Mechanical properties and morphologies of PP/mPE/filler composites

Because of the poor impact behavior of polypropylene (PP) at low temperatures, the blending of PP with metallocene‐polymerized polyethylene (mPE) elastomers was investigated in this study. However, a reduced modulus of the overall blend was inevitable because of the addition to elastomers. To obtain a balance of the properties, we introduced rigid inorganic fillers to PP/mPE blends. The performance of the composites was characterized with tensile and Charpy notched impact tests, and the fracture morphology was examined with scanning electron microscopy. The results showed that the effects of fillers in a brittle matrix and in a ductile matrix were quantitatively different. For PP/mPE/filler ternary composites, the dependence of Young's modulus and yield strength on CaCO₃ content was not significant compared with that of PP/filler binary composites, whereas the elongation at break and tensile toughness at room temperature for PP/mPE/filler systems were more improved. The impact strength of the PP/mPE blends filled with untreated glass beads and CaCO₃ at a low temperature was lowered because of the weak interfacial bond. However, the values of the impact strength of the PP/mPE/filler composites at a low temperature remained at a high level compared with that of pure PP. In particular, a PP/mPE blend filled with surface‐treated kaolin had a higher low‐temperature impact toughness than the unfilled blend. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3029–3035, 2002; DOI 10.1002/app.2333     

Quantum Dot Infrared Photodetectors: Photoresponse Enhancement Due to Potential Barriers

Potential barriers around quantum dots (QDs) play a key role in kinetics of photoelectrons. These barriers are always created, when electrons from dopants outside QDs fill the dots. Potential barriers suppress the capture processes of photoelectrons and increase the photoresponse. To directly investigate the effect of potential barriers on photoelectron kinetics, we fabricated several QD structures with different positions of dopants and various levels of doping. The potential barriers as a function of doping and dopant positions have been determined using nextnano³ software. We experimentally investigated the photoresponse to IR radiation as a function of the radiation frequency and voltage bias. We also measured the dark current in these QD structures. Our investigations show that the photoresponse increases ~30 times as the height of potential barriers changes from 30 to 130 meV.     

Chemical and electrochemical syntheses of a graphite fluoro-tris(pentafluoroethyl)borate intercalation compound

Graphite intercalation compounds (GICs) of composition C_x[FB(C₂F₅)₃] · δF are prepared for the first time by the intercalation of fluoro-tris(pentafluoroethyl)borate anion, [FB(C₂F₅)₃]⁻_, under ambient conditions in 48% hydrofluoric acid containing the oxidant K₂[MnF₆]. Powder XRD data indicate that products are of mixed stages 2 and 3 after reactions for 1-20 h, with a gallery height of 0.87 nm. The intercalate orientation is modeled using an energy-minimized anion structure. Microwave digestion followed by B and F elemental analyses, along with thermogravimetric analyses provide compositional x and δ parameters for the GICs obtained. In addition, C_x[FB(C₂F₅)₃] · δCH₃NO₂ with stage 2 is prepared by electrochemical oxidation of graphite in a nitromethane solution and characterized as above.     

Structural and optical properties of soluble melanin analogues with enhanced photoluminescence quantum efficiency

Melanin is a functional material of growing interest for bioelectronics. Several melanin analogues have been employed in order to fully explore its potential; in this work melanin was synthesized using dimethylsulfoxide (DMSO) and O₂ under pressure as oxidizing agent. It is shown that the products have similar functional groups and solubility; however, O₂ pressure produces more carboxylated structures and improves the synthesis reaction rate. The photoluminescence of all sulfonated melanin analogues was studied. It is shown that the material synthesized in DMSO has photoluminescence in the visible region (487 nm) with a quantum yield of (2.12 ± 0.02)%. This good quantum yield compared to natural and synthetic melanin may open new perspectives for its use in optoelectronics applications. The origin of this effect is discussed in terms of the polymer structure. © 2018 Society of Chemical Industry     

Selective activation of cAMP-dependent protein kinase type I inhibits rat natural killer cell cytotoxicity

The present study examines the expression and involvement of cAMP-dependent protein kinase (PKA) isozymes in cAMP-induced inhibition of natural killer (NK) cell-mediated cytotoxicity. Rat interleukin-2-activated NK cells express the PKA alpha-isoforms RIalpha, RIIalpha, and Calpha and contain both PKA type I and type II. Prostaglandin E2, forskolin, and cAMP analogs all inhibit NK cell lysis of major histocompatibility complex class I mismatched allogeneic lymphocytes as well as of standard tumor target cells. Specific involvement of PKA in the cAMP-induced inhibition of NK cell cytotoxicity is demonstrated by the ability of a cAMP antagonist, (Rp)-8-Br-adenosine 3',5'-cyclic monophosphorothioate, to reverse the inhibitory effect of complementary cAMP agonist (Sp)-8-Br-adenosine 3',5'-cyclic monophosphorothioate. Furthermore, the use of cAMP analog pairs selective for either PKA isozyme (PKA type I or PKA type II), shows a preferential involvement of the PKA type I isozyme, indicating that PKA type I is necessary and sufficient to completely abolish killer activatory signaling leading to NK cell cytotoxicity. Finally, combined treatment with phorbol ester and ionomycin maintains NK cell cytotoxicity and eliminates the cAMP-mediated inhibition, demonstrating that protein kinase C and Ca2+-dependent events stimulate the cytolytic activity of NK cells at a site distal to the site of cAMP/PKA action.     

Culture collections and the biotechnology deal

Culture collections provide starting material for life science research, development and production. Especially in biotechnology, well characterised and pure microbial strains are essential for reproducible and safe bioprocesses. Culture collections also play a role as repositories of biological material for future applications and help to preserve biological diversity. In addition, they also maintain the know-how needed for more complex identification methods and help to develop new techniques. To enable culture collections to achieve higher quality standards, new certification guidelines for biological resource centres are currently being developed.     

Near-infrared spectroscopy of H3+ above the barrier to linearity

Since the Royal Society Discussion Meeting on H3+ in 2000, the laboratory spectroscopy of H3+ has entered a new regime. For the first time, transitions of H3+ above the barrier to linearity have been observed. A highly sensitive near-infrared spectrometer based on a titanium:sapphire laser and incorporating a dual-beam, double-modulation technique with bidirectional optical multi-passing has been developed in order to detect these transitions, which are more than 4600 times weaker than the fundamental band. We discuss our recent work on the 2v1 + 2v2(2) <-- 0, 3v1 + v2(1) <-- 0, v1 + 4v2(2) <-- 0, v1 + 4V2(4) <-- 0 and 2v1 + 3v2(1) <-- 0 combination bands and the 5v2(1) <-- 0, 5v2(3) <-- 0, 52(5) <-- 0 and 6v2(2) <-- 0 overtone bands. Experimentally determined energy levels provide a critical test of ab initio calculations in this challenging energy regime (greater than 10,000 cm(-1)). By comparing the experimental energy levels and theoretical energy levels from ab initio calculations in which the adiabatic and relativistic corrections are incorporated, the extent of higher-order effects such as non-adiabatic and radiative corrections is revealed.     

Wiener predistorter for nonlinear satellite downlinks

The nonlinear power amplifier and the analogue output channel filter with nonconstant group delay add nonlinear and linear distortions to the satellite transmitted signal, respectively. Recently, there has been growing interest in using Wiener predistorters, consisting of separate nonlinear and linear components, to compensate for these distortions in the satellite downlinks. The Wiener predistorter has been shown to effectively deal with signal distortions and has lower complexity compared to other state-of-the-art methods. In this paper, we argue that fully compensating the nonconstant group-delay distortion degrades the overall performance of the Wiener predistortion systems. This is primarily due to the increased peak-to-average power ratio of the signal at the output of the linear predistorter. We show that the overall performance of the Wiener predistorter can be improved by undercompensating the group-delay distortion. We propose two optimizations to address the PAPR growth problem and show using simulations that our approach leads to significant improvement in predistortion performance. Using our Wiener predistorter, the total degradation gap to the ideal limiter channel can be reduced to merely 0.34 dB for 64-APSK modulated signals.     

Home environment and cognitive development in the first 3 years of life: A collaborative study involving six sites and three ethnic groups in North America.

Attempted to examine the generalizability of environment/development relationships among 3 ethnic groups across the first 3 years of life. Social status did not show a consistent relationship to either quality of home environment or children's developmental status across the various groups. Results indicated a fairly consistent relationship between HOME scores and children's developmental status, although there were some ethnic and social status differences in the relationship. Measures of specific aspects of the child's home environment, such as parental responsivity and availability of stimulating play materials, were more strongly related to child developmental status than global measures of environmental quality such as SES. When the child's developmental status and early home environment were both very low, the likelihood of poor developmental outcomes was markedly increased compared with cases when only one was low. (PsycINFO Database Record (c) 2010 APA, all rights reserved)