A Wilcoxon–Mann–Whitney Test for Latent Variables

We propose an extension of the Wilcoxon–Mann–Whitney test to compare two groups when the outcome variable is latent. We empirically demonstrate that the test can have superior power properties relative to tests based on Structural Equation Modeling for a variety of settings. In addition, several other advantages of the Wilcoxon–Mann–Whitney test are retained such as robustness to outliers and good small sample performance. We demonstrate the proposed methodology on a case study.

Choosing Interim Sample Sizes in Group Sequential Designs

This manuscript investigates sample sizes for interim analyses in group sequential designs. Traditional group sequential designs (GSD) rely on “information fraction” arguments to define the interim sample sizes. Then, interim maximum likelihood estimators (MLEs) are used to decide whether to stop early or continue the data collection until the next interim analysis. The possibility of early stopping changes the distribution of interim and final MLEs: possible interim decisions on trial stopping excludes some sample space elements. At each interim analysis the distribution of an interim MLE is a mixture of truncated and untruncated distributions. The distributional form of an MLE becomes more and more complicated with each additional interim analysis. Test statistics that are asymptotically normal without a possibly of early stopping, become mixtures of truncated normal distributions under local alternatives. Stage-specific information ratios are equivalent to sample size ratios for independent and identically distributed data. This equivalence is used to justify interim sample sizes in GSDs. Because stage-specific information ratios derived from normally distributed data differ from those derived from non-normally distributed data, the former equivalence is invalid when there is a possibility of early stopping. Tarima and Flournoy [3] have proposed a new GSD where interim sample sizes are determined by a pre-defined sequence of ordered alternative hypotheses, and the calculation of information fractions is not needed. This innovation allows researchers to prescribe interim analyses based on desired power properties. This work compares interim power properties of a classical one-sided three stage Pocock design with a one-sided three stage design driven by three ordered alternatives.

Особенности механического поведения силовых приводов кольцевой формы, действующих в режиме обратимой памяти формы

The possibility of increasing the deformation-power properties of TiNi ring-shaped drives operating in the two-way shape memory effect (TWSME) has been studied. For this purpose, thermal cycling of an oval sample was used with the transfer of material from the low-temperature martensite phase to the high-temperature austenitic phase in the free state and cooling through the transformation temperature range under load. The possibility of force generation in ring-shaped structures, the shape change of which is caused by the TWSME process, both during heating and during cooling, is shown. Data on the asymmetry of these properties with respect to the direction of temperature change are presented. The significant influence of the cooling rate on the deformation-power properties of the ring-shaped drives is shown.

Non-lithium based metal ion capacitors: recent advances and perspectives

Metal ion capacitors (MICs), as the combination of supercapacitors and rechargeable batteries, are endowed with higher energy density and longer cycle life but not at the expense of high-power properties....