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Relaxation
Kinds of Relaxation Terms modified by Relaxation Selected AbstractsManometric study in Kearns,Sayre syndromeDISEASES OF THE ESOPHAGUS, Issue 1 2001K. H. Katsanos Although swallowing difficulties have been described in patients with Kearns,Sayre syndrome (KSS), the spectrum of manometric characteristics of dysphagia is not yet well known. Moreover, it is conceivable that a combination of various degrees of swallowing difficulties with different patterns in manometric studies exist, each playing a major role in the prognosis, natural history, and quality of life of KSS patients. An 18-year-old girl diagnosed at the age of 5 years with KSS (muscle biopsy) was admitted to our department with an upper respiratory tract infection and dysphagia. Clinical examination revealed growth retardation, external ophthalmoplegia, pigmentary retinopathy, impaired hearing, and ataxia. An electrocardiogram revealed cardiac conduction defects (long Q-T), and brain magnetic resonance imaging showed abnormalities in the cerebellar hemispheres. A manometric and motility study for dysphagia was conducted and the pharynx and upper esophageal sphincter (UES) resting pressures were similar to control group values, but the swallowing peak contraction pressure of the pharynx and the closing pressure of the UES were very low and could not promote effective peristaltic waves. Relaxation and coordination of the UES were not affected although pharyngeal and upper esophagus peristaltic waves proved to be very low and, consequently, were practically ineffective. The patient was started on treatment comprising a diet rich in potassium, magnesium, and calcium, and oral administration of vitamin D and co-enzyme Q10 100 mg daily; she was discharged 6 days later with apparent clinical improvement. [source] Hysteresis in Conjugated Polymer Thin Film Transistors Generated by Chain RelaxationADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Neng-Jye Yang Abstract The hysteresis phenomenon in a polymer thin film transistor (PTFT) with either poly(3-hexylthiophene), poly(3-dodecylthiophene), or poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] is investigated over a wide range of temperatures, and found to be generated by the delay in main chain ring distortion with an applied electric field. In the temperature range for side chain relaxation, main chain motion induced by side chain motion already starts such that polarization of the main chain by the applied electric field is permitted but in a limited extent and is not in phase with the variation in electric field. In the main chain relaxation temperature range, the extent of segmental motion increases, which leads to the main chain being more realignable by the applied electric field and thus a reduced hysteresis. After main chain relaxation is complete, the ring can distort more freely and chain segments are able to realign in phase with the applied electric field, which leads to a leveling off of the hysteresis. This investigation shows for first time that the chain relaxation in conjugated polymers is the origin of the hysteresis in PTFT devices. [source] Photo-induced Charge Transfer and Relaxation of Persistent Charge Carriers in Polymer/Nanocrystal Composites for Applications in Hybrid Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Marc Daniel Heinemann Abstract The photo-induced charge transfer and the dynamics of persistent charge carriers in blends of semiconducting polymers and nanocrystals are investigated. Regioregular poly(3-hexylthiophene) (P3HT) is used as the electron donor material, while the acceptor moiety is established by CdSe nanocrystals (nc-CdSe) prepared via colloidal synthesis. As a reference system, organic blends of P3HT and [6,6]-phenyl C61 -butyric acid methyl ester (PCBM) are studied as well. The light-induced charge transfer between P3HT and the acceptor materials is studied by photoluminescence (PL), photo-induced absorption (PIA) and light-induced electron spin resonance spectroscopy (LESR). Compared to neat P3HT samples, both systems show an intensified formation of polarons in the polymer upon photo-excitation, pointing out successful separation of photogenerated charge carriers. Additionally, relaxation of the persistent charge carriers is investigated, and significant differences are found between the hybrid composite and the purely organic system. While relaxation, reflected in the transient signal decay of the polaron signal, is fast in the organic system, the hybrid blends exhibit long-term persistence. The appearance of a second, slow recombination channel indicates the existence of deep trap states in the hybrid system, which leads to the capture of a large fraction of charge carriers. A change of polymer conformation due to the presence of nc-CdSe is revealed by low temperature LESR measurements and microwave saturation techniques. The impact of the different recombination behavior on the photovoltaic efficiency of both systems is discussed. [source] Tuning 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] Mechanical deformation model of the western United States instantaneous strain-rate fieldGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2006Fred F. Pollitz SUMMARY We present a relationship between the long-term fault slip rates and instantaneous velocities as measured by Global Positioning System (GPS) or other geodetic measurements over a short time span. The main elements are the secularly increasing forces imposed by the bounding Pacific and Juan de Fuca (JdF) plates on the North American plate, viscoelastic relaxation following selected large earthquakes occurring on faults that are locked during their respective interseismic periods, and steady slip along creeping portions of faults in the context of a thin-plate system. In detail, the physical model allows separate treatments of faults with known geometry and slip history, faults with incomplete characterization (i.e. fault geometry but not necessarily slip history is available), creeping faults, and dislocation sources distributed between the faults. We model the western United States strain-rate field, derived from 746 GPS velocity vectors, in order to test the importance of the relaxation from historic events and characterize the tectonic forces imposed by the bounding Pacific and JdF plates. Relaxation following major earthquakes (M, 8.0) strongly shapes the present strain-rate field over most of the plate boundary zone. Equally important are lateral shear transmitted across the Pacific,North America plate boundary along ,1000 km of the continental shelf, downdip forces distributed along the Cascadia subduction interface, and distributed slip in the lower lithosphere. Post-earthquake relaxation and tectonic forcing, combined with distributed deep slip, constructively interfere near the western margin of the plate boundary zone, producing locally large strain accumulation along the San Andreas fault (SAF) system. However, they destructively interfere further into the plate interior, resulting in smaller and more variable strain accumulation patterns in the eastern part of the plate boundary zone. Much of the right-lateral strain accumulation along the SAF system is systematically underpredicted by models which account only for relaxation from known large earthquakes. This strongly suggests that in addition to viscoelastic-cycle effects, steady deep slip in the lower lithosphere is needed to explain the observed strain-rate field. [source] Biofeedback-Assisted Relaxation in Migraine Headache: Relationship to Cerebral Blood Flow Velocity in the Middle Cerebral ArteryHEADACHE, Issue 3 2003Sachinder Vasudeva MD Objective.,To determine if migraineurs with aura respond differently to biofeedback/relaxation than those without aura and, if so, whether the variability in outcome can be explained by blood flow velocity. Background.,The relationship between cerebral blood flow velocity and treatment response to biofeedback/relaxation in migraine with and without aura is uncertain. Method.,Twenty migraineurs underwent 12 sessions of biofeedback/relaxation therapy, while 20 controls simply were told to relax on their own. Cerebral blood flow velocity was measured bilaterally in the middle cerebral artery with transcranial Doppler. Results.,The biofeedback group showed significant (P < .05) reductions in pain, depression, and anxiety compared to the control group. Patients with and without aura did equally well. There were significant (P < .05) left to right blood flow velocity differences only in the migraine with aura group. Maximum blood flow velocities were significantly higher (P < .05) in the migraine with aura group than in the cohort without aura. There was an inverse correlation between indicators of anxiety and blood flow velocity, perhaps related to hyperventilation-induced constriction in the small vessels distal to the middle cerebral artery. Conclusion.,The positive treatment response to biofeedback/relaxation in migraine headache is not related to presence of aura, nor to changes in blood flow velocity, but may be associated with reduction in anxiety and depression. [source] Saturation, Relaxation, and Dissociation of Excited Triplet Excitons in Conjugated PolymersADVANCED MATERIALS, Issue 8 2009Xudong Yang Femtosecond pump-probe spectroscopy is used to measure the excited state absorption dynamics in triplet excitons generated by continuous wave excitation of a conjugated polymer. Saturation of the T1,Tn transition is observed, allowing a cross-section of 2.0,×,10,16,cm2 to be established. Relaxation to T1 occurs with a 300,fs timescale, but 20% of Tn states dissociate into charges. [source] Dielectric Relaxation in CaO,Bi2O3,B2O3 GlassesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2010Koushik Majhi Glasses in the system CaO,Bi2O3,B2O3 (in molar ratio) have been prepared using melt-quenching route. Ion transport characteristics were investigated for this glass using electric modulus, ac conductivity and impedance measurements. The ac conductivity was rationalized using Almond,West power law. Dielectric relaxation has been analyzed based on the behavior of electric modulus behavior. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.76 eV, close to that the activation energy for dc conductivity (1.71 eV) indicating that the same species took part in both the processes. The stretched exponent , (0.5,0.6) is invariant with temperature for the present glasses. [source] Shock tube study of 1,3,5-triazine dissociation and relaxation and relaxation of pyrazineINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2010Hui Xu The three-body dissociation of 1,3,5-triazine (s-triazine, s-C3H3N3 , 3HCN) has been observed in incident shock waves with the laser-schlieren technique. The experiments use 5% triazine/Kr and cover 1630,2350 K for 100,600 Torr. These experiments show dissociation rates with strong falloff and a slight but fully expected pressure dependence. The dissociation is without secondary reaction save for a possible, but rather unlikely, contribution from the isomerization HCN , HNC. Electronic structure calculations of the transition-state properties (G3B3, HL1, Eo = 84.6 kcal/mol) are used to construct a Rice,Ramsperger,Kassel,Marcus (RRKM) model whose fit to the rate measurements suggests a ,,E,down of 1200 cm,1. However, a seemingly better fit is achieved using the barrier of 81 kcal/mol proposed by Dyakov et al. (J. Phys. Chem. A 2007, 111, 9591,9599). With this barrier k, (s,1) = 5.3 × 1016 exp(,86.6(kcal/mol)/RT), and the fit now accepts the more routine ,,E,down = 126(T/298)0.9. It seems the dissociation most likely occurs by a direct, one-step, "triple" dissociation to 3HCN, although the present experiments cannot rule out a multistep process. Vibrational relaxation of the triazine was also examined in 5% and 20% mixtures with Kr over 770,1500 K for pressures between 6 and 14 Torr. Relaxation is very fast, with a slight inverse temperature dependence, P, rising from 100 to 200 ns-atm over the full temperature range. Integrated gradients are in good accord with calculated total changes in density, indicating a single exponential relaxation. A separate investigation of relaxation in the related molecule pyrazine (500,1300 K, in 1% and 5% in Kr, between 13 and 66 Torr) is included. Again relaxation is rapid, but here the temperature dependence seems more normal, the relaxation times decreasing slightly with temperature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 211,220, 2010 [source] Actuation in Crosslinked Polymers via Photoinduced Stress Relaxation,ADVANCED MATERIALS, Issue 16 2006F. Scott Photoinduced polymer actuation by relieving stress unevenly through the thickness of a chemically crosslinked, rubbery polymer upon light exposure is demonstrated (see figure). The sensitivity of this method to light is greater than previously developed photoinduced actuation techniques, as the recurring chain-transfer reactions amplify the effects of each absorbed photon and subsequently generated radical on the stress-relief and actuation processes. [source] Templated Self-Assembly: Formation of Folded Structures by Relaxation of Pre-stressed, Planar Tapes,ADVANCED MATERIALS, Issue 5 2005M. Boncheva A strategy for the formation of three-dimensional (3D) structures based on the spontaneous folding of elastomeric tapes is described. These tapes are fabricated in crimped, quasi-3D forms, and carry metal features supporting liquid solder. Self-assembly based on capillary interactions between drops of liquid solder results in folding of the tapes into structures that have quasi- and true 3D topology (see Figure). [source] Relaxation of quantum hydrodynamic modesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2002Eric R. Bittner Abstract In this article, we develop a series of hierarchical mode-coupling equations for the momentum cumulants and moments of the density matrix for a mixed quantum system. Working in the Lagrange representation, we show how these can be used to compute quantum trajectories for dissipative and nondissipative systems. This approach is complementary to the de Broglie,Bohm approach in that the moments evolve along hydrodynamic/Lagrangian paths. In the limit of no dissipation, the paths are the Bohmian paths. However, the "quantum force" in our case is represented in terms of momentum fluctuations and an osmotic pressure. Representative calculations for the relaxation of a harmonic system are presented to illustrate the rapid convergence of the cumulant expansion in the presence of a dissipative environment. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] Comments on the mechanism of attachment in species of the monogenean genus GyrodactylusINVERTEBRATE BIOLOGY, Issue 1 2003Andrew P. Shinn Abstract. In species of the monogenean helminth Gyrodactylus, the opisthaptor is the main organ of attachment to the host. The opisthaptor comprises two large centrally positioned hooks or hamuli and sixteen peripherally distributed marginal hooks. This paper describes the functional morphology and the mechanism and sequence of attachment in this species. Information on the attachment process was gathered from observations of live gyrodactylids, from transmission electron microscopy, from scanning electron microscopy of skeletal elements, and by histochemical and X-ray elemental analysis of hook chemical composition. The marginal hooks provide the principal force of attachment whilst the hamuli are not actively employed in the process of attachment. Instead, the hamuli provide a system preventing accidental dislodgement and assist the action of the marginal hooks. Attachment is achieved by the alternating action of two systems of muscles attached respectively to the hamuli and to the marginal hooks. Relaxation or contraction of the muscles connected to the hamuli manoeuvres the hamuli over the extremities of the accessory ventral bar and allows them to pivot around their longitudinal axis, effectively raising or lowering the opisthaptoral dome. Under reduced opisthaptoral tension, the independent gaffing activity of the marginal hooks ensures a secure attachment to the host's epidermis. Repositioning of the hamuli then raises the opisthaptoral dome to tension the peripheral marginal hooks. The sequence of attachment is complete when all the muscles associated with the hooks are in a state of relaxation but are held securely and under tension by the surrounding, stretched, opisthaptoral dome. [source] Impaired EDHF-Mediated Relaxation in Porcine Pulmonary Micro-Arteries by Cold Storage with University of Wisconsin and Euro-Collins SolutionsJOURNAL OF CARDIAC SURGERY, Issue 6 2002Wei Zou Background: Vascular endothelium plays a key role in regulation of vascular tone. Hyperkalemia has been demonstrated to impair the EDHF-mediated endothelial function in coronary circulation. University of Wisconsin (UW) and Eruo-collins (EC) solutions are used for organ preservation in transplantation surgery. The potassium concentration in UW or EC solutions is as high as 125 mmol/L or 115 mmol/L, respectively. This study was designed to examine whether hyperkalemia or storage with UW and EC solutions affects the relaxation mediated by EDHF in the porcine pulmonary micro-arteries. Methods: Porcine pulmonary micro-artery rings (diameter 200,450 ,m) were studied in myograph (n = 8 in each group). After incubation with hyperkalemia (K+ 125 mmol/L, at 37° C), UW or EC solutions (at 4° C for 4 hours), EDHF-mediated relaxation induced by bradykinin (BK, ,10 to ,6.5 log M) in the presence of inhibitors for cyclooxygenase (Indomethacin, 7 ,M), nitric oxide synthase (NG -nitro- L -arginine, 300 ,M), and oxyhemoglobin (20 ,M) was compared with control (Krebs' solution) in precontraction with U46619 (,7.5 log M). Results: The EDHF-mediated relaxation to BK was 69.6 ± 6.3% compared with 97.1 ± 1.7% (p= 0.003) in control (no inhibitors). After incubation with hyperkalemia, the relaxation significantly decreased (38.6 ± 3.0% vs. 59.1 ± 7.4%, p= 0.03). Storage with UW or EC solutions also significantly decreased the relaxation (49.3 ± 7.3% vs. 65.2 ± 3.5%, p= 0.04 and 51.9 ± 8.4% vs. 60.3 ± 6.1%, p= 0.02, respectively). Conclusions: In porcine pulmonary micro-arteries, exposure to hyperkalemia or storage with UW or EC solutions at 4°C for 4 hours impairs the EDHF-mediated endothelial function. The clinical significance of this effect should be further studied. [source] Progressive muscle relaxation, breathing exercises, and ABC relaxation theoryJOURNAL OF CLINICAL PSYCHOLOGY, Issue 12 2001Mia Matsumoto This study compared the psychological effects of Progressive Muscle Relaxation (PMR) and breathing exercises. Forty-two students were divided randomly into two groups and taught PMR or breathing exercises. Both groups practiced for five weeks and were given the Smith Relaxation States Inventory before and after each session. As hypothesized, PMR practitioners displayed greater increments in relaxation states (R-States) Physical Relaxation and Disengagement, while breathing practitioners displayed higher levels of R-State Strength and Awareness. Slight differences emerged at Weeks 1 and 2; major differences emerged at Weeks 4 and 5. A delayed and potentially reinforcing aftereffect emerged for PMR only after five weeks of training,increased levels of Mental Quiet and Joy. Clinical and theoretical implications are discussed. © 2001 John Wiley & Sons, Inc. J Clin Psychol 57: 1551,1557, 2001. [source] Double-deck aerated biofilm membrane bioreactor with sludge control for municipal wastewater treatmentAICHE JOURNAL, Issue 5 2009Jirachote Phattaranawik Abstract Alternative designs of an aerated moving-bed biofilm reactor and a flat-sheet membrane module for a biofilm membrane bioreactor process have been investigated to overcome a membrane clogging problem and to determine the performance of a new membrane module. Double-deck aerated biofilm reactor with integrated designs of sludge hopper, thickener, and velocity-zone concept for particle settlement was evaluated for the suspended solid control and removal. Hydrodynamics of bubbling, liquid, and solid particles were arranged in the bioreactor to obtain a particle settlement. New membrane modules used under low suspended solid environment having smaller membrane gaps were evaluated for filtration performance and clogging problems for long-term operation. The average suspended solids concentration in the bioreactor effluent was 44.6 mg/L. Relaxation applied with the membrane module provided the most optimum result for fouling control, and no clogging problems in the modules were observed in the system after continuous operation of 3 weeks. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Correlation Between Thermal and Mechanical Relaxation in Chalcogenide Glass FibersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2009Pierre Lucas Enthalpy relaxation processes in chalcogenide fibers at room temperature are investigated by differential scanning calorimetry and compared with bending-stress relaxation measurements obtained by rolling fibers on a mandrel and recording the viscoelastic relaxation parameters. While the kinetics of the two processes is very different, several qualitative correlations are demonstrated between the enthalpy state and the mechanical properties of chalcogenide glass fibers. It is observed that the ability to undergo stress relaxation is dependent upon the fictive temperature of the glass. Stress relaxation in a glass far from thermodynamic equilibrium is contingent upon its ability to undergo enthalpy relaxation and is minimal in glasses that have already relaxed enthalpy or in which relaxation time is overwhelmingly large. [source] Crystallization Kinetics and Electrical Relaxation of BaO,0.5Li2O,4.5B2O3 GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2009Rahul Vaish Transparent glasses in the composition BaO,0.5Li2O,4.5B2O3 (BLBO) were fabricated via the conventional melt-quenching technique. X-ray powder diffraction combined with differential scanning calorimetric (DSC) studies carried out on the as-quenched samples confirmed their amorphous and glassy nature, respectively. The crystallization behavior of these glasses has been studied by isothermal and nonisothermal methods using DSC. Crystallization kinetic parameters were evaluated from the Johnson,Mehl,Avrami equation. The value of the Avrami exponent (n) was found to be 3.6±0.1, suggesting that the process involves three-dimensional bulk crystallization. The average value of activation energy associated with the crystallization of BLBO glasses was 317±10 kJ/mol. Transparent glass,ceramics were fabricated by controlled heat-treatment of the as-quenched glasses at 845 K/40 min. The dielectric constants for BLBO glasses and glass,ceramics in the 100 Hz,10 MHz frequency range were measured as a function of the temperature (300,925 K). The electrical relaxation and dc conductivity characteristics were rationalized using electric modulus formalism. The imaginary part of the electric modulus spectra was modeled using an approximate solution of the Kohlrausch,Williams,Watts relation. The temperature-dependent behavior of stretched exponent (,) was discussed for the as-quenched and heat-treated BLBO glasses. [source] Relaxation and Glass Transition in an Isostatically Compressed Diopside GlassJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2007Lothar Wondraczek Relaxation of isostatically compressed CaMgSi2O6 (diopside) glass is explored by ex situ differential scanning calorimetric (DSC) experiments. A diopside melt was compressed above its glass transition temperature under isostatic conditions at a pressure of 500 MPa. DSC analysis was performed at ambient pressure after slowly cooling the compressed melt under pressure (i.e., after freezing-in the densified state). Compression-induced enhancement of the overshoot in heat capacity was observed in the glass transition region. This indicates that a densified, quenched glass possesses a lower apparent fictive temperature, TfA, than a glass that was cooled under ambient pressure at the same cooling rate. However, a thermodynamic analysis indicates that the fictive temperature produced under pressure, Tf0, is actually much higher than that determined from DSC experiments at ambient pressure (Tf0>TfA). [source] Dielectric Relaxation in Layer-Structured SrBi2,xNdxNb2O9 Ceramics (x=0, 0.05, 0.2, 0.35)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007Lin Sun SrBi2,xNdxNb2O9 (x=0, 0.05, 0.2, 0.35) ceramics were synthesized by the traditional solid-state sintering method. X-ray diffraction analysis showed that single-phase-layered perovskites were obtained for all compositions. The substitution of Nd3+ for Bi3+ induced a relaxor behavior of frequency dispersion for Nd-doped SrBi2Nb2O9. The parameter of frequency dispersion ,Tm, which is the Tm between 1 kHz and 1 MHz, increases from 0°C for x=0 to 13°C for x=0.35, and the degree of relaxor behavior , increases from 0.96 for x=0 to 2.02 for x=0.35. The temperature of the maximum dielectric constant Tm decreases linearly with an increase in the Nd content (x). [source] High-Temperature Creep Behavior of Mixed Conducting La0.5Sr0.5Fe1,xCoxO3-, (0.5,x,1) MaterialsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Hilde Lea Lein Steady-state compressive creep rate of La0.5Sr0.5Fe0.5Co0.5O3,, (LSFC) and La0.5Sr0.5CoO3,, (LSC) is reported in the temperature region 900°,1050°C and stress range 5,28 MPa. The stress exponents for the two materials were 1.71±0.18 and 1.24±0.15, respectively. The activation energy for creep was considerably higher for LSC (619±56 kJ/mol) than for LSFC (392±28 kJ/mol). The grain size exponent for LSC was 1.28±0.14. Considerably higher creep rates were observed for both materials in N2 compared with air. Relaxation by creep of chemical-induced stresses in oxygen-permeable membranes is addressed, especially at low partial pressure of oxygen. [source] A Nonequilibrium Statistical Mechanical Model of Structural Relaxation in GlassJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006John C. Mauro We derive a new model of structural relaxation in glass based on nonequilibrium statistical mechanics and the Stillinger model of inherent structures. Our model follows the evolution of a system from its equilibrium liquid state through an arbitrary cooling path and allows for the computation of macroscopic properties as a function of time. Using this new model, we have numerically demonstrated for the first time the connection between the topography of a potential energy landscape in 1-D and its corresponding fragility. [source] Decoupling between Enthalpy Relaxation and Viscous Flow and Its Structural Origin in Fragile Oxide Glass-Forming LiquidsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002Takayuki Komatsu The structural relaxation kinetics at the glass transition in tellurium oxide (TeO2)-based glasses has been examined from viscosity and heat-capacity measurements to clarify the features of the structural relaxation in fragile oxide glass-forming liquids. A large decoupling between enthalpy relaxation and viscous flow, i.e., a large discrepancy between the activation energies for the enthalpy relaxation (recovery), ,H, and viscous flow, E,, has been demonstrated in TeO2 -based glasses. The values in xK2O·xMgO·(100 , 2x)TeO2 glasses, for example, are ,919,1051 kJ/mol for ,H and , 577,701 kJ/mol for E,, given the ratio of ,H/E,, 1.44,1.59. Some viscosity and heat-capacity data (all data have been reported previously) obtained from similar experiments in Sb2O3,B2O3 glasses belonging to the category of strong glass-forming liquids have been reanalyzed in this paper for comparison; a strong coupling was found to exist between ,H and E,, i.e., ,H/E,, 0.98,1.18. An origin of decoupling between ,H and E, in fragile glass-forming systems such as TeO2 -based glasses has been discussed by considering the glass structure model for fragile glasses; strongly bonded correlated (highly constrained) regions are surrounded or connected by weakly bonded noncorrelated (unconstrained) parts. [source] Long-term efficacy of a fractional resurfacing device,,§LASERS IN SURGERY AND MEDICINE, Issue 2 2010Arisa E. Ortiz MD Abstract Background and Objective Recently, there has been much debate regarding the long-term efficacy of fractional resurfacing devices. While pulsed CO2 laser resurfacing is considered a highly effective treatment, fractionated resurfacing is a newer modality and its long-term efficacy has yet to be assessed. We report the long-term outcomes of subjects previously treated with fractional CO2 resurfacing for photodamaged skin and acne scars. Study Design/Materials and Methods Ten subjects from our previous studies who received fractional resurfacing for the treatment of acne scarring and photodamage returned for long-term follow-up visits at 1 and 2 years, respectively. Investigators graded maintenance of improvement on a quartile scale based on clinical photography. Results Subjects maintained 74% of their overall improvement at their long-term visits compared to 3-month follow-up visits. While clinical improvement was maintained long-term, the results were not as remarkable as those seen at 3-month visits. The authors speculate that results seen at 3 months may be enhanced by persistent inflammatory changes, as evidenced by heat shock protein 47 activity and ongoing collagen remodeling seen in previous histologic studies. Relaxation of tightening is to be expected with any procedure along with the natural progression of aging. However, patient satisfaction was upheld long-term. Conclusion Fractional CO2 laser resurfacing does have long-term efficacy and persistence of improvement of acne scarring and photodamage compared to baseline. However, additional treatments may be necessary to enhance long-term results. Lasers Surg. Med. 42:168,170, 2010. © 2010 Wiley-Liss, Inc. [source] Technology and Stress Relaxation of Biaxially Oriented Polyolefin Shrink FilmsMACROMOLECULAR SYMPOSIA, Issue 1 2004Arthur Bobovitch Abstract In the present study the influence of the heating rate on the stability of the double bubble technological process was investigated. It was shown that increasing the heating rate decreases the stability of the process and causes the lower elongation of the films produced. The morphological transformations of linear low density polyethylene (LLDPE) film were explained using X-ray and transmission electrom microscopy (TEM) methods. The stress relaxation behavior of co-extruded LLDPE/ethylene-vinyl-acetate (EVA) film was studied using the relaxation time spectrum approach. The influence of vinyl-acetate (VA) content in EVA copolymers on the relaxation time spectrum was observed. [source] Guest editor's foreword: Relaxation in NMRMAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2003Jozef Kowalewski [source] Rapid and efficient mapping of regional ventilation in the rat lung using hyperpolarized 3He with Flip angle variation for offset of RF and relaxation (FAVOR)MAGNETIC RESONANCE IN MEDICINE, Issue 6 2008Giles E. Santyr Abstract A novel imaging method is presented, Flip Angle Variation for Offset of RF and Relaxation (FAVOR), for rapid and efficient measurement of rat lung ventilation using hyperpolarized helium-3 (3He) gas. The FAVOR technique utilizes variable flip angles to remove the cumulative effect of RF pulses and T1 relaxation on the hyperpolarized gas signal and thereby eliminates the need for intervening air wash-out breaths and multiple cycles of 3He wash-in breaths before each image. The former allows an improvement in speed (by a factor of ,30) while the latter reduces the cost of each measurement (by a factor of ,5). The FAVOR and conventional ventilation methods were performed on six healthy male Brown Norway rats (190,270 g). Lobar measurements of ventilation, r, obtained with the FAVOR method were not significantly different from those obtained with the conventional method for the right middle and caudal and left lobes (P > 0.05 by a Wilcoxon matched pairs test). A methacholine challenge test was also administered to an animal and reduction and recovery of r was detected by the FAVOR method. The reduced 3He consumption and the improvement in speed provided by FAVOR suggest that it may allow measurement of ventilation in human subjects not previously possible. Magn Reson Med 59:1304,1310, 2008. © 2008 Wiley-Liss, Inc. [source] Time-Course and Mechanisms of Restored Vascular Relaxation by Reduced Salt Intake and Angiotensin II Infusion in Rats Fed a High-Salt DietMICROCIRCULATION, Issue 3 2009SCOTT T. MCEWEN ABSTRACT Objective: This study determined the mechanisms and time-course of recovery of vascular relaxation in middle cerebral arteries (MCAs) of salt-fed Sprague-Dawley rats returned to a low-salt (LS) diet (0.4% NaCl) or infused with low-dose angiotensin II (ANG II). Methods: Rats were fed a high-salt (HS) diet (4% NaCl) for 3 days or 4 weeks before returning to an LS diet for various periods. Other rats fed a HS diet (HS+ANG II) received a chronic (3 days) intravenous (i.v.) infusion of a low dose of ANG II (5 ng kg,1 min,1) to prevent salt-induced ANG II suppression. Results: The HS diet eliminated the increase in cerebral blood flow in response to acetylcholine (ACh) infusion and the relaxation of MCA in response to ACh, iloprost, cholera toxin, and reduced PO2. Recovery of vascular relaxation was slow, requiring at least 2 weeks of the LS diet, regardless of the duration of exposure to a HS diet. Hypoxic dilation was mediated by cyclo-oxygenase metabolites and ACh-induced dilation was mediated via nitric oxide in LS rats and in HS rats returned to the LS diet or receiving ANG II infusion. Conclusions: Returning to a LS diet for 2 weeks or chronic 3-day ANG II infusion restores the mechanisms that normally mediate cerebral vascular relaxation. [source] On Spectral Relaxation in Proteins,,§PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2000Joseph R. Lakowicz ABSTRACT During the past several years there has been debate about the origins of nonexponential intensity decays of intrinsic tryptophan (trp) fluorescence of proteins, especially for single tryptophan proteins (STP). In this review we summarize the data from diverse sources suggesting that time-dependent spectral relaxation is a ubiquitous feature of protein fluorescence. For most proteins, the observations from numerous laboratories have shown that for trp residues in proteins (1) the mean decay times increase with increasing observation wavelength; (2) decay associated spectra generally show longer decay times for the longer wavelength components; and (3) collisional quenching of proteins usually results in emission spectral shifts to shorter wavelengths. Additional evidence for spectral relaxation comes from the time-resolved emission spectra that usually shows time-dependent shifts to longer wavelengths. These overall observations are consistent with spectral relaxation in proteins occurring on a subnanosecond timescale. These results suggest that spectral relaxation is a significant if not dominant source of nonexponential decay in STP, and should be considered in any interpretation of nonexponential decay of intrinsic protein fluorescence. [source] Projected Gradient Flows for BV/Level Set RelaxationPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Martin Burger This paper introduces a new level set method based on projected gradient flows for problems that can be solved by a recently introduced relaxation approach. For the class of problems the relaxation is exact, it can be shown that the solution of the flow converges to a solution of the relaxed problem for large time, and the level sets of the limit are solutions of the original problem. We introduce a simple computational scheme based on explicit time discretization and apply the method to imaging examples. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||