The simple equation used to calculate the intrinsic photopeak efficiency of a semiconductor germanium detector consisting of one factor which allows for the x‐ray transmission through the window and another factor which takes into account the photoelectric interaction in the active volume of the detector has proved to be insufficient since it does not consider the escape of photons with characteristic line energies. An analytical expression embodying all physical processes for photon interaction, including the escape of characteristic photons, is proposed; such an expression corrects the simplified equation shown in modern textbooks. When the detector’s thickness is known, the model can be reduced to an expression with one free parameter, which was chosen to be the equivalent beryllium thickness, in order to describe the attenuation of the incident photon beam. The value of the parameter is finally obtained by comparison of the tabulated Kα/Kβ as compared to the measured Kα/Kβ values for thin, high‐purity samples. The efficiency curves for two cylindrical 5 and 7 mm thick germanium detectors were obtained with the sole assumption that photons escape from the upper, or radiation entrance, detector face. Finally, Monte Carlo simulations of the detection of x‐rays with these detectors with an ad hoc developed program show that the proposed parametric function is useful to fit results over a broad range of energies. © 1998 John Wiley & Sons, Ltd.

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The fundamental parameters method has been extensively used for XRF analysis applications. One of the method's requirements is an explicit knowledge of the excitation beam used, which is not always available. Recently, a methodology that avoids the direct reconstruction of the x-ray beam using a non-explicit representation was published. In this paper the results of a multicomponent analysis of stainless-steel samples with this methodology are presented. The concentrations obtained were compared with NBS certified values and very good agreement was found. Two parameteric models of beam description were also used in order to compare the goodness of each spectral representation (the non-explicit model and the parametric ones) to perform x-ray fluorescence analysis. The proposed methodology showed better results, in terms of accuracy and precision, than the standard methodology, in the case of a continuous spectrum of the exciting beam. When the spectrum of the exciting beam exhibits discontinuities (i.e. absorption edges and characteristic lines), the results of the three descriptions are comparable. It was demonstrated that the fundamental parameters method without an explicit knowledge of the excitation beam is suitable for use in x-ray fluorescence analysis.

Clear epigenetic signatures were found in hypertensive and pre-hypertensive patients using DNA methylation data and neural networks in a classification algorithm. It is shown how by selecting an appropriate subset of CpGs it is possible to achieve a mean accuracy classification of 86% for distinguishing control and hypertensive (and pre-hypertensive) patients using only 2239 CpGs. Furthermore, it is also possible to obtain a statistically comparable model achieving an 83% mean accuracy using only 22 CpGs. Both of these approaches represent a substantial improvement over using the entire amount of available CpGs, which resulted in the neural network not generating accurate classifications. An optimization approach is followed to select the CpGs to be used as the base for a model distinguishing between hypertensive and pre-hypertensive individuals. It is shown that it is possible to find methylation signatures using machine learning techniques, which can be applied to distinguish between control (healthy) individuals, pre-hypertensive individuals and hypertensive individuals, illustrating an associated epigenetic impact. Identifying epigenetic signatures might lead to more targeted treatments for patients in the future.

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This work suggests a theoretical approach for the description of a primary x‐ray beam by means of the K fluorescence which it excites on a set of thin targets made of pure elements. Physical quantities, defined as weighted integrals over hv of the photon spectral distribution, are obtained directly as weighted integrals of the Kα yields over the variable Ez (the ionization energy of the K shell of the element with atomic number Z), without needing any explicit reconstruction of the spectral distribution. The set of Kα yields produced by an x‐ray beam as a function of Ez is a functional description of the exciting beam. Theoretically, such a description is suited to x‐ray fluorescence analysis.