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Few Degrees (few + degree)
Selected AbstractsPolymers derived from N -isopropylacrylamide and azobenzene-containing acrylamides: Photoresponsive affinity to waterJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2004Haruhisa Akiyama N -Isopropylacryamide was copolymerized by free-radical polymerization with N -[2-(4-phenylazophenoxy)ethyl]acrylamide derivatives that were substituted at their 4,-position with ethoxy, methoxyethoxy, or isopropyl units, or with N -{2-[4-(pyridin-2-ylazo)phenoxy]ethyl}acrylamide. The polymers were soluble in cold water and possessed lower critical solution temperatures (LCSTs). The value of the LCST rose a few degrees after UV irradiation and dropped after irradiation with visible light, reversibly, in processes that corresponded to the isomerization of the azobenzene units. The polymers became increasingly hydrophobic after increasing their azobenzene content. The difference of hydrophobicity correlates with the absorption band height at about 400 nm. The structure of the substituent on the azobenzene unit affected both the transition temperature and the hydrophobicity. A change in photoinduced wettability for water was observed to occur on a prepared film at a temperature different from the LCST determined in water. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5200,5214, 2004 [source] Rheological Investigation of Shear Induced-Mixing and Shear Induced-Demixing for Polystyrene/Poly(vinyl methyl ether) BlendMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2004Samy A. Madbouly Abstract Full Paper: The phase behavior of polystyrene (PS) and poly(vinyl methyl ether) (PVME) blend has been investigated rheologically as a function of temperature, composition and oscillating shear rate as well as different heating rates. An LCST (lower critical solution temperature)-type phase diagram was detected rheologically from the sudden changes in the slopes of the dynamic temperature ramps of G, at given heating and shear rate values. The rheological cloud points were dependent on the heating rate, , and oscillating shear rate, . The cloud points shifted a few degrees to higher temperatures with increasing and reached an equilibrium value (heating rate independent) at ,°C/min. The phase diagrams of the blends detected at ,=,0.1 and 1 rad/s were located in lower temperature ranges than the quiescent phase diagram, i.e., oscillating shear rate induced-demixing at these two values for the shear rate. On the other hand, at ,=,10 rad/s, the phase diagram shifted to higher temperatures, higher than the corresponding values found under quiescent conditions, i.e., shear induced-mixing took place. Based on these two observations, shear induced-demixing and shear induced-mixing can be detected rheologically within a single composition at low and high shear rate values, respectively, and this is in good agreement with the previous investigation using simple shear flow techniques. In addition, the William, Landel and Ferry (WLF)-superposition principle was found to be applicable only in the single-phase regime; however, the principle broke-down at a temperature higher than or equal to the cloud point. Furthermore, different spinodal phase diagrams were estimated at different oscillating shear rates based on the theoretical approach of Ajji and Choplin. Spinodal phase diagrams at different oscillating shear rates. [source] Characterisation of indomethacin and nifedipine using variable-temperature solid-state NMRMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2005David C. Apperley Abstract We have characterised the stable polymorphic forms of two drug molecules, indomethacin (1) and nifedipine (2) by 13C CPMAS NMR and the resonances have been assigned. The signal for the CCl carbon of indomethacin has been studied as a function of applied magnetic field, and the observed bandshapes have been simulated. Variable-temperature 1H relaxation measurements of static samples have revealed a T1, minimum for indomethacin at 17.8 °C. The associated activation energy is 38 kJ mol,1. The relevant motion is probably an internal rotation and it is suggested that this involves the COCH3 group. Since the two drug compounds are potential candidates for formulation in the amorphous state, we have examined quench-cooled melts in detail by variable-temperature 13C and 1H NMR. There is a change in slope for and at the glass transition temperature (Tg) for indomethacin, but this occurs a few degrees below Tg for nifedipine, which is perhaps relevant to the lower real-time stability of the amorphous form for the latter compound. Comparison of relaxation time data for the crystalline and amorphous forms of each compound reveals a greater difference for nifedipine than for indomethacin, which again probably relates to real-time stabilities. Recrystallisation of the two drugs has been followed by proton bandshape measurements at higher temperatures. It is shown that, under the conditions of the experiments, recrystallisation of nifedipine can be detected already at 70 °C, whereas this does not occur until 110 °C for indomethacin. The effect of crushing the amorphous samples has been studied by 13C NMR; nifedipine recrystallises but indomethacin does not. The results were supported by DSC, powder XRD, FTIR and solution-state NMR measurements. Copyright © 2005 John Wiley & Sons, Ltd. [source] Bulk motion of ultrarelativistic conical blazar jetsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006Gopal-Krishna ABSTRACT Allowing for the conical shape of ultrarelativistic blazar jets with opening angles of a few degrees on parsec-scales, we show that their bulk Lorentz factors and viewing angles can be much larger than the values usually inferred by combining their flux-variability and proper-motion measurements. This is in accord with our earlier finding that such ultrarelativistic (Lorentz factor, , > 30) conical jets can reconcile the relatively slow apparent motions of Very Long Baseline Interferometry (VLBI) knots in TeV blazars with the extremely fast flows implied by their rapid ,-ray variability. This jet geometry also implies that de-projected jet opening angles will typically be significantly underestimated from VLBI measurements. In addition, de-projected jet lengths will be considerably overestimated if high Lorentz factors and significant opening angles are not taken into account. [source] Declines in Leaf Litter Nitrogen Linked to Rising Temperatures in a Wet Tropical ForestBIOTROPICA, Issue 5 2010Katherine Tully ABSTRACT In the tropics rainfall can vary by hundreds of millimeters from month to month, while mean temperatures fluctuate by only a few degrees. Nevertheless, during this 7-year study, we observed 35,52 percent declines in litter nitrogen concentrations in response to small increases in minimum temperature, with no response to the larger oscillations in rainfall. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp. [source] | ||||||||||