing salmon spawning in riverbeds where redd building by female salmon is inhibited by sediment that is too big for fish to move. Yet the conditions necessary for productive spawning remain unclear. There is no gauge for quantifying how grain size influences the reproductive potential of coarse-bedded rivers. Hence, managers lack a quantitative basis for optimizing spawning habitat restoration for reproductive value. To overcome this limitation, we studied spawning by Chinook, sockeye, and pink salmon (Oncorhynchus tshawytscha, O. nerka, and O. gorbuscha) in creeks and rivers of California and the Pacific Northwest. Our analysis shows that coarse substrates have been substantially undervalued as spawning habitat in previous work. We present a field-calibrated approach for estimating the number of redds and eggs a substrate can accommodate from measurements of grain size and fish length. Bigger fish can move larger sediment and thus use more riverbed area for spawning. They also tend to have higher fecundity, and so can deposit more eggs per redd. However, because redd area increases with fish length, the number of eggs a substrate can accommodate is maximized for moderate-sized fish. This previously unrecognized tradeoff raises the possibility that differences in grain size help regulate river-to-river differences in salmon size. Thus, population diversity and species resilience may be linked to lithologic, geomorphic, and climatic factors that determine grain size in rivers. Our approach provides a tool for managing grain-size distributions in support of optimal reproductive potential and species resilience.

  1. Automatic River Bed Grain Size Measurement Using Image Processing and Support Vector Machines

    NASA Astrophysics Data System (ADS)

    Bellugi, D.; Nelson, P. A.; Dietrich, W. E.

    2010-12-01

    Gravel-bedded rivers cut through hilly and mountainous areas, driving landscape evolution and creating a diverse habitat upon which river food web ecosystems develop. Our understanding of the mechanics underlying important processes in fluvial geomorphology, hydrodynamics, and aquatic ecology inevitably requires knowledge about the grain size distribution of river bed material. Standard methods of sampling bed surface material may introduce errors due to biases and inadequate sample size. Alternative areal or volumetric sampling procedures are often impractical, particularly in coarse channel beds. Furthermore, all invasive sampling techniques can compromise laboratory flume experiments. These concerns suggest that there is a practical need for a reliable, automated, non-invasive procedure for obtaining the grain size distribution of bed surface material. Although considerable effort has been made to automatically generate grain size distributions using image processing and analysis techniques, the problem remains quite challenging: issues such as varying lighting conditions, partial immersion of particles in water, and heterogeneous mineralogy result in ambiguities that cannot be easily resolved. Feature extraction introduces further biases due to over- or under-segmentation of the image. Moreover, unless the grain distributions are fairly homogeneous between different locations, and images are collected in similar fashion, it is difficult to parametrize any such method in a transferable manner. In this study we present an image processing and machine learning procedure to automatically identify and measure grains from photographic images of gravel-bedded rivers. We apply the state-of-the-art of image segmentation techniques, making use of local cues such as brightness, color, and texture in a multi-scale approach. These cues are globalized using a graph partitioning method on the oriented contour signal. The resulting boundary probability signal is treated by a

  2. Sintering Trajectories: Description on How Density, Surface Area, and Grain Size Change

    NASA Astrophysics Data System (ADS)

    German, Randall M.

    2016-03-01

    Sintering is a mainstay production step in forming metal, ceramic, polymer, and composite components from particles. Since the 1940s, the sintering process is treated using a matrix of mathematical relationships that include at least seven atomic transport mechanisms, several options on powder characteristics, and three pore-grain morphology options. The interplay of these relationships is handled by numerical solutions to predict property development. An alternative approach is to track the sintering trajectory using relatively simple relationships based on bulk measures. Energy minimization dictates that initial stage sintering acts to reduce surface area. In late stage sintering, the energy minimization turns to grain boundary area reduction via grain growth. Accordingly, relationships result between density, surface area, and grain size, which largely ignore mechanistic details. These relationships are applicable to a wide variety of materials and consolidation conditions, including hot pressing, and spark sintering.

  3. The effect of bleaching on toothbrush abrasion of resin composites

    PubMed Central

    Hajizadeh, Hila; Ameri, Hamideh; Eslami, Samaneh; Mirzaeepoor, Behnam

    2013-01-01

    Aim: This experimental study was designed to focus on the effects of bleaching on toothbrush abrasion in three types of composites with different filler size. Materials and Methods: Forty eight disks were prepared from three types of composite and divided into 6 groups. In the first three groups the abrasion test was done. The remaining groups were bleached and the abrasion test was performed. The weight of the samples before and after abrasion was measured. Statistical analysis was done with one-way ANOVA and Duncan test. Results: There was a significant difference in abrasion of composites with different filler size (P < 0.05). The most amount of abrasion was observed in Z100 after being bleached. An increase in abrasion was noticed in all three types of tested composite after bleaching. Conclusion: According to the findings, it is suggested to use a nano filled resin composite for restoration if the bleaching treatment is required. PMID:23349570

  4. The Effect of Fuel Grain Size on the Combustion Characteristics in the Primary Combustion Chamber of Staged Combustion Hybrid Rocket

    NASA Astrophysics Data System (ADS)

    Nagata, Harunori; Hashiba, Kenta; Sakai, Hiroya; Totani, Tsuyoshi; Wakita, Masashi

    To clarify the fuel gasification characteristics in a primary combustion chamber of a staged combustion hybrid rocket, the effect of fuel grain size on the regression rate of a grain was investigated experimentally. The grain size distribution in the combustion region achieved a steady state in 30 seconds burning duration. Examining fuel size distributions and fuel consumption rate at steady states, we obtained a history of fuel size and the regression rate of a grain in the combustion region. Regression rate increases with decreasing grain size. With a constant oxidizer flow rate, the regression rate is a function of grain size and independent to the initial grain size. After an initial transient the grain size decreases following the classical d-square law in droplet combustion: The square of the grain size decreases linearly with time. Although why the regression history of a grain in the combustion region follows the d-square law is not clear, this result is useful to estimate the fuel gasification rate of a staged combustion hybrid rocket.

  5. EPR investigation of UV light effect on calcium carbonate powders with different grain sizes.

    PubMed

    Kabacińska, Zuzanna; Krzyminiewski, Ryszard; Dobosz, Bernadeta

    2014-06-01

    This study is based on investigation of calcium carbonate powders with different grain sizes exposed to UV light. Calcium carbonate is widely used in many branches of industry, e.g. as a filler for polymer materials; therefore, knowing its properties, among them also its reaction to UV light, is essential. Samples of powdered calcium carbonate with average grain sizes of 69 and 300 nm and 2.1, 6, 16, 25 µm were used in this investigation. Measurements were performed at room temperature using EPR X-band spectrometer, and they have shown the additional signals induced by the light from Hg lamp. The effect of annealing of the micro-grain samples was also studied. The spectra of four micro-grain samples after irradiation are similar, but there are differences between them and the other two powders, which could be related to the different sizes of their grains. Further studies based on these preliminary results may prove useful in research of photodegradation of CaCO3-filled materials, as well as helpful in increasing the accuracy of dating of archaeological and geological objects.

  6. Mechanical spectroscopy of nanocrystalline aluminum films: effects of frequency and grain size on internal friction.

    PubMed

    Sosale, Guruprasad; Almecija, Dorothée; Das, Kaushik; Vengallatore, Srikar

    2012-04-20

    Energy dissipation by internal friction is a property of fundamental interest for probing the effects of scale on mechanical behavior in nanocrystalline metallic films and for guiding the use of these materials in the design of high-Q micro/nanomechanical resonators. This paper describes an experimental study to measure the effects of frequency, annealing and grain size on internal friction at room temperature in sputter-deposited nanocrystalline aluminum films with thicknesses ranging from 60 to 120 nm. Internal friction was measured using a single-crystal silicon microcantilever platform that calibrates dissipation against the fundamental limits of thermoelastic damping. Internal friction was a weak function of frequency, reducing only by a factor of two over three decades of frequency (70 Hz to 44 kHz). Annealing led to significant grain growth and the average grain size of 100 nm thick films increased from 90 to 390 nm after annealing for 1 h at 450 (∘)C. This increase in grain size was accompanied by a decrease in internal friction from 0.05 to 0.02. Taken together, these results suggest that grain-boundary sliding, characterized by a spectrum of relaxation times, contributes to internal friction in these films. PMID:22436133

  7. Physical conditions in three high-z H2-bearing DLAs: implications for grain size

    NASA Astrophysics Data System (ADS)

    Shaw, Gargi; Rawlins, Katherine; Srianand, Raghunathan

    2016-07-01

    We present results of our numerical simulation of three H2-bearing damped Lyman α absorbers (DLAs) in the redshift interval ˜ 2-3. The systems we have modelled are the DLAs at zabs = 2.3377 towards the quasar LBQS 1232 + 0815, at zabs = 2.418 37 towards SDSS J143912.04 + 111740.5 and at zabs = 2.6265 towards FBQS J081240.6 + 320808. We have used the spectral synthesis code CLOUDY to simulate the physical environment of these DLAs, and constrain the density, radiation field, geometry and dust-grain properties of the DLAs self-consistently based on the observed column densities of various atomic and molecular species such as H I, fine structure lines of C I and the rotational level population of H2. In our models, we explore the effect of grain size distribution on the predicted column densities of different species. Within the allowed uncertainties in the inferred dust-to-gas ratio, both models with standard interstellar medium grains and smaller sized grains reproduce the observations equally well. Improved constraints on dust-to-gas ratio and line-of-sight extinction are important for probing the grain size distribution in high-z DLAs. We find the H2-bearing clouds to have line-of-sight thickness in the range 1-6 pc, consistent with what has been found using partial coverage or 21-cm observations in some high-z DLAs.

  8. Cleaning power and abrasivity of European toothpastes.

    PubMed

    Wülknitz, P

    1997-11-01

    For 41 toothpastes available to European consumers in 1995, the cleaning efficacy was evaluated in comparison with abrasivity on dentin (RDA value). For cleaning power assessment, a modified pellicle cleaning ratio (PCR) measurement method was developed. The method is characterized by a five-day tea-staining procedure on bovine front teeth slabs on a rotating wheel, standardized brushing of the slabs in a V8 cross-brushing machine, and brightness measurement by a chromametric technique. All tested products were in accordance with the new DIN/ISO standard 11,609 for toothpastes in terms of dentin abrasivity. Not a single product exceeded an RDA value of 200. The majority of toothpastes (80%) had an RDA value below 100. Only three products surpassed the reference in cleaning power. Most products (73%) had a cleaning power (PCR value) between 20 and 80. The correlation between cleaning power and dentin abrasion was low (r = 0.66), which can be explained with the different influence on dentin and stains by factors like abrasive type, particle surface and size, as well as the chemical influence of other toothpaste ingredients. Some major trends could be shown on the basis of abrasive types. The ratio PCR to RDA was rather good in most silica-based toothpastes. A lower ratio was found in some products containing calcium carbonate or aluminum trihydrate as the only abrasive. The addition of other abrasives, such as polishing alumina, showed improved cleaning power. Some active ingredients, especially sequenstrants such as sodium tripolyphosphate or AHBP, also improve the PCR/RDA ratio by stain-dissolving action without being abrasive. The data for some special anti-stain products did not differ significantly from standard products. Compared with data measured in 1988, a general trend toward reduced abrasivity without loss of cleaning efficacy could be noticed on the European toothpaste market. This may be mostly due to the increased use of high-performance abrasives such

  9. Space Weathering of Intermediate-Size Soil Grains in Immature Apollo 17 Soil 71061

    NASA Technical Reports Server (NTRS)

    Wentworth, S. J.; Robinson, G. A.; McKay, D. S.

    2005-01-01

    Understanding space weathering, which is caused by micrometeorite impacts, implantation of solar wind gases, radiation damage, chemical effects from solar particles and cosmic rays, interactions with the lunar atmosphere, and sputter erosion and deposition, continues to be a primary objective of lunar sample research. Electron beam studies of space weathering have focused on space weathering effects on individual glasses and minerals from the finest size fractions of lunar soils [1] and patinas on lunar rocks [2]. We are beginning a new study of space weathering of intermediate-size individual mineral grains from lunar soils. For this initial work, we chose an immature soil (see below) in order to maximize the probability that some individual grains are relatively unweathered. The likelihood of identifying a range of relatively unweathered grains in a mature soil is low, and we plan to study grains ranging from pristine to highly weathered in order to determine the progression of space weathering. Future studies will include grains from mature soils. We are currently in the process of documenting splash glass, glass pancakes, craters, and accretionary particles (glass and mineral grains) on plagioclase from our chosen soil using high-resolution field emission scanning electron microscopy (FESEM). These studies are being done concurrently with our studies of patinas on larger lunar rocks [e.g., 3]. One of our major goals is to correlate the evidence for space weathering observed in studies of the surfaces of samples with the evidence demonstrated at higher resolution (TEM) using cross-sections of samples. For example, TEM studies verified the existence of vapor deposits on soil grains [1]; we do not yet know if they can be readily distinguished by surfaces studies of samples. A wide range of textures of rims on soil grains is also clear in TEM [1]; might it be possible to correlate them with specific characteristics of weathering features seen in SEM?

  10. Geochemistry of grain-size fractions of soils from the Taurus-Littrow valley floor

    NASA Technical Reports Server (NTRS)

    Korotev, R. L.

    1976-01-01

    Results are presented for a study in which high-precision instrumental neutron activation analysis was applied to determine the abundances of seven rare-earth and nine other elements in two grain-size fractions (90 to 150 microns and less than 20 microns) of eight soils from the Taurus-Littrow Valley floor and one Apollo 11 bulk-soil fraction with grain sizes of less than 1 mm. Compositional differences between the two size fractions of two valley-floor soils are examined, and mixing of soil components is investigated. It is found that a five-component mixing model describes very adequately the chemical composition of bulk soils with grain sizes of less than 1 mm as mixtures of local Apollo 17 rock types (basalt, anorthositic gabbro, noritic breccia), orange glass, and meteorites, but does not describe well the chemical compositions of the other two size fractions. A ten-component model is used to show that the compositions of those two size fractions can be well represented as mixtures of the five components if the mineralogy and chemical composition of the basalt component are allowed to vary in the size fractions.

  11. A model for estimating the hydraulic conductivity of granular material based on grain shape, grain size, and porosity

    SciTech Connect

    Sperry, J.M.; Peirce, J.J.

    1995-11-01

    Particle shape is an important parameter in numerous civil, environmental, and petroleum engineering applications. In ground-water flow, the shape of individual particles comprising the soil affects the soil`s pore size distribution and, hence, the important flow characteristics such as hydraulic conductivity and headloss. A model for delineating the relative importance of particle size, particle shape, and porosity, (and their interactions), in explaining the variability of hydraulic conductivity of a granular porous medium is developed and tested. Three types of porous media are considered in this work: spherical glass beads; granular sand; and irregularly shaped, shredded glass particles. A reliable method for quantifying the three-dimensional shape and packing of large samples of irregular particles based on their angle of repose is presented. The results of column experiments indicate that in the size range examined (i.e., 149 {micro}m to 2,380 {micro}m), the single most important predictor of hydraulic conductivity is seen to be particle size, explaining 69% of the variability. Porous media comprising irregular particles exhibit lower hydraulic conductivity only for the larger (707 to 841 {micro}m) particles. For the smaller (149 to 177 {micro}m) particles, particle shape has no observable influence on hydraulic conductivity. The results of the regression analysis reveal the importance off the interaction between particle size and porosity, indicating that similar pore configurations for a given type of particle are not achieved at different sizes. This empirical model seems to provide better estimates of the hydraulic conductivity of granular porous media comprising irregular particles than selected models based solely on grain size, including Hazen, Kozeny-Carman, and more recently Alyamani and Sen.

  12. Abrasives in snuff?

    PubMed

    Dahl, B L; Stølen, S O; Oilo, G

    1989-08-01

    The purpose of this study was to determine and calculate the inorganic contents of four brands of snuff. Visual inspection of wet snuff showed fairly large, yellow crystal-like particles. Scanning electron microscopy and X-ray dispersive (EDX) analyses were used to study both wet snuff and ashes of snuff, whereas light emission spectrography was used to determine elements in the ashes. The crystal-like particles did not dissolve in distilled water or in ethanol heated to 60 degrees C. EDX analyses showed that most elements remained in the particles after washing. The total weight percentage of inorganic material in snuff was calculated after burning dried snuff until constant weight was obtained. The ashes of snuff did not contain any crystal-like particles but consisted of a small-grained amorphous mass. The following elements were detected: Ag, Al, Ba, Ca, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, P, Pb, Si, Sr, Ti, Va, and Zr. Other elements such as rare earths were not searched for. The weight percentage of inorganic elements ranged between 12.35 +/- 0.69 and 20.95 +/- 0.81. Provided snuff is used in the same manner as chewing tobacco, and some people admit to doing so, there is a risk that its relatively high contents of inorganic material and heavily soluble salts may be conducive to excessive abrasion of teeth and restorations. PMID:2782061

  13. The ubiquity of micrometer-sized dust grains in the dense interstellar medium.

    PubMed

    Pagani, Laurent; Steinacker, Jürgen; Bacmann, Aurore; Stutz, Amelia; Henning, Thomas

    2010-09-24

    Cold molecular clouds are the birthplaces of stars and planets, where dense cores of gas collapse to form protostars. The dust mixed in these clouds is thought to be made of grains of an average size of 0.1 micrometer. We report the widespread detection of the coreshine effect as a direct sign of the existence of grown, micrometer-sized dust grains. This effect is seen in half of the cores we have analyzed in our survey, spanning all Galactic longitudes, and is dominated by changes in the internal properties and local environment of the cores, implying that the coreshine effect can be used to constrain fundamental core properties such as the three-dimensional density structure and ages and also the grain characteristics themselves.

  14. Frost grain size metamorphism - Implications for remote sensing of planetary surfaces

    NASA Technical Reports Server (NTRS)

    Clark, R. N.; Fanale, F. P.; Zent, A. P.

    1983-01-01

    The effective grain size of a material on a planetary surface affects the strength of absorption features observed in the reflectance of a particulate surface. In the case of a planetary surface containing volatile ices, the absorption characteristics can change in connection with processes leading to a change in the grain size of the material. The present investigation is concerned with an evaluation regarding the occurrence of such processes and the implications for remote sensing applications. It is found that quantitative modeling of the kinetics of grain growth and destruction by thermal and nonthermal processes can provide a means to reconcile apparent optical paths in the volatile portions of planetary surfaces with the physical history of those surfaces. Attention is also given to conditions in the case of the Pluto/Triton system, Uranus and Saturnian satellites, and the Galilean system.

  15. Influence of Processing Parameters on Grain Size Evolution of a Forged Superalloy

    NASA Astrophysics Data System (ADS)

    Reyes, L. A.; Páramo, P.; Salas Zamarripa, A.; de la Garza, M.; Guerrero-Mata, M. P.

    2016-01-01

    The microstructure evolution of nickel-based superalloys has a great influence on the mechanical behavior during service conditions. Microstructure modification and the effect of process variables such as forging temperature, die-speed, and tool heating were evaluated after hot die forging of a heat-resistant nickel-based alloy. Forging sequences in a temperature range from 1253 to 1323 K were considered through experimental trials. An Avrami model was applied using finite element data to evaluate the average grain size and recrystallization at different evolution zones. It was observed that sequential forging at final temperatures below 1273 K provided greater grain refinement through time-dependent recrystallization phenomena. This investigation was aim to explore the influence of forging parameters on grain size evolution in order to design a fully homogenous and refined microstructure after hot die forging.

  16. Influence of precipitate size and morphology on grain refinement in nickel aluminium bronze

    NASA Astrophysics Data System (ADS)

    Barr, C. J.; Xia, K.

    2015-08-01

    Nickel aluminium bronze (NAB) was subjected to equal channel angular pressing (ECAP) using routes BA and C at 400°C to investigate the effect of precipitate size and morphology on grain refinement in low stacking fault energy alloys. Both routes produced dynamically recrystallised grains of ∼550 nm in size although only route BA was able to create a uniform distribution of the refined grains. The large unrefined regions in NAB processed via route C was thought to arise from its inability to redistribute the various precipitate phases, as recrystallisation was enhanced around the coarse κII rosettes and refined κIII lamellae but reduced in the areas containing fine κIV precipitates.

  17. The Smallest Lunar Grains: Analytical TEM Characterization of the Sub-micron Size Fraction of a Mare Soil

    NASA Technical Reports Server (NTRS)

    Thompson, M.; Christoffersen, R.

    2010-01-01

    The chemical composition, mineralogical type, and morphology of lunar regolith grains changes considerably with decreasing size, and below the approx.25 m size range the correlation between these parameters and remotely-sensed lunar surface properties connected to space weathering increases significantly. Although trends for these parameters across grain size intervals greater than 20 m are now well established, the 0 to 20 m size interval remains relatively un-subdivided with respect to variations in grain modal composition, chemistry and microstructure. Of particular interest in this size range are grains in the approximate < 1 m diameter class, whose fundamental properties are now the focus of lunar research pertaining to electrostatic grain transport, dusty plasmas, and lunar dust effects on crew health and exploration systems. In this study we have used analytical transmission electron microscopy (TEM) to characterize the mineralogy, microstructure and major element composition of grains below the 1 m size threshold in lunar soil 10084.

  18. Grain-Size Effects on Field Capacity of Soil-Biochar Mixtures

    NASA Astrophysics Data System (ADS)

    Liu, Z.; Dugan, B.; Masiello, C. A.; Gonnermann, H. M.

    2014-12-01

    While it is known that under some circumstances amending soil with biochar improves soil hydrologic properties, the mechanisms driving these improvements are not well-understood. This is a serious gap: without mechanism understanding, it is much harder to predict when biochar will improve soil properties. Grain size likely plays a key role in controlling biochar effects on water movement and storage, because grain size (of both biochar and soils) plays a major role in soil porosity. Here we report water potential of soil-biochar mixtures in the context of grain size and porosity measurements to better understand the mechanisms controlling how pores in biochar and soil store water. Our soil-biochar mixtures are sand (0.251-0.853 mm) with 2 wt% biochar; we used two separate biochar grain size ranges. Comparison of pure sand with biochar+sand mixtures shows a field capacity (θfc, water content at soil water potential = 33 kPa) increase from 0.014 to 0.027 kgwater/kgsoil+water (increase of 93%) when biochar is 0.251-0.853 mm (same size as sand) and a field capacity increase from 0.014 to 0.032 kgwater/kgsoil+water (increase of 129%) when biochar is 0.853-2.00 mm (larger than sand). Thus when biochar is larger than sand, θfc of biochar+sand mixtures (0.032 kgwater/kgsoil+water) is higher than θfc of biochar+sand mixtures (0.027 kgwater/kgsoil+water) when biochar is the same size as sand. Biochar+sand mixtures have interporosity (porosity between grains) and intraporosity (pores inside biochar particles). The average intraporosity of our biochars is 0.61±0.01 (61±1% of the biochar volume is pore space). Based our results we interpret that this intraporosity can store water and drives the increase of θfc for biochar-amended sand. Field capacity also increases with pore size decreases because smaller pores tend to hold water tightly due to higher capillary forces. The increase of θfc with increased biochar grain size may be caused by the bimodal particle size

  19. Luminescence dating of glacial deposits near the eastern Himalayan syntaxis using different grain-size fractions

    NASA Astrophysics Data System (ADS)

    Hu, Gang; Yi, Chao-Lu; Zhang, Jia-Fu; Liu, Jin-Hua; Jiang, Tao

    2015-09-01

    Numerical dating of glacial deposits is important for understanding Quaternary glacial evolution. Optically stimulated luminescence (OSL) dating is one of the techniques widely used on such sediments. Owing to the short distances traveled before deposition, the incomplete bleaching of luminescence signals in glacial sediments may introduce serious dating problems vis-à-vis glacial and any associated sediments. Here, we report a comparison of OSL ages obtained from the fine (4-11 μm) and medium (38-63 μm) grain size fractions of quartz extracted from glaciofluvial sediments and from glacial tills in the Basongcuo catchment near the eastern Himalayan syntaxis. Initially, four glacial stages were identified based on field observations of moraine distribution and geomorpho-stratigraphic relations. A total of 39 OSL samples were then collected from glaciofluvial sand layers or lenses and from till. Quartz grains in the fine (4-11 μm) and medium (38-63 μm) size fractions were extracted from each sample, and dated using the single-aliquot regeneration (SAR) protocol. The modern supraglacial sediment sample was dated to ˜0.2 (fine grain) to ˜0.7 (medium grain) ka, suggesting that the sediment was not completely bleached on deposition. Contrary to previous experience suggesting that coarse grains are usually better bleached than fine grains prior to deposition, our results show that estimated OSL ages for fine grains are generally younger than those for medium grains. This suggests that the two fractions may have come from different sources and thus have different bleaching histories, and that fine-grained quartz may be more suitable for OSL dating of these materials. Applying the minimum age model to data from medium-grained quartz yields ages close to those obtained from fine-grained quartz, suggesting that both can be used for dating glacial advances. The OSL dates suggest that glaciers in the studied area advanced at 0.1-1.3 ka, ˜7.5 ka and 11-13 ka, and were

  20. H2O grain size and the amount of dust in Mars' residual North polar cap

    USGS Publications Warehouse

    Kieffer, H.H.

    1990-01-01

    In Mars' north polar cap the probable composition of material residual from the annual condensation cycle is a mixture of fine dust and H2O grains of comparable size and abundance. However, metamorphism of such material will gradually lower its albedo by increasing the size of the H2O grains only. If the cap is undergoing net annual sublimation (as inferred from water vapor observations), late summer observations should be of old ice with H2O grain sizes of 100 ??m or more. Ice of this granularity containing 30% fine dust has a reflectivity similar to that of dust alone; the observed albedo and computed ice grain size imply dust concentrations of 1 part per 1000 or less. The brightness of the icy areas conflicts with what would be expected for a residual cap deposited by an annual cycle similar to that observed by Viking and aged for thousands of years. The residual cap surface cannot be "old dirty' ice. It could be old, coarse, and clean; or it could be young, fine, and dirty. This brings into question both the source of the late summer water vapor and the formation rate of laminated terrain. -Author

  1. TOC as a regional sediment condition indicator: Parsing effects of grain size and organic content

    EPA Science Inventory

    TOC content of sediments is often used as an indicator of benthic condition. Percent TOC is generally positively correlated with sediment percent fines. While sediment grain size may have impacts on benthic organisms independent of organic content, it is often not explicitly co...

  2. TOC as a regional sediment conditionindicator: Parsing effects of grain size and organic content

    EPA Science Inventory

    TOC content of sediments is often used as an indicator of benthic condition. Percent TOC is generally positively correlated with sediment percent fines. While sediment grain size may have impacts on benthic organisms independent of organic content, it is often not explicitly co...

  3. Agriproteomics of Bread Wheat: Comparative Proteomics and Network Analyses of Grain Size Variation.

    PubMed

    Dawkar, Vishal V; Dholakia, Bhushan B; Gupta, Vidya S

    2015-07-01

    Agriproteomics signifies the merging of agriculture research and proteomics systems science and is impacting plant research and societal development. Wheat is a frequently consumed foodstuff, has highly variable grain size that in effect contributes to wheat grain yield and the end-product quality. Very limited information is available on molecular basis of grain size due to complex multifactorial nature of this trait. Here, using liquid chromatography-mass spectrometry, we investigated the proteomics profiles from grains of wheat genotypes, Rye selection 111 (RS111) and Chinese spring (CS), which differ in their size. Significant differences in protein expression were found, including 33 proteins uniquely present in RS111 and 32 only in CS, while 54 proteins were expressed from both genotypes. Among differentially expressed proteins, 22 were upregulated, while 21 proteins were downregulated in RS111 compared to CS. Functional classification revealed their role in energy metabolism, seed storage, stress tolerance and transcription. Further, protein interactive network analysis was performed to predict the targets of identified proteins. Significantly different interactions patterns were observed between these genotypes with detection of proteins such as Cyp450, Sus2, and WRKY that could potentially affect seed size. The present study illustrates the potentials of agriproteomics as a veritable new frontier of plant omics research.

  4. Subpixel Snow-Covered-Area and Snow Grain Size From Mixture Analysis with AVIRIS Data

    NASA Technical Reports Server (NTRS)

    Green Robert O.; Painter, Thomas H.; Roberts, Dar A.; Dozier, Jeff

    1996-01-01

    Snow-covered-area (SCA) and snow grain size are crucial inputs to hydrologic and climatologic modeling of alpine and other seasonally snow-covered regions. SCA is necessary to parameterize energy budget calculations in climate models, to determine in which regions point snowmelt models are to be run for distributed snowmelt modeling efforts and to provide a basis from which estimates of snow water equivalent (SWE) may be made. Snow grain size, SWE and snow impurities determine the spectral albedo of snow, which controls the net solar flux at the snowpack surface. Snow albedo is of the utmost importance in snowmelt modeling, yet the difficulty with which grain size, SWE, and impurities are mapped has left the spatial distribution of snow albedo in alpine catchments poorly understood. The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) has been used to estimate sub-pixel snow-covered-area and snow grain size independently. In this paper we present a technique which improves estimates of both snow parameters by treating their mapping simultaneously.

  5. Agriproteomics of Bread Wheat: Comparative Proteomics and Network Analyses of Grain Size Variation.

    PubMed

    Dawkar, Vishal V; Dholakia, Bhushan B; Gupta, Vidya S

    2015-07-01

    Agriproteomics signifies the merging of agriculture research and proteomics systems science and is impacting plant research and societal development. Wheat is a frequently consumed foodstuff, has highly variable grain size that in effect contributes to wheat grain yield and the end-product quality. Very limited information is available on molecular basis of grain size due to complex multifactorial nature of this trait. Here, using liquid chromatography-mass spectrometry, we investigated the proteomics profiles from grains of wheat genotypes, Rye selection 111 (RS111) and Chinese spring (CS), which differ in their size. Significant differences in protein expression were found, including 33 proteins uniquely present in RS111 and 32 only in CS, while 54 proteins were expressed from both genotypes. Among differentially expressed proteins, 22 were upregulated, while 21 proteins were downregulated in RS111 compared to CS. Functional classification revealed their role in energy metabolism, seed storage, stress tolerance and transcription. Further, protein interactive network analysis was performed to predict the targets of identified proteins. Significantly different interactions patterns were observed between these genotypes with detection of proteins such as Cyp450, Sus2, and WRKY that could potentially affect seed size. The present study illustrates the potentials of agriproteomics as a veritable new frontier of plant omics research. PMID:26134253

  6. Effect of grain size on thermal shock property of alumina ceramic

    NASA Astrophysics Data System (ADS)

    Xu, Xianghong; Sheng, Shilong; Yuan, Wenjun; Lin, Zhongkang

    2016-04-01

    Ceramic has a great broad application in high-temperature environment due to its favorable mechanical, antioxidant and corrosion resistance properties. However, it tends to exhibit severe crack or fail under thermal shock resulting from its inherent brittleness. Microstructure property is a vital factor and plays a critical role in influencing thermal shock property of ceramic. The present study experimentally tested and characterized thermal-shock crack and residual strength of ceramic under different quench temperature, while two kinds of alumina ceramics with different grain size are employed. A two-dimensional (2D) numerical model based on statistical mesoscopic damage mechanics is introduced to depict the micro-crack propagation of ceramic sheet under water quenching. The effects of grain size on critical thermal shock temperature, crack characteristics and residual strength are studied. And the microscopic mechanism of the influence of grain size on thermal shock resistance of ceramic is discussed based on the crack propagation path obtained from experimental and simulation results. The qualitative effect and evolution change of grain size on thermal shock property of alumina ceramic will be summarized.

  7. Effect Of Grain Size-Distribution And Nonthermal Ion Distribution On Dust Acoustic Solitons

    SciTech Connect

    Annou, K.; Annou, R.

    2005-10-31

    The investigation of the formation of non-linear coherent structures in dusty plasmas taking into account the dust size and non-thermal ion distributions is conducted. Conditions of the existence of solitons in terms of the Mach number, concentration of non-thermal ions, dust charge and the permeability of the grains are evaluated.

  8. Discrimination of sediment provenance in the Yellow Sea: Secondary grain-size effect and REE proxy

    NASA Astrophysics Data System (ADS)

    Jung, Hoi-Soo; Lim, Dhongil; Jeong, Do-Hyun; Xu, Zhaokai; Li, Tiegang

    2016-06-01

    This study analyzed grain size and elemental concentrations (Al, Mg, Fe, and rare earth elements (REEs)) in 91 surface sediments to elucidate sediment provenance in the Yellow Sea. Elemental concentrations were normalized by Al concentration (Celement/CAl) to minimize the sediment grain-size effect (GSE). However, noticeable linear relationships between Al concentration (or mean grain size) and the ratio (e.g., Mg/Al or Fe/Al) appeared unexpectedly in pair diagrams. The spatial distribution patterns of Fe/Al and Mg/Al ratios were also similar to the pattern of mean grain size. This implies that the GSE was not removed completely, even after the normalization process. Thus, great care must be taken when applying the ratios of Celement/CAl as a proxy of sediment provenance. To improve provenance discrimination of the sediments in the Yellow Sea, the difference between the REE distribution patterns of Chinese and Korean river sediments, expressed as δ (δ = REE∗(La) - REE∗(Lu)), was calculated, and the spatial distribution patterns of the δ values were mapped. The δ values gradually increased from the western to the eastern part of the Yellow Sea, except for low δ values in the southeastern part of the Yellow Sea. This result indicates that the majority of Chinese and Korean river sediments are accumulating near to their respective coasts, except for a deposit along the southwestern coast of Korea in which a considerable amount of sediment from Chinese rivers has been accumulating.

  9. Grain size dependence of dielectric relaxation in cerium oxide as high-k layer

    PubMed Central

    2013-01-01

    Cerium oxide (CeO2) thin films used liquid injection atomic layer deposition (ALD) for deposition and ALD procedures were run at substrate temperatures of 150°C, 200°C, 250°C, 300°C, and 350°C, respectively. CeO2 were grown on n-Si(100) wafers. Variations in the grain sizes of the samples are governed by the deposition temperature and have been estimated using Scherrer analysis of the X-ray diffraction patterns. The changing grain size correlates with the changes seen in the Raman spectrum. Strong frequency dispersion is found in the capacitance-voltage measurement. Normalized dielectric constant measurement is quantitatively utilized to characterize the dielectric constant variation. The relationship extracted between grain size and dielectric relaxation for CeO2 suggests that tuning properties for improved frequency dispersion can be achieved by controlling the grain size, hence the strain at the nanoscale dimensions. PMID:23587419

  10. Effects of grain size on the spallation behavior of pure copper under plate-impact loading

    NASA Astrophysics Data System (ADS)

    Jiang, ZhaoXiu; Peng, Hui; Xing, MingZhi; Shen, HaiTing; He, HongLiang; Wang, YongGang

    2015-09-01

    The effects of grain size on the dynamic tensile fracture (or spall) response were investigated for high purity copper materials by plate-impact experiments. The spall strength estimated from the free surface velocity profile is nearly constant with no significant effect from the grain size. However, differences are observed in the acceleration rate of velocity rebound beyond the minima. This may be attributed to the effect of grain size on the growth rate of damage. Metallographic analyses of the fracture surface show that the characteristic feature of the fracture surface clearly depends on the grain size. In the smaller samples, the fracture surfaces are decorated with large, high-density ductile dimples suggesting that the preferential failure mode is ductile intergranular fracture. In the larger samples, the fracture surfaces have a rock candy appearance with small, brittle, high density dimples as well as large ductile dimples suggesting that the fracture mode is a mix of both brittle intergranular fracture and ductile transgranular fracture.

  11. Kinetics of HMX and Phase Transitions: Effects of Grain Size at Elevated Temperature

    SciTech Connect

    Saw, C K

    2002-06-13

    To date a global kinetic rate law has not been written to accurately describe solid-solid phase transformations of HMX and TATB where contributions from grain size effects, binder contents, and impurity levels are explicitly defined. Our recent work presented at the 2001 SCCM topical APS meeting, Atlanta, GA, demonstrated one can not confidently use the second harmonic generation (SHG) diagnostic to study energetic material phase transitions where non-uniform grain size distributions are present. For example, in HMX, the early arrival of SHG before the XRD in the SHG/XRD simultaneous high temperature experiment clearly indicates the partial molecular conversion from centrosymmetric to non-centrosymmetric without any structural changes as exhibit by the XRD pattern. This conversion is attributed to the changes of the surface molecules due to the differences in potential between the surface and the bulk. The present paper reports on accurate XRD measurements following changes of {beta}-HMX to {delta}-HMX at elevated temperature. The results are compared for sample with 2 different grain sizes for HMX. We report accurate temperature dependent lattice parameters and hence volume and linear thermal expansion coefficients along each crystallographic axis. We have also conducted kinetic studies of the behavior of 2 grain-sizes of HMX and concluded that their kinetics, are drastically different.

  12. Sediment supply and grain size export from normal fault footwalls in Southern Italy

    NASA Astrophysics Data System (ADS)

    Roda-Boluda, Duna; D'Arcy, Mitch; Whittaker, Alex; Allen, Philip

    2015-04-01

    The sedimentary record is the only physical evidence we have of mass transfer across the Earth's surface. In order to understand and ultimately decode this record, it is of key importance to characterize the sediment fluxes that generate stratigraphy. Sediment fluxes from catchments to basins, and their grain size distribution, can be highly sensitive to tectonic, geomorphic and lithological boundary conditions. However, the way in which these variables interact to determine the volume, locus and calibre of sediment released from catchments to basins remains unclear. Here we use a combination of DEM analysis and fieldwork to quantify the controls on sediment export from catchments crossing tectonically active faults in the Southern Apennines, where fault throw rates along strike, landslide abundances and hanging-wall stratigraphies are well-constrained, over timescales up to 1 Myr. We first use catchment drainage areas and estimates of fault throw rate and channel transport capacities as the main variables to estimate sediment supply along the fault footwalls. Sediment volumes, flux rates, and grain sizes are estimated using three complementary methodologies: 1) based on fault slip rates and topographic steady-state; 2) the BQART model*; 3) Shields stress-based approaches. We then compare these predictions with field data of the grain size distributions exported along the fault footwall catchments; the sediment volumes and grain sizes supplied by landslide populations in the field area; and the volumes and grain sizes of sediments stored in the hangingwall basins. Our analysis shows that 1) fault throw rates strongly influence channel and hillslope gradients and hence they exert a critical control on the calibre of the sediment released from footwall catchments; 2) grain size distributions correlate with the magnitudes of the sediment fluxes exported from catchments, and both vary significantly along the strike of active faults; 3) bedrock lithology modulates the

  13. Dolomite microstructures between 390° and 700 °C: Indications for deformation mechanisms and grain size evolution

    NASA Astrophysics Data System (ADS)

    Berger, Alfons; Ebert, Andreas; Ramseyer, Karl; Gnos, Edwin; Decrouez, Danielle

    2016-08-01

    Dolomitic marble on the island of Naxos was deformed at variable temperatures ranging from 390 °C to >700 °C. Microstructural investigations indicate two end-member of deformation mechanisms: (1) Diffusion creep processes associated with small grain sizes and weak or no CPO (crystallographic preferred orientation), whereas (2) dislocation creep processes are related with larger grain sizes and strong CPO. The change between these mechanisms depends on grain size and temperature. Therefore, sample with dislocation and diffusion creep microstructures and CPO occur at intermediate temperatures in relative pure dolomite samples. The measured dolomite grain size ranges from 3 to 940 μm. Grain sizes at Tmax >450 °C show an Arrhenius type evolution reflecting the stabilized grain size in deformed and relative pure dolomite. The stabilized grain size is five times smaller than that of calcite at the same temperature and shows the same Arrhenius-type evolution. In addition, the effect of second phase particle influences the grain size evolution, comparable with calcite. Calcite/dolomite mixtures are also characterized by the same difference in grain size, but recrystallization mechanism including chemical recrystallization induced by deformation may contribute to apparent non-temperature equilibrated Mg-content in calcite.

  14. Refinement of Ferrite Grain Size near the Ultrafine Range by Multipass, Thermomechanical Compression

    NASA Astrophysics Data System (ADS)

    Patra, S.; Neogy, S.; Kumar, Vinod; Chakrabarti, D.; Haldar, A.

    2012-11-01

    Plane-strain compression testing was carried out on a Nb-Ti-V microalloyed steel, in a GLEEBLE3500 simulator using a different amount of roughing, intermediate, and finishing deformation over the temperature range of 1373 K to 1073 K (1100 °C to 800 °C). A decrease in soaking temperature from 1473 K to 1273 K (1200 °C to 1000 °C) offered marginal refinement in the ferrite ( α) grain size from 7.8 to 6.6 μm. Heavy deformation using multiple passes between A e3 and A r3 with true strain of 0.8 to 1.2 effectively refined the α grain size (4.1 to 3.2 μm) close to the ultrafine size by dynamic-strain-induced austenite ( γ) → ferrite ( α) transformation (DSIT). The intensities of microstructural banding, pearlite fraction in the microstructure (13 pct), and fraction of the harmful "cube" texture component (5 pct) were reduced with the increase in finishing deformation. Simultaneously, the fractions of high-angle (>15 deg misorientation) boundaries (75 to 80 pct), beneficial gamma-fiber (ND//<111>) texture components, along with {332}<133> and {554}<225> components were increased. Grain refinement and the formation of small Fe3C particles (50- to 600-nm size) increased the hardness of the deformed samples (184 to 192 HV). For the same deformation temperature [1103 K (830 °C)], the difference in α-grain sizes obtained after single-pass (2.7 μm) and multipass compression (3.2 μm) can be explained in view of the static- and dynamic-strain-induced γ → α transformation, strain partitioning between γ and α, dynamic recovery and dynamic recrystallization of the deformed α, and α-grain growth during interpass intervals.

  15. Theoretical effects of mechanical grain-size reduction on GEM domain states in pyrrhotite

    NASA Astrophysics Data System (ADS)

    Ye, Jun; Halgedahl, Susan L.

    2000-05-01

    Recent laboratory experiments by Halgedahl and Ye (1999) show that domain widths in pyrrhotite change very little, or not at all, as a grain is mechanically thinned along one or two directions. In their experiments, particles were initially demagnetized in an alternating field until a global energy minimum (GEM) domain state was attained. Surprisingly, the overall positions of surviving walls and many small-scale details in the shapes of curved walls were remarkably insensitive to thinning. Thus, domain states that survived thinning were interpreted to be local energy minimum (LEM) states. As a first step toward providing a theoretical reference frame for the thinning results, GEM domain widths in pyrrhotite have been calculated here as grains are thinned to one-fourth or less of their original size. Nine models assume one-dimensional (1D) thinning, which greatly changes both particle size and shape. Two other models address the effects of three-dimensional (3D) thinning, in which particles retain a cubic shape as their sizes are reduced. If a particle can maintain a GEM state while it is thinned, seven of the nine 1D models and both 3D models predict that domain widths will adjust by amounts that are readily detected experimentally. Thus, results of these calculations support the interpretation that LEM states in pyrrhotite can be stable over a broad range of grain sizes and shapes. The primary origin of this stability remains an unsolved problem, however. If this stability is intrinsic to the pure material, then future micromagnetic models for pyrrhotite are required to investigate LEM states and their stability as functions of grain size and grain shape. On the other hand, this stability could originate from the pinning of preexisting walls by defects [Halgedahl and Ye, 1999]. Whatever their origins, the energy barriers that inhibit LEM-LEM transitions could play a significant role in the acquisition of remanence and the temporal stability of the paleomagnetic

  16. Enhanced Sucrose Loading Improves Rice Yield by Increasing Grain Size1[OPEN

    PubMed Central

    Wang, Liang; Lu, Qingtao

    2015-01-01

    Yield in cereals is a function of grain number and size. Sucrose (Suc), the main carbohydrate product of photosynthesis in higher plants, is transported long distances from source leaves to sink organs such as seeds and roots. Here, we report that transgenic rice plants (Oryza sativa) expressing the Arabidopsis (Arabidopsis thaliana) phloem-specific Suc transporter (AtSUC2), which loads Suc into the phloem under control of the phloem protein2 promoter (pPP2), showed an increase in grain yield of up to 16% relative to wild-type plants in field trials. Compared with wild-type plants, pPP2::AtSUC2 plants had larger spikelet hulls and larger and heavier grains. Grain filling was accelerated in the transgenic plants, and more photoassimilate was transported from the leaves to the grain. In addition, microarray analyses revealed that carbohydrate, amino acid, and lipid metabolism was enhanced in the leaves and grain of pPP2::AtSUC2 plants. Thus, enhancing Suc loading represents a promising strategy to improve rice yield to feed the global population. PMID:26504138

  17. Magnetic properties in an ash flow tuff with continuous grain size variation: a natural reference for magnetic particle granulometry

    USGS Publications Warehouse

    Till, J.L.; Jackson, M.J.; Rosenbaum, J.G.; Solheid, P.

    2011-01-01

    The Tiva Canyon Tuff contains dispersed nanoscale Fe-Ti-oxide grains with a narrow magnetic grain size distribution, making it an ideal material in which to identify and study grain-size-sensitive magnetic behavior in rocks. A detailed magnetic characterization was performed on samples from the basal 5 m of the tuff. The magnetic materials in this basal section consist primarily of (low-impurity) magnetite in the form of elongated submicron grains exsolved from volcanic glass. Magnetic properties studied include bulk magnetic susceptibility, frequency-dependent and temperature-dependent magnetic susceptibility, anhysteretic remanence acquisition, and hysteresis properties. The combined data constitute a distinct magnetic signature at each stratigraphic level in the section corresponding to different grain size distributions. The inferred magnetic domain state changes progressively upward from superparamagnetic grains near the base to particles with pseudo-single-domain or metastable single-domain characteristics near the top of the sampled section. Direct observations of magnetic grain size confirm that distinct transitions in room temperature magnetic susceptibility and remanence probably denote the limits of stable single-domain behavior in the section. These results provide a unique example of grain-size-dependent magnetic properties in noninteracting particle assemblages over three decades of grain size, including close approximations of ideal Stoner-Wohlfarth assemblages, and may be considered a useful reference for future rock magnetic studies involving grain-size-sensitive properties.

  18. Settling equivalence of detrital minerals and grain-size dependence of sediment composition

    NASA Astrophysics Data System (ADS)

    Garzanti, Eduardo; Andò, Sergio; Vezzoli, Giovanni

    2008-08-01

    This study discusses the laws which govern sediment deposition, and consequently determine size-dependent compositional variability. A theoretical approach is substantiated by robust datasets on major Alpine, Himalayan, and African sedimentary systems. Integrated (bulk-petrography, heavy-mineral, X-ray powder diffraction) multiple-window analyses at 0.25ϕ to 0.50ϕ sieve interval of eighty-five fluvial, beach, and eolian-dune samples, ranging from very fine silt to coarse sand, document homologous intrasample compositional trends, revealed by systematic concentration of denser grains in finer-grained fractions (“size-density sorting”). These trends are explained by the settling-equivalence principle, stating that detrital minerals are deposited together if their settling velocity is the same. Settling of silt is chiefly resisted by fluid viscosity, and Stokes' law predicts that size differences between detrital minerals in ϕ units (“size shifts”) are half the difference between the logarithms of their submerged densities. Settling of pebbles is chiefly resisted by turbulence effects, and the Impact law predicts double size shifts than Stokes' law. Settling of sand is resisted by both viscosity and turbulence, the settling-equivalence formula is complex, and size shifts increase - with increasing settling velocity and grain size - from those predicted by Stokes' law to those predicted by the Impact law. In wind-laid sands, size shifts match those predicted by the Impact law; size-density sorting is thus greater than in water-laid fine sands. New analytical, graphical, and statistical techniques for rigorous settling-equivalence analysis of terrigenous sediments are illustrated. Deviations associated with non-spherical shape, density anomalies, inheritance from source rocks, or mixing of detrital species with contrasting provenance and different size distribution are also tentatively assessed. Such integrated theoretical and experimental approach allows us

  19. Evolutionary models of the Earth with a grain size-dependent rheology

    NASA Astrophysics Data System (ADS)

    Rozel, Antoine; Golabek, Gregor; Tackley, Paul

    2015-04-01

    Thermodynamically consistent models of single phase grain size evolution have been proposed in the past years [Austin and Evans (2007), Ricard and Bercovici (2009), Rozel et al. (2011), Rozel (2012)]. Following the same physical approach, the mechanics of two-phase grain aggregates has been formulated [Bercovici and Ricard (2012a)]. Several non-linear mechanisms such as dynamic recrystallization or Zener pinning are now available in a single non-equilibrium formulation of grain size distributions evolution. The self-consistent generation of localized plate boundaries is predicted in [Bercovici and Ricard (2012b)] using this model, but it has not been tested in a dynamically consistent way. Our preliminary results have shown that out of equilibrium grain size dynamics leads to localization of deformation below the lithosphere rather than subduction initiation. Yet this result was obtained assuming indealized conditions. We study here, for the first time, the evolution of grain size in the mantle and lithosphere in evolutionary models, starting from a just-frozen magma ocean until the present day situation. Following complexities are considered in these models: melting, phase transitions, compressible convection, and different pressure-temperature-dependent composite rheologies in upper and lower mantles. We use a visco-plastic rheology in which the viscous strain rate is obtained by summation of dislocation and diffusion creep. Pressure and velocity fields are solved on a staggered grid using a SIMPLER-like method. Multigrid W-cycles and extra coarse-grid relaxations are employed to enhance the convergence of Stokes and continuity equations. The grain size is stored on a large number of tracers advected through the computational domain (a 2D spherical annulus), which prevent numerical diffusion and allows a high resolution. We also describe the physical formalism itself and derive a set of free parameters for the model. The results show that Normal growth, dynamic

  20. Dam impacts on downstream sediment grain size in a dryland river

    NASA Astrophysics Data System (ADS)

    Dekker, F. J.; Wilcox, A. C.

    2011-12-01

    We examined sediment characteristics on a dammed, sand dominated, dryland river to determine the pattern of grain size adjustment and the extent of sediment deficit resulting from dam-induced changes in water and sediment fluxes. We expected that conditions of sediment deficit would be manifested by coarsening immediately downstream of the dam, but that downstream fining would occur as a function of both tributary inputs and landform heterogeneity, such as canyon and wide floodplain reaches. Grain size data were collected longitudinally downstream on the Bill Williams River (BWR), a major tributary of the Colorado River in Arizona that was dammed in 1968 by Alamo Dam. We took photographs at 30m intervals for digital grain size analysis and collected bulk samples or pebble counts every 300m, for over 20% of the 58km long BWR. We used GIS to delineate the contributing area of approximately 60 ephemeral tributaries entering the BWR mainstem below the dam and to identify canyon and wide floodplain reaches. Whereas upstream of Alamo Dam, bed materials are predominantly sand-sized, in the 4km canyon reach downstream of the dam, the bed material coarsens, with an average size of 72 mm along bars, and >1 m of incision is evident. Bars fine to 33 mm and 23 mm at 8km and 28km downstream of the dam, respectively. Decreasing bar grain size downstream is explained to some extent by an exponential model with a fining coefficient of 0.033km^-1 (r^2=0.50). The grain size variation within gravel samples also decreases downstream. The gravel-dominated reach downstream of the dam lacks tributary inputs of sediments; 75% of the tributary area of the dammed BWR enters the mainstem in the river's lower half. The lower BWR is more sand dominated, which is possibly controlled by a wide, 8km long floodplain reach where surface flow is often discontinuous. Further analysis of sediment dynamics in the BWR using reservoir sedimentation and cosmogenic nuclide data are being used to determine

  1. Absorption Efficiencies of Forsterite. I. Discrete Dipole Approximation Explorations in Grain Shape and Size

    NASA Astrophysics Data System (ADS)

    Lindsay, Sean S.; Wooden, Diane H.; Harker, David E.; Kelley, Michael S.; Woodward, Charles E.; Murphy, Jim R.

    2013-03-01

    We compute the absorption efficiency (Q abs) of forsterite using the discrete dipole approximation in order to identify and describe what characteristics of crystal grain shape and size are important to the shape, peak location, and relative strength of spectral features in the 8-40 μm wavelength range. Using the DDSCAT code, we compute Q abs for non-spherical polyhedral grain shapes with a eff = 0.1 μm. The shape characteristics identified are (1) elongation/reduction along one of three crystallographic axes; (2) asymmetry, such that all three crystallographic axes are of different lengths; and (3) the presence of crystalline faces that are not parallel to a specific crystallographic axis, e.g., non-rectangular prisms and (di)pyramids. Elongation/reduction dominates the locations and shapes of spectral features near 10, 11, 16, 23.5, 27, and 33.5 μm, while asymmetry and tips are secondary shape effects. Increasing grain sizes (0.1-1.0 μm) shifts the 10 and 11 μm features systematically toward longer wavelengths and relative to the 11 μm feature increases the strengths and slightly broadens the longer wavelength features. Seven spectral shape classes are established for crystallographic a-, b-, and c-axes and include columnar and platelet shapes plus non-elongated or equant grain shapes. The spectral shape classes and the effects of grain size have practical application in identifying or excluding columnar, platelet, or equant forsterite grain shapes in astrophysical environs. Identification of the shape characteristics of forsterite from 8 to 40 μm spectra provides a potential means to probe the temperatures at which forsterite formed.

  2. Absorption Efficiencies of Forsterite. I: DDA Explorations in Grain Shape and Size

    NASA Technical Reports Server (NTRS)

    Lindsay, Sean S.; Wooden, Diane; Harker, David E.; Kelley, Michael S.; Woodward, Charles E.; Murphy, Jim R.

    2013-01-01

    We compute the absorption efficiency (Q(sub abs)) of forsterite using the discrete dipole approximation (DDA) in order to identify and describe what characteristics of crystal grain shape and size are important to the shape, peak location, and relative strength of spectral features in the 8 - 40 micron wavelength range. Using the DDSCAT code, we compute Q(sub abs) for non-spherical polyhedral grain shapes with a(sub eff) = 0.1 micron. The shape characteristics identified are: 1) elongation/reduction along one of three crystallographic axes; 2) asymmetry, such that all three crystallographic axes are of different lengths; and 3) the presence of crystalline faces that are not parallel to a specific crystallographic axis, e.g., non-rectangular prisms and (di)pyramids. Elongation/reduction dominates the locations and shapes of spectral features near 10, 11, 16, 23.5, 27, and 33.5 micron, while asymmetry and tips are secondary shape effects. Increasing grain sizes (0.1 - 1.0 micron) shifts the 10, 11 micron features systematically towards longer wavelengths and relative to the 11 micron feature increases the strengths and slightly broadens the longer wavelength features. Seven spectral shape classes are established for crystallographic a-, b-, and c-axes and include columnar and platelet shapes plus non-elongated or equant grain shapes. The spectral shape classes and the effects of grain size have practical application in identifying or excluding columnar, platelet or equant forsterite grain shapes in astrophysical environs. Identification of the shape characteristics of forsterite from 8 - 40 micron spectra provides a potential means to probe the temperatures at which forsterite formed.

  3. ABSORPTION EFFICIENCIES OF FORSTERITE. I. DISCRETE DIPOLE APPROXIMATION EXPLORATIONS IN GRAIN SHAPE AND SIZE

    SciTech Connect

    Lindsay, Sean S.; Wooden, Diane H.; Harker, David E.; Kelley, Michael S.; Woodward, Charles E.; Murphy, Jim R. E-mail: diane.h.wooden@nasa.gov E-mail: msk@astro.umd.edu E-mail: murphy@nmsu.edu

    2013-03-20

    We compute the absorption efficiency (Q{sub abs}) of forsterite using the discrete dipole approximation in order to identify and describe what characteristics of crystal grain shape and size are important to the shape, peak location, and relative strength of spectral features in the 8-40 {mu}m wavelength range. Using the DDSCAT code, we compute Q{sub abs} for non-spherical polyhedral grain shapes with a{sub eff} = 0.1 {mu}m. The shape characteristics identified are (1) elongation/reduction along one of three crystallographic axes; (2) asymmetry, such that all three crystallographic axes are of different lengths; and (3) the presence of crystalline faces that are not parallel to a specific crystallographic axis, e.g., non-rectangular prisms and (di)pyramids. Elongation/reduction dominates the locations and shapes of spectral features near 10, 11, 16, 23.5, 27, and 33.5 {mu}m, while asymmetry and tips are secondary shape effects. Increasing grain sizes (0.1-1.0 {mu}m) shifts the 10 and 11 {mu}m features systematically toward longer wavelengths and relative to the 11 {mu}m feature increases the strengths and slightly broadens the longer wavelength features. Seven spectral shape classes are established for crystallographic a-, b-, and c-axes and include columnar and platelet shapes plus non-elongated or equant grain shapes. The spectral shape classes and the effects of grain size have practical application in identifying or excluding columnar, platelet, or equant forsterite grain shapes in astrophysical environs. Identification of the shape characteristics of forsterite from 8 to 40 {mu}m spectra provides a potential means to probe the temperatures at which forsterite formed.

  4. Size distribution of dust grains: A problem of self-similarity

    NASA Technical Reports Server (NTRS)

    Henning, TH.; Dorschner, J.; Guertler, J.

    1989-01-01

    Distribution functions describing the results of natural processes frequently show the shape of power laws, e.g., mass functions of stars and molecular clouds, velocity spectrum of turbulence, size distributions of asteroids, micrometeorites and also interstellar dust grains. It is an open question whether this behavior is a result simply coming about by the chosen mathematical representation of the observational data or reflects a deep-seated principle of nature. The authors suppose the latter being the case. Using a dust model consisting of silicate and graphite grains Mathis et al. (1977) showed that the interstellar extinction curve can be represented by taking a grain radii distribution of power law type n(a) varies as a(exp -p) with 3.3 less than or equal to p less than or equal to 3.6 (example 1) as a basis. A different approach to understanding power laws like that in example 1 becomes possible by the theory of self-similar processes (scale invariance). The beta model of turbulence (Frisch et al., 1978) leads in an elementary way to the concept of the self-similarity dimension D, a special case of Mandelbrot's (1977) fractal dimension. In the frame of this beta model, it is supposed that on each stage of a cascade the system decays to N clumps and that only the portion beta N remains active further on. An important feature of this model is that the active eddies become less and less space-filling. In the following, the authors assume that grain-grain collisions are such a scale-invarient process and that the remaining grains are the inactive (frozen) clumps of the cascade. In this way, a size distribution n(a) da varies as a(exp -(D+1))da (example 2) results. It seems to be highly probable that the power law character of the size distribution of interstellar dust grains is the result of a self-similarity process. We can, however, not exclude that the process leading to the interstellar grain size distribution is not fragmentation at all. It could be, e

  5. Time-evolution of grain size distributions in random nucleation and growth crystallization processes

    NASA Astrophysics Data System (ADS)

    Teran, Anthony V.; Bill, Andreas; Bergmann, Ralf B.

    2010-02-01

    We study the time dependence of the grain size distribution N(r,t) during crystallization of a d -dimensional solid. A partial differential equation, including a source term for nuclei and a growth law for grains, is solved analytically for any dimension d . We discuss solutions obtained for processes described by the Kolmogorov-Avrami-Mehl-Johnson model for random nucleation and growth (RNG). Nucleation and growth are set on the same footing, which leads to a time-dependent decay of both effective rates. We analyze in detail how model parameters, the dimensionality of the crystallization process, and time influence the shape of the distribution. The calculations show that the dynamics of the effective nucleation and effective growth rates play an essential role in determining the final form of the distribution obtained at full crystallization. We demonstrate that for one class of nucleation and growth rates, the distribution evolves in time into the logarithmic-normal (lognormal) form discussed earlier by Bergmann and Bill [J. Cryst. Growth 310, 3135 (2008)]. We also obtain an analytical expression for the finite maximal grain size at all times. The theory allows for the description of a variety of RNG crystallization processes in thin films and bulk materials. Expressions useful for experimental data analysis are presented for the grain size distribution and the moments in terms of fundamental and measurable parameters of the model.

  6. Magnetic ejection of submilimeter-sized diamagnetic grains observed in a chamber-type drop shaft

    NASA Astrophysics Data System (ADS)

    Hisayoshi, K.; Uyeda, C.; Kuwada, K.; Mamiya, M.; H; Nagai

    2011-12-01

    Mass dependence of magnetically induced translation is examined for submilimeter-sized diamagnetic grain, which is floated in a diffused gas medium of 70 Pa by the use of microgravity μG condition. Here the grains are ejected from field-center of a pole-piece magnetic circuit by field-gradient force in a direction of decreasing field; maximum field-intensity at initial point is about 0.6T. It was deduced from an energy conservation rule that magnetic potential of the grain at initial position was partially converted to kinetic energy during translation. Therefore, observed velocity was expected to be independent to mass of particle; this is because magnetic potential is proportional to mass of particle. In a given field distribution, the velocity was uniquely determined by intrinsic magnetic susceptibility χ DIA of material. We report here that the magnetic ejection in μ G condition is realized for sub-mm sized crystals of bismuth, graphite and magnesia. The χ DIA values obtained from the ejection agreed fairly well with the published values for the three materials. The mass-independent property of translation was examined by observing the translation of two bismuth grains with different sizes. A chamber-type drop shaft having a height of 1.5 m was introduced to produce the μ G condition. By the use of this drop shaft, study of field-induced motion of a single diamagnetic particle becomes possible in an ordinary laboratory.

  7. The influence of phase and grain size distribution on the dynamics of strain localization in polymineralic rocks

    NASA Astrophysics Data System (ADS)

    Czaplińska, Daria; Piazolo, Sandra; Zibra, Ivan

    2015-03-01

    Deformation microstructures of a quartzo-feldspathic pegmatite deformed at mid-crustal levels allow the study of the dynamics of strain localization in polymineralic rocks. Strain localization results from (i) difference in grain sizes between phases, both original and obtained during fluid present reactions and (ii) initial compositional banding. Due to original difference in grain size stress concentrates in the initially finer-grained phases resulting in their intense grain size reduction via subgrain rotation recrystallization (SGR). When the grain size is sufficiently reduced through either deformation or interphase coupled dissolution-precipitation replacement of the coarse grained feldspar, aggregates start to deform by dominantly diffusion accommodated grain boundary sliding (GBS). Phase mixing inhibits grain growth and sustains a grain size allowing GBS. Consequently, discontinuous microscale shear zones form locally within initially coarse grained areas. At the same time difference in strain rate between feldspar-rich and quartz-rich domains needs to be accommodated at domain boundaries. This results in the formation of continuous mesoscale shear zones deformed by GBS. Once these are formed, deformation in the coarse grained parts is arrested and strain is mainly accommodated in the mesoscale shear zones resulting in "superplastic" behaviour consistent with diffusion creep.

  8. [Effects of irrigation scheme on the grain glutenin macropolymer's size distribution and the grain quality of winter wheat with strong gluten].

    PubMed

    Zhou, Xiao-Yan; Jia, Dian-Yong; Dai, Xing-Long; He, Ming-Rong

    2013-09-01

    Taking two winter wheat (Triticum aestivum L.) cultivars (Gaocheng 8901 and Jimai 20) with high quality strong gluten as test materials, a 2-year field experiment was conducted to study the grain glutenin macropolymer (GMP)'s content and size distribution, grain quality, and grain yield under effects of different irrigation schemes. The schemes included no irrigation in whole growth period (W0), irrigation once at jointing stage (W1), irrigation two times at wintering and jointing stages (W2), respectively, and irrigation three times at wintering, jointing, and filling stages (W3), respectively, with the irrigation amount in each time being 675 m3 x hm(-2). Among the test irrigation schemes, W2 had the best effects on the dough development time, dough stability time, loaf volume, grain yield, GMP content, weighted average surface area of particle D(3,2), weighted average volume of particle D(4,3), and volume percent and surface area percent of particle size >100 microm of the two cultivars. The dough development time, dough stability time, and loaf volume were negatively correlated with the volume percent of GMP particle size <10 microm and 10-100 microm, while positively correlated with the volume percent of GMP particle size >100 microm, D(3,2), and D(4,3). It was suggested that both water deficit and water excess had detrimental effects on the grain yield and grain quality, and irrigation level could affect the wheat grain quality through altering GMP particle size distribution.

  9. On Techniques to Characterize and Correlate Grain Size, Grain Boundary Orientation and the Strength of the SiC Layer of TRISO Coated Particles: A Preliminary Study

    SciTech Connect

    I.J.van Rooyen; J.L. Dunzik Gougar; T. Trowbridge; Philip M van Rooyen

    2012-10-01

    The mechanical properties of the silicon carbide (SiC) layer of the TRi-ISOtropic (TRISO) coated particle (CP) for high temperature gas reactors (HTGR) are performance parameters that have not yet been standardized by the international HTR community. Presented in this paper are the results of characterizing coated particles to reveal the effect of annealing temperature (1000 to 2100°C) on the strength and grain size of unirradiated coated particles. This work was further expanded to include possible relationships between the grain size and strength values. The comparative results of two strength measurement techniques and grain size measured by the Lineal intercept method are included. Preliminary grain boundary characterization results determined by electron backscatter diffraction (EBSD) are included. These results are also important for future fission product transport studies, as grain boundary diffusion is identified as a possible mechanism by which 110mAg, one of the fission activation products, might be released through intact SiC layers. Temperature is a parameter known to influence the grain size of SiC and therefore it is important to investigate the effect of high temperature annealing on the SiC grain size. Recommendations and future work will also be briefly discussed.

  10. Method to grow carbon thin films consisting entirely of diamond grains 3-5 nm in size and high-energy grain boundaries

    DOEpatents

    Carlisle, John A.; Auciello, Orlando; Birrell, James

    2006-10-31

    An ultrananocrystalline diamond (UNCD) having an average grain size between 3 and 5 nanometers (nm) with not more than about 8% by volume diamond having an average grain size larger than 10 nm. A method of manufacturing UNCD film is also disclosed in which a vapor of acetylene and hydrogen in an inert gas other than He wherein the volume ratio of acetylene to hydrogen is greater than 0.35 and less than 0.85, with the balance being an inert gas, is subjected to a suitable amount of energy to fragment at least some of the acetylene to form a UNCD film having an average grain size of 3 to 5 nm with not more than about 8% by volume diamond having an average grain size larger than 10 nm.

  11. Amphipod sediment bioassays: effects on response of methodology, grain size, organic content, and cadmium

    SciTech Connect

    Ott, F.S.

    1986-01-01

    Ten day sediment bioassays and behavioral tests were conducted with the phoxocephalid amphipod Rhepoxynius abronius to determine individual and interactive effects on response of grain size, cadmium (Cd), and organic content in static and flow-through systems. Effects of freezing sediment and variations in animal sensitivity (due to age and season) were also examined. In addition, bioassays were conducted biannually over a 2-yr period using sediments from 27 stations in central Puget Sound, Washington. Sterile sediments with a mean grain size <29-54 um were acutely toxic to amphipods. The 96-h LC50 for water-borne Cd was 1.7 ppm; the 10-day LC50 for Cd in native sand was 8.8 ppm. Toxicity from Cd and tissue Cd uptake were a direct function of the seawater Cd concentration which decreased with decreasing grain size and increasing organic content. Therefore, Cd bioavailability was not correlated with total Cd in sediment. Survival was similar or lower in a static versus a flow-through system with the magnitude of the difference in response between systems being greatest in contaminated fine-grain sediments. Amphipods were more sensitive during Jan-March then Oct-Nov. Shifts in sensitivity may be related to the recruitment/growth pattern and the overwintering habits of this animal. In bioassays conducted with field sediments, geographic patterns of sediment toxicity were apparent. Survival was negatively correlated with mean grain size and priority pollutant load of 15 heavy metals and 50 organic compounds, although response could not be attributed to any single parameter.

  12. Estimating sand grain sizes from digital imagery via chord-distribution functions

    NASA Astrophysics Data System (ADS)

    Bartlett, M.

    2007-12-01

    Variations in beach sediment size, supply, and composition are important parameters in understanding patterns of sediment transport and erosion. Traditional methods of characterizing sediments (including mechanical sieving, water column settlement, and laser diffraction) involve recovery of a sample and its removal to the lab for measurement, a time and labor intensive process. Consequently, despite the evidence suggesting the importance of grain size and variability in sediment transport and morphodynamic processes and the inherent spatial and temporal variability of sediments at many locales, most studies are based on relatively few samples. In-situ, rapid characterization of sediments would allow greater spatial data coverage and, consequently, tighter constraints in sediment transport and erosion models. Rubin (J. Sediment. Res., 74, 160-165, 2004) suggested one approach, analyzing the autocorrelation of digital images of sediments to determine grain size distribution rapidly. The technique has the advantages of rapid data collection (via a digital camera) and a relatively straight forward data processing algorithm. However, the autocorrelation technique is not always able to discriminate robustly between different grain morphologies. Using the same tools (digital imagery and computational resources), I examine an alternative approach to characterization of beach sediments: using chord-distribution functions to discriminate grain size distribution and variability. Chord-distribution functions have been shown to be extremely sensitive to small changes in particle morphology in biphasic media (Levitz and Tchoubar, J. Phyisque I, 2, 771-790, 1992). Initial results indicate that with proper pre-processing of the digital image, the technique robustly characterizes the distribution of grains in beach sediment samples from Oahu's north shore.

  13. Glacial-Interglacial Climate Changes Recorded by Debris Flow Grain Size, Eastern Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    D'Arcy, M. K.; Whittaker, A. C.; Roda Boluda, D. C.

    2015-12-01

    Uncertainties remain about the sensitivity of eroding landscapes to climate changes over a range of frequencies and amplitudes. Numerical models suggest that simple catchment-fan systems should be responsive to glacial-interglacial climate cycles, recording them in both sediment flux and the grain size distribution of their deposits. However these models are largely untested and the propagation of climatic signals through simple sediment routing systems remains contentious. Here, we present detailed sedimentological data from 8 debris flow fans in Owens Valley, eastern California. These fans have an exceptionally well-constrained depositional record spanning the last 120 ka, which we use to examine how sediment export has varied as a function of high-amplitude climate changes. We find a strong and sustained relationship between debris flow grain size and paleoclimate proxies over an entire glacial-interglacial cycle, with significantly coarser-grained deposits correlated with warm and dry conditions. Our data suggest these systems are highly reactive to climate forcing, with a short response timescale of <10 ka and no evidence of signal buffering, which we interpret to be driven by rapid sediment transfer from source to sink. We demonstrate that debris flow grain size follows an exponential relationship with temperature, coarsening at a rate of ~10 % per °C. Using this observation, and a known relationship between temperature and storm intensity, we propose that the climate signal recorded in these fan deposits captures changing storm intensity during the last glacial-interglacial cycle. This study offers a direct test of existing models of catchment-fan systems, confirming that glacial-interglacial climate changes can be clearly expressed in their grain size records. Our results also suggest that these debris flow deposits contain a high-resolution, testable record of past storm intensity, and that storminess is the primary control on their sedimentological

  14. Relationship among grain size, annealing twins and shape memory effect in Fe–Mn–Si based shape memory alloys

    NASA Astrophysics Data System (ADS)

    Wang, Gaixia; Peng, Huabei; Zhang, Chengyan; Wang, Shanling; Wen, Yuhua

    2016-07-01

    In order to clarify the relationship among grain size, annealing twins and the shape memory effect in Fe–Mn–Si based shape memory alloys, the Fe–21.63Mn–5.60Si–9.32Cr–5.38Ni (weight %) alloy with a grain size ranging from 48.9 μm–253.6 μm was obtained by adjusting the heating temperature or heating time after 20% cold-rolling. The densities of grain boundaries and annealing twins increase with a decrease in grain size, whereas the volume fraction and width of stress-induced ε martensite after 9% deformation at Ms + 10 K decrease. This result indicates that grain refinement raises the constraint effects of grain boundaries and annealing twins upon martensitic transformation. In this case, the ability to suppress the plastic deformation and facilitate the stress-induced ε martensite transformation deteriorates after grain refinement owing to the enhancement of the constraint effects. It is demonstrated by the result that the difference at Ms + 10 K between the critical stress for plastic yielding and that for inducing martensitic transformation is smaller for the specimen with a grain size of 48.9 μm than for the specimen with a grain size of 253.6 μm. Therefore, the shape memory effect declined by decreasing the grain size.

  15. Relationship among grain size, annealing twins and shape memory effect in Fe-Mn-Si based shape memory alloys

    NASA Astrophysics Data System (ADS)

    Wang, Gaixia; Peng, Huabei; Zhang, Chengyan; Wang, Shanling; Wen, Yuhua

    2016-07-01

    In order to clarify the relationship among grain size, annealing twins and the shape memory effect in Fe-Mn-Si based shape memory alloys, the Fe-21.63Mn-5.60Si-9.32Cr-5.38Ni (weight %) alloy with a grain size ranging from 48.9 μm-253.6 μm was obtained by adjusting the heating temperature or heating time after 20% cold-rolling. The densities of grain boundaries and annealing twins increase with a decrease in grain size, whereas the volume fraction and width of stress-induced ɛ martensite after 9% deformation at Ms + 10 K decrease. This result indicates that grain refinement raises the constraint effects of grain boundaries and annealing twins upon martensitic transformation. In this case, the ability to suppress the plastic deformation and facilitate the stress-induced ɛ martensite transformation deteriorates after grain refinement owing to the enhancement of the constraint effects. It is demonstrated by the result that the difference at Ms + 10 K between the critical stress for plastic yielding and that for inducing martensitic transformation is smaller for the specimen with a grain size of 48.9 μm than for the specimen with a grain size of 253.6 μm. Therefore, the shape memory effect declined by decreasing the grain size.

  16. Calcinations effect on the grain size distributions Al2O3 powder

    NASA Astrophysics Data System (ADS)

    Issa, Tarik Talib; Mohammed, Awattif A.; Kamil, Dunia

    2012-09-01

    Fine of Al2O3 Powder was calcined at 200°C, 400°C, 600°C, and 800°C respectively for 2 hours under static air, x-ray diffraction, optical microscope and grain size distribution were done to analysis the resulting data after calcinations process. Batter particle size was achieved at 800°C of value (0.486) μm, while batter particles mean value of size 7.18 μm was found at 400°C. SEM micrographs shows that the agglomerate particles were vanished due to the calcinations process.

  17. Ultralow thermal conductivity in polycrystalline CdSe thin films with controlled grain size.

    PubMed

    Feser, Joseph P; Chan, Emory M; Majumdar, Arun; Segalman, Rachel A; Urban, Jeffrey J

    2013-05-01

    Polycrystallinity leads to increased phonon scattering at grain boundaries and is known to be an effective method to reduce thermal conductivity in thermoelectric materials. However, the fundamental limits of this approach are not fully understood, as it is difficult to form uniform sub-20 nm grain structures. We use colloidal nanocrystals treated with functional inorganic ligands to obtain nanograined films of CdSe with controlled characteristic grain size between 3 and 6 nm. Experimental measurements demonstrate that thermal conductivity in these composites can fall beneath the prediction of the so-called minimum thermal conductivity for disordered crystals. The measurements are consistent, however, with diffuse boundary scattering of acoustic phonons. This apparent paradox can be explained by an overattribution of transport to high-energy phonons in the minimum thermal conductivity model where, in compound semiconductors, optical and zone edge phonons have low group velocity and high scattering rates.

  18. Processing Variables of Alumina Slips and Their Effects on the Density and Grain Size of the Sintered Sample

    SciTech Connect

    Rowley, R.; Chu, H.

    2002-01-01

    High densities and small grain size of alumina ceramic bodies provide high strength and better mechanical properties than lower density and larger grain size bodies. The final sintered density and grain size of slip-cast, alumina samples depends greatly on the processing of the slip and the alumina powder, as well as the sintering schedule. There were many different variables explored that include initial powder particle size, slurry solids percent, amount and type of dispersant used, amount and type of binder used, and sintering schedule. Although the experimentation is not complete, to this point the sample with the highest density and smallest grain size has been a SM8/Nano mixture with Darvan C as the dispersant and Polyvinyl Alcohol (PVA) as the binder, with a solids loading of 70 wt% and a 1500 C for 2 hours sintering schedule. The resultant density was 98.81% of theoretical and the average grain size was approximately 2.5 {micro}m.

  19. Distribution of garnet grain sizes and morphologies across the Moine Supergroup, northern Scottish Caledonides

    NASA Astrophysics Data System (ADS)

    Ashley, Kyle T.; Thigpen, J. Ryan; Law, Richard D.

    2016-04-01

    Garnet is used in a wide range of geologic studies due to its important physical and chemical characteristics. While the mineral is useful for thermobarometry and geochronology constraints and can often be correlated to deformation and fabric development, difficulties remain in making meaningful interpretations of such data. In this study, we characterize garnet grain sizes and crystal morphologies from 141 garnet-bearing metasedimentary rock samples collected from the northern part of the Moine Supergroup in the Scottish Caledonides. Larger, euhedral crystals are indicative of prograde metamorphic growth and are typically associated with the most recent phase of orogenesis (Scandian, ˜430 Ma). Small, rounded ("pin-head") garnets are interpreted as detrital in origin. A subhedral classification is more subjective and is used when garnets contains portions of straight boundaries but have rounded edges or rims that have been altered through retrograde metamorphic reactions. From our collection, 88 samples contain anhedral garnets (maximum measured grain size d = 0.46 ± 0.21 mm), 34 bear subhedral garnets (d = 2.0 ± 1.0 mm), and the remaining 19 samples contain garnets with euhedral grains (d = 4.4 ± 2.6 mm). Plotting the distribution of garnets relative to the mapped thrust contacts reveals an abrupt change in morphology and grain size when traced from the Moine thrust sheet across the Ben Hope and Sgurr Beag thrusts into the higher-grade, more hinterland-positioned thrust sheets. The dominance of anhedral garnets in the Moine thrust sheet suggests that these grains should not be used for peak P - T estimation associated with relatively low temperature (<500 ° C) Scandian metamorphism, as they are likely detrital in origin and contain protolith chemical signatures that would not have been reset due to sluggish diffusivities at greenschist facies temperatures. However, chemical and isotopic data from these grains may provide information into the provenance of

  20. Grain Size Distribution in Mudstones: A Question of Nature vs. Nurture

    NASA Astrophysics Data System (ADS)

    Schieber, J.

    2011-12-01

    Grain size distribution in mudstones is affected by the composition of the source material, the processes of transport and deposition, and post-depositional diagenetic modification. With regard to source, it does make a difference whether for example a slate belt is eroded vs a stable craton. The former setting tends to provide a broad range of detrital quartz in the sub 62 micron size range in addition to clays and greenschist grade rock fragments, whereas the latter may be biased towards coarser quartz silt (30-60 microns), in addition to clays and mica flakes. In flume experiments, when fine grained materials are transported in turbulent flows at velocities that allow floccules to transfer to bedload, a systematic shift of grain size distribution towards an increasingly finer grained suspended load is observed as velocity is lowered. This implies that the bedload floccules are initially constructed of only the coarsest clay particles at high velocities, and that finer clay particles become incorporated into floccules as velocity is lowered. Implications for the rock record are that clay beds deposited from decelerating flows should show subtle internal grading of coarser clay particles; and that clay beds deposited from continuous fast flows should show a uniform distribution of coarse clays. Still water settled clays should show a well developed lower (coarser) and upper (finer) subdivision. A final complication arises when diagenetic processes, such as the dissolution of biogenic silica, give rise to diagenetic quartz grains in the silt to sand size range. This diagenetic silica precipitates in fossil cavities and pore spaces of uncompacted muds, and on casual inspection can be mistaken for detrital quartz. In distal mudstone successions close to 100 % of "apparent" quartz silt can be of that origin, and reworking by bottom currents can further enhance a detrital perception by producing rippled and laminated silt beds. Although understanding how size

  1. Linking differential domain functions of the GS3 protein to natural variation of grain size in rice.

    PubMed

    Mao, Hailiang; Sun, Shengyuan; Yao, Jialing; Wang, Chongrong; Yu, Sibin; Xu, Caiguo; Li, Xianghua; Zhang, Qifa

    2010-11-01

    Grain yield in many cereal crops is largely determined by grain size. Here we report the genetic and molecular characterization of GS3, a major quantitative trait locus for grain size. It functions as a negative regulator of grain size and organ size. The wild-type isoform is composed of four putative domains: a plant-specific organ size regulation (OSR) domain in the N terminus, a transmembrane domain, a tumor necrosis factor receptor/nerve growth factor receptor (TNFR/NGFR) family cysteine-rich domain, and a von Willebrand factor type C (VWFC) in the C terminus. These domains function differentially in grain size regulation. The OSR domain is both necessary and sufficient for functioning as a negative regulator. The wild-type allele corresponds to medium grain. Loss of function of OSR results in long grain. The C-terminal TNFR/NGFR and VWFC domains show an inhibitory effect on the OSR function; loss-of-function mutations of these domains produced very short grain. This study linked the functional domains of the GS3 protein to natural variation of grain size in rice. PMID:20974950

  2. MinSORTING: an Excel macro for modelling sediment composition and grain-size distribution

    NASA Astrophysics Data System (ADS)

    Resentini, Alberto; Malusà, Marco G.; Garzanti, Eduardo

    2013-04-01

    Detrital mineral analyses are gaining increasing attention in the geosciences as new single-grain analytical techniques are constantly improving their resolution, and consequently widening their range of application, including sedimentary petrology, tectonic geomorphology and archaeology (Mange and Wright, 2007; von Eynatten and Dunkl, 2012). We present here MinSORTING, a new tool to quickly predict the size distribution of various minerals and rock fragments in detrital sediments, based on the physical laws that control sedimentation by tractive wind or water currents (Garzanti et al., 2008). The input values requested by the software are the sediment mean size, sorting, fluid type (seawater, freshwater, air) and standard sediment composition chosen from a given array including nine diverse tectonic settings. MinSORTING calculates the bulk sediment density and the settling velocity. The mean size of each single detrital component, assumed as lognormally-distributed, is calculated from its characteristic size-shift with respect to bulk sediment mean size, dependent in turn on its density and shape. The final output of MinSORTING is the distribution of each single detrital mineral in each size classes (at the chosen 0.25, 0.5 or 1 phi intervals). This allows geochronolgists to select the most suitable grain size of sediment to be sampled in the field, as well as the most representative size-window for analysis. Also, MinSORTING provides an estimate of the volume/weight of the fractions not considered in both sizes finer and coarser than the selected size-window. A beta version of the software is available upon request from: alberto.resentini@unimib.it Mange, M., and Wright, D. (eds), 2007. Heavy minerals in use. Developments in Sedimentology Series, 58. Elsevier, Amsterdam. Garzanti, E., Andò, S., Vezzoli, G., 2008. Settling-equivalence of detrital minerals and grain-size dependence of sediment composition. Earth and Planetary Science Letters 273, 138-151. von

  3. Can sediment total organic carbon and grain size be used to diagnose organic enrichment in estuaries?

    PubMed

    Pelletier, Marguerite C; Campbell, Daniel E; Ho, Kay T; Burgess, Robert M; Audette, Charles T; Detenbeck, Naomi E

    2011-03-01

    Eutrophication (i.e., nutrient enrichment, organic enrichment, and oxygen depletion) is one of the most common sources of impairment in Clean Water Act 303(d)-listed waters in the United States. Although eutrophication can eventually cause adverse effects to the benthos, it may be difficult to diagnose. Sediment organic carbon (OC) content has been used as an indicator of enrichment in sediments, but the amount of surface area available for carbon adsorption must be considered. We investigated the utility of the relationship between OC and sediment grain size as an indicator of eutrophication. Data from the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program was used to test this relationship. However, anthropogenic contaminants are also capable of causing adverse effects to the benthos and often co-occur with elevated levels of OC. Contaminant analysis and toxicity tests were not consistently related to enrichment status as defined by relationship between total OC and grain size. Although variability in response occurred, reflecting the variance in the water column factors (dissolved oxygen, chlorophyll a, and nutrients) and limited sample sizes, the data supported the hypothesis that sites designated as enriched were eutrophied. Dissolved oxygen levels were reduced at enriched sites, whereas chlorophyll a and nutrients were higher at enriched sites. This suggests that the relationship of OC to grain size can be used as a screening tool to diagnose eutrophication. PMID:21298700

  4. The origin of bimodal grain-size distribution for aeolian deposits

    NASA Astrophysics Data System (ADS)

    Lin, Yongchong; Mu, Guijin; Xu, Lishuai; Zhao, Xue

    2016-03-01

    Atmospheric dust deposition is a common phenomenon in arid and semi-arid regions. Bimodal grain size distribution (BGSD) (including the fine component and coarse component) of aeolian deposits has been widely reported. But the origin of this pattern is still debated. Here, we focused on the sedimentary process of modern dust deposition, and analyzed the grain size distribution of modern dust deposition, foliar dust, and aggregation of the aeolian dust collected in Cele Oasis, southern margin of Tarim Basin. The results show that BGSD also appear in a dust deposition. The content of fine components (<20 μm size fraction) change with temporal and spatial variation. Fine component from dust storm is significant less than that from subsequent floating dust. Fine component also varies with altitude. These indicate that modern dust deposition have experienced changing aerodynamic environment and be reworked during transportation and deposition, which is likely the main cause for BGSD. The dusts from different sources once being well-mixed in airflow are hard to form multiple peaks respectively corresponding with different sources. In addition, the dust deposition would appear BGSD whether aggregation or not. Modern dust deposition is the continuation of ancient dust deposition. They both may have the same cause of formation. Therefore, the origin of BGSD should provide a theoretical thinking for reconstructing the palaeo-environmental changes with the indicator of grain size.

  5. Variations in CYP78A13 coding region influence grain size and yield in rice.

    PubMed

    Xu, Fan; Fang, Jun; Ou, Shujun; Gao, Shaopei; Zhang, Fengxia; Du, Lin; Xiao, Yunhua; Wang, Hongru; Sun, Xiaohong; Chu, Jinfang; Wang, Guodong; Chu, Chengcai

    2015-04-01

    Grain size is one of the most important determinants of crop yield in cereals. Here, we identified a dominant mutant, big grain2 (bg2-D) from our enhancer-trapping population. Genetic analysis and SiteFinding PCR (polymerase chain reaction) revealed that BG2 encodes a cytochrome P450, OsCYP78A13. Sequence search revealed that CYP78A13 has a paralogue Grain Length 3.2 (GL3.2, LOC_Os03g30420) in rice with distinct expression patterns, analysis of transgenic plants harbouring either CYP78A13 or GL3.2 showed that both can promote grain growth. Sequence polymorphism analysis with 1529 rice varieties showed that the nucleotide diversity at CYP78A13 gene body and the 20 kb flanking region in the indica varieties were markedly higher than those in japonica varieties. Further, comparison of the genomic sequence of CYP78A13 in the japonica cultivar Nipponbare and the indica cultivar 9311 showed that there were three InDels in the promoter region and eight SNPs (single nucleotide polymorphism) in its coding sequence. Detailed examination of the transgenic plants with chimaeric constructs suggested that variation in CYP78A13 coding region is responsible for the variation of grain yield. Taken together, our results suggest that the variations in CYP78A13 in the indica varieties hold potential in rice breeding for application of grain yield improvement.

  6. Influence of grain size on transition temperature of thermochromic VO{sub 2}

    SciTech Connect

    Miller, Mark J.; Wang, Junlan

    2015-01-21

    Vanadium(IV) oxide (VO{sub 2}) is a unique material that undergoes a reversible phase transformation around 68 °C. The material could potentially be used as an energy-efficient coating for windows since its reflectance in the infrared (IR) increases significantly more than in the visible region. Currently, VO{sub 2} is limited by a transition temperature (τ{sub c}) that is too high, luminous transmittance that is too low or both. In this study, a transition temperature of 45 °C is achieved for a reactively sputtered, undoped film by restricting grain size to approximately 30 nm. It is concluded that a higher density of grain boundaries (smaller grain size) provides a greater number of nucleating defects which in turn reduces τ{sub c}. Similarly, a higher density of grain boundaries may reduce the hysteresis width (difference between transition temperatures in heating and cooling). Also in this study, a new set of optical performance metrics is proposed in which the solar spectrum is divided into the ultraviolet (UV), visible and near infrared (NIR) regions. This approach is more closely aligned with the goals of limiting UV, allowing luminous and modulating NIR transmission. Using these metrics, the optical properties of the low-τ{sub c} sample were: 2% UV transmittance, 47% luminous transmittance, and 23% NIR modulation (decrease from 43 to 33%). This study demonstrates that the grain size of VO{sub 2} should be viewed as an important parameter for controlling the transition temperature of the material.

  7. Importance of Pore Size Distribution of Fine-grained Sediments on Gas Hydrate Equilibrium

    NASA Astrophysics Data System (ADS)

    Kwon, T. H.; Kim, H. S.; Cho, G. C.; Park, T. H.

    2015-12-01

    Gas hydrates have been considered as a new source of natural gases. For the gas hydrate production, the gas hydrate reservoir should be depressurized below the equilibrium pressure of gas hydrates. Therefore, it is important to predict the equilibrium of gas hydrates in the reservoir conditions because it can be affected by the pore size of the host sediments due to the capillary effect. In this study, gas hydrates were synthesized in fine-grained sediment samples including a pure silt sample and a natural clayey silt sample cored from a hydrate occurrence region in Ulleung Basin, East Sea, offshore Korea. Pore size distributions of the samples were obtained by the nitrogen adsorption and desorption test and the mercury intrusion porosimetry. The equilibrium curve of gas hydrates in the fine-grained sediments were found to be significantly influenced by the clay fraction and the corresponding small pores (>50 nm in diameter). For the clayey silt sample, the equilibrium pressure was higher by ~1.4 MPa than the bulk equilibrium pressure. In most cases of oceanic gas hydrate reservoirs, sandy layers are found interbedded with fine-grained sediment layers while gas hydrates are intensively accumulated in the sandy layers. Our experiment results reveal the inhibition effect of fine-grained sediments against gas hydrate formation, in which greater driving forces (e.g., higher pressure or lower temperature) are required during natural gas migration. Therefore, gas hydrate distribution in interbedded layers of sandy and fine-grained sediments can be explained by such capillary effect induced by the pore size distribution of host sediments.

  8. Grain size reduction and shear heating: a recipe for intermediate-depth earthquake generation?

    NASA Astrophysics Data System (ADS)

    Thielmann, Marcel; Rozel, Antoine

    2016-04-01

    The mechanisms resulting in intermediate-depth earthquakes remain enigmatic, with two processes - dehydration embrittlement and thermal runaway - being the most promising candidates. Using a simple shear one-dimensional model, Thielmann et al. (2015) have shown that the feedback between grain size evolution and shear heating significantly reduces the stress needed to initiate thermal runaway. However, at intermediate depths, Peierls creep as well as dislocation accommodated grain boundary sliding (disGBS) are also viable deformation mechanisms. Here we investigate the impact of those additional creep mechanisms (grain boundary sliding and Peierls creep) on the formation of shear zones. As in Thielmann et al. (2015), we consider both thermal and microstructural damage mechanisms (shear heating and grain size reduction). Depending on material and deformation parameters different creep mechanisms are dominant during deformation, which affects the occurrence and timing of thermal runaway (e.g. at low temperatures and/or high strain rates Peierls creep is dominant and limits the strength of the material which delays thermal runaway). We derive regime diagrams and from them regime boundaries that allow for easy determination of the governing mechanisms and of the localization potential for given material parameters. In one-dimensional models however, the shear zone - once formed - extends infinitely. In nature however, this is not the case. This has potentially a large impact on rupture velocities during shear zone formation. For this reason, we compare the 1D predictions to 2D simulations where fault length is finite.

  9. Size and shape of grain boundary network components and their atomic structures in polycrystalline nanoscale materials

    SciTech Connect

    Xu, Tao; Li, Mo

    2015-10-28

    Microstructure in polycrystalline materials is composed of grain boundary plane, triple junction line, and vertex point. They are the integral parts of the grain boundary network structure and the foundation for the structure-property relations. In polycrystalline, especially nanocrystalline, materials, it becomes increasingly difficult to probe the atomistic structure of the microstructure components directly in experiment due to the size limitation. Here, we present a numerical approach using pair correlation function from atomistic simulation to obtain the detailed information for atomic order and disorder in the grain boundary network in nanocrystalline materials. We show that the atomic structures in the different microstructural components are related closely to their geometric size and shape, leading to unique signatures for atomic structure in microstructural characterization at nanoscales. The dependence varies systematically with the characteristic dimension of the microstructural component: liquid-like disorder is found in vertex points, but a certain order persists in triple junctions and grain boundaries along the extended dimensions of these microstructure components.

  10. [The application of air abrasion in dentistry].

    PubMed

    Mandinić, Zoran; Vulićević, Zoran R; Beloica, Milos; Radović, Ivana; Mandić, Jelena; Carević, Momir; Tekić, Jasmina

    2014-01-01

    One of the main objectives of contemporary dentistry is to preserve healthy tooth structure by applying techniques of noninvasive treatment. Air abrasion is a minimally invasive nonmechanical technique of tooth preparation that uses kinetic energy to remove carious tooth structure. A powerful narrow stream of moving aluminum-oxide particles hit the tooth surface and they abrade it without heat, vibration or noise. Variables that affect speed of cutting include air pressure, particle size, powder flow, tip's size, angle and distance from the tooth. It has been proposed that air abrasion can be used to diagnose early occlusal-surface lesions and treat them with minimal tooth preparation using magnifier. Reported advantages of air abrasion include reduced noise, vibration and sensitivity. Air abrasion cavity preparations have more rounded internal contours than those prepared with straight burs. This may increase the longevity of placed restorations because it reduces the incidence of fractures and a consequence of decreased internal stresses. However, air abrasion cannot be used for all patients, i.e. in cases involving severe dust allergy, asthma, chronic obstructive lung disease, recent extraction or other oral surgery, open wounds, advanced periodontal disease, recent placement of orthodontic appliances and oral abrasions, or subgingival caries removal. Many of these conditions increase the risk of air embolism in the oral soft tissues. Dust control is a challenge, and it necessitates the use of rubber dam, high-volume evacuation, protective masks and safety eyewear for both the patient and the therapist.

  11. Turbidite systems in deep-water basin margins classified by grain size and feeder system

    SciTech Connect

    Reading, H.G. ); Richards, M. )

    1994-05-01

    Depositional system in deep-water basin margins can be classified on the basis of grain size and feeder system into 12 classes: mud-rich, mud/sand-rich, sand-rich, and gravel-rich [open quotes]point-source submarine fans,[close quotes] mud-rich, mud/sand-rich, sand-rich, and gravel-rich [open quotes]multiple-source submarine ramps;[close quotes] and mud-rich, mud/sand-rich, sand-rich, and gravel-rich [open quotes]linear-source slope aprons.[close quotes] The size and stability of channels and the organization of the depositional sequences decreases toward a linear source as does the length:width ratio of the system. As grain size increases, so does slope gradient, impersistence of channel systems, and tendency for channels to migrate. As grain size diminishes, there is an increase in the size of the source area, the size of the depositional system, the downcurrent length, the persistence and size of flows, fan channels, channel-levee systems, and in the tendency to meander and for major slumps and sheet sands to reach the lower fan and basin plan. The exact positioning of any one depositional system within the scheme cannot always be precise and the position may be altered by changes in tectonic, climate, supply, and sea level. The models derived from each system are sufficiently different to significantly affect the nature of petroleum prospectivity and reservoir pattern. Understanding and recognizing this variability is crucial to all elements of the exploration-production chain. In exploration, initial evaluations of prospectivity and commerciality rely on the accurate stratigraphic prediction of reservoir facies, architecture, and trapping styles. For field appraisal and reservoir development, a similar appreciation of variability aids reservoir description by capturing the distribution and architecture of reservoir and nonreservoir facies and their impact on reservoir delineation, reservoir behavior, and production performance. 161 refs., 19 figs., 4 tabs.

  12. Determination of grain size distribution function using two-dimensional Fourier transforms of tone pulse encoded images

    NASA Technical Reports Server (NTRS)

    Generazio, E. R.

    1986-01-01

    Microstructural images may be tone pulse encoded and subsequently Fourier transformed to determine the two-dimensional density of frequency components. A theory is developed relating the density of frequency components to the density of length components. The density of length components corresponds directly to the actual grain size distribution function from which the mean grain shape, size, and orientation can be obtained.

  13. Sediment grain size and surface textural observations of quartz grains in late quaternary lacustrine sediments from Schirmacher Oasis, East Antarctica: Paleoenvironmental significance

    NASA Astrophysics Data System (ADS)

    Warrier, Anish Kumar; Pednekar, Hemant; Mahesh, B. S.; Mohan, Rahul; Gazi, Sahina

    2016-03-01

    In this study we report the sediment grain size parameters and surface textural observations (using scanning electron microscopy (SEM)) of quartz grains from sediments of Sandy Lake, Schirmacher Oasis, East Antarctica. The sediment core spans the last 43 cal ka B.P. The statistical parameters of grain size data (sorting, skewness, kurtosis, mean grain size, D10, D50, D90 and SPAN index) indicate that the sediments are primarily transported by melt-water streams and glaciers. However, during the last glacial period, sediments seem to be transported due to wind activity as evident by the good correlation between rounded quartz data and dust flux data from EPICA ice-core data. The mean grain size values are low during the last glacial period indicating colder climatic conditions and the values increase after the last glacial maximum suggesting an increase in the energy of the transporting medium, i.e., melt-water streams. The sediments are poorly sorted and finely skewed and show different modes of grain size distribution throughout the last 43 cal ka B.P. SEM studies of selected quartz grains and analyses of various surface textures indicate that glacigenic conditions must have prevailed at the time of their transport. Semi-quantitative analyses of mineral (quartz, feldspar, mica, garnet and rock fragments & other minerals) counts suggest a mixed population of minerals with quartz being the dominant mineral. Higher concentration of quartz grains over other minerals indicates that the sediments are compositionally mature. The study reveals the different types of physical weathering, erosive signatures, and chemical precipitation most of them characteristic of glacial environment which affected these quartz grains before final deposition as lake sediments. The palaeoclimatic signals obtained from this study show similarities with ice-core and lake sediment records from Schirmacher Oasis and other ice-free regions in East Antarctica.

  14. Using stream sediment lithology to explore the roles of abrasion and channel network structure in shaping downstream sediment yields

    NASA Astrophysics Data System (ADS)

    Mueller, E. R.; Smith, M. E.; Pitlick, J.

    2012-12-01

    Both the flux and characteristics of stream sediment evolve downstream in response to variations in sediment supply, abrasion rate, and channel network structure. We use a simple erosion-abrasion mass balance to model the downstream evolution of sediment flux in two adjacent watersheds draining differing mixtures of soft and resistant rock types in the northern Rocky Mountains. Measurements of bed sediment grain size and lithology are used in conjunction with measured bed load and suspended load sediment fluxes to constrain the model. The results show that the downstream evolution in bed load flux and composition can be strongly influenced by subtle differences in underlying geology, which shapes both the abrasion characteristics and travel path lengths of individual rock types. In the Big Wood basin, abrasion rapidly reduces the size of soft sedimentary and volcanic rocks exposed in headwater areas, concentrating resistant granitic rocks in the stream bed and depressing bed load in favor of suspended load. Alternatively, in the North Fork Big Lost basin, volcanic and sedimentary lithologies are exposed throughout the catchment, and the bed material becomes dominated by erodible but resistant quartzitic sandstones. The result is a much higher bed load flux best modeled with modest abrasion rates. In both cases, the best-fit model can reproduce within 5% the composition of the stream bed substrate using realistic erosion and abrasion parameters. The results also demonstrate a strong linkage between modern hillslopes and channel systems even in these formerly glaciated landscapes, as the sediment signature of the primary streams reflects the systematic tapping of distinct source areas. While this work shows promise, measurement of the spatial patterns in the size and composition of bed and suspended load fluxes at locations throughout a channel network would better elucidate that relative importance of supply, sorting, and abrasion processes.

  15. Porosity and grain size controls on compaction band formation in Jurassic Navajo Sandstone

    USGS Publications Warehouse

    Schultz, Richard A.; Okubo, Chris H.; Fossen, Haakon

    2010-01-01

    Determining the rock properties that permit or impede the growth of compaction bands in sedimentary sequences is a critical problem of importance to studies of strain localization and characterization of subsurface geologic reservoirs. We determine the porosity and average grain size of a sequence of stratigraphic layers of Navajo Sandstone that are then used in a critical state model to infer plastic yield envelopes for the layers. Pure compaction bands are formed in layers having the largest average grain sizes (0.42–0.45 mm) and porosities (28%), and correspondingly the smallest values of critical pressure (-22 MPa) in the sequence. The results suggest that compaction bands formed in these layers after burial to -1.5 km depth in association with thrust faulting beneath the nearby East Kaibab monocline, and that hardening of the yield caps accompanied compactional deformation of the layers.

  16. Effect of grain size distribution on the development of compaction localization in porous sandstone

    NASA Astrophysics Data System (ADS)

    Cheung, Cecilia S. N.; Baud, Patrick; Wong, Teng-fong

    2012-11-01

    Compaction bands are strain localization structures that are relatively impermeable and can act as barriers to fluid flow in reservoirs. Laboratory studies have shown that discrete compaction bands develop in several sandstones with porosities of 22-25%, at stress states in the transitional regime between brittle faulting and cataclastic flow. To identify the microstructural parameters that influence compaction band formation, we conducted a systematic study of mechanical deformation, failure mode and microstructural evolution in Bleurswiller and Boise sandstones, of similar porosity (˜25%) and mineralogy but different sorting. Discrete compaction bands were observed to develop over a wide range of pressure in the Bleurswiller sandstone that has a relatively uniform grain size distribution. In contrast, compaction localization was not observed in the poorly sorted Boise sandstone. Our results demonstrate that grain size distribution exerts important influence on compaction band development, in agreement with recently published data from Valley of Fire and Buckskin Gulch, as well as numerical studies.

  17. Reading acquisition, developmental dyslexia, and skilled reading across languages: a psycholinguistic grain size theory.

    PubMed

    Ziegler, Johannes C; Goswami, Usha

    2005-01-01

    The development of reading depends on phonological awareness across all languages so far studied. Languages vary in the consistency with which phonology is represented in orthography. This results in developmental differences in the grain size of lexical representations and accompanying differences in developmental reading strategies and the manifestation of dyslexia across orthographies. Differences in lexical representations and reading across languages leave developmental "footprints" in the adult lexicon. The lexical organization and processing strategies that are characteristic of skilled reading in different orthographies are affected by different developmental constraints in different writing systems. The authors develop a novel theoretical framework to explain these cross-language data, which they label a psycholinguistic grain size theory of reading and its development.

  18. Effect of grain size and heavy metals on As immobilization by marble particles.

    PubMed

    Simón, M; García, I; González, V; Romero, A; Martín, F

    2015-05-01

    The effect of grain size and the interaction of heavy metals on As sorption by marble waste with different particle sizes was investigated. Acidic solutions containing only arsenic and a mixture of arsenic, lead, zinc, and cadmium were put in contact with the marble waste. The amount of metal(loid)s that were immobilized was calculated using the difference between the concentration in the acidic solution and in the liquid phase of the suspensions. Approximately 420 μg As m(-2) was sorbed onto the marble grains, both nonspecifically and specifically, where ≥ 80 % of the total arsenic in the acidic solution remained soluble, which suggests that this amendment is not effective to immobilize arsenic. However, in mixed contamination, relatively stable Pb-Ca arsenates were formed on the surface of the marble particles, and the soluble arsenic was reduced by 95 %, which indicates that marble particles can effectively immobilize arsenic and lead when both appear together.

  19. Grain size disposed structural, optical and polarization tuning in ZnO

    NASA Astrophysics Data System (ADS)

    Para, Touseef Ahmad; Reshi, Hilal Ahmad; Pillai, Shreeja; Shelke, Vilas

    2016-08-01

    Structural, optical and polarization properties were investigated in different batches of ZnO synthesized by sol-gel method at varying sintering temperature. The structural visualization and charge scattering density analysis on the basis of X-ray diffraction data indicate polarized nature of sample. The structure- and polarization-related parameters were determined from Raman and Fourier transformed infrared spectroscopy data. Urbach energies and band gap were calculated using UV-visible spectroscopy. We observed increase in polarization, decrease in optical activity and band gap with increasing grain size without any increase in defects. Distortion in ZnO tetrahedra resulted in nonlinear optical behaviour above band edges. The results show direct correlation between grain size, band gap, optical behaviour and polarization. Low band gap and high polarization in ZnO can be employed for the production of opto-electronic devices.

  20. Low pressure shock initiation of porous HMX for two grain size distributions and two densities

    SciTech Connect

    Gustavsen, R.L.; Sheffield, S.A.; Alcon, R.R.

    1995-09-01

    Shock initiation measurements have been made on granular HMX (octotetramethylene tetranitrainine) for two particle size distributions and two densities. Samples were pressed to either 65% or 73% of crystal density from fine ({approx} 10 {mu}m grain size) and coarse (broad distribution of grain sizes peaking at {approx} 150 {mu}m) powders. Planar shocks of 0.2--1 GPa were generated by impacting gas gun driven projectiles on plastic targets containing the HMX. Wave profiles were measured at the input and output of the {approx} 3.9 mm thick HMX layer using electromagnetic particle velocity gauges. The initiation behavior for the two particle size distributions was very different. The coarse HMX began initiating at input pressures as low as 0.5 GPa. Transmitted wave profiles showed relatively slow reaction with most of the buildup occurring at the shock front. In contrast, the fine particle HMX did not begin to initiate at pressures below 0.9 GPa. When the fine powder did react, however, it did so much faster than the coarse HMX. These observations are consistent with commonly held ideas about bum rates being correlated to surface area, and initiation thresholds being correlated with the size and temperature of the hot spots created by shock passage. For each size, the higher density pressings were less sensitive than the lower density pressings.

  1. Disk Radii and Grain Sizes in Herschel-resolved Debris Disks

    NASA Astrophysics Data System (ADS)

    Pawellek, Nicole; Krivov, Alexander V.; Marshall, Jonathan P.; Montesinos, Benjamin; Ábrahám, Péter; Moór, Attila; Bryden, Geoffrey; Eiroa, Carlos

    2014-09-01

    The radii of debris disks and the sizes of their dust grains are important tracers of the planetesimal formation mechanisms and physical processes operating in these systems. Here we use a representative sample of 34 debris disks resolved in various Herschel Space Observatory (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA) programs to constrain the disk radii and the size distribution of their dust. While we modeled disks with both warm and cold components, and identified warm inner disks around about two-thirds of the stars, we focus our analysis only on the cold outer disks, i.e., Kuiper-belt analogs. We derive the disk radii from the resolved images and find a large dispersion for host stars of any spectral class, but no significant trend with the stellar luminosity. This argues against ice lines as a dominant player in setting the debris disk sizes, since the ice line location varies with the luminosity of the central star. Fixing the disk radii to those inferred from the resolved images, we model the spectral energy distribution to determine the dust temperature and the grain size distribution for each target. While the dust temperature systematically increases toward earlier spectral types, the ratio of the dust temperature to the blackbody temperature at the disk radius decreases with the stellar luminosity. This is explained by a clear trend of typical sizes increasing toward more luminous stars. The typical grain sizes are compared to the radiation pressure blowout limit s blow that is proportional to the stellar luminosity-to-mass ratio and thus also increases toward earlier spectral classes. The grain sizes in the disks of G- to A-stars are inferred to be several times s blow at all stellar luminosities, in agreement with collisional models of debris disks. The sizes, measured in the units of s blow, appear to decrease with the luminosity

  2. Disk radii and grain sizes in Herschel-resolved debris disks

    SciTech Connect

    Pawellek, Nicole; Krivov, Alexander V.; Marshall, Jonathan P.; Montesinos, Benjamin; Ábrahám, Péter; Moór, Attila; Bryden, Geoffrey; Eiroa, Carlos

    2014-09-01

    The radii of debris disks and the sizes of their dust grains are important tracers of the planetesimal formation mechanisms and physical processes operating in these systems. Here we use a representative sample of 34 debris disks resolved in various Herschel Space Observatory (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA) programs to constrain the disk radii and the size distribution of their dust. While we modeled disks with both warm and cold components, and identified warm inner disks around about two-thirds of the stars, we focus our analysis only on the cold outer disks, i.e., Kuiper-belt analogs. We derive the disk radii from the resolved images and find a large dispersion for host stars of any spectral class, but no significant trend with the stellar luminosity. This argues against ice lines as a dominant player in setting the debris disk sizes, since the ice line location varies with the luminosity of the central star. Fixing the disk radii to those inferred from the resolved images, we model the spectral energy distribution to determine the dust temperature and the grain size distribution for each target. While the dust temperature systematically increases toward earlier spectral types, the ratio of the dust temperature to the blackbody temperature at the disk radius decreases with the stellar luminosity. This is explained by a clear trend of typical sizes increasing toward more luminous stars. The typical grain sizes are compared to the radiation pressure blowout limit s {sub blow} that is proportional to the stellar luminosity-to-mass ratio and thus also increases toward earlier spectral classes. The grain sizes in the disks of G- to A-stars are inferred to be several times s {sub blow} at all stellar luminosities, in agreement with collisional models of debris disks. The sizes, measured in the units of s {sub blow}, appear to decrease

  3. Effects of the Depth-Dependent Grain Size on the Evolution of Earth's Mantle: Linking Mantle Rheology and Geophysical Observations

    NASA Astrophysics Data System (ADS)

    Glisovic, P.; Forte, A. M.

    2014-12-01

    The effects of the grain size variations on the viscosity are comparable to that of temperature and pressure. A detailed depth-profile of the grain size in the mantle is, however, unknown. To explore the possible depth-dependence of grain size, we use models of coupled core-mantle evolution that include the dynamic effect of surface tectonic plates. We developed an algorithm for modelling: 1) the surface yield stress in a dynamically consistent manner, and 2) the diffusion creep, that is based on the following ingredients: vacancy diffusion in perovskite, depth-dependent grain size, temperature and pressure. This algorithm is able to provide a fit to a wide set of geodynamical observations. Time-dependent convection simulations reveal that the thermal evolution of the mantle is very sensitive to depth-variations in the grain size. We also explore the important feedbacks of thermal convection on the evolution of Earth's mantle rheology.

  4. Grain Size Effect on the Microhardness of BCC Metal Vapor Deposits

    SciTech Connect

    Jankowski, A F; Hayes, J P; Saw, C K; Vallier, R F; Go, J; Bliss, R A

    2004-09-08

    The physical vapor deposition methods of evaporation and sputtering are used to prepare foils of the body-centered-cubic metals, vanadium and tantalum. A two-fold increase in the micro-hardness is measured as the grain size decreases to the sub-micron scale. The micro-hardness of vanadium increases to 2.7 GPa and for tantalum to 2.9 GPa.

  5. Simulating the grain-size distribution of Wisconsinan age glaciofluvial sediments: Applications to fluid transport

    SciTech Connect

    Webb, E.K.; Anderson, M.P. )

    1991-03-01

    A sedimentary deposition model, SEDSIM, was used to simulate the deposition of glaciofluvial sediments in south-central Wisconsin. These types of deposits are present at or near the surface over much of the northern United States and have a high contamination potential. They also represent relatively recent analogs for ancient braided stream systems. Sixty sediment samples were used to determine the average sediment properties for a facies assemblage located 8-10 km from the ice margin. A regional depositional system was simulated, using SEDSIM, to determine the range of input values that reproduced the observed average sediment characteristics. Progressively smaller scale models were constructed to produce more detailed estimates of the grain-size distribution. the grain-size estimates from the finest scale model were translated into relative hydraulic conductivity values using the method of Hazen. The resulting conductivities were incorporated into a fluid flow model to illustrate the control that heterogeneity of petrologic properties has on the direction and rate of fluid movement. This work indicates that a wide range of input parameters will reproduce the bulk sediment properties. Furthermore, small-scale features may not be reproduced under the assumptions incorporated in the current SEDSIM code. Thus, for sedimentary depositional models to be used to predict permeability and porosity distributions, or to interpret paleo-flow conditions, one must determine calibration targets that are more sensitive to flow parameters than bulk grain-size distributions.

  6. Determination of hydraulic conductivity from grain-size distribution for different depositional environments.

    PubMed

    Rosas, Jorge; Lopez, Oliver; Missimer, Thomas M; Coulibaly, Kapo M; Dehwah, Abdullah H A; Sesler, Kathryn; Lujan, Luis R; Mantilla, David

    2014-01-01

    Over 400 unlithified sediment samples were collected from four different depositional environments in global locations and the grain-size distribution, porosity, and hydraulic conductivity were measured using standard methods. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations (e.g., Hazen, Carman-Kozeny) commonly used to estimate hydraulic conductivity from grain-size distribution. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly to the measured hydraulic conductivity values with errors ranging to over 500%. To improve the empirical estimation methodology, the samples were grouped by depositional environment and subdivided into subgroups based on lithology and mud percentage. The empirical methods were then analyzed to assess which methods best estimated the measured values. Modifications of the empirical equations, including changes to special coefficients and addition of offsets, were made to produce modified equations that considerably improve the hydraulic conductivity estimates from grain size data for beach, dune, offshore marine, and river sediments. Estimated hydraulic conductivity errors were reduced to 6 to 7.1 m/day for the beach subgroups, 3.4 to 7.1 m/day for dune subgroups, and 2.2 to 11 m/day for offshore sediments subgroups. Improvements were made for river environments, but still produced high errors between 13 and 23 m/day.

  7. Regolith grain size and cohesive strength of near-Earth Asteroid (29075) 1950 DA

    NASA Astrophysics Data System (ADS)

    Gundlach, B.; Blum, J.

    2015-09-01

    Due to its fast rotation period of 2.12 h, about half of the surface of near-Earth Asteroid (29075) 1950 DA experiences negative (i.e., outward directed) acceleration levels (Rozitis, B., Maclennan, E., Emery, J.P. [2014]. Nature 512, 174-176). Thus, cohesion of the surface material is mandatory to prevent rotational breakup of the asteroid. Rozitis et al. (Rozitis, B., Maclennan, E., Emery, J.P. [2014]. Nature 512, 174-176) concluded that a grain size of ∼6 cm or lower is needed to explain the required cohesive strength of 64-20+12Pa . Here, we present another approach to determine the grain size of near-Earth Asteroid (29075) 1950 DA by using the thermal inertia value from Rozitis et al. (Rozitis, B., Maclennan, E., Emery, J.P. [2014]. Nature 512, 174-176) and a model of the heat conductivity of the surface regolith (Gundlach, B., Blum, J. [2013]. Icarus 223, 479-492). This method yields a mean particle radius ranging from 32 μm to 117 μm. The derived grain sizes are then used to infer the cohesive strength of the surface material of Asteroid (29075) 1950 DA (ranging from 24 Pa to 88 Pa), by using laboratory measurements of the tensile strength of powders.

  8. The influence of grain size coating and shaft angulation of different diamond tips on dental cutting

    PubMed Central

    Santos-Pinto, Lourdes; Bortoletto, Carolina Carvalho; Oliveira, Ana Carolina Mascarenhas; Santos-Pinto, Ary; Zuanon, Angela Cristina Cilense; Lima, Luciana Monti

    2011-01-01

    Objectives: To evaluate the influence of the grain size coating and shaft angulation of ultrasonic and high-speed diamond burs on the dental cutting effectiveness. Materials and Methods: For the grain size evaluation, cavities were prepared on 40 incisors using high-speed (1092 and 1093F KG Sorensen®) and ultrasonic tips (8.2142 and 6.2142-CVDentus®). For the shaft angulation evaluation, cavities were prepared on 40 incisors using uniangulated (T1-CVDentus®) and biangulated (T1-A CVDentus®) ultrasonic tips. The cavities were bisected and examined at ×50 magnification. The width and depth of cavities were measured by Leica QWin software. Kruskal–Wallis non-parametric test was used for analysis. Results: The grain size did not affect the cutting effectiveness, but the high-speed burs promoted deeper and wider cavities than the ultrasonic tips. The shaft angulation did not affect the cutting effectiveness; both the angulated and biangulated tips had greater cutting efficiency in dentin than in enamel. Conclusions: Ultrasonic tips promoted more conservative preparations and seemed promising for cavity preparation. PMID:21814352

  9. Reflectance Spectra of Regolith Analogs in the middle-IR: Influence of Grain Size

    NASA Astrophysics Data System (ADS)

    Le Bras, A.

    1999-09-01

    Reflectance spectroscopy of asteroids permits to infer the mineral composition of their surface. Since spectral mineral features are sensitive to surface parameters such as grain size, regolith compactness, temperature, maturity,... the interpretation of remote-sensing asteroids spectra is not easy nor unique. Asteroids family members show a continuous dispersion of their spectral characteristics (Doressoudiram et al., 1997) which seems to be due first to a compositional variation but also to some space weathering processes. Space weathering may contribute to the spectral dispersion of the smallest S-type asteroids too. New laboratory spectra are required in order to understand the influence of surface parameters and space weathering effects, and to interpret the recent high-spectral resolution observations from ISO. We started an experimental program at Institut d'Astrophysique Spatiale (Orsay, France), using the 2.5-120 microns interferometer spectrometer, to study the influence of surface parameters on mineral features. First, we study grain size effects with two types of terrestrial rocks: anorthosite (bright) and basalt (dark) in the 2-40 microns range. In a second part, we will extend our experiments to other samples (meteorites and asteroid-like mixtures), and to the visible and NIR range. We present the experimental setup and the preliminary results obtained for 6 different grain size ranges with basalt and anorthosite.

  10. Computer program for the calculation of grain size statistics by the method of moments

    USGS Publications Warehouse

    Sawyer, Michael B.

    1977-01-01

    A computer program is presented for a Hewlett-Packard Model 9830A desk-top calculator (1) which calculates statistics using weight or point count data from a grain-size analysis. The program uses the method of moments in contrast to the more commonly used but less inclusive graphic method of Folk and Ward (1957). The merits of the program are: (1) it is rapid; (2) it can accept data in either grouped or ungrouped format; (3) it allows direct comparison with grain-size data in the literature that have been calculated by the method of moments; (4) it utilizes all of the original data rather than percentiles from the cumulative curve as in the approximation technique used by the graphic method; (5) it is written in the computer language BASIC, which is easily modified and adapted to a wide variety of computers; and (6) when used in the HP-9830A, it does not require punching of data cards. The method of moments should be used only if the entire sample has been measured and the worker defines the measured grain-size range. (1) Use of brand names in this paper does not imply endorsement of these products by the U.S. Geological Survey.

  11. Prediction of grain size of nanocrystalline nickel coatings using adaptive neuro-fuzzy inference system

    NASA Astrophysics Data System (ADS)

    Hayati, M.; Rashidi, A. M.; Rezaei, A.

    2011-01-01

    This paper presents application of adaptive neuro-fuzzy inference system (ANFIS) for prediction of the grain size of nanocrystalline nickel coatings as a function of current density, saccharin concentration and bath temperature. For developing ANFIS model, the current density, saccharin concentration and bath temperature are taken as input, and the resulting grain size of the nanocrystalline coating as the output of the model. In order to provide a consistent set of experimental data, the nanocrystalline nickel coatings have been deposited from Watts-type bath using direct current electroplating within a large range of process parameters i.e., current density, saccharin concentration and bath temperature. Variation of the grain size because of the electroplating parameters has been modeled using ANFIS, and the experimental results and theoretical approaches have been compared to each other as well. Also, we have compared the proposed ANFIS model with artificial neural network (ANN) approach. The results have shown that the ANFIS model is more accurate and reliable compared to the ANN approach.

  12. An attempt to detect sedimentary materials grain size using texture analysis of FCIR orthophotos

    NASA Astrophysics Data System (ADS)

    Deluigi, Nicola; Lambiel, Christophe

    2014-05-01

    Grain size is one of the main factors controlling the ground (surface) temperature, and thus the permafrost occurrence in mountain areas. Its automatic detection may thus help to improve the distribution models of the phenomenon. The physical properties of the ground surface can be detected by performing image texture analysis. As texture is usually defined as the spatial variation of the gray values in an image or the variation of its spectral radiance, texture operators can provide useful information about the spatial variation of the ground surface characteristics. For this study false-color infrared (FCIR) orthophotos were used (0.25 meters resolution). These five channels (PAN, NIR, R, G, B) images were recorded with airborne digital sensor (ADS) digital cameras by the Swiss federal office of topography (swisstopo). They cover two test sites located in the Western Valais Alps (Switzerland). In a preliminary step some regions of interest were delineated. Hydrography network, glaciers and human infrastructures (buildings, roads, etc.) were masked from FCIR images by extraction from a primary surfaces map (swisstopo). Vegetation was distinguished and extracted thanks to the Normalized Difference of Vegetation Index (NDVI), calculated with the NIR and Red bands. Finally, the resulting dataset was only composed by mineral-covered surfaces. In a second step, we computed a Principal Component Analysis (PCA) in order to find the combination of bands that contain most spectral information. Various texture operators such tonal features (mean, variance, skewness and kurtosis of gray levels) as well as texture features computed from gray level co-occurrence matrices (entropy, homogeneity, energy, etc.) were performed on the first principal component using different moving windows (3x3, 5x5, 7x7, 9x9). The grain size classification was lately performed on a new dataset whose variables correspond to the various combinations of moving window sizes and the corresponding

  13. How well does end-member modelling analysis of grain size data work?

    NASA Astrophysics Data System (ADS)

    Schulte, Philipp; Dietze, Michael; Dietze, Elisabeth

    2014-05-01

    End-member modelling analysis (EMMA) is a powerful and flexible statistic approach to identify and quantify generic sediment transport processes from multimodal grain-size distributions. EMMA has been introduced over 15 years ago and is now available in different approaches as encapsulated FORTRAN code (Weltje, 1997), Matlab-script (Dietze et al., 2012) and the R-package EMMAgeo (Dietze and Dietze, 2013). EMMA was mainly used to reconstruct past sedimentation processes in a variety of sedimentary environments (marine, aeolian, lacustrine). Typically, it is rather difficult to assess how meaningful and well the model performs in a certain environment, since neither the actual process end-members (generic grain-size distributions sorted by a certain sediment transport) nor their individual contributions to each sample are known a priori. To allow a comprehensive performance test, we sampled a set of four known process end-members: alluvial sand (main mode: 0.70±0.55 φ), dune sand (main mode: 1.35±0.60 φ), loess (main mode: 4.71±0.65 φ) and overbank deposit (main mode: 5.81±1.62 φ). High resolution grain-size information is based on laser-diffraction analysis (116 classes). The four process end-members were artificially mixed with random, but known proportions to yield 100 samples. This mixed data set was measured again with the laser particle size analyser and served as input for EMMA within the R-package EMMAgeo. This contribution discusses the ability of EMMA to identify and characterise the four distinct process end-members and quantify their contributions to each sample. Different ways to estimate uncertainties are presented. Further evaluations focus on the influence of numbers of included samples, numbers of grain-size classes, vertical mixing of samples (simulating turbation) and self-similarity of process end-members. Dietze E, et al. 2012. An end-member algorithm for deciphering modern detrital processes from lake sediments of Lake Donggi Cona, NE

  14. Grain size distribution and composition of modern dune and beach sediments, Malindi Bay coast, Kenya

    NASA Astrophysics Data System (ADS)

    Abuodha, J. O. Z.

    2003-02-01

    Grain size distribution and heavy mineral content of beach and dune sediments from the Malindi Bay coast, Kenya were determined. Grain sizes were determined by dry sieving sediments; samples represent the upper 5 mm of surficial sediment, collected from the four main geomorphological units (beach, berm zone, foredune and dunefield), during three observation periods, covering the southeast and northeast monsoon seasons. Sediment samples were grouped according to whether they were collected from the northern or southern sector of the Sabaki river. The heavy mineral content of several samples collected from the beach, berm zone and sand dunes was obtained by using separating funnels and tetrabromomethane to gain insight into the mineral distribution, the mineralogy and comment on the economic potential of prospecting for the heavy minerals. The petrographic parameters determined include the heavy mineral weight percentages and the mineral composition of the heavy fractions obtained using a petrographic microscope. The Malindi Bay shore is dominated by terrigenous deposits brought in by the Sabaki river which consist mainly of fine- to medium-grained quartz sand. The sediments also contain heavy minerals averaging about 15%, with highest concentration being 67% by weight for the samples analyzed. The heavy mineral suite here is dominated by opaque iron-titanium minerals as well as some red garnet and zircon. The results demonstrate a good relationship between the heavy mineral concentrations and the corresponding geomorphological elements. There are some differences between the various geomorphological units, with a subtle trend from the beach to the dunes. During all three observation periods grain size decreases slightly from the beach to the foredune. The sediment size fraction 0.625∅, present on the beach, was absent in the immediate aeolian environments, except for the steep slopes of sand sheets and interdune valleys. The berm zone rarely has sediments coarser

  15. Only pick the right grains: Modelling the bias due to subjective grain-size interval selection for chronometric and fingerprinting approaches.

    NASA Astrophysics Data System (ADS)

    Dietze, Michael; Fuchs, Margret; Kreutzer, Sebastian

    2016-04-01

    Many modern approaches of radiometric dating or geochemical fingerprinting rely on sampling sedimentary deposits. A key assumption of most concepts is that the extracted grain-size fraction of the sampled sediment adequately represents the actual process to be dated or the source area to be fingerprinted. However, these assumptions are not always well constrained. Rather, they have to align with arbitrary, method-determined size intervals, such as "coarse grain" or "fine grain" with partly even different definitions. Such arbitrary intervals violate principal process-based concepts of sediment transport and can thus introduce significant bias to the analysis outcome (i.e., a deviation of the measured from the true value). We present a flexible numerical framework (numOlum) for the statistical programming language R that allows quantifying the bias due to any given analysis size interval for different types of sediment deposits. This framework is applied to synthetic samples from the realms of luminescence dating and geochemical fingerprinting, i.e. a virtual reworked loess section. We show independent validation data from artificially dosed and subsequently mixed grain-size proportions and we present a statistical approach (end-member modelling analysis, EMMA) that allows accounting for the effect of measuring the compound dosimetric history or geochemical composition of a sample. EMMA separates polymodal grain-size distributions into the underlying transport process-related distributions and their contribution to each sample. These underlying distributions can then be used to adjust grain-size preparation intervals to minimise the incorporation of "undesired" grain-size fractions.

  16. Effects of particle optical properties on grain size measurements of aeolian dust deposits

    NASA Astrophysics Data System (ADS)

    Varga, György; Újvári, Gábor; Kovács, János; Szalai, Zoltán

    2015-04-01

    Particle size data are holding crucial information on the sedimentary environment at the time the aeolian dust deposits were accumulated. Various aspects of aeolian sedimentation (wind strength, distance to source(s), possible secondary source regions and modes of sedimentation and transport) can be reconstructed from proper grain size distribution data. Laser diffraction methods provide much more accurate and reliable information on the major granulometric properties of wind-blown sediments compared to the sieve and pipette methods. The Fraunhofer and Mie scattering theories are generally used for laser diffraction grain size measurements. () The two different approaches need different 'background' information on the medium measured. During measurements following the Fraunhofer theory, the basic assumption is that parcticles are relatively large (over 25-30 µm) and opaque. The Mie theory could offer more accurate data on smaller fractions (clay and fine silt), assuming that a proper, a'priori knowledge on refraction and absorption indices exists, which is rarely the case for polymineral samples. This study is aimed at determining the effects of different optical parameters on grain size distributions (e.g. clay-content, median, mode). Multiple samples collected from Hungarian red clay and loess-paleosol records have been analysed using a Malvern Mastersizer 3000 laser diffraction particle sizer (with a Hydro LV unit). Additional grain size measurements have been made on a Fritsch Analysette 22 Microtec and a Horiba Partica La-950 v2 instrument to investigate possible effects of the used laser sources with different wavelengths. XRF and XRD measurements have also been undertaken to gain insight into the geochemical/mineralogical compositions of the samples studied. Major findings include that measurements using the Mie theory provide more accurate data on the grain size distribution of aeolian dust deposits, when we use a proper optical setting. Significant

  17. Grain-size and grain-shape analyses using digital imaging technology: Application to the fluvial formation of the Ngandong paleoanthropological site in Central Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Sipola, Maija

    2013-04-01

    This study implements grain-size and grain-shape analyses to better understand the fluvial processes responsible for forming the Ngandong paleoanthropological site along the Solo River in Central Java. The site was first discovered and excavated by the Dutch Geological Survey in the early 1930's, during which fourteen Homo erectus fossils and thousands of other macrofaunal remains were uncovered. The Homo erectus fossils discovered at Ngandong are particularly interesting to paleoanthropologists because the morphology of the excavated crania suggests they are from a recently-living variety of the species. The primary scientific focus for many years has been to determine the absolute age of the Ngandong fossils, while the question of exactly how the Ngandong site itself formed has been frequently overlooked. In this study I use Retsch CAMSIZER digital imaging technology to conduct grain-size and grain-shape analyses of sediments from the terrace stratigraphy at the Ngandong site to understand if there are significant differences between sedimentary layers in grain-size and/or grain-shape, and what these differences mean in terms of local paleoflow dynamics over time. Preliminary analyses indicate there are four distinct sedimentary layers present at Ngandong with regard to size sorting, with the fossil-bearing layers proving to be the most poorly-sorted and most similar to debris-flow deposits. These results support hypotheses by geoarchaeologists that the fossil-bearing layers present at Ngandong were deposited during special flow events rather than under normal stream flow conditions.

  18. Grain-size signature of Saharan dust over the Atlantic Ocean at 12°N

    NASA Astrophysics Data System (ADS)

    van der Does, Michelle; Korte, Laura; Munday, Chris; Brummer, Geert-Jan; Stuut, Jan-Berend

    2015-04-01

    Every year, an estimated 200 million tons of Saharan dust are deposited in the Atlantic Ocean. On its way from source to sink, the dust can be influenced by many climatic processes, but it also affects climate itself in various ways that are far from understood. In order to constrain the relations between atmospheric dust and climate, we deployed ten submarine sediment traps along a transect in the Atlantic Ocean at 12˚N, at 1200m and 3500m water depth. These have been sampling Saharan dust settling in the ocean since October 2012. Samples of seven of these sediment traps have been successfully recovered during RV Pelagia cruise 64PE378 in November 2013. The transect also includes three floating dust collectors and two on-land dust collectors, and all the instruments lie directly underneath the largest dust plume originating from the African continent. This study focuses on the size of the dust particles, which can have an effect on the positive or negative radiation balance in the atmosphere. Small particles in the high atmosphere can reflect incoming radiation and therefore have a cooling effect on climate. Large particles in the lower atmosphere have the opposite effect by absorbing reflected radiation from the Earth's surface. Mineral dust also affects carbon export to the deep ocean by providing mineral ballast for organic particles, and the size of the dust particles directly relates to the downward transport velocity. Here I will present the measured grain-size distributions of samples from seven sediment traps recovered from the 12°N-latitude transect. The data show seasonal variations, with finer grained dust particles during winter and spring, and coarser grained particles during summer and fall. Samples from multiple years should give more details about the dust's seasonality. Also a fining trend of the grain sizes of the dust particles from source (Africa) to sink (Caribbean) is observed, which is also expected due to intuitive relationships between

  19. Debris flow grain size scales with sea surface temperature over glacial-interglacial timescales

    NASA Astrophysics Data System (ADS)

    D'Arcy, Mitch; Roda Boluda, Duna C.; Whittaker, Alexander C.; Araújo, João Paulo C.

    2015-04-01

    Debris flows are common erosional processes responsible for a large volume of sediment transfer across a range of landscapes from arid settings to the tropics. They are also significant natural hazards in populated areas. However, we lack a clear set of debris flow transport laws, meaning that: (i) debris flows remain largely neglected by landscape evolution models; (ii) we do not understand the sensitivity of debris flow systems to past or future climate changes; and (iii) it remains unclear how to interpret debris flow stratigraphy and sedimentology, for example whether their deposits record information about past tectonics or palaeoclimate. Here, we take a grain size approach to characterising debris flow deposits from 35 well-dated alluvial fan surfaces in Owens Valley, California. We show that the average grain sizes of these granitic debris flow sediments precisely scales with sea surface temperature throughout the entire last glacial-interglacial cycle, increasing by ~ 7 % per 1 ° C of climate warming. We compare these data with similar debris flow systems in the Mediterranean (southern Italy) and the tropics (Rio de Janeiro, Brazil), and find equivalent signals over a total temperature range of ~ 14 ° C. In each area, debris flows are largely governed by rainfall intensity during triggering storms, which is known to increase exponentially with temperature. Therefore, we suggest that these debris flow systems are transporting predictably coarser-grained sediment in warmer, stormier conditions. This implies that debris flow sedimentology is governed by discharge thresholds and may be a sensitive proxy for past changes in rainfall intensity. Our findings show that debris flows are sensitive to climate changes over short timescales (≤ 104 years) and therefore highlight the importance of integrating hillslope processes into landscape evolution models, as well as providing new observational constraints to guide this. Finally, we comment on what grain size

  20. Interpreting Hydraulic Conditions from Morphology, Sedimentology, and Grain Size of Sand Bars in the Colorado River in Grand Canyon

    NASA Astrophysics Data System (ADS)

    Rubin, D. M.; Topping, D. J.; Schmidt, J. C.; Grams, P. E.; Buscombe, D.; East, A. E.; Wright, S. A.

    2015-12-01

    During three decades of research on sand bars and sediment transport in the Colorado River in Grand Canyon, we have collected unprecedented quantities of data on bar morphology, sedimentary structures, grain size of sand on the riverbed (~40,000 measurements), grain size of sand in flood deposits (dozens of vertical grain-size profiles), and time series of suspended sediment concentration and grain size (more than 3 million measurements using acoustic and laser-diffraction instruments sampling every 15 minutes at several locations). These data, which include measurements of flow and suspended sediment as well as sediment within the deposits, show that grain size within flood deposits generally coarsens or fines proportionally to the grain size of sediment that was in suspension when the beds were deposited. The inverse problem of calculating changing flow conditions from a vertical profile of grain size within a deposit is difficult because at least two processes can cause similar changes. For example, upward coarsening in a deposit can result from either an increase in discharge of the flow (causing coarser sand to be transported to the depositional site), or from winnowing of the upstream supply of sand (causing suspended sand to coarsen because a greater proportion of the bed that is supplying sediment is covered with coarse grains). These two processes can be easy to distinguish where suspended-sediment observations are available: flow-regulated changes cause concentration and grain size of sand in suspension to be positively correlated, whereas changes in supply can cause concentration and grain size of sand in suspension to be negatively correlated. The latter case (supply regulation) is more typical of flood deposits in Grand Canyon.

  1. Reproductive Potential of Salmon Spawning Substrates Inferred from Grain Size and Fish Length

    NASA Astrophysics Data System (ADS)

    Riebe, C. S.; Sklar, L. S.; Overstreet, B. T.; Wooster, J. K.; Bellugi, D. G.

    2014-12-01

    The river restoration industry spends millions of dollars every year on improving salmon spawning in riverbeds where sediment is too big for fish to move and thus use during redd building. However, few studies have addressed the question of how big is too big in salmon spawning substrates. Hence managers have had little quantitative basis for gauging the amount of spawning habitat in coarse-bedded rivers. Moreover, the scientific framework has remained weak for restoration projects that seek to improve spawning conditions. To overcome these limitations, we developed a physically based, field-calibrated model for the fraction of the bed that is fine-grained enough to support spawning by fish of a given size. Model inputs are fish length and easy-to-measure indices of bed-surface grain size. Model outputs include the number of redds and eggs the substrate can accommodate when flow depth, temperature, and other environmental factors are not limiting. The mechanistic framework of the model captures the biophysical limits on sediment movement and the space limitations on redd building and egg deposition in riverbeds. We explored the parameter space of the model and found a previously unrecognized tradeoff in salmon size: bigger fish can move larger sediment and thus use more riverbed area for spawning; they also tend to have higher fecundity, and so can deposit more eggs per redd; however, because redd area increases with fish length, the number of eggs a substrate can accommodate is highest for moderate-sized fish. One implication of this tradeoff is that differences in grain size may help regulate river-to-river differences in salmon size. Thus, our model suggests that population diversity and, by extension, species resilience are linked to lithologic, geomorphic, and climatic factors that determine grain size in rivers. We cast the model into easy-to-use look-up tables, charts, and computer applications, including a JavaScript app that works on tablets and mobile

  2. Modelling the size and composition of fruit, grain and seed by process-based simulation models.

    PubMed

    Martre, Pierre; Bertin, Nadia; Salon, Christophe; Génard, Michel

    2011-08-01

    Understanding what determines the size and composition of fruit, grain and seed in response to the environment and genotype is challenging, as these traits result from several linked processes controlled at different levels of organization, from the subcellular to the crop level, with subtle interactions occurring at or between the levels of organization. Process-based simulation models (PBSMs) implement algorithms to simulate metabolic and biophysical aspects of cell, tissue and organ behaviour. In this review, fruit, grain and seed PBSMs describing the main phases of growth, development and storage metabolism are discussed. From this concurrent work, it is possible to identify generic storage organ processes which can be modelled similarly for fruit, grain and seed. Spatial heterogeneity at the tissue and whole-plant level is found to be a key consideration in modelling the effects of the environment and genotype on fruit, grain and seed end-use value. In the future, PBSMs may well become the main link between studies at the molecular and whole-plant levels. To bridge this phenotype-to-genotype gap, future models need to remain plastic without becoming overparameterized.

  3. Effect of Grain Size on Uranium(VI) Surface Complexation Kinetics and Adsorption Additivity

    SciTech Connect

    Shang, Jianying; Liu, Chongxuan; Wang, Zheming; Zachara, John M.

    2011-07-27

    Laboratory experiments were performed to investigate the contribution of variable grain sizes to uranium adsorption/desorption in a sediment collected from the US DOE Hanford site. The sediment was wet-sieved into four size fractions: coarse sand (1-2 mm), medium sand (0.2-1 mm), fine sand (0.05-0.2 mm), and clay/silt fraction (< 0.05mm). For each size fraction and their composite (sediment), batch experiments were performed to determine uranium adsorption isotherms, and stirred flow-cell experiments were conducted to derive kinetic data of uranium adsorption and subsequent desorption. The results showed that uranium adsorption isotherms and adsorption/desorption kinetics were size-specific, reflecting the effects of size-specific adsorption site concentration and kinetic rate constants. The larger-size fraction had a larger mass percentage in the sediment, but with a smaller adsorption site concentration and generally a slower uranium adsorption/desorption rate. The same equilibrium surface complexation reaction and reaction constant could describe uranium adsorption isotherms for all size fractions and the composite after accounting for the effect of adsorption site concentration. Mass-weighted, linear additivity was observed for both uranium adsorption isotherms and adsorption/desorption kinetics in the composite. Our analysis also showed that uranium adsorption site concentration estimated from the adsorption isotherms was 3 orders of magnitude less than a site concentration estimated from sediment surface area and generic site density. One important implication of this study is that grain size distribution may be used to estimate uranium adsorption site, and adsorption/desorption kinetic rates in heterogeneous sediments from a common location.

  4. Determination of the total grain size distribution in a vulcanian eruption column, and its implications to stratospheric aerosol perturbation

    NASA Astrophysics Data System (ADS)

    Murrow, P. J.; Rose, W. I., Jr.; Self, S.

    1980-11-01

    The total grain distribution of tephra from the eruption by the Fuego volcano in Guatemala on Oct. 14, 1974 was determined by grain size analysis. The region within each isopach has a grain distribution which was weighted proportionally to its percentage volume; the total distribution had a median grain size of 0.6 mm and a sorting coefficient of 2.3. The ash composed of fine particles did not fall in the volcano area as part of the recognizable tephra blanket; the eruption column reached well into the stratosphere to the height of 10-12 km above sea level, with mass flux rate estimated altitudes of 18-23 km

  5. The Influence of Grain Size on Twinning and Microstructure Refinement During Cold Rolling of Commercial-Purity Titanium

    NASA Astrophysics Data System (ADS)

    Zherebtsov, S. V.; Dyakonov, G. S.; Salishchev, G. A.; Salem, A. A.; Semiatin, S. L.

    2016-08-01

    Microstructure evolution in commercial-purity titanium (CP Ti) with various initial grain sizes (1, 7, 15, and 30 μm) during plane-strain multipass rolling to a true thickness strain of 2.66 at 293 K (20 °C) was established. The degree of deformation twinning was found to be strongly dependent on grain size. Twinning was rare in the material with a grain size of 1 μm. For all grain sizes >15 μm, the occurrence of twinning reached a similar, maximum level. Concurrently, the propensity for twinning enhanced the kinetics of microstructure refinement particularly for the initially coarse-grain materials. Due to the extensive twinning-induced microstructure refinement, rolling of coarse-grain (15 μm) CP Ti to a true thickness strain of 2.66 resulted in the formation of an ultrafine microstructure with a grain/subgrain size of 200-300 nm, a value similar to that attained for the initially micrometer-scale microstructure. The effect of grain size on twinning in titanium was discussed in the context of a disclination model.

  6. The Influence of Grain Size on Twinning and Microstructure Refinement During Cold Rolling of Commercial-Purity Titanium

    NASA Astrophysics Data System (ADS)

    Zherebtsov, S. V.; Dyakonov, G. S.; Salishchev, G. A.; Salem, A. A.; Semiatin, S. L.

    2016-10-01

    Microstructure evolution in commercial-purity titanium (CP Ti) with various initial grain sizes (1, 7, 15, and 30 μm) during plane-strain multipass rolling to a true thickness strain of 2.66 at 293 K (20 °C) was established. The degree of deformation twinning was found to be strongly dependent on grain size. Twinning was rare in the material with a grain size of 1 μm. For all grain sizes >15 μm, the occurrence of twinning reached a similar, maximum level. Concurrently, the propensity for twinning enhanced the kinetics of microstructure refinement particularly for the initially coarse-grain materials. Due to the extensive twinning-induced microstructure refinement, rolling of coarse-grain (15 μm) CP Ti to a true thickness strain of 2.66 resulted in the formation of an ultrafine microstructure with a grain/subgrain size of 200-300 nm, a value similar to that attained for the initially micrometer-scale microstructure. The effect of grain size on twinning in titanium was discussed in the context of a disclination model.

  7. Dependence of Grain Size on the Performance of a Polysilicon Channel TFT for 3D NAND Flash Memory.

    PubMed

    Kim, Seung-Yoon; Park, Jong Kyung; Hwang, Wan Sik; Lee, Seung-Jun; Lee, Ki-Hong; Pyi, Seung Ho; Cho, Byung Jin

    2016-05-01

    We investigated the dependence of grain size on the performance of a polycrystalline silicon (poly-Si) channel TFT for application to 3D NAND Flash memory devices. It has been found that the device performance and memory characteristics are strongly affected by the grain size of the poly-Si channel. Higher on-state current, faster program speed, and poor endurance/reliability properties are observed when the poly-Si grain size is large. These are mainly attributed to the different local electric field induced by an oxide valley at the interface between the poly-Si channel and the gate oxide. In addition, the trap density at the gate oxide interface was successfully measured using a charge pumping method by the separation between the gate oxide interface traps and traps at the grain boundaries in the poly-Si channel. The poly-Si channel with larger grain size has lower interface trap density. PMID:27483868

  8. Effect of specimen size and grain orientation on the mechanical and physical properties of NBG-18 nuclear graphite

    NASA Astrophysics Data System (ADS)

    Vasudevamurthy, G.; Byun, T. S.; Pappano, P.; Snead, L. L.; Burchell, T. D.

    2015-07-01

    We present here a comparison of the measured baseline mechanical and physical properties of with grain (WG) and against grain (AG) non-ASTM size NBG-18 graphite. The objectives of the experiments were twofold: (1) assess the variation in properties with grain orientation; (2) establish a correlation between specimen tensile strength and size. The tensile strength of the smallest sized (4 mm diameter) specimens were about 5% higher than the standard specimens (12 mm diameter) but still within one standard deviation of the ASTM specimen size indicating no significant dependence of strength on specimen size. The thermal expansion coefficient and elastic constants did not show significant dependence on specimen size. Experimental data indicated that the variation of thermal expansion coefficient and elastic constants were still within 5% between the different grain orientations, confirming the isotropic nature of NBG-18 graphite in physical properties.

  9. Effect of specimen size and grain orientation on the mechanical and physical properties of NBG-18 nuclear graphite

    SciTech Connect

    Vasudevamurthy, Gokul; Byun, Thak Sang; Pappano, Pete; Snead, Lance L.; Burchell, Tim D.

    2015-03-13

    We present here a comparison of the measured baseline mechanical and physical properties of with grain (WG) and against grain (AG) non-ASTM size NBG-18 graphite. The objectives of the experiments were twofold: (1) assess the variation in properties with grain orientation; (2) establish a correlation between specimen tensile strength and size. The tensile strength of the smallest sized (4 mm diameter) specimens were about 5% higher than the standard specimens (12 mmdiameter) but still within one standard deviation of the ASTM specimen size indicating no significant dependence of strength on specimen size. The thermal expansion coefficient and elastic constants did not show significant dependence on specimen size. Experimental data indicated that the variation of thermal expansion coefficient and elastic constants were still within 5% between the different grain orientations, confirming the isotropic nature of NBG-18 graphite in physical properties.

  10. Trends in grain size and surface area of glacial and non-glacial alluvial sediments: Building a paleoclimate proxy for deep-time

    NASA Astrophysics Data System (ADS)

    Marra, K. R.; Keiser, L.; Soreghan, G. S.; Elwood-Madden, M.

    2011-12-01

    Extent of chemical and physical weathering in sediments depends upon climatic factors, which affect both the mode of sediment production and the rate of chemical reactions. Most glacial systems are capable of producing large amounts of fine-grained sediments, due to glacial grinding and abrasion, which increases the surface area of mineral constituents. Increased surface area enhances rates of chemical weathering despite cold temperatures, which are typically considered to limit rates of chemical reactions due to relatively high activation energies. The amount of chemical weathering in non-glacial systems depends upon erosion rates, although modes of sediment production differ, with temperature exerting a secondary control. To assess variations in weathering rates and products in cold-arid relative to semi-arid climates, sediment samples were collected every 500 m along 5-7 km fluvial transects in the Dry Valleys, Antarctica and the Wichita Mountains of Oklahoma, where bedrock (granitoid), drainage area, and relief are similar. Sediments were sieved for the gravel, sand, and mud (< 63 μm) fractions. The mud fraction was treated with acetic acid and hydrogen peroxide to remove carbonate and organics, and then analyzed for surface area (nitrogen absorption BET) and grain size. Preliminary grain size analysis of sediments from Clark Glacier stream (Wright Valley, Antarctica) shows the mud fraction coarsens with distance along a 5 km transect and surface area correspondingly decreases, suggesting weathering products (clays) are not being produced in this climate but are being dissolved. Sediments collected along a 5 km transect from Blue Beaver Creek in the Wichita Mountains show the opposite, wherein a downstream decrease in grain size and increase in surface area likely relate to precipitation of secondary weathering phases. XRD and whole-rock geochemical analyses are currently underway to further assess chemical weathering signatures in glacial and non

  11. Convergent evolution of abrading flow obstacles: Insights from analogue modelling of fluvial bedrock abrasion by coarse bedload

    NASA Astrophysics Data System (ADS)

    Wilson, Andrew; Lavé, Jérôme

    2014-03-01

    Upstream-facing convex surfaces (UFCS) are formed by bedload abrasion in bedrock rivers and indicate the recent, significant action of bedload abrasion in causing channel incision. Beyond this, little is known of the dynamics of UFCS and the effect of substrate and bedload properties on rates and distribution of bedload abrasion for these bed roughness elements. Grain size populations from 1 to 8 cm (b-axis, in 1- or 2-cm bin widths) were used to bombard preshaped marble and limestone targets bolted to the base of an annular flume. The control of initial shape and lithology of the target and the erodent grain size and lithology were investigated by monitoring the evolution of the target form using laser scanning at predefined time intervals. Eleven experiment suites were carried out containing three initial target shapes constructed from two lithologies, four bedload (erodent) grain sizes of either granodiorites or limestone, or clear water flow. All 10 targets abraded by bedload evolved from their initial form into a steady state (time invariant) form, producing UFCSs. Steady state forms were closely similar for all targets despite different initial conditions. Bedload grain size has a strong control on this equilibrium form, related to the transit path of the grains when moving over the target, whilst initial target form has only a weak control. Steady state morphology is achieved more rapidly with harder erodent bedload particles and/or softer targets. Upstream-facing convex surface stoss sides were characterised by a brighter, sugary, granular appearance on the rock-forming grain scale. Increasing erodent grain size, for a fixed bedload mass, increased the bulk abrasion rate at fixed flow speed and discharge. No detectable erosion occurred for a limestone block in clear water flows under the same flow conditions, indicating solution and cavitation were insignificant mechanisms of erosion in this study. During the experiment suites, suspended load abrasion was

  12. Microplastics in the Mediterranean Sea: Deposition in coastal shallow sediments, spatial variation and preferential grain size.

    PubMed

    Alomar, Carme; Estarellas, Fernando; Deudero, Salud

    2016-04-01

    Marine litter loads in sea compartments are an emergent issue due to their ecological and biological consequences. This study addresses microplastic quantification and morphological description to test spatial differences along an anthropogenic gradient of coastal shallow sediments and further on to evaluate the preferential deposition of microplastics in a given sediment grain fraction. Sediments from Marine Protected Areas (MPAs) contained the highest concentrations of microplastics (MPs): up to 0.90 ± 0.10 MPs/g suggesting the transfer of microplastics from source areas to endpoint areas. In addition, a high proportion of microplastic filaments were found close to populated areas whereas fragment type microplastics were more common in MPAs. There was no clear trend between sediment grain size and microplastic deposition in sediments, although microplastics were always present in two grain size fractions: 2 mm > x > 1 mm and 1 mm > x 0.5 mm. PMID:26803229

  13. Influence of metal grain size on surface-enhanced Raman scattering

    SciTech Connect

    XDawson, P. ); Alexander, K.B.; Thompson, J.R.; Haas, J.W. III; Ferrell, T.L. )

    1991-09-15

    The surface roughness of nominally smooth and of randomly roughened thin silver films is characterized using scanning tunneling microscopy and the metal grain size is assessed using transmission electron microscopy. On each type of substrate used, glass or CaF{sub 2}-roughened glass, the silver films are deposited either very slowly ({similar to}0.15 nm s{sup {minus}1}) or quite quickly ({similar to}2.0 nm s{sup {minus}1}). Only silver films deposited on CaF{sub 2}-roughened glass yield measurable surface-enhanced Raman signals for benzoic acid; the enhancement is brought about by surface field amplification due to the excitation of delocalized surface-plasmon polaritons. However, the surface-enhanced Raman signals obtained from the slow-deposited silver films are significantly better (by about a factor of 3) than those obtained from the fast-deposited silver films on a given CaF{sub 2}-roughened substrate. The explanation of this observation does not lie with different surface roughness; both types of film yield closely similar data on the scanning tunneling microscope. Rather, it is suggested that the relatively small grain size of the fast-deposited silver films leads to increased elastic scattering of surface-plasmon polaritons at the grain boundaries, with a consequent increase of internal damping. This results in a reduction of the scattered Raman signal.

  14. Microplastics in the Mediterranean Sea: Deposition in coastal shallow sediments, spatial variation and preferential grain size.

    PubMed

    Alomar, Carme; Estarellas, Fernando; Deudero, Salud

    2016-04-01

    Marine litter loads in sea compartments are an emergent issue due to their ecological and biological consequences. This study addresses microplastic quantification and morphological description to test spatial differences along an anthropogenic gradient of coastal shallow sediments and further on to evaluate the preferential deposition of microplastics in a given sediment grain fraction. Sediments from Marine Protected Areas (MPAs) contained the highest concentrations of microplastics (MPs): up to 0.90 ± 0.10 MPs/g suggesting the transfer of microplastics from source areas to endpoint areas. In addition, a high proportion of microplastic filaments were found close to populated areas whereas fragment type microplastics were more common in MPAs. There was no clear trend between sediment grain size and microplastic deposition in sediments, although microplastics were always present in two grain size fractions: 2 mm > x > 1 mm and 1 mm > x 0.5 mm.

  15. Grain size effect on electrical resistivity of bulk nanograined Bi{sub 2}Te{sub 3} material

    SciTech Connect

    Ivanov, Oleg Maradudina, Oxana; Lyubushkin, Roman

    2015-01-15

    The bulk nanograined Bi{sub 2}Te{sub 3} material with various mean grain sizes changing from ~ 97 nm to ~ 51 nm was prepared by microwave assisted solvothermal method and hot pseudo-isostatic pressure. It was found that the specific electrical resistivity of the material increases as mean grain size decreases. Such kind of the grain effect on the resistivity can be attributed to enhanced electron scattering at the grain boundaries. The Mayadas–Shatzkes model was applied to explain experimental results. In this model the grain boundaries are regarded as potential barriers which have to be overcome by the electrons. The reflectivity R of the grain boundaries for the material under study was estimated to be equal to ~ 0.7. - Highlights: • The bulk nanograined Bi{sub 2}Te{sub 3} material with various mean grain sizes was prepared. • It was found that the electrical resistivity of the material increases as grain size decreases. • The Mayadas–Shatzkes model was applied to explain experimental results. • The reflectivity R of the grain boundaries was estimated to be equal to ~ 0.7.

  16. Physics-Based Reactive Burn Model: Grain size effects and binder effects

    NASA Astrophysics Data System (ADS)

    Lu, Xia; Hamate, Yuichio; Horie, Yasuyuki

    2007-06-01

    We have been developing a physics-based reactive burn (PBRB) model aiming at expanding predictive capability. The PBRB model was formulated based on the concept of a statistical hot spot cell. In the model, thermomechanics and physiochemical features are explicitly modeled. In this paper, we have extended the statistical hot spot model to explicitly describe the ignition and growth of hot spots. In particular, grain size effects are explicitly delineated through introduction of a size-dependent thickness of the hot-region thickness, a size-dependent energy deposition criterion, and a specific surface area. Besides the linear relationships between the run distance to detonation and critical diameter with the reciprocal specific surface area of HE, as discussed in a parallel paper in this meeting, parametric studies have also shown that the PBRB can predict a non-monotonous variation of shock sensitivity with grain size, as observed by Moulard et al. The purpose of this work is to extend the model to include the effects of explosive binders explicitly. As a first step we investigate the thermomechanical effects of a binder by using direct mesoscale simulations. The results will be used in the extending the PBRB model to include binder thermomechanics explicitly.

  17. Location, Identification, and Size Distribution of Depleted Uranium Grains in Reservoir Sediments

    NASA Astrophysics Data System (ADS)

    Lo, D.; Fleischer, R. L.; Albert, E. A.; Arnason, J. G.

    2006-05-01

    The location, isotopic composition, and size distribution of uranium-rich grains in sediment layers can be identified by analysis of etched particle tracks. Samples are pressed against track detectors, irradiated with thermal neutrons, and the detectors are chemically etched to reveal fission tracks. The total track abundance from the sample is a measure of the U-235 content; hence, if the bulk uranium (mostly U-238) has been measured, the two sets of results give the depletion or enrichment of the uranium. Each uranium-rich particle produces a sunburst of tracks where the number of tracks is proportional to the size of the particle. From 1958 to 1984, National Lead Industries processed depleted uranium (DU) at its plant in Colonie, NY (just west of Albany). Radioactive materials, principally DU, that were emitted from its exhaust stacks have been found 40 km away (Dietz, 1981). We have studied a sediment core taken by Arnason and Fletcher (2003, 2004) from a small body of water, the Patroon Reservoir, which is 1 km east-southeast of the National Lead plant. Examination of portions of that core demonstrates the usefulness of induced nuclear tracks (1) to locate microscopic high-uranium grains for further mineralogical study ; (2) to determine the size distribution of uranium grains; and (3) to help analyze the average isotopic depletion of the uranium when total U concentrations are known. We infer that the size of DU particles in the sediment was controlled by both atmospheric transport from stack to reservoir and fluvial transport within the reservoir.

  18. The potential for adaptive evolution of pollen grain size in Mimulus guttatus.

    PubMed

    Lamborn, Ellen; Cresswell, James E; Macnair, Mark R

    2005-07-01

    We tested whether pollen grain size (PGS) shows heritable variation in three independent populations of Mimulus guttatus by imposing artificial selection for this character. In addition, we looked for correlated responses to selection in a range of 15 other floral characters. Heritable variation in PGS was found in all three populations, with heritabilities of between 19 and 40% (average 30%). After three generations, upward and downward lines differed on average by 30% in pollen volume. No consistent patterns of correlated response were found in other characters, indicating that PGS can respond to selective forces acting on PGS alone. Possible selection mechanisms on PGS in this species could include intermale selection, if large pollen grains produce more competitive gametophytes; or optimization of patterns of resource allocation, if local mate competition varies.

  19. Estimation of Fracture Toughness of Small-Sized Ultrafine-Grained Specimens

    NASA Astrophysics Data System (ADS)

    Deryugin, E. E.; Suvorov, B. I.

    2015-10-01

    The results obtained from measurements of the crack resistance of a VT6 alloy (Ti-6.46Al-3.84V in wt.%) produced by refining coarse-crystalline structure down to an ultrafine-grained state, using a triaxial forging technique, are presented. The specific fracture energy γc is calculated by means of a new procedure developed for small-sized chevron-notched specimens. Severe plastic deformation is shown to cause a substantial reduction in γc at room temperature. Fracture surface structure found in the ultrafine-grained alloy under study contains local zones of a severely deformed material characterized by high pore concentration. This type of structure cannot be formed solely by crystallographic shearing along densely packed lattice planes. This is evidence for a significant role of rotation deformation modes in crack nucleation and growth on different structural scales of the material.

  20. SLG controls grain size and leaf angle by modulating brassinosteroid homeostasis in rice.

    PubMed

    Feng, Zhiming; Wu, Chuanyin; Wang, Chunming; Roh, Jeehee; Zhang, Long; Chen, Jun; Zhang, Shengzhong; Zhang, Huan; Yang, Chunyan; Hu, Jinlong; You, Xiaoman; Liu, Xi; Yang, Xiaoming; Guo, Xiuping; Zhang, Xin; Wu, Fuqing; Terzaghi, William; Kim, Seong-Ki; Jiang, Ling; Wan, Jianmin

    2016-07-01

    Grain size and leaf angle are two important traits determining grain yield in rice. However, the mechanisms regulating the two traits remain largely unknown. Here, we characterized a rice gain-of-function mutant, slender grain Dominant (slg-D), which exhibited longer and narrower grains and larger leaf angles, similar to plants with elevated brassinosteroid (BR) levels or strengthened BR signaling. The increased cell length is responsible for the mutant phenotypes in slg-D We demonstrated that the phenotype of slg-D is caused by enhanced expression of SLG, a BAHD acyltransferase-like protein gene. SLG is preferentially expressed in young panicles and lamina joints, implying its role in controlling cell growth in those two tissues. slg-D was restored to wild type by treatment with brassinazole, an inhibitor of BR biosynthesis. Overexpression of SLG in d11-2 (deficient in BR synthesis) and d61-1 (deficient in BR signaling) did not change the existing phenotypes. The slg-D plants had elevated BR contents and, accordingly, expression of BR-related genes was changed in a manner similar to BR treatment. Moreover, SLG RNAi plants displayed mild BR-deficient phenotypes including shorter grains, smaller leaf angles, and compact semi-dwarf plant types. The in vitro biochemical assays and transgenic approaches collectively demonstrated that SLG functions as homomers. Taken together, we conclude that SLG is an important regulator in BR homeostasis and that manipulation of SLG expression to an optimal level may provide a way to develop an ideal plant type. PMID:27252468

  1. Influence of Grain Size Distribution on the Mechanical Behavior of Light Alloys in Wide Range of Strain Rates

    NASA Astrophysics Data System (ADS)

    Skripnyak, Vladimir A.; Skripnyak, Natalia V.; Skripnyak, Evgeniya G.; Skripnyak, Vladimir V.

    2015-06-01

    Inelastic deformation and damage at the mesoscale level of ultrafine grained (UFG) Al 1560 aluminum and Ma2-1 magnesium alloys with distribution of grain size were investigated in wide loading conditions by experimental and computer simulation methods. The computational multiscale models of representative volume element (RVE) with the unimodal and bimodal grain size distributions were developed using the data of structure researches aluminum and magnesium UFG alloys. The critical fracture stress of UFG alloys on mesoscale level depends on relative volumes of coarse grains. Microcracks nucleation at quasi-static and dynamic loading is associated with strain localization in UFG partial volumes with bimodal grain size distribution. Microcracks arise in the vicinity of coarse and ultrafine grains boundaries. It is revealed that the occurrence of bimodal grain size distributions causes the increasing of UFG alloys ductility, but decreasing of the tensile strength. The increasing of fine precipitations concentration not only causes the hardening but increasing of ductility of UFG alloys with bimodal grain size distribution. This research carried out in 2014-2015 was supported by grant from ``The Tomsk State University Academic D.I. Mendeleev Fund Program''.

  2. Exploring the effects of temperature and grain size on plumes associated with PDCs through analogue experimentation

    NASA Astrophysics Data System (ADS)

    Mitchell, S. J.; Eychenne, J.; Rust, A.

    2015-12-01

    Pyroclastic density currents (PDCs) often loft upwards into convective, buoyant co-PDC plumes. Recent analogue experiments using a unimodal grain size of 22 ± 6 μm (Andrews & Manga, 2012) have established that plume generation is aided by PDC interaction with a topographic barrier. Here, we have simulated the onset of co-PDC plumes from the collapse of concentrated particle-gas mixtures comprised of unimodal or bimodal grain size distributions (GSD) of glass beads, using combinations of lognormal populations with modes of 35, 195 and 590 μm. The collapse of a mixture, with constant mass 2950 ± 150 g, induced the propagation of a gravity current channelized down a 13° sloping tank; a barrier in the tank caused the gravity current to produce a plume of particles. Experiments were recorded with high speed visible and thermal-infrared cameras. Initial GSD and temperature of the mixture were varied to assess the effects of the addition of a coarser component on plume generation. Analogue co-PDC plumes were only produced when a proportion of fine grains (35 μm) was present in the initial granular mixture. Sampling of the particles entrained in the co-PDC plumes revealed that fine grains (35 μm) are preferentially lofted, although a few coarser particles (195 or 590 μm) are also entrained in the co-PDC plumes and settle closer to the area of uplift. Increasing the initial temperature of the mixture increases plume height measured at 1 and 2s after onset; this is supported by repeat experiments at specific conditions. Bimodal mixtures containing both fine (35 μm) and coarser (195 or 590 μm) grains result in plume heights and initial flow velocities higher than observed in unimodal fine-grained experiments of the same total mass of particles. Repeat experiments identify the natural variability in plume generation under the same nominal conditions, which is likely due to the combined variations of momentum during flow propagation and heat-driven buoyancy, as well

  3. The Influence of Grain Size and Crystal Content on Rheology and Deformation of Pyroclastic Material

    NASA Astrophysics Data System (ADS)

    Paquereau-Lebti, P.; Robert, G.; Grunder, A. L.; Russell, K. J.

    2007-12-01

    Pyroclastic deposits undergo variable degrees of sintering, viscous deformation of particles and loss of pore space, which combine to produce the dramatic textural variations that define welded facies. We here investigate the effects of grain size and crystal content on the rheology and welding of pyroclastic material.Uniaxial deformation experiments were conducted using sintered cores of natural rhyolite ash under conditions consistent with welding. Experiments were done in the University of British Columbia Volcanology Deformation Rig (VDR). This apparatus is designed to run experiments relevant to volcanology, by supporting low-load, high temperature, deformation experiments (Quane et al., 2004). We ran experiments at constant displacement rate (2.5.10-6 m.s-1), under ambient water pressure ("Dry"), at temperatures of 850 and 900°C and to maximal strain of 50%. Grain-size effect was investigated using sintered cores from three different sieving fractions of Rattlesnake Tuff (RST, Eastern Oregon, USA) ash: fine ash (grain size < 0.6 mm), coarse ash (0.6 to 2mm) and row unsieved ash. The effect of crystal content was explored using cores of sintered unsieved RST ash, variably enriched in crystals of feldspars and quartz.Unsieved and fine ash cores suffered higher total porosity reduction than coarse ash cores during deformation experiments. For cores of unsieved ash, porosity loss is facilitated by mechanical compaction, which includes orientation and organisation of different size clasts to a compact assemblage, without any deformation of individual particles. Isolated porosity decreases faster than connected porosity in coarse and fine ash cores, whereas cores of raw ash mainly loose connected porosity. This is also consistent with mechanical compaction for cores of unsieved ash, in which isolated porosity of weakly deformed individual pumice clasts or glass shards is maintained. Increasing strain causes a reduction in porosity and correlates with increase in

  4. Characterization of pore scale NAPL morphology in homogeneous sands as a function of grain size and NAPL dissolution.

    PubMed

    Cho, Jaehyun; Annable, Michael D

    2005-11-01

    In this study, we investigate pore scale morphology of nonaqueous phase liquids (NAPLs) trapped in different pore sizes using tracer techniques. Specific interfacial area and saturation of NAPL trapped in homogeneous sands were measured using the interfacial and partitioning tracer techniques. The observed NAPL-water interfacial areas increased in a log-linear fashion with decreasing sand grain size, but showed no clear trend with residual NAPL saturation formed in the various grain sizes. The measured values were used to calculate the NAPL morphology index, which characterizes the spatial NAPL distribution within the pore space. The NAPL morphology indices, increased exponentially with decreasing grain size, indicating that the NAPL becomes smaller, but more blobs. For a fixed grain size, the specific interfacial area and saturation of the NAPL were measured following changes caused by dissolution using alcohol. The observed interfacial areas showed a decrease linearly as a function of the NAPL saturation.

  5. Thermoelectric properties of n-Type Mg2Si-Mg2Sn solid solutions with different grain sizes

    NASA Astrophysics Data System (ADS)

    Samunin, A. Yu.; Zaitsev, V. K.; Pshenay-Severin, D. A.; Konstantinov, P. P.; Isachenko, G. N.; Fedorov, M. I.; Novikov, S. V.

    2016-08-01

    Influence of the grain sizes on thermoelectric parameters of pressurized solid solutions of the composition Mg2Si0.8Sn0.2 was studied. The Seebeck coefficient, electric conductivity, thermal conductivity, and Hall coefficient were determined. Decreasing the grain size to the nanoscale was found to decrease the mobility at low temperatures and resulted in a peculiar temperature dependence of the electric conductivity, but did not lead to a decrease in the thermo EMF. It was found that the grain size had no effect on the thermoelectric efficiency of the investigated solid solution in the operating temperature range.

  6. The Effect of Grain Size and Phosphorous-doping of Polycrystalline 3C-SiC on Infrared Reflectance Spectra

    SciTech Connect

    I. J. van Rooyen; J. A. A. Engelbrecht; A. Henry; E. Janzen; J. H. Neethling; P. M. van Rooyen

    2012-03-01

    The effect of P-doping and grain size of polycrystalline 3C-SiC on the infrared reflectance spectra is reported. The relationship between grain size and full width at half maximum (FWHM) suggest that the behaviour of the 3C-SiC with the highest phosphorous doping level (of 1.2 x 10{sup 19} at. cm{sup -3}) is different from those with lower doping levels (< 6.6 x 10{sup 18} at. cm{sup -3}). It is also further demonstrated that the plasma resonance frequency (w{sub p}) is not influenced by the grain size.

  7. In vitro evaluation of the microbiota modulation abilities of different sized whole oat grain flakes.

    PubMed

    Connolly, Michael L; Lovegrove, Julie A; Tuohy, Kieran M

    2010-10-01

    Epidemiological studies and healthy eating guidelines suggest a positive correlation between ingestion of whole grain cereal and food rich in fibre with protection from chronic diseases. The prebiotic potential of whole grains may be related, however, little is known about the microbiota modulatory capability of oat grain or the impact processing has on this ability. In this study the fermentation profile of whole grain oat flakes, processed to produce two different sized flakes (small and large), by human faecal microbiota was investigated in vitro. Simulated digestion and subsequent fermentation by gut bacteria was investigated using pH controlled faecal batch cultures inoculated with human faecal slurry. The different sized oat flakes, Oat 23's (0.53-0.63 mm) and Oat 25's/26's (0.85-1.0 mm) were compared to oligofructose, a confirmed prebiotic, and cellulose, a poorly fermented carbohydrate. Bacterial enumeration was carried out using the culture independent technique, fluorescent in situ hybridisation, and short chain fatty acid (SCFA) production monitored by gas chromatography. Significant changes in total bacterial populations were observed after 24 h incubation for all substrates except Oat 23's and cellulose. Oats 23's fermentation resulted in a significant increase in the Bacteroides-Prevotella group. Oligofructose and Oats 25's/26's produced significant increases in Bifidobacterium in the latter stages of fermentation while numbers declined for Oats 23's between 5 h and 24 h. This is possibly due to the smaller surface area of the larger flakes inhibiting the simulated digestion, which may have resulted in increased levels of resistant starch (Bifidobacterium are known to ferment this dietary fibre). Fermentation of Oat 25's/26's resulted in a propionate rich SCFA profile and a significant increase in butyrate, which have both been linked to benefiting host health. The smaller sized oats did not produce a significant increase in butyrate

  8. Abrasive drill for resilient materials

    NASA Technical Reports Server (NTRS)

    Koch, A. J.

    1981-01-01

    Resilient materials normally present problem in obtaining accurate and uniform hole size and position. Tool is fabricated from stiff metal rod such as tungsten or carbon steel that has diameter slightly smaller than required hole. Piercing/centering point is ground on one end of rod. Rod is then plasma-sprayed (flame-sprayed) with suitable hard abrasive coating. High-speed, slow-feed operation of tool is necessary for accurate holes, and this can be done with drill press, hard drill, or similar machines.

  9. Grain-size-induced weakening of H2O ices I and II and associated anisotropic recrystallization

    USGS Publications Warehouse

    Stern, L.A.; Durham, W.B.; Kirby, S.H.

    1997-01-01

    Grain-size-dependent flow mechanisms tend to be favored over dislocation creep at low differential stresses and can potentially influence the rheology of low-stress, low-strain rate environments such as those of planetary interiors. We experimentally investigated the effect of reduced grain size on the solid-state flow of water ice I, a principal component of the asthenospheres of many icy moons of the outer solar system, using techniques new to studies of this deformation regime. We fabricated fully dense ice samples of approximate grain size 2 ?? 1 ??m by transforming "standard" ice I samples of 250 ?? 50 ??m grain size to the higher-pressure phase ice II, deforming them in the ice II field, and then rapidly releasing the pressure deep into the ice I stability field. At T ??? 200 K, slow growth and rapid nucleation of ice I combine to produce a fine grain size. Constant-strain rate deformation tests conducted on these samples show that deformation rates are less stress sensitive than for standard ice and that the fine-grained material is markedly weaker than standard ice, particularly during the transient approach to steady state deformation. Scanning electron microscope examination of the deformed fine-grained ice samples revealed an unusual microstructure dominated by platelike grains that grew normal to the compression direction, with c axes preferentially oriented parallel to compression. In samples tested at T ??? 220 K the elongation of the grains is so pronounced that the samples appear finely banded, with aspect ratios of grains approaching 50:1. The anisotropic growth of these crystallographically oriented neoblasts likely contributes to progressive work hardening observed during the transient stage of deformation. We have also documented remarkably similar microstructural development and weak mechanical behavior in fine-grained ice samples partially transformed and deformed in the ice II field.

  10. A study on the correlation between the grain size and the conversion efficiency of Mc-Si solar cells.

    PubMed

    Lee, Myoung-Bok; Song, Kyu-Ho; Park, Kwang-Mook; Jung, Ji-Hee; Bae, So-Ik

    2012-07-01

    For grain size estimation, a prototype system was developed by integrating a vision-acquiring hardware and a vision-assistant-processing module based on the platform software package of LabVIEW, to systematically estimate the average grain size of solar-grade multicrystalline (mc)-Si wafers. Three groups of 156 x 156 mm mc-Si wafers were selected to produce the average grain sizes of 3.4 mm (Group 1), 3.8 mm (Group II), and 4.6 mm (Group III), and were used for the fabrication of mc-Si solar cells by employing the standard mc-Si cell fabrication procedure of the 30 MW mass production line. The conversion efficiency including Jsc and Pmax, showed a quasi linear dependence on the mean grain size, with a correlation factor of 0.525%/mm. By combining the EL image and the grain size/position-dependent EQE spectra in a wavelength range of 400-1100 nm, the conversion efficiency of uniformly-surface-texturized mc-Si solar cells with larger grain sizes can be made much higher as a result of the much-reduced spatial density of the nano/microscope grain boundaries acting as recombination centers or traps.

  11. Grain size dependence of dynamic mechanical behavior of AZ31B magnesium alloy sheet under compressive shock loading

    SciTech Connect

    Asgari, H.; Odeshi, A.G.; Szpunar, J.A.; Zeng, L.J.; Olsson, E.

    2015-08-15

    The effects of grain size on the dynamic deformation behavior of rolled AZ31B alloy at high strain rates were investigated. Rolled AZ31B alloy samples with grain sizes of 6, 18 and 37 μm, were subjected to shock loading tests using Split Hopkinson Pressure Bar at room temperature and at a strain rate of 1100 s{sup −} {sup 1}. It was found that a double-peak basal texture formed in the shock loaded samples. The strength and ductility of the alloy under the high strain-rate compressive loading increased with decreasing grain size. However, twinning fraction and strain hardening rate were found to decrease with decreasing grain size. In addition, orientation imaging microscopy showed a higher contribution of double and contraction twins in the deformation process of the coarse-grained samples. Using transmission electron microscopy, pyramidal dislocations were detected in the shock loaded sample, proving the activation of pyramidal slip system under dynamic impact loading. - Highlights: • A double-peak basal texture developed in all shock loaded samples. • Both strength and ductility increased with decreasing grain size. • Twinning fraction and strain hardening rate decreased with decreasing grain size. • ‘g.b’ analysis confirmed the presence of dislocations in shock loaded alloy.

  12. Extending and simplifying the standard Köhn-pipette technique for grain size analysis

    NASA Astrophysics Data System (ADS)

    Hirsch, Florian; Raab, Thomas

    2014-05-01

    Grain size distribution is a fundamental parameter to characterize physical properties of soils and sediments. Manifold approaches exist and according to the DIN ISO 11277 soil texture is analyzed by default with the combined pipette sieving and sedimentation method developed by Köhn. With this standard technique subfractions of sand and silt as well as the total clay content can be determined but the differentiation of clay subfractions is impossible. As the differentiation of the clay subfractions yields relevant information about pedogenesis, we present a protocol basing on standard techniques of granulometry with easy to handle and low cost equipment. The protocol was tested on a set of soil samples to cover the range of grain size distributions. We used a three-step procedure for achieving the grain size distribution of soil samples taking into account the subfractions of sand, silt and clay by a combination of sedimentation, centrifugal sedimentation and wet sieving. The pipetting was done with a piston-stroke pipette instead of the referred complex pipette from the DIN ISO 11277. Our first results show that the applied protocol is less prone to operating errors than the standard Köhn-pipette technique. Furthermore, even a less experienced laboratory worker can handle 10 samples in one day. Analyses of a luvisol profile, sampled in high spatial resolution, showed that the lessivation process is characterized by translocation of fine clay from the eluvial horizon to the illuvial horizon. Therefore our protocol is a fast alternative to detect lessivation, which is otherwise only clearly identifiable by micromorphological investigation and not by the standard Köhn-pipette technique.

  13. Grain size trends reveal alluvial fan sensitivity to late Pleistocene climate change

    NASA Astrophysics Data System (ADS)

    Whittaker, A. C.; D'Arcy, M. K.; Roda Boluda, D. C.

    2015-12-01

    The effects of climate change on eroding landscapes and the sedimentary record remain poorly understood. The measurement of grain size fining rates in stream-flow dominated deposits provides one way to address this issue because, in principle, these trends embed important information about the dynamics of sediment routing systems and their sensitivities to external forcing. At a fundamental level, downstream fining is often driven by selective deposition of sediment. The relative efficiency of this process is determined by the physical characteristics of the input sediment supply and the spatial distribution of subsidence rate, which generates the accommodation necessary for mass extraction. Here, we measure grain size fining rates from apex to toe on two alluvial fan systems in northern Death Valley, California, which have well-exposed modern and 70 ka surfaces, where the long-term tectonic boundary conditions are known and where climatic variation over this time period is well-constrained. We integrate a self-similar gravel fraction fining model, based on selective sediment extraction, with cosmogenically-derived catchment erosion rates and gravel fining data, to estimate the change in sediment flux that occurred between 70 ka and the present day. Our results show that a 30 % decrease in average precipitation rate led to a 20 % decrease in sediment flux and a clear increase in the down-fan rate of fining. This supports existing landscape evolution models that relate a decrease in precipitation rate to a decrease in sediment flux, but implies that this relationship may be sub-linear. This study offers a new approach to applying grain size fining models to mountain catchments and their alluvial fan systems, and shows fan stratigraphy can be highly sensitive to climate changes over <105 years. However we also observe that this sensitivity is lost when sediment is remobilised and recycled over a time period longer than the duration of the climatic perturbation.

  14. The referential grain size and effective porosity in the Kozeny-Carman model

    NASA Astrophysics Data System (ADS)

    Urumović, Kosta; Urumović, Kosta, Sr.

    2016-05-01

    In this paper, the results of permeability and specific surface area analyses as functions of granulometric composition of various sediments (from silty clays to very well graded gravels) are presented. The effective porosity and the referential grain size are presented as fundamental granulometric parameters expressing an effect of the forces operating on fluid movement through the saturated porous media. This paper suggests procedures for calculating referential grain size and determining effective (flow) porosity, which result in parameters that reliably determine the specific surface area and permeability. These procedures ensure the successful application of the Kozeny-Carman model up to the limits of validity of Darcy's law. The value of effective porosity in the referential mean grain size function was calibrated within the range of 1.5 µm to 6.0 mm. The reliability of the parameters applied in the KC model was confirmed by a very high correlation between the predicted and tested hydraulic conductivity values (R2 = 0.99 for sandy and gravelly materials; R2 = 0.70 for clayey-silty materials). The group representation of hydraulic conductivity (ranging from 10-12 m s-1 up to 10-2 m s-1) presents a coefficient of correlation of R2 = 0.97 for a total of 175 samples of various deposits. These results present new developments in the research of the effective porosity, the permeability and the specific surface area distributions of porous materials. This is important because these three parameters are critical conditions for successful groundwater flow modeling and contaminant transport. Additionally, from a practical viewpoint, it is very important to identify these parameters swiftly and very accurately.

  15. [Effectiveness of arsenite adsorption by ferric and alum water treatment residuals with different grain sizes].

    PubMed

    Lin, Lu; Xu, Jia-Rui; Wu, Hao; Wang, Chang-Hui; Pei, Yuan-Sheng

    2013-07-01

    Effectiveness of arsenite adsorption by ferric and alum water treatment residuals (FARs) with different grain sizes was studied. The results indicated that the content of active Fe and Al, the specific surface area and pore volume in FARs with different grain sizes were in the range of 523.72-1 861.72 mmol x kg(-1), 28.15-265.59 m2 x g(-1) and 0.03-0.09 cm3 x g(-1), respectively. The contents of organic matter, fulvic acid, humic acid and humin were in the range of 46.97-91.58 mg x kg(-1), 0.02-32.27 mg x kg(-1), 22.27-34.09 mg x kg(-1) and 10.76-34.22 mg x kg(-1), respectively. Results of SEM and XRD analysis further demonstrated that FARs with different grain sizes were amorphousness. Batch experiments suggested that both the pseudo-first-order and pseudo-second-order equations could well describe the kinetics adsorption processes of arsenite by FARs. Moreover, the contents of arsenite absorbed by FARs increased with the increase of arsenite concentrations. The theoretical saturated adsorption capacities calculated from Langmuir isotherm model were in the range of 6.72-21.79 mg x g(-1). Interestingly, pH showed little effect on the arsenite adsorption capability of FARs. The capability of FARs had a close relationship with their physicochemical properties. Correlation analysis showed that the active Fe and Al contents and pore volume had major effects on the arsenite adsorption capability of FARs.

  16. GRAIN SIZING AND CALIBRATING OF DISTORTION BY IMAGE PROCESSING WITH INCLINED PHOTOGRAPH

    NASA Astrophysics Data System (ADS)

    Yasuda, Shingo; Ohashi, Keisuke; Ihara, Kazuki

    River bed material is normally heterogeneous, and the grain size distribution shows some features of each rivers. The information of distribution is, therefore, important factor in river engineering, and several traditional methods is practically used. Image processing method with digital photograph is modern analysis by using computer and replaced traditional analog photograph method. In image processing, however, optical distortion brings measurement error. We present a calibration of the distortion with optical theorem. In laboratory experiment with balls supposed river bed gravel, the theoretical calibration is considered to be appropriate. In field experiment, actual coefficient to calibrate distortion is estimated. In consequence of the investigation, it makes image processing method more accurate.

  17. Sediment transport modelling based on grain size trend analysis in Augusta Harbour (Sicily)

    NASA Astrophysics Data System (ADS)

    Barbera, Giuseppe; Feo, Roberto; Freni, Gabriele

    2015-12-01

    To support marine civil engineer in pollutant studies, sediment management or dredging operations, is useful to know how the sediments move in accumulation basin. This paper investigates the dynamic of the sediment path using a two-dimensional numeric model: the Grain Size Trend Analysis (GSTA). The GSTA was applied using GiSedTrend plugin, under GIS software. The case study is the Augusta Harbour, which is one of the most polluted Italian harbours. It is the marine part of the Site of National Interest (SNI) of Priolo Gargallo (Siracusa, Italy) and it can be hydrodynamically considered as a lagoon. Two scenarios were obtained by using different geostatistical criteria.

  18. The effect of pH, grain size, and organic ligands on biotite weathering rates

    NASA Astrophysics Data System (ADS)

    Bray, Andrew W.; Oelkers, Eric H.; Bonneville, Steeve; Wolff-Boenisch, Domenik; Potts, Nicola J.; Fones, Gary; Benning, Liane G.

    2015-09-01

    Biotite dissolution rates were determined at 25 °C, at pH 2-6, and as a function of mineral composition, grain size, and aqueous organic ligand concentration. Rates were measured using both open- and closed-system reactors in fluids of constant ionic strength. Element release was non-stoichiometric and followed the general trend of Fe, Mg > Al > Si. Biotite surface area normalised dissolution rates (ri) in the acidic range, generated from Si release, are consistent with the empirical rate law:

  19. Delineation of river bed-surface patches by clustering high-resolution spatial grain size data

    NASA Astrophysics Data System (ADS)

    Nelson, Peter A.; Bellugi, Dino; Dietrich, William E.

    2014-01-01

    The beds of gravel-bed rivers commonly display distinct sorting patterns, which at length scales of ~ 0.1 - 1 channel widths appear to form an organization of patches or facies. This paper explores alternatives to traditional visual facies mapping by investigating methods of patch delineation in which clustering analysis is applied to a high-resolution grid of spatial grain-size distributions (GSDs) collected during a flume experiment. Specifically, we examine four clustering techniques: 1) partitional clustering of grain-size distributions with the k-means algorithm (assigning each GSD to a type of patch based solely on its distribution characteristics), 2) spatially-constrained agglomerative clustering ("growing" patches by merging adjacent GSDs, thus generating a hierarchical structure of patchiness), 3) spectral clustering using Normalized Cuts (using the spatial distance between GSDs and the distribution characteristics to generate a matrix describing the similarity between all GSDs, and using the eigenvalues of this matrix to divide the bed into patches), and 4) fuzzy clustering with the fuzzy c-means algorithm (assigning each GSD a membership probability to every patch type). For each clustering method, we calculate metrics describing how well-separated cluster-average GSDs are and how patches are arranged in space. We use these metrics to compute optimal clustering parameters, to compare the clustering methods against each other, and to compare clustering results with patches mapped visually during the flume experiment.All clustering methods produced better-separated patch GSDs than the visually-delineated patches. Although they do not produce crisp cluster assignment, fuzzy algorithms provide useful information that can characterize the uncertainty of a location on the bed belonging to any particular type of patch, and they can be used to characterize zones of transition from one patch to another. The extent to which spatial information influences

  20. A study of the effect of grain size on the ballistic performance of silicon carbide

    SciTech Connect

    Cline, C.F.

    1995-03-01

    The depth of penetration method was used to ballistically evaluate the performance of silicon carbide as a function of grain size. The hot-pressed silicon carbide was backed by 4340 steel Rc = 35 and impacted by tungsten heavy metal projectiles of L/D = 4 at velocities of 1.6 and 1/75 km/s. The hot-pressed silicon carbide was also compared with reaction-sintered silicon carbide of identical thickness in the current study. Results are compared with data previously reported by others.

  1. Effect of Grain Size on Bacterial Penetration, Reproduction, and Metabolic Activity in Porous Glass Bead Chambers

    PubMed Central

    Sharma, Pramod K.; McInerney, Michael J.

    1994-01-01

    We determined the effects of grain size and nutritional conditions on the penetration rate and metabolic activity of Escherichia coli strains in anaerobic, nutrient-saturated chambers packed with different sizes of glass beads (diameters, 116 to 767 μm) under static conditions. The chambers had nearly equal porosities (38%) but different calculated pore sizes (range, 10 to 65 μm). Motile strains always penetrated faster than nonmotile strains, and nutrient conditions that resulted in faster growth rates (fermentative conditions versus nitrate-respiring conditions) resulted in faster penetration rates for both motile and nonmotile strains for all of the bead sizes tested. The penetration rate of nonmotile strains increased linearly when bead size was increased, while the penetration rate of motile strains became independent of the bead size when beads having diameters of 398 μm or greater were used. The rate of H2 production and the final amount of H2 produced decreased when bead size was decreased. However, the final protein concentrations were similar in chambers packed with 116-, 192-, and 281-μm beads and were only slightly higher in chambers packed with 398- and 767-μm beads. Our data indicated that conditions that favored faster growth rates also resulted in faster penetration times and that the lower penetration rates observed in chambers packed with small beads were due to restriction of bacterial activity in the small pores. The large increases in the final amount of hydrogen produced without corresponding increases in the final amount of protein made indicated that metabolism became uncoupled from cell mass biosynthesis as bead size increased, suggesting that pore size influenced the efficiency of substrate utilization. PMID:16349250

  2. Laboratory Measurements on Charging of Individual Micron-Size Apollo-11 Dust Grains by Secondary Electron Emissions

    NASA Technical Reports Server (NTRS)

    Tankosic, D.; Abbas, M. M.

    2012-01-01

    Observations made during Apollo missions, as well as theoretical models indicate that the lunar surface and dust grains are electrostatically charged, levitated and transported. Lunar dust grains are charged by UV photoelectric emissions on the lunar dayside and by the impact of the solar wind electrons on the nightside. The knowledge of charging properties of individual lunar dust grains is important for developing appropriate theoretical models and mitigating strategies. Currently, very limited experimental data are available for charging of individual micron-size size lunar dust grains in particular by low energy electron impact. However, experimental results based on extensive laboratory measurements on the charging of individual 0.2-13 micron size lunar dust grains by the secondary electron emissions (SEE) have been presented in a recent publication. The SEE process of charging of micron-size dust grains, however, is found to be very complex phenomena with strong particle size dependence. In this paper we present some examples of the complex nature of the SEE properties of positively charged individual lunar dust grains levitated in an electrodynamic balance (EDB), and show that they remain unaffected by the variation of the AC field employed in the above mentioned measurements.

  3. Development of a System to Measure Austenite Grain Size of Plate Steel Using Laser-Based Ultrasonics

    SciTech Connect

    Lim, C. S.; Hong, S. T.; Yi, J. K.; Choi, S. G.; Oh, K. J.; Nagata, Y.; Yamada, H.; Hamada, N.

    2007-03-21

    A measurement system for austenite grain size of plate steel using laser-based ultrasonics has been developed. At first, the relationship between the ultrasonic attenuation coefficients using longitudinal waves and austenite grain size of samples was investigated in the laboratory experiments. According to the experimental results, the ultrasonic attenuation coefficients showed a good correlation with actual austenite grain sizes. For the next step, the system was installed in a hot rolling pilot plant of plate steel, and it was verified that the austenite grain size could be measured even in the environment of a hot rolling pilot plant. In the experiments, it was also confirmed that the fiber delivery system could deliver Nd:YAG laser beam of 810 mJ/pulse and ultrasonic signals could be obtained successfully.

  4. Can grain size sensitive flow lubricate faults during the initial stages of earthquake propagation?

    NASA Astrophysics Data System (ADS)

    De Paola, Nicola; Holdsworth, Robert E.; Viti, Cecilia; Collettini, Cristiano; Bullock, Rachael

    2015-12-01

    Recent friction experiments carried out under upper crustal P-T conditions have shown that microstructures typical of high temperature creep develop in the slip zone of experimental faults. These mechanisms are more commonly thought to control aseismic viscous flow and shear zone strength in the lower crust/upper mantle. In this study, displacement-controlled experiments have been performed on carbonate gouges at seismic slip rates (1 m s-1), to investigate whether they may also control the frictional strength of seismic faults at the higher strain rates attained in the brittle crust. At relatively low displacements (<1 cm) and temperatures (≤100 °C), brittle fracturing and cataclasis produce shear localisation and grain size reduction in a thin slip zone (150 μm). With increasing displacement (up to 15 cm) and temperatures (T up to 600 °C), due to frictional heating, intracrystalline plasticity mechanisms start to accommodate intragranular strain in the slip zone, and play a key role in producing nanoscale subgrains (≤100 nm). With further displacement and temperature rise, the onset of weakening coincides with the formation in the slip zone of equiaxial, nanograin aggregates exhibiting polygonal grain boundaries, no shape or crystal preferred orientation and low dislocation densities, possibly due to high temperature (>900 °C) grain boundary sliding (GBS) deformation mechanisms. The observed micro-textures are strikingly similar to those predicted by theoretical studies, and those observed during experiments on metals and fine-grained carbonates, where superplastic behaviour has been inferred. To a first approximation, the measured drop in strength is in agreement with our flow stress calculations, suggesting that strain could be accommodated more efficiently by these mechanisms within the weaker bulk slip zone, rather than by frictional sliding along the main slip surfaces in the slip zone. Frictionally induced, grainsize-sensitive GBS deformation

  5. Effects of grain size and humidity on fretting wear in fine-grained alumina, Al{sub 2}O{sub 3}/TiC, and zirconia

    SciTech Connect

    Krell, A.; Klaffke, D.

    1996-05-01

    Friction and wear of sintered alumina with grain sizes between 0.4 and 3 {micro}m were measured in comparison with Al{sub 2}O{sub 3}/TiC composites and with tetragonal ZrO{sub 2} (3 mol% Y{sub 2}O{sub 3}). The dependence on the grain boundary toughness and residual microstresses is investigated, and a hierarchical order of influencing parameters is observed. In air, reduced alumina grain sizes improve the micromechanical stability of the grain boundaries and the hardness, and reduced wear is governed by microplastic deformation, with few pullout events. Humidity and water slightly reduce the friction of all of the investigated ceramics. In water, this effect reduces the wear of coarser alumina microstructures. The wear of aluminas and of the Al{sub 2}O{sub 3}/TiC composite is similar; it is lower than observed in zirconia, where extended surface cracking occurs at grain sizes as small as 0.3 {micro}m.

  6. The effects of mineral fraction on the rheological properties of forsterite-enstatite rocks during grain size sensitive creep

    NASA Astrophysics Data System (ADS)

    Tasaka, M.; Hiraga, T.

    2012-12-01

    Since the majority of crustal and mantle rocks are polymineralic, it is important to consider the effects of secondary mineral phases on their rheological properties. To examine these effects, we have conducted grain growth and deformation experiments on samples composed of different volumetric fractions of forsterite (Fo) and enstatite (En) at 1 atmosphere and temperatures of 1260, 1310 and 1360 C. The results of our grain growth experiments indicate that the grain size ratios of Fo and En in annealed (reference) and deformed samples follow a Zener relationship with d1/d2 = b/f2z, where di is the grain size of the primary or secondary phase, b and z are the Zener parameters relating grain boundary energies, and f is the volume fraction of the associated phase. Grain growth in the reference samples conforms to the relationship d4-d04 = kt, where d is the grain size under static conditions, d0 is the initial grain size, k is the grain growth coefficient, and t is time. The growth coefficient of Fo decrease with increasing En volume fraction (fEn), and is consistent with theoretical predictions of Ardell's grain growth model that incorporates physical parameters such as diffusivity and interfacial energy of the mineral phases. The results of our deformation experiments at constant temperature and strain rate indicate that the flow stress decreases with increasing fEn, for samples with 0 < fEn < 0.5, and increases with increasing fEn, for samples with 0.5 < fEn < 1. The values of the pre-exponential term, stress and grain size exponents, and activation energy in the constitutive equation for a wide range of fEn were determined. The majority of samples exhibited diffusion accommodated grain boundary sliding creep (i.e., stress exponent = 1). The viscosity measured for all samples is fit well by a model that takes into account (1) grain size calculated from grain growth laws established in our experiments and (2) the flow laws for monomineralic systems of forsterite and

  7. Importance of suspended sediment (SPS) composition and grain size in the bioavailability of SPS-associated pyrene to Daphnia magna.

    PubMed

    Xia, Xinghui; Zhang, Xiaotian; Zhou, Dong; Bao, Yimeng; Li, Husheng; Zhai, Yawei

    2016-07-01

    Hydrophobic organic compounds (HOCs) tend to associate with suspended sediment (SPS) in aquatic environments; the composition and grain size of SPS will affect the bioavailability of SPS-associated HOCs. However, the bioavailability of HOCs sorbed on SPS with different compositions and grain sizes is not well understood. In this work, passive dosing devices were made to control the freely dissolved concentration of pyrene, a typical HOC, in the exposure systems. The effect of pyrene associated with amorphous organic carbon (AOC), black carbon (BC), and minerals of SPS with grain sizes of 0-50 μm and 50-100 μm on the immobilization and enzymatic activities of Daphnia magna was investigated to quantify the bioavailability of pyrene sorbed on SPS with different grain sizes and compositions. The results showed that the contribution of AOC-, BC-, and mineral-associated pyrene to the total bioavailability of SPS-associated pyrene was approximately 50%-60%, 10%-29%, and 20%-30%, respectively. The bioavailable fraction of pyrene sorbed on the three components of SPS was ordered as AOC (22.4%-67.3%) > minerals (20.1%-46.0%) > BC (9.11%-16.8%), and the bioavailable fraction sorbed on SPS of 50-100 μm grain size was higher than those of 0-50 μm grain size. This is because the SPS grain size will affect the ingestion of SPS and the SPS composition will affect the desorption of SPS-associated pyrene in Daphnia magna. According to the results obtained in this study, a model has been developed to calculate the bioavailability of HOCs to aquatic organisms in natural waters considering both SPS grain size and composition. PMID:27112726

  8. Assessing tephra total grain-size distribution: Insights from field data analysis

    NASA Astrophysics Data System (ADS)

    Costa, A.; Pioli, L.; Bonadonna, C.

    2016-06-01

    The Total Grain-Size Distribution (TGSD) of tephra deposits is crucial for hazard assessment and provides fundamental insights into eruption dynamics. It controls both the mass distribution within the eruptive plume and the sedimentation processes and can provide essential information on the fragmentation mechanisms. TGSD is typically calculated by integrating deposit grain-size at different locations. The result of such integration is affected not only by the number, but also by the spatial distribution and distance from the vent of the sampling sites. In order to evaluate the reliability of TGSDs, we assessed representative sampling distances for pyroclasts of different sizes through dedicated numerical simulations of tephra dispersal. Results reveal that, depending on wind conditions, a representative grain-size distribution of tephra deposits down to ∼100 μm can be obtained by integrating samples collected at distances from less than one tenth up to a few tens of the column height. The statistical properties of TGSDs representative of a range of eruption styles were calculated by fitting the data with a few general distributions given by the sum of two log-normal distributions (bi-Gaussian in Φ-units), the sum of two Weibull distributions, and a generalized log-logistic distribution for the cumulative number distributions. The main parameters of the bi-lognormal fitting correlate with height of the eruptive columns and magma viscosity, allowing general relationships to be used for estimating TGSD generated in a variety of eruptive styles and for different magma compositions. Fitting results of the cumulative number distribution show two different power law trends for coarse and fine fractions of tephra particles, respectively. Our results shed light on the complex processes that control the size of particles being injected into the atmosphere during volcanic explosive eruptions and represent the first attempt to assess TGSD on the basis of pivotal physical

  9. An estimate of field size distributions for selected sites in the major grain producing countries

    NASA Technical Reports Server (NTRS)

    Podwysocki, M. H.

    1977-01-01

    The field size distributions for the major grain producing countries of the World were estimated. LANDSAT-1 and 2 images were evaluated for two areas each in the United States, People's Republic of China, and the USSR. One scene each was evaluated for France, Canada, and India. Grid sampling was done for representative sub-samples of each image, measuring the long and short axes of each field; area was then calculated. Each of the resulting data sets was computer analyzed for their frequency distributions. Nearly all frequency distributions were highly peaked and skewed (shifted) towards small values, approaching that of either a Poisson or log-normal distribution. The data were normalized by a log transformation, creating a Gaussian distribution which has moments readily interpretable and useful for estimating the total population of fields. Resultant predictors of the field size estimates are discussed.

  10. High contrast hollow-cone dark field transmission electron microscopy for nanocrystalline grain size quantification.

    PubMed

    Yao, Bo; Sun, Tik; Warren, Andrew; Heinrich, Helge; Barmak, Katayun; Coffey, Kevin R

    2010-04-01

    In this paper, we describe hollow-cone dark field (HCDF) transmission electron microscopy (TEM) imaging, with a slightly convergent beam, as an improved technique that is suitable to form high contrast micrographs for nanocrystalline grain size quantification. We also examine the various factors that influence the HCDF TEM image quality, including the conditions of microscopy (alignment, focus and objective aperture size), the properties of the materials imaged (e.g., atomic number, strain, defects), and the characteristics of the TEM sample itself (e.g., thickness, ion milling artifacts). Sample preparation was found to be critical and an initial thinning by wet etching of the substrate (for thin film samples) or tripod polishing (for bulk samples), followed by low-angle ion milling was found to be the preferred approach for preparing high-quality electron transparent samples for HCDF imaging. PMID:20018512

  11. Downwind changes in grain size of aeolian dust; examples from marine and terrestrial archives

    NASA Astrophysics Data System (ADS)

    Stuut, Jan-Berend; Prins, Maarten

    2013-04-01

    Aeolian dust in the atmosphere may have a cooling effect when small particles in the high atmosphere block incoming solar energy (e.g., Claquin et al., 2003) but it may also act as a 'greenhouse gas' when larger particles in the lower atmosphere trap energy that was reflected from the Earth's surface (e.g., Otto et al., 2007). Therefore, it is of vital importance to have a good understanding of the particle-size distribution of aeolian dust in space and time. As wind is a very size-selective transport mechanism, the sediments it carries typically have a very-well sorted grain-size distribution, which gradually fines from proximal to distal deposition sites. This fact has been used in numerous paleo-environmental studies to both determine source-to-sink changes in the particle size of aeolian dust (e.g., Weltje and Prins, 2003; Holz et al., 2004; Prins and Vriend, 2007) and to quantify mass-accumulation rates of aeolian dust (e.g., Prins and Weltje 1999; Stuut et al., 2002; Prins et al., 2007; Prins and Vriend, 2007; Stuut et al., 2007; Tjallingii et al., 2008; Prins et al., 2009). Studies on modern wind-blown particles have demonstrated that particle size of dust not only is a function of lateral but also vertical transport distance (e.g., Torres-Padron et al., 2002; Stuut et al., 2005). Nonetheless, there are still many unresolved questions related to the physical properties of wind-blown particles like e.g., the case of "giant" quartz particles found on Hawaii (Betzer et al., 1988) that can only originate from Asia but have a too large size for the distance they travelled through the atmosphere. Here, we present examples of dust particle-size distributions from terrestrial (loess) as well as marine (deep-sea sediments) sedimentary archives and their spatial and temporal changes. With this contribution we hope to provide quantitative data for the modelling community in order to get a better grip on the role of wind-blown particles in the climate system. Cited

  12. Grain-size dependence of the magnetic properties of street dusts from Warsaw, Poland

    NASA Astrophysics Data System (ADS)

    Dytłow, Sylwia; Winkler, Aldo; Sagnotti, Leonardo

    2015-04-01

    In recent years, in connection with a substantial development of transportation in urban areas, vehicular traffic increased its importance as source of pollution and consequent cause of health problems in urban environments. In fact, it is well established that the concentration and size of pollution related particulate matter (PM) are important factors affecting human health. The aim of this study is to identify the variations of the magnetic properties and of the chemical composition of different granulometric fractions from street dusts collected at four locations in Warsaw: the city center, a suburb, a tramline and a big crossroad. Dust samples were mechanically sieved and classified using the laboratory shaker with a standard sieve set (0.5 mm, 0.25 mm, 0.1 mm and 0.071 mm). Data show a distribution of magnetic susceptibility (χ) in the wide range of 80-370 × 10-8 m3kg-1. Comparison of magnetic parameters shows that the street dust contains the pollution characteristics for air and soil. The samples were characterized by uniform magnetic mineralogy, typical for fine-grained magnetite, in a grain size range between pseudo-single-domain and fine multi-domain, with a small contribution from ultrafine superparamagnetic particles (~2-3.5 %). The street dust contains, as usual for the urban areas, spherical magnetic particles produced by fossil fuel combustion processes and mixture of irregular angular iron-oxides grains containing other elements. The magnetic susceptibility and hysteresis properties of the dusts have been analyzed in detail; the temperature variation of the saturation of remanent magnetization and of the magnetic susceptibility revealed that the main magnetic mineral, for all the fractions, is almost stoichiometric magnetite, with the finest fractions (d=0.1 mm, 0.071 mm and d

  13. Correlation between Al grain size, grain boundary grooves and local variations in oxide barrier thickness of Al/AlOx/Al tunnel junctions by transmission electron microscopy.

    PubMed

    Nik, Samira; Krantz, Philip; Zeng, Lunjie; Greibe, Tine; Pettersson, Henrik; Gustafsson, Stefan; Delsing, Per; Olsson, Eva

    2016-01-01

    A thickness variation of only one Ångström makes a significant difference in the current through a tunnel junction due to the exponential thickness dependence of the current. It is thus important to achieve a uniform thickness along the barrier to enhance, for example, the sensitivity and speed of single electron transistors based on the tunnel junctions. Here, we have observed that grooves at Al grain boundaries are associated with a local increase of tunnel barrier thickness. The uniformity of the barrier thickness along the tunnel junction thus increases with increasing Al grain size. We have studied the effect of oxidation time, partial oxygen pressure and also temperature during film growth on the grain size. The implications are that the uniformity improves with higher temperature during film growth. PMID:27462515

  14. Characterizing 3D grain size distributions from 2D sections in mylonites using a modified version of the Saltykov method

    NASA Astrophysics Data System (ADS)

    Lopez-Sanchez, Marco; Llana-Fúnez, Sergio

    2016-04-01

    The understanding of creep behaviour in rocks requires knowledge of 3D grain size distributions (GSD) that result from dynamic recrystallization processes during deformation. The methods to estimate directly the 3D grain size distribution -serial sectioning, synchrotron or X-ray-based tomography- are expensive, time-consuming and, in most cases and at best, challenging. This means that in practice grain size distributions are mostly derived from 2D sections. Although there are a number of methods in the literature to derive the actual 3D grain size distributions from 2D sections, the most popular in highly deformed rocks is the so-called Saltykov method. It has though two major drawbacks: the method assumes no interaction between grains, which is not true in the case of recrystallised mylonites; and uses histograms to describe distributions, which limits the quantification of the GSD. The first aim of this contribution is to test whether the interaction between grains in mylonites, i.e. random grain packing, affects significantly the GSDs estimated by the Saltykov method. We test this using the random resampling technique in a large data set (n = 12298). The full data set is built from several parallel thin sections that cut a completely dynamically recrystallized quartz aggregate in a rock sample from a Variscan shear zone in NW Spain. The results proved that the Saltykov method is reliable as long as the number of grains is large (n > 1000). Assuming that a lognormal distribution is an optimal approximation for the GSD in a completely dynamically recrystallized rock, we introduce an additional step to the Saltykov method, which allows estimating a continuous probability distribution function of the 3D grain size population. The additional step takes the midpoints of the classes obtained by the Saltykov method and fits a lognormal distribution with a trust region using a non-linear least squares algorithm. The new protocol is named the two-step method. The

  15. A theoretical explanation of grain size distributions in explosive rock fragmentation

    NASA Astrophysics Data System (ADS)

    Fowler, A. C.; Scheu, Bettina

    2016-06-01

    We have measured grain size distributions of the results of laboratory decompression explosions of volcanic rock. The resulting distributions can be approximately represented by gamma distributions of weight per cent as a function of ϕ =-log2⁡d , where d is the grain size in millimetres measured by sieving, with a superimposed long tail associated with the production of fines. We provide a description of the observations based on sequential fragmentation theory, which we develop for the particular case of `self-similar' fragmentation kernels, and we show that the corresponding evolution equation for the distribution can be explicitly solved, yielding the long-time lognormal distribution associated with Kolmogorov's fragmentation theory. Particular features of the experimental data, notably time evolution, advection, truncation and fines production, are described and predicted within the constraints of a generalized, `reductive' fragmentation model, and it is shown that the gamma distribution of coarse particles is a natural consequence of an assumed uniform fragmentation kernel. We further show that an explicit model for fines production during fracturing can lead to a second gamma distribution, and that the sum of the two provides a good fit to the observed data.

  16. A CONCENTRATION OF CENTIMETER-SIZED GRAINS IN THE OPHIUCHUS IRS 48 DUST TRAP

    SciTech Connect

    Marel, N. van der; Pinilla, P.; Tobin, J.; Kempen, T. van; Andrews, S.; Ricci, L.; Birnstiel, T.

    2015-09-01

    Azimuthally asymmetric dust distributions observed with the Atacama Large Millimeter/submillimeter Array (ALMA) in transition disks have been interpreted as dust traps. We present Very Large Array Ka band (34 GHz or 0.9 cm) and ALMA Cycle 2 Band 9 (680 GHz or 0.45 mm) observations at a 0.″2 resolution of the Oph IRS 48 disk, which suggest that larger particles could be more azimuthally concentrated than smaller dust grains, assuming an axisymmetric temperature field or optically thin 680 GHz emission. Fitting an intensity model to both data demonstrates that the azimuthal extent of the millimeter emission is 2.3 ± 0.9 times as wide as the centimeter emission, marginally consistent with the particle trapping mechanism under the above assumptions. The 34 GHz continuum image also reveals evidence for ionized gas emission from the star. Both the morphology and the spectral index variations are consistent with an increase of large particles in the center of the trap, but uncertainties remain due to the continuum optical depth at 680 GHz. Particle trapping has been proposed in planet formation models to allow dust particles to grow beyond millimeter sizes in the outer regions of protoplanetary disks. The new observations in the Oph IRS 48 disk provide support for the dust trapping mechanism for centimeter-sized grains, although additional data are required for definitive confirmation.

  17. The Impact of Li Grain Size on Coulombic Efficiency in Li Batteries

    PubMed Central

    Mehdi, B. Layla; Stevens, Andrew; Qian, Jiangfeng; Park, Chiwoo; Xu, Wu; Henderson, Wesley A.; Zhang, Ji-Guang; Mueller, Karl T.; Browning, Nigel D.

    2016-01-01

    One of the most promising means to increase the energy density of state-of-the-art lithium Li-ion batteries is to replace the graphite anode with a Li metal anode. While the direct use of Li metal may be highly advantageous, at present its practical application is limited by issues related to dendrite growth and low Coulombic efficiency, CE. Here operando electrochemical scanning transmission electron microscopy (STEM) is used to directly image the deposition/stripping of Li at the anode-electrolyte interface in a Li-based battery. A non-aqueous electrolyte containing small amounts of H2O as an additive results in remarkably different deposition/stripping properties as compared to the “dry” electrolyte when operated under identical electrochemical conditions. The electrolyte with the additive deposits more Li during the first cycle, with the grain sizes of the Li deposits being significantly larger and more variable. The stripping of the Li upon discharge is also more complete, i.e., there is a higher cycling CE. This suggests that larger grain sizes are indicative of better performance by leading to more uniform Li deposition and an overall decrease in the formation of Li dendrites and side reactions with electrolyte components, thus potentially paving the way for the direct use of Li metal in battery technologies. PMID:27703188

  18. The Impact of Li Grain Size on Coulombic Efficiency in Li Batteries

    NASA Astrophysics Data System (ADS)

    Mehdi, B. Layla; Stevens, Andrew; Qian, Jiangfeng; Park, Chiwoo; Xu, Wu; Henderson, Wesley A.; Zhang, Ji-Guang; Mueller, Karl T.; Browning, Nigel D.

    2016-10-01

    One of the most promising means to increase the energy density of state-of-the-art lithium Li-ion batteries is to replace the graphite anode with a Li metal anode. While the direct use of Li metal may be highly advantageous, at present its practical application is limited by issues related to dendrite growth and low Coulombic efficiency, CE. Here operando electrochemical scanning transmission electron microscopy (STEM) is used to directly image the deposition/stripping of Li at the anode-electrolyte interface in a Li-based battery. A non-aqueous electrolyte containing small amounts of H2O as an additive results in remarkably different deposition/stripping properties as compared to the “dry” electrolyte when operated under identical electrochemical conditions. The electrolyte with the additive deposits more Li during the first cycle, with the grain sizes of the Li deposits being significantly larger and more variable. The stripping of the Li upon discharge is also more complete, i.e., there is a higher cycling CE. This suggests that larger grain sizes are indicative of better performance by leading to more uniform Li deposition and an overall decrease in the formation of Li dendrites and side reactions with electrolyte components, thus potentially paving the way for the direct use of Li metal in battery technologies.

  19. Exceptional high fatigue strength in Cu-15at.%Al alloy with moderate grain size

    PubMed Central

    Liu, Rui; Tian, Yanzhong; Zhang, Zhenjun; An, Xianghai; Zhang, Peng; Zhang, Zhefeng

    2016-01-01

    It is commonly proposed that the fatigue strength can be enhanced by increasing the tensile strength, but this conclusion needs to be reconsidered according to our study. Here a recrystallized α-Cu-15at.%Al alloy with moderate grain size of 0.62 μm was fabricated by cold rolling and annealing, and this alloy achieved exceptional high fatigue strength of 280 MPa at 107 cycles. This value is much higher than the fatigue strength of 200 MPa for the nano-crystalline counterpart (0.04 μm in grain size) despite its higher tensile strength. The remarkable improvement of fatigue strength should be mainly attributed to the microstructure optimization, which helps achieve the reduction of initial damage and the dispersion of accumulated damage. A new strategy of “damage reduction” was then proposed for fatigue strength improvement, to supplement the former strengthening principle. The methods and strategies summarized in this work offer a general pathway for further improvement of fatigue strength, in order to ensure the long-term safety of structural materials. PMID:27264347

  20. Exceptional high fatigue strength in Cu-15at.%Al alloy with moderate grain size

    NASA Astrophysics Data System (ADS)

    Liu, Rui; Tian, Yanzhong; Zhang, Zhenjun; An, Xianghai; Zhang, Peng; Zhang, Zhefeng

    2016-06-01

    It is commonly proposed that the fatigue strength can be enhanced by increasing the tensile strength, but this conclusion needs to be reconsidered according to our study. Here a recrystallized α-Cu-15at.%Al alloy with moderate grain size of 0.62 μm was fabricated by cold rolling and annealing, and this alloy achieved exceptional high fatigue strength of 280 MPa at 107 cycles. This value is much higher than the fatigue strength of 200 MPa for the nano-crystalline counterpart (0.04 μm in grain size) despite its higher tensile strength. The remarkable improvement of fatigue strength should be mainly attributed to the microstructure optimization, which helps achieve the reduction of initial damage and the dispersion of accumulated damage. A new strategy of “damage reduction” was then proposed for fatigue strength improvement, to supplement the former strengthening principle. The methods and strategies summarized in this work offer a general pathway for further improvement of fatigue strength, in order to ensure the long-term safety of structural materials.

  1. Significant enhancement of the thermoelectric figure of merit of polycrystalline Si films by reducing grain size

    NASA Astrophysics Data System (ADS)

    Valalaki, K.; Vouroutzis, N.; Nassiopoulou, A. G.

    2016-08-01

    The thermoelectric properties of p-type polycrystalline silicon thin films deposited by low pressure chemical vapour deposition (LPCVD) were accurately determined at room temperature and the thermoelectric figure of merit was deduced as a function of film thickness, ranging from 100 to 500 nm. The effect of film thickness on their thermoelectric performance is discussed. More than threefold increase in the thermoelectric figure of merit of the 100 nm thick polysilicon film was observed compared to the 500 nm thick film, reaching a value as high as 0.033. This enhancement is mainly the result of the smaller grain size in the thinner films. With the decrease in grain size the resistivity of the films is increased twofold and electrical conductivity decreased, however the Seebeck coefficient is increased by 30% and the thermal conductivity is decreased eightfold, being mainly at the origin of the increased figure of merit of the 100 nm film. Our experimental results were compared to known theoretical models and the possible mechanisms involved are presented and discussed.

  2. Functional outlier detection in grain-size distribution curves of detrital sediments

    NASA Astrophysics Data System (ADS)

    Sierra, Carlos; Ordóñez, Celestino; Gallego, José Luis Rodríguez

    2013-11-01

    This article introduces functional outlier detection as a mathematical tool for the recognition of outliers in grain-size distribution curves. Two methods, namely the functional high density region (HDR) boxplot and functional bagplot, were applied for outlier detection in detrital sediment grain-size curves. The results of these two approaches were compared with those obtained with a classical modified z-score method. In this regard, while the HDR and functional bagplots revealed a significant number of curves as outliers, the former showed superior sensitivity. Despite the visual appreciation of differences between the curves produced by the classical method, this technique was not able to detect outliers on the basis of just one characteristic parameter of the curves (the median in our case). None of the sedimentary structures (eolian and tidal) addressed was detected as outliers by the algorithms, thus these structures were incorporated into natural variability. The results suggest that the HDR bagplot and the functional bagplot could be introduced as a preceding outlier detection step in geochemical, sedimentological and coastal studies.

  3. Exceptional high fatigue strength in Cu-15at.%Al alloy with moderate grain size.

    PubMed

    Liu, Rui; Tian, Yanzhong; Zhang, Zhenjun; An, Xianghai; Zhang, Peng; Zhang, Zhefeng

    2016-01-01

    It is commonly proposed that the fatigue strength can be enhanced by increasing the tensile strength, but this conclusion needs to be reconsidered according to our study. Here a recrystallized α-Cu-15at.%Al alloy with moderate grain size of 0.62 μm was fabricated by cold rolling and annealing, and this alloy achieved exceptional high fatigue strength of 280 MPa at 10(7) cycles. This value is much higher than the fatigue strength of 200 MPa for the nano-crystalline counterpart (0.04 μm in grain size) despite its higher tensile strength. The remarkable improvement of fatigue strength should be mainly attributed to the microstructure optimization, which helps achieve the reduction of initial damage and the dispersion of accumulated damage. A new strategy of "damage reduction" was then proposed for fatigue strength improvement, to supplement the former strengthening principle. The methods and strategies summarized in this work offer a general pathway for further improvement of fatigue strength, in order to ensure the long-term safety of structural materials. PMID:27264347

  4. Transient response in longitudinal grain size to reduced sediment supply in a large river

    NASA Astrophysics Data System (ADS)

    Singer, Michael

    2010-05-01

    Bed material grain size is an important degree of freedom in fluvial systems as they adjust to system-wide perturbations such as sediment supply changes. However, little is known about processes and patterns of such adjustment in longitudinal grain size sorting in large rivers. This research uses unprecedented datasets collected in a large fluvial system to investigate transient response to recent supply changes associated with anthropogenic activities. Separate fining trends for gravel and fines, a protracted gravel-sand (G-S) transition, and bed patchiness identified in Singer (2008) were interrogated using output from a hydraulic model with grain size distributions (GSDs) extracted from ~125 cross sections spanning ~400 river kilometers of the Sacramento River, California. The analysis suggests that interactions between hydraulics, bed material sorting, and sediment flux explain these previously identified anomalies. Highest values of sorting occur in the G-S transition and represent the overlap of separate fining trends for gravel and fines, where the long profile is jagged with evidence of progressive incision. Much of the sediment in this poorly sorted zone is organized into patches, where transport apparently occurs as bedload sheets. Patchiness occurs over short length scales leading to strong differences in entrainment and flux, regardless of hydraulic conditions. A modified Shields stress is proposed that is scaled by GSD sorting to improve characterization of entrainment/disentrainment. Sediment flux calculations based on an equation sensitive bed material conditions (Singer and Dunne, 2004) reveal a strong relationship between fine sediment flux and d90, suggesting that the efficiency of fine patch flux controls bed material bed surface roughness. Results are in part consistent with Paola and Seal (1995) suggesting that patches are a result of overlapping pdfs of shear stress and sorting and with Ferguson (2003) in that the final end of the protracted G

  5. Experimental Investigations of the Physical and Optical Properties of Individual Micron/Submicron-Size Dust Grains in Astrophysical Environments

    NASA Technical Reports Server (NTRS)

    Abbas, M. M.; Tankosic, D.; LeClair, A.

    2014-01-01

    Dust grains constitute a significant component of matter in the universe, and play an important and crucial role in the formation and evolution of the stellar/planetary systems in interstellar dust clouds. Knowledge of physical and optical properties of dust grains is required for understanding of a variety of processes in astrophysical and planetary environments. The currently available and generally employed data on the properties of dust grains is based on bulk materials, with analytical models employed to deduce the corresponding values for individual small micron/submicron-size dust grains. However, it has been well-recognized over a long period, that the properties of individual smallsize dust grains may be very different from those deduced from bulk materials. This has been validated by a series of experimental investigations carried out over the last few years, on a laboratory facility based on an Electrodynamic Balance at NASA, which permits levitation of single small-size dust grains of desired composition and size, in vacuum, in simulated space environments. In this paper, we present a brief review of the results of a series of selected investigations carried out on the analogs of interstellar and planetary dust grains, as well as dust grains obtained by Apollo-l1-17 lunar missions. The selected investigations, with analytical results and discussions, include: (a) Direct measurements of radiation on individual dust grains (b) Rotation and alignments of dust grains by radiative torque (c) Charging properties of dust grains by: (i) UV Photo-electric emissions (ii) Electron Impact. The results from these experiments are examined in the light of the current theories of the processes involved.

  6. Remote Analysis of Grain Size Characteristic in Submarine Pyroclastic Deposits from Kolumbo Volcano, Greece

    NASA Astrophysics Data System (ADS)

    Smart, C.; Whitesell, D. P.; Roman, C.; Carey, S.

    2011-12-01

    Grain size characteristics of pyroclastic deposits provide valuable information about source eruption energetics and depositional processes. Maximum size and sorting are often used to discriminate between fallout and sediment gravity flow processes during explosive eruptions. In the submarine environment the collection of such data in thick pyroclastic sequences is extremely challenging and potentially time consuming. A method has been developed to extract grain size information from stereo images collected by a remotely operated vehicle (ROV). In the summer of 2010 the ROV Hercules collected a suite of stereo images from a thick pumice sequence in the caldera walls of Kolumbo submarine volcano located about seven kilometers off the coast of Santorini, Greece. The highly stratified, pumice-rich deposit was likely created by the last explosive eruption of the volcano that took place in 1650 AD. Each image was taken from a distance of only a few meters from the outcrop in order to capture the outlines of individual clasts with relatively high resolution. Mosaics of individual images taken as the ROV transected approximately 150 meters of vertical outcrop were used to create large-scale vertical stratigraphic columns that proved useful for overall documentation of the eruption sequence and intracaldera correlations of distinct tephra units. Initial image processing techniques, including morphological operations, edge detection, shape and size estimation were implemented in MatLab and applied to a subset of individual images of the mosiacs. A large variety of algorithms were tested in order to best discriminate the outlines of individual pumices. This proved to be challenging owing to the close packing and overlapping of individual pumices. Preliminary success was achieved in discriminating the outlines of the large particles and measurements were carried out on the largest clasts present at different stratigraphic levels. In addition, semi-quantitative analysis of the

  7. Valve for abrasive material

    DOEpatents

    Gardner, Harold S.

    1982-01-01

    A ball valve assembly for controlling the flow of abrasive particulates including an enlarged section at the bore inlet and an enlarged section at the bore outlet. A refractory ceramic annular deflector is positioned in each of the enlarged sections, substantially extending the useful life of the valve.

  8. The Evolution of Grain Size Distribution in Explosive Rock Fragmentation - Sequential Fragmentation Theory Revisited

    NASA Astrophysics Data System (ADS)

    Scheu, B.; Fowler, A. C.

    2015-12-01

    Fragmentation is a ubiquitous phenomenon in many natural and engineering systems. It is the process by which an initially competent medium, solid or liquid, is broken up into a population of constituents. Examples occur in collisions and impacts of asteroids/meteorites, explosion driven fragmentation of munitions on a battlefield, as well as of magma in a volcanic conduit causing explosive volcanic eruptions and break-up of liquid drops. Besides the mechanism of fragmentation the resulting frequency-size distribution of the generated constituents is of central interest. Initially their distributions were fitted empirically using lognormal, Rosin-Rammler and Weibull distributions (e.g. Brown & Wohletz 1995). The sequential fragmentation theory (Brown 1989, Wohletz at al. 1989, Wohletz & Brown 1995) and the application of fractal theory to fragmentation products (Turcotte 1986, Perfect 1997, Perugini & Kueppers 2012) attempt to overcome this shortcoming by providing a more physical basis for the applied distribution. Both rely on an at least partially scale-invariant and thus self-similar random fragmentation process. Here we provide a stochastic model for the evolution of grain size distribution during the explosion process. Our model is based on laboratory experiments in which volcanic rock samples explode naturally when rapidly depressurized from initial pressures of several MPa to ambient conditions. The physics governing this fragmentation process has been successfully modelled and the observed fragmentation pattern could be numerically reproduced (Fowler et al. 2010). The fragmentation of these natural rocks leads to grain size distributions which vary depending on the experimental starting conditions. Our model provides a theoretical description of these different grain size distributions. Our model combines a sequential model of the type outlined by Turcotte (1986), but generalized to cater for the explosive process appropriate here, in particular by

  9. Effect of Freeze-Thaw Cycles on Grain Size of Biochar

    NASA Astrophysics Data System (ADS)

    Dugan, B.; Liu, Z.; Masiello, C. A.; Gonnermann, H. M.; Nittrouer, J. A.

    2015-12-01

    Biochar may improve soil performance by altering soil physical properties such as porosity, density, hydraulic conductivity, and water holding capacity. Because these physical properties of soil-biochar mixtures are associated with the grain size of the soil and the biochar, they may change if biochar particles are physically broken down in the environment. In cold regions, biochar may be fragmented into smaller particles when water in biochar's internal pores expands during freezing. This expansion may mechanically break particles. In this study we investigate if freeze-thaw cycles affect grain size of biochars produced at two temperatures (350°C and 500°C) from four types of feedstock (mesquite, pine, sewage waste, and miscanthus). Prior to freeze-thaw cycles, biochar's internal porosity increases with pyrolysis temperature and also varies with feedstock type. In our study, the highest internal porosity is 0.82±0.11 for 500 °C miscanthus biochar and the lowest internal porosity is 0.27±0.01 for 350 °C sewage waste biochar. Our biochars also have different median grain diameter (D50) and aspect ratio (AR). The largest D50 is 4836±132 μm for 350 °C miscanthus biochar and the smallest D50 is 2238±13 μm for 350°C sewage waste biochar. The highest AR is 0.85±0.01 for 500 °C sewage waste biochar and the lowest AR is 0.31±0.01 for 350 °C miscanthus biochar. After characterizing the initial properties of biochars, we saturated our biochar using synthetic rain water and subjected them to 10 freeze-thaw cycles (freeze at -19±3°C for 8 hours and thaw at 20±0°C for 16 hours). We expect that D50 will be reduced and AR will be changed by freeze-thaw cycles and the effect will vary with biochar porosity. Ultimately this work will help constrain how biochar particle size changes due to freezing, which can be extrapolated to understand transients in soil performance associated with biochar particle size.

  10. Tracking eolian dust with helium and thorium: Impacts of grain size and provenance

    NASA Astrophysics Data System (ADS)

    McGee, David; Winckler, Gisela; Borunda, Alejandra; Serno, Sascha; Anderson, Robert F.; Recasens, Cristina; Bory, Aloys; Gaiero, Diego; Jaccard, Samuel L.; Kaplan, Michael; McManus, Jerry F.; Revel, Marie; Sun, Youbin

    2016-02-01

    Reconstructions of the deposition rate of windblown mineral dust in ocean sediments offer an important means of tracking past climate changes and of assessing the radiative and biogeochemical impacts of dust in past climates. Dust flux estimates in ocean sediments have commonly been based on the operationally defined lithogenic fraction of sediment samples. More recently, dust fluxes have been estimated from measurements of helium and thorium, as rare isotopes of these elements (He-3 and Th-230) allow estimates of sediment flux, and the dominant isotopes (He-4 and Th-232) are uniquely associated with the lithogenic fraction of marine sediments. In order to improve the fidelity of dust flux reconstructions based on He and Th, we present a survey of He and Th concentrations in sediments from dust source areas in East Asia, Australia and South America. Our data show systematic relationships between He and Th concentrations and grain size, with He concentrations decreasing and Th concentrations increasing with decreasing grain size. We find consistent He and Th concentrations in the fine fraction (<5 μm) of samples from East Asia, Australia and Central South America (Puna-Central West Argentina), with Th concentrations averaging 14 μg/g and He concentrations averaging 2 μcc STP/g. We recommend use of these values for estimating dust fluxes in sediments where dust is dominantly fine-grained, and suggest that previous studies may have systematically overestimated Th-based dust fluxes by 30%. Source areas in Patagonia appear to have lower He and Th contents than other regions, as fine fraction concentrations average 0.8 μcc STP/g and 9 μg/g for 4He and 232Th, respectively. The impact of grain size on lithogenic He and Th concentrations should be taken into account in sediments proximal to dust sources where dust grain size may vary considerably. Our data also have important implications for the hosts of He in long-traveled dust and for the 3He/4He ratio used for

  11. Influence of grain size on optical properties of Sr{sub 2}CeO{sub 4} nanocrystals

    SciTech Connect

    Stefanski, M.; Marciniak, L. Hreniak, D.; Strek, W.

    2015-05-14

    The absorption, excitation, and emission spectra of the Sr{sub 2}CeO{sub 4} nanocrystals prepared by the modified sol–gel method were investigated. The impact of the average grain size of Sr{sub 2}CeO{sub 4} nanocrystals on their optical properties was investigated. It was observed that with increasing the average grain size of Sr{sub 2}CeO{sub 4} nanocrystals, the emission decay times decreased significantly. A similar behavior was observed for the emission quantum efficiencies and the Huang–Rhys factors. The grain size dependence of optical parameters of Sr{sub 2}CeO{sub 4} nanocrystals was found well fitted by functions of the reciprocal of the grain diameter. It was shown that this dependence may be rationalized assuming that the correction for electric local field associated with effective refractive index affecting the spherical nanoparticle is governed by its shell.

  12. State-of-the-art of Grain-Size Analyses Using Laser Diffractometry

    NASA Astrophysics Data System (ADS)

    Machalett, Bjoern

    2013-04-01

    Laser diffractometry is based on the principle that particles of a given size diffract light through a given angle: large particles scatter light at small angles, while small particles scatter light at big angles. The method has become accepted to measure grain-size distributions as it offers important advantages compared with traditional sieve-pipette methods or image particle analyses. Laser diffractometry allows fast measurements of large sample sets with high reproducibility and accuracy. Furthermore, this method needs only small amounts of sample material and offers a dynamic measuring range from around 0.04 to 2000 µm. This paper summarizes improvements in lab procedures and methodology, as well as comprehensive experimental results using laser diffractometry leading towards a standardized protocol for applying laser particle size analysis in geomorphic and paleoenvironmental studies. It will be demonstrated that advances in measurement technologies as well as in sample collection and sample preparation reveal much more complex particle size distributions than it has been hitherto suspected.

  13. State-of-the-art of Grain-Size Analyses Using Laser Diffractometry

    NASA Astrophysics Data System (ADS)

    Rosmayev, P.; Machalett, B.

    2011-12-01

    Laser diffractometry is based on the principle that particles of a given size diffract light through a given angle: large particles scatter light at small angles, while small particles scatter light at big angles. The method has become accepted to measure grain-size distributions as it offers important advantages compared with traditional sieve-pipette methods or image particle analyses. Laser diffractometry allows fast measurements of large sample sets with high reproducibility and accuracy. Furthermore, this method needs only small amounts of sample material and offers a dynamic measuring range from around 0.04 to 2000 μm. This paper summarizes improvements in lab procedures and methodology, as well as comprehensive experimental results using laser diffractometry leading towards a standardized protocol for applying laser particle size analysis in geomorphic and paleoenvironmental studies. It will be demonstrated that advances in measurement technologies as well as in sample collection and sample preparation reveal much more complex particle size distributions than it has been hitherto suspected.

  14. Heavy metal speciation in various grain sizes of industrially contaminated street dust using multivariate statistical analysis.

    PubMed

    Yıldırım, Gülşen; Tokalıoğlu, Şerife

    2016-02-01

    A total of 36 street dust samples were collected from the streets of the Organised Industrial District in Kayseri, Turkey. This region includes a total of 818 work places in various industrial areas. The modified BCR (the European Community Bureau of Reference) sequential extraction procedure was applied to evaluate the mobility and bioavailability of trace elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in street dusts of the study area. The BCR was classified into three steps: water/acid soluble fraction, reducible and oxidisable fraction. The remaining residue was dissolved by using aqua regia. The concentrations of the metals in street dust samples were determined by flame atomic absorption spectrometry. Also the effect of the different grain sizes (<38µm, 38-53µm and 53-74µm) of the 36 street dust samples on the mobility of the metals was investigated using the modified BCR procedure. The mobility sequence based on the sum of the first three phases (for <74µm grain size) was: Cd (71.3)>Cu (48.9)>Pb (42.8)=Cr (42.1)>Ni (41.4)>Zn (40.9)>Co (36.6)=Mn (36.3)>Fe (3.1). No significant difference was observed among metal partitioning for the three particle sizes. Correlation, principal component and cluster analysis were applied to identify probable natural and anthropogenic sources in the region. The principal component analysis results showed that this industrial district was influenced by traffic, industrial activities, air-borne emissions and natural sources. The accuracy of the results was checked by analysis of both the BCR-701 certified reference material and by recovery studies in street dust samples. PMID:26595510

  15. Heavy metal speciation in various grain sizes of industrially contaminated street dust using multivariate statistical analysis.

    PubMed

    Yıldırım, Gülşen; Tokalıoğlu, Şerife

    2016-02-01

    A total of 36 street dust samples were collected from the streets of the Organised Industrial District in Kayseri, Turkey. This region includes a total of 818 work places in various industrial areas. The modified BCR (the European Community Bureau of Reference) sequential extraction procedure was applied to evaluate the mobility and bioavailability of trace elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in street dusts of the study area. The BCR was classified into three steps: water/acid soluble fraction, reducible and oxidisable fraction. The remaining residue was dissolved by using aqua regia. The concentrations of the metals in street dust samples were determined by flame atomic absorption spectrometry. Also the effect of the different grain sizes (<38µm, 38-53µm and 53-74µm) of the 36 street dust samples on the mobility of the metals was investigated using the modified BCR procedure. The mobility sequence based on the sum of the first three phases (for <74µm grain size) was: Cd (71.3)>Cu (48.9)>Pb (42.8)=Cr (42.1)>Ni (41.4)>Zn (40.9)>Co (36.6)=Mn (36.3)>Fe (3.1). No significant difference was observed among metal partitioning for the three particle sizes. Correlation, principal component and cluster analysis were applied to identify probable natural and anthropogenic sources in the region. The principal component analysis results showed that this industrial district was influenced by traffic, industrial activities, air-borne emissions and natural sources. The accuracy of the results was checked by analysis of both the BCR-701 certified reference material and by recovery studies in street dust samples.

  16. Field test comparison of an autocorrelation technique for determining grain size using a digital 'beachball' camera versus traditional methods

    USGS Publications Warehouse

    Barnard, P.L.; Rubin, D.M.; Harney, J.; Mustain, N.

    2007-01-01

    This extensive field test of an autocorrelation technique for determining grain size from digital images was conducted using a digital bed-sediment camera, or 'beachball' camera. Using 205 sediment samples and >1200 images from a variety of beaches on the west coast of the US, grain size ranging from sand to granules was measured from field samples using both the autocorrelation technique developed by Rubin [Rubin, D.M., 2004. A simple autocorrelation algorithm for determining grain size from digital images of sediment. Journal of Sedimentary Research, 74(1): 160-165.] and traditional methods (i.e. settling tube analysis, sieving, and point counts). To test the accuracy of the digital-image grain size algorithm, we compared results with manual point counts of an extensive image data set in the Santa Barbara littoral cell. Grain sizes calculated using the autocorrelation algorithm were highly correlated with the point counts of the same images (r2 = 0.93; n = 79) and had an error of only 1%. Comparisons of calculated grain sizes and grain sizes measured from grab samples demonstrated that the autocorrelation technique works well on high-energy dissipative beaches with well-sorted sediment such as in the Pacific Northwest (r2 ??? 0.92; n = 115). On less dissipative, more poorly sorted beaches such as Ocean Beach in San Francisco, results were not as good (r2 ??? 0.70; n = 67; within 3% accuracy). Because the algorithm works well compared with point counts of the same image, the poorer correlation with grab samples must be a result of actual spatial and vertical variability of sediment in the field; closer agreement between grain size in the images and grain size of grab samples can be achieved by increasing the sampling volume of the images (taking more images, distributed over a volume comparable to that of a grab sample). In all field tests the autocorrelation method was able to predict the mean and median grain size with ???96% accuracy, which is more than

  17. Effect of sputtering target's grain size on the sputtering yield, particle size and coercivity (Hc) of Ni and Ni20Al thin films

    NASA Astrophysics Data System (ADS)

    Reza, M.; Sajuri, Z.; Yunas, J.; Syarif, J.

    2016-02-01

    Researches on magnetic thin films concentrated mainly on optimizing the sputtering parameters to obtain the desired thin film's properties. However, the effect of the sputtering target's properties towards the thin film's properties is not well established. This study is focused on analysing the effect of sputtering target's grain size towards the sputtering yield, particle size and the magnetic coercivity (Hc) of thin film. Two sets of sputtering targets; pure Ni (magnetic) and Ni20Al (at.%) (non-magnetic) were prepared. Each target has 2 sets of samples with different grain sizes; (a) 30 to 50μm and (b) 80 to 100μm. Thin films from each target were sputtered onto glass substrates under fixed sputtering parameters. The initial results suggested that the sputtering target's grain size has significant effect on the thin film's sputtering yield, particle size and Hc. Sputtering target with smaller grain size has 12% (pure Ni) to 60% (Ni20Al) higher sputtering yield, which produces thin films with smaller particle size and larger Hc value. These initial findings provides a basis for further magnetic thin film research, particularly for the seed layer in hard disk drive (HDD) media, where seed layer with smaller particle size is essential in reducing signal-to-noise ratio (SNR).

  18. Effect of grain size on stability of X-ray diffraction patterns used for threat detection

    NASA Astrophysics Data System (ADS)

    Ghammraoui, B.; Rebuffel, V.; Tabary, J.; Paulus, C.; Verger, L.; Duvauchelle, Ph.

    2012-08-01

    Energy Dispersive X-ray Diffraction (EDXRD) is well-suited to detecting narcotics and a wide range of explosives. The integrated intensity of an X-ray diffraction peak is proportional to the number of grains in the inspected object which are oriented such that they satisfy Bragg's condition. Several parameters have a significant influence on this number. Among them, we can list grain size and the fill rate for polycrystalline materials that both may significantly vary for a same material according to its way of production. Consequently, peak intensity may change significantly from one measurement to another one, thus increasing the risk of losing peaks. This instability is one of the many causes of false alarms. To help avoid these, we have developed a model to quantify the stability of the diffraction patterns measured. Two methods (extension of the detector in a direction perpendicular to the diffractometer plane and slow rotation of both source and detector) can be used to decrease the coefficient of variation, leading to a more stable spectral measurement.

  19. Evaporative Deposition of Aluminum Coatings and Shapes with Grain Size Control

    SciTech Connect

    Jankowski, A F; Hayes, J P

    2003-02-19

    The direct deposition of coatings with variable cross-section profiles presents a challenge for the use of physical vapor deposition technology. Coatings with constant and variable cross-section profiles are of interest for advancing the evaluation of material behavior under extreme loading conditions, as for example under high strain rate. The synthesis of a variable cross-section profile by design in the as-deposited condition requires process innovation. It is demonstrated that a thickness gradient in cross-section can be produced when the substrate is exposed to a highly collimated evaporation source. The exposure is governed using a variable position shutter as driven by a computer-controlled stepper motor. An example is shown for aluminum deposition in which the coating thickness varies linearly from one plateau to another forming a wedge shape. To deposit a controlled grain size in coatings as these wedge shapes, first requires an understanding of the affect of time at temperature. An examination of aluminum coatings with constant cross-section reveals that ideal-grain growth behavior is observed from the micron-to-millimeter scale for depositions at temperatures in excess of half the melt point.

  20. Experimental investigation of suspended particles transport through porous media: particle and grain size effect.

    PubMed

    Liu, Quansheng; Cui, Xianze; Zhang, Chengyuan; Huang, Shibing

    2016-01-01

    Particle and grain size may influence the transportation and deposition characteristics of particles within pollutant transport and within granular filters that are typically used in wastewater treatment. We conducted two-dimensional sandbox experiments using quartz powder as the particles and quartz sand as the porous medium to study the response of transportation and deposition formation to changes in particle diameter (ds, with median diameter 18, 41, and 82 μm) and grain diameter (dp, with median diameter 0.36, 1.25, and 2.82 mm) considering a wide range of diameter ratios (ds/dp) from 0.0064 to 0.228. Particles were suspended in deionized water, and quartz sand was used as the porous medium, which was meticulously cleaned to minimize any physicochemical and impurities effects that could result in indeterminate results. After the experiments, the particle concentration of the effluent and particle mass per gram of dry sands were measured to explore changes in transportation and deposition characteristics under different conditions. In addition, a micro-analysis was conducted to better analyse the results on a mesoscopic scale. The experimental observation analyses indicate that different diameter ratios (ds/dp) may lead to different deposit formations. As ds/dp increased, the deposit formation changed from 'Random Deposition Type' to 'Gradient Deposition Type', and eventually became 'Inlet Deposition Type'.

  1. Superior Mobility in Chemical Vapor Deposition Synthesized Graphene by Grain Size Engineering

    NASA Astrophysics Data System (ADS)

    Petrone, Nicholas; Dean, Cory; Meric, Inanc; van der Zande, Arend; Huang, Pinshane; Wang, Lei; Muller, David; Shepard, Kenneth; Hone, James

    2012-02-01

    Chemical vapor deposition (CVD) offers a promising method to produce large-area films of graphene, crucial for commercial realization of graphene-based applications. However, electron transport in CVD grown graphene has continued to fall short of the performance demonstrated by graphene derived from mechanical exfoliation. Lattice defects and grain boundaries developed during growth, structural defects and chemical contamination introduced during transfer, and charged scatterers present in sub-optimal dielectric substrates have all been identified as sources of disorder in CVD grown graphene devices. We grow CVD graphene and fabricate field-effect transistors, attempting to minimize potential sources of disorder. We reduce density of grain boundaries in CVD graphene by controlling domain sizes up to 250 microns. By transferring CVD graphene onto h-BN utilizing a dry-transfer method, we minimize trapped charges at the interface between graphene and in the underlying substrate. We report field-effect mobilities up to 110,000 cm2V-1s-1 and oscillations in magnetotransport measurements below 1 T, confirming the high quality and low disorder in our CVD graphene devices.

  2. Experimental investigation of suspended particles transport through porous media: particle and grain size effect.

    PubMed

    Liu, Quansheng; Cui, Xianze; Zhang, Chengyuan; Huang, Shibing

    2016-01-01

    Particle and grain size may influence the transportation and deposition characteristics of particles within pollutant transport and within granular filters that are typically used in wastewater treatment. We conducted two-dimensional sandbox experiments using quartz powder as the particles and quartz sand as the porous medium to study the response of transportation and deposition formation to changes in particle diameter (ds, with median diameter 18, 41, and 82 μm) and grain diameter (dp, with median diameter 0.36, 1.25, and 2.82 mm) considering a wide range of diameter ratios (ds/dp) from 0.0064 to 0.228. Particles were suspended in deionized water, and quartz sand was used as the porous medium, which was meticulously cleaned to minimize any physicochemical and impurities effects that could result in indeterminate results. After the experiments, the particle concentration of the effluent and particle mass per gram of dry sands were measured to explore changes in transportation and deposition characteristics under different conditions. In addition, a micro-analysis was conducted to better analyse the results on a mesoscopic scale. The experimental observation analyses indicate that different diameter ratios (ds/dp) may lead to different deposit formations. As ds/dp increased, the deposit formation changed from 'Random Deposition Type' to 'Gradient Deposition Type', and eventually became 'Inlet Deposition Type'. PMID:26323505

  3. Size and grain morphology dependent magnetic behaviour of Co-doped ZnO

    SciTech Connect

    Vagadia, Megha; Ravalia, Ashish; Khachar, Uma; Solanki, P.S.; Doshi, R.R.; Rayaprol, S.; Kuberkar, D.G.

    2011-11-15

    Highlights: {yields} Structure and magnetic studies on Co-doped ZnO. {yields} Synthesis method dependent comparison of magnetic properties. {yields} Grain size and morphology affect the magnetic properties of Co-doped ZnO. -- Abstract: We have carried out a comparative study of structural, microstructural and magnetic properties of the two sets of Co-doped ZnO samples synthesized using solid state reaction and sol-gel method. Rietveld refinement of the X-ray diffraction data reveals single phase hexagonal wurtzite structure for all the samples, while the tunnelling electron microscopy measurements show the presence of nano-phase in the sol-gel grown Co-doped ZnO samples. It is found that, the microstructure strongly depends on the synthesis method adopted. Samples with higher Co-concentration synthesized by SSR route exhibit antiferromagnetism while SG grown Co-doped ZnO samples exhibit weak ferromagnetic behaviour. Improved magnetic phase in the SG grown samples has been attributed to the grain morphology.

  4. Grain Size and Field Dependence of the Morin Transition and Mössbauer Spectroscopy of Synthetic Hematite

    NASA Astrophysics Data System (ADS)

    Volk, M. W. R.; Egli, R.; Gilder, S.

    2012-04-01

    Hematite is a common magnetic mineral occurring in sediments, both in detrital and authigenic form. The dependence of its magnetic properties on grain size and particle surface are not yet fully understood. Here we present a systematic investigation of magnetic properties of synthetic hematite particles (14 nm, 22 nm, 34 nm, 147 nm, 11 μm) across the so-called Morin transition, focusing on the transition temperature and amplitude, transition hysteresis, and defect moment remaining in the antiferromagnetic phase below the transition temperature. While hysteresis parameters above and below the Morin transition did not show well-defined systematic grain size trends, we found a clear relation between grain size, applied field, and transition temperature along with results shown by previous studies. The field dependence of the transition was found to be stronger in smaller particles. We measured Mössbauer spectra at room and low temperatures, finding a clear grain size dependence of Mössbauer parameters. We also found a second sextet in the smallest particles, whose relative contribution is inversely proportional to the size of the sample. The hyperfine field - the magnetic field at the Fe3+ atom in the lattice - decreases with decreasing grain size. We also found a linear correlation between the transition temperature and the magnetic hypefine field.

  5. Extracting magnetic cluster size and its distributions in advanced perpendicular recording media with shrinking grain size using small angle x-ray scattering

    SciTech Connect

    Mehta, Virat; Ikeda, Yoshihiro; Takano, Ken; Terris, Bruce D.; Hellwig, Olav; Wang, Tianhan; Wu, Benny; Graves, Catherine; Dürr, Hermann A.; Scherz, Andreas; Stöhr, Jo

    2015-05-18

    We analyze the magnetic cluster size (MCS) and magnetic cluster size distribution (MCSD) in a variety of perpendicular magnetic recording (PMR) media designs using resonant small angle x-ray scattering at the Co L{sub 3} absorption edge. The different PMR media flavors considered here vary in grain size between 7.5 and 9.5 nm as well as in lateral inter-granular exchange strength, which is controlled via the segregant amount. While for high inter-granular exchange, the MCS increases rapidly for grain sizes below 8.5 nm, we show that for increased amount of segregant with less exchange the MCS remains relatively small, even for grain sizes of 7.5 and 8 nm. However, the MCSD still increases sharply when shrinking grains from 8 to 7.5 nm. We show evidence that recording performance such as signal-to-noise-ratio on the spin stand correlates well with the product of magnetic cluster size and magnetic cluster size distribution.

  6. New Technology/Old Technology: Comparing Lunar Grain Size Distribution Data and Methods

    NASA Technical Reports Server (NTRS)

    Fruland, R. M.; Cooper, Bonnie L.; Gonzalexz, C. P.; McKay, David S.

    2011-01-01

    Laser diffraction technology generates reproducible grain size distributions and reveals new structures not apparent in old sieve data. The comparison of specific sieve fractions with the Microtrac distribution curve generated for those specific fractions shows a reasonable match for the mean of each fraction between the two techniques, giving us confidence that the large existing body of sieve data can be cross-correlated with new data based on laser diffraction. It is well-suited for lunar soils, which have as much as 25% of the material in the less than 20 micrometer fraction. The fines in this range are of particular interest because they may contain a record of important space weathering processes.

  7. Stimulated Brillouin scattering of laser in semiconductor plasma embedded with nano-sized grains

    SciTech Connect

    Sharma, Giriraj; Dad, R. C.; Ghosh, S.

    2015-07-31

    A high power laser propagating through semiconductor plasma undergoes Stimulated Brillouin scattering (SBS) from the electrostrictively generated acoustic perturbations. We have considered that nano-sized grains (NSGs) ions are embedded in semiconductor plasma by means of ion implantation. The NSGs are bombarded by the surrounding plasma particles and collect electrons. By considering a negative charge on the NSGs, we present an analytically study on the effects of NSGs on threshold field for the onset of SBS and Brillouin gain of generated Brillouin scattered mode. It is found that as the charge on the NSGs builds up, the Brillouin gain is significantly raised and the threshold pump field for the onset of SBS process is lowered.

  8. Vibracore, Radiocarbon, Microfossil, and Grain-Size Data from Apalachicola Bay, Florida

    USGS Publications Warehouse

    Twichell, D.C.; Pendleton, E.A.; Poore, R.Z.; Osterman, L.E.; Kelso, K.W.

    2009-01-01

    In 2007, the U.S. Geological Survey collected 24 vibracores within Apalachicola Bay, Florida. The vibracores were collected by using a Rossfelder electric percussive (P-3) vibracore system during a cruise on the Research Vessel (R/V) G.K. Gilbert. Selection of the core sites was based on a geophysical survey that was conducted during 2005 and 2006 in collaboration with the National Oceanic and Atmospheric Administration's (NOAA) Coastal Services Center (CSC) and the Apalachicola Bay National Estuarine Research Reserve. This report contains the vibracore data logs, photographs, and core-derived data including grain-size analyses, radiocarbon ages, microfossil counts, and sedimentological interpretations. The long-term goal of this study is to provide maps, data, and assistance to the Apalachicola Bay National Estuarine Research Reserve in their effort to monitor and understand the geology and ecology of Apalachicola Bay Estuary. These data will inform coastal managers charged with the responsibility for resource preservation.

  9. Reference-Free XRF - Soft X-ray Experiments and Grain Size Effects

    NASA Astrophysics Data System (ADS)

    Beckhoff, B.; Kolbe, M.; Müller, M.

    2010-03-01

    The plane grating monochromator (PGM) beamline for undulator radiation of the Physikalisch-Technische Bundesanstalt (PTB) at BESSY provides tunable excitation radiation of well-known radiant power and spectral purity in the soft x-ray range. In conjunction with calibrated instrumentation, i.e. photodiodes, energy- dispersive detectors and apertures defining the solid angle of detection, reference-free X-Ray Fluorescence (XRF) investigations of rock samples were performed for different beam geometries. Both the angle of incidence of the radiation with respect to the sample surface as well as the angle of detection of element- specific fluorescence radiation could be easily varied. A set of specimens based on rock materials of the same basalt in different configurations ranging from unpolished and polished cut rocks and from pellets of differently sized grains to a smooth glass bead were investigated to study the effects of specimen flatness and roughness.

  10. Statistical relationship between pyrite grain size distribution and pyritic sulfur reduction in Ohio coal

    USGS Publications Warehouse

    Mazumdar, M.; Carlton, R.W.; Irdi, G.A.

    1988-01-01

    This paper presents a statistical relationship between the pyrite particle size distribution and the potential amount of pyritic sulfur reduction achieved by specific-gravity-based separation. This relationship is obtained from data on 26 Ohio coal samples crushed to 14 ?? 28 mesh. In this paper a prediction equation is developed that considers the complete statistical distribution of all the pyrite particle sizes in the coal sample. Assuming that pyrite particles occurring in coal have a lognormal distribution, the information about the particle size distribution can be encapsulated in terms of two parameters only, the mean and the standard deviation of the logarithms of the grain diameters. When the pyritic sulfur reductions of the 26 coal samples are related to these two parameters, a very satisfactory regression equation (R2 = 0.91) results. This equation shows that information on both these parameters is needed for an accurate prediction of potential sulfur reduction, and that the mean and the standard deviation interact negatively insofar as their influence on pyritic sulfur reduction is concerned. ?? 1988.

  11. Relationship of manganese-iron oxides and associated heavy metals to grain size in stream sediments

    USGS Publications Warehouse

    Whitney, P.R.

    1975-01-01

    The distribution of ammonium citrate-leachable lead, zinc and cadmium among size fractions in stream sediments is strongly influenced by the presence of hydrous Mn-Fe oxides in the form of coatings on sediment grains. Distribution curves showing leachable metals as a function of particle size are given for eight samples from streams in New York State. These show certain features in common; in particular two concentrations of metals, one in the finest fractions, and a second peak in the coarse sand and gravel fraction. The latter can be explained as a result of the increasing prevalence and thickness of oxide coatings with increasing particle size, with the oxides serving as collectors for the heavy metals. The distribution of Zn and Cd in most of the samples closely parallels that of Mn; the distribution of Pb is less regular and appears to be related to Fe in some samples and Mn in others. The concentration of metals in the coarse fractions due to oxide coatings, combined with the common occurrence of oxide deposition in streams of glaciated regions, raises the possibility of using coarse materials for geochemical surveys and environmental heavy-metal studies. ?? 1975.

  12. Trace, isotopic analysis of micron-sized grains -- Mo, Zr analysis of stardust (SiC and graphite grains).

    SciTech Connect

    Pellin, M. J.; Nicolussi, G. K.

    1998-02-19

    Secondary Neutral Mass Spectrometry using resonant laser ionization can provide for both high useful yields and high discrimination while maintaining high lateral and depth resolutions. An example of the power of the method is measurement of the isotopic composition of Mo and Zr in 1-5 {micro}m presolar SiC and graphite grains isolated from the Murchison CM2 meteorite for the first time. These grains have survived the formation of the Solar System and isotopic analysis reveals a record of the stellar nucleosynthesis present during their formation. Mo and Zr, though present at less than 10 ppm in some grains, are particularly useful in that among their isotopes are members that can only be formed by distinct nucleosynthetic processes known as s-, p-, and r-process. Successful isotopic analysis of these elements requires both high selectivity (since these are trace elements) and high efficiency (since the total number of atoms available are limited). Resonant Ionization Spectroscopy is particularly useful and flexible in this application. While the sensitivity of this t.edmique has often been reported in the past, we focus hereon the very low noise properties of the technique. We further demonstrate the efficacy of noise removal by two complimentary methods. First we use the resonant nature of the signal to subtract background signal. Second we demonstrate that by choosing the appropriate resonance scheme background can often be dramatically reduced.

  13. Investigation and modelling of the effects of solidification time and grain refinement on the grain size of a sand-cast Al4Cu alloy

    NASA Astrophysics Data System (ADS)

    Colak, M.; Sirin, S.; Kocaman, E.; Kayıkcı, R.

    2015-03-01

    It is well known that adding small amounts of Ti and B into aluminium casting alloys increase the fluidity, feedability, strength, fatigue resistance and pressure tightness. These occur because of Ti and B within the master alloys create heterogeneous nucleation sites by forming such intermetallic compounds as TiB2, Al3Ti and AlB2. It is also known that the solidification time is influential on the formation of final grain size of aluminium cast parts. However the combining effects of both grain refining and solidification time has not been studied properly. Therefore, in this work, the effects of the grain refining and solidification time have been investigated on a sand-cast Al-4wt%Cu alloy. To determine solidification time effect, a tests mould having different section thickness has been used.

  14. Orthographic transparency modulates the grain size of orthographic processing: behavioral and ERP evidence from bilingualism.

    PubMed

    Lallier, Marie; Carreiras, Manuel; Tainturier, Marie-Josèphe; Savill, Nicola; Thierry, Guillaume

    2013-04-10

    Grapheme-to-phoneme mapping regularity is thought to determine the grain size of orthographic information extracted whilst encoding letter strings. Here we tested whether learning to read in two languages differing in their orthographic transparency yields different strategies used for encoding letter-strings as compared to learning to read in one (opaque) language only. Sixteen English monolingual and 16 early Welsh-English bilingual readers undergoing event-related brain potentials (ERPs) recordings were asked to report whether or not a target letter displayed at fixation was present in either a nonword (consonant string) or an English word presented immediately before. Bilinguals and monolinguals showed similar behavioural performance on target detection presented in words and nonwords, suggesting similar orthographic encoding in the two groups. By contrast, the amplitude of ERPs locked to the target letters (P3b, 340-570 ms post target onset, and a late frontal positive component 600-1,000 ms post target onset) were differently modulated by the position of the target letter in words and nonwords between bilinguals and monolinguals. P3b results show that bilinguals who learnt to read simultaneously in an opaque and a transparent orthographies encoded orthographic information presented to the right of fixation more poorly than monolinguals. On the opposite, only monolinguals exhibited a position effect on the late positive component for both words and nonwords, interpreted as a sign of better re-evaluation of their responses. The present study shed light on how orthographic transparency constrains grain size and visual strategies underlying letter-string encoding, and how those constraints are influenced by bilingualism. PMID:23419894

  15. Airway size and the rate of pulmonary function decline in grain handlers

    SciTech Connect

    Vedal, S.; Enarson, D.A.; Chan-Yeung, M.

    1988-12-01

    Tracheal diameter and chest dimensions were measured from postero-anterior chest radiographs in grain handlers to prospectively identify airway size and chest size-related predictors of the rate of pulmonary function decline. A total of 634 grain workers were studied at the initial survey, of whom 239 satisfied the following inclusion criteria: (1) had a satisfactory chest radiograph taken at the initial survey in 1975, (2) performed spirometry at the 1975, 1978, and 1981 surveys, and (3) had no change in smoking status from 1975 to 1981. Radiographic measurements consisted of height of the right lung, transverse diameter of the chest at the level of the right diaphragm and at a level two-thirds up the right lung, and tracheal diameter (Tr). Areas of both lungs were measured by planimetry. Tr was only weakly related to height (r = 0.24). Increasing age was strongly associated with faster rates of FEV1 decline. After adjusting for the effects of age and cigarette smoking, Tr was the only radiographic measurement associated with FEV1 decline. Workers with Tr of 16 mm or less lost an average of 0.2% of their FEV1 per year compared to 0.9% per year for those with larger tracheas. This association was not modified by dust exposure estimates based on measurements of total dust. However, the strength of the association did depend upon smoking status, being strongest in current cigarette smokers (Tr less than or equal to 16 mm lost 0.2% annually and Tr greater than or equal to 21 mm lost 1.4% annually).

  16. Orthographic transparency modulates the grain size of orthographic processing: behavioral and ERP evidence from bilingualism.

    PubMed

    Lallier, Marie; Carreiras, Manuel; Tainturier, Marie-Josèphe; Savill, Nicola; Thierry, Guillaume

    2013-04-10

    Grapheme-to-phoneme mapping regularity is thought to determine the grain size of orthographic information extracted whilst encoding letter strings. Here we tested whether learning to read in two languages differing in their orthographic transparency yields different strategies used for encoding letter-strings as compared to learning to read in one (opaque) language only. Sixteen English monolingual and 16 early Welsh-English bilingual readers undergoing event-related brain potentials (ERPs) recordings were asked to report whether or not a target letter displayed at fixation was present in either a nonword (consonant string) or an English word presented immediately before. Bilinguals and monolinguals showed similar behavioural performance on target detection presented in words and nonwords, suggesting similar orthographic encoding in the two groups. By contrast, the amplitude of ERPs locked to the target letters (P3b, 340-570 ms post target onset, and a late frontal positive component 600-1,000 ms post target onset) were differently modulated by the position of the target letter in words and nonwords between bilinguals and monolinguals. P3b results show that bilinguals who learnt to read simultaneously in an opaque and a transparent orthographies encoded orthographic information presented to the right of fixation more poorly than monolinguals. On the opposite, only monolinguals exhibited a position effect on the late positive component for both words and nonwords, interpreted as a sign of better re-evaluation of their responses. The present study shed light on how orthographic transparency constrains grain size and visual strategies underlying letter-string encoding, and how those constraints are influenced by bilingualism.

  17. Repeated growth and bubbling transfer of graphene with millimetre-size single-crystal grains using platinum.

    PubMed

    Gao, Libo; Ren, Wencai; Xu, Huilong; Jin, Li; Wang, Zhenxing; Ma, Teng; Ma, Lai-Peng; Zhang, Zhiyong; Fu, Qiang; Peng, Lian-Mao; Bao, Xinhe; Cheng, Hui-Ming

    2012-02-28

    Large single-crystal graphene is highly desired and important for the applications of graphene in electronics, as grain boundaries between graphene grains markedly degrade its quality and properties. Here we report the growth of millimetre-sized hexagonal single-crystal graphene and graphene films joined from such grains on Pt by ambient-pressure chemical vapour deposition. We report a bubbling method to transfer these single graphene grains and graphene films to arbitrary substrate, which is nondestructive not only to graphene, but also to the Pt substrates. The Pt substrates can be repeatedly used for graphene growth. The graphene shows high crystal quality with the reported lowest wrinkle height of 0.8 nm and a carrier mobility of greater than 7,100 cm(2) V(-1) s(-1) under ambient conditions. The repeatable growth of graphene with large single-crystal grains on Pt and its nondestructive transfer may enable various applications.

  18. The effects of snowpack grain size on satellite passive microwave observations from the Upper Colorado River Basin

    USGS Publications Warehouse

    Josberger, E.G.; Gloersen, P.; Chang, A.; Rango, A.

    1996-01-01

    Understanding the passive microwave emissions of a snowpack, as observed by satellite sensors, requires knowledge of the snowpack properties: water equivalent, grain size, density, and stratigraphy. For the snowpack in the Upper Colorado River Basin, measurements of snow depth and water equivalent are routinely available from the U.S. Department of Agriculture, but extremely limited information is available for the other properties. To provide this information, a field program from 1984 to 1995 obtained profiles of snowpack grain size, density, and temperature near the time of maximum snow accumulation, at sites distributed across the basin. A synoptic basin-wide sampling program in 1985 showed that the snowpack exhibits consistent properties across large regions. Typically, the snowpack in the Wyoming region contains large amounts of depth hoar, with grain sizes up to 5 mm, while the snowpack in Colorado and Utah is dominated by rounded snow grains less than 2 mm in diameter. In the Wyoming region, large depth hoar crystals in shallow snowpacks yield the lowest emissivities or coldest brightness temperatures observed across the entire basin. Yearly differences in the average grain sizes result primarily from variations in the relative amount of depth hoar within the snowpack. The average grain size for the Colorado and Utah regions shows much less variation than do the grain sizes from the Wyoming region. Furthermore, the greatest amounts of depth hoar occur in the Wyoming region during 1987 and 1992, years with strong El Nin??o Southern Oscillation, but the Colorado and Utah regions do not show this behavior.

  19. Determination of the total grain size distributionin a vulcanian eruption column, and its implications to stratospheric aerosol perturbation

    SciTech Connect

    Murrow, P.J.; Rose, W.I. Jr.; Self, S.

    1980-11-01

    Grain size analysis of samples representing all sampleable portions of the airfall deposit produced by the Fuego volcano in Guatemala on 14 October 1974 form the basis for estimating the total grain size distribution of tephra from this eruption. The region enclosed by each isopach has a particular average grain size distribution which can be weighted proportionally to its percentage volume. The grain size of pyroclastic avalanche deposits produced during the eruption are also included. The total grain size distribution calculated as a sum of weighted distributions has a median grain size of 0.80 (0.6mm) and a sorting coefficient (sigma0) of 2.3. The size distribution seems to approximate Rosin and Rammler's law of crushing and this observation allows us to estimate that no more than 15% volume of the fine tail of the total size distribution is likely to be missing. The ash composed of these fine particles did not fall in the region of the volcano as part of the recognizable tephra blanket. The eruption column reached well into the stratosphere: heights estimated from the ground were 10 to 12 km above sea level but estimated heights based on mass flux rates are higher (18 to 23 km). The proportion of ash smaller than 2 ..mu..m, which could remain for substantial periods in the stratosphere, is no more than 0.8% volume of the total. It seems probable that acid aerosol particles from vulcanian type eruptions are more important to stratospheric aerosol perturbation than fine silicate ash particles by at least an order of magnitude.

  20. Genotypic variation in spike fertility traits and ovary size as determinants of floret and grain survival rate in wheat.

    PubMed

    Guo, Zifeng; Slafer, Gustavo A; Schnurbusch, Thorsten

    2016-07-01

    Spike fertility traits are critical attributes for grain yield in wheat (Triticum aestivum L.). Here, we examine the genotypic variation in three important traits: maximum number of floret primordia, number of fertile florets, and number of grains. We determine their relationship in determining spike fertility in 30 genotypes grown under two contrasting conditions: field and greenhouse. The maximum number of floret primordia per spikelet (MFS), fertile florets per spikelet (FFS), and number of grains per spikelet (GS) not only exhibited large genotypic variation in both growth conditions and across all spikelet positions studied, but also displayed moderate levels of heritability. FFS was closely associated with floret survival and only weakly related to MFS. We also found that the post-anthesis process of grain set/abortion was important in determining genotypic variation in GS; an increase in GS was mainly associated with improved grain survival. Ovary size at anthesis was associated with both floret survival (pre-anthesis) and grain survival (post-anthesis), and was thus believed to 'connect' the two traits. In this work, proximal florets (i.e. the first three florets from the base of a spikelet: F1, F2, and F3) produced fertile florets and set grains in most cases. The ovary size of more distal florets (F4 and beyond) seemed to act as a decisive factor for grain setting and effectively reflected pre-anthesis floret development. In both growth conditions, GS positively correlated with ovary size of florets in the distal position (F4), suggesting that assimilates allocated to distal florets may play a critical role in regulating grain set. PMID:27279276

  1. Abrasion resistant heat pipe

    DOEpatents

    Ernst, Donald M.

    1984-10-23

    A specially constructed heat pipe for use in fluidized bed combustors. Two distinct coatings are spray coated onto a heat pipe casing constructed of low thermal expansion metal, each coating serving a different purpose. The first coating forms aluminum oxide to prevent hydrogen permeation into the heat pipe casing, and the second coating contains stabilized zirconium oxide to provide abrasion resistance while not substantially affecting the heat transfer characteristics of the system.

  2. Abrasion resistant heat pipe

    DOEpatents

    Ernst, D.M.

    1984-10-23

    A specially constructed heat pipe is described for use in fluidized bed combustors. Two distinct coatings are spray coated onto a heat pipe casing constructed of low thermal expansion metal, each coating serving a different purpose. The first coating forms aluminum oxide to prevent hydrogen permeation into the heat pipe casing, and the second coating contains stabilized zirconium oxide to provide abrasion resistance while not substantially affecting the heat transfer characteristics of the system.

  3. Abrasive Wear Behavior of WC Reinforced Ni-BASED Composite Coating Sprayed and Fused by Oxy-Acetylene Flame

    NASA Astrophysics Data System (ADS)

    Wang, Qun; Chen, Zhenhua; Ding, Zhang Xiong; Chen, Ding

    Microstructure of WC reinforced Ni-based self-fluxing alloy composite coating sprayed and fused by oxy-acetylene flame was investigated by scanning electron microscopy and energy dispersive X-ray Spectrometry, X-ray diffraction, and transmission electron microscopy. The wear performance of the coating was studied by a MLS-225 wet sand rubber wheel abrasive wear tester at various loads and sizes of abrasive particles. Also, the wear resistance of the coating was compared with uncoated ASTM1020 steel. The results indicated that the coating is bonded metallurgically to the substrate and has a homogeneous microstructure composed of both coarse WC and fine carbide and boride grains such as Cr7C3, Cr23C6, and Ni2B which disperse uniformly in the matrix of γ-Ni solid solution and Ni3B. The worn mass loss of the coating and ASTM1020 steel both increased with the load and size of abrasive particles, also, the coating has exhibited excellent abrasive wear resistance compared with ASTM1020 steel.

  4. Comparison of hydraulic conductivities by grain-size analysis pumping, and slug tests in Quaternary gravels, NE Slovenia

    NASA Astrophysics Data System (ADS)

    Pucko, Tatjana; Verbovšek, Timotej

    2015-08-01

    Hydraulic conductivities (K) can be obtained from pumping and slug tests as well as grain size analysis. Although empirical methods for such estimations are longstanding, there is still insufficient comparison of K values among the various approaches. Six grain-size analysis methods were tested on coarse-grained alluvial sediments from 12 water wells in NE Slovenia. Values of K from grainsize methods were compared to those of pumping tests and slug tests. Six grain-size methods (USBR, Slichter, Hazen, Beyer, Kozeny-Carman, and Terzaghi) were used for comparison with the Theis and Neuman pumping test method and the Bouwer-Rice method for slug tests. The results show that the USBR (US Bureau of Reclamation) method overestimates K values and there is no correlation with other results, so its use is not advised. Conversely, whilst the Slichter method gives much lower estimates of K, it is the only one to completely fulfill the grain size requirements. Other methods (Hazen, Beyer, Kozeny- Carman, and Terzaghi) result in intermediate values and are similar to the Slichter method; however they should be used for smaller-sized sediments. Due to their high transmissivity and small radius of inffiuence, slug tests should be avoided in the analysis of gravels, as they only test a small portion of the aquifer compared to pumping tests. This is confirmed by the low correlation coefficients between hydraulic conductivities obtained from pumping tests and slug tests.

  5. Significant contribution of stacking faults to the strain hardening behavior of Cu-15%Al alloy with different grain sizes.

    PubMed

    Tian, Y Z; Zhao, L J; Chen, S; Shibata, A; Zhang, Z F; Tsuji, N

    2015-11-19

    It is commonly accepted that twinning can induce an increase of strain-hardening rate during the tensile process of face-centered cubic (FCC) metals and alloys with low stacking fault energy (SFE). In this study, we explored the grain size effect on the strain-hardening behavior of a Cu-15 at.%Al alloy with low SFE. Instead of twinning, we detected a significant contribution of stacking faults (SFs) irrespective of the grain size even in the initial stage of tensile process. In contrast, twinning was more sensitive to the grain size, and the onset of deformation twins might be postponed to a higher strain with increasing the grain size. In the Cu-15 at.%Al alloy with a mean grain size of 47 μm, there was a stage where the strain-hardening rate increases with strain, and this was mainly induced by the SFs instead of twinning. Thus in parallel with the TWIP effect, we proposed that SFs also contribute significantly to the plasticity of FCC alloys with low SFE.

  6. Assessing grain-size correspondence between flow and deposits of controlled floods in the Colorado River, USA

    USGS Publications Warehouse

    Draut, Amy; Rubin, David M.

    2013-01-01

    Flood-deposited sediment has been used to decipher environmental parameters such as variability in watershed sediment supply, paleoflood hydrology, and channel morphology. It is not well known, however, how accurately the deposits reflect sedimentary processes within the flow, and hence what sampling intensity is needed to decipher records of recent or long-past conditions. We examine these problems using deposits from dam-regulated floods in the Colorado River corridor through Marble Canyon–Grand Canyon, Arizona, U.S.A., in which steady-peaked floods represent a simple end-member case. For these simple floods, most deposits show inverse grading that reflects coarsening suspended sediment (a result of fine-sediment-supply limitation), but there is enough eddy-scale variability that some profiles show normal grading that did not reflect grain-size evolution in the flow as a whole. To infer systemwide grain-size evolution in modern or ancient depositional systems requires sampling enough deposit profiles that the standard error of the mean of grain-size-change measurements becomes small relative to the magnitude of observed changes. For simple, steady-peaked floods, 5–10 profiles or fewer may suffice to characterize grain-size trends robustly, but many more samples may be needed from deposits with greater variability in their grain-size evolution.

  7. OsMAPK6, a mitogen-activated protein kinase, influences rice grain size and biomass production.

    PubMed

    Liu, Shuying; Hua, Lei; Dong, Sujun; Chen, Hongqi; Zhu, Xudong; Jiang, Jun'e; Zhang, Fang; Li, Yunhai; Fang, Xiaohua; Chen, Fan

    2015-11-01

    Grain size is an important agronomic trait in determining grain yield. However, the molecular mechanisms that determine the final grain size are not well understood. Here, we report the functional analysis of a rice (Oryza sativa L.) mutant, dwarf and small grain1 (dsg1), which displays pleiotropic phenotypes, including small grains, dwarfism and erect leaves. Cytological observations revealed that the small grain and dwarfism of dsg1 were mainly caused by the inhibition of cell proliferation. Map-based cloning revealed that DSG1 encoded a mitogen-activated protein kinase (MAPK), OsMAPK6. OsMAPK6 was mainly located in the nucleus and cytoplasm, and was ubiquitously distributed in various organs, predominately in spikelets and spikelet hulls, consistent with its role in grain size and biomass production. As a functional kinase, OsMAPK6 interacts strongly with OsMKK4, indicating that OsMKK4 is likely to be the upstream MAPK kinase of OsMAPK6 in rice. In addition, hormone sensitivity tests indicated that the dsg1 mutant was less sensitive to brassinosteroids (BRs). The endogenous BR levels were reduced in dsg1, and the expression of several BR signaling pathway genes and feedback-inhibited genes was altered in the dsg1 mutant, with or without exogenous BRs, indicating that OsMAPK6 may contribute to influence BR homeostasis and signaling. Thus, OsMAPK6, a MAPK, plays a pivotal role in grain size in rice, via cell proliferation, and BR signaling and homeostasis. PMID:26366992

  8. Grain-size reduction mechanisms and rheological consequences in high-temperature gabbro mylonites of Hidaka, Japan

    NASA Astrophysics Data System (ADS)

    Raimbourg, Hugues; Toyoshima, Tsuyoshi; Harima, Yuta; Kimura, Gaku

    2008-03-01

    The study of microstructures and crystallographic fabrics in a granulite-facies shear zone of the Hidaka Metamorphic Belt showed that the strong shearing localized within the mylonite resulted in the asymmetrical elongation of the inherited orthopyroxene porphyroclasts and the generation of fine-grained plagioclase and orthopyroxene layers as asymmetric tails of orthopyroxene porphyroclasts. The orthopyroxene porphyroclasts and the coarse plagioclase matrix surrounding them have a strong crystallographic preferred orientation acquired through deformation by dislocation creep. In contrast, the small orthopyroxene and plagioclase grains located in the tails have equant shapes and random fabric that are interpreted as the result of deformation by grain-boundary sliding. The small orthopyroxene grains are generated on the sheared rims of the orthopyroxene porphyroclasts by subgrain rotation, inheriting the orientation of the porphyroclasts before deforming by grain-boundary sliding (GBS) and losing this fabric. Additional mechanism of grain-size reduction is the disruption of orthopyroxene porphyroclasts by synthetic shear zones localized on clinopyroxene exsolutions. The switch in deformation mechanism from dislocation creep to GBS, associated with the grain-size reduction, yielded estimates of deviatoric stress one order smaller than lithostatic pressure. Besides, such rheological evolution attests of the mechanical softening during deformation, which contributed to the localization of the strain within the mylonite.

  9. Size effects of nano-scale pinning centers on the superconducting properties of YBCO single grains

    NASA Astrophysics Data System (ADS)

    Moutalbi, Nahed; Noudem, Jacques G.; M'chirgui, Ali

    2014-08-01

    High pinning superconductors are the most promising materials for power engineering. Their superconducting properties are governed by the microstructure quality and the vortex pinning behavior. We report on a study of the vortex pinning in YBa2Cu3O7-x (YBCO) single grain with defects induced through the addition of insulating nano-particles. In order to improve the critical current density, YBCO textured bulk superconductors were elaborated using the Top Seeded Melt Texture and Growth process with different addition amounts of Al2O3 nano-particles. Serving as strong pinning centers, 0.05% excess of Al2O3 causes a significant enhancement of the critical current density Jc under self field and in magnetic fields at 77 K. The enhanced flux pinning achieved with the low level of alumina nano-particles endorses the effectiveness of insulating nano-inclusions to induce effectives pinning sites within the superconducting matrix. On the other side, we focused on the effect of the size of pinning centers on the critical current density. This work was carried out using two batches of alumina nano-particles characterized by two different particle size distributions with mean diameters PSD1 = 20 nm and PSD2 = 2.27 μm. The matching effects of the observed pinning force density have been compared. The obtained results have shown that the flux pinning is closely dependent on the size of the artificial pinning centers. Our results suggest that the optimization of the size of the artificial pinning centers is crucial to a much better understanding of the pinning mechanisms and therefore to insure high superconducting performance for the practical application of superconducting materials.

  10. Kinetics of phosphorus release from a natural mixed grain-size sediment with associated algal biofilms.

    PubMed

    Gainswin, B E; House, W A; Leadbeater, B S C; Armitage, P D

    2006-05-01

    Experiments using flumes containing mixed grain-size sediment with an associated algal biofilm, from two sites on the R. Tame, investigated the sediment-water exchanges in heterogeneous sediment deposits. These results were considered in the light of findings of a companion study [Gainswin BE, et al. The effects of sediment size fraction and associated algal biofilms on the kinetics of phosphorus release. Sci Total Environ, this issue.] by considering this natural system in relation to the effects of the different sizes of material comprising the sediment. Sediment samples were collected in trays installed in the river over a period of one growth cycle (March 2001-April 2002) and placed in flume channels with controlled water flow. The temperature, pH, and dissolved oxygen of the solution overlying the sediment were monitored automatically whilst filtered samples were obtained at 2-0h intervals over 48 h. The biomass, expressed as chlorophyll a, of the algal component of the biofilm from the surface of the sediment was estimated using methanol extraction. The composition of the sediment, viz. size fractions, organic matter and porosity, were determined at the end of the experiments. The equilibrium phosphate concentration and a phosphorus transfer index were used to establish that a net uptake of phosphorus by some of the samples that occurred at the time of sampling. The results were modelled using a Diffusion Boundary Layer model and the maximum flux from the sediment (or limiting diffusion flux) compared for each of the samples. The limiting diffusion flux was highest at the most contaminated site--reaching approximately 180 nmol m(-2) s(-1) (normalised with respect to the river bed area). The limiting diffusion flux calculated for the composite samples was in agreement with the flux estimated from the contributions expected from the individual size fractions [Gainswin BE, et al. The effects of sediment size fraction and associated algal biofilms on the kinetics

  11. Effect of particles attachment to multi-sized dust grains present in electrostatic sheaths of discharge plasmas

    SciTech Connect

    Zaham, B.; Tahraoui, A. Chekour, S.; Benlemdjaldi, D.

    2014-12-15

    The loss of electrons and ions due to their attachment to a Gauss-distributed sizes of dust grains present in electrostatic sheaths of discharge plasmas is investigated. A uni-dimensional, unmagnetized, and stationary multi-fluid model is proposed. Forces acting on the dust grain along with its charge are self-consistently calculated, within the limits of the orbit motion limited model. The dynamic analysis of dust grains shows that the contribution of the neutral drag force in the net force acting on the dust grain is negligible, whereas the contribution of the gravity force is found considerable only for micrometer particles. The dust grains trapping is only possible when the electrostatic force is balanced by the ion drag and the gravity forces. This trapping occurs for a limited radius interval of micrometer dust grains, which is around the most probable dust grain radius. The effect of electron temperature and ion density at the sheath edge is also discussed. It is shown that the attachment of particles reduces considerably the sheath thickness and induces dust grain deceleration. The increase of the lower limit as well as the upper limit of the dust radius reduces also the sheath thickness.

  12. Abrasion of 6 dentifrices measured by vertical scanning interference microscopy

    PubMed Central

    PASCARETTI-GRIZON, Florence; MABILLEAU, Guillaume; CHAPPARD, Daniel

    2013-01-01

    Objectives The abrasion of dentifrices is well recognized to eliminate the dental plaque. The aims of this study were to characterize the abrasive powders of 6 dentifrices (3 toothpastes and 3 toothpowders) and to measure the abrasion on a test surface by Vertical Scanning Interference microscopy (VSI). Material and Methods Bright field and polarization microscopy were used to identify the abrasive particles on the crude dentifrices and after prolonged washes. Scanning electron microscopy and microanalysis characterized the shape and nature of the particles. Standardized and polished blocks of poly(methylmethacrylate) were brushed with a commercial electric toothbrush with the dentifrices. VSI quantified the mean roughness (Ra) and illustrated in 3D the abraded areas. Results Toothpastes induced a limited abrasion. Toothpowders induced a significantly higher roughness linked to the size of the abrasive particles. One powder (Gencix® produced a high abrasion when used with a standard testing weight. However, the powder is based on pumice particles covered by a plant homogenate that readily dissolves in water. When used in the same volume, or after dispersion in water, Ra was markedly reduced. Conclusion Light and electron microscopy characterize the abrasive particles and VSI is a new tool allowing the analysis of large surface of abraded materials. PMID:24212995

  13. Incorporating gold into nanocrystalline silver dressings reduces grain boundary size and maintains suitable antimicrobial properties.

    PubMed

    Unrau, Kevin R; Cavanagh, Marion H; Cheng, On Kwan; Wang, Shiman; Burrell, Robert E

    2013-12-01

    Nanocrystalline silver dressings are widely known to be potent antimicrobial and anti-inflammatory agents and have long been used to treat topical wounds. Gold is known to be a strong anti-inflammatory agent and has been used in the treatment of rheumatoid arthritis for >70 years. The purpose of this work was to study the effect of incorporating gold into nanocrystalline silver dressings from antimicrobial and anti-inflammatory perspectives. Gold and silver dressing alloys were created by direct current magnetron sputtering and compared with pure silver nanocrystalline dressings using conventional biological (log reduction and corrected zone of inhibition) and physical (X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, atomic absorption spectroscopy, atomic force microscopy and scanning electron microscopy) characterisation techniques. While the gold/silver dressings were slightly weaker antimicrobials than the pure silver nanocrystalline structures, the addition of gold to the nanostructure reduces the minimum crystallite size from 17 to 4 nm. This difference increases the number of grain boundary atoms from 12% to 40% which could augment the anti-inflammatory properties of the dressings. The formation of gold oxide (Au2O3) was thought to be responsible for the observed decrease in crystallite size.

  14. GaN photovoltaic leakage current and correlation to grain size

    SciTech Connect

    Matthews, K. D.; Chen, X.; Hao, D.; Schaff, W. J.; Eastman, L. F.

    2010-10-15

    GaN p-i-n solar PV structures grown by rf plasma assisted molecular beam epitaxy (MBE) produce high performance IV characteristics with a leakage current density of less than 1x10{sup -4} mA cm{sup -2} at 0.1 V forward bias and an on-resistance of 0.039 {Omega} cm{sup 2}. Leakage current measurements taken for different size diodes processed on the same sample containing the solar cells reveal that current density increases with diode area, indicating that leakage is not a large function of surface leakage along the mesa. Nonannealed Pt/Au Ohmic p-contacts produce a contact resistivity of 4.91x10{sup -4} {Omega} cm{sup -2} for thin Mg doped contact layers with sheet resistivity of 62196 {Omega}/{open_square}. Under concentrated sunlight the cells produce an open-circuit voltage of 2.5 V and short circuit currents as high as 30 mA cm{sup -2}. Multiple growths comprised the study and on each wafer the IV curves representing several diodes showed considerable variation in parasitic leakage current density at low voltages on some wafers and practically no variation on others. It appears that a smaller grain size within the GaN thin film accounts for higher levels of dark current.

  15. Effects of grain size and temperature on virus attachment onto quartz sand

    NASA Astrophysics Data System (ADS)

    Aravantinou, Andriana F.; Chrysikopoulos, Constantinos V.

    2014-05-01

    Virus transport in groundwater is controlled mainly by attachment onto the solid matrix and inactivation. Therefore, understanding how the various parameters affect virus attachment can lead to improved virus transport predictions and better health risk evaluations. This study is focused on the attachment of viruses onto quartz sand under batch experimental conditions. The bacteriophages ΦX174 and MS2 were used as model viruses. Three different sand grain sizes were employed for the static and dynamic experiments. The batch sorption experiments were performed under static conditions at 4°C and 20°C and dynamic conditions at 4°C. The experimental data were adequately described by the Freudlich isotherm. It was shown that temperature significantly affects virus attachment under static conditions. The attachment of both MS2 and ΦX174 onto quartz sand was greater at 20°C than 4°C. Higher virus attachment was observed under dynamic than static conditions, and in all cases, the affinity of MS2 for quartz sand was greater than that of ΦX174. Furthermore, in most of the cases considered, bacteriophage attachment was shown to decrease with increasing quartz sand size.

  16. Prediction of as-cast grain size of inoculated aluminum alloys melt solidified under non-isothermal conditions

    NASA Astrophysics Data System (ADS)

    Du, Qiang; Li, Yanjun

    2015-06-01

    In this paper, a multi-scale as-cast grain size prediction model is proposed to predict as-cast grain size of inoculated aluminum alloys melt solidified under non-isothermal condition, i.e., the existence of temperature gradient. Given melt composition, inoculation and heat extraction boundary conditions, the model is able to predict maximum nucleation undercooling, cooling curve, primary phase solidification path and final as-cast grain size of binary alloys. The proposed model has been applied to two Al-Mg alloys, and comparison with laboratory and industrial solidification experimental results have been carried out. The preliminary conclusion is that the proposed model is a promising suitable microscopic model used within the multi-scale casting simulation modelling framework.

  17. Influence of Shock Prestraining and Grain Size on the Dynamic Tensile Extrusion Response of Copper: Experiments, Modeling and Simulation

    NASA Astrophysics Data System (ADS)

    Gray, George, III

    2005-07-01

    The mechanical behavior and damage evolution response of high-purity Cu are influenced by strain rate, temperature, stress state, grain size, and shock prestraining. The effects of grain size on the mechanical response of high-purity Cu have been probed and are correlated with the substructural evolution during deformation. The dynamic extrusion response of shock prestrained Cu demonstrates the significant influence of grain size on the large-strain dynamic tensile ductility of high-purity copper. Eulerian hydrocode simulations utilizing the Mechanical Threshold Stress flow stress model were performed to provide insight into the dynamic extrusion process. Quantitative comparisons between the predicted and measured deformation topologies and extrusion rate will be presented. Predictions of the texture evolution (based upon the deformation rate history and the rigid body rotations experienced by the Cu during the extrusion process) are compared with texture measurements.

  18. Influence of Shock Prestraining and Grain Size on the Dynamic-Tensile-Extrusion Response of Copper: Experiments and Simulation

    SciTech Connect

    Gray, G. T. III; Cerreta, E.; Yablinsky, C. A.; Addessio, L. B.; Henrie, B. L.; Sencer, B. H.; Maloy, S. A.; Trujillo, C. P.; Lopez, M. F.; Burkett, M.; Maudlin, P. J.

    2006-07-28

    The mechanical behavior of, and damage evolution in high-purity Cu is influenced by strain rate, temperature, stress state, grain size, and shock prestraining. The effects of grain size on the tensile mechanical response of high-purity Cu have been probed and are correlated with the evolution of the substructure. The dynamic extrusion response of shock prestrained Cu demonstrates the significant influence of grain size on the large-strain dynamic tensile ductility of high-purity copper. Eulerian hydrocode simulations utilizing the Mechanical Threshold Stress constitutive model were performed to provide insight into the dynamic extrusion process. Quantitative comparisons between the predicted and measured deformation topologies and extrusion rates are presented.

  19. Influence of Shock Prestraining and Grain Size on the Dynamic-Tensile-Extrusion Response of Copper: Experiments and Simulation

    NASA Astrophysics Data System (ADS)

    Gray, G. T.; Cerreta, E.; Yablinsky, C. A.; Addessio, L. B.; Henrie, B. L.; Sencer, B. H.; Burkett, M.; Maudlin, P. J.; Maloy, S. A.; Trujillo, C. P.; Lopez, M. F.

    2006-07-01

    The mechanical behavior of, and dam