WorldWideScience

Sample records for void size distributions

  1. Size effects on void growth in single crystals with distributed voids

    DEFF Research Database (Denmark)

    Borg, Ulrik; Niordson, Christian Frithiof; Kysar, J.W.

    2008-01-01

    The effect of void size on void growth in single crystals with uniformly distributed cylindrical voids is studied numerically using a finite deformation strain gradient crystal plasticity theory with an intrinsic length parameter. A plane strain cell model is analyzed for a single crystal...

  2. Magnetic pattern at supergranulation scale: the Void Size Distribution

    CERN Document Server

    Berrilli, Francesco; Del Moro, Dario

    2014-01-01

    The large-scale magnetic pattern of the quiet sun is dominated by the magnetic network. This network, created by photospheric magnetic fields swept into convective downflows, delineates the boundaries of large scale cells of overturning plasma and exhibits voids in magnetic organization. Such voids include internetwork fields, a mixed-polarity sparse field that populate the inner part of network cells. To single out voids and to quantify their intrinsic pattern a fast circle packing based algorithm is applied to 511 SOHO/MDI high resolution magnetograms acquired during the outstanding solar activity minimum between 23 and 24 cycles. The computed Void Distribution Function shows a quasi-exponential decay behavior in the range 10-60 Mm. The lack of distinct flow scales in such a range corroborates the hypothesis of multi-scale motion flows at the solar surface. In addition to the quasi-exponential decay we have found that the voids reveal departure from a simple exponential decay around 35 Mm.

  3. A variational constitutive model for the distribution and interactions of multi-sized voids

    KAUST Repository

    Liu, Jinxing

    2013-07-29

    The evolution of defects or voids, generally recognized as the basic failure mechanism in most metals and alloys, has been intensively studied. Most investigations have been limited to spatially periodic cases with non-random distributions of the radii of the voids. In this study, we use a new form of the incompressibility of the matrix to propose the formula for the volumetric plastic energy of a void inside a porous medium. As a consequence, we are able to account for the weakening effect of the surrounding voids and to propose a general model for the distribution and interactions of multi-sized voids. We found that the single parameter in classical Gurson-type models, namely void volume fraction is not sufficient for the model. The relative growth rates of voids of different sizes, which can in principle be obtained through physical or numerical experiments, are required. To demonstrate the feasibility of the model, we analyze two cases. The first case represents exactly the same assumption hidden in the classical Gurson\\'s model, while the second embodies the competitive mechanism due to void size differences despite in a much simpler manner than the general case. Coalescence is implemented by allowing an accelerated void growth after an empirical critical porosity in a way that is the same as the Gurson-Tvergaard-Needleman model. The constitutive model presented here is validated through good agreements with experimental data. Its capacity for reproducing realistic failure patterns is shown by simulating a tensile test on a notched round bar. © 2013 The Author(s).

  4. Microstructural characterization of XLPE electrical insulation in power cables: determination of void size distributions using TEM

    Science.gov (United States)

    Markey, L.; Stevens, G. C.

    2003-10-01

    In an effort to progress in our understanding of the ageing mechanisms of high voltage cables submitted to electrical and thermal stresses, we present a quantitative study of voids, the defects which are considered to be partly responsible for cable failure. We propose a method based on large data sets of transmission electron microscopy (TEM) observations of replicated samples allowing for the determination of void concentration distribution as a function of void size in the mesoscopic to microscopic range at any point in the cable insulation. A theory is also developed to calculate the effect of etching on the apparent size of the voids observed. We present the first results of this sort ever obtained on two industrial cables, one of which was aged in an AC field. Results clearly indicate that a much larger concentration of voids occur near the inner semiconductor compared to the bulk of the insulation, independently of ageing. An effect of ageing can also be seen near the inner semiconductor, resulting in an increase in the total void internal surface area and a slight shift of the concentration curve towards larger voids, with the peak moving from about 40 nm to about 50 nm.

  5. Why a steady state void size distribution in irradiated UO2? A modeling approach

    Science.gov (United States)

    Maillard, S.; Martin, G.; Sabathier, C.

    2016-05-01

    In UO2 pellets irradiated in standard water reactor, Xe nano-bubbles nucleate, grow, coarsen and finally reach a quasi steady state size distribution: transmission electron microscope (TEM) observations typically report a concentration around 10-4 nm-3 and a radius around 0.5 nm. This phenomenon is often considered as a consequence of radiation enhanced diffusion, precipitation of gas atoms and ballistic mixing. However, in UO2 thin foils irradiated with energetic ions at room temperature, a nano-void population whose size distribution reaches a similar steady state can be observed, although quasi no foreign atoms are implanted nor significant cation vacancy diffusion expected in conditions. Atomistic simulations performed at low temperature only address the first stage of the process, supporting the assumption of void heterogeneous nucleation: 25 keV sub-cascades directly produce defect aggregates (loops and voids) even in the absence of gas atoms and thermal diffusion. In this work a semi-empirical stochastic model is proposed to enlarge the time scale covered by simulation up to damage levels where every point in the material undergoes the superposition of a large number of sub-cascade impacts. To account for the accumulation of these impacts, simple rules inferred from the atomistic simulation results are used. The model satisfactorily reproduces the TEM observations of nano-voids size and concentration, which paves the way for the introduction of a more realistic damage term in rate theory models.

  6. Ultrasonic Techniques for Air Void Size Distribution and Property Evaluation in Both Early-Age and Hardened Concrete Samples

    Directory of Open Access Journals (Sweden)

    Shuaicheng Guo

    2017-03-01

    Full Text Available Entrained air voids can improve the freeze-thaw durability of concrete, and also affect its mechanical and transport properties. Therefore, it is important to measure the air void structure and understand its influence on concrete performance for quality control. This paper aims to measure air void structure evolution at both early-age and hardened stages with the ultrasonic technique, and evaluates its influence on concrete properties. Three samples with different air entrainment agent content were specially prepared. The air void structure was determined with optimized inverse analysis by achieving the minimum error between experimental and theoretical attenuation. The early-age sample measurement showed that the air void content with the whole size range slightly decreases with curing time. The air void size distribution of hardened samples (at Day 28 was compared with American Society for Testing and Materials (ASTM C457 test results. The air void size distribution with different amount of air entrainment agent was also favorably compared. In addition, the transport property, compressive strength, and dynamic modulus of concrete samples were also evaluated. The concrete transport decreased with the curing age, which is in accordance with the air void shrinkage. The correlation between the early-age strength development and hardened dynamic modulus with the ultrasonic parameters was also evaluated. The existence of clustered air voids in the Interfacial Transition Zone (ITZ area was found to cause severe compressive strength loss. The results indicated that this developed ultrasonic technique has potential in air void size distribution measurement, and demonstrated the influence of air void structure evolution on concrete properties during both early-age and hardened stages.

  7. Size-Effects in Void Growth

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof

    2005-01-01

    The size-effect on ductile void growth in metals is investigated. The analysis is based on unit cell models both of arrays of cylindrical voids under plane strain deformation, as well as arrays of spherical voids using an axisymmetric model. A recent finite strain generalization of two higher order...

  8. Size-Effects in Void Growth

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof

    2005-01-01

    The size-effect on ductile void growth in metals is investigated. The analysis is based on unit cell models both of arrays of cylindrical voids under plane strain deformation, as well as arrays of spherical voids using an axisymmetric model. A recent finite strain generalization of two higher order...... strain gradient plasticity models is implemented in a finite element program, which is used to study void growth numerically. The results based on the two models are compared. It is shown how gradient effects suppress void growth on the micron scale when compared to predictions based on conventional...... models. This increased resistance to void growth, due to gradient hardening, is accompanied by an increase in the overall strength for the material. Furthermore, for increasing initial void volume fraction, it is shown that the effect of gradients becomes more important to the overall response but less...

  9. New Statistical Perspective to The Cosmic Void Distribution

    CERN Document Server

    Pycke, Jean-Renaud

    2016-01-01

    In this study, we obtain the size distribution of voids as a 3-parameter redshift independent log-normal void probability function (VPF) directly from the Cosmic Void Catalog (CVC). Although many statistical models of void distributions are based on the counts in randomly placed cells, the log-normal VPF that we here obtain is independent of the shape of the voids due to the parameter-free void finder of the CVC. We use three void populations drawn from the CVC generated by the Halo Occupation Distribution (HOD) Mocks which are tuned to three mock SDSS samples to investigate the void distribution statistically and the effects of the environments on the size distribution. As a result, it is shown that void size distributions obtained from the HOD Mock samples are satisfied by the 3-parameter log-normal distribution. In addition, we find that there may be a relation between hierarchical formation, skewness and kurtosis of the log-normal distribution for each catalog. We also show that the shape of the 3-paramet...

  10. Coupling effects of void size and void shape on the growth of prolate ellipsoidal microvoid

    Institute of Scientific and Technical Information of China (English)

    Minsheng Huang; Zhenhuan Li; Cheng Wang

    2005-01-01

    The combined effects of void size and void shape on the void growth are studied by using the classical spectrum method. An infinite solid containing an isolated prolate spheroidal void is considered to depict the void shape effect and the Fleck-Hutchinson phenomenological strain gradient plasticity theory is employed to capture the size effects. It is found that the combined effects of void size and void shape are mainly controlled by the remote stress triaxiality. Based on this, a new size-dependent void growth model similar to the Rice-Tracey model is proposed and an important conclusion about the size-dependent void growth is drawn: the growth rate of the void with radius smaller than a critical radius rc may be ignored. It is interesting that rc is a material constant independent of the initial void shape and the remote stress triaxiality.

  11. Scaling of voids and fractality in the galaxy distribution

    CERN Document Server

    Gaite, J; Gaite, Jose; Manrubia, Susanna C.

    2002-01-01

    We study here, from first principles, what properties of voids are to be expected in a fractal point distribution and how the void distribution is related to its morphology. We show this relation in various examples and apply our results to the distribution of galaxies. If the distribution of galaxies forms a fractal set, then this property results in a number of scaling laws to be fulfilled by voids. Consider a fractal set of dimension $D$ and its set of voids. If voids are ordered according to decreasing sizes (largest void has rank R=1, second largest R=2 and so on), then a relation between size $\\Lambda$ and rank of the form $\\Lambda (R) \\propto R^{-z}$ must hold, with $z = d/D$, and where $d$ is the euclidean dimension of the space where the fractal is embedded. The physical restriction $D 1$ in a fractal set. The average size $\\bar \\Lambda$ of voids depends on the upper ($\\Lambda_u$) and the lower ($\\Lambda_l$) cut-off as ${\\bar \\Lambda} \\propto \\Lambda_u^{1-D/d} \\Lambda_l^{D/d}$. Current analysis of v...

  12. Plasticity size effects in voided crystals

    DEFF Research Database (Denmark)

    Hussein, M. I.; Borg, Ulrik; Niordson, Christian Frithiof;

    The shear and equi-biaxial straining responses of periodic voided single crystals are analysed using discrete dislocation plasticity and a continuum strain gradient crystal plasticity theory. In the discrete dislocation formulation the dislocations are all of edge character and are modelled as line...... predictions of the two formulations for all crystal types and void volume fractions considered when the material length scale in the non-local plasticity model chosen to be $0.325\\mu m$ (around ten times the slip plane spacing in the discrete dislocation models)....

  13. Plasticity size effects in voided crystals

    DEFF Research Database (Denmark)

    Hussein, M. I.; Borg, Ulrik; Niordson, Christian Frithiof

    singularities in an elastic material. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and annihilation are incorporated through a set of constitutive rules. Over the range of length scales investigated, both the discrete dislocation and strain...... predictions of the two formulations for all crystal types and void volume fractions considered when the material length scale in the non-local plasticity model chosen to be $0.325\\mu m$ (around ten times the slip plane spacing in the discrete dislocation models)....

  14. Plasticity size effects in voided crystals

    DEFF Research Database (Denmark)

    Hussein, M.I.; Borg, Ulrik; Niordson, Christian Frithiof

    2008-01-01

    as line singularities in an elastic material. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and annihilation are incorporated through a set of constitutive rules. Over the range of length scales investigated, both the discrete dislocation...... between predictions of the two formulations for all crystal types and void volume fractions considered when the material length scale in the non-local plasticity model is chosen to be 0.325 mu m (about 10 times the slip plane spacing in the discrete dislocation models)....

  15. Constitutive modeling of rate dependence and microinertia effects in porous-plastic materials with multi-sized voids (MSVs)

    KAUST Repository

    Liu, Jinxing

    2012-11-27

    Micro-voids of varying sizes exist in most metals and alloys. Both experiments and numerical studies have demonstrated the critical influence of initial void sizes on void growth. The classical Gurson-Tvergaard-Needleman model summarizes the influence of voids with a single parameter, namely the void-volume fraction, excluding any possible effects of the void-size distribution. We extend our newly proposed model including the multi-sized void (MSV) effect and the void-interaction effect for the capability of working for both moderate and high loading rate cases, where either rate dependence or microinertia becomes considerable or even dominant. Parametric studies show that the MSV-related competitive mechanism among void growth leads to the dependence of the void growth rate on void size, which directly influences the void\\'s contribution to the total energy composition. We finally show that the stress-strain constitutive behavior is also affected by this MSV-related competitive mechanism. The stabilizing effect due to rate sensitivity and microinertia is emphasized. © 2013 IOP Publishing Ltd.

  16. Constitutive modeling of rate dependence and microinertia effects in porous-plastic materials with multi-sized voids (MSVs)

    Science.gov (United States)

    Liu, J. X.; El Sayed, T.

    2013-01-01

    Micro-voids of varying sizes exist in most metals and alloys. Both experiments and numerical studies have demonstrated the critical influence of initial void sizes on void growth. The classical Gurson-Tvergaard-Needleman model summarizes the influence of voids with a single parameter, namely the void-volume fraction, excluding any possible effects of the void-size distribution. We extend our newly proposed model including the multi-sized void (MSV) effect and the void-interaction effect for the capability of working for both moderate and high loading rate cases, where either rate dependence or microinertia becomes considerable or even dominant. Parametric studies show that the MSV-related competitive mechanism among void growth leads to the dependence of the void growth rate on void size, which directly influences the void's contribution to the total energy composition. We finally show that the stress-strain constitutive behavior is also affected by this MSV-related competitive mechanism. The stabilizing effect due to rate sensitivity and microinertia is emphasized.

  17. Effects of void size and gas content on electrical breakdown in lightweight, mechanically compliant, void-filled dielectrics

    Science.gov (United States)

    Anderson, R. A.; Lagasse, R. R.; Russick, E. M.; Schroeder, J. L.

    2002-03-01

    Dielectric potting materials (encapsulants) are used to prevent air breakdown in high-voltage electrical devices. We report breakdown strengths in void-filled encapsulants, stressed with unipolar voltage pulses of the order of 10 μs duration. High strengths, on the order of 100 kV mm-1, are measured under these test conditions. The materials studied include low-density open celled gel-derived foams with cell sizes of 4 μm or less, closed celled CO2-blown polystyrene and urethane foams, and epoxies containing 48 vol % of hollow glass microballoon (GMB) fillers. These last specimens varied the void gas (N2 or SO2) and also the void diameters (tens to hundreds of μm). Our measurements are thought to be directly sensitive to the rate of field-induced ionization events in the void gas; however, the breakdown strengths of the materials tested appeared to vary in direct proportion with the conventional Paschen-law gas-discharge inception threshold, the electric stress at which gas-ionization avalanches become possible. The GMB-epoxy specimens displayed this type of dependence of breakdown strength on the void-gas density and void size, but the measurements were an order of magnitude above the conventional predictions. Small-celled foams also showed increased breakdown strengths with decreased cell size, although their irregular void geometry prevented a direct comparison with the more uniformly structured microballoon-filled encapsulants. The experimental observations are consistent with a breakdown mechanism in which the discharge of a few voids can launch a full breakdown in the composite material.

  18. Nonlocal plasticity effects on interaction of different size voids

    DEFF Research Database (Denmark)

    Tvergaard, Viggo; Niordson, Christian Frithiof

    2004-01-01

    A nonlocal elastic-plastic material model is used to show that the rate of void growth is significantly reduced when the voids are small enough to be comparable with a characteristic material length. For a very small void in the material between much larger voids the competition between...... an increased growth rate due to the stress concentrations around the larger voids and a reduced growth rate due to the nonlocal effects is studied. The analyses are based on an axisymmetric unit cell model with special boundary conditions, which allow for a relatively simple investigation of a full three...

  19. Effects of Heterogeneous Sink Distribution on Void Swelling

    DEFF Research Database (Denmark)

    Leffers, Torben; Volobuyev, A. V.; Gann, V. V.

    1986-01-01

    Swelling rates are calculated for two types of material with heterogeneous distributions of dislocations and voids, namely copper irradiated with neutrons to low dose at 250 degree C and heavily cold-worked copper irradiated with 1 MeV electrons in a HVEM at 250 degree C. Both materials...... are considered to consist of non-interacting spherical components with a wall and an inner cell with different dislocation and/or void densities. We subdivide the sphere (wall plus cell) in a number of concentric shells and find a quasi-static solution for the interstitial and vacancy concentrations...

  20. Shapes and Sizes of Voids in the LCDM Universe: Excursion Set Approach

    CERN Document Server

    Shandarin, S; Heitmann, K; Habib, S; Shandarin, Sergei; Feldman, Hume A.; Heitmann, Katrin

    2006-01-01

    We study the global distribution and morphology of dark matter voids in a LCDM universe using density fields generated by N-body simulations. Voids are defined as isolated regions of the low-density excursion set specified via density thresholds, the density thresholds being quantified by the corresponding filling factors, i.e., the fraction of the total volume in the excursion set. Our work encompasses a systematic investigation of the void volume function, the volume fraction in voids, and the fitting of voids to corresponding ellipsoids and spheres. We emphasize the relevance of the percolation threshold to the void volume statistics of the density field both in the high redshift, Gaussian random field regime, as well as in the present epoch. By using measures such as the Inverse Porosity, we characterize the quality of ellipsoidal fits to voids, finding that such fits are a poor representation of the larger voids that dominate the volume of the void excursion set.

  1. Study of void sizes and loading configurations effects on shock initiation due to void collapse in heterogeneous energetic materials

    Science.gov (United States)

    Roy, Sidhartha; Rai, Nirmal; Udaykumar, H. S.

    2015-06-01

    In heterogeneous energetic materials, presence of porosity has been seen to increase its sensitivity towards shock initiation and ignition. Under the application of shock load, the viscoplastic deformation of voids and its collapse leads to the formation of local high temperature regions known as hot spots. The chemical reaction triggers at the hot spot depending on the local temperature and grows eventually leading to ignition and formation of detonation waves in the material. The temperature of the hot spot depends on various factors such as shock strength, void size, void arrangements, loading configuration etc. Hence, to gain deeper understanding on shock initiation and ignition study due to void collapse, a parametric study involving various factors which can affect the hot spot temperature is desired. In the current work, effects of void sizes, shock strength and loading configurations has been studied for shock initiation in HMX using massively parallel Eulerian code, SCIMITAR3D. The chemical reaction and decomposition for HMX has been modeled using Henson-Smilowitz multi step mechanism. The effect of heat conduction has also been taken into consideration. Ignition threshold criterion has been established for various factors as mentioned. The critical hot spot temperature and its size which can lead to ignition has been obtained from numerical experiments.

  2. Luminosity distance in Swiss cheese cosmology with randomized voids. II. Magnification probability distributions

    CERN Document Server

    Flanagan, Éanna É; Wasserman, Ira; Vanderveld, R Ali

    2011-01-01

    We study the fluctuations in luminosity distances due to gravitational lensing by large scale (> 35 Mpc) structures, specifically voids and sheets. We use a simplified "Swiss cheese" model consisting of a \\Lambda -CDM Friedman-Robertson-Walker background in which a number of randomly distributed non-overlapping spherical regions are replaced by mass compensating comoving voids, each with a uniform density interior and a thin shell of matter on the surface. We compute the distribution of magnitude shifts using a variant of the method of Holz & Wald (1998), which includes the effect of lensing shear. The standard deviation of this distribution is ~ 0.027 magnitudes and the mean is ~ 0.003 magnitudes for voids of radius 35 Mpc, sources at redshift z_s=1.0, with the voids chosen so that 90% of the mass is on the shell today. The standard deviation varies from 0.005 to 0.06 magnitudes as we vary the void size, source redshift, and fraction of mass on the shells today. If the shell walls are given a finite thic...

  3. The void-size effect on plastic flow localization in the Gurson model

    Science.gov (United States)

    Jie, Wen; Yonggang, Huang; Keh-Chih, Hwang

    2004-08-01

    Recent studies have shown that the size of microvoids has a significant effect on the void growth rate. The purpose of this paper is to explore whether the void size effect can influence the plastic flow localization in ductile materials. We have used the extended Gurson's dilatational plasticity theory, which accounts for the void size effect, to study the plastic flow localization in porous solids with long cylindrical voids. The localization model of Rice is adopted, in which the material inside the band may display a different response from that outside the band at the incipient plastic flow localization. The present study shows that it has little effect on the shear band angle.

  4. THE VOID-SIZE EFFECT ON PLASTIC FLOW LOCALIZATION IN THE GURSON MODEL

    Institute of Scientific and Technical Information of China (English)

    WEN Jie; HUANG Yonggang; HWANG Keh-Chih

    2004-01-01

    Recent studies have shown that the size of microvoids has a significant effect on the void growth rate. The purpose of this paper is to explore whether the void size effect can influence the plastic flow localization in ductile materials. We have used the extended Gurson's dilatational plasticity theory, which accounts for the void size effect, to study the plastic flow localization in porous solids with long cylindrical voids. The localization model of Rice is adopted, in which the material inside the band may display a different response from that outside the band at the incipient plastic flow localization. The present study shows that it has little effect on the shear band angle.

  5. Validation uncertainty of MATRA code for subchannel void distributions

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Dae-Hyun; Kim, S. J.; Kwon, H.; Seo, K. W. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2014-10-15

    To extend code capability to the whole core subchannel analysis, pre-conditioned Krylov matrix solvers such as BiCGSTAB and GMRES are implemented in MATRA code as well as parallel computing algorithms using MPI and OPENMP. It is coded by fortran 90, and has some user friendly features such as graphic user interface. MATRA code was approved by Korean regulation body for design calculation of integral-type PWR named SMART. The major role subchannel code is to evaluate core thermal margin through the hot channel analysis and uncertainty evaluation for CHF predictions. In addition, it is potentially used for the best estimation of core thermal hydraulic field by incorporating into multiphysics and/or multi-scale code systems. In this study we examined a validation process for the subchannel code MATRA specifically in the prediction of subchannel void distributions. The primary objective of validation is to estimate a range within which the simulation modeling error lies. The experimental data for subchannel void distributions at steady state and transient conditions was provided on the framework of OECD/NEA UAM benchmark program. The validation uncertainty of MATRA code was evaluated for a specific experimental condition by comparing the simulation result and experimental data. A validation process should be preceded by code and solution verification. However, quantification of verification uncertainty was not addressed in this study. The validation uncertainty of the MATRA code for predicting subchannel void distribution was evaluated for a single data point of void fraction measurement at a 5x5 PWR test bundle on the framework of OECD UAM benchmark program. The validation standard uncertainties were evaluated as 4.2%, 3.9%, and 2.8% with the Monte-Carlo approach at the axial levels of 2216 mm, 2669 mm, and 3177 mm, respectively. The sensitivity coefficient approach revealed similar results of uncertainties but did not account for the nonlinear effects on the

  6. Enthalpy and void distributions in subchannels of PHWR fuel bundles

    Energy Technology Data Exchange (ETDEWEB)

    Park, J. W.; Choi, H.; Rhee, B. W. [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1998-12-31

    Two different types of the CANDU fuel bundles have been modeled for the ASSERT-IV code subchannel analysis. From calculated values of mixture enthalpy and void fraction distribution in the fuel bundles, it is found that net buoyancy effect is pronounced in the central region of the DUPIC fuel bundle when compared with the standard CANDU fuel bundle. It is also found that the central region of the DUPIC fuel bundle can be cooled more efficiently than that of the standard fuel bundle. From the calculated mixture enthalpy distribution at the exit of the fuel channel, it is found that the mixture enthalpy and void fraction can be highest in the peripheral region of the DUPIC fuel bundle. On the other hand, the enthalpy and the void fraction were found to be highest in the central region of the standard CANDU fuel bundle at the exit of the fuel channel. This study shows that the subchannel analysis is very useful in assessing thermal behavior of the fuel bundle that could be used in CANDU reactors. 10 refs., 4 figs., 2 tabs. (Author)

  7. Experimental and numerical investigation of voids distribution in VPI for ITER correction coil

    Energy Technology Data Exchange (ETDEWEB)

    Li, Juping, E-mail: ljping@ipp.ac.cn; Wu, Jiefeng; Yu, Xiaowu

    2015-06-15

    Highlights: • A sample of correction coil was treated by vacuum pressure impregnation. • The voids in sample were observed by computed tomography. • The voids distributions were simulated in 2-D and 3-D model. • The calculated voids locations had a good agreement with experiment. • The simulation was not accurate in calculating the voids content. - Abstract: The experimental and numerical investigations were conducted to study the voids distribution in VPI (Vacuum Pressure Impregnation) process for correction coil. A sample of correction coil was manufactured by VPI. The voids in sample were observed with computed tomography and the average voids content was tested. The voids content is closely related to infiltration velocity and fluid properties. In former researches, the parameters affecting voids content were combined into a single parameter, namely capillary number. By calculating the capillary numbers in different areas of the sample, the voids distribution could be acquired. The corresponding numerical analyses based on Darcy law were conducted in 2-D and 3-D models. The 2-D case was used to simulate the voids distribution on the section as a simplified model, while the 3-D case demonstrated the spatial distribution of voids. The voids locations were similar in 2-D and 3-D cases, but the voids contents were different. The numerical results were compared with the actual voids distribution in sample. It was found the voids locations were close in numerical and experimental results, but the voids content did not match. The numerical simulations are available for predicting the voids locations in VPI, but not accurate in calculating the voids content.

  8. Extension of the gurson model accounting for the void size effect

    Institute of Scientific and Technical Information of China (English)

    Jie Wen; Keh-Chih Hwang; Yonggang Huang

    2005-01-01

    A continuum model of solids with cylindrical microvoids is proposed based on the Taylor dislocation model.The model is an extension of Gurson model in the sense that the void size effect is accounted for. Beside the void volume fraction f, the intrinsic material length l becomes a parameter representing voids since the void size comes into play in the Gurson model. Approximate yield functions in analytic forms are suggested for both solids with cylindrical microvoids and with spherical microvoids. The application to uniaxial tension curves shows a precise agreement between the approximate analytic yield function and the "exact" parametric form of integrals.

  9. Effect of Void Size on the Detonation Pressure of Emulsion Explosives

    Science.gov (United States)

    Hirosaki, Yoshikazu; Murata, Kenji; Kato, Yukio; Itoh, Shigeru

    2002-07-01

    To study the effect of void size, detonation pressure as well as detonation velocity was measured using PVDF pressure gauge for the emulsion explosives sensitized with plastic balloons of five different size ranging from 0.05mm to 2.42mm. The experimental results were compared with the detonation pressure and velocity calculated using KHT code. The experimental results showed that the detonation pressure and velocity were strongly affected by void size, and that the fraction of ammonium nitrate reacted in the reaction zone was strongly dependent on void size.

  10. Geometry and scaling of cosmic voids

    CERN Document Server

    Gaite, Jose

    2008-01-01

    CONTEXT: Cosmic voids are observed in the distribution of galaxies and, to some extent, in the dark matter distribution. If these distributions have fractal geometry, it must be reflected in the geometry of voids; in particular, we expect scaling sizes of voids. However, this scaling is not well demonstrated in galaxy surveys yet. AIMS: Our objective is to understand the geometry of cosmic voids in relation to a fractal structure of matter. We intend to distinguish monofractal voids from multifractal voids, regarding their scaling properties. We plan to analyse voids in the distributions of mass concentrations (halos) in a multifractal and their relation to galaxy voids. METHODS: We make a statistical analysis of point distributions based on the void probability function and correlation functions. We assume that voids are spherical and devise a simple spherical void finder. For continuous mass distributions, we employ the methods of fractal geometry. We confirm the analytical predictions with numerical simula...

  11. Effect of endocrine treatment on voiding and prostate size in men with prostate cancer

    DEFF Research Database (Denmark)

    Klarskov, Louise L; Klarskov, Peter; Mommsen, Søren

    2012-01-01

    The aim of this study was to assess and quantify changes in voiding parameters and prostate size in men with prostate cancer from before the start of endocrine treatment and during long-term follow-up.......The aim of this study was to assess and quantify changes in voiding parameters and prostate size in men with prostate cancer from before the start of endocrine treatment and during long-term follow-up....

  12. Calculated Grain Size-Dependent Vacancy Supersaturation and its Effect on Void Formation

    DEFF Research Database (Denmark)

    Singh, Bachu Narain; Foreman, A. J. E.

    1974-01-01

    In order to study the effect of grain size on void formation during high-energy electron irradiations, the steady-state point defect concentration and vacancy supersaturation profiles have been calculated for three-dimensional spherical grains up to three microns in size. In the calculations...... of vacancy supersaturation as a function of grain size, the effects of internal sink density and the dislocation preference for interstitial attraction have been included. The computations show that the level of vacancy supersaturation achieved in a grain decreases with decreasing grain size. The grain size...... dependence of the maximum vacancy supersaturation in the centre of the grains is found to be very similar to the grain size dependence of the maximum void number density and void volume swelling measured in the central regions of austenitic stainless steel grains. This agreement reinforces the interpretation...

  13. Effect of Grain Size on Void Formation during High-Energy Electron Irradiation of Austenitic Stainless Steel

    DEFF Research Database (Denmark)

    Singh, Bachu Narain

    1974-01-01

    Thin foils of an ‘ experimental ’ austenitic stainless steel, with and without dispersions of aluminium oxide particles, are irradiated with 1 MeV electrons in a High Voltage Electron Microscope at 600°C. Evidence of grain size dependent void nucleation, void concentration, and void volume swelling...

  14. Pore size distribution mapping

    OpenAIRE

    Strange, John H.; J. Beau W. WEBBER; Schmidt, S.D.

    1996-01-01

    Pore size distribution mapping has been demonstrated using NMR cryoporometry\\ud in the presence of a magnetic field gradient, This novel method is extendable to 2D and 3D mapping. It offers a unique nondestructive method of obtaining full pore-size distributions in the range 3 to 100 nm at any point within a bulk sample. \\ud

  15. Study on void fraction distribution in the moderator cell of Cold Neutron Source systems in China Advanced Research Reactor

    Science.gov (United States)

    Li, Liangxing; Li, Huixiong; Hu, Jinfeng; Bi, Qincheng; Chen, Tingkuan

    2007-04-01

    A physical model is developed for analyzing and evaluating the void fraction profiles in the moderator cell of the Cold Neutron Source (CNS) of the China Advanced Research Reactor (CARR), which is now constructing in the China Institute of Atomic Energy (CIAE). The results derived from the model are compared with the related experimental data and its propriety is verified. The model is then used to explore the influence of various factors, including the diameter of boiling vapor bubbles, liquid density, liquid viscosity and the total heating power acted on the moderator cell, on the void fraction profiles in the cell. The results calculated with the present model indicate that the void fraction in the moderator cell increases linearly with heating power, and increases with the liquid viscosity, but decreases as the size of bubbles increases, and increases linearly with heating power. For the case where hydrogen is being used as a moderator, calculation results show that the void fraction in the moderator cell may be less than 30%, which is the maximum void fraction permitted from the nuclear physics point of view. The model and the calculation results will help to obtain insight of the mechanism that controls the void fraction distribution in the moderator cell, and provide theoretical supports for the moderator cell design.

  16. Cosmological Black Holes as Seeds of Voids in Galaxy Distribution

    CERN Document Server

    Capozziello, S; Stornaiolo, C; Capozziello, Salvatore; Funaro, Maria; Stornaiolo, Cosimo

    2004-01-01

    Deep surveys indicate a bubbly structure of cosmological large scale which should be the result of evolution of primordial density perturbations. Several models have been proposed to explain origin and dynamics of such features but, till now, no exhaustive and fully consistent theory has been found. We discuss a model where cosmological black holes, deriving from primordial perturbations, are the seeds for large-scale-structure voids. We give details of dynamics and accretion of the system voids-cosmological black holes from the epochs $(z\\simeq10^{3})$ till now finding that void of $40h^{-1}Mpc$ of diameter and under-density of -0.9 will fits the observations without conflicting with the homogeneity and isotropy of cosmic microwave background radiation.

  17. Numerical Study of Void Fraction Distribution Propagation in Gas-Liquid Two-Phase Flow

    Institute of Scientific and Technical Information of China (English)

    YANG Jianhui; LI Qing; LU Wenqiang

    2005-01-01

    A dynamic propagation model was developed for waves in two-phase flows by assuming that continuity waves and dynamic waves interact nonlinearly for certain flow conditions. The drift-flux model is solved with the one-dimensional continuity equation for gas-liquid two-phase flows as an initial-boundary value problem solved using the characteristic-curve method. The numerical results give the void fraction distribution propagation in a gas-liquid two-phase flow which shows how the flow pattern transition occurs. The numerical simulations of different flow patterns show that the void fraction distribution propagation is determined by the characteristics of the drift-flux between the liquid and gas flows and the void fraction range. Flow pattern transitions begin around a void fraction of 0.27 and end around 0.58. Flow pattern transitions do not occur for very high void concentrations.

  18. Void probability as a function of the void's shape and scale-invariant models. [in studies of spacial galactic distribution

    Science.gov (United States)

    Elizalde, E.; Gaztanaga, E.

    1992-01-01

    The dependence of counts in cells on the shape of the cell for the large scale galaxy distribution is studied. A very concrete prediction can be done concerning the void distribution for scale invariant models. The prediction is tested on a sample of the CfA catalog, and good agreement is found. It is observed that the probability of a cell to be occupied is bigger for some elongated cells. A phenomenological scale invariant model for the observed distribution of the counts in cells, an extension of the negative binomial distribution, is presented in order to illustrate how this dependence can be quantitatively determined. An original, intuitive derivation of this model is presented.

  19. In search of empty places: Voids in the distribution of galaxies

    Science.gov (United States)

    Bucklein, Brian K.

    2010-12-01

    We investigate several techniques to identify voids in the galaxy distribution of matter in the universe. We utilize galaxy number counts as a function of apparent magnitude and Wolf plots to search a two- or three-dimensional data set in a pencil-beam fashion to locate voids within the field of view. The technique is able to distinguish between voids that represent simply a decrease in density as well as those that show a build up of galaxies on the front or back side of the void. This method turns out to be primarily useable only at relatively short range (out to about 200 Mpc). Beyond this distance, the characteristics indicating a void become increasingly difficult to separate from the statistical background noise. We apply the technique to a very simplified model as well as to the Millennium Run dark matter simulation. We then compare results with those obtained on the Sloan Digital Sky Survey. We also created the Watershed Void Examiner (WaVE) which treats densities in a fashion similar to elevation on a topographical map, and then we allow the "terrain" to flood. The flooded low-lying regions are identified as voids, which are allowed to grow and merge as the level of flooding becomes higher (the overdensity threshold increases). Void statistics can be calculated for each void. We also determine that within the Millennium Run semi-analytic galaxy catalog, the walls that separate the voids are permeable at a scale of 4 Mpc. For each resolution that we tested, there existed a characteristic density at which the walls could be penetrated, allowing a single void to grow to dominate the volume. With WaVE, we are able to get comparable results to those previously published, but often with fewer choices of parameters that could bias the results. We are also able to determine the the density at which the number of voids peaks for different resolutions as well as the expected number of void galaxies. The number of void galaxies is amazingly consistent at an

  20. Packing fraction of particles with a Weibull size distribution

    Science.gov (United States)

    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.

  1. Business size distributions

    Science.gov (United States)

    D'Hulst, R.; Rodgers, G. J.

    2001-10-01

    In a recent work, we introduced two models for the dynamics of customers trying to find the business that best corresponds to their expectation for the price of a commodity. In agreement with the empirical data, a power-law distribution for the business sizes was obtained, taking the number of customers of a business as a proxy for its size. Here, we extend one of our previous models in two different ways. First, we introduce a business aggregation rate that is fitness dependent, which allows us to reproduce a spread in empirical data from one country to another. Second, we allow the bankruptcy rate to take a different functional form, to be able to obtain a log-normal distribution with power-law tails for the size of the businesses.

  2. Size-effects at a crack-tip interacting with a number of voids

    DEFF Research Database (Denmark)

    Tvergaard, Viggo; Niordson, Christian Frithiof

    2008-01-01

    of the characteristic material length relative to the initial void radius. For a case showing the multiple void mechanism, it is found that the effect of the material length can change the behaviour towards the void by void mechanism. A material model with three characteristic length scales is compared with a one...

  3. Hail Size Distribution Mapping

    Science.gov (United States)

    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.

  4. CT measurements of SAP voids in concrete

    DEFF Research Database (Denmark)

    Laustsen, Sara; Bentz, Dale P.; Hasholt, Marianne Tange

    2010-01-01

    X-ray computed tomography (CT) scanning is used to determine the SAP void distribution in hardened concrete. Three different approaches are used to analyse a binary data set created from CT measurement. One approach classifies a cluster of connected, empty voxels (volumetric pixel of a 3D image......) as one void, whereas the other two approaches are able to classify a cluster of connected, empty voxels as a number of individual voids. Superabsorbent polymers (SAP) have been used to incorporate air into concrete. An advantage of using SAP is that it enables control of the amount and size...... of the created air voids. The results indicate the presence of void clusters. To identify the individual voids, special computational approaches are needed. The addition of SAP results in a dominant peak in two of the three air void distributions. Based on the position (void diameter) of the peak, it is possible...

  5. CT measurements of SAP voids in concrete

    DEFF Research Database (Denmark)

    Laustsen, Sara; Bentz, Dale P.; Hasholt, Marianne Tange;

    2010-01-01

    X-ray computed tomography (CT) scanning is used to determine the SAP void distribution in hardened concrete. Three different approaches are used to analyse a binary data set created from CT measurement. One approach classifies a cluster of connected, empty voxels (volumetric pixel of a 3D image......) as one void, whereas the other two approaches are able to classify a cluster of connected, empty voxels as a number of individual voids. Superabsorbent polymers (SAP) have been used to incorporate air into concrete. An advantage of using SAP is that it enables control of the amount and size...... of the created air voids. The results indicate the presence of void clusters. To identify the individual voids, special computational approaches are needed. The addition of SAP results in a dominant peak in two of the three air void distributions. Based on the position (void diameter) of the peak, it is possible...

  6. Distribution of void fraction for gas-liquid slug flow in an inclined pipe

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In order to investigate the effect of inclination angle on the spatial distribution of phases, experiments on gas-liquid two-phase slug flow in an inclined pipe were carried out by using the optical probe and an EKTAPRO 1000 high speed motion analyzer. It has been demonstrated that the inclination angle and the mixture velocity are important parameters to influence the distribution of void fraction for upward slug flow in the inclined pipe. At high mixture velocity, the gas phase profile is axial symmetry in the cross-section of the pipe. This is similar to that for vertical slug flow. In contrast, most of the gas phase is located near the upper pipe wall at low mixture velocity. By measuring the axial variation of void fraction along the liquid slug, it can be concluded that there is a high void fraction wake region with length of 3~4D in the front of liquid slug. In the fully developed zone of liquid slug, the peak value of the void fraction is near the upper wall.

  7. Neutron Tomography Using Mobile Neutron Generators for Assessment of Void Distributions in Thermal Hydraulic Test Loops

    OpenAIRE

    Andersson, Peter; Bjelkenstedt, Tom; Andersson Sundén, Erik; Sjöstrand, Henrik; Jacobsson, Staffan

    2015-01-01

    Detailed knowledge of the lateral distribution of steam (void) and water in a nuclear fuel assembly is of great value for nuclear reactor operators and fuel manufacturers, with consequences for both reactor safety and economy of operation. Therefore, nuclear relevant two-phase flows are being studied at dedicated thermal-hydraulic test loop, using twophase flow systems ranging from simplified geometries such as heated circular pipes to full scale mock-ups of nuclear fuel assemblies. Neutron t...

  8. A new geometrical approach to void statistics

    CERN Document Server

    Werner, M C

    2014-01-01

    Modelling cosmic voids as spheres in Euclidean space, the notion of a de-Sitter configuration space is introduced. It is shown that a uniform distribution over this configuration space yields a power-law approximating the void size distribution in an intermediate range of volumes, as well as an estimate for the fractal dimension of the large scale structure.

  9. Towards a better understanding of dielectric barrier discharges in ferroelectrets: Paschen breakdown fields in micrometer sized voids

    Science.gov (United States)

    Harris, Scott; Mellinger, Axel

    2014-04-01

    Charged cellular polypropylene foams (i.e., ferro- or piezoelectrets) demonstrate high piezoelectric activity upon being electrically charged. When an external electric field is applied, dielectric barrier discharges (DBDs) occur, resulting in a separation of charges which are subsequently deposited on dielectric surfaces of internal micrometer sized voids. This deposited space charge is responsible for the piezoelectric activity of the material. Previous studies have indicated charging fields larger than predicted by Townsend's model of Paschen breakdown applied to a multilayered electromechanical model; a discrepancy which prompted the present study. The actual breakdown fields for micrometer sized voids were determined by constructing single cell voids using polypropylene spacers with heights ranging from 8 to 75 μm, "sandwiched" between two polypropylene dielectric barriers and glass slides with semi-transparent electrodes. Subsequently, a bipolar triangular charging waveform with a peak voltage of 6 kV was applied to the samples. The breakdown fields were determined by monitoring the emission of light due to the onset of DBDs using an electron multiplying CCD camera. The breakdown fields at absolute pressures from 101 to 251 kPa were found to be in good agreement with the standard Paschen curves. Additionally, the magnitude of the light emission was found to scale linearly with the amount of gas, i.e., the height of the voids. Emissions were homogeneous over the observed regions of the voids for voids with heights of 25 μm or less and increasingly inhomogeneous for void heights greater than 40 μm at high electric fields.

  10. On grain size dependent void swelling in pure copper irradiated with fission neutrons

    DEFF Research Database (Denmark)

    Singh, B.N.; Eldrup, Morten Mostgaard; Zinkle, S.J.

    2001-01-01

    in pure copper irradiated with fission neutrons at 623K to a dose level of approx0.3 dpa (displacement peratom). The post-irradiation defect microstructure including voids was investigated using transmission electron microscopy and positron annihilation spectroscopy. The evolution of void swelling...

  11. On grain-size-dependent void swelling in pure copper irradiated with fission neutrons

    DEFF Research Database (Denmark)

    Singh, Bachu Narain; Eldrup, Morten Mostgaard; Zinkle, S.J.

    2002-01-01

    in pure copper irradiated with fission neutrons at 623 K to a dose level of about 0.3 displacement per atom. The post-irradiation defect microstructure including voids was investigated using transmission electron microscopy and positron annihilation spectroscopy. The evolution of void swelling...

  12. Electrochemical charging of CdSe quantum dot films: dependence on void size and counterion proximity.

    Science.gov (United States)

    Boehme, Simon C; Wang, Hai; Siebbeles, Laurens D A; Vanmaekelbergh, Daniel; Houtepen, Arjan J

    2013-03-26

    Films of colloidal quantum dots (QDs) show great promise for application in optoelectronic devices. Great advances have been made in recent years in designing efficient QD solar cells and LEDs. A very important aspect in the design of devices based on QD films is the knowledge of their absolute energy levels. Unfortunately, reported energy levels vary markedly depending on the employed measurement technique and the environment of the sample. In this report, we determine absolute energy levels of QD films by electrochemical charge injection. The concomitant change in optical absorption of the film allows quantification of the number of charges in quantum-confined levels and thereby their energetic position. We show here that the size of voids in the QD films (i.e., the space between the quantum dots) determines the amount of charges that may be injected into the films. This effect is attributed to size exclusion of countercharges from the electrolyte solution. Further, the energy of the QD levels depends on subtle changes in the QD film and the supporting electrolyte: the size of the cation and the QD ligand length. These nontrivial effects can be explained by the proximity of the cation to the QD surface and a concomitant lowering of the electrochemical potential. Our findings help explain the wide range of reported values for QD energy levels and redefine the limit of applicability of electrochemical measurements on QD films. Finally, the finding that the energy of QD levels depends on ligand length and counterion size may be exploited in optimized designs of QD sensitized solar cells.

  13. Gas-liquid Phase Distribution and Void Fraction Measurements Using the MRI

    Science.gov (United States)

    Daidzic, N. E.; Schmidt, E.; Hasan, M. M.; Altobelli, S.

    2004-01-01

    We used a permanent-magnet MRI system to estimate the integral and spatially- and/or temporally-resolved void-fraction distributions and flow patterns in gas-liquid two-phase flows. Air was introduced at the bottom of the stagnant liquid column using an accurate and programmable syringe pump. Air flow rates were varied between 1 and 200 ml/min. The cylindrical non-conducting test tube in which two-phase flow was measured was placed in a 2.67 kGauss MRI with MRT spectrometer/imager. Roughly linear relationship has been obtained for the integral void-fraction, obtained by volume-averaging of the spatially-resolved signals, and the air flow rate in upward direction. The time-averaged spatially-resolved void fraction has also been obtained for the quasi-steady flow of air in a stagnant liquid column. No great accuracy is claimed as this was an exploratory proof-of-concept type of experiment. Preliminary results show that MRI a non-invasive and non-intrusive experimental technique can indeed provide a wealth of different qualitative and quantitative data and is especially well suited for averaged transport processes in adiabatic and diabatic multi-phase and/or multi-component flows.

  14. Kinetic narrowing of size distribution

    Science.gov (United States)

    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. The sizes of mini-voids in the local universe: an argument in favor of a warm dark matter model?

    CERN Document Server

    Tikhonov, A V; Yepes, G; Hoffman, Y

    2009-01-01

    Using high-resolution simulations within the Cold and Warm Dark Matter models we study the evolution of small scale structure in the Local Volume, a sphere of 8 Mpc radius around the Local Group. We compare the observed spectrum of mini-voids in the Local Volume with the spectrum of mini-voids determined from the simulations. We show that the \\LWDM model can easily explain both the observed spectrum of mini-voids and the presence of low-mass galaxies observed in the Local Volume, provided that all haloes with circular velocities greater than 20 km/s host galaxies. On the contrary within the \\LCDM model the distribution of the simulated mini-voids reflects the observed one if haloes with maximal circular velocities larger than $35 \\kms$ host galaxies. This assumption is in contradiction with observations of galaxies with circular velocities as low as 20 km/s in our Local Universe. A potential problem of the \\LWDM model could be the late formation of the haloes in which the gas can be efficiently photo-evaporat...

  16. Centaur size distribution with DECam

    Science.gov (United States)

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

    2014-11-01

    We present the results of the 2014 centaur search campaign on the Dark Energy Camera (DECam) in Tololo, Chile. This is the largest debiased Centaur survey to date, measuring for the first time the size distribution of small Centaurs (1-10km) and the first time the sizes of planetesimals from which the entire Solar System formed are directly detected.The theoretical model for the coagulation and collisional evolution of the outer solar system proposed in Schlichting et al. 2013 predicts a steep rise in the size distribution of TNOs smaller than 10km. These objects are below the detection limit of current TNO surveys but feasible for the Centaur population. By constraining the number of Centaurs and this feature in their size distribution we can confirm the collisional evolution of the Solar System and estimate the rate at which material is being transferred from the outer to the inner Solar System. If the shallow power law behavior from the TNO size distribution at ~40km can be extrapolated to 1km, the size of the Jupiter Family of Comets (JFC), there would not be enough small TNOs to supply the JFC population (Volk & Malhotra, 2008), debunking the link between TNOs and JFCs.We also obtain the colors of small Centaurs and TNOs, providing a signature of collisional evolution by measuring if there is in fact a relationship between color and size. If objects smaller than the break in the TNO size distribution are being ground down by collisions then their surfaces should be fresh, and then appear bluer in the optical than larger TNOs that are not experiencing collisions.

  17. Acoustic characterization of void distributions across carbon-fiber composite layers

    Science.gov (United States)

    Tayong, Rostand B.; Smith, Robert A.; Pinfield, Valerie J.

    2016-02-01

    Carbon Fiber Reinforced Polymer (CFRP) composites are often used as aircraft structural components, mostly due to their superior mechanical properties. In order to improve the efficiency of these structures, it is important to detect and characterize any defects occurring during the manufacturing process, removing the need to mitigate the risk of defects through increased thicknesses of structure. Such defects include porosity, which is well-known to reduce the mechanical performance of composite structures, particularly the inter-laminar shear strength. Previous work by the authors has considered the determination of porosity distributions in a fiber-metal laminate structure [1]. This paper investigates the use of wave-propagation modeling to invert the ultrasonic response and characterize the void distribution within the plies of a CFRP structure. Finite Element (FE) simulations are used to simulate the ultrasonic response of a porous composite laminate to a typical transducer signal. This simulated response is then applied as input data to an inversion method to calculate the distribution of porosity across the layers. The inversion method is a multi-dimensional optimization utilizing an analytical model based on a normal-incidence plane-wave recursive method and appropriate mixture rules to estimate the acoustical properties of the structure, including the effects of plies and porosity. The effect of porosity is defined through an effective wave-number obtained from a scattering model description. Although a single-scattering approach is applied in this initial study, the limitations of the method in terms of the considered porous layer, percentage porosity and void radius are discussed in relation to single- and multiple-scattering methods. A comparison between the properties of the modeled structure and the void distribution obtained from the inversion is discussed. This work supports the general study of the use of ultrasound methods with inversion to

  18. CFD Analysis of a Void Distribution Benchmark of the NUPEC PSBT Tests: Model Calibration and Influence of Turbulence Modelling

    Directory of Open Access Journals (Sweden)

    E. Krepper

    2012-01-01

    Full Text Available The paper presents CFD calculations of the void distribution tests of the PSBT benchmark using ANSYS CFX-12.1. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncertainties in several model parameters. It is then shown that the measured cross-sectionally averaged values can be reproduced well with a single set of calibrated model parameters for different test cases. For the reproduction of patterns of void distribution cross-sections, attention has to be focussed on the modelling of turbulence in the narrow channel. Only a turbulence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns.

  19. Research on segregation evaluation methods of asphalt pavement based on air voids distribution

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Eye observation was used to evaluate the segregation degree of asphalt pavement, which was not much creditable. To the asphalt pavement, road surface texture measuring method which has appeared recently can identify gradational segregation; but it can't reflect the influence of the temperature segregation. However,using infrared temperature detector to evaluate the segregation must be taken during paving, which brings much inconvenience. In this paper, measuring the air voids distribution using non-nuclear density gauge to evaluate asphalt pavement segregation was introduced. Result shows that this method can directly reflect the comprehensive results of the two types of segregation in a high efficient and accurate way. Moreover, using the sketch map of segregation area can help to analyze the segregation reason visually.

  20. Packing fraction of particles with lognormal size distribution.

    Science.gov (United States)

    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.

  1. Packing fraction of particles with lognormal size distribution

    Science.gov (United States)

    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.

  2. Effect of pore-size distribution on the collapse behaviour of anthropogenic sandy soil deposits

    Directory of Open Access Journals (Sweden)

    Baille Wiebke

    2016-01-01

    Full Text Available In the former open-pit mines of the Lusatian region in Germany, several liquefaction events have occurred during the recent years in the anthropogenic deposits made of very loose sandy soils. These events are related to the rising ground water table after the stop of controlled ground water lowering. The very loose state is due to the formation of sand aggregates (pseudo-grains during the deposition process. The pseudo-grains enclose larger voids of dimension greater than the single sand grain. Wetting induced collapse of the pseudo-grains is presumed to be one of the possible mechanisms triggering liquefaction. In the present study, the effect of larger voids on the wetting induced deformation behaviour of sandy soils is experimentally investigated by laboratory box tests. The deformation field in the sample during wetting was measured using Digital Image Correlation (DIC technique. The results show that the observed deformations are affected by the pore size distribution, thus the amount of voids between the pseudo-grains (macro-void ratio and the voids inside the pseudo-grains (matrix void ratio. The global void ratio of a sandy soil is not sufficient as single state parameter, but the pore size distribution has to be taken into account, experimentally as well as in modelling.

  3. Urban aerosol number size distributions

    Directory of Open Access Journals (Sweden)

    T. Hussein

    2004-01-01

    Full Text Available Aerosol number size distributions have been measured since 5 May 1997 in Helsinki, Finland. The presented aerosol data represents size distributions within the particle diameter size range 8-400nm during the period from May 1997 to March 2003. The daily, monthly and annual patterns of the aerosol particle number concentrations were investigated. The temporal variation of the particle number concentration showed close correlations with traffic activities. The highest total number concentrations were observed during workdays; especially on Fridays, and the lowest concentrations occurred during weekends; especially Sundays. Seasonally, the highest total number concentrations were observed during winter and spring and lower concentrations were observed during June and July. More than 80% of the number size distributions had three modes: nucleation mode (30nm, Aitken mode (20-100nm and accumulation mode (}$'>90nm. Less than 20% of the number size distributions had either two modes or consisted of more than three modes. Two different measurement sites were used; in the first (Siltavuori, 5.5.1997-5.3.2001, the arithmetic means of the particle number concentrations were 7000cm, 6500cm, and 1000cm respectively for nucleation, Aitken, and accumulation modes. In the second site (Kumpula, 6.3.2001-28.2.2003 they were 5500cm, 4000cm, and 1000cm. The total number concentration in nucleation and Aitken modes were usually significantly higher during workdays than during weekends. The temporal variations in the accumulation mode were less pronounced. The lower concentrations at Kumpula were mainly due to building construction and also the slight overall decreasing trend during these years. During the site changing a period of simultaneous measurements over two weeks were performed showing nice correlation at both sites.

  4. The Void Galaxy Survey

    CERN Document Server

    van de Weygaert, R; Platen, E; Beygu, B; van Gorkom, J H; van der Hulst, J M; Aragon-Calvo, M A; Peebles, P J E; Jarrett, T; Rhee, G; Kovac, K; Yip, C -W

    2011-01-01

    The Void Galaxy Survey (VGS) is a multi-wavelength program to study $\\sim$60 void galaxies. Each has been selected from the deepest interior regions of identified voids in the SDSS redshift survey on the basis of a unique geometric technique, with no a prior selection of intrinsic properties of the void galaxies. The project intends to study in detail the gas content, star formation history and stellar content, as well as kinematics and dynamics of void galaxies and their companions in a broad sample of void environments. It involves the HI imaging of the gas distribution in each of the VGS galaxies. Amongst its most tantalizing findings is the possible evidence for cold gas accretion in some of the most interesting objects, amongst which are a polar ring galaxy and a filamentary configuration of void galaxies. Here we shortly describe the scope of the VGS and the results of the full analysis of the pilot sample of 15 void galaxies.

  5. Void Statistics and Void Galaxies in the 2dFGRS

    CERN Document Server

    von Benda-Beckmann, Alexander M

    2007-01-01

    For the 2dFGRS we study the properties of voids and of fainter galaxies within voids that are defined by brighter galaxies. Our results are compared with simulated galaxy catalogues from the Millenium simulation coupled with a semianalytical galaxy formation recipe. We derive the void size distribution and discuss its dependence on the faint magnitude limit of the galaxies defining the voids. While voids among faint galaxies are typically smaller than those among bright galaxies, the ratio of the void sizes to the mean galaxy separation reaches larger values. This is well reproduced in the mock galaxy samples studied. We provide analytic fitting functions for the void size distribution. Furthermore, we study the galaxy population inside voids defined by objects with $B_J -5\\log{h}< -20$ and diameter larger than 10 \\hMpc. We find a clear bimodality of the void galaxies similar to the average comparison sample. We confirm the enhanced abundance of galaxies in the blue cloud and a depression of the number of ...

  6. Void Dynamics

    Science.gov (United States)

    Padilla, Nelson D.; Paz, Dante; Lares, Marcelo; Ceccarelli, Laura; Lambas, Diego Garcí A.; Cai, Yan-Chuan; Li, Baojiu

    2016-10-01

    Cosmic voids are becoming key players in testing the physics of our Universe.Here we concentrate on the abundances and the dynamics of voids as these are among the best candidatesto provide information on cosmological parameters. Cai, Padilla & Li (2014)use the abundance of voids to tell apart Hu & Sawicki f(R) models from General Relativity. An interestingresult is that even though, as expected, voids in the dark matter field are emptier in f(R) gravity due to the fifth force expellingaway from the void centres, this result is reversed when haloes are used to find voids. The abundance of voids in this casebecomes even lower in f(R) compared to GR for large voids. Still, the differences are significant and thisprovides a way to tell apart these models. The velocity field differences between f(R) and GR, on the other hand, arethe same for halo voids and for dark matter voids.Paz et al. (2013), concentrate on the velocity profiles around voids. First they show the necessityof four parameters to describe the density profiles around voids given two distinct voidpopulations, voids-in-voids and voids-in-clouds. This profile is used to predict peculiar velocities around voids,and the combination of the latter with void density profiles allows the construction of modelvoid-galaxy cross-correlation functions with redshift space distortions. When these modelsare tuned to fit the measured correlation functions for voids and galaxies in the SloanDigital Sky Survey, small voids are found to be of the void-in-cloud type, whereas largerones are consistent with being void-in-void. This is a novel result that is obtaineddirectly from redshift space data around voids. These profiles can be used toremove systematics on void-galaxy Alcock-Pacinsky tests coming from redshift-space distortions.

  7. DIVE in the cosmic web: voids with Delaunay triangulation from discrete matter tracer distributions

    Science.gov (United States)

    Zhao, Cheng; Tao, Charling; Liang, Yu; Kitaura, Francisco-Shu; Chuang, Chia-Hsun

    2016-07-01

    We present a novel parameter-free cosmological void finder (DIVE, Delaunay TrIangulation Void findEr) based on Delaunay Triangulation (DT), which efficiently computes the empty spheres constrained by a discrete set of tracers. We define the spheres as DT voids, and describe their properties, including a universal density profile together with an intrinsic scatter. We apply this technique on 100 halo catalogues with volumes of 2.5 h-1Gpc side each, with a bias and number density similar to the Baryon Oscillation Spectroscopic Survey CMASS luminous red galaxies, performed with the PATCHY code. Our results show that there are two main species of DT voids, which can be characterized by the radius: they have different responses to halo redshift space distortions, to number density of tracers, and reside in different dark matter environments. Based on dynamical arguments using the tidal field tensor, we demonstrate that large DT voids are hosted in expanding regions, whereas the haloes used to construct them reside in collapsing ones. Our approach is therefore able to efficiently determine the troughs of the density field from galaxy surveys, and can be used to study their clustering. We further study the power spectra of DT voids, and find that the bias of the two populations are different, demonstrating that the small DT voids are essentially tracers of groups of haloes.

  8. Void effects and the determination of ''patches'' for radiation distribution in heterogeneous multilayer shields

    Energy Technology Data Exchange (ETDEWEB)

    Sayedahmed, F.M.; Makarious, A.S.; Kansouh, W.A. (Atomic Energy Authority, Cairo (Egypt). Reactor and Neutron Physics Dept.)

    1989-01-01

    The effect on radiation distribution in heterogeneous multilayer shield configurations containing cylindrical air-filled voids of different diameters have been investigated. The heterogeneous shield assemblies were placed in front of one of the horizontal channels of the ET-RR-1 reactor. The measurements of {delta}-rays and slow neutrons were carried out using LiF-7 and LiF-6 Teflon disc dosimeters, respectively. It was found that the presence of air-filled voids increases the radiation along and perpendicular to the void axis. An empirical formula has been derived to calculate the radiation distribution in the multilayer shields and a good agreement between the measured and calculated values was obtained. The formulae developed by Chase have been checked experimentally to determine the minimum amount of ''patching'' required on the outside of the voided shields to maintain a uniform emergent radiation distribution on the outer surface of the shielding assembly. The applicability of this formula has been defined and a semi-empirical formula developed to describe the experimental results obtained for the required ''patching''. (author).

  9. Urban aerosol number size distributions

    Directory of Open Access Journals (Sweden)

    T. Hussein

    2003-10-01

    Full Text Available Aerosol number size distributions were measured continuously in Helsinki, Finland from 5 May 1997 to 28 February 2003. The daily, monthly and annual patterns were investigated. The temporal variation of the particle number concentration was seen to follow the traffic density. The highest total particle number concentrations were usually observed during workdays; especially on Fridays, and the lower concentrations occurred during weekends; especially Sundays. Seasonally, the highest total number concentrations were usually observed during winter and spring and the lowest during June and July. More than 80\\% of the particle number size distributions were tri-modal: nucleation mode (Dp < 30 nm, Aitken mode (20–100 nm and accumulation mode (Dp > 90 nm. Less than 20% of the particle number size distributions have either two modes or consisted of more than three modes. Two different measurement sites are used; in the first place (Siltavuori, 5 May 1997–5 March 2001, the overall means of the integrated particle number concentrations were 7100 cm−3, 6320 cm−3, and 960 cm−3, respectively, for nucleation, Aitken, and accumulation modes. In the second site (Kumpula, 6 March 2001–28 February 2003 they were 5670 cm−3, 4050 cm−3, and 900 cm−3. The total number concentration in nucleation and Aitken modes were usually significantly higher during weekdays than during weekends. The variations in accumulation mode were less pronounced. The smaller concentrations in Kumpula were mainly due to building construction and also slight overall decreasing trend during these years. During the site changing a period of simultaneous measurements over two weeks were performed showing nice correlation in both sites.

  10. TRANSVERSELY ISOTROPIC HYPER-ELASTIC MATERIAL RECTANGULAR PLATE WITH VOIDS UNDER A UNIAXIAL EXTENSION

    Institute of Scientific and Technical Information of China (English)

    程昌钧; 任九生

    2003-01-01

    The finite deformation and stress analyses for a transversely isotropic rectangularplate with voids and made of hyper-elastic material with the generalized neo-Hookean strainenergy function under a uniaxial extension are studied. The deformation functions of plateswith voids that are symmetrically distributed in a certain manner are given and the functionsare expressed by two parameters by solving the differential equations. The solution may beapproximately obtained from the minimum potential energy principle. Thus, the analyticsolutions of the deformation and stress of the plate are obtained. The growth of the void.s andthe distribution of stresses along the voids are analyzed and the influences of the degree ofanisotropy, the size of the voids and the distance between the voids are discussed. Thecharacteristics of the growth of the voids and the distribution of stresses of the plates with onevoid, three or five voids are obtained and compared.

  11. Structure in the 3D Galaxy Distribution. II. Voids and Watersheds of Local Maxima and Minima

    Science.gov (United States)

    Way, M. J.; Gazis, P. R.; Scargle, Jeffrey D.

    2015-01-01

    The major uncertainties in studies of the multi-scale structure of the universe arise not from observational errors but from the variety of legitimate definitions and detection methods for individual structures. To facilitate the study of these methodological dependencies, we have carried out 12 different analyses defining structures in various ways. This has been done in a purely geometrical way by utilizing the HOP algorithm as a unique parameter-free method of assigning groups of galaxies to local density maxima or minima. From three density estimation techniques (smoothing kernels, Bayesian blocks, and self-organizing maps) applied to three data sets (the Sloan Digital Sky Survey Data Release 7, the Millennium simulation, and randomly distributed points) we tabulate information that can be used to construct catalogs of structures connected to local density maxima and minima. We also introduce a void finder that utilizes a method to assemble Delaunay tetrahedra into connected structures and characterizes regions empty of galaxies in the source catalog.

  12. STRUCTURE IN THE 3D GALAXY DISTRIBUTION. II. VOIDS AND WATERSHEDS OF LOCAL MAXIMA AND MINIMA

    Energy Technology Data Exchange (ETDEWEB)

    Way, M. J. [Also at NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA. (United States); Gazis, P. R.; Scargle, Jeffrey D., E-mail: Michael.J.Way@nasa.gov, E-mail: PGazis@sbcglobal.net, E-mail: Jeffrey.D.Scargle@nasa.gov [NASA Ames Research Center, Space Science Division, Moffett Field, CA 94035 (United States)

    2015-01-20

    The major uncertainties in studies of the multi-scale structure of the universe arise not from observational errors but from the variety of legitimate definitions and detection methods for individual structures. To facilitate the study of these methodological dependencies, we have carried out 12 different analyses defining structures in various ways. This has been done in a purely geometrical way by utilizing the HOP algorithm as a unique parameter-free method of assigning groups of galaxies to local density maxima or minima. From three density estimation techniques (smoothing kernels, Bayesian blocks, and self-organizing maps) applied to three data sets (the Sloan Digital Sky Survey Data Release 7, the Millennium simulation, and randomly distributed points) we tabulate information that can be used to construct catalogs of structures connected to local density maxima and minima. We also introduce a void finder that utilizes a method to assemble Delaunay tetrahedra into connected structures and characterizes regions empty of galaxies in the source catalog.

  13. Effects of Cure Pressure Induced Voids on the Mechanical Strength of Carbon/Epoxy Laminates

    Institute of Scientific and Technical Information of China (English)

    Ling LIU; Boming ZHANG; Zhanjun WU; Dianfu WANG

    2005-01-01

    This work aims at designing a set of curing pressure routes to produce laminates with various void contents. The effects of various consolidation pressures resulting in different void contents on mechanical strength of carbon/epoxy laminates have been examined. Characterization of the voids, in terms of void volume fraction, void distribution,size, and shape, was performed by standard test, ultrasonic inspection and metallographic analysis. The interlaminar shear strength was measured by the short-beam method. An empirical model was used to predict the strength vs porosity. The predicted strengths conform well with the experimental data and voids were found to be uniformly distributed throughout the laminate.

  14. Detection of atomic scale changes in the free volume void size of three-dimensional colorectal cancer cell culture using positron annihilation lifetime spectroscopy.

    Science.gov (United States)

    Axpe, Eneko; Lopez-Euba, Tamara; Castellanos-Rubio, Ainara; Merida, David; Garcia, Jose Angel; Plaza-Izurieta, Leticia; Fernandez-Jimenez, Nora; Plazaola, Fernando; Bilbao, Jose Ramon

    2014-01-01

    Positron annihilation lifetime spectroscopy (PALS) provides a direct measurement of the free volume void sizes in polymers and biological systems. This free volume is critical in explaining and understanding physical and mechanical properties of polymers. Moreover, PALS has been recently proposed as a potential tool in detecting cancer at early stages, probing the differences in the subnanometer scale free volume voids between cancerous/healthy skin samples of the same patient. Despite several investigations on free volume in complex cancerous tissues, no positron annihilation studies of living cancer cell cultures have been reported. We demonstrate that PALS can be applied to the study in human living 3D cell cultures. The technique is also capable to detect atomic scale changes in the size of the free volume voids due to the biological responses to TGF-β. PALS may be developed to characterize the effect of different culture conditions in the free volume voids of cells grown in vitro.

  15. Comparative Analysis of CTF and Trace Thermal-Hydraulic Codes Using OECD/NRC PSBT Benchmark Void Distribution Database

    Directory of Open Access Journals (Sweden)

    M. Avramova

    2013-01-01

    Full Text Available The international OECD/NRC PSBT benchmark has been established to provide a test bed for assessing the capabilities of thermal-hydraulic codes and to encourage advancement in the analysis of fluid flow in rod bundles. The benchmark was based on one of the most valuable databases identified for the thermal-hydraulics modeling developed by NUPEC, Japan. The database includes void fraction and departure from nucleate boiling measurements in a representative PWR fuel assembly. On behalf of the benchmark team, PSU in collaboration with US NRC has performed supporting calculations using the PSU in-house advanced thermal-hydraulic subchannel code CTF and the US NRC system code TRACE. CTF is a version of COBRA-TF whose models have been continuously improved and validated by the RDFMG group at PSU. TRACE is a reactor systems code developed by US NRC to analyze transient and steady-state thermal-hydraulic behavior in LWRs and it has been designed to perform best-estimate analyses of LOCA, operational transients, and other accident scenarios in PWRs and BWRs. The paper presents CTF and TRACE models for the PSBT void distribution exercises. Code-to-code and code-to-data comparisons are provided along with a discussion of the void generation and void distribution models available in the two codes.

  16. Neutron Tomography Using Mobile Neutron Generators for Assessment of Void Distributions in Thermal Hydraulic Test Loops

    Science.gov (United States)

    Andersson, P.; Bjelkenstedt, T.; Sundén, E. Andersson; Sjöstrand, H.; Jacobsson-Svärd, S.

    Detailed knowledge of the lateral distribution of steam (void) and water in a nuclear fuel assembly is of great value for nuclear reactor operators and fuel manufacturers, with consequences for both reactor safety and economy of operation. Therefore, nuclear relevant two-phase flows are being studied at dedicated thermal-hydraulic test loop, using two-phase flow systems ranging from simplified geometries such as heated circular pipes to full scale mock-ups of nuclear fuel assemblies. Neutron tomography (NT) has been suggested for assessment of the lateral distribution of steam and water in such test loops, motivated by a good ability of neutrons to penetrate the metallic structures of metal pipes and nuclear fuel rod mock-ups, as compared to e.g. conventional X-rays, while the liquid water simultaneously gives comparatively good contrast. However, these stationary test loops require the measurement setup to be mobile, which is often not the case for NT setups. Here, it is acknowledged that fast neutrons of 14 MeV from mobile neutron generators constitute a viable option for a mobile NT system. We present details of the development of neutron tomography for this purpose at the division of Applied Nuclear Physics at Uppsala University. Our concept contains a portable neutron generator, exploiting the fusion reaction of deuterium and tritium, and a detector with plastic scintillator elements designed to achieveadequate spatial and energy resolution, all mounted in a light-weight frame without collimators or bulky moderation to allow for a mobile instrument that can be moved about the stationary thermal hydraulic test sections. The detector system stores event-to-event pulse-height information to allow for discrimination based on the energy deposition in the scintillator elements.

  17. Tracing the gravitational potential using cosmic voids

    CERN Document Server

    Nadathur, Seshadri; Crittenden, Robert

    2016-01-01

    The properties of large underdensities in the distribution of galaxies in the Universe, known as cosmic voids, are potentially sensitive probes of fundamental physics. We use data from the MultiDark suite of N-body simulations and multiple halo occupation distribution mocks to study the relationship between galaxy voids and the gravitational potential $\\Phi$. We find that the majority of galaxy voids correspond to local density minima in larger-scale overdensities, and thus lie in potential wells. However, a subset of voids can be identified that closely trace maxima of the gravitational potential and thus stationary points of the velocity field. We identify a new void observable, $\\lambda_v$, which depends on a combination of the void size and the average galaxy density contrast within the void, and show that it provides a good proxy indicator of the potential at the void location. A simple linear scaling of $\\Phi$ as a function of $\\lambda_v$ is found to hold, independent of the redshift and properties of t...

  18. DIVE in the cosmic web: voids with Delaunay Triangulation from discrete matter tracer distributions

    CERN Document Server

    Zhao, Cheng; Liang, Yu; Kitaura, Francisco-Shu; Chuang, Chia-Hsun

    2015-01-01

    We present a novel parameter-free cosmological void finder (\\textsc{dive}, Delaunay TrIangulation Void findEr) based on Delaunay Triangulation (DT), which efficiently computes the empty spheres constrained by a discrete set of tracers. We define the spheres as DT voids, and describe their properties, including an universal density profile together with an intrinsic scatter. We apply this technique on 100 halo catalogues with volumes of 2.5\\,$h^{-1}$Gpc side each, with a bias and number density similar to the BOSS CMASS Luminous Red Galaxies, performed with the \\textsc{patchy} code. Our results show that there are two main species of DT voids, which can be characterised by the radius: they have different responses to halo redshift space distortions, to number density of tracers, and reside in different dark matter environments. Based on dynamical arguments using the tidal field tensor, we demonstrate that large DT voids are hosted in expanding regions, whereas the haloes used to construct them reside in collap...

  19. A Cosmic Void Catalog of SDSS DR12 BOSS Galaxies

    Science.gov (United States)

    Mao, Qingqing; Berlind, Andreas A.; Scherrer, Robert J.; Neyrinck, Mark C.; Scoccimarro, Román; Tinker, Jeremy L.; McBride, Cameron K.; Schneider, Donald P.; Pan, Kaike; Bizyaev, Dmitry; Malanushenko, Elena; Malanushenko, Viktor

    2017-02-01

    We present a cosmic void catalog using the large-scale structure galaxy catalog from the Baryon Oscillation Spectroscopic Survey (BOSS). This galaxy catalog is part of the Sloan Digital Sky Survey (SDSS) Data Release 12 and is the final catalog of SDSS-III. We take into account the survey boundaries, masks, and angular and radial selection functions, and apply the ZOBOV void finding algorithm to the Galaxy catalog. We identify a total of 10,643 voids. After making quality cuts to ensure that the voids represent real underdense regions, we obtain 1,228 voids with effective radii spanning the range 20–100 {h}-1 {Mpc} and with central densities that are, on average, 30% of the mean sample density. We release versions of the catalogs both with and without quality cuts. We discuss the basic statistics of voids, such as their size and redshift distributions, and measure the radial density profile of the voids via a stacking technique. In addition, we construct mock void catalogs from 1000 mock galaxy catalogs, and find that the properties of BOSS voids are in good agreement with those in the mock catalogs. We compare the stellar mass distribution of galaxies living inside and outside of the voids, and find no large difference. These BOSS and mock void catalogs are useful for a number of cosmological and galaxy environment studies.

  20. Particle-size distribution and packing fraction of geometric random packings

    NARCIS (Netherlands)

    Brouwers, H.J.H.

    2006-01-01

    This paper addresses the geometric random packing and void fraction of polydisperse particles. It is demonstrated that the bimodal packing can be transformed into a continuous particle-size distribution of the power law type. It follows that a maximum packing fraction of particles is obtained when t

  1. The Distribution of Bubble Sizes During Reionization

    CERN Document Server

    Lin, Yin; Furlanetto, Steven R; Sutter, P M

    2015-01-01

    A key physical quantity during reionization is the size of HII 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 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 those 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, HI...

  2. Microbubble Size Distributions Data Collection and Analysis

    Science.gov (United States)

    2016-06-13

    ABSTRACT A technique for determining the size distribution of micron-size bubbles from underway measurements at sea is described. A camera...Blank TM 841204 INTRODUCTION Properties of micron-sized bubble aggregates in sea water were investigated to determine their influence on the...problem during this study. This paper will discuss bubble size and size distribution measurements in sea water while underway. A technique to detect

  3. Structure in the 3D Galaxy Distribution: II. Voids and Watersheds of Local Maxima and Minima

    CERN Document Server

    Way, M J; Scargle, Jeffrey D

    2014-01-01

    The major uncertainties in studies of the multi-scale structure of the Universe arise not from observational errors but from the variety of legitimate definitions and detection methods for individual structures. To facilitate the study of these methodological dependencies we have carried out 12 different analyses defining structures in various ways. This has been done in a purely geometrical way by utilizing the HOP algorithm as a unique parameter-free method of assigning groups of galaxies to local density maxima or minima. From three density estimation techniques (smoothing kernels, Bayesian Blocks and self organizing maps) applied to three data sets (the Sloan Digital Sky Survey Data Release 7, the Millennium Simulation and randomly distributed points) we tabulate information that can be used to construct catalogs of structures connected to local density maxima and minima. The resulting sizes follow continuous multi-scale distributions with no indication of the presence of a discrete hierarchy. We also int...

  4. City-size distribution and the size of urban systems.

    Science.gov (United States)

    Thomas, I

    1985-07-01

    "This paper is an analysis of the city-size distribution for thirty-five countries of the world in 1975; the purpose is to explain statistically the regularity of the rank-size distribution by the number of cities included in the urban systems. The rank-size parameters have been computed for each country and also for four large urban systems in which several population thresholds have been defined. These thresholds seem to have more influence than the number of cities included in the urban system on the regularity of the distribution." The data are from the U.N. Demographic Yearbook. excerpt

  5. Modeling cosmic void statistics

    Science.gov (United States)

    Hamaus, Nico; Sutter, P. M.; Wandelt, Benjamin D.

    2016-10-01

    Understanding the internal structure and spatial distribution of cosmic voids is crucial when considering them as probes of cosmology. We present recent advances in modeling void density- and velocity-profiles in real space, as well as void two-point statistics in redshift space, by examining voids identified via the watershed transform in state-of-the-art ΛCDM n-body simulations and mock galaxy catalogs. The simple and universal characteristics that emerge from these statistics indicate the self-similarity of large-scale structure and suggest cosmic voids to be among the most pristine objects to consider for future studies on the nature of dark energy, dark matter and modified gravity.

  6. Modeling particle size distributions by the Weibull distribution function

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Zhigang (Rogers Tool Works, Rogers, AR (United States)); Patterson, B.R.; Turner, M.E. Jr (Univ. of Alabama, Birmingham, AL (United States))

    1993-10-01

    A method is proposed for modeling two- and three-dimensional particle size distributions using the Weibull distribution function. Experimental results show that, for tungsten particles in liquid phase sintered W-14Ni-6Fe, the experimental cumulative section size distributions were well fit by the Weibull probability function, which can also be used to compute the corresponding relative frequency distributions. Modeling the two-dimensional section size distributions facilitates the use of the Saltykov or other methods for unfolding three-dimensional (3-D) size distributions with minimal irregularities. Fitting the unfolded cumulative 3-D particle size distribution with the Weibull function enables computation of the statistical distribution parameters from the parameters of the fit Weibull function.

  7. FRACTAL SCALING OF PARTICLE AND PORE SIZE DISTRIBUTIONS AND ITS RELATION TO SOIL HYDRAULIC CONDUCTIVITY

    Directory of Open Access Journals (Sweden)

    BACCHI O.O.S.

    1996-01-01

    Full Text Available Fractal scaling has been applied to soils, both for void and solid phases, as an approach to characterize the porous arrangement, attempting to relate particle-size distribution to soil water retention and soil water dynamic properties. One important point of such an analysis is the assumption that the void space geometry of soils reflects its solid phase geometry, taking into account that soil pores are lined by the full range of particles, and that their fractal dimension, which expresses their tortuosity, could be evaluated by the fractal scaling of particle-size distribution. Other authors already concluded that although fractal scaling plays an important role in soil water retention and porosity, particle-size distribution alone is not sufficient to evaluate the fractal structure of porosity. It is also recommended to examine the relationship between fractal properties of solids and of voids, and in some special cases, look for an equivalence of both fractal dimensions. In the present paper data of 42 soil samples were analyzed in order to compare fractal dimensions of pore-size distribution, evaluated by soil water retention curves (SWRC of soils, with fractal dimensions of soil particle-size distributions (PSD, taking the hydraulic conductivity as a standard variable for the comparison, due to its relation to tortuosity. A new procedure is proposed to evaluate the fractal dimension of pore-size distribution. Results indicate a better correlation between fractal dimensions of pore-size distribution and the hydraulic conductivity for this set of soils, showing that for most of the soils analyzed there is no equivalence of both fractal dimensions. For most of these soils the fractal dimension of particle-size distribution does not indicate properly the pore trace tortuosity. A better equivalence of both fractal dimensions was found for sandy soils.

  8. Image analysis of aggregate,mastic and air void phases for asphalt mixture%Image analysis of aggregate, mastic and air void phases for asphalt mixture

    Institute of Scientific and Technical Information of China (English)

    ADHIKARI Sanjeev; YOU Zhan-ping; HAO Pei-wen; WANG Hai-nian

    2013-01-01

    The shape characterization and spatial distribution of aggregate,mastic and air void phases for asphalt mixture were analyzed.Three air void percentage asphalt mixtures,4%,7% and 8%,respectively,were cut into cross sections and polished.X-ray scanning microscope was used to capture aggregate,mastic,air void phase by the image.The average of polygon diameter was chosen as a threshold to determine which aggregates would be retained on a given sieve.The aggregate morphological image from scanned image was utilized by digital image processing method to calculate the gradation of aggregate and simulate the real gradation.Analysis result shows that the air void of asphalt mixture has influence on the correlation between calculation gradation and actual gradation.When comparing 4.75 mm sieve size of 4%,7% and 8% air void asphalt mixtures,7% air void asphalt mixture has 55% higher than actual size gradation,8% air void asphalt mixture has 8% higher than actual size gradation,and 4% air void asphalt mixture has 3.71% lower than actual size gradation.4% air void asphalt mixture has the best correlation between calculation gradation and actual gradation comparing to other specimens.The air void percentage of asphalt mixture has no obvious influence on the air void orientation,and three asphalt mixtures show the similar air orientation along the same direction.4 tabs,7 figs,17 refs.

  9. Aggregate size distributions in hydrophobic flocculation

    Directory of Open Access Journals (Sweden)

    Chairoj Rattanakawin

    2003-07-01

    Full Text Available The evolution of aggregate (floc size distributions resulting from hydrophobic flocculation has been investigated using a laser light scattering technique. By measuring floc size distributions it is possible to distinguish clearly among floc formation, growth and breakage. Hydrophobic flocculation of hematite suspensions with sodium oleate under a variety of agitating conditions produces uni-modal size distributions. The size distribution of the primary particles is shifted to larger floc sizes when the dispersed suspension is coagulated by pH adjustment. By adding sodium oleate to the pre-coagulated suspension, the distribution progresses further to the larger size. However, prolonged agitation degrades the formed flocs, regressing the distribution to the smaller size. Median floc size derived from the distribution is also used as performance criterion. The median floc size increases rapidly at the initial stage of the flocculation, and decreases with the extended agitation time and intensity. Relatively weak flocs are produced which may be due to the low dosage of sodium oleate used in this flocculation study. It is suggested that further investigation should focus on optimum reagent dosage and non-polar oil addition to strengthen these weak flocs.

  10. Body size distribution of the dinosaurs.

    Directory of Open Access Journals (Sweden)

    Eoin J O'Gorman

    Full Text Available 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.

  11. Body size distribution of the dinosaurs.

    Science.gov (United States)

    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.

  12. City size distributions and spatial economic change.

    Science.gov (United States)

    Sheppard, E

    1982-10-01

    "The concept of the city size distribution is criticized for its lack of consideration of the effects of interurban interdependencies on the growth of cities. Theoretical justifications for the rank-size relationship have the same shortcomings, and an empirical study reveals that there is little correlation between deviations from rank-size distributions and national economic and social characteristics. Thus arguments suggesting a close correspondence between city size distributions and the level of development of a country, irrespective of intranational variations in city location and socioeconomic characteristics, seem to have little foundation." (summary in FRE, ITA, JPN, ) excerpt

  13. City-size distribution and the size of urban systems

    OpenAIRE

    Thomas, I.

    1985-01-01

    This paper is an analysis of the city-size distribution for thirty-five countries of the world in 1975; the purpose is to explain statistically the regularity of the rank-size distribution by the number of cities included in the urban systems. The rank-size parameters have been computed for each country and also for four large urban systems in which several population thresholds have been defined. These thresholds seem to have more influence than the number of cities included in the urban sys...

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

    Science.gov (United States)

    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.

  15. Dark matter in voids

    Science.gov (United States)

    Fong, Richard; Doroshkevich, Andrei G.; Turchaninov, Victor I.

    1995-07-01

    The theory of the formation of large-scale structure in the universe through the action of gravitational instability imply the existence of substantial amounts of baryonic dark matter, of the order of 50% of the total baryon content in the universe, in the ``voids'' or under-dense regions seen in the large-scale distribution of galaxies. We discuss also the large-scale structure of dark matter expected in voids and the present and future possibilities for the observation of this baryonic dark matter in ``voids.''

  16. Dark matter in voids

    Energy Technology Data Exchange (ETDEWEB)

    Fong, R. [Department of Physics, University of Durham, Durham, DH1 3LE (United Kingdom); Doroshkevich, A.G. [Keldysh Institute of Applied Mathematics, 125047 Moscow (Russian Federation)]|[Teoretical Astrophysics Centrum, Blegsdamsvej 17, Copenhagen DK 2100 (Denmark); Turchaninov, V.I. [Keldysh Institute of Applied Mathematics, 125047 Moscow (Russian Federation)

    1995-07-01

    The theory of the formation of large-scale structure in the universe through the action of gravitational instability imply the existence of substantial amounts of baryonic dark matter, of the order of 50% of the total baryon content in the universe, in the ``voids`` or under-dense regions seen in the large-scale distribution of galaxies. We discuss also the large-scale structure of dark matter expected in voids and the present and future possibilities for the observation of this baryonic dark matter in ``voids.`` {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  17. Aggregate size distributions in sweep flocculation

    Directory of Open Access Journals (Sweden)

    Chairoj Rattanakawin

    2005-09-01

    Full Text Available The evolution of aggregate size distributions resulting from sweep flocculation has been investigated using laser light scattering technique. By measuring the (volume distributions of floc size, it is possible to distinguish clearly among floc formation, growth and breakage. Sweep flocculation of stable kaolin suspensions with ferric chloride under conditions of the rapid/slow mixing protocol produces uni-modal size distributions. The size distribution is shifted to larger floc size especially during the rapid mixing step. The variation of the distributions is also shown in the plot of cumulative percent finer against floc size. From this plot, the distributions maintain the same S-shape curves over the range of the mixing intensities/times studied. A parallel shift of the curves indicates that self-preserving size distribution occurred in this flocculation. It is suggested that some parameters from mathematical functions derived from the curves could be used to construct a model and predict the flocculating performance. These parameters will be useful for a water treatment process selection, design criteria, and process control strategies. Thus the use of these parameters should be employed in any further study.

  18. An experimental study of the size effect on adiabatic gas-liquid two-phase flow patterns and void fraction in microchannels

    Science.gov (United States)

    Xiong, Renqiang; Chung, J. N.

    2007-03-01

    Adiabatic gas-liquid flow patterns and void fractions in microchannels were experimentally investigated. Using nitrogen and water, experiments were conducted in rectangular microchannels with hydraulic diameters of 0.209mm, 0.412mm and 0.622mm, respectively. Gas and liquid superficial velocities were varied from 0.06-72.3m/s and 0.02-7.13m/s, respectively. The main objective is focused on the effects of microscale channel sizes on the flow regime map and void fraction. The instability of flow patterns was observed. Four groups of flow patterns including bubbly slug flow, slug-ring flow, dispersed-churn flow, and annular flow were observed in microchannels of 0.412mm and, 0.622mm. In the microchannel of 0.209mm, the bubbly slug flow became the slug flow and the dispersed-churn flow disappeared. The current flow regime maps showed the transition lines shifted to higher gas superficial velocity due to a dominant surface tension effect as the channel size was reduced. The regime maps presented by other authors for minichannels were found to not be applicable for microchannels. Time-averaged void fractions were measured by analyzing 8000 high speed video images for each flow condition. The void fractions hold a nonlinear relationship with the homogeneous void fraction as opposed to the relatively linear trend for the minichannels. A new correlation was developed to predict the nonlinear relationship that fits most of the current experimental data and those of the 0.1mm diameter tube reported by Kawahara et al. [Int. J. Multiphase Flow 28, 1411 (2002)] within ±15%.

  19. On the Deepwater Horizon drop size distributions

    Science.gov (United States)

    Ryerson, T. B.; Atlas, E. L.; Blake, D. R.; De Gouw, J. A.; Warneke, C.; Peischl, J.; Brock, C. A.; McKeen, S. A.

    2014-12-01

    Model simulations of the fate of gas and oil released following the Deepwater Horizon blowout in 2012 depend critically on the assumed drop size distributions. We use direct observations of surfacing time, surfacing location, and atmospheric chemical composition to infer an average drop size distribution for June 10, 2012, providing robust first-order constraints on parameterizations in models. We compare the inferred drop size distribution to published work on Deepwater Horizon and discuss the ability of this approach to determine the efficacy of subsurface dispersant injection.

  20. Particle size distribution instrument. Topical report 13

    Energy Technology Data Exchange (ETDEWEB)

    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.

  1. On the Size Distribution of Sand

    DEFF Research Database (Denmark)

    Sørensen, Michael

    2016-01-01

    -distribution, by taking into account that individual grains do not have the same travel time from the source to the deposit. The travel time is assumed to be random so that the wear on the individual grains vary randomly. The model provides an interpretation of the parameters of the NIG-distribution, and relates the mean......A model is presented of the development of the size distribution of sand while it is transported from a source to a deposit. The model provides a possible explanation of the log-hyperbolic shape that is frequently found in unimodal grain size distributions in natural sand deposits, as pointed out...

  2. The distribution of bubble sizes during reionization

    Science.gov (United States)

    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.

  3. The exponential age distribution and the Pareto firm size distribution

    OpenAIRE

    Coad, Alex

    2008-01-01

    Recent work drawing on data for large and small firms has shown a Pareto distribution of firm size. We mix a Gibrat-type growth process among incumbents with an exponential distribution of firm’s age, to obtain the empirical Pareto distribution.

  4. Bubble Size Distributions in Coastal Seas

    NARCIS (Netherlands)

    Leeuw, G. de; Cohen, L.H.

    1995-01-01

    Bubble size distributions have been measured with an optical system that is based on imaging of a small sample volume with a CCD camera system, and processing of the images to obtain the size of individual bubbles in the diameter range from 30 to lOOO^m. This bubble measuring system is deployed from

  5. Alignment of voids in the cosmic web

    NARCIS (Netherlands)

    Platen, Erwin; van de Weygaert, Rien; Jones, Bernard J. T.

    2008-01-01

    We investigate the shapes and mutual alignment of voids in the large-scale matter distribution of a Lambda cold dark matter (Lambda CDM) cosmology simulation. The voids are identified using the novel watershed void finder (WVF) technique. The identified voids are quite non-spherical and slightly pro

  6. Alignment of voids in the cosmic web

    NARCIS (Netherlands)

    Platen, Erwin; van de Weygaert, Rien; Jones, Bernard J. T.

    2008-01-01

    We investigate the shapes and mutual alignment of voids in the large-scale matter distribution of a Lambda cold dark matter (Lambda CDM) cosmology simulation. The voids are identified using the novel watershed void finder (WVF) technique. The identified voids are quite non-spherical and slightly

  7. Quantifying Effects of Voids in Woven Ceramic Matrix Composites

    Science.gov (United States)

    Goldsmith, Marlana B.; Sankar, Bhavani V.; Haftka, Raphael T.; Goldberg, Robert K.

    2013-01-01

    Randomness in woven ceramic matrix composite architecture has been found to cause large variability in stiffness and strength. The inherent voids are an aspect of the architecture that may cause a significant portion of the variability. A study is undertaken to investigate the effects of many voids of random sizes and distributions. Response surface approximations were formulated based on void parameters such as area and length fractions to provide an estimate of the effective stiffness. Obtaining quantitative relationships between the properties of the voids and their effects on stiffness of ceramic matrix composites are of ultimate interest, but the exploratory study presented here starts by first modeling the effects of voids on an isotropic material. Several cases with varying void parameters were modeled which resulted in a large amount of variability of the transverse stiffness and out-of-plane shear stiffness. An investigation into a physical explanation for the stiffness degradation led to the observation that the voids need to be treated as an entity that reduces load bearing capabilities in a space larger than what the void directly occupies through a corrected length fraction or area fraction. This provides explanation as to why void volume fraction is not the only important factor to consider when computing loss of stiffness.

  8. Experimental Study of Three-Dimensional Void Fraction Distribution in Heated Tight-Lattice Rod Bundles Using Three-Dimensional Neutron Tomography

    Science.gov (United States)

    Kureta, Masatoshi

    Three-dimensional (3D) void fraction distributions in a tight-lattice of heated 7- or 14-rod bundles were measured using 3D neutron tomography. The distribution was also studied parametrically from the thermal-hydraulic point of view in order to elucidate boiling phenomena in a fuel assembly of the FLWR which is being developed as an advanced BWR-type reactor. 7-rod tests were carried out to obtain high void fraction data. 14-rod tests were conducted for visualization and discussion of the 3D distribution extending from the vapor generation region to the high void fraction region at one time. Experimental data were obtained under atmospheric pressure with mass velocity, heater power and inlet quality as the test parameters. It was found from the visualization of data that the void fraction at the channel center became higher than that at the periphery, high void fraction spots appeared in narrow regions at the inlet, and a so-called 'vapor chimney' was generated at the center of a subchannel.

  9. Spectro-ellipsometric studies of sputtered amorphous Titanium dioxide thin films: simultaneous determination of refractive index, extinction coefficient, and void distribution

    CERN Document Server

    Lee, S I; Oh, S G

    1999-01-01

    Amorphous titanium dioxide thin films were deposited onto silicon substrates by using RF magnetron sputtering, and the index of refraction, the extinction coefficient, and the void distribution of these films were simultaneously determined from the analyses of there ellipsometric spectra. In particular, our novel strategy, which combines the merits of multi-sample fitting, the dual dispersion function, and grid search, was proven successful in determining optical constants over a wide energy range, including the energy region where the extinction coefficient was large. Moreover, we found that the void distribution was dependent on the deposition conditions, such as the sputtering power, the substrate temperature, and the substrate surface.

  10. CTF Void Drift Validation Study

    Energy Technology Data Exchange (ETDEWEB)

    Salko, Robert K. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Gosdin, Chris [Pennsylvania State Univ., University Park, PA (United States); Avramova, Maria N. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Gergar, Marcus [Pennsylvania State Univ., University Park, PA (United States)

    2015-10-26

    This milestone report is a summary of work performed in support of expansion of the validation and verification (V&V) matrix for the thermal-hydraulic subchannel code, CTF. The focus of this study is on validating the void drift modeling capabilities of CTF and verifying the supporting models that impact the void drift phenomenon. CTF uses a simple turbulent-diffusion approximation to model lateral cross-flow due to turbulent mixing and void drift. The void drift component of the model is based on the Lahey and Moody model. The models are a function of two-phase mass, momentum, and energy distribution in the system; therefore, it is necessary to correctly model the ow distribution in rod bundle geometry as a first step to correctly calculating the void distribution due to void drift.

  11. Size dependent pore size distribution of shales by gas physisorption

    Science.gov (United States)

    Roshan, Hamid; Andersen, Martin S.; Yu, Lu; Masoumi, Hossein; Arandian, Hamid

    2017-04-01

    Gas physisorption, in particular nitrogen adsorption-desorption, is a traditional technique for characterization of geomaterials including the organic rich shales. The low pressure nitrogen is used together with adsorption-desorption physical models to study the pore size distribution (PSD) and porosity of the porous samples. The samples are usually crushed to a certain fragment size to measure these properties however there is not yet a consistent standard size proposed for sample crushing. Crushing significantly increases the surface area of the fragments e.g. the created surface area is differentiated from that of pores using BET technique. In this study, we show that the smaller fragment sizes lead to higher cumulative pore volume and smaller pore diameters. It is also shown that some of the micro-pores are left unaccounted because of the correction of the external surface area. In order to illustrate this, the nitrogen physisorption is first conducted on the identical organic rich shale samples with different sizes: 20-25, 45-50 and 63-71 µm. We then show that such effects are not only a function of pore structure changes induced by crushing, but is linked to the inability of the physical models in differentiating between the external surface area (BET) and micro-pores for different crushing sizes at relatively low nitrogen pressure. We also discuss models currently used in nano-technology such as t-method to address this issue and their advantages and shortcoming for shale rock characterization.

  12. Responsibility voids

    NARCIS (Netherlands)

    van Hees, M.V.B.P.M; Braham, Matthew

    We present evidence for the existence of 'responsibility voids' in committee decision-making, that is, the existence of situations where no member of a committee can individually be held morally responsible for the outcome. We analyse three types of reasons (causal, normative and epistemic) for the

  13. Development and validation of advanced CFD models for detailed predictions of void distribution in a BWR bundle

    Science.gov (United States)

    Neykov, Boyan

    , it is important to extend validity of the current correlations for the lift coefficients to higher void (gas) phase fractions. After investigating the underlying physics and analyzing a large amount of experimental data, an improved model for lift force at different void fraction levels, including large bubbles and slug flow regime, is proposed. The model is implemented in STAR-CD and validated. The validation of the models is performed against five different experiments, characterized by different geometries at different boundary conditions. Comparison with the already existing models in STAR-CD code is performed and it is found that the newly integrated force models for drag and lift forces leads to more accurate void distribution predictions.

  14. Modelling the void deformation and closure by hot forging of ingot castings

    DEFF Research Database (Denmark)

    Christiansen, Peter; Hattel, Jesper Henri; Kotas, Petr;

    2012-01-01

    After solidification and cooling cast ingots contain voids due to improper feeding and volume shrinkage. Such voids are normally unwanted, so besides of forming the ingot to the desired shape, one of the purposes of the post processing of the ingot by hot forging is to close such voids by mechani......After solidification and cooling cast ingots contain voids due to improper feeding and volume shrinkage. Such voids are normally unwanted, so besides of forming the ingot to the desired shape, one of the purposes of the post processing of the ingot by hot forging is to close such voids...... and focuses on how the voids deform depending on their size and distribution in the ingot as well ashow the forging forces are applied....

  15. Determination of size distribution using neural networks

    NARCIS (Netherlands)

    Stevens, JH; Nijhuis, JAG; Spaanenburg, L; Mohammadian, M

    1999-01-01

    In this paper we present a novel approach to the estimation of size distributions of grains in water from images. External conditions such as the concentrations of grains in water cannot be controlled. This poses problems for local image analysis which tries to identify and measure single grains.

  16. Size from Specular Highlights for Analyzing Droplet Size Distributions

    Science.gov (United States)

    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.

  17. A Cosmic Void Catalog of SDSS DR12 BOSS Galaxies

    CERN Document Server

    Mao, Qingqing; Scherrer, Robert J; Scoccimarro, Roman; Tinker, Jeremy L; McBride, Cameron K; Neyrinck, Mark C; Schneider, Donald P; Pan, Kaike; Bizyaev, Dmitry; Malanushenko, Elena; Malanushenko, Viktor

    2016-01-01

    We present a cosmic void catalog using the large-scale structure galaxy catalog from the Baryon Oscillation Spectroscopic Survey (BOSS). This galaxy catalog is part of the Sloan Digital Sky Survey (SDSS) Data Release 12 and is the final catalog of SDSS-III. We take into account the survey boundaries, masks, and angular and radial selection functions, and apply the ZOBOV void finding algorithm to the galaxy catalog. After making quality cuts to ensure that the voids represent real underdense regions, we identify 1228 voids with effective radii spanning the range 20-100Mpc/h and with central densities that are, on average, 30% of the mean sample density. We discuss the basic statistics of voids, such as their size and redshift distributions, and measure the radial density profile of the voids via a stacking technique. In addition, we construct mock void catalogs from 1000 mock galaxy catalogs, and find that the properties of BOSS voids are in good agreement with those in the mock catalogs. We compare the stella...

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

    Science.gov (United States)

    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.

  19. Velocity Distributions in Inelastic Granular Gases with Continuous Size Distributions

    Institute of Scientific and Technical Information of China (English)

    LI Rui; ZHANG Duan-Ming; LI Zhi-Hao

    2011-01-01

    We study by numerical simulation the property of velocity distributions of granular gases with a power-law size distribution, driven by uniform heating and boundary heating. It is found that the form of velocity distribution is primarily controlled by the restitution coefficient -q and q, the ratio between the average number of heatings and the average number of collisions in the system. Furthermore, we show that uniform and boundary heating can be understood as different limits of q, with q ? 1 and q >1 and q≤1,respectively.

  20. Prediction of the size distribution of precipitates

    Energy Technology Data Exchange (ETDEWEB)

    Prikhodovsky, A. [Forschungszentrum Juelich GmbH (Germany). Inst. fuer Werkstoffe und Verfahren der Energietechnik 2: Werkstoffstruktur und Eigenschaften

    2001-12-01

    Modelling has proven to be an efficient way of cutting the time and costs associated with the investigation of materials properties. A new mathematical model for the prediction of the particle size distribution of precipitates has been developed. The model allows the description of all stages of the precipitation process: nucleation, growth and Ostwald ripening of particles. The incorporation of existing thermodynamic databases allows the simulation of a formation of dispersed phases in commercial multicomponent alloys. The influence of the model parameters on the final particle size distribution was investigated with the example of NbC formation in austenite. It was shown that the interfacial energy of a particle-matrix interface has the most significant effect on the final particle arrangement. A pre-exponential factor, which is the subject of nucleation theories, plays a less significant role in the final particle arrangement. (orig.)

  1. Crystallite size distributions of marine gas hydrates

    Energy Technology Data Exchange (ETDEWEB)

    Klapp, S.A.; Bohrmann, G.; Abegg, F. [Bremen Univ., Bremen (Germany). Research Center of Ocean Margins; Hemes, S.; Klein, H.; Kuhs, W.F. [Gottingen Univ., Gottingen (Germany). Dept. of Crystallography

    2008-07-01

    Experimental studies were conducted to determine the crystallite size distributions of natural gas hydrate samples retrieved from the Gulf of Mexico, the Black Sea, and a hydrate ridge located near offshore Oregon. Synchrotron radiation technology was used to provide the high photon fluxes and high penetration depths needed to accurately analyze the bulk sediment samples. A new beam collimation diffraction technique was used to measure gas hydrate crystallite sizes. The analyses showed that gas hydrate crystals were globular in shape. Mean crystallite sizes ranged from 200 to 400 {mu}m for hydrate samples taken from the sea floor. Larger grain sizes in the hydrate ridge samples suggested differences in hydrate formation ages or processes. A comparison with laboratory-produced methane hydrate samples showed half a lognormal curve with a mean value of 40{mu}m. Results of the study showed that a cautious approach must be adopted when transposing crystallite-size sensitive physical data from laboratory-made gas hydrates to natural settings. It was concluded that crystallite size information may also be used to resolve the formation ages of gas hydrates when formation processes and conditions are constrained. 48 refs., 1 tab., 9 figs.

  2. Remote Laser Diffraction Particle Size Distribution Analyzer

    Energy Technology Data Exchange (ETDEWEB)

    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.

  3. Measurement of nonvolatile particle number size distribution

    Science.gov (United States)

    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

  4. Landslide size distribution in seismic areas

    Science.gov (United States)

    Valagussa, Andrea; Frattini, Paolo; Crosta, Giovanni B.

    2015-04-01

    In seismic areas, the analysis of the landslides size distribution with the distance from the seismic source is very important for hazard zoning and land planning. From numerical modelling (Bourdeau et al., 2004), it has been observed that the area of the sliding mass tends to increase with the ground-motion amplitude up to a certain threshold input acceleration. This has been also observed empirically for the 1989 Loma Prieta earthquake (Keefer and Manson, 1998) and 1999 Chi Chi earthquake (Khazai and Sitar, 2003). Based on this, it possible to assume that the landslide size decreases with the increase of the distance from the seismic source. In this research, we analysed six earthquakes-induced landslides inventories (Papua New Guinea Earthquake, 1993; Northridge Earthquake, 1994; Niigata-Chuetsu Earthquake 2004; Iwate-Miyagi Nairiku Earthquake, 2008; Wenchuan Earthquake, 2008; Tohoku Earthquake, 2011) with a magnitude ranging between 6.6 and 9.0 Mw. For each earthquake, we first analysed the size of landslides as a function of different factors such as the lithology, the PGA, the relief, the distance from the seismic sources (both fault and epicentre). Then, we analysed the magnitude frequency curves for different distances from the source area and for each lithology. We found that a clear relationship between the size distribution and the distance from the seismic source is not evident, probably due to the combined effect of the different influencing factors and to the non-linear relationship between the ground-motion intensity and the distance from the seismic source.

  5. Aerosol Size Distribution in the marine regions

    Science.gov (United States)

    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

  6. Charge and Size Distributions of Electrospray Drops

    Science.gov (United States)

    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.

  7. Bimodal micropore size distribution in active carbons

    Energy Technology Data Exchange (ETDEWEB)

    Vartapetyan, R.S.; Voloshchuk, A.M.; Limonov, N.A.; Romanov, Y.A. (Russian Academy of Sciences, Moscow (Russian Federation). Inst. of Physical Chemistry)

    1993-03-01

    The porous structure of active carbon was compared with that of the original mineral coal and its carbonization products. The parameters of the porous structure were calculated from the adsorption isotherms of CO[sub 2] (298 K) and H[sub 2]O (293 K). It was shown that carbonization of the original coal at 1120 K causes changes in the chemical composition, consolidation of the part which is amorphous to X-rays, generation of an ordered defect-containing structure on its basis, an increase in the volume of the micropores, and a decrease in the mean diameter. Activation of the carbonized coal affords a microporous structure with a bimodal size distribution.

  8. Void growth to coalescence in a non-local material

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof

    The size-effect in metals containing distributed spherical voids is analyzed numerically using a finite strain generalization of a length scale dependent plasticity theory. Results are obtained for stress-triaxialities relevant in front of a crack tip in an elastic-plastic metal. The influence...

  9. Void growth to coalescence in a non-local material

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof

    2008-01-01

    The size-effect in metals containing distributed spherical voids is analyzed numerically using a finite strain generalization of a length scale dependent plasticity theory. Results are obtained for stress-triaxialities relevant in front of a crack tip in an elastic-plastic metal. The influence...

  10. The life and death of cosmic voids

    CERN Document Server

    Sutter, P M; Falck, Bridget; Onions, Julian; Hamaus, Nico; Knebe, Alexander; Srisawat, Chaichalit; Schneider, Aurel

    2014-01-01

    We investigate the formation, growth, merger history, movement, and destruction of cosmic voids detected via the watershed transform in a cosmological N-body dark matter {\\Lambda}CDM simulation. By adapting a method used to construct halo merger trees, we are able to trace individual voids back to their initial appearance and record the merging and evolution of their progenitors at high redshift. For the scales of void sizes captured in our simulation, we find that the void formation rate peaks at scale factor 0.3, which coincides with a growth in the void hierarchy and the emergence of dark energy. Voids of all sizes appear at all scale factors, though the median initial void size decreases with time. When voids become detectable they have nearly their present-day volumes. Almost all voids have relatively stable growth rates and suffer only infrequent minor mergers. Dissolution of a void via merging is very rare. Instead, most voids maintain their distinct identity as annexed subvoids of a larger parent. The...

  11. Cross-sectional void fraction distribution measurements in a vertical annulus two-phase flow by high speed X-ray computed tomography and real-time neutron radiography techniques

    Energy Technology Data Exchange (ETDEWEB)

    Harvel, G.D. [McMaster Univ., Ontario (Canada)]|[Combustion and Heat Transfer Lab., Takasago (Japan); Hori, K.; Kawanishi, K. [Combustion and Heat Transfer Lab., Takasago (Japan)] [and others

    1995-09-01

    A Real-Time Neutron Radiography (RTNR) system and a high speed X-ray Computed tomography (X-CT) system are compared for measurement of two-phase flow. Each system is used to determine the flow regime, and the void fraction distribution in a vertical annulus flow channel. A standard optical video system is also used to observe the flow regime. The annulus flow channel is operated as a bubble column and measurements obtained for gas flow rates from 0.0 to 30.01/min. The flow regimes observed by all three measurement systems through image analysis shows that the two-dimensional void fraction distribution can be obtained. The X-CT system is shown to have a superior temporal resolution capable of resolving the void fraction distribution in an (r,{theta}) plane in 33.0 ms. Void fraction distribution for bubbly flow and slug flow is determined.

  12. Parameterizing Size Distribution in Ice Clouds

    Energy Technology Data Exchange (ETDEWEB)

    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

  13. Comparative Analysis of CTF and Trace Thermal-Hydraulic Codes Using OECD/NRC PSBT Benchmark Void Distribution Database

    OpenAIRE

    2013-01-01

    The international OECD/NRC PSBT benchmark has been established to provide a test bed for assessing the capabilities of thermal-hydraulic codes and to encourage advancement in the analysis of fluid flow in rod bundles. The benchmark was based on one of the most valuable databases identified for the thermal-hydraulics modeling developed by NUPEC, Japan. The database includes void fraction and departure from nucleate boiling measurements in a representative PWR fuel assembly. On behalf of the be...

  14. Development of Criteria and Identification of Particle Cluster Size Based on Measurements of Void Fraction in Gas-Solid Systems

    Energy Technology Data Exchange (ETDEWEB)

    David Roelant; Seckin Gokaltun

    2009-06-30

    A circulating fluidized bed (CFB) built at FIU was used to study particle motion in the riser in order to simulate flow regimes in a cold gasifier. High speed imaging was used in order to capture the dynamics of the particles flowing in the riser. The imaging method used here is called the shadow sizing technique which allowed the determination of particle areas and trajectories at various flow rates in the riser. The solid volume fraction and particle velocities calculated using the images acquired during the experiments can be related to granular temperature in order to detect formations of clusters in the riser section of the CFB. The shadow sizing technique was observed to be an effective method in detecting dynamics of particles in motion and formation of clusters when supported with high-speed imaging.

  15. Effects of nano-void density, size and spatial population on thermal conductivity: a case study of GaN crystal

    Science.gov (United States)

    Zhou, X. W.; Jones, R. E.

    2012-08-01

    The thermal conductivity of a crystal is sensitive to the presence of surfaces and nanoscale defects. While this opens tremendous opportunities to tailor thermal conductivity, true ‘phonon engineering’ of nanocrystals for a specific electronic or thermoelectric application can only be achieved when the dependence of thermal conductivity on the defect density, size and spatial population is understood and quantified. Unfortunately, experimental studies of the effects of nanoscale defects are quite challenging. While molecular dynamics simulations are effective in calculating thermal conductivity, the defect density range that can be explored with feasible computing resources is unrealistically high. As a result, previous work has not generated a fully detailed understanding of the dependence of thermal conductivity on nanoscale defects. Using GaN as an example, we have combined a physically motivated analytical model and highly converged large-scale molecular dynamics simulations to study the effects of defects on thermal conductivity. An analytical expression for thermal conductivity as a function of void density, size, and population has been derived and corroborated with the model, simulations, and experiments.

  16. Atomistic insights into dislocation-based mechanisms of void growth and coalescence

    Science.gov (United States)

    Mi, Changwen; Buttry, Daniel A.; Sharma, Pradeep; Kouris, Demitris A.

    2011-09-01

    One of the low-temperature failure mechanisms in ductile metallic alloys is the growth of voids and their coalescence. In the present work we attempt to obtain atomistic insights into the mechanisms underpinning cavitation in a representative metal, namely Aluminum. Often the pre-existing voids in metallic alloys such as Al have complex shapes (e.g. corrosion pits) and the defromation/damage mechanisms exhibit a rich size-dependent behavior across various material length scales. We focus on these two issues in this paper through large-scale calculations on specimens of sizes ranging from 18 thousand to 1.08 million atoms. In addition to the elucidation of the dislocation propagation based void growth mechanism we highlight the observed length scale effect reflected in the effective stress-strain response, stress triaxiality and void fraction evolution. Furthermore, as expected, the conventionally used Gurson's model fails to capture the observed size-effects calling for a mechanistic modification that incorporates the mechanisms observed in our (and other researchers') simulation. Finally, in our multi-void simulations, we find that, the splitting of a big void into a distribution of small ones increases the load-carrying capacity of specimens. However, no obvious dependence of the void fraction evolution on void coalescence is observed.

  17. Flow Characteristics and Grain Size Distribution of Granular Gangue Mineral by Compaction Treatment

    Directory of Open Access Journals (Sweden)

    Ran Yuan

    2017-01-01

    Full Text Available A test system for water flow in granular gangue mineral was designed to study the flow characteristics by compaction treatment. With the increase of the compaction displacement, the porosity decreases and void in granular gangue becomes less. The main reason causing initial porosity decrease is that the void of larger size is filled with small particles. Permeability tends to decrease and non-Darcy flow factor increases under the compaction treatment. The change trend of flow characteristics shows twists and turns, which indicate that flow characteristics of granular gangue mineral are related to compaction level, grain size distribution, crushing, and fracture structure. During compaction, larger particles are crushed, which in turn causes the weight of smaller particles to increase, and water flow induces fine particles to migrate (weight loss; meanwhile, a sample with more weight of size (0–2.5 mm has a higher amount of weight loss. Water seepage will cause the decrease of some chemical components, where SiO2 decreased the highest in these components; the components decreased are more likely locked at fragments rather than the defect of the minerals. The variation of the chemical components has an opposite trend when compared with permeability.

  18. The dark matter of galaxy voids

    CERN Document Server

    Sutter, P M; Wandelt, Benjamin D; Weinberg, David H; Warren, Michael S

    2013-01-01

    How do observed voids relate to the underlying dark matter distribution? To examine the spatial distribution of dark matter contained within voids identified in galaxy surveys, we apply Halo Occupation Distribution models representing sparsely and densely sampled galaxy surveys to a high-resolution N-body simulation. We compare these galaxy voids to voids found in the halo distribution, low-resolution dark matter, and high-resolution dark matter. We find that voids at all scales in densely sampled surveys - and medium- to large-scale voids in sparse surveys - trace the same underdensities as dark matter, but they are larger in radius by ~20%, they have somewhat shallower density profiles, and they have centers offset by ~0.4Rv rms. However, in void-to-void comparison we find that shape estimators are less robust to sampling, and the largest voids in sparsely sampled surveys suffer fragmentation at their edges. We find that voids in galaxy surveys always correspond to underdensities in the dark matter, though ...

  19. The dark matter of galaxy voids

    Science.gov (United States)

    Sutter, P. M.; Lavaux, Guilhem; Wandelt, Benjamin D.; Weinberg, David H.; Warren, Michael S.

    2014-03-01

    How do observed voids relate to the underlying dark matter distribution? To examine the spatial distribution of dark matter contained within voids identified in galaxy surveys, we apply Halo Occupation Distribution models representing sparsely and densely sampled galaxy surveys to a high-resolution N-body simulation. We compare these galaxy voids to voids found in the halo distribution, low-resolution dark matter and high-resolution dark matter. We find that voids at all scales in densely sampled surveys - and medium- to large-scale voids in sparse surveys - trace the same underdensities as dark matter, but they are larger in radius by ˜20 per cent, they have somewhat shallower density profiles and they have centres offset by ˜ 0.4Rv rms. However, in void-to-void comparison we find that shape estimators are less robust to sampling, and the largest voids in sparsely sampled surveys suffer fragmentation at their edges. We find that voids in galaxy surveys always correspond to underdensities in the dark matter, though the centres may be offset. When this offset is taken into account, we recover almost identical radial density profiles between galaxies and dark matter. All mock catalogues used in this work are available at http://www.cosmicvoids.net.

  20. Atmospheric Ion Clusters: Properties and Size Distributions

    Science.gov (United States)

    D'Auria, R.; Turco, R. P.

    2002-12-01

    Ions are continuously generated in the atmosphere by the action of galactic cosmic radiation. Measured charge concentrations are of the order of 103 ~ {cm-3} throughout the troposphere, increasing to about 5 x 103 ~ {cm-3} in the lower stratosphere [Cole and Pierce, 1965; Paltridge, 1965, 1966]. The lifetimes of these ions are sufficient to allow substantial clustering with common trace constituents in air, including water, nitric and sulfuric acids, ammonia, and a variety of organic compounds [e.g., D'Auria and Turco, 2001 and references cited therein]. The populations of the resulting charged molecular clusters represent a pre-nucleation phase of particle formation, and in this regard comprise a key segment of the over-all nucleation size spectrum [e.g., Castleman and Tang, 1972]. It has been suggested that these clusters may catalyze certain heterogeneous reactions, and given their characteristic crystal-like structures may act as freezing nuclei for supercooled droplets. To investigate these possibilities, basic information on cluster thermodynamic properties and chemical kinetics is needed. Here, we present new results for several relevant atmospheric ion cluster families. In particular, predictions based on quantum mechanical simulations of cluster structure, and related thermodynamic parameters, are compared against laboratory data. We also describe a hybrid approach for modeling cluster sequences that combines laboratory measurements and quantum predictions with the classical liquid droplet (Thomson) model to treat a wider range of cluster sizes. Calculations of cluster mass distributions based on this hybrid model are illustrated, and the advantages and limitations of such an analysis are summarized. References: Castelman, A. W., Jr., and I. N. Tang, Role of small clusters in nucleation about ions, J. Chem. Phys., 57, 3629-3638, 1972. Cole, R. K., and E. T. Pierce, Electrification in the Earth's atmosphere for altitudes between 0 and 100 kilometers, J

  1. Evaluation of Factors Affecting Size and Size Distribution of Chitosan-Electrosprayed Nanoparticles.

    Science.gov (United States)

    Abyadeh, Morteza; Karimi Zarchi, Ali Akbar; Faramarzi, Mohammad Ali; Amani, Amir

    2017-01-01

    Size and size distribution of polymeric nanoparticles have important effect on their properties for pharmaceutical application. In this study, Chitosan nanoparticles were prepared by electrospray method (electrohydrodynamic atomization) and parameters that simultaneously affect size and/or size distribution of chitosan nanoparticles were optimized. Effect of formulation/processing three independent formulation/processing parameters, namely concentration, flow rate and applied voltage was investigated on particle size and size distribution of generated nanoparticles using a Box-Behnken experimental design. All the studied factors showed important effects on average size and size distribution of nanoparticles. A decrease in size and size distribution was obtainable with decreasing flow rate and concentration and increasing applied voltage. Eventually, a sample with minimum size and polydispersity was obtained with polymer concentration, flow rate and applied voltage values of 0.5 %w/v, 0.05 ml/hr and 15 kV, respectively. The experimentally prepared nanoparticles, expected having lowest size and size distribution values had a size of 105 nm, size distribution of 36 and Zeta potential of 59.3 mV. Results showed that optimum condition for production of chitosan nanoparticles with the minimum size and narrow size distribution was a minimum value for flow rate and highest value for applied voltage along with an optimum chitosan concentration.

  2. The star formation activity in cosmic voids

    CERN Document Server

    Ricciardelli, Elena; Varela, Jesus; Quilis, Vicent

    2014-01-01

    Using a sample of cosmic voids identified in the Sloan Digital Sky Survey Data Release 7, we study the star formation activity of void galaxies. The properties of galaxies living in voids are compared with those of galaxies living in the void shells and with a control sample, representing the general galaxy population. Void galaxies appear to form stars more efficiently than shell galaxies and the control sample. This result can not be interpreted as a consequence of the bias towards low masses in underdense regions, as void galaxy subsamples with the same mass distribution as the control sample also show statistically different specific star formation rates. This highlights the fact that galaxy evolution in voids is slower with respect to the evolution of the general population. Nevertheless, when only the star forming galaxies are considered, we find that the star formation rate is insensitive to the environment, as the main sequence is remarkably constant in the three samples under consideration. This fact...

  3. Computerized voiding diary.

    Science.gov (United States)

    Rabin, J M; McNett, J; Badlani, G H

    1993-01-01

    An electronic, computerized voiding diary, "Compu-Void" (patent pending) was developed in order to simplify, augment, and automate patients' recording of bladder symptomatology. A voiding diary as a tool has the potential to provide essential information for a more complete diagnostic and therefore therapeutic picture for each patient. Two major problems with the standard written voiding diary have been a lack of patient compliance and the limited amount of information it garners. Twenty-five women with various types of voiding dysfunctions were compared to twenty-five age and parity-matched control women in order to determine patient preferences of the Compu-Void when compared to the standard written voiding diary, compliance with each method, and amount and quality of information obtained with each method. Over 90% of subjects and over 70% of control group patients preferred the Compu-Void over the written diary (P Compu-Void exceeded that obtained with the written method.

  4. Cosmology with void-galaxy correlations.

    Science.gov (United States)

    Hamaus, Nico; Wandelt, Benjamin D; Sutter, P M; Lavaux, Guilhem; Warren, Michael S

    2014-01-31

    Galaxy bias, the unknown relationship between the clustering of galaxies and the underlying dark matter density field is a major hurdle for cosmological inference from large-scale structure. While traditional analyses focus on the absolute clustering amplitude of high-density regions mapped out by galaxy surveys, we propose a relative measurement that compares those to the underdense regions, cosmic voids. On the basis of realistic mock catalogs we demonstrate that cross correlating galaxies and voids opens up the possibility to calibrate galaxy bias and to define a static ruler thanks to the observable geometric nature of voids. We illustrate how the clustering of voids is related to mass compensation and show that volume-exclusion significantly reduces the degree of stochasticity in their spatial distribution. Extracting the spherically averaged distribution of galaxies inside voids from their cross correlations reveals a remarkable concordance with the mass-density profile of voids.

  5. Evaluation of droplet size distributions using univariate and multivariate approaches.

    Science.gov (United States)

    Gaunø, Mette Høg; Larsen, Crilles Casper; Vilhelmsen, Thomas; Møller-Sonnergaard, Jørn; Wittendorff, Jørgen; Rantanen, Jukka

    2013-01-01

    Pharmaceutically relevant material characteristics are often analyzed based on univariate descriptors instead of utilizing the whole information available in the full distribution. One example is droplet size distribution, which is often described by the median droplet size and the width of the distribution. The current study was aiming to compare univariate and multivariate approach in evaluating droplet size distributions. As a model system, the atomization of a coating solution from a two-fluid nozzle was investigated. The effect of three process parameters (concentration of ethyl cellulose in ethanol, atomizing air pressure, and flow rate of coating solution) on the droplet size and droplet size distribution using a full mixed factorial design was used. The droplet size produced by a two-fluid nozzle was measured by laser diffraction and reported as volume based size distribution. Investigation of loading and score plots from principal component analysis (PCA) revealed additional information on the droplet size distributions and it was possible to identify univariate statistics (volume median droplet size), which were similar, however, originating from varying droplet size distributions. The multivariate data analysis was proven to be an efficient tool for evaluating the full information contained in a distribution.

  6. Constraints on Cosmology and Gravity from the Dynamics of Voids

    Science.gov (United States)

    Hamaus, Nico; Pisani, Alice; Sutter, P. M.; Lavaux, Guilhem; Escoffier, Stéphanie; Wandelt, Benjamin D.; Weller, Jochen

    2016-08-01

    The Universe is mostly composed of large and relatively empty domains known as cosmic voids, whereas its matter content is predominantly distributed along their boundaries. The remaining material inside them, either dark or luminous matter, is attracted to these boundaries and causes voids to expand faster and to grow emptier over time. Using the distribution of galaxies centered on voids identified in the Sloan Digital Sky Survey and adopting minimal assumptions on the statistical motion of these galaxies, we constrain the average matter content Ωm=0.281 ±0.031 in the Universe today, as well as the linear growth rate of structure f /b =0.417 ±0.089 at median redshift z ¯=0.57 , where b is the galaxy bias (68% C.L.). These values originate from a percent-level measurement of the anisotropic distortion in the void-galaxy cross-correlation function, ɛ =1.003 ±0.012 , and are robust to consistency tests with bootstraps of the data and simulated mock catalogs within an additional systematic uncertainty of half that size. They surpass (and are complementary to) existing constraints by unlocking cosmological information on smaller scales through an accurate model of nonlinear clustering and dynamics in void environments. As such, our analysis furnishes a powerful probe of deviations from Einstein's general relativity in the low-density regime which has largely remained untested so far. We find no evidence for such deviations in the data at hand.

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

    Directory of Open Access Journals (Sweden)

    Yue Bin

    Full Text Available 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.

  8. Universal void density profiles from simulation and SDSS

    CERN Document Server

    Nadathur, S; Diego, J M; Iliev, I T; Gottlöber, S; Watson, W A; Yepes, G

    2014-01-01

    We discuss the universality and self-similarity of void density profiles, for voids in realistic mock luminous red galaxy (LRG) catalogues from the Jubilee simulation, as well as in void catalogues constructed from the SDSS LRG and Main Galaxy samples. Voids are identified using a modified version of the ZOBOV watershed transform algorithm, with additional selection cuts. We find that voids in simulation are self-similar, meaning that their average rescaled profile does not depend on the void size, or -- within the range of the simulated catalogue -- on the redshift. Comparison of the profiles obtained from simulated and real voids shows an excellent match. The profiles of real voids also show a universal behaviour over a wide range of galaxy luminosities, number densities and redshifts. This points to a fundamental property of the voids found by the watershed algorithm, which can be exploited in future studies of voids.

  9. Universal void density profiles from simulation and SDSS

    Science.gov (United States)

    Nadathur, S.; Hotchkiss, S.; Diego, J. M.; Iliev, I. T.; Gottlöber, S.; Watson, W. A.; Yepes, G.

    2016-10-01

    We discuss the universality and self-similarity of void density profiles, for voids in realistic mock luminous red galaxy (LRG) catalogues from the Jubilee simulation, as well as in void catalogues constructed from the SDSS LRG and Main Galaxy samples. Voids are identified using a modified version of the ZOBOV watershed transform algorithm, with additional selection cuts. We find that voids in simulation are self-similar, meaning that their average rescaled profile does not depend on the void size, or - within the range of the simulated catalogue - on the redshift. Comparison of the profiles obtained from simulated and real voids shows an excellent match. The profiles of real voids also show a universal behaviour over a wide range of galaxy luminosities, number densities and redshifts. This points to a fundamental property of the voids found by the watershed algorithm, which can be exploited in future studies of voids.

  10. Analysis of Void Fraction Distribution and Departure from Nucleate Boiling in Single Subchannel and Bundle Geometries Using Subchannel, System, and Computational Fluid Dynamics Codes

    Directory of Open Access Journals (Sweden)

    Taewan Kim

    2012-01-01

    Full Text Available In order to assess the accuracy and validity of subchannel, system, and computational fluid dynamics codes, the Paul Scherrer Institut has participated in the OECD/NRC PSBT benchmark with the thermal-hydraulic system code TRACE5.0 developed by US NRC, the subchannel code FLICA4 developed by CEA, and the computational fluid dynamic code STAR-CD developed by CD-adapco. The PSBT benchmark consists of a series of void distribution exercises and departure from nucleate boiling exercises. The results reveal that the prediction by the subchannel code FLICA4 agrees with the experimental data reasonably well in both steady-state and transient conditions. The analyses of single-subchannel experiments by means of the computational fluid dynamic code STAR-CD with the CD-adapco boiling model indicate that the prediction of the void fraction has no significant discrepancy from the experiments. The analyses with TRACE point out the necessity to perform additional assessment of the subcooled boiling model and bulk condensation model of TRACE.

  11. How dense can one pack spheres of arbitrary size distribution?

    Science.gov (United States)

    Reis, S. D. S.; Araújo, N. A. M.; Andrade, J. S., Jr.; Herrmann, Hans J.

    2012-01-01

    We present the first systematic algorithm to estimate the maximum packing density of spheres when the grain sizes are drawn from an arbitrary size distribution. With an Apollonian filling rule, we implement our technique for disks in 2d and spheres in 3d. As expected, the densest packing is achieved with power-law size distributions. We also test the method on homogeneous and on empirical real distributions, and we propose a scheme to obtain experimentally accessible distributions of grain sizes with low porosity. Our method should be helpful in the development of ultra-strong ceramics and high-performance concrete.

  12. The Development of Voiding

    DEFF Research Database (Denmark)

    Olsen, Lars Henning

    2011-01-01

    The thesis addresses some new aspeccts in the development of voiding function from midgestation into early childhood.......The thesis addresses some new aspeccts in the development of voiding function from midgestation into early childhood....

  13. Pareto tails and lognormal body of US cities size distribution

    Science.gov (United States)

    Luckstead, Jeff; Devadoss, Stephen

    2017-01-01

    We consider a distribution, which consists of lower tail Pareto, lognormal body, and upper tail Pareto, to estimate the size distribution of all US cities. This distribution fits the data more accurately than a distribution that comprises of only lognormal and the upper tail Pareto.

  14. Effect of void cluster on ductile failure evolution

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2016-01-01

    The behavior of a non-uniform void distribution in a ductile material is investigated by using a cell model analysis to study a material with a periodic pattern of void clusters. The special clusters considered consist of a number of uniformly spaced voids located along a plane perpendicular...... to the maximum principal tensile stress. A plane strain approximation is used, where the voids are parallel cylindrical holes. Clusters with different numbers of voids are compared with the growth of a single void, such that the total initial volume of the voids, and thus also the void volume fractions...... understanding, different transverse stresses on the unit cell are considered to see the influence of different levels of stress triaxiality. Also considered are different initial ratios of the void spacing to the void radius inside the clusters. And results are shown for different levels of strain hardening...

  15. Changes of firm size distribution: The case of Korea

    Science.gov (United States)

    Kang, Sang Hoon; Jiang, Zhuhua; Cheong, Chongcheul; Yoon, Seong-Min

    2011-01-01

    In this paper, the distribution and inequality of firm sizes is evaluated for the Korean firms listed on the stock markets. Using the amount of sales, total assets, capital, and the number of employees, respectively, as a proxy for firm sizes, we find that the upper tail of the Korean firm size distribution can be described by power-law distributions rather than lognormal distributions. Then, we estimate the Zipf parameters of the firm sizes and assess the changes in the magnitude of the exponents. The results show that the calculated Zipf exponents over time increased prior to the financial crisis, but decreased after the crisis. This pattern implies that the degree of inequality in Korean firm sizes had severely deepened prior to the crisis, but lessened after the crisis. Overall, the distribution of Korean firm sizes changes over time, and Zipf’s law is not universal but does hold as a special case.

  16. Supplemental topics on voids

    Energy Technology Data Exchange (ETDEWEB)

    Rood, H.J.

    1988-09-01

    Several topics concerning voids are presented, supplementing the report of Rood (1988). The discovery of the Coma supercluster and void and the recognition of the cosmological significance of superclusters and voids are reviewed. Galaxy redshift surveys and redshift surveys for the Abell clusters and very distant objects are discussed. Solar system and extragalactic dynamics are examined. Also, topics for future observational research on voids are recommended. 50 references.

  17. Universal density profile for cosmic voids.

    Science.gov (United States)

    Hamaus, Nico; Sutter, P M; Wandelt, Benjamin D

    2014-06-27

    We present a simple empirical function for the average density profile of cosmic voids, identified via the watershed technique in ΛCDM N-body simulations. This function is universal across void size and redshift, accurately describing a large radial range of scales around void centers with only two free parameters. In analogy to halo density profiles, these parameters describe the scale radius and the central density of voids. While we initially start with a more general four-parameter model, we find two of its parameters to be redundant, as they follow linear trends with the scale radius in two distinct regimes of the void sample, separated by its compensation scale. Assuming linear theory, we derive an analytic formula for the velocity profile of voids and find an excellent agreement with the numerical data as well. In our companion paper [Sutter et al., arXiv:1309.5087 [Mon. Not. R. Astron. Soc. (to be published)

  18. A study of process induced voids in resistance welding of thermoplastic composites

    OpenAIRE

    Shi, H.; Fernandez Villegas, I.; Bersee, H.E.N.

    2015-01-01

    Void formation in resistance welding of woven fabric reinforced thermoplastic composites was investigated. Void contents were measured using optical microscopy and digital image process. Un-even void distributions were observed in the joints, and more voids were found in the middle of the joints than the edges. A higher welding pressure was shown to help reduce the void generation. The mechanisms of void formation, in particular fibre de-compaction induced voids and residual moisture induced ...

  19. Effect of the Entrained Air Void on Strength and Interfacial Transition Zone of Air-Entrained Mortar

    Institute of Scientific and Technical Information of China (English)

    GAO Hui; ZHANG Xiong; ZHANG Yongjuan

    2015-01-01

    In order to facilitate the development and application of air entraining agents (AEA) in the high performance concrete, entrained air void structure parameters (air void size range from 10 to 1 600 μm) of 28 d sifted mortar were measured by image analysis method. The relationship between the air void size distribution and strength of mortar was studied by methods of grey connection analysis and multiple linear regression analysis. The multiple linear regression equation was established with a correlation coefifcient of 0.966. The weight of the affection of hierarchical porosity on the compressive strength ratio was also obtained. In addition, the effect of air voids on the paste-aggregate interfacial transition zone (ITZ) was analyzed by microhardness. The results show that the correlation between different pore size range and the compressive strength is negative. The effect of air void size distribution on 28 days compressive strength is different: under the condition of similar total porosity, with the increase of the porosity of the air void size, ranging from 10 to 200 μm, and the decrease of the porosity, ranging from 200 to 1 600 μm, the average air void diameter and mean free spacing are decreased; as well as the width of ITZ. On the contrary, the microhardness of the ITZ is increased while the compressive strength loss is decreased.

  20. 导流介质对VARTM复合材料纤维分布及空隙率的影响%Effects of Infusion Media on Fiber Volume Fraction Distribution and Void Content in Vacuum Assisted Resin Transfer Molding

    Institute of Scientific and Technical Information of China (English)

    赖家美; 陈显明; 王德盼; 鄢冬冬; 王科

    2014-01-01

    Effects of the size of infusion media on resin flow behavior,fiber volume fraction distribution and void content in vacuum assisted resin transfer molding(VARTM) were studied.The results showed that with the increase of infusion media size, the resin flow rate increased exponentially;the fiber volume fraction showed a tendency to increase after the first decrease,and the infusion media boundary was just the high and low fiber volume fraction line;the void content increased first and then decreased and increased tremendously at last,varied from 3.86% to 19.92%.%研究了导流介质尺寸对真空辅助树脂传递模塑(VARTM)工艺中树脂流动行为的影响,以及对复合材料制品中纤维分布和空隙率的影响。结果表明,随着导流介质尺寸的增加,树脂在增强体中的流动速度加快,并呈现指数加速趋势;制品中纤维体积含量呈现先减少后增大的趋势,并且以导流介质边界为纤维体积含量高低的分界线;复合材料制品的空隙率范围在3.86%~19.92%,空隙率呈现先增大后减小再加速增大的趋势。

  1. The size distribution of inhabited planets

    Science.gov (United States)

    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 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.

  2. Estimation of Nanoparticle Size Distributions by Image Analysis

    DEFF Research Database (Denmark)

    Fisker, Rune; Carstensen, Jens Michael; Hansen, Mikkel Fougt

    2000-01-01

    Knowledge of the nanoparticle size distribution is important for the interpretation of experimental results in many studies of nanoparticle properties. An automated method is needed for accurate and robust estimation of particle size distribution from nanoparticle images with thousands of particl...

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

    Science.gov (United States)

    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.

  4. Droplet size distribution in homogeneous isotropic turbulence

    Science.gov (United States)

    Perlekar, Prasad; Biferale, Luca; Sbragaglia, Mauro; Srivastava, Sudhir; Toschi, Federico

    2012-06-01

    We study the physics of droplet breakup in a statistically stationary homogeneous and isotropic turbulent flow by means of high resolution numerical investigations based on the multicomponent lattice Boltzmann method. We verified the validity of the criterion proposed by Hinze [AIChE J. 1, 289 (1955)] for droplet breakup and we measured the full probability distribution function of droplets radii at different Reynolds numbers and for different volume fractions. By means of a Lagrangian tracking we could follow individual droplets along their trajectories, define a local Weber number based on the velocity gradients, and study its cross-correlation with droplet deformation.

  5. Voids in cosmological simulations over cosmic time

    Science.gov (United States)

    Wojtak, Radosław; Powell, Devon; Abel, Tom

    2016-06-01

    We study evolution of voids in cosmological simulations using a new method for tracing voids over cosmic time. The method is based on tracking watershed basins (contiguous regions around density minima) of well-developed voids at low redshift, on a regular grid of density field. It enables us to construct a robust and continuous mapping between voids at different redshifts, from initial conditions to the present time. We discuss how the new approach eliminates strong spurious effects of numerical origin when voids' evolution is traced by matching voids between successive snapshots (by analogy to halo merger trees). We apply the new method to a cosmological simulation of a standard Λ-cold-dark-matter cosmological model and study evolution of basic properties of typical voids (with effective radii 6 h-1 Mpc < Rv < 20 h-1 Mpc at redshift z = 0) such as volumes, shapes, matter density distributions and relative alignments. The final voids at low redshifts appear to retain a significant part of the configuration acquired in initial conditions. Shapes of voids evolve in a collective way which barely modifies the overall distribution of the axial ratios. The evolution appears to have a weak impact on mutual alignments of voids implying that the present state is in large part set up by the primordial density field. We present evolution of dark matter density profiles computed on isodensity surfaces which comply with the actual shapes of voids. Unlike spherical density profiles, this approach enables us to demonstrate development of theoretically predicted bucket-like shape of the final density profiles indicating a wide flat core and a sharp transition to high-density void walls.

  6. A RELATION FOR THE VOID FRACTION OF RANDOMLY PACKED PARTICLE BEDS

    NARCIS (Netherlands)

    HOFFMANN, AC; FINKERS, HJ

    1995-01-01

    The void fractions of loosely packed and tapped beds of particles of continuous size distributions are correlated by means of a proposed new semi-empirical relation. In this relation four parameters describing the following particle properties are included: (i) mean particle size, (ii) spread of the

  7. Cosmic voids and void lensing in the Dark Energy Survey Science Verification data

    Energy Technology Data Exchange (ETDEWEB)

    Sánchez, C.; Clampitt, J.; Kovacs, A.; Jain, B.; García-Bellido, J.; Nadathur, S.; Gruen, D.; Hamaus, N.; Huterer, D.; Vielzeuf, P.; Amara, A.; Bonnett, C.; DeRose, J.; Hartley, W. G.; Jarvis, M.; Lahav, O.; Miquel, R.; Rozo, E.; Rykoff, E. S.; Sheldon, E.; Wechsler, R. H.; Zuntz, J.; Abbott, T. M. C.; Abdalla, F. B.; Annis, J.; Benoit-Lévy, A.; Bernstein, G. M.; Bernstein, R. A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Crocce, M.; Cunha, C. E.; D' Andrea, C. B.; da Costa, L. N.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Evrard, A. E.; Neto, A. Fausti; Flaugher, B.; Fosalba, P.; Frieman, J.; Gaztanaga, E.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Krause, E.; Kuehn, K.; Lima, M.; Maia, M. A. G.; Marshall, J. L.; Melchior, P.; Plazas, A. A.; Reil, K.; Romer, A. K.; Sanchez, E.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Tarle, G.; Thomas, D.; Walker, A. R.; Weller, J.

    2016-10-26

    Galaxies and their dark matter halos populate a complicated filamentary network around large, nearly empty regions known as cosmic voids. Cosmic voids are usually identified in spectroscopic galaxy surveys, where 3D information about the large-scale structure of the Universe is available. Although an increasing amount of photometric data is being produced, its potential for void studies is limited since photometric redshifts induce line-of-sight position errors of $\\sim50$ Mpc/$h$ or more that can render many voids undetectable. In this paper we present a new void finder designed for photometric surveys, validate it using simulations, and apply it to the high-quality photo-$z$ redMaGiC galaxy sample of the Dark Energy Survey Science Verification (DES-SV) data. The algorithm works by projecting galaxies into 2D slices and finding voids in the smoothed 2D galaxy density field of the slice. Fixing the line-of-sight size of the slices to be at least twice the photo-$z$ scatter, the number of voids found in these projected slices of simulated spectroscopic and photometric galaxy catalogs is within 20% for all transverse void sizes, and indistinguishable for the largest voids of radius $\\sim 70$ Mpc/$h$ and larger. The positions, radii, and projected galaxy profiles of photometric voids also accurately match the spectroscopic void sample. Applying the algorithm to the DES-SV data in the redshift range $0.2voids with comoving radii spanning the range 18-120 Mpc/$h$, and carry out a stacked weak lensing measurement. With a significance of $4.4\\sigma$, the lensing measurement confirms the voids are truly underdense in the matter field and hence not a product of Poisson noise, tracer density effects or systematics in the data. It also demonstrates, for the first time in real data, the viability of void lensing studies in photometric surveys.

  8. Zipf's law for fractal voids and a new void-finder

    CERN Document Server

    Gaite, J

    2005-01-01

    Voids are a prominent feature of fractal point distributions but there is no precise definition of what is a void (except in one dimension). Here we propose a definition of voids that uses methods of discrete stochastic geometry, in particular, Delaunay and Voronoi tessellations, and we construct a new algorithm to search for voids in a point set. We find and rank-order the voids of suitable examples of fractal point sets in one and two dimensions to test whether Zipf's power-law holds. We conclude affirmatively and, furthermore, that the rank-ordering of voids conveys similar information to the number-radius function, as regards the scaling regime and the transition to homogeneity. So it is an alternative tool in the analysis of fractal point distributions with crossover to homogeneity and, in particular, of the distribution of galaxies.

  9. Powder Size and Distribution in Ultrasonic Gas Atomization

    Science.gov (United States)

    Rai, G.; Lavernia, E.; Grant, N. J.

    1985-08-01

    Ultrasonic gas atomization (USGA) produces powder sizes dependent on the ratio of the nozzle jet diameter to the distance of spread dt/R, Powder size distribution is attributed to the spread of atomizing gas jets during travel from the nozzle exit to the metal stream. The spread diminishes at higher gas atomization pressures. In this paper, calculated powder sizes and distribution are compared with experimentally determined values.

  10. Vapor intrusion in soils with multimodal pore-size distribution

    OpenAIRE

    Alfaro Soto Miguel; Hung Kiang Chang

    2016-01-01

    The Johnson and Ettinger [1] model and its extensions are at this time the most widely used algorithms for estimating subsurface vapor intrusion into buildings (API [2]). The functions which describe capillary pressure curves are utilized in quantitative analyses, although these are applicable for porous media with a unimodal or lognormal pore-size distribution. However, unaltered soils may have a heterogeneous pore distribution and consequently a multimodal pore-size distribution [3], which ...

  11. The Collisional Divot in the Kuiper belt Size Distribution

    CERN Document Server

    Fraser, Wesley C

    2009-01-01

    This paper presents the results of collisional evolution calculations for the Kuiper belt starting from an initial size distribution similar to that produced by accretion simulations of that region - a steep power-law large object size distribution that breaks to a shallower slope at r ~1-2 km, with collisional equilibrium achieved for objects r ~0.5 km. We find that the break from the steep large object power-law causes a divot, or depletion of objects at r ~10-20 km, which in-turn greatly reduces the disruption rate of objects with r> 25-50 km, preserving the steep power-law behavior for objects at this size. Our calculations demonstrate that the roll-over observed in the Kuiper belt size distribution is naturally explained as an edge of a divot in the size distribution; the radius at which the size distribution transitions away from the power-law, and the shape of the divot from our simulations are consistent with the size of the observed roll-over, and size distribution for smaller bodies. Both the kink r...

  12. Evaluation of droplet size distributions using univariate and multivariate approaches

    DEFF Research Database (Denmark)

    Gauno, M.H.; Larsen, C.C.; Vilhelmsen, T.

    2013-01-01

    of the distribution. The current study was aiming to compare univariate and multivariate approach in evaluating droplet size distributions. As a model system, the atomization of a coating solution from a two-fluid nozzle was investigated. The effect of three process parameters (concentration of ethyl cellulose....... Investigation of loading and score plots from principal component analysis (PCA) revealed additional information on the droplet size distributions and it was possible to identify univariate statistics (volume median droplet size), which were similar, however, originating from varying droplet size distributions....... The multivariate data analysis was proven to be an efficient tool for evaluating the full information contained in a distribution. © 2013 Informa Healthcare USA, Inc....

  13. Inversion of spheroid particle size distribution in wider size range and aspect ratio range

    Directory of Open Access Journals (Sweden)

    Tang Hong

    2013-01-01

    Full Text Available The non-spherical particle sizing is very important in the aerosol science, and it can be determined by the light extinction measurement. This paper studies the effect of relationship of the size range and aspect ratio range on the inversion of spheroid particle size distribution by the dependent mode algorithm. The T matrix method and the geometric optics approximation method are used to calculate the extinction efficiency of the spheroids with different size range and aspect ratio range, and the inversion of spheroid particle size distribution in these different ranges is conducted. Numerical simulation indicates that a fairly reasonable representation of the spheroid particle size distribution can be obtained when the size range and aspect ratio range are suitably chosen.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  15. Pore-size-distribution of cationic polyacrylamide hydrogels

    Energy Technology Data Exchange (ETDEWEB)

    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.

  16. The darkness that shaped the void: dark energy and cosmic voids

    CERN Document Server

    Bos, E G Patrick; Dolag, Klaus; Pettorino, Valeria

    2012-01-01

    Aims: We assess the sensitivity of void shapes to the nature of dark energy that was pointed out in recent studies. We investigate whether or not void shapes are useable as an observational probe in galaxy redshift surveys. We focus on the evolution of the mean void ellipticity and its underlying physical cause. Methods: We analyse the morphological properties of voids in five sets of cosmological N-body simulations, each with a different nature of dark energy. Comparing voids in the dark matter distribution to those in the halo population, we address the question of whether galaxy redshift surveys yield sufficiently accurate void morphologies. Voids are identified using the parameter free Watershed Void Finder. The effect of redshift distortions is investigated as well. Results: We confirm the statistically significant sensitivity of voids in the dark matter distribution. We identify the level of clustering as measured by \\sigma_8(z) as the main cause of differences in mean void shape . We find that in the h...

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

    Science.gov (United States)

    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.

  18. Cosmic voids and void lensing in the Dark Energy Survey Science Verification data

    Science.gov (United States)

    Sánchez, C.; Clampitt, J.; Kovacs, A.; Jain, B.; García-Bellido, J.; Nadathur, S.; Gruen, D.; Hamaus, N.; Huterer, D.; Vielzeuf, P.; Amara, A.; Bonnett, C.; DeRose, J.; Hartley, W. G.; Jarvis, M.; Lahav, O.; Miquel, R.; Rozo, E.; Rykoff, E. S.; Sheldon, E.; Wechsler, R. H.; Zuntz, J.; Abbott, T. M. C.; Abdalla, F. B.; Annis, J.; Benoit-Lévy, A.; Bernstein, G. M.; Bernstein, R. A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Evrard, A. E.; Neto, A. Fausti; Flaugher, B.; Fosalba, P.; Frieman, J.; Gaztanaga, E.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Krause, E.; Kuehn, K.; Lima, M.; Maia, M. A. G.; Marshall, J. L.; Melchior, P.; Plazas, A. A.; Reil, K.; Romer, A. K.; Sanchez, E.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Tarle, G.; Thomas, D.; Walker, A. R.; Weller, J.; DES Collaboration

    2017-02-01

    Cosmic voids are usually identified in spectroscopic galaxy surveys, where 3D information about the large-scale structure of the Universe is available. Although an increasing amount of photometric data is being produced, its potential for void studies is limited since photometric redshifts induce line-of-sight position errors of ≥50 Mpc h-1which can render many voids undetectable. We present a new void finder designed for photometric surveys, validate it using simulations, and apply it to the high-quality photo-z redMaGiC galaxy sample of the DES Science Verification data. The algorithm works by projecting galaxies into 2D slices and finding voids in the smoothed 2D galaxy density field of the slice. Fixing the line-of-sight size of the slices to be at least twice the photo-z scatter, the number of voids found in simulated spectroscopic and photometric galaxy catalogues is within 20 per cent for all transverse void sizes, and indistinguishable for the largest voids (Rv ≥ 70 Mpc h-1). The positions, radii, and projected galaxy profiles of photometric voids also accurately match the spectroscopic void sample. Applying the algorithm to the DES-SV data in the redshift range 0.2 < z < 0.8, we identify 87 voids with comoving radii spanning the range 18-120 Mpc h-1, and carry out a stacked weak lensing measurement. With a significance of 4.4σ, the lensing measurement confirms that the voids are truly underdense in the matter field and hence not a product of Poisson noise, tracer density effects or systematics in the data. It also demonstrates, for the first time in real data, the viability of void lensing studies in photometric surveys.

  19. Environmental control of natural gap size distribution in tropical forests

    Science.gov (United States)

    Goulamoussène, Youven; Bedeau, Caroline; Descroix, Laurent; Linguet, Laurent; Hérault, Bruno

    2017-01-01

    Natural disturbances are the dominant form of forest regeneration and dynamics in unmanaged tropical forests. Monitoring the size distribution of treefall gaps is important to better understand and predict the carbon budget in response to land use and other global changes. In this study, we model the size frequency distribution of natural canopy gaps with a discrete power law distribution. We use a Bayesian framework to introduce and test, using Monte Carlo Markov chain and Kuo-Mallick algorithms, the effect of local physical environment on gap size distribution. We apply our methodological framework to an original light detecting and ranging dataset in which natural forest gaps were delineated over 30 000 ha of unmanaged forest. We highlight strong links between gap size distribution and environment, primarily hydrological conditions and topography, with large gaps being more frequent on floodplains and in wind-exposed areas. In the future, we plan to apply our methodological framework on a larger scale using satellite data. Additionally, although gap size distribution variation is clearly under environmental control, variation in gap size distribution in time should be tested against climate variability.

  20. Effects of Data Frame Size Distribution on Wireless Lans | Aneke ...

    African Journals Online (AJOL)

    Effects of Data Frame Size Distribution on Wireless Lans. ... Nigerian Journal of Technology ... to replace cables and deploy mobile devices in the communications industry has led to very active research on the utilization of wireless networks.

  1. The sparkling Universe: a scenario for cosmic void motions

    Science.gov (United States)

    Ceccarelli, Laura; Ruiz, Andrés N.; Lares, Marcelo; Paz, Dante J.; Maldonado, Victoria E.; Luparello, Heliana E.; Garcia Lambas, Diego

    2016-10-01

    Cosmic voids are prominent features of the Universe, encoding relevant information of the growth and evolution of structure through their dynamics. Here, we perform a statistical study of the global motion of cosmic voids using both a numerical simulation and observational data. Their relation to large-scale mass flows and the physical effects that drive those motions. We analyse the bulk motions of voids, finding void mean bulk velocities in the range 300-400 km s-1, depending on void size and the large-scale environment. Statistically, small voids move faster, and voids in relatively higher density environments have higher bulk velocities. Also, we find large-scale overdensities (underdensities) along (opposite to) the void motion direction, suggesting that void motions respond to a pull-push mechanism. Our analysis suggests that their relative motions are generated by large-scale density fluctuations. In agreement with linear theory, voids embedded in low (high) density regions mutually recede (attract) each other, providing the general mechanism to understand the bimodal behaviour of void motions. We have also inferred void motions in the Sloan Digital Sky Survey using linear theory, finding that their estimated motions are in qualitatively agreement with the results of the simulation. Our results suggest a scenario of galaxies and galaxy systems flowing away from void centres with the additional, and more relevant, contribution of the void bulk motion to the total velocity.

  2. Size distribution measurements and chemical analysis of aerosol components

    Energy Technology Data Exchange (ETDEWEB)

    Pakkanen, T.A.

    1995-12-31

    The principal aims of this work were to improve the existing methods for size distribution measurements and to draw conclusions about atmospheric and in-stack aerosol chemistry and physics by utilizing size distributions of various aerosol components measured. A sample dissolution with dilute nitric acid in an ultrasonic bath and subsequent graphite furnace atomic absorption spectrometric analysis was found to result in low blank values and good recoveries for several elements in atmospheric fine particle size fractions below 2 {mu}m of equivalent aerodynamic particle diameter (EAD). Furthermore, it turned out that a substantial amount of analyses associated with insoluble material could be recovered since suspensions were formed. The size distribution measurements of in-stack combustion aerosols indicated two modal size distributions for most components measured. The existence of the fine particle mode suggests that a substantial fraction of such elements with two modal size distributions may vaporize and nucleate during the combustion process. In southern Norway, size distributions of atmospheric aerosol components usually exhibited one or two fine particle modes and one or two coarse particle modes. Atmospheric relative humidity values higher than 80% resulted in significant increase of the mass median diameters of the droplet mode. Important local and/or regional sources of As, Br, I, K, Mn, Pb, Sb, Si and Zn were found to exist in southern Norway. The existence of these sources was reflected in the corresponding size distributions determined, and was utilized in the development of a source identification method based on size distribution data. On the Finnish south coast, atmospheric coarse particle nitrate was found to be formed mostly through an atmospheric reaction of nitric acid with existing coarse particle sea salt but reactions and/or adsorption of nitric acid with soil derived particles also occurred. Chloride was depleted when acidic species reacted

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

    Science.gov (United States)

    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.

  4. Size Segregation in Rapid Flows of Inelastic Particles with Continuous Size Distributions

    Institute of Scientific and Technical Information of China (English)

    LI Rui; ZHANG Duan-Ming; LI Zhi-Hao

    2012-01-01

    Two-dimensional numerical simulations are employed to gain insight into the segregation behavior of granular mixtures with a power-law particle size distribution in the presence of a granular temperature gradient.It is found that particles of all sizes move toward regions of low granular temperature.Species segregation is also observed.Large particles demonstrate a higher affinity for the low-temperature regions and accumulate in these cool regions to a greater extent than their smaller counterparts.Furthermore,the local particle size distribution maintains the same form as the overall (including all particles) size distribution.%Two-dimensional numerical simulations are employed to gain insight into the segregation behavior of granular mixtures with a power-law particle size distribution in the presence of a granular temperature gradient. It is found that particles of all sizes move toward regions of low granular temperature. Species segregation is also observed. Large particles demonstrate a higher affinity for the low-temperature regions and accumulate in these cool regions to a greater extent than their smaller counterparts. Furthermore, the local particle size distribution maintains the same form as the overall (including all particles) size distribution.

  5. Vapor intrusion in soils with multimodal pore-size distribution

    Directory of Open Access Journals (Sweden)

    Alfaro Soto Miguel

    2016-01-01

    Full Text Available The Johnson and Ettinger [1] model and its extensions are at this time the most widely used algorithms for estimating subsurface vapor intrusion into buildings (API [2]. The functions which describe capillary pressure curves are utilized in quantitative analyses, although these are applicable for porous media with a unimodal or lognormal pore-size distribution. However, unaltered soils may have a heterogeneous pore distribution and consequently a multimodal pore-size distribution [3], which may be the result of specific granulometry or the formation of secondary porosity related to genetic processes. The present paper was designed to present the application of the Vapor Intrusion Model (SVI_Model to unsaturated soils with multimodal pore-size distribution. Simulations with data from the literature show that the use of a multimodal model in soils with such pore distribution characteristics could provide more reliable results for indoor air concentration, rather than conventional models.

  6. A multivariate rank test for comparing mass size distributions

    KAUST Repository

    Lombard, F.

    2012-04-01

    Particle size analyses of a raw material are commonplace in the mineral processing industry. Knowledge of particle size distributions is crucial in planning milling operations to enable an optimum degree of liberation of valuable mineral phases, to minimize plant losses due to an excess of oversize or undersize material or to attain a size distribution that fits a contractual specification. The problem addressed in the present paper is how to test the equality of two or more underlying size distributions. A distinguishing feature of these size distributions is that they are not based on counts of individual particles. Rather, they are mass size distributions giving the fractions of the total mass of a sampled material lying in each of a number of size intervals. As such, the data are compositional in nature, using the terminology of Aitchison [1] that is, multivariate vectors the components of which add to 100%. In the literature, various versions of Hotelling\\'s T 2 have been used to compare matched pairs of such compositional data. In this paper, we propose a robust test procedure based on ranks as a competitor to Hotelling\\'s T 2. In contrast to the latter statistic, the power of the rank test is not unduly affected by the presence of outliers or of zeros among the data. © 2012 Copyright Taylor and Francis Group, LLC.

  7. Modelling complete particle-size distributions from operator estimates of particle-size

    Science.gov (United States)

    Roberson, Sam; Weltje, Gert Jan

    2014-05-01

    Estimates of particle-size made by operators in the field and laboratory represent a vast and relatively untapped data archive. The wide spatial distribution of particle-size estimates makes them ideal for constructing geological models and soil maps. This study uses a large data set from the Netherlands (n = 4837) containing both operator estimates of particle size and complete particle-size distributions measured by laser granulometry. This study introduces a logit-based constrained-cubic-spline (CCS) algorithm to interpolate complete particle-size distributions from operator estimates. The CCS model is compared to four other models: (i) a linear interpolation; (ii) a log-hyperbolic interpolation; (iii) an empirical logistic function; and (iv) an empirical arctan function. Operator estimates were found to be both inaccurate and imprecise; only 14% of samples were successfully classified using the Dutch classification scheme for fine sediment. Operator estimates of sediment particle-size encompass the same range of values as particle-size distributions measured by laser analysis. However, the distributions measured by laser analysis show that most of the sand percentage values lie between zero and one, so the majority of the variability in the data is lost because operator estimates are made to the nearest 1% at best, and more frequently to the nearest 5%. A method for constructing complete particle-size distributions from operator estimates of sediment texture using a logit constrained cubit spline (CCS) interpolation algorithm is presented. This model and four other previously published methods are compared to establish the best approach to modelling particle-size distributions. The logit-CCS model is the most accurate method, although both logit-linear and log-linear interpolation models provide reasonable alternatives. Models based on empirical distribution functions are less accurate than interpolation algorithms for modelling particle-size distributions in

  8. VIDE: The Void IDentification and Examination toolkit

    CERN Document Server

    Sutter, P M; Hamaus, Nico; Pisani, Alice; Wandelt, Benjamin D; Warren, Michael S; Villaescusa-Navarro, Francisco; Zivick, Paul; Mao, Qingqing; Thompson, Benjamin B

    2014-01-01

    We present VIDE, the Void IDentification and Examination toolkit, an open-source Python/C++ code for finding cosmic voids in galaxy redshift surveys and N-body simulations, characterizing their properties, and providing a platform for more detailed analysis. At its core, VIDE uses a greatly enhanced version of ZOBOV (Neyinck 2008) to calculate a Voronoi tessellation for estimating the density field and a watershed transform to construct voids. The watershed levels are used to place voids in a hierarchical tree. VIDE provides significant additional functionality for both pre- and post-processing: for example, VIDE can work with volume- or magnitude-limited galaxy samples with arbitrary survey geometries, or dark matter particles or halo catalogs in a variety of common formats. It can also randomly subsample inputs and includes a Halo Occupation Distribution model for constructing mock galaxy populations. VIDE outputs a summary of void properties in plain ASCII, and provides a Python API to perform many analysi...

  9. Voids in the SDSS DR9: observations, simulations, and the impact of the survey mask

    CERN Document Server

    Sutter, P M; Wandelt, Benjamin D; Weinberg, David H; Warren, Michael S

    2013-01-01

    We present and study cosmic voids identified using the watershed void finder ZOBOZ in the Sloan Digital Sky Survey Data Release 9, compare these voids to ones identified in mock catalogs, and assess the impact of the survey mask on void statistics such as number functions, ellipticity distributions, and radial density profiles. The nearly 1,000 identified voids span three volume-limited samples from redshift z=0.43 to 0.7. For comparison we use 98 of the publicly available 2LPT-based mock galaxy catalogs of Manera et al. (2012), and also generate our own mock catalogs by applying a Halo Occupation Distribution model to an N-body simulation. We find that the mask reduces the number density of voids at all scales by a factor of three and slightly skews the relative size distributions. This engenders an increase in the mean ellipticity by roughly 30%. However, we find that radial density profiles are largely robust to the effects of the mask. We see excellent agreement between the data and both mock catalogs, an...

  10. SANDY: A Matlab tool to estimate the sediment size distribution from a sieve analysis

    Science.gov (United States)

    Ruiz-Martínez, Gabriel; Rivillas-Ospina, Germán Daniel; Mariño-Tapia, Ismael; Posada-Vanegas, Gregorio

    2016-07-01

    This paper presents a new computational tool called SANDY© which calculates the sediment size distribution and its textural parameters from a sieved sediment sample using Matlab®. The tool has been developed for professionals involved in the study of sediment transport along coastal margins, estuaries, rivers and desert dunes. The algorithm uses several types of statistical analyses to obtain the main textural characteristics of the sediment sample (D50, mean, sorting, skewness and kurtosis). SANDY© includes the method of moments (geometric, arithmetic and logarithmic approaches) and graphical methods (geometric, arithmetic and mixed approaches). In addition, it provides graphs of the sediment size distribution and its classification. The computational tool automatically exports all the graphs as enhanced metafile images and the final report is also exported as a plain text file. Parameters related to bed roughness such as Nikuradse and roughness length are also computed. Theoretical depositional environments are established by a discriminant function analysis. Using the uniformity coefficient the hydraulic conductivity of the sand as well as the porosity and void ratio of the sediment sample are obtained. The maximum relative density related to sand compaction is also computed. The Matlab® routine can compute one or several samples. SANDY© is a useful tool for estimating the sediment textural parameters which are the basis for studies of sediment transport.

  11. Granule Size Distribution and Porosity of Granule Packing

    Institute of Scientific and Technical Information of China (English)

    DAI Shu-hua; SHEN Feng-man; YU Ai-bing

    2008-01-01

    The granule size distribution and the porosity of the granule packing process were researched.For realizing the optimizing control of the whole sintering production process,researchers must know the factors influencing the granule size distribution and the porosity.Therefore,tests were carried out in the laboratory with regard to the influences of the size and size distribution of raw materials and the total moisture content on the size and size distribution of granule.Moreover,tests for finding out the influences of the moisture content and the granule volume fraction on the porosity were also carried out.The results show that (1) the raw material has little influence on granulation when its size is in the range of 0.51 mm to 1.0 mm;(2) the influence of the material size on granule size plays a dominant role,and in contrast,the moisture content creates a minor effect on granule size;(3) in binary packing system,with the increase in the constituent volume fraction,the porosity initially increases and then decreases,and there is a minimum value on the porosity curve of the binary mixture system;(4) the minimum value of the porosity in binary packing system occurs at different locations for different moisture contents,and this value shifts from right to left on the porosity curve with increasing the moisture content;(5) the addition of small granules to the same size component cannot create a significant influence on the porosity,whereas the addition of large granules to the same system can greatly change the porosity.

  12. Particle size and shape distributions of hammer milled pine

    Energy Technology Data Exchange (ETDEWEB)

    Westover, Tyler Lott [Idaho National Lab. (INL), Idaho Falls, ID (United States); Matthews, Austin Colter [Idaho National Lab. (INL), Idaho Falls, ID (United States); Williams, Christopher Luke [Idaho National Lab. (INL), Idaho Falls, ID (United States); Ryan, John Chadron Benjamin [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    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.

  13. Particle size and shape distributions of hammer milled pine

    Energy Technology Data Exchange (ETDEWEB)

    Westover, Tyler Lott [Idaho National Lab. (INL), Idaho Falls, ID (United States); Matthews, Austin Colter [Idaho National Lab. (INL), Idaho Falls, ID (United States); Williams, Christopher Luke [Idaho National Lab. (INL), Idaho Falls, ID (United States); Ryan, John Chadron Benjamin [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    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.

  14. Voiding dysfunction - A review

    Directory of Open Access Journals (Sweden)

    Sripathi V

    2005-01-01

    Full Text Available In a child who is toilet trained the sudden onset of daytime wetting with frequency or urgency is alarming to the parents. Initially this subject was subdivided into a number of descriptive clinical conditions which led to a lot of confusion in recognition and management. Subsequently, the term elimination dysfunction was coined by Stephen Koff to emphasise the association between recurrent urinary infection, wetting, constipation and bladder overactivity. From a urodynamic point of view, in voiding dysfunction, there is either detrusor overactivity during bladder filling or dyssynergic action between the detrusor and the external sphincter during voiding. Identifying a given condition as a ′filling phase dysfunction′ or ′voiding phase dysfunction′ helps to provide appropriate therapy. Objective clinical criteria should be used to define voiding dysfunction. These include bladder wall thickening, large capacity bladder and infrequent voiding, bladder trabeculation and spinning top deformity of the urethra and a clinically demonstrated Vincent′s curtsy. The recognition and treatment of constipation is central to the adequate treatment of voiding dysfunction. Transcutaneous electric nerve stimuation for the treatment of detrusor overactivity, biofeedback with uroflow EMG to correct dyssynergic voiding, and behavioral therapy all serve to correct voiding dysfunction in its early stages. In established neurogenic bladder disease the use of Botulinum Toxin A injections into the detrusor or the external sphincter may help in restoring continence especially in those refractory to drug therapy. However in those children in whom the upper tracts are threatened, augmentation of the bladder may still be needed.

  15. Voids in cosmological simulations over cosmic time

    CERN Document Server

    Wojtak, Radosław; Abel, Tom

    2016-01-01

    We study evolution of voids in cosmological simulations using a new method for tracing voids over cosmic time. The method is based on tracking watershed basins (contiguous regions around density minima) of well developed voids at low redshift, on a regular grid of density field. It enables us to construct a robust and continuous mapping between voids at different redshifts, from initial conditions to the present time. We discuss how the new approach eliminates strong spurious effects of numerical origin when voids evolution is traced by matching voids between successive snapshots (by analogy to halo merger trees). We apply the new method to a cosmological simulation of a standard LambdaCDM cosmological model and study evolution of basic properties of typical voids (with effective radii between 6Mpc/h and 20Mpc/h at redshift z=0) such as volumes, shapes, matter density distributions and relative alignments. The final voids at low redshifts appear to retain a significant part of the configuration acquired in in...

  16. Measuring nanoparticles size distribution in food and consumer products: a review.

    Science.gov (United States)

    Calzolai, L; Gilliland, D; Rossi, F

    2012-08-01

    Nanoparticles are already used in several consumer products including food, food packaging and cosmetics, and their detection and measurement in food represent a particularly difficult challenge. In order to fill the void in the official definition of what constitutes a nanomaterial, the European Commission published in October 2011 its recommendation on the definition of 'nanomaterial'. This will have an impact in many different areas of legislation, such as the European Cosmetic Products Regulation, where the current definitions of nanomaterial will come under discussion regarding how they should be adapted in light of this new definition. This new definition calls for the measurement of the number-based particle size distribution in the 1-100 nm size range of all the primary particles present in the sample independently of whether they are in a free, unbound state or as part of an aggregate/agglomerate. This definition does present great technical challenges for those who must develop valid and compatible measuring methods. This review will give an overview of the current state of the art, focusing particularly on the suitability of the most used techniques for the size measurement of nanoparticles when addressing this new definition of nanomaterials. The problems to be overcome in measuring nanoparticles in food and consumer products will be illustrated with some practical examples. Finally, a possible way forward (based on the combination of different measuring techniques) for solving this challenging analytical problem is illustrated.

  17. Cell-size distribution in epithelial tissue formation and homeostasis.

    Science.gov (United States)

    Puliafito, Alberto; Primo, Luca; Celani, Antonio

    2017-03-01

    How cell growth and proliferation are orchestrated in living tissues to achieve a given biological function is a central problem in biology. During development, tissue regeneration and homeostasis, cell proliferation must be coordinated by spatial cues in order for cells to attain the correct size and shape. Biological tissues also feature a notable homogeneity of cell size, which, in specific cases, represents a physiological need. Here, we study the temporal evolution of the cell-size distribution by applying the theory of kinetic fragmentation to tissue development and homeostasis. Our theory predicts self-similar probability density function (PDF) of cell size and explains how division times and redistribution ensure cell size homogeneity across the tissue. Theoretical predictions and numerical simulations of confluent non-homeostatic tissue cultures show that cell size distribution is self-similar. Our experimental data confirm predictions and reveal that, as assumed in the theory, cell division times scale like a power-law of the cell size. We find that in homeostatic conditions there is a stationary distribution with lognormal tails, consistently with our experimental data. Our theoretical predictions and numerical simulations show that the shape of the PDF depends on how the space inherited by apoptotic cells is redistributed and that apoptotic cell rates might also depend on size.

  18. Recurrent frequency-size distribution of characteristic events

    Directory of Open Access Journals (Sweden)

    S. G. Abaimov

    2009-04-01

    Full Text Available Statistical frequency-size (frequency-magnitude properties of earthquake occurrence play an important role in seismic hazard assessments. The behavior of earthquakes is represented by two different statistics: interoccurrent behavior in a region and recurrent behavior at a given point on a fault (or at a given fault. The interoccurrent frequency-size behavior has been investigated by many authors and generally obeys the power-law Gutenberg-Richter distribution to a good approximation. It is expected that the recurrent frequency-size behavior should obey different statistics. However, this problem has received little attention because historic earthquake sequences do not contain enough events to reconstruct the necessary statistics. To overcome this lack of data, this paper investigates the recurrent frequency-size behavior for several problems. First, the sequences of creep events on a creeping section of the San Andreas fault are investigated. The applicability of the Brownian passage-time, lognormal, and Weibull distributions to the recurrent frequency-size statistics of slip events is tested and the Weibull distribution is found to be the best-fit distribution. To verify this result the behaviors of numerical slider-block and sand-pile models are investigated and the Weibull distribution is confirmed as the applicable distribution for these models as well. Exponents β of the best-fit Weibull distributions for the observed creep event sequences and for the slider-block model are found to have similar values ranging from 1.6 to 2.2 with the corresponding aperiodicities CV of the applied distribution ranging from 0.47 to 0.64. We also note similarities between recurrent time-interval statistics and recurrent frequency-size statistics.

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

    Science.gov (United States)

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

    2016-12-01

    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.

  20. Modelling and validation of particle size distributions of supported nanoparticles using the pair distribution function technique

    Energy Technology Data Exchange (ETDEWEB)

    Gamez-Mendoza, Liliana; Terban, Maxwell W.; Billinge, Simon J. L.; Martinez-Inesta, Maria

    2017-04-13

    The particle size of supported catalysts is a key characteristic for determining structure–property relationships. It is a challenge to obtain this information accurately andin situusing crystallographic methods owing to the small size of such particles (<5 nm) and the fact that they are supported. In this work, the pair distribution function (PDF) technique was used to obtain the particle size distribution of supported Pt catalysts as they grow under typical synthesis conditions. The PDF of Pt nanoparticles grown on zeolite X was isolated and refined using two models: a monodisperse spherical model (single particle size) and a lognormal size distribution. The results were compared and validated using scanning transmission electron microscopy (STEM) results. Both models describe the same trends in average particle size with temperature, but the results of the number-weighted lognormal size distributions can also accurately describe the mean size and the width of the size distributions obtained from STEM. Since the PDF yields crystallite sizes, these results suggest that the grown Pt nanoparticles are monocrystalline. This work shows that refinement of the PDF of small supported monocrystalline nanoparticles can yield accurate mean particle sizes and distributions.

  1. Voids' System in the Woven Composite Structure

    Institute of Scientific and Technical Information of China (English)

    Pavla VOZKOVA

    2006-01-01

    Composites are common material constructions for high-tech use now. Mechanical properties of woven reinforced composites are influenced by voids inside the structure.Voids could be classified to the two sections. Long and thin cracks are more dangerous than pores. It is important to find relations between preparation and place of occurrence of voids. This paper classifies defects according to rise mechanism, point of occurrence, orientation, size and affect to the properties. Image analysis was used for observing samples. Future work would be oriented not only to observing real samples, but also to calculate mechanical properties from real and ideal structures in 3D woven reinforced composites.

  2. Size Dependency of Income Distribution and Its Implications

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jiang; WANG You-Gui

    2011-01-01

    We systematically study the size dependency of income distributions, i.e. income distribution versus the population of a country. Using the generalized Lotka--Uolterra model to fit the empirical income data for 1996-2007 in the U.S.A,we find an important parameter A that can scale with a βpower of the size(population) of the U.S.A.in that year. We point out that the size dependency of income distributions, which is a very important property but seldom addressed in previous studies, has two non-trivial implications:(1) the allometric growth pattern,i.e. the power-law relationship between population and GDP in different years, can be mathematically derived from the size-dependent income distributions and also supported by the empirical data;(2)the connection with the anomalous scaling for the probability density function in critical phenomena, since the re-scaled form of the income distributions has asymptotically exactly the same mathematical expression for the limit distribution of the sum of many correlated random variables.

  3. Lognormal Behavior of the Size Distributions of Animation Characters

    Science.gov (United States)

    Yamamoto, Ken

    This study investigates the statistical property of the character sizes of animation, superhero series, and video game. By using online databases of Pokémon (video game) and Power Rangers (superhero series), the height and weight distributions are constructed, and we find that the weight distributions of Pokémon and Zords (robots in Power Rangers) follow the lognormal distribution in common. For the theoretical mechanism of this lognormal behavior, the combination of the normal distribution and the Weber-Fechner law is proposed.

  4. Particle size distribution in ferrofluid macro-clusters

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Wah-Keat, E-mail: wklee@bnl.gov [X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, 9700S. Cass Avenue, Argonne, IL 60439 (United States); Ilavsky, Jan [X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, 9700S. Cass Avenue, Argonne, IL 60439 (United States)

    2013-03-15

    Under an applied magnetic field, many commercial and concentrated ferrofluids agglomerate and form large micron-sized structures. Although large diameter particles have been implicated in the formation of these macro-clusters, the question of whether the particle size distribution of the macro-clusters are the same as the original fluid remains open. Some studies suggest that these macro-clusters consist of larger particles, while others have shown that there is no difference in the particle size distribution between the macro-clusters and the original fluid. In this study, we use X-ray imaging to aid in a sample (diluted EFH-1 from Ferrotec) separation process and conclusively show that the average particle size in the macro-clusters is significantly larger than those in the original sample. The average particle size in the macro-clusters is 19.6 nm while the average particle size of the original fluid is 11.6 nm. - Highlights: Black-Right-Pointing-Pointer X-ray imaging was used to isolate ferrofluid macro-clusters under an applied field. Black-Right-Pointing-Pointer Small angle X-ray scattering was used to determine particle size distributions. Black-Right-Pointing-Pointer Results show that macro-clusters consist of particles that are larger than average.

  5. Formation and size distribution of self-assembled vesicles

    Science.gov (United States)

    Huang, Changjin; Quinn, David; Suresh, Subra

    2017-01-01

    When detergents and phospholipid membranes are dispersed in aqueous solutions, they tend to self-assemble into vesicles of various shapes and sizes by virtue of their hydrophobic and hydrophilic segments. A clearer understanding of such vesiculation processes holds promise for better elucidation of human physiology and disease, and paves the way to improved diagnostics, drug development, and drug delivery. Here we present a detailed analysis of the energetics and thermodynamics of vesiculation by recourse to nonlinear elasticity, taking into account large deformation that may arise during the vesiculation process. The effects of membrane size, spontaneous curvature, and membrane stiffness on vesiculation and vesicle size distribution were investigated, and the critical size for vesicle formation was determined and found to compare favorably with available experimental evidence. Our analysis also showed that the critical membrane size for spontaneous vesiculation was correlated with membrane thickness, and further illustrated how the combined effects of membrane thickness and physical properties influenced the size, shape, and distribution of vesicles. These findings shed light on the formation of physiological extracellular vesicles, such as exosomes. The findings also suggest pathways for manipulating the size, shape, distribution, and physical properties of synthetic vesicles, with potential applications in vesicle physiology, the pathobiology of cancer and other diseases, diagnostics using in vivo liquid biopsy, and drug delivery methods. PMID:28265065

  6. Mass size distribution of particle-bound water

    Science.gov (United States)

    Canepari, S.; Simonetti, G.; Perrino, C.

    2017-09-01

    The thermal-ramp Karl-Fisher method (tr-KF) for the determination of PM-bound water has been applied to size-segregated PM samples collected in areas subjected to different environmental conditions (protracted atmospheric stability, desert dust intrusion, urban atmosphere). This method, based on the use of a thermal ramp for the desorption of water from PM samples and the subsequent analysis by the coulometric KF technique, had been previously shown to differentiate water contributes retained with different strength and associated to different chemical components in the atmospheric aerosol. The application of the method to size-segregated samples has revealed that water showed a typical mass size distribution in each one of the three environmental situations that were taken into consideration. A very similar size distribution was shown by the chemical PM components that prevailed during each event: ammonium nitrate in the case of atmospheric stability, crustal species in the case of desert dust, road-dust components in the case of urban sites. The shape of the tr-KF curve varied according to the size of the collected particles. Considering the size ranges that better characterize the event (fine fraction for atmospheric stability, coarse fraction for dust intrusion, bi-modal distribution for urban dust), this shape is coherent with the typical tr-KF shape shown by water bound to the chemical species that predominate in the same PM size range (ammonium nitrate, crustal species, secondary/combustion species - road dust components).

  7. Molecular theory of size exclusion chromatography for wide pore size distributions.

    Science.gov (United States)

    Sepsey, Annamária; Bacskay, Ivett; Felinger, Attila

    2014-02-28

    Chromatographic processes can conveniently be modeled at a microscopic level using the molecular theory of chromatography. This molecular or microscopic theory is completely general; therefore it can be used for any chromatographic process such as adsorption, partition, ion-exchange or size exclusion chromatography. The molecular theory of chromatography allows taking into account the kinetics of the pore ingress and egress processes, the heterogeneity of the pore sizes and polymer polydispersion. In this work, we assume that the pore size in the stationary phase of chromatographic columns is governed by a wide lognormal distribution. This property is integrated into the molecular model of size exclusion chromatography and the moments of the elution profiles were calculated for several kinds of pore structure. Our results demonstrate that wide pore size distributions have strong influence on the retention properties (retention time, peak width, and peak shape) of macromolecules. The novel model allows us to estimate the real pore size distribution of commonly used HPLC stationary phases, and the effect of this distribution on the size exclusion process. Copyright © 2014 Elsevier B.V. All rights reserved.

  8. Global patterns of city size distributions and their fundamental drivers.

    Directory of Open Access Journals (Sweden)

    Ethan H Decker

    Full Text Available Urban areas and their voracious appetites are increasingly dominating the flows of energy and materials around the globe. Understanding the size distribution and dynamics of urban areas is vital if we are to manage their growth and mitigate their negative impacts on global ecosystems. For over 50 years, city size distributions have been assumed to universally follow a power function, and many theories have been put forth to explain what has become known as Zipf's law (the instance where the exponent of the power function equals unity. Most previous studies, however, only include the largest cities that comprise the tail of the distribution. Here we show that national, regional and continental city size distributions, whether based on census data or inferred from cluster areas of remotely-sensed nighttime lights, are in fact lognormally distributed through the majority of cities and only approach power functions for the largest cities in the distribution tails. To explore generating processes, we use a simple model incorporating only two basic human dynamics, migration and reproduction, that nonetheless generates distributions very similar to those found empirically. Our results suggest that macroscopic patterns of human settlements may be far more constrained by fundamental ecological principles than more fine-scale socioeconomic factors.

  9. Production, depreciation and the size distribution of firms

    Science.gov (United States)

    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.

  10. Draining the Local Void

    CERN Document Server

    Rizzi, Luca; Shaya, Edward J; Kourkchi, Ehsan; Karachentsev, Igor D

    2016-01-01

    Two galaxies that lie deep within the Local Void provide a test of the expectation that voids expand. The modest (M_B~-14) HI bearing dwarf galaxies ALFAZOAJ1952+1428 and KK246 have been imaged with Hubble Space Telescope in order to study the stellar populations and determine distances from the luminosities of stars at the tip of the red giant branch. The mixed age systems have respective distances of 8.39 Mpc and 6.95 Mpc and inferred line-of-sight peculiar velocities of -114 km/s and -66 km/s toward us and away from the void center. These motions compound on the Milky Way motion of ~230 km/s away from the void. The orbits of the two galaxies are reasonably constrained by a numerical action model encompassing an extensive region that embraces the Local Void. It is unambiguously confirmed that these two void galaxies are moving away from the void center at several hundred km/s.

  11. The mechanism and kinetics of void formation and growth in particulate filled PE composites

    Directory of Open Access Journals (Sweden)

    2007-11-01

    Full Text Available Volume strain measurements were carried out on PE/CaCO3 composites prepared with three different matrix polymers, containing various amounts of filler. The analysis of the debonding process and the various stages of void formation proved that the model developed for the prediction of the initiation of debonding is valid also for the studied PE/CaCO3 composites. Debonding stress is determined by the strength of interfacial adhesion, particle size and the stiffness of the matrix. In thermoplastic matrices usually two competitive processes take place: debonding and the plastic deformation of the polymer. The relative magnitude of the two processes strongly influences the number and size of the voids formed. Because of this competition and due to the wide particle size distribution of commercial fillers, only a certain fraction of the particles initiate the formation of voids. The number of voids formed is inversely proportional to the stiffness of the matrix polymer. In stiff matrices almost the entire amount of filler separates from the matrix under the effect of external load, while less than 30% debond in a PE which has an initial modulus of 0.4 GPa. Further decrease of matrix stiffness may lead to the complete absence of debonding and the composite would deform exclusively by shear yielding. Voids initiated by debonding grow during the further deformation of the composite. The size of the voids also depends on the modulus of the matrix. The rate of volume increase considerably exceeds the value predicted for cross-linked rubbers. At the same deformation and filler content the number of voids is smaller and their size is larger in soft matrices than in polymers with larger inherent modulus.

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

    Science.gov (United States)

    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.

  13. Practical Statistics for the Voids Between Galaxies

    Directory of Open Access Journals (Sweden)

    Zaninetti, L.

    2010-12-01

    Full Text Available The voids between galaxies are identified withthe volumes of the Poisson Voronoi tessellation.Two new survival functions for the apparent radii of voids are derived. The sectional normalized area ofthe Poisson Voronoi tessellation is modelledby the Kiang function and by the exponential function. Two new survival functions with equivalent sectional radius are therefore derived; they represent an alternative to the survival function of voids between galaxies as given by the self-similar distribution. The spatial appearance of slices of the 2dF Galaxy Redshift Survey is simulated.

  14. Theory of Nanocluster Size Distributions from Ion Beam Synthesis

    Energy Technology Data Exchange (ETDEWEB)

    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.

  15. Particle size distributions in the Eastern Mediterranean troposphere

    Science.gov (United States)

    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 population was governed mainly by coagulation and that particle formation was absent during most days.

  16. Modal character of atmospheric black carbon size distributions

    Science.gov (United States)

    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.

  17. Correction of bubble size distributions from transmission electron microscopy observations

    Energy Technology Data Exchange (ETDEWEB)

    Kirkegaard, P.; Eldrup, M.; Horsewell, A.; Skov Pedersen, J.

    1996-01-01

    Observations by transmission electron microscopy of a high density of gas bubbles in a metal matrix yield a distorted size distribution due to bubble overlap and bubble escape from the surface. A model is described that reconstructs 3-dimensional bubble size distributions from 2-dimensional projections on taking these effects into account. Mathematically, the reconstruction is an ill-posed inverse problem, which is solved by regularization technique. Extensive Monte Carlo simulations support the validity of our model. (au) 1 tab., 32 ills., 32 refs.

  18. Size distribution of Portuguese firms between 2006 and 2012

    Science.gov (United States)

    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.

  19. Void growth in metals: Atomistic calculations

    Energy Technology Data Exchange (ETDEWEB)

    Traiviratana, Sirirat [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States); Bringa, Eduardo M. [Materials Science Department, Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Benson, David J. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States); Meyers, Marc A. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States); NanoEngineering, University of California, San Diego, La Jolla, CA 92093 (United States)], E-mail: mameyers@ucsd.edu

    2008-09-15

    Molecular dynamics simulations in monocrystalline and bicrystalline copper were carried out with LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) to reveal void growth mechanisms. The specimens were subjected to tensile uniaxial strains; the results confirm that the emission of (shear) loops is the primary mechanism of void growth. It is observed that many of these shear loops develop along two slip planes (and not one, as previously thought), in a heretofore unidentified mechanism of cooperative growth. The emission of dislocations from voids is the first stage, and their reaction and interaction is the second stage. These loops, forming initially on different {l_brace}1 1 1{r_brace} planes, join at the intersection, if the Burgers vector of the dislocations is parallel to the intersection of two {l_brace}1 1 1{r_brace} planes: a <1 1 0> direction. Thus, the two dislocations cancel at the intersection and a biplanar shear loop is formed. The expansion of the loops and their cross slip leads to the severely work-hardened region surrounding a growing void. Calculations were carried out on voids with different sizes, and a size dependence of the stress threshold to emit dislocations was obtained by MD, in disagreement with the Gurson model which is scale independent. This disagreement is most marked for the nanometer sized voids. The scale dependence of the stress required to grow voids is interpreted in terms of the decreasing availability of optimally oriented shear planes and increased stress required to nucleate shear loops as the void size is reduced. The growth of voids simulated by MD is compared with the Cocks-Ashby constitutive model and significant agreement is found. The density of geometrically necessary dislocations as a function of void size is calculated based on the emission of shear loops and their outward propagation. Calculations are also carried out for a void at the interface between two grains to simulate polycrystalline

  20. The degree distribution of fixed act-size collaboration networks

    Indian Academy of Sciences (India)

    Qinggui Zhao; Xiangxing Kong; Zhenting Hou

    2009-11-01

    In this paper, we investigate a special evolving model of collaboration net-works, where the act-size is fixed. Based on the first-passage probability of Markov chain theory, this paper provides a rigorous proof for the existence of a limiting degree distribution of this model and proves that the degree distribution obeys the power-law form with the exponent adjustable between 2 and 3.

  1. Properties of Galaxies in and around Voids

    CERN Document Server

    Hopp, U

    1997-01-01

    Two surveys for intrinsically faint galaxies towards nearby voids have been conducted at the MPI für Astronomie, Heidelberg. One selected targets from a new diameter limited ($\\Phi \\ge 5''$) catalog with morphological criteria while the other used digitized objective prism Schmidt plates to select mainly HII dwarf galaxies. For some 450 galaxies, redshifts and other optical data were obtained. We studied the spatial distribution of the sample objects, their luminosity function, and their intrinsic properties. Most of the galaxies belong to already well known sheets and filaments. But we found about a dozen highly isolated galaxies in each sample (nearest neighborhood distance $\\ge 3 h_{75}^{-1} Mpc$). These tend to populate additional structures and are not distributed homogeneously throughout the voids. As our results on 'void galaxies' still suffer from small sample statistics, I also tried to combine similar existing surveys of nearby voids to get further hints on the larger structure and on the luminosit...

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  4. Aerosol mobility imaging for rapid size distribution measurements

    Science.gov (United States)

    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.

  5. Quantifying the PAH Size Distribution in H II-Regions

    Science.gov (United States)

    Allamandola, Louis

    We propose to determine the astronomical PAH size distribution for 20 compact H II-regions from the ISO H II-regions spectroscopic archive (catalog). The selected sample includes H IIregions at a range of distances, all with angular sizes captured by the ISO aperture. This is the first time that the PAH size distribution will be put on an accurate, quantitative footing and that a breakdown of the overall PAH population into different size bins is possible. Since the PAH properties that influence the astronomical environment are PAH-size dependent, this new knowledge will provide a deeper understanding of the specific, and sometimes critical, roles that PAHs play in different astronomical environments. This research will be carried out using the PAH spectra and tools that are available through the NASA Ames PAH IR Spectroscopic Database (www.astrochemistry.org/pahdb/). The ISO compact, H II-regions spectroscopic catalog contains the 2.3 196 µm spectra from some 45 H II-regions. Of these, 20 capture the PAH spectrum with high enough quality between 2.5 15 µm to carry out the proposed work. From the outset of the PAH hypothesis it has been thought that the 3.3/11.2 µm PAH band strength ratio is a qualitative proxy for PAH size and a rough measure of variations in the astronomical PAH size distribution between objects or within extended objects. However, because of the intrinsic uncertainties for most of the observational data available for these two bands, and the very limited spectroscopic data available for PAHs representative of the astronomical PAH population, only very crude estimates of the astronomical PAH size distribution have been possible up to now. The work proposed here overcomes these two limitations, allowing astronomers to quantitatively and accurately determine the astronomical PAH size distribution for the first time. The spectra and tools from the NASA Ames PAH IR Spectroscopic Database will be used to determine the astronomical PAH size

  6. Selecting series size where the generalized Pareto distribution best fits

    Science.gov (United States)

    Ben-Zvi, Arie

    2016-10-01

    Rates of arrival and magnitudes of hydrologic variables are frequently described by the Poisson and the generalized Pareto (GP) distributions. Variations of their goodness-of-fit to nested series are studied here. The variable employed is depth of rainfall events at five stations of the Israel Meteorological Service. Series sizes range from about 50 (number of years on records) to about 1000 (total number of recorded events). The goodness-of-fit is assessed by the Anderson-Darling test. Three versions of this test are applied here. These are the regular two-sided test (of which the statistic is designated here by A2), the upper one-sided test (UA2) and the adaptation to the Poisson distribution (PA2). Very good fits, with rejection significance levels higher than 0.5 for A2 and higher than 0.25 for PA2, are found for many series of different sizes. Values of the shape parameter of the GP distribution and of the predicted rainfall depths widely vary with series size. Small coefficients of variation are found, at each station, for the 100-year rainfall depths, predicted through the series with very good fit of the GP distribution. Therefore, predictions through series of very good fit appear more consistent than through other selections of series size. Variations of UA2, with series size, are found narrower than those of A2. Therefore, it is advisable to predict through the series of low UA2. Very good fits of the Poisson distribution to arrival rates are found for series with low UA2. But, a reversed relation is not found here. Thus, the model of Poissonian arrival rates and GP distribution of magnitudes suits here series with low UA2. It is recommended to predict through the series, to which the lowest UA2 is obtained.

  7. Global abundance and size distribution of streams and rivers

    NARCIS (Netherlands)

    Downing, J.A.; Cole, J.J.; Duarte, C.M.; Middelburg, J.J.; Melack, J.M.; Prairie, Y.T.; Kortelainen, P.; Striegl, R.G.; McDowell, W.H.; Tranvik, L.J.

    2012-01-01

    To better integrate lotic ecosystems into global cycles and budgets, we provide approximations of the size-distribution and areal extent of streams and rivers. One approach we used was to employ stream network theory combined with data on stream width. We also used detailed stream networks on 2 cont

  8. Comparison of aerosol size distribution in coastal and oceanic environments

    NARCIS (Netherlands)

    Kusmierczyk-Michulec, J.T.; Eijk, A.M.J. van

    2006-01-01

    The results of applying the empirical orthogonal functions (EOF) method to decomposition and approximation of aerosol size distributions are presented. A comparison was made for two aerosol data sets, representing coastal and oceanic environments. The first data set includes measurements collected a

  9. Casein Micelles: Size Distribution in Milks from Individual Cows

    NARCIS (Netherlands)

    de Kruif, C.G.; Huppertz, T.

    2012-01-01

    The size distribution and protein composition of casein micelles in the milk of Holstein-Friesian cows was determined as a function of stage and number of lactations. Protein composition did not vary significantly between the milks of different cows or as a function of lactation stage. Differences i

  10. Global abundance and size distribution of streams and rivers

    NARCIS (Netherlands)

    Downing, J.A.; Cole, J.J.; Duarte, C.M.; Middelburg, J.J.; Melack, J.M.; Prairie, Y.T.; Kortelainen, P.; Striegl, R.G.; McDowell, W.H.; Tranvik, L.J.

    2012-01-01

    To better integrate lotic ecosystems into global cycles and budgets, we provide approximations of the size-distribution and areal extent of streams and rivers. One approach we used was to employ stream network theory combined with data on stream width. We also used detailed stream networks on 2

  11. Effects of Mixtures on Liquid and Solid Fragment Size Distributions

    Science.gov (United States)

    2016-05-01

    Bath of an Immiscible Liquid, Physical Review Letters, 110, 264503, 2013 X. Li and R. S. Tankin, Droplet Size Distribution: A Derivation of a...10), 811-823, 1969 C. R. Hoggatt and R. F. Recht, Fracture Behavior of Tubular Bombs , Journal of Applied Physics, 39(3), 1856-1862, 1968

  12. Modeling of Microporosity Size Distribution in Aluminum Alloy A356

    Science.gov (United States)

    Yao, Lu; Cockcroft, Steve; Zhu, Jindong; Reilly, Carl

    2011-12-01

    Porosity is one of the most common defects to degrade the mechanical properties of aluminum alloys. Prediction of pore size, therefore, is critical to optimize the quality of castings. Moreover, to the design engineer, knowledge of the inherent pore population in a casting is essential to avoid potential fatigue failure of the component. In this work, the size distribution of the porosity was modeled based on the assumptions that the hydrogen pores are nucleated heterogeneously and that the nucleation site distribution is a Gaussian function of hydrogen supersaturation in the melt. The pore growth is simulated as a hydrogen-diffusion-controlled process, which is driven by the hydrogen concentration gradient at the pore liquid interface. Directionally solidified A356 (Al-7Si-0.3Mg) alloy castings were used to evaluate the predictive capability of the proposed model. The cast pore volume fraction and size distributions were measured using X-ray microtomography (XMT). Comparison of the experimental and simulation results showed that good agreement could be obtained in terms of both porosity fraction and size distribution. The model can effectively evaluate the effect of hydrogen content, heterogeneous pore nucleation population, cooling conditions, and degassing time on microporosity formation.

  13. Collisional processes and size distribution in spatially extended debris discs

    CERN Document Server

    Thebault, Philippe

    2007-01-01

    We present a new multi-annulus code for the study of collisionally evolving extended debris discs. We first aim to confirm results obtained for a single-annulus system, namely that the size distribution in "real" debris discs always departs from the theoretical collisional equilibrium $dN\\proptoR^{-3.5}dR$ power law, especially in the crucial size range of observable particles (<1cm), where it displays a characteristic wavy pattern. We also aim at studying how debris discs density distributions, scattered light luminosity profiles, and SEDs are affected by the coupled effect of collisions and radial mixing due to radiation pressure affected small grains. The size distribution evolution is modeled from micron-sized grains to 50km-sized bodies. The model takes into account the crucial influence of radiation pressure-affected small grains. We consider the collisional evolution of a fiducial a=120AU radius disc with an initial surface density in $\\Sigma(a)\\propto a^{\\alpha}$. We show that the system's radial e...

  14. The Detection and Measurement of the Activity Size Distributions

    Science.gov (United States)

    Ramamurthi, Mukund

    The infiltration of radon into the indoor environment may cause the exposure of the public to excessive amounts of radioactivity and has spurred renewed research interest over the past several years into the occurrence and properties of radon and its decay products in indoor air. The public health risks posed by the inhalation and subsequent lung deposition of the decay products of Rn-222 have particularly warranted the study of their diffusivity and attachment to molecular cluster aerosols in the ultrafine particle size range (0.5-5 nm) and to accumulation mode aerosols. In this research, a system for the detection and measurement of the activity size distributions and concentration levels of radon decay products in indoor environments has been developed. The system is microcomputer-controlled and involves a combination of multiple wire screen sampler -detector units operated in parallel. The detection of the radioactivity attached to the aerosol sampled in these units permits the determination of the radon daughter activity -weighted size distributions and concentration levels in indoor air on a semi-continuous basis. The development of the system involved the design of the detection and measurement system, its experimental characterization and testing in a radon-aerosol chamber, and numerical studies for the optimization of the design and operating parameters of the system. Several concepts of utility to aerosol size distribution measurement methods sampling the ultrafine cluster size range evolved from this study, and are discussed in various chapters of this dissertation. The optimized multiple wire screen (Graded Screen Array) system described in this dissertation is based on these concepts. The principal facet of the system is its ability to make unattended measurements of activity size distributions and concentration levels of radon decay products on a semi-continuous basis. Thus, the capability of monitoring changes in the activity concentrations and size

  15. Remnant lipoprotein size distribution profiling via dynamic light scattering analysis.

    Science.gov (United States)

    Chandra, Richa; Mellis, Birgit; Garza, Kyana; Hameed, Samee A; Jurica, James M; Hernandez, Ana V; Nguyen, Mia N; Mittal, Chandra K

    2016-11-01

    Remnant lipoproteins (RLP) are a metabolically derived subpopulation of triglyceride-rich lipoproteins (TRL) in human blood that are involved in the metabolism of dietary fats or triglycerides. RLP, the smaller and denser variants of TRL particles, are strongly correlated with cardiovascular disease (CVD) and were listed as an emerging atherogenic risk factor by the AHA in 2001. Varying analytical techniques used in clinical studies in the size determination of RLP contribute to conflicting hypotheses in regard to whether larger or smaller RLP particles contribute to CVD progression, though multiple pathways may exist. We demonstrated a unique combinatorial bioanalytical approach involving the preparative immunoseparation of RLP, and dynamic light scattering for size distribution analysis. This is a new facile and robust methodology for the size distribution analysis of RLP that in conjunction with clinical studies may reveal the mechanisms by which RLP cause CVD progression. Copyright © 2016 Elsevier B.V. All rights reserved.

  16. Size distribution and structure of Barchan dune fields

    Directory of Open Access Journals (Sweden)

    O. Durán

    2011-07-01

    Full Text Available Barchans are isolated mobile dunes often organized in large dune fields. Dune fields seem to present a characteristic dune size and spacing, which suggests a cooperative behavior based on dune interaction. In Duran et al. (2009, we propose that the redistribution of sand by collisions between dunes is a key element for the stability and size selection of barchan dune fields. This approach was based on a mean-field model ignoring the spatial distribution of dune fields. Here, we present a simplified dune field model that includes the spatial evolution of individual dunes as well as their interaction through sand exchange and binary collisions. As a result, the dune field evolves towards a steady state that depends on the boundary conditions. Comparing our results with measurements of Moroccan dune fields, we find that the simulated fields have the same dune size distribution as in real fields but fail to reproduce their homogeneity along the wind direction.

  17. Casein micelles: size distribution in milks from individual cows.

    Science.gov (United States)

    de Kruif, C G Kees; Huppertz, Thom

    2012-05-09

    The size distribution and protein composition of casein micelles in the milk of Holstein-Friesian cows was determined as a function of stage and number of lactations. Protein composition did not vary significantly between the milks of different cows or as a function of lactation stage. Differences in the size and polydispersity of the casein micelles were observed between the milks of different cows, but not as a function of stage of milking or stage of lactation and not even over successive lactations periods. Modal radii varied from 55 to 70 nm, whereas hydrodynamic radii at a scattering angle of 73° (Q² = 350 μm⁻²) varied from 77 to 115 nm and polydispersity varied from 0.27 to 0.41, in a log-normal distribution. Casein micelle size in the milks of individual cows was not correlated with age, milk production, or lactation stage of the cows or fat or protein content of the milk.

  18. Size distribution and structure of Barchan dune fields

    DEFF Research Database (Denmark)

    Duran, O.; Schwämmle, Veit; Lind, P. G.;

    2011-01-01

    Barchans are isolated mobile dunes often organized in large dune fields. Dune fields seem to present a characteristic dune size and spacing, which suggests a co-operative behavior based on dune interaction. In Duran et al. (2009), we propose that the redistribution of sand by collisions between...... dunes is a key element for the stability and size selection of barchan dune fields. This approach was based on a mean-field model ignoring the spatial distribution of dune fields. Here, we present a simplified dune field model that includes the spatial evolution of individual dunes as well...... as their interaction through sand exchange and binary collisions. As a result, the dune field evolves towards a steady state that depends on the boundary conditions. Comparing our results with measurements of Moroccan dune fields, we find that the simulated fields have the same dune size distribution as in real fields...

  19. Thoron progeny size distribution in monazite storage facility.

    Science.gov (United States)

    Rogozina, Marina; Zhukovsky, Michael; Ekidin, Aleksey; Vasyanovich, Maksim

    2014-11-01

    Field experiments in the atmosphere of monazite warehouses with a high content of (220)Rn progeny concentration were conducted. Size distribution of aerosol particles was measured with the combined use of diffusion battery with varied capture elements and cascade impactor. Four (212)Pb aerosol modes were detected-three in the ultrafine region (aerosol median thermodynamic diameters ∼0.3, 1 and 5 nm) and one with an aerosol median aerodynamic diameter of 500 nm. The activity fraction of aerosol particles with the size <10 nm is nearly 20-25 %. The dose conversion factor for EEC₂₂₀Rn exposure, obtained on the basis of the aerosol size distribution and existing research data on lung absorption types of (212)Pb aerosols, is close to 180 nSv per Bq h m(-3).

  20. Thresholded Power Law Size Distributions of Instabilities in Astrophysics

    CERN Document Server

    Aschwanden, Markus J

    2015-01-01

    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 $x_0$; (3) contamination by an event-unrelated background $x_b$; and (4) truncation effects at the largest events due to a finite system size. These effects can be modeled in 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 $x_0 > 0$ is positive for a threshold effect, while $x_0 < 0$ 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 $x_0$. We app...

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  3. A study of process induced voids in resistance welding of thermoplastic composites

    NARCIS (Netherlands)

    Shi, H.; Fernandez Villegas, I.; Bersee, H.E.N.

    2015-01-01

    Void formation in resistance welding of woven fabric reinforced thermoplastic composites was investigated. Void contents were measured using optical microscopy and digital image process. Un-even void distributions were observed in the joints, and more voids were found in the middle of the joints tha

  4. Particle size distributions in the Eastern Mediterranean troposphere

    Directory of Open Access Journals (Sweden)

    N. Kalivitis

    2008-04-01

    Full Text Available 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.

  5. Particle size distributions in the Eastern Mediterranean troposphere

    Directory of Open Access Journals (Sweden)

    N. Kalivitis

    2008-11-01

    Full Text Available 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.

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

    Science.gov (United States)

    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.

  7. MOLECULAR THERMODYNAMICS OF MICELLIZATION: MICELLE SIZE DISTRIBUTIONS AND GEOMETRY TRANSITIONS

    Directory of Open Access Journals (Sweden)

    M. S. Santos

    Full Text Available Abstract Surfactants are amphiphilic molecules that can spontaneously self-assemble in solution, forming structures known as micelles. Variations in temperature, pH, and electrolyte concentration imply changes in the interactions between surfactants and micelle stability conditions, including micelle size distribution and micelle shape. Here, molecular thermodynamics is used to describe and predict conditions of micelle formation in surfactant solutions by directly calculating the minimum Gibbs free energy of the system, corresponding to the most stable condition of the surfactant solution. In order to find it, the proposed methodology takes into account the micelle size distribution and two possible geometries (spherical and spherocylindrical. We propose a numerical optimization methodology where the minimum free energy can be reached faster and in a more reliable way. The proposed models predict the critical micelle concentration well when compared to experimental data, and also predict the effect of salt on micelle geometry transitions.

  8. Size distribution of FeNiB nanoparticles

    Directory of Open Access Journals (Sweden)

    Lackner P.

    2014-07-01

    Full Text Available Two samples of amorphous nanoparticles FeNiB, one of them with SiO2 sheath around the core and one without, were investigated by transmission electron microscopy and magnetic measurements. The coating gives mean particle diameters of 4.3 nm compared to 7.2 nm for the uncoated particles. Magnetic measurements prove superparamagnetic behaviour above 160 K (350 K for the coated (uncoated sample. With use of effective anisotropy constant Keff – determined from hysteresis loops – size distributions are determined both from ZFC curves, as well as from relaxation measurements. Both are in good agreement and are very similar for both samples. Comparison with the size distribution determined from TEM pictures shows that magnetic clusters consist of only few physical particles.

  9. Energy conservation potential of Portland Cement particle size distribution control

    Energy Technology Data Exchange (ETDEWEB)

    Tresouthick, S.W.

    1985-01-01

    The main objective of Phase 3 is to develop practical economic methods of controlling the particle size distribution of portland cements using existing or modified mill circuits with the principal aim of reducing electrical energy requirements for cement manufacturing. The work of Phase 3, because of its scope, will be carried out in 10 main tasks, some of which will be handled simultaneously. Progress on each of these tasks is discussed in this paper.

  10. Power law olivine crystal size distributions in lithospheric mantle xenoliths

    Science.gov (United States)

    Armienti, P.; Tarquini, S.

    2002-12-01

    Olivine crystal size distributions (CSDs) have been measured in three suites of spinel- and garnet-bearing harzburgites and lherzolites found as xenoliths in alkaline basalts from Canary Islands, Africa; Victoria Land, Antarctica; and Pali Aike, South America. The xenoliths derive from lithospheric mantle, from depths ranging from 80 to 20 km. Their textures vary from coarse to porphyroclastic and mosaic-porphyroclastic up to cataclastic. Data have been collected by processing digital images acquired optically from standard petrographic thin sections. The acquisition method is based on a high-resolution colour scanner that allows image capturing of a whole thin section. Image processing was performed using the VISILOG 5.2 package, resolving crystals larger than about 150 μm and applying stereological corrections based on the Schwartz-Saltykov algorithm. Taking account of truncation effects due to resolution limits and thin section size, all samples show scale invariance of crystal size distributions over almost three orders of magnitude (0.2-25 mm). Power law relations show fractal dimensions varying between 2.4 and 3.8, a range of values observed for distributions of fragment sizes in a variety of other geological contexts. A fragmentation model can reproduce the fractal dimensions around 2.6, which correspond to well-equilibrated granoblastic textures. Fractal dimensions >3 are typical of porphyroclastic and cataclastic samples. Slight bends in some linear arrays suggest selective tectonic crushing of crystals with size larger than 1 mm. The scale invariance shown by lithospheric mantle xenoliths in a variety of tectonic settings forms distant geographic regions, which indicate that this is a common characteristic of the upper mantle and should be taken into account in rheological models and evaluation of metasomatic models.

  11. Measurement of air distribution and void fraction of an upwards air-water flow using electrical resistance tomography and a wire-mesh sensor

    Science.gov (United States)

    Olerni, Claudio; Jia, Jiabin; Wang, Mi

    2013-03-01

    Measurements on an upwards air-water flow are reported that were obtained simultaneously with a dual-plane electrical resistance tomograph (ERT) and a wire-mesh sensor (WMS). The ultimate measurement target of both ERT and WMS is the same, the electrical conductivity of the medium. The ERT is a non-intrusive device whereas the WMS requires a net of wires that physically crosses the flow. This paper presents comparisons between the results obtained simultaneously from the ERT and the WMS for evaluation and calibration of the ERT. The length of the vertical testing pipeline section is 3 m with an internal diameter of 50 mm. Two distinct sets of air-water flow rate scenarios, bubble and slug regimes, were produced in the experiments. The fast impedance camera ERT recorded the data at an approximate time resolution of 896 frames per second (fps) per plane in contrast with the 1024 fps of the wire-mesh sensor WMS200. The set-up of the experiment was based on well established knowledge of air-water upwards flow, particularly the specific flow regimes and wall peak effects. The local air void fraction profiles and the overall air void fraction were produced from two systems to establish consistency for comparison of the data accuracy. Conventional bulk flow measurements in air mass and electromagnetic flow metering, as well as pressure and temperature, were employed, which brought the necessary calibration to the flow measurements. The results show that the profiles generated from the two systems have a certain level of inconsistency, particularly in a wall peak and a core peak from the ERT and WMS respectively, whereas the two tomography instruments achieve good agreement on the overall air void fraction for bubble flow. For slug flow, when the void fraction is over 30%, the ERT underestimates the void fraction, but a linear relation between ERT and WMS is still observed.

  12. An overview of aerosol particle sensors for size distribution measurement

    Directory of Open Access Journals (Sweden)

    Panich Intra

    2007-08-01

    Full Text Available Fine aerosols are generally referred to airborne particles of diameter in submicron or nanometer size range. Measurement capabilities are required to gain understanding of these particle dynamics. One of the most important physical and chemical parameters is the particle size distribution. The aim of this article is to give an overview of recent development of already existing sensors for particle size distribution measurement based on electrical mobility determination. Available instruments for particle size measurement include a scanning mobility particle sizer (SMPS, an electrical aerosol spectrometer (EAS, an engine exhaust particle sizer (EEPS, a bipolar charge aerosol classifier (BCAC, a fast aerosol spectrometer (FAS a differential mobility spectrometer (DMS, and a CMU electrical mobility spectrometer (EMS. The operating principles, as well as detailed physical characteristics of these instruments and their main components consisting of a particle charger, a mobility classifier, and a signal detector, are described. Typical measurements of aerosol from various sources by these instruments compared with an electrical low pressure impactor (ELPI are also presented.

  13. Estimation of coal particle size distribution by image segmentation

    Institute of Scientific and Technical Information of China (English)

    Zhang Zelin; Yang Jianguo; Ding Lihua; Zhao Yuemin

    2012-01-01

    Several industrial coal processes are largely determined by the distribution of particle sizes in their feed.Currently these parameters are measured by manual sampling,which is time consuming and cannot provide real time feedback for automatic control purposes.In this paper,an approach using image segmentation on images of overlapped coal particles is described.The estimation of the particle size distribution by number is also described.The particle overlap problem was solved using image enhancement algorithms that converted those image parts representing material in lower layers to black.Exponential high-pass filter (EHPF) algorithms were used to remove the texture from particles on the surface.Finally,the edges of the surface particles were identified by morphological edge detection.These algorithms are described in detail as is the method of extracting the coal particle size.Tests indicate that using more coal images gives a higher accuracy estimate.The positive absolute error of 50 random tests was consistently less than 2.5% and the errors were reduced as the size of the fraction increased.

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

    Science.gov (United States)

    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.

  15. Application of flower pollination algorithm for optimal placement and sizing of distributed generation in Distribution systems

    Directory of Open Access Journals (Sweden)

    P. Dinakara Prasad Reddy

    2016-05-01

    Full Text Available Distributed generator (DG resources are small, self contained electric generating plants that can provide power to homes, businesses or industrial facilities in distribution feeders. By optimal placement of DG we can reduce power loss and improve the voltage profile. However, the values of DGs are largely dependent on their types, sizes and locations as they were installed in distribution feeders. The main contribution of the paper is to find the optimal locations of DG units and sizes. Index vector method is used for optimal DG locations. In this paper new optimization algorithm i.e. flower pollination algorithm is proposed to determine the optimal DG size. This paper uses three different types of DG units for compensation. The proposed methods have been tested on 15-bus, 34-bus, and 69-bus radial distribution systems. MATLAB, version 8.3 software is used for simulation.

  16. Universal functional form of 1-minute raindrop size distribution?

    Science.gov (United States)

    Cugerone, Katia; De Michele, Carlo

    2015-04-01

    Rainfall remains one of the poorly quantified phenomena of the hydrological cycle, despite its fundamental role. No universal laws describing the rainfall behavior are available in literature. This is probably due to the continuous description of rainfall, which is a discrete phenomenon, made by drops. From the statistical point of view, the rainfall variability at particle size scale, is described by the drop size distribution (DSD). With this term, it is generally indicated as the concentration of raindrops per unit volume and diameter, as the probability density function of drop diameter at the ground, according to the specific problem of interest. Raindrops represent the water exchange, under liquid form, between atmosphere and earth surface, and the number of drops and their size have impacts in a wide range of hydrologic, meteorologic, and ecologic phenomena. DSD is used, for example, to measure the multiwavelength rain attenuation for terrestrial and satellite systems, it is an important input for the evaluation of the below cloud scavenging coefficient of the aerosol by precipitation, and is of primary importance to make estimates of rainfall rate through radars. In literature, many distributions have been used to this aim (Gamma and Lognormal above all), without statistical supports and with site-specific studies. Here, we present an extensive investigation of raindrop size distribution based on 18 datasets, consisting in 1-minute disdrometer data, sampled using Joss-Waldvogel or Thies instrument in different locations on Earth's surface. The aim is to understand if an universal functional form of 1-minute drop diameter variability exists. The study consists of three main steps: analysis of the high order moments, selection of the model through the AIC index and test of the model with the use of goodness-of-fit tests.

  17. Fog-Influenced Submicron Aerosol Number Size Distributions

    Science.gov (United States)

    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.

  18. Measuring Technique of Bubble Size Distributions in Dough

    Science.gov (United States)

    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.

  19. Universal scaling of grain size distributions during dislocation creep

    Science.gov (United States)

    Aupart, Claire; Dunkel, Kristina G.; Angheluta, Luiza; Austrheim, Håkon; Ildefonse, Benoît; Malthe-Sørenssen, Anders; Jamtveit, Bjørn

    2017-04-01

    Grain size distributions are major sources of information about the mechanisms involved in ductile deformation processes and are often used as paleopiezometers (stress gauges). Several factors have been claimed to influence the stress vs grain size relation, including the water content (Jung & Karato 2001), the temperature (De Bresser et al., 2001), the crystal orientation (Linckens et al., 2016), the presence of second phase particles (Doherty et al. 1997; Cross et al., 2015), and heterogeneous stress distributions (Platt & Behr 2011). However, most of the studies of paleopiezometers have been done in the laboratory under conditions different from those in natural systems. It is therefore essential to complement these studies with observations of naturally deformed rocks. We have measured olivine grain sizes in ultramafic rocks from the Leka ophiolite in Norway and from Alpine Corsica using electron backscatter diffraction (EBSD) data, and calculated the corresponding probability density functions. We compared our results with samples from other studies and localities that have formed under a wide range of stress and strain rate conditions. All distributions collapse onto one universal curve in a log-log diagram where grain sizes are normalized by the mean grain size of each sample. The curve is composed of two straight segments with distinct slopes for grains above and below the mean grain size. These observations indicate that a surprisingly simple and universal power-law scaling describes the grain size distribution in ultramafic rocks during dislocation creep irrespective of stress levels and strain rates. Cross, Andrew J., Susan Ellis, and David J. Prior. 2015. « A Phenomenological Numerical Approach for Investigating Grain Size Evolution in Ductiley Deforming Rocks ». Journal of Structural Geology 76 (juillet): 22-34. doi:10.1016/j.jsg.2015.04.001. De Bresser, J. H. P., J. H. Ter Heege, and C. J. Spiers. 2001. « Grain Size Reduction by Dynamic

  20. Effects of Voids on Concrete Tensile Fracturing: A Mesoscale Study

    Directory of Open Access Journals (Sweden)

    Lei Xu

    2017-01-01

    Full Text Available A two-dimensional mesoscale modeling framework, which considers concrete as a four-phase material including voids, is developed for studying the effects of voids on concrete tensile fracturing under the plane stress condition. Aggregate is assumed to behave elastically, while a continuum damaged plasticity model is employed to describe the mechanical behaviors of mortar and ITZ. The effects of voids on the fracture mechanism of concrete under uniaxial tension are first detailed, followed by an extensive investigation of the effects of void volume fraction on concrete tensile fracturing. It is found that both the prepeak and postpeak mesoscale cracking in concrete are highly affected by voids, and there is not a straightforward relation between void volume fraction and the postpeak behavior due to the randomness of void distribution. The fracture pattern of concrete specimen with voids is controlled by both the aggregate arrangement and the distribution of voids, and two types of failure modes are identified for concrete specimens under uniaxial tension. It is suggested that voids should be explicitly modeled for the accurate fracturing simulation of concrete on the mesoscale.

  1. Multimodal Dispersion of Nanoparticles: A Comprehensive Evaluation of Size Distribution with 9 Size Measurement Methods.

    Science.gov (United States)

    Varenne, Fanny; Makky, Ali; Gaucher-Delmas, Mireille; Violleau, Frédéric; Vauthier, Christine

    2016-05-01

    Evaluation of particle size distribution (PSD) of multimodal dispersion of nanoparticles is a difficult task due to inherent limitations of size measurement methods. The present work reports the evaluation of PSD of a dispersion of poly(isobutylcyanoacrylate) nanoparticles decorated with dextran known as multimodal and developed as nanomedecine. The nine methods used were classified as batch particle i.e. Static Light Scattering (SLS) and Dynamic Light Scattering (DLS), single particle i.e. Electron Microscopy (EM), Atomic Force Microscopy (AFM), Tunable Resistive Pulse Sensing (TRPS) and Nanoparticle Tracking Analysis (NTA) and separative particle i.e. Asymmetrical Flow Field-Flow Fractionation coupled with DLS (AsFlFFF) size measurement methods. The multimodal dispersion was identified using AFM, TRPS and NTA and results were consistent with those provided with the method based on a separation step prior to on-line size measurements. None of the light scattering batch methods could reveal the complexity of the PSD of the dispersion. Difference between PSD obtained from all size measurement methods tested suggested that study of the PSD of multimodal dispersion required to analyze samples by at least one of the single size particle measurement method or a method that uses a separation step prior PSD measurement.

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

    Science.gov (United States)

    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

  3. Building predictive models of soil particle-size distribution

    Directory of Open Access Journals (Sweden)

    Alessandro Samuel-Rosa

    2013-04-01

    Full Text Available Is it possible to build predictive models (PMs of soil particle-size distribution (psd in a region with complex geology and a young and unstable land-surface? The main objective of this study was to answer this question. A set of 339 soil samples from a small slope catchment in Southern Brazil was used to build PMs of psd in the surface soil layer. Multiple linear regression models were constructed using terrain attributes (elevation, slope, catchment area, convergence index, and topographic wetness index. The PMs explained more than half of the data variance. This performance is similar to (or even better than that of the conventional soil mapping approach. For some size fractions, the PM performance can reach 70 %. Largest uncertainties were observed in geologically more complex areas. Therefore, significant improvements in the predictions can only be achieved if accurate geological data is made available. Meanwhile, PMs built on terrain attributes are efficient in predicting the particle-size distribution (psd of soils in regions of complex geology.

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

    Science.gov (United States)

    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.

  5. Grain size effects on He bubbles distribution and evolution

    Energy Technology Data Exchange (ETDEWEB)

    Wang, J. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); School of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China); Gao, X.; Gao, N. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Wang, Z.G., E-mail: zhgwang@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Cui, M.H.; Wei, K.F.; Yao, C.F.; Sun, J.R.; Li, B.S.; Zhu, Y.B.; Pang, L.L. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Li, Y.F. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); School of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China); Wang, D. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Xie, E.Q. [School of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China)

    2015-02-15

    Highlights: • SMAT treated T91 and conventional T91 were implanted by 200 keV He{sup 2+} to 1 × 10{sup 21} He m{sup −2} at room temperature and annealed at 450 °C for 3.5 h. • He bubbles in nanometer-size-grained T91 are smaller in as-implanted case. • The bubbles in the matrix of nanograins were hard to detect and those along the nanograin boundaries coalesced and filled with the grain boundaries after annealing. • Brownian motion and coalescence and Ostwald ripening process might lead to bubbles morphology presented in the nanometer-size-grained T91 after annealing. - Abstract: Grain boundary and grain size effects on He bubble distribution and evolution were investigated by He implantation into nanometer-size-grained T91 obtained by Surface Mechanical Attrition Treatment (SMAT) and the conventional coarse-grained T91. It was found that bubbles in the nanometer-size-grained T91 were smaller than those in the conventional coarse-grained T91 in as-implanted case, and bubbles in the matrix of nanograins were undetectable while those at nanograin boundaries (GBs) coalesced and filled in GBs after heat treatment. These results suggested that the grain size of structural material should be larger than the mean free path of bubble’s Brownian motion and/or denuded zone around GBs in order to prevent bubbles accumulation at GBs, and multiple instead of one type of defects should be introduced into structural materials to effectively reduce the susceptibility of materials to He embrittlement and improve the irradiation tolerance of structural materials.

  6. Method for measuring the size distribution of airborne rhinovirus

    Energy Technology Data Exchange (ETDEWEB)

    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. Size distribution of wet crushed waste printed circuit boards

    Institute of Scientific and Technical Information of China (English)

    Tan Zhihai; He Yaqun; Xie Weining; Duan Chenlong; Zhou Enhui; Yu Zheng

    2011-01-01

    A wet impact crusher was used to breakdown waste printed circuit boards (PCB's) in a water medium.The relationship between the yield of crushed product and the operating parameters was established.The crushing mechanism was analyzed and the effects of hammerhead style,rotation speed,and inlet water volume on particle size distribution were investigated.The results show that the highest yield of -1 + 0.75 mm sized product was obtained with an inlet water volume flow rate of 5.97 m3/h and a smooth hammerhead turning at 1246.15 r/min.Cumulative undersize-product yield curves were fitted to a nonlinear function:the fitting correlation coefficient was greater than 0.998.These research results provide a theoretical basis for the highly effective wet crushing of PCB's.

  8. Dust generation in powders: Effect of particle size distribution

    Directory of Open Access Journals (Sweden)

    Chakravarty Somik

    2017-01-01

    Full Text Available This study explores the relationship between the bulk and grain-scale properties of powders and dust generation. A vortex shaker dustiness tester was used to evaluate 8 calcium carbonate test powders with median particle sizes ranging from 2μm to 136μm. Respirable aerosols released from the powder samples were characterised by their particle number and mass concentrations. All the powder samples were found to release respirable fractions of dust particles which end up decreasing with time. The variation of powder dustiness as a function of the particle size distribution was analysed for the powders, which were classified into three groups based on the fraction of particles within the respirable range. The trends we observe might be due to the interplay of several mechanisms like de-agglomeration and attrition and their relative importance.

  9. Cosmic Voids and Void Lensing in the Dark Energy Survey Science Verification Data

    CERN Document Server

    Sánchez, C; Kovacs, A; Jain, B; García-Bellido, J; Nadathur, S; Gruen, D; Hamaus, N; Huterer, D; Vielzeuf, P; Amara, A; Bonnett, C; DeRose, J; Hartley, W G; Jarvis, M; Lahav, O; Miquel, R; Rozo, E; Rykoff, E S; Sheldon, E; Wechsler, R H; Zuntz, J; Abbott, T M C; Abdalla, F B; Annis, J; Benoit-Lévy, A; Bernstein, G M; Bernstein, R A; Bertin, E; Brooks, D; Buckley-Geer, E; Rosell, A Carnero; Kind, M Carrasco; Carretero, J; Crocce, M; Cunha, C E; D'Andrea, C B; da Costa, L N; Desai, S; Diehl, H T; Dietrich, J P; Doel, P; Evrard, A E; Neto, A Fausti; Flaugher, B; Fosalba, P; Frieman, J; Gaztanaga, E; Gruendl, R A; Gutierrez, G; Honscheid, K; James, D J; Krause, E; Kuehn, K; Lima, M; Maia, M A G; Marshall, J L; Melchior, P; Plazas, A A; Reil, K; Romer, A K; Sanchez, E; Schubnell, M; Sevilla-Noarbe, I; Smith, R C; Soares-Santos, M; Sobreira, F; Suchyta, E; Tarle, G; Thomas, D; Walker, A R; Weller, J

    2016-01-01

    Galaxies and their dark matter halos populate a complicated filamentary network around large, nearly empty regions known as cosmic voids. Cosmic voids are usually identified in spectroscopic galaxy surveys, where 3D information about the large-scale structure of the Universe is available. Although an increasing amount of photometric data is being produced, its potential for void studies is limited since photometric redshifts induce line-of-sight position errors of $\\sim50$ Mpc/$h$ or more that can render many voids undetectable. In this paper we present a new void finder designed for photometric surveys, validate it using simulations, and apply it to the high-quality photo-$z$ redMaGiC galaxy sample of the Dark Energy Survey Science Verification (DES-SV) data. The algorithm works by projecting galaxies into 2D slices and finding voids in the smoothed 2D galaxy density field of the slice. Fixing the line-of-sight size of the slices to be at least twice the photo-$z$ scatter, the number of voids found in these ...

  10. Measurement of non-volatile particle number size distribution

    Science.gov (United States)

    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

  11. Simulation study of territory size distributions in subterranean termites.

    Science.gov (United States)

    Jeon, Wonju; Lee, Sang-Hee

    2011-06-21

    In this study, on the basis of empirical data, we have simulated the foraging tunnel patterns of two subterranean termites, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar), using a two-dimensional model. We have defined a territory as a convex polygon containing a tunnel pattern and explored the effects of competition among termite territory colonies on the territory size distribution in the steady state that was attained after a sufficient simulation time. In the model, territorial competition was characterized by a blocking probability P(block) that quantitatively describes the ease with which a tunnel stops its advancement when it meets another tunnel; higher P(block) values imply easier termination. In the beginning of the simulation run, N=10, 20,…,100 territory seeds, representing the founding pair, were randomly distributed on a square area. When the territory density was less (N=20), the differences in the territory size distributions for different P(block) values were small because the territories had sufficient space to grow without strong competitions. Further, when the territory density was higher (N>20), the territory sizes increased in accordance with the combinational effect of P(block) and N. In order to understand these effects better, we introduced an interference coefficient γ. We mathematically derived γ as a function of P(block) and N: γ(N,P(block))=a(N)P(block)/(P(block)+b(N)). a(N) and b(N) are functions of N/(N+c) and d/(N+c), respectively, and c and d are constants characterizing territorial competition. The γ function is applicable to characterize the territoriality of various species and increases with both the P(block) values and N; higher γ values imply higher limitations of the network growth. We used the γ function, fitted the simulation results, and determined the c and d values. In addition, we have briefly discussed the predictability of the present model by comparing it with our previous lattice model

  12. Simulation of soot size distribution in an ethylene counterflow flame

    KAUST Repository

    Zhou, Kun

    2014-01-06

    Soot, an aggregate of carbonaceous particles produced during the rich combustion of fossil fuels, is an undesirable pollutant and health hazard. Soot evolution involves various dynamic processes: nucleation soot formation from polycyclic aromatic hydrocarbons (PAHs) condensation PAHs condensing on soot particle surface surface processes hydrogen-abstraction-C2H2-addition, oxidation coagulation two soot particles coagulating to form a bigger particle This simulation work investigates soot size distribution and morphology in an ethylene counterflow flame, using i). Chemkin with a method of moments to deal with the coupling between vapor consumption and soot formation; ii). Monte Carlo simulation of soot dynamics.

  13. A Maximum Entropy Modelling of the Rain Drop Size Distribution

    Directory of Open Access Journals (Sweden)

    Francisco J. Tapiador

    2011-01-01

    Full Text Available This paper presents a maximum entropy approach to Rain Drop Size Distribution (RDSD modelling. It is shown that this approach allows (1 to use a physically consistent rationale to select a particular probability density function (pdf (2 to provide an alternative method for parameter estimation based on expectations of the population instead of sample moments and (3 to develop a progressive method of modelling by updating the pdf as new empirical information becomes available. The method is illustrated with both synthetic and real RDSD data, the latest coming from a laser disdrometer network specifically designed to measure the spatial variability of the RDSD.

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

    Science.gov (United States)

    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

  15. Mass size distributions of elemental aerosols in industrial area

    Directory of Open Access Journals (Sweden)

    Mona Moustafa

    2015-11-01

    Full Text Available 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.

  16. Empirical Reference Distributions for Networks of Different Size

    CERN Document Server

    Smith, Anna; Browning, Christopher R

    2015-01-01

    Network analysis has become an increasingly prevalent research tool across a vast range of scientific fields. Here, we focus on the particular issue of comparing network statistics, i.e. graph-level measures of network structural features, across multiple networks that differ in size. Although "normalized" versions of some network statistics exist, we demonstrate via simulation why direct comparison of raw and normalized statistics is often inappropriate. We examine a recent suggestion to normalize network statistics relative to Erdos-Renyi random graphs and demonstrate via simulation how this is an improvement over direct comparison, but still sometimes problematic. We propose a new adjustment method based on a reference distribution constructed as a mixture model of random graphs which reflect the dependence structure exhibited in the observed networks. We show that using simple Bernoulli models as mixture components in this reference distribution can provide adjusted network statistics that are relatively ...

  17. Void shape effects and voids starting from cracked inclusion

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2011-01-01

    Numerical, axisymmetric cell model analyses are used to study the growth of voids in ductile metals, until the mechanism of coalescence with neighbouring voids sets in. A special feature of the present analyses is that extremely small values of the initial void volume fraction are considered, dow...

  18. Evolution of Pore Size Distribution and Mean Pore Size in Lotus-type Porous Magnesium Fabricated with Gasar Process

    Institute of Scientific and Technical Information of China (English)

    Yuan LIU; Yanxiang LI; Huawei ZHANG; Jiang WAN

    2006-01-01

    The effect of gas pressures on the mean pore size, the porosity and the pore size distribution of lotus-type porous magnesium fabricated with Gasar process were investigated. The theoretical analysis and the experimental results all indicate that there exists an optimal ratio of the partial pressures of hydrogen pH2 to argon pAr for producing lotus-type structures with narrower pore size distribution and smaller pore size. The effect of solidification mode on the pore size distribution and pore size was also discussed.

  19. Voids in Ly{\\alpha} Forest Tomographic Maps

    CERN Document Server

    Stark, Casey W; White, Martin; Lee, Khee-Gan

    2015-01-01

    We present a new method of finding cosmic voids using tomographic maps of Ly{\\alpha} forest flux. We identify cosmological voids with radii of 2 - 12 $h^{-1}$Mpc in a large N-body simulation at $z = 2.5$, and characterize the signal of the high-redshift voids in density and Ly{\\alpha} forest flux. The void properties are similar to what has been found at lower redshifts, but they are smaller and have steeper radial density profiles. Similarly to what has been found for low-redshift voids, the radial velocity profiles have little scatter and agree very well with the linear theory prediction. We run the same void finder on an ideal Ly{\\alpha} flux field and tomographic reconstructions at various spatial samplings. We compare the tomographic map void catalogs to the density void catalog and find good agreement even with modest-sized voids ($r > 6 \\, h^{-1}$Mpc). Using our simple void-finding method, the configuration of the ongoing CLAMATO survey covering 1 deg$^2$ would provide a sample of about 100 high-redshi...

  20. Optimal placement and sizing of multiple distributed generating units in distribution

    Directory of Open Access Journals (Sweden)

    D. Rama Prabha

    2016-06-01

    Full Text Available Distributed generation (DG is becoming more important due to the increase in the demands for electrical energy. DG plays a vital role in reducing real power losses, operating cost and enhancing the voltage stability which is the objective function in this problem. This paper proposes a multi-objective technique for optimally determining the location and sizing of multiple distributed generation (DG units in the distribution network with different load models. The loss sensitivity factor (LSF determines the optimal placement of DGs. Invasive weed optimization (IWO is a population based meta-heuristic algorithm based on the behavior of weeds. This algorithm is used to find optimal sizing of the DGs. The proposed method has been tested for different load models on IEEE-33 bus and 69 bus radial distribution systems. This method has been compared with other nature inspired optimization methods. The simulated results illustrate the good applicability and performance of the proposed method.

  1. Vertical Raindrop Size Distribution in Central Spain: A Case Study

    Directory of Open Access Journals (Sweden)

    Roberto Fraile

    2015-01-01

    Full Text Available A precipitation event that took place on 12 October 2008 in Madrid, Spain, is analyzed in detail. Three different devices were used to characterize the precipitation: a disdrometer, a rain gauge, and a Micro Rain Radar (MRR. These instruments determine precipitation intensity indirectly, based on measuring different parameters in different sampling points in the atmosphere. A comparative study was carried out based on the data provided by each of these devices, revealing that the disdrometer and the rain gauge measure similar precipitation intensity values, whereas the MRR measures different rain fall volumes. The distributions of drop sizes show that the mean diameter of the particles varied considerably depending on the altitude considered. The level at which saturation occurs in the atmosphere is decisive in the distribution of drop sizes between 2,700 m and 3,000 m. As time passes, the maximum precipitation intensities are registered at a lower height and are less intense. The maximum precipitation intensities occurred at altitudes above 1,000 m, while the maximum fall speeds are typically found at altitudes below 700 m.

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

    CERN Document Server

    Terai, Tsuyoshi

    2010-01-01

    We investigated the size distribution of high-inclination main-belt asteroids (MBAs) to explore asteroid collisional evolution under hypervelocity collisions of around 10 km/s. 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 deg^2 with a limiting magnitude of 24.0 mag in the SDSS r filter. Most of 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 deg) 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 inclinatio...

  3. Ductile damage of porous materials with two populations of voids

    Science.gov (United States)

    Vincent, Pierre-Guy; Monerie, Yann; Suquet, Pierre

    2008-01-01

    This study is devoted to the modelling of ductile damage in uranium dioxide. This polycrystalline material contains two populations of voids of well separated size. The problem addressed here is the prediction of the effective flow surface of a Gurson material containing randomly oriented oblate voids. The case of spherical voids is considered first and the variational approach of Gurson is generalized by adding a compressible component to his original velocity field. The case of aligned oblate voids is then considered and a suitable generalization of a velocity field due to Gologanu et al. (ASME J. Engrg. Mater. Technol. 116 (1994) 290-297) is proposed. The extension to randomly oriented voids is achieved by averaging over all orientations. In each case, rigorous upper bounds and approximate estimates are derived and compared (in the case of spherical voids) with Finite Element simulations. To cite this article: P.-G. Vincent et al., C. R. Mecanique 336 (2008).

  4. The sparkling Universe: the coherent motions of cosmic voids

    CERN Document Server

    Lambas, Diego G; Ceccarelli, Laura; Ruiz, Andrés N; Paz, Dante J; Maldonado, Victoria E; Luparello, Heliana E

    2015-01-01

    We compute the bulk motions of cosmic voids, using a $\\Lambda$CDM numerical simulation considering the mean velocities of the dark matter inside the void itself and that of the haloes in the surrounding shell. We find coincident values of these two measures in the range $\\sim$ 300-400 km/s, not far from the expected mean peculiar velocities of groups and galaxy clusters. When analysing the distribution of the pairwise relative velocities of voids, we find a remarkable bimodal behaviour consistent with an excess of both systematically approaching and receding voids. We determine that the origin of this bimodality resides in the void large scale environment, since once voids are classified into void-in-void (R-type) or void-in-cloud (S-type), R-types are found mutually receding away, while S-types approach each other. The magnitude of these systematic relative velocities account for more than 100 km/s, reaching large coherence lengths of up to 200 h$^{-1}$ Mpc . We have used samples of voids from the Sloan Digi...

  5. Failure by void coalescence in metallic materials containing primary and secondary voids subject to intense shearing

    DEFF Research Database (Denmark)

    Nielsen, Kim Lau; Tvergaard, Viggo

    2011-01-01

    , subject to shear dominated loading. To account for both length scales involved in this study, a continuum model that includes the softening effect of damage evolution in shear is used to represent the matrix material surrounding the primary voids. Here, a recently extended Gurson-type model is used, which......Failure under intense shearing at close to zero stress triaxiality is widely observed for ductile metallic materials, and is identified in experiments as smeared-out dimples on the fracture surface. Numerical cell-model studies of equal sized voids have revealed that the mechanism governing...... secondary damage that co-exists with or nucleation in the ligaments between larger voids that coalesce during intense shearing. A numerical cell-model study is carried out to gain a parametric understanding of the overall material response for different initial conditions of the two void populations...

  6. Size Distribution of Chlorinated Polycyclic Aromatic Hydrocarbons in Atmospheric Particles.

    Science.gov (United States)

    Kakimoto, Kensaku; Nagayoshi, Haruna; Konishi, Yoshimasa; Kajimura, Keiji; Ohura, Takeshi; Nakano, Takeshi; Hata, Mitsuhiko; Furuuchi, Masami; Tang, Ning; Hayakawa, Kazuichi; Toriba, Akira

    2017-01-01

    The particle size distribution of chlorinated polycyclic aromatic hydrocarbons (ClPAHs) in particulate matter (PM) in Japan is examined for the first time. PM was collected using a PM0.1 air sampler with a six-stage filter. PM was collected in October 2014 and January 2015 to observe potential seasonal variation in the atmospheric behavior and size of PM, including polycyclic aromatic hydrocarbons (PAHs) and ClPAHs. We found that the concentration of PAHs and ClPAHs between 0.5-1.0 μm and 1.0-2.5 μm markedly increase in January (i.e., the winter season). Among the ClPAHs, 1-ClPyrene and 6-ClBenzo[a]Pyrene were the most commonly occurring compounds; further, approximately 15% of ClPAHs were in the nanoparticle phase (<0.1 μm). The relatively high presence of nanoparticles is a potential human health concern because these particles can easily be deposited in the lung periphery. Lastly, we evaluated the aryl hydrocarbon receptor (AhR) ligand activity of PM extracts in each size fraction. The result indicates that PM < 2.5 μm has the strong AhR ligand activity.

  7. Bble Size Distribution for Waves Propagating over A Submerged Breakwater

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Experiments are carried out to study the characteristics of active bubbles entrained by breaking waves as these propagate over an abruptly topographical change or a submerged breakwater. Underwater sounds generated by the entrained air bubbles are detected by a hydrophone connected to a charge amplifier and a data acquisition system. The size distribution of the bubbles is then determined inversely from the received sound frequencies. The sound signals are converted from time domain to time-frequency domain by applying Gabor transform. The number of bubbles with different sizes are counted from the signal peaks in the time-frequency domain. The characteristics of the bubbles are in terms of bubble size spectra, which account for the variation in bubble probability density related to the bubble radius r. The experimental data demonstrate that the bubble probability density function shows a-2.39 power-law scaling with radius for r>0.8 mm, and a-1.11 power law for r<0.8 mm.

  8. Locating voids beneath pavement using pulsed electromagnetic waves

    Science.gov (United States)

    Steinway, W. J.; Echard, J. D.; Luke, C. M.

    1981-11-01

    The feasibility of using pulsed electromagnetic wave technology for locating and sizing voids beneath reinforced and nonreinforced portland cement concrete pavements is determined. The data processing techniques developed can be implemented to provide information for void depth and sizing to + or - 1/2 in. and spatial location within + or - 6 in. A very short pulse radar directly connected to a microcomputer was chosen as the equipment necessary to obtain measurements. This equipment has the required accuracy and reliability, and is a cost effective solution for the void locating problem. The radar provides a signal return from voids that has unique characteristics that can be examined to provide information regarding the location, depth, and shape of the void. The microcomputer provides a means of real time processing to extract the information from the radar signal return and record the results. Theoretical modeling of signal returns from voids led to suitable techniques for locating and sizing voids beneath the pavement. Analysis and application of these techniques to radar measurements verified the theoretical predictions that radar can be used to determine the location, size, and shape of actual voids.

  9. Neurogenic voiding dysfunction.

    Science.gov (United States)

    Georgopoulos, Petros; Apostolidis, Apostolos

    2017-05-01

    This review aims to analyze and discuss all recently published articles associated with neurogenic voiding discussion providing readers with the most updated knowledge and trigger for further research. They include the proposal of a novel classification system for the pathophysiology of neurogenic lower urinary tract dysfunction (NLUTD) which combines neurological defect in a distinct anatomic location, and data on bowel dysfunction, autonomic dysreflexia and urine biomarkers; review of patient-reported outcome measures in NLUTD; review of the criteria for the diagnosis of clinically significant urinary infections; novel research findings on the pathophysiology of NLUTD; and review of data on minimally and more invasive treatments. Despite the extended evidence base on NLUTD, there is a paucity of high-quality new research concerning voiding dysfunction as opposed to storage problems. The update aims to inform clinicians about new developments in clinical practice, as well as ignite discussion for further clinical and basic research in the aforementioned areas of NLUTD.

  10. On de-Sitter Geometry in Cosmic Void Statistics

    CERN Document Server

    Gibbons, Gary W; Yoshida, Naoki; Chon, Sunmyon

    2013-01-01

    Starting from the geometrical concept of a 4-dimensional de-Sitter configuration of spheres in Euclidean 3-space and modelling voids in the Universe as spheres, we show that a uniform distribution over this configuration space implies a power-law for the void number density which is consistent with results from the excursion set formalism and from data, for an intermediate range of void volumes. We also discuss the effect of restricting the survey geometry on the void statistics. This work is a new application of de-Sitter geometry to cosmology and also provides a new geometrical perspective on self-similarity in cosmology.

  11. Voids and the Cosmic Web: cosmic depressions & spatial complexity

    CERN Document Server

    van de Weygaert, Rien

    2016-01-01

    Voids form a prominent aspect of the Megaparsec distribution of galaxies and matter. Not only do they represent a key constituent of the Cosmic Web, they also are one of the cleanest probes and measures of global cosmological parameters. The shape and evolution of voids are highly sensitive to the nature of dark energy, while their substructure and galaxy population provides a direct key to the nature of dark matter. Also, the pristine environment of void interiors is an important testing ground for our understanding of environmental influences on galaxy formation and evolution. In this paper, we review the key aspects of the structure and dynamics of voids, with a particular focus on the hierarchical evolution of the void population. We demonstrate how the rich structural pattern of the Cosmic Web is related to the complex evolution and buildup of voids.

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

    Science.gov (United States)

    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.

  13. A computerized voiding diary.

    Science.gov (United States)

    Rabin, J M; McNett, J; Badlani, G H

    1996-11-01

    To examine a group of subject and control patient's preferences and compliance with regard to the Compu-Void (CV) electronic voiding diary as compared to the written diary (WD) and to compare the two methods with respect to the type of information obtained and whether the order of use of each method influenced results in the subject group. Thirty-six women between the ages of 20 and 84 with bladder symptoms were compared to a group of 36 age-matched women. In 100% of subjects and 95% of control patients, CV entries exceeded the number made with the WD in voiding events and, in subjects, in incontinence episodes recorded (P < .005 and P < .005, respectively). Over 98% of subjects and over 80% of controls preferred the CV (P < .0005). The order of use of each method in subjects made no significant difference with regard to the volume of information obtained (P < .407), number of leakage events recorded (P < .494) or fluid intake patterns (P < .410). Patients' compliance with each method was not affected by the order of use. Our results suggest an increased volume of data and greater patient compliance in reporting bladder symptoms and events using the CV and that the order of use is not important.

  14. Voids and the Cosmic Web: cosmic depression & spatial complexity

    NARCIS (Netherlands)

    van de Weygaert, Rien; Shandarin, S.; Saar, E.; Einasto, J.

    2016-01-01

    Voids form a prominent aspect of the Megaparsec distribution of galaxies and matter. Not only do theyrepresent a key constituent of the Cosmic Web, they also are one of the cleanest probesand measures of global cosmological parameters. The shape and evolution of voids are highly sensitive tothe natu

  15. Mechanical Stress Effects on Electromigration Voiding in a Meandering Test Stripe

    Science.gov (United States)

    Lowry, L. E.; Tai, B. H.; Mattila, J.; Walsh, L. H.

    1993-01-01

    Earlier experimental findings concluded that electromigratin voids in these meandering stripe test structures were not randomly distributed and that void nucleation frequenly occurred sub-surface at the metal/thermal oxide interface.

  16. Bubble size distribution in surface wave breaking entraining process

    Institute of Scientific and Technical Information of China (English)

    HAN; Lei; YUAN; YeLi

    2007-01-01

    From the similarity theorem,an expression of bubble population is derived as a function of the air entrainment rate,the turbulent kinetic energy (TKE) spectrum density and the surface tension.The bubble size spectrum that we obtain has a dependence of a-2.5+nd on the bubble radius,in which nd is positive and dependent on the form of TKE spectrum within the viscous dissipation range.To relate the bubble population with wave parameters,an expression about the air entrainment rate is deduced by introducing two statistical relations to wave breaking.The bubble population vertical distribution is also derived,based on two assumptions from two typical observation results.

  17. Raindrop size distributions and storm classification in Mexico City

    Science.gov (United States)

    Amaro-Loza, Alejandra; Pedrozo-Acuña, Adrián; Agustín| Breña-Naranjo, José

    2017-04-01

    Worldwide, the effects of urbanization and land use change have caused alterations to the hydrological response of urban catchments. This observed phenomenon implies high resolution measurements of rainfall patterns. The work provides the first dataset of raindrop size distributions and storm classification, among others, across several locations of Mexico City. Data were derived from a recent established network of laser optical disdrometers (LOD) and retrieving measurements of rainrate, reflectivity, number of drops, drop diameter & velocity, and kinetic energy, at a 1-minute resolution. Moreover, the comparison of hourly rainfall patterns revealed the origin and classification of storms into three types: stratiform, transition and convective, by means of its corresponding reflectivity and rainrate relationship (Z-R). Finally, a set of rainfall statistics was applied to evaluate the performance of the LOD disdrometer and weighing precipitation gauge (WPG) data at different aggregated timescales. It was found that WPG gauge estimates remain below the precipitation amounts measured by the LOD.

  18. Pore Size Distribution of High Performance Metakaolin Concrete

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The Compressive strength, porosity and pore size distribution of high performance metakaolin (MK) concrete were investigated. Concretes containing 0,5%,10% and 20% metakaolin were prepared at a water/cementitious material ratio (W/C) of 0.30. In parallel, concrete mixtures with the replacement of cement by 20% fly ash or 5 and 10% silica fume were prepared for comparison. The specimens were cured in water at 27℃ for 3 to 90 days. The results show that at the early age of curing (3 days and 7 days), metakaolin replacements increase the compressive strength, but silica fume replacement slightly reduces the compressive strength. At the age of and after 28 days, the compressive strength of the concrete with metakaolin and silica fume replacement increases.A strong reduction in the total porosity and average pore diameter were observed in the concrete with MK 20% and 10% in the first 7 days.

  19. Influence of particle size distribution on nanopowder cold compaction processes

    Science.gov (United States)

    Boltachev, G.; Volkov, N.; Lukyashin, K.; Markov, V.; Chingina, E.

    2017-06-01

    Nanopowder uniform and uniaxial cold compaction processes are simulated by 2D granular dynamics method. The interaction of particles in addition to wide-known contact laws involves the dispersion forces of attraction and possibility of interparticle solid bridges formation, which have a large importance for nanopowders. Different model systems are investigated: monosized systems with particle diameter of 10, 20 and 30 nm; bidisperse systems with different content of small (diameter is 10 nm) and large (30 nm) particles; polydisperse systems corresponding to the log-normal size distribution law with different width. Non-monotone dependence of compact density on powder content is revealed in bidisperse systems. The deviations of compact density in polydisperse systems from the density of corresponding monosized system are found to be minor, less than 1 per cent.

  20. Cosmic Voids: structure, dynamics and galaxies

    CERN Document Server

    van de Weygaert, Rien

    2009-01-01

    In this review we discuss several aspects of Cosmic Voids. Voids are a major component of the large scale distribution of matter and galaxies in the Universe. They are of instrumental importance for understanding the emergence of the Cosmic Web. Their relatively simple shape and structure makes them into useful tools for extracting the value of a variety cosmic parameters, possibly including even that of the influence of dark energy. Perhaps most promising and challenging is the issue of the galaxies found within their realm. Not only does the pristine environment of voids provide a promising testing ground for assessing the role of environment on the formation and evolution of galaxies, the dearth of dwarf galaxies may even represent a serious challenge to the standard view of cosmic structure formation.

  1. Void coalescence within periodic clusters of particles

    Science.gov (United States)

    Thomson, C. I. A.; Worswick, M. J.; Pilkey, A. K.; Lloyd, D. J.

    2003-01-01

    The effect of particle clustering on void damage rates in a ductile material under triaxial loading conditions is examined using three-dimensional finite element analysis. An infinite material containing a regular distribution of clustered particles is modelled using a unit cell approach. Three discrete particles are introduced into each unit cell while a secondary population of small particles within the surrounding matrix is represented using the Gurson-Tvergaard-Needleman (GTN) constitutive equations. Deformation strain states characteristic of sheet metal forming are considered; that is, deep drawing, plane strain and biaxial stretching. Uniaxial tensile stress states with varying levels of superimposed hydrostatic tension are also examined. The orientation of a particle cluster with respect to the direction of major principal loading is shown to significantly influence failure strains. Coalescence of voids within a first-order particle cluster (consisting of three particles) is a stable event while collapse of inter-cluster ligaments leads to imminent material collapse through void-sheeting.

  2. Size distribution and seasonal variation of atmospheric cellulose

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  4. Vesicle Size Distribution as a Novel Nuclear Forensics Tool

    Science.gov (United States)

    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

  5. Airborne Measurements of Aerosol Size Distributions During PACDEX

    Science.gov (United States)

    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.

  6. Rank-size Distributions of Chinese Cities: Macro and Micro Patterns

    Institute of Scientific and Technical Information of China (English)

    LI Shujuan

    2016-01-01

    A large number of studies have been conducted to find a better fit for city rank-size distributions in different countries.Many theoretical curves have been proposed,but no consensus has been reached.This study argues for the importance of examining city rank-size distribution across different city size scales.In addition to focusing on macro patterns,this study examines the micro patterns of city rank-size distributions in China.A moving window method is developed to detect rank-size distributions of cities in different sizes incrementally.The results show that micro patterns of the actual city rank-size distributions in China are much more complex than those suggested by the three theoretical distributions examined (Pareto,quadratic,and q-exponential distributions).City size distributions present persistent discontinuities.Large cities are more evenly distributed than small cities and than that predicted by Zipf's law.In addition,the trend is becoming more pronounced over time.Medium-sized cities became evenly distributed first and then unevenly distributed thereafter.The rank-size distributions of small cities are relatively consistent.While the three theoretical distributions examined in this study all have the ability to detect the overall dynamics of city rank-size distributions,the actual macro distribution may be composed of a combination of the three theoretical distributions.

  7. An observational detection of the bridge effect of void filaments

    CERN Document Server

    Shim, Junsup; Hoyle, Fiona

    2015-01-01

    The bridge effect of void filaments is a phrase coined by Park & Lee (2009b) to explain the correlations found in a numerical experiment between the luminosity of the void galaxies and the degree of the straightness of their host filaments. Their numerical finding implies that a straight void filament provides a narrow channel for the efficient transportation of gas and matter particles from the surroundings into the void galaxies. To observationally confirm the presence of the bridge effect of void filaments, we identify the filamentary structures from the Sloan void catalog and determine the specific size of each void filament as a measure of its straightness. Using both classical and Bayesian statistics, we indeed detect a strong tendency that the void galaxies located in the more straight filaments are on average more luminous, which is in agreement with the numerical prediction. It is also shown that the strength of correlation increases with the spatial extent of the void filaments, which can be phy...

  8. The sparkling Universe: a scenario for cosmic void motions

    CERN Document Server

    Ceccarelli, Laura; Lares, Marcelo; Paz, Dante J; Maldonado, Victoria E; Luparello, Heliana E; Lambas, Diego Garcia

    2015-01-01

    We perform a statistical study of the global motion of cosmic voids using both a numerical simulation and observational data. We analyse their relation to large--scale mass flows and the physical effects that drive those motions. We analyse the bulk motions of voids, defined by the mean velocity of haloes in the surrounding shells in the numerical simulation, and by galaxies in the Sloan Digital Sky Survey Data Release 7. We find void mean bulk velocities close to 400 km/s, comparable to those of haloes (~ 500-600 km/s), depending on void size and the large--scale environment. Statistically, small voids move faster than large ones, and voids in relatively higher density environments have higher bulk velocities than those placed in large underdense regions. Also, we analyze the mean mass density around voids finding, as expected, large--scale overdensities (underdensities) along (opposite to) the void motion direction, suggesting that void motions respond to a pull--push mechanism. This contrasts with massive ...

  9. Crystal Size Distributions in Igneous rocks: Where are we now?

    Science.gov (United States)

    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

  10. Statistical properties of the normalized ice particle size distribution

    Science.gov (United States)

    Delanoë, Julien; Protat, Alain; Testud, Jacques; Bouniol, Dominique; Heymsfield, A. J.; Bansemer, A.; Brown, P. R. A.; Forbes, R. M.

    2005-05-01

    Testud et al. (2001) have recently developed a formalism, known as the "normalized particle size distribution (PSD)", which consists in scaling the diameter and concentration axes in such a way that the normalized PSDs are independent of water content and mean volume-weighted diameter. In this paper we investigate the statistical properties of the normalized PSD for the particular case of ice clouds, which are known to play a crucial role in the Earth's radiation balance. To do so, an extensive database of airborne in situ microphysical measurements has been constructed. A remarkable stability in shape of the normalized PSD is obtained. The impact of using a single analytical shape to represent all PSDs in the database is estimated through an error analysis on the instrumental (radar reflectivity and attenuation) and cloud (ice water content, effective radius, terminal fall velocity of ice crystals, visible extinction) properties. This resulted in a roughly unbiased estimate of the instrumental and cloud parameters, with small standard deviations ranging from 5 to 12%. This error is found to be roughly independent of the temperature range. This stability in shape and its single analytical approximation implies that two parameters are now sufficient to describe any normalized PSD in ice clouds: the intercept parameter N*0 and the mean volume-weighted diameter Dm. Statistical relationships (parameterizations) between N*0 and Dm have then been evaluated in order to reduce again the number of unknowns. It has been shown that a parameterization of N*0 and Dm by temperature could not be envisaged to retrieve the cloud parameters. Nevertheless, Dm-T and mean maximum dimension diameter -T parameterizations have been derived and compared to the parameterization of Kristjánsson et al. (2000) currently used to characterize particle size in climate models. The new parameterization generally produces larger particle sizes at any temperature than the Kristjánsson et al. (2000

  11. Reconciliation between experimental and Monte Carlo-based simulation of the pore size distribution in mesoporous silicon.

    Science.gov (United States)

    Tadvani, Jalil Khajepour; Falamaki, Cavus

    2008-07-23

    It is demonstrated for the first time that mesoporous PS structures obtained by the electrochemical etching of p(+)(100) oriented silicon wafers might assume the peculiarity of invariance of the first peak positions in their pore size distribution curves, albeit for current densities far from the electropolishing region and at constant electrolyte composition. A new Monte Carlo-based simulation model is presented that predicts reasonably the pore size distribution of the PS layers and the observed invariance of peak position with respect to changes in current density. The main highlight of the new model is the introduction of a 'light avalanche breakdown' process in a mathematical fashion. The model is also able to predict an absolute value of 4.23 Å for the smallest pore created experimentally. It is discussed that the latter value has an exact physical meaning: it corresponds with great accuracy to the width of a void created on the surface due to the exclusion of one Si atom.

  12. Reconciliation between experimental and Monte Carlo-based simulation of the pore size distribution in mesoporous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Tadvani, Jalil Khajepour [Ceramics Department, Materials and Energy Research Center, PO Box 14155-4777, Tehran (Iran, Islamic Republic of); Falamaki, Cavus [Chemical Engineering Department, Amirkabir University of Technology, Hafez Avenue, PO Box 15875-4413, Tehran (Iran, Islamic Republic of)

    2008-07-23

    It is demonstrated for the first time that mesoporous PS structures obtained by the electrochemical etching of p{sup +}(100) oriented silicon wafers might assume the peculiarity of invariance of the first peak positions in their pore size distribution curves, albeit for current densities far from the electropolishing region and at constant electrolyte composition. A new Monte Carlo-based simulation model is presented that predicts reasonably the pore size distribution of the PS layers and the observed invariance of peak position with respect to changes in current density. The main highlight of the new model is the introduction of a 'light avalanche breakdown' process in a mathematical fashion. The model is also able to predict an absolute value of 4.23 A for the smallest pore created experimentally. It is discussed that the latter value has an exact physical meaning: it corresponds with great accuracy to the width of a void created on the surface due to the exclusion of one Si atom.

  13. Into the Void

    Science.gov (United States)

    2006-01-01

    17 May 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a portion of a chain of pits on a lava- and dust-covered plain northwest of Tharsis Tholus -- one of the many volcanic constructs in the Tharsis region of Mars. Pit chains, such as this one, are associated with the collapse of surface materials into subsurface voids formed by faulting and expansion -- or extension -- of the bedrock. Location near: 16.4oN, 92.6oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Winter

  14. Carbon-based phytoplankton size classes retrieved via ocean color estimates of the particle size distribution

    Science.gov (United States)

    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 text">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 are mostly due to the

  15. Dislocation and void segregation in copper during neutron irradiation

    DEFF Research Database (Denmark)

    Singh, Bachu Narain; Leffers, Torben; Horsewell, Andy

    1986-01-01

    High-purity (99. 999%) and fully annealed copper specimens have been irradiated in the DR-3 reactor at Riso to doses of 1 multiplied by 10**2**2 and 5 multiplied by 10**2**2 neutrons (fast)m** minus **2(2 multiplied by 10** minus **3 dpa and 1 multiplied by 10** minus **2 dpa, respectively...... were distributed between these walls. The dislocation walls were practically free of voids and generally had a void-denuded zone along them. The density of dislocations (loops and segments) was very low in the region containing voids (i. e. between the dislocation walls). Even with this low dislocation...... density, the void swelling rate was very high (approximately 2. 5% per dpa). The implications of the segregated distribution of sinks for void formation and growth are briefly discussed....

  16. Void-induced dissolution in molecular dynamics simulations of NaCl and water.

    Science.gov (United States)

    Bahadur, Ranjit; Russell, Lynn M; Alavi, Saman; Martin, Scot T; Buseck, Peter R

    2006-04-21

    To gain a better understanding of the interaction of water and NaCl at the surface during dissolution, we have used molecular dynamics to simulate the interface with two equal-sized slabs of solid NaCl and liquid water in contact. The introduction of voids in the bulk of the salt, as well as steps or pits on the surface of the NaCl slab results in a qualitative change of system structure, as defined by radial distribution functions (RDFs). As an example, the characteristic Na-Na RDF for the system changes from regularly spaced narrow peaks (corresponding to an ordered crystalline structure), to a broad primary and smaller secondary peak (corresponding to a disordered structure). The change is observed at computationally short time scales of 100 ps, in contrast with a much longer time scale of 1 mus expected for complete mixing in the absence of defects. The void fraction (which combines both bulk and surface defects) required to trigger dissolution varies between 15%-20% at 300 K and 1 atm, and has distinct characteristics for the physical breakdown of the crystal lattice. The void fraction required decreases with temperature. Sensitivity studies show a strong dependence of the critical void fraction on the quantity and distribution of voids on the surface, with systems containing a balanced number of surface defects and a rough surface showing a maximum tendency to dissolve. There is a moderate dependence on temperature, with a 5% decrease in required void fraction with a 100 K increase in temperature, and a weak dependence on water potential model used, with the SPC, SPC/E, TIP4P, and RPOL models giving qualitatively identical results. The results were insensitive to the total quantity of water available for dissolution and the duration of the simulation.

  17. Void-induced dissolution in molecular dynamics simulations of NaCl and water

    Science.gov (United States)

    Bahadur, Ranjit; Russell, Lynn M.; Alavi, Saman; Martin, Scot T.; Buseck, Peter R.

    2006-04-01

    To gain a better understanding of the interaction of water and NaCl at the surface during dissolution, we have used molecular dynamics to simulate the interface with two equal-sized slabs of solid NaCl and liquid water in contact. The introduction of voids in the bulk of the salt, as well as steps or pits on the surface of the NaCl slab results in a qualitative change of system structure, as defined by radial distribution functions (RDFs). As an example, the characteristic Na-Na RDF for the system changes from regularly spaced narrow peaks (corresponding to an ordered crystalline structure), to a broad primary and smaller secondary peak (corresponding to a disordered structure). The change is observed at computationally short time scales of 100ps, in contrast with a much longer time scale of 1μs expected for complete mixing in the absence of defects. The void fraction (which combines both bulk and surface defects) required to trigger dissolution varies between 15%-20% at 300K and 1atm, and has distinct characteristics for the physical breakdown of the crystal lattice. The void fraction required decreases with temperature. Sensitivity studies show a strong dependence of the critical void fraction on the quantity and distribution of voids on the surface, with systems containing a balanced number of surface defects and a rough surface showing a maximum tendency to dissolve. There is a moderate dependence on temperature, with a 5% decrease in required void fraction with a 100K increase in temperature, and a weak dependance on water potential model used, with the SPC, SPC/E, TIP4P, and RPOL models giving qualitatively identical results. The results were insensitive to the total quantity of water available for dissolution and the duration of the simulation.

  18. Void formation in pure aluminium irradiated with high-energetic electron beams and gamma-quanta

    DEFF Research Database (Denmark)

    Gan, V. V.; Ozhigou, L. S.; Yamnitsky, V. A.

    1983-01-01

    The spatial distribution of displaced atoms and helium atoms and also the spectra of damaging energies of primary displaced atoms in a thick aluminium target irradiated with electrons of 225 MeV energy were calculated. Pure aluminium (99.9999%) irradiated up to 0.04 dose was studied by electron-m......-microscopy. Voids of size 5 to 40 nm were obtained and their vacancy nature was estimated. The dislocation structure of the material was studied...

  19. Determination of Size Distribution of Nano-particles by Capillary Zone Electrophoresis

    Institute of Scientific and Technical Information of China (English)

    Yan XUE; Hai Ying YANG; Yong Tan YANG

    2005-01-01

    A new method was developed for the determination of the size distribution of nano-particles by capillary zone electrophoresis (CZE). Scattering effect of nanoparticles was studied. This method for the determination of size distribution was statistical.

  20. Analytical Approach for Loss Minimization in Distribution Systems by Optimum Placement and Sizing of Distributed Generation

    Directory of Open Access Journals (Sweden)

    Bakshi Surbhi

    2016-01-01

    Full Text Available Distributed Generation has drawn the attention of industrialists and researchers for quite a time now due to the advantages it brings loads. In addition to cost-effective and environmentally friendly, but also brings higher reliability coefficient power system. The DG unit is placed close to the load, rather than increasing the capacity of main generator. This methodology brings many benefits, but has to address some of the challenges. The main is to find the optimal location and size of DG units between them. The purpose of this paper is distributed generation by adding an additional means to reduce losses on the line. This paper attempts to optimize the technology to solve the problem of optimal location and size through the development of multi-objective particle swarm. The problem has been reduced to a mathematical optimization problem by developing a fitness function considering losses and voltage distribution line. Fitness function by using the optimal value of the size and location of this algorithm was found to be minimized. IEEE-14 bus system is being considered, in order to test the proposed algorithm and the results show improved performance in terms of accuracy and convergence rate.

  1. ESTIMATING SOIL PARTICLE-SIZE DISTRIBUTION FOR SICILIAN SOILS

    Directory of Open Access Journals (Sweden)

    Vincenzo Bagarello

    2009-09-01

    Full Text Available The soil particle-size distribution (PSD is commonly used for soil classification and for estimating soil behavior. An accurate mathematical representation of the PSD is required to estimate soil hydraulic properties and to compare texture measurements from different classification systems. The objective of this study was to evaluate the ability of the Haverkamp and Parlange (HP and Fredlund et al. (F PSD models to fit 243 measured PSDs from a wide range of 38 005_Bagarello(547_33 18-11-2009 11:55 Pagina 38 soil textures in Sicily and to test the effect of the number of measured particle diameters on the fitting of the theoretical PSD. For each soil textural class, the best fitting performance, established using three statistical indices (MXE, ME, RMSE, was obtained for the F model with three fitting parameters. In particular, this model performed better in the fine-textured soils than the coarse-textured ones but a good performance (i.e., RMSE < 0.03 was detected for the majority of the investigated soil textural classes, i.e. clay, silty-clay, silty-clay-loam, silt-loam, clay-loam, loamy-sand, and loam classes. Decreasing the number of measured data pairs from 14 to eight determined a worse fitting of the theoretical distribution to the measured one. It was concluded that the F model with three fitting parameters has a wide applicability for Sicilian soils and that the comparison of different PSD investigations can be affected by the number of measured data pairs.

  2. Single and Joint Multifractal Analysis of Soil Particle Size Distributions

    Institute of Scientific and Technical Information of China (English)

    LI Yi; LI Min; R.HORTON

    2011-01-01

    It is noted that there has been little research to compare volume-based and number-based soil particle size distributions (PSDs).Our objectives were to characterize the scaling properties and the possible connections between volume-based and number-based PSDs by applying single and joint multifractal analysis.Twelve soil samples were taken from selected sites in Northwest China and their PSDs were analyzed using laser diffractometry.The results indicated that the volume-based PSDs of all 12 samples and thc number-based PSDs of 4 samples had multifractal scalings for moment order -6 < q < 6.Some empirical relationships were identified between the extreme probability values, maximum probability (Pmax), minimum probability (Pmin), and Pmax/Pmin, and the multifractal indices,the difference and the ratio of generalized dimensions at q=0 and 1(D0-D1 and D1/D0), maximum and minimum singularity strength (αmax and αmin) and their difference (αmax - αmin, spectrum width), and asymmetric index (RD).An increase in Pmax generally resulted in corresponding increases of D0 - D1, αmax, αmax - αmin, and RD, which indicated that a large Pmax increased the multifractality of a distribution.Joint multifractal analysis showed that there was significant correlation between the scaling indices of volume-based and number-based PSDs.The multifractality indices indicated that for a given soil, the volume-based PSD was more homogeneous than the number-based PSD, and more likely to display monofractal rather than multifractal scaling.

  3. Elastic–plastic void expansion in near-self-similar shapes

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2011-01-01

    For void growth in an elastic–plastic strain hardening material the preferred shape of the void is calculated, dependent on the macroscopic stress state. Axisymmetric cell model analyses are carried out with a very small initial void size relative to the cell dimensions. Large deformations of the...

  4. Optimal Placement and Sizing of Renewable Distributed Generations and Capacitor Banks into Radial Distribution Systems

    Directory of Open Access Journals (Sweden)

    Mahesh Kumar

    2017-06-01

    Full Text Available In recent years, renewable types of distributed generation in the distribution system have been much appreciated due to their enormous technical and environmental advantages. This paper proposes a methodology for optimal placement and sizing of renewable distributed generation(s (i.e., wind, solar and biomass and capacitor banks into a radial distribution system. The intermittency of wind speed and solar irradiance are handled with multi-state modeling using suitable probability distribution functions. The three objective functions, i.e., power loss reduction, voltage stability improvement, and voltage deviation minimization are optimized using advanced Pareto-front non-dominated sorting multi-objective particle swarm optimization method. First a set of non-dominated Pareto-front data are called from the algorithm. Later, a fuzzy decision technique is applied to extract the trade-off solution set. The effectiveness of the proposed methodology is tested on the standard IEEE 33 test system. The overall results reveal that combination of renewable distributed generations and capacitor banks are dominant in power loss reduction, voltage stability and voltage profile improvement.

  5. Aerosol size distribution seasonal characteristics measured in Tiksi, Russian Arctic

    Directory of Open Access Journals (Sweden)

    E. Asmi

    2015-07-01

    Full Text Available Four years of continuous aerosol number size distribution measurements from an Arctic Climate Observatory in Tiksi Russia are analyzed. Source region effects on particle modal features, and number and mass concentrations are presented for different seasons. The monthly median total aerosol number concentration in Tiksi ranges from 184 cm-3 in November to 724 cm-3 in July with a local maximum in March of 481 cm-3. The total mass concentration has a distinct maximum in February–March of 1.72–2.38 μg m-3 and two minimums in June of 0.42 μg m-3 and in September–October of 0.36–0.57 μg m-3. These seasonal cycles in number and mass concentrations are related to isolated aerosol sources such as Arctic haze in early spring which increases accumulation and coarse mode numbers, and biogenic emissions in summer which affects the smaller, nucleation and Aitken mode particles. The impact of temperature dependent natural emissions on aerosol and cloud condensation nuclei numbers was significant. Therefore, in addition to the precursor emissions of biogenic volatile organic compounds, the frequent Siberian forest fires, although far are suggested to play a role in Arctic aerosol composition during the warmest months. During calm and cold months aerosol concentrations were occasionally increased by nearby aerosol sources in trapping inversions. These results provide valuable information on inter-annual cycles and sources of Arctic aerosols.

  6. Controllable microgels from multifunctional molecules: structure control and size distribution

    Science.gov (United States)

    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.

  7. Bubble Size Distribution in a Vibrating Bubble Column

    Science.gov (United States)

    Mohagheghian, Shahrouz; Wilson, Trevor; Valenzuela, Bret; Hinds, Tyler; Moseni, Kevin; Elbing, Brian

    2016-11-01

    While vibrating bubble columns have increased the mass transfer between phases, a universal scaling law remains elusive. Attempts to predict mass transfer rates in large industrial scale applications by extrapolating laboratory scale models have failed. In a stationary bubble column, mass transfer is a function of phase interfacial area (PIA), while PIA is determined based on the bubble size distribution (BSD). On the other hand, BSD is influenced by the injection characteristics and liquid phase dynamics and properties. Vibration modifies the BSD by impacting the gas and gas-liquid dynamics. This work uses a vibrating cylindrical bubble column to investigate the effect of gas injection and vibration characteristics on the BSD. The bubble column has a 10 cm diameter and was filled with water to a depth of 90 cm above the tip of the orifice tube injector. BSD was measured using high-speed imaging to determine the projected area of individual bubbles, which the nominal bubble diameter was then calculated assuming spherical bubbles. The BSD dependence on the distance from the injector, injector design (1.6 and 0.8 mm ID), air flow rates (0.5 to 5 lit/min), and vibration conditions (stationary and vibration conditions varying amplitude and frequency) will be presented. In addition to mean data, higher order statistics will also be provided.

  8. An alternative method for determining particle-size distribution of forest road aggregate and soil with large-sized particles

    Science.gov (United States)

    Hakjun Rhee; Randy B. Foltz; James L. Fridley; Finn Krogstad; Deborah S. Page-Dumroese

    2014-01-01

    Measurement of particle-size distribution (PSD) of soil with large-sized particles (e.g., 25.4 mm diameter) requires a large sample and numerous particle-size analyses (PSAs). A new method is needed that would reduce time, effort, and cost for PSAs of the soil and aggregate material with large-sized particles. We evaluated a nested method for sampling and PSA by...

  9. Comprehensive Characterization of Voids and Microstructure in TATB-based Explosives from 10 nm to 1 cm: Effects of Temperature Cycling and Compressive Creep

    Energy Technology Data Exchange (ETDEWEB)

    Willey, T M; Lauderbach, L; Gagliardi, F; Cunningham, B; Lorenz, K T; Lee, J I; van Buuren, T; Call, R; Landt, L; Overturf, G

    2010-02-26

    This paper outlines the characterization of voids and Microstructure in TATB-based Explosives over several orders of magnitude, from sizes on the order of 10 nm to about 1 cm. This is accomplished using ultra small angle x-ray scattering to investigate voids from a few nm to a few microns, ultra small angle neutron scattering for voids from 100 nm to 10 microns, and x-ray computed microtomography to investigate microstructure from a few microns to a few centimeters. The void distributions of LX-17 are outlined, and the microstructure of LX-17 is presented. Temperature cycling and compressive creep cause drastically different damage to the microstructure. Temperature cycling leads to a volume expansion (ratchet growth) in TATB-based explosives, and x-ray scattering techniques that are sensitive to sizes up to a few microns indicated changes to the void volume distribution that had previously accounted for most, but not all of the change in density. This paper presents the microstructural damage larger than a few microns caused by ratchet growth. Temperature cycling leads to void creation in the binder poor regions associated with the interior portion of formulated prills. Conversely, compressive creep causes characteristically different changes to microstructure; fissures form at binder-rich prill boundaries prior to mechanical failure.

  10. Comparisons of Particulate Size Distributions from Multiple Combustion Strategies

    Science.gov (United States)

    Zhang, Yizhou

    In this study, a comparison of particle size distribution (PSD) measurements from eight different combustion strategies was conducted at four different load-speed points. The PSDs were measured using a scanning mobility particle sizer (SMPS) together with a condensation particle counter (CPC). To study the influence of volatile particles, PSD measurements were performed with and without a volatile particle remover (thermodenuder, TD) at both low and high dilution ratios. The common engine platform utilized in the experiment helps to eliminate the influence of background particulate and ensures similarity in dilution conditions. The results show a large number of volatile particles were present under LDR sample conditions for most of the operating conditions. The use of a TD, especially when coupled with HDR, was demonstrated to be effective at removing volatile particles and provided consistent measurements across all combustion strategies. The PSD comparison showed that gasoline premixed combustion strategies such as HCCI and GCI generally have low PSD magnitudes for particle sizes greater than the Particle Measurement Programme (PMP) cutoff diameter (23 nm), and the PSDs were highly nuclei-mode particle dominated. The strategies using diesel as the only fuel (DLTC and CDC) generally showed the highest particle number emissions for particles larger than 23 nm and had accumulation-mode particle dominated PSDs. A consistent correlation between the increase of the direct-injection of diesel fuel and a higher fraction of accumulation-mode particles was observed over all combustion strategies. A DI fuel substitution study and injector nozzle geometry study were conducted to better understand the correlation between PSD shape and DI fueling. It was found that DI fuel properties has a clear impact on PSD behavior for CDC and NG DPI. Fuel with lower density and lower sooting tendency led to a nuclei-mode particle dominated PSD shape. For NG RCCI, accumulation

  11. Single-peak distribution model of particulate size for welding aerosols

    Institute of Scientific and Technical Information of China (English)

    施雨湘; 李爱农

    2003-01-01

    A large number of particulate size distributions of welding aerosols are measured by means of DMPS method, several distribution types are presented. Among them the single-peak distribution is the basic composing unit of particulate size. The research on the mathematic models and distributions functions shows that the single-peak distribution features the log-normal distribution. The diagram-estimating method (DEM) is a concise approach to dealing with distribution types, obtaining distribution functions for the particulate sizes of welding aerosols. It proves that the distribution function of particulate size possesses the extending property, being from quantity distribution to volume, as well as high-order moment distributions, with K-S method verifying the application of single-peak distribution and of DEM.

  12. Simulation of 2D Fields of Raindrop Size Distributions

    Science.gov (United States)

    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

  13. Rank-size distribution and primate city characteristics in India--a temporal analysis.

    Science.gov (United States)

    Das, R J; Dutt, A K

    1993-02-01

    "This paper is an analysis of the historical change in city size distribution in India....Rank-size distribution at national level and primate city-size distribution at regional levels are examined....The paper also examines, in the Indian context, the relation between rank-size distribution and an integrated urban system, and the normative nature of the latter as a spatial organization of human society. Finally, we have made a modest attempt to locate the research on city-size distribution...." excerpt

  14. Properties of galaxy halos in Clusters and Voids

    CERN Document Server

    Antonuccio-Delogu, V; Pagliaro, A; Van Kampen, E; Colafrancesco, Sergio; Germaná, A; Gambera, M

    2000-01-01

    We use the results of a high resolution N-body simulation to investigate the role of the environment on the formation and evolution of galaxy-sized halos. Starting from a set of constrained initial conditions, we have produced a final configuration hosting a double cluster in one octant and a large void extending over two octants of the simulation box. In this paper we concentrate on {\\em gravitationally bound} galaxy-sized halos extracted from the two regions. Exploiting the high mass resolution of our simulation ($m_{body} = 2.1\\times 10^{9} h^{-1} M_{\\odot}$), we focus on halos with a relatively small mass: $5\\times 10^{10} \\leq M \\leq 2\\times 10^{12} M_{\\odot}$. We present results for two statistics: the relationship between 1-D velocity dispersion and mass and the probability distribution of the spin parameter $P(\\lambda)$. We do find a clear difference between halos lying in overdense regions and in voids. The \\svm relationship is well described by the Truncated Isothermal Sphere (TIS) model introduced ...

  15. A constitutive model for elastoplastic solids containing primary and secondary voids

    Science.gov (United States)

    Fabrègue, D.; Pardoen, T.

    In many ductile metallic alloys, the damage process controlled by the growth and coalescence of primary voids nucleated on particles with a size varying typically between 1 and 100 μm, is affected by the growth of much smaller secondary voids nucleated on inclusions with a size varying typically between 0.1 and 3 μm. The goal of this work is first to quantify the potential effect of the growth of these secondary voids on the coalescence of primary voids using finite element (FE) unit cell calculations and second to formulate a new constitutive model incorporating this effect. The nucleation and growth of secondary voids do essentially not affect the growth of the primary voids but mainly accelerate the void coalescence process. The drop of the ductility caused by the presence of secondary voids increases if the nucleation strain decreases and/or if their volume fraction increases and/or if the primary voids are flat. A strong coupling is indeed observed between the shape of the primary voids and the growth of the second population enhancing the anisotropy of the ductility induced by void shape effects. The new micromechanics-based coalescence condition for internal necking introduces the softening induced by secondary voids growing in the ligament between two primary voids. The FE cell calculations were used to guide and assess the development of this model. The use of the coalescence condition relies on a closed-form model for estimating the evolution of the secondary voids in the vicinity of a primary cavity. This coalescence criterion is connected to an extended Gurson model for the first population including the effect of the void aspect ratio. With respect to classical models for single void population, this new constitutive model improves the predictive potential of damage constitutive models devoted to ductile metal while requiring only two new parameters, i.e. the initial porosity of second population and a void nucleation stress, without any additional

  16. Two new methods to detect cosmic voids without density measurements

    CERN Document Server

    Elyiv, Andrii; Pollina, Giorgia; Baldi, Marco; Branchini, Enzo; Cimatti, Andrea; Moscardini, Lauro

    2014-01-01

    Cosmic voids are effective cosmological probes to discriminate among competing world models. Their precise and unbiased identification is a prerequisite to perform accurate observational tests. The identification is generally based on density or geometry criteria that, because of their very nature, are prone to shot noise errors. In this work we propose two new void finders that are based on dynamical and clustering criteria to select voids in the Lagrangian coordinates and minimise the impact of sparse sampling. The first approach exploits the Zeldovich approximation to trace back in time the orbits of galaxies located in the voids and their surroundings, whereas the second uses the observed galaxy-galaxy correlation function to relax the objects' spatial distribution to homogeneity and isotropy. In both cases voids are defined as regions of the negative velocity divergence in Lagrangian coordinates, that can be regarded as sinks of the back-in-time streamlines of the mass tracers. To assess the performance ...

  17. Voids and the Cosmic Web: cosmic depression & spatial complexity

    Science.gov (United States)

    van de Weygaert, Rien

    2016-10-01

    Voids form a prominent aspect of the Megaparsec distribution of galaxies and matter. Not only do theyrepresent a key constituent of the Cosmic Web, they also are one of the cleanest probesand measures of global cosmological parameters. The shape and evolution of voids are highly sensitive tothe nature of dark energy, while their substructure and galaxy population provides a direct key to thenature of dark matter. Also, the pristine environment of void interiors is an important testing groundfor our understanding of environmental influences on galaxy formation and evolution. In this paper, we reviewthe key aspects of the structure and dynamics ofvoids, with a particular focus on the hierarchical evolution of the void population. We demonstratehow the rich structural pattern of the Cosmic Web is related to the complex evolution and buildupof voids.

  18. Thermal Properties, Sizes, and Size Distribution of Jupiter-Family Cometary Nuclei

    CERN Document Server

    Fernandez, Y R; Lamy, P L; Toth, I; Groussin, O; Lisse, C M; A'Hearn, M F; Bauer, J M; Campins, H; Fitzsimmons, A; Licandro, J; Lowry, S C; Meech, K J; Pittichova, J; Reach, W T; Snodgrass, C; Weaver, H A

    2013-01-01

    We present results from SEPPCoN, an on-going Survey of the Ensemble Physical Properties of Cometary Nuclei. In this report we discuss mid-infrared measurements of the thermal emission from 89 nuclei of Jupiter-family comets (JFCs). All data were obtained in 2006 and 2007 with the Spitzer Space Telescope. For all 89 comets, we present new effective radii, and for 57 comets we present beaming parameters. Thus our survey provides the largest compilation of radiometrically-derived physical properties of nuclei to date. We conclude the following. (a) The average beaming parameter of the JFC population is 1.03+/-0.11, consistent with unity, and indicating low thermal inertia. (b) The known JFC population is not complete even at 3 km radius, and even for comets with perihelia near ~2 AU. (c) We find that the JFC nuclear cumulative size distribution (CSD) has a power-law slope of around -1.9. (d) This power-law is close to that derived from visible-wavelength observations, suggesting that there is no strong dependenc...

  19. "Dark energy" in the Local Void

    Science.gov (United States)

    Villata, M.

    2012-05-01

    The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence of an unidentified "dark energy", or cosmological constant, devoid of any physical meaning. While this standard cosmology seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can account for some of the features that are unexplained by the standard model. Through simple dynamical considerations, we find that the Local Void could host an amount of antimatter (˜5×1015 M ⊙) roughly equivalent to the mass of a typical supercluster, thus restoring the matter-antimatter symmetry. The antigravity field produced by this "dark repulsor" can explain the anomalous motion of the Local Sheet away from the Local Void, as well as several other properties of nearby galaxies that seem to require void evacuation and structure formation much faster than expected from the standard model. At the global cosmological level, gravitational repulsion from antimatter hidden in voids can provide more than enough potential energy to drive both the cosmic expansion and its acceleration, with no need for an initial "explosion" and dark energy. Moreover, the discrete distribution of these dark repulsors, in contrast to the uniformly permeating dark energy, can also explain dark flows and other recently observed excessive inhomogeneities and anisotropies of the Universe.

  20. Evaluating the role of genome downsizing and size thresholds from genome size distributions in angiosperms.

    Science.gov (United States)

    Zenil-Ferguson, Rosana; Ponciano, José M; Burleigh, J Gordon

    2016-07-01

    Whole-genome duplications (WGDs) can rapidly increase genome size in angiosperms. Yet their mean genome size is not correlated with ploidy. We compared three hypotheses to explain the constancy of genome size means across ploidies. The genome downsizing hypothesis suggests that genome size will decrease by a given percentage after a WGD. The genome size threshold hypothesis assumes that taxa with large genomes or large monoploid numbers will fail to undergo or survive WGDs. Finally, the genome downsizing and threshold hypothesis suggests that both genome downsizing and thresholds affect the relationship between genome size means and ploidy. We performed nonparametric bootstrap simulations to compare observed angiosperm genome size means among species or genera against simulated genome sizes under the three different hypotheses. We evaluated the hypotheses using a decision theory approach and estimated the expected percentage of genome downsizing. The threshold hypothesis improves the approximations between mean genome size and simulated genome size. At the species level, the genome downsizing with thresholds hypothesis best explains the genome size means with a 15% genome downsizing percentage. In the genus level simulations, the monoploid number threshold hypothesis best explains the data. Thresholds of genome size and monoploid number added to genome downsizing at species level simulations explain the observed means of angiosperm genome sizes, and monoploid number is important for determining the genome size mean at the genus level. © 2016 Botanical Society of America.

  1. Growth and change in the analysis of rank - size distributions: empirical findings

    OpenAIRE

    Malecki, E.J.

    1980-01-01

    This paper analyzes the interrelationships of city size and growthin the American Midwest from 1940 to 1970 in an effort to synthesize the study of urban growth rates and of city-size distributions. Changes in the rank - size distribution are related to the differential growth of different-size urban places; some relationship in changes over time is evident, but there is little correspondence in static analyses. The urban system analyzed by various threshold sizes examines the sensitivity of ...

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

    Science.gov (United States)

    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

  3. Raindrop size distribution variability estimated using ensemble statistics

    Directory of Open Access Journals (Sweden)

    C. R. Williams

    2009-02-01

    Full Text Available Before radar estimates of the raindrop size distribution (DSD can be assimilated into numerical weather prediction models, the DSD estimate must also include an uncertainty estimate. Ensemble statistics are based on using the same observations as inputs into several different models with the spread in the outputs providing an uncertainty estimate. In this study, Doppler velocity spectra from collocated vertically pointing profiling radars operating at 50 and 920 MHz were the input data for 42 different DSD retrieval models. The DSD retrieval models were perturbations of seven different DSD models (including exponential and gamma functions, two different inverse modeling methodologies (convolution or deconvolution, and three different cost functions (two spectral and one moment cost functions.

    Two rain events near Darwin, Australia, were analyzed in this study producing 26 725 independent ensembles of mass-weighted mean raindrop diameter Dm and rain rate R. The mean and the standard deviation (indicated by the symbols <x> and σx of Dm and R were estimated for each ensemble. For small ranges of <Dm> or <R>, histograms of σDm and σR were found to be asymmetric, which prevented Gaussian statistics from being used to describe the uncertainties. Therefore, 10, 50, and 90 percentiles of σDm and σR were used to describe the uncertainties for small intervals of <Dm> or <R>. The smallest Dm uncertainty occurred for <Dm> between 0.8 and 1.8 mm with the 90th and 50th percentiles being less than 0.15 and 0.11 mm, which correspond to relative errors of less than 20% and 15%, respectively. The uncertainty increased for smaller and larger <Dm> values. The uncertainty of R increased with <R>. While the 90th percentile

  4. Measuring Baryon Acoustic Oscillations from the clustering of voids

    CERN Document Server

    Liang, Yu; Chuang, Chia-Hsun; Kitaura, Francisco-Shu; Tao, Charling

    2015-01-01

    We investigate the necessary methodology to optimally measure the baryon acoustic oscillation (BAO) signal, from voids based on galaxy redshift catalogues. To this end, we study the dependency of the BAO signal on the population of voids classified by their sizes. We find for the first time the characteristic features of the correlation function of voids including the first robust detection of BAOs in mock galaxy catalogues. These show an anti-correlation around the scale corresponding to the smallest size of voids in the sample (the void exclusion effect), and dips at both sides of the BAO peak, which can be used to determine the significance of the BAO signal without any priori model. Furthermore, our analysis demonstrates that there is a scale dependent bias for different populations of voids depending on the radius, with the peculiar property that the void population with the largest BAO significance corresponds to tracers with approximately zero bias on the largest scales. We further investigate the meth...

  5. The Hierarchy Model of the Size Distribution of Centres

    NARCIS (Netherlands)

    J. Tinbergen (Jan)

    1968-01-01

    textabstractWe know that human beings live in centres, that is, cities, towns and villages of different size. Both large and small centres have a number of advantages and disadvantages, different for different people and this is why we have a whole range of sizes. Statistically, we even find that th

  6. Theoretical Study on the Effects of Particle Size Distribution on the Optical Properties of Colloidal Gold

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyo Jeong; Chandra, Saha Leton; Jang, Joon Kyung [Pusan National University, Busan (Korea, Republic of)

    2007-10-15

    Mie theory has been used to calculate the extinction of a gold nanoparticle in water by varying its diameter from 1 to 1000 nm. Utilizing this size-dependent theoretical spectrum, we have calculated the extinction spectrum of a colloidal gold by taking into account the size distribution of particle. Such calculation is in better agreement with experiment than the calculation without considering the size distribution. A least-squares fitting is used to deduce the size distribution from an experimental extinction spectrum. For particles with their diameters ranging from 10 to 28 nanometers, the fitting gives reasonable agreement with the size distribution obtained from tunneling electron microscope images.

  7. Calculation method for particle mean diameter and particle size distribution function under dependent model algorithm

    Institute of Scientific and Technical Information of China (English)

    Hong Tang; Xiaogang Sun; Guibin Yuan

    2007-01-01

    In total light scattering particle sizing technique, the relationship among Sauter mean diameter D32, mean extinction efficiency Q, and particle size distribution function is studied in order to inverse the mean diameter and particle size distribution simply. We propose a method which utilizes the mean extinction efficiency ratio at only two selected wavelengths to solve D32 and then to inverse the particle size distribution associated with (Q) and D32. Numerical simulation results show that the particle size distribution is inversed accurately with this method, and the number of wavelengths used is reduced to the greatest extent in the measurement range. The calculation method has the advantages of simplicity and rapidness.

  8. A grain size distribution model for non-catalytic gas-solid reactions

    NARCIS (Netherlands)

    Heesink, Albertus B.M.; Prins, W.; van Swaaij, Willibrordus Petrus Maria

    1993-01-01

    A new model to describe the non-catalytic conversion of a solid by a reactant gas is proposed. This so-called grain size distribution (GSD) model presumes the porous particle to be a collection of grains of various sizes. The size distribution of the grains is derived from mercury porosimetry measur

  9. A generalized statistical model for the size distribution of wealth

    Science.gov (United States)

    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.

  10. Particle size distribution and physico-chemical composition of clay.

    African Journals Online (AJOL)

    HP USER

    obtained after acid digestion of clay samples were used in determining the elements by Atomic. Absorption ... ignition (LOI) reveal a general reduction in composition as particles sizes reduces. However, Mg .... Murray, H.H. Diagnostic Tests for.

  11. Testing Gravity using Void Profiles

    Science.gov (United States)

    Cai, Yan-Chuan; Padilla, Nelson; Li, Baojiu

    2016-10-01

    We investigate void properties in f(R) models using N-body simulations, focusing on their differences from General Relativity (GR) and their detectability. In the Hu-Sawicki f(R) modified gravity (MG) models, the halo number density profiles of voids are not distinguishable from GR. In contrast, the same f(R) voids are more empty of dark matter, and their profiles are steeper. This can in principle be observed by weak gravitational lensing of voids, for which the combination of a spectroscopic redshift and a lensing photometric redshift survey over the same sky is required. Neglecting the lensing shape noise, the f(R) model parameter amplitudes fR0=10-5 and 10-4 may be distinguished from GR using the lensing tangential shear signal around voids by 4 and 8 σ for a volume of 1 (Gpc/h)3. The line-of-sight projection of large-scale structure is the main systematics that limits the significance of this signal for the near future wide angle and deep lensing surveys. For this reason, it is challenging to distinguish fR0=10-6 from GR. We expect that this can be overcome with larger volume. The halo void abundance being smaller and the steepening of dark matter void profiles in f(R) models are unique features that can be combined to break the degeneracy between fR0 and σ8.

  12. PRECISION COSMOGRAPHY WITH STACKED VOIDS

    Energy Technology Data Exchange (ETDEWEB)

    Lavaux, Guilhem [Department of Physics, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States); Wandelt, Benjamin D. [UPMC Univ Paris 06, UMR 7095, Institut d' Astrophysique de Paris, 98 bis, boulevard Arago, 75014 Paris (France)

    2012-08-01

    We present a purely geometrical method for probing the expansion history of the universe from the observation of the shape of stacked voids in spectroscopic redshift surveys. Our method is an Alcock-Paczynski (AP) test based on the average sphericity of voids posited on the local isotropy of the universe. It works by comparing the temporal extent of cosmic voids along the line of sight with their angular, spatial extent. We describe the algorithm that we use to detect and stack voids in redshift shells on the light cone and test it on mock light cones produced from N-body simulations. We establish a robust statistical model for estimating the average stretching of voids in redshift space and quantify the contamination by peculiar velocities. Finally, assuming that the void statistics that we derive from N-body simulations is preserved when considering galaxy surveys, we assess the capability of this approach to constrain dark energy parameters. We report this assessment in terms of the figure of merit (FoM) of the dark energy task force and in particular of the proposed Euclid mission which is particularly suited for this technique since it is a spectroscopic survey. The FoM due to stacked voids from the Euclid wide survey may double that of all other dark energy probes derived from Euclid data alone (combined with Planck priors). In particular, voids seem to outperform baryon acoustic oscillations by an order of magnitude. This result is consistent with simple estimates based on mode counting. The AP test based on stacked voids may be a significant addition to the portfolio of major dark energy probes and its potentialities must be studied in detail.

  13. Simulating the particle size distribution of rockfill materials based on its statistical regularity

    Institute of Scientific and Technical Information of China (English)

    YAN Zongling; QIU Xiande; YU Yongqiang

    2003-01-01

    The particle size distribution of rockfill is studied by using granular mechanics, mesomechanics and probability statistics to reveal the relationship of the distribution of particle size to that of the potential energy intensity before fragmentation,which finds out that the potential energy density has a linear relation to the logarithm of particle size and deduces that the distribution of the logarithm of particle size conforms to normal distribution because the distribution of the potential energy density does so. Based on this finding and by including the energy principle of rock fragmentation, the logarithm distribution model of particle size is formulated, which uncovers the natural characteristics of particle sizes on statistical distribution. Exploring the properties of the average value, the expectation, and the unbiased variance of particle size indicates that the expectation does notequal to the average value, but increases with increasing particle size and its ununiformity, and is always larger than the average value, and the unbiased variance increases as the ununiformity and geometric average value increase. A case study proves that the simulated results by the proposed logarithm distribution model accord with the actual data. It is concluded that the logarithm distribution model and Kuz-Ram model can be used to forecast the particle-size distribution of inartificial rockfill while for blasted rockfill, Kuz-Ram model is an option, and in combined application of the two models, it is necessary to do field tests to adjust some parameters of the model.

  14. Size distribution of rare earth elements in coal ash

    Science.gov (United States)

    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. 

  15. The void galaxy survey: photometry, structure and identity of void galaxies

    Science.gov (United States)

    Beygu, B.; Peletier, R. F.; van der Hulst, J. M.; Jarrett, T. H.; Kreckel, K.; van de Weygaert, R.; van Gorkom, J. H.; Aragon-Calvo, M. A.

    2017-01-01

    We analyse photometry from deep B-band images of 59 void galaxies in the Void Galaxy Survey (VGS), together with their near-infrared 3.6 μm and 4.5 μm Spitzer photometry. The VGS galaxies constitute a sample of void galaxies that were selected by a geometric-topological procedure from the Sloan Digital Sky Survey Data Release 7 data release, and which populate the deep interior of voids. Our void galaxies span a range of absolute B-magnitude from MB = -15.5 to -20, while at the 3.6 μm band their magnitudes range from M3.6 = -18 to -24. Their B-[3.6] colour and structural parameters indicate these are star-forming galaxies. A good reflection of the old stellar population, the near-infrared band photometry also provide a robust estimate of the stellar mass, which for the VGS galaxies we confirm to be smaller than 3 × 1010 M⊙. In terms of the structural parameters and morphology, our findings align with other studies in that our VGS galaxy sample consists mostly of small late-type galaxies. Most of them are similar to Sd-Sm galaxies, although a few are irregularly shaped galaxies. The sample even includes two early-type galaxies, one of which is an AGN. Their Sérsic indices are nearly all smaller than n = 2 in both bands and they also have small half-light radii. In all, we conclude that the principal impact of the void environment on the galaxies populating them mostly concerns their low stellar mass and small size.

  16. Multi-component Erlang distribution of plant seed masses and sizes

    Science.gov (United States)

    Fan, San-Hong; Wei, Hua-Rong

    2012-12-01

    The mass and the size distributions of plant seeds are very similar to the multi-component Erlang distribution of final-state particle multiplicities in high-energy collisions. We study the mass, length, width, and thickness distributions of pumpkin and marrow squash seeds in this paper. The corresponding distribution curves are obtained and fitted by using the multi-component Erlang distribution. In the comparison, the method of χ2-testing is used. The mass and the size distributions of the mentioned seeds are shown to obey approximately the multi-component Erlang distribution with the component number being 1.

  17. Particle size distributions in and exhausted from a poultry house

    Science.gov (United States)

    Here we describe a study looking at the full particulate size range of particles in a poultry house. Agricultural particulates are typically thought of as coarse mode dust. But recent emphasis of PM2.5 regulations on pre-cursors such as ammonia and volatile organic compounds increasingly makes it ne...

  18. Effect of the Size Distribution of Nanoscale Dispersed Particles on the Zener Drag Pressure

    Science.gov (United States)

    Eivani, A. R.; Valipour, S.; Ahmed, H.; Zhou, J.; Duszczyk, J.

    2011-04-01

    In this article, a new relationship for the calculation of the Zener drag pressure is described in which the effect of the size distribution of nanoscale dispersed particles is taken into account, in addition to particle radius and volume fraction, which have been incorporated in the existing relationships. Microstructural observations indicated a clear correlation between the size distribution of dispersed particles and recrystallized grain sizes in the AA7020 aluminum alloy. However, the existing relationship to calculate the Zener drag pressure yielded a negligible difference of 0.016 pct between the two structures homogenized at different conditions resulting in totally different size distributions of nanoscale dispersed particles and, consequently, recrystallized grain sizes. The difference in the Zener drag pressure calculated by the application of the new relationship was 5.1 pct, being in line with the experimental observations of the recrystallized grain sizes. Mathematical investigations showed that the ratio of the Zener drag pressure from the new equation to that from the existing equation is maximized when the number densities of all the particles with different sizes are equal. This finding indicates that in the two structures with identical parameters except the size distribution of nanoscale dispersed particles, the one that possesses a broader size distribution of particles, i.e., the number densities of particles with different sizes being equal, gives rise to a larger Zener drag pressure than that having a narrow size distribution of nanoscale dispersed particles, i.e., most of the particles being in the same size range.

  19. Degree Distribution, Rank-size Distribution, and Leadership Persistence in Mediation-Driven Attachment Networks

    CERN Document Server

    Hassan, Md Kamrul; Haque, Syed Arefinul

    2016-01-01

    We investigate the growth of a class of networks in which a new node first picks a mediator at random and connects with $m$ randomly chosen neighbors of the mediator at each time step. We show that degree distribution in such a mediation-driven attachment (MDA) network exhibits power-law $P(k)\\sim k^{-\\gamma(m)}$ with a spectrum of exponents depending on $m$. To appreciate the contrast between MDA and Barab\\'{a}si-Albert (BA) networks, we then discuss their rank-size distribution. To quantify how long a leader, the node with the maximum degree, persists in its leadership as the network evolves, we investigate the leadership persistence probability $F(\\tau)$ i.e. the probability that a leader retains its leadership up to time $\\tau$. We find that it exhibits a power-law $F(\\tau)\\sim \\tau^{-\\theta(m)}$ with persistence exponent $\\theta(m) \\approx 1.51 \\ \\forall \\ m$ in the MDA networks and $\\theta(m) \\rightarrow 1.53$ exponentially with $m$ in the BA networks.

  20. Degree distribution, rank-size distribution, and leadership persistence in mediation-driven attachment networks

    Science.gov (United States)

    Hassan, Md. Kamrul; Islam, Liana; Haque, Syed Arefinul

    2017-03-01

    We investigate the growth of a class of networks in which a new node first picks a mediator at random and connects with m randomly chosen neighbors of the mediator at each time step. We show that the degree distribution in such a mediation-driven attachment (MDA) network exhibits power-law P(k) ∼k - γ(m) with a spectrum of exponents depending on m. To appreciate the contrast between MDA and Barabási-Albert (BA) networks, we then discuss their rank-size distribution. To quantify how long a leader, the node with the maximum degree, persists in its leadership as the network evolves, we investigate the leadership persistence probability F(τ) i.e. the probability that a leader retains its leadership up to time τ. We find that it exhibits a power-law F(τ) ∼τ - θ(m) with persistence exponent θ(m) ≈ 1.51 ∀ m in MDA networks and θ(m) → 1.53 exponentially with m in BA networks.

  1. City-size distributions and the world urban system in the twentieth century.

    Science.gov (United States)

    Ettlinger, N; Archer, J C

    1987-09-01

    "In this paper we trace and interpret changes in the geographical pattern and city-size distribution of the world's largest cities in the twentieth century. Since 1900 the geographical distribution of these cities has become increasingly dispersed; their city-size distribution by rank was nearly linear in 1900 and 1940, and convex in 1980. We interpret the convex distribution which emerged following World War 2 as reflecting an economically integrated but politically and demographically partitioned global urban system. Our interpretation of changes in size distribution of cities emphasizes demographic considerations, largely neglected in previous investigations, including migration and relative rates of population change."

  2. Size distribution of particle systems analyzed with organic photodetectors

    CERN Document Server

    Sentis, Matthias

    2015-01-01

    As part of a consortium between academic and industry, this PhD work investigates the interest and capabilities of organic photo-sensors (OPS) for the optical characterization of suspensions and two-phase flows. The principle of new optical particle sizing instruments is proposed to characterize particle systems confined in a cylinder glass (standard configuration for Process Analytical Technologies). To evaluate and optimize the performance of these systems, a Monte-Carlo model has been specifically developed. This model accounts for the numerous parameters of the system: laser beam profile, mirrors, lenses, sample cell, particle medium properties (concentration, mean & standard deviation, refractive indices), OPS shape and positions, etc. Light scattering by particles is treated either by using Lorenz-Mie theory, Debye, or a hybrid model (that takes into account the geometrical and physical contributions). For diluted media (single scattering), particle size analysis is based on the inversion of scatter...

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

    Science.gov (United States)

    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

  4. Convergence of the frequency-size distribution of global earthquakes

    Science.gov (United States)

    Bell, Andrew F.; Naylor, Mark; Main, Ian G.

    2013-06-01

    The Gutenberg-Richter (GR) frequency-magnitude relation is a fundamental empirical law of seismology, but its form remains uncertain for rare extreme events. Here, we show that the temporal evolution of model likelihoods and parameters for the frequency-magnitude distribution of the global Harvard Centroid Moment Tensor catalog is inconsistent with an unbounded GR relation, despite if being the preferred model at the current time. During the recent spate of 12 great earthquakes in the last 8 years, record-breaking events result in profound steps in favor of the unbounded GR relation. However, between such events the preferred model gradually converges to the tapered GR relation, and the form of the convergence cannot be explained by random sampling of an unbounded GR distribution. The convergence properties are consistent with a global catalog composed of superposed randomly-sampled regional catalogs, each with different upper bounds, many of which have not yet sampled their largest event.

  5. Evolution of shock through a void in foam

    Science.gov (United States)

    Kim, Y.; Smidt, J. M.; Murphy, T. J.; Douglass, M. R.; Devolder, B. G.; Fincke, J. R.; Schmidt, D. W.; Cardenas, T.; Newman, S. G.; Hamilton, C. E.; Sedillo, T. J.; Los Alamos, NM 87544 Team

    2016-10-01

    Marble implosion is an experimental campaign intended to study the effects of heterogeneous mix on fusion burn. A spherical capsule is composed of deuterated plastic foam of controlled pore (or void) size with tritium fill in pores. As capsule implosion evolves, the initially separated deuterium and tritium will mix, producing DT yields. Void evolution during implosion is of interest for the Marble campaign. A shock tube, driven by the laser at Omega, was designed to study the evolution of a shock through a foam-filled ``void'' and subsequent void evolution. Targets were comprised of a 100 mg/cc CH foam tube containing a 200-µm diameter, lower density doped foam sphere. High-quality, radiographic images were obtained from both 2% iodine-doped in plastic foam and 15% tin-doped in aerogel foam. These experiments will be used to inform simulations.

  6. Void Growth in Single and Bicrystalline Metals: Atomistic Calculations

    Science.gov (United States)

    Traiviratana, Sirirat; Bringa, Eduardo M.; Benson, David J.; Meyers, Marc A.

    2007-12-01

    MD simulations in monocrystalline and bicrystalline copper were carried out with LAMMPS to reveal void growth mechanisms. The specimens were subjected to both tensile uniaxial and hydrostatic strains; the results confirm that the emission of (shear) loops is the primary mechanism of void growth. However, these shear loops develop along two slip planes (and not one, as previously thought), in a heretofore unidentified mechanism of cooperative growth. The emission of dislocations from voids is the first stage, and their reaction and interaction is the second stage. These loops, forming initially on different {111} planes, join at the intersection, the Burgers vector of the dislocations being parallel to the intersection of two {111} planes: a direction. Thus, the two dislocations cancel at the intersection and a biplanar shear loop is formed. The expansion of the loops and their cross slip leads to the severely work hardened layer surrounding a growing void. Calculations were carried out on voids with different sizes, and a size dependence of the stress response to emitted dislocations was observed, in disagreement with the Gurson model[1] which is scale independent. Calculations were also carried out for a void at the interface between two grains.

  7. Number size distributions and seasonality of submicron particles in Europe 2008-2009

    NARCIS (Netherlands)

    Asmi, A.; Wiedensohler, A.; Laj, P.; Fjaeraa, A.-M.; Sellegri, K.; Birmili, W.; Weingartner, E.; Baltensperger, U.; Zdimal, V.; Zikova, N.; Putaud, J.-P.; Marinoni, A.; Tunved, P.; Hansson, H.-C.; Fiebig, M.; Kivekäs, N.; Lihavainen, H.; Asmi, E.; Ulevicius, V.; Aalto, P.P.; Swietlicki, E.; Kristensson, A.; Mihalopoulos, N.; Kalivitis, N.; Kalapov, I.; Kiss, G.; Leeuw, G. de; Henzing, B.; Harrison, R.M.; Beddows, D.; O'Dowd, C.; Jennings, S.G.; Flentje, H.; Weinhold, K.; Meinhardt, F.; Ries, L.; Kulmala, M.

    2011-01-01

    Two years of harmonized aerosol number size distribution data from 24 European field monitoring sites have been analysed. The results give a comprehensive overview of the European near surface aerosol particle number concentrations and number size distributions between 30 and 500 nm of dry particle

  8. An analysis of the size distribution of Italian firms by age

    Science.gov (United States)

    Cirillo, Pasquale

    2010-02-01

    In this paper we analyze the size distribution of Italian firms by age. In other words, we want to establish whether the way that the size of firms is distributed varies as firms become old. As a proxy of size we use capital. In [L.M.B. Cabral, J. Mata, On the evolution of the firm size distribution: Facts and theory, American Economic Review 93 (2003) 1075-1090], the authors study the distribution of Portuguese firms and they find out that, while the size distribution of all firms is fairly stable over time, the distributions of firms by age groups are appreciably different. In particular, as the age of the firms increases, their size distribution on the log scale shifts to the right, the left tails becomes thinner and the right tail thicker, with a clear decrease of the skewness. In this paper, we perform a similar analysis with Italian firms using the CEBI database, also considering firms’ growth rates. Although there are several papers dealing with Italian firms and their size distribution, to our knowledge a similar study concerning size and age has not been performed yet for Italy, especially with such a big panel.

  9. A model study of the size and composition distribution of aerosols in an aircraft exhaust

    Energy Technology Data Exchange (ETDEWEB)

    Sorokin, A.A. [SRC `ECOLEN`, Moscow (Russian Federation)

    1997-12-31

    A two-dimensional, axisymmetric flow field model which includes water and sulphate aerosol formation represented by moments of the size and composition distribution function is used to calculate the effect of radial turbulent jet mixing on the aerosol size distribution and mean modal composition. (author) 6 refs.

  10. The Effects of Mergers and Acquisitions on the Firm Size Distribution

    NARCIS (Netherlands)

    Cefis, E.; Marsili, O.; Schenk, E.J.J

    2006-01-01

    This paper provides new empirical evidence on the effects of mergers and acquisitions on the shape of the firm size distribution (FSD), by using data of the population of manufacturing firms in the Netherlands. Our analysis shows that M&As do not affect the size distribution when we consider the

  11. The effects of mergers and acquisitions on the firm size distribution

    NARCIS (Netherlands)

    Cefis, E.; Marsili, Orietta; Schenk, E.J.J.

    2008-01-01

    This paper provides new empirical evidence on the effects of mergers and acquisitions (M&As) on the shape of the firm size distribution, by using data of the population of manufacturing firms in the Netherlands. Our analysis shows that M&As do not affect the size distribution when we consider the

  12. The effects of mergers and acquisitions on the firm size distribution

    NARCIS (Netherlands)

    E. Cefis (Elena); O. Marsili (Orietta); H. Schenk (Hans)

    2009-01-01

    textabstractThis paper provides new empirical evidence on the effects of mergers and acquisitions (M&As) on the shape of the firm size distribution, by using data of the population of manufacturing firms in the Netherlands. Our analysis shows that M&As do not affect the size distribution when we

  13. [Mathematical processing of human platelet distribution according to size for determination of cell heterogeneity].

    Science.gov (United States)

    Kosmovskiĭ, S Iu; Vasin, S L; Rozanova, I B; Sevast'ianov, V I

    1999-01-01

    The paper proposes a method for mathematical treatment of the distribution of human platelets by sizes to detect the heterogeneity of cell populations. Its use allowed the authors to identify three platelet populations that have different parameters of size distribution. The proposed method opens additional vistas for analyzing the heterogeneity of platelet populations without sophisticating experimental techniques.

  14. Control over Particle Size Distribution by Autoclaving Poloxamer-Stabilized Trimyristin Nanodispersions.

    Science.gov (United States)

    Göke, Katrin; Roese, Elin; Arnold, Andreas; Kuntsche, Judith; Bunjes, Heike

    2016-09-06

    Lipid nanoparticles are under investigation as delivery systems for poorly water-soluble drugs. The particle size in these dispersions strongly influences important pharmaceutical properties like biodistribution and drug loading capacity; it should be below 500 nm for direct injection into the bloodstream. Consequently, small particles with a narrow particle size distribution are desired. Hitherto, there are, however, only limited possibilities for the preparation of monodisperse, pharmaceutically relevant dispersions. In this work, the effect of autoclaving at 121 °C on the particle size distribution of lipid nanoemulsions and -suspensions consisting of the pharmaceutically relevant components trimyristin and poloxamer 188 was studied. Additionally, the amount of emulsifier needed to stabilize both untreated and autoclaved particles was assessed. In our study, four dispersions of mean particle sizes from 45 to 150 nm were prepared by high-pressure melt homogenization. The particle size distribution before and after autoclaving was characterized using static and dynamic light scattering, differential scanning calorimetry, and transmission electron microscopy. Asymmetrical flow field-flow fractionation was used for particle size distribution analyses and for the determination of free poloxamer 188. Upon autoclaving, the mean particle size increased to up to 200 nm, but not proportionally to the initial size. At the same time, the particle size distribution width decreased remarkably. Heat treatment thus seems to be a promising approach to achieve the desired narrow particle size distribution of such dispersions. Related to the lipid content, suspension particles needed more emulsifier for stabilization than emulsion droplets, and smaller particles more than larger ones.

  15. 3D Hail Size Distribution Interpolation/Extrapolation Algorithm

    Science.gov (United States)

    Lane, John

    2013-01-01

    Radar data can usually detect hail; however, it is difficult for present day radar to accurately discriminate between hail and rain. Local ground-based hail sensors are much better at detecting hail against a rain background, and when incorporated with radar data, provide a much better local picture of a severe rain or hail event. The previous disdrometer interpolation/ extrapolation algorithm described a method to interpolate horizontally between multiple ground sensors (a minimum of three) and extrapolate vertically. This work is a modification to that approach that generates a purely extrapolated 3D spatial distribution when using a single sensor.

  16. On cavitation instabilities with interacting voids

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2012-01-01

    voids so far apart that the radius of the plastic zone around each void is less than 1% of the current spacing between the voids, can still affect each others at the occurrence of a cavitation instability such that one void stops growing while the other grows in an unstable manner. On the other hand...

  17. New algorithm and system for measuring size distribution of blood cells

    Institute of Scientific and Technical Information of China (English)

    Cuiping Yao(姚翠萍); Zheng Li(李政); Zhenxi Zhang(张镇西)

    2004-01-01

    In optical scattering particle sizing, a numerical transform is sought so that a particle size distribution can be determined from angular measurements of near forward scattering, which has been adopted in the measurement of blood cells. In this paper a new method of counting and classification of blood cell, laser light scattering method from stationary suspensions, is presented. The genetic algorithm combined with nonnegative least squared algorithm is employed to inverse the size distribution of blood cells. Numerical tests show that these techniques can be successfully applied to measuring size distribution of blood cell with high stability.

  18. Evidence of bimodal crystallite size distribution in {mu}c-Si:H films

    Energy Technology Data Exchange (ETDEWEB)

    Ram, Sanjay K. [Laboratoire de Physique des Interfaces et des Couches Minces (UMR 7647 du CNRS), Ecole Polytechnique, 91128 Palaiseau Cedex (France); Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016 (India)], E-mail: sanjayk.ram@gmail.com; Islam, Md. Nazrul [QAED-SRG, Space Application Centre (ISRO), Ahmedabad 380015 (India); Kumar, Satyendra [Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016 (India); Roca i Cabarrocas, P. [Laboratoire de Physique des Interfaces et des Couches Minces (UMR 7647 du CNRS), Ecole Polytechnique, 91128 Palaiseau Cedex (France)

    2009-03-15

    We report on the microstructural characterization studies carried out on plasma deposited highly crystalline undoped microcrystalline silicon films to explore the crystallite size distribution present in this material. The modeling of results of spectroscopic ellipsometry using two different sized crystallites is corroborated by the deconvolution of experimental Raman profiles using a modeling method that incorporates a bimodal size distribution of crystallites. The presence of a bimodal size distribution of crystallites is demonstrated as well by the results of atomic force microscopy and X-ray diffraction studies. The qualitative agreement between the results of different studies is discussed.

  19. The catalytic diversity of zeolites: confinement and solvation effects within voids of molecular dimensions.

    Science.gov (United States)

    Gounder, Rajamani; Iglesia, Enrique

    2013-05-01

    chemical composition, thus enabling voids of a given size and shape to provide the "right fit" for a given elementary step, defined as that which minimizes Gibbs free energies of activation. Tighter confinement is preferred at low temperatures because enthalpic gains prevail over concomitant entropic losses, while looser fits are favored at high temperatures because entropy gains offset losses in enthalpic stabilization. Confinement and solvation by van der Waals forces are not directly involved in the making or breaking of strong chemical bonds; yet, they confer remarkable diversity to zeolites, in spite of their structural rigidity and their common aluminosilicate composition. A single zeolite can itself contain a range of local void environments, each with distinct reactivity and selectivity; as a result, varying the distribution of protons among these locations within a given framework or modifying a given location by partial occlusion of the void space can extend the range of catalytic opportunities for zeolites. Taken together with theoretical tools that accurately describe van der Waals interactions between zeolite voids and confined guests and with synthetic protocols that place protons or space-filling moieties at specific locations, these concepts promise to broaden the significant impact and catalytic diversity already shown by microporous solids.

  20. Experimental study on bubble size distributions in a direct-contact evaporator

    Directory of Open Access Journals (Sweden)

    Ribeiro Jr. C. P.

    2004-01-01

    Full Text Available Experimental bubble size distributions and bubble mean diameters were obtained by means of a photographic technique for a direct-contact evaporator operating in the quasi-steady-state regime. Four gas superficial velocities and three different spargers were analysed for the air-water system. In order to assure the statistical significance of the determined size distributions, a minimum number of 450 bubbles was analysed for each experimental condition. Some runs were also conducted with an aqueous solution of sucrose to study the solute effect on bubble size distribution. For the lowest gas superficial velocity considered, at which the homogeneous bubbling regime is observed, the size distribution was log-normal and depended on the orifice diameter in the sparger. As the gas superficial velocity was increased, the size distribution progressively acquired a bimodal shape, regardless of the sparger employed. The presence of sucrose in the continuous phase led to coalescence hindrance.

  1. ON ESTIMATION AND HYPOTHESIS TESTING OF THE GRAIN SIZE DISTRIBUTION BY THE SALTYKOV METHOD

    Directory of Open Access Journals (Sweden)

    Yuri Gulbin

    2011-05-01

    Full Text Available The paper considers the problem of validity of unfolding the grain size distribution with the back-substitution method. Due to the ill-conditioned nature of unfolding matrices, it is necessary to evaluate the accuracy and precision of parameter estimation and to verify the possibility of expected grain size distribution testing on the basis of intersection size histogram data. In order to review these questions, the computer modeling was used to compare size distributions obtained stereologically with those possessed by three-dimensional model aggregates of grains with a specified shape and random size. Results of simulations are reported and ways of improving the conventional stereological techniques are suggested. It is shown that new improvements in estimating and testing procedures enable grain size distributions to be unfolded more efficiently.

  2. Simulation-aided constitutive law development - Assessment of low triaxiality void nucleation models via extended finite element method

    Science.gov (United States)

    Zhao, Jifeng; Kontsevoi, Oleg Y.; Xiong, Wei; Smith, Jacob

    2017-05-01

    In this work, a multi-scale computational framework has been established in order to investigate, refine and validate constitutive behaviors in the context of the Gurson-Tvergaard-Needleman (GTN) void mechanics model. The eXtended Finite Element Method (XFEM) has been implemented in order to (1) develop statistical volume elements (SVE) of a matrix material with subscale inclusions and (2) to simulate the multi-void nucleation process due to interface debonding between the matrix and particle phases. Our analyses strongly suggest that under low stress triaxiality the nucleation rate of the voids f˙ can be well described by a normal distribution function with respect to the matrix equivalent stress (σe), as opposed to that proposed (σbar + 1 / 3σkk) in the original form of the single void GTN model. The modified form of the multi-void nucleation model has been validated based on a series of numerical experiments with different loading conditions, material properties, particle shape/size and spatial distributions. The utilization of XFEM allows for an invariant finite element mesh to represent varying microstructures, which implies suitability for drastically reducing complexity in generating the finite element discretizations for large stochastic arrays of microstructure configurations. The modified form of the multi-void nucleation model is further applied to study high strength steels by incorporating first principles calculations. The necessity of using a phenomenological interface separation law has been fully eliminated and replaced by the physics-based cohesive relationship obtained from Density Functional Theory (DFT) calculations in order to provide an accurate macroscopic material response.

  3. Iteration method for the inversion of simulated multiwavelength lidar signals to determine aerosol size distribution

    Institute of Scientific and Technical Information of China (English)

    Tao Zong-Ming; Zhang Yin-Chao; Liu Xiao-Qin; Tan Kun; Shao Shi-Sheng; Hu Huan-Ling; Zhang Gai-Xia; Lü Yong-Hui

    2004-01-01

    A new method is proposed to derive the size distribution of aerosol from the simulated multiwavelength lidar extinction coefficients. The basis for this iteration is to consider the extinction efficiency factor of particles as a set of weighting function covering the entire radius region of a distribution. The weighting functions are calculated exactly from Mie theory. This method extends the inversion region by subtracting some extinction coefficient. The radius range of simulated size distribution is 0.1-10.0μm, the inversion radius range is 0.1-2.0μm, but the inverted size distributions are in good agreement with the simulated one.

  4. Droplet breakup in subsea oil releases--part 2: predictions of droplet size distributions with and without injection of chemical dispersants.

    Science.gov (United States)

    Johansen, Øistein; Brandvik, Per Johan; Farooq, Umer

    2013-08-15

    A new method for prediction of droplet size distributions from subsea oil and gas releases is presented in this paper. The method is based on experimental data obtained from oil droplet breakup experiments conducted in a new test facility at SINTEF. The facility is described in a companion paper, while this paper deals with the theoretical basis for the model and the empirical correlations used to derive the model parameters from the available data from the test facility. A major issue dealt with in this paper is the basis for extrapolation of the data to full scale (blowout) conditions. Possible contribution from factors such as buoyancy flux and gas void fraction are discussed and evaluated based on results from the DeepSpill field experiment.

  5. Porosity and pore size distribution in a sedimentary rock: Implications for the distribution of chlorinated solvents

    Science.gov (United States)

    Shapiro, Allen M.; Evans, Chrsitopher E.; Hayes, Erin C.

    2017-01-01

    Characterizing properties of the rock matrix that control retention and release of chlorinated solvents is essential in evaluating the extent of contamination and the application of remediation technologies in fractured rock. Core samples from seven closely spaced boreholes in a mudstone subject to trichloroethene (TCE) contamination were analyzed using Mercury Intrusion Porosimetry to investigate porosity and pore size distribution as a function of mudstone characteristics, and depth and lateral extent in the aquifer; organic carbon content was also evaluated to identify the potential for adsorption. Porosity and retardation factor varied over two orders of magnitude, with the largest porosities and largest retardation factors associated with carbon-rich mudstone layers. Larger porosities were also measured in the shallow rock that has been subject to enhanced groundwater flow. Porosity also varied over more than an order of magnitude in spatially continuous mudstone layers. The analyses of the rock cores indicated that the largest pore diameters may be accessible to entry of the nonaqueous form of TCE. Although the porosity associated with the largest pore diameters is small (~ 0.1%), that volume of TCE can significantly affect the total TCE that is retained in the rock matrix. The dimensions of the largest pore diameters may also be accessible to microbes responsible for reductive dechlorination; however, the small percentage of the pore space that can accommodate microbes may limit the extent of reductive dechlorination in the rock matrix.

  6. Porosity and pore size distribution in a sedimentary rock: Implications for the distribution of chlorinated solvents.

    Science.gov (United States)

    Shapiro, Allen M; Evans, Christopher E; Hayes, Erin C

    2017-08-01

    Characterizing properties of the rock matrix that control retention and release of chlorinated solvents is essential in evaluating the extent of contamination and the application of remediation technologies in fractured rock. Core samples from seven closely spaced boreholes in a mudstone subject to trichloroethene (TCE) contamination were analyzed using Mercury Intrusion Porosimetry to investigate porosity and pore size distribution as a function of mudstone characteristics, and depth and lateral extent in the aquifer; organic carbon content was also evaluated to identify the potential for adsorption. Porosity and retardation factor varied over two orders of magnitude, with the largest porosities and largest retardation factors associated with carbon-rich mudstone layers. Larger porosities were also measured in the shallow rock that has been subject to enhanced groundwater flow. Porosity also varied over more than an order of magnitude in spatially continuous mudstone layers. The analyses of the rock cores indicated that the largest pore diameters may be accessible to entry of the nonaqueous form of TCE. Although the porosity associated with the largest pore diameters is small (~0.1%), that volume of TCE can significantly affect the total TCE that is retained in the rock matrix. The dimensions of the largest pore diameters may also be accessible to microbes responsible for reductive dechlorination; however, the small percentage of the pore space that can accommodate microbes may limit the extent of reductive dechlorination in the rock matrix. Published by Elsevier B.V.

  7. Why liquid displacement methods are sometimes wrong in estimating the pore-size distribution

    NARCIS (Netherlands)

    Gijsbertsen-Abrahamse, A.J.; Boom, R.M.; Padt, van der A.

    2004-01-01

    The liquid displacement method is a commonly used method to determine the pore size distribution of micro- and ultrafiltration membranes. One of the assumptions for the calculation of the pore sizes is that the pores are parallel and thus are not interconnected. To show that the estimated pore size

  8. A facile synthesis of Te nanoparticles with binary size distribution by green chemistry.

    Science.gov (United States)

    He, Weidong; Krejci, Alex; Lin, Junhao; Osmulski, Max E; Dickerson, James H

    2011-04-01

    Our work reports a facile route to colloidal Te nanocrystals with binary uniform size distributions at room temperature. The binary-sized Te nanocrystals were well separated into two size regimes and assembled into films by electrophoretic deposition. The research provides a new platform for nanomaterials to be efficiently synthesized and manipulated.

  9. Bipartite Producer-Consumer Networks and the Size Distribution of Firms

    CERN Document Server

    Dahui, W; Zengru, D; Dahui, Wang; Li, Zhou; Zengru, Di

    2005-01-01

    A bipartite producer-consumer network is constructed to describe the industrial structure. The edges from consumer to producer represent the choices of the consumer for the final products and the degree of producer can represent its market share. So the size distribution of firms can be characterized by producer's degree distribution. The probability for a producer receiving a new consumption is determined by its competency described by initial attractiveness and the self-reinforcing mechanism in the competition described by preferential attachment. The cases with constant total consumption and with growing market are studied. The following results are obtained: 1, Without market growth and a uniform initial attractiveness $a$, the final distribution of firm sizes is Gamma distribution for $a>1$ and is exponential for $a=1$. If $a<1$, the distribution is power in small size and exponential in upper tail; 2, For a growing market, the size distribution of firms obeys the power law. The exponent is affected b...

  10. RESUSPENSION METHOD FOR ROAD SURFACE DUST COLLECTION AND AERODYNAMIC SIZE DISTRIBUTION CHARACTERIZATION

    Institute of Scientific and Technical Information of China (English)

    Jianhua Chen; Hongfeng Zheng; Wei Wang; Hongjie Liu; Ling Lu; Linfa Bao; Lihong Ren

    2006-01-01

    Traffic-generated fugitive dust is a source of urban atmospheric particulate pollution in Beijing. This paper introduces the resuspension method, recommended by the US EPA in AP-42 documents, for collecting Beijing road-surface dust. Analysis shows a single-peak distribution in the number size distribution and a double-peak mode for mass size distribution of the road surface dust. The median diameter of the mass concentration distribution of the road dust on a high-grade road was higher than that on a low-grade road. The ratio of PM2.5 to PM10 was consistent with that obtained in a similar study for Hong Kong. For the two selected road samples, the average relative deviation of the size distribution was 10.9% and 11.9%. All results indicate that the method introduced in this paper can effectively determine the size distribution of fugitive dust from traffic.

  11. On bimodal size distribution of spin clusters in the one dimensional Ising model

    OpenAIRE

    Ivanytskyi, A. I.; Chelnokov, V. O.

    2015-01-01

    The size distribution of geometrical spin clusters is exactly found for the one dimensional Ising model of finite extent. For the values of lattice constant $\\beta$ above some "critical value" $\\beta_c$ the found size distribution demonstrates the non-monotonic behavior with the peak corresponding to the size of largest available cluster. In other words, at high values of lattice constant there are two ways to fill the lattice: either to form a single largest cluster or to create many cluster...

  12. Effect of the size distribution of nanoscale dispersed particles on the Zener drag pressure

    OpenAIRE

    Eivani, A.R.; Valipour, S.; Ahmed, H.; Zhou, J; Duszczyk, J.

    2010-01-01

    In this article, a new relationship for the calculation of the Zener drag pressure is described in which the effect of the size distribution of nanoscale dispersed particles is taken into account, in addition to particle radius and volume fraction, which have been incorporated in the existing relationships. Microstructural observations indicated a clear correlation between the size distribution of dispersed particles and recrystallized grain sizes in the AA7020 aluminum alloy. However, the ex...

  13. Bimodal distribution of the magnetic dipole moment in nanoparticles with a monomodal distribution of the physical size

    NARCIS (Netherlands)

    van Rijssel, Jozef; Kuipers, Bonny W M; Erne, Ben

    2015-01-01

    High-frequency applications of magnetic nanoparticles, such as therapeutic hyperthermia and magnetic particle imaging, are sensitive to nanoparticle size and dipole moment. Usually, it is assumed that magnetic nanoparticles with a log-normal distribution of the physical size also have a log-normal d

  14. Bimodal distribution of the magnetic dipole moment in nanoparticles with a monomodal distribution of the physical size

    Energy Technology Data Exchange (ETDEWEB)

    Rijssel, Jos van; Kuipers, Bonny W.M.; Erné, Ben H., E-mail: B.H.Erne@uu.nl

    2015-04-15

    High-frequency applications of magnetic nanoparticles, such as therapeutic hyperthermia and magnetic particle imaging, are sensitive to nanoparticle size and dipole moment. Usually, it is assumed that magnetic nanoparticles with a log-normal distribution of the physical size also have a log-normal distribution of the magnetic dipole moment. Here, we test this assumption for different types of superparamagnetic iron oxide nanoparticles in the 5–20 nm range, by multimodal fitting of magnetization curves using the MINORIM inversion method. The particles are studied while in dilute colloidal dispersion in a liquid, thereby preventing hysteresis and diminishing the effects of magnetic anisotropy on the interpretation of the magnetization curves. For two different types of well crystallized particles, the magnetic distribution is indeed log-normal, as expected from the physical size distribution. However, two other types of particles, with twinning defects or inhomogeneous oxide phases, are found to have a bimodal magnetic distribution. Our qualitative explanation is that relatively low fields are sufficient to begin aligning the particles in the liquid on the basis of their net dipole moment, whereas higher fields are required to align the smaller domains or less magnetic phases inside the particles. - Highlights: • Multimodal fits of dilute ferrofluids reveal when the particles are multidomain. • No a priori shape of the distribution is assumed by the MINORIM inversion method. • Well crystallized particles have log-normal TEM and magnetic size distributions. • Defective particles can combine a monomodal size and a bimodal dipole moment.

  15. Geospatial modeling of fire-size distributions in historical low-severity fire regimes

    Science.gov (United States)

    McKenzie, D.; Kellogg, L. B.; Larkin, N. K.

    2006-12-01

    Low-severity fires are recorded by fire-scarred trees. These records can provide temporal depth for reconstructing fire history because one tree may record dozens of separate fires over time, thereby providing adequate sample size for estimating fire frequency. Estimates of actual fire perimeters from these point-based records are uncertain, however, because fire boundaries can only be located approximately. We indirectly estimate fire-size distributions without attempting to establish individual fire perimeters. The slope and intercept of the interval-area function, a power-law relationship between sample area and mean fire-free intervals for that area, provide surrogates for the moments of a fire-size distribution, given a distribution of fire- free intervals. Analogously, by deconstructing variograms that use a binary distance measure (Sorensen's index) for the similarity of the time-series of fires recorded by pairs of recorder trees, we provide estimates of modal fire size. We link both variograms and interval-area functions to fire size distributions by simulating fire size distributions on neutral landscapes with and without right- censoring to represent topographic controls on maximum fire size. From parameters of the two functions produced by simulations we can back-estimate means and variances of fire sizes on real landscapes. This scale-based modeling provides a robust alternative to empirical and heuristic methods and a means to extrapolate estimates of fire-size distributions to unsampled landscapes.

  16. Vertical profile and aerosol size distribution measurements in Iceland (LOAC)

    Science.gov (United States)

    Dagsson Waldhauserova, Pavla; Olafsson, Haraldur; Arnalds, Olafur; Renard, Jean-Baptiste; Vignelles, Damien; Verdier, Nicolas

    2014-05-01

    Cold climate and high latitudes regions contain important dust sources where dust is frequently emitted, foremost from glacially-derived sediments of riverbeds or ice-proximal areas (Arnalds, 2010; Bullard, 2013). Iceland is probably the most active dust source in the arctic/sub-arctic region (Dagsson-Waldhauserova, 2013). The frequency of days with suspended dust exceeds 34 dust days annually. Icelandic dust is of volcanic origin; it is very dark in colour and contains sharp-tipped shards with bubbles. Such properties allow even large particles to be easily transported long distances. Thus, there is a need to better understand the spatial and temporal variability of these dusts. Two launch campaigns of the Light Optical Aerosols Counter (LOAC) were conducted in Iceland with meteorological balloons. LOAC use a new optical design that allows to retrieve the size concentrations in 19 size classes between 0.2 and 100 microm, and to provide an estimate of the main nature of aerosols. Vertical stratification and aerosol composition of the subarctic atmosphere was studied in detail. The July 2011 launch represented clean non-dusty season with low winds while the November 2013 launch was conducted during the high winds after dusty period. For the winter flight (performed from Reykjavik), the nature of aerosols strongly changed with altitude. In particular, a thin layer of volcanic dust was observed at an altitude of 1 km. Further LOAC measurements are needed to understand the implication of Icelandic dust to the Arctic warming and climate change. A new campaign of LAOC launches is planned for May 2014. Reference: Arnalds, O., 2010. Dust sources and deposition of aeolian materials in Iceland. Icelandic Agricultural Sciences 23, 3-21. Bullard, J.E., 2013. Contemporary glacigenic inputs to the dust cycle. Earth Surface Processes and Landforms 38, 71-89. Dagsson-Waldhauserova, P., Arnalds O., Olafsson H. 2013. Long-term frequency and characteristics of dust storm events in

  17. Precision cosmography with stacked voids

    CERN Document Server

    Lavaux, Guilhem

    2011-01-01

    We present a purely geometrical method for probing the expansion history of the Universe from the observation of the shape of stacked voids in spectroscopic re dshift surveys. Our method is an Alcock-Pasczinsky test based on the average sphericity of voids posited on the local isotropy of the Universe. It works by comparing the temporal extent of cosmic voids along the line of sight with their angular, spatial extent. We describe the algorithm that we use to detect and stack voids in redshift shells on the light cone and test it on mock light cones produced from N-body simulations. We establish a robust statistical model for estimating the average stretching of voids in redshift space and quantify the contamination by peculiar velocities. Finally, we assess the capability of this approach to constrain dark energy parameters in terms of the figure of merit (FoM) of the dark energy task force and in particular of the proposed Euclid mission which is particularly suited for this technique since it is a spectrosc...

  18. Size-selected genomic libraries: the distribution and size-fractionation of restricted genomic DNA fragments by gel electrophoresis.

    Science.gov (United States)

    Gondo, Y

    1995-02-01

    By using one-dimensional genome scanning, it is possible to directly identify the restricted genomic DNA fragment that reflects the site of genetic change. The subsequent strategies to obtain the molecular clones of the corresponding restriction fragment are usually as follows: (i) the restriction of a mass quantity of an appropriate genomic DNA, (ii) the size-fractionation of the restricted DNA on a preparative electrophoresis gel in order to enrich the corresponding restriction fragment, (iii) the construction of the size-selected libraries from the fractionated genomic DNA, and (iv) the screening of the library to obtain an objective clone which is identified on the analytical genome scanning gel. A knowledge of the size distribution pattern of restriction fragments of the genomic DNA makes it possible to calculate the heterogeneity or complexity of the restriction fragment in each size-fraction. This manuscript first describes the distribution of the restriction fragments with respect to their length. Some examples of the practical application of this theory to genome scanning is then discussed using presumptive genome scanning gels. The way to calculate such DNA complexities in the prepared size-fractionated samples is also demonstrated. Such information should greatly facilitate the design of experimental strategies for the cloning of a certain size of genomic DNA after digestion with restriction enzyme(s) as is the case with genome scanning.

  19. Self-similarity and universality of void density profiles in simulation and SDSS data

    CERN Document Server

    Nadathur, S; Diego, J M; Iliev, I T; Gottlöber, S; Watson, W A; Yepes, G

    2014-01-01

    The stacked density profile of cosmic voids in the galaxy distribution provides an important tool for the use of voids for precision cosmology. We study the density profiles of voids identified using the ZOBOV watershed transform algorithm in realistic mock luminous red galaxy (LRG) catalogues from the Jubilee simulation, as well as in void catalogues constructed from the SDSS LRG and Main Galaxy samples. We compare different methods for reconstructing density profiles scaled by the void radius and show that the most commonly used method based on counts in shells and simple averaging is statistically flawed as it underestimates the density in void interiors. We provide two alternative methods that do not suffer from this effect; one based on Voronoi tessellations is also easily able to account from artefacts due to finite survey boundaries and so is more suitable when comparing simulation data to observation. Using this method we show that voids in simulation are exactly self-similar, meaning that their avera...

  20. Uncertainty in volcanic ash particle size distribution and implications for infrared remote sensing and airspace management

    Science.gov (United States)

    Western, L.; Watson, M.; Francis, P. N.

    2014-12-01

    Volcanic ash particle size distributions are critical in determining the fate of airborne ash in drifting clouds. A significant amount of global airspace is managed using dispersion models that rely on a single ash particle size distribution, derived from a single source - Hobbs et al., 1991. This is clearly wholly inadequate given the range of magmatic compositions and eruptive styles that volcanoes present. Available measurements of airborne ash lognormal particle size distributions show geometric standard deviation values that range from 1.0 - 2.5, with others showing mainly polymodal distributions. This paucity of data pertaining to airborne sampling of volcanic ash results in large uncertainties both when using an assumed distribution to retrieve mass loadings from satellite observations and when prescribing particle size distributions of ash in dispersion models. Uncertainty in the particle size distribution can yield order of magnitude differences to mass loading retrievals of an ash cloud from satellite observations, a result that can easily reclassify zones of airspace closure. The uncertainty arises from the assumptions made when defining both the geometric particle size and particle single scattering properties in terms of an effective radius. This has significant implications for airspace management and emphasises the need for an improved quantification of airborne volcanic ash particle size distributions.

  1. Fissure formation in coke. 3: Coke size distribution and statistical analysis

    Energy Technology Data Exchange (ETDEWEB)

    D.R. Jenkins; D.E. Shaw; M.R. Mahoney [CSIRO, North Ryde, NSW (Australia). Mathematical and Information Sciences

    2010-07-15

    A model of coke stabilization, based on a fundamental model of fissuring during carbonisation is used to demonstrate the applicability of the fissuring model to actual coke size distributions. The results indicate that the degree of stabilization is important in determining the size distribution. A modified form of the Weibull distribution is shown to provide a better representation of the whole coke size distribution compared to the Rosin-Rammler distribution, which is generally only fitted to the lump coke. A statistical analysis of a large number of experiments in a pilot scale coke oven shows reasonably good prediction of the coke mean size, based on parameters related to blend rank, amount of low rank coal, fluidity and ash. However, the prediction of measures of the spread of the size distribution is more problematic. The fissuring model, the size distribution representation and the statistical analysis together provide a comprehensive capability for understanding and predicting the mean size and distribution of coke lumps produced during carbonisation. 12 refs., 16 figs., 4 tabs.

  2. Estimating Functions of Distributions Defined over Spaces of Unknown Size

    Directory of Open Access Journals (Sweden)

    David H. Wolpert

    2013-10-01

    Full Text Available We consider Bayesian estimation of information-theoretic quantities from data, using a Dirichlet prior. Acknowledging the uncertainty of the event space size m and the Dirichlet prior’s concentration parameter c, we treat both as random variables set by a hyperprior. We show that the associated hyperprior, P(c, m, obeys a simple “Irrelevance of Unseen Variables” (IUV desideratum iff P(c, m = P(cP(m. Thus, requiring IUV greatly reduces the number of degrees of freedom of the hyperprior. Some information-theoretic quantities can be expressed multiple ways, in terms of different event spaces, e.g., mutual information. With all hyperpriors (implicitly used in earlier work, different choices of this event space lead to different posterior expected values of these information-theoretic quantities. We show that there is no such dependence on the choice of event space for a hyperprior that obeys IUV. We also derive a result that allows us to exploit IUV to greatly simplify calculations, like the posterior expected mutual information or posterior expected multi-information. We also use computer experiments to favorably compare an IUV-based estimator of entropy to three alternative methods in common use. We end by discussing how seemingly innocuous changes to the formalization of an estimation problem can substantially affect the resultant estimates of posterior expectations.

  3. Can the Size Distributions of Talus Particles be Predicted from Fracture Spacing Distributions on Adjacent Bedrock Cliffs?

    Science.gov (United States)

    Verdian, J. P.; Sklar, L. S.; Moore, J. R.; Rosenberg, D. J.

    2016-12-01

    What controls the size of sediments produced on hillslopes and supplied to river channels? This is an important but unanswered question in geomorphology and sedimentology. One hypothesis is that the initial size distribution of rock fragments eroded from bedrock is related to the distribution of spacing between pre-existing fractures in the bedrock. Slopes of talus that accumulate below eroding cliffs provide a simple natural experiment to test this hypothesis. We studied talus slopes and cliff faces at more than 20 locations in California, USA, where cliff retreat rates were previously measured by Moore et al., 2009. Rock types included andesite, basalt, granodiorite and meta-sediment. To quantify fracture spacing we measured fracture frequency and orientation along scan lines at the base of the cliff. We also used scaled photographs of the cliff face to characterize the shape, size and surface area of discrete blocks. We measured talus particle size distributions using surface point counts along transects oriented downslope from the cliff face, and mapped facies of distinct size distributions. To explore the effect of chemical weathering on talus size we sampled cliff faces and talus particles for x-ray fluorescence analysis to test for depletion of labile cations relative to source rock. Preliminary results suggest that talus size distributions are strongly correlated with bedrock fracture spacing, although systematic differences do occur. In some cases, talus sizes are larger than the spacing between fractures because the detached particles still retain truncated fractures. In other cases, talus is smaller than cliff fracture spacing, presumably because particle size is reduced by fragmentation on impact and weathering during transport down the talus slope. Further analysis will explore whether cliff retreat rate and extent of chemical weathering, as well as rock type and local climate, can explain between-site differences in the size of particles produced.

  4. Are range-size distributions consistent with species-level heritability?

    DEFF Research Database (Denmark)

    Borregaard, Michael Krabbe; Gotelli, Nicholas; Rahbek, Carsten

    2012-01-01

    been that it is not compatible with the observed shape of present-day species range-size distributions (SRDs), a claim that has never been tested. To assess this claim, we used forward simulation of range-size evolution in clades with varying degrees of range-size heritability, and compared the output...... of three different models to the range-size distribution of the South American avifauna. Although there were differences among the models, a moderate-to-high degree of range-size heritability consistently leads to SRDs that were similar to empirical data. These results suggest that range-size heritability......The concept of species-level heritability is widely contested. Because it is most likely to apply to emergent, species-level traits, one of the central discussions has focused on the potential heritability of geographic range size. However, a central argument against range-size heritability has...

  5. Size Distributions and Characterization of Native and Ground Samples for Toxicology Studies

    Science.gov (United States)

    McKay, David S.; Cooper, Bonnie L.; Taylor, Larry A.

    2010-01-01

    This slide presentation shows charts and graphs that review the particle size distribution and characterization of natural and ground samples for toxicology studies. There are graphs which show the volume distribution versus the number distribution for natural occurring dust, jet mill ground dust, and ball mill ground dust.

  6. Methods for determining particle size distribution and growth rates between 1 and 3 nm using the Particle Size Magnifier

    CERN Document Server

    Lehtipalo, Katrianne; Kontkanen, Jenni; Kangasluoma, Juha; Franchin, Alessandro; Wimmer, Daniela; Schobesberger, Siegfried; Junninen, Heikki; Petäjä, Tuukka; Sipilä, Mikko; Mikkilä, Jyri; Vanhanen, Joonas; Worsnop, Douglas R; Kulmala, Markku

    2014-01-01

    The most important parameters describing the atmospheric new particle formation process are the particle formation and growth rates. These together determine the amount of cloud condensation nuclei attributed to secondary particle formation. Due to difficulties in detecting small neutral particles, it has previously not been possible to derive these directly from measurements in the size range below about 3 nm. The Airmodus Particle Size Magnifier has been used at the SMEAR II station in Hyytiälä, southern Finland, and during nucleation experiments in the CLOUD chamber at CERN for measuring particles as small as about 1 nm in mobility diameter. We developed several methods to determine the particle size distribution and growth rates in the size range of 1–3 nm from these data sets. Here we introduce the appearance-time method for calculating initial growth rates. The validity of the method was tested by simulations with the Ion-UHMA aerosol dynamic model.

  7. Sifting attacks in finite-size quantum key distribution

    Science.gov (United States)

    Pfister, Corsin; Lütkenhaus, Norbert; Wehner, Stephanie; Coles, Patrick J.

    2016-05-01

    A central assumption in quantum key distribution (QKD) is that Eve has no knowledge about which rounds will be used for parameter estimation or key distillation. Here we show that this assumption is violated for iterative sifting, a sifting procedure that has been employed in some (but not all) of the recently suggested QKD protocols in order to increase their efficiency. We show that iterative sifting leads to two security issues: (1) some rounds are more likely to be key rounds than others, (2) the public communication of past measurement choices changes this bias round by round. We analyze these two previously unnoticed problems, present eavesdropping strategies that exploit them, and find that the two problems are independent. We discuss some sifting protocols in the literature that are immune to these problems. While some of these would be inefficient replacements for iterative sifting, we find that the sifting subroutine of an asymptotically secure protocol suggested by Lo et al (2005 J. Cryptol. 18 133-65), which we call LCA sifting, has an efficiency on par with that of iterative sifting. One of our main results is to show that LCA sifting can be adapted to achieve secure sifting in the finite-key regime. More precisely, we combine LCA sifting with a certain parameter estimation protocol, and we prove the finite-key security of this combination. Hence we propose that LCA sifting should replace iterative sifting in future QKD implementations. More generally, we present two formal criteria for a sifting protocol that guarantee its finite-key security. Our criteria may guide the design of future protocols and inspire a more rigorous QKD analysis, which has neglected sifting-related attacks so far.

  8. Electrostatic Barrier Against Dust Growth in Protoplanetary Disks. I. Classifying the Evolution of Size Distribution

    CERN Document Server

    Okuzumi, Satoshi; Takeuchi, Taku; Sakagami, Masa-aki

    2010-01-01

    Collisional growth of submicron-sized dust grains into macroscopic aggregates is the first step of planet formation in protoplanetary disks. These aggregates are considered to carry nonzero negative charges in the weakly ionized gas disks, but its effect on their collisional growth has not been fully understood so far. In this paper, we investigate how the charging of dust aggregates affects the evolution of their size distribution properly taking into account the charging mechanism in a weakly ionized gas. To clarify the role of the size distribution, we divide our analysis into two steps. First, we analyze the collisional growth of charged aggregates assuming a monodisperse (i.e., narrow) size distribution. We show that the monodisperse growth stalls due to the electrostatic repulsion when a certain condition is met, as is already expected in the previous work. Second, we numerically simulate dust coagulation using Smoluchowski's method to see how the outcome changes when the size distribution is allowed to...

  9. Earthquake Size Distribution: Power-Law with Exponent Beta = 1/2 ?

    CERN Document Server

    Kagan, Yan Y

    2009-01-01

    We propose that the widely observed and universal Gutenberg-Richter relation is a mathematical consequence of the critical branching nature of earthquake process in a brittle fracture environment. These arguments, though preliminary, are confirmed by recent investigations of the seismic moment distribution in global earthquake catalogs and by the results on the distribution in crystals of dislocation avalanche sizes. We consider possible systematic and random errors in determining earthquake size, especially its seismic moment. These effects increase the estimate of the parameter beta of the power-law distribution of earthquake sizes. In particular we find that the decrease in relative moment uncertainties with earthquake size causes inflation in the beta-value by about 1-3%. Moreover, earthquake clustering greatly influences the beta-parameter. If clusters (aftershock sequences) are taken as the entity to be studied, then the exponent value for their size distribution would decrease by 5-10%. The complexity ...

  10. Does the size distribution of mineral dust aerosols depend on the wind speed at emission?

    Directory of Open Access Journals (Sweden)

    J. F. Kok

    2011-07-01

    Full Text Available The size distribution of mineral dust aerosols greatly affects their interactions with clouds, radiation, ecosystems, and other components of the Earth system. Several theoretical dust emission models predict that the dust size distribution depends on the wind speed at emission, with larger wind speeds predicted to produce smaller aerosols. The present study investigates this prediction using a compilation of published measurements of the size-resolved vertical dust flux emitted by eroding soils. Surprisingly, these measurements indicate that the size distribution of naturally emitted dust aerosols is independent of the wind speed. This finding is consistent with the recently formulated brittle fragmentation theory of dust emission, but inconsistent with other theoretical dust emission models. The independence of the emitted dust size distribution with wind speed simplifies both the parameterization of dust emission in atmospheric circulation models as well as the interpretation of geological records of dust deposition.

  11. Does the size distribution of mineral dust aerosols depend on the wind speed at emission?

    CERN Document Server

    Kok, Jasper F

    2011-01-01

    The size distribution of mineral dust aerosols partially determines their interactions with clouds, radiation, ecosystems, and other components of the Earth system. Several theoretical models predict that the dust size distribution depends on the wind speed at emission, with larger wind speeds predicted to produce smaller aerosols. The present study investigates this prediction using a compilation of published measurements of the size-resolved vertical dust flux emitted by eroding soils. Surprisingly, these measurements indicate that the size distribution of naturally emitted dust aerosols is independent of the wind speed. The recently formulated brittle fragmentation theory of dust emission is consistent with this finding, whereas other theoretical dust emission models are not. The independence of the emitted dust size distribution with wind speed simplifies both the interpretation of geological records of dust deposition and the parameterization of dust emission in atmospheric circulation models.

  12. Distribution and Size of Pyroxenite Bodies in the Mantle

    Science.gov (United States)

    Herzberg, C.

    2006-12-01

    lower in pyroxenite-source lavas owing to higher melt fractions. Peridotite-source lavas for the above-mentioned OIB from the Atlantic, Cook-Austral in the Pacific, and Turkana in East Africa have HIMU and FOZO isotopic characteristics, and have low Y/Nb and Zr/Nb. In contrast, peridotite-source lavas from the Caribbean, Ontong Java and North Atlantic display greater isotopic and trace element variability, indicating variable mixing and degradation of subducted crust. Pyroxenite is likely to range in size from grain boundary films to shield volcanoes.

  13. Two-size approximation: a simple way of treating the evolution of grain size distribution in galaxies

    CERN Document Server

    Hirashita, Hiroyuki

    2014-01-01

    Full calculations of the evolution of grain size distribution in galaxies are in general computationally heavy. In this paper, we propose a simple model of dust enrichment in a galaxy with a simplified treatment of grain size distribution by imposing a `two-size approximation'; that is, all the grain population is represented by small (grain radius a 0.03 micron) grains. We include in the model dust supply from stellar ejecta, destruction in supernova shocks, dust growth by accretion, grain growth by coagulation and grain disruption by shattering, considering how these processes work on the small and large grains. We show that this simple framework reproduces the main features found in full calculations of grain size distributions as follows. The dust enrichment starts with the supply of large grains from stars. At a metallicity level referred to as the critical metallicity of accretion, the abundance of the small grains formed by shattering becomes large enough to rapidly increase the grain abundance by acc...

  14. Intensity and degree of segregation in bimodal and multimodal grain size distributions

    Science.gov (United States)

    Katra, Itzhak; Yizhaq, Hezi

    2017-08-01

    The commonly used grain size analysis technique which applies moments (sorting, skewness and kurtosis) is less useful in the case of sediments with bimodal size distributions. Herein we suggest a new simple method for analyzing the degree of grain size segregation in sand-sized sediment that has clear bimodal size distributions. Two main features are used to characterize the bimodal distribution: grain diameter segregation, which is the normalized difference between coarse and fine grain diameters, and the frequency segregation which is the normalized difference in frequencies between two modes. The new defined indices can be calculated from frequency plot curves and can be graphically represented on a two dimensional coordinate system showing the dynamical aspects of the size distribution. The results enable comparison between granular samples from different locations and/or times to shed new light on the dynamic processes involved in grain size segregation of sediments. We demonstrate here the use of this method to analyze bimodal distributions of aeolian granular samples mostly from aeolian megaripples. Six different aeolian cases were analyzed to highlight the method's applicability, which is relevant to wide research themes in the Earth and environmental sciences, and can furthermore be easily adapted to analyze polymodal grain size distributions.

  15. Influence of stress-path on pore size distribution in granular materials

    Directory of Open Access Journals (Sweden)

    Das Arghya

    2017-01-01

    Full Text Available Pore size distribution is an important feature of granular materials in the context of filtration and erosion in soil hydraulic structures. Present study focuses on the evolution characteristics of pore size distribution for numerically simulated granular assemblies while subjected to various compression boundary constrain, namely, conventional drained triaxial compression, one-dimensional or oedometric compression and isotropic compression. We consider the effects initial packing of the granular assembly, loose or dense state. A simplified algorithm based on Delaunay tessellation is used for the estimation of pore size distribution for the deforming granular assemblies at various stress states. The analyses show that, the evolution of pore size is predominantly governed by the current porosity of the granular assembly while the stress path or loading process has minimal influence. Further it has also been observed that pore volume distribution reaches towards a critical distribution at the critical porosity during shear enhanced loading process irrespective of the deformation mechanism either compaction or dilation.

  16. Influence of stress-path on pore size distribution in granular materials

    Science.gov (United States)

    Das, Arghya; Kumar, Abhinav

    2017-06-01

    Pore size distribution is an important feature of granular materials in the context of filtration and erosion in soil hydraulic structures. Present study focuses on the evolution characteristics of pore size distribution for numerically simulated granular assemblies while subjected to various compression boundary constrain, namely, conventional drained triaxial compression, one-dimensional or oedometric compression and isotropic compression. We consider the effects initial packing of the granular assembly, loose or dense state. A simplified algorithm based on Delaunay tessellation is used for the estimation of pore size distribution for the deforming granular assemblies at various stress states. The analyses show that, the evolution of pore size is predominantly governed by the current porosity of the granular assembly while the stress path or loading process has minimal influence. Further it has also been observed that pore volume distribution reaches towards a critical distribution at the critical porosity during shear enhanced loading process irrespective of the deformation mechanism either compaction or dilation.

  17. The Effect of Nearby Voids on Galaxy Number Counts

    CERN Document Server

    Bucklein, Brian K; Hintz, Eric G

    2016-01-01

    The size, shape and degree of emptiness of void interiors sheds light on the details of galaxy formation. A particularly interesting question is whether void interiors are completely empty or contain a dwarf population. However the nearby voids that are most conducive for dwarf searches have large angular diameters, on the order of a steradian, making it difficult to redshift-map a statistically significant portion of their volume to the magnitude limit of dwarf galaxies. As part of addressing this problem, we investigate here the usefulness of number counts in establishing the best locations to search inside nearby (d < 300 Mpc) galaxy voids, utilizing Wolf plots of log(n < m) vs. m as the basic diagnostic. To illustrate expected signatures, we consider the signature of three void profiles, "cut out", "built up", and "universal profile" carved into Monte-Carlo Schechter function models. We then investigate the signatures of voids in the Millennium Run dark matter simulation and the Sloan Digital Sky Su...

  18. ACK filling void first algorithm and performance for asynchronous OPS

    Science.gov (United States)

    Liu, Huanlin; Shi, Yonghe; Chen, Qianbin; Pan, Yingjun

    2007-11-01

    OPS with feedback shared FDL buffer produce large voids due to FDL buffers only supplying discrete step delay and causing FDL queue virtually occupation. By analyzing the TCP traffic and ACK packets feature, the ACK packet void filling first scheduling is presented to decrease packet loss rate and to reduce the FDL voids. When the FDL buffer void size is fit for the ACK packet, the ACK packet is scheduled to FDL immediately. An ACK and non-ACK packets difference and process flow is designed according the TCP packet frame structure. Compared with the conventional FIFO scheduling and smallest FDL void first scheduling, the algorithm reduces greatly the number of ACK occupying the FDL buffer and eliminates large numbers of ACK's bad influence on efficiency of IP data transmission under different FDL buffer depth and traffic load. The results of simulation show that the proposed scheduling makes use of ACK packets first void filling scheduling mechanism to reduce FDL excess load, increases output utilization and reduce packet loss ratio for asynchronous optical network. This approach is shown to minimize the FDL numbers with the feature of high stabilization and photonic integration and to improve real time TCP traffic performance for Internet network.

  19. Geometric and Chemical Composition Effects on Healing Kinetics of Voids in Mg-bearing Al Alloys

    Science.gov (United States)

    Song, Miao; Du, Kui; Wang, Chunyang; Wen, Shengping; Huang, Hui; Nie, Zuoren; Ye, Hengqiang

    2016-05-01

    The healing kinetics of nanometer-scale voids in Al-Mg-Er and Al-Mg-Zn-Er alloy systems were investigated with a combination of in situ transmission electron microscopy and electron tomography at different temperatures. Mg was observed completely healing the voids, which were then rejuvenated to the alloy composition with further aging, in the Al-Mg-Er alloy. On the contrary, Mg51Zn20 intermetallic compound was formed in voids in the Al-Mg-Zn-Er alloy, which leads to complete filling of the voids but not rejuvenation for the material. For voids with different geometrical aspects, different evolution processes were observed, which are related to the competition between bulk and surface diffusion of the alloys. For voids with a large size difference in their two ends, a viscous flow of surface atoms can be directly observed with in situ electron microscopy, when the size of one end becomes less than tens of nanometers.

  20. Nanovoid growth in BCC α-Fe: influences of initial void geometry

    Science.gov (United States)

    Xu, Shuozhi; Su, Yanqing

    2016-12-01

    The growth of voids has a great impact on the mechanical properties of ductile materials by altering their microstructures. Exploring the process of void growth at the nanoscale helps in understanding the dynamic fracture of metals. While some very recent studies looked into the effects of the initial geometry of an elliptic void on the plastic deformation of face-centered cubic metals, a systematic study of the initial void ellipticity and orientation angle in body-centered cubic (BCC) metals is still lacking. In this paper, large scale molecular dynamics simulations with millions of atoms are conducted, investigating the void growth process during tensile loading of metallic thin films in BCC α-Fe. Our simulations elucidate the intertwined influences on void growth of the initial ellipticity and initial orientation angle of the void. It is shown that these two geometric parameters play an important role in the stress-strain response, the nucleation and evolution of defects, as well as the void size/outline evolution in α-Fe thin films. Results suggest that, together with void size, different initial void geometries should be taken into account if a continuum model is to be applied to nanoscale damage progression.

  1. [Size distributions of organic carbon (OC) and elemental carbon (EC) in Shanghai atmospheric particles].

    Science.gov (United States)

    Wang, Guang-Hua; Wei, Nan-Nan; Liu, Wei; Lin, Jun; Fan, Xue-Bo; Yao, Jian; Geng, Yan-Hong; Li, Yu-Lan; Li, Yan

    2010-09-01

    Size distributions of organic carbon (OC), elemental carbon (EC) and secondary organic carbon (SOC) in atmospheric particles with size range from 7.20 microm, collected in Jiading District, Shanghai were determined. For estimating size distribution of SOC in these atmospheric particles, a method of determining (OC/EC)(pri) in atmospheric particles with different sizes was discussed and developed, with which SOC was estimated. According to the correlation between OC and EC, main sources of the particles were also estimated roughly. The size distributions of OC and SOC showed a bi-modal with peaks in the particles with size of 3.0 microm, respectively. EC showed both of a bi-modal and tri-modal. Compared with OC, EC was preferably enriched in particles with size of particles (particles. OC and EC were preferably enriched in fine particles (particles with different sizes accounted for 15.7%-79.1% of OC in the particles with corresponding size. Concentrations of SOC in fine aerosols ( 3.00 microm) accounted for 41.4% and 43.5% of corresponding OC. Size distributions of OC, EC and SOC showed time-dependence. The correlation between OC and EC showed that the main contribution to atmospheric particles in Jiading District derived from light petrol vehicles exhaust.

  2. Nanomaterial size distribution analysis via liquid nebulization coupled with ion mobility spectrometry (LN-IMS).

    Science.gov (United States)

    Jeon, Seongho; Oberreit, Derek R; Van Schooneveld, Gary; Hogan, Christopher J

    2016-02-21

    We apply liquid nebulization (LN) in series with ion mobility spectrometry (IMS, using a differential mobility analyzer coupled to a condensation particle counter) to measure the size distribution functions (the number concentration per unit log diameter) of gold nanospheres in the 5-30 nm range, 70 nm × 11.7 nm gold nanorods, and albumin proteins originally in aqueous suspensions. In prior studies, IMS measurements have only been carried out for colloidal nanoparticles in this size range using electrosprays for aerosolization, as traditional nebulizers produce supermicrometer droplets which leave residue particles from non-volatile species. Residue particles mask the size distribution of the particles of interest. Uniquely, the LN employed in this study uses both online dilution (with dilution factors of up to 10(4)) with ultra-high purity water and a ball-impactor to remove droplets larger than 500 nm in diameter. This combination enables hydrosol-to-aerosol conversion preserving the size and morphology of particles, and also enables higher non-volatile residue tolerance than electrospray based aerosolization. Through LN-IMS measurements we show that the size distribution functions of narrowly distributed but similarly sized particles can be distinguished from one another, which is not possible with Nanoparticle Tracking Analysis in the sub-30 nm size range. Through comparison to electron microscopy measurements, we find that the size distribution functions inferred via LN-IMS measurements correspond to the particle sizes coated by surfactants, i.e. as they persist in colloidal suspensions. Finally, we show that the gas phase particle concentrations inferred from IMS size distribution functions are functions of only of the liquid phase particle concentration, and are independent of particle size, shape, and chemical composition. Therefore LN-IMS enables characterization of the size, yield, and polydispersity of sub-30 nm particles.

  3. Linear and nonlinear excitations in complex plasmas with nonadiabatic dust charge fluctuation and dust size distribution

    Institute of Scientific and Technical Information of China (English)

    Zhang Li-Ping; Xue Ju-Kui; Li Yan-Long

    2011-01-01

    Both linear and nonlinear excitation in dusty plasmas have been investigated including the nonadiabatic dust charge fluctuation and Gaussian size distribution dust particles.A linear dispersion relation and a Korteweg-de VriesBurgers equation governing the dust acoustic shock waves are obtained.The relevance of the instability of wave and the wave evolution to the dust size distribution and nonadiabatic dust charge fluctuation is illustrated both analytically and numerically.The numerical results show that the Gaussian size distribution of dust particles and the nonadiabatic dust charge fluctuation have strong common influence on the propagation of both linear and nonlinear excitations.

  4. Determination of Size Distributions in Nanocrystalline Powders by TEM, XRD and SAXS

    DEFF Research Database (Denmark)

    Jensen, Henrik; Pedersen, Jørgen Houe; Jørgensen, Jens Erik

    2006-01-01

    available powders showed different morphologies. The SSEC78 powder showed the narrowest sizes distribution while UV100 and TiO2_5nm consisted of the smallest primary particles. SSEC78, UV100, and TiO2_5nm consisted of both primary particles as well as a secondary structure comprised of nanosized primary......Crystallite size distributions and particle size distributions were determined by TEM, XRD, and SAXS for three commercially available TiO2 samples and one homemade. The theoretical Guinier Model was fitted to the experimental data and compared to analytical expressions. Modeling of the XRD spectra...

  5. The dipole moment of a wall-charged void in a bulk dielectric

    DEFF Research Database (Denmark)

    McAllister, Iain Wilson

    1993-01-01

    The dipole moment of a wall-charged void is examined with reference to the spatial extent of the surface charge density σ and the distribution of this charge. The salient factors influencing the void dipole moment are also examined. From a study of spherical voids, it is shown that, although the σ......-distribution influences the dipole moment, the spatial extent of σ has a greater influence. This behavior is not unexpected. For a void of fixed dimensions, the smaller the charged surface area, the greater is the charges, and thus the greater the dipole moment...

  6. Particle size distributions by transmission electron microscopy: an interlaboratory comparison case study.

    Science.gov (United States)

    Rice, Stephen B; Chan, Christopher; Brown, Scott C; Eschbach, Peter; Han, Li; Ensor, David S; Stefaniak, Aleksandr B; Bonevich, John; Vladár, András E; Hight Walker, Angela R; Zheng, Jiwen; Starnes, Catherine; Stromberg, Arnold; Ye, Jia; Grulke, Eric A

    2013-11-01

    This paper reports an interlaboratory comparison that evaluated a protocol for measuring and analysing the particle size distribution of discrete, metallic, spheroidal nanoparticles using transmission electron microscopy (TEM). The study was focused on automated image capture and automated particle analysis. NIST RM8012 gold nanoparticles (30 nm nominal diameter) were measured for area-equivalent diameter distributions by eight laboratories. Statistical analysis was used to (1) assess the data quality without using size distribution reference models, (2) determine reference model parameters for different size distribution reference models and non-linear regression fitting methods and (3) assess the measurement uncertainty of a size distribution parameter by using its coefficient of variation. The interlaboratory area-equivalent diameter mean, 27.6 nm ± 2.4 nm (computed based on a normal distribution), was quite similar to the area-equivalent diameter, 27.6 nm, assigned to NIST RM8012. The lognormal reference model was the preferred choice for these particle size distributions as, for all laboratories, its parameters had lower relative standard errors (RSEs) than the other size distribution reference models tested (normal, Weibull and Rosin-Rammler-Bennett). The RSEs for the fitted standard deviations were two orders of magnitude higher than those for the fitted means, suggesting that most of the parameter estimate errors were associated with estimating the breadth of the distributions. The coefficients of variation for the interlaboratory statistics also confirmed the lognormal reference model as the preferred choice. From quasi-linear plots, the typical range for good fits between the model and cumulative number-based distributions was 1.9 fitted standard deviations less than the mean to 2.3 fitted standard deviations above the mean. Automated image capture, automated particle analysis and statistical evaluation of the data and fitting coefficients provide a

  7. "Compu-Void II": the computerized voiding diary.

    Science.gov (United States)

    Rabin, J M; McNett, J; Badlani, G H

    1996-02-01

    We have previously described an electronic voiding diary, "Compu-Void" (Copyright, 1990) developed to automate recording of bladder symptoms (Rabin et al., 1993). Our objectives in this, the second phase of this study, were to examine a group of subject and control patients' preference and compliance with regard to the "Compu-Void" (CV) compared to the standard written voiding diary (WD), to compare the two methods with respect to the amount and type of information obtained and to determine whether or not the order of use of each recording method influenced results in the subject group. Thirty-six women between the ages of 20 and 84 with bladder symptomatology were compared to a group 36 age-matched women. In 100% of subjects and 95% of control patients, CV entries exceeded the number made with the WD in voiding events and in subjects, in incontinent episodes recorded (P < 0.0005 and P < 0.005, respectively). Over 98% of subjects and over 80% of control patients preferred CV over the WD (p < 0.0005). The order of use of each recording method in subjects made no significant difference with regard to the volume of information obtained (p < 0.407), number of urinary leakage events recorded (p < 0.494), and fluid intake patterns (p < 0.410). Patient impressions of, and compliance with each method were not affected by order of use. The only difference regarding order of use was that most subjects who used the CV first also found the WD to be tedious (61% vs 14%). Our results suggest increased volume of data and of patient compliance in reporting bladder symptoms and events using CV, and that order of use is not an important factor in determining patient impressions of the two methods. The majority of subject and control patients preferred CV over traditional methods. An updated version of the software and hardware is also included.

  8. Grain size distribution of quartz isolated from Chinese loess/paleosol

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Grain size distribution of bulk loess-paleosol and quartz chemically extracted from the loess/paleosol shows that mean size of the bulk samples is always finer than that of the quartz. The original aeolian depositions have been modified to various degrees by post-depositional weathering and pedogenic processes. The grain size distribution of the isolated quartz should be close to that of the primary aeolian sediment because the chemical pretreatment excludes secondary produced minerals. Therefore, the grain size of the quartz may be considered to more clearly reflect the variations of winter monsoon intensity.

  9. Mass size distributions and size resolved chemical composition of fine particulate matter at the Pittsburgh supersite

    Science.gov (United States)

    Cabada, Juan C.; Rees, Sarah; Takahama, Satoshi; Khlystov, Andrey; Pandis, Spyros N.; Davidson, Cliff I.; Robinson, Allen L.

    Size-resolved aerosol mass and chemical composition were measured during the Pittsburgh Air Quality Study. Daily samples were collected for 12 months from July 2001 to June 2002. Micro-orifice uniform deposit impactors (MOUDIs) were used to collect aerosol samples of fine particulate matter smaller than 10 μm. Measurements of PM 0.056, PM 0.10, PM 0.18, PM 0.32, PM 0.56, PM 1.0, PM 1.8 and PM 2.5 with the MOUDI are available for the full study period. Seasonal variations in the concentrations are observed for all size cuts. Higher concentrations are observed during the summer and lower during the winter. Comparison between the PM 2.5 measurements by the MOUDI and other integrated PM samplers reveals good agreement. Good correlation is observed for PM 10 between the MOUDI and an integrated sampler but the MOUDI underestimates PM 10 by 20%. Bouncing of particles from higher stages of the MOUDI (>PM 2.5) is not a major problem because of the low concentrations of coarse particles in the area. The main cause of coarse particle losses appears to be losses to the wall of the MOUDI. Samples were collected on aluminum foils for analysis of carbonaceous material and on Teflon filters for analysis of particle mass and inorganic anions and cations. Daily samples were analyzed during the summer (July 2001) and the winter intensives (January 2002). During the summer around 50% of the organic material is lost from the aluminum foils as compared to a filter-based sampler. These losses are due to volatilization and bounce-off from the MOUDI stages. High nitrate losses from the MOUDI are also observed during the summer (above 70%). Good agreement between the gravimetrically determined mass and the sum of the masses of the individual compounds is obtained, if the lost mass from organics and the aerosol water content are included for the summer. For the winter no significant losses of material are detected and there exists reasonable agreement between the gravimetrical mass and the

  10. Influence of particle size on the distributions of liposomes to atherosclerotic lesions in mice.

    Science.gov (United States)

    Chono, Sumio; Tauchi, Yoshihiko; Morimoto, Kazuhiro

    2006-01-01

    In order to confirm the efficacy of liposomes as a drug carrier for atherosclerotic therapy, the influence of particle size on the distribution of liposomes to atherosclerotic lesions in mice was investigated. In brief, liposomes of three different particle sizes (500, 200, and 70 nm) were prepared, and the uptake of liposomes by the macrophages and foam cells in vitro and the biodistributions of liposomes administered intravenously to atherogenic mice in vivo were examined. The uptake by the macrophages and foam cells increased with the increase in particle size. Although the elimination rate from the blood circulation and the hepatic and splenic distribution increased with the increase in particle size in atherogenic mice, the aortic distribution was independent of the particle size. The aortic distribution of 200 nm liposomes was the highest in comparison with the other sizes. Surprisingly, the aortic distribution of liposomes in vivo did not correspond with the uptake by macrophages and foam cells in vitro. These results suggest that there is an optimal size for the distribution of liposomes to atherosclerotic lesions.

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

    Science.gov (United States)

    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.

  12. Effects of grain size distribution on the packing fraction and shear strength of frictionless disk packings

    Science.gov (United States)

    Estrada, Nicolas

    2016-12-01

    Using discrete element methods, the effects of the grain size distribution on the density and the shear strength of frictionless disk packings are analyzed. Specifically, two recent findings on the relationship between the system's grain size distribution and its rheology are revisited, and their validity is tested across a broader range of distributions than what has been used in previous studies. First, the effects of the distribution on the solid fraction are explored. It is found that the distribution that produces the densest packing is not the uniform distribution by volume fractions as suggested in a recent publication. In fact, the maximal packing fraction is obtained when the grading curve follows a power law with an exponent close to 0.5 as suggested by Fuller and Thompson in 1907 and 1919 [Trans Am. Soc. Civ. Eng. 59, 1 (1907) and A Treatise on Concrete, Plain and Reinforced (1919), respectively] while studying mixtures of cement and stone aggregates. Second, the effects of the distribution on the shear strength are analyzed. It is confirmed that these systems exhibit a small shear strength, even if composed of frictionless particles as has been shown recently in several works. It is also found that this shear strength is independent of the grain size distribution. This counterintuitive result has previously been shown for the uniform distribution by volume fractions. In this paper, it is shown that this observation keeps true for different shapes of the grain size distribution.

  13. 3D Property Modeling of Void Ratio by Cokriging

    Institute of Scientific and Technical Information of China (English)

    Yao Lingqing; Pan Mao; Cheng Qiuming

    2008-01-01

    Void ratio measures compactness of ground soil in geotechnical engineering. When samples are collected in certain area for mapping void ratios, other relevant types of properties such as water content may be also analyzed. To map the spatial distribution of void ratio in the area based on these types of point, observation data interpolation is often needed. Owing to the variance of sampling density along the horizontal and vertical directions, special consideration is required to handle anisotropy of estimator. 3D property modeling aims at predicting the overall distribution of property values from limited samples, and geostatistical method can he employed naturally here because they help to minimize the mean square error of estimation. To construct 3D property model of void ratio, cokriging was used considering its mutual correlation with water content, which is another important soil parameter. Moreover, K-D tree was adopted to organize the samples to accelerate neighbor query in 3D space during the above modeling process. At last, spatial configuration of void ratio distribution in an engineering body was modeled through 3D visualization, which provides important information for civil engineering purpose.

  14. Measuring coral size-frequency distribution using stereo video technology, a comparison with in situ measurements.

    Science.gov (United States)

    Turner, Joseph A; Polunin, Nicholas V C; Field, Stuart N; Wilson, Shaun K

    2015-05-01

    Coral colony size-frequency distribution data offer valuable information about the ecological status of coral reefs. Such data are usually collected by divers in situ, but stereo video is being increasingly used for monitoring benthic marine communities and may be used to collect size information for coral colonies. This study compared the size-frequency distributions of coral colonies obtained by divers measuring colonies 'in situ' with digital video imagery collected using stereo video and later processed using computer software. The size-frequency distributions of the two methods were similar for corymbose colonies, although distributions were different for massive, branching and all colonies combined. The differences are mainly driven by greater abundance of colonies >50 cm and fewer colonies 5 cm and was able to record measurements on 87% of the colonies detected. However, stereo video only detected 57% of marked colonies coral recruits. Estimates of colony size made with the stereo video were smaller than the in situ technique for all growth forms, particularly for massive morphologies. Despite differences in size distributions, community assessments, which incorporated genera, growth forms and size, were similar between the two techniques. Stereo video is suitable for monitoring coral community demographics and provided data similar to in situ measure for corymbose corals, but the ability to accurately measure massive and branching coral morphologies appeared to decline with increasing colony size.

  15. Cloud particle size distributions measured with an airborne digital in-line holographic instrument

    Directory of Open Access Journals (Sweden)

    J. P. Fugal

    2009-03-01

    Full Text Available Holographic data from the prototype airborne digital holographic instrument HOLODEC (Holographic Detector for Clouds, taken during test flights are digitally reconstructed to obtain the size (equivalent diameters in the range 23 to 1000 μm, three-dimensional position, and two-dimensional profile of ice particles and then ice particle size distributions and number densities are calculated using an automated algorithm with minimal user intervention. The holographic method offers the advantages of a well-defined sample volume size that is not dependent on particle size or airspeed, and offers a unique method of detecting shattered particles. The holographic method also allows the volume sample rate to be increased beyond that of the prototype HOLODEC instrument, limited solely by camera technology.

    HOLODEC size distributions taken in mixed-phase regions of cloud compare well to size distributions from a PMS FSSP probe also onboard the aircraft during the test flights. A conservative algorithm for detecting shattered particles utilizing the particles depth-position along the optical axis eliminates the obvious ice particle shattering events from the data set. In this particular case, the size distributions of non-shattered particles are reduced by approximately a factor of two for particles 15 to 70 μm in equivalent diameter, compared to size distributions of all particles.

  16. Ultrafine particle size distributions near freeways: Effects of differing wind directions on exposure

    Science.gov (United States)

    Kozawa, Kathleen H.; Winer, Arthur M.; Fruin, Scott A.

    2012-12-01

    High ambient ultrafine particle (UFP) concentrations may play an important role in the adverse health effects associated with living near busy roadways. However, UFP size distributions change rapidly as vehicle emissions dilute and age. These size changes can influence UFP lung deposition rates and dose because deposition in the respiratory system is a strong function of particle size. Few studies to date have measured and characterized changes in near-road UFP size distributions in real-time, thus missing transient variations in size distribution due to short-term fluctuations in wind speed, direction, or particle dynamics. In this study we measured important wind direction effects on near-freeway UFP size distributions and gradients using a mobile platform with 5-s time resolution. Compared to more commonly measured perpendicular (downwind) conditions, parallel wind conditions appeared to promote formation of broader and larger size distributions of roughly one-half the particle concentration. Particles during more parallel wind conditions also changed less in size with downwind distance and the fraction of lung-deposited particle number was calculated to be 15% lower than for downwind conditions, giving a combined decrease of about 60%. In addition, a multivariate analysis of several variables found meteorology, particularly wind direction and temperature, to be important in predicting UFP concentrations within 150 m of a freeway (R2 = 0.46, p = 0.014).

  17. Particle Size Distributions Measured in the Stratospheric Plumes of Three Rockets During the ACCENT Missions

    Science.gov (United States)

    Wiedinmyer, C.; Brock, C. A.; Reeves, J. M.; Ross, M. N.; Schmid, O.; Toohey, D.; Wilson, J. C.

    2001-12-01

    The global impact of particles emitted by rocket engines on stratospheric ozone is not well understood, mainly due to the lack of comprehensive in situ measurements of the size distributions of these emitted particles. During the Atmospheric Chemistry of Combustion Emissions Near the Tropopause (ACCENT) missions in 1999, the NASA WB-57F aircraft carried the University of Denver N-MASS and FCAS instruments into the stratospheric plumes from three rockets. Size distributions of particles with diameters from 4 to approximately 2000 nm were calculated from the instrument measurements using numerical inversion techniques. The data have been averaged over 30-second intervals. The particle size distributions observed in all of the rocket plumes included a dominant mode near 60 nm diameter, probably composed of alumina particles. A smaller mode at approximately 25 nm, possibly composed of soot particles, was seen in only the plumes of rockets that used liquid oxygen and kerosene as a propellant. Aircraft exhaust emitted by the WB-57F was also sampled; the size distributions within these plumes are consistent with prior measurements in aircraft plumes. The size distributions for all rocket intercepts have been fitted to bimodal, lognormal distributions to provide input for global models of the stratosphere. Our data suggest that previous estimates of the solid rocket motor alumina size distributions may underestimate the alumina surface area emission index, and so underestimate the particle surface area available for heterogeneous chlorine activation reactions in the global stratosphere.

  18. Species sensitivity distribution for chlorpyrifos to aquatic organisms: Model choice and sample size.

    Science.gov (United States)

    Zhao, Jinsong; Chen, Boyu

    2016-03-01

    Species sensitivity distribution (SSD) is a widely used model that extrapolates the ecological risk to ecosystem levels from the ecotoxicity of a chemical to individual organisms. However, model choice and sample size significantly affect the development of the SSD model and the estimation of hazardous concentrations at the 5th centile (HC5). To interpret their effects, the SSD model for chlorpyrifos, a widely used organophosphate pesticide, to aquatic organisms is presented with emphases on model choice and sample size. Three subsets of median effective concentration (EC50) with different sample sizes were obtained from ECOTOX and used to build SSD models based on parametric distribution (normal, logistic, and triangle distribution) and nonparametric bootstrap. The SSD models based on the triangle distribution are superior to the normal and logistic distributions according to several goodness-of-fit techniques. Among all parametric SSD models, the one with the largest sample size based on the triangle distribution gives the most strict HC5 with 0.141μmolL(-1). The HC5 derived from the nonparametric bootstrap is 0.159μmol L(-1). The minimum sample size required to build a stable SSD model is 11 based on parametric distribution and 23 based on nonparametric bootstrap. The study suggests that model choice and sample size are important sources of uncertainty for application of the SSD model. Copyright © 2015 Elsevier Inc. All rights reserved.

  19. Rumen Contents and Ruminal Digesta Particle Size Distribution in Buffalo Steers Fed Three Different Size of Alfalfa

    Directory of Open Access Journals (Sweden)

    A. Teimouri Yansari

    2010-02-01

    Full Text Available This study was conducted to investigate the effects of three sizes of alfalfa and time post-feeding on rumen contents and on particle size distribution of ruminal digesta. Three ruminally fistulated buffalo steers received a diet consisting just alfalfa that was harvested at 15% of flowering and chopped in three sizes. Individual small rectangular bales were chopped with a forage field harvester for theoretical cut length 19 and 10 mm for preparation of long and medium particle size, also the fine particles were prepared by milling. The geometric means and its standard deviation were 8.5, 5.5 and 2.5 mm; and 1.24, 1.16 and 1.06 mm, in coarse, medium and fine, respectively. The experimental design was a repeated 3×3 Latin squares with 21 day periods. The diets were offered twice daily at 09:00 and 21:00 h at ad libitum level. The rumens were evacuated manually at 3, 7.5 and 12h post-feeding and total ruminal contents separated into mat and bailable liquids. Dry matter weight distribution of total recovered particles was determined by a wet-sieving procedure and used to partition ruminal mat and bailable liquids among percentages of large (≥4.0 mm, medium (<4.0mm and ≥1.18 mm, and fine (<1.18 mm and ≥0.05 mm particles. Intake did not influence markedly the distribution of different particle fractions, whereas particle size and time post-feeding had a pronounced effect. With increasing time after feeding, percentage of large and medium particles significantly decreased, whereas the percentage of fine particles significantly increased. The ruminal digesta particle distributions illustrated intensive particle breakdown in the reticulo-rumen for coarse particle more than others. Dry matter contents and the proportion of particulate dry matter in the rumen increased as intake increased, i.e. ruminal mat increased at the expense of bailable liquids. It can be concluded that reduction of forage particle size for buffaloes at maintenance level

  20. Statistical geometry of lattice chain polymers with voids of defined shapes: Sampling with strong constraints

    Science.gov (United States)

    Lin, Ming; Chen, Rong; Liang, Jie

    2008-02-01

    Proteins contain many voids, which are unfilled spaces enclosed in the interior. A few of them have shapes compatible to ligands and substrates and are important for protein functions. An important general question is how the need for maintaining functional voids is influenced by, and affects other aspects of proteins structures and properties (e.g., protein folding stability, kinetic accessibility, and evolution selection pressure). In this paper, we examine in detail the effects of maintaining voids of different shapes and sizes using two-dimensional lattice models. We study the propensity for conformations to form a void of specific shape, which is related to the entropic cost of void maintenance. We also study the location that voids of a specific shape and size tend to form, and the influence of compactness on the formation of such voids. As enumeration is infeasible for long chain polymer, a key development in this work is the design of a novel sequential Monte Carlo strategy for generating large number of sample conformations under very constraining restrictions. Our method is validated by comparing results obtained from sampling and from enumeration for short polymer chains. We succeeded in accurate estimation of entropic cost of void maintenance, with and without an increasing number of restrictive conditions, such as loops forming the wall of void with fixed length, with additionally fixed starting position in the sequence. Additionally, we have identified the key structural properties of voids that are important in determining the entropic cost of void formation. We have further developed a parametric model to predict quantitatively void entropy. Our model is highly effective, and these results indicate that voids representing functional sites can be used as an improved model for studying the evolution of protein functions and how protein function relates to protein stability.

  1. Nanoparticles and metrology: a comparison of methods for the determination of particle size distributions

    Science.gov (United States)

    Coleman, Victoria A.; Jämting, Åsa K.; Catchpoole, Heather J.; Roy, Maitreyee; Herrmann, Jan

    2011-10-01

    Nanoparticles and products incorporating nanoparticles are a growing branch of nanotechnology industry. They have found a broad market, including the cosmetic, health care and energy sectors. Accurate and representative determination of particle size distributions in such products is critical at all stages of the product lifecycle, extending from quality control at point of manufacture to environmental fate at the point of disposal. Determination of particle size distributions is non-trivial, and is complicated by the fact that different techniques measure different quantities, leading to differences in the measured size distributions. In this study we use both mono- and multi-modal dispersions of nanoparticle reference materials to compare and contrast traditional and novel methods for particle size distribution determination. The methods investigated include ensemble techniques such as dynamic light scattering (DLS) and differential centrifugal sedimentation (DCS), as well as single particle techniques such as transmission electron microscopy (TEM) and microchannel resonator (ultra high-resolution mass sensor).

  2. PARTICLE SIZE DISTRIBUTIONS FROM SELECT RESIDENCES PARTICIPATING IN THE NERL RTP PM PANEL STUDY

    Science.gov (United States)

    Particle Size Distributions from Select Residences Participating in the NERL RTP PM Panel Study. Alan Vette, Ronald Williams, and Michael Riediker, U.S. Environmental Protection Agency, National Exposure Research Laboratory, Research Triangle Park, NC 27711; Jonathan Thornburg...

  3. Geostatistical modeling of regionalized grain-size distributions using Min/Max Autocorrelation Factors

    National Research Council Canada - National Science Library

    Desbarats, A J

    2001-01-01

    .... Since the number of classes may be large and abundances in adjacent classes may be highly cross-correlated, practical simulation of regionalized grain-size distributions requires an efficient method...

  4. A SURFACTANT-ASSISTED APPROACH FOR PREPARING COLLOIDAL AZO POLYMER SPHERES WITH NARROW SIZE DISTRIBUTION

    Institute of Scientific and Technical Information of China (English)

    Xiao-lan Tong; Yao-bang Li; Ya-ning He; Xiao-gong Wang

    2006-01-01

    A surfactant-assisted method for preparing colloidal spheres with narrow size distribution from a polydispersed azo polymer has been developed in this work. The colloidal spheres were formed through gradual hydrophobic aggregation of the polymeric chains in THF-H2O dispersion media, which was induced by a steady increase in the water content. Results showed that the addition of a small amount of surfactant (SDBS) could significantly narrow the size distribution of the colloidal spheres. The size distribution of the colloidal spheres was determined by the concentrations of azo polymer and the amount of surfactant in the systems. When the concentrations of polymer and surfactant amount were in a proper range,colloidal spheres with narrow size distribution could be obtained. The colloidal spheres formed by this method could be elongated along the polarization direction of the laser beams upon Ar+ laser irradiation. The colloidal spheres are considered to be a new type of the colloid-based functional materials.

  5. MetaZipf. A dynamic meta-analysis of city size distributions

    National Research Council Canada - National Science Library

    Clémentine Cottineau

    2017-01-01

    .... However, little evidence exists as to the factors which influence the level of urban unevenness, as expressed by the slope of the rank-size distribution, partly because the diversity of results found...

  6. Solitary waves in a dusty plasma with charge fluctuation and dust size distribution and vortex like ion distribution

    Energy Technology Data Exchange (ETDEWEB)

    Roy Chowdhury, K. [Department of Physics, J.C.C. College, Kolkata 700 033 (India); Mishra, Amar P. [High Energy Physics Division, Department of Physics Jadavpur University, Kolkata 700 032 (India); Roy Chowdhury, A. [High Energy Physics Division, Department of Physics Jadavpur University, Kolkata 700 032 (India)

    2006-07-15

    A modified KdV equation is derived for the propagation of non-linear waves in a dusty plasma, containing N different dust grains with a size distribution and charge fluctuation with electrons in the background. The ions are assumed to obey a vortex like distribution due to their non-isothermal nature. The standard distribution for the dust size is a power law. The variation of the soliton width is studied with respect to normalized size of the dust grains. A numerical solution of the equation is done by considering the soliton solution of the modified KdV as the initial pulse. It shows considerable broadening of the pulse variation of width with {beta} {sub 1} is shown.

  7. Effect of Lithium Ions on Copper Nanoparticle Size, Shape, and Distribution

    Directory of Open Access Journals (Sweden)

    Kyung-Deok Jang

    2012-01-01

    Full Text Available Copper nanoparticles were synthesized using lithium ions to increase the aqueous electrical conductivity of the solution and precisely control the size, shape, and size distribution of the particles. In this study, the conventional approach of increasing particle size by the concentration of copper ions and PGPPE in a copper chloride solution was compared to increasing the concentration of lithium chloride when the copper chloride concentration was held constant. Particle size and shape were characterized by TEM, and the size distribution of the particles at different concentrations was obtained by particle size analysis. Increasing the concentration of copper ion in the solution greatly increased the aqueous electric conductivity and the size of the particles but led to a wide size distribution ranging from 150 nm to 400 nm and rough particle morphology. The addition of lithium ions increased the size of the particles, but maintains them in a range of 250 nm. In addition the particles exhibited spherical shape as determined by TEM. The addition of lithium ions to the solution has the potential to synthesize nanoparticles with optimal characteristics for printing applications by maintaining a narrow size range and spherical shape.

  8. Calibration of the passive cavity aerosol spectrometer probe for airborne determination of the size distribution

    Directory of Open Access Journals (Sweden)

    Y. Cai

    2013-09-01

    Full Text Available This work describes calibration methods for the particle sizing and particle concentration systems of the passive cavity aerosol spectrometer probe (PCASP. Laboratory calibrations conducted over six years, in support of the deployment of a PCASP on a cloud physics research aircraft, are analyzed. Instead of using the many calibration sizes recommended by the PCASP manufacturer, a relationship between particle diameter and scattered light intensity is established using three sizes of mobility-selected polystyrene latex particles, one for each amplifier gain stage. In addition, studies of two factors influencing the PCASP's determination of the particle size distribution – amplifier baseline and particle shape – are conducted. It is shown that the PCASP-derived size distribution is sensitive to adjustments of the sizing system's baseline voltage, and that for aggregates of spheres, a PCASP-derived particle size and a sphere-equivalent particle size agree within uncertainty dictated by the PCASP's sizing resolution. Robust determinations of aerosol concentration, and size distribution, also require calibration of the PCASP's aerosol flowrate sensor. Sensor calibrations, calibration drift, and the sensor's non-linear response are documented.

  9. Quality of the log-geometric distribution extrapolation for smaller undiscovered oil and gas pool size

    Science.gov (United States)

    Chenglin, L.; Charpentier, R.R.

    2010-01-01

    The U.S. Geological Survey procedure for the estimation of the general form of the parent distribution requires that the parameters of the log-geometric distribution be calculated and analyzed for the sensitivity of these parameters to different conditions. In this study, we derive the shape factor of a log-geometric distribution from the ratio of frequencies between adjacent bins. The shape factor has a log straight-line relationship with the ratio of frequencies. Additionally, the calculation equations of a ratio of the mean size to the lower size-class boundary are deduced. For a specific log-geometric distribution, we find that the ratio of the mean size to the lower size-class boundary is the same. We apply our analysis to simulations based on oil and gas pool distributions from four petroleum systems of Alberta, Canada and four generated distributions. Each petroleum system in Alberta has a different shape factor. Generally, the shape factors in the four petroleum systems stabilize with the increase of discovered pool numbers. For a log-geometric distribution, the shape factor becomes stable when discovered pool numbers exceed 50 and the shape factor is influenced by the exploration efficiency when the exploration efficiency is less than 1. The simulation results show that calculated shape factors increase with those of the parent distributions, and undiscovered oil and gas resources estimated through the log-geometric distribution extrapolation are smaller than the actual values. ?? 2010 International Association for Mathematical Geology.

  10. Aged boreal biomass-burning aerosol size distributions from BORTAS 2011

    OpenAIRE

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

    2015-01-01

    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 (cloud condensation nuclei) concentrations and forcing estima...

  11. Placement and Sizing of DG Using PSO&HBMO Algorithms in Radial Distribution Networks

    Directory of Open Access Journals (Sweden)

    M. A.Taghikhani

    2012-09-01

    Full Text Available Optimal placement and sizing of DG in distribution network is an optimization problem with continuous and discrete variables. Many researchers have used evolutionary methods for finding the optimal DG placement and sizing. This paper proposes a hybrid algorithm PSO&HBMO for optimal placement and sizing of distributed generation (DG in radial distri-bution system to minimize the total power loss and improve the voltage profile. The proposed method is tested on a standard 13 bus radial distribution system and simulation results carried out using MATLAB software. The simulation results indicate that PSO&HBMO method can obtain better results than the simple heuristic search method and PSO algorithm. The method has a potential to be a tool for identifying the best location and rating of a DG to be installed for improving voltage profile and line losses reduction in an electrical power system. Moreover, current reduction is obtained in distribution system.

  12. Modeling Size-number Distributions of Seeds for Use in Soil Bank Studies

    Institute of Scientific and Technical Information of China (English)

    Hugo Casco; Alexandra Soveral Dias; Luís Silva Dias

    2008-01-01

    Knowledge of soil seed banks is essential to understand the dynamics of plant populations and communities and would greatly benefit from the integration of existing knowledge on ecological correlations of seed size and shape. The present study aims to establish a feasible and meaningful method to describe size-number distributions of seeds in multi-species situations. For that purpose, size-number distributions of seeds with known length, width and thickness were determined by sequential sieving. The most appropriate combination of sieves and seeds dimensions was established, and the adequacy of the power function and the Weibull model to describe size-number distributions of spherical, non.spherical, and all seeds was investigated. We found that the geometric mean of seed length, width and thickness was the most adequate size estimator, providing shape-independent measures of seeds volume directly related to sieves mesh side, and that both the power function and the Weibuli model provide high quality descriptions of size-number distributions of spherical,non-spherical, and all seeds. We also found that, in spite of its slightly lower accuracy, the power function is, at this stage, a more trustworthy model to characterize size-number distributions of seeds in soil banks because in some Weibull equations the estimates of the scale parameter were not acceptable.

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

    Science.gov (United States)

    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.

  14. A facile synthesis of Tenanoparticles with binary size distribution by green chemistry

    Science.gov (United States)

    He, Weidong; Krejci, Alex; Lin, Junhao; Osmulski, Max E.; Dickerson, James H.

    2011-04-01

    Our work reports a facile route to colloidal Tenanocrystals with binary uniform size distributions at room temperature. The binary-sized Tenanocrystals were well separated into two size regimes and assembled into films by electrophoretic deposition. The research provides a new platform for nanomaterials to be efficiently synthesized and manipulated.Our work reports a facile route to colloidal Tenanocrystals with binary uniform size distributions at room temperature. The binary-sized Tenanocrystals were well separated into two size regimes and assembled into films by electrophoretic deposition. The research provides a new platform for nanomaterials to be efficiently synthesized and manipulated. Electronic supplementary information (ESI) available: Synthetic procedures, FTIR analysis, ED pattern, AFM image, and EPD current curve. See DOI: 10.1039/c1nr10025d

  15. Void/Pore Distributions and Ductile Fracture.

    Science.gov (United States)

    1985-11-01

    three holes was never observed remote from the final fracture surface indicates that. the imperfection consists of three linked holes plus a zig - zag ...the sheet and plane strain for the plate). Specimen preparation was performed in a numerically controlled milling machine with the holes being

  16. Maximum size distributions in tropical forest communities: relationships with rainfall and disturbance

    NARCIS (Netherlands)

    Poorter, L.; Hawthorne, W.D.; Sheil, D.; Bongers, F.J.J.M.

    2008-01-01

    The diversity and structure of communities are partly determined by how species partition resource gradients. Plant size is an important indicator of species position along the vertical light gradient in the vegetation. 2. Here, we compared the size distribution of tree species in 44 Ghanaian

  17. Evaluation of 1H NMR relaxometry for the assessment of pore size distribution in soil samples

    NARCIS (Netherlands)

    Jaeger, F.; Bowe, S.; As, van H.; Schaumann, G.E.

    2009-01-01

    1H NMR relaxometry is used in earth science as a non-destructive and time-saving method to determine pore size distributions (PSD) in porous media with pore sizes ranging from nm to mm. This is a broader range than generally reported for results from X-ray computed tomography (X-ray CT) scanning, wh

  18. Aerosol size distribution and classification. (Latest citations from the NTIS bibliographic database). Published Search

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1996-11-01

    The bibliography contains citations concerning aerosol particle size distribution and classification pertaining to air pollution detection and health studies. Aerosol size measuring methods, devices, and apparatus are discussed. Studies of atmospheric, industrial, radioactive, and marine aerosols are presented.(Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)

  19. How dispersal limitation shapes species-body size distributions in local communities

    NARCIS (Netherlands)

    Etienne, R.S.; Olff, H.

    2004-01-01

    A critical but poorly understood pattern in macroecology is the often unimodal species - body size distribution ( also known as body size - diversity relationship) in a local community ( embedded in a much larger regional species pool). Purely neutral community models that assume functional

  20. A simple algorithm for measuring particle size distributions on an uneven background from TEM images

    DEFF Research Database (Denmark)

    Gontard, Lionel Cervera; Ozkaya, Dogan; Dunin-Borkowski, Rafal E.

    2011-01-01

    Nanoparticles have a wide range of applications in science and technology. Their sizes are often measured using transmission electron microscopy (TEM) or X-ray diffraction. Here, we describe a simple computer algorithm for measuring particle size distributions from TEM images in the presence of a...

  1. Model independent determination of colloidal silica size distributions via analytical ultracentrifugation

    NARCIS (Netherlands)

    Planken, K.L.; Kuipers, B.W.M.; Philipse, A.P.

    2008-01-01

    We report a method to determine the particle size distribution of small colloidal silica spheres via analytical ultracentrifugation and show that the average particle size, variance, standard deviation, and relative polydispersity can be obtained from a single sedimentation velocity (SV) analytical

  2. The dune size distribution and scaling relations of barchan dune fields

    NARCIS (Netherlands)

    Durán, O.; Schwämmle, V.; Lind, P.G.; Herrmann, H.J.

    2009-01-01

    Barchan dunes emerge as a collective phenomena involving the generation of thousands of them in so called barchan dune fields. By measuring the size and position of dunes in Moroccan barchan dune fields, we find that these dunes tend to distribute uniformly in space and follow an unique size distrib

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

    Science.gov (United States)

    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

  4. Synthesis of iron oxide nanoparticles of narrow size distribution on polysaccharide templates

    Indian Academy of Sciences (India)

    M Nidhin; R Indumathy; K J Sreeram; Balachandran Unni Nair

    2008-02-01

    We report here the preparation of nanoparticles of iron oxide in the presence of polysaccharide templates. Interaction between iron (II) sulfate and template has been carried out in aqueous phase, followed by the selective and controlled removal of the template to achieve narrow distribution of particle size. Particles of iron oxide obtained have been characterized for their stability in solvent media, size, size distribution and crystallinity and found that when the negative value of the zeta potential increases, particle size decreases. A narrow particle size distribution with 100 = 275 nm was obtained with chitosan and starch templates. SEM measurements further confirm the particle size measurement. Diffuse reflectance UV–vis spectra values show that the template is completely removed from the final iron oxide particles and powder XRD measurements show that the peaks of the diffractogram are in agreement with the theoretical data of hematite. The salient observations of our study shows that there occurs a direct correlation between zeta potential, polydispersity index, bandgap energy and particle size. The crystallite size of the particles was found to be 30–35 nm. A large negative zeta potential was found to be advantageous for achieving lower particle sizes, owing to the particles remaining discrete without agglomeration.

  5. A Possible Divot in the Size Distribution of the Kuiper Belt's Scattering Objects

    Science.gov (United States)

    Shankman, C.; Gladman, B. J.; Kaib, N.; Kavelaars, J. J.; Petit, J. M.

    2013-02-01

    Via joint analysis of a calibrated telescopic survey, which found scattering Kuiper Belt objects, and models of their expected orbital distribution, we explore the scattering-object (SO) size distribution. Although for D > 100 km the number of objects quickly rise as diameters decrease, we find a relative lack of smaller objects, ruling out a single power law at greater than 99% confidence. After studying traditional "knees" in the size distribution, we explore other formulations and find that, surprisingly, our analysis is consistent with a very sudden decrease (a divot) in the number distribution as diameters decrease below 100 km, which then rises again as a power law. Motivated by other dynamically hot populations and the Centaurs, we argue for a divot size distribution where the number of smaller objects rises again as expected via collisional equilibrium. Extrapolation yields enough kilometer-scale SOs to supply the nearby Jupiter-family comets. Our interpretation is that this divot feature is a preserved relic of the size distribution made by planetesimal formation, now "frozen in" to portions of the Kuiper Belt sharing a "hot" orbital inclination distribution, explaining several puzzles in Kuiper Belt science. Additionally, we show that to match today's SO inclination distribution, the supply source that was scattered outward must have already been vertically heated to the of order 10°.

  6. Evaluation of eruptive energy of a pyroclastic deposit applying fractal geometry to fragment size distributions

    Science.gov (United States)

    Paredes Marino, Joali; Morgavi, Daniele; Di Vito, Mauro; de Vita, Sandro; Sansivero, Fabio; Perugini, Diego

    2016-04-01

    Fractal fragmentation theory has been applied to characterize the particle size distribution of pyroclastic deposits generated by volcanic explosions. Recent works have demonstrated that fractal dimension on grain size distributions can be used as a proxy for estimating the energy associated with volcanic eruptions. In this work we seek to establish a preliminary analytical protocol that can be applied to better characterize volcanic fall deposits and derive the potential energy for fragmentation that was stored in the magma prior/during an explosive eruption. The methodology is based on two different techniques for determining the grain-size distribution of the pyroclastic samples: 1) dry manual sieving (particles larger than 297μm), and 2) automatic grain size analysis via a CamSizer-P4®device, the latter measure the distribution of projected area, obtaining a cumulative distribution based on volume fraction for particles up to 30mm. Size distribution data have been analyzed by applying the fractal fragmentation theory estimating the value of Df, i.e. the fractal dimension of fragmentation. In order to test our protocol we studied the Cretaio eruption, Ischia island, Italy. Results indicate that size distributions of pyroclastic fall deposits follow a fractal law, indicating that the fragmentation process of these deposits reflects a scale-invariant fragmentation mechanism. Matching the results from manual and automated techniques allows us to obtain a value of the "fragmentation energy" from the explosive eruptive events that generate the Cretaio deposits. We highlight the importance of these results, based on fractal statistics, as an additional volcanological tool for addressing volcanic risk based on the analyses of grain size distributions of natural pyroclastic deposits. Keywords: eruptive energy, fractal dimension of fragmentation, pyroclastic fallout.

  7. Subcritical, Critical and Supercritical Size Distributions in Random Coagulation-Fragmentation Processes

    Institute of Scientific and Technical Information of China (English)

    Dong HAN; Xin Sheng ZHANG; Wei An ZHENG

    2008-01-01

    We consider the asymptotic probability distribution of the size of a reversible random coagula-tion-fragmentation process in the thermodynamic limit.We prove that the distributions of small,medium and the largest clusters converge to Gaussian,Poisson and 0-1 distributions in the supercritical stage (post-gelation),respectively.We show also that the mutually dependent distributions of clusters will become independent after the occurrence of a gelation transition.Furthermore,it is proved that all the number distributions of clusters are mutually independent at the critical stage (gelation),but the distributions of medium and the largest clusters are mutually dependent with positive correlation coe .cient in the supercritical stage.When the fragmentation strength goes to zero,there will exist only two types of clusters in the process,one type consists of the smallest clusters, the other is the largest one which has a size nearly equal to the volume (total number of units).

  8. Influence of ageing, inclusions and voids on ductile fracture mechanism in commercial Al-alloys

    Indian Academy of Sciences (India)

    A Chennakesava Reddy; S Sundar Rajan

    2005-02-01

    The objective of the paper is to study the effect of ageing, inclusions and voids on the mechanism of fracture and resultant toughness. It has been found that the voids are initiated at only a fraction of the larger inclusions present. The initiation of voids at small particles in the ductile fracture process appears to have little effect on fracture toughness. The strain hardening capacity has a marked effect on void size, and is an indicator of fracture toughness in the commercial Al alloy.

  9. Effects of transverse electron beam size on transition radiation angular distribution

    Energy Technology Data Exchange (ETDEWEB)

    Chiadroni, E., E-mail: enrica.chiadroni@lnf.infn.it [Laboratori Nazionali di Frascati-INFN, via E. Fermi, 40, 00044 Frascati (Italy); Castellano, M. [Laboratori Nazionali di Frascati-INFN, via E. Fermi, 40, 00044 Frascati (Italy); Cianchi, A. [University of Rome ' Tor Vergata' and INFN-Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome (Italy); Honkavaara, K.; Kube, G. [Deutsches Elektronen-Synchrotron, Notkestrasse 85, 22607 Hamburg (Germany)

    2012-05-01

    In this paper we consider the effect of the transverse electron beam size on the Optical Transition Radiation (OTR) angular distribution in case of both incoherent and coherent emission. Our results confute the theoretical argumentations presented first in Optics Communications 211, 109 (2002), which predicts a dependence of the incoherent OTR angular distribution on the beam size and emission wavelength. We present here theoretical and experimental data not only to validate the well-established Ginzburg-Frank theory, but also to show the impact of the transverse beam size in case of coherent emission.

  10. Inference of stratospheric aerosol composition and size distribution from SAGE II satellite measurements

    Science.gov (United States)

    Wang, Pi-Huan; Mccormick, M. P.; Fuller, W. H.; Yue, G. K.; Swissler, T. J.; Osborn, M. T.

    1989-01-01

    A method for inferring stratospheric aerosol composition and size distribution from the water vapor concentration and aerosol extinction measurements obtained in the Stratospheric Aerosol and Gas Experiment (SAGE) II and the associated temperature from the NMC. The aerosols are assumed to be sulfuric acid-water droplets. A modified Levenberg-Marquardt algorithm is used to determine model size distribution parameters based on the SAGE II multiwavelength aerosol extinctions. It is found that the best aerosol size information is contained in the aerosol radius range between about 0.25 and 0.80 micron.

  11. Size distribution of aerosol particles: comparison between agricultural and industrial areas in Egypt

    Energy Technology Data Exchange (ETDEWEB)

    Tadros, M.T.Y.; Madkour, M. [Mansoura Univ., Physics Dept., Mansoura (Egypt); Elmetwally, M. [Egyptian Meteorological Authority, Abbasyia-Cairo (Egypt)

    1999-07-01

    Mie theory has been used in this work to obtain a theoretical calculation of the size distribution of aerosol particles by using tabulated mean of the Angstrom wavelength exponent {alpha}{sub o}. Comparison was done between an industrial polluted area (Helwan, which is a neighbor to Cairo city), and an agricultural relatively unpolluted area (Mansoura, about 140 km from Cairo). The results show that the size distribution obeys the Junge power law. The size of particles in the polluted area is larger than that in the unpolluted area. (Author)

  12. Size distribution of a metallic polydispersion through capacitive measurements in a sedimentation experiment

    Science.gov (United States)

    Salazar-Neumann, E.; Nahmad-Molinari, Y.; Ruiz-Suárez, J. C.; Ardisson, P.-L.; Arancibia-Bulnes, C. A.; Rechtman, R.

    2001-07-01

    We present a simple experimental technique to determine size distributions of metallic polydispersions. The particles are first suspended in a viscous fluid-like glycerol and then their sedimentation is followed by measuring the effective dielectric constant in a cylindrical cell at a fixed frequency. Thereafter, an inversion procedure of the data, based on the Maxwell-Garnett effective medium theory and Stokes law, is used to directly obtain the size distribution. The technique is applied to three different stainless steel dispersions and compares very well with a traditional sizing method based in microphotography.

  13. Exact Solution of the Cluster Size Distribution for Multi-polymer Coagulation Process

    Institute of Scientific and Technical Information of China (English)

    KE Jian-Hong; LIN Zhen-Quan; WANG Xiang-Hong

    2003-01-01

    We propose a simple irreversible multi-polymer coagulation model in which m polymers consist of multiple components bond spontaneously to form a larger cluster. We solve the generalized Smoluchowski rate equation with constant reaction rates to obtain the exact solution of the cluster size distribution. The results indicate that the evolution behaviour of the system depends crucially on the polymer number m of the coagulation reaction. The cluster concentrations decay as t~m/(m~l) ; anc; tne typical size S(t) of the m-polymer coagulation system grows as t /'m~1'. On the other hand, the cluster size distribution may approach unusual scaling form in some cases.

  14. Effect of particle size distributions on absorbance spectra of gold nanoparticles

    Science.gov (United States)

    Doak, J.; Gupta, R. K.; Manivannan, K.; Ghosh, K.; Kahol, P. K.

    2010-03-01

    In this paper, a method is developed to calculate the absorbance spectra of nanoparticles solution containing a size distribution of particles using the Mie theory. The standard gold nanoparticles solutions were purchased and characterized with the UV-visible absorption spectroscopy and dynamic light scattering size measurements techniques. Model size distributions were fit to the experimental absorbance spectra using the method described herein. Good semi-quantitative fits were found, which elucidate qualitative differences between “small” and “large” gold nanoparticles.

  15. The temperature and size distribution of large water clusters from a non-equilibrium model

    Energy Technology Data Exchange (ETDEWEB)

    Gimelshein, N. [Gimel, Inc., San Jose, California 95124 (United States); Gimelshein, S., E-mail: gimelshe@usc.edu [University of Southern California, Los Angeles, California 90089 (United States); Pradzynski, C. C.; Zeuch, T., E-mail: tzeuch1@gwdg.de [Institut für Physikalische Chemie, Universität Göttingen, Tammanstr. 6, D-37077 Göttingen (Germany); Buck, U., E-mail: ubuck@gwdg.de [Max-Planck-Institut für Dynamik und Selbstorganisation, Am Faßberg 17, D-37077 Göttingen (Germany)

    2015-06-28

    A hybrid Lagrangian-Eulerian approach is used to examine the properties of water clusters formed in neon-water vapor mixtures expanding through microscale conical nozzles. Experimental size distributions were reliably determined by the sodium doping technique in a molecular beam machine. The comparison of computed size distributions and experimental data shows satisfactory agreement, especially for (H{sub 2}O){sub n} clusters with n larger than 50. Thus validated simulations provide size selected cluster temperature profiles in and outside the nozzle. This information is used for an in-depth analysis of the crystallization and water cluster aggregation dynamics of recently reported supersonic jet expansion experiments.

  16. A void ratio dependent water retention curve model including hydraulic hysteresis

    Directory of Open Access Journals (Sweden)

    Pasha Amin Y.

    2016-01-01

    Full Text Available Past experimental evidence has shown that Water Retention Curve (WRC evolves with mechanical stress and structural changes in soil matrix. Models currently available in the literature for capturing the volume change dependency of WRC are mainly empirical in nature requiring an extensive experimental programme for parameter identification which renders them unsuitable for practical applications. In this paper, an analytical model for the evaluation of the void ratio dependency of WRC in deformable porous media is presented. The approach proposed enables quantification of the dependency of WRC on void ratio solely based on the form of WRC at the reference void ratio and requires no additional parameters. The effect of hydraulic hysteresis on the evolution process is also incorporated in the model, an aspect rarely addressed in the literature. Expressions are presented for the evolution of main and scanning curves due to loading and change in the hydraulic path from scanning to main wetting/drying and vice versa as well as the WRC parameters such as air entry value, air expulsion value, pore size distribution index and slope of the scanning curve. The model is validated using experimental data on compacted and reconstituted soils subjected to various hydro-mechanical paths. Good agreement is obtained between model predictions and experimental data in all the cases considered.

  17. Testing the imprint of nonstandard cosmologies on void profiles using Monte Carlo random walks

    Science.gov (United States)

    Achitouv, Ixandra

    2016-11-01

    Using Monte Carlo random walks of a log-normal distribution, we show how to qualitatively study void properties for nonstandard cosmologies. We apply this method to an f (R ) modified gravity model and recover the N -body simulation results of [1 I. Achitouv, M. Baldi, E. Puchwein, and J. Weller, Phys. Rev. D 93, 103522 (2016).] for the void profiles and their deviation from GR. This method can potentially be extended to study other properties of the large scale structures such as the abundance of voids or overdense environments. We also introduce a new way to identify voids in the cosmic web, using only a few measurements of the density fluctuations around random positions. This algorithm allows us to select voids with specific profiles and radii. As a consequence, we can target classes of voids with higher differences between f (R ) and standard gravity void profiles. Finally, we apply our void criteria to galaxy mock catalogues and discuss how the flexibility of our void finder can be used to reduce systematic errors when probing the growth rate in the galaxy-void correlation function.

  18. Testing the imprint of non-standard cosmologies on void profiles using Monte Carlo random walks

    CERN Document Server

    Achitouv, Ixandra

    2016-01-01

    Using a Monte Carlo random walks of a log-normal distribution, we show how to qualitatively study void properties for non-standard cosmologies. We apply this method to an f(R) modified gravity model and recover the N-body simulation results of (Achitouv et al. 2016) for the void profiles and their deviation from GR. This method can potentially be extended to study other properties of the large scale structures such as the abundance of voids or overdense environments. We also introduce a new way to identify voids in the cosmic web, using only a few measurements of the density fluctuations around random positions. This algorithm allows to select voids with specific profiles and radii. As a consequence, we can target classes of voids with higher differences between f(R) and standard gravity void profiles. Finally we apply our void criteria to galaxy mock catalogues and discuss how the flexibility of our void finder can be used to reduce systematics errors when probing the growth rate in the galaxy-void correlati...

  19. Quantification of the evolution of firm size distributions due to mergers and acquisitions

    Science.gov (United States)

    Sornette, Didier

    2017-01-01

    The distribution of firm sizes is known to be heavy tailed. In order to account for this stylized fact, previous economic models have focused mainly on growth through investments in a company’s own operations (internal growth). Thereby, the impact of mergers and acquisitions (M&A) on the firm size (external growth) is often not taken into consideration, notwithstanding its potential large impact. In this article, we make a first step into accounting for M&A. Specifically, we describe the effect of mergers and acquisitions on the firm size distribution in terms of an integro-differential equation. This equation is subsequently solved both analytically and numerically for various initial conditions, which allows us to account for different observations of previous empirical studies. In particular, it rationalises shortcomings of past work by quantifying that mergers and acquisitions develop a significant influence on the firm size distribution only over time scales much longer than a few decades. This explains why M&A has apparently little impact on the firm size distributions in existing data sets. Our approach is very flexible and can be extended to account for other sources of external growth, thus contributing towards a holistic understanding of the distribution of firm sizes. PMID:28841683

  20. Quantification of the evolution of firm size distributions due to mergers and acquisitions.

    Science.gov (United States)

    Lera, Sandro Claudio; Sornette, Didier

    2017-01-01

    The distribution of firm sizes is known to be heavy tailed. In order to account for this stylized fact, previous economic models have focused mainly on growth through investments in a company's own operations (internal growth). Thereby, the impact of mergers and acquisitions (M&A) on the firm size (external growth) is often not taken into consideration, notwithstanding its potential large impact. In this article, we make a first step into accounting for M&A. Specifically, we describe the effect of mergers and acquisitions on the firm size distribution in terms of an integro-differential equation. This equation is subsequently solved both analytically and numerically for various initial conditions, which allows us to account for different observations of previous empirical studies. In particular, it rationalises shortcomings of past work by quantifying that mergers and acquisitions develop a significant influence on the firm size distribution only over time scales much longer than a few decades. This explains why M&A has apparently little impact on the firm size distributions in existing data sets. Our approach is very flexible and can be extended to account for other sources of external growth, thus contributing towards a holistic understanding of the distribution of firm sizes.

  1. Size distributions of major elements in residual ash particles from coal combustion

    Institute of Scientific and Technical Information of China (English)

    YU DunXi; XU MingHou; YAO Hong; LIU XiaoWei

    2009-01-01

    Combustion experiments for three coals of different ranks were conducted in an electrically-heated drop tube furnace. The size distributions of major elements in the residual ash particles (>0.4μm) such as AI, Si, S, P, Na, Mg, K, Ca and Fe were investigated. The experimental results showed that the concentrations of AI and Si in the residual ash particles decreased with decreasing particle size, while the concentrations of S and P increased with decreasing particle size. No consistent size distributions were obtained for Na, Mg, K, Ca and Fe. The established deposition model accounting for trace element distributions was demonstrated to be applicable to some major elements as well. The modeling results indicated that the size distributions of the refractory elements, AI and Si, were mainly influenced by the deposition of vaporized elements on particle surfaces. A dominant fraction of S and P vaporized during coal combustion. Their size distributions were determined by surface condensation, reaction or adsorption. The partitioning mechanisms of Na, Mg, K, Ca and Fe were more complex.

  2. Some comments on the characterization of drop-size distribution in sprays

    Science.gov (United States)

    Chin, J. S.; Lefebvre, A. H.

    An attempt is made to explain and clarify some of the anomalies and misconceptions that are encountered in the literature on drop-size distributions in sprays. The key features and relative merits of the various parameters that have been put forward to describe drop-size distribution, such as the Rosin-Rammler equation, Droplet Uniformity Index, Relative Span Factor, Dispersion Index, and MMD/SMD ratio, are discussed. It is shown that although any suitable diameter may be used as the representative diameter in the Rosin-Rammler distribution function, the Sauter mean diameter (SMD) provides the best indication of the atomization quality of a spray.

  3. The relation between pre-eruptive bubble size distribution, ash particle morphology, and their internal density: Implications to volcanic ash transport and dispersion models

    Science.gov (United States)

    Proussevitch, Alexander

    2014-05-01

    Parameterization of volcanic ash transport and dispersion (VATD) models strongly depends on particle morphology and their internal properties. Shape of ash particles affects terminal fall velocities (TFV) and, mostly, dispersion. Internal density combined with particle size has a very strong impact on TFV and ultimately on the rate of ash cloud thinning and particle sedimentation on the ground. Unlike other parameters, internal particle density cannot be measured directly because of the micron scale sizes of fine ash particles, but we demonstrate that it varies greatly depending on the particle size. Small simple type ash particles (fragments of bubble walls, 5-20 micron size) do not contain whole large magmatic bubbles inside and their internal density is almost the same as that of volcanic glass matrix. On the other side, the larger compound type ash particles (>40 microns for silicic fine ashes) always contain some bubbles or the whole spectra of bubble size distribution (BSD), i.e. bubbles of all sizes, bringing their internal density down as compared to simple ash. So, density of the larger ash particles is a function of the void fraction inside them (magmatic bubbles) which, in turn, is controlled by BSD. Volcanic ash is a product of the fragmentation of magmatic foam formed by pre-eruptive bubble population and characterized by BSD. The latter can now be measured from bubble imprints on ash particle surfaces using stereo-scanning electron microscopy (SSEM) and BubbleMaker software developed at UNH, or using traditional high-resolution X-Ray tomography. In this work we present the mathematical and statistical formulation for this problem connecting internal ash density with particle size and BSD, and demonstrate how the TFV of the ash population is affected by variation of particle density.

  4. A Stochastic Theory for Deep Bed Filtration Accounting for Dispersion and Size Distributions

    DEFF Research Database (Denmark)

    Shapiro, Alexander; Bedrikovetsky, P. G.

    2010-01-01

    We develop a stochastic theory for filtration of suspensions in porous media. The theory takes into account particle and pore size distributions, as well as the random character of the particle motion, which is described in the framework of the theory of continuous-time random walks (CTRW......). In the limit of the infinitely many small walk steps we derive a system of governing equations for the evolution of the particle and pore size distributions. We consider the case of concentrated suspensions, where plugging the pores by particles may change porosity and other parameters of the porous medium....... A procedure for averaging of the derived system of equations is developed for polydisperse suspensions with several distinctive particle sizes. A numerical method for solution of the flow equations is proposed. Sample calculations are applied to compare the roles of the particle size distribution...

  5. Influence of pore size distribution on the adsorption of phenol on PET-based activated carbons.

    Science.gov (United States)

    Lorenc-Grabowska, Ewa; Diez, María A; Gryglewicz, Grazyna

    2016-05-01

    The role of pore size distribution in the adsorption of phenol in aqueous solutions on polyethylene terephthalate (PET)-based activated carbons (ACs) has been analyzed. The ACs were prepared from PET and mixtures of PET with coal-tar pitch (CTP) by means of carbonization and subsequent steam and carbon dioxide activation at 850 and 950 °C, respectively. The resultant ACs were characterized on the basis of similarities in their surface chemical features and differences in their micropore size distributions. The adsorption of phenol was carried out in static conditions at ambient temperature. The pseudo-second order kinetic model and Langmuir model were found to fit the experimental data very well. The different adsorption capacities of the ACs towards phenol were attributed to differences in their micropore size distributions. Adsorption capacity was favoured by the volume of pores with a size smaller than 1.4 nm; but restricted by pores smaller than 0.8 nm.

  6. Control over particle size distribution by autoclaving poloxamer-stabilized trimyristin nanodispersions

    DEFF Research Database (Denmark)

    Göke, Katrin; Roese, Elin; Arnold, Andreas

    2016-01-01

    into the bloodstream. Consequently, small particles with a narrow particle size distribution are desired. Hitherto, there are, however, only limited possibilities for the preparation of monodisperse, pharmaceutically relevant dispersions. In this work, the effect of autoclaving at 121 °C on the particle size...... distribution of lipid nanoemulsions and -suspensions consisting of the pharmaceutically relevant components trimyristin and poloxamer 188 was studied. Additionally, the amount of emulsifier needed to stabilize both untreated and autoclaved particles was assessed. In our study, four dispersions of mean particle...... sizes from 45 to 150 nm were prepared by high-pressure melt homogenization. The particle size distribution before and after autoclaving was characterized using static and dynamic light scattering, differential scanning calorimetry, and transmission electron microscopy. Asymmetrical flow field...

  7. Planar dust-acoustic waves in electron-positron-ion-dust plasmas with dust size distribution

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Hong-Yan; Zhang, Kai-Biao [Sichuan University of Science and Engineering, Zigong (China)

    2014-06-15

    Nonlinear dust-acoustic solitary waves which are described with a Kortweg-de vries (KdV) equation by using the reductive perturbation method, are investigated in a planar unmagnetized dusty plasma consisting of electrons, positrons, ions and negatively-charged dust particles of different sizes and masses. The effects of the power-law distribution of dust and other plasma parameters on the dust-acoustic solitary waves are studied. Numerical results show that the dust size distribution has a significant influence on the propagation properties of dust-acoustic solitons. The amplitudes of solitary waves in the case of a power-law distribution is observed to be smaller, but the soliton velocity and width are observed to be larger, than those of mono-sized dust grains with an average dust size. Our results indicate that only compressed solitary waves exist in dusty plasma with different dust species. The relevance of the present investigation to interstellar clouds is discussed.

  8. New method to estimate the sample size for calculation of a proportion assuming binomial distribution.

    Science.gov (United States)

    Vallejo, Adriana; Muniesa, Ana; Ferreira, Chelo; de Blas, Ignacio

    2013-10-01

    Nowadays the formula to calculate the sample size for estimate a proportion (as prevalence) is based on the Normal distribution, however it would be based on a Binomial distribution which confidence interval was possible to be calculated using the Wilson Score method. By comparing the two formulae (Normal and Binomial distributions), the variation of the amplitude of the confidence intervals is relevant in the tails and the center of the curves. In order to calculate the needed sample size we have simulated an iterative sampling procedure, which shows an underestimation of the sample size for values of prevalence closed to 0 or 1, and also an overestimation for values closed to 0.5. Attending to these results we proposed an algorithm based on Wilson Score method that provides similar values for the sample size than empirically obtained by simulation.

  9. Comparison of outdoor activity size distributions of {sup 220}Rn and {sup 222}Rn progeny

    Energy Technology Data Exchange (ETDEWEB)

    Mohamed, A. [Physics Department, Faculty of Science, El-Minia University (Egypt)]. E-mail: amermohamed6@hotmail.com; El-Hussein, A. [Physics Department, Faculty of Science, El-Minia University (Egypt)

    2005-06-01

    Inhalation of {sup 222}Rn and {sup 220}Rn progeny from the domestic environment contributes the greatest fraction of the natural radiation exposure to the public. Dosimetric models are most often used in the assessment of human lung doses due to inhaled radioactivity because of the difficulty in making direct measurements. These models require information about the parameters of activity size distributions of thoron and radon progeny. The present study presents measured data on the attached and unattached activity size distributions of thoron and radon progeny in outdoor air in El-Minia, Egypt. The attached fraction was collected using a low-pressure Berner cascade impactor technique. A screen diffusion battery was used for collecting the unattached fraction. Most of the attached activities for {sup 222}Rn and {sup 220}Rn progeny were associated with aerosol particles of the accumulation mode. The activity size distribution of thoron progeny was found to be shifted to slightly smaller particle size compared to radon progeny.

  10. Detailed mass size distributions of atmospheric aerosol species in the Negev desert, Israel, during ARACHNE-96

    Science.gov (United States)

    Maenhaut, Willy; Ptasinski, Jacek; Cafmeyer, Jan

    1999-04-01

    As part of the 1996 summer intensive of the Aerosol, RAdiation and CHemistry Experiment (ARACHNE-96), the mass size distribution of various airborne particulate elements was studied at a remote site in the Negev Desert, Israel. Aerosol collections were made with 8-stage PIXE International cascade impactors (PCIs) and 12-stage small deposit area low pressure impactors (SDIs) and the samples were analyzed by PIXE for about 20 elements. The mineral elements (Al, Si, Ca, Ti, Fe) exhibited a unimodal size distribution which peaked at about 6 μm, but the contribution of particles larger than 10 μm was clearly more pronounced during the day than during night. Sulphur and Br had a tendency to exhibit two modes in the submicrometer size range, with diameters at about 0.3 and 0.6 μm, respectively. The elements V and Ni, which are indicators of residual fuel burning, showed essentially one fine mode (at 0.3 μm) in addition to a coarse mode which represented the mineral dust contribution. Overall, good agreement was observed between the mass size distributions from the PCI and SDI devices. The PCI was superior to the SDI for studying the size distribution in the coarse size range, but the SDI was clearly superior for unravelling the various modes in the submicrometer size range.

  11. Detailed mass size distributions of atmospheric aerosol species in the Negev desert, Israel, during ARACHNE-96

    Energy Technology Data Exchange (ETDEWEB)

    Maenhaut, Willy E-mail: maenhaut@inwchem.rug.ac.be; Ptasinski, Jacek; Cafmeyer, Jan

    1999-04-02

    As part of the 1996 summer intensive of the Aerosol, RAdiation and CHemistry Experiment (ARACHNE-96), the mass size distribution of various airborne particulate elements was studied at a remote site in the Negev Desert, Israel. Aerosol collections were made with 8-stage PIXE International cascade impactors (PCIs) and 12-stage small deposit area low pressure impactors (SDIs) and the samples were analyzed by PIXE for about 20 elements. The mineral elements (Al, Si, Ca, Ti, Fe) exhibited a unimodal size distribution which peaked at about 6 {mu}m, but the contribution of particles larger than 10 {mu}m was clearly more pronounced during the day than during night. Sulphur and Br had a tendency to exhibit two modes in the submicrometer size range, with diameters at about 0.3 and 0.6 {mu}m, respectively. The elements V and Ni, which are indicators of residual fuel burning, showed essentially one fine mode (at 0.3 {mu}m) in addition to a coarse mode which represented the mineral dust contribution. Overall, good agreement was observed between the mass size distributions from the PCI and SDI devices. The PCI was superior to the SDI for studying the size distribution in the coarse size range, but the SDI was clearly superior for unravelling the various modes in the submicrometer size range.

  12. Deconvolution of the particle size distribution of ProRoot MTA and MTA Angelus.

    Science.gov (United States)

    Ha, William Nguyen; Shakibaie, Fardad; Kahler, Bill; Walsh, Laurence James

    2016-01-01

    Objective Mineral trioxide aggregate (MTA) cements contain two types of particles, namely Portland cement (PC) (nominally 80% w/w) and bismuth oxide (BO) (20%). This study aims to determine the particle size distribution (PSD) of PC and BO found in MTA. Materials and methods The PSDs of ProRoot MTA (MTA-P) and MTA Angelus (MTA-A) powder were determined using laser diffraction, and compared to samples of PC (at three different particle sizes) and BO. The non-linear least squares method was used to deconvolute the PSDs into the constituents. MTA-P and MTA-A powders were also assessed with scanning electron microscopy. Results BO showed a near Gaussian distribution for particle size, with a mode distribution peak at 10.48 μm. PC samples milled to differing degrees of fineness had mode distribution peaks from 19.31 down to 4.88 μm. MTA-P had a complex PSD composed of both fine and large PC particles, with BO at an intermediate size, whereas MTA-A had only small BO particles and large PC particles. Conclusions The PSD of MTA cement products is bimodal or more complex, which has implications for understanding how particle size influences the overall properties of the material. Smaller particles may be reactive PC or unreactive radiopaque agent. Manufacturers should disclose particle size information for PC and radiopaque agents to prevent simplistic conclusions being drawn from statements of average particle size for MTA materials.

  13. An Empirical Bayes Mixture Model for Effect Size Distributions in Genome-Wide Association Studies

    DEFF Research Database (Denmark)

    Thompson, Wesley K.; Wang, Yunpeng; Schork, Andrew J.

    2015-01-01

    Characterizing the distribution of effects from genome-wide genotyping data is crucial for understanding important aspects of the genetic architecture of complex traits, such as number or proportion of non-null loci, average proportion of phenotypic variance explained per non-null effect, power...... for discovery, and polygenic risk prediction. To this end, previous work has used effect-size models based on various distributions, including the normal and normal mixture distributions, among others. In this paper we propose a scale mixture of two normals model for effect size distributions of genome...... of variance explained by genotyped SNPs, CD and SZ have a broadly dissimilar genetic architecture, due to differing mean effect size and proportion of non-null loci....

  14. Evaluation of the effective thermal conductivity of composite polymers by considering the filler size distribution law

    Institute of Scientific and Technical Information of China (English)

    Sorin HOLOTESCU; Floriana D.STOIAN

    2009-01-01

    We present an empirical model for the effective thermal conductivity(ETC)of a polymer composite that includes dependency on the filler size distribution-chosen as the Rosin-Rammler distribution.The ETC is determined based on certain hypotheses that connect the behavior of a real composite matefial A.to that of a model composite material B,filled with mono-dimensional filler.The application of these hypotheses to the Maxwell model for ETC is presented.The validation of the new model and its characteristic equation was carried out using experimental data from the reference.The comparison showed that by using the size distribution law a very good fit between the equation of the new model(the size distribution model for the ETC)and the reference experimental results is obtained,even for high volume fractions,up to about 50%.

  15. Simulation and analysis of the soot particle size distribution in a turbulent nonpremixed flame

    KAUST Repository

    Lucchesi, Marco

    2017-02-05

    A modeling framework based on Direct Simulation Monte Carlo (DSMC) is employed to simulate the evolution of the soot particle size distribution in turbulent sooting flames. The stochastic reactor describes the evolution of soot in fluid parcels following Lagrangian trajectories in a turbulent flow field. The trajectories are sampled from a Direct Numerical Simulation (DNS) of a n-heptane turbulent nonpremixed flame. The DSMC method is validated against experimentally measured size distributions in laminar premixed flames and found to reproduce quantitatively the experimental results, including the appearance of the second mode at large aggregate sizes and the presence of a trough at mobility diameters in the range 3–8 nm. The model is then applied to the simulation of soot formation and growth in simplified configurations featuring a constant concentration of soot precursors and the evolution of the size distribution in time is found to depend on the intensity of the nucleation rate. Higher nucleation rates lead to a higher peak in number density and to the size distribution attaining its second mode sooner. The ensemble-averaged PSDF in the turbulent flame is computed from individual samples of the PSDF from large sets of Lagrangian trajectories. This statistical measure is equivalent to time-averaged, scanning mobility particle size (SMPS) measurements in turbulent flames. Although individual trajectories display strong bimodality as in laminar flames, the ensemble-average PSDF possesses only one mode and a long, broad tail, which implies significant polydispersity induced by turbulence. Our results agree very well with SMPS measurements available in the literature. Conditioning on key features of the trajectory, such as mixture fraction or radial locations does not reduce the scatter in the size distributions and the ensemble-averaged PSDF remains broad. The results highlight and explain the important role of turbulence in broadening the size distribution of

  16. Reynolds number scaling to predict droplet size distribution in dispersed and undispersed subsurface oil releases.

    Science.gov (United States)

    Li, Pu; Weng, Linlu; Niu, Haibo; Robinson, Brian; King, Thomas; Conmy, Robyn; Lee, Kenneth; Liu, Lei

    2016-12-15

    This study was aimed at testing the applicability of modified Weber number scaling with Alaska North Slope (ANS) crude oil, and developing a Reynolds number scaling approach for oil droplet size prediction for high viscosity oils. Dispersant to oil ratio and empirical coefficients were also quantified. Finally, a two-step Rosin-Rammler scheme was introduced for the determination of droplet size distribution. This new approach appeared more advantageous in avoiding the inconsistency in interfacial tension measurements, and consequently delivered concise droplet size prediction. Calculated and observed data correlated well based on Reynolds number scaling. The relation indicated that chemical dispersant played an important role in reducing the droplet size of ANS under different seasonal conditions. The proposed Reynolds number scaling and two-step Rosin-Rammler approaches provide a concise, reliable way to predict droplet size distribution, supporting decision making in chemical dispersant application during an offshore oil spill.

  17. Particle size distributions and the sequential fragmentation/transport theory applied to volcanic ash

    Energy Technology Data Exchange (ETDEWEB)

    Wohletz, K.H. (Earth and Space Science Division Los Alamos National Laboratory, New Mexico (USA)); Sheridan, M.F. (Department of Geology, Arizona State University, Tempe (USA)); Brown, W.K. (Math/Science Division, Lassen College, Susanville, California (USA))

    1989-11-10

    The assumption that distributions of mass versus size interval for fragmented materials fit the log normal distribution is empirically based and has historical roots in the late 19th century. Other often used distributions (e.g., Rosin-Rammler, Weibull) are also empirical and have the general form for mass per size interval: {ital n}({ital l})={ital kl}{sup {alpha}} exp(-{ital l}{beta}), where {ital n}({ital l}) represents the number of particles of diameter {ital l}, {ital l} is the normalized particle diameter, and {ital k}, {alpha}, and {beta} are constants. We describe and extend the sequential fragmentation distribution to include transport effects upon observed volcanic ash size distributions. The sequential fragmentation/transport (SFT) distribution is also of the above mathematical form, but it has a physical basis rather than empirical. The SFT model applies to a particle-mass distribution formed by a sequence of fragmentation (comminution) and transport (size sorting) events acting upon an initial mass {ital m}{prime}: {ital n}({ital x}, {ital m})={ital C} {integral}{integral} {ital n}({ital x}{prime}, {ital m}{prime}){ital p}({xi}) {ital dx}{prime} {ital dm}{prime}, where {ital x}{prime} denotes spatial location along a linear axis, {ital C} is a constant, and integration is performed over distance from an origin to the sample location and mass limits from 0 to {ital m}.

  18. NUMBER CONCENTRATION, SIZE DISTRIBUTION AND FINE PARTICLE FRACTION OF TROPOSPHERIC AND STRATOSPHERIC AEROSOLS

    Institute of Scientific and Technical Information of China (English)

    Li Xu; Guangyu Shi; Li Zhang; Jun Zhou; Yasunobu Iwasaka

    2003-01-01

    Aerosol observations were carried out at Xianghe Scientific Balloon Base (39.45°N, 117°E) using a stratospheric balloon. The particle number concentrations of the tropospheric and stratospheric aerosols were directly explored.The vertical distributions of the number concentration, number-size (that is, particle number versus particle size)distribution, and the fraction of fine particles (0.5 μm>r>0.15 μm/r>0.15 μm) are reported in this paper. The profiles of particle concentration present multi-peak phenomenon. The pattern of size distribution for atmospheric aerosol indicates a tri-modal (r=~0.2 μm, ~0.88 μm and ~7.0 μm) and a bi-modal (r=~0.13 μm and 2.0 μm). The number-size distribution almost fits the Junge distribution for particles with r<0.5 μm in the stratosphere of 1993 and the troposphere of 1994. But the distributions of coarse particles (r>0.5 μm) are not uniform. The number-size distribution exhibits also a wide size range in the troposphere of 1993. The results demonstrate that fine particles represent the major portion in the troposphere during the measurement period, reaching as high as 95% in 1994. Certain coarse particle peaks in the troposphere were attributed to clouds and other causes, and in the stratosphere to volcanic eruption. The stratospheric aerosol layer consists of unique fractions of fine or coarse particles depending on their sources. In summary, the process of gas-to-particles conversion was active and the coarse particles were rich over the Xianghe area. The measurements also demonstrate that the spatial and temporal atmospheric aerosol distributions are nonuniform and changeful.

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

    Science.gov (United States)

    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

  20. Numerical Simulation of Dust Void Evolution in Complex Plasmas with Ionization Effect

    Institute of Scientific and Technical Information of China (English)

    LIU Yue; WANG Zheng-Xiong; WANG Xiao-Gang

    2006-01-01

    We develop the nonlinear theory of dust voids [Phys. Rev. Lett. 90 (2003) 075001], focusing particularly on effects of the ionization, to investigate numerically the void evolution under cylindrical coordinates [Phys. Plasmas 13(2006) 064502]. The ion velocity profile is solved by a more accurate ion motion equation with the ion convection and ionization terms. It is shown that the differences between the previous result and the one obtained with ionizations are significant for the distributions of the ion and dust velocities, the dust density, and etc., in the void formation process. Furthermore, the ionization can slow down the void formation process effectively.