Experimental Study of a Vacuum Spark Discharge over a Dielectric Surface

A decrease in the amplitude of the current of a vacuum spark discharge over a dielectric surface with increasing discharge gap length is established. It is shown that, in the presence of a longitudinal magnetic field, the leading edge of the discharge voltage pulse is extended, whereas the clearly pronounced current pulse transforms into a train of alternating current oscillations. The discharge is found to decelerate when the spark is preceded by a low-current discharge.     

Inferential Clustering Approach for Microarray Experiments with Replicated Measurements

Cluster analysis has proven to be a useful tool for investigating the association structure among genes in a microarray data set. There is a rich literature on cluster analysis and various techniques have been developed. Such analyses heavily depend on an appropriate (dis)similarity measure. In this paper, we introduce a general clustering approach based on the confidence interval inferential methodology, which is applied to gene expression data of microarray experiments. Emphasis is placed on data with low replication (three or five replicates). The proposed method makes more efficient use of the measured data and avoids the subjective choice of a dissimilarity measure. This new methodology, when applied to real data, provides an easy-to-use bioinformatics solution for the cluster analysis of microarray experiments with replicates (see the Appendix). Even though the method is presented under the framework of microarray experiments, it is a general algorithm that can be used to identify clusters in any situation. The method's performance is evaluated using simulated and publicly available data set. Our results also clearly show that our method is not an extension of the conventional clustering method based on correlation or euclidean distance.     

Biological Control of Crown Gall: Field Measurements and Glasshouse Experiments

S ummary : An ecological study showed that the pathogeniec form of Agrobacterium radiobacter (A.r. var. tumefaciens ), biotype 2 was present in soil near galled almond seedlings, where it formed a significant proportion of the total biotype 2 population; the pathogen was not detected near healthy plants. One nonpathogenic biotype 2 isolate was able, when present in numbers approximately equal to the pathogen, to prevent crown gall induction in tomato and peach seedlings. This isolate gave complete biological control of crown gall in a glasshouse test. Six other nonpathogenic isolates did not significantly inhibit gall induction by equal numbers of the pathogen. In the field, gall induction probably depends on the size of the population of the pathogen (both absolutely and relative to that of the nonpathogen) at a wound site and on the inhibitory efficiency of the nonpathogen.     

The Design and Analysis of Experiments with Grouped Measurements. II. Comparison of Means

The method of grouped measurements, described in part one of this article, is worked out for some important comparisons of means. Methods for design of experiments for the multiple t-Test are given. Two approximate solutions are proposed. An extensive table facilitate to find out the approximate optimal design in the set of designs with preliminated precision.     

Biases and Power for Groups Comparison on Subjective Health Measurements

Subjective health measurements are increasingly used in clinical research, particularly for patient groups comparisons. Two main types of analytical strategies can be used for such data: so-called classical test theory (CTT), relying on observed scores and models coming from Item Response Theory (IRT) relying on a response model relating the items responses to a latent parameter, often called latent trait. Whether IRT or CTT would be the most appropriate method to compare two independent groups of patients on a patient reported outcomes measurement remains unknown and was investigated using simulations. For CTT-based analyses, groups comparison was performed using t-test on the scores. For IRT-based analyses, several methods were compared, according to whether the Rasch model was considered with random effects or with fixed effects, and the group effect was included as a covariate or not. Individual latent traits values were estimated using either a deterministic method or by stochastic approaches. Latent traits were then compared with a t-test. Finally, a two-steps method was performed to compare the latent trait distributions, and a Wald test was performed to test the group effect in the Rasch model including group covariates. The only unbiased IRT-based method was the group covariate Wald’s test, performed on the random effects Rasch model. This model displayed the highest observed power, which was similar to the power using the score t-test. These results need to be extended to the case frequently encountered in practice where data are missing and possibly informative.     

The Power and the Pitfalls of Large-scale,Unreplicated Natural Experiments

Large-scale, unreplicated natural experiments (LUNEs) have a unique power to test hypotheses at ecologically realistic scales and have delivered insights of great power into cosmology, evolution and geology. Yet, LUNEs are relatively rare in the field of ecology and continue to meet resistance due to their lack of replication. However, in the vast majority of cases, large-scale experiments cannot be replicated for practical and ethical reasons. Here, we make the case that LUNEs have had a disproportionately positive effect on conservation policy and are a crucial next step in the extrapolation of our understanding of ecological processes from small-scale experiments to relevant scales, particularly in the context of the current “replication crisis” affecting many sciences. Greater inclusion of LUNEs in mainstream ecology will help humanity to solve global problems as human transformation of the planet accelerates in coming decades.     

Precision and Agreement of Corneal Power Measurements Obtained Using a New Corneal Topographer OphthaTOP

Purpose

To evaluate repeatability and reproducibility of anterior corneal power measurements obtained with a new corneal topographer OphthaTOP (Hummel AG, Germany) and agreement with measurements by a rotating Scheimpflug camera (Pentacam HR, Oculus, Germany) and an automated keratometer (IOLMaster, Carl Zeiss Meditec, Germany).

Methods

The right eyes of 79 healthy subjects were prospectively measured three times with all three devices. Another examiner performed three additional scans with the OphthaTOP in the same session. Within one week, the first examiner repeated the measurements using the OphthaTOP. The flat simulated keratometry (Kf), steep K (Ks), mean K (Km), J₀, and J₄₅ were noted. Repeatability and reproducibility of measurements were assessed by within-subject standard deviation (Sw), repeatability (2.77 Sw), coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Agreement between devices was assessed using 95% limits of agreement (LoA).

Results

Intraobserver repeatability and interobserver and intersession reproducibility of all measured parameters showed a 2.77 Sw of 0.29 diopter or less, a CoV of less than 0.24%, and an ICC of more than 0.906. Statistically significant differences (P<0.001) were found between the parameters analyzed by the three devices, except J₀ and J₄₅. The mean differences between OphthaTOP and the other two devices were small, and the 95% LoA was narrow for all results.

Conclusions

The OphthaTOP showed excellent intraobserver repeatability and interobserver and intersession reproducibility of corneal power measurements. Good agreements with the other two devices in these parameters were found in healthy eyes.     

Measurements of Microwave Power Absorbed during ECR Plasma Heating at the L-2M Stellarator

Plasma Physics Reports - The results are presented from measurements of the power absorbed in plasma of the L-2M stellarator in experiments on the electron cyclotron resonance (ECR) plasma heating...     

Experiments

In this article, I have provided a brief history of my life. After tracing my family background and my early interest in physical sciences, I discuss how I entered biology under the influence of Robert Emerson. I have always enjoyed doing experiments and this led to new measurements and analyses of chlorophyll unit, efficiency of photosynthesis, excitation energy transfer, delayed light emission, thermoluminescence and electroluminescence in photosynthetic organisms. It is my view that discoveries are made because we follow our scientific curiosities.This article was written at the invitation of Govindjee.     

Spark channel propagation in a microbubble liquid

Experimental study on the development of the spark channel from the anode needle under pulsed electrical breakdown of isopropyl alcohol solution in water with air microbubbles has been performed. The presence of the microbubbles increases the velocity of the spark channel propagation and increases the current in the discharge gap circuit. The observed rate of spark channel propagation in microbubble liquid ranges from 4 to 12 m/s, indicating the thermal mechanism of the spark channel development in a microbubble liquid.     

Effect of Directional Nature of Antenna and Magnetic Field Strength on Optimal Power Absorption in a Helicon Discharge

Plasma Physics Reports - The study of power absorption in a helicon plasma source excited by 13.56 MHz frequency is reported. Numerical analysis is carried out to determine the power absorption in...