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A practical approach to using statistics in health research : from planning to reporting
\"This book provides an outline with methodological steps of how to use statistics to analyze your research data. The book begins with a general introduction, which discusses what you should be trying to achieve with your statistical analysis. This involves describing the subjects you investigated and their outcomes, determining whether there is statistically significant evidence of differences in outcomes between groups of subjects, quantitatively describing effect sizes, and also determining whether any changes are large enough to be of clinical significance. Next, the authors cover data types and choosing statistical tests. This includes identifying the factor and outcome, and also identifying the type of data used to record the outcome. Readers are then introduced to multiple testing, the Chi-square test, and independent samples and the two-sample t-test. The Man-Whitney test is discussed, as well as the One-way ANOVA. Readers are taught how to Carrying out the Kruskal-Wallis test and the McNemar's test. The Paired t-test is covered, as well as how to carry out the Wilcoxon paired samples test. Readers are shown how to carry out the repeated measures ANOVA and the Friedman test. This includes discussion of merits of change in median, change in proportions in categories, and changes in high/low categories. The book concludes with a discussion on correlation and regression methods, and a detailed analysis on Cronbach's alpha\"-- Provided by publisher.
Book
Impact of Submodule Faults on the Performance of Modular Multilevel Converters
Modular multilevel converter (MMC) is well suited for high-power and medium-voltage applications. However, its performance is adversely affected by asymmetry that might be introduced by the failure of a limited number of submodules (SMs) or even by severe deviations in the values of SM capacitors and arm inductors, particularly when the number of SMs per arm is relatively low. Although a safe-failed operation is easily achieved through the incorporation of redundant SMs, the SMs’ faults make MMC arms present unequal impedances, which leads to undesirable internal dynamics because of unequal power distribution between the arms. The severity of these undesirable dynamics varies with the implementation of auxiliary controllers that regulate the MMC internal dynamics. This paper studied the impact of SMs failure on the MMC internal dynamics performance, considering two implementations of internal dynamics control, including a direct control method for suppressing the fundamental component that may arise in the dc-link current. Performances of the presented and widely-appreciated conventional methods for regulating MMC internal dynamics were assessed under normal and SM fault conditions, using detailed time-domain simulations and considering both active and reactive power applications. The effectiveness of control methods is also verified by the experiment. Related trade-offs of the control methods are presented, whereas it is found that the adverse impact of SMs failure on MMC ac and dc side performances could be minimized with appropriate control countermeasures.
Journal Article
Mixed gain detector configurations for time‐resolved X‐ray solution scattering
X‐ray detection at X‐ray free‐electron lasers is challenging in part due to the XFEL's extremely short and intense X‐ray pulses. Experimental measurements are further complicated by the large fluctuations inherent to the self‐amplified spontaneous emission process producing the X‐rays. At the Linac Coherent Light Source the ePix10ka2M detector offers multiple gain modes, and auto‐ranging between these, to increase the dynamic range while retaining low noise. For diffuse scattering techniques, such as time‐resolved X‐ray solution scattering, where the shape of the scattering pattern largely does not change between exposures, a fixed mix of different gain modes offers many of the same advantages as auto‐ranging. We find that configuring individual ASICs in separate gain modes does not impact the intensity linearity of the gain response and has a limited effect on the effective dynamic range in regions with different gain mode settings while avoiding the complexities of auto‐ranging. Small (<5%) non‐linear gain contributions arise when pixels on the same ASIC are configured in different gain modes. We present a configuration scheme that is designed to select the optimal mixed gain configuration to minimize effects of saturation in the high‐/medium‐gain region, while maximizing the number of pixels with higher gain to improve the signal‐to‐noise ratio. The linearity of the intensity response of the ePix10k detector in mixed gain configurations is evaluated for solution phase scattering experiments at the LCLS.
Journal Article
Multi-Port DC-DC and DC-AC Converters for Large-Scale Integration of Renewable Power Generation
Numerous research studies on high capacity DC-DC converters have been put forward in recent years, targeting multi-terminal medium-voltage direct current (MVDC) and high-voltage direct current (HVDC) systems, in which renewable power plants can be integrated at both medium-voltage (MV) and high-voltage (HV) DC and AC terminals; hence, leading to complex hybrid AC-DC systems. Multi-port converters (MPCs) offer the means to promote and accelerate renewable energy and smart grids applications due to their increased control flexibilities. In this paper, a family of MPCs is proposed in order to act as a hybrid hub at critical nodes of complex multi-terminal MVDC and HVDC grids. The proposed MPCs provide several controllable DC voltages from constant or variable DC or AC voltage sources. The theoretical analysis and operation scenarios of the proposed MPC are discussed and validated with the aid of MATLAB-SIMULINK simulations, and further corroborated using experimental results from scale down prototype. Theoretical analysis and discussions, quantitative simulations, and experimental results show that the MPCs offer high degree of control flexibilities during normal operation, including the capacity to reroute active or DC power flow between any arbitrary AC and DC terminals, and through a particular sub-converter with sufficient precision. Critical discussions of the experimental results conclude that the DC fault responses of the MPCs vary with the topology of the converter adopted in the sub-converters. It has been established that a DC fault at high-voltage DC terminal exposes sub-converters 1 and 2 to extremely high currents; therefore, converters with DC fault current control capability are required to decouple the healthy sub-converters from the faulted one and their respective fault dynamics. On the other hand, a DC fault at the low-voltage DC terminal exposes the healthy upper sub-converter to excessive voltage stresses; therefore, sub-converters with bipolar cells, which possess the capacity for controlled operation with variable and reduced DC voltage over wide range are required. In both fault causes, continued operation without interruption to power flow during DC fault is not possible due to excessive over-current or over-voltage during fault period; however, it is possible to minimize the interruption. The above findings and contributions of this work have been further elaborated in the conclusions.
Journal Article
Novel Enhanced Modular Multilevel Converter for High-Voltage Direct Current Transmission Systems
This paper proposes an enhanced modular multilevel converter as an alternative to the conventional half-bridge modular multilevel converter that employs a reduced number of medium-voltage cells, with the aim of improving waveforms quality in its AC and DC sides. Each enhanced modular multilevel converter arm consists of high-voltage and low-voltage chain-links. The enhanced modular multilevel converter uses the high-voltage chain-links based on medium-voltage half-bridge cells to synthesize the fundamental voltage using nearest level modulation. Although the low-voltage chain-links filter out the voltage harmonics from the voltage generated by the high-voltage chain-links, which are rough and stepped approximations of the fundamental voltage, the enhanced modular multilevel converter uses the nested multilevel concept to dramatically increase the number of voltage levels per phase compared to half-bridge modular multilevel converter. The aforementioned improvements are achieved at the cost of a small increase in semiconductor losses. Detailed simulations conducted in EMPT-RV and experimental results confirm the validity of the proposed converter.
Journal Article
Comparative Analysis of Convergent Jellyfish Eyes Reveals Extensive Differences in Expression of Vision‐Related Genes
Quantifying gene expression across convergent origins of traits clarifies the degree to which those traits arise from shared versus distinct genetic programs, revealing how gene reuse relates to the repeatability of evolution. Eyes are important traits that evolved in many distantly related lineages, including at least nine times within cnidarians. Here, we investigate gene expression in eye‐bearing and nonvisual tissues from three cnidarian species representing long‐diverged lineages where eyes evolved convergently (Cubozoa, Scyphozoa, and Hydrozoa). We find gene expression in eye‐bearing tissues to be mostly lineage‐specific, with only a small proportion of genes having convergent expression across species. Nevertheless, all species express homologs of deeply conserved vision‐related genes known from Bilateria, which likely reflects deep homology (parallel evolution across vast phylogenetic distances) of a metazoan phototransduction toolkit. A gene tree analysis of opsins—the prototypical animal photosensors—shows that convergent eyes recruited different opsin paralogs, with the potential exception of an opsin ortholog shared between scyphozoan and cubozoan eyes. Our results suggest that eyes have mostly lineage‐specific patterns of gene expression, yet some key phototransduction components are repeatedly recruited across multiple independent eye origins in Medusozoa. Eyes have evolved in many different lineages, including several times within jellyfish, yet the relative contributions of shared and lineage‐specific genes to convergent eyes are not known. We find that three long‐diverged species of jellyfish have mostly divergent patterns of gene expression in their eye‐bearing tissues, suggesting a major role for lineage‐specific novelty in eye evolution. However, all three species also expressed homologs of bilaterian light perception genes, indicating some components of early animal phototransduction toolkits have likely been recruited into eyes repeatedly in Bilateria and Cnidaria.
Journal Article