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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. Growth kinetics of Listeria monocytogenes in broth and beef frankfurters--determination of lag phase duration and exponential growth rate under isothermal conditions.

    PubMed

    Huang, L

    2008-06-01

    The objective of this study was to develop a new kinetic model to describe the isothermal growth of microorganisms. The new model was tested with Listeria monocytogenes in tryptic soy broth and frankfurters, and compared with 2 commonly used models-Baranyi and modified Gompertz models. Bias factor (BF), accuracy factor (AF), and root mean square errors (RMSE) were used to evaluate the 3 models. Either in broth or in frankfurter samples, there were no significant differences in BF (approximately 1.0) and AF (1.02 to 1.04) among the 3 models. In broth, the mean RMSE of the new model was very close to that of the Baranyi model, but significantly lower than that of the modified Gompertz model. However, in frankfurters, there were no significant differences in the mean RMSE values among the 3 models. These results suggest that these models are equally capable of describing isothermal bacterial growth curves. Almost identical to the Baranyi model in the exponential and stationary phases, the new model has a more identifiable lag phase and also suggests that the bacteria population would increase exponentially until the population approaches to within 1 to 2 logs from the stationary phase. In general, there is no significant difference in the means of the lag phase duration and specific growth rate between the new and Baranyi models, but both are significantly lower than those determined from the modified Gompertz models. The model developed in this study is directly derived from the isothermal growth characteristics and is more accurate in describing the kinetics of bacterial growth in foods.

  3. 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…

  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.

  5. 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.

  6. Teaching about Exponential Growth in Social Studies.

    ERIC Educational Resources Information Center

    Allen, Rodney F.; LaHart, David E.

    1984-01-01

    Characteristics of exponential growth which should be taught in social studies classes are listed, and learning activities dealing with exponential growth which can be used in secondary social studies classes are provided. (RM)

  7. 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)...

  8. 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)

  9. 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.

  10. 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…

  11. 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…

  12. A Simple Mechanical Experiment on Exponential Growth

    NASA Astrophysics Data System (ADS)

    McGrew, Ralph

    2015-04-01

    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 activity are accessible to students in physical science and environmental science courses.

  13. Is it growing exponentially fast? -- Impact of assuming exponential growth for characterizing and forecasting epidemics with initial near-exponential growth dynamics.

    PubMed

    Chowell, Gerardo; Viboud, Cécile

    2016-10-01

    The increasing use of mathematical models for epidemic forecasting has highlighted the importance of designing models that capture the baseline transmission characteristics in order to generate reliable epidemic forecasts. Improved models for epidemic forecasting could be achieved by identifying signature features of epidemic growth, which could inform the design of models of disease spread and reveal important characteristics of the transmission process. In particular, it is often taken for granted that the early growth phase of different growth processes in nature follow early exponential growth dynamics. In the context of infectious disease spread, this assumption is often convenient to describe a transmission process with mass action kinetics using differential equations and generate analytic expressions and estimates of the reproduction number. In this article, we carry out a simulation study to illustrate the impact of incorrectly assuming an exponential-growth model to characterize the early phase (e.g., 3-5 disease generation intervals) of an infectious disease outbreak that follows near-exponential growth dynamics. Specifically, we assess the impact on: 1) goodness of fit, 2) bias on the growth parameter, and 3) the impact on short-term epidemic forecasts. Designing transmission models and statistical approaches that more flexibly capture the profile of epidemic growth could lead to enhanced model fit, improved estimates of key transmission parameters, and more realistic epidemic forecasts.

  14. Exponentiated exponential model (Gompertz kinetics) of Na+ and K+ conductance changes in squid giant axon.

    PubMed Central

    Easton, D M

    1978-01-01

    The conductance changes, gK(t) and gNa(t), of squid giant axon under voltage clamp (Hodgkin and Huxley, 1952) may be modeled by exponentiated exponential functions (Gompertz kinetics) from any holding potential VO to any membrane clamp potential V. The equation constants are set by the membrane potential V, and include, for any voltage step in the case of gK, the initial conductance, gO, the asymptote conductance g, and rate constant k: gK = g exp(-be-kt) where b = 1n g/gO. Equations of similar form relate g and k to the voltage V, and govern the corresponding parameters of the gNa system. For the gNa, the fast phase y = y exp (-be-kt) is cut down in proportion to a slow process p = (1 - p)e-k't + p, and thus gNa = py. The expo-exponential functions involve fewer constants than the Hodgkin-Huxley model. In particular, the role of the n, m, h parameters appears to be filled largely by 1n (g/gO) in the case of gK and by 1n (y/yO) in the case of gNa. Membrane action potentials during current clamp may be computed from the conductances generated by use of the appropriate differential forms of the equations; diverse other membrane behaviors may be predicted. PMID:638223

  15. A Learning Cycle on Exponential Growth and the Energy Crises.

    ERIC Educational Resources Information Center

    Dykstra, D. I., Jr.

    1982-01-01

    Describes nature and logistics of a learning cycle approach to teaching exponential growth and the energy crisis. Used with both science and nonscience majors, the cycle uses no algebra, never mentions the terms exponential or logarithmic, and requires a calculator. Instructions for obtaining student and instructor materials are provided.…

  16. Generalized exponential function and discrete growth models

    NASA Astrophysics Data System (ADS)

    Souto Martinez, Alexandre; Silva González, Rodrigo; Lauri Espíndola, Aquino

    2009-07-01

    Here we show that a particular one-parameter generalization of the exponential function is suitable to unify most of the popular one-species discrete population dynamic models into a simple formula. A physical interpretation is given to this new introduced parameter in the context of the continuous Richards model, which remains valid for the discrete case. From the discretization of the continuous Richards’ model (generalization of the Gompertz and Verhulst models), one obtains a generalized logistic map and we briefly study its properties. Notice, however that the physical interpretation for the introduced parameter persists valid for the discrete case. Next, we generalize the (scramble competition) θ-Ricker discrete model and analytically calculate the fixed points as well as their stabilities. In contrast to previous generalizations, from the generalized θ-Ricker model one is able to retrieve either scramble or contest models.

  17. 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.

  18. 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.

  19. 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)

  20. Growth Kinetics in Epitaxial Growth

    NASA Astrophysics Data System (ADS)

    Hessinger, Uwe

    Growth kinetics in heteroepitaxial growth are related to the nucleation and growth of atomic-height islands during the deposition of a material on a dissimilar substrate. Experimental measurements of the initial morphology of CaF_2 films deposited on Si(111) substrates were performed. These measurements consisted of photoemission spectroscopy and diffraction, which give sub-nanometer scale information averaged over the entire sample, and plan-view transmission electron microscopy, which gives localized information on a scale of several nanometers. These results, combined with others in the literature, revealed four distinct growth morphologies dependent on the deposition rate, substrate temperature and spacing between atomic-height steps on the surface, two of which had not been previously explained. A model based on two extant theories of homoepitaxial growth kinetics was developed to explain the different observed growth morphologies for the heteroepitaxial system CaF_2/Si(111). The first theory deals with whether the initial nucleation will occur at substrate steps or through adatom collisions on flat terraces, while the second deals with the nucleation of subsequent layers as these initial atomic islands increase in size. In extending these theories to heteroepitaxy, very different rates of upper-layer nucleation for the different size islands that nucleated at steps and on terraces are predicted. By applying this theory to CaF_2/Si(111), the diffusion barriers for CaF_2 molecule migration both on the reacted Si-Ca-F interface layer and on subsequent CaF_2 layers was extracted. The four different growth morphologies are explained within a common framework. The theory is quite general, and should apply to most heteroepitaxial systems. These theories were extended to predict a means by which the upper-layer nucleation may be inhibited while the underlying layer is completed. This method involves initiating the growth at conditions favoring many, small islands on

  1. Solving Point-Reactor Kinetics Equations Using Exponential Moment Methods

    DTIC Science & Technology

    2013-03-21

    equations of the following form: ( ) ( ) ( ) ( ) ( )i i i dn t t n t c t S t dt               (2) ( ) ( ) ( )i ii i dc t c t n...presented in the function. Exponential moment functions are orderless; that is, the value of the function is invariant under permutations of its...turned into an integral equation by   ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) i i i i i i i i i i i i dn

  2. Exponential growth combined with exponential decline explains lifetime performance evolution in individual and human species.

    PubMed

    Berthelot, Geoffroy; Len, Stéphane; Hellard, Philippe; Tafflet, Muriel; Guillaume, Marion; Vollmer, Jean-Claude; Gager, Bruno; Quinquis, Laurent; Marc, Andy; Toussaint, Jean-François

    2012-08-01

    The physiological parameters characterizing human capacities (the ability to move, reproduce or perform tasks) evolve with ageing: performance is limited at birth, increases to a maximum and then decreases back to zero at the day of death. Physical and intellectual skills follow such a pattern. Here, we investigate the development of sport and chess performances during the lifetime at two different scales: the individual athletes' careers and the world record by age class in 25 Olympic sports events and in grandmaster chess players. For all data sets, a biphasic development of growth and decline is described by a simple model that accounts for 91.7% of the variance at the individual level and 98.5% of the variance at the species one. The age of performance peak is computed at 26.1 years old for the events studied (26.0 years old for track and field, 21.0 years old for swimming and 31.4 years old for chess). The two processes (growth and decline) are exponential and start at age zero. Both were previously demonstrated to happen in other human and non-human biological functions that evolve with age. They occur at the individual and species levels with a similar pattern, suggesting a scale invariance property.

  3. 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.

  4. 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.

  5. Stretched exponential kinetics for photoinduced birefringence in azo dye doped PVA films

    NASA Astrophysics Data System (ADS)

    Yang, Hye Ri; Kim, Eun Ju; Lee, Sang Jo; Kim, Gun Yeup; Kwak, Chong Hoon

    2009-05-01

    We fabricated azo dye (methylorange) doped poly vinyl alcohol (MO/PVA) thin films and measured the photoinduced birefringence (PIB) kinetics for several pump beam intensities and for various MO concentrations by using the pump-probe technique. A novel approach to explain the transient behaviors of the photoinduced anisotropy is presented by employing an empirical stretched exponential time response in the course of the trans-cis-trans photoisomerization of azo molecules and is compared with the experimental data, showing excellent agreement. The stretched exponent is estimated to be β = 0.34 ± 0.04, revealing amorphous nature of the MO/PVA system.

  6. 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.

  7. A kinetic theory for nonanalog Monte Carlo algorithms: Exponential transform with angular biasing

    SciTech Connect

    Ueki, T.; Larsen, E.W.

    1998-11-01

    A new Boltzmann Monte Carlo (BMC) equation is proposed to describe the transport of Monte Carlo particles governed by a set of nonanalog rules for the transition of space, velocity, and weight. The BMC equation is a kinetic equation that includes weight as an extra independent variable. The solution of the BMC equation is the pointwise distribution of velocity and weight throughout the physical system. The BMC equation is derived for the simulation of a transmitted current, utilizing the exponential transform with angular biasing. The weight moments of the solution of the BMC equation are used to predict the score moments of the transmission current. (Also, it is shown that an adjoint BMC equation can be used for this purpose.) Integrating the solution of the forward BMC equation over space, velocity, and weight, the mean number of flights per history is obtained. This is used to determine theoretically the figure of merit for any choice of biasing parameters. Also, a maximum safe value of the exponential transform parameter is proposed, which ensure the finite variance of variance estimate (sample variance) for any penetration distance. Finally, numerical results that validate the new theory are provided.

  8. 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.

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

    DOE PAGES

    Li, Yuelin; Jiang, Zhang; Lin, Xiao -Min; ...

    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

  10. The role of multiple modeling perspectives in students' learning of exponential growth.

    PubMed

    Castillo-Garsow, Carlos

    2013-01-01

    The exponential is among the most important family functions in mathematics; the foundation for the solution of linear differential equations, linear difference equations, and stochastic processes. However there is little research and superficial agreement on how the concepts of exponential growth are learned and/or should be taught initially. In order to investigate these issues, I preformed a teaching experiment with two high school students, which focused on building understandings of exponential growth leading up to the (nonlinear) logistic differential equation model. In this paper, I highlight some of the ways of thinking used by participants in this teaching experiment. From these results I discuss how mathematicians using exponential growth routinely make use of multiple--sometimes contradictory--ways of thinking, as well as the danger that these multiple ways of thinking are not being made distinct to students.

  11. [Growth and development kinetics of Bacillus thuringiensis in batch culture].

    PubMed

    Sakharova, Z V; Ignatenko, Iu N; Schulz, F; Khovrychev, M P; Rabotnova, I L

    1985-01-01

    The kinetics of Bacillus thuringiensis growth and its assimilation of nutrient substances were studied under the conditions of batch cultivation in a complex medium containing yeast extract and in a chemically defined medium with amino acids. The growth of B. thuringiensis can be divided into five phases: exponential growth; decelerated growth; stationary phase when protein crystals are formed; stationary phase when spores are formed; lysis of sporangia releasing spores. The first phase may in turn be subdivided into three stages according to changes in the specific growth rate and substrate assimilation: a high specific growth rate and no glucose assimilation; an abrupt drop in mu and the beginning of intensive glucose assimilation from the medium; a new rise in the specific growth rate. As follows from the results of studying the kinetics of B. thuringiensis growth in a chemically defined medium, the above changes in the exponential growth phase are due to the fact that the culture assimilates yeast extract components in the complex medium or amino acids in the chemically defined medium during this phase, and then starts to assimilate glucose and ammonium in the following phases of growth.

  12. 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.

  13. Characterizing the Growth Kinetics in Estrogen Responsive ...

    EPA Pesticide Factsheets

    There is a need to develop high-throughput screening (HTS) tests capable of testing thousands of environmental chemicals for endocrine disrupting potential. The estrogen signaling pathway is a known xenobiotic target that has been implicated in a variety of adverse health effects including reproductive deficits and cancer promotion. Using real-time measurements of growth kinetics by electrode impedance, the estrogen-responsive human ductal carcinoma cell line, T47D, was treated with 2000 chemicals of environmental relevance. Cells were treated in concentration response and measurements of cellular impedance were recorded every hour for six days. Exponential impedance, signifying increased proliferation, was observed by prototypical estrogen receptor agonists (17β-estradiol, genestein, bisphenol-A, nonylphenol, 4-tert-octylphenol). Several compounds, including bisphenol-A and genestein, induced cell proliferation at comparable levels to 17β-estradiol, although at much higher concentrations. Progestins, and mineralocortocoids (progesterone, dihydrotestosterone, aldosterone) invoked a biphasic impedance signature. In conclusion, the real-time nature of this assay allows for rapid detection of differential growth characteristics shows potential, in combination with other ToxCast HTS assays, to detect environmental chemicals with potential endocrine activity. [This abstract does not necessarily reflect Agency policy]. Several compounds, including bisphenol-A and

  14. Reduced heme levels underlie the exponential growth defect of the Shewanella oneidensis hfq mutant.

    PubMed

    Brennan, Christopher M; Mazzucca, Nicholas Q; Mezoian, Taylor; Hunt, Taylor M; Keane, Meaghan L; Leonard, Jessica N; Scola, Shelby E; Beer, Emma N; Perdue, Sarah; Pellock, Brett J

    2014-01-01

    The RNA chaperone Hfq fulfills important roles in small regulatory RNA (sRNA) function in many bacteria. Loss of Hfq in the dissimilatory metal reducing bacterium Shewanella oneidensis strain MR-1 results in slow exponential phase growth and a reduced terminal cell density at stationary phase. We have found that the exponential phase growth defect of the hfq mutant in LB is the result of reduced heme levels. Both heme levels and exponential phase growth of the hfq mutant can be completely restored by supplementing LB medium with 5-aminolevulinic acid (5-ALA), the first committed intermediate synthesized during heme synthesis. Increasing expression of gtrA, which encodes the enzyme that catalyzes the first step in heme biosynthesis, also restores heme levels and exponential phase growth of the hfq mutant. Taken together, our data indicate that reduced heme levels are responsible for the exponential growth defect of the S. oneidensis hfq mutant in LB medium and suggest that the S. oneidensis hfq mutant is deficient in heme production at the 5-ALA synthesis step.

  15. Reduced Heme Levels Underlie the Exponential Growth Defect of the Shewanella oneidensis hfq Mutant

    PubMed Central

    Mezoian, Taylor; Hunt, Taylor M.; Keane, Meaghan L.; Leonard, Jessica N.; Scola, Shelby E.; Beer, Emma N.; Perdue, Sarah; Pellock, Brett J.

    2014-01-01

    The RNA chaperone Hfq fulfills important roles in small regulatory RNA (sRNA) function in many bacteria. Loss of Hfq in the dissimilatory metal reducing bacterium Shewanella oneidensis strain MR-1 results in slow exponential phase growth and a reduced terminal cell density at stationary phase. We have found that the exponential phase growth defect of the hfq mutant in LB is the result of reduced heme levels. Both heme levels and exponential phase growth of the hfq mutant can be completely restored by supplementing LB medium with 5-aminolevulinic acid (5-ALA), the first committed intermediate synthesized during heme synthesis. Increasing expression of gtrA, which encodes the enzyme that catalyzes the first step in heme biosynthesis, also restores heme levels and exponential phase growth of the hfq mutant. Taken together, our data indicate that reduced heme levels are responsible for the exponential growth defect of the S. oneidensis hfq mutant in LB medium and suggest that the S. oneidensis hfq mutant is deficient in heme production at the 5-ALA synthesis step. PMID:25356668

  16. 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.

  17. Molecular basis for the explanation of the exponential growth of polyelectrolyte multilayers

    PubMed Central

    Picart, C.; Mutterer, J.; Richert, L.; Luo, Y.; Prestwich, G. D.; Schaaf, P.; Voegel, J.-C.; Lavalle, P.

    2002-01-01

    The structure of poly(l-lysine) (PLL)/hyaluronan (HA) polyelectrolyte multilayers formed by electrostatic self-assembly is studied by using confocal laser scanning microscopy, quartz crystal microbalance, and optical waveguide lightmode spectroscopy. These films exhibit an exponential growth regime where the thickness increases exponentially with the number of deposited layers, leading to micrometer thick films. Previously such a growth regime was suggested to result from an “in” and “out” diffusion of the PLL chains through the film during buildup, but direct evidence was lacking. The use of dye-conjugated polyelectrolytes now allows a direct three-dimensional visualization of the film construction by introducing fluorescent polyelectrolytes at different steps during the film buildup. We find that, as postulated, PLL diffuses throughout the film down into the substrate after each new PLL injection and out of the film after each PLL rinsing and further after each HA injection. As PLL reaches the outer layer of the film it interacts with the incoming HA, forming the new HA/PLL layer. The thickness of this new layer is thus proportional to the amount of PLL that diffuses out of the film during the buildup step, which explains the exponential growth regime. HA layers are also visualized but no diffusion is observed, leading to a stratified film structure. We believe that such a diffusion-based buildup mechanism explains most of the exponential-like growth processes of polyelectrolyte multilayers reported in the literature. PMID:12237412

  18. 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…

  19. 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…

  20. A Precalculus Project on Exponential Population Growth and Linear Food Production.

    ERIC Educational Resources Information Center

    McDonald, Michael A.; And Others

    1996-01-01

    Discusses a precalculus project in which students create a model United Nations to present and discuss the long-term prognosis for individual countries given data on population growth and food production. Students compare exponential and linear functions to determine whether starvation will occur and prepare oral and written presentations of their…

  1. Transition from exponential to linear photoautotrophic growth changes the physiology of Synechocystis sp. PCC 6803.

    PubMed

    Schuurmans, R M; Matthijs, J C P; Hellingwerf, K J

    2017-04-01

    Phototrophic microorganisms like cyanobacteria show growth curves in batch culture that differ from the corresponding growth curves of chemotrophic bacteria. Instead of the usual three phases, i.e., lag-, log-, and stationary phase, phototrophs display four distinct phases. The extra growth phase is a phase of linear, light-limited growth that follows the exponential phase and is often ignored as being different. Results of this study demonstrate marked growth phase-dependent alterations in the photophysiology of the cyanobacterium Synechocystis sp. PCC 6803 between cells harvested from the exponential and the linear growth phase. Notable differences are a gradual shift in the energy transfer of the light-harvesting phycobilisomes to the photosystems and a distinct change in the redox state of the plastoquinone pool. These differences will likely affect the result of physiological studies and the efficiency of product formation of Synechocystis in biotechnological applications. Our study also demonstrates that the length of the period of exponential growth can be extended by a gradually stronger incident light intensity that matches the increase of the cell density of the culture.

  2. Assessment of antitumor activity for tumor xenograft studies using exponential growth models.

    PubMed

    Wu, Jianrong

    2011-05-01

    In preclinical tumor xenograft experiments, the antitumor activity of the tested agents is often assessed by endpoints such as tumor doubling time, tumor growth delay (TGD), and log10 cell kill (LCK). In tumor xenograft literature, the values of these endpoints are presented without any statistical inference, which ignores the noise in the experimental data. However, using exponential growth models, these endpoints can be quantified by their growth curve parameters, thus allowing parametric inference, such as an interval estimate, to be used to assess the antitumor activity of the treatment.

  3. Growth and dissolution kinetics of tetragonal lysozyme

    NASA Technical Reports Server (NTRS)

    Monaco, L. A.; Rosenberger, F.

    1993-01-01

    The growth and dissolution kinetics of lysozyme in a 25 ml solution bridge inside a closed growth cell was investigated. It was found that, under all growth conditions, the growth habit forming (110) and (101) faces grew through layer spreading with different growth rate dependence on supersaturation/temperature. On the other hand, (100) faces which formed only at low temperatures underwent a thermal roughening transition around 12 C.

  4. Effects of penconazole on two yeast strains: growth kinetics and molecular studies.

    PubMed

    Jawich, Dalal; Lteif, Roger; Pfohl-Leszkowicz, Annie; Strehaiano, Pierre

    2006-05-01

    The aim of this study consisted to evaluate the impact of a pesticide (penconazole) on the growth kinetics and genotoxicity on two yeast strains (Saccharomyces cerevisiae and Metschnikowia pulcherrima). When the penconazole was added at different phases of the growth of M. pulcherrima, no effect was noticed on the kinetics of yeast growth but DNA adducts were observed when penconazole was added in the exponential phase. Increasing doses (1-15 maximum residue limit) of the pesticide added at the beginning of the fermentation did not induce DNA adducts while kinetics were affected.

  5. 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.

  6. Exponential model describing methane production kinetics in batch anaerobic digestion: a tool for evaluation of biochemical methane potential assays.

    PubMed

    Brulé, Mathieu; Oechsner, Hans; Jungbluth, Thomas

    2014-09-01

    Biochemical methane potential assays, usually run in batch mode, are performed by numerous laboratories to characterize the anaerobic degradability of biogas substrates such as energy crops, agricultural residues, and organic wastes. Unfortunately, the data obtained from these assays lacks common, universal bases for comparison, because standard protocols did not diffuse to the entire scientific community. Results are usually provided as final values of the methane yields of substrates. However, methane production curves generated in these assays also provide useful information about substrate degradation kinetics, which is rarely exploited. A basic understanding of the kinetics of the biogas process may be a first step towards a convergence of the assay methodologies on an international level. Following this assumption, a modeling toolbox containing an exponential model adjusted with a simple data-fitting method has been developed. This model should allow (a) quality control of the assays according to the goodness of fit of the model onto data series generated from the digestion of standard substrates, (b) interpretation of substrate degradation kinetics, and (c) estimate of the ultimate methane yield at infinite time. The exponential model is based on two assumptions: (a) the biogas process is a two-step reaction yielding VFA as intermediate products, and methane as the final product, and (b) the digestible substrate can be divided into a rapidly degradable and a slowly degradable fraction.

  7. Cost of unneeded proteins in E. coli is reduced after several generations in exponential growth.

    PubMed

    Shachrai, Irit; Zaslaver, Alon; Alon, Uri; Dekel, Erez

    2010-06-11

    When E. coli cells express unneeded protein, they grow more slowly. Such penalty to fitness associated with making proteins is called protein cost. Protein cost is an important component in the cost-benefit tradeoffs that underlie the evolution of protein circuits, but its origins are still poorly understood. Here, we ask how the protein cost varies during the exponential growth phase of E. coli. We find that cells growing exponentially following an upshift from overnight culture show a large cost when producing unneeded proteins. However, after several generations, while still in exponential growth, the cells enter a phase where cost is much reduced despite vigorous unneeded protein production. We find that this reduced-cost phase depends on the ppGpp system, which adjusts the amount of ribosomes in the cell and does not occur after a downshift from rich to poor medium. These findings suggest that protein cost is a transient phenomenon that happens upon an upshift in conditions and that cost is reduced when ribosomes and other cellular systems have increased to their appropriate steady-state level in the new condition.

  8. 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

  9. 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.

  10. 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.

  11. Inference of Super-exponential Human Population Growth via Efficient Computation of the Site Frequency Spectrum for Generalized Models.

    PubMed

    Gao, Feng; Keinan, Alon

    2016-01-01

    The site frequency spectrum (SFS) and other genetic summary statistics are at the heart of many population genetic studies. Previous studies have shown that human populations have undergone a recent epoch of fast growth in effective population size. These studies assumed that growth is exponential, and the ensuing models leave an excess amount of extremely rare variants. This suggests that human populations might have experienced a recent growth with speed faster than exponential. Recent studies have introduced a generalized growth model where the growth speed can be faster or slower than exponential. However, only simulation approaches were available for obtaining summary statistics under such generalized models. In this study, we provide expressions to accurately and efficiently evaluate the SFS and other summary statistics under generalized models, which we further implement in a publicly available software. Investigating the power to infer deviation of growth from being exponential, we observed that adequate sample sizes facilitate accurate inference; e.g., a sample of 3000 individuals with the amount of data expected from exome sequencing allows observing and accurately estimating growth with speed deviating by ≥10% from that of exponential. Applying our inference framework to data from the NHLBI Exome Sequencing Project, we found that a model with a generalized growth epoch fits the observed SFS significantly better than the equivalent model with exponential growth (P-value [Formula: see text]). The estimated growth speed significantly deviates from exponential (P-value [Formula: see text]), with the best-fit estimate being of growth speed 12% faster than exponential.

  12. Ammonium Removal from Aqueous Solutions by Clinoptilolite: Determination of Isotherm and Thermodynamic Parameters and Comparison of Kinetics by the Double Exponential Model and Conventional Kinetic Models

    PubMed Central

    Tosun, İsmail

    2012-01-01

    The adsorption isotherm, the adsorption kinetics, and the thermodynamic parameters of ammonium removal from aqueous solution by using clinoptilolite in aqueous solution was investigated in this study. Experimental data obtained from batch equilibrium tests have been analyzed by four two-parameter (Freundlich, Langmuir, Tempkin and Dubinin-Radushkevich (D-R)) and four three-parameter (Redlich-Peterson (R-P), Sips, Toth and Khan) isotherm models. D-R and R-P isotherms were the models that best fitted to experimental data over the other two- and three-parameter models applied. The adsorption energy (E) from the D-R isotherm was found to be approximately 7 kJ/mol for the ammonium-clinoptilolite system, thereby indicating that ammonium is adsorbed on clinoptilolite by physisorption. Kinetic parameters were determined by analyzing the nth-order kinetic model, the modified second-order model and the double exponential model, and each model resulted in a coefficient of determination (R2) of above 0.989 with an average relative error lower than 5%. A Double Exponential Model (DEM) showed that the adsorption process develops in two stages as rapid and slow phase. Changes in standard free energy (∆G°), enthalpy (∆H°) and entropy (∆S°) of ammonium-clinoptilolite system were estimated by using the thermodynamic equilibrium coefficients. PMID:22690177

  13. Ammonium removal from aqueous solutions by clinoptilolite: determination of isotherm and thermodynamic parameters and comparison of kinetics by the double exponential model and conventional kinetic models.

    PubMed

    Tosun, Ismail

    2012-03-01

    The adsorption isotherm, the adsorption kinetics, and the thermodynamic parameters of ammonium removal from aqueous solution by using clinoptilolite in aqueous solution was investigated in this study. Experimental data obtained from batch equilibrium tests have been analyzed by four two-parameter (Freundlich, Langmuir, Tempkin and Dubinin-Radushkevich (D-R)) and four three-parameter (Redlich-Peterson (R-P), Sips, Toth and Khan) isotherm models. D-R and R-P isotherms were the models that best fitted to experimental data over the other two- and three-parameter models applied. The adsorption energy (E) from the D-R isotherm was found to be approximately 7 kJ/mol for the ammonium-clinoptilolite system, thereby indicating that ammonium is adsorbed on clinoptilolite by physisorption. Kinetic parameters were determined by analyzing the nth-order kinetic model, the modified second-order model and the double exponential model, and each model resulted in a coefficient of determination (R(2)) of above 0.989 with an average relative error lower than 5%. A Double Exponential Model (DEM) showed that the adsorption process develops in two stages as rapid and slow phase. Changes in standard free energy (∆G°), enthalpy (∆H°) and entropy (∆S°) of ammonium-clinoptilolite system were estimated by using the thermodynamic equilibrium coefficients.

  14. Physiological adaptation of growth kinetics in activated sludge.

    PubMed

    Friedrich, M; Takács, I; Tränckner, J

    2015-11-15

    Physiological adaptation as it occurs in bacterial cells at variable environmental conditions influences characteristic properties of growth kinetics significantly. However, physiological adaptation to growth related parameters in activated sludge modelling is not yet recognised. Consequently these parameters are regarded to be constant. To investigate physiological adaptation in activated sludge the endogenous respiration in an aerobic degradation batch experiment and simultaneous to that the maximum possible respiration in an aerobic growth batch experiment was measured. The activated sludge samples were taken from full scale wastewater treatment plants with different sludge retention times (SRTs). It could be shown that the low SRT sludge adapts by growth optimisation (high maximum growth rate and high decay rate) to its particular environment where a high SRT sludge adapts by survival optimization (low maximum growth rate and low decay rate). Thereby, both the maximum specific growth rate and the decay rate vary in the same pattern and are strongly correlated to each other. To describe the physiological state of mixed cultures like activated sludge quantitatively a physiological state factor (PSF) is proposed as the ratio of the maximum specific growth rate and the decay rate. The PSF can be expressed as an exponential function with respect to the SRT.

  15. Kinetics of microbial growth on pentachlorophenol.

    PubMed Central

    Klecka, G M; Maier, W J

    1985-01-01

    Batch and fed-batch experiments were conducted to examine the kinetics of pentachlorophenol utilization by an enrichment culture of pentachlorophenol-degrading bacteria. The Haldane modification of the Monod equation was found to describe the relationship between the specific growth rate and substrate concentration. Analysis of the kinetic parameters indicated that the maximum specific growth rate and yield coefficients are low, with values of 0.074 h-1 and 0.136 g/g, respectively. The Monod constant (Ks) was estimated to be 60 micrograms/liter, indicating a high affinity of the microorganisms for the substrate. However, high concentrations (KI = 1,375 micrograms/liter) were shown to be inhibitory for metabolism and growth. These kinetic parameters can be used to define the optimal conditions for the removal of pentachlorophenol in biological treatment systems. PMID:3977315

  16. Dynamic proteome changes of Shigella flexneri 2a during transition from exponential growth to stationary phase.

    PubMed

    Zhu, Li; Liu, Xian-Kai; Zhao, Ge; Zhi, Yi-Dan; Bu, Xin; Ying, Tian-Yi; Feng, Er-Ling; Wang, Jie; Zhang, Xue-Min; Huang, Pei-Tang; Wang, Heng-Liang

    2007-05-01

    Shigella flexneri is an infectious pathogen that causes dysentery to human, which remains a serious threat to public health, particularly in developing countries. In this study, the global protein expression patterns of S. flexneri during transition from exponential growth to stationary phase in vitro were analyzed by using 2-D PAGE combined with MALDI-TOF MS. In a time-course experiment with five time points, the relative abundance of 49 protein spots varied significantly. Interestingly, a putative outer membrane protein YciD (OmpW) was almost not detected in the exponential growth phase but became one of the most abundant proteins in the whole stationary-phase proteome. Some proteins regulated by the global regulator FNR were also significantly induced (such as AnsB, AspA, FrdAB, and KatG) or repressed (such as AceEF, OmpX, SodA, and SucAB) during the growth phase transition. These proteins may be the key effectors of the bacterial cell cycle or play important roles in the cellular maintenance and stress responses. Our expression profile data provide valuable information for the study of bacterial physiology and form the basis for future proteomic analyses of this pathogen.

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

    PubMed

    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.

  18. Postdiffusion of oligo-peptide within exponential growth multilayer films for localized peptide delivery.

    PubMed

    Wang, Xuefei; Ji, Jian

    2009-10-06

    The multilayers of poly(L-lysine) (PLL) and hyaluronic acid (HA) were constructed by alternating deposition of PLL at high pH and HA at low pH. The exponential growth of the multilayer was proved to be amplified by increasing the pH difference between the two deposition solutions. The exponential growth multilayers of PLL/HA assembled at different pH were utilized as reservoirs for loading a trans-activating transcriptional factor (TAT) peptide. The confocal laser scanning microscopy (CLSM) results indicated that the FITC-labeled TAT could diffuse throughout the exponentially growing PLL/HA film. The amount of peptide embedded within multilayer could be adjusted by both multilayer assembly pH and the TAT loading pH. Compared with (PLL/HA 6.5/6.5)5 multilayer (PLL/HA a/b means that the multilayer film was constructed by using PLL at pH a and HA at pH b), the (PLL/HA 9.5/2.9)5 film can be loaded with more TAT peptide at the same loading pH 6.5. The excess of positively charged TAT peptide within (PLL/HA 9.5/2.9)5 film could not only be ascribed to its extraordinary thickness but also be attributed to its uncompensated negative charge density enhanced by the pH difference between film buildup and peptide loading process. Increasing of the TAT loading pH from 6.5 to 9.5, which increases the pH difference between multilayer assembly and peptide loading process, enhances the uncompensated charge density within (PLL/HA 9.5/2.9)5 film and elevates the peptide density from 13.8 to 25.0 microg/cm2. Compared with direct layer-by-layer assembly of TAT and HA, the postdiffusion of TAT into (PLL/HA 9.5/2.9)5 film was loaded much more peptide. The postdiffusion of peptide into a rapid growth multilayer can be more favorable to load and sustainedly release functional oligo-peptide. The cell culture results indicated that the TAT embedded within the film maintained the ability to traverse across the Hep G2 cell membrane. The functionalized (PLL/HA 9.5/2.9)5 TAT 9.5 film was more

  19. Bioassays with unicellular algae: deviations from exponential growth and its implications for toxicity test results.

    PubMed

    Altenburger, Rolf; Schmitt-Jansen, Mechthild; Riedl, Janet

    2008-01-01

    Growth assays with unicellular green algae are an established tool in ecotoxicological effect assessment for chemicals and environmental samples. From an ecological perspective it seems appropriate to use the growth rate as a process variable rather than a measure of biomass gain for calculating inhibitory effects of contaminants. The notion of simple exponential growth for the description of the population increase in undisturbed suspension cultures of unicellular green algae, however, seems to be an oversimplification. Experimental findings describe the increase in biomass, cell number, the development of cell volume distributions of populations, and the relationship between cell size and chlorophyll content for individual cells over one generation at a time resolution of 2-h intervals. It was observed that algal populations of Desmodesmus subspicatus show a time pattern of cell size growth; the average cell volume increases about sixfold, without corresponding increase in population size. This is followed by a distinct cell division phase with little gain in biomass. This synchronous growth behavior despite continuous illumination may be explained by the multiple fission characteristic of unicellular green algae which is an adaptation to cyclic light-dark changes in the environment. It might be controlled by an independent cell cycle clock. For routine regulatory testing fluorescence-based measurements rather than cell counting minimizes the confounding effect on toxicity determination. For investigations of time-dependent effects, e.g., by pulsed exposure, an alternative mechanistically based growth function for unicellular algae is proposed that accommodates for the observed growth pattern.

  20. 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.

  1. [Chemo- and endocrino-therapy of breast carcinoma xenografts in the dormant or exponential growth phase].

    PubMed

    Takeuchi, T

    1995-06-01

    In case of concerning about recurrence case after operative treatment of breast cancer, we must suppose existence of dormant breast cancer cell. To elucidate a rational treatment of the breast cancer in the dormant stage, we have developed a new treatment model using human breast carcinoma xenografts (MCF-7, R-27 and Br-10) in nude mice. After the sc inoculation of the tumors, the treatment was initiated with or without the previous estradiol (E2) stimulation. While MCF-7 was sensitive to mitomycin C (6 mg/kg i.p.) and and tamoxifen pellet (2.5 mg/mouse s.c.) in the dormant and exponential growth phase, R-27 and Br-10 were sensitive to the drugs only in the exponential growth phase but not in the dormant stage. These results suggested that the sensitivity of human breast carcinoma cells in the dormant stage is rather low, however some strain would be also sensitive to the treatment. This model seems to be useful in evaluating the adjuvant therapy of breast carcinoma after surgery.

  2. Translational resistivity/conductivity of coding sequences during exponential growth of Escherichia coli.

    PubMed

    Takai, Kazuyuki

    2017-01-21

    Codon adaptation index (CAI) has been widely used for prediction of expression of recombinant genes in Escherichia coli and other organisms. However, CAI has no mechanistic basis that rationalizes its application to estimation of translational efficiency. Here, I propose a model based on which we could consider how codon usage is related to the level of expression during exponential growth of bacteria. In this model, translation of a gene is considered as an analog of electric current, and an analog of electric resistance corresponding to each gene is considered. "Translational resistance" is dependent on the steady-state concentration and the sequence of the mRNA species, and "translational resistivity" is dependent only on the mRNA sequence. The latter is the sum of two parts: one is the resistivity for the elongation reaction (coding sequence resistivity), and the other comes from all of the other steps of the decoding reaction. This electric circuit model clearly shows that some conditions should be met for codon composition of a coding sequence to correlate well with its expression level. On the other hand, I calculated relative frequency of each of the 61 sense codon triplets translated during exponential growth of E. coli from a proteomic dataset covering over 2600 proteins. A tentative method for estimating relative coding sequence resistivity based on the data is presented.

  3. Non-exponential growth of Mycobacterium leprae Thai-53 strain cultured in vitro.

    PubMed

    Amako, Kazunobu; Iida, Ken-Ichiro; Saito, Mitsumasa; Ogura, Yoshitoshi; Hayashi, Tetsuya; Yoshida, Shin-Ichi

    2016-12-01

    In this study, attempts were made to culture this bacterium in media supplemented with a variety of biological materials to determine why cultivation of Mycobacterium leprae in vitro has not this far been successful. A slight increase in the number of cells in medium supplemented with human blood plasma and an extract of nude mouse tissue as observed after more than 3 months of cultivation at 30 °C. To ascertain whether this increase was real growth, the growth was analyzed by droplet digital PCR, which showed a slow increase in the copy number of cell-associated DNA and the release of a large amount of DNA into the culture medium from bacterial cells during cultivation. These results were supported by electron microscopic examination of M. leprae in infected mouse tissues, which showed that most of the replicated bacteria had degenerated and only a few cells survived. Based on these results, it was postulated that many of the replicated cells degenerate during M. leprae growth and that only a few cells remain to participate in the next growth stage. This means that, unlike other cultivable bacteria, the growth of M. leprae is not exponential and the number of cells therefore increase extremely slowly. Thus, accurate judging of the success of M. leprae cultivation requires observation of growth over a long period of time and careful measurement of the increase in number of viable cells.

  4. Non‐exponential growth of Mycobacterium leprae Thai‐53 strain cultured in vitro

    PubMed Central

    Iida, Ken‐ichiro; Saito, Mitsumasa; Ogura, Yoshitoshi; Hayashi, Tetsuya; Yoshida, Shin‐ichi

    2017-01-01

    ABSTRACT In this study, attempts were made to culture this bacterium in media supplemented with a variety of biological materials to determine why cultivation of Mycobacterium leprae in vitro has not this far been successful. A slight increase in the number of cells in medium supplemented with human blood plasma and an extract of nude mouse tissue as observed after more than 3 months of cultivation at 30 °C. To ascertain whether this increase was real growth, the growth was analyzed by droplet digital PCR, which showed a slow increase in the copy number of cell‐associated DNA and the release of a large amount of DNA into the culture medium from bacterial cells during cultivation. These results were supported by electron microscopic examination of M. leprae in infected mouse tissues, which showed that most of the replicated bacteria had degenerated and only a few cells survived. Based on these results, it was postulated that many of the replicated cells degenerate during M. leprae growth and that only a few cells remain to participate in the next growth stage. This means that, unlike other cultivable bacteria, the growth of M. leprae is not exponential and the number of cells therefore increase extremely slowly. Thus, accurate judging of the success of M. leprae cultivation requires observation of growth over a long period of time and careful measurement of the increase in number of viable cells. PMID:27925336

  5. 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).

  6. Evidence of exponential growth of an anammox population in an anaerobic batch culture.

    PubMed

    Yasuda, Tomoko; Waki, Miyoko; Yoshinaga, Ikuo; Amano, Teruki; Suzuki, Kazuyoshi; Tanaka, Yasuo; Yamagishi, Takao; Suwa, Yuichi

    2011-01-01

    Twenty-five replicates of growth medium for anaerobic ammonium oxidation (anammox) containing (15)N-labeled ammonium and non-labeled nitrite were inoculated into an anammox enrichment culture at low density, and anaerobically incubated batchwise. In the headspace, (29)N(2) partial pressure linearly increased via anammox in 25 vials, confirming that anammox populations were viable in all subcultures. On prolonged incubation, exponential increases in (29)N(2) were not observed in all but 13 subcultures, suggesting that the anammox population may not proliferate unless all conditions for growth are satisfied. The estimated first-order rate coefficients in those 13 subcultures varied from 0.0029 to 0.0048 h(-1).

  7. 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...

  8. Modeling the pre-industrial roots of modern super-exponential population growth.

    PubMed

    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

  9. 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.

  10. Analysis of the lag phase to exponential growth transition by incorporating inoculum characteristics.

    PubMed

    Verhulst, A J; Cappuyns, A M; Van Derlinden, E; Bernaerts, K; Van Impe, J F

    2011-06-01

    During the last decade, individual-based modelling (IbM) has proven to be a valuable tool for modelling and studying microbial dynamics. As each individual is considered as an independent entity with its own characteristics, IbM enables the study of microbial dynamics and the inherent variability and heterogeneity. IbM simulations and (single-cell) experimental research form the basis to unravel individual cell characteristics underlying population dynamics. In this study, the IbM framework MICRODIMS, i.e., MICRObial Dynamics Individual-based Model/Simulator, is used to investigate the system dynamics (with respect to the model and the system modelled). First, the impact of the time resolution on the simulation accuracy is discussed. Second, the effect of the inoculum state and size on emerging individual dynamics, such as individual mass, individual age and individual generation time distribution dynamics, is studied. The distributions of individual characteristics are more informative during the lag phase and the transition to the exponential growth phase than during the exponential phase. The first generation time distributions are strongly influenced by the inoculum state. All inocula with a pronounced heterogeneity, except the inocula starting from a uniform distribution, exhibit commonly observed microbial behaviour, like a more spread first generation time distribution compared to following generations and a fast stabilisation of biomass and age distributions.

  11. Intensification of β-poly(L: -malic acid) production by Aureobasidium pullulans ipe-1 in the late exponential growth phase.

    PubMed

    Cao, Weifeng; Luo, Jianquan; Zhao, Juan; Qiao, Changsheng; Ding, Luhui; Qi, Benkun; Su, Yi; Wan, Yinhua

    2012-07-01

    β-Poly(malic acid) (PMLA) has attracted industrial interest because this polyester can be used as a prodrug or for drug delivery systems. In PMLA production by Aureobasidium pullulans ipe-1, it was found that PLMA production was associated with cell growth in the early exponential growth phase and dissociated from cell growth in the late exponential growth phase. To enhance PMLA production in the late phase, different fermentation modes and strategies for controlling culture redox potential (CRP) were studied. The results showed that high concentrations of produced PMLA (above 40 g/l) not only inhibited PMLA production, but also was detrimental to cell growth. Moreover, when CRP increased from 57 to 100 mV in the late exponential growth phase, the lack of reducing power in the broth also decreased PMLA productivity. PMLA productivity could be enhanced by repeated-batch culture to maintain cell growth in the exponential growth phase, or by cell-recycle culture with membrane to remove the produced PMLA, or by maintaining CRP below 70 mV no matter which kind of fermentation mode was adopted. Repeated-batch culture afforded a high PMLA concentration (up to 63.2 g/l) with a productivity of 1.15 g l(-1) h(-1). Cell-recycle culture also confirmed that PMLA production by the strain ipe-1 was associated with cell growth.

  12. Development of a chemically defined minimal medium for the exponential growth of Leuconostoc mesenteroides ATCC8293.

    PubMed

    Kim, Yu Jin; Eom, Hyun-Ju; Seo, Eun-Young; Lee, Dong Yup; Kim, Jeong Hwan; Han, Nam Soo

    2012-11-01

    Leuconostoc mesenteroides is a heterofermentative Grampositive bacterium that plays key roles in fermentation of foods such as kimchi, sauerkraut, and milk, leading to the production of various organic acids and aromatic compounds. To study the microbiological and genomic characteristics of L. mesenteroides, we have developed a new chemically defined minimal medium by using the single omission technique. During the exponential cell growth, this species required glutamine, methionine, valine, and nicotinic acid as essential nutrients and 8 amino acids (arginine, cysteine, histidine, leucine, phenylalanine, proline, threonine, and tryptophan), 5 vitamins (ascorbic acid, folic acid, inosine, calcium panthothenate, and thiamine), and others (manganese, magnesium, adenine, uracil, and Tween 80) as supplemental nutrients. This medium is useful to study the metabolic characteristics of L. mesenteroides and to explain its role in food fermentation.

  13. 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

  14. Dependence of morphometric allometries on the growth kinetics of body parts.

    PubMed

    Nijhout, H Frederik

    2011-11-07

    As overall size varies, the sizes of body parts of many animals often appear to be related to each other by a power law, commonly called the allometric equation. Orderly scaling relationships among body parts are widespread in the animal world, but there is no general agreement about how these relationships come about. Presumably they depend on the patterns of growth of body parts, and simple analyses have shown that exponential growth can lead to size relationships that are well-described by the allometric equation. Exponential growth kinetics also allow for a simple biological interpretation of the coefficients of the power relationship. Nevertheless, many tissues do not grow with exponential kinetics, nor do they grow for the same period of time, and the consequences of more realistic growth patterns on the resulting allometric relationships of body parts are not well understood. In this paper I derive a set of allometric equations that assume different kinetics of growth: linear, exponential and sigmoidal. In these derivations I also include differences in development times as a variable, in addition to differences in the growth rates and initial sizes of the two structures whose allometric relationship is compared. I show how these equations can be used to deduce the effect of different causes of variation in absolute size on the resulting allometry. Variation in size can be due to variation in the duration of development, variation in growth rate or variation in initial size. I show that the meaning of the coefficients of the allometric equation depends on exactly how size variation comes about. I show that if two structures are assumed to grow with sigmoidal kinetics (logistic and Gompertz) the resulting allometric equations do not have a simple and intuitive structure and produce graphs that, over a sufficiently large range of sizes, can vary from linear, to sigmoidal to hump-shaped. Over a smaller range of absolute sizes, these sigmoid growth kinetics can

  15. [Natural history of non specific neuralgias of the limbs. Exponential kinetics of the root pain recovery in sciatica and femoral neuralgia; uncertain kinetics for brachial neuralgia].

    PubMed

    Paolaggi, Jean-Baptiste

    2003-01-01

    Very few studies are dedicated to the natural history of sciatica, and none to femoral neuralgia or brachial neuralgia natural course. Hence, the results of a collection of five studies on these topics appear worth being published. A rheumatology department. The first study was a retrospective comparison of sciatica (145 patients) and femoral neuralgia (63 patients). The second study was a retrospective study concerning 107 patients with sciatica observed in a second different period. A third and a fourth retrospective studies were carried out on 38 femoral neuralgia and 69 brachial neuralgia patients. The fifth study was a prospective cohort study on patients with sciatica. As there are no diagnosis criteria for non specific neuralgias, the diagnosis was based on seniors' opinion. Neuralgia due to specific causes were carefully excluded. As there are no relevant outcomes measures specially dedicated to idiopathic acute root pain, the full recovery of root pain was used as endpoint. The kinetics of sciatica and of femoral neuralgia recoveries are related Plotted as neuralgia survival sciatica as well as femoral neuralgia exhibited a decreasing, exponential kinetics curve. Half sciatica disappear each 6 to 7 weeks. Half femoral neuralgia disappear each 5 to 6 weeks. The brachial neuralgia survival exhibited a more complex kinetics. These pilot studies, do not allow definitive conclusions. Nevertheless, given the scarcity of available data, they may be used as a factual basis for perfectly designed prospective inception cohort studies.

  16. Growth and nitrogen acquisition strategies of Acacia senegal seedlings under exponential phosphorus additions.

    PubMed

    Isaac, M E; Harmand, J M; Drevon, J J

    2011-05-15

    There remains conflicting evidence on the relationship between P supply and biological N(2)-fixation rates, particularly N(2)-fixing plant adaptive strategies under P limitation. This is important, as edaphic conditions inherent to many economically and ecologically important semi-arid leguminous tree species, such as Acacia senegal, are P deficient. Our research objective was to verify N acquisition strategies under phosphorus limitations using isotopic techniques. Acacia senegal var. senegal was cultivated in sand culture with three levels of exponentially supplied phosphorus [low (200 μmol of P seedling(-1) over 12 weeks), mid (400 μmol) and high (600 μmol)] to achieve steady-state nutrition over the growth period. Uniform additions of N were also supplied. Plant growth and nutrition were evaluated. Seedlings exhibited significantly greater total biomass under high P supply compared to low P supply. Both P and N content significantly increased with increasing P supply. Similarly, N derived from solution increased with elevated P availability. However, both the number of nodules and the N derived from atmosphere, determined by the (15)N natural abundance method, did not increase along the P gradient. Phosphorus stimulated growth and increased mineral N uptake from solution without affecting the amount of N derived from the atmosphere. We conclude that, under non-limiting N conditions, A. senegal N acquisition strategies change with P supply, with less reliance on N(2)-fixation when the rhizosphere achieves a sufficient N uptake zone.

  17. 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.

  18. 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.

  19. Multiple factors underlying the maximum motility of Escherichia coli as cultures enter post-exponential growth.

    PubMed Central

    Amsler, C D; Cho, M; Matsumura, P

    1993-01-01

    Motility and chemotaxis allow cells to move away from stressful microenvironments. Motility of Escherichia coli in batch cultures, as measured by cell swimming speed, was low in early-exponential-phase cells, peaked as the cells entered post-exponential phase, and declined into early stationary phase. Transcription from the flhB operon and synthesis of flagellin protein similarly peaked in late exponential and early post-exponential phases, respectively. The increase in swimming speed between early-exponential and post-exponential phases was correlated with twofold increases in both flagellar length and flagellar density per cell volume. This increased investment in flagella probably reflects the increased adaptive value of motility in less favorable environments. The decrease in speed between post-exponential and stationary phases was correlated with a threefold decrease in torque produced by the flagellar motors and presumably reflects decreased proton motive force available to stationary-phase cells. Images PMID:8407796

  20. 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.

  1. 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.

  2. Growth morphology with anisotropic surface kinetics

    NASA Technical Reports Server (NTRS)

    Xiao, Rong-Fu; Alexander, J. Iwan D.; Rosenberger, Franz

    1990-01-01

    The morphological evolution of crystals growing from an incongruent vapor phase is studied using a Monte Carlo model, and the full range of growth morphologies is recovered. The diffusion in the bulk nutrient and the anisotropy in the interface kinetics are morphologically destabilizing and stabilizing, respectively. For a given set of simulation parameters and lattice symmetries there is a critical size, which scales linearly with the mean free path in the vapor, beyond which a crystal cannot retain its stable, macroscopically faceted growth shape. Surface diffusion stabilizes faceted growth on the shorter scale of the mean surface diffusion length. In simulations with a uniform drift superimposed on the random walk nutrient transport, crystal faces oriented toward the drift show enhanced morphological stability compared to the purely diffusive situation. Rotational drifts with periodic reversal of direction are morphologically stabilizing for all crystal facets.

  3. Polyamine metabolism during exponential growth transition in Scots pine embryogenic cell culture.

    PubMed

    Vuosku, Jaana; Suorsa, Marja; Ruottinen, Maria; Sutela, Suvi; Muilu-Mäkelä, Riina; Julkunen-Tiitto, Riitta; Sarjala, Tytti; Neubauer, Peter; Häggman, Hely

    2012-10-01

    Polyamine (PA) metabolism was studied in liquid cultures of Scots pine (Pinus sylvestris L.) embryogenic cells. The focus of the study was on the metabolic changes at the interphase between the initial lag phase and the exponential growth phase. PA concentrations fluctuated in the liquid cultures as follows. Putrescine (Put) concentrations increased, whereas spermidine (Spd) concentrations decreased in both free and soluble conjugated PA fractions. The concentrations of free and soluble conjugated spermine (Spm) remained low, and small amounts of excreted PAs were also found in the culture medium. The minor production of secondary metabolites reflected the undifferentiated stage of the embryogenic cell culture. Put was produced via the arginine decarboxylase (ADC) pathway. Futhermore, the gene expression data suggested that the accumulation of Put was caused neither by an increase in Put biosynthesis nor by a decrease in Put catabolism, but resulted mainly from the decrease in the biosynthesis of Spd and Spm. Put seemed to play an important role in cell proliferation in Scots pine embryogenic cells, but the low pH of the culture medium could also, at least partially, be the reason for the accumulation of endogenous Put. High Spd concentrations at the initiation of the culture, when cells were exposed to stress and cell death, suggested that Spd may act not only as a protector against stress but also as a growth suppressor, when proliferative growth is not promoted. All in all, Scots pine embryogenic cell culture was proved to be a favourable experimental platform to study PA metabolism and, furthermore, the developed system may also be beneficial in experiments where, e.g., the effect of specific stressors on PA metabolism is addressed.

  4. 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…

  5. Metabolic flux analysis during the exponential growth phase of Saccharomyces cerevisiae in wine fermentations.

    PubMed

    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.

  6. 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

  7. 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

  8. Shewanella oneidensis Hfq promotes exponential phase growth, stationary phase culture density, and cell survival

    PubMed Central

    2013-01-01

    Background Hfq is an RNA chaperone protein that has been broadly implicated in sRNA function in bacteria. Here we describe the construction and characterization of a null allele of the gene that encodes the RNA chaperone Hfq in Shewanella oneidensis strain MR-1, a dissimilatory metal reducing bacterium. Results Loss of hfq in S. oneidensis results in a variety of mutant phenotypes, all of which are fully complemented by addition of a plasmid-borne copy of the wild type hfq gene. Aerobic cultures of the hfq∆ mutant grow more slowly through exponential phase than wild type cultures, and hfq∆ cultures reach a terminal cell density in stationary phase that is ~2/3 of that observed in wild type cultures. We have observed a similar growth phenotype when the hfq∆ mutant is cultured under anaerobic conditions with fumarate as the terminal electron acceptor, and we have found that the hfq∆ mutant is defective in Cr(VI) reduction. Finally, the hfq∆ mutant exhibits a striking loss of colony forming units in extended stationary phase and is highly sensitive to oxidative stress induced by H2O2 or methyl viologen (paraquat). Conclusions The hfq mutant in S. oneidensis exhibits pleiotropic phenotypes, including a defect in metal reduction. Our results also suggest that hfq mutant phenotypes in S. oneidensis may be at least partially due to increased sensitivity to oxidative stress. PMID:23394078

  9. 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.

  10. 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.

  11. 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.

  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. On new non-modal hydrodynamic stability modes and resulting non-exponential growth rates - a Lie symmetry approach

    NASA Astrophysics Data System (ADS)

    Oberlack, Martin; Nold, Andreas; Sanjon, Cedric Wilfried; Wang, Yongqi; Hau, Jan

    2016-11-01

    Classical hydrodynamic stability theory for laminar shear flows, no matter if considering long-term stability or transient growth, is based on the normal-mode ansatz, or, in other words, on an exponential function in space (stream-wise direction) and time. Recently, it became clear that the normal mode ansatz and the resulting Orr-Sommerfeld equation is based on essentially three fundamental symmetries of the linearized Euler and Navier-Stokes equations: translation in space and time and scaling of the dependent variable. Further, Kelvin-mode of linear shear flows seemed to be an exception in this context as it admits a fourth symmetry resulting in the classical Kelvin mode which is rather different from normal-mode. However, very recently it was discovered that most of the classical canonical shear flows such as linear shear, Couette, plane and round Poiseuille, Taylor-Couette, Lamb-Ossen vortex or asymptotic suction boundary layer admit more symmetries. This, in turn, led to new problem specific non-modal ansatz functions. In contrast to the exponential growth rate in time of the modal-ansatz, the new non-modal ansatz functions usually lead to an algebraic growth or decay rate, while for the asymptotic suction boundary layer a double-exponential growth or decay is observed.

  14. Modeling the lag period and exponential growth of Listeria monocytogenes under conditions of fluctuating temperature and water activity values.

    PubMed

    Muñoz-Cuevas, Marina; Fernández, Pablo S; George, Susan; Pin, Carmen

    2010-05-01

    The dynamic model for the growth of a bacterial population described by Baranyi and Roberts (J. Baranyi and T. A. Roberts, Int. J. Food Microbiol. 23:277-294, 1994) was applied to model the lag period and exponential growth of Listeria monocytogenes under conditions of fluctuating temperature and water activity (a(w)) values. To model the duration of the lag phase, the dependence of the parameter h(0), which quantifies the amount of work done during the lag period, on the previous and current environmental conditions was determined experimentally. This parameter depended not only on the magnitude of the change between the previous and current environmental conditions but also on the current growth conditions. In an exponentially growing population, any change in the environment requiring a certain amount of work to adapt to the new conditions initiated a lag period that lasted until that work was finished. Observations for several scenarios in which exponential growth was halted by a sudden change in the temperature and/or a(w) were in good agreement with predictions. When a population already in a lag period was subjected to environmental fluctuations, the system was reset with a new lag phase. The work to be done during the new lag phase was estimated to be the workload due to the environmental change plus the unfinished workload from the uncompleted previous lag phase.

  15. Staphylococcus aureus aconitase inactivation unexpectedly inhibits post-exponential-phase growth and enhances stationary-phase survival.

    PubMed

    Somerville, Greg A; Chaussee, Michael S; Morgan, Carrie I; Fitzgerald, J Ross; Dorward, David W; Reitzer, Lawrence J; Musser, James M

    2002-11-01

    Staphylococcus aureus preferentially catabolizes glucose, generating pyruvate, which is subsequently oxidized to acetate under aerobic growth conditions. Catabolite repression of the tricarboxylic acid (TCA) cycle results in the accumulation of acetate. TCA cycle derepression coincides with exit from the exponential growth phase, the onset of acetate catabolism, and the maximal expression of secreted virulence factors. These data suggest that carbon and energy for post-exponential-phase growth and virulence factor production are derived from the catabolism of acetate mediated by the TCA cycle. To test this hypothesis, the aconitase gene was genetically inactivated in a human isolate of S. aureus, and the effects on physiology, morphology, virulence factor production, virulence for mice, and stationary-phase survival were examined. TCA cycle inactivation prevented the post-exponential growth phase catabolism of acetate, resulting in premature entry into the stationary phase. This phenotype was accompanied by a significant reduction in the production of several virulence factors and alteration in host-pathogen interaction. Unexpectedly, aconitase inactivation enhanced stationary-phase survival relative to the wild-type strain. Aconitase is an iron-sulfur cluster-containing enzyme that is highly susceptible to oxidative inactivation. We speculate that reversible loss of the iron-sulfur cluster in wild-type organisms is a survival strategy used to circumvent oxidative stress induced during host-pathogen interactions. Taken together, these data demonstrate the importance of the TCA cycle in the life cycle of this medically important pathogen.

  16. Modeling the Lag Period and Exponential Growth of Listeria monocytogenes under Conditions of Fluctuating Temperature and Water Activity Values▿

    PubMed Central

    Muñoz-Cuevas, Marina; Fernández, Pablo S.; George, Susan; Pin, Carmen

    2010-01-01

    The dynamic model for the growth of a bacterial population described by Baranyi and Roberts (J. Baranyi and T. A. Roberts, Int. J. Food Microbiol. 23:277-294, 1994) was applied to model the lag period and exponential growth of Listeria monocytogenes under conditions of fluctuating temperature and water activity (aw) values. To model the duration of the lag phase, the dependence of the parameter h0, which quantifies the amount of work done during the lag period, on the previous and current environmental conditions was determined experimentally. This parameter depended not only on the magnitude of the change between the previous and current environmental conditions but also on the current growth conditions. In an exponentially growing population, any change in the environment requiring a certain amount of work to adapt to the new conditions initiated a lag period that lasted until that work was finished. Observations for several scenarios in which exponential growth was halted by a sudden change in the temperature and/or aw were in good agreement with predictions. When a population already in a lag period was subjected to environmental fluctuations, the system was reset with a new lag phase. The work to be done during the new lag phase was estimated to be the workload due to the environmental change plus the unfinished workload from the uncompleted previous lag phase. PMID:20208022

  17. 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…

  18. RpoS regulation of gene expression during exponential growth of Escherichia coli K12.

    PubMed

    Dong, Tao; Kirchhof, Mark G; Schellhorn, Herb E

    2008-03-01

    RpoS is a major regulator of genes required for adaptation to stationary phase in E. coli. However, the exponential phase expression of some genes is affected by rpoS mutation, suggesting RpoS may also have an important physiological role in growing cells. To test this hypothesis, we examined the regulatory role of RpoS in exponential phase using both genomic and biochemical approaches. Microarray expression data revealed that, in the rpoS mutant, the expression of 268 genes was attenuated while the expression of 24 genes was enhanced. Genes responsible for carbon source transport (the mal operon for maltose), protein folding (dnaK and mopAB), and iron acquisition (fepBD, entCBA, fecI, and exbBD) were positively controlled by RpoS. The importance of RpoS-mediated control of iron acquisition was confirmed by cellular metal analysis which revealed that the intracellular iron content of wild type cells was two-fold higher than in rpoS mutant cells. Surprisingly, many previously identified RpoS stationary-phase dependent genes were not controlled by RpoS in exponential phase and several genes were RpoS-regulated only in exponential phase, suggesting the involvement of other regulators. The expression of RpoS-dependent genes osmY, tnaA and malK was controlled by Crl, a transcriptional regulator that modulates RpoS activity. In summary, the identification of a group of exponential phase genes controlled by RpoS reveals a novel aspect of RpoS function.

  19. [Activation of the expression of the microcin C51 operon upon glucose starvation of cells at the exponential growth phase].

    PubMed

    Veselovskiĭ, A M; Metlitskaia, A Z; Lipasova, V A; Bass, I A; Khmel', I A

    2005-01-01

    It was earlier shown that expression of the microcin C51 operon in Escherichia coli cells is activated upon decelerated growth of cells during their transition to the stationary growth phase and depends on the sigmaS subunit of RNA polymerase. Using a single-copy construct containing the cloned promoter region of the microcin C51 operon and a promoterless lac operon (P(mcc)-lac), it was shown that the promoter of the microcin operon was also induced by stress caused by the transition of cells at the exponential growth phase into the medium without glucose as a sole carbon source. Activation of P(mcc)-lac expression upon severe glucose starvation occurred in rpoS+ and rpoS- strains. In cells carrying the rpoD800 mutation that renders the sigma70 subunit of RNA polymerase temperature-sensitive, an activation of P(mcc)-lac expression was observed at nonpermissive temperature, in contrast to its complete inhibition in E. coli cells at the phase of delayed growth. Other stressors-nitrogen starvation, high temperatures, osmotic shock, tetracycline and chloramphenicol-did not activate P(mcc)-lac expression in cells at the exponential growth phase.

  20. Antioxidant defence system during exponential and stationary growth phases of Phycomyces blakesleeanus: response to oxidative stress by hydrogen peroxide.

    PubMed

    de Castro, Cristina; del Valle, Pilar; Rúa, Javier; García-Armesto, María Rosario; Gutiérrez-Larraínzar, Marta; Busto, Félix; de Arriaga, Dolores

    2013-04-01

    An analysis of the components of the antioxidant defence system in exponential and stationary growth phases of filamentous fungus Phycomyces blakesleeanus and the response to the oxidative stress hydrogen peroxide were performed. There is a strong positive correlation between mycelial antioxidant capacity and the contents of gallic acid, d-erythroascorbate (d-EAA) or d-erythroascorbate monoglucoside (d-EAAG). These secondary metabolites are specifically synthesized by this fungus and reach maximal values in the stationary growth phase, suggesting that they can play some role in the antioxidant defence system of this fungus. There is a differential expression of the two more notable antioxidant activities, catalase (CAT) and superoxide dismutase (SOD), depending of the growth stage of P. blakesleeanus, CAT being expressed in the exponential and SOD in the stationary phase. Phycomyces blakesleeanus showed a high resistance to the oxidative stress caused by H2O2 (50 and 200 mM) which was higher in exponential phase. This higher resistance can be explained by the presence of CAT, glutathione peroxidase (GPx), and the probable contribution of glutathione-S-transferase (GST) and high levels of reduced form of glutathione (GSH). The transition to stationary phase was accompanied with a higher physiological oxidative damage illustrated by the higher protein carbonylation. In this growth stage the resistance of the fungus to the oxidative stress caused by H2O2 could be explained by the presence of SOD, GPx, and the probable contribution of GST as well as of secondary metabolites, mainly d-EAA and d-EAAG. These results highlight a specific response to oxidative stress by H2O2 depending on the growth phase of P. blakesleeanus.

  1. 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.

  2. On the origin of stretched exponential (Kohlrausch) relaxation kinetics in the room temperature luminescence decay of colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Bodunov, E. N.; Antonov, Yu. A.; Simões Gamboa, A. L.

    2017-03-01

    The non-exponential room temperature luminescence decay of colloidal quantum dots is often well described by a stretched exponential function. However, the physical meaning of the parameters of the function is not clear in the majority of cases reported in the literature. In this work, the room temperature stretched exponential luminescence decay of colloidal quantum dots is investigated theoretically in an attempt to identify the underlying physical mechanisms associated with the parameters of the function. Three classes of non-radiative transition processes between the excited and ground states of colloidal quantum dots are discussed: long-range resonance energy transfer, multiphonon relaxation, and contact quenching without diffusion. It is shown that multiphonon relaxation cannot explain a stretched exponential functional form of the luminescence decay while such dynamics of relaxation can be understood in terms of long-range resonance energy transfer to acceptors (molecules, quantum dots, or anharmonic molecular vibrations) in the environment of the quantum dots acting as energy-donors or by contact quenching by acceptors (surface traps or molecules) distributed statistically on the surface of the quantum dots. These non-radiative transition processes are assigned to different ranges of the stretching parameter β.

  3. On the origin of stretched exponential (Kohlrausch) relaxation kinetics in the room temperature luminescence decay of colloidal quantum dots.

    PubMed

    Bodunov, E N; Antonov, Yu A; Simões Gamboa, A L

    2017-03-21

    The non-exponential room temperature luminescence decay of colloidal quantum dots is often well described by a stretched exponential function. However, the physical meaning of the parameters of the function is not clear in the majority of cases reported in the literature. In this work, the room temperature stretched exponential luminescence decay of colloidal quantum dots is investigated theoretically in an attempt to identify the underlying physical mechanisms associated with the parameters of the function. Three classes of non-radiative transition processes between the excited and ground states of colloidal quantum dots are discussed: long-range resonance energy transfer, multiphonon relaxation, and contact quenching without diffusion. It is shown that multiphonon relaxation cannot explain a stretched exponential functional form of the luminescence decay while such dynamics of relaxation can be understood in terms of long-range resonance energy transfer to acceptors (molecules, quantum dots, or anharmonic molecular vibrations) in the environment of the quantum dots acting as energy-donors or by contact quenching by acceptors (surface traps or molecules) distributed statistically on the surface of the quantum dots. These non-radiative transition processes are assigned to different ranges of the stretching parameter β.

  4. Multiple semiclassical states for coupled Schrödinger-Poisson equations with critical exponential growth

    NASA Astrophysics Data System (ADS)

    Liu, Zhisu; Guo, Shangjiang; Fang, Yanqin

    2015-04-01

    In this paper, we study the multiplicity of positive solutions for a class of Schrödinger-Poisson systems. Working in a variational setting, we prove the existence and multiplicity of positive solutions for the system when the Plank's constant is small and the potential satisfies some suitable conditions. We show that the number of positive solutions depends on the profile of the potential and that each solution concentrates around its corresponding global minimum point of the potential in the semi-classical limit. We also study the exponential decay.

  5. The exponential growth of autophagy-related research: from the humble yeast to the Nobel Prize.

    PubMed

    Mizushima, Noboru

    2017-03-01

    Autophagy was discovered more than half a century ago. In the early days, autophagy was studied mostly through the use of biochemical methods and electron microscopy. In the 1990s, yeast genetics was introduced to this field and brought about an exponential expansion. The 2016 Nobel Prize in Physiology or Medicine was eventually awarded to the scientist who spearheaded the rapid development of the field: Yoshinori Ohsumi. Here, I describe in a Nutshell how the autophagy machinery was discovered and how the autophagy research field has grown following the breakthroughs from yeast studies.

  6. 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.

  7. Thermal transitions in dry and hydrated layer-by-layer assemblies exhibiting linear and exponential growth.

    PubMed

    Vidyasagar, Ajay; Sung, Choonghyun; Gamble, Randall; Lutkenhaus, Jodie L

    2012-07-24

    Layer-by-layer (LbL) assemblies are remarkable materials, known for their tunable mechanical, optical, and surface properties in nanoscale films. However, questions related to their thermal properties still remain unclear. Here, the thermal properties of a model LbL assembly of strong polyelectrolytes, poly(diallyldimethylammonium chloride)/poly(styrene sulfonate) (PDAC/PSS), assembled from solutions of varying ionic strength (0-1.25 M NaCl) are investigated using quartz crystal microbalance with dissipation (QCM-D) and modulated differential scanning calorimetry. Hydrated exponentially growing films (assembled from 0.25 to 1.25 M NaCl) exhibited distinct thermal transitions akin to a glass transition at 49-56 °C; linearly growing films (assembled without added salt) did not exhibit a transition in the temperature range investigated and were glassy. Results support the idea that exponentially growing films have greater segmental mobility than that of linearly growing films. On the other hand, all dry LbL assemblies investigated were glassy at room temperature and did not exhibit a T(g) up to 250 °C, independent of ionic strength. For the first time, thermal transitions such as T(g) values can be measured for LbL assemblies using QCM-D by monitoring fluctuations in changes in dissipation, allowing us to probe the film's internal structure as a function of film depth.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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.

  9. 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.

  10. Modeling growth kinetics and statistical distribution of oligometastases.

    PubMed

    Withers, H Rodney; Lee, Steve P

    2006-04-01

    The kinetics of development of micrometastases, and especially of small numbers of metastases (oligometastases), was explored by using simple assumptions to develop concepts that may be useful for framing future research. The conclusions depend on the assumptions and hence must be considered speculative. It is assumed that beyond a threshold size for initiation of metastatic spread, which varies widely from tumor to tumor, the rate at which a primary tumor sheds new metastases increases exponentially, in parallel with its exponential growth. This increasing rate of release of new metastatic clonogens from the primary tumor is accompanied by a similar exponential growth of each of the micrometastases newly established at a secondary site. This creates a log-log linear relationship between the volume distribution of metastases and number of metastases, there being one largest metastasis followed by an exponentially expanding number of logarithmically smaller micrometastases. For example, if the micrometastases and the primary tumor grew at the same rate for 6 doublings after initiation of the first metastasis, then the primary tumor would have increased its volume by a factor of 64 (2(6)) and would be shedding metastatic clonogens at 64 times the initial rate. The first metastasis would undergo 6 doublings and contain 64 cells; the succeeding 2 metastases, released as the primary doubled in volume, would undergo 5 doublings and each would contain 32 cells; and so forth down to the 64 most recently developed single-cell metastases. However, the growth rate of metastases is expected to be faster than that of the primary tumor so that the rate of increase in volume of the micrometastases would be faster than the rate of increase in their numbers (through release of new metastases from the primary). Thus, although the log-log linear relationship is maintained, the slope of the volume frequency curve is changed; if the micrometastases grew 5 times faster than the primary

  11. Growth kinetics of Listeria monocytogenes and spoilage microorganisms in fresh-cut cantaloupe.

    PubMed

    Fang, Ting; Liu, Yanhong; Huang, Lihan

    2013-05-01

    The main objective of this study was to investigate the growth kinetics of Listeria monocytogenes and background microorganisms in fresh-cut cantaloupe. Fresh-cut cantaloupe samples, inoculated with three main serotypes (1/2a, 1/2b, and 4b) of L. monocytogenes, were incubated at different temperatures, ranging from 4 to 43 °C, to develop kinetic growth models. During storage studies, the population of both background microorganisms and L. monocytogenes began to increase almost immediately, with little or no lag phase for most growth curves. All growth curves, except for two growth curves of L. monocytogenes 1/2a at 4 °C, developed to full curves (containing exponential and stationary phases), and can be described by a 3-parameter logistic model. There was no significant difference (P = 0.28) in the growth behaviors and the specific growth rates of three different serotypes of L. monocytogenes inoculated to fresh-cut cantaloupe. The effect of temperature on the growth of L. monocytogenes and spoilage microorganisms was evaluated using three secondary models. For L. monocytogenes, the minimum and maximum growth temperatures were estimated by both the Ratkowsky square-root and Cardinal parameter models, and the optimum temperature and the optimum specific growth rate by the Cardinal parameter model. An Arrhenius-type model provided more accurate estimation of the specific growth rate of L. monocytogenes at temperatures <4 °C. The kinetic models developed in this study can be used by regulatory agencies and food processors for conducting risk assessment of L. monocytogenes in fresh-cut cantaloupe, and for estimating the shelf-life of fresh-cut products.

  12. Early sub-exponential epidemic growth: Simple models, nonlinear incidence rates, and additional mechanisms. Reply to comments on "Mathematical models to characterize early epidemic growth: A review"

    NASA Astrophysics Data System (ADS)

    Chowell, Gerardo; Sattenspiel, Lisa; Bansal, Shweta; Viboud, Cécile

    2016-09-01

    We would like to thank all of the commentators for their insightful and positive reactions to our review paper [1]. Their comments touch on both theoretical and applied aspects of sub-exponential growth dynamics and the mechanisms that generate them, and have greatly enhanced and broadened the discussion. Here we aim to further discuss key points raised by Brauer [2], Danon and Brooks-Pollock [3], Allen [4], Merler [5], Champredon and Earn [6], and House [7].

  13. 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.

  14. 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...

  15. Understanding Linear and Exponential Growth: Searching for the Roots in 6- To 9-Year-Olds

    ERIC Educational Resources Information Center

    Ebersbach, Mirjam; Van Dooren, Wim; Van den Noortgate, Wim; Resing, Wilma C. M.

    2008-01-01

    Previous studies have suggested that children as young as 9 years old have developed an understanding of non-linear growth processes prior to formal education. The present experiment aimed at investigating this competency in even younger samples (i.e., in kindergartners, first, and third graders, ages 6, 7 and 9, respectively). Children (N=90)…

  16. 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...

  17. The Growth Kinetics of Salmonella Enteritidis in Raw Ground Beef.

    PubMed

    Sabike, Islam I; Fujikawa, Hiroshi; Edris, Abobakr M

    2015-01-01

    The growth kinetics of Salmonella Enteritidis in raw beef has been little studied so far. Thus, this study aimed to clarify the growth kinetics of the pathogen in ground beef using a growth model. When Salmonella cells inoculated at various initial doses into ground beef were incubated at a given temperature (24℃), the maximum population (Nmax) of the microbe at the stationary phase varied with the doses. This relationship was expressed with a polynomialequation for Nmax using the initial dose. The combination of the growth model and the polynomial equation successfully predicted Salmonella growth at a given initial dose. When Salmonella cells inoculated in ground beef were incubated at various constant temperatures, the growth curves of the pathogen and natural microflora (NM) were well described with the growth model. The rate constant of growth and the Nmax values for Salmonella and NM were then analyzed kinetically. From these results, growth curves of Salmonella and NM in ground beef stored at dynamic temperatures were successfully predicted. Competition between Salmonella and NM in ground beef was also found during the storage. This study could give usable information on the growth of Salmonella and NM in ground beef at various temperatures.

  18. The Oenococcus oeni clpX Homologue Is a Heat Shock Gene Preferentially Expressed in Exponential Growth Phase

    PubMed Central

    Jobin, Michel-Philippe; Garmyn, Dominique; Diviès, Charles; Guzzo, Jean

    1999-01-01

    Using degenerated primers from conserved regions of previously studied clpX gene products, we cloned the clpX gene of the malolactic bacterium Oenococcus oeni. The clpX gene was sequenced, and the deduced protein of 413 amino acids (predicted molecular mass of 45,650 Da) was highly similar to previously analyzed clpX gene products from other organisms. An open reading frame located upstream of the clpX gene was identified as the tig gene by similarity of its predicted product to other bacterial trigger factors. ClpX was purified by using a maltose binding protein fusion system and was shown to possess an ATPase activity. Northern analyses indicated the presence of two independent 1.6-kb monocistronic clpX and tig mRNAs and also showed an increase in clpX mRNA amount after a temperature shift from 30 to 42°C. The clpX transcript is abundant in the early exponential growth phase and progressively declines to undetectable levels in the stationary phase. Thus, unlike hsp18, the gene encoding one of the major small heat shock proteins of Oenococcus oeni, clpX expression is related to the exponential growth phase and requires de novo protein synthesis. Primer extension analysis identified the 5′ end of clpX mRNA which is located 408 nucleotides upstream of a putative AUA start codon. The putative transcription start site allowed identification of a predicted promoter sequence with a high similarity to the consensus sequence found in the housekeeping gene promoter of gram-positive bacteria as well as Escherichia coli. PMID:10542163

  19. Expression of Escherichia coli cspA during early exponential growth at 37 °C.

    PubMed

    Brandi, Anna; Pon, Cynthia L

    2012-01-25

    CspA is a small (7.4 kDa) nucleic acid binding protein of Escherichia coli whose expression is stimulated after cold-stress but whose level is also extraordinarily high during the early phase of growth of non-stressed cells. In this study the relationship existing between cspA transcription/translation on the one hand and the acquisition of critical mass for cell division and chromosome replication, on the other, in stationary phase cells subjected to a nutritional up-shift at 37 °C has been analyzed. Measurements of optical density and viable counts, pulse-chase, real-time PCR and immunodetection experiments, as well as cytofluorimetric and DNA duplication analyses show that synthesis of new CspA molecules at 37 °C is not only restricted to the lag phase ensuing the nutritional up-shift, but continues also during the first stages of logarithmic growth, when cells have already started dividing; although the early synthesized molecules are diluted by the following cell divisions and new synthesis occurs at an extremely low level, cspA mRNA and CspA continue to be present. A possible explanation for the apparent paradox that cspA is activated not only following cold stress, but also under non-stress and other stress conditions which entail a down-regulation of bulk gene expression and protein synthesis is presented.

  20. Janus particle rotator-to-lamellar nucleation and growth kinetics

    NASA Astrophysics Data System (ADS)

    Beltran-Villegas, Daniel J.; Zhang, Yulei; Larson, Ronald G.

    2017-03-01

    We determine the free energy barrier, critical nucleus size, and kinetics of a Janus particle solid-solid transition by nucleation and growth of lamellar clusters within a metastable rotator phase. The transition involves negligible change in particle position and phase volume and entails only particle orientational ordering. Fast kinetics enable the analysis of unbiased crystal growth and shrinkage trajectories from Brownian dynamic simulations. By fitting simulation trajectories to a diffusion-migration equation, the nucleus free energy and growth coefficient as a function of nucleus size are extracted. Observed transition times are on the order of hundreds of characteristic particle rotation times. Lamellar crystal nuclei are oblate rather than spherical, but otherwise classical nucleation theory applies, with the bulk free energy contribution following closely the Maier-Saupe theory for purely orientational transitions and the interfacial energy contribution following trends from 3-dimensional Ising spin kinetics.

  1. Growth kinetic models of five species of Lactobacilli and lactose consumption in batch submerged culture.

    PubMed

    Rezvani, Fazlollah; Ardestani, Fatemeh; Najafpour, Ghasem

    Kinetic behaviors of five Lactobacillus strains were investigated with Contois and Exponential models. Awareness of kinetic behavior of microorganisms is essential for their industrial process design and scale up. The consistency of experimental data was evaluated using Excel software. L. bulgaricus was introduced as the most efficient strain with the highest biomass and lactic acid yield of 0.119 and 0.602gg(-1) consumed lactose, respectively. The biomass and carbohydrate yield of L. fermentum and L. lactis were slightly less and close to L. bulgaricus. Biomass and lactic acid production yield of 0.117 and 0.358 for L. fermentum and 0.114 and 0.437gg(-1) for L.actobacillus lactis were obtained. L. casei and L. delbrueckii had the less biomass yield, nearly 11.8 and 22.7% less than L. bulgaricus, respectively. L. bulgaricus (R(2)=0.9500 and 0.9156) and L. casei (R(2)=0.9552 and 0.8401) showed acceptable consistency with both models. The investigation revealed that the above mentioned models are not suitable to describe the kinetic behavior of L. fermentum (R(2)=0.9367 and 0.6991), L. delbrueckii (R(2)=0.9493 and 0.7724) and L. lactis (R(2)=0.8730 and 0.6451). Contois rate equation is a suitable model to describe the kinetic of Lactobacilli. Specific cell growth rate for L. bulgaricus, L. casei, L. fermentum, L. delbrueckii and L. lactis with Contois model in order 3.2, 3.9, 67.6, 10.4 and 9.8-fold of Exponential model.

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

    PubMed

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

    2013-12-31

    Fermenting cells growing exponentially on rich (YPAD) medium underwent a transition 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 transition period, the high-affinity Fe import rate declined slower than the cell-growth rate declined, causing Fe to accumulate, initially as Fe(III) oxyhydroxide nanoparticles but eventually as mitochondrial and vacuolar Fe. Once the cells had reached 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 the exponential phase and underwent a transition to a true stationary state as glucose levels declined. The Fe concentration of MM cells that just entered the stationary state was similar to that of YPAD cells, but MM cells continued to accumulate Fe in the stationary state. Fe initially accumulated as nanoparticles and high-spin Fe(II) species, but vacuolar Fe(III) also eventually accumulated. Surprisingly, Fe-packed 5-day-old MM cells suffered no more reactive oxygen species (ROS) damage than younger cells, suggesting that the 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 the import of Fe via a regulated high-affinity pathway and an unregulated low-affinity pathway. The import of Fe from the cytosol to 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

  3. Thermodynamic and kinetic control of the lateral Si wire growth

    SciTech Connect

    Dedyulin, Sergey N. Goncharova, Lyudmila V.

    2014-03-24

    Reproducible lateral Si wire growth has been realized on the Si (100) surface. In this paper, we present experimental evidence showing the unique role that carbon plays in initiating lateral growth of Si wires on a Si (100) substrate. Once initiated in the presence of ≈5 ML of C, lateral growth can be achieved in the range of temperatures, T = 450–650 °C, and further controlled by the interplay of the flux of incoming Si atoms with the size and areal density of Au droplets. Critical thermodynamic and kinetic aspects of the growth are discussed in detail.

  4. An autocatalytic kinetic model for describing microbial growth during fermentation.

    PubMed

    Ibarz, Albert; Augusto, Pedro E D

    2015-01-01

    The mathematical modelling of the behaviour of microbial growth is widely desired in order to control, predict and design food and bioproduct processing, stability and safety. This work develops and proposes a new semi-empirical mathematical model, based on an autocatalytic kinetic, to describe the microbial growth through its biomass concentration. The proposed model was successfully validated using 15 microbial growth patterns, covering the three most important types of microorganisms in food and biotechnological processing (bacteria, yeasts and moulds). Its main advantages and limitations are discussed, as well as the interpretation of its parameters. It is shown that the new model can be used to describe the behaviour of microbial growth.

  5. 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.

  6. 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

  7. 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.

  8. Nucleation and growth kinetics of biochemicals measured at high supersaturations

    NASA Astrophysics Data System (ADS)

    Mahajan, Amarjit J.; Kirwan, Donald J.

    1994-12-01

    A grid mixer device (characteristic micromixing time < 3 ms) was successfully used to measure both nucleation and growth kinetics of lovastatin in 60 vol% methanol and asparagine monohydrate in 50 vol% 2-propanol at 23°C at high supersaturations but in the absence of mixing limitations. The supersaturation ratios investigated were in the range 1.25-8.8 for the lovastatin system and 1.17-4.1 for the asparagine system. When plotted according to primary nucleation theory, the induction time and nucleation rate measurements for both systems exhibited a homogeneous nucleation region at high supersaturations and a heterogeneous nucleation region at low supersaturations. The values of interfacial free energy extracted from these measurements for lovastatin (1.4-1.6 mJ/m 2) and asparagine (4.5-6.1 mJ/m 2) were an order-of-magnitude lower than those for inorganic salts reflecting the weaker intermolecular bonding in such biochemical solutes. The measured crystal growth rates for both solutes over the entire range of supersaturation could be represented with a power law dependence on chemical potential driving force. The kinetic orders of crystal growth were found to be 6.7 and 2.9 for lovastatin and asparagine, respectively. These unusually high kinetic orders could be represented by a polynuclear surface nucleation growth mechanism. The activation energy for the growth of lovastatin was measured as 280 kJ/mol.

  9. 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

  10. Lag phase is a distinct growth phase that prepares bacteria for exponential growth and involves transient metal accumulation.

    PubMed

    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; Hinton, Jay C D

    2012-02-01

    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.

  11. Differential expression profiles of Streptococcus mutans ftf, gtf and vicR genes in the presence of dietary carbohydrates at early and late exponential growth phases.

    PubMed

    Shemesh, Moshe; Tam, Avshalom; Feldman, Mark; Steinberg, Doron

    2006-09-04

    Dental caries is one of the most common infectious diseases that affects humans. Streptococcus mutans, the main pathogenic bacterium associated with dental caries, produces a number of extracellular sucrose-metabolizing enzymes, such as glucosyltransferases (GTFB, GTFC and GTFD) and fructosyltransferase (FTF). The cooperative action of these enzymes is essential for sucrose-dependent cellular adhesion and biofilm formation. A global response regulator (vicR) plays important roles in S. mutans ftf and gtf expression in response to a variety of stimuli. A real-time reverse-transcription polymerase chain-reaction was used to quantify the relative levels of ftf, gtfB, gtfC, gtfD and vicR transcription of S. mutans in the presence of various dietary carbohydrates: sucrose, D-glucose, D-fructose, D-glucitol (D-sorbitol), D-mannitol and xylitol. Ftf was highly expressed at late exponential phase in the presence of sorbitol and mannitol. GtfB was highly expressed in the presence of all the above carbohydrates except for xylitol at early exponential growth phase and glucose and fructose at late exponential growth phase. Similar to gtfB, the expression of gtfC was also induced with the presence of all the tested carbohydrates except for xylitol at early growth and glucose and fructose at late exponential phase. In addition, no effect of mannitol on gtfC expression at early exponential phase was observed. GtfD was less influenced compared to the gtfB and gtfC, demonstrating enhanced expression especially in the presence of sorbitol, glucose, mannitol and xylitol at early exponential phase and mannitol at late exponential phase. VicR expression was induced only at the presence of xylitol at late exponential phase, and a decrease in expression was recorded at early exponential phase. Our findings show that dietary carbohydrates have a major influence on the transcription of ftf, gtfB, gtfC and gtfD, but less on vicR. Sorbitol and mannitol, which are considered as noncariogenic

  12. Dendritic growth shapes in kinetic Monte Carlo models

    NASA Astrophysics Data System (ADS)

    Krumwiede, Tim R.; Schulze, Tim P.

    2017-02-01

    For the most part, the study of dendritic crystal growth has focused on continuum models featuring surface energies that yield six pointed dendrites. In such models, the growth shape is a function of the surface energy anisotropy, and recent work has shown that considering a broader class of anisotropies yields a correspondingly richer set of growth morphologies. Motivated by this work, we generalize nanoscale models of dendritic growth based on kinetic Monte Carlo simulation. In particular, we examine the effects of extending the truncation radius for atomic interactions in a bond-counting model. This is done by calculating the model’s corresponding surface energy and equilibrium shape, as well as by running KMC simulations to obtain nanodendritic growth shapes. Additionally, we compare the effects of extending the interaction radius in bond-counting models to that of extending the number of terms retained in the cubic harmonic expansion of surface energy anisotropy in the context of continuum models.

  13. 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.

  14. Kinetics of Denitrifying Growth by Fast-Growing Cowpea Rhizobia

    PubMed Central

    El Hassan, G. A.; Zablotowicz, R. M.; Focht, D. D.

    1985-01-01

    Two fast-growing strains of cowpea rhizobia (A26 and A28) were found to grow anaerobically at the expense of NO3−, NO2−, and N2O as terminal electron acceptors. The two major differences between aerobic and denitrifying growth were lower yield coefficients (Y) and higher saturation constants (Ks) with nitrogenous oxides as electron acceptors. When grown aerobically, A26 and A28 adhered to Monod kinetics, respectively, as follows: Ks, 3.4 and 3.8 μM; Y, 16.0 and 14.0 g · cells eq−1; μmax, 0.41 and 0.33 h−1. Yield coefficients for denitrifying growth ranged from 40 to 70% of those for aerobic growth. Only A26 adhered to Monod kinetics with respect to growth on all three nitrogenous oxides. The apparent Ks values were 41, 270, and 460 μM for nitrous oxide, nitrate, and nitrite, respectively; the Ks for A28 grown on nitrate was 250 μM. The results are kinetically and thermodynamically consistent in explaining why O2 is the preferred electron acceptor. Although no definitive conclusions could be drawn regarding preferential utilization of nitrogenous oxides, nitrite was inhibitory to both strains and effected slower growth. However, growth rates were identical (μmax, 0.41 h−1) when A26 was grown with either O2 or NO3− as an electron acceptor and were only slightly reduced when A28 was grown with NO3− (0.25 h−1) as opposed to O2 (0.33 h−1). PMID:16346745

  15. Kinetic model for microbial growth and desulphurisation with Enterobacter sp.

    PubMed

    Liu, Long; Guo, Zhiguo; Lu, Jianjiang; Xu, Xiaolin

    2015-02-01

    Biodesulphurisation was investigated by using Enterobacter sp. D4, which can selectively desulphurise and convert dibenzothiophene into 2-hydroxybiphenyl (2-HBP). The experimental values of growth, substrate consumption and product generation were obtained at 95 % confidence level of the fitted values using three models: Hinshelwood equation, Luedeking-Piret and Luedeking-Piret-like equations. The average error values between experimental values and fitted values were less than 10 %. These kinetic models describe all the experimental data with good statistical parameters. The production of 2-HBP in Enterobacter sp. was by "coupled growth".

  16. 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.

  17. A DNA-binding peroxiredoxin of Coxiella burnetii is involved in countering oxidative stress during exponential-phase growth.

    PubMed

    Hicks, Linda D; Raghavan, Rahul; Battisti, James M; Minnick, Michael F

    2010-04-01

    Coxiella burnetii is a Gram-negative, obligate intracellular bacterial pathogen that resides within the harsh, acidic confines of a lysosome-like compartment of the host cell that is termed a parasitophorous vacuole. In this study, we characterized a thiol-specific peroxidase of C. burnetii that belongs to the atypical 2-cysteine subfamily of peroxiredoxins, commonly referred to as bacterioferritin comigratory proteins (BCPs). Coxiella BCP was initially identified as a potential DNA-binding protein by two-dimensional Southwestern (SW) blots of the pathogen's proteome, probed with biotinylated C. burnetii genomic DNA. Confirmation of the identity of the DNA-binding protein as BCP (CBU_0963) was established by matrix-assisted laser desorption ionization-tandem time of flight mass spectrometry (MALDI-TOF/TOF MS). Recombinant Coxiella BCP (rBCP) was generated, and its DNA binding was demonstrated by two independent methods, including SW blotting and electrophoretic mobility shift assays (EMSAs). rBCP also demonstrated peroxidase activity in vitro that required thioredoxin-thioredoxin reductase (Trx-TrxR). Both the DNA-binding and peroxidase activities of rBCP were lost upon heat denaturation (100 degrees C, 10 min). Functional expression of Coxiella bcp was demonstrated by trans-complementation of an Escherichia coli bcp mutant, as evidenced by the strain's ability to grow in an oxidative-stress growth medium containing tert-butyl hydroperoxide to levels that were indistinguishable from, or significantly greater than, those observed with its wild-type parental strain and significantly greater than bcp mutant levels (P < 0.05). rBCP was also found to protect supercoiled plasmid DNA from oxidative damage (i.e., nicking) in vitro. Maximal expression of the bcp gene coincided with the pathogen's early (day 2 to 3) exponential-growth phase in an experiment involving synchronized infection of an epithelial (Vero) host cell line. Taken as a whole, the results show that

  18. 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

  19. Comparison of methods for measuring viable E. coli cells during cultivation: great differences in the early and late exponential growth phases.

    PubMed

    Wang, Hengwei; Cheng, Hairong; Wei, Dongzhi; Wang, Fengqing

    2011-01-01

    Four methods, namely enumeration of colony-forming units (CFU), aerobic respiration, MTT reduction capacity and succinate dehydrogenase activity were compared to determine the viability of E. coli cells at the early and late exponential growth phases. Our results revealed that great differences in cell viability existed between these methods and that the choice of method to determine cell viability must be made with caution.

  20. Hydromagnesite solubility product and growth kinetics in aqueous solution from 25 to 75 °C

    NASA Astrophysics Data System (ADS)

    Gautier, Quentin; Bénézeth, Pascale; Mavromatis, Vasileios; Schott, Jacques

    2014-08-01

    Hydromagnesite Mg5(CO3)4(OH)2·4H2O is the most widespread form of hydrated Mg-carbonate minerals. To better understand the factors controlling the precipitation of hydrated Mg-carbonates, we measured hydromagnesite solubility product at 25 and 50 °C and its growth rate between 25 and 75 °C, using natural hydromagnesite from a cave as seed material. The solubility products values derived in this study, Ksp-Hmgs = -37.08 ± 0.50 and -38.90 ± 0.54 at 25 and 50 °C, respectively, are in the upper range of published values. Hydromagnesite growth rate normalized to the BET surface area at 8 ⩽ pH ⩽ 10 is consistent with the direct and reversible attachment of the reactants at the solid surface being rate-limiting. It may be described by: RHmgs=A0·e(ΩHmgs1/5-1) where A0, the pre-exponential factor, and Ea, the activation energy, are equal to 5.12 × 10-7 mol/cm2/s and 45.5 ± 9 kJ/mol, respectively, and ΩHmgs stands for the saturation state of the solution with respect to hydromagnesite. Comparison of hydromagnesite growth rates with recently published magnesite growth rates (Saldi et al., 2009, 2012) show that: (1) hydromagnesite apparent growth activation energy is lower by more than 100 kJ/mol compared to the activation energy for magnesite obtuse step advancement, and (2) hydromagnesite growth rate constant extrapolated to 90 °C is 2.5 orders of magnitude higher than corresponding magnesite growth rate constant. Thus, our results confirm the long-standing hypothesis that the slow dehydration kinetics of the Mg2+ cation is responsible for the sluggish magnesite formation at low temperature, and that the kinetic barrier for hydromagnesite growth is much lower. Nevertheless, simulation of hydromagnesite and magnesite growth rates as a function of solution composition at 50 and 90 °C, and pH 7 and 9 reveal that, because of its much higher solubility, hydromagnesite would grow more quickly than magnesite in natural or industrial environments only at 50 °C and

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

    PubMed

    Huang, Lihan

    2011-06-01

    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 exponential growth rate of a growth curve were simultaneously determined by nonlinear regression. The new model was validated using Listeria monocytogenes and Escherichia coli O157:H7 in broth or meat. Statistical results suggested that both bias factor (B(f)) and accuracy factor (A(f)) of the new model were very close to 1.0. A new Bĕlehdrádek-type rate model and the Ratkowsky square-root model were used to describe the temperature dependence of bacterial growth rate. It was observed that the maximum and minimum temperatures were more accurately estimated by a new Bĕlehdrádek-type rate model. Further, the inverse of square-roots of lag phases was found proportional to temperature, making it possible to estimate the lag phase duration from the growth temperature.

  2. Effect of Na+ Concentration and Nutritional Factors on the Lag Phase and Exponential Growth Rates of the Marine Bacterium Deleya aesta and of Other Marine Species

    PubMed Central

    Berthelet, Marc; MacLeod, Robert A.

    1989-01-01

    Growth of the marine bacterium Deleya aesta in a succinate minimal medium showed increasingly long lag phases as Na+ was decreased below the optimum (200 to 500 mM). The minimum Na+ concentration permitting growth consistently was 15 mM. Supplementation of the medium with KHCO3 (as a source of CO2) or yeast extract, especially in combination, reduced the lag phase, increased the rate of exponential growth, and allowed growth at 8 mM Na+. KHCO3 did not reduce the lag period but did increase the rate of exponential growth of Deleya venusta, Deleya pacifica, and Alteromonas haloplanktis 214. Yeast extract was active for all three. The effect of yeast extract on D. aesta could be reproduced by a mixture of amino acids approximating its amino acid composition. l-Alanine, l-aspartate, and l-methionine, in combination, were the most effective in reducing the lag phase, although not as effective as the complete mixture. Succinate, l-aspartate, and l-alanine were transported into the cells by largely independent pathways and oxidized at rates which were much lower at 10 than at 200 mM Na+. l-Methionine was transported at a low rate in the absence of Na+ and at a higher rate at 10 mM but was not oxidized. Above 25 mM Na+, the rate of transport of the carbon source was not the rate-limiting step for growth. It is concluded that a combination of transportable carbon sources reduced the lag period and increased the rate of exponential growth because they can be taken up independently and at low Na+ utilized simultaneously. PMID:16347969

  3. 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 .

  4. Kinetic growth walk on critical percolation clusters and lattice animals

    NASA Astrophysics Data System (ADS)

    Lam, P. M.; Zhang, Z. Q.

    1984-03-01

    The statistics of recently proposed kinetic growth walk (KGW) model for linear polymers (or growing self avoiding walk (GSAW)) on two dimensional critical percolation clusters and lattice animals are studied using real-space renormalization group method. The correlation length exponents ν's are found to be ν{KGW/ Pc } = 0.68 and ν{KGW/LA} respectively for the critical percolation clusters and lattice animals. Close agreements are found between these results and a generalized Flory formula for linear polymers at theta point ν{KGW/F} = 2/bar d+1),, wherebar d is the fractal dimension of the fractal object F.

  5. Kinetic 15N-isotope effects on algal growth

    PubMed Central

    Andriukonis, Eivydas; Gorokhova, Elena

    2017-01-01

    Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism metabolism and growth, which is not consistent with current theoretical and empirical knowledge on kinetic isotope effects. Here, we demonstrate profound changes in growth dynamics of the green alga Raphidocelis subcapitata grown in 15N-enriched media. With increasing 15N concentration (0.37 to 50 at%), the lag phase increased, whereas maximal growth rate and total yield decreased; moreover, there was a negative relationship between the growth and the lag phase across the treatments. The latter suggests that a trade-off between growth rate and the ability to adapt to the high 15N environment may exist. Remarkably, the lag-phase response at 3.5 at% 15N was the shortest and deviated from the overall trend, thus providing partial support to the recently proposed Isotopic Resonance hypothesis, which predicts that certain isotopic composition is particularly favorable for living organisms. These findings confirm the occurrence of KIE in isotopically enriched algae and underline the importance of considering these effects when using stable isotope labeling in field and experimental studies. PMID:28281640

  6. Kinetic 15N-isotope effects on algal growth

    NASA Astrophysics Data System (ADS)

    Andriukonis, Eivydas; Gorokhova, Elena

    2017-03-01

    Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism metabolism and growth, which is not consistent with current theoretical and empirical knowledge on kinetic isotope effects. Here, we demonstrate profound changes in growth dynamics of the green alga Raphidocelis subcapitata grown in 15N-enriched media. With increasing 15N concentration (0.37 to 50 at%), the lag phase increased, whereas maximal growth rate and total yield decreased; moreover, there was a negative relationship between the growth and the lag phase across the treatments. The latter suggests that a trade-off between growth rate and the ability to adapt to the high 15N environment may exist. Remarkably, the lag-phase response at 3.5 at% 15N was the shortest and deviated from the overall trend, thus providing partial support to the recently proposed Isotopic Resonance hypothesis, which predicts that certain isotopic composition is particularly favorable for living organisms. These findings confirm the occurrence of KIE in isotopically enriched algae and underline the importance of considering these effects when using stable isotope labeling in field and experimental studies.

  7. Steps in Cu(111) thin films affect graphene growth kinetics

    NASA Astrophysics Data System (ADS)

    Miller, David L.; Gannett, Will; Keller, Mark W.

    2014-03-01

    The kinetics of chemical vapor deposition of graphene on Cu substrates depend on the relative rates of C diffusion on the surface, C attachment to graphene islands, and removal of C from the surface or from graphene islands by etching processes involving H atoms. Using Cu(111) thin films with centimeter-sized grains, we have grown graphene under a variety of conditions and examined the edges of graphene islands with SEM and AFM. The Cu surface shows a series of regular steps, roughly 2 nm in height, and the graphene islands are diamond-shaped with faster growth along the edges of Cu steps. In contrast, growth on polycrystalline Cu foils under the same conditions shows hexagonal graphene islands with smooth edges.

  8. Relationship between grain boundary complexion and grain growth kinetics in alumina

    NASA Astrophysics Data System (ADS)

    Dillon, Shen J.

    2007-12-01

    This work investigated the effect of different grain boundary phases (complexions) on the grain growth kinetics of doped and undoped aluminas. This was achieved by relating quantitative grain growth kinetics to high-resolution electron microscopy of the grain boundaries. It was found that there are 6 different regimes into which the grain growth kinetics may be categorized. These regimes corresponded to the existence of six different grain boundary complexions. Grain boundaries in alumina were observed to show sub-monolayer adsorption, 'clean' intrinsic behavior, bilayer adsorption, multilayer adsorption, equilibrium thickness intergranular films, and wetting intergranular films. These different grain boundary types are listed in order of increasing grain boundary mobility. In general there is an increase in grain boundary mobility with an increase in the disorder within the core of the grain boundary. This broad range of grain boundaries produces a multiplicity of different microstructural effects that until now have been difficult to understand experimentally or theoretically. For example, abnormal grain growth in alumina simply results from the coexistence of two or more different complexions within the same microstructure. Therefore, there may be multiple distinct types of normal and abnormal grain growth behavior. Transitions from one type of boundary to another are chemically and thermally activated, and depend on the crystallography of the adjacent grains. It is found that the number of transitions that occur increases linearly with increasing grain size, and exponentially with temperature. In this regard, different dopants produce very different effects, which appear to be the major role of most dopants in affecting the grain boundary transport kinetics. Low energy planes and grain boundaries are the least likely to undergo such transitions. This experimental data compliments some theoretical derivations within the literature and has provided new insight

  9. 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/.

  10. Kinetics of growth and sugar consumption in yeasts.

    PubMed

    van Dijken, J P; Weusthuis, R A; Pronk, J T

    1993-01-01

    An overview is presented of the steady- and transient state kinetics of growth and formation of metabolic byproducts in yeasts. Saccharomyces cerevisiae is strongly inclined to perform alcoholic fermentation. Even under fully aerobic conditions, ethanol is produced by this yeast when sugars are present in excess. This so-called 'Crabtree effect' probably results from a multiplicity of factors, including the mode of sugar transport and the regulation of enzyme activities involved in respiration and alcoholic fermentation. The Crabtree effect in S. cerevisiae is not caused by an intrinsic inability to adjust its respiratory activity to high glycolytic fluxes. Under certain cultivation conditions, for example during growth in the presence of weak organic acids, very high respiration rates can be achieved by this yeast. S. cerevisiae is an exceptional yeast since, in contrast to most other species that are able to perform alcoholic fermentation, it can grow under strictly anaerobic conditions. 'Non-Saccharomyces' yeasts require a growth-limiting supply of oxygen (i.e. oxygen-limited growth conditions) to trigger alcoholic fermentation. However, complete absence of oxygen results in cessation of growth and therefore, ultimately, of alcoholic fermentation. Since it is very difficult to reproducibly achieve the right oxygen dosage in large-scale fermentations, non-Saccharomyces yeasts are therefore not suitable for large-scale alcoholic fermentation of sugar-containing waste streams. In these yeasts, alcoholic fermentation is also dependent on the type of sugar. For example, the facultatively fermentative yeast Candida utilis does not ferment maltose, not even under oxygen-limited growth conditions, although this disaccharide supports rapid oxidative growth.

  11. Growth kinetics of Salmonella spp. pre- and post-thermal treatment.

    PubMed

    Juneja, Vijay K; Marks, Harry M

    2006-05-25

    This paper reports estimated growth kinetic parameters for a cocktail of stationary phase Salmonella serotypes, pre- and post-thermal inactivation treatment. Cells were grown in brain-heart infusion broth at 25 or 37 degrees Celsius and then destruction of the cells was quantified at 55 degrees Celsius using a submerged coil heating apparatus. The surviving cells (about 1-2 log(10) cfu/ml) were subsequently grown at 25 or 37 degrees Celsius. The results indicated that lag phase duration times for the post- heat treated cells increased at 25 and 37 degrees Celsius by about 6.2 h and at least 3 to 4 h, respectively, and thus the increases appear to be truly different. However, when considering the ratios of the lag phase duration times for post-treated to pre-treated cells, a significant difference was not found, where estimated ratios could exceed 4. Estimated exponential growth rates, EGR, were not affected by the treatment, where for 37 degrees Celsius, EGR was estimated to be 0.9 log(10) (cfu/ml)/h, and at 25 degrees Celsius, the EGR was estimated at 0.45 log(10) (cfu/ml)/h.

  12. 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.

  13. 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.

  14. Elevated acetyl-CoA by amino acid recycling fuels microalgal neutral lipid accumulation in exponential growth phase for biofuel production.

    PubMed

    Yao, Lina; Shen, Hui; Wang, Nan; Tatlay, Jaspaul; Li, Liang; Tan, Tin Wee; Lee, Yuan Kun

    2017-04-01

    Microalgal neutral lipids [mainly in the form of triacylglycerols (TAGs)], feasible substrates for biofuel, are typically accumulated during the stationary growth phase. To make microalgal biofuels economically competitive with fossil fuels, generating strains that trigger TAG accumulation from the exponential growth phase is a promising biological approach. The regulatory mechanisms to trigger TAG accumulation from the exponential growth phase (TAEP) are important to be uncovered for advancing economic feasibility. Through the inhibition of pyruvate dehydrogenase kinase by sodium dichloroacetate, acetyl-CoA level increased, resulting in TAEP in microalga Dunaliella tertiolecta. We further reported refilling of acetyl-CoA pool through branched-chain amino acid catabolism contributed to an overall sixfold TAEP with marginal compromise (4%) on growth in a TAG-rich D. tertiolecta mutant from targeted screening. Herein, a three-step α loop-integrated metabolic model is introduced to shed lights on the neutral lipid regulatory mechanism. This article provides novel approaches to compress lipid production phase and heightens lipid productivity and photosynthetic carbon capture via enhancing acetyl-CoA level, which would optimize renewable microalgal biofuel to fulfil the demanding fuel market.

  15. Rethinking growth and decay kinetics in activated sludge - towards a new adaptive kinetics approach.

    PubMed

    Friedrich, Michael; Jimenez, Jose; Pruden, Amy; Miller, Jennifer H; Metch, Jacob; Takács, Imre

    2017-02-01

    Growth kinetics in activated sludge modelling (ASM) are typically assumed to be the result of intrinsic growth and decay properties and thus process parameters are deemed to be constant. The activity change in a microbial population is expressed in terms of variance of the active biomass fraction and not actual shifts in bacterial cellular activities. This approach is limited, in that it does not recognise the reality that active biomass is highly physiologically adaptive. Here, a strong correlation between maximum specific growth rate (μmax) and decay rate (be) of ordinary heterotrophic organisms was revealed in both low solids retention times (SRT) and high SRT activated sludge systems. This relationship is indicative of physiological adaptation either for growth (high μmax and be) or survival optimization (low μmax and be). Further, the nitrifier decay process was investigated using molecular techniques to measure decay rates of ammonia oxidizing bacteria and nitrite oxidizing bacteria over a range of temperatures. This approach revealed decay rates 10-12% lower than values previously accepted and used in ASM. These findings highlight potential benefits of incorporating physiological adaptation of heterotrophic and nitrifying populations in future ASM.

  16. Kinetics of droplet growth observed in recent field campaigns

    NASA Astrophysics Data System (ADS)

    Mei, F.; Wang, J.

    2012-12-01

    Atmospheric aerosols can indirectly influence global climate budget by changing the microphysical structure, lifetime, and coverage of clouds. While it is generally agreed that aerosol indirect effects act to cool the Earth-atmosphere system by increasing cloud reflectivity and coverage, the magnitudes of the indirect effects are poorly understood. The formation of cloud droplets from aerosol particles is kinetically controlled by the availability of water vapor, equilibrium water vapor pressure above the growing droplet surface, and both the gas phase and aerosol phase mass transfer resistances. It has been hypothesized that the formation of surface organic films or the delay in dissolution of solute could significantly delay the growth of cloud droplets. Such delay could lead to a higher maximum supersaturation within a rising cloud parcel, therefore higher droplet number concentration and smaller droplet size at constant liquid water content. When only a subset of the droplets experiences significant growth delay, the overall droplet size spectrum will be broadened, which facilitates the formation of precipitation. During three recent field campaigns (CalNex-LA, CARES, and Aerosol Intensive Observation Period at Brookhaven National Laboratory), the CCN activity and droplet growth of size selected particles ranging from 25 to 320 nm were characterized by a CCN counter under supersaturations from 0.1% to 0.8%. The three campaigns allow us to examine the droplet growth for many representative organic aerosol types, including biogenic SOA, anthropogenic SOA, and organic aerosols from biomass burning. The droplet growth of size-selected ambient particles inside the CCN counter was found to be influenced by a number of parameters, including particle critical supersaturation, heterogeneity in particle composition, and particle concentration. For example, reduced droplet growth due to water vapor depletion was observed when particle concentration was higher than 200 cm

  17. Growth Kinetics and Morphology of Barite Crystals Derived from Face-Specific Growth Rates

    DOE PAGES

    Godinho, Jose R. A.; Stack, Andrew G.

    2015-03-30

    Here we investigate the growth kinetics and morphology of barite (BaSO4) crystals by measuring the growth rates of the (001), (210), (010), and (100) surfaces using vertical scanning interferometry. Solutions with saturation indices 1.1, 2.1, and 3.0 without additional electrolyte, in 0.7 M NaCl, or in 1.3 mM SrCl2 are investigated. Face-specific growth rates are inhibited in the SrCl2 solution relative to a solution without electrolyte, except for (100). Contrarily, growth of all faces is promoted in the NaCl solution. The variation of face-specific rates is solution-specific, which leads to a. change of the crystal morphology and overall growth ratemore » of crystals. The measured face-specific growth rates are used to model the growth of single crystals. Modeled crystals have a morphology and size similar to those grown from solution. Based on the model the time dependence of surface area and growth rates is analyzed. Growth rates change with time due to surface area normalization for small crystals and large growth intervals. By extrapolating rates to crystals with large surfaces areas, time-independent growth rates are 0.783, 2.96, and 0.513 mmol∙m-2∙h-1, for saturation index 2.1 solutions without additional electrolyte, NaCl, and SrCl2, respectively.« less

  18. Growth Kinetics and Morphology of Barite Crystals Derived from Face-Specific Growth Rates

    SciTech Connect

    Godinho, Jose R. A.; Stack, Andrew G.

    2015-03-30

    Here we investigate the growth kinetics and morphology of barite (BaSO4) crystals by measuring the growth rates of the (001), (210), (010), and (100) surfaces using vertical scanning interferometry. Solutions with saturation indices 1.1, 2.1, and 3.0 without additional electrolyte, in 0.7 M NaCl, or in 1.3 mM SrCl2 are investigated. Face-specific growth rates are inhibited in the SrCl2 solution relative to a solution without electrolyte, except for (100). Contrarily, growth of all faces is promoted in the NaCl solution. The variation of face-specific rates is solution-specific, which leads to a. change of the crystal morphology and overall growth rate of crystals. The measured face-specific growth rates are used to model the growth of single crystals. Modeled crystals have a morphology and size similar to those grown from solution. Based on the model the time dependence of surface area and growth rates is analyzed. Growth rates change with time due to surface area normalization for small crystals and large growth intervals. By extrapolating rates to crystals with large surfaces areas, time-independent growth rates are 0.783, 2.96, and 0.513 mmol∙m-2∙h-1, for saturation index 2.1 solutions without additional electrolyte, NaCl, and SrCl2, respectively.

  19. Kinetics of faceting of crystals in growth, etching, and equilibrium

    NASA Astrophysics Data System (ADS)

    Vlachos, D. G.; Schmidt, L. D.; Aris, R.

    1993-03-01

    The faceting of crystals in equilibrium with the gas phase and also during crystal growth and etching conditions is studied using the Monte Carlo method. The dynamics of the transformation of unstable crystallographic orientations into hill and valley structures and the spatial patterns that develop are examined as functions of surface temperature, crystallographic orientation, and strength of interatomic potential for two transport processes: adsorption-desorption and surface diffusion. The results are compared with the continuum theory for facet formation. Thermodynamically unstable orientations break into hill and valley structures, and faceting exhibits three time regimes: disordering, facet nucleation, and coarsening of small facets to large facets. Faceting is accelerated as temperature increases, but thermal roughening can occur at high temperatures. Surface diffusion is the dominant mechanism at short times and small facets but adsorption-desorption becomes important at long times and large facets. Growth and etching promote faceting for conditions close to equilibrium but induce kinetic roughening for conditions far from equilibrium. Simultaneous irreversible growth and etching conditions with fast surface diffusion result in enhanced faceting.

  20. 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.

  1. 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.

  2. Kinetic transition during the growth of proeutectoid ferrite in Fe-C-Mn-Si quaternary steel

    NASA Astrophysics Data System (ADS)

    Zhang, Guo-Hong; Heo, Yoon-Uk; Song, Eun-Ju; Suh, Dong-Woo

    2013-03-01

    The kinetics of ferrite growth in Fe-0.1C-1.5Mn-0.94Si (mass pct) quaternary steel is investigated through the characterization of isothermal growth behavior, the thermodynamic prediction of kinetic boundary and the diffusional growth simulations using DICTRA. The change in microstructural evolution from slow growth to fast one is consistent with the calculated change of interface condition from the partitioning local equilibrium (PLE) to the negligible partitioning local equilibrium (NPLE). Compared with the DICTRA simulation, the observed growth kinetics of ferrite are between the calculated ones assuming local equilibrium (LE) and paraequilibrium (PE) criterions. At temperatures below the PLE/NPLE kinetic boundary, the observed growth behavior can be reasonably described by kinetic transition from PE to NPLE condition as isothermal time elapses, taking into account the critical velocity of interface at which trans-interface diffusion of subsitutional element permits the transition from PE to NPLE growth.

  3. Enhancerless cytomegalovirus is capable of establishing a low-level maintenance infection in severely immunodeficient host tissues but fails in exponential growth.

    PubMed

    Podlech, Jürgen; Pintea, Rares; Kropp, Kai A; Fink, Annette; Lemmermann, Niels A W; Erlach, Katja C; Isern, Elena; Angulo, Ana; Ghazal, Peter; Reddehase, Matthias J

    2010-06-01

    Major immediate-early transcriptional enhancers are genetic control elements that act, through docking with host transcription factors, as a decisive regulatory unit for efficient initiation of the productive virus cycle. Animal models are required for studying the function of enhancers paradigmatically in host organs. Here, we have sought to quantitatively assess the establishment, maintenance, and level of in vivo growth of enhancerless mutants of murine cytomegalovirus in comparison with those of an enhancer-bearing counterpart in models of the immunocompromised or immunologically immature host. Evidence is presented showing that enhancerless viruses are capable of forming restricted foci of infection but fail to grow exponentially.

  4. [Role of catalase and superoxide dismutase in the yeast Saccharomyces cerevisiae response to hydrogen peroxide in exponential phase of growth].

    PubMed

    Baĭliak, M M; Semchyshyn, H M; Lushchak, V I

    2006-01-01

    The role of catalase and superoxide dismutase (SOD) in response of the yeast Saccharomyces cerevisiae to oxidative stress induced by hydrogen peroxide in the middle-exponential phase has been investigated. It was shown that cell survival is significantly decreased after yeast exposure to hydrogen peroxide in the strains defective in cytosolic or peroxisomal catalases. Treatment of the wild-type cells with 0.5 mM H2O2 for 30 min causes an increase in the activity of catalase and superoxide dismutase, but the effect was not observed in all strains investigated. It was also shown that hydrogen peroxide leads to an increase in the activities of both catalases and Cu,Zn-containing SOD. The effect was cancelled by cycloheximide, an inhibitor of protein synthesis.

  5. 2-DE based proteomic analysis of Saccharomyces cerevisiae wild and K+ transport-affected mutant (trk1,2) strains at the growth exponential and stationary phases.

    PubMed

    Curto, Miguel; Valledor, Luis; Navarrete, Clara; Gutiérrez, Dolores; Sychrova, Hana; Ramos, José; Jorrin, Jesús

    2010-11-10

    By using a 2-DE based workflow, the proteome of wild and potassium transport mutant trk1,2 under optimal growth potassium concentration (50mM) has been analyzed. At the exponential and stationary phases, both strains showed similar growth, morphology potassium content, and Vmax of rubidium transport, the only difference found being the Km values for this potassium analogue transport, higher for the mutant (20mM) than for the wild (3-6mM) cells. Proteins were buffer-extracted, precipitated, solubilized, quantified, and subjected to 2-DE analysis in the 5-8 pH range. More differences in protein content (37-64mgg(-1) cell dry weight) and number of resolved spots (178-307) were found between growth phases than between strains. In all, 164 spots showed no differences between samples and a total of 105 were considered to be differential after ANOVA test. 171 proteins, corresponding to 71 unique gene products have been identified, this set being dominated by cytosolic species and glycolitic enzymes. The ranking of the more abundant spots revealed no differences between samples and indicated fermentative metabolism, and active cell wall biosynthesis, redox homeostasis, biosynthesis of amino acids, coenzymes, nucleotides, and RNA, and protein turnover, apart from cell division and growth. PCA analysis allowed the separation of growth phases (PC1 and 2) and strains at the stationary phase (PC3 and 4), but not at the exponential one. These results are also supported by clustering analysis. As a general tendency, a number of spots newly appeared at the stationary phase in wild type, and to a lesser extent, in the mutant. These up-accumulated spots corresponded to glycolitic enzymes, indicating a more active glucose catabolism, accompanied by an accumulation of methylglyoxal detoxification, and redox-homeostasis enzymes. Also, more extensive proteolysis was observed at the stationary phase with this resulting in an accumulation of low Mr protein species.

  6. Exact solutions of kinetic equations in an autocatalytic growth model.

    PubMed

    Jędrak, Jakub

    2013-02-01

    Kinetic equations are introduced for the transition-metal nanocluster nucleation and growth mechanism, as proposed by Watzky and Finke [J. Am. Chem. Soc. 119, 10382 (1997)]. Equations of this type take the form of Smoluchowski coagulation equations supplemented with the terms responsible for the chemical reactions. In the absence of coagulation, we find complete analytical solutions of the model equations for the autocatalytic rate constant both proportional to the cluster mass, and the mass-independent one. In the former case, ξ(k)=s(k)(ξ(1))[proportionality]ξ(1)(k)/k was obtained, while in the latter, the functional form of s(k)(ξ(1)) is more complicated. In both cases, ξ(1)(t)=h(μ)(M(μ)(t)) is a function of the moments of the mass distribution. Both functions, s(k)(ξ(1)) and h(μ)(M(μ)), depend on the assumed mechanism of autocatalytic growth and monomer production, and not on other chemical reactions present in a system.

  7. Pattern formation and growth kinetics in eutectic systems

    NASA Astrophysics Data System (ADS)

    Teng, Jing

    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 rod, 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

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. Growth kinetics and inhibition of growth of chemical vapor deposited thin tungsten films on silicon from tungsten hexafluoride

    NASA Astrophysics Data System (ADS)

    Leusink, G. J.; Kleijn, C. R.; Oosterlaken, T. G. M.; Janssen, G. C. A. M.; Radelaar, S.

    1992-07-01

    The growth kinetics and inhibition of growth of chemical vapor deposited thin W films on Si(100) from WF6 was studied with in situ growth stress and reflectivity measurements and ex situ weight gain measurements. A systematic series of experiments at varying WF6 flow, total pressure, and temperature show that the thickening kinetics and inhibition of the growth are controlled by two processes: WF6 diffusion through the gas phase and Si diffusion through the thickening columnar film. The steady state growth kinetics are controlled by WF6 diffusion in the gas phase whereas inhibition of the growth occurs at the transition from WF6 gas diffusion limited to Si solid state diffusion limited growth. A simple model based on WF6 gas phase diffusion and Si solid state diffusion is presented which gives a quantitative description of the experimental results.

  14. The H-NS-like protein StpA represses the RpoS (sigma 38) regulon during exponential growth of Salmonella Typhimurium.

    PubMed

    Lucchini, Sacha; McDermott, Paul; Thompson, Arthur; Hinton, Jay C D

    2009-12-01

    StpA is a paralogue of the nucleoid-associated protein H-NS that is conserved in a range of enteric bacteria and had no known function in Salmonella Typhimurium. We show that 5% of the Salmonella genome is regulated by StpA, which contrasts with the situation in Escherichia coli where deletion of stpA only had minor effects on gene expression. The StpA-dependent genes of S. Typhimurium are a specific subset of the H-NS regulon that are predominantly under the positive control of sigma(38) (RpoS), CRP-cAMP and PhoP. Regulation by StpA varied with growth phase; StpA controlled sigma(38) levels at mid-exponential phase by preventing inappropriate activation of sigma(38) during rapid bacterial growth. In contrast, StpA only activated the CRP-cAMP regulon during late exponential phase. ChIP-chip analysis revealed that StpA binds to PhoP-dependent genes but not to most genes of the CRP-cAMP and sigma(38) regulons. In fact, StpA indirectly regulates sigma(38)-dependent genes by enhancing sigma(38) turnover by repressing the anti-adaptor protein rssC. We discovered that StpA is essential for the dynamic regulation of sigma(38) in response to increased glucose levels. Our findings identify StpA as a novel growth phase-specific regulator that plays an important physiological role by linking sigma(38) levels to nutrient availability.

  15. Heat and pulsed electric field resistance of pigmented and non-pigmented enterotoxigenic strains of Staphylococcus aureus in exponential and stationary phase of growth.

    PubMed

    Cebrián, G; Sagarzazu, N; Pagán, R; Condón, S; Mañas, P

    2007-09-30

    The survival of four enterotoxigenic strains of Staphylococcus aureus (with different pigment content) to heat and to pulsed electric fields (PEF) treatments, and the increase in resistance to both processing stresses associated with entrance into stationary phase was examined. Survival curves to heat (58 degrees C) and to PEF (26 kV/cm) of cells in the stationary and in the exponential phase of growth were obtained. Whereas a wide variation in resistance to heat treatments was detected amongst the four strains, with decimal reduction time values at 58 degrees C (D(58 degrees C)) ranging from 0.93 to 0.20 min, the resistance to PEF was very similar. The occurrence of a higher tolerance to heat in stationary phase was coincident with a higher content in carotenoid pigmentation in S. aureus colonies. However, cells of the most heat resistant (pigmented) and the most heat sensitive (non-pigmented) strains in the mid-exponential phase of growth showed similar resistance to heat and to PEF. Therefore the increase in thermotolerance upon entrance into stationary phase of growth was more marked for the pigmented strains. Recovery in anaerobic conditions particularly enhanced survival to heat treatments in a non-pigmented strain. Strain CECT 4630, which possess a deficient sigma B activity, showed low heat resistance, low pigmentation, and reduced increase in thermotolerance in stationary phase. These results indicate that the magnitude of the development of a higher heat resistance in S. aureus in stationary phase is positively related to the carotenoid content of the strain. The development of tolerance to pulsed electric field was less relevant and not linked to the carotenoid content.

  16. Nucleation kinetics and crystal growth with fluctuating rates at the intermediate stage of phase transitions

    NASA Astrophysics Data System (ADS)

    Alexandrov, D. V.; Malygin, A. P.

    2014-01-01

    Crystal growth kinetics accompanied by particle growth with fluctuating rates at the intermediate stage of phase transitions is analyzed theoretically. The integro-differential model of governing equations is solved analytically for size-independent growth rates and arbitrary dependences of the nucleation frequency on supercooling/supersaturation. Two important cases of Weber-Volmer-Frenkel-Zel'dovich and Mier nucleation kinetics are detailed. A Fokker-Plank type equation for the crystal-size density distribution function is solved explicitly.

  17. Menaquinone synthesis is critical for maintaining mycobacterial viability during exponential growth and recovery from non-replicating persistence.

    PubMed

    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

    2009-04-01

    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 microM concentrations of aminoalkoxydiphenylmethane derivatives inhibited both the aerobic growth and survival of non-replicating, persistent M. tuberculosis. Metabolic labelling studies and quantification 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.

  18. 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.

  19. 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

  20. The influence of crystal morphology on the kinetics of growth of calcium oxalate monohydrate

    NASA Astrophysics Data System (ADS)

    Millan, A.; Sohnel, O.; Grases, F.

    1997-08-01

    The growth of several calcium oxalate monohydrate seeds in the presence and absence of additives (phytate, EDTA and citrate) has been followed by potentiometry measurements. Growth rates have been calculated from precipitate curves by a cubic spline method and represented in logarithmic plots versus supersaturation. Crystal growth kinetics were found to be dependent on crystal morphology, crystal perfection and degree of aggregation. Some seeds were dissolving in supersaturated solutions. Other seeds showed an initial growth phase of high-order kinetics. The effect of the additives was also different on each seed. Three alternative mechanisms for calcium oxalate crystal growth are proposed.

  1. 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.

  2. Notes on Interface Growth Kinetics 50 Years After Burton, Cabrera and Frank

    NASA Technical Reports Server (NTRS)

    Chernov, A. A.

    2003-01-01

    This is an overview of basic problems of crystal growth kinetics controlled by processes on the crystal interface with solution and melt. Included, also, are results on fundamental issues concerning morphological stability of crystal-solution interface that engage both interface kinetics and mass transport by diffusion and convection.

  3. Development of tolerogenic dendritic cells and regulatory T cells favors exponential bacterial growth and survival during early respiratory tularemia.

    PubMed

    Periasamy, Sivakumar; Singh, Anju; Sahay, Bikash; Rahman, Tabassum; Feustel, Paul J; Pham, Giang H; Gosselin, Edmund J; Sellati, Timothy J

    2011-09-01

    Tularemia is a vector-borne zoonosis caused by Ft, a Gram-negative, facultative intracellular bacterium. Ft exists in two clinically relevant forms, the European biovar B (holarctica), which produces acute, although mild, self-limiting infections, and the more virulent United States biovar A (tularensis), which is often associated with pneumonic tularemia and more severe disease. In a mouse model of tularemia, respiratory infection with the virulence-attenuated Type B (LVS) or highly virulent Type A (SchuS4) strain engenders peribronchiolar and perivascular inflammation. Paradoxically, despite an intense neutrophilic infiltrate and high bacterial burden, T(h)1-type proinflammatory cytokines (e.g., TNF, IL-1β, IL-6, and IL-12) are absent within the first ∼72 h of pulmonary infection. It has been suggested that the bacterium has the capacity to actively suppress or block NF-κB signaling, thus causing an initial delay in up-regulation of inflammatory mediators. However, our previously published findings and those presented herein contradict this paradigm and instead, strongly support an alternative hypothesis. Rather than blocking NF-κB, Ft actually triggers TLR2-dependent NF-κB signaling, resulting in the development and activation of tDCs and the release of anti-inflammatory cytokines (e.g., IL-10 and TGF-β). In turn, these cytokines stimulate development and proliferation of T(regs) that may restrain T(h)1-type proinflammatory cytokine release early during tularemic infection. The highly regulated and overall anti-inflammatory milieu established in the lung is permissive for unfettered growth and survival of Ft. The capacity of Ft to evoke such a response represents an important immune-evasive strategy.

  4. Development of tolerogenic dendritic cells and regulatory T cells favors exponential bacterial growth and survival during early respiratory tularemia

    PubMed Central

    Periasamy, Sivakumar; Singh, Anju; Sahay, Bikash; Rahman, Tabassum; Feustel, Paul J.; Pham, Giang H.; Gosselin, Edmund J.; Sellati, Timothy J.

    2011-01-01

    Tularemia is a vector-borne zoonosis caused by Ft, a Gram-negative, facultative intracellular bacterium. Ft exists in two clinically relevant forms, the European biovar B (holarctica), which produces acute, although mild, self-limiting infections, and the more virulent United States biovar A (tularensis), which is often associated with pneumonic tularemia and more severe disease. In a mouse model of tularemia, respiratory infection with the virulence-attenuated Type B (LVS) or highly virulent Type A (SchuS4) strain engenders peribronchiolar and perivascular inflammation. Paradoxically, despite an intense neutrophilic infiltrate and high bacterial burden, Th1-type proinflammatory cytokines (e.g., TNF, IL-1β, IL-6, and IL-12) are absent within the first ∼72 h of pulmonary infection. It has been suggested that the bacterium has the capacity to actively suppress or block NF-κB signaling, thus causing an initial delay in up-regulation of inflammatory mediators. However, our previously published findings and those presented herein contradict this paradigm and instead, strongly support an alternative hypothesis. Rather than blocking NF-κB, Ft actually triggers TLR2-dependent NF-κB signaling, resulting in the development and activation of tDCs and the release of anti-inflammatory cytokines (e.g., IL-10 and TGF-β). In turn, these cytokines stimulate development and proliferation of Tregs that may restrain Th1-type proinflammatory cytokine release early during tularemic infection. The highly regulated and overall anti-inflammatory milieu established in the lung is permissive for unfettered growth and survival of Ft. The capacity of Ft to evoke such a response represents an important immune-evasive strategy. PMID:21724804

  5. 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

  6. Metabolic profiling and flux analysis of MEL-2 human embryonic stem cells during exponential growth at physiological and atmospheric oxygen concentrations.

    PubMed

    Turner, Jennifer; Quek, Lake-Ee; Titmarsh, Drew; Krömer, Jens O; Kao, Li-Pin; Nielsen, Lars; Wolvetang, Ernst; Cooper-White, Justin

    2014-01-01

    As human embryonic stem cells (hESCs) steadily progress towards regenerative medicine applications there is an increasing emphasis on the development of bioreactor platforms that enable expansion of these cells to clinically relevant numbers. Surprisingly little is known about the metabolic requirements of hESCs, precluding the rational design and optimisation of such platforms. In this study, we undertook an in-depth characterisation of MEL-2 hESC metabolic behaviour during the exponential growth phase, combining metabolic profiling and flux analysis tools at physiological (hypoxic) and atmospheric (normoxic) oxygen concentrations. To overcome variability in growth profiles and the problem of closing mass balances in a complex environment, we developed protocols to accurately measure uptake and production rates of metabolites, cell density, growth rate and biomass composition, and designed a metabolic flux analysis model for estimating internal rates. hESCs are commonly considered to be highly glycolytic with inactive or immature mitochondria, however, whilst the results of this study confirmed that glycolysis is indeed highly active, we show that at least in MEL-2 hESC, it is supported by the use of oxidative phosphorylation within the mitochondria utilising carbon sources, such as glutamine to maximise ATP production. Under both conditions, glycolysis was disconnected from the mitochondria with all of the glucose being converted to lactate. No difference in the growth rates of cells cultured under physiological or atmospheric oxygen concentrations was observed nor did this cause differences in fluxes through the majority of the internal metabolic pathways associated with biogenesis. These results suggest that hESCs display the conventional Warburg effect, with high aerobic activity despite high lactate production, challenging the idea of an anaerobic metabolism with low mitochondrial activity. The results of this study provide new insight that can be used in

  7. 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.

  8. Measurement of the Dewetting, Nucleation, and Deactivation Kinetics of Carbon Nanotube Population Growth by Environmental Transmission Electron Microscopy

    DOE PAGES

    Bedewy, Mostafa; Viswanath, B.; Meshot, Eric R.; ...

    2016-05-23

    In order to understand the collective growth of carbon nanotube (CNT) populations tailoring their properties for many applications is key. During the initial stages of CNT growth by chemical vapor deposition, catalyst nanoparticle formation by thin-film dewetting and the subsequent CNT nucleation processes dictate the CNT diameter distribution, areal density, and alignment. We use in situ environmental transmission electron microscopy (E-TEM) to observe the catalyst annealing, growth, and deactivation stages for a population of CNTs grown from a thin-film catalyst. Complementary in situ electron diffraction and TEM imaging show that, during the annealing step in hydrogen, reduction of the ironmore » oxide catalyst is concomitant with changes in the thin-film morphology; complete dewetting and the formation of a population of nanoparticles is only achieved upon the introduction of the carbon source, acetylene. The dewetting kinetics, i.e., the appearance of distinct nanoparticles, exhibits a sigmoidal (autocatalytic) curve with 95% of all nanoparticles appearing within 6 s. After nanoparticles form, they either nucleate CNTs or remain inactive, with incubation times measured to be as small as 3.5 s. Via E-TEM we also directly observe the crowding and self-alignment of CNTs after dewetting and nucleation. Additionally, in situ electron energy loss spectroscopy reveals that the collective rate of carbon accumulation decays exponentially. We conclude that the kinetics of catalyst formation and CNT nucleation must both be addressed in order to achieve uniform and high CNT density, and their transient behavior may be a primary cause of the well-known nonuniform density of CNT forests.« less

  9. Measurement of the Dewetting, Nucleation, and Deactivation Kinetics of Carbon Nanotube Population Growth by Environmental Transmission Electron Microscopy

    SciTech Connect

    Bedewy, Mostafa; Viswanath, B.; Meshot, Eric R.; Zakharov, Dmitri N.; Stach, Eric A.; Hart, A. John

    2016-05-23

    In order to understand the collective growth of carbon nanotube (CNT) populations tailoring their properties for many applications is key. During the initial stages of CNT growth by chemical vapor deposition, catalyst nanoparticle formation by thin-film dewetting and the subsequent CNT nucleation processes dictate the CNT diameter distribution, areal density, and alignment. We use in situ environmental transmission electron microscopy (E-TEM) to observe the catalyst annealing, growth, and deactivation stages for a population of CNTs grown from a thin-film catalyst. Complementary in situ electron diffraction and TEM imaging show that, during the annealing step in hydrogen, reduction of the iron oxide catalyst is concomitant with changes in the thin-film morphology; complete dewetting and the formation of a population of nanoparticles is only achieved upon the introduction of the carbon source, acetylene. The dewetting kinetics, i.e., the appearance of distinct nanoparticles, exhibits a sigmoidal (autocatalytic) curve with 95% of all nanoparticles appearing within 6 s. After nanoparticles form, they either nucleate CNTs or remain inactive, with incubation times measured to be as small as 3.5 s. Via E-TEM we also directly observe the crowding and self-alignment of CNTs after dewetting and nucleation. Additionally, in situ electron energy loss spectroscopy reveals that the collective rate of carbon accumulation decays exponentially. We conclude that the kinetics of catalyst formation and CNT nucleation must both be addressed in order to achieve uniform and high CNT density, and their transient behavior may be a primary cause of the well-known nonuniform density of CNT forests.

  10. 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…

  11. 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…

  12. New observations and insights into the morphology and growth kinetics of hydrate films.

    PubMed

    Li, Sheng-Li; Sun, Chang-Yu; Liu, Bei; Li, Zhi-Yun; Chen, Guang-Jin; Sum, Amadeu K

    2014-02-19

    The kinetics of film growth of hydrates of methane, ethane, and methane-ethane mixtures were studied by exposing a single gas bubble to water. The morphologies, lateral growth rates, and thicknesses of the hydrate films were measured for various gas compositions and degrees of subcooling. A variety of hydrate film textures was revealed. The kinetics of two-dimensional film growth was inferred from the lateral growth rate and initial thickness of the hydrate film. A clear relationship between the morphology and film growth kinetics was observed. The shape of the hydrate crystals was found to favour heat or mass transfer and favour further growth of the hydrate film. The quantitative results on the kinetics of film growth showed that for a given degree of subcooling, the initial film thicknesses of the double hydrates were larger than that of pure methane or ethane hydrate, whereas the thickest hydrate film and the lowest lateral growth rate occurred when the methane mole fraction was approximately 0.6.

  13. Hypothesized kinetic models for describing the growth of globular and encrusting demosponges.

    PubMed

    Sipkema, Detmer; Yosef, Nejla A M; Adamczewski, Marcin; Osinga, Ronald; Mendola, Dominick; Tramper, Johannes; Wijffels, René H

    2006-01-01

    The marine sponges Dysidea avara and Chondrosia reniformis (globular forms) were cultured in the laboratory on a diet of viable Phaeodactylum tricornutum cells and dissolved nutrients (algae and fish powders). Our growth data were combined with literature data for Pseudosuberites andrewsi (a globular sponge) and for the encrusting sponges Oscarella lobularis, Hemimycale columella, and Crambe crambe. The suitability of three growth models-linear, exponential, and radial accretive-for describing the growth of globular and encrusting sponges was assessed. Radial accretive growth was determined to be the best model to describe growth of both encrusting and globular sponges. Average growth rates of 0.051+/-0.016 and 0.019+/-0.003 mm/day (calculated as the increase of the radius of the sponge per day) were obtained experimentally for D. avara and C. reniformis, respectively.

  14. Time-Lapse Imaging to Examine the Growth Kinetics of Arabidopsis Seedlings in Response to Ethylene.

    PubMed

    Binder, Brad M

    2017-01-01

    Ethylene is well known to inhibit the growth of dark-grown eudicot seedlings. Most studies examine this inhibition after several days of exposure to ethylene. However, such end-point analysis misses transient responses and the dynamic nature of growth regulation. Here, high-resolution, time-lapse imaging is described as a method to gather data about ethylene growth kinetics and movement responses of the hypocotyls of dark-grown seedlings of Arabidopsis thaliana. These methods allow for the characterization of short-term kinetic responses and can be modified for the analysis of roots and seedlings from other species.

  15. Modeling of scale-dependent bacterial growth by chemical kinetics approach.

    PubMed

    Martínez, Haydee; Sánchez, Joaquín; Cruz, José-Manuel; Ayala, Guadalupe; Rivera, Marco; Buhse, Thomas

    2014-01-01

    We applied the so-called chemical kinetics approach to complex bacterial growth patterns that were dependent on the liquid-surface-area-to-volume ratio (SA/V) of the bacterial cultures. The kinetic modeling was based on current experimental knowledge in terms of autocatalytic bacterial growth, its inhibition by the metabolite CO2, and the relief of inhibition through the physical escape of the inhibitor. The model quantitatively reproduces kinetic data of SA/V-dependent bacterial growth and can discriminate between differences in the growth dynamics of enteropathogenic E. coli, E. coli JM83, and Salmonella typhimurium on one hand and Vibrio cholerae on the other hand. Furthermore, the data fitting procedures allowed predictions about the velocities of the involved key processes and the potential behavior in an open-flow bacterial chemostat, revealing an oscillatory approach to the stationary states.

  16. Influence of Glucose Supplementation and Inoculum Size on Growth Kinetics and Antifungal Susceptibility Testing of Candida spp.

    PubMed Central

    Cuenca-Estrella, Manuel; Díaz-Guerra, Teresa M.; Mellado, Emilia; Rodríguez-Tudela, Juan L.

    2001-01-01

    The influences of inoculum size and glucose supplementation on the growth kinetics of 60 Candida spp. clinical isolates (Candida albicans, Candida tropicalis, Candida parapsilosis, Candida glabrata, Candida krusei, and Candida lusitaniae [10 isolates each]) are assessed. The combined influence of growth and reading method (visual or spectrophotometric) on the determination of the MICs of amphotericin B, flucytosine, fluconazole, itraconazole, ketoconazole, and voriconazole is also analyzed, and the MICs are compared with those determined by the National Committee for Clinical Laboratory Standards standard microdilution method (NCCLS document M27-A). Glucose supplementation and inoculum size had a significant influence on the growth cycles of these yeasts, and a statistically significant denser growth (optical density at 540 nm) was seen for both incubation periods, 24 and 48 h (P < 0.01). A longer exponential phase and shorter lag phase were also observed. The A540 values at 24 h of incubation with medium containing glucose and an inoculum of 105 CFU/ml were >0.4 U for all species, with the exception of that for C. parapsilosis (A540 = 0.26 ± 0.025). The MICs at 24 h determined by testing with 2% glucose and an inoculum of 105 CFU/ml showed the strongest agreement (96.83%) with MICs determined by the reference method. MICs were not falsely elevated, and good correlation indexes were obtained. The reproducibility of results with this medium-inoculum combination was high (intraclass correlation coefficient, 0.955). The best agreement and reproducibility of results for spectrophotometric readings were achieved with endpoints of 50% growth inhibition for flucytosine and azoles and 95% for amphotericin B. Supplementation of test media with glucose and an inoculum size of 105 CFU/ml yielded a reproducible technique that shows elevated agreement with the reference procedures and a shorter incubation period for obtaining reliable MIC determinations. The spectrophotometric

  17. 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.)

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

    SciTech Connect

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

    2016-03-15

    Here, 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.

  19. 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.

  20. 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.

  1. Flowtube experiments on diamond formation: separating the growth and nucleation kinetics

    NASA Astrophysics Data System (ADS)

    Martin, L. R.; Hill, Michael W.

    1990-12-01

    We have done a series of experiments on diamond microcrystal formation in flowtubes. The system is designed to separate the discharge used to create atomic hydrogen from the organic molecules used as a carbon source. This creates a simplified chemical environment in which the species concentrations are kinetically rather than thermodynamically controlled. The flowtube enables us to examine kinetics of diamond formation under a variety of conditions and gives us some information about the rate of nucleation independently of the growth rate. 1.

  2. 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

  3. 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

  4. 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.

  5. 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…

  6. Growth kinetics of hydrogen sulfide oxidizing bacteria in corroded concrete from sewers.

    PubMed

    Jensen, Henriette Stokbro; Lens, Piet N L; Nielsen, Jeppe L; Bester, Kai; Nielsen, Asbjørn Haaning; Hvitved-Jacobsen, Thorkild; Vollertsen, Jes

    2011-05-30

    Hydrogen sulfide oxidation by microbes present on concrete surfaces of sewer pipes is a key process in sewer corrosion. The growth of aerobic sulfur oxidizing bacteria from corroded concrete surfaces was studied in a batch reactor. Samples of corrosion products, containing sulfur oxidizing bacteria, were suspended in aqueous solution at pH similar to that of corroded concrete. Hydrogen sulfide was supplied to the reactor to provide the source of reduced sulfur. The removal of hydrogen sulfide and oxygen was monitored. The utilization rates of both hydrogen sulfide and oxygen suggested exponential bacterial growth with median growth rates of 1.25 d(-1) and 1.33 d(-1) as determined from the utilization rates of hydrogen sulfide and oxygen, respectively. Elemental sulfur was found to be the immediate product of the hydrogen sulfide oxidation. When exponential growth had been achieved, the addition of hydrogen sulfide was terminated leading to elemental sulfur oxidation. The ratio of consumed sulfur to consumed oxygen suggested that sulfuric acid was the ultimate oxidation product. To the knowledge of the authors, this is the first study to determine the growth rate of bacteria involved in concrete corrosion with hydrogen sulfide as source of reduced sulfur.

  7. Quantitative Polymerase Chain Reaction for Microbial Growth Kinetics of Mixed Culture System.

    PubMed

    Cotto, Ada; Looper, Jessica K; Mota, Linda C; Son, Ahjeong

    2015-11-01

    Microbial growth kinetics is often used to optimize environmental processes owing to its relation to the breakdown of substrate (contaminants). However, the quantification of bacterial populations in the environment is difficult owing to the challenges of monitoring a specific bacterial population within a diverse microbial community. Conventional methods are unable to detect and quantify the growth of individual strains separately in the mixed culture reactor. This work describes a novel quantitative PCR (qPCR)-based genomic approach to quantify each species in mixed culture and interpret its growth kinetics in the mixed system. Batch experiments were performed for both single and dual cultures of Pseudomonas putida and Escherichia coli K12 to obtain Monod kinetic parameters (μmax and Ks). The growth curves and kinetics obtained by conventional methods (i.e., dry weight measurement and absorbance reading) were compared with that obtained by qPCR assay. We anticipate that the adoption of this qPCR-based genomic assay can contribute significantly to traditional microbial kinetics, modeling practice, and the operation of bioreactors, where handling of complex mixed cultures is required.

  8. Crystal nucleation and cluster-growth kinetics in a model glass under shear

    NASA Astrophysics Data System (ADS)

    Mokshin, Anatolii V.; Barrat, Jean-Louis

    2010-08-01

    Crystal nucleation and growth processes induced by an externally applied shear strain in a model metallic glass are studied by means of nonequilibrium molecular dynamics simulations, in a range of temperatures. We observe that the nucleation-growth process takes place after a transient, induction regime. The critical cluster size and the lag-time associated with this induction period are determined from a mean first-passage time analysis. The laws that describe the cluster-growth process are studied as a function of temperature and strain rate. A theoretical model for crystallization kinetics that includes the time dependence for nucleation and cluster growth is developed within the framework of the Kolmogorov-Johnson-Mehl-Avrami scenario and is compared with the molecular dynamics data. Scalings for the cluster-growth laws and for the crystallization kinetics are also proposed and tested. The observed nucleation rates are found to display a nonmonotonic strain rate dependency.

  9. 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.

  10. Reactive Dependent Growth Kinetics and Morphology of A-B Ternary Mixtures

    NASA Astrophysics Data System (ADS)

    Feng, Wen-Qiang; Wang, Kai-Ming; Zhu, Yue-Jin

    2013-08-01

    In this paper, we present Monte Carlo simulations of A-B-diblock-copolymer ternary mixtures simultaneously undergoing phase separation and reversible chemical reaction A + B ⇌ C. The results demonstrate that the competition of chemical reaction and thermal diffusion dynamics co-determine the self-assembling morphology and growth kinetics of the reactive ternary mixtures. The role of the chemical reaction on the growth kinetics count mainly on the copolymer-polymer interaction strength Jp. If Jp < 1.0, the introduction of chemical reaction speeds up the domain growth; while for Jp > 1.0, the chemical reaction slows down the domain growth. The domain growth exponent decreases linearly with increasing of the copolymer-polymer interaction strength. At a later stage, <1, 0> and <0, 1> oriented strip pattern formations are observed when Jp is strong.

  11. Relationship between kinetics of growth and production of exo-electrons: Case study with Geobacter toluenoxydans.

    PubMed

    Szöllősi, Attila; Narr, László; Kovács, Attila G; Styevkó, Gabriella

    2015-09-01

    Kinetics of growth and product formation of G. toluenoxydans DSMZ 19350 strain were investigated using sodium-acetate as substrate and Fe(3+)-ions and fumarate as electron acceptor. Response surface method was adapted for evaluation of growth of bacteria. Results showed that maximum growth was detected in the case of 2.2 g/L substrate concentration. Application of higher substrate concentration (>2.5 g/L sodium acetate) significantly inhibits the bacterial growth. Luong's model was found to be the most suitable to determine kinetic parameters (μ(max) = 0.033 1/h, KS = 0.205 g/L) of growth of G.toluenoxydans strain, and the growth was completely inhibited at substrate concentration higher than 3.1 g/L. In the case of product formation the Haldane model was used and kinetic parameters are μ(Pmax) = 0.123 mg/h, K(PS)= 0.184 g/L. Correlation between microbial growth and product formation was observed using the Luedeking-Piret empirical method. Both factors (growth and number of cells) affected significantly iron(III)-reduction, thus the product formation. These results are important and open the possibility to design a continuous MFC setting operating with G. toluenoxydans as biocatalyst.

  12. 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.

  13. 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

  14. 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.

  15. Exponential splines: A survey

    SciTech Connect

    McCartin, B.J.

    1996-12-31

    Herein, we discuss a generalization of the semiclassical cubic spline known in the literature as the exponential spline. 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 {open_quotes}tension{close_quotes} parameters. We first outline the theoretical underpinnings of the exponential spline. 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. We next discuss the numerical computation of the exponential spline. 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. We conclude with a consideration of the broad spectrum of possible uses of exponential splines in the applications. Our primary emphasis is on computational fluid dynamics although the imaginative reader will recognize the wider generality of the techniques developed.

  16. Domain and rim growth kinetics in stratifying foam films

    NASA Astrophysics Data System (ADS)

    Zhang, Yiran; Yilixiati, Subinuer; Sharma, Vivek

    Foam films are freely standing thin liquid films that typically 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. During the initial expansion, a rim forms near the contact line between the growing thinner domain and the surrounding region, which influences the dynamics of domain growth as well as stratification Using newly developed interferometry digitial imaging optical microscopy (IDIOM) technique, we capture the rim evolution dynamics. Finally, we also develop a theoretical model to describe both rim evolution and domain growth dynamics.

  17. Phosphate-limited continuous culture of Rhodotorula rubra: kinetics of transport, leakage, and growth.

    PubMed Central

    Robertson, B R; Button, D K

    1979-01-01

    The phosphate-limited growth kinetics of Rhodotorula rubra, a small yeast of marine origin, were examined by analysis of 32P distributions in continuous cultures. Isotope relaxation procedures were used to identify unidirectional flows of Pi and organic phosphate among compartments modeled during growth. The concentrations of phosphates in these compartments at various growth rates were used, together with attendant flows, to produce a mathematical model of growth. Both Pi and phosphate-containing metabolic intermediates leaked from cells during growth. Total leakage ranged from 4 to 10% of influx and was comprised mostly of Pi. Transport capacity was at least 10 times that required for growth at saturating Pi concentrations, so that influx was linear with concentration during growth. This led to the realization that the curvature of Monod plots (Kmu = 12 nM mumax = 0.18/h, and the threshold At = 2.5 nM) is due to change in yield with growth rate. Growth rate related to Pi by the affinity, aA (= 0.43 liter/mg of cells.h) of cells for Pi and the growth rate-dependent yield. It was also specified by a series of kinetic constants that specified flow among the various compartments and equilibrium compartment concentrations as they were set by extracellular Pi. The importance of leakage by healthy cells to the organic chemistry of aquatic systems is noted. PMID:37231

  18. Pyridine nucleotide cycling and control of intracellular redox state in relation to poly (ADP-ribose) polymerase activity and nuclear localization of glutathione during exponential growth of Arabidopsis cells in culture.

    PubMed

    Pellny, Till K; Locato, Vittoria; Vivancos, Pedro Diaz; Markovic, Jelena; De Gara, Laura; Pallardó, Federico V; Foyer, Christine H

    2009-05-01

    Pyridine nucleotides, ascorbate and glutathione are major redox metabolites in plant cells, with specific roles in cellular redox homeostasis and the regulation of the cell cycle. However, the regulation of these metabolite pools during exponential growth and their precise functions in the cell cycle remain to be characterized. The present analysis of the abundance of ascorbate, glutathione, and pyridine nucleotides during exponential growth of Arabidopsis cells in culture provides evidence for the differential regulation of each of these redox pools. Ascorbate was most abundant early in the growth cycle, but glutathione was low at this point. The cellular ascorbate to dehydroascorbate and reduced glutathione (GSH) to glutathione disulphide ratios were high and constant but the pyridine nucleotide pools were largely oxidized over the period of exponential growth and only became more reduced once growth had ceased. The glutathione pool increased in parallel with poly (ADP-ribose) polymerase (PARP) activities and with increases in the abundance of PARP1 and PARP2 mRNAs at a time of high cell cycle activity as indicated by transcriptome information. Marked changes in the intracellular partitioning of GSH between the cytoplasm and nucleus were observed. Extension of the exponential growth phase by dilution or changing the media led to increases in the glutathione and nicotinamide adenine dinucleotide, oxidized form (NAD)-plus-nicotinamide adenine dinucleotide, reduced form (NADH) pools and to higher NAD/NADH ratios but the nicotinamide adenine dinucleotide phosphate, oxidized form (NADP)-plus-nicotinamide adenine dinucleotide phosphate, reduced form (NADPH) pool sizes, and NAPD/NADPH ratios were much less affected. The ascorbate, glutathione, and pyridine nucleotide pools and PARP activity decreased before the exponential growth phase ended. We conclude that there are marked changes in intracellular redox state during the growth cycle but that redox homeostasis is

  19. Kinetic growth mode of epitaxial GaAs on Si(001) micro-pillars

    NASA Astrophysics Data System (ADS)

    Bergamaschini, Roberto; Bietti, Sergio; Castellano, Andrea; Frigeri, Cesare; Falub, Claudiu V.; Scaccabarozzi, Andrea; Bollani, Monica; von Känel, Hans; Miglio, Leo; Sanguinetti, Stefano

    2016-12-01

    Three-dimensional, epitaxial GaAs crystals are fabricated on micro-pillars patterned into Si(001) substrates by exploiting kinetically controlled growth conditions in Molecular Beam Epitaxy. The evolution of crystal morphology during growth is assessed by considering samples with increasing GaAs deposit thickness. Experimental results are interpreted by a kinetic growth model, which takes into account the fundamental aspects of the growth and mutual deposition flux shielding between neighboring crystals. Different substrate pattern geometries with dissimilar lateral sizes and periodicities of the Si micro-pillars are considered and self-similar crystal structures are recognized. It is demonstrated that the top faceting of the GaAs crystals is tunable, which can pave the way to locally engineer compound semiconductor quantum structures on Si(001) substrates.

  20. 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.

  1. A growth kinetic model of Kluyveromyces marxianus cultures on cheese whey as substrate.

    PubMed

    Longhi, Luís G S; Luvizetto, Débora J; Ferreira, Luciane S; Rech, Rosane; Ayub, Marco A Z; Secchi, Argimiro R

    2004-01-01

    This work presents a multi-route, non-structured kinetic model for determination of microbial growth and substrate consumption in an experimental batch bioreactor in which beta-galactosidase is produced by Kluyveromyces marxianus growing on cheese whey. The main metabolic routes for lactose, and oxygen consumption, cell growth, and ethanol production are derived based on experimental data. When these individual rates are combined into a single growth rate, by rewriting the model equations, the model re-interpretation has a complexity similar to that of the usual variations of the Monod kinetic model, available in the literature. Furthermore, the proposed model is in good agreement with the experimental data for different growth temperatures, being acceptable for dynamic simulations, processes optimization, and implementations of model-based control technologies.

  2. Effect of wall growth on the kinetic modeling of nitrite oxidation in a CSTR.

    PubMed

    Dokianakis, Spiros N; Kornaros, Michael; Lyberatos, Gerasimos

    2006-03-05

    A simple kinetic model was developed for describing nitrite oxidation by autotrophic aerobic nitrifiers in a continuous stirred tank reactor (CSTR), in which mixed (suspended and attached) growth conditions prevail. The CSTR system was operated under conditions of constant nitrite feed concentration and varying volumetric flow rates. Experimental data from steady-state conditions in the CSTR system and from batch experiments were used for the determination of the model's kinetic parameters. Model predictions were verified against experimental data obtained under transient operating conditions, when volumetric flow rate and nitrite feed concentration disturbances were imposed on the CSTR. The presented kinetic modeling procedure is quite simple and general and therefore can also be applied to other mixed growth biological systems.

  3. 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.

  4. 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...

  5. Dynamic identification of growth and survival kinetic parameters of microorganisms in foods

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Inverse analysis is a mathematical method used in predictive microbiology to determine the kinetic parameters of microbial growth and survival in foods. The traditional approach in inverse analysis relies on isothermal experiments that are time-consuming and labor-intensive, and errors are accumula...

  6. 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…

  7. Understanding the isothermal growth kinetics of cdse quantum dots through microfluidic reactor assisted combinatorial synthesis

    NASA Astrophysics Data System (ADS)

    Swain, Basudev; Hong, Myung Hwan; Kang, Lee-Seung; Lee, Chan Gi

    2016-11-01

    With the use of a microfluidic-assisted combinatorial reactor, the synthesis of CdSe quantum dots was optimized by varying one parameter at a time, and the isothermal growth kinetics of CdSe quantum dots using various models was analyzed. To understand precisely the nucleation and growth characteristics of CdSe quantum dots (QDs), we synthesized the CdSe QDs using various experimental conditions. Different model equations, like acceleratory growth-time curves, sigmoidal growth-time curves or Johnson-Mehl-Avrami-Kolmogorov (JMAK), acceleratory growthtime curves based on diffusion, geometric model growth-time curves, and nth order growth-time curves were fitted. Among all growth models, the JMAK model with α = 1 - {e^{ - {{(kt)}^n}}}, and n = 1 was the best fitting model with the MATLAB interactive curve-fitting procedure were used. Errors associated with the best-fitting model and statistics for the goodness of fit were analyzed. Most of the models were not as good as the other than the proposed model. The errors associated with the proposed model were minimal, and the growth kinetics and other associated statistical factors are very similar, for all the variables investigated. The minimal error associated with the reproducibility and the similar data for growth kinetics for all studied parameters indicated that microfluidic-assisted combinatorial synthesis can be used in the industrial production of QDs. By using the proposed model to obtain an understanding of growth of QDs, their size and properties can be managed and simulated.

  8. 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%).

  9. Analytical solution of Luedeking-Piret equation for a batch fermentation obeying Monod growth kinetics.

    PubMed

    Garnier, Alain; Gaillet, Bruno

    2015-12-01

    Not so many fermentation mathematical models allow analytical solutions of batch process dynamics. The most widely used is the combination of the logistic microbial growth kinetics with Luedeking-Piret bioproduct synthesis relation. However, the logistic equation is principally based on formalistic similarities and only fits a limited range of fermentation types. In this article, we have developed an analytical solution for the combination of Monod growth kinetics with Luedeking-Piret relation, which can be identified by linear regression and used to simulate batch fermentation evolution. Two classical examples are used to show the quality of fit and the simplicity of the method proposed. A solution for the combination of Haldane substrate-limited growth model combined with Luedeking-Piret relation is also provided. These models could prove useful for the analysis of fermentation data in industry as well as academia.

  10. 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.

  11. 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

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

    PubMed

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

    2016-03-28

    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.

  13. Edge-controlled growth and kinetics of single-crystal graphene domains by chemical vapor deposition.

    PubMed

    Ma, Teng; Ren, Wencai; Zhang, Xiuyun; Liu, Zhibo; Gao, Yang; Yin, Li-Chang; Ma, Xiu-Liang; Ding, Feng; Cheng, Hui-Ming

    2013-12-17

    The controlled growth of large-area, high-quality, single-crystal graphene is highly desired for applications in electronics and optoelectronics; however, the production of this material remains challenging because the atomistic mechanism that governs graphene growth is not well understood. The edges of graphene, which are the sites at which carbon accumulates in the two-dimensional honeycomb lattice, influence many properties, including the electronic properties and chemical reactivity of graphene, and they are expected to significantly influence its growth. We demonstrate the growth of single-crystal graphene domains with controlled edges that range from zigzag to armchair orientations via growth-etching-regrowth in a chemical vapor deposition process. We have observed that both the growth and the etching rates of a single-crystal graphene domain increase linearly with the slanted angle of its edges from 0° to ∼19° and that the rates for an armchair edge are faster than those for a zigzag edge. Such edge-structure-dependent growth/etching kinetics of graphene can be well explained at the atomic level based on the concentrations of the kinks on various edges and allow the evolution and control of the edge and morphology in single-crystal graphene following the classical kinetic Wulff construction theory. Using these findings, we propose several strategies for the fabrication of wafer-sized, high-quality, single-crystal graphene.

  14. Monte Carlo simulation of the kinetic effects on GaAs/GaAs(001) MBE growth

    NASA Astrophysics Data System (ADS)

    Ageev, Oleg A.; Solodovnik, Maxim S.; Balakirev, Sergey V.; Mikhaylin, Ilya A.; Eremenko, Mikhail M.

    2017-01-01

    The molecular beam epitaxial growth of GaAs on the GaAs(001)-(2×4) surface is investigated using a kinetic Monte Carlo-based method. The developed algorithm permits to focus on the kinetic effects in a wide range of growth conditions and enables considerable computational speedup. The simulation results show that the growth rate has a dramatic influence upon both the island morphology and Ga surface diffusion length. The average island size reduces with increasing growth rate while the island density increases with increasing growth rate as well as As4/Ga beam equivalent pressure ratio. As the growth rate increases, the island density becomes weaker dependent upon the As4/Ga pressure ratio and approaches to a saturation value. We also discuss three characteristics of Ga surface diffusion, namely a diffusion length of a Ga adatom deposited first, an average diffusion length, and an island spacing as an average distance between islands. The calculations show that the As4/Ga pressure ratio dependences of these characteristics obey the same law, but with different coefficients. An increase of the As4/Ga pressure ratio leads to a decrease in both the diffusion length and island spacing. However, its influence becomes stronger with increasing growth rate for the first Ga adatom diffusion length and weaker for the average diffusion length and for the island spacing.

  15. A Kinetic Model for GaAs Growth by Hydride Vapor Phase Epitaxy

    SciTech Connect

    Schulte, Kevin L.; Simon, John; Jain, Nikhil; Young, David L.; Ptak, Aaron J.

    2016-11-21

    Precise control of the growth of III-V materials by hydride vapor phase epitaxy (HVPE) is complicated by the fact that the growth rate depends on the concentrations of nearly all inputs to the reactor and also the reaction temperature. This behavior is in contrast to metalorganic vapor phase epitaxy (MOVPE), which in common practice operates in a mass transport limited regime where growth rate and alloy composition are controlled almost exclusively by flow of the Group III precursor. In HVPE, the growth rate and alloy compositions are very sensitive to temperature and reactant concentrations, which are strong functions of the reactor geometry. HVPE growth, particularly the growth of large area materials and devices, will benefit from the development of a growth model that can eventually be coupled with a computational fluid dynamics (CFD) model of a specific reactor geometry. In this work, we develop a growth rate law using a Langmuir-Hinshelwood (L-H) analysis, fitting unknown parameters to growth rate data from the literature that captures the relevant kinetic and thermodynamic phenomena of the HVPE process. We compare the L-H rate law to growth rate data from our custom HVPE reactor, and develop quantitative insight into reactor performance, demonstrating the utility of the growth model.

  16. Exponentially fitted symplectic integrator

    NASA Astrophysics Data System (ADS)

    Simos, T. E.; Vigo-Aguiar, Jesus

    2003-01-01

    In this paper a procedure for constructing efficient symplectic integrators for Hamiltonian problems is introduced. This procedure is based on the combination of the exponential fitting technique and symplecticness conditions. Based on this procedure, a simple modified Runge-Kutta-Nyström second-order algebraic exponentially fitted method is developed. We give explicitly the symplecticness conditions for the modified Runge-Kutta-Nyström method. We also give the exponential fitting and trigonometric fitting conditions. Numerical results indicate that the present method is much more efficient than the “classical” symplectic Runge-Kutta-Nyström second-order algebraic method introduced by M.P. Calvo and J.M. Sanz-Serna [J. Sci. Comput. (USA) 14, 1237 (1993)]. We note that the present procedure is appropriate for all near-unimodal systems.

  17. Kinetics of grain-growth in wadsleyite: implications for point defect chemistry

    NASA Astrophysics Data System (ADS)

    Nishihara, Y.; Shinmei, T.; Karato, S.

    2003-12-01

    We investigate the kinetics of grain-growth in wadsleyite for two reasons. First, grain-growth kinetics controls the grain-size of wadsleyite in the mantle transition zone which in turn controls the rheology in that region. Second, the detailed knowledge of grain-growth kinetics will provide us with important constraints on the defect-related properties of this mineral which may control other properties such as diffusion, electrical conductivity and creep. We carried out the grain-growth experiments by using KIWI 1000-ton Kawai-type multi-anvil apparatus installed at Yale University. Starting material was synthesized from powdered San Carlos olivine. The grain-growth experiments were conducted at 15 GPa and 1100-1500° C for 1-24 hours. We used Mo, Ni and Re foil capsules, in order to control the oxygen fugacity by metal-oxide buffer. For ''wet'' experiments (water-saturated), a mixture of talc and brucite was packed into a capsule together with a wadsleyite sample separated by metal foils. We used a Au-Pd outer capsule which is known to be a good barrier for hydrogen diffusion. Water content in each sample was determined after an experiment by FTIR analysis of a doubly polished thin section. Grain-size was measured on a polished section using an intercept method. One of the difficulties in these experiments is to reduce the amount of water in wadsleyite. Even in nominally ''dry'' experiments in which no water is added, a significant amount of water (upto ˜25,000 H/106 Si) was detected, which comes presumably from some components in the sample assembly such as the cement. This water-uptake by wadsleyite can be minimized by surrounding it with a Au-Pd capsule. In this truly ''dry'' sample assembly, the water content of wadsleyite (after an experiment) is reduced to less than ˜100 H/106 Si, a water content similar to typical ''dry'' experiments on olivine. Compared at similar water content, the kinetics of grain-growth in wadsleyite is significantly slower than

  18. 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…

  19. A kinetic model to simulate protein crystal growth in an evaporation-based crystallization platform

    SciTech Connect

    Talreja, S.; Kenis, P; Zukoski, C

    2007-01-01

    The quality, size, and number of protein crystals grown under conditions of continuous solvent extraction are dependent on the rate of solvent extraction and the initial protein and salt concentration. An increase in the rate of solvent extraction leads to a larger number of crystals. The number of crystals decreases, however, when the experiment is started with an initial protein concentration that is closer to the solubility boundary. Here we develop a kinetic model capable of predicting changes in the number and size of protein crystals as a function of time under continuous evaporation. Moreover, this model successfully predicts the initial condition of drops that will result in gel formation. We test this model with experimental crystal growth data of hen egg white lysozyme for which crystal nucleation and growth rate parameters are known from other studies. The predicted and observed rates of crystal growth are in excellent agreement, which suggests that kinetic constants for nucleation and crystal growth for different proteins can be extracted by applying a kinetic model in combination with observations from a few evaporation-based crystallization experiments.

  20. Growth kinetics of cubic carbide free layers in graded cemented carbides

    NASA Astrophysics Data System (ADS)

    Shi, Liu-Yong; Liu, Yi-Min; Huang, Ji-Hua; Zhang, Shou-Quan; Zhao, Xing-Ke

    2012-01-01

    In order to reveal the formation mechanism of cubic carbide free layers (CCFL), graded cemented carbides with CCFL in the surface zone were fabricated by a one-step sintering procedure in vacuum, and the analysis on microstructure and element distribution were performed by scanning electron microscopy (SEM) and electron probe micro-analyzer (EPMA), respectively. A new physical model and kinetic equation were established based on experimental results. Being different from previous models, this model suggests that nitrogen diffusion outward is only considered as an induction factor, and the diffusion of titanium through liquid phase plays a dominative role. The driving force of diffusion is expressed as the differential value between nitrogen partial pressure and nitrogen equilibrium pressure essentially. Simulation results by the kinetic equation are in good agreement with experimental values, and the effect of process parameters on the growth kinetics of CCFL can also be explained reasonably by the current model.

  1. Analysis of Arabidopsis thaliana root growth kinetics with high temporal and spatial resolution

    PubMed Central

    Yazdanbakhsh, Nima; Fisahn, Joachim

    2010-01-01

    Background Methods exist to quantify the distribution of growth rate over the root axis. However, non-destructive, high-throughput evaluations of total root elongation in controlled environments and the field are lacking in growth studies. A new imaging approach to analyse total root elongation is described. Scope High pixel resolution of the images enables the study of growth in short time intervals and provides high temporal resolution. Using the method described, total root elongation rates are calculated from the displacement of the root tip. Although the absolute root elongation rate changes in response to growth conditions, this set-up enables root growth of Arabidopsis wild-type seedlings to be followed for more than 1 month after germination. The method provides an easy approach to decipher root extension rate and much simpler calculations compared with other methods that use segmental growth to address this question. Conclusions The high temporal resolution allows small modifications of total root elongation growth to be revealed. Furthermore, with the options to investigate growth of various mutants in diverse growth conditions the present tool allows modulations in root growth kinetics due to different biotic and abiotic stimuli to be unravelled. Measurements performed on Arabidopsis thaliana wild-type (Col0) plants revealed rhythms superimposed on root elongation. Results obtained from the starchless mutant pgm, however, present a clearly modified pattern. As expected, deviation is strongest during the dark period. PMID:20421235

  2. 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.

  3. Catastrophic growth of gas hydrates in the presence of kinetic hydrate inhibitors.

    PubMed

    Cha, Minjun; Shin, Kyuchul; Seo, Yutaek; Shin, Ju-Young; Kang, Seong-Pil

    2013-12-27

    The effect of the concentration of kinetic hydrate inhibitors, polyvinylpyrrolidone (PVP), and polyvinylcaprolactam (PVCap) on the onset and growth of synthetic natural gas hydrates is investigated by measuring the hydrate onset time and gas consumption rate. Although the hydrate onset time is extended by increasing the concentration from 0.5 to 3.0 wt % for both PVP and PVCap, the growth rate of hydrates shows that the different tendency depends on the type of kinetic hydrate inhibitor and its concentration. For PVCap solution, the hydrate growth was slow for more than 1000 min after the onset at the concentration of 0.5 and 1.5 wt %. However, the growth rate becames almost 8 times faster at the concentration of 3.0 wt %, representing the catastrophic growth of hydrate just after the hydrate onset. (13)C NMR spectra of hydrates formed at 3.0 wt % of PVP and PVCap indicate the existence of both structures I and II. Cage occupancy of methane in large cages of structure II decreases significantly when compared to that for pure water. These results suggest that increasing the concentration of KHI up to 3.0 wt % may induce the earlier appearance of catastrophic hydrate growth and the existence of metastable structure I; thus, there needs to be an upper limit for using KHI to manage the formation of gas hydrates.

  4. 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.

  5. 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.

  6. Quantitative nucleation and growth kinetics of gold nanoparticles via model-assisted dynamic spectroscopic approach.

    PubMed

    Zhou, Yao; Wang, Huixuan; Lin, Wenshuang; Lin, Liqin; Gao, Yixian; Yang, Feng; Du, Mingming; Fang, Weiping; Huang, Jiale; Sun, Daohua; Li, Qingbiao

    2013-10-01

    Lacking of quantitative experimental data and/or kinetic models that could mathematically depict the redox chemistry and the crystallization issue, bottom-to-up formation kinetics of gold nanoparticles (GNPs) remains a challenge. We measured the dynamic regime of GNPs synthesized by l-ascorbic acid (representing a chemical approach) and/or foliar aqueous extract (a biogenic approach) via in situ spectroscopic characterization and established a redox-crystallization model which allows quantitative and separate parameterization of the nucleation and growth processes. The main results were simplified as the following aspects: (I) an efficient approach, i.e., the dynamic in situ spectroscopic characterization assisted with the redox-crystallization model, was established for quantitative analysis of the overall formation kinetics of GNPs in solution; (II) formation of GNPs by the chemical and the biogenic approaches experienced a slow nucleation stage followed by a growth stage which behaved as a mixed-order reaction, and different from the chemical approach, the biogenic method involved heterogeneous nucleation; (III) also, biosynthesis of flaky GNPs was a kinetic-controlled process favored by relatively slow redox chemistry; and (IV) though GNPs formation consists of two aspects, namely the redox chemistry and the crystallization issue, the latter was the rate-determining event that controls the dynamic regime of the whole physicochemical process.

  7. Semirigorous synchronous sublattice algorithm for parallel kinetic Monte Carlo simulations of thin film growth

    NASA Astrophysics Data System (ADS)

    Shim, Yunsic; Amar, Jacques G.

    2005-03-01

    The standard kinetic Monte Carlo algorithm is an extremely efficient method to carry out serial simulations of dynamical processes such as thin film growth. However, in some cases it is necessary to study systems over extended time and length scales, and therefore a parallel algorithm is desired. Here we describe an efficient, semirigorous synchronous sublattice algorithm for parallel kinetic Monte Carlo simulations. The accuracy and parallel efficiency are studied as a function of diffusion rate, processor size, and number of processors for a variety of simple models of epitaxial growth. The effects of fluctuations on the parallel efficiency are also studied. Since only local communications are required, linear scaling behavior is observed, e.g., the parallel efficiency is independent of the number of processors for fixed processor size.

  8. 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.

  9. Exponential Localization of Photons

    NASA Astrophysics Data System (ADS)

    Bialynicki-Birula, Iwo

    1998-06-01

    It is shown that photons can be localized in space with an exponential falloff of the energy density and photodetection rates. The limits of localization are determined by the fundamental Paley-Wiener theorem. A direct mathematical connection between the spatial localization of photons and the decay in time of quantum mechanical systems is established.

  10. 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.

  11. Nonlinear Response of Layer Growth Dynamics in the Mixed Kinetics-Bulk-Transport Regime

    NASA Technical Reports Server (NTRS)

    Vekilov, Peter G.; Alexander, J. Iwan D.; Rosenberger, Franz

    1996-01-01

    In situ high-resolution interferometry on horizontal facets of the protein lysozyme reveal that the local growth rate R, vicinal slope p, and tangential (step) velocity v fluctuate by up to 80% of their average values. The time scale of these fluctuations, which occur under steady bulk transport conditions through the formation and decay of step bunches (macrosteps), is of the order of 10 min. The fluctuation amplitude of R increases with growth rate (supersaturation) and crystal size, while the amplitude of the v and p fluctuations changes relatively little. Based on a stability analysis for equidistant step trains in the mixed transport-interface-kinetics regime, we argue that the fluctuations originate from the coupling of bulk transport with nonlinear interface kinetics. Furthermore, step bunches moving across the interface in the direction of or opposite to the buoyancy-driven convective flow increase or decrease in height, respectively. This is in agreement with analytical treatments of the interaction of moving steps with solution flow. Major excursions in growth rate are associated with the formation of lattice defects (striations). We show that, in general, the system-dependent kinetic Peclet number, Pe(sub k) , i.e., the relative weight of bulk transport and interface kinetics in the control of the growth process, governs the step bunching dynamics. Since Pe(sub k) can be modified by either forced solution flow or suppression of buoyancy-driven convection under reduced gravity, this model provides a rationale for the choice of specific transport conditions to minimize the formation of compositional inhomogeneities under steady bulk nutrient crystallization conditions.

  12. Prediction of microbial growth rate versus biomass yield by a metabolic network with kinetic parameters.

    PubMed

    Adadi, Roi; Volkmer, Benjamin; Milo, Ron; Heinemann, Matthias; Shlomi, Tomer

    2012-01-01

    Identifying the factors that determine microbial growth rate under various environmental and genetic conditions is a major challenge of systems biology. While current genome-scale metabolic modeling approaches enable us to successfully predict a variety of metabolic phenotypes, including maximal biomass yield, the prediction of actual growth rate is a long standing goal. This gap stems from strictly relying on data regarding reaction stoichiometry and directionality, without accounting for enzyme kinetic considerations. Here we present a novel metabolic network-based approach, MetabOlic Modeling with ENzyme kineTics (MOMENT), which predicts metabolic flux rate and growth rate by utilizing prior data on enzyme turnover rates and enzyme molecular weights, without requiring measurements of nutrient uptake rates. The method is based on an identified design principle of metabolism in which enzymes catalyzing high flux reactions across different media tend to be more efficient in terms of having higher turnover numbers. Extending upon previous attempts to utilize kinetic data in genome-scale metabolic modeling, our approach takes into account the requirement for specific enzyme concentrations for catalyzing predicted metabolic flux rates, considering isozymes, protein complexes, and multi-functional enzymes. MOMENT is shown to significantly improve the prediction accuracy of various metabolic phenotypes in E. coli, including intracellular flux rates and changes in gene expression levels under different growth rates. Most importantly, MOMENT is shown to predict growth rates of E. coli under a diverse set of media that are correlated with experimental measurements, markedly improving upon existing state-of-the art stoichiometric modeling approaches. These results support the view that a physiological bound on cellular enzyme concentrations is a key factor that determines microbial growth rate.

  13. Linking genes to microbial growth kinetics: an integrated biochemical systems engineering approach.

    PubMed

    Koutinas, Michalis; Kiparissides, Alexandros; Silva-Rocha, Rafael; Lam, Ming-Chi; Martins Dos Santos, Vitor A P; de Lorenzo, Victor; Pistikopoulos, Efstratios N; Mantalaris, Athanasios

    2011-07-01

    The majority of models describing the kinetic properties of a microorganism for a given substrate are unstructured and empirical. They are formulated in this manner so that the complex mechanism of cell growth is simplified. Herein, a novel approach for modelling microbial growth kinetics is proposed, linking biomass growth and substrate consumption rates to the gene regulatory programmes that control these processes. A dynamic model of the TOL (pWW0) plasmid of Pseudomonas putida mt-2 has been developed, describing the molecular interactions that lead to the transcription of the upper and meta operons, known to produce the enzymes for the oxidative catabolism of m-xylene. The genetic circuit model was combined with a growth kinetic model decoupling biomass growth and substrate consumption rates, which are expressed as independent functions of the rate-limiting enzymes produced by the operons. Estimation of model parameters and validation of the model's predictive capability were successfully performed in batch cultures of mt-2 fed with different concentrations of m-xylene, as confirmed by relative mRNA concentration measurements of the promoters encoded in TOL. The growth formation and substrate utilisation patterns could not be accurately described by traditional Monod-type models for a wide range of conditions, demonstrating the critical importance of gene regulation for the development of advanced models closely predicting complex bioprocesses. In contrast, the proposed strategy, which utilises quantitative information pertaining to upstream molecular events that control the production of rate-limiting enzymes, predicts the catabolism of a substrate and biomass formation and could be of central importance for the design of optimal bioprocesses.

  14. Retrospective growth kinetics and radiosensitivity analysis of various human xenograft models

    PubMed Central

    Lee, Ji Young; Kim, Eun Ho; Chung, Namhyun

    2016-01-01

    The purpose of this study was to delineate the various factors that affect the growth characteristics of human cancer xenografts in nude mice and to reveal the relationship between the growth characteristics and radiosensitivity. We retrospectively analyzed 390 xenografts comprising nine different human cancer lines grown in nude mice used in our institute between 2009 and 2015. Tumor growth rate (TGR) was calculated using exponential growth equations. The relationship between the TGR of xenografts and the proliferation of the cells in vitro was examined. Additionally, we examined the correlations between the surviving fractions of cells after 2 Gy irradiation in vitro and the response of the xenograft to radiation. The TGR of xenografts was positively related to the proliferation of the cells in vitro (rP=0.9714, p<0.0001), whereas it was independent of the histological type of the xenografts. Radiation-induced suppression of the growth rate (T/C%) of xenografts was positively related to the radiosensitivity of the cells in vitro (SF2; rP=0.8684, p=0.0284) and TGR (rP=0.7623, p=0.0780). The proliferation of human cancer cells in vitro and the growth rate of xenografts were positively related. The radiosensitivity of cancer cells, as judged from the SF2 values in vitro, and the radiation-induced suppression of xenograft growth were positively related. In conclusion, the growth rate of human xenografts was independent of histological type and origin of the cancer cells, and was positively related to the proliferation of the cancer cells in vitro. PMID:28053611

  15. Growth kinetics of biopigment production by Thai isolated Monascus purpureus in a stirred tank bioreactor.

    PubMed

    Kongruang, Sasithorn

    2011-01-01

    Monascus purpureus is a biopigment-producing fungi whose pigments can be used in many biotechnological and food industries. The growth kinetics of biopigment production were investigated in a liquid fermentation medium in a 5-l stirred tank bioreactor at 30°C, pH 7, for 8 days with 100 rpm agitation and 1.38 × 10(5) N/m(2) aeration. Thai Monascus purpureus strains TISTR 3002, 3180, 3090 and 3385 were studied for color production, growth kinetics and productivity. Citrinin as a toxic metabolite was measured from the Monascus fermentation broth. The biopigment productions were detected from fermentation broth by scanning spectra of each strain produced. Results showed a mixture of yellow, orange and red pigments with absorption peaks of pigments occurring at different wavelengths for the four strains. It was found that for each pigment color, the color production from the strains increased in the order TISTR 3002, 3180, 3090, 3385 with 3385 production being approximately 10 times that of 3002. Similar results were found for growth kinetics and productivity. HPLC results showed that citrinin was not produced under the culture conditions of this study. The L*, a* and b* values of the CIELAB color system were also obtained for the yellow, orange and red pigments produced from the TISTR 3002, 3180, 3090 and 3385 strains. The colors of the pigments ranged from burnt umber to deep red.

  16. 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

  17. 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.

  18. Kinetic simulation of filament growth dynamics in memristive electrochemical metallization devices

    NASA Astrophysics Data System (ADS)

    Dirkmann, Sven; Ziegler, Martin; Hansen, Mirko; Kohlstedt, Hermann; Trieschmann, Jan; Mussenbrock, Thomas

    2015-12-01

    In this work, we report on kinetic Monte-Carlo calculations of resistive switching and the underlying growth dynamics of filaments in an electrochemical metallization device consisting of an Ag/TiO2/Pt sandwich-like thin film system. The developed model is not limited to (i) fast time scale dynamics and (ii) only one growth and dissolution cycle of metallic filaments. In particular, we present results from the simulation of consecutive cycles. We find that the numerical results are in excellent agreement with experimentally obtained data. Additionally we observe an unexpected filament growth mode that is in contradiction to the widely acknowledged picture of filament growth but consistent with recent experimental findings.

  19. In situ X-ray diffraction study on the growth kinetics of NiO nanoparticles.

    PubMed

    Meneses, C T; Almeida, J M A; Sasaki, J M

    2010-05-01

    The growth kinetics of NiO nanoparticles have been studied by in situ X-ray diffraction using two detection systems (conventional and imaging plate). NiO nanoparticles were formed by thermal decomposition after heating of an amorphous compound formed by the coprecipitation method. It was found that the detection method using an imaging plate is more efficient than the conventional detection mode for observing changes in the crystallite growth of nanocrystalline materials. Studies have been carried out to investigate the effects of the heating rates on the particles growth. The results suggest that the growth process of the particles is accelerated when the samples are treated at low heating rates. The evolution of particles size and the diffusion coefficient obtained from X-ray powder diffraction patterns are discussed in terms of the thermal conditions for the two types of detection.

  20. Altered Cellular Kinetics in Growth Plate according to Alterations in Weight Bearing

    PubMed Central

    Park, Hoon; Kong, Sun Young; Kim, Hyun Woo

    2012-01-01

    Purpose To examine the effects of change in weight bearing on the growth plate metabolism, a simulated animal model of weightlessness was introduced and the chondrocytes' cellular kinetics was evaluated. Materials and Methods Unloading condition on the hind-limb of Sprague-Dawley rats was created by fixing a tail and lifting the hind-limb. Six rats aged 6 weeks old were assigned to each group of unloading, reloading, and control groups of unloading or reloading. Unloading was maintained for three weeks, and then reloading was applied for another one week thereafter. Histomorphometry for the assessment of vertical length of the growth plate, 5-bromo-2'-deoxyuridin immunohistochemistry for cellular kinetics, and biotin nick end labeling transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) assay for chondrocytes apoptosis in the growth plate were performed. Results The vertical length of the growth plate and the proliferative potential of chondrocytes were decreased in the unloading group compared to those of control groups. Inter-group differences were more significant in the proliferative and hypertrophic zones. Reloading increased the length of growth plate and proliferative potential of chondrocytes. However, apoptotic changes in the growth plate were not affected by the alterations of weight bearing. Conclusion Alterations in the weight bearing induced changes in the chondrocytic proliferative potential of the growth plate, however, had no effects on the apoptosis. This may explain why non-weight bearing in various clinical situations hampers normal longitudinal bone growth. Further studies on the factors for reversibility of chondrocytic proliferation upon variable mechanical stresses are needed. PMID:22477008

  1. 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.

  2. 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.

  3. Release kinetics of platelet-derived and plasma-derived growth factors from autologous plasma rich in growth factors.

    PubMed

    Anitua, Eduardo; Zalduendo, Mari Mar; Alkhraisat, Mohammad Hamdan; Orive, Gorka

    2013-10-01

    Many studies have evaluated the biological effects of platelet rich plasma reporting the final outcomes on cell and tissues. However, few studies have dealt with the kinetics of growth factor delivery by plasma rich in growth factors. Venous blood was obtained from three healthy volunteers and processed with PRGF-Endoret technology to prepare autologous plasma rich in growth factors. The gel-like fibrin scaffolds were then incubated in triplicate, in a cell culture medium to monitor the release of PDGF-AB, VEGF, HGF and IGF-I during 8 days of incubation. A leukocyte-platelet rich plasma was prepared employing the same technology and the concentrations of growth factors and interleukin-1β were determined after 24h of incubation. After each period, the medium was collected, fibrin clot was destroyed and the supernatants were stored at -80°C until analysis. The growth factor delivery is diffusion controlled with a rapid initial release by 30% of the bioactive content after 1h of incubation and a steady state release when almost 70% of the growth factor content has been delivered. Autologous fibrin matrix retained almost 30% of the amount of the growth factors after 8 days of incubation. The addition of leukocytes to the formula of platelet rich plasma did not increase the concentration of the growth factors, while it drastically increased the presence of pro-inflammatory IL-1β. Further studies employing an in vitro inflammatory model would be interesting to study the difference in growth factors and pro-inflammatory cytokines between leukocyte-free and leukocyte-rich platelet rich plasma.

  4. Altered hypertrophic chondrocyte kinetics in GDF-5 deficient murine tibial growth plates.

    PubMed

    Mikic, B; Clark, R T; Battaglia, T C; Gaschen, V; Hunziker, E B

    2004-05-01

    The growth/differentiation factors (GDFs) are a subgroup of the bone morphogenetic proteins best known for their role in joint formation and chondrogenesis. Mice deficient in one of these signaling proteins, GDF-5, exhibit numerous skeletal abnormalities, including shortened limb bones. The primary aim of this study was determine whether GDF-5 deficiency would alter the growth rate in growth plates from the long bones in mice and, if so, how this is achieved. Stereologic and cell kinetic parameters in proximal tibial growth plates from 5-week-old female GDF-5 -/- mice and control littermates were examined. GDF-5 deficiency resulted in a statistically significant reduction in growth rate (-14%, p=0.03). The effect of genotype on growth rate was associated with an altered hypertrophic phase duration, with hypertrophic cells from GDF-5 deficient mice exhibiting a significantly longer phase duration compared to control littermates (+25%, p=0.006). These data suggest that one way in which GDF-5 might modulate the rate of endochondral bone growth could be by affecting the duration of the hypertrophic phase in growth plate chondrocytes.

  5. Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

    SciTech Connect

    Ubnoske, Stephen M.; Radauscher, Erich J.; Meshot, Eric R.; Stoner, Brian R.; Parker, Charles B.; Glass, Jeffrey T.

    2016-11-19

    The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100) and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. As a result, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.

  6. Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

    DOE PAGES

    Ubnoske, Stephen M.; Radauscher, Erich J.; Meshot, Eric R.; ...

    2016-11-19

    The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100)more » and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. As a result, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.« less

  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. 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. ...

  9. Role of Step and Terrace Nucleation in Heteroepitaxial Growth Morphology: Growth Kinetics of CaF2/Si(111)

    NASA Astrophysics Data System (ADS)

    Hessinger, Uwe; Leskovar, M.; Olmstead, Marjorie A.

    1995-09-01

    The thickness uniformity and the spatial distribution of lattice relaxation in thin ( <8 nm) CaF2/Si(111) films, observed with photoelectron spectroscopy and transmission electron microscopy, are seen to depend strongly on the initial nucleation kinetics. We develop a general model for heteroepitaxial growth that explains both these and literature results. Terrace or step nucleation leads to laminar films, although with different relaxation patterns; combined step and terrace nucleation leads to rough films due to different upper-layer nucleation rates on the differently sized islands.

  10. Temperature-dependent growth kinetics of Escherichia coli ML 30 in glucose-limited continuous culture.

    PubMed Central

    Kovárová, K; Zehnder, A J; Egli, T

    1996-01-01

    Detailed comparison of growth kinetics at temperatures below and above the optimal temperature was carried out with Escherichia coli ML 30 (DSM 1329) in continuous culture. The culture was grown with glucose as the sole limiting source of carbon and energy (100 mg liter(-1) in feed medium), and the resulting steady-state concentrations of glucose were measured as a function of the dilution rate at 17.4, 28.4, 37, and 40 degrees C. The experimental data could not be described by the conventional Monod equation over the entire temperature range, but an extended form of the Monod model [mu = mu(max) x (s - s(min))/(Ks + s - s(min))], which predicts a finite substrate concentration at 0 growth rate (s(min)), provided a good fit. The two parameters mu(max) and s(min) were temperature dependent, whereas, surprisingly, fitting the model to the experimental data yielded virtually identical Ks values (approximately 33 microg liter(-1)) at all temperatures. A model that describes steady-state glucose concentrations as a function of temperature at constant growth rates is presented. In similar experiments with mixtures of glucose and galactose (1:1 mixture), the two sugars were utilized simultaneously at all temperatures examined, and their steady-state concentrations were reduced compared with to growth with either glucose or galactose alone. The results of laboratory-scale kinetic experiments are discussed with respect to the concentrations observed in natural environments. PMID:8755881

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

    PubMed

    Benjamin, Ronald; Horbach, Jürgen

    2015-07-07

    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.

  12. 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...

  13. 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

  14. A mathematical model of the kinetics of beta-amyloid fibril growth from the denatured state.

    PubMed Central

    Pallitto, M M; Murphy, R M

    2001-01-01

    Spontaneous conversion of beta-amyloid peptide (Abeta) from soluble monomer to insoluble fibril may underlie the neurodegeneration associated with Alzheimer's disease. A complete description of Abeta self-association kinetics requires identification of the oligomeric species present and the pathway of association, as well as quantitation of rate constants and reaction order. Abeta was rendered monomeric and denatured by dissolution in 8 M urea, pH 10. "Refolding" and fibrillization were initiated by rapid dilution into phosphate-buffered saline, pH 7.4. The kinetics of growth were followed at three different concentrations, using size exclusion chromatography, dynamic light scattering, and static light scattering. A multi-step pathway for fibril formation and growth was postulated. This pathway included 1) rapid commitment to either stable monomer/dimer or unstable intermediate, 2) cooperative association of intermediate into a multimeric "nucleus," 3) elongation of the "nucleus" into filaments via addition of intermediate, 4) lateral aggregation of filaments into fibrils, and 5) fibril elongation via end-to-end association. Differential and algebraic equations describing this kinetic pathway were derived, and model parameters were determined by fitting the data. The utility of the model for identifying toxic Abeta oligomeric specie(s) is demonstrated. The model should prove useful for designing compounds that inhibit Abeta aggregation and/or toxicity. PMID:11509390

  15. Theoretical consideration of the growth kinetics for GaAs and GaSb

    NASA Astrophysics Data System (ADS)

    Kaneko, T.; Asahi, H.; Gonda, S.

    1992-05-01

    An extended MOMBE growth kinetics model is proposed, based on the Robertson model, to explain both the GaAs growth rate variation and modulated beam mass spectroscopy data reported by Martin and Whitehouse. In this model, we assume that (1) MEGa molecules react with ethyl-radicals to form DEGa, (2) excessive group-V molecules on the surface suppress the decomposition of DEGa and enhance the desorption of DEGa, (3) reaction of DEGa with ethyl-radicals to form TEGa is negligible, and (4) effective surface coverage of excessive group-V atoms during growth is determined by the double layer adsorption model including desorption parameters for group-V molecules. The first assumption (1) is found to be a dominant process to explain the behaviour of DEGa desorption at high temperatures. This model can reproduce the dependences of both growth rate and desorbing rate of Ga alkyls on substrate temperature during GaAs MOMBE growth. The use of Sb instead of As produces a significant change in the growth rate variation with substrate temperature and group-V flux for the growth of GaSb, in spite of the use of the same TEGa flow rate. This can be rationalized by the difference in the desorption parameters for Sb and As.

  16. 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.

  17. 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

  18. 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

    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.

  19. 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.

  20. Nucleation and growth kinetics of struvite in a fluidized bed reactor

    NASA Astrophysics Data System (ADS)

    Bhuiyan, M. Iqbal H.; Mavinic, D. S.; Beckie, R. D.

    2008-03-01

    Kinetics of struvite crystallization were studied to gain a better understanding of intentional struvite formation in fluidized bed reactors. Mechanisms controlling nucleation were studied in the laboratory by induction time experiments. pH monitoring proved to be an effective method of induction time determination, during the induction period. The induction period, when nucleation was the controlling process for struvite crystal formation, was found to be primarily reaction controlled, with minor transport influence. The metastable region for struvite was explored in this study. The solubility and supersolubility curves, which are the boundaries of the metastable region, were observed to be almost parallel straight lines in the concentration range studied. The growth rate of struvite determined in a fluidized bed reactor was mainly transport controlled. With the determination of the mass-transfer coefficient and surface-reaction coefficient for a specified condition, a two-step linear growth rate model for struvite growth determination in a fluidized bed reactor has been proposed.

  1. 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.

  2. Altered Cellular Kinetics in the Growth Plate of the Femoral Head of Spontaneously Hypertensive Rats

    PubMed Central

    Park, Hoon; Kong, Sun Young

    2012-01-01

    Purpose Pathologic changes in the growth plate remain unknown in Legg-Calvé-Perthes (LCP) disease. Spontaneously hypertensive rats have proven to be a good model for studying LCP disease. This study investigated the histopathologic changes and the expression of vascular endothelial growth factor in the growth plate of spontaneously hypertensive rats (SHR). Materials and Methods Sixty SHR rats were divided into two groups: those showing osteonecrosis (SHR+n group: 32), and those showing normal ossification (SHR-n group: 28). Thirty Wister Kyoto rats served as a control. For histomorphological measurement, the length of each zone of the growth plate was measured. Cell kinetics was measured by 5-bromo-2'-deoxyuridin (BrdU) immunohistochemistry and transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) assays. Vascular endothelial growth factor (VEGF) immunohistochemistry was used to identify of expression of VEGF. Results The lengths of growth plates of the SHR+n group were significantly shorter in the initial growth period than those of the other groups. The lowest proliferative rate and the highest apoptosis rate were observed in the SHR+n group at the initial growth period. The expression of VEGF in the growth plate of the SHR group was lower than the control group, and it was lower in the SHR+n group than in the SHR-n group. Conclusion The growth plate of the SHR+n group was found to be affected by disease process of ischemic necrosis of the femoral head, and this might explain the relative overgrowth of the greater trochanter in the later stages of LCP disease. PMID:22477009

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

    PubMed

    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.

  4. The growth kinetics and metabolic and antioxidant activities of the functional synbiotic combination of Lactobacillus gasseri 505 and Cudrania tricuspidata leaf extract.

    PubMed

    Oh, Nam Su; Lee, Ji Young; Kim, Younghoon

    2016-12-01

    In a previous study, the synbiotic combination of selected Lactobacillus gasseri strains and Cudrania tricuspidata leaf extract (CT) was shown to significantly improve the functionality of fermented milk, and the greatest synbiotic effect was exhibited with L. gasseri 505. The aim of the present study was to investigate the growth kinetics and fermentation metabolism of this specific synbiotic combination. Fermentation was carried out in synthetic media and milk with or without CT supplementation using L. gasseri 505. Whole genome sequencing and comparative genomics analyses were conducted to verify the novelty of strain. Titratable acidity, pH, microbial population, and organic acid production were measured during the fermentation period. The addition of CT accelerated the acidification rate, supporting the growth of L. gasseri 505, and the production of fermentation metabolites such as lactic acid and pyruvic acid also significantly increased during fermentation of both of CT-supplemented synthetic media and milk. In particular, the formic acid and propionic acid in CT were significantly utilized during fermentation of milk by L. gasseri 505. Moreover, the antioxidant capacity of CT-supplemented fermented milk increased due to the release of bioactive compounds until the exponential growth phase, after which the antioxidant activity declined due to degradation and loss of potency. Therefore, this study established that L. gasseri 505 efficiently utilized the CT-related nutrients during fermentation producing resulting metabolites with health-promoting effects, although it is necessary to control the fermentation time to obtain dairy products with optimum functionality.

  5. Modification of bone-like apatite nanoparticle size and growth kinetics by alizarin red S

    NASA Astrophysics Data System (ADS)

    Ibsen, Casper Jon Steenberg; Birkedal, Henrik

    2010-11-01

    The formation of nanocrystals in biomineralization such as in bone occurs under the influence of organic molecules. Prompted by this fact, the effect of alizarin red S, a dye used in in vivo bone labeling methods, on bone-like carbonated apatite nanocrystal formation was investigated as a function of alizarin red S additive concentration. The obtained nanoparticles were investigated by powder X-ray diffraction (XRD), FTIR as well thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) while the kinetics of nanoparticle formation was investigated by in situ pH and synchrotron XRD measurements. Increasing alizarin red S concentration lead to amorphous particles over a threshold concentration and to smaller crystallites in a dose-dependent fashion. Alizarin red S induced a macroscopic lattice strain that scaled linearly with the alizarin red S concentration; this effect is reminiscent of that seen in biogenic calcium carbonates. TGA showed that the amorphous particles contained significantly more water than the crystalline samples and the DSC data showed that crystallization occurs after loss of most of the included organic material. The in situ studies showed that the formation of apatite goes via the very rapid formation of an amorphous precursor that after a certain nucleation time crystallizes into apatite. This nucleation time increased exponentially with alizarin red S concentration showing that this additive strongly stabilizes the amorphous precursor phase.

  6. Kinetics of gypsum nucleation and crystal growth from Dead Sea brine

    NASA Astrophysics Data System (ADS)

    Reznik, Itay J.; Gavrieli, Ittai; Ganor, Jiwchar

    2009-10-01

    The Dead Sea brine is supersaturated with respect to gypsum ( Ω = 1.42). Laboratory experiments and evaluation of historical data show that gypsum nucleation and crystal growth kinetics from Dead Sea brine are both slower in comparison with solutions at a similar degree of supersaturation. The slow kinetics of gypsum precipitation in the Dead Sea brine is mainly attributed to the low solubility of gypsum which is due to the high Ca 2+/SO 42- molar ratio (115), high salinity (˜280 g/kg) and to Na + inhibition. Experiments with various clay minerals (montmorillonite, kaolinite) indicate that these minerals do not serve as crystallization seeds. In contrast, calcite and aragonite which contain traces of gypsum impurities do prompt precipitation of gypsum but at a considerable slower rate than with pure gypsum. This implies that transportation inflow of clay minerals, calcite and local crystallization of minerals in the Dead Sea does not prompt significant heterogeneous precipitation of gypsum. Based on historical analyses of the Dead Sea, it is shown that over the last decades, as inflows to the lake decreased and its salinity increased, gypsum continuously precipitated from the brine. The increasing salinity and Ca 2+/SO 42- ratio, which results from the precipitation of gypsum, lead to even slower kinetics of nucleation and crystal growth, which resulted in an increasing degree of supersaturation with respect to gypsum. Therefore, we predict that as the salinity of the Dead Sea brine continues to increase (accompanied by Dead Sea water level decline), although gypsum will continuously precipitate, the degree of supersaturation will increase furthermore due to progressively slower kinetics.

  7. Does viscosity describe the kinetic barrier for crystal growth from the liquidus to the glass transition?

    PubMed

    Nascimento, Marcio Luis Ferreira; Zanotto, Edgar Dutra

    2010-11-07

    An analysis of the kinetic coefficient of crystal growth U(kin), recently proposed by Ediger et al. [J. Chem. Phys. 128, 034709 (2008)], indicates that the Stokes-Einstein/Eyring (SE/E) equation does not describe the diffusion process controlling crystal growth rates in fragile glass-forming liquids. U(kin) was defined using the normal growth model and tested for crystal data for inorganic and organic liquids covering a viscosity range of about 10(4)-10(12) Pa  s. Here, we revisit their interesting finding considering two other models: the screw dislocation (SD) and the two-dimensional surface nucleated (2D) growth models for nine undercooled oxide liquids, in a wider temperature range, from slightly below the melting point down to the glass transition region T(g), thus covering a wider viscosity range: 10(1)-10(13) Pa  s. We then propose and use normalized kinetic coefficients (M(kin)) for the SD and 2D growth models. These new kinetic coefficients restore the ability of viscosity to describe the transport part of crystal growth rates (M(kin)∼1/η and ξ∼1) from low to moderate viscosities (η<10(6) Pa  s), and thus the SE/E equation works well in this viscosity range for all systems tested. For strong glasses, the SE/E equation works well from low to high viscosities, from the melting point down to T(g)! However, for at least three fragile liquids, diopside (kink at 1.08T(g), η=1.6×10(8) Pa  s), lead metasilicate (kink at 1.14T(g), η=4.3×10(6) Pa  s), and lithium disilicate (kink at 1.11T(g), η=1.6×10(8) Pa  s), there are clear signs of a breakdown of the SE/E equation at these higher viscosities. Our results corroborate the findings of Ediger et al. and demonstrate that viscosity data cannot be used to describe the transport part of the crystal growth (via the SE/E equation) in fragile glasses in the neighborhood of T(g).

  8. 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.

  9. Correlation between former alpha boundary growth kinetics and superplastic flow in Zn-22 pct Al

    SciTech Connect

    Yousefiani, A.; Mohamed, F.A.

    2000-01-01

    Former {alpha} boundaries (F{alpha}Bs) are residual grain boundaries that develop in Zn-22 pct Al during a heat treatment, which is normally applied to produce the fine structure necessary for micrograin superplasticity. They represent domains consisting of fine elongated {alpha} grains, which encompass groups of fine {alpha} (Al-rich) and {beta} (Zn-rich) phases (the superplastic microstructure). The results of a detailed investigation conducted on F{alpha}B growth kinetics in five grades of Zn-22 pct Al with various impurity contents reveal a direct correspondence between the level of impurities in the alloy and the characteristics associated with F{alpha}Bs (average size of F{alpha}Bs and the value of the F{alpha} B growth exponent). This correspondence, which, according to available evidence, is the result of impurity segregation at F{alpha}Bs, lends strong support to the interpretation of superplastic behavior at low stresses in terms of phenomena arising from boundary segregation. It is suggested that information on F{alpha}B growth kinetics in Zn-22 pct Al can be utilized to predict the low-stress superplastic characteristics of the alloy, such as the existence of region 1 or the occurrence of extensive cavitation.

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

    PubMed

    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

    2013-06-07

    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.

  11. Model-driven experimental evaluation of struvite nucleation, growth and aggregation kinetics.

    PubMed

    Galbraith, S C; Schneider, P A; Flood, A E

    2014-06-01

    Nutrient stewardship is emerging as an issue of global importance, which will drive the development of nutrient recovery in the near to medium future. This will impact wastewater treatment practices, environmental protection, sustainable agriculture and global food security. A modelling framework for precipitation-based nutrient recovery systems has been developed, incorporating non-ideal solution thermodynamics, a dynamic mass balance and a dynamic population balance to track the development of the precipitating particles. The mechanisms of crystal nucleation and growth and, importantly, aggregation are considered. A novel approach to the population balance embeds the nucleation rate into the model, enabling direct regression of its kinetic parameters. The case study chosen for the modelling framework is that of struvite precipitation, given its wide interest and commercial promise as one possible nutrient recovery pathway. Power law kinetic parameters for nucleation, crystal growth and particle aggregation rates were regressed from an ensemble data set generated from 14 laboratory seeded batch experiments using synthetic solutions. These experiments were highly repeatable, giving confidence to the regressed parameter values. The model successfully describes the dynamic responses of solution pH, the evolving particle size distribution subject to nucleation, growth and aggregation effects and the aqueous magnesium concentration in the liquid phase. The proposed modelling framework could well be extended to other, more complex systems, leading to an improved understanding and commensurately greater confidence in the design, operation and optimisation of large-scale nutrient recovery processes from complex effluents.

  12. 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.

  13. Controlling the Growth of Au on Icosahedral Seeds of Pd by Manipulating the Reduction Kinetics

    DOE PAGES

    Lv, Tian; Yang, Xuan; Zheng, Yiqun; ...

    2016-03-29

    This article reports a systematic study of how Au atoms nucleate and grow on Pd icosahedral seeds with a multiply twinned structure. By manipulating the reduction kinetics, we obtained Pd–Au bimetallic nanocrystals with two distinct shapes and structures. Specifically, Pd@Au core–shell icosahedra were formed when a relatively fast reduction rate was used for the HAuCl4 precursor. At a slow reduction rate, in contrast, the nucleation and growth of Au atoms were mainly confined to one of the vertices of a Pd icosahedral seed, resulting in the formation of a Au icosahedron by sharing five adjacent faces with the Pd seed.more » The same growth pattern was observed for Pd icosahedral seeds with both sizes of 32 and 20 nm. Also, we have also investigated the effects of other kinetic parameters, including the concentration of reducing agent and reaction temperature, on the growth pathway undertaken by the Au atoms. In conclusion, we believe that the mechanistic insights obtained from this study can be extended to other systems, including the involvement of different metals and/or seeds with different morphologies.« less

  14. Controlling the Growth of Au on Icosahedral Seeds of Pd by Manipulating the Reduction Kinetics

    SciTech Connect

    Lv, Tian; Yang, Xuan; Zheng, Yiqun; Huang, Hongwen; Zhang, Lei; Tao, Jing; Pan, Likun; Xia, Younan

    2016-03-29

    This article reports a systematic study of how Au atoms nucleate and grow on Pd icosahedral seeds with a multiply twinned structure. By manipulating the reduction kinetics, we obtained Pd–Au bimetallic nanocrystals with two distinct shapes and structures. Specifically, Pd@Au core–shell icosahedra were formed when a relatively fast reduction rate was used for the HAuCl4 precursor. At a slow reduction rate, in contrast, the nucleation and growth of Au atoms were mainly confined to one of the vertices of a Pd icosahedral seed, resulting in the formation of a Au icosahedron by sharing five adjacent faces with the Pd seed. The same growth pattern was observed for Pd icosahedral seeds with both sizes of 32 and 20 nm. Also, we have also investigated the effects of other kinetic parameters, including the concentration of reducing agent and reaction temperature, on the growth pathway undertaken by the Au atoms. In conclusion, we believe that the mechanistic insights obtained from this study can be extended to other systems, including the involvement of different metals and/or seeds with different morphologies.

  15. 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.

  16. Nutritional versatility and growth kinetics of an Aeromonas hydrophila strain isolated from drinking water.

    PubMed Central

    van der Kooij, D; Hijnen, W A

    1988-01-01

    The nutritional versatility and growth kinetics of Aeromonas hydrophila were studied to determine the nature and the growth-promoting properties of organic compounds which may serve as substrates for the growth of this organism in drinking water during treatment and distribution. As an initial screening, a total of 69 different organic compounds were tested at a concentration of 2.5 g/liter as growth substrates for 10 A. hydrophila strains. Of these strains, strain M800 attained the highest maximum colony counts in various types of drinking water and river water and was therefore used in further measurements of growth at low substrate concentrations. A mixture of 21 amino acids and a mixture of 10 long-chain fatty acids, when added to drinking water, promoted growth of strain M800 at individual compound concentrations as low as 0.1 microgram of C per liter. Mixtures of 18 carbohydrates and 18 carboxylic acids clearly enhanced growth of the organism at individual compound concentrations above 1 microgram of C per liter. Growth measurements with 63 individual substrates at a concentration of 10 micrograms of C per liter gave growth rates of greater than or equal to 0.1/h with two amino acids, nine carbohydrates, and six long-chain fatty acids. Ks values were determined for arginine (less than or equal to 0.3 micrograms of C per liter), glucose (15.9 micrograms of C per liter), acetate (11.1 micrograms of C per liter), and oleate (2.1 micrograms of C per liter). The data obtained indicate that biomass components, such as amino acids and long-chain fatty acids, can promote multiplication of aeromonads in drinking water distribution systems at concentrations as low as a few micrograms per liter. PMID:3214162

  17. 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.

  18. Growth kinetics and processings of copper indium diselenide-based thin films

    NASA Astrophysics Data System (ADS)

    Kim, Suku

    CuInSe2 (CIS)-based compound semiconductors are increasingly important absorber layer materials for thin film solar cells. A better understanding of the growth kinetics of CuInSe2 thin films as a function of the process parameters would benefit the development of this technology. The reaction kinetics for formation of CuInSe2 from the bilayer structure InSe/CuSe was studied in-situ by high-temperature X-ray diffraction. The reaction pathway produces a diffusion barrier layer that can be schematically represented as InSe|CuSe → InSe|CuInSe 2|CuSe. Two different analyses based on the Avrami and the parabolic rate laws suggest that the reaction is one-dimensional diffusion controlled. The estimated apparent activation energy from each model is 66.0 and 65.2 kJ/mol, respectively. The result demonstrates that the time-resolved high temperature X-ray diffraction provides a powerful method for studying the reaction kinetics of CuInSe2 growth. The thermodynamic driving force for formation of copper selenide phase and the grain size distribution in CuInSe2 films was investigated. Large grains (˜a few mum) were observed in the CuInSe2 films annealed with a CuSe layer while films annealed without this layer exhibited very small grain size (<0.2 mum). This result suggests a secondary grain growth mechanism driven by the surface-energy anisotropy is responsible for the increased grain size. Epitaxial growth of CuInSe2 and CuGaSe2 on (001) GaAs substrates was attempted. The result shows that the crystalline structure and its quality strongly depends on the film stoichiometry, especially the [Cu]/[III] atomic ratio, with Cu-rich compositions showing higher crystalline quality. A two-dimensional model of heat transfer in the growth reactor was developed for a rotating platen/substrate in the molecular beam epitaxial reactor that was used for film growth. Time-varying view factors were included in the model to solve the problem dynamically and to account for the fact that the

  19. 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.

  20. 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

  1. Dynamic Scaling and Island Growth Kinetics in Pulsed Laser Deposition of SrTiO3

    NASA Astrophysics Data System (ADS)

    Eres, Gyula; Tischler, J. Z.; Rouleau, C. M.; Lee, Ho Nyung; Christen, H. M.; Zschack, P.; Larson, B. C.

    2016-11-01

    We use real-time diffuse surface x-ray diffraction to probe the evolution of island size distributions and its effects on surface smoothing in pulsed laser deposition (PLD) of SrTiO3 . We show that the island size evolution obeys dynamic scaling and two distinct regimes of island growth kinetics. Our data show that PLD film growth can persist without roughening despite thermally driven Ostwald ripening, the main mechanism for surface smoothing, being shut down. The absence of roughening is concomitant with decreasing island density, contradicting the prevailing view that increasing island density is the key to surface smoothing in PLD. We also report a previously unobserved crossover from diffusion-limited to attachment-limited island growth that reveals the influence of nonequilibrium atomic level surface transport processes on the growth modes in PLD. We show by direct measurements that attachment-limited island growth is the dominant process in PLD that creates step flowlike behavior or quasistep flow as PLD "self-organizes" local step flow on a length scale consistent with the substrate temperature and PLD parameters.

  2. Influence of heavy metals on microbial growth kinetics including lag time: mathematical modeling and experimental verification.

    PubMed

    Sengör, S Sevinç; Barua, Sutapa; Gikas, Petros; Ginn, Timothy R; Peyton, Brent; Sani, Rajesh K; Spycher, Nicolas F

    2009-10-01

    Heavy metals can significantly affect the kinetics of substrate biodegradation and microbial growth, including lag times and specific growth rates. A model to describe microbial metabolic lag as a function of the history of substrate concentration has been previously described by Wood et al. (Water Resour Res 31:553-563) and Ginn (Water Resour Res 35:1395-1408). In the present study, this model is extended by including the effect of heavy metals on metabolic lag by developing an inhibitor-dependent functional to account for the metabolic state of the microorganisms. The concentration of the inhibiting metal is explicitly incorporated into the functional. The validity of the model is tested against experimental data on the effects of zinc on Pseudomonas species isolated from Lake Coeur d'Alene sediments, Idaho, U.S.A., as well as the effects of nickel or cobalt on a mixed microbial culture collected from the aeration tank of a wastewater treatment plant in Athens, Greece. The simulations demonstrate the ability to incorporate the effect of metals on metabolism through lag, yield coefficient, and specific growth rates. The model includes growth limitation due to insufficient transfer of oxygen into the growth medium.

  3. Predicting crystal growth via a unified kinetic three-dimensional partition model.

    PubMed

    Anderson, Michael W; Gebbie-Rayet, James T; Hill, Adam R; Farida, Nani; Attfield, Martin P; Cubillas, Pablo; Blatov, Vladislav A; Proserpio, Davide M; Akporiaye, Duncan; Arstad, Bjørnar; Gale, Julian D

    2017-04-03

    Understanding and predicting crystal growth is fundamental to the control of functionality in modern materials. Despite investigations for more than one hundred years, it is only recently that the molecular intricacies of these processes have been revealed by scanning probe microscopy. To organize and understand this large amount of new information, new rules for crystal growth need to be developed and tested. However, because of the complexity and variety of different crystal systems, attempts to understand crystal growth in detail have so far relied on developing models that are usually applicable to only one system. Such models cannot be used to achieve the wide scope of understanding that is required to create a unified model across crystal types and crystal structures. Here we describe a general approach to understanding and, in theory, predicting the growth of a wide range of crystal types, including the incorporation of defect structures, by simultaneous molecular-scale simulation of crystal habit and surface topology using a unified kinetic three-dimensional partition model. This entails dividing the structure into 'natural tiles' or Voronoi polyhedra that are metastable and, consequently, temporally persistent. As such, these units are then suitable for re-construction of the crystal via a Monte Carlo algorithm. We demonstrate our approach by predicting the crystal growth of a diverse set of crystal types, including zeolites, metal-organic frameworks, calcite, urea and l-cystine.

  4. 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).

  5. Growth behavior and kinetics of self-assembled silica-carbonate biomorphs.

    PubMed

    Kellermeier, Matthias; Melero-García, Emilio; Glaab, Fabian; Eiblmeier, Josef; Kienle, Lorenz; Rachel, Reinhard; Kunz, Werner; García-Ruiz, Juan Manuel

    2012-02-20

    Upon slow crystallization from silica-containing solutions or gels at elevated pH, alkaline-earth carbonates spontaneously self-assemble into remarkable nanocrystalline ultrastructures. These so-called silica biomorphs exhibit curved morphologies beyond crystallographic symmetry and ordered textures reminiscent of the hierarchical design found in many biominerals. The formation of these fascinating materials is thought to be driven by a dynamic coupling of the components' speciations in solution, which causes concerted autocatalytic mineralization of silica-stabilized nanocrystals over hours. In the present work, we have studied the precipitation kinetics of this unique system by determining growth rates of individual aggregates using video microscopy, and correlated the results with time-dependent data on the concentration of metal ions and pH acquired online during crystallization. In this manner, insight to the evolution of chemical conditions during growth was gained. It is shown that crystallization proceeds linearly with time and is essentially reaction controlled, which fits well in the proposed morphogenetic scenario, and thus, indirectly supports it. Measurements of the silica concentration in solution, combined with analyses of crystal aggregates isolated at distinct stages of morphogenesis, further demonstrate that the fraction of silica coprecipitated with carbonate during active growth is rather small. We discuss our findings with respect to the role of silica in the formation of biomorphs, and moreover, prove that the external silica skins that occasionally sheath the aggregates--previously supposed to be involved in the growth mechanism--originate from secondary precipitation after growth is already terminated.

  6. Dynamic Scaling and Island Growth Kinetics in Pulsed Laser Deposition of SrTiO3

    DOE PAGES

    Eres, Gyula; Tischler, J. Z.; Rouleau, C. M.; ...

    2016-11-11

    We use real-time diffuse surface x-ray diffraction to probe the evolution of island size distributions and its effects on surface smoothing in pulsed laser deposition (PLD) of SrTiO3. In this study, we show that the island size evolution obeys dynamic scaling and two distinct regimes of island growth kinetics. Our data show that PLD film growth can persist without roughening despite thermally driven Ostwald ripening, the main mechanism for surface smoothing, being shut down. The absence of roughening is concomitant with decreasing island density, contradicting the prevailing view that increasing island density is the key to surface smoothing in PLD.more » We also report a previously unobserved crossover from diffusion-limited to attachment-limited island growth that reveals the influence of nonequilibrium atomic level surface transport processes on the growth modes in PLD. We show by direct measurements that attachment-limited island growth is the dominant process in PLD that creates step flowlike behavior or quasistep flow as PLD “self-organizes” local step flow on a length scale consistent with the substrate temperature and PLD parameters.« less

  7. 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

  8. Growth and Magnetic Properties of Mn-doped Germanium near the Kinetic Solubility Limit

    SciTech Connect

    Ozer, Mustafa M; Thompson, James R; Weitering, Harm H

    2012-01-01

    Growth of high-quality dilute magnetic semiconductor (DMS) material is often compromised by the low solubility of magnetic dopants, leading to formation of precipitates. Here, we explore the feasibility of growing precipitate-free Mn-doped Ge at doping levels near the kinetic solubility limit. Ge:Mn DMS films were grown at low temperature so as to minimize precipitate formation. Meanwhile, epitaxial quality was maintained by employing a very low growth rate. The magnetic properties of these lightly doped films exhibit both interesting contrasts and similarities with those of heavily-doped DMS reported in the literature, indicating that the substitutional Mn contents are very similar. Films grown at 95 degree C are free of intermetallic precipitates, offering useful opportunities for studying the fundamentals of carrier mediated exchange and metal insulator transitions without complications arising from precipitate formation.

  9. 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

  10. 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...

  11. Kinetic modeling of the SWNT growth by CO disproportionation on CoMo catalysts.

    PubMed

    Monzon, A; Lolli, G; Cosma, S; Mohamed, S B; Resasco, D E

    2008-11-01

    A kinetic model has been developed to describe the growth of single-walled carbon nanotubes (SWNT) in the CoMoCAT method, which is based on the disproportionation of CO on supported CoMo catalysts. The model attempts to capture mathematically the different stages involved in this method: (i) catalyst activation or in-situ creation of active sites, i.e., reduced Co clusters by transformation of CoMoOx precursor species, or oxidized sites; (ii) CO decomposition over active sites, which increases the surface fugacity of carbon until reaching a certain threshold; (iii) nucleation of ordered forms of carbon; (iv) C diffusion (both across the surface and into the metal particle); (v) SWNT growth; (vi) termination, by either deactivation of the catalyst active sites or by increase in the carbon concentration at the metal/SWNT interface, approaching that of the metal/gas interface and eliminating the driving force for diffusion. Previous investigations have only explained the growth termination by the former. Here, we emphasize the possible contribution of the later and propose a novel "hindrance factor" to quantify the effect of nanotube interaction with its surroundings on the growth termination. To test the kinetic model and obtain typical values of the physical parameters, experiments have been conducted on a CoMo/SiO2 catalyst in a laboratory flow reactor, in which the rate of carbon deposition was continuously evaluated by the direct measurement of the CO2 evolution as a function of time. The experimental data are fitted very well with model.

  12. 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.

  13. Theory of Crystal Growth, Kinetics of Dissolution and Transformation of Calcium Phosphates.

    NASA Astrophysics Data System (ADS)

    Zhang, Jingwu

    The kink density along a (01) step on the (001) face of a Kossel crystal is derived from a kinetic steady state approach by considering the elementary events at the step. When the kink formation energy, epsilon , is very high compared with the thermal energy kT, the kink density, rho, is found to be a function of the saturation ratio, S. For S > 1, rho = 2a-1S^ {1over 2}exp(-epsilon /kT) while for S < 1, rho = 2a^{-1}exp( -epsilon/kT)/(2-S)^ {1over 2}. This finding may provide a theoretical background for interpreting the observed growth kinetics of many sparingly soluble salts in aqueous solutions. The above approach is extended to analyze the configuration of a surface step of an AB crystal with NaCl type of lattice. It is found that the growth rate of an electrolyte crystal cannot be defined solely by the thermodynamic driving forces even when integration is the rate determining step. The rate also depends on the lattice ion activity ratio and relative frequencies of integration of A and B ions into kink sites on a step. At a given driving force, a maximum growth rate can be attained at a certain ratio of lattice ion activities. The dual constant composition (DCC) method is developed which enables the kinetics of phase transformation to be studied at constant driving forces. The applicability of this novel approach is verified in the investigation of dicalcium phosphate dihydrate (DCPD) to octacalcium phosphate (OCP) transformation. In these studies, the concentrations of total calcium and phosphate are maintained constant to within 2% with the pH held to within +/-0.003 during the reaction. The dissolution kinetics of DCPD and OCP has been investigated using CC method at 37^circ C over a wide range of experimental conditions. Both processes can be generally described by a combined volume and surface diffusion mechanism with varying degrees of volume resistance at different pH's and solution hydrodynamics. The decrease in the dissolution rate with the extent of

  14. Controlled growth and kinetics of porous hydroxyapatite spheres by a template-directed method

    NASA Astrophysics Data System (ADS)

    He, Qian Jun; Huang, Zhi Liang

    2007-03-01

    Porous hydroxyapatite (HA) spheres with high purity of phase and well-controlled pore size were grown by a template-directed method. We studied for the initial concentration of Ca-P how to control the chemical component of the products, and for the concentration of template how to control the aperture and the morphology of porous HA spheres. The experimental results indicated that the lower concentration of Ca-P was prone to pure HA phase and the aperture decreased gradually with the increase of the concentration of template. Correspondingly, the crystallization thermodynamics and template-directed growth kinetics were discussed in details. The solubility isotherms of HA and dicalcium phosphate (DCPD) were calculated based on classical crystallization theories of thermodynamics. The results suggested that there was a critical concentration of P=0.048 M in the case of Ca:P=5:3 and thus DCPD could be avoided only when P⩽0.048 M in this given reaction system. Kinetic analysis of HA crystal growth revealed that the template depressed the interfacial potential energy E, then enhanced the roughness on the surface of crystal nucleus and directed HA crystal to selectively grow along the [0 0 0 1] direction, and consequently governed the aperture of porous HA spheres. The experimental results were in agreement with the theoretical analysis.

  15. Macrotransport-solidification kinetics modeling of equiaxed dendritic growth. Part 1: Model development and discussion

    SciTech Connect

    Nastac, L.; Stefanescu, D.M.

    1996-12-01

    An analytical model that describes solidification of equiaxed dendrites has been developed for use in solidification kinetics-macrotransport modeling. It relaxes some of the assumptions made in previous models, such as the Dustin-Kurz, Rappaz-Thevoz, and Kanetkar-Stefanescu models. It is assumed that nuclei grow as unperturbed spheres until the radius of the sphere becomes larger than the minimum radius of instability. Then, growth of the dendrites is related to morphological instability and is calculated as a function of melt undercooling around the dendrite tips, which is controlled by the bulk temperature and the intrinsic volume average concentration of the liquid phase. When the general morphology of equiaxed dendrites is considered, the evolution of the fraction of solid is related to the interdendritic branching and dynamic coarsening (through the evolution of the specific interfacial areas) and to the topology and movement of the dendrite envelope (through the tip growth velocity and dendrite shape factor). The particular case of this model is the model for globulitic an overall solute and thermal balance around a growing equiaxed dendrite grain within a spherical closed system. Overall solute balance in the integral form is obtained by a complete analytical solution of the diffusion field in both liquid and solid phases. The bulk temperature is obtained from the solution of the macrotransport-solidification kinetics problem.

  16. Investigation of equilibration and growth of stepped surfaces by Kinetic Monte Carlo in one dimension

    NASA Astrophysics Data System (ADS)

    Türkan, A.; Esen, M.; Tüzemen, A. Türker; Özdemir, M.

    2017-02-01

    In this study, the equilibration and in the case of a particle flux to the surface, the growth of a one dimensional semi-conductor surface of "V" initial shape is investigated by kinetic Monte Carlo method. The initial surface is assumed to consist of atomic height steps separated by terraces. In Monte Carlo simulations, the following processes are considered: the diffusion of free particles on the surface, the attachment/detachment of particles to/from step edges from/to a terrace in front of a step or to a terrace above the step. In the simulations the Ehrlich-Schwoebel barrier is also taken into account. The equilibration of "V" initial shape at various temperatures is investigated. Moreover, the effect of particle bonding energy on the surface profile and on the evolution of the surface is also investigated. In the case of a particle flux to the surface, the surface profile and its growth kinetics are investigated at various temperatures and flux values.

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

    NASA Astrophysics Data System (ADS)

    Benisti, Didier; Morice, Olivier; Gremillet, Laurent; Siminos, Evangelos; Strozzi, David

    2010-11-01

    Using a nonlinear kinetic analysis, we provide a theoretical description for the nonlinear Landau damping rate, frequency, and group velocity of a slowly varying electron plasma wave (EPW). In particular, we show that the nonlinear group velocity of the EPW is not the derivative of its frequency with respect to its wave number, and we discuss previous results on the nonlinear Landau damping rate and on the nonlinear frequency shift of the EPW. Our theoretical predictions are moreover very carefully compared against results from Vlasov simulations of stimulated Raman scattering (SRS), and an excellent agreement is found between numerical and theoretical results. We use the previous analysis to derive envelope equations modeling SRS in the nonlinear kinetic regime. These equations provide very accurate predictions regarding threshold intensities for SRS and the growth time of SRS beyond threshold, provided that one uses the ansatz of self-optimization that we detail. Finally, we discuss saturation of SRS and, in particular, we derive growth rates for sidebands using a spectral method.

  18. Global Genome Response of Escherichia coli O157∶H7 Sakai during Dynamic Changes in Growth Kinetics Induced by an Abrupt Downshift in Water Activity

    PubMed Central

    Kocharunchitt, Chawalit; King, Thea; Gobius, Kari; Bowman, John P.; Ross, Tom

    2014-01-01

    The present study was undertaken to investigate growth kinetics and time-dependent change in global expression of Escherichia coli O157∶H7 Sakai upon an abrupt downshift in water activity (aw). Based on viable count data, shifting E. coli from aw 0.993 to aw 0.985 or less caused an apparent loss, then recovery, of culturability. Exponential growth then resumed at a rate characteristic for the aw imposed. To understand the responses of this pathogen to abrupt osmotic stress, we employed an integrated genomic and proteomic approach to characterize its cellular response during exposure to a rapid downshift but still within the growth range from aw 0.993 to aw 0.967. Of particular interest, genes and proteins with cell envelope-related functions were induced during the initial loss and subsequent recovery of culturability. This implies that cells undergo remodeling of their envelope composition, enabling them to adapt to osmotic stress. Growth at low aw, however, involved up-regulating additional genes and proteins, which are involved in the biosynthesis of specific amino acids, and carbohydrate catabolism and energy generation. This suggests their important role in facilitating growth under such stress. Finally, we highlighted the ability of E. coli to activate multiple stress responses by transiently inducing the RpoE and RpoH regulons to control protein misfolding, while simultaneously activating the master stress regulator RpoS to mediate long-term adaptation to hyperosmolality. This investigation extends our understanding of the potential mechanisms used by pathogenic E. coli to adapt, survive and grow under osmotic stress, which could potentially be exploited to aid the selection and/or development of novel strategies to inactivate this pathogen. PMID:24594867

  19. 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

  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. 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.

  2. Combined Experimental and Theoretical Approach to the Kinetics of Magnetite Crystal Growth from Primary Particles

    PubMed Central

    2017-01-01

    It is now recognized that nucleation and growth of crystals can occur not only by the addition of solvated ions but also by accretion of nanoparticles, in a process called nonclassical crystallization. The theoretical framework of such processes has only started to be described, partly due to the lack of kinetic or thermodynamic data. Here, we study the growth of magnetite nanoparticles from primary particles—nanometer-sized amorphous iron-rich precursors—in aqueous solution at different temperatures. We propose a theoretical framework to describe the growth of the nanoparticles and model both a diffusion-limited and a reaction-limited pathway to determine which of these best describes the rate-limiting step of the process. We show that, based on the measured iron concentration and the related calculated concentration of primary particles at the steady state, magnetite growth is likely a reaction-limited process, and within the framework of our model, we propose a phase diagram to summarize the observations.

  3. Kinetic modelling of epitaxial film growth with up- and downward step barriers

    NASA Astrophysics Data System (ADS)

    Leal, F. F.; Oliveira, T. J.; Ferreira, S. C.

    2011-09-01

    The formation of three-dimensional structures during the epitaxial growth of films is associated with the reflection of diffusing particles in descending terraces due to the presence of the so-called Ehrlich-Schwoebel (ES) barrier. We generalize this concept in a solid-on-solid growth model, in which a barrier dependent on the particle coordination (number of lateral bonds) exists whenever the particle performs an interlayer diffusion. The rules do not distinguish explicitly if the particle is executing a descending or an ascending interlayer diffusion. We show that the usual model, with a step barrier in descending steps, produces spurious, columnar and highly unstable morphologies if the growth temperature is varied in a usual range of mound formation experiments. Our model generates well-behaved mounded morphologies for the same ES barriers that produce anomalous morphologies in the standard model. Moreover, mounds are also obtained when the step barrier has an equal value for all particles independently of whether they are free or bonded. Kinetic roughening is observed at long times, when the surface roughness w and the characteristic length ξ scale as w ~ tβ and ξ ~ tζ, where β≈0.31 and ζ≈0.22, independently of the growth temperature.

  4. 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.

  5. 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.

  6. Quantifying Variability in Growth and Thermal Inactivation Kinetics of Lactobacillus plantarum

    PubMed Central

    Aryani, D. C.; den Besten, H. M. W.

    2016-01-01

    experimental variability with respect to the growth and thermal inactivation kinetics of Lactobacillus plantarum and to quantify the variability in thermal resistance attributed to growth history. The quantitative knowledge obtained on experimental, reproduction, and strain variabilities can be used to improve experimental designs and to adequately select strains for challenge growth and inactivation tests. Moreover, the integration of strain variability in prediction of microbial growth and inactivation kinetics will result in more realistic predictions of L. plantarum dynamics along the food production chain. PMID:27260362

  7. Kinetics of octacalcium phosphate crystal growth in the presence of organic acids

    NASA Astrophysics Data System (ADS)

    Grossl, Paul R.; Inskeep, William P.

    1992-05-01

    Octacalcium phosphate (OCP) is an important P solid phase in geochemical and biological systems and has been recognized as a precursor phase to the formation of thermodynamically more stable hydroxyapatite (HAP). Metastability of OCP with respect to HAP may be explained by precipitation kinetics and the influence of dissolved organic C (DOC) on crystal growth. Octacalcium phosphate precipitation was measured at pH 6.0 and 25°C in the absence and presence of organic acids commonly found in natural waters and soil solutions using a seeded crystal growth constant composition method. Rate constants for OCP precipitation were calculated from the following expression: Rate = kS(IAP 1/8 - K sp1/8) n, where k is the rate constant (L 7 mol -6 m -2 s -1), S is OCP seed crystal surface area (m 2 L -1), IAP = ion activity product, Ksp = OCP solubility constant (mol 8 L -8), and n is the rate reaction order. The rate constant for OCP precipitation in the absence of organic acids was 10 34.93·L 7 mol -6 m -2 s -1. Humic, fulvic, tannic, and citric acids were added to OCP crystal growth experiments at total soluble (C TS) C levels ranging from 20 μM to 2 mM. Inhibition of OCP precipitation was nearly complete (99% ) in the presence of 1.0 mM C TS as humic acid. At the same level of C TS, OCP precipitation was inhibited by 97,88, and 68% in the presence of fulvic, citric, and tannic acids, respectively. Inhibition of precipitation is caused by adsorption of organic acids onto OCP surfaces blocking active crystal growth sites. The ability of organic acids to inhibit OCP crystal growth is related to their hydrophobicity, functional group content, size, geometry, and orientation on the crystal surface. Precipitation kinetics and crystal growth inhibition by organic acids may explain the metastability of dicalcium phosphate dihydrate (DCPD) and OCP with respect to thermodynamically more stable HAP often observed in geochemical environments.

  8. Troilite formation kinetics and growth mechanism in the solar nebula. [Abstract only

    NASA Technical Reports Server (NTRS)

    Lauretta, D. S.; Fegley, B., Jr.

    1994-01-01

    Troilite formation via the reaction Fe(s) + H2S(g) + H2(g) is the major mechanism for S retention in grains in the solar nebula. Thermodynamic calculations predict that troilite condenses from a solar composition gas. We present experimental results on the kinetics and growth of troilite crystals on Fe metal at temperature (450-650 C) and composition (50-1000 ppm H2S in H2) conditions similar to those in the solar nebula. The fraction of Fe reacted (based on gravimetric data) is plotted at 450, 505, 575, and 650 C. The thickness change of unreacted iron (measured by optical microscopy) is plotted at 575 and 650 C vs. time. the weight change per unit area varies as the square root of time at the lower temperatures and varies linearly with time at the highest temperature. The growth behavior along the lower isotherms is due to diffusion. This behavior suggests sulfide diffusion to the metal-sulfide interface and suggests Fe(2+) diffusion to the sulfide-gas interface. The reaction along the highest isotherm appears to be interface controlled. The formation of troilite crystals is a rapid process forming measurable layers in a few hours. The crystalgrowth is complicated. Initially there are intergrowths of troilite into the pure Fe metal. As the reaction progresses two distinct layers of troilite crystals form. One is in contact with the Fe metal and consists of small randomly oriented crystals with pore space between them. The outermost layer contains large crystals that are all oriented in the same direction. The intergrowth layer is much smaller at 650 C than at 575 C. This suggest that FeS nucleation is inhibited at the higher temperature, accounting for the initially slower reaction rate. Once nucleated, the reaction kinetics are apparently controlled by the growth of the crystals at the interface.

  9. Inhibition of the sodium-translocating NADH-ubiquinone oxidoreductase [Na+-NQR] decreases cholera toxin production in Vibrio cholerae O1 at the late exponential growth phase.

    PubMed

    Minato, Yusuke; Fassio, Sara R; Reddekopp, Rylan L; Häse, Claudia C

    2014-01-01

    Two virulence factors produced by Vibrio cholerae, cholera toxin (CT) and toxin-corregulated pilus (TCP), are indispensable for cholera infection. ToxT is the central regulatory protein involved in activation of CT and TCP expression. We previously reported that lack of a respiration-linked sodium-translocating NADH-ubiquinone oxidoreductase (Na(+)-NQR) significantly increases toxT transcription. In this study, we further characterized this link and found that Na(+)-NQR affects toxT expression only at the early-log growth phase, whereas lack of Na(+)-NQR decreases CT production after the mid-log growth phase. Such decreased CT production was independent of toxT and ctxB transcription. Supplementing a respiratory substrate, l-lactate, into the growth media restored CT production in the nqrA-F mutant, suggesting that decreased CT production in the Na(+)-NQR mutant is dependent on electron transport chain (ETC) activity. This notion was supported by the observations that two chemical inhibitors, a Na(+)-NQR specific inhibitor 2-n-Heptyl-4-hydroxyquinoline N-oxide (HQNO) and a succinate dehydrogenase (SDH) inhibitor, thenoyltrifluoroacetone (TTFA), strongly inhibited CT production in both classical and El Tor biotype strains of V. cholerae. Accordingly, we propose the main respiratory enzyme of V. cholerae, as a potential drug target to treat cholera because human mitochondria do not contain Na(+)-NQR orthologs.

  10. Test Exponential Pile

    NASA Astrophysics Data System (ADS)

    Fermi, Enrico

    The Patent contains an extremely detailed description of an atomic pile employing natural uranium as fissile material and graphite as moderator. It starts with the discussion of the theory of the intervening phenomena, in particular the evaluation of the reproduction or multiplication factor, K, that is the ratio of the number of fast neutrons produced in one generation by the fissions to the original number of fast neutrons, in a system of infinite size. The possibility of having a self-maintaining chain reaction in a system of finite size depends both on the facts that K is greater than unity and the overall size of the system is sufficiently large to minimize the percentage of neutrons escaping from the system. After the description of a possible realization of such a pile (with many detailed drawings), the various kinds of neutron losses in a pile are depicted. Particularly relevant is the reported "invention" of the exponential experiment: since theoretical calculations can determine whether or not a chain reaction will occur in a give system, but can be invalidated by uncertainties in the parameters of the problem, an experimental test of the pile is proposed, aimed at ascertaining if the pile under construction would be divergent (i.e. with a neutron multiplication factor K greater than 1) by making measurements on a smaller pile. The idea is to measure, by a detector containing an indium foil, the exponential decrease of the neutron density along the length of a column of uranium-graphite lattice, where a neutron source is placed near its base. Such an exponential decrease is greater or less than that expected due to leakage, according to whether the K factor is less or greater than 1, so that this experiment is able to test the criticality of the pile, its accuracy increasing with the size of the column. In order to perform this measure a mathematical description of the effect of neutron production, diffusion, and absorption on the neutron density in the

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. Growth kinetics and hydrolytic enzyme production of Pseudomonas spp. isolated from pasteurized milk.

    PubMed

    Stevenson, R Gregory; Rowe, Michael T; Wisdom, G Brian; Kilpatrick, David

    2003-08-01

    Psychrotrophs, particularly Pseudomonas spp. are known to be the main determinants of the shelf-life of pasteurized milk and refrigerated raw milk. It is presumed that they mainly cause spoilage through the elaboration of proteinase and lipase enzymes. At the time of this research, under the relevant European Directive, one of the means of determining the quality of pasteurized milk was the pre-incubated count, which involves incubating the milk sample for 5 d at 6 degrees C followed by a plate count. Examination of numerous pre-incubated counts revealed a bimodal rather than a normal distribution indicating that the types of contaminants in pasteurized milk may be as important as their initial concentration. Pseudomonads that gave particularly high (> 5 x 10(6) cfu/ml) and low (< 10(3) cfu/ml) pre-incubated counts were isolated (high and low count isolates respectively). After the organisms had been subjected to a cold shock no consistent trend between the groups of isolates was detected with respect to lag phase duration. However, the high count isolates consistently had a faster exponential growth rate. Unexpectedly, with the exception of one isolate, the low count isolates produced detectable proteinase and lipase earlier. In addition, with one exception, maximal proteinase and lipase production was observed with the low count isolates. These findings indicate that there is no causal relationship between selective growth advantage and ability to produce proteinase and lipase. It also indicates that the spoilage of pasteurized milk is a complex phenomenon and is worthy of further research.

  16. Growth kinetics and energetics of a deep-sea hyperthermophilic methanogen under varying environmental conditions.

    PubMed

    Ver Eecke, Helene C; Akerman, Nancy H; Huber, Julie A; Butterfield, David A; Holden, James F

    2013-10-01

    A hyperthermophilic deep-sea methanogen, Methanocaldococcus strain JH146, was isolated from 26°C hydrothermal fluid at Axial Volcano to model high temperature methanogenesis in the subseafloor. Emphasis was placed on defining growth kinetics, cell yields and growth energy demand (GE) across a range of conditions. The organism uses H2 and CO2 as its sole carbon and energy sources. At various temperatures, pHs, and chlorinities, its growth rates and cell yields co-varied while GE remained uniform at 1.69 × 10(-11) J cell(-1)s(-1) ± 0.68 × 10(-11) J cell(-1)s(-1) (s.d., n = 23). An exception was at superoptimal growth temperatures where GE increased to 7.25 × 10(-11) J cell(-1)s(-1) presumably due to heat shock. GE also increased from 5.1 × 10(-12) J cell(-1)s(-1) to 7.61 × 10(-11) J cell(-1)s(-1) as NH4 (+) concentrations decreased from 9.4 mM to 0.14 mM. JH146 did not fix N2 or assimilate NO3 (-), lacked the N2-fixing (cluster II) nifH gene, and became nitrogen limited below 0.14 mM NH4Cl. Nitrogen availability may impact growth in situ since ammonia concentrations at Axial Volcano are < 18 μM. Our approach contributes to refining bioenergetic and carbon flux models for methanogens and other organisms in hydrothermal vents and other environments.

  17. Diffusion-induced growth of nanowires: Generalized boundary conditions and self-consistent kinetic equation

    NASA Astrophysics Data System (ADS)

    Dubrovskii, V. G.; Hervieu, Yu. Yu.

    2014-09-01

    In this work, we present a theoretical analysis of the diffusion-induced growth of "vapor-liquid-solid" nanowires, based on the stationary equations with generalized boundary conditions. We discuss why and how the earlier results are modified when the adatom chemical potential is discontinuous at the nanowire base. Several simplified models for the adatom diffusion flux are discussed, yielding the 1 /Rp radius dependence of the length, with p ranging from 0.5 to 2. The self-consistent approach is used to couple the diffusion transport with the kinetics of 2D nucleation under the droplet. This leads to a new growth equation that contains only two dimensional parameters and the power exponents p and q, where q=1 or 2 depends on the nucleus position. We show that this equation describes the size-dependent depression of the growth rate of narrow nanowires much better than the Gibbs-Thomson correction in several important cases. Overall, our equation fits very well the experimental data on the length-radius correlations of III-V and group IV nanowires obtained by different epitaxy techniques.

  18. Nonisothermal Austenite Grain Growth Kinetics in a Microalloyed X80 Linepipe Steel

    NASA Astrophysics Data System (ADS)

    Banerjee, Kumkum; Militzer, Matthias; Perez, Michel; Wang, Xiang

    2010-12-01

    Nonisothermal austenite grain growth kinetics under the influence of several combinations of Nb, Ti, and Mo containing complex precipitates has been studied in a microalloyed linepipe steel. The goal of this study is the development of a grain growth model to predict the austenite grain size in the weld heat affected zone (HAZ). Electron microscopy investigations of the as-received steel proved the presence of Ti-rich, Nb-rich, and Mo-rich precipitates. The steel has then been subjected to austenitizing heat treatments to selected peak temperatures at various heating rates that are typical for thermal cycles in the HAZ. Thermal cycles have a strong effect on the final austenite grain size. Using a mean field approach, a model is proposed for the dissolution of Nb-rich precipitates. This model has been coupled to a Zener-type austenite grain growth model in the presence of pinning particles. This coupling leads to accurate prediction of the austenite grain size along the nonisothermal heating path simulating selected thermal profiles of the HAZ.

  19. Pattern, growth, and aging in aggregation kinetics of a Vicsek-like active matter model

    NASA Astrophysics Data System (ADS)

    Das, Subir K.

    2017-01-01

    Via molecular dynamics simulations, we study kinetics in a Vicsek-like phase-separating active matter model. Quantitative results, for isotropic bicontinuous pattern, are presented on the structure, growth, and aging. These are obtained via the two-point equal-time density-density correlation function, the average domain length, and the two-time density autocorrelation function. Both the correlation functions exhibit basic scaling properties, implying self-similarity in the pattern dynamics, for which the average domain size exhibits a power-law growth in time. The equal-time correlation has a short distance behavior that provides reasonable agreement between the corresponding structure factor tail and the Porod law. The autocorrelation decay is a power-law in the average domain size. Apart from these basic similarities, the overall quantitative behavior of the above-mentioned observables is found to be vastly different from those of the corresponding passive limit of the model which also undergoes phase separation. The functional forms of these have been quantified. An exceptionally rapid growth in the active system occurs due to fast coherent motion of the particles, mean-squared-displacements of which exhibit multiple scaling regimes, including a long time ballistic one.

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

    PubMed

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

    2014-04-21

    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.

  1. Effect of moderate electric field frequency on growth kinetics and metabolic activity of Lactobacillus acidophilus.

    PubMed

    Loghavi, Laleh; Sastry, Sudhir K; Yousef, Ahmed E

    2008-01-01

    Moderate electric fields (MEF) have been previously shown to alter the metabolic activity of microbial cells; thus, the effect of frequency and electric field would be of considerable interest. We investigated herein the effects of MEF frequency on microbial growth kinetics and bacteriocin (Lacidin A) production of Lactobacillus acidophilus OSU 133 during fermentation. The following fermentation treatments were compared: conventional (for 40 h), MEF (1 V cm(-1), for 40 h), combination of MEF (1 V cm(-1), for the first 5 h) and conventional (for 35 h) at various frequency levels (45, 60, and 90 Hz) all at 30 degrees C, and control (conventional) fermentation at 37 degrees C. MEF treatments with purely sinusoidal waveforms at all frequencies at 30 degrees C produced a shorter lag phase than conventional fermentation. However, no lag phase reduction was found for a 60 Hz waveform that contained high-frequency harmonics. There was, however, a significant increase in the bacteriocin production under early MEF treatment at 60 Hz with high-frequency harmonics. On the basis of these observations, the fermentation process is accelerated by applying pure sinusoidal MEF at the early stage of growth while a significant increase in the bacteriocin production occurs when sinusoidal field at 60 Hz with harmonics is applied at the early stage of the growth.

  2. Growth Kinetics of In Situ Fabricated Dense NbC Coatings on Gray Cast Iron

    NASA Astrophysics Data System (ADS)

    Shen, Liuliu; Xu, Yunhua; Zhao, Nana; Zhao, Ziyuan; Zhong, Lisheng; Song, Ke; Cai, Xiaolong; Wang, Juan

    2016-12-01

    In the present study, dense niobium carbide (NbC) coatings are fabricated by in situ techniques on gray cast iron (Fe) substrates at 1150 °C for 5 min, followed by a heat treatment at 990, 1010 and 1030 °C for 5, 10, 15 and 20 min. The microstructure, element composition and metallographic phase of the coating are characterized by scanning electron microscope, energy dispersive spectral and x-ray diffraction, respectively. Results show that the coating consists of NbC and α-Fe phases. NbC coating thickness ranges from 12.51 ± 1.4 to 29.17 ± 2.0 µm depending on the heat treatment temperature and time. In addition, the growth kinetics of dense niobium carbide coatings are estimated. A diffusion model based on Fick's laws is used to explore the carbon diffusion coefficients of the dense NbC coating in the range of heat treatment temperatures in which the experimental results of the kinetics of the niobium carbide coating are in good agreement with those estimated using diffusion model.

  3. Modeling of the Kinetics of Metal Film Growth on 5-Fold Surfaces of Icosohedral Quasicrystals

    NASA Astrophysics Data System (ADS)

    Evans, J. W.; Unal, B.; Fournee, V.; Ghosh, C.; Liu, D.-J.; Jenks, C. J.; Thiel, P. A.

    2007-03-01

    During submonolayer deposition of metals on 5-f icosohedral Al- Pd-Mn and Al-Cu-Fe surfaces, experimental evidence for several system points to heterogeneous nucleation of islands at specific ``dark star'' trap sites. We model this phenomenon using a mean-field rate equation formulation for Ag on Al-Pd-Mn, where data is available for both the flux and temperature dependence of the island density. We also utilize a more sophisticated kinetic Monte Carlo simulation approach to analyze an atomistic lattice-gas model (for an appropriate ``disordered-bond-network'' of nearest-neighbor adsorption sites) describing nucleation of starfish islands observed by STM for Al on Al-Cu-Fe. Finally, we briefly describe multilayer growth morphologies (which can display kinetic roughening or quantum size effects), but which also generally reflect the submonolayer island distribution. B. Unal et al. PRB 75 (2007); C. Ghosh et al. Phil. Mag. 86 (2006) 831; Surf. Sci. 600 (2006) 1110; V. Fournee et al. PRL 95 (2005) 155504.

  4. 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.

  5. Growth kinetics of an indigenous mixed microbial consortium during phenol degradation in a batch reactor.

    PubMed

    Saravanan, Pichiah; Pakshirajan, K; Saha, Prabirkumar

    2008-01-01

    Biodegradation of phenol by a mixed microbial culture, isolated from a sewage treatment plant, was investigated in batch shake flasks. A minimum concentration of 100 and a maximum of 800 mg 1(-1) of phenol in the media were adapted in the degradation study. The phenol degradation rate varied largely and was less than 10 mg l(-1)h(-1) at both extremes of the initial concentrations in the media. The degradation rate was maximum 15.7 mg l(-1)h(-1) at 400 mg l(-1) phenol. The culture followed substrate inhibition kinetics and the specific growth rate were fitted to Haldane and Han-Levenspiel models. Between the two models the Han-Levenspiel was found to be a better fit with a root mean square error of 0.0211. The biokinetics constants estimated using these models showed good potential of the mixed microbial culture in phenol degradation.

  6. Solution-growth kinetics and thermodynamics of nanoporous self-assembled molecular monolayers

    NASA Astrophysics Data System (ADS)

    Bellec, Amandine; Arrigoni, Claire; Schull, Guillaume; Douillard, Ludovic; Fiorini-Debuisschert, Céline; Mathevet, Fabrice; Kreher, David; Attias, André-Jean; Charra, Fabrice

    2011-03-01

    The temperature and concentration dependences of the self-assembly onto graphite from solution of a series of molecular building blocks able to form nanoporous structures are analyzed experimentally by in situ scanning tunneling microscopy. It is shown that the commonly observed coexistence of dense and nanoporous domains results from kinetic blockades rather than a thermodynamic equilibrium. The ripening can be favored by high densities of domain boundaries, which can be obtained by cooling the substrate before the nucleation and growth. Then ripening at higher-temperature yields large defect-free domains of a single structure. This thermodynamically stable structure can be either the dense or the nanoporous one, depending on the tecton concentration in the supernatant solution. A sharp phase transition from dense to honeycomb structures is observed at a critical concentration. This collective phenomenon is explained by introducing interactions between adsorbed molecules in the thermodynamic description of the whole system.

  7. Solubility, phase transition, kinetic ripening and growth rates of porcine pancreatic α-amylase isoenzymes

    NASA Astrophysics Data System (ADS)

    Boistelle, Roland; Astier, Jean Pierre; Marchis-Mouren, Guy; Desseaux, Véronique; Haser, Richard

    1992-09-01

    Two polymorphic modifications, A and B, of porcine pancreatic α-amylase were grown between 4 and 30°C. A and B crystals are made up by two isoenzymes so that four crystal varieties (AI, AII, BI, BII) exist. A and B are easily distinguished due to their typical crystal habits but there is no difference between AI and AII or BI and BII respectively at least as concerns their unit cells, crystal habits and solubilities for instance. On the other hand, the growth rates are somewhat different, even if the overall rate determining step is volume diffusion. The transition temperature between A and B polymorphs is 18°C, A being stable above this temperature. A and B can undergo a phase transition by slightly changing the temperature around the transition point. Kinetic ripening experiments show that ripening can be used for growing larger crystals at the expenses of smaller ones.

  8. 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

  9. The kinetics of the hydrogen/deuterium exchange of epidermal growth factor receptor ligands.

    PubMed

    Iloro, Ibon; Narváez, Daniel; Guillén, Nancy; Camacho, Carlos M; Guillén, Lalisse; Cora, Elsa; Pastrana-Ríos, Belinda

    2008-05-15

    Five highly homologous epidermal growth factor receptor ligands were studied by mass spectral analysis, hydrogen/deuterium (H/D) exchange via attenuated total reflectance Fourier transform-infrared spectroscopy, and two-dimensional correlation analysis. These studies were performed to determine the order of events during the exchange process, the extent of H/D exchange, and associated kinetics of exchange for a comparative analysis of these ligands. Furthermore, the secondary structure composition of amphiregulin (AR) and heparin-binding-epidermal growth factor (HB-EGF) was determined. All ligands were found to have similar contributions of 3(10)-helix and random coil with varying contributions of beta-sheets and beta-turns. The extent of exchange was 40%, 65%, 55%, 65%, and 98% for EGF, transforming growth factor-alpha (TGF-alpha), AR, HB-EGF, and epiregulin (ER), respectively. The rate constants were determined and classified as fast, intermediate, and slow: for EGF the 0.20 min(-1) (Tyr), 0.09 min(-1) (Arg, beta-turns), and 1.88 x 10(-3) min(-1) (beta-sheets and 3(10)-helix); and for TGF-alpha 0.91 min(-1) (Tyr), 0.27 min(-1) (Arg, beta-turns), and 1.41 x 10(-4) min(-1) (beta-sheets). The time constants for AR 0.47 min(-1) (Tyr), 0.04 min(-1) (Arg), and 1.00 x 10(-4) min(-1) (buried 3(10)-helix, beta-turns, and beta-sheets); for HB-EGF 0.89 min(-1) (Tyr), 0.14 min(-1) (Arg and 3(10)-helix), and 1.00 x 10(-3) min(-1) (buried 3(10)-helix, beta-sheets, and beta-turns); and for epiregulin 0.16 min(-1) (Tyr), 0.03 min(-1) (Arg), and 1.00 x 10(-4) min(-1) (3(10)-helix and beta-sheets). These results provide essential information toward understanding secondary structure, H/D exchange kinetics, and solvation of these epidermal growth factor receptor ligands in their unbound state.

  10. Kinetic Monte Carlo simulations of surface growth during plasma deposition of silicon thin films

    NASA Astrophysics Data System (ADS)

    Pandey, Sumeet C.; Singh, Tejinder; Maroudas, Dimitrios

    2009-07-01

    Based on an atomically detailed surface growth model, we have performed kinetic Monte Carlo (KMC) simulations to determine the surface chemical composition of plasma deposited hydrogenated amorphous silicon (a-Si:H) thin films as a function of substrate temperature. Our surface growth kinetic model consists of a combination of various surface rate processes, including silyl (SiH3) radical chemisorption onto surface dangling bonds or insertion into Si-Si surface bonds, SiH3 physisorption, SiH3 surface diffusion, abstraction of surface H by SiH3 radicals, surface hydride dissociation reactions, as well as desorption of SiH3, SiH4, and Si2H6 species into the gas phase. Transition rates for the adsorption, surface reaction and diffusion, and desorption processes accounted for in the KMC simulations are based on first-principles density-functional-theory computations of the corresponding optimal pathways on the H-terminated Si(001)-(2×1) surface. Results are reported for two types of KMC simulations. The first employs a fully ab initio database of activation energy barriers for the surface rate processes involved and is appropriate for modeling the early stages of growth. The second uses approximate rates for all the relevant processes to account properly for the effects on the activation energetics of interactions between species adsorbed at neighboring surface sites and is appropriate to model later stages of growth toward a steady state of the surface composition. The KMC predictions for the temperature dependence of the surface concentration of SiHx(s) (x =1,2,3) species, the surface hydrogen content, and the surface dangling-bond coverage are compared to experimental measurements on a-Si:H films deposited under operating conditions for which the SiH3 radical is the dominant deposition precursor. The predictions of both KMC simulation types are consistent with the reported experimental data, which are based on in situ attenuated total reflection Fourier transformed

  11. 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.

  12. PAH growth initiated by propargyl addition: mechanism development and computational kinetics.

    PubMed

    Raj, Abhijeet; Al Rashidi, Mariam J; Chung, Suk Ho; Sarathy, S Mani

    2014-04-24

    Polycyclic aromatic hydrocarbon (PAH) growth is known to be the principal pathway to soot formation during fuel combustion, as such, a physical understanding of the PAH growth mechanism is needed to effectively assess, predict, and control soot formation in flames. Although the hydrogen abstraction C2H2 addition (HACA) mechanism is believed to be the main contributor to PAH growth, it has been shown to under-predict some of the experimental data on PAHs and soot concentrations in flames. This article presents a submechanism of PAH growth that is initiated by propargyl (C3H3) addition onto naphthalene (A2) and the naphthyl radical. C3H3 has been chosen since it is known to be a precursor of benzene in combustion and has appreciable concentrations in flames. This mechanism has been developed up to the formation of pyrene (A4), and the temperature-dependent kinetics of each elementary reaction has been determined using density functional theory (DFT) computations at the B3LYP/6-311++G(d,p) level of theory and transition state theory (TST). H-abstraction, H-addition, H-migration, β-scission, and intramolecular addition reactions have been taken into account. The energy barriers of the two main pathways (H-abstraction and H-addition) were found to be relatively small if not negative, whereas the energy barriers of the other pathways were in the range of (6-89 kcal·mol(-1)). The rates reported in this study may be extrapolated to larger PAH molecules that have a zigzag site similar to that in naphthalene, and the mechanism presented herein may be used as a complement to the HACA mechanism to improve prediction of PAH and soot formation.

  13. 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.

  14. 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

    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.

  15. Temperature dependence of hole growth kinetics in aluminum-phthalocyanine-tetrasulfonate in hyperquenched glassy water.

    PubMed

    Dang, N C; Reinot, T; Reppert, M; Jankowiak, R

    2007-02-22

    The temperature (T) dependence of hole growth kinetics (HGK) data that span more than four decades of burn fluence are reported for aluminum-phthalocyanine tetrasulfonate (APT) in fresh and annealed hyperquenched glassy water (HGW) for temperatures between 5 and 20 K. The highly dispersive HGK data are modeled by using the "master" equation based on the two level system (TLS) model described in 2000 by Reinot and Small [J. Chem. Phys. 2000, 113, 10207]. We have demonstrated that thermal line broadening is not enough to account for temperature-dependent HGK for temperatures greater than 10 K. To overcome the discrepancy, the hole growth model must account for thermal hole filling (THF) processes. For the first time, the "master" equation used for HGK simulations is modified to take into account both the temperature dependence of the (single site) absorption spectrum and THF processes, effectively turning off those TLS which do not participate in the hole burning process at higher temperatures. A single set of parameters, some of which were determined directly from the hole spectra, was found to provide satisfactory fits to the HGK data for APT in fresh and annealed HGW for holes burned in the 679.7-676.9 nm range from the high to low energy sides of the Qx absorption band. Furthermore, we propose that HGK modeling at high burn fluences requires that the TLS model be further modified to take into account the existence of extrinsic multiple level systems.

  16. Growth kinetics and competition between Methanosarcina and Methanosaeta in mesophilic anaerobic digestion.

    PubMed

    Conklin, Anne; Stensel, H David; Ferguson, John

    2006-05-01

    Methanosarcina species with a high maximum specific growth rate (mumax) and high half-saturation coefficient (KS) and Methanosaeta species with a low mumax and low KS are the only known aceticlastic methanogens. Because of Methanosaeta's low KS, the low acetate concentrations in conventional, mesophilic anaerobic digestion yield Methanosaeta dominance. However, Methanosarcina absorbs increases in acetate more efficiently and thus promotes more stable digestion. This paper tests the hypothesis that decreasing digester feeding frequencies can increase Methanosarcina predominance. Two acetate-fed reactors were established at a 17-day solids retention time. One reactor was fed hourly, and one was fed once daily. Microscopic and molecular methods were used to verify that the hourly fed reactor enriched for Methanosaeta, while the daily fed reactor enriched for Methanosarcina. Growth and substrate-use kinetics were measured for each reactor. A digester overload condition was simulated, and the Methanosarcina-enriched reactor was found to perform better than the Methanosaeta-enriched reactor. These findings indicate that Methanosarcina dominance can be achieved with infrequent feedings, leading to more stable digestion.

  17. Estimation of the growth kinetic parameters of Bacillus cereus spores as affected by pulsed light treatment.

    PubMed

    Aguirre, Juan S; de Fernando, Gonzalo García; Hierro, Eva; Hospital, Xavier F; Ordóñez, Juan A; Fernández, Manuela

    2015-06-02

    Quantitative microbial risk assessment requires the knowledge of the effect of food preservation technologies on the growth parameters of the survivors of the treatment. This is of special interest in the case of the new non-thermal technologies that are being investigated for minimal processing of foods. This is a study on the effect of pulsed light technology (PL) on the lag phase of Bacillus cereus spores surviving the treatment and the maximum growth rate (μmax) of the survivors after germination. The D value was estimated as 0.35 J/cm(2) and our findings showed that PL affected the kinetic parameters of the microorganism. A log linear relationship was observed between the lag phase and the intensity of the treatment. Increasing the lethality lengthened the mean lag phase and proportionally increased its variability. A polynomial regression was fitted between the μmax of the survivors and the inactivation achieved. The μmax decreased as intensity increased. From these data, and their comparison to published results on the effect of heat and e-beam irradiation on B. cereus spores, it was observed that the shelf-life of PL treated foods would be longer than those treated with heat and similar to irradiated ones. These findings offer information of interest for the implementation of PL for microbial decontamination in the food industry.

  18. 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

  19. 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.

  20. The use of real-time PCR to study Penicillium chrysogenum growth kinetics on solid food at different water activities.

    PubMed

    Arquiza, J M R Apollo; Hunter, Jean

    2014-09-18

    Fungal growth on solid foods can make them unfit for human consumption, but certain specialty foods require fungi to produce their characteristic properties. In either case, a reliable way of measuring biomass is needed to study how various factors (e.g. water activity) affect fungal growth rates on these substrates. Biochemical markers such as chitin, glucosamine or ergosterol have been used to estimate fungal growth, but they cannot distinguish between individual species in mixed culture. In this study, a real-time polymerase chain reaction (rt-PCR) protocol specific for a target fungal species was used to quantify its DNA while growing on solid food. The measured amount of DNA was then related to the biomass present using an experimentally determined DNA-to-biomass ratio. The highly sensitive rt-PCR biomass assay was found to have a wide range, able to quantify the target DNA within a six orders-of-magnitude difference. The method was used to monitor germination and growth of Penicillium chrysogenum spores on a model porous food (cooked wheat flour) at 25°C and different water activities of 0.973, 0.936, and 0.843. No growth was observed at 0.843, but lag, exponential and stationary phases were identified in the growth curves for the higher water activities. The calculated specific growth rates (μ) during the exponential phase were almost identical, at 0.075/h and 0.076/h for aw=0.973 and 0.936, respectively. The specificity of the method was demonstrated by measuring the biomass of P. chrysogenum while growing together with Aspergillus niger on solid media at aw=0.973.

  1. 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.

  2. 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...

  3. High-throughput quantitative analysis with cell growth kinetic curves for low copy number mutant cells.

    PubMed

    Xing, James Z; Gabos, Stephan; Huang, Biao; Pan, Tianhong; Huang, Min; Chen, Jie

    2012-10-01

    The mutation rate in cells induced by environmental genotoxic hazards is very low and difficult to detect using traditional cell counting assays. The established genetic toxicity tests currently recognized by regulatory authorities, such as conventional Ames and hypoxanthine guanine phosphoribosyl-transferase (HPRT) assays, are not well suited for higher-throughput screening as they require large amounts of test compounds and are very time consuming. In this study, we developed a novel cell-based assay for quantitative analysis of low numbers of cell copies with HPRT mutation induced by an environmental mutagen. The HPRT gene mutant cells induced by the mutagen were selected by 6-thioguanine (6-TG) and the cell's kinetic growth curve monitored by a real-time cell electronic sensor (RT-CES) system. When a threshold is set at a certain cell index (CI) level, samples with different initial mutant cell copies take different amounts of time in order for their growth (or CI accumulation) to cross this threshold. The more cells that are initially seeded in the test well, the faster the cell accumulation and therefore the shorter the time required to cross this threshold. Therefore, the culture time period required to cross the threshold of each sample corresponds to the original number of cells in the sample. A mutant cell growth time threshold (MT) value of each sample can be calculated to predict the number of original mutant cells. For mutagenesis determination, the RT-CES assay displayed an equal sensitivity (p > 0.05) and coefficients of variation values with good correlation to conventional HPRT mutagenic assays. Most importantly, the RT-CES mutation assay has a higher throughput than conventional cellular assays.

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

    PubMed Central

    Focht, D D; Shelton, D

    1987-01-01

    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

  5. 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

  6. Effect of native microflora on the growth kinetics of salmonella enteritidis strain 04-137 in raw ground chicken.

    PubMed

    Zaher, Sakha M; Fujikawa, Hiroshi

    2011-05-01

    Effects of native microflora (NM) on growth kinetics of Salmonella Enteritidis strain 04-137 were studied in raw ground chicken. First, samples of ground chicken with high and low levels of NM (10(7.1) and 10(4.9) CFU/g, respectively) were spiked with Salmonella at doses ranging from 10(1) to 10(4) CFU/g. The growth kinetics, including the rate constant of growth, r, and the lag period, were similar, but the maximum cell level, N(max), was higher at higher initial Salmonella doses for both NM levels. Second, samples of ground chicken with high and low NM levels (10(6.8) and 10(4.7) CFU/g, respectively) were spiked with Salmonella and then stored at various constant temperatures ranging from 8 to 32°C. Both N(max) and r for Salmonella were higher at higher temperatures for both NM levels. Although r for total bacteria, which consisted of NM and Salmonella, was also higher at higher temperatures, N(max) was constant at all temperatures for both NM levels. Further, Salmonella growth was compared among samples of ground chicken with high and low NM levels and samples of sterilized chicken. Salmonella growth, characterized by both N(max) and r, was highest in sterilized chicken, followed by chicken with the low NM level. Our growth model successfully described and analyzed the growth of Salmonella and total bacteria in chicken at constant temperatures; using the data obtained, the model also successfully predicted the growth of Salmonella and total bacteria in chicken stored at dynamic temperatures. Our study clarified the effects that different doses of NM in ground chicken had on the growth kinetics of the Salmonella strain and demonstrated the usability of the growth model for foods with NM.

  7. Mathematical models to predict kinetic behavior and growth probabilities of Listeria monocytogenes on pork skin at constant and dynamic temperatures.

    PubMed

    Lee, Soomin; Lee, Heeyoung; Lee, Joo-Yeon; Skandamis, Panagiotis; Park, Beom-Young; Oh, Mi-Hwa; Yoon, Yohan

    2013-11-01

    In this study, mathematical models were developed to predict the growth probability and kinetic behavior of Listeria monocytogenes on fresh pork skin during storage at different temperatures. A 10-strain mixture of L. monocytogenes was inoculated on fresh pork skin (3 by 5 cm) at 4 log CFU/cm(2). The inoculated samples were stored aerobically at 4, 7, and 10 °C for 240 h, at 15 and 20 °C for 96 h, and at 25 and 30 °C for 12 h. The Baranyi model was fitted to L. monocytogenes growth data on PALCAM agar to calculate the maximum specific growth rate, lag-phase duration, the lower asymptote, and the upper asymptote. The kinetic parameters were then further analyzed as a function of storage temperature. The model simulated growth of L. monocytogenes under constant and changing temperatures, and the performances of the models were evaluated by the root mean square error and bias factor (Bf). Of the 49 combinations (temperature × sampling time), the combinations with significant growth (P < 0.05) of L. monocytogenes were assigned a value of 1, and the combinations with nonsignificant growth (P > 0.05) were given a value of 0. These data were analyzed by logistic regression to develop a model predicting the probabilities of L. monocytogenes growth. At 4 to 10 °C, obvious L. monocytogenes growth was observable after 24 h of storage; but, at other temperatures, the pathogen had obvious growth after 12 h of storage. Because the root mean square error value (0.184) and Bf (1.01) were close to 0 and 1, respectively, the performance of the developed model was acceptable, and the probabilistic model also showed good performance. These results indicate that the developed model should be useful in predicting kinetic behavior and calculating growth probabilities of L. monocytogenes as a function of temperature and time.

  8. Synthesis of Graphene Layers from Metal-Carbon Melts: Nucleation and Growth Kinetics

    NASA Astrophysics Data System (ADS)

    Amini, Shaahin

    A new method for growth of large-area graphene, which can lead to a scalable low-cost high-throughput production technology, was demonstrated. The method is based on growing of graphene films on the surface of metal-carbon melts and involves dissolving carbon in a molten metal at a specified temperature and then allowing the dissolved carbon to nucleate and grow on top of the melt at a lower temperature. The synthesized graphene layers were subjected to detailed microscopic and Raman spectroscopic characterizations. The deconvolution of the Raman 2D band was used to accurately determine the number of atomic planes in the resulting graphene layers and access their quality. The results indicated that the technology can provide bulk graphite films, few-layer graphene as well as high-quality single layer graphene on metals. It was also shown that upon cooling of supersaturated metal-carbon melts; graphite would also grow inside the melt either with flake or sphere morphology, depending on the solidification rate and degree of supersaturation. At small solidification rates, graphite crystals are normally bounded by faceted low index basal and prismatic planes which grow by lateral movement of ledges produced by 2D-nucleation or dislocations. At higher growth rates, however, both interfaces become kinetically rough, and growth becomes limited by diffusion of carbon to the growing interface. The roughening transition from faceted to non-faceted was found to depend on the driving force and nature of growing plane. Due to high number of C-C dangling bonds in prismatic face, its roughening transition occurs at smaller driving forces. At intermediate rates, the prismatic interfaces become rough and grow faster while the basal plane is still faceted, leading to formation of flake graphite. At higher growth rates, both interfaces grow with a relatively similar rate leading to initiation of graphite sphere formation, which later grows by a multi-stage growth mechanism. An

  9. Optimized growth kinetics of Pichia pastoris and recombinant Candida rugosa LIP1 production by RSM.

    PubMed

    Chang, Shu-Wei; Shieh, Chwen-Jen; Lee, Guan-Chiun; Akoh, Casimir C; Shaw, Jei-Fu

    2006-01-01

    A predictive model for Pichia pastoris expression of highly active recombinant Candida rugosa LIP1 was developed by combining the Gompertz function and response surface methodology (RSM) to evaluate the effect of yeast extract concentration, glucose concentration, temperature, and pH on specific responses. Each of the responses (maximum population densities, specific growth rate (mumax), protein concentration, and minimum lag phase duration) was determined using the modified Gompertz function. RSM and 4-factor-5-level central composite rotatable design (CCRD) were adopted to evaluate the effects of growth parameters, such as temperature (21.6-38.4 degrees C), glucose concentration (0.3-3.7%), yeast extract (0.16-1.84%), and pH (5.3-8.7) on the responses of P. pastoris growth kinetics. Based on ridge maximum analysis, the optimum population density conditions were: temperature 24.4 degrees C, glucose concentration 2.0%, yeast extract 1.5%, and pH 7.6. The optimum specific growth rate conditions were: temperature 28.9 degrees C, glucose concentration 2.0%, yeast extract 1.1%, and pH 6.9. The optimum protein concentration conditions were: temperature 24.2 degrees C, glucose concentration 1.9%, yeast extract 1.5%, and pH 7.6. Based on ridge minimum analysis, the minimal lag phase conditions were: temperature 32.3 degrees C, glucose concentration 2.1%, yeast extract 1.1%, and pH 5.4. For the predicted value, the maximum population density, specific growth rate, protein concentration, and minimum lag phase duration were 15.7 mg/ml, 3.4 h(-1), 0.78 mg/ml, and 4.2 h, and the actual values were 14.3 +/- 3.5 mg/ml, 3.6 +/- 0.6 h(-1), 0.72 +/- 0.2 mg/ml, and 4.4 +/- 1.6 h, respectively.

  10. 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.

  11. 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.

  12. 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

  13. Dynamo theory, vorticity generation, and exponential stretching.

    PubMed

    Friedlander, Susan; Vishik, Misha M.

    1991-08-01

    A discussion is given of the analogy between the dynamo equation for the generation of a magnetic field by the motion of an electrically conducting fluid and the equation for the evolution of vorticity of a viscous fluid. In both cases exponential stretching is an important feature of the underlying instability problem. For the "fast" dynamo problem, the existence of exponential stretching (i.e., the positivity of the Lyapunov exponent) somewhere in the flow is a necessary condition when the flow is smooth. An example is presented of a flow with exponential stretching (an Anosov flow) that supports fast dynamo action. A parallel treatment is described for the linearized Navier-Stokes equations for the motion of a viscous fluid. In this problem the analogous necessary condition for "fast vorticity generation" is the existence of some instability in the corresponding Euler (i.e., inviscid) equation. Dynamo theory methods give a second related result, namely a universal geometric estimate from below on the growth rate of a small perturbation in an inviscid fluid. This bound gives an effective sufficient condition for local instability for Eulers equations. In particular, it is proved that a steady flow with a hyperbolic stagnation point is unstable. The growth rate of an infinitesimal perturbation in a metric with derivatives depends on this metric. This dependence is completely described.

  14. Discovery of Novel Insulin-Like Growth Factor-1 Receptor Inhibitors with Unique Time-Dependent Binding Kinetics

    PubMed Central

    2013-01-01

    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 (t1/2) 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

  15. 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.

  16. Is radioactive decay really exponential?

    NASA Astrophysics Data System (ADS)

    Aston, P. J.

    2012-03-01

    Radioactive decay of an unstable isotope is widely believed to be exponential. This view is supported by experiments on rapidly decaying isotopes but is more difficult to verify for slowly decaying isotopes. The decay of 14C can be calibrated over a period of 12550 years by comparing radiocarbon dates with dates obtained from dendrochronology. It is well known that this approach shows that radiocarbon dates of over 3000 years are in error, which is generally attributed to past variation in atmospheric levels of 14C. We note that predicted atmospheric variation (assuming exponential decay) does not agree with results from modelling, and that theoretical quantum mechanics does not predict exact exponential decay. We give mathematical arguments that non-exponential decay should be expected for slowly decaying isotopes and explore the consequences of non-exponential decay. We propose an experimental test of this prediction of non-exponential decay for 14C. If confirmed, a foundation stone of current dating methods will have been removed, requiring a radical reappraisal both of radioisotope dating methods and of currently predicted dates obtained using these methods.

  17. Classification and kinetic analysis of viscosity growth processes for NaOH-gelatinized rice starches.

    PubMed

    Yamamoto, Hisashi; Sawai, Nozomi; Seo, Kanako

    2013-09-12

    Using capillary viscometry, viscosity growth processes were studied for non-glutinous rice starches gelatinized with different NaOH solution concentrations. The viscosity-time data series generally conformed to sigmoid curves with an arbitrary inflection point (IP) for each curve, and were analyzed using a kinetic model that incorporated a first-order reaction rate equation and a mixing rule of a power-law type. The shapes of curves were classified with the exponent ν or the ratio η(*)/ηG, where η(*) and ηG were viscosities at IP and at equilibrium, respectively. It was argued that these parameters were related to the complex formation arising from NaOH-starch interactions. The rate constant K defined uniformly for an entire process increased with NaOH concentration and was power-law dependent. Furthermore, it was suggested that gelatinization evolved non-uniformly over time. A non-uniform analysis was then performed by disassembling the entire process into several elementary stages and revealed the evolutionary process for K.

  18. 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.

  19. Post-deposition growth kinetics of Ge on Ge(0 0 1)

    NASA Astrophysics Data System (ADS)

    Tinkham, B. P.; Jenichen, B.; Kaganer, V. M.; Shayduk, R.; Braun, W.; Ploog, K. H.

    2008-07-01

    We study the nucleation and growth kinetics on the Ge(0 0 1) surface at elevated temperatures using in situ surface X-ray diffraction. The time evolution of characteristic length scales on the surface is analyzed through the widths of the different components of the integer-order (morphology sensitive) and fractional-order (reconstruction sensitive) diffraction peaks. We find an activation energy of 0.58 eV for Ge island nucleation during homoepitaxy, which implies a diffusion activation energy higher than that obtained for both adatom and dimer diffusion on Ge(0 0 1) in previous studies. Sub-monolayer homoepitaxial Ge islands coarsen according to a power law, with a relatively low time exponent of n=0.2. The coarsening of small 2×1 reconstruction domains on a flat surface prepared by deposition of an integer number of layers shows a strong temperature dependence, whereby the coarsening exponent decreases from 0.41 to 0.2 as the temperature is increased.

  20. Mechanism and kinetics of biofilm growth process influenced by shear stress in sewers.

    PubMed

    Ai, Hainan; Xu, Jingwei; Huang, Wei; He, Qiang; Ni, Bingjie; Wang, Yinliang

    2016-01-01

    Sewer biofilms play an important role in the biotransformation of substances for methane and sulfide emission in sewer networks. The dynamic flows and the particular shear stress in sewers are the key factors determining the growth of the sewer biofilm. In this work, the development of sewer biofilm with varying shear stress is specifically investigated to gain a comprehensive understanding of the sewer biofilm dynamics. Sewer biofilms were cultivated in laboratory-scale gravity sewers under different hydraulic conditions with the corresponding shell stresses are 1.12 Pa, 1.29 Pa and 1.45 Pa, respectively. The evolution of the biofilm thickness were monitored using microelectrodes, and the variation in total solids (TS) and extracellular polymer substance (EPS) levels in the biofilm were also measured. The results showed that the steady-state biofilm thickness were highly related to the corresponding shear stresses with the biofilm thickness of 2.4 ± 0.1 mm, 2.7 ± 0.1 mm and 2.2 ± 0.1 mm at shear stresses of 1.12 Pa, 1.29 Pa and 1.45 Pa, respectively, which the chemical oxygen demand concentration is 400 mg/L approximately. Based on these observations, a kinetic model for describing the development of sewer biofilms was developed and demonstrated to be capable of reproducing all the experimental data.

  1. 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.

  2. 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.

  3. Cell growth kinetics of the human cell line Colo-205 irradiated with photons and astatine-211 alpha-particles.

    PubMed

    Palm, S; Andersson, H; Bäck, T; Claesson, I; Delle, U; Hultborn, R; Jacobsson, L; Köpf, I; Lindegren, S

    2000-01-01

    Cell growth kinetics following Astatine-211 (211At, alpha-particle emitter) and photon irradiation were studied for the human colorectal cell line Colo-205. A growth assay using 96-well plates was chosen. The growth kinetics could be simulated by assuming certain fractions of cells with various proliferative capacities, i.e. from none up to 5 cell doublings, in addition to the defined survivors with remaining unlimited clonogenic capacity. No significant difference in cell growth characteristics was seen between 211At and photon irradiation. The cell doubling time, as calculated from the increment in optical density, was compared with the results from BrdU experiments in the early phases of growth (Tpot = 18.5 +/- 0.6 h for LDR (low dose rate) photon irradiated and 20.3 +/- 0.8 hours for sham-irradiated cells 40-45 hours post-irradiation) confirming the transient accelerated growth of irradiated cells. No statistically significant difference in growth was found between LDR, MDR (medium dose rate) and HDR (high dose rate) photon irradiation.

  4. Growth kinetics of Ge islands during Ga-surfactant-mediated ultrahigh vacuum chemical vapor deposition on Si(001)

    NASA Astrophysics Data System (ADS)

    Portavoce, A.; Kammler, M.; Hull, R.; Reuter, M. C.; Copel, M.; Ross, F. M.

    2004-11-01

    The surfactant effect of Ga pre-deposited prior to ultrahigh vacuum (UHV) chemical vapor deposition (CVD) of Ge on Si(001) is investigated using in situ transmission electron microscopy. Island shape, nucleation and growth kinetics, and the influence of growth temperature and pressure are studied. When 1 monolayer of Ga covers the surface, Ge island nucleation occurs after a 5-10× longer growth time than without Ga for the same growth temperature and pressure, and the island density then varies with time in a more complex way than for Ga-free growth. The islands formed have a different shape and aspect ratio compared to conventional hut and dome clusters, and the critical lateral size for dislocation nucleation is reduced. Ex situ medium energy ion scattering and x-ray photoelectron scattering measurements of the total amount of Ge deposited before island nucleation demonstrate that the Ga layer decreases the surface reactivity and inhibits Ge growth. We discuss a simple model in which the surfactant-mediated growth kinetics are principally driven by the balance between Ge deposition and Ga desorption. We show that Ga surfactant-mediated UHV CVD can be used to produce Ge quantum dots with a higher surface density and a thinner wetting layer than is possible using conventional CVD.

  5. Nucleation and growth in materials and on surfaces: Kinetic Monte Carlo simulations and rate equation theory

    NASA Astrophysics Data System (ADS)

    Shi, Feng

    This dissertation is organized in two parts, the first part is about fundamental characteristics of multiple dimensional systems, the second part is about parallel KMC calculation of coarsening process. In Part I, we first study the fundamental characteristics of nucleation and growth in 3 dimensional (3D) systems using a simplified model of nucleation and growth. One of the main goals of this work is to compare with previous work on 2D nucleation and growth in order to understand the effects of dimensionality. The scaling of the average island-size, island density, monomer density, island-size distribution (ISD), capture number distribution (CND), and capture zone distribution (CZD) are studied as a function of the fraction of occupied sites (coverage) and the ratio D/F of the monomer hopping rate D to the (per site) monomer creation rate F. Our model may be viewed as a simple model of the early-stages of vacancy cluster nucleation and growth under irradiation. Good agreement is found between our mean-field (MF) rate-equation results for the average island and monomer densities and our simulation results. In addition, we find that due to the decreased influence of correlations and fluctuations in 3D as compared to 2D, the scaled CND depends only weakly on the island-size. As a result the scaled ISD is significantly sharper than obtained in 2D and diverges with increasing D/F. However, the scaled ISD obtained in kinetic Monte Carlo (KMC) simulations appears to diverge more slowly with increasing D/F than the MF prediction while the divergence occurs at a value of the scaled island-size which is somewhat beyond the MF prediction. These results are supported by an analysis of the asymptotic CND. The final goal for understanding the mechanism of nucleation and growth is to develop a theory to concisely and precisely disclose the law underlying the nucleation and growth process. From the theoretical point view, dimension can be taken as a variable to develop theory. In

  6. Comparative studies on phosphorus uptake and growth kinetics of the microalga Tetraselmis subcordiformis and the macroalga Ulva pertusa

    NASA Astrophysics Data System (ADS)

    Nan, Chunrong; Dong, Shuanglin

    2004-04-01

    Short-term uptake experiments and long-term semicontinuous culture experiments were performed under the condition of phosphorus (P) limitation to estimate and compare the P uptake and growth kinetics of the microalga Tetraselmis subcordiformis and the macroalga Ulva pertusa. Two new parameters, the maximum specific uptake rate ( V {m/sp}) and the maximal growth efficiency (β), are introduced to achieve uniformity for the comparison of nutrient uptake and growth efficiency between microalgae and macroalgae. T. subcordiformis possesses 3 times lower half saturation uptake constant, 4 times higher maximal growth rate and 20 times higher maximum specific uptake rate than U. pertusa, while U. pertusa possesses 4 times higher maximal growth efficiency than T. subcordiformis.

  7. Sputtering temperature dependent growth kinetics and CO2 sensing properties of ZnO deposited over porous silicon

    NASA Astrophysics Data System (ADS)

    Martínez, L.; Holguín-Momaca, J. T.; Karthik, T. V. K.; Olive-Méndez, S. F.; Campos-Alvarez, J.; Agarwal, V.

    2016-10-01

    We report the growth kinetics and sensing properties of ZnO deposited over macro-porous silicon substrates at 400 and 600 °C using magnetron-sputtering technique. Scanning electron microscopy was employed to investigate the morphology and the particle size of the ZnO nanoparticles (NPs). The grain growth kinetics was analyzed with the help of the phenomenological equation rn =k0 texp(- Q / RT) finding an activation energy Q = 13.92 kJ/mol. The grain growth exponent (n = 2.85) for the growth at 400 °C corresponds to an Ostwald ripening process, while the growth at 600 °C is described by n = 1.66 implying a higher growth rate attributed to a high surface diffusion of add-atoms contributing to the formation of larger grains. The sensing response of the complete structure has been tested at different temperatures. The highest sensitivity, S ∼10, was obtained at a sensor temperature of 300 °C on the ZnO NPs sputtered on to the porous silicon substrate at 400 °C. The high response is attributed to the infiltration, uniform and homogenous distribution of the ZnO NPs into the pores. ZnO NPs sputtered at 400 °C are found to be smaller than those grown at 600 °C, exhibiting a larger surface-area/volume ratio and hence increasing the oxygen adsorption resulting in an enhanced CO2 sensitivity.

  8. Growth kinetics of CaF2/Si(111) heteroepitaxy: An x-ray photoelectron diffraction study

    NASA Astrophysics Data System (ADS)

    Denlinger, J. D.; Rotenberg, Eli; Hessinger, U.; Leskovar, M.; Olmstead, Marjorie A.

    1995-02-01

    Kinetic variations of the initial stages of CaF2 growth on Si(111) by molecular-beam epitaxy are studied with the in situ combination of x-ray photoelectron spectroscopy and diffraction. After the formation of a chemically reacted interface layer, the morphology of the subsequent bulk layers is found to be dependent on the substrate temperature and incident flux rate, as well as the initial interface structure. For substrate temperatures above ~600 °C, subsequent layers do not easily wet the interface layer, and a transition is observed from a three-dimensional island formation at low flux to a laminar growth following the coalescence of bilayer islands at higher flux. At lower substrate temperatures (~450 °C), a different stoichiometry and structure of the interface layer leads to laminar growth at all fluxes, but with a different bulk nucleation behavior. Crystalline heteroepitaxy is not observed when growth initiates at room temperature, but homoepitaxy does proceed at room temperature if the first few layers are deposited at a high temperature. The different growth regimes are discussed in terms of a kinetic model separating step and terrace nucleation where, contrary to homoepitaxy, step nucleation leads to islanded growth.

  9. Structure and growth kinetics of the oxidation process of Fe(001) whisker surfaces over a 10-decade pressure range

    NASA Astrophysics Data System (ADS)

    Ferrer, Salvador; Robach, Odile; Balmes, Olivier; Isern, Helena; Popa, Iona; Ackerman, Marcelo

    2010-10-01

    Fe(001) surfaces of whiskers of good crystalline quality were oxidized in a pressure range from 10 - 7 mbar to 1 bar at different temperatures. Epitaxial Fe 3O 4 and FeO thin films with negligible strain were grown depending on the oxidation temperatures. The kinetics of the oxide thickness growth was measured and compared with the predictions of the Fromhold-Cook theory for oxidation of metals. Some discrepancies were found and a possible explanation is presented.

  10. Simulation of the growth kinetics of boride layers formed on Fe during gas boriding in H2-BCl3 atmosphere

    NASA Astrophysics Data System (ADS)

    Kulka, M.; Makuch, N.; Pertek, A.; Małdziński, L.

    2013-03-01

    The modeling of the boriding kinetics is considered as a necessary tool to select the suitable process parameters for obtaining boride layer of an adequate thickness. Therefore, the simulation of the growth kinetics of boride layers has gained much attention for last years. The majority of the published works described the kinetics of the pack-boriding or paste-boriding. In this study, the model of growth kinetics of two-phase boride layer (FeB+Fe2B) on pure Fe was proposed for gas boriding. Displacements of the two interfaces (FeB/Fe2B and Fe2B/substrate) resulted from a difference of the arrival flux of interstitial boron atoms to one phase and the departure flux of the boron atoms from this phase to the second phase. The mass balance equations were formulated. The measurements of thickness of both zones (FeB and Fe2B), for different temperature of boriding, were used for calculations. Based on the experimental data, the parabolic growth constants AFeB and B versus the temperature of boriding were determined. The linear relationships were accepted. As a consequence, the activation energies (QFeB and Q) were calculated. The calculated values were comparable to other data derived from gas boriding. The presented model can predict the thicknesses of the FeB and Fe2B zones (XFeB and Y, respectively) formed on pure Fe during gas boriding. Additionally, the diffusion annealing after boriding was analyzed. This process was carried out in order to obtain a single-phase boride layer (Fe2B). The relationship between the reduction in FeB zone (dXFeB) and the growth in Fe2B phase (dY) was determined. The time tXFeB=0, needed for the total elimination of FeB phase in the boride layer was calculated and compared to the experimental data.

  11. 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.

  12. Batch growth kinetics of an indigenous mixed microbial culture utilizing m-cresol as the sole carbon source.

    PubMed

    Saravanan, Pichiah; Pakshirajan, K; Saha, Prabirkumar

    2009-02-15

    An indigenous mixed microbial culture, isolated from a sewage treatment plant located in Guwahati was used to study biodegradation of m-cresol in batch shake flasks. m-Cresol concentration in the growth media was varied from 100mg/L to 900mg/L. The degradation kinetics was found to follow a three-half-order model at all initial m-cresol concentrations with regression values greater than 0.97. A maximum observed specific degradation rate of 0.585h(-1) was observed at 200mg/L m-cresol concentration in the medium. In the range of m-cresol concentrations used in the study, specific growth rate of the culture and specific degradation rates were observed to follow substrate inhibition kinetics. These two rates were fitted to kinetic models of Edward, Haldane, Luong, Han-Levenspiel, and Yano-Koga that are used to explain substrate inhibition on growth of microbial culture. Out of these models Luong and Han-Levenspiel models fitted the experimental data best with lowest root mean square error values. Biokinetic constants estimated from these two models showed good potential of the indigenous mixed culture in degrading m-cresol in wastewaters.

  13. Co-optimizing carbon nanotube synthesis: control of diameter, structural quality, and growth kinetics along with simultaneous cost minimization

    NASA Astrophysics Data System (ADS)

    Meshot, Eric R.; Plata, Desireé L.; Reddy, Christopher M.; Gschwend, Philip M.; Hart, A. John

    2009-03-01

    We employ a decoupled CVD method that not only facilitates control of mean diameter and structural quality of vertically aligned CNTs, but also co-optimization of kinetics for efficient growth to ``forest'' heights of several millimeters. The growth substrate temperature (Ts) governs agglomeration of the catalyst film which primarily determines CNT diameter, while structural quality monotonically increases with Ts. Independent heating (Tp) of the reactant mixture generates a strikingly diverse population of active hydrocarbons. These analyses, in concert with real-time laser measurements of forest growth rate and height suggest that select products of gas treatment promote growth, while excessive gas-phase pyrolysis of hydrocarbons adversely affects the CNT structure. Further, we directly inject select compounds in the absence of thermal treatment, thus minimizing energetic costs.

  14. 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.

  15. 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).

  16. Quantification of epidermal growth factor receptor expression level and binding kinetics on cell surfaces by surface plasmon resonance imaging.

    PubMed

    Zhang, Fenni; Wang, Shaopeng; Yin, Linliang; Yang, Yunze; Guan, Yan; Wang, Wei; Xu, Han; Tao, Nongjian

    2015-10-06

    Epidermal growth factor receptor (EGFR, also known as ErbB-1 or HER-1) is a membrane bound protein that has been associated with a variety of solid tumors and the control of cell survival, proliferation, and metabolism. Quantification of the EGFR expression level in cell membranes and the interaction kinetics with drugs are thus important for cancer diagnosis and treatment. Here we report mapping of the distribution and interaction kinetics of EGFR in their native environment with the surface plasmon resonance imaging (SPRi) technique. The monoclonal anti-EGFR antibody was used as a model drug in this study. The binding of the antibody to EGFR overexpressed A431 cells was monitored in real time, which was found to follow the first-order kinetics with an association rate constant (ka) and dissociation rate constant (kd) of (2.7 ± 0.6) × 10(5) M(-1) s(-1) and (1.4 ± 0.5) × 10(-4) s(-1), respectively. The dissociation constant (KD) was determined to be 0.53 ± 0.26 nM with up to seven-fold variation among different individual A431 cells. In addition, the averaged A431 cell surface EGFR density was found to be 636/μm(2) with an estimation of 5 × 10(5) EGFR per cell. Additional measurement also revealed that different EGFR positive cell lines (A431, HeLa, and A549) show receptor density dependent anti-EGFR binding kinetics. The results demonstrate that SPRi is a valuable tool for direct quantification of membrane protein expression level and ligand binding kinetics at single cell resolution. Our findings show that the local environment affects the drug-receptor interactions, and in situ measurement of membrane protein binding kinetics is important.

  17. Quantum properties of exponential states

    SciTech Connect

    Luis, Alfredo

    2007-05-15

    The use of Renyi entropy as an uncertainty measure alternative to variance leads to the study of states with quantum fluctuations below the levels established by Gaussian states, which are the position-momentum minimum uncertainty states according to variance. We examine the quantum properties of states with exponential wave functions, which combine reduced fluctuations with practical feasibility.

  18. 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…

  19. Approximating Functions with Exponential Functions

    ERIC Educational Resources Information Center

    Gordon, Sheldon P.

    2005-01-01

    The possibility of approximating a function with a linear combination of exponential functions of the form e[superscript x], e[superscript 2x], ... is considered as a parallel development to the notion of Taylor polynomials which approximate a function with a linear combination of power function terms. The sinusoidal functions sin "x" and cos "x"…

  20. The Effect of Growth Kinetics on the Development of Element- and Isotope Profiles in Single Mineral Grains

    NASA Astrophysics Data System (ADS)

    Watson, E. B.; Mueller, T.

    2008-12-01

    The formation of a rock texture is the consequence of multiple interacting processes controlling the crystallization history of minerals, and is typically recorded in several ways and on different scales. Recent advances in microanalysis enable observation of compositional (elemental as well as isotopic) variations on progressively decreasing (sub-mm) scales, and theoretical approaches for simulating realistic, disequilibrium kinetic effects are becoming increasingly sophisticated. Here we present some new perspectives arising from the continuing development of our numerical approach for describing kinetically controlled element uptake and isotope fractionation during diffusion-controlled mineral growth. We assume a spherical grain growing under local equilibrium at the interface with a spherical matrix of a given size and composition. It has been shown previously that the uptake of a component in a growing crystal depends critically upon the ratio of the crystal growth rate (R) to the diffusivity (D) of that component in the growth medium. Highly compatible (or incompatible) elements potentially will be depleted (or accumulated) near the surface of the growing crystal, forming a disequilibrium compositional boundary layer against the advancing interface. Equilibration of this boundary layer with the bulk reservoir depends mainly on D of the species of interest, and because D is now known to vary with mass of an isotope of a given element, signficant isotope fractionation is predicted to occur during progressive mineral growth under some circumstances. In the present study we focus specifically on the role of crystal-growth kinetics [R=f(time)] in controlling isotope profiles recorded in crystals. We show that the amount of fractionation, and especially the shape of the resulting radial isotope profiles, is quite sensitive to the assumed growth law or history. Differences in the initial grain size - as might apply in the case of xenocrysts in magma - have a

  1. 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

    2013-02-07

    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

  2. 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.

  3. 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.

  4. 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.

  5. Kinetic analysis of platelet-derived growth factor receptor/phosphoinositide 3-kinase/Akt signaling in fibroblasts.

    PubMed

    Park, Chang Shin; Schneider, Ian C; Haugh, Jason M

    2003-09-26

    Isoforms of the serine-threonine kinase Akt coordinate multiple cell survival pathways in response to stimuli such as platelet-derived growth factor (PDGF). Activation of Akt is a multistep process, which relies on the production of 3'-phosphorylated phosphoinositide (PI) lipids by PI 3-kinases. To quantitatively assess the kinetics of PDGF receptor/PI 3-kinase/Akt signaling in fibroblasts, a systematic study of this pathway was performed, and a mechanistic mathematical model that describes its operation was formulated. We find that PDGF receptor phosphorylation exhibits positive cooperativity with respect to PDGF concentration, and its kinetics are quantitatively consistent with a mechanism in which receptor dimerization is initially mediated by the association of two 1:1 PDGF/PDGF receptor complexes. Receptor phosphorylation is transient at high concentrations of PDGF, consistent with the loss of activated receptors upon endocytosis. By comparison, Akt activation responds to lower PDGF concentrations and exhibits more sustained kinetics. Further analysis and modeling suggest that the pathway is saturated at the level of PI 3-kinase activation, and that the p110alpha catalytic subunit of PI 3-kinase contributes most to PDGF-stimulated 3'-PI production. Thus, at high concentrations of PDGF the kinetics of 3'-PI production are limited by the turnover rate of these lipids, while the Akt response is additionally influenced by the rate of Akt deactivation.

  6. Biochemical kinetics in changing volumes.

    PubMed

    Pawłowski, Piotr H; Zielenkiewicz, Piotr

    2004-01-01

    The need of taking into account the change of compartment volume when developing chemical kinetics analysis inside the living cell is discussed. Literature models of a single enzymatic Michaelis-Menten process, glycolytic oscillations, and mitotic cyclin oscillations were tested with appropriate theoretical extension in the direction of volume modification allowance. Linear and exponential type of volume increase regimes were compared. Due to the above, in a growing cell damping of the amplitude, phase shift, and time pattern deformation of the metabolic rhythms considered were detected, depending on the volume change character. The performed computer simulations allow us to conclude that evolution of the cell volume can be an essential factor of the chemical kinetics in a growing cell. The phenomenon of additional metabolite oscillations caused by the periodic cell growth and division was theoretically predicted and mathematically described. Also, the hypothesis of the periodized state in the growing cell as the generalization of the steady-state was formulated.

  7. In situ and time resolved quantification of the kinetics and mechanisms of CaCO3 nucleation and growth

    NASA Astrophysics Data System (ADS)

    Rodriguez-Blanco, J. D.; Shaw, S.; Benning, L. G.

    2009-04-01

    The crystal chemistry, occurrence and relevance of amorphous CaCO3 and its crystalline polymorphs in inorganic and organic environments have been studied for decades and are nowadays relatively well known [1]. However, due to the fast kinetics of the reactions that take place in solution [2], there is virtually no quantitative data available about the kinetics and mechanisms of the nucleation, growth and transformation of these phases in aqueous solutions. In this study we demonstrate that in situ and time resolved synchrotron-based Energy Dispersive X-Ray Diffraction combined with the corresponding solution chemistry and imaging can be successfully applied to evaluate quantitatively kinetic rates and mechanisms of the crystallization and transformation of CaCO3 phases in solution. The precipitation of amorphous calcium carbonate (ACC) and its crystallization to vaterite and calcite was followed in closed thermostated reactors at temperatures between 7.5 and 40˚ C with the time-resolved data collected every 15 secs. The growth/decay of vaterite and calcite diffraction peaks was fitted using a Johnson-Mehl-Avrami-Kolmogorov model [3] to evaluate the kinetics and mechanisms of crystallization [4]. The results show that vaterite grows fast via a 3D growth process following a first order reaction and the subsequent transformation to calcite takes place slower, being controlled by the dissolution of the vaterite precursor. From the temperature dependent data apparent activation energies of nucleation and crystallization for both crystalline CaCO3 polymorphs have been calculated. In addition, wet chemical data and imaging also confirm these findings. Finally, this approach was applied also to other carbonate systems (i.e., dolomite , Ca/Mg carbonates). [1] Reeder R. (1983) Rev. Mineral, 11. [2] Ogino et al. (1987) Geochim. Cosmochim. Acta 51, 2757-2767. [3] Johnson, P.F. and Mehl, R.F. (1939) Reaction kinetics in processes of nucleation and growth. American Institute

  8. Kinetics of copper growth on graphene revealed by time-resolved small-angle x-ray scattering

    NASA Astrophysics Data System (ADS)

    Hodas, M.; Siffalovic, P.; Jergel, M.; Pelletta, M.; Halahovets, Y.; Vegso, K.; Kotlar, M.; Majkova, E.

    2017-01-01

    Metal growth on graphene has many applications. Transition metals are known to favor three-dimensional (3D) cluster growth on graphene. Copper is of particular interest for cost-effective surface-supported catalysis applications and as a contact material in electronics. This paper presents an in situ real-time study of Cu growth kinetics on graphene covering all stages preceding formation of a continuous film performed by laboratory-based grazing-incidence small-angle x-ray scattering (GISAXS) technique. In particular, nucleation and 3D cluster growth, coalescence, and percolation stages were identified. The cluster nucleation saturates after reaching a density of 1012c m-2 at ≈1 monolayer thickness. A Kratky plot and a paracrystal model with cumulative structural disorder were necessary to evaluate properly cluster growth and coalescence, respectively. The power law scaling constants 0.27 ±0.05 and 0.81 ±0.02 of the temporal evolution of Cu cluster size suggest the growth of isolated clusters and dynamic cluster coalescence keeping the cluster shape, respectively. Coalescence and percolation thresholds occur at Cu thicknesses of 2 ±0.4 and 8.8 ±0.7 nm , respectively. This paper demonstrates the potential of laboratory-based in situ GISAXS as a vital diagnostic tool for tailoring a large variety of Cu nanostructures on graphene based on an in situ Cu growth monitoring which is applicable in a broad range of deposition times.

  9. 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.

  10. 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

  11. Robust exponential acceleration in time-dependent billiards.

    PubMed

    Gelfreich, Vassili; Rom-Kedar, Vered; Shah, Kushal; Turaev, Dmitry

    2011-02-18

    A class of nonrelativistic particle accelerators in which the majority of particles gain energy at an exponential rate is constructed. The class includes ergodic billiards with a piston that moves adiabatically and is removed adiabatically in a periodic fashion. The phenomenon is robust: deformations that keep the chaotic character of the billiard retain the exponential energy growth. The growth rate is found analytically and is, thus, controllable. Numerical simulations corroborate the analytic predictions with good precision. The acceleration mechanism has a natural thermodynamical interpretation and is applied to a hot dilute gas of repelling particles.

  12. Exponentially Stabilizing Robot Control Laws

    NASA Technical Reports Server (NTRS)

    Wen, John T.; Bayard, David S.

    1990-01-01

    New class of exponentially stabilizing laws for joint-level control of robotic manipulators introduced. In case of set-point control, approach offers simplicity of proportion/derivative control architecture. In case of tracking control, approach provides several important alternatives to completed-torque method, as far as computational requirements and convergence. New control laws modified in simple fashion to obtain asymptotically stable adaptive control, when robot model and/or payload mass properties unknown.

  13. 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.

  14. 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.

  15. Influence of synthesis parameters on the growth of CdS nanoparticles in colloidal solution and determination of growth kinetics using Karhunen Loeve decomposition

    NASA Astrophysics Data System (ADS)

    Barglik-Chory, Ch.; Münster, A. F.; Strohm, H.; Remenyi, Ch.; Müller, G.

    2003-06-01

    The growth of CdS nanoparticles during aging at ambient temperature is investigated with respect to the type of stabilizer, the concentration of the colloidal solution, and the molar ratio of sulfide to cadmium. The UV/Vis absorption spectra recorded within a period of seven days are analyzed by Karhunen-Loeve decomposition. It revealed a single process with first-order decomposition kinetics for each of the measured time series, and the respective rate constants are calculated. An explanation describing possible mechanisms for the observed ripening of the colloids is given.

  16. 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).

  17. 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

  18. Submonolayer nucleation and growth and the initial stage of multilayer kinetic roughening during Ag/Ag (100) homoepitaxy

    SciTech Connect

    Zhang, C.

    1996-08-01

    A comprehensive Scanning Tunneling Microscopy (STM) study of submonolayer nucleation and growth of 2D islands in Ag/Ag(100) homoepitaxy for temperature between 295K and 370K is presented. The initial stages of multilayer kinetic roughening is also studied. Analysis of an appropriate model for metal (100) homoepitaxy, produces estimates of 350 meV for the terrace diffusion barrier, 400 meV for the adatom bond energy, and 25 meV for the additional Ehrlich-Schwoebel step-edge barrier.

  19. Growth kinetics of 1-2 mm and 3-4 mm colonies of Nostoc sphaeroides (Cyanophyta) in outdoor culture.

    PubMed

    Deng, Zhongyang; Yan, Chunlan; Lu, Fan; Hu, Qiang; Hu, Zhengyu

    2008-10-01

    Nostoc sphaeroides Kützing was cultivated in paddlewheel-driven raceway ponds and the growth kinetics of 1-2 mm and 3-4 mm colonies of N. sphaeroides was studied. The biomass productivities in 2.5 m(2) raceway ponds inoculated with 1-2 mm and 3-4 mm colonies were 5.2 and 0.25 g dry wt m(-2) d(-1), respectively. Furthermore, differently sized colonies showed different relative water content, total soluble carbohydrates, chlorophyll a content and density of filaments. This is the first report on mass culture of N. sphaeroides under outdoor conditions.

  20. Emergence of protocellular growth laws.

    PubMed

    Rocheleau, Tristan; Rasmussen, Steen; Nielsen, Peter E; Jacobi, Martin N; Ziock, Hans

    2007-10-29

    Template-directed replication is known to obey a parabolic growth law due to product inhibition (Sievers & Von Kiedrowski 1994 Nature 369, 221; Lee et al. 1996 Nature 382, 525; Varga & Szathmáry 1997 Bull. Math. Biol. 59, 1145). We investigate a template-directed replication with a coupled template catalysed lipid aggregate production as a model of a minimal protocell and show analytically that the autocatalytic template-container feedback ensures balanced exponential replication kinetics; both the genes and the container grow exponentially with the same exponent. The parabolic gene replication does not limit the protocellular growth, and a detailed stoichiometric control of the individual protocell components is not necessary to ensure a balanced gene-container growth as conjectured by various authors (Gánti 2004 Chemoton theory). Our analysis also suggests that the exponential growth of most modern biological systems emerges from the inherent spatial quality of the container replication process as we show analytically how the internal gene and metabolic kinetics determine the cell population's generation time and not the growth law (Burdett & Kirkwood 1983 J. Theor. Biol. 103, 11-20; Novak et al. 1998 Biophys. Chem. 72, 185-200; Tyson et al. 2003 Curr. Opin. Cell Biol. 15, 221-231). Previous extensive replication reaction kinetic studies have mainly focused on template replication and have not included a coupling to metabolic container dynamics (Stadler et al. 2000 Bull. Math. Biol. 62, 1061-1086; Stadler & Stadler 2003 Adv. Comp. Syst. 6, 47). The reported results extend these investigations. Finally, the coordinated exponential gene-container growth law stemming from catalysis is an encouraging circumstance for the many experimental groups currently engaged in assembling self-replicating minimal artificial cells (Szostak 2001 et al. Nature 409, 387-390; Pohorille & Deamer 2002 Trends Biotech. 20 123-128; Rasmussen et al. 2004 Science 303, 963-965; Szathma ry

  1. 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

  2. Dissolution Kinetics of IMX-101 and IMX-104; Operating Procedure Series: Characterization of IMX Dissolution

    DTIC Science & Technology

    2016-07-01

    RDX. An exponential kinetic model is fitted to a small data sample to demonstrate one of many possible interpretations. DISCLAIMER: The...paddle rod also may suppress any microbial growth , particularly over very long experiments (up to five to six weeks); initial testing shows this is...sufficient to inhibit microbial growth , without introducing new transformation products. ERDC/EL TR-16-9 8 • Sample vials: 1.5–2.0 mL, amber glass

  3. Crystal growth kinetics of ultra-thin ZrO2 film on Si by differential scanning calorimetry

    NASA Astrophysics Data System (ADS)

    Faruque, Sk Abdul Kader Md; Debnath, Debika; Giri, Bimalesh; Chakraborty, Supratic

    2017-02-01

    Crystal growth kinetics of thin ZrO2 film deposited on Si is described in the framework of Johnson, Mehl and Avrami (JMA) equation and Kissinger method. Differential scanning calorimetry is employed here to determine the Avrami exponent and the activation energy of crystalline transition from the amorphous nature of ZrO2/Si. The activation energy is found to be 0.77 ± 0.06 eV, estimated from the slope of Kissinger plot. From the variation of Avrami exponent, it is observed that the crystallization of ZrO2 begins at the ZrO2/Si interface and grows normal to the interface at lower temperature range. The crystallization grows laterally, identified as heterogeneous nucleation at the grain boundary that dominates at higher temperature range indicating an increase in its grain size without increasing the number of grains. Only the growth along the grain boundary occurs during heterogeneous crystallization.

  4. 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.

  5. In Situ Atomic Scale Visualization Of Surface Kinetics Driven Dynamics Of Oxide Growth On A Ni–Cr Surface

    SciTech Connect

    Luo, Langli; Zou, Lianfeng; Schreiber, Daniel K.; Olszta, Matthew J.; Baer, Donald R.; Bruemmer, Stephen M.; Zhou, Guangwen; Wang, Chong M.

    2016-01-20

    We report in situ atomic-scale visualization of the dynamical three-dimensional (3D) growth of NiO during initial oxidation of Ni-10at%Cr using environmental transmission electron microscopy (ETEM). Despite the thermodynamic preference for Cr2O3 formation, cubic NiO oxides nucleated and grew epitaxially as the dominating oxide phase on the Ni-Cr (100) surface during initial oxidation. The growth of NiO islands proceeds through step-by-step adatom mechanism in 3D, which is sustained by surface diffusion of Ni and O atoms. Although the shapes of oxide islands are controlled by strain energy between oxide and alloy substrate, local surface kinetic variations can lead to the change of surface planes of oxide islands. These results demonstrate that surface diffusion dominates initial oxidation of Ni-Cr in these test conditions.

  6. 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.

  7. 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).

  8. 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

  9. Growth kinetics of coliform bacteria under conditions relevant to drinking water distribution systems.

    PubMed

    Camper, A K; McFeters, G A; Characklis, W G; Jones, W L

    1991-08-01

    The growth of environmental and clinical coliform bacteria under conditions typical of drinking water distribution systems was examined. Four coliforms (Klebsiella pneumoniae, Escherichia coli, Enterobacter aerogenes, and Enterobacter cloacae) were isolated from an operating drinking water system for study; an enterotoxigenic E. coli strain and clinical isolates of K. pneumoniae and E. coli were also used. All but one of the coliforms tested were capable of growth in unsupplemented mineral salts medium; the environmental isolates had greater specific growth rates than did the clinical isolates. This trend was maintained when the organisms were grown with low levels (less than 1 mg liter-1) of yeast extract. The environmental K. pneumoniae isolate had a greater yield, higher specific growth rates, and a lower Ks value than the other organisms. The environmental E. coli and the enterotoxigenic E. coli strains had comparable yield, growth rate, and Ks values to those of the environmental K. pneumoniae strain, and all three showed significantly more successful growth than the clinical isolates. The environmental coliforms also grew well at low temperatures on low concentrations of yeast extract. Unsupplemented distribution water from the collaborating utility supported the growth of the environmental isolates. Growth of the K. pneumoniae water isolate was stimulated by the addition of autoclaved biofilm but not by tubercle material. These findings indicate that growth of environmental coliforms is possible under the conditions found in operating municipal drinking water systems and that these bacteria could be used in tests to determine assimilable organic carbon in potable water.

  10. A 9-pool metabolic structured kinetic model describing days to seconds dynamics of growth and product formation by Penicillium chrysogenum.

    PubMed

    Tang, Wenjun; Deshmukh, Amit T; Haringa, Cees; Wang, Guan; van Gulik, Walter; van Winden, Wouter; Reuss, Matthias; Heijnen, Joseph J; Xia, Jianye; Chu, Ju; Noorman, Henk J

    2017-03-21

    A powerful approach for the optimization of industrial bioprocesses is to perform detailed simulations integrating large scale computational fluid dynamics (CFD) and cellular reaction dynamics (CRD). However, complex metabolic kinetic models containing a large number of equations pose formidable challenges in CFD-CRD coupling and computation time afterward. This necessitates to formulate a relatively simple but yet representative model structure. Such a kinetic model should be able to reproduce metabolic responses for short-term (mixing time scale of tens of seconds) and long-term (fed-batch cultivation of hours/days) dynamics in industrial bioprocesses. In this paper, we used Penicillium chrysogenum as a model system and developed a metabolically structured kinetic model for growth and production. By lumping the most important intracellular metabolites in 5 pools and 4 intracellular enzyme pools, linked by 10 reactions, we succeeded in maintaining the model structure relatively simple, while providing informative insight into the state of the organism. The performance of this 9-pool model was validated with a periodic glucose feast-famine cycle experiment at the minute time scale. Comparison of this model and a reported black box model for this strain shows the necessity of employing a structured model under feast-famine conditions. This proposed model provides deeper insight into the in vivo kinetics and, most importantly, can be straightforwardly integrated into a computational fluid dynamic framework for simulating complete fermentation performance and cell population dynamics in large scale and small scale fermentors. This article is protected by copyright. All rights reserved.

  11. Growth kinetics and characterization of human dental pulp stem cells: Comparison between third molar and first premolar teeth

    PubMed Central

    Mehrabani, Davood; Mahdiyar, Parisa; Robati, Reza; Zare, Shahrokh; Dianatpour, Mehdi; Tamadon, Amin

    2017-01-01

    Background Dental pulp stem cells (DPSCs) play an important role in tissue regeneration. This study compares the growth kinetics and characterization of third molar and first premolar human DPSCs. Material and Methods Dental pulp tissues were isolated from human first premolar and third molar teeth and were digested by treating them with collagenase type I. Single-cell suspensions from each dental pulp were seeded in T25 culture flasks and the media were replaced every 3 days until 70% confluence. The cells were enumerated to determine the population doubling time (PDT). Cells were characterized using flow cytometry, RT-PCR and osteogenic medium for differentiation of DPSCs. Karyotyping assay was also performed till passage 7th. Results The DPSCs had spindle-shaped morphology. There was an increase in PDT in third molar DPSCs when compared to first premolar teeth. Positive expression of CD44, CD73, and CD90 and negative expression of CD34 and CD45 were illustrated. A normal karyotype was visible for all seven passages. The Alizarin red staining was positive for osteogenic induction of DPSCs. Conclusions When DPSCs are needed, third molar teeth can be a good and convenient candidate for cell transplantation, yielding high number of cells with mesenchymal characteristics. They can be a source for further investigations in vitro and work on tissue engineering protocols. Key words:Stem cells, dental pulp, growth kinetics, characterization. PMID:28210430

  12. Caprine Endometrial Mesenchymal Stromal Stem Cell: Multilineage Potential, Characterization, and Growth Kinetics in Breeding and Anestrous Stages

    PubMed Central

    Zarezadeh, Younes; Dianatpour, Mehdi; Zare, Shahrokh

    2017-01-01

    The endometrial layer of the uterus contains a population of cells with similar characteristics of mesenchymal stem cells (MSCs). In the present study, caprine endometrial mesenchymal stromal stem cells (En-MSCs) characters and differentiation potential to chondrogenic, osteogenic, and adipogenic cell lines as well as their growth kinetics in breeding and anestrous stages were evaluated. En-MSCs were enzymatically isolated from endometrial layer of the uterus of adult goats and were cultured and subcultured until passage 4. The growth kinetics and population doubling time (PDT) of caprine En-MSCs in breeding and anestrous stages were determined. En-MSCs in passage 4 were used for the karyotyping and differentiation into chondrocytes, osteocytes, and adipocytes. The PDT in anestrus phase was 40.6 h and in cyclic goats was 53 h. En-MSCs were fibroblast-like in all passages. The number of chromosomes was normal (2n = 60) with no chromosomal instability. Chondrogenic, osteogenic, and adipogenic differentiation of En-MSCs was confirmed by staining with Alcian blue, Alizarin red, and Oil Red O, respectively. Caprine En-MSCs demonstrated to be an alternative source of MSCs for cell therapy purposes in regenerative medicine. PMID:28357151

  13. 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

  14. SU-E-T-751: Three-Component Kinetic Model of Tumor Growth and Radiation Response for Stereotactic Radiosurgery

    SciTech Connect

    Watanabe, Y; Dahlman, E; Leder, K; Hui, S

    2015-06-15

    Purpose: To develop and study a kinetic model of tumor growth and its response to stereotactic radiosurgery (SRS) by assuming that the cells in irradiated tumor volume were made of three types. Methods: A set of ordinary differential equations (ODEs) were derived for three types of cells and a tumor growth rate. It is assumed that the cells were composed of actively proliferating cells, lethally damaged-dividing cells, and non-dividing cells. We modeled the tumor volume growth with a time-dependent growth rate to simulate the saturation of growth. After SRS, the proliferating cells were permanently damaged and converted to the lethally damaged cells. The amount of damaged cells were estimated by the LQ-model. The damaged cells gradually stopped dividing/proliferating and died with a constant rate. The dead cells were cleared from their original location with a constant rate. The total tumor volume was the sum of the three components. The ODEs were numerically solved with appropriate initial conditions for a given dosage. The proposed model was used to model an animal experiment, for which the temporal change of a rhabdomyosarcoma tumor volume grown in a rat was measured with time resolution sufficient to test the model. Results: To fit the model to the experimental data, the following characteristics were needed with the model parameters. The α-value in the LQ-model was smaller than the commonly used value; furthermore, it decreased with increasing dose. At the same time, the tumor growth rate after SRS had to increase. Conclusions: The new 3-component model of tumor could simulate the experimental data very well. The current study suggested that the radiation sensitivity and the growth rate of the proliferating tumor cells may change after irradiation and it depended on the dosage used for SRS. These preliminary observations must be confirmed by future animal experiments.

  15. 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.

  16. Differential expression of secretion machinery during bacterial growth: SecY and SecF decrease while SecA increases during transition from exponential phase to stationary phase.

    PubMed

    Yang, Chun-Kai; Lu, Chung-Dar; Tai, Phang C

    2013-12-01

    Transcription of many house-keeping genes, including secY and some other sec genes, decreases in the transition from the exponential phase to the stationary phase (feast to famine) in Bacillus subtilis. Unexpectedly and in contradiction to earlier reports, enhanced transcription was observed for another group of sec genes, including secA which codes for an essential ATPase for protein secretion. Consistent with the transcription data, the SecA protein of B. subtilis increases significantly in the stationary phase. Immunoblot analyses of Sec proteins during the transition in Escherichia coli also revealed the pronounced decreases of SecY and SecF and the increase of SecA, resulting in drastic increases of SecA/SecY and SecA/SecF ratios from exponential to stationary phases. The differential expression of Sec proteins in the stationary phase suggests the possibility of specific physiological functions.

  17. Enhancing the growth of Physcomitrella patens by combination of monochromatic red and blue light - a kinetic study.

    PubMed

    Cerff, Martin; Posten, Clemens

    2012-04-01

    In the current work we demonstrate the relevance of monochromatic light conditions in moss plant cell culture. Light intensity and illumination wavelength are important cultivation parameters due to their impact on growth and chlorophyll formation kinetics of the moss Physcomitrella patens. This moss was chosen as a model organism due to its capability to produce complex recombinant pharmaceutical proteins. Filamentous moss cells were cultivated in mineral medium in shaking flasks. The flasks were illuminated by light emitting diodes (LED) providing nearly monochromatic red and blue light as well as white light as a reference. A maximum growth rate of 0.78 day((1) was achieved under additional CO(2) aeration and no growth inhibition was observed under high light illumination. The application of dual red and blue light is the most effective way to reach high growth and chlorophyll formation rates while minimizing energy consumption of the LEDs. These observations are discussed as effects of photo sensory pigments in the moss. The combination of monochromatic red and blue light should be considered when a large scale process is set up.

  18. KMCThinFilm: A C++ Framework for the Rapid Development of Lattice Kinetic Monte Carlo (kMC) Simulations of Thin Film Growth

    DTIC Science & Technology

    2015-09-01

    Monte Carlo (kMC) Simulations of Thin Film Growth by James J Ramsey Approved for public release; distribution is...Research Laboratory KMCThinFilm: A C++ Framework for the Rapid Development of Lattice Kinetic Monte Carlo (kMC) Simulations of Thin Film Growth by...Simulations of Thin Film Growth 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) James J Ramsey 5d. PROJECT

  19. Growth and Grazing Kinetics of the Facultative Anaerobic Nanoflagellate, Suigetsumonas clinomigrationis.

    PubMed

    Kondo, Ryuji; Okamura, Takahiko

    2017-03-31

    The functional and numerical responses of the facultative anaerobic heterotrophic nanoflagellate, Suigetsumonas clinomigrationis NIES-3647 to prey density were examined under oxic and anoxic conditions. S. clinomigrationis grew at temperatures between 10 and 30°C and in the salinity range of 3.9-36.9 psu. The maximum specific growth and ingestion rates of S. clinomigrationis were lower under anoxic conditions than under oxic conditions. Half-saturation constants for the growth of S. clinomigrationis were within or greater than the range of bacterial densities in the water column of Lake Suigetsu, suggesting that its growth rate is limited by bacterial prey densities in natural environments.

  20. Growth and Grazing Kinetics of the Facultative Anaerobic Nanoflagellate, Suigetsumonas clinomigrationis

    PubMed Central

    Kondo, Ryuji; Okamura, Takahiko

    2017-01-01

    The functional and numerical responses of the facultative anaerobic heterotrophic nanoflagellate, Suigetsumonas clinomigrationis NIES-3647 to prey density were examined under oxic and anoxic conditions. S. clinomigrationis grew at temperatures between 10 and 30°C and in the salinity range of 3.9–36.9 psu. The maximum specific growth and ingestion rates of S. clinomigrationis were lower under anoxic conditions than under oxic conditions. Half-saturation constants for the growth of S. clinomigrationis were within or greater than the range of bacterial densities in the water column of Lake Suigetsu, suggesting that its growth rate is limited by bacterial prey densities in natural environments. PMID:28190796

  1. Exponential self-replication enabled through a fibre elongation/breakage mechanism

    NASA Astrophysics Data System (ADS)

    Colomb-Delsuc, Mathieu; Mattia, Elio; Sadownik, Jan W.; Otto, Sijbren

    2015-06-01

    Self-replicating molecules are likely to have played a central role in the origin of life. Most scenarios of Darwinian evolution at the molecular level require self-replicators capable of exponential growth, yet only very few exponential replicators have been reported to date and general design criteria for exponential replication are lacking. Here we show that a peptide-functionalized macrocyclic self-replicator exhibits exponential growth when subjected to mild agitation. The replicator self-assembles into elongated fibres of which the ends promote replication and fibre growth. Agitation results in breakage of the growing fibres, generating more fibre ends. Our data suggest a mechanism in which mechanical energy promotes the liberation of the replicator from the inactive self-assembled state, thereby overcoming self-inhibition that prevents the majority of self-replicating molecules developed to date from attaining exponential growth.

  2. Exponential self-replication enabled through a fibre elongation/breakage mechanism

    PubMed Central

    Colomb-Delsuc, Mathieu; Mattia, Elio; Sadownik, Jan W.; Otto, Sijbren

    2015-01-01

    Self-replicating molecules are likely to have played a central role in the origin of life. Most scenarios of Darwinian evolution at the molecular level require self-replicators capable of exponential growth, yet only very few exponential replicators have been reported to date and general design criteria for exponential replication are lacking. Here we show that a peptide-functionalized macrocyclic self-replicator exhibits exponential growth when subjected to mild agitation. The replicator self-assembles into elongated fibres of which the ends promote replication and fibre growth. Agitation results in breakage of the growing fibres, generating more fibre ends. Our data suggest a mechanism in which mechanical energy promotes the liberation of the replicator from the inactive self-assembled state, thereby overcoming self-inhibition that prevents the majority of self-replicating molecules developed to date from attaining exponential growth. PMID:26081104

  3. Effects of crystal-melt interfacial energy anisotropy on dendritic morphology and growth kinetics

    NASA Technical Reports Server (NTRS)

    Glicksman, M. E.; Singh, N. B.

    1989-01-01

    Morphological and kinetic studies of succinonitrile, a BCC crystal with a low (0.5 percent) anisotropy and pivalic acid, and FCC crystal with relatively large (5 percent) anisotropy in solid-liquid interfacial energy, show clearly that anisotropy in the solid-liquid interfacial energy does not affect the tip radius-velocity relationship, but has a profound influence on the tip region and the rate of amplification of branching waves. Anisotropy of the solid-liquid interfacial energy may be one of the key factors by which the microstructural characteristics of cast structures reflect individual material behavior, especially crystal symmetry.

  4. 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.

  5. Modified growth kinetics of ion induced yttrium--silicide layers during subsequent thermal annealing

    SciTech Connect

    Alford, T.L.; Mayer, J.W. )

    1991-12-02

    Yttrium and amorphous silicon bilayers were irradiated with 600-keV inert ions between {minus}190 and 265 {degree}C. Ion-induced YSi{sub 1.7} layers occurred in those samples irradiated above {ge} (R18)205 {degree}C. These ion-mixed samples were thermally annealed at temperatures between 325 and 380 {degree}C. The diffusion-limited growth was observed only in those samples which had an ion-induced YSi{sub 1.7} layer present prior to thermal annealing. This type of growth is distinctly different from the interface limited, nonuniform, and irreproducible growth seen during typical thermal annealing of yttrium and silicon bilayers. This type of growth still occurred in those samples annealed after ion irradiations at {le}190 {degree}C.

  6. Measurements of crystal growth kinetics at extreme deviations from equilibrium. [Rapid solidification processing

    SciTech Connect

    Aziz, M.J.

    1993-05-07

    We have measured solute trapping of Sn in Al over a wide enough range of velocities to make a quantitative test of theory. The Continuous Growth Model of Aziz is the only one-parameter model that fits the data. We have also measured the diffusive speed - the growth rate at which interfacial partitioning is in mid-transition between equilibrium partitioning and complete solute trapping - for several solutes in A1. We have found an inverse correlation between the equilibrium partition coefficient and the diffusive speed. Taken together, these results give us heretofore unprecedented predictive capability in modeling rapid solidification processing. We have also examined theoretically short-range diffusion-limited growth, characteristic of incomplete solute trapping, and interface-limited growth, characteristic of complete solute trapping, in alloy solidification and have shown that the two regimes fall naturally out of a single unified theory of solidification.

  7. 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.

  8. 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.

  9. Observational constraints on exponential gravity

    SciTech Connect

    Yang, Louis; Lee, Chung-Chi; Luo, Ling-Wei; Geng, Chao-Qiang

    2010-11-15

    We study the observational constraints on the exponential gravity model of f(R)=-{beta}R{sub s}(1-e{sup -R/R}{sub s}). We use the latest observational data including Supernova Cosmology Project Union2 compilation, Two-Degree Field Galaxy Redshift Survey, Sloan Digital Sky Survey Data Release 7, and Seven-Year Wilkinson Microwave Anisotropy Probe in our analysis. From these observations, we obtain a lower bound on the model parameter {beta} at 1.27 (95% C.L.) but no appreciable upper bound. The constraint on the present matter density parameter is 0.245<{Omega}{sub m}{sup 0}<0.311 (95% C.L.). We also find out the best-fit value of model parameters on several cases.

  10. Continued Development of a Coupled Instrument Model for Quantifying Droplet Activation and Growth Kinetics in the DMT CCN Counter

    NASA Astrophysics Data System (ADS)

    Lathem, T. L.; Raatikainen, T. E.; Moore, R.; Nenes, A.

    2011-12-01

    The continuous-flow streamwise thermal gradient cloud condensation nuclei (CCN) chamber (CFSTGC1) and its commercialization by Droplet Measurement Technologies (DMT) has enabled large strides in measuring and parameterizing the CCN activity of atmospheric aerosol. The fast time response of the DMT CCN coupled with its ability to both count and size the activated droplets exiting the flow chamber have facilitated studies on CCN activation kinetics. Such studies are increasing in importance because changes in the kinetics of cloud droplet growth may have large impacts on cloud droplet number concentrations and climate. However, we find that activated droplet sizes in the DMT CCN are also strongly dependent on the instrument operating conditions and dry aerosol properties. A detailed numerical instrument model1 is utilized to account for these dependences, thereby enabling the quantification of an empirical water uptake coefficient and detection of changes in droplet growth arising from particle composition-dependent mechanisms.
    We present improvements to the coupled instrument and droplet growth model of Roberts and Nenes (2005)1, which include significantly reducing computing time, enhancing convergence stability, and incorporating an explicit treatment of water vapor depletion effects2. We apply the model to a variety of field campaign data and find that water vapor depletion effects can explain a large portion of the observed variability in CCN droplet sizes, which might have otherwise been incorrectly attributed to slow activation kinetics. Model accuracy is assessed through comparison of measured and model predicted droplet sizes for ammonium sulfate calibration experiments at a variety of instrument flow rates, pressures, and supersaturations. The accuracy of CCN optical particle counter (OPC) is also assessed using polystyrene latex and glass spheres (2-10 μm), which indicate a small but significant bias toward under-sizing. This suggests that while the

  11. 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.

  12. Growth kinetics of a single InP1-xAsx nanowire

    NASA Astrophysics Data System (ADS)

    Harmand, Jean-Christophe; Glas, Frank; Patriarche, Gilles

    2010-06-01

    Semiconductor nanowires offer additional properties and more flexibility for many potential applications. However the precise control of their growth is very challenging and much more complex than for two-dimensional layers. Here, we present a method which provides detailed information on their formation. The method is implemented with In(P,As) nanowires grown by Au-catalyzed molecular beam epitaxy. Controlled and periodic modulations of the incident vapor phase are generated. Due to these modulations, the nanowires show small and short oscillations of composition along their growth axis. These oscillations furnish a time scale which is recorded in the nanowire solid phase. The instantaneous growth rate and the total length of the nanowire at any time of the growth are accessible. The experimental data are fitted with models. The adatom diffusion lengths on the different surfaces and the chemical potentials in the adsorbed and liquid phases are extracted. It appears that the vapor flux intercepted by the nanowire sidewalls is the dominant contribution to their elongation. We discuss which contribution allows one initiating their growth from the catalyst drop.

  13. 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.

  14. A heterogeneous population model for the analysis of bacterial growth kinetics.

    PubMed

    McKellar, R C

    1997-05-20

    A two-compartment, heterogeneous population model (HPM) was derived using the simulation software SB ModelMaker to describe the growth of Listeria monocytogenes in bacteriological media at 5-35 degrees C. The model assumed that, at time t = 0, the inoculum was distributed between two distinct compartments, Non-Growing and Growing, and that growth could be described by four parameters: initial total cell population (N0), final maximum cell population (Nmax), maximum specific growth rate (mu(max)), and initial cell population in the Growing compartment (G0). The model was fitted to the data by optimizing the four parameters, and lag phase duration (lambda) was calculated. The resulting values of mu(max) and lambda were similar to those determined using the modified Gompertz equation. A new parameter, w0, was defined which relates to the proportion of the initial cell population capable of growth, and is a measure of the initial physiological state of the cells. A modified model in which mu(max) was replaced with a temperature function, and w0 replaced G0, was used to predict the effect of temperature on the growth of L. monocytogenes. The results of this study raise questions concerning the current definition of the lag phase.

  15. Influence of Thawing Methods and Storage Temperatures on Bacterial Diversity, Growth Kinetics, and Biogenic Amine Development in Atlantic Mackerel.

    PubMed

    Onyango, S; Palmadottir, H; Tómason, T; Marteinsson, V T; Njage, P M K; Reynisson, E

    2016-11-01

    Limited knowledge is currently available on the influence of fish thawing and subsequent storage conditions on bacterial growth kinetics, succession, and diversity alongside the production of biogenic amines. This study aimed to address these factors during the thawing and subsequent storage of mackerel. Thawing was either done fast in 18°C water for 2 h or slowly at 30°C overnight. Subsequent storage was at 30°C (ambient) for 36 h and 2 to 5°C (refrigerated) for 12 days. The cultivation methods used were total viable counts, hydrogen sulfide-producing bacteria, and Pseudomonas . Maximum growth rate, population density, and lag time were fitted on the counts using the Baranyi model. The bacterial diversity and succession were based on sequencing of 16S rRNA amplicons, and biogenic amines were quantified on high-pressure liquid chromatography-UV. The results show that lag time of hydrogen sulfide-producing bacteria was significantly affected by both thawing methods, and further, the interaction between thawing and storage significantly affected the maximum growth rate of these bacteria. However, the maximum growth rate of Pseudomonas was higher during refrigerated storage compared with storage at ambient temperature. Total viable counts showed longer lag time and reduced growth rate under refrigerated storage. Higher bacterial diversity was correlated to slow thawing and storage at ambient temperature compared with slow thawing and refrigerated storage. Overall, Acinetobacter and Psychrobacter genera were the dominant bacterial populations. The amine levels were low and could not be differentiated along the thawing and storage approaches, despite a clear increase in bacterial load, succession, and diversity. This corresponded well with the low abundance of biogenic amine-producing bacteria, with the exception of the genus Proteus , which was 8.6% in fast-thawed mackerel during storage at ambient temperature. This suggests that the decarboxylation potential is

  16. Growth kinetics of white graphene (h-BN) on a planarised Ni foil surface.

    PubMed

    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

    2015-07-09

    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.

  17. 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.

  18. 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.

  19. 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

  20. Kinetic Monte Carlo studies of early surface morphology in diamond film growth by chemical vapor deposition of methyl radical

    NASA Astrophysics Data System (ADS)

    Clark, M. M.; Raff, L. M.; Scott, H. L.

    1996-08-01

    We present results of off-lattice kinetic Monte Carlo simulations of early stages of low-pressure diamond film growth from a C[111] substrate via methyl radical and hydrogen vapor deposition. Interactions are governed by a semiempirical interatomic potential energy function. Rates for surface chemisorption and desorption of hydrogen and chemisorption of methyl radical that have been calculated by Raff and co-workers are used to assign real time to the Monte Carlo steps. The rate-determining step is the deposition or attempted deposition of methyl radical. Between CH3 surface events, the surface is relaxed by standard Monte Carlo methods. During the relaxation process C-C bonds may form and break, and surface diffusion occurs. We study the rate of formation of pair bonds and larger clusters of chemisorbed carbon over a 20-ms simulation, during which the initial surface becomes covered and small diamond ledges begin to form. This rate of growth is in accord with observed rates for diamond film growth from methyl radical.

  1. Kinetics of growth and ethanol production on different carbon substrates using genetically engineered xylose-fermenting yeast.

    PubMed

    Govindaswamy, Shekar; Vane, Leland M

    2007-02-01

    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 concentration of 20+/-0.8 g/L. Growth rates obtained in pure xylose-based medium were less than those for media containing pure glucose and glucose-xylose mixtures. A maximum specific growth rate micro(max) of 0.291 h(-1) was obtained in YPD medium containing 20 g/L glucose as compared to 0.206 h(-1) in YPX medium containing 20 g/L xylose. In media containing combinations of glucose and xylose, glucose was exhausted first followed by xylose. Ethanol production on pure xylose entered log phase during the 12-24h period as compared to the 4-10h for pure glucose based medium using 2% inoculum. When glucose was added to fermentation flasks which had been initiated on a pure xylose-based medium, the rate of xylose usage was reduced indicating cosubstrate inhibition of xylose consumption by glucose.

  2. 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

  3. [Kinetics of the growth of Ca oxalate crystals from supersaturated solutions].

    PubMed

    Leskovar, P; Hartung, R

    1979-04-01

    Several factors influencing the nucleation and growth of Ca-oxalate crystals from metastable and instable solutions were studied in some detail. Factors of interest were the absolute concentration of calcium respectively oxalate, the quotient oxalate/calcium, repeated additions of calcium and/or oxalate, the presence or absence of crystal seeds, the agitation respectively stagnation of the metastable Ca-oxalate solution, the duration of crystallization, etc. The striking findings are the eminent role of oxalate in the formation of big crystals and crystal aggregates, the distinct inhibition of crystal growth at higher and very high calcium concentrations, as well as the substantial crystal enlargement at the presistent oxalate load.

  4. 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.

  5. Low temperature reaction kinetics of CN- + HC3N and implications for the growth of anions in Titan's atmosphere

    NASA Astrophysics Data System (ADS)

    Biennier, Ludovic; Carles, Sophie; Cordier, Daniel; Guillemin, Jean-Claude; Le Picard, Sébastien D.; Faure, Alexandre

    2014-01-01

    The Cassini-Huygens probe has uncovered the existence of a profusion of negatively charged molecular species in the upper atmosphere of Titan (˜950 km). The presence of large amounts of anions was unexpected and the chemical pathways leading to their formation mostly unknown. The investigation of the negative ion chemistry appears therefore to be a key factor for modeling Titan's upper atmosphere. We present here the first low temperature experimental kinetic study involving CN-, proposed by Vuitton et al. (2009) to be one of the negative ions detected by the CAPS-ELS instrument onboard the Cassini spacecraft. The temperature dependence of the rate coefficient of the reaction CN- + HC3N, was explored over the 49-294 K temperature range in uniform supersonic flows using the CRESU technique. We find that the kinetics of this reaction is fast (k ≳ 4 × 10-9 cm3 molecule-1 s-1) and presents a weak negative temperature dependence which, considering the experimental error bars, agrees with long-range based capture theory. We also observe that C3N- + HCN represents the main exit channel demonstrating that the studied reaction participates efficiently to the chemical growth of negative ions in the atmosphere of Titan.

  6. 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.

  7. Conductive atomic force microscopy study of InAs growth kinetics on vicinal GaAs (110)

    NASA Astrophysics Data System (ADS)

    Tejedor, Paloma; Díez-Merino, Laura; Beinik, Igor; Teichert, Christian

    2009-09-01

    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 [11¯0]-multiatomic step edges, where preferential nucleation of InAs nanowires takes place by step decoration. On H-terminated substrates with triangular terraces bounded by [11¯5]-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 AsHx intermediate species and a reduction in the surface free energy.

  8. 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...

  9. Growth kinetics of protein single crystals in the gel acupuncture technique

    NASA Astrophysics Data System (ADS)

    García-Ruiz, Juan Manuel; Moreno, Abel

    1997-07-01

    The growth of single crystals of tetragonal HEW lysozyme and thaumatin I into glass capillaries was monitored by time lapse video-microscopy. The crystals were obtained by unidirectional transport of the precipitating agent through capillaries of internal diameter ranging from 0.2 to 1.2 mm, using the gel acupuncture technique. For crystals growing from true protein solutions, the measured average growth rates varies with capillary diameter from 1.7 to 3.7 Å/s for thaumatin and from 2.8 to 22 Å/s for lysozyme. The measured average growth rates for crystals growing into gelled protein solutions were 1.8 Å/s for thaumatin and 2.5 Å/s for lysozyme. The trend in the variation of the growth rate with time is similar and suggests that, for capillaries with internal radius lower than 0.8 mm, diffusion dominates the global mass transport control. However, the existence of convection rolls near the crystal-solution interface and close to zones with high density gradient cannot be discarded.

  10. 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.

  11. Fast and slow crystal growth kinetics in glass-forming melts.

    PubMed

    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(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.

  12. Chirality-Controlled Growth of Single-Wall Carbon Nanotubes Using Vapor Phase Epitaxy: Mechanistic Understanding and Scalable Production

    DTIC Science & Technology

    2016-09-15

    period, that is, growth plus termination, we assume the average growth rate (R̅t) of a (n, m) SWCNT at time t follows exponential kinetics ?̅?...AFRL-AFOSR-VA-TR-2016-0319 Chirality-Controlled Growth of Single-Wall Carbon Nanotubes Using Vapor Phase Epitaxy: Mechanistic Understanding and...controlled growth of single-wall carbon nanotubes using vapor phase epitaxy: mechanistic understanding and scalable production FA9550-14-1-0115 Zhou

  13. Two-tank suspended growth process for accelerating the detoxification kinetics of hydrocarbons requiring initial monooxygenation reactions.

    PubMed

    Dahlen, Elizabeth P; Rittmann, Bruce E

    2002-01-01

    An experimental evaluation demonstrated that suspended growth systems operated in a two-tank accelerator/aerator configuration significantly increased the overall removal rates for phenol and 2,4-dichlorophenol (2,4-DCP), aromatic hydrocarbons that require initial monooxygenations. The accelerator tank is a small volume that receives the influent and recycled biomass. It has a high ratio of electron donor (BOD) to electron acceptor (O2). Biomass in the accelerator should be enriched in reduced nicotinamide adenine dinucleotide (NADH + H+) and have a very high specific growth rate, conditions that should accelerate the kinetics of monooxygenation reactions. For the more slowly degraded 2,4-DCP, the average percentage removal increased from 74% to 93%, even though the volume of the two-tank system was smaller than that of the one-tank system in most experiments. The average volumetric and biomass-specific removal rates increased by 50% and 100%, respectively, in the two-tank system, compared to a one-tank system. The greatest enhancement in 2,4-DCP removal occurred when the accelerator tank comprised approximately 20% of the system volume. Biomass in the accelerator tank was significantly enriched in NADH + H+ when its dissolved oxygen (DO) concentration was below 0.25 mg/L, a situation having a high ratio of donor to acceptor. The accelerator biomass had its highest NADH + H+ content for the experiments that had the highest rate of 2,4-DCP removal. Biomass in the accelerator also had a much higher specific growth rate than in the aerator or the system overall, and the specific growth rate in the accelerator was inversely correlated to the accelerator volume.

  14. 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.

  15. 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.

  16. Control of heterogeneous nucleation and growth kinetics of dopamine-melanin by altering substrate chemistry.

    PubMed

    Klosterman, Luke; Riley, John K; Bettinger, Christopher John

    2015-03-24

    Dopamine-melanin (DM or "polydopamine") can be deposited on virtually any substrate from solution through autoxidation of dopamine. The versatility of this process has allowed surface-mediated assembly of DM for a wide variety of functional coatings. Here we report the impact of well-defined surface chemistries on the nucleation and growth of such films. DM was deposited on silicon dioxide (SiO2) and SiO2 substrates modified with self-assembled monolayers (SAMs) bearing octadecyl (C18), phenethyl, and aminopropyl functional groups. Atomic force microscopy revealed three-dimensional islands whose areal density and surface coverage are lowest on bare SiO2 substrates and highest on the neutral aromatic and aliphatic substrates. Increasing the pH of the solution from 8.2 to 10 dissociates catechol moieties in DM and inhibits adsorption on negatively charged SiO2 substrates. The growth rate of DM films on SAM-modified SiO2 is maximized at pH 9.5 and almost completely abolished at pH 10 because of increased DM solubility. The initial rates of DM adsorption were measured using quartz crystal microbalance with dissipation measurements. The initial adsorption rate is proportional to the nucleation density, which increases as the hydrophobicity of the substrate increases. Taken together, these data provide insight into the rates of heterogeneous nucleation and growth of DM on substrates with well-defined chemistries.

  17. Effects of nitrogen sources on the nitrate assimilation in Haloferax mediterranei: growth kinetics and transcriptomic analysis.

    PubMed

    Esclapez, Julia; Bravo-Barrales, Gloria; Bautista, Vanesa; Pire, Carmen; Camacho, Mónica; Bonete, María J

    2014-01-01

    The haloarchaeon Haloferax mediterranei is able to grow in a defined culture media not only in the presence of inorganic nitrogen salt but also with amino acid as the sole nitrogen source. Assimilatory nitrate and nitrite reductases, respectively, catalyze the first and second reactions. The genes involved in this process are nasA, which encodes nitrate reductase and is found within the operon nasABC, and nasD, which encodes nitrite reductase. These genes are subjected to transcriptional regulation, being repressed in the presence of ammonium and induced with either nitrate or nitrite. This type of regulation has also been described when the amino acids are used as nitrogen source in the minimal media. Furthermore, it has been observed that the microorganism growth depends on nitrogen source, obtaining the lowest growth rate in the presence of nitrate and aspartate. In this paper, we present the results of a comparative study of microorganism growth and transcriptomic analysis of the operon nasABC and gene nasD in different nitrogen sources. The results are the first ever produced in relation to amino acids as nitrogen sources within the Halobacteriaceae family.

  18. Formation and Growth Kinetics of Reverted Austenite During Tempering of a High Co-Ni Steel

    NASA Astrophysics Data System (ADS)

    Gruber, Marina; Ressel, Gerald; Méndez Martín, Francisca; Ploberger, Sarah; Marsoner, Stefan; Ebner, Reinhold

    2016-12-01

    It is well known that high Co-Ni steels exhibit excellent toughness. Since the good toughness in these steels is supposed to be related to thin layers of austenite between martensite crystals, this work presents an experimental study corroborated with diffusional calculations to characterize the evolution of reverted austenite. Atom probe measurements were conducted for analyzing the element distribution in austenite and martensite during tempering. These results were correlated with crystallographic information, which was obtained by using transmission electron microscopy investigations. Additionally, the experimental findings were compared with kinetic calculations with DICTRA™. The investigations reveal that reverted austenite formation during tempering is connected with a redistribution of Ni, Co, Cr, and Mo atoms. The austenite undergoes a Ni and Cr enrichment and a Co depletion, while in the neighboring martensite, a zone of Ni and Cr depletion and Co enrichment is formed. The changes in the chemical composition of austenite during tempering affect the stability of the austenite against phase transformation to martensite during plastic deformation and have thus decisive influence on the toughness of the material.

  19. 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.

  20. 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.

  1. Anomalous Phase Separation Kinetics Observed in a Micelle Solution

    NASA Astrophysics Data System (ADS)

    Wilcoxon, Jess P.; Martin, James E.; Odinek, Judy

    1995-08-01

    We report a real-time, two-dimensional light scattering study of the evolution of structure in a two-component nonionic micelle system undergoing phase separation. We find that the structure of the domains is qualitatively similar to that observed in binary fluid systems, with some anomalies observed. However, compared to the Lifshitz-Slyozov prediction for simple binary fluids, the domain growth is unexpectedly slow. In fact, the growth kinetics can be empirically described as a stretched exponential approach to a pinned domain size. This anomalous behavior may be due to the ability of the spherical micelles to reorganize into more complex structures.

  2. Parametric Investigation of the Isothermal Kinetics of Growth of Graphene on a Nickel Catalyst in the Process of Chemical Vapor Deposition of Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Futko, S. I.; Shulitskii, B. G.; Labunov, V. A.; Ermolaeva, E. M.

    2016-11-01

    A kinetic model of isothermal synthesis of multilayer graphene on the surface of a nickel foil in the process of chemical vapor deposition, on it, of hydrocarbons supplied in the pulsed regime is considered. The dependences of the number of graphene layers formed and the time of their growth on the temperature of the process, the concentration of acetylene, and the thickness of the nickel foil were calculated. The regime parameters of the process of chemical vapor deposition, at which single-layer graphene and bi-layer graphene are formed, were determined. The dynamics of growth of graphene domains at chemical-vapor-deposition parameters changing in wide ranges was investigated. It is shown that the time dependences of the rates of growth of single-layer graphene and bi-layer graphene are nonlinear in character and that they are determined by the kinetics of nucleation and growth of graphene and the diffusion flow of carbon atoms in the nickel foil.

  3. Equivalences between nonuniform exponential dichotomy and admissibility

    NASA Astrophysics Data System (ADS)

    Zhou, Linfeng; Lu, Kening; Zhang, Weinian

    2017-01-01

    Relationship between exponential dichotomies and admissibility of function classes is a significant problem for hyperbolic dynamical systems. It was proved that a nonuniform exponential dichotomy implies several admissible pairs of function classes and conversely some admissible pairs were found to imply a nonuniform exponential dichotomy. In this paper we find an appropriate admissible pair of classes of Lyapunov bounded functions which is equivalent to the existence of nonuniform exponential dichotomy on half-lines R± separately, on both half-lines R± simultaneously, and on the whole line R. Additionally, the maximal admissibility is proved in the case on both half-lines R± simultaneously.

  4. 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.

  5. 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.

  6. Treatment of agro based industrial wastewater in sequencing batch reactor: performance evaluation and growth kinetics of aerobic biomass.

    PubMed

    Lim, J X; Vadivelu, V M

    2014-12-15

    A sequencing batch reactor (SBR) with a working volume of 8 L and an exchange ratio of 25% was used to enrich biomass for the treatment of the anaerobically treated low pH palm oil mill effluent (POME). The influent concentration was stepwise increased from 5000 ± 500 mg COD/L to 11,500 ± 500 mg COD/L.