Fluctuations In Growth Rate Research Articles

Initiation and propagation behaviour of microcracks in Ni-base superalloy Udimet 720 Li

In order to clarify the fatigue behaviour of polycrystalline Ni-base superalloy Udimet 720 Li and its statistical characteristics, four point bending fatigue test of plain specimens were carried out at room temperature. Initiation and propagation behaviour of all the cracks in each specimen was observed using the plastic replication technique. At extremely early stages of cycling, cracking of some TiN particles occurred. Fatigue cracks were initiated from these cracked particles. The growth rate of a small crack can be determined by a term σ n a l, not by Δ K, where n is the material constant and is 3.6 for this alloy. Moreover, the relationship between the small crack growth law and fluctuation of growth rate caused by the inhomogeneity of the microstructure was studied. With regard to statistical characteristics of fatigue behaviour, the investigation of initiation lifetime of cracks and crack density was performed. The distribution characteristics of crack length, microcrack propagation life and growth rate of microcracks was examined by assuming a Weibull distribution and log-normal distribution.

Algal growth rate fluctuations observed under uniform ambient test conditions using static and semicontinuous assay techniques

A simple, manually diluted, semicontinuous, 96-h algal growth assay technique was developed to measure changing rates of population growth following sublethal chemical exposure. Rates were estimated directly from changing cell counts in a fixed volume of cell suspension. Short-term rate fluctuations in exponential rate parameters were observed in Selenastrum capricornutum populations using this method and similar fluctuations were also documented by reanalyzing conventional static culture assay data. Replicate cultures tended to fluctuate in unison, and patterns of population increase were similar in static assays initiated on different dates. The latter suggested that nonuniform rates of S. capricornutum population increase were not due simply to environmental variation. All populations were preacclimated to test conditions, but growth lags were consistently observed for 12–24 h following inoculation. Subsequent rate fluctuations probably resulted from a high degree of cell-cycle synchronization. Treating systematic rate fluctuations as random error lowered measurement precision, especially with respect to estimates of rate changes over time. Systematic variance may be difficult to eliminate in practice, but repeated-measures regression methods can account for this effect and substantially reduce rate parameter confidence intervals. Findings are expected to apply to endpoints such as dry weight, total cell volume, chlorophyll, or DNA.

Corrosion Fatigue Crack Initiation and Early Growth Behavior in Stainless Steels. 2nd Report, Influence of Microstructure on Early Crack Growth.

Fatigue tests have been conducted on a duplex stainless steel, SUS 329 J 4 L, and an austenitic stainless steel, SUS 304, in order to clarify the influence of microstructure on crack initiation and early growth. Crack initiation of SUS 329 J 4 L occurred principally at austenite phase in room air and in 3% NaCl solution. In SUS 304, cracks were generated within austenite phase and at austenite grain boundary in room air and in 3% NaCl solution, respectively. The early crack growth behavior in the microstructurally small crack region was influenced by the phase change at crack front for SUS 329 J 4 L, and the crack hesitated at the phase boundary. Also in SUS 304 the fluctuations in crack growth rate were found at austenite grain boundaries, which were less remarkable in 3%NaCl solution than in room air. Early crack growth immediately after the initiation was enhanced in 3% NaCl solution for both stainless steels.

Crystal growth studies in microgravity with the APCF. II. Image analysis studies

Lysozyme crystallization experiments performed in the Advanced Protein Crystallization Facility during SpaceHab-01 mission are analyzed using pictures obtained during the flight. The temporal evolution of experiments performed using free interface diffusion (FID) and dialysis (DIA) techniques was studied to gain a deeper insight into the processes of nucleation and growth. Heterogeneous nucleation on the walls of the reactor predominates over nucleation in the bulk solution. Nucleation takes place simultaneously throughout the protein chamber, which means that the supersaturation inside the reactors has reached homogeneity before nucleation. In terms of precipitation behavior this means that the APCF reactors are working as very slow-mixing batch experiments. Measured growth rates range from 10 to 50Å/s and decrease asymptotically to zero. L (a linear dimension of the crystals) versus time1/2 plots are discussed. Large-scale growth rate fluctuations are observed and explained by the interaction between diffusive fields of neighboring crystals. Crystals not attached to the reactor walls are observed to move, with varying velocities and directions of movement, and at a given time, undergo a fast acceleration that projects them towards the walls of the reactor. The amount of information that can be derived from the final data set supplied after the space experiment is limited by the technical features implemented in the APCF. Some recommendations to enhance these features are proposed.

Microzooplankton grazing in the surface water of the Southern Ocean during an austral summer

Microzooplankton grazing was investigated in surface waters of the Indo-Pacific and Atlantic sectors of the Southern Ocean by the dilution method. Phytoplankton growth varied mainly between 0.1 and 0.4 day−1, and microzooplankton grazing between 0.0 and 0.3 day−1. Great fluctuations in phytoplankton growth rate were observed at one station within 3 weeks and between closely spaced stations. Microzooplankton grazing rates were similar to phytoplankton growth rate despite the variation of phytoplankton growth rates, although in some cases, phytoplankton growth overwhelmed microzooplankton grazing. These observations suggest that microzooplankton are the main consumers of primary producers, and that steady state between phytoplankton growth and microzooplankton grazing is usually established in the Southern Ocean in austral summer.

Crop load and water stress effects on daily stem growth in peach (Prunus persica)

We investigated crop load and water stress effects on diurnal stem extension growth of field-grown peach (Prunus persica (L.) Batsch) trees. Neither the presence of fruit nor reduced irrigation significantly altered the timing of diurnal fluctuations in stem growth rate. Stems with subtending fruit had significantly reduced growth compared to stems with no subtending fruit. Crop load had no significant effect on relative stem extension rates and the majority of the reduction in absolute growth was the result of a smaller zone of elongation in fruit-bearing stems than in stems with no subtending fruit. Fruit removal did not increase growth rates within 24 h. When irrigation was reduced, the length of the stem elongation zone and total daily stem growth were significantly decreased relative to well-irrigated controls and the decreases were highly correlated with stem water potential. Compared with well-irrigated controls, relative stem extension rates of water-stressed trees were reduced at several times during the 24-h period, but the degree of reduction was not proportional to the difference in stem water potentials between the treatments.

Demography of the Marine Bivalve Yoldia notabilis in Fluctuating Environments: An Analysis Using a Stochastic Matrix Model

A population of the marine bivalve Yoldia notabilis in Otsuchi Bay, northeastern Japan shows large interannual fluctuations in recruitment rate and individual growth rate. The effects of these fluctuations on population growth rate were examined using a stochastic size-classified matrix model. Stochastic population growth rate (In Xs) estimated by numerical iterations differed greatly between models with lognormal distributions and normal distributions fitted to the fluctuating recruitment rate. The estimates of In Xs, its confidence interval and In g (growth rate of average population size) increased greatly with an arbitrary increase in the variance of recruitment rate, while the variance in individual growth rate has less effects on the estimates of these parameters. The fluctuation in recruitment has therefore more impact on the population dynamics. The stochastic growth rate In Xs was always no greater than In I, the latter equivalent to the deterministic growth rate, and their difference increased with the variance in the recruitment rate and the individual growth rate, suggesting that the population growth rate estimate based on average vital rates may be an overestimate. These findings demonstrate that the estimates of population growth rates are greatly influenced by the types of probability distributions fitted to fluctuat

The 1991–1992 atmospheric methane anomaly: Southern hemisphere 13C decrease and growth rate fluctuations

Measurements of atmospheric methane from 1989–1996 at Baring Head, New Zealand, and at Scott Base, Antarctica show a seasonal cycle in the mixing ratio with a peak to peak amplitude of 28 ppb. This is superposed on a trend varying between 16 ppb yr−1 and near zero. δ13C values also show a seasonal cycle, with an amplitude of 0.1–0.3‰, approximately 6 months out of phase with the mixing ratio cycle. A pronounced negative anomaly in δ13C occurred in 1992 with annual average values dropping from −47.08‰ to −47.28‰. From 1992 to 1996, average δ13C values recovered slowly at an average rate of about 0.04‰ yr−1. The simultaneous changes in the mixing ratio growth rate and δ13C together with the rapid drop and slow recovery in the latter provide a stringent test of possible causes. Although a combination of causes cannot be ruled out, decreased emissions from an isotopically heavy source such as biomass burning best meet the constraints of the data.

Unsteady crystal growth due to step-bunch cascading

Based on our experimental findings of growth rate fluctuations during the crystallization of the protein lysozyme [Vekilov, Alexander, and Rosenberger, Phys. Rev. 54, 6650 (1996)], we have developed a numerical model that combines diffusion in the bulk of a solution with diffusive transport to microscopic growth steps that propagate on a finite crystal facet. Nonlinearities in layer growth kinetics arising from step interaction by bulk and surface diffusion, and from step generation by surface nucleation, are taken into account. On evaluation of the model with properties characteristic for the solute transport, and the generation and propagation of steps in the lysozyme system, growth rate fluctuations of the same magnitude and characteristic time, as in the experiments, are obtained. The fluctuation time scale is large compared to that of step generation. Variations of the governing parameters of the model reveal that both the nonlinearity in step kinetics and mixed transport-kinetics control of the crystallization process are necessary conditions for the fluctuations. On a microscopic scale, the fluctuations are associated with a morphological instability of the vicinal face, in which a step bunch triggers a cascade of new step bunches through the microscopic interfacial supersaturation distribution.

Generation of biogenic hydrocarbons during a spring bloom in Newfoundland coastal (NW Atlantic) waters

The distribution and carbon isotopic composition of biogenic hydrocarbons in spring bloom plankton, bottom sediments, and benthic macrobiota in Conception Bay, Newfoundland (NW Atlantic) were determined by gas chromatography/mass spectrometry and gas chromatography/combustion/isotope ratio mass spectrometry. Although individual hydrocarbons were generally depleted by at least 3‰ relative to bulk organic matter, significant variations and temporal fluctuations in compound-specific carbon isotopic compositions were documented in bloom samples and laboratory cultures. Marked 13C depletions in a suite of eight C 25 highly branched isoprenoid alkenes, as well as a temporal shift in the 13C composition of spring bloom n-alkanes are suggested to be related to changes in the growth rates of bloom organisms. The input of multiple sources of organic matter into deep bay sediments could be recognized in the isotopic compositions of sedimentary n-alkanes. Overall, the carbon isotopic composition appeared to be primarily a reflection of the carbon fixing pathway of source organisms, with superimposed variations caused by fluctuations in growth rates and [CO 2(aq)]. These findings highlight the need for more study of contemporary biogenic hydrocarbons; specifically of the influence of growth rate and timing of synthesis on the carbon isotopic composition of biomarkers over the course of phytoplankton blooms.

Fatigue of a nickel base superalloy with bimodal grain size

Room temperature fatigue tests in the form of four point bending were performed at a frequency of 20 Hz and a load ratio R= +0·1 on electropolished Waspaloy specimens taken from a forged turbine disc. Samples, which had a partially recrystallised microstructure with a bimodal grain size, were removed from the outer rim of the disc. The S-N curve was similar to that reported for a fully recrystallised structure with a coarse grain size, from the same turbine disc. The dominant crack initiation sites were found to be inclusions with a subsequent stage I crack growth generally along slip bands. Other crack initiation sites observed included slip bands, annealing twins, and grain boundaries. Fatigue deformation occurred by the propagation of planar slip bands. Slip band cracks formed more frequently in coarse grains than expected from their volume fraction. Fluctuations in short crack growth rate were observed and were associated with microstructural features such as grain boundaries and twin boundaries, both of which acted as barriers in the early stages of crack growth. The short crack growth rate versus stress intensity range graph was similar to those from uniform fine grained Waspaloy.MST/3413

Fatigue of a nickel base superalloy with bimodal grain size

Room temperature fatigue tests in the form of four point bending were performed at a frequency of 20 Hz and a load ratio R= +0·1 on electropolished Waspaloy specimens taken from a forged turbine disc. Samples, which had a partially recrystallised microstructure with a bimodal grain size, were removed from the outer rim of the disc. The S-N curve was similar to that reported for a fully recrystallised structure with a coarse grain size, from the same turbine disc. The dominant crack initiation sites were found to be inclusions with a subsequent stage I crack growth generally along slip bands. Other crack initiation sites observed included slip bands, annealing twins, and grain boundaries. Fatigue deformation occurred by the propagation of planar slip bands. Slip band cracks formed more frequently in coarse grains than expected from their volume fraction. Fluctuations in short crack growth rate were observed and were associated with microstructural features such as grain boundaries and twin boundaries, both of which acted as barriers in the early stages of crack growth. The short crack growth rate versus stress intensity range graph was similar to those from uniform fine grained Waspaloy.MST/3413

Enforced growth-rate fluctuation causes pectin ring formation in the cell wall of Lilium longiflorum pollen tubes

Normally growing lily (Lilium longiflorum Thunb.) pollen tubes cultured in standard sucrose medium display a relatively steady tip-growth pattern and a rather even pectin sheath in the cell wall. In an attempt to better understand pulsatory growth, observed in some species, e.g., Petunia, and its possible role in causing the formation of thickened cell wall rings, we have imposed marked fluctuations in the growth-rate of lily pollen tubes. The appropriate growth-perturbing conditions were achieved by modulating the medium osmolarity or by applying caffeine, a non-turgor inhibitor, in a specially designed incubation chamber with a controlled medium flow. The relatively non-esterified pectin deposition in the wall of the growth-interrupted pollen tubes was detected by immunofluorescence microscopy using a monoclonal antibody, JIM 5. The observations show that the periods of slow or inhibited growth correspond to the times when the thickened walls are deposited. Since the growth fluctuations were induced by both turgor- and non-turgor-related means, the proposed endogenous regulatory role of turgor pressure is questioned. Other factors, such as the tip-focused Ca2+ gradient which was demonstrated by ratiometric ion imaging, and the alteration in the extensibility of the cell wall, which correlated with pectin esterification/de-esterification, emerge as candidates for the regulation of growth fluctuations.

Continuous-Time Sunspot Equilibria and Dynamics in a Model of Growth

This article is concerned with the existence of sunspot equilibria in a continuous-time growth setting. It brings alternative approaches in the self-fulfilling prophecies literature: continuous time, global dynamics, and non-stationarity. The main contribution of the use of continuous-time methods is to allow for a complete understanding of the global dynamical properties of these stochastic equilibria within a non-stationary economy. In this model, fluctuations in growth rates occur through a self-fulfilling prophecies mechanism.Journal of Economic LiteratureClassification Numbers: E12, E32, O41.

Real Interest Differentials and Macro Fundamentals: Empirical Estimates

This paper explores the implications of an open-economy version of the Lucas asset pricing model for the empirical relationship between pairwise real interest rate differentials and macroeconomic fundamentals for the United States, West Germany, and the United Kingdom from 1974 to 1989. Using Hansen's Generalized Method of Moments, the model's overidentifying restrictions cannot be rejected, while exclusion restrictions on the effect of fluctuations in money and output growth rates on real interest differentials are rejected in the majority of cases. These results are encouraging for those who believe that structural models driven by fundamental macroeconomic variables can help explain price determination in international financial markets.

Real Interest Differentials and Macro Fundamentals: Empirical Estimates

This paper explores the implications of an open-economy version of the Lucas asset pricing model for the empirical relationship between pairwise real interest rate differentials and macroeconomic fundamentals for the United States, West Germany, and the United Kingdom from 1974 to 1989. Using Hansen's Generalized Method of Moments, the model's overidentifying restrictions cannot be rejected, while exclusion restrictions on the effect of fluctuations in money and output growth rates on real interest differentials are rejected in the majority of cases. These results are encouraging for those who believe that structural models driven by fundamental macroeconomic variables can help explain price determination in international financial markets.

Oscillatory, stochastic and chaotic growth rate fluctuations in permittistatically controlled yeast cultures

We describe a continuous culture system related to the turbidostat, but using a feedback system based on biomass estimation from the dielectric permittivity of the cell suspension rather than its optical density. It is shown that this system provides an excellent method of maintaining a constant biomass level within a fermentor. The computer-controlled system was able to effect the essentially continuous registration of growth rate by monitoring the rate of medium addition via the time-dependent activity of the pump. At some biomass setpoints for aerobically grown cultures of baker's yeast substantial time-dependent fluctuations in the growth rate of the culture were thereby observed. At some biomass setpoints, however, or under anaerobic conditions, or when using a non-Crabtree yeast, the growth rate was constant, indicating that the fluctuations were inherent to the biological system and not simply a property of the fermentor and control system. A variety of time series analyses (Fourier transformations, Hurst and Lyapunov exponents, the determination of embedding dimension, and non-linear time series predictions based on the methodology of Sugihara and May) were used to demonstrate, for the first time, that as well as stochastic and periodic components these fluctuations exhibited deterministic chaos. ‘Trivial predictors’ were unable to give accurate predictions of the growth rate in these cultures. The growth rate fluctuations were studied further by means of offline measurements of changes in percentage viability, bud count, and in the external ethanol and glucose concentrations; these data and other evidence suggested that the growth rate fluctuations were closely linked to the primary respiro-fermentative metabolism of this organism. The identification of chaotic growth rates in cell cultures suggests that there may be novel methods for controlling the growth of such cultures.

Macroeconomic determinants of exchange rates: a frequency-specific analysis

This paper applies a new methodology, rolling spectral regression, to investigate currency movements at various frequencies. This technique generates efficient and frequency-band estimates of the regression coefficients between three major exchange rates and their determinants from a generic monetary model. Empirical results reported in this study suggest that the variations of the yen/dollar and pound/dollar exchange rates can be explained by changes in monetary policy in the long run and fluctuations in economic growth and long-term interest rates in the medium run

Temporal and spatial stability of bacterioplankton biomass and productivity in an atoll lagoon

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 11:251-261 (1996) - doi:10.3354/ame011251 Temporal and spatial stability of bacterioplankton biomass and productivity in an atoll lagoon Torréton JP, Dufour P Spatial and temporal variations of bacterioplankton biomass, production and growth rates were investigated 6 times from 1991 to 1994 in Tikehau lagoon (Tuamotu, French Polynesia). The water column was homogeneous from the surface to the bottom (20 m) at the reference station but some horizontal variations were detected, with biomass and production increasing from the reef-flat spillways (oceanic water inflow) to the main part of the lagoon and decreasing from the relatively eutrophic shore (near the village) to the main part of the lagoon. However, both of these perturbations were limited to the immediate vicinity of these areas. Diel fluctuations of bacterial biomass and growth rate were slight (coefficient of variation, CV < 20%) and showed no significant pattern. Day-to-day variations recorded over periods of up to 20 consecutive days appeared also to be limited (CV < 25%). A significant correlation between wind and total abundance of bacteria in the water column suggested that these day-to-day variations may be in part explained by wind, probably inducing resuspension of sediments. No significant pattern appeared from comparison of the 6 cruises spread over different seasons. Cruise averages differed slightly from each other, with CV for all cruises averaging 34, 10 and 41% for bacterioplankton biomass, production and growth rate, respectively. Tikehau lagoon appears to be a very stable ecosystem for bacterioplankton processes and therefore differs strongly from other reef water column systems. This untypical stability might be explained by the long residence time of water (170 d), the strong stability of the oceanic surrounding water (South Pacific Gyre), the weak seasonality of primary producers and the limited inputs from corals, bordering islands and sediments. Bacterioplankton · Bacterial production · Thymidine incorporation · Leucine incorporation · Atoll lagoon · Pacific Ocean Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 11, No. 3. Publication date: December 31, 1996 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1996 Inter-Research.

Daily dynamics in xylem cell radial growth of Scots pine (Pinus sylvestris L.)

Daily dynamics of radial cell expansion during wood formation within the stems of 25-year-old Scots pine trees (Pinus sylvestris L.), growing in field conditions, were studied. The samples of forming wood layers were extracted 4 times per day for 3 days. Possible variations in the growth on different sides of the stem, duration of cell development in radial cell expansion phase and dynamics of cell growth in this phase were taken into account. The perimeters of tracheid cross-sections as a reflection of primary cell wall growth were the criterion of growth in a radial direction. For the evaluation of growing cell perimeters a special system for digital processing and image analysis of tracheid cross-sections of the forming wood was used. Growth rate for certain time intervals was estimated by the change in the relation of the perimeter of each observed cell in each of ten tracheid rows in each of 12 trees to the perimeter of the xylem cell of the same row before the expansion. Temporal differences in average values of the relations were estimated by Analyses of Variance. The existence of daily dynamics of Scots pine xylem cell radial growth has been proved. Intensive growth of pine tracheids has been shown to occur at any time of the day and to depend on the temperature regime of the day and the night as well as water supply of stem tissues. Moreover, reliable differences (P = 0.95) in the increment of cell walls during tracheid radial expansion have been found. Pulsing changes of the water potentials both of the cell and the apoplast, as the reason for the fluctuations of radial cell growth rate, were discussed.