Effects of Cyclic Loading on the Uniaxial Behavior of Nitinol

The widespread development and use of implants made from NiTi is accompanied by the publication of many NiTi material characterization studies. These publications have increased significantly the knowledge about the mechanical properties of NiTi. However, this knowledge also increased the complexity of the numerical simulation of NiTi implants or devices. This study is focused on the uniaxial behavior of NiTi tubing due to cyclic loading and had the goal to deliver both precise and application-oriented results. Single aspects of this study have already been published (Wagner in Ein Beitrag zur strukturellen und funktionalen Ermüdung von Drähten und Federn aus NiTi-Formgedaechtnislegierungen, Ph.D. Thesis, 2005; Eucken and Duerig in Acta Metall 37:2245-2252, 1989; Yawny et al. in Z Metallkd 96:608-618, 2005); however, there is no publication known that shows all the single effects combined in a ??duty cycle case.?? It was of particular importance to summarize the main effects of pre-strain and subsequent small or large strain amplitudes on the material properties. The phenomena observed were captured in an extended Abaqus^® Nitinol material model, presented by Rebelo et al. (A Material Model for the Cyclic Behavior of Nitinol, SMST Extended Abstracts 2010). The cyclic tensile tests were performed using a video extensometer to obtain accurate strain measurement on small electro-polished dog-bone specimen that were incorporated into a stent framework so that standard manufacturing methods could be used for the fabrication. This study indicates that a prestrain beyond 6% strain alters the transformation plateaus and if the cyclic displacement amplitude is large enough, additional permanent deformations are observed, the lower plateau and most notably the upper plateau change. The changes to the upper plateau are very interesting in the sense that an additional stress plateau develops: its ??start stress?? is lowered thereby creating a new plateau up to the highest level of cyclic strain, followed by resuming the original plateau until full transformation. This study was conducted in the course of the work of a consortium of several stent manufacturers, SAFE Technology Limited and Dassault Systèmes Simulia Corp., dedicated to the development of fatigue laws suitable for life prediction of Nitinol devices.     

Hydrogeochemische Hintergrundwerte der Grundw?sser Deutschlands als Web Map Service

One of the main objectives of the EC water framework directive is to ensure good chemical status for all groundwater bodies. For this reason the geological surveys of Germany have produced a nationwide map of the background values of groundwater. Only naturally occurring inorganic parameters were taken into account, including the relevant major and trace elements. Based on the hydrogeological map of Germany at the scale of 1:200,000 (HüK 200), and its delimited hydrogeological regions, a total of 186 hydrogeochemical units were defined and mapped geochemically. This involved collection of more than 52,000 groundwater samples in a database and allocation to their appropriate hydrogeochemical units. In order to separate anomalies within the data-sets from the underlying normal population, probability nets were used as a statistical tool. The procedure allowed to determine the normal populations of the investigated parameters within the hydrogeochemical units and to quantify them in the form of percentiles. The resulting hydrogeochemical background values are accessible through an internet web map service that includes an online map application. The main intention of this technical note is to inform the reader about the existing internet service, which necessitates some web-site content duplication.     

Specific site selection in RNA resulting from a combination of nonspecific secondary structure and -CCR- boxes: initiation of minus strand synthesis by turnip yellow mosaic virus RNA-dependent RNA polymerase

A turnip yellow mosaic virus RNA-dependent RNA polymerase activity was used to study the template requirements for in vitro minus strand synthesis, which is initiated specifically opposite the 3'-CCA that terminates the 3'-tRNA-like structure. A deletion survey confirmed earlier results suggesting the absence of minus strand promoter elements upstream of the pseudoknotted acceptor stem and 3'-terminus. Reiteration of this 27-nt domain provided two competing initiation sites. By varying the added downstream element, it was shown that the pseudoknotted domain could be functionally replaced by various simple stem/loops, although with some decrease in activity. The addition of varying numbers of consecutive -CCA- triplets to the 3' end of the tRNA-like structure resulted in accurate initiation from each added triplet. A similar spectrum of initiations occurred with an unstructured RNA consisting of 12 consecutive -CCA- triplets and no additional viral sequence. Substitution mutations revealed no influence on minus strand synthesis of the identity of the nucleotide immediately upstream of a -CC- initiation site, but a preference for a purine immediately downstream. The introduction of secondary structure into the linear template showed that the usage of potential -CCR- initiation sites is influenced by nonspecific secondary structure. We conclude that specificity arises from the requirement that a -CCR- sequence be sterically accessible. This mechanism is only applicable to interactions that do not involve RNA unwinding during site selection, but may be used commonly in positive strand RNA virus replication and be applicable to other RNA-protein interactions.     

Lethal tuberculosis in interleukin-6-deficient mutant mice

Tuberculosis is a chronic infectious disease which causes major health problems globally. Acquired resistance is mediated by T lymphocytes and executed by activated macrophages. In vitro studies have emphasized the importance of macrophage activation for mycobacterial growth inhibition. In vivo, the protective host response is focused on granulomatous lesions in which Mycobacterium tuberculosis is contained. A cellular immune response of the T helper 1 (Th1) type is considered central for control of tuberculosis. Using interleukin-6 (IL-6)-deficient mice, we here demonstrate a crucial role of this pluripotent cytokine in protection against M. tuberculosis but not against Mycobacterium bovis BCG. Infection with M. tuberculosis was lethal for the IL-6-deficient mice at inocula that were still controlled by IL-6-competent mice. Spleen cells from M. tuberculosis-infected IL-6-/- mouse mutants produced elevated levels of IL-4 and reduced levels of gamma interferon compared to the control levels. Cytofluorometric analyses of spleen cells from M. tuberculosis-infected mice revealed more-profound alterations in T-cell ratios in IL-6-/- mice than in control mice. We assume that IL-6 contributes to host resistance by its proinflammatory activity and by its influence on cytokine secretion.     

The TYMV tRNA-like structure

The genomic RNA from turnip yellow mosaic virus presents a 3'-end functionally and structurally related to tRNAs. This report summarizes our knowledge about the peculiar structure of the tRNA-like domain and its interaction with tRNA specific proteins, like RNAse P, tRNA nucleotidyl-transferase, aminoacyl-tRNA synthetases, and elongation factors. It discusses also the biological role of this structure in the viral life cycle. A brief survey of our knowledge of other tRNA mimicries in biological systems, as well as their relevance for understanding canonical tRNA, will also be presented.     

Specifity and sensitivity of the inhibition of drug metabolism following inhalation of carbon disulphide-air mixtures

A single 8-h exposure of adult female Wistar rats to 20 ppm carbon disulphide (CS2), the threshold limit value (TLV) in several countries, was sufficient to cause inhibition of the following drug-metabolizing reactions: formation of trichloroethanol and trichloroacetic acid from trichloroethylene (aliphatic C-hydroxylation), formation of 4-hydroxyantipyrine from antipyrine (quasi-aromatic C-hydroxylation), formation of acetaminophenol from acetanilid (aromatic C-hydroxylation) and phenacetin (oxidative odealkylation), respectively, and formation of 4-aminoantipyrine from aminopyrine (oxidative N-demethylation). The behaviour of these effects was dependent on the dose of CS2 administered in that the inhibitory process was enhanced when increasing the concentration to (50), 100, 200, and 400 ppm. The respective changes could be demonstrated by a short-duration (6-h) reduction in the urinary excretion of the metabolites. In the case of trichloroethylene the limitation in metabolite formation persisted for as long as 36 h due to the varying rate of formation of trichloroethanol and trichloroacetic acid. This deficiency in excretion was compensated in part during the subsequent elimination phase (up to 24 and 36 h, respectively), an observation which suggests the rapid reversibility of the alteration. As shown by the respective prolongation of the hexobarbital sleeping time in the rat, the side-chain oxidation of hexobarbital to ketohexobarbital was increasingly inhibited by rising concentrations of CS2 in the range of 20 to 400 ppm/8 h. On the basis of the present results it is concluded that CS2 also inhibits various oxygenases of the microsomal enzyme system. In adult female NMRI mice a significant inhibition of the microsomal procaine-hydrolyzing esterase of the liver was observed only after 400 ppm/8 h; however, this limitation did not affect the LD50 of procaine-HCl, particularly as the corresponding serum esterase activity also remained uninfluenced. The aromatic N-acetylation of sulphisomidine and the quasi-aromatic N-acetylation of 4-aminoantipyrine in rats failed to be significantly reduced by CS2 even after 400 ppm/8 h, nor did the same dose of CS2 affect the glucuronidation of 4-hydroxyantipyrine in the same animal species. It is concluded from the above results that the specificity and sensitivity of the inhibition of drug metabolism observed in small laboratory animals is probably similar to that prevailing in man. This assumption has already been substantiated for the oxidative N-demethylation of aminopyrine.     

Characterization of Laminar Transient Flow Regimes and Mixing in T-shaped Micromixers

Convective micromixers create vortices in curved channel elements allowing characteristic mixing times below 1 millisecond for gaseous and liquid media. This contribution gives an overview about the flow regimes of symmetrical 1:1 mixing in T-shaped micromixers with rectangular cross-sections for Reynolds numbers (Re) from 0.01 to 1000 in the mixing channel. First, symmetrical vortices are formed for Re > 10 in the so-called Dean flow. At Re > 140, fluid from one side swaps to the opposite side and creates a double vortex, which enhances mixing. For Re > 240, the flow becomes unsteady, and a kind of wake flow establishes. From 240 < Re < 500, the wake flow is periodic with a Strouhal number of about 0.23. The mixing quality also shows a periodic behavior and reaches its maximum at this point. With further increasing the Re number, the flow becomes chaotic, and the two components are often flowing parallel in the mixing channel, which decreases the mixing quality. Besides detailed CFD simulations, the periodic flow is observed in experimental studies with stroboscopic imaging. The decreasing mixing quality is also reflected in a lower selectivity of parallel chemical test reactions for Re > 500. With the knowledge of the flow regimes in microchannels, design criteria can be formulated for efficient mixing devices.     

THE CONVERSION OF Rh(m) CHLOROCOMPLEXES TO BROMOCOMPLEXES AND THEIR SOLVENT EXTRACTION BEHAVIOUR

ABSTRACT

This paper details investigations on the conversion of Rh(HI) chlorocomplexes to bromocomplexes, followed by the extraction of the tatter with an alkylated 8-hydroxyquinoline and their subsequent stripping with hydrobromic acid. It was found that in contrast to Rh(III) chlorocomplexes, the analogous bromocomplexes underwent significantly less aquation, thus rendering themselves to qualitative solvent extraction. Of the extractants tested, Kelex 100 proved to give the best performance. On the other hand, stripping was problematic. It was apparent that complex transformation of the extracted Rh(HI) occurred in the organic phase upon aging, which resulted in metal lock up.     

Epigenetic Clocks Are Not Accelerated in COVID-19 Patients

Age is a major risk factor for severe outcome of the 2019 coronavirus disease (COVID-19). In this study, we followed the hypothesis that particularly patients with accelerated epigenetic age are affected by severe outcomes of COVID-19. We investigated various DNA methylation datasets of blood samples with epigenetic aging signatures and performed targeted bisulfite amplicon sequencing. Overall, epigenetic clocks closely correlated with the chronological age of patients, either with or without acute respiratory distress syndrome. Furthermore, lymphocytes did not reveal significantly accelerated telomere attrition. Thus, these biomarkers cannot reliably predict higher risk for severe COVID-19 infection in elderly patients.