Measurement Uncertainty of Liquid Chromatographic Analyses Visualized by Ishikawa Diagrams

Ishikawa, or cause-and-effect diagrams, help to visualize the parameters that influence a chromatographic analysis. Therefore, they facilitate the set up of the uncertainty budget of the analysis, which can then be expressed in mathematical form. If the uncertainty is calculated as the Gaussian sum of all uncertainty parameters, it is necessary to quantitate them all, a task that is usually not practical. The other possible approach is to use the intermediate precision as a base for the uncertainty calculation. In this case, it is at least necessary to consider the uncertainty of the purity of the reference material in addition to the precision data. The Ishikawa diagram is then very simple, and so is the uncertainty calculation. This advantage is given by the loss of information about the parameters that influence the measurement uncertaint

The h Index – Help or Hype?

Three years ago a bibliometric index for the qualification of a person's scientific output was proposed by Hirsch, the so-called h index. This is an integer number which combines the number of papers of an author and the number of citations they gathered. Thus the h index is an indicator for both the productivity and the impact of a scientist. This paper presents the properties of the h index and the great attention it attracted within a short time. Numerous other indices, claimed to be better than the original, were proposed in the meantime. These developments are discussed critically

Error Tracking Down: A Peculiar Playground?

Errors in an analytical method are often not recognized as such or are underrated. Therefore, it is useful to compile and publish them. Error tracking down can even be an exciting field of research. Two different errors which can occur in chromatography are presented: The area of poorly resolved peaks cannot be integrated accurately by the usual integrators or data systems due to geometrical reasons. Second, injected air can give rise to a retained peak in HPLC. Air injection can happen during a malfunction of the autosampler but the extra peak is unwanted because it can overlap with the analyte peaks

The Uncertainty of Weighing Data Obtained with Electronic Analytical Balances

Abstract.: Weighing is a common task in any chemical laboratory and weighing data are associated with some uncertainty, as this is common with all other working procedures and their data. This paper presents the influence factors which are part of the combined measurement uncertainty of a mass determination and their interplay, namely the technical specifications of the balance (repeatability, nonlinearity, sensitivity tolerance, and temperature coefficient of the sensitivity) and the effect of air buoyancy. Depending on the net and gross weight, the densities involved (density of air and of the weighing object in relation to the density of the reference weights) and the uncertainties of these densities the relative uncertainty of weighing data is often in the 10−5 to 10−4 range (10 to 100 ppm). It must be kept in mind that such low values can only be obtained with simple weighing goods, i.e. in the absence of disturbances such as electrostatic charges, air drafts, evaporation, or water adsorption phenomen

The Influence of Climate Conditions on Weighing Results

Abstract.: The influence of atmospheric pressure, air temperature, and relative air humidity on weighing results was determined in a long-term experiment. Two magnesium and three aluminium cylinders were weighed in a room without air conditioning over a period of more than three months. The climate parameters were automatically registered every 10 minutes. The climate data allow to calculate the masses from the weighing values which are subject to air buoyancy. It is then possible to check the validity of the empirical Schwartz equation for the calculation of the air density. The match between theory and experimental results is excellent for the influence of pressure and temperature and is weaker for the influence of humidity. The influence of this latter parameter on weight values is rather low and may be corrupted by water adsorption effects on the surfaces. It was found that the climate parameters can be looked at as triangular distributions rather than the previously proposed rectangular ones for the calculation of the weighing uncertainty budge

A cell atlas of human thymic development defines T cell repertoire formation.

The thymus provides a nurturing environment for the differentiation and selection of T cells, a process orchestrated by their interaction with multiple thymic cell types. We used single-cell RNA sequencing to create a cell census of the human thymus across the life span and to reconstruct T cell differentiation trajectories and T cell receptor (TCR) recombination kinetics. Using this approach, we identified and located in situ CD8αα+ T cell populations, thymic fibroblast subtypes, and activated dendritic cell states. In addition, we reveal a bias in TCR recombination and selection, which is attributed to genomic position and the kinetics of lineage commitment. Taken together, our data provide a comprehensive atlas of the human thymus across the life span with new insights into human T cell development

The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder