Decrease In Relaxation Time Research Articles

Investigation of the adsorption of Sb(III) from chloride solutions at the DME by ac measurements

Impedance measurements were performed to study the reduction of Sb(III) ions at a DME from 4.3 M H(Cl, ClO 4) solutions at the peak potential of the ac polarogram. The frequency dependence of the interfacial admittance corresponds to that of a charge transfer and diffusion-controlled process parallel to an adsorption-controlled adsorption process. It was found that with increasing concentration of HCl up to 0.4 M both the charge transfer resistance and the adsorption relaxation time decrease and then both quantities remain constant up to 3 M. This tendency is discussed in terms of different Sb(III) halide complexes.

Bone marrow: ultrasmall superparamagnetic iron oxide for MR imaging.

An ultrasmall superparamagnetic iron oxide (USPIO) preparation was evaluated as a potential intravenous contrast agent for magnetic resonance (MR) imaging of bone marrow. One hour after administration of USPIO (40, 80, and 160 mumols of iron per kilogram body weight) in rats and rabbits, T1 and T2 relaxation times were, respectively, approximately 30%, 50%, and 65% lower than precontrast relaxation times. Maximum decrease in relaxation times of marrow occurred within 1-24 hours after intravenous administration; thereafter, relaxation times slowly returned to normal within 7 days. In vivo MR imaging of rabbits and rats confirmed that USPIO decreases signal intensity of red and yellow marrow. The decrease was most marked with gradient echo pulse sequences. An animal model of intramedullary tumor demonstrated the potential of USPIO to enable differentiation between tumor and normal red marrow. USPIO-enhanced MR imaging improves detection of smaller tumors and allows differentiation of tumor deposits from islands of hyperplastic or normal red marrow.

Low resolution pulse nuclear magnetic resonance study of water equilibration in dried carrots

SummarySamples taken during air drying of carrots were analysed after different equilibration times. Low resolution NMR measurements were made and the longitudinal (T1) and the transverse (T2) relaxation times calculated. Both T1 and T2 decreased with the equilibration time for water contents above 0.30 and 0.47 kg water kg‐1 dry matter, respectively. The decrease in relaxation time increased with the water content. For the same water contents, grated carrots gave lower T1 values and smaller T1 decreases with equilibration time than 3‐mm cubes. Low resolution NMR is a technique which is well suited to the monitoring of the tempering phases of industrial drying cycles.

ＭＲ‐ＣＴ画像（ＭＲＩ）による顎関節内障の診断学的研究 Ｔ１・Ｔ２について

The T1 and T2 relaxation times of the phantom were measured in the magnetic resonance imaging (MRI) using the headcoil and the surface coil for the temporomandibular joint (TMJ). The purpose of this study on the phantom was to investigate the feature of the surface coil for TMJ (TMJ-coil). Two spin echo (TR=2, 000 msec, TE=30 msec and TR=2, 000 msec, TE=80 msec) and one inversion recovery (TR=2, 000 msec, TI=-500 msec) pulse sequence with a 256×256 matrix and two excitations were used, and the T1 and T2 values were obtained by the ROI (region of interest) in the maps of T1 and T2. As a result of the phantom study, I acquired the knowledge that I have to set an object on the center of the TMJ-coil with a distance more than 3 cm.With the TMJ-coil, measurements of T1and T2 relaxation times of meniscus and lateral pterygoid muscle were performed on 30 normal volunteers and 30 patients who had been diagnosed internal derangement of the TMJ. The 30 patients were classified into two groups; one composed of 15 patients diagnosed meniscal displacement with reduction (goup MDWR) and the other was of 15 patients diagnosed meniscal displacement without reduction (group MDWOR).Between the volunteers and patients, there was a significant decrease in T1 and T2 relaxation times of meniscus and Ti relaxation times of lateral pterygoid muscle. There was no significant difference between group NIDWR and group MDWOR. There was no significant difference in sex or age, either. The more long-term the patients were, the more the T1 relaxation times decreased. The decrease in T1 and T2 relaxation times of meniscus probably represented water loss.The decrease in T1 and T2 relaxation times of lateral pterygoid muscle was slight compared with that of meniscus.

Transient photoconductivity in amorphous Si 1− xC x:H

We have studied the picosecond dynamics of the photoconductivity of a-Si:H and a-Si1−xCx:H alloys at room-temperature by using a photocurrent correlation technique. The carbon content in the amorphous silicon-carbon alloys has been varied between x=0.05 and x=0.29. We find a pronounced decrease of the photoconductivity relaxation time with increasing carbon content. The experimental results can be described within a multiple trapping model taking into account free carrier capture into additional defect states above midgap and carrier trapping and reemission within shallow tail states.

Experimental study of ion-drag pumping using various working fluids

An ion-drag pump in a vertical axisymmetric configuration was built. Different dielectric fluids were compared to establish which produced the best pumping performance. Experimental results showed that pumping performance depended on fluid properties, primarily fluid viscosity and electrical conductivity. Two fluids, dodecylbenzine and Envirotemp 200, were studied at various doping levels. In both fluids a decrease in the charge relaxation time caused a decrease in efficiency. >

Characterization of viscoelastic surfactant mixtures part II: Rheological studies

The temperature dependence of the rheological behavior of worm-like aggregates formed in 0.3 M C 16TAB/0.05 M SXS mixtures is examined. Three distinct regions are observed for all of the rheological parameters studied (η 0, G′, G″, Δ, τ s). Region I, belo the critical micellization temperature ( T< 18°C) is characterized by highly rigid elastic coagels. In Region II (18≤ T≤40°C) Maxwell body behavior is observed, with a rapid decrease in the structural relaxation time, and a change in the phase angle from ≈ 3 to 90°. In Region III ( T40°C), the aggregates exhibit terminal region behavior, yielding viscoelastic properties only at very high oscillation frequencies. The data can be interpreted in terms of a repeating chain model for worm-like aggregates above the overlap concentration. The increase in interior fluidity of the aggregates observed by FT-IR spectroscopy (Part I) causes a continuous change in the overall flexibility and morphology of these micelles, and a consequent drop in the relaxation time with increasing temperature. The concept of temperature- and compositional-dependent flexibility for worm-like surfactant aggregates serves as a link between the viscoelastic behavior of these systems and ordinary concentrated polymer solutions, and can qualitatively explain the large variations in the relaxation time of surfactant aggregates with small changes in temperature, methylene chain length, or cationic surfactant head group size.

Effect of sodium selenite and vitamin E treatment in myotonic dystrophy

Fifteen patients with myotonic dystrophy, seven men and eight women, of age range 15-55 years, were treated with sodium selenite and vitamin E for 2 years. The patients were examined using a number of tests to assess muscle force and function at the start of the treatment period and 6, 12 and 24 months thereafter. Myotonia gives an increased relaxation time. The latter was measured in the adductor pollicis. There was a significant decrease in half relaxation time before treatment compared with the values during treatment. In summary, the results indicate that selenium and vitamin E therapy may have an effect on myotonia. The effects of treatment on motor functions were minimal, and overall motor performance was not improved.

Radical intermediates in veratryl alcohol oxidation by ligninase. NMR evidence

Proton nuclear magnetic resonance (NMR) spectra of veratryl alcohol (3,4-dimethoxybenzyl alcohol) were obtained during its oxidation by ligninase. It was observed that a substantial increase in the linewidths of the resonances occurred only in the presence of both the enzyme and hydrogen peroxide. Quenching the reaction by the addition of alkali immediately restored the normal linewidths of the resonances. Furthermore, inversion-recovery experiments showed a decrease in the longitudinal relaxation time of the substrate when the enzyme was actively turning over. Changes in both these NMR parameters are consistent with the generation of radical intermediates during the ligninase-catalysed oxidation of veratryl alcohol.

Magnetic Resonance Imaging of the Bone Marrow in Patients with Acute Leukemia during and after Chemotherapy Changes in T1 Relaxation

Twenty-seven patients with acute leukemia were examined at the time of diagnosis with MR imaging and in vivo T1 relaxation time measurements of the hemopoietic bone marrow. A 1.5 T whole body magnetic resonance scanner was used. Twenty of the patients had follow-up examinations in relation to chemotherapy. Bone marrow biopsies from the posterior iliac crest were obtained within a short time interval of all MR examinations. At the time of diagnosis, T1 relaxation times were increased significantly in all the leukemic patients, compared with 24 age-matched controls. A decrease in T1 relaxation time towards or into the normal range was observed in 10 patients who obtained remission. The T1 relaxation time remained prolonged in 6 patients who failed to obtain remission during chemotherapy. Four patients, who obtained remission with concomitant decrease of T1 values towards or into the normal range, also showed prolongation of T1 relaxation time in relation to leukemic relapse. The results indicate that changes observed in T1 relaxation times of the hemopoietic bone marrow in patients with acute leukemia reflect changes in disease activity, and, that serial measurements of T1 values may provide clinically useful information with the possibility for identification of residual disease in regions inaccessible for biopsy.

NMR imaging of diffusion processes in polymers: measurement of the spatial dependence of solvent mobility in partially swollen PMMA rods

The spin-spin and spin-lattice relaxation times and self-diffusion coefficients of acetone and methanol are measured as a function of distance from the glassy core of the polymer. The results show decreases in all three parameters toward the glassy core, indicating that the solvent motions are decreasing in this direction. A conceptual model is proposed which attributes the decrease in relaxation times to the decrease in mobility, of the polymer chain toward the core

Twitch response in a myopathy with impaired relaxation but no myotonia

A patient with slow muscle relaxation but without accompanying motor unit or myotonic electrical activity had a unique staircase twitch response to repeated nerve stimulation. During 1-Hz stimulation, twitches recorded by measurement of the ankle dorsiflexor group displayed progressively increasing relaxation times with successive stimuli (37% increase) unlike the progressively decreasing relaxation time of the normal response (12-37% decrease). The response may be diagnostic of this unusual myopathy; the test methods are noninvasive and easily tolerated.

The Biphasic Effect of Amrinone on Tension Development in Newborn Mammalian Myocardium

The effect of the bipyridine compound, amrinone, on tension generation in neonatal and adult myocardium was studied over the concentration range 30-500 micrograms/mL. Increasing concentrations of amrinone caused a monotonic increase in twitch tension and the rate of tension development in adult papillary muscles. In contrast, lower concentrations of amrinone (30 and 100 micrograms/mL) caused a decrease in twitch tension and dP/dt in newborn papillary muscles, whereas 500 micrograms/mL amrinone caused a significant increase in both parameters in the younger age group. Lactic acid, used to dissolve amrinone, was shown to have no effect on tension development. Half relaxation time was decreased in adult preparations at all concentrations of amrinone. In comparison, the decrease in half relaxation time produced by amrinone in the newborn was significant only at a concentration of 500 micrograms/mL. Action potential duration in the newborn was significantly shortened by 30 micrograms/mL amrinone. In voltage clamp experiments, 30 micrograms/mL amrinone was shown to have no effect on tension accompanying two second voltage clamp steps to the plateau potential in newborn myocardium. Developed tension at 400 ms into the clamp step, final tension, and the ratio of early peak tension to final tension were all unchanged by the low concentration of amrinone. In contrast, 500 micrograms/mL amrinone in the newborn increased tension at 400 ms and final tension but had no effect on the ratio of early peak tension to final tension. These results suggest that the negative inotropic effect of lower concentrations of amrinone on neonatal myocardium is the result of changes in action potential configuration and not a true alteration in basic mechanisms of intracellular Ca2+ regulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dipole position on relaxation parameters

Dielectric absorption studies have been made on numerous monobromoalkanes and twoα,ω-dibromoalkanes dispersed in polystyrene and polypropylene matrices in the frequency range 10–105 Hz between 80-285 K. All compounds exhibited two clear cut dispersion regions in polystyrene except 3-bromopentane, 4-bromoheptane and 4-bromooctane. Nevertheless, when these three solute molecules are dispersed in polypropylene, they then show two dispersion regions. The low temperature process (LT) has been attributed to -CHzBr group rotation about the C-C bonds and the high temperature (HT) process to molecular rotation. In the case ofα,ω-dibromoalkanes, both -CH2Br groups contribute to the low temperature absorption. For a bromoalkane of a given chain length the relaxation time alters with variation of the main dipole position from the terminal carbon atom to the middle of the chain for the low temperature absorption; this is related to the change in the size of the reorientating unit containing the -CHzBr group. The effect of the same variation of the dipole position on the high temperature absorption is that the relaxation time decreases which is attributed to the decrease in volume swept out on molecular rotation. The ratio,ɛ″maxLT/ɛ″(max)HT, increases with the variation of the dipole from the terminal to the middle of the chain.

Magnetic resonance imaging of the bone marrow in patients with acute leukemia during and after chemotherapy

Twenty-seven patients with acute leukemia were examined at the time of diagnosis with MR imaging and in vivo T1 relaxation time measurements of the hemopoietic bone marrow. A 1.5 T whole body magnetic resonance scanner was used. Twenty of the patients had follow-up examinations in relation to chemotherapy. Bone marrow biopsies from the posterior iliac crest were obtained within a short time interval of all MR examinations. at the time of diagnosis, T1 relaxation times were increased significantly in all the leukemic patients, compared with 24 age-matched controls. A decrease in T1 relaxation time towards or into the normal range was observed in 10 patients who obtained remission. the T1 relaxation time remained prolonged in 6 patients who failed to obtain remission during chemotherapy. Four patients, who obtained remission with concomitant decrease of T1 values towards or into the normal range, also showed prolongation of T1 relaxation time in relation to leukemic relapse. the results indicate that change...

Electrokinetic Decay in Zero-Current and Zero-Potential Conditions

The zero-current and zero-potential electrokinetic decay process are studied from the point of view of linear non-equilibrium thermodynamics, in terms of the degree of coupling. A time scale is established for weakly coupled systems by comparing the dissipation of energy due to dipole-reorientation and charge-conduction. Two electrokinetic systems from literature have been studied. It is demonstrated that the degree of coupling decreases with concentration, while relaxation times increase or decrease depending on the molecular dipole of the solute as compared with that of the solvent

Studies on the mechanism of action of the bipyridine milrinone on the heart

Milrinone is a positive inotropic and vasodilator agent when tested in experimental animals and in human heart-failure patients. It is generally believed that milrinone acts by inhibiting phosphodiesterase IV, thus increasing cyclic AMP, [Ca++]i and cardiac contractile force and relaxation. Maximal force produced by milrinone is greater when single-dose response curves are compared to cumulative dose-response curves. In vitro, milrinone produces a tachyphylaxis, the extent of which is both dose- and time-dependent. Recovery of tachyphylaxis is both dose- and time-dependent and is not influenced by inhibitors of protein or RNA synthesis. There is a specific cross-tachyphylaxis between milrinone and amrinone, theophylline, papaverine, and Bay K8644. This tachyphylaxis may explain the low maximal contractile response of the cumulative dose-response observed in isolated tissues. Milrinone increased cyclic AMP in dog and guinea pig cardiac muscle. As previously shown by Endoh et al., milrinone in low doses produced a biphasic effect on cyclic AMP. The early increase (first 60-70 s) in cyclic AMP shows a good correlation with contractile force changes. If cyclic AMP is determined at maximal contractile force this correlation was poor. Here we also present instances where the increase in cyclic AMP after milrinone (determined at maximal effect) does not correlate with the contractile response. The cross-tachyphylaxis of milrinone with Bay K8644 suggests that milrinone has an action on the sarcolemmal Ca++ channels. Bay K8644 suppresses the positive inotropic effect of catecholamines by 50%, but not the cyclic AMP response. The inotropic effect of milrinone, in contrast to norepinephrine is highly sensitive to [Ca++]0, stimulation rate, and [K+]0. In this respect milrinone behaves more like Bay K8644. We postulate that the main inotropic action of milrinone is due to a sarcolemmal effect. The early cyclic AMP production described could be in the sarcolemmal compartment and this may explain some of the similarities of milrinone's actions with those of Bay K8644. The tachyphylaxis observed with the inotropic effect of milrinone does not extend to the decreases in relaxation time. This and other findings to be discussed suggest that the positive inotropic and reduction in relaxation time by milrinone depend on different mechanisms, possibly through differential compartmentalization of cyclic AMP.

MAS n.m.r. and e.s.r. studies of MnAlPO5

27Al and 31P magic angle spinning ( MAS) n.m.r. and e.s.r. measurements have been performed on MnAlPO5 in order to obtain direct evidence for Mn +2 incorporation into tetrahedral sites in the framework. Two samples differing in their Mn content have been studied, and their results were compared with those obtained from impregnated Mn-AlPO5 and exchanged Mn-SAPO5 where the Mn +2 does not occupy framework sites. The MAS n.m.r. spectrum showed a large anisotropy, manifested in numerous side bands due to the paramagnetic shifts induced by dipolar interactions between the unpaired electrons of the Mn +2 and the 31P and 27Al nuclei in its vicinity. On dehydration, a considerable linewidth narrowing has been observed, attributed to a decrease in the electronic relaxation time induced by increase in Mn +2 spin-exchange interaction. Calculated 31P MAS n.m.r spectra, where the paramagnetic shift anisotropy was obtained from X-ray diffraction data of AlPO5 and taking into account the Mn content obtained from the chemical analysis, showed qualitative agreement with the experimental spectra. Comparison of the simulated and experimental spectra indicates that, indeed, part of the Mn +2 cations occupy framework sites; it does, however, also suggest that extraframework Mn +2 cations are present as well. These conclusions are further supported by e.s.r. measurements. The e.s.r. spectrum of MnAlPO5 shows resolved hyperfine lines with splitting characteristics of octahedral Mn +2, supporting the existence of extraframework Mn +2. On dehydration, the spectrum of MnAlPO5 coalesce into a single absorption line. This coalescence is attributed to increase in the spin-exchange interaction due to migration of probably extraframework Mn +2 toward the framework.

The vibrational relaxation of highly excited Freon-22 molecules

The V–T relaxation from Freon-22 molecules has been studied by using an interferometric technique. By raising the excitation energy from 500 cm−1 up to 3000 cm−1 (about three photons) a decrease of the effective relaxation time followed by a leveling off, has been observed. In agreement with this behavior, the average energy 〈ΔE〉 transferred per collision was found to depend linearly on 〈E〉 for extremal values of the energy absorbed, and stronger than linearly for intermediate energy values. This behavior parallels that observed in SF6 and other polyatomic molecules, and confirms the role played by the sparse and quasicontinuum regions of the vibrational spectrum.

Carcinogen-nucleic acid interactions: equilibrium binding studies of aflatoxin B1 with the oligodeoxynucleotide d(ATGCAT)2 and with plasmid pBR322 support intercalative association with the B-DNA helix

Equilibrium binding of aflatoxin B1 (AFB1) to the oligodeoxynucleotide d(ATGCAT)2 was examined by using 1H NMR. AFB1 binds to double-stranded d(ATGCAT)2 with an apparent binding constant of 3.7 x 10(3) M-1. The equilibrium is rapid on the NMR time scale; the observed 1H NMR spectrum represents the population-weighted average of the chemical shifts arising from the free and bound states of the oligodeoxynucleotide and the AFB1. The spectrum of d(ATGCAT)2 exhibits exchange broadening in the presence of AFB1, manifested as decreases in apparent T2 relaxation times for the d(ATGCAT)2 base protons. Upon binding to d(ATGCAT)2, the AFB1 signals are shifted upfield, indicative of increased shielding. The adenine H2 protons are also shifted upfield in the presence of the carcinogen. Small changes in chemical shift are observed for other d(ATGCAT)2 protons. A substantial decrease in the nonselective T1 relaxation time is observed for the adenine H2 protons in the presence of AFB1. Competition binding experiments in which the competing ligands actinomycin D, ethidium bromide, and spermidine were individually added to an AFB1-d(ATGCAT)2 equilibrium mixture showed that addition of 1 equiv of actinomycin D or 4 equiv of ethidium bromide was sufficient to displace bound AFB1 from d(ATGCAT)2. In contrast, the addition of spermidine did not result in the displacement of bound AFB1 molecules and may have slightly enhanced binding, presumably due to stabilization of the DNA duplex. 1H NOESY experiments confirmed that the overall conformation for the d(ATGCAT)2 duplex was right-handed both in the absence and in the presence of AFB1. Equilibrium binding of AFB1 to d(ATGCAT)2 is greatly diminished at higher temperatures at which the oligodeoxynucleotide is single-stranded.(ABSTRACT TRUNCATED AT 250 WORDS)