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Strong Temperature Dependence (strong + temperature_dependence)
Selected AbstractsThe helix nucleation site and propensity of the synthetic mitochondrial presequence of ornithine carbamoyltransferaseFEBS JOURNAL, Issue 18 2000Harmen H. J. De Jongh This study describes the helix nucleation site and helix propagation of the amphiphilic helical structure of the mitochondrial presequence of rat ornithine carbamoyltransferase. We investigated this property of the 32-residue synthetic presequence using CD and 2D-HR NMR techniques by determining the structure as a function of the concentration of trifluoroethanol. It was found that the hydrophobic cluster Ile7-Leu8-Leu9 forms the helix nucleation site, expanding to include residues Asn4 to Lys16 when the concentration of trifluoroethanol is increased from 10 to 30%. At higher trifluoroethanol concentrations an increased ,stiffening' of the polypeptide backbone (to Arg26) is observed. In addition, by recording CD spectra at different trifluoroethanol concentrations as a function of temperature, it was found that the equilibrium constant between helix and random coil formation for this peptide exhibits a strong temperature dependence with maximum values between 20 and 30 °C. Comparison of these equilibrium constants with those of homopolymers stressed the unique character of the mitochondrial presequence. The findings are discussed in relation to the molecular recognition events at different stages of the transport process of this protein into mitochondria. [source] Electrocaloric effect in antiferroelectric PbZrO3 thin filmsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 5 2008Jayanta Parui Abstract Antiferroelectric PbZrO3 thin films have been deposited on Pt(111)/Ti/SiO2/Si substrate by polymer modified sol,gel route. Temperature dependent P ,E hysteresis loops have been measured at 51 MV/m within a temperature range of 40 °C to 330 °C. The maximum electrocaloric effect ,0.224 × 10,6 K mV,1 has been observed near the dielectric phase transition temperature (235 °C) of the thin films. The electrocaloric effect and its strong temperature dependence have been attributed to nearly first-order phase transition. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Two mechanisms of 1D2 fluorescence quenching of Pr3+ -doped Y2SiO5 crystalPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2003Yu. V. Malyukin Abstract In Y2SiO5:Pr3+ crystals (0.1 at%, 0.3 at%, 0.6 at% , and 1.8 at% Pr3+) characterized by the existence of two types of Pr3+ optical centers, the energy transfer has been investigated using time-resolved site-selective spectroscopy techniques. The results obtained show that at certain conditions there are two different mechanisms of fluorescence quenching of the excited 1D2 states of Pr3+ ions. At 0.3 at% Pr3+ and under the excitation of 1D2 states as the result of 3P0 , 1D2 nonradiative relaxation, the phonon-assisted energy transfer from 1D2 states of the I-type Pr3+ ions to the II-type ones has been found. The nonexponential part of donor fluorescence decay was described by the law t0.5. and the transfer efficiency exhibits a strong temperature dependence in the range of 1.5,80 K. At the direct selective excitation of the 1D2 states of one type Pr3+ optical centers it was possible to observe only their own fluorescence which quenched at a concentration above 0.6 at% Pr3+. The donor fluorescence decay was not fit by the law t0.5 and the quenching efficiency was characterized by the square-loaw dependence on the concentration and a very poor dependency on the temperature. The analysis of some models allows us to assume, that in this case, the cooperative quenching of the 1D2 states of both type Pr3+ optical centers can take place. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetization and FMR studies of [Fe/Cr]n structures with ultrathin iron layersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2006A. B. Drovosekov Abstract Magnetic multilayer structures [Fe(tFe)/Cr(tCr)]n with ultrathin (tFe < 5 Å) iron layers prepared by a molecular beam epitaxy were studied using SQUID-magnetometry and ferromagnetic resonance technique. For the samples with tFe , 3 Å, the obtained magnetization curves and resonance spectra are typical for regular magnetic superlattices. On the contrary, the samples with tFe , 3 Å demonstrate superparamagnetic-like behavior. These samples show a strong temperature dependence of their static and resonance magnetic properties. To explain the obtained results, we propose a theoretical model considering a cluster structure of thin iron layers. Magnetization curves and resonance spectra are calculated using an effective field approximation taking into account an interlayer interaction and cluster size distribution. The calculated dependencies show a qualitative agreement with the experimental data. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature dependence of electrical resistivity in carbon nanofiber/unsaturated polyester nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 7 2008Toshiaki Natsuki This article described the temperature dependence of electrical resistivity for carbon nanofiber (CNF)/unsaturated polyester resin (UPR) nanocomposites prepared by a solvent evaporation method. It was found that the CNF/UPR nanocomposites had quite low electrical percolation threshold due to CNFs having a large aspect ratio and being well dispersed into the UPR matrix. A sharp decrease in the electrical resistivity was observed at about 1 wt% CNF content. The influence of CNF content on the electrical resistivity was investigated as a function of temperature in detail. The nanocomposites showed a positive temperature coefficient effect for the resistivity, and had a strong temperature dependence near the percolation threshold. When the number of thermal cycles was increased, the electrical resistivity decreased and had a weak temperature dependence, especially in the case of melting temperature. Moreover, the size influences of CNFs on the electrical properties of nanocomposites were analyzed and discussed. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] On helical flows of polymer fluidsPOLYMER ENGINEERING & SCIENCE, Issue 6 2001Jae-Hyeuk Jeong Isothermal and non-isothermal steady helical flows are theoretically investigated under the assumption that the flow is fully developed in both the thermal and hydrodynamic senses. It is well known that the basic gross characteristics of steady isothermal helical flows of non-Newtonian liquids can be found relatively easily if the flow curve (or non-Newtonian viscosity) in simple shearing is known. Nevertheless, evaluation of more detailed viscoelastic properties in this type of flow is also sometimes desirable. These properties are shown to be exactly determined in both the isothermal and non-isothermal cases as soon as a nonlinear viscoelatic constitutive equation is specified. Shear thinning due to fluid rotation and strong temperature dependence of Newtonian viscosity highly increase dissipative heat. This can produce significant non-isothermal effects in intense helical flows, even when the wall temperature is kept uniform and constant. It is shown that the energy consumption in isothermal and non-isothermal helical flows is always higher than in respective annular flows with the same flow rate. Comparisons between our calculations and available experimental data are also discussed. [source] Ground-State Equilibrium Thermodynamics and Switching Kinetics of Bistable [2]Rotaxanes Switched in Solution, Polymer Gels, and Molecular Electronic DevicesCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2006Jang Wook Choi Abstract We report on the kinetics and ground-state thermodynamics associated with electrochemically driven molecular mechanical switching of three bistable [2]rotaxanes in acetonitrile solution, polymer electrolyte gels, and molecular-switch tunnel junctions (MSTJs). For all rotaxanes a ,-electron-deficient cyclobis(paraquat- p -phenylene) (CBPQT4+) ring component encircles one of two recognition sites within a dumbbell component. Two rotaxanes (RATTF4+ and RTTF4+) contain tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units, but different hydrophilic stoppers. For these rotaxanes, the CBPQT4+ ring encircles predominantly (>90,%) the TTF unit at equilibrium, and this equilibrium is relatively temperature independent. In the third rotaxane (RBPTTF4+), the TTF unit is replaced by a ,-extended analogue (a bispyrrolotetrathiafulvalene (BPTTF) unit), and the CBPQT4+ ring encircles almost equally both recognition sites at equilibrium. This equilibrium exhibits strong temperature dependence. These thermodynamic differences were rationalized by reference to binding constants obtained by isothermal titration calorimetry for the complexation of model guests by the CBPQT4+ host in acetonitrile. For all bistable rotaxanes, oxidation of the TTF (BPTTF) unit is accompanied by movement of the CBPQT4+ ring to the DNP site. Reduction back to TTF0 (BPTTF0) is followed by relaxation to the equilibrium distribution of translational isomers. The relaxation kinetics are strongly environmentally dependent, yet consistent with a single electromechanical-switching mechanism in acetonitrile, polymer electrolyte gels, and MSTJs. The ground-state equilibrium properties of all three bistable [2]rotaxanes were reflective of molecular structure in all environments. These results provide direct evidence for the control by molecular structure of the electronic properties exhibited by the MSTJs. [source] | |||||||||||||