Growth, current size and the role of the 'reversal paradox' in the foetal origins of adult disease: an illustration using vector geometry

BACKGROUND Numerous studies have reported inverse associations between birth weight and a range of diseases in later life. These have led to the development of the 'foetal origins of adult disease hypothesis'. However, many such studies have only been able to demonstrate a statistically significant association between birth weight and disease in later life by adjusting for current size. This has been interpreted as evidence that the impact of low birth weight on subsequent disease is somehow dependent on subsequent weight gain, and has led to a broadening of the hypothesis into the 'developmental origins of health and disease'. Unfortunately, much of the epidemiological evidence used for both of these interpretations is prone to a statistical artefact known as the 'reversal paradox'. The aim of this paper is to illustrate why, using vector geometry. MATERIALS AND METHODS This paper introduces the key concepts of vector geometry as applied to multiple regression analysis. This approach is then used to illustrate the similar statistical problems encountered when adjusting for current size or growth when exploring the association between birth weight and disease in later life. RESULTS Geometrically, the three covariates – birth size, growth, and current size – span only 2-dimensional space. Regressing disease in later life (i.e. the outcome variable) on any two of these covariates equates to projecting the disease variable onto the plane spanned by the three covariate vectors. The three possible regression models – where any two covariates are considered – are therefore equivalent and yield exactly the same model fit (R2). CONCLUSION Vector geometry illustrates why it is impossible to differentiate between the effects of growth from the effects of current size in studies exploring the relationship between size at birth and subsequent disease. For similar reasons, it is impossible to differentiate between the effects of growth and the effects of birth weight. Assessing the 'independent' impact of growth on later disease by adjusting for either birth weight or current size is therefore illusory

Vibration signature analysis of multistage gear transmission

An analysis is presented for multistage multimesh gear transmission systems. The analysis predicts the overall system dynamics and the transmissibility to the gear box or the enclosed structure. The modal synthesis approach of the analysis treats the uncoupled lateral/torsional model characteristics of each stage or component independently. The vibration signature analysis evaluates the global dynamics coupling in the system. The method synthesizes the interaction of each modal component or stage with the nonlinear gear mesh dynamics and the modal support geometry characteristics. The analysis simulates transient and steady state vibration events to determine the resulting torque variations, speeds, changes, rotor imbalances, and support gear box motion excitations. A vibration signature analysis examines the overall dynamic characteristics of the system, and the individual model component responses. The gear box vibration analysis also examines the spectral characteristics of the support system

Dynamics of Multistage Gear Transmission with Effects of Gearbox Vibrations

A comprehensive approach is presented in analyzing the dynamic behavior of multistage gear transmission systems with the effects of gearbox induced vibrations and mass imbalances of the rotor. The modal method, with undamped frequencies and planar mode shapes, is used to reduce the degrees of freedom of the gear system for time-transient dynamic analysis. Both the lateral and torsional vibration modes of each rotor-bearing-gear stage as well as the interstage vibrational characteristics are coupled together through localized gear mesh tooth interactions. In addition, gearbox vibrations are also coupled to the rotor-bearing-gear system dynamics through bearing support forces between the rotor and the gearbox. Transient and steady state dynamics of lateral and torsional vibrations of the geared system are examined in both time and frequency domains to develop interpretations of the overall modal dynamic characteristics under various operating conditions. A typical three-stage geared system is used as an example. Effects of mass imbalance and gearbox vibrations on the system dynamic behavior are presented in terms of modal excitation functions for both lateral and torsional vibrations. Operational characteristics and conclusions are drawn from the results presented

Modal analysis of multistage gear systems coupled with gearbox vibrations

An analytical procedure to simulate vibrations in gear transmission systems is presented. This procedure couples the dynamics of the rotor-bearing gear system with the vibration in the gear box structure. The model synthesis method is used in solving the overall dynamics of the system, and a variable time-stepping integration scheme is used in evaluating the global transient vibration of the system. Locally each gear stage is modeled as a multimass rotor-bearing system using a discrete model. The modal characteristics are calculated using the matrix-transfer technique. The gearbox structure is represented by a finite element models, and modal parameters are solved by using NASTRAN. The rotor-gear stages are coupled through nonlinear compliance in the gear mesh while the gearbox structure is coupled through the bearing supports of the rotor system. Transient and steady state vibrations of the coupled system are examined in both time and frequency domains. A typical three-geared system is used as an example for demonstration of the developed procedure

Observation of indirect ionization of W7+ in an electron-beam ion-trap plasma

In this work, visible and extreme ultraviolet spectra of W7+ are measured using the high-temperature superconducting electron-beam ion trap (EBIT) at the Shanghai EBIT Laboratory under extremely low-energy conditions (lower than the nominal electron-beam energy of 130 eV). The relevant atomic structure is calculated using the flexible atomic code package based on the relativistic configuration interaction method. The GRASP2K code, in the framework of the multiconfiguration Dirac-Hartree-Fock method, is employed as well for calculating the wavelength of the M1 transition in the ground configuration of W7+. A line from the W7+ ions is observed at a little higher electron-beam energy than the ionization potential for W4+, making this line appear to be from W5+. A hypothesis for the charge-state evolution of W7+ is proposed based on our experimental and theoretical results; that is, the occurrence of W7+ ions results from indirect ionization caused by stepwise excitation between some metastable states of lower-charge-state W ions, at the nominal electron-beam energy of 59 eV

Response to: Simpson’s Paradox is suppression, but Lord’s Paradox is neither: clarification of and correction to Tu, Gunnell, and Gilthorpe (2008) by Nickerson CA & Brown NJL (https://doi.org/10.1186/1742-7622-5-2)

We commend Nickerson and Brown on their insightful exposition of the mathematical algebra behind Simpson’s paradox, suppression and Lord’s paradox; we also acknowledge there can be differences in how Lord’s paradox is approached analytically, compared to Simpson’s paradox and suppression, though not in every example of Lord’s paradox. Furthermore, Simpson’s paradox, suppression and Lord’s paradox ask the same contextual questions, seeking to understand if statistical adjustment is valid and meaningful, identifying which analytical option is correct. In our exposition of this, we focus on the perspective of context, which must invoke causal thinking. From a causal thinking perspective, Simpson’s paradox, suppression and Lord’s paradox present very similar analytical challenges

Efficacy of preharvest spraying with Pichia guilliermondii on postharvest decay and quality of cherry tomato fruit during storage

This study investigated the effects of preharvest spraying with Pichia guilliermondii on postharvest natural decay of cherry tomato fruit, and evaluated the quality attributes during storage. Preharvest spraying with P. guilliermondii significantly decreased the decay index. Moreover, the efficacy of this biological control was positively correlated with spraying frequency. However, preharvest spraying with P. guilliermondii and spraying frequency did not significantly affect fruit quality attributes regardless of whether the cherry tomato fruit was grown or stored after harvest. This observation indicates that preharvest spraying with P. guilliermondii does not influence the quality attributes of the fruit. In addition, the activities of peroxidase (POD), phenylalanine ammonia-lyase (PAL), and β-1,3-glucanase increased in all P. guilliermondii treatments, suggesting a positive correlation with spraying frequency. The results suggest that cherry tomato fruit is capable of responding to preharvest spraying with P. guilliermondii, which can activate its defensive enzymes and thus induce host disease resistance.Key words: Preharvest, Pichia guilliermondii, cherry tomato fruit, decay, quality

Fractionation of Asphaltenes in Understanding Their Role in Petroleum Emulsion Stability and Fouling

SARA fractionation separates crude oil into fractions of saturates (S), aromatics (A), resins (R), and asphaltenes (A) based on the differences in their polarizability and polarity. Defined as a solubility class, asphaltenes are normally considered as a nuisance in the petroleum industry mainly as a result of their problematic precipitation and adsorption at oil–water and oil–solid interfaces. Because a broad range of molecules fall within the group of asphaltenes with distinct sizes and structures, considering the asphaltenes as a whole was noted to limit the deep understanding of governing mechanisms in asphaltene-induced problems. Extended-SARA (E-SARA) is proposed as a concept of asphaltene fractionation according to their interfacial activities and adsorption characteristics, providing critical information to correlate specific functional groups with certain characteristics of asphaltene aggregation, precipitation, and adsorption. Such knowledge is essential to addressing asphaltene-related problems by targeting specific subfractions of asphaltenes

Genetic variation of indigenous chicken breeds in China and a Recessive White breed using AFLP fingerprinting

Amplified fragment length polymorphism (AFLP) using six marker combinations were applied to detect genetic variation and phylo genetic relationships among 12 indigenous Chinese chicken breeds and a Recessive White chicken breed introduced from France. The DNA was pooled for each group. Polymorphic bands, breed-specific bands and genetic similarity coefficients of 13 chicken breeds were derived from the AFLP data. A total of 280 polymorphic bands was generated from which nine specific bands were observed for the Shouguang and the Dongxiang Dark chicken. One specific band was observed in the pooled DNA of the Jiuyuan Dark chicken, the Xingyi Bantam chicken and the Recessive White chicken. The genetic similarity coefficients among the 12 indigenous Chinese chicken breeds varied between 0.635 - 0.860, and 0.188 - 0.360 between the Recessive White and the indigenous Chinese chicken breeds. The UPGMA based tree yielded two clusters for the 13 chicken breeds, with the Recessive White chickens forming a distinct cluster. In summary, the genetic similarity coefficients and the UPGMA tree of the 13 chicken breeds were consistent with their breeding history and geographical distribution. These results provide useful data with regard to the genetic diversity, genetic relationships and identification of chicken breeds in China. Keywords: Indigenous chicken breeds, AFLP markers, genetic variation, genetic relationshipsSouth African Journal of Animal Science Vol. 38 (3) 2008: pp. 193-20

CFD Simulations on the Heating Capability in a Human Nasal Cavity

The air conditioning capability of the nose is dependent on the nasal mucosal temperature and the airflow dynamics caused by the airway geometry. A computational model of a human nasal cavity obtained through CT scans was produced and CFD techniques were applied to study the effects of morphological differences in the left and right nasal cavity on the airflow and heat transfer of inhaled air. A laminar steady flow of 10L/min was applied and two inhalation conditions were investigated: normal conditions, 25°C, 35% relative humidity and cold dry air conditions, 12°C, 13% relative humidity. It was found that the frontal regions of the nasal cavity exhibited greater secondary cross flows compared to the middle and back regions. The left cavity in the front region had a smaller cross-sectional area compared to the right which allowed greater heating as the heat source from the wall was closer to the bulk flow regions. Additionally it was found that the residence time of the inhaled air was important for the heating ability in laminar flows