Quantum counter for correcting fluorescence excitation spectra at 320- to 800-nm wavelengths

A procedure for recording corrected fluorescence excitation spectra to wavelengths as long as 800 nm is described. The procedure involves the use of a commercial spectrofluorometer, which is modified by substituting 1,1',3,3,3',3'-hexamethylindotricarbocyanine perchlorate in place of rhodamine B as the quantum counter dye. This modification is applicable to spectrofluorometers supplied by several different manufacturers and can be accomplished by a user having only modest technical skills. A study of the fluorescence excitation spectrum of bacteriochlorophyll a is presented as an illustration of the use of the procedure. The procedure will be valuable in biological and biochemical studies that involve the use of long-wavelength fluorescent probes of either natural or synthetic origin.     

Nonparametric identification of the minimum effective dose

We consider identifying the minimum effective dose (MED) in a dose-response study, where the MED is defined to be the lowest dose level producing an effect over that of the zero-dose control. Proposed herein is a nonparametric procedure based on the Mann-Whitney statistic incorporated with the step-down closed testing scheme. A numerical example demonstrates the feasibility of the proposed nonparametric procedure. Finally, the comparative results of a Monte Carlo level and power study for small sample sizes are presented and discussed.     

High Throughput Screening of Signal Transduction Mutants With Luciferase Imaging

A detailed procedure for high throughput genetic screening of hormone and environmental stress signal transduction mutants of Arabidopsis thaliana is described. The screen was carried out with mutagenized plants expressing the firefly luciferase reporter under control of a cold, osmotic stress, and absciscic acid responsive promoter. A thermoelectrically cooled CCD camera was used to detect luminescence emitted by the plants in response to stresses or ABA. Advantages of the screening procedure include high throughput, capability to identify low as well as high expression mutants and employment of a highly sensitive but affordable imaging system and software. This procedure can be used to study complex signal transduction networks in higher plants.     

A Two-Way Analysis of Covariance Model for Classification of Stability Data

This paper proposes a procedure for testing and classifying data with multiple factors. A two-way analysis of covariance is used to classify the differences among the batches as well as another factor such as package type and/or product strength. In the test procedure, slopes and intercepts of the main effects are tested using a combination of simultaneous and sequential F-tests. Based on the test procedure results, the data are classified into one of four different groups. For each group, shelf life can be calculated accordingly. We examine if the procedure produces satisfactory control of the probability of a Type I error and the power of detecting the difference of degradation rates and intercepts for different nominal levels. The method is evaluated with a Monte Carlo simulation study. The proposed procedure is compared with the current FDA procedure using real data.     

The determination of folylpolyglutamate synthetase.

A relatively rapid radiochemical procedure for the determination of folylpolyglutamate synthetase activity is presented in this communication. The procedure is based on measurement of the incorporation of radioactive l-glutamate into tetrahydropteroylpolyglutamate on incubation with a tetrahydrofolate. After deproteinating the incubation mixtures with trichloroacetic acid, folate is separated from radioactive glutamate by an adaptation of a procedure generally employed in the isolation of folate from natural materials, i.e., adsorption on columns of charcoal from which it is subsequently eluted with aqueous-alcoholic ammonia containing mercaptoethanol and counted. The procedure is applicable to monitoring purification of the enzymes and to the study of their properties.The technique for separating a radioactive product of enzyme action from a radioactive precursor with a column of charcoal, that has been developed for this procedure is applicable also to other radiochemical enzyme determinations requiring the separation of an aromatic from an aliphatic metabolite.     

The use of the maharanobis and modified distances for the improvement of simulation of glutamic acid production

A modified simulation procedure based on a statistical approach was investigated. The procedure predicts the time course of fed-batch culture for glutamic acid production by a temperature-sensitive strain of Brevibacterium flavum. The statistical approach requires only a data base of state points obtained in experiments, and not perfect identification of fermentation models. The simulation procedure is based on regression analysis to estimate specific rate parameters of system equations using the data points selected with reference to the Euclid distance. It was modified in that the data selection procedure included the use of the Maharanobis distance as well as a modified distance defined in this study. Simulation results using the modified procedure allow reasonable prediction of the time course of fed-batch culture for glutamic acid compared to that involving the Euclid distance alone.     

Incorporating Prior Beliefs in Treatment Allocation for Clinical Trials

Recently Faraggi and Reiser (1991) introduced a general dynamic treatment allocation scheme which incorporates the permuted block allocation procedure and the Begg Iglewicz procedure as special cases. A drawback of previous allocation methods is that they did not allow incorporation of prior knowledge of the relative importance of the prognostic factors. In this paper we extend our allocation model to incorporate the weighting of prognostic factors. A simulation study examines the effects of this procedure and an example of its implementation is given.     

Thermal gels: A procedure for determination of heat-inactivation temperature of enzymes

A facile procedure for the study of inactivation temperatures of enzymes that could be stained for activity after electrophoresis is described. This is particularly suitable for enzymes that have multiple electrophoretic forms. The results of studies on Drosophila dehydrogenases and acetylcholinesterase are presented. The procedure may be useful in the study of genetic variants.     

An Approximate EM Algorithm for Nonlinear Mixed Effects Models

In this article, we construct an approximate EM algorithm to estimate the parameters of a nonlinear mixed effects model. The iterative procedure can be viewed as an iterative method of moments procedure for estimating the variance components and an iterative reweighted least squares estimates for estimating the fixed effects. Therefore, it is valid without the normality assumptions on the random components. A computationally simple method of moments estimates of the model parameters are used as the starting values for our iterative procedure. A simulation study was conducted to compare the performances of the proposed procedure with the procedure proposed by Lindstrom and Bates (1990) for some normal models and nonnormal models.     

Tests for Ordered Alternatives with Right Censored Data

A procedure is presented to test for ordered alternatives in the k-sample case when the observations are subject to right censorship. This procedure is an extension of the one proposed by Hettmansperger and Norton (1987). The nondecreasing and umbrella alternatives are of particular interest. A Monte Carlo simulation study is done comparing this procedure with two other existing ones in the nondecreasing case.     

A two-stage procedure for bioequivalence studies

A two-stage experimental procedure for bioequivalence studies is proposed. The procedure is based on the idea that information from a first-stage experiment can be used to form a predictive distribution for the outcome of a second-stage experiment, thus permitting an assessment of the probability of a successful overall outcome. A systematic numerical study of a variety of possible strategies results in the identification of procedures that lead to substantial increases in efficiency compared with single-stage studies.     

Determination of CoASH by high-performance liquid chromatography and its application in the assay of long-chain acyl-CoA derivatives.

A high-performance liquid chromatographic procedure is described for the determination of picomole amounts of CoASH, using a microparticulate, strong anion-exchange resin. The method was applied in a systematic study to optimize the conditions for alkaline hydrolysis of palmitoyl-CoA. The procedure, which ensures 100% recovery of CoASH by hydrolysis of paimitoyl-CoA, was found to be convenient also for the assay of the endogenous content of long-chain acyl-CoA derivatives in biological material.     

Order-preserving dimension reduction procedure for the dominance of two mean curves with application to tidal volume curves

Summary .   The paper here presented was motivated by a case study involving high-dimensional and high-frequency tidal volume traces measured during induced panic attacks. The focus was to develop a procedure to determine the significance of whether a mean curve dominates another one. The key idea of the suggested method relies on preserving the order in mean while reducing the dimension of the data. The observed data matrix is projected onto a set of lower rank matrices with a positive constraint. A multivariate testing procedure is then applied in the lower dimension. We use simulated data to illustrate the statistical properties of the proposed testing procedure. Results on the case study confirm the preliminary hypothesis of the investigators and provide critical support to their overall goal of creating an experimental model of the clinical panic attack in normal subjects.     

Efficiency of a Two-Stage Procedure for Survival Studies

A two-stage procedure using occurrences of a surrogate endpoint regarding a true clinical endpoint has been proposed (FLANDRE, O'QUIGLEY and BROOKMEYER, 1994). The procedure allows estimation of the survival function S(t) reliably and comparison of treatment groups. The aim of this paper is to investigate the efficiency of such a two-stage procedure compared to a one stage procedure, i.e. a classical study. The efficiency is estimated by the ratio of the standard derivation of S(t) for the classical procedure to the standard derivation of S(t) for the two-stage procedure and represents the precision on the estimation of S(t). Standard deviation of S(t) is approximate by the delta-method. Using the exponential model. some numerical results are presented.     

A two-step procedure for automatic and accurate segmentation of volumetric CLSM biofilm images

This paper presents a robust two-step segmentation procedure for the study of biofilm structure. Without user intervention, the procedure segments volumetric biofilm images generated by a confocal laser scanning microscopy (CLSM). This automated procedure implements an anisotropic diffusion filter as a preprocessing step and a 3D extension of the Otsu method for thresholding. Applying the anisotropic diffusion filter to even low-contrast CLSM images significantly improves the segmentation obtained with the 3D Otsu method. A comparison of the results for several CLSM data sets demonstrated that the accuracy of this procedure, unlike that of the objective threshold selection algorithm (OTS), is not affected by biofilm coverage levels and thus fills an important gap in developing a robust and objective segmenting procedure. The effectiveness of the present segmentation procedure is shown for CLSM images containing different bacterial strains. The image saturation handling capability of this procedure relaxes the constraints on user-selected gain and intensity settings of a CLSM. Therefore, this two-step procedure provides an automatic and accurate segmentation of biofilms that is independent of biofilm coverage levels and, in turn, lays a solid foundation for achieving objective analysis of biofilm structural parameters.     

Reproducibility of the tensile properties of spider (Argiope trifasciata) silk obtained by forced silking

A modified forced silking procedure was developed to allow an accurate study of the tensile properties of spider (Argiope trifasciata) silk, especially the characterization of the variability of the tensile properties of forcibly silked fibers. The procedure involves an immobilization technique that does not require anesthetization of the spider, a mode of collection that allows immediate access to any silk sample with a minimum manipulation, and a technique to measure the diameters of the spider silk fibers systematically. The forcibly silked fibers obtained by this procedure show reproducible tensile properties in terms of force-displacement curves as well as stress-strain curves. Furthermore, reproducibility also extends to forcibly silked fibers obtained from different spiders when stress-strain is considered.     

Photolabelling of membrane proteins with photoactive phospholipids.

Photoactive probes have been introduced recently to study the hydrophobic sector of integral membrane proteins. A simple procedure to synthesize a new series of highly radioactive aryl azido-phospholipids is presented. They effectively exchange with the boundary lipids and, on illumination, the cross-link to several membrane proteins with high efficiency. The procedure and analysis of labelling of ATPase from sarcoplasmic reticulum is reported as an example. The advantages in using these photoactive phospholipids are discussed together with some information obtained on their use.     

On Significance Testing in Comparative Epidemiologic Research

The choice of the referent entity in comparative epidemiologic studies is, of course, crucial to the attainment of a valid and sharp contrast. A commonplace procedure in large sample significance testing for (multiple) fourfold (and extended) tables is to base the estimation of the expected value (and/or the variance) on the combined study and comparison experience. This procedure is, however, deplorable in that in interim stages of the study it may hide the underlying difference in rates. The notion that the probability of the realization of the observed number of exposed cases be evaluated unconditionally assuming a binomial model with the Bernoulli parameter estimated solely by the rate in the referent series is considered. This outlook is carried over to bilateral testing. A chi square criterion accommodating this viewpoint could be used to canvass the accrued data for deciding on the prospects of continuing the data collection. A test employing exact variance estimates is derived and various methods for computing an ‘exact’ significance probability are developed. The procedure is exemplified by artificial data and accompanied by a discussion of its applicability.     

Stepwise Procedures under Unknown Variances for Toxicological Evaluation

Toxicological study is of practical importance in modern drug development. Proper statistical methodologies for toxicological evaluation of new developed drugs are undoubtedly necessary. In toxicological studies, it is practically desirable for a method to not declare the safety of a developed drug at a higher dosage prior to the declaration of the safety at lower dosages. Hsu and Berger 's stepwise confidence interval method was recently proposed for this purpose. Unfortunately, their procedure necessitates the homogeneity of variances among dosages, which is seldom satisfied in practice. In this article, via the application of the Stein 's two‐stage sampling method, we propose a stepwise confidence interval procedure for the same task without the homoscedasticity restriction. In addition, our procedure is shown to control its family‐wise type I error rate at the pre‐chosen nominal level. A simulation study will be conducted to compare our method, Hsu and Berger 's stepwise confidence interval method, and a single stage stepwise testing procedure based on Welch 's approximation. Our procedure is empirically shown to outperform Hsu and Berger 's procedure under heteroscedasticity and perform similarly with Welch 's procedure. An example will be used to illustrate our method.     

Stepwise Variable Selection in Classification Problems

Two variable selection procedures are evaluated for classification problems: a forward stepwise discrimination procedure, and a stepwise procedure preceded by a preliminary screening of variables on the basis of individual t statistics. Expected probability of correct classification is used as the measure of performance. A comparison is made of the procedures using samples from multi-variate normal populations and from several nonnormal populations. The study demonstrated some situations where the use of all variables is preferable to the use of a stepwise discriminant procedure stopping after a few steps, though usually the latter procedure was superior in performance. However where the stepwise procedure performed better than using all variables, the modified stepwise procedure performed still better. The use of modified stepwise procedures in which not all the covariances of the problem need be estimated seems promising.