Science.gov

Sample records for size distribution dependence

  1. Bayesian analysis of size-dependent overwinter mortality from size-frequency distributions.

    PubMed

    Carlson, Stephanie M; Kottas, Athanasios; Mangel, Marc

    2010-04-01

    Understanding the relationship between body size and mortality is an important problem in ecology. We introduce a novel Bayesian method that can be used to quantify this relationship when the only data available are size-frequency distributions of unmarked individuals measured at two successive time periods. The inverse Gaussian distribution provides a parametric form for the statistical model development, and we use Markov chain Monte Carlo methods to evaluate posterior distributions. We illustrate the method using data on threespine stickleback (Gasterosteus aculeatus) collected before and after the winter season in an Alaskan lake. Our method allows us to compare the intensity of size-biased mortality in different years. We discuss generalizations that include more complicated relationships between size and survival as well as time-series modeling.

  2. A study of SS size distribution during runoff and fractionation of phosphates depending on soil size in agricultural watershed.

    PubMed

    Sa, S H; Masuda, T; Hosoi, Y

    2005-01-01

    Characterization of the differences and algal-available fractions of P in soils, suspended solids, and bottom sediments have been the main topics of research during the past decade. However, the size distribution and properties of particulate matter in runoff have not been much studied in Japan. Here we study particle size distribution during runoff and the chemical characteristics of P in each soil size fraction and relate them to land use. The temporal variation of particulate sizes during rain events is different in each watershed. Most particles have the size in the range of 10-100 microm. Also, the percentage of BAP in TP as well as percentage of PCOD in SS also varies temporally and spatially during runoff. To investigate how soil particles characteristics depend on land use, soil samples from two watersheds are examined. For particle size distribution and specific gravity, no significant difference among watersheds is found. However, C, N, and P content are indirectly proportional to the particle size, which means smaller particle size results in larger. H2O-extracted P, NH4Cl-extracted P, NAI-P, Apatite-P, Organic-P, and TP contents in each soil particle sample vary depending on particle size, land use, and watershed.

  3. Introduction of a nozzle throat diameter dependency into the SRM dust size distribution

    NASA Astrophysics Data System (ADS)

    Stabroth, S.; Wegener, P.; Oswald, M.; Wiedemann, C.; Klinkrad, H.; Vörsmann, P.

    2006-01-01

    The ESA space debris population model MASTER (Meteoroid and Space Debris Terrestrial Environment Reference) considers 1032 firings of solid rocket motors (SRM) with the associated generation of SRM slag and dust particles in its current version. The resulting dust population is a major contribution to the sub-millimetre size space debris environment in Earth orbit. For the modelling of each SRM dust release event a detailed knowledge of the particle size distribution is essential. However, the knowledge of the particle sizes after passing the nozzle throat is poor. The current dust implementation in the MASTER model assumes a fixed size distribution which is identically used for both large upper stages and small apogee motors. This assumption can lead to an over-representation of large dust particles in regions, where mainly apogee motors are used (i.e., Geostationary Earth Orbit) and an under-representation in lower altitudes, where large stages predominate. In this paper, a concept for the improvement of SRM dust size modelling is discussed. It will be shown that an introduction of a nozzle throat diameter dependency into the dust size distribution enables a more precise modelling of SRM dust release events. The improved SRM dust size distribution is going to be used by the MASTER-2005 space debris model which is currently under development by the Institute of Aerospace Systems and QinetiQ (UK) under ESA contract.

  4. Introduction of a Nozzle Throat Diameter Dependency into the SRM Dust Size Distribution

    NASA Astrophysics Data System (ADS)

    Stabroth, S.; Wegener, P.; Oswald, M.; Wiedemann, C.; Klinkrad, H.; Vörsmann, P.

    In the exhaust gas of SRM (Solid Rocket Motor) firings, a considerable amount of very small aluminium oxide (Al2O3) particles is generally included. In order to increase motor performance and to dampen burn instabilities, aluminium is used as an additive in the propellant. During the burn process this aluminium is transformed into Al2O3. A large number of small dust particles (< 1 μ m up to about 50 μ m) is generated continuously during a burn. At the end of a burn, a second group of much larger fragments from an Al2O3 slag pool clustering inside the motor leaves the nozzle. The ESA space debris population model MASTER-2001 considers 1,032 SRM firings with the associated generation of SRM slag and dust. The resulting Al2O3 population is a major contribution to the micron size space debris environment in Earth orbit. For the modelling of each SRM dust release event a detailed knowledge of the size distribution is essential. However, the knowledge of the particle size distribution after passing the nozzle throat is poor. The current dust implementation in the MASTER-2001 space debris model therefore assumes an average motor size, since information on the actual motor size is normally not available in common databases. Thus, a fixed distribution is identically used for large upper stages as well as small apogee motors. This assumption can lead to an over-representation of large dust in regions, where mainly apogee motors are used (i.e. GEO) and an under-representation in lower altitudes, where large stages predominate. In this paper, a concept for the improvement of SRM dust size modelling is discussed. It will be shown that an introduction of a nozzle throat diameter dependency into the dust size distribution could lead to a more precise modelling of SRM dust release events. Investigations showed that there is a good correlation between the propellant mass flow and the nozzle's throat diameter, which is in turn the determining term for the actual diameter

  5. Nanoparticle distribution during systemic inflammation is size-dependent and organ-specific

    NASA Astrophysics Data System (ADS)

    Chen, K.-H.; Lundy, D. J.; Toh, E. K.-W.; Chen, C.-H.; Shih, C.; Chen, P.; Chang, H.-C.; Lai, J. J.; Stayton, P. S.; Hoffman, A. S.; Hsieh, P. C.-H.

    2015-09-01

    This study comprehensively investigates the changing biodistribution of fluorescent-labelled polystyrene latex bead nanoparticles in a mouse model of inflammation. Since inflammation alters systemic circulatory properties, increases vessel permeability and modulates the immune system, we theorised that systemic inflammation would alter nanoparticle distribution within the body. This has implications for prospective nanocarrier-based therapies targeting inflammatory diseases. Low dose lipopolysaccharide (LPS), a bacterial endotoxin, was used to induce an inflammatory response, and 20 nm, 100 nm or 500 nm polystyrene nanoparticles were administered after 16 hours. HPLC analysis was used to accurately quantify nanoparticle retention by each vital organ, and tissue sections revealed the precise locations of nanoparticle deposition within key tissues. During inflammation, nanoparticles of all sizes redistributed, particularly to the marginal zones of the spleen. We found that LPS-induced inflammation induces splenic macrophage polarisation and alters leukocyte uptake of nanoparticles, with size-dependent effects. In addition, spleen vasculature becomes significantly more permeable following LPS treatment. We conclude that systemic inflammation affects nanoparticle distribution by multiple mechanisms, in a size dependent manner.This study comprehensively investigates the changing biodistribution of fluorescent-labelled polystyrene latex bead nanoparticles in a mouse model of inflammation. Since inflammation alters systemic circulatory properties, increases vessel permeability and modulates the immune system, we theorised that systemic inflammation would alter nanoparticle distribution within the body. This has implications for prospective nanocarrier-based therapies targeting inflammatory diseases. Low dose lipopolysaccharide (LPS), a bacterial endotoxin, was used to induce an inflammatory response, and 20 nm, 100 nm or 500 nm polystyrene nanoparticles were administered

  6. Temperature Dependence of Particle Size Distribution in Transformer Oil-Based Ferrofluid

    NASA Astrophysics Data System (ADS)

    Józefczak, Arkadiusz; Hornowski, Tomasz; Skumiel, Andrzej

    2011-04-01

    The temperature dependence of the particle size distribution (PSD) of a transformer oil-based ferrofluid was studied using an ultrasound method. The measurements of the ultrasound velocity and attenuation were carried out in the absence of an external magnetic field as a function of the volume concentration of magnetite particles at temperatures ranging from 10 °C to 80 °C. The experimental results of ultrasound measurements were analyzed within the framework of the Vinogradov-Isakovich theory which takes into account contributions to acoustical parameters due to friction and heat exchange between magnetic particles and the surrounding carrier liquid. From the best fit of the experimental results and theoretical predictions, the parameters characterizing the PSD at different temperatures were determined. In order to analyze ultrasonic data, the density and viscosity of ferrofluid samples and the transformer oil were also measured.

  7. Dependence of pulsed focused ultrasound induced thrombolysis on duty cycle and cavitation bubble size distribution.

    PubMed

    Xu, Shanshan; Zong, Yujin; Feng, Yi; Liu, Runna; Liu, Xiaodong; Hu, Yaxin; Han, Shimin; Wan, Mingxi

    2015-01-01

    In this study, we investigated the relationship between the efficiency of pulsed, focused ultrasound (FUS)-induced thrombolysis, the duty cycle (2.3%, 9%, and 18%) and the size distribution of cavitation bubbles. The efficiency of thrombolysis was evaluated through the degree of mechanical fragmentation, namely the number, mass, and size of clot debris particles. First, we found that the total number and mass of clot debris particles were highest when a duty cycle of 9% was used and that the mean diameter of clot debris particles was smallest. Second, we found that the size distribution of cavitation bubbles was mainly centered around the linear resonance radius (2.5μm) of the emission frequency (1.2MHz) of the FUS transducer when a 9% duty cycle was used, while the majority of cavitation bubbles became smaller or larger than the linear resonance radius when a 2.3% or 18% duty cycle was used. In addition, the inertial cavitation dose from the treatment performed at 9% duty cycle was much higher than the dose obtained with the other two duty cycles. The data presented here suggest that there is an optimal duty cycle at which the thrombolysis efficiency and cavitation activity are strongest. They further indicate that using a pulsed FUS may help control the size distribution of cavitation nuclei within an active size range, which we found to be near the linear resonance radius of the emission frequency of the FUS transducer.

  8. COLOR DEPENDENCE IN THE SIZE DISTRIBUTION OF MAIN BELT ASTEROIDS REVISITED

    SciTech Connect

    August, Tyler M.; Wiegert, Paul A.

    2013-06-15

    The size distribution of the asteroid belt is examined with 16956 main belt asteroids detected in data taken from the Canada-France-Hawaii Telescope Legacy Survey in two filters (g' and r'). The cumulative H (absolute magnitude) distribution is examined in both filters, and both match well to simple power laws down to H = 17, with slopes in rough agreement with those reported the literature. This implies that disruptive collisions between asteroids are gravitationally dominated down to at least this size, and probably sub-kilometer scales. The slopes of these distributions appear shallower in the outer belt than the inner belt, and the g' distributions appear slightly steeper than the r'. The slope shallowing in the outer belt may reflect a real compositional difference: the inner asteroid belt has been suggested to consist mostly of stony and/or metallic S-type asteroids, whereas carbonaceous C-types are thought to be more prevalent further from the Sun. No waves are seen in the size distribution above H = 15. Since waves are expected to be produced at the transition from gravitationally-dominated to internal strength-dominated collisions, their absence here may imply that the transition occurs at sub-kilometer scales, much smaller than the H = 17 (diameter {approx} 1.6 km) cutoff of this study.

  9. The evolution of biomass-burning aerosol size distributions due to coagulation: dependence on fire and meteorological details and parameterization

    NASA Astrophysics Data System (ADS)

    Sakamoto, Kimiko M.; Laing, James R.; Stevens, Robin G.; Jaffe, Daniel A.; Pierce, Jeffrey R.

    2016-06-01

    Biomass-burning aerosols have a significant effect on global and regional aerosol climate forcings. To model the magnitude of these effects accurately requires knowledge of the size distribution of the emitted and evolving aerosol particles. Current biomass-burning inventories do not include size distributions, and global and regional models generally assume a fixed size distribution from all biomass-burning emissions. However, biomass-burning size distributions evolve in the plume due to coagulation and net organic aerosol (OA) evaporation or formation, and the plume processes occur on spacial scales smaller than global/regional-model grid boxes. The extent of this size-distribution evolution is dependent on a variety of factors relating to the emission source and atmospheric conditions. Therefore, accurately accounting for biomass-burning aerosol size in global models requires an effective aerosol size distribution that accounts for this sub-grid evolution and can be derived from available emission-inventory and meteorological parameters. In this paper, we perform a detailed investigation of the effects of coagulation on the aerosol size distribution in biomass-burning plumes. We compare the effect of coagulation to that of OA evaporation and formation. We develop coagulation-only parameterizations for effective biomass-burning size distributions using the SAM-TOMAS large-eddy simulation plume model. For the most-sophisticated parameterization, we use the Gaussian Emulation Machine for Sensitivity Analysis (GEM-SA) to build a parameterization of the aged size distribution based on the SAM-TOMAS output and seven inputs: emission median dry diameter, emission distribution modal width, mass emissions flux, fire area, mean boundary-layer wind speed, plume mixing depth, and time/distance since emission. This parameterization was tested against an independent set of SAM-TOMAS simulations and yields R2 values of 0.83 and 0.89 for Dpm and modal width, respectively. The

  10. The weather dependence of particle size distribution of indoor radioactive aerosol associated with radon decay products.

    PubMed

    Mostafa, A M A; Tamaki, K; Moriizumi, J; Yamazawa, H; Iida, T

    2011-07-01

    This study was performed to measure the activity size distribution of aerosol particles associated with short-lived radon decay products in indoor air at Nagoya University, Nagoya, Japan. The measurements were performed using a low pressure Andersen cascade impactor under variable meteorological conditions. The results showed that the greatest activity fraction was associated with aerosol particles in the accumulation size range (100-1000 nm) with a small fraction of nucleation mode (10-100 nm). Regarding the influence of the weather conditions, the decrease in the number of accumulation particles was observed clearly after rainfall without significant change in nucleation particles, which may be due to a washout process for the large particles.

  11. Spatial distribution of steep lunar craters may be linked to size-dependent orbital distribution of impactors

    NASA Astrophysics Data System (ADS)

    JeongAhn, Youngmin; Malhotra, Renu; Werner, Stephanie; Lee, Jui-Chi; Trang, David; Ip, Wing-Huen; Reyes-Ruiz, Mauricio

    2016-10-01

    The depth/diameter (d/D) ratio of simple lunar craters (D<15km) is known to be ~0.2 at the time of formation; larger complex craters (D>15km) have smaller d/D ratios. We examine the spatial distribution of high d/D ratio (>0.18) craters using LU60645GT catalogue (Salamunićcar et al. 2012). We select craters larger than 8km for which the census is known to be almost complete over the whole lunar surface. We find that the number density of steep craters in maria is significantly lower than in highlands, which may be explained by the age differences of the background surfaces. We also find that the spatial density of steep craters in the equatorial region is lower than in the polar region. On the contrary, higher cratering flux on the lunar equator has been claimed: from the numerical calculations with the orbital distribution of observed Earth Crossing Objects (ECOs) larger than 1km (Le Feuvre & Wieczorek 2008; Ito & Malhotra 2010) and from the distribution of steepest slopes at a 25m baseline (Kreslavsky & Head, 2016). In order to reconcile our findings with previous observations, we hypothesize that the cratering rate at low latitudes has been higher for meter to decameter size ECOs than for kilometer size objects since the Late Imbrian epoch; smaller objects have triggered more frequent mass wasting on the pre-existing large steep craters (D>8km, d/D>0.18) at low latitudes, thereby reducing the surviving number of steep craters. Our hypothesis is supported by the finding that the power-law slope in the H magnitude distribution for the low inclination ECOs (i<15 deg) is steeper than for the high inclination objects. Renu Malhotra acknowledges research support from NSF (grant AST-1312498).

  12. Effect of magnetic anisotropy and particle size distribution on temperature dependent magnetic hyperthermia in Fe3O4 ferrofluids

    NASA Astrophysics Data System (ADS)

    Palihawadana Arachchige, Maheshika; Nemala, Humeshkar; Naik, Vaman; Naik, Ratna

    Magnetic hyperthermia (MHT) has a great potential as a non-invasive cancer therapy technique. Specific absorption rate (SAR) which measures the efficiency of heat generation, mainly depends on magnetic properties of nanoparticles such as saturation magnetization (Ms) and magnetic anisotropy (K) which depend on the size and shape. Therefore, MHT applications of magnetic nanoparticles often require a controllable synthesis to achieve desirable magnetic properties. We have synthesized Fe3O4 nanoparticles using two different methods, co-precipitation (CP) and hydrothermal (HT) techniques to produce similar XRD crystallite size of 12 nm, and subsequently coated with dextran to prepare ferrofluids for MHT. However, TEM measurements show average particle sizes of 13.8 +/-3.6 nm and 14.6 +/-3.6 nm for HT and CP samples, implying the existence of an amorphous surface layer for both. The MHT data show the two samples have very different SAR values of 110 W/g (CP) and 40W/g (HT) at room temperature, although they have similar Ms of 70 +/-4 emu/g regardless of their different TEM sizes. We fitted the temperature dependent SAR using linear response theory to explain the observed results. CP sample shows a larger magnetic core with a narrow size distribution and a higher K value compared to that of HT sample.

  13. Island-size distribution and capture numbers in three-dimensional [corrected] nucleation: dependence on island morphology.

    PubMed

    Royston, John; Amar, Jacques G

    2009-10-01

    The scaling of the monomer and island densities, island-size distribution (ISD), and capture-number distribution (CND) as a function of the fraction of occupied sites (coverage) and ratio D(h)/F of the monomer hopping rate D(h) to the (per site) monomer creation rate F are studied for the case of irreversible nucleation and growth of fractal islands in three dimensions (d=3) . We note that our model is a three-dimensional analog of submonolayer growth in the absence of island relaxation and may also be viewed as a simplified model of the early stages of vacancy cluster nucleation and growth under irradiation. In contrast to results previously obtained for point-islands in d=3 , for which mean-field behavior corresponding to a CND which is independent of island size was observed, our results indicate that for fractal islands the scaled CND increases approximately linearly with island size in the asymptotic limit of large D(h)/F . In addition, while the peak height of the scaled ISD for fractal islands appears to diverge with increasing D(h)/F , the dependence on D(h)/F is much weaker than for point-islands in d=3 . The results of a self-consistent rate-equation calculation for the coverage and D(h)/F dependence of the average island and monomer densities are also presented and good agreement with simulation results is obtained. For the case of point-islands, the value of the exponent chi describing the D(h)/F dependence of the island density at fixed coverage, e.g., N(sat) approximately (D(h)/F)-chi , is in good agreement with the value (chi=1/3) expected for irreversible growth. However, for both compact and fractal islands in d=3 , our results indicate that the value of chi (chi approximately 0.42) is significantly larger. In order to explain this behavior, an analytical expression [e.g., chi=d(f)/(3d(f)-2) ] for the dependence of chi on island fractal dimension d(f) in d=3 is derived and found to give reasonable agreement with our simulation and rate

  14. Kinetic narrowing of size distribution

    NASA Astrophysics Data System (ADS)

    Dubrovskii, V. G.

    2016-05-01

    We present a model that reveals an interesting possibility for narrowing the size distribution of nanostructures when the deterministic growth rate changes its sign from positive to negative at a certain stationary size. Such a behavior occurs in self-catalyzed one-dimensional III-V nanowires and more generally whenever a negative "adsorption-desorption" term in the growth rate is compensated by a positive "diffusion flux." By asymptotically solving the Fokker-Planck equation, we derive an explicit representation for the size distribution that describes either Poissonian broadening or self-regulated narrowing depending on the parameters. We show how the fluctuation-induced spreading of the size distribution can be completely suppressed in systems with size self-stabilization. These results can be used for obtaining size-uniform ensembles of different nanostructures.

  15. Particle-size dependence on metal(loid) distributions in mine wastes: Implications for water contamination and human exposure

    USGS Publications Warehouse

    Kim, C.S.; Wilson, K.M.; Rytuba, J.J.

    2011-01-01

    The mining and processing of metal-bearing ores has resulted in contamination issues where waste materials from abandoned mines remain in piles of untreated and unconsolidated material, posing the potential for waterborne and airborne transport of toxic elements. This study presents a systematic method of particle size separation, mass distribution, and bulk chemical analysis for mine tailings and adjacent background soil samples from the Rand historic mining district, California, in order to assess particle size distribution and related trends in metal(loid) concentration as a function of particle size. Mine tailings produced through stamp milling and leaching processes were found to have both a narrower and finer particle size distribution than background samples, with significant fractions of particles available in a size range (???250 ??m) that could be incidentally ingested. In both tailings and background samples, the majority of trace metal(loid)s display an inverse relationship between concentration and particle size, resulting in higher proportions of As, Cr, Cu, Pb and Zn in finer-sized fractions which are more susceptible to both water- and wind-borne transport as well as ingestion and/or inhalation. Established regulatory screening levels for such elements may, therefore, significantly underestimate potential exposure risk if relying solely on bulk sample concentrations to guide remediation decisions. Correlations in elemental concentration trends (such as between As and Fe) indicate relationships between elements that may be relevant to their chemical speciation. ?? 2011 Elsevier Ltd.

  16. Size-dependent distribution and feeding habits of Terebralia palustris in mangrove habitats of Gazi Bay, Kenya

    NASA Astrophysics Data System (ADS)

    Pape, Ellen; Muthumbi, Agnes; Kamanu, Chomba Peter; Vanreusel, Ann

    2008-03-01

    The gastropod Terebralia palustris often dominates the surface of muddy to sandy substrates of intertidal mudflats and mangrove forests, where they clearly destabilize the sediment. In the present study, it was investigated whether and to what extent the behaviour of juvenile and adult snails differs among habitats (mudflat vs. mangrove stand) in a Sonneratia alba mangal at Gazi Bay, Kenya. For this purpose we: (1) examined their distribution along three land-sea transects; and (2) applied stable isotope analysis to determine the feeding patterns of different-sized snails from the mangrove and mudflat habitats. Additionally, we investigated if these gastropods exert an impact on microphytobenthic (diatom) biomass, and whether this is size-dependent. The latter objective was met by either enclosing or excluding different-sized snails from experimental cages on the intertidal mudflat and the subsequent assessment of a change in pigment concentration of the sediment surface. In agreement with several previous studies conducted in other mangroves and geographical locations, a spatial segregation was demonstrated between juveniles (more common on the mudflat) and adults (more common in the mangrove forest). On the intertidal mudflat juveniles avoided sediment patches characterized by highly saline water in intertidal pools and a high mud content, while adults tended to dwell on substrates covered by a high amount of leaf litter. Stable carbon isotope analysis of the foot tissue of snails sampled from the S. alba stand and the mudflat indicated a transition in food source when a shell length of 51 mm is reached. Considering the δ13C value of juveniles, it seems they might be selecting for microphytobenthos, which might explain their preference for the mudflat. The diet of size classes found in both habitats did not differ significantly, although juveniles inhabiting the mangrove forest were slightly more depleted in 13C compared to those residing on the mudflat

  17. Dependence of the thermal conductivity of two-dimensional graphite nanoplatelet-based composites on the nanoparticle size distribution.

    PubMed

    Sun, Xiaobo; Ramesh, Palanisamy; Itkis, Mikhail E; Bekyarova, Elena; Haddon, Robert C

    2010-08-25

    We report the thermal conductivities of graphite nanoplatelet-epoxy composites prepared by exfoliation of natural graphite flakes of varying lateral sizes. We found that utilization of natural graphite flakes of the optimum lateral dimensions (∼200-400 µm) as a starting material for exfoliation significantly enhanced the thermal conductivity of the composite. In order to understand this enhancement we developed a procedure for evaluation of the particle size distribution of graphite nanoplatelets and correlated the measured distributions with the resulting thermal conductivities. In order to expand the scope of our study we applied our statistical and thermal analysis to commercially available graphite nanoplatelet materials.

  18. Multi-Scale Particle Size Distributions of Mars, Moon and Itokawa based on a time-maturation dependent fragmentation model

    NASA Astrophysics Data System (ADS)

    Charalambous, C. A.; Pike, W. T.

    2013-12-01

    We present the development of a soil evolution framework and multiscale modelling of the surface of Mars, Moon and Itokawa thus providing an atlas of extra-terrestrial Particle Size Distributions (PSD). These PSDs are profoundly based on a tailoring method which interconnects several datasets from different sites captured by the various missions. The final integrated product is then fully justified through a soil evolution analysis model mathematically constructed via fundamental physical principles (Charalambous, 2013). The construction of the PSD takes into account the macroscale fresh primary impacts and their products, the mesoscale distributions obtained by the in-situ data of surface missions (Golombek et al., 1997, 2012) and finally the microscopic scale distributions provided by Curiosity and Phoenix Lander (Pike, 2011). The distribution naturally extends at the magnitudinal scales at which current data does not exist due to the lack of scientific instruments capturing the populations at these data absent scales. The extension is based on the model distribution (Charalambous, 2013) which takes as parameters known values of material specific probabilities of fragmentation and grinding limits. Additionally, the establishment of a closed-form statistical distribution provides a quantitative description of the soil's structure. Consequently, reverse engineering of the model distribution allows the synthesis of soil that faithfully represents the particle population at the studied sites (Charalambous, 2011). Such representation essentially delivers a virtual soil environment to work with for numerous applications. A specific application demonstrated here will be the information that can directly be extracted for the successful drilling probability as a function of distance in an effort to aid the HP3 instrument of the 2016 Insight Mission to Mars. Pike, W. T., et al. "Quantification of the dry history of the Martian soil inferred from in situ microscopy

  19. Hail Size Distribution Mapping

    NASA Technical Reports Server (NTRS)

    2008-01-01

    A 3-D weather radar visualization software program was developed and implemented as part of an experimental Launch Pad 39 Hail Monitor System. 3DRadPlot, a radar plotting program, is one of several software modules that form building blocks of the hail data processing and analysis system (the complete software processing system under development). The spatial and temporal mapping algorithms were originally developed through research at the University of Central Florida, funded by NASA s Tropical Rainfall Measurement Mission (TRMM), where the goal was to merge National Weather Service (NWS) Next-Generation Weather Radar (NEXRAD) volume reflectivity data with drop size distribution data acquired from a cluster of raindrop disdrometers. In this current work, we adapted these algorithms to process data from a cluster of hail disdrometers positioned around Launch Pads 39A or 39B, along with the corresponding NWS radar data. Radar data from all NWS NEXRAD sites is archived at the National Climatic Data Center (NCDC). That data can be readily accessed at . 3DRadPlot plots Level III reflectivity data at four scan elevations (this software is available at Open Channel Software, ). By using spatial and temporal interpolation/extrapolation based on hydrometeor fall dynamics, we can merge the hail disdrometer array data coupled with local Weather Surveillance Radar-1988, Doppler (WSR-88D) radial velocity and reflectivity data into a 4-D (3-D space and time) picture of hail size distributions. Hail flux maps can then be generated and used for damage prediction and assessment over specific surfaces corresponding to structures within the disdrometer array volume. Immediately following a hail storm, specific damage areas and degree of damage can be identified for inspection crews.

  20. Nanophase cobalt, nickel and zinc ferrites: synchrotron XAS study on the crystallite size dependence of metal distribution.

    PubMed

    Nordhei, Camilla; Ramstad, Astrid Lund; Nicholson, David G

    2008-02-21

    Nanophase cobalt, nickel and zinc ferrites, in which the crystallites are in the size range 4-25 nm, were synthesised by coprecipitation and subsequent annealing. X-Ray absorption spectroscopy using synchrotron radiation (supported by X-ray powder diffraction) was used to study the effects of particle size on the distributions of the metal atoms over the tetrahedral and octahedral sites of the spinel structure. Deviations from the bulk structure were found which are attributed to the significant influence of the surface on very small particles. Like the bulk material, nickel ferrite is an inverse spinel in the nanoregime, although the population of metals on the octahedral sites increases with decreasing particle size. Cobalt ferrite and zinc ferrite take the inverse and normal forms of the spinel structure respectively, but within the nanoregime both systems show similar trends in being partially inverted. Further, in zinc ferrite, unlike the normal bulk structure, the nanophase system involves mixed coordinations of zinc(ii) and iron(iii) consistent with increasing partial inversion with size.

  1. System Size, Energy, and Centrality Dependence of Pseudorapidity Distributions of Charged Particles in Relativistic Heavy-Ion Collisions

    SciTech Connect

    Alver, B.; Back, B. B.; Baker, M. D.; Barton, D. S.; Chai, Z.; Holzman, B.; Nouicer, R.; Pak, R.; Sedykh, I.; Stankiewicz, M. A.; Steinberg, P.; Sukhanov, A.; Szostak, A.; Wyngaardt, S.; Ballintijn, M.; Busza, W.; Gulbrandsen, K.; Henderson, C.; Kane, J. L.; Kulinich, P.

    2009-04-10

    We present the first measurements of the pseudorapidity distribution of primary charged particles in Cu+Cu collisions as a function of collision centrality and energy, {radical}(s{sub NN})=22.4, 62.4, and 200 GeV, over a wide range of pseudorapidity, using the PHOBOS detector. A comparison of Cu+Cu and Au+Au results shows that the total number of produced charged particles and the rough shape (height and width) of the pseudorapidity distributions are determined by the number of nucleon participants. More detailed studies reveal that a more precise matching of the shape of the Cu+Cu and Au+Au pseudorapidity distributions over the full range of pseudorapidity occurs for the same N{sub part}/2A rather than the same N{sub part}. In other words, it is the collision geometry rather than just the number of nucleon participants that drives the detailed shape of the pseudorapidity distribution and its centrality dependence at RHIC energies.

  2. Thermal fluctuations of vesicles and nonlinear curvature elasticity--implications for size-dependent renormalized bending rigidity and vesicle size distribution.

    PubMed

    Ahmadpoor, Fatemeh; Sharma, Pradeep

    2016-03-01

    Both closed and open biological membranes noticeably undulate at physiological temperatures. These thermal fluctuations influence a broad range of biophysical phenomena, ranging from self-assembly to adhesion. In particular, the experimentally measured thermal fluctuation spectra also provide a facile route to the assessment of mechanical and certain other physical properties of biological membranes. The theoretical assessment of thermal fluctuations, be it for closed vesicles or the simpler case of flat open lipid bilayers, is predicated upon assuming that the elastic curvature energy is a quadratic functional of the curvature tensor. However, a qualitatively correct description of several phenomena such as binding-unbinding transition, vesicle-to-bicelle transition, appearance of hats and saddles among others, appears to require consideration of constitutively nonlinear elasticity that includes fourth order curvature contributions rather than just quadratic. In particular, such nonlinear considerations are relevant in the context of large-curvature or small-sized vesicles. In this work we discuss the statistical mechanics of closed membranes (vesicles) incorporating both constitutive and geometrical nonlinearities. We derive results for the renormalized bending rigidity of small vesicles and show that significant stiffening may occur for sub-20 nm vesicle sizes. Our closed-form results may also be used to determine nonlinear curvature elasticity properties from either experimentally measured fluctuation spectra or microscopic calculations such as molecular dynamics. Finally, in the context of our results on thermal fluctuations of vesicles and nonlinear curvature elasticity, we reexamine the problem of determining the size distribution of vesicles and obtain results that reconcile well with experimental observations. However, our results are somewhat paradoxical. Specifically, the molecular dynamics predictions for the thermo-mechanical behavior of small vesicles

  3. Dependence on Crystal Size of the Nanoscale Chemical Phase Distribution and Fracture in LixFePO₄.

    PubMed

    Yu, Young-Sang; Kim, Chunjoong; Shapiro, David A; Farmand, Maryam; Qian, Danna; Tyliszczak, Tolek; Kilcoyne, A L David; Celestre, Rich; Marchesini, Stefano; Joseph, John; Denes, Peter; Warwick, Tony; Strobridge, Fiona C; Grey, Clare P; Padmore, Howard; Meng, Ying Shirley; Kostecki, Robert; Cabana, Jordi

    2015-07-01

    The performance of battery electrode materials is strongly affected by inefficiencies in utilization kinetics and cycle life as well as size effects. Observations of phase transformations in these materials with high chemical and spatial resolution can elucidate the relationship between chemical processes and mechanical degradation. Soft X-ray ptychographic microscopy combined with X-ray absorption spectroscopy and electron microscopy creates a powerful suite of tools that we use to assess the chemical and morphological changes in lithium iron phosphate (LiFePO4) micro- and nanocrystals that occur upon delithiation. All sizes of partly delithiated crystals were found to contain two phases with a complex correlation between crystallographic orientation and phase distribution. However, the lattice mismatch between LiFePO4 and FePO4 led to severe fracturing on microcrystals, whereas no mechanical damage was observed in nanoplates, indicating that mechanics are a principal driver in the outstanding electrode performance of LiFePO4 nanoparticles. These results demonstrate the importance of engineering the active electrode material in next generation electrical energy storage systems, which will achieve theoretical limits of energy density and extended stability. This work establishes soft X-ray ptychographic chemical imaging as an essential tool to build comprehensive relationships between mechanics and chemistry that guide this engineering design.

  4. Determination of size-dependent metal distribution in dissolved organic matter by SEC-UV/VIS-ICP-MS with special focus on changes in seawater.

    PubMed

    Rathgeb, Anna; Causon, Tim; Krachler, Regina; Hann, Stephan

    2016-04-01

    Iron is an essential micronutrient for all marine organisms, but it is also a growth limiting factor as the iron concentrations in the open ocean are below 1 nmol/L in sea water iron is almost entirely bound to organic ligands of the dissolved organic matter fraction, which are mostly of unknown structure. The input from rivers was traditionally considered as less important due to estuarine sedimentation processes of the mainly colloidal iron particles. However, recent studies have shown that this removal is not complete and riverine input may represent an important iron source in the open ocean. In this context, iron transport by land-derived natural organic matter (NOM), and dissolved organic matter (DOM) have been identified as carrier mechanisms for riverine iron. The aim of this work is to characterize complexes containing iron and other metals in waters simulating estuarine conditions in order to help understand which role iron-DOM compounds play in the open ocean. A method based on size-exclusion chromatography (SEC) with sequential UV/VIS and ICP-MS detection was developed for investigation of DOM size distribution and for assessment of the size-dependent metal distribution in NOM-rich surface water. Furthermore, sample matrix experiments were also performed revealing a dependence of DOM size distribution upon seawater concentration and different compounds present in seawater. Finally, efforts toward determination of DOM size with standardization with typical SEC standards indicate that only relative comparisons are possible with this approach, and that the sample matrix composition strongly influences obtained results. PMID:26814136

  5. Determination of size-dependent metal distribution in dissolved organic matter by SEC-UV/VIS-ICP-MS with special focus on changes in seawater.

    PubMed

    Rathgeb, Anna; Causon, Tim; Krachler, Regina; Hann, Stephan

    2016-04-01

    Iron is an essential micronutrient for all marine organisms, but it is also a growth limiting factor as the iron concentrations in the open ocean are below 1 nmol/L in sea water iron is almost entirely bound to organic ligands of the dissolved organic matter fraction, which are mostly of unknown structure. The input from rivers was traditionally considered as less important due to estuarine sedimentation processes of the mainly colloidal iron particles. However, recent studies have shown that this removal is not complete and riverine input may represent an important iron source in the open ocean. In this context, iron transport by land-derived natural organic matter (NOM), and dissolved organic matter (DOM) have been identified as carrier mechanisms for riverine iron. The aim of this work is to characterize complexes containing iron and other metals in waters simulating estuarine conditions in order to help understand which role iron-DOM compounds play in the open ocean. A method based on size-exclusion chromatography (SEC) with sequential UV/VIS and ICP-MS detection was developed for investigation of DOM size distribution and for assessment of the size-dependent metal distribution in NOM-rich surface water. Furthermore, sample matrix experiments were also performed revealing a dependence of DOM size distribution upon seawater concentration and different compounds present in seawater. Finally, efforts toward determination of DOM size with standardization with typical SEC standards indicate that only relative comparisons are possible with this approach, and that the sample matrix composition strongly influences obtained results.

  6. Temperature induced changes in size dependent distributions of two boreal and three Lusitanian flatfish species: A comparative study

    NASA Astrophysics Data System (ADS)

    van Hal, Ralf; van Kooten, Tobias; Rijnsdorp, Adriaan D.

    2016-01-01

    Changes in spatial distribution in several fish species have been related to recent increase in global temperature. In the North Sea, both a poleward shift and a shift to deeper water have been observed. Here, we study the underlying mechanism of these shifts in a comparative study of the changes in distribution of two boreal flatfish species (plaice Pleuronectes platessa and dab Limanda limanda) and three Lusitanian flatfish species (sole Solea solea, solenette Buglossidium luteum, and scaldfish Arnoglossus laterna) as recorded in annual bottom trawl surveys carried out in the North Sea in late summer since 1985. The distribution is analysed in relation to the bottom temperature at the time of the survey as well as to the seasonal maximum bottom temperature earlier in the year. It is shown that the boreal species plaice and dab moved to deeper water and maintained the seasonal maximum temperature that they experienced in earlier periods, while the Lusitanian species sole, solenette, and scaldfish experienced an increase in the seasonal maximum temperature that they experienced while maintaining their depth distribution. This overall response varied between length classes, reflecting a preference for higher temperature of the smaller length classes. The results lend support to the hypothesis that the fish displayed a direct response to the maximum temperature that occurred during the growth season before the time of sampling.

  7. Experimental determination of size distributions: analyzing proper sample sizes

    NASA Astrophysics Data System (ADS)

    Buffo, A.; Alopaeus, V.

    2016-04-01

    The measurement of various particle size distributions is a crucial aspect for many applications in the process industry. Size distribution is often related to the final product quality, as in crystallization or polymerization. In other cases it is related to the correct evaluation of heat and mass transfer, as well as reaction rates, depending on the interfacial area between the different phases or to the assessment of yield stresses of polycrystalline metals/alloys samples. The experimental determination of such distributions often involves laborious sampling procedures and the statistical significance of the outcome is rarely investigated. In this work, we propose a novel rigorous tool, based on inferential statistics, to determine the number of samples needed to obtain reliable measurements of size distribution, according to specific requirements defined a priori. Such methodology can be adopted regardless of the measurement technique used.

  8. Size Distribution of Bacterial Cells

    PubMed Central

    Stull, V. R.

    1972-01-01

    By using differential light-scattering measurements of single cells suspended in a laser beam, an effective cell radius has been determined for 141 individual bacteria from suspensions of Staphylococcus epidermidis. The accumulation of these measurements has provided the size distribution for the sampling. PMID:4551753

  9. Size distribution of ring polymers

    NASA Astrophysics Data System (ADS)

    Medalion, Shlomi; Aghion, Erez; Meirovitch, Hagai; Barkai, Eli; Kessler, David A.

    2016-06-01

    We present an exact solution for the distribution of sample averaged monomer to monomer distance of ring polymers. For non-interacting and local-interaction models these distributions correspond to the distribution of the area under the reflected Bessel bridge and the Bessel excursion respectively, and are shown to be identical in dimension d ≥ 2, albeit with pronounced finite size effects at the critical dimension, d = 2. A symmetry of the problem reveals that dimension d and 4 - d are equivalent, thus the celebrated Airy distribution describing the areal distribution of the d = 1 Brownian excursion describes also a polymer in three dimensions. For a self-avoiding polymer in dimension d we find numerically that the fluctuations of the scaled averaged distance are nearly identical in dimension d = 2, 3 and are well described to a first approximation by the non-interacting excursion model in dimension 5.

  10. Parameterizing the Raindrop Size Distribution

    NASA Technical Reports Server (NTRS)

    Haddad, Ziad S.; Durden, Stephen L.; Im, Eastwood

    1996-01-01

    This paper addresses the problem of finding a parametric form for the raindrop size distribution (DSD) that(1) is an appropriate model for tropical rainfall, and (2) involves statistically independent parameters. Such a parameterization is derived in this paper. One of the resulting three "canonical" parameters turns out to vary relatively little, thus making the parameterization particularly useful for remote sensing applications. In fact, a new set of r drop-size-distribution-based Z-R and k-R relations is obtained. Only slightly more complex than power laws, they are very good approximations to the exact radar relations one would obtain using Mie scattering. The coefficients of the new relations are directly related to the shape parameters of the particular DSD that one starts with. Perhaps most important, since the coefficients are independent of the rain rate itself, the relations are ideally suited for rain retrieval algorithms.

  11. Exponential Size Distribution of von Willebrand Factor

    PubMed Central

    Lippok, Svenja; Obser, Tobias; Müller, Jochen P.; Stierle, Valentin K.; Benoit, Martin; Budde, Ulrich; Schneppenheim, Reinhard; Rädler, Joachim O.

    2013-01-01

    Von Willebrand Factor (VWF) is a multimeric protein crucial for hemostasis. Under shear flow, it acts as a mechanosensor responding with a size-dependent globule-stretch transition to increasing shear rates. Here, we quantify for the first time, to our knowledge, the size distribution of recombinant VWF and VWF-eGFP using a multilateral approach that involves quantitative gel analysis, fluorescence correlation spectroscopy, and total internal reflection fluorescence microscopy. We find an exponentially decaying size distribution of multimers for recombinant VWF as well as for VWF derived from blood samples in accordance with the notion of a step-growth polymerization process during VWF biosynthesis. The distribution is solely described by the extent of polymerization, which was found to be reduced in the case of the pathologically relevant mutant VWF-IIC. The VWF-specific protease ADAMTS13 systematically shifts the VWF size distribution toward smaller sizes. This dynamic evolution is monitored using fluorescence correlation spectroscopy and compared to a computer simulation of a random cleavage process relating ADAMTS13 concentration to the degree of VWF breakdown. Quantitative assessment of VWF size distribution in terms of an exponential might prove to be useful both as a valuable biophysical characterization and as a possible disease indicator for clinical applications. PMID:24010664

  12. Size distribution of ring polymers

    PubMed Central

    Medalion, Shlomi; Aghion, Erez; Meirovitch, Hagai; Barkai, Eli; Kessler, David A.

    2016-01-01

    We present an exact solution for the distribution of sample averaged monomer to monomer distance of ring polymers. For non-interacting and local-interaction models these distributions correspond to the distribution of the area under the reflected Bessel bridge and the Bessel excursion respectively, and are shown to be identical in dimension d ≥ 2, albeit with pronounced finite size effects at the critical dimension, d = 2. A symmetry of the problem reveals that dimension d and 4 − d are equivalent, thus the celebrated Airy distribution describing the areal distribution of the d = 1 Brownian excursion describes also a polymer in three dimensions. For a self-avoiding polymer in dimension d we find numerically that the fluctuations of the scaled averaged distance are nearly identical in dimension d = 2, 3 and are well described to a first approximation by the non-interacting excursion model in dimension 5. PMID:27302596

  13. Power laws, discontinuities and regional city size distributions

    USGS Publications Warehouse

    Garmestani, A.S.; Allen, C.R.; Gallagher, C.M.

    2008-01-01

    Urban systems are manifestations of human adaptation to the natural environment. City size distributions are the expression of hierarchical processes acting upon urban systems. In this paper, we test the entire city size distributions for the southeastern and southwestern United States (1990), as well as the size classes in these regions for power law behavior. We interpret the differences in the size of the regional city size distributions as the manifestation of variable growth dynamics dependent upon city size. Size classes in the city size distributions are snapshots of stable states within urban systems in flux. ?? 2008.

  14. Size-dependent distribution of radiocesium in riverbed sediments and its relevance to the migration of radiocesium in river systems after the Fukushima Daiichi Nuclear Power Plant accident.

    PubMed

    Tanaka, Kazuya; Iwatani, Hokuto; Sakaguchi, Aya; Fan, Qiaohui; Takahashi, Yoshio

    2015-01-01

    We investigated the particle size distribution of radiocesium in riverbed sediments after the Fukushima Daiichi Nuclear Power Plant accident. Riverbed sediments were collected in the Abukuma River system in Fukushima and Miyagi Prefectures. The collected sediments were separated into 11 fractions, ranging from granular size (>2000 μm) to clay size (<2 μm) fractions. Cesium-137 concentrations were higher in the smaller particle size fractions, possibly reflecting specific surface areas and the mineralogy, in particular the clay mineral content. A gap in (137)Cs concentration was observed between the silt size and sand size fractions of riverbed sediments at downstream sites, whereas riverbed sediments at an upstream site did not show such a concentration gap. It is likely that selective transport of small particles in suspended state from upstream areas resulted in an accumulation of radiocesium in downstream areas. PMID:24874435

  15. Spatial Structure of Seagrass Suggests That Size-Dependent Plant Traits Have a Strong Influence on the Distribution and Maintenance of Tropical Multispecies Meadows

    PubMed Central

    Ooi, Jillian L. S.; Van Niel, Kimberly P.; Kendrick, Gary A.; Holmes, Karen W.

    2014-01-01

    Background Seagrass species in the tropics occur in multispecies meadows. How these meadows are maintained through species co-existence and what their ecological drivers may be has been an overarching question in seagrass biogeography. In this study, we quantify the spatial structure of four co-existing species and infer potential ecological processes from these structures. Methods and Results Species presence/absence data were collected using underwater towed and dropped video cameras in Pulau Tinggi, Malaysia. The geostatistical method, utilizing semivariograms, was used to describe the spatial structure of Halophila spp, Halodule uninervis, Syringodium isoetifolium and Cymodocea serrulata. Species had spatial patterns that were oriented in the along-shore and across-shore directions, nested with larger species in meadow interiors, and consisted of multiple structures that indicate the influence of 2–3 underlying processes. The Linear Model of Coregionalization (LMC) was used to estimate the amount of variance contributing to the presence of a species at specific spatial scales. These distances were <2.5 m (micro-scale), 2.5–50 m (fine-scale) and >50 m (broad-scale) in the along-shore; and <2.5 m (micro-scale), 2.5–140 m (fine-scale) and >140 m (broad-scale) in the across-shore. The LMC suggests that smaller species (Halophila spp and H. uninervis) were most influenced by broad-scale processes such as hydrodynamics and water depth whereas large, localised species (S. isoetifolium and C. serrulata) were more influenced by finer-scale processes such as sediment burial, seagrass colonization and growth, and physical disturbance. Conclusion In this study, we provide evidence that spatial structure is distinct even when species occur in well-mixed multispecies meadows, and we suggest that size-dependent plant traits have a strong influence on the distribution and maintenance of tropical marine plant communities. This study offers a contrast from previous spatial

  16. 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.

  17. Determination of the cumulus size distribution from LANDSAT pictures

    NASA Technical Reports Server (NTRS)

    Karg, E.; Mueller, H.; Quenzel, H.

    1983-01-01

    Varying insolation causes undesirable thermic stress to the receiver of a solar power plant. The rapid change of insolation depends on the size distribution of the clouds; in order to measure these changes, it is suitable to determine typical cumulus size distributions. For this purpose, LANDSAT-images are adequate. Several examples of cumulus size distributions will be presented and their effects on the operation of a solar power plant are discussed.

  18. Imaging widespread seismicity at midlower crustal depths beneath Long Beach, CA, with a dense seismic array: Evidence for a depth-dependent earthquake size distribution

    NASA Astrophysics Data System (ADS)

    Inbal, Asaf; Clayton, Robert W.; Ampuero, Jean-Paul

    2015-08-01

    We use a dense seismic array composed of 5200 vertical geophones to monitor microseismicity in Long Beach, California. Poor signal-to-noise ratio due to anthropogenic activity is mitigated via downward-continuation of the recorded wavefield. The downward-continued data are continuously back projected to search for coherent arrivals from sources beneath the array, which reveals numerous, previously undetected events. The spatial distribution of seismicity is uncorrelated with the mapped fault traces, or with activity in the nearby oil-fields. Many events are located at depths larger than 20 km, well below the commonly accepted seismogenic depth for that area. The seismicity exhibits temporal clustering consistent with Omori's law, and its size distribution obeys the Gutenberg-Richter relation above 20 km but falls off exponentially at larger depths. The dense array allows detection of earthquakes two magnitude units smaller than the permanent seismic network in the area. Because the event size distribution above 20 km depth obeys a power law whose exponent is near one, this improvement yields a hundred-fold decrease in the time needed for effective characterization of seismicity in Long Beach.

  19. Size-dependent properties of semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Kwak, Hyun Wook

    Doping is crucial to many potential applications of nanometer-sized semiconductors. Since their properties are strongly affected by both doping and quantum size effect, it is important to understand how dopants will influence its media under strong quantum confinement. In this dissertation, we will discuss the role of quantum confinement in the properties of nanometer-sized semiconductors doped with impurities. It is well-known that electronic and optical properties of nanometer-sized semiconductors can vary with size. We present size-dependent properties of lithium doped silicon and zinc oxide nanocrystals as examples. With the help of first-principles methods based on real space approach, we find that not only the size itself but also the chemical nature of the impurity is important to determine the properties of nanometer-sized semiconductors. We will also discuss size-induced magnetism in semiconductor nanostructures doped with non-magnetic impurities. From recent studies, it has been proposed that magnetic semiconductors can be designed by using non-magnetic defects, e.g., through the introduction of an extrinsic impurity atom that does not exhibit magnetism by itself. We examine this idea with silicon and zinc oxide nanostructures doped with impurities. We find that quantum size effect may induce magnetism in doped nanostructures. The evidence of the size-dependent magnetic properties offers a new perspective for the design of semiconductor-based spintronic materials.

  20. Unimodal tree size distributions possibly result from relatively strong conservatism in intermediate size classes.

    PubMed

    Bin, Yue; Ye, Wanhui; Muller-Landau, Helene C; Wu, Linfang; Lian, Juyu; Cao, Honglin

    2012-01-01

    Tree size distributions have long been of interest to ecologists and foresters because they reflect fundamental demographic processes. Previous studies have assumed that size distributions are often associated with population trends or with the degree of shade tolerance. We tested these associations for 31 tree species in a 20 ha plot in a Dinghushan south subtropical forest in China. These species varied widely in growth form and shade-tolerance. We used 2005 and 2010 census data from that plot. We found that 23 species had reversed J shaped size distributions, and eight species had unimodal size distributions in 2005. On average, modal species had lower recruitment rates than reversed J species, while showing no significant difference in mortality rates, per capita population growth rates or shade-tolerance. We compared the observed size distributions with the equilibrium distributions projected from observed size-dependent growth and mortality. We found that observed distributions generally had the same shape as predicted equilibrium distributions in both unimodal and reversed J species, but there were statistically significant, important quantitative differences between observed and projected equilibrium size distributions in most species, suggesting that these populations are not at equilibrium and that this forest is changing over time. Almost all modal species had U-shaped size-dependent mortality and/or growth functions, with turning points of both mortality and growth at intermediate size classes close to the peak in the size distribution. These results show that modal size distributions do not necessarily indicate either population decline or shade-intolerance. Instead, the modal species in our study were characterized by a life history strategy of relatively strong conservatism in an intermediate size class, leading to very low growth and mortality in that size class, and thus to a peak in the size distribution at intermediate sizes. PMID:23300714

  1. Aerosol Size Distribution in the marine regions

    NASA Astrophysics Data System (ADS)

    Markuszewski, Piotr; Petelski, Tomasz; Zielinski, Tymon; Pakszys, Paulina; Strzalkowska, Agata; Makuch, Przemyslaw; Kowalczyk, Jakub

    2014-05-01

    We would like to present the data obtained during the regular research cruises of the S/Y Oceania over a period of time between 2009 - 2012. The Baltic Sea is a very interesting polygon for aerosol measurements, however, also difficult due to the fact that mostly cases of a mixture of continental and marine aerosols are observed. It is possible to measure clear marine aerosol, but also advections of dust from southern Europe or even Africa. This variability of data allows to compare different conditions. The data is also compared with our measurements from the Arctic Seas, which have been made during the ARctic EXperiment (AREX). The Arctic Seas are very suitable for marine aerosol investigations since continental advections of aerosols are far less frequent than in other European sea regions. The aerosol size distribution was measured using the TSI Laser Aerosol Spectrometer model 3340 (99 channels, measurement range 0.09 μm to 7 μm), condensation particle counter (range 0.01 μm to 3 μm) and laser particle counter PMS CSASP-100-HV-SP (range 0.5 μm to 47 μm in 45 channels). Studies of marine aerosol production and transport are important for many Earth sciences such as cloud physics, atmospheric optics, environmental pollution studies and interaction between ocean and atmosphere. All equipment was placed on one of the masts of S/Y Oceania. Measurements using the laser aerosol spectrometer and condensation particle counter were made on one level (8 meters above sea level). Measurements with the laser particle counter were performed at five different levels above the sea level (8, 11, 14, 17 and 20 m). Based on aerosol size distribution the parameterizations with a Log-Normal and a Power-Law distributions were made. The aerosol source functions, characteristic for the region were also determined. Additionally, poor precision of the sea spray emission determination was confirmed while using only the aerosol concentration data. The emission of sea spray depends

  2. The size dependence of sublimation rates for interplanetary ice particles

    NASA Technical Reports Server (NTRS)

    Patashnick, H.; Rupprecht, G.

    1975-01-01

    The sublimation rates for water ice have been computed as a function of particle size for various solar distances. Because of the size dependence of the absorption and emission properties of the particles, a sublimation-rate minimum evolves whose depth and position are sensitive to the spectral-absorption properties of the particle in combination with the spectral distribution of solar radiation. As a consequence, a quasistable size of interplanetary ice particles is predicted which is independent of solar distance.

  3. Body size distribution of the dinosaurs.

    PubMed

    O'Gorman, Eoin J; Hone, David W E

    2012-01-01

    The distribution of species body size is critically important for determining resource use within a group or clade. It is widely known that non-avian dinosaurs were the largest creatures to roam the Earth. There is, however, little understanding of how maximum species body size was distributed among the dinosaurs. Do they share a similar distribution to modern day vertebrate groups in spite of their large size, or did they exhibit fundamentally different distributions due to unique evolutionary pressures and adaptations? Here, we address this question by comparing the distribution of maximum species body size for dinosaurs to an extensive set of extant and extinct vertebrate groups. We also examine the body size distribution of dinosaurs by various sub-groups, time periods and formations. We find that dinosaurs exhibit a strong skew towards larger species, in direct contrast to modern day vertebrates. This pattern is not solely an artefact of bias in the fossil record, as demonstrated by contrasting distributions in two major extinct groups and supports the hypothesis that dinosaurs exhibited a fundamentally different life history strategy to other terrestrial vertebrates. A disparity in the size distribution of the herbivorous Ornithischia and Sauropodomorpha and the largely carnivorous Theropoda suggests that this pattern may have been a product of a divergence in evolutionary strategies: herbivorous dinosaurs rapidly evolved large size to escape predation by carnivores and maximise digestive efficiency; carnivores had sufficient resources among juvenile dinosaurs and non-dinosaurian prey to achieve optimal success at smaller body size.

  4. Body Size Distribution of the Dinosaurs

    PubMed Central

    O’Gorman, Eoin J.; Hone, David W. E.

    2012-01-01

    The distribution of species body size is critically important for determining resource use within a group or clade. It is widely known that non-avian dinosaurs were the largest creatures to roam the Earth. There is, however, little understanding of how maximum species body size was distributed among the dinosaurs. Do they share a similar distribution to modern day vertebrate groups in spite of their large size, or did they exhibit fundamentally different distributions due to unique evolutionary pressures and adaptations? Here, we address this question by comparing the distribution of maximum species body size for dinosaurs to an extensive set of extant and extinct vertebrate groups. We also examine the body size distribution of dinosaurs by various sub-groups, time periods and formations. We find that dinosaurs exhibit a strong skew towards larger species, in direct contrast to modern day vertebrates. This pattern is not solely an artefact of bias in the fossil record, as demonstrated by contrasting distributions in two major extinct groups and supports the hypothesis that dinosaurs exhibited a fundamentally different life history strategy to other terrestrial vertebrates. A disparity in the size distribution of the herbivorous Ornithischia and Sauropodomorpha and the largely carnivorous Theropoda suggests that this pattern may have been a product of a divergence in evolutionary strategies: herbivorous dinosaurs rapidly evolved large size to escape predation by carnivores and maximise digestive efficiency; carnivores had sufficient resources among juvenile dinosaurs and non-dinosaurian prey to achieve optimal success at smaller body size. PMID:23284818

  5. Size-dependent mortality rate profiles.

    PubMed

    Roa-Ureta, Ruben H

    2016-08-01

    Knowledge of mortality rates is crucial to the understanding of population dynamics in populations of free-living fish and invertebrates in marine and freshwater environments, and consequently to sustainable resource management. There is a well developed theory of population dynamics based on age distributions that allow direct estimation of mortality rates. However, for most cases the aging of individuals is difficult or age distributions are not available for other reasons. The body size distribution is a widely available alternative although the theory underlying the formation of its shape is more complicated than in the case of age distributions. A solid theory of the time evolution of a population structured by any physiological variable has been developed in 1960s and 1970s by adapting the Hamilton-Jacobi formulation of classical mechanics, and equations to estimate the body size-distributed mortality profile have been derived for simple cases. Here I extend those results with regards to the size-distributed mortality profile to complex cases of non-stationary populations, individuals growing according to a generalised growth model and seasonally patterned recruitment pulses. I apply resulting methods to two cases in the marine environment, a benthic crustacean population that was growing during the period of observation and whose individuals grow with negative acceleration, and a sea urchin coastal population that is undergoing a stable cycle of two equilibrium points in population size whose individuals grow with varying acceleration that switches sign along the size range. The extension is very general and substantially widens the applicability of the theory. PMID:27164999

  6. Asteroid Size-Frequency Distribution

    NASA Technical Reports Server (NTRS)

    Tedesco, Edward F.

    2001-01-01

    A total of six deep exposures (using AOT CAM01 with a 6 inch PFOV) through the ISOCAM LW10 filter (IRAS Band 1, i.e. 12 micron) were obtained on an approximately 15 arcminute square field centered on the ecliptic plane. Point sources were extracted using the technique described. Two known asteroids appear in these frames and 20 sources moving with velocities appropriate for main belt asteroids are present. Most of the asteroids detected have flux densities less than 1 mJy, i,e., between 150 and 350 times fainter than any of the asteroids observed by IRAS. These data provide the first direct measurement of the 12 pm sky-plane density for asteroids on the ecliptic equator. The median zodiacal foreground, as measured by ISOCAM during this survey, is found to be 22.1 +/- 1.5 mJy per pixel, i.e., 26.2 +/- 1.7 MJy/sr. The results presented here imply that the actual number of kilometer-sized asteroids is significantly greater than previously believed and in reasonable agreement with the Statistical Asteroid Model.

  7. Optical heterodyne measurement of cloud droplet size distributions.

    PubMed

    Gollub, J P; Chabay, L; Flygare, W H

    1973-12-01

    Optical heterodyne spectra of laser light quasi-elastically scattered by falling water droplets (1-10-micro radius) in a diffusion cloud chamber were used to determine the droplet size distribution. The rate of fall depends on radius in a known way, thus yielding a heterodyne spectrum manifesting a distribution of Doppler shifts. This spectrum, in conjunction with the calculated Mie scattering intensity as a function of droplet radius, provides a direct measure of the droplet size distribution for droplets large enough that Brownian motion is negligible. The experiments described in this paper demonstrate the technique and establish the potential for further more quantitative studies of size distributions.

  8. Size distribution of planetary nebulae

    NASA Astrophysics Data System (ADS)

    Asvarov, Abdul; Allahverdiyev, Ahad

    2015-08-01

    Despite a very long history of investigations, the nature and origin of planetary nebulae (PNe) are not fully understood. It is obvious that the observational properties of PNe are influenced by the properties of the central star and the conditions in the environment. In this presentation in order to understand the effects of these components we have modeled the evolution of radio luminosity and the expansion of PNe in the framework of different hypothesis on the origin of these objects. In this we have used the observational data on the central stars and clustered this data into gourps with the similar parameters of the central stars. For the each of these groups of PNe we have built statistical dependences radio luminosity - diameter, number of PNe - diameter which are then compared to the modeled ones. Unfortunately, the comparison of simulations with observations did not allow us to choose between the known models of the evolution of the PN shell. However with the increase of statistics the approach considered in this presentation may become more productive.

  9. Analytic scaling function for island-size distributions.

    PubMed

    Dubrovskii, V G; Sibirev, N V

    2015-04-01

    We obtain an explicit solution for the island-size distribution described by the rate equations for irreversible growth with the simplified capture rates of the form σ(s)(Θ)∝Θ(p)(a+s-1) for all s≥1, where s is the size and Θ is the time-dependent coverage. The intrinsic property of this solution is its scaling form in the continuum limit. The analytic scaling function depends on the two parameters a and p and is capable of describing very dissimilar distribution shapes, both monomodal and monotonically decreasing. The obtained results suggest that the scaling features of the size distributions are closely related to the size linearity of the capture rates. A simple analytic scaling is obtained rigorously here and helps to gain a better theoretical understanding of possible origins of the scaling behavior of the island-size distributions. PMID:25974509

  10. Size-Dependent Raman Shifts for nanocrystals

    PubMed Central

    Gao, Yukun; Zhao, Xinmei; Yin, Penggang; Gao, Faming

    2016-01-01

    Raman spectroscopy is a very sensitive tool for probing semiconductor nanocrystals. The underlying mechanism behind the size-dependent Raman shifts is still quite controversial. Here we offer a new theoretical method for the quantum confinement effects on the Raman spectra of semiconductor nanocrystals. We propose that the shift of Raman spectra in nanocrystals can result from two overlapping effects: the quantum effect shift and surface effect shift. The quantum effect shift is extracted from an extended Kubo formula, the surface effect shift is determined via the first principles calculations. Fairly good prediction of Raman shifts can be obtained without the use of any adjustable parameter. Closer analysis shows that the size-dependent Raman shifts in Si nanocrystals mainly result from the quantum effect shifts. For nanodiamond, the proportion of surface effect shift in Raman shift is up to about 40%. Such model can also provide a good baseline for using Raman spectroscopy as a tool to measure size. PMID:27102066

  11. Size-dependent melting of Bi nanoparticles

    NASA Astrophysics Data System (ADS)

    Olson, E. A.; Efremov, M. Yu.; Zhang, M.; Zhang, Z.; Allen, L. H.

    2005-02-01

    Nanocalorimetry was used to investigate the melting of Bi nanoparticles. The particles were formed by evaporating Bi onto a silicon nitride substrate, which was then heated. The particles self-assemble into truncated spherical particles. Below 5-nm average film thickness, mean particle sizes increased linearly with deposition thickness but increased rapidly for 10-nm-thick films. As expected, small particles were found to exhibit size-dependent melting temperatures less than the bulk melting temperature (e.g., ΔT =67K for a 3-nm radius particle). The measured melting temperatures for particles below ˜7nm in radius, however, were ˜50K above the value predicted by the homogeneous melting model. We discuss this discrepancy in terms of a possible size-dependent crystal structure change and the superheating of the solid phase.

  12. Size-Dependent Raman Shifts for nanocrystals.

    PubMed

    Gao, Yukun; Zhao, Xinmei; Yin, Penggang; Gao, Faming

    2016-04-22

    Raman spectroscopy is a very sensitive tool for probing semiconductor nanocrystals. The underlying mechanism behind the size-dependent Raman shifts is still quite controversial. Here we offer a new theoretical method for the quantum confinement effects on the Raman spectra of semiconductor nanocrystals. We propose that the shift of Raman spectra in nanocrystals can result from two overlapping effects: the quantum effect shift and surface effect shift. The quantum effect shift is extracted from an extended Kubo formula, the surface effect shift is determined via the first principles calculations. Fairly good prediction of Raman shifts can be obtained without the use of any adjustable parameter. Closer analysis shows that the size-dependent Raman shifts in Si nanocrystals mainly result from the quantum effect shifts. For nanodiamond, the proportion of surface effect shift in Raman shift is up to about 40%. Such model can also provide a good baseline for using Raman spectroscopy as a tool to measure size.

  13. High frequency variability of particle size distribution and its dependency on turbulence over the sea bottom during re-suspension processes

    NASA Astrophysics Data System (ADS)

    Renosh, P. R.; Schmitt, François G.; Loisel, Hubert; Sentchev, Alexei; Mériaux, Xavier

    2014-04-01

    The impact of tidal current, waves and turbulence on particles re-suspension over the sea bottom is studied through Eulerian high frequency measurements of velocity and particle size distribution (PSD) during 5 tidal cycles (65 h) in a coastal environment of the eastern English Channel. High frequency variability of PSD is observed along with the velocity fluctuations. Power spectral analysis shows that turbulent velocity and PSD parameters have similarities in their spectral behaviour over the whole range of examined temporal scales. The low frequency variability of particles is controlled by turbulence (β≃-5/3) and the high frequency is partly driven by dynamical processes impacted by the sea bottom interactions with turbulence (wall turbulence). Stokes number (St), rarely measured in situ, exhibits very low values, emphasizing that these particles can be considered as passive tracers. The effect of tide and waves on turbidity and PSD is highlighted. During slack tide, when the current reaches its minimum value, we observe a higher proportion of small particles compared to larger ones. To a lower extent, high significant wave heights are also associated with a greater concentration of suspended sediments and the presence of larger particles (larger Sauter's diameter DA, and lower PSD slope ξ).

  14. Size-dependent distribution and inhalation cancer risk of particle-bound polycyclic aromatic hydrocarbons at a typical e-waste recycling and an urban site.

    PubMed

    Luo, Pei; Bao, Lian-Jun; Li, Shao-Meng; Zeng, Eddy Y

    2015-05-01

    Atmospheric particle size distribution of polycyclic aromatic hydrocarbons (PAHs) in a typical e-waste recycling zone and an urban site (Guangzhou) in southern China featured a unimodal peak in 0.56-1.8 μm for 4-6 ring PAHs but no obvious peak for 2-3 ring PAHs at both sites. The atmospheric deposition fluxes of PAHs were estimated at 5.4 ± 2.3 μg m(-2) d(-1) in the e-waste recycling zone and 3.1 ± 0.6 μg m(-2) d(-1) in Guangzhou. In addition, dry and wet deposition fluxes of PAHs were dominated by coarse (Dp > 1.8 μm) and fine particles (Dp < 1.8 μm), respectively. Fine particles predominated the deposition of PAHs in the lung. The results estimated by incremental inhalation cancer risk suggested that particle-bound PAHs posed serious threat to human health within the e-waste recycling zone and Guangzhou.

  15. Particle size distribution instrument. Topical report 13

    SciTech Connect

    Okhuysen, W.; Gassaway, J.D.

    1995-04-01

    The development of an instrument to measure the concentration of particles in gas is described in this report. An in situ instrument was designed and constructed which sizes individual particles and counts the number of occurrences for several size classes. Although this instrument was designed to detect the size distribution of slag and seed particles generated at an experimental coal-fired magnetohydrodynamic power facility, it can be used as a nonintrusive diagnostic tool for other hostile industrial processes involving the formation and growth of particulates. Two of the techniques developed are extensions of the widely used crossed beam velocimeter, providing simultaneous measurement of the size distribution and velocity of articles.

  16. Size-dependent thermopower of nickel nanoparticles

    SciTech Connect

    Singh, Jaiveer; Kaurav, N.; Okram, Gunadhor S.

    2014-04-24

    Nickel nanoparticles (Ni-NPs) were prepared by thermal decomposition method using Trioctylphosphine (TOP) and Oleylamine (OA). The average particle size (D) estimated from X-ray diffraction (XRD) using Scherrer equation, to be 1-10nm, systematically decreases with increasing concentration of TOP at constant OA concentration. The observed thermopower strongly depends on particle size particularly at low temperatures reaching a very high value of ∼ 10{sup 5} μV/K (at 20 K), and is attributed to the enhanced grain-boundary scattering combined with quantum confinement.

  17. Domain Size Distribution in Segregating Binary Superfluids

    NASA Astrophysics Data System (ADS)

    Takeuchi, Hiromitsu

    2016-05-01

    Domain size distribution in phase separating binary Bose-Einstein condensates is studied theoretically by numerically solving the Gross-Pitaevskii equations at zero temperature. We show that the size distribution in the domain patterns arising from the dynamic instability obeys a power law in a scaling regime according to the dynamic scaling analysis based on the percolation theory. The scaling behavior is kept during the relaxation dynamics until the characteristic domain size becomes comparable to the linear size of the system, consistent with the dynamic scaling hypothesis of the phase-ordering kinetics. Our numerical experiments indicate the existence of a different scaling regime in the size distribution function, which can be caused by the so-called coreless vortices.

  18. Analytic modeling of aerosol size distributions

    NASA Technical Reports Server (NTRS)

    Deepack, A.; Box, G. P.

    1979-01-01

    Mathematical functions commonly used for representing aerosol size distributions are studied parametrically. Methods for obtaining best fit estimates of the parameters are described. A catalog of graphical plots depicting the parametric behavior of the functions is presented along with procedures for obtaining analytical representations of size distribution data by visual matching of the data with one of the plots. Examples of fitting the same data with equal accuracy by more than one analytic model are also given.

  19. Size-Dependent Accuracy of Nanoscale Thermometers.

    PubMed

    Alicki, Robert; Leitner, David M

    2015-07-23

    The accuracy of two classes of nanoscale thermometers is estimated in terms of size and system-dependent properties using the spin-boson model. We consider solid state thermometers, where the energy splitting is tuned by thermal properties of the material, and fluorescent organic thermometers, in which the fluorescence intensity depends on the thermal population of conformational states of the thermometer. The results of the theoretical model compare well with the accuracy reported for several nanothermometers that have been used to measure local temperature inside living cells.

  20. Size dependence of non-magnetic thickness in YIG nanoparticles

    NASA Astrophysics Data System (ADS)

    Niyaifar, M.; Mohammadpour, H.; Dorafshani, M.; Hasanpour, A.

    2016-07-01

    This study is focused on particle size dependence of structural and magnetic properties in yttrium iron garnet (Y3Fe5O12) nanoparticles. A series of YIG samples with different particle size were produced by varying the annealing temperatures. The X-ray analysis revealed an inverse correlation between lattice parameter and the crystallite size. The normal distribution is used for fitting the particles size distribution which is extracted from scanning electron micrographs. Also, by using the results of vibrating sample magnetometer, the magnetic diameter was calculated based on Langevin model in order to investigate the variation of dead layer thickness. Furthermore, the observed line broadening in Mössbauer spectra confirmed the increase of non-magnetic thickness due to the reduction of particle size.

  1. Resonance-induced multimodal body-size distributions in ecosystems

    PubMed Central

    Lampert, Adam; Tlusty, Tsvi

    2013-01-01

    The size of an organism reflects its metabolic rate, growth rate, mortality, and other important characteristics; therefore, the distribution of body size is a major determinant of ecosystem structure and function. Body-size distributions often are multimodal, with several peaks of abundant sizes, and previous studies suggest that this is the outcome of niche separation: species from distinct peaks avoid competition by consuming different resources, which results in selection of different sizes in each niche. However, this cannot explain many ecosystems with several peaks competing over the same niche. Here, we suggest an alternative, generic mechanism underlying multimodal size distributions, by showing that the size-dependent tradeoff between reproduction and resource utilization entails an inherent resonance that may induce multiple peaks, all competing over the same niche. Our theory is well fitted to empirical data in various ecosystems, in which both model and measurements show a multimodal, periodically peaked distribution at larger sizes, followed by a smooth tail at smaller sizes. Moreover, we show a universal pattern of size distributions, manifested in the collapse of data from ecosystems of different scales: phytoplankton in a lake, metazoans in a stream, and arthropods in forests. The demonstrated resonance mechanism is generic, suggesting that multimodal distributions of numerous ecological characters emerge from the interplay between local competition and global migration. PMID:23248320

  2. Population size, distribution and growth in Iran.

    PubMed

    Kamiar, M

    1985-01-01

    The author examines population size, distribution, and growth in Iran using data for 1966, 1976 census data, and some historical data for the nineteenth century. "This paper discusses changes in the size of population through time, population distribution, and regional patterns of population growth of the 23 provinces. It has been argued in this paper that because of a large family size norm as a religious duty to increase the numbers of the Islamic faith, early age at marriage, especially among females, common practice of polygamy, and the war with Iraq, population will grow even faster. It is concluded that population policy must be integrated into the national development plans."

  3. Particle Size Distributions in Atmospheric Clouds

    NASA Technical Reports Server (NTRS)

    Paoli, Roberto; Shariff, Karim

    2003-01-01

    In this note, we derive a transport equation for a spatially integrated distribution function of particles size that is suitable for sparse particle systems, such as in atmospheric clouds. This is done by integrating a Boltzmann equation for a (local) distribution function over an arbitrary but finite volume. A methodology for evolving the moments of the integrated distribution is presented. These moments can be either tracked for a finite number of discrete populations ('clusters') or treated as continuum variables.

  4. Size distributions of chemically synthesized Ag nanocrystals

    NASA Astrophysics Data System (ADS)

    Thøgersen, Annett; Bonsak, Jack; Fosli, Carl Huseby; Muntingh, Georg

    2011-08-01

    Silver nanocrystals made by a chemical reduction of silver salts (AgNO3) by sodium borohydride (NaBH4) were studied using transmission electron microscopy and light scattering simulations. For various AgNO3/NaBH4 molar ratios, the size distributions of the nanocrystals were found to be approximately log-normal. In addition, a linear relation was found between the mean nanocrystal size and the molar ratio. In order to relate the size distribution of Ag nanocrystals of the various molar ratios to the scattering properties of Ag nanocrystals in solar cell devices, light scattering simulations of Ag nanocrystals in Si, SiO2, SiN, and Al2O3 matrices were carried out using MiePlot. These light scattering spectra for the individual nanocrystal sizes were combined into light scattering spectra for the fitted size distributions. The evolution of these scattering spectra with respect to an increasing mean nanocrystal size was then studied. From these findings, it is possible to find the molar ratio for which the corresponding nanocrystal size distribution has maximum scattering at a particular wavelength in the desired matrix.

  5. Scale invariance of incident size distributions in response to sizes of their causes.

    PubMed

    Englehardt, James D

    2002-04-01

    Incidents can be defined as low-probability, high-consequence events and lesser events of the same type. Lack of data on extremely large incidents makes it difficult to determine distributions of incident size that reflect such disasters, even though they represent the great majority of total losses. If the form of the incident size distribution can be determined, then predictive Bayesian methods can be used to assess incident risks from limited available information. Moreover, incident size distributions have generally been observed to have scale invariant, or power law, distributions over broad ranges. Scale invariance in the distributions of sizes of outcomes of complex dynamical systems has been explained based on mechanistic models of natural and built systems, such as models of self-organized criticality. In this article, scale invariance is shown to result also as the maximum Shannon entropy distribution of incident sizes arising as the product of arbitrary functions of cause sizes. Entropy is shown by simulation and derivation to be maximized as a result of dependence, diversity, abundance, and entropy of multiplicative cause sizes. The result represents an information-theoretic explanation of invariance, parallel to those of mechanistic models. For example, distributions of incident size resulting from 30 partially dependent causes are shown to be scale invariant over several orders of magnitude. Empirical validation of power law distributions of incident size is reviewed, and the Pareto (power law) distribution is validated against oil spill, hurricane, and insurance data. The applicability of the Pareto distribution, in particular, for assessment of total losses over a planning period is discussed. Results justify the use of an analytical, predictive Bayesian version of the Pareto distribution, derived previously, to assess incident risk from available data.

  6. Clouds of venus: particle size distribution measurements.

    PubMed

    Knollenberg, R G; Hunten, D M

    1979-02-23

    Data from the Pioneer Venus cloud particle size spectrometer experiment has revealed the Venus cloud system to be a complicated mixture of particles of various chemical composition distinguishable by their multimodal size distributions. The appearance, disappearance, growth, and decay of certain size modes has aided the preliminary identification of both sulfuric acid and free sulfur cloud regions. The discovery of large particles > 30 micrometers, significant particle mass loading, and size spectral features suggest that precipitation is likely produced; a peculiar aerosol structure beneath the lowest cloud layer could be residue from a recent shower.

  7. Correlating size and composition-dependent effects with magnetic, Mössbauer, and pair distribution function measurements in a family of catalytically active ferrite nanoparticles

    DOE PAGES

    Wong, Stanislaus; Papaefthymiou, Georgia C.; Lewis, Crystal S.; Han, Jinkyu; Zhang, Cheng; Li, Qiang; Shi, Chenyang; Abeykoon, A. M.Milinda; Billinge, Simon J.L.; Stach, Eric; et al

    2015-05-06

    The magnetic spinel ferrites, MFe₂O₄ (wherein 'M' = a divalent metal ion such as but not limited to Mn, Co, Zn, and Ni), represent a unique class of magnetic materials in which the rational introduction of different 'M's can yield correspondingly unique and interesting magnetic behaviors. Herein we present a generalized hydrothermal method for the synthesis of single-crystalline ferrite nanoparticles with 'M' = Mg, Fe, Co, Ni, Cu, and Zn, respectively, which can be systematically and efficaciously produced simply by changing the metal precursor. Our protocol can moreover lead to reproducible size control by judicious selection of various surfactants. Asmore » such, we have probed the effects of both (i) size and (ii) chemical composition upon the magnetic properties of these nanomaterials using complementary magnetometry and Mössbauer spectroscopy techniques. The structure of the samples was confirmed by atomic PDF analysis of X-ray and electron powder diffraction data as a function of particle size. These materials retain the bulk spinel structure to the smallest size (i.e., 3 nm). In addition, we have explored the catalytic potential of our ferrites as both (a) magnetically recoverable photocatalysts and (b) biological catalysts, and noted that many of our as-prepared ferrite systems evinced intrinsically higher activities as compared with their iron oxide analogues.« less

  8. Correlating size and composition-dependent effects with magnetic, Mössbauer, and pair distribution function measurements in a family of catalytically active ferrite nanoparticles

    SciTech Connect

    Wong, Stanislaus; Papaefthymiou, Georgia C.; Lewis, Crystal S.; Han, Jinkyu; Zhang, Cheng; Li, Qiang; Shi, Chenyang; Abeykoon, A. M.Milinda; Billinge, Simon J.L.; Stach, Eric; Thomas, Justin; Guerrero, Kevin; Munayco, Pablo; Munayco, Jimmy; Scorzelli, Rosa B.; Burnham, Philip; Viescas, Arthur J; Tiano, Amanda L.

    2015-05-06

    The magnetic spinel ferrites, MFe₂O₄ (wherein 'M' = a divalent metal ion such as but not limited to Mn, Co, Zn, and Ni), represent a unique class of magnetic materials in which the rational introduction of different 'M's can yield correspondingly unique and interesting magnetic behaviors. Herein we present a generalized hydrothermal method for the synthesis of single-crystalline ferrite nanoparticles with 'M' = Mg, Fe, Co, Ni, Cu, and Zn, respectively, which can be systematically and efficaciously produced simply by changing the metal precursor. Our protocol can moreover lead to reproducible size control by judicious selection of various surfactants. As such, we have probed the effects of both (i) size and (ii) chemical composition upon the magnetic properties of these nanomaterials using complementary magnetometry and Mössbauer spectroscopy techniques. The structure of the samples was confirmed by atomic PDF analysis of X-ray and electron powder diffraction data as a function of particle size. These materials retain the bulk spinel structure to the smallest size (i.e., 3 nm). In addition, we have explored the catalytic potential of our ferrites as both (a) magnetically recoverable photocatalysts and (b) biological catalysts, and noted that many of our as-prepared ferrite systems evinced intrinsically higher activities as compared with their iron oxide analogues.

  9. Size distributions of quantum islands on stepped substrates.

    PubMed

    Liang, S; Zhu, H L; Wang, W

    2009-10-21

    The size distributions of self-assembled quantum islands on stepped substrates are studied using kinetic Monte Carlo simulations. It is found that the energy barrier E(SW) between the step and the terrace region is the key factor in affecting the size distribution of islands. With small E(SW) (< or = 0.1 eV), lines of uniform islands can be obtained at relative low surface coverage. As the surface coverage is increased, wirelike islands can be obtained. Scaling behavior is obeyed for the size distributions of the wirelike islands. When the size distributions are separated into their width and length components, however, scaling is only observed in the length distribution of the wirelike islands. With larger E(SW), the size distribution of islands shows a clear bimodal size distribution and anomalous growth temperature dependent island size evolutions are observed. The simulation results reproduce qualitatively the phenomena observed in the cases of InAs islands grown on stepped GaAs substrates.

  10. Comparison of drop size distributions from two droplet sizing systems

    NASA Technical Reports Server (NTRS)

    Oldenburg, John R.; Ide, Robert F.

    1990-01-01

    A comparison between the Phase Doppler Particle Analyzer and the combined measurements from Particle Measuring Systems' Forward Scattering Spectrometer Probe and the Optical Array Probe was conducted in an icing wind tunnel using NASA Icing Research Tunnel spray nozzles to produce the supercooled water droplet cloud. Clouds having a range of volume median diameters from 10 to greater than 50 microns were used for the instrument comparisons. A volume median diameter was calculated from combining the droplet distributions of the Optical Array Probe and the Forward Scattering Spectrometer Probe. A comparison of the combined volume median diameters and the Phase Doppler Particle Analyzer volume median diameters showed agreement from 10 microns up to 30 microns. Typical drop size distributions from the Phase Doppler Particle Analyzer, the Forward Scattering Spectrometer Probe, and Optical Array Probe are presented for several median volume diameters. A comparison of the distributions illustrates regions of the distributions where there is good agreement and other regions where there are discrepancies between the Phase Doppler Particle Analyzer and the Particle Measuring Systems' droplet size instruments.

  11. Particle size dependent response of aerosol counters

    NASA Astrophysics Data System (ADS)

    Ankilov, A.; Baklanov, A.; Colhoun, M.; Enderle, K.-H.; Gras, J.; Julanov, Yu.; Kaller, D.; Lindner, A.; Lushnikov, A. A.; Mavliev, R.; McGovern, F.; O'Connor, T. C.; Podzimek, J.; Preining, O.; Reischl, G. P.; Rudolf, R.; Sem, G. J.; Szymanski, W. W.; Vrtala, A. E.; Wagner, P. E.; Winklmayr, W.; Zagaynov, V.

    During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions. The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles.

  12. The size-distribution of Earth's lakes.

    PubMed

    Cael, B B; Seekell, D A

    2016-01-01

    Globally, there are millions of small lakes, but a small number of large lakes. Most key ecosystem patterns and processes scale with lake size, thus this asymmetry between area and abundance is a fundamental constraint on broad-scale patterns in lake ecology. Nonetheless, descriptions of lake size-distributions are scarce and empirical distributions are rarely evaluated relative to theoretical predictions. Here we develop expectations for Earth's lake area-distribution based on percolation theory and evaluate these expectations with data from a global lake census. Lake surface areas ≥8.5 km(2) are power-law distributed with a tail exponent (τ = 1.97) and fractal dimension (d = 1.38), similar to theoretical expectations (τ = 2.05; d = 4/3). Lakes <8.5 km(2) are not power-law distributed. An independently developed regional lake census exhibits a similar transition and consistency with theoretical predictions. Small lakes deviate from the power-law distribution because smaller lakes are more susceptible to dynamical change and topographic behavior at sub-kilometer scales is not self-similar. Our results provide a robust characterization and theoretical explanation for the lake size-abundance relationship, and form a fundamental basis for understanding and predicting patterns in lake ecology at broad scales. PMID:27388607

  13. Acoustical concept for measuring particle size distributions

    SciTech Connect

    Mahler, D.S.; Kaufman, M.

    1981-02-01

    A new concept is investigated for measuring particle size and distribution for air pollution control applications. This study illustrates that the proposed device--the Acoustic Particulate Monitor (APM)--can measure total mass loading, mean particle diameter, and width of particle size distributions on an in-situ basis. The concept for such an instrument is based upon experimental and theoretical observations that the presence of dust in air causes a reduction in the speed of sound as a function of the transmitted frequency. These percentage reductions in the speed of sound are small and the research results illustrate how the accompanying shift in the acoustical phase is a highly sensitive method for detecting such effects. The magnitudes of the phase shift are related to mass loading. The frequency associated with the maximum phase shift is defined as the acoustic frequency, fA. Experimentally determining fA provides a measure of the mean particle size of the distribution. The detailed shape of the phase shift as a function of frequency is a measure of the spread in the size distribution of the entrained particulate. Experiments were performed using several configurations. Results were verified using direct mass measurements and microphotographs.

  14. PARTICLE SIZE DISTRIBUTIONS FOR AN OFFICE AEROSOL

    EPA Science Inventory

    The article discusses an evaluation of the effect of percent outdoor air supplied and occupation level on the particle size distributions and mass concentrations for a typical office building. (NOTE: As attention has become focused on indoor air pollution control, it has become i...

  15. SELF-CONSISTENT SIZE AND VELOCITY DISTRIBUTIONS OF COLLISIONAL CASCADES

    SciTech Connect

    Pan, Margaret; Schlichting, Hilke E. E-mail: hilke@ucla.edu

    2012-03-10

    The standard theoretical treatment of collisional cascades derives a steady-state size distribution assuming a single constant velocity dispersion for all bodies regardless of size. Here we relax this assumption and solve self-consistently for the bodies' steady-state size and size-dependent velocity distributions. Specifically, we account for viscous stirring, dynamical friction, and collisional damping of the bodies' random velocities in addition to the mass conservation requirement typically applied to find the size distribution in a steady-state cascade. The resulting size distributions are significantly steeper than those derived without velocity evolution. For example, accounting self-consistently for the velocities can change the standard q = 3.5 power-law index of the Dohnanyi differential size spectrum to an index as large as q = 4. Similarly, for bodies held together by their own gravity, the corresponding power-law index range 2.88 < q < 3.14 of Pan and Sari can steepen to values as large as q = 3.26. Our velocity results allow quantitative predictions of the bodies' scale heights as a function of size. Together with our predictions, observations of the scale heights for different-sized bodies for the Kuiper belt, the asteroid belt, and extrasolar debris disks may constrain the mass and number of large bodies stirring the cascade as well as the colliding bodies' internal strengths.

  16. Raindrop Size Distribution Measurements in Tropical Cyclones

    NASA Technical Reports Server (NTRS)

    Tokay, Ali; Bashor, Paul G.; Habib, Emad; Kasparis, Takis

    2008-01-01

    Characteristics of the raindrop size distribution in seven tropical cyclones have been studied through impact-type disdrometer measurements at three different sites during the 2004-06 Atlantic hurricane seasons. One of the cyclones has been observed at two different sites. High concentrations of small and/or midsize drops were observed in the presence or absence of large drops. Even in the presence of large drops, the maximum drop diameter rarely exceeded 4 mm. These characteristics of raindrop size distribution were observed in all stages of tropical cyclones, unless the storm was in the extratropical stage where the tropical cyclone and a midlatitude frontal system had merged. The presence of relatively high concentrations of large drops in extratropical cyclones resembled the size distribution in continental thunderstorms. The integral rain parameters of drop concentration, liquid water content, and rain rate at fixed reflectivity were therefore lower in extratropical cyclones than in tropical cyclones. In tropical cyclones, at a disdrometercalculated reflectivity of 40 dBZ, the number concentration was 700 plus or minus 100 drops m(sup -3), while the liquid water content and rain rate were 0.90 plus or minus 0.05 g m(sup -3) and 18.5 plus or minus 0.5 mm h(sup -1), respectively. The mean mass diameter, on the other hand, was 1.67 plus or minus 0.3 mm. The comparison of raindrop size distributions between Atlantic tropical cyclones and storms that occurred in the central tropical Pacific island of Roi-Namur revealed that the number density is slightly shifted toward smaller drops, resulting in higher-integral rain parameters and lower mean mass and maximum drop diameters at the latter site. Considering parameterization of the raindrop size distribution in tropical cyclones, characteristics of the normalized gamma distribution parameters were examined with respect to reflectivity. The mean mass diameter increased rapidly with reflectivity, while the normalized

  17. Size from Specular Highlights for Analyzing Droplet Size Distributions

    NASA Astrophysics Data System (ADS)

    Jalba, Andrei C.; Westenberg, Michel A.; Grooten, Mart H. M.

    In mechanical engineering, heat-transfer models by dropwise condensation are under development. The condensation process is captured by taking many pictures, which show the formation of droplets, of which the size distribution and area coverage are of interest for model improvement. The current analysis method relies on manual measurements, which is time consuming. In this paper, we propose an approach to automatically extract the positions and radii of the droplets from an image. Our method relies on specular highlights that are visible on the surfaces of the droplets. We show that these highlights can be reliably extracted, and that they provide sufficient information to infer the droplet size. The results obtained by our method compare favorably with those obtained by laborious and careful manual measurements. The processing time per image is reduced by two orders of magnitude.

  18. Dependence of sandpile avalanche frequency-size distribution on coverage extent and compactness of embedded toppling threshold heterogeneity: implications for the variation of Gutenberg-Richter b value

    NASA Astrophysics Data System (ADS)

    Chiao, L.-Y.; Liu, Q.

    2014-12-01

    The effects of the spatiotemporal evolution of failure threshold heterogeneity on the dynamics of fault criticality, and thus on regional seismogenesis, have attracted strong interest in the field of regional seismotectonics. The heterogeneity might be a manifestation of the macroscopic distribution and multiscale strength variation of asperities, the distinct regional stress level, and (microscopically) heterogeneous fault surface roughness or friction regimes. In this study, rather than attempting to mimic the complex microscale slipping physics on a fault surface, sandpile cellular automata were implemented with a straightforward toppling rule. The objective is to examine the influence of distinct configurations of the embedded heterogeneous toppling threshold field on the global system avalanche event statistics. The examination results revealed that increasing the coverage extent and decreasing the compactness of the heterogeneous failure threshold, rather than the magnitude, range of contrast, diversity, or the geometric configuration of the threshold heterogeneity, leads to a systematic increase in the scaling exponent of the avalanche event power law statistics, implying the importance of mutual interaction among toppling sites with distinct thresholds. For tectonic provinces with differing stress regimes evolving spatio temporally, it is postulated that the distinct extent and compactness of the heterogeneous failure threshold are critical factors that manifest in the reported dynamic variations of seismicity scaling.

  19. Theory of Nanocluster Size Distributions from Ion Beam Synthesis

    SciTech Connect

    Yuan, C.W.; Yi, D.O.; Sharp, I.D.; Shin, S.J.; Liao, C.Y.; Guzman, J.; Ager III, J.W.; Haller, E.E.; Chrzan, D.C.

    2008-06-13

    Ion beam synthesis of nanoclusters is studied via both kinetic Monte Carlo simulations and the self-consistent mean-field solution to a set of coupled rate equations. Both approaches predict the existence of a steady state shape for the cluster size distribution that depends only on a characteristic length determined by the ratio of the effective diffusion coefficient to the ion flux. The average cluster size in the steady state regime is determined by the implanted species/matrix interface energy.

  20. Size distributions of submicrometer aerosols from cooking

    SciTech Connect

    Li, C.S.; Lin, W.H.; Jeng, F.T. )

    1993-01-01

    Although gas stove usage varies from country to country, it is still one of the major indoor combustion sources. In order to assess the health effects of using gas stoves, the physical characteristics of the particle emissions from cooking were conducted in a first-floor apartment in the Taipei area. The particle size distributions from scrambling eggs, frying chicken, and cooking soup were measured in the kitchen by a high resolution particle sizer, which could measure the particles in the size range of 0.01 [mu]m to 1 [mu]m. The concentrations of the submicrometer particles increased significantly from 15,000 cm[sup [minus]3] to 150,000 cm[sup [minus]3] during cooking. Additionally, the ultrafine particles constituted 60%--70% of the total submicron aerosols. The changes in the size distributions and the concentrations of the submicrometer aerosols before, during, and after the aerosol generations were compared. On the average, the median diameters of scrambling eggs, frying chicken, cooking soup, and of the background conditions were 40 nm, 50 nm, 30 nm, and 70 nm, respectively. Regarding the surface area-weighted size distributions, the surface median diameters of the four situations were 180 nm, 300 nm, 150 nm, and 220 nm, respectively. Furthermore, the volume median diameters in the conditions mentioned above were almost similar, namely 300--350 nm. 10 refs., 6 figs., 2 tabs.

  1. The size distribution of 'gold standard' nanoparticles.

    PubMed

    Bienert, Ralf; Emmerling, Franziska; Thünemann, Andreas F

    2009-11-01

    The spherical gold nanoparticle reference materials RM 8011, RM 8012, and RM 8013, with a nominal radius of 5, 15, and 30 nm, respectively, have been available since 2008 from NIST. These materials are recommended as standards for nanoparticle size measurements and for the study of the biological effects of nanoparticles, e.g., in pre-clinical biomedical research. We report on determination of the size distributions of these gold nanoparticles using different small-angle X-ray scattering (SAXS) instruments. Measurements with a classical Kratky type SAXS instrument are compared with a synchrotron SAXS technique. Samples were investigated in situ, positioned in capillaries and in levitated droplets. The number-weighted size distributions were determined applying model scattering functions based on (a) Gaussian, (b) log-normal, and (c) Schulz distributions. The mean radii are 4.36 +/- 0.04 nm (RM 8011), 12.20 +/- 0.03 nm (RM 8012), and 25.74 +/- 0.27 nm (RM 8013). Low polydispersities, defined as relative width of the distributions, were detected with values of 0.067 +/- 0.006 (RM 8011), 0.103 +/- 0.003, (RM 8012), and 0.10 +/- 0.01 (RM 8013). The results are in agreement with integral values determined from classical evaluation procedures, such as the radius of gyration (Guinier) and particle volume (Kratky). No indications of particle aggregation and particle interactions--repulsive or attractive--were found. We recommend SAXS as a standard method for a fast and precise determination of size distributions of nanoparticles.

  2. Company size distribution in different countries

    NASA Astrophysics Data System (ADS)

    Ramsden, J. J.; Kiss-Haypál, Gy.

    2000-03-01

    The distribution of companies in a country, ranked in order of size (annual net revenue) s, follows the simplified canonical law s r∼(r+ρ) -1/θ remarkably well, where r is the rank, and θ and ρ are the parameters of the distribution. These parameters have been determined for 20 countries in America, Asia and Europe. Significant differences between countries are found. Neither θ nor ρ appears to correlate well with traditional economic indicators; indeed some countries often thought to be economically and politically, but not necessarily socially, similar show surprising differences, suggesting that wealth and prosperity are influenced by hidden layers hitherto inaccessible through standard economic theory.

  3. Particle size distribution and particle size-related crystalline silica content in granite quarry dust.

    PubMed

    Sirianni, Greg; Hosgood, Howard Dean; Slade, Martin D; Borak, Jonathan

    2008-05-01

    Previous studies indicate that the relationship between empirically derived particle counts, particle mass determinations, and particle size-related silica content are not constant within mines or across mine work tasks. To better understand the variability of particle size distributions and variations in silica content by particle size in a granite quarry, exposure surveys were conducted with side-by-side arrays of four closed face cassettes, four cyclones, four personal environmental monitors, and a real-time particle counter. In general, the proportion of silica increased as collected particulate size increased, but samples varied in an inconstant way. Significant differences in particle size distributions were seen depending on the extent of ventilation and the nature and activity of work performed. Such variability raises concerns about the adequacy of silica exposure assessments based on only limited numbers of samples or short-term samples.

  4. Average size and size distribution of large droplets produced in a free-jet expansion of a liquid

    NASA Astrophysics Data System (ADS)

    Knuth, E. L.; Henne, U.

    1999-02-01

    The experimental parameters and fluid properties affecting the average size N¯ and the size distribution P(N) of droplets formed by fragmentation of a liquid after expansion into a vacuum are investigated. The mean droplet size is found to be a function of the surface tension of the liquid, the nozzle diameter, and a characteristic flow speed. The size distribution is found to be a linear exponential distribution; measurements deviate from this distribution at small sizes if a factor which is a function of the cluster size is included in the measuring process. Good agreement with measured distributions of both positive and negative droplet ions formed from neutral 4He droplets by electron impact is found. The strong dependence of mean droplet size on source-orifice diameter found in the present analysis indicates that earlier correlations of droplet size with specific entropy in the source were useful at best only for a fixed nozzle size.

  5. Remote Laser Diffraction Particle Size Distribution Analyzer

    SciTech Connect

    Batcheller, Thomas Aquinas; Huestis, Gary Michael; Bolton, Steven Michael

    2001-03-01

    In support of a radioactive slurry sampling and physical characterization task, an “off-the-shelf” laser diffraction (classical light scattering) particle size analyzer was utilized for remote particle size distribution (PSD) analysis. Spent nuclear fuel was previously reprocessed at the Idaho Nuclear Technology and Engineering Center (INTEC—formerly recognized as the Idaho Chemical Processing Plant) which is on DOE’s INEEL site. The acidic, radioactive aqueous raffinate streams from these processes were transferred to 300,000 gallon stainless steel storage vessels located in the INTEC Tank Farm area. Due to the transfer piping configuration in these vessels, complete removal of the liquid can not be achieved. Consequently, a “heel” slurry remains at the bottom of an “emptied” vessel. Particle size distribution characterization of the settled solids in this remaining heel slurry, as well as suspended solids in the tank liquid, is the goal of this remote PSD analyzer task. A Horiba Instruments Inc. Model LA-300 PSD analyzer, which has a 0.1 to 600 micron measurement range, was modified for remote application in a “hot cell” (gamma radiation) environment. This technology provides rapid and simple PSD analysis, especially down in the fine and microscopic particle size regime. Particle size analysis of these radioactive slurries down in this smaller range was not previously achievable—making this technology far superior than the traditional methods used. Successful acquisition of this data, in conjunction with other characterization analyses, provides important information that can be used in the myriad of potential radioactive waste management alternatives.

  6. Particle size distributions and the vertical distribution of suspended matter in the upwelling region off Oregon

    NASA Technical Reports Server (NTRS)

    Kitchen, J. C.

    1977-01-01

    Various methods of presenting and mathematically describing particle size distribution are explained and evaluated. The hyperbolic distribution is found to be the most practical but the more complex characteristic vector analysis is the most sensitive to changes in the shape of the particle size distributions. A method for determining onshore-offshore flow patterns from the distribution of particulates was presented. A numerical model of the vertical structure of two size classes of particles was developed. The results show a close similarity to the observed distributions but overestimate the particle concentration by forty percent. This was attributed to ignoring grazing by zooplankton. Sensivity analyses showed the size preference was most responsive to the maximum specific growth rates and nutrient half saturation constants. The verical structure was highly dependent on the eddy diffusivity followed closely by the growth terms.

  7. Particle size distribution of indoor aerosol sources

    SciTech Connect

    Shah, K.B.

    1990-10-24

    As concern about Indoor Air Quality (IAQ) has grown in recent years, it has become necessary to determine the nature of particles produced by different indoor aerosol sources and the typical concentration that these sources tend to produce. These data are important in predicting the dose of particles to people exposed to these sources and it will also enable us to take effective mitigation procedures. Further, it will also help in designing appropriate air cleaners. A new state of the art technique, DMPS (Differential Mobility Particle Sizer) System is used to determine the particle size distributions of a number of sources. This system employs the electrical mobility characteristics of these particles and is very effective in the 0.01--1.0 {mu}m size range. A modified system that can measure particle sizes in the lower size range down to 3 nm was also used. Experimental results for various aerosol sources is presented in the ensuing chapters. 37 refs., 20 figs., 2 tabs.

  8. Measurement of nonvolatile particle number size distribution

    NASA Astrophysics Data System (ADS)

    Gkatzelis, G. I.; Papanastasiou, D. K.; Florou, K.; Kaltsonoudis, C.; Louvaris, E.; Pandis, S. N.

    2016-01-01

    An experimental methodology was developed to measure the nonvolatile particle number concentration using a thermodenuder (TD). The TD was coupled with a high-resolution time-of-flight aerosol mass spectrometer, measuring the chemical composition and mass size distribution of the submicrometer aerosol and a scanning mobility particle sizer (SMPS) that provided the number size distribution of the aerosol in the range from 10 to 500 nm. The method was evaluated with a set of smog chamber experiments and achieved almost complete evaporation (> 98 %) of secondary organic as well as freshly nucleated particles, using a TD temperature of 400 °C and a centerline residence time of 15 s. This experimental approach was applied in a winter field campaign in Athens and provided a direct measurement of number concentration and size distribution for particles emitted from major pollution sources. During periods in which the contribution of biomass burning sources was dominant, more than 80 % of particle number concentration remained after passing through the thermodenuder, suggesting that nearly all biomass burning particles had a nonvolatile core. These remaining particles consisted mostly of black carbon (60 % mass contribution) and organic aerosol (OA; 40 %). Organics that had not evaporated through the TD were mostly biomass burning OA (BBOA) and oxygenated OA (OOA) as determined from AMS source apportionment analysis. For periods during which traffic contribution was dominant 50-60 % of the particles had a nonvolatile core while the rest evaporated at 400 °C. The remaining particle mass consisted mostly of black carbon with an 80 % contribution, while OA was responsible for another 15-20 %. Organics were mostly hydrocarbon-like OA (HOA) and OOA. These results suggest that even at 400 °C some fraction of the OA does not evaporate from particles emitted from common combustion processes, such as biomass burning and car engines, indicating that a fraction of this type of OA

  9. Particle Size Distribution in Aluminum Manufacturing Facilities

    PubMed Central

    Liu, Sa; Noth, Elizabeth M.; Dixon-Ernst, Christine; Eisen, Ellen A.; Cullen, Mark R.; Hammond, S. Katharine

    2015-01-01

    As part of exposure assessment for an ongoing epidemiologic study of heart disease and fine particle exposures in aluminum industry, area particle samples were collected in production facilities to assess instrument reliability and particle size distribution at different process areas. Personal modular impactors (PMI) and Minimicro-orifice uniform deposition impactors (MiniMOUDI) were used. The coefficient of variation (CV) of co-located samples was used to evaluate the reproducibility of the samplers. PM2.5 measured by PMI was compared to PM2.5 calculated from MiniMOUDI data. Mass median aerodynamic diameter (MMAD) and concentrations of sub-micrometer (PM1.0) and quasi-ultrafine (PM0.56) particles were evaluated to characterize particle size distribution. Most of CVs were less than 30%. The slope of the linear regression of PMI_PM2.5 versus MiniMOUDI_PM2.5 was 1.03 mg/m3 per mg/m3 (± 0.05), with correlation coefficient of 0.97 (± 0.01). Particle size distribution varied substantively in smelters, whereas it was less variable in fabrication units with significantly smaller MMADs (arithmetic mean of MMADs: 2.59 μm in smelters vs. 1.31 μm in fabrication units, p = 0.001). Although the total particle concentration was more than two times higher in the smelters than in the fabrication units, the fraction of PM10 which was PM1.0 or PM0.56 was significantly lower in the smelters than in the fabrication units (p < 0.001). Consequently, the concentrations of sub-micrometer and quasi-ultrafine particles were similar in these two types of facilities. It would appear, studies evaluating ultrafine particle exposure in aluminum industry should focus on not only the smelters, but also the fabrication facilities. PMID:26478760

  10. Charge and Size Distributions of Electrospray Drops

    PubMed

    de Juan L; de la Mora JF

    1997-02-15

    The distributions of charge q and diameter d of drops emitted from electrified liquid cones in the cone-jet mode are investigated with two aerosol instruments. A differential mobility analyzer (DMA, Vienna type) first samples the spray drops, selects those with electrical mobilities within a narrow band, and either measures the associated current or passes them to a second instrument. The drops may also be individually counted optically and sized by sampling them into an aerodynamic size spectrometer (API's Aerosizer). For a given cone-jet, the distribution of charge q for the main electrospray drops is some 2.5 times broader than their distribution of diameters d, with qmax/qmin approximately 4. But mobility-selected drops have relative standard deviations of only 5% for both d and q, showing that the support of the (q, d) distribution is a narrow band centered around a curve q(d). The approximate one-dimensionality of this support region is explained through the mechanism of jet breakup, which is a random process with only one degree of freedom: the wavelength of axial modulation of the jet. The observed near constancy of the charge over volume ratio (q approximately d3) shows that the charge is frozen in the liquid surface at the time scale of the breakup process. The charge over volume ratio of the primary drops varies between 98 and 55% of the ratio of spray current I over liquid flow rate Q, and decreases at increasing Q. I/Q is therefore an unreliable measure of the charge density of these drops.

  11. Dense medium radiative transfer theory for two scattering layers with a Rayleigh distribution of particle sizes

    SciTech Connect

    West, R.; Tsang, Leung; Winebrenner, D.P. )

    1993-03-01

    Dense medium radiative transfer theory is applied to a three-layer model consisting of two scattering layers overlying a homogeneous half space with a size distribution of particles in each layer. A model with a distribution of sizes gives quite different results than those obtained from a model with a single size. The size distribution is especially important in the low frequency limit when scattering is strongly dependent on particle size. The size distribution and absorption characteristics also affect the extinction behavior as a function of fractional volume. Theoretical results are also compared with experimental data. The sizes, permittivities, and densities used in the numerical illustrations are typical values for snow.

  12. Packing fraction of particles with a Weibull size distribution.

    PubMed

    Brouwers, H J H

    2016-07-01

    This paper addresses the void fraction of polydisperse particles with a Weibull (or Rosin-Rammler) size distribution. It is demonstrated that the governing parameters of this distribution can be uniquely related to those of the lognormal distribution. Hence, an existing closed-form expression that predicts the void fraction of particles with a lognormal size distribution can be transformed into an expression for Weibull distributions. Both expressions contain the contraction coefficient β. Likewise the monosized void fraction φ_{1}, it is a physical parameter which depends on the particles' shape and their state of compaction only. Based on a consideration of the scaled binary void contraction, a linear relation for (1-φ_{1})β as function of φ_{1} is proposed, with proportionality constant B, depending on the state of compaction only. This is validated using computational and experimental packing data concerning random close and random loose packing arrangements. Finally, using this β, the closed-form analytical expression governing the void fraction of Weibull distributions is thoroughly compared with empirical data reported in the literature, and good agreement is found. Furthermore, the present analysis yields an algebraic equation relating the void fraction of monosized particles at different compaction states. This expression appears to be in good agreement with a broad collection of random close and random loose packing data. PMID:27575204

  13. Packing fraction of particles with a Weibull size distribution

    NASA Astrophysics Data System (ADS)

    Brouwers, H. J. H.

    2016-07-01

    This paper addresses the void fraction of polydisperse particles with a Weibull (or Rosin-Rammler) size distribution. It is demonstrated that the governing parameters of this distribution can be uniquely related to those of the lognormal distribution. Hence, an existing closed-form expression that predicts the void fraction of particles with a lognormal size distribution can be transformed into an expression for Weibull distributions. Both expressions contain the contraction coefficient β. Likewise the monosized void fraction φ1, it is a physical parameter which depends on the particles' shape and their state of compaction only. Based on a consideration of the scaled binary void contraction, a linear relation for (1 - φ1)β as function of φ1 is proposed, with proportionality constant B, depending on the state of compaction only. This is validated using computational and experimental packing data concerning random close and random loose packing arrangements. Finally, using this β, the closed-form analytical expression governing the void fraction of Weibull distributions is thoroughly compared with empirical data reported in the literature, and good agreement is found. Furthermore, the present analysis yields an algebraic equation relating the void fraction of monosized particles at different compaction states. This expression appears to be in good agreement with a broad collection of random close and random loose packing data.

  14. Optical Sizing of Ultrafine Metallic Particles: Retrieval of Particle Size Distribution from Spectral Extinction Measurements.

    PubMed

    Oshchepkov; Sinyuk

    1998-12-01

    The inverse problem of optical sizing of ultrafine metallic particles from the spectral extinction measurements in the visible range is investigated. Solving the inverse problem becomes possible due to the strong size effect which in the framework of classical electrodynamics can be described by the dependence of complex refractive index on the particle size. It is shown that the size effect leads to the considerable increase of information content of spectral extinction data with respect to desired size composition of the particles. This makes it possible to retrieve the size distribution of ultrafine metallic particles with reasonably high accuracy, including the Rayleigh size region. The analysis is performed mainly within the framework of numerical tests by the typical example of ultrafine silver particles in a gelatin matrix. The results in retrieving of size distribution from experimentally measured extinction spectra are also presented. Calculations of spectral extinction coefficient are made by means of Mie theory. In so doing, the dielectric function of particles is modified by using the electron's mean free path limitation model. Copyright 1998 Academic Press.

  15. Nanocatalysis: size- and shape-dependent chemisorption and catalytic reactivity

    NASA Astrophysics Data System (ADS)

    Roldan Cuenya, Beatriz; Behafarid, Farzad

    2015-06-01

    In recent years, the field of catalysis has experienced an astonishing transformation, driven in part by more demanding environmental standards and critical societal and industrial needs such as the search for alternative energy sources. Thanks to the advent of nanotechnology, major steps have been made towards the rational design of novel catalysts. Striking new catalytic properties, including greatly enhanced reactivities and selectivities, have been reported for nanoparticle (NP) catalysts as compared to their bulk counterparts. However, in order to harness the power of these nanocatalysts, a detailed understanding of the origin of their enhanced performance is needed. The present review focuses on the role of the NP size and shape on chemisorption and catalytic performance. Since homogeneity in NP size and shape is a prerequisite for the understanding of structure-reactivity correlations, we first review different synthesis methods that result in narrow NP size distributions and shape controlled NPs. Next, size-dependent phenomena which influence the chemical reactivity of NPs, including quantum size-effects and the presence of under-coordinated surface atoms are examined. The effect of the NP shape on catalytic performance is discussed and explained based on the existence of different atomic structures on the NP surface with distinct chemisorption properties. The influence of additional factors, such as the oxidation state of the NPs and NP-support interactions, is also considered in the frame of the size- and shape-dependency that these phenomena present. Ultimately, our review highlights the importance of achieving a systematic understanding of the factors that control the activity and selectivity of a catalyst in order to avoid trial and error methods in the rational design of the new generation of nanocatalysts with properties tunable at the atomic level.

  16. Theory of Nanocluster Size Distributions from Ion Beam Synthesis

    SciTech Connect

    Yuan, C. W.; Yi, D. O.; Shin, S. J.; Liao, C. Y.; Guzman, J.; Haller, E. E.; Chrzan, D. C.; Sharp, I. D.; Ager, J. W. III

    2009-04-10

    Ion beam synthesis of nanoclusters is studied via both kinetic Monte Carlo simulations and the self-consistent mean-field solution to a set of coupled rate equations. Both approaches predict the existence of a steady-state shape for the cluster-size distribution that depends only on a characteristic length determined by the effective diffusion coefficient, the ion solubility, and the volumetric ion flux. The average cluster size in the steady-state regime is determined by the implanted species or matrix interface energy.

  17. Aggregate size distribution of the soil loss

    NASA Astrophysics Data System (ADS)

    Szabó, Judit Alexandra; Jakab, Gergely; Szabó, Boglárka; Józsa, Sándor; Szalai, Zoltán; Centeri, Csaba

    2016-04-01

    aggregate size distribution which is led to nutrient and organic matter redistribution is one of a key questions to improve erosion estimation. G. Jakab was supported by the János Bolyai fellowship of the HAS.

  18. Size dependent polaronic conduction in hematite

    NASA Astrophysics Data System (ADS)

    Sharma, Monika; Banday, Azeem; Murugavel, Sevi

    2016-05-01

    Lithium Ion Batteries have been attracted as the major renewable energy source for all portable electronic devices because of its advantages like superior energy density, high theoretical capacity, high specific energy, stable cycling and less memory effects. Recently, α-Fe2O3 has been considered as a potential anode material due to high specific capacity, low cost, high abundance and environmental benignity. We have synthesized α-Fe2O3 with various sizes by using the ball milling and sol-gel procedure. Here, we report the dc conductivity measurement for the crystallite size ranging from 15 nm to 50nm. It has been observed that the enhancement in the polaronic conductivity nearly two orders in magnitude while reducing the crystallite size from bulk into nano scale level. The enhancement in the conductivity is due to the augmented to compressive strain developed in the material which leads to pronounced decrease in the hopping length of polarons. Thus, nanocrystaline α-Fe2O3 may be a better alternative anode material for lithium ion batteries than earlier reported systems.

  19. Particle Size Distribution in Saturn’s Ring C

    NASA Astrophysics Data System (ADS)

    Marouf, Essam A.; Wong, K.; French, R.; Rappaport, N.

    2012-10-01

    Information about particle sizes in Saturn’s rings is provided by two complementary types of Cassini radio occultation measurements. The first is differential extinction of three coherent sinusoidal signals transmitted by Cassini through the rings back to Earth (wavelength = 0.94, 3.6, and 13 cm, respectively). The differential measurements strongly constraint three parameters of an assumed power-law size distribution n(a) = n0 (a/a0)q, amin ≤ a ≤ amax: namely, the power law index q, the minimum radius amin, and reference abundance n0 at reference radius a0. The differential measurements are particularly sensitive to radii in the range 0.1 mm < a < 1 m. Complementing this capability, is a second type of measurements that is particularly sensitive to the larger radii 1 m < a < 20 m and their abundance. Signature of the collective near-forward scattering by these particles is captured in power spectrum measurements as broadened component of width, shape, and strength that depend on ring particle sizes, their spatial distribution, and observation geometry. Contributions of ring features of width as small several hundred kilometers can be identified and isolated in the measured spectra for a small subset of Cassini orbits of favorable geometry. We use three inverse scattering algorithms (Bayes, constrained linear inversion, generalized singular-value-decomposition) to recover the size distribution of particles of resolved ring features over the size range 1 m < a < 20 m without assuming an explicit size distribution model. We also investigate consistency of the results with a single power-law model extending over 0.1 mm < a < 20 m and implications to the spatial distribution of ring particles normal to the ring plane (vertical ring thickness). We present example results for selected features across Saturn’s Ring C where little evidence for gravitational wakes is present, hence the approaches above are applicable.

  20. Pore-size distributions of N-isopropylacrylamide (NIPA) hydrogels

    SciTech Connect

    Walther, D.H.; Blanch, H.W.; Prausnitz, J.M. |

    1993-11-01

    Pore-size distributions have been measured for N-isopropylacrylamide (NIPA) hydrogels at 25 and 32{degrees}C with swelling capacities 11.3 and 6.0 g swollen gel per g dry gel. The mixed-solute-exclusion method (introduced by Kuga) was used to obtain the experimental solute-exclusion curve which represents the amount of imbibed liquid inside the gel inaccessible for a solute of radius r. The pore-size distributions were obtained by using Casassa`s Brownian-motion model and numerically solving the Fredholm integral equation. The pore-size distributions of temperature-sensitive NIPA hydrogels are strongly dependent on temperature which determines swelling capacity. With increasing swelling capacity (from 6.0 to 11.3), the pore-size distribution shifts to higher mode values (27.3 to 50.6 {angstrom}) and to higher variance (1.07{center_dot}10{sup 3} to 3.58{center_dot}10{sup 3} {angstrom}{sup 2}).

  1. Asymmetric competition causes multimodal size distributions in spatially structured populations.

    PubMed

    Velázquez, Jorge; Allen, Robert B; Coomes, David A; Eichhorn, Markus P

    2016-01-27

    Plant sizes within populations often exhibit multimodal distributions, even when all individuals are the same age and have experienced identical conditions. To establish the causes of this, we created an individual-based model simulating the growth of trees in a spatially explicit framework, which was parametrized using data from a long-term study of forest stands in New Zealand. First, we demonstrate that asymmetric resource competition is a necessary condition for the formation of multimodal size distributions within cohorts. By contrast, the legacy of small-scale clustering during recruitment is transient and quickly overwhelmed by density-dependent mortality. Complex multi-layered size distributions are generated when established individuals are restricted in the spatial domain within which they can capture resources. The number of modes reveals the effective number of direct competitors, while the separation and spread of modes are influenced by distances among established individuals. Asymmetric competition within local neighbourhoods can therefore generate a range of complex size distributions within even-aged cohorts.

  2. Parameterizing Size Distribution in Ice Clouds

    SciTech Connect

    DeSlover, Daniel; Mitchell, David L.

    2009-09-25

    PARAMETERIZING SIZE DISTRIBUTIONS IN ICE CLOUDS David L. Mitchell and Daniel H. DeSlover ABSTRACT An outstanding problem that contributes considerable uncertainty to Global Climate Model (GCM) predictions of future climate is the characterization of ice particle sizes in cirrus clouds. Recent parameterizations of ice cloud effective diameter differ by a factor of three, which, for overcast conditions, often translate to changes in outgoing longwave radiation (OLR) of 55 W m-2 or more. Much of this uncertainty in cirrus particle sizes is related to the problem of ice particle shattering during in situ sampling of the ice particle size distribution (PSD). Ice particles often shatter into many smaller ice fragments upon collision with the rim of the probe inlet tube. These small ice artifacts are counted as real ice crystals, resulting in anomalously high concentrations of small ice crystals (D < 100 µm) and underestimates of the mean and effective size of the PSD. Half of the cirrus cloud optical depth calculated from these in situ measurements can be due to this shattering phenomenon. Another challenge is the determination of ice and liquid water amounts in mixed phase clouds. Mixed phase clouds in the Arctic contain mostly liquid water, and the presence of ice is important for determining their lifecycle. Colder high clouds between -20 and -36 oC may also be mixed phase but in this case their condensate is mostly ice with low levels of liquid water. Rather than affecting their lifecycle, the presence of liquid dramatically affects the cloud optical properties, which affects cloud-climate feedback processes in GCMs. This project has made advancements in solving both of these problems. Regarding the first problem, PSD in ice clouds are uncertain due to the inability to reliably measure the concentrations of the smallest crystals (D < 100 µm), known as the “small mode”. Rather than using in situ probe measurements aboard aircraft, we employed a treatment of ice

  3. Lognormal field size distributions as a consequence of economic truncation

    USGS Publications Warehouse

    Attanasi, E.D.; Drew, L.J.

    1985-01-01

    The assumption of lognormal (parent) field size distributions has for a long time been applied to resource appraisal and evaluation of exploration strategy by the petroleum industry. However, frequency distributions estimated with observed data and used to justify this hypotheses are conditional. Examination of various observed field size distributions across basins and over time shows that such distributions should be regarded as the end result of an economic filtering process. Commercial discoveries depend on oil and gas prices and field development costs. Some new fields are eliminated due to location, depths, or water depths. This filtering process is called economic truncation. Economic truncation may occur when predictions of a discovery process are passed through an economic appraisal model. We demonstrate that (1) economic resource appraisals, (2) forecasts of levels of petroleum industry activity, and (3) expected benefits of developing and implementing cost reducing technology are sensitive to assumptions made about the nature of that portion of (parent) field size distribution subject to economic truncation. ?? 1985 Plenum Publishing Corporation.

  4. Size-dependent structure of silver nanoparticles under high pressure

    SciTech Connect

    Koski, Kristie Jo

    2008-12-31

    Silver noble metal nanoparticles that are<10 nm often possess multiply twinned grains allowing them to adopt shapes and atomic structures not observed in bulk materials. The properties exhibited by particles with multiply twinned polycrystalline structures are often far different from those of single-crystalline particles and from the bulk. I will present experimental evidence that silver nanoparticles<10 nm undergo a reversible structural transformation under hydrostatic pressures up to 10 GPa. Results for nanoparticles in the intermediate size range of 5 to 10 nm suggest a reversible linear pressure-dependent rhombohedral distortion which has not been previously observed in bulk silver. I propose a mechanism for this transitiion that considers the bond-length distribution in idealized multiply twinned icosahedral particles. Results for nanoparticles of 3.9 nm suggest a reversible linear pressure-dependent orthorhombic distortion. This distortion is interpreted in the context of idealized decahedral particles. In addition, given these size-dependent measurements of silver nanoparticle compression with pressure, we have constructed a pressure calibration curve. Encapsulating these silver nanoparticles in hollow metal oxide nanospheres then allows us to measure the pressure inside a nanoshell using x-ray diffraction. We demonstrate the measurement of pressure gradients across nanoshells and show that these nanoshells have maximum resolved shear strengths on the order of 500 MPa to IGPa.

  5. 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

  6. Asteroid collisions: Target size effects and resultant velocity distributions

    NASA Astrophysics Data System (ADS)

    Ryan, Eileen V.

    1993-03-01

    To study the dynamic fragmentation of rock to simulate asteroid collisions, we use a 2-D, continuum damage numerical hydrocode which models two-body impacts. This hydrocode monitors stress wave propagation and interaction within the target body, and includes a physical model for the formation and growth of cracks in rock. With this algorithm we have successfully reproduced fragment size distributions and mean ejecta speeds from laboratory impact experiments using basalt, and weak and strong mortar as target materials. Using the hydrocode, we have determined that the energy needed to fracture a body has a much stronger dependence on target size than predicted from most scaling theories. In addition, velocity distributions obtained indicate that mean ejecta speeds resulting from large-body collisions do not exceed escape velocities.

  7. Transverse Momentum Dependent Distributions in Hard Scattering

    SciTech Connect

    Alexie Prokudin

    2011-05-01

    Transverse Momentum Dependent Distributions (TMDs) describe the spin structure of the proton. At leading twist spin structure of spin-1/2 hadron can be described by 8 TMDs. TMDs reveal three-dimensional distribution of partons inside polarised nucleon. Experimentally these functions can be studied in polarised experiments using Spin Asymmetries in particular Single Spin Asymmetries (SSAs). We discuss transversity that measures distribution of transversely polarised quarks in a transversely polarised nucleon and Sivers distribution function that describes distribution of unpolarised quarks in a transversely polarised nucleon.

  8. Size distributions and failure initiation of submarine and subaerial landslides

    USGS Publications Warehouse

    ten Brink, U.S.; Barkan, R.; Andrews, B.D.; Chaytor, J.D.

    2009-01-01

    Landslides are often viewed together with other natural hazards, such as earthquakes and fires, as phenomena whose size distribution obeys an inverse power law. Inverse power law distributions are the result of additive avalanche processes, in which the final size cannot be predicted at the onset of the disturbance. Volume and area distributions of submarine landslides along the U.S. Atlantic continental slope follow a lognormal distribution and not an inverse power law. Using Monte Carlo simulations, we generated area distributions of submarine landslides that show a characteristic size and with few smaller and larger areas, which can be described well by a lognormal distribution. To generate these distributions we assumed that the area of slope failure depends on earthquake magnitude, i.e., that failure occurs simultaneously over the area affected by horizontal ground shaking, and does not cascade from nucleating points. Furthermore, the downslope movement of displaced sediments does not entrain significant amounts of additional material. Our simulations fit well the area distribution of landslide sources along the Atlantic continental margin, if we assume that the slope has been subjected to earthquakes of magnitude ??? 6.3. Regions of submarine landslides, whose area distributions obey inverse power laws, may be controlled by different generation mechanisms, such as the gradual development of fractures in the headwalls of cliffs. The observation of a large number of small subaerial landslides being triggered by a single earthquake is also compatible with the hypothesis that failure occurs simultaneously in many locations within the area affected by ground shaking. Unlike submarine landslides, which are found on large uniformly-dipping slopes, a single large landslide scarp cannot form on land because of the heterogeneous morphology and short slope distances of tectonically-active subaerial regions. However, for a given earthquake magnitude, the total area

  9. Aged Boreal Biomass Burning Size Distributions from Bortas 2011

    NASA Astrophysics Data System (ADS)

    Pierce, J. R.; Sakamoto, K.; Allan, J. D.; Coe, H.; Taylor, J.; Duck, T.

    2014-12-01

    Biomass-burning aerosols contribute to aerosol radiative forcing on the climate system. The magnitude of this effect is partially determined by aerosol size distributions, which are strong functions of source fire characteristics (e.g. fuel type, MCE) and in-plume microphysical processing. The uncertainties in biomass-burning emission number size-distributions in climate model inventories lead to uncertainties in the CCN concentrations and forcing estimates derived from these models. The BORTAS-B measurement campaign was designed to sample boreal biomass-burning outflow over Eastern Canada in the summer of 2011. Using these BORTAS-B data, we implement plume criteria to isolate the characteristic size-distribution of aged biomass-burning emissions (aged ~ 1.5 - 2 days) from boreal wildfires in Northwestern Ontario. The composite median size-distribution yields a single dominant accumulation mode with Dpm = 232 nm, σ = 1.7, which are comparable to literature values of other aged plumes of a similar type. The organic aerosol enhancement ratios (ΔOA/ΔCO) along the path of Flight b622 show values of 0.08-0.18 μg m-3 ppbv-1 with no significant trend with distance from the source. This lack of enhancement ratio increase/decrease with distance suggests no detectable net OA production/evaporation within the aged plume over the sampling period. A Lagrangian microphysical model was used to determine an estimate of the freshly emitted size distribution and flux corresponding to the BORTAS-B aged size-distributions. The model was restricted to coagulation and dilution processes only based on the insignificant net OA production/evaporation derived from the ΔOA/ΔCO enhancement ratios. Depending on the, we estimate that the fresh-plume median diameter was in the range of 59-94 nm with modal widths in the range of 1.7-2.8. Thus, the size of the freshly emitted particles is somewhat unconstrained due to the uncertainties in the plume dilution rates.

  10. Evolution of Particle Size Distributions in Fragmentation Over Time

    NASA Astrophysics Data System (ADS)

    Charalambous, C. A.; Pike, W. T.

    2013-12-01

    We present a new model of fragmentation based on a probabilistic calculation of the repeated fracture of a particle population. The resulting continuous solution, which is in closed form, gives the evolution of fragmentation products from an initial block, through a scale-invariant power-law relationship to a final comminuted powder. Models for the fragmentation of particles have been developed separately in mainly two different disciplines: the continuous integro-differential equations of batch mineral grinding (Reid, 1965) and the fractal analysis of geophysics (Turcotte, 1986) based on a discrete model with a single probability of fracture. The first gives a time-dependent development of the particle-size distribution, but has resisted a closed-form solution, while the latter leads to the scale-invariant power laws, but with no time dependence. Bird (2009) recently introduced a bridge between these two approaches with a step-wise iterative calculation of the fragmentation products. The development of the particle-size distribution occurs with discrete steps: during each fragmentation event, the particles will repeatedly fracture probabilistically, cascading down the length scales to a final size distribution reached after all particles have failed to further fragment. We have identified this process as the equivalent to a sequence of trials for each particle with a fixed probability of fragmentation. Although the resulting distribution is discrete, it can be reformulated as a continuous distribution in maturity over time and particle size. In our model, Turcotte's power-law distribution emerges at a unique maturation index that defines a regime boundary. Up to this index, the fragmentation is in an erosional regime with the initial particle size setting the scaling. Fragmentation beyond this index is in a regime of comminution with rebreakage of the particles down to the size limit of fracture. The maturation index can increment continuously, for example under

  11. Reversing the size-dependence of surface plasmon resonances

    PubMed Central

    Peng, Sheng; McMahon, Jeffrey M.; Schatz, George C.; Gray, Stephen K.; Sun, Yugang

    2010-01-01

    The size-dependence of surface plasmon resonances (SPRs) is poorly understood in the small particle limit due to complex physical/chemical effects and uncertainties in experimental samples. In this article, we report an approach for synthesizing an ideal class of colloidal Ag nanoparticles with highly uniform morphologies and narrow size distributions. Optical measurements and theoretical analyses for particle diameters in the d ≈ 2–20 nm range are presented. The SPR absorption band exhibits an exceptional behavior: As size decreases from d ≈ 20 nm it blue-shifts but then turns over near d ≈ 12 nm and strongly red-shifts. A multilayer Mie theory model agrees well with the observations, indicating that lowered electron conductivity in the outermost atomic layer, due to chemical interactions, is the cause of the red-shift. We corroborate this picture by experimentally demonstrating precise chemical control of the SPR peak positions via ligand exchange. PMID:20671201

  12. Temperature and size-dependent Hamaker constants for metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Jiang, K.; Pinchuk, P.

    2016-08-01

    Theoretical values of the Hamaker constant have been calculated for metal nanoparticles using Lifshitz theory. The theory describes the Hamaker constant in terms of the permittivity of the interacting bodies. Metal nanoparticles exhibit an internal size effect that alters the dielectric permittivity of the particle when its size falls below the mean free path of the conducting electrons. This size dependence of the permittivity leads to size-dependence of the Hamaker constant for metal nanoparticles. Additionally, the electron damping and the plasma frequency used to model the permittivity of the particle exhibit temperature-dependence, which lead to temperature dependence of the Hamaker constant. In this work, both the size and temperature dependence for gold, silver, copper, and aluminum nanoparticles is demonstrated. The results of this study might be of interest for studying the colloidal stability of nanoparticles in solution.

  13. The Dependence of Cirrus Gamma Size Distributions Expressed as Volumes in N(sub 0)-Lambda-Mu Phase Space and Bulk Cloud Properties on Environmental Conditions: Results from the Small Ice Particles in Cirrus Experiment (SPARTICUS)

    NASA Technical Reports Server (NTRS)

    Jackson, Robert C.; McFarquhar, Greg M.; Fridlind, Ann M.; Atlas, Rachel

    2015-01-01

    The variability of cirrus ice microphysical properties is investigated using observations obtained during the Small Particles in Cirrus (SPARTICUS) campaign. An existing approach that represents a size distribution (SD) as a single gamma function using an ellipsoid of equally realizable solutions in (N(sub 0), lambda, mu) phase space is modified to automatically identify multiple modes in SDs and characterize each mode by such an ellipsoid. The modified approach is applied to ice crystals with maximum dimension D greater than15 micrometers collected by the 2-D stereo and 2-D precipitation probes on the Stratton Park Engineering Company Learjet. The dependencies of N(sub 0), mu, and lambda from each mode, total number concentration, bulk extinction, ice water content (IWC), and mass median maximum dimension D(sub mm) as a function of temperature T and cirrus type are then analyzed. The changes in the observed codependencies between N(sub 0), mu, and lambda, bulk extinction, IWC, and D(sub mm) with environmental conditions indicate that particles were larger at higher T during SPARTICUS. At most two modes were observed in any SD during SPARTICUS, with the average boundary between them at 115 micrometers, similar to past studies not using probes with shatter mitigating tips and artifact removal algorithms. The bimodality of the SDs increased with T. This and the differences in N(sub 0), mu, and lambda between the modes suggest that particles with smaller D nucleated more recently than particles with larger D, which grew via vapor deposition and aggregation. Because smaller crystals, whose concentrations are uncertain, make marginal contributions to higher order moments, the use of higher moments for evaluating model fields is suggested.

  14. Effects of particle size distribution in thick film conductors

    NASA Technical Reports Server (NTRS)

    Vest, R. W.

    1983-01-01

    Studies of particle size distribution in thick film conductors are discussed. The distribution of particle sizes does have an effect on fired film density but the effect is not always positive. A proper distribution of sizes is necessary, and while the theoretical models can serve as guides to selecting this proper distribution, improved densities can be achieved by empirical variations from the predictions of the models.

  15. Establishing different size distributions in the asteroid belt

    NASA Astrophysics Data System (ADS)

    Jacobson, Seth A.; Morbidelli, Alessandro

    2016-05-01

    While gas is present in the protoplanetary disk, aerodynamic drag circularizes, equatorializes and shrinks planetesimal orbits. The strength of this effect is size-dependent effecting smaller planetesimals more severely. During planet formation debris from giant impacts amongst the growing terrestrial embryos can be transported to the asteroid belt via scattering events and secular resonances. The effectiveness of this transport is strongly size dependent due to the aforementioned gas drag. Thus transported debris in the asteroid belt can have a strong size sorting. Further processing due to collisions and YORP-induced rotational fission during the lifetime of the solar system must be taken into account before a model population of debris can be compared to suspected planetary debris in the asteroid belt, such as the A-type asteroids. Furthermore, scenarios such as the Grand Tack may establish size distributions since they predict that S-type asteroids are transported from an inner planetesimal disk while C-type asteroids are transporeted from an outer planetesimal disk.

  16. Size and Age Dependence of Koronis Family Colors

    NASA Astrophysics Data System (ADS)

    Molnar, L. A.

    2011-10-01

    The ancient and massive Koronis family now has four identified subfamilies (asteroid families made by the breakup of fragments of the ancient collision), with ages running from 5.7 to 290 My. This presents unique opportunities to explore space weathering processes, along with dynamical processes such as collisions and binary formation and destruction. Analysis of family members with accurate SDSS measurements shows a correlation of average subfamily color with age that for the first time is highly statistically significant. Yet Thomas et al. (2011) report a size dependence of the colors of the ancient family that demands caution when comparing subfamilies with differing size distributions. Reanalyis of the Thomas et al. data show the reported break near asteroid diameter 5 km is not significant. However, analysis of the much more extensive SDSS data set show a significant break past diameter 2.5 km, with smaller objects systematically bluer. The break is not present in the Karin subfamily (the youngest at 5.7 My), but is already fully developed in the Eriphyla subfamily (only 220 My). The reddening trend with age remains even when comparing only asteroids of similar size, confirming the presence of space weathering phenomena. The meaning of the trend with size is not immediately clear. We consider briefly the strengths and weaknesses of several interpretations of the bluer colors for small objects: 1) those objects receive more jolts from random collisions capable of shaking the regolith and exposing fresh material beneath; 2) those objects receive more jolts from the cycle of fission and recombination driven by YORP; and 3) the lower gravity on those objects retains regolith less well.

  17. Size- and temperature-dependent Young's modulus and size-dependent thermal expansion coefficient of thin films.

    PubMed

    Zhou, Xiao-Ye; Huang, Bao-Ling; Zhang, Tong-Yi

    2016-08-21

    Nanomaterials possess a high surface/volume ratio and surfaces play an essential role in size-dependent material properties. In the present study, nanometer-thick thin films were taken as an ideal system to investigate the surface-induced size- and temperature-dependent Young's modulus and size-dependent thermal expansion coefficient. The surface eigenstress model was further developed with the consideration of thermal expansion, leading to analytic formulas of size- and temperature-dependent Young's modulus, and size-dependent thermal expansion coefficient of thin films. Molecular dynamics (MD) simulations on face-centered cubic (fcc) Ag, Cu, and Ni(001) thin films were conducted at temperatures ranging from 300 K to 600 K. The MD simulation results are perfectly consistent with the theoretical predictions, thereby verifying the theoretical approach. The newly developed surface eigenstress model will be able to attack similar problems in other types of nanomaterials. PMID:27426852

  18. Time-dependent photoelectron angular distributions

    NASA Astrophysics Data System (ADS)

    Wang, Xiangyang

    1999-09-01

    I show that the angular distribution of electrons photoionized from gas phase targets by short light pulses is time-dependent, when the orbital momentum composition of the photocurrent changes with excitation energy so evolves with the time of detection. A theory of time- dependent photoionization is outlined and general formulas of time-dependent photoelectron flux and angular distribution are given. Two general propagator methods suitable to describe the time-dependent photoionization and scattering processes are developed. The photoionization process is viewed as a local excitation followed by a half scattering. The local excitation process is solved theoretically in a small region around the target core. This approach has been generalized to describe the evolution of a wavepacket in an unbound system. An asymptotic propagator theorem is discovered and used to derive analytic expressions for asymptotic propagators. The origin of the time dependence is explored by parameterizing the time delay and orbital momentum coupling in a two channel model. K-shell photoionization of N2 and CO are calculated with this time- dependent photoionization theory, implemented using a multiple scattering model. Numerical results demonstrate that the time dependence of photoelectron angular distributions is a realistic effect.

  19. The determination and optimization of (rutile) pigment particle size distributions

    NASA Technical Reports Server (NTRS)

    Richards, L. W.

    1972-01-01

    A light scattering particle size test which can be used with materials having a broad particle size distribution is described. This test is useful for pigments. The relation between the particle size distribution of a rutile pigment and its optical performance in a gray tint test at low pigment concentration is calculated and compared with experimental data.

  20. Monte Carlo predictions of DNA fragment-size distributions for large sizes after HZE particle irradiation

    NASA Technical Reports Server (NTRS)

    Ponomarev, A. L.; Cucinotta, F. A.; Sachs, R. K.; Brenner, D. J.

    2001-01-01

    DSBs (double-strand breaks) produced by densely ionizing space radiation are not located randomly in the genome: recent data indicate DSB clustering along chromosomes. DSB clustering at large scales, from >100 Mbp down to approximately 2 kbp, is modeled using a Monte-Carlo algorithm. A random-walk model of chromatin is combined with a track model, that predicts the radial distribution of energy from an ion, and the RLC (randomly-located-clusters) formalism, in software called DNAbreak. This model generalizes the random-breakage model, whose broken-stick fragment-size distribution is applicable to low-LET radiation. DSB induction due to track interaction with the DNA volume depends on the radiation quality parameter Q. This dose-independent parameter depends only weakly on LET. Multi-track, high-dose effects depend on the cluster intensity parameter lambda, proportional to fluence as defined by the RLC formalism. After lambda is determined by a numerical experiment, the model reduces to one adjustable parameter Q. The best numerical fits to the experimental data, determining Q, are obtained. The knowledge of lambda and Q allows us to give biophysically based extrapolations of high-dose DNA fragment-size data to low doses or to high LETs.

  1. Approximate sample sizes required to estimate length distributions

    USGS Publications Warehouse

    Miranda, L.E.

    2007-01-01

    The sample sizes required to estimate fish length were determined by bootstrapping from reference length distributions. Depending on population characteristics and species-specific maximum lengths, 1-cm length-frequency histograms required 375-1,200 fish to estimate within 10% with 80% confidence, 2.5-cm histograms required 150-425 fish, proportional stock density required 75-140 fish, and mean length required 75-160 fish. In general, smaller species, smaller populations, populations with higher mortality, and simpler length statistics required fewer samples. Indices that require low sample sizes may be suitable for monitoring population status, and when large changes in length are evident, additional sampling effort may be allocated to more precisely define length status with more informative estimators. ?? Copyright by the American Fisheries Society 2007.

  2. Size-dependent concentrations of thermal vacancies in solid films.

    PubMed

    Gao, Panpan; Wu, Quan; Li, Xi; Ma, Hongxin; Zhang, Hao; Volinsky, Alex A; Qiao, Lijie; Su, Yanjing

    2016-08-10

    Solid films are considered as typical model systems to study size effects on thermal vacancy concentration in nanomaterials. By combining the generalized Young-Laplace equation with the chemical potential of vacancies, a strict size-dependent thermodynamic model of vacancies, which includes the surface intrinsic elastic parameters of the eigenstress, Young's modulus and the geometric size of the solid films, was established. The vacancy concentration changes in the film with respect to the bulk value, depending on the geometric size and surface stress sign of the solid films. Atomistic simulations of Au and Pt films verified the developed thermodynamic model. These results provide physical insights into the size-dependent thermal vacancy concentration in nanomaterials.

  3. Size-dependent concentrations of thermal vacancies in solid films.

    PubMed

    Gao, Panpan; Wu, Quan; Li, Xi; Ma, Hongxin; Zhang, Hao; Volinsky, Alex A; Qiao, Lijie; Su, Yanjing

    2016-08-10

    Solid films are considered as typical model systems to study size effects on thermal vacancy concentration in nanomaterials. By combining the generalized Young-Laplace equation with the chemical potential of vacancies, a strict size-dependent thermodynamic model of vacancies, which includes the surface intrinsic elastic parameters of the eigenstress, Young's modulus and the geometric size of the solid films, was established. The vacancy concentration changes in the film with respect to the bulk value, depending on the geometric size and surface stress sign of the solid films. Atomistic simulations of Au and Pt films verified the developed thermodynamic model. These results provide physical insights into the size-dependent thermal vacancy concentration in nanomaterials. PMID:27476928

  4. Zipf Distribution of U.S. Firm Sizes

    NASA Astrophysics Data System (ADS)

    Axtell, Robert L.

    2001-09-01

    Analyses of firm sizes have historically used data that included limited samples of small firms, data typically described by lognormal distributions. Using data on the entire population of tax-paying firms in the United States, I show here that the Zipf distribution characterizes firm sizes: the probability a firm is larger than size s is inversely proportional to s. These results hold for data from multiple years and for various definitions of firm size.

  5. Binary nucleation kinetics. I. Self-consistent size distribution

    SciTech Connect

    Wilemski, G.; Wyslouzil, B.E. ||

    1995-07-15

    Using the principle of detailed balance, we derive a new self-consistency requirement, termed the kinetic product rule, relating the evaporation coefficients and equilibrium cluster distribution for a binary system. We use this result to demonstrate and resolve an inconsistency for an idealized Kelvin model of nucleation in a simple binary mixture. We next examine several common forms for the equilibrium distribution of binary clusters based on the capillarity approximation and ideal vapor behavior. We point out fundamental deficiencies for each expression. We also show that each distribution yields evaporation coefficients that formally satisfy the new kinetic product rule but are physically unsatisfactory because they depend on the monomer vapor concentrations. We then propose a new form of the binary distribution function that is free of the deficiencies of the previous functions except for its reliance on the capillarity approximation. This new self-consistent classical (SCC) size distribution for binary clusters has the following properties: It satisfies the law of mass action; it reduces to an SCC unary distribution for clusters of a single component; and it produces physically acceptable evaporation rate coefficients that also satisfy the new kinetic product rule. Since it is possible to construct other examples of similarly well-behaved distributions, our result is not unique in this respect, but it does give reasonable predictions. As an illustration, we calculate binary nucleation rates and vapor activities for the ethanol--hexanol system at 260 K using the new SCC distribution and compare them to experimental results. The theoretical rates are uniformly higher than the experimental values over the entire vapor composition range. Although the predicted activities are lower, we find good agreement between the measured and theoretical slope of the critical vapor activity curve at a constant nucleation rate of 10{sup 7} cm{sup {minus}3} s{sup {minus}2}.

  6. Size dependence of microscopic Hall sensor detection limits.

    PubMed

    Vervaeke, K; Simoen, E; Borghs, G; Moshchalkov, V V

    2009-07-01

    In this paper the magnetic field detection limits of microscopic Hall sensors are investigated as a function of their lateral size. Hall sensors fabricated from GaAs/AlGaAs heterostructures and silicon are experimentally investigated at different temperatures using Hall effect and noise spectrum measurements. At room temperature a clear size dependence of the detection limit is observed, whereas at low temperatures this dependence is found to disappear. The results are explained using the theory of noise in semiconductors.

  7. Energy dependent 4-dimensional multiple scattering distributions

    NASA Astrophysics Data System (ADS)

    Tschalär, C.

    1984-12-01

    A complete analytic solution in Fourier space is presented of the four dimensional small angle, multiple scattering distribution MSD in angle and space, produced by an energy dependent single scattering cross section from an initial pencil beam of heavy particles. Independently, simple integrals are derived for the central moments of the energy dependent MSD in the continuous-slowing-down approximation. The distributions of the projections t and x of the scattering angle and displacement into a plane through the axis of propagation are evaluated numerically for a truncated Rutherford scattering cross section using a fast Fourier transform. The resulting MSDs for a wide range of particles, initial and final momenta, and scattering materials are found to be approximately represented by one-dimensional set of standard distributions symmetrized by a linear transformation in t- x-space.

  8. Cluster size distribution in Gaussian glasses

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.

    2011-03-01

    A simple method for the estimation of the asymptotics of the cluster numbers in Gaussian glasses is described. Validity of the method was tested by the comparison with the exact analytic result for the non-correlated field and simulation data for the distribution of random energies in strongly spatially correlated dipolar glass model.

  9. Source distribution dependent scatter correction for PVI

    SciTech Connect

    Barney, J.S.; Harrop, R.; Dykstra, C.J. . School of Computing Science TRIUMF, Vancouver, British Columbia )

    1993-08-01

    Source distribution dependent scatter correction methods which incorporate different amounts of information about the source position and material distribution have been developed and tested. The techniques use image to projection integral transformation incorporating varying degrees of information on the distribution of scattering material, or convolution subtraction methods, with some information about the scattering material included in one of the convolution methods. To test the techniques, the authors apply them to data generated by Monte Carlo simulations which use geometric shapes or a voxelized density map to model the scattering material. Source position and material distribution have been found to have some effect on scatter correction. An image to projection method which incorporates a density map produces accurate scatter correction but is computationally expensive. Simpler methods, both image to projection and convolution, can also provide effective scatter correction.

  10. The distribution of bubble sizes during reionization

    NASA Astrophysics Data System (ADS)

    Lin, Yin; Oh, S. Peng; Furlanetto, Steven R.; Sutter, P. M.

    2016-09-01

    A key physical quantity during reionization is the size of H II regions. Previous studies found a characteristic bubble size which increases rapidly during reionization, with apparent agreement between simulations and analytic excursion set theory. Using four different methods, we critically examine this claim. In particular, we introduce the use of the watershed algorithm - widely used for void finding in galaxy surveys - which we show to be an unbiased method with the lowest dispersion and best performance on Monte Carlo realizations of a known bubble size probability density function (PDF). We find that a friends-of-friends algorithm declares most of the ionized volume to be occupied by a network of volume-filling regions connected by narrow tunnels. For methods tuned to detect the volume-filling regions, previous apparent agreement between simulations and theory is spurious, and due to a failure to correctly account for the window function of measurement schemes. The discrepancy is already obvious from visual inspection. Instead, H II regions in simulations are significantly larger (by factors of 10-1000 in volume) than analytic predictions. The size PDF is narrower, and evolves more slowly with time, than predicted. It becomes more sharply peaked as reionization progresses. These effects are likely caused by bubble mergers, which are inadequately modelled by analytic theory. Our results have important consequences for high-redshift 21 cm observations, the mean free path of ionizing photons, and the visibility of Lyα emitters, and point to a fundamental failure in our understanding of the characteristic scales of the reionization process.

  11. Lunar soil: Size distribution and mineralogical constituents

    USGS Publications Warehouse

    Duke, M.B.; Woo, C.C.; Bird, M.L.; Sellers, G.A.; Finkelman, R.B.

    1970-01-01

    The lunar soil collected by Apollo 11 consists primarily of submillimeter material and is finer in grain size than soil previously recorded photographically by Surveyor experiments. The main constituents are fine-grained to glassy rocks of basaltic affinity and coherent breccia of undetermined origin. Dark glass, containing abundant nickel-iron spheres, coats many rocks, mineral, and breccia fragments. Several types of homogeneous glass occur as fragments and spheres. Colorless spheres, probably an exotic component, are abundant in the fraction finer than 20 microns.

  12. Dependency of Lipid Raft Diffusion on System Size

    NASA Astrophysics Data System (ADS)

    Davis, Ryan

    2009-11-01

    An inherit limitation in molecular dynamics is a finite system size. Although periodic boundary conditions can be used to mimic an infinite space, minimizing the artificial effects created by the physical dimensions of the system still remains an issue. Here I will discuss the undesirable relationship between system properties and system size observed via a dissipative particle dynamics approach. In particular, results illustrate a strong dependence between the diffusion of a lipid raft along a membrane and the length of the axis perpendicular to it, even at relatively large system sizes. Methods for obtaining system properties independently of simulation size are crucial for accurate results.

  13. The size distribution of inhabited planets

    NASA Astrophysics Data System (ADS)

    Simpson, Fergus

    2016-02-01

    Earth-like planets are expected to provide the greatest opportunity for the detection of life beyond the Solar system. However, our planet cannot be considered a fair sample, especially if intelligent life exists elsewhere. Just as a person's country of origin is a biased sample among countries, so too their planet of origin may be a biased sample among planets. The magnitude of this effect can be substantial: over 98 per cent of the world's population live in a country larger than the median. In the context of a simple model where the mean population density is invariant to planet size, we infer that a given inhabited planet (such as our nearest neighbour) has a radius r < 1.2r⊕ (95 per cent confidence bound). We show that this result is likely to hold not only for planets hosting advanced life, but also for those which harbour primitive life forms. Further, inferences may be drawn for any variable which influences population size. For example, since population density is widely observed to decline with increasing body mass, we conclude that most intelligent species are expected to exceed 300 kg.

  14. Investigating the Size Dependent Material Properties of Nanoceria

    NASA Astrophysics Data System (ADS)

    Alam, Bushra B.

    Nanoceria is widely being investigated for applications as support materials for fuel cell catalysts, free radical scavengers, and as chemical and mechanical abrasives due to its high antioxidant capacity and its oxygen buffering capacity. This antioxidant or oxygen buffering capacity has been reported to be highly size dependent and related to its redox properties. However, the quantification of this antioxidant capacity has not been well defined or understood and has been often been carried out using colorimetric assays which do not directly correlate to ceria nanoparticle properties. Fabrication rules for developing materials with optimal antioxidant/oxygen buffering capacities are not yet defined and one of the limitations has been the challenge of obtaining quantitative measurements of the antioxidant properties. In this work, we create our own library of ceria nanoparticles of various size distributions by two synthesis methods: sol-gel peroxo and thermal decomposition/calcination and annealing in open atmosphere at three different temperatures. The synthesis methods and conditions produce characteristic sizes and morphologies of ceria nanoparticles. Qualitative and quantitative approaches are used for characterization and to predict reactivity. Qualitative approaches include Brunauer-Emmett-Teller (BET) surface area measurements and Raman analysis while quantitative approaches include a combination of powder X-ray diffraction (XRD) Rietveld analysis, Transmission Electron Microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) to measure crystallite sizes, lattice parameters, oxygen site occupancies, and the relative abundance of Ce(III) ions in a nanoceria sample. These methods are discussed in detail in addition to their limitations and challenges. These methods are used to predict nanocrystalline or bulk-like behavior of ceria nanoparticles. The investigation of the material properties is also extended to test the redox properties of ceria

  15. Knife mill operating factors effect on switchgrass particle size distributions

    SciTech Connect

    Bitra, V.S.P.; Womac, A.R.; Yang, Y.T.; Igathinathane, C.; Miu, P.I; Chevanan, Nehru; Sokhansanj, Shahabaddine

    2009-06-01

    Biomass particle size impacts handling, storage, conversion, and dust control systems. Switchgrass (Panicum virgatum L.) particle size distributions created by a knife mill were determined for integral classifying screen sizes from 12.7 to 50.8 mm, operating speeds from 250 to 500 rpm, and mass input rates from 2 to 11 kg/min. Particle distributions were classified with standardized sieves for forage analysis that included horizontal sieving motion with machined-aluminum sieves of thickness proportional to sieve opening dimensions. Then, a wide range of analytical descriptors were examined to mathematically represent the range of particle sizes in the distributions. Correlation coefficient of geometric mean length with knife mill screen size, feed rate, and speed were 0.872, 0.349, and 0.037, respectively. Hence, knife mill screen size largely determined particle size of switchgrass chop. Feed rate had an unexpected influence on particle size, though to a lesser degree than screen size. The Rosin Rammler function fit the chopped switchgrass size distribution data with an R2 > 0.982. Mass relative span was greater than 1, which indicated a wide distribution of particle sizes. Uniformity coefficient was more than 4.0, which indicated a large assortment of particles and also represented a well-graded particle size distribution. Knife mill chopping of switchgrass produced strongly fine skewed mesokurtic particles with 12.7 25.4 mm screens and fine skewed mesokurtic particles with 50.8 mm screen. Results of this extensive analysis of particle sizes can be applied to selection of knife mill operating parameters to produce a particular size of switchgrass chop, and will serve as a guide for relations among the various analytic descriptors of biomass particle distributions.

  16. Knife mill operating factors effect on switchgrass particle size distributions.

    PubMed

    Bitra, Venkata S P; Womac, Alvin R; Yang, Yuechuan T; Igathinathane, C; Miu, Petre I; Chevanan, Nehru; Sokhansanj, Shahab

    2009-11-01

    Biomass particle size impacts handling, storage, conversion, and dust control systems. Switchgrass (Panicum virgatum L.) particle size distributions created by a knife mill were determined for integral classifying screen sizes from 12.7 to 50.8 mm, operating speeds from 250 to 500 rpm, and mass input rates from 2 to 11 kg/min. Particle distributions were classified with standardized sieves for forage analysis that included horizontal sieving motion with machined-aluminum sieves of thickness proportional to sieve opening dimensions. Then, a wide range of analytical descriptors were examined to mathematically represent the range of particle sizes in the distributions. Correlation coefficient of geometric mean length with knife mill screen size, feed rate, and speed were 0.872, 0.349, and 0.037, respectively. Hence, knife mill screen size largely determined particle size of switchgrass chop. Feed rate had an unexpected influence on particle size, though to a lesser degree than screen size. The Rosin-Rammler function fit the chopped switchgrass size distribution data with an R(2)>0.982. Mass relative span was greater than 1, which indicated a wide distribution of particle sizes. Uniformity coefficient was more than 4.0, which indicated a large assortment of particles and also represented a well-graded particle size distribution. Knife mill chopping of switchgrass produced 'strongly fine skewed mesokurtic' particles with 12.7-25.4 mm screens and 'fine skewed mesokurtic' particles with 50.8 mm screen. Results of this extensive analysis of particle sizes can be applied to selection of knife mill operating parameters to produce a particular size of switchgrass chop, and will serve as a guide for relations among the various analytic descriptors of biomass particle distributions.

  17. Transverse-momentum-dependent parton distributions (TMDs)

    NASA Astrophysics Data System (ADS)

    Bacchetta, Alessandro

    2011-10-01

    Transverse-momentum-dependent parton distributions (TMDs) provide three-dimensional images of the partonic structure of the nucleon in momentum space. We made impressive progress in understanding TMDs, both from the theoretical and experimental point of view. This brief overview on TMDs is divided in two parts: in the first, an essential list of achievements is presented. In the second, a selection of open questions is discussed.

  18. Calculating Confidence Intervals for Effect Sizes Using Noncentral Distributions.

    ERIC Educational Resources Information Center

    Norris, Deborah

    This paper provides a brief review of the concepts of confidence intervals, effect sizes, and central and noncentral distributions. The use of confidence intervals around effect sizes is discussed. A demonstration of the Exploratory Software for Confidence Intervals (G. Cuming and S. Finch, 2001; ESCI) is given to illustrate effect size confidence…

  19. Size-dependent pyroelectric properties of gallium nitride nanowires

    NASA Astrophysics Data System (ADS)

    Zhang, Jin; Wang, Chengyuan

    2016-04-01

    The size scale effect on the pyroelectric properties is studied for gallium nitride (GaN) nanowires (NWs) based on molecular dynamics simulations and the theoretical analysis. Due to the significant influence of the surface thermoelasticity and piezoelectricity at the nanoscale, the pyroelectric coefficient of GaN NWs is found to depend on the cross-sectional size. This size-dependent pyroelectric coefficient of GaN NWs together with the size-dependent dielectric constant reported in our previous study is employed to study the pyroelectric potential of GaN NWs subjected to heating. The results show that the size scale effect is significant for thin NWs (cross-sectional size in nanometers) and may raise the pyroelectric potential of GaN NWs by over 10 times. Such a size scale effect on the pyroelectric properties of NWs originates from the influence of thermoelasticity, piezoelectricity, and dielectricity at the nanoscale and decreases with increasing cross-section of GaN NWs. It is expected that the present study may have strong implication in the field of energy harvesting at the nanoscale, as pyroelectricity offers a new avenue to the design of novel nanogenerators.

  20. Diffusion in nanoporous phases: size dependence and levitation effect.

    PubMed

    Yashonath, S; Ghorai, Pradip Kr

    2008-01-24

    Self-diffusivity, D, of diffusants in widely differing mediums such as liquids (e.g., solution), porous solids (e.g., guests in zeolites), or ions in polar solvents exhibit strong size dependence. We discuss the nature of the size dependence observed in these systems. Altogether, different theoretical approaches have been proposed to understand the nature of size dependence of D not only across these widely differing systems but even in just one medium or class of systems such as, for example, ions in polar solvents. But molecular dynamics investigations in the past decade have shown that the size dependence of self-diffusion in guest-porous solids could have origins in the mutual cancellation of forces that occurs when the size of the diffusant is comparable to the size of the void. The effect leading to the maximum in D is known as the levitation effect (LE). Such a cancellation is a consequence of symmetry. This effect exists in all porous solids irrespective of the geometrical and topological details of the pore network provided by the solid. Recent studies show that the levitation effect and size-dependent diffusivity maximum exists for uncharged solutes in solvents. One of the consequences of this is the breakdown in the Stokes-Einstein relationship over a certain range of solute-solvent size ratio. Experimental measurements of ionic conductivity over the past hundred years have found the existence of a size-dependent diffusivity maximum leading to violation of the Walden's rule for ions in polar solvents. Molecular dynamics simulations and experimental data suggest that even this maximum has its origin in LE. Simulation studies of impurity atom diffusion in close-packed solids as well as ions in superionic and other solids suggest the existence of a size-dependent diffusivity maximum in these materials as well. The levitation effect is a universal effect leading to a maximum in diffusivity of a diffusant in a variety of condensed matter phases. The only

  1. Size distribution of Amazon River bed sediment

    USGS Publications Warehouse

    Nordin, C.F.; Meade, R.H.; Curtis, W.F.; Bosio, N.J.; Landim, P.M.B.

    1980-01-01

    The first recorded observations of bed material of the Amazon River were made in 1843 by Lt William Lewis Herndon of the US Navy, when he travelled the river from its headwaters to its mouth, sounding its depths, and noting the nature of particles caught in a heavy grease smeared to the bottom of his sounding weight1. He reported the bed material of the river to be mostly sand and fine gravel. Oltman and Ames took samples at a few locations in 1963 and 1964, and reported the bed material at O??bidos, Brazil, to be fine sands, with median diameters ranging from 0.15 to 0.25 mm (ref. 2). We present here a summary of particle-size analyses of samples of streambed material collected from the Amazon River and its major tributaries along a reach of the river from Iquitos in Peru, ???3,500 km above Macapa?? Brazil, to a point 220 km above Macapa??3. ?? 1980 Nature Publishing Group.

  2. Size-dependent magnetic properties of iron oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Patsula, Vitalii; Moskvin, Maksym; Dutz, Silvio; Horák, Daniel

    2016-01-01

    Uniform iron oxide nanoparticles in the size range from 10 to 24 nm and polydisperse 14 nm iron oxide particles were prepared by thermal decomposition of Fe(III) carboxylates in the presence of oleic acid and co-precipitation of Fe(II) and Fe(III) chlorides by ammonium hydroxide followed by oxidation, respectively. While the first method produced hydrophobic oleic acid coated particles, the second one formed hydrophilic, but uncoated, nanoparticles. To make the iron oxide particles water dispersible and colloidally stable, their surface was modified with poly(ethylene glycol) and sucrose, respectively. Size and size distribution of the nanoparticles was determined by transmission electron microscopy, dynamic light scattering and X-ray diffraction. Surface of the PEG-functionalized and sucrose-modified iron oxide particles was characterized by Fourier transform infrared (FT-IR) and Raman spectroscopy and thermogravimetric analysis (TGA). Magnetic properties were measured by means of vibration sample magnetometry and specific absorption rate in alternating magnetic fields was determined calorimetrically. It was found, that larger ferrimagnetic particles showed higher heating performance than smaller superparamagnetic ones. In the transition range between superparamagnetism and ferrimagnetism, samples with a broader size distribution provided higher heating power than narrow size distributed particles of comparable mean size. Here presented particles showed promising properties for a possible application in magnetic hyperthermia.

  3. The explicit dependence of quadrat variance on the ratio of clump size to quadrat size.

    PubMed

    Ferrandino, Francis J

    2005-05-01

    ABSTRACT In the past decade, it has become common practice to pool mapped binary epidemic data into quadrats. The resultant "quadrat counts" can then be analyzed by fitting them to a probability distribution (i.e., betabinomial). Often a binary form of Taylor's power law is used to relate the quadrat variance to the quadrat mean. The fact that there is an intrinsic dependence of such analyses on quadrat size and shape is well known. However, a clear-cut exposition of the direct connection between the spatial properties of the two-dimensional pattern of infected plants in terms of the geometry of the quadrat and the results of quadrat-based analyses is lacking. This problem was examined both empirically and analytically. The empirical approach is based on a set of stochastically generated "mock epidemics" using a Neyman-Scott cluster process. The resultant spatial point-patterns of infected plants have a fixed number of disease foci characterized by a known length scale (monodisperse) and saturated to a known disease level. When quadrat samples of these epidemics are fit to a beta-binomial distribution, the resulting measures of aggregation are totally independent of disease incidence and most strongly dependent on the ratio of the length scale of the quadrat to the length scale of spatial aggregation and to a lesser degree on disease saturation within individual foci. For the analytical approach, the mathematical form for the variation in the sum of random variates is coupled to the geometry of a quadrat through an assumed exponential autocorrelation function. The net result is an explicit equation expressing the intraquadrat correlation, quadrat variance, and the index of dispersion in terms of the ratio of the quadrat length scale to the correlative length scale.

  4. Determination of particle size distributions from acoustic wave propagation measurements

    SciTech Connect

    Spelt, P.D.; Norato, M.A.; Sangani, A.S.; Tavlarides, L.L.

    1999-05-01

    The wave equations for the interior and exterior of the particles are ensemble averaged and combined with an analysis by Allegra and Hawley [J. Acoust. Soc. Am. {bold 51}, 1545 (1972)] for the interaction of a single particle with the incident wave to determine the phase speed and attenuation of sound waves propagating through dilute slurries. The theory is shown to compare very well with the measured attenuation. The inverse problem, i.e., the problem of determining the particle size distribution given the attenuation as a function of frequency, is examined using regularization techniques that have been successful for bubbly liquids. It is shown that, unlike the bubbly liquids, the success of solving the inverse problem is limited since it depends strongly on the nature of particles and the frequency range used in inverse calculations. {copyright} {ital 1999 American Institute of Physics.}

  5. The Angstrom Exponent and Bimodal Aerosol Size Distributions

    NASA Technical Reports Server (NTRS)

    Schuster, Gregory L.; Dubovik, Oleg; Holben, Brent H.

    2005-01-01

    Powerlaws have long been used to describe the spectral dependence of aerosol extinction, and the wavelength exponent of the aerosol extinction powerlaw is commonly referred to as the Angstrom exponent. The Angstrom exponent is often used as a qualitative indicator of aerosol particle size, with values greater than two indicating small particles associated with combustion byproducts, and values less than one indicating large particles like sea salt and dust. In this study, we investigate the relationship between the Angstrom exponent and the mode parameters of bimodal aerosol size distributions using Mie theory calculations and Aerosol Robotic Network (AERONET) retrievals. We find that Angstrom exponents based upon seven wavelengths (0.34, 0.38, 0.44, 0.5, 0.67, 0.87, and 1.02 micrometers) are sensitive to the volume fraction of aerosols with radii less then 0.6 micrometers, but not to the fine mode effective radius. The Angstrom exponent is also known to vary with wavelength, which is commonly referred to as curvature; we show how the spectral curvature can provide additional information about aerosol size distributions for intermediate values of the Angstrom exponent. Curvature also has a significant effect on the conclusions that can be drawn about two-wavelength Angstrom exponents; long wavelengths (0.67, 0.87 micrometers) are sensitive to fine mode volume fraction of aerosols but not fine mode effective radius, while short wavelengths (0.38, 0.44 micrometers) are sensitive to the fine mode effective radius but not the fine mode volume fraction.

  6. Microfluidic-Enabled Liposomes Elucidate Size-Dependent Transdermal Transport

    PubMed Central

    Junqueira, Mariana; Vreeland, Wyatt N.; Quezado, Zenaide; Finkel, Julia C.; DeVoe, Don L.

    2014-01-01

    Microfluidic synthesis of small and nearly-monodisperse liposomes is used to investigate the size-dependent passive transdermal transport of nanoscale lipid vesicles. While large liposomes with diameters above 105 nm are found to be excluded from deeper skin layers past the stratum corneum, the primary barrier to nanoparticle transport, liposomes with mean diameters between 31–41 nm exhibit significantly enhanced penetration. Furthermore, multicolor fluorescence imaging reveals that the smaller liposomes pass rapidly through the stratum corneum without vesicle rupture. These findings reveal that nanoscale liposomes with well-controlled size and minimal size variance are excellent vehicles for transdermal delivery of functional nanoparticle drugs. PMID:24658111

  7. Intercomparison of 15 aerodynamic particle size spectrometers (APS 3321): uncertainties in particle sizing and number size distribution

    NASA Astrophysics Data System (ADS)

    Pfeifer, Sascha; Müller, Thomas; Weinhold, Kay; Zikova, Nadezda; Martins dos Santos, Sebastiao; Marinoni, Angela; Bischof, Oliver F.; Kykal, Carsten; Ries, Ludwig; Meinhardt, Frank; Aalto, Pasi; Mihalopoulos, Nikolaos; Wiedensohler, Alfred

    2016-04-01

    Aerodynamic particle size spectrometers are a well-established method to measure number size distributions of coarse mode particles in the atmosphere. Quality assurance is essential for atmospheric observational aerosol networks to obtain comparable results with known uncertainties. In a laboratory study within the framework of ACTRIS (Aerosols, Clouds, and Trace gases Research Infrastructure Network), 15 aerodynamic particle size spectrometers (APS model 3321, TSI Inc., St. Paul, MN, USA) were compared with a focus on flow rates, particle sizing, and the unit-to-unit variability of the particle number size distribution. Flow rate deviations were relatively small (within a few percent), while the sizing accuracy was found to be within 10 % compared to polystyrene latex (PSL) reference particles. The unit-to-unit variability in terms of the particle number size distribution during this study was within 10 % to 20 % for particles in the range of 0.9 up to 3 µm, which is acceptable for atmospheric measurements. For particles smaller than that, the variability increased up to 60 %, probably caused by differences in the counting efficiencies of individual units. Number size distribution data for particles smaller than 0.9 µm in aerodynamic diameter should only be used with caution. For particles larger than 3 µm, the unit-to-unit variability increased as well. A possible reason is an insufficient sizing accuracy in combination with a steeply sloping particle number size distribution and the increasing uncertainty due to decreasing counting. Particularly this uncertainty of the particle number size distribution must be considered if higher moments of the size distribution such as the particle volume or mass are calculated, which require the conversion of the aerodynamic diameter measured to a volume equivalent diameter. In order to perform a quantitative quality assurance, a traceable reference method for the particle number concentration in the size range 0.5-3 µm

  8. Oligogermanes as molecular precursors for germanium(0) nanoparticles: Size control and size-dependent fluorescence

    SciTech Connect

    Schrick, Aaron C.; Weinert, Charles S.

    2013-10-15

    Graphical abstract: Catenated germanium compounds are employed as molecular precursors for germanium(0) nanoparticles. The size of the nanoparticles, and their fluorescence spectra, depend on the number of catenated germanium atoms present in the precursor. - Highlights: • We have used oligogermanes for the size-specific synthesis of germanium(0) nanoparticles. • The size of the nanomaterials obtained depends directly on the degree of catenation present in the oligogermane precursor. • The nanoparticles are shown to exhibit size-dependent fluorescence. • Oligogermanes will function as useful precursors for the synthesis of a variety of nanomaterials. - Abstract: Germanium nanoparticles were synthesized in solution from novel oligogermane molecular precursors. The size of the nanoparticles obtained is directly related to the number of catenated germanium atoms present in the oligogermane precursor and the nanoparticles exhibit size-dependent fluorescence. The germanium nanoparticles were also characterized by TEM, powder XRD, FTIR, EDS and XPS methods. This method appears to be a promising new route for the synthesis of germanium nanoparticles since the size of the materials obtained can be controlled by the choice of the oligogermane used as the precursor.

  9. Asymmetric Colloidal Janus Particle Formation Is Core-Size-Dependent.

    PubMed

    Landon, Preston B; Mo, Alexander H; Printz, Adam D; Emerson, Chris; Zhang, Chen; Janetanakit, Woraphong; Colburn, David A; Akkiraju, Siddhartha; Dossou, Samuel; Chong, Baxi; Glinsky, Gennadi; Lal, Ratnesh

    2015-08-25

    Colloidal particles with asymmetric surface chemistry (Janus particles) have unique bifunctional properties. The size of these particles is an important determinant for their applications in diverse fields from drug delivery to chemical catalysis. The size of Janus particles, with a core surface coated with carboxylate and a partially encapsulating silica shell, depends upon several factors, including the core size and the concentration of carboxylate coating. The role of the carboxylate coating on the Janus particle size is well-understood; however, the role of the core size is not well defined. The role of the carboxylated polystyrene (cPS) core size on the cPS-silica Janus particle morphology (its size and shape) was examined by testing two different silica sizes and five different cPS core sizes. Results from electron microscopy (EM) and dynamic light scattering (DLS) analysis indicate that the composite cPS-silica particle acquires two distinct shapes: (i) when the size of the cPS core is much smaller than the non-cPS silica (b-SiO2) sphere, partially encapsulated Janus particles are formed, and (ii) when the cPS core is larger than or equal to the b-SiO2 sphere, a raspberry-like structure rather than a Janus particle is formed. The cPS-silica Janus particles of ∼100-500 nm size were obtained when the size of the cPS core was much smaller than the non-cPS silica (b-SiO2) sphere. These scalable nanoscale Janus particles will have wide application in a multifunctional delivery platform and catalysis. PMID:26244597

  10. Pore-size-distribution of cationic polyacrylamide hydrogels

    SciTech Connect

    Kremer, M.; Prausnitz, J.M.

    1992-06-01

    The pore size distribution of a AAm/MAPTAC (acrylamide copolymerized with (3-methacrylamidopropyl)trimethylammonium chloride) hydrogel was investigated using Kuga's mixed-solute-exclusion method, taking into account the wall effect. A Brownian-motion model is also used. Results show the feasibility of determining pore-size distribution of porous materials using the mixed-solute-exclusion method in conjunction with solution of the Fredholm equation; good agreement was obtained with experiment, even for bimodal pore structures. However, different pore size distributions were calculated for the two different probe-solutes (Dextran and poly(ethylene glycol/oxide)). Future work is outlined. 32 figs, 25 refs.

  11. Pore-size-distribution of cationic polyacrylamide hydrogels. Progress report

    SciTech Connect

    Kremer, M.; Prausnitz, J.M.

    1992-06-01

    The pore size distribution of a AAm/MAPTAC (acrylamide copolymerized with (3-methacrylamidopropyl)trimethylammonium chloride) hydrogel was investigated using Kuga`s mixed-solute-exclusion method, taking into account the wall effect. A Brownian-motion model is also used. Results show the feasibility of determining pore-size distribution of porous materials using the mixed-solute-exclusion method in conjunction with solution of the Fredholm equation; good agreement was obtained with experiment, even for bimodal pore structures. However, different pore size distributions were calculated for the two different probe-solutes (Dextran and poly(ethylene glycol/oxide)). Future work is outlined. 32 figs, 25 refs.

  12. The Size Distribution of Jupiter-Family Cometary Nuclei

    NASA Technical Reports Server (NTRS)

    Weissman, Paul R.; Lowry, Stephen C.

    2003-01-01

    Introduction: We are continuing our program to determine the size distribution of cometary nuclei. We have compiled a catalog of 105 measurements of 57 cometary nuclei, drawn from the general literature, from our own program of CCD photometry of distant cometary nuclei (Lowry and Weissman), and from unpublished observations by colleagues. We model the cumulative size distribution of the nuclei as a power law. Previous determinations of the size distribution slope do not agree. Fernandez et al. found a slope of alpha = 2.65+/-0.25 whereas Lowry et al. and Weissman and Lowry each found a slope of alpha = 1.60+/-0.10.

  13. Time-dependent species sensitivity distributions.

    PubMed

    Fox, David R; Billoir, Elise

    2013-02-01

    Time is a central component of toxicity assessments. However, current ecotoxicological practice marginalizes time in concentration-response (C-R) modeling and species sensitivity distribution (SSD) analyses. For C-R models, time is invariably fixed, and toxicity measures are estimated from a function fitted to the data at that time. The estimated toxicity measures are used as inputs to the SSD modeling phase, which similarly avoids explicit recognition of the temporal component. The present study extends some commonly employed probability models for SSDs to derive theoretical results that characterize the time-dependent nature of hazardous concentration (HCx) values. The authors' results show that even from very simple assumptions, more complex patterns in the SSD time dependency can be revealed.

  14. What We Can Learn From Supernova Remnant Size Distributions

    NASA Astrophysics Data System (ADS)

    Elwood, Benjamin; Murphy, Jeremiah; Diaz, Mariangelly

    2016-01-01

    Previous literature regarding size distributions of supernova remnants generally discuss a uniform distribution for the radius, occasionally considering a Gaussian alternative. We indeed show that these distributions are consistent with log-normal, which can be considered a natural consequence of the Central Limit Theorem and Sedov expansion. Modeling explosion energy, remnant age, and ambient density as independent, random distributions, we show, using simple Monte Carlo simulations, that the size distribution is indistinguishable from log-normal when the SNR sample size is of order three hundred. This implies that these SNR distributions provide only information on the mean and variance, yielding additional information only when the sample size grows large. We then proceed to Bayesian statistical inference to characterize the information provided by the size distributions. In particular, we use the mean and variance of sizes and explosion energies to subsequently estimate the mean and variance of the ambient medium surrounding SNR progenitors. This in turn allows us to characterize potential bias in studies involving samples of supernova remnants.

  15. Size-dependent Strain in Epitaxial (001)Gadolinium-doped Ceria Nanoislands

    SciTech Connect

    V Solovyov; M Gibert; T Puig; X Obradors

    2011-12-31

    We report size-dependent strain in epitaxial gadolinium doped ceria nanoislands, which was determined by synchrotron x-ray diffraction. Reciprocal space sections of symmetric, (004) and asymmetric, (224) reflections are approximated by a model assuming size-dependent strain of the islands using real-space size distribution obtained by atomic force microscopy. We show that the islands smaller than 40 nm are subjected to a high level of lateral tensile strain and normal compression. The lateral to normal strain ratio determined from the reciprocal map analysis suggests that lateral tension is the primary stress generator, possibly due to oxygen vacancy ordering on the island-substrate interface.

  16. Determination of aerosol size distributions from spectral attenuation measurements.

    PubMed

    Grassl, H

    1971-11-01

    An iteration method for the determination of size distributions of aerosols from spectral attenuation data, similar to the one previously published for clouds, is presented. The basis for this iteration is to consider the extinction efficiency factor of particles as a set of weighting functions covering the entire radius region of a distribution. The weighting functions were calculated exactly from the Mie theory. Aerosol distributions are shown derived from tests with analytical size distributions and also generated from measured aerosol extinction data in seven spectral channels from 0.4-microto 10-micro wavelength in continental aerosols. The influence of relative humidity on the complex index of refraction is also discussed.

  17. Liquid crystal size selection of large-size graphene oxide for size-dependent N-doping and oxygen reduction catalysis.

    PubMed

    Lee, Kyung Eun; Kim, Ji Eun; Maiti, Uday Narayan; Lim, Joonwon; Hwang, Jin Ok; Shim, Jongwon; Oh, Jung Jae; Yun, Taeyeong; Kim, Sang Ouk

    2014-09-23

    Graphene oxide (GO) is aqueous-dispersible oxygenated graphene, which shows colloidal discotic liquid crystallinity. Many properties of GO-based materials, including electrical conductivity and mechanical properties, are limited by the small flake size of GO. Unfortunately, typical sonochemical exfoliation of GO from graphite generally leads to a broad size and shape distribution. Here, we introduce a facile size selection of large-size GO exploiting liquid crystallinity and investigate the size-dependent N-doping and oxygen reduction catalysis. In the biphasic GO dispersion where both isotropic and liquid crystalline phases are equilibrated, large-size GO flakes (>20 μm) are spontaneously concentrated within the liquid crystalline phase. N-Doping and reduction of the size-selected GO exhibit that N-dopant type is highly dependent on GO flake size. Large-size GO demonstrates quaternary dominant N-doping and the lowest onset potential (-0.08 V) for oxygen reduction catalysis, signifying that quaternary N-dopants serve as principal catalytic sites in N-doped graphene. PMID:25145457

  18. INITIAL PLANETESIMAL SIZES AND THE SIZE DISTRIBUTION OF SMALL KUIPER BELT OBJECTS

    SciTech Connect

    Schlichting, Hilke E.; Fuentes, Cesar I.; Trilling, David E.

    2013-08-01

    The Kuiper Belt is a remnant from the early solar system and its size distribution contains many important constraints that can be used to test models of planet formation and collisional evolution. We show, by comparing observations with theoretical models, that the observed Kuiper Belt size distribution is well matched by coagulation models, which start with an initial planetesimal population with radii of about 1 km, and subsequent collisional evolution. We find that the observed size distribution above R {approx} 30 km is primordial, i.e., it has not been modified by collisional evolution over the age of the solar system, and that the size distribution below R {approx} 30 km has been modified by collisions and that its slope is well matched by collisional evolution models that use published strength laws. We investigate in detail the resulting size distribution of bodies ranging from 0.01 km to 30 km and find that its slope changes several times as a function of radius before approaching the expected value for an equilibrium collisional cascade of material strength dominated bodies for R {approx}< 0.1 km. Compared to a single power-law size distribution that would span the whole range from 0.01 km to 30 km, we find in general a strong deficit of bodies around R {approx} 10 km and a strong excess of bodies around 2 km in radius. This deficit and excess of bodies are caused by the planetesimal size distribution left over from the runaway growth phase, which left most of the initial mass in small planetesimals while only a small fraction of the total mass is converted into large protoplanets. This excess mass in small planetesimals leaves a permanent signature in the size distribution of small bodies that is not erased after 4.5 Gyr of collisional evolution. Observations of the small Kuiper Belt Object (KBO) size distribution can therefore test if large KBOs grew as a result of runaway growth and constrained the initial planetesimal sizes. We find that results from

  19. A statistical approach to estimate the 3D size distribution of spheres from 2D size distributions

    USGS Publications Warehouse

    Kong, M.; Bhattacharya, R.N.; James, C.; Basu, A.

    2005-01-01

    Size distribution of rigidly embedded spheres in a groundmass is usually determined from measurements of the radii of the two-dimensional (2D) circular cross sections of the spheres in random flat planes of a sample, such as in thin sections or polished slabs. Several methods have been devised to find a simple factor to convert the mean of such 2D size distributions to the actual 3D mean size of the spheres without a consensus. We derive an entirely theoretical solution based on well-established probability laws and not constrained by limitations of absolute size, which indicates that the ratio of the means of measured 2D and estimated 3D grain size distribution should be r/4 (=.785). Actual 2D size distribution of the radii of submicron sized, pure Fe0 globules in lunar agglutinitic glass, determined from backscattered electron images, is tested to fit the gamma size distribution model better than the log-normal model. Numerical analysis of 2D size distributions of Fe0 globules in 9 lunar soils shows that the average mean of 2D/3D ratio is 0.84, which is very close to the theoretical value. These results converge with the ratio 0.8 that Hughes (1978) determined for millimeter-sized chondrules from empirical measurements. We recommend that a factor of 1.273 (reciprocal of 0.785) be used to convert the determined 2D mean size (radius or diameter) of a population of spheres to estimate their actual 3D size. ?? 2005 Geological Society of America.

  20. THE EFFECT OF THE DUST SIZE DISTRIBUTION ON ASTEROID POLARIZATION

    SciTech Connect

    Masiero, Joseph; Hartzell, Christine; Scheeres, Daniel J. E-mail: christine.hartzell@colorado.edu

    2009-12-15

    We have developed a theoretical description of how of an asteroid's polarization-phase curve will be affected by the removal of the dust from the surface due to a size-dependent phenomenon such as radiation pressure-driven escape of levitated particles. We test our calculations against new observations of four small (D {approx} 1 km) near-Earth asteroids (NEAs; (85236), (142348), (162900), and 2006 SZ{sub 217}) obtained with the Dual Beam Imaging Polarimeter on the University of Hawaii's 2.2 m telescope, as well as previous observations of (25143) Itokawa and (433) Eros. We find that the polarization of the light reflected from an asteroid is controlled by the mineralogical and chemical composition of the surface and is independent of dust particle. The relation between the slope of the polarization-phase curve beyond the inversion angle and the albedo of an asteroid is thus independent of the surface regolith size distribution and is valid for both Main Belt and NEAs.

  1. Laser induced mechanisms controlling the size distribution of metallic nanoparticles.

    PubMed

    Liu, Zeming; Vitrant, Guy; Lefkir, Yaya; Bakhti, Said; Destouches, Nathalie

    2016-09-21

    This paper describes a model to simulate changes in the size distribution of metallic nanoparticles (NPs) in TiO2 films upon continuous wave light excitation. Interrelated laser induced physical and chemical processes initiated directly by photon absorption or by plasmon induced thermal heating are considered. Namely the model takes into account the NP coalescence, Ostwald ripening, the reduction of silver ions and the oxidation of metallic NPs, competitive mechanisms that can lead to counter-intuitive behaviors depending on the exposure conditions. Theoretical predictions are compared successfully to the experimental results deduced from a thorough analysis of scanning transmission electron microscopy (STEM) pictures of Ag:TiO2 films processed with a scanning visible laser beam at different speeds. Ag:TiO2 systems are considered for many applications in solar energy conversion, photocatalysis or secured data printing. Numerical investigations of such a system provide a better understanding of light induced growth and shrinking processes and open up prospects for designing more efficient photocatalytic devices based on metal NP doped TiO2 or for improving the size homogeneity in self-organized metallic NP patterns, for instance. PMID:27539293

  2. Nanocrystal size distribution analysis from transmission electron microscopy images

    NASA Astrophysics Data System (ADS)

    van Sebille, Martijn; van der Maaten, Laurens J. P.; Xie, Ling; Jarolimek, Karol; Santbergen, Rudi; van Swaaij, René A. C. M. M.; Leifer, Klaus; Zeman, Miro

    2015-12-01

    We propose a method, with minimal bias caused by user input, to quickly detect and measure the nanocrystal size distribution from transmission electron microscopy (TEM) images using a combination of Laplacian of Gaussian filters and non-maximum suppression. We demonstrate the proposed method on bright-field TEM images of an a-SiC:H sample containing embedded silicon nanocrystals with varying magnifications and we compare the accuracy and speed with size distributions obtained by manual measurements, a thresholding method and PEBBLES. Finally, we analytically consider the error induced by slicing nanocrystals during TEM sample preparation on the measured nanocrystal size distribution and formulate an equation to correct this effect.We propose a method, with minimal bias caused by user input, to quickly detect and measure the nanocrystal size distribution from transmission electron microscopy (TEM) images using a combination of Laplacian of Gaussian filters and non-maximum suppression. We demonstrate the proposed method on bright-field TEM images of an a-SiC:H sample containing embedded silicon nanocrystals with varying magnifications and we compare the accuracy and speed with size distributions obtained by manual measurements, a thresholding method and PEBBLES. Finally, we analytically consider the error induced by slicing nanocrystals during TEM sample preparation on the measured nanocrystal size distribution and formulate an equation to correct this effect. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06292f

  3. A multiscale gradient-dependent plasticity model for size effects

    NASA Astrophysics Data System (ADS)

    Lyu, Hao; Taheri-Nassaj, Nasrin; Zbib, Hussein M.

    2016-06-01

    The mechanical behaviour of polycrystalline material is closely correlated to grain size. In this study, we investigate the size-dependent phenomenon in multi-phase steels using a continuum dislocation dynamic model coupled with viscoplastic self-consistent model. We developed a dislocation-based strain gradient plasticity model and a stress gradient plasticity model, as well as a combined model, resulting in a theory that can predict size effect over a wide range of length scales. Results show that strain gradient plasticity and stress gradient plasticity are complementary rather than competing theories. The stress gradient model is dominant at the initial strain stage, and is much more effective for predicting yield strength than the strain gradient model. For larger deformations, the strain gradient model is dominant and more effective for predicting size-dependent hardening. The numerical results are compared with experimental data and it is found that they have the same trend for the yield stress. Furthermore, the effect of dislocation density at different strain stages is investigated, and the findings show that the Hall-Petch relation holds for the initial strain stage and breaks down for higher strain levels. Finally, a power law to describe the size effect and the transition zone between the strain gradient and stress gradient dominated regions is developed.

  4. Narrow size distributed Ag nanoparticles grown by spin coating and thermal reduction: effect of processing parameters

    NASA Astrophysics Data System (ADS)

    Ansari, A. A.; Sartale, S. D.

    2016-08-01

    A simple method to grow uniform sized Ag nanoparticles with narrow size distribution on flat support (glass and Si substrates) via spin coating of Ag+ ions (AgNO3) solution followed by thermal reduction in H2 is presented. These grown nanoparticles can be used as model catalytic system to study size dependent oxygen reduction reaction (ORR) activity. Ag nanoparticles formation was confirmed by local surface plasmon resonance and x-ray photoelectron spectroscopy measurements. Influences of process parameters (revolution per minute (rpm), ramp and salt concentration) on grown Ag nanoparticles size, density and size uniformity are studied. With increase in rpm and ramp the size decreases and the particle number density increases, whereas the size dispersion improves. The catalytic activity of the grown Ag particles for ORR is studied and it is found that the catalytic performance is dependent on the size as well as the number density of the grown Ag nanoparticles.

  5. Does Nanoparticle Activity Depend upon Size and Crystal Phase?

    PubMed Central

    Jiang, Jingkun; Oberdörster, Günter; Elder, Alison; Gelein, Robert; Mercer, Pamela; Biswas, Pratim

    2010-01-01

    A method to investigate the dependence of the physicochemical properties of nanoparticles (e.g. size, surface area and crystal phase) on their oxidant generating capacity is proposed and demonstrated for TiO2 nanoparticles. Gas phase synthesis methods that allow for strict control of size and crystal phase were used to prepare TiO2 nanoparticles. The reactive oxygen species (ROS) generating capacity of these particles was then measured. The size dependent ROS activity was established using TiO2 nanoparticles of 9 different sizes (4 – 195 nm) but the same crystal phase. For a fixed total surface area, an S-shaped curve for ROS generation per unit surface area was observed as a function of particle size. The highest ROS activity per unit area was observed for 30 nm particles, and observed to be constant above 30 nm. There was a decrease in activity per unit area as size decreased from 30 nm to 10 nm; and again constant for particles smaller than 10 nm. The correlation between crystal phase and oxidant capacity was established using TiO2 nanoparticles of 11 different crystal phase combinations but similar size. The ability of different crystal phases of TiO2 nanoparticles to generate ROS was highest for amorphous, followed by anatase, and then anatase/rutile mixtures, and lowest for rutile samples. Based on evaluation of the entire dataset, important dose metrics for ROS generation are established. Their implications of these ROS studies on biological and toxicological studies using nanomaterials are discussed. PMID:20827377

  6. Distribution of cooperative unit size of amphiphilic molecules in the phase coexistence region in Langmuir monolayers.

    PubMed

    Hatta, E; Nishimura, T

    2013-02-01

    The dependence of the size of the cooperative unit (C.U.) of amphiphilic molecules on surface pressure (π) in the liquid expanded (LE)-liquid condensed (LC) phase coexistence region of Langmuir monolayers has been formulated and calculated using measured isotherm data. The C.U. size changes largely depending on the surface pressure in the coexistence region: these submicroscopic molecular aggregates are not static objects, but dynamic ones characterized by large fluctuations in size. It has been found that the C.U. size distribution can be a natural consequence of the significant change of monolayer compressibility, which reflects large molecular area density fluctuations, in the coexistence region.

  7. Airborne Particle Size Distribution Measurements at USDOE Fernald

    SciTech Connect

    Harley, N.H.; Chittaporn, P.; Heikkinen, M.; Medora, R.; Merrill, R.

    2003-03-27

    There are no long term measurements of the particle size distribution and concentration of airborne radionuclides at any USDOE facility except Fernald. Yet the determinant of lung dose is the particle size, determining the airway and lower lung deposition. Beginning in 2000, continuous (6 to 8 weeks) measurements of the aerosol particle size distribution have been made with a miniature sampler developed under EMSP. Radon gas decays to a chain of four short lived solid radionuclides that attach immediately to the resident atmospheric aerosol. These in turn decay to long lived polonium 210. Alpha emitting polonium is a tracer for any atmospheric aerosol. Six samplers at Fernald and four at QC sites in New Jersey show a difference in both polonium concentration and size distribution with the winter measurements being higher/larger than summer by almost a factor of two at all locations. EMSP USDOE Contract DE FG07 97ER62522.

  8. Characterization of events by aerosol mass size distributions.

    PubMed

    Nicolás, José; Yubero, Eduardo; Galindo, Nuria; Giménez, Joaquín; Castañer, Ramón; Carratalá, Adoración; Crespo, Javier; Pastor, Carlos

    2009-02-01

    Continuous measurements of particle mass size distributions were carried out in summer 2004 at an urban location in the western Mediterranean using an optical particle counter. In this work we propose a simple methodology to identify PM episodes and determine their influence on mass size distributions. During the study period three types of event produced a significant increase in TSP daily levels: Saharan dust intrusions, firework displays and strong winds, modifying size distributions in different ways. As well, a traffic-related mass size spectrum was obtained showing road dust particles injected into the atmosphere by vehicle-induced resuspension having mainly aerodynamic diameters between 5 and 15 microm. This was confirmed by principal component and conditional probability function analyses.

  9. Particle size and shape distributions of hammer milled pine

    SciTech Connect

    Westover, Tyler Lott; Matthews, Austin Colter; Williams, Christopher Luke; Ryan, John Chadron Benjamin

    2015-04-01

    Particle size and shape distributions impact particle heating rates and diffusion of volatized gases out of particles during fast pyrolysis conversion, and consequently must be modeled accurately in order for computational pyrolysis models to produce reliable results for bulk solid materials. For this milestone, lodge pole pine chips were ground using a Thomas-Wiley #4 mill using two screen sizes in order to produce two representative materials that are suitable for fast pyrolysis. For the first material, a 6 mm screen was employed in the mill and for the second material, a 3 mm screen was employed in the mill. Both materials were subjected to RoTap sieve analysis, and the distributions of the particle sizes and shapes were determined using digital image analysis. The results of the physical analysis will be fed into computational pyrolysis simulations to create models of materials with realistic particle size and shape distributions. This milestone was met on schedule.

  10. Size distribution of microbubbles as a function of shell composition.

    PubMed

    Dicker, Stephen; Mleczko, Michał; Schmitz, Georg; Wrenn, Steven P

    2013-09-01

    The effect of modifying the shell composition of a population of microbubbles on their size demonstrated through experiment. Specifically, these variations include altering both the mole fraction and molecular weight of functionalized polymer, polyethylene glycol (PEG) in the microbubble phospholipid monolayer shell (1-15 mol% PEG, and 1000-5000 g/mole, respectively). The size distribution is measured with an unbiased image segmentation program written in MATLAB which identifies and sizes bubbles from micrographs. For a population of microbubbles with a shell composition of 5 mol% PEG2000, the mean diameter is 1.42 μm with a variance of 0.244 μm. For the remainder of the shell compositions studied herein, we find that the size distributions do not show a statistically significant correlation to either PEG molecular weight or mole fraction. All the measured distributions are nearly Gaussian in shape and have a monomodal peak.

  11. Nano-material size dependent laser-plasma thresholds

    NASA Astrophysics Data System (ADS)

    EL Sherbini, Ashraf M.; Parigger, Christian G.

    2016-10-01

    The reduction of laser fluence for initiation of plasma was measured for zinc monoxide nanoparticles of diameters in the range of 100 to 20 nm. In a previous work by EL Sherbini and Parigger [Wavelength Dependency and Threshold Measurements for Nanoparticle-enhanced Laser-induced Breakdown Spectroscopy, Spectrochim. Acta Part B 116 (2016) 8-15], the hypothesis of threshold dependence on particle size leads to the interpretation of the experiments for varying excitation wavelengths with fixed, 30 nm nanomaterial. The experimental results presented in this work were obtained with 1064 nm Nd:YAG radiation and confirm and validate the suspected reduction due to quenching of the thermal conduction length to the respective sizes of the nanoparticles.

  12. Inferring Volcanic Degassing Processes From Vesicle Size Distributions

    NASA Astrophysics Data System (ADS)

    Blower, J. D.; Keating, J. P.; Mader, H. M.; Phillips, J. C.

    2001-12-01

    Both power law and exponential vesicle size distributions (VSDs) have been observed in many different types of volcanic rocks. We present results of laboratory analogue experiments, of the type pioneered by Brad Sturtevant, which reproduce these observations, and use experimental results and computer simulations to show that the distributions can be interpreted as the product of continuous bubble nucleation resulting from non-equilibrium degassing. This ongoing nucleation causes the bubbles to evolve through an exponential size distribution into a power law size distribution as nucleation and growth progress. The process of continuous nucleation is a mechanism whereby the volcanic system maintains near-equilibrium in the case of rapid depressurisation and slow volatile diffusion.

  13. Packing fraction of particles with lognormal size distribution.

    PubMed

    Brouwers, H J H

    2014-05-01

    This paper addresses the packing and void fraction of polydisperse particles with a lognormal size distribution. It is demonstrated that a binomial particle size distribution can be transformed into a continuous particle-size distribution of the lognormal type. Furthermore, an original and exact expression is derived that predicts the packing fraction of mixtures of particles with a lognormal distribution, which is governed by the standard deviation, mode of packing, and particle shape only. For a number of particle shapes and their packing modes (close, loose) the applicable values are given. This closed-form analytical expression governing the packing fraction is thoroughly compared with empirical and computational data reported in the literature, and good agreement is found.

  14. Density, chemistry, and size distribution of interplanetary dust

    NASA Technical Reports Server (NTRS)

    Brownlee, D. E.; Horz, F.; Hartung, J. B.; Gault, D. E.

    1975-01-01

    Depth/diameter ratios measured for 98 craters in lunar glass targets reveal a broad distribution with a single strong peaking between 0.55 and 0.8. The measured values indicate a mean meteoroid density greater than 1 g/cu cm and probably less than 4 g/cu cm. Microprobe analyses show that typical glass pit liners on silicate targets contain only approximately 0.1% or less of meteoritic material. The size-frequency distribution of meteoroids was analyzed for a fractured glass surface of 60095, and a very steep size distribution of submicron meteoroids is indicated. As in the case of 15205, a dip at approximately 5 micron in the size-frequency distribution is detected.

  15. Size-dependent diffusion promotes the emergence of spatiotemporal patterns.

    PubMed

    Zhang, Lai; Thygesen, Uffe Høgsbro; Banerjee, Malay

    2014-07-01

    Spatiotemporal patterns, indicating the spatiotemporal variability of individual abundance, are a pronounced scenario in ecological interactions. Most of the existing models for spatiotemporal patterns treat species as homogeneous groups of individuals with average characteristics by ignoring intraspecific physiological variations at the individual level. Here we explore the impacts of size variation within species resulting from individual ontogeny, on the emergence of spatiotemporal patterns in a fully size-structured population model. We found that size dependency of animal's diffusivity greatly promotes the formation of spatiotemporal patterns, by creating regular spatiotemporal patterns out of temporal chaos. We also found that size-dependent diffusion can substitute large-amplitude base harmonics with spatiotemporal patterns with lower amplitude oscillations but with enriched harmonics. Finally, we found that the single-generation cycle is more likely to drive spatiotemporal patterns compared to predator-prey cycles, meaning that the mechanism of Hopf bifurcation might be more common than hitherto appreciated since the former cycle is more widespread than the latter in case of interacting populations. Due to the ubiquity of individual ontogeny in natural ecosystems we conclude that diffusion variability within populations is a significant driving force for the emergence of spatiotemporal patterns. Our results offer a perspective on self-organized phenomena, and pave a way to understand such phenomena in systems organized as complex ecological networks. PMID:25122357

  16. Population dynamic theory of size-dependent cannibalism.

    PubMed Central

    Claessen, David; de Roos, André M.; Persson, Lennart

    2004-01-01

    Cannibalism is characterized by four aspects: killing victims, gaining energy from victims, size-dependent interactions and intraspecific competition. In this review of mathematical models of cannibalistic populations, we relate the predicted population dynamic consequences of cannibalism to its four defining aspects. We distinguish five classes of effects of cannibalism: (i) regulation of population size; (ii) destabilization resulting in population cycles or chaos; (iii) stabilization by damping population cycles caused by other interactions; (iv) bistability such that, depending on the initial conditions, the population converges to one of two possible stable states; and (v) modification of the population size structure. The same effects of cannibalism may be caused by different combinations of aspects of cannibalism. By contrast, the same combination of aspects may lead to different effects. For particular cannibalistic species, the consequences of cannibalism will depend on the presence and details of the four defining aspects. Empirical evidence for the emerged theory of cannibalism is discussed briefly. The implications of the described dynamic effects of cannibalism are discussed in the context of community structure, making a comparison with the community effects of intraguild predation. PMID:15101690

  17. On the origin of size-dependent and size-independent crystal growth: Influence of advection and diffusion

    USGS Publications Warehouse

    Kile, D.E.; Eberl, D.D.

    2003-01-01

    Crystal growth experiments were conducted using potassium alum and calcite crystals in aqueous solution under both non-stirred and stirred conditions to elucidate the mechanism for size-dependent (proportionate) and size-independent (constant) crystal growth. Growth by these two laws can be distinguished from each other because the relative size difference among crystals is maintained during proportionate growth, leading to a constant crystal size variance (??2) for a crystal size distribution (CSD) as the mean size increases. The absolute size difference among crystals is maintained during constant growth, resulting in a decrease in size variance. Results of these experiments show that for centimeter-sized alum crystals, proportionate growth occurs in stirred systems, whereas constant growth occurs in non-stirred systems. Accordingly, the mechanism for proportionate growth is hypothesized to be related to the supply of reactants to the crystal surface by advection, whereas constant growth is related to supply by diffusion. Paradoxically, micrometer-sized calcite crystals showed proportionate growth both in stirred and in non-stirred systems. Such growth presumably results from the effects of convection and Brownian motion, which promote an advective environment and hence proportionate growth for minute crystals in non-stirred systems, thereby indicating the importance of solution velocity relative to crystal size. Calcite crystals grown in gels, where fluid motion was minimized, showed evidence for constant, diffusion-controlled growth. Additional investigations of CSDs of naturally occurring crystals indicate that proportionate growth is by far the most common growth law, thereby suggesting that advection, rather than diffusion, is the dominant process for supplying reactants to crystal surfaces.

  18. Crater size distributions on Ganymede and Callisto: fundamental issues

    NASA Astrophysics Data System (ADS)

    Wagner, Roland; Schmedemann, Nico; Werner, Stefanie; Ivanov, Boris; Stephan, Katrin; Jaumann, Ralf

    2015-04-01

    Crater size distributions on the two largest Jovian satellites Ganymede and Callisto and the origin of impactors are subject of intense and controversial debates. In this paper, we reinvestigate crater size distributions measured in surface units derived from a recently published global geologic map, based on Voyager and Galileo SSI images at a scale of 1 km/pxl (Collins G. C. et al. (2013), U. S. Geol. Surv., Sci. Inv. Map 3237). These units are used as a context to units mapped in more detail at higher resolution in Galileo SSI images. We focus on the following fundamental issues: (1) Similarity between shapes of crater distributions on the Galilean satellites and on inner solar system bodies; (2) production versus equilibrium distributions; (3) apex/antapex variations in crater distributions. First, our results show a strong similarity in shape between the crater distributions on the most densely cratered regions on Ganymede and Callisto with those in the lunar highlands. We conclude that the shape of the crater distributions on these two Jovian satellites implies the craters were preferentially formed from members of a collisionally evolved projectile family, derived either from Main Belt asteroids as candidates of impactors on the Jovian satellites, or from projectiles stemming from the outer solar system which have undergone collisional evolution, resulting in a size distribution similar to those of Main Belt asteroids. Second, the complex shape of the crater distributions on Ganymede and Callisto indicates they are mostly production distributions and can be used to infer the underlying shape of the projectile size distribution. Locally, equilibrium distributions occur, especially at smaller sub-kilometer diameters. Third, the most densely cratered regions on both satellites do not show apex-antapex variations in crater frequency, as inferred for bodies from heliocentric orbits (e.g., Zahnle K. et al. (2003), Icarus 163, 263-289). This indicates that these

  19. Anomalous size dependence of the thermal conductivity of graphene ribbons.

    PubMed

    Nika, Denis L; Askerov, Artur S; Balandin, Alexander A

    2012-06-13

    We investigated the thermal conductivity K of graphene ribbons and graphite slabs as the function of their lateral dimensions. Our theoretical model considered the anharmonic three-phonon processes to the second-order and included the angle-dependent phonon scattering from the ribbon edges. It was found that the long mean free path of the long-wavelength acoustic phonons in graphene can lead to an unusual nonmonotonic dependence of the thermal conductivity on the length L of a ribbon. The effect is pronounced for the ribbons with the smooth edges (specularity parameter p > 0.5). Our results also suggest that, contrary to what was previously thought, the bulk-like three-dimensional phonons in graphite make a rather substantial contribution to its in-plane thermal conductivity. The Umklapp-limited thermal conductivity of graphite slabs scales, for L below ∼30 μm, as log(L), while for larger L, the thermal conductivity approaches a finite value following the dependence K(0) - A × L(-1/2), where K(0) and A are parameters independent of the length. Our theoretical results clarify the scaling of the phonon thermal conductivity with the lateral sizes in graphene and graphite. The revealed anomalous dependence K(L) for the micrometer-size graphene ribbons can account for some of the discrepancy in reported experimental data for graphene.

  20. Size Distributions of Solar Proton Events: Methodological and Physical Restrictions

    NASA Astrophysics Data System (ADS)

    Miroshnichenko, L. I.; Yanke, V. G.

    2016-10-01

    Based on the new catalogue of solar proton events (SPEs) for the period of 1997 - 2009 (Solar Cycle 23) we revisit the long-studied problem of the event-size distributions in the context of those constructed for other solar-flare parameters. Recent results on the problem of size distributions of solar flares and proton events are briefly reviewed. Even a cursory acquaintance with this research field reveals a rather mixed and controversial picture. We concentrate on three main issues: i) SPE size distribution for > 10 MeV protons in Solar Cycle 23; ii) size distribution of > 1 GV proton events in 1942 - 2014; iii) variations of annual numbers for > 10 MeV proton events on long time scales (1955 - 2015). Different results are critically compared; most of the studies in this field are shown to suffer from vastly different input datasets as well as from insufficient knowledge of underlying physical processes in the SPEs under consideration. New studies in this field should be made on more distinct physical and methodological bases. It is important to note the evident similarity in size distributions of solar flares and superflares in Sun-like stars.

  1. Size dependent strengthening mechanisms in sputtered Fe/W multilayers

    NASA Astrophysics Data System (ADS)

    Li, Nan; Yu, K. Y.; Lee, J.; Wang, H.; Zhang, X.

    2010-05-01

    We investigate size dependent strengthening mechanisms in sputtered Fe/W multilayers with individual layer thickness, h, varying from 1 to 200 nm. Microstructure analyses reveal that Fe/W has incoherent bcc/bcc interface when h is greater than 5 nm. When h decreases to 1-2.5 nm, the interface becomes semicoherent, and Fe and W show significant lattice distortions comparing to their bulk counterpart due to interface constraint. The layer thickness dependent drastic variations in x-ray diffraction profiles are simulated well by using an analytical model. Film hardness increases with decreasing h, and approaches a maximum value of 12.5 GPa when h is 1 nm. The layer thickness dependent film hardnesses are compared with analytical models. Koehler's image force plays a major role in determining the maximum strength of composites at smaller h.

  2. Auxin regulates SNARE-dependent vacuolar morphology restricting cell size.

    PubMed

    Löfke, Christian; Dünser, Kai; Scheuring, David; Kleine-Vehn, Jürgen

    2015-03-05

    The control of cellular growth is central to multicellular patterning. In plants, the encapsulating cell wall literally binds neighbouring cells to each other and limits cellular sliding/migration. In contrast to its developmental importance, growth regulation is poorly understood in plants. Here, we reveal that the phytohormone auxin impacts on the shape of the biggest plant organelle, the vacuole. TIR1/AFBs-dependent auxin signalling posttranslationally controls the protein abundance of vacuolar SNARE components. Genetic and pharmacological interference with the auxin effect on vacuolar SNAREs interrelates with auxin-resistant vacuolar morphogenesis and cell size regulation. Vacuolar SNARE VTI11 is strictly required for auxin-reliant vacuolar morphogenesis and loss of function renders cells largely insensitive to auxin-dependent growth inhibition. Our data suggests that the adaptation of SNARE-dependent vacuolar morphogenesis allows auxin to limit cellular expansion, contributing to root organ growth rates.

  3. Integrated microfluidic system capable of size-specific droplet generation with size-dependent droplet separation.

    PubMed

    Lee, Sangmin; Hong, Seok Jun; Yoo, Hyung Jung; Ahn, Jae Hyun; Cho, Dong-il Dan

    2013-06-01

    Droplet-based microfluidics is receiving much attention in biomedical research area due to its advantage in uniform size droplet generation. Our previous results have reported that droplet size plays an important role in drug delivery actuated by flagellated bacteria. Recently, many research groups have been reported the size-dependent separation of emulsion droplets by a microfluidic system. In this paper, an integrated microfluidic system is proposed to produce and sort specificsized droplets sequentially. Operation of the system relies on two microfluidic transport processes: initial generation of droplets by hydrodynamic focusing and subsequent separation of droplets by a T-junction channel. The microfluidic system is fabricated by the SU-8 rapid prototyping method and poly-di-methyl-siloxane (PDMS) replica molding. A biodegradable polymer, poly-capro-lactone (PCL), is used for the droplet material. Using the proposed integrated microfluidic system, specific-sized droplets which can be delivered by flagellated bacteria are successfully generated and obtained. PMID:23858958

  4. Thresholded Power law Size Distributions of Instabilities in Astrophysics

    NASA Astrophysics Data System (ADS)

    Aschwanden, Markus J.

    2015-11-01

    Power-law-like size distributions are ubiquitous in astrophysical instabilities. There are at least four natural effects that cause deviations from ideal power law size distributions, which we model here in a generalized way: (1) a physical threshold of an instability; (2) incomplete sampling of the smallest events below a threshold x0; (3) contamination by an event-unrelated background xb; and (4) truncation effects at the largest events due to a finite system size. These effects can be modeled in the simplest terms with a “thresholded power law” distribution function (also called generalized Pareto [type II] or Lomax distribution), N(x){dx}\\propto {(x+{x}0)}-a{dx}, where x0 > 0 is positive for a threshold effect, while x0 < 0 is negative for background contamination. We analytically derive the functional shape of this thresholded power law distribution function from an exponential growth evolution model, which produces avalanches only when a disturbance exceeds a critical threshold x0. We apply the thresholded power law distribution function to terrestrial, solar (HXRBS, BATSE, RHESSI), and stellar flare (Kepler) data sets. We find that the thresholded power law model provides an adequate fit to most of the observed data. Major advantages of this model are the automated choice of the power law fitting range, diagnostics of background contamination, physical instability thresholds, instrumental detection thresholds, and finite system size limits. When testing self-organized criticality models that predict ideal power laws, we suggest including these natural truncation effects.

  5. On the Challenge of Fitting Tree Size Distributions in Ecology

    PubMed Central

    Taubert, Franziska; Hartig, Florian; Dobner, Hans-Jürgen; Huth, Andreas

    2013-01-01

    Patterns that resemble strongly skewed size distributions are frequently observed in ecology. A typical example represents tree size distributions of stem diameters. Empirical tests of ecological theories predicting their parameters have been conducted, but the results are difficult to interpret because the statistical methods that are applied to fit such decaying size distributions vary. In addition, binning of field data as well as measurement errors might potentially bias parameter estimates. Here, we compare three different methods for parameter estimation – the common maximum likelihood estimation (MLE) and two modified types of MLE correcting for binning of observations or random measurement errors. We test whether three typical frequency distributions, namely the power-law, negative exponential and Weibull distribution can be precisely identified, and how parameter estimates are biased when observations are additionally either binned or contain measurement error. We show that uncorrected MLE already loses the ability to discern functional form and parameters at relatively small levels of uncertainties. The modified MLE methods that consider such uncertainties (either binning or measurement error) are comparatively much more robust. We conclude that it is important to reduce binning of observations, if possible, and to quantify observation accuracy in empirical studies for fitting strongly skewed size distributions. In general, modified MLE methods that correct binning or measurement errors can be applied to ensure reliable results. PMID:23469137

  6. Body size distributions of the pale grass blue butterfly in Japan: Size rules and the status of the Fukushima population.

    PubMed

    Taira, Wataru; Iwasaki, Mayo; Otaki, Joji M

    2015-07-22

    The body size of the pale grass blue butterfly, Zizeeria maha, has been used as an environmental indicator of radioactive pollution caused by the Fukushima nuclear accident. However, geographical and temporal size distributions in Japan and temperature effects on size have not been established in this species. Here, we examined the geographical, temporal, and temperature-dependent changes of the forewing size of Z. maha argia in Japan. Butterflies collected in 2012 and 2013 from multiple prefectures throughout Japan demonstrated an inverse relationship of latitude and forewing size, which is the reverse of Bergmann's cline. The Fukushima population was significantly larger than the Aomori and Miyagi populations and exhibited no difference from most of the other prefectural populations. When monitored at a single geographic locality every other month, forewing sizes were the largest in April and the smallest in August. Rearing larvae at a constant temperature demonstrated that forewing size followed the temperature-size rule. Therefore, the converse Bergmann's rule and the temperature-size rule coexist in this multivoltine species. Our study establishes this species as a useful environmental indicator and supports the idea that the size reduction observed only in Fukushima Prefecture in 2011 was caused by the environmental stress of radioactive pollution.

  7. Body size distributions of the pale grass blue butterfly in Japan: Size rules and the status of the Fukushima population

    NASA Astrophysics Data System (ADS)

    Taira, Wataru; Iwasaki, Mayo; Otaki, Joji M.

    2015-07-01

    The body size of the pale grass blue butterfly, Zizeeria maha, has been used as an environmental indicator of radioactive pollution caused by the Fukushima nuclear accident. However, geographical and temporal size distributions in Japan and temperature effects on size have not been established in this species. Here, we examined the geographical, temporal, and temperature-dependent changes of the forewing size of Z. maha argia in Japan. Butterflies collected in 2012 and 2013 from multiple prefectures throughout Japan demonstrated an inverse relationship of latitude and forewing size, which is the reverse of Bergmann’s cline. The Fukushima population was significantly larger than the Aomori and Miyagi populations and exhibited no difference from most of the other prefectural populations. When monitored at a single geographic locality every other month, forewing sizes were the largest in April and the smallest in August. Rearing larvae at a constant temperature demonstrated that forewing size followed the temperature-size rule. Therefore, the converse Bergmann’s rule and the temperature-size rule coexist in this multivoltine species. Our study establishes this species as a useful environmental indicator and supports the idea that the size reduction observed only in Fukushima Prefecture in 2011 was caused by the environmental stress of radioactive pollution.

  8. Body size distributions of the pale grass blue butterfly in Japan: Size rules and the status of the Fukushima population

    PubMed Central

    Taira, Wataru; Iwasaki, Mayo; Otaki, Joji M.

    2015-01-01

    The body size of the pale grass blue butterfly, Zizeeria maha, has been used as an environmental indicator of radioactive pollution caused by the Fukushima nuclear accident. However, geographical and temporal size distributions in Japan and temperature effects on size have not been established in this species. Here, we examined the geographical, temporal, and temperature-dependent changes of the forewing size of Z. maha argia in Japan. Butterflies collected in 2012 and 2013 from multiple prefectures throughout Japan demonstrated an inverse relationship of latitude and forewing size, which is the reverse of Bergmann’s cline. The Fukushima population was significantly larger than the Aomori and Miyagi populations and exhibited no difference from most of the other prefectural populations. When monitored at a single geographic locality every other month, forewing sizes were the largest in April and the smallest in August. Rearing larvae at a constant temperature demonstrated that forewing size followed the temperature-size rule. Therefore, the converse Bergmann’s rule and the temperature-size rule coexist in this multivoltine species. Our study establishes this species as a useful environmental indicator and supports the idea that the size reduction observed only in Fukushima Prefecture in 2011 was caused by the environmental stress of radioactive pollution. PMID:26197998

  9. Body size distributions of the pale grass blue butterfly in Japan: Size rules and the status of the Fukushima population.

    PubMed

    Taira, Wataru; Iwasaki, Mayo; Otaki, Joji M

    2015-01-01

    The body size of the pale grass blue butterfly, Zizeeria maha, has been used as an environmental indicator of radioactive pollution caused by the Fukushima nuclear accident. However, geographical and temporal size distributions in Japan and temperature effects on size have not been established in this species. Here, we examined the geographical, temporal, and temperature-dependent changes of the forewing size of Z. maha argia in Japan. Butterflies collected in 2012 and 2013 from multiple prefectures throughout Japan demonstrated an inverse relationship of latitude and forewing size, which is the reverse of Bergmann's cline. The Fukushima population was significantly larger than the Aomori and Miyagi populations and exhibited no difference from most of the other prefectural populations. When monitored at a single geographic locality every other month, forewing sizes were the largest in April and the smallest in August. Rearing larvae at a constant temperature demonstrated that forewing size followed the temperature-size rule. Therefore, the converse Bergmann's rule and the temperature-size rule coexist in this multivoltine species. Our study establishes this species as a useful environmental indicator and supports the idea that the size reduction observed only in Fukushima Prefecture in 2011 was caused by the environmental stress of radioactive pollution. PMID:26197998

  10. Isometric size-scaling of metabolic rate and the size abundance distribution of phytoplankton

    PubMed Central

    Huete-Ortega, María; Cermeño, Pedro; Calvo-Díaz, Alejandra; Marañón, Emilio

    2012-01-01

    The relationship between phytoplankton cell size and abundance has long been known to follow regular, predictable patterns in near steady-state ecosystems, but its origin has remained elusive. To explore the linkage between the size-scaling of metabolic rate and the size abundance distribution of natural phytoplankton communities, we determined simultaneously phytoplankton carbon fixation rates and cell abundance across a cell volume range of over six orders of magnitude in tropical and subtropical waters of the Atlantic Ocean. We found an approximately isometric relationship between carbon fixation rate and cell size (mean slope value: 1.16; range: 1.03–1.32), negating the idea that Kleiber's law is applicable to unicellular autotrophic protists. On the basis of the scaling of individual resource use with cell size, we predicted a reciprocal relationship between the size-scalings of phytoplankton metabolic rate and abundance. This prediction was confirmed by the observed slopes of the relationship between phytoplankton abundance and cell size, which have a mean value of −1.15 (range: −1.29 to −0.97), indicating that the size abundance distribution largely results from the size-scaling of metabolic rate. Our results imply that the total energy processed by carbon fixation is constant along the phytoplankton size spectrum in near steady-state marine ecosystems. PMID:22171079

  11. Isometric size-scaling of metabolic rate and the size abundance distribution of phytoplankton.

    PubMed

    Huete-Ortega, María; Cermeño, Pedro; Calvo-Díaz, Alejandra; Marañón, Emilio

    2012-05-01

    The relationship between phytoplankton cell size and abundance has long been known to follow regular, predictable patterns in near steady-state ecosystems, but its origin has remained elusive. To explore the linkage between the size-scaling of metabolic rate and the size abundance distribution of natural phytoplankton communities, we determined simultaneously phytoplankton carbon fixation rates and cell abundance across a cell volume range of over six orders of magnitude in tropical and subtropical waters of the Atlantic Ocean. We found an approximately isometric relationship between carbon fixation rate and cell size (mean slope value: 1.16; range: 1.03-1.32), negating the idea that Kleiber's law is applicable to unicellular autotrophic protists. On the basis of the scaling of individual resource use with cell size, we predicted a reciprocal relationship between the size-scalings of phytoplankton metabolic rate and abundance. This prediction was confirmed by the observed slopes of the relationship between phytoplankton abundance and cell size, which have a mean value of -1.15 (range: -1.29 to -0.97), indicating that the size abundance distribution largely results from the size-scaling of metabolic rate. Our results imply that the total energy processed by carbon fixation is constant along the phytoplankton size spectrum in near steady-state marine ecosystems.

  12. Initial drop size and velocity distributions for airblast coaxial atomizers

    NASA Technical Reports Server (NTRS)

    Eroglu, H.; Chigier, N.

    1991-01-01

    Phase Doppler measurements were used to determine initial drop size and velocity distributions after a complete disintegration of coaxial liquid jets. The Sauter mean diameter (SMD) distribution was found to be strongly affected by the structure and behavior of the preceding liquid intact jet. The axial measurement stations were determined from the photographs of the coaxial liquid jet at very short distances (1-2 mm) downstream of the observed break-up locations. Minimum droplet mean velocities were found at the center, and maximum velocities were near the spray boundary. Size-velocity correlations show that the velocity of larger drops did not change with drop size. Drop rms velocity distributions have double peaks whose radial positions coincide with the maximum mean velocity gradients.

  13. Production, depreciation and the size distribution of firms

    NASA Astrophysics Data System (ADS)

    Ma, Qi; Chen, Yongwang; Tong, Hui; Di, Zengru

    2008-05-01

    Many empirical researches indicate that firm size distributions in different industries or countries exhibit some similar characters. Among them the fact that many firm size distributions obey power-law especially for the upper end has been mostly discussed. Here we present an agent-based model to describe the evolution of manufacturing firms. Some basic economic behaviors are taken into account, which are production with decreasing marginal returns, preferential allocation of investments, and stochastic depreciation. The model gives a steady size distribution of firms which obey power-law. The effect of parameters on the power exponent is analyzed. The theoretical results are given based on both the Fokker-Planck equation and the Kesten process. They are well consistent with the numerical results.

  14. The Size Frequency Distribution of Small Main-Belt Asteroids

    NASA Technical Reports Server (NTRS)

    Burt, Brian J.; Trilling, David E.; Hines, Dean C.; Stapelfeldt, Karl R.; Rebull, Luisa M.; Fuentes, Cesar I.; Hulsebus, Alan

    2012-01-01

    The asteroid size distribution informs us about the formation and composition of the Solar System. We build on our previous work in which we harvest serendipitously observed data of the Taurus region and measure the brightness and size distributions of Main-belt asteroids. This is accomplished with the highly sensitive MIPS 24 micron channel. We expect to catalog 104 asteroids, giving us a statistically significant data set. Results from this investigation will allow us to characterize the total population of small, Main-belt asteroids. Here we will present new results on the completeness of our study; on the presence of size distribution variations with inclination and radial distance in the belt; and early result on other archival fields.

  15. Extrahypophysial distribution of corticotropin as a function of brain size.

    PubMed Central

    Moldow, R; Yalow, R S

    1978-01-01

    Determination by radioimmunoassay of corticotropin in the brains of rats, rabbits, dogs, monkeys, and human beings reveals that the dimensions within which the hormone is found is about the same for each of these species but that the anatomical regions in which the hormone is found depends on brain size. Corticotropin is widely distributed in the brain of rats but is found only in the hypothalamic region of the primate brain. The patterns of immunoreactivity observed after Sephadex gel filtration confirm that the molecular forms of corticotropin found in extrahypophysial regions are similar to those in the pituitary of each species. These findings suggest that the mammalian pituitary is the sole site of synthesis of the hormone. The observation of persistence of corticotropin in the brains of commerically hypophysectomized rats has been interpreted by others as suggesting diencephalic as well as pituitary origin for this peptide. However, our studies demonstrate that 8 weeks after hypophysectomy the rats we have received from commerical sources manifest stress-stimulated plasma corticotropin concentrations about 80% of that found in intact rats in spite of the fact that residual pituitary tissue was not found by visual inspection of the sella. Scrapings from the sella revealed a corticotropin content up to 5% that of the average rat pituitary. Images PMID:204943

  16. Variations in earthquake-size distribution across different stress regimes.

    PubMed

    Schorlemmer, Danijel; Wiemer, Stefan; Wyss, Max

    2005-09-22

    The earthquake size distribution follows, in most instances, a power law, with the slope of this power law, the 'b value', commonly used to describe the relative occurrence of large and small events (a high b value indicates a larger proportion of small earthquakes, and vice versa). Statistically significant variations of b values have been measured in laboratory experiments, mines and various tectonic regimes such as subducting slabs, near magma chambers, along fault zones and in aftershock zones. However, it has remained uncertain whether these differences are due to differing stress regimes, as it was questionable that samples in small volumes (such as in laboratory specimens, mines and the shallow Earth's crust) are representative of earthquakes in general. Given the lack of physical understanding of these differences, the observation that b values approach the constant 1 if large volumes are sampled was interpreted to indicate that b = 1 is a universal constant for earthquakes in general. Here we show that the b value varies systematically for different styles of faulting. We find that normal faulting events have the highest b values, thrust events the lowest and strike-slip events intermediate values. Given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress.

  17. Size-dependent two-photon absorption in circular graphene quantum dots.

    PubMed

    Feng, Xiaobo; Li, Xin; Li, Zhisong; Liu, Yingkai

    2016-02-01

    We investigate theoretically the size-dependence of two-photon absorption (TPA) for circular graphene quantum dots (GQDs) on the basis of electronic energy states obtained by solving the Dirac-Weyl equation analytically under infinite-mass boundary condition. The analytical expressions for TPA coefficient are derived with an arbitrary size-distribution and the transition selection rules are obtained. Results reveal that the intraband transitions in conduction band and valence band contribute much more to TPA than interband transitions. The energy spectrum and TPA peaks are tuned by the size of GQDs. PMID:26906856

  18. Three optical methods for remotely measuring aerosol size distributions.

    NASA Technical Reports Server (NTRS)

    Reagan, J. A.; Herman, B. M.

    1971-01-01

    Three optical probing methods for remotely measuring atmospheric aerosol size distributions are discussed and contrasted. The particular detection methods which are considered make use of monostatic lidar (laser radar), bistatic lidar, and solar radiometer sensing techniques. The theory of each of these measurement techniques is discussed briefly, and the necessary constraints which must be applied to obtain aerosol size distribution information from such measurements are pointed out. Theoretical and/or experimental results are also presented which demonstrate the utility of the three proposed probing methods.

  19. Modal character of atmospheric black carbon size distributions

    NASA Astrophysics Data System (ADS)

    Berner, A.; Sidla, S.; Galambos, Z.; Kruisz, C.; Hitzenberger, R.; ten Brink, H. M.; Kos, G. P. A.

    1996-08-01

    Samples of atmospheric aerosols, collected with cascade impactors in the urban area of Vienna (Austria) and at a coastal site on the North Sea, were investigated for black carbon (BC) as the main component of absorbing material and for mass. The size distributions are structured. The BC distributions of these samples show a predominant mode, the accumulation aerosol, in the upper submicron size range, a less distinct finer mode attributable to fresh emissions from combustion sources, and a distinct coarse mode of unclear origin. It is important to note that some parameters of the accumulation aerosol are related statistically, indicating the evolution of the atmospheric accumulation aerosol.

  20. Space Shuttle exhausted aluminum oxide - A measured particle size distribution

    NASA Technical Reports Server (NTRS)

    Cofer, W. R., III; Purgold, G. C.; Edahl, R. A.; Winstead, E. L.

    1991-01-01

    Aluminum oxide (A2O3) particles were collected from the Space Shuttle exhaust plume immediately following the launch of STS-34 on October 18, 1989. A2O3 samples were obtained at 2.4, 3.0, 3.2, and 7.4 km in altitude. The samples were analyzed using SEM to develope particle size distributions. There were no indications that the particle size distribution changed as a function of altitude. The particle number concentrations per cubic meter of air sampled for the four collections was found to fit an exponential expression.

  1. Saturn's rings - Particle size distributions for thin layer model

    NASA Technical Reports Server (NTRS)

    Zebker, H. A.; Marouf, E. A.; Tyler, G. L.

    1985-01-01

    A model incorporating limited interaction between the incident energy and particles in the ring is considered which appears to be consistent with the multiple scattering process in Saturn's rings. The model allows for the small physical thickness of the rings and can be used to relate Voyager 1 observations of 3.6- and 13-cm wavelength microwave scatter from the rings to the ring particle size distribution function for particles with radii ranging from 0.001 to 20 m. This limited-scatter model yields solutions for particle size distribution functions for eight regions in the rings, which exhibit approximately inverse-cubic power-law behavior.

  2. Size distribution of Portuguese firms between 2006 and 2012

    NASA Astrophysics Data System (ADS)

    Pascoal, Rui; Augusto, Mário; Monteiro, A. M.

    2016-09-01

    This study aims to describe the size distribution of Portuguese firms, as measured by annual sales and total assets, between 2006 and 2012, giving an economic interpretation for the evolution of the distribution along the time. Three distributions are fitted to data: the lognormal, the Pareto (and as a particular case Zipf) and the Simplified Canonical Law (SCL). We present the main arguments found in literature to justify the use of distributions and emphasize the interpretation of SCL coefficients. Methods of estimation include Maximum Likelihood, modified Ordinary Least Squares in log-log scale and Nonlinear Least Squares considering the Levenberg-Marquardt algorithm. When applying these approaches to Portuguese's firms data, we analyze if the evolution of estimated parameters in both lognormal power and SCL is in accordance with the known existence of a recession period after 2008. This is confirmed for sales but not for assets, leading to the conclusion that the first variable is a best proxy for firm size.

  3. Time evolution of cell size distributions in dense cell cultures

    NASA Astrophysics Data System (ADS)

    Khain, Evgeniy

    2015-03-01

    Living cells in a dense system are all in contact with each other. The common assumption is that such cells stop dividing due to a lack of space. Recent experimental observations have shown, however, that cells continue dividing for a while, but other cells in the system must shrink, to allow the newborn cells to grow to a normal size. Due to these ``pressure'' effects, the average cell size dramatically decreases with time, and the dispersion in cell sizes decreases, too. The collective cell behavior becomes even more complex when the system is expanding: cells near the edges are larger and migrate faster, while cells deep inside the colony are smaller and move slower. This exciting experimental data still needs to be described theoretically, incorporating the distribution of cell sizes in the system. We propose a mathematical model for time evolution of cell size distribution both in a closed and open system. The model incorporates cell proliferation, cell growth after division, cell shrinking due to ``pressure'' from other cells, and possible cell detachment from the interface of a growing colony. This research sheds light on physical and biological mechanisms of cell response to a dense environment and on the role of mechanical stresses in determining the distribution of cell sizes in the system.

  4. Particle size distributions of several commonly used seeding aerosols

    NASA Technical Reports Server (NTRS)

    Crosswy, F. L.

    1985-01-01

    During the course of experimentation, no solid particle powder could be found which produced an aerosol with a narrow particle size distribution when fluidization was the only flow process used in producing the aerosol. The complication of adding particle size fractionation processes to the aerosol generation effort appears to be avoidable. In this regard, a simple sonic orifice is found to be effective in reducing the percentage of agglomerates in the several metal oxide powders tested. Marginally beneficial results are obtained for a 0.5/99.5 percent by weight mixture of the flow agent and metal oxide powder. However, agglomeration is observed to be enhanced when the flow agent percentage is increased to 5 percent. Liquid atomization using the Collison nebulizer as well as a version of the Laskin nozzle resulted in polydispersed aerosols with particle size distributions heavily weighted by the small particle end of the size spectrum. The aerosol particle size distributions produced by the vaporization/condensation seeder are closer to the ideal monodispersed aerosol than any of the other aerosols tested. In addition, this seeding approach affords a measure of control over particle size and particle production rate.

  5. Enhanced size-dependent trapping of particles using microvortices

    PubMed Central

    Zhou, Jian; Kasper, Susan; Papautsky, Ian

    2013-01-01

    Inertial microfluidics has been attracting considerable interest for size-based separation of particles and cells. The inertial forces can be manipulated by expanding the microchannel geometry, leading to formation of microvortices which selectively isolate and trap particles or cells from a mixture. In this work, we aim to enhance our understanding of particle trapping in such microvortices by developing a model of selective particle trapping. Design and operational parameters including flow conditions, size of the trapping region, and target particle concentration are explored to elucidate their influence on trapping behavior. Our results show that the size dependence of trapping is characterized by a threshold Reynolds number, which governs the selective entry of particles into microvortices from the main flow. We show that concentration enhancement on the order of 100,000× and isolation of targets at concentrations in the 1/mL is possible. Ultimately, the insights gained from our systematic investigation suggest optimization solutions that enhance device performance (efficiency, size selectivity, and yield) and are applicable to selective isolation and trapping of large rare cells as well as other applications. PMID:24187531

  6. Size Evolution and Stochastic Models: Explaining Ostracod Size through Probabilistic Distributions

    NASA Astrophysics Data System (ADS)

    Krawczyk, M.; Decker, S.; Heim, N. A.; Payne, J.

    2014-12-01

    The biovolume of animals has functioned as an important benchmark for measuring evolution throughout geologic time. In our project, we examined the observed average body size of ostracods over time in order to understand the mechanism of size evolution in these marine organisms. The body size of ostracods has varied since the beginning of the Ordovician, where the first true ostracods appeared. We created a stochastic branching model to create possible evolutionary trees of ostracod size. Using stratigraphic ranges for ostracods compiled from over 750 genera in the Treatise on Invertebrate Paleontology, we calculated overall speciation and extinction rates for our model. At each timestep in our model, new lineages can evolve or existing lineages can become extinct. Newly evolved lineages are assigned sizes based on their parent genera. We parameterized our model to generate neutral and directional changes in ostracod size to compare with the observed data. New sizes were chosen via a normal distribution, and the neutral model selected new sizes differentials centered on zero, allowing for an equal chance of larger or smaller ostracods at each speciation. Conversely, the directional model centered the distribution on a negative value, giving a larger chance of smaller ostracods. Our data strongly suggests that the overall direction of ostracod evolution has been following a model that directionally pushes mean ostracod size down, shying away from a neutral model. Our model was able to match the magnitude of size decrease. Our models had a constant linear decrease while the actual data had a much more rapid initial rate followed by a constant size. The nuance of the observed trends ultimately suggests a more complex method of size evolution. In conclusion, probabilistic methods can provide valuable insight into possible evolutionary mechanisms determining size evolution in ostracods.

  7. Size distribution of native cytosolic proteins of Thermoplasma acidophilum.

    PubMed

    Sun, Na; Tamura, Noriko; Tamura, Tomohiro; Knispel, Roland Wilhelm; Hrabe, Thomas; Kofler, Christine; Nickell, Stephan; Nagy, István

    2009-07-01

    We used molecular sieve chromatography in combination with LC-MS/MS to identify protein complexes that can serve as templates in the template matching procedures of visual proteomics approaches. By this method the sample complexity was lowered sufficiently to identify 464 proteins and - on the basis of size distribution and bioinformatics analysis - 189 of them could be assigned as subunits of macromolecular complexes over the size of 300 kDa. From these we purified six stable complexes of Thermoplasma acidophilum whose size and subunit composition - analyzed by electron microscopy and MALDI-TOF-MS, respectively - verified the accuracy of our method.

  8. Size distributions of gold nanoclusters studied by liquid chromatography

    SciTech Connect

    WILCOXON,JESS P.; MARTIN,JAMES E.; PROVENCIO,PAULA P.

    2000-05-23

    The authors report high pressure liquid chromatography, (HPLC), and transmission electron microscopy, (TEM), studies of the size distributions of nanosize gold clusters dispersed in organic solvents. These metal clusters are synthesized in inverse micelles at room temperature and those investigated range in diameter from 1--10 nm. HPLC is sensitive enough to discern changes in hydrodynamic volume corresponding to only 2 carbon atoms of the passivating agent or metal core size changes of less than 4 {angstrom}. The authors have determined for the first time how the total cluster volume (metal core + passivating organic shell) changes with the size of the passivating agent.

  9. The size-distribution of Earth’s lakes

    PubMed Central

    Cael, B. B.; Seekell, D. A.

    2016-01-01

    Globally, there are millions of small lakes, but a small number of large lakes. Most key ecosystem patterns and processes scale with lake size, thus this asymmetry between area and abundance is a fundamental constraint on broad-scale patterns in lake ecology. Nonetheless, descriptions of lake size-distributions are scarce and empirical distributions are rarely evaluated relative to theoretical predictions. Here we develop expectations for Earth’s lake area-distribution based on percolation theory and evaluate these expectations with data from a global lake census. Lake surface areas ≥8.5 km2 are power-law distributed with a tail exponent (τ = 1.97) and fractal dimension (d = 1.38), similar to theoretical expectations (τ = 2.05; d = 4/3). Lakes <8.5 km2 are not power-law distributed. An independently developed regional lake census exhibits a similar transition and consistency with theoretical predictions. Small lakes deviate from the power-law distribution because smaller lakes are more susceptible to dynamical change and topographic behavior at sub-kilometer scales is not self-similar. Our results provide a robust characterization and theoretical explanation for the lake size-abundance relationship, and form a fundamental basis for understanding and predicting patterns in lake ecology at broad scales. PMID:27388607

  10. The size-distribution of Earth’s lakes

    NASA Astrophysics Data System (ADS)

    Cael, B. B.; Seekell, D. A.

    2016-07-01

    Globally, there are millions of small lakes, but a small number of large lakes. Most key ecosystem patterns and processes scale with lake size, thus this asymmetry between area and abundance is a fundamental constraint on broad-scale patterns in lake ecology. Nonetheless, descriptions of lake size-distributions are scarce and empirical distributions are rarely evaluated relative to theoretical predictions. Here we develop expectations for Earth’s lake area-distribution based on percolation theory and evaluate these expectations with data from a global lake census. Lake surface areas ≥8.5 km2 are power-law distributed with a tail exponent (τ = 1.97) and fractal dimension (d = 1.38), similar to theoretical expectations (τ = 2.05 d = 4/3). Lakes <8.5 km2 are not power-law distributed. An independently developed regional lake census exhibits a similar transition and consistency with theoretical predictions. Small lakes deviate from the power-law distribution because smaller lakes are more susceptible to dynamical change and topographic behavior at sub-kilometer scales is not self-similar. Our results provide a robust characterization and theoretical explanation for the lake size-abundance relationship, and form a fundamental basis for understanding and predicting patterns in lake ecology at broad scales.

  11. Aggregation dynamics explain vegetation patch-size distributions.

    PubMed

    Irvine, M A; Bull, J C; Keeling, M J

    2016-04-01

    Vegetation patch-size distributions have been an intense area of study for theoreticians and applied ecologists alike in recent years. Of particular interest is the seemingly ubiquitous nature of power-law patch-size distributions emerging in a number of diverse ecosystems. The leading explanation of the emergence of these power-laws is due to local facilitative mechanisms. There is also a common transition from power law to exponential distribution when a system is under global pressure, such as grazing or lack of rainfall. These phenomena require a simple mechanistic explanation. Here, we study vegetation patches from a spatially implicit, patch dynamic viewpoint. We show that under minimal assumptions a power-law patch-size distribution appears as a natural consequence of aggregation. A linear death term also leads to an exponential term in the distribution for any non-zero death rate. This work shows the origin of the breakdown of the power-law under increasing pressure and shows that in general, we expect to observe a power law with an exponential cutoff (rather than pure power laws). The estimated parameters of this distribution also provide insight into the underlying ecological mechanisms of aggregation and death.

  12. Aerosol mobility imaging for rapid size distribution measurements

    DOEpatents

    Wang, Jian; Hering, Susanne Vera; Spielman, Steven Russel; Kuang, Chongai

    2016-07-19

    A parallel plate dimensional electrical mobility separator and laminar flow water condensation provide rapid, mobility-based particle sizing at concentrations typical of the remote atmosphere. Particles are separated spatially within the electrical mobility separator, enlarged through water condensation, and imaged onto a CCD array. The mobility separation distributes particles in accordance with their size. The condensation enlarges size-separated particles by water condensation while they are still within the gap of the mobility drift tube. Once enlarged the particles are illuminated by a laser. At a pre-selected frequency, typically 10 Hz, the position of all of the individual particles illuminated by the laser are captured by CCD camera. This instantly records the particle number concentration at each position. Because the position is directly related to the particle size (or mobility), the particle size spectra is derived from the images recorded by the CCD.

  13. Size distributions of metal nanoparticles in polyelectrolyte gels

    NASA Astrophysics Data System (ADS)

    Svergun, D. I.; Shtykova, E. V.; Dembo, A. T.; Bronstein, L. M.; Platonova, O. A.; Yakunin, A. N.; Valetsky, P. M.; Khokhlov, A. R.

    1998-12-01

    Small-angle x-ray scattering is used to study size distributions of noble metal nanoparticles embedded in polyelectrolyte hydrogels with oppositely charged surfactants. A procedure is proposed to subtract matrix scattering and to extract pure scattering due to the nanoparticles allowing to evaluate their size distribution functions by means of a regularization technique. Two kinds of collapsed gel-surfactant complexes were studied: a complex of a cationic gel of poly(diallyldimethylammonium chloride) with an anionic surfactant sodium dodecyl sulfate (PDADMACl/SDS), and that of an anionic gel of poly(methacrylic acid) with a cationic surfactant cetylpyridinium chloride (PMA/CPC). Addition of a gold compound (HAuCl4ṡ3H2O) to the PDADMACl/SDS system forms the metal compound clusters and leads to a partial distortion of the gel structure. After subsequent reduction of the gold compound with sodium borohydride (NaBH4) ordering in the gel disappears and gold nanoparticles are formed. Their size distribution includes a fraction of small particles with approximately the same size as the compound clusters before reduction and a fraction of larger particles with the radii up to 40 nm. For the collapsed PDADMACl/SDS gels, aging does not change the size distribution profile; for the noncollapsed PDADMACl gels without surfactant, metal particles are found to grow with time. This suggests that the aggregation of metal colloids is prevented by the ordering in the collapsed gel-surfactant complex. The addition of HAuCl4ṡ3H2O and the subsequent reduction of the metal ions in the PMA/CPC system does not distort the gel structure as the degree of incorporation of AuCl4- ions is very low. Particle sizes in the PMA/CPC system are found to be somewhat larger than those in the PDADMACl/SDS system. The PDADMACl/SDS gels loaded with the PtCl4 compound were also studied to analyze the influence of the reducing agent type on the particle size distribution distributions. Fast reduction

  14. Size and voltage dependence of effective anisotropy in sub-100-nm perpendicular magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Piotrowski, Stephan K.; Bapna, Mukund; Oberdick, Samuel D.; Majetich, Sara A.; Li, Mingen; Chien, C. L.; Ahmed, Rizvi; Victora, R. H.

    2016-07-01

    Magnetic tunnel junctions with perpendicular magnetic anisotropy are investigated using a conductive atomic force microscope. The 1.23 -nm Co40Fe40B20 recording layer coercivity exhibits a size dependence which suggests single-domain behavior for diameters ≤100 nm. Focusing on devices with diameters smaller than 100 nm, we determine the effect of voltage and size on the effective device anisotropy Keff using two different techniques. Keff is extracted both from distributions of the switching fields of the recording and reference layers and from measurement of thermal fluctuations of the recording layer magnetization when a field close to the switching field is applied. The results from both sets of measurements reveal that Keff increases monotonically with decreasing junction diameter, consistent with the size dependence of the demagnetization energy density. We demonstrate that Keff can be controlled with a voltage down to the smallest size measured, 64 nm.

  15. 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.

  16. Distributional shifts in size structure of phytoplankton community

    NASA Astrophysics Data System (ADS)

    Waga, H.; Hirawake, T.; Fujiwara, A.; Nishino, S.; Kikuchi, T.; Suzuki, K.; Takao, S.

    2015-12-01

    Increased understanding on how marine species shift their distribution is required for effective conservation of fishery resources under climate change. Previous studies have often predicted distributional shifts of fish using satellite derived sea surface temperature (SST). However, SST may not fully represent the changes in species distribution through food web structure and as such this remains an open issue due to lack of ecological perspective on energy transfer process in the earlier studies. One of the most important factors in ecosystem is composition of phytoplankton community, and its size structure determines energy flow efficiency from base to higher trophic levels. To elucidate spatiotemporal variation in phytoplankton size structure, chlorophyll-a size distribution (CSD) algorithm was developed using spectral variance of phytoplankton absorption coefficient through principal component analysis. Slope of CSD (CSD slope) indicates size structure of phytoplankton community where, strong and weak magnitudes of CSD slope indicate smaller and larger phytoplankton structure, respectively. Shifts in CSD slope and SST were derived as the ratio of temporal trend over the 12-year period (2003-2014) to 2-dimensional spatial gradient and the resulting global median velocity of CSD slope and SST were 0.361 and 0.733 km year-1, respectively. In addition, the velocity of CSD slope monotonically increases with increasing latitude, while relatively complex latitudinal pattern for SST emerged. Moreover, angle of shifts suggest that species are required to shift their distribution toward not limited to simple pole-ward migration, and some regions exhibit opposite direction between the velocity of CSD slope and SST. These findings further imply that combined phytoplankton size structure and SST may contribute for more accurate prediction of species distribution shifts relative to existing studies which only considering variations in thermal niches.

  17. Elemental composition and size distribution of particulates in Cleveland, Ohio

    NASA Technical Reports Server (NTRS)

    King, R. B.; Fordyce, J. S.; Neustadter, H. E.; Leibecki, H. F.

    1975-01-01

    Measurements were made of the elemental particle size distribution at five contrasting urban environments with different source-type distributions in Cleveland, Ohio. Air quality conditions ranged from normal to air pollution alert levels. A parallel network of high-volume cascade impactors (5-state) were used for simultaneous sampling on glass fiber surfaces for mass determinations and on Whatman-41 surfaces for elemental analysis by neutron activation for 25 elements. The elemental data are assessed in terms of distribution functions and interrelationships and are compared between locations as a function of resultant wind direction in an attempt to relate the findings to sources.

  18. Novel magnetic Fe onion-like fullerene micrometer-sized particles of narrow size distribution

    NASA Astrophysics Data System (ADS)

    Snovski, Ron; Grinblat, Judith; Margel, Shlomo

    2012-01-01

    Magnetic polydivinylbenzene (PDVB)/magnetite micrometer-sized particles of narrow size distribution were prepared by entrapping Fe(CO)5 within the pores of uniform porous PDVB particles, followed by the thermal decomposition of the encapsulated Fe(CO)5 at 300 °C in a sealed cell under inert atmosphere. Magnetic Fe onion-like fullerene micrometer-sized particles of narrow size distribution have been prepared by the thermal decomposition of the PDVB/magnetite magnetic microspheres at 1100 °C under inert atmosphere. The graphitic coating protects the elemental iron particles from oxidation and thereby preserves their very high magnetic moment for at least a year. Characterization of these unique magnetic carbon graphitic particles was also performed.

  19. Tracing Particle Size Distribution Curves Using an Analogue Circuit.

    ERIC Educational Resources Information Center

    Bisschop, F. De; Segaert, O.

    1986-01-01

    Proposes an analog circuit for use in sedimentation analysis of finely divided solid materials. Discusses a method of particle size distribution analysis and provides schematics of the circuit with list of components as well as a discussion about the operation of the circuit. (JM)

  20. Factors influencing the effect size distribution of adaptive substitutions.

    PubMed

    Dittmar, Emily L; Oakley, Christopher G; Conner, Jeffrey K; Gould, Billie A; Schemske, Douglas W

    2016-04-13

    The distribution of effect sizes of adaptive substitutions has been central to evolutionary biology since the modern synthesis. Early theory proposed that because large-effect mutations have negative pleiotropic consequences, only small-effect mutations contribute to adaptation. More recent theory suggested instead that large-effect mutations could be favoured when populations are far from their adaptive peak. Here we suggest that the distributions of effect sizes are expected to differ among study systems, reflecting the wide variation in evolutionary forces and ecological conditions experienced in nature. These include selection, mutation, genetic drift, gene flow, and other factors such as the degree of pleiotropy, the distance to the phenotypic optimum, whether the optimum is stable or moving, and whether new mutation or standing genetic variation provides the source of adaptive alleles. Our goal is to review how these factors might affect the distribution of effect sizes and to identify new research directions. Until more theory and empirical work is available, we feel that it is premature to make broad generalizations about the effect size distribution of adaptive substitutions important in nature.

  1. Factors influencing the effect size distribution of adaptive substitutions

    PubMed Central

    Oakley, Christopher G.; Gould, Billie A.; Schemske, Douglas W.

    2016-01-01

    The distribution of effect sizes of adaptive substitutions has been central to evolutionary biology since the modern synthesis. Early theory proposed that because large-effect mutations have negative pleiotropic consequences, only small-effect mutations contribute to adaptation. More recent theory suggested instead that large-effect mutations could be favoured when populations are far from their adaptive peak. Here we suggest that the distributions of effect sizes are expected to differ among study systems, reflecting the wide variation in evolutionary forces and ecological conditions experienced in nature. These include selection, mutation, genetic drift, gene flow, and other factors such as the degree of pleiotropy, the distance to the phenotypic optimum, whether the optimum is stable or moving, and whether new mutation or standing genetic variation provides the source of adaptive alleles. Our goal is to review how these factors might affect the distribution of effect sizes and to identify new research directions. Until more theory and empirical work is available, we feel that it is premature to make broad generalizations about the effect size distribution of adaptive substitutions important in nature. PMID:27053750

  2. Sample Size Tables, "t" Test, and a Prevalent Psychometric Distribution.

    ERIC Educational Resources Information Center

    Sawilowsky, Shlomo S.; Hillman, Stephen B.

    Psychology studies often have low statistical power. Sample size tables, as given by J. Cohen (1988), may be used to increase power, but they are based on Monte Carlo studies of relatively "tame" mathematical distributions, as compared to psychology data sets. In this study, Monte Carlo methods were used to investigate Type I and Type II error…

  3. Turbulent Concentration of Chondrules: Size Distribution and Multifractal Scaling

    NASA Technical Reports Server (NTRS)

    Cuzzi, Jeffrey N.; Hogan, Robert C.; Paque, Julie M.; Dobrovolskis, Anthony R.

    1999-01-01

    Size-selective concentration of particles in 3D turbulence may be related to collection of chondrules and other constituents into primitive bodies in a weakly turbulent protoplanetary nebula. In the terrestrial planet region, both the characteristic size and narrow size distribution of chondrules are explained, whereas "fluffier" particles would be concentrated in lower density, or more intensely turbulent, regions of the nebula. The spatial distribution of concentrated particle density obeys multifractal scaling, suggesting a dose tie to the turbulent cascade process. This scaling behavior allows predictions of the concentration probabilities to be made in the protoplanetary nebula, which are so large (> 10(exp 3) - 10(exp 4)) that further studies must be made of the role of mass loading.

  4. Size and dimensionality dependent phonon conductivity in nanocomposites.

    PubMed

    Al-Otaibi, Jawaher; Srivastava, G P

    2016-04-13

    We have studied size and dimensionality dependent phonon conductivity of PbTe-PbSe nanocomposites by considering three configurations: superlattice, embedded nanowire and embedded nanodot. Calculations have been performed in the framework of an effective medium theory. The required bulk thermal conductivities of PbTe and PbSe are evaluated by using Callaway's effective relaxation-time theory, and by accounting for relevant scattering mechanism including three-phonon Normal and Umklapp interactions involving acoustic as well as optical branches. The thermal interface resistance is computed using the diffuse mismatch theory. It is found that the size (thickness) and volume fraction of PbSe are the two main factors that control the effective thermal conductivity in these nanocomposites. In particular, for PbSe size d = 10 nm and volume fraction Vf = 0.1, our results predict significant reductions over the weighted average of room-temperature bulk results of 9%, 17% and 15% in the conductivity across the interfaces for the superlattice, embedded nanowire, and nanosphere structures, respectively. For a given Vf, an increase in d reduces the interface density and the effective conductivity varies approximately as [Formula: see text]. It is shown that nanocompositing in any of the three configurations can beat the alloy limit for lattice thermal conductivity. PMID:26974428

  5. Size- and structure-dependent toxicity of silica particulates

    NASA Astrophysics Data System (ADS)

    Hanada, Sanshiro; Miyaoi, Kenichi; Hoshino, Akiyoshi; Inasawa, Susumu; Yamaguchi, Yukio; Yamamoto, Kenji

    2011-03-01

    Nano- and micro-particulates firmly attach with the surface of various biological systems. In some chronic pulmonary disease such as asbestosis and silicosis, causative particulates will induce chronic inflammatory disorder, followed by poor prognosis diseases. However, nano- and micro-scale specific toxicity of silica particulates is not well examined enough to recognize the risk of nano- and micro-particulates from the clinical aspect. To clarify the effect of the size and structure of silica particulates on the cellular damage and the biological response, we assessed the cytotoxicity of the various kinds of silica particles including amorphous and crystalline silica, in mouse alveolar macrophage culture, focusing on the fibrotic and inflammatory response. Our study showed that the cytotoxicity, which depends on the particle size and surface area, is correlated with their inflammatory response. By contrast, production of TGF-β, which is one of the fibrotic agents in lung, by addition of crystal silica was much higher than that of amorphous silica. We conclude that fibrosis and inflammation are induced at different phases and that the size- and structure-differences of silica particulates affect the both biological responses, caused by surface activity, radical species, and so on.

  6. A new stochastic algorithm for inversion of dust aerosol size distribution

    NASA Astrophysics Data System (ADS)

    Wang, Li; Li, Feng; Yang, Ma-ying

    2015-08-01

    Dust aerosol size distribution is an important source of information about atmospheric aerosols, and it can be determined from multiwavelength extinction measurements. This paper describes a stochastic inverse technique based on artificial bee colony (ABC) algorithm to invert the dust aerosol size distribution by light extinction method. The direct problems for the size distribution of water drop and dust particle, which are the main elements of atmospheric aerosols, are solved by the Mie theory and the Lambert-Beer Law in multispectral region. And then, the parameters of three widely used functions, i.e. the log normal distribution (L-N), the Junge distribution (J-J), and the normal distribution (N-N), which can provide the most useful representation of aerosol size distributions, are inversed by the ABC algorithm in the dependent model. Numerical results show that the ABC algorithm can be successfully applied to recover the aerosol size distribution with high feasibility and reliability even in the presence of random noise.

  7. Size distribution of iron and manganese species in freshwaters

    NASA Astrophysics Data System (ADS)

    Laxen, Duncan P. H.; Chandler, I. Michael

    1983-04-01

    A recently established technique for size fractionation of particulate matter in freshwaters, based on low volume filtration through Nuclepore filters in the field, has been applied to the study of Fe and Mn species in 3 freshwater lakes and a stream feeding one of the lakes. The technique has also been used in a series of laboratory experiments to provide further insight into the process of particle formation. The results are complemented with scanning electron microscope examination of the particles. The raw data are transformed into mass size distributions, which are generally unimodal, with the major part of the mass confined to a single log unit size range. These size distributions are compared and contrasted with a theoretical model of particle behaviour in a lake. The results suggest that particulate Fe and Mn behave according to particle theory. The observed size distributions represent a balance between hydraulic input/output, aggregation, and gravitational settling, as well as chemical precipitation and dissolution processes. Overall particle aggregation is shown to be a slow process in the waters examined, with a time constant of the order of days. There is evidence for a fairly stable particle regime in the 0.05-0.4 μm size range. Deviations from the unimodal distribution in the epilimnion of the lakes indicate the association of Fe, but not Mn, with phytoplankton. In the waters examined Mn was most frequently found in solution, while Fe was predominantly particulate. These findings are interpreted in terms of the differing redox behaviour of the metals.

  8. Cell Size Distributions of Soil Bacterial and Archaeal Taxa

    PubMed Central

    Portillo, Maria C.; Leff, Jonathan W.; Lauber, Christian L.

    2013-01-01

    Cell size is a key ecological trait of soil microorganisms that determines a wide range of life history attributes, including the efficiency of nutrient acquisition. However, because of the methodological issues associated with determining cell sizes in situ, we have a limited understanding of how cell abundances vary across cell size fractions and whether certain microbial taxa have consistently smaller cells than other taxa. In this study, we extracted cells from three distinct soils and fractionated them into seven size ranges (5 μm to 0.2 μm) by filtration. Cell abundances in each size fraction were determined by direct microscopy, with the taxonomic composition of each size fraction determined by high-throughput sequencing of the 16S rRNA gene. Most of the cells were smaller than cells typically grown in culture, with 59 to 67% of cells <1.2 μm in diameter. Furthermore, each size fraction harbored distinct bacterial and archaeal communities in each of the three soils, and many of the taxa exhibited distinct size distribution patterns, with the smaller size fractions having higher relative abundances of taxa that are rare or poorly characterized (including Acidobacteria, Gemmatimonadetes, Crenarchaeota, Verrucomicrobia, and Elusimicrobia). In general, there was a direct relationship between average cell size and culturability, with those soil taxa that are poorly represented in culture collections tending to be smaller. Size fractionation not only provides important insight into the life history strategies of soil microbial taxa but also is a useful tool to enable more focused investigations into those taxa that remain poorly characterized. PMID:24077710

  9. Undersampling power-law size distributions: effect on the assessment of extreme natural hazards

    USGS Publications Warehouse

    Geist, Eric L.; Parsons, Thomas E.

    2014-01-01

    The effect of undersampling on estimating the size of extreme natural hazards from historical data is examined. Tests using synthetic catalogs indicate that the tail of an empirical size distribution sampled from a pure Pareto probability distribution can range from having one-to-several unusually large events to appearing depleted, relative to the parent distribution. Both of these effects are artifacts caused by limited catalog length. It is more difficult to diagnose the artificially depleted empirical distributions, since one expects that a pure Pareto distribution is physically limited in some way. Using maximum likelihood methods and the method of moments, we estimate the power-law exponent and the corner size parameter of tapered Pareto distributions for several natural hazard examples: tsunamis, floods, and earthquakes. Each of these examples has varying catalog lengths and measurement thresholds, relative to the largest event sizes. In many cases where there are only several orders of magnitude between the measurement threshold and the largest events, joint two-parameter estimation techniques are necessary to account for estimation dependence between the power-law scaling exponent and the corner size parameter. Results indicate that whereas the corner size parameter of a tapered Pareto distribution can be estimated, its upper confidence bound cannot be determined and the estimate itself is often unstable with time. Correspondingly, one cannot statistically reject a pure Pareto null hypothesis using natural hazard catalog data. Although physical limits to the hazard source size and by attenuation mechanisms from source to site constrain the maximum hazard size, historical data alone often cannot reliably determine the corner size parameter. Probabilistic assessments incorporating theoretical constraints on source size and propagation effects are preferred over deterministic assessments of extreme natural hazards based on historic data.

  10. Particle-Size-Distribution of Nevada Test Site Soils

    SciTech Connect

    Spriggs, G; Ray-Maitra, A

    2007-09-17

    The amount of each size particle in a given soil is called the particle-size distribution (PSD), and the way it feels to the touch is called the soil texture. Sand, silt, and clay are the three particle sizes of mineral material found in soils. Sand is the largest sized particle and it feels gritty; silt is medium sized and it feels floury; and clay is the smallest and if feels sticky. Knowing the particle-size distribution of a soil sample helps to understand many soil properties such as how much water, heat, and nutrients the soil will hold, how fast water and heat will move through the soil, and what kind of structure, bulk density and consistence the soil will have. Furthermore, the native particle-size distribution of the soil in the vicinity of ground zero of a nuclear detonation plays a major role in nuclear fallout. For soils that have a high-sand content, the near-range fallout will be relatively high and the far-range fallout will be relatively light. Whereas, for soils that have a high-silt and high-clay content, the near-range fallout will be significantly lower and the far-range fallout will be significantly higher. As part of a program funded by the Defense Threat Reduction Agency (DTRA), the Lawrence Livermore National Laboratory (LLNL) has recently measured the PSDs from the various major areas at the Nevada Test Site where atmospheric detonations and/or nuclear weapon safety tests were performed back in the 50s and 60s. The purpose of this report is to document those results.

  11. Experimental study of the relationship between local particle-size distributions and local ordering in random close packing.

    PubMed

    Kurita, Rei

    2015-12-01

    We experimentally study the structural properties of a sediment of size distributed colloids. By determining each particle size using a size estimation algorithm, we are able to investigate the relationship between local environment and local ordering. Our results show that ordered environments of particles tend to generate where the local particle-size distribution is within 5%. In addition, we show that particles whose size is close to the average size have 12 coordinate neighbors, which matches the coordination number of the fcc and hcp crystals. On the other hand, bcc structures are observed around larger particles. Our results represent experiments to show a size dependence of the specific ordering in colloidal systems.

  12. Size and DNA distributions of electrophoretically separated cultured human kidney cells

    NASA Technical Reports Server (NTRS)

    Kunze, M. E.; Plank, L. D.; Todd, P. W.

    1985-01-01

    Electrophoretic purification of purifying cultured cells according to function presumes that the size of cycle phase of a cell is not an overriding determinant of its electrophoretic velocity in an electrophoretic separator. The size distributions and DNA distributions of fractions of cells purified by density gradient electrophoresis were determined. No systematic dependence of electrophoretic migration upward in a density gradient column upon either size or DNA content were found. It was found that human leukemia cell populations, which are more uniform function and found in all phases of the cell cycle during exponential growth, separated on a vertical sensity gradient electrophoresis column according to their size, which is shown to be strictly cell cycle dependent.

  13. Aged boreal biomass burning aerosol size distributions from BORTAS 2011

    NASA Astrophysics Data System (ADS)

    Sakamoto, K. M.; Allan, J. D.; Coe, H.; Taylor, J. W.; Duck, T. J.; Pierce, J. R.

    2014-09-01

    Biomass-burning aerosols contribute to aerosol radiative forcing on the climate system. The magnitude of this effect is partially determined by aerosol size distributions, which are functions of source fire characteristics (e.g. fuel type, MCE) and in-plume microphysical processing. The uncertainties in biomass-burning emission number size-distributions in climate model inventories lead to uncertainties in the CCN concentrations and forcing estimates derived from these models. The BORTAS-B measurement campaign was designed to sample boreal biomass-burning outflow over Eastern Canada in the summer of 2011. Using these BORTAS-B data, we implement plume criteria to isolate the characteristic size-distribution of aged biomass-burning emissions (aged ∼1-2 days) from boreal wildfires in Northwestern Ontario. The composite median size-distribution yields a single dominant accumulation mode with Dpm = 230 nm (number-median diameter), σ = 1.7, which are comparable to literature values of other aged plumes of a similar type. The organic aerosol enhancement ratios (ΔOA / ΔCO) along the path of Flight b622 show values of 0.05-0.18 μg m-3 ppbv-1 with no significant trend with distance from the source. This lack of enhancement ratio increase/decrease with distance suggests no detectable net OA production/evaporation within the aged plume over the sampling period. A Lagrangian microphysical model was used to determine an estimate of the freshly emitted size distribution corresponding to the BORTAS-B aged size-distributions. The model was restricted to coagulation and dilution processes based on the insignificant net OA production/evaporation derived from the ΔOA / ΔCO enhancement ratios. We estimate that the fresh-plume median diameter was in the range of 59-94 nm with modal widths in the range of 1.7-2.8 (the ranges are due to uncertainty in the entrainment rate). Thus, the size of the freshly emitted particles is relatively unconstrained due to the uncertainties in

  14. Transneptunians as probes of planet building: The Plutino size distribution

    NASA Astrophysics Data System (ADS)

    Alexandersen, M.; Gladman, B.; Kavelaars, J.; Petit, J.; Gwyn, S.

    2014-07-01

    Planetesimals that formed during planet formation are the building blocks of giant planet cores; some are preserved as large transneptunian objects (TNOs). Previous work has shown steep power-law size distributions for TNOs of diameters > 100 km. Recent results claim a dramatic roll-over or divot in the size distribution of Neptunian Trojans (1:1 resonance with Neptune) and scattering TNOs, with a significant lack of intermediate-size D < 100 km planetesimals [1,2,3]. One theoretical explanation for this is that planetesimals were born big, skipping the intermediate sizes, contrary to the expectation of bottom-up planetesimal formation. Exploration of the TNO size distribution requires more precisely calibrated detections in order to improve statistics on these results. We have searched a 32 sq.deg. area near RA=2 hr to an r-band limiting magnitude of m_r=24.6 using the Canada-France-Hawaii Telescope. This coverage was near the Neptunian L4 region to maximise our detection rate, as this is where Neptunian Trojans reside and where Plutinos (and several other resonant populations) come to perihelion. This program successfully detected and tracked 77 TNOs and Centaurs for up to 17 months, giving us both the high-quality orbits and the quantitative detection efficiency needed for precise modelling. Among our detections were one Uranian Trojan, two Neptunian Trojans, 18 Plutinos (3:2 resonance with Neptune) and other resonant objects. We test TNO size and orbital-distribution models using a survey simulator, which simulates the detectability of model objects, accounting for the survey biases. We show that the Plutino size distribution cannot continue as a rising power law past H_r˜8.3 (equivalent to ˜100 km). A single power law is found rejectable at 99.5 % confidence, and a knee (a broken power law to a softer slope) is also rejectable. A divot (sudden drop in number of objects at a transition size), with parameters found independently for scattering TNOs by Shankman

  15. Evaluation of the Malvern optical particle monitor. [Volumetric size distribution

    SciTech Connect

    Anderson, R. J.; Johnson, E.

    1983-07-01

    The Malvern 2200/3300 Particle Sizer is a laser-based optical particle sizing device which utilizes the principle of Fraunhofer Diffraction as the means of particle size measurement. The instrument is designed to analyze particle sizes in the range of 1 to 1800 microns diameter through a selection of lenses for the receiving optics. It is not a single-particle counter but rather an ensemble averager over the distribution of particles present in the measuring volume. Through appropriate measurement techniques, the instrument can measure the volumetric size distribution of: solids in gas or liquid suspension; liquid droplets in gas or other immiscible liquids; and, gas bubbles in liquid. (Malvern Handbook, Version 1.5). This report details a limited laboratory evaluation of the Malvern system to determine its operational characteristics, limitations, and accuracy. This investigation focused on relatively small particles in the range of 5 to 150 microns. Primarily, well characterized particles of coal in a coal and water mixture were utilized, but a selection of naturally occurring, industrially generated, and standard samples (i.e., glass beads) wer also tested. The characteristic size parameter from the Malvern system for each of these samples was compared with the results of a Coulter particle counter (Model TA II) analysis to determine the size measurement accuracy. Most of the particulate samples were suspended in a liquid media (water or isoton, plus a dispersant) for the size characterization. Specifically, the investigations contained in this report fall into four categories: (a) Sample-to-lense distance and sample concentration studies, (b) studies testing the applicability to aerosols, (c) tests of the manufacturer supplied software, and (d) size measurement comparisons with the results of Coulter analysis. 5 references, 15 figures, 2 tables.

  16. Raindrop size distribution: Fitting performance of common theoretical models

    NASA Astrophysics Data System (ADS)

    Adirosi, E.; Volpi, E.; Lombardo, F.; Baldini, L.

    2016-10-01

    Modelling raindrop size distribution (DSD) is a fundamental issue to connect remote sensing observations with reliable precipitation products for hydrological applications. To date, various standard probability distributions have been proposed to build DSD models. Relevant questions to ask indeed are how often and how good such models fit empirical data, given that the advances in both data availability and technology used to estimate DSDs have allowed many of the deficiencies of early analyses to be mitigated. Therefore, we present a comprehensive follow-up of a previous study on the comparison of statistical fitting of three common DSD models against 2D-Video Distrometer (2DVD) data, which are unique in that the size of individual drops is determined accurately. By maximum likelihood method, we fit models based on lognormal, gamma and Weibull distributions to more than 42.000 1-minute drop-by-drop data taken from the field campaigns of the NASA Ground Validation program of the Global Precipitation Measurement (GPM) mission. In order to check the adequacy between the models and the measured data, we investigate the goodness of fit of each distribution using the Kolmogorov-Smirnov test. Then, we apply a specific model selection technique to evaluate the relative quality of each model. Results show that the gamma distribution has the lowest KS rejection rate, while the Weibull distribution is the most frequently rejected. Ranking for each minute the statistical models that pass the KS test, it can be argued that the probability distributions whose tails are exponentially bounded, i.e. light-tailed distributions, seem to be adequate to model the natural variability of DSDs. However, in line with our previous study, we also found that frequency distributions of empirical DSDs could be heavy-tailed in a number of cases, which may result in severe uncertainty in estimating statistical moments and bulk variables.

  17. Particle size distributions of polyaniline-silica colloidal composites

    SciTech Connect

    Gill, M.; Armes, S.P. ); Fairhurst, D. ); Emmett, S.N. ); Idzorek, G.; Pigott, T. )

    1992-09-01

    We have characterized a new polyaniline-silica composite colloid by various particle sizing techniques. Our transmission electron microscopy studies have confirmed for the first time an unusual raspberry morphology, with the small silica particles held together by the polyaniline [open quotes]binder[close quotes]. These particles have average diameters in the size range 150-500 nm. Charge-velocity analysis experiments indicated a number-average particle diameter of 300 [plus minus] 80 nm, but only poor statistics were obtained (172 particles counted). Photon correlation spectroscopy studies suggested an intensity-average particle diameter of 380 nm. Disk centrifuge photosedimentometry (DCP) turned out to be our preferred sizing technique for the polyaniline-silica colloids, since it was both quick and reliable and, more importantly, produced the true particle size distribution (PSD) curve with excellent statistics. The DCP data indicated a weight-average and number-average particle diameter of 330 [plus minus] 70 nm and 280 [plus minus] 70 nm, respectively, and moreover confirmed the PSD to be both broad and unimodal. Finally, these colloidal composites were sized using the Malvern Aerosizer. Using this instrument in conjunction with a nebulizer attachment (which allowed particle sizing of the [open quotes]wet[close quotes] dispersion) rather than in the conventional [open quotes]dry powder[close quotes] mode, we obtained particle size data which were in reasonable agreement with the DCP results. 31 refs., 5 figs., 1 tab.

  18. Particle size distributions in the Eastern Mediterranean troposphere

    NASA Astrophysics Data System (ADS)

    Kalivitis, N.; Birmili, W.; Stock, M.; Wehner, B.; Massling, A.; Wiedensohler, A.; Gerasopoulos, E.; Mihalopoulos, N.

    2008-11-01

    Atmospheric particle size distributions were measured on Crete island, Greece in the Eastern Mediterranean during an intensive field campaign between 28 August and 20 October, 2005. Our instrumentation combined a differential mobility particle sizer (DMPS) and an aerodynamic particle sizer (APS) and measured number size distributions in the size range 0.018 μm 10 μm. Four time periods with distinct aerosol characteristics were discriminated, two corresponding to marine and polluted air masses, respectively. In marine air, the sub-μm size distributions showed two particle modes centered at 67 nm and 195 nm having total number concentrations between 900 and 2000 cm-3. In polluted air masses, the size distributions were mainly unimodal with a mode typically centered at 140 nm, with number concentrations varying between 1800 and 2900 cm-3. Super-μm particles showed number concentrations in the range from 0.01 to 2.5 cm-3 without any clear relation to air mass origin. A small number of short-lived particle nucleation events were recorded, where the calculated particle formation rates ranged between 1.1 1.7 cm-3 s-1. However, no particle nucleation and growth events comparable to those typical for the continental boundary layer were observed. Particles concentrations (Diameter <50 nm) were low compared to continental boundary layer conditions with an average concentration of 300 cm-3. The production of sulfuric acid and its subsequently condensation on preexisting particles was examined with the use of a simplistic box model. These calculations suggested that the day-time evolution of the Aitken particle population was governed mainly by coagulation and that particle formation was absent during most days.

  19. Particle size distributions in the Eastern Mediterranean troposphere

    NASA Astrophysics Data System (ADS)

    Kalivitis, N.; Birmili, W.; Stock, M.; Wehner, B.; Massling, A.; Wiedensohler, A.; Gerasopoulos, E.; Mihalopoulos, N.

    2008-04-01

    Atmospheric particle size distributions were measured on Crete island, Greece in the Eastern Mediterranean during an intensive field campaign between 28 August and 20 October 2005. Our instrumentation combined a differential mobility particle sizer (DMPS) and an aerodynamic particle sizer (APS) and measured number size distributions in the size range 0.018 μm-10 μm. Four time periods with distinct aerosol characteristics were discriminated, two corresponding to marine and polluted air masses, respectively. In marine air, the sub-μm size distributions showed two particle modes centered at 67 nm and 195 nm having total number concentrations between 900 and 2000 cm-3. In polluted air masses, the size distributions were mainly unimodal with a mode typically centered at 140 nm, with number concentrations varying between 1800 and 2900 cm-3. Super-μm particles showed number concentrations in the range from 0.01 to 2.5 cm-3 without any clear relation to air mass origin. A small number of short-lived particle nucleation events were recorded, where the calculated particle formation rates ranged between 1.1-1.7 cm-3 s-1. However, no particle nucleation and growth events comparable to those typical for the continental boundary layer were observed. Particles concentrations (Diameter <50 nm) were low compared to continental boundary layer conditions with an average concentration of 300 cm-3. The production of sulfuric acid and its subsequently condensation on preexisting particles was examined with the use of a simplistic box model. These calculations suggested that the day-time evolution of the Aitken particle population was governed mainly by coagulation and that particle formation was absent during most days.

  20. Aerosol size distribution, composition, and CO2 backscatter

    NASA Astrophysics Data System (ADS)

    Clarke, Antony D.; Porter, John N.

    1991-03-01

    The aerosol size distribution, composition, and CO2 backscatter at 10.6 microns (beta-CO2) were measured continuosly at the Mauna Loa Observatory (Hawaii) during January-March and November-December, 1988 periods to compare the characteristics of periods associated with appreciable Asian dust transport to that site (January-March) with those of periods characterized by low-dust condition. The aerosol size distribution in the range 0.15 micron to 7.6 microns was measured at temperatures of 40, 150, and 340 C to differentiate between volatile and nonvolatile aerosols. Large ranges of variability was found in measurements of aerosol size distribution during both periods, but the average distributions were similar for both the high-dust and the low-dust periods. However, values for beta-CO2 were more elevated (by about six times) during periods associated with active Asian dust transport to the observatory site than during the low-dust periods.

  1. Maintenance of phenotypic variation: Repeatability, heritability and size-dependent processes in a wild brook trout population

    USGS Publications Warehouse

    Letcher, B.H.; Coombs, J.A.; Nislow, K.H.

    2011-01-01

    Phenotypic variation in body size can result from within-cohort variation in birth dates, among-individual growth variation and size-selective processes. We explore the relative effects of these processes on the maintenance of wide observed body size variation in stream-dwelling brook trout (Salvelinus fontinalis). Based on the analyses of multiple recaptures of individual fish, it appears that size distributions are largely determined by the maintenance of early size variation. We found no evidence for size-dependent compensatory growth (which would reduce size variation) and found no indication that size-dependent survival substantially influenced body size distributions. Depensatory growth (faster growth by larger individuals) reinforced early size variation, but was relatively strong only during the first sampling interval (age-0, fall). Maternal decisions on the timing and location of spawning could have a major influence on early, and as our results suggest, later (>age-0) size distributions. If this is the case, our estimates of heritability of body size (body length=0.25) will be dominated by processes that generate and maintain early size differences. As a result, evolutionary responses to environmental change that are mediated by body size may be largely expressed via changes in the timing and location of reproduction. Published 2011. This article is a US Government work and is in the public domain in the USA.

  2. Effect of a RF Wave on Ion Cyclotron Instability in Size Distributed Impurities Containing Plasmas

    SciTech Connect

    Sharma, A. K.; Tripathi, V. K.; Annou, R.

    2008-09-07

    The effect of a large amplitude lower hybrid wave on current driven ion cyclotron waves in a dusty plasma where dust grains are size distributed is examined. The influence of the lower hybrid wave on the stabilization of the instability is studied. The efficacy of rf is dust density dependent.

  3. Simulation of 2D Fields of Raindrop Size Distributions

    NASA Astrophysics Data System (ADS)

    Berne, A.; Schleiss, M.; Uijlenhoet, R.

    2008-12-01

    The raindrop size distribution (DSD hereafter) is of primary importance for quantitative applications of weather radar measurements. The radar reflectivity~Z (directly measured by radar) is related to the power backscattered by the ensemble of hydrometeors within the radar sampling volume. However, the rain rate~R (the flux of water to the surface) is the variable of interest for many applications (hydrology, weather forecasting, air traffic for example). Usually, radar reflectivity is converted into rain rate using a power law such as Z=aRb. The coefficients a and b of the Z-R relationship depend on the DSD. The variability of the DSD in space and time has to be taken into account to improve radar rain rate estimates. Therefore, the ability to generate a large number of 2D fields of DSD which are statistically homogeneous provides a very useful simulation framework that nicely complements experimental approaches based on DSD data, in order to investigate radar beam propagation through rain as well as radar retrieval techniques. The proposed approach is based on geostatistics for structural analysis and stochastic simulation. First, the DSD is assumed to follow a gamma distribution. Hence a 2D field of DSDs can be adequately described as a 2D field of a multivariate random function consisting of the three DSD parameters. Such fields are simulated by combining a Gaussian anamorphosis and a multivariate Gaussian random field simulation algorithm. Using the (cross-)variogram models fitted on data guaranties that the spatial structure of the simulated fields is consistent with the observed one. To assess its validity, the proposed method is applied to data collected during intense Mediterranean rainfall. As only time series are available, Taylor's hypothesis is assumed to convert time series in 1D range profile. Moreover, DSD fields are assumed to be isotropic so that the 1D structure can be used to simulate 2D fields. A large number of 2D fields of DSD parameters are

  4. Rock sampling. [method for controlling particle size distribution

    NASA Technical Reports Server (NTRS)

    Blum, P. (Inventor)

    1971-01-01

    A method for sampling rock and other brittle materials and for controlling resultant particle sizes is described. The method involves cutting grooves in the rock surface to provide a grouping of parallel ridges and subsequently machining the ridges to provide a powder specimen. The machining step may comprise milling, drilling, lathe cutting or the like; but a planing step is advantageous. Control of the particle size distribution is effected primarily by changing the height and width of these ridges. This control exceeds that obtainable by conventional grinding.

  5. Method for determining the droplet size distribution of emulsified water

    SciTech Connect

    Rzaev, A.G.

    1988-09-10

    Accelerating crude-oil processing requires estimation of the major parameters, including the droplet size distribution of the oil emulsion (OE) in the flow ahead of the settlers. This is handled here as follows. Under industrial conditions, samples are taken ahead of the settler into a calibrated vessel specially designed for the purpose and allowed to separate at a temperature equal to the flow temperature, where the amount of water deposited and the settling time are recorded. A hyperbolic relation applies quite closely to those data. The model expresses the droplet size as a function of the hydrodynamic parameters and can be used in optimizing dewatering and desalting oil.

  6. Collagen fibril arrangement and size distribution in monkey oral mucosa

    PubMed Central

    OTTANI, V.; FRANCHI, M.; DE PASQUALE, V.; LEONARDI, L.; MOROCUTTI, M.; RUGGERI, A.

    1998-01-01

    Collagen fibre organisation and fibril size were studied in the buccal gingival and hard palate mucosa of Macacus rhesus monkey. Light and electron microscopy analysis showed connective papillae exhibiting a similar inner structure in the different areas examined, but varying in distribution, shape and size. Moving from the deep to surface layers of the buccal gingival mucosa (free and attached portions), large collagen fibril bundles became smaller and progressively more wavy with decreasing collagen fibril diameter. This gradual diameter decrease did not occur in the hard palate mucosa (free portion, rugae and interrugal regions) where the fibril diameter remained constant. A link between collagen fibril diameter and mechanical function is discussed. PMID:9688498

  7. The measurement of the size distribution of artificial fogs

    NASA Technical Reports Server (NTRS)

    Deepak, A.; Cliff, W. C.; Mcdonald, J. R.; Ozarski, R.; Thomson, J. A. L.; Huffaker, R. M.

    1974-01-01

    The size-distribution of the fog droplets at various fog particle concentrations in fog chamber was determined by two methods: (1) the Stokes' velocity photographic method and (2) using the active scattering particle spectrometer. It is shown that the two techniques are accurate in two different ranges of particle size - the former in the radii range (0.1 micrometers to 10.0 micrometers), and the latter for radii greater than 10.0 micrometers. This was particularly true for high particle concentration, low visibility fogs.

  8. TIME DELAY SYSTEMS WITH DISTRIBUTION DEPENDENT DYNAMICS

    PubMed Central

    Banks, H. T.; Dediu, Sava; Nguyen, Hoan K.

    2009-01-01

    General delay dynamical systems in which uncertainty is present in the form of probability measure dependent dynamics are considered. Several motivating examples arising in biology are discussed. A functional analytic framework for investigating well–posedness (existence, uniqueness and continuous dependence of solutions), inverse problems, sensitivity analysis and approximations of the measures for computational purposes is surveyed. PMID:19865602

  9. TIME DELAY SYSTEMS WITH DISTRIBUTION DEPENDENT DYNAMICS.

    PubMed

    Banks, H T; Dediu, Sava; Nguyen, Hoan K

    2007-01-01

    General delay dynamical systems in which uncertainty is present in the form of probability measure dependent dynamics are considered. Several motivating examples arising in biology are discussed. A functional analytic framework for investigating well-posedness (existence, uniqueness and continuous dependence of solutions), inverse problems, sensitivity analysis and approximations of the measures for computational purposes is surveyed.

  10. Size dependent elastic modulus and mechanical resilience of dental enamel.

    PubMed

    O'Brien, Simona; Shaw, Jeremy; Zhao, Xiaoli; Abbott, Paul V; Munroe, Paul; Xu, Jiang; Habibi, Daryoush; Xie, Zonghan

    2014-03-21

    Human tooth enamel exhibits a unique microstructure able to sustain repeated mechanical loading during dental function. Although notable advances have been made towards understanding the mechanical characteristics of enamel, challenges remain in the testing and interpretation of its mechanical properties. For example, enamel was often tested under dry conditions, significantly different from its native environment. In addition, constant load, rather than indentation depth, has been used when mapping the mechanical properties of enamel. In this work, tooth specimens are prepared under hydrated conditions and their stiffnesses are measured by depth control across the thickness of enamel. Crystal arrangement is postulated, among other factors, to be responsible for the size dependent indentation modulus of enamel. Supported by a simple structure model, effective crystal orientation angle is calculated and found to facilitate shear sliding in enamel under mechanical contact. In doing so, the stress build-up is eased and structural integrity is maintained.

  11. The flexoelectric effect associated size dependent pyroelectricity in solid dielectrics

    SciTech Connect

    Bai, Gang; Liu, Zhiguo; Xie, Qiyun; Guo, Yanyan; Li, Wei; Yan, Xiaobing

    2015-09-15

    A phenomenological thermodynamic theory is used to investigate the effect of strain gradient on the pyroelectric effect in centrosymmetric dielectric solids. Direct pyroelectricity can exist as external mechanical stress is applied to non-pyroelectric dielectrics with shapes such as truncated pyramids, due to elastic strain gradient induced flexoelectric polarization. Effective pyroelectric coefficient was analyzed in truncated pyramids. It is found to be controlled by size, ambient temperature, stress, and aspect ratio and depends mainly on temperature sensitivity of flexoelectric coefficient (TSFC) and strain gradient of the truncated pyramids dielectric solids. These results show that the pyroelectric property of Ba{sub 0.67}Sr{sub 0.33}TiO{sub 3} above T{sub c} similar to PZT and other lead-based ferroelectrics can be obtained. This feature might widely broaden the selection of materials for infrared detectors with preferable properties.

  12. Microscopic probing of the size dependence in hydrophobic solvation

    SciTech Connect

    Huang Ningdong; Nordlund, Dennis; Huang Congcong; Weiss, Thomas M.; Acremann, Yves; Schlesinger, Daniel; Pettersson, Lars G. M.; Tyliszczak, Tolek; Nilsson, Anders

    2012-02-21

    We report small angle x-ray scattering data demonstrating the direct experimental microscopic observation of the small-to-large crossover behavior of hydrophobic effects in hydrophobic solvation. By increasing the side chain length of amphiphilic tetraalkyl-ammonium (C{sub n}H{sub 2n+1}){sub 4}N{sup +} (R{sub 4}N{sup +}) cations in aqueous solution we observe diffraction peaks indicating association between cations at a solute size between 4.4 and 5 A, which show temperature dependence dominated by hydrophobic attraction. Using O K-edge x-ray absorption we show that small solutes affect hydrogen bonding in water similar to a temperature decrease, while large solutes affect water similar to a temperature increase. Molecular dynamics simulations support, and provide further insight into, the origin of the experimental observations.

  13. Size Dependent Cation Channel in Nanoporous Prussian Blue Lattice

    NASA Astrophysics Data System (ADS)

    Moritomo, Yutaka; Igarashi, Kazuhiro; Kim, Jungeun; Tanaka, Hiroshi

    2009-08-01

    Cation and/or molecule transfer within nanoporous materials can be utilized in, for example, electrochromic devices, hydrogen storage, molecular sensors, and molecular filters. Here, we investigated the mobilities of cations, Na+, K+, and Rb+, in vacancy-controlled Prussian blue film, NaxCo[Fe(CN)6]1-vzH2O (v is vacancy concentration) with a jungle gym structure. We found that only the smallest Na+ ions pass through the cubic planes of the lattice, while the larger cations, i.e., K+ and Rb+, take a detour channel along the [Fe(CN)6] vacancy. The size-dependent cation channel is well understood in terms of the potential curve derived by an ab initio total energy calculation.

  14. Droplet Size Distributions in Atomization of Dilute Viscoelastic Solutions

    NASA Astrophysics Data System (ADS)

    Keshavarz, Bavand; McKinley, Gareth; Houze, Eric; Moore, John; Pottiger, Michael; Cotts, Patricia; M. I. T. Collaboration; DuPont Collaboration

    2012-11-01

    The droplet size probability distribution functions (PDF) for atomization/fragmentation processes in Newtonian fluids are now generally accepted to be close to Gamma distributions. Despite the great practical importance, little is known about the nature of corresponding distributions for viscoelastic liquids, e.g. polymeric solutions such as pesticide sprays and paints. We present data from air-assisted atomization experiments for model viscoelastic solutions composed of very dilute solutions of polyethylene oxide. Although the addition of small amounts of high molecular weight polymer keeps the fluid shear viscosity and surface tension close to the solvent values, the size distributions are skewed towards higher values of the Sauter mean diameter. We show that the PDF curves for these weakly-elastic fluids are well described by Gamma distributions, but the exponent n is systematically decreased by fluid elasticity. Flow visualization images show that this behavior arises from the non-linear dynamics close to the break-up point which are dominated by an elasto-capillary force balance within the thinning ligaments and the magnitude of the extensional viscosity in the viscoelastic fluid. Mechanical Engineering Department, Cambridge, MA.

  15. Size dependent nanomechanics of coil spring shaped polymer nanowires

    PubMed Central

    Ushiba, Shota; Masui, Kyoko; Taguchi, Natsuo; Hamano, Tomoki; Kawata, Satoshi; Shoji, Satoru

    2015-01-01

    Direct laser writing (DLW) via two-photon polymerization (TPP) has been established as a powerful technique for fabrication and integration of nanoscale components, as it enables the production of three dimensional (3D) micro/nano objects. This technique has indeed led to numerous applications, including micro- and nanoelectromechanical systems (MEMS/NEMS), metamaterials, mechanical metamaterials, and photonic crystals. However, as the feature sizes decrease, an urgent demand has emerged to uncover the mechanics of nanosized polymer materials. Here, we fabricate coil spring shaped polymer nanowires using DLW via two-photon polymerization. We find that even the nanocoil springs follow a linear-response against applied forces, following Hooke’s law, as revealed by compression tests using an atomic force microscope. Further, the elasticity of the polymer material is found to become significantly greater as the wire radius is decreased from 550 to 350 nm. Polarized Raman spectroscopy measurements show that polymer chains are aligned in nanowires along the axis, which may be responsible for the size dependence. Our findings provide insight into the nanomechanics of polymer materials fabricated by DLW, which leads to further applications based on nanosized polymer materials. PMID:26612544

  16. Size dependent nanomechanics of coil spring shaped polymer nanowires

    NASA Astrophysics Data System (ADS)

    Ushiba, Shota; Masui, Kyoko; Taguchi, Natsuo; Hamano, Tomoki; Kawata, Satoshi; Shoji, Satoru

    2015-11-01

    Direct laser writing (DLW) via two-photon polymerization (TPP) has been established as a powerful technique for fabrication and integration of nanoscale components, as it enables the production of three dimensional (3D) micro/nano objects. This technique has indeed led to numerous applications, including micro- and nanoelectromechanical systems (MEMS/NEMS), metamaterials, mechanical metamaterials, and photonic crystals. However, as the feature sizes decrease, an urgent demand has emerged to uncover the mechanics of nanosized polymer materials. Here, we fabricate coil spring shaped polymer nanowires using DLW via two-photon polymerization. We find that even the nanocoil springs follow a linear-response against applied forces, following Hooke’s law, as revealed by compression tests using an atomic force microscope. Further, the elasticity of the polymer material is found to become significantly greater as the wire radius is decreased from 550 to 350 nm. Polarized Raman spectroscopy measurements show that polymer chains are aligned in nanowires along the axis, which may be responsible for the size dependence. Our findings provide insight into the nanomechanics of polymer materials fabricated by DLW, which leads to further applications based on nanosized polymer materials.

  17. Size-dependent symmetry breaking in models for morphogenesis

    NASA Astrophysics Data System (ADS)

    Barrio, R. A.; Maini, P. K.; Aragón, J. L.; Torres, M.

    2002-08-01

    A general property of dynamical systems is the appearance of spatial and temporal patterns due to a change of stability of a homogeneous steady state. Such spontaneous symmetry breaking is observed very frequently in all kinds of real systems, including the development of shape in living organisms. Many nonlinear dynamical systems present a wide variety of patterns with different shapes and symmetries. This fact restricts the applicability of these models to morphogenesis, since one often finds a surprisingly small variation in the shapes of living organisms. For instance, all individuals in the Phylum Echinodermata share a persistent radial fivefold symmetry. In this paper, we investigate in detail the symmetry-breaking properties of a Turing reaction-diffusion system confined in a small disk in two dimensions. It is shown that the symmetry of the resulting pattern depends only on the size of the disk, regardless of the boundary conditions and of the differences in the parameters that differentiate the interior of the domain from the outer space. This study suggests that additional regulatory mechanisms to control the size of the system are of crucial importance in morphogenesis.

  18. Size dependent nanomechanics of coil spring shaped polymer nanowires.

    PubMed

    Ushiba, Shota; Masui, Kyoko; Taguchi, Natsuo; Hamano, Tomoki; Kawata, Satoshi; Shoji, Satoru

    2015-01-01

    Direct laser writing (DLW) via two-photon polymerization (TPP) has been established as a powerful technique for fabrication and integration of nanoscale components, as it enables the production of three dimensional (3D) micro/nano objects. This technique has indeed led to numerous applications, including micro- and nanoelectromechanical systems (MEMS/NEMS), metamaterials, mechanical metamaterials, and photonic crystals. However, as the feature sizes decrease, an urgent demand has emerged to uncover the mechanics of nanosized polymer materials. Here, we fabricate coil spring shaped polymer nanowires using DLW via two-photon polymerization. We find that even the nanocoil springs follow a linear-response against applied forces, following Hooke's law, as revealed by compression tests using an atomic force microscope. Further, the elasticity of the polymer material is found to become significantly greater as the wire radius is decreased from 550 to 350 nm. Polarized Raman spectroscopy measurements show that polymer chains are aligned in nanowires along the axis, which may be responsible for the size dependence. Our findings provide insight into the nanomechanics of polymer materials fabricated by DLW, which leads to further applications based on nanosized polymer materials. PMID:26612544

  19. Size dependent nanomechanics of coil spring shaped polymer nanowires.

    PubMed

    Ushiba, Shota; Masui, Kyoko; Taguchi, Natsuo; Hamano, Tomoki; Kawata, Satoshi; Shoji, Satoru

    2015-11-27

    Direct laser writing (DLW) via two-photon polymerization (TPP) has been established as a powerful technique for fabrication and integration of nanoscale components, as it enables the production of three dimensional (3D) micro/nano objects. This technique has indeed led to numerous applications, including micro- and nanoelectromechanical systems (MEMS/NEMS), metamaterials, mechanical metamaterials, and photonic crystals. However, as the feature sizes decrease, an urgent demand has emerged to uncover the mechanics of nanosized polymer materials. Here, we fabricate coil spring shaped polymer nanowires using DLW via two-photon polymerization. We find that even the nanocoil springs follow a linear-response against applied forces, following Hooke's law, as revealed by compression tests using an atomic force microscope. Further, the elasticity of the polymer material is found to become significantly greater as the wire radius is decreased from 550 to 350 nm. Polarized Raman spectroscopy measurements show that polymer chains are aligned in nanowires along the axis, which may be responsible for the size dependence. Our findings provide insight into the nanomechanics of polymer materials fabricated by DLW, which leads to further applications based on nanosized polymer materials.

  20. Effects of pore-size and shape distributions on diffusion pore imaging by nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Kuder, Tristan Anselm; Laun, Frederik Bernd

    2015-08-01

    In medical imaging and porous media research, NMR diffusion measurements are extensively used to investigate the structure of diffusion restrictions such as cell membranes. Recently, several methods have been proposed to unambiguously determine the shape of arbitrary closed pores or cells filled with an NMR-visible medium by diffusion experiments. The first approach uses a combination of a long and a short diffusion-weighting gradient pulse, while the other techniques employ short gradient pulses only. While the eventual aim of these methods is to determine pore-size and shape distributions, the focus has been so far on identical pores. Thus, the aim of this work is to investigate the ability of these different methods to resolve pore-size and orientation distributions. Simulations were performed comparing the various pore imaging techniques employing different distributions of pore size and orientation and varying timing parameters. The long-narrow gradient profile is most advantageous to investigate pore distributions, because average pore images can be directly obtained. The short-gradient methods suppress larger pores or induce a considerable blurring. Moreover, pore-shape-specific artifacts occur; for example, the central part of a distribution of cylinders may be largely underestimated. Depending on the actual pore distribution, short-gradient methods may nonetheless yield good approximations of the average pore shape. Furthermore, the application of short-gradient methods can be advantageous to differentiate whether pore-size distributions or intensity distributions, e.g., due to surface relaxation, are predominant.

  1. Rapid determination of particle size distribution of microbead catalysts

    SciTech Connect

    Mirshii, Y.V.; Goos, T.V.; Kaviev, V.M.; Kazahov, G.I.; Klimov, A.V.; Nesmeyanova, T.S.

    1986-05-01

    The authors have developed a rapid method for the determination of the particle size distribution of microbead catalysts by a photosedimentation method. This method is based on a determination of the settling velocity of the particles according to the change in optical density of the suspension as the particles settle. The design of the instrument was modified for application to the analysis of microbead cracking catalysts and microbead zeolites; it was originally developed for studies of particle size distribution in other materials. The measuring part of the AFS-2M photosedimentograph is shown schematically. For the high-zeolite catalysts, the results obtained by photosedimenation analysis are somewhat different from those obtained by the pipette method. The photosedimentation method can also be used in the analysis of microbead zeolites that are intended for use in the fluid-bed recovery of liquid paraffins.

  2. The fossilized size distribution of the main asteroid belt

    NASA Astrophysics Data System (ADS)

    Bottke, William F.; Durda, Daniel D.; Nesvorný, David; Jedicke, Robert; Morbidelli, Alessandro; Vokrouhlický, David; Levison, Hal

    2005-05-01

    Planet formation models suggest the primordial main belt experienced a short but intense period of collisional evolution shortly after the formation of planetary embryos. This period is believed to have lasted until Jupiter reached its full size, when dynamical processes (e.g., sweeping resonances, excitation via planetary embryos) ejected most planetesimals from the main belt zone. The few planetesimals left behind continued to undergo comminution at a reduced rate until the present day. We investigated how this scenario affects the main belt size distribution over Solar System history using a collisional evolution model (CoEM) that accounts for these events. CoEM does not explicitly include results from dynamical models, but instead treats the unknown size of the primordial main belt and the nature/timing of its dynamical depletion using innovative but approximate methods. Model constraints were provided by the observed size frequency distribution of the asteroid belt, the observed population of asteroid families, the cratered surface of differentiated Asteroid (4) Vesta, and the relatively constant crater production rate of the Earth and Moon over the last 3 Gyr. Using CoEM, we solved for both the shape of the initial main belt size distribution after accretion and the asteroid disruption scaling law QD∗. In contrast to previous efforts, we find our derived QD∗ function is very similar to results produced by numerical hydrocode simulations of asteroid impacts. Our best fit results suggest the asteroid belt experienced as much comminution over its early history as it has since it reached its low-mass state approximately 3.9-4.5 Ga. These results suggest the main belt's wavy-shaped size-frequency distribution is a "fossil" from this violent early epoch. We find that most diameter D≳120 km asteroids are primordial, with their physical properties likely determined during the accretion epoch. Conversely, most smaller asteroids are byproducts of fragmentation

  3. Domain-size-dependent exchange bias in Co/LaFeO3

    SciTech Connect

    Scholl, A.; Nolting, F.; Seo, J.W.; Ohldag, H.; Stohr, J.; Raoux,S.; Locquet, J.-P.; Fompeyrine, J.

    2004-09-22

    X-ray microscopy using magnetic linear dichroism of a zero-field-grown, multi-domain Co/LaFeO{sub 3} ferromagnet/antiferromagnet sample shows a local exchange bias of random direction and magnitude. A statistical analysis of the local bias of individual, micron-size magnetic domains demonstrates an increasing bias field with decreasing domain size as expected for a random distribution of pinned, uncompensated spins, which are believed to mediate the interface coupling. A linear dependence with the inverse domain diameter is found.

  4. Size-dependant heating rates of iron oxide nanoparticles for magnetic fluid hyperthermia

    PubMed Central

    Gonzales-Weimuller, Marcela; Zeisberger, Matthias; Krishnan, Kannan M.

    2015-01-01

    Using the thermal decomposition of organometallics method we have synthesized high-quality, iron oxide nanoparticles of tailorable size up to ~15nm and transferred them to a water phase by coating with a biocompatible polymer. The magnetic behavior of these particles was measured and fit to a log-normal distribution using the Chantrell method and their polydispersity was confirmed to be very narrow. By performing calorimetry measurements with these monodisperse particles we have unambiguously demonstrated, for the first time, that at a given frequency, heating rates of superparamagnetic particles are dependent on particle size, in agreement with earlier theoretical predictions. PMID:26405373

  5. Size-dependent mobility of gold nano-clusters during growth on chemically modified graphene

    SciTech Connect

    Bell, Gavin R. Dawson, Peter M.; Pandey, Priyanka A.; Wilson, Neil R.; Mulheran, Paul A.

    2014-01-01

    Gold nano-clusters were grown on chemically modified graphene by direct sputter deposition. Transmission electron microscopy of the nano-clusters on these electron-transparent substrates reveals an unusual bimodal island size distribution (ISD). A kinetic Monte Carlo model of growth incorporating a size-dependent cluster mobility rule uniquely reproduces the bimodal ISD, providing strong evidence for the mobility of large clusters during surface growth. The cluster mobility exponent of −5/3 is consistent with cluster motion via one-dimensional diffusion of gold atoms around the edges of the nano-clusters.

  6. 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.

  7. Ultrasonic Backscattering from Suspended Erythrocytes: Dependence on Frequency and Size.

    NASA Astrophysics Data System (ADS)

    Kuo, Ihyuan

    The ultrasonic scattering properties of blood have been intensively investigated since the echo signal from red blood cells carries abundant diagnostic information for the study of blood flow and blood properties in the vessels. Recently, ultrasound of frequency higher than 20 MHz has been implemented in intravascular imaging to obtain better images of the vessel wall. In this research measurements were extended to 30 MHz to better understand the effect of blood on the operation of these intravascular devices. The experimentally measured backscatter of saline suspended porcine erythrocytes for frequency up to 30 MHz agrees very well with the theoretical analysis which indicate that Rayleigh scattering is still valid below this frequency. The analysis utilize the T-matrix method to calculate the backscattering cross section of an erythrocyte modeled as a fluid sphere, disk, and biconcave disk. Measurements on the backscattering coefficients of porcine, bovine, and lamb erythrocytes reveal that the backscatter has a square dependence on cell volume. The cell size dependent backscatter is also analyzed via a continuum approach. It is found that the echo intensity of high frequency ultrasound suffers greatly from the attenuation. The dilemma may be solved by using a spherically focused transducer. An analysis of the focused beam reflected from a perfect planar reflector leads to the modification of the standard substitution method for the backscatter measurement since the "image source" theory is found to be inappropriate for the focused beam. Reflection of the focused beam near the focal point is described based on Huygens' principle. Experimental and theoretical results indicate that the backscatter is dependent upon the position of the scatterer and the geometry of the transducer if a focused beam is used. Since ultrasound velocity information is needed for scattering measurements, an innovative method for measuring the acoustic speed and the attenuation coefficient

  8. The Dependence of Atomic Oxygen Undercutting of Protected Polyimide Kapton(tm) H upon Defect Size

    NASA Technical Reports Server (NTRS)

    Snyder, Aaron; deGroh, Kim K.

    2001-01-01

    Understanding the behavior of polymeric materials when exposed to the low-Earth-orbit (LEO) environment is important in predicting performance characteristics such as in-space durability. Atomic oxygen (AO) present in LEO is known to be the principal agent in causing undercutting erosion of SiO(x) protected polyimide Kapton(R) H film, which serves as a mechanically stable blanket material in solar arrays. The rate of undercutting is dependent on the rate of arrival, directionality and energy of the AO with respect to the film surface. The erosion rate also depends on the distribution of the size of defects existing in the protective coating. This paper presents results of experimental ground testing using low energy, isotropic AO flux together with numerical modeling to determine the dependence of undercutting erosion upon defect size.

  9. Comparison of photon correlation spectroscopy with photosedimentation analysis for the determination of aqueous colloid size distributions

    USGS Publications Warehouse

    Rees, T.F.

    1990-01-01

    Photon correlation spectroscopy (PCS) utilizes the Doppler frequency shift of photons scattered off particles undergoing Brownian motion to determine the size of colloids suspended in water. Photosedimentation analysis (PSA) measures the time-dependent change in optical density of a suspension of colloidal particles undergoing centrifugation. A description of both techniques, important underlying assumptions, and limitations are given. Results for a series of river water samples show that the colloid-size distribution means are statistically identical as determined by both techniques. This also is true of the mass median diameter (MMD), even though MMD values determined by PSA are consistently smaller than those determined by PCS. Because of this small negative bias, the skew parameters for the distributions are generally smaller for the PCS-determined distributions than for the PSA-determined distributions. Smaller polydispersity indices for the distributions are also determined by PCS. -from Author

  10. Exploiting Size-Dependent Drag and Magnetic Forces for Size-Specific Separation of Magnetic Nanoparticles

    PubMed Central

    Rogers, Hunter B.; Anani, Tareq; Choi, Young Suk; Beyers, Ronald J.; David, Allan E.

    2015-01-01

    Realizing the full potential of magnetic nanoparticles (MNPs) in nanomedicine requires the optimization of their physical and chemical properties. Elucidation of the effects of these properties on clinical diagnostic or therapeutic properties, however, requires the synthesis or purification of homogenous samples, which has proved to be difficult. While initial simulations indicated that size-selective separation could be achieved by flowing magnetic nanoparticles through a magnetic field, subsequent in vitro experiments were unable to reproduce the predicted results. Magnetic field-flow fractionation, however, was found to be an effective method for the separation of polydisperse suspensions of iron oxide nanoparticles with diameters greater than 20 nm. While similar methods have been used to separate magnetic nanoparticles before, no previous work has been done with magnetic nanoparticles between 20 and 200 nm. Both transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis were used to confirm the size of the MNPs. Further development of this work could lead to MNPs with the narrow size distributions necessary for their in vitro and in vivo optimization. PMID:26307980

  11. Controls on phytoplankton cell size distributions in contrasting physical environments

    NASA Astrophysics Data System (ADS)

    Clark, J. R.; Daines, S. J.; Lenton, T. M.

    2012-04-01

    A key challenge for marine ecosystem and biogeochemical models is to capture the multiple ecological and evolutionary processes driving the adaptation of diverse communities to changed environmental conditions over different spatial and temporal scales. These range from short-term acclimation in individuals, to population-level selection, immigration and ecological succession on intermediate scales, to shifts in the global biogeochemical cycling of key elements. As part of the "EVE" project, we have been working toward improving the representation of ecological and evolutionary processes in models, with a focus on understanding the role of marine ecosystems in the past, present, and future Earth system. Our approach is to develop a mechanistic understanding of trade-offs between different functional traits through the explicit representation of resource investment in sub-cellular components controlled by a synthetic genome. Trait expression (including size, metabolic strategies on a continuum from autotrophy to heterotrophy, and predation strategies) and adaptation to the environment are then emergent properties of the model, following from natural selection operating in the model environment. Here we show results relating to controls on phytoplankton cell size - a key phytoplankton trait which is inextricably linked to the structuring and functioning of marine ecosystems. Coupled to the MIT OGCM, we use the model to derive dynamic optimal size-class distributions at representative oligotrophic and high-latitude time series sites, which are then compared with in situ data. Particular attention is given to the relative importance of top-down vs bottom-up drivers for phytoplankton cell size, and their influence on global patterns in phytoplankton cell size, as well as changes in the cell size distribution during phytoplankton bloom periods.

  12. Measurements of Aerosol Charge and Size Distribution for Graphite, Gold, Palladium, and Silver Nanoparticles

    SciTech Connect

    Simones, Matthew P.; Gutti, Veera R.; Meyer, Ryan M.; Loyalka, Sudarshan K.

    2011-11-01

    The role of charge on aerosol evolution and hence the nuclear source term has been an issue of interest, and there is a need for both experimental techniques and modeling for quantifying this role. Our focus here is on further exploration of a tandem differential mobility analyzer (TDMA) technique to simultaneously measure both the size and charge (positive, negative and neutral) dependent aerosol distributions. We have generated graphite, gold, silver, and palladium nanoparticles (aerosol) using a spark generator. We measure the electrical mobility-size distributions for these aerosols using a TDMA, and from these data we deduce the full charge-size distributions. We observe asymmetry in the particle size distributions for negative and positive charges. This asymmetry could have a bearing on the dynamics of charged aerosols, indicating that the assumption of symmetry for size distributions of negatively and positively charged particles in source term simulations may not be always appropriate. Also, the experimental technique should find applications in measurements of aerosol rate processes that are affected by both particle charge and size (e.g. coagulation, deposition, resuspension), and hence in modeling and simulation of the nuclear source term.

  13. SIZE DEPENDENCE OF FLEXURAL STRENGTH AND FATIGUE STRENGTH OF PAVEMENT CONCRETE

    NASA Astrophysics Data System (ADS)

    Yoshimoto, Toru; Sato, Ryoichi

    The size effect on flexural fatigue strength of concrete was experime ntally investigated. For this purpose, specimens of two sizes were prepared: 150mm x 150mm x 530mm (span=450mm) and 200mm x 450mm x 1800mm (span=1350mm). The stress levels were set at 70%, 80% and 90% of the compressive strength. Experimental results showed that the number of loading cycles at failure increased with the enlargement of specimens. Based on a fracture mechanics approach, with a stress level of 70%, this dependence of flexural fatigue strength on size was explained by the difference in the stress distributions in the sections of small and large sized specimens. A te nsion softening stress region was formed in the section of the small specimen, whereas elastic stress was produced over the full section in the large specimen.

  14. Sensitivity of Satellite-Retrieved Cloud Properties to the Effective Variance of Cloud Droplet Size Distribution

    SciTech Connect

    Arduini, R.F.; Minnis, P.; Smith, W.L.Jr.; Ayers, J.K.; Khaiyer, M.M.; Heck, P.

    2005-03-18

    Cloud reflectance models currently used in cloud property retrievals from satellites have been developed using size distributions defined by a set of fixed effective radii with a fixed effective variance. The satellite retrievals used for the Atmospheric Radiation Measurement (ARM) program assume droplet size distributions with an effective variance value of 0.10 (Minnis et al. 1998); the International Satellite Cloud Climatology Project uses 0.15 (Rossow and Schiffer 1999); and the Moderate Resolution Imaging Spectroradiometer (MODIS) team uses 0.13 (Nakajima and King 1990). These distributions are not necessarily representative of the actual sizes present in the clouds being observed. Because the assumed distributions can affect the reflectance patterns and near-infrared absorption, even for the same droplet effective radius reff, it is desirable to use the optimal size distributions in satellite retrievals of cloud properties. Collocated observations of the same clouds from different geostationary satellites, at different viewing angles, indicate that the current models may not be optimal (Ayers et al. 2005). Similarly, hour-to-hour variations in effective radius and optical depth reveal an unexplained dependence on scattering angle. To explore this issue, this paper examines the sensitivity of the cloud reflectance at 0.65 and 3.90-{micro}m to changes in the effective variance, or the spectral dispersion, of the modeled size distributions. The effects on the scattering phase functions and on the cloud reflectances are presented, as well as some resultant effects on the retrieved cloud properties.

  15. Single-size thermometric measurements on a size distribution of neutral fullerenes.

    PubMed

    Cauchy, C; Bakker, J M; Huismans, Y; Rouzée, A; Redlich, B; van der Meer, A F G; Bordas, C; Vrakking, M J J; Lépine, F

    2013-05-10

    We present measurements of the velocity distribution of electrons emitted from mass-selected neutral fullerenes, performed at the intracavity free electron laser FELICE. We make use of mass-specific vibrational resonances in the infrared domain to selectively heat up one out of a distribution of several fullerene species. Efficient energy redistribution leads to decay via thermionic emission. Time-resolved electron kinetic energy distributions measured give information on the decay rate of the selected fullerene. This method is generally applicable to all neutral species that exhibit thermionic emission and provides a unique tool to study the stability of mass-selected neutral clusters and molecules that are only available as part of a size distribution.

  16. Truncated shifted pareto distribution in assessing size distribution of oil and gas fields

    SciTech Connect

    Houghton, J.C.

    1988-11-01

    The truncated shifted Pareto (TSP) distribution, a variant of the two-parameter Pareto distribution, in which one parameter is added to shift the distribution right and left and the right-hand side is truncated, is used to model size distributions of oil and gas fields for resource assessment. Assumptions about limits to the left-hand and right-hand side reduce the number of parameters to two. The TSP distribution has advantages over the more customary lognormal distribution because it has a simple analytic expression, allowing exact computation of several statistics of interest, has a J-shape, and has more flexibility in the thickness of the right-hand tail. Oil field sizes from the Minnelusa play in the Powder River Basin, Wyoming and Montana, are used as a case study. Probability plotting procedures allow easy visualization of the fit and help the assessment.

  17. Use of the truncated shifted Pareto distribution in assessing size distribution of oil and gas fields

    USGS Publications Warehouse

    Houghton, J.C.

    1988-01-01

    The truncated shifted Pareto (TSP) distribution, a variant of the two-parameter Pareto distribution, in which one parameter is added to shift the distribution right and left and the right-hand side is truncated, is used to model size distributions of oil and gas fields for resource assessment. Assumptions about limits to the left-hand and right-hand side reduce the number of parameters to two. The TSP distribution has advantages over the more customary lognormal distribution because it has a simple analytic expression, allowing exact computation of several statistics of interest, has a "J-shape," and has more flexibility in the thickness of the right-hand tail. Oil field sizes from the Minnelusa play in the Powder River Basin, Wyoming and Montana, are used as a case study. Probability plotting procedures allow easy visualization of the fit and help the assessment. ?? 1988 International Association for Mathematical Geology.

  18. A diagnostic stratospheric aerosol size distribution inferred from SAGE II measurements

    NASA Technical Reports Server (NTRS)

    Thomason, Larry W.

    1991-01-01

    An aerosol size distribution model for the stratosphere is inferred based on 5 years of Stratospheric Aerosol and Gas Experiment (SAGE) II measurements of multispectral aerosol and water vapor extinction. The SAGE II aerosol and water vapor extinction data strongly suggest that there is a critical particle radius below which there is a relatively weak dependence of particle number density with size and above which there are few, if any, particles. A segmented power law model, as a simple representation of this dependence, is used in theoretical calculations and intercomparisons with a variety of aerosol measurements including dustsondes, longwave lidar, and wire impactors and shows a consistently good agreement.

  19. Nanogeochemistry: Size-dependent mineral-fluid interface chemistry

    NASA Astrophysics Data System (ADS)

    Wang, Y.

    2012-12-01

    Nanostructures and nanometer mineral phases, both widely present in geologic materials, can potentially affect many geochemical processes. It is known that at nanometer scales a material tends to exhibit chemical properties distinct from the corresponding bulk phase. Understanding of this size-dependent property change will help us to bridge the existing knowledge gap between the molecular level understanding and the macro-scale laboratory/field observations of a geochemical process. In this presentation, I will review of the recent progresses in nanoscience and provide a perspective on how these progresses can potentially impact geochemical studies. My presentation will be focused the following areas: (1) the characterization of nanostructures in natural systems, (2) the study of fluids and chemical species in nanoconfinement, (3) the effects of nanopores on geochemical reaction and mass transfers, and (4) the use nanostructured materials for environmental management. I will demonstrate that the nanopore confinement can significantly modify geochemical reactions in porous geologic media. As the pore size is reduced to a few nanometers, the difference between surface acidity constants of a mineral (pK2 - pK1) decreases, giving rise to a higher surface charge density on a nanopore surface than that on an unconfined mineral-water interface. The change in surface acidity constants results in a shift of ion sorption edges and enhances ion sorption on nanopore surfaces. This effect causes preferential enrichment of trace elements in nanopores. I will then discuss the implications of this emergent nanometer-scale property to radionuclide transport and carbon dioxide storage in geologic media. This work was performed at Sandia National Laboratories, which is a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the DOE under contract DE-AC04-94AL8500.

  20. Size dependence of cavity volume: a molecular dynamics study.

    PubMed

    Patel, Nisha; Dubins, David N; Pomès, Régis; Chalikian, Tigran V

    2012-02-01

    Partial molar volume, V°, has been used as a tool to sample solute hydration for decades. The efficacy of volumetric investigations of hydration depends on our ability to reliably discriminate between the cavity, V(C), and interaction, V(I), contributions to the partial molar volume. The cavity volume, V(C), consists of the intrinsic volume, V(M), of a solute molecule and the thermal volume, V(T), with the latter representing the volume of the effective void created around the solute. In this work, we use molecular dynamics simulations in conjunction with the Kirkwood-Buff theory to compute the partial molar volumes for organic solutes of varying sizes in water. We perform our computations using the Lennard-Jones and Coulombic pair potentials as well as truncated potentials which contain only the Lennard-Jones but not the Coulombic contribution. The partial molar volume computed with the Lennard-Jones potentials in the absence of the Coulombic term nearly coincides with the cavity volume, V(C). We determine the thermal volume, V(T), for each compound by subtracting its van der Waals volume, V(W), from V(C). Finally, we apply the spherical approximation of solute geometry to evaluate the thickness of the thermal volume, δ. Our results reveal an increase in the thickness of thermal volume, δ, with an increase in the size of the solute. This finding may be related to dewetting of large nonpolar solutes and the concomitant increase in the compressibility of water of hydration. PMID:22133917

  1. Measuring Technique of Bubble Size Distributions in Dough

    NASA Astrophysics Data System (ADS)

    Maeda, Tatsurou; Do, Gab-Soo; Sugiyama, Junichi; Oguchi, Kosei; Tsuta, Mizuki

    A novel technique to recognize bubbles in bread dough and analyze their size distribution was developed by using a Micro-Slicer Image Processing System (MSIPS). Samples were taken from the final stage of the mixing process of bread dough which generally consists of four distinctive stages. Also, to investigate the effect of freeze preservation on the size distribution of bubbles, comparisons were made between fresh dough and the dough that had been freeze preserved at .30°C for three months. Bubbles in the dough samples were identified in the images of MSIPS as defocusing spots due to the difference in focal distance created by vacant spaces. In case of the fresh dough, a total of 910 bubbles were recognized and their maximum diameter ranged from 0.4 to 70.5μm with an average of 11.1μm. On the other hand, a total of 1,195 bubbles were recognized from the freeze-preserved sample, and the maximum diameter ranged from 0.9 to 32.7μm with an average of 6.7μm. Small bubbles with maximum diameters less than 10μm comprised approximately 59% and 78% of total bubbles for fresh and freeze-preserved dough samples, respectively. The results indicated that the bubble size of frozen dough is smaller than that of unfrozen one. The proposed method can provide a novel tool to investigate the effects of mixing and preservation treatments on the size, morphology and distribution of bubbles in bread dough.

  2. Fog-Influenced Submicron Aerosol Number Size Distributions

    NASA Astrophysics Data System (ADS)

    Zikova, N.; Zdimal, V.

    2013-12-01

    The aim of this work is to evaluate the influence of fog on aerosol particle number size distributions (PNSD) in submicron range. Thus, five-year continuous time series of the SMPS (Scanning Mobility Particle Sizer) data giving information on PNSD in five minute time step were compared with detailed meteorological records from the professional meteorological station Kosetice in the Czech Republic. The comparison included total number concentration and PNSD in size ranges between 10 and 800 nm. The meteorological records consist from the exact times of starts and ends of individual meteorological phenomena (with one minute precision). The records longer than 90 minutes were considered, and corresponding SMPS spectra were evaluated. Evaluation of total number distributions showed considerably lower concentration during fog periods compared to the period when no meteorological phenomenon was recorded. It was even lower than average concentration during presence of hydrometeors (not only fog, but rain, drizzle, snow etc. as well). Typical PNSD computed from all the data recorded in the five years is in Figure 1. Not only median and 1st and 3rd quartiles are depicted, but also 5th and 95th percentiles are plotted, to see the variability of the concentrations in individual size bins. The most prevailing feature is the accumulation mode, which seems to be least influenced by the fog presence. On the contrary, the smallest aerosol particles (diameter under 40 nm) are effectively removed, as well as the largest particles (diameter over 500 nm). Acknowledgements: This work was supported by the projects GAUK 62213 and SVV-2013-267308. Figure 1. 5th, 25th, 50th, 75th and 95th percentile of aerosol particle number size distributions recorded during fog events.

  3. INITIAL SIZE DISTRIBUTION OF THE GALACTIC GLOBULAR CLUSTER SYSTEM

    SciTech Connect

    Shin, Jihye; Kim, Sungsoo S.; Yoon, Suk-Jin; Kim, Juhan

    2013-01-10

    Despite the importance of their size evolution in understanding the dynamical evolution of globular clusters (GCs) of the Milky Way, studies that focus specifically on this issue are rare. Based on the advanced, realistic Fokker-Planck (FP) approach, we theoretically predict the initial size distribution (SD) of the Galactic GCs along with their initial mass function and radial distribution. Over one thousand FP calculations in a wide parameter space have pinpointed the best-fit initial conditions for the SD, mass function, and radial distribution. Our best-fit model shows that the initial SD of the Galactic GCs is of larger dispersion than today's SD, and that the typical projected half-light radius of the initial GCs is {approx}4.6 pc, which is 1.8 times larger than that of the present-day GCs ({approx}2.5 pc). Their large size signifies greater susceptibility to the Galactic tides: the total mass of destroyed GCs reaches 3-5 Multiplication-Sign 10{sup 8} M {sub Sun }, several times larger than previous estimates. Our result challenges a recent view that the Milky Way GCs were born compact on the sub-pc scale, and rather implies that (1) the initial GCs were generally larger than the typical size of the present-day GCs, (2) the initially large GCs mostly shrank and/or disrupted as a result of the galactic tides, and (3) the initially small GCs expanded by two-body relaxation, and later shrank by the galactic tides.

  4. Size distribution of submarine landslides along the U.S. Atlantic margin

    USGS Publications Warehouse

    Chaytor, J.D.; ten Brink, U.S.; Solow, A.R.; Andrews, B.D.

    2009-01-01

    Assessment of the probability for destructive landslide-generated tsunamis depends on the knowledge of the number, size, and frequency of large submarine landslides. This paper investigates the size distribution of submarine landslides along the U.S. Atlantic continental slope and rise using the size of the landslide source regions (landslide failure scars). Landslide scars along the margin identified in a detailed bathymetric Digital Elevation Model (DEM) have areas that range between 0.89??km2 and 2410??km2 and volumes between 0.002??km3 and 179??km3. The area to volume relationship of these failure scars is almost linear (inverse power-law exponent close to 1), suggesting a fairly uniform failure thickness of a few 10s of meters in each event, with only rare, deep excavating landslides. The cumulative volume distribution of the failure scars is very well described by a log-normal distribution rather than by an inverse power-law, the most commonly used distribution for both subaerial and submarine landslides. A log-normal distribution centered on a volume of 0.86??km3 may indicate that landslides preferentially mobilize a moderate amount of material (on the order of 1??km3), rather than large landslides or very small ones. Alternatively, the log-normal distribution may reflect an inverse power law distribution modified by a size-dependent probability of observing landslide scars in the bathymetry data. If the latter is the case, an inverse power-law distribution with an exponent of 1.3 ?? 0.3, modified by a size-dependent conditional probability of identifying more failure scars with increasing landslide size, fits the observed size distribution. This exponent value is similar to the predicted exponent of 1.2 ?? 0.3 for subaerial landslides in unconsolidated material. Both the log-normal and modified inverse power-law distributions of the observed failure scar volumes suggest that large landslides, which have the greatest potential to generate damaging tsunamis

  5. Non-monotonic size dependence of diffusion and levitation effect: A mode-coupling theory analysis

    NASA Astrophysics Data System (ADS)

    Nandi, Manoj Kumar; Banerjee, Atreyee; Bhattacharyya, Sarika Maitra

    2013-03-01

    We present a study of diffusion of small tagged particles in a solvent, using mode coupling theory (MCT) analysis and computer simulations. The study is carried out for various interaction potentials. For the first time, using MCT, it is shown that only for strongly attractive interaction potential with allowing interpenetration between the solute-solvent pair the diffusion exhibits a non-monotonic solute size dependence which has earlier been reported in simulation studies [P. K. Ghorai and S. Yashonath, J. Phys. Chem. B 109, 5824-5835 (2005), 10.1021/jp046312w]. For weak attractive and repulsive potential the solute size dependence of diffusion shows monotonic behaviour. It is also found that for systems where the interaction potential does not allow solute-solvent interpenetration, the solute cannot explore the neck of the solvent cage. Thus these systems even with strong attractive interaction will never show any non-monotonic size dependence of diffusion. This non-monotonic size dependence of diffusion has earlier been connected to levitation effect [S. Yashonath and P. Santikary, J. Phys. Chem. 98, 6368 (1994), 10.1021/j100076a022]. We also show that although levitation is a dynamic phenomena, the effect of levitation can be obtained in the static radial distribution function.

  6. Scale-Dependent Habitat Selection and Size-Based Dominance in Adult Male American Alligators.

    PubMed

    Strickland, Bradley A; Vilella, Francisco J; Belant, Jerrold L

    2016-01-01

    Habitat selection is an active behavioral process that may vary across spatial and temporal scales. Animals choose an area of primary utilization (i.e., home range) then make decisions focused on resource needs within patches. Dominance may affect the spatial distribution of conspecifics and concomitant habitat selection. Size-dependent social dominance hierarchies have been documented in captive alligators, but evidence is lacking from wild populations. We studied habitat selection for adult male American alligators (Alligator mississippiensis; n = 17) on the Pearl River in central Mississippi, USA, to test whether habitat selection was scale-dependent and individual resource selectivity was a function of conspecific body size. We used K-select analysis to quantify selection at the home range scale and patches within the home range to determine selection congruency and important habitat variables. In addition, we used linear models to determine if body size was related to selection patterns and strengths. Our results indicated habitat selection of adult male alligators was a scale-dependent process. Alligators demonstrated greater overall selection for habitat variables at the patch level and less at the home range level, suggesting resources may not be limited when selecting a home range for animals in our study area. Further, diurnal habitat selection patterns may depend on thermoregulatory needs. There was no relationship between resource selection or home range size and body size, suggesting size-dependent dominance hierarchies may not have influenced alligator resource selection or space use in our sample. Though apparent habitat suitability and low alligator density did not manifest in an observed dominance hierarchy, we hypothesize that a change in either could increase intraspecific interactions, facilitating a dominance hierarchy. Due to the broad and diverse ecological roles of alligators, understanding the factors that influence their social dominance

  7. Scale-Dependent Habitat Selection and Size-Based Dominance in Adult Male American Alligators

    PubMed Central

    Strickland, Bradley A.; Vilella, Francisco J.; Belant, Jerrold L.

    2016-01-01

    Habitat selection is an active behavioral process that may vary across spatial and temporal scales. Animals choose an area of primary utilization (i.e., home range) then make decisions focused on resource needs within patches. Dominance may affect the spatial distribution of conspecifics and concomitant habitat selection. Size-dependent social dominance hierarchies have been documented in captive alligators, but evidence is lacking from wild populations. We studied habitat selection for adult male American alligators (Alligator mississippiensis; n = 17) on the Pearl River in central Mississippi, USA, to test whether habitat selection was scale-dependent and individual resource selectivity was a function of conspecific body size. We used K-select analysis to quantify selection at the home range scale and patches within the home range to determine selection congruency and important habitat variables. In addition, we used linear models to determine if body size was related to selection patterns and strengths. Our results indicated habitat selection of adult male alligators was a scale-dependent process. Alligators demonstrated greater overall selection for habitat variables at the patch level and less at the home range level, suggesting resources may not be limited when selecting a home range for animals in our study area. Further, diurnal habitat selection patterns may depend on thermoregulatory needs. There was no relationship between resource selection or home range size and body size, suggesting size-dependent dominance hierarchies may not have influenced alligator resource selection or space use in our sample. Though apparent habitat suitability and low alligator density did not manifest in an observed dominance hierarchy, we hypothesize that a change in either could increase intraspecific interactions, facilitating a dominance hierarchy. Due to the broad and diverse ecological roles of alligators, understanding the factors that influence their social dominance

  8. Cloud droplet size distributions in low-level stratiform clouds

    SciTech Connect

    Miles, N.L.; Verlinde, J.; Clothiaux, E.E.

    2000-01-15

    A database of stratus cloud droplet size distribution parameters, derived from in situ data reported in the existing literature, was created, facilitating intercomparison among datasets and quantifying typical values and their variability. From the datasets, which were divided into marine and continental groups, several parameters are presented, including the total number concentration, effective diameter, mean diameter, standard deviation of the droplet diameters about the mean diameter, and liquid water content, as well as the parameters of modified gamma and lognormal distributions. In light of these results, the appropriateness of common assumptions used in remote sensing of cloud droplet size distributions is discussed. For example, vertical profiles of mean diameter, effective diameter, and liquid water content agreed qualitatively with expectations based on the current paradigm of cloud formation. Whereas parcel theory predicts that the standard deviation about the mean diameter should decrease with height, the results illustrated that the standard deviation generally increases with height. A feature common to all marine clouds was their approximately constant total number concentration profiles; however, the total number concentration profiles of continental clouds were highly variable. Without cloud condensation nuclei spectra, classification of clouds into marine and continental groups is based on indirect methods. After reclassification of four sets of measurements in the database, there was a fairly clear dichotomy between marine and continental clouds, but a great deal of variability within each classification. The relevant applications of this study lie in radiative transfer and climate issues, rather than in cloud formation and dynamics. Techniques that invert remotely sensed measurements into cloud droplet size distributions frequently rely on a priori assumptions, such as constant number concentration profiles and constant spectral width. The

  9. Drop Size Distribution - Based Separation of Stratiform and Convective Rain

    NASA Technical Reports Server (NTRS)

    Thurai, Merhala; Gatlin, Patrick; Williams, Christopher

    2014-01-01

    For applications in hydrology and meteorology, it is often desirable to separate regions of stratiform and convective rain from meteorological radar observations, both from ground-based polarimetric radars and from space-based dual frequency radars. In a previous study by Bringi et al. (2009), dual frequency profiler and dual polarization radar (C-POL) observations in Darwin, Australia, had shown that stratiform and convective rain could be separated in the log10(Nw) versus Do domain, where Do is the mean volume diameter and Nw is the scaling parameter which is proportional to the ratio of water content to the mass weighted mean diameter. Note, Nw and Do are two of the main drop size distribution (DSD) parameters. In a later study, Thurai et al (2010) confirmed that both the dual-frequency profiler based stratiform-convective rain separation and the C-POL radar based separation were consistent with each other. In this paper, we test this separation method using DSD measurements from a ground based 2D video disdrometer (2DVD), along with simultaneous observations from a collocated, vertically-pointing, X-band profiling radar (XPR). The measurements were made in Huntsville, Alabama. One-minute DSDs from 2DVD are used as input to an appropriate gamma fitting procedure to determine Nw and Do. The fitted parameters - after averaging over 3-minutes - are plotted against each other and compared with a predefined separation line. An index is used to determine how far the points lie from the separation line (as described in Thurai et al. 2010). Negative index values indicate stratiform rain and positive index indicate convective rain, and, moreover, points which lie somewhat close to the separation line are considered 'mixed' or 'transition' type precipitation. The XPR observations are used to evaluate/test the 2DVD data-based classification. A 'bright-band' detection algorithm was used to classify each vertical reflectivity profile as either stratiform or convective

  10. Fine structure of mass size distributions in an urban environment

    NASA Astrophysics Data System (ADS)

    Salma, Imre; Ocskay, Rita; Raes, Nico; Maenhaut, Willy

    As part of an urban aerosol research project, aerosol samples were collected by a small deposit area low-pressure impactor and a micro-orifice uniform deposit impactor in downtown Budapest in spring 2002. A total number of 23 samples were obtained with each device for separate daytime periods and nights. The samples were analysed by particle-induced X-ray emission spectrometry for 29 elements, or by gravimetry for particulate mass. The raw size distribution data were processed by the inversion program MICRON utilising the calibrated collection efficiency curve for each impactor stage in order to study the mass size distributions in the size range of about 50 nm to 10 μm in detail. Concentration, geometric mean aerodynamic diameter, and geometric standard deviation for each contributing mode were determined and further evaluated. For the crustal elements, two modes were identified in the mass size distributions: a major coarse mode and a (so-called) intermediate mode, which contained about 4% of the elemental mass. The coarse mode was associated with suspension, resuspension, and abrasion processes, whereby the major contribution likely came from road dust, while the particles of the intermediate mode may have originated from the same but also from the other sources. The typical anthropogenic elements exhibited usually trimodal size distributions including a coarse mode and two submicrometer modes instead of a single accumulation mode. The mode diameter of the upper submicrometer mode was somewhat lower for the particulate mass (PM) and S than for the anthropogenic metals, suggesting different sources and/or source processes. The different relative intensities of the two submicrometer modes for the anthropogenic elements and the PM indicate that the elements and PM have multiple sources. An Aitken mode was unambiguously observed for S, Zn, and K, but in a few cases only. The relatively large coarse mode of Cu and Zn, and the small night-to-daytime period

  11. Shape, size, and distribution of magnetic particles in Bjurbole chondrules

    NASA Technical Reports Server (NTRS)

    Nava, David F.

    1994-01-01

    Chondrules from the Bjurbole chondritic meteorite (L4) exhibit saturation remanence magnetization (SIRM) values which vary over three orders of magnitude. REM values (Natural Remanence Magnetization/SIRM) for Allende (C3V) and Chainpur (LL3) are less than 0.01 but in Bjurbole some chondrules were found to have REM values greater than 0.1 with several greater than 0.2. REM values greater than 0.1 are abnormal and cannot be acquired during weak field cooling. If exposure to a strong field (whatever the source) during the chondrules' history is responsible for the high REM values, was such history associated with a different processing which might have resulted in different shape, size, and distribution of metal particles compared to chondrules having REM values of less than 0.01? Furthermore, magnetic hysteresis results show a broad range of magnetic hardness and other intrinsic magnetic properties. These features must be related to (1) size and amount of metal; and (2) properties of, and amount of, tetrataenite in the chondrules (all chondrules thus far subjected to thermomagnetic analysis show the presence of tetrataenite). A scanning electron microscopy (SEM) study is underway to determine the relationship between the shape, size, and distribution of metal particles within individual chondrules and the magnetic properties of these chondrules. Results from the SEM study in conjunction with magnetic property data may also help to discern effects from possible lightning strikes in the nebula prior to incorporation of the chondrules into the parent body.

  12. Characterization of particleboard aerosol - size distribution and formaldehyde content

    SciTech Connect

    Stumpf, J.M.; Blehm, K.D.; Buchan, R.M.; Gunter, B.J.

    1986-12-01

    Health hazards unique to particleboard include the generation of urea-formaldehyde resin bound in wood aerosol and release of formaldehyde gas that can be inhaled by the worker. A particleboard aerosol was generated by a sanding process and collected under laboratory conditions that determined the particle size distribution and formaldehyde content. Three side-by-side Marple 296 personal cascade impactors with midget impingers attached downstream collected particleboard aerosol and gaseous formaldehyde for ten sample runs. Gravimetric analysis quantified the collected aerosol mass, and chromotropic acid/spectrophotometric analytical methods were employed for formaldehyde content in particleboard aerosol and gaseous formaldehyde liberated from sanded particleboard. Significant variations (p<.005) were observed for the particleboard mass and gaseous formaldehyde collected between sample runs. No significant differences (..cap alpha.. = .05) were observed for the aerosol size distribution determined and formaldehyde content in particle board aerosol per unit mass for sampling trials. The overall MMAD of particleboard aerosol was 8.26 ..mu..mAED with a sigmag of 2.01. A predictive model was derived for determining the expected formaldehyde content (..mu..g) by particleboard aerosol mass (mg) collected and particulate size (..mu..mAED).

  13. Size Distributions of Solar Flares and Solar Energetic Particle Events

    NASA Technical Reports Server (NTRS)

    Cliver, E. W.; Ling, A. G.; Belov, A.; Yashiro, S.

    2012-01-01

    We suggest that the flatter size distribution of solar energetic proton (SEP) events relative to that of flare soft X-ray (SXR) events is primarily due to the fact that SEP flares are an energetic subset of all flares. Flares associated with gradual SEP events are characteristically accompanied by fast (much > 1000 km/s) coronal mass ejections (CMEs) that drive coronal/interplanetary shock waves. For the 1996-2005 interval, the slopes (alpha values) of power-law size distributions of the peak 1-8 Angs fluxes of SXR flares associated with (a) >10 MeV SEP events (with peak fluxes much > 1 pr/sq cm/s/sr) and (b) fast CMEs were approx 1.3-1.4 compared to approx 1.2 for the peak proton fluxes of >10 MeV SEP events and approx 2 for the peak 1-8 Angs fluxes of all SXR flares. The difference of approx 0.15 between the slopes of the distributions of SEP events and SEP SXR flares is consistent with the observed variation of SEP event peak flux with SXR peak flux.

  14. SIZE DISTRIBUTIONS OF SOLAR FLARES AND SOLAR ENERGETIC PARTICLE EVENTS

    SciTech Connect

    Cliver, E. W.; Ling, A. G.; Belov, A.; Yashiro, S.

    2012-09-10

    We suggest that the flatter size distribution of solar energetic proton (SEP) events relative to that of flare soft X-ray (SXR) events is primarily due to the fact that SEP flares are an energetic subset of all flares. Flares associated with gradual SEP events are characteristically accompanied by fast ({>=}1000 km s{sup -1}) coronal mass ejections (CMEs) that drive coronal/interplanetary shock waves. For the 1996-2005 interval, the slopes ({alpha} values) of power-law size distributions of the peak 1-8 A fluxes of SXR flares associated with (a) >10 MeV SEP events (with peak fluxes {>=}1 pr cm{sup -2} s{sup -1} sr{sup -1}) and (b) fast CMEs were {approx}1.3-1.4 compared to {approx}1.2 for the peak proton fluxes of >10 MeV SEP events and {approx}2 for the peak 1-8 A fluxes of all SXR flares. The difference of {approx}0.15 between the slopes of the distributions of SEP events and SEP SXR flares is consistent with the observed variation of SEP event peak flux with SXR peak flux.

  15. Marked point process models of raindrop-size distributions

    SciTech Connect

    Smith, J.A. )

    1993-02-01

    The principal process considered in this paper is the flux of raindrops through a volume of the atmosphere. This process is of fundamental importance for a wide variety of engineering and environmental problems, notably remote sensing of precipitation, infiltration of rainfall, soil erosion, atmospheric deposition of pollutants, and design of microwave communication systems. A marked point process model is developed in which the point process represents the arrival times of drops at the upper surface of a sample volume and the mark associated with a drop is its diameter. In the model, both the rate of occurrence of raindrops and the distribution of drop diameters vary randomly over time. Results that relate the drop-size distribution within the sample volume to the probability law of the drop-arrival process are presented. These results allow straightforward comparisons between temporal characterizations of drop-size distributions and spatial characterizations. Representations for derived processes such as rainfall rate and reflectivity are shown to be quite accurate using raindrop data from North Carolina. 30 refs.

  16. Marked point process models of raindrop-size distributions

    NASA Technical Reports Server (NTRS)

    Smith, James A.

    1993-01-01

    The principal process considered in this paper is the flux of raindrops through a volume of the atmosphere. This process is of fundamental importance for a wide variety of engineering and environmental problems, notably remote sensing of precipitation, infiltration of rainfall, soil erosion, atmospheric deposition of pollutants, and design of microwave communication systems. A marked point process model is developed in which the point process represents the arrival times of drops at the upper surface of a sample volume and the mark associated with a drop is its diameter. In the model, both the rate of occurrence of raindrops and the distribution of drop diameters vary randomly over time. Results that relate the drop-size distribution within the sample volume to the probability law of the drop-arrival process are presented. These results allow straightforward comparisons between temporal characterizations of drop-size distributions and spatial characterizations. Representations for derived processes such as rainfall rate and reflectivity are shown to be quite accurate using raindrop data from North Carolina.

  17. Inferring local competition intensity from patch size distributions: a test using biological soil crusts

    USGS Publications Warehouse

    Bowker, Matthew A.; Maestre, Fernando T.

    2012-01-01

    Dryland vegetation is inherently patchy. This patchiness goes on to impact ecology, hydrology, and biogeochemistry. Recently, researchers have proposed that dryland vegetation patch sizes follow a power law which is due to local plant facilitation. It is unknown what patch size distribution prevails when competition predominates over facilitation, or if such a pattern could be used to detect competition. We investigated this question in an alternative vegetation type, mosses and lichens of biological soil crusts, which exhibit a smaller scale patch-interpatch configuration. This micro-vegetation is characterized by competition for space. We proposed that multiplicative effects of genetics, environment and competition should result in a log-normal patch size distribution. When testing the prevalence of log-normal versus power law patch size distributions, we found that the log-normal was the better distribution in 53% of cases and a reasonable fit in 83%. In contrast, the power law was better in 39% of cases, and in 8% of instances both distributions fit equally well. We further hypothesized that the log-normal distribution parameters would be predictably influenced by competition strength. There was qualitative agreement between one of the distribution's parameters (μ) and a novel intransitive (lacking a 'best' competitor) competition index, suggesting that as intransitivity increases, patch sizes decrease. The correlation of μ with other competition indicators based on spatial segregation of species (the C-score) depended on aridity. In less arid sites, μ was negatively correlated with the C-score (suggesting smaller patches under stronger competition), while positive correlations (suggesting larger patches under stronger competition) were observed at more arid sites. We propose that this is due to an increasing prevalence of competition transitivity as aridity increases. These findings broaden the emerging theory surrounding dryland patch size distributions

  18. Estimation of Raindrop size Distribution over Darjeeling (India)

    NASA Astrophysics Data System (ADS)

    Mehta, Shyam; Mitra, Amitabha

    2016-07-01

    A study of rain drop size distribution (DSD) model over Darjeeling (27001'N, 88015'E), India, has been carried out using a Micro Rain Radar (MRR). In this article on the basis of MRR which measured DSD (number of rain drop size and rain rates with the time interval of one minute), at the particular heights and the different rain rates. It starts the simulating data for using the general formula moment of the gamma DSD; however, Applying the method by DSD model of exponential, lognormal, and gamma, to check the true estimation of drop size distributions and it has been estimated by the lower order moments and higher order moments for gamma Distributions. It shows the DSD at different altitudes from 150 m to 2000 m, in the vertical steps of 500 m. however it has been simulated the DSD data about 2 km out of 4.5 km. (I). At the height of 150 m where most of DSD behaves gamma Distributions according to the moments order of low and the moments order of high, However, where occupying low concentrations for any rain rates, (ii). Upper altitudes from 450 m to 2000 m as where as shown most of DSD behaves gamma Distributions according to the moments order of high only, However, where occupying high concentrations for any rain rates. DSD at the altitudes of 2 km and even more 4.5 km (as not shown) but every height behaves more or less similar manner except at the height of 150 m, The DSD of empirical model has been derived on the basis of fit parameters evaluated from experimental data. It is observed that data fits well in gamma distribution for Darjeeling. And relation between slope (ΛɅ) and shape (μµ) which bears the best resemblance at the height of 150m (ground surface) at the lower order moments by the linear fit for any rain rates. In higher altitudes obtained where shape (μ) and slope (ΛɅ) which is not making any resemblance by the linear fit or polynomial fit for any rain rates in Darjeeling.

  19. Size distribution of particles in Saturn’s rings from aggregation and fragmentation

    PubMed Central

    Brilliantov, Nikolai; Krapivsky, P. L.; Bodrova, Anna; Spahn, Frank; Hayakawa, Hisao; Stadnichuk, Vladimir; Schmidt, Jürgen

    2015-01-01

    Saturn’s rings consist of a huge number of water ice particles, with a tiny addition of rocky material. They form a flat disk, as the result of an interplay of angular momentum conservation and the steady loss of energy in dissipative interparticle collisions. For particles in the size range from a few centimeters to a few meters, a power-law distribution of radii, ∼r−q with q≈3, has been inferred; for larger sizes, the distribution has a steep cutoff. It has been suggested that this size distribution may arise from a balance between aggregation and fragmentation of ring particles, yet neither the power-law dependence nor the upper size cutoff have been established on theoretical grounds. Here we propose a model for the particle size distribution that quantitatively explains the observations. In accordance with data, our model predicts the exponent q to be constrained to the interval 2.75≤q≤3.5. Also an exponential cutoff for larger particle sizes establishes naturally with the cutoff radius being set by the relative frequency of aggregating and disruptive collisions. This cutoff is much smaller than the typical scale of microstructures seen in Saturn’s rings. PMID:26183228

  20. Fast Airborne Size Distribution Measurements of an Aerosol Processes and Aging

    NASA Astrophysics Data System (ADS)

    Kapustin, V.; Clarke, A. D.; Zhou, J.; Brekhovskikh, V.; McNaughton, C. S.; Howell, S.

    2009-12-01

    During MILAGRO/INTEX experiment the Hawaii Group for Environmental Aerosol Research (HIGEAR) deployed a wide range of aerosol instrumentation aboard NSF C-130 and NASA DC-8. These were designed to provide rapid information on aerosol composition, state of mixing (internal or external), spectral optical properties (scattering and absorption), the humidity dependence of light scattering - f(RH), and the role of condensed species in changing the absorption properties of black carbon (BC) and inferred properties of organic carbon (OC). We also flew the Fast Mobility Particle Spectrometer (FMPS, TSI Inc.) to measure aerosol size distributions in a range 5.6 - 560 nm. For all our flights around Mexico City, an aerosol number concentration usually was well above the nominal FMPS sensitivity (from ~100 particles/cc @ Dp = 5.6 nm to 1 part/cc @ 560nm), providing us with reliable size distributions even at 1 sec resolution. FMPS measurements revealed small scale structure of an aerosol and allowed us to examine size distributions varying over space and time associated with mixing processes previously unresolved. These 1-Hz measurements during aircraft profiles captured variations in size distributions within shallow layers. Other dynamic processes observed included orography induced aerosol layers and evolution of the nanoparticles formed by nucleation. We put FMPS high resolution size distribution data in a context of aerosol evolution and aging, using a range of established (for MIRAGE/INTEX) chemical, aerosol and transport aging parameters.

  1. Size-dependent standard deviation for growth rates: empirical results and theoretical modeling.

    PubMed

    Podobnik, Boris; Horvatic, Davor; Pammolli, Fabio; Wang, Fengzhong; Stanley, H Eugene; Grosse, I

    2008-05-01

    We study annual logarithmic growth rates R of various economic variables such as exports, imports, and foreign debt. For each of these variables we find that the distributions of R can be approximated by double exponential (Laplace) distributions in the central parts and power-law distributions in the tails. For each of these variables we further find a power-law dependence of the standard deviation sigma(R) on the average size of the economic variable with a scaling exponent surprisingly close to that found for the gross domestic product (GDP) [Phys. Rev. Lett. 81, 3275 (1998)]. By analyzing annual logarithmic growth rates R of wages of 161 different occupations, we find a power-law dependence of the standard deviation sigma(R) on the average value of the wages with a scaling exponent beta approximately 0.14 close to those found for the growth of exports, imports, debt, and the growth of the GDP. In contrast to these findings, we observe for payroll data collected from 50 states of the USA that the standard deviation sigma(R) of the annual logarithmic growth rate R increases monotonically with the average value of payroll. However, also in this case we observe a power-law dependence of sigma(R) on the average payroll with a scaling exponent beta approximately -0.08 . Based on these observations we propose a stochastic process for multiple cross-correlated variables where for each variable (i) the distribution of logarithmic growth rates decays exponentially in the central part, (ii) the distribution of the logarithmic growth rate decays algebraically in the far tails, and (iii) the standard deviation of the logarithmic growth rate depends algebraically on the average size of the stochastic variable. PMID:18643131

  2. Size-dependent standard deviation for growth rates: Empirical results and theoretical modeling

    NASA Astrophysics Data System (ADS)

    Podobnik, Boris; Horvatic, Davor; Pammolli, Fabio; Wang, Fengzhong; Stanley, H. Eugene; Grosse, I.

    2008-05-01

    We study annual logarithmic growth rates R of various economic variables such as exports, imports, and foreign debt. For each of these variables we find that the distributions of R can be approximated by double exponential (Laplace) distributions in the central parts and power-law distributions in the tails. For each of these variables we further find a power-law dependence of the standard deviation σ(R) on the average size of the economic variable with a scaling exponent surprisingly close to that found for the gross domestic product (GDP) [Phys. Rev. Lett. 81, 3275 (1998)]. By analyzing annual logarithmic growth rates R of wages of 161 different occupations, we find a power-law dependence of the standard deviation σ(R) on the average value of the wages with a scaling exponent β≈0.14 close to those found for the growth of exports, imports, debt, and the growth of the GDP. In contrast to these findings, we observe for payroll data collected from 50 states of the USA that the standard deviation σ(R) of the annual logarithmic growth rate R increases monotonically with the average value of payroll. However, also in this case we observe a power-law dependence of σ(R) on the average payroll with a scaling exponent β≈-0.08 . Based on these observations we propose a stochastic process for multiple cross-correlated variables where for each variable (i) the distribution of logarithmic growth rates decays exponentially in the central part, (ii) the distribution of the logarithmic growth rate decays algebraically in the far tails, and (iii) the standard deviation of the logarithmic growth rate depends algebraically on the average size of the stochastic variable.

  3. Size distribution of luteal cells during pseudopregnancy in domestic cats.

    PubMed

    Arikan, S; Yigit, A A; Kalender, H

    2009-10-01

    Experiments were designed to investigate the size distribution of queen steroidogenic luteal cells throughout pseudopregnancy. Corpora lutea were obtained from the queens following ovariohysterectomy on days 7, 15 or 25 of pseudopregnancy. Luteal cells were isolated from the ovary by collagenase digestion. Steriodogenic cells were identified by staining of cells for 3beta-HSD activity. Cell diameters were measured using a microscope. Luteal cells having steroidogenic capacity covered a wide spectrum of sizes ranging from 3 to 35 mum in diameter. There was a significant increase in mean cell diameters (p < 0.01) as pseudopregnancy progressed. Mean diameter of 3beta-HSD positive cells increased from 10.41 +/- 0.7 microm, on day 7 of pseudopregnancy, to 19.72 +/- 1.3 microm on day 25 of pseudopregnancy. The ratio of large (>20 microm in diameter) to small (3-20 microm in diameter) luteal cells was 0.08 : 1.0 on day 7 of pseudopregnancy, with the 7.5-10 microm cell size class predominant. By day 25 of pseudopregnancy, the ratio of large-to-small cells was increased to 0.87 : 1.0, and 20-25 microm cell sizes become predominant. In conclusion, this study has demonstrated that the cells of the corpus luteum undergo continuous differentiation during pseudopregnancy in queen. This study also demonstrates that luteal cells dissociated from pseudopregnant queen can be used as a model to study the physiology of corpus luteum in pregnant cats.

  4. Ultrasonically controlled particle size distribution of explosives: a safe method.

    PubMed

    Patil, Mohan Narayan; Gore, G M; Pandit, Aniruddha B

    2008-03-01

    Size reduction of the high energy materials (HEM's) by conventional methods (mechanical means) is not safe as they are very sensitive to friction and impact. Modified crystallization techniques can be used for the same purpose. The solute is dissolved in the solvent and crystallized via cooling or is precipitated out using an antisolvent. The various crystallization parameters such as temperature, antisolvent addition rate and agitation are adjusted to get the required final crystal size and morphology. The solvent-antisolvent ratio, time of crystallization and yield of the product are the key factors for controlling antisolvent based precipitation process. The advantages of cavitationally induced nucleation can be coupled with the conventional crystallization process. This study includes the effect of the ultrasonically generated acoustic cavitation phenomenon on the solvent antisolvent based precipitation process. CL20, a high-energy explosive compound, is a polyazapolycyclic caged polynitramine. CL-20 has greater energy output than existing (in-use) energetic ingredients while having an acceptable level of insensitivity to shock and other external stimuli. The size control and size distribution manipulation of the high energy material (CL20) has been successfully carried out safely and quickly along with an increase in the final mass yield, compared to the conventional antisolvent based precipitation process. PMID:17532248

  5. 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.

  6. Method for measuring the size distribution of airborne rhinovirus

    SciTech Connect

    Russell, M.L.; Goth-Goldstein, R.; Apte, M.G.; Fisk, W.J.

    2002-01-01

    About 50% of viral-induced respiratory illnesses are caused by the human rhinovirus (HRV). Measurements of the concentrations and sizes of bioaerosols are critical for research on building characteristics, aerosol transport, and mitigation measures. We developed a quantitative reverse transcription-coupled polymerase chain reaction (RT-PCR) assay for HRV and verified that this assay detects HRV in nasal lavage samples. A quantitation standard was used to determine a detection limit of 5 fg of HRV RNA with a linear range over 1000-fold. To measure the size distribution of HRV aerosols, volunteers with a head cold spent two hours in a ventilated research chamber. Airborne particles from the chamber were collected using an Andersen Six-Stage Cascade Impactor. Each stage of the impactor was analyzed by quantitative RT-PCR for HRV. For the first two volunteers with confirmed HRV infection, but with mild symptoms, we were unable to detect HRV on any stage of the impactor.

  7. Measurement of non-volatile particle number size distribution

    NASA Astrophysics Data System (ADS)

    Gkatzelis, G. I.; Papanastasiou, D. K.; Florou, K.; Kaltsonoudis, C.; Louvaris, E.; Pandis, S. N.

    2015-06-01

    An experimental methodology was developed to measure the non-volatile particle number concentration using a thermodenuder (TD). The TD was coupled with a high-resolution time-of-flight aerosol mass spectrometer, measuring the chemical composition and mass size distribution of the submicrometer aerosol and a scanning mobility particle sizer (SMPS) that provided the number size distribution of the aerosol in the range from 10 to 500 nm. The method was evaluated with a set of smog chamber experiments and achieved almost complete evaporation (> 98 %) of secondary organic as well as freshly nucleated particles, using a TD temperature of 400 °C and a centerline residence time of 15 s. This experimental approach was applied in a winter field campaign in Athens and provided a direct measurement of number concentration and size distribution for particles emitted from major pollution sources. During periods in which the contribution of biomass burning sources was dominant, more than 80 % of particle number concentration remained after passing through the thermodenuder, suggesting that nearly all biomass burning particles had a non-volatile core. These remaining particles consisted mostly of black carbon (60 % mass contribution) and organic aerosol, OA (40 %). Organics that had not evaporated through the TD were mostly biomass burning OA (BBOA) and oxygenated OA (OOA) as determined from AMS source apportionment analysis. For periods during which traffic contribution was dominant 50-60 % of the particles had a non-volatile core while the rest evaporated at 400 °C. The remaining particle mass consisted mostly of black carbon (BC) with an 80 % contribution, while OA was responsible for another 15-20 %. Organics were mostly hydrocarbon-like OA (HOA) and OOA. These results suggest that even at 400 °C some fraction of the OA does not evaporate from particles emitted from common combustion processes, such as biomass burning and car engines, indicating that a fraction of this type

  8. Decomposition of biospeckle signals through granulometric size distribution.

    PubMed

    Blotta, Eduardo; Ballarin, Virginia; Rabal, Hector

    2009-04-15

    We present a method for the analysis of dynamic speckle signals based on morphological granulometry. We obtain selected information differentiating the morphological patterns of the temporal history of each pixel through the granulometric size distribution. The method is exemplified by detecting bruised regions on apples and studying the germination of corn seeds. Different levels of activity are observed in the bruised and healthy areas of the apple, within a certain range of the morphological spectrum. Likewise, the activity of the corn seed embryo can also be distinguished from the endosperm area. PMID:19370117

  9. Connecting Aerosol Size Distributions at Three Arctic Stations

    NASA Astrophysics Data System (ADS)

    Freud, E.; Krejci, R.; Tunved, P.; Barrie, L. A.

    2015-12-01

    Aerosols play an important role in Earth's energy balance mainly through interactions with solar radiation and cloud processes. There is a distinct annual cycle of arctic aerosols, with greatest mass concentrations in the spring and lowest in summer due to effective wet removal processes - allowing for new particles formation events to take place. Little is known about the spatial extent of these events as no previous studies have directly compared and linked aerosol measurements from different arctic stations during the same times. Although the arctic stations are hardly affected by local pollution, it is normally assumed that their aerosol measurements are indicative of a rather large area. It is, however, not clear if that assumption holds all the time, and how large may that area be. In this study, three different datasets of aerosol size distributions from Mt. Zeppelin in Svalbard, Station Nord in northern Greenland and Alert in the Canadian arctic, are analyzed for the measurement period of 2012-2013. All stations are 500 to 1000 km from each other, and the travel time from one station to the other is typically between 2 to 5 days. The meteorological parameters along the calculated trajectories are analyzed in order to estimate their role in the modification of the aerosol size distribution while the air is traveling from one field station to another. In addition, the exposure of the sampled air to open waters vs. frozen sea is assessed, due to the different fluxes of heat, moisture, gases and particles, that are expected to affect the aerosol size distribution. The results show that the general characteristics of the aerosol size distributions and their annual variation are not very different in all three stations, with Alert and Station Nord being more similar. This is more pronounced when looking into the cases for which the trajectory calculations indicated that the air traveled from one of the latter stations to the other. The probable causes for the

  10. Saharan Dust Particle Size And Concentration Distribution In Central Ghana

    NASA Astrophysics Data System (ADS)

    Sunnu, A. K.

    2010-12-01

    A.K. Sunnu*, G. M. Afeti* and F. Resch+ *Department of Mechanical Engineering, Kwame Nkrumah University of Science and Technology (KNUST) Kumasi, Ghana. E-mail: albertsunnu@yahoo.com +Laboratoire Lepi, ISITV-Université du Sud Toulon-Var, 83162 La Valette cedex, France E-mail: resch@univ-tln.fr Keywords: Atmospheric aerosol; Saharan dust; Particle size distributions; Particle concentrations. Abstract The Saharan dust that is transported and deposited over many countries in the West African atmospheric environment (5°N), every year, during the months of November to March, known locally as the Harmattan season, have been studied over a 13-year period, between 1996 and 2009, using a location at Kumasi in central Ghana (6° 40'N, 1° 34'W) as the reference geographical point. The suspended Saharan dust particles were sampled by an optical particle counter, and the particle size distributions and concentrations were analysed. The counter gives the total dust loads as number of particles per unit volume of air. The optical particle counter used did not discriminate the smoke fractions (due to spontaneous bush fires during the dry season) from the Saharan dust. Within the particle size range measured (0.5 μm-25 μm.), the average inter-annual mean particle diameter, number and mass concentrations during the northern winter months of January and February were determined. The average daily number concentrations ranged from 15 particles/cm3 to 63 particles/cm3 with an average of 31 particles/cm3. The average daily mass concentrations ranged from 122 μg/m3 to 1344 μg/m3 with an average of 532 μg/m3. The measured particle concentrations outside the winter period were consistently less than 10 cm-3. The overall dust mean particle diameter, analyzed from the peak representative Harmattan periods over the 13-year period, ranged from 0.89 μm to 2.43 μm with an average of 1.5 μm ± 0.5. The particle size distributions exhibited the typical distribution pattern for

  11. 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.

  12. Mass size distributions of elemental aerosols in industrial area

    PubMed Central

    Moustafa, Mona; Mohamed, Amer; Ahmed, Abdel-Rahman; Nazmy, Hyam

    2014-01-01

    Outdoor aerosol particles were characterized in industrial area of Samalut city (El-minia/Egypt) using low pressure Berner cascade impactor as an aerosol sampler. The impactor operates at 1.7 m3/h flow rate. Seven elements were investigated including Ca, Ba, Fe, K, Cu, Mn and Pb using atomic absorption technique. The mean mass concentrations of the elements ranged from 0.42 ng/m3 (for Ba) to 89.62 ng/m3 (for Fe). The mass size distributions of the investigated elements were bi-modal log normal distribution corresponding to the accumulation and coarse modes. The enrichment factors of elements indicate that Ca, Ba, Fe, K, Cu and Mn are mainly emitted into the atmosphere from soil sources while Pb is mostly due to anthropogenic sources. PMID:26644919

  13. Size dependence of yield strength simulated by a dislocation-density function dynamics approach

    NASA Astrophysics Data System (ADS)

    Leung, P. S. S.; Leung, H. S.; Cheng, B.; Ngan, A. H. W.

    2015-04-01

    The size dependence of the strength of nano- and micron-sized crystals is studied using a new simulation approach in which the dynamics of the density functions of dislocations are modeled. Since any quantity of dislocations can be represented by a density, this approach can handle large systems containing large quantities of dislocations, which may handicap discrete dislocation dynamics schemes due to the excessive computation time involved. For this reason, pillar sizes spanning a large range, from the sub-micron to micron regimes, can be simulated. The simulation results reveal the power-law relationship between strength and specimen size up to a certain size, beyond which the strength varies much more slowly with size. For specimens smaller than ∼4000b, their strength is found to be controlled by the dislocation depletion condition, in which the total dislocation density remains almost constant throughout the loading process. In specimens larger than ∼4000b, the initial dislocation distribution is of critical importance since the presence of dislocation entanglements is found to obstruct deformation in the neighboring regions within a distance of ∼2000b. This length scale suggests that the effects of dense dislocation clusters are greater in intermediate-sized specimens (e.g. 4000b and 8000b) than in larger specimens (e.g. 16 000b), according to the weakest-link concept.

  14. Probe measurements and numerical model predictions of evolving size distributions in premixed flames

    SciTech Connect

    De Filippo, A.; Sgro, L.A.; Lanzuolo, G.; D'Alessio, A.

    2009-09-15

    Particle size distributions (PSDs), measured with a dilution probe and a Differential Mobility Analyzer (DMA), and numerical predictions of these PSDs, based on a model that includes only coagulation or alternatively inception and coagulation, are compared to investigate particle growth processes and possible sampling artifacts in the post-flame region of a C/O = 0.65 premixed laminar ethylene-air flame. Inputs to the numerical model are the PSD measured early in the flame (the initial condition for the aerosol population) and the temperature profile measured along the flame's axial centerline. The measured PSDs are initially unimodal, with a modal mobility diameter of 2.2 nm, and become bimodal later in the post-flame region. The smaller mode is best predicted with a size-dependent coagulation model, which allows some fraction of the smallest particles to escape collisions without resulting in coalescence or coagulation through the size-dependent coagulation efficiency ({gamma}{sub SD}). Instead, when {gamma} = 1 and the coagulation rate is equal to the collision rate for all particles regardless of their size, the coagulation model significantly under predicts the number concentration of both modes and over predicts the size of the largest particles in the distribution compared to the measured size distributions at various heights above the burner. The coagulation ({gamma}{sub SD}) model alone is unable to reproduce well the larger particle mode (mode II). Combining persistent nucleation with size-dependent coagulation brings the predicted PSDs to within experimental error of the measurements, which seems to suggest that surface growth processes are relatively insignificant in these flames. Shifting measured PSDs a few mm closer to the burner surface, generally adopted to correct for probe perturbations, does not produce a better matching between the experimental and the numerical results. (author)

  15. Debiased Orbital and Size Distributions of the NEOs

    NASA Astrophysics Data System (ADS)

    Bottke, W. F.; Morbidelli, A.; Jedicke, R.; Petit, J. M.; Levison, H. F.

    2001-11-01

    The orbital and absolute magnitude distribution of the Near-Earth Objects (NEOs) is difficult to compute, partly because known NEOs are biased by complicated observational selection effects but also because only a modest fraction of the entire NEO population has been discovered so far. To circumvent these problems, we created a model NEO population which was fit to known NEOs discovered or accidentally rediscovered by Spacewatch. Our method was to numerically integrate thousands of test bodies from four ``intermediate sources'': three in or adjacent to the main asteroid belt (Bottke et al. 2000, Science 288, 2190.) and one in the Kuiper belt (Levison and Duncan 1997, Icarus 127, 13). The test bodies which passed into the NEO region were tracked until they were eliminated. Next, we calculated the observational biases and assumed a functional form for the absolute magnitude (H) distribution associated with objects on those orbits. By merging the observational biases with our NEO dynamical ``roadmaps'' and an observed NEO H distribution, we produced a probability distribution which was fit to the biased NEO population. By testing a range of possible source combinations, a ``best-fit'' distribution was then deconvolved to provide the debiased orbital and H distributions for the NEO population as well as the relative importance of each NEO replenishment source. Our best-fit model predicts there are ~ 1010 H < 18 NEOs out to T > 2 (i.e., a < ~ 7.4 AU), with ~ 55% coming from the inner main belt (a < 2.5 AU), ~ 30% from the central main belt (2.5 < a < 2.8 AU), and ~ 15% from the Jupiter-family comet region. These results suggest that roughly 40% of the H < 18 NEOs have been found. The Amor, Apollo, and Aten populations contain 30%, 64%, and 6% of the H < 22 NEO population, respectively. The population of objects inside Earth's orbit (IEOs) are about 2% the size of the NEO population. Active and extinct comets make up a third of the entire km-sized NEO population with T

  16. The Distribution and Evolution of Lyman- Alpha Forest Cloud Sizes

    NASA Astrophysics Data System (ADS)

    Foltz, Craig

    1997-07-01

    Our ongoing program to measure the sizes of Ly-alpha forest clouds by looking for common absorption in close pairs of quasars using FOS UV spectroscopy {GO Programs 5320 and 6100} has yielded dramatic and unexpected results: {1} Observations of the pair Q0107-025A, B {z_em eq 0.95} give a firm and model-independent lower limit on the transverse size of the absorbers of more than 300 kpc and suggest a characteristic radius of the clouds of 600 , h^-1 kpc {h = 100 kms Mpc^-1; q_0 = 0.5} at 0.5 <= z <= 0.9. {2} Similar observations of the higher redshift pair LB 9605 {z_ em = 1.834} and LB 9612 {z_ em = 1.898} imply a characteristic radius of about half that inferred at lower redshift. Together with ground-based observations, these results imply an evolution of cloud radii with redshift, with the characteristic size of the Ly-alpha absorbers decreasing with increasing redshift. {3} Evidence is also found for a possible dependence of cloud radii on column density, with the high column density clouds being larger in extent than the lower column density clouds. Additional observations of these quasars, as well as a third quasar LBQS 0107-0232 within 3' of Q0107-025A, B, will establish whether the correlation with column density is real, further constrain the size of the clouds at two different redshift ranges, and probe cloud sizes on scales up to 1 Mpc.

  17. The Distribution and Evolution of Lyman- Alpha Forest Cloud Sizes

    NASA Astrophysics Data System (ADS)

    Foltz, Craig

    1996-07-01

    Our ongoing program to measure the sizes of Ly-alpha forest clouds by looking for common absorption in close pairs of quasars using FOS UV spectroscopy {GO Programs 5320 and 6100} has yielded dramatic and unexpected results: {1} Observations of the pair Q0107-025A,B {z_em eq 0.95} give a firm and model-independent lower limit on the transverse size of the absorbers of more than 300 kpc and suggest a characteristic radius of the clouds of 600 ,h^-1 kpc {h = 100 kms Mpc^-1; q_0 = 0.5} at 0.5 <= z <= 0.9. {2} Similar observations of the higher redshift pair LB 9605 {z_ em = 1.834} and LB 9612 {z_ em = 1.898} imply a characteristic radius of about half that inferred at lower redshift. Together with ground-based observations, these results imply an evolution of cloud radii with redshift, with the characteristic size of the Ly-alpha absorbers decreasing with increasing redshift. {3} Evidence is also found for a possible dependence of cloud radii on column density, with the high column density clouds being larger in extent than the lower column density clouds. Additional observations of these quasars, as well as a third quasar LBQS 0107-0232 within 3' of Q0107-025A,B, will establish whether the correlation with column density is real, further constrain the size of the clouds at two different redshift ranges, and probe cloud sizes on scales up to 1 Mpc.

  18. 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.

  19. Light scattering by lunar-like particle size distributions

    NASA Technical Reports Server (NTRS)

    Goguen, Jay D.

    1991-01-01

    A fundamental input to models of light scattering from planetary regoliths is the mean phase function of the regolith particles. Using the known size distribution for typical lunar soils, the mean phase function and mean linear polarization for a regolith volume element of spherical particles of any composition were calculated from Mie theory. The two contour plots given here summarize the changes in the mean phase function and linear polarization with changes in the real part of the complex index of refraction, n - ik, for k equals 0.01, the visible wavelength 0.55 micrometers, and the particle size distribution of the typical mature lunar soil 72141. A second figure is a similar index-phase surface, except with k equals 0.1. The index-phase surfaces from this survey are a first order description of scattering by lunar-like regoliths of spherical particles of arbitrary composition. They form the basis of functions that span a large range of parameter-space.

  20. Influence of molecular size on tissue distribution of antibody fragments

    PubMed Central

    Li, Zhe; Krippendorff, Ben-Fillippo; Sharma, Sharad; Walz, Antje C.; Lavé, Thierry; Shah, Dhaval K.

    2016-01-01

    Biodistribution coefficients (BC) allow estimation of the tissue concentrations of proteins based on the plasma pharmacokinetics. We have previously established the BC values for monoclonal antibodies. Here, this concept is extended by development of a relationship between protein size and BC values. The relationship was built by deriving the BC values for various antibody fragments of known molecular weight from published biodistribution studies. We found that there exists a simple exponential relationship between molecular weight and BC values that allows the prediction of tissue distribution of proteins based on molecular weight alone. The relationship was validated by a priori predicting BC values of 4 antibody fragments that were not used in building the relationship. The relationship was also used to derive BC50 values for all the tissues, which is the molecular weight increase that would result in 50% reduction in tissue uptake of a protein. The BC50 values for most tissues were found to be ~35 kDa. An ability to estimate tissue distribution of antibody fragments based on the BC vs. molecular size relationship established here may allow better understanding of the biologics concentrations in tissues responsible for efficacy or toxicity. This relationship can also be applied for rational development of new biotherapeutic modalities with optimal biodistribution properties to target (or avoid) specific tissues. PMID:26496429

  1. 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

  2. PMSE dependence on aerosol charge number density and aerosol size

    NASA Astrophysics Data System (ADS)

    Rapp, Markus; Lübken, Franz-Josef; Hoffmann, Peter; Latteck, Ralph; Baumgarten, Gerd; Blix, Tom A.

    2003-04-01

    It is commonly accepted that the existence of polar mesosphere summer echoes (PMSEs) depends on the presence of charged aerosols since these are comparatively heavy and reduce the diffusion of free electrons due to ambipolar forces. Simple microphysical modeling suggests that this diffusivity reduction is proportional to rA2 (rA = aerosol radius) but only if a significant amount of charges is bound on the aerosols such that NA∣ZA∣/ne > 1.2 (NA = number of aerosols, ZA = aerosol charge, ne = number of free electrons). The fact that the background electron profile frequently shows large depletions ("biteouts") at PMSE altitudes is taken as a support for this idea since within biteouts a major fraction of free electrons is missing, i.e., bound on aerosols. In this paper, we show from in situ measurements of electron densities and from radar and lidar observations that PMSEs can also exist in regions where only a minor fraction of free electrons is bound on aerosols, i.e., with no biteout and with NA∣ZA∣/ne ≪ 1. We show strong experimental evidence that it is instead the product NA∣ZA∣rA2 that is crucial for the existence of PMSEs. For example, small aerosol charge can be compensated by large aerosol radius. We show that this product replicates the main features of PMSEs, in particular the mean altitude distribution and the altitude of PMSEs in the presence of noctilucent clouds (NLCs). We therefore take this product as a "proxy" for PMSE. The agreement between this proxy and the main characteristics of PMSEs implies that simple microphysical models do not satisfactorily describe PMSE physics and need to be improved. The proxy can easily be used in models of the upper atmosphere to better understand seasonal and geographical variations of PMSEs, for example, the long debated difference between Northern and Southern hemisphere PMSEs.

  3. A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials.

    PubMed

    Félix, V; Jannot, Y; Degiovanni, A

    2012-05-01

    Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10(-1) to 10(5) Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent. PMID:22667640

  4. A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials

    NASA Astrophysics Data System (ADS)

    Félix, V.; Jannot, Y.; Degiovanni, A.

    2012-05-01

    Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10-1 to 105 Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent.

  5. A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials

    SciTech Connect

    Felix, V.; Jannot, Y.; Degiovanni, A.

    2012-05-15

    Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10{sup -1} to 10{sup 5} Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent.

  6. Algorithm-dependent fault tolerance for distributed computing

    SciTech Connect

    P. D. Hough; M. e. Goldsby; E. J. Walsh

    2000-02-01

    Large-scale distributed systems assembled from commodity parts, like CPlant, have become common tools in the distributed computing world. Because of their size and diversity of parts, these systems are prone to failures. Applications that are being run on these systems have not been equipped to efficiently deal with failures, nor is there vendor support for fault tolerance. Thus, when a failure occurs, the application crashes. While most programmers make use of checkpoints to allow for restarting of their applications, this is cumbersome and incurs substantial overhead. In many cases, there are more efficient and more elegant ways in which to address failures. The goal of this project is to develop a software architecture for the detection of and recovery from faults in a cluster computing environment. The detection phase relies on the latest techniques developed in the fault tolerance community. Recovery is being addressed in an application-dependent manner, thus allowing the programmer to take advantage of algorithmic characteristics to reduce the overhead of fault tolerance. This architecture will allow large-scale applications to be more robust in high-performance computing environments that are comprised of clusters of commodity computers such as CPlant and SMP clusters.

  7. Throughfall Drop Size Distribution in relation to Leaf Canopy State

    NASA Astrophysics Data System (ADS)

    Hudson, S.; Nanko, K.; Levia, D. F., Jr.

    2014-12-01

    The partitioning of incident precipitation by a forest canopy into throughfall and stemflow varies as a function of meteorological conditions, tree species, leaf morphology and surface roughness. Little work quantified the throughfall drop size signature of precipitation events relative to changes in leaf canopy state of deciduous forests. This is the first study to compare throughfall drop size distributions in the presence and absence of foliage. To quantify individual throughfall drops, a laser disdrometer gauge was deployed below an observed drip point under a Liriodendron tulipifera L. (yellow poplar) tree, in northeastern Maryland, USA. More than 750,000 individual throughfall droplets have been counted and measured from precipitation events generating more than 5 mm gross rainfall over a period of 12 months. Throughfall during leafless events had significantly larger maximum drop diameters (6.74mm leafless, 5.55mm leafed) and median volume diameter of drops (5.44mm leafless, 3.31mm leafed) than throughfall generated when leaves were present. Statistical techniques have demonstrated the substantial influence of canopy state over the drop size spectra. Principal component analysis and factor analysis both resulted in canopy state loading positively with increases in maximum drop diameter while loading negatively with air temperature. Boosted regression trees analysis corroborated these findings. Our findings correspond with the physical conditions of a leafless canopy, and illustrated the greater extent of surface adhesion of intercepted water films on woody surfaces as opposed to foliar surfaces, thereby underscoring the importance of canopy state on throughfall inputs.

  8. Bubble size distribution in acoustic droplet vaporization via dissolution using an ultrasound wide-beam method.

    PubMed

    Xu, Shanshan; Zong, Yujin; Li, Wusong; Zhang, Siyuan; Wan, Mingxi

    2014-05-01

    Performance and efficiency of numerous cavitation enhanced applications in a wide range of areas depend on the cavitation bubble size distribution. Therefore, cavitation bubble size estimation would be beneficial for biological and industrial applications that rely on cavitation. In this study, an acoustic method using a wide beam with low pressure is proposed to acquire the time intensity curve of the dissolution process for the cavitation bubble population and then determine the bubble size distribution. Dissolution of the cavitation bubbles in saline and in phase-shift nanodroplet emulsion diluted with undegassed or degassed saline was obtained to quantify the effects of pulse duration (PD) and acoustic power (AP) or peak negative pressure (PNP) of focused ultrasound on the size distribution of induced cavitation bubbles. It was found that an increase of PD will induce large bubbles while AP had only a little effect on the mean bubble size in saline. It was also recognized that longer PD and higher PNP increases the proportions of large and small bubbles, respectively, in suspensions of phase-shift nanodroplet emulsions. Moreover, degassing of the suspension tended to bring about smaller mean bubble size than the undegassed suspension. In addition, condensation of cavitation bubble produced in diluted suspension of phase-shift nanodroplet emulsion was involved in the calculation to discuss the effect of bubble condensation in the bubble size estimation in acoustic droplet vaporization. It was shown that calculation without considering the condensation might underestimate the mean bubble size and the calculation with considering the condensation might have more influence over the size distribution of small bubbles, but less effect on that of large bubbles. Without or with considering bubble condensation, the accessible minimum bubble radius was 0.4 or 1.7 μm and the step size was 0.3 μm. This acoustic technique provides an approach to estimate the size

  9. The Fossilized Size Distribution of the Main Asteroid Belt

    NASA Astrophysics Data System (ADS)

    Bottke, W. F.; Durda, D.; Nesvorny, D.; Jedicke, R.; Morbidelli, A.

    2004-05-01

    The main asteroid belt evolved into its current state via two processes: dynamical depletion and collisional evolution. During the planet formation epoch, the primordial main belt (PMB) contained several Earth masses of material, enough to allow the asteroids to accrete on relatively short timescales (e.g., Weidenschilling 1977). The present-day main belt, however, only contains 5e-4 Earth masses of material (Petit et al. 2002). To explain this mass loss, we suggest the PMB evolved in the following manner: Planetesimals and planetary embryos accreted (and differentiated) in the PMB during the first few Myr of the solar system. Gravitational perturbations from these embryos dynamically stirred the main belt, enough to initiate fragmentation. When Jupiter reached its full size, some 10 Myr after the solar system's birth, its perturbations, together with those of the embryos, dynamically depleted the main belt region of > 99% of its bodies. Much of this material was sent to high (e,i) orbits, where it continued to pummel the surviving main belt bodies at high impact velocities for more than 100 Myr. While some differentiated bodies in the PMB were disrupted, most were instead scattered; only small fragments from this population remain. This period of comminution and dynamical evolution in the PMB created, among other things, the main belt's wavy size-frequency distribution, such that it can be considered a "fossil" from this violent early epoch. From this time forward, however, relatively little collisional evolution has taken place in the main belt, consistent with the surprising paucity of prominent asteroid families. We will show that the constraints provided by asteroid families and the shape of the main belt size distribution are essential to obtaining a unique solution from our model's initial conditions. We also use our model results to solve for the asteroid disruption scaling law Q*D, a critical function needed in all planet formation codes that include

  10. 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.

  11. Particulate matter neurotoxicity in culture is size-dependent

    EPA Science Inventory

    Exposure to particulate matter (PM) air pollution produces inflammatory damage to the cardiopulmonary system. This toxicity appears to be inversely related to the size of the PM particles, with the ultrafine particle being more inflammatory than larger sizes. Exposure to PM has m...

  12. Size distribution analysis of influenza virus particles using size exclusion chromatography.

    PubMed

    Vajda, Judith; Weber, Dennis; Brekel, Dominik; Hundt, Boris; Müller, Egbert

    2016-09-23

    Size exclusion chromatography is a standard method in quality control of biopharmaceutical proteins. In contrast, vaccine analysis is often based on activity assays. The hemagglutination assay is a widely accepted influenza quantification method, providing no insight in the size distribution of virus particles. Capabilities of size exclusion chromatography to complement the hemagglutination assay are investigated. The presented method is comparatively robust regarding different buffer systems, ionic strength and additive concentrations. Addition of 200mM arginine or sodium chloride is necessary to obtain complete virus particle recovery. 0.5 and 1.0M arginine increase the hydrodynamic radius of the whole virus particles by 5nm. Sodium citrate induces virus particle aggregation. Results are confirmed by dynamic light scattering. Retention of a H1N1v strain correlates with DNA contents between 5ng/mL and 670ng/mL. Quantitative elution of the virus preparations is verified on basis of hemagglutination activity. Elution of hemagglutination inducing compounds starts at a flow channel diameter of 7000nm. The universal applicability is demonstrated with three different influenza virus samples, including an industrially produced, pandemic vaccine strain. Size distribution of the pandemic H1N1v 5258, H1N1 PR/8/34, and H3N2 Aichi/2/68 preparations spreads across inter- and intra-particle volume and extends to the secondary interaction dominated range. Thus, virus particle debris seems to induce hemagglutination. Fragments generated by 0.5% Triton™ X-100 treatment increase overall hemagglutination activity. PMID:27578410

  13. Estimating the 3D pore size distribution of biopolymer networks from directionally biased data.

    PubMed

    Lang, Nadine R; Münster, Stefan; Metzner, Claus; Krauss, Patrick; Schürmann, Sebastian; Lange, Janina; Aifantis, Katerina E; Friedrich, Oliver; Fabry, Ben

    2013-11-01

    The pore size of biopolymer networks governs their mechanical properties and strongly impacts the behavior of embedded cells. Confocal reflection microscopy and second harmonic generation microscopy are widely used to image biopolymer networks; however, both techniques fail to resolve vertically oriented fibers. Here, we describe how such directionally biased data can be used to estimate the network pore size. We first determine the distribution of distances from random points in the fluid phase to the nearest fiber. This distribution follows a Rayleigh distribution, regardless of isotropy and data bias, and is fully described by a single parameter--the characteristic pore size of the network. The bias of the pore size estimate due to the missing fibers can be corrected by multiplication with the square root of the visible network fraction. We experimentally verify the validity of this approach by comparing our estimates with data obtained using confocal fluorescence microscopy, which represents the full structure of the network. As an important application, we investigate the pore size dependence of collagen and fibrin networks on protein concentration. We find that the pore size decreases with the square root of the concentration, consistent with a total fiber length that scales linearly with concentration. PMID:24209841

  14. A prognostic model of the sea ice floe size and thickness distribution

    NASA Astrophysics Data System (ADS)

    Horvat, C.; Tziperman, E.

    2015-05-01

    Sea ice exhibits considerable seasonal and longer-term variations in extent, concentration, thickness and age, and is characterized by a complex and continuously changing distribution of floe sizes and thicknesses. Models of sea ice used in current climate models keep track of its concentration and of the distribution of ice thicknesses, but do not account for the floe size distribution and its potential effects on air-sea exchange and sea-ice evolution. Accurately capturing sea-ice variability in climate models may require a better understanding and representation of the distribution of floe sizes and thicknesses. We develop and demonstrate a model for the evolution of the joint sea-ice floe size and thickness distribution that depends on atmospheric and oceanic forcing fields. The model accounts for effects due to multiple processes that are active in the marginal and seasonal ice zones: freezing and melting along the lateral side and base of floes, mechanical interactions due to floe collisions (ridging and rafting) and sea-ice fracture due to swell propagation into the ice pack. The model is then examined and demonstrated in a series of idealized test cases.

  15. Size Distribution of Possible Dust Carriers for the Extended Red Emission

    NASA Astrophysics Data System (ADS)

    Mahapatra, D. P.; Chutjian, A.; Machacek, J. R.; Mangina, R. S.

    2014-08-01

    Power-law size distributions expected to be applicable to possible carriers of extended red emission (ERE) have been examined using Monte Carlo (MC) simulations. Si nanoparticles and some polycyclic aromatic hydrocarbon complexes such as oligoacene and oligorylenes with energy gaps close to 2 eV have been considered. In the simplest case of unit quantum efficiency, the MC-generated size distributions are used to obtain photoluminescence (PL) spectra that are then corrected for dust extinction and reddening effects for comparison with observed ERE spectra. It is shown that a power-law size distribution with a decay exponent of α = 7/2, which closely agrees with starlight extinction data, fails to produce an ERE-like spectrum. However, size distributions with decay exponents of α = 19/12 and 3/2 are found to lead to acceptable spectra. Results indicate that energetic photon-induced breakup and competing aggregation effects dominate collisional effects in producing the observed steady-state mass distribution. It is shown that the peak wavelength of emission critically depends on the band gap, rather than cluster mass, which for oligoacenes and oligorylenes is widely different. The peak wavelength is also shown to be insensitive to dust attenuation.

  16. Size distribution of possible dust carriers for the extended red emission

    SciTech Connect

    Mahapatra, D. P.; Chutjian, A.; Machacek, J. R.; Mangina, R. S.

    2014-08-01

    Power-law size distributions expected to be applicable to possible carriers of extended red emission (ERE) have been examined using Monte Carlo (MC) simulations. Si nanoparticles and some polycyclic aromatic hydrocarbon complexes such as oligoacene and oligorylenes with energy gaps close to 2 eV have been considered. In the simplest case of unit quantum efficiency, the MC-generated size distributions are used to obtain photoluminescence (PL) spectra that are then corrected for dust extinction and reddening effects for comparison with observed ERE spectra. It is shown that a power-law size distribution with a decay exponent of α = 7/2, which closely agrees with starlight extinction data, fails to produce an ERE-like spectrum. However, size distributions with decay exponents of α = 19/12 and 3/2 are found to lead to acceptable spectra. Results indicate that energetic photon-induced breakup and competing aggregation effects dominate collisional effects in producing the observed steady-state mass distribution. It is shown that the peak wavelength of emission critically depends on the band gap, rather than cluster mass, which for oligoacenes and oligorylenes is widely different. The peak wavelength is also shown to be insensitive to dust attenuation.

  17. Asymptotic Distributions of Coalescence Times and Ancestral Lineage Numbers for Populations with Temporally Varying Size

    PubMed Central

    Chen, Hua; Chen, Kun

    2013-01-01

    The distributions of coalescence times and ancestral lineage numbers play an essential role in coalescent modeling and ancestral inference. Both exact distributions of coalescence times and ancestral lineage numbers are expressed as the sum of alternating series, and the terms in the series become numerically intractable for large samples. More computationally attractive are their asymptotic distributions, which were derived in Griffiths (1984) for populations with constant size. In this article, we derive the asymptotic distributions of coalescence times and ancestral lineage numbers for populations with temporally varying size. For a sample of size n, denote by Tm the mth coalescent time, when m + 1 lineages coalesce into m lineages, and An(t) the number of ancestral lineages at time t back from the current generation. Similar to the results in Griffiths (1984), the number of ancestral lineages, An(t), and the coalescence times, Tm, are asymptotically normal, with the mean and variance of these distributions depending on the population size function, N(t). At the very early stage of the coalescent, when t → 0, the number of coalesced lineages n − An(t) follows a Poisson distribution, and as m → n, n(n−1)Tm/2N(0) follows a gamma distribution. We demonstrate the accuracy of the asymptotic approximations by comparing to both exact distributions and coalescent simulations. Several applications of the theoretical results are also shown: deriving statistics related to the properties of gene genealogies, such as the time to the most recent common ancestor (TMRCA) and the total branch length (TBL) of the genealogy, and deriving the allele frequency spectrum for large genealogies. With the advent of genomic-level sequencing data for large samples, the asymptotic distributions are expected to have wide applications in theoretical and methodological development for population genetic inference. PMID:23666939

  18. Break of slope in earthquake size distribution and creep rate along the San Andreas Fault system

    NASA Astrophysics Data System (ADS)

    Vorobieva, Inessa; Shebalin, Peter; Narteau, Clément

    2016-07-01

    Crustal faults accommodate slip either by a succession of earthquakes or continuous slip, and in most instances, both these seismic and aseismic processes coexist. Recorded seismicity and geodetic measurements are therefore two complementary data sets that together document ongoing deformation along active tectonic structures. Here we study the influence of stable sliding on earthquake statistics. We show that creep along the San Andreas Fault is responsible for a break of slope in the earthquake size distribution. This slope increases with an increasing creep rate for larger magnitude ranges, whereas it shows no systematic dependence on creep rate for smaller magnitude ranges. This is interpreted as a deficit of large events under conditions of faster creep where seismic ruptures are less likely to propagate. These results suggest that the earthquake size distribution does not only depend on the level of stress but also on the type of deformation.

  19. Avalanche-size distributions in mean-field plastic yielding models.

    PubMed

    Jagla, E A

    2015-10-01

    We discuss the size distribution N(S) of avalanches occurring at the yielding transition of mean-field (i.e., Hebraud-Lequeux) models of amorphous solids. The size distribution follows a power law dependence of the form N(S)∼S(-τ). However (contrary to what is found in its depinning counterpart), the value of τ depends on details of the dynamic protocol used. For random triggering of avalanches we recover the τ=3/2 exponent typical of mean-field models, which, in particular, is valid for the depinning case. However, for the physically relevant case of external loading through a quasistatic increase of applied strain, a smaller exponent (close to 1) is obtained. This result is rationalized by mapping the problem to an effective random walk in the presence of a moving absorbing boundary. PMID:26565196

  20. Laser damage dependence on the size and concentration of precursor defects in KDP crystals: view through differently sized filter pores.

    PubMed

    Wang, Yueliang; Zhao, Yuanan; Xie, Xiaoyi; Hu, Guohang; Yang, Liujiang; Xu, Ziyuan; Shao, Jianda

    2016-04-01

    We investigate the laser-induced damage performance at 1064 nm of potassium dihydrogen phosphate (KDP) crystals grown using filters of different pore sizes. The aim is to explore a novel method for understanding laser-matter interactions with regard to physical parameters affecting the ability of damage precursors to initiate damage. By reducing the pore size of filters in continuous filtration growth, we can improve laser damage resistance. Furthermore, we develop a model based on a Gaussian distribution of precursor thresholds and heat transfer to obtain a size distribution of the precursor defects. Smaller size and/or lower concentration of precursor defects could lead to better damage resistance. PMID:27192280

  1. Is Foreshock Area Dependent on the Size of the Mainshock?

    NASA Astrophysics Data System (ADS)

    Papadopoulos, G. A.; Minadakis, G.

    2012-12-01

    A global overview of studies about foreshock activity preceding strong mainshocks has indicated the next main patterns: (1) foreshock detection strongly depends on monitoring capabilities but in well monitored areas foreshocks are detected in about 50% of strong, shallow foreshocks; (2) foreshocks occur in the close area of mainshock in a time frame ranging from hours to a few weeks before the mainshock but mainly in about the last ten days; (3) when abundant foreshocks are in place the event rate tends to increase with the inverse of time towards the mainshock; (4) the b parameter of G-R in foreshock sequences usually drops with respect to b parameter in aftershock sequences or in the background seismicity in the same area. These features imply that precursory quantitative changes related to foreshock activity may indicate the place and approximate time of the mainshock occurrence. However, no quantitative relations were found so far between the mainshock size and the foreshock area. This issue has been investigated by using data from selected mainshocks preceded by well shaped foreshock sequences in Greece (Ionian Sea, 12 April 2006, Ms5.6), Italy (L' Aquila, 6 April 2010, Mw6.3), Japan (Tohoku, 13 March 2011, Mw9.0) and a Southern California waveform relocated earthquake catalogue from SCSN covering the time period from 1981 to 2011 and provided by E. Hauksson et al., 2012. Only earthquakes are included in the catalogue given that the catalogue authors removed quarry blasts and other events. It was found that in the S. California catalogue the three largest mainshocks of 26 April 1981, Mw5.75; 24 November 1987, Mw6.60 and 4 April 2010, Mw7.20, were also preceded by well shaped foreshock sequences. Systematic search for the spatial extend of event rate and b-value changes before the mainshocks showed that the foreshock area increases systematically with the increase of the mainshock magnitude ranging from about 15 km in the Ionian Sea case to over than 400 km in

  2. Scale effects on the variability of the raindrop size distribution

    NASA Astrophysics Data System (ADS)

    Raupach, Timothy; Berne, Alexis

    2016-04-01

    The raindrop size distribution (DSD) is of utmost important to the study of rainfall processes and microphysics. All important rainfall variables can be calculated as weighted moments of the DSD. Qualitative precipitation estimation (QPE) algorithms and numerical weather prediction (NWP) models both use the DSD in order to calculate quantities such as the rain rate. Often these quantities are calculated at a pixel scale: radar reflectivities, for example, are integrated over a volume, so a DSD for the volume must be calculated or assumed. We present results of a study in which we have investigated the change of support problem with respect to the DSD. We have attempted to answer the following two questions. First, if a DSD measured at point scale is used to represent an area, how much error does this introduce? Second, how representative are areal DSDs calculated by QPE and NWP algorithms of the microphysical process happening inside the pixel of interest? We simulated fields of DSDs at two representative spatial resolutions: at the 2.1x2.1 km2 resolution of a typical NWP pixel, and at the 5x5 km2 resolution of a Global Precipitation Mission (GPM) satellite-based weather radar pixel. The simulation technique uses disdrometer network data and geostatistics to simulate the non-parametric DSD at 100x100 m2 resolution, conditioned by the measured DSD values. From these simulations, areal DSD measurements were derived and compared to point measurements of the DSD. The results show that the assumption that a point represents an area introduces error that increases with areal size and drop size and decreases with integration time. Further, the results show that current areal DSD estimation algorithms are not always representative of sub-grid DSDs. Idealised simulations of areal DSDs produced representative values for rain rate and radar reflectivity, but estimations of drop concentration and characteristic drop size that were often outside the sub-grid value ranges.

  3. Size dependence of the radio-luminosity-mechanical-power correlation in radio galaxies

    SciTech Connect

    Shabala, S. S.; Godfrey, L. E. H.

    2013-06-01

    We examine the relationship between source radio luminosity and kinetic power in active galactic nucleus jets. We show that neglecting various loss processes can introduce a systematic bias in the jet powers inferred from radio luminosities for a sample of radio galaxies. This bias can be corrected for by considering source size as well as radio luminosity; effectively the source size acts as a proxy for source age. Based on a sample of Fanaroff-Riley Type II radio sources with jet powers derived from the measured hotspot parameters, we empirically determine a new expression for jet power that accounts for the source size, (Q{sub jet}/10{sup 36} W)=1.5{sub −0.8}{sup +1.8}(L{sub 151}/10{sup 27} W Hz{sup −1}){sup 0.8}(1+z){sup 1.0}(D/kpc){sup 0.58±0.17}, where D is source size and L {sub 151} the 151 MHz radio luminosity. By comparing a flux-limited and volume-limited sample, we show that any derived radio-luminosity-jet-power relation depends sensitively on sample properties, in particular the source size distribution and the size-luminosity correlation inherent in the sample. Such bias will affect the accuracy of the kinetic luminosity function derived from lobe radio luminosities and should be treated with caution.

  4. Decoding size distribution patterns in marine and transitional water phytoplankton: from community to species level.

    PubMed

    Roselli, Leonilde; Basset, Alberto

    2015-01-01

    Understanding the mechanisms of phytoplankton community assembly is a fundamental issue of aquatic ecology. Here, we use field data from transitional (e.g. coastal lagoons) and coastal water environments to decode patterns of phytoplankton size distribution into organization and adaptive mechanisms. Transitional waters are characterized by higher resource availability and shallower well-mixed water column than coastal marine environments. Differences in physico-chemical regime between the two environments have been hypothesized to exert contrasting selective pressures on phytoplankton cell morphology (size and shape). We tested the hypothesis focusing on resource availability (nutrients and light) and mixed layer depth as ecological axes that define ecological niches of phytoplankton. We report fundamental differences in size distributions of marine and freshwater diatoms, with transitional water phytoplankton significantly smaller and with higher surface to volume ratio than marine species. Here, we hypothesize that mixing condition affecting size-dependent sinking may drive phytoplankton size and shape distributions. The interplay between shallow mixed layer depth and frequent and complete mixing of transitional waters may likely increase the competitive advantage of small phytoplankton limiting large cell fitness. The nutrient regime appears to explain the size distribution within both marine and transitional water environments, while it seem does not explain the pattern observed across the two environments. In addition, difference in light availability across the two environments appear do not explain the occurrence of asymmetric size distribution at each hierarchical level. We hypothesize that such competitive equilibria and adaptive strategies in resource exploitation may drive by organism's behavior which exploring patch resources in transitional and marine phytoplankton communities. PMID:25974052

  5. Decoding Size Distribution Patterns in Marine and Transitional Water Phytoplankton: From Community to Species Level

    PubMed Central

    Roselli, Leonilde; Basset, Alberto

    2015-01-01

    Understanding the mechanisms of phytoplankton community assembly is a fundamental issue of aquatic ecology. Here, we use field data from transitional (e.g. coastal lagoons) and coastal water environments to decode patterns of phytoplankton size distribution into organization and adaptive mechanisms. Transitional waters are characterized by higher resource availability and shallower well-mixed water column than coastal marine environments. Differences in physico-chemical regime between the two environments have been hypothesized to exert contrasting selective pressures on phytoplankton cell morphology (size and shape). We tested the hypothesis focusing on resource availability (nutrients and light) and mixed layer depth as ecological axes that define ecological niches of phytoplankton. We report fundamental differences in size distributions of marine and freshwater diatoms, with transitional water phytoplankton significantly smaller and with higher surface to volume ratio than marine species. Here, we hypothesize that mixing condition affecting size-dependent sinking may drive phytoplankton size and shape distributions. The interplay between shallow mixed layer depth and frequent and complete mixing of transitional waters may likely increase the competitive advantage of small phytoplankton limiting large cell fitness. The nutrient regime appears to explain the size distribution within both marine and transitional water environments, while it seem does not explain the pattern observed across the two environments. In addition, difference in light availability across the two environments appear do not explain the occurrence of asymmetric size distribution at each hierarchical level. We hypothesize that such competitive equilibria and adaptive strategies in resource exploitation may drive by organism’s behavior which exploring patch resources in transitional and marine phytoplankton communities. PMID:25974052

  6. Stationary Size Distributions of Growing Cells with Binary and Multiple Cell Division

    NASA Astrophysics Data System (ADS)

    Rading, M. M.; Engel, T. A.; Lipowsky, R.; Valleriani, A.

    2011-10-01

    Populations of unicellular organisms that grow under constant environmental conditions are considered theoretically. The size distribution of these cells is calculated analytically, both for the usual process of binary division, in which one mother cell produces always two daughter cells, and for the more complex process of multiple division, in which one mother cell can produce 2 n daughter cells with n=1,2,3,… . The latter mode of division is inspired by the unicellular algae Chlamydomonas reinhardtii. The uniform response of the whole population to different environmental conditions is encoded in the individual rates of growth and division of the cells. The analytical treatment of the problem is based on size-dependent rules for cell growth and stochastic transition processes for cell division. The comparison between binary and multiple division shows that these different division processes lead to qualitatively different results for the size distribution and the population growth rates.

  7. Observations of the spatial and temporal distribution of lightning flash sizes

    NASA Astrophysics Data System (ADS)

    Bruning, E. C.; Berkseth, S.; Salinas, V.; Chmielewski, V.; Ware, P. J.

    2015-12-01

    Recent work has shown that lightning flash sizes exhibit organization that parallels the meteorological organization of thunderstorms. Two- or three-dimensional grids of flash size and rate allow for spatial diagnosis of actively convecting regions and those with advection- or sedimentation-dominated motions. A time series of statistical moments of the flash size distribution is useful in discrimination of stages in the cellular lifecycle. Finally, ensembles of flashes exhibit a scale-dependent distribution of electrical energy like that of a turbulent energy cascade. The role of turbulence in organizing charge into small pockets is under ongoing investigation as part of the Kinematic Texture and Lightning Experiment (KTaL), where the primary observational tools are the TTU Ka-band mobile Doppler radars and the West Texas Lightning Mapping Array. Preliminary results from these new field observations will be discussed and used to illustrate the methods of interpretation described above.

  8. Measurement of particle size distribution of soil and selected aggregate sizes using the hydrometer method and laser diffractometry

    NASA Astrophysics Data System (ADS)

    Guzmán, G.; Gómez, J. A.; Giráldez, J. V.

    2010-05-01

    Soil particle size distribution has been traditionally determined by the hydrometer or the sieve-pipette methods, both of them time consuming and requiring a relatively large soil sample. This might be a limitation in situations, such as for instance analysis of suspended sediment, when the sample is small. A possible alternative to these methods are the optical techniques such as laser diffractometry. However the literature indicates that the use of this technique as an alternative to traditional methods is still limited, because the difficulty in replicating the results obtained with the standard methods. In this study we present the percentages of soil grain size determined using laser diffractometry within ranges set between 0.04 - 2000 μm. A Beckman-Coulter ® LS-230 with a 750 nm laser beam and software version 3.2 in five soils, representative of southern Spain: Alameda, Benacazón, Conchuela, Lanjarón and Pedrera. In three of the studied soils (Alameda, Benacazón and Conchuela) the particle size distribution of each aggregate size class was also determined. Aggregate size classes were obtained by dry sieve analysis using a Retsch AS 200 basic ®. Two hundred grams of air dried soil were sieved during 150 s, at amplitude 2 mm, getting nine different sizes between 2000 μm and 10 μm. Analyses were performed by triplicate. The soil sample preparation was also adapted to our conditions. A small amount each soil sample (less than 1 g) was transferred to the fluid module full of running water and disaggregated by ultrasonication at energy level 4 and 80 ml of sodium hexametaphosphate solution during 580 seconds. Two replicates of each sample were performed. Each measurement was made for a 90 second reading at a pump speed of 62. After the laser diffractometry analysis, each soil and its aggregate classes were processed calibrating its own optical model fitting the optical parameters that mainly depends on the color and the shape of the analyzed particle. As a

  9. Five-years of atmospheric aerosol number size distribution measurements in Eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Kalivitis, Nikolaos; Kouvarakis, Giorgos; Bougiatioti, Aikaterini; Stavroulas, Iasonas; Wiedensohler, Alfred; Mihalopoulos, Nikolaos

    2014-05-01

    The first long term measurements of atmospheric particle size distributions from the Eastern Mediterranean region are reported. Atmospheric aerosol number size distributions have been measured at the environmental research station of University of Crete at Finokalia, Crete, Greece (35° 20' N, 25° 40' E, 250m a.s.l) on a continuous base since 2008. A custom built (TROPOS type) scanning mobility particle sizer (SMPS) is used covering size ranges from 8 to 900 nm. The system is humidity controlled so that relative humidity is kept below 40% most of the time. Throughout the measuring period the average number concentration of the particles in the studied size range was found to be 2354 ± 1332 cm-3 (median of 2098 cm-3). Maximum concentrations are observed during summer while minimum during winter, reflecting the effectiveness of the removal processes in the region. Clear annual circles are found for the number concentrations of nucleation, Aitken and accumulation mode particles. Nucleation mode is presenting different pattern from the other two modes, with the highest concentrations during winter (and March) and the lowest during summer. New particle formation events are more frequently observed during March and October. The number size distributions present different seasonal patterns. During summer, unimodal distributions centering on the lower end of the accumulation mode size range are dominant in our observations. The prevailing meteorology characterized by the Etesian winds (Meltemi) and the lack of precipitation along the trajectory results to the arrival of well mixed air masses at Finokalia, carrying aged aerosol mainly from central and Eastern Europe. Regarding the other seasons, the shape of the distributions is more variable and strongly dependent on the air mass history: When the air masses are of marine origin or precipitation has affected them, the size distributions are mainly bimodal (peaking both in Aitken and in Accumulation mode). These

  10. 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.

  11. Atmospheric mass and metal size distributions measured around Lake Michigan

    SciTech Connect

    Seung-Muk Yi; Sofuoglu, S.C.; Holsen, T.M.

    1996-12-31

    This study, which was part of a multi-university AEOLOS investigation, involved an assessment of the spatial and temporal variations in the dry deposition fluxes and mass size distributions (MSDs) of total mass, crustal (aluminum and magnesium), and anthropogenic (lead and copper) metals over the southern basin of Lake Michigan. The work included measurement of deposition fluxes and MSDs during winter, summer and fall, concurrently, in Chicago, IL, over Lake Michigan, and in South Haven, MI. A Cascade impactor was used to determine the size distribution in the fine particles (<2.5 {mu}m), while Noll Rotary Impactor (NRI) was used to collect coarse particles (>2.5 {mu}m). The flux of these metals was substantially higher in Chicago than at either South Haven or over Lake Michigan. The measured average aluminum and magnesium fluxes were 2.23 and 5.32 mg/m{sup 2}-day over Chicago, and 0.24 and 0.28 mg/m{sup 2}-day over Lake Michigan, while the average aluminum and magnesium fluxes in South Haven were 0.17 and 0.12 mg/m{sup 2}-day respectively. The measured average lead and copper fluxes were 0.07 and 0.06 mg/m{sup 2}-day in Chicago, 0.003 and 0.01 mg/m{sup 2}-day over Lake Michigan, and 0.004 and 0.003 mg/m{sup 2}-day in South Haven. This research provided evidence of three possible peaks in the MSDs: the first in the 0-1 {mu}m range, the second in the 1-10 {mu}m region, and the third in the > 10-50 {mu}m range, with the MSDs being unimodal, bimodal or trimodal. Temporal variations in flux were not evident in this study. The wind direction (e.g., from over land, or from over lake) had large impact on both fluxes and size distributions. 5 refs., 10 figs., 1 tab.

  12. Condensation on surface energy gradient shifts drop size distribution toward small drops.

    PubMed

    Macner, Ashley M; Daniel, Susan; Steen, Paul H

    2014-02-25

    During dropwise condensation from vapor onto a cooled surface, distributions of drops evolve by nucleation, growth, and coalescence. Drop surface coverage dictates the heat transfer characteristics and depends on both drop size and number of drops present on the surface at any given time. Thus, manipulating drop distributions is crucial to maximizing heat transfer. On earth, manipulation is achieved with gravity. However, in applications with small length scales or in low gravity environments, other methods of removal, such as a surface energy gradient, are required. This study examines how chemical modification of a cooled surface affects drop growth and coalescence, which in turn influences how a population of drops evolves. Steam is condensed onto a horizontally oriented surface that has been treated by silanization to deliver either a spatially uniform contact angle (hydrophilic, hydrophobic) or a continuous radial gradient of contact angles (hydrophobic to hydrophilic). The time evolution of number density and associated drop size distributions are measured. For a uniform surface, the shape of the drop size distribution is unique and can be used to identify the progress of condensation. In contrast, the drop size distribution for a gradient surface, relative to a uniform surface, shifts toward a population of small drops. The frequent sweeping of drops truncates maturation of the first generation of large drops and locks the distribution shape at the initial distribution. The absence of a shape change indicates that dropwise condensation has reached a steady state. Previous reports of heat transfer enhancement on chemical gradient surfaces can be explained by this shift toward smaller drops, from which the high heat transfer coefficients in dropwise condensation are attributed to. Terrestrial applications using gravity as the primary removal mechanism also stand to benefit from inclusion of gradient surfaces because the critical threshold size required for

  13. Size Distribution of Main-Belt Asteroids with High Inclination

    NASA Astrophysics Data System (ADS)

    Terai, Tsuyoshi; Itoh, Yoichi

    2011-04-01

    We investigated the size distribution of high-inclination main-belt asteroids (MBAs) so as to explore asteroid collisional evolution under hypervelocity collisions of around 10 km s-1. We performed a wide-field survey for high-inclination sub-km MBAs using the 8.2-m Subaru Telescope with the Subaru Prime Focus Camera (Suprime-Cam). Suprime-Cam archival data were also used. A total of 616 MBA candidates were detected in an area of 9.0 deg² with a limiting magnitude of 24.0 mag in the SDSS r filter. Most of the candidate diameters were estimated to be smaller than 1 km. We found a scarcity of sub-km MBAs with high inclination. Cumulative size distributions (CSDs) were constructed using Subaru data and published asteroid catalogs. The power-law indexes of the CSDs were 2.17±0.02 for low-inclination (<15°) MBAs and 2.02±0.03 for high-inclination (>15°) MBAs in the 0.7-50 km diameter range. The high-inclination MBAs had a shallower CSD. We also found that the CSD of S-like MBAs had a small slope with high inclination, whereas the slope did not vary with the inclination in the C-like group. The most probable cause of the shallow CSD of the high-inclination S-like MBAs is the large power-law index in the diameter-impact strength curve in hypervelocity collisions. The collisional evolution of MBAs may have advanced with oligopolistic survival during the dynamical excitation phase in the final stage of planet formation.

  14. Measurements of Gas Bubble Size Distributions in Flowing Liquid Mercury

    SciTech Connect

    Wendel, Mark W; Riemer, Bernie; Abdou, Ashraf A

    2012-01-01

    ABSTRACT Pressure waves created in liquid mercury pulsed spallation targets have been shown to induce cavitation damage on the target container. One way to mitigate such damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, measuring such a population in mercury is difficult since it is opaque and the mercury is involved in a turbulent flow. Ultrasonic measurements have been attempted on these types of flows, but the flow noise can interfere with the measurement, and the results are unverifiable and often unrealistic. Recently, a flow loop was built and operated at Oak Ridge National Labarotory to assess the capability of various bubbler designs to deliver an adequate population of bubbles to mitigate cavitation damage. The invented diagnostic technique involves flowing the mercury with entrained gas bubbles in a steady state through a horizontal piping section with a glass-window observation port located on the top. The mercury flow is then suddenly stopped and the bubbles are allowed to settle on the glass due to buoyancy. Using a bright-field illumination and a high-speed camera, the arriving bubbles are detected and counted, and then the images can be processed to determine the bubble populations. After using this technique to collect data on each bubbler, bubble size distributions were built for the purpose of quantifying bubbler performance, allowing the selection of the best bubbler options. This paper presents the novel procedure, photographic technique, sample visual results and some example bubble size distributions. The best bubbler options were subsequently used in proton beam irradiation tests performed at the Los Alamos National Laboratory. The cavitation damage results from the irradiated test plates in contact with the mercury are available for correlation with the bubble populations. The most effective mitigating population can now be designed into prototypical geometries for implementation into

  15. On geological interpretations of crystal size distributions: Constant vs. proportionate growth

    USGS Publications Warehouse

    Eberl, D.D.; Kile, D.E.; Drits, V.A.

    2002-01-01

    Geological interpretations of crystal size distributions (CSDs) depend on understanding the crystal growth laws that generated the distributions. Most descriptions of crystal growth, including a population-balance modeling equation that is widely used in petrology, assume that crystal growth rates at any particular time are identical for all crystals, and, therefore, independent of crystal size. This type of growth under constant conditions can be modeled by adding a constant length to the diameter of each crystal for each time step. This growth equation is unlikely to be correct for most mineral systems because it neither generates nor maintains the shapes of lognormal CSDs, which are among the most common types of CSDs observed in rocks. In an alternative approach, size-dependent (proportionate) growth is modeled approximately by multiplying the size of each crystal by a factor, an operation that maintains CSD shape and variance, and which is in accord with calcite growth experiments. The latter growth law can be obtained during supply controlled growth using a modified version of the Law of Proportionate Effect (LPE), an equation that simulates the reaction path followed by a CSD shape as mean size increases.

  16. SIZE DISTRIBUTION AND RATE OF PRODUCTION OF AIRBORNE PARTICULATE MATTER GENERATED DURING METAL CUTTING

    SciTech Connect

    M.A. Ebadian, Ph.D.; S.K. Dua, Ph.D., C.H.P.; Hillol Guha, Ph.D.

    2001-01-01

    During deactivation and decommissioning activities, thermal cutting tools, such as plasma torch, laser, and gasoline torch, are used to cut metals. These activities generate fumes, smoke and particulates. These airborne species of matter, called aerosols, may be inhaled if suitable respiratory protection is not used. Inhalation of the airborne metallic aerosols has been reported to cause ill health effects, such as acute respiratory syndrome and chromosome damage in lymphocytes. In the nuclear industry, metals may be contaminated with radioactive materials. Cutting these metals, as in size reduction of gloveboxes and tanks, produces high concentrations of airborne transuranic particles. Particles of the respirable size range (size < 10 {micro}m) deposit in various compartments of the respiratory tract, the fraction and the site in the respiratory tract depending on the size of the particles. The dose delivered to the respiratory tract depends on the size distribution of the airborne particulates (aerosols) and their concentration and radioactivity/toxicity. The concentration of airborne particulate matter in an environment is dependent upon the rate of their production and the ventilation rate. Thus, measuring aerosol size distribution and generation rate is important for (1) the assessment of inhalation exposures of workers, (2) the selection of respiratory protection equipment, and (3) the design of appropriate filtration systems. Size distribution of the aerosols generated during cutting of different metals by plasma torch was measured. Cutting rates of different metals, rate of generation of respirable mass, as well as the fraction of the released kerf that become respirable were determined. This report presents results of these studies. Measurements of the particles generated during cutting of metal plates with a plasma arc torch revealed the presence of particles with mass median aerodynamic diameters of particles close to 0.2 {micro}m, arising from

  17. Passive acoustic inversion to estimate bedload size distribution in rivers

    NASA Astrophysics Data System (ADS)

    Petrut, Teodor; Geay, Thomas; Belleudy, Philippe; Gervaise, Cédric

    2016-04-01

    The knowledge of sediment transport rate in rivers is related to issues like changes in channel forms, inundation risks and river's ecological functions. The passive acoustic method introduced here measures the bedload processes by recording the noise generated by the inter-particle collisions. In this research, an acoustic inversion is proposed to estimate the size distribution of mobile particles. The theoretical framework of Hertz's impact between two solids rigid is used to model the sediment-generated noise. This model combined with the acoustical power spectrum density gives the information on the particle sizes. The sensitivity of the method is performed and finally the experimental validation is done through a series of tests in the laboratory as well in a natural stream. The limitations of the proposed inversion method are drawn assuming the wave propagation effects in the channel. It is stated that propagation effects limit the applicability of the method to large rivers, like fluvial channels, in the detriment of mountain torrents.

  18. Size distribution and seasonal variation of atmospheric cellulose

    NASA Astrophysics Data System (ADS)

    Puxbaum, Hans; Tenze-Kunit, Monika

    Atmospheric cellulose is a main constituent of the insoluble organic aerosol and a "macrotracer" for plant debris. A time series of the cellulose concentration at a downtown site in Vienna showed a maximum concentration during fall and a secondary maximum during spring. The fall maximum appears to be associated with leaf litter production, the spring maximum with increased biological activity involving repulsion of cellulose-containing particles, e.g. seed production. The grand average of the time series over 9 months was 0.374 μg m -3 cellulose, respectively, 0.75 μg m -3 plant debris. Compared to an annual average of 5.7 μg m -3 organic carbon as observed at a Vienna downtown site it becomes clear that plant debris is a major contributor to the organic aerosol and has to be considered in source attribution studies. Simultaneous measurements at the downtown and a suburban site indicated that particulate cellulose is obviously not produced within the city in notable amounts, at least during the campaign in December. Size distribution measurements with impactors showed the unexpected result that "fine aerosol" size particles (0.1- 1.6 μm aerodynamic diameter) contained 0.7% "free cellulose" on a mass basis, forming a wettable, but insoluble part of the accumulation mode aerosol.

  19. Airborne Measurements of Aerosol Size Distributions During PACDEX

    NASA Astrophysics Data System (ADS)

    Rogers, D. C.; Gandrud, B.; Campos, T.; Kok, G.; Stith, J.

    2007-12-01

    The Pacific Dust Experiment (PACDEX) is an airborne project that attempts to characterize the indirect aerosol effect by tracing plumes of dust and pollution across the Pacific Ocean. This project occurred during April-May 2007 and used the NSF/NCAR HIAPER research aircraft. When a period of strong generation of dust particles and pollution was detected by ground-based and satellite sensors, then the aircraft was launched from Colorado to Alaska, Hawaii, and Japan. Its mission was to intercept and track these plumes from Asia, across the Pacific Ocean, and ultimately to the edges of North America. For more description, see the abstract by Stith and Ramanathan (this conference) and other companion papers on PACDEX. The HIAPER aircraft carried a wide variety of sensors for measuring aerosols, cloud particles, trace gases, and radiation. Sampling was made in several weather regimes, including clean "background" air, dust and pollution plumes, and regions with cloud systems. Altitude ranges extended from 100 m above the ocean to 13.4 km. This paper reports on aerosol measurements made with a new Ultra-High Sensitivity Aerosol Spectrometer (UHSAS), a Radial Differential Mobility Analyzer (RDMA), a water-based CN counter, and a Cloud Droplet Probe (CDP). These cover the size range 10 nm to 10 um diameter. In clear air, dust was detected with the UHSAS and CDP. Polluted air was identified with high concentrations of carbon monoxide, ozone, and CN. Aerosol size distributions will be presented, along with data to define the context of weather regimes.

  20. Vesicle Size Distribution as a Novel Nuclear Forensics Tool

    PubMed Central

    Simonetti, Antonio

    2016-01-01

    The first nuclear bomb detonation on Earth involved a plutonium implosion-type device exploded at the Trinity test site (33°40′38.28″N, 106°28′31.44″W), White Sands Proving Grounds, near Alamogordo, New Mexico. Melting and subsequent quenching of the local arkosic sand produced glassy material, designated “Trinitite”. In cross section, Trinitite comprises a thin (1–2 mm), primarily glassy surface above a lower zone (1–2 cm) of mixed melt and mineral fragments from the precursor sand. Multiple hypotheses have been put forward to explain these well-documented but heterogeneous textures. This study reports the first quantitative textural analysis of vesicles in Trinitite to constrain their physical and thermal history. Vesicle morphology and size distributions confirm the upper, glassy surface records a distinct processing history from the lower region, that is useful in determining the original sample surface orientation. Specifically, the glassy layer has lower vesicle density, with larger sizes and more rounded population in cross-section. This vertical stratigraphy is attributed to a two-stage evolution of Trinitite glass from quench cooling of the upper layer followed by prolonged heating of the subsurface. Defining the physical regime of post-melting processes constrains the potential for surface mixing and vesicle formation in a post-detonation environment. PMID:27658210

  1. Comparison of Raindrop Size Distribution Measurements by Collocated Disdrometers

    NASA Technical Reports Server (NTRS)

    Tokay, Ali; Petersen, Walter A.; Gatlin, Patrick; Wingo, Matthew

    2013-01-01

    An impact-type Joss-Waldvogel disdrometer (JWD), a two-dimensional video disdrometer (2DVD), and a laser optical OTT Particle Size and Velocity (PARSIVEL) disdrometer (PD) were used to measure the raindrop size distribution (DSD) over a 6-month period in Huntsville, Alabama. Comparisons indicate event rain totals for all three disdrometers that were in reasonable agreement with a reference rain gauge. In a relative sense, hourly composite DSDs revealed that the JWD was more sensitive to small drops (,1 mm), while the PD appeared to severely underestimate small drops less than 0.76mm in diameter. The JWD and 2DVD measured comparable number concentrations of midsize drops (1-3mm) and large drops (3-5 mm), while the PD tended to measure relatively higher drop concentrations at sizes larger than 2.44mm in diameter. This concentration disparity tended to occur when hourly rain rates and drop counts exceeded 2.5mm/h and 400/min, respectively. Based on interactions with the PD manufacturer, the partially inhomogeneous laser beam is considered the cause of the PD drop count overestimation. PD drop fall speeds followed the expected terminal fall speed relationship quite well, while the 2DVD occasionally measured slower drops for diameters larger than 2.4mm, coinciding with events where wind speeds were greater than 4m/s. The underestimation of small drops by the PD had a pronounced effect on the intercept and shape of parameters of gamma-fitted DSDs, while the overestimation of midsize and larger drops resulted in higher mean values for PD integral rain parameters

  2. Size dependent differences in litter consumption of isopods: preliminary results

    PubMed Central

    Vilisics, Ferenc; Szekeres, Sándor; Hornung, Elisabeth

    2012-01-01

    Abstract A series of experiments were applied to test how leaf orientation within microcosms affect consumption rates (Experiment 1), and to discover intra-specific differences in leaf litter consumption (Experiment 2) of the common isopod species Porcellio scaber and Porcellionides pruinosus. A standardised microcosm setup was developed for feeding experiments to maintain standard conditions. A constant amount of freshly fallen black poplar litter was provided to three distinct size class (small, medium, large) of woodlice. We measured litter consumption after a fortnight. We maintained appr. constant isopod biomass for all treatments, and equal densities within each size class. We hypothesized that different size classes differ in their litter consumption, therefore such differences should occur even within populations of the species. We also hypothesized a marked difference in consumption rates for different leaf orientation within microcosms. Our results showed size-specific consumption patterns for Porcellio scaber: small adults showed the highest consumption rates (i.e. litter mass loss / isopod biomass) in high density microcosms, while medium-sized adults of lower densities ate the most litter in containers. Leaf orientation posed no significant effect on litter consumption. PMID:22536112

  3. Size dependent differences in litter consumption of isopods: preliminary results.

    PubMed

    Vilisics, Ferenc; Szekeres, Sándor; Hornung, Elisabeth

    2012-01-01

    A series of experiments were applied to test how leaf orientation within microcosms affect consumption rates (Experiment 1), and to discover intra-specific differences in leaf litter consumption (Experiment 2) of the common isopod species Porcellio scaber and Porcellionides pruinosus. A standardised microcosm setup was developed for feeding experiments to maintain standard conditions. A constant amount of freshly fallen black poplar litter was provided to three distinct size class (small, medium, large) of woodlice. We measured litter consumption after a fortnight. We maintained appr. constant isopod biomass for all treatments, and equal densities within each size class. We hypothesized that different size classes differ in their litter consumption, therefore such differences should occur even within populations of the species. We also hypothesized a marked difference in consumption rates for different leaf orientation within microcosms. Our results showed size-specific consumption patterns for Porcellio scaber: small adults showed the highest consumption rates (i.e. litter mass loss / isopod biomass) in high density microcosms, while medium-sized adults of lower densities ate the most litter in containers. Leaf orientation posed no significant effect on litter consumption.

  4. Evaluation and interpretation of bubble size distributions in pulsed megasonic fields

    NASA Astrophysics Data System (ADS)

    Hauptmann, M.; Struyf, H.; De Gendt, S.; Glorieux, C.; Brems, S.

    2013-05-01

    The occurrence of acoustic cavitation is incorporating a multitude of interdependent effects that strongly depend on the bubble size. Therefore, bubble size control would be beneficial for biological and industrial processes that rely on acoustic cavitation. A pulsed acoustic field can result in bubble size control and the repeated dissolution and reactivation ("recycling") of potentially active bubbles. As a consequence, a pulsed field can strongly enhance cavitation activity. In this paper, we present a modified methodology for the evaluation of the active bubble size distribution by means of a combination of cavitation noise measurements and ultrasonic pulsing. The key component of this modified methodology is the definition of an upper size limit, below which bubbles—in between subsequent pulses—have to dissolve, in order to be sustainably recycled. This upper limit makes it possible to explain and link the enhancement of cavitation activity to a bubble size distribution. The experimentally determined bubble size distributions for different power densities are interpreted in the frame of numerical calculations of the oscillatory responses of the bubbles to the intermittent driving sound field. The distributions are found to be shaped by the size dependent interplay between bubble pulsations, rectified diffusion, coalescence, and the development of parametrically amplified shape instabilities. Also, a phenomenological reactivation-deactivation model is proposed to explain and quantify the observed enhancement of cavitation activity under pulsed, with respect to continuous sonication. In this model, the pulse-duration determines the magnitude of the reactivation of partially dissolved bubbles and the deactivation of activated bubbles by coalescence. It is shown that the subsequent recycling of previously active bubbles leads to an accumulation of cavitation activity, which saturates after a certain number of pulses. The model is fitted to the experimental

  5. Event-based total suspended sediment particle size distribution model

    NASA Astrophysics Data System (ADS)

    Thompson, Jennifer; Sattar, Ahmed M. A.; Gharabaghi, Bahram; Warner, Richard C.

    2016-05-01

    One of the most challenging modelling tasks in hydrology is prediction of the total suspended sediment particle size distribution (TSS-PSD) in stormwater runoff generated from exposed soil surfaces at active construction sites and surface mining operations. The main objective of this study is to employ gene expression programming (GEP) and artificial neural networks (ANN) to develop a new model with the ability to more accurately predict the TSS-PSD by taking advantage of both event-specific and site-specific factors in the model. To compile the data for this study, laboratory scale experiments using rainfall simulators were conducted on fourteen different soils to obtain TSS-PSD. This data is supplemented with field data from three construction sites in Ontario over a period of two years to capture the effect of transport and deposition within the site. The combined data sets provide a wide range of key overlooked site-specific and storm event-specific factors. Both parent soil and TSS-PSD in runoff are quantified by fitting each to a lognormal distribution. Compared to existing regression models, the developed model more accurately predicted the TSS-PSD using a more comprehensive list of key model input parameters. Employment of the new model will increase the efficiency of deployment of required best management practices, designed based on TSS-PSD, to minimize potential adverse effects of construction site runoff on aquatic life in the receiving watercourses.

  6. Using radial NMR profiles to characterize pore size distributions

    NASA Astrophysics Data System (ADS)

    Deriche, Rachid; Treilhard, John

    2012-02-01

    Extracting information about axon diameter distributions in the brain is a challenging task which provides useful information for medical purposes; for example, the ability to characterize and monitor axon diameters would be useful in diagnosing and investigating diseases like amyotrophic lateral sclerosis (ALS)1 or autism.2 Three families of operators are defined by Ozarslan,3 whose action upon an NMR attenuation signal extracts the moments of the pore size distribution of the ensemble under consideration; also a numerical method is proposed to continuously reconstruct a discretely sampled attenuation profile using the eigenfunctions of the simple harmonic oscillator Hamiltonian: the SHORE basis. The work presented here extends Ozarlan's method to other bases that can offer a better description of attenuation signal behaviour; in particular, we propose the use of the radial Spherical Polar Fourier (SPF) basis. Testing is performed to contrast the efficacy of the radial SPF basis and SHORE basis in practical attenuation signal reconstruction. The robustness of the method to additive noise is tested and analysed. We demonstrate that a low-order attenuation signal reconstruction outperforms a higher-order reconstruction in subsequent moment estimation under noisy conditions. We propose the simulated annealing algorithm for basis function scale parameter estimation. Finally, analytic expressions are derived and presented for the action of the operators on the radial SPF basis (obviating the need for numerical integration, thus avoiding a spectrum of possible sources of error).

  7. Direct correlation of diffusion and pore size distributions with low field NMR

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Xiao, Lizhi; Liao, Guangzhi; Song, Yi-Qiao

    2016-08-01

    The time-dependent diffusion coefficient (D) is a powerful tool to probe microstructure in porous media, and can be obtained by the NMR method. In a real porous sample, molecular diffusion is very complex. Here we present a new method which directly measures the relationship between effective diffusion coefficients and pore size distributions without knowing surface relaxivity. This method is used to extract structural information and explore the relationship between D and a in porous media having broad pore size distributions. The diffusion information is encoded by the Pulsed Field Gradient (PFG) method and the pore size distributions are acquired by the Decay due to Diffusion in the Internal Field (DDIF) method. Two model samples were measured to verify this method. Restricted diffusion was analyzed, and shows that most fluid molecules experience pore wall. The D(a) curves obtained from correlation maps were fitted to the Padé approximant equation and a good agreement was found between the fitting lines and the measured data. Then a sandstone sample with unknown structure was measured. The state of confined fluids was analyzed and structural information, such as pore size distributions, were extracted. The D - T1 correlation maps were also obtained using the same method, which yielded surface relaxivities for different samples. All the experiments were conducted on 2 MHz NMR equipment to obtain accurate diffusion information, where internal gradients can be neglected. This method is expected to have useful applications in the oil industry, particularly for NMR logging in the future.

  8. Direct correlation of diffusion and pore size distributions with low field NMR.

    PubMed

    Zhang, Yan; Xiao, Lizhi; Liao, Guangzhi; Song, Yi-Qiao

    2016-08-01

    The time-dependent diffusion coefficient (D) is a powerful tool to probe microstructure in porous media, and can be obtained by the NMR method. In a real porous sample, molecular diffusion is very complex. Here we present a new method which directly measures the relationship between effective diffusion coefficients and pore size distributions without knowing surface relaxivity. This method is used to extract structural information and explore the relationship between D and a in porous media having broad pore size distributions. The diffusion information is encoded by the Pulsed Field Gradient (PFG) method and the pore size distributions are acquired by the Decay due to Diffusion in the Internal Field (DDIF) method. Two model samples were measured to verify this method. Restricted diffusion was analyzed, and shows that most fluid molecules experience pore wall. The D(a) curves obtained from correlation maps were fitted to the Padé approximant equation and a good agreement was found between the fitting lines and the measured data. Then a sandstone sample with unknown structure was measured. The state of confined fluids was analyzed and structural information, such as pore size distributions, were extracted. The D - T1 correlation maps were also obtained using the same method, which yielded surface relaxivities for different samples. All the experiments were conducted on 2MHz NMR equipment to obtain accurate diffusion information, where internal gradients can be neglected. This method is expected to have useful applications in the oil industry, particularly for NMR logging in the future. PMID:27371788

  9. Ultrashort laser ablation of bulk copper targets: Dynamics and size distribution of the generated nanoparticles

    SciTech Connect

    Tsakiris, N.; Gill-Comeau, M.; Lewis, L. J.; Anoop, K. K.; Ausanio, G.; Bruzzese, R.; Amoruso, S.

    2014-06-28

    We address the role of laser pulse fluence on expansion dynamics and size distribution of the nanoparticles produced by irradiating a metallic target with an ultrashort laser pulse in a vacuum, an issue for which contrasting indications are present in the literature. To this end, we have carried out a combined theoretical and experimental analysis of laser ablation of a bulk copper target with ≈50 fs, 800 nm pulses, in an interval of laser fluencies going from few to several times the ablation threshold. On one side, molecular dynamics simulations, with two-temperature model, describe the decomposition of the material through the analysis of the evolution of thermodynamic trajectories in the material phase diagram, and allow estimating the size distribution of the generated nano-aggregates. On the other side, atomic force microscopy of less than one layer nanoparticles deposits on witness plates, and fast imaging of the nanoparticles broadband optical emission provide the corresponding experimental characterization. Both experimental and numerical findings agree on a size distribution characterized by a significant fraction (≈90%) of small nanoparticles, and a residual part (≈10%) spanning over a rather large size interval, evidencing a weak dependence of the nanoparticles sizes on the laser pulse fluence. Numerical and experimental findings show a good degree of consistency, thus suggesting that modeling can realistically support the search for experimental methods leading to an improved control over the generation of nanoparticles by ultrashort laser ablation.

  10. The Fossilized Size Distribution of the Main Asteroid Belt

    NASA Astrophysics Data System (ADS)

    Bottke, W. F.; Durda, D.; Nesvorny, D.; Jedicke, R.; Morbidelli, A.

    2003-05-01

    At present, we do not understand how the main asteroid belt evolved into its current state. During the planet formation epoch, the primordial main belt (PMB) contained several Earth masses of material, enough to allow the asteroids to accrete on relatively short timescales (e.g., Weidenschilling 1977). The present-day main belt, however, only contains 5e-4 Earth masses of material (Petit et al. 2002). Constraints on this evolution come from (i) the observed fragments of differentiated asteroids, (ii) meteorites collected from numerous differentiated parent bodies, (iii) the presence of ˜ 10 prominent asteroid families, (iv) the "wavy" size-frequency distribution of the main belt, which has been shown to be a by-product of substantial collisional evolution (e.g., Durda et al. 1997), and (v) the still-intact crust of (4) Vesta. To explain the contradictions in the above constraints, we suggest the PMB evolved in this fashion: Planetesimals and planetary embryos accreted (and differentiated) in the PMB during the first few Myr of the solar system. Gravitational perturbations from these embryos dynamically stirred the main belt, enough to initiate fragmentation. When Jupiter reached its full size, some 10 Myr after the solar system's birth, its perturbations, together with those of the embryos, dynamically depleted the main belt region of ˜ 99% of its bodies. Much of this material was sent to high (e,i) orbits, where it continued to pummel the surviving main belt bodies at high impact velocities for more than 100 Myr. While some differentiated bodies in the PMB were disrupted, most were instead scattered; only small fragments from this population remain. This period of comminution and dynamical evolution in the PMB created, among other things, the main belt's wavy size distribution, such that it can be considered a "fossil" from this violent early epoch. From this time forward, however, relatively little collisional evolution has taken place in the main belt

  11. Size Dependent Phase Diagrams of Nickel-Carbon Nanoparticles

    NASA Astrophysics Data System (ADS)

    Magnin, Y.; Zappelli, A.; Amara, H.; Ducastelle, F.; Bichara, C.

    2015-11-01

    The carbon rich phase diagrams of nickel-carbon nanoparticles, relevant to catalysis and catalytic chemical vapor deposition synthesis of carbon nanotubes, are calculated for system sizes up to about 3 nm (807 Ni atoms). A tight binding model for interatomic interactions drives the grand canonical Monte Carlo simulations used to locate solid, core shell and liquid stability domains, as a function of size, temperature, and carbon chemical potential or concentration. Melting is favored by carbon incorporation from the nanoparticle surface, resulting in a strong relative lowering of the eutectic temperature and a phase diagram topology different from the bulk one. This should lead to a better understanding of the nanotube growth mechanisms.

  12. Crystal Size Distributions in Igneous rocks: Where are we now?

    NASA Astrophysics Data System (ADS)

    Higgins, M.

    2003-12-01

    Modern Crystal Size Distributions (CSD) studies started in 1988 and have expanded since then, albeit somewhat slowly. We have now measured CSDs in a variety of different compositions and for both plutonic and volcanic rocks. However, the subject still lags far behind chemical petrology and we need many more studies. CSD methodology has advanced considerably, both for 3D and 2D methods, but it is unfortunate that some 2D studies still do not use appropriate stereological conversions or publish their raw data. The nature of the lower size limit is very important, real or measurement artefact, but is not commonly stated. All this is especially important for comparing data with earlier studies. Individual CSDs of minerals are not always very informative. A much better approach is to look at suites of related CSDs. For instance, different minerals within a single sample, ensembles of related whole rock samples, comparison of late and early textures as preserved in oikocrysts, dykes or volcanic rocks. As more data become available it will be possible to compare usefully unrelated suites of rocks. Straight or nearly straight CSDs in volcanic rocks can be produced by steady-state crystallisation. If the growth rate is known then the residence time can be determined. In some rocks there is a good agreement with other chronometric techniques, but others show no such concordance. In the latter case another model may be more appropriate, such as textural coarsening. This model has been applied in some cases in inappropriate situations, which has cast doubt on the whole subject of CSDs. For plutonic rocks exponentially increasing undercooling can also produce straight CSDs. However, many CSDs are slightly curved and other models are possible, especially if no small crystals are present. Within ensembles of straight CSDs the slope and intercept are commonly correlated. This is mostly accounted for by closure and hence this correlation is not significant, although the variation

  13. Interpolation of the raindrop size distribution over a GPM-pixel-sized region.

    NASA Astrophysics Data System (ADS)

    Berne, A.; Raupach, T.

    2014-12-01

    The raindrop size distribution (DSD) is crucial information on the structure of rainfall. All bulk rainfall variables of interest can be derived as weighted moments of the DSD. Usually the DSD is measured at point locations using disdrometers. In some contexts, such as the investigation of scale-change effects, it would be useful to be able to interpolate the DSD across space between point measurements. Traditionally such studies are performed by interpolating bulk variables individually. Such an approach fails to take into account any interrelationships between the bulk variables and information is lost. We present a spatial interpolation method for the whole drop size distribution. Instead of using multivariate geostatistics, we use a principle component analysis (PCA) to identify orthogonal components of the DSD. These components are independent, and thus we can apply univariate geostatistics to each one individually. Interpolation is carried out using ordinary kriging. Once components are interpolated, the interpolation of the DSD can be recovered at any requested point by recombining and back-transforming the components. The advantages of the method are that the DSD is interpolated in full, the use of PCA allows us to control and quantify the amount of information loss that occurs, and relationships between any bulk variables are maintained through the process. An important feature of rainfall that is considered in the proposed interpolation method is the intermittency and its influence on the spatial distribution of raindrops. We have applied this technique to DSDs recorded at point locations in a GPM-pixel sized area in Ardèche, France in the framework of the HyMeX project. To test the results we use leave-one-out testing and compare to interpolation of individual bulk variables; the results are favourable. An investigation of the radar reflectivity to rain-rate (Z-R) relationship shows that our DSD interpolation technique maintains the relationships

  14. Carbon-based phytoplankton size classes retrieved via ocean color estimates of the particle size distribution

    NASA Astrophysics Data System (ADS)

    Kostadinov, Tihomir S.; Milutinović, Svetlana; Marinov, Irina; Cabré, Anna

    2016-04-01

    Owing to their important roles in biogeochemical cycles, phytoplankton functional types (PFTs) have been the aim of an increasing number of ocean color algorithms. Yet, none of the existing methods are based on phytoplankton carbon (C) biomass, which is a fundamental biogeochemical and ecological variable and the "unit of accounting" in Earth system models. We present a novel bio-optical algorithm to retrieve size-partitioned phytoplankton carbon from ocean color satellite data. The algorithm is based on existing methods to estimate particle volume from a power-law particle size distribution (PSD). Volume is converted to carbon concentrations using a compilation of allometric relationships. We quantify absolute and fractional biomass in three PFTs based on size - picophytoplankton (0.5-2 µm in diameter), nanophytoplankton (2-20 µm) and microphytoplankton (20-50 µm). The mean spatial distributions of total phytoplankton C biomass and individual PFTs, derived from global SeaWiFS monthly ocean color data, are consistent with current understanding of oceanic ecosystems, i.e., oligotrophic regions are characterized by low biomass and dominance of picoplankton, whereas eutrophic regions have high biomass to which nanoplankton and microplankton contribute relatively larger fractions. Global climatological, spatially integrated phytoplankton carbon biomass standing stock estimates using our PSD-based approach yield ˜ 0.25 Gt of C, consistent with analogous estimates from two other ocean color algorithms and several state-of-the-art Earth system models. Satisfactory in situ closure observed between PSD and POC measurements lends support to the theoretical basis of the PSD-based algorithm. Uncertainty budget analyses indicate that absolute carbon concentration uncertainties are driven by the PSD parameter No which determines particle number concentration to first order, while uncertainties in PFTs' fractional contributions to total C biomass

  15. Density-dependent effects on growth, body size, and clutch size in black brant

    USGS Publications Warehouse

    Sedinger, J.S.; Lindberg, M.S.; Person, B.T.; Eichholz, M.W.; Herzog, M.P.; Flint, P.L.

    1998-01-01

    We documented gosling size in late summer, adult body size, and clutch size of known-age Black Brant (Branta bernicla nigricans) females nesting on the Tutakoke River colony between 1986 and 1995. During this period, the colony increased from 1,100 to >5,000 nesting pairs. Gosling mass at 30 days of age declined from 764 ?? SE of 13 g and 723 ?? 15 g for males and females, respectively, in the 1986 cohort, to 665 ?? 18 g and 579 ?? 18 g in the 1994 cohort. Gosling size was directly negatively correlated with number of Black Brant broods. We detected no trend in adult body size for individuals from these cohorts; in fact, adults from the 1992 and 1994 cohorts had the largest overall masses. Clutch size increased with age from 3.4 eggs for 2-year-old females to 4.4 eggs for 5-year-old females. Clutch size declined during the study by 0.20 (3-year-old females) to 0.45 (2-year-old females) eggs. Clutch size did not decline between the 1986 and 1990 cohorts for females that were >5 years old. Our results for clutch size and gosling size are similar to those recorded for Lesser Snow Geese (Chen caerulescens caerulescens). Our failure to detect a trend in adult body size, however, differs from the response of other geese to increasing population density. We interpret this difference in effects of density on adult size between Black Brant and other geese as an indication of stronger selection against the smallest individuals in Black Brant relative to other species of geese.

  16. Size Distribution of Sea-Salt Emissions as a Function of Relative Humidity

    NASA Astrophysics Data System (ADS)

    Zhang, K. M.; Knipping, E. M.; Wexler, A. S.; Bhave, P. V.; Tonnesen, G. S.

    2004-12-01

    Here we introduced a simple method for correcting sea-salt particle-size distributions as a function of relative humidity. Distinct from previous approaches, our derivation uses particle size at formation as the reference state rather than dry particle size. The correction factors, corresponding to the size at formation and the size at 80% RH, are given as polynomial functions of local relative humidity which are straightforward to implement. Without major compromises, the correction factors are thermodynamically accurate and can be applied between 0.45 and 0.99 RH. Since the thermodynamic properties of sea-salt electrolytes are weakly dependent on ambient temperature, these factors can be regarded as temperature independent. The correction factor w.r.t. to the size at 80% RH is in excellent agreement with those from Fitzgerald's and Gerber's growth equations; while the correction factor w.r.t. the size at formation has the advantage of being independent of dry size and relative humidity at formation. The resultant sea-salt emissions can be used directly in atmospheric model simulations at urban, regional and global scales without further correction. Application of this method to several common open-ocean and surf-zone sea-salt-particle source functions is described.

  17. 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

  18. Determining the size distribution of core-shell spheres and other complex particles by laser diffraction.

    PubMed

    Lagasse, R R; Richards, D Wayne

    2003-11-01

    The goal of this work is to determine the size distribution of hollow glass spheres by laser diffraction, an experiment which involves measuring angle-dependent scattering of light from particles dispersed in a liquid. The proprietary software supplied with commercial instruments is not strictly applicable to our two-layer, glass-shell, hollow-core spheres because it requires that the particles have spatially homogeneous properties. We therefore developed Fortran code to compute the scattering from core-shell spherical particles. The results show that the scattering from representative hollow glass particles diverges from homogeneous sphere scattering when the radius decreases from 10 to 3 microm. Additionally, scattering measurements on two core-shell hollow glass powders were analyzed using the exact core-shell optical model and homogeneous sphere approximations. In both cases, the size distribution determined using the exact core-shell model differs from that determined using the homogeneous-sphere approximation when the distribution covers radii smaller than about 10 microm, as expected. The size distribution based on the exact core-shell optical model was determined using a new algorithm. Although the basic equations used in the algorithm have been published previously, they are developed here in a different form, which can be implemented using Fortran and MatLab routines available commercially and in the public domain. This algorithm could be used to determine the size distribution of other kinds of particles, such as cylindrical rods, as long as their angle-dependent scattering could be computed. PMID:14554168

  19. Analysis of a Stochastic Model for Bacterial Growth and the Lognormality of the Cell-Size Distribution

    NASA Astrophysics Data System (ADS)

    Yamamoto, Ken; Wakita, Jun-ichi

    2016-07-01

    This paper theoretically analyzes a phenomenological stochastic model for bacterial growth. This model comprises cell division and the linear growth of cells, where growth rates and cell cycles are drawn from lognormal distributions. We find that the cell size is expressed as a sum of independent lognormal variables. We show numerically that the quality of the lognormal approximation greatly depends on the distributions of the growth rate and cell cycle. Furthermore, we show that actual parameters of the growth rate and cell cycle take values that give a good lognormal approximation; thus, the experimental cell-size distribution is in good agreement with a lognormal distribution.

  20. Size Dependent Phase Diagrams of Nickel-Carbon Nanoparticles.

    PubMed

    Magnin, Y; Zappelli, A; Amara, H; Ducastelle, F; Bichara, C

    2015-11-13

    The carbon rich phase diagrams of nickel-carbon nanoparticles, relevant to catalysis and catalytic chemical vapor deposition synthesis of carbon nanotubes, are calculated for system sizes up to about 3 nm (807 Ni atoms). A tight binding model for interatomic interactions drives the grand canonical Monte Carlo simulations used to locate solid, core shell and liquid stability domains, as a function of size, temperature, and carbon chemical potential or concentration. Melting is favored by carbon incorporation from the nanoparticle surface, resulting in a strong relative lowering of the eutectic temperature and a phase diagram topology different from the bulk one. This should lead to a better understanding of the nanotube growth mechanisms. PMID:26613451

  1. Particle size dependent chemistry from laser ablation of brass.

    PubMed

    Liu, Chunyi; Mao, Xianglei; Mao, Sam S; Greif, Ralph; Russo, Richard E

    2005-10-15

    The proportion of zinc and copper in particles formed by laser ablation of brass was found to vary with the particle diameter. Energy-dispersive X-ray analysis showed that smaller particles were zinc enhanced while larger particles were composed mostly of copper. A model based on condensation of vapor onto large droplets ejected from a melted liquid layer is proposed to describe the change in particle composition versus size. PMID:16223257

  2. Particle size dependent rheological property in magnetic fluid

    NASA Astrophysics Data System (ADS)

    Wu, Jie; Pei, Lei; Xuan, Shouhu; Yan, Qifan; Gong, Xinglong

    2016-06-01

    The influence of the particle size on the rheological property of magnetic fluid was studied both by the experimental and computer simulation methods. Firstly, the magnetic fluids were prepared by dispersing Fe3O4 nanospheres with size varied from 40 nm to 100 nm and 200 nm in the solution. Then, the rheological properties were investigated and it was found that the relative magnetorheological effects increased with increasing the particle size. Finally, the molecular dynamic simulation was used to analyze the mechanical characteristics of the magnetic fluid and the chain-like model agreed well with the experimental result. The authentic chain-like structure observed by a microscope agreed with the simulation results. The three particles composed of the similar cluster nanostructure, thus they exhibited similar magnetic property. To this end, the unique assembling microstructures was the origination of the mechanical difference. And it was found that the higher MR (magnetorheological) effects of the large particle based magnetic fluid was originated from the stronger assembling microstructure under the applying magnetic field.

  3. Size-dependent protein segregation at membrane interfaces

    NASA Astrophysics Data System (ADS)

    Schmid, Eva M.; Bakalar, Matthew H.; Choudhuri, Kaushik; Weichsel, Julian; Ann, Hyoung Sook; Geissler, Phillip L.; Dustin, Michael L.; Fletcher, Daniel A.

    2016-07-01

    Membrane interfaces formed at cell-cell junctions are associated with characteristic patterns of membrane proteins whose organization is critical for intracellular signalling. To isolate the role of membrane protein size in pattern formation, we reconstituted model membrane interfaces in vitro using giant unilamellar vesicles decorated with synthetic binding and non-binding proteins. We show that size differences between membrane proteins can drastically alter their organization at membrane interfaces, with as little as a ~5 nm increase in non-binding protein size driving its exclusion from the interface. Combining in vitro measurements with Monte Carlo simulations, we find that non-binding protein exclusion is also influenced by lateral crowding, binding protein affinity, and thermally driven membrane height fluctuations that transiently limit access to the interface. This sensitive and highly effective means of physically segregating proteins has implications for cell-cell contacts such as T-cell immunological synapses (for example, CD45 exclusion) and epithelial cell junctions (for example, E-cadherin enrichment), as well as for protein sorting at intracellular contact points between membrane-bound organelles.

  4. Molecular size and molecular size distribution affecting traditional balsamic vinegar aging.

    PubMed

    Falcone, Pasquale Massimiliano; Giudici, Paolo

    2008-08-27

    A first attempt at a semiquantitative study of molecular weight (MW) and molecular weight distribution (MWD) in cooked grape must and traditional balsamic vinegar (TBV) with increasing well-defined age was performed by high-performance liquid size exclusion chromatography (SEC) using dual detection, that is, differential refractive index (DRI) and absorbance (UV-vis) based detectors. With this aim, MW and MWD, including number- and weight-average MW and polydispersity, were determined with respect to a secondary standard and then analyzed. All investigated vinegar samples were recognized as compositionally and structurally heterogeneous blends of copolymers (melanoidins) spreading over a wide range of molecular sizes: the relative MW ranged from 2 to >2000 kDa. The extent of the polymerization reactions was in agreement with the TBV browning kinetics. MWD parameters varied asymptotically toward either upper or lower limits during aging, reflecting a nonequilibrium status of the balance between polymerization and depolymerization reactions in TBV. MWD parameters were proposed as potential aging markers of TBV. PMID:18656930

  5. Mars: New Determination of Impact Crater Production Function Size Distribution

    NASA Astrophysics Data System (ADS)

    Hartmann, William K.

    2006-12-01

    Several authors have questioned our knowledge of Martian impact crater production function size-frequency distribution (PFSFD), especially at small diameters D. Plescia (2005) questioned whether any area of Mars shows size distributions used for estimating crater retention ages on Mars. McEwen et al. (2005) and McEwen and Bierhaus (2006) suggested existing PFSFD’s are hopelessly confused by the presence of secondaries, and that my isochrons give primary crater densities off by factors of several thousand at small D. In 2005, I addressed some of these concerns, noting my curves do not estimate primary crater densities per se, but show total numbers of primaries + semi-randomly “distant secondaries” (negating many McEwen et al. critiques). In 2006 I have conducted new crater counts on a PFSFD test area suggested by Ken Tanaka. This area shows young lava flows of similar crater density, west of Olympus Mons (around 30 deg N, 100 deg W). Multiple crater counts were made on several adjacent Odyssey THEMIS images and MGS MOC images, giving the SFD over a range of 11m

  6. Can vesicle size distributions predict eruption intensity during volcanic activity?

    NASA Astrophysics Data System (ADS)

    LaRue, A.; Baker, D. R.; Polacci, M.; Allard, P.; Sodini, N.

    2013-06-01

    We studied three-dimensional (3-D) vesicle size distributions by X-ray microtomography in scoria collected during the relatively quiescent Phase II of the 2010 eruption at Eyjafjallajökull volcano, Iceland. Our goal was to compare the vesicle size distributions (VSDs) measured in these samples with those found in Stromboli volcano, Italy. Stromboli was chosen because its VSDs are well-characterized and show a correlation with eruption intensity: typical Strombolian activity produces VSDs with power-law exponents near 1, whereas larger and more energetic Vulcanian-type explosions and Plinian eruptions produce VSDs with power-law exponents near 1.5. The hypothesis to be tested was whether or not the samples studied in this work would contain VSDs similar to normal Strombolian products, display higher power-law exponents, or be described by exponential functions. Before making this comparison we tested the hypothesis that the phreatomagmatic nature of the Eyjafjallajökull eruption might have a significant effect on the VSDs. We performed 1 atm bubble-growth experiments in which the samples were inundated with water and compared them to similar, control, experiments without water inundation. No significant differences between the VSDs of the two sets of experiments were found, and the hypothesis is not supported by the experimental evidence; therefore, VSDs of magmatic and phreatomagmatic eruptions can be directly compared. The Phase II Eyjafjallajökull VSDs are described by power law exponents of ~ 0.8, typical of normal Strombolian eruptions. The comparable VSDs and behavior of Phase II of the Eyjafjallajökull 2010 eruption to Stromboli are interpreted to be a reflection of similar conduit systems in both volcanoes that are being constantly fed by the ascent of deep magma that mixes with resident magma at shallow depths. Such behavior implies that continued activity during Phase II of the Eyjafjallajökull eruption could be expected and would have been predicted

  7. Dependence of SAW resonator 1/f noise on device size.

    PubMed

    Parker, T E

    1993-01-01

    Experiments were conducted with eight 450-MHz surface acoustic wave (SAW) resonators which demonstrate that a resonator's 1/f noise depends approximately inversely on the active acoustic area of the device. This observation is consistent with a proposed theory that 1/f noise in acoustic resonators is caused by localized velocity or dimensional fluctuations. PMID:18263254

  8. SILICATE DUST SIZE DISTRIBUTION FROM HYPERVELOCITY COLLISIONS: IMPLICATIONS FOR DUST PRODUCTION IN DEBRIS DISKS

    SciTech Connect

    Takasawa, S.; Nakamura, A. M.; Arakawa, M.; Seto, Y.; Sangen, K.; Setoh, M.; Machii, N.; Kadono, T.; Shigemori, K.; Hironaka, Y.; Fujioka, S.; Sano, T.; Watari, T.; Dohi, K.; Ohno, S.; Maeda, M.; Sakaiya, T.; Otani, K.; Takeuchi, T.

    2011-06-01

    Fragments generated by high-velocity collisions between solid planetary bodies are one of the main sources of new interplanetary dust particles. However, only limited ranges of collision velocity, ejecta size, and target materials have been studied in previous laboratory experiments, and the collision condition that enables the production of dust-sized particles remains unclear. We conducted hypervelocity impact experiments on silicate rocks at relative velocities of 9 to 61 km s{sup -1}, which is beyond the upper limit of previous laboratory studies. Sub-millimeter-diameter aluminum and gold spheres were accelerated by laser ablation and were shot into dunite and basalt targets. We analyzed the surfaces of aerogel blocks deployed near the targets using an electron probe micro analyzer and counted the number of particles that contained the target material. The size distributions of ejecta ranged from five to tens of microns in diameter. The total cross-sectional area of dust-sized ejecta monotonically increased with the projectile kinetic energy, independent of impact velocity, projectile diameter, and projectile and target material compositions. The slopes of the cumulative ejecta-size distributions ranged from -2 to -5. Most of the slopes were steeper than the -2.5 or -2.7 that is expected for a collisional equilibrium distribution in a collision cascade with mass-independent or mass-dependent catastrophic disruption thresholds, respectively. This suggests that the steep dust size-distribution proposed for the debris disk around HD172555 (an A5V star) could be due to a hypervelocity collision.

  9. Deposition Rate and Size Distribution of Volcanic Ash

    NASA Astrophysics Data System (ADS)

    Hikida, M.

    2006-12-01

    Sakurajima Volcano has been in violent activity since 1955 and erupting large amount of volcanic ash and stones from the crater. Volcanic fallouts have caused damages to the agricaltural products in the area and denuded the mountainside of vegitation. Deposited ash and stones on the mountainside has also caused hazardrous debris flows in the rivers. Therefore, it is necessary to know the deposition rate of the fallouts in prediction of debris flow. Due to the violent volcanic activity, however, it is prohibited to enter within two kilometers of the crater, making it impossible to measure the depth of deposited fallouts in the area. Theoretical study on deposition rate of volcanic fallouts should be needed to estimate the amount of fallouts in the upstream area. At first, motion of a particle erupted from the crater into the air was computed to examine its trajectory. From the simulation of the trajectory, a particle was assumed to fall at its terminal veloctity, and theoretical equation which give the deposition rate of volcanic ash and the distribution of deposited ash were obtained. In the derivation of these equations, the probability density functions of eruption column height, the terminal velocity of the erupted particles and the wind velocity were introduced. The computed values of amount of deposited ash show good agreement with the data taken from 93 collection points around Sakurajima Volcano. The annual amount of erupted volcanic ash was estimated to be about thirteen millions tons. The sample of deposited fallouts were taken to analize the size distribution. The data was also used to check the applicability of the theory presented.

  10. Population size and winter distribution of eastern American oystercatchers

    USGS Publications Warehouse

    Brown, S.C.; Schulte, Shiloh A.; Harrington, B.; Winn, Brad; Bart, J.; Howe, M.

    2005-01-01

    Conservation of the eastern subspecies of the American oystercatcher (Haematopus palliatus palliatus) is a high priority in the U.S. Shorebird Conservation Plan, but previous population estimates were unreliable, information on distribution and habitat associations during winter was incomplete, and methods for long-term monitoring had not been developed prior to this survey. We completed the aerial survey proposed in the U.S. Shorebird Conservation Plan to determine population size, winter distribution, and habitat associations. We conducted coastal aerial surveys from New Jersey to Texas during November 2002 to February 2003. This area comprised the entire wintering range of the eastern American oystercatcher within the United States. Surveys covered all suitable habitat in the United States for the subspecies, partitioned into 3 survey strata: known roost sites, high-use habitat, and inter-coastal tidal habitat. We determined known roost sites from extensive consultation with biologists and local experts in each state. High-use habitat included sand islands, sand spits at inlets, shell rakes, and oyster reefs. Partner organizations conducted ground counts in most states. We used high resolution still photography to determine detection rates for estimates of the number of birds in particular flocks, and we used ground counts to determine detection rates of flocks. Using a combination of ground and aerial counts, we estimated the population of eastern American oystercatchers to be 10,971 +/- 298. Aerial surveys can serve an important management function for shorebirds and possibly other coastal waterbirds by providing population status and trend information across a wide geographic scale.

  11. Microsphere size, precipitation kinetics and drug distribution control drug release from biodegradable polyanhydride microspheres.

    PubMed

    Berkland, Cory; Kipper, Matt J; Narasimhan, Balaji; Kim, Kyekyoon Kevin; Pack, Daniel W

    2004-01-01

    A thorough understanding of the factors affecting drug release mechanisms from surface-erodible polymer devices is critical to the design of optimal delivery systems. Poly(sebacic anhydride) (PSA) microspheres were loaded with three model drug compounds (rhodamine B, p-nitroaniline and piroxicam) with a range of polarities (water solubilities). The drug release profiles from monodisperse particles of three different sizes were compared to release from polydisperse microspheres. Each of the model drugs exhibited different release mechanisms. Drug distribution within the polymer was investigated by laser scanning confocal microscopy and scanning electron microscopy. Rhodamine, the most hydrophilic compound investigated, was localized strongly toward the microsphere surface, while the much more hydrophobic compound, piroxicam, distributed more evenly. Furthermore, all three compounds were most uniformly distributed in the smallest microspheres, most likely due to the competing effects of drug diffusion out of the nascent polymer droplets and the precipitation of polymer upon solvent extraction, which effectively "traps" the drug in the polymer matrix. The differing drug distributions were manifested in the drug release profiles. Rhodamine was released very quickly independent of microsphere size. Thus, extended release profiles may not be obtainable if the drug strongly redistributes in the microspheres. The release of p-nitroaniline was more prolonged, but still showed little dependence on microsphere size. Hence, when water-soluble drugs are encapsulated with hydrophobic polymers, it may be difficult to tailor release profiles by controlling microsphere size. The piroxicam-loaded microspheres exhibit the most interesting release profiles, showing that release duration can be increased by decreasing microsphere size, resulting in a more uniform drug distribution. PMID:14684277

  12. On the annual maximum distribution in dependent partial duration series

    NASA Astrophysics Data System (ADS)

    Rosbjerg, D.

    1987-03-01

    As a basis for development of the annual maximum distribution the so-called partial duration series with Poissonian occurrence times and exponentially distributed peak exceedance values has been selected. The model is generalized by allowing for a Markov dependence between succeeding peak values. Correlation values from p=0 to p=1 can be accounted for by introducing the Marshall-Olkin bivariate exponential distribution, which is presented in detail. The developed distribution function for the annual maximum is throughly analysed and a variety of distribution forms depending on the value of the correlation coefficient and the intensity in the Poisson process is hereby recognized. To a certain extent this might be considered as parallel to the scattering of hydrological regions with different generating mechanisms for the annual maxima.

  13. Carbon-based phytoplankton size classes retrieved via ocean color estimates of the particle size distribution

    NASA Astrophysics Data System (ADS)

    Kostadinov, T. S.; Milutinović, S.; Marinov, I.; Cabré, A.

    2015-05-01

    Owing to their important roles in biogeochemical cycles, phytoplankton functional types (PFTs) have been the aim of an increasing number of ocean color algorithms. Yet, none of the existing methods are based on phytoplankton carbon (C) biomass, which is a fundamental biogeochemical and ecological variable and the "unit of accounting" in Earth System models. We present a novel bio-optical algorithm to retrieve size-partitioned phytoplankton carbon from ocean color satellite data. The algorithm is based on existing algorithms to estimate particle volume from a power-law particle size distribution (PSD). Volume is converted to carbon concentrations using a compilation of allometric relationships. We quantify absolute and fractional biomass in three PFTs based on size - picophytoplankton (0.5-2 μm in diameter), nanophytoplankton (2-20 μm) and microphytoplankton (20-50 μm). The mean spatial distributions of total phytoplankton C biomass and individual PFTs, derived from global SeaWiFS monthly ocean color data, are consistent with current understanding of oceanic ecosystems, i.e. oligotrophic regions are characterized by low biomass and dominance of picoplankton, whereas eutrophic regions have large biomass to which nanoplankton and microplankton contribute relatively larger fractions. Global spatially integrated phytoplankton carbon biomass standing stock estimates using our PSD-based approach yield on average ~0.2-0.3 Gt of C, consistent with analogous estimates from two other ocean color algorithms, and several state-of-the-art Earth System models. However, the range of phytoplankton C biomass spatial variability globally is larger than estimated by any other models considered here, because the PSD-based algorithm is not a priori empirically constrained and introduces improvement over the assumptions of the other approaches. Satisfactory in situ closure observed between PSD and POC measurements lends support to the theoretical basis of the PSD-based algorithm

  14. Size-dependent bistability of an electrostatically actuated arch NEMS based on strain gradient theory

    NASA Astrophysics Data System (ADS)

    Tajaddodianfar, Farid; Nejat Pishkenari, Hossein; Hairi Yazdi, Mohammad Reza; Maani Miandoab, Ehsan

    2015-06-01

    This paper deals with the investigation of the size-dependent nature of nonlinear dynamics, in a doubly clamped shallow nano-arch actuated by spatially distributed electrostatic force. We employ strain gradient theory together with the Euler-Bernoulli and shallow arch assumptions in order to derive the nonlinear partial differential equation governing the transverse motion of the arch with mid-plane stretching effects. Using the Galerkin projection method, we derive the lumped single degree of freedom model which is then used for the study of the size effects on the nonlinear snap-through and pull-in instabilities of the arch nano-electro-mechanical-system (NEMS). Moreover, using strain gradient theory, the size-dependent bistability and fundamental frequencies of the nano-arch are scrutinized, revealing that, despite what is predicted by the classical theory, the bistability region in the parameter space of the nano-structure shrinks as the structure scales down. Also, we show that the minimum initial elevation, required for bistability, increases as the nano-arch scales down.

  15. Size-dependent thermo-electrical buckling analysis of functionally graded piezoelectric nanobeams

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Farzad; Salari, Erfan

    2015-12-01

    In the present study, thermo-electrical buckling characteristics of functionally graded piezoelectric (FGP) Timoshenko nanobeams subjected to in-plane thermal loads and applied electric voltage are carried out by presenting a Navier type solution for the first time. Three kinds of thermal loading, namely, uniform, linear and nonlinear temperature rises through the thickness direction are considered. Thermo-electro-mechanical properties of FGP nanobeam are supposed to vary smoothly and continuously throughout the thickness based on power-law model. Eringen’s nonlocal elasticity theory is exploited to describe the size dependency of nanobeam. Using Hamilton’s principle, the nonlocal governing equations together with corresponding boundary conditions based on Timoshenko beam theory are obtained for the thermal buckling analysis of graded piezoelectric nanobeams including size effect and they are solved applying analytical solution. According to the numerical results, it is revealed that the proposed modeling can provide accurate critical buckling temperature results of the FG nanobeams as compared some cases in the literature. In following a parametric study is accompanied to examine the effects of the several parameters such as various temperature distributions, external electric voltage, power-law index, nonlocal parameter and aspect ratio on the critical buckling temperature difference of the size-dependent FGP nanobeams in detail. It is found that the small scale effect and electrical loading have a significant effect on buckling temperatures of FGP nanobeams.

  16. Size-dependent electromechanical coupling behaviors of circular micro-plate due to flexoelectricity

    NASA Astrophysics Data System (ADS)

    Li, Anqing; Zhou, Shenjie; Qi, Lu

    2016-10-01

    In this paper, the flexoelectric theory is re-expressed by a set of orthogonal components of strain gradient tensor. The general formulations of flexoelectric theory in orthogonal curvilinear coordinates are derived and, then, are specified for the case of cylindrical coordinates. A flexoelectric circular micro-plate model is established based on the current formulations in cylindrical coordinates to evaluate its size-dependent static and dynamic responses. The governing equations, boundary conditions and initial conditions are obtained according to the Hamilton's principle. A static bending problem of simply supported axisymmetric circular micro-plate is solved in two cases, of which one is subjected to a distributed load and the other is subjected to a voltage across the plate thickness. And the free vibration problem of a simply supported circular micro-plate is also analyzed. The bending numerical results show that both the deflection and the electric potential exhibit obvious size dependency in the two cases. Both the induced electric potential in direct flexoelectric effect and the induced deflection in inverse flexoelectric effect decrease as the decrease in flexoelectric coefficient and even disappear when the flexoelectric coefficient equals zero. Moreover, the numerical results of free vibration demonstrate the dimensionless natural frequency shows obvious size effect, while the influence of flexoelectric coefficient on dimensionless natural frequency is negligible.

  17. 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

  18. Size dependence of magnetorheological properties of cobalt ferrite ferrofluid

    NASA Astrophysics Data System (ADS)

    Radhika, B.; Sahoo, Rasmita; Srinath, S.

    2015-06-01

    Cobalt Ferrite nanoparticles were synthesized using co-precipitation method at reaction temperatures of 40°C and 80°C. X-Ray diffraction studies confirm cubic phase formation. The average crystallite sizes were found to be ˜30nm and ˜48nm for 40°C sample and 80°C sample respectively. Magnetic properties measured using vibrating sample magnetometer show higher coercivety and magnetization for sample prepared at 80°C. Magnetorheological properties of CoFe2O4 ferrofluids were measured and studied.

  19. Size dependence of magnetorheological properties of cobalt ferrite ferrofluid

    SciTech Connect

    Radhika, B.; Sahoo, Rasmita; Srinath, S.

    2015-06-24

    Cobalt Ferrite nanoparticles were synthesized using co-precipitation method at reaction temperatures of 40°C and 80°C. X-Ray diffraction studies confirm cubic phase formation. The average crystallite sizes were found to be ∼30nm and ∼48nm for 40°C sample and 80°C sample respectively. Magnetic properties measured using vibrating sample magnetometer show higher coercivety and magnetization for sample prepared at 80°C. Magnetorheological properties of CoFe2O4 ferrofluids were measured and studied.

  20. Simulated airborne particle size distributions over Greenland during Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Unnerstad, Lars; Hansson, Margareta

    Polar ice cores indicate that the deposition of dust from the atmosphere was strongly enhanced during Last Glacial Maximum (LGM). The concentration of dust in the ice sheets and in the overlaying atmosphere are not proportional to each other but are dependent, among other things, on the relative magnitudes of dry and wet deposition which change with climate. Observed dust particle size distributions in the Greenland ice sheet are shifted toward larger particles during LGM. By applying common theories for particle removal processes we show that the airborne particle size distributions over Greenland probably remained the same in the two different climates. This leads to the conclusion that the airborne dust concentration was even higher during LGM than indicated by the enhancement in deposition flux. We suggest a LGM/pre-industrial current climate aerosol ratio (including the soluble fraction) over Greenland of about 90-125 by mass and 75-100 by number.

  1. Size-dependent absolute quantum yields for size-separated colloidally-stable silicon nanocrystals.

    PubMed

    Mastronardi, Melanie L; Maier-Flaig, Florian; Faulkner, Daniel; Henderson, Eric J; Kübel, Christian; Lemmer, Uli; Ozin, Geoffrey A

    2012-01-11

    Size-selective precipitation was used to successfully separate colloidally stable allylbenzene-capped silicon nanocrystals into several visible emitting monodisperse fractions traversing the quantum size effect range of 1-5 nm. This enabled the measurement of the absolute quantum yield and lifetime of photoluminescence of allylbenzene-capped silicon nanocrystals as a function of size. The absolute quantum yield and lifetime are found to monotonically decrease with decreasing nanocrystal size, which implies that nonradiative vibrational and surface defect effects overwhelm spatial confinement effects that favor radiative relaxation. Visible emission absolute quantum yields as high as 43% speak well for the development of "green" silicon nanocrystal color-tunable light emitting diodes that can potentially match the performance of their toxic heavy metal chalcogenide counterparts.

  2. Aerosol Size Distribution in a City Influenced by Both Rural and Urban Regions

    NASA Astrophysics Data System (ADS)

    Fitzgerald, R. M.; Polanco, J.; Lozano, A.

    2006-12-01

    Most atmospheric studies have focused on sites located in either rural or urban areas. However, there are regions affected by air from both, such as the city of El Paso. Adjacent to the neighboring city of Juarez, Mexico, and in close proximity to rural areas, it is affected by desert particles and both biogenic, anthropogenic emissions. Aerosol properties largely depend upon particle size and this makes it the most important parameter for characterizing the aerosol. We focus on studies using inverse reconstruction models for particle size distribution using aerosol optical depth data. Our methodology uses Twomey's regularization technique that suppresses ill-posedness by imposing smoothing and non-negativity constraints on the desired size distributions. We have also applied T-matrix codes to study the scattering from irregularly shaped particles that exhibit rotational symmetry. Furthermore, our studies include analysis of aerosol size distributions using optic probes and soot photometers, sampled from aircraft at different heights. This work will lead to better characterization of aerosols and their impact in our rural-urban interface region. In addition, it will provide a more accurate assessment of regional transport and better boundary conditions for air quality models.

  3. Size and spacial distribution of micropores in SBA-15 using CM-SANS

    SciTech Connect

    Pollock, Rachel A; Walsh, Brenna R; Fry, Jason A; Ghampson, Tyrone; Centikol, Ozgul; Melnichenko, Yuri B; Kaiser, Helmut; Pynn, Roger; Frederick, Brian G

    2011-01-01

    Diffraction intensity analysis of small-angle neutron scattering measurements of dry SBA-15 have been combined with nonlocal density functional theory (NLDFT) analysis of nitrogen desorption isotherms to characterize the micropore, secondary mesopore, and primary mesopore structure. The radial dependence of the scattering length density, which is sensitive to isolated surface hydroxyls, can only be modeled if the NLDFT pore size distribution is distributed relatively uniformly throughout the silica framework, not localized in a 'corona' around the primary mesopores. Contrast matching-small angle neutron scattering (CM-SANS) measurements, using water, decane, tributylamine, cyclohexane, and isooctane as direct probes of the size of micropores indicate that the smallest pores in SBA-15 have diameter between 5.7 and 6.2 {angstrom}. Correlation of the minimum pore size with the onset of the micropore size distribution provides direct evidence that the shape of the smallest micropores is cylinderlike, which is consistent with their being due to unraveling of the polymer template.

  4. Xenon porometry: a novel method for the derivation of pore size distributions.

    PubMed

    Telkki, Ville-Veikko; Lounila, Juhani; Jokisaari, Jukka

    2007-05-01

    Xenon porometry is a novel method used for characterizing porous materials by the (129)Xe nuclear magnetic resonance of xenon gas. With the method, the diffusion of gas is slowed down by immersing the material in a medium, which can be in liquid or solid state during measurements. Because of slow diffusion, the signal of a xenon atom is characteristic of the properties of only one pore, and the composite signal of all atoms represents the distribution of properties. The method is especially applicable for determining pore size distribution because the chemical shifts of two different xenon signals (one from liquid and the other from gas pockets in solid) are dependent on pore size. Therefore, the shapes of these signals represent pore size distribution function. In addition, the porosity of the material can be determined by comparing the intensities of two signals. This article focuses on describing xenon signals observed from gas pockets in a solid medium, which has turned out to be most convenient for pore size determination. PMID:17466763

  5. Variability of the raindrop size distribution at small spatial scales

    NASA Astrophysics Data System (ADS)

    Berne, A.; Jaffrain, J.

    2010-12-01

    Because of the interactions between atmospheric turbulence and cloud microphysics, the raindrop size distribution (DSD) is strongly variable in space and time. The spatial variability of the DSD at small spatial scales (below a few km) is not well documented and not well understood, mainly because of a lack of adequate measurements at the appropriate resolutions. A network of 16 disdrometers (Parsivels) has been designed and set up over EPFL campus in Lausanne, Switzerland. This network covers a typical operational weather radar pixel of 1x1 km2. The question of the significance of the variability of the DSD at such small scales is relevant for radar remote sensing of rainfall because the DSD is often assumed to be uniform within a radar sample volume and because the Z-R relationships used to convert the measured radar reflectivity Z into rain rate R are usually derived from point measurements. Thanks to the number of disdrometers, it was possible to quantify the spatial variability of the DSD at the radar pixel scale and to show that it can be significant. In this contribution, we show that the variability of the total drop concentration, of the median volume diameter and of the rain rate are significant, taking into account the sampling uncertainty associated with disdrometer measurements. The influence of this variability on the Z-R relationship can be non-negligible. Finally, the spatial structure of the DSD is quantified using a geostatistical tool, the variogram, and indicates high spatial correlation within a radar pixel.

  6. Regional variability of raindrop size distribution over Indonesia

    NASA Astrophysics Data System (ADS)

    Marzuki, M.; Hashiguchi, H.; Yamamoto, M. K.; Mori, S.; Yamanaka, M. D.

    2013-11-01

    Regional variability of raindrop size distribution (DSD) along the Equator was investigated through a network of Parsivel disdrometers in Indonesia. The disdrometers were installed at Kototabang (KT; 100.32° E, 0.20° S), Pontianak (PT; 109.37° E, 0.00° S), Manado (MN; 124.92° E, 1.55° N) and Biak (BK; 136.10° E, 1.18° S). It was found that the DSD at PT has more large drops than at the other three sites. The DSDs at the four sites are influenced by both oceanic and continental systems, and majority of the data matched the maritime-like DSD that was reported in a previous study. Continental-like DSDs were somewhat dominant at PT and KT. Regional variability of DSD is closely related to the variability of topography, mesoscale convective system propagation and horizontal scale of landmass. Different DSDs at different sites led to different Z-R relationships in which the radar reflectivity at PT was much larger than at other sites, at the same rainfall rate.

  7. Controllable microgels from multifunctional molecules: structure control and size distribution

    NASA Astrophysics Data System (ADS)

    Gu, Zhenyu; Patterson, Gary; Cao, Rong; Armitage, Bruce

    2004-03-01

    Supramolecular microgels with fractal structures were produced by engineered multifunctional molecules. The combination of static and dynamic light scattering was utilized to characterize the fractal dimension (Df) of the microgels and analyze the aggregation process of the microgels. The microgels are assembled from (1) a tetrafunctional protein (avidin), (2) a trifunctional DNA construct known as a three-way junction, and (3) a biotinylated peptide nucleic acid (PNA) that acts as a crosslinker by binding irreversibly to four equivalent binding sites on the protein and thermoreversibly to three identical binding sites on the DNA. The structure of microgels can be controlled through different aggregation mechanisms. The initial microgels formed by titration have a compact structure with Df ˜2.6; while the reversible microgels formed from melted aggregates have an open structure with Df ˜1.8. The values are consistent with the point-cluster and the cluster-cluster aggregation mechanisms, respectively. A narrow size distribution of microgels was observed and explained in terms of the Flory theory of reversible self-assembly.

  8. Size-dependent electrocatalytic activity of gold nanoparticles on HOPG and highly boron-doped diamond surfaces.

    PubMed

    Brülle, Tine; Ju, Wenbo; Niedermayr, Philipp; Denisenko, Andrej; Paschos, Odysseas; Schneider, Oliver; Stimming, Ulrich

    2011-12-06

    Gold nanoparticles were prepared by electrochemical deposition on highly oriented pyrolytic graphite (HOPG) and boron-doped, epitaxial 100-oriented diamond layers. Using a potentiostatic double pulse technique, the average particle size was varied in the range from 5 nm to 30 nm in the case of HOPG as a support and between < 1 nm and 15 nm on diamond surfaces, while keeping the particle density constant. The distribution of particle sizes was very narrow, with standard deviations of around 20% on HOPG and around 30% on diamond. The electrocatalytic activity towards hydrogen evolution and oxygen reduction of these carbon supported gold nanoparticles in dependence of the particle sizes was investigated using cyclic voltammetry. For oxygen reduction the current density normalized to the gold surface (specific current density) increased for decreasing particle size. In contrast, the specific current density of hydrogen evolution showed no dependence on particle size. For both reactions, no effect of the different carbon supports on electrocatalytic activity was observed.

  9. Evolution of density- and patch-size-dependent dispersal rates.

    PubMed Central

    Poethke, Hans Joachim; Hovestadt, Thomas

    2002-01-01

    Based on a marginal value approach, we derive a nonlinear expression for evolutionarily stable (ES) dispersal rates in a metapopulation with global dispersal. For the general case of density-dependent population growth, our analysis shows that individual dispersal rates should decrease with patch capacity and-beyond a certain threshold-increase with population density. We performed a number of spatially explicit, individual-based simulation experiments to test these predictions and to explore further the relevance of variation in the rate of population increase, density dependence, environmental fluctuations and dispersal mortality on the evolution of dispersal rates. They confirm the predictions of our analytical approach. In addition, they show that dispersal rates in metapopulations mostly depend on dispersal mortality and inter-patch variation in population density. The latter is dominantly driven by environmental fluctuations and the rate of population increase. These conclusions are not altered by the introduction of neighbourhood dispersal. With patch capacities in the order of 100 individuals, kin competition seems to be of negligible importance for ES dispersal rates except when overall dispersal rates are low. PMID:11916481

  10. Effect of the slope and initial moisture content on soil loss, aggregate and particle size distribution

    NASA Astrophysics Data System (ADS)

    Szabó, Judit Alexandra; Jakab, Gergely; Szabó, Boglárka

    2015-04-01

    Soil structure degradation has effect through the soil water balance and nutrient supply on the agricultural potential of an area. The soil erosion process comprises two phases: detachment and transport by water. To study the transport phase nozzle type laboratory-scale rainfall simulator was used with constant 80 mmhr-1 intensity on an arable haplic Cambisol. Measuring the aggregate and particle size distribution of the soil loss gives a good approach the erosion process. The primary objective of this study was to examine the sediment concentration, and detect the quality and quantity change of the soil loss during a single precipitation under six treatment combinations (recently tilled and crusty soil surface on two different slope steepness, inland inundation and drought soil conditions). Soil loss were collected continually, and separated per aggregate size fractions with sieves in three rounds during a rain to measure the weights. The particle size distribution was measured with Horiba LA-950 particle size analyzer. In general the ratio of the macro aggregates decreases and the ratio of the micro aggregates and clay fraction increases in the sediment with time during the precipitation due to the raindrop impact. Sediment concentration depends on the slope steepness, as from steeper slopes the runoff can transport bigger amount of sediment, but from the tilled surface bigger aggregates were washing down. Micro aggregate fraction is one of the indicators of good soil structure. The degradation of micro aggregates occurs in steeper slopes and the most erosive time period depends on the micromorphology of the surface. And while the aggregate size distribution of the soil loss of the treatments shows high variety of distribution and differs from the original soil, the particle size distribution of each aggregate size fraction shows similar trends except the 50-250 µm fraction where the fine sand fraction is dominating instead of the loam. This anomaly may be

  11. Size dependence of phosphorus doping in silicon nanocrystals

    NASA Astrophysics Data System (ADS)

    He, Wei; Li, Zhengping; Wen, Chao; Liu, Hong; Shen, Wenzhong

    2016-10-01

    Doping of silicon nanocrystals (Si-NCs) is one of the major challenges for silicon nanoscale devices. In this work, phosphorus (P) doping in Si-NCs which are embedded within an amorphous silicon matrix is realized together with the growth of Si-NCs by plasma-enhanced chemical vapor deposition under a tunable substrate direct current (DC) bias. The variation of phosphorus concentration with substrate bias can be explained by the competition of bonding processes of Si–Si and P–Si bonds. The formation of Si–Si and P–Si bonds is differently influenced by the ion bombardment controlled by the substrate bias, due to their bonding energy difference. We have studied the influences of grain size on P doping in Si-NCs. Free carrier concentration, which is provided by activated P atoms, decreases with decreasing grain size due to increasing formation energy and activation energy of P atoms incorporated in Si-NCs. Furthermore, we have studied the P locations inside Si-NCs and hydrogen passivation of P in the form of P–Si–H complexes using the first-principles method. Hydrogen passivation of P can also contribute to the reduced free carrier concentration in smaller Si-NCs. These results provide valuable understanding of P doping in Si-NCs.

  12. Size-dependent water structures in carbon nanotubes.

    PubMed

    Ohba, Tomonori

    2014-07-28

    Water surrounded by hydrophobic interfaces affects a variety of chemical reactions and biological activities. Carbon nanotubes (CNTs) can be used to investigate the behavior of water at hydrophobic interfaces. Here, we determined the fundamental unit of water by evaluating the ice-like cluster formation of water in the limited hydrophobic nanospaces of CNTs, using X-ray diffraction and molecular simulation analysis. The water in CNTs with a diameter of 1 nm had fewer hydrogen bonds than bulk water under ambient conditions. In CNTs with diameters of 2 and 3 nm, water formed nanoclusters even under ambient conditions, because of prolific hydrogen bonding; predominant ice-like cluster formation was induced in the 2-3 nm nanospaces. The results confirming the cluster formation in the CNTs also demonstrated that the critical cluster size was 0.8-3.4 nm. The fundamental cluster size was 0.8 nm; these results indicated that 0.8 nm clusters are the fundamental units of water assemblies.

  13. Size dependence of phosphorus doping in silicon nanocrystals.

    PubMed

    He, Wei; Li, Zhengping; Wen, Chao; Liu, Hong; Shen, Wenzhong

    2016-10-21

    Doping of silicon nanocrystals (Si-NCs) is one of the major challenges for silicon nanoscale devices. In this work, phosphorus (P) doping in Si-NCs which are embedded within an amorphous silicon matrix is realized together with the growth of Si-NCs by plasma-enhanced chemical vapor deposition under a tunable substrate direct current (DC) bias. The variation of phosphorus concentration with substrate bias can be explained by the competition of bonding processes of Si-Si and P-Si bonds. The formation of Si-Si and P-Si bonds is differently influenced by the ion bombardment controlled by the substrate bias, due to their bonding energy difference. We have studied the influences of grain size on P doping in Si-NCs. Free carrier concentration, which is provided by activated P atoms, decreases with decreasing grain size due to increasing formation energy and activation energy of P atoms incorporated in Si-NCs. Furthermore, we have studied the P locations inside Si-NCs and hydrogen passivation of P in the form of P-Si-H complexes using the first-principles method. Hydrogen passivation of P can also contribute to the reduced free carrier concentration in smaller Si-NCs. These results provide valuable understanding of P doping in Si-NCs. PMID:27632417

  14. Size dependence of phosphorus doping in silicon nanocrystals.

    PubMed

    He, Wei; Li, Zhengping; Wen, Chao; Liu, Hong; Shen, Wenzhong

    2016-10-21

    Doping of silicon nanocrystals (Si-NCs) is one of the major challenges for silicon nanoscale devices. In this work, phosphorus (P) doping in Si-NCs which are embedded within an amorphous silicon matrix is realized together with the growth of Si-NCs by plasma-enhanced chemical vapor deposition under a tunable substrate direct current (DC) bias. The variation of phosphorus concentration with substrate bias can be explained by the competition of bonding processes of Si-Si and P-Si bonds. The formation of Si-Si and P-Si bonds is differently influenced by the ion bombardment controlled by the substrate bias, due to their bonding energy difference. We have studied the influences of grain size on P doping in Si-NCs. Free carrier concentration, which is provided by activated P atoms, decreases with decreasing grain size due to increasing formation energy and activation energy of P atoms incorporated in Si-NCs. Furthermore, we have studied the P locations inside Si-NCs and hydrogen passivation of P in the form of P-Si-H complexes using the first-principles method. Hydrogen passivation of P can also contribute to the reduced free carrier concentration in smaller Si-NCs. These results provide valuable understanding of P doping in Si-NCs.

  15. Size and rate dependent necking in thin metallic films

    NASA Astrophysics Data System (ADS)

    Pardoen, T.

    2014-01-01

    The control of the ductility of thin metallic films is a major issue in a variety of technologies involving flexible electronics, MEMS and deformable coatings. An enhanced closed form 1D imperfection based localization analysis is developed in order to investigate the mechanics of diffuse necking in metallic films. The model relies on a description of the localization process in a finite length specimen using either a 2- or 3-zone model, under plane stress or plane strain tension conditions. A strain gradient plasticity contribution to the stabilization of the localization process is taken into account in the hardening response through a simple estimate of the deformation gradient inside the necking zone. The model, with gradient plasticity effects, is validated towards 2D finite element simulations. The response of the material involves both strain-hardening and rate sensitivity, as well as possible creep relaxation. The plastic flow parameters are related to the grain size and film thickness. The model shows, in agreement with experiments, that the ductility can either drop to small values for very small grain sizes and/or film thickness due to the high strength and to the presence of imperfections, or can remain constant or even increase owing to an increased rate sensitivity resulting from thermally activated mechanisms. This last stabilization effect can be reinforced by gradient plasticity effects if allowed by the dominant deformation mechanism.

  16. Distributed energy storage: Time-dependent tree flow design

    NASA Astrophysics Data System (ADS)

    Bejan, A.; Ziaei, S.; Lorente, S.

    2016-05-01

    This article proposes "distributed energy storage" as a basic design problem of distributing energy storage material on an area. The energy flows by fluid flow from a concentrated source to points (users) distributed equidistantly on the area. The flow is time-dependent. Several scenarios are analyzed: sensible-heat storage, latent-heat storage, exergy storage vs energy storage, and the distribution of a finite supply of heat transfer surface between the source fluid and the distributed storage material. The chief conclusion is that the finite amount of storage material should be distributed proportionally with the distribution of the flow rate of heating agent arriving on the area. The total time needed by the source stream to "invade" the area is cumulative (the sum of the storage times required at each storage site) and depends on the energy distribution paths and the sequence in which the users are served by the source stream. Directions for future designs of distributed storage and retrieval are outlined in the concluding section.

  17. Influence of size distribution and field amplitude on specific loss power

    NASA Astrophysics Data System (ADS)

    Boskovic, M.; Goya, G. F.; Vranjes-Djuric, S.; Jovic, N.; Jancar, B.; Antic, B.

    2015-03-01

    Herein we present the results of specific loss power (SLP) analysis of polydisperse water based ferrofluids, Fe3O4/PEG200 and Fe3O4/PEG6000, with average Fe3O4 particle size of 9 nm and 11 nm, respectively. Specific loss power was measured in alternating magnetic field of various amplitudes and at fixed frequency of 580.5 kHz. Maximum SLP values acquired were 195 W/g for Fe3O4/PEG200 and 60 W/g for Fe3O4/PEG6000 samples. The samples were labeled as superparamagnetic by magnetization measurements, but SLP field dependence showed deviation from the behavior predicted by the commonly employed linear response theory. The scope of this theory for both samples with wide particle size distribution is discussed. Deviation from the expected behavior is explained by referring to polydisperse nature of the samples and field dependent relaxation rates.

  18. Size-dependent knockdown potential of siRNA-loaded cationic nanohydrogel particles.

    PubMed

    Nuhn, Lutz; Tomcin, Stephanie; Miyata, Kanjiro; Mailänder, Volker; Landfester, Katharina; Kataoka, Kazunori; Zentel, Rudolf

    2014-11-10

    To overcome the poor pharmacokinetic conditions of short double-stranded RNA molecules in RNA interference therapies, cationic nanohydrogel particles can be considered as alternative safe and stable carriers for oligonucleotide delivery. For understanding key parameters during this process, two different types of well-defined cationic nanohydrogel particles were synthesized, which provided nearly identical physicochemical properties with regards to their material composition and resulting siRNA loading characteristics. Yet, according to the manufacturing process using amphiphilic reactive ester block copolymers of pentafluorophenyl methacrylate (PFPMA) and tri(ethylene glycol)methyl ether methacrylate (MEO3MA) with similar compositions but different molecular weights, the resulting nanohydrogel particles differed in size after cross-linking with spermine (average diameter 40 vs 100 nm). This affected their knockdown potential significantly. Only the 40 nm sized cationic nanogel particles were able to generate moderate gene knockdown levels, which lasted, however, up to 3 days. Interestingly, primary cell uptake and colocalization studies with lysosomal compartments revealed that only these small sized nanogels were able to avoid acidic compartments of endolysosomal uptake pathways, which may contribute to their knockdown ability exclusively. To that respect, this size-dependent intracellular distribution behavior may be considered as an essential key parameter for tuning the knockdown potential of siRNA nanohydrogel particles, which may further contribute to the development of advanced siRNA carrier systems with improved knockdown potential.

  19. CaCO3 size distribution: A paleocarbonate ion proxy?

    NASA Astrophysics Data System (ADS)

    Broecker, W. S.; Clark, E.

    1999-10-01

    Lysocline reconstructions play an important role in scenarios purporting to explain the lowered atmospheric CO2 content of glacial time. These reconstructions are based on indicators such as the CaCO3 content, the percent of coarse fraction, the ratio of fragments to whole foraminifera shells, the ratio of solution-susceptible to solution-resistant species, and the ratio of coarse to fine CaCO3. All assume that changes with time in the composition of the input material do not bias the result. However, as the composition of the input material does depend on climate, none of these indicators provides an absolute measure of the extent of dissolution. In this paper we evaluate the reliability of the ratio of >63 µm CaCO3 to total CaCO3 as a dissolution indicator. We present here results that suggest that in today's tropics this ratio appears to be determined solely by CO3= ion concentration and water depth (i.e., the saturation state of bottom waters). This finding offers the possibility that the size fraction index can be used to reconstruct CO3= ion concentrations for the late Quaternary ocean to an accuracy of ±5 µmol kg-1.

  20. Influence of load on particle size distribution of lactose-crystalline cellulose mixed powder.

    PubMed

    Nakamori, Takahiko; Miyagishim, Atsuo; Nozawa, Yasuo; Sadzuka, Yasuyuki; Sonobe, Takashi

    2008-04-16

    Effects of loads applied to a powdery layer of a mixture of lactose and crystalline cellulose (granules) on the microparticle formation were evaluated. In a 1:1 mixture, the number of particles size, 20 microm or smaller in diameter, was reduced under loading compared with the standard value. It tended to increase with increasing ratio of lactose. In samples with a particle size of 350 microm or less, the shear friction coefficient increased with increase in the load, reached a peak at a mixing ratio of 50%, and decreased with increase in the mixing ratio. These changes were similar to those of the number of particles 20 microm or smaller. These results suggest that particle formation and aggregation under loads are dependent on the mixing rate and that there is a range of mixing rates in which no changes in the particle size distribution are observed.

  1. Field size dependent mapping of medical linear accelerator radiation leakage.

    PubMed

    Bezin, Jérémi Vũ; Veres, Attila; Lefkopoulos, Dimitri; Chavaudra, Jean; Deutsch, Eric; de Vathaire, Florent; Diallo, Ibrahima

    2015-03-01

    The purpose of this study was to investigate the suitability of a graphics library based model for the assessment of linear accelerator radiation leakage. Transmission through the shielding elements was evaluated using the build-up factor corrected exponential attenuation law and the contribution from the electron guide was estimated using the approximation of a linear isotropic radioactive source. Model parameters were estimated by a fitting series of thermoluminescent dosimeter leakage measurements, achieved up to 100 cm from the beam central axis along three directions. The distribution of leakage data at the patient plane reflected the architecture of the shielding elements. Thus, the maximum leakage dose was found under the collimator when only one jaw shielded the primary beam and was about 0.08% of the dose at isocentre. Overall, we observe that the main contributor to leakage dose according to our model was the electron beam guide. Concerning the discrepancies between the measurements used to calibrate the model and the calculations from the model, the average difference was about 7%. Finally, graphics library modelling is a readily and suitable way to estimate leakage dose distribution on a personal computer. Such data could be useful for dosimetric evaluations in late effect studies.

  2. Particle size distribution of rice flour affecting the starch enzymatic hydrolysis and hydration properties.

    PubMed

    de la Hera, Esther; Gomez, Manuel; Rosell, Cristina M

    2013-10-15

    Rice flour is becoming very attractive as raw material, but there is lack of information about the influence of particle size on its functional properties and starch digestibility. This study evaluates the degree of dependence of the rice flour functional properties, mainly derived from starch behavior, with the particle size distribution. Hydration properties of flours and gels and starch enzymatic hydrolysis of individual fractions were assessed. Particle size heterogeneity on rice flour significantly affected functional properties and starch features, at room temperature and also after gelatinization; and the extent of that effect was grain type dependent. Particle size heterogeneity on rice flour induces different pattern in starch enzymatic hydrolysis, with the long grain having slower hydrolysis as indicated the rate constant (k). No correlation between starch digestibility and hydration properties or the protein content was observed. It seems that in intact granules interactions with other grain components must be taken into account. Overall, particle size fractionation of rice flour might be advisable for selecting specific physico-chemical properties.

  3. System Size, Energy, Pseudorapidity, and Centrality Dependence of Elliptic Flow

    SciTech Connect

    Alver, B.; Ballintijn, M.; Busza, W.; Decowski, M. P.; Gulbrandsen, K.; Henderson, C.; Kane, J. L.; Kulinich, P.; Li, W.; Loizides, C.; Reed, C.; Roland, C.; Roland, G.; Stephans, G. S. F.; Vale, C.; Nieuwenhuizen, G. J. van; Vaurynovich, S. S.; Verdier, R.; Veres, G. I.; Wenger, E.

    2007-06-15

    This Letter presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider. The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events. For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects. A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.

  4. Pore size distribution and supercritical hydrogen adsorption in activated carbon fibers.

    PubMed

    Purewal, J J; Kabbour, H; Vajo, J J; Ahn, C C; Fultz, B

    2009-05-20

    Pore size distributions (PSD) and supercritical H2 isotherms have been measured for two activated carbon fiber (ACF) samples. The surface area and the PSD both depend on the degree of activation to which the ACF has been exposed. The low-surface-area ACF has a narrow PSD centered at 0.5 nm, while the high-surface-area ACF has a broad distribution of pore widths between 0.5 and 2 nm. The H2 adsorption enthalpy in the zero-coverage limit depends on the relative abundance of the smallest pores relative to the larger pores. Measurements of the H2 isosteric adsorption enthalpy indicate the presence of energy heterogeneity in both ACF samples. Additional measurements on a microporous, coconut-derived activated carbon are presented for reference.

  5. Partial slip in mesoscale contacts: dependence on contact size.

    PubMed

    Hanke, Sylvia; Petri, Judith; Johannsmann, Diethelm

    2013-09-01

    Using acoustic resonators, we have studied the occurrence and the magnitude of partial slip between glass spheres and polymer surfaces. The measurement relies on the shifts of resonance frequency and bandwidth, Δf and ΔΓ, induced by the contact as well as the dependence of Δf and ΔΓ on the amplitude of oscillation. One often finds a decrease of Δf at elevated amplitudes, which goes back to partial slip (also "microslip"). Building on two different models of partial slip, we derive the frequency-amplitude relation from the force-displacement relation. In accordance with both models, the bandwidth is found to increase with amplitude in the partial slip regime. For the highest amplitudes and largest spheres investigated, one observes a decrease of bandwidth with amplitude, which is interpreted as a transition to gross slip. Deviating from both models of partial slip, Δf is sometimes found to be independent of amplitude in the low-amplitude range. Constant Δf implies linear force-displacement relations. The critical amplitude for the onset of partial slip depends on the contact radius, where partial slip is more pronounced for larger contacts. This finding can be explained by a smooth stress profile at the edge of the contact with no singularity. The stress at the edge might be lowered by nanoscale roughness, by capillary forces, or by the inability of the two surfaces to reestablish a sticking contact at the turning point of the oscillation.

  6. Optimal Estimation Retrieval of Cloud Ice Particle Size Distributions

    NASA Astrophysics Data System (ADS)

    Griffith, B. D.; Kummerow, C.

    2006-12-01

    An optimal estimation retrieval technique has been applied to a multi-frequency airborne radar and radiometer data set from the Wakasa Bay AMSR-E validation experiment. First, airborne radar observations at 13.4, 35.6 and 94.9 GHz were integrated to retrieve all three parameters of a normalized gamma ice particle size distribution (PSD). The retrieved PSD was validated against near-simultaneous in situ cloud probe observations. The differences between the retrieved and in situ measured PSDs were explored through sensitivity analysis, and the sources of uncertainty were found to be the bulk density of the cloud ice and the aspect ratio of aspherical particles modeled as oblate spheroids. The optimal estimation technique was then applied to select an optimal density and aspect ratio for the cloud under study through integration of the in situ and radar observations. The optimal ice size-density relationship was found to be ρ(D)=0.07×D^{- 1.58} g cm-3 where the diameter, D, is in mm, and the oblate spheroid aspect ratio was found to be 0.53. The use of these optimal values, as improved assumptions in the PSD retrieval, reduced the uncertainty in the optimized forward model from ± 6 dB to ± 2 dB. Next, the retrieval technique was expanded to include passive microwave observations and retrieve a full column vertical hydrometeor profile. Eleven airborne passive microwave frequencies from 10.7 to 340 GHz were integrated with the airborne radar observations to retrieve all three parameters of a normalized gamma PSD at each vertical level in the column. The retrieved vertical profile was validated against a clear sky scene before being applied to the horizontal extent of an ice cloud. The retrieved PSD showed vertical structure consistent with cloud microphysical processes. PSDs were retrieved using both the general and improved assumption case-specific density and shape models. A comparison revealed an order of magnitude difference in ice water path between the two

  7. Predicting predation through prey ontogeny using size-dependent functional response models.

    PubMed

    McCoy, Michael W; Bolker, Benjamin M; Warkentin, Karen M; Vonesh, James R

    2011-06-01

    The functional response is a critical link between consumer and resource dynamics, describing how a consumer's feeding rate varies with prey density. Functional response models often assume homogenous prey size and size-independent feeding rates. However, variation in prey size due to ontogeny and competition is ubiquitous, and predation rates are often size dependent. Thus, functional responses that ignore prey size may not effectively predict predation rates through ontogeny or in heterogeneous populations. Here, we use short-term response-surface experiments and statistical modeling to develop and test prey size-dependent functional responses for water bugs and dragonfly larvae feeding on red-eyed treefrog tadpoles. We then extend these models through simulations to predict mortality through time for growing prey. Both conventional and size-dependent functional response models predicted average overall mortality in short-term mixed-cohort experiments, but only the size-dependent models accurately captured how mortality was spread across sizes. As a result, simulations that extrapolated these results through prey ontogeny showed that differences in size-specific mortality are compounded as prey grow, causing predictions from conventional and size-dependent functional response models to diverge dramatically through time. Our results highlight the importance of incorporating prey size when modeling consumer-prey dynamics in size-structured, growing prey populations. PMID:21597252

  8. One Size Does Not Fit All: The Impact of Primary Vaccine Container Size on Vaccine Distribution and Delivery

    PubMed Central

    Haidari, Leila A.; Wahl, Brian; Brown, Shawn T.; Privor-Dumm, Lois; Wallman-Stokes, Cecily; Gorham, Katie; Connor, Diana L.; Wateska, Angela R.; Schreiber, Benjamin; Dicko, Hamadou; Jaillard, Philippe; Avella, Melanie; Lee, Bruce Y.

    2015-01-01

    BACKGROUND While the size and type of a vaccine container (i.e., primary container) can have many implications on the safety and convenience of a vaccination session, another important but potentially overlooked consideration is how the design of the primary container may affect the distribution of the vaccine, its resulting cost, and whether the vial is ultimately opened. METHODS Using our HERMES software platform, we developed a simulation model of the World Health Organization Expanded Program on Immunization supply chain for the Republic of Benin and used the model to explore the effects of different primary containers for various vaccine antigens. RESULTS Replacing vaccines with presentations containing fewer doses per vial reduced vaccine availability (proportion of people arriving for vaccines who are successfully immunized) by as much as 13% (from 73% at baseline) and raised logistics costs by up to $0.06 per dose administered (from $0.25 at baseline) due to increased bottlenecks, while reducing total costs by as much as $0.15 per dose administered (from $2.52 at baseline) due to lower open vial wastage. Primary containers with a greater number of doses per vial each improved vaccine availability by 19% and reduced logistics costs by $0.05 per dose administered, while raising the total costs by up to $0.25 per dose administered due to greater vaccine procurement needs. Changes in supply chain performance were more extreme in departments with greater constraints. Implementing a vial opening threshold reversed the direction of many of these effects. CONCLUSIONS Our results show that one size may not fit all when choosing a primary vaccine container. Rather, the choice depends on characteristics of the vaccine, the vaccine supply chain, immunization session size, and goals of decision-makers. In fact, the optimal vial size may vary among locations within a country. Simulation modeling can help identify tailored approaches to improve availability and efficiency

  9. Lung deposited surface area size distributions of particulate matter in different urban areas

    NASA Astrophysics Data System (ADS)

    Kuuluvainen, Heino; Rönkkö, Topi; Järvinen, Anssi; Saari, Sampo; Karjalainen, Panu; Lähde, Tero; Pirjola, Liisa; Niemi, Jarkko V.; Hillamo, Risto; Keskinen, Jorma

    2016-07-01

    Lung deposited surface area (LDSA) concentration is considered as a relevant metric for the negative health effects of aerosol particles. We report for the first time the size distributions of the LDSA measured in urban air. The measurements were carried out in the metropolitan area of Helsinki, including mobile laboratory and stationary measurements in different outdoor environments, such as traffic sites, a park area, the city center and residential areas. The main instrument in this study was an electrical low pressure impactor (ELPI), which was calibrated in the field to measure the LDSA concentration. The calibration factor was determined to be 60 μm2/(cm3 pA). In the experiments, the LDSA size distributions were found to form two modes at the traffic sites and in the city center. Both of these traffic related particle modes, the nucleation mode and the soot mode, had a clear contribution to the total LDSA concentration. The average total concentrations varied from 12 to 94 μm2/cm3, measured in the park area and at the traffic site next to a major road, respectively. The LDSA concentration was found to correlate with the mass of fine particles (PM2.5), but the relation of these two metrics varied between different environments, emphasizing the influence of traffic on the LDSA. The results of this study provide valuable information on the total concentrations and size distributions of the LDSA for epidemiological studies. The size distributions are especially important in estimating the contribution of outdoor concentrations on the concentrations inside buildings and vehicles through size-dependent penetration factors.

  10. Characterizing the particle size distribution of Saturn's A ring with Cassini UVIS occultation data

    NASA Astrophysics Data System (ADS)

    Becker, Tracy M.; Colwell, Joshua E.; Esposito, Larry W.; Bratcher, Allison D.

    2016-11-01

    Stellar occultation data from Cassini's Ultraviolet Imaging Spectrograph (UVIS) have revealed diffraction spikes near sharp edges in Saturn's rings. The UVIS High Speed Photometer (HSP) observes these spikes as signals at ring edges that surpass measurements of the unocculted stellar signal. In Saturn's A ring, diffracted light can augment the direct stellar signal by up to 6% and can be detected tens of kilometers radially from the edge. The radial profile of the diffraction signal is dependent on the size distribution of the particle population near the ring edge. These diffraction signals are clearly observed at sharp edges throughout Saturn's ring system. In this paper we focus on the clearest detections at the outer edge of the A ring and at the edges of the Encke Gap. We present a forward model in which we reconstruct the spacecraft's observations for each stellar occultation by ring edges. The model produces a synthetic diffraction signal for a given truncated power-law particle size distribution, which we compare with the observed signal. We find an overall steepening of the power-law size distribution and a decrease in the minimum particle size at the outer edge of the A ring when compared with the Encke Gap edges. This suggests that interparticle collisions caused by satellite perturbations in the region result in more shedding of regolith or fragmentation of particles in the outermost parts of the A ring. We rule out any significant population of sub-millimeter-sized particles in Saturn's A ring, placing a lower limitation of 1-mm on the minimum particle size in the ring.

  11. Numerical simulation and sensitivity analysis of detailed soot particle size distribution in laminar premixed ethylene flames

    SciTech Connect

    Singh, Jasdeep; Patterson, Robert I.A.; Kraft, Markus; Wang, Hai

    2006-04-15

    In this paper, the prediction of a soot model [J. Appel, H. Bockhorn, M. Frenklach, Combust. Flame 121 (2000) 122-136] is compared to a recently published set of highly detailed soot particle size distributions [B. Zhao, Z. Yang, Z. Li, M.V. Johnston, H. Wang, Proc. Combust. Inst. 30 (2005)]. A stochastic approach is used to obtain soot particle size distributions (PSDs). The key features of the measured and simulated particle size distributions are identified and used as a simple way of comparing PSDs. The sensitivity of the soot PSDs to the parameters defining parts of the soot model, such as soot inception, particle and PAH collision efficiency and enhancement, and surface activity is investigated. Incepting soot particle size is found to have a very significant effect on the small-size end of the PSDs, especially the position of the trough for a bimodal soot PSDs. A new model for the decay in the surface activity is proposed in which the activity of the soot particle depends only on the history of that particle and the local temperature in the flame. This is a first attempt to use local flame variables to define the surface aging which has major impact on the prediction of the large-size end of the PSDs. Using these modifications to the soot model it is possible to improve the agreement between some of the points of interest in the simulated and measured PSDs. The paper achieves the task to help advance the soot models to predict soot PSD in addition to soot volume fraction and number density, which has been the focus of the literature. (author)

  12. Size-dependent color tuning of efficiently luminescent germanium nanoparticles.

    PubMed

    Shirahata, Naoto; Hirakawa, Daigo; Masuda, Yoshitake; Sakka, Yoshio

    2013-06-18

    It is revealed that rigorous control of the size and surface of germanium nanoparticles allows fine color tuning of efficient fluorescence emission in the visible region. The spectral line widths of each emission were very narrow (<500 meV). Furthermore, the absolute fluorescence quantum yields of each emission were estimated to be 4-15%, which are high enough to be used as fluorescent labeling tags. In this study, a violet-light-emitting nanoparticle is demonstrated to be a new family of luminescent Ge. Such superior properties of fluorescence were observed from the fractions separated from one mother Ge nanoparticle sample by the fluorescent color using our developed combinatorial column technique. It is commonly believed that a broad spectral line width frequently observed from Ge nanoparticle appears because of an indirect band gap nature inherited even in nanostructures, but the present study argues that such a broad luminescence spectrum is expressed as an ensemble of different spectral lines and can be separated into the fractions emitting light in each wavelength region by the appropriate postsynthesis process.

  13. The temperature size rule in arthropods: independent of macro-environmental variables but size dependent.

    PubMed

    Klok, C Jaco; Harrison, Jon F

    2013-10-01

    Temperature is a key factor that affects the rates of growth and development in animals, which ultimately determine body size. Although not universal, a widely documented and poorly understood pattern is the inverse relationship between the temperature at which an ectothermic animal is reared and its body size (temperature size rule [TSR]). The proximate and ultimate mechanisms for the TSR remain unclear. To explore possible explanations for the TSR, we tested for correlations between the magnitude/direction of the TSR and latitude, temperature, elevation, habitat, availability of oxygen, capacity for flight, and taxonomic grouping in 98 species/populations of arthropods. The magnitude and direction of the TSR was not correlated with any of the macro-environmental variables we examined, supporting the generality of the TSR. However, body size affected the magnitude and direction of the TSR, with smaller arthropods more likely to demonstrate a classic TSR. Considerable variation among species exists in the TSR, suggesting either strong interactions with nutrition, or selection based on microclimatic or seasonal variation not captured in classic macro-environmental variables.

  14. Moments of nucleon spin-dependent generalized parton distributions

    SciTech Connect

    Wolfram Schroers; Richard Brower; Patrick Dreher; Robert Edwards; George Fleming; P. Hagler; Urs Heller; Thomas Lippert; John Negele; Andrew Pochinsky; Dru Renner; David Richards; Klaus Schilling

    2004-03-01

    We present a lattice measurement of the first two moments of the spin-dependent GPD H-tilde(x,xi,t). From these we obtain the axial coupling constant and the second moment of the spin-dependent forward parton distribution. The measurements are done in full QCD using Wilson fermions. In addition, we also present results from a first exploratory study of full QCD using Asqtad sea and domain-wall valence fermions.

  15. Size-distribution analysis of proteins by analytical ultracentrifugation: strategies and application to model systems.

    PubMed Central

    Schuck, Peter; Perugini, Matthew A; Gonzales, Noreen R; Howlett, Geoffrey J; Schubert, Dieter

    2002-01-01

    Strategies for the deconvolution of diffusion in the determination of size-distributions from sedimentation velocity experiments were examined and developed. On the basis of four different model systems, we studied the differential apparent sedimentation coefficient distributions by the time-derivative method, g(s*), and by least-squares direct boundary modeling, ls-g*(s), the integral sedimentation coefficient distribution by the van Holde-Weischet method, G(s), and the previously introduced differential distribution of Lamm equation solutions, c(s). It is shown that the least-squares approach ls-g*(s) can be extrapolated to infinite time by considering area divisions analogous to boundary divisions in the van Holde-Weischet method, thus allowing the transformation of interference optical data into an integral sedimentation coefficient distribution G(s). However, despite the model-free approach of G(s), for the systems considered, the direct boundary modeling with a distribution of Lamm equation solutions c(s) exhibited the highest resolution and sensitivity. The c(s) approach requires an estimate for the size-dependent diffusion coefficients D(s), which is usually incorporated in the form of a weight-average frictional ratio of all species, or in the form of prior knowledge of the molar mass of the main species. We studied the influence of the weight-average frictional ratio on the quality of the fit, and found that it is well-determined by the data. As a direct boundary model, the calculated c(s) distribution can be combined with a nonlinear regression to optimize distribution parameters, such as the exact meniscus position, and the weight-average frictional ratio. Although c(s) is computationally the most complex, it has the potential for the highest resolution and sensitivity of the methods described. PMID:11806949

  16. Concentration, Size Distribution, and Infectivity of Airborne Particles Carrying Swine Viruses

    PubMed Central

    Alonso, Carmen; Raynor, Peter C.; Davies, Peter R.; Torremorell, Montserrat

    2015-01-01

    When pathogens become airborne, they travel associated with particles of different size and composition. Particle size determines the distance across which pathogens can be transported, as well as the site of deposition and the survivability of the pathogen. Despite the importance of this information, the size distribution of particles bearing viruses emitted by infectious animals remains unknown. In this study we characterized the concentration and size distribution of inhalable particles that transport influenza A virus (IAV), porcine reproductive and respiratory syndrome virus (PRRSV), and porcine epidemic diarrhea virus (PEDV) generated by acutely infected pigs and assessed virus viability for each particle size range. Aerosols from experimentally infected pigs were sampled for 24 days using an Andersen cascade impactor able to separate particles by size (ranging from 0.4 to 10 micrometer (μm) in diameter). Air samples collected for the first 9, 20 and the last 3 days of the study were analyzed for IAV, PRRSV and PEDV, respectively, using quantitative reverse transcription polymerase chain reaction (RT-PCR) and quantified as geometric mean copies/m3 within each size range. IAV was detected in all particle size ranges in quantities ranging from 5.5x102 (in particles ranging from 1.1 to 2.1μm) to 4.3x105 RNA copies/m3 in the largest particles (9.0–10.0μm). PRRSV was detected in all size ranges except particles between 0.7 and 2.1μm in quantities ranging from 6x102 (0.4–0.7μm) to 5.1x104 RNA copies/m3 (9.0–10.0μm). PEDV, an enteric virus, was detected in all particle sizes and in higher quantities than IAV and PRRSV (p < 0.0001) ranging from 1.3x106 (0.4–0.7μm) to 3.5x108 RNA copies/m3 (9.0–10.0μm). Infectious status was demonstrated for the 3 viruses, and in the case of IAV and PRRSV, viruses were isolated from particles larger than 2.1μm. In summary, our results indicated that airborne PEDV, IAV and PRRSV can be found in a wide range of

  17. Note on a Strongly Unimodal Bibliometric Size Frequency Distribution.

    ERIC Educational Resources Information Center

    Sichel, H. S.

    1992-01-01

    This study demonstrates that the number of references at the end of scientific research papers forms a strongly unimodal frequency distribution and that the generalized Gaussian-Poisson distribution fits such unimodal data extremely well. (three references) (Author/MES)

  18. New insight on the Sivers transverse momentum dependent distribution function

    SciTech Connect

    M. Anselmino, M. Boglione, U. D'Alesio, S. Melis, F. Murgia, A. Prokudin

    2011-05-01

    Polarised Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes allow to study Transverse Momentum Dependent partonic distributions (TMDs), which reveal a non trivial three dimensional internal structure of the hadrons in momentum space. One of the most representative of the TMDs is the so-called Sivers function that describes the distribution of unpolarized quarks inside a transversely polarized proton. We present a novel extraction of the Sivers distribution functions from the most recent experimental data of HERMES and COMPASS experiments. Using suitable parametrizations, within the TMD factorization scheme, and a simple fitting strategy, we also perform a preliminary exploration of the role of the proton sea quarks.

  19. Pore-size-dependent calcium carbonate precipitation controlled by surface chemistry.

    PubMed

    Stack, Andrew G; Fernandez-Martinez, Alejandro; Allard, Lawrence F; Bañuelos, José L; Rother, Gernot; Anovitz, Lawrence M; Cole, David R; Waychunas, Glenn A

    2014-06-01

    Induced mineral precipitation is potentially important for the remediation of contaminants, such as during mineral trapping during carbon or toxic metal sequestration. The prediction of precipitation reactions is complicated by the porous nature of rocks and soils and their interaction with the precipitate, introducing transport and confinement effects. Here X-ray scattering measurements, modeling, and electron microscopies were used to measure the kinetics of calcium carbonate precipitation in a porous amorphous silica (CPG) that contained two discrete distributions of pore sizes: nanopores and macropores. To examine the role of the favorability of interaction between the substrate and precipitate, some of the CPG was functionalized with a self-assembled monolayer (SAM) similar to those known to enhance nucleation densities on planar substrates. Precipitation was found to occur exclusively in macropores in the native CPG, while simultaneous precipitation in nanopores and macropores was observed in the functionalized CPG. The rate of precipitation in the nanopores estimated from the model of the X-ray scattering matched that measured on calcite single crystals. These results suggest that the pore-size distribution in which a precipitation reaction preferentially occurs depends on the favorability of interaction between substrate and precipitate, something not considered in most studies of precipitation in porous media.

  20. Retrieval of spheroidal particle size distribution using the approximate method in spectral extinction technique

    NASA Astrophysics Data System (ADS)

    Wang, Li; Sun, Xiaogang; Xing, Jian

    2012-04-01

    Retrieval of spheroidal particle size distribution using an approximate method in spectral extinction technique is proposed. The combined approximate method, which is the combination of Mie method and generalized eikonal approximation (GEA) method, is used as an alternative to the rigorous solutions to calculate the averaging extinction efficiency of spheroid. Based on the averaging extinction efficiency, the accuracy and limitations of the retrieval are then investigated. Moreover, the validity range and effect of the refractive index are also examined. The Johnson's SB function in this paper is used as a versatile function to fit the commonly used particle size distribution functions in the dependent model. Simulations and experimental results show that the combined approximate method can be successfully applied to retrieval of spheroidal particle size distribution. In certain constraint conditions, the retrieval results demonstrate the high reliability and stability of the method. By using the combined approximate method, the complexity and computation time of the retrieval are significantly reduced, which is more suitable for quick and easy measurement. The method can also be used as a replacement when the rigorous solutions suffer computationally intractable difficulties.

  1. Direct Observation of Aggregative Nanoparticle Growth: Kinetic Modeling of the Size Distribution and Growth Rate

    SciTech Connect

    Woehl, Taylor J.; Park, Chiwoo; Evans, James E.; Arslan, Ilke; Ristenpart, William D.; Browning, Nigel D.

    2014-01-08

    Direct observations of solution-phase nanoparticle growth using in situ liquid transmission electron microscopy (TEM) have demonstrated the importance of “non-classical” growth mechanisms, such as aggregation and coalescence, on the growth and final morphology of nanocrystals at the atomic and single nanoparticle scales. To date, groups have quantitatively interpreted the mean growth rate of nanoparticles in terms of the Lifshitz-Slyozov-Wagner (LSW) model for Ostwald ripening, but less attention has been paid to modeling the corresponding particle size distribution. Here we use in situ fluid stage scanning TEM to demonstrate that silver nanoparticles grow by a length-scale dependent mechanism, where individual nanoparticles grow by monomer attachment but ensemble-scale growth is dominated by aggregation. Although our observed mean nanoparticle growth rate is consistent with the LSW model, we show that the corresponding particle size distribution is broader and more symmetric than predicted by LSW. Following direct observations of aggregation, we interpret the ensemble-scale growth using Smoluchowski kinetics and demonstrate that the Smoluchowski model quantitatively captures the mean growth rate and particle size distribution.

  2. Large Scale Behavior and Droplet Size Distributions in Crude Oil Jets and Plumes

    NASA Astrophysics Data System (ADS)

    Katz, Joseph; Murphy, David; Morra, David

    2013-11-01

    The 2010 Deepwater Horizon blowout introduced several million barrels of crude oil into the Gulf of Mexico. Injected initially as a turbulent jet containing crude oil and gas, the spill caused formation of a subsurface plume stretching for tens of miles. The behavior of such buoyant multiphase plumes depends on several factors, such as the oil droplet and bubble size distributions, current speed, and ambient stratification. While large droplets quickly rise to the surface, fine ones together with entrained seawater form intrusion layers. Many elements of the physics of droplet formation by an immiscible turbulent jet and their resulting size distribution have not been elucidated, but are known to be significantly influenced by the addition of dispersants, which vary the Weber Number by orders of magnitude. We present experimental high speed visualizations of turbulent jets of sweet petroleum crude oil (MC 252) premixed with Corexit 9500A dispersant at various dispersant to oil ratios. Observations were conducted in a 0.9 m × 0.9 m × 2.5 m towing tank, where large-scale behavior of the jet, both stationary and towed at various speeds to simulate cross-flow, have been recorded at high speed. Preliminary data on oil droplet size and spatial distributions were also measured using a videoscope and pulsed light sheet. Sponsored by Gulf of Mexico Research Initiative (GoMRI).

  3. How the Assumed Size Distribution of Dust Minerals Affects the Predicted Ice Forming Nuclei

    NASA Astrophysics Data System (ADS)

    Perlwitz, J. P.; Fridlind, A. M.; Pérez García-Pando, C.; Miller, R. L.; Knopf, D. A.

    2015-12-01

    The formation of ice in clouds depends on the availability of ice forming nuclei (IFN). Dust aerosol particles are considered the most important source of IFN at a global scale. Recent laboratory studies have demonstrated that the mineral feldspar provides the most efficient dust IFN for immersion freezing and together with kaolinite for deposition ice nucleation, and that the phyllosilicates illite and montmorillonite (a member of the smectite group) are of secondary importance.A few studies have applied global models that simulate mineral specific dust to predict the number and geographical distribution of IFN. These studies have been based on the simple assumption that the mineral composition of soil as provided in data sets from the literature translates directly into the mineral composition of the dust aerosols. However, these tables are based on measurements of wet-sieved soil where dust aggregates are destroyed to a large degree. In consequence, the size distribution of dust is shifted to smaller sizes, and phyllosilicates like illite, kaolinite, and smectite are only found in the size range <2 μm. In contrast, in measurements of the mineral composition of dust aerosols, the largest mass fraction of these phyllosilicates is found in the size range >2 μm as part of dust aggregates. Conversely, the mass fraction of feldspar is smaller in this size range, varying with the geographical location. This may have a significant effect on the predicted IFN number and its geographical distribution.An improved mineral specific dust aerosol module has been recently implemented in the NASA GISS Earth System ModelE2. The dust module takes into consideration the disaggregated state of wet-sieved soil, on which the tables of soil mineral fractions are based. To simulate the atmospheric cycle of the minerals, the mass size distribution of each mineral in aggregates that are emitted from undispersed parent soil is reconstructed. In the current study, we test the null

  4. How the Assumed Size Distribution of Dust Minerals Affects the Predicted Ice Forming Nuclei

    NASA Technical Reports Server (NTRS)

    Perlwitz, Jan P.; Fridlind, Ann M.; Garcia-Pando, Carlos Perez; Miller, Ron L.; Knopf, Daniel A.

    2015-01-01

    The formation of ice in clouds depends on the availability of ice forming nuclei (IFN). Dust aerosol particles are considered the most important source of IFN at a global scale. Recent laboratory studies have demonstrated that the mineral feldspar provides the most efficient dust IFN for immersion freezing and together with kaolinite for deposition ice nucleation, and that the phyllosilicates illite and montmorillonite (a member of the smectite group) are of secondary importance.A few studies have applied global models that simulate mineral specific dust to predict the number and geographical distribution of IFN. These studies have been based on the simple assumption that the mineral composition of soil as provided in data sets from the literature translates directly into the mineral composition of the dust aerosols. However, these tables are based on measurements of wet-sieved soil where dust aggregates are destroyed to a large degree. In consequence, the size distribution of dust is shifted to smaller sizes, and phyllosilicates like illite, kaolinite, and smectite are only found in the size range 2 m. In contrast, in measurements of the mineral composition of dust aerosols, the largest mass fraction of these phyllosilicates is found in the size range 2 m as part of dust aggregates. Conversely, the mass fraction of feldspar is smaller in this size range, varying with the geographical location. This may have a significant effect on the predicted IFN number and its geographical distribution.An improved mineral specific dust aerosol module has been recently implemented in the NASA GISS Earth System ModelE2. The dust module takes into consideration the disaggregated state of wet-sieved soil, on which the tables of soil mineral fractions are based. To simulate the atmospheric cycle of the minerals, the mass size distribution of each mineral in aggregates that are emitted from undispersed parent soil is reconstructed. In the current study, we test the null

  5. Size-dependent nonlinear weak-field magnetic behavior of maghemite nanoparticles.

    PubMed

    de Montferrand, Caroline; Lalatonne, Yoann; Bonnin, Dominique; Lièvre, Nicole; Lecouvey, Marc; Monod, Philippe; Russier, Vincent; Motte, Laurence

    2012-06-25

    The magnetic behavior at room temperature of maghemite nanoparticles of variable sizes (from 7 to 20 nm) is compared using a conventional super quantum interference device (SQUID) and a recently patented technology, called MIAplex. The SQUID usually measures the magnetic response versus an applied magnetic field in a quasi-static mode until high field values (from -4000 to 4000 kA m(-1)) to determine the field-dependence and saturation magnetization of the sample. The MIAplex is a handheld portable device that measures a signal corresponding to the second derivative of the magnetization around zero field (between -15 and 15 kA m(-1)). In this paper, the magnetic response of the size series is correlated, both in diluted and powder form, between the SQUID and MIAplex. The SQUID curves are measured at room temperature in two magnetic field ranges from -4000 to 4000 kA m(-1) (-5T to 5T) and from -15 to 15 kA m(-1). Nonlinear behavior at weak fields is highlighted and the magnetic curves for diluted solutions evolve from quasi-paramagnetic to superparamagnetic behavior when the size of the nanoparticles increases. For the 7-nm sample, the fit of the magnetization with the Langevin model weighted with log-normal distribution corresponds closely to the magnetic size. This confirms the accuracy of the model of non-interacting superparamagnetic particles with a magnetically frustrated surface layer of about 0.5 nm thickness. For the other samples (10-nm to 21-nm), the experimental weak-field magnetization curves are modeled by more than one population of magnetically responding species. This behavior is consistent with a chemically uniform but magnetically distinct structure composed of a core and a magnetically active nanoparticle canted shell. Accordingly the weak-field signature corresponds to the total assembly of the nanoparticles. The impact of size polydispersity is also discussed.

  6. Thermal simulation of magnetization reversals for size-distributed assemblies of core-shell exchange biased nanoparticles

    NASA Astrophysics Data System (ADS)

    Richy, J.; Jay, J.-Ph.; Pogossian, S. P.; Ben Youssef, J.; Sheppard, C. J.; Prinsloo, A. R. E.; Spenato, D.; Dekadjevi, D. T.

    2016-08-01

    A temperature dependent coherent magnetization reversal model is proposed for size-distributed assemblies of ferromagnetic nanoparticles and ferromagnetic-antiferromagnetic (AF) core-shell nanoparticles. The nanoparticles are assumed to be of uniaxial anisotropy and all aligned along their easy axis. The thermal dependence is included by considering thermal fluctuations, implemented via the Néel-Arrhenius theory. Thermal and angular dependence of magnetization reversal loops, coercive field, and exchange-bias field are obtained, showing that ferromagnetic-antiferromagnetic size-distributed exchange-coupled nanoparticles exhibit temperature-dependent asymmetric magnetization reversal. Also, non-monotonic evolutions of exchange-bias and coercive fields with temperature are demonstrated. The angular dependence of coercive field with temperature exhibits a complex behavior, with the presence of an apex, whose position and amplitude are strongly temperature-dependent. The angular dependence of exchange bias with temperature exhibits complex behaviors, which depends on the AF anisotropy and exchange coupling. The resulting angular behavior demonstrates the key role of the size distribution and temperature in the magnetic response of nanoparticles.

  7. 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.

  8. Determination of particle nucleation and growth rates from measured aerosol size distributions

    NASA Astrophysics Data System (ADS)

    Verheggen, B.; Mozurkewich, M.

    2003-04-01

    The effects of aerosols on atmospheric chemistry, health and climate are dependent on particle size and composition, and therefore on particle nucleation and growth. An analytical model has been developed to determine nucleation and growth rates from measurements of consecutive aerosol size distributions. The evolution of an aerosol population in time is described by the General Dynamic Equation (GDE). Wall loss, coagulation loss and coagulation production are determined, based on the measured aerosol size distributions. Taking their contributions into account, a non-linear regression analysis of the GDE is performed for each time interval to find the value of the growth rate, that gives best agreement between the measured and calculated change in the size distribution. Other parameters can also be verified and/or optimized by regression analysis. Knowing the growth rate as a function of time (and size) from the regression analysis, each measured cohort of particles is tracked backwards in time to their time of formation, where the radius of the critical cluster is assumed to be 0.5 nm. The number density of each cohort has decreased since their formation, due to wall losses and coagulation processes. Perturbation theory is used to approximate the contribution of within mode coagulation in decreasing the number density. Wall losses and coagulation scavenging are well characterized for each time interval. The integrated losses, from time of formation to time of measurement, are used to obtain the number of nucleated particles, and ultimately the -empirically determined- nucleation rate. The analysis is applied to measurements made in Calspan's 590 m3 smog chamber, following SO2 nucleation.

  9. Predicting hillslope sediment size distribution using remote sensing data, Inyo Creek, California

    NASA Astrophysics Data System (ADS)

    Leclere, S.; Genetti, J. R.; Sklar, L. S.

    2015-12-01

    The size distribution of sediments produced on hillslopes and supplied to channels depends on the geomorphic processes that weather, detach and transport rock fragments down slopes. Little in the way of theory or data is available to predict patterns in hillslope size distributions at the catchment scale from topographic and geologic maps. To address this knowledge gap, we map the steep granitic catchment of Inyo Creek, eastern Sierra Nevada, California and categorize geomorphic landscape units (GLUs) by overlaying basic GIS attributes to create polygons of similar inferred sediment production process regimes. Key attributes include elevation, slope, aspect, and land cover, which varies across 2 km of relief from bare bedrock cliffs at higher elevations to vegetated, regolith-covered slopes at lower elevations. We expect that factors that influence temperature and water residence time, and thus the intensity of chemical versus mechanical weathering, will correlate with resulting hillslope sediment size. For example, GLUs constructed from binned combinations of slope, elevation and aspect were used to predict three categories of sediment size on an ordinal scale. We used a map of predicted sediment size to guide field measurements, using point counts and photogrammetry to quantify hillslope surface size distributions. Areas predicted to have relatively large sediments were primarily covered in boulders and cobble-sized particles, whereas areas predicted to have small sediments were primarily covered in scree and gruss. Although hillslope sediment size at Inyo Creek correlates strongly with elevation, incorporation of slope and aspect creates a significantly better predictive model. We combine this result with supervised classification of aerial images using eCognition to estimate that more than half the catchment area produces boulder and cobble-rich sediment. Further analysis will include characterizing the local contributing areas to each field sampling point to

  10. A transition in mechanisms of size dependent electrical transport at nanoscale metal-oxide interfaces

    SciTech Connect

    Hou, Jiechang; Nonnenmann, Stephen S.; Qin, Wei; Bonnell, Dawn A.

    2013-12-16

    As device miniaturization approaches nanoscale dimensions, interfaces begin to dominate electrical properties. Here the system archetype Au/SrTiO{sub 3} is used to examine the origin of size dependent transport properties along metal-oxide interfaces. We demonstrate that a transition between two classes of size dependent electronic transport mechanisms exists, defined by a critical size ε. At sizes larger than ε an edge-related tunneling effect proportional to 1/D (the height of the supported Au nanoparticle) is observed; interfaces with sizes smaller than ε exhibit random fluctuations in current. The ability to distinguish between these mechanisms is important to future developments in nanoscale device design.

  11. Cluster size distributions: signatures of self-organization in spatial ecologies.

    PubMed Central

    Pascual, Mercedes; Roy, Manojit; Guichard, Frédéric; Flierl, Glenn

    2002-01-01

    Three different lattice-based models for antagonistic ecological interactions, both nonlinear and stochastic, exhibit similar power-law scalings in the geometry of clusters. Specifically, cluster size distributions and perimeter-area curves follow power-law scalings. In the coexistence regime, these patterns are robust: their exponents, and therefore the associated Korcak exponent characterizing patchiness, depend only weakly on the parameters of the systems. These distributions, in particular the values of their exponents, are close to those reported in the literature for systems associated with self-organized criticality (SOC) such as forest-fire models; however, the typical assumptions of SOC need not apply. Our results demonstrate that power-law scalings in cluster size distributions are not restricted to systems for antagonistic interactions in which a clear separation of time-scales holds. The patterns are characteristic of processes of growth and inhibition in space, such as those in predator-prey and disturbance-recovery dynamics. Inversions of these patterns, that is, scalings with a positive slope as described for plankton distributions, would therefore require spatial forcing by environmental variability. PMID:12079527

  12. A statistical mechanical model for drug release: Investigations on size and porosity dependence

    NASA Astrophysics Data System (ADS)

    Gomes Filho, Márcio Sampaio; Oliveira, Fernando Albuquerque; Barbosa, Marco Aurélio Alves

    2016-10-01

    A lattice gas model is proposed for investigating the release of drug molecules in capsules covered with semi-permeable membranes. Release patterns in one and two dimensional systems are obtained with Monte Carlo simulations and adjusted to the semi-empirical Weibull distribution function. An analytical solution to the diffusion equation is used to complement and guide simulations in one dimension. Size and porosity dependence analysis was made on the two semi-empirical parameters of the Weibull function, which are related to characteristic time and release mechanism, and our results indicate that a simple scaling law occurs only for systems with almost impermeable membranes, represented in our model by capsules with a single leaking site.

  13. One-pot, high-yield synthesis of size-controlled gold particles with narrow size distribution.

    PubMed

    Guo, Shaojun; Wang, Erkang

    2007-08-01

    Here, we first report a facile one-step one-phase synthetic route to achieve size-controlled gold micro/nanoparticles with narrow size distribution by using o-diaminobenzene as a reducing agent in the presence of poly(N-vinyl-2-pyrrolidone) via a simple wet-chemical approach. All experimental data including that from scanning-electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction techniques indicates that the gold micro/nanoparticles with a narrow size distribution were produced in high yield (approximately 100%).

  14. A Program for Partitioning Shifted Truncated Lognormal Distributions into Size-Class Bins

    USGS Publications Warehouse

    Attanasi, E.D.; Charpentier, Ronald R.

    2007-01-01

    In recent years, oil and gas accumulation-size frequency distributions have become a standard way to characterize undiscovered conventional oil and gas resources that have been postulated by geologic assessments. The preparation of such distributions requires the assessment geologists to explicitly choose parameters for the probability distribution for the sizes of undiscovered accumulations. The purpose of this report is to present a computational scheme for obtaining a binned size frequency distribution of undiscovered accumulations when the undiscovered accumulation size distribution is shifted truncated lognormal.

  15. Measurement of size-dependent composition variations for gamma prime (γ') precipitates in an advanced nickel-based superalloy.

    PubMed

    Chen, Y Q; Slater, T J A; Lewis, E A; Francis, E M; Burke, M G; Preuss, M; Haigh, S J

    2014-09-01

    Energy-dispersive X-ray (EDX) spectroscopy in the scanning transmission electron microscope (STEM) has been used to demonstrate the presence of size-dependent compositional variation for L12-structured Ni3Al-type gamma-prime (γ') precipitates within a commercial RR1000 Ni-based superalloy. This semi-quantitative elemental analysis has been achieved using electrochemical extraction of the γ' precipitates from the γ matrix. The applicability of this approach to size-dependent compositional analysis of precipitates was confirmed by a comparison of the size distribution for the extracted precipitates with those present in traditional electropolished foil specimens in the size range 20-250nm. By applying suitable thickness-dependent absorption-corrections we have demonstrated that the composition of γ' precipitates in our material depends on the size of the precipitate in the range of 5nm to 3μm. In particular, the Al content was observed to increase in smaller γ' precipitates while Ti and Ta contents are constant for all sizes of precipitate. Hf was observed to be present only in the largest precipitates. This type of local compositional information provides invaluable input to assess the accuracy of microstructural modelling for these complex alloys and provides new evidence supporting the importance of anti-site diffusion. PMID:24814008

  16. Measurement of size-dependent composition variations for gamma prime (γ') precipitates in an advanced nickel-based superalloy.

    PubMed

    Chen, Y Q; Slater, T J A; Lewis, E A; Francis, E M; Burke, M G; Preuss, M; Haigh, S J

    2014-09-01

    Energy-dispersive X-ray (EDX) spectroscopy in the scanning transmission electron microscope (STEM) has been used to demonstrate the presence of size-dependent compositional variation for L12-structured Ni3Al-type gamma-prime (γ') precipitates within a commercial RR1000 Ni-based superalloy. This semi-quantitative elemental analysis has been achieved using electrochemical extraction of the γ' precipitates from the γ matrix. The applicability of this approach to size-dependent compositional analysis of precipitates was confirmed by a comparison of the size distribution for the extracted precipitates with those present in traditional electropolished foil specimens in the size range 20-250nm. By applying suitable thickness-dependent absorption-corrections we have demonstrated that the composition of γ' precipitates in our material depends on the size of the precipitate in the range of 5nm to 3μm. In particular, the Al content was observed to increase in smaller γ' precipitates while Ti and Ta contents are constant for all sizes of precipitate. Hf was observed to be present only in the largest precipitates. This type of local compositional information provides invaluable input to assess the accuracy of microstructural modelling for these complex alloys and provides new evidence supporting the importance of anti-site diffusion.

  17. Density-dependent effects on group size are sex-specific in a gregarious ungulate.

    PubMed

    Vander Wal, Eric; van Beest, Floris M; Brook, Ryan K

    2013-01-01

    Density dependence can have marked effects on social behaviors such as group size. We tested whether changes in population density of a large herbivore (elk, Cervus canadensis) affected sex-specific group size and whether the response was density- or frequency-dependent. We quantified the probability and strength of changes in group sizes and dispersion as population density changed for each sex. We used group size data from a population of elk in Manitoba, Canada, that was experimentally reduced from 1.20 to 0.67 elk/km(2) between 2002 and 2009. Our results indicated that functional responses of group size to population density are sex-specific. Females showed a positive density-dependent response in group size at population densities ≥0.70 elk/km(2) and we found evidence for a minimum group size at population density ≤0.70 elk/km(2). Changes in male group size were also density-dependent; however, the strength of the relationship was lower than for females. Density dependence in male group size was predominantly a result of fusion of solitary males into larger groups, rather than fusion among existing groups. Our study revealed that density affects group size of a large herbivore differently between males and females, which has important implications for the benefits e.g., alleviating predation risk, and costs of social behaviors e.g., competition for resources and mates, and intra-specific pathogen transmission. PMID:23326502

  18. Density-Dependent Effects on Group Size Are Sex-Specific in a Gregarious Ungulate

    PubMed Central

    Vander Wal, Eric; van Beest, Floris M.; Brook, Ryan K.

    2013-01-01

    Density dependence can have marked effects on social behaviors such as group size. We tested whether changes in population density of a large herbivore (elk, Cervus canadensis) affected sex-specific group size and whether the response was density- or frequency-dependent. We quantified the probability and strength of changes in group sizes and dispersion as population density changed for each sex. We used group size data from a population of elk in Manitoba, Canada, that was experimentally reduced from 1.20 to 0.67 elk/km2 between 2002 and 2009. Our results indicated that functional responses of group size to population density are sex-specific. Females showed a positive density-dependent response in group size at population densities ≥0.70 elk/km2 and we found evidence for a minimum group size at population density ≤0.70 elk/km2. Changes in male group size were also density-dependent; however, the strength of the relationship was lower than for females. Density dependence in male group size was predominantly a result of fusion of solitary males into larger groups, rather than fusion among existing groups. Our study revealed that density affects group size of a large herbivore differently between males and females, which has important implications for the benefits e.g., alleviating predation risk, and costs of social behaviors e.g., competition for resources and mates, and intra-specific pathogen transmission. PMID:23326502

  19. Size distribution and scattering phase function of aerosol particles retrieved from sky brightness measurements

    NASA Technical Reports Server (NTRS)

    Kaufman, Y. J.; Gitelson, A.; Karnieli, A.; Ganor, E. (Editor); Fraser, R. S.; Nakajima, T.; Mattoo, S.; Holben, B. N.

    1994-01-01

    Ground-based measurements of the solar transmission and sky radiance in a horizontal plane through the Sun are taken in several geographical regions and aerosol types: dust in a desert transition zone in Israel, sulfate particles in Eastern and Western Europe, tropical aerosol in Brazil, and mixed continental/maritime aerosol in California. Stratospheric aerosol was introduced after the eruption of Mount Pinatubo in June 1991. Therefore measurements taken before the eruption are used to analyze the properties of tropospheric aerosol; measurements from 1992 are also used to detect the particle size and concentration of stratospheric aerosol. The measurements are used to retrieve the size distribution and the scattering phase function at large scattering angles of the undisturbed aerosol particles. The retrieved properties represent an average on the entire atmospheric column. A comparison between the retrieved phase function for a scattering angle of 120 deg, with phase function predicted from the retrieved size distribution, is used to test the assumption of particle homogeneity and sphericity in radiative transfer models (Mie theory). The effect was found to be small (20% +/- 15%). For the stratospheric aerosol (sulfates), as expected, the phase function was very well predicted using the Mie theory. A model with a power law distribution, based on the spectral dependence of the optical thickness, alpha, cannot estimate accurately the phase function (up to 50% error for lambda = 0.87 microns). Before the Pinatubo eruption the ratio between the volumes of sulfate and coarse particles was very well correlated with alpha. The Pinatubo stratospheric aerosol destroyed this correlation. The aerosol optical properties are compared with analysis of the size, shape, and composition of the individual particles by electron microscopy of in situ samples. The measured volume size distribution before the injection of stratospheric aerosol consistently show two modes, sulfate

  20. A generalized statistical model for the size distribution of wealth

    NASA Astrophysics Data System (ADS)

    Clementi, F.; Gallegati, M.; Kaniadakis, G.

    2012-12-01

    In a recent paper in this journal (Clementi et al 2009 J. Stat. Mech. P02037), we proposed a new, physically motivated, distribution function for modeling individual incomes, having its roots in the framework of the κ-generalized statistical mechanics. The performance of the κ-generalized distribution was checked against real data on personal income for the United States in 2003. In this paper we extend our previous model so as to be able to account for the distribution of wealth. Probabilistic functions and inequality measures of this generalized model for wealth distribution are obtained in closed form. In order to check the validity of the proposed model, we analyze the US household wealth distributions from 1984 to 2009 and conclude an excellent agreement with the data that is superior to any other model already known in the literature.

  1. Inverse size scaling of the nucleolus by a concentration-dependent phase transition.

    PubMed

    Weber, Stephanie C; Brangwynne, Clifford P

    2015-03-01

    Just as organ size typically increases with body size, the size of intracellular structures changes as cells grow and divide. Indeed, many organelles, such as the nucleus [1, 2], mitochondria [3], mitotic spindle [4, 5], and centrosome [6], exhibit size scaling, a phenomenon in which organelle size depends linearly on cell size. However, the mechanisms of organelle size scaling remain unclear. Here, we show that the size of the nucleolus, a membraneless organelle important for cell-size homeostasis [7], is coupled to cell size by an intracellular phase transition. We find that nucleolar size directly scales with cell size in early C. elegans embryos. Surprisingly, however, when embryo size is altered, we observe inverse scaling: nucleolar size increases in small cells and decreases in large cells. We demonstrate that this seemingly contradictory result arises from maternal loading of a fixed number rather than a fixed concentration of nucleolar components, which condense into nucleoli only above a threshold concentration. Our results suggest that the physics of phase transitions can dictate whether an organelle assembles, and, if so, its size, providing a mechanistic link between organelle assembly and cell size. Since the nucleolus is known to play a key role in cell growth, this biophysical readout of cell size could provide a novel feedback mechanism for growth control.

  2. Machine vision based particle size and size distribution determination of airborne dust particles of wood and bark pellets

    SciTech Connect

    Igathinathane, C; Pordesimo, L.O.

    2009-08-01

    Dust management strategies in industrial environment, especially of airborne dust, require quantification and measurement of size and size distribution of the particles. Advanced specialized instruments that measure airborne particle size and size distribution apply indirect methods that involve light scattering, acoustic spectroscopy, and laser diffraction. In this research, we propose a simple and direct method of airborne dust particle dimensional measurement and size distribution analysis using machine vision. The method involves development of a user-coded ImageJ plugin that measures particle length and width and analyzes size distribution of particles based on particle length from high-resolution scan images. Test materials were airborne dust from soft pine wood sawdust pellets and ground pine tree bark pellets. Subsamples prepared by dividing the actual dust using 230 mesh (63 m) sieve were analyzed as well. A flatbed document scanner acquired the digital images of the dust particles. Proper sampling, layout of dust particles in singulated arrangement, good contrast smooth background, high resolution images, and accurate algorithm are essential for reliable analysis. A halo effect around grey-scale images ensured correct threshold limits. The measurement algorithm used Feret s diameter for particle length and pixel-march technique for particle width. Particle size distribution was analyzed in a sieveless manner after grouping particles according to their distinct lengths, and several significant dimensions and parameters of particle size distribution were evaluated. Results of the measurement and analysis were presented in textual and graphical formats. The developed plugin was evaluated to have a dimension measurement accuracy in excess of 98.9% and a computer speed of analysis of <8 s/image. Arithmetic mean length of actual wood and bark pellets airborne dust particles were 0.1138 0.0123 and 0.1181 0.0149 mm, respectively. The airborne dust particles of

  3. Number size distribution measurements of biological aerosols under contrasting environments and seasons from southern tropical India

    NASA Astrophysics Data System (ADS)

    Valsan, Aswathy; Cv, Biju; Krishna, Ravi; Huffman, Alex; Poschl, Ulrich; Gunthe, Sachin

    2016-04-01

    Biological aerosols constitute a wide range of dead and alive biological materials and structures that are suspended in the atmosphere. They play an important role in the atmospheric physical, chemical and biological processes and health of living being by spread of diseases among humans, plants, and, animals. The atmospheric abundance, sources, physical properties of PBAPs as compared to non-biological aerosols, however, is poorly characterized. Though omnipresent, their concentration and composition exhibit large spatial and temporal variations depending up on their sources, land-use, and local meteorology. The Indian tropical region, which constitutes approximately 18% of the world's total population exhibits vast geographical extend and experiences a distinctive meteorological phenomenon by means of Indian Summer Monsoon (IMS). Thus, the sources, properties and characteristics of biological aerosols are also expected to have significant variations over the Indian subcontinent depending upon the location and seasons. Here we present the number concentration and size distribution of Fluorescent Biological Aerosol Particles (FBAP) from two contrasting locations in Southern tropical India measured during contrasting seasons using Ultra Violet Aerodynamic Particle Sizer (UV-APS). Measurements were carried out at a pristine high altitude continental site, Munnar (10.09 N, 77.06 E; 1605 m asl) during two contrasting seasons, South-West Monsoon (June-August, 2014) and winter (Jan - Feb, 2015) and in Chennai, a coastal urban area, during July - November 2015. FBAP concentrations at both the locations showed large variability with higher concentrations occurring at Chennai. Apart from regional variations, the FBAP concentrations also exhibited variations over two different seasons under the same environmental condition. In Munnar the FBAP concentration increased by a factor of four from South-West Monsoon to winter season. The average size distribution of FBAP at both

  4. 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

  5. Comparison of Drop Size Distribution Measurements by Impact and Optical Disdrometers.

    NASA Astrophysics Data System (ADS)

    Tokay, Ali; Kruger, Anton; Krajewski, Witold F.

    2001-11-01

    Simultaneous observations made with optical- and impact-type disdrometers were analyzed to broaden knowledge of these instruments. These observations were designed to test how accurately they measure drop size distributions (DSDs). The instruments' use in determining radar rainfall relations such as that between reflectivity and rainfall rate also was analyzed. A unique set of instruments, including two video and one Joss-Waldvogel disdrometer along with eight tipping-bucket rain gauges, was operated within a small area of about 100 × 50 m2 during a 2-month-long field campaign in central Florida. The disdrometers were evaluated by comparing their rain totals with the rain gauges. Both disdrometers underestimated the rain totals, but the video disdrometers had higher readings, resulting in a better agreement with the gauges. The disdrometers underreported small- to medium-size drops, which most likely caused the underestimation of rain totals. However, more medium-size drops were measured by the video disdrometer, thus producing higher rain rates for that instrument. The comparison of DSDs, averaged at different timescales, showed good agreement between the two types of disdrometers. A continuous increase in the number of drops toward smaller sizes was only evident in the video disdrometers at rain rates above 20 mm h1. Otherwise, the concentration of small drops remained the same or decreased to the smallest measurable size. The Joss-Waldvogel disdrometer severely underestimated only at very small drop size (diameter 0.5 mm). Beyond the Joss-Waldvogel disdrometer measurement limit were very large drops that fell during heavy and extreme rain intensities. The derived parameters of exponential and gamma distributions reflect the good agreement between the disdrometers' DSD measurements. The parameters of fitted distributions were close to each other, especially when all the coincident measurements were averaged. The low concentrations of very large drops observed by

  6. Size distribution of rare earth elements in coal ash

    USGS Publications Warehouse

    Scott, Clinton T.; Deonarine, Amrika; Kolker, Allan; Adams, Monique; Holland, James F.

    2015-01-01

    Rare earth elements (REEs) are utilized in various applications that are vital to the automotive, petrochemical, medical, and information technology industries. As world demand for REEs increases, critical shortages are expected. Due to the retention of REEs during coal combustion, coal fly ash is increasingly considered a potential resource. Previous studies have demonstrated that coal fly ash is variably enriched in REEs relative to feed coal (e.g, Seredin and Dai, 2012) and that enrichment increases with decreasing size fractions (Blissett et al., 2014). In order to further explore the REE resource potential of coal ash, and determine the partitioning behavior of REE as a function of grain size, we studied whole coal and fly ash size-fractions collected from three U.S commercial-scale coal-fired generating stations burning Appalachian or Powder River Basin coal. Whole fly ash was separated into , 5 um, to 5 to 10 um and 10 to 100 um particle size fractions by mechanical shaking using trace-metal clean procedures. In these samples REE enrichments in whole fly ash ranges 5.6 to 18.5 times that of feedcoals. Partitioning results for size separates relative to whole coal and whole fly ash will also be reported. 

  7. Transverse Momentum-Dependent Parton Distributions From Lattice QCD

    SciTech Connect

    Michael Engelhardt, Bernhard Musch, Philipp Haegler, Andreas Schaefer

    2012-12-01

    Starting from a definition of transverse momentum-dependent parton distributions for semi-inclusive deep inelastic scattering and the Drell-Yan process, given in terms of matrix elements of a quark bilocal operator containing a staple-shaped Wilson connection, a scheme to determine such observables in lattice QCD is developed and explored. Parametrizing the aforementioned matrix elements in terms of invariant amplitudes permits a simple transformation of the problem to a Lorentz frame suited for the lattice calculation. Results for the Sivers and Boer-Mulders transverse momentum shifts are presented, focusing in particular on their dependence on the staple extent and the Collins-Soper evolution parameter.

  8. Transverse Momentum-Dependent Parton Distributions from Lattice QCD

    NASA Astrophysics Data System (ADS)

    Engelhardt, M.; Musch, B.; Hägler, P.; Negele, J.; Schäfer, A.

    Starting from a definition of transverse momentum-dependent parton distributions for semi-inclusive deep inelastic scattering and the Drell-Yan process, given in terms of matrix elements of a quark bilocal operator containing a staple-shaped Wilson connection, a scheme to determine such observables in lattice QCD is developed and explored. Parametrizing the aforementioned matrix elements in terms of invariant amplitudes permits a simple transformation of the problem to a Lorentz frame suited for the lattice calculation. Results for the Sivers and Boer-Mulders transverse momentum shifts are presented, focusing in particular on their dependence on the staple extent and the Collins-Soper evolution parameter.

  9. Tropospheric aerosols: size-differentiated chemistry and large-scale spatial distributions.

    PubMed

    Hidy, George M; Mohnen, Volker; Blanchard, Charles L

    2013-04-01

    Worldwide interest in atmospheric aerosols has emerged since the late 20th century as a part of concerns for air pollution and radiative forcing of the earth's climate. The use of aircraft and balloons for sampling and the use of remote sensing have dramatically expanded knowledge about tropospheric aerosols. Our survey gives an overview of contemporary tropospheric aerosol chemistry based mainly on in situ measurements. It focuses on fine particles less than 1-2.5 microm in diameter. The physical properties of particles by region and altitude are exemplified by particle size distributions, total number and volume concentration, and optical parameters such as extinction coefficient and aerosol optical depth. Particle chemical characterization is size dependent, differentiated by ubiquitous sulfate, and carbon, partially from anthropogenic activity. Large-scale particle distributions extend to intra- and intercontinental proportions involving plumes from population centers to natural disturbances such as dust storms and vegetation fires. In the marine environment, sea salt adds an important component to aerosols. Generally, aerosol components, most of whose sources are at the earth's surface, tend to dilute and decrease in concentration with height, but often show different (layered) profiles depending on meteorological conditions. Key microscopic processes include new particle formation aloft and cloud interactions, both cloud initiation and cloud evaporation. Measurement campaigns aloft are short term, giving snapshots of inherently transient phenomena in the troposphere. Nevertheless, these data, combined with long-term data at the surface and optical depth and transmission observations, yield a unique picture of global tropospheric particle chemistry. PMID:23687724

  10. Size distribution of water-soluble components in particulate matter emitted from biomass burning

    NASA Astrophysics Data System (ADS)

    Park, Seung-Shik; Sim, Soo Young; Bae, Min-Suk; Schauer, James J.

    2013-07-01

    Size-resolved measurements of particulate matter (PM) emissions from 10 biomass materials (rice straw, soybean stem, green perilla stem, red pepper stem, pine needles, cherry leaves, cherry stem, maple leaves, gingko leaves and gingko stem) were conducted in a laboratory hood chamber environment using a 10-stage MOUDI. Samples were analyzed to determine the mass, water soluble organic carbon (WSOC), and water soluble inorganic species. This study examines how particle emissions and size distributions of chemical components vary with biomass materials. Mass fractions of water soluble organic mass (WSOM) (=1.6 × WSOC) and ionic species to the PM1.8 emissions varied significantly depending on the biomass type burned. The percent mass of WSOM in PM1.8 emissions ranged from 19.8% (green perilla stem) to 41.9% (red pepper stem) for agricultural crop residues, while the tree category accounted for 9.6% (gingko leaves) to 44.0% (gingko stem) of the PM1.8 emissions. Total ionic species contents in the PM1.8 mass ranged from 7.4% (rice straw) to 26.9% (green perilla stem) for the agricultural waste category, and 5.8% (maple leaves) to 23.5% (gingko stem) for the tree category. The ionic species fraction of the PM1.8 emission was dominated by K+, Cl-, and SO, while Ca2+ was important in the coarse mode particles (>3.1 μm). PM1.8 emissions of K+, Cl-, and SO were as high as 16.9%, 9.0%, and 5.8%, respectively, and were from the green perilla stem, red pepper stem, and gingko stem emissions. Normalized size distributions of mass, WSOC, K+, Cl-, SO, and oxalate in the biomass burning emissions showed a unimodal size distribution, peaking in the size ranges of 0.32-0.55 μm and 0.55-1.0 μm. Size-resolved PM mass fractions of WSOM, K+, Cl-, and SO showed fairly consistent distributions for each biomass type, with higher fractions in the ultrafine mode (<0.10 μm) and lower fractions in the accumulation mode of 0.32-1.0 μm. The size distributions of WSOC were strongly

  11. Size-dependent reproductive pattern and short-term reproductive cost in Rumex obtusifolius L

    NASA Astrophysics Data System (ADS)

    Pino, Joan; Sans, F. Xavier; Masalles, Ramon M.

    2002-10-01

    This paper analyses the size-dependent reproductive pattern of Rumex obtusifolius L. growing in lucerne crops ( Medicago sativa L.), and its importance in determining the existence of a short-term reproductive cost. Size effects on reproductive pattern were evaluated by determining the role of plant size at the time of first reproduction, and the size-dependency of flowering probability (estimated as the proportion of flowering plants), plant fecundity, and reproductive effort (estimated as the ratio between reproductive and vegetative biomass). These parameters were recorded over the reproductive episodes determined by crop harvesting during the reproductive period. The results showed that size was much more important than age in determining time of first reproduction. Seed output decreased progressively over the reproductive period, probably in relation to an increasing short-term reproductive cost caused by a gradual depletion of plant resources. Probability of flowering over the successive reproductive episodes increased with plant size. The allometric relationship of vegetative versus reproductive biomass indicated that reproductive biomass increased less sharply than vegetative biomass and, consequently, reproductive effort decreased as plant size increased. Assuming a direct relationship between reproductive effort and reproductive cost, the size-dependent flowering probability could reflect, in turn, the existence of a size-dependent reproductive cost that would decrease as plant size increased. Ecological implications of these results are discussed.

  12. Iterative method for the inversion of multiwavelength lidar signals to determine aerosol size distribution.

    PubMed

    Rajeev, K; Parameswaran, K

    1998-07-20

    Two iterative methods of inverting lidar backscatter signals to determine altitude profiles of aerosol extinction and altitude-resolved aerosol size distribution (ASD) are presented. The first method is for inverting two-wavelength lidar signals in which the shape of the ASD is assumed to be of power-law type, and the second method is for inverting multiwavelength lidar signals without assuming any a priori analytical form of ASD. An arbitrary value of the aerosol extinction-to-backscatter ratio (S(1)) is assumed initially to invert the lidar signals, and the ASD determined by use of the spectral dependence of the retrieved aerosol extinction coefficients is used to improve the value of S(1) iteratively. The methods are tested for different forms of altitude-dependent ASD's by use of simulated lidar-backscatter-signal profiles. The effect of random noise on the lidar backscatter signals is also studied.

  13. Airborne brake wear debris: size distributions, composition, and a comparison of dynamometer and vehicle tests.

    PubMed

    Sanders, Paul G; Xu, Ning; Dalka, Tom M; Maricq, M Matti

    2003-09-15

    Particle size distributions of light-duty vehicle brake wear debris are reported with careful attention paid to avoid sampling biases. Electrical low-pressure impactor and micro-orifice uniform deposit impactor measurements yield consistent size distributions, and the net particulate matter mass from each method is in good agreement with gravimetric filter measurements. The mass mean diameter of wear debris from braking events representative of urban driving is 6 microm, and the number-weighted mean is 1-2 microm for three currently used classes of lining materials: low metallic, semimetallic, and non-asbestos organic (NAO). In contrast, the wear rates are very material dependent, both in number and mass of particles, with 3-4 times higher emissions observed from the low metallic linings as compared to the semimetallic and NAO linings. Wind tunnel and test track measurements demonstrate the appearance of micron size particles that correlate with braking events, with approximately 50% of the wear debris being airborne for the test vehicle in this study. Elemental analysis of the wear debris reveals a consistent presence of the elements Fe, Cu, and Ba in both dynamometer and test track samples. PMID:14524436

  14. A Review of Discrete Element Method (DEM) Particle Shapes and Size Distributions for Lunar Soil

    NASA Technical Reports Server (NTRS)

    Lane, John E.; Metzger, Philip T.; Wilkinson, R. Allen

    2010-01-01

    As part of ongoing efforts to develop models of lunar soil mechanics, this report reviews two topics that are important to discrete element method (DEM) modeling the behavior of soils (such as lunar soils): (1) methods of modeling particle shapes and (2) analytical representations of particle size distribution. The choice of particle shape complexity is driven primarily by opposing tradeoffs with total number of particles, computer memory, and total simulation computer processing time. The choice is also dependent on available DEM software capabilities. For example, PFC2D/PFC3D and EDEM support clustering of spheres; MIMES incorporates superquadric particle shapes; and BLOKS3D provides polyhedra shapes. Most commercial and custom DEM software supports some type of complex particle shape beyond the standard sphere. Convex polyhedra, clusters of spheres and single parametric particle shapes such as the ellipsoid, polyellipsoid, and superquadric, are all motivated by the desire to introduce asymmetry into the particle shape, as well as edges and corners, in order to better simulate actual granular particle shapes and behavior. An empirical particle size distribution (PSD) formula is shown to fit desert sand data from Bagnold. Particle size data of JSC-1a obtained from a fine particle analyzer at the NASA Kennedy Space Center is also fitted to a similar empirical PSD function.

  15. Turbulent crude oil jets in crossflow: holographic measurements of droplet size distributions

    NASA Astrophysics Data System (ADS)

    Xue, Xinzhi; Murphy, David; Katz, Joseph

    2015-11-01

    Buoyant, immiscible jets and plumes are created by subsurface oil well blowouts. In this experimental study, high speed visualizations and digital holography follow vertical crude oil turbulent jets of varying Reynolds and Ohnesorge numbers, all falling in the atomization range, while being towed in a towing tank generating `crossflows' at varying crossflow-to-exit speed velocity ratios. The droplet size distributions are measured using a submerged miniature holographic microscopy system, enabling comparison between the plume behavior and the droplet size distributions. Due to variations in rise-velocity with droplet size, the shape and dispersion rate of the plume depends on the interfacial tension. Hence, the crude oil plume rises faster than a `control' miscible oil analog with the same density and viscosity. Premixing the oil with dispersant (Corexit 9500A) at dispersant to oil (DOR) ratios of 1:100 and 1:25 reduces the oil-seawater interfacial tension by up to two orders of magnitude, promoting formation of micro-droplets. Hence, the plume rises at a slower rate, with the large droplets rapidly escaping, leaving smaller ones behind. Furthermore, for the DOR 1:25 case, some of the microdroplets are entrained into the vortices prominent in the wake region under the plume. Funding provided by the Gulf of Mexico Research Initiative.

  16. The Floe Size Distribution in the Marginal Ice Zone of the Beaufort and Chukchi Seas

    NASA Astrophysics Data System (ADS)

    Schweiger, A. J. B.; Stern, H. L., III; Stark, M.; Zhang, J.; Steele, M.; Hwang, P. B.

    2014-12-01

    Several key processes in the Marginal Ice Zone (MIZ) of the Arctic Ocean are related to the size of the ice floes, whose diameters range from meters to tens of kilometers. The floe size distribution (FSD) influences the mechanical properties of the ice cover, air-sea momentum and heat transfer, lateral melting, and light penetration. However, no existing sea-ice/ocean models currently simulate the FSD in the MIZ. Model development depends on observations of the FSD for parameterization, calibration, and validation. To support the development and implementation of the FSD in the Marginal Ice Zone Modeling and Assimilation System (MIZMAS), we have analyzed the FSD in the Beaufort and Chukchi seas using multiple sources of satellite imagery: NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites (250 m pixel size), the USGS Landsat 8 satellite (80 m pixel size), the Canadian Space Agency's synthetic aperture radar (SAR) on RADARSAT (50 meter pixel size), and declassified National Technical Means imagery from the Global Fiducials Library (GFL) of the USGS (1 m pixel size). The procedure for identifying ice floes in the imagery begins with manually delineating cloud-free regions (if necessary). A threshold is then chosen to separate ice from water. Morphological operations and other semi-automated techniques are used to identify individual floes, whose properties are then easily calculated. We use the mean caliper diameter as the measure of floe size. The FSD is adequately described by a power-law in which the exponent characterizes the relative number of large and small floes. Changes in the exponent over time and space reflect changes in physical processes in the MIZ, such as sea-ice deformation, fracturing, and melting. We report results of FSD analysis for the spring and summer of 2013 and 2014, and show how the FSD will be incorporated into the MIZMAS model.

  17. A comparison of TEM and DLS methods to characterize size distribution of ceramic nanoparticles

    NASA Astrophysics Data System (ADS)

    Souza, T. G. F.; Ciminelli, V. S. T.; Mohallem, N. D. S.

    2016-07-01

    The accuracy of dynamic light scattering (DLS) measurements are compared with transmission electron microscopy (TEM) studies for characterization of size distributions of ceramic nanoparticles. It was found that measurements by DLS using number distribution presented accurate results when compared to TEM. The presence of dispersants and the enlargement of size distributions induce errors to DLS particle sizing measurements and shifts its results to higher values.

  18. Proper definition and evolution of generalized transverse momentum dependent distributions

    NASA Astrophysics Data System (ADS)

    Echevarria, Miguel G.; Idilbi, Ahmad; Kanazawa, Koichi; Lorcé, Cédric; Metz, Andreas; Pasquini, Barbara; Schlegel, Marc

    2016-08-01

    We consider one of the most fundamental sets of hadronic matrix elements, namely the generalized transverse momentum dependent distributions (GTMDs), and argue that their existing definitions lack proper evolution properties. By exploiting the similarity of GTMDs with the much better understood transverse momentum distributions, we argue that the existing definitions of GTMDs have to include an additional dependence on soft gluon radiation in order to render them properly defined. With this, we manage to obtain the evolution kernel of all (un)polarized quark and gluon GTMDs, which turns out to be spin independent. As a byproduct, all large logarithms can be resummed up to next-to-next-to-leading-logarithmic accuracy with the currently known perturbative ingredients.

  19. Hydrometeor Size Distribution Measurements by Imaging the Attenuation of a Laser Spot

    NASA Technical Reports Server (NTRS)

    Lane, John

    2013-01-01

    The optical extinction of a laser due to scattering of particles is a well-known phenomenon. In a laboratory environment, this physical principle is known as the Beer-Lambert law, and is often used to measure the concentration of scattering particles in a fluid or gas. This method has been experimentally shown to be a usable means to measure the dust density from a rocket plume interaction with the lunar surface. Using the same principles and experimental arrangement, this technique can be applied to hydrometeor size distributions, and for launch-pad operations, specifically as a passive hail detection and measurement system. Calibration of a hail monitoring system is a difficult process. In the past, it has required comparison to another means of measuring hydrometeor size and density. Using a technique recently developed for estimating the density of surface dust dispersed during a rocket landing, measuring the extinction of a laser passing through hail (or dust in the rocket case) yields an estimate of the second moment of the particle cloud, and hydrometeor size distribution in the terrestrial meteorological case. With the exception of disdrometers, instruments that measure rain and hail fall make indirect measurements of the drop-size distribution. Instruments that scatter microwaves off of hydrometeors, such as the WSR-88D (Weather Surveillance Radar 88 Doppler), vertical wind profilers, and microwave disdrometers, measure the sixth moment of the drop size distribution (DSD). By projecting a laser onto a target, changes in brightness of the laser spot against the target background during rain and hail yield a measurement of the DSD's second moment by way of the Beer-Lambert law. In order to detect the laser attenuation within the 8-bit resolution of most camera image arrays, a minimum path length is required. Depending on the intensity of the hail fall rate for moderate to heavy rainfall, a laser path length of 100 m is sufficient to measure variations in

  20. Surface structures of cerium oxide nanocrystalline particles from the size dependence of the lattice parameters

    NASA Astrophysics Data System (ADS)

    Tsunekawa, S.; Ito, S.; Kawazoe, Y.

    2004-10-01

    Cerium oxide nanocrystalline particles are synthesized and monodispersed in the size range from 2 to 8nm in diameter. The dependence of the lattice parameters on particle size is obtained by x-ray and electron diffraction analyses. The size dependence well coincides with the estimation based on the assumption that the surface is composed of one layer of Ce2O3 and the inside consists of CeO2. The effect of particle size on lattice parameters is discussed from the differences in the fabrication method and the surface structure.

  1. The stress-strain behavior of coronary stent struts is size dependent.

    PubMed

    Murphy, B P; Savage, P; McHugh, P E; Quinn, D F

    2003-06-01

    Coronary stents are used to re-establish the vascular lumen and flow conditions within the coronary arteries; the typical thickness of a stent strut is 100 microm, and average grain sizes of approximately 25 microm exist in stainless steel stents. The purpose of this study is to investigate the effect of strut size on the stress strain behavior of 316 L stainless steel. Other materials have shown a size dependence at the micron size scale; however, at present there are no studies that show a material property size dependence in coronary stents. Electropolished stainless steel stent struts within the size range of 60-500 microm were tensile tested. The results showed that within the size range of coronary stent struts a size dependent stress-strain relationship is required to describe the material. Finite element models of the final phase of fracture, i.e., void growth models, explained partially the reason for this size effect. This study demonstrated that a size based stress-strain relationship must be used to describe the tensile behavior material of 316 L stainless steel at the size scale of coronary stent struts.

  2. New real-time technique to measure the size distribution of water-insoluble aerosols.

    PubMed

    Greenwald, Roby; Bergin, Michael H; Carrico, Christian M; Grant, Don

    2005-07-01

    To date, there has been much research into the size distribution of ambient atmospheric aerosols, particularly either the total aerosol population or water-soluble ionic species such as sulfate or nitrate. Meanwhile, there have been virtually no size-resolved measurements of water-insoluble aerosols (WIA). This has been due to a lack of practical measurement technology rather than a reflection of the importance of WIA to climate and health. Particle solubility influences the planetary radiation balance both directly and indirectly: solubility influences both the amount of hygroscopic growth (and thus light scattering) that occurs as a function of relative humidity and the ability of particles to serve as cloud condensation nuclei (and thus the lifetime and albedo of clouds). Also, recent information suggests that WIA may be harmful to human health. To address these concerns, a new real-time technique has been developed to measure the size-resolved concentration of WIA. This technique involves the entrainment of particles into a liquid stream and measurement of the WIA size distribution using a liquid optical particle counter. The time resolution of this instrumentation is approximately 4 min (depending on flow rate) and is capable of sizing and counting insoluble particles with diameters of 0.25-2.0 microm at atmospheric concentrations as low as 0.1 cm(-3). Laboratory characterization using polystyrene latex spheres shows agreement within +/-5% of the liquid stream and air stream particle concentrations when adjusted for flow rate. The instrumentation was field-tested at a rural site on the edge of the metro-Atlanta urban area. During this test, the WIA concentration averaged 5% of the total particle concentration between 0.25 and 2.0 microm but reached as high as 35%.

  3. 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.