Viscoelastic study of ionomers

Stress-relaxation curves were obtained for ionomers containing different cations, per cents of ionization, and thermal treatments. Differences in the rheological behavior were found to depend more on the ionization level than on the ion. A recently proposed model for ionomers is discussed and found to be consistent with these results. In terms of this model the degree of ionization in the polymer acts as a regulator for the growth of small oriented lamellar (crystalline) regions. In the most general terms, the mechanical behavior and strength of ionomers appears dominated by the existence of “hard” regions interspersed among “soft” regions. In the polymers studied here there was some slight crystallinity; however, similar effects and explanations are probably suitable for amorphous “ionomers.” Toughness was also found in some completely amorphous carboxylcontaining copolymers without added ionic salts. The same explanation of “hard” regions interspersed among soft regions is also valid here. The “blocky” nature of the copolymerization may play a role in setting up this type of structure.     

Examining cognitive function across the lifespan using a mobile application

Many studies conducted in a laboratory or university setting are limited by funding, personnel, space, and time constraints. In the present study, we introduce a method of data collection using a mobile application that circumvents these typical experiment administration issues. Using the application, we examined cross-sectional age differences in cognitive function. We obtained data from more than 15,000 participants and replicated specific patterns of age-related differences in cognition. Using a subset of these participants, we also examined the processing speed account of age-related cognitive differences, and the association of exercise and leisure activity with cognitive function across the lifespan. We discuss the relative advantages and disadvantages of data collection with a mobile application, and provide recommendations for the use of this method in research.     

Review on direct metal laser deposition manufacturing technology for the Ti-6Al-4V alloy

Direct laser metal deposition (DLMD) is a breaking edge laser-based additive manufacturing (LAM) technique with the possibility of changing the perception     

喧嚣中的静谧生活

由于地面和墙面都是浅色的缘故，一进房间就可以感受到宽敞明亮。融入着欧式元素的房间透露着高贵气质、繁茂的花朵使房间不至于显得过于沉静。整个房间的风格一致，浅色地面及墙面、银灰色的窗帘、红橡木饰面的家具、金色边框、简约而大气，沉稳而舒适，没有一丝压抑感，落地窗外的绿色风光随时使你感到清新。[编者按]     

Functional and ultrastructural effects of essential fatty acid deficiency in kidney epithelial cells

Madin-Darby canine kidney (MDCK) epithelial cells were grown in culture medium supplemented with 1% fetal bovine serum (FBS) to provide a cell culture model of essential fatty acid deficiency (EFAD). 5,8,11-Eicosatrienoic acid (20∶3n−9) accumulated in cellular phospholipids, and arachidonic acid (20∶4) decreased. A large increase in cellular cholesterol/phospholipid ratio was observed. Hemicyst formation was greatly reduced from normal levels in the EFAD-MDCK cells. Scanning and transmission electron microscopy revealed that EFAD-MDCK were much flatter than their normal counterparts. They had much less dense surface microvilli, mitochondria and other organelles were very sparse, except in the perinuclear area, and much of the peripheral cytoplasm was amorphous. The EFAD was rapidly reversed by the addition of as little as 10 μM linoleic or arachidonic acid to the medium. Cells supplemented with 10% FBS, the usual culture condition, displayed borderline EFAD, with intermediate levels of 20∶3n−9 and 20∶4 and hemicyst formation. These studies suggest that EFAD reduces water and electrolyte transport in renal tubular epithelium.     

The application of reactive dyes to cotton by a wet-on-wet cold pad-batch method

Cotton ha been dyed with reactive dyes by both wet-on-wet (WOW) and wet-on-dry (WOD) cold pad-batch processes, and by conventional exhaust methods. The colour yields, in terms of the Kubelka-Munk values as a function of the amount of fixed dye, showed that the WOW method required less fixed dye to produce a given depth of shade than the other methods. It is proposed that the higher colour yields are a consequence of limited dye penetration into the cotton fibre. Compared with exhaust dyeings, WOW and WOD dyeings were clearly ring dyed but, unfortunately, no definitive difference in the degree of dye penetration into the cotton fibres was found despite their colour yield differences. Although ring dyeings often have inferior fastness properties, the WOW dyeings were of equal or slightly superior fastness to repeated washing and to normal daylight in comparison with the other dyeings     

Effects of Heat Treatment in a Wet Hydrogen Atmosphere on the Reliability of Sintered α-Silicon Carbide

Sintered α-SiC was exposed, for times up to 2 h, to a flowing wet H₂ atmosphere ( P _H2O= 1 × 10^-4 MPa) at temperatures of 1300°, 1400°, and 1500°C. The effect of such conditions on the reliability of the ceramic was estimated by comparing the Weibull modulus of the groups of specimens, tested in four-point flexure, before and after exposure. The Weibull modulus of as-polished specimens was 6.7, indicating a wide variation in room-temperature flexural strength. The Weibull modulus was increased to 14.2 by the heat treatment for 2 h in wet H₂ at 1400°C. The average strength was also improved from 347 to 446 MPa by such exposure. Heat treatment at 1300° and 1500°C also improved the reliability of the material, as indicated by increases in the Weibull modulus, but to less a degree than did exposure at 1400°C. The increases in reliability and average strength were attributed to the blunting of surface flaws by the formation of a thin SiO₂ layer on the sample surface.     

Recent advances in atomic-scale spin-polarized scanning tunneling microscopy

The Mn3N2 (010) surface has been studied using spin-polarized scanning tunneling microscopy at the atomic scale. The principle objective of this work is to elucidate the properties and potential of this technique to measure atomic-scale magnetic structures. The experimental approach involves the use of a combined molecular beam epitaxy/scanning tunneling microscopy system that allows the study of atomically clean magnetic surfaces. Several key findings have been obtained. First, both magnetic and non-magnetic atomic-scale information has been obtained in a single spin-polarized image. Magnetic modulation of the height profile having an antiferromagnetic super-period of c = 12.14 A (6 atomic rows) together with a non-magnetic superstructure having a period of c/2 = 6.07 A (3 atomic rows) was observed. Methods of separation of magnetic and non-magnetic profiles are presented. Second, bias voltage-dependent spin-polarized images show a reversal of the magnetic modulation at a particular voltage. This reversal is clearly due to a change in the sign of the magnetic term in the tunnel current. Since this term depends on both the tip's as well as the sample's magnetic local density of states, the reversal can be caused by either the sample or the tip. Third, the shape of the line profile was found to vary with the bias voltage, which is related to the energy-dependent spin contribution from the 2 chemically inequivalent Mn sites on the surface. Overall, the results shown here expand the application of the method of spin-polarized scanning tunneling microscopy to measure atomic-scale magnetic structures.