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Thermal Relaxation (thermal + relaxation)
Selected AbstractsTuning the Thermal Relaxation of a Photochromic Dye in Functionalized Mesoporous SilicaADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Lea A. Mühlstein Abstract In this study, it is shown that the kinetics of the back-switching reaction of a photochromic spirooxazine dye encapsulated in mesoporous silica materials can be significantly influenced both by the space available to the dye molecules and by the functionalization of the silica wall. Steric hindrance of the ring-closing process due to high dye content or small pore size leads to a slow fading speed of the irradiated dye species. Further, the density of surface silanol-groups present at the silica walls has an effect on the switching behavior of the dye because of their ability to stabilize the zwitterionic merocyanine isomers, thereby slowing the fading process from the open to the closed form. This stabilization effect is further enhanced in the presence of acidic functional groups, while, in contrast, basic functional groups reduce the stabilization of the open-from dye isomers, and thus a faster decay of the irradiated species is observed. Control over the fading speed of photochromic dyes is interesting for applications requiring a particularly fast or slow fading speed. [source] Thermal relaxation and coherence dynamics of spin 3/2.CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2003Abstract The relaxation dynamics of the spin 3/2 density operator in the presence of fluctuating and static quadrupolar interactions is reviewed. The nuclear magnetic resonance (NMR) line shapes are analyzed for any value of the static quadrupolar interaction, ranging from isotropic systems to systems exhibiting large splitting far exceeding the line widths. Pulse sequences optimized for the elimination of line broadening due to an inhomogeneous static quadrupolar interaction and for the detection of nuclei involved in slow molecular motion and/or in anisotropic, liquid crystalline environment are discussed. In Part II, the dynamics of spin 3/2 in the presence of a (pulsed) radio frequency (RF) field is reviewed. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 97,116, 2003. [source] First-order reversal curve diagrams and thermal relaxation effects in magnetic particlesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Christopher R. Pike Summary We have recently developed a technique for characterizing the magnetic components within natural particle assemblages. This technique is based on the transformation of magnetization data from first-order reversal curves (FORCs) into contour plots of a 2-D distribution function (FORC diagrams). FORC diagrams are useful for obtaining information about switching fields and interactions in magnetic particle systems. Here, we examine experimental data and a theoretical model in order to provide a rigorous framework for interpreting FORC diagrams for samples that contain superparamagnetic particles. We have found four distinct manifestations of thermal relaxation on FORC diagrams. First, thermal relaxation will shift the FORC distribution to lower coercivities. Second, at intermediate temperatures, thermal relaxation can generate a secondary peak about the origin of a FORC diagram. This secondary peak indicates that part of a single-domain particle assemblage has become superparamagnetic. At high enough temperatures, the primary peak of the FORC distribution will be located about the origin of a FORC diagram. Third, thermal relaxation can produce a small, but systematic, upward shift of a FORC distribution. Fourth, thermal relaxation will produce contours that lie near and parallel to the vertical axis in the lower quadrant of a FORC diagram. These manifestations make FORC diagrams a powerful tool for studying the effects of thermal relaxation (superparamagnetism) in bulk natural samples, particularly when the samples contain mixed magnetic particle assemblages. [source] Photoresponsive Ferroelectric Liquid-Crystalline PolymersADVANCED FUNCTIONAL MATERIALS, Issue 1 2007P. Beyer Abstract The photoresponse of ferroelectric smectic side-chain liquid-crystalline (LC) polymers containing a photoisomerizable azobenzene derivative as a covalently linked photochromic side group is investigated. By static measurements in different photostationary states, the effect of trans,cis isomerization on the material's phase-transition temperatures and its ferroelectric properties (spontaneous electric polarization PS and director tilt angle ,) are analyzed. It turns out that the Curie temperature (transition SC* to SA) can be reversibly shifted by up to 17,°C. The molecular mechanism of this "photoferroelectric effect" is studied in detail using time-resolved measurements of the dye's optical absorbance, the director tilt angle, and the spontaneous polarization, which show a direct response of the ferroelectric parameters to the molecular isomerization. The kinetics of the thermal reisomerization of the azo dye in the LC matrix are evaluated. A comparison to the reisomerization reaction in isotropic solution (toluene) reveals a faster thermal relaxation of the dye in the LC phase. [source] Cooling and inferred exhumation history of the Ryoke metamorphic belt in the Yanai district, south-west Japan: Constraints from Rb,Sr and fission-track ages of gneissose granitoid and numerical modelingISLAND ARC, Issue 2 2001Takamoto Okudaira Abstract The Ryoke metamorphic belt in south-west Japan consists mainly of I-type granitoids and associated low-pressure/high-temperature metamorphic rocks. In the Yanai district, it has been divided into three structural units: northern, central and southern units. In this study, we measured the Rb,Sr whole-rock,mineral isochron ages and fission-track ages of the gneissose granodiorite in the central structural unit. Four Rb,Sr ages fall in a range of ca 89,87 Ma. The fission-track ages of zircon and apatite are 68.9 ± 2.6 Ma and 57.4 ± 2.5 Ma (1, error), respectively. Combining the newly obtained ages with previously reported (Th,)U,Pb ages from the same unit, thermochronologic study revealed two distinctive cooling stages; 1) a rapid cooling (> 40°C/Myr) for a period (~7 Myr) soon after the peak metamorphism (~ 95 Ma) and 2) the subsequent slow cooling stage (~ 5°C/Myr) after ca 88 Ma. The first rapid cooling stage corresponds to thermal relaxation of the intruded granodiorite magma and its associated metamorphic rocks, and to the uplift by a displacement along low-angle faults which initiated soon after the intrusion of the magma. Uplift by the later stage deformation having formed large-scale upright folds resulted in progress of the exhumation during the first stage. The average exhumation velocity of the stage is , 2 mm/yr. During the second stage, the rocks were not accompanied by ductile deformation and were exhumed with the rate of 0.1,0.2 mm/yr. The difference in the exhumation velocity between the first and second cooling stages resulted from the difference in the thickness of the crust and in the activity of ductile deformation between the early and later stages of the orogenesis. [source] Microstrain and grain-size analysis from diffraction peak width and graphical derivation of high-pressure thermomechanicsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008Yusheng Zhao An analytical method is presented for deriving the thermomechanical properties of polycrystalline materials under high-pressure (P) and high-temperature (T) conditions. This method deals with non-uniform stress among heterogeneous crystal grains and surface strain in nanocrystalline materials by examining peak-width variation under different P,T conditions. Because the method deals directly with lattice d spacing and local deformation caused by stress, it can be applied to process any diffraction profile, independent of detection mode. In addition, a correction routine is developed using diffraction elastic ratios to deal with severe surface strain and/or strain anisotropy effects related to nano-scale grain sizes, so that significant data scatter can be reduced in a physically meaningful way. Graphical illustration of the resultant microstrain analysis can identify micro/local yields at the grain-to-grain interactions resulting from high stress concentration, and macro/bulk yield of the plastic deformation over the entire sample. This simple and straightforward approach is capable of revealing the corresponding micro and/or macro yield stresses, grain crushing or growth, work hardening or softening, and thermal relaxation under high- P,T conditions, as well as the intrinsic residual strain and/or surface strain in the polycrystalline bulk. In addition, this approach allows the instrumental contribution to be illustrated and subtracted in a straightforward manner, thus avoiding the potential complexities and errors resulting from instrument correction. Applications of the method are demonstrated by studies of ,-SiC (6H, moissanite) and of micro- and nanocrystalline nickel by synchrotron X-ray and time-of-flight neutron diffraction. [source] The P,T path of the ultra-high pressure Lago Di Cignana and adjoining high-pressure meta-ophiolitic units: insights into the evolution of the subducting Tethyan slabJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2009C. GROPPO Abstract The Lago di Cignana ultra-high-pressure unit (LCU), which consists of coesite,eclogite facies metabasics and metasediments, preserves the most deeply subducted oceanic rocks worldwide. New constraints on the prograde and early retrograde evolution of this ultra-high pressure unit and adjoining units provide important insights into the evolution of the Piemontese,Ligurian palaeo-subduction zone, active in Paleocene,Eocene times. In the LCU, a first prograde metamorphic assemblage, consisting of omphacite + Ca-amphibole + epidote + rare biotite + ilmenite, formed during burial at estimated P < 1.7 GPa and 350 < T < 480 °C. Similar metamorphic conditions of 400 < T < 650 °C and 1.0 < P < 1.7 GPa have been estimated for the meta-ophiolitic rocks juxtaposed to the LCU. The prograde assemblage is partially re-equilibrated into the peak assemblage garnet + omphacite + Na-amphibole + lawsonite + coesite + rutile, whose conditions were estimated at 590 < T < 605 °C and P > 3.2 GPa. The prograde path was characterized by a gradual decrease in the thermal gradient from ,9,10 to ,5,6 °C km,1. This variation is interpreted as the evidence of an increase in the rate of subduction of the Piemonte,Ligurian oceanic slab in the Eocene. Accretion of the Piemontese oceanic rocks to the Alpine orogen and thermal relaxation were probably related to the arrival of more buoyant continental crust at the subduction zone. Subsequent deformation of the orogenic wedge is responsible for the present position of the LCU, sandwiched between two tectonic slices of meta-ophiolites, named the Lower and Upper Units, which experienced peak pressures of 2.7,2.8 and <2.4 GPa respectively. [source] Activity Switches of Rhodopsin,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2008Eglof Ritter Rhodopsin, the visual pigment of the rod photoreceptor cell contains as its light-sensitive cofactor 11- cis retinal, which is bound by a protonated Schiff base between its aldehyde group and the Lys296 side chain of the apoprotein. Light activation is achieved by 11- cis to all- trans isomerization and subsequent thermal relaxation into the active, G protein-binding metarhodopsin II state. Metarhodopsin II decays via two parallel pathways, which both involve hydrolysis of the Schiff base eventually to opsin and released all- trans retinal. Subsequently, rhodopsin's dark state is regenerated by a complicated retinal metabolism, termed the retinoid cycle. Unlike other retinal proteins, such as bacteriorhodopsin, this regeneration cycle cannot be short cut by light, because blue illumination of active metarhodopsin II does not lead back to the ground state but to the formation of largely inactive metarhodopsin III. In this review, mechanistic details of activating and deactivating pathways of rhodopsin, particularly concerning the roles of the retinal, are compared. Based on static and time-resolved UV/Vis and FTIR spectroscopic data, we discuss a model of the light-induced deactivation. We describe properties and photoreactions of metarhodopsin III and suggest potential roles of this intermediate for vision. [source] | ||||||||||