Entropy as a measure of the performance of phosphor materials used in medical imaging radiation detectors

In information theory, entropy expresses the information gain obtained after detection of a signal concerning the state of a parameter of interest. In this study, entropy has been expressed in terms of physical quantities (emitted optical fluence and MTF) related to the imaging performance of phosphor materials, which are employed in medical imaging radiation detectors. Four phosphor materials, used in the form of laboratory-prepared fluorescent layers (screens), were compared on the basis of their entropy performance. Measurements were performed using 30- and 80-kVp X-ray beams often employed in X-ray imaging. Results showed that phosphor materials with high density and effective atomic number exhibit high entropy performance, especially at the higher X-ray tube voltage of 80 kVp. Entropy values are also affected by the type of activator, which determines the intrinsic X-ray-to-light conversion efficiency, and the spectrum of emitted light. The proximity of the incident X-ray quanta energy to the energy of the K-shell threshold for photoelectric absorption is an additional important factor which increases entropy. This effect was more apparent in the performance of yttrium-based phosphors at the lower voltage of 30 kVp. Received: 7 January 2000 / Accepted: 28 March 2000 / Published online: 23 August 2000     

The epistemic gossip problem

In the gossip problem information (‘secrets’) must be shared among a certain number of agents using the minimum number of calls. We extend the gossip problem to arbitrary epistemic depths. For example, we may require not only that all agents know all secrets but also that all agents know that all agents know all secrets. We give optimal protocols for various versions of this epistemic gossip problem, depending on the graph of communication links, in the case of two-way communication, one-way communication and parallel communication. We show, among other things, that increasing epistemic depth from 1 (all agents know all secrets) to 2 (so that all agents know that all agents know all secrets) does not double the required number of calls but increases this number by $3∕2$ (for a complete graph). We also show that the following counter-intuitive result generalises to the epistemic gossip problem: asymptotically the same number of calls are required whether calls are two-way or one-way.     

(E)‐4,4′‐Bis(1,3‐benzoxazol‐2‐yl)stilbene at 150 and 375 K

The title compound, a chromophore of formula C₂₈H₁₈N₂O₂, crystallizes with the molecule lying on an inversion centre to give one‐half of a crystallographically independent molecule in the asymmetric unit. The molecule is almost planar, with slight deviation of the benzene rings from the mean molecular plane. The structure is characterized by a herringbone packing arrangement arising from C—H...π and π–π intermolecular interactions. The benzoxazole group is disordered between two orientations, with occupancy factors of 0.669 (10) and 0.331 (10) at 150 K [0.712 (7) and 0.288 (7) at 375 K].     

Volatile profiling reveals intracellular metabolic changes in <Emphasis Type="Italic">Aspergillus parasiticus</Emphasis>: <Emphasis Type="Italic">veA</Emphasis> regulates branched chain amino acid and ethanol metabolism

Background  

Filamentous fungi in the genus Aspergillus produce a variety of natural products, including aflatoxin, the most potent naturally occurring carcinogen known. Aflatoxin biosynthesis, one of the most highly characterized secondary metabolic pathways, offers a model system to study secondary metabolism in eukaryotes. To control or customize biosynthesis of natural products we must understand how secondary metabolism integrates into the overall cellular metabolic network. By applying a metabolomics approach we analyzed volatile compounds synthesized by Aspergillus parasiticus in an attempt to define the association of secondary metabolism with other metabolic and cellular processes.     

The multicriteria analysis for construction of benchmarkers to support the Clinical Engineering in the Healthcare Technology Management

In developing countries, approximately half of the healthcare equipments are not in full use and the main cause of this is the inadequate management of them. The Clinical Engineering might face this problem in the healthcare environment analyzing the equipment with a health technological process perspective to identify opportunities of improvements. Generally, the inadequate management is a result of lack of systemized and contextualized information about the health technological process. The effort to make an adequate management generates an increasing interest in the use of benchmarker. Currently, the benchmarkers used by the Clinical Engineering are not representative of a health technological process as a whole. Health technological process concept is stated in this article. The multicriteria analysis methodology MCDA (Multicriteria Decision Aid) is used to obtain benchmarkers and to identify opportunities of improvements, thus generating conditions for that the Clinical Engineering consolidates its relevant contribution for the healthcare.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

Observation of a new type of electron bubble in superfluid helium

We report on the observation of a new type of electron bubble in superfluid helium-4. This object appears to be larger than the normal electron bubble and is associated with the presence of quantized vortices in the liquid.