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Relaxation Time (relaxation + time)
Kinds of Relaxation Time Terms modified by Relaxation Time Selected AbstractsInvestigation of the Influence of Overvoltage, Auxiliary Glow Current and Relaxation Time on the Electrical Breakdown Time Delay Distributions in NeonCONTRIBUTIONS TO PLASMA PHYSICS, Issue 2 2005. A. Maluckov Abstract Results of the statistical analysis of the electrical breakdown time delay for neon-filled tube at 13.3 mbar are presented in this paper. Experimental distributions of the breakdown time delay were established on the basis of 200 successive and independent measurements, for different overvoltages, relaxation times and auxiliary glows. Obtained experimental distributions deviate from usual exponential distribution. Breakdown time delay distributions are numerically generated, usingMonte-Carlo method, as the compositions of the two independent random variables with an exponential and a Gaussian distribution. Theoretical breakdown time delay distribution is obtained from the convolution of the exponential and Gaussian distribution. Performed analysis shows that the crucial parameter that determines the complex structure of time delay is the overvoltage and if it is of the order of few percentage, then distribution of time delay must be treated as an convolution of two random variables. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Scavenging Free Radicals To Preserve Enhancement and Extend Relaxation Times in NMR using Dynamic Nuclear Polarization,ANGEWANDTE CHEMIE, Issue 35 2010Pascal Miéville Länger leben dank Vitamin,C: N -Oxid-Radikale, die weithin zur dynamischen Kernpolarisation eingesetzt werden, können beim Auflösen durch Abfangreagentien wie Natriumascorbat (Vitamin,C) reduziert werden, wodurch Polarisierungsverluste während des Transfers vermieden und transversale wie longitudinale Relaxationszeiten in NMR-spektroskopischen Experimenten verlängert werden (siehe Bild). [source] Local dynamics in epoxy coatings containing iron oxide nanoparticles by dielectric relaxation spectroscopyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008G. Kortaberria Abstract Nanocomposites of photocurable epoxy resin and epoxy-modified iron oxide magnetic nanoparticles were analyzed by dielectric relaxation spectroscopy to study the local dynamics at temperatures well below the glass-transition temperature. Two secondary processes were detected, , and , processes, but the second one was just detected at lower temperatures in the high-frequency part of the spectra and moved out of the frequency range at higher temperatures. Data were fitted to the Havriliak,Negami and Arrhenius models, and the obtained parameters were analyzed. Relaxation times of the , secondary relaxation did not change with the nanoparticle content, but the relaxation strength increased. The increase could not be explained when we took into account the molecular origin of the relaxation. The presence of ferromagnetic nanoparticles enhanced the internal field and increased the relaxation strengths. Transmission electron microscopy images showed that the nanoparticles were well dispersed in the matrix, without magnetic agglomerates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Proton spectroscopic metabolite signal relaxation times in preterm infants: A prerequisite for quantitative spectroscopy in infant brainJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2003Harald Kugel PhD Abstract Purpose To determine relaxation times of metabolite signals in proton magnetic resonance (MR) spectra of immature brain, which allow a correction of relaxation that is necessary for a quantitative evaluation of spectra acquired with long TE. Proton MR spectra acquired with long TE allow a better definition of metabolites as N-acetyl aspartate (NAA) and lactate especially in children. Materials and Methods Relaxation times were determined in the basal ganglia of 84 prematurely born infants at a postconceptional age of 37.8 ± 2.2 (mean ± SD) weeks. Metabolite resonances were investigated using the double-spin-echo volume selection method (PRESS) at 1.5 T. T1 was determined from intensity ratios of signals obtained with TRs of 1884 and 6000 msec, measured at 3 TEs (25 msec, 136 msec, 272 msec). T2 was determined from signal intensity ratios obtained with TEs of 136 msec and 272 msec, measured at 2 TR. Taking only long TEs reduced baseline distortions by macromolecules and lipids. For myo-inositol (MI), an apparent T2 for short TE was determined from the ratio of signals obtained with TE = 25 msec and 136 msec. Intensities were determined by fitting a Lorentzian to the resonance, and by integration. Results Relaxation times were as follows: trimethylamine-containing compounds (Cho): T1 = 1217 msec/T2 = 273 msec; total creatine (Cr) at 3.9 ppm: 1010 msec/111 msec; Cr at 3.0 ppm: 1388 msec/224 msec; NAA: 1171 msec/499 msec; Lac: 1820 msec/1022 msec; MI: 1336 msec/173 msec; apparent T2 at short TE: 68 msec. Conclusion T1 and T2 in the basal ganglia of premature infants do not differ much from previously published data from basal ganglia of older children and adults. T2 of Cho was lower than previous values. T2 of Cr at 3.9 ppm and Lac have been measured under different conditions before, and present values differ from these data. J. Magn. Reson. Imaging 2003;17:634,640. © 2003 Wiley-Liss, Inc. [source] Effect of Green Density on the Thermomechanical Properties of a Ceramic During SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Sam E. Schoenberg The thermomechanical properties of a commercial barium titanate were experimentally or theoretically determined for samples with green densities ranging from 45% to 55%. For stresses less than 300 kPa, sample deformation was determined to be linear viscous for all three stages of sintering. The shrinkage rates at a given temperature can differ by up to ,25% as the green density changes from 45% to 55%, and the maximum shrinkage rate increased with decreasing green density. The increase in shrinkage rate with lower green density samples persisted through the final sintering stage. The viscosity was determined by cyclic loading dilatometry to range from 5 to 6 GPa·s in the initial stage of sintering, to 2 GPa·s in the intermediate stage, and to increase to 10,20 GPa·s for all specimens in the final stage of sintering. Differences in the final-stage viscosity were attributed to grain size differences. Relaxation times for the sintering body were estimated to be less than 1 s, indicating that viscous behavior is dominant throughout the sintering process. [source] The effect of experimental conditions on the detection of spermine in cell extracts and tissuesNMR IN BIOMEDICINE, Issue 2 2010Nicholas G. Spencer Abstract The aim of this work was to investigate the effect of experimental conditions on the visibility of polyamines. In solution the chemical shift of the three groups of peaks (at approximately 1.8, 2.1 and 3.1,ppm) were found to be pH dependent. Relaxation times in aqueous solution at pH 7.0, 298,K and 11.74,T were measured to be: putrescine (T1,=,2.49,s, T2,=,2.07,s), spermidine (T1,=,1.27,s, T2,=,1.05,s) and spermine (T1,=,1.02,s, T2,=,0.82,s). Simple spin-echo sequences could not be used to measure T2 as the spins also experience phase evolution from homonuclear coupling which imposes a modulation on the T2 decay curve. This modulation is eliminated by using CPMG sequences with an echo spacing of <500,µs. Relaxation times for spermine in solution in presence of metal ions and protein showed that metal ions had little effect on T2; however, addition of 15,mg/ml bovine serum albumin reduced T2 of spermine (0.41,s at 298,K and 0.19,s at 277,K) but was not as short as the T2 of the polyamine peak in prostatic tissue (0.03,s at 277,K). The MR visibility of polyamines in prostate cell extracts, PC-3 xenograft (intact as well as extracted) and intact human prostatic tissues were investigated. Polyamines were not detected in methanol/chloroform extracts, but were visible in perchloric acid extracts of prostate tumour cells. No polyamines were detected in the HR MAS spectra of three samples of whole PC-3 xenograft tissue studied. In summary, the chemical shift of polyamine species is pH dependent, while protein binding causes peak broadening and reduction in T2. Perchloric acid extraction improves visibility of intracellular polyamines, but whole tissue polyamines are not seen in xenografts without epithelial/ ductal structure. Copyright © 2009 John Wiley & Sons, Ltd. [source] Relaxation times of choline, creatine and N -acetyl aspartate in human cerebral white matter at 1.5 TNMR IN BIOMEDICINE, Issue 3 2002D. R. Rutgers Abstract Several studies have investigated the T1 and T2 relaxation time of choline, creatine and N -acetyl aspartate in cerebral white matter in normal human subjects. However, these studies demonstrate a large variation in T1 and T2 values. In the present study, relaxation times of choline, creatine and N -acetyl aspartate were determined in cerebral white matter in 15 control subjects (age 21,±,2 y, mean,±,SD) at 1.5 T. Using PRESS, seven or eight data points were obtained to fit the T1 and T2 relaxation curves to, respectively. The mean voxel size was 14,cm3. The T1 relaxation times of choline, creatine and N -acetyl aspartate were 1091,±,132 (mean,±,SD), 1363,±,137 and 1276,±,132,ms. The T2 relaxation times were 352,±,52, 219,±,29 and 336,±,46,ms, respectively. Copyright © 2002 John Wiley & Sons, Ltd. [source] Optical spin orientation of a single manganese atomPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2010C. Le Gall Abstract An optical spin orientation is achieved for a Mn atom localized in a semiconductor quantum dot using quasiresonant excitation at zero magnetic field. Optically created spin polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy. The dynamics and the magnetic field dependence of the optical pumping mechanism shows that the spin lifetime of an isolated Mn atom at zero magnetic field is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots. Relaxation times exceeding the micro-second range are measured (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Stress relaxation behavior of glass fiber-reinforced polyester composites prepared by the newly proposed rubber pressure moldingPOLYMER COMPOSITES, Issue 10 2008Kamal K. Kar Stress-relaxation behavior of glass fiber-reinforced polyester composites, prepared by a recently developed manufacturing method called rubber pressure molding (RPM), is investigated with special reference to the effect of environmental temperature (,70°C to +100°C), fiber volume fraction (30,60%), and initial load level (1,5 kN). It is found that the stress-relaxation rate decreases with an increase in the applied load of composites and a decrease in temperature. Below glass transition temperature, the rate of stress relaxation increases with an increase in volume fraction of fibers in the composites, whereas above glass transition temperature, it increases with a decrease in the volume fraction of fibers. The experimental results for a given composites are summarized by four values, the slopes of the two straight lines (two separate relaxation processes), and their intercepts upon the stress axis. Both the slopes are dependent upon the applied load, temperature, and volume fraction of fibers in the composites. Relaxation times in both primary and secondary are calculated over the wide range of temperatures, loads, and volume fraction of fibers in the composites. It depends strongly on the temperature, but does not depend strongly on the applied load and volume fraction of fibers. The performances of the composites are also evaluated through conventional compression-molding process. The rate of stress relaxation is small when the composites are made of newly proposed RPM technique when compared with the conventional process. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source] Introducing dimensionless parameters into the correlation of NMR relaxation time to transport properties of porous mediaCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2007Manolis M. Tomadakis Abstract Dimensionless parameters representing the viscous permeability (k) and NMR relaxation time (T1) of particle beds, while accounting also for the particle size, are shown to improve drastically the accuracy of k-T1 correlations in the slow diffusion regime, in the absence of bulk relaxation effects. The finding is based on a regression analysis of numerical results for k and T1 in both random and ordered isotropic and anisotropic beds of fibers. Use of the formation factor (F) improves further the accuracy of the correlations only for the strongly anisotropic unidirectional arrays of fibers. A survey of related literature reveals an extensive effort in recent years in upgrading k-T1 correlations, driven primarily by applications in petroleum and gas field exploration and recovery. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 154,164, 2007. [source] Acute Adaptation to Volume Unloading of the Functional Single Ventricle in Children Undergoing Bidirectional Glenn AnastomosisCONGENITAL HEART DISEASE, Issue 2 2009Catherine Ikemba MD ABSTRACT Objective., Volume unloading of the functional single ventricle after a bidirectional Glenn anastomosis (BDG) prior to 1 year of age leads to improved global ventricular function as measured by the myocardial performance index (MPI), a Doppler-derived measurement of combined systolic and diastolic ventricular function. Systolic function remains unchanged after BDG according to previous studies; however, acute changes in global and diastolic function have not been previously investigated in this cohort. Our objective was to assess the short-term effects of the BDG on global ventricular function in patients with a functional single ventricle. Design., Echocardiograms to obtain MPI, isovolumic contraction time, and isovolumic relaxation time were performed at four time periods: in the operating room, in the operating room prior to BDG, shortly after separation from cardiopulmonary bypass, less than 24 hours postoperatively, and either prior to hospital discharge or at the first clinic follow-up visit. Results., Twenty-six patients were enrolled. There was significant ventricular dysfunction noted shortly after separation from cardiopulmonary bypass, median MPI 0.63 (0.39,0.81), that persisted in the short term postoperatively median MPI 0.50 (0.40,0.63). Isovolumic contraction time did not change, however, isovolumic relaxation time was significantly prolonged following BDG. Conclusion., In the postoperative patient after BDG, systolic function is preserved; however, there is evidence of diastolic and global ventricular dysfunction, at least in the short term. [source] Dependency of Tritium Retention in Graphite on Temperature Control of Molecular DynamicsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-5 2010A. Ito Abstract We have investigated the carbon plasma facing material and hydrogen atom interaction by the use of molecular dynamics simulation to clarify chemical erosion processes on divertor plate. The present paper is our first try at elucidation of temperature dependence by the molecular dynamics. Temperature was controlled by using Langevin thermostat method. As a result, the retention of hydrogen atom achieve steady state, and the CH4 was generated, which was not found MD simulations without a temperature control method. About 30 percent of injected hydrogen atoms are retained. CH4 yields has a peak at 600 K, which accords with experimental results. A dominant path of CH4 generation found by the present molecular dynamics simulation is as follows: a CH is detached from eroded surface and then it grows into CH4 adsorbing hydrogen atoms via CH2 and CH3. In addition, we propose the problem that the hydrogen atom retention and CH,, yields depend on the thermal relaxation time in MD simulation using temperature control methods (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Correlations of ELM Frequency with Pedestal Plasma CharacteristicsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 2 2005G. Kamberov Abstract JET and ASDEX data for the correlations of ELM's frequency with pedestal plasma temperature and density are compared with a corresponding functional dependence predicted by a classical Fokker-Planck approach. Deviations of the predicted relaxation time from the experimental data are found to increase with the input power. They are discussed in relation with a possible non-diffusional transport of plasma into the SOL. This approach gives opportunity to express the impact of the main engineering factors on ELM's frequency and to extrapolate it for ITER scenaria. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characteristics and dynamics of multiple intertidal bars, north Lincolnshire, EnglandEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2006Selma van Houwelingen Abstract Multiple intertidal bars and troughs, often referred to as ,ridges and runnels', are significant features on many macrotidal sandy beaches. Along the coastline of England and Wales, they are particularly prevalent in the vicinity of estuaries, where the nearshore gradient is gentle and a large surplus of sediment is generally present. This paper examines the dynamics of such bar systems along the north Lincolnshire coast. A digital elevation model of the intertidal morphology obtained using LIDAR demonstrates that three to five intertidal bars are consistently present with a spacing of approximately 100 m. The largest and most pronounced bars (height = 0·5,0·8 m) are found around mean sea level, whereas the least developed bars (height = 0·2,0·5 m) occur in the lower intertidal zone. Annual aerial photographs of the intertidal bar morphology were inspected to try to track individual bars from year to year to derive bar migration rates; however, there is little resemblance between concurrent photographs, and ,resetting' of the intertidal profile occurs on an annual basis. Three-dimensional beach surveys were conducted monthly at three locations along the north Lincolnshire coast over a one-year period. The intertidal bar morphology responds strongly to the seasonal variation in the forcing conditions, and bars are least numerous and flattest during the more energetic winter months. Morphological changes over the monthly time scale are strongly affected by longshore sediment transport processes and the intertidal bar morphology can migrate along the beach at rates of up to 30 m per month. The behaviour of intertidal bars is complex and varies over a range of spatial and temporal scales in response to a combination of forcing factors (e.g. incident wave energy, different types of wave processes, longshore and cross-shore sediment transport), relaxation time and morphodynamic feedback. Copyright © 2005 John Wiley & Sons, Ltd. [source] Initial hydrologic and geomorphic response following a wildfire in the Colorado Front RangeEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2001John A. Moody Abstract A wildfire in May 1996 burned 4690 hectares in two watersheds forested by ponderosa pine and Douglas fir in a steep, mountainous landscape with a summer, convective thunderstorm precipitation regime. The wildfire lowered the erosion threshold in the watersheds, and consequently amplified the subsequent erosional response to shorter time interval episodic rainfall and created both erosional and depositional features in a complex pattern throughout the watersheds. The initial response during the first four years was an increase in runoff and erosion rates followed by decreases toward pre-fire rates. The maximum unit-area peak discharge was 24 m3 s,1 km,2 for a rainstorm in 1996 with a rain intensity of 90 mm h,1. Recovery to pre-fire conditions seems to have occurred by 2000 because for a maximum 30-min rainfall intensity of 50 mm h,1, the unit-area peak discharge in 1997 was 6.6 m3 s,1 km,2, while in 2000 a similar intensity produced only 0.11 m3 s,1 km,2. Rill erosion accounted for 6 per cent, interrill erosion for 14 per cent, and drainage erosion for 80 per cent of the initial erosion in 1996. This represents about a 200-fold increase in erosion rates on hillslopes which had a recovery or relaxation time of about three years. About 67 per cent of the initially eroded sediment is still stored in the watersheds after four years with an estimated residence time greater than 300 years. This residence time is much greater than the fire recurrence interval so erosional and depositional features may become legacies from the wildfire and may affect landscape evolution by acting as a new set of initial conditions for subsequent wildfire and flood sequences. Published in 2001 by John Wiley & Sons, Ltd. [source] Effects of Continuous Positive Airway Pressure Therapy on Right Ventricular Function Assessment by Tissue Doppler Imaging in Patients with Obstructive Sleep Apnea SyndromeECHOCARDIOGRAPHY, Issue 10 2008Nihal Akar Bayram M.D. Objectives: The effects of continuous positive airway pressure (CPAP) therapy on right ventricular (RV) function in patients with obstructive sleep apnea syndrome (OSAS) has not been previously studied by tissue Doppler imaging (TDI). The aim of this study was to assess RV function using TDI in patients with OSAS before and after CPAP therapy. Methods: Twenty-eight patients with newly diagnosed OSAS in the absence of any confounding factors and 18 controls were included in this study. The peak systolic velocity (S,m), early (E,m) and late (A,m) diastolic myocardial peak velocities at tricuspid lateral annulus, isovolumic acceleration (IVA), myocardial precontraction time (PCT,m), myocardial contraction time (CT,m), and myocardial relaxation time (RT,m) were measured. All echocardiographic parameters were calculated 6 months after CPAP therapy. Results: The RV diastolic parameters such as E,m velocity and E,m-to-A,m ratio were significantly lower, RT,m was significantly prolonged, A,m velocity was similar in patients with OSAS compared to controls; and the RV systolic parameters such as IVA and CT,m were significantly lower and S,m was similar in patients with OSAS compared to controls. At the end of the treatment, 20 of 28 patients were compliant with CPAP therapy. E,m velocity, E,m-to-A,m ratio, IVA, and CT,m increased, PCT,m, PCT,m-to-CT,m ratio, and RT,m decreased significantly after therapy, whereas S,m velocity and A,m velocity did not change after CPAP treatment in the compliant patients. Conclusion: OSAS is associated with RV systolic and diastolic dysfunction, and 6 months of CPAP therapy improves the RV systolic and diastolic dysfunction. [source] Relationship between Slow Coronary Flow and Left Atrial Appendage Blood Flow VelocitiesECHOCARDIOGRAPHY, Issue 1 2007Recep Demirbag M.D. Aims: This study was undertaken to assess whether slow coronary flow (SCF)is related to low left atrial appendage (LAA) blood flow velocities. Methods: Study subjects consist of 44 patients with SCF and 11 volunteer subjects with normal coronary angiogram. The diagnosis of SCF was made using the TIMI frame count method. The blood flow velocities were obtained by placing a pulsed-wave Doppler sample volume inside the proximal third of the LAA. Results: The mean LAA emptying velocities (MEV)were significantly lower in patients than control subjects (34.5 ± 9.9 cm/sec vs 84.0 ± 12.1 cm/sec; P < 0.001). In bivariate analysis, significant correlation was found between MEV, and systolic pulmonary venous flow, mean TIMI frame count, deceleration time, and isovolumetric relaxation time (P < 0.05). By multiple linear regression analysis, mean TIMI frame count (ß=,0.865, P < 0.001) was identified as independent predictors of MEV. Conclusion: This study indicates that SCF phenomenon may be related to low LAA blood flows. [source] Correlation between Right Ventricular Indices and Clinical Improvement in Epoprostenol Treated Pulmonary Hypertension PatientsECHOCARDIOGRAPHY, Issue 5 2005Jayant Nath M.D. The aim of this study was to evaluate which parameter of right ventricular (RV) echocardiographic best mirrors the clinical status of patients with pulmonary arterial hypertension. Patients with pulmonary arterial hypertension on epoprostenol therapy were identified via hospital registry. Twenty patients, (16 females, 4 males) were included in the study, 9 with primary pulmonary hypertension and 11 with other diseases. Echocardiograms before therapy and at 22.7 (±9.3) months into therapy were compared. The right ventricular myocardial performance index (RVMPI) was measured as the sum of the isometric contraction time and the isometric relaxation time divided by right ventricular ejection time. Other measures included peak tricuspid regurgitation jet velocity (TRV), pulmonary artery systolic pressure (PASP), pulmonary valve velocity time integral (PVVTI), PASP/PVVTI (as an index of total pulmonary resistance) and symptoms by New York Heart Association (NYHA) functional class. Echo parameters of right ventricular function were analyzed in patients, before and during therapy. There was significant improvement of NYHA class in patients following epoprostenol therapy (P < 0.0001). Peak tricuspid regurgitant jet velocity (pre 4.2 ± 0.6 m/sec, post 3.8 ± 0.7 m/sec, P = 0.02) and PASP/PVVTI (pre 6.7 ± 3.3 mmHg/m per second, post 4.8 ± 2.2 mmHg/m per second, P < 0.0001) were significantly improved during treatment. RVMPI did not improve (pre 0.6 ± 0.3, post 0.6 ± 0.3, P = 0.54). Changes in NYHA class did not correlate with changes in RVMPI (P = 0.33) or changes in PASP/PVVTI (P = 0.58). Despite significant improvements in TRV, PASP/PVVTI, and NYHA class, there was no significant change in RVMPI on epoprostenol therapy. Changes in right ventricular indices were not correlated with changes in NYHA class. [source] The Myocardial Performance Index in Patients with Aortic StenosisECHOCARDIOGRAPHY, Issue 4 2002Jude A. Mugerwa M.D. Objectives: This study was designed to determine the effect of chronic afterload on a Doppler-derived myocardial performance index (MPI) combining both systolic and diastolic left ventricular dysfunction. Methods: The study included 36 patients with a diagnosis of aortic stenosis and 36 normal subjects. Doppler-derived myocardial performance index (MPI), defined as the sum of the isovolumic contraction time and isovolumic relaxation time divided by ejection time, was measured from the mitral valve inflow and left ventricular outflow velocity patterns and was then related to the aortic valve area, valve gradient, and other echocardiographic variables. Results: The values of the Doppler-derived MPI in the patients with aortic stenosis were significantly higher than those in the controls (0.54 ± 0.20 vs 0.38 ± 0.04, respectively; P < 0.001). Transmitral deceleration time and the E/A ratio (r = 0.47 and r = 0.35, respectively; P < 0.05) were significant univariate correlates, and mitral deceleration time was the only significant correlate of MPI. However the index did not correlate with aortic valve area, peak and mean valve gradients, left ventricular mass, or age. Conclusions: Doppler-derived MPI reflects severity of global left ventricular dysfunction in patients with aortic stenosis and may be of clinical value in this patient population. [source] Tissue inhibitor of metalloproteinse-1 is a marker of diastolic dysfunction using tissue doppler in patients with type 2 diabetes and hypertensionEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 1 2005M. H. Tayebjee Abstract Background, Tissue inhibitor of metalloproteinase-1 (TIMP-1) is associated with increased fibrosis of the extracellular matrix (ECM). Myocardial stiffness is a feature of diastolic dysfunction. We assessed circulating TIMP-1 as a marker of diastolic dysfunction in patients with type 2 diabetes mellitus (DM) and hypertension, who were compared with healthy controls. Methods, We recruited 54 patients (43 males; mean age 68 ± 5 years) with treated type 2 DM (i.e. controlled glycaemia, hypertension, hyperlipidaemia), 35 (30 males; 69 ± 8 years) treated nondiabetic hypertensives, and 31 healthy controls (18 males; 66 ± 5 years). Circulating TIMP-1 was measured by ELISA. Using transthoracic echocardiography, the early (E) diastolic mitral inflow velocity was measured with pulse wave Doppler, and the early mitral annular velocity (e,), a recognized index of diastolic relaxation, was measured with tissue Doppler. The E/A ratio was also calculated and isovolumic relaxation time measured. Results, Mean e, levels differed significantly between controls, diabetics and hypertensives (P < 0·0001). Circulating TIMP-1 was significantly different between patients and controls (P = 0·006), but there was no statistically significant difference between the DM and hypertension group. In both groups, only e, was negatively correlated with TIMP-1 levels, with a stronger correlation among the hypertensive patients (Spearman r = ,0·544, P = 0·001) when compared with the diabetic group (r = ,0·341, P = 0·011). Conclusion, Diastolic relaxation is impaired in diabetes and hypertensive patients. The relationship between TIMP-1 and e, may reflect increased myocardial fibrosis and consequent diastolic dysfunction, which may be more prominent in hypertension. [source] Age-associated changes in viscoelastic properties of the bovine temporomandibular joint discEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2006Eiji Tanaka To test the hypothesis that compressive properties of the temporomandibular joint (TMJ) disc change with age, we investigated its viscoelastic properties and stress-relaxation behavior under compression. Compressive stress-relaxation tests were performed in different regions of bovine discs of various ages. For each disc, specimens were derived from three different regions (anterior, central, and posterior). For four strain levels (5, 10, 15, and 20%), a stress-relaxation test was conducted over a 5-min period. Values of the instantaneous modulus, E0, appeared to be larger in the anterior than in the posterior region of the disc, irrespective of age. The E0 value increased with age, especially in the central region. Values of the relaxed modulus, ER, also increased significantly with age. There were no regional differences in values of the relaxed modulus. Under stress-relaxation, the relaxation time became longer with age, especially in the posterior region. The results suggest that the compressive properties, instantaneous and relaxed moduli, increase with age, while the relaxation time becomes longer. This implies that the TMJ disc becomes harder with age. Furthermore, the compressive properties of the TMJ disc are region-specific. As a result of the harder disc, it is likely that the TMJ becomes more vulnerable to secondary damage, such as fracture and tissue degradation. [source] Measurement of the size distribution of water-filled pores at different matric potentials by stray field nuclear magnetic resonanceEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2005N. R. A. Bird Summary The water retention characteristic provides the traditional data set for the derivation of a soil's pore-size distribution. However, the technique employed to achieve this requires that assumptions be made about the way pores interconnect. We explore an alternative approach based on stray field nuclear magnetic resonance (STRAFI-NMR) to probe the water-filled pores of both saturated and unsaturated soils, which does not require information relating to pore connectivity. We report the relative size distributions of water-occupied pores in saturated and unsaturated samples of two sets of glass beads of known particle size, two sands, and three soils (a silty loam, a sandy loam and a loamy sand), using measurements of the NMR T1 proton relaxation time of water. The T1 values are linearly related to pore size and consequently measured T1 distributions provide a measure of the pore-size distribution. For both the sands and the glass beads at saturation the T1 distributions are unimodal, and the samples with small particle sizes show a shift to small T1 values indicating smaller voids relative to the samples with larger particles. Different matric potentials were used to reveal how the water-occupied pore-size distribution changes during drainage. These changes are inconsistent with, and demonstrate the inadequacies of, the commonly employed parallel-capillary tube model of a soil pore space. We find that not all pores of the same size drain at the same matric potential. Further, we observe that the T1 distribution is shifted to smaller values beyond the distribution at saturation. This shift is explained by a change in the weighted average of the relaxation rates as the proportion of water in the centre of water-filled pores decreases. This is evidence for the presence of pendular structures resulting from incomplete drainage of pores. For the soils the results are similar except that at saturation the T1 distributions are bimodal or asymmetrical, indicative of inter-aggregate and intra-aggregate pore spaces. We conclude that the NMR method provides a characterization of the water-filled pore space which complements that derived from the water retention characteristic and which can provide insight into the way pore connectivity impacts on drainage. [source] Pressure-exploration of the 33-kDa protein from the spinach photosystem II particleFEBS JOURNAL, Issue 9 2001Kangcheng Ruan The 33-kDa protein isolated from the spinach photosystem II particle is an ideal model to explore high-pressure protein-unfolding. The protein has a very low free energy as previously reported by chemical unfolding studies, suggesting that it must be easy to modulate its unfolding transition by rather mild pressure. Moreover, the protein molecule consists of only one tryptophan residue (Trp241) and eight tyrosine residues, which can be conveniently used to probe the protein conformation and structural changes under pressure using either fluorescence spectroscopy or fourth derivative UV absorbance spectroscopy. The different experimental methods used in the present study indicate that at 20 °C and pH 6, the 33-kDa protein shows a reversible two-state unfolding transition from atmospheric pressure to about 180 MPa. This value is much lower than those found for the unfolding of most proteins studied so far. The unfolding transition induces a large red shift of the maximum fluorescence emission of 34 nm (from 316 nm to 350 nm). The change in standard free energy (,Go) and in volume (,V) for the transition at pH 6.0 and 20 °C are ,14.6 kJ·mol,1 and ,120 mL·mol,1, respectively, in which the ,Go value is consistent with that obtained by chemical denaturation. We found that pressure-induced protein unfolding is promoted by elevated temperatures, which seem largely attributed to the decrease in the absolute value of ,Go (only a minor variation was observed for the ,V value). However, the promotion of the unfolding by alkaline pH seems mainly related to the increase in ,V without any significant changes in ,Go. It was also found that NaCl significantly protects the protein from pressure-induced unfolding. In the presence of 1 m NaCl, the pressure needed to induce the half-unfold of the protein is shifted to a higher value (shift of 75 MPa) in comparison with that observed without NaCl. Interestingly, in the presence of NaCl, the value of ,V is significantly reduced whilst that of ,Go remains as before. The unfolding-refolding kinetics of the protein has also been studied by pressure-jump, in which it was revealed that both reactions are a two-state transition process with a relatively slow relaxation time of about 102 s. [source] Modulation of Viscoelasticity and HIV Transport as a Function of pH in a Reversibly Crosslinked HydrogelADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Julie I. Jay Abstract Materials that respond to physiological stimuli are important in developing advanced biomaterials for modern therapies. The reversibility of covalent crosslinks formed by phenylboronate (PBA) and salicylhydroxamate (SHA) has been exploited to provide a pH-responsive gel for application to the vaginal tract. Dynamic rheology reveals that the gel frequency-dependent viscoelastic properties are modulated by pH. At pH 4.8 the viscous component dominates throughout most of the frequency range. As the pH increases, the characteristic relaxation time continues to increase while the G,Plateau levels off above pH 6. At pH 7.5, the elastic component dominates throughout the frequency sweep and is predominately independent of frequency. Particle tracking assesses the transport of both fluorescently labeled HIV-1 and 100-nm latex particles in the PBA,SHA crosslinked gel as a function of pH. At pH 4.8 the ensemble-averaged mean squared displacement at lag times greater than three seconds reveals that transport of the HIV-1 and 100-nm particles becomes significantly impeded by the matrix, exhibiting diffusion coefficients less than 0.0002,µm2 s,1. This pH-responsive gel thus displays properties that have the potential to significantly reduce the transport of HIV-1 to susceptible tissues and thus prevent the first stage of male-to-female transmission of HIV-1. [source] Viscoelastic,afterslip concurrence: a possible mechanism in the early post-seismic deformation of the Mw 7.6, 1999 Chi-Chi (Taiwan) earthquakeGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Shyh-Yang Sheu SUMMARY Observed coseismic data as well as 97 days of post-seismic GPS data for the Chi-Chi earthquake are used as constraints in the modelling of crustal evolution using the 3-D finite-element method. First, the coseismic GPS data are used to justify the use of the elastic earth model and the source rupture model. Subsequently, the most likely rheological model is determined by analysing several modelled time-dependent displacements for various viscosity structures. The range of viscosities of the lower crust in central Taiwan is determined in advance from laboratory measurements and the long-term strain rate. The estimated viscosity of 5.0 × 1017 Pa s seems to be very low and a relaxation time of 116 days seems very short, but the latter approximates the GPS measurement of 86 days. Since earlier studies have indicated that both the viscoelastic response model and the afterslip model may affect post-seismic deformation, we compare theoretical surface displacements for each of the two models that we evaluate. The results reveal that there is little doubt that while neither of these models alone is able to predict the GPS measurements well in a 97-day period, the combination of the two models improves the predictions considerably. We conclude that the afterslip mainly dominated Chi-Chi post-seismic deformation in the rupture area while the viscoelastic model did so elsewhere. [source] Combined Optical and MR Bioimaging Using Rare Earth Ion Doped NaYF4 NanocrystalsADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Rajiv Kumar Abstract Here, novel nanoprobes for combined optical and magnetic resonance (MR) bioimaging are reported. Fluoride (NaYF4) nanocrystals (20,30,nm size) co-doped with the rare earth ions Gd3+ and Er3+/Yb3+/Eu3+ are synthesized and dispersed in water. An efficient up- and downconverted photoluminescence from the rare-earth ions (Er3+ and Yb3+ or Eu3+) doped into fluoride nanomatrix allows optical imaging modality for the nanoprobes. Upconversion nanophosphors (UCNPs) show nearly quadratic dependence of the photoluminescence intensity on the excitation light power, confirming a two-photon induced process and allowing two-photon imaging with UCNPs with low power continuous wave laser diodes due to the sequential nature of the two-photon process. Furthermore, both UCNPs and downconversion nanophosphors (DCNPs) are modified with biorecognition biomolecules such as anti-claudin-4 and anti-mesothelin, and show in vitro targeted delivery to cancer cells using confocal microscopy. The possibility of using nanoprobes for optical imaging in vivo is also demonstrated. It is also shown that Gd3+ co-doped within the nanophosphors imparts strong T1 (Spin-lattice relaxation time) and T2 (spin-spin relaxation time) for high contrast MR imaging. Thus, nanoprobes based on fluoride nanophosphors doped with rare earth ions are shown to provide the dual modality of optical and magnetic resonance imaging. [source] Quantitative T1 mapping of hepatic encephalopathy using magnetic resonance imagingHEPATOLOGY, Issue 5 2003Nadim Joni Shah M.D. Changes are shown in the spin-lattice (T1) relaxation time caused by the putative deposition of manganese in various brain regions of hepatic encephalopathy (HE) patients using a novel and fast magnetic resonance imaging (MRI) method for quantitative relaxation time mapping. A new method, T1 mapping with partial inversion recovery (TAPIR), was used to obtain a series of T1 -weighted images to produce T1 maps. Imaging of 15 control subjects and 11 patients was performed on a 1.5T MRI scanner. The measurement time per patient with this technique, including adjustments, was ,5 minutes. Regions of interest in the globus pallidus, the caudate nucleus, the posterior and anterior limbs of the internal capsule, the putamen, the frontal and occipital white matter, the white matter of the corona radiata, the occipital visual and frontal cortices, and the thalamus were interactively defined in the left hemisphere and analyzed with respect to their T1 values. T1 changes in the brains of HE patients can be determined quantitatively with TAPIR in short, clinically relevant measurement times. Significant correlations between the change in T1 and HE severity have been shown in the globus pallidus, the caudate nucleus, and the posterior limb of the internal capsule. No significant correlation of T1 with grade of HE was found in the putamen, frontal white matter, white matter of the corona radiata, white matter in the occipital lobe, the anterior limb of the internal capsule, visual cortex, thalamus, or frontal cortex. In conclusion, these measurements show that T1 mapping is feasible in short, clinically relevant acquisition times. [source] High-Modulus Organic Glasses Prepared by Physical Vapor DepositionADVANCED MATERIALS, Issue 1 2010Kenneth L. Kearns Extraordinarily stable organic glasses are prepared by physical vapor deposition using indomethacin (IMC) or trisnaphthylbenzene. Utilizing Brillouin light scattering (BLS), the elastic moduli of these stable glasses (SG) are found to exceed those of ordinary glass (OG) by up to 19%. Such high-modulus glasses take more than 104 times longer than the structural relaxation time to transform to the supercooled liquid (SCL). [source] Assessment of algorithms for the no-slip boundary condition in the lattice Boltzmann equation of BGK modelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2008Yong Kweon Suh Abstract Three kinds of algorithms for the lattice Boltzmann equation of the BGK model in the implementation of the no-slip boundary condition on the wall are assessed by using the analytical formula for the slip velocity of the fully developed pressure-driven channel flow. It is shown that the bounce-back algorithm results in the spatial accuracy of 1st order, except for the case when the wall is located at half way between the two grid lines. The interpolation scheme proposed by Yu et al. (Prog. Aerospace Sci. 2003; 39:329,367) and the similar one by Bouzidi et al. (Phys. Fluids 2001; 13(11):3452,3459) are of 2nd order, but the error increases quadratically with the relaxation time. The extrapolation scheme of Guo et al. (Phys. Fluids 2002; 14(6):2007,2010) is also shown to be of 2nd order, and the error level increases linearly with the relaxation time, but it turns out that this scheme is unstable for a certain range of parameter values. Numerical experiments with various parameter sets have been performed to obtain the stability diagram. Three algorithms are then applied to a circular-Couette flow and their performance is also studied in terms of the numerical accuracy and stability. Copyright © 2008 John Wiley & Sons, Ltd. [source] Use of associating polymers as multifunctional thickeners: studies of Their structure in aqueous solutions via nmr, qels, fluorescence, And rheology measurementsINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 5 2007Katsunori Yoshida The solution properties of an associating polymer were studied by NMR, quasi-elastic light scattering (QELS), fluorescence, and rheology measurements. An associative thickening (AT) polymer was designed having a nonionic poly(ethylene oxide) backbone with long alkyl chains at both ends to achieve high viscosity even at relatively high salt concentrations and over a wide pH range. This study focuses on the associative state of the polymer in aqueous solutions at various polymer concentrations. In a fluorescence probe study using pyrene a spectral change in the I3/I1 ratio was observed for pyrene at a polymer concentration (Cp) of 3 x 10 -4%, indicating an apparent critical concentration (cmc) of the amphiphilic polymer. The viscosity, self-diffusion coefficient (Dsel), and hydrodynamic size (Rh) distribution measurements at various Cp all suggest that there is a second transition at Cp, 0.4%. Although we observed the discontinuity in viscosity, Dsel, and Rh at Cp, 0.4%, no changes in the relaxation times (T1 and T2) were recognized for either the alkyl chain or the ethylene oxide moiety of the polymer at C p= 0.1,1%. These data suggest that there are no structural changes or phase transitions at Cp, 0.4%, but that intermicellar networks are presumably formed by bridging of the end alkyl groups of the polymer, which is driven by hydrophobic forces. Because the polymer forms networks by hydrophobic interaction and the polymer itself is nonionic, the viscosity of the polymer solution was influenced very little by either the addition of salt or a pH change, as would be expected. The dynamic viscoelastic study revealed that the polymer solution exhibits a single mode Maxwell type relaxation behavior with a terminal relaxation time of about 0.61 s, which imparts a unique flow appearance to the polymer solutions. The time course measurements of the dynamic elastic modulus of the stratum corneum revealed that the polymer has excellent potential for skin softening. It was concluded that the associative thickening polymer not only is a useful thickener with a salt and pH tolerance but also has beneficial skincare effects. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||