Surveillance in longitudinal models: detection of intrauterine growth restriction

A new methodology for online detection of intrauterine growth restriction (IUGR) is proposed where traditional methods for statistical surveillance are applied. Here, deficient growth rate is used to detect IUGR instead of the common surrogate measure "small for gestational age" (SGA). Fetal growth is estimated by repeated measurements of symphysis-fundus (SF) height. At each time point the new method, based on the Shiryaev-Roberts method, is used to evaluate the growth in SF height. We use Swedish data to model a normal growth pattern, which is used to evaluate the capability of the new method to detect IUGR in comparison with a method used in practice today. Results from simulations indicate that the new method performs considerably better than the method used today. We also illustrate the effect of some important factors which influence the detection ability and illuminate the tendency of the method used today to misclassify SGA cases as IUGR.     

Statistical method for detecting structural change in the growth process

Summary .   Due to competition among individual trees and other exogenous factors that change the growth environment, each tree grows following its own growth trend with some structural changes in growth over time. In the present article, a new method is proposed to detect a structural change in the growth process. We formulate the method as a simple statistical test for signal detection without constructing any specific model for the structural change. To evaluate the p -value of the test, the tube method is developed because the regular distribution theory is insufficient. Using two sets of tree diameter growth data sampled from planted forest stands of Cryptomeria japonica in Japan, we conduct an analysis of identifying the effect of thinning on the growth process as a structural change. Our results demonstrate that the proposed method is useful to identify the structural change caused by thinning. We also provide the properties of the method in terms of the size and power of the test.     

Determination of the Monod substrate saturation constant for microbial growth

Abstract Methods used to determine the Monod substrate saturation constant for microbial growth are surveyed. The preferred and most accurate method is to assay the concentrations of growth rate-limiting nutrients in steady-state continuous cultures. But, this is not always possible due to the lack of sufficiently sensitive assay methods or due to high nutrient fluxes in rapidly growing cultures. It is suggested that an acceptable and simple alternative method for aerobic microorganisms is to measure initial oxygen uptake rates during growth in the presence of different initial concentrations of growth rate-limiting nutrient. It is important in this method that the microbial cells are taken from rapidly growing cultures and are suspended in a medium permitting growth.     

KymoRod: a method for automated kinematic analysis of rod‐shaped plant organs

A major challenge in plant systems biology is the development of robust, predictive multiscale models for organ growth. In this context it is important to bridge the gap between the, rather well‐documented molecular scale and the organ scale by providing quantitative methods to study within‐organ growth patterns. Here, we describe a simple method for the analysis of the evolution of growth patterns within rod‐shaped organs that does not require adding markers at the organ surface. The method allows for the simultaneous analysis of root and hypocotyl growth, provides spatio‐temporal information on curvature, growth anisotropy and relative elemental growth rate and can cope with complex organ movements. We demonstrate the performance of the method by documenting previously unsuspected complex growth patterns within the growing hypocotyl of the model species Arabidopsis thaliana during normal growth, after treatment with a growth‐inhibiting drug or in a mechano‐sensing mutant. The method is freely available as an intuitive and user‐friendly Matlab application called KymoRod.     

Determination of the unknown age at first capture of western rock lobsters (Panulirus cygnus) by random effects model

We propose a method for fitting growth curves to multiple recapture data of lobsters when the age at first capture is unknown. The von Bertalanffy growth curve is used to model the growth. To account for individual variability, the unknown age in logarithmic scale of a lobster at first capture, the individual asymptotic size, and the individual growth coefficient of its carapace length are modeled as random effects with a trivariate normal distribution. Unlike previously suggested models, the present model permits correlation between the growth coefficient and the age at first capture and can be fitted readily using existing software. The error structures between consecutive recaptures of a lobster are assumed to be a first-order autoregressive process with unequally spaced time points. A comparison between this model and the Fabens growth equation is given. The proposed method is a flexible method and can be applied to fit different growth equations when the age at first capture is unknown.     

Method for the quantitative study of the growth of fibroblastic cells in tissue culture

The method is elaborated for a quantitative evaluation of hypodermic fibroblast element growth in tissue culture of albino rats. The method is based on determination of the growth activity and intensity for each of the explant growth zones (compact, necwork-like zones and zone of migrating elements). The method permits a rapid and an exact evaluation of the influence of different substances added to the culture medium.     

The tensor-based model of plant growth applied to leaves of Arabidopsis thaliana: A two-dimensional computer model

Plant organs grow in coordinated and continuous way. Such growth is of a tensor nature, hence there is an infinite number of different directions of growth rate in each point of the growing organ. Three mutually orthogonal directions of growth can be recognized in which growth achieves extreme values (principal directions of growth [PDGs]). Models based on the growth tensor have already been successfully applied to the root and shoot apex. This paper presents the 2D model of growth applied to the arabidopsis leaf. The model employs the growth tensor method with a non-stationary velocity field. The postulated velocity functions are confirmed by growth measurements with the aid of the replica method.     

陕北白桦个体生长过程的谐波分析

利用波谱分析方法中的谐波分析原理, 对陕北白桦个体生长过程进行了不同层次的分析。结果表明:白桦个体的树高、胸径和材积生长动态波动规律与Logistic 模型不完全相同, 树高在20 年后与Logistic 模型吻合, 胸径整个过程均不吻合, 但材积生长与Logistic 模型基本一致;应用波谱分析方法分析树木生长过程的动态规律, 比Logistic 模型更准确。     

Modelling count and growth data with many zeros

We discuss the problem of modelling survival/mortality and growth data that are skewed with excess zeros. This type of data is a common occurrence in biological and environmental studies. The method presented here allows us to utilize both the survival/mortality and growth data when both data sets contain a large proportion of zeros. The method consists of four stages. Firstly the original data is divided into two sets; one contains all the surviving organisms and the other all of the mortalities. Secondly we calculate the actual growth of the surviving organisms and of the mortalities. Thirdly we count the number of surviving organisms for which growth has occurred and the number where no growth occurred, and the same count procedure is carried out on the mortalities. Next we model the survival/mortality data and growth/no growth data using logistic regression, and separately model the growth data using an ordinary regression. Finally we combine the three models to estimate the expected growth for a specific set of values of the explanatory variables. If we used another statistical method that did not involve the dead mussels or the ones with no growth, some of the information provided by these mussels would be lost. However, using the method we propose, all of the data collected are used to achieve an optimal estimation of the mussel growth. A case study of survival and growth of blue mussels (Mytilus galloprovincialis) and ribbed mussels (Aulacomya atra maoriana) trans-located from their natural distribution to different depths and sites along the axis of Doubtful Sound, New Zealand, is used for illustration.     

A new method to determine mean adult height from incomplete follow-up data

BACKGROUND/AIM: In long-term growth studies with adult height (AH) as outcome, reporting is often required while data are incomplete because some participants have not yet reached AH whereas others might be lost to follow-up. Current practice is to analyze only participants who did reach AH, which can easily give biased results. We introduce a new method into the area of growth research. METHODS: We used the data of patients from a registration database and a growth study. The new method uses growth data in time intervals. The percentage of children still growing and the mean growth at each interval are used to determine mean AH. RESULTS: With the new method, estimated mean AHs had smaller bias and standard error than with commonly used methods. The method is not hampered by a correlation between AH and age at reaching AH, unlike methods merely using patients who have reached AH. CONCLUSION: In contrast to commonly used methods, the new method provides valid results on mean AH when complete actual measurements of AH are not (yet) available, provided that drop-out, if any, is not related to (disappointing) growth. As it also uses observed data of children with incomplete follow-up, the method employs the data more effectively.     

A pseudo-exponential feeding method for control of specific growth rate in fed-batch cultures

A simple feeding method for controlling specific growth rate in fed-batch culture was developed. This method applies a constant feed rate using a concentrate reservoir and two mixing chambers in series to simulate the exponential feeding. Fed-batch cultures with Escherichia coli showed that the present feeding method could sustain the cells growing at predetermined specific growth rates, where the time length for exponential growth was dependent on the magnitude of the growth rate. The present feeding method is convenient to operate, requires no computerized control equipments, and thus could expect an extensive application in fed-batch culture.     

A quantitative method for the analysis of mammalian cell proliferation in culture in terms of dividing and non-dividing cells

The application of the exponential growth equation is the standard method employed in the quantitative analyses of mammalian cell proliferation in culture. This method is based on the implicit assumption that, within a cell population under study, all division events give rise to daughter cells that always divide. When a cell population does not adhere to this assumption, use of the exponential growth equation leads to errors in the determination of both population doubling time and cell generation time. We have derived a more general growth equation that defines cell growth in terms of the dividing fraction of daughter cells. This equation can account for population growth kinetics that derive from the generation of both dividing and non-dividing cells. As such, it provides a sensitive method for detecting non-exponential division dynamics. In addition, this equation can be used to determine when it is appropriate to use the standard exponential growth equation for the estimation of doubling time and generation time.     

A comparison of the traditional method of counting viable cells and a quick microplate method for monitoring the growth characteristics of Listeria monocytogenes

AIMS: To determine: (i) the growth parameters (specific growth rate, lag time, asymptotic amount of growth, generation time and time for maximum growth rate) of Listeria monocytogenes in different broths by standard cultivation methods and (ii) whether a microplate method in conjunction with a standard nondedicated plate reader could be adapted to routine assay. METHODS AND RESULTS: Growth curves were determined from cell numbers in a standard tube method at 2 h intervals by serial dilution and plating, and in a microplate method by absorbance measurements. Growth curves were fitted with a modified Gompertz function. CONCLUSIONS: The microplate method was similar to the standard cultivation methods in accuracy, required less chemical reagents, and considerably reduced the time required for analyses. This work also illustrates that growth characteristics of bacteria are not necessarily constant, and depend on the methodology used. SIGNIFICANCE AND IMPACT OF THE STUDY: It is not the intended purpose of this paper to present all the data for the media tested but instead to illustrate the success of the microplate method for studying growth kinetics compared to a standard cultivation method and system precision. The method will be of considerable benefit to laboratories unable to afford dedicated workstations.     

Analysis of exponential growth data for yoghurt cultures

Obtaining accurate estimates of maximum specific growth rate, growth yield, and product yield is important for many fermentation processes. A systematic procedure is presented to select the exponential growth region and estimate the maximum specific growth rate using the covariate adjustment method with all the available measured variables (i.e. biomass, substrate, and product). The procedure is applied to data collected during growth of pure and mixed cultures of Lactobacillus bulgaricus and Streptococcus thermophilus on 3% dry milk under anaerobic conditions. The estimation procedure gives good estimates with relatively narrow confidence intervals even though biomass concentration is measured by an indirect method. The estimated values of maximum specific growth rate range from 0.2805 h(-1) for S. thermophilus (ATCC-19258) to 0.4672 h(-1) for S. thermophilus (Microlife). Growth and product yields are estimated using regression analysis and the data for the exponential growth region. The growth yields are compared to their theoretical maximum values.     

A novel isotope labeling protocol for bacterially expressed proteins

Summary A novel protocol for isotopically labeling bacterially expressed proteins is presented. This method circumvents problems related to poor cell growth, commonly associated with the use of minimal labeled media, and problems with protein induction encountered, less commonly, when using enriched labeled media. The method involves initially growing the bacterial cells to high optical density in a commercially available enriched labeled medium. Following a suitable growth period, the cells are transferred to a different (minimal) labeled medium, appropriate for induction. The method is demonstrated using the protein melanoma growth stimulating activity (MGSA).     

The effect of 60Co gamma-radiation and hydroxyurea on the in vivo chain growth of DNA in crypt cells of the small intestine of the mouse.

DNA chain growth has been studied in small intestinal crypt cells of the mouse in vivo using a sensitive method. The method is designed primarily to study radiation-induced DNA-breaks and their repair; but since there are breaks in DNA at the replicating fork, it is also possible to study DNA chain growth after a 3H-thymidine pulse. We found that DNA chain growth is not depressed by 200 rad of 60Co gamma radiation. This finding supports the hypothesis that irradiation interfers mainly with the initiation of new replicons in mammalian cells affecting DNA chain growth only at higher doses. Hydroxyurea at sufficient dosage, however, depresses or even stops DNA chain growth in mouse crypt cells in vivo.     

A novel approach for estimating growth phases and parameters of bacterial population in batch culture

Using mathematical analysis, a new method has been developed for studying the growth kinetics of bacterial populations in batch culture. First, sampling data were smoothed with the spline interpolation method. Second, the instantaneous rates were derived by numerical differential techniques and finally, the derived data were fitted with the Gaussian function to obtain growth parameters. We named this the Spline-Numerical-Gaussian or SNG method. This method yielded more accurate estimates of the growth rates of bacterial populations and new parameters. It was possible to divide the growth curve into four different but continuous phases based on changes in the instantaneous rates. The four phases are the accelerating growth phase, the constant growth phase, the decelerating growth phase and the declining phase. Total DNA content was measured by flow cytometry and varied depending on the growth phase. The SNG system provides a very powerful tool for describing the kinetics of bacterial population growth. The SNG method avoids the unrealistic assumptions generally used in the traditional growth equations.     

A novel approach for estimating growth phases and parameters of bacterial population in batch culture

Traditionally, microbiologists divided bacterial growth in batch cultures into lag, exponential, station-ary and death phases[1], following the Logistic equa-tion that has been applied to the growth of human populations. The growth curves can always be ch…