Influence of the residual stress state of coatings on the wear behavior in external turning of AISI 4140 and Ti–6Al–4V

The residual stress state of coatings influences tool life and performance in machining significantly. Due to thermo-mechanical loads during the cutting process the coatings require tailored properties. Beside the coating structure the two most important properties are the residual stress state and the chemical composition of the coating. Therefore, the influence of these two properties is investigated in this study, comparing the cutting performance in continuous and interrupted cutting of 42CrMo4 (AISI 4140) and Ti–6Al–4V. It is shown that the residual stress states of the coating close to the surface and close to the substrate are important for the wear behavior. High compressive residual stresses near the substrate combined with a material-optimized composition increase the resistance against chipping. Flank wear resistance increases with high compressive residual stresses near the surface and decreasing stresses towards the substrate.     

13C-NMR Spectroscopic Detection of Malto-oligosaccharide Complexes

Fragments of amylose were enzymatically synthesized and purified to α-(a→4)-glucans of well defined degress of polymerization by preparative size exclusion chromatography. Maltooligosaccharides from DP 3 to 12 were subjected to ¹³C-NMR-spectroscopy. The addition of iodine as a complexing agent selectively affected the carbon atoms involved in the glycosidic bond. Resonances of C-1 and C-4 experienced a dramatic downfield shift. This is interpreted as a change of conformation of the amylose helix. The shift differences can be measured conveniently and be used for calculations of complex stability constants. Maltohexaose and higher saccharides gave strong effects upon complexation, indicating that one helical turn brings about a gain in helical stability. No lower chain-length limit for the complex-forming capacity was observed. Even the smallest fragments of amylose showed complexing behaviour.     

C/C-SiC component for metallic phase change materials

Thanks to their high energy density and thermal conductivity, metallic Phase Change Materials (mPCM) have shown great potential to improve the performance of thermal energy storage systems. However, the commercial application of mPCM is still limited due to their corrosion behavior with conventional container materials. This work first addresses on a fundamental level, whether carbon-based composite-ceramics are suitable for corrosion critical components in a thermal storage system. The compatibility between the mPCM AlSi₁₂ and the Liquid Silicon Infiltration (LSI)-based carbon fiber reinforced silicon carbide (C/C-SiC) composite is then investigated via contact angle measurements, microstructure analysis, and mechanical testing after exposure. The results reveal that the C/C-SiC composite maintains its mechanical properties and microstructure after exposure in the strongly corrosive mPCM. Based on these results, efforts were made to design and manufacture a container out of C/C-SiC for the housing of mPCM in vehicle application. The stability of the component filled with mPCM was proven nondestructively via computer tomography (CT). Successful thermal input- and output as well as thermal storage ability were demonstrated using a system calorimeter under conditions similar to the application. The investigated C/C-SiC composite has significant application potential as a structural material for thermal energy storage systems with mPCM.     

Bolus ingestion of white and green tea increases the concentration of several flavan‐3‐ols in plasma,but does not affect markers of oxidative stress in healthy non‐smokers

White tea (WT) is rich in flavan‐3‐ols as green tea (GT) and might provide health protective effects due to the strong antioxidant properties of flavan‐3‐ols. Since intervention studies with WT are lacking, we evaluated the effects of WT consumption on antioxidant status, antioxidant capacity and biomarkers of oxidative stress compared to water and GT. After an overnight fast, 70 healthy non‐smokers were randomized to consume 600 mL of WT, GT or water (control). Plasma (epi‐)catechin and epi(gallo)catechingallate, antioxidant capacity (Folin assay, trolox equivalent antioxidant capacity test), 8‐iso‐prostaglandin F_2α, ascorbic acid and uric acid were determined before and several times within 8 h after consumption. DNA strand breaks were measured in vivo and ex vivo (H₂O₂ stimulation) in leukocytes. Plasma flavan‐3‐ols significantly increased after WT and GT ingestion. Trolox equivalent antioxidant capacity was lower after 5 h in controls versus WT (p=0.031) and GT (p=0.005). Folin‐Ciocalteu reducing capacity, ascorbic and uric acid as well as markers of oxidative stress (8‐iso‐prostaglandin‐F_2α, DNA strand breaks) were not affected by the beverages. A short‐term increase of catechins does not change plasma antioxidant capacity in healthy subjects. Conclusions with respect to health protective effects of WT and GT on the basis of these biomarkers can, thus, not be drawn.     

Elucidation of a polychlorinated bipyrrole structure using enantioselective GC

A hexachloro congener (Q1-hex) of the natural heptachloro-1'-methyl-1,2'-bipyrrole Q1 was recently observed as a byproduct of the Q1 synthesis. NMR investigation confirmed that Q1-hex has a proton on a carbon in beta-position to a nitrogen. Three isomers are possible that fulfill this prerequisite; unfortunately, however, the NMR data were not sufficient to distinguish among the three structural variants. Because only one isomer of Q1-hex is expected to be chiral, we utilized enantioselective gas chromatography and two chiral stationary phases to separate the atropisomers. Baseline separation of the Q1-hex atropisomers was obtained on 10% chemically bonded permethyl-beta-cyclodextrin. In the full-scan mode, it was found that Q1-hex was racemic and that both atropisomers had identical mass fragmentation patterns. Partial resolution of the Q1-hex atropisomers was obtained on 25% tert-butyldimethylsilylated beta-cyclodextrin diluted in PS086. In concert with previous NMR data, these enantioseparations prove that the structure of Q1-hex is 2,3,3',4',5,5'-hexachloro-1'-methyl-1,2'-bipyrrole (5). To our knowledge, this is the first gas chromatographic separation of atropisomers of an axially chiral 1,2'-bipyrrole derivative.     

An Integrated Framework for Implementing Quality of Network Concepts

This paper presents an integrated framework for describing and implementing quality of network (QoN) concepts. It focuses on identifying a systems engineering framework for better understanding how to specify and implement QoN concepts. We demonstrate, by means of several examples, that the quality of service interfaces between the end user and the underlying network are very important. Finally, we provide insights as to future development efforts needed to realize the goal of high quality networks.     

Observer of the human cardiac sympathetic nerve activity using noncausal blind source separation

We present a novel method for the blind reconstruction of the cardiac sympathetic nerve activity (CSNA) in the low-frequency (LF) band (0.04-0.15 Hz) using only heart rate and arterial blood pressure. The originality of the method consists in the application of blind source separation techniques to obtain an observer of CSNA. We show how this observer can be deduced from a linear model of the cardiovascular system by introduction of the fundamental assumptions about the independence of the cardiac sympathetic an parasympathetic outflow. In cardiovascular applications, the reliability of the observer has been assessed by verification of the fundamental assumption for the given data. A primer qualitative validation has been performed using the muscle sympathetic nerve activity as an indirect indicator of CSNA. Very satisfying and promising results have been obtained. Moreover, we have performed quantitative validations of the observer in various experimental conditions known to elicit selectively cardiac sympathetic or parasympathetic response. The experimental conditions include a supine-to-60 degrees tilt test, indirect sympathetic stimulation/inhibition by medication, and sympathetic stimulation by isometric handgrip. We show that the observer allows to highlight changing levels of the cardiac sympathetic activity in the LF band in all these experimental conditions.     

Effect of dissociation pulse circuit inductance on the CuCl laser

The performance of the double-pulsed CuCI laser is improved by a decrease in the inductance of the dissociation pulse circuit. Higher efficiency is obtained due to a larger ground state copper atom population and lower optimum dissociation energy.