Changes In Relaxation Rate Research Articles

Photodissociation and vibrational relaxation of I−2 in water, ethanol, and ethanol-d1

We have investigated the photodissociation and vibrational relaxation of I−2 in water, ethanol, and ethanol-d1. Internal conversion, geminate recombination, and vibrational relaxation in the top 70% of the ground state potential in water are complete within the time resolution of our apparatus ( <0.3 ps). Vibrational relaxation down the remainder of the potential (ν⩽10) occurs with a time constant of ≈3 ps, very similar to the value of ≈4 ps previously observed in ethanol. Deuteration of the alcoholic proton in ethanol causes no measurable change in the vibrational relaxation rate at the bottom of the well (3.4 ± 0.4 ps in ethanol, 4.0 ± 0.4 ps, ethanol-d1), indicating that the solvent degrees of freedom involved in accepting the I−2 vibrational energy at the bottom of the well do not involve inertial hydrogenic motions of the hydroxyl group. Simple spectral and kinetic modeling is employed to help interpret the data.

Laser induced dynamics of atomic sublevel coherences

In atomic media, the interaction with resonant light leads to optical pumping and light shift effects which modify not only the static optical and magneto-optical properties of the media, but also the dynamics of multipole moments that are present in the electronic ground state as well as in electronically excited states. These modified dynamics include changes in precession frequencies and relaxation rates, but also laser-induced exchange of coherences between different atomic multipole moments. Using the Na ground state as an example, a theoretical analysis of these modified dynamics is presented, as well as experimental measurements of the laser induced coherence transfer.

Resistivity in the spin-gap phase of strongly correlated fermions.

In the gauge theories of strongly correlated electrons, the linear-[ital T] resistivity observed in high-temperature-superconductor cuprates is attributed to the scattering of charge carriers by low-frequency long-wavelength gauge fluctuations. We discuss the change in resistivity from the strange-metal to the spin-gap phase, where, in mean-field theory, the fermion liquid becomes superfluid, and its correlation with the change in nuclear relaxation rate [ital T][sub 1]. The effect of fluctuations is qualitatively described. We also discuss the low-temperature resistivity. Experimental data is not in disagreement with the gauge-fluctuation theory.

Effects of chronic mitral regurgitation on diastolic function in isolated cardiocytes.

We have previously shown that chronic mitral regurgitation (MR) increases the rate of left ventricular early diastolic filling. These changes in chamber diastolic function were felt to be secondary to alterations in left ventricular loading conditions. Therefore, cellular diastolic function measured in cardiac muscle cells (cardiocytes) isolated from animals with chronic MR (absent alterations in loading conditions) was expected to be normal. However, chronic MR caused a decrease in sarcomere lengthening rate. The purpose of the current study was to define the mechanisms causing this decreased sarcomere lengthening rate in chronic MR cardiocytes and to explain the apparent dichotomy between chamber and cellular diastolic properties. Accordingly, sarcomere motion was measured using laser diffraction techniques in enzymatically isolated cardiocytes from seven control dogs and 11 dogs with chronic MR (produced by closed-chest transection of the mitral chordae). In the MR cardiocytes, there were abnormalities in cellular systolic function (decreased extent and velocity of shortening) and in cellular diastolic function (decreased velocity of sarcomere lengthening). Because studies in papillary muscles have shown that there is a direct relation between abnormal diastolic function (decreased velocity of muscle lengthening) and abnormal systolic function (decreased extent of muscle shortening), it was unclear whether the changes in cellular relaxation rate observed in chronic MR merely reflected a concomitant decrease in the extent of shortening or instead reflected an impairment in intrinsic relaxation properties. To make this distinction, the relation between relaxation velocity (measured as peak sarcomere lengthening rate) and sarcomere shortening extent was examined in MR cardiocytes and compared with that in control cardiocytes. There was a direct relation between sarcomere relaxation velocity and sarcomere shortening extent in both control and MR cardiocytes. Over a wide range of shortening extent, the slopes and y intercepts of this relation were similar in control and MR cardiocytes (slope, 27.7 sec-1 in control cells versus 28.1 sec-1 in MR cells; y intercept, -1.1 microns/sec in control cells versus -1.7 microns/sec in MR cells; p = NS). At any common shortening extent, relaxation velocity was the same in control and MR cardiocytes. To prove that this relation could detect abnormalities in the intrinsic myocardial relaxation process, interventions known to produce primary alterations in the intrinsic myocardial relaxation process were examined: the effects of hypothermia (30 degrees C) and isoproterenol (10(-6) M) on the relaxation velocity-shortening extent relation were studied in normal and MR cardiocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Test Machine and Control System Interactions in the Evaluation of Rate-Dependent Metal Flow

Although rate-change experiments are essential for characterizing rate-dependent flow, certain nonobvious aspects of test machine dynamic response and control system strategies can distort rate-change data. These distortions are large enough to cause rate-change experiments to characterize the test system dynamic response instead of the test material’s rate dependence. We demonstrate that both relaxation and strain rate change experiments exhibit this potential distortion of test data. Investigators performing these experiments must therefore examine control error carefully to assure that the experiments are valid. We demonstrate that the standard PID control modes normally used in servocontrolled mechanical test equipment will generate error. Either P or PD control modes are more appropriate for rate-change experiments.

The Effect of Respiratory and Lactic Acidosis on Diaphragm Function

The relative effects of respiratory and metabolic acidosis on diaphragm function are not known. To determine these effects, we compared the effects of respiratory and lactic acidosis on the contractile properties of the diaphragm. We estimated diaphragmatic performance from the change in transdiaphragmatic pressure after supramaximal stimulation of the phrenic nerves in an open-chested, casted-abdomen dog. Similarly, we stimulated the gastrocnemius motor nerve and examined force production and relaxation rate to determine if there was a difference in the response of this skeletal muscle. There was a fall in diaphragm performance with respiratory acidosis (77.1 +/- 16.9 cm H2O versus 93.8 +/- 15.0 cm H2O baseline), but not with lactic acidosis (96.7 +/- 15.7 cm H2O versus 93.8 +/- 15.0 cm H2O baseline); and the gastrocnemius was unaffected by either acidosis. The changes with respiratory acidosis were similar to those seen with diaphragmatic fatigue and had similar relaxation rate changes, suggesting that intracellular pH may play a mechanistic role in respiratory muscle fatigue. In addition, the absence of a respiratory acidosis effect on a non-diaphragmatic skeletal muscle's function represents another physiologic difference between the diaphragm and other skeletal muscles.

Counterion affinity orders in aqueous micellar solutions of sodium decyl phosphate and sodium dodecyl sulfate determined by changes in sodium-23 NMR relaxation rates: a surprising dependence on head group charge

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCounterion affinity orders in aqueous micellar solutions of sodium decyl phosphate and sodium dodecyl sulfate determined by changes in sodium-23 NMR relaxation rates: a surprising dependence on head group chargeLaurence S. Romsted and Choon Ock YoonCite this: J. Am. Chem. Soc. 1993, 115, 3, 989–994Publication Date (Print):February 1, 1993Publication History Published online1 May 2002Published inissue 1 February 1993https://doi.org/10.1021/ja00056a025RIGHTS & PERMISSIONSArticle Views364Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (848 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

Effect of Inspiratory Muscle Fatigue on Inspiratory Muscle Relaxation Rates in Healthy Subjects

Simple methods to diagnose inspiratory muscle fatigue in the clinical setting would be of considerable benefit. Inspiratory muscle relaxation rates are known to slow following induction of fatigue. Inspiratory muscle relaxation rates have been measured following a short sharp inspiratory effort against an occluded airway (sniffmouth) or through the unoccluded nostrils (sniffnostrils). Relaxation rates in the absence of fatigue are faster when sniffs are performed through the unoccluded nostrils. While both methods have been shown to be capable of detecting inspiratory muscle fatigue, there may be quantitative or qualitative differences between the two techniques in their ability to detect fatigue similar to the differences observed in the fresh state. Accordingly, we measured relaxation rates with the two sniff techniques in five healthy naive male subjects before and after induction of fatigue. Inspiratory muscle fatigue was induced by threshold loading at 80 percent of Pesmax until the subjects were unable to generate the target pressure. For those trials in which sniffnostrils were performed, the maximum relaxation rate from the esophageal pressure curve (MRRes) was significantly decreased following induction of fatigue in nine of ten trials, while the exponential time constant (taues) was significantly increased in all ten trials. In contrast, for those trials in which sniffmouth were performed, the MRRes was significantly decreased following induction of fatigue in only six of ten trials. Similarly, taues was significantly increased following induction of fatigue in only six of ten trials. In addition, the magnitude of change in the MRR or tau following induction of fatigue was quantitatively greater with sniffnostrils compared with sniffmouth. Similar findings were obtained when relaxation rates were measured from the diaphragmatic pressure tracing. In conclusion, changes in relaxation rate following induction of fatigue were quantitatively greater and more consistently observed when sniffs were performed through the unoccluded nostrils rather than against an occluded airway.

Enhanced inotropic responsiveness to alpha 1-adrenoceptor stimulation in isolated working hearts from diabetic rats.

We compared the inotropic responsiveness to the alpha 1-adrenoceptor agonist cirazoline and the calcium entry promoter Bay K 8644 in isolated working hearts from streptozotocin (STZ) diabetic rats and age-matched controls. The maximal rate of contraction and cardiac output (CO) were unaffected by diabetes. The maximal rate of relaxation was significantly decreased in diabetic hearts as compared with controls. Cirazoline (10(-9)-10(-6) M) induced an increase in both maximal rate of contraction and relaxation in diabetic and control hearts. Notably, the maximal rate of contraction was significantly greater in diabetic hearts. Changes in maximal rate of relaxation were similar in both preparations. A significant increase in CO was observed in diabetic hearts, but not in controls. With Bay K 8644 (10(-9)-10(-6) M) added, the increase in maximal rate of contraction and relaxation as well as CO were not significantly different in the two preparations although the changes in maximal rate of relaxation tended to be decreased in diabetic hearts. Our results indicate that cardiac alpha 1-adrenoceptors appear to gain greater functional importance in regulation of myocardial inotropism in diabetes mellitus.

Low-temperature vibrational relaxation in crystalline carbon disulfide at high pressure

Picosecond coherent Raman measurements are made on crystalline CS{sub 2} in a high-pressure diamond anvil cell at low temperature as a sensitive probe of the intermolecular interactions which give rise to relaxation phenomena. The authors observe density-dependent changes in the low-temperature vibrational relaxation rate of the v{sub 1} and 2v{sub 2} vibrational modes and analyze these results in terms of pressure-induced changes in intermolecular anharmonicities and pressure-induced shifts in the phonon density of states. 46 refs., 4 figs., 1 tab.

Picosecond Photon Echo and Coherent Raman Measurements on Molecular Solids in a High Pressure Diamond Anvil Cell

Abstract We report the first picosecond photon echo measurements on a molecular solid in a high pressure diamond anvil cell at low temperature. We also present time-resolved coherent Raman measurements of vibrational relaxation in pure molecular crystals as a function of pressure in a diamond anvil cell at low temperature. Since photon echo spectroscopy eliminates inhomogeneous dephasing, we utilize this technique to yield the homogeneous dephasing rate for high pressure samples where sample inhomogeneities and inhomogeneous pressure gradients may exist. Since the Fourier transform of the photon echo decay yields the absorption lineshape, these experiments provide a means of obtaining high resolution spectra under extreme high pressure conditions. In addition, pressure induced changes in vibrational relaxation rates observed by picosecond coherent Raman measurements are used as a sensitive probe of the intermolecular interactions that give rise to relaxation phenomena.

Confined geometry effects on reorientational dynamics of molecular liquids in porous silica glasses

This work investigates the relative role of the pure geometrical confinement and the strength of the surface effect on the dynamics of liquids in porous silica glasses prepared by the sol-gel process. The deuteron NMR spin-lattice relaxation times T1 of several molecular liquids in porous silica glasses are reported as function of pore size in the range from 18 to 143 Å over the temperature range from 260 to 310 K. Molecular liquids studied include strongly interacting polar liquids such as pyridine-d5, aniline-d5, and nitrobenzene-d5, whereas the saturated cyclic hydrocarbon liquids of cyclohexane-d12 and cis-decalin-d18 represent the weakly interacting liquids. In a first approximation, toluene-d1 and dioxane-d18 are chosen as examples of liquids with intermediate interactions with the silica surface. The experimental relaxation data are analyzed by using the two-state, fast-exchange model which is found to be valid for the strongly interacting liquids and liquids with intermediate interactions. In terms of this model, the viscosity of the surface layer for pyridine-d5 is about 30 times higher than that for bulk liquid pyridine. The importance of the two-dimensional approach to describe motional dynamics of liquids confined to pores smaller than 30 Å is illustrated in the case of weakly interacting liquid of cyclohexane-d12. Additional information on the relative role of surface interactions and the pure topological effects on the dynamics of liquids in confined geometries was obtained by using surface-modified glasses in which the surface hydroxyl groups were replaced by OSi(CH3)2OC2H5 groups. Indeed, the effects of surface modifications on the 2H T−11 are most pronounced for strongly interacting liquids whereas they are absent for cyclohexane. In agreement with the concept of two-dimensional behavior of liquids in small pores, one finds that the low-frequency relaxation times, namely, the spin–spin relaxation time T2, and the spin-lattice relaxation time in the rotating coordinate frame, T1ρ, remain unchanged by surface modification. In fact, this is a consequence of logarithmic enhancement of the spectral density at low frequencies so that the effect of pure geometrical confinement on the T−12 and T−11ρ relaxation rates is much larger than any relaxation rate changes arising from surface modification. Several selected NMR T1 experiments on pyridine-d5 confined to anopore and zeolites are also presented.

Gating current "fractionation" in crayfish giant axons

Effects of changes in initial conditions on the magnitude and kinetics of gating current and sodium current were studied in voltage-clamped, internally-perfused, crayfish giant axons. We examined the effects of changes in holding potential, inactivating prepulses, and recovery from inactivation in axons with intact fast inactivation. We also studied the effects of brief interpulse intervals in axons pretreated with chloramine-T for removal of fast inactivation. We find marked effects of gating current kinetics induced by both prepulse inactivation and brief interpulse intervals. The apparent changes in gating current relaxation rates cannot be explained simply by changes in gating charge magnitude (charge immobilization) combined with "Cole-Moore-type" time shifts. Rather they appear to indicate selective suppression of kinetically-identifiable components within the control gating currents. Our results provide additional support for a model involving parallel, nonidentical, gating particles.

Parvalbumin content and Ca2+ and Mg2+ dissociation rates correlated with changes in relaxation rate of frog muscle fibres.

1. Experiments were done to test the hypothesis that parvalbumin (PA) promotes relaxation in frog skeletal muscle. Single fibres and purified PA from Rana temporaria skeletal muscle were used to determine the relationship between PA concentration ( [PA] ), Ca2+ and Mg2+ dissociation rates from PA and changes in rate of relaxation as a function of tetanus duration at 0 degrees C. 2. Total [PA] in fibres from tibialis anterior muscles is 0.76 +/- 0.20 mmol PA l-1 myoplasmic water (mean +/- S.D., n = 25) with 65% PA IVa and 35% PA IVb, where PA IVa and PA IVb are PA isoforms. 3. Relaxation rate from an isometric tetanus shows progressively as a function of tetanus duration with an exponential time course and a rate constant of 1.18 +/- 0.35 s-1 (n = 17). Time course of recovery of relaxation rate after a prolonged tetanus is exponential with a rate constant of 0.12 +/- 0.02 s-1 (n = 14). 4. The extent of recovery of relaxation rate after a prolonged tetanus was correlated with total [PA] in fibres (correlation coefficient (r) = 0.80, n = 7; P less than 0.05). 5. Dissociation rate constants for Mg2+ and Ca2+ from purified PA are 0.93 +/- 0.02 s-1 (n = 5) and 0.19 +/- 0.01 s-1 (n = 5), respectively. Dissociation rate constants were not significantly different for PA isoforms IVa and IVb. These rate constants are similar to the rate constants determined for the time courses of slowing and recovery of relaxation rate, respectively. 6. Results suggest that the time courses of slowing and recovery of relaxation rate may be controlled, to a large extent, by Mg2+ and Ca2+ dissociation from PA, respectively. This evidence supports a role for PA in facilitating relaxation during a tetanus in frog skeletal muscle at 0 degrees C.

Inspiratory muscle relaxation rate after voluntary maximal isocapnic ventilation in humans

We have investigated whether the capacity of the inspiratory muscles to generate pressure and flow during a ventilatory load is related to changes in inspiratory muscle relaxation rate. Five highly motivated normal subjects performed voluntary maximal isocapnic ventilation (MIV) for 2 min. Minute ventilation and esophageal, gastric, and transdiaphragmatic pressures were measured breath by breath. We observed that ventilation, peak inspiratory and expiratory pressures, and inspiratory flow rate declined from the start of the run to reach a plateau at 60 s that was sustained for the remainder of the exercise. In a subsequent series of studies, MIV was performed for variable durations between 15 and 120 s. The normalized maximum relaxation rate of unoccluded inspiratory sniffs (sniff MRR, %pressure loss/10 ms) was determined immediately on stopping MIV. Sniff MRR slowed as the duration of MIV increased and paralleled the decline in inspiratory pressure and ventilation observed during the 2-min exercise. No further slowing in MRR occurred when ventilation became sustainable. We conclude that, during MIV, the progressive loss of ventilation and capacity to generate pressure is associated with the early onset and progression of a peripheral fatiguing process within the inspiratory muscles.

MR Contrast Due to Microscopically Heterogeneous Magnetic Susceptibility: Numerical Simulations and Applications to Cerebral Physiology

We calculate the effects of subvoxel variations in magnetic susceptibility on MR image intensity for spin-echo (SE) and gradient-echo (GE) experiments for a range of microscopic physical parameters. The model used neglects the overlap of gradients from one magnetic inclusion to the next, and so is valid for low volume fractions and weak perturbations of the magnetic field. Transverse relaxation is predicted to deviate significantly from linear exponential decay in both SE and GE at a particle radius of 2.5 microns. Calculated changes in transverse relaxation rates for SE and GE increase linearly with volume fraction of high-susceptibility regions of 5 microns diameter, but increase with about the 3/2 power of volume fraction of regions with 15 micron spacing between centers. This sensitivity to the actual size and spacing of magnetized regions may allow them to be measured on the basis of contrast. without being resolved in images. GE and SE decay rates are approximately twice as sensitive to long cylinders of 5 microns diameter than to spheres of the same size, for diffusion constants of 2.5 micron 2/ms. Calculated changes in transverse decay rates increase with approximately the square of field and susceptibility variation for 5-microns spheres and a diffusion constant of 2.5 microns 2/ms. This exponent is smaller for cylindrical magnetized regions of the same size, and also depends on the diffusion constant. We discuss possible applications of our theoretical results to the analysis of the effects of high-susceptibility contrast agents in brain. Experimental data from the literature are compared with calculated signal changes according to the model. The monotonic dependence of decay rates on the volume of distribution of the contrast agent suggests that cerebral blood volume and flow could be measured using MR contrast.

Magnetic Resonance Imaging of Blood and Clots In Vitro

The effects of variations in blood clot composition on magnetic relaxation rates and magnetic resonance (MR) image have been characterized in vitro. Both 1/T1 and 1/T2 were found to be linear functions of hematocrit for blood and clot, with increases in hematocrit resulting in progressive decreases in image signal intensity. Clot formation in fully oxygenated samples produced no change in relaxation rates or MR images compared with unclotted blood, but clot retraction was associated with a significant increase in 1/T2 that resulted in a decreased signal. Retraction resulted in a heterogenous image with appearance of a hypointense peripheral rim; differences in the method of clot preparation resulted in significant image inhomogeneity. The pattern of fibrinolysis was found to depend on the type of plasminogen activator used and its site of initial application. Injection of tissue plasminogen activator into the clot resulted in lysis, primarily in the clot interior, whereas placing the enzyme in the surrounding serum caused degradation from the outside of the clot. Both observations are consistent with the high binding affinity of tissue plasminogen activator for fibrin. By comparison, streptokinase, with low fibrin binding affinity, dissolved thrombi in a peripheral pattern whether injected into the thrombus or introduced in the serum. These findings identify several variables of clot composition and structure that influence MR images of thrombi and should be considered in their interpretation.

The effect of 4He on the relaxation rates of the two-level systems in porous vycor glass

Abstract The sound speed in porous Vycor glass is strongly dependent on the amount of 4He adsorbed in the pores. This is due to the interaction between the Two-Level Systems (TLS) in the glass and excitations in the helium film. As helium is added, the TLS relaxation rates gradually increase, to reach a maximum at approximately 90% of ncrit, the critical coverage for the onset of superfluidity. Very close to ncrit a local minimum in the relaxation rates is found. A further increase in the coverage causes again an increase in the relaxation rates. For thicker films and filled pores, the relaxation rates become essentially independent of the amount of helium adsorbed. We then find a new behavior in which the relaxation contribution to the sound speed scales with temperature and frequency as T/ω l 4 . This indicates that an efficient relaxation channel becomes available for the TLS when there is superfluid in the pores. The rapid change in relaxation rates seen close to the completion of the “inert layer” indicates a change in excitation spectrum in the helium film at the onset of superfluidity.

The effect of 4He on the relaxation rates of the two-level systems in porous Vycor glass

The sound speed in porous Vycor glass is strongly dependent on the amount of 4He adsorbed in the pores. This is due to the interaction between the Two-Level Systems (TLS) in the glass and excitations in the helium film. As helium is added, the TLS relaxation rates gradually increase, to reach a maximum at approximately 90% of ncrit, the critical coverage for the onset of superfluidity. Very close to ncrit a local minimum in the relaxation rates is found. A further increase in the coverage causes again an increase in the relaxation rates. For thicker films and filled pores, the relaxation rates become essentially independent of the amount of helium adsorbed. We then find a new behavior in which the relaxation contribution to the sound speed scales with temperature and frequency as T/ωl4. This indicates that an efficient relaxation channel becomes available for the TLS when there is superfluid in the pores. The rapid change in relaxation rates seen close to the completion of the “inert layer” indicates a change in excitation spectrum in the helium film at the onset of superfluidity.

Solubilization equilibria of alcohols and polymers in micellar solutions: NMR paramagnetic relaxation studies

The solubilization equilibria of some typical alcohols in cationic, anionic, and nonionic surfactant micellar solutions were investigated using the NMR paramagnetic relaxation method [J. Phys. Chem., 93 (1989) 2190]. The degree of solubilization of solubilizate in the micellar phase, p, was determined by monitoring the change in the 1H spin-lattice relaxation rate of the solubilizate upon the addition of paramagnetic ions to the aqueous phase. Hydrophilic paramagnetic ions, which should have the same sign of charge as the micellar surface for the case of ionic surfactant systems, were used to enhance the spin-lattice relaxation rate of solubulizate in the aqueous phase. The degree of solubilization obtained is, within experimental error, independent of the concentration of the paramagnetic ions. The error in the degree of solubilization, p, decreases with increasing paramagnetic ion concentration. The results obtained using different paramagnetic ions (i.e., 3-carboxylate-PROXYL (charge: − 1) and Mn (EDTA) 2− in anionic micellar systems, and Mn (D 2O) 2+ 6 and Mn (EDTA) 2− in nonionic micellar systems) are in good agreement. The paramagnetic relaxation method was also used to determine the degree of solubilization of poly (ethylene oxide) in two surfactant solutions, sodium ω-phenyldecanoate and sodium dodecyl sulfate.