Quick Relaxation Research Articles

Kinetics of short- and long-range B2 ordering in the pair approximation

The kinetic master equation is developed in the pair approximation to study disorder ⇉ B2 order transformations in bee binary alloys. Coupled sets of rate equations for the pair variables are obtained for atom movements by either the direct interchange mechanism or the vacancy mechanism. Numerical integrations provide the nonequilibrium relaxations of short- and long-range order (SRO and LRO) and the vacancy balances between the two sublattices. For binary alloys, disorder ⇉ order transformations were studied for all combinations of interatomic interaction strengths, activation barrier heights, and alloy stoichiometry variations. After a transient vacancy relaxation, all cases began with a quick relaxation of SRO, followed later and independently by the growth of LRO and additional SRO. There were some variations in kinetic path through SRO and LRO, moderate variations in overall kinetics, and large variations in vacancy balance. Some nonphysical aspects of kinetics in the pair approximation are discussed.

Kinetics of B2 and D03 Ordering: Theory

AbstractMonte-Carlo simulations (MCS) and the path probability method (PPM) were used to study disorder→order transformations in bcc alloys having the AB3 stoichiometry. Both methods used an explicit vacancy mechanism of ordering and an activated-state rate theory for the vacancy jumps. We studied the evolution of short-range order (SRO) as well as B2 and D03 long-range order (LRO) in alloys that began as random solid solutions. The growth rates of SRO and LRO were significantly higher for the PPM than for the MCS. We attribute this difference to improper handling of correlated vacancy motions in the PPM. The PPM also suffered from an artificial incubation time for the initiation of LRO. Both the MCS and the PPM showed that SRO has a tendency to develop in two stages. In the first stage there is a quick relaxation of the SRO by itself. In the second stage, which occurs with a longer time constant, the SRO and LRO grow simultaneously. Parametric plots of one order parameter against another, here termed “kinetic paths”, are discussed. A variety of different kinetic paths through the B2 and D03 order parameters can be predicted theoretically, depending on the choice of interatomic potentials. This range of calculated kinetic paths is broad enough to encompass our experimental results of SRO and LRO evolution in Fe3Al.

The process of spontaneous vitrification evaluated by calorimetry

The Cr 40Ti 60 and Cr 28Fe 8Ti 64 high temperature b.c.c. solid solutions, if properly quenched to room temperature, transform into an amorphous structure on subsequent annealing. Here we report on calorimetric studies of this vitrification process. The specific heat was measured during temperature cycling between 50 °C and 600 °C. In the first heating cycle, the crystal phase undergoes quick stress relaxation and subsequently exhibits the thermal and elastic behaviour of the vitrified state. However, X-ray diffraction still shows predominantly crystalline features which then progressively disappear in the following heating cycles. We conclude that vitrification—with respect to different system variables — evolves on different time scales. A possible mechanism for the vitrification phenomenon is proposed on the basis of statistical mechanics.

Formation of cylindrical shock waves in nonequilibrium magnetogasdynamic flow

Following Chu [in Non-Equilibrium Flows, edited by P. P. Wegener (Dekker, New York, 1970), Vol. II, p. 37], the phenomena associated with the propagation of acceleration waves in nonequilibrium magnetogasdynamic flow, which is induced by the motion of a piston advancing with finite acceleration into a constant state of rest, are studied. Also studied is the characteristic path by using the characteristics of the governing quasilinear system as the reference coordinate system. A differential equation governing the growth and decay of an acceleration wave is derived. The critical time when the breakdown of the characteristic solution occurs in the neighborhood of the leading frozen characteristic is obtained; that is, when all the characteristics will pile up at the wave front to form a shock wave. It is shown that for the slow relaxation process the effect of the magnetic field is to slow down the motion of the breakdown point along the leading frozen characteristic, and thus to increase the cylindrical shock formation time. However, the effect of the magnetic field on expansion waves is to enhance the decay rate. For the quick relaxation process, however, the effect of the magnetic field on compressive waves is to cause an early shock formation, while the effect on expansion waves is to decrease the decay rate.

Temperature Stability of Piezoelectric Ceramics

This paper reports an investigation into the fundamental temperature stability of piezoelectric ceramics through thermal aging and thermal shock tests. The dependence of piezoelectricity on thermal aging and thermal shock of low Qm and high Qm materials was clarified. The surface charges generated by the thermal shock caused depolarization of the ceramic elements. In particular, it was found that space charges promoted depolarization in the high Qm materials. A resistor inserted in parallel with the element for the thermal shock test improved piezoelectricity by causing quick relaxation of the induced charges.

THE EFFECT OF VARIOUS PURINERGIC RECEPTOR BLOCKING AGENTS ON ADENOSINE 5'-TRIPHOSPHATE INDUCED RESPONSES OF THE GUINEA-PIG GALLBLADDER

Exogenously applied adenosine 5'-triphosphate (ATP) caused a biphasic response;a quick relaxation followed by a slow contraction . This response was not affected by atropine, phentolamine, propranolol and tetrodotoxin .Theophylline, quinidine and IBMX reduced ATP-induced contraction and had no effect on ATP-induced relaxation . On the other hand, apamin reduced ATP-induced relaxation and had no effect on ATP-induced contraction .Indomethacin remarkedly reduced ATP-induced contraction without affecting the relaxation.It was suggested that there were two types of receptors (apamin sensitive and apamin resistant) in the guinea-pig gallbladder .

Species differences in the sensitivity of small intestine to the spasmogenic effect of K-free solution.

Effect of removal of the external Potassium ion (K removal) was examined on the mechanical response of the ileum isolated from thirteen animal species; monkey, dog, cat, rabbit, guinea pig, rat, mouse, volt, deer, cock, pigeon, frog and toad. In isotonic recording, K removal induced a sustained contraction in ileum isolated from cat and deer, however, a transient contraction followed by a relaxation in the ileum isolated from other species. Readmission of potassium to the K-free solution produced a quick relaxation in the muscles of pigeon, frog, guinea pig, rat and mouse. Ouabain (1×10-5 M) inhibited the relaxation induced by the readmission of K. There were species differences in contractile activity to K removal; the relative height of ileal contraction induced by K removal was in the order of pigeon, frog, vole, dog, cat, deer, monkey, cock, guinea pig, rat, rabbit, mouse and toad, respectively. Furthermore, the magnitude of the contractile responses to K removal in the ilea isolated from the various kinds of animals correlated with the ED50 of ouabain for a contractile response in the ilea from these animals, as reported by Shimizu et al. (1979). These results probably confirm the concept that K removal and ouabain induce a contraction which is due to the inhibition on an electrogenic Na pump in muscle cells of the ileum.

Neurotensin is a potent inhibitor of guinea-pig colon contractile activity

The investigation concerned the effects of neurotensin (NT) on the mechanical activity of segments of guinea-pig proximal colon. The peptide, in concentrations ranging from 0.1 nM to 100 nM, induced a quick relaxation of the preparations which was followed upon washout by a rebound contraction. Tetrodotoxin had no effect on either the NT-induced relaxation or the rebound contraction. Blocking agents of α- and β-adrenoceptors were also without effect. The bee venom toxin apamin inhibited and even converted to contractions the NT-induced relaxations in the guinea-pig colon. Concentration-response curves for the inhibitory effect of NT, adrenaline and ATP indicated that NT (IC 50 0.32 nM) was 100 times more potent that adrenaline (IC 50 32 nM) and 50 000 times more potent than ATP (IC 50 16 μM). The data show that NT exerts a potent myogenic relaxing effect on the longitudinal smooth muscle of the guinea-pig proximal colon. The properties of this effect suggest the presence of high affinity NT receptors on colonic smooth muscle cells and this points to a possible role for NT as a modulator of guinea-pig proximal colon motility.

The Schultz-Dale reaction of the guinea-pig ileum: influence by beta-adrenoceptor agonists and theophylline.

One of the organs that can be used to study the Schultz-Dale reaction, is the guinea-pig ileum. The reaction is characterized by a specific pattern: a quick contraction, followed by a quick relaxation and a second, more slow contraction. A description is given of this typical reaction. Selective inhibition of the slow contraction could be obtained using beta-adrenoceptor agonists. Also theophylline inhibited the slow contraction, but this inhibition was only selective within a narrow range of concentration. These findings encourage further investigation about a possible involvement of cyclic nucleotides in the liberation of the mediators involved in the Schultz-Dale reaction of the guinea-pig ileum. Furthermore they provide more information about this preparation which could be used as a screening model for anti-allergic drugs of distinct pharmacological groups.

Relaxation of splenic strips during wash out with amine-free solution after an exposure to noradrenaline

1. Strips were prepared from the spleens of normal or of reserpine-pretreated cats or rabbits. The strips were first exposed to (-)noradrenaline and then washed out with amine-free solution. 2. After inhibition of monoamine oxidase by pargyline "secondary sensitization" was prominent during the incubation with noradrenaline, and the early phase of quick relaxation was followed by a late phase of slow relaxation. The latter was cocaine-sensitive and has to be attributed to a slowly declining efflux of noradrenaline from adrenergic nerve endings. 3. Inhibition of catechol-O-methyl transferase by U-0521 or inhibition of extraneuronal uptake by hydrocortisone (cat) or corticosterone (rabbit) failed to alter relaxation. Apparently, an efflux of noradrenaline from extraneuronal stores plays little or no role in the relaxation of splenic strips. 4. During prolonged exposure to noradrenaline strips become desensitized to noradrenaline; on wash out of the amine, sensitivity is restored. As a consequence of this temporary desensitization the response to noradrenaline is not well maintained during prolonged exposure to this amine (when MAO is intact), and the relaxation curve is distorted (whenever a late phase of slow relaxation is prominent). 5. Indometacin enhances the sensitivity of rabbit (but not of cat) splenic strips to noradrenaline but fails to substantially alter relaxation curves. 6. When the distribution of noradrenaline is restricted to the extracellular space and when the concentration of the amine is varied over a wide range, essentially parallel relaxation curves are obtained on wash out, provided the initial contraction does not exceed 80% of maximum. For higher initial contractions relaxation is slowed during the first minute of wash out, probably because of the sigmoid shape of the dose-response curve.

Blood Pressure Recording In the Tense Patient

To the Editor.— Dr. Klinefelter described (226:81, 1973) a practical maneuver that can produce quick relaxation in a tense patient, before measuring his blood pressure. This consisted of a few preliminary deep breaths. I have used this method for many years and have often been impressed by the rapid reduction of the pressure after such deep breathing. Some apprehensive patients tend to undergo contraction of muscles, including diaphragms, and to hold the breath in reaction to some fear provoked by the taking of the blood pressure. In my opinion, the explanation does not lie in the effect of hyperventilation or associated change in the blood oxygen or carbon dioxide tension, but merely in a state of muscle relaxation (including the diaphragm), combined with the diversion created by taking two deep breaths. I believe that Dr. Klinefelter's suggestion should be followed whenever there are doubts about an elevated pressure reading.

Platelets and Clot Retraction

SummaryThe effect of Ca2+, Mg2+, Mn2+ and some drugs known to influence smooth muscle behaviour on human and rat whole blood and PRP clot retraction was studied.The force of the retraction was measured by a dynographic apparatus using electrical transduction. Clot retraction was studied by thrombelastographic method as well.The results obtained by using EDTA and EGT A show that both Ca2+ and Mg2+ are necessary for the normal development of clot retraction. They suggest the coexistence in the platelets of an accessible calcium fraction and a fraction not readily accessible to chelating agents, which is released following the calcium chelation in the first fraction.MnCl2 inhibits clot retraction and induced a quick, complete and irreversible relaxation of fully contracted clots. It is concluded that there are some analogies between blood clots and smooth muscle.The absence of any effect of adrenaline, noradrenaline and ADP, which strongly modify smooth muscle contraction, is not surprising. This is probably because clotting caused by thrombin-triggered platelets has already produced a maximal clot retraction.

Inhibitory postsynaptic potentials in the abducens motoneurons associated with the quick relaxation phase of vestibular nystagmus

Inhibitory postsynaptic potentials in the abducens motoneurons associated with the quick relaxation phase of vestibular nystagmus

Inhibitory postsynaptic potentials in the abducens motoneurons associated with the quick relaxation phase of vestibular nystagmus

Inhibitory postsynaptic potentials in the abducens motoneurons associated with the quick relaxation phase of vestibular nystagmus

The Schultz-Dale response of the longitudinal muscle strip preparation of guinea-pig ileum.

1. The mast-cell distribution in the various layers of the ileum has been described.2. Histamine-content, anaphylactic histamine-release and the anaphylactic dose-response curve of the full-thickness ileum and of the longitudinal muscle strip have been measured and compared.3. Tetrodotoxin 10(-7) g/ml had no obvious effect on the anaphylactic dose-response curve of either preparation. This suggests that the plexus is not of any great importance in the Schultz-Dale reaction.4. Exposure of the longitudinal muscle strip to octylamine 10(-3) g/ml for 1 min reduced the mast cell content by 95-100%. After this treatment the dose-response curve to antigen was eliminated, although the muscle still responded to small doses of histamine and to anaphylactic mediators. Pretreatment of antibody with octylamine did not impair passive sensitization and subsequent response to antigenic challenge. This suggests that the classical Schultz-Dale reaction in the strip is mediated mainly by mast cells, and possibly other cells, and is probably not due to a direct effect of the antigen-antibody reaction on the smooth muscle.5. The typical three-phase anaphylactic response (quick contraction, quick relaxation, slow contraction) of full-thickness ileum is discussed and compared with the predominantly two-phase response of the longitudinal muscle strip. No evidence was found for the release of a relaxation-factor. It is suggested that the initial fast phase may be due to mediators released from mast cells among the longitudinal muscle fibres, and the sustained contraction to a second wave of mediators reaching the longitudinal muscle from deeper layers of the ileum.

Inhibition of central vestibular neurons from the contralateral labyrinth and its mediating pathway.

Inhibition of central vestibular neurons from the contralateral labyrinth and its mediating pathway.

CONTRACTION AND RELAXATION OF THE GUINEA-PIG'S TAENIA COLI IN RELATION TO SPIKE DISCHARGES

1. In the isolated preparation of guinea-pig's taenia coli the tension and the spike discharge have been recorded simultaneously.2. When the muscle was stretched, the frequency of spike discharge increased with the increase in tension developed by stretch, but the maximum frequency of spike discharge during the spontaneous contraction did not alter, and even decreased at the extremely stretched muscle.3. The magnitude of spontaneous contraction decreased by synchronization of spike discharges.4. On application of electrical stimulus the evoked contraction was followed by the quick and deep relaxation. At least a part of this deep relaxation is neither the result of cessation of spike discharge nor the result of adrenaline release. Strong contraction inhibited further contraction probably by lowering the inner visco-elasticity of muscle cell.

A new biological method for the assay of depolarizing substances using the isolated semispinalis muscle of the chick.

The isolated semispinalis cervicis muscle of a 3 to 10 days old chick has been found to provide a very useful assay method for depolarizing substances. There are three main advantages of this preparation over that of the rectus abdominis of the frog: (a) quick relaxation without any artificial stretching of the muscle, (b) greater sensitivity to depolarizing drugs, and (c) no falling off in sensitivity for at least 2 hr.

Changes in twitch tension induced by quick stretch and stress relaxation.

The triceps surae of male rats was prepared in situ for isometric recording and for stimulation through the cut sciatic nerve. A study was made on changes of twitch tension induced by quick stretch, stress relaxation and slow stretch. Quick stretch applied immediately before the twitch response produces changes of twitch tension similar to those obtained by slow stretch. Stress relaxation after quick stretch is accompanied by twitch tension greater than that obtainable after slow stretch at all lengths of the muscle observed. The amount of increase of twitch tension induced by stress relaxation is large below the optimum length and small beyond the optimum length of the muscle. When stress relaxation is virtually complete, this increase of twitch tension disappears, the magnitude of the twitch being thereafter equal to that obtainable by slow stretch. It is suggested that the increase is due to a dynamic state of the length-resting tension relationship during stress relaxation when length is increasing and tension is decreasing. Disappearance of the increase of twitch tension when length-resting tension equilibrium is established after stress relaxation supports this suggestion.

ANALYSIS OF THE ACTIVITY OF THE CHAINS OF INTERNUNCIAL NEURONS

ANALYSIS OF THE ACTIVITY OF THE CHAINS OF INTERNUNCIAL NEURONS