Magnitude Of Relaxation Research Articles

Dielectric relaxation due to interfacial polarization for heat-treated wood

The dielectric properties of totally dried sugi ( Cryptomeria japonica) wood block and powder specimens treated at various temperatures up to 800 °C were measured in the range from 20 Hz to 1 MHz and from −150 to 20 °C. Relaxation ascribed to the motion of methylol groups was detected in specimens treated at temperatures below 300 °C and its magnitude decreased with increasing temperature. The electric conductivity decreased with increasing temperature up to 400 °C. Another form of relaxation was recognized for block specimens treated at temperatures between 500 and 600 °C. Cole–Cole’s circular arc law was applied to the experimental results. The relaxation magnitude was 60–75 and 24–28 in the longitudinal and radial directions of the block specimens, respectively. Identical relaxation was also observed in the powder specimen. The electric conductivity began to increase remarkably from 500 °C. These results suggested that a small volume fraction of particles with large conductivity is formed at microscopic levels in the cell walls. It is considered that this relaxation is due to interfacial polarization.

03/02501 Long-term fatigue life loss of turbine blades owing to non-characteristic harmonic currents in asynchronous HVDC links: Tsai, J.-T. et al. Electric Power Systems Research, 2003, 65, (2), 135–147

Foreign-object damage associated with the ingestion of debris into aircraft turbine engines can lead to a marked degradation in the high-cycle fatigue (HCF) life of turbine components. This degradation is generally considered to be associated with the premature initiation of fatigue cracks at or near the damage sites; this is suspected to be due to, at least in part, the impact-induced residual stress state, which can be strongly tensile in these locations. However, recent experimental studies have shown the unexpected propensity for impact-induced fatigue crack formation at locations of compressive residual stress in the vicinity of the impact site. To address this issue, in situ and ex situ spatially-resolved X-ray diffraction and numerical modeling are utilized to show that the initial residual stress state can be strongly relaxed during the fatigue loading process. The magnitude and rate of relaxation is strongly dependent on the applied loads. For a Ti–6Al–4V turbine blade alloy, little relaxation was observed for an applied maximum stress of 325 MPa (0.35σy, where σy is the yield stress), and cracks tended to form in subsurface zones of tensile residual stress away from the damage sites. In contrast, at an applied maximum stress of 500 MPa (0.54σy), equal to the smooth-bar 107-cycle endurance strength, cracks tended to form at the damage sites in zones of high stress concentration that had initially been in strong compression, but had relaxed during the fatigue loading.

Accessibility of solid core tablet for dissolution in an asymmetric triple-layer matrix system.

The importance of glassy matrix surface area to ensure constant drug release and the effect of barrier layer thickness on the duration of linear release in an asymmetric triple-layer tablet with zero-order release kinetics were investigated. Poly(ethylene oxide) of different molecular weights and hydroxypropylmethylcellulose K4M were the major polymeric constituents, and verapamil hydrochloride was used as a drug model. The contribution of diffusion and polymer relaxation towards drug release was evaluated based on drug release data using a non-linear regression analysis algorithm. The results demonstrated that application of barrier layers to the central core tablet enables polymer relaxation to be the predominant mechanism in controlling drug release and leads to the often desired zero-order release kinetics. The duration of linear release from the asymmetric triple-layer tablet depends on the barrier layer thickness and composition. It was further indicated that the magnitude of diffusion and polymer relaxation in controlling drug release is affected by the accessibility of the drug core tablet for dissolution, as well as the inherent swelling and erosion characteristics of the release rate-controlling polymer.

Mechanical relaxation of localized residual stresses associated with foreign object damage

Foreign-object damage associated with the ingestion of debris into aircraft turbine engines can lead to a marked degradation in the high-cycle fatigue (HCF) life of turbine components. This degradation is generally considered to be associated with the premature initiation of fatigue cracks at or near the damage sites; this is suspected to be due to, at least in part, the impact-induced residual stress state, which can be strongly tensile in these locations. However, recent experimental studies have shown the unexpected propensity for impact-induced fatigue crack formation at locations of compressive residual stress in the vicinity of the impact site. To address this issue, in situ and ex situ spatially-resolved X-ray diffraction and numerical modeling are utilized to show that the initial residual stress state can be strongly relaxed during the fatigue loading process. The magnitude and rate of relaxation is strongly dependent on the applied loads. For a Ti–6Al–4V turbine blade alloy, little relaxation was observed for an applied maximum stress of 325 MPa (0.35σy, where σy is the yield stress), and cracks tended to form in subsurface zones of tensile residual stress away from the damage sites. In contrast, at an applied maximum stress of 500 MPa (0.54σy), equal to the smooth-bar 107-cycle endurance strength, cracks tended to form at the damage sites in zones of high stress concentration that had initially been in strong compression, but had relaxed during the fatigue loading.

The viscoelastic compression behavior of liquid composite molding preforms

The compressive deformation of reinforcements is an important consideration for many composites manufacturing processes. The apparent viscoelastic behavior of three common Liquid Composite Molding reinforcements has been studied, and the implications for modeling mold filling processes discussed. Though no resin was present, these fibrous structures have displayed complex time-dependent response, including loading hysteresis, stress relaxation, and strain rate dependent loading behavior. Stress relaxations have been observed to be as high as 64% of the peak stress, with the magnitude of relaxation being dependent on the preform fiber volume fraction. Increasing peak stresses are generated with faster strain rates, and two of the materials studied displayed stress relaxation sensitive to the initial strain rate. Two mold filling experiments are also presented, demonstrating the significant influence of preform viscoelasticity, and providing motivation for further study of these effects.

Thiorphan enhances bradykinin-induced vascular relaxation in hypoxic/hyperkalaemic porcine coronary artery.

Relaxation induced by bradykinin is diminished by hypoxia in epicardial coronary arteries. The bradykinin-degrading enzyme, neutral endopeptidase (NEP, EC.3.4.24.11), is a potential target for coronary artery vasodilators. In this study, we examined the effect of thiorphan, an inhibitor of NEP, on the tone of porcine isolated coronary artery under hypoxic conditions. Endothelium-intact porcine isolated coronary artery rings were isometrically contracted with a prostaglandin F(2alpha) analogue (U46619, 0.75 microM) and potassium chloride (KCl, 30 mM), and relaxed with bradykinin (1-1000 nM) under normoxic (partial pressure of oxygen, pO(2) approximately 90-100 mmHg) and moderately hypoxic (pO(2) approximately 50-60 mmHg) conditions. Experiments were performed to study the effects of 30 min pre-treatment with the NEP-inhibitor, thiorphan (10 microM), both at physiological and at low pO(2)s. Hypoxia inhibited the bradykinin-induced relaxation in porcine epicardial coronary arteries. In normoxia, thiorphan significantly enhanced the decrease of coronary tone produced by bradykinin (1-10 nM) when U46619 was used as contractile agent. Under hypoxic conditions, in U46619 contracture, thiorphan did not influence, but in KCl contracture it enhanced the magnitude of relaxations induced by bradykinin. In the absence of bradykinin, thiorphan had no significant effect on the basal, KCl- and U46619-elevated tones and on the hypoxia-induced decrease of coronary artery tone. Inhibition of NEP-enzyme activity may effectively improve the relaxing capacity of epicardial coronary arteries under hypoxic/hyperkalemic conditions. This effect could be potentially utilized when the endothelial function and relaxation of the coronary arteries are impaired under clinical conditions.

Dielectric properties of chemically treated wood

Dielectric properties along the grain for absolutely dried untreated and seven kinds of chemically treated Sitka spruce (Picea sitchensis Carr.) woods were measured. Cole-Cole's circular arc law was applied to the results of the relaxation due to the motions of methylol groups. The following changes were caused by chemical treatments. In polyethylene glycol (PEG) impregnation, the distribution of relaxation times became very narrow, the generalized relaxation time (τm) was considerably decreased, and the relaxation magnitude (e0 − e∞) was slightly increased. In acetylation, the distribution of relaxation times became very broad, τm was considerably increased, and (e0 − e∞) was remarkably decreased. In propylene oxide treatment, the distribution of relaxation times became slightly narrow and τm was decreased. τm was slightly decreased in formalization, phenol-formaldehyde (PF) resin treatment and wood methyl methacrylate (MMA) composite. (e0 − e∞) was decreased in formalization and PF-resin treatment and was hardly changed in wood-MMA composite and heat treatment. The distribution of relaxation times was almost unchanged in formalization, PF-resin treatment, wood-MMA composite and heat treatment.

熱処理木材の誘電緩和

Changes in the dielectric relaxation of sugi (Cryptomeria japonica) specimens by heat treatment were investigated. Dielectric properties in the longitudinal direction for the oven-dried specimens were measured in the range from 20Hz to 1MHz and from -150°C to 20°C. The relaxation due to the orientation of methylol groups was observed for the specimens treated at the temperature up to 300°C. The relaxation magnitude obtained from the Cole-Cole plots did not change by the heat treatment up to 200°C, but it decreased remarkably above 200°C and became 0 at 300°C, showing the disappearance of methylol groups. Any relaxation was not detected within the range measured for the specimens treated at the temperature between 300°C and 450°C. However, one relaxation was recognized for the specimens treated at the temperature between 500°C and 600°C. Regarding the specimen treated at 500°C as a system in which a small amount of ellipsoids of graphite disperses in the medium of an insulator, the applicability of the Maxwell-Wagner's theory to the tanδ versus logarithmic frequency curve at 20°C was examined. A good agreement between the experimental and calculated results was obtained in the case that long and narrow ellipsoids oriente to the direction of the electrical field. These results suggested that the relaxation was due to the interfacial polarization.

A micro-mechanism model of residual stress reduction by low frequency alternating magnetic field treatment

Low frequency alternating magnetic field treatment is a non-thermal method used to process welded samples with internal residual stress. The purpose of the paper is to investigate the quantitative correlation between magnetic treating parameters, magnitude of stress relaxation and the stress relaxation mechanism. The microstructure change of the material during magnetic treatment is also observed by TEM and discussed from the point of view of dislocation behavior in the processed material. The experimental results indicate that low frequency alternating magnetic field treatment is an effective method in reducing residual stress in steels. The main reason for the stress reduction is the even-distribution of dislocation due to magnetic treatment. A physical model of residual stress relaxation by magnetic treatment is raised based on the experimental results and microstructural observation that well explain the micro-mechanism of this method.

Central orexin facilitates gastric relaxation and contractility in rats

The effects of the intracisternal administration of synthetic orexin-A (3 nmol) on gastric motility were examined in rats. The administration of orexin but not a vehicle induced relaxation of the proximal stomach lasting for more than 30 min. Phasic contractions in the distal stomach were facilitated in response to the administration of orexin but not a vehicle. Facilitation in the distal stomach was not observed in the animals which underwent the sectioning of the bilateral vagi at the subdiaphragmatic level. Relaxation of the proximal stomach was observed in vagotomized animals but the magnitude of relaxation was significantly smaller than that in intact animals. These results suggest that central orexin facilitates distal stomach motility and relaxation of the proximal stomach via vagi.

Micromechanism of residual stress reduction by low frequency alternating magnetic field treatment

Low frequency alternating magnetic field is used to process welded samples having internal residual stress. Magnetic treatment parameters and the magnitude of stress relaxation are investigated quantitatively. The microstructural change of the material during magnetic treatment is observed by TEM and discussed from the point of view of the dislocation behavior in the processed material. A physical model of residual stress relaxation produced by magnetic treatment is presented based on the experimental results and microstructural observation.

Multilayer relaxation of the Cu(2 1 0) surface

Low-energy electron diffraction (LEED) I– V has been utilized to determine the surface structure of Cu(2 1 0). The surface structure is found to exhibit multilayer relaxation following the trend − − + (− is contraction and + is expansion in the interlayer spacing). The magnitude of interplanar relaxation is found to be damped, where | Δd 12|>| Δd 23|>| Δd 34|, etc. This kind of behavior is quite different from that observed on Al(2 1 0) [Phys. Rev. B 38 (1988) 7913], where the magnitude of interplanar relaxation in the third interlayer is larger than that in the second interlayer (i.e., | Δd 23|<| Δd 34|). The difference of damped multilayer relaxation behavior of Cu(2 1 0) and Al(2 1 0) could be related to a charge density oscillation perpendicular to the surface.

Functional Study on Nitroxidergic Nerve in Isolated Dog Pulmonary Arteries and Veins

In dog pulmonary arterial and venous strips without endothelium under treatment with prazosin, nicotine induced relaxation that was abolished by NG-nitro-L-arginine, hexamethonium and methylene blue. L-Arginine antagonized the NG-nitro-L-arginine action. Neurogenic relaxations tended to be more evident in the vein. Nitric oxide (NO)-induced relaxations were greater in the veins than in the arteries. Concentrations of NO to induce the same magnitude of relaxation as that to nicotine were higher in the arteries. In conclusion, dog pulmonary arteries and veins are innervated by nitroxidergic (nitrergic) nerves, and NO is released by nerve stimulation with nicotine in a larger amount in the artery than the vein.

Role of mitogen-activated protein kinase pathway in acetylcholine-mediated in vitro relaxation of rat pulmonary artery

This study was designed to characterise the muscarinic receptor subtype responsible for acetylcholine-mediated in vitro pulmonary artery relaxation in rats and the importance of the presence of neostigmine (an anti-cholinesterase) during receptor characterisation. Cumulative administration of acetylcholine elicited concentration-dependent relaxation of phenylephrine (1 μM) precontracted preparations. Inclusion of neostigmine (10 μM) caused a parallel leftward shift with an increase of the p D 2 value (7.09 vs. 6.43) of the concentration–response curve of acetylcholine. The magnitude of maximum relaxation, however, was not affected. Using a range of conventional muscarinic receptor antagonists (atropine, pirenzepine, methoctramine, p-FHHSiD and tropicamide) and the highly selective Green Mamba muscarinic toxins (MT-3 and MT-7), it was found that muscarinic M 3 receptors are probably responsible for endothelium-dependent relaxation of the pulmonary artery upon acetylcholine challenge. Preincubation with N G-nitro- l-arginine methyl ester ( l-NAME, 20 μM, a nitric oxide synthase inhibitor), but not N G-nitro- d-arginine methyl ester ( d-NAME, 20 μM), abolished acetylcholine-elicited relaxation. Moreover, 6-anilino-5,8-quinolinedione (LY 83583, 1 μM) and methylene blue (1 μM) (both are guanylate cyclase inhibitors) markedly attenuated acetylcholine-elicited relaxation. However, the presence of indomethacin (3 μM, a cyclo-oxygenase inhibitor), (−)-perillic acid (30 μM, a p21 ras blocker), 2-[2′-amino-3′-methoxy-phenyl]-oxana-phthalen-4-one (PD 98059) (10 μM, a p42/p44 mitogen-activated protein kinase inhibitor), 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1 H-imidazole (SB 203580) (1 μM, a p38 mitogen-activated protein kinase blocker), wortmannin (500 nM, a phosphatidylinositol-3 kinase inhibitor) and genistein (10 μM, a tyrosine kinase blocker) failed to alter acetylcholine-provoked pulmonary arterial relaxation. These results suggest that acetylcholine caused pulmonary arterial relaxation through the activation of muscarinic M 3 receptors in the endothelium. Moreover, the p21 ras/mitogen-activated protein kinase pathway seems to play no role in mediating acetylcholine-elicited relaxation.

Acute, nongenomic vasodilatory action of estradiol is attenuated by chronic estradiol treatment.

Deficiency of estradiol or chronic estrogen treatment may alter the responses to this hormone in many tissues. A possible interaction between the acute nongenomic and the chronic effects of estradiol on microvessels have not been investigated yet. In the present study we have investigated whether acute in vitro vasodilatory action of estradiol on a small artery is altered by chronic estradiol pretreatment. Female rats were surgically ovariectomized and subjected to either estradiol replacement therapy (estradiol propionate, 450 micrograms/kg/week) or vehicle administration for 5 weeks. Cylindrical segments of the saphenous artery were studied using videocomputerized microarteriography in vitro. Estradiol, in concentrations of 10(-6) to 10(-4) M relaxed norepinephrine precontracted vessel segments in a dose-dependent manner. Magnitude of relaxation observed in arteries of estradiol replaced animals was significantly smaller at all concentrations than that of nonreplaced ovariectomized rats; maximal relaxation in the control ovariectomized group was 64.5% +/- 3.6%, while it was 34.3% +/- 4.2% only in the ovariectomized and estradiol replaced group (P < 0.001). Comparison of acute relaxations in response to papaverine and nifedipine failed to prove a reduced activity of the general relaxation machinery in estradiol replaced animals. We conclude that chronic estradiol replacement can downregulate the acute nongenomic vasorelaxation effect of this hormone in small arteries of ovariectomized rats.

Modifications by sumatriptan and acetylcholine of nitric oxide-mediated neurogenic dilatation in dog cerebral arteries

Canine cerebral arterial strips denuded of endothelium responded to nicotine and transmural electrical stimulation with relaxations, which were abolished by N G-nitro- l-arginine and methylene blue. Magnitudes of relaxation did not differ in the arteries contracted with prostaglandin F 2α and sumatriptan, an effective therapeutic of migraine. Sumatriptan concentration-dependently contracted the arteries responding to 2 Hz stimulation with persistent relaxations, and the concentration of this 5-HT 1B/1D/1F receptor agonist to overcome the relaxation averaged 1.06×10 −7 M. Acetylcholine inhibited the response to nerve stimulation due possibly to its action on prejunctional nitroxidergic nerves; the inhibition did not differ in the arteries contracted with prostaglandin F 2α and K +. It appears that sumatriptan does not interfere with the release of nitric oxide from nerves but counteracts the neurogenic relaxation by functional antagonistic action on smooth muscle. Prejunctional inhibition by muscarinic receptor activation is unlikely associated with opening of neuronal K + channels.

E2 and not P4 increases NO release from NANC nerves of the gastrointestinal tract: implications in pregnancy.

In women, during pregnancy, there is decreased motility of the gastrointestinal tract leading to a delay in gastric emptying and an increase in colonic transit time. Whether the rise in estradiol (E2) or progesterone (P4) is responsible for this effect is controversial. As the nitrergic component of the nonadrenergic, noncholinergic (NANC) nerves is responsible for modulating gastrointestinal motility in vivo, the purpose of this study was to evaluate whether the increased release of nitric oxide (NO) from the nitrergic component of the NANC nerves innervating the gastric fundus and colon that occurs during late pregnancy in rats is mediated by E2 or P4. Ovariectomized rats treated with E2 or P4 alone or in combination were used for our studies. We also wanted to assess the cellular and molecular mechanisms involved. The NANC activity was studied by assessing changes in tone after application of electric field stimulation (EFS). The role of NO was determined by observing the effects of EFS in the presence and absence of the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) and the reversibility of the effects of L-NAME by L-arginine. Our studies indicated that there was increased magnitude of relaxation of isolated strips of rat gastric fundus and rat colon after application of EFS to tissues obtained from animals treated with E2 alone or a combination of E2 + P4 but not from those treated with P4 alone. L-NAME attenuated relaxation responses in E2- and E2 + P4-treated animals. To elucidate whether the increased NO release may be due to an increase in neuronal NOS (nNOS) protein, we used both Western blot analysis and immunohistochemistry. We also used RT-PCR to determine whether there was an increase in nNOS mRNA after treatment with sex steroids. In nonpregnant animals, nNOS was detected by Western blot in the fundus and the colon and was barely detectable in the ileum. In pregnancy, there was an increase in nNOS in both the gastric fundus and the colon. The nNOS protein was also increased in ovariectomized animals treated with either E2 alone or E2 + P4 but not P4 alone when compared with ovariectomized animals receiving vehicle. Our results indicated that there was an increase in nNOS protein that was localized to the neurons of the myenteric plexus in the gastric fundus and colon in E2- and E2 + P4-treated animals, but this increase was not observed in animals treated with P4 alone. This increase in nNOS protein was accompanied by an increase in nNOS mRNA. These results suggest the possibility that E2, rather than P4, may be responsible for the delay in gastric emptying and increase in colonic transit time observed in pregnancy.

Dielectric Relaxation Behavior of Cationic Micellar Solutions: 2

Dielectric relaxation behavior was examined, in the frequency range from 1 MHz to 20 GHz, for an aqueous micellar system of cetyltrimethylammonium bromide (CTAB) with the concentration (CD) from 2 to 1000 m mol kg-1. The system exhibited three dielectric relaxation modes. The fastest mode, with a relaxation time around 1 ns, had relaxation strength proportional to CD up to CD values of 100 m mol kg-1, and showed a constant relaxation strength independent of CD above that concentration. The fastest relaxation mode attributed to the rotational relaxation mode of ionic pairs formed between CTA+ and Br- in spherical micelles is considerably depressed in contact areas on the micellar surface of two micelles in contact with each other at CD values higher than 100 m mol kg-1. This is likely the reason for the leveling-off in the magnitude of the fastest relaxation at high CD and the appearance of the slowest relaxation mode, which has a relaxation time of about 20 ns and increases in strength with increasing CD. The intermediate relaxation mode (with a relaxation time around 8 ns, and strength which decreases with increasing with CD) is attributed to the migration of electrically bound Br- ions around spherical micelles. The average number of Br- ions bound into an ionic cloud covering a micelle was estimated to be less than unity (from the values of direct current electric conductance and Br- concentration determined by use of a Br- selective ion electrode), and a small number of micelles possessed ionic clouds which showed dielectric relaxation behavior.

Morphology and relaxation in In yGa 1− yAs/GaAs multi-layer structures

Metastable InGaAs/GaAs multi-layer structures (MLS) on GaAs substrates with a constant interfacial strain and number of periods varying from 14 to 75 are studied by high-resolution X-ray reciprocal-space maps (HRXRSM), transmission electron microscopy, and differential contrast microscopy. These characterization techniques are used to monitor both the magnitude of relaxation and the change in crystalline state from a coherent “pseudomorphic” growth to a dislocated condition as the number of periods increases. For 14-periods, the diffuse intensity emanating from the entire MLS region arises from periodic, coherent crystallites. For 17- and 30-period, the displacement fields around the active region transition to coherent random crystallites (mosaic blocks). At 50-periods, displacement fields of overlapping dislocations from relaxation of the random crystallites cause the initial stages of relaxation of the active region. At 75-periods, relaxation of the strained region becomes bi-modal characterized by overlapping dislocations caused by mosaic block relaxation and periodically spaced misfit dislocations formed by 60°-type dislocations. The relaxation of the MLS has an exponential dependence on the diffuse scatter length-scale which is shown to be a sensitive measure of the onset of relaxation.

The effect of cold expansion on fatigue crack growth from open holes at room and high temperature

In this paper a series of residual stress measurements and fatigue crack growth tests have been carried out using aluminium alloy 2650 specimens containing cold expanded and non cold expanded holes. Residual stress measurements have been done after cold expansion and after various loading and temperature conditions. In order to measure an angular variation of residual stresses, X-ray and a new technique called the Garcia–Sachs method have been employed. Results revealed that residual stress relaxation occurred as a result of exposure at 150°C. The magnitude of relaxation was shown to be dependent on the level and the sign of externally applied load. Fatigue crack growth tests have been carried out at 20°C and 150°C for both cold expanded and non-cold expanded conditions. Fatigue crack growth rates in specimens containing cold expanded fastener holes were affected significantly by elevated temperature exposure. Depending on the exposure time and loading conditions the fatigue life improvement was found to be between one and greater than 10 for tests at 20°C.