Crack growth in ultrafine-grained AA6063 produced by equal-channel angular pressing

Crack growth behaviour of ultrafine-grained AA6063, processed by equal-channel angular pressing (ECAP) via route E at room temperature, was evaluated with special emphasis on the effect of grain size distribution and work hardening. A bimodal, two times ECAPed condition and a monomodal ultrafine-grained condition after eight ECAP passes are compared with the coarse grained peak aged material. Depending on their microstructure, the ECAPed materials show significantly lower fatigue threshold values (ΔK _th) and higher crack growth rates (da/dN) than their coarse grained counterparts. Micrographs of the crack propagation surfaces reveal the reduced grain size as major key to increased crack growth rates of the ECAPed material, as it influences roughness-induced crack closure and crack deflections. Furthermore, the effects of other features, such as ductility, work hardening capability and grain boundary characteristics, are discussed.     

UV inactivation, liquid-holding recovery, and photoreactivation of Escherichia coli O157 and other pathogenic Escherichia coli strains in water

Drinking water, water used in food production and for irrigation, water for fish farming, waste water, surface water, and recreational water have been recently recognized as a vector for the transmission of pathogenic Escherichia coli, especially serotype O157:H7. We investigated the UV (253.7 nm) inactivation behavior and the capability of dark repair (liquid-holding recovery) and photoreactivation of seven pathogenic (including three enterohemorrhagic E. coli) strains and one nonpathogenic strain of E. coli (ATCC 11229) with respect to the use of UV light for water disinfection purposes. Because most bacteria and yeast are known to be able to repair UV damage in their nucleic acids, repair mechanisms have to be considered to ensure safe water disinfection. We found a wide divergence in the UV susceptibility within the strains tested. A 6-log reduction of bacteria that fulfills the requirement for safe water disinfection was reached for the very most susceptible strain O157:H7 (CCUG 29199) at a UV fluence of 12 J/m2, whereas for the most resistant strain, O25:K98:NM, a UV fluence of about 125 J/m2 was needed. Except for one strain (O50:H7) liquid-holding recovery did not play an important role in recovery after UV irradiation. By contrast, all strains, particularly strains O25:K98:NM, O78:K80:H12, and O157:H7 (CCUG 29193), demonstrated photorepair ability. For a 6-log reduction of these strains, a UV fluence (253.7 nm) up to 300 J/m2 is required. The results reveal that the minimum fluence of 400 J/m2 demanded in the Austrian standard for water disinfection is sufficient to inactivate pathogenic E. coli. A fluence of 160 J/m2 (recommendation in Norway) or 250 J/m2 (recommendation in Switzerland) cannot be regarded as safe in that respect.     

Short communication: Evidence for methylglyoxal-mediated browning of Parmesan cheese during low temperature storage

Brown pigmentation can occasionally form in Parmesan cheese during the ripening process, creating an unappealing appearance and associated off-flavors. The browning reactions proceed at refrigerated temperatures and in the relative absence of reducing sugar, contrary to typical Maillard browning. Residual sugars, lipid oxidation products, byproducts of fermentation, and (or) enzymes may react with primary amines in cheese to form brown pigmentation and concomitantly generate volatile compounds unique to each of these reactions. Determining the volatile profiles provides a means of understanding the potential substrates involved and causative reaction pathways. This work is divided into 2 segments. The first portion characterized the pigmentation and the browning index of Parmesan cheeses with and without extensive browning. The second phase examined the volatile character of the cheeses using gas chromatography-mass spectrometry. Various pyrazines, such as 2,3,5-trimethylpyrazine and 3,5-diethyl-2-methylpyrazine, were found in the brown cheeses but were not present in the white samples. The formation of pyrazines is proposed to result from the spontaneous condensation of aminoacetone. Aminoacetone can be formed by the Strecker degradation of amino acids with methylglyoxal, the latter a byproduct of sugar fermentation. Evidence is provided to support a browning pathway mediated by the production of methylglyoxal in Parmesan cheese.     

Using Mean Field Theory to Guide Biofunctional Materials Design

Cell‐instructive characteristics of extracellular matrices (ECM) resulting from a subtle balance of biomolecular and biophysical signals must be recapitulated in engineered biomaterials to facilitate regenerative therapies. However, no material explored so far allows the independent tuning of the involved molecular and physical cues due to the inherent correlation between biopolymer concentration and material properties. Addressing the resulting challenge, a rational design strategy for ECM‐inspired biohybrid hydrogels based on multi‐armed poly(ethylene glycol) and heparin, adapting a mean field approach to identify conditions at which the balance of elastic, electrostatic, and excluded volume forces results in constant heparin concentrations within swollen polymer networks with gradually varied physical properties is introduced. Applying heparin‐based biofunctionalization schemes, multiple distinct combinations of matrix parameters could be identified to effectively stimulate the pro‐angiogenic state of human endothelial cells and the differentiation of human mesenchymal stem cells. The study demonstrates the power of joint theoretical and experimental efforts in creating bioactive materials with specifically and independently controllable characteristics.     

Investigation of a BeO-based optically stimulated luminescence dosemeter

The optical sensitivity of BeO-based luminophors has been well-known for many years. The optical stimulation of BeO with blue light is most effective. Then the dosemeters emit luminescent light in the ultraviolet-range around 325 nm. Matched on these facts a simple optically stimulated luminescence (OSL) treatment has been developed. Intense blue light-emitting diodes are used for cw-stimulation. A Hamamatsu solar blind photomultiplier detects the OSL-light. Good separation of both spectral ranges by optical filters is very important. The dosemeter has a linear dose response between approximately 20 muGy and >10 Gy. It was suggested, that a modification of stimulation conditions would allow measurements down to 1 muGy. Fading, photon energy dependence and reproducibility of OSL-signal correspond well with requirements to clinical and personal dosemeters. In addition, basic questions of the OSL-process in BeO have been investigated. A relevant point of interest was the dependency of the OSL-signal on stimulation power.     

Disinfection by-products in ballast water treatment: An evaluation of regulatory data

To reduce the global spread of invasive aquatic species, international regulations will soon require reductions of the number of organisms in ballast water discharged by ships. For this purpose, ballast water treatment systems were developed and approved by an international procedure. These systems rely on established water treatment principles which, to different degrees, have been proven to generate disinfection by-products with hazardous properties but have only scarcely been investigated in marine environments. Our study evaluates the publicly available documentation about approved ballast water treatment systems with regard to by-product formation. The most commonly employed methods are chlorination, ozonation, and ultraviolet (UV) irradiation. Chlorination systems generate trihalomethanes, halogenated acetic acids, and bromate in substantially larger quantities than reported for other areas of application. Levels are highest in brackish water, and brominated species predominate, in particular bromoform and dibromoacetic acid. Ozonation, which is less frequently utilized, produces bromoform in lower concentrations but forms higher levels of bromate, both of which were effectively reduced by active carbon treatment. In systems based on UV radiation, medium pressure lamps are employed as well as UV-induced advanced oxidation. For all UV systems, by-product formation is reported only occasionally. The most notable observations were small increases in nitrite, hydrogen peroxide, halogenated methanes and acetic acids. The assessment of by-product formation during ballast water treatment is limited by the lacking completeness and quality of available information. This concerns the extent and statistical characterisation of chemical analysis as well as the documentation of the test water parameters.     

维生素A强化主食的国际研究

世界卫生组织1995年报道，维生素A缺乏是60个发展中国家的一个主要公共卫生问题，估计受影响的学龄前儿童约为0．78亿；而联合国儿童基金会（UNICEF）的微量营养素项目1998年报道，维生素A缺乏是78个发展中国家的主要公共卫生问题之一，估计受影响学龄前儿童为2．63亿；此外，发展中国家的孕妇和育龄妇女也是VA缺乏的高危人群。     

Consciousness of attention and expectancy as reflected in event-related potentials and reaction times.

The effects of conscious expectancies and attention on event-related potentials (ERPs) and choice reaction times (RTs) and their modulation by stimulus sequence were studied. Ss retrospectively reported their expectancy of, and attention to, the terminal tones of short series. ERPs and RTs showed the usual sequential effects that were modulated by practice. As ratings were affected by only a few of the stimulus sequence, conscious access to sequence-based expectancy or attention appears to be fragmentary. Increased P300 amplitude with attention indicates conscious access to processing capacity. RTs and P300 latencies suggest stimulus processing time to decrease with sequence-based and consciously accessible expectancy. Differential effects of stimulus sequences and conscious expectancies on P300 amplitude indicate influences of two varieties of expectancy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

3D Printing of Dual-Cure Networks Based on (Meth)acrylate/Bispropargyl Ether Building Blocks

In recent years, dual-cure chemistry has been exploited to realize interpenetrating networks (IPNs) that provide enhanced thermo-mechanical properties. In this contribution, photoinduced curing of (meth)acrylates is used to build the desired 3D structure, whereas the thermally triggered polymerization reaction of 2H-chromene functionalized building blocks is utilized to create the IPN. This strategy combines the advantages of traditional UV-curable monomers with high-performance thermosets. After the successful synthesis of the bispropargyl ether derivative, i.e., 4,4′-(propane-2,2-diyl)bis((ethynyloxy)benzene), its thermally induced conversion to the corresponding 2H chromene functionalized prepolymer is studied by Fourier-transform infrared spectroscopy and gel permeation chromatography. The network formation as well as the printability of various formulations containing different amounts of the thermo-curable building block is investigated. The obtained IPNs provide enhanced thermo-mechanical properties making these resins suitable for the additive manufacturing of functional 3D parts for high-performance applications.     

High-Throughput Alloy Development Using Advanced Characterization Techniques During Directed Energy Deposition Additive Manufacturing

In laser-based direct energy deposition (DED-LB) additive manufacturing (AM), wire or powder materials are melted by a high-power laser beam. Process-specific characteristics enable robust in situ fabrication of compositionally graded materials, e.g., through an adaption of powder mass flow from independent hoppers. Based on the high flexibility of this approach, pathways toward multimaterial AM have been unlocked. Obviously, such characteristics enable high-throughput alloy development. However, rapid alloy development demands substantial characterization efforts to assess phase and microstructural evolution. So far, property analysis is considered as the limiting factor for these high-throughput approaches. Herein, the use of high-brilliance X-Ray analysis and subsequent micropillar compression testing are introduced to tackle these challenges. As a proof of concept, their application to a compositionally graded material made from AISI 316L stainless steel and a CoCrMo alloy is presented. The results obtained reveal that X-Ray analysis can be exploited to evaluate process robustness, chemical characteristics, and phase composition within the gradient regions. Moreover, the use of micropillar compression testing provides spatially resolved insights into the mechanical properties of the gradient regions. The combination of both characterization techniques eventually opens pathways toward a robust and time-efficient alloy development using powder-fed DED-LB (DED-LB/P).