Science.gov

Sample records for exponential growth kinetics

  1. Noise in Exponential Growth

    NASA Astrophysics Data System (ADS)

    Iyer-Biswas, Srividya; Wright, Charles; Henry, Jon; Burov, Stas; Lin, Yihan; Crosson, Sean; Dinner, Aaron; Scherer, Norbert

    2013-03-01

    The interplay between growth and division of cells is has been studied in the context of exponential growth of bacterial cells (in suitable conditions) for decades. However, bulk culture studies obscure phenomena that manifest in single cells over many generations. We introduce a unique technology combining microfluidics, single-cell imaging, and quantitative analysis. This enables us to track the growth of single Caulobacter crescentus stalked cells over hundreds of generations. The statistics that we extract indicate a size thresholding mechanism for cell division and a non-trivial scaling collapse of division time distributions at different temperatures. In this talk I shall discuss these observations and a stochastic model of growth and division that captures all our observations with no free parameters.

  2. Modeling Exponential Population Growth

    ERIC Educational Resources Information Center

    McCormick, Bonnie

    2009-01-01

    The concept of population growth patterns is a key component of understanding evolution by natural selection and population dynamics in ecosystems. The National Science Education Standards (NSES) include standards related to population growth in sections on biological evolution, interdependence of organisms, and science in personal and social…

  3. Universality in Stochastic Exponential Growth

    NASA Astrophysics Data System (ADS)

    Iyer-Biswas, Srividya; Crooks, Gavin E.; Scherer, Norbert F.; Dinner, Aaron R.

    2014-07-01

    Recent imaging data for single bacterial cells reveal that their mean sizes grow exponentially in time and that their size distributions collapse to a single curve when rescaled by their means. An analogous result holds for the division-time distributions. A model is needed to delineate the minimal requirements for these scaling behaviors. We formulate a microscopic theory of stochastic exponential growth as a Master Equation that accounts for these observations, in contrast to existing quantitative models of stochastic exponential growth (e.g., the Black-Scholes equation or geometric Brownian motion). Our model, the stochastic Hinshelwood cycle (SHC), is an autocatalytic reaction cycle in which each molecular species catalyzes the production of the next. By finding exact analytical solutions to the SHC and the corresponding first passage time problem, we uncover universal signatures of fluctuations in exponential growth and division. The model makes minimal assumptions, and we describe how more complex reaction networks can reduce to such a cycle. We thus expect similar scalings to be discovered in stochastic processes resulting in exponential growth that appear in diverse contexts such as cosmology, finance, technology, and population growth.

  4. Universality in stochastic exponential growth.

    PubMed

    Iyer-Biswas, Srividya; Crooks, Gavin E; Scherer, Norbert F; Dinner, Aaron R

    2014-07-11

    Recent imaging data for single bacterial cells reveal that their mean sizes grow exponentially in time and that their size distributions collapse to a single curve when rescaled by their means. An analogous result holds for the division-time distributions. A model is needed to delineate the minimal requirements for these scaling behaviors. We formulate a microscopic theory of stochastic exponential growth as a Master Equation that accounts for these observations, in contrast to existing quantitative models of stochastic exponential growth (e.g., the Black-Scholes equation or geometric Brownian motion). Our model, the stochastic Hinshelwood cycle (SHC), is an autocatalytic reaction cycle in which each molecular species catalyzes the production of the next. By finding exact analytical solutions to the SHC and the corresponding first passage time problem, we uncover universal signatures of fluctuations in exponential growth and division. The model makes minimal assumptions, and we describe how more complex reaction networks can reduce to such a cycle. We thus expect similar scalings to be discovered in stochastic processes resulting in exponential growth that appear in diverse contexts such as cosmology, finance, technology, and population growth. PMID:25062238

  5. Exponential Growth of Nonlinear Ballooning Instability

    SciTech Connect

    Zhu, P.; Hegna, C. C.; Sovinec, C. R.

    2009-06-12

    Recent ideal magnetohydrodynamic (MHD) theory predicts that a perturbation evolving from a linear ballooning instability will continue to grow exponentially in the intermediate nonlinear phase at the same linear growth rate. This prediction is confirmed in ideal MHD simulations. When the Lagrangian compression, a measure of the ballooning nonlinearity, becomes of the order of unity, the intermediate nonlinear phase is entered, during which the maximum plasma displacement amplitude as well as the total kinetic energy continues to grow exponentially at the rate of the corresponding linear phase.

  6. Growth Kinetics of Listeria monocytogenes in Broth and Beef Frankfurters– Determination of Lag Phase Duration and Exponential Growth Rate under Isothermal Conditions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The objective of this research was to develop a new kinetic model to describe the isothermal growth of microorganisms. The new model was tested with Listeria monocytogenes in broth and frankfurters, and compared with two commonly used models - Baranyi and modified Gompertz models. Bias factor (BF)...

  7. A Simulation To Model Exponential Growth.

    ERIC Educational Resources Information Center

    Appelbaum, Elizabeth Berman

    2000-01-01

    Describes a simulation using dice-tossing students in a population cluster to model the growth of cancer cells. This growth is recorded in a scatterplot and compared to an exponential function graph. (KHR)

  8. Exponential kinetics of formation of organic microstructures

    NASA Technical Reports Server (NTRS)

    Fraser, C. L.; Folsome, C. E.

    1975-01-01

    Organic microstructure production in Miller-Urey spark discharge flasks is an energy-dependent, autocatalytic process which follows first order kinetics similar to microbial growth curves. These relationships hold for all three major morphological types of microstructures observed. The three types are assembled from smaller precursor subunits which associate according to a binomial distribution. These structures could have formed bounded systems in which pre-biological processes might have occurred.

  9. Exponential kinetics of formation or organic microstructures.

    PubMed

    Fraser, C L; Folsome, C E

    1975-07-01

    Organic microstructure production in Miller-Urey spark discharge flasks in an energy-dependent, autocatalytic process which follows first order kinetics similar to microbial growth curves. These relationships hold for all three major morphological types of microstructures observed. The three types are assembled from smaller precursor subunits which associate according to a binomial distribution. These structures could have formed bounded systems in which pre-biological processes might have occurred. PMID:1187106

  10. Segregated growth kinetics of Escherichia coli DH5α-NH36 in exponential-fed perfusion culture for pDNA vaccine production.

    PubMed

    Munguía-Soto, Rodolfo; García-Rendón, Aurora; Garibay-Escobar, Adriana; Guerrero-Germán, Patricia; Tejeda-Mansir, Armando

    2015-01-01

    The clinical demand of plasmid DNA (pDNA) has been increasing constantly. An exponential-fed perfusion (EFP) culture is a new mode for plasmid production for clinical trials and commercialization. However, the culture conditions may lead to cell filamentation and growth cessation. In this study, the variation of the physiological state and the plasmid contents of Escherichia coli DH5α hosting pVAX1-NH36 in an EFP culture for application as a Leishmaniasis vaccine was investigated. The culture performance was monitored using flow cytometry (FC) and real-time quantitative PCR. The FC studies showed a high viability of cell population and a constant distribution of complexity and size. A high homogeneity of pDNA (>95 % of supercoiled) was obtained, which might be attributed to a better culture environment. The obtained plasmid specific and volumetric yields of 1.8 mg/g dcw and 36.5 mg/L represent typical values for laboratory-scale plasmid production in a defined medium. A segregated kinetic model of the perfusion system was developed and fitted to the experimental data (R(2) > 0.96). A practical conclusion of this work is that a space-time yield analysis of a bioprocess requires a viability evaluation. This new strategy of culture operation might help in the efficient production of pDNA for therapeutic use. PMID:25556882

  11. An Exponential Growth Learning Trajectory: Students' Emerging Understanding of Exponential Growth through Covariation

    ERIC Educational Resources Information Center

    Ellis, Amy B.; Ozgur, Zekiye; Kulow, Torrey; Dogan, Muhammed F.; Amidon, Joel

    2016-01-01

    This article presents an Exponential Growth Learning Trajectory (EGLT), a trajectory identifying and characterizing middle grade students' initial and developing understanding of exponential growth as a result of an instructional emphasis on covariation. The EGLT explicates students' thinking and learning over time in relation to a set of tasks…

  12. A Simple Mechanical Experiment on Exponential Growth

    ERIC Educational Resources Information Center

    McGrew, Ralph

    2015-01-01

    With a rod, cord, pulleys, and slotted masses, students can observe and graph exponential growth in the cord tension over a factor of increase as large as several hundred. This experiment is adaptable for use either in algebra-based or calculus-based physics courses, fitting naturally with the study of sliding friction. Significant parts of the…

  13. 101 Ways to Teach About Exponential Growth and Its Consequences.

    ERIC Educational Resources Information Center

    Allen, Rodney F., Ed.

    Exponential growth is a mega-concept which has many applications. It is fundamental to understanding how and why systems work and fail, be they natural or man-made systems. Lessons/activities in this booklet are designed for Florida teachers to help provide their students with an understanding of the nature and implications of exponential growth.…

  14. Exponential growth of bacteria: Constant multiplication through division

    NASA Astrophysics Data System (ADS)

    Hagen, Stephen J.

    2010-12-01

    The growth of a bacterial culture is one of the most familiar examples of exponential growth, with important consequences in biology and medicine. Bacterial growth involves more than just a rate constant. To sustain exponential growth, the cell must carefully coordinate the accumulation of mass, constant replication of the chromosome, and physical division. Hence, the growth rate is centrally important in any physical and chemical description of a bacterial cell. These aspects of bacterial growth can be described by empirical laws that suggest simple and intuitive models. Therefore, a quantitative discussion of bacterial growth could be a part of any undergraduate biophysics course. We present a general overview of some classic experimental studies and mathematical models of bacterial growth from a mostly physical perspective.

  15. Exponential order statistic models of software reliability growth

    NASA Technical Reports Server (NTRS)

    Miller, D. R.

    1986-01-01

    Failure times of a software reliability growth process are modeled as order statistics of independent, nonidentically distributed exponential random variables. The Jelinsky-Moranda, Goel-Okumoto, Littlewood, Musa-Okumoto Logarithmic, and Power Law models are all special cases of Exponential Order Statistic Models, but there are many additional examples also. Various characterizations, properties and examples of this class of models are developed and presented.

  16. Exponential order statistic models of software reliability growth

    NASA Technical Reports Server (NTRS)

    Miller, D. R.

    1985-01-01

    Failure times of a software reliabilty growth process are modeled as order statistics of independent, nonidentically distributed exponential random variables. The Jelinsky-Moranda, Goel-Okumoto, Littlewood, Musa-Okumoto Logarithmic, and Power Law models are all special cases of Exponential Order Statistic Models, but there are many additional examples also. Various characterizations, properties and examples of this class of models are developed and presented.

  17. Teaching Exponential Growth and Decay: Examples from Medicine

    ERIC Educational Resources Information Center

    Hobbie, Russell K.

    1973-01-01

    A treatment of exponential growth and decay is sketched which does not require knowledge of calculus, and hence, it can be applied to many cases in the biological and medical sciences. Some examples are bacterial growth, sterilization, clearance, and drug absorption. (DF)

  18. Exponential energy growth in adiabatically changing Hamiltonian systems

    NASA Astrophysics Data System (ADS)

    Pereira, Tiago; Turaev, Dmitry

    2015-01-01

    We show that the mixed phase space dynamics of a typical smooth Hamiltonian system universally leads to a sustained exponential growth of energy at a slow periodic variation of parameters. We build a model for this process in terms of geometric Brownian motion with a positive drift, and relate it to the steady entropy increase after each period of the parameters variation.

  19. Iterative exponential growth of stereo- and sequence-controlled polymers

    NASA Astrophysics Data System (ADS)

    Barnes, Jonathan C.; Ehrlich, Deborah J. C.; Gao, Angela X.; Leibfarth, Frank A.; Jiang, Yivan; Zhou, Erica; Jamison, Timothy F.; Johnson, Jeremiah A.

    2015-10-01

    Chemists have long sought sequence-controlled synthetic polymers that mimic nature's biopolymers, but a practical synthetic route that enables absolute control over polymer sequence and structure remains a key challenge. Here, we report an iterative exponential growth plus side-chain functionalization (IEG+) strategy that begins with enantiopure epoxides and facilitates the efficient synthesis of a family of uniform >3 kDa macromolecules of varying sequence and stereoconfiguration that are coupled to produce unimolecular polymers (>6 kDa) with sequences and structures that cannot be obtained using traditional polymerization techniques. Selective side-chain deprotection of three hexadecamers is also demonstrated, which imbues each compound with the ability to dissolve in water. We anticipate that these new macromolecules and the general IEG+ strategy will find broad application as a versatile platform for the scalable synthesis of sequence-controlled polymers.

  20. Exponential potential for an inflaton with nonminimal kinetic coupling and its supergravity embedding

    NASA Astrophysics Data System (ADS)

    Dalianis, Iannis; Farakos, Fotis

    2014-10-01

    In the light of new observational results, we discuss the status of the exponential potentials driving inflation. We depart from the minimal scenario and study an inflaton kinetically coupled to the Einstein tensor. We find that in this case, the exponential potentials are well compatible with observations. Their predictions coincide with those of the chaotic-type quadratic potential for an inflaton minimally coupled to gravity. We show that there exists a simple mapping between the two models. Moreover, a novel aspect of our model is that it features a natural exit from the inflationary phase even in the absence of a minimum. We also turn to supergravity and motivate this sort of potential and the nonminimal kinetic coupling as possible effective dilaton theories.

  1. Integration of large chemical kinetic mechanisms via exponential methods with Krylov approximations to Jacobian matrix functions

    NASA Astrophysics Data System (ADS)

    Bisetti, Fabrizio

    2012-06-01

    Recent trends in hydrocarbon fuel research indicate that the number of species and reactions in chemical kinetic mechanisms is rapidly increasing in an effort to provide predictive capabilities for fuels of practical interest. In order to cope with the computational cost associated with the time integration of stiff, large chemical systems, a novel approach is proposed. The approach combines an exponential integrator and Krylov subspace approximations to the exponential function of the Jacobian matrix. The components of the approach are described in detail and applied to the ignition of stoichiometric methane-air and iso-octane-air mixtures, here described by two widely adopted chemical kinetic mechanisms. The approach is found to be robust even at relatively large time steps and the global error displays a nominal third-order convergence. The performance of the approach is improved by utilising an adaptive algorithm for the selection of the Krylov subspace size, which guarantees an approximation to the matrix exponential within user-defined error tolerance. The Krylov projection of the Jacobian matrix onto a low-dimensional space is interpreted as a local model reduction with a well-defined error control strategy. Finally, the performance of the approach is discussed with regard to the optimal selection of the parameters governing the accuracy of its individual components.

  2. Exponential growth of codimensions of identities of algebras with unity

    NASA Astrophysics Data System (ADS)

    Zaicev, M. V.; Repovš, D.

    2015-10-01

    The asymptotic behaviour is studied of exponentially bounded sequences of codimensions of identities of algebras with unity. A series of algebras is constructed for which the base of the exponential increases by exactly 1 when an outer unity is adjoined to the original algebra. It is shown that the PI-exponents of unital algebras can take any value greater than 2, and the exponents of finite-dimensional unital algebras form a dense subset in the domain \\lbrack 2,∞). Bibliography: 34 titles.

  3. Exponential growth of publications on carbon nanodots by Chinese authors

    PubMed Central

    Wang, Junqing; Choi, Hak Soo

    2015-01-01

    Publication statistics was retrieved on carbon nanodots (C-dots) from 2004 up till 2014 using the web of ScienceTM search engine. The number of publications from Chinese authors increased exponentially during this period. Till 2014 China mainland authors contributed 47% of the total publications. Publications on pharmacology and toxicology lagged far behind the publications on chemistry and material science, indicating that research is not solidly moving toward the direction of application. PMID:26380753

  4. Nucleation and growth transformation kinetics

    NASA Astrophysics Data System (ADS)

    Erukhimovitch, V.; Baram, J.

    1995-03-01

    As a result of the reassessment of the Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory for the kinetics of nucleation and growth transformations, an integral-equation formulation has been developed instead of the well-known and widely used Avrami equation. The presented formulation considers interfacial and diffusional growths, in one, two, and three dimensions, with both time-dependent and time-invariant nucleation and growth rates. The integral-equation model corrects reported inadequacies of the KJMA theory when applied in numerous experiments and various solid-state transformations. It is shown that in the example cases examined in this paper, crystallization from the amorphous state in melt-spun ribbons, isothermal aging of CuAlZn, pearlitic transition in an eutectoid steel, and crystallization in a PEKK polymer, the thermodynamic and kinetic interpretation and parameters extracted from best fits of the Avrami equations to the experimental data are erroneous. The KJMA formulation is a simplification of the real physical conditions. The main limitation of the new model is that almost all the integral equations representing the kinetics of solid-state transformations have no analytical solutions.

  5. A routine fitting of kinetic data to sums of exponentials with a programmable calculator.

    PubMed

    Ristanović, D; Ristanović, D; Milutinović, B; Maleŝević, J; Milin, J

    1984-01-01

    The effects of prolonged ingestion of ethyl alcohol on the elimination kinetics of bromsulphalein (BSP) from the plasma and the excretion of the dye into bile after a single intravenous injection into the circulation of the rat were examined by means of the colorimetrical technique. Simple numerical methods for fitting the experimental data to polyexponential and convex upward functions were also proposed. Two multioptional programs written for the Texas Instrument 59 programmable calculator and for the Sharp 1500 pocket computer were developed which provide for fully automated exponential stripping of pharmacokinetic data and which will allow workers to calculate the numerical values of all the coefficients and exponents for the tracer function fitting the monotone sequences of data. PMID:6547894

  6. Femtosecond laser pulse driven melting in gold nanorod aqueous colloidal suspension: Identification of a transition from stretched to exponential kinetics

    DOE PAGESBeta

    Li, Yuelin; Jiang, Zhang; Lin, Xiao -Min; Wen, Haidan; Walko, Donald A.; Deshmukh, Sanket A.; Subbaraman, Ram; Sankaranarayanan, Subramanian K. R. S.; Gray, Stephen K.; Ho, Phay

    2015-01-30

    Many potential industrial, medical, and environmental applications of metal nanorods rely on the physics and resultant kinetics and dynamics of the interaction of these particles with light. We report a surprising kinetics transition in the global melting of femtosecond laser-driven gold nanorod aqueous colloidal suspension. At low laser intensity, the melting exhibits a stretched exponential kinetics, which abruptly transforms into a compressed exponential kinetics when the laser intensity is raised. It is found the relative formation and reduction rate of intermediate shapes play a key role in the transition. Supported by both molecular dynamics simulations and a kinetic model, themore » behavior is traced back to the persistent heterogeneous nature of the shape dependence of the energy uptake, dissipation and melting of individual nanoparticles. These results could have significant implications for various applications such as water purification and electrolytes for energy storage that involve heat transport between metal nanorod ensembles and surrounding solvents.« less

  7. Femtosecond laser pulse driven melting in gold nanorod aqueous colloidal suspension: Identification of a transition from stretched to exponential kinetics

    SciTech Connect

    Li, Yuelin; Jiang, Zhang; Lin, Xiao -Min; Wen, Haidan; Walko, Donald A.; Deshmukh, Sanket A.; Subbaraman, Ram; Sankaranarayanan, Subramanian K. R. S.; Gray, Stephen K.; Ho, Phay

    2015-01-30

    Many potential industrial, medical, and environmental applications of metal nanorods rely on the physics and resultant kinetics and dynamics of the interaction of these particles with light. We report a surprising kinetics transition in the global melting of femtosecond laser-driven gold nanorod aqueous colloidal suspension. At low laser intensity, the melting exhibits a stretched exponential kinetics, which abruptly transforms into a compressed exponential kinetics when the laser intensity is raised. It is found the relative formation and reduction rate of intermediate shapes play a key role in the transition. Supported by both molecular dynamics simulations and a kinetic model, the behavior is traced back to the persistent heterogeneous nature of the shape dependence of the energy uptake, dissipation and melting of individual nanoparticles. These results could have significant implications for various applications such as water purification and electrolytes for energy storage that involve heat transport between metal nanorod ensembles and surrounding solvents.

  8. Femtosecond Laser Pulse Driven Melting in Gold Nanorod Aqueous Colloidal Suspension: Identification of a Transition from Stretched to Exponential Kinetics

    PubMed Central

    Li, Yuelin; Jiang, Zhang; Lin, Xiao-Min; Wen, Haidan; Walko, Donald A.; Deshmukh, Sanket A.; Subbaraman, Ram; Sankaranarayanan, Subramanian K. R. S.; Gray, Stephen K.; Ho, Phay

    2015-01-01

    Many potential industrial, medical, and environmental applications of metal nanorods rely on the physics and resultant kinetics and dynamics of the interaction of these particles with light. We report a surprising kinetics transition in the global melting of femtosecond laser-driven gold nanorod aqueous colloidal suspension. At low laser intensity, the melting exhibits a stretched exponential kinetics, which abruptly transforms into a compressed exponential kinetics when the laser intensity is raised. It is found the relative formation and reduction rate of intermediate shapes play a key role in the transition. Supported by both molecular dynamics simulations and a kinetic model, the behavior is traced back to the persistent heterogeneous nature of the shape dependence of the energy uptake, dissipation and melting of individual nanoparticles. These results could have significant implications for various applications such as water purification and electrolytes for energy storage that involve heat transport between metal nanorod ensembles and surrounding solvents. PMID:25634673

  9. Cancer Progression and Tumor Growth Kinetics

    NASA Astrophysics Data System (ADS)

    Blagoev, Krastan; Kalpathy-Cramer, Jayashree; Wilkerson, Julia; Sprinkhuizen, Sara; Song, Yi-Qiao; Bates, Susan; Rosen, Bruce; Fojo, Tito

    2013-03-01

    We present and analyze tumor growth data from prostate and brain cancer. Scaling the data from different patients shows that early stage prostate tumors show non-exponential growth while advanced prostate and brain tumors enter a stage of exponential growth. The scaling analysis points to the existence of cancer stem cells and/or massive apoptosis in early stage prostate cancer and that late stage cancer growth is not dominated by cancer stem cells. Statistical models of these two growth modes are discussed. Work supported by the National Science Foundation and the National Institutes of Health

  10. Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 1; Analysis

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

    2002-01-01

    Extensive slow-crack-growth (SCG) analysis was made using a primary exponential crack-velocity formulation under three widely used load configurations: constant stress rate, constant stress, and cyclic stress. Although the use of the exponential formulation in determining SCG parameters of a material requires somewhat inconvenient numerical procedures, the resulting solutions presented gave almost the same degree of simplicity in both data analysis and experiments as did the power-law formulation. However, the fact that the inert strength of a material should be known in advance to determine the corresponding SCG parameters was a major drawback of the exponential formulation as compared with the power-law formulation.

  11. Rapid growth of seed black holes in the early universe by supra-exponential accretion.

    PubMed

    Alexander, Tal; Natarajan, Priyamvada

    2014-09-12

    Mass accretion by black holes (BHs) is typically capped at the Eddington rate, when radiation's push balances gravity's pull. However, even exponential growth at the Eddington-limited e-folding time t(E) ~ few × 0.01 billion years is too slow to grow stellar-mass BH seeds into the supermassive luminous quasars that are observed when the universe is 1 billion years old. We propose a dynamical mechanism that can trigger supra-exponential accretion in the early universe, when a BH seed is bound in a star cluster fed by the ubiquitous dense cold gas flows. The high gas opacity traps the accretion radiation, while the low-mass BH's random motions suppress the formation of a slowly draining accretion disk. Supra-exponential growth can thus explain the puzzling emergence of supermassive BHs that power luminous quasars so soon after the Big Bang. PMID:25103410

  12. Rapid growth of seed black holes in the early universe by supra-exponential accretion

    NASA Astrophysics Data System (ADS)

    Alexander, Tal; Natarajan, Priyamvada

    2014-09-01

    Mass accretion by black holes (BHs) is typically capped at the Eddington rate, when radiation's push balances gravity's pull. However, even exponential growth at the Eddington-limited e-folding time tE ~ few × 0.01 billion years is too slow to grow stellar-mass BH seeds into the supermassive luminous quasars that are observed when the universe is 1 billion years old. We propose a dynamical mechanism that can trigger supra-exponential accretion in the early universe, when a BH seed is bound in a star cluster fed by the ubiquitous dense cold gas flows. The high gas opacity traps the accretion radiation, while the low-mass BH's random motions suppress the formation of a slowly draining accretion disk. Supra-exponential growth can thus explain the puzzling emergence of supermassive BHs that power luminous quasars so soon after the Big Bang.

  13. Exponential Growth and the Shifting Global Center of Gravity of Science Production, 1900-2011

    ERIC Educational Resources Information Center

    Zhang, Liang; Powell, Justin J. W.; Baker, David P.

    2015-01-01

    Long historical trends in scientific discovery led mid-20th century scientometricians to mark the advent of "big science"--extensive science production--and predicted that over the next few decades, the exponential growth would slow, resulting in lower rates of increase in production at the upper limit of a logistic curve. They were…

  14. Understanding Exponential Growth: As Simple as a Drop in a Bucket.

    ERIC Educational Resources Information Center

    Goldberg, Fred; Shuman, James

    1984-01-01

    Provides procedures for a simple laboratory activity on exponential growth and its characteristic doubling time. The equipment needed consists of a large plastic bucket, an eyedropper, a stopwatch, an assortment of containers and graduated cylinders, and a supply of water. (JN)

  15. Implicit and Explicit Knowledge of Linear and Exponential Growth in 5- and 9-Year-Olds

    ERIC Educational Resources Information Center

    Ebersbach, Mirjam; Resing, Wilma C. M.

    2008-01-01

    The present study examined children's implicit and explicit knowledge of linear and non-linear processes. Five- and nine-year-olds (N = 60) were asked to forecast linear and exponential growth by providing the corresponding number of beads. Implicit knowledge was assessed via the magnitudes of the forecasts; explicit knowledge was investigated…

  16. The mechanism of double-exponential growth in hyper-inflation

    NASA Astrophysics Data System (ADS)

    Mizuno, T.; Takayasu, M.; Takayasu, H.

    2002-05-01

    Analyzing historical data of price indices, we find an extraordinary growth phenomenon in several examples of hyper-inflation in which, price changes are approximated nicely by double-exponential functions of time. In order to explain such behavior we introduce the general coarse-graining technique in physics, the Monte Carlo renormalization group method, to the price dynamics. Starting from a microscopic stochastic equation describing dealers’ actions in open markets, we obtain a macroscopic noiseless equation of price consistent with the observation. The effect of auto-catalytic shortening of characteristic time caused by mob psychology is shown to be responsible for the double-exponential behavior.

  17. Deoxyribonucleic Acid Synthesis During Exponential Growth and Microcyst Formation in Myxococcus xanthus

    PubMed Central

    Rosenberg, Eugene; Katarski, Mary; Gottlieb, Peter

    1967-01-01

    Myxococcus xanthus in exponential phase with a generation time of 270 min contained a period of 50 min during which deoxyribonucleic acid (DNA) synthesis did not take place. After induction of microcysts by the glycerol technique, the DNA content increased 19%. Autoradiographic experiments demonstrated that the DNA made after glycerol induction was not evenly distributed among the microcysts. The distribution of grains per microcyst fits the following model of chromosome replication: in exponential phase, each daughter cell receives two chromosomes which are replicated sequentially during 80% of the divison cycle; after microcyst induction, no chromosomes are initiated. Mathematical formulas were derived which predict the kinetics and discrete probability distribution for several chromosome models. PMID:6032514

  18. A magnetosome-associated cytochrome MamP is critical for magnetite crystal growth during the exponential growth phase.

    PubMed

    Taoka, Azuma; Eguchi, Yukako; Mise, Shingo; Oestreicher, Zachery; Uno, Fumio; Fukumori, Yoshihiro

    2014-09-01

    Magnetotactic bacteria use a specific set of conserved proteins to biomineralize crystals of magnetite or greigite within their cells in organelles called magnetosomes. Using Magnetospirillum magneticum AMB-1, we examined one of the magnetotactic bacteria-specific conserved proteins named MamP that was recently reported as a new type of cytochrome c that has iron oxidase activity. We found that MamP is a membrane-bound cytochrome, and the MamP content increases during the exponential growth phase compared to two other magnetosome-associated proteins on the same operon, MamA and MamK. To assess the function of MamP, we overproduced MamP from plasmids in wild-type (WT) AMB-1 and found that during the exponential phase of growth, these cells contained more magnetite crystals that were the same size as crystals in WT cells. Conversely, when the heme c-binding motifs within the mamP on the plasmid was mutated, the cells produced the same number of crystals, but smaller crystals than in WT cells during exponential growth. These results strongly suggest that during the exponential phase of growth, MamP is crucial to the normal growth of magnetite crystals during biomineralization. PMID:25048532

  19. Growth potential of exponential- and stationary-phase Salmonella Typhimurium during sausage fermentation.

    PubMed

    Birk, T; Henriksen, S; Müller, K; Hansen, T B; Aabo, S

    2016-11-01

    Raw meat for sausage production can be contaminated with Salmonella. For technical reasons, meat is often frozen prior to mincing but it is unknown how growth of Salmonella in meat prior to freezing affects its growth potential during sausage fermentation. We investigated survival of exponential- and stationary-phase Salmonella Typhimurium (DT12 and DTU292) during freezing at -18°C and their subsequent growth potential during 72h sausage fermentation at 25°C. After 0, 7 and >35d of frozen storage, sausage batters were prepared with NaCl (3%) and NaNO2 (0, 100ppm) and fermented with and without starter culture. With no starter culture, both strains grew in both growth phases. In general, a functional starter culture abolished S. Typhimurium growth independent of growth phase and we concluded that ensuring correct fermentation is important for sausage safety. However, despite efficient fermentation, sporadic growth of exponential-phase cells of S. Typhimurium was observed drawing attention to the handling and storage of sausage meat. PMID:27423056

  20. Growth kinetics and morphology of polymer crystals

    NASA Astrophysics Data System (ADS)

    Toda, Akihiko

    2007-03-01

    Originating from the nature of chain folding, polymer single crystals are quite unique in the growth kinetics and morphology. The developments of the understanding in the past 50 years are discussed and the unsolved important issues will be suggested. Polymer single crystals are thin lamellae with the thickness in the order of 10nm determined by the period of chain folding, which keeps a constant value for the isothermal crystallization. The growth of polymer single crystals is modeled by the kinetics of creation and annihilation of growth steps on a rectangular substrate with the pre-determined thickness. The growth face is therefore regarded as a one-dimensional substrate and the kinks and anti-kinks on the substrate correspond to the growth steps propagating in the opposite directions. The kinetic equations of those kinks proposed by Seto and Frank well describe the transition of growth regime as a crossover from single nucleation to multi-nucleation on the basis of the standard model of chain-folded polymer crystallization with surface nucleation proposed by Lauritzen and Hoffman. However, the analysis of the growth kinetics and morphology of single crystals having curved growth front suggests an unusual behavior of the step propagation velocity. The anomaly can be accounted for by a self-poisoning of the growth step interrupted by polymer chains with folding shorter than required. An entropic barrier of pinning proposed by Sadler and Gilmer is a possible candidate of the self-poisoning and is in accordance with recent computer simulation results suggesting the kinetics on a rugged free energy landscape having a resemblance to protein folding. Therefore, the quantitative evaluation of the kinetic barriers of surface nucleation and pinning has been an important issue. In addition, examination of the kinetics of melting will have valuable information because melting of a crystal must be free from nucleation but can still be limited by the entropic barrier.

  1. Exponential-fitted methods for integrating stiff systems of ordinary differential equations: Applications to homogeneous gas-phase chemical kinetics

    NASA Technical Reports Server (NTRS)

    Pratt, D. T.

    1984-01-01

    Conventional algorithms for the numerical integration of ordinary differential equations (ODEs) are based on the use of polynomial functions as interpolants. However, the exact solutions of stiff ODEs behave like decaying exponential functions, which are poorly approximated by polynomials. An obvious choice of interpolant are the exponential functions themselves, or their low-order diagonal Pade (rational function) approximants. A number of explicit, A-stable, integration algorithms were derived from the use of a three-parameter exponential function as interpolant, and their relationship to low-order, polynomial-based and rational-function-based implicit and explicit methods were shown by examining their low-order diagonal Pade approximants. A robust implicit formula was derived by exponential fitting the trapezoidal rule. Application of these algorithms to integration of the ODEs governing homogenous, gas-phase chemical kinetics was demonstrated in a developmental code CREK1D, which compares favorably with the Gear-Hindmarsh code LSODE in spite of the use of a primitive stepsize control strategy.

  2. Power Law Versus Exponential Form of Slow Crack Growth of Advanced Structural Ceramics: Dynamic Fatigue

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Gyekenyesi, John P.

    2002-01-01

    The life prediction analysis based on an exponential crack velocity formulation was examined using a variety of experimental data on glass and advanced structural ceramics in constant stress-rate ("dynamic fatigue") and preload testing at ambient and elevated temperatures. The data fit to the strength versus In (stress rate) relation was found to be very reasonable for most of the materials. It was also found that preloading technique was equally applicable for the case of slow crack growth (SCG) parameter n > 30. The major limitation in the exponential crack velocity formulation, however, was that an inert strength of a material must be known priori to evaluate the important SCG parameter n, a significant drawback as compared to the conventional power-law crack velocity formulation.

  3. Forecasting Financial Extremes: A Network Degree Measure of Super-Exponential Growth.

    PubMed

    Yan, Wanfeng; van Tuyll van Serooskerken, Edgar

    2015-01-01

    Investors in stock market are usually greedy during bull markets and scared during bear markets. The greed or fear spreads across investors quickly. This is known as the herding effect, and often leads to a fast movement of stock prices. During such market regimes, stock prices change at a super-exponential rate and are normally followed by a trend reversal that corrects the previous overreaction. In this paper, we construct an indicator to measure the magnitude of the super-exponential growth of stock prices, by measuring the degree of the price network, generated from the price time series. Twelve major international stock indices have been investigated. Error diagram tests show that this new indicator has strong predictive power for financial extremes, both peaks and troughs. By varying the parameters used to construct the error diagram, we show the predictive power is very robust. The new indicator has a better performance than the LPPL pattern recognition indicator. PMID:26339793

  4. Forecasting Financial Extremes: A Network Degree Measure of Super-Exponential Growth

    PubMed Central

    Yan, Wanfeng; van Tuyll van Serooskerken, Edgar

    2015-01-01

    Investors in stock market are usually greedy during bull markets and scared during bear markets. The greed or fear spreads across investors quickly. This is known as the herding effect, and often leads to a fast movement of stock prices. During such market regimes, stock prices change at a super-exponential rate and are normally followed by a trend reversal that corrects the previous overreaction. In this paper, we construct an indicator to measure the magnitude of the super-exponential growth of stock prices, by measuring the degree of the price network, generated from the price time series. Twelve major international stock indices have been investigated. Error diagram tests show that this new indicator has strong predictive power for financial extremes, both peaks and troughs. By varying the parameters used to construct the error diagram, we show the predictive power is very robust. The new indicator has a better performance than the LPPL pattern recognition indicator. PMID:26339793

  5. Observation of Self-Amplified Spontaneous Emission and Exponential Growth at 530 nm

    NASA Astrophysics Data System (ADS)

    Milton, S. V.; Gluskin, E.; Biedron, S. G.; Dejus, R. J.; den Hartog, P. K.; Galayda, J. N.; Kim, K.-J.; Lewellen, J. W.; Moog, E. R.; Sajaev, V.; Sereno, N. S.; Travish, G.; Vinokurov, N. A.; Arnold, N. D.; Benson, C.; Berg, W.; Biggs, J. A.; Borland, M.; Carwardine, J. A.; Chae, Y.-C.; Decker, G.; Deriy, B. N.; Erdmann, M. J.; Friedsam, H.; Gold, C.; Grelick, A. E.; Hahne, M. W.; Harkay, K. C.; Huang, Z.; Lessner, E. S.; Lill, R. M.; Lumpkin, A. H.; Makarov, O. A.; Markovich, G. M.; Meyer, D.; Nassiri, A.; Noonan, J. R.; Pasky, S. J.; Pile, G.; Smith, T. L.; Soliday, R.; Tieman, B. J.; Trakhtenberg, E. M.; Trento, G. F.; Vasserman, I. B.; Walters, D. R.; Wang, X. J.; Wiemerslage, G.; Xu, S.; Yang, B.-X.

    2000-07-01

    Experimental evidence for self-amplified spontaneous emission (SASE) at 530 nm is reported. The measurements were made at the low-energy undulator test line facility at the Advanced Photon Source, Argonne National Laboratory. The experimental setup and details of the experimental results are presented, as well as preliminary analysis. This experiment extends to shorter wavelengths the operational knowledge of a linac-based SASE free-electron laser and explicitly shows the predicted exponential growth in intensity of the optical pulse as a function of length along the undulator.

  6. Exponential energy growth due to slow parameter oscillations in quantum mechanical systems

    NASA Astrophysics Data System (ADS)

    Turaev, Dmitry

    2016-05-01

    It is shown that a periodic emergence and destruction of an additional quantum number leads to an exponential growth of energy of a quantum mechanical system subjected to a slow periodic variation of parameters. The main example is given by systems (e.g., quantum billiards and quantum graphs) with periodically divided configuration space. In special cases, the process can also lead to a long period of cooling that precedes the acceleration, and to the desertion of the states with a particular value of the quantum number.

  7. Exponential growth of dental schools in Chile: effects on academic, economic and workforce issues.

    PubMed

    Cartes-Velásquez, Ricardo Andrés

    2013-01-01

    In the last 30 years, Chile has undergone noteworthy economic development and an exponential growth in the access of its population to higher education. The aim of this paper was to review the changes in academic, economic and workforce issues that occurred as a consequence of the growth in supply of undergraduate dental vacancies between 1997 and 2011. Data collected from the Consejo de Educación Superior - CES, Comisión Nacional de Acreditación - CNA, and Instituto Nacional de Estadísticas de Chile - INE included these variables: number of dental schools, school type (private or traditional, see explanation below), city where the school is located, entry vacancies, total student enrollment, admission scores, percentile rank of dentistry as a university career, tuition fees, accreditation status, and number of inhabitants. There was an exponential increase in dental schools in Chile (5 to 34) that occurred in association with the rise in tuition fees (US$ 3900 to US$ 9800), a deterioration in the academic level of dental students (650 to 550 points in admission scores) and a predicted 77.5% oversupply of dentists by 2025, according to WHO criteria. The exponential increase in dental schools in Chile brought about negative consequences, such as increasing career costs, deterioration in the academic level of dental students, and an oversupply of dentists, associated with lower incomes and possibly leading to unemployment. Additional research should be conducted to determine whether an increase in the number of dentists can improve the population's access to dental care and reduce the oral disease burden. PMID:24346044

  8. An integrated model for predictive microbiology and simultaneous determination of lag phase duration and exponential growth rate

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A new mechanistic growth model was developed to describe microbial growth under isothermal conditions. The development of the mathematical model was based on the fundamental phenomenon of microbial growth, which is normally a three-stage process that includes lag, exponential, and stationary phases...

  9. Transport and Growth Kinetics in Microgravity Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Otalora, F.; Garcia-Ruiz, J. M.; Carotenuto, L.; Castagnolo, D.; Novella, M. L.; Chernov, A. A.

    2002-01-01

    The dynamic coupling between mass transport and incorporation of growth units into the surface of a crystal growing from solution in microgravity is used to derive quantitative information on the crystal growth kinetics. To this end, new procedures for experiment preparation, interferometric data processing and model fitting have been developed. The use of experimental data from the bulk diffusive maw transport together with a model for steady state stagnant crystal growth allows the detailed quantitative understanding of the kinetics of both the concentration depletion zone around the crystal and the growth of the crystal interface. The protein crystal used in the experiment is shown to be growing in the mixed kinetic regime (0.2 x 10(exp -6) centimeters per second less than beta R/D less than 0.9 x 10(exp -6) centimeters per second).

  10. Stretching of single poly-ubiquitin molecules revisited: Dynamic disorder in the non-exponential unfolding kinetics

    NASA Astrophysics Data System (ADS)

    Zheng, Yue; Bian, Yukun; Zhao, Nanrong; Hou, Zhonghuai

    2014-03-01

    A theoretical framework based on a generalized Langevin equation (GLE) with fractional Gaussian noise (fGn) and a power-law memory kernel is presented to describe the non-exponential kinetics of the unfolding of a single poly-ubiquitin molecule under a constant force [T.-L. Kuo, S. Garcia-Manyes, J. Li, I. Barel, H. Lu, B. J. Berne, M. Urbakh, J. Klafter, and J. M. Fernández, Proc. Natl. Acad. Sci. U.S.A. 107, 11336 (2010)]. Such a GLE-fGn strategy is made on the basis that the pulling coordinate variable x undergoes subdiffusion, usually resulting from conformational fluctuations, over a one-dimensional force-modified free-energy surface U(x, F). By using the Kramers' rate theory, we have obtained analytical formulae for the time-dependent rate coefficient k(t, F), the survival probability S(t, F) as well as the waiting time distribution function f(t, F) as functions of time t and force F. We find that our results can fit the experimental data of f(t, F) perfectly in the whole time range with a power-law exponent γ = 1/2, the characteristic of typical anomalous subdiffusion. In addition, the fitting of the survival probabilities for different forces facilitates us to reach rather reasonable estimations for intrinsic properties of the system, such as the free-energy barrier and the distance between the native conformation and the transition state conformation along the reaction coordinate, which are in good agreements with molecular dynamics simulations in the literatures. Although static disorder has been implicated in the original work of Kuo et al., our work suggests a sound and plausible alternative interpretation for the non-exponential kinetics in the stretching of poly-ubiquitin molecules, associated with dynamic disorder.

  11. Volumetric analysis of syringomyelia following hindbrain decompression for Chiari malformation Type I: syringomyelia resolution follows exponential kinetics

    PubMed Central

    Coumans, Jean-Valery; Walcott, Brian P.; Butler, William E.; Nahed, Brian V.; Kahle, Kristopher T.

    2013-01-01

    Object Resolution of syringomyelia is common following hindbrain decompression for Chiari malformation, yet little is known about the kinetics governing this process. The authors sought to establish the volumetric rate of syringomyelia resolution. Methods A retrospective cohort of patients undergoing hindbrain decompression for a Chiari malformation Type I with preoperative cervical or thoracic syringomyelia was identified. Patients were included in the study if they had at least 3 neuroimaging studies that detailed the entirety of their preoperative syringomyelia over a minimum of 6 months postoperatively. The authors reconstructed the MR images in 3 dimensions and calculated the volume of the syringomyelia. They plotted the syringomyelia volume over time and constructed regression models using the method of least squares. The Akaike information criterion and Bayesian information criterion were used to calculate the relative goodness of fit. The coefficients of determination R2 (unadjusted and adjusted) were calculated to describe the proportion of variability in each individual data set accounted for by the statistical model. Results Two patients were identified as meeting inclusion criteria. Plots of the least-squares best fit were identified as 4.01459e−0.0180804x and 13.2556e−0.00615859x. Decay of the syringomyelia followed an exponential model in both patients (R2 = 0.989582 and 0.948864). Conclusions Three-dimensional analysis of syringomyelia resolution over time enables the kinetics to be estimated. This technique is yet to be validated in a large cohort. Because syringomyelia is the final common pathway for a number of different pathological processes, it is possible that this exponential only applies to syringomyelia related to treatment of Chiari malformation Type I. PMID:21882909

  12. Modeling the Pre-Industrial Roots of Modern Super-Exponential Population Growth

    PubMed Central

    Stutz, Aaron Jonas

    2014-01-01

    To Malthus, rapid human population growth—so evident in 18th Century Europe—was obviously unsustainable. In his Essay on the Principle of Population, Malthus cogently argued that environmental and socioeconomic constraints on population rise were inevitable. Yet, he penned his essay on the eve of the global census size reaching one billion, as nearly two centuries of super-exponential increase were taking off. Introducing a novel extension of J. E. Cohen's hallmark coupled difference equation model of human population dynamics and carrying capacity, this article examines just how elastic population growth limits may be in response to demographic change. The revised model involves a simple formalization of how consumption costs influence carrying capacity elasticity over time. Recognizing that complex social resource-extraction networks support ongoing consumption-based investment in family formation and intergenerational resource transfers, it is important to consider how consumption has impacted the human environment and demography—especially as global population has become very large. Sensitivity analysis of the consumption-cost model's fit to historical population estimates, modern census data, and 21st Century demographic projections supports a critical conclusion. The recent population explosion was systemically determined by long-term, distinctly pre-industrial cultural evolution. It is suggested that modern globalizing transitions in technology, susceptibility to infectious disease, information flows and accumulation, and economic complexity were endogenous products of much earlier biocultural evolution of family formation's embeddedness in larger, hierarchically self-organizing cultural systems, which could potentially support high population elasticity of carrying capacity. Modern super-exponential population growth cannot be considered separately from long-term change in the multi-scalar political economy that connects family formation and

  13. Microscopic kinetic model for polymer crystal growth

    NASA Astrophysics Data System (ADS)

    Hu, Wenbing

    2011-03-01

    Linear crystal growth rates characterize the net result of competition between growth and melting at the liquid-solid interfaces. The rate equation for polymer crystal growth can be derived with a barrier term for crystal growth and with a driving force term of excess lamellar thickness, provided that growth and melting share the same rate-determining steps at the growth front. Such an ansatz can be verified by the kinetic symmetry between growth and melting around the melting point of lamellar crystals, as made in our recent dynamic Monte Carlo simulations. The profile of the growth/melting front appears as wedge-shaped, with the free energy barrier for intramolecular secondary crystal nucleation at its top, and with the driving force gained via instant thickening at its bottom. Such a scenario explains unique phenomena on polymer crystal growth, such as chain folding, regime transitions, molecular segregation of polydisperse polymers, self-poisoning with integer-number chain-folding of short chains, and colligative growth rates of binary mixtures of two chain lengths. Financial support from NNSFC No. 20825415 and NBRPC No. 2011CB606100 is acknowledged.

  14. Can the Site-Frequency Spectrum Distinguish Exponential Population Growth from Multiple-Merger Coalescents?

    PubMed Central

    Eldon, Bjarki; Birkner, Matthias; Blath, Jochen; Freund, Fabian

    2015-01-01

    The ability of the site-frequency spectrum (SFS) to reflect the particularities of gene genealogies exhibiting multiple mergers of ancestral lines as opposed to those obtained in the presence of population growth is our focus. An excess of singletons is a well-known characteristic of both population growth and multiple mergers. Other aspects of the SFS, in particular, the weight of the right tail, are, however, affected in specific ways by the two model classes. Using an approximate likelihood method and minimum-distance statistics, our estimates of statistical power indicate that exponential and algebraic growth can indeed be distinguished from multiple-merger coalescents, even for moderate sample sizes, if the number of segregating sites is high enough. A normalized version of the SFS (nSFS) is also used as a summary statistic in an approximate Bayesian computation (ABC) approach. The results give further positive evidence as to the general eligibility of the SFS to distinguish between the different histories. PMID:25575536

  15. A Minimal Model of the E. Coli Bacterium in Exponential Phase Growth

    NASA Astrophysics Data System (ADS)

    Maitra, Arijit; Dill, Ken

    2013-03-01

    We study the fundamental process of exponential cell growth in the E. Coli bacterium under conditions of extracellular glucose limitations using a minimalistic reaction framework by accounting for energy metabolism and protein synthesis. The cell model has three nodes: ATP, the ribosomal and the non-ribosomal proteins. Their interdependencies and dynamics are wrapped in a system of ordinary differential equations. The formulations of their interactive fluxes capture the essence of cellular physiology under conditions of growth. We solve the model numerically for different glucose concentrations, and, where possible, explore the cell states analytically under steady state conditions. We verify the model predictions with available experimental data. The model lets us quantify the coupling between energy generation and biomass growth. An implication of this model is that it provides a layout to compute the fitness landscape in terms of the parameters of the cells, such as the protein translation rates, to make hypotheses about possible routes for cellular evolution under glucose limitation. Laufer Center for Phys. and Quant. Biology.

  16. Protein crystal growth - Growth kinetics for tetragonal lysozyme crystals

    NASA Technical Reports Server (NTRS)

    Pusey, M. L.; Snyder, R. S.; Naumann, R.

    1986-01-01

    Results are reported from theoretical and experimental studies of the growth rate of lysozyme as a function of diffusion in earth-gravity conditions. The investigations were carried out to form a comparison database for future studies of protein crystal growth in the microgravity environment of space. A diffusion-convection model is presented for predicting crystal growth rates in the presence of solutal concentration gradients. Techniques used to grow and monitor the growth of hen egg white lysozyme are detailed. The model calculations and experiment data are employed to discuss the effects of transport and interfacial kinetics in the growth of the crystals, which gradually diminished the free energy in the growth solution. Density gradient-driven convection, caused by presence of the gravity field, was a limiting factor in the growth rate.

  17. Growth kinetics of Bacillus stearothermophilus BR219

    SciTech Connect

    Worden, R.M.; Subramanian, R.; Bly, M.J.; Winter, S.; Aronson, C.L.

    1991-12-31

    Bacillus stearothermophilus BR219, a phenol-resistant thermophile, can convert phenol to the specialty chemical catechol. The growth kinetics of this organism were studied in batch, continuous, and immobilized-cell culture. Batch growth was insensitive to pH between 6.0 and 8.0, but little growth occurred at 5.5. In continuous culture on a dilute medium supplemented with 10 mM phenol, several steady states were achieved between dilution rates of 0.25 and 1.3 h{sup -1}. Phenol degradation was found to be uncoupled from growth. Immobilized cells grew rapidly in a rich medium, but cell viability plummeted following a switch to a dilute medium supplemented with 5 mM phenol.

  18. Morphological stability and kinetics in crystal growth from vapors

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz

    1990-01-01

    The following topics are discussed: (1) microscopy image storage and processing system; (2) growth kinetics and morphology study with carbon tetrabromide; (3) photothermal deflection vapor growth setup; (4) bridgman growth of iodine single crystals; (5) vapor concentration distribution measurement during growth; and (6) Monte Carlo modeling of anisotropic growth kinetics and morphology. A collection of presentations and publications of these results are presented.

  19. Entrainability of cell cycle oscillator models with exponential growth of cell mass.

    PubMed

    Nakao, Mitsuyuki; Enkhkhudulmur, Tsog-Erdene; Katayama, Norihiro; Karashima, Akihiro

    2014-01-01

    Among various aspects of cell cycle, understanding synchronization mechanism of cell cycle is important because of the following reasons. (1)Cycles of cell assembly should synchronize to form an organ. (2) Synchronizing cell cycles are required to experimental analysis of regulatory mechanisms of cell cycles. (3) Cell cycle has a distinct phase relationship with the other biological rhythms such as circadian rhythm. However, forced as well as mutual entrainment mechanisms are not clearly known. In this study, we investigated entrainability of cell cycle models of yeast cell under the periodic forcing to both of the cell mass and molecular dynamics. Dynamics of models under study involve the cell mass growing exponentially. In our result, they are shown to allow only a limited frequency range for being entrained by the periodic forcing. In contrast, models with linear growth are shown to be entrained in a wider frequency range. It is concluded that if the cell mass is included in the cell cycle regulation, its entrainability is sensitive to a shape of growth curve assumed in the model. PMID:25571564

  20. Teaching the Verhulst Model: A Teaching Experiment in Covariational Reasoning and Exponential Growth

    ERIC Educational Resources Information Center

    Castillo-Garsow, Carlos

    2010-01-01

    Both Thompson and the duo of Confrey and Smith describe how students might be taught to build "ways of thinking" about exponential behavior by coordinating the covariation of two changing quantities, however, these authors build exponential behavior from different meanings of covariation. Confrey and Smith advocate beginning with discrete additive…

  1. Droplet Growth Kinetics in Various Environments

    NASA Astrophysics Data System (ADS)

    Raatikainen, T. E.; Lathem, T. L.; Moore, R.; Lin, J. J.; Cerully, K. M.; Padro, L.; Lance, S.; Cozic, J.; Anderson, B. E.; Nenes, A.

    2012-12-01

    The largest uncertainties in the effects of atmospherics aerosols on the global radiation budget are related to their indirect effects on cloud properties (IPCC, the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007). Cloud formation is a kinetic process where the resulting cloud properties depend on aerosol properties and meteorological parameters such as updraft velocity (e.g. McFiggans et al., Atmos. Chem. Phys., 6, 2593-2649, 2006). Droplet growth rates are limited by the water vapor diffusion, but additional kinetic limitations, e.g., due to organic surface films, slow solute dissociation or highly viscous or glassy aerosol states have been hypothesized. Significant additional kinetic limitations can lead to increased cloud droplet number concentration, thus the effect is similar to those of increased aerosol number concentration or changes in vertical velocity (e.g. Nenes et al., Geophys. Res. Lett., 29, 1848, 2002). There are a few studies where slow droplet growth has been observed (e.g. Ruehl et al., Geophys. Res. Lett., 36, L15814, 2009), however, little is currently known about their global occurrence and magnitude. Cloud micro-physics models often describe kinetic limitations by an effective water vapor uptake coefficient or similar parameter. Typically, determining aerosol water vapor uptake coefficients requires experimental observations of droplet growth which are interpreted by a numerical droplet growth model where the uptake coefficient is an adjustable parameter (e.g. Kolb et al., Atmos. Chem. Phys., 10, 10561-10605, 2010). Such methods have not been practical for high time-resolution or long term field measurements, until a model was recently developed for analyzing Droplet Measurement Technologies (DMT) cloud condensation nuclei (CCN) counter data (Raatikainen et al., Atmos. Chem. Phys., 12, 4227-4243, 2012). Model verification experiments showed that the calibration aerosol droplet size can be predicted accurately

  2. Metabolic Flux Analysis during the Exponential Growth Phase of Saccharomyces cerevisiae in Wine Fermentations

    PubMed Central

    Quirós, Manuel; Martínez-Moreno, Rubén; Albiol, Joan; Morales, Pilar; Vázquez-Lima, Felícitas; Barreiro-Vázquez, Antonio; Ferrer, Pau; Gonzalez, Ramon

    2013-01-01

    As a consequence of the increase in global average temperature, grapes with the adequate phenolic and aromatic maturity tend to be overripe by the time of harvest, resulting in increased sugar concentrations and imbalanced C/N ratios in fermenting musts. This fact sets obvious additional hurdles in the challenge of obtaining wines with reduced alcohols levels, a new trend in consumer demands. It would therefore be interesting to understand Saccharomyces cerevisiae physiology during the fermentation of must with these altered characteristics. The present study aims to determine the distribution of metabolic fluxes during the yeast exponential growth phase, when both carbon and nitrogen sources are in excess, using continuous cultures. Two different sugar concentrations were studied under two different winemaking temperature conditions. Although consumption and production rates for key metabolites were severely affected by the different experimental conditions studied, the general distribution of fluxes in central carbon metabolism was basically conserved in all cases. It was also observed that temperature and sugar concentration exerted a higher effect on the pentose phosphate pathway and glycerol formation than on glycolysis and ethanol production. Additionally, nitrogen uptake, both quantitatively and qualitatively, was strongly influenced by environmental conditions. This work provides the most complete stoichiometric model used for Metabolic Flux Analysis of S. cerevisiae in wine fermentations employed so far, including the synthesis and release of relevant aroma compounds and could be used in the design of optimal nitrogen supplementation of wine fermentations. PMID:23967264

  3. The Cultural Divide: Exponential Growth in Classical 2D and Metabolic Equilibrium in 3D Environments

    PubMed Central

    Kanlaya, Rattiyaporn; Borkowski, Kamil; Schwämmle, Veit; Dai, Jie; Joensen, Kira Eyd; Wojdyla, Katarzyna; Carvalho, Vasco Botelho; Fey, Stephen J.

    2014-01-01

    Introduction Cellular metabolism can be considered to have two extremes: one is characterized by exponential growth (in 2D cultures) and the other by a dynamic equilibrium (in 3D cultures). We have analyzed the proteome and cellular architecture at these two extremes and found that they are dramatically different. Results Structurally, actin organization is changed, microtubules are increased and keratins 8 and 18 decreased. Metabolically, glycolysis, fatty acid metabolism and the pentose phosphate shunt are increased while TCA cycle and oxidative phosphorylation is unchanged. Enzymes involved in cholesterol and urea synthesis are increased consistent with the attainment of cholesterol and urea production rates seen in vivo. DNA repair enzymes are increased even though cells are predominantly in Go. Transport around the cell – along the microtubules, through the nuclear pore and in various types of vesicles has been prioritized. There are numerous coherent changes in transcription, splicing, translation, protein folding and degradation. The amount of individual proteins within complexes is shown to be highly coordinated. Typically subunits which initiate a particular function are present in increased amounts compared to other subunits of the same complex. Summary We have previously demonstrated that cells at dynamic equilibrium can match the physiological performance of cells in tissues in vivo. Here we describe the multitude of protein changes necessary to achieve this performance. PMID:25222612

  4. Long-wave theory for a new convective instability with exponential growth normal to the wall.

    PubMed

    Healey, J J

    2005-05-15

    A linear stability theory is presented for the boundary-layer flow produced by an infinite disc rotating at constant angular velocity in otherwise undisturbed fluid. The theory is developed in the limit of long waves and when the effects of viscosity on the waves can be neglected. This is the parameter regime recently identified by the author in a numerical stability investigation where a curious new type of instability was found in which disturbances propagate and grow exponentially in the direction normal to the disc, (i.e. the growth takes place in a region of zero mean shear). The theory describes the mechanisms controlling the instability, the role and location of critical points, and presents a saddle-point analysis describing the large-time evolution of a wave packet in frames of reference moving normal to the disc. The theory also shows that the previously obtained numerical solutions for numerically large wavelengths do indeed lie in the asymptotic long-wave regime, and so the behaviour and mechanisms described here may apply to a number of cross-flow instability problems. PMID:16105773

  5. Volume Diffusion Growth Kinetics and Step Geometry in Crystal Growth

    NASA Technical Reports Server (NTRS)

    Mazuruk, Konstantin; Ramachandran, Narayanan

    1998-01-01

    The role of step geometry in two-dimensional stationary volume diff4sion process used in crystal growth kinetics models is investigated. Three different interface shapes: a) a planar interface, b) an equidistant hemispherical bumps train tAx interface, and c) a train of right angled steps, are used in this comparative study. The ratio of the super-saturation to the diffusive flux at the step position is used as a control parameter. The value of this parameter can vary as much as 50% for different geometries. An approximate analytical formula is derived for the right angled steps geometry. In addition to the kinetic models, this formula can be utilized in macrostep growth models. Finally, numerical modeling of the diffusive and convective transport for equidistant steps is conducted. In particular, the role of fluid flow resulting from the advancement of steps and its contribution to the transport of species to the steps is investigated.

  6. Amyloid growth: combining experiment and kinetic theory

    NASA Astrophysics Data System (ADS)

    Knowles, Tuomas; Cohen, Samuel; Vendruscolo, Michele; Dobson, Christopher

    2012-02-01

    The conversion of proteins from their soluble forms into fibrillar amyloid nanostructures is a general type of behaviour encountered for many different proteins in the context of disease as well as for the generation of a select class of functional materials in nature. This talk focuses on the problem of defining the rates of the individual molecular level processes involved in the overall conversion reaction. A master equation approach is discussedootnotetextCohen et al, J Chem Phys 2011, 135, 065106 ootnotetextKnowles et al, Science, 2009, 326, 1533-1537 and used in combination with kinetic measurements to yield mechanistic insights into the amyloid growth phenomenon.

  7. Growth kinetics of Si and Ge nanowires

    NASA Astrophysics Data System (ADS)

    Kodambaka, S.; Tersoff, J.; Reuter, M. C.; Ross, F. M.

    2009-02-01

    Si and Ge nanowires have potential applications in a wide variety of areas including thermoelectrics, optoelectronics, and sensors. Nanowires are most commonly grown via the vapor-liquid-solid (VLS) process. In this method, a vapor phase containing the material of interest preferentially dissociates at a liquid catalyst and is incorporated as a solid at the solid-liquid interface. However, despite 40 years of research in this area, several aspects of nanowire growth remain unclear, even for relatively simple elemental Si and Ge wires. Here, we will review our in situ transmission electron microscopy (TEM) investigations of Si and Ge nanowire growth kinetics. The observations are carried out in an ultra-high vacuum TEM (the IBM UHV-TEM) equipped with facilities for deposition during observation. Using Au as the catalyst, we study the VLS growth of Si and Ge nanowires as a function of disilane or digermane pressure and substrate temperature. We find surprisingly different growth mechanisms for the two materials. The insights gained from in situ results may help devise methods for large-scale fabrication of wires with controlled architecture.

  8. Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 2; Constant Stress Rate Experiments

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

    2002-01-01

    The previously determined life prediction analysis based on an exponential crack-velocity formulation was examined using a variety of experimental data on glass and advanced structural ceramics in constant stress rate and preload testing at ambient and elevated temperatures. The data fit to the relation of strength versus the log of the stress rate was very reasonable for most of the materials. Also, the preloading technique was determined equally applicable to the case of slow-crack-growth (SCG) parameter n greater than 30 for both the power-law and exponential formulations. The major limitation in the exponential crack-velocity formulation, however, was that the inert strength of a material must be known a priori to evaluate the important SCG parameter n, a significant drawback as compared with the conventional power-law crack-velocity formulation.

  9. Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 3; Constant Stress and Cyclic Stress Experiments

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

    2002-01-01

    The previously determined life prediction analysis based on an exponential crack-velocity formulation was examined using a variety of experimental data on advanced structural ceramics tested under constant stress and cyclic stress loading at ambient and elevated temperatures. The data fit to the relation between the time to failure and applied stress (or maximum applied stress in cyclic loading) was very reasonable for most of the materials studied. It was also found that life prediction for cyclic stress loading from data of constant stress loading in the exponential formulation was in good agreement with the experimental data, resulting in a similar degree of accuracy as compared with the power-law formulation. The major limitation in the exponential crack-velocity formulation, however, was that the inert strength of a material must be known a priori to evaluate the important slow-crack-growth (SCG) parameter n, a significant drawback as compared with the conventional power-law crack-velocity formulation.

  10. Finite amplitude folding: transition from exponential to layer length controlled growth

    NASA Astrophysics Data System (ADS)

    Schmalholz, Stefan M.; Podladchikov, Yuri Yu.

    2000-06-01

    A new finite amplitude theory of folding has been developed by the combined application of analytical, asymptotic and numerical methods. The existing linear folding theory has been improved by considering nonlinear weakening of membrane stresses, which is caused by the stretching of the competent layer during folding. The resulting theory is simple and accurate for finite amplitude folding and is not restricted to infinitesimal amplitudes, as is the classical linear theory of folding. Two folding modes relevant to most natural settings were considered: (i) both membrane and fiber stresses are viscous during folding (the 'viscous' mode); (ii) membrane stresses are viscous whereas fiber stresses are elastic (the 'viscoelastic' mode). For these two modes, the new theory provided a nonlinear, ordinary differential equation for fold amplification during shortening and an estimate for crossover amplitude and strain where the linear theory breaks down. A new analytical relationship for amplitude versus strain was derived for strains much larger than the crossover strain. The new relationship agrees well with complete 2D numerical solutions for up to threefold shortening, whereas the exponential solution predicted by the linear theory is inaccurate by orders of magnitude for strains larger than the crossover value. Analysis of the crossover strain and amplitude as a function of the controlling parameters demonstrates that the linear theory is only applicable for a small range of amplitudes and strains. This renders unreliable the large strain prediction of wavelength selection based on the linear theory, especially for folding at high competence contrasts. To resolve this problem, the new finite amplitude theory is used to calculate the evolution of the growth rate spectra during progressive folding. The growth rate spectra exhibited splitting of a single maximum (predicted by the linear theory) into two maxima at large strains. This bifurcation occurred for both

  11. Finite amplitude folding: transition from exponential to layer length controlled growth

    NASA Astrophysics Data System (ADS)

    Schmalholz, Stefan M.; Podladchikov, Yuri Yu.

    2000-09-01

    A new finite amplitude theory of folding has been developed by the combined application of analytical, asymptotic and numerical methods. The existing linear folding theory has been improved by considering nonlinear weakening of membrane stresses, which is caused by the stretching of the competent layer during folding. The resulting theory is simple and accurate for finite amplitude folding and is not restricted to infinitesimal amplitudes, as is the classical linear theory of folding. Two folding modes relevant to most natural settings were considered: (i) both membrane and fiber stresses are viscous during folding (the 'viscous' mode); (ii) membrane stresses are viscous whereas fiber stresses are elastic (the 'viscoelastic' mode). For these two modes, the new theory provided a nonlinear, ordinary differential equation for fold amplification during shortening and an estimate for crossover amplitude and strain where the linear theory breaks down. A new analytical relationship for amplitude versus strain was derived for strains much larger than the crossover strain. The new relationship agrees well with complete 2D numerical solutions for up to threefold shortening, whereas the exponential solution predicted by the linear theory is inaccurate by orders of magnitude for strains larger than the crossover value. Analysis of the crossover strain and amplitude as a function of the controlling parameters demonstrates that the linear theory is only applicable for a small range of amplitudes and strains. This renders unreliable the large strain prediction of wavelength selection based on the linear theory, especially for folding at high competence contrasts. To resolve this problem, the new finite amplitude theory is used to calculate the evolution of the growth rate spectra during progressive folding. The growth rate spectra exhibited splitting of a single maximum (predicted by the linear theory) into two maxima at large strains. This bifurcation occurred for both

  12. Domain Growth Kinetics in Stratifying Foam Films

    NASA Astrophysics Data System (ADS)

    Zhang, Yiran; Sharma, Vivek

    2015-03-01

    Baking bread, brewing cappuccino, pouring beer, washing dishes, shaving, shampooing, whipping eggs and blowing bubbles all involve creation of aqueous foam films. Typical foam films consist of two surfactant-laden surfaces that are μ 5 nm - 10 micron apart. Sandwiched between these interfacial layers is a fluid that drains primarily under the influence of viscous and interfacial forces, including disjoining pressure. Interestingly, for certain low molecular weight surfactants, a layered ordering of micelles inside the foam films (thickness <100 nm) leads to a stepwise thinning phenomena called stratification. We experimentally elucidate the influence of these different driving forces, and confinement on drainage kinetics of horizontal stratifying foam films. Thinner, darker domains spontaneously grow within foam films. Quantitative characterization of domain growth visualized in a using Scheludko-type thin film cell and a theoretical model based on lubrication analysis, provide critical insights into hydrodynamics of thin foam films, and the strength and nature of surface forces, including supramolecular oscillatory structural forces.

  13. Determining the Kinetic Parameters Characteristic of Microalgal Growth.

    ERIC Educational Resources Information Center

    Martinez Sancho, Maria Eugenie; And Others

    1991-01-01

    An activity in which students obtain a growth curve for algae, identify the exponential and linear growth phases, and calculate the parameters which characterize both phases is described. The procedure, a list of required materials, experimental conditions, analytical technique, and a discussion of the interpretations of individual results are…

  14. Domain growth kinetics in stratifying foam films

    NASA Astrophysics Data System (ADS)

    Zhang, Yiran; Sharma, Vivek

    2015-11-01

    Baking bread, brewing cappuccino, pouring beer, washing dishes, shaving, shampooing, whipping eggs and blowing bubbles all involve creation of aqueous foam films. Typical foam films consist of two surfactant-laden surfaces that are ~ 5 nm - 10 micron apart. Sandwiched between these interfacial layers is a fluid that drains primarily under the influence of viscous and interfacial forces, including disjoining pressure. Interestingly, a layered ordering of micelles inside the foam films (thickness <100 nm) leads to a stepwise thinning phenomena called stratification, which results in a thickness-dependent variation in reflected light intensity, visualized as progressively darker shades of gray. Thinner, darker domains spontaneously grow within foam films. We show that the domain expansion dynamics exhibit two distinct growth regimes with characteristic scaling laws. Though several studies have focused on the expansion dynamics of isolated domains that exhibit a diffusion-like scaling, the change in expansion kinetics observed after domains contact with the Plateau border has not been reported and analyzed before.

  15. Large-scale epitaxial growth kinetics of graphene: A kinetic Monte Carlo study

    SciTech Connect

    Jiang, Huijun; Hou, Zhonghuai

    2015-08-28

    Epitaxial growth via chemical vapor deposition is considered to be the most promising way towards synthesizing large area graphene with high quality. However, it remains a big theoretical challenge to reveal growth kinetics with atomically energetic and large-scale spatial information included. Here, we propose a minimal kinetic Monte Carlo model to address such an issue on an active catalyst surface with graphene/substrate lattice mismatch, which facilitates us to perform large scale simulations of the growth kinetics over two dimensional surface with growth fronts of complex shapes. A geometry-determined large-scale growth mechanism is revealed, where the rate-dominating event is found to be C{sub 1}-attachment for concave growth-front segments and C{sub 5}-attachment for others. This growth mechanism leads to an interesting time-resolved growth behavior which is well consistent with that observed in a recent scanning tunneling microscopy experiment.

  16. Approximate models for the study of exponential changed quantities: Application on the plasma waves growth rate or damping

    SciTech Connect

    Xaplanteris, C. L.; Xaplanteris, L. C.; Leousis, D. P.

    2014-03-15

    Many physical phenomena that concern the research these days are basically complicated because of being multi-parametric. Thus, their study and understanding meets with big if not unsolved obstacles. Such complicated and multi-parametric is the plasmatic state as well, where the plasma and the physical quantities that appear along with it have chaotic behavior. Many of those physical quantities change exponentially and at most times they are stabilized by presenting wavy behavior. Mostly in the transitive state rather than the steady state, the exponentially changing quantities (Growth, Damping etc) depend on each other in most cases. Thus, it is difficult to distinguish the cause from the result. The present paper attempts to help this difficult study and understanding by proposing mathematical exponential models that could relate with the study and understanding of the plasmatic wavy instability behavior. Such instabilities are already detected, understood and presented in previous publications of our laboratory. In other words, our new contribution is the study of the already known plasmatic quantities by using mathematical models (modeling and simulation). These methods are both useful and applicable in the chaotic theory. In addition, our ambition is to also conduct a list of models useful for the study of chaotic problems, such as those that appear into the plasma, starting with this paper's examples.

  17. Determining crystal growth kinetic parameters using optical fibre sensors

    NASA Astrophysics Data System (ADS)

    Boerkamp, M.; Lamb, D. W.; Lye, P. G.

    2012-12-01

    The capability of an 'intrinsic exposed core optical fibre sensor' (IECOFS) as a monitoring device of scale formation has been evaluated. The IECOFS has been used to measure kinetics parameters of calcium carbonate heterogeneous crystal growth such as the activation energy, the crystal growth rate and the induction time. The IECOFS was able to evaluate crystal growth inhibition through the use of chemical inhibitors.

  18. Growth Kinetics of Suspended Microbial Cells: From Single-Substrate-Controlled Growth to Mixed-Substrate Kinetics

    PubMed Central

    Kovárová-Kovar, Karin; Egli, Thomas

    1998-01-01

    Growth kinetics, i.e., the relationship between specific growth rate and the concentration of a substrate, is one of the basic tools in microbiology. However, despite more than half a century of research, many fundamental questions about the validity and application of growth kinetics as observed in the laboratory to environmental growth conditions are still unanswered. For pure cultures growing with single substrates, enormous inconsistencies exist in the growth kinetic data reported. The low quality of experimental data has so far hampered the comparison and validation of the different growth models proposed, and only recently have data collected from nutrient-controlled chemostat cultures allowed us to compare different kinetic models on a statistical basis. The problems are mainly due to (i) the analytical difficulty in measuring substrates at growth-controlling concentrations and (ii) the fact that during a kinetic experiment, particularly in batch systems, microorganisms alter their kinetic properties because of adaptation to the changing environment. For example, for Escherichia coli growing with glucose, a physiological long-term adaptation results in a change in KS for glucose from some 5 mg liter−1 to ca. 30 μg liter−1. The data suggest that a dilemma exists, namely, that either “intrinsic” KS (under substrate-controlled conditions in chemostat culture) or μmax (under substrate-excess conditions in batch culture) can be measured but both cannot be determined at the same time. The above-described conventional growth kinetics derived from single-substrate-controlled laboratory experiments have invariably been used for describing both growth and substrate utilization in ecosystems. However, in nature, microbial cells are exposed to a wide spectrum of potential substrates, many of which they utilize simultaneously (in particular carbon sources). The kinetic data available to date for growth of pure cultures in carbon-controlled continuous culture

  19. How well can the exponential-growth coalescent approximate constant-rate birth–death population dynamics?

    PubMed Central

    Stadler, Tanja; Vaughan, Timothy G.; Gavryushkin, Alex; Guindon, Stephane; Kühnert, Denise; Leventhal, Gabriel E.; Drummond, Alexei J.

    2015-01-01

    One of the central objectives in the field of phylodynamics is the quantification of population dynamic processes using genetic sequence data or in some cases phenotypic data. Phylodynamics has been successfully applied to many different processes, such as the spread of infectious diseases, within-host evolution of a pathogen, macroevolution and even language evolution. Phylodynamic analysis requires a probability distribution on phylogenetic trees spanned by the genetic data. Because such a probability distribution is not available for many common stochastic population dynamic processes, coalescent-based approximations assuming deterministic population size changes are widely employed. Key to many population dynamic models, in particular epidemiological models, is a period of exponential population growth during the initial phase. Here, we show that the coalescent does not well approximate stochastic exponential population growth, which is typically modelled by a birth–death process. We demonstrate that introducing demographic stochasticity into the population size function of the coalescent improves the approximation for values of R0 close to 1, but substantial differences remain for large R0. In addition, the computational advantage of using an approximation over exact models vanishes when introducing such demographic stochasticity. These results highlight that we need to increase efforts to develop phylodynamic tools that correctly account for the stochasticity of population dynamic models for inference. PMID:25876846

  20. Lack of synchronization between iron uptake and cell growth leads to iron overload in Saccharomyces cerevisiae during post-exponential growth modes

    PubMed Central

    Park, Jinkyu; McCormick, Sean P.; Chakrabarti, Mrinmoy; Lindahl, Paul A.

    2014-01-01

    Fermenting cells growing exponentially on rich (YPAD) medium transitioned to a slow-growing state as glucose levels declined and their metabolism shifted to respiration. During exponential growth, Fe import and cell growth rates were matched, affording an approximately invariant cellular Fe concentration. During the transitionary period, the high-affinity Fe import rate declined slower than the cell growth rate declined, causing Fe to accumulate, initially as FeIII oxyhydroxide nanoparticles but eventually as mitochondrial and vacuolar Fe. Once in slow-growth mode, Fe import and cell growth rates were again matched, and the cellular Fe concentration was again approximately invariant. Fermenting cells grown on minimal medium (MM) grew more slowly during exponential phase and transitioned to a true stationary state as glucose levels declined. The Fe concentration of MM cells that just entered stationary state was similar to that of YPAD cells, but MM cells continued to accumulate Fe in stationary state. Fe initially accumulated as nanoparticles and high-spin FeII species, but vacuolar FeIII also eventually accumulated. Surprisingly, Fe-packed 5-day-old MM cells suffered no more ROS damage than younger cells, suggesting that Fe concentration alone does not accurately predict the extent of ROS damage. The mode and rate of growth at the time of harvesting dramatically affected cellular Fe content. A mathematical model of Fe metabolism in a growing cell was developed. The model included Fe import via a regulated high-affinity pathway and an unregulated low-affinity pathway. Fe import from the cytosol into vacuoles and mitochondria, and nanoparticle formation were also included. The model captured essential trafficking behavior, demonstrating that cells regulate Fe import in accordance with their overall growth rate and that they misregulate Fe import when nanoparticles accumulate. The lack of regulation of Fe in yeast is perhaps unique compared to the tight regulation of

  1. A new mechanistic growth model for simultaneous determination of lag phase duration and exponential growth rate and a new Belehdradek-type model for evaluating the effect of temperature on growth rate

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A new mechanistic growth model was developed to describe microbial growth under isothermal conditions. The new mathematical model was derived from the basic observation of bacterial growth that may include lag, exponential, and stationary phases. With this model, the lag phase duration and exponen...

  2. Kinetics of growth and caffeine demethylase production of Pseudomonas sp. in bioreactor.

    PubMed

    Gummadi, Sathyanarayana N; Santhosh, Devarai

    2010-09-01

    The effect of various initial caffeine concentrations on growth and caffeine demethylase production by Pseudomonas sp. was studied in bioreactor. At initial concentration of 6.5 g l(-1) caffeine, Pseudomonas sp. showed a maximum specific growth rate of 0.2 h(-1), maximum degradation rate of 1.1 g h(-1), and caffeine demethylase activity of 18,762 U g CDW(-1) (CDW: cell dry weight). Caffeine degradation rate was 25 times higher in bioreactor than in shake flask. For the first time, we show highest degradation of 75 g caffeine (initial concentration 20 g l(-1)) in 120 h, suggesting that the tested strain has potential for successful bioprocess for caffeine degradation. Growth kinetics showed substrate inhibition phenomenon. Various substrate inhibition models were fitted to the kinetic data, amongst which the double-exponential (R(2) = 0.94), Luong (R(2) = 0.92), and Yano and Koga 2 (R(2) = 0.94) models were found to be the best. The Luedeking-Piret model showed that caffeine demethylase production kinetics was growth related. This is the first report on production of high levels of caffeine demethylase in batch bioreactor with faster degradation rate and high tolerance to caffeine, hence clearly suggesting that Pseudomonas sp. used in this study is a potential biocatalyst for industrial decaffeination. PMID:20495941

  3. Production of Thiol Species From An Exponential Growth Diatom Under Copper Exposure

    NASA Astrophysics Data System (ADS)

    Tang, D.; Shafer, M. M.; Karner, D. A.; Armstrong, D. E.; Schauer, J.

    2003-12-01

    The intracellar induction of phytochelatins is a well documented response of eukaryotic microorganisms to aqueous metal exposure. The extracellular release of thiolic compounds from algal species has been observed; and in some cases, this release can contribute a significant fraction of the uncharacterized metal-complexing ligands. Glutathione (GSH) or cysteine is among the detectable thiols excreted. A quantitative assessment of the excretion of thiols from algae cells into growth media is needed to assess the significance of biogenic-thiols as a source of strong ligands in natural waters and as a "forgotten" route in sulfur biogeochemical cycle. Unbuffered growth media (e.g., without adding complexing ligand such as EDTA) have only rarely been used to study the possible release of metal-complexing ligands from algal species, and the ligand titration techniques used varied considerably. The majority of culture studies have applied metal-buffered media. A direct comparison of released ligands under buffered and unbuffered conditions is lacking, partially due to the inherent difficulties of the titration methods applied. Using HPLC with fluorescence detection of thiol-monobromobimane derivatives, we were able to follow the dynamic change of GSH released in both media types during algal growth: (1) the cell quotas for thiols and pigments varied (mostly decreases) with growth time. Therefore, pigment-normalized cellular thiol concentrations were more or less conservative. (2) GSH was released into both the EDTA-buffered and -unbuffered growth media at similar concentrations. (3) at similar available Cu concentrations, EDTA possibly enhanced, rather than hindered, the release of GSH.

  4. Growth of Listeria monocytogenes in Salmon Roe - a kinetic analysis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The objective of this study was to investigate the growth kinetics of Listeria monocytogenes in unsalted and salted (3%) salmon roe. Growth curves, developed using inoculated samples incubated at constant temperatures between 5 and 30 degrees C, were analyzed by curve-fitting to the Huang and Baran...

  5. Controlled positions and kinetic analysis of spontaneous tin whisker growth

    NASA Astrophysics Data System (ADS)

    Su, Chien-Hao; Chen, Hao; Lee, Hsin-Yi; Wu, Albert T.

    2011-09-01

    This study achieved controlling the positions of spontaneous growth of tin whiskers. We surmounted the unpredictable growing nature of such whiskers and performed accurately quantitative analyses of the growth kinetics and yielded precise measurement of the growth rate. Furthermore, using synchrotron radiation x-ray, this study determined the stress variations in conjunction with whisker growth that fitted appropriately to the model. Accordingly, the results could address the debate held for decades and prove that forming a surface oxide layer is one of the required and necessary conditions for controlling the positions of spontaneous growth of tin whiskers.

  6. Multiple substrate growth kinetics of Leptothrix discophora SP-6.

    PubMed

    Yurt, Nurdan; Sears, John; Lewandowski, Zbigniew

    2002-01-01

    The growth parameters of Leptothrix discophora SP-6 were quantified on the basis of the steady-state concentrations and utilization rates of pyruvate, dissolved oxygen, and concentration of microorganisms in a chemostat operated at 25 degrees C, pH 7.2, and an agitation rate of 350 rpm. The results showed that the microbial growth was limited by both pyruvate and dissolved oxygen. A combined growth kinetics model using Monod growth kinetics for pyruvate and Tessier growth kinetics for oxygen showed the best correlation with the experimental data when analyzed using an interactive multiple substrate model. The growth kinetics parameters and the respective confidence limits, estimated using the Monte Carlo simulation, were mu(max) = 0.576 +/- 0.021 h(-1), K(sMp) = 38.81 +/- 4.24 mg L(-1), K(sTo) = 0.39 +/- 0.04 mg L(-1), Y(X/p) = 0.150 (mg microorganism mg(-1) pyruvate), Y(X/o) = 1.24 (mg microorganism mg(-1) oxygen), the maintenance factors for pyruvate and oxygen were m(p) = 0.129 (mg pyruvate consumed mg(-1) microorganism h(-1)) and m(o) = 0.076 (mg oxygen consumed mg(-1) microorganism h(-1)), respectively. PMID:12363350

  7. Growth and Nitrogen Uptake Kinetics in Cultured Prorocentrum donghaiense

    PubMed Central

    Hu, Zhangxi; Duan, Shunshan; Xu, Ning; Mulholland, Margaret R.

    2014-01-01

    We compared growth kinetics of Prorocentrum donghaiense cultures on different nitrogen (N) compounds including nitrate (NO3−), ammonium (NH4+), urea, glutamic acid (glu), dialanine (diala) and cyanate. P. donghaiense exhibited standard Monod-type growth kinetics over a range of N concentraions (0.5–500 μmol N L−1 for NO3− and NH4+, 0.5–50 μmol N L−1 for urea, 0.5–100 μmol N L−1 for glu and cyanate, and 0.5–200 μmol N L−1 for diala) for all of the N compounds tested. Cultures grown on glu and urea had the highest maximum growth rates (μm, 1.51±0.06 d−1 and 1.50±0.05 d−1, respectively). However, cultures grown on cyanate, NO3−, and NH4+ had lower half saturation constants (Kμ, 0.28–0.51 μmol N L−1). N uptake kinetics were measured in NO3−-deplete and -replete batch cultures of P. donghaiense. In NO3−-deplete batch cultures, P. donghaiense exhibited Michaelis-Menten type uptake kinetics for NO3−, NH4+, urea and algal amino acids; uptake was saturated at or below 50 μmol N L−1. In NO3−-replete batch cultures, NH4+, urea, and algal amino acid uptake kinetics were similar to those measured in NO3−-deplete batch cultures. Together, our results demonstrate that P. donghaiense can grow well on a variety of N sources, and exhibits similar uptake kinetics under both nutrient replete and deplete conditions. This may be an important factor facilitating their growth during bloom initiation and development in N-enriched estuaries where many algae compete for bioavailable N and the nutrient environment changes as a result of algal growth. PMID:24710151

  8. Kinetic model of particle-inhibited grain growth

    NASA Astrophysics Data System (ADS)

    Thompson, Gary Scott

    The effects of second phase particles on matrix grain growth kinetics were investigated using Al2O3-SiC as a model system. In particular, the validity of the conclusion drawn from a previous kinetic analysis that the kinetics of particle-inhibited grain growth in Al2 O3-SiC samples with an intermediate volume fraction of second phase could be well quantified by a modified-Zener model was investigated. A critical analysis of assumptions made during the previous kinetic analysis revealed oversimplifications which affect the validity of the conclusion. Specifically, the degree of interaction between particles and grain boundaries was assumed to be independent of the mean second phase particle size and size distribution. In contrast, current measurements indicate that the degree of interaction in Al2O3-SiC is dependent on these parameters. An improved kinetic model for particle-inhibited grain growth in Al 2O3-SiC was developed using a modified-Zener approach. The comparison of model predictions with experimental grain growth data indicated that significant discrepancies (as much as 4--5 orders of magnitude) existed. Based on this, it was concluded that particles had a much more significant effect on grain growth kinetics than that caused by a simple reduction of the boundary driving force due to the removal of boundary area. Consequently, it was also concluded that the conclusion drawn from the earlier kinetic analysis regarding the validity of a modified-Zener model was incorrect. Discrepancies between model and experiment were found to be the result of a significant decrease in experimental growth rate constant not predicted by the model. Possible physical mechanisms for such a decrease were investigated. The investigation of a small amount of SiO2 on grain growth in Al2O3 indicated that the decrease was not the result of a decrease in grain boundary mobility due to impurity contamination by particles. By process of elimination and based on previous observations

  9. Metastable Solution Thermodynamic Properties and Crystal Growth Kinetics

    NASA Technical Reports Server (NTRS)

    Kim, Soojin; Myerson, Allan S.

    1996-01-01

    The crystal growth rates of NH4H2PO4, KH2PO4, (NH4)2SO4, KAl(SO4)2 central dot 12H2O, NaCl, and glycine and the nucleation rates of KBr, KCl, NaBr central dot 2H2O, (NH4)2Cl, and (NH4)2SO4 were expressed in terms of the fundamental driving force of crystallization calculated from the activity of supersaturated solutions. The kinetic parameters were compared with those from the commonly used kinetic expression based on the concentration difference. From the viewpoint of thermodynamics, rate expressions based on the chemical potential difference provide accurate kinetic representation over a broad range of supersaturation. The rates estimated using the expression based on the concentration difference coincide with the true rates of crystallization only in the concentration range of low supersaturation and deviate from the true kinetics as the supersaturation increases.

  10. Kinetics of laser-assisted carbon nanotube growth.

    PubMed

    van de Burgt, Y; Bellouard, Y; Mandamparambil, R

    2014-03-21

    Laser-assisted chemical vapour deposition (CVD) growth is an attractive mask-less process for growing locally aligned carbon nanotubes (CNTs) in selected places on temperature sensitive substrates. The nature of the localized process results in fast carbon nanotube growth with high experimental throughput. Here, we report on the detailed investigation of growth kinetics related to physical and chemical process characteristics. Specifically, the growth kinetics is investigated by monitoring the dynamical changes in reflected laser beam intensity during growth. Benefiting from the fast growth and high experimental throughput, we investigate a wide range of experimental conditions and propose several growth regimes. Rate-limiting steps are determined using rate equations linked to the proposed growth regimes, which are further characterized by Raman spectroscopy and Scanning Electron Microscopy (SEM), therefore directly linking growth regimes to the structural quality of the CNTs. Activation energies for the different regimes are found to be in the range of 0.3-0.8 eV. PMID:24481313

  11. Grain boundary curvature and grain growth kinetics with particle pinning

    NASA Astrophysics Data System (ADS)

    Shahandeh, Sina; Militzer, Matthias

    2013-08-01

    Second-phase particles are used extensively in design of polycrystalline materials to control the grain size. According to Zener's theory, a distribution of particles creates a pinning pressure on a moving grain boundary. As a result, a limiting grain size is observed, but the effect of pinning on the detail of grain growth kinetics is less known. The influence of the particles on the microstructure occurs in multiple length scales, established by particle radius and the grain size. In this article, we use a meso-scale phase-field model that simulates grain growth in the presence of a uniform pinning pressure. The curvature of the grain boundary network is measured to determine the driving pressure of grain growth in 2D and 3D systems. It was observed that the grain growth continues, even under conditions where the average driving pressure is smaller than the pinning pressure. The limiting grain size is reached when the maximum of driving pressure distribution in the structure is equal to the pinning pressure. This results in a limiting grain size, larger than the one predicted by conventional models, and further analysis shows consistency with experimental observations. A physical model is proposed for the kinetics of grain growth using parameters based on the curvature analysis of the grain boundaries. This model can describe the simulated grain growth kinetics.

  12. Kinetics of bacterial growth on chlorinated aliphatic compounds

    SciTech Connect

    Wijngaard, A.J. van den; Wind, R.E.; Janssen, D.B. )

    1993-07-01

    Halogenated aliphatic compounds are frequent constituents of industrial waste gases. Because of the environmental and biological toxic effects of these compounds, there is a growing interest in technologies for their removal. Biological waste gas purification is an option if specialized bacterial strains that use halogenated aliphatics as sole carbon and energy sources can be used. Elimination efficiency of the compounds depends not only on the process technology but on the degradation properties of the bacterial strains. Important aspects of bacterial growth are the Monod half-saturation constant and the maximum growth rate. In this study the kinetic properties of the organisms (Ancylobacter aquaticus AD20 and AD25, Xanthobacter autotrophicus GJ10, Pseudomonas sp. strain AD1) weree measured during growth in continuous cultures and wer compared with the kinetic properties of the first catabolic enzyme involved in the degradation of the growth substrate. The results indicate that the growth of the strains examined followed Monod kinetics. Stains AD20 and GJ10 showed growth rates on DCE somewhat higher than predicted from the amount of haloalkane dehalogenase present in the cells, while strain AD25 was much lower. 33 refs., 3 figs., 4 tabs.

  13. Subdiffusion kinetics of nanoprecipitate growth and destruction in solid solutions

    NASA Astrophysics Data System (ADS)

    Sibatov, R. T.; Svetukhin, V. V.

    2015-06-01

    Based on fractional differential generalizations of the Ham and Aaron-Kotler precipitation models, we study the kinetics of subdiffusion-limited growth and dissolution of new-phase precipitates. We obtain the time dependence of the number of impurities and dimensions of new-phase precipitates. The solutions agree with the Monte Carlo simulation results.

  14. Growth Kinetics and Modeling of ZnO Nanoparticles

    ERIC Educational Resources Information Center

    Hale, Penny S.; Maddox, Leone M.; Shapter, Joe G.; Voelcker, Nico H.; Ford, Michael J.; Waclawik, Eric R.

    2005-01-01

    The technique for producing quantum-sized zinc oxide (ZnO) particles is much safer than a technique that used hydrogen sulfide gas to produce cadmium sulfide and zinc sulfide nanoparticles. A further advantage of this method is the ability to sample the solution over time and hence determine the growth kinetics.

  15. A novel microculture kinetic assay (MiCK assay) for malignant cell growth and chemosensitivity.

    PubMed

    Kravtsov, V D

    1994-01-01

    The THERMOmax microplate reader was adapted for monitoring the growth kinetics of human leukaemic OCI/AML-2 and mouse tumour J-774.1 cell lines in continuous culture. Fluid evaporation from wells, CO2 escape and contamination were prevented by hermetic sealing of the microcultures in wells of a 96-well microplate, thus enabling the cells to grow exponentially for 72 h under the conditions of the incubated microplate reader. For both OCI/AML-2 cells, which grow in suspension, and adherent J-774.1 cells, a linear correlation was demonstrated between the number of unstained cells seeded in a given microplate well and the optical density (OD) of that well. Therefore, the OD/time curve of the culture could be deemed to be its growth curve. By the use of the linear fit equation, the actual number of the cells in the wells was computable at any time point of the assay. In the chemosensitivity test, an inhibitory effect of ARA-C on the growth of the cells could be estimated by viewing of the growth curves plotted on the screen. The maximum kinetic rates (Vmax) of the curves in the control and the ARA-C-treated wells were compared, yielding a growth inhibition index (GII). Comparison of results of the kinetic chemosensitivity assay with those of a [3H]thymidine incorporation assay revealed that the novel assay is suitable for precise quantitation of the cell chemosensitivity, is more informative and has the added technical advantage of performance without recourse to radioactive or chemically hazardous substances. PMID:7833120

  16. Lag Phase Is a Distinct Growth Phase That Prepares Bacteria for Exponential Growth and Involves Transient Metal Accumulation

    PubMed Central

    Rolfe, Matthew D.; Rice, Christopher J.; Lucchini, Sacha; Pin, Carmen; Thompson, Arthur; Cameron, Andrew D. S.; Alston, Mark; Stringer, Michael F.; Betts, Roy P.; Baranyi, József; Peck, Michael W.

    2012-01-01

    Lag phase represents the earliest and most poorly understood stage of the bacterial growth cycle. We developed a reproducible experimental system and conducted functional genomic and physiological analyses of a 2-h lag phase in Salmonella enterica serovar Typhimurium. Adaptation began within 4 min of inoculation into fresh LB medium with the transient expression of genes involved in phosphate uptake. The main lag-phase transcriptional program initiated at 20 min with the upregulation of 945 genes encoding processes such as transcription, translation, iron-sulfur protein assembly, nucleotide metabolism, LPS biosynthesis, and aerobic respiration. ChIP-chip revealed that RNA polymerase was not “poised” upstream of the bacterial genes that are rapidly induced at the beginning of lag phase, suggesting a mechanism that involves de novo partitioning of RNA polymerase to transcribe 522 bacterial genes within 4 min of leaving stationary phase. We used inductively coupled plasma mass spectrometry (ICP-MS) to discover that iron, calcium, and manganese are accumulated by S. Typhimurium during lag phase, while levels of cobalt, nickel, and sodium showed distinct growth-phase-specific patterns. The high concentration of iron during lag phase was associated with transient sensitivity to oxidative stress. The study of lag phase promises to identify the physiological and regulatory processes responsible for adaptation to new environments. PMID:22139505

  17. Growth kinetics of sulfur nanoparticles in aqueous surfactant solutions.

    PubMed

    Chaudhuri, Rajib Ghosh; Paria, Santanu

    2011-02-15

    Sulfur is an important element has many practical applications when present as nanoparticles. Despite the practicable applications, limited studies are available in the literature related to synthesis of sulfur nanoparticles. Growth kinetics of colloidal sulfur particles synthesized from aqueous solutions using different surfactants have been studied here. The effects of different parameters such as reactant concentration, temperature, sonication, types of acids, types of surfactants, and even surfactant concentration are studied on the growth kinetics. Since the reaction rate is fast, particle growth depends on the parameters which affect diffusion of sulfur molecules. There is a linear relationship found among the reactant concentration and the particle coarsening rate constant. The growth kinetics was studied in the presence of different surfactants such as nonionic (poly(oxyethylene) p-tert-octylphenyl ether, TX-100), anionic (sodium dodecylbenzene sulfonate, SDBS), cationic (cetyltrimethyammonium bromide, CTAB) and results show the coarsening constant changes according to the following order: water>TX-100>SDBS>CTAB. The particle growth rate also depends on the surfactant concentration, coarsening rate constant decreases with the increase in surfactant concentration and become constant close to the critical micellar concentration (CMC). The coarsening rate constant also highly depends on the types of acid used as catalyst. PMID:21147482

  18. Growth kinetics of Staphylococcus aureus on Brie and Camembert cheeses.

    PubMed

    Lee, Heeyoung; Kim, Kyungmi; Lee, Soomin; Han, Minkyung; Yoon, Yohan

    2014-05-01

    In this study, we developed mathematical models to describe the growth kinetics of Staphylococcus aureus on natural cheeses. A five-strain mixture of Staph. aureus was inoculated onto 15 g of Brie and Camembert cheeses at 4 log CFU/g. The samples were then stored at 4, 10, 15, 25, and 30 °C for 2-60 d, with a different storage time being used for each temperature. Total bacterial and Staph. aureus cells were enumerated on tryptic soy agar and mannitol salt agar, respectively. The Baranyi model was fitted to the growth data of Staph. aureus to calculate kinetic parameters such as the maximum growth rate in log CFU units (r max; log CFU/g/h) and the lag phase duration (λ; h). The effects of temperature on the square root of r max and on the natural logarithm of λ were modelled in the second stage (secondary model). Independent experimental data (observed data) were compared with prediction and the respective root mean square error compared with the RMSE of the fit on the original data, as a measure of model performance. The total growth of bacteria was observed at 10, 15, 25, and 30 °C on both cheeses. The r max values increased with storage temperature (P<0·05), but a significant effect of storage temperature on λ values was only observed between 4 and 15 °C (P<0·05). The square root model and linear equation were found to be appropriate for description of the effect of storage temperature on growth kinetics (R 2=0·894-0·983). Our results indicate that the models developed in this study should be useful for describing the growth kinetics of Staph. aureus on Brie and Camembert cheeses. PMID:24731395

  19. Growth Morphologies of Wax in the Presence Kinetic Inhibitors

    NASA Astrophysics Data System (ADS)

    Tetervak, Alexander; Hutter, Jeffrey

    2004-03-01

    Kinetic inhibitors are molecules that alter crystal growth rates and morphologies by adsorbing to growth faces. Such species are used in many commercial processes to control microsctructure, and in other cases to prevent crystallization altogether. Despite their importance, the details of their mechanisms are largely unverified. We are studying the effects of such inhibitors on the crystallization of normal alkanes from solution. We find that inhibitors drastically alter the crystal morphology. As in similar systems, we see ``burst growth,'' in which newly formed solid is able to grow faster due to lower inhibitor coverage. Our experiments show several growth morphologies as a function of conditions: a tree-like structure that in some cases forms bands, and spherulites with characteristics very similar to those seen in polymers. Here, we characterize the front morphology as a function of these conditions and compare the results to numerical models that capture the essential growth behavior.

  20. Kinetic Roughening Transition and Energetics of Tetragonal Lysozyme Crystal Growth

    NASA Technical Reports Server (NTRS)

    Gorti, Sridhar; Forsythe, Elizabeth L.; Pusey, Marc L.

    2004-01-01

    Interpretation of lysozyme crystal growth rates using well-established physical theories enabled the discovery of a phenomenon possibly indicative of kinetic roughening. For example, lysozyme crystals grown above a critical supersaturation sigma, (where supersaturation sigma = ln c/c(sub eq), c = the protein concentration and c(sub eq) = the solubility concentration) exhibit microscopically rough surfaces due to the continuous addition of growth units anywhere on the surface of a crystal. The rate of crystal growth, V(sub c), for the continuous growth process is determined by the continuous flux of macromolecules onto a unit area of the crystal surface, a, from a distance, xi, per unit time due to diffusion, and a probability of attachment onto the crystal surface, expressed. Based upon models applied, the energetics of lysozyme crystal growth was determined. The magnitudes of the energy barriers of crystal growth for both the (110) and (101) faces of tetragonal lysozyme crystals are compared. Finally, evidence supportive of the kinetic roughening hypothesis is presented.

  1. The stretching of single poly-ubiquitin molecules: Static versus dynamic disorder in the non-exponential kinetics of chain unfolding

    NASA Astrophysics Data System (ADS)

    Chatterjee, Debarati; Cherayil, Binny J.

    2011-04-01

    Static disorder has recently been implicated in the non-exponential kinetics of the unfolding of single molecules of poly-ubiquitin under a constant force [Kuo, Garcia-Manyes, Li, Barel, Lu, Berne, Urbakh, Klafter, and Fernández, Proc. Natl. Acad. Sci. U.S.A. 107, 11336 (2010), 10.1073/pnas.1006517107]. In the present paper, it is suggested that dynamic disorder may provide a plausible, alternative description of the experimental observations. This suggestion is made on the basis of a model in which the barrier to chain unfolding is assumed to be modulated by a control parameter r that evolves in a parabolic potential under the action of fractional Gaussian noise according to a generalized Langevin equation. The treatment of dynamic disorder within this model is pursued using Zwanzig's indirect approach to noise averaging [Acc. Chem. Res. 23, 148 (1990)]. In conjunction with a self-consistent closure scheme developed by Wilemski and Fixman [J. Chem. Phys. 58, 4009 (1973), 10.1063/1.1679757; ibid. 60, 866 (1974), 10.1063/1.1681162], this approach eventually leads to an expression for the chain unfolding probability that can be made to fit the corresponding experimental data very closely.

  2. Coalescence kinetics under the action of alternative grain growth mechanisms

    SciTech Connect

    Gubanov, P. Yu. Maksimov, I. L.

    2008-01-15

    The coalescence process is considered for the case where the prevailing grain growth mechanism is block-to-block diffusion, during which the motion of atoms in a solution occurs in the form of diffusion flux along the block boundaries. Numerical and analytical investigation of the coalescence kinetics in a homogeneous supersaturated solution is performed with allowance for the finite maximum grain size, and the time evolution of the size distribution function of new-phase grains is theoretically described. Possible transition regimes arising during coalescence at a change in the dominant grain growth mechanism are considered.

  3. Growth morphologies of wax in the presence of kinetic inhibitors

    NASA Astrophysics Data System (ADS)

    Tetervak, Alexander A.

    Driven by the need to prevent crystallization of normal alkanes from diesel fuels in cold climates, the petroleum industry has developed additives to slow the growth of these crystals and alter their morphologies. Although the utility of these kinetic inhibitors has been well demonstrated in the field, few studies have directly monitored their effect at microscopic morphology, and the mechanisms by which they act remain poorly understood. Here we present a study of the effects of such additives on the crystallization of long-chain n-alkanes from solution. The additives change the growth morphology from plate-like crystals to a microcrystalline mesh. When we impose a front velocity by moving the sample through a temperature gradient, the mesh growth may form a macroscopic banded pattern and also exhibit a burst-crystallization behavior. In this study, we characterize these crystallization phenomena and also two growth models: a continuum model that demonstrates the essential behavior of the banded crystallization, and a simple qualitative cellular automata model that captures basics of the burst-crystallization process. Keywords: solidification; mesh crystallization; kinetic inhibitor; burst growth.

  4. Role of Transport and Kinetics in Growth of Renal Stones

    NASA Technical Reports Server (NTRS)

    Kassemi, Mohammad; Iskovitz, Ilana

    2012-01-01

    Renal stone disease is not only a concern on earth but could conceivably pose as a serious risk to the astronauts health and safety in Space. In this paper, a combined transport-kinetics model for growth of calcium oxalate crystals is presented. The model is used to parametrically investigate the growth of renal calculi in urine with a focus on the coupled effects of transport and surface reaction on the ionic concentrations at the surface of the crystal and their impact on the resulting growth rates. It is shown that under nominal conditions of low solution supersaturation and low Damkohler number that typically exist on Earth, the surface concentrations of calcium and oxalate approach their bulk solution values in the urine and the growth rate is most likely limited by the surface reaction kinetics. But for higher solution supersaturations and larger Damkohler numbers that may be prevalent in the microgravity environment of Space, the calcium and oxalate surface concentrations tend to shift more towards their equilibrium or saturation values and thus the growth process may be limited by the transport through the medium. Furthermore, parametric numerical studies suggest that changes to the renal biochemistry of astronauts due in space may promote development of renal calculi during long duration space expeditions.

  5. Computer Simulation of Grain Growth Kinetics with Solute Drag

    SciTech Connect

    Chen, L.; Chen, S.P.; Fan, D.

    1998-12-23

    The effects of solute dragon grain growth kinetics were studied in two dimensional (2-D) computer simulations by using a diffuse-interface field model. It is shown that, in the low velocity / low driving force regime, the velocity of a grain boundary motion departs from a linear relation with driving force (curvature) with solute drag. The nonlinear relation of migration velocity and driving force comes from the dependence of grain boundary energy and width on the curvature. The growth exponent m of power growth law for a polycrystalline system is affected by the segregation of solutes to grain boundaries. With the solute drag, the growth exponent m can take any value between 2 and 3 depending on the ratio of lattice diffusion to grain boundary mobility. The grain size and topological distributions are unaffected by solute drag, which are the same as those in a pure system.

  6. Grain Growth Kinetics of BaTiO3 Nanocrystals During Calcining Process

    NASA Astrophysics Data System (ADS)

    Song, Xiao-lan; He, Xi; Yang, Hai-ping; Qu, Yi-xin; Qiu, Guan-zhou

    2008-06-01

    BaTiO3 nanocrystals were synthesized by sol-gel method using barium acetate (Ba(CH3COO)2) and tetra-butyl titanate (Ti(OC4H9)4) as raw materials. Xerogel precursors and products were characterized by means of thermogravimetric/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD) and transmission electron microscope (TEM). The influence of the calcination temperature and duration on the lattice constant, the lattice distortion, and the grain size of BaTiO3 nanocrystals was discussed based on the XRD results. The grain growth kinetics of BaTiO3 nanocrystals during the calcination process were simulated with a conventional grain growth model which only takes into account diffusion, and an isothermal model proposed by Qu and Song, which takes into account both diffusion and surface reactions. Using these models, the pre-exponential factor and the activation energy of the rate constant were estimated. The simulation results indicate that the isothermal model is superior to the conventional one in describing the grain growth process, implying that both diffusion and surface reactions play important roles in the grain growth process.

  7. Diverse Growth Kinetics in Suspension Culture of a Model Eukaryote Dictyostelium discoideum, Confirmation of Lagless Growth

    NASA Astrophysics Data System (ADS)

    Franck, Carl; Zhou, Xaio-Qiao S.; Deshmukh, Amrish; Bogart, Elijah; Lau, Sharon; Daie, Kayvon; Bae, Albert

    2010-03-01

    In recent work we explored the notion that the transition between slow and fast growth, the lag-log transition, with increasing density seen in shaken cell culture represents a collective effect. (Phys. Rev. E 77, 041905 (2008)). We reported preliminary observations in which the lag phase was apparently missing. Here, we present significantly more measurements than in our original work as well as increased sensitivity at low densities. We confirm that instances of nearly exponential (``log'') growth do in fact appear, but more frequently, we find evidence of lagging. The degree of lagging fluctuates significantly from run to run, in contrast to our earlier observations and theory, but in all cases exponential growth is established with increasing density once the range of 10^4 to 10^5 cells/ml is reached. We present evidence against two natural explanations for these fluctuations: 1) a mixture of strains which have different growth phenotypes or 2) a single strain variation due to an epigenetic switch which can be set to the low growth state by subjecting cells to high density environments. The appearance of such growth variations has considerable practical significance and suggests that there is an additional dynamical variable besides density in play.

  8. Morphology and Growth Kinetics of Straight and Kinked Tin Whiskers

    NASA Astrophysics Data System (ADS)

    Susan, Donald; Michael, Joseph; Grant, Richard P.; McKenzie, Bonnie; Yelton, W. Graham

    2013-03-01

    Time-lapse SEM studies of Sn whiskers were conducted to estimate growth kinetics and document whisker morphologies. For straight whiskers, growth rates of 3 to 4 microns per day were measured at room temperature. Two types of kinked whiskers were observed. For Type A kinks, the original growth segment spatial orientation remains unchanged, there are no other changes in morphology or diameter, and growth continues. For Type B kinks, the spatial orientation of the original segment changes and it appears that the whisker bends over. Whiskers with Type B kinks show changes in morphology and diameter at the base, indicating grain boundary motion in the film, which eliminates the conditions suitable for long-term whisker growth. To estimate the errors in the whisker growth measurements, a technique is presented to correct for SEM projection effects. With this technique, the actual growth angles and lengths of a large number of whiskers were collected. It was found that most whiskers grow at moderate or shallow angles with respect to the surface; few straight whiskers grow nearly normal to the surface. In addition, there is no simple correlation between growth angles and lengths for whiskers observed over an approximate 2-year period.

  9. Calcite growth kinetics: Modeling the effect of solution stoichiometry

    NASA Astrophysics Data System (ADS)

    Wolthers, Mariëtte; Nehrke, Gernot; Gustafsson, Jon Petter; Van Cappellen, Philippe

    2012-01-01

    Until recently the influence of solution stoichiometry on calcite crystal growth kinetics has attracted little attention, despite the fact that in most aqueous environments calcite precipitates from non-stoichiometric solution. In order to account for the dependence of the calcite crystal growth rate on the cation to anion ratio in solution, we extend the growth model for binary symmetrical electrolyte crystals of Zhang and Nancollas (1998) by combining it with the surface complexation model for the chemical structure of the calcite-aqueous solution interface of Wolthers et al. (2008). To maintain crystal stoichiometry, the rate of attachment of calcium ions to step edges is assumed to equal the rate of attachment of carbonate plus bicarbonate ions. The model parameters are optimized by fitting the model to the step velocities obtained previously by atomic force microscopy (AFM, Teng et al., 2000; Stack and Grantham, 2010). A variable surface roughness factor is introduced in order to reconcile the new process-based growth model with bulk precipitation rates measured in seeded calcite growth experiments. For practical applications, we further present empirical parabolic rate equations fitted to bulk growth rates of calcite in common background electrolytes and in artificial seawater-type solutions. Both the process-based and empirical growth rate equations agree with measured calcite growth rates over broad ranges of ionic strength, pH, solution stoichiometry and degree of supersaturation.

  10. The small RNA, DsrA, is essential for the low temperature expression of RpoS during exponential growth in Escherichia coli.

    PubMed Central

    Sledjeski, D D; Gupta, A; Gottesman, S

    1996-01-01

    dsrA encodes a small, untranslated RNA. When over-expressed, DsrA antagonizes the H-NS-mediated silencing of numerous promoters. Cells devoid of DsrA grow normally and show little change in the expression of a number of H-NS-silenced genes. Expression of a transcriptional fusion of lacZ to dsrB, the gene next to dsrA, is significantly lower in cells carrying mutations in dsrA. All expression of beta-galactosidase from the dsrB::lacZ fusion is also dependent on the stationary phase sigma factor, RpoS. DsrA RNA was found to regulate dsrB::lacZ indirectly, by modulating RpoS synthesis. Levels of RpoS protein are substantially lower in a dsrA mutant, both in stationary and exponential phase cells. Mutations in dsrA decrease the expression of an RpoS::LacZ translational fusion, but not a transcriptional fusion, suggesting that DsrA is acting after transcription initiation. While RpoS expression is very low in exponential phase at temperatures of 30 degrees C and above, at 20 degrees C there is substantial synthesis of RpoS during exponential growth, all dependent on DsrA RNA. dsrA expression is also increased at low temperatures. These results suggest a new role for RpoS during exponential growth at low temperatures, mediated by DsrA. Images PMID:8670904

  11. Analysis of Network Topologies Underlying Ethylene Growth Response Kinetics.

    PubMed

    Prescott, Aaron M; McCollough, Forest W; Eldreth, Bryan L; Binder, Brad M; Abel, Steven M

    2016-01-01

    Most models for ethylene signaling involve a linear pathway. However, measurements of seedling growth kinetics when ethylene is applied and removed have resulted in more complex network models that include coherent feedforward, negative feedback, and positive feedback motifs. The dynamical responses of the proposed networks have not been explored in a quantitative manner. Here, we explore (i) whether any of the proposed models are capable of producing growth-response behaviors consistent with experimental observations and (ii) what mechanistic roles various parts of the network topologies play in ethylene signaling. To address this, we used computational methods to explore two general network topologies: The first contains a coherent feedforward loop that inhibits growth and a negative feedback from growth onto itself (CFF/NFB). In the second, ethylene promotes the cleavage of EIN2, with the product of the cleavage inhibiting growth and promoting the production of EIN2 through a positive feedback loop (PFB). Since few network parameters for ethylene signaling are known in detail, we used an evolutionary algorithm to explore sets of parameters that produce behaviors similar to experimental growth response kinetics of both wildtype and mutant seedlings. We generated a library of parameter sets by independently running the evolutionary algorithm many times. Both network topologies produce behavior consistent with experimental observations, and analysis of the parameter sets allows us to identify important network interactions and parameter constraints. We additionally screened these parameter sets for growth recovery in the presence of sub-saturating ethylene doses, which is an experimentally-observed property that emerges in some of the evolved parameter sets. Finally, we probed simplified networks maintaining key features of the CFF/NFB and PFB topologies. From this, we verified observations drawn from the larger networks about mechanisms underlying ethylene

  12. Analysis of Network Topologies Underlying Ethylene Growth Response Kinetics

    PubMed Central

    Prescott, Aaron M.; McCollough, Forest W.; Eldreth, Bryan L.; Binder, Brad M.; Abel, Steven M.

    2016-01-01

    Most models for ethylene signaling involve a linear pathway. However, measurements of seedling growth kinetics when ethylene is applied and removed have resulted in more complex network models that include coherent feedforward, negative feedback, and positive feedback motifs. The dynamical responses of the proposed networks have not been explored in a quantitative manner. Here, we explore (i) whether any of the proposed models are capable of producing growth-response behaviors consistent with experimental observations and (ii) what mechanistic roles various parts of the network topologies play in ethylene signaling. To address this, we used computational methods to explore two general network topologies: The first contains a coherent feedforward loop that inhibits growth and a negative feedback from growth onto itself (CFF/NFB). In the second, ethylene promotes the cleavage of EIN2, with the product of the cleavage inhibiting growth and promoting the production of EIN2 through a positive feedback loop (PFB). Since few network parameters for ethylene signaling are known in detail, we used an evolutionary algorithm to explore sets of parameters that produce behaviors similar to experimental growth response kinetics of both wildtype and mutant seedlings. We generated a library of parameter sets by independently running the evolutionary algorithm many times. Both network topologies produce behavior consistent with experimental observations, and analysis of the parameter sets allows us to identify important network interactions and parameter constraints. We additionally screened these parameter sets for growth recovery in the presence of sub-saturating ethylene doses, which is an experimentally-observed property that emerges in some of the evolved parameter sets. Finally, we probed simplified networks maintaining key features of the CFF/NFB and PFB topologies. From this, we verified observations drawn from the larger networks about mechanisms underlying ethylene

  13. Spherulitic growth of wax in the presence of kinetic inhibitors

    NASA Astrophysics Data System (ADS)

    Hutter, Jeffrey L.; Smith, Chris; Khmaladze, Alexander

    2001-03-01

    The petroleum industry has developed polymeric additives to prevent the precipitation of wax from diesel fuels in cold climates. These additives affect the crystallization kinetics of wax growth without affecting the thermodynamics. Some additives apparently operate by adsorbing to crystalline surfaces and blocking step flow, though direct evidence is lacking. We have used optical microscopy to study this process in model n-alkane systems with inhibitors added as a 1 wt% impurity. We find that the presence of the polymer dramatically alters the growth morphology of the wax --- rather than the usual plate-like growth, we see forms with all of the attributes of spherulites typical of bulk polymer growth, including radially oriented lamellae and banding. Since models for spherulitic growth postulate lamellar alignment by entropic pressure due to dangling polymer chains, the surface-adsorbed polymers are likely responsible for the similar alignment in wax spherulites. The banding seen in this case, however, results from periodic growth, rather than from the lamellar twisting seen in traditional polymer spherulites. We have modeled this effect as a coupling between the polymer adsorption rate and the growth rate of wax crystals.

  14. Solution growth kinetics and mechanism: Prismatic face of ADP

    NASA Astrophysics Data System (ADS)

    Chernov, A. A.; Rashkovich, L. N.; Mkrtchan, A. A.

    1986-01-01

    Laser Michelson interferometry has been applied to in situ study the (001) ADP growth kinetics in aqueous solution in the kinetic regime. The technique allows one to simultaneously measure the slope p of a growth hillock and normal growth rate R provided by this hillock. From these data, the average step growth rate v=R/p has been determined as a function of relative supersaturation σ. The dependencev(σ) is found to be linear, demonstrating the unimportance of surface and bulk diffusion. The direct incorporation at steps is characterized by the step kinetic coefficient βl=(5.1-6.4)X10-3 cm/s. The specific step free energy αl=(1.2-1.9) X10-6 erg/cm was determined from the measured linear dependence of the hillock slope on supersaturation for the hillock around presumably single elementary dislocation. For complex dislocation sources with large total Burgers vectors, the tendency to saturationin the hillock slope-supersaturation curves has been found. The curve perfectly fits the BCF expression which takes into account the perimeter 2L of the region occupied by the points in which the dislocation of the complex step source cross the growing face. For two dislocation sources,L=0.92 μm andL=0.31 μm and total Burgers vectors ⋍12h and 6h (h=7.53Å) have been found. The supersaturation dependence of activities for various complex dislocation sources have been directly demonstrated.

  15. A dynamic void growth model governed by dislocation kinetics

    NASA Astrophysics Data System (ADS)

    Wilkerson, J. W.; Ramesh, K. T.

    2014-10-01

    Here we examine the role of dislocation kinetics and substructure evolution on the dynamic growth of voids under very high strain rates, and develop a methodology for accounting for these effects in a computationally efficient manner. In particular, we account for the combined effects of relativistic dislocation drag and an evolving mobile dislocation density on the dynamics of void growth. We compare these effects to the constraints imposed by micro-inertia and discuss the conditions under which each mechanism governs the rate of void growth. The consequences of these constraints may be seen in a number of experimental observations associated with dynamic tensile failure, including the extreme rate-sensitivity of spall strength observed in laser shock experiments, an apparent anomalous temperate dependence of spall strength, and some particular features of void size distributions on spall surfaces.

  16. Kinetics of growth and aniline degradation by Stenotrophomonas maltophilia

    SciTech Connect

    Zissi, U.S.; Lyberatos, G.C.

    1999-01-01

    A pure bacterial culture of Stenotrophomonas maltophilia, capable of using aniline as a sole carbon source, was isolated. Kinetic experiments were conducted to develop a mathematical model that describes accurately the growth and utilization rates of the microorganism on the aniline and an alternate carbon source (glucose) individually and on their mixture. The growth of microorganisms and substrate utilization could be well described by using Monod expressions for limiting substrates. The presence of glucose in the culture medium did not repress aniline catabolism but simultaneous utilization was observed. When both substrates were present, the utilization of one substrate had a considerable effect on the utilization of the other. These effects were shown to be predicted by a mathematical model based on a modified Monod expression. The proposed model was found capable of describing accurately cellular growth as well as aniline and glucose biodegradation.

  17. Energetics and kinetics unveiled on helium cluster growth in tungsten

    NASA Astrophysics Data System (ADS)

    Wang, Jinlong; Niu, Liang-Liang; Shu, Xiaolin; Zhang, Ying

    2015-09-01

    The energetics and kinetics regarding helium (He) cluster growth in bcc tungsten (W) are unveiled using combined techniques of molecular statics and molecular dynamics. The principal mechanisms accounting for the decrease of system potential energy are identified to be trap mutation, < 100>   →  1/2< 111> cluster transformation, loop punching, coalescence between 1/2[1 1-1] and 1/2[1-1-1] loops, and loop capturing. The kinetic barriers associated with these key atomistic events are estimated. This work provides new insights into the complex yet intriguing atomistic evolution sequence of the He cluster and interstitial loop in W-based nuclear fusion materials under irradiation.

  18. Correlation between PLD repair capacity and the survival curve of human fibroblasts in exponential growth phase: analysis in terms of several parameters

    SciTech Connect

    Fertil, B.; Deschavanne, P.J.; Debieu, D.; Malaise, E.P.

    1988-10-01

    Published data on the in vitro radiosensitivity of 46 nontransformed fibroblasts of different genetic origins studied in plateau phase with immediate or delayed plating were used to investigate to what extent potentially lethal damage repair capacity is related to intrinsic radiosensitivity (i.e., irradiated in exponential growth phase). While most of the survival curve analysis is conducted in terms of D0, Dq, and the mean inactivation dose D, some of the data are also discussed in terms of the linear-quadratic model parameter alpha. Using D it is shown that: (i) the radiosensitivity of human fibroblasts in exponential growth phase does not significantly differ from that of plateau-phase fibroblasts with immediate plating; (ii) the radiosensitivity of plateau-phase cells with delayed plating is correlated to the radiosensitivity of cells with immediate plating: the more radioresistant the cell strain in exponential growth phase, the higher its repair capacity; (iii) the repair capacity of the cell strains is related to their genetic origin. In conclusion, we suggest that the survival curve of growing cells depends on the repair capacity of the cells.

  19. Kinetic model of impurity poisoning during growth of calcite

    SciTech Connect

    DeYoreo, J; Wasylenki, L; Dove, P; Wilson, D; Han, N

    2004-05-18

    The central role of the organic component in biologically controlled mineralization is widely recognized. These proteins are characterized by a high proportion of acidic amino acid residues, especially aspartate, Asp. At the same time, biomineralization takes place in the presence of a number of naturally-occurring, inorganic impurities, particularly Mg and Sr. In an attempt to decipher the controls on calcite growth imposed by both classes of modifiers, we have used in situ AFM to investigate the dependence of growth morphology and step kinetics on calcite in the presence of Sr{sup 2+}, as well as a wide suite of Aspartic acid-bearing polypeptides. In each case, we observe a distinct and step-specific modification. Most importantly, we find that the step speed exhibits a characteristic dependence on impurity concentration not predicted by existing crystal growth models. While all of the impurities clearly induce appearance of a 'dead zone,' neither the width of that dead zone nor the dependence of step speed on activity or impurity content can be explained by invoking the Gibbs-Thomson effect, which is the basis for the Cabrera-Vermilyea model of impurity poisoning. Common kink-blocking models also fail to explain the observed dependencies. Here we propose a kinetic model of inhibition based on a 'cooperative' effect of impurity adsorption at adjacent kink sites. The model is in qualitative agreement with the experimental results in that it predicts a non-linear dependence of dead zone width on impurity concentration, as well as a sharp drop in step speed above a certain impurity content. However, a detailed model of impurity adsorption kinetics that give quantitative agreement with the data has yet to be developed.

  20. Glass susceptibility: Growth kinetics and saturation under shear

    NASA Astrophysics Data System (ADS)

    Nandi, Saroj Kumar; Ramaswamy, Sriram

    2016-07-01

    We study the growth kinetics of glassy correlations in a structural glass by monitoring the evolution, within mode-coupling theory, of a suitably defined three-point function χC(t ,tw) with time t and waiting time tw. From the complete wave-vector-dependent equations of motion for domain growth, we pass to a schematic limit to obtain a numerically tractable form. We find that the peak value χCP of χC(t ,tw) , which can be viewed as a correlation volume, grows as tw0.5, and the relaxation time as tw0.8, following a quench to a point deep in the glassy state. These results constitute a theoretical explanation of the simulation findings of Parisi [J. Phys. Chem. B 103, 4128 (1999), 10.1021/jp983967m] and Kob and Barrat [Phys. Rev. Lett. 78, 4581 (1997), 10.1103/PhysRevLett.78.4581], and they are also in qualitative agreement with Parsaeian and Castillo [Phys. Rev. E 78, 060105(R) (2008), 10.1103/PhysRevE.78.060105]. On the other hand, if the quench is to a point on the liquid side, the correlation volume grows to saturation. We present a similar calculation for the growth kinetics in a p -spin spin glass mean-field model where we find a slower growth, χCP˜tw0.13 . Further, we show that a shear rate γ ˙ cuts off the growth of glassy correlations when tw˜1 /γ ˙ for quench in the glassy regime and tw=min(tr,1 /γ ˙) in the liquid, where tr is the relaxation time of the unsheared liquid. The relaxation time of the steady-state fluid in this case is ∝γ˙-0.8 .

  1. Leuconostoc mesenteroides growth kinetics with application to bacterial profile modification

    SciTech Connect

    Lappan, R.E.; Fogler, H.S. . Dept. of Chemical Engineering)

    1994-04-15

    Bacterial profile modification (BPM) is being developed as an oil recovery technique that uses bacteria to selectively plug oil depleted zones within a reservoir to divert displacing fluids into oil-rich zones. Leuconostoc mesenteroides, which produces dextran when supplied with sucrose, is a bacterium that is technically feasible for use in profile modification. However, the technique requires controlled bacterial growth to produce selective plugging. A kinetic model for the production of cells and polysaccharides has been developed for L. mesenteroides bacteria. This model, based on data from batch growth experiments, predicts saccharide utilization, cell generation, and dextran production. The underlying mechanism is the extracellular breakdown of sucrose into glucose and fructose and the subsequent production of polysaccharide. The monosaccharides are then available for growth. Accompanying sucrose consumption is the utilization of yeast extract. The cell requires a complex media that is provided by yeast extract as a source of vitamins and amino acids. Varying the concentration ratio of yeast extract to sucrose in the growth media provides a means of controlling the amount of polymer produced per cell. Consequently, in situ bacteria growth can be controlled by the manipulation of nutrient media composition, thereby providing the ability to create an overall strategy for the use of L. mesenteroides bacteria for profile modification.

  2. Radiochemical study of the kinetics of crystal growth in gels

    NASA Astrophysics Data System (ADS)

    Cecal, Alexandru; Palamaru, Mircea; Juverdeanu, Anca; Giosan, Marcel

    1996-01-01

    A kinetic study was performed on nucleation and growth of crystals containing radioactive ions in gelatin and agar gels. The investigated crystals were: 60CoHPO 4, 60CoS, 60Co(OH) 2, 60Co(SCN) 2, 204Tl(OH) 3, and 204Tl[(C 2H 5) 2NCS 2] 3. The study shows that the crystal growth rate depends on the cation size and charge, the nature of anion as well as on the colloidal medium. The crystallisation process in the gel has two distinctive steps: diffusion of reactant ions in the gel followed by a chemical reaction which leads to nucleation of the crystal. Both steps are described quantitatively.

  3. Kinetically controlled growth of gallium on stepped Si (553) surface

    NASA Astrophysics Data System (ADS)

    Kumar, Mukesh; Pasha, Syed Khalid; Govind

    2013-10-01

    Kinetically controlled growth of gallium (Ga) metal has been reported on high index stepped Si (553) surface and its thermal stability with various novel superstructural phases has been analyzed. Auger electron spectroscopy studies revealed that the adsorption of Ga at room temperature (RT) follows Frank-van der Merwe (FM) growth mode while for higher substrate temperature, Ga adsorption remains within the submonolayer range. Thermal desorption and low energy electron diffraction studies investigated the formation of thermally stable Ga-islands and the various Ga induced superstructural phase on Si (553). During room temperature adsorption, (1 1 1)7 × 7 facet of Si (553) reconstructed into (1 1 1)6 × 6 facet while during desorption process, stable (1 1 1)6 × 6 and (1 1 1)√3 × √3-R30° surface reconstructions has been observed.

  4. Continuous growth kinetics of Candida utilis in pineapple cannery effluent

    SciTech Connect

    Prior, B.A.

    1984-01-01

    Candida utilis was grown on a pineapple cannery effluent as the sole carbon and energy source in a chemostat at dilution rates between 0.10 and 0.62 h/sup -1/ to determine the growth kinetics. The principal sugars in the effluent were sucrose, glucose, and fructose. The cell yield coefficient on carbohydrate varied with dilution rate and a maximum value of 0.63 was observed at a dilution rate of 0.33 h/sup -1/. The steady-state concentrations of carbohydrate, reducing sugar, and chemical oxygen demand (COD) appeared to follow Monod saturation kinetics with increasing dilution rate, although none of the measured parameters represented a pure substrate. The maximum specific growth rate and reducing sugar saturation constant were 0.64 h/sup -1/ and 0.060 g/L, respectively. A maximum cell mass productivity of 2.3 g/L h was observed at a dilution rate of 0.51 h/sup -1/. At this dilution rate, only 68% of the COD was removed. A 95% COD removal was attained at a dilution rate of 0.10 h/sup -1/. Optimal yeast productivity and COD reduction occurred at a dilution rate of 0.33 h/sup -1/.

  5. Thermodynamic-kinetic simulation of constrained dendrite growth in steels

    SciTech Connect

    Miettinen, J.

    2000-04-01

    A model of constrained dendritic growth for steels, based on thermodynamic and kinetic theory, is presented. The model links thermodynamic chemical potential-equality equations to an existing, approximate treatment of constrained dendritic growth in multicomponent steels, taking into account the deviation from the local thermodynamic equilibrium of the phase interface caused by interface friction, capillarity, and solute trapping. Due to the thermodynamic approach, with a thermodynamic model and recently assessed data, the present treatment yields a more accurate determination of phase stabilities than the earlier methods. Depending on the steel composition and the growth conditions (growth rate and temperature gradient), the model determines the dendrite tip undercooling, the primary solid phase (ferrite or austenite), the stability of that phase, certain dimensions of the microstructure, and the solute accumulation ahead of the dendrite tip. A special optional calculations is that of the equally probable formation of ferrite and austenite in stainless steels. Calculations for testing the model and for validation it with experimental data are presented.

  6. The mathematical properties of the quasi-chemical model for microorganism growth-death kinetics in foods.

    PubMed

    Ross, E W; Taub, I A; Doona, C J; Feeherry, F E; Kustin, K

    2005-03-15

    Knowledge of the mathematical properties of the quasi-chemical model [Taub, Feeherry, Ross, Kustin, Doona, 2003. A quasi-chemical kinetics model for the growth and death of Staphylococcus aureus in intermediate moisture bread. J. Food Sci. 68 (8), 2530-2537], which is used to characterize and predict microbial growth-death kinetics in foods, is important for its applications in predictive microbiology. The model consists of a system of four ordinary differential equations (ODEs), which govern the temporal dependence of the bacterial life cycle (the lag, exponential growth, stationary, and death phases, respectively). The ODE system derives from a hypothetical four-step reaction scheme that postulates the activity of a critical intermediate as an antagonist to growth (perhaps through a quorum sensing biomechanism). The general behavior of the solutions to the ODEs is illustrated by several examples. In instances when explicit mathematical solutions to these ODEs are not obtainable, mathematical approximations are used to find solutions that are helpful in evaluating growth in the early stages and again near the end of the process. Useful solutions for the ODE system are also obtained in the case where the rate of antagonist formation is small. The examples and the approximate solutions provide guidance in the parameter estimation that must be done when fitting the model to data. The general behavior of the solutions is illustrated by examples, and the MATLAB programs with worked examples are included in the appendices for use by predictive microbiologists for data collected independently. PMID:15734564

  7. Kinetic model of nucleation and growth in silicate melts: Implications for igneous textures and their quantitative description

    NASA Astrophysics Data System (ADS)

    Špillar, Václav; Dolejš, David

    2014-04-01

    We present a new high-resolution numerical model for the simulation of crystallization and texture evolution using arbitrary rates of crystal nucleation and growth. The algorithm models single or multiphase solidification in a three-dimensional domain and 17 simulations using constant, linearly increasing, exponential, and Gaussian functions for the rates of nucleation and growth yield equigranular to seriate textures. Conventional crystal size distributions of all textures are nearly linear to concave-down (previously interpreted as formed by equilibration coarsening), and identical distribution patterns can result from multiple non-unique combinations of nucleation and growth rates. The clustering index is always a non-monotonous function, which initially increases then decreases with increasing crystal fraction. For texture from random homogeneous nucleation the index is substantially lower than previous predictions based on a random sphere distribution line, hence, natural samples interpreted as clustered now have greater degrees of randomness or ordering. The average number of contact neighbors and the average neighbor distance of a crystal depend linearly on crystal size, but one of the two remains insensitive to nucleation and growth kinetics and represents potential indicator of other crystallization processes than random nucleation and crystal growth. Simultaneous comparison of size, spatial and clustering patterns and of their departures from expected values are suggested to allow for separation of effects of crystallization kinetics, melt-mineral mechanical interactions, suspension mixing, or postcrystallization re-equilibration and coarsening on natural igneous rocks.

  8. Glass susceptibility: Growth kinetics and saturation under shear.

    PubMed

    Nandi, Saroj Kumar; Ramaswamy, Sriram

    2016-07-01

    We study the growth kinetics of glassy correlations in a structural glass by monitoring the evolution, within mode-coupling theory, of a suitably defined three-point function χ_{C}(t,t_{w}) with time t and waiting time t_{w}. From the complete wave-vector-dependent equations of motion for domain growth, we pass to a schematic limit to obtain a numerically tractable form. We find that the peak value χ_{C}^{P} of χ_{C}(t,t_{w}), which can be viewed as a correlation volume, grows as t_{w}^{0.5}, and the relaxation time as t_{w}^{0.8}, following a quench to a point deep in the glassy state. These results constitute a theoretical explanation of the simulation findings of Parisi [J. Phys. Chem. B 103, 4128 (1999)JPCBFK1520-610610.1021/jp983967m] and Kob and Barrat [Phys. Rev. Lett. 78, 4581 (1997)PRLTAO0031-900710.1103/PhysRevLett.78.4581], and they are also in qualitative agreement with Parsaeian and Castillo [Phys. Rev. E 78, 060105(R) (2008)PLEEE81539-375510.1103/PhysRevE.78.060105]. On the other hand, if the quench is to a point on the liquid side, the correlation volume grows to saturation. We present a similar calculation for the growth kinetics in a p-spin spin glass mean-field model where we find a slower growth, χ_{C}^{P}∼t_{w}^{0.13}. Further, we show that a shear rate γ[over ̇] cuts off the growth of glassy correlations when t_{w}∼1/γ[over ̇] for quench in the glassy regime and t_{w}=min(t_{r},1/γ[over ̇]) in the liquid, where t_{r} is the relaxation time of the unsheared liquid. The relaxation time of the steady-state fluid in this case is ∝γ[over ̇]^{-0.8}. PMID:27575179

  9. Different isotope and chemical patterns of pyrite oxidation related to lag and exponential growth phases of Acidithiobacillus ferrooxidans reveal a microbial growth strategy

    NASA Astrophysics Data System (ADS)

    Brunner, Benjamin; Yu, Jae-Young; Mielke, Randall E.; MacAskill, John A.; Madzunkov, Stojan; McGenity, Terry J.; Coleman, Max

    2008-06-01

    The solution chemistry during the initial (slow increase of dissolved iron and sulfate) and main stage (rapid increase of dissolved iron and sulfate) of pyrite leaching by Acidithiobacillus ferrooxidans (Af) at a starting pH of 2.05 shows significant differences. During the initial stage, ferrous iron (Fe2+) is the dominant iron species in solution and the molar ratio of produced sulfate (SO42-) and total iron (Fetot) is 1.1, thus does not reflect the stoichiometry of pyrite (FeS2). During the main stage, ferric iron (Fe3+) is the dominant iron species in solution and the SO42-:Fetot ratio is with 1.9, close to the stoichiometry of FeS2. Another difference between initial and main stage is an initial trend to slightly higher pH values followed by a drop during the main stage to pH 1.84. These observations raise the question if there are different modes of bioleaching of pyrite, and if there are, what those modes imply in terms of leaching mechanisms. Different oxygen and sulfur isotope trends of sulfate during the initial and main stages of pyrite oxidation confirm that there are two pyrite bioleaching modes. The biochemical reactions during initial stage are best explained by the net reaction FeS2 + 3O2 ⇒ Fe2+ + SO42- + SO2(g). The degassing of sulfur dioxide (SO2) acts as sink for sulfur depleted in 34S compared to pyrite, and is the cause of the SO42-:Fetot ratio of 1.1 and the near constant pH. During the exponential phase, pyrite sulfur is almost quantitatively converted to sulfate, according to the net reaction FeS2 + 15/4O2 + 1/2H2O ⇒ Fe3+ + 2SO42- + H+. We hypothesize that the transition between the modes of bioleaching of pyrite is due to the impact of the accumulation of ferrous iron, which induces changes in the metabolic activity of Af and may act as an inhibitor for the oxidation of sulfur species. This transition defines a fundamental change in the growth strategy of Af. A mode, where bacteria gain energy by oxidation of elemental sulfur to

  10. Arabidopsis thaliana root growth kinetics and lunisolar tidal acceleration.

    PubMed

    Fisahn, Joachim; Yazdanbakhsh, Nima; Klingele, Emile; Barlow, Peter

    2012-07-01

    • All living organisms on Earth are continually exposed to diurnal variations in the gravitational tidal force due to the Sun and Moon. • Elongation of primary roots of Arabidopsis thaliana seedlings maintained at a constant temperature was monitored for periods of up to 14 d using high temporal- and spatial-resolution video imaging. The time-course of the half-hourly elongation rates exhibited an oscillation which was maintained when the roots were placed in the free-running condition of continuous illumination. • Correlation between the root growth kinetics collected from seedlings initially raised under several light protocols but whose roots were subsequently in the free-running condition and the lunisolar tidal profiles enabled us to identify that the latter is the probable exogenous determinant of the rhythmic variation in root elongation rate. Similar observations and correlations using roots of Arabidopsis starch mutants suggest a central function of starch metabolism in the response to the lunisolar tide. The periodicity of the lunisolar tidal signal and the concomitant adjustments in root growth rate indicate that an exogenous timer exists for the modulation of root growth and development. • We propose that, in addition to the sensitivity to Earthly 1G gravity, which is inherent to all animals and plants, there is another type of responsiveness which is attuned to the natural diurnal variations of the lunisolar tidal force. PMID:22583121

  11. Growth kinetics in a phase field model with continuous symmetry

    NASA Astrophysics Data System (ADS)

    Marini Bettolo Marconi, Umberto; Crisanti, Andrea

    1996-07-01

    We discuss the static and kinetic properties of a Ginzburg-Landau spherically symmetric O(N) model recently introduced [U. Marini Bettolo Marconi and A. Crisanti, Phys. Rev. Lett. 75, 2168 (1995)] in order to generalize the so-called phase field model of Langer [Rev. Mod. Phys. 52, 1 (1980); Science 243, 1150 (1989)]. The Hamiltonian contains two O(N) invariant fields φ and U bilinearly coupled. The order parameter field φ evolves according to a nonconserved dynamics, whereas the diffusive field U follows a conserved dynamics. In the limit N-->∞ we obtain an exact solution, which displays an interesting kinetic behavior characterized by three different growth regimes. In the early regime the system displays normal scaling and the average domain size grows as t1/2; in the intermediate regime one observes a finite wave-vector instability, which is related to the Mullins-Sekerka instability; finally, in the late stage the structure function has a multiscaling behavior, while the domain size grows as t1/4.

  12. Screening and kinetic studies of catharanthine and ajmalicine accumulation and their correlation with growth biomass in Catharanthus roseus hairy roots.

    PubMed

    Benyammi, Roukia; Paris, Cédric; Khelifi-Slaoui, Majda; Zaoui, Djamila; Belabbassi, Ouarda; Bakiri, Nouara; Meriem Aci, Myassa; Harfi, Boualem; Malik, Sonia; Makhzoum, Abdullah; Desobry, Stéphane; Khelifi, Lakhdar

    2016-10-01

    Context Catharanthus roseus (L.) G. Don (Apocynaceae) is still one of the most important sources of terpene indole alkaloids including anticancer and hypertensive drugs as vincristine and vinblastine. These final compounds have complex pathway and many enzymes are involved in their biosynthesis. Indeed, ajmalicine and catharanthine are important precursors their increase can lead to enhance levels of molecules of interest. Objective This study aims at selecting the highest yield of hairy root line(s) and at identifying best times for further treatments. We study kinetics growth and alkaloids (ajmalicine and catharanthine) accumulation of three selected hairy root lines during the culture cycle in order to determine the relationship between biomass production and alkaloids accumulation. Materials and methods Comparative analysis has been carried out on three selected lines of Catharanthus roseus hairy roots (LP10, LP21 and L54) for their kinetics of growth and the accumulation of ajamalicine and catharanthine, throughout a 35-day culture cycle. The methanolic extract for each line in different times during culture cycle is analyzed using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Results Maximum accumulation of the alkaloids is recorded for LP10 line in which the peak of ajmalicine and catharanthine accumulation reached to 3.8 and 4.3 mg/g dry weight (DW), respectively. This increase coincides with an exponential growth phase. Discussion and conclusion Our results suggest that the evolution of accumulation of ajmalicine and catharanthine are positively correlated with the development of the biomass growth. Significantly, for LP10 line the most promising line to continue optimizing the production of TIAs. Additionally, the end of exponential phase remains the best period for elicitor stimuli. PMID:26983347

  13. Oxidation kinetics and chemostat growth kinetics of Thiobacillus ferrooxidans on tetrathionate and thiosulfate.

    PubMed

    Eccleston, M; Kelly, D P

    1978-06-01

    Growth of Thiobacillus ferrooxidans in batch culture on 10 mM potassium tetrathionate was optimal at pH 2.5 (specific growth rate, 0.092 h-1). Oxygen electrode studies on resting cell suspensions showed that the apparent Km for tetrathionate oxidation (0.13 to 8.33 mM) was pH dependent, suggesting higher substrate affinity at higher pH. Conversely, oxidation rates were greatest at low pH. High substrate concentrations (7.7 to 77 mM) did not affect maximum oxidation rates at pH 3.0, but produced substrate inhibition at other pH values. Tetrathionate-grown cell suspensions also oxidized thiosulfate at pH 2.0 to 4.0. Apparent Km values (1.2 to 25 mM) were of the same order as for tetrathionate, but kinetics were complex. Continuous culture on growth-limiting tetrathionate at pH 2.5, followed by continuous culture on growth-limiting thiosulfate at pH 2.5, indicated true growth yield values (grams [dry weight] per gram-molecule of substrate) of 12.2 and 7.5, and maintenance coefficient values (millimoles of substrate per gram [dry weight) of organisms per hour) of 1.01 and 0.97 for tetrathionate and thiosulfate, respectively. Yield was increased on both media at low dilution rates by increase in CO2 supply. The apparent maintenance coefficient was lowered without affecting YG, suggesting better energy coupling in CO2-rich environments. Prolonged continuous cultivation on tetrathionate or thiosulfate did not affect the ability of the organism to grow subsequently in ferrous iron medium. PMID:26665

  14. Energy and fluxes of thermal runaway electrons produced by exponential growth of streamers during the stepping of lightning leaders and in transient luminous events

    NASA Astrophysics Data System (ADS)

    Celestin, Sebastien; Pasko, Victor P.

    2011-03-01

    In the present paper, we demonstrate that the exponential expansion of streamers propagating in fields higher than the critical fields for stable propagation of streamers of a given polarity leads to the exponential growth of electric potential differences in streamer heads. These electric potential differences are directly related to the energy that thermal runaway electrons can gain once created. Using full energy range relativistic Monte Carlo simulations, we show that the exponential growth of potential differences in streamers gives rise to the production of runaway electrons with energies as high as ˜100 keV, with most of electrons residing in energy range around several tens of keVs. We apply these concepts in the case of lightning stepped leaders during the stage of negative corona flash. The computation of electric field produced by stepped leaders demonstrates for the first time that those energetic electrons are capable of further acceleration up to the MeV energies. Moreover, the flux of runaway electrons produced by streamers suggests that stepped leaders produce a considerable number of energetic electrons, which is in agreement with the number of energetic photons observed from satellites in terrestrial gamma ray flashes (TGFs). The results suggest that previously proposed process of relativistic runaway electron avalanche is difficult to sustain in the low-electric fields observed in thunderclouds and is generally not needed for explanation of TGFs. The present work also gives insights on relations between physical properties of energetic electrons produced in streamers and the internal electrical properties of streamer discharges, which can further help development and interpretation of X-ray diagnostics of these discharges.

  15. Pattern Formation and Growth Kinetics in Eutectic Systems

    SciTech Connect

    Teng, Jing

    2007-01-01

    Growth patterns during liquid/solid phase transformation are governed by simultaneous effects of heat and mass transfer mechanisms, creation of new interfaces, jump of the crystallization units from liquid to solid and their rearrangement in the solid matrix. To examine how the above processes influence the scale of microstructure, two eutectic systems are chosen for the study: a polymeric system polyethylene glycol-p-dibromobenzene (PEG-DBBZ) and a simple molecular system succinonitrile (SCN)-camphor. The scaling law for SCN-camphor system is found to follow the classical Jackson-Hunt model of circular rod eutectic, where the diffusion in the liquid and the interface energy are the main physics governing the two-phase pattern. In contrast, a significantly different scaling law is observed for the polymer system. The interface kinetics of PEG phase and its solute concentration dependence thus have been critically investigated for the first time by directional solidification technique. A model is then proposed that shows that the two-phase pattern in polymers is governed by the interface diffusion and the interface kinetics. In SCN-camphor system, a new branch of eutectic, elliptical shape rodl, is found in thin samples where only one layer of camphor rods is present. It is found that the orientation of the ellipse can change from the major axis in the direction of the thickness to the direction of the width as the velocity and/or the sample thickness is decreased. A theoretical model is developed that predicts the spacing and orientation of the elliptical rods in a thin sample. The single phase growth patterns of SCN-camphor system were also examined with emphasis on the three-dimensional single cell and cell/dendrite transition. For the 3D single cell in a capillary tube, the entire cell shape ahead of the eutectic front can be described by the Saffmann-Taylor finger only at extremely low growth rate. A 3D directional solidification model is developed to

  16. Direct Observation of Aggregative Nanoparticle Growth: Kinetic Modeling of the Size Distribution and Growth Rate

    SciTech Connect

    Woehl, Taylor J.; Park, Chiwoo; Evans, James E.; Arslan, Ilke; Ristenpart, William D.; Browning, Nigel D.

    2014-01-08

    Direct observations of solution-phase nanoparticle growth using in situ liquid transmission electron microscopy (TEM) have demonstrated the importance of “non-classical” growth mechanisms, such as aggregation and coalescence, on the growth and final morphology of nanocrystals at the atomic and single nanoparticle scales. To date, groups have quantitatively interpreted the mean growth rate of nanoparticles in terms of the Lifshitz-Slyozov-Wagner (LSW) model for Ostwald ripening, but less attention has been paid to modeling the corresponding particle size distribution. Here we use in situ fluid stage scanning TEM to demonstrate that silver nanoparticles grow by a length-scale dependent mechanism, where individual nanoparticles grow by monomer attachment but ensemble-scale growth is dominated by aggregation. Although our observed mean nanoparticle growth rate is consistent with the LSW model, we show that the corresponding particle size distribution is broader and more symmetric than predicted by LSW. Following direct observations of aggregation, we interpret the ensemble-scale growth using Smoluchowski kinetics and demonstrate that the Smoluchowski model quantitatively captures the mean growth rate and particle size distribution.

  17. Physiologic growth hormone replacement improves fasting lipid kinetics in patients with HIV lipodystrophy syndrome

    Technology Transfer Automated Retrieval System (TEKTRAN)

    HIV lipodystrophy syndrome (HLS) is characterized by accelerated lipolysis, inadequate fat oxidation, increased hepatic reesterification, and a high frequency of growth hormone deficiency (GHD). The effect of growth hormone (GH) replacement on these lipid kinetic abnormalities is unknown. We aimed ...

  18. Growth kinetics of forsterite reaction rims at high-pressure

    NASA Astrophysics Data System (ADS)

    Nishihara, Yu; Maruyama, Genta; Nishi, Masayuki

    2016-08-01

    Growth kinetics of forsterite (Fo) reaction rims between periclase (Per) and enstatite (En) were studied experimentally at pressure (P) and temperature (T) conditions of 3.0-11.1 GPa and 1473-1873 K, respectively. Pt markers originally placed at the Per-En interface were always observed at the Per-Fo interface, which indicates that Mg and O are the diffusing species in Fo rim growth (Mg-O coupled diffusion). The presence of some En inclusions in Fo grains and the growth rate of the Fo rim suggests that grain boundary diffusion is dominant rather than lattice diffusion. Considering the very fast grain boundary diffusion of O in olivine, the Mg-O coupled grain boundary diffusion in Fo is deduced to be rate-limited by the diffusivity of Mg. Based on an analysis of data collected under dry conditions, the product of the Mg grain boundary diffusion coefficient (Dgb) and the effective grain boundary width (δ) was determined to be δDgb = δDgb,0exp[-(E∗ + PV∗)/RT] with δDgb,0 = 10-9.68 ± 1.51 m3/s, E∗ = 379 ± 44 kJ/mol and V∗ = -1.9 ± 1.4 cm3/mol. Our results, combined with previously reported data on Mg lattice diffusion in Fo, suggest that for Mg, the significance of grain boundary diffusion increases with depth in the Earth's upper mantle, although lattice diffusion is still dominant for typical mantle grain sizes of 1-10 mm.

  19. End-growth/evaporation living polymerization kinetics revisited

    NASA Astrophysics Data System (ADS)

    Semenov, A. N.; Nyrkova, I. A.

    2011-03-01

    End-growth/evaporation kinetics in living polymer systems with "association-ready" free unimers (no initiator) is considered theoretically. The study is focused on the systems with long chains (typical aggregation number N ≫ 1) at long times. A closed system of continuous equations is derived and is applied to study the kinetics of the chain length distribution (CLD) following a jump of a parameter (T-jump) inducing a change of the equilibrium mean chain length from N0 to N. The continuous approach is asymptotically exact for t ≫ t1, where t1 is the dimer dissociation time. It yields a number of essentially new analytical results concerning the CLD kinetics in some representative regimes. In particular, we obtained the asymptotically exact CLD response (for N ≫ 1) to a weak T-jump (ɛ = N0/N - 1 ≪ 1). For arbitrary T-jumps we found that the longest relaxation time tmax = 1/γ is always quadratic in N (γ is the relaxation rate of the slowest normal mode). More precisely tmax ∝4N2 for N0 < 2N and tmax ∝NN0/(1 - N/N0) for N0 > 2N. The mean chain length Nn is shown to change significantly during the intermediate slow relaxation stage t1 ≪ t ≪ tmax . We predict that N_n(t)-N_n(0)∝ √{t} in the intermediate regime for weak (or moderate) T-jumps. For a deep T-quench inducing strong increase of the equilibrium Nn (N ≫ N0 ≫ 1), the mean chain length follows a similar law, N_n(t)∝ √{t}, while an opposite T-jump (inducing chain shortening, N0 ≫ N ≫ 1) leads to a power-law decrease of Nn: Nn(t)∝t-1/3. It is also shown that a living polymer system gets strongly polydisperse in the latter regime, the maximum polydispersity index r = Nw/Nn being r* ≈ 0.77N0/N ≫ 1. The concentration of free unimers relaxes mainly during the fast process with the characteristic time tf ˜ t1N0/N2. A nonexponential CLD dominated by short chains develops as a result of the fast stage in the case of N0 = 1 and N ≫ 1. The obtained analytical results are supported

  20. The effect of inorganic and organic mercury on growth kinetics of Nitzschia accicularis W. Sm. and Tetraselmis suecica Butch.

    PubMed

    Mora, B; Fábregas, J

    1980-08-01

    Studies have been made on the toxicities of three inorganic (HgCl2, HgSO4, and NH2HgCl) and two organic (CH3HgCl and phenyl mercuric acetate (PMA)) mercury derivatives on planktonic algae (Nitzschia acicularis W. Sm. and Tetraselmis suecica Butch.) Growth kinetics and flourescence changes were used as criteria for assessing algal-metal responses. Methylmercury chloride was found to be the more toxic form, inhibiting growth of both species at levels of 0.025 ppm Hg. PMA inhibited Nitzschia at the same concentration. Inorganic forms prevent growth of the diatom at 0.15-0.20 ppm Hg. Addition of inorganic mercury at concentrations of 0.05 ppm Hg resulted in reduction of the lag phase, increase in exponential growth rate, or both. Increasing mercury concentrations caused a gradual increase in the lag phase in T. suecica and in N. acicularis only with mercuric sulphate. Populations recovered from this initial effect and started to grow. The effect of inoculum size on mercurial toxicity was tested. The higher concentrations of mercury that still permit growth restricted the chlorophyll fluorescence to the central cellular area and the cells appear slimmed. This effect is highest in concentrations that inhibit growth. PMID:6450629

  1. Callus Growth Kinetics of Physic Nut (Jatropha curcas L.) and Content of Fatty Acids from Crude Oil Obtained In Vitro.

    PubMed

    da Luz Costa, Jefferson; da Silva, André Luís Lopes; Bier, Mário César Jucoski; Brondani, Gilvano Ebling; Gollo, André Luiz; Letti, Luiz Alberto Junior; Erasmo, Eduardo Andrea Lemus; Soccol, Carlos Ricardo

    2015-06-01

    The callus growth kinetics allows identifying the appropriate moment for callus pealing and monitoring the accumulation of primary and secondary metabolites. The physic nut (Jatropha curcas L.) is a plant species used for biofuel production due to its high oil content; however, this plant presents a great amount of bioactive compounds which can be useful for industry. The aim of this research was to establish a calli growth curve and to evaluate the fatty acid profile of crude oil extracted from callus. The callus growth kinetics presented a sigmoid standard curve with six distinct phases: lag, exponential, linear, deceleration, stationary, and decline. Total soluble sugars were higher at the inoculation day. Reducing sugars were higher at the inoculation day and at the 80th day. The highest percentage of ethereal extract (oil content) was obtained at the 120th day of culture, reaching 18 % of crude oil from the callus. The calli produced medium-chain and long-chain fatty acids (from 10 to 18 carbon atoms). The palmitic acid was the fatty acid with the highest proportion in oil (55.4 %). The lipid profile obtained in callus oil was different from the seed oil profile. PMID:25917545

  2. Influence of deformation on dolomite rim growth kinetics

    NASA Astrophysics Data System (ADS)

    Helpa, Vanessa; Rybacki, Erik; Grafulha Morales, Luiz Fernando; Dresen, Georg

    2015-04-01

    Using a gas-deformation apparatus stacks of oriented calcite (CaCO3) and magnesite (MgCO3) single crystals were deformed at T = 750° C and P = 400 MPa to examine the influence of stress and strain on magnesio-calcite and dolomite (CaMg[CO3]2) growth kinetics. Triaxial compression and torsion tests performed at constant stresses between 7 and 38 MPa and test durations between 4 and 171 hours resulted in bulk strains of 0.03-0.2 and maximum shear strains of 0.8-5.6, respectively. The reaction rims consist of fine-grained (2-7 μm) dolomite with palisade-shaped grains growing into magnesite reactants and equiaxed granular dolomite grains next to calcite. In between dolomite and pure calcite, magnesio-calcite grains evolved with an average grain size of 20-40 μm. Grain boundaries tend to be straighter at high bulk strains and equilibrium angles at grain triple junctions are common within the magnesio-calcite layer. Transmission electron microscopy shows almost dislocation free palisades and increasing dislocation density within granular dolomite towards the magnesio-calcite boundary. Within magnesio-calcite grains, dislocations are concentrated at grain boundaries. Variation of time at fixed stress (˜17 MPa) yields a parabolic time dependence of dolomite rim width, indicating diffusion-controlled growth, similar to isostatic rim growth behavior. In contrast, the magnesio-calcite layer growth is enhanced compared to isostatic conditions. Triaxial compression at given time shows no significant change of dolomite rim thickness (11±2 μm) and width of magnesio-calcite layers (33±5 μm) with increasing stress. In torsion experiments, reaction layer thickness and grain size decrease from the center (low stress/strain) to the edge (high strain/stress) of samples. Chemical analysis shows nearly stoichiometric composition of dolomite palisades, but enhanced Ca content within granular grains, indicating local disequilibrium with magnesio-calcite, in particular for twisted

  3. Kinetics of Ni2Si growth from pure Ni and Ni(V) films on (111) and (100) Si

    NASA Astrophysics Data System (ADS)

    Harith, M. A.; Zhang, J. P.; Campisano, S. U.; Klaar, H.-J.

    1987-01-01

    The kinetics of Ni2Si growth from pure Ni and from Ni0.93V0.07 films on (111) and (100) silicon has been studied by the combination of He+ backscattering, x-ray diffraction, Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) techniques. The activation energies are 1.5 and 1.0 eV for pure Ni and Ni(V) films, respectively while the pre-exponential factors in Ni(V) are 4 5 orders of magnitude smaller than in the pure Ni case. The variations in the measured rates are related to the different grain size of the growing suicide layers. The vanadium is rejected from the silicide layer and piles up at the metalsilicide interface.

  4. Menaquinone Synthesis is Critical for Maintaining Mycobacterial Viability During Exponential Growth and Recovery from Non-Replicating Persistence

    PubMed Central

    Dhiman, Rakesh K.; Mahapatra, Sebabrata; Slayden, Richard A.; Boyne, Melissa E.; Lenaerts, Anne; Hinshaw, Jerald C.; Angala, Shiva K.; Chatterjee, Delphi; Biswas, Kallolmay; Narayanasamy, Prabagaran; Kurosu, Michio; Crick, Dean C.

    2016-01-01

    Summary Understanding the basis of bacterial persistence in latent infections is critical for eradication of tuberculosis. Analysis of Mycobacterium tuberculosis mRNA expression in an in vitro model of non-replicating persistence indicated that the bacilli require electron transport chain components and ATP synthesis for survival. Additionally, low μM concentrations of aminoalkoxydiphenylmethane derivatives inhibited both the aerobic growth and survival of non-replicating, persistent M. tuberculosis. Metabolic labeling studies and quantitation of cellular menaquinone levels suggested that menaquinone synthesis, and consequently electron transport, is the target of the aminoalkoxydiphenylmethane derivatives. This hypothesis is strongly supported by the observations that treatment with these compounds inhibits oxygen consumption and that supplementation of growth medium with exogenous menaquinone rescued both growth and oxygen consumption of treated bacilli. In vitro assays indicate that the aminoalkoxydiphenylmethane derivatives specifically inhibit MenA, an enzyme involved in the synthesis of menaquinone. Thus, the results provide insight into the physiology of mycobacterial persistence and a basis for the development of novel drugs that enhance eradication of persistent bacilli and latent tuberculosis. PMID:19220750

  5. Kinetics and mechanisms of creep crack growth in a creep-resisting steel

    SciTech Connect

    Vainshtok, V.A.; Baumshtein, M.V.; Makovetskaya, I.A.; Man'ko, V.D.

    1986-02-01

    This paper discusses the nature of kinetic diagrams of growth of fatigue cracks in the temperature range typical of operation of important components of power equipment and examines the proportion of the incubation period of crack growth in the total life. The relationship of the kinetic diagrams of crack growth with the fracture mechanisms are examined and the effect of running life on creep crack propagation is reviewed.

  6. Exploring growth kinetics of carbon nanotube arrays by in situ optical diagnostics and modeling

    SciTech Connect

    Puretzky, Alexander A; Geohegan, David B; Pannala, Sreekanth; Rouleau, Christopher

    2014-01-01

    Simple kinetic models of carbon nanotube growth have been able to successfully link together many experimental parameters involved in the growth of carbon nanotubes for practical applications including the prediction of growth rates, terminal lengths, number of walls, activation energies, and their dependences on the growth environment. The implications of recent experiments utilizing in situ monitoring of carbon nanotube growth on our past kinetic model are first reviewed. Then, sub-second pulsed feedstock gas introduction is discussed to explore the nucleation and initial growth of carbon nanotubes in the context of the kinetic model. Moreover, kinetic effects in "pulsed CVD" - using repeated pulsed gas introduction to stop and restart nanotube growth - are explored to understand renucleation, the origin of alignment in nanotube arrays, and incremental growth. Time-resolved reflectivity of the surface is used to remotely understand the kinetics of nucleation and the coordinated growth of arrays. This approach demonstrates that continuous vertically aligned single wall carbon nanotubes can be grown incrementally by pulsed CVD, and that the first exposure of fresh catalyst to feedstock gas is critical to nanotubes site density required for coordinated growth. Aligned nanotube arrays (as short as 60 nm) are shown to nucleate and grow within single, sub-second gas pulses. The multiple-pulse growth experiments (> 100 pulses) show that a high fraction of nanotubes renucleate on subsequent gas pulses.

  7. Kinetics of gypsum formation and growth during the dissolution of colemanite in sulfuric acid

    NASA Astrophysics Data System (ADS)

    Çetin, E.; Eroğlu, İ.; Özkar, S.

    2001-11-01

    One of the most important boron minerals, colemanite, is dissolved in aqueous sulfuric acid to produce boric acid whereby gypsum is formed as byproduct. Filtration of gypsum has an important role in boric acid production because gypsum affects the efficiency, purity and crystallization of boric acid. The formation and growth kinetics of gypsum during the dissolution of colemanite in aqueous sulfuric acid were studied in a batch reactor by varying the temperature (60-90°C), stirring rate (150-400 rpm), and initial concentrations of the reactants. The initial CaO/H 2SO 4 molar ratio was varied between 0.21-0.85 by keeping the initial concentration of sulfate ion at [SO 42-] o=0.623 mol/l, and 0.85-3.41 by keeping the initial concentration of colemanite at [B 2O 3] o=0.777 mol/l. The crystallization of gypsum from the solution was followed by monitoring the calcium ion concentration in the solution as it is decreased by the formation of calcium sulfate precipitate. The calcium ion concentration in the liquid phase first undergoes a rapid exponential decay and then slowly approaches an asymptotic value of the saturation concentration at the respective temperature. The saturation concentration decreases with the increasing temperature from 5.2 mmol/l at 60°C to 3.1 mmol/l at 80°C, however, further increase in the temperature up to 90°C causes an increase in the saturation concentration to 5.1 mmol/l. The stirring rate was found to have no significant effect on dissolution in the range of 150-400 rpm. The minimum saturation concentration of the calcium ion was obtained at 80°C when the initial CaO/H 2SO 4 molar ratio is 0.85. The boric acid concentration in the solution decreases with the decreasing initial concentration of sulfuric acid. After the fast dissolution reaction of colemanite in aqueous sulfuric acid, the nucleation of the gypsum crystals first occurs from the supersaturated solution and then the crystals grow on these nuclei. The needle like crystals

  8. Free convection and surface kinetics in crystal growth from solution

    NASA Astrophysics Data System (ADS)

    Baird, James K.; Guo, Lihong

    1998-08-01

    As a crystal grows from solution, there is ordinarily a boundary layer depleted in solute, which forms at the crystal-solution interface. When the normal to the growing crystal surface is oriented in any direction other than parallel to gravity, the boundary layer is set into motion by the force of buoyancy. Using a similarity transformation and a boundary layer approximation, we have solved the Navier-Stokes equation and the equation for convective diffusion for a crystal in the form of a flat plate growing with normal perpendicular to gravity. Parameters in the theory include solute concentration, c0, and diffusion coefficient, D; solution shear viscosity, μ, mass density, ρ, and logarithmic density derivative with respect to concentration, α; crystal solubility, cs, height, h, and linear growth rate, kG; the specific rate, k (sticking coefficient), of the reaction which transfers molecules from the solution to the crystal and the kinetic order, n, of this reaction; and the acceleration due to gravity, g. We find these parameters to be related by the equation log[1-Sh/a (Sc) 1/4(Gr) 1/4φ s1/4]=(1/n) log[a(5/4) n(D/hkc 0n-1)(Sc)1/4(Gr) 1/4]+[(5/4-n)/n]log φs, where a=0.9, Sh=kGh/D, Sc=μ/ρD, Gr=gαh3ρ2/4μ2, and φs=(c0-cs)/c0. Given a knowledge of the solution physical properties, if Sh is measured as a function of φs and the results plotted in accord with the above equation, both n and k can be determined.

  9. A kinetic theory for nonanalog Monte Carlo particle transport algorithms: Exponential transform with angular biasing in planar-geometry anisotropically scattering media

    SciTech Connect

    Ueki, T.; Larsen, E.W.

    1998-09-01

    The authors show that Monte Carlo simulations of neutral particle transport in planargeometry anisotropically scattering media, using the exponential transform with angular biasing as a variance reduction device, are governed by a new Boltzman Monte Carlo (BMC) equation, which includes particle weight as an extra independent variable. The weight moments of the solution of the BMC equation determine the moments of the score and the mean number of collisions per history in the nonanalog Monte Carlo simulations. Therefore, the solution of the BMC equation predicts the variance of the score and the figure of merit in the simulation. Also, by (1) using an angular biasing function that is closely related to the ``asymptotic`` solution of the linear Boltzman equation and (2) requiring isotropic weight changes as collisions, they derive a new angular biasing scheme. Using the BMC equation, they propose a universal ``safe`` upper limit of the transform parameter, valid for any type of exponential transform. In numerical calculations, they demonstrate that the behavior of the Monte Carlo simulations and the performance predicted by deterministically solving the BMC equation agree well, and that the new angular biasing scheme is always advantageous.

  10. Kinetics of Austenite Grain Growth During Heating and Its Influence on Hot Deformation of LZ50 Steel

    NASA Astrophysics Data System (ADS)

    Du, Shiwen; Li, Yongtang; Zheng, Yi

    2016-07-01

    Grain growth behaviors of LZ50 have been systematically investigated for various temperatures and holding times. Quantitative evaluations of the grain growth kinetics over a wide range of temperature (950-1200 °C) and holding time (10-180 min) have been performed. With the holding time kept constant, the average austenite grain size has an exponential relationship with the heating temperature, while with the heating temperature kept constant, the relationship between the austenite average grain size and holding time is a parabolic curve approximately. The holding time dependence of average austenite grain size obeys the Beck's equation. As the heating temperature increases, the time exponent for grain growth n increases from 0.21 to 0.39. On the basis of previous models and experimental results, taking the initial grain size into account, the mathematical model for austenite grain growth of LZ50 during isothermal heating and non-isothermal heating is proposed. The effects of initial austenite grain size on hot deformation behavior of LZ50 are analyzed through true stress-strain curves under different deformation conditions. Initial grain size has a slight effect on peak stress.

  11. Phase-field Model for Interstitial Loop Growth Kinetics and Thermodynamic and Kinetic Models of Irradiated Fe-Cr Alloys

    SciTech Connect

    Li, Yulan; Hu, Shenyang Y.; Sun, Xin; Khaleel, Mohammad A.

    2011-06-15

    Microstructure evolution kinetics in irradiated materials has strongly spatial correlation. For example, void and second phases prefer to nucleate and grow at pre-existing defects such as dislocations, grain boundaries, and cracks. Inhomogeneous microstructure evolution results in inhomogeneity of microstructure and thermo-mechanical properties. Therefore, the simulation capability for predicting three dimensional (3-D) microstructure evolution kinetics and its subsequent impact on material properties and performance is crucial for scientific design of advanced nuclear materials and optimal operation conditions in order to reduce uncertainty in operational and safety margins. Very recently the meso-scale phase-field (PF) method has been used to predict gas bubble evolution, void swelling, void lattice formation and void migration in irradiated materials,. Although most results of phase-field simulations are qualitative due to the lake of accurate thermodynamic and kinetic properties of defects, possible missing of important kinetic properties and processes, and the capability of current codes and computers for large time and length scale modeling, the simulations demonstrate that PF method is a promising simulation tool for predicting 3-D heterogeneous microstructure and property evolution, and providing microstructure evolution kinetics for higher scale level simulations of microstructure and property evolution such as mean field methods. This report consists of two parts. In part I, we will present a new phase-field model for predicting interstitial loop growth kinetics in irradiated materials. The effect of defect (vacancy/interstitial) generation, diffusion and recombination, sink strength, long-range elastic interaction, inhomogeneous and anisotropic mobility on microstructure evolution kinetics is taken into account in the model. The model is used to study the effect of elastic interaction on interstitial loop growth kinetics, the interstitial flux, and sink

  12. Interactive effects of temperature, pH, and water activity on the growth kinetics of Shiga toxin-producing Escherichia coli O104:H4 3.

    PubMed

    Juneja, Vijay K; Mukhopadhyay, Sudarsan; Ukuku, Dike; Hwang, Cheng-An; Wu, Vivian C H; Thippareddi, Harshavardhan

    2014-05-01

    The risk of non-O157 Shiga toxin-producing Escherichia coli strains has become a growing public health concern. Several studies characterized the behavior of E. coli O157:H7; however, no reports on the influence of multiple factors on E. coli O104:H4 are available. This study examined the effects and interactions of temperature (7 to 46°C), pH (4.5 to 8.5), and water activity (aw ; 0.95 to 0.99) on the growth kinetics of E. coli O104:H4 and developed predictive models to estimate its growth potential in foods. Growth kinetics studies for each of the 23 variable combinations from a central composite design were performed. Growth data were used to obtain the lag phase duration (LPD), exponential growth rate, generation time, and maximum population density (MPD). These growth parameters as a function of temperature, pH, and aw as controlling factors were analyzed to generate second-order response surface models. The results indicate that the observed MPD was dependent on the pH, aw, and temperature of the growth medium. Increasing temperature resulted in a concomitant decrease in LPD. Regression analysis suggests that temperature, pH, and aw significantly affect the LPD, exponential growth rate, generation time, and MPD of E. coli O104:H4. A comparison between the observed values and those of E. coli O157:H7 predictions obtained by using the U. S. Department of Agriculture Pathogen Modeling Program indicated that E. coli O104:H4 grows faster than E. coli O157:H7. The developed models were validated with alfalfa and broccoli sprouts. These models will provide risk assessors and food safety managers a rapid means of estimating the likelihood that the pathogen, if present, would grow in response to the interaction of the three variables assessed. PMID:25198132

  13. Non-exponential relaxation, fictive temperatures, and dispersive kinetics in the liquid-glass-liquid transition range of acetaminophen, sulfathiazole, and their mixtures.

    PubMed

    Aji, D P B; Khouri, J; Johari, G P

    2014-11-01

    To investigate the effects of added molecular heterogeneity on the hysteretic features of liquid-glass-liquid transition, we studied acetaminophen, sulfathiazole, and three of their mixtures by calorimetry, and determined the T(g) and the fictive temperature, T(f), from changes in the enthalpy and entropy on the cooling and heating paths, as well as the non-exponential parameter, β(cal). We find that, (i) T(f) for cooling is within 1-3 K of T(f) for heating and both are close to T(g), (ii) the closed loop entropy change in the liquid-glass-liquid range is negligibly small, (iii) T(g) and T(f) increase on increasing sulfathiazole in the mixture, (iv) β(cal) first slightly increases when the second component is added and then decreases, and (v) ageing causes deviations from a non-exponential, nonlinear behavior of the glass. In terms of fluctuations in a potential energy landscape, adding a solute heterogeneity would shift the state point to another part of the landscape with a different distribution of barrier heights and a different number of minima accessible to the state point. Part of the change in β(cal) is attributed to hydrogen-bond formation between the two components. Ageing changes the relaxation times distribution, more at short relaxation times than at long relaxation times, and multiplicity of relaxation modes implied by β(cal) < 1 indicates that each mode contributing to the enthalpy has its own T(g) or T(f). β(cal) differs from β(age) determined from isothermal ageing, and the distribution parameter of α-relaxation times would differ from both β(cal) and β(age). PMID:25381531

  14. Temperature dependence of protein solubility-determination, application to crystallization, and growth kinetics studies

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz

    1993-01-01

    A scintillation method was developed for determinations of the temperature dependence of the solubility, and of nucleation induction times of proteins, in 50-100 mu(l) volumes of solution. Solubility data for lysozyme and horse serum albumin were obtained for various combinations of pH and precipitant concentrations. These data and the nucleation induction information were used for dynamic crystallization control, that is, for the controlled separation of nucleation and growth stages. Individual lysozyme and horse serum albumin crystals were grown in 15-20 mu(l) solution volumes contained in x-ray capillaries. The morphology and kinetics of the growth and dissolution of lysozyme in aqueous solutions with 2.5 percent NaCl and at pH = 4.5 was studied in situ with a depth resolution of 300 A (4 unit cells) by high resolution optical microscopy and digital image processing. The bulk super- or under saturation, sigma, of the solution inside a closed growth cell was controlled by temperature. The growth habit was bound by (110) and (101) faces that grew through layer spreading, although with different growth rate dependencies on supersaturation/temperature. At sigma less than 10 (obtained at higher temperatures) growth was purely kinetic ally controlled, with impurity effects (macrostep formation and kinetic hindrance) becoming significant for sigma less than 2. At sigma greater than 10 (lower temperatures), anisotropies in the interfacial kinetics were more pronounced, with interfacial kinetics and bulk transport becoming equally important to the growth morphology. Growth rates were growth history dependent. The formation of striations (layers of irregularly incorporated solution) was unambiguously correlated with growth temperature variations. Etching exposed dislocations and various high-index faces whose growth morphologies were studied during return to the steady state growth form. Growth steps were observed to originate from two-dimensional nuclei or from outcrops

  15. Correlated responses in body composition to divergent selection for exponential growth rate to 14 or 42 days of age in chickens.

    PubMed

    Sizemore, F G; Barbato, G F

    2002-07-01

    Chicks divergently selected for 14-d (14H and 14L) or 42-d (42H and 42L) exponential growth rate (EGR) over five generations were used to determine correlated responses between growth at different ages and body composition. Regression coefficient estimates across five generations of selection were not significant for any line at either age for percentage total body water or protein. Genetic correlations between EGR from hatching to 14 d of age (EGR14) and 42-d percentage carcass fat were -0.18, -0.57, 0.63, and -0.79 among the 14H, 14L, 42H, and 42L lines, respectively. Genetic correlations between EGR from hatching to 42 d of age (EGR42) and 42-d percentage carcass fat were 0.09, -0.67,0.50, and -0.75 among the 14H, 14L, 42H, and 42L lines, respectively. During the short-term selection experiment, selection for fast EGR14 or EGR42 increased fat at the age of selection. However, selection for fast EGR42 increased body weight and percentage fat at 42 d of age (DOA), whereas selection for fast EGR14 increased body weight but not fat at 42 DOA. Therefore, it is possible to simultaneously select for high body weight at, or near, the inflection point of the growth curve without increasing fat deposition or obesity by taking advantage of the lack of a genetic correlation between EGR14 and body fat percentage at later ages. PMID:12162352

  16. Computer Simulations of Interstitial Loop Growth Kinetics in irradiated bcc Fe

    SciTech Connect

    Li, Yulan; Hu, Shenyang Y.; Henager, Charles H.; Deng, Huiqiu; Gao, Fei; Sun, Xin; Khaleel, Mohammad A.

    2012-08-01

    The growth kinetics of (001) [001] interstitial loops in bcc Fe is studied by phase-field modeling. The effect of defect (vacancy/interstitial) concentration, generation, recombination, sink strength, and elastic interaction on the growth kinetics of interstitial loops is systematically simulated. Results show that the elastic interaction between the defects and interstitial loops speeds up the growth kinetics and affects the morphology of the interstitial loops. Linear growth rate, i.e., the loop average radius is linear to time, under both aging and irradiation are predicted, which is in agreement with experimental observation. The results also show that the interstitial loop growth rate, which is directly related to the sink strength of the interstitial loop for interstitials, increases linearly with the initial interstitial concentration during aging while changing logarithmically with the interstitial generation rate under irradiation.

  17. Recognizing Exponential Growth. Classroom Notes

    ERIC Educational Resources Information Center

    Dobbs, David E.

    2004-01-01

    Two heuristic and three rigorous arguments are given for the fact that functions of the form Ce[kx], with C an arbitrary constant, are the only solutions of the equation dy/dx=ky where k is constant. Various of the proofs in this self-contained note could find classroom use in a first-year calculus course, an introductory course on differential…

  18. Exponential Growth through Pattern Exploration

    ERIC Educational Resources Information Center

    Brown, Betty

    2005-01-01

    Participants at the Summer Institute Pattern Exploration: Integration Math and Science in the Middle Grades used and developed a method treat arithmetic, algebra and geometry as one entity. The use of iterative geometric constructions is seen to reinforce the concepts of exponents, ratios and algebraic expressions for the nth stage of the…

  19. Kinetics of nickel silicide growth in silicon nanowires: From linear to square root growth

    NASA Astrophysics Data System (ADS)

    Yaish, Y. E.; Katsman, A.; Cohen, G. M.; Beregovsky, M.

    2011-05-01

    The common practice for nickel silicide formation in silicon nanowires (SiNWs) relies on axial growth of silicide along the wire that is initiated from nickel reservoirs at the source and drain contacts. In the present work the silicide intrusions were studied for various parameters including wire diameter (25-50 nm), annealing time (15-120 s), annealing temperature (300-440∘C), and the quality of the initial Ni/Si interface. The silicide formation was investigated by high-resolution scanning electron microscopy, high-resolution transmission electron microscopy (TEM), and atomic force microscopy. The main part of the intrusion formed at 420∘C consists of monosilicide NiSi, as was confirmed by energy dispersive spectroscopy STEM, selected area diffraction TEM, and electrical resistance measurements of fully silicided SiNWs. The kinetics of nickel silicide axial growth in the SiNWs was analyzed in the framework of a diffusion model through constrictions. The model calculates the time dependence of the intrusion length, L, and predicts crossover from linear to square root time dependency for different wire parameters, as confirmed by the experimental data.

  20. The Escherichia coli FIS protein is not required for the activation of tyrT transcription on entry into exponential growth.

    PubMed Central

    Lazarus, L R; Travers, A A

    1993-01-01

    The Escherichia coli DNA bending protein factor for inversion stimulation (FIS), is neither necessary nor responsible for the stimulation of transcription from the wild type promoter for the tyrT operon (encoding a species of tyrosine tRNA) that occurs upon resumption of exponential growth. This conclusion is unexpected given that the regulatory element required for optimal transcription of tyrT contains three binding sites for FIS protein. In addition, it is in apparent conflict with reports from other laboratories which have described FIS-dependent activation of the stable RNA promoters rrnB P1 and thrU(tufB) in vivo. However, tyrT transcription is stimulated in a FIS-dependent manner both in vivo and in vitro when promoter function is impaired by mutation of the promoter itself or by the addition of the polymerase effector guanosine 5'-diphosphate 3'-diphosphate. These conditions, which expose a requirement for activation of stable RNA synthesis by FIS, suggest that FIS serves an adaptive role permitting high levels of stable RNA transcription on nutritional shift-up when RNA polymerase levels are depleted. In principle such a mechanism could confer a significant selective advantage thus accounting for the conservation of FIS binding sites in the regulatory regions of stable RNA promoters. Images PMID:7685276

  1. Modeling of kinetically limited growth rate for solution-synthesized germanium nanocrystals

    NASA Astrophysics Data System (ADS)

    Shoop, Nicholas; Tribby, Louis J.; Han, Sang M.

    2015-08-01

    Solution synthesis is a common method for preparing semiconductor nanocrystals (NCs). For such solution synthesis, many investigations have considered diffusion-limited growth, in which the diffusion of reactants through the boundary layer (BL) limits the NC growth rate. These studies often model the growth rate with a diffusion BL thickness much larger than the NC size and with unphysically low diffusion constants on the order of 10-12 cm2 s-1. In this work, we have examined the growth of Ge NCs synthesized by injecting Ge amide precursors into a solution of 1-octadecene, oleylamine, and hexadecylamine. We have previously established this low-temperature, low-pressure synthesis route. The resulting Ge growth rate compares well with our model, in which we consider both BL diffusion and surface kinetics of Ge precursors and organic ligand adsorbates. Our modeling results suggest that the NC growth is limited not by diffusion, but by the surface adsorption and desorption kinetics. The BL thickness in the stirred reaction vessel is calculated to be on the same order of magnitude as the crystal radius; therefore, the surface kinetics cannot be ignored. Furthermore, the synthesis temperature is near 300 °C, where the Ge monomer diffusion coefficient within the growth solution is substantially increased and estimated to be on the order of 10-5 cm2 s-1. These considerations agree well with our experimentally measured growth rate and strongly suggest that the NC size evolution is controlled primarily by the surface kinetics.

  2. COMPARATIVE KINETIC STUDIES OF NITRATE-LIMITED GROWTH AND NITRATE UPTAKE IN PHYTOPLANKTON IN CONTINUOUS CULTURE

    EPA Science Inventory

    A comparative kinetic study of nitrate-limited growth and nitrate uptake was carried out in chemostat cultures of Ankistrodesmus falcatus, Asterionella formosa, Fragilaria crotonensis. In each species growth rate (microgram) was related to total cell nitrogen or cell quota (q) by...

  3. Domain growth and ordering kinetics in dense quark matter

    SciTech Connect

    Singh, A.; Puri, S.; Mishra, H.

    2012-06-15

    The kinetics of chiral transitions in quark matter is studied in a two-flavor Nambu-Jona-Lasinio model. We focus on the phase-ordering dynamics subsequent to a temperature quench from the massless quark phase to the massive quark phase. We study the dynamics by considering a phenomenological model (Ginzburg-Landau free-energy functional). The morphology of the ordering system is characterized by the scaling of the order-parameter correlation function.

  4. Nanowire growth kinetics in aberration corrected environmental transmission electron microscopy.

    PubMed

    Chou, Yi-Chia; Panciera, Federico; Reuter, Mark C; Stach, Eric A; Ross, Frances M

    2016-04-14

    We visualize atomic level dynamics during Si nanowire growth using aberration corrected environmental transmission electron microscopy, and compare with lower pressure results from ultra-high vacuum microscopy. We discuss the importance of higher pressure observations for understanding growth mechanisms and describe protocols to minimize effects of the higher pressure background gas. PMID:27041654

  5. Giving Exponential Functions a Fair Shake

    ERIC Educational Resources Information Center

    Wanko, Jeffrey J.

    2005-01-01

    This article details an exploration of exponential decay and growth relationships using M&M's and dice. Students collect data for mathematical models and use graphing calculators to make sense of the general form of the exponential functions. (Contains 10 figures and 2 tables.)

  6. Kinetics of monolayer graphene growth by segregation on Pd(111)

    SciTech Connect

    Mok, H. S.; Murata, Y.; Kodambaka, S.; Ebnonnasir, A.; Ciobanu, C. V.; Nie, S.; McCarty, K. F.

    2014-03-10

    Using in situ low-energy electron microscopy and density functional theory calculations, we follow the growth of monolayer graphene on Pd(111) via surface segregation of bulk-dissolved carbon. Upon lowering the substrate temperature, nucleation of graphene begins on graphene-free Pd surface and continues to occur during graphene growth. Measurements of graphene growth rates and Pd surface work functions establish that this continued nucleation is due to increasing C adatom concentration on the Pd surface with time. We attribute this anomalous phenomenon to a large barrier for attachment of C adatoms to graphene coupled with a strong binding of the non-graphitic C to the Pd surface.

  7. Monoculture parameters successfully predict coculture growth kinetics of Bacteroides thetaiotaomicron and two Bifidobacterium strains.

    PubMed

    Van Wey, A S; Cookson, A L; Roy, N C; McNabb, W C; Soboleva, T K; Shorten, P R

    2014-11-17

    Microorganisms rarely live in isolation but are most often found in a consortium. This provides the potential for cross-feeding and nutrient competition among the microbial species, which make it challenging to predict the growth kinetics in coculture. In this paper we developed a mathematical model to describe substrate consumption and subsequent microbial growth and metabolite production for bacteria grown in monoculture. The model characterized substrate utilization kinetics of 18 Bifidobacterium strains. Some bifidobacterial strains demonstrated preferential degradation of oligofructose in that sugars with low degree of polymerization (DP) (DP≤3 or 4) were metabolized before sugars of higher DP, or vice versa. Thus, we expanded the model to describe the preferential degradation of oligofructose. In addition, we adapted the model to describe the competition between human colonic bacteria Bacteroides thetaiotaomicron LMG 11262 and Bifidobacterium longum LMG 11047 or Bifidobacterium breve Yakult for inulin as well as cross-feeding of breakdown products from the extracellular hydrolysis of inulin by B. thetaiotaomicron LMG 11262. We found that the coculture growth kinetics could be predicted based on the respective monoculture growth kinetics. Using growth kinetics from monoculture experiments to predict coculture dynamics will reduce the number of in vitro experiments required to parameterize multi-culture models. PMID:25282609

  8. Kinetic constants of abnormal grain growth in nanocrystalline nickel

    NASA Astrophysics Data System (ADS)

    Aleshin, A. N.

    2016-02-01

    The grain growth in nanocrystalline nickel with a purity of 99.5 at % during non-isothermal annealing was experimentally investigated using differential scanning calorimetry and transmission electron microscopy. Nanocrystalline nickel was prepared by electrodeposition and had an average grain size of approximately 20 nm. It was shown that, at a temperature corresponding to the calorimetric signal peak, abnormal grain growth occurs with the formation of a bimodal grain microstructure. Calorimeters signals were processed within the Johnson-Mehl-Avrami formalism. This made it possible to determine the exponent of the corresponding equation, the frequency factor, and the activation energy of the grain growth, which was found to be equal to the activation energy of the vacancy migration. The reasons for the abnormal grain growth in nanocrystalline nickel were discussed.

  9. Growth kinetics and H-shaped crystals of SAPO-40

    NASA Astrophysics Data System (ADS)

    Di Renzo, F.; Dumont, Nathalie; Trens, P.; Gabelica, Zelimir

    2003-11-01

    Crystal morphologies with well-defined macroscopic cavities are very rare occurrences. Tabular crystals of SAPO-40 with a symmetrical notch at each end have been obtained by selective inhibition of the growth of the large-pore faces. Crystal growth has continued on the small-pores (0 1 0) faces, circumvented the inhibited sphenoidal faces formed a protruding tab at the corners of the crystals.

  10. An exponential growth of computational phantom research in radiation protection, imaging, and radiotherapy: a review of the fifty-year history.

    PubMed

    Xu, X George

    2014-09-21

    Radiation dose calculation using models of the human anatomy has been a subject of great interest to radiation protection, medical imaging, and radiotherapy. However, early pioneers of this field did not foresee the exponential growth of research activity as observed today. This review article walks the reader through the history of the research and development in this field of study which started some 50 years ago. This review identifies a clear progression of computational phantom complexity which can be denoted by three distinct generations. The first generation of stylized phantoms, representing a grouping of less than dozen models, was initially developed in the 1960s at Oak Ridge National Laboratory to calculate internal doses from nuclear medicine procedures. Despite their anatomical simplicity, these computational phantoms were the best tools available at the time for internal/external dosimetry, image evaluation, and treatment dose evaluations. A second generation of a large number of voxelized phantoms arose rapidly in the late 1980s as a result of the increased availability of tomographic medical imaging and computers. Surprisingly, the last decade saw the emergence of the third generation of phantoms which are based on advanced geometries called boundary representation (BREP) in the form of Non-Uniform Rational B-Splines (NURBS) or polygonal meshes. This new class of phantoms now consists of over 287 models including those used for non-ionizing radiation applications. This review article aims to provide the reader with a general understanding of how the field of computational phantoms came about and the technical challenges it faced at different times. This goal is achieved by defining basic geometry modeling techniques and by analyzing selected phantoms in terms of geometrical features and dosimetric problems to be solved. The rich historical information is summarized in four tables that are aided by highlights in the text on how some of the most

  11. An exponential growth of computational phantom research in radiation protection, imaging, and radiotherapy: A review of the fifty-year history

    PubMed Central

    Xu, X. George

    2014-01-01

    Radiation dose calculation using models of the human anatomy has been a subject of great interest to radiation protection, medical imaging, and radiotherapy. However, early pioneers of this field did not foresee the exponential growth of research activity as observed today. This review article walks the reader through the history of the research and development in this field of study which started some 50 years ago. This review identifies a clear progression of computational phantom complexity which can be denoted by three distinct generations. The first generation of stylized phantoms, representing a grouping of less than dozen models, was initially developed in the 1960s at Oak Ridge National Laboratory to calculate internal doses from nuclear medicine procedures. Despite their anatomical simplicity, these computational phantoms were the best tools available at the time for internal/external dosimetry, image evaluation, and treatment dose evaluations. A second generation of a large number of voxelized phantoms arose rapidly in the late 1980s as a result of the increased availability of tomographic medical imaging and computers. Surprisingly, the last decade saw the emergence of the third generation of phantoms which are based on advanced geometries called boundary representation (BREP) in the form of Non-Uniform Rational B-Splines (NURBS) or polygonal meshes. This new class of phantoms now consists of over 287 models including those used for non-ionizing radiation applications. This review article aims to provide the reader with a general understanding of how the field of computational phantoms came about and the technical challenges it faced at different times. This goal is achieved by defining basic geometry modeling techniques and by analyzing selected phantoms in terms of geometrical features and dosimetric problems to be solved. The rich historical information is summarized in four tables that are aided by highlights in the text on how some of the most well

  12. Growth Kinetics and Mechanics of Hydrate Films by Interfacial Rheology.

    PubMed

    Leopércio, Bruna C; de Souza Mendes, Paulo R; Fuller, Gerald G

    2016-05-01

    A new approach to study and understand the kinetics and mechanical properties of hydrates by interfacial rheology is presented. This is made possible using a "double wall ring" interfacial rheology cell that has been designed to provide the necessary temperature control. Cyclopentane and water are used to form hydrates, and this model system forms these structures at ambient pressures. Different temperature and water/hydrocarbon contact protocols are explored. Of particular interest is the importance of first contacting the hydrocarbon against ice crystals in order to initiate hydrate formation. Indeed, this is found to be the case, even though the hydrates may be created at temperatures above the melting point of ice. Once hydrates completely populate the hydrocarbon/water interface, strain sweeps of the interfacial elastic and viscous moduli are conducted to interrogate the mechanical response and fragility of the hydrate films. The dependence on temperature, Tf, by the kinetics of formation and the mechanical properties is reported, and the cyclopentane hydrate dissociation temperature was found to be between 6 and 7 °C. The formation time (measured from the moment when cyclopentane first contacts ice crystals) as well as the elastic modulus and the yield strain increase as Tf increases. PMID:27076092

  13. In Bacillus subtilis LutR is part of the global complex regulatory network governing the adaptation to the transition from exponential growth to stationary phase.

    PubMed

    Irigül-Sönmez, Öykü; Köroğlu, Türkan E; Öztürk, Büşra; Kovács, Ákos T; Kuipers, Oscar P; Yazgan-Karataş, Ayten

    2014-02-01

    The lutR gene, encoding a product resembling a GntR-family transcriptional regulator, has previously been identified as a gene required for the production of the dipeptide antibiotic bacilysin in Bacillus subtilis. To understand the broader regulatory roles of LutR in B. subtilis, we studied the genome-wide effects of a lutR null mutation by combining transcriptional profiling studies using DNA microarrays, reverse transcription quantitative PCR, lacZ fusion analyses and gel mobility shift assays. We report that 65 transcriptional units corresponding to 23 mono-cistronic units and 42 operons show altered expression levels in lutR mutant cells, as compared with lutR(+) wild-type cells in early stationary phase. Among these, 11 single genes and 25 operons are likely to be under direct control of LutR. The products of these genes are involved in a variety of physiological processes associated with the onset of stationary phase in B. subtilis, including degradative enzyme production, antibiotic production and resistance, carbohydrate utilization and transport, nitrogen metabolism, phosphate uptake, fatty acid and phospholipid biosynthesis, protein synthesis and translocation, cell-wall metabolism, energy production, transfer of mobile genetic elements, induction of phage-related genes, sporulation, delay of sporulation and cannibalism, and biofilm formation. Furthermore, an electrophoretic mobility shift assay performed in the presence of both SinR and LutR revealed a close overlap between the LutR and SinR targets. Our data also revealed a significant overlap with the AbrB regulon. Together, these findings reveal that LutR is part of the global complex, interconnected regulatory systems governing adaptation of bacteria to the transition from exponential growth to stationary phase. PMID:24196425

  14. Kinetic-structural analysis of neuronal growth cone veil motility.

    PubMed

    Mongiu, Anne K; Weitzke, Elizabeth L; Chaga, Oleg Y; Borisy, Gary G

    2007-03-15

    Neuronal growth cone advance was investigated by correlative light and electron microscopy carried out on chick dorsal root ganglion cells. Advance was analyzed in terms of the two principal organelles responsible for protrusive motility in the growth cone - namely, veils and filopodia. Veils alternated between rapid phases of protrusion and retraction. Electron microscopy revealed characteristic structural differences between the phases. Our results provide a significant advance in three respects: first, protruding veils are comprised of a densely branched network of actin filaments that is lamellipodial in appearance and includes the Arp2/3 complex. On the basis of this structural and biomarker evidence, we infer that the dendritic nucleation and/or array-treadmilling mechanism of protrusive motility is conserved in veil protrusion of growth cones as in the motility of fibroblasts; second, retracting veils lack dendritic organization but contain a sparse network of long filaments; and third, growth cone filopodia have the capacity to nucleate dendritic networks along their length, a property consistent with veil formation seen at the light microscopic level but not previously understood in supramolecular terms. These elements of veil and filopodial organization, when taken together, provide a conceptual framework for understanding the structural basis of growth cone advance. PMID:17327278

  15. Kinetic Monte Carlo Simulation of Epitaxial Thin Film Growth: Formation of Submonolayer Islands and Multilayer Mounds

    SciTech Connect

    Evans, J. W.; Thiel, P. A.; Li, Maozhi

    2007-06-14

    We consider homoepitaxy (or low-misfit heteroepitaxy) via vapor deposition or MBE under UHV conditions. Thin film growth is initiated by nucleation and growth of 2D islands in the submonolayer regime. For atoms subsequently deposited on top of islands, a step edge barrier often inhibits downward transport and produces kinetic roughening during multilayer growth. Such unstable growth is characterized by the formation of 3D mounds (multilayer stacks of 2D islands). Kinetic Monte Carlo (KMC) simulation of suitable atomistic lattice-gas models can address fundamental or general issues related to both submonolayer and multilayer film evolution, and can also provide a predictive tool for morphological evolution in specific systems. Examples of the successes of KMC modeling are provided for metal homoepitaxial film growth, specifically for contrasting behavior in the classic Ag/Ag(100) and Ag/Ag(111) systems.

  16. Natural History, Growth Kinetics and Outcomes of Untreated Clinically Localized Renal Tumors Under Active Surveillance

    PubMed Central

    Crispen, Paul L.; Viterbo, Rosalia; Boorjian, Stephen A.; Greenberg, Richard E.; Chen, David Y.T.; Uzzo, Robert G.

    2010-01-01

    Background The growth kinetics of untreated solid organ malignancies are not defined. Radiographic active surveillance (AS) of renal tumors in patient unfit or unwilling to undergo intervention provides an opportunity to quantitate the natural history of untreated localized tumors. Here we report the radiographic growth kinetics of renal neoplasms during a period of surveillance. Methods We identified patients with enhancing renal masses who were radiographically observed for at least 12 months. Clinical and pathological records were reviewed to determine tumor growth kinetics and clinical outcomes. Tumor growth kinetics were expressed in terms of absolute and relative linear and volumetric growth. Results We identified 172 renal tumors in 154 patients under AS. Median tumor diameter and volume on presentation was 2.0 cm (mean 2.5, range 0.4 - 12.0) and 4.18 cm3 (mean 20.0, range 0.0033 – 904). Median duration of follow-up was 24 months (mean 31, range 12 – 156). A significant association between presenting tumor size and proportional growth was noted, with smaller tumors growing faster than larger tumors. 39% (68/173) of tumors underwent delayed intervention and 84% (57/68) were pathologically malignant. Progression to metastatic disease was noted in 1.3% (2/154) of patients. Conclusions We demonstrate the association between a tumor’s volume and subsequent growth with smaller tumors exhibiting significantly faster volumetric growth than larger tumors, consistent with Gompertzian kinetics. Surveillance of localized renal tumors is associated with a low rate of disease progression in the intermediate term and suggests potential over-treatment biases in select patients. PMID:19402168

  17. Graphene CVD growth on copper and nickel: role of hydrogen in kinetics and structure.

    PubMed

    Losurdo, Maria; Giangregorio, Maria Michela; Capezzuto, Pio; Bruno, Giovanni

    2011-12-14

    Understanding the chemical vapor deposition (CVD) kinetics of graphene growth is important for advancing graphene processing and achieving better control of graphene thickness and properties. In the perspective of improving large area graphene quality, we have investigated in real-time the CVD kinetics using CH(4)-H(2) precursors on both polycrystalline copper and nickel. We highlighted the role of hydrogen in differentiating the growth kinetics and thickness of graphene on copper and nickel. Specifically, the growth kinetics and mechanism is framed in the competitive dissociative chemisorption of H(2) and dehydrogenating chemisorption of CH(4), and in the competition of the in-diffusion of carbon and hydrogen, being hydrogen in-diffusion faster in copper than nickel, while carbon diffusion is faster in nickel than copper. It is shown that hydrogen acts as an inhibitor for the CH(4) dehydrogenation on copper, contributing to suppress deposition onto the copper substrate, and degrades quality of graphene. Additionally, the evidence of the role of hydrogen in forming C-H out of plane defects in CVD graphene on Cu is also provided. Conversely, resurfacing recombination of hydrogen aids CH(4) decomposition in the case of Ni. Understanding better and providing other elements to the kinetics of graphene growth is helpful to define the optimal CH(4)/H(2) ratio, which ultimately can contribute to improve graphene layer thickness uniformity even on polycrystalline substrates. PMID:22006173

  18. Role of plasma activation in the kinetics of CNT growth in PECVD process

    NASA Astrophysics Data System (ADS)

    Lebedeva, Irina; Gavrikov, Alexey; Baranov, Alexey; Belov, Maxim; Knizhnik, Andrey; Potapkin, Boris; Sommerer, Timothy

    2009-10-01

    The work presents kinetic modeling of the effect of acceleration for the growth kinetics of carbon nanotubes by hydrocarbon gas mixture modification with plasma discharge. The plasma activation creates active species in hydrocarbon gas mixture, which can easily adsorb and dissociate on the catalyst surface. So plasma treatment of the gas mixture in the CVD process allows to increase the carbon supply rate by a few orders of magnitude compared to that in thermal CVD process. On the other hand, plasma can also provide etching of carbon species from the catalyst surface. To correctly reproduce both of these effects of plasma, the kinetic model of growth of carbon nanotubes is developed based on first-principles analysis of heterogeneous processes on the catalyst surface and detailed kinetics of gas phase chemistry. The model is used to compare the growth rates of carbon nanotubes in thermal and plasma-enhanced CVD processes and to determine critical gas pressures, at which CNT growth kinetics switches from the adsorption limitation to the limitation by reaction and diffusion on the catalyst.

  19. Crystallization of pumpkin seed globulin: growth and dissolution kinetics

    NASA Astrophysics Data System (ADS)

    Malkin, Alexander J.; McPherson, Alexander

    1993-10-01

    Quasi-elastic light scattering was used to investigate the nucleation and crystallization of pumpkin ( Cucurbita) seed globulin. The diameter of the pumpkin globulin monomer was measured to be ≈ 5-6 nm. The supersaturation dependence of critical nucleus size was obtained, and this allowed an estimate of the interfacial free energy to be α ≈ 6.1 x 10 -2 erg/cm 2. The crystallization and dissolution kinetics were investigated for 4.9-16 mg/ml protein solutions containing 1-7% NaCl. The solubility data as a function of precipitant concentration and temperature were obtained and these will be utilized for optimization of the crystallization conditions for the pumpkin globulin.

  20. Self-consistent ion-by-ion growth model for kinetic isotopic fractionation during calcite precipitation

    NASA Astrophysics Data System (ADS)

    Nielsen, Laura C.; DePaolo, Donald J.; De Yoreo, James J.

    2012-06-01

    Microscopic mechanisms operating at the mineral-aqueous interface control rates of growth and dissolution, isotope fractionation and trace element partitioning during crystal growth. Despite the importance of characterizing surface kinetic controls on isotopic partitioning, no self-consistent microscopic theory has yet been presented which can simultaneously model both mineral growth rate and isotopic composition. Using a kinetic theory for AB or di-ionic crystal growth, we derive a model to predict precipitation rate and isotope fractionation as a function of growth solution oversaturation and solution stoichiometry and apply the theory to calcium isotope fractionation during calcite precipitation. Our model assimilates the current understanding of surface controlled isotope fractionation with kinetic theories of ion-by-ion mineral growth to predict isotopic partitioning during the growth of ionic crystals. This approach accounts for the effect of solution composition on microscopic mineral surface structure and composition, providing numerous testable hypotheses for growth of sparingly soluble AB crystals such as calcite, namely: Both oversaturation and solution stoichiometry control growth rate and partitioning of isotopes during precipitation; for growth driven primarily by step propagation, distinct expressions describe dislocation- and 2D nucleation-driven growth rates, while the expression for isotope fractionation is the same for both mechanisms; mineral precipitation occurring via the formation of an amorphous precursor will generate isotope effects that are not compatible with ion-by-ion growth theory and may therefore be excluded from comparison; and, the absolute kinetic limit of isotope fractionation may not be accessible at high oversaturation due to the formation of amorphous precursors. Using calcite as a model system, we derive expressions for growth rate and isotopic fractionation as a function of oversaturation and Ca:CO32- in solution

  1. An Exceptional Exponential Function

    ERIC Educational Resources Information Center

    Curgus, Branko

    2006-01-01

    We show that there is a link between a standard calculus problem of finding the best view of a painting and special tangent lines to the graphs of exponential functions. Surprisingly, the exponential function with the "best view" is not the one with the base "e." A similar link is established for families of functions obtained by composing…

  2. The kinetics of parasitic growth in GaAs MOVPE

    NASA Astrophysics Data System (ADS)

    Clayton, A. J.; Irvine, S. J. C.

    2007-03-01

    Gallium arsenide (GaAs) deposition was carried out in a horizontal quartz reactor tube with trimethylgallium (TMGa) and arsine (AsH 3) as precursors, using a hydrogen (H 2) carrier gas. Temperatures were in the range 400-500 °C, where surface reactions limit deposition rate. Nucleation time and deposition rate were monitored using laser interferometry, optimum reflectance was gained by aligning a quartz wafer to back reflect the incident beam. The 980 nm infrared laser beam was sufficiently long in wavelength to be able to penetrate the wall deposit. Results showing the effect of temperature and V/III ratio on the nucleation time and deposition rate are presented, where with temperature the nucleation delay was observed to reduce and the growth rate to increase. The nucleation delay is consistent with a thermally activated surface nucleation for the parasitic GaAs. A theoretical growth rate model, based on a restricted set of reaction steps was used to compare with the experimental growth rates. Without any free parameters, the growth rates from theoretical calculation and experiment agreed within a factor of two and showed the same trends with V/III ratio and temperature. The non-linearity of the theoretical growth rates on an Arrhenius plot indicates that there is more than one dominant reaction step over the temperature range investigated. The range of experimental activation energies, calculated from Arrhenius plots, was 17.56-23.59 kJ mol -1. A comparison of these activation energies and minimum deposition temperature with the literature indicates that the wall temperature measurement on an Aixtron reactor is over 100 °C higher than previously reported.

  3. Crystal Growth Kinetics and Viscous Behavior in Ge2Sb2Se5 Undercooled Melt.

    PubMed

    Barták, Jaroslav; Koštál, Petr; Podzemná, Veronika; Shánělová, Jana; Málek, Jiří

    2016-08-18

    Crystal growth, viscosity, and melting were studied in Ge2Sb2Se5 bulk samples. The crystals formed a compact layer on the surface of the sample and then continued to grow from the surface to the central part of the sample. The formed crystalline layer grew linearly with time, which suggests that the crystal growth is controlled by liquid-crystal interface kinetics. Combining the growth data with the measured viscosities and melting data, crystal growth could be described on the basis of standard crystal growth models. The screw dislocation growth model seems to be operative in describing the temperature dependence of the crystal growth rate in the studied material in a wide temperature range. A detailed discussion on the relation between the kinetic coefficient of crystal growth and viscosity (ukin ∝ η(-ξ)) is presented. The activation energy of crystal growth was found to be higher than the activation energy of crystallization obtained from differential scanning calorimetry, which covers the whole nucleation-growth process. This difference is considered and explained under the experimental conditions. PMID:27441575

  4. Modified Gompertz equation for electrotherapy murine tumor growth kinetics: predictions and new hypotheses

    PubMed Central

    2010-01-01

    Background Electrotherapy effectiveness at different doses has been demonstrated in preclinical and clinical studies; however, several aspects that occur in the tumor growth kinetics before and after treatment have not yet been revealed. Mathematical modeling is a useful instrument that can reveal some of these aspects. The aim of this paper is to describe the complete growth kinetics of unperturbed and perturbed tumors through use of the modified Gompertz equation in order to generate useful insight into the mechanisms that underpin this devastating disease. Methods The complete tumor growth kinetics for control and treated groups are obtained by interpolation and extrapolation methods with different time steps, using experimental data of fibrosarcoma Sa-37. In the modified Gompertz equation, a delay time is introduced to describe the tumor's natural history before treatment. Different graphical strategies are used in order to reveal new information in the complete kinetics of this tumor type. Results The first stage of complete tumor growth kinetics is highly non linear. The model, at this stage, shows different aspects that agree with those reported theoretically and experimentally. Tumor reversibility and the proportionality between regions before and after electrotherapy are demonstrated. In tumors that reach partial remission, two antagonistic post-treatment processes are induced, whereas in complete remission, two unknown antitumor mechanisms are induced. Conclusion The modified Gompertz equation is likely to lead to insights within cancer research. Such insights hold promise for increasing our understanding of tumors as self-organizing systems and, the possible existence of phase transitions in tumor growth kinetics, which, in turn, may have significant impacts both on cancer research and on clinical practice. PMID:21029411

  5. Model for computing kinetics of the graphene edge epitaxial growth on copper

    NASA Astrophysics Data System (ADS)

    Khenner, Mikhail

    2016-06-01

    A basic kinetic model that incorporates a coupled dynamics of the carbon atoms and dimers on a copper surface is used to compute growth of a single-layer graphene island. The speed of the island's edge advancement on Cu[111] and Cu[100] surfaces is computed as a function of the growth temperature and pressure. Spatially resolved concentration profiles of the atoms and dimers are determined, and the contributions provided by these species to the growth speed are discussed. Island growth under the conditions of a thermal cycling is studied.

  6. Integrated kinetic and probabilistic modeling of the growth potential of bacterial populations.

    PubMed

    George, S M; Métris, A; Baranyi, J

    2015-05-01

    When bacteria are exposed to osmotic stress, some cells recover and grow, while others die or are unculturable. This leads to a viable count growth curve where the cell number decreases before the onset of the exponential growth phase. From such curves, it is impossible to estimate what proportion of the initial cells generates the growth because it leads to an ill-conditioned numerical problem. Here, we applied a combination of experimental and statistical methods, based on optical density measurements, to infer both the probability of growth and the maximum specific growth rate of the culture. We quantified the growth potential of a bacterial population as a quantity composed from the probability of growth and the "suitability" of the growing subpopulation to the new environment. We found that, for all three laboratory media studied, the probability of growth decreased while the "work to be done" by the growing subpopulation (defined as the negative logarithm of their suitability parameter) increased with NaCl concentration. The results suggest that the effect of medium on the probability of growth could be described by a simple shift parameter, a differential NaCl concentration that can be accounted for by the change in the medium composition. Finally, we highlighted the need for further understanding of the effect of the osmoprotectant glycine betaine on metabolism. PMID:25747002

  7. How exponential are FREDs?

    NASA Astrophysics Data System (ADS)

    Schaefer, Bradley E.; Dyson, Samuel E.

    1996-08-01

    A common Gamma-Ray Burst-light curve shape is the ``FRED'' or ``fast-rise exponential-decay.'' But how exponential is the tail? Are they merely decaying with some smoothly decreasing decline rate, or is the functional form an exponential to within the uncertainties? If the shape really is an exponential, then it would be reasonable to assign some physically significant time scale to the burst. That is, there would have to be some specific mechanism that produces the characteristic decay profile. So if an exponential is found, then we will know that the decay light curve profile is governed by one mechanism (at least for simple FREDs) instead of by complex/multiple mechanisms. As such, a specific number amenable to theory can be derived for each FRED. We report on the fitting of exponentials (and two other shapes) to the tails of ten bright BATSE bursts. The BATSE trigger numbers are 105, 257, 451, 907, 1406, 1578, 1883, 1885, 1989, and 2193. Our technique was to perform a least square fit to the tail from some time after peak until the light curve approaches background. We find that most FREDs are not exponentials, although a few come close. But since the other candidate shapes come close just as often, we conclude that the FREDs are misnamed.

  8. The logistic growth of duckweed (Lemna minor) and kinetics of ammonium uptake.

    PubMed

    Zhang, Kun; Chen, You-Peng; Zhang, Ting-Ting; Zhao, Yun; Shen, Yu; Huang, Lei; Gao, Xu; Guo, Jin-Song

    2014-01-01

    Mathematical models have been developed to describe nitrogen uptake and duckweed growth experimentally to study the kinetics of ammonium uptake under various concentrations. The kinetics of duckweed ammonium uptake was investigated using the modified depletion method after plants were grown for two weeks at different ammonium concentrations (0.5-14 mg/L) in the culture medium. The maximum uptake rate and Michaelis-Menten constant for ammonium were estimated as 0.082 mg/(g fresh weight x h) and 1.877 mg/L, respectively. Duckweed growth was assessed when supplied at different total nitrogen (TN) concentrations (1-5 mg/L) in the culture medium. The results showed that the intrinsic growth rate was from 0.22 to 0.26 d(-1), and TN concentrations had no significant influence on the duckweed growth rate. PMID:24645435

  9. Nonlinear estimation of Monod growth kinetic parameters from a single substrate depletion curve.

    PubMed Central

    Robinson, J A; Tiedje, J M

    1983-01-01

    Monod growth kinetic parameters were estimated by fitting sigmoidal substrate depletion data to the integrated Monod equation, using nonlinear least-squares analysis. When the initial substrate concentration was in the mixed-order region, nonlinear estimation of simulated data sets containing known measurement errors provided accurate estimates of the mu max, Ks, and Y values used to create these data. Nonlinear regression analysis of sigmoidal substrate depletion data was also evaluated for H2-limited batch growth of Desulfovibrio sp. strain G11. The integrated Monod equation can be more convenient for the estimation of growth kinetic parameters, particularly for gaseous substrates, but it must be recognized that the estimates of mu max, Ks, and Y obtained may be influenced by the growth rate history of the inoculum. PMID:6870238

  10. Kinetic Roughening and Energetics of Tetragonal Lysozyme Crystal Growth: A Preliminary Atomic Force Microscopy Investigation

    NASA Technical Reports Server (NTRS)

    Gorti, Sridhar; Forsythe, Elizabeth L.; Pusey, Marc L.

    2004-01-01

    We examined particulars of crystal growth from measurements obtained at both microscopic and molecular levels. The crystal growth measurements performed at the microscopic level are well characterized by a model that balances the flux of macromolecules towards the crystal surface with the flux of the crystal surface. Numerical evaluation of model with measurements of crystal growth, in time, provided accurate estimates for the average growth velocities. Growth velocities thus obtained were also interpreted using well-established phenomenological theories. Moreover, we find that microscopic measurements of growth velocity measurements obtained as a function of temperature best characterizes changes in crystal growth modes, when present. We also examined the possibility of detecting a change in crystal growth modes at the molecular level using atomic force microscopy, AFM. From preliminary AFM measurements performed at various supersaturations, we find that magnitude of surface height fluctuations, h(x), increases with supersaturation. Further examination of surface height fluctuations using methods established for fluctuation spectroscopy also enabled the discovery of the existence of a characteristic length, c, which may possibly determine the mode of crystal growth. Although the results are preliminary, we establish the non- critical divergence of 5 and the root-mean-square (rms) magnitude of height-height fluctuations as the kinetic roughening transition temperatures are approached. Moreover, we also examine approximate models for interpreting the non-critical behavior of both 6 and rms magnitude of height-height fluctuations, as the solution supersaturation is increased towards the kinetic roughening supersaturation.

  11. Growth Kinetics of Intracellular RNA/Protein Droplets: Signature of a Liquid-Liquid Phase Transition?

    NASA Astrophysics Data System (ADS)

    Berry, Joel; Weber, Stephanie C.; Vaidya, Nilesh; Zhu, Lian; Haataja, Mikko; Brangwynne, Clifford P.

    2015-03-01

    Nonmembrane-bound organelles are functional, dynamic assemblies of RNA and/or protein that can self-assemble and disassemble within the cytoplasm or nucleoplasm. The possibility that underlying intracellular phase transitions may drive and mediate the morphological evolution of some membrane-less organelles has been supported by several recent studies. In this talk, results from a collaborative experimental-theoretical study of the growth and dissolution kinetics of nucleoli and extranucleolar droplets (ENDs) in C. elegans embryos will be presented. We have employed Flory-Huggins solution theory, reaction-diffusion kinetics, and quantitative statistical dynamic scaling analysis to characterize the specific growth mechanisms at work. Our findings indicate that both in vivo and in vitro droplet scaling and growth kinetics are consistent with those resulting from an equilibrium liquid-liquid phase transition mediated by passive nonequilibrium growth mechanisms - simultaneous Brownian coalescence and Ostwald ripening. This supports a view in which cells can employ phase transitions to drive structural organization, while utilizing active processes, such as local transcriptional activity, to fine tune the kinetics of these phase transitions in response to given conditions.

  12. Growth kinetics of Al–Fe intermetallic compounds during annealing treatment of friction stir lap welds

    SciTech Connect

    Movahedi, M.; Kokabi, A.H.; Seyed Reihani, S.M.; Najafi, H.; Farzadfar, S.A.; Cheng, W.J.; Wang, C.J.

    2014-04-01

    In this study, we explored the growth kinetics of the Al–Fe intermetallic (IM) layer at the joint interface of the St-12/Al-5083 friction stir lap welds during post-weld annealing treatment at 350, 400 and 450 °C for 30 to 180 min. Optical microscope (OM), field emission gun scanning electron microscope (FEG-SEM) and transmission electron microscope (TEM) were employed to investigate the structure of the weld zone. The thickness and composition of the IM layers were evaluated using image analysis system and electron back-scatter diffraction (EBSD), respectively. Moreover, kernel average misorientation (KAM) analysis was performed to evaluate the level of stored energy in the as-welded state. The results showed that the growth kinetics of the IM layer was not governed by a parabolic diffusion law. Presence of the IM compounds as well as high stored energy near the joint interface of the as-welded sample was recognized to be the origin of the observed deviation from the parabolic diffusion law. - Highlights: • This work provided a new insight into growth kinetics of Al–Fe IM thickness. • The growth kinetics of IM layer was not governed by a parabolic diffusion law. • IM near the joint interface was the origin of deviation from the parabolic law. • High stored energy at joint interface was origin of deviation from parabolic law.

  13. Mathematical modeling and growth kinetics of Clostridium sporogenes in cooked beef

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Clostridium sporogenes PA 3679 is a common surrogate for proteolytic Clostridium botulinum for thermal process development and validation. However, little information is available concerning the growth kinetics of C. sporogenes in food. Therefore, the objective of this study was to investigate the...

  14. COMPARATIVE KINETIC STUDIES OF PHOSPHATE-LIMITED GROWTH AND PHOSPHATE UPTAKE IN PHYTOPLANKTON IN CONTINUOUS CULTURE

    EPA Science Inventory

    A comparative kinetic study of phosphate-limited growth and phosphate uptake was carried out in chemostat cultures of Anabaena flos-aquae Lyng. Breb., Ankistrodesmus falcatus (Corda) Ralfs, Asterionella formosa Hass., Fragilaria crotonensis Kitt., and Microcystis sp. Lemm. For ea...

  15. An Unusual Exponential Graph

    ERIC Educational Resources Information Center

    Syed, M. Qasim; Lovatt, Ian

    2014-01-01

    This paper is an addition to the series of papers on the exponential function begun by Albert Bartlett. In particular, we ask how the graph of the exponential function y = e[superscript -t/t] would appear if y were plotted versus ln t rather than the normal practice of plotting ln y versus t. In answering this question, we find a new way to…

  16. Growth kinetics of three species of Tetrahymena on solid agar

    SciTech Connect

    Dobra, K.W.; McArdle, E.W.; Ehret, C.F.

    1980-01-01

    A nutrient-agar method without liquid overlay has been developed for cultivation of ciliates. Three species of Tetrahymena-T. pyriformis strain W, T. rostrata strain UNI, and T. vorax strain V/sub 2/S, representing the 3 main groups of Tetrahymena species, were used; however the method should apply to other ciliates. Growth on the surface of the agar was facilitated by an optimal surface-to-volume ratio yielding a high density of ciliates and short generation times. At the highest density achieved, the cells became irregularly hexagonal and formed a monolayer tissue on the agar. Ciliates grown on agar were like those in liquid culture, typical oral ciliature, food-vacuole formation, and typical cortical patterns being retained. Advantages of this method include high cell density, easy recovery, and optimal O/sub 2/ supply. The organisms can also be cultivated on the surface of sterile cellulose-nitrate filters, facilitating in situ fixation and staining as well as transfer into different media by transfer of filters with cells, without prior centrifugation and resuspension.

  17. The kinetic boundary layer around an absorbing sphere and the growth of small droplets

    SciTech Connect

    Widder, M.E.; Titulaer, U.M. )

    1989-06-01

    Deviations from the classical Smoluchowski expression for the growth rate of a droplet in a supersaturated vapor can be expected when the droplet radius is not large compared to the mean free path of a vapor molecule. The growth rate then depends significantly on the structure of the kinetic boundary layer around a sphere. The authors consider this kinetic boundary layer for a dilute system of Brownian particles. For this system a large class of boundary layer problems for a planar wall have been solved. They show how the spherical boundary layer can be treated by a perturbation expansion in the reciprocal droplet radius. In each order one has to solve a finite number of planar boundary layer problems. The first two corrections to the planar problem are calculated explicitly. For radii down to about two velocity persistence lengths (the analog of the mean free path for a Brownian particle) the successive approximations for the growth rate agree to within a few percent. A reasonable estimate of the growth rate for all radii can be obtained by extrapolating toward the exactly known value at zero radius. Kinetic boundary layer effects increase the time needed for growth from 0 to 10 (or 2{1/2}) velocity persistence lengths by roughly 35% (or 175%).

  18. Intermetallic compound layer growth kinetics in non-lead bearing solders

    SciTech Connect

    Vianco, P.T.; Kilgo, A.C.; Grant, R.

    1995-04-01

    The introduction of alternative, non-lead bearing solders into electronic assemblies requires a thorough investigation of product manufacturability and reliability. Both of these attributes can be impacted by the excessive growth of intermetallic compound (IMC) layers at the solder/substrate interface. An extensive study has documented the stoichiometry and solid state growth kinetics of IMC layers formed between copper and the lead-free solders: 96.5Sn-3.5Ag (wt.%), 95Sn-5Sb, 100Sn, and 58Bi-42Sn. Aging temperatures were 70--205 C for the Sn-based solders and 55--120 C for the Bi-rich solder. Time periods were 1--400 days for all of the alloys. The Sn/Cu, Sn-Ag/Cu, and Sn-Sb/Cu IMC layers exhibited sub-layers of Cu{sub 6}Sn{sub 5} and Cu{sub 3}Sn; the latter composition was present only following prolonged aging times or higher temperatures. The total layer growth exhibited a time exponent of n = 0.5 at low temperatures and a value of n = 0.42 at higher temperatures in each of the solder/Cu systems. Similar growth kinetics were observed with the low temperature 58Bi-42Sn solder; however, a considerably more complex sub-layer structure was observed. The kinetic data will be discussed with respect to predicting IMC layer growth based upon solder composition.

  19. Diameter-Independent Kinetics in the Vapor-Liquid-Solid Growth of Si Nanowires

    NASA Astrophysics Data System (ADS)

    Kodambaka, S.; Tersoff, J.; Reuter, M. C.; Ross, F. M.

    2006-03-01

    We examine individual Si nanowires grown by the vapor-liquid-solid mechanism, using real-time in situ ultra high vacuum transmission electron microscopy. By directly observing Au-catalyzed growth of Si wires from disilane, we show that the growth rate is independent of wire diameter, contrary to the expected behavior. Our measurements show that the unique rate-limiting step here is the irreversible, kinetically limited, dissociative adsorption of disilane directly on the catalyst surface. We also identify a novel dependence of growth rate on wire taper.

  20. Diameter-independent kinetics in the vapor-liquid-solid growth of Si nanowires.

    PubMed

    Kodambaka, S; Tersoff, J; Reuter, M C; Ross, F M

    2006-03-10

    We examine individual Si nanowires grown by the vapor-liquid-solid mechanism, using real-time in situ ultra high vacuum transmission electron microscopy. By directly observing Au-catalyzed growth of Si wires from disilane, we show that the growth rate is independent of wire diameter, contrary to the expected behavior. Our measurements show that the unique rate-limiting step here is the irreversible, kinetically limited, dissociative adsorption of disilane directly on the catalyst surface. We also identify a novel dependence of growth rate on wire taper. PMID:16606284

  1. Kinetic Simulation of Gold Nanorod Growth in Solution Based on Optical Spectra

    NASA Astrophysics Data System (ADS)

    Wang, Ying-ying; Li, Bo-xuan; Vdovic, Silvije; Wang, Xue-fei; Xia, An-dong

    2012-04-01

    By monitoring the time evolution of the optical absorption spectrum corresponding to dynamic information of aspect ratio (AR) and volume, we succeeded in following the growth kinetics of gold nanorods. The results indicate that the rods growth consists of two stages: seeds develop into rods with a fast AR increase and the rods grow big with constant AR. Here, a charge transfer model, involving positive charge transfer from Au(I) to seed and neutralization by electron from ascorbic acid, has been introduced to explain the autocatalysis mechanism of rod growth. The good agreement between the numerical simulation based on this model and experimental results supports the proposed mechanism.

  2. Kinetic characteristics and modelling of growth and substrate removal by Alcaligenes faecalis strain NR.

    PubMed

    Chen, Jie; Zhao, Bin; An, Qiang; Wang, Xia; Zhang, Yi Xin

    2016-04-01

    Alcaligenes faecalis strain NR has the capability of simultaneous ammonium and organic carbon removal under sole aerobic conditions. The growth and substrate removal characteristics of A. faecalis strain NR were studied and appropriate kinetic models were developed. The maximum substrate removal rate of NH4 (+)-N and TOC were determined as 2.27 mg NH4 (+)-N/L/h and 30.00 mg TOC/L/h, respectively with initial NH4 (+)-N = 80 mg/L and TOC = 800 mg/L. Single-substrate models and double-substrate models based on Monod, Contois, Moser and Teissier were employed to describe the bioprocess kinetic coefficients. As a result, two double-substrate models, Teissier-Contois and Contois-Contois, were considered to be appropriate to model growth kinetics with both NH4 (+)-N and TOC as limiting substrates. The kinetic constants of maximum growth rate (μ max) and half-saturation constant (K S and B S) were obtained by solving multiple equations with regression. This work can be used to further understand and predict the performance of heterotrophic nitrifiers, and thus provides specific guidance of these functional strains in practical wastewater treatment process. PMID:26796583

  3. Lack of a unique kinetic pathway in the growth and decay of Pluronic micelles.

    PubMed

    Arranja, Alexandra; Waton, Gilles; Schosseler, François; Mendes, Eduardo

    2016-01-21

    We report kinetic experiments on dilute brine solutions of P84, P94 and P104 Pluronic copolymer micelles. The growth and the decay of micelles after temperature steps are measured by non-standard time resolved multi-angle photon correlation spectroscopy. Several concurrent mechanisms are at work during the very slow equilibration of solutions, namely insertion/expulsion of unimers, aggregation/dissociation of micellar aggregates, and fusion/budding of micellar aggregates. Their relative rates determine both the kinetic pathways and the morphologies of the micellar assemblies, which depend markedly on modest changes in the copolymer molecular weight. For the typical Pluronic copolymers investigated here, none of these elementary processes can be neglected if the resulting morphology is to be explained. This feature imposes multiple kinetic behaviours where growth and decay of Pluronic micelles become strongly dependent on the thermal history. We point out to some possible shortcomings in the studies of micellar growth kinetics by light scattering techniques. Extensive time-resolved multiangle measurements are a prerequisite for avoiding these pitfalls. PMID:26523415

  4. Kinetics of cesium lead halide perovskite nanoparticle growth; focusing and de-focusing of size distribution

    NASA Astrophysics Data System (ADS)

    Koolyk, Miriam; Amgar, Daniel; Aharon, Sigalit; Etgar, Lioz

    2016-03-01

    In this work we study the kinetics of cesium lead halide perovskite nanoparticle (NP) growth; the focusing and de-focusing of the NP size distribution. Cesium lead halide perovskite NPs are considered to be attractive materials for optoelectronic applications. Understanding the kinetics of the formation of these all-inorganic perovskite NPs is critical for reproducibly and reliably generating large amounts of uniformly sized NPs. Here we investigate different growth durations for CsPbI3 and CsPbBr3 NPs, tracking their growth by high-resolution transmission electron microscopy and size distribution analysis. As a result, we are able to provide a detailed model for the kinetics of their growth. It was observed that the CsPbI3 NPs exhibit focusing of the size distribution in the first 20 seconds of growth, followed by de-focusing over longer growth durations, while the CsPbBr3 NPs show de-focusing of the size distribution starting from the beginning of the growth. The monomer concentration is depleted faster in the case of CsPbBr3 than in the case of CsPbI3, due to faster diffusion of the monomers, which increases the critical radius and results in de-focusing of the population. Accordingly, focusing is not observed within 40 seconds of growth in the case of CsPbBr3. This study provides important knowledge on how to achieve a narrow size distribution of cesium lead halide perovskite NPs when generating large amounts of these promising, highly luminescent NPs.In this work we study the kinetics of cesium lead halide perovskite nanoparticle (NP) growth; the focusing and de-focusing of the NP size distribution. Cesium lead halide perovskite NPs are considered to be attractive materials for optoelectronic applications. Understanding the kinetics of the formation of these all-inorganic perovskite NPs is critical for reproducibly and reliably generating large amounts of uniformly sized NPs. Here we investigate different growth durations for CsPbI3 and CsPbBr3 NPs, tracking

  5. Insitu Measurements and Modeling of Carbon Nanotube Array Growth Kinetics during Chemical Vapor Deposition

    SciTech Connect

    Puretzky, Alexander A; Geohegan, David B; Jesse, Stephen; Ivanov, Ilia N; Eres, Gyula

    2005-01-01

    Direct measurements of carbon nanotube growth kinetics are described based upon time-resolved reflectivity (TRR) of a HeNe laser beam from vertically aligned nanotube arrays (VANTAs) as they grow during chemical vapor deposition (CVD). Growth rates and terminal lengths were measured in situ for VANTAs growing during CVD between 535 C and 900 C on Si substrates with evaporated Al/Fe/Mo multi-layered catalysts and acetylene feedstock at different feedstock partial pressures. Methods of analysis of the TRR signals are presented to interpret catalyst particle formation and oxidation, as well as the porosity of the VANTAs. A rate-equation model is developed to describe the measured kinetics in terms of activation energies and rate constants for surface carbon formation and diffusion on the catalyst nanoparticle, nanotube growth, and catalyst over-coating. Taken together with the TRR data, this model enables basic understanding and optimization of growth conditions for any catalyst/feedstock combination. The model lends insight into the main processes responsible for the growth of VANTAs, the measured number of walls in the nanotubes at different temperatures, conditions for growth of single-wall carbon nanotube arrays, and likely catalyst poisoning mechanisms responsible for the sharp decline in growth rates observed at high temperatures.

  6. Phosphate-limited growth of the marine diatom Thalassiosira weissflogii (Bacillariophyceae): evidence of non-monod growth kinetics(1).

    PubMed

    Laws, Edward A; Pei, Shaofeng; Bienfang, Paul

    2013-04-01

    The marine diatom Thalassiosira weissflogii (Grunow) G. A. Fryxell & Hasle was grown in a chemostat over a series of phosphate-limited growth rates. Ambient substrate concentrations were determined from bioassays involving picomolar spikes of (33) P-labeled phosphate, and maximum uptake rates were determined from analogous bioassays that included the addition of micromolar concentrations of unlabeled phosphate and tracer concentrations of (33) P. The relationship between cell phosphorus quotas and growth rates was well described by the Droop equation. Maximum uptake rates of phosphate spikes were several orders of magnitude higher than steady state uptake rates. Despite the large size of the T. weissflogii cells, diffusion of phosphate through the boundary layer around the cells had little effect on growth kinetics, in part because the cellular N:P ratios exceeded the Redfield ratio at all growth rates. Fitting the Monod equation to the experimental data produced an estimate of the nutrient-saturated growth rate that was ~50% greater than the maximum growth rate observed in batch culture. A modified hyperbolic equation with a curvature that is a maximum in magnitude at positive growth rates gave a better fit to the data and an estimate of the maximum growth rate that was consistent with observations. The failure of the Monod equation to describe the data may reflect a transition from substrate to co-substrate limitation and/or the presence of an inducible uptake system. PMID:27008513

  7. Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

    PubMed Central

    Gokhale, Shreyas; Nagamanasa, K. Hima; Santhosh, V.; Sood, A. K.; Ganapathy, Rajesh

    2012-01-01

    The fabrication of functional materials via grain growth engineering implicitly relies on altering the mobilities of grain boundaries (GBs) by applying external fields. Although computer simulations have alluded to kinetic roughening as a potential mechanism for modifying GB mobilities, its implications for grain growth have remained largely unexplored owing to difficulties in bridging the widely separated length and time scales. Here, by imaging GB particle dynamics as well as grain network evolution under shear, we present direct evidence for kinetic roughening of GBs and unravel its connection to grain growth in driven colloidal polycrystals. The capillary fluctuation method allows us to quantitatively extract shear-dependent effective mobilities. Remarkably, our experiments reveal that for sufficiently large strains, GBs with normals parallel to shear undergo preferential kinetic roughening, resulting in anisotropic enhancement of effective mobilities and hence directional grain growth. Single-particle level analysis shows that the mobility anisotropy emerges from strain-induced directional enhancement of activated particle hops normal to the GB plane. We expect our results to influence materials fabrication strategies for atomic and block copolymeric polycrystals as well. PMID:23169661

  8. On the Effect of Atoms in Solid Solution on Grain Growth Kinetics

    NASA Astrophysics Data System (ADS)

    Hersent, Emmanuel; Marthinsen, Knut; Nes, Erik

    2014-10-01

    The discrepancy between the classical grain growth law in high purity metals (grain size ) and experimental measurements has long been a subject of debate. It is generally believed that a time growth exponent less than 1/2 is due to small amounts of impurity atoms in solid solution even in high purity metals. The present authors have recently developed a new approach to solute drag based on solute pinning of grain boundaries, which turns out to be mathematically simpler than the classic theory for solute drag. This new approach has been combined with a simple parametric law for the growth of the mean grain size to simulate the growth kinetics in dilute solid solution metals. Experimental grain growth curves in the cases of aluminum, iron, and lead containing small amounts of impurities have been well accounted for.

  9. Investigation of nucleation and crystal growth kinetics of nickel manganese oxalates

    NASA Astrophysics Data System (ADS)

    Aoun-Habbache, Montaha; Guillemet-Fritsch, Sophie; Lemaître, Jacques; Jones, Alan

    2005-06-01

    The nucleation and the crystal growth rates of mixed nickel manganese oxalates have been determined from the changes of the ionic concentration of the solution and the crystal size distribution during the precipitation process within a supersaturation range 0-0.1 M. Thermodynamic solubility calculations have been used to identify the different species contributing the precipitation reaction and for estimation of the thermodynamic constant. Experimental data show that the nucleation rate of mixed nickel manganese oxalate in this supersaturation range is consistent with a primary heterogeneous mechanism and was found to obey to an exponential law. The crystal growth rates indicate a surface-integration-controlled mechanism with a first-order law with respect to the supersaturation.

  10. Growth kinetics and complex characterization of PECVD SiO x N y dielectric films

    NASA Astrophysics Data System (ADS)

    Pereyaslavtsev, A.; Sokolov, I.

    2016-05-01

    This paper is devoted to the study of patterns of dielectric film growth depending on the parameters of the plasma chemical deposition process. The study has revealed the influence of the basic reagents’ content on the changes in surface morphology, breakdown voltage and stoichiometry (transition to the intermediate oxidation states of silicon) of dielectric films. Furthermore, an exponential pattern of the change in the films’ growth rate has been registered. When increasing the N/Si ratio, a nonlinear dependence of the change in the dielectric films’ band gap has been recorded. When increasing the SiH4/N2O ratio, a shift of the peak positions of the interband interactions relative to the band gap boundaries has been detected. The dataset on breakdown voltage and band structure suggests a certain optimum of barrier properties of SiO x N y dielectric films at the basic reagents’ ratio close to 0.3–0.4.

  11. Kinetic modeling of Moorella thermoacetica growth on single and dual-substrate systems.

    PubMed

    Schmitt, Elliott; Bura, Renata; Gustafson, Rick; Ehsanipour, Mandana

    2016-10-01

    Acetic acid is an important chemical raw material that can be produced directly from sugars in lignocellulosic biomass. Development of kinetic models that capture the bioconversion dynamics of multiple sugar systems will be critical to optimization and process control in future lignocellulosic biorefinery processes. In this work, a kinetic model was developed for the single- and dual-substrate conversion of xylose and glucose to acetic acid using the acetogen Moorella thermoacetica. Batch fermentations were performed experimentally at 20 g L(-1) total sugar concentration using synthetic glucose, xylose, and a mixture of glucose and xylose at a 1:1 ratio. The product yield, calculated as total product formed divided by total sugars consumed, was 79.2, 69.9, and 69.7 % for conversion of glucose, xylose, and a mixture of glucose and xylose (1:1 ratio), respectively. During dual-substrate fermentation, M. thermoacetica demonstrated diauxic growth where xylose (the preferred substrate) was almost entirely consumed before consumption of glucose began. Kinetic parameters were similar for the single-substrate fermentations, and a strong linear correlation was determined between the maximum specific growth rate μ max and substrate inhibition constant, K s . Parameters estimated for the dual-substrate system demonstrated changes in the specific growth rate of both xylose and glucose consumption. In particular, the maximum growth rate related to glucose tripled compared to the single-substrate system. Kinetic growth is affected when multiple substrates are present in a fermentation system, and models should be developed to reflect these features. PMID:27262717

  12. Review of "Going Exponential: Growing the Charter School Sector's Best"

    ERIC Educational Resources Information Center

    Garcia, David

    2011-01-01

    This Progressive Policy Institute report argues that charter schools should be expanded rapidly and exponentially. Citing exponential growth organizations, such as Starbucks and Apple, as well as the rapid growth of molds, viruses and cancers, the report advocates for similar growth models for charter schools. However, there is no explanation of…

  13. Kinetics and mechanisms of cadmium carbonate heteroepitaxial growth at the calcite (10 1bar 4) surface

    NASA Astrophysics Data System (ADS)

    Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien

    2014-06-01

    Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at calcite-water interfaces was investigated by exposing calcite (10 1bar 4) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the calcite substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and calcite shows perfect, dislocation-free epitaxy.

  14. Kinetics and Mechanisms of Cadmium Carbonate Heteroepitaxial Growth at the Calcite (101¯4) Surface

    SciTech Connect

    Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.

    2014-06-01

    Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at calcite-water interfaces was investigated by exposing calcite (10-14) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the calcite substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and calcite shows perfect, dislocation-free epitaxy.

  15. Estimation of the growth kinetics for the cooling crystallisation of paracetamol and ethanol solutions

    NASA Astrophysics Data System (ADS)

    Mitchell, Niall A.; Ó'Ciardhá, Clifford T.; Frawley, Patrick J.

    2011-08-01

    This work details the estimation of the growth kinetics of paracetamol in ethanol solutions for cooling crystallisation processes, by means of isothermal seeded batch experiments. The growth kinetics of paracetamol crystals were evaluated in isolation, with the growth rate assumed to be size independent. Prior knowledge of the Metastable Zone Width (MSZW) was required, so that supersaturation ratios of 1.7-1.1 could be induced in solution without the occurrence of nucleation. The technique involved the utilisation of two in-situ Process Analytical Techniques (PATs), with a Focused Beam Reflectance Measurement (FBRM ®) utilised to ensure that negligible nucleation occurred and an Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) probe employed for online monitoring of solute concentration. Initial Particle Size Distributions (PSDs) were used in conjunction with desupersaturation profiles to determine the growth rate as a function of temperature and supersaturation. Furthermore, the effects of seed loading and size on the crystal growth rate were investigated. A numerical model, incorporating the population balance equation and the method of moments, was utilised to describe the crystal growth process. Experimental parameters were compared to the model simulation, with the accuracy of the model validated by means of the final product PSDs and solute concentration.

  16. Nonlinear Growth Kinetics of Breast Cancer Stem Cells: Implications for Cancer Stem Cell Targeted Therapy

    NASA Astrophysics Data System (ADS)

    Liu, Xinfeng; Johnson, Sara; Liu, Shou; Kanojia, Deepak; Yue, Wei; Singn, Udai; Wang, Qian; Wang, Qi; Nie, Qing; Chen, Hexin

    2013-08-01

    Cancer stem cells (CSCs) have been identified in primary breast cancer tissues and cell lines. The CSC population varies widely among cancerous tissues and cell lines, and is often associated with aggressive breast cancers. Despite of intensive research, how the CSC population is regulated within a tumor is still not well understood so far. In this paper, we present a mathematical model to explore the growth kinetics of CSC population both in vitro and in vivo. Our mathematical models and supporting experiments suggest that there exist non-linear growth kinetics of CSCs and negative feedback mechanisms to control the balance between the population of CSCs and that of non-stem cancer cells. The model predictions can help us explain a few long-standing questions in the field of cancer stem cell research, and can be potentially used to predict the efficicacy of anti-cancer therapy.

  17. Growth kinetics and island evolution during double-pulsed molecular beam epitaxy of InN

    NASA Astrophysics Data System (ADS)

    Kraus, A.; Hein, C.; Bremers, H.; Rossow, U.; Hangleiter, A.

    2016-06-01

    The kinetic processes of InN growth using alternating source fluxes with sub-monolayer In pulses in plasma-assisted molecular beam epitaxy have been investigated. Growth at various temperatures reveals the existence of two growth regimes. While growth at low temperatures is solely governed by surface diffusion, a combination of decomposition, desorption, and diffusion becomes decisive at growth temperatures of 470 °C and above. At this critical temperature, the surface morphology changes from a grainy structure to a structure made of huge islands. The formation of those islands is attributed to the development of an indium adlayer, which can be observed via reflection high energy electron diffraction monitoring. Based on the growth experiments conducted at temperatures below TGrowth = 470 °C, an activation energy for diffusion of 0.54 ± 0.02 eV has been determined from the decreasing InN island density. A comparison between growth on metalorganic vapor phase epitaxy GaN templates and pseudo bulk GaN indicates that step edges and dislocations are favorable nucleation sites. Based on the results, we developed a growth model, which describes the main mechanisms of the growth.

  18. Intrinsic Kinetics Fluctuations as Cause of Growth Inhomogeneity in Protein Crystals

    NASA Technical Reports Server (NTRS)

    Vekilov, Peter G.; Rosenberger, Franz

    1998-01-01

    Intrinsic kinetics instabilities in the form of growth step bunching during the crystallization of the protein lysozyme from solution were characterized by in situ high-resolution optical interferometry. Compositional variations (striations) in the crystal, which potentially decrease its utility, e.g., for molecular structure studies by diffraction methods, were visualized by polarized light reflection microscopy. A spatiotemporal correlation was established between the sequence of moving step bunches and the striations.

  19. Mg doping and its effect on the semipolar GaN(1122) growth kinetics

    SciTech Connect

    Lahourcade, L.; Wirthmueller, A.; Monroy, E.; Chauvat, M. P.; Ruterana, P.; Laufer, A.; Eickhoff, M.

    2009-10-26

    We report the effect of Mg doping on the growth kinetics of semipolar GaN(1122) synthesized by plasma-assisted molecular-beam epitaxy. Mg tends to segregate on the surface, inhibiting the formation of the self-regulated Ga film which is used as a surfactant for the growth of undoped and Si-doped GaN(1122). We observe an enhancement of Mg incorporation in GaN(1122) compared to GaN(0001). Typical structural defects or polarity inversion domains found in Mg-doped GaN(0001) were not observed for the semipolar films investigated in the present study.

  20. Effect of clofibrate on the growth-kinetics of the murine P 1798(sc) lymphoma.

    PubMed Central

    Ubeira, F. M.; Seoane, R.; Puentes, E.; Faro, J.; Regueiro, B. J.

    1983-01-01

    Clofibrate (CPIB) is a drug applied as an antilipidaemic agent in mammals. In this work we have tested its efficacy in vivo on the growth kinetics of P 1798(sc) lymphoma transplanted to recipient (BALB/c x AKR)F1 mice. Our results show a facilitation of the tumour growth rate in treated recipients. This fact may be related to an effect of the agent on the recipient which produces a decrease in the immune response as was confirmed on testing CPIB on thymus-dependent antigens in haemolytic plaque assays. Images Figure 3 PMID:6351886

  1. Generalization of Monod kinetics for analysis of growth data with substrate inhibition

    SciTech Connect

    Luong, J.H.T.

    1987-02-05

    The inhibitory effect of butanol on yeast growth has been studied for the strain Candida utilis ATCC 8205 growing aerobically on butanol under batch conditions. A mathematical expression was then proposed to fit the kinetic pattern of butanol inhibition on the specific growth rate. The maximum allowable butanol concentration above which cells do not grow was predicted to be 9.16 g/l. The proposed model appears to accurately represent the experimental data obtained in this study and the literature data developed for a variety of batch culture systems at widely ranging substrate concentrations. 20 references.

  2. Investigation of the kinetics of surface-limited thin film growth of SiGe alloys

    SciTech Connect

    Sharp, J.W. . Dept. of Physics and Astronomy); Eres, G. )

    1992-11-01

    The kinetics of surface-limited thin film growth of SiGe alloys was investigated by time-resolved surface differential reflectometry. The source gas, mixtures of disilane and digermane in ratios from 1:1 to 6:1 in helium carrier gas, was delivered to a heated substrate by a fast-acting pulsed molecular jet valve. The adsorption and desorption kinetics were determined from the surface differential reflectance signal obtained using a polarized, high-stability HeNe probe laser. Thin film growth was studied in the temperature range of 400--600[degrees]C on Si(001) substrates. Preferential incorporation of digermane into the film produces an alloy composition that depends upon but does not mirror the gas composition. For all gas mixtures, there is a strong temperature dependence of the rate at which the adsorption layer decomposes into film plus by-product. The kinetic data and the alloy compositions provide a basis for deducing some of the characteristics of the reaction sequence that leads to SiGe alloy thin film growth.

  3. Investigation of the kinetics of surface-limited thin film growth of SiGe alloys

    SciTech Connect

    Sharp, J.W.; Eres, G.

    1992-11-01

    The kinetics of surface-limited thin film growth of SiGe alloys was investigated by time-resolved surface differential reflectometry. The source gas, mixtures of disilane and digermane in ratios from 1:1 to 6:1 in helium carrier gas, was delivered to a heated substrate by a fast-acting pulsed molecular jet valve. The adsorption and desorption kinetics were determined from the surface differential reflectance signal obtained using a polarized, high-stability HeNe probe laser. Thin film growth was studied in the temperature range of 400--600{degrees}C on Si(001) substrates. Preferential incorporation of digermane into the film produces an alloy composition that depends upon but does not mirror the gas composition. For all gas mixtures, there is a strong temperature dependence of the rate at which the adsorption layer decomposes into film plus by-product. The kinetic data and the alloy compositions provide a basis for deducing some of the characteristics of the reaction sequence that leads to SiGe alloy thin film growth.

  4. Exponential increases of RNA virus fitness during large population transmissions.

    PubMed Central

    Novella, I S; Duarte, E A; Elena, S F; Moya, A; Domingo, E; Holland, J J

    1995-01-01

    The great adaptability shown by RNA viruses is a consequence of their high mutation rates. Here we investigate the kinetics of virus fitness gains during repeated transfers of large virus populations in cell culture. Results always show that fitness increases exponentially. Low fitness clones exhibit regular increases observed as biphasic periods of exponential evolutionary improvement, while neutral clones show monophasic kinetics. These results are significant for RNA virus epidemiology, optimal handling of attenuated live virus vaccines, and routine laboratory procedures. PMID:7597039

  5. Effect of nitrogen and vanadium on austenite grain growth kinetics of a low alloy steel

    SciTech Connect

    Stasko, Renata . E-mail: rstasko@ap.Cracow.pl; Adrian, Henryk . E-mail: adrian@uci.agh.edu.pl; Adrian, Anna . E-mail: adrian@metal.agh.edu.pl

    2006-06-15

    Austenite grain growth kinetics in a steel containing 0.4% C, 1.8% Cr with different nitrogen contents (in the range 0.0038-0.0412%) and a micralloying addition of 0.078% V were investigated. The investigations were carried out in an austenitising temperature range of 840-1200 deg. C for 30 min. The results of investigations showed that N promotes the grain growth of austenite. The microalloying addition of vanadium protects the austenite grain growth because of carbonitride V(C,N) precipitation and the grain boundary pinning effect of undissolved particles of V(C,N). Using a thermodynamic model, the carbonitride V(C,N) content, undissolved at the austenitising temperature was calculated. At temperatures when a coarsening and dissolution of carbonitride occurs, the austenite grains start to growth. The effect of nitrogen on the type of chord length distribution of austenite grains was analysed.

  6. Effects of Alloying on Nanoscale Grain Growth in Substitutional Binary Alloy System: Thermodynamics and Kinetics

    NASA Astrophysics Data System (ADS)

    Peng, Haoran; Chen, Yuzeng; Liu, Feng

    2015-11-01

    Applying the regular solution model, the Gibbs free energy of mixing for substitutional binary alloy system was constructed. Then, thermodynamic and kinetic parameters, e.g., driving force and solute drag force, controlling nanoscale grain growth of substitutional binary alloy systems were derived and compared to their generally accepted definitions and interpretations. It is suggested that for an actual grain growth process, the classical driving force P = γ/D ( γ the grain boundary (GB) energy, D the grain size) should be replaced by a new expression, i.e., P^' = γ /D - Δ P . Δ P represents the energy required to adjust nonequilibrium solute distribution to equilibrium solute distribution, which is equivalent to the generally accepted solute drag force impeding GB migration. By incorporating the derived new driving force for grain growth into the classical grain growth model, the reported grain growth behaviors of nanocrystalline Fe-4at. pct Zr and Pd-19at. pct Zr alloys were analyzed. On this basis, the effect of thermodynamic and kinetic parameters ( i.e., P, Δ P and the GB mobility ( M GB)) on nanoscale grain growth, were investigated. Upon grain growth, the decrease of P is caused by the reduction of γ as a result of solute segregation in GBs; the decrease of Δ P is, however, due to the decrease of grain growth velocity; whereas the decrease of M GB is attributed to the enhanced difference of solute molar fractions between the bulk and the GBs as well as the increased activation energy for GB diffusion.

  7. A phase-field model coupled with lattice kinetics solver for modeling crystal growth in furnaces

    SciTech Connect

    Lin, Guang; Bao, Jie; Xu, Zhijie; Tartakovsky, Alexandre M.; Henager, Charles H.

    2014-02-02

    In this study, we present a new numerical model for crystal growth in a vertical solidification system. This model takes into account the buoyancy induced convective flow and its effect on the crystal growth process. The evolution of the crystal growth interface is simulated using the phase-field method. Two novel phase-field models are developed to model the crystal growth interface in vertical gradient furnaces with two temperature profile setups: 1) fixed wall temperature profile setup and 2) time-dependent temperature profile setup. A semi-implicit lattice kinetics solver based on the Boltzmann equation is employed to model the unsteady incompressible flow. This model is used to investigate the effect of furnace operational conditions on crystal growth interface profiles and growth velocities. For a simple case of macroscopic radial growth, the phase-field model is validated against an analytical solution. Crystal growth in vertical gradient furnaces with two temperature profile setups have been also investigated using the developed model. The numerical simulations reveal that for a certain set of temperature boundary conditions, the heat transport in the melt near the phase interface is diffusion dominant and advection is suppressed.

  8. Comparison of growth kinetics for healthy and heat-injured Listeria monocytogenes in eight enrichment broths.

    PubMed

    Silk, Todd M; Roth, Tatiana M T; Donnelly, C W

    2002-08-01

    Detection of Listeria in food products is often limited by performance of enrichment media used to support growth of Listeria to detectable levels. In this study, growth curves were generated using healthy and heat-injured Listeria monocytogenes strain F5069 in three nonselective and five selective enrichment broths. Nonselective enrichment media included the current Food and Drug Administration Bacteriological Analytical Manual Listeria enrichment broth base (BAM), Listeria repair broth (LRB), and Trypticase soy broth. Selective enrichment media included BAM with selective agents and LRB with selective agents, BCM L. monocytogenes preenrichment broth, Fraser broth, and UVM-modified Listeria enrichment broth. The Gompertz equation was used to model the growth of L. monocytogenes. Gompertz parameters were used to calculate exponential growth rate, lag-phase duration (LPD), generation time, maximum population density (MPD), and time required for repair of injured cells. Statistical differences (P < 0.05) in broth performance were noted for LPD and MPD when healthy and injured cells were inoculated into the broths. With the exception of Fraser broth, there were no significant differences in the time required for the repair of injured cells. Results indicate that the distinction between selective and nonselective broths in their ability to grow healthy Listeria and to repair sublethally injured cells is not solely an elementary issue of presence or absence of selective agents. PMID:12182490

  9. Quantifying the Nucleation and Growth Kinetics of Microwave Nanochemistry Enabled by in Situ High-Energy X-ray Scattering.

    PubMed

    Liu, Qi; Gao, Min-Rui; Liu, Yuzi; Okasinski, John S; Ren, Yang; Sun, Yugang

    2016-01-13

    The fast reaction kinetics presented in the microwave synthesis of colloidal silver nanoparticles was quantitatively studied, for the first time, by integrating a microwave reactor with in situ X-ray diffraction at a high-energy synchrotron beamline. Comprehensive data analysis reveals two different types of reaction kinetics corresponding to the nucleation and growth of the Ag nanoparticles. The formation of seeds (nucleation) follows typical first-order reaction kinetics with activation energy of 20.34 kJ/mol, while the growth of seeds (growth) follows typical self-catalytic reaction kinetics. Varying the synthesis conditions indicates that the microwave colloidal chemistry is independent of concentration of surfactant. These discoveries reveal that the microwave synthesis of Ag nanoparticles proceeds with reaction kinetics significantly different from the synthesis present in conventional oil bath heating. The in situ X-ray diffraction technique reported in this work is promising to enable further understanding of crystalline nanomaterials formed through microwave synthesis. PMID:26625184

  10. Dynamic kinetic analysis of growth of Listeria monocytogenes in a simulated comminuted, non-cured cooked pork product

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The objective of this study was to directly construct a tertiary growth model for Listeria monocytogenes in cooked pork and simultaneously determine the kinetic parameters using a combination of dynamic and isothermal growth curves. Growth studies were conducted using a cocktail of 5 strains of L. ...

  11. Simulation studies on shape and growth kinetics for fractal aggregates in aerosol and colloidal systems

    NASA Astrophysics Data System (ADS)

    Heinson, William Raymond

    The aim of this work is to explore, using computational techniques that simulate the motion and subsequent aggregation of particles in aerosol and colloidal systems, many common but not well studied systems that form fractal clusters. Primarily the focus is on cluster shape and growth kinetics. The structure of clusters made under diffusion limited cluster-cluster aggregation (DLCA) is looked at. More specifically, the shape anisotropy is found to have an inverse relationship on the scaling prefactor k0 and have no effect on the fractal dimension Df . An analytical model that predicts the shape and fractal dimension of diffusion limited cluster-cluster aggregates is tested and successfully predicts cluster shape and dimensionality. Growth kinetics of cluster-cluster aggregation in the free molecular regime where the system starts with ballistic motion and then transitions to diffusive motion as the aggregates grow in size is studied. It is shown that the kinetic exponent will crossover from the ballistic to the diffusional values and the onset of this crossover is predicted by when the nearest neighbor Knudsen number reaches unity. Simulations were carried out for a system in which molten particles coalesce into spheres, then cool till coalescing stops and finally the polydispersed monomers stick at point contacts to form fractal clusters. The kinetic exponent and overall cluster structure for these aggregates was found to be in agreement with DLCA that started with monodispersed monomers. Colloidal aggregation in the presence of shear was studied in detail. Study of a colloidal system characterized a by short-range attractive potential showed that weak shear enhanced the aggregation process. Strong shear led to fragmentation and subsequent nucleation as cluster growth rebounded after an induction time.

  12. Deletion of the Escherichia coli pseudouridine synthase gene truB blocks formation of pseudouridine 55 in tRNA in vivo, does not affect exponential growth, but confers a strong selective disadvantage in competition with wild-type cells.

    PubMed Central

    Gutgsell, N; Englund, N; Niu, L; Kaya, Y; Lane, B G; Ofengand, J

    2000-01-01

    Previous work from this laboratory (Nurse et al., RNA, 1995, 1:102-112) established that TruB, a pseudouridine (psi) synthase from Escherichia coli, was able to make psi55 in tRNA transcripts but not in transcripts of full-length or fragmented 16S or 23S ribosomal RNAs. By deletion of the truB gene, we now show that TruB is the only protein in E. coli able to make psi55 in vivo. Lack of TruB and psi55 did not affect the exponential growth rate but did confer a strong selective disadvantage on the mutant when it was competed against wild-type. The negative selection did not appear to be acting at either the exponential or stationary phase. Transformation with a plasmid vector conferring carbenicillin resistance and growth in carbenicillin markedly increased the selective disadvantage, as did growth at 42 degrees C, and both together were approximately additive such that three cycles of competitive growth sufficed to reduce the mutant strain to approximately 0.2% of its original value. The most striking finding was that all growth effects could be reversed by transformation with a plasmid carrying a truB gene coding for a D48C mutation in TruB. Direct analysis showed that this mutant did not make psi55 under the conditions of the competition experiment. Therefore, the growth defect due to the lack of TruB must be due to the lack of some other function of the protein, possibly an RNA chaperone activity, but not to the absence of psi55. PMID:11142385

  13. Implications of solution chemistry effects: Direction-specific restraints on the step kinetics of calcite growth

    NASA Astrophysics Data System (ADS)

    Hong, Mina; Teng, H. Henry

    2014-09-01

    Classical crystallization models successfully depict the dependence of growth kinetics on thermodynamic driving force but cannot predict the roles of solution chemistry. Yet, it has become increasingly clear that crystal growth rate at fixed supersaturations depends on pH, ionic strength, and the relative abundance of cations and anions in the parent solutions. We conducted experiments to isolate the effect of individual solution-chemistry parameters on calcite step growth kinetics. Our results revealed a distinct correlation between step velocity and pH in acute and obtuse directions and a simultaneous trend change at pH ∼9.5. Step speeds varied with solution stoichiometry, and each direction reached its maximal rate at a different [Ca]/[CO32-] value. In addition, the solution cation/anion at which maximal step speed occurred appeared to be pH dependent as well. Limited effect of ionic strength on step growth was observed in the obtuse direction at low background electrolyte concentrations, but no obvious change was found for growth at the acute side. We proposed a growth model based upon independent incorporation of cations and anions and interpreted these observations as: (1) solute constituents enter kinks through direct solution diffusion at obtuse steps but surface diffusion at acute steps; (2) growth is limited by Ca2+ dehydration at the obtuse side, but by surface adsorption and reorientation and rearrangement of CO32- in the acute direction; and (3) background electrolyte (NaCl in our study) competes with solutes for surface sites at more easily accessible kinks.

  14. Kinetics of grain growth in the weld heat-affected zone of Alloy 718

    SciTech Connect

    Radhakrishnan, B.; Thompson, R.G.

    1993-12-01

    Grain-boundary liquation occurs in the weld heat-affected zone (HAZ) of the Ni-base superalloy 718 at locations where the peak temperatures are greater than about 1,200 C. The evolution of the grain structure at the HAZ locations depends upon the interaction between the grains and the grain-boundary liquid. The evolution of grain structure in the presence of grain-boundary liquid was simulated by subjecting samples to controlled thermal cycles using resistance heating. A measurement of grain size as a function of isothermal hold at two peak temperatures of 1,200 C and 1,227 C indicated that in alloy 718, the kinetics of grain growth depended upon the prior thermal history of the alloy. In the solution-treated alloy, the presence of grain-boundary liquid did not arrest grain growth at either peak temperature. In the homogenized and aged alloy, a grain refinement was observed at the peak temperature of 1,227 C, while an arrest of grain growth was observed at a peak temperature of 1,200 C. Liquid film migration (LFM) and subgrain coalescence, either acting alone or simultaneously, are shown to explain most of the observed microstructural phenomena and the kinetics of grain growth in the alloy.

  15. Kinetics of grain growth in the weld heat-affected zone of alloy 718

    NASA Astrophysics Data System (ADS)

    Radhakrishnan, B.; Thompson, R. G.

    1993-12-01

    Grain-boundary liquation occurs in the weld heat-affected zone (HAZ) of the Ni-base superalloy 718 at locations where the peak temperatures are greater than about 1200 ‡C. The evolution of the grain structure at these HAZ locations depends upon the interaction between the grains and the grain-boundary liquid. The evolution of grain structure in the presence of grain-boundary liquid was simulated by subjecting samples to controlled thermal cycles using resistance heating. A measurement of grain size as a function of isothermal hold at two peak temperatures of 1200 ‡C and 1227 ‡C indicated that in alloy 718, the kinetics of grain growth depended upon the prior thermal history of the alloy. In the solution-treated alloy, the presence of grain-boundary liquid did not arrest grain growth at either peak temperature. In the homogenized and aged alloy, a grain refinement was observed at the peak temperature of 1227 ‡C, while an arrest of grain growth was observed at a peak temperature of 1200‡C. Liquid film migration (LFM) and subgrain coalescence, either acting alone or simultaneously, are shown to explain most of the observed microstructural phenomena and the kinetics of grain growth in the alloy.

  16. From atoms to layers: in situ gold cluster growth kinetics during sputter deposition

    NASA Astrophysics Data System (ADS)

    Schwartzkopf, Matthias; Buffet, Adeline; Körstgens, Volker; Metwalli, Ezzeldin; Schlage, Kai; Benecke, Gunthard; Perlich, Jan; Rawolle, Monika; Rothkirch, André; Heidmann, Berit; Herzog, Gerd; Müller-Buschbaum, Peter; Röhlsberger, Ralf; Gehrke, Rainer; Stribeck, Norbert; Roth, Stephan V.

    2013-05-01

    The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction of morphological real space parameters, such as cluster size and shape, correlation distance, layer porosity and surface coverage, directly from reciprocal space scattering data. This approach enables a large variety of future investigations of the influence of different process parameters on the thin metal film morphology. Furthermore, our study allows for deducing the wetting behavior of gold cluster films on solid substrates and provides a better understanding of the growth kinetics in general, which is essential for optimization of manufacturing parameters, saving energy and resources.The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction

  17. Evaluation of a kinetic model for computer simulation of growth and fermentation by Scheffersomyces (Pichia) stipitis fed D-xylose

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Scheffersomyces (formly Pichia) stipitis is a potential biocatalyst for converting lignocelluloses to ethanol because the yeast natively ferments xylose. An unstructured kinetic model based upon a system of linear differential equations has been formulated that describes growth and ethanol productio...

  18. Crystal growth kinetics in Lennard-Jones and Weeks-Chandler-Andersen systems along the solid-liquid coexistence line

    NASA Astrophysics Data System (ADS)

    Benjamin, Ronald; Horbach, Jürgen

    2015-07-01

    Kinetics of crystal-growth is investigated along the solid-liquid coexistence line for the (100), (110), and (111) orientations of the Lennard-Jones (LJ) and Weeks-Chandler-Andersen (WCA) fcc crystal-liquid interface, using non-equilibrium molecular dynamics simulations. A slowing down of the growth kinetics along the coexistence line is observed, which is due to the decrease of the melting enthalpy with increasing coexistence temperature and pressure. Other quantities such as the melting pressure and liquid self-diffusion coefficient have a comparatively lesser impact on the kinetic growth coefficient. Growth kinetics of the LJ and WCA potentials become similar at large values of the melting temperature and pressure, when both resemble a purely repulsive soft-sphere potential. Classical models of crystallization from the melt are in reasonable qualitative agreement with our simulation data. Finally, several one-phase empirical melting/freezing rules are studied with respect to their validity along the coexistence line.

  19. Control of Electron Beam-Induced Au Nanocrystal Growth Kinetics through Solution Chemistry.

    PubMed

    Park, Jeung Hun; Schneider, Nicholas M; Grogan, Joseph M; Reuter, Mark C; Bau, Haim H; Kodambaka, Suneel; Ross, Frances M

    2015-08-12

    Measurements of solution-phase crystal growth provide mechanistic information that is helpful in designing and synthesizing nanostructures. Here, we examine the model system of individual Au nanocrystal formation within a defined liquid geometry during electron beam irradiation of gold chloride solution, where radiolytically formed hydrated electrons reduce Au ions to solid Au. By selecting conditions that favor the growth of well-faceted Au nanoprisms, we measure growth rates of individual crystals. The volume of each crystal increases linearly with irradiation time at a rate unaffected by its shape or proximity to neighboring crystals, implying a growth process that is controlled by the arrival of atoms from solution. Furthermore, growth requires a threshold dose rate, suggesting competition between reduction and oxidation processes in the solution. Above this threshold, the growth rate follows a power law with dose rate. To explain the observed dose rate dependence, we demonstrate that a reaction-diffusion model is required that explicitly accounts for the species H(+) and Cl(-). The model highlights the necessity of considering all species present when interpreting kinetic data obtained from beam-induced processes, and suggest conditions under which growth rates can be controlled with higher precision. PMID:26207841

  20. Domain growth kinetics in the isosceles triangular Ising antiferromagnet CoNb2O6

    NASA Astrophysics Data System (ADS)

    Kobayashi, S.; Okano, H.; Jogetsu, T.; Miyamoto, J.; Mitsuda, S.

    2004-04-01

    We have studied the domain-growth kinetics of fourfold-degenerate antiferromagnetic (AF) and threefold-degenerate ferrimagnetic states in the isosceles triangular Ising antiferromagnet CoNb2O6 by ac susceptibility measurements and Monte Carlo simulations. In both magnetic phases ac susceptibility after the field quench is found to decrease with time according to the power-growth law with an universal growth exponent n=0.21±0.01. The prefactor in the power-growth law suggests that the zero-field growth of the AF state is strongly suppressed by the application of magnetic fields along the direction perpendicular to the frustrated isosceles-triangular lattice. Monte Carlo results show the unusual domain growth dominated by the reversal of the free magnetic spins near favorable domain walls where the exchange field is effectively canceled out due to the isosceles triangular geometry of spins. The obtained domain configuration strongly supports our neutron-diffraction results that revealed the temporal shift of the magnetic Bragg peak position during the growth.

  1. Antifreeze effect of carboxylated ε-poly-L-lysine on the growth kinetics of ice crystals.

    PubMed

    Vorontsov, Dmitry A; Sazaki, Gen; Hyon, Suong-Hyu; Matsumura, Kazuaki; Furukawa, Yoshinori

    2014-08-28

    Some biological substances control the nucleation and growth of inorganic crystals. Antifreeze proteins, which prohibit ice crystal growth in living organisms, promise are also important as biological antifreezes for medical applications and in the frozen food industries. In this work, we investigated the crystallization of ice in the presence of a new cryoprotector, carboxylated ε-poly-L-lysine (COOH-PLL). In order to reveal the characteristics and the mechanism of its antifreeze effect, free-growth experiments of ice crystals were carried out in solutions with various COOH-PLL concentrations and degrees of supercooling, and the depression of the freezing point and growth rates of the tips of ice dendrites were obtained using optical microscopy. Hysteresis of growth rates and depression of the freezing point was revealed in the presence of COOH-PLL. The growth-inhibition effect of COOH-PLL molecules could be explained on the basis of the Gibbs-Thomson law and the use of Langmuir's adsorption isotherm. Theoretical kinetic curves for hysteresis calculated on the basis of Punin-Artamonova's model were in good agreement with experimental data. We conclude that adsorption of large biological molecules in the case of ice crystallization has a non-steady-state character and occurs more slowly than the process of embedding of crystal growth units. PMID:25113284

  2. Growth Kinetics and Transmission Potential of Existing and Emerging Field Strains of Infectious Laryngotracheitis Virus

    PubMed Central

    Coppo, Mauricio J. C.; Vaz, Paola K.; Legione, Alistair R.; Quinteros, José A.; Noormohammadi, Amir H.; Markham, Phillip F.; Browning, Glenn F.; Devlin, Joanne M.

    2015-01-01

    Attenuated live infectious laryngotracheitis virus (ILTV) vaccines are widely used in the poultry industry to control outbreaks of disease. Natural recombination between commercial ILTV vaccines has resulted in virulent recombinant viruses that cause severe disease, and that have now emerged as the dominant field strains in important poultry producing regions in Australia. Genotype analysis using PCR—restriction fragment length polymorphism has shown one recombinant virus (class 9) has largely replaced the previously dominant class 2 field strain. To examine potential reasons for this displacement we compared the growth kinetics and transmission potential of class 2 and class 9 viruses. The class 9 ILTV grew to higher titres in cell culture and embryonated eggs, but no differences were observed in entry kinetics or egress into the allantoic fluid from the chorioallantoic membrane. In vivo studies showed that birds inoculated with class 9 ILTV had more severe tracheal pathology and greater weight loss than those inoculated with the class 2 virus. Consistent with the predominance of class 9 field strains, birds inoculated with 102 or 103 plaque forming units of class 9 ILTV consistently transmitted virus to in-contact birds, whereas this could only be seen in birds inoculated with 104 PFU of the class 2 virus. Taken together, the improved growth kinetics and transmission potential of the class 9 virus is consistent with improved fitness of the recombinant virus over the previously dominant field strain. PMID:25785629

  3. Growth kinetics and transmission potential of existing and emerging field strains of infectious laryngotracheitis virus.

    PubMed

    Lee, Sang-Won; Hartley, Carol A; Coppo, Mauricio J C; Vaz, Paola K; Legione, Alistair R; Quinteros, José A; Noormohammadi, Amir H; Markham, Phillip F; Browning, Glenn F; Devlin, Joanne M

    2015-01-01

    Attenuated live infectious laryngotracheitis virus (ILTV) vaccines are widely used in the poultry industry to control outbreaks of disease. Natural recombination between commercial ILTV vaccines has resulted in virulent recombinant viruses that cause severe disease, and that have now emerged as the dominant field strains in important poultry producing regions in Australia. Genotype analysis using PCR-restriction fragment length polymorphism has shown one recombinant virus (class 9) has largely replaced the previously dominant class 2 field strain. To examine potential reasons for this displacement we compared the growth kinetics and transmission potential of class 2 and class 9 viruses. The class 9 ILTV grew to higher titres in cell culture and embryonated eggs, but no differences were observed in entry kinetics or egress into the allantoic fluid from the chorioallantoic membrane. In vivo studies showed that birds inoculated with class 9 ILTV had more severe tracheal pathology and greater weight loss than those inoculated with the class 2 virus. Consistent with the predominance of class 9 field strains, birds inoculated with 10(2) or 10(3) plaque forming units of class 9 ILTV consistently transmitted virus to in-contact birds, whereas this could only be seen in birds inoculated with 10(4) PFU of the class 2 virus. Taken together, the improved growth kinetics and transmission potential of the class 9 virus is consistent with improved fitness of the recombinant virus over the previously dominant field strain. PMID:25785629

  4. Kinetics of substrate utilization and bacterial growth of crude oil degraded by Pseudomonas aeruginosa.

    PubMed

    Talaiekhozani, Amirreza; Jafarzadeh, Nematollah; Fulazzaky, Mohamad Ali; Talaie, Mohammad Reza; Beheshti, Masoud

    2015-01-01

    Pollution associated with crude oil (CO) extraction degrades the quality of waters, threatens drinking water sources and may ham air quality. The systems biology approach aims at learning the kinetics of substrate utilization and bacterial growth for a biological process for which very limited knowledge is available. This study uses the Pseudomonas aeruginosa to degrade CO and determines the kinetic parameters of substrate utilization and bacterial growth modeled from a completely mixed batch reactor. The ability of Pseudomonas aeruginosa can remove 91 % of the total petroleum hydrocarbons and 83 % of the aromatic compounds from oily environment. The value k of 9.31 g of substrate g(-1) of microorganism d(-1) could be far higher than the value k obtained for petrochemical wastewater treatment and that for municipal wastewater treatment. The production of new cells of using CO as the sole carbon and energy source can exceed 2(3) of the existing cells per day. The kinetic parameters are verified to contribute to improving the biological removal of CO from oily environment. PMID:26413306

  5. A Kinetic and Factorial Approach to Study the Effects of Temperature and Salinity on Growth and Toxin Production by the Dinoflagellate Alexandrium ostenfeldii from the Baltic Sea

    PubMed Central

    Salgado, Pablo; Vázquez, José A.; Riobó, Pilar; Franco, José M.; Figueroa, Rosa I.; Kremp, Anke; Bravo, Isabel

    2015-01-01

    Alexandrium ostenfeldii is present in a wide variety of environments in coastal areas worldwide and is the only dinoflagellate known species that produces paralytic shellfish poisoning (PSP) toxins and two types of cyclic imines, spirolides (SPXs) and gymnodimines (GYMs). The increasing frequency of A. ostenfeldii blooms in the Baltic Sea has been attributed to the warming water in this region. To learn more about the optimal environmental conditions favoring the proliferation of A. ostenfeldii and its complex toxicity, the effects of temperature and salinity on the kinetics of both the growth and the net toxin production of this species were examined using a factorial design and a response-surface analysis (RSA). The results showed that the growth of Baltic A. ostenfeldii occurs over a wide range of temperatures and salinities (12.5–25.5°C and 5–21, respectively), with optimal growth conditions achieved at a temperature of 25.5°C and a salinity of 11.2. Together with the finding that a salinity > 21 was the only growth-limiting factor detected for this strain, this study provides important insights into the autecology and population distribution of this species in the Baltic Sea. The presence of PSP toxins, including gonyautoxin (GTX)-3, GTX-2, and saxitoxin (STX), and GYMs (GYM-A and GYM-B/-C analogues) was detected under all temperature and salinity conditions tested and in the majority of the cases was concomitant with both the exponential growth and stationary phases of the dinoflagellate’s growth cycle. Toxin concentrations were maximal at temperatures and salinities of 20.9°C and 17 for the GYM-A analogue and > 19°C and 15 for PSP toxins, respectively. The ecological implications of the optimal conditions for growth and toxin production of A. ostenfeldii in the Baltic Sea are discussed. PMID:26636674

  6. Kinetic Analysis of Spontaneous Whisker Growth on Pre-treated Surfaces with Weak Oxide

    NASA Astrophysics Data System (ADS)

    Su, Chien-Hao; Chen, Hao; Lee, Hsin-Yi; Liu, Cheng Yi; Ku, Ching-Shun; Wu, Albert T.

    2014-09-01

    This study sought to clarify the relationship between cracks in surface oxide layers and the growth behavior of tin whiskers. The number, length, and total volume of extrusions were precisely calculated and residual stress was measured using synchrotron radiation x-ray diffractometry. The aim was to elucidate the influence of stress on the driving force and flux involved in atomic diffusion. The distance between weak spots was shown to be the most significant factor involved in the growth of whiskers. The results could explain why increasing the density of the surface weak spots could reduce the number of long whiskers. Measuring the dimensions of whiskers yielded a precise kinetic model capable of describing the migration of atoms to the root of whiskers, resulting in their spontaneous growth.

  7. Kinetics of crystal nucleation and growth in Pd(40)Ni(40)P(20) glass

    NASA Technical Reports Server (NTRS)

    Drehman, A. J.; Greer, A. L.

    1984-01-01

    Samples of Pd(40)Ni(40)P(20) glass, produced by cooling the melt at 1 or 800 K/s, are heated in a differential scanning calorimeter to determine the crystallization kinetics. Optical microscopy shows that eutectic crystallization proceeds both by growth from the surface of the samples and by the growth of spherical regions around preexisting nuclei in the interior. A modified Kissinger (1957) analysis is used to obtain the activation energy for crystal growth (3.49 eV). The steady state homogeneous nucleation frequency at 590 K is about 10 million/cu m per sec. This is estimated to be the maximum nucleation frequency: it is too low to account for the observed population of quenched-in nuclei, which are therefore presumed to be heterogeneous. The major practical obstacle to glass formation in this system is heterogeneous nucleation.

  8. Impact of sustaining a controlled residual growth on polyhydroxybutyrate yield and production kinetics in Cupriavidus necator.

    PubMed

    Grousseau, Estelle; Blanchet, Elise; Déléris, Stéphane; Albuquerque, Maria G E; Paul, Etienne; Uribelarrea, Jean-Louis

    2013-11-01

    In this study a complementary modeling and experimental approach was used to explore how growth controls the NADPH generation and availability, and the resulting impact on PHB (polyhydroxybutyrate) yields and kinetics. The results show that the anabolic demand allowed the NADPH production through the Entner-Doudoroff (ED) pathway, leading to a high maximal theoretical PHB production yield of 0.89 C mole C mole(-1); whereas without biomass production, NADPH regeneration is only possible via the isocitrate dehydrogenase leading to a theoretical yield of 0.67 C mole C mole(-1). Furthermore, the maximum specific rate of NADPH produced at maximal growth rate (to fulfil biomass requirement) was found to be the maximum set in every conditions, which by consequence determines the maximal PHB production rate. These results imply that sustaining a controlled residual growth improves the PHB specific production rate without altering production yield. PMID:24035890

  9. Effects of substrate crystallinity and dopant on the growth kinetics of platinum silicides

    NASA Astrophysics Data System (ADS)

    Takai, H.; Psaras, P. A.; Tu, K. N.

    1985-12-01

    The growth kinetics of platinum silicides have been studied on four substrate categories: single-crystal, amorphous, undoped polycrystalline, and phosphorus-doped (8×1020 at./cm3) polycrystalline silicon. The sequential growth of Pt2Si and PtSi were analyzed by Rutherford backscattering spectroscopy (RBS), Seeman-Bohlin x-ray diffraction, and cross-section transmission electron microscopy. Phosphorus depth profiles were measured by secondary ion mass spectroscopy (SIMS). Our results conclude that the activation energies for the growth of Pt2Si and PtSi are not affected by substrate crystallinity and doping of phosphorus. Analysis of the phosphorus profile by SIMS clearly showed that phosphorus atoms are segregated near the interface between PtSi and polycrystalline silicon, but not at the Pt2Si/polycrystalline silicon interface.

  10. Growth of Ni2Si by rapid thermal annealing: Kinetics and moving species

    NASA Astrophysics Data System (ADS)

    Ma, E.; Lim, B. S.; Nicolet, M.-A.; Natan, M.

    1987-10-01

    The growth kinetics is characterized and the moving species is identified for the formation of Ni2Si by Rapid Thermal Annealing (RTA) of sequentially deposited Si and Ni films on a <100> Si substrate. The interfacial Ni2Si layer grows as the square root of time, indicating that the suicide growth process is diffusion-limited. The activation energy is 1.25±0.2 eV in the RTA temperature range of 350 450° C. The results extend those of conventional steady-state furnace annealing quite fittingly, and a common activation energy of 1.3±0.2 eV is deduced from 225° to 450° C. The marker experiment shows that Ni is the dominant moving species during Ni2Si formation by RTA, as is the case for furnace annealing. It is concluded that the two annealing techniques induce the same growth mechanisms in Ni2Si formation.

  11. The importance of growth kinetic analysis in determining bacterial susceptibility against antibiotics and silver nanoparticles

    PubMed Central

    Theophel, Karsten; Schacht, Veronika J.; Schlüter, Michael; Schnell, Sylvia; Stingu, Catalina-Suzana; Schaumann, Reiner; Bunge, Michael

    2014-01-01

    Routine antibiotics susceptibility testing still relies on standardized cultivation-based analyses, including measurement of inhibition zones in conventional agar diffusion tests and endpoint turbidity-based measurements. Here, we demonstrate that common off-line monitoring and endpoint determination after 18–24 h could be insufficient for reliable growth-dependent evaluation of antibiotic susceptibility. Different minimal inhibitory concentrations were obtained in 20- and 48 h microdilution plate tests using an Enterococcus faecium clinical isolate (strain UKI-MB07) as a model organism. Hence, we used an on-line kinetic assay for simultaneous cultivation and time-resolved growth analysis in a 96-well format instead of off-line susceptibility testing. Growth of the Enterococcus test organism was delayed up to 30 h in the presence of 0.25 μg mL-1 of vancomycin and 8 μg mL-1 of fosfomycin, after which pronounced growth was observed. Despite the delayed onset of growth, treatment with fosfomycin, daptomycin, fusidic acid, cefoxitin, or gentamicin resulted in higher maximum growth rates and/or higher final optical density values compared with antibiotic-free controls, indicating that growth stimulation and hormetic effects may occur with extended exposure to sublethal antibiotic concentrations. Whereas neither maximum growth rate nor final cell density correlated with antibiotic concentration, the lag phase duration for some antibiotics was a more meaningful indicator of dose-dependent growth inhibition. Our results also reveal that non-temporal growth profiles are only of limited value for cultivation-based antimicrobial silver nanoparticle susceptibility testing. The exposure to Ag(0) nanoparticles led to plasma membrane damage in a concentration-dependent manner and induced oxidative stress in Enterococcus faecium UKI-MB07, as shown by intracellular ROS accumulation. PMID:25426104

  12. Kinetically Controlled Sequential Growth of Surface-Grafted Chiral Supramolecular Copolymers.

    PubMed

    Frisch, Hendrik; Fritz, Eva-Corinna; Stricker, Friedrich; Schmüser, Lars; Spitzer, Daniel; Weidner, Tobias; Ravoo, Bart Jan; Besenius, Pol

    2016-06-13

    We report a facile strategy to grow supramolecular copolymers on Au surfaces by successively exposing a surface-anchored monomer to solutions of oppositely charged peptide comonomers. Charge regulation on the active chain end of the polymer sufficiently slows down the kinetics of the self-assembly process to produce kinetically trapped copolymers at near-neutral pH. We thereby achieve architectural control at three levels: The β-sheet sequences direct the polymerization away from the surface, the height of the supramolecular copolymer brushes is well-controlled by the stepwise nature of the alternating copolymer growth, and 2D spatial resolution is realized by using micropatterned initiating monomers. The programmable nature of the resulting architectures renders this concept attractive for the development of customized biomaterials or chiral interfaces for optoelectronics and sensor applications. PMID:26989886

  13. Nonlinear kinetic description of Raman growth using an envelope code, and comparisons with Vlasov simulations

    NASA Astrophysics Data System (ADS)

    Bénisti, Didier; Morice, Olivier; Gremillet, Laurent; Siminos, Evangelos; Strozzi, David J.

    2010-10-01

    In this paper, we present our nonlinear kinetic modeling of stimulated Raman scattering in a uniform and collisionless plasma using envelope equations. We recall the derivation of these equations, as well as our theoretical predictions for each of the nonlinear kinetic terms, the precision of which having been carefully checked against Vlasov simulations. We particularly focus here on the numerical resolution of these equations, which requires the additional concept of "self-optimization" that we explain, and we describe the envelope code BRAMA that we used. As an application of our modeling, we present one-dimensional BRAMA simulations of stimulated Raman scattering which predict threshold intensities, as well as time scales for Raman growth above threshold, in very good agreement with those inferred from Vlasov simulations. Finally, we discuss the differences between our modeling and other published ones.

  14. Growth kinetics of CVD TiO sub 2; Influence of carrier gas

    SciTech Connect

    Siefering, K.L.; Griffin, G.L. )

    1990-04-01

    This paper reports on the growth rate of TiO{sub 2} thin films deposited by the decomposition of titanium tetraisopropoxide (TTIP) in the presence of N{sub 2} carrier gas. Experiments are performed at TTIP partial pressures between 0.005 and 0.7 torr and a substrate temperature of 573 K, conditions where second-order kinetics have previously been observed in the presence of TTIP alone. When 5 torr of N{sub 2} is present as a carrier gas, the kinetics become first order in TTIP concentration. By fitting the observed rates to the rate expression for the bimolecular reaction mechanism proposed in the earlier study, the authors obtain a value of {phi} = 0.43 for the relative efficiency of N{sub 2} for collisional energy transfer, compared to TTIP.

  15. Effects of spill-treating agents on growth kinetics of marine microalgae.

    PubMed

    Rial, Diego; Murado, Miguel A; Menduiña, Araceli; Fuciños, Pablo; González, Pilar; Mirón, Jesús; Vázquez, José A

    2013-12-15

    The effects of four spill-treating agents (STAs) (CytoSol, Finasol(®) OSR 51, Agma OSD 569 and OD4000) on the growth kinetics of three marine microalgae (Isochrysis galbana, Chaetoceros gracilis, Phaeodactylum tricornutum) were studied. Chlorophyll a concentration and optical density at 700 nm were assessed to describe the logistic growth of algae in batch cultures. The optical density data were initially analyzed as described for standard algal growth inhibition tests and subsequently modelled by a bivariate model, as a function of time and dose, to assess the toxic effects on growth parameters. Increasing trends in EC50 and EC10 values with time were found with the standard approach. In 8 of the 11 tests, the lag phase (λ) or the time required to achieve half the maximum biomass (τ) was significantly dependent on the STA concentration. A global parameter (EC50,τ) was calculated to summarize the effects of STAs on growth parameters in the bivariate model. The ranking of sensitivity as EC50,τ values was I. galbana>C. gracilis>P. tricornutum. For all species tested, the least toxic agent was Agma OSD 569, followed by CytoSol. The mathematical model allowed successful ecotoxicological evaluation of chemicals on microalgal growth. PMID:23911058

  16. Growth kinetics of a diesel-degrading bacterial strain from petroleum-contaminated soil.

    PubMed

    Dahalan, S F A; Yunus, I; Johari, W L W; Shukor, M Y; Halmi, M I E; Shamaan, N A; Syed, M A

    2014-03-01

    A diesel-degrading bacterium was isolated from a diesel-contaminated site in Selangor, Malaysia. The isolate was tentatively identified as Acinetobacter sp. strain DRY12 based on partial 16S rDNA molecular phylogeny and Biolog GN microplate panels and Microlog database. Optimum growth occurred from 3 to 5% diesel and the strain was able to tolerate as high as 8% diesel. The optimal pH that supported growth of the bacterium was between pH 7.5 to 8.0. The isolate exhibited optimal growth in between 30 and 35 degrees C. The best nitrogen source was potassium nitrate (between 0.6 and 0.9% (w/v)) followed by ammonium chloride, sodium nitrite and ammonium sulphate in descending order. An almost complete removal of diesel components was seen from the reduction in hydrocarbon peaks observed using Solid Phase Microextraction Gas Chromatography analysis after 10 days of incubation. The best growth kinetic model to fit experimental data was the Haldane model of substrate inhibiting growth with a correlation coefficient value of 0.97. The maximum growth rate- micromax was 0.039 hr(-1) while the saturation constant or half velocity constant Ks and inhibition constant Ki, were 0.387% and 4.46%, respectively. MATH assays showed that 75% of the bacterium was found in the hexadecane phase indicating that the bacterium was hydrophobic. The characteristics of this bacterium make it useful for bioremediation works in the Tropics. PMID:24665769

  17. Step-flow kinetics model for the vapor-solid-solid Si nanowires growth.

    PubMed

    Cui, H; Lü, Y Y; Yang, G W; Chen, Y M; Wang, C X

    2015-05-13

    Vapor-solid-solid (VSS) process has recently received continued attention as an alternative to grow Si nanowire. In comparison with common vapor-liquid-solid (VLS) growth with liquid catalyst, VSS growth can prevent the catalyst species from incorporating into nanowires with deep-level impurity, and achieve the compositionally abrupt interfaces by restraining the so-called "reservoir effect". However, despite the huge advances in experimental observations with in situ electron microscopy, VSS growth still remains much less understood in theory. Here, we developed a general mass-transport-limited kinetic model to describe the VSS growth process of Si nanowires by considering three surface diffusion processes and a slow interface diffusion process, where the former determines the atoms supplies way, while the latter dominates the growth of nanowires. The present model is not only well consistent with the available experimental data of Si nanowire, but also gives a clear physical image for the successive side-to-side ledge flow VSS growth. PMID:25928836

  18. Growth kinetics of physical vapor transport processes: Crystal growth of the optoelectronic material mercurous chloride

    NASA Technical Reports Server (NTRS)

    Singh, N. B.; Duval, W. M.

    1991-01-01

    Physical vapor transport processes were studied for the purpose of identifying the magnitude of convective effects on the crystal growth process. The effects of convection on crystal quality were were studied by varying the aspect ratio and those thermal conditions which ultimately affect thermal convection during physical vapor transport. An important outcome of the present study was the observation that the convection growth rate increased up to a certain value and then dropped to a constant value for high aspect ratios. This indicated that a very complex transport had occurred which could not be explained by linear stability theory. Better quality crystals grown at a low Rayleigh number confirmed that improved properties are possible in convectionless environments.

  19. The Powder-Pack Nitriding Process: Growth Kinetics of Nitride Layers on Pure Iron

    NASA Astrophysics Data System (ADS)

    Campos-Silva, I.; Ortiz-Dominguez, M.; Elias-Espinosa, M.; Vega-Morón, R. C.; Bravo-Bárcenas, D.; Figueroa-López, U.

    2015-09-01

    In this study, the growth kinetics of nitride layers that develop during the powder-pack nitriding process on the surface of ARMCO pure iron was estimated. The powder-pack nitriding of pure iron was performed according to the Pulnieren© (H.E.F. Durferrit) method using a "Pulnier" powder and an activator, at 798-848 K with different exposure times (2-12 h) for each temperature. In addition, for the entire set of nitriding conditions, three different activator/"Pulnier" powder ratios (0.20, 0.25, and 0.35) were used to evaluate the activation level during the growth of nitride layers. The kinetics of the nitride layers over the surface of ARMCO pure iron were estimated by two mathematical approaches, that consider the mass balance equations at the growth interphases. The resulting expressions for the effective diffusion coefficients in the nitride layers were evaluated as a function of nitriding temperatures and activator/"Pulnier" powder ratio. Finally, based on the experimental parameters ascribed to the powder-pack nitriding process, two expressions were proposed to estimate the nitride layer thicknesses at 798 and 823 K after 9 h of exposure for each temperature, to validate the diffusion models used in this work.

  20. [Growth kinetics and phenol degradation of highly efficient phenol-degrading Ochrobactrum sp. CH10].

    PubMed

    Chen, Xiao-Hua; Wei, Gang; Liu, Si-Yuan; Sun, Jiang-Man; Wang, Fang-Fang; Li, Hao-Yuan; Liu, Yu-Jun

    2012-11-01

    The strain Ochrobactrum sp. CH10 was a highly efficient phenol degrading bacterial strain isolated from soil in a constructed wetland in Yuan Dynasty Capital City Wall Relics in Beijing. Growth and biodegradation were investigated in details with phenol as the sole carbon and energy source. The best growth and most efficient phenol biodegradation occurred when the strain was cultured in medium containing 400 mg x L(-1) phenol at initial pH of 7.0 and 30 degrees C, with 5% inoculation volume. The phenol degradation rate was around 100% , 92.3 and 82.2% with an initial concentration of 400, 900 and 1 000 mg x L(-1) phenol in 24, 44 and 48 h, respectively. Phenol degradation kinetic studies indicated that the strain followed Haldane's model, and the parameters were: upsilon(max) (maximum specific rate) = 0.126 h(-1), K(s) (half-saturation constant) = 23.53 mg x L(-1) and K(I) (inhibition constant) = 806.1 mg x L(-1). The phenol-limited growth kinetics of CH10 by Andrews's model also followed a similar trend to that of phenol degradation. Among all the strains belonging to Ochrobactrum genus, this strain is the most efficient at present. The strain has a good application potential for the phenolic wastewater treatment. PMID:23323431

  1. The effect of Co alloying content on the kinetics of reaction zone growth in tungsten fiber reinforced superalloy composites

    NASA Technical Reports Server (NTRS)

    Rodriguez, A.; Tien, J. K.; Caulfield, T.; Petrasek, D. W.

    1988-01-01

    A Co-free modified superalloy similar in composition to Waspaloy is investigated in an effort to understand the effect of Co on reaction zone growth kinetics and verify the chemistry dependence of reaction zone growth in the matrix of tungsten fiber reinforced superalloy composites. The values of the parabolic rate constant, characterizing the kinetics of reaction zone growth, for the Waspaloy matrix and the C-free alloy as well as five other alloys from a previous study confirm the dependence of reaction zone growth kinetics on cobalt content of the matrix. The Co-free alloy composite exhibits the slowest reaction zone growth among all tungsten fiber reinforced composites studied to date.

  2. Polymorph-specific kinetics and thermodynamics of β-amyloid fibril growth

    PubMed Central

    Qiang, Wei; Kelley, Kevin; Tycko, Robert

    2013-01-01

    Amyloid fibrils formed by the 40-residue β-amyloid peptide (Aβ1–40) are highly polymorphic, with molecular structures that depend on the details of growth conditions. Underlying differences in physical properties are not well understood. Here, we investigate differences in growth kinetics and thermodynamic stabilities of two Aβ1–40 fibril polymorphs for which detailed structural models are available from solid state nuclear magnetic resonance (NMR) studies. Rates of seeded fibril elongation in the presence of excess soluble Aβ1–40 and shrinkage in the absence of soluble Aβ1–40 are determined with atomic force microscopy (AFM). From these rates, we derive polymorph-specific values for the soluble Aβ1–40 concentration at quasi-equilibrium, from which relative stabilities can be derived. The AFM results are supported by direct measurements by ultraviolet absorbance, using a novel dialysis system to establish quasi-equilibrium. At 24° C, the two polymorphs have significantly different elongation and shrinkage kinetics but similar thermodynamic stabilities. At 37° C, differences in kinetics are reduced, and thermodynamic stabilities are increased significantly. Fibril length distributions in AFM images provide support for an intermittent growth model, in which fibrils switch randomly between an "on" state (capable of elongation) and an "off" state (incapable of elongation). We also monitor interconversion between polymorphs at 24° C by solid state NMR, showing that the two-fold symmetric "agitated" () polymorph is more stable than the three-fold symmetric "quiescent" polymorph. Finally, we show that the two polymorphs have significantly different rates of fragmentation in the presence of shear forces, a difference that helps explain the observed predominance of the structure when fibrils are grown in agitated solutions. PMID:23627695

  3. Kinetics of phase growth in Nb3Sn formation for heat treatment optimization

    SciTech Connect

    Emanuela Barzi; Sara Mattafirri

    2002-10-25

    The kinetics of growth and superconducting properties of Nb{sub 3}Sn are investigated as a function of the heat treatment (HT) duration and temperature for Internal Tin and Powder-in-Tube strands at 650, 700 and 750 C. For all times and temperatures, the Nb{sub 3}Sn layer thickness is measured, the critical current at 4.2 K is tested as a function of magnetic field, and the upper critical field is evaluated. Results of the layer critical current density are also shown as a function of HT duration and temperature.

  4. Exponentiated power Lindley distribution.

    PubMed

    Ashour, Samir K; Eltehiwy, Mahmoud A

    2015-11-01

    A new generalization of the Lindley distribution is recently proposed by Ghitany et al. [1], called as the power Lindley distribution. Another generalization of the Lindley distribution was introduced by Nadarajah et al. [2], named as the generalized Lindley distribution. This paper proposes a more generalization of the Lindley distribution which generalizes the two. We refer to this new generalization as the exponentiated power Lindley distribution. The new distribution is important since it contains as special sub-models some widely well-known distributions in addition to the above two models, such as the Lindley distribution among many others. It also provides more flexibility to analyze complex real data sets. We study some statistical properties for the new distribution. We discuss maximum likelihood estimation of the distribution parameters. Least square estimation is used to evaluate the parameters. Three algorithms are proposed for generating random data from the proposed distribution. An application of the model to a real data set is analyzed using the new distribution, which shows that the exponentiated power Lindley distribution can be used quite effectively in analyzing real lifetime data. PMID:26644927

  5. Exponentiated power Lindley distribution

    PubMed Central

    Ashour, Samir K.; Eltehiwy, Mahmoud A.

    2014-01-01

    A new generalization of the Lindley distribution is recently proposed by Ghitany et al. [1], called as the power Lindley distribution. Another generalization of the Lindley distribution was introduced by Nadarajah et al. [2], named as the generalized Lindley distribution. This paper proposes a more generalization of the Lindley distribution which generalizes the two. We refer to this new generalization as the exponentiated power Lindley distribution. The new distribution is important since it contains as special sub-models some widely well-known distributions in addition to the above two models, such as the Lindley distribution among many others. It also provides more flexibility to analyze complex real data sets. We study some statistical properties for the new distribution. We discuss maximum likelihood estimation of the distribution parameters. Least square estimation is used to evaluate the parameters. Three algorithms are proposed for generating random data from the proposed distribution. An application of the model to a real data set is analyzed using the new distribution, which shows that the exponentiated power Lindley distribution can be used quite effectively in analyzing real lifetime data. PMID:26644927

  6. Comparison of the growth kinetics and proteolytic activities of Chryseobacterium species and Pseudomonas fluorescens.

    PubMed

    Bekker, A; Steyn, L; Charimba, G; Jooste, P; Hugo, C

    2015-12-01

    The effect of temperature on the growth kinetics and proteolytic activity of Chryseobacterium joostei and Chryseobacterium bovis was determined during this study. The results were compared with the activities of Pseudomonas fluorescens, which is regarded to be a major food spoilage psychrotolerant microorganism. For the growth studies, cultures were incubated in nutrient broth in a temperature gradient incubator (from 9 to 50 °C) and separately at 4 °C, and the optical density was measured at different time intervals. Growth temperature profiles for each organism were constructed. For determination of proteolytic activity, the cultures were incubated in fat-free ultra-high temperature processed milk in the temperature gradient incubator for 72 h (temperature range as above). Cell-free extracts were used to determine the proteolytic activity using the azocasein method. Results of the growth studies showed that C. joostei had the ability to grow over a wider temperature range than C. bovis and P. fluorescens without being affected by changes in the temperature. For the proteolytic activity, C. joostei had significantly (p < 0.001) higher activity per milligram of protein at 15.5 °C, followed by C. bovis and P. fluorescens. The results showed that C. joostei potentially has an even greater spoilage capacity in milk on the basis of growth rate and proteolytic activity than did P. fluorescens. PMID:26451905

  7. Alginate Sulfates Mitigate Binding Kinetics of Proangiogenic Growth Factors with Receptors toward Revascularization.

    PubMed

    Schmidt, John; Lee, Min Kyung; Ko, Eunkyung; Jeong, Jae Hyun; DiPietro, Luisa A; Kong, Hyunjoon

    2016-07-01

    Ever since proangiogenic growth factors have been used as a vascular medicine to treat tissue ischemia, efforts have been increasingly made to develop a method to enhance efficacy of growth factors in recreating microvascular networks, especially at low dose. To this end, we hypothesized that polysaccharides substituted with sulfate groups would amplify growth factor receptor activation and stimulate phenotypic activities of endothelial cells involved in neovascularization. We examined this hypothesis by modifying alginate with a controlled number of sulfates and using it to derive a complex with vascular endothelial growth factor (VEGF), as confirmed with fluorescence resonance energy transfer (FRET) assay. Compared with the bare VEGF and with a mixture of VEGF and unmodified alginates, the VEGF complexed with alginate sulfates significantly reduced the dissociation rate with the VEGFR-2, elevated VEGFR-2 phosphorylation level, and increased the number of endothelial sprouts in vitro. Furthermore, the VEGF-alginate sulfate complex improved recovery of perfusion in an ischemic hindlimb of a mouse due to the increase of the capillary density. Overall, this study not only demonstrates an important cofactor of VEGF but also uncovers an underlying mechanism by which the cofactor mitigates the VEGF-induced signaling involved in the binding kinetics and activation of VEGFR. We therefore believe that the results of this study will be highly useful in improving the therapeutic efficacy of various growth factors and expediting their uses in clinical treatments of wounds and tissue defects. PMID:26881299

  8. Kinetics of Bacillus thuringiensis var. israelensis growth on high glucose concentrations.

    PubMed

    Berbert-Molina, M A; Prata, A M R; Pessanha, L G; Silveira, M M

    2008-11-01

    The kinetic and general growth features of Bacillus thuringiensis var. israelensis were evaluated. Initial glucose concentration (S0) in fermentation media varied from 10 to 152 g/l. The results afforded to characterize four morphologically and physiologically well-defined culture phases, independent of S0 values: Phase I, vegetative growth; Phase II, transition to sporulation; Phase III, sporulation; and Phase IV, spores maturation and cell lysis. Important process parameters were also determined. The maximum specific growth rates (microX,m) were not affected with S0 up to 75 g/l (1.0-1.1 per hour), but higher glucose concentrations resulted in growth inhibition by substrate, revealed by a reduction in microX,m values. These higher S0 values led to longer Phases III and IV and delayed sporulation. Similar biomass concentrations (Xm=15.2-15.9 g/l) were achieved with S0 over 30.8 g/l, with increasing residual substrate, suggesting a limitation in some other nutrients and the use of glucose to form other metabolites. In this case, with S0 from 30.8 to 152 g/l, cell yield (YX/S) decreased from 0.58 to 0.41 g/g. On the other hand, with S0=10 g/l growth was limited by substrate, and YX/S has shown its maximum value (0.83 g/g). PMID:18712542

  9. Flux-Dependent Growth Kinetics and Diameter Selectivity in Single-Wall Carbon Nanotube Arrays

    SciTech Connect

    Geohegan, David B; Puretzky, Alexander A; Jackson, Jeremy Joseph; Rouleau, Christopher M; Eres, Gyula; More, Karren Leslie

    2011-01-01

    The nucleation and growth kinetics of single-wall carbon nanotubes in aligned arrays have been measured using fast pulses of acetylene and in situ optical diagnostics in conjunction with low pressure chemical vapor deposition (CVD). Increasing the acetylene partial pressure is shown to decrease nucleation times by three orders of magnitude, permitting aligned nanotube arrays to nucleate and grow to microns lengths within single gas pulses at high (up to 7 micron/s) peak growth rates and short ~ 0.5 s times.Low-frequency Raman scattering (> 10 cm-1) and transmission electron microscopy measurements show that increasing the feedstock flux in both continuous-CVD and pulsed-CVD shifts the product distribution to large single-wall carbon nanotube diameters > 2.5 nm. Sufficiently high acetylene partial pressures in pulsed-CVD appear to temporarily terminate the growth of the fastest- growing, small-diameter nanotubes by overcoating the more catalytically-active, smaller catalyst nanoparticles within the ensemble with non-nanotube carbon in agreement with a growth model. The results indicate that subsets of catalyst nanoparticle ensembles nucleate, grow, and terminate growth within different flux ranges according to their catalytic activity.

  10. An identification algorithm of model kinetic parameters of the interfacial layer growth in fiber composites

    NASA Astrophysics Data System (ADS)

    Zubov, V.; Lurie, S.; Solyaev, Y.

    2016-04-01

    This paper considers the identification algorithm of parameters included in a parabolic law that is often used to predict the time dependence of the thickness of the interfacial layers in the structure of composite materials based on a metal matrix. The incubation period of the process and the speed of reaction and pressure are taken into account. The proposed algorithm of identification is based on the introduction of a minimized objective function of a special kind. The problem of identification of unknown parameters in the parabolic law is formulated in a variational form. The authors of the paper have determined the desired parameters, under which the objective function has a minimum value. It is shown that on the basis of four known experimental values of the interfacial layer thickness, corresponding to different values of temperature, pressure and the time of the interfacial layer growth, it is possible to identified four model parameters. They are the activation energy, a pre-exponential parameter, the delay time of the start of the interfacial layer formation, and the parameter determining the pressure effect on the rate of interfacial layer growth. The stability of the proposed identification algorithm is also studied.

  11. Kinetics and mechanisms of crystal growth inhibition of indomethacin by model precipitation inhibitors

    NASA Astrophysics Data System (ADS)

    Patel, Dhaval

    Supersaturating Drug Delivery Systems (SDDS) could enhance oral bioavailability of poorly water soluble drugs (PWSD). Precipitation inhibitors (PIs) in SDDS could maintain supersaturation by inhibiting nucleation, crystal growth, or both. The mechanisms by which these effects are realized are generally unknown. The goal of this dissertation was to explore the mechanisms underpinning the effects of model PIs including hydroxypropyl beta-cyclodextrins (HP-beta-CD), hydroxypropyl methylcellulose (HPMC), and polyvinylpyrrolidone (PVP) on the crystal growth of indomethacin, a model PWSD. At high degrees of supersaturation (S), the crystal growth kinetics of indomethacin was bulk diffusion-controlled, which was attributed to a high energy form deposited on the seed crystals. At lower S, indomethacin growth kinetics was surface integration-controlled. The effect of HP-beta-CD at high S was successfully modeled using the reactive diffusion layer theory. The superior effects of PVP and HPMC as compared to HP-beta-CD at high S were attributed to a change in the rate limiting step from bulk diffusion to surface integration largely due to prevention of the high energy form formation. The effects of PIs at low S were attributed to significant retardation of the surface integration rate, a phenomenon that may reflect the adsorption of PIs onto the growing surface. PVP was selected to further understand the relationship between adsorption and crystal growth inhibition. The Langmuir adsorption isotherm model fit the adsorption isotherms of PVP and N-vinylpyrrolidone well. The affinity and extent of adsorption of PVP were significantly higher than those of N-vinylpyrrolidone, which was attributed to cooperative interactions between PVP and indomethacin. The extent of PVP adsorption on a weight-basis was greater for higher molecular weight PVP but less on a molar-basis indicating an increased percentage of loops and tails for higher molecular weight PVPs. PVP significantly inhibited

  12. [Kinetic patterns in the growth of transplantable mouse tumor RShM-1].

    PubMed

    Svinogeeva, T P; Konopliannikov, A G; Shtein, L V

    1976-01-01

    Under study was the kinetics of growth of cervical cancer (CCM-1) transplanted on mice CBA, also the mitotic cycle and diurnal activity of tumor cells division. The tumor growth can well be described with the Hompertz equation, the constants of acceleration and retardation being equal to 0.34 day-1 and 0.004 day-1 accordingly. A linear dependence between the size, weight and number of CCM-1 celos is shown. In the tumor under study a persistant diurnal rhythm of the cell division was found with the maximum at 7 and 19 hours and the minimum at 13. The basis parameters of the mitotic cycle of tumor cells were determined: Tc=17.8 hr., G2 approximately 40 min.; S=9 hr., M approximately 24 min., G1 approximately 18.4 hr. The time of tumor doubling was 48.7 hr. The cell loss factor is as much as 42.1 per cent. PMID:1034368

  13. Experimental Studies of the Growth Kinetics of Methane Clathrate Hydrates & Superfluid Hydrodynamics on the Nanoscale

    NASA Astrophysics Data System (ADS)

    Botimer, Jeffrey David

    This thesis details the experimental findings of three distinct research projects. The first studies the growth kinetics of methane clathrate hydrates grown under the influence of multiple factors including surfactants, porous media, substrate wetting properties, and salt content. The second investigates the flow behaviors of superfluid helium through single, high aspect ratio nanopipes. The third models the frequency response of a quartz tuning fork in high pressure normal and superfluid helium and demonstrates how quartz tuning forks can be used as cheap, small, in situ, cryogenic pressure gauges. The first project reports studies of the kinetics of growth of methane hydrates from liquid water containing small amounts of surfactant (<500 ppm of sodium dodecyl sulfate, SDS). The kinetics are monitored using simultaneous measurements of the uptake of methane detected by a pressure drop in the gas phase, and either visual observations of the amount of liquid water and solid phase in the reaction vessel, or in situ micro-Raman measurements or in situ NMR measurements. These diagnostics show that the uptake of methane and the conversion of liquid water to a solid phase do not occur simultaneously; the uptake of gas always lags the visual and spectroscopic signatures of the disappearance of liquid water and the formation of solid. The evidence suggests that the SDS causes water to form an intermediate immobile solid-like state before combining with the methane to form hydrate. The growth mechanism is related to the surfactant and disappears for low SDS concentrations (<25 ppm). Also reported are studies of the growth rates of methane hydrates as a function of substrate wetting properties, driving force, and growth media. The second project studies pressure driven flow of superfluid helium through single high aspect ratio glass nanopipes into a vacuum has been studied for a wide range of pressure drop (0--30 atm), reservoir temperature (0.8--2.5K), pipe lengths (1-30mm

  14. Direct dynamic kinetic analysis and computer simulation of growth of Clostridium perfringens in cooked turkey during cooling

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This research applied a new one-step methodology to directly construct a tertiary model for describing the growth of C. perfringens in cooked turkey meat under dynamically cooling conditions. The kinetic parameters of the growth models were determined by numerical analysis and optimization using mu...

  15. Shape transition of endotaxial islands growth from kinetically constrained to equilibrium regimes

    SciTech Connect

    Li, Zhi-Peng; Tok, Engsoon; Foo, Yonglim

    2013-09-01

    Graphical abstract: - Highlights: • All Fe{sub 13}Ge{sub 8} islands will grow into Ge(0 0 1) substrate at temperatures from 350 to 675 °C. • Shape transition occurred from kinetically constrained to equilibrium regime. • All endotaxial islands can be clarified into two types. • The mechanisms of endotaxial growth and shape transition have been rationalized. - Abstract: A comprehensive study of Fe grown on Ge(0 0 1) substrates has been conducted at elevated temperatures, ranging from 350 to 675 °C. All iron germinide islands, with the same Fe{sub 13}Ge{sub 8} phase, grow into the Ge substrate with the same epitaxial relationship. Shape transition occurs from small square islands (low temperatures), to elongated orthogonal islands or orthogonal nanowires (intermediate temperatures), and then finally to large square orthogonal islands (high temperatures). According to both transmission electron microscopy (TEM) and atomic force microscopy (AFM) investigations, all islands can be defined as either type-I or type-II. Type-I islands usually form at kinetically constrained growth regimes, like truncated pyramids. Type-II islands usually appear at equilibrium growth regimes forming a dome-like shape. Based on a simple semi-quantitative model, type-II islands have a lower total energy per volume than type-I, which is considered as the dominant mechanism for this type of shape transition. Moreover, this study not only elucidates details of endotaxial growth in the Fe–Ge system, but also suggests the possibility of controlled fabrication of temperature-dependent nanostructures, especially in materials with dissimilar crystal structures.

  16. Effects of Kinetic Roughening and Liquid-Liquid Phase Transition on Lysozyme Crystal Growth Velocities

    NASA Technical Reports Server (NTRS)

    Gorti, Sridhar; Konnert, John; Forsythe, Elizabeth L.; Pusey, Marc L.

    2004-01-01

    We measured the growth velocities of the (110) face of tetragonal lysozyme, V (centimeters per second), at four different concentrations, c (milligrams per milliliter), as the solution temperature, T (Centigrade), was reduced. For a broad range of T dependent on c, we find that the growth velocities increased as the solution temperature was reduced. The initial increase in V is well characterized by the 2D nucleation model for crystal growth, yielding the magnitude of an effective barrier for growth, gamma(sub s) = 1.2 plus or minus 0.1 x 10(exp -13) erg/molecule. Below certain temperatures, T(sub cr), dependent on c, however, a kinetic roughening hypothesis that considers the continuous addition of molecules anywhere on the crystal surface better describes the observed growth velocities. The application of the continuous growth model, up to the solution cloud-point temperatures, T(sub cl), enabled the determinations of the crossover concentration, c(sub r), from estimated values of T(sub cr). For all conditions presented, we find that the crossover from growth by 2D nucleation to continuous addition occurs at a supersaturation, sigma (sub c), = 2.0 plus or minus 0.1. Moreover, we find the energy barrier for the continuous addition, E(sub c), within the temperature range T(sub cl) less than T less than T less than T (sub cr), to be 6 plus or minus 1 x 10(exp -13) erg/molecule. Further reduction of T below approximately 2-3 C of T(sub cl), also revealed a rapid slowing of crystal growth velocities. From quasi-elastic light scattering investigations, we find that the rapid diminishment of crystal growth velocities can be accounted for by the phase behavior of lysozyme solutions. Namely, we find the reversible formation of dense fluid proto-droplets comprised of lysozyme molecules to occur below approximately 0.3 C of T(sub cl). Hence, the rapid slowing of growth velocities may occur as a result of the sudden depletion of "mobile" molecules within crystal growth

  17. Confined growth of poly(butylene succinate) in its miscible blends with poly(vinylidene fluoride): morphology and growth kinetics.

    PubMed

    Wang, Tianchang; Li, Huihui; Wang, Feng; Yan, Shouke; Schultz, Jerold M

    2011-06-23

    The morphology and confined crystallization behavior of poly(butylene succinate) (PBS) in miscible poly(vinylidene fluoride) (PVDF)/PBS blends has been studied using differential scanning calorimetry (DSC) and optical and atomic force microscopy (OM and AFM). It was found that PBS crystal lamellae nucleated and grew confined inside the matrix of PVDF spherulites. Crystallized PBS domains grow with an ellipsoidal outline within PVDF spherulites formed at a relatively high PVDF crystallization temperature (T(c,PVDF)), while circular domains, engulfing several PVDF spherulites, are seen when growing in the PVDF spherulites created at lower T(c,PVDF). The growth kinetics of PBS confined in the PVDF matrix was investigated under various conditions. The growth rate of PBS (G(PBS)) increases with decreasing crystallization temperature and increasing PBS content under a given PVDF crystallization temperature (T(c,VDF)). For T(c,PVDF) above 145 °C, G(PBS) decreases with T(c,PVDF) for both 50:50 and 30:70 PVDF/PBS blends. However, for T(c,PVDF) below 145 °C, 50:50 and 30:70 PVDF/PBS blends exhibit the opposite G(PBS) trend; that is, G(PBS) for the 50:50 blend decreases with decreasing T(c,PVDF), while for the 30:70 PVDF/PBS blend G(PBS) increases with decreasing T(c,PVDF). It is shown that this behavior cannot be associated with the effect of crossing the boundary of smaller PVDF spherulites formed at a lower temperature. Rather, the behavior appears to be related to the interleaving growth of PBS lamellae among PVDF lamellae or between bundles of PVDF lamellae (fibrils), as in situ AFM observation shows. It is found that the interconnectedness of the molten pockets within the PVDF spherulites, which depends on the PVDF crystallization temperature, is an important factor determining the growth kinetics of PBS confined within the PVDF scaffold. PMID:21595485

  18. Process development for hydrogen production with Chlamydomonas reinhardtii based on growth and product formation kinetics.

    PubMed

    Lehr, Florian; Morweiser, Michael; Rosello Sastre, Rosa; Kruse, Olaf; Posten, Clemens

    2012-11-30

    Certain strains of microalgae are long known to produce hydrogen under anaerobic conditions. In Chlamydomonas reinhardtii the oxygen-sensitive hydrogenase enzyme recombines electrons from the chloroplast electron transport chain with protons to form molecular hydrogen directly inside the chloroplast. A sustained hydrogen production can be obtained under low sulfur conditions in C. reinhardtii, reducing the net oxygen evolution by reducing the photosystem II activity and thereby overcoming the inhibition of the hydrogenases. The development of specially adapted hydrogen production strains led to higher yields and optimized biological process preconditions. So far sustainable hydrogen production required a complete exchange of the growth medium to establish sulfur-deprived conditions after biomass growth. In this work we demonstrate the transition from the biomass growth phase to the hydrogen production phase in a single batch culture only by exact dosage of sulfur. This eliminates the elaborate and energy intensive solid-liquid separation step and establishes a process strategy to proceed further versus large scale production. This strategy has been applied to determine light dependent biomass growth and hydrogen production kinetics to assess the potential of H₂ production with C. reinhardtii as a basis for scale up and further process optimization. PMID:22750091

  19. Cell growth kinetics of Chlorella sorokiniana and nutritional values of its biomass.

    PubMed

    Kumar, Kanhaiya; Dasgupta, Chitralekha Nag; Das, Debabrata

    2014-09-01

    The present study investigates the effects of different physico-chemical parameters for the growth of Chlorella sorokiniana and subsequently determination of nutritional values of its biomass. Most suitable temperature, light intensity, pH, and acetic acid concentration were 30°C, 100 μmol m(-2)s(-1), pH 7.5, and 34.8mM, respectively for the growth of this microorganism. Arrhenius growth activation energy, Ea was calculated as 7.08 kJ mol(-1). Monod kinetics constants: maximum specific growth rate (μ max) and substrate (acetic acid) affinity coefficient (Ks) were determined as 0.1 ± 0.01 h(-1) and 76 ± 8 mg L(-1), respectively. Stoichiometric analysis revealed the capture of 1.83 g CO2 and release of 1.9 g O2 for 1g algal biomass synthesis. Algal biomass of C. sorokiniana was found rich in protein and several important minerals such as Mg, Ca, and Fe. Astaxanthin and β-carotene were extracted and quantified using high performance liquid chromatography. PMID:24997380

  20. Three-dimensional kinetic Monte Carlo simulations of cubic transition metal nitride thin film growth

    NASA Astrophysics Data System (ADS)

    Nita, F.; Mastail, C.; Abadias, G.

    2016-02-01

    A three-dimensional kinetic Monte Carlo (KMC) model has been developed and used to simulate the microstructure and growth morphology of cubic transition metal nitride (TMN) thin films deposited by reactive magnetron sputtering. Results are presented for the case of stoichiometric TiN, chosen as a representative TMN prototype. The model is based on a NaCl-type rigid lattice and includes deposition and diffusion events for both N and Ti species. It is capable of reproducing voids and overhangs, as well as surface faceting. Simulations were carried out assuming a uniform flux of incoming particles approaching the surface at normal incidence. The ballistic deposition model is parametrized with an interaction parameter r0 that mimics the capture distance at which incoming particles may stick on the surface, equivalently to a surface trapping mechanism. Two diffusion models are implemented, based on the different ways to compute the site-dependent activation energy for hopping atoms. The influence of temperature (300-500 K), deposition flux (0.1-100 monolayers/s), and interaction parameter r0 (1.5-6.0 Å) on the obtained growth morphology are presented. Microstructures ranging from highly porous, [001]-oriented straight columns with smooth top surface to rough columns emerging with different crystallographic facets are reproduced, depending on kinetic restrictions, deposited energy (seemingly captured by r0), and shadowing effect. The development of facets is a direct consequence of the diffusion model which includes an intrinsic (minimum energy-based) diffusion anisotropy, although no crystallographic diffusion anisotropy was explicitly taken into account at this stage. The time-dependent morphological evolution is analyzed quantitatively to extract the growth exponent β and roughness exponent α , as indicators of kinetic roughening behavior. For dense TiN films, values of α ≈0.7 and β =0.24 are obtained in good agreement with existing experimental data. At this

  1. Revealing the surface and bulk regimes of isothermal graphene growth on Ni with in situ kinetic measurements and modeling

    SciTech Connect

    Puretzky, Alexander A; Merkulov, Igor A; Rouleau, Christopher M; Eres, Gyula; Geohegan, David B

    2014-01-01

    In situ optical diagnostics are used to reveal the isothermal nucleation and growth mechanisms of graphene on Ni across a wide temperature range (560 C < T < 840 C) by chemical vapor deposition from single, sub-second pulses of acetylene. An abrupt, two-orders of magnitude change in growth times (~ 100s to 1s) is revealed at T = 680 C. Below and above this temperature, similar sigmoidal kinetics are measured and attributed to autocatalytic growth reactions but by two different mechanisms, surface assembly and dissolution/precipitation, respectively. These data are used to develop a simple and general kinetic model for graphene growth that includes the nucleation phase and includes the effects of carbon solubility in metals, describes delayed nucleation, and allows the interpretation of the competition between surface and bulk growth modes. The sharp transition in growth kinetics at T = 680 C is explained by a change in defect site density required for nucleation due to a transition in the carbon-induced mobility of the Ni surface. The easily-implemented optical reflectivity diagnostics and the simple kinetic model described here allow a pathway to optimize the growth of graphene on metals with arbitrary carbon solubility.

  2. Kinetics-controlled growth of bimetallic RhAg on Au nanorods and their catalytic properties

    NASA Astrophysics Data System (ADS)

    Ye, Wei; Guo, Xia; Xie, Fang; Zhu, Rui; Zhao, Qing; Yang, Jian

    2014-03-01

    Controlled growth of hybrid metallic nanocomposites for a desirable structure in a combination of selected components is highly important for their applications. Herein, the controllable growth of RhAg on the gold nanorods is achieved from the dumbbell-like RhAg-tipped nanorods to the brushy RhAg-coated nanorods, or the rod-like Au@Ag-Rh nanorattles. These different growth modes of RhAg on the gold nanorods are correlated with the reducing kinetics of RhCl3 and AgNO3. In view of the promising catalytic properties of Rh, the gold nanorods modified by RhAg in different structures are examined as catalysts for the oxidation of o-phenylenediamine. It is found that brushy RhAg-coated nanorods present a higher catalytic efficiency than dumbbell-like RhAg-tipped nanorods and rod-like Au@Ag-Rh nanorattles. These results would benefit the overgrowth control on the one-dimensional metallic nanorods and the rational design of new generation heterogeneous catalysts and optical devices.Controlled growth of hybrid metallic nanocomposites for a desirable structure in a combination of selected components is highly important for their applications. Herein, the controllable growth of RhAg on the gold nanorods is achieved from the dumbbell-like RhAg-tipped nanorods to the brushy RhAg-coated nanorods, or the rod-like Au@Ag-Rh nanorattles. These different growth modes of RhAg on the gold nanorods are correlated with the reducing kinetics of RhCl3 and AgNO3. In view of the promising catalytic properties of Rh, the gold nanorods modified by RhAg in different structures are examined as catalysts for the oxidation of o-phenylenediamine. It is found that brushy RhAg-coated nanorods present a higher catalytic efficiency than dumbbell-like RhAg-tipped nanorods and rod-like Au@Ag-Rh nanorattles. These results would benefit the overgrowth control on the one-dimensional metallic nanorods and the rational design of new generation heterogeneous catalysts and optical devices. Electronic

  3. Suppression in droplet growth kinetics by the addition of organics to sulfate particles

    NASA Astrophysics Data System (ADS)

    Wong, Jenny P. S.; Liggio, John; Li, Shao-Meng; Nenes, Athanasios; Abbatt, Jonathan P. D.

    2014-11-01

    Aerosol-cloud interactions are affected by the rate at which water vapor condenses onto particles during cloud droplet growth. Changes in droplet growth rates can impact cloud droplet number and size distribution. The current study investigated droplet growth kinetics of acidic and neutral sulfate particles which contained various amounts and types of organic compounds, from model compounds (carbonyls) to complex mixtures (α-pinene secondary organic aerosol and diesel engine exhaust). In most cases, the formed droplet size distributions were shifted to smaller sizes relative to control experiments (pure sulfate particles), due to suppression in droplet growth rates in the cloud condensation nuclei counter. The shift to smaller droplets correlated with increasing amounts of organic material, with the largest effect observed for acidic seed particles at low relative humidity. For all organics incorporated onto acidic particles, formation of high molecular weight compounds was observed, probably by acid-catalyzed Aldol condensation reactions in the case of carbonyls. To test the reversibility of this process, carbonyl experiments were conducted with acidic particles exposed to higher relative humidity. High molecular weight compounds were not measured in this case and no shift in droplet sizes was observed, suggesting that high molecular weight compounds are the species affecting the rate of water uptake. While these results provide laboratory evidence that organic compounds can slow droplet growth rates, the modeled mass accommodation coefficient of water on these particles (α > 0.1) indicates that this effect is unlikely to significantly affect cloud properties, consistent with infrequent field observations of slower droplet growth rates.

  4. [The kinetic characteristics of mycelium growth of medicinal mushroom Ganoderma sinense in liquid-submerged cultivation].

    PubMed

    Gong, Jianhua; Wang, Yijun

    2002-02-01

    The study was carried out to investigate the kinetic characteristics of Ganoderma sinense mycelium growth in liquid-submerged cultivation, using a air-lift bioreactor ALR/ff specially designed for the cultivation of mushrooms' suspending mycelia cultures. Mycelia of G. sinense grew in the range of 25 degrees C-35 degrees C, and at the different temperature in which the specific growth rate showed by the mycelia much differed. The specific growth rates with the maximum of 0.0444(h-1) at 1.64 vvm of aeration in the cultivation were more than at 0.93 vvm, also more than at 2.50 vvm. In comparison with the less glucose concentration, the culture of 2.80 g glucose/100 mL in the medium had a shorter lag-period, and the more concentration of glucose favoured mycelia growth in the latter cultivation course with the denser pellets of mycelia. Then the culture of the less concentration of glucose in the medium had the higher conversion-rates of glucose to G. sinense biomass all along the cultivation course, than of the more concentration of glucose. Futhermore, in the continuous cultivations with growth-limiting substrate of carbon source the mycelia displaying different growing activities, demonstrated the varied forms of mycelium-gathering. In that cases the relationships among mycelia biomass, growth-limiting substrate and productivity of mycelium biomass obviously differed from the ones in the case of bacteria. Also in the range of dilution rates 0.010-0.220 (h-1) the growing of G. sinense mycelia followed the function of Contois equation. PMID:12557355

  5. Prognostic markers and tumour growth kinetics in melanoma patients progressing on vemurafenib.

    PubMed

    Seifert, Heike; Fisher, Rosalie; Martin-Liberal, Juan; Edmonds, Kim; Hughes, Peta; Khabra, Komel; Gore, Martin; Larkin, James

    2016-04-01

    The BRAF inhibitor vemurafenib is an effective drug in patients with BRAF mutant metastatic melanoma, but resistance occurs after a median of 6 months. The anti-CTLA4-antibody, ipilimumab, is a standard first-line and second-line treatment option in Europe, with a median time to response of 2-3 months, but some patients show rapid clinical deterioration before that. The aim of this analysis was to identify prognostic markers for survival after failure of vemurafenib treatment to identify patients who have a sufficient life expectancy to respond to new immunotherapy treatments. We retrospectively analysed 101 consecutive unselected patients treated with vemurafenib for metastatic melanoma at a single institution. The association between clinical parameters and death within 3 months after cessation of vemurafenib (n=69) was assessed by binary logistic and Cox regression. Of the patients, 45% died within 3 months of progression on vemurafenib. Elevated baseline serum lactate dehydrogenase, absence of normalization of serum lactate dehydrogenase on vemurafenib therapy, performance status of at least 2 at progression and time from primary tumour to metastatic disease less than 5 years were identified as poor prognostic markers. In an exploratory tumour growth kinetics analysis (n=16), we found that following cessation of vemurafenib, approximately a third each showed a stable, decelerated or accelerated rate of tumour growth. Patients with these poor prognostic markers are unlikely to have sufficient life expectancy to complete ipilimumab treatment after failure with vemurafenib. Consideration needs to be given to the elective use of immunotherapy before patients become resistant to vemurafenib. This requires prospective randomized evaluation. Our tumour growth kinetics analysis requires confirmation; however, it may suggest that intermittent vemurafenib treatment should be investigated in clinical trials. PMID:26684061

  6. The petroleum exponential (again)

    NASA Astrophysics Data System (ADS)

    Bell, Peter M.

    The U.S. production and reserves of liquid and gaseous petroleum have declined since 1960, at least in the lower 48 states. This decline stems from decreased discovery rates, as predicted by M. King Hubbert in the mid-1950's. Hubbert's once unpopular views were based on statistical analysis of the production history of the petroleum industry, and now, even with inclusion of the statistical perturbation caused by the Prudhoe Bay-North Alaskan Slope discovery (the largest oil field ever found in the United States), it seems clear again that production is following the exponential curve to depletion of the resource—to the end of the ultimate yield of petroleum from wells in the United States.In a recent report, C. Hall and C. Cleveland of Cornell University show that large atypical discoveries, such as the Prudhoe Bay find, are but minor influences on what now appears to be the crucial intersection of two exponentials [Science, 211, 576-579, 1981]: the production-per-drilled-foot curve of Hubbert, which crosses zero production no later than the year 2005; the other, a curve that plots the energy cost of drilling and extraction with time; that is, the cost-time rate of how much oil is used to drill and extract oil from the ground. The intersection, if no other discoveries the size of the Prudhoe Bay field are made, could be as early as 1990, the end of the present decade. The inclusion of each Prudhoe-Bay-size find extends the year of intersection by only about 6 years. Beyond that point, more than one barrel of petroleum would be expended for each barrel extracted from the ground. The oil exploration-extraction and refining industry is currently the second most energy-intensive industry in the U.S., and the message seems clear. Either more efficient drilling and production techniques are discovered, or domestic production will cease well before the end of this century if the Hubbert analysis modified by Hall and Cleveland is correct.

  7. The Influence of Kinetic Growth Factors on the Clumped Isotope Composition of Calcite

    NASA Astrophysics Data System (ADS)

    Hunt, J. D.; Watkins, J. M.; Tripati, A.; Ryerson, F. J.; DePaolo, D. J.

    2014-12-01

    Clumped isotope paleothermometry is based on the association of 13C and 18O within carbonate minerals. Although the influence of temperature on equilibrium 13C-18O bond ordering has been studied, recent oxygen isotope studies of inorganic calcite demonstrate that calcite grown in laboratory experiments and in many natural settings does not form in equilibrium with water. It is therefore likely that the carbon and clumped isotope composition of these calcite crystals are not representative of true thermodynamic equilibrium. To isolate kinetic clumped isotope effects that arise at the mineral-solution interface, clumped isotopic equilibrium of DIC species must be maintained. This can be accomplished by dissolving the enzyme carbonic anhydrase (CA) into the solution, thereby reducing the time required for isotopic equilibration of DIC species by approximately two orders of magnitude between pH 7.7 and 9.3. We conduct calcite growth experiments aimed specifically at measuring the pH-dependence of kinetic clumped isotope effects during non-equilibrium precipitation of calcite. We precipitated calcite from aqueous solution at a constant pH and controlled supersaturation over the pH range 7.7-9.3 in the presence of CA. For each experiment, a gas mixture of N2 and CO2 is bubbled through a beaker of solution without seed crystals. As CO2 from the gas dissolves into solution, calcite crystals grow on the beaker walls. The pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. We control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate, and monitor the total alkalinity, the pCO2 of the gas outflow, and the amount of NaOH added. A constant crystal growth rate of ~1.6 mmol/m2/hr is maintained over all experiments. Results from these experiments are compared to predictions from a recently-developed isotopic ion-by-ion growth model of calcite. The model describes the rate, temperature and pH dependence of oxygen isotope uptake

  8. Notes on Interface Growth Kinetics 50 Years after Burton, Cabrera and Frank

    NASA Technical Reports Server (NTRS)

    Chernov, A. A.

    2004-01-01

    This overview is devoted to some unresolved basic problems in crystal growth kinetics. The density wave approach to propagation of a spatially diffuse interface between a growing crystal and its simple (e.g., metallic) melt is discussed is Section 2. This approach allows for the calculation of kinetic coefficients and is an alternative to the localized interface concept in which each atom belongs to either a solid or a liquid. Sections 3 and 4 deals mainly with layer growth from solution. Mutual retardation of the growth steps via their bulk and d a c e diffusion fields is the major subject. The influence of solution flow on step bunching (Section 4) suggests the essential influence of bulk diffusion on the surface morphology. The flow within the solution boundary layer enhances step-step interaction, influences the step bunching process and the resulting step pattern morphology on the growing surface. Recent experiments on the rates at which strongly polygonized steps on protein and small molecule crystals propagate during growth from solution are analyzed in Section 5 . We have shown that the step segments may be "singular" and that "one-dimensional nucleation" may be the rate limiting stage for the segments that are shorter or comparable in length to the thermodynamically equilibrium interlink distance. In this case, the reciprocal dependence of the segment propagation rate on the segment length that follow from the Gibbs-Thompson law, should be replaced by an abrupt switch from zero to a finite constant velocity. Until recently, the Kossel crystal remained the only model used in crystal growth theory. In such Kossel Gibbs-Thomson law, should be replaced by an abrupt switch &om zero to a finite constant velocity. crystals, all kinks at the steps are identical and the kink rate is a linear function of the supersaturation. In the non-Kossel crystals, there may be several kink configurations characterized by different geometries and energies. These configurations

  9. OPINION: Safe exponential manufacturing

    NASA Astrophysics Data System (ADS)

    Phoenix, Chris; Drexler, Eric

    2004-08-01

    In 1959, Richard Feynman pointed out that nanometre-scale machines could be built and operated, and that the precision inherent in molecular construction would make it easy to build multiple identical copies. This raised the possibility of exponential manufacturing, in which production systems could rapidly and cheaply increase their productive capacity, which in turn suggested the possibility of destructive runaway self-replication. Early proposals for artificial nanomachinery focused on small self-replicating machines, discussing their potential productivity and their potential destructiveness if abused. In the light of controversy regarding scenarios based on runaway replication (so-called 'grey goo'), a review of current thinking regarding nanotechnology-based manufacturing is in order. Nanotechnology-based fabrication can be thoroughly non-biological and inherently safe: such systems need have no ability to move about, use natural resources, or undergo incremental mutation. Moreover, self-replication is unnecessary: the development and use of highly productive systems of nanomachinery (nanofactories) need not involve the construction of autonomous self-replicating nanomachines. Accordingly, the construction of anything resembling a dangerous self-replicating nanomachine can and should be prohibited. Although advanced nanotechnologies could (with great difficulty and little incentive) be used to build such devices, other concerns present greater problems. Since weapon systems will be both easier to build and more likely to draw investment, the potential for dangerous systems is best considered in the context of military competition and arms control.

  10. Growth rate for blackhole instabilities

    NASA Astrophysics Data System (ADS)

    Prabhu, Kartik; Wald, Robert

    2015-04-01

    Hollands and Wald showed that dynamic stability of stationary axisymmetric black holes is equivalent to positivity of canonical energy on a space of linearised axisymmetric perturbations satisfying certain boundary and gauge conditions. Using a reflection isometry of the background, we split the energy into kinetic and potential parts. We show that the kinetic energy is positive. In the case that potential energy is negative, we show existence of exponentially growing perturbations and further obtain a variational formula for the growth rate.

  11. A diffusion-controlled kinetic model for growth of Au-catalyzed ZnO nanorods: Theory and experiment

    NASA Astrophysics Data System (ADS)

    Hejazi, S. R.; Madaah Hosseini, H. R.

    2007-11-01

    A kinetic model for growth of ZnO nanorods via vapor-liquid-solid (VLS) mechanism based on the bulk diffusion of Zn atoms through the Au-Zn droplet is presented. The dependences of the growth rate on size are given quantitatively. A general expression for the growth rate of nanorods during VLS process is derived. The derived formula shows the dependences of growth rate on lateral size of nanorods, concentration and supersaturation of Zn atoms in the liquid droplet. Based on the presented kinetic model the smaller nanorods have faster growth rate. Au-catalyzed ZnO nanorods are grown by chemical vapor transport and condensation (CVTC) process experimentally. Theoretical and experimental rate/radius curves are compared to each other. Theoretical predictions are in good agreement with the experimental results.

  12. The Catalytic Properties of Hybrid Rubisco Comprising Tobacco Small and Sunflower Large Subunits Mirror the Kinetically Equivalent Source Rubiscos and Can Support Tobacco Growth1[W][OA

    PubMed Central

    Sharwood, Robert Edward; von Caemmerer, Susanne; Maliga, Pal; Whitney, Spencer Michael

    2008-01-01

    Plastomic replacement of the tobacco (Nicotiana tabacum) Rubisco large subunit gene (rbcL) with that from sunflower (Helianthus annuus; rbcLS) produced tobaccoRst transformants that produced a hybrid Rubisco consisting of sunflower large and tobacco small subunits (LsSt). The tobaccoRst plants required CO2 (0.5% v/v) supplementation to grow autotrophically from seed despite the substrate saturated carboxylation rate, Km, for CO2 and CO2/O2 selectivity of the LsSt enzyme mirroring the kinetically equivalent tobacco and sunflower Rubiscos. Consequently, at the onset of exponential growth when the source strength and leaf LsSt content were sufficient, tobaccoRst plants grew to maturity without CO2 supplementation. When grown under a high pCO2, the tobaccoRst seedlings grew slower than tobacco and exhibited unique growth phenotypes: Juvenile plants formed clusters of 10 to 20 structurally simple oblanceolate leaves, developed multiple apical meristems, and the mature leaves displayed marginal curling and dimpling. Depending on developmental stage, the LsSt content in tobaccoRst leaves was 4- to 7-fold less than tobacco, and gas exchange coupled with chlorophyll fluorescence showed that at 2 mbar pCO2 and growth illumination CO2 assimilation in mature tobaccoRst leaves remained limited by Rubisco activity and its rate (approximately 11 μmol m−2 s−1) was half that of tobacco controls. 35S-methionine labeling showed the stability of assembled LsSt was similar to tobacco Rubisco and measurements of light transient CO2 assimilation rates showed LsSt was adequately regulated by tobacco Rubisco activase. We conclude limitations to tobaccoRst growth primarily stem from reduced rbcLS mRNA levels and the translation and/or assembly of sunflower large with the tobacco small subunits that restricted LsSt synthesis. PMID:17993544

  13. Effects of Gypsophila saponins on bacterial growth kinetics and on selection of subterranean clover rhizosphere bacteria.

    PubMed

    Fons, F; Amellal, N; Leyval, C; Saint-Martin, N; Henry, M

    2003-06-01

    Plant secondary metabolites, such as saponins, have a considerable impact in agriculture because of their allelopathic effects. They also affect the growth of soil microorganisms, especially fungi. We investigated the influence of saponins on rhizosphere bacteria in vitro and in soil conditions. The effects of gypsophila saponins on the growth kinetics of rhizosphere bacteria were studied by monitoring the absorbance of the cultures in microtiter plates. Gypsophila saponins (1%) increased the lag phase of bacterial growth. The impact of gypsophila saponins on subterranean clover rhizosphere was also investigated in a pot experiment. The addition of gypsophila saponins did not modify clover biomass but significantly increased (twofold with 1% saponins) the weight of adhering soil. The number of culturable heterotrophic bacteria of the clover rhizosphere was not affected by the addition of gypsophila saponins. Nevertheless, the phenotypical characterization of the dominant Gram-negative strains of the clover rhizosphere, using the Biolog system, showed qualitative and quantitative differences induced by 1% saponins. With the addition of saponins, the populations of Chryseomonas spp. and Acinetobacter spp., the two dominant culturable genera of control clover, were no longer detectable or were significantly decreased, while that of Aquaspirillum dispar increased and Aquaspirillum spp. became the major genus. Aquaspirillum dispar and Aquaspirillum spp. were also the dominant rhizosphere bacteria of Gypsophila paniculata, which greatly accumulates these saponins in its roots. These results suggest that saponins may control rhizosphere bacteria in soil through rhizodeposition mechanisms. PMID:14569290

  14. Influence of Nitrogen Content on Thermal Stability and Grain Growth Kinetics of Cryomilled Al Nanocomposites

    NASA Astrophysics Data System (ADS)

    Hashemi-Sadraei, L.; Mousavi, S. E.; Vogt, R.; Li, Y.; Zhang, Z.; Lavernia, E. J.; Schoenung, J. M.

    2012-02-01

    Nanocomposite powders of Al 5083/B4C were produced via cryogenic milling (cryomilling) of boron carbide (B4C) particles in Al 5083 matrix. The effect of milling time (up to 24 hours), and consequential nitrogen content, on grain growth in the nanocrystalline Al 5083 matrix was investigated. Thermal stability was studied at temperatures as high as ~0.96 T m and annealing times of up to 24 hours. Average grain sizes increased with time and temperature and tended to stabilize after longer annealing times, regardless of nitrogen content. Higher thermal stability was observed in samples with higher nitrogen content, with the average grain size remaining in the range of 30 nm, even after exposure to the most extreme annealing conditions. This behavior was attributed to the retarding effect that nitrides have on grain growth, as a result of pinning grain boundaries. Kinetic studies based on the Burke equation showed two thermally activated grain growth regimes—a low-temperature regime with an activation energy of 15 kJ/mol and a high-temperature regime with an activation energy of 58 kJ/mol.

  15. Use of fermentative metabolites for heterotrophic microalgae growth: Yields and kinetics.

    PubMed

    Turon, V; Baroukh, C; Trably, E; Latrille, E; Fouilland, E; Steyer, J-P

    2015-01-01

    The growth of two lipid-producing Chlorella species on fermentative end-products acetate, butyrate and lactate, was investigated using a kinetic modeling approach. Chlorella sorokiniana and Auxenochlorella protothecoides were grown on synthetic media with various (acetate:butyrate:lactate) ratios. Both species assimilated efficiently acetate and butyrate with yields between 0.4 and 0.5g carbon of biomass/g carbon of substrate, but did not use lactate. The highest growth rate on acetate, 2.23d(-1), was observed for C. sorokiniana, and on butyrate, 0.22d(-1), for A. protothecoides. Butyrate removal started after complete acetate exhaustion (diauxic effect). However, butyrate consumption may be favored by the increase of biomass concentration induced by the initial use of acetate. A model combining Monod and Haldane functions was then built and fitted the experimental data well for both species. Butyrate concentration and (acetate:butyrate) ratios were identified as key parameters for heterotrophic growth of microalgae on fermentative metabolites. PMID:25459841

  16. Photobiotreatment: influence of nitrogen and phosphorus ratio in wastewater on growth kinetics of Scenedesmus obliquus.

    PubMed

    Arbib, Z; Ruiz, J; Alvarez-Díaz, Pablo; Garrido-Pérez, C; Barragan, J; Perales, J A

    2013-01-01

    Nitrogen and phosphorus concentration in the effluent of a wastewater treatment plant can vary significantly, which could affect the growth kinetic and chemical composition of microalgae when cultivated in this medium. The aim of this work was to study the rate of growth, nutrient removal and carbon dioxide biofixation as well as biomass composition of Scenedesmus obliquus (S. obliquus) when it is cultivated in wastewater at different nitrogen and phosphorus ratio, from 1:1 to 35:1. A more homogeneous method for calculating productivities in batch reactors was proposed. The proper N:P ratio for achieving optimum batch biomass productivity ranged between 9 and 13 (263 and 322 mg L(-1) d(-1) respectively). This was also the ratio range for achieving a total N and P removal. Above and below this range (9-13) the maximum biomass concentration changed, instead of the specific growth rate.The maximum carbon dioxide biofixation rate was achieved at N:P ratio between 13 and 22 (553 and 557 mg CO2 L(-1) d(-1) respectively). Lipid and crude protein content, both depend on the aging culture, reaching the maximum lipid content (34%) at the lowest N:P (1:1) and the maximum crude protein content (34.2%) at the highest N:P (35:1). PMID:23819274

  17. The kinetics of dolomite reaction rim growth under isostatic and non-isostatic pressure conditions

    NASA Astrophysics Data System (ADS)

    Helpa, V.; Rybacki, E.; Morales, L. G.; Abart, R.; Dresen, G. H.

    2013-12-01

    During burial and exhumation, rocks are simultaneously exposed to metamorphic reactions and tectonic stresses. Therefore, the reaction rate of newly formed minerals may depend on chemical and mechanical driving forces. Here, we investigate the reaction kinetics of dolomite (CaMg[CO3]2) rim growth by solid-state reactions experiments on oriented calcite (CaCO3) and magnesite (MgCO3) single crystals under isostatic and non-isostatic pressure conditions. Cylindrical samples of 3-5 mm length and 7 mm diameter were drilled and polished perpendicular to the rhombohedral cleavage planes of natural clear crystals. The tests were performed using a Paterson-type deformation apparatus at P = 400 MPa confining pressure, temperatures, T, between 750 and 850°C, and reaction durations, t, of 2 - 146 h to calculate the kinetic parameters of dolomite rim growth under isostatic stress conditions. For non-isostatic reaction experiments we applied in addition differential stresses, σ, up to 40 MPa perpendicular to the contact interface at T = 750°C for 4 - 171 h duration, initiating minor inelastic deformation of calcite. The thickness of the resulting dolomite reaction rims increases linearly with the square root of time, indicating a diffusion-controlled reaction. The rims consist of two different textural domains. Granular dolomite grains (≈ 2 -5 μm grain size) form next to calcite and elongated palisade-shaped grains (1-6 μm diameter) grow perpendicular to the magnesite interface. Texture measurements with the electron backscatter diffraction technique indicate that the orientations of dolomite grains are mainly influenced by the orientation of the calcite educt crystal, in particular in the granular rim. To some extent, the texture of dolomite palisades is also influenced by the orientation of magnesite. The thickness of the two individual layers increases with temperature. At 400 MPa isostatic pressure, T = 750°C and t = 29 hours, a 5 μm thick granular dolomite layer

  18. Kinetics of subdiffusive growth of new phase particles in supersaturated solid solutions

    NASA Astrophysics Data System (ADS)

    Svetukhin, V. V.; Sibatov, R. T.

    2015-04-01

    The kinetics of the subdiffusion-limited growth of spherical precipitates is studied. The process is described by the equation of anomalous diffusion with a fractional derivative with respect to time. It is shown that a decrease in the concentration of monomers is described by the law exp(- kt 3α/2) at the initial stage and the power law t -α at large times, where 0 < α ≤ 1 is the dispersion parameter coinciding with the order of time derivative in the subdiffusion equation. The time dependence of the size of a spherical precipitate is obtained. The results generalize the Ham diffusion theory and are in agreement with the Monte Carlo simulation data.

  19. Kinetics of subdiffusive growth of new phase particles in supersaturated solid solutions

    SciTech Connect

    Svetukhin, V. V. Sibatov, R. T.

    2015-04-15

    The kinetics of the subdiffusion-limited growth of spherical precipitates is studied. The process is described by the equation of anomalous diffusion with a fractional derivative with respect to time. It is shown that a decrease in the concentration of monomers is described by the law exp(−kt{sup 3α/2}) at the initial stage and the power law t{sup −α} at large times, where 0 < α ≤ 1 is the dispersion parameter coinciding with the order of time derivative in the subdiffusion equation. The time dependence of the size of a spherical precipitate is obtained. The results generalize the Ham diffusion theory and are in agreement with the Monte Carlo simulation data.

  20. Kinetics of low pressure CVD growth of SiO2 on InP and Si

    NASA Technical Reports Server (NTRS)

    Iyer, R.; Lile, D. L.

    1988-01-01

    The kinetics of low pressure CVD growth of SiO2 from SiH4 and O2 has been investigated for the case of an indirect (remote) plasma process. Homogeneous (gas phase) and heterogeneous operating ranges have been experimentally identified. The process was shown to be consistent within the heterogeneous surface-reaction dominated range of operation. A kinetic rate equation is given for growth at 14 W RF power input and 400 mtorr total pressure on both InP and Si substrates. The process exhibits an activation energy of 8.4 + or - 0.6 kcal/mol.

  1. Enhanced Generic Phase-field Model of Irradiation Materials: Fission Gas Bubble Growth Kinetics in Polycrystalline UO2

    SciTech Connect

    Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert O.; Gao, Fei; Sun, Xin

    2012-05-30

    Experiments show that inter-granular and intra-granular gas bubbles have different growth kinetics which results in heterogeneous gas bubble microstructures in irradiated nuclear fuels. A science-based model predicting the heterogeneous microstructure evolution kinetics is desired, which enables one to study the effect of thermodynamic and kinetic properties of the system on gas bubble microstructure evolution kinetics and morphology, improve the understanding of the formation mechanisms of heterogeneous gas bubble microstructure, and provide the microstructure to macroscale approaches to study their impact on thermo-mechanical properties such as thermo-conductivity, gas release, volume swelling, and cracking. In our previous report 'Mesoscale Benchmark Demonstration, Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing', we developed a phase-field model to simulate the intra-granular gas bubble evolution in a single crystal during post-irradiation thermal annealing. In this work, we enhanced the model by incorporating thermodynamic and kinetic properties at grain boundaries, which can be obtained from atomistic simulations, to simulate fission gas bubble growth kinetics in polycrystalline UO2 fuels. The model takes into account of gas atom and vacancy diffusion, vacancy trapping and emission at defects, gas atom absorption and resolution at gas bubbles, internal pressure in gas bubbles, elastic interaction between defects and gas bubbles, and the difference of thermodynamic and kinetic properties in matrix and grain boundaries. We applied the model to simulate gas atom segregation at grain boundaries and the effect of interfacial energy and gas mobility on gas bubble morphology and growth kinetics in a bi-crystal UO2 during post-irradiation thermal annealing. The preliminary results demonstrate that the model can produce the equilibrium thermodynamic properties and the morphology of gas bubbles at

  2. Kinetics and gas-surface dynamics of GaN homoepitaxial growth using NH 3-seeded supersonic molecular beams

    NASA Astrophysics Data System (ADS)

    McGinnis, A. J.; Thomson, D.; Davis, R. F.; Chen, E.; Michel, A.; Lamb, H. H.

    2001-11-01

    The kinetics of homoepitaxial growth of GaN thin films on metal-organic chemical vapor deposition (MOCVD)-grown GaN(0 0 0 1)/AlN/6H-SiC substrates was probed using NH 3-seeded supersonic molecular beams. NH 3 was seeded in H 2 and He and antiseeded in N 2 and Ar in order to obtain incident kinetic energies of 0.08-1.8 eV. Nozzle temperatures of 35-600 °C were used to adjust the NH 3 internal energy. Intense NH 3 beams (fluxes >2×10 15 cm-2 s-1 at the substrate) are produced for low seeding percentages (<5%) in the lighter carrier gases, because the heavier species (NH 3) is focused along the centerline of the beam. The NH 3 flux is proportional to the ratio of its molecular weight to the average molecular weight of the binary gas mixture. A steady-state Langmuir-Hinshelwood kinetics model was used to extract zero-coverage NH 3 sticking coefficient ( αNH 30) values from GaN growth kinetics data. An αNH 30 value of 0.14 at 750 °C was determined using seeded supersonic beams of NH 3 in He with incident kinetic energies of 0.4-0.5 eV. In comparison, GaN growth rates using low-energy NH 3 molecules (0.03 eV) from a leak valve indicate an αNH 30 of 0.29. Growth rate measurements using NH 3 beams with kinetic energies of 0.08-1.8 eV confirmed that αNH 30 generally decreases with increasing incident kinetic energy, leading us to conclude that NH 3 chemisorption on GaN(0 0 0 1) is unactivated and occurs via a precursor-mediated mechanism. Internal energy enhancement of NH 3 chemisorption via a precursor-mediated channel is proposed to explain the effects of nozzle temperature on GaN growth kinetics. The effects of NH 3 incident kinetic energy on film morphology are indirect. Rough, highly faceted films are observed under Ga-limited growth conditions. The surface morphology of films grown under NH 3-limited conditions changes from rough to smooth as the effective V/III ratio is decreased.

  3. Non-classical nuclei and growth kinetics of Cr precipitates in FeCr alloys during ageing

    SciTech Connect

    Li, Yulan; Hu, Shenyang Y.; Zhang, Lei; Sun, Xin

    2014-01-10

    In this manuscript, we quantitatively calculated the thermodynamic properties of critical nuclei of Cr precipitates in FeCr alloys. The concentration profiles of the critical nuclei and nucleation energy barriers were predicted by the constrained shrinking dimer dynamics (CSDD) method. It is found that Cr concentration distribution in the critical nuclei strongly depend on the overall Cr concentration as well as temperature. The critical nuclei are non-classical because the concentration in the nuclei is smaller than the thermodynamic equilibrium value. These results are in agreement with atomic probe observation. The growth kinetics of both classical and non-classical nuclei was investigated by the phase field approach. The simulations of critical nucleus evolution showed a number of interesting phenomena: 1) a critical classical nucleus first shrinks toward its non-classical nucleus and then grows; 2) a non-classical nucleus has much slower growth kinetics at its earlier growth stage compared to the diffusion-controlled growth kinetics. 3) a critical classical nucleus grows faster at the earlier growth stage than the non-classical nucleus. All of these results demonstrate that it is critical to introduce the correct critical nuclei in order to correctly capture the kinetics of precipitation.

  4. Non-classical nuclei and growth kinetics of Cr precipitates in FeCr alloys during ageing

    NASA Astrophysics Data System (ADS)

    Li, Yulan; Hu, Shenyang; Zhang, Lei; Sun, Xin

    2014-03-01

    In this manuscript, we have quantitatively calculated the thermodynamic properties of the critical nuclei of Cr precipitates in FeCr alloys. The concentration profiles of the critical nuclei and nucleation energy barriers were predicted by the constrained shrinking dimer dynamics method. It is found that Cr concentration distribution in the critical nuclei strongly depends on the overall Cr concentration as well as on the temperature. The critical nuclei are non-classical because the concentration in the nuclei is smaller than the thermodynamic equilibrium value. These results are in agreement with atomic probe observation. The growth kinetics of both classical and non-classical nuclei was investigated by the phase-field approach. The simulations of critical nucleus evolution showed a number of interesting phenomena: (1) a critical classical nucleus first shrinks toward its non-classical nucleus and then grows; (2) a non-classical nucleus has much slower growth kinetics at its earlier growth stage compared to the diffusion-controlled growth kinetics and (3) a critical classical nucleus grows faster at the earlier growth stage than does a non-classical nucleus. All of these results demonstrate that it is critical to introduce the correct critical nuclei in order to correctly capture the kinetics of precipitation.

  5. Growth of Staphylococcus aureus in Cooked Potato and Potato Salad--A One-Step Kinetic Analysis.

    PubMed

    Huang, Lihan

    2015-12-01

    Staphylococcus aureus is a Gram-positive spherically-shaped bacterium capable of producing heat-stable enterotoxins that cause acute gastrointestinal diseases. The growth of this pathogen in food is a major threat to public health worldwide. Potato salad is a frequent vehicle for infection and food poisoning caused by S. aureus. Therefore, the objective of this study was to investigate the growth kinetics of S. aureus in cooked potato and potato salad. Samples of potato cubes and potato salad inoculated with S. aureus were incubated at temperatures between 8 and 43 °C to observe its growth for developing growth models. No growth was observed at 8 °C. The experimental results showed that the growth curves did not exhibit lag phases, and can be described by a 3-parameter logistic model. A one-step kinetic analysis approach was used to simultaneously analyze all growth curves by direct construction of both the primary and secondary (Ratkowsky square root) models using nonlinear regression to minimize the global residual error. The estimated nominal minimum growth temperature of S. aureus was 6.12 °C in potato cubes and 8.80 °C in potato salad. The estimated maximum growth temperatures of S. aureus in potato cubes and potato salad were very close to each other (46.3 and 46.8 °C, respectively). On the average, the specific growth rates of S. aureus in potato cubes were approximately 70% higher than those in potato salad. This study suggests that cooked potato and potato salad should be stored below 6 °C or above 47 °C to prevent the growth of S. aureus. The mathematical models and kinetic parameters can be used to accurately evaluate the effect of temperature abuse on the growth of S. aureus and conduct risk assessments of S. aureus in cooked potato and potato salad. PMID:26539902

  6. A growth kinetics model of rate decomposition for Si1-xGex alloy based on dimer theory

    NASA Astrophysics Data System (ADS)

    Dai, Xian-Ying; Ji, Yao; Hao, Yue

    2014-01-01

    According to the dimer theory on semiconductor surface and chemical vapor deposition(CVD) growth characteristics of Si1-xGex, two mechanisms of rate decomposition and discrete flow density are proposed. Based on these two mechanisms, the Grove theory and Fick's first law, a CVD growth kinetics model of Si1-xGex alloy is established. In order to make the model more accurate, two growth control mechanisms of vapor transport and surface reaction are taken into account. The paper also considers the influence of the dimer structure on the growth rate. The results show that the model calculated value is consistent with the experimental values at different temperatures.

  7. D-Alanylation of Teichoic Acids and Loss of Poly-N-Acetyl Glucosamine in Staphylococcus aureus during Exponential Growth Phase Enhance IL-12 Production in Murine Dendritic Cells

    PubMed Central

    Lund, Lisbeth Drozd; Ingmer, Hanne; Frøkiær, Hanne

    2016-01-01

    Staphylococcus aureus is a major human pathogen that has evolved very efficient immune evading strategies leading to persistent colonization. During different stages of growth, S. aureus express various surface molecules, which may affect the immune stimulating properties, but very little is known about their role in immune stimulation and evasion. Depending on the growth phase, S. aureus may affect antigen presenting cells differently. Here, the impact of growth phases and the surface molecules lipoteichoic acid, peptidoglycan and poly-N-acetyl glucosamine on the induction of IL-12 imperative for an efficient clearance of S. aureus was studied in dendritic cells (DCs). Exponential phase (EP) S. aureus was superior to stationary phase (SP) bacteria in induction of IL-12, which required actin-mediated endocytosis and endosomal acidification. Moreover, addition of staphylococcal cell wall derived peptidoglycan to EP S. aureus stimulated cells increased bacterial uptake but abrogated IL-12 induction, while addition of lipoteichoic acid increased IL-12 production but had no effect on the bacterial uptake. Depletion of the capability to produce poly-N-acetyl glucosamine increased the IL-12 inducing activity of EP bacteria. Furthermore, the mutant dltA unable to produce D-alanylated teichoic acids failed to induce IL-12 but like peptidoglycan and the toll-like receptor (TLR) ligands LPS and Pam3CSK4 the mutant stimulated increased macropinocytosis. In conclusion, the IL-12 response by DCs against S. aureus is highly growth phase dependent, relies on cell wall D-alanylation, endocytosis and subsequent endosomal degradation, and is abrogated by receptor induced macropinocytosis. PMID:26872029

  8. Kinetic aspects of the thermostatted growth of ice from supercooled water in simulations

    NASA Astrophysics Data System (ADS)

    Weiss, Volker C.; Rullich, Markus; Köhler, Christof; Frauenheim, Thomas

    2011-07-01

    In experiments, the growth rate of ice from supercooled water is seen to increase with the degree of supercooling, that is, the lower the temperature, the faster the crystallization takes place. In molecular dynamics simulations of the freezing process, however, the temperature is usually kept constant by means of a thermostat that artificially removes the heat released during the crystallization by scaling the velocities of the particles. This direct removal of energy from the system replaces a more realistic heat-conduction mechanism and is believed to be responsible for the curious observation that the thermostatted ice growth proceeds fastest near the melting point and more slowly at lower temperatures, which is exactly opposite to the experimental findings [M. A. Carignano, P. B. Shepson, and I. Szleifer, Mol. Phys. 103, 2957 (2005), 10.1080/00268970500243796]. This trend is explained by the diffusion and the reorientation of molecules in the liquid becoming the rate-determining steps for the crystal growth, both of which are slower at low temperatures. Yet, for a different set of simulations, a kinetic behavior analogous to the experimental finding has been reported [H. Nada and Y. Furukawa, J. Crystal Growth 283, 242 (2005), 10.1016/j.jcrysgro.2005.05.057]. To clarify this apparent contradiction, we perform relatively long simulations of the TIP4P/Ice model in an extended range of temperatures. The temperature dependence of the thermostatted ice growth is seen to be more complex than was previously reported: The crystallization process is very slow close to the melting point at 270 K, where the thermodynamic driving force for the phase transition is weak. On lowering the temperature, the growth rate initially increases, but displays a maximum near 260 K. At even lower temperatures, the freezing process slows down again due to the reduced diffusivity in the liquid. The velocity of the thermostatted melting process, in contrast, shows a monotonic increase upon

  9. Kinetic aspects of the thermostatted growth of ice from supercooled water in simulations.

    PubMed

    Weiss, Volker C; Rullich, Markus; Köhler, Christof; Frauenheim, Thomas

    2011-07-21

    In experiments, the growth rate of ice from supercooled water is seen to increase with the degree of supercooling, that is, the lower the temperature, the faster the crystallization takes place. In molecular dynamics simulations of the freezing process, however, the temperature is usually kept constant by means of a thermostat that artificially removes the heat released during the crystallization by scaling the velocities of the particles. This direct removal of energy from the system replaces a more realistic heat-conduction mechanism and is believed to be responsible for the curious observation that the thermostatted ice growth proceeds fastest near the melting point and more slowly at lower temperatures, which is exactly opposite to the experimental findings [M. A. Carignano, P. B. Shepson, and I. Szleifer, Mol. Phys. 103, 2957 (2005)]. This trend is explained by the diffusion and the reorientation of molecules in the liquid becoming the rate-determining steps for the crystal growth, both of which are slower at low temperatures. Yet, for a different set of simulations, a kinetic behavior analogous to the experimental finding has been reported [H. Nada and Y. Furukawa, J. Crystal Growth 283, 242 (2005)]. To clarify this apparent contradiction, we perform relatively long simulations of the TIP4P/Ice model in an extended range of temperatures. The temperature dependence of the thermostatted ice growth is seen to be more complex than was previously reported: The crystallization process is very slow close to the melting point at 270 K, where the thermodynamic driving force for the phase transition is weak. On lowering the temperature, the growth rate initially increases, but displays a maximum near 260 K. At even lower temperatures, the freezing process slows down again due to the reduced diffusivity in the liquid. The velocity of the thermostatted melting process, in contrast, shows a monotonic increase upon raising the temperature beyond the normal melting point

  10. On the Matrix Exponential Function

    ERIC Educational Resources Information Center

    Hou, Shui-Hung; Hou, Edwin; Pang, Wan-Kai

    2006-01-01

    A novel and simple formula for computing the matrix exponential function is presented. Specifically, it can be used to derive explicit formulas for the matrix exponential of a general matrix A satisfying p(A) = 0 for a polynomial p(s). It is ready for use in a classroom and suitable for both hand as well as symbolic computation.

  11. Effects of 3-D microwell culture on growth kinetics and metabolism of human embryonic stem cells

    PubMed Central

    Azarin, Samira M.; Larson, Elise A.; Almodóvar-Cruz, Janice M; de Pablo, Juan J.; Palecek, Sean P.

    2013-01-01

    Human embryonic stem cells (hESCs) hold potential in the field of tissue engineering given their capacity for both limitless self-renewal and differentiation to any adult cell type. However, several limitations, including the ability to expand undifferentiated cells and efficiently direct differentiation at scales needed for commercial cell production, prevent realizing the potential of hESCs in tissue engineering. Numerous studies have illustrated that 3-D culture systems provide microenvironmental cues that affect hESC pluripotency and differentiation fates, but little is known about how 3-D culture affects cell expansion. Here we have used a 3-D microwell array to model the differences in hESC growth kinetics and metabolism in 2-D vs. 3-D cultures. Our results demonstrated that 3-D microwell culture reduced hESC size and proliferative capacity, and impacted cell cycle dynamics, lengthening the G1 phase and shortening the G2/M phase of the cell cycle. However, glucose and lactate metabolism were similar in 2-D and 3-D cultures. Elucidating the effects of 3-D culture on growth and metabolism of hESCs may facilitate efforts for developing integrated, scalable cell expansion and differentiation processes with these cells. PMID:23586789

  12. Kinetic Mie ellipsometry to determine the time-resolved particle growth in nanodusty plasmas

    NASA Astrophysics Data System (ADS)

    Groth, Sebastian; Greiner, Franko; Tadsen, Benjamin; Piel, Alexander

    2015-11-01

    The growth of nanometer-sized particles in a reactive argon-acetylene plasma is investigated by means of kinetic single-wavelength Mie ellipsometry from the change of the polarization state of scattered light. This requires advanced measurement techniques as well as complex methods for the analysis of the measured data. Today commercial devices reduce the metrological effort, but the data analysis is still a challenging topic. We present a scheme to gain time-resolved information about the size evolution of monodisperse spherical particles and to determine their optical properties, represented by the complex refractive index N, without limiting assumptions concerning the evolution of the particle size or the need for additional ex situ diagnostics. The method is applied on typical particle growth processes at varying optical depth and compared to ex situ SEM measurements. It is shown that more complex processes, including particle etching, can be analyzed. This demonstrates the applicability of the analysis on a strongly non-linear process.

  13. Biomineralization: Systematics of organic-directed controls on carbonate growth morphologies and kinetics determined by in situ AFM. Final report

    SciTech Connect

    Dove, P.M.

    1998-12-01

    During the three years of this project, tremendous progress has been made in understanding the microscopic kinetic controls on calcite growth and in investigations of amino acid controls on modifying crystal growth and dissolution. The project began with a focus on the aspartate-calcite system because previous studies have found that acidic matrix macromolecules involved in the regulation of biological crystal growth usually contain aspartic acid-rick domains. Indeed, several studies have shown that aspartate (Asp) modifies the growth morphology of calcite. Aspartate-rich proteins and {beta}-sheet polyaspartate adsorbed on sulfonated polystyrene surfaces were shown to stabilize {l_brace}0001{r_brace} growth surfaces. It was also shown that aspartate also stabilizes the prismatic {l_brace}1{bar 1}00{r_brace} growth forms. For the first time, the author has an understanding of the microscopic controls of aspartate on growth and dissolution.

  14. Growth kinetics of gamma-prime precipitates in a directionally solidified eutectic, gamma/gamma-prime-delta

    NASA Technical Reports Server (NTRS)

    Tewari, S. N.

    1976-01-01

    A directionally solidified eutectic alloy (DSEA), of those viewed as potential candidates for the next generation of aircraft gas turbine blade materials, is studied for the gamma-prime growth kinetics, in the system Ni-Nb-Cr-Al, specifically: Ni-20 w/o Nb-6 w/o Cr-2.5 w/o Al gamma/gamma-prime-delta DSEA. Heat treatment, polishing and etching, and preparation for electron micrography are described, and the size distribution of gamma-prime phase following various anneals is plotted, along with gamma-prime growth kinetics in this specific DSEA, and the cube of gamma-prime particle size vs anneal time. Activation energies and coarsening kinetics are studied.

  15. KINETICS OF GROWTH AND ETHANOL PRODUCTION ON DIFFERENT CARBON SUBSTRATES USING GENETICALLY ENGINEERED XYLOSE-FERMENTING YEAST

    EPA Science Inventory

    Saccharomyces cerevisiae 424A (LNH-ST) strain was used for fermentation of glucose and xylose. Growth kinetics and ethanol productivity were calculated for batch fermentation on media containing different combinations of glucose and xylose to give a final sugar concentra...

  16. Phase-field Modeling of Void Migration and Growth Kinetics in Materials under Irradiation and Temperature Field

    SciTech Connect

    Li, Yulan; Hu, Shenyang Y.; Sun, Xin; Gao, Fei; Henager, Charles H.; Khaleel, Mohammad A.

    2010-12-15

    A phase-field model is developed to investigate the migration of vacancies, interstitials, and voids as well as void growth kinetics in materials under radiation and temperature field. The model takes into account the generation of vacancies and interstitials associated with the irradiation damage, the recombination between vacancies and interstitials, defect diffusion, and defect sinks. The effect of void sizes, vacancy concentration, vacancy generation rate, recombination rate, and temperature gradient on a single void migration and growth kinetics is parametrically studied. The results demonstrate that the temperature gradient causes void migration and defect fluxes, i.e., the Soret effect, which affects void stability and growth kinetics. It is found that 1) the void migration mobility is independent of the void size, which is in agreement with the theoretical prediction with the assumption of bulk diffusion controlled migration; 2) the void migration mobility strongly depends on temperature gradient; and 3) the effect of defect concentration, generation rate, and recombination rate on void migration mobility is minor although they strongly influence the void growth kinetics.

  17. Kinetics of Nucleation and Crystal Growth in Glass Forming Melts in Microgravity

    NASA Technical Reports Server (NTRS)

    Day, Delbert E.; Ray, Chandra S.

    1999-01-01

    The following list summarizes the most important results that have been consistently reported for glass forming melts in microgravity: (1) Glass formation is enhanced for melts prepared in space; (2) Glasses prepared in microgravity are more chemically homogeneous and contain fewer and smaller chemically heterogeneous regions than identical glasses prepared on earth; (3) Heterogeneities that are deliberately introduced such as Pt particles are more uniformly distributed in a glass melted in space than in a glass melted on earth; (4) Glasses prepared in microgravity are more resistant to crystallization and have a higher mechanical strength and threshold energy for radiation damage; and (5) Glasses crystallized in space have a different microstructure, finer grains more uniformly distributed, than equivalent samples crystallized on earth. The preceding results are not only scientifically interesting, but they have considerable practical implications. These results suggest that the microgravity environment is advantageous for developing new and improved glasses and glass-ceramics that are difficult to prepare on earth. However, there is no suitable explanation at this time for why a glass melted in microgravity will be more chemically homogeneous and more resistant to crystallization than a glass melted on earth. A fundamental investigation of melt homogenization, nucleation, and crystal growth processes in glass forming melts in microgravity is important to understanding these consistently observed, but yet unexplained results. This is the objective of the present research. A lithium disilicate (Li2O.2SiO2) glass will be used for this investigation, since it is a well studied system, and the relevant thermodynamic and kinetic parameters for nucleation and crystal growth at 1-g are available. The results from this research are expected to improve our present understanding of the fundamental mechanism of nucleation and crystal growth in melts and liquids, and to lead

  18. Growth kinetics of Pseudomonas alcaligenes C-0 relative to inoculation and 3-chlorobenzoate metabolism in soil.

    PubMed

    Focht, D D; Shelton, D

    1987-08-01

    Pseudomonas alcaligenes C-0 was isolated from activated sewage sludge by enrichment with 3-chlorobenzoate (3CB) as the sole carbon source. The carbon balance from [14C]3CB in pure culture could be accounted for in substrate, biomass, and CO2 from all sampling periods and inoculum densities (0.012, 0.092, 0.20, and 0.92 micrograms of dry cells X ml-1), and inorganic chloride was produced stoichiometrically. Monod parameters as determined in culture were compared with the kinetics of 3CB metabolism in soil with decreasing inoculum densities (1.9 X 10(-1), 1.9 X 10(-3), and 1.9 X 10(-5) micrograms of cells X g-1). 3CB was refractile to attack in soil by indigenous microflora, but it was completely metabolized upon inoculation with P. alcaligenes C-0. The saturation constant KS was much higher in soil than in culture, but the yield coefficient Y and the growth rate constant were the same in both systems: mu max = 0.32 h-1; Y = 34 micrograms cells X mumol-1; KS = 0.18 mM in culture and 6.0 mM in soil solution (1.1 mumol X g-1 of soil). The parameter estimates obtained from the highest inoculum density could be used for the lower inoculum densities with reasonable agreement between predicted and observed 3CB concentrations in soil, although the residual sum of squares was progressively higher. Since the growth rate of P. alcaligenes C-0 in soil was comparable to its growth rate in culture, inoculation should be a viable strategy for biodegradation of 3CB in soil if indigenous microflora are unable to exploit this metabolic niche. PMID:3662518

  19. Growth Kinetics, Characterization, and Plasticity of Human Menstrual Blood Stem Cells.

    PubMed

    Mehrabani, Davood; Nazarabadi, Roshanak Bahrami; Kasraeian, Maryam; Tamadon, Amin; Dianatpour, Mehdi; Vahdati, Akbar; Zare, Shahrokh; Ghobadi, Farnaz

    2016-03-01

    One of the readily available sources of mesenchymal stem cells (MSCs) is menstrual blood-derived stem cells (Men-SCs), which exhibit characteristics similar to other types of MSCs. This study was performed to determine the growth kinetics, plasticity, and characterization of Men-SCs in women. During spring 2014 in the southern Iranian city of Shiraz, menstrual blood (5 mL) was obtained from 10 women on their third day of menstruation in 2 age groups of 30 to 40 and 40 to 50 years old. Ficoll was used to separate the mononuclear cell fraction. After the Men-SCs were cultured, they were subcultured up to passage 4. Growth behavior and population doubling time were evaluated by seeding 5×10(4) cells into 12- and 24-well culture plates, and the colonies were enumerated. The expression of CD44, CD90, and CD34 was evaluated. The osteogenic potential was assessed by alizarin red staining. The Men-SCs were shown to be plastic adherent and spindle-shaped. Regarding the growth curves in the 12- and 24-well culture plates, it was demonstrated that in the women aged between 30 and 40 years, population doubling time was 55.5 and 62 hours, respectively, while these values in the women aged between 40 and 50 years were 70.4 and 72.4 hours, correspondingly. Positive expression of CD44 and CD90 and negative expression of CD34 were noted. In the osteogenic differentiation medium, the cells differentiated toward osteoblasts. As human Men-SCs are easily collectable without any invasive procedure and are a safe and rapid source of MSCs, they can be a good candidate for stem cell banking and cell transplantation in women. PMID:26989284

  20. Growth Kinetics, Characterization, and Plasticity of Human Menstrual Blood Stem Cells

    PubMed Central

    Mehrabani, Davood; Nazarabadi, Roshanak Bahrami; Kasraeian, Maryam; Tamadon, Amin; Dianatpour, Mehdi; Vahdati, Akbar; Zare, Shahrokh; Ghobadi, Farnaz

    2016-01-01

    One of the readily available sources of mesenchymal stem cells (MSCs) is menstrual blood-derived stem cells (Men-SCs), which exhibit characteristics similar to other types of MSCs. This study was performed to determine the growth kinetics, plasticity, and characterization of Men-SCs in women. During spring 2014 in the southern Iranian city of Shiraz, menstrual blood (5 mL) was obtained from 10 women on their third day of menstruation in 2 age groups of 30 to 40 and 40 to 50 years old. Ficoll was used to separate the mononuclear cell fraction. After the Men-SCs were cultured, they were subcultured up to passage 4. Growth behavior and population doubling time were evaluated by seeding 5×104 cells into 12- and 24-well culture plates, and the colonies were enumerated. The expression of CD44, CD90, and CD34 was evaluated. The osteogenic potential was assessed by alizarin red staining. The Men-SCs were shown to be plastic adherent and spindle-shaped. Regarding the growth curves in the 12- and 24-well culture plates, it was demonstrated that in the women aged between 30 and 40 years, population doubling time was 55.5 and 62 hours, respectively, while these values in the women aged between 40 and 50 years were 70.4 and 72.4 hours, correspondingly. Positive expression of CD44 and CD90 and negative expression of CD34 were noted. In the osteogenic differentiation medium, the cells differentiated toward osteoblasts. As human Men-SCs are easily collectable without any invasive procedure and are a safe and rapid source of MSCs, they can be a good candidate for stem cell banking and cell transplantation in women. PMID:26989284

  1. Role of adsorption kinetics in the low-temperature Si growth by gas-source molecular beam epitaxy: In situ observations and detailed modeling of the growth

    SciTech Connect

    Murata, Takeshi; Nakazawa, Hideki; Tsukidate, Yoshikazu; Suemitsu, Maki

    2001-08-06

    The growth rate and surface hydrogen coverage during Si gas-source molecular beam epitaxy using disilane have been obtained as functions of both the growth temperature and the source-gas pressure. The activation energy of the low-temperature (<600{sup o}C) growth rate was found to increase with the source-gas pressure, indicating a contribution by the adsorption process in these low-temperature growth kinetics. Several growth models have been constructed based on the results, among which the two-site/four-site-adsorption model [M. Suemitsu Jpn. J. Appl. Phys., Part 236, L625 (1997)] showed the best fit to both the growth rate and the hydrogen coverage. {copyright} 2001 American Institute of Physics.

  2. Phytochrome-controlled extension growth of Avena sativa L. seedlings : I. Kinetic characterization of mesocotyl, coleoptile, and leaf responses.

    PubMed

    Schopfer, P; Fidelak, K H; Schäfer, E

    1982-05-01

    The effects of continuous red and far-red light and of brief light pulses on the growth kinetics of the mesocotyl, coleoptile, and primary leaf of intact oat (Avena sativa L.) seedlings were investigated. Mesocotyl lengthening is strongly inhibited, even by very small amounts of Pfr, the far-red light absorbing form of phytochrome (e.g., by [Pfr]≈0.1% of total phytochrome, established by a 756-nm light pulse). Coleoptile growth is at first promoted by Pfr, but apparently inhibited later. This inhibition is correlated in time with the rupturing of the coleoptile tip by the primary leaf, the growth of which is also promoted by phytochrome. The growth responses of all three seedling organs are fully reversible by far-red light. The apparent lack of photoreversibility observed by some previous investigators of the mesocotyl inhibition can be explained by an extremely high sensitivity to Pfr. Experiments with different seedling parts failed to demonstrate any further obvious interorgan relationship in the light-mediated growth responses of the mesocotyl and coleoptile. The organspecific growth kinetics, don't appear to be influenced by Pfr destruction. Following an irradiation, the growth responses are quantitatively determined by the level of Pfr established at the onset of darkness rather than by the actual Pfr level present during the growth period. PMID:24276065

  3. Direct Dynamic Kinetic Analysis and Computer Simulation of Growth of Clostridium perfringens in Cooked Turkey during Cooling.

    PubMed

    Huang, Lihan; Vinyard, Bryan T

    2016-03-01

    This research applied a new 1-step methodology to directly construct a tertiary model that describes the growth of Clostridium perfringens in cooked turkey meat under dynamically cooling conditions. The kinetic parameters of the growth models were determined by numerical analysis and optimization using multiple dynamic growth curves. The models and kinetic parameters were validated using independent growth curves obtained under various cooling conditions. The results showed that the residual errors (ε) of the predictions followed a Laplace distribution that is symmetric with respect to ε = 0. For residual errors, 90.6% are within ±0.5 Log CFU/g and 73.4% are ±0.25 Log CFU/g for all growth curves used for validation. For relative growth <1.0 Log CFU/g, 88.9% of the residual errors are within ±0.5 Log CFU/g, and 63.0% are within ±0.25 Log CFU/g. For relative growth of <2.0 Log CFU/g, 92.7% of the residual errors are within ±0.5 Log CFU/g, and 70.3% are within ±0.25 Log CFU/g. The scale and distribution of residual errors clearly suggests that the models and estimated kinetic parameters are reasonably accurate in predicting the growth of C. perfringens. Monte Carlo simulation was used to estimate the probabilities of >1.0 and 2.0 Log CFU/g relative growth of C. perfringens in the final products at the end of cooling. This probabilistic process analysis approach provides a new alternative for estimating and managing the risk of a product and can help the food industry and regulatory agencies assess the safety of cooked meat in the event of cooling deviation. PMID:26801359

  4. Determination of kinetic parameters of crystal growth rate of borax in aqueous solution by using the rotating disc technique

    NASA Astrophysics Data System (ADS)

    Sahin, Omer; Aslan, Fevzi; Ozdemir, Mustafa; Durgun, Mustafa

    2004-10-01

    Growth rate of polycrystalline disc of borax compressed at different pressure and rotated at various speed has been measured in a rotating disc crystallizer under well-defined conditions of supersaturation. It was found that the mass transfer coefficient, K, increased while overall growth rate constant, Kg, and surface reaction constant, kr, decreased with increasing smoothness of the disc. It was also determined that kinetic parameters (kr , r , K , g) of crystal growth rate of borax decreased with increasing rotating speed of the polycrystalline disc. The effectiveness factor was calculated from the growth rate data to evaluate the relative magnitude of the steps in series bulk diffusion through the mass transfer boundary layer and the surface integration. At low rotating speed of disc, the crystal growth rate of borax is mainly controlled by integration. However, both diffusion and integration steps affect the growth rate of borax at higher rotating speed of polycrystalline disc.

  5. Anisotropic growth kinetics in the geometrically frustrated isosceles triangular Ising antiferromagnet CoNb2O6

    NASA Astrophysics Data System (ADS)

    Kobayashi, S.; Mitsuda, S.; Jogetsu, T.; Miyamoto, J.; Katagiri, H.; Kohn, K.

    1999-10-01

    The growth kinetics in the geometrically frustrated isosceles triangular Ising antiferromagnet CoNb2O6 has been studied by neutron scattering and ac susceptibility measurements under magnetic fields. Spatially anisotropic growth of fourfold degenerate ground states is found to proceed according to the power law tn with anomalously low growth exponent n~=0.2 compared with 1/2 of the conventional Ising magnets. This anomalous power law is independent of both the strength of applied field and the degree of ground-state degeneracy.

  6. Kinetics of Nucleation and Crystal Growth in Glass Forming Melts in Microgravity

    NASA Technical Reports Server (NTRS)

    Day, Delbert E.; Ray, Chandra S.

    2003-01-01

    This flight definition project has the specific objective of investigating the kinetics of nucleation and crystal growth in high temperature inorganic oxide, glass forming melts in microgravity. It is related to one1 of our previous NASA projects that was concerned with glass formation for high temperature containerless melts in microgravity. The previous work culminated in two experiments which were conducted aboard the space shuttle in 1983 and 1985 and which consisted of melting (at 1500 C) and cooling levitated 6 to 8 mm diameter spherical samples in a Single Axis Acoustic Levitator (SAAL) furnace. Compared to other types of materials, there have been relatively few experiments, 6 to 8, conducted on inorganic glasses in space. These experiments have been concerned with mass transport (alkali diffusion), containerless melting, critical cooling rate for glass formation, chemical homogeneity, fiber pulling, and crystallization of glass forming melts. One of the most important and consistent findings in all of these experiments has been that the glasses prepared in microgravity are more resistant to crystallization (better glass former) and more chemically homogeneous than equivalent glasses made on earth (1g). The chemical composition of the melt appears relatively unimportant since the same general results have been reported for oxide, fluoride and chalcogenide melts. These results for space-processed glasses have important implications, since glasses with a higher resistance to crystallization or higher chemical homogeneity than those attainable on earth can significantly advance applications in areas such as fiber optics communications, high power laser glasses, and other photonic devices where glasses are the key functional materials. The classical theories for nucleation and crystal growth for a glass or melt do not contain any parameter that is directly dependent upon the g-value, so it is not readily apparent why glasses prepared in microgravity should be

  7. Kinetic model of growth and coalescence of oxygen and carbon precipitates during cooling of As-grown silicon crystals

    NASA Astrophysics Data System (ADS)

    Talanin, V. I.; Talanin, I. E.

    2011-01-01

    A kinetic model of growth and coalescence of oxygen and carbon precipitates has been proposed. This model in combination with the kinetic model of the formation of oxygen and carbon precipitates represents a unified model of precipitation in as-grown dislocation-free silicon single crystals during their cooling in the temperature range from 1683 to 300 K. It has been demonstrated that the results of the calculations are in good agreement with the experimental data obtained from investigations of grown-in microdefects.

  8. Discovery of novel insulin-like growth factor-1 receptor inhibitors with unique time-dependent binding kinetics.

    PubMed

    Jin, Meizhong; Petronella, Brenda A; Cooke, Andy; Kadalbajoo, Mridula; Siu, Kam W; Kleinberg, Andrew; May, Earl W; Gokhale, Prafulla C; Schulz, Ryan; Kahler, Jennifer; Bittner, Mark A; Foreman, Kenneth; Pachter, Jonathan A; Wild, Robert; Epstein, David; Mulvihill, Mark J

    2013-07-11

    This letter describes a series of small molecule inhibitors of IGF-1R with unique time-dependent binding kinetics and slow off-rates. Structure-activity and structure-kinetic relationships were elucidated and guided further optimizations within the series, culminating in compound 2. With an IGF-1R dissociative half-life (t 1/2) of >100 h, compound 2 demonstrated significant and extended PD effects in conjunction with tumor growth inhibition in xenograft models at a remarkably low and intermittent dose, which correlated with the observed in vitro slow off-rate properties. PMID:24900721

  9. Understanding growth kinetics of nanorods in microemulsion: a combined fluorescence correlation spectroscopy, dynamic light scattering, and electron microscopy study.

    PubMed

    Sharma, Soma; Pal, Nibedita; Chowdhury, Pramit K; Sen, Sobhan; Ganguli, Ashok K

    2012-12-01

    Even though nanostructures of various shapes and sizes can be controlled by microemulsions, there is substantial difficulty in understanding their growth mechanism. The evolution of nanostructures from the time of mixing of reactants to their final stage is a heterogeneous process involving a variety of intermediates. To obtain a deeper insight into these kinetic steps, we studied the slow growth kinetics (extending over eight days) of iron oxalate nanorods inside the polar core of water-in-oil microemulsion droplets made of cetyltrimethylammonium bromide/1-butanol/isooctane. Fluorescence correlation spectroscopy (FCS), dynamic light scattering (DLS), and transmission electron microscopy (TEM) have been employed to monitor the nanostructure growth at (near) the single-droplet level and in an ensemble. Analyzing FCS data with suitable kinetic model we obtain transient dimer lifetime (28 μs) and the droplet fusion rates (and fusion tendency) on each day as the reaction proceeds. The droplet fusion rate is found to directly control the nanorod growth in microemulsion solution and attains its maximum value (3.55 × 10(4) s(-1)) on day 6, when long nanorods are found in TEM data, implying that more and more reactants are fed into the growing system at this stage. Combining FCS, DLS, and TEM results, we find three distinct periods in the entire growth process: a long nucleation-dominant nanoparticle growth period which forms nanoparticles of critical (average) size of ∼53 nm, followed by a short period where isotropic nanoparticles switch to anisotropic growth to form nanorods, and finally elongation of nanorods and growth (and shrinking) of nanoparticles. PMID:23140268

  10. Modified energetics and growth kinetics on H-terminated GaAs (110)

    NASA Astrophysics Data System (ADS)

    Galiana, B.; Benedicto, M.; Díez-Merino, L.; Lorbek, S.; Hlawacek, G.; Teichert, C.; Tejedor, P.

    2013-10-01

    Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As4, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

  11. Kinetics of Diffusional Droplet Growth in a Liquid/Liquid Two-Phase System

    NASA Technical Reports Server (NTRS)

    Glicksman, M. E.; Fradkov, V. E.

    1996-01-01

    We address the problem of diffusional interactions in a finite sized cluster of spherical particles for volume fractions, V(sub v) in the range 0-0.01. We determined the quasi-static monopole diffusion solution for n particles distributed at random in a continuous matrix. A global mass conservation condition is employed, obviating the need for any external boundary condition. The numerical results provide the instantaneous (snapshot) growth or shrinkage rate of each particle, precluding the need for extensive time-dependent computations. The close connection between these snapshot results and the coarsegrained kinetic constants are discussed. A square-root dependence of the deviations of the rate constants from their zero volume fraction value is found for the higher V(sub v) investigated. This behavior is consistent with predictions from diffusion Debye-Huckel screening theory. By contrast, a cube-root dependence, reported in earlier numerical studies, is found for the lower V(sub v) investigated. The roll-over region of the volume fraction where the two asymptotics merge depends on the number of particles, n, alone. A theoretical estimate for the roll-over point predicts that the corresponding V(sub v) varies as n(sup -2), in good agreement with the numerical results.

  12. Modified energetics and growth kinetics on H-terminated GaAs (110)

    SciTech Connect

    Galiana, B.; Benedicto, M.; Díez-Merino, L.; Tejedor, P.; Lorbek, S.; Hlawacek, G.; Teichert, C.

    2013-10-28

    Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As{sub 4}, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å{sup 2} measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As{sub 4} molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

  13. Different antibacterial activity of novel theophylline-based ionic liquids - Growth kinetic and cytotoxicity studies.

    PubMed

    Borkowski, Andrzej; Ławniczak, Łukasz; Cłapa, Tomasz; Narożna, Dorota; Selwet, Marek; Pęziak, Daria; Markiewicz, Bartosz; Chrzanowski, Łukasz

    2016-08-01

    The aim of this study was to investigate novel theophylline-based ionic liquids and their cytotoxic effects towards model Gram-positive and Gram-negative bacteria (Bacillus cereus and Escherichia coli, respectively). Growth kinetics, respiratory rates and dehydrogenase activities were studied in the presence of ionic liquids at concentrations ranging from 10 to 1000mg/L. Additionally, the influence of ionic liquids on bacterial cells associated with specific interactions based on the structure of cell wall was evaluated. This effect was assessed by viability tests and scanning electron microscope observations. The obtained results confirmed that ionic liquids exhibit different levels of toxicity in relation to Gram-positive and Gram-negative bacteria. Those effects are associated with the chemical structure of the cationic species of the ionic liquids and their critical micelle concentration value. It was established that the presence of an alkyl or allyl group increased the toxicity, whereas the presence of an aryl group in the cation decreased the toxic effect of ILs. Results presented in this study also revealed unexpected effects of self-aggregation of E. coli cells. Overall, it was established that the studied ILs exhibited higher toxicity towards Gram-positive bacteria due to different interactions between the ILs and the cell membranes. These findings may be of importance for the design of ILs with targeted antimicrobial properties. PMID:27082812

  14. Cellular kinetics in growth anomalies of the scleractinian corals Porites australiensis and Montipora informis .

    PubMed

    Yasuda, Naoko; Hidaka, Michio

    2012-12-01

    Growth anomalies (GAs) in corals are characterized by morphological abnormalities of the skeleton as well as polyps and coenosarcs. GAs commonly appear as protuberances with fewer polyps and are paler in color due to decreased zooxanthellae density. To test the hypothesis that morphological anomalies in GAs may be caused by unregulated cellular kinetics, the relative abundances of apoptotic cells and proliferating cells were compared between GAs and apparently healthy regions in 2 corals, Porites australiensis and Montipora informis. Apoptotic cells and proliferating cells were detected using TUNEL assays and BrdU incorporation assays, respectively. The labeling indices for apoptotic nuclei and BrdU-labeled nuclei were measured in the epidermis, oral gastrodermis, aboral gastrodermis, and calicodermis. The labeling index for apoptotic nuclei in the oral gastrodermis and the calicodermis was significantly lower in GAs than in healthy regions in both coral species. The index for BrdU-labeled cells in the calicodermis was significantly higher in GAs than in healthy regions in both coral species. When GA regions partially died, the GA tissues directly adjacent to the dead areas exhibited signs of necrosis, although some apoptotic cells were also present. Healthy oral gastrodermis adjacent to the border between the healthy and GA regions exhibited higher frequencies of apoptotic cells. These results suggest that apoptotic pathways were suppressed and cell proliferation was promoted in GA regions, although cells in GAs may die through both necrosis and apoptosis. PMID:23209073

  15. Kinetic modeling of tumor growth and dissemination in the craniospinal axis: implications for craniospinal irradiation

    PubMed Central

    Meyer, Jeffrey J; Marks, Lawrence B; Halperin, Edward C; Kirkpatrick, John P

    2006-01-01

    Background Medulloblastoma and other types of tumors that gain access to the cerebrospinal fluid can spread throughout the craniospinal axis. The purpose of this study was to devise a simple multi-compartment kinetic model using established tumor cell growth and treatment sensitivity parameters to model the complications of this spread as well as the impact of treatment with craniospinal radiotherapy. Methods A two-compartment mathematical model was constructed. Rate constants were derived from previously published work and the model used to predict outcomes for various clinical scenarios. Results The model is simple and with the use of known and estimated clinical parameters is consistent with known clinical outcomes. Treatment outcomes are critically dependent upon the duration of the treatment break and the radiosensitivity of the tumor. Cross-plot analyses serve as an estimate of likelihood of cure as a function of these and other factors. Conclusion The model accurately describes known clinical outcomes for patients with medulloblastoma. It can help guide treatment decisions for radiation oncologists treating patients with this disease. Incorporation of other treatment modalities, such as chemotherapy, that enhance radiation sensitivity and/or reduce tumor burden, are predicted to significantly increase the probability of cure. PMID:17187666

  16. Exponential approximations in optimal design

    NASA Technical Reports Server (NTRS)

    Belegundu, A. D.; Rajan, S. D.; Rajgopal, J.

    1990-01-01

    One-point and two-point exponential functions have been developed and proved to be very effective approximations of structural response. The exponential has been compared to the linear, reciprocal and quadratic fit methods. Four test problems in structural analysis have been selected. The use of such approximations is attractive in structural optimization to reduce the numbers of exact analyses which involve computationally expensive finite element analysis.

  17. Understanding the performance of sulfate reducing bacteria based packed bed reactor by growth kinetics study and microbial profiling.

    PubMed

    Dev, Subhabrata; Roy, Shantonu; Bhattacharya, Jayanta

    2016-07-15

    A novel marine waste extract (MWE) as alternative nitrogen source was explored for the growth of sulfate reducing bacteria (SRB). Variation of sulfate and nitrogen (MWE) showed that SRB growth follows an uncompetitive inhibition model. The maximum specific growth rates (μmax) of 0.085 and 0.124 h(-1) and inhibition constants (Ki) of 56 and 4.6 g/L were observed under optimized sulfate and MWE concentrations, respectively. The kinetic data shows that MWE improves the microbial growth by 27%. The packed bed bioreactor (PBR) under optimized sulfate and MWE regime showed sulfate removal efficiency of 62-66% and metals removal efficiency of 66-75% on using mine wastewater. The microbial community analysis using DGGE showed dominance of SRB (87-89%). The study indicated the optimum dosing of sulfate and cheap organic nitrogen to promote the growth of SRB over other bacteria. PMID:27085153

  18. Effect of interwire separation on growth kinetics and properties of site-selective GaAs nanowires

    SciTech Connect

    Rudolph, D.; Schweickert, L.; Morkötter, S.; Loitsch, B.; Hertenberger, S.; Becker, J.; Bichler, M.; Finley, J. J.; Koblmüller, G.; Abstreiter, G.

    2014-07-21

    We report tuning of the growth kinetics, geometry, and properties of autocatalytic GaAs nanowires (NW) by precisely controlling their density on SiO{sub 2}-mask patterned Si (111) substrates using selective area molecular beam epitaxy. Using patterned substrates with different mask opening size (40–120 nm) and pitch (0.25–3 μm), we find that the NW geometry (length, diameter) is independent of the opening size, in contrast to non-catalytic GaAs NWs, whereas the NW geometry strongly depends on pitch, i.e., interwire separation and NW density. In particular, two distinct growth regimes are identified: a diffusion-limited regime for large pitches (low NW density) and a competitive growth regime for smaller pitches (high NW density), where axial and radial NW growth rates are reduced. The transition between these two regimes is significantly influenced by the growth conditions and shifts to smaller pitches with increasing As/Ga flux ratio. Ultimately, the pitch-dependent changes in growth kinetics lead to distinctly different photoluminescence properties, highlighting that mask template design is a very critical parameter for tuning intrinsic NW properties.

  19. Plagioclase nucleation and growth kinetics in a hydrous basaltic melt by decompression experiments

    NASA Astrophysics Data System (ADS)

    Arzilli, Fabio; Agostini, C.; Landi, P.; Fortunati, A.; Mancini, L.; Carroll, M. R.

    2015-12-01

    Isothermal single-step decompression experiments (at temperature of 1075 °C and pressure between 5 and 50 MPa) were used to study the crystallization kinetics of plagioclase in hydrous high-K basaltic melts as a function of pressure, effective undercooling (Δ T eff) and time. Single-step decompression causes water exsolution and a consequent increase in the plagioclase liquidus, thus imposing an effective undercooling (∆ T eff), accompanied by increased melt viscosity. Here, we show that the decompression process acts directly on viscosity and thermodynamic energy barriers (such as interfacial-free energy), controlling the nucleation process and favoring the formation of homogeneous nuclei also at high pressure (low effective undercoolings). In fact, this study shows that similar crystal number densities ( N a) can be obtained both at low and high pressure (between 5 and 50 MPa), whereas crystal growth processes are favored at low pressures (5-10 MPa). The main evidence of this study is that the crystallization of plagioclase in decompressed high-K basalts is more rapid than that in rhyolitic melts on similar timescales. The onset of the crystallization process during experiments was characterized by an initial nucleation event within the first hour of the experiment, which produced the largest amount of plagioclase. This nucleation event, at short experimental duration, can produce a dramatic change in crystal number density ( N a) and crystal fraction ( ϕ), triggering a significant textural evolution in only 1 h. In natural systems, this may affect the magma rheology and eruptive dynamics on very short time scales.

  20. Kinetics of Nucleation and Crystal Growth in Glass Forming Melts in Microgravity

    NASA Technical Reports Server (NTRS)

    Day, Delbert E.; Ray, Chandra S.

    2001-01-01

    This flight definition project has the specific objective of investigating the kinetics of nucleation and crystal growth in high temperature inorganic oxide, glass forming melts in microgravity. It is related to one of our previous NASA projects that was concerned with glass formation for high temperature containerless melts in microgravity. The previous work culminated in two experiments which were conducted aboard the space shuttle in 1983 and 1985 and which consisted of melting (at 1500 C) and cooling levitated 6 to 8 mm diameter spherical samples in a Single Axis Acoustic Levitator (SAAL) furnace. Compared to other types of materials, there have been relatively few experiments, 6 to 8, conducted on inorganic glasses in space. These experiments have been concerned with mass transport (alkali diffusion), containerless melting, critical cooling rate for glass formation, chemical homogeneity, fiber pulling, and crystallization of glass forming melts. One of the most important and consistent findings in all of these experiments has been that the glasses prepared in microgravity are more resistant to crystallization (better glass former) and more chemically homogeneous than equivalent glasses made on Earth (1 g). The chemical composition of the melt appears relatively unimportant since the same general results have been reported for oxide, fluoride and chalcogenide melts. These results for space-processed glasses have important implications, since glasses with a higher resistance to crystallization or higher chemical homogeneity than those attainable on Earth can significantly advance applications in areas such as fiber optics communications, high power laser glasses, and other photonic devices where glasses are the key functional materials.

  1. Substrate uptake tests and quantitative FISH show differences in kinetic growth of bulking and non-bulking activated sludge.

    PubMed

    Lou, Inchio; de Los Reyes, Francis L

    2005-12-20

    The competition between filaments and floc formers in activated sludge has been historically described using kinetic selection. However, recent studies have suggested that bacterial storage may also be an important factor in microbial selection, since the dynamic nature of substrate flows into wastewater treatment plants elicit transient responses from microorganisms. Respirometry-based kinetic selection should thus be reevaluated by considering cell storage, and a more reliable method should be developed to include bacterial storage in the analysis of growth of filaments and floc formers in activated sludge. In this study, we applied substrate uptake tests combined with metabolic modeling to determine the growth rates, yields and maintenance coefficients of bulking and non-bulking activated sludge developed in lab scale reactors under feast and famine conditions. The results of quantitative fluorescence in situ hybridization (FISH) showed that the filaments Eikelboom Type 1851, Type 021N, and Thiothrix nivea were dominant in bulking sludge, comprising 42.0 % of mixed liquor volatile suspended solids (MLVSS), with 61.6% of the total filament length extending from flocs into bulk solution. Only low levels of Type 1851 filament length (4.9% of MLVSS) occurred in non-bulking sludge, 83.0% of which grew inside the flocs. The kinetic parameters determined from the substrate uptake tests were consistent with those from respirometry and showed that filamentous bulking sludge had lower growth rates and maintenance coefficients than non-bulking sludge. These results provide support for growth kinetic differences in explaining the competitive strategy of filamentous bacteria. PMID:16155949

  2. Layer-growth kinetics on gaseous nitriding of pure iron: Evaluation of diffusion coefficients for nitrogen in iron nitrides

    NASA Astrophysics Data System (ADS)

    Somers, Marcel A. J.; Mittemeijer, Eric J.

    1995-01-01

    Models were derived for monolayer and bilayer growth into a substrate in which diffusion of the solute governs the growth kinetics, as in gas-solid reactions, for example. In the models, the composition dependence of the solute diffusivity in the phases constituting the layers was accounted for by appropriate definition of an effective diffusion coefficient for a (sub)layer. This effective diffusion coefficient is the intrinsic diffusion coefficient weighted over the composition range of the (sub)layer. The models were applied for analyzing the growth kinetics of a γ'-Fe4N1-x monolayer on an α-Fe substrate and the growth kinetics of an ɛ-Fe2N1-z/γ'-Fe4N1-x bilayer on an α-Fe substrate, as observed by gaseous nitriding in an NH3/H2-gas mixture at 843 K. The kinetics of layer development and the evolution of the microstructure were investigated by means of thermogravimetry, layer-thickness measurements, light microscopy, and electron probe X-ray microanalysis (EPMA). The effective and self-diffusion coefficients were determined for each of the nitride layers. The composition dependence of the intrinsic (and effective) diffusion coefficients was established. Re-evaluating literature data for diffusion in γ'-Fe4N1-x on the basis of the present model, it followed that the previous and present data are consistent. The activation energy for diffusion of nitrogen in γ'-Fe4N1-x was determined from the temperature dependence of the self-diffusion coefficient. The self-diffusion coefficient for nitrogen in ɛ-Fe2N1-z was significantly larger than that for γ'-Fe4N1-x. This was explained qualitatively, considering the possible mechanisms for interstitial diffusion of nitrogen atoms in the close-packed iron lattices of the ɛ and γ' iron nitrides.

  3. Discussion on the Alloying Element Partition and Growth Kinetics of Proeutectoid Ferrite in Fe-C-Mn-X Alloys

    NASA Astrophysics Data System (ADS)

    Wei, R.; Enomoto, M.

    2011-12-01

    Experimental data on alloying element partition and growth kinetics of proeutectoid ferrite in quaternary Fe-C-Mn-Si, Ni, and Co alloys were reanalyzed using an approximate method, which permits a quick evaluation of alloy partitioning to be made. The method yielded results in good agreement with DICTRA and is applicable to Fe-C base multicomponent alloys. Differences of the predicted local condition at the α/ γ boundary from those previously presented in the alloys are noted.

  4. Atmospheric pressure flow reactor / aerosol mass spectrometer studies of tropospheric aerosol nucleat and growth kinetics. Final report, June, 2001

    SciTech Connect

    Worsnop, Douglas R.

    2001-06-01

    The objective of this program was to determine the mechanisms and rates of growth and transformation and growth processes that control secondary aerosol particles in both the clear and polluted troposphere. The experimental plan coupled an aerosol mass spectrometer (AMS) with a chemical ionization mass spectrometer to provide simultaneous measurement of condensed and particle phases. The first task investigated the kinetics of tropospheric particle growth and transformation by measuring vapor accretion to particles (uptake coefficients, including mass accommodation coefficients and heterogeneous reaction rate coefficients). Other work initiated investigation of aerosol nucleation processes by monitoring the appearance of submicron particles with the AMS as a function of precursor gas concentrations. Three projects were investigated during the program: (1) Ozonolysis of oleic acid aerosols as model of chemical reactivity of secondary organic aerosol; (2) Activation of soot particles by measurement deliquescence in the presence of sulfuric acid and water vapor; (3) Controlled nucleation and growth of sulfuric acid aerosols.

  5. About the interest of a zooplankton compartment in pond systems: methodology to study the growth kinetic of Daphnia pulex on Scenedesmus sp.

    PubMed

    Liady, M N D; Tangou, T T; Fiogbe, E D; Cauchie, H-M; Vasel, J-L

    2015-01-01

    A reliable characterization of cladocerans' growth kinetic on their substrates is crucial for the estimation of their biochemical conversion rate in pond models. Although many studies reported cladocerans' growth inhibitions by high chlorophyceae contents, their growth kinetics had continued to be described in many pond system models by Monod-type kinetic, which describes growth saturation by high substrate contents, but fails to explain the disappearance of cladocerans observed during chlorophyceae's bloom periods. This study aimed to develop a methodology and assess whether growth-inhibition-type models used to describe microbial growth kinetics can be applicable to cladocerans. Experiments were carried out using Daphnia pulex populations and Scenedesmus sp. First, biomass of D. pulex was measured through digital image processing (DIP) during growth experiments. Then, three candidate models (i.e., Andrews, Edward and Haldane models), along with the Monod model, were fitted to the observed data and compared. The results showed that the DIP technique provided reliable results for estimating the biomass of D. pulex. Our findings show that the candidate growth inhibition-type models satisfactorily described D. pulex's growth kinetic (86% variance accounted for). Scenesdemus sp. were not strong inhibitors of the growth of D. pulex (high inhibition constant and low half-saturation constant found). PMID:26442483

  6. Exponential Finite-Difference Technique

    NASA Technical Reports Server (NTRS)

    Handschuh, Robert F.

    1989-01-01

    Report discusses use of explicit exponential finite-difference technique to solve various diffusion-type partial differential equations. Study extends technique to transient-heat-transfer problems in one dimensional cylindrical coordinates and two and three dimensional Cartesian coordinates and to some nonlinear problems in one or two Cartesian coordinates.

  7. Linear or Exponential Number Lines

    ERIC Educational Resources Information Center

    Stafford, Pat

    2011-01-01

    Having decided to spend some time looking at one's understanding of numbers, the author was inspired by "Alex's Adventures in Numberland," by Alex Bellos to look at one's innate appreciation of number. Bellos quotes research studies suggesting that an individual's natural appreciation of numbers is more likely to be exponential rather than linear,…

  8. Dynamic determination of kinetic parameters, computer simulation, and probabilistic analysis of growth of Clostridium perfringens in cooked beef during cooling.

    PubMed

    Huang, Lihan

    2015-02-16

    The objective of this research was to develop a new one-step methodology that uses a dynamic approach to directly construct a tertiary model for prediction of the growth of Clostridium perfringens in cooked beef. This methodology was based on simultaneous numerical analysis and optimization of both primary and secondary models using multiple dynamic growth curves obtained under different conditions. Once the models were constructed, the bootstrap method was used to calculate the 95% confidence intervals of kinetic parameters, and a Monte Carlo simulation method was developed to validate the models using the growth curves not previously used in model development. The results showed that the kinetic parameters obtained from this study accurately matched the common characteristics of C. perfringens, with the optimum temperature being 45.3°C. The results also showed that the predicted growth curves matched accurately with experimental observations used in validation. The mean of residuals of the predictions is -0.02logCFU/g, with a standard deviation of only 0.23logCFU/g. For relative growths <1logCFU/g, the residuals of predictions are <0.4logCFU/g. Overall, 74% of the residuals of predictions are <0.2logCFU/g, 7.7% are >0.4logCFU/g, while only 1.5% are >0.8logCFU/g. In addition, the dynamic model also accurately predicted four isothermal growth curves arbitrarily chosen from the literature. Finally, the Monte Carlo simulation was used to provide the probability of >1 and 2logCFU/g relative growths at the end of cooling. The results of this study will provide a new and accurate tool to the food industry and regulatory agencies to assess the safety of cooked beef in the event of cooling deviation. PMID:25500276

  9. New insight into the ZnO sulfidation reaction: mechanism and kinetics modeling of the ZnS outward growth.

    PubMed

    Neveux, Laure; Chiche, David; Pérez-Pellitero, Javier; Favergeon, Loïc; Gay, Anne-Sophie; Pijolat, Michèle

    2013-02-01

    Zinc oxide based materials are commonly used for the final desulfurization of synthesis gas in Fischer-Tropsch based XTL processes. Although the ZnO sulfidation reaction has been widely studied, little is known about the transformation at the crystal scale, its detailed mechanism and kinetics. A model ZnO material with well-determined characteristics (particle size and shape) has been synthesized to perform this study. Characterizations of sulfided samples (using XRD, TEM and electron diffraction) have shown the formation of oriented polycrystalline ZnS nanoparticles with a predominant hexagonal form (wurtzite phase). TEM observations also have evidenced an outward development of the ZnS phase, showing zinc and oxygen diffusion from the ZnO-ZnS internal interface to the surface of the ZnS particle. The kinetics of ZnO sulfidation by H(2)S has been investigated using isothermal and isobaric thermogravimetry. Kinetic tests have been performed that show that nucleation of ZnS is instantaneous compared to the growth process. A reaction mechanism composed of eight elementary steps has been proposed to account for these results, and various possible rate laws have been determined upon approximation of the rate-determining step. Thermogravimetry experiments performed in a wide range of H(2)S and H(2)O partial pressures have shown that the ZnO sulfidation reaction rate has a nonlinear variation with H(2)S partial pressure at the same time no significant influence of water vapor on reaction kinetics has been observed. From these observations, a mixed kinetics of external interface reaction with water desorption and oxygen diffusion has been determined to control the reaction kinetics and the proposed mechanism has been validated. However, the formation of voids at the ZnO-ZnS internal interface, characterized by TEM and electron tomography, strongly slows down the reaction rate. Therefore, the impact of the decreasing ZnO-ZnS internal interface on reaction kinetics has been

  10. Correlation between growth kinetics and nanoscale resistive switching properties of SrTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Muenstermann, Ruth; Menke, Tobias; Dittmann, Regina; Mi, Shaobo; Jia, Chun-Lin; Park, Daesung; Mayer, Joachim

    2010-12-01

    We deliberately fabricated SrTiO3 thin films deviating from ideal stoichiometry and from two-dimensional layer-by-layer growth mode, in order to study the impact of well pronounced defect arrangements on the nanoscale electrical properties. By combining transmission electron microscopy with conductive-tip atomic force microscopy we succeeded to elucidate the microstructure of thin films grown by pulsed laser deposition under kinetically limited growth conditions and to correlate it with the local electrical properties. SrTiO3 thin films, grown in a layer-by-layer growth mode, exhibit a defect structure and conductivity pattern close to single crystals, containing irregularly distributed, resistive switching spots. In contrast to this, Ti-rich films exhibit short-range-ordered, well-conducting resistive switching units. For Ti-rich films grown in a kinetically more restricted island growth mode, we succeeded to identify defective island boundaries with the location of tip-induced resistive switching. The observed nanoscale switching behavior is consistent with a voltage driven oxygen vacancy movement that induces a local redox-based metal-to-insulator transition. Switching occurs preferentially in defect-rich regions, that exhibit a high concentration of oxygen vacancies and might act as easy-diffusion-channels.

  11. Kinetic modeling of anthocyanin degradation and microorganism growth during postharvest storage of açai fruits (Euterpe oleracea).

    PubMed

    Rogez, Hervé; Akwie, Santuscha N L T; Moura, Fábio G; Larondelle, Yvan

    2012-12-01

    The unavoidable damage of açai (Euterpe oleracea) fruits (AF) during picking leads to microbial contamination and anthocyanin degradation, which prejudice the consumed fruit drink. Thirteen lots of AF (24 kg) from different municipal districts of the Pará State (Brazil) were monitored during a 75-h-long storage in the dark at 30 °C for microbial growth, and 7 lots for anthocyanin degradation. On arrival at the laboratory, anthocyanins presented a mean concentration of 828 mg kg(-1) fruits with a standard deviation of 323 mg kg(-1) fruits whereas mean microbial contamination was 2.64 10(6) CFU g(-1) of dry matter for total mesophilic bacteria, 1.98 10(3) MPN g(-1) DM for fecal coliforms, and 1.11 10(5) CFU g(-1) DM for moulds and yeasts. Kinetic growth of the microbes could be fitted to a quadratic equation with an unusual rapid growth during the 1st 24 h. The kinetics of anthocyanin degradation fitted a 1st-order equation. The mean velocity constant of the reaction (k(1)) was of 0.0137 h(-1) and the mean half-life (t(½)) of the anthocyanins was 50 h. These results indicate that the AF simultaneously suffer extensive anthocyanin degradation and explosive microbial growth during the postharvest period needing a special care. PMID:23240969

  12. Activation of oxygen-mediating pathway using copper ions: fine-tuning of growth kinetics in gold nanorod overgrowth.

    PubMed

    Liu, Wenqi; Zhang, Hui; Wen, Tao; Yan, Jiao; Hou, Shuai; Shi, Xiaowei; Hu, Zhijian; Ji, Yinglu; Wu, Xiaochun

    2014-10-21

    Growth kinetics plays an important role in the shape control of nanocrystals (NCs). Herein, we presented a unique way to fine-tune the growth kinetics via oxidative etching activated by copper ions. For the overgrowth of gold nanorods (Au NRs), competitive adsorption of dissolved oxygen on rod surface was found to slow down the overgrowth rate. Copper ions were able to remove the adsorbed oxygen species from the Au surface via oxidative etching, thus exposing more reaction sites for Au deposition. In this way, copper ions facilitated the overgrowth process. Furthermore, Cu(2+) rather than Cu(+) acted as the catalyst for the oxidative etching. Comparative study with Ag(+) indicated that Cu(2+) cannot regulate NC shapes via an underpotential deposition mechanism. In contrast, Ag(+) led to the formation of Au tetrahexahedra (THH) and a slight decrease of the growth rate at similar growth conditions. Combining the distinct roles of the two ions enabled elongated THH to be produced. Copper ions activating the O2 pathway suggested that dissolved oxygen has a strong affinity for the Au surface. Moreover, the results of NC-sensitized singlet oxygen ((1)O2) indicated that the absorbed oxygen species on the surface of Au NCs bounded with low-index facets mainly existed in the form of molecular O2. PMID:25244407

  13. Study of oxide and α-Zr(O) growth kinetics from high temperature steam oxidation of Zircaloy-4 cladding

    NASA Astrophysics Data System (ADS)

    Sawarn, Tapan K.; Banerjee, Suparna; Samanta, Akanksha; Rath, B. N.; Kumar, Sunil

    2015-12-01

    Oxidation kinetics of Zircaloy-4 cladding of fuel pins of Indian pressurized heavy water reactors (IPHWRs) under a simulated loss of coolant accident (LOCA) condition was investigated. The kinetic rate constants for the oxide and oxygen stabilized α-Zr phase growth were established from the isothermal metal-steam reaction at high temperatures (900-1200 °C) with soaking periods in the range of 60-900 s. Oxide and α-Zr(O) layer thickness were measured to derive the respective growth rates. The observed rates obeyed a parabolic law and Arrhenius expressions of rate constants were established. Percentage equivalent clad reacted (%ECR) was calculated using Baker-Just equation. Hydrogen estimation was carried out on the oxidized samples using inert gas fusion technique. The hydrogen pick up was found to be in the range 10-30 ppm. The measured values of oxide and α-Zr(O) layer thickness were compared with the results obtained using OXYCON, an indigenously developed model. The model predicts the oxide growth reasonably well but under predicts the α-Zr(O) growth significantly at thickness values higher than 80 μm.

  14. Effect of GaAs substrate orientation on the growth kinetic of GaN layer grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Laifi, J.; Chaaben, N.; Bouazizi, H.; Fourati, N.; Zerrouki, C.; El Gmili, Y.; Bchetnia, A.; Salvestrini, J. P.; El Jani, B.

    2016-06-01

    We have investigated the kinetic growth of low temperature GaN nucleation layers (LT-GaN) grown on GaAs substrates with different crystalline orientations. GaN nucleation layers were grown by metal organic vapor phase epitaxy (MOVPE) in a temperature range of 500-600 °C on oriented (001), (113), (112) and (111) GaAs substrates. The growth was in-situ monitored by laser reflectometry (LR). Using an optical model, including time-dependent surface roughness and growth rate profiles, simulations were performed to best approach the experimental reflectivity curves. Results are discussed and correlated with ex-situ analyses, such as atomic force microscopy (AFM) and UV-visible reflectance (SR). We show that the GaN nucleation layers growth results the formation of GaN islands whose density and size vary greatly with both growth temperature and substrate orientation. Arrhenius plots of the growth rate for each substrate give values of activation energy varying from 0.20 eV for the (001) orientation to 0.35 eV for the (113) orientation. Using cathodoluminescence (CL), we also show that high temperature (800-900 °C) GaN layers grown on top of the low temperature (550 °C) GaN nucleation layers, grown themselves on the GaAs substrates with different orientations, exhibit cubic or hexagonal phase depending on both growth temperature and substrate orientation.

  15. Modeling of Fusarium redolens Dzf2 mycelial growth kinetics and optimal fed-batch fermentation for beauvericin production.

    PubMed

    Xu, Li-Jian; Liu, Yuan-Shuai; Zhou, Li-Gang; Wu, Jian-Yong

    2011-09-01

    Beauvericin (BEA) is a cyclic hexadepsipeptide mycotoxin with notable phytotoxic and insecticidal activities. Fusarium redolens Dzf2 is a highly BEA-producing fungus isolated from a medicinal plant. The aim of the current study was to develop a simple and valid kinetic model for F. redolens Dzf2 mycelial growth and the optimal fed-batch operation for efficient BEA production. A modified Monod model with substrate (glucose) and product (BEA) inhibition was constructed based on the culture characteristics of F. redolens Dzf2 mycelia in a liquid medium. Model parameters were derived by simulation of the experimental data from batch culture. The model fitted closely with the experimental data over 20-50 g l(-1) glucose concentration range in batch fermentation. The kinetic model together with the stoichiometric relationships for biomass, substrate and product was applied to predict the optimal feeding scheme for fed-batch fermentation, leading to 54% higher BEA yield (299 mg l(-1)) than in the batch culture (194 mg l(-1)). The modified Monod model incorporating substrate and product inhibition was proven adequate for describing the growth kinetics of F. redolens Dzf2 mycelial culture at suitable but not excessive initial glucose levels in batch and fed-batch cultures. PMID:21082211

  16. Growth kinetic study of Tetratrichomonas didelphidis isolated from opossum Lutreolina crassicaudata and interaction with a prokaryotic cell.

    PubMed

    Tasca, T; DeCarli, G A

    2001-08-01

    Tetratrichomonas didelphidis is a flagellate protozoan found in the intestine, cecum and colon of opossums, Didelphis marsupialis. This work reports the occurrence of T. didelphidis in another opossum species, Lutreolina crassicaudata. The strain was cultivated in monoxenic culture with Escherichia coli in Diamond (TYM) medium without maltose and with starch solution (trypticase-yeast extract-starch), pH 7.5 at 28 degrees C. The growth kinetic study of T. didelphidis showed a longer time of growth and a higher number of trophozoites when inoculated with E. coli than in axenic cultures, in aerobiosis as well as under anaerobic conditions. Scanning electron microscopy showed that the bacteria adhered throughout the protozoan body and probably evoked endocytic channels, strongly suggesting the existence of endocytosis of rods by T. didelphidis. Our preliminary results suggest that the in vitro culture of T. didelphidis depends on E. coli as a growth-promoting partner, and requires monoxenic cultivation. PMID:11510998

  17. Enzyme-linked immunosorbent assay for detection of type A streptococcal exotoxin: kinetics and regulation during growth of Streptococcus pyogenes.

    PubMed Central

    Houston, C W; Ferretti, J J

    1981-01-01

    We describe the detection and quantitation of type A streptococcal exotoxin (erythrogenic toxin, streptococcal pyrogenic exotoxin) by an enzyme-linked immunosorbent assay. This sensitive and specific technique detected microgram amounts of type A exotoxin and was useful for studying the kinetics and regulation of type A exotoxin production during the growth of Streptococcus pyogenes NY5. Maximum production of type A exotoxin was observed during the mid-log phase of growth, similar to the production of other streptococcal extracellular products. When S. pyogenes NY5 was grown at 42 degrees C, decreases in both growth and type A exotoxin production were observed. The results obtained when we studied the influence of nutrient additives and metal ions on the production of type A exotoxin led to the conclusion that none of these factors significantly affected type A exotoxin synthesis and that regulation was constitutive. Images PMID:7026447

  18. Growth Kinetics of Microscopic Silicon Rods Grown on Silicon Substrates by the Pyrolytic Laser-Induced Chemical Vapor Deposition Process

    NASA Astrophysics Data System (ADS)

    Park, Se Il; Lee, Sang Soo

    1990-01-01

    By using a cw Ar+ ion laser beam, microscopic crystalline silicon rods ≈ 102 μm in diameter and ≈ 103 μm in height have been grown on a silicon substrate by pyrolytic dissociation of SiH4. The kinetics of lateral growth of the silicon rods is derived from the time integration of the Arrhenius equation using a reasonable assumption that the temperature on the edge of the deposit saturates inversely to the substrate temperature with illumination time. For the axial growth, excluding the initial transient growth, the same result as Bäuerle and his collaborators is derived. The influences of laser power and illumination time on the deposited diameter and height are found experimentally, and it is found that the derived theory agrees well with the experimental results.

  19. Optimization of growth medium for Sporosarcina pasteurii in bio-based cement pastes to mitigate delay in hydration kinetics.

    PubMed

    Williams, Sarah L; Kirisits, Mary Jo; Ferron, Raissa Douglas

    2016-04-01

    Microbial-induced calcium carbonate precipitation has been identified as a novel method to improve durability and remediate cracks in concrete. One way to introduce microorganisms to concrete is by replacing the mixing water with a bacterial culture in nutrient medium. In the literature, yeast extract often has been used as a carbon source for this application; however, severe retardation of hydration kinetics has been observed when yeast extract is added to cement. This study investigates the suitability of alternative carbon sources to replace yeast extract for microbial-induced calcium carbonate precipitation in cement-based materials. A combination of meat extract and sodium acetate was identified as a suitable replacement in growth medium for Sporosarcina pasteurii; this alternative growth medium reduced retardation by 75 % (as compared to yeast extract) without compromising bacterial growth, urea hydrolysis, cell zeta potential, and ability to promote calcium carbonate formation. PMID:26795346

  20. Growth kinetics of low temperature single-wall and few walled carbon nanotubes grown by plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Gohier, A.; Minea, T. M.; Djouadi, M. A.; Jiménez, J.; Granier, A.

    2007-03-01

    Single-wall, double walled or few walled nanotubes (FWNT) are grown by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) at temperature as low as 600 °C. Most of these structures are isolated and self-oriented perpendicular to the substrate. The growth mechanism observed for single-wall and few walled (less than seven walls) nanotubes is the “base-growth” mode. Their grow kinetics is investigated regarding two parameters namely the growth time and the synthesis temperature. It is shown that nucleation and growth rate is correlated with the number of walls into FWNT. It also provides an evidence of a critical temperature for FWNT synthesis.

  1. Biodegradation kinetics of benzene, toluene and xylene compounds: microbial growth and evaluation of models.

    PubMed

    Feisther, Vódice Amoroz; Ulson de Souza, Antônio Augusto; Trigueros, Daniela Estelita Goes; de Mello, Josiane Maria Muneronde; de Oliveira, Déborade; Guelli Ulson de Souza, Selene M A

    2015-07-01

    The biodegradation kinetics of BTX compounds (benzene, toluene, and xylene) individually and as mixtures was studied using models with different levels of sophistication. To compare the performance of the unstructured models applied in this work we used experimental data obtained here and some results published in the literature. The system description was based on the material balances of key components for batch operations, where the Monod and Andrews models were applied to predict the biodegradation of individual substrates. To simulate the biodegradation kinetics of substrate mixtures, models of substrate inhibition were applied along with the Sum Kinetics with Interaction Parameters (SKIP) models, where for two-component association toluene-xylene SKIP model presented better performance and for tri-component association benzene-toluene-xylene, the uncompetitive inhibition model was better. The kinetic parameters were estimated via a global search method known as Particle Swarm Optimization (PSO). The main result of this study is that the sophisticated biodegradation kinetics of BTX mixtures can be successfully described by applying the SKIP model, with the main advantage being the consideration of the substrate interactions. PMID:25627469

  2. Sequential and coordinated action of phytochromes A and B during Arabidopsis stem growth revealed by kinetic analysis

    NASA Technical Reports Server (NTRS)

    Parks, B. M.; Spalding, E. P.; Evans, M. L. (Principal Investigator)

    1999-01-01

    Photoreceptor proteins of the phytochrome family mediate light-induced inhibition of stem (hypocotyl) elongation during the development of photoautotrophy in seedlings. Analyses of overt mutant phenotypes have established the importance of phytochromes A and B (phyA and phyB) in this developmental process, but kinetic information that would augment emerging molecular models of phytochrome signal transduction is absent. We have addressed this deficiency by genetically dissecting phytochrome-response kinetics, after having solved the technical issues that previously limited growth studies of small Arabidopsis seedlings. We show here, with resolution on the order of minutes, that phyA initiated hypocotyl growth inhibition upon the onset of continuous red light. This primary contribution of phyA began to decrease after 3 hr of irradiation, the same time at which immunochemically detectable phyA disappeared and an exclusively phyB-dependent phase of inhibition began. The sequential and coordinated actions of phyA and phyB in red light were not observed in far-red light, which inhibited growth persistently through an exclusively phyA-mediated pathway.

  3. Effect of oxidation kinetics on the near threshold fatigue crack growth behavior of a nickel base superalloy

    SciTech Connect

    Yuen, J.L.; Roy, P.; Nix, W.D.

    1984-09-01

    The influence of oxidation kinetics on the near threshold fatigue crack growth behavior of a nickel base precipitation hardened superalloy was studied in air from 427 to 649 C. The tests were conducted at 100 Hz and at load ratios of 0.1 and 0.5. The threshold values of the alternating stress intensity factor were found to increase with temperature. This behavior is attributed to oxide deposits that form on the freshly created fracture surfaces which enhance crack closure. As determined from secondary ion mass spectrometry, the oxide thickness was uniform over the crack length and was of the order of the maximum crack tip opening displacement at threshold. Oxidation kinetics were important in thickening the oxide on the fracture surfaces at elevated temperatures, whereas at room temperature, the oxide deposits at near threshold fatigue crack growth rates and at low load ratios were thickened by an oxide fretting mechanism. The effect of fracture surface roughness-induced crack closure on the near threshold fatigue crack growth behavior is also discussed. 27 references.

  4. Effect of oxidation kinetics on the near threshold fatigue crack growth behavior of a nickel base superalloy

    NASA Astrophysics Data System (ADS)

    Yuen, J. L.; Roy, P.; Nix, W. D.

    1984-09-01

    The influence of oxidation kinetics on the near threshold fatigue crack growth behavior of a nickel base precipitation hardened superalloy was studied in air from 427° to 649 °C. The tests were conducted at 100 Hz and at load ratios of 0.1 and 0.5. The threshold ΔK values were found to increase with temperature. This behavior is attributed to oxide deposits that form on the freshly created fracture surfaces which enhance crack closure. As determined from secondary ion mass spectrometry, the oxide thickness was uniform over the crack length and was of the order of the maximum crack tip opening displacement at threshold. Oxidation kinetics were important in thickening the oxide on the fracture surfaces at elevated temperatures, whereas at room temperature, the oxide deposits at near threshold fatigue crack growth rates and at low load ratios were thickened by an oxide fretting mechanism. The effect of fracture surface roughness-induced crack closure on the near threshold fatigue crack growth behavior is also discussed.

  5. Exponential tilting in Bayesian asymptotics

    PubMed Central

    Kharroubi, S. A.; Sweeting, T. J.

    2016-01-01

    We use exponential tilting to obtain versions of asymptotic formulae for Bayesian computation that do not involve conditional maxima of the likelihood function, yielding a more stable computational procedure and significantly reducing computational time. In particular we present an alternative version of the Laplace approximation for a marginal posterior density. Implementation of the asymptotic formulae and a modified signed root based importance sampler are illustrated with an example. PMID:27279661

  6. Effects of Bonding Wires and Epoxy Molding Compound on Gold and Copper Ball Bonds Intermetallic Growth Kinetics in Electronic Packaging

    NASA Astrophysics Data System (ADS)

    Gan, C. L.; Classe, F. C.; Chan, B. L.; Hashim, U.

    2014-04-01

    This paper discusses the influence of bonding wires and epoxy mold compounds (EMC) on intermetallic compound (IMC) diffusion kinetics and apparent activation energies ( E aa) of CuAl and AuAl IMCs in a fineline ball grid array package. The objective of this study is to study the CuAl and AuAl IMC growth rates with different epoxy mold compounds and to determine the apparent activation energies of different combination of package bills of materials. IMC thickness measurement has been carried out to estimate the coefficient of diffusion ( D o) and E aa various aging conditions of different EMCs and bonding wires. Apparent activation energies ( E aa) of both wire types were investigated after high temperature storage life tests (HTSL) for both molding compounds. Au bonds were identified to have faster IMC formation, compared to slower IMC growth of Cu. The E aa obtained for CuAl IMC diffusion kinetics are 1.08 and 1.04 eV with EMC A and EMC B, respectively. For AuAl IMC diffusion kinetics, the E aa obtained are 1.04 and 0.98 eV, respectively, on EMC A and EMC B. These values are close to previous HTSL studies conducted on Au and Cu ball bonds and are in agreement to the theory of HTSL performance of Au and Cu bonding wires.Overall, EMC B shows slightly lower apparent activation energy ( E aa) valueas in CuAl and AuAl IMCs. This proves that the different types of epoxy mold compounds have some influence on IMC growth rates.

  7. Barrierless growth of precursor-free, ultrafast laser-fragmented noble metal nanoparticles by colloidal atom clusters - A kinetic in situ study.

    PubMed

    Jendrzej, Sandra; Gökce, Bilal; Amendola, Vincenzo; Barcikowski, Stephan

    2016-02-01

    Unintended post-synthesis growth of noble metal colloids caused by excess amounts of reactants or highly reactive atom clusters represents a fundamental problem in colloidal chemistry, affecting product stability or purity. Hence, quantified kinetics could allow defining nanoparticle size determination in dependence of the time. Here, we investigate in situ the growth kinetics of ps pulsed laser-fragmented platinum nanoparticles in presence of naked atom clusters in water without any influence of reducing agents or surfactants. The nanoparticle growth is investigated for platinum covering a time scale of minutes to 50days after nanoparticle generation, it is also supplemented by results obtained from gold and palladium. Since a minimum atom cluster concentration is exceeded, a significant growth is determined by time resolved UV/Vis spectroscopy, analytical disc centrifugation, zeta potential measurement and transmission electron microscopy. We suggest a decrease of atom cluster concentration over time, since nanoparticles grow at the expense of atom clusters. The growth mechanism during early phase (<1day) of laser-synthesized colloid is kinetically modeled by rapid barrierless coalescence. The prolonged slow nanoparticle growth is kinetically modeled by a combination of coalescence and Lifshitz-Slyozov-Wagner kinetic for Ostwald ripening, validated experimentally by the temperature dependence of Pt nanoparticle size and growth quenching by Iodide anions. PMID:26555960

  8. Integration of biological kinetics and computational fluid dynamics to model the growth of Nannochloropsis salina in an open channel raceway.

    PubMed

    Park, Stephen; Li, Yebo

    2015-05-01

    Microalgal growth and systemic productivity is not only affected by environmental conditions such as temperature, irradiance, and nutrient concentrations, but also by physical processes such as fluid flow and particulate sedimentation. Modeling and simulating the system is a cost-effective way to predict the growth behavior under various environmental and physical conditions while determining effective engineering approaches to maximize productivity. Many mathematical models have been proposed to describe microalgal growth, while computational fluid dynamics (CFD) have been used to model the behavior of many fluid systems. Integrating the growth kinetics into a CFD model can help researchers understand the impact of a variety of parameters and determine what measures can be taken to overcome some obstacles in the aquaculture industry--self-shading, biomass sedimentation, and contamination--which prevent the production of high biomass yields. The aim of this study was to integrate physical and environmental effects to predict space- and time-dependent algal growth in industrial scale raceways. A commercial CFD software, ANSYS-Fluent 14.5, was used to solve the proposed models in regards to fluid flow, heat transfer, and nutrient balance. User-defined functions written in C language were used to incorporate the kinetic equations into a three-dimensional standard k-ε turbulence model of an open channel raceway system driven by a single paddlewheel. Simulated results were compared with light intensity, temperature, nutrient concentration, and algal biomass data acquired for 56 day from an industrial scale raceway pond constructed for the growth of Nannochloropsis salina and were observed to be in good agreement with one another. There was up to a 17.6% increase in simulated productivity when the incoming CO2 concentration was increased from 0.0006 to 0.150 g L(-1), while the effect of paddlewheel velocity was not significant. Sensitivity analysis showed that the model

  9. X-ray photoelectron spectroscopy study of the growth kinetics of biomimetically grown hydroxyapatite thin-film coatings

    NASA Astrophysics Data System (ADS)

    McLeod, K.; Kumar, S.; Dutta, N. K.; Smart, R. St. C.; Voelcker, N. H.; Anderson, G. I.

    2010-09-01

    Hydroxyapatite (HA) thin-film coatings grown biomimetically using simulated body fluid (SBF) are desirable for a range of applications such as improved fixation of fine- and complex-shaped orthopedic and dental implants, tissue engineering scaffolds and localized and sustained drug delivery. There is a dearth of knowledge on two key aspects of SBF-grown HA coatings: (i) the growth kinetics over short deposition periods, hours rather than weeks; and (ii) possible difference between the coatings deposited with and without periodic SBF replenishment. A study centred on these aspects is reported. X-ray photoelectron spectroscopy (XPS) has been used to study the growth kinetics of SBF-grown HA coatings for deposition periods ranging from 0.5 h to 21 days. The coatings were deposited with and without periodic replenishment of SBF. The XPS studies revealed that: (i) a continuous, stable HA coating fully covered the titanium substrate after a growth period of 13 h without SBF replenishment; (ii) thicker HA coatings about 1 μm in thickness resulted after a growth period of 21 days, both with and without SBF replenishment; and (iii) the Ca/P ratio at the surface of the HA coating was significantly lower than that in its bulk. No significant difference between HA grown with and without periodic replenishment of SBF was found. The coatings were determined to be carbonated, a characteristic desirable for improved implant fixation. The atomic force and scanning electron microscopies results suggested that heterogeneous nucleation and growth are the primary deposition mode for these coatings. Primary osteoblast cell studies demonstrated the biocompatibility of these coatings, i.e., osteoblast colony coverage of approximately 80%, similar to the control substrate (tissue culture polystyrene).

  10. Kinetics of hydrogen desorption in surface-limited thin-film growth of SiGe alloys

    SciTech Connect

    Sharp, J.W. ); Eres, G. )

    1993-05-31

    The kinetics of hydrogen desorption in surface-limited thin-film growth of SiGe alloys from binary mixtures of disilane and digermane was investigated by surface differential reflectance. The hydrogen desorption process from the alloy surface was found to consist of two components. Both components are thermally activated, but the activation energies appear to equal neither the hydrogen desorption energy from pure silicon nor that from pure germanium surfaces. We suggest that the two components represent Ge- and Si-mediated hydrogen desorption, with the former being more rapid than the latter.

  11. Effects of Temperature and Packaging on the Growth Kinetics of Clostridium perfringens in Ready-to-eat Jokbal (Pig's Trotters)

    PubMed Central

    Cho, Joon-Il; Lee, Soon-Ho

    2014-01-01

    Ready-to-eat (RTE) Jokbal (Pig's trotter), which consists of pig's feet cooked in soy sauce and various spices, is a very popular and widely sold in Korean retail markets. Commercially, the anaerobically packed Jokbal have also become a popular RTE food in several convenience stores. This study evaluates the effects of storage temperature and packaging methods for the growth of C. perfringens in Jokbal. Growth kinetic parameters of C. perfringens in aerobically and anaerobically packed Jokbals are determined at each temperature by the modified Gompertz equation. The lag time, specific growth rate, and maximum population density of C. perfringens are being analyzed as a function of temperature and packaging method. The minimum growth temperature of C. perfringens in aerobically and anaerobically packed Jokbal is 24℃ and 18℃, respectively. The C. perfringens in Jokbal did not grow under conditions of over 50℃ regardless of the packaging methods, indicating that the holding temperature of Jokbal in markets must be maintained at above 50℃ or below 18℃. Growth of C. perfringens in anaerobically packed Jokbal is faster than in aerobically packed Jokbal when stored under the same conditions. This indicates that there are a higher risks associated with C. perfringens for anaerobically packed meat products. PMID:26760749

  12. Growth kinetics of the (001) face of TGS below the ferroelectric transition temperature

    NASA Technical Reports Server (NTRS)

    Reiss, D. A.; Kroes, R. L.; Anderson, E. E.

    1987-01-01

    The growth rates of the (001) face of triglycine sulfate (TGS) from aqueous solutions were measured at 33.55 C in an apparatus which produced a laminar flow of solution past the crystal. The data of growth rate as a function of relative supersaturation were compared with the results of two well-known models: the Burton-Cabrera-Frank (1951) surface diffusion model and the birth-and-spreading growth model. Both models produced good fits to the growth rate data. However, on the basis of the qualitative aspects of the experimentally-observed growth, it is suggested that the correct growth model for these crystals is the Burton-Cabrera-Frank model.

  13. Growth kinetics response of a Salmonella typhimurium poultry marker strain to fresh produce extracts.

    PubMed

    Nutt, J D; Li, X; Woodward, C L; Zabala-Díaz, I B; Ricke, S C

    2003-09-01

    The purpose of this research was to assess growth response of a Salmonella typhimurium poultry marker strain to fresh homogenized vegetables. Salmonella growth rates were significantly higher (p<0.05) in jalapeno extracts than any other produce extract examined. Growth rates on samples of broccoli and lettuce extracts were greater (p<0.05) than the respective growth rates on bell pepper and tomato. Broccoli extracts yielded the highest extent of growth (4 h optical density) followed by jalapeno and bell pepper extracts. From this study, it appears that fresh produce extracts have different abilities to significantly alter growth response in Salmonella. This could potentially be explained by the variations of pH, nutrient availability to the bacteria, or unknown components found within fresh produce. PMID:12798123

  14. Defect, Kinetics and Heat Transfer of CDTE Bridgman Growth without Wall Contact

    NASA Technical Reports Server (NTRS)

    Larson, D. J., Jr.; Zhang, H.

    2003-01-01

    A detached growth mechanism has been proposed, which is similar to that proposed by Duffar et al. and used to study the current detached growth system. From numerical results, we can conclude that detached growth will more likely appear if the growth and wetting angles are large and meniscus is flat. Detached thickness is dependent on growth angle, wetting angle, and gap width and shape of the fins. The model can also explain why the detached growth will not happen for metals in which the growth angle is almost zero. Since the growth angle of CdZnTe cannot be changed, to promote detached growth, the number density of the fins should be low and the wetting angle should be high. Also, a much smaller gap width of the fins should be used in the ground experiment and the detached gap width is much smaller. The shape of the fins has minor influence on detached growth. An integrated numerical model for detached solidification has been developed combining a global heat transfer sub-model and a wall contact sub-model. The global heat transfer sub-model accounts for heat and mass transfer in the multiphase system, convection in the melt, macro-segregation, and interface dynamics. The location and dynamics of the solidification interface are accurately tracked by a multizone adaptive grid generation scheme. The wall contact sub-model accounts for the meniscus dynamics at the three-phase boundary. Simulations have been performed for crystal growth in a conventional ampoule and a designed ampoule to understand the benefits of detached solidification and its impacts on crystalline structural quality, e.g., stoichiometry, macro-segregation, and stress. From simulation results, both the Grashof and Marangoni numbers will have significant effects on the shape of growth front, Zn concentration distribution, and radial segregation. The integrated model can be used in designing apparatus and determining the optimal geometry for detached solidification in space and on the ground.

  15. Morphological Manipulation of Solvothermal Prepared CdSe Nanostructures by Controlling the Growth Rate of Nanocrystals as a Kinetic Parameter

    NASA Astrophysics Data System (ADS)

    Zarghami, V.; Mohammadi, M. R.; Fray, D. J.

    2012-11-01

    The morphological manipulation, structural characterization, and optical properties of different cadmium selenide (CdSe) nanostructures are reported. Two different CdSe nanostructures, i.e., nanorods and nanoparticles, were grown by controlling the concentration of precursors (i.e., cadmium nitrate and selenium dioxide) in ethanolamine solvent. By manipulating the kinetic parameter of the process (i.e., growth rate) under constant growth driving force (i.e., degree of supersaturation), the morphology of CdSe nanostructures can be tailored from nanorods to nanoparticles. The optical properties of CdSe nanostructures were investigated using ultraviolet-visible (UV-vis) spectroscopy. The absorption edge of the samples showed a blue-shift. CdSe nanostructures prepared under optimized conditions showed good microstructural and optical properties for solar cell applications.

  16. Growth kinetics of potassium alum crystal in a well-agitated vessel

    NASA Astrophysics Data System (ADS)

    Tai, Clifford Y.; Yu, K. H.

    1989-08-01

    Growth rates of potassium alum crystal in a well-agitated vessel were determined from the de-supersaturation curve of the solution. The mass transfer and surface integration coefficients were then estimated using the two-step model. Both coefficients were found to increase with increasing crystal size. Judging from the Damköhler number for crystal growth and the over-all order of the growth rate equation, it is concluded that both mass transfer resistance and surface integration resistance are significant in the growth process.

  17. Exponential Size Distribution of von Willebrand Factor

    PubMed Central

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

    2013-01-01

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

  18. Kinetically-controlled growth of cubic and octahedral Rh-Pd alloy oxygen reduction electrocatalysts with high activity and durability

    NASA Astrophysics Data System (ADS)

    Yan, Yucong; Zhan, Fangwei; Du, Jingshan; Jiang, Yingying; Jin, Chuanhong; Fu, Maoshen; Zhang, Hui; Yang, Deren

    2014-11-01

    Rh is a promising candidate as an indispensible component in bimetallic catalysts due to its unique capability to resist against the aggressive corrosion from the reaction medium. However, Rh has a very strong oxygen binding ability and is generally not suitable for the oxygen reduction reaction (ORR). Here, we have demonstrated shape-controlled synthesis of Rh-Pd alloy nanocrystals with high activity and durability for ORR by retarding the reaction kinetics at an ultra-slow injection rate of metal salts using a syringe pump. Under precise control of sluggish reaction kinetics, Pd followed a preferential overgrowth along the <100> direction, whereas the growth behavior of Rh was dominant along the <111> direction. These different kinetically-controlled growth behaviors associated with Rh and Pd were essential for achieving the shape transition between the cube and the octahedron of their alloys. The Rh8Pd92 alloy octahedra exhibited the highest mass activity with a value of 0.18 mA μg-1 in terms of the equivalent Pt cost, and were two-fold higher than that of commercial Pt/C. Significantly, all Rh-Pd alloy nanocrystals were highly stable with only less than 25% loss in mass activity after 30 000 CV cycles in O2 saturated acid solution compared to ~56% loss of the commercial Pt/C (E-TEK). Indeed, the mass activity of Rh8Pd92 was 3.3 times higher than that of commercial Pt/C after the accelerated stability test (ADT). This improvement in activity and durability may arise possibly from synergistic effects between the facet and the surface composition.Rh is a promising candidate as an indispensible component in bimetallic catalysts due to its unique capability to resist against the aggressive corrosion from the reaction medium. However, Rh has a very strong oxygen binding ability and is generally not suitable for the oxygen reduction reaction (ORR). Here, we have demonstrated shape-controlled synthesis of Rh-Pd alloy nanocrystals with high activity and durability for

  19. Growth kinetics of nickel microstructures produced by laser-induced decomposition of nickel tetracarbonyl

    NASA Astrophysics Data System (ADS)

    Tonneau, D.; Auvert, G.; Pauleau, Y.

    1988-11-01

    Nickel dots and films were deposited on Si-coated quartz plates by the cw Ar+ laser-induced decomposition of Ni(CO)4 at a temperature in the range of 200-400 °C. The deposited material was characterized by x-ray diffraction, Auger spectroscopy, nuclear reaction analyses, and scanning electron microscopy. The deposition kinetics of Ni dots formed in the laser-heated area of 200 μm in diameter was investigated as a function of irradiation time, output laser power, and Ni(CO)4 pressure. The laser-induced deposition of Ni dots was demonstrated to occur via a purely pyrolytic decomposition of Ni(CO)4. At low Ni(CO)4 pressures (typically below 0.3 Torr) and high output laser powers (above 1 W), the deposition rate of flat-topped Ni dots was found to be independent of the deposition temperature and proportional to Ni(CO)4 pressure. The deposition kinetics of these dots was limited by the number of molecules colliding with the heated area. At reactant pressures ranging from 0.3 to 10 Torr, the deposition rate of Gaussian Ni dots was found to be independent of Ni(CO)4 pressure, and the apparent activation energy was 11.6 kcal mol-1. The deposition kinetics of these Gaussian dots was controlled by the desorption of CO molecules.

  20. Exponential Formulae and Effective Operations

    NASA Technical Reports Server (NTRS)

    Mielnik, Bogdan; Fernandez, David J. C.

    1996-01-01

    One of standard methods to predict the phenomena of squeezing consists in splitting the unitary evolution operator into the product of simpler operations. The technique, while mathematically general, is not so simple in applications and leaves some pragmatic problems open. We report an extended class of exponential formulae, which yield a quicker insight into the laboratory details for a class of squeezing operations, and moreover, can be alternatively used to programme different type of operations, as: (1) the free evolution inversion; and (2) the soft simulations of the sharp kicks (so that all abstract results involving the kicks of the oscillator potential, become realistic laboratory prescriptions).

  1. Radial expansion rates and tumor growth kinetics predict malignant transformation in contrast-enhancing low-grade diffuse astrocytoma

    PubMed Central

    Hathout, Leith; Pope, Whitney B; Lai, Albert; Nghiemphu, Phioanh L; Cloughesy, Timothy F; Ellingson, Benjamin M

    2015-01-01

    Summary Background Contrast-enhancing low-grade diffuse astrocytomas are an understudied, aggressive subtype at increased risk because of few radiographic indications of malignant transformation. In the current study, we tested whether tumor growth kinetics could identify tumors that undergo malignant transformation to higher grades. Methods Thirty patients with untreated diffuse astrocytomas (WHO II) that underwent tumor progression were enrolled. Contrast-enhancing and T2 hyperintense tumor regions were segmented and the radius of tumor at two time points leading to progression was estimated. Radial expansion rates were used to estimate proliferation and invasion rates using a biomathematical model. Results Radial expansion rates for both contrast-enhancing (p = 0.0040) and T2 hyperintense regions (p = 0.0016) were significantly higher in WHO II–IV tumors compared with nontransformers. Similarly, model estimates showed a significantly higher proliferation (p = 0.0324) and invasion rate (p = 0.0050) in WHO II–IV tumors compared with nontransformers. Conclusion Tumor growth kinetics can identify contrast-enhancing diffuse astrocytomas undergoing malignant transformation. PMID:26095141

  2. Kinetics of microbial growth and biodegradation of methanol and toluene in biofilters and an analysis of the energetic indicators.

    PubMed

    Avalos Ramirez, Antonio; Bénard, Sandrine; Giroir-Fendler, Anne; Jones, J Peter; Heitz, Michèle

    2008-11-25

    The kinetics of microbial growth and the biodegradation of methanol and toluene in (a) biofilters (BFs), and (b) biotrickling filters (BTFs), packed with inert materials, has been studied and analyzed. The specific growth rate, mu, for the treatment of methanol was 0.037h(-1) for a wide range of operating conditions. In the BF, mu was found to be a function of the methanol and toluene concentrations in the biofilm. In the BF used for treating methanol, mu was found to be affected by (1) the nitrogen concentration present in the nutrient solution, and (2) the kind of packing material employed. The kinetics of the methanol and toluene biodegradations were also analyzed using "mixed order" models. A Michaelis-Menten model type provided a good fit for the elimination capacity (EC) of the BTF treating methanol, while a Haldane model type provided a good fit to the EC of the BF treating methanol and toluene. The carbon dioxide production rate was related to the packed bed temperature and the content of the volatile solids within the biofilm. For the BF, the ratio of temperature/carbon dioxide production rate (PCO(2)) was 0.024 degrees C per unit of PCO(2), and for the BTF it was 0.15 degrees C per unit of PCO(2). PMID:18778740

  3. Priming Adipose-Derived Mesenchymal Stem Cells with Hyaluronan Alters Growth Kinetics and Increases Attachment to Articular Cartilage.

    PubMed

    Succar, Peter; Medynskyj, Michael; Breen, Edmond J; Batterham, Tony; Molloy, Mark P; Herbert, Benjamin R

    2016-01-01

    Background. Biological therapeutics such as adipose-derived mesenchymal stem cell (MSC) therapy are gaining acceptance for knee-osteoarthritis (OA) treatment. Reports of OA-patients show reductions in cartilage defects and regeneration of hyaline-like-cartilage with MSC-therapy. Suspending MSCs in hyaluronan commonly occurs in animals and humans, usually without supporting data. Objective. To elucidate the effects of different concentrations of hyaluronan on MSC growth kinetics. Methods. Using a range of hyaluronan concentrations, we measured MSC adherence and proliferation on culture plastic surfaces and a novel cartilage-adhesion assay. We employed time-course and dispersion imaging to assess MSC binding to cartilage. Cytokine profiling was also conducted on the MSC-secretome. Results. Hyaluronan had dose-dependent effects on growth kinetics of MSCs at concentrations of entanglement point (1 mg/mL). At higher concentrations, viscosity effects outweighed benefits of additional hyaluronan. The cartilage-adhesion assay highlighted for the first time that hyaluronan-primed MSCs increased cell attachment to cartilage whilst the presence of hyaluronan did not. Our time-course suggested patients undergoing MSC-therapy for OA could benefit from joint-immobilisation for up to 8 hours. Hyaluronan also greatly affected dispersion of MSCs on cartilage. Conclusion. Our results should be considered in future trials with MSC-therapy using hyaluronan as a vehicle, for the treatment of OA. PMID:26981136

  4. Priming Adipose-Derived Mesenchymal Stem Cells with Hyaluronan Alters Growth Kinetics and Increases Attachment to Articular Cartilage

    PubMed Central

    Succar, Peter; Medynskyj, Michael; Breen, Edmond J.; Batterham, Tony; Molloy, Mark P.; Herbert, Benjamin R.

    2016-01-01

    Background. Biological therapeutics such as adipose-derived mesenchymal stem cell (MSC) therapy are gaining acceptance for knee-osteoarthritis (OA) treatment. Reports of OA-patients show reductions in cartilage defects and regeneration of hyaline-like-cartilage with MSC-therapy. Suspending MSCs in hyaluronan commonly occurs in animals and humans, usually without supporting data. Objective. To elucidate the effects of different concentrations of hyaluronan on MSC growth kinetics. Methods. Using a range of hyaluronan concentrations, we measured MSC adherence and proliferation on culture plastic surfaces and a novel cartilage-adhesion assay. We employed time-course and dispersion imaging to assess MSC binding to cartilage. Cytokine profiling was also conducted on the MSC-secretome. Results. Hyaluronan had dose-dependent effects on growth kinetics of MSCs at concentrations of entanglement point (1 mg/mL). At higher concentrations, viscosity effects outweighed benefits of additional hyaluronan. The cartilage-adhesion assay highlighted for the first time that hyaluronan-primed MSCs increased cell attachment to cartilage whilst the presence of hyaluronan did not. Our time-course suggested patients undergoing MSC-therapy for OA could benefit from joint-immobilisation for up to 8 hours. Hyaluronan also greatly affected dispersion of MSCs on cartilage. Conclusion. Our results should be considered in future trials with MSC-therapy using hyaluronan as a vehicle, for the treatment of OA. PMID:26981136

  5. Growth kinetics and characterizations of gallium nitride thin films by remote PECVD

    NASA Technical Reports Server (NTRS)

    Choi, S. W.; Bachmann, K. J.; Lucovsky, G.

    1993-01-01

    Thin films of GaN have been deposited at relatively low growth temperatures by remote plasma-enhanced chemical-vapor deposition (RPECVD), using a plasma excited NH3, and trimethylgallium (TMG), injected downstream from the plasma. The activation energy for GaN growth has been tentatively assigned to the dissociation of NH groups as the primary N-atom precursors in the surface reaction with adsorbed TMG, or TMG fragments. At high He flow rates, an abrupt increase in the growth rate is observed and corresponds to a change in the reaction mechanism attributed to the formation of atomic N. XRD reveals an increased tendency to ordered growth in the (0001) direction with increasing growth temperature, He flow rate, and RF plasma power. IR spectra show the fundamental lattice mode of GaN at 530 cm without evidence for vibrational modes of hydrocarbon groups.

  6. The growth scale and kinetics of WS2 monolayers under varying H2 concentration.

    PubMed

    Kang, Kyung Nam; Godin, Kyle; Yang, Eui-Hyeok

    2015-01-01

    The optical and electronic properties of tungsten disulfide monolayers (WS2) have been extensively studied in the last few years, yet growth techniques for WS2 remain behind other transition metal dichalcogenides (TMDCs) such as MoS2. Here we demonstrate chemical vapor deposition (CVD) growth of continuous monolayer WS2 films on mm(2) scales and elucidate effects related to hydrogen (H2) gas concentration during growth. WS2 crystals were grown by reduction and sulfurization of WO3 using H2 gas and sulfur evaporated from solid sulfur powder. Several different growth formations (in-plane shapes) were observed depending on the concentration of H2. Characterization using atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed etching of the SiO2 substrate at low concentrations of H2 and in the presence of an Ar carrier gas. We attribute this to insufficient reduction of WO3 during growth. High H2 concentrations resulted in etching of the grown WS2 crystals after growth. The two dimensional X-ray diffraction (2D XRD) pattern demonstrates that the monolayer WS2 was grown with the (004) plane normal to the substrate, showing that the WS2 conforms to the growth substrate. PMID:26279085

  7. The growth scale and kinetics of WS2 monolayers under varying H2 concentration

    NASA Astrophysics Data System (ADS)

    Kang, Kyung Nam; Godin, Kyle; Yang, Eui-Hyeok

    2015-08-01

    The optical and electronic properties of tungsten disulfide monolayers (WS2) have been extensively studied in the last few years, yet growth techniques for WS2 remain behind other transition metal dichalcogenides (TMDCs) such as MoS2. Here we demonstrate chemical vapor deposition (CVD) growth of continuous monolayer WS2 films on mm2 scales and elucidate effects related to hydrogen (H2) gas concentration during growth. WS2 crystals were grown by reduction and sulfurization of WO3 using H2 gas and sulfur evaporated from solid sulfur powder. Several different growth formations (in-plane shapes) were observed depending on the concentration of H2. Characterization using atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed etching of the SiO2 substrate at low concentrations of H2 and in the presence of an Ar carrier gas. We attribute this to insufficient reduction of WO3 during growth. High H2 concentrations resulted in etching of the grown WS2 crystals after growth. The two dimensional X-ray diffraction (2D XRD) pattern demonstrates that the monolayer WS2 was grown with the (004) plane normal to the substrate, showing that the WS2 conforms to the growth substrate.

  8. Grain growth kinetics in liquid-phase-sintered zinc oxide-barium oxide ceramics

    NASA Technical Reports Server (NTRS)

    Yang, Sung-Chul; German, Randall M.

    1991-01-01

    Grain growth of ZnO in the presence of a liquid phase of the ZnO-BaO system has been studied for temperatures from 1300 to 1400 C. The specimens were treated in boiling water and the grains were separated by dissolving the matrix phase in an ultrasonic bath. As a consequence 3D grain size measurements were possible. Microstructural examination shows some grain coalescence with a wide range of neck size ratios and corresponding dihedral angles, however, most grains are isolated. Lognormal grain size distributions show similar shapes, indicating that the growth mechanism is invariant over this time and temperature. All regressions between G exp n and time for n = 2 and 3 proved statistically significant. The rate constants calculated with the growth exponent set to n = 3 are on the same order of magnitude as in metallic systems. The apparent activation energy for growth is estimated between 355 and 458 kJ/mol.

  9. [Features of kinetics of thrombocytic thrombi growth in the microcirculatory system].

    PubMed

    Kondrat'ev, A S; Mikhaĭlova, I A; Petrishchev, N N

    1998-01-01

    The nonuniform distribution of thrombocytes in a microvessel is considered in terms of a previously advanced phenomenological theory, which describes the relationship between the mean blood velocity and thrombus growth rate. PMID:9567187

  10. Biphasic kinetics of growth and bacteriocin production with Lactobacillus amylovorus DCE 471 occur under stress conditions.

    PubMed

    Neysens, Patricia; Messens, Winy; Gevers, Dirk; Swings, Jean; De Vuyst, Luc

    2003-04-01

    Micro-organisms used during the production of fermented foods are subjected to several abiotic stresses. Microbial survival during these processes strongly depends on the ability of the cells to adapt and become more tolerant to the environmental conditions. Cultivation of Lactobacillus amylovorus DCE 471, a potential strain for use during type II sourdough fermentations, at low temperatures, unfavourable pH and high salt concentrations resulted in biphasic growth patterns. In addition, two separate bacteriocin peaks, as well as a dramatic change in cellular morphology, were observed. In general, an increase of the specific bacteriocin production occurred during the second growth phase. Finally, the observed sugar consumption profiles were affected by the applied fermentation temperature. Moreover, the highest bacteriocin activity occurred during maltose consumption at a low constant temperature of 28 degrees C and a constant pH of 5.4. Plate counts from both growth phases revealed the existence of two colony types. Irregular colonies were found to outnumber smoother colonies during the first growth phase, while the second growth phase was characterized by a greater number of smooth colonies. Electron microscopy was used to investigate the observed morphological switch at the single-cell level. Single, rod-shaped cells changed into elongated cells that grew in chains. Colony and cell morphology changes coincided with the biphasic growth pattern. PMID:12686649

  11. Sensitivity analysis of dendritic growth kinetics in a Bridgman furnace front tracking model

    NASA Astrophysics Data System (ADS)

    Mooney, R. P.; McFadden, S.

    2016-03-01

    A directional solidification experiment of a Ti-Al-Nb-B-C alloy by power down method is simulated using a Bridgman furnace front tracking model. The effect of varying the dendritic growth parameters; C, the columnar dendrite growth coefficient, and n, the undercooling exponent, is investigated. A matrix of growth coefficients and undercooling exponents - at three levels each, based around a growth law for Ti-46wt.%Al - is applied in simulations, and the effect on columnar dendrite tip temperature, tip velocity, and tip temperature gradient is observed. The simulation results show that the dendrite tip velocity and temperature gradient at the tip are practically unaffected by the use of different growth parameters. However, the predicted columnar dendrite tip undercooling did vary to give the required dendrite tip velocity. This finding has implications for the analysis of microstructural transitions, such as the Columnar to Equiaxed Transition (CET). In conclusion, it is suggested that, for transient solidification conditions, a CET prediction criterion based on tip undercooling is preferable to one that uses growth velocity.

  12. Kinetics and heat transfer of CdZnTe Bridgman growth without wall contact

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Larson, D. J.; Wang, C. L.; Chen, T. H.

    2003-03-01

    We have proposed to grow a CdZnTe crystal without wall contact (detached solidification) using a unique soft wall technique. An integrated numerical model for detached solidification has been developed combining a global heat transfer sub-model and a wall contact sub-model for the proposed modified Bridgman system. The global heat transfer sub-model accounts for heat and mass transfer in the multiphase system, convection in the melt, macro-segregation, and interface dynamics. The wall contact sub-model accounts for detached growth process. The detached growth mechanism is similar to that proposed by Duffar et al. Simulations have been performed to understand the effects of various parameters, e.g., growth angle, wetting angle, geometric configuration, and gravity on CdZnTe detached growth. Results show that detached gap width is dependent on growth angle, wetting angle, and gap width and shape of the fins. The effects of the Grashof and Marangoni numbers on the shape of growth front, Zn concentration distribution, and radial segregation are studied.

  13. Kinetically Controlled Growth of Fine Gold Nanofractals from Au(I) via Indirect Galvanic Replacement Reaction.

    PubMed

    Zhou, Yao; Zeng, Hua Chun

    2015-09-30

    Two of the most important features of Au nanostructures, size and shape, are significantly affected by the reduction kinetics of the relevant metal precursors. Because of the high standard oxidative potential of gold ionic species, AuCl4(-) in particular, Au fractals formed via various chemical or electrochemical approaches often have very coarse branches with diameters varying from tens of nanometers to submicrometers, even though extensive chemicals and/or complicated processes have been deployed to control the reduction kinetics. Herein we report an indirect galvanic replacement (IGR) strategy where the electrons generated in a galvanic replacement reaction from anode oxidation are channeled out to a separate conducting film on which the cathodic metal can be deposited. Reduction of Au(I) ionic species with relatively low standard oxidative potential has been conducted with the IGR experimental setting. 2D finely hyperbranched Au fractals (4.0 nm in diameter and a few micrometers in length) with high structural integrity were produced. Controls over the deposition density, location, and microfeatures of Au nanofractals were demonstrated through a mechanistic study. In addition, the thus-prepared Au nanofractals were also thoroughly tested in electrochemical sensing of H2O2. PMID:26360961

  14. Urea modulation of β-amyloid fibril growth: Experimental studies and kinetic models

    PubMed Central

    Kim, Jin Ryoun; Muresan, Adrian; Lee, Ka Yee C.; Murphy, Regina M.

    2004-01-01

    Aggregation of β-amyloid (Aβ) into fibrillar deposits is widely believed to initiate a cascade of adverse biological responses associated with Alzheimer’s disease. Although it was once assumed that the mature fibril was the toxic form of Aβ, recent evidence supports the hypothesis that Aβ oligomers, intermediates in the fibrillogenic pathway, are the dominant toxic species. In this work we used urea to reduce the driving force for Aβ aggregation, in an effort to isolate stable intermediate species. The effect of urea on secondary structure, size distribution, aggregation kinetics, and aggregate morphology was examined. With increasing urea concentration, β-sheet content and the fraction of aggregated peptide decreased, the average size of aggregates was reduced, and the morphology of aggregates changed from linear to a globular/linear mixture and then to globular. The data were analyzed using a previously published model of Aβ aggregation kinetics. The model and data were consistent with the hypothesis that the globular aggregates were intermediates in the amyloidogenesis pathway rather than alternatively aggregated species. Increasing the urea concentration from 0.4 M to 2 M decreased the rate of filament initiation the most; between 2 M and 4 M urea the largest change was in partitioning between the nonamyloid and amyloid pathways, and between 4 M and 6 M urea, the most significant change was a reduction in the rate of filament elongation. PMID:15459334

  15. Real-Time Exponential Curve Fits Using Discrete Calculus

    NASA Technical Reports Server (NTRS)

    Rowe, Geoffrey

    2010-01-01

    An improved solution for curve fitting data to an exponential equation (y = Ae(exp Bt) + C) has been developed. This improvement is in four areas -- speed, stability, determinant processing time, and the removal of limits. The solution presented avoids iterative techniques and their stability errors by using three mathematical ideas: discrete calculus, a special relationship (be tween exponential curves and the Mean Value Theorem for Derivatives), and a simple linear curve fit algorithm. This method can also be applied to fitting data to the general power law equation y = Ax(exp B) + C and the general geometric growth equation y = Ak(exp Bt) + C.

  16. Fully exponentially correlated wavefunctions for small atoms

    SciTech Connect

    Harris, Frank E.

    2015-01-22

    Fully exponentially correlated atomic wavefunctions are constructed from exponentials in all the interparticle coordinates, in contrast to correlated wavefunctions of the Hylleraas form, in which only the electron-nuclear distances occur exponentially, with electron-electron distances entering only as integer powers. The full exponential correlation causes many-configuration wavefunctions to converge with expansion length more rapidly than either orbital formulations or correlated wavefunctions of the Hylleraas type. The present contribution surveys the effectiveness of fully exponentially correlated functions for the three-body system (the He isoelectronic series) and reports their application to a four-body system (the Li atom)

  17. Kinetics of gypsum crystal growth from high ionic strength solutions: A case study of Dead Sea - seawater mixtures

    NASA Astrophysics Data System (ADS)

    Reznik, Itay J.; Gavrieli, Ittai; Antler, Gilad; Ganor, Jiwchar

    2011-04-01

    Gypsum precipitation kinetics were examined from a wide range of chemical compositions (11growth theory ( Burton et al., 1951) and other layer-by-layer growth mechanisms ( Goto and Ridge, 1967; Van Rosmalen et al., 1981; Bosbach and Rammensee, 1994). Under further-away-from-equilibrium conditions, the reaction is dominated by an apparent 10th order reaction. A conceptual model for gypsum growth kinetics is presented. The model is based on the 2nd order kinetic coefficients determined in the present study and data from the literature and is valid under a wide range of ionic strengths and Ca/SO42- ratios. According to this model, the integration of SO42- to kinks on the surface of the growing crystals is the rate-limiting step in the precipitation reaction. At ionic strengths above 8.5 m the precipitation rate of gypsum is enhanced, possibly due to the formation of CaSO4° ion pairs and/or a decrease in hydration frequencies.

  18. Kinetics modeling and growth of Si layers by Liquid Phase Epitaxy Driven by Solvent Evaporation (LPESE)

    NASA Astrophysics Data System (ADS)

    Giraud, S.; Duffar, T.; Pihan, E.; Fave, A.

    2015-12-01

    Crystalline Si thin films on low-cost substrates are expected to be an alternative to bulk Si for PV applications. Liquid Phase Epitaxy (LPE) is one of the most suitable techniques for the growth of high quality Si layers since LPE is performed under almost equilibrium conditions. We investigated a growth technology which allows growing Si epitaxial thin films in steady temperature conditions through the control of solvent evaporation from a metallic solution saturated with silicon: Liquid Phase Epitaxy by Solvent Evaporation (LPESE). An analytical model aiming to predict solvent evaporation and Si crystallization rate is described and discussed for three solvents (Sn, In and Cu). Growth experiments are implemented in order to check the validity of the model. Experimental set up and growth procedure are presented. Si thin films were grown from Sn-Si and In-Si solution at temperatures between 900 and 1200 °C under high vacuum. The predicted solvent evaporation rate and Si growth rate are in agreement with the experimental measurements.

  19. Fast and slow crystal growth kinetics in glass-forming melts

    NASA Astrophysics Data System (ADS)

    Orava, J.; Greer, A. L.

    2014-06-01

    Published values of crystal growth rates are compared for supercooled glass-forming liquids undergoing congruent freezing at a planar crystal-liquid interface. For the purposes of comparison pure metals are considered to be glass-forming systems, using data from molecular-dynamics simulations. For each system, the growth rate has a maximum value Umax at a temperature Tmax that lies between the glass-transition temperature Tg and the melting temperature Tm. A classification is suggested, based on the lability (specifically, the propensity for fast crystallization), of the liquid. High-lability systems show "fast" growth characterized by a high Umax, a low Tmax / Tm, and a very broad peak in U vs. T / Tm. In contrast, systems showing "slow" growth have a low Umax, a high Tmax / Tm, and a sharp peak in U vs. T / Tm. Despite the difference of more than 11 orders of magnitude in Umax seen in pure metals and in silica, the range of glass-forming systems surveyed fit into a common pattern in which the lability increases with lower reduced glass-transition temperature (Tg / Tm) and higher fragility of the liquid. A single parameter, a linear combination of Tg / Tm and fragility, can show a good correlation with Umax. For all the systems, growth at Umax is coupled to the atomic/molecular mobility in the liquid. It is found that, across the diversity of glass-forming systems, Tmax / Tg = 1.48 ± 0.15.

  20. Kinetic theory of protein filament growth: Self-consistent methods and perturbative techniques

    NASA Astrophysics Data System (ADS)

    Michaels, Thomas C. T.; Knowles, Tuomas P. J.

    2015-12-01

    Filamentous protein structures are of high relevance for the normal functioning of the cell, where they provide the structural component for the cytoskeleton, but are also implicated in the pathogenesis of many disease states. The self-assembly of these supra-molecular structures from monomeric proteins has been studied extensively in the past 50 years and much interest has focused on elucidating the microscopic events that drive linear growth phenomena in a biological setting. Master equations have proven to be particularly fruitful in this context, allowing specific assembly mechanisms to be linked directly to experimental observations of filamentous growth. Recently, these approaches have increasingly been applied to aberrant protein polymerization, elucidating potential implications for controlling or combating the formation of pathological filamentous structures. This article reviews recent theoretical advances in the field of filamentous growth phenomena through the use of the master-equation formalism. We use perturbation and self-consistent methods for obtaining analytical solutions to the rate equations describing fibrillar growth and show how the resulting closed-form expressions can be used to shed light on the general physical laws underlying this complex phenomenon. We also present a connection between the underlying ideas of the self-consistent analysis of filamentous growth and the perturbative renormalization group.

  1. Growth kinetics and yield study on Chlorella pyrenoidosa in chemically defined media

    SciTech Connect

    Joung, J.J.; Akin, C.

    1983-01-01

    A Chlorella culture free from heterotrophic bacteria was obtained by eliminating the bacteria with successive use of antibiotics and agar plants. The purified Chlorella was cultured in chemically defined media. Under a photon flux (16.7 mw/cmS) similar to insolation, both heterotrophic and mixotrophic cultures were luxurious but the growth rates of autotrophic cultures were reduced substantially. The Chlorella culture grew most rapidly at 30 C in the absence of heterotrophic bacteria, and the highest specific growth rates were 1.43 x 10 h and 0.46 x 10 h for mixotrophic and autotrophic cultures, respectively. The highest photosynthetic efficiency over its growth period was 2.9% for autotrophic cultures. Elimination of heterotrophic bacteria from Chlorella cultures improved the algal growth rate as well as biomass yield significantly. A parasite of 0.1- m size was identified. The motile microorganism played an important role in the growth of the Chlorella and appeared to be common to green algae. 16 references, 2 tables.

  2. Growth kinetics of white graphene (h-BN) on a planarised Ni foil surface

    PubMed Central

    Cho, Hyunjin; Park, Sungchan; Won, Dong-Il; Kang, Sang Ook; Pyo, Seong-Soo; Kim, Dong-Ik; Kim, Soo Min; Kim, Hwan Chul; Kim, Myung Jong

    2015-01-01

    The morphology of the surface and the grain orientation of metal catalysts have been considered to be two important factors for the growth of white graphene (h-BN) by chemical vapour deposition (CVD). We report a correlation between the growth rate of h-BN and the orientation of the nickel grains. The surface of the nickel (Ni) foil was first polished by electrochemical polishing (ECP) and subsequently annealed in hydrogen at atmospheric pressure to suppress the effect of the surface morphology. Atmospheric annealing with hydrogen reduced the nucleation sites of h-BN, which induced a large crystal size mainly grown from the grain boundary with few other nucleation sites in the Ni foil. A higher growth rate was observed from the Ni grains that had the {110} or {100} orientation due to their higher surface energy. PMID:26156068

  3. Growth Kinetics of the S Sub H Center on Magnesium Oxide Using Electron Paramagnetic Resonance

    NASA Technical Reports Server (NTRS)

    Jayne, J. P.

    1971-01-01

    Electron paramagnetic resonance spectroscopy was used to study the growth of S sub H centers on magnesium oxide powder which had hydrogen adsorbed on its surface. The centers were produced by ultraviolet radiation. The effects of both radiation intensity and hydrogen pressure were also studied. At constant hydrogen pressure and radiation dose, the initial S sub H center growth rate was found to be zero order. Beyond the initial region the growth rate deviated from zero order and finally approached saturation. The results are interpreted in terms of a model which assumes that the S sub H center is a hydrogen atom associated with a surface vacancy. Saturation appears to result from a limited supply of surface vacancies.

  4. Nucleation and growth mechanisms of nano magnesium hydride from the hydrogen sorption kinetics.

    PubMed

    Mooij, Lennard; Dam, Bernard

    2013-07-21

    We use a combination of hydrogenography and Johnson-Mehl-Avrami-Kolmogorov (JMAK) analyses to identify (1) the driving force dependence of the nucleation and growth mechanism of MgH2 in thin film multilayers of Mg (10 nm) and (2) the nucleation and growth mechanism of Mg in the earlier formed MgH2, i.e. the hydrogen desorption process. We conclude that JMAK may be successfully applied to obtain the nucleation and growth mechanism of hydrogen absorption. The desorption mechanism, however, is not simply the reverse of the absorption mechanism. We find evidence that the barrier for nucleation of Mg is small. The dehydrogenation probably involves the formation of voids, which is energetically more favorable than elastic and plastic deformation of the multilayer. PMID:23749082

  5. Two-stream Maxwellian kinetic theory of cloud droplet growth by condensation

    NASA Technical Reports Server (NTRS)

    Robinson, N. F.; Scott, W. T.

    1981-01-01

    A new growth rate formula (NGRF) is developed for the rate of growth of cloud droplets by condensation. The theory used is a modification of the Lees-Shankar theory in which the two-stream Maxwellian distribution function of Lees is used in Maxwell's method of moments to determine the transport of water vapor to and heat away from the droplet. Boundary conditions at the droplet are the usual conditions set in terms of accommodation coefficients, and the solution passes smoothly into diffusion flow in the far region. Comparisons are given between NGRF and the conventional formula showing close agreement (approximately 0.1%) for large radii with significant difference (approximately 5%) for small radii (not greater than 1 micron). Growth times for haze droplets in a Laktionov chamber are computed.

  6. Grain growth kinetics during ion beam irradiation of chemical vapor deposited amorphous silicon

    SciTech Connect

    Spinella, C.; Lombardo, S. ); Campisano, S.U. )

    1990-08-06

    The amorphous to polycrystal transition during Kr ion beam irradiation of chemical vapor deposited silicon layers has been studied in the temperature range 320--480 {degree}C. At each irradiation temperature the average grain diameter increases linearly with the Kr dose, while the grain density remains constant within the experimental accuracy. The growth rate follows a complex behavior which can be described by dynamic defect generation and annihilation. The absolute value of the grain growth rate is equal to that of the ion-assisted epitaxial layer by layer crystallization in the silicon (111) orientation. This result can be related to the crystal grain structure and morphology.

  7. Growth kinetics, effect of carbon substrate in biosynthesis of mcl-PHA by Pseudomonas putida Bet001

    PubMed Central

    Gumel, A.M.; Annuar, M.S.M.; Heidelberg, T.

    2014-01-01

    Growth associated biosynthesis of medium chain length poly-3-hydroxyalkanoates (mcl-PHA) in Pseudomonas putida Bet001 isolated from palm oil mill effluent was studied. Models with substrate inhibition terms described well the kinetics of its growth. Selected fatty acids (C8:0 to C18:1) and ammonium were used as carbon and nitrogen sources during growth and PHA biosynthesis, resulting in PHA accumulation of about 50 to 69% (w/w) and PHA yields ranging from 10.12 g L−1 to 15.45 g L−1, respectively. The monomer composition of the PHA ranges from C4 to C14, and was strongly influenced by the type of carbon substrate fed. Interestingly, an odd carbon chain length (C7) monomer was also detected when C18:1 was fed. Polymer showed melting temperature (Tm) of 42.0 (± 0.2) °C, glass transition temperature (Tg) of −1.0 (± 0.2) °C and endothermic melting enthalpy of fusion (ΔHf) of 110.3 (± 0.1) J g−1. The molecular weight (Mw) range of the polymer was relatively narrow between 55 to 77 kDa. PMID:25242925

  8. Evolution of Li2O2 growth and its effect on kinetics of Li-O2 batteries.

    PubMed

    Xia, Chun; Waletzko, Michael; Chen, Limei; Peppler, Klaus; Klar, Peter J; Janek, Jürgen

    2014-08-13

    Lithium peroxide (Li2O2), the solid and intrinsically electronic insulating discharge product of Li-O2 batteries strongly influences the discharge and charge kinetics. In a series of experiments, we investigated the growth of Li2O2 upon discharge and the corresponding reduction and oxidation processes by varying the depth of discharge. The results indicate that insulating Li2O2 particles with a disc-like shape were formed during the initial discharge stage. Afterward, the nucleation and growth of Li2O2 resulted in the formation of conducting Li2O2 shells. When the discharge voltage dropped below 2.65 V, the Li2O2 discs evolved to toroid-shaped particles and defective superoxide-like phase presumably with high conductivity was formed on the rims of Li2O2 toroids. Both Li2O2 and the superoxide-like phase are unstable in ether-based electrolytes resulting in the degradation of the corresponding cells. Nevertheless, by controlling the growth of Li2O2, the chemical reactivity of the discharge product can be suppressed to improve the reversibility of Li-O2 batteries. PMID:25006701

  9. Growth kinetics of micron-size nickel lines produced by laser-assisted decomposition of nickel tetracarbonyl

    NASA Astrophysics Data System (ADS)

    Boughaba, S.; Auvert, G.

    1993-06-01

    Polycrystalline nickel lines as small as 1 μm in width were deposited by pyrolysis of nickel tetracarbonyl [Ni(CO)4] on polysilicon/silicon dioxide/monosilicon substrates. As heat source, a cw argon-ion laser operating at several wavelengths around 0.5 μm was used. The growth kinetics, morphology, and electrical resistivity of the nickel microstructures were investigated at various scanning speeds of the laser spot, laser beam powers, and reactant gas pressures. From the deposition kinetics, the vertical deposition rate of nickel was calculated. For Ni(CO)4 pressures below 0.3 mbar, deposition of flat-topped nickel lines occurs. The deposition rate was proportional to the Ni(CO)4 pressure and independent of the laser output power. For Ni(CO)4 pressures above 0.3 mbar, lines with a Gaussian profile are obtained. The deposition rate was found to be independent of the Ni(CO)4 pressure and exhibits an activation energy of 11.5 kcal mol-1. The measured electrical resistivity of the flat-topped lines was about ten times higher than that of the bulk (7 μΩ cm) while for the Gaussian lines this ratio falls below 1.5. Kinetic measurements with carbon monoxide (CO) as buffer gas were also performed. The nickel deposition rate was found to decrease as the CO partial pressure increases for all the Ni(CO)4 partial pressures considered (0.2-20 mbar). The morphology and roughness of the deposited lines were investigated using both a scanning electron microscope and an atomic force microscope. The effect of the laser beam on the quality of the interfaces underlying the deposited lines was investigated by means of a focused ion beam system. On the basis of the experimental results, a decomposition mechanism of the Ni(CO)4 molecules was elaborated.

  10. Surface kinetics in AlN growth: A universal model for the control of surface morphology in III-nitrides

    NASA Astrophysics Data System (ADS)

    Bryan, Isaac; Bryan, Zachary; Mita, Seiji; Rice, Anthony; Tweedie, James; Collazo, Ramón; Sitar, Zlatko

    2016-03-01

    AlN epitaxial thin films were grown on both vicinal (0001)-oriented native single crystal AlN substrates and AlN templates grown on vicinal (0001)-oriented sapphire to develop a surface kinetic framework for the control of surface morphology. A Burton, Cabrera, and Frank (BCF) theory-based model is formulated and utilized to understand the dependence of the surface kinetics on the vapor supersaturation, σ, and substrate misorientation angle, α. The surface energy of the Al-polar surface of AlN was experimentally determined using BCF theory to be 149±8 meV/Å2. The critical misorientation angle for the onset of step-bunching was determined to be ~0.25° for a growth rate of 500 nm/h and temperature of 1250 °C. Transitioning from a surface with 2D nuclei to one with bilayer steps required a decrease in σ or an increase in α, whereas the suppression of step-bunching required an increase in σ or a decrease in α.

  11. Kinetics of growth and enhanced sophorolipids production by Candida bombicola using a low-cost fermentative medium.

    PubMed

    Daverey, Achlesh; Pakshirajan, Kannan

    2010-04-01

    In this study, effect of various parameters on sophorolipid (SL) production by the yeast Candida bombicola was investigated for the enhancing of its production by employing L18 orthogonal array design of experiments. At optimum conditions of sugarcane molasses 50 g l(-1), soybean oil 50 g l(-1), inoculum size 5% (v/v), temperature 30 degrees C, inoculum age 2 days, and agitation 200 rpm, the yeast produced almost equal amounts of the product in batch shake flasks and in a 3-l fermentor without any pH control (45 and 47 g l(-1), respectively). However, the yield increased to 60 g l(-1) in the fermentor under controlled pH environment. Time course of SL production, yeast biomass growth, and utilization of sugarcane molasses and soybean oil at these optimized conditions were fitted to existing kinetic models reported in the literature. Estimated kinetic parameters from these models suggested that conventional medium containing glucose can very well be replaced with the present low-cost fermentative medium. PMID:19834651

  12. Dynamic determination of kinetic parameters and computer simulation of growth of Clostridium perfringens in cooked beef

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The objective of this research was to develop a new one-step methodology that uses a dynamic approach to directly construct a tertiary model for prediction of the growth of C. perfringens in cooked beef. This methodology was based on numerical analysis and optimization of both primary and secondary...

  13. Structure and kinetics of Sn whisker growth on Pb-free solder finish

    SciTech Connect

    Choi, W.J.; Lee, T.Y.; Tu, K.N.; Tamura, N.; Celestre, R.S.; MacDowell, A.A.; Bong, Y.Y.; Nguyen, L.; Sheng, G.T.T.

    2002-07-11

    Standard Leadframes used in surface mount technology are finished with a layer of eutectic SnPb for passivation and for enhancing solder wetting during reflow. When eutectic SnPb is replaced by Pb-free solder, especially the eutectic SnCu, a large number of Sn whiskers are found on the Pb-free finish. Some of the whiskers are long enough to become shorts between the neighboring legs of the leadframe. How to suppress their growth and how to perform accelerated test of Sn whisker growth are crucial reliability issues in the electronic packaging industry. In this paper, we report the study of spontaneous Sn whisker growth at room temperature on eutectic SnCu and pure Sn finishes. Both compressive stress and surface oxide on Sn are necessary conditions for whisker growth. Structure and stress analyses by using the micro-diffraction in synchrotron radiation are reported. Cross-sectional electron microscopy, with samples prepared by focused ion beam, are included.

  14. Kinetics of phase growth in the Cu-Sn system and application to composite Nb3Sn strands

    SciTech Connect

    Emanuela Barzi et al.1

    2002-11-18

    Nb{sub 3}Sn is the superconductor most used in the R and D of high field accelerator magnets by either the wind and react or the react and wind technique. In order to program the low temperature steps of the heat treatment, the growth kinetics of Cu-Sn intermetallics was investigated as a function of duration and temperature. The diffusion constants of {eta}, {var_epsilon} and {delta} phases between 150 and 550 C were evaluated using Cu-Sn model samples. Statistical and systematic errors were thoroughly evaluated for an accurate data analysis. Next the behavior of Internal Tin and Modified Jelly Roll Nb{sub 3}Sn composites was compared with the model predictions.

  15. Conductive atomic force microscopy study of InAs growth kinetics on vicinal GaAs (110)

    SciTech Connect

    Tejedor, Paloma; Diez-Merino, Laura; Beinik, Igor; Teichert, Christian

    2009-09-21

    Conductive atomic force microscopy has been used to investigate the effect of atomic hydrogen and step orientation on the growth behavior of InAs on GaAs (110) misoriented substrates. Samples grown by conventional molecular beam epitaxy exhibit higher conductivity on [110]-multiatomic step edges, where preferential nucleation of InAs nanowires takes place by step decoration. On H-terminated substrates with triangular terraces bounded by [115]-type steps, three-dimensional InAs clusters grow selectively at the terrace apices as a result of a kinetically driven enhancement in upward mass transport via AsH{sub x} intermediate species and a reduction in the surface free energy.

  16. Kinetics of disilane molecule decomposition on the growth surface of silicon in vacuum gas-phase epitaxy reactors

    NASA Astrophysics Data System (ADS)

    Orlov, L. K.; Smyslova, T. N.

    2012-11-01

    The range of the characteristic decomposition rates of dihydride molecule radicals adsorbed by the silicon surface in the temperature interval 450-700°C is experimentally found for a number of kinetic models. A relationship between the rate of silicon atom incorporation into a growing crystal and the characteristic rate of disilane molecule pyrolysis on the silicon surface is found. The temperature dependence of the rate of disilane fragment decomposition on the silicon surface is nonmonotonic, and its run depends on temperature conditions. It is shown that the temperature dependence of the molecular decomposition rate on the growth surface is described by a superposition of two activation curves with various activation energies. The activation energies depend on the peculiarity of interaction between the molecular beam and the silicon surface when the filling of surface states with hydrogen is low and high.

  17. Software tools that facilitate kinetic modelling with large data sets: an example using growth modelling in sugarcane.

    PubMed

    Uys, L; Hofmeyr, J H S; Snoep, J L; Rohwer, J M

    2006-09-01

    A solution to manage cumbersome data sets associated with large modelling projects is described. A kinetic model of sucrose accumulation in sugarcane is used to predict changes in sucrose metabolism with sugarcane internode maturity. This results in large amounts of output data to be analysed. Growth is simulated by reassigning maximal activity values, specific to each internode of the sugarcane plant, to parameter attributes of a model object. From a programming perspective, only one model definition file is required for the simulation software used; however, the amount of input data increases with each extra interrnode that is modelled, and likewise the amount of output data that is generated also increases. To store, manipulate and analyse these data, the modelling was performed from within a spreadsheet. This was made possible by the scripting language Python and the modelling software PySCeS through an embedded Python interpreter available in the Gnumeric spreadsheet program. PMID:16986323

  18. In situ real-time investigation of kinetics of nucleation and growth of sol-gel-derived functional oxide thin films

    NASA Astrophysics Data System (ADS)

    Sun, Tao; Hu, Hao; Pan, Zixiao; Li, Xuefa; Wang, Jin; Dravid, Vinayak P.

    2008-05-01

    Early-stage nucleation and growth kinetics of sol-gel-derived multiferroic BiFeO3 thin films were investigated in situ and in real time by combining transmission electron microscopy and grazing-incidence small-angle x-ray scattering (GISAXS). While the initial phase of the nuclei was identified to be Bi2O2CO3 , the quantitative GISAXS analysis unambiguously revealed that the early-stage kinetic nucleation growth in the thin films was dominated by an oriented-attachment mechanism as opposed to the conventional Ostwald ripening in metallic and ceramic systems.

  19. Fast and slow crystal growth kinetics in glass-forming melts

    SciTech Connect

    Orava, J.; Greer, A. L.

    2014-06-07

    Published values of crystal growth rates are compared for supercooled glass-forming liquids undergoing congruent freezing at a planar crystal-liquid interface. For the purposes of comparison pure metals are considered to be glass-forming systems, using data from molecular-dynamics simulations. For each system, the growth rate has a maximum value U{sub max} at a temperature T{sub max} that lies between the glass-transition temperature T{sub g} and the melting temperature T{sub m}. A classification is suggested, based on the lability (specifically, the propensity for fast crystallization), of the liquid. High-lability systems show “fast” growth characterized by a high U{sub max}, a low T{sub max} / T{sub m}, and a very broad peak in U vs. T / T{sub m}. In contrast, systems showing “slow” growth have a low U{sub max}, a high T{sub max} / T{sub m}, and a sharp peak in U vs. T / T{sub m}. Despite the difference of more than 11 orders of magnitude in U{sub max} seen in pure metals and in silica, the range of glass-forming systems surveyed fit into a common pattern in which the lability increases with lower reduced glass-transition temperature (T{sub g} / T{sub m}) and higher fragility of the liquid. A single parameter, a linear combination of T{sub g} / T{sub m} and fragility, can show a good correlation with U{sub max}. For all the systems, growth at U{sub max} is coupled to the atomic/molecular mobility in the liquid. It is found that, across the diversity of glass-forming systems, T{sub max} / T{sub g} = 1.48 ± 0.15.

  20. Fast and slow crystal growth kinetics in glass-forming melts.

    PubMed

    Orava, J; Greer, A L

    2014-06-01

    Published values of crystal growth rates are compared for supercooled glass-forming liquids undergoing congruent freezing at a planar crystal-liquid interface. For the purposes of comparison pure metals are considered to be glass-forming systems, using data from molecular-dynamics simulations. For each system, the growth rate has a maximum value U(max) at a temperature T(max) that lies between the glass-transition temperature T(g) and the melting temperature T(m). A classification is suggested, based on the lability (specifically, the propensity for fast crystallization), of the liquid. High-lability systems show "fast" growth characterized by a high U(max), a low T(max)/T(m), and a very broad peak in U vs. T/T(m). In contrast, systems showing "slow" growth have a low U(max), a high T(max)/T(m), and a sharp peak in U vs. T/T(m). Despite the difference of more than 11 orders of magnitude in U(max) seen in pure metals and in silica, the range of glass-forming systems surveyed fit into a common pattern in which the lability increases with lower reduced glass-transition temperature (T(g)/T(m)) and higher fragility of the liquid. A single parameter, a linear combination of T(g)/T(m) and fragility, can show a good correlation with U(max). For all the systems, growth at U(max) is coupled to the atomic/molecular mobility in the liquid. It is found that, across the diversity of glass-forming systems, T(max)/T(g) = 1.48 ± 0.15. PMID:24908023

  1. Growth kinetics of grain boundary allotriomorphs of proeutectoid ferrite in Fe-C-Mn-X{sub 2} alloys

    SciTech Connect

    Tanaka, T.; Aaronson, H.I.; Enomoto, M.

    1995-03-01

    The parabolic rate constant for the thickening of grain boundary ferrite allotriomorphs at the faces of austenite grain boundaries was measured as a function of isothermal transformation temperature in three Fe-C-X{sub 1}-X{sub 2} alloys where X{sub 1} is Mn and X{sub 2} is successively Si, Ni, and Co. The results were compared with the predictions of the local equilibrium model for multi-component systems and with those derived from the theory of growth under paraequilibrium conditions. The distribution of Mn and Si in ferrite and austenite in the Fe-C-Mn-Si alloy was also measured as a function of reaction temperature with transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The observed temperature below which alloying element partition ceased was in good agreement with the local equilibrium model. Whereas the parabolic rate constant for thickening was considerably larger than the amount predicted by this theory in the alloying element diffusion-controlled regime, the opposite was true in the carbon diffusion-controlled regime. Similarly, the calculated paraequilibrium constant was usually considerably larger than that measured experimentally. Synergistic enhancements of the effects of Mn and X{sub 2} in diminishing thickening kinetics were observed for each X{sub 2}. The time-temperature-transformation (TTT) curves for the beginning of transformation were calculated from a modified Cahn analysis for the overall kinetics of grain-boundary-nucleated reactions using values of the nucleation rate and the parabolic growth rate constant computed from various models and compared with experimentally determined TTT curves.

  2. Specific heat capacity and dendritic growth kinetics of liquid peritectic Fe-Cu alloys

    NASA Astrophysics Data System (ADS)

    Xia, Z. C.; Wang, W. L.; Luo, S. B.; Wei, B.

    2016-08-01

    The specific heat and dendritic growth of highly undercooled peritectic Fe-Cu alloys were investigated by electromagnetic levitation technique. The specific heat values of liquid peritectic Fe92.8Cu7.2 and hyperperitectic Fe88.5Cu11.5 alloys were determined to be 40.4 and 39.58 J·mol-1·K-1 over wide temperature ranges. The measured growth velocities rose rapidly with increasing undercooling, which reached 69 and 68 m·s-1 at the maximum undercoolings of 401 K (0.23 TL) and 468 K (0.27 TL). The microstructures of peritectic Fe-Cu alloys were refined significantly with enhanced undercooling. Theoretical analyses showed that almost segregationless solidification was realized if undercooling was sufficiently large.

  3. Kinetic modeling of growth and lipid body induction in Chlorella pyrenoidosa under heterotrophic conditions.

    PubMed

    Sachdeva, Neha; Kumar, G Dinesh; Gupta, Ravi Prakash; Mathur, Anshu Shankar; Manikandan, B; Basu, Biswajit; Tuli, Deepak Kumar

    2016-10-01

    The aim of the present work was to develop a mathematical model to describe the biomass and (total) lipid productivity of Chlorella pyrenoidosa NCIM 2738 under heterotrophic conditions. Biomass growth rate was predicted by Droop's cell quota model, while changes observed in cell quota (utilization) under carbon excess conditions were used for the modeling and predicting the lipid accumulation rate. The model was simulated under non-limiting (excess) carbon and limiting nitrate concentration and validated with experimental data for the culture grown in batch (flask) mode under different nitrate concentrations. The present model incorporated two modes (growth and stressed) for the prediction of endogenous lipid synthesis/induction and aimed to predict the effect and response of the microalgae under nutrient starvation (stressed) conditions. MATLAB and Genetic Algorithm were employed for the prediction and validation of the model parameters. PMID:27450124

  4. Growth kinetics of Salmonella enterica in Hajna tetrathionate broth, Rappaport broth and modified semisolid Rappaport agar

    PubMed Central

    FUJIHARA, Masatoshi; TABUCHI, Hiroyuki; UEGAKI, Kaho

    2015-01-01

    To determine the appropriate method for isolating Salmonella enterica, we compared the growth of S. enterica serovars using three selective enrichment media. S. enterica was more successfully isolated from artificially contaminated fecal samples after enrichment in Hajna tetrathionate broth or modified semisolid Rappaport agar than in Rappaport broth. Since most bacteria (other than motile S. enterica) do not migrate on modified semisolid Rappaport agar, the growth characteristics of S. enterica can be interpreted easily and quickly. Two S. enterica isolates did not migrate on modified semisolid Rappaport agar, but did grow in Hajna tetrathionate broth, which suggests that the combined use of these selective enrichment media is appropriate for isolating S. enterica. PMID:26498402

  5. Kinetic surface roughening and wafer bow control in heteroepitaxial growth of 3C-SiC on Si(111) substrates.

    PubMed

    Wang, Li; Walker, Glenn; Chai, Jessica; Iacopi, Alan; Fernandes, Alanna; Dimitrijev, Sima

    2015-01-01

    A thin, chemically inert 3C-SiC layer between GaN and Si helps not only to avoid the "melt-back" effect, but also to inhibit the crack generation in the grown GaN layers. The quality of GaN layer is heavily dependent on the unique properties of the available 3C-SiC/Si templates. In this paper, the parameters influencing the roughness, crystalline quality, and wafer bow are investigated and engineered to obtain high quality, low roughness 3C-SiC/Si templates suitable for subsequent GaN growth and device processing. Kinetic surface roughening and SiC growth mechanisms, which depend on both deposition temperature and off-cut angle, are reported for heteroepitaxial growth of 3C-SiC on Si substrates. The narrower terrace width on 4° off-axis Si enhances the step-flow growth at 1200 °C, with the roughness of 3C-SiC remaining constant with increasing thickness, corresponding to a scaling exponent of zero. Crack-free 3C-SiC grown on 150-mm Si substrate with a wafer bow of less than 20 μm was achieved. Both concave and convex wafer bow can be obtained by in situ tuning of the deposited SiC layer thicknesses. The 3C-SiC grown on off-axis Si, compared to that grown on on-axis Si, has lower surface roughness, better crystallinity, and smaller bow magnitude. PMID:26487465

  6. Kinetic surface roughening and wafer bow control in heteroepitaxial growth of 3C-SiC on Si(111) substrates

    PubMed Central

    Wang, Li; Walker, Glenn; Chai, Jessica; Iacopi, Alan; Fernandes, Alanna; Dimitrijev, Sima

    2015-01-01

    A thin, chemically inert 3C-SiC layer between GaN and Si helps not only to avoid the “melt-back” effect, but also to inhibit the crack generation in the grown GaN layers. The quality of GaN layer is heavily dependent on the unique properties of the available 3C-SiC/Si templates. In this paper, the parameters influencing the roughness, crystalline quality, and wafer bow are investigated and engineered to obtain high quality, low roughness 3C-SiC/Si templates suitable for subsequent GaN growth and device processing. Kinetic surface roughening and SiC growth mechanisms, which depend on both deposition temperature and off-cut angle, are reported for heteroepitaxial growth of 3C-SiC on Si substrates. The narrower terrace width on 4° off-axis Si enhances the step-flow growth at 1200 °C, with the roughness of 3C-SiC remaining constant with increasing thickness, corresponding to a scaling exponent of zero. Crack-free 3C-SiC grown on 150-mm Si substrate with a wafer bow of less than 20 μm was achieved. Both concave and convex wafer bow can be obtained by in situ tuning of the deposited SiC layer thicknesses. The 3C-SiC grown on off-axis Si, compared to that grown on on-axis Si, has lower surface roughness, better crystallinity, and smaller bow magnitude. PMID:26487465

  7. First principles kinetic Monte Carlo study on the growth patterns of WSe2 monolayer

    NASA Astrophysics Data System (ADS)

    Nie, Yifan; Liang, Chaoping; Zhang, Kehao; Zhao, Rui; Eichfeld, Sarah M.; Cha, Pil-Ryung; Colombo, Luigi; Robinson, Joshua A.; Wallace, Robert M.; Cho, Kyeongjae

    2016-06-01

    The control of domain morphology and defect level of synthesized transition metal dichalcogenides (TMDs) is of crucial importance for their device applications. However, current TMDs synthesis by chemical vapor deposition and molecular beam epitaxy is in an early stage of development, where much of the understanding of the process-property relationships is highly empirical. In this work, we use a kinetic Monte Carlo coupled with first principles calculations to study one specific case of the deposition of monolayer WSe2 on graphene, which can be expanded to the entire TMD family. Monolayer WSe2 domains are investigated as a function of incident flux, temperature and precursor ratio. The quality of the grown WSe2 domains is analyzed by the stoichiometry and defect density. A phase diagram of domain morphology is developed in the space of flux and the precursor stoichiometry, in which the triangular compact, fractal and dendritic domains are identified. The phase diagram has inspired a new synthesis strategy for large TMD domains with improved quality.

  8. Kinetics of biphenyl and polychlorinated biphenyl metabolism in soil

    SciTech Connect

    Focht, D.D.; Brunner, W.

    1985-10-01

    The metabolism of /sup 14/C-labeled PCBs (polychlorinated biphenyls), which comprised the Aroclor 1242 mixture, was greatly enhanced by the addition of biphenyl (BP) to soil. After 49 days, only 25 to 35% of the original PCBs remained in the soil, and 48 to 49% was converted to /sup 14/CO/sub 2/ (including soil carbonates) in treatment enriched with BP; by contrast, 92% of the PCBs remained and less than 2% was converted to /sup 14/CO/sub 2/ in the unenriched control. Although the mineralization of PCBs in soils inoculated with Acinetobacter strain P6 was not greater than that in uninoculated BP-enriched soils, the initial and maximum mineralization rates and mineralization of BP was consistent with kinetic models based upon linear-no growth and exponential growth; lower cell densities (< 10/sup 6//g) of BP-oxidizing bacteria gave a better fit for exponential growth, whereas the highest cell density (10/sup 9//g) gave a better fit for linear-no growth. The numbers of BP-oxidizing bacteria declined exponentially upon depletion of the substrate. Since the mineralization of the chlorinated cometabolites was brought about by microorganisms (comensals) other than BP oxidizers, /sup 14/CO/sub 2/ production could not be fit to either of the two growth models. However, /sup 14/CO/sub 2/ production from the highest-density inoculum could be fit to a first-order (no-growth) sequential-reaction series.

  9. Theory, computation, and application of exponential splines

    NASA Technical Reports Server (NTRS)

    Mccartin, B. J.

    1981-01-01

    A generalization of the semiclassical cubic spline known in the literature as the exponential spline is discussed. In actuality, the exponential spline represents a continuum of interpolants ranging from the cubic spline to the linear spline. A particular member of this family is uniquely specified by the choice of certain tension parameters. The theoretical underpinnings of the exponential spline are outlined. This development roughly parallels the existing theory for cubic splines. The primary extension lies in the ability of the exponential spline to preserve convexity and monotonicity present in the data. Next, the numerical computation of the exponential spline is discussed. A variety of numerical devices are employed to produce a stable and robust algorithm. An algorithm for the selection of tension parameters that will produce a shape preserving approximant is developed. A sequence of selected curve-fitting examples are presented which clearly demonstrate the advantages of exponential splines over cubic splines.

  10. EXPONENTIAL GALAXY DISKS FROM STELLAR SCATTERING

    SciTech Connect

    Elmegreen, Bruce G.; Struck, Curtis E-mail: curt@iastate.edu

    2013-10-01

    Stellar scattering off of orbiting or transient clumps is shown to lead to the formation of exponential profiles in both surface density and velocity dispersion in a two-dimensional non-self gravitating stellar disk with a fixed halo potential. The exponential forms for both nearly flat rotation curves and near-solid-body rotation curves. The exponential does not depend on initial conditions, spiral arms, bars, viscosity, star formation, or strong shear. After a rapid initial development, the exponential saturates to an approximately fixed scale length. The inner exponential in a two-component profile has a break radius comparable to the initial disk radius; the outer exponential is primarily scattered stars.

  11. Real-time x-ray studies of indium island growth kinetics

    SciTech Connect

    Demasi, Alexander; Rainville, Meliha G.; Ludwig, Karl F.

    2015-03-15

    The authors have investigated the early stages of indium island formation and growth by vapor phase deposition on room temperature sapphire using real-time grazing incidence small angle x-ray scattering (GISAXS), followed by ex-situ atomic force microscopy and scanning electron microscopy. The results are consistent with the formation and coalescence of hemispherical islands, as described by Family and Meakin. Monte Carlo simulations of systems of coalescing islands were used to supplement and quantify the results of GISAXS, and a good agreement is seen between the data and the simulations.

  12. Nuclei growth kinetics during the nucleation of gold on UHV-cleaved mica substrates

    NASA Technical Reports Server (NTRS)

    Elliot, A. G.

    1974-01-01

    Measurements of crystalline sizes during nucleation of gold on mica surfaces cleaved in ultra-high vacuum (UHV) reveal the presence of symmetric, sharply peaked distributions which flatten and broaden with increasing nucleation time. When the number density of nuclei increases, the growth rate is suppressed. The time taken to reach a given size increases with increasing temperature when the nuclei are growing as isolated particles. When the nuclei are spaced so far that their diffusion fields overlap, then the time taken to reach a given size decreases with increasing temperature.

  13. Imaging System to Measure Kinetics of Material Cluster Ejection During Exit-Surface Damage Initiation and Growth in Fused Silica

    SciTech Connect

    Raman, R N; Negres, R A; Demos, S G

    2009-10-29

    Laser-induced damage on the surface of optical components typically is manifested by the formation of microscopic craters that can ultimately degrade the optics performance characteristics. It is believed that the damage process is the result of the material exposure to high temperatures and pressures within a volume on the order of several cubic microns located just below the surface. The response of the material following initial localized energy deposition by the laser pulse, including the timeline of events and the individual processes involved during this timeline, is still largely unknown. In this work we introduce a time-resolved microscope system designed to enable a detailed investigation of the sequence of dynamic events involved during surface damage. To best capture individual aspects of the damage timeline, this system is employed in multiple imaging configurations (such as multi-view image acquisition at a single time point and multi-image acquisition at different time points of the same event) and offers sensitivity to phenomena at very early delay times. The capabilities of this system are demonstrated with preliminary results from the study of exit-surface damage in fused silica. The time-resolved images provide information on the material response immediately following laser energy deposition, the processes later involved during crater formation or growth, the material ejecta kinetics, and overall material motion and transformation. Such results offer insight into the mechanisms governing damage initiation and growth in the optical components of ICF class laser systems.

  14. Growth and uptake kinetics of nitrate and phosphate by benthic microalgae for phytoremediation of eutrophic coastal sediments.

    PubMed

    Kwon, Hyeong Kyu; Oh, Seok Jin; Yang, Han-Soeb

    2013-02-01

    In the present study, the effect of monochromatic light (blue, yellow and red) and mixed wavelength on the nutrient uptake and growth kinetics of benthic microalgae Achnanthes sp., Amphora sp., Navicula sp. and Nitzschia sp. were investigated. The maximum uptake rate (ρmax) for nitrate and phosphate obtained by short-term experiments were high in the order of blue, mixed, red, yellow wavelength, and among the 4 benthic microalgae, Nitzschia sp. was the highest ρmax. The half-saturation constant (Ks) was higher than other taxon. The specific maximum growth rate (μmax') and minimum cell quota (q0) for the nitrogen and phosphorus-limited condition, Nitzschia sp. showed the highest μmax' and q0 values among the 4 benthic microalgae. These results suggest that the benthic microalgae are adapted to high nutrient concentration. In particular, Nitzschia sp., which have a higher capability of storage and uptake, may be a useful species for phytoremediation. PMID:23262016

  15. BiOI/TiO2-nanorod array heterojunction solar cell: Growth, charge transport kinetics and photoelectrochemical properties

    NASA Astrophysics Data System (ADS)

    Wang, Lingyun; Daoud, Walid A.

    2015-01-01

    A series of BiOI/TiO2-nanorod array photoanodes were grown on fluorine-doped tin oxide (FTO) glass using a simple two-step solvothermal/hydrothermal method. The effects of the hydrothermal process, such as TiO2 nanorod growth time, BiOI concentration and the role of surfactant, polyvinylpyrrolidone (PVP), on the growth of BiOI, were investigated. The heterojunctions were characterized by X-ray diffraction, UV-vis absorbance spectroscopy and scanning electron microscopy. The photoelectrochemical properties of the as-grown junctions, such as linear sweep voltammetry (LSV) behavior, photocurrent response and incident photon-to-electron conversion efficiency (IPCE) under Xenon lamp illumination, are presented. The cell with BiOI/TiO2 (PVP) as photoanode can reach a short current density (Jsc) of 0.13 mA/cm2 and open circuit voltage (Voc) of 0.46 V vs. Ag/AgCl under the irradiation of a 300 W Xenon lamp. Compared to bare TiO2, the IPCE of BiOI/TiO2 (PVP) increased 4-5 times at 380 nm. Furthermore, the charge transport kinetics within the heterojunction is also discussed.

  16. Nucleation kinetics, growth, crystalline perfection, mechanical, thermal, optical and electrical characterization of brucinium 2-carboxy-6-nitrophthalate dihydrate single crystal

    NASA Astrophysics Data System (ADS)

    Krishnan, P.; Gayathri, K.; Sivakumar, N.; Gunasekaran, S.; Anbalagan, G.

    2014-06-01

    Single crystals of brucinium 2-carboxy-6-nitrophthalate dihydrate (B2C6ND) have been grown by the slow evaporation solution technique at room temperature using water-ethanol (1:1) mixed solvent. The metastable zone width and induction period have been experimentally determined for the growth conditions. Nucleation kinetics and fundamental growth parameters such as surface free energy, critical radius and critical free energy change are also evaluated according to the experimental data. The crystal system and the lattice parameters have been confirmed by single crystal X-ray diffraction. The crystalline perfection of the grown B2C6ND crystals has been characterized by HRXRD method. Optical band gap and Urbach tail width of the sample have been studied employing UV-Vis absorption spectroscopy. The Vickers microhardness number (Hv), yield strength (σv) and stiffness constant (C11) of the grown crystal have been evaluated. The dielectric permittivity and dielectric loss of the grown B2C6ND crystal have been investigated as a function of frequency in the temperature range 313-353 K. The laser damage threshold value of B2C6ND crystal was estimated to be 2.8 GW/cm2 using a Nd:YAG laser.

  17. Growth kinetics and mechanistic action of reactive oxygen species released by silver nanoparticles from Aspergillus niger on Escherichia coli.

    PubMed

    Ninganagouda, Shivaraj; Rathod, Vandana; Singh, Dattu; Hiremath, Jyoti; Singh, Ashish Kumar; Mathew, Jasmine; ul-Haq, Manzoor

    2014-01-01

    Silver Nanoparticles (AgNPs), the real silver bullet, are known to have good antibacterial properties against pathogenic microorganisms. In the present study AgNPs were prepared from extracellular filtrate of Aspergillus niger. Characterization of AgNPs by UV-Vis spectrum reveals specific surface plasmon resonance at peak 416 nm; TEM photographs revealed the size of the AgNPs to be 20-55 nm. Average diameter of the produced AgNPs was found to be 73 nm with a zeta potential that was -24 mV using Malvern Zetasizer. SEM micrographs showed AgNPs to be spherical with smooth morphology. EDS revealed the presence of pure metallic AgNPs along with carbon and oxygen signatures. Of the different concentrations (0, 2.5, 5, 10, and 15 μg/mL) used 10 μg/mL were sufficient to inhibit 10(7) CFU/mL of E. coli. ROS production was measured using DCFH-DA method and the the free radical generation effect of AgNPs on bacterial growth inhibition was investigated by ESR spectroscopy. This paper not only deals with the damage inflicted on microorganisms by AgNPs but also induces cell death through the production of ROS released by AgNPs and also growth kinetics of E. coli supplemented with AgNPs produced by A. niger. PMID:25028666

  18. Growth Kinetics and Mechanistic Action of Reactive Oxygen Species Released by Silver Nanoparticles from Aspergillus niger on Escherichia coli

    PubMed Central

    Ninganagouda, Shivaraj; Rathod, Vandana; Singh, Dattu; Hiremath, Jyoti; Singh, Ashish Kumar; Mathew, Jasmine; ul-Haq, Manzoor

    2014-01-01

    Silver Nanoparticles (AgNPs), the real silver bullet, are known to have good antibacterial properties against pathogenic microorganisms. In the present study AgNPs were prepared from extracellular filtrate of Aspergillus niger. Characterization of AgNPs by UV-Vis spectrum reveals specific surface plasmon resonance at peak 416 nm; TEM photographs revealed the size of the AgNPs to be 20–55 nm. Average diameter of the produced AgNPs was found to be 73 nm with a zeta potential that was −24 mV using Malvern Zetasizer. SEM micrographs showed AgNPs to be spherical with smooth morphology. EDS revealed the presence of pure metallic AgNPs along with carbon and oxygen signatures. Of the different concentrations (0, 2.5, 5, 10, and 15 μg/mL) used 10 μg/mL were sufficient to inhibit 107 CFU/mL of E. coli. ROS production was measured using DCFH-DA method and the the free radical generation effect of AgNPs on bacterial growth inhibition was investigated by ESR spectroscopy. This paper not only deals with the damage inflicted on microorganisms by AgNPs but also induces cell death through the production of ROS released by AgNPs and also growth kinetics of E. coli supplemented with AgNPs produced by A. niger. PMID:25028666

  19. CO2 Biofixation and Growth Kinetics of Chlorella vulgaris and Nannochloropsis gaditana.

    PubMed

    Adamczyk, Michał; Lasek, Janusz; Skawińska, Agnieszka

    2016-08-01

    CO2 biofixation was investigated using tubular bioreactors (15 and 1.5 l) either in the presence of green algae Chlorella vulgaris or Nannochloropsis gaditana. The cultivation was carried out in the following conditions: temperature of 25 °C, inlet-CO2 of 4 and 8 vol%, and artificial light enhancing photosynthesis. Higher biofixation were observed in 8 vol% CO2 concentration for both microalgae cultures than in 4 vol%. Characteristic process parameters such as productivity, CO2 fixation, and kinetic rate coefficient were determined and discussed. Simplified and advanced methods for determination of CO2 fixation were compared. In a simplified method, it is assumed that 1 kg of produced biomass equals 1.88 kg recycled CO2. Advance method is based on empirical results of the present study (formula with carbon content in biomass). It was observed that application of the simplified method can generate large errors, especially if the biomass contains a relatively low amount of carbon. N. gaditana is the recommended species for CO2 removal due to a high biofixation rate-more than 1.7 g/l/day. On day 10 of cultivation, the cell concentration was more than 1.7 × 10(7) cells/ml. In the case of C. vulgaris, the maximal biofixation rate and cell concentration did not exceed 1.4 g/l/day and 1.3 × 10(7) cells/ml, respectively. PMID:27052208

  20. Non-magnetic impurity effect on domain growth kinetics in an isosceles triangular Ising antiferromagnet CoNb2O6

    NASA Astrophysics Data System (ADS)

    Mitsuda, S.; Okano, H.; Kobayashi, S.; Prokes, K.

    2004-05-01

    By neutron diffraction and ac susceptibility measurements we have investigated non-magnetic impurity effect on domain-growth-kinetics specific to an isosceles-triangular geometry of frustrated spins, using the Co1-xMgxNb2O6 sample with x=0.005, where, preserving anomalously low growth exponent n~0.2, anisotropic pinning effect for domain-wall-motion by non-magnetic impurity was clearly observed.

  1. Vacuum hydride epitaxy of silicon: kinetics of monosilane pyrolysis on the growth surface

    SciTech Connect

    Orlov, L. K.; Ivin, S. V.

    2011-04-15

    Analytical expressions relating the rate of silicon atom incorporation into a growing crystal to the typical frequency of silane molecule pyrolysis on the silicon surface in the growth temperature range are derived. Based on currently available experimental data, the range of typical decomposition frequencies of hydride molecule radicals adsorbed at the silicon wafer surface in the temperature range of 450-700 Degree-Sign C is determined for the most widely used physicochemical models. It is shown that the most probable molecular decomposition model can be chosen based on the experimental study of the temperature dependence of the decomposition rate of adsorbed hydride molecules. A change in the silane molecule pyrolysis rate or the hydrogen desorption rate from the surface in principle makes it possible to increase the Si layer growth rate without additional substrate heating under conditions of low-temperature epitaxy (450-550 Degree-Sign C), but no larger than by a factor of 2-3 in the former case and up to 100 times in the latter case. The analysis performed shows that physicochemical pyrolysis models in which hydrogen is trapped by the surface, mostly at the stage of decomposition of silane radicals adsorbed by the surface, are more realistic.

  2. Kinetics of protein crystal nucleation and growth in the batch method

    NASA Astrophysics Data System (ADS)

    Baird, James K.; Hill, Susan C.; Clunie, John C.

    1999-01-01

    We have applied the Johnson-Mehl-Avrami-Kolomogorov (JMAK) theory of crystal nucleation and growth to the problem of protein crystallization in the batch method. Without integrating the JMAK equation explicitly, we use dimensional analysis to derive a general formula for the half-life for decay of the protein supersaturation. This formula includes a dimensioned group and an arbitrary dimensionless function. We integrate the JMAK equation exactly for the special case where the growth rate is independent of the supersaturation and the nucleation rate is proportional to its square. This gives an equation for the time decay of the supersaturation and a formula for the half-life in which all arbitrary dimensionless functions are evaluated. The results are consistent not only with Von Weimarn's rule, which asserts that the average size of a crystal increases as the supersaturation decreases, but also with our experimental results for crystallization of lysozyme, in which the half-life at fixed pH decreases with increasing ionic strength and decreasing temperature.

  3. Growth kinetics of Chlorococcum humicola - A potential feedstock for biomass with biofuel properties.

    PubMed

    Thomas, Jibu; Jayachithra, E V

    2015-11-01

    Economically viable production facilities for microalgae depend on the optimization of growth parameters with regard to nutrient requirements. Using microalgae to treat industrial effluents containing heavy metals presents an alternative to the current practice of using physical and chemical methods. Present work focuses on the statistical optimization of growth of Chlorococcum humicola to ascertain the maximum production of biomass. Plackett Burman design was carried out to screen the significant variables influencing biomass production. Further, Response Surface Methodology was employed to optimize the effect of inoculum, light intensity and pH on net biomass yield. Optimum conditions for maximum biomass yield were identified to be inoculum at 15%, light intensity to be 1500lx and pH 8.5. Theoretical and predicted values were in agreement and thus the model was found to be significant. Gas chromatography analyses of the FAME derivatives showed a high percentage of saturated fatty acids thereby confirming the biofuel properties of the oil derived from algal biomass. PMID:25791468

  4. Experimental and numerical analysis of coupled interfacial kinetics and heat transport during the axial heat flux close to the phase interface growth of BGO single crystals

    NASA Astrophysics Data System (ADS)

    Bykova, S. V.; Golyshev, V. D.; Gonik, M. A.; Tsvetovsky, V. B.; Deshko, V. I.; Karvatskii, A. Ya.; Lenkin, A. V.; Brandon, S.; Weinstein, O.; Virozub, A.; Derby, J. J.; Yeckel, A.; Sonda, P.

    2004-05-01

    Combined experimental and numerical tools are used to analyze the effect of convective and radiative heat transport, faceting phenomena, and the optical thickness of the Bi 4Ge 3O 12 (BGO) crystal on the measurement and calculation of melt/crystal interface kinetics during the axial heat flux close to the phase interface growth of BGO single crystals. Results show that, in the general case, accurate determination of growth kinetic relations requires the application of models which account for all of the above phenomena (radiative and convective heat transport, faceting phenomena, etc.). Failure to take these into account may result not only in quantitative errors, but also even in qualitatively wrong determination of interfacial kinetic mechanisms.

  5. Kinetics of growth of thin-films of Co2Si, Ni2Si, WSi2 and VSi2 during a reactive diffusion process

    NASA Astrophysics Data System (ADS)

    Akintunde, S. O.; Selyshchev, P. A.

    A theoretical approach is developed which describes the growth kinetics of thin films of near noble metal silicide (especially of cobalt silicide (Co2Si) and nickel silicide (Ni2Si)) and refractory metal silicide (particularly of tungsten disilicide (WSi2) and vanadium disilicide (VSi2)) at the interfaces of metal-silicon system. In this approach, metal species are presented as A-atoms, silicon as B-atoms, and silicide as AB-compound. The AB-compound is formed as a result of chemical transformation between A- and B-atoms at the reaction interfaces A/AB and AB/B. The growth of AB-compound at the interfaces occurs in two stages. The first growth stage is reaction controlled stage which takes place at the interface with excess A or B-atoms and the second stage is diffusion limited stage which occurs at both interfaces. The critical thickness of AB-compound and the corresponding time is determined at the transition point between the two growth stages. The result that follows from this approach shows that the growth kinetics of any growing silicides depends on the number of kinds of dominant diffusing species in the silicide layer and also on their number densities at the reaction interface. This result shows a linear-parabolic growth kinetics for WSi2, VSi2, Co2Si, and Ni2Si and it is in good agreement with experiment.

  6. Isolation and growth kinetics of a novel phenol-degrading bacterium Microbacterium oxydans from the sediment of Taihu Lake (China).

    PubMed

    Wang, Linqiong; Li, Yi; Niu, Lihua; Dai, Yu; Wu, Yue; Wang, Qing

    2016-01-01

    Seven phylogenetically diverse phenol-degrading bacterial strains designated as P1 to P7 were isolated from the industry-effluent dump sites of an industrial area near Taihu Lake, China. Through the 16S rDNA sequence analysis, these strains were widely distributed among five different genera: Rhodococcus (P1), Pseudomonas (P2-P4), Acinetobacter (P5), Alcaligenes (P6), and Microbacterium (P7). All seven isolates were capable of growing with phenol as the sole carbon source. Strain P7 was found to be a novel phenol-degrading strain by detailed morphological, physiological and biochemical characteristic analysis as well as the 16S rDNA sequence analyses, and was named Microbacterium oxydans LY1 (M. oxydans LY1 in its short form). Degradation experiments of phenol at various initial concentrations (20-1,000 mg/L) revealed that phenol is an inhibitory substrate to M. oxydans LY1. In a batch culture experiment, more than 95% of the phenol (500 mg/L) was degraded by M. oxydans LY1 at 30°C, pH 7.0 and 120 rpm within 88 h. Phenol concentration higher than 200 mg/L was found to inhibit the bacterial growth. The growth kinetics correlated well with the Haldane model with μmax (maximum specific cell growth rate) = 0.243 h(-1), Ks (saturation constant) = 25.7 mg/L, and Ki (self-inhibition constant) = 156.3 mg/L. This is the first report of the ability of M. oxydans to degrade phenol, and the results could provide important information for bioremediation of phenol-contaminated environments. PMID:27120643

  7. Kinetics of Growth Retardant and Hormone Interactions in Affecting Cucumber Hypocotyl Elongation 1

    PubMed Central

    Moore, Thomas C.

    1967-01-01

    The capacities of indole-3-acetic acid (IAA) and gibberellin A3 (GA3) to counteract the inhibitory effects of (2-chloroethyl) trimethylammonium chloride (CCC), 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride (Amo-1618), and N,N-dimethylaminosuccinamic acid (B-995) on hypocotyl elongation in light-grown cucumber (Cucumis sativus L.) seedlings were investigated. One μg of GA3 applied to the shoot tip was sufficient to completely nullify the effect of 10 μg of Amo-1618 or 25 μg of B-995 applied simultaneously to the shoot tip, and 10 μg of GA3 completely counteracted the effect of 10−3 m CCC added to the root medium. One μg of IAA counteracted the effect of 10−3 m CCC in the root medium, but IAA did not nullify the action of either Amo-1618 or B-995. Experiments were conducted using 2 growth retardants simultaneously, which indicated that Amo-1618 and CCC inhibit a common process, namely GA biosynthesis, essential to hypocotyl elongation. However, since the effect of CCC was overcome by applications of both GA and IAA, growth retardation resulting from treatment with CCC apparently is not due solely to inhibition of GA biosynthesis. B-995 did not interact additively with either Amo-1618 or CCC, which suggests that B-995 affects a process different from those affected by the other 2 retardants. Thus, while inhibition evoked by B-995 is reversible by applied GA, the action of B-995 does not appear to be inhibition of GA biosynthesis. PMID:16656555

  8. Contrasting effects of basic fibroblast growth factor and neurotrophin 3 on cell cycle kinetics of mouse cortical stem cells

    PubMed Central

    Lukaszewicz, Agnès; Savatier, Pierre; Cortay, Véronique; Kennedy, Henry; Dehay, Colette

    2002-01-01

    Basic fibroblast growth factor (bFGF) exerts a mitogenic effect on cortical neuroblasts, whereas neurotrophin 3 (NT3) promotes differentiation in these cells. Here we provide evidence that both the mitogenic effect of bFGF and the differentiation-promoting effect of NT3 are linked with modifications of cell cycle kinetics in mouse cortical precursor cells. We adapted an in vitro assay, which makes it possible to evaluate (1) the speed of progression of the cortical precursors through the cell cycle, (2) the duration of individual phases of the cell cycle, (3) the proportion of proliferative versus differentiative divisions, and (4) the influence on neuroglial differentiation. Contrary to what has been claimed previously, bFGF promotes proliferation via a change in cell cycle kinetics by simultaneously decreasing G1 duration and increasing the proportion of proliferative divisions. In contrast, NT3 lengthens G1 and promotes differentiative divisions. We investigated the molecular foundations of these effects and show that bFGF downregulates p27kip1 and upregulates cyclin D2 expression. This contrasts with NT3, which upregulates p27kip1 and downregulates cyclin D2 expression. Neither bFGF nor NT3 influences the proportion of glia or neurons in short to medium term cultures. The data point to links between the length of the G1 phase and the type of division of cortical precursors: differentiative divisions are correlated with long G1 durations, whereas proliferative divisions correlate with short G1 durations. The present results suggest that concerted mechanisms control the progressive increase in the cell cycle duration and proportion of differentiative divisions that is observed as corticogenesis proceeds. PMID:12151540

  9. Epidemics, Exponential Functions, and Modeling

    ERIC Educational Resources Information Center

    Bush, Sarah B.; Gibbons, Katie; Karp, Karen S.; Dillon, Fred

    2015-01-01

    The phenomenon of outbreaks of dangerous diseases is both intriguing to students and of mathematical significance, which is exactly why the authors engaged eighth graders in an introductory activity on the growth that occurs as an epidemic spreads. Various contexts can set the stage for such an exploration. Reading adolescent literature like…

  10. Dynamics of Seeded Aβ40-Fibril Growth from Atomistic Molecular Dynamics Simulations: Kinetic Trapping and Reduced Water Mobility in the Locking Step.

    PubMed

    Schwierz, Nadine; Frost, Christina V; Geissler, Phillip L; Zacharias, Martin

    2016-01-20

    Filamentous β-amyloid aggregates are crucial for the pathology of Alzheimer's disease. Despite the tremendous biomedical importance, the molecular pathway of growth propagation is not completely understood and remains challenging to investigate by simulations due to the long time scales involved. Here, we apply extensive all-atom molecular dynamics simulations in explicit water to obtain free energy profiles and kinetic information from position-dependent diffusion profiles for three different Aβ9-40-growth processes: fibril elongation by single monomers at the structurally unequal filament tips and association of larger filament fragments. Our approach provides insight into the molecular steps of the kinetic pathway and allows close agreement with experimental binding free energies and macroscopic growth rates. Water plays a decisive role, and solvent entropy is identified as the main driving force for assembly. Fibril growth is disfavored energetically due to cancellation of direct peptide-peptide interactions and solvation effects. The kinetics of growth is consistent with the characteristic dock/lock mechanism, and docking is at least 2 orders of magnitude faster. During initial docking, interactions are mediated by transient non-native hydrogen bonds, which efficiently catch the incoming monomer or fragment already at separations of about 3 nm. In subsequent locking, the dynamics is much slower due to formation of kinetically trapped conformations caused by long-lived non-native hydrogen bonds. Fibril growth additionally requires collective motion of water molecules to create a dry binding interface. Fibril growth is further retarded due to reduced mobility of the involved hydration water, evident from a 2-fold reduction of the diffusion coefficient. PMID:26694883

  11. Kinetic and Stochastic Models of 1D yeast ``prions"

    NASA Astrophysics Data System (ADS)

    Kunes, Kay

    2005-03-01

    Mammalian prion proteins (PrP) are of public health interest because of mad cow and chronic wasting diseases. Yeasts have proteins, which can undergo similar reconformation and aggregation processes to PrP; yeast ``prions" are simpler to experimentally study and model. Recent in vitro studies of the SUP35 protein (1), showed long aggregates and pure exponential growth of the misfolded form. To explain this data, we have extended a previous model of aggregation kinetics along with our own stochastic approach (2). Both models assume reconformation only upon aggregation, and include aggregate fissioning and an initial nucleation barrier. We find for sufficiently small nucleation rates or seeding by small dimer concentrations that we can achieve the requisite exponential growth and long aggregates.

  12. Interpretation of orbital scale variability in mid-latitude speleothem δ18O: Significance of growth rate controlled kinetic fractionation effects

    NASA Astrophysics Data System (ADS)

    Stoll, Heather; Mendez-Vicente, Ana; Gonzalez-Lemos, Saul; Moreno, Ana; Cacho, Isabel; Cheng, Hai; Edwards, R. Lawrence

    2015-11-01

    Oxygen isotopes have been the most widely used climate indicator in stalagmites, applied to reconstruct past changes in rainfall δ18O and cave temperature. However, the δ18O signal in speleothems may also be influenced by variable kinetic fractionation effects, here conceived broadly as fractionation effects not arising from temperature variation. The regional reproducibility of speleothem δ18O signals has been proposed as a way to distinguish the δ18O variations arising directly from changes rainfall δ18O and cave temperature, from variations due to kinetic effects which may nonetheless be influenced by climate. Here, we compare isotopic records from 5 coeval stalagmites from two proximal caves in NW Spain covering the interval 140 to 70 ka, which experienced the same primary variations in temperature and rainfall δ18O, but exhibit a large range in growth rates and temporal trends in growth rate. Stalagmites growing at faster rates near 50 μm/yr have oxygen isotopic ratios over 1‰ more negative than coeval stalagmites with very slow (5 μm/yr) growth rates. Because growth rate variations also occur over time within any given stalagmite, the measured oxygen isotopic time series for a given stalagmite includes both climatic and kinetic components. Removal of the kinetic component of variation in each stalagmite, based on the dependence of the kinetic component on growth rate, is effective at distilling a common temporal evolution of among the oxygen isotopic records of the multiple stalagmites. However, this approach is limited by the quality of the age model. For time periods characterized by very slow growth and long durations between dates, the presence of crypto-hiatus may result in average growth rates which underestimate the instantaneous speleothem deposition rates and which therefore underestimate the magnitude of kinetic effects. The stacked growth rate-corrected speleothem δ18O is influenced by orbital scale variation in the cave temperature and

  13. Decarburization and grain growth kinetics during the annealing of electrical steels

    SciTech Connect

    Oldani, C.R.

    1996-12-01

    Electrical steels are generally described as thin steel sheets of variable thickness (from 0.27 to 0.76 mm), whose function is to efficiently transport the magnetic flux in electrical equipments. The electromagnetic properties expected from these materials are low magnetic losses and a high permeability. It can be said that a cyclically magnetized-demagnetized material is not free of energy losses because a portion of the power, the loss, is irreversibly transformed into heat. These steels are usually produced in a partially processed condition and they reach their maximum magnetic potential during the final steps of manufacture at the user`s plant. Efficient control of the operations by which the sheets are submitted is essential to obtain the optimum steel yield in the magnetic circuit they are made for. In these operations a decarburization annealing heat treatment produces important effects such as removing punching residual tensions, decarburization to very low carbon content, ferritic grain growth and a favorable magnetic crystallographic texture.

  14. Modeling Growth and Dissolution Kinetics of Grain-Boundary Cementite in Cyclic Carburizing

    NASA Astrophysics Data System (ADS)

    Ikehata, Hideaki; Tanaka, Kouji; Takamiya, Hiroyuki; Mizuno, Hiroyuki; Shimada, Takeyuki

    2013-08-01

    In vacuum carburizing of steels, short-time carburizing is usually followed by a diffusion period to eliminate the filmlike cementite ( θ GB ) grown on the austenite ( γ) grain boundary surface. In order to obtain the θ GB amount during the process, the conventional model estimates the amount of cementite ( θ) with the equilibrium fractions for local C contents within a framework of the finite difference method (FDM), which overestimates the amount of θ GB observed after several minutes of carburizing. In our newly developed model, a parabolic law is assumed for the growth of θ GB and the rate controlling process is considered to be Si diffusion rejected from θ under the isoactivity condition. In contrast, the rate constant for the dissolution of θ GB is considered to be controlled by Cr diffusion of θ. Both rate coefficients ( α) were validated using multicomponent diffusion simulation for the moving velocity of the γ/ θ interface. A one-dimensional (1-D) FDM program calculates an increment of θ GB for all grid points by the updated diffusivities and local equilibrium using coupled CALPHAD software. Predictions of the carbon (C) profile and volume fraction of cementite represent the experimental analysis much better than the existing models, especially for both short-time carburization and the cyclic procedure of carburization and diffusion processes.

  15. Kinetics of some immunological and biochemical changes of immunocompetent cells during tumor growth in rats.

    PubMed

    Koníková, E; Hrivnáková, A; Babusíková, O

    1986-01-01

    The dynamics of lymphocyte response in peripheral blood, the tumor draining lymph node, spleen and thymus, was followed in a model system of syngeneically transplanted rat MC-1 tumor. Electrophoretic mobility (EPM) of lymphoid cells was determined by the automatic mode of measurement. The results revealed a two-phase pattern of EPM changes during the course of cancer growth. The first phase (day 3 to 6 following intramuscular injection of tumor cells) was characterized by a prevalence of high-mobility cells, while in the second phase (day 14 to 20), depletion of high-mobility cells was compensated for by an increased number of low-mobility cells. The mean EPM value was found to be increased only in the thymus at that time. Changes in the adenosine deaminase activity proved to be most expressive in the tumor draining lymph node and in the second phase also in splenic and thymic lymphocytes. An increased percentage of active lymphocytes with compact nucleoli with nucleolonemas became evident already on the 3rd day in all the lymphoid organs followed. The response was two-phasic only in the lymphocyte population of the peripheral blood, while their percentage in the other organs remained higher even on day 20. Changes in the proportion of high- and low-mobility cells in the lymphoid organs followed here, in correlation with the adenosine deaminase activity and the percentage of active lymphocytes, were interpreted as a response of immunocompetent cells in animals with a growing tumor. PMID:3785465

  16. Quantification of cell lysis during CHO bioprocesses: Impact on cell count, growth kinetics and productivity.

    PubMed

    Klein, Tobias; Heinzel, Nicole; Kroll, Paul; Brunner, Matthias; Herwig, Christoph; Neutsch, Lukas

    2015-08-10

    High cell densities and high viability are critical quality attributes for mammalian bioprocesses. Determination of living and dead cell numbers is nowadays routinely performed by automated image-based cell analyzers or flow cytometry. However, complete lysis of cells is usually neglected by these devices. We present a novel method for robust quantification of lysed cell populations over the course of a CHO bioprocess. The release of lactate dehydrogenase (LDH) and double stranded genomic DNA in culture supernatants were used as markers for cell lysis. We considered the degradation of both markers over cultivation time, which significantly increased the amount of released LDH and DNA. For correct and robust estimation of lysed cell fractions, degradation of both markers over cultivation time was considered, where redundancy of markers allowed data reconciliation. Calculating the number of cells which were subject to complete cell lysis, we could show that this fraction makes up as much as 30% of the total produced biomass and is not described by measurements of image-based analyzers. Finally, we demonstrate that disregarding cell lysis heavily affects the calculation of biomass yields and growth rates and that increasing levels of cell lysis are related to decreased productivity. PMID:25956245

  17. Cloud condensation nuclei activity, droplet growth kinetics, and hygroscopicity of biogenic and anthropogenic secondary organic aerosol (SOA)

    NASA Astrophysics Data System (ADS)

    Zhao, D. F.; Buchholz, A.; Kortner, B.; Schlag, P.; Rubach, F.; Fuchs, H.; Kiendler-Scharr, A.; Tillmann, R.; Wahner, A.; Watne, Å. K.; Hallquist, M.; Flores, J. M.; Rudich, Y.; Kristensen, K.; Hansen, A. M. K.; Glasius, M.; Kourtchev, I.; Kalberer, M.; Mentel, Th. F.

    2016-02-01

    Interaction of biogenic volatile organic compounds (VOCs) with Anthropogenic VOC (AVOC) affects the physicochemical properties of secondary organic aerosol (SOA). We investigated cloud droplet activation (CCN activity), droplet growth kinetics, and hygroscopicity of mixed anthropogenic and biogenic SOA (ABSOA) compared to pure biogenic SOA (BSOA) and pure anthropogenic SOA (ASOA). Selected monoterpenes and aromatics were used as representative precursors of BSOA and ASOA, respectively.

    We found that BSOA, ASOA, and ABSOA had similar CCN activity despite the higher oxygen to carbon ratio (O/C) of ASOA compared to BSOA and ABSOA. For individual reaction systems, CCN activity increased with the degree of oxidation. Yet, when considering all different types of SOA together, the hygroscopicity parameter, κCCN, did not correlate with O/C. Droplet growth kinetics of BSOA, ASOA, and ABSOA were comparable to that of (NH4)2SO4, which indicates that there was no delay in the water uptake for these SOA in supersaturated conditions.

    In contrast to CCN activity, the hygroscopicity parameter from a hygroscopic tandem differential mobility analyzer (HTDMA) measurement, κHTDMA, of ASOA was distinctively higher (0.09-0.10) than that of BSOA (0.03-0.06), which was attributed to the higher degree of oxidation of ASOA. The ASOA components in mixed ABSOA enhanced aerosol hygroscopicity. Changing the ASOA fraction by adding biogenic VOC (BVOC) to ASOA or vice versa (AVOC to BSOA) changed the hygroscopicity of aerosol, in line with the change in the degree of oxidation of aerosol. However, the hygroscopicity of ABSOA cannot be described by a simple linear combination of pure BSOA and ASOA systems. This indicates that additional processes, possibly oligomerization, affected the hygroscopicity.

    Closure analysis of CCN and HTDMA data showed κHTDMA was lower than κCCN by 30-70 %. Better closure was achieved for ASOA compared to BSOA. This

  18. Stretched Exponential relaxation in pure Se glass

    NASA Astrophysics Data System (ADS)

    Dash, S.; Ravindren, S.; Boolchand, P.

    A universal feature of glasses is the stretched exponential relaxation, f (t) = exp[ - t / τ ] β . The model of diffusion of excitations to randomly distributed traps in a glass by Phillips1 yields the stretched exponent β = d[d +2] where d, the effective dimensionality. We have measured the enthalpy of relaxation ΔHnr (tw) at Tg of Se glass in modulated DSC experiments as glasses age at 300K and find β = 0.43(2) for tw in the 0 growth of interchain structural correlations mediated by both long range (van der Waals forces) and short-range (covalent) interactions. A striking consequence of this relaxation is a narrowing of the glass transition width from 7.1°C to 1.4°C, and the ΔHnr term increasing from 0.21 cal/gm to 0.92 cal/gm. In bulk GexSe100-x glasses as x increases to 20%, the length of the polymeric Sen chains between the Ge-crosslinks decreases to n = 2. and the striking relaxation effects nearly vanish. J.C. Phillips, Rep.Prog.Phys. 59 , 1133 (1996). Supported by NSF Grant DMR 08-53957.

  19. Molecular weight and concentration of heparin in hyaluronic acid-based matrices modulates growth factor retention kinetics and stem cell fate.

    PubMed

    Jha, Amit K; Mathur, Anurag; Svedlund, Felicia L; Ye, Jianqin; Yeghiazarians, Yerem; Healy, Kevin E

    2015-07-10

    Growth factors are critical for regulating and inducing various stem cell functions. To study the effects of growth factor delivery kinetics and presentation on stem cell fate, we developed a series of heparin-containing hyaluronic acid (HyA)-based hydrogels with various degrees of growth factor affinity and retention. To characterize this system, we investigated the effect of heparin molecular weight, fractionation, and relative concentration on the loading efficiency and retention kinetics of TGFβ1 as a model growth factor. At equal concentrations, high MW heparin both loaded and retained the greatest amount of TGFβ1, and had the slowest release kinetics, primarily due to the higher affinity with TGFβ1 compared to low MW or unfractionated heparin. Subsequently, we tested the effect of TGFβ1, presented from various heparin-containing matrices, to differentiate a versatile population of Sca-1(+)/CD45(-) cardiac progenitor cells (CPCs) into endothelial cells and form vascular-like networks in vitro. High MW heparin HyA hydrogels stimulated more robust differentiation of CPCs into endothelial cells, which formed vascular-like networks within the hydrogel. This observation was attributed to the ability of high MW heparin HyA hydrogels to sequester endogenously synthesized angiogenic factors within the matrix. These results demonstrate the importance of molecular weight, fractionation, and concentration of heparin on presentation of heparin-binding growth factors and their effect on stem cell differentiation and lineage specification. PMID:25931306

  20. Characterization of exposure dependent fatigue crack growth kinetics and damage mechanisms for aluminum alloys

    NASA Astrophysics Data System (ADS)

    Ro, Yunjo

    The effect of environmental exposure [given by the ratio of water vapor pressure to the loading frequency (PH2O/f)] on fatigue crack growth rates (FCGR) and damage mechanisms has been investigated for Al-Cu-Li/Mg alloys tested at constant stress intensity range (DeltaK = KMAX - KMIN). Different exposure dependences of the FCGR are explained by H-embrittlement and 3 rate-limiting processes that are similar for each alloy and aging condition. It is shown that the dislocation slip character (heterogeneous planar vs. wavy) controls FCGR at low to moderate exposures, rather than alloy composition and strengthening precipitate reactivity. However, the benefit of planar slip is significantly reduced at higher exposures. An SEM-based electron backscattered diffraction (EBSD)/stereology method was used to successfully quantify changes in fatigue fracture surface crystallography as a function of exposure for a peak aged Al-Cu-Li alloy and an under-aged Al-Cu-Mg alloy. Near-{111} slip band cracking (SBC) observed under high vacuum conditions is gradually replaced by near-{001}/{011} and high index, {hkl}, cracking planes as PH2O/f is increased. The complete absence of near-{111} SBC at higher exposures suggests H enhanced decohesion rather than slip based damage process enhanced by H. This conclusion was substantiated by direct TEM observation. Focused Ion Beam (FIB) milling was used to produce thin foils for TEM, which successfully revealed the underlying dislocation structure at the crack surface and within surrounding materials in under-aged Al-Cu-Mg tested at exposure conditions of ˜10 -8 and 50 Pa·sec. Both conditions exhibit a similar layer of dislocation cells just below the fracture surface which abruptly changes to localized slip bands away from the fracture surface, confirming the presence of a strain gradient at the crack tip. However, the thickness of the substructure layer and slip band width observed at ˜10-8 Pa·sec was larger than those observed at 50 Pa

  1. Kinetics of fluid demixing in complex plasmas: Domain growth analysis using Minkowski tensors.

    PubMed

    Böbel, A; Räth, C

    2016-07-01

    A molecular dynamics simulation of the demixing process of a binary complex plasma is analyzed and the role of distinct interaction potentials is discussed by using morphological Minkowski tensor analysis of the minority phase domain growth in a demixing simulated binary complex plasma. These Minkowski tensor methods are compared with previous results that utilized a power spectrum method based on the time-dependent average structure factor. It is shown that the Minkowski tensor methods are superior to the previously used power-spectrum method in the sense of higher sensitivity to changes in domain size. By analysis of the slope of the temporal evolution of Minkowski tensor measures, qualitative differences between the case of particle interaction with a single length scale compared to particle interactions with two different length scales (dominating long-range interaction) are revealed. After proper scaling the graphs for the two length scale scenarios coincide, pointing toward universal behavior. The qualitative difference in demixing scenarios is evidenced by distinct demixing behavior: in the long-range dominated cases demixing occurs in two stages. At first, neighboring particles agglomerate, then domains start to merge in cascades. However, in the case of only one interaction length scale only agglomeration but no merging of domains can be observed. Thus, Minkowski tensor analysis is likely to become a useful tool for further investigation of this (and other) demixing processes. It is capable to reveal (nonlinear) local topological properties, probing deeper than (linear) global power-spectrum analysis, however, still providing easily interpretable results founded on a solid mathematical framework. PMID:27575224

  2. Film growth, adsorption and desorption kinetics of indigo on SiO2

    NASA Astrophysics Data System (ADS)

    Scherwitzl, Boris; Resel, Roland; Winkler, Adolf

    2014-05-01

    Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer desorption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption.

  3. Film growth, adsorption and desorption kinetics of indigo on SiO{sub 2}

    SciTech Connect

    Scherwitzl, Boris Resel, Roland; Winkler, Adolf

    2014-05-14

    Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer desorption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption.

  4. Kinetics of fluid demixing in complex plasmas: Domain growth analysis using Minkowski tensors

    NASA Astrophysics Data System (ADS)

    Böbel, A.; Räth, C.

    2016-07-01

    A molecular dynamics simulation of the demixing process of a binary complex plasma is analyzed and the role of distinct interaction potentials is discussed by using morphological Minkowski tensor analysis of the minority phase domain growth in a demixing simulated binary complex plasma. These Minkowski tensor methods are compared with previous results that utilized a power spectrum method based on the time-dependent average structure factor. It is shown that the Minkowski tensor methods are superior to the previously used power-spectrum method in the sense of higher sensitivity to changes in domain size. By analysis of the slope of the temporal evolution of Minkowski tensor measures, qualitative differences between the case of particle interaction with a single length scale compared to particle interactions with two different length scales (dominating long-range interaction) are revealed. After proper scaling the graphs for the two length scale scenarios coincide, pointing toward universal behavior. The qualitative difference in demixing scenarios is evidenced by distinct demixing behavior: in the long-range dominated cases demixing occurs in two stages. At first, neighboring particles agglomerate, then domains start to merge in cascades. However, in the case of only one interaction length scale only agglomeration but no merging of domains can be observed. Thus, Minkowski tensor analysis is likely to become a useful tool for further investigation of this (and other) demixing processes. It is capable to reveal (nonlinear) local topological properties, probing deeper than (linear) global power-spectrum analysis, however, still providing easily interpretable results founded on a solid mathematical framework.

  5. Is Anatomic Complexity Associated with Renal Tumor Growth Kinetics Under Active Surveillance?

    PubMed Central

    Mehrazin, Reza; Smaldone, Marc C.; Egleston, Brian; Tomaszewski, Jeffrey J.; Concodora, Charles W.; Ito, Timothy K.; Abbosh, Philip H.; Chen, David Y.T.; Kutikov, Alexander; Uzzo, Robert G.

    2015-01-01

    Introduction Linear growth rate (LGR) is the most commonly employed trigger for definitive intervention in patients with renal masses managed with an initial period of active surveillance (AS). Using our institutional cohort, we explored the association between tumor anatomic complexity at presentation and LGR in patients managed with AS. Methods and Materials Enhancing renal masses managed expectantly for at least 6 months were included for analysis. The association between NS and LGR was assessed using generalized estimating equations, adjusting for age, Charlson score, race, sex, and initial tumor size. Results 346 patients (401 masses) met inclusion criteria (18% ≥cT1b), with a median follow-up of 37 months (range: 6-169). 44% of patients progressed to definitive intervention with a median duration of 27 months (range: 6-130). Comparing patients managed expectantly to those requiring intervention, no difference was seen in median tumor size at presentation (2.2 vs. 2.2 cm), while significant differences in median age (74 vs. 65 years, p<0.001), Charlson co-morbidity score (3 vs. 2, p<0.001), and average LGR (0.23 vs. 0.49 cm/year, p<0.001) were observed between groups. Following adjustment, for each 1-point increase in NS sum, the average tumor LGR increased by 0.037 cm/year (p=0.002). Of the entire cohort, 6 patients (1.7%) progressed to metastatic disease. Conclusions The demonstrated association between anatomic tumor complexity at presentation and LGR of clinical stage 1 renal masses under AS may afford a clinically useful cue to tailor individual patient radiographic surveillance schedules and warrants further evaluation. PMID:25778696

  6. Film growth, adsorption and desorption kinetics of indigo on SiO2

    PubMed Central

    Scherwitzl, Boris; Resel, Roland; Winkler, Adolf

    2015-01-01

    Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer des orption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption. PMID:24832297

  7. The matrix exponential in transient structural analysis

    NASA Technical Reports Server (NTRS)

    Minnetyan, Levon

    1987-01-01

    The primary usefulness of the presented theory is in the ability to represent the effects of high frequency linear response with accuracy, without requiring very small time steps in the analysis of dynamic response. The matrix exponential contains a series approximation to the dynamic model. However, unlike the usual analysis procedure which truncates the high frequency response, the approximation in the exponential matrix solution is in the time domain. By truncating the series solution to the matrix exponential short, the solution is made inaccurate after a certain time. Yet, up to that time the solution is extremely accurate, including all high frequency effects. By taking finite time increments, the exponential matrix solution can compute the response very accurately. Use of the exponential matrix in structural dynamics is demonstrated by simulating the free vibration response of multi degree of freedom models of cantilever beams.

  8. Irreversible kinetics on a one-dimensional lattice: Comparison of exact result with a point-process nucleation-growth-collision model

    NASA Astrophysics Data System (ADS)

    Fletcher, S.

    1983-02-01

    In this paper we discuss irreversible kinetics on a one-dimensional lattice. We compare the expectation value of the coverage of the lattice, as a function of time, with that predicted by a point-process nucleation-growth-collision model. We conclude that the nucleation-growth-collision model is only applicable to lattice kinetics when the spreading rate of clusters is much greater than their nucleation rate. Although the kinetics of coverage of a one-dimensional lattice are known exactly, the complete solution turns out to be rather complex. In order to facilitate comparison with the point-process nucleation and growth model, we calculate an approximation to the lattice kinetics which is valid when the collision rate of clusters is very fast. The result is complementary to an earlier approximation of McQuarrie, McTague and Reiss, which described the case when the collision rate of clusters was comparable with the spreading rate. We also consider an integral geometrical approach to discreteness effects in lattice models. The general approach which we suggest is to calculate coefficients of variation of the numbers of lattice sites covered by various geometric shapes as a measure of "discreteness". This method uses some mathematical results of Kendall et al.

  9. Comparison of the growth kinetics of In2O3 and Ga2O3 and their suboxide desorption during plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Vogt, Patrick; Bierwagen, Oliver

    2016-08-01

    We present a comprehensive study of the In2O3 growth kinetics during plasma-assisted molecular beam epitaxy and compare it to that of the related oxide Ga2O3 [P. Vogt and O. Bierwagen, Appl. Phys. Lett. 108, 072101 (2016)]. The growth rate and desorbing fluxes were measured during growth in-situ by a laser reflectometry set-up and line-of-sight quadrupole mass spectrometer, respectively. We extracted the In incorporation as a function of the provided In flux, different growth temperatures TG, and In-to-O flux ratios r. The data are discussed in terms of the competing formation of In2O3 and desorption of the suboxide In2O and O. The same three growth regimes as in the case of Ga2O3 can be distinguished: (i) In-transport limited, O-rich (ii) In2O-desorption limited, O-rich, and (iii) O-transport limited, In-rich. In regime (iii), In droplets are formed on the growth surface at low TG. The growth kinetics follows qualitatively that of Ga2O3 in agreement with their common oxide and suboxide stoichiometry. The quantitative differences are mainly rationalized by the difference in In2O and Ga2O desorption rates and vapor pressures. For the In2O, Ga2O, and O desorption, we extracted the activation energies and frequency factors by means of Arrhenius-plots.

  10. Macrotransport-solidification kinetics modeling of equiaxed dendritic growth: Part II. Computation problems and validation on INCONEL 718 superalloy castings

    NASA Astrophysics Data System (ADS)

    Nastac, L.; Stefanescu, D. M.

    1996-12-01

    In Part I of the article, a new analytical model that describes solidification of equiaxed dendrites was presented. In this part of the article, the model is used to simulate the solidification of INCONEL 718 superalloy castings. The model was incorporated into a commercial finite-element code, PROCAST. A special procedure called microlatent heat method (MLHM) was used for coupling between macroscopic heat flow and microscopic growth kinetics. A criterion for time-stepping selection in microscopic modeling has been derived in conjunction with MLHM. Reductions in computational (CPU) time up to 90 pct over the classic latent heat method were found by adopting this coupling. Validation of the model was performed against experimental data for an INCONEL 718 superalloy casting. In the present calculations, the model for globulitic dendrite was used. The evolution of fraction of solid calculated with the present model was compared with Scheil’s model and experiments. An important feature in solidification of INCONEL 718 is the detrimental Laves phase. Laves phase content is directly related to the intensity of microsegregation of niobium, which is very sensitive to the evolution of the fraction of solid. It was found that there is a critical cooling rate at which the amount of Laves phase is maximum. The critical cooling rate is not a function of material parameters (diffusivity, partition coefficient, etc.). It depends only on the grain size and solidification time. The predictions generated with the present model are shown to agree very well with experiments.

  11. Macrotransport-solidification kinetics modeling of equiaxed dendritic growth. Part 2: Computation problems and validation on INCONEL 718 superalloy castings

    SciTech Connect

    Nastac, L.; Stefanescu, D.M.

    1996-12-01

    In Part 1 of the article, a new analytical model that describes solidification of equiaxed dendrites was presented. In this part of the article, the model is used to simulate the solidification of INCONEL 718 superalloy castings. The model was incorporated into a commercial finite-element code, PROCAST. A special procedure called microlatent heat method (MLHM) was used for coupling between macroscopic heat flow and microscopic growth kinetics. A criterion for time-stepping selection in microscopic modeling has been derived in conjunction with MLHM. Reductions in computational (CPU) time up to 90 pct over the classic latent heat method were found by adopting this coupling. Validation of the model was performed against experimental data for an INCONEL 718 superalloy casting. In the present calculations, the model for globulitic dendrite was used. The evolution of fraction of solid calculated with the present model was compared with Scheil`s model and experiments. An important feature in solidification of INCONEL 718 is the detrimental Laves phase. Laves phase content is directly related to the intensity of microsegregation of niobium, which is very sensitive to the evolution of the fraction of solid. It was found that thee is a critical cooling rate at which the amount of Laves phase is maximum. The critical cooling rate is not a function of material parameters (diffusivity, partition coefficient, etc.). It depends only on the grain size and solidification time. The predictions generated with the present model are shown to agree very well with experiments.

  12. Modeling of helium bubble nucleation and growth in austenitic stainless steels using an Object Kinetic Monte Carlo method

    NASA Astrophysics Data System (ADS)

    De Backer, A.; Adjanor, G.; Domain, C.; Lescoat, M. L.; Jublot-Leclerc, S.; Fortuna, F.; Gentils, A.; Ortiz, C. J.; Souidi, A.; Becquart, C. S.

    2015-06-01

    Implantation of 10 keV helium in 316L steel thin foils was performed in JANNuS-Orsay facility and modeled using a multiscale approach. Density Functional Theory (DFT) atomistic calculations [1] were used to obtain the properties of He and He-vacancy clusters, and the Binary Collision Approximation based code MARLOWE was applied to determine the damage and He-ion depth profiles as in [2,3]. The processes involved in the homogeneous He bubble nucleation and growth were defined and implemented in the Object Kinetic Monte Carlo code LAKIMOCA [4]. In particular as the He to dpa ratio was high, self-trapping of He clusters and the trap mutation of He-vacancy clusters had to be taken into account. With this multiscale approach, the formation of bubbles was modeled up to nanometer-scale size, where bubbles can be observed by Transmission Electron Microscopy. Their densities and sizes were studied as functions of fluence (up to 5 × 1019 He/m2) at two temperatures (473 and 723 K) and for different sample thicknesses (25-250 nm). It appears that the damage is not only due to the collision cascades but is also strongly controlled by the He accumulation in pressurized bubbles. Comparison with experimental data is discussed and sensible agreement is achieved.

  13. Growth kinetics of MPS-capped CdS quantum dots in self-assembled thin films

    PubMed Central

    2012-01-01

    For this study, we prepared colloidal CdS quantum dots using 3-mercaptopropyltrimethoxysilane as capping agent. Colloidal CdS quantum dots were directly deposited on glass substrates by a spin-coating process. Coated substrates were heat-treated between 225°C and 325°C for various heat treatment time intervals to investigate the growth kinetics of the quantum dots. Results showed that sizes of the CdS quantum dots grew approximately from 2.9 to 4.6 nm, and the E1s1s energy values shifted approximately from 3.3 to 2.7 eV. Results showed that the average size of quantum dots increase by thermal treatment due to Ostwald ripening. The thermal process used to grow the size of quantum dots was examined according to the Lifshitz-Slyozov-Wagner theory. The activation energy of CdS quantum dots in thin films was calculated at approximately 44 kJ/mol. PMID:23127193

  14. Growth from Solutions: Kink dynamics, Stoichiometry, Face Kinetics and stability in turbulent flow

    NASA Technical Reports Server (NTRS)

    Chernov, A. A.; DeYoreo, J. J.; Rashkovich, L. N.; Vekilov, P. G.

    2005-01-01

    1. Kink dynamics. The first segment of a polygomized dislocation spiral step measured by AFM demonstrates up to 60% scattering in the critical length l*- the length when the segment starts to propagate. On orthorhombic lysozyme, this length is shorter than that the observed interkink distance. Step energy from the critical segment length based on the Gibbs-Thomson law (GTL), l* = 20(omega)alpha/(Delta)mu is several times larger than the energy from 2D nucleation rate. Here o is tine building block specific voiume, a is the step riser specific free energy, Delta(mu) is the crystallization driving force. These new data support our earlier assumption that the classical Frenkel, Burton -Cabrera-Frank concept of the abundant kink supply by fluctuations is not applicable for strongly polygonized steps. Step rate measurements on brushite confirms that statement. This is the1D nucleation of kinks that control step propagation. The GTL is valid only if l* growth velocity vk. This is equivalent to supersaturations sigma less than approx. alpha/2l*, where alpha is the building block size. For lysozyme, sigma much less than (1%). Conventionally used interstep distance generated by screw dislocation, 19(omega)alpha/Delta(mu) should be replaced by the very different real one, approx.4l*. 2. Stoichiometry. Kink, and thus step and face rates of a non-Kossel complex molecular monocomponent or any binary, AB, lattice was found theoretically to be proportional to 1/(zeta(sup 1/2) + zeta(sup - 1/2)), where zeta = [B]/[A] is the stoichiometry ratio in solution. The velocities reach maxima at zeta = 1. AFM studies of step rates on CaOxalate monohydrate (kidney stones) from aqueous solution was found to obey the law mentioned above. Generalization for more complex lattice will be discussed. 3. Turbulence. In agreement with theory, high precision in-situ laser interferometry of the (101) KDP crystal face shows step

  15. Root-zone acidity and nitrogen source affects Typha latifolia L. growth and uptake kinetics of ammonium and nitrate.

    PubMed

    Brix, Hans; Dyhr-Jensen, Kirsten; Lorenzen, Bent

    2002-12-01

    The NH(4)(+) and NO(3)(-) uptake kinetics by Typha latifolia L. were studied after prolonged hydroponics growth at constant pH 3.5, 5.0, 6.5 or 7.0 and with NH(4)(+) or NO(3)(-) as the sole N-source. In addition, the effects of pH and N source on H(+) extrusion and adenine nucleotide content were examined. Typha latifolia was able to grow with both N sources at near neutral pH levels, but the plants had higher relative growth rates, higher tissue concentrations of the major nutrients, higher contents of adenine nucleotides, and higher affinity for uptake of inorganic nitrogen when grown on NH(4)(+). Growth almost completely stopped at pH 3.5, irrespective of N source, probably as a consequence of pH effects on plasma membrane integrity and H(+) influx into the root cells. Tissue concentrations of the major nutrients and adenine nucleotides were severely reduced at low pH, and the uptake capacity for inorganic nitrogen was low, and more so for NO(3)(-)-fed than for NH(4)(+)-fed plants. The maximum uptake rate, V(max), was highest for NH(4)(+) at pH 6.5 (30.9 micro mol h(-1) g(-1) root dry weight) and for NO(3)(-) at pH 5.0 (31.7 micro mol h(-1) g(-1) root dry weight), and less than 10% of these values at pH 3.5. The affinity for uptake as estimated by the half saturation constant, K((1/2)), was lowest at low pH for NH(4)(+) and at high pH for NO(3)(-). The changes in V(max) and K((1/2)) were thus consistent with the theory of increasing competition between cations and H(+) at low pH and between anions and OH(-) at high pH. C(min) was independent of pH, but slightly higher for NO(3)(-) than for NH(4)(+) (C(min)(NH(4)(+)) approximately 0.8 mmol m(-3); C(min)(NO(3)(-)) approximately 2.8 mmol m(-3)). The growth inhibition at low pH was probably due to a reduced nutrient uptake and a consequential limitation of growth by nutrient stress. Typha latifolia seems to be well adapted to growth in wetland soils where NH(4)(+) is the prevailing nitrogen compound, but very low p

  16. Kinetics of photoacclimation in corals.

    PubMed

    Anthony, Kenneth R N; Hoegh-Guldberg, Ove

    2003-01-01

    Traditional models describing the relationship between photosynthesis (P) and irradiance (I) do not account for photoacclimation to short-term variation in irradiance. Here we develop and test a model that predicts the rate of photosynthesis under fluctuating irradiances at the scale of days to weeks. Using oxygen respirometry, we measured the rates of change in the P-I model parameters P(max) (maximum rate of gross photosynthesis) and I(k) (sub-saturation irradiance) of the photo-symbiotic coral Turbinaria mesenterina (Lamarck) following large and small increases and decreases in growth irradiance. We analyse the behaviour of the dynamic P-I model in turbid-water conditions using a dataset of 3-month continuous irradiance as the input variable. In response to upward or downward changes in experimental growth irradiance, I(k) values decreased or increased exponentially, reaching new and stable levels within 5-10 days. I(k) responded 4 times stronger than P(max) to changes in growth irradiance. The kinetics of I(k) did not show hysteresis, and changed in similar ways when irradiance was increased or decreased in small or large amounts. This suggests that mechanisms associated with photo-protection during increases in irradiance, and the maximisation of photosynthetic efficiency during decreases in irradiance, are equally potent. On the scale of months, the dynamic P-I model did not predict higher rates of photosynthesis than the static P-I model, but buffered the variation in photosynthesis during periods of reduced irradiance. Fourier analysis indicated that the kinetics of I(k) closely matches the main periodicities in daily irradiance (1-2 weeks). The recorded kinetics of photoacclimation in the Turbinaria-zooxanthella symbiosis is comparable to that of free-living phytoplankton and faster than that of higher plants. PMID:12647175

  17. Kinetic characteristics and modeling of microalgae Chlorella vulgaris growth and CO2 biofixation considering the coupled effects of light intensity and dissolved inorganic carbon.

    PubMed

    Chang, Hai-Xing; Huang, Yun; Fu, Qian; Liao, Qiang; Zhu, Xun

    2016-04-01

    Understanding and optimizing the microalgae growth process is an essential prerequisite for effective CO2 capture using microalgae in photobioreactors. In this study, the kinetic characteristics of microalgae Chlorella vulgaris growth in response to light intensity and dissolved inorganic carbon (DIC) concentration were investigated. The greatest values of maximum biomass concentration (Xmax) and maximum specific growth rate (μmax) were obtained as 2.303 g L(-1) and 0.078 h(-1), respectively, at a light intensity of 120 μmol m(-2) s(-1) and DIC concentration of 17 mM. Based on the results, mathematical models describing the coupled effects of light intensity and DIC concentration on microalgae growth and CO2 biofixation are proposed. The models are able to predict the temporal evolution of C. vulgaris growth and CO2 biofixation rates from lag to stationary phases. Verification experiments confirmed that the model predictions agreed well with the experimental results. PMID:26866758

  18. Exponential fitting quadrature rule for functional equations

    NASA Astrophysics Data System (ADS)

    Cardone, A.; Paternoster, B.; Santomauro, G.

    2012-09-01

    A Gaussian quadrature rule for periodic integrand function is presented. The weights and nodes depend on the frequency of the problem and they are constructed by following the exponential fitting theory. The composite rule based on this formula is derived. The analysis of the error is carried out and it proves that the exponentially fitted Gaussian rule is more accurate than the classical Gauss-Legendre rule when oscillatory functions are treated. Some numerical tests are presented.

  19. In situ high-temperature scanning tunneling microscopy studies of early stage growth kinetics during titanium nitride epitaxy

    NASA Astrophysics Data System (ADS)

    Kodambaka, Suneel Kumar

    NaCl-structure TiN is widely used as a hard wear-resistant coating on cutting tools, as a diffusion-barrier layer in microelectronic devices, as a corrosion-resistant coating on mechanical components, and as an abrasion-resistant layer on optics and architectural glass. Even though its diffusion barrier and elastic properties are known to be anisotropic, and hence depend upon grain orientation, little is known regarding the mechanisms and reaction paths leading to the development of preferred orientation in polycrystalline TiN layers deposited by reactive evaporation and sputter deposition. Efforts to model polycrystalline growth as a function of deposition conditions is a complex problem. As a minimum set, one requires adatom transport parameters---activation barriers for surface diffusion step edge attachment/detachment, the adatom formation energy, the step edge Ehrlich barrier, and the step formation energy---all as a function of orientation. Unfortunately, very little data, either experimental or theoretical, is available concerning these parameters for TiN. During the course of my research, I have developed methods to grow atomically-smooth TiN(001) and (111) single-crystal layers with simple well-defined single-atom-high 2D island configurations on large atomically-smooth terraces. I used in situ scanning tunneling microscopy to study time- and temperature-dependent 2D island coarsening/decay kinetics, obtain 2D equilibrium island shapes, and follow temporal fluctuations of island shapes on both TiN(001) and (111) surfaces. I have developed a combination of experimental and theoretical techniques to analyze the surface dynamics measurements and determined adatom surface transport parameters, step energies, step stiffnesses, and kink formation energies on TiN(001) and TiN(111) surfaces.

  20. Si(001):B gas-source molecular-beam epitaxy: Boron surface segregation and its effect on film growth kinetics

    NASA Astrophysics Data System (ADS)

    Kim, H.; Glass, G.; Spila, T.; Taylor, N.; Park, S. Y.; Abelson, J. R.; Greene, J. E.

    1997-09-01

    B-doped Si(001) films, with concentrations CB up to 1.7×1022cm-3, were grown by gas-source molecular-beam epitaxy from Si2H6 and B2H6 at Ts=500-800 °C. D2 temperature-programed desorption (TPD) spectra were then used to determine B coverages θB as a function of CB and Ts. In these measurements, as-deposited films were flash heated to desorb surface hydrogen, cooled, and exposed to atomic deuterium until saturation coverage. Strong B surface segregation was observed with surface-to-bulk B concentration ratios ranging up to 1200. TPD spectra exhibited β2 and β1 peaks associated with dideuteride and monodeuteride desorption as well as lower-temperature B-induced peaks β2* and β1*. Increasing θB increased the area under β2* and β1* at the expense of β2 and β1 and decreased the total D coverage θD. The TPD results were used to determine the B segregation enthalpy, -0.53 eV, and to explain and model the effects of high B coverages on Si(001) growth kinetics. Film deposition rates R increase by ⩾50% with increasing CB>˜1×1019 cm-3 at Ts⩽550 °C, due primarily to increased H desorption rates from B-backbonded Si adatoms, and decrease by corresponding amounts at Ts⩾600 °C due to decreased adsorption site densities. At Ts⩾700 °C, high B coverages also induce {113} facetting.

  1. Kinetics of aggregation and growth processes of PEG-stabilised mono- and multivalent gold nanoparticles in highly concentrated halide solutions.

    PubMed

    Stein, Benjamin; Zopes, David; Schmudde, Madlen; Schneider, Ralf; Mohsen, Ahmed; Goroncy, Christian; Mathur, Sanjay; Graf, Christina

    2015-01-01

    5-6 nm gold nanoparticles were prepared by hydrolytic decomposition of [NMe4][Au(CF3)2] and functionalized in situ with mono- and multivalent thiolated PEG ligands. Time-dependent changes of the nanoparticles were monitored in aqueous NaCl, NaBr, and NaI solutions by UV-Vis spectroscopy, TEM, and HRTEM. The purely sterically protected particles are stable in ≤1 M NaCl and NaBr solutions, regardless of the valence of the ligands. At higher concentrations (≥2 M), the monovalent stabilized particles show minor reaction limited colloidal aggregation. In NaBr but not in NaCl solutions a minor Ostwald ripening also occurs. The divalent stabilized particles remain colloidally stable in both halide solutions, even if the temperature is raised or the concentration is increased above 2 M. In ≤1 M aqueous NaI solutions the particles remain stable. Above, the monovalent stabilized particles undergo an oxidative reaction, resulting in a time-dependent shift and broadening of the absorbance spectrum. Finally, this process slows down while the width of the spectra slightly narrows. The kinetics of this process can be described by a two-step sigmoidal process, comprising a slow induction period where active species are formed, followed by a fast growth and aggregation process. The increasing concentration of fused structures from the aggregates during this process results in a narrowing of the size distributions. The divalent stabilized particles show only some minor broadening and a slight shift of the absorbance spectra in ≤3 M NaI solutions. These observations confirm the excellent stability of the multivalent stabilized particles from this chloride-free particle synthesis. PMID:25972038

  2. Kinetic model of Chlorella vulgaris growth with and without extremely low frequency-electromagnetic fields (EM-ELF).

    PubMed

    Beruto, Dario T; Lagazzo, Alberto; Frumento, Davide; Converti, Attilio

    2014-01-01

    Chlorella vulgaris was grown in two bench-scale photobioreactors with and without the application of a low intensity, low frequency electromagnetic field (EM-ELF) of about 3mT. Cell concentration and tendency of cells to form aggregates inside the reactor were recorded over a 30 days-time period at 0.5L-constant medium volume in the temperature range 289-304K. At 304K, after a cultivation period of 15 days, the rate of cell death became predominant over that of growth. In the temperature range 289-299K, a two step-kinetic model based on the mitotic division and the clusterization processes was developed and critically discussed. The best-fitted curves turned out to have a sigmoid shape, and the competition between mitosis and clusterization was investigated. Without EM-ELF, the temperature dependence of the specific rate constant of the mitotic step yielded an apparent total enthalpy of 15±6kJmol(-1), whose value was not influenced by the EM-ELF application. The electromagnetic field was shown to exert a significant effect on the exothermic clusterization step. The heat exchange due to binding between cells and liquid medium turned out to be -44±5kJmol(-1) in the absence of EM-ELF and -68±8kJmol(-1) when it was active. Optical microscopy observations were in agreement with the model predictions and confirmed that EM-ELF was able to enhance cell clusterization. PMID:24216340

  3. Mutation in continuous cultures of Schizosaccharomyces pombe. I. Dependence of the kinetics of mutation accumulation upon the growth-limiting nutrilite.

    PubMed

    McAthey, P; Kilbey, B J

    1977-08-01

    The rate of spontaneous mutation to resistance to the 12,13-epoxytrichothecene trichodermin has been determined under different growth limiting conditions in continuous cultures of the microbial eukaryote Schizosaccharomyces pombe. In agreement with data obtained in bacterial systems by previous workers the kinetics observed for the accumulation of mutations is found to be dependent upon the nutrient used to limit the growth of the population. Under conditions of glucose-limitation mutation accumulation is directly proportional to the rate of cell division, while under histidine-limitation it is proportional to chronological time. Various possible explanations for these observations are discussed. PMID:895757

  4. Quantum Dots: Growth of InAs Quantum Dots on GaAs (511)A Substrates: The Competition between Thermal Dynamics and Kinetics (Small 31/2016).

    PubMed

    Wen, Lei; Gao, Fangliang; Zhang, Shuguang; Li, Guoqiang

    2016-08-01

    On page 4277, G. Li and co-workers aim to promote III-V compound semiconductors and devices for a broad range of applications with various technologies. The growth process of InAs quantum dots on GaAs (511)A substrates is systematically studied. By carefully controlling the competition between growth thermal-dynamics and kinetics, InAs quantum dots with high size uniformity are prepared, which are highly desirable for the fabrication of high-efficiency solar cells. PMID:27510365

  5. The Existence of Weak D-Pullback Exponential Attractor for Nonautonomous Dynamical System.

    PubMed

    Li, Yongjun; Wei, Xiaona; Zhang, Yanhong

    2016-01-01

    First, for a process {U(t, τ)∣t ≥ τ}, we introduce a new concept, called the weak D-pullback exponential attractor, which is a family of sets {ℳ(t)∣t ≤ T}, for any T ∈ ℝ, satisfying the following: (i) ℳ(t) is compact, (ii) ℳ(t) is positively invariant, that is, U(t, τ)ℳ(τ) ⊂ ℳ(t), and (iii) there exist k, l > 0 such that dist(U(t, τ)B(τ), ℳ(t)) ≤ ke (-(t-τ)); that is, ℳ(t) pullback exponential attracts B(τ). Then we give a method to obtain the existence of weak D-pullback exponential attractors for a process. As an application, we obtain the existence of weak D-pullback exponential attractor for reaction diffusion equation in H 0 (1) with exponential growth of the external force. PMID:27119090

  6. Hexagonal-Rod Growth Mechanism and Kinetics of the Primary Cu6Sn5 Phase in Liquid Sn-Based Solder

    NASA Astrophysics Data System (ADS)

    Zhang, Z. H.; Cao, H. J.; Yang, H. F.; Li, M. Y.; Yu, Y. X.

    2016-08-01

    A hexagonal-rod growth mechanism is proposed to describe the growth behavior of the primary Cu6Sn5 phase in liquid Sn-based solder. After Sn-6.5 at.%Cu solder had been maintained at 250°C for 10 h, a large number of hexagonal-rod-type Cu6Sn5 grains were found to have separated within it. Our observations show that these hexagonal rods had side facets in the { 10overline{1} 0}_{η } family and round ends close to the {0002}η family. Moreover, the nucleation of the hexagonal rods was studied, and the corresponding growth kinetics found to be governed by a Cu-supply-controlled mechanism rather than an interfacial-reaction-controlled or Cu-diffusion-limited mechanism. More importantly, the anisotropic growth of the Cu6Sn5 phase was confirmed to be the dominant reason for production of these primary hexagonal rods with high aspect ratio. This may represent an avenue for synthesis of nanosized Cu6Sn5 single crystals for use as anode materials in lithium-ion batteries. Additionally, our Cu6Sn5 hexagonal-rod growth mechanism may provide insight into morphological and kinetic studies on interfacial Cu6Sn5 grains and similar intermetallics.

  7. A three-dimensional phase field model coupled with lattice kinetics solver for modeling crystal growth in furnaces with accelerated crucible rotation and traveling magnetic field

    SciTech Connect

    Lin, Guang; Bao, Jie; Xu, Zhijie

    2014-11-01

    In this study, which builds on other related work, we present a new three-dimensional numerical model for crystal growth in a vertical solidification system. This model accounts for buoyancy, accelerated crucible rotation technique (ACRT), and traveling magnetic field (TMF) induced convective flow and their effect on crystal growth and the chemical component's transport process. The evolution of the crystal growth interface is simulated using the phase field method. A semi-implicit lattice kinetics solver based on the Boltzmann equation is employed to model the unsteady incompressible flow. A one-way coupled concentration transport model is used to simulate the component fraction variation in both the liquid and solid phases, which can be used to check the quality of the crystal growth.

  8. Growth of InAs Quantum Dots on GaAs (511)A Substrates: The Competition between Thermal Dynamics and Kinetics.

    PubMed

    Wen, Lei; Gao, Fangliang; Zhang, Shuguang; Li, Guoqiang

    2016-08-01

    The growth process of InAs quantum dots grown on GaAs (511)A substrates has been studied by atomic force microscopy. According to the atomic force microscopy studies for quantum dots grown with varying InAs coverage, a noncoherent nucleation of quantum dots is observed. Moreover, due to the long migration length of In atoms, the Ostwald ripening process is aggravated, resulting in the bad uniformity of InAs quantum dots on GaAs (511)A. In order to improve the uniformity of nucleation, the growth rate is increased. By studying the effects of increased growth rates on the growth of InAs quantum dots, it is found that the uniformity of InAs quantum dots is greatly improved as the growth rates increase to 0.14 ML s(-1) . However, as the growth rates increase further, the uniformity of InAs quantum dots becomes dual-mode, which can be attributed to the competition between Ostwald ripening and strain relaxation processes. The results in this work provide insights regarding the competition between thermal dynamical barriers and the growth kinetics in the growth of InAs quantum dots, and give guidance to improve the size uniformity of InAs quantum dots on (N11)A substrates. PMID:27348495

  9. Temperature effect on the build-up of exponentially growing polyelectrolyte multilayers. An exponential-to-linear transition point.

    PubMed

    Vikulina, Anna S; Anissimov, Yuri G; Singh, Prateek; Prokopović, Vladimir Z; Uhlig, Katja; Jaeger, Magnus S; von Klitzing, Regine; Duschl, Claus; Volodkin, Dmitry

    2016-03-21

    In this study, the effect of temperature on the build-up of exponentially growing polyelectrolyte multilayer films was investigated. It aims at understanding the multilayer growth mechanism as crucially important for the fabrication of tailor-made multilayer films. Model poly(L-lysine)/hyaluronic acid (PLL/HA) multilayers were assembled in the temperature range of 25-85 °C by layer-by-layer deposition using a dipping method. The film growth switches from the exponential to the linear regime at the transition point as a result of limited polymer diffusion into the film. With the increase of the build-up temperature the film growth rate is enhanced in both regimes; the position of the transition point shifts to a higher number of deposition steps confirming the diffusion-mediated growth mechanism. Not only the faster polymer diffusion into the film but also more porous/permeable film structure are responsible for faster film growth at higher preparation temperature. The latter mechanism is assumed from analysis of the film growth rate upon switching of the preparation temperature during the film growth. Interestingly, the as-prepared films are equilibrated and remain intact (no swelling or shrinking) during temperature variation in the range of 25-45 °C. The average activation energy for complexation between PLL and HA in the multilayers calculated from the Arrhenius plot has been found to be about 0.3 kJ mol(-1) for monomers of PLL. Finally, the following processes known to be dependent on temperature are discussed with respect to the multilayer growth: (i) polymer diffusion, (ii) polymer conformational changes, and (iii) inter-polymer interactions. PMID:26911320

  10. Determination of oxygen diffusion kinetics during thin film ruthenium oxidation

    SciTech Connect

    Coloma Ribera, R. Kruijs, R. W. E. van de; Yakshin, A. E.; Bijkerk, F.

    2015-08-07

    In situ X-ray reflectivity was used to reveal oxygen diffusion kinetics for thermal oxidation of polycrystalline ruthenium thin films and accurate determination of activation energies for this process. Diffusion rates in nanometer thin RuO{sub 2} films were found to show Arrhenius behaviour. However, a gradual decrease in diffusion rates was observed with oxide growth, with the activation energy increasing from about 2.1 to 2.4 eV. Further exploration of the Arrhenius pre-exponential factor for diffusion process revealed that oxidation of polycrystalline ruthenium joins the class of materials that obey the Meyer-Neldel rule.

  11. Phylogenetic Stochastic Mapping Without Matrix Exponentiation

    PubMed Central

    Irvahn, Jan; Minin, Vladimir N.

    2014-01-01

    Abstract Phylogenetic stochastic mapping is a method for reconstructing the history of trait changes on a phylogenetic tree relating species/organism carrying the trait. State-of-the-art methods assume that the trait evolves according to a continuous-time Markov chain (CTMC) and works well for small state spaces. The computations slow down considerably for larger state spaces (e.g., space of codons), because current methodology relies on exponentiating CTMC infinitesimal rate matrices—an operation whose computational complexity grows as the size of the CTMC state space cubed. In this work, we introduce a new approach, based on a CTMC technique called uniformization, which does not use matrix exponentiation for phylogenetic stochastic mapping. Our method is based on a new Markov chain Monte Carlo (MCMC) algorithm that targets the distribution of trait histories conditional on the trait data observed at the tips of the tree. The computational complexity of our MCMC method grows as the size of the CTMC state space squared. Moreover, in contrast to competing matrix exponentiation methods, if the rate matrix is sparse, we can leverage this sparsity and increase the computational efficiency of our algorithm further. Using simulated data, we illustrate advantages of our MCMC algorithm and investigate how large the state space needs to be for our method to outperform matrix exponentiation approaches. We show that even on the moderately large state space of codons our MCMC method can be significantly faster than currently used matrix exponentiation methods. PMID:24918812

  12. Finite Higher Spin Transformations from Exponentiation

    NASA Astrophysics Data System (ADS)

    Monnier, Samuel

    2015-05-01

    We study the exponentiation of elements of the gauge Lie algebras hs(λ) of three-dimensional higher spin theories. Exponentiable elements generate one-parameter groups of finite higher spin symmetries. We show that elements of hs(λ) in a dense set are exponentiable, when pictured in certain representations of hs(λ), induced from representations of in the complementary series. We also provide a geometric picture of higher spin gauge transformations clarifying the physical origin of these representations. This allows us to construct an infinite-dimensional topological group HS(λ) of finite higher spin symmetries. Interestingly, this construction is possible only for 0 ≤ λ ≤ 1, which are the values for which the higher spin theory is believed to be unitary and for which the Gaberdiel-Gopakumar duality holds. We exponentiate explicitly various commutative subalgebras of hs(λ). Among those, we identify families of elements of hs(λ) exponentiating to the unit of HS(λ), generalizing the logarithms of the holonomies of BTZ black hole connections. Our techniques are generalizable to the Lie algebras relevant to higher spin theories in dimensions above three.

  13. Theoretical analysis of impurity precipitation in nanopores in crystals. II: Kinetics of impurity cluster growth in pores

    NASA Astrophysics Data System (ADS)

    Lubov, M. N.; Kulikov, D. V.; Trushin, Yu. V.; Kurnosikov, O.

    2013-03-01

    The kinetics of the formation of impurity clusters in subsurface nanopores in crystals is studied theoretically. A physical model of precipitation of the impurity phase in nanopores in a sample with sinks of various types is developed. This model forms the basis for the calculation of the annealing kinetics of copper containing subsurface pores and cobalt impurity atoms. The optimal annealing conditions are determined in which cobalt atoms diffuse predominantly into pores and form impurity clusters in them.

  14. Decoherence and Exponential Law: A Solvable Model

    NASA Technical Reports Server (NTRS)

    Pascazio, Saverio; Namiki, Mikio

    1996-01-01

    We analyze a modified version of the 'AgBr' Hamiltonian, solve exactly the equations of motion in terms of SU(2) coherent states, and study the weak-coupling, macroscopic limit of the model, obtaining an exponential behavior at all times. The asymptotic dominance of the exponential behavior is representative of a purely stochastic evolution and can be derived quantum mechanically in the so-called van Hove's limit (which is a weak-coupling, macroscopic limit). At the same time, a temporal behavior of the exponential type, yielding a 'probability dissipation' is closely related to dephasing ('decoherence') effects and one can expect a close connection with a dissipative and irreversible behavior. We stress the central relevance of the problem of dissipation to the quantum measurement theory and to the general topic of decoherence.

  15. Why does human culture increase exponentially?

    PubMed

    Enquist, M; Ghirlanda, S; Jarrick, A; Wachtmeister, C-A

    2008-08-01

    Historical records show that culture can increase exponentially in time, e.g., in number of poems, musical works, scientific discoveries. We model how human capacities for creativity and cultural transmission may make such an increase possible, suggesting that: (1) creativity played a major role at the origin of human culture and for its accumulation throughout history, because cultural transmission cannot, on its own, generate exponentially increasing amounts of culture; (2) exponential increase in amount of culture can only occur if creativity is positively influenced by culture. The evolution of cultural transmission is often considered the main genetic bottleneck for the origin of culture, because natural selection cannot favor cultural transmission without any culture to transmit. Our models suggest that an increase in individual creativity may have been the first step toward human culture, because in a population of creative individuals there may be enough non-genetic information to favor the evolution of cultural transmission. PMID:18571686

  16. Modeling aftershocks as a stretched exponential relaxation

    NASA Astrophysics Data System (ADS)

    Mignan, A.

    2015-11-01

    The decay rate of aftershocks has been modeled as a power law since the pioneering work of Omori in the late nineteenth century. Although other expressions have been proposed in recent decades to describe the temporal behavior of aftershocks, the number of model comparisons remains limited. After reviewing the aftershock models published from the late nineteenth century until today, I solely compare the power law, pure exponential and stretched exponential expressions defined in their simplest forms. By applying statistical methods recommended recently in applied mathematics, I show that all aftershock sequences tested in three regional earthquake catalogs (Southern and Northern California, Taiwan) and with three declustering techniques (nearest-neighbor, second-order moment, window methods) follow a stretched exponential instead of a power law. These results infer that aftershocks are due to a simple relaxation process, in accordance with most other relaxation processes observed in Nature.

  17. Method for exponentiating in cryptographic systems

    DOEpatents

    Brickell, Ernest F.; Gordon, Daniel M.; McCurley, Kevin S.

    1994-01-01

    An improved cryptographic method utilizing exponentiation is provided which has the advantage of reducing the number of multiplications required to determine the legitimacy of a message or user. The basic method comprises the steps of selecting a key from a preapproved group of integer keys g; exponentiating the key by an integer value e, where e represents a digital signature, to generate a value g.sup.e ; transmitting the value g.sup.e to a remote facility by a communications network; receiving the value g.sup.e at the remote facility; and verifying the digital signature as originating from the legitimate user. The exponentiating step comprises the steps of initializing a plurality of memory locations with a plurality of values g.sup.xi ; computi The United States Government has rights in this invention pursuant to Contract No. DE-AC04-76DP00789 between the Department of Energy and AT&T Company.

  18. Reaction kinetics and growth window for plasma-assisted molecular beam epitaxy of Ga2O3: Incorporation of Ga vs. Ga2O desorption

    NASA Astrophysics Data System (ADS)

    Vogt, Patrick; Bierwagen, Oliver

    2016-02-01

    A detailed study of the reaction kinetics of the plasma-assisted molecular beam epitaxy (MBE) growth of the n-type semiconducting oxide Ga2O3 is presented. The growth rate as a function of gallium flux is measured in situ by laser reflectometry at different growth temperatures (TG) and gallium-to-oxygen ratios (rGa). The flux of the suboxide Ga2O desorbed off the growth surface is identified in situ by line-of-sight quadrupole mass spectroscopy. The measurements reveal the influence of TG and rGa on the competing formation of Ga2O3 and desorption of Ga2O resulting in three different growth regimes: (i) Ga transport limited, (ii) Ga2O desorption limited, and (iii) O transport limited. As a result, we present a growth diagram of gallium oxide. This diagram illustrates the regimes of complete, partial, and no Ga incorporation as a function of TG and rGa, and thus provides guidance for the MBE growth of Ga2O3.

  19. Simulating Population Growth.

    ERIC Educational Resources Information Center

    Byington, Scott

    1997-01-01

    Presents a strategy to help students grasp the important implications of population growth. Involves an interactive demonstration that allows students to experience exponential and logistic population growth followed by a discussion of the implications of population-growth principles. (JRH)

  20. Dissolution and Growth of (10(1) over-bar4) Calcite in Flowing Water: Estimation of Back Reaction Rates via Kinetic Monte Carlo Simulations

    SciTech Connect

    Williford, Rick E.; Baer, Donald R.; Amonette, James E.; Lea, Alan S.

    2004-02-15

    Although calcite is an important mineral for many processes, there have been relatively few simulations of it's growth and dissolution behavior. Such simulations are complicated by the multitude of defect types and by the asymmetry of the crystal. The present work combined a kinetic Monte Carlo (KMC) technique with the Kossel crystal (100) simple cubic concept and the Blasius boundary layer model to simulate the simultaneous growth and dissolution of the (1014)calcite cleavage surface in flowing water. The objective was to determine the activation energies of the back reaction (growth) from those of the forward reaction (dissolution) by obtaining agreement with cleavage-step morphologies and step dissolution velocities previously measured using an atomic force microscope (AFM). Blasius boundary layer conditions for the flowing fluid defined a model that treated the solid, the dissolution/growth interface, and the fluid kinetics. Microscopic reversibility and the laws of large number s gave an expression for the back reaction activation energies in terms of the forward reaction energies and the entropy of mixing, a quantity estimated from the concentration of desorbates in a very small fluid layer adjacent to the interface. The KMC simulations produced cleavage-step morphologies that were in qualitative agreement with observations from AFM. The kinetics were dominated by diffusion events on the solid/fluid interface and in the fluid, as expected. The relative magnitudes of the desorption and adsorption activation energies were consistent with experimental data, entropic arguments, and crystal roughening theories. Qualitative agreement with measured step velocities was best when the boundary layer parameters were given physically reasonable values, indicating that the model is self consistent.