Ultrahigh Electrical Resistance of Poly(cyclohexyl methacrylate)/Carbon Nanotube Composites Prepared Using Surface‐Initiated Polymerization

Multiwalled carbon nanotubes on which poly(cyclohexyl methacrylate)s are densely grafted (PCHMA‐CNTs), are synthesized using a modified surface‐initiated atom transfer radical polymerization technique. The electrical resistance of PCHMA‐CNT is systematically characterized under direct current (DC) and alternating current and compared to that of conventional nanocomposites prepared by blending PCHMA with the CNT (PCHMA/CNT). At a comparable volume fraction of CNT, DC volume resistivity of PCHMA‐CNT is 14 orders of magnitude higher than that of PCHMA/CNT. This is because the grafted polymer with a combination of the high molecular weight and the high grafting density isolates individual CNTs at a long distance in the PCHMA‐CNT system. In addition, impedance analysis reveals that the highly insulated PCHMA‐CNT has the same electrical nature as neat PCHMA, i.e., it is a dielectric. Furthermore, dynamic mechanical analysis shows PCHMA‐CNT has a good mechanical properties as well as ultrahigh electrical resistance.     

Stabilization of Microcapsules Using a Freeze-Dried Gelatin Matrix: Aqueous Redispersibility and the Ingredient Activity

Microcapsules are of great interest to the food and pharmaceutical industries as vehicles to deliver active ingredients to the gastrointestinal tract. Drying plays an important role in stabilizing microcapsules to prolong their lifetime; however, drying often produces undesirable changes in the microcapsules, such as irreversible aggregation of the microcapsules and activity loss of the encapsulated ingredient. In this work, poly(epsilon-caprolactone) microcapsules containing a model bioactive compound (tocopherol) were prepared and stabilized in a freeze-dried gelatin matrix. This dried product was rehydrated and the aqueous redispersibility of the microcapsules and the tocopherol activity were investigated. The experimental results suggested that a kinetic balance between dehydration (caused by freezing) and gel network formation is a critical factor that affects the redispersibility and ingredient activity of the products. It was further suggested that a hydrogel-based product could be strategically freeze dried to maximize product quality by tuning its freezing process; that is, by employing a controllable dehydration process.     

Planning in human children (Homo sapiens) assessed by maze problems on the touch screen.

The authors examined how human children perform on maze tasks on the touch screen and whether the children plan the solution of the mazes. In Experiment 1, the authors exposed children around 3 years of age to a maze having an L-shaped line as a barrier that can be solved by moving an illustration of a dog (the target) to that of a bone (the goal) with their fingers. The participants successfully solved the maze by taking efficient routes more frequently than chance, although the authors found no evidence that a preview of the maze before starting to solve the task facilitated their performance. In Experiment 2, using a plus-shaped maze, the authors found that 3- and 4-year-old children plan and adjust their moves while solving the maze, with 4-year-olds showing more advanced and higher-level planning than 3-year-olds. Similarity of these results to what the authors previously found in pigeons tested in the same tasks may suggest an analogy for planning capacity in the behavioral level across taxa and developmental stages. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mixed alkali effect in elastic properties of glasses in the ZrF4-BaF2- AlF3-RF system (RF = LiF-NaF,NaF-KF)

The elastic properties, such as Poisson's ratios, shear modulus, Young's modulus and bulk modulus, have been determined with glasses of the compositions 48ZrF₄ · 24BaF₂ · 8AlF₃ · 20RF, where RF is the LiF-NaF or NaF-KF pair, and 42ZrF₄ · 21BaFe₂· 7AIF₃ · 30RF, where RF is the LiF-NaF pair, by measuring sound wave velocities. Non-linear variations, i.e. mixed alkali elects, were found in the sound velocities, shear modulus, Young's modulus and bulk modulus. The mixed alkali effect in the present systems is attributed to the strengthening of the glass structure and not to the mere compaction of the glass structure. The thermal expansion coefficient becomes higher when the two alkalis are mixed contrary to expectation from the change of the elastic moduli, indicating that the structural elements controlling the elastic moduli re different from those affecting the thermal expansion.     

Photoelectrochemical properties of sol–gel-derived anatase and rutile TiO2 films

Anatase and rutile film electrodes with comparable porosities were prepared by the sol–gel dip-coating method, and the photoelectrochemical properties were studied based on photocurrent measurement and impedance analysis in a three-electrode wet cell. The photocurrent was found to increase with the donor density, both in anatase and rutile electrodes. For the same donor density, however, rutile electrodes exhibited higher photocurrents than anatase electrodes, which was ascribed to the more beneficial bandgap structure of the former.     

The determination of Gibbs energy of the exchange reaction of sulphides using beta-alumina solid electrolyte

EMF measurements of the cell Na (l) |-alumina | Na₂S + A9₂S + Ag were carried out in the temperature range of 463.4 to 843.7 K. The results were represented by the equationE/V (±0.00057) = 1.75793(±0.00086) – 4.452(±0.014) × 10^–4(T) where 463.4 < T < 737.7 K. The Gibbs energy of the exchange reaction 1/2Ag₂S(s) + Na(l) 1/2Na₂S(s) + Ag(s) was determined from the EMFs. The standard Gibbs energy of formation of Na₂S in the reaction 2Na(l) + 1/2S₂(g) = Na₂S(s) was obtained from the values of EMF and in the literature as (J mol^–1 ± 1160) = –427940 + 124.92T where 463.4 < T < 737.7 K. The eutectic temperature of the Ag₂S-Na₂S system was estimated to be 738 ± 5 K.     

Preparation of superconducting Bi-Sr-Ca-Cu-O ceramics by the sol-gel method

Superconducting Bi-(Pb)-Sr-Ca-Cu-O ceramics were prepared through the sol-gel method using an aqueous solution of metal acetates containing acetic acid and tartaric acid. The conditions of gelation and conversion of gel to Bi₂Sr₂CaCu₂O_x phase were studied by thermal analysis, infrared absorption spectroscopy and X-ray diffraction technique. It was found that transparent gels were obtained from the solutions containing tartaric acid, with a molar ratio of C₄H₆O₆/Cu of about 0.4. The gel matrix was assumed to be composed of carboxylate anions and metal cations. A gel of molar composition BiSrCaCu = 2223 was decomposed to CaCO₃, CaO, CuO and Bi_1-x Sr_xO_y (x = 0.2 to 0.3) at low temperatures of 270 to 600 ° C and produced Bi₂Sr₂CaCu₂O_x phase at 800 ° C via complex intermediate states. A rapid cooling of the heated product increasedT _c (end) in the gel of molar composition BiSrCaCu = 2223, while a slow cooling increasedT _c (end) in the lead-containing gel of molar composition BiPbSrCaCu = 1.850.351.92.03.1. The latter showedT _c (onset) at 115 K andT _c (end) at 105K.     

Experimental Comparison of Load/Unload Slider Dynamics For Two Different Pico-Slider Designs

A comparison of Laser-Doppler vibrometry (LDV) and acoustic emission (AE) data is presented for two different slider designs during load/unload (L/UL). The behavior of the slider is measured for three different vertical load/unload velocities using a transparent glass disk with the slider flying at the bottom surface of the disk. The LDV laser spot can be positioned on the slider alrbearing surface during the complete load/unload process with the help of a so-called “periscope.” A characteristic velocity peak during unloading is observed that is caused by the slider pull-off force.