Damping efficiency of two-layer polyurethane composites

In this work, based on the results of dynamic mechanical studies, the damping efficiency of two-layer polyurethane (PU) composites designed by gluing two films of synthesized PU with different glass transition temperatures (Tg) was estimated. The damping efficiency was estimated by the parameters of the mechanical losses (tanδ) peak. To vary Tg, three types of PU with different chemical nature and structure were synthesized. The effect of an increase in the difference between the Tg of the initial PU (ΔTg) on the damping efficiency of the two-layer PU composites formed from them is analyzed. The effective damping temperature range (ΔT) was estimated as the temperature range under conditions tanδ ≥ 0,3 and tanδ ≥ 0,6. It was shown that at ΔТg = 7 °С a two-layer PU composite has one relaxation maximum, and its temperature range of damping efficiency expands in comparison with ΔТ for individual PU. Under the conditions ΔТg = 23 °С and ΔТg = 30 °С, two-layer PU composites exhibit damping efficiency in two temperature regions at tanδ ≥ 0,3, which provides an additional temperature range of effective damping. The essential role of the PU structure of each of the layers in the formation of a two-layer composite by gluing has been determined. Easier penetration of residues of the adhesive organic solvent into the surface of the PU film with a linear structure leads to plasticization of the corresponding layer in the composite and reduces Tg. It is shown that a two-layer structure can be used to solve specific problems related to the adjustment or broadening the effective damping temperature range.

Change in hamstrings flexibility: A comparison between three different manual therapeutic techniques in normal individuals

Objectives: The objectives of the study were to find the effective techniques out of post isometric relaxation, Maximum voluntary isometric contraction and PNF hold relax in increasing the flexibility of hamstring muscles. Materials and Methods: An observational study on 90 subjects (both sexes; between 18 and 30 years) was given one of three interventions – PIR, 10 Sec MVIC, and PNF HR and assigned into three groups – Group A, B, and C (each group with 30 subjects). Three repetitions of the protocol were given to each subject for regular 2 days. Active knee extension ROM was measured by the AKE test (90–90 test) before and after the treatment session both days. The data were collected, and percentage analysis was used to interpret the results. Results: All the groups showed a significant increase in active knee extension ROM. However, the results were more significant for Group B than Group A than Group C with mean differences 5.53, 4.97, and 3.83, respectively. Conclusion: Hence, it is concluded that 10 s, MVIC was the most effective among the three manual techniques.

Nanoscale rotational dynamics of four independent rotators confined in crowded crystalline layers

Car–Parrinello molecular dynamics unravels a microscopic model of correlated motion within a set of four rotors whose similar rotational barriers (at 6 kcal mol−1) are encapsulated within a broad 1H spin–lattice relaxation maximum.

Features of Polarization Processes in Thin Films Poly(Diphenylene Phthalide)

The paper presents the results of investigation of polarization processes in poly (diphenylene phthalide) films in a wide frequency range (10-1-106Hz) and temperatures (273-373K). The thickness of the films varied from 5 μm to 100 μm. An increase in the dielectric constant, which may be associated with the manifestation of the dipole-relaxation polarization mechanism, is observed. The temperature dependence of the loss factor for the investigated PDF films revealed a relaxation maximum in the studied temperature region. This anomaly is caused by relaxation processes in the polymer structure. The frequency dependence of the conductivity was σ'~ωs type, that indicates the existence of hopping mechanism of charge transfer. The values of the exponent was s<1.0 and decreased with the increase of temperature. The observed linear dependence of the temperature of change in the conductivity type on the film thickness may be associated with transition of the polymer system from the dielectric to conducting state. This feature can be used to estimate the sample thickness for this system.

Involvement of Potassium Channels in Vasorelaxant Effect Induced byValeriana prionophyllaStandl. in Rat Mesenteric Artery

Assaysin vitroandin vivowere performed on extract from roots and leaves from theValeriana prionophyllaStandl. (VPR and VPF, resp.). In phenylephrine (1 μM) precontracted rings, VPR (0.01–300 μg/mL) induced a concentration-dependent relaxation (maximum response (MR) = 75.4 ± 4.0%, EC50= 5.97 (3.8–9.3)μg/mL,n=6]); this effect was significantly modified after removal of the endothelium (EC50= 39.6 (27.2–57.6)μg/mL,P<0.05). However, VPF-induced vasorelaxation was less effective compared to VPR. When rings were preincubated with L-NAME (100 μM) or indomethacin (10 μM), the endothelium-dependent relaxation induced by VPR was significantly attenuated (MR = 20.9 ± 2.3%, 34.2 ± 2.9%, resp.,P<0.001). In rings denuded endothelium, precontracted with KCl (80 mM), or in preparations pretreated with KCl (20 mM) or tetraethylammonium (1 or 3 mM), the vasorelaxant activity of VPR was significantly attenuated (MR = 40.0 ± 8.2,n=5; 50.5 ± 6.0%; 49.3 ± 6.4%; 46.8 ± 6.2%; resp.,P<0.01). In contrast, neither glibenclamide (10 μM), barium chloride (30 μM), nor 4-aminopyridine (1 mM) affected VPR-induced relaxation. Taken together, these results demonstrate that hypotension induced by VPR seems to involve, at least in part, a vascular component. Furthermore, endothelium-independent relaxation induced by VPR involves K+channels activation, most likely due to BKCachannels, in the rat superior mesenteric artery.

Absence of adenosine-mediated aortic relaxation in A2A adenosine receptor knockout mice

Adenosine mediates vascular responses through four receptor subtypes: A1, A2A, A2B, and A3. The role of A2A receptors in aortic vascular tone was investigated using A2A adenosine receptor (AR) knockout (A2AKO) and corresponding wild-type (A2AWT) mice. Isolated aortic rings from A2AWT and A2AKO mice were precontracted with phenylephrine (10−7 M), and concentration responses for adenosine analogs and selective agonists/antagonists were obtained. Nonselective adenosine analog (NECA; EC50 = 6.78 μM) and CGS-21680 (A2AAR selective agonist; EC50 = 0.013 μM) produced concentration-dependent relaxation (maximum of 25% and 28% relaxation at 10−5 M NECA and CGS-21680, respectively) in A2AWT aorta. In A2AKO aorta, NECA (EC50 = 0.075 μM) induced concentration-dependent contraction (maximum contraction of 47% at 10−6 M; P < 0.05 compared with A2AWT), whereas CGS-21680 produced no response. SCH-58261 (10−6 M; A2AAR selective antagonist) abolished both NECA- and CGS-21680-mediated vasorelaxation in A2AWT ( P < 0.05), whereas no change was observed in A2AKO. When DPCPX (10−5 M; A1 selective antagonist) was used in NECA concentration response, greater vasorelaxation was observed in A2AWT (50% vs. 25% in controls at 10−5 M; P < 0.05), whereas lower contraction was seen in A2AKO tissues (5% vs. 47% in controls at 10−6 M; P < 0.05). Aortic endothelial function, determined by response to acetylcholine, was significantly higher in WT compared with KO (66% vs. 51%; P < 0.05). BAY 60–6583 (A2B selective agonist) produced similar relaxation in both KO and WT tissues. In conclusion, A2AAR KO mice had significantly lower aortic relaxation and endothelial function, suggesting that the A2AAR plays an important role in vasorelaxation, probably through an endothelium-dependent mechanism.

Modulation of left ventricular relaxation in isolated ejecting heart by endogenous nitric oxide

Nitric oxide (NO) modulates myocardial contractile behavior in several isolated preparations, e.g., cardiac myocytes and papillary muscles, via elevation of intracellular guanosine 3',5'-cyclic monophosphate (cGMP). We have recently reported that the exogenous NO donor, sodium nitroprusside, selectively modulates left ventricular (LV) relaxation in the isolated ejecting guinea pig heart, independent of coronary flow. We now report the effects of endogenously released NO on LV performance in this preparation (constant heart rate and loading). Both bradykinin (1 nM, n = 6) and substance P (100 nM, n = 6) accelerated early LV relaxation (maximum change in time constant, tE, -10.5 +/- 1.6 and -13.4 +/- 2.1%, respectively; both P < 0.05), without significantly altering early systolic parameters (e.g., rate of LV pressure development). These effects were inhibited by hemoglobin (P < 0.05; n > or = 6), which inactivates NO. Bradykinin (100 nM, n = 10) had an additional negative inotropic effect, which was not inhibited by hemoglobin. Neither agonist altered relaxation in isolated papillary muscles. These data suggest that endogenous NO, probably released from coronary microvascular endothelial cells, modulates LV relaxation in the intact heart.

THE EFFECT OF GAMMA IRRADIATION ON THE DISLOCATION RELAXATION PEAK OF COPPER

The effect of gamma irradiation on the dislocation relaxation maximum, i.e. the Bordoni peak, of two high purity copper single crystals of orientation <110> has been studied at a frequency of 10 MHz. It was found that as the irradiation dose increases the Bordoni peak height [Formula: see text] and its temperature Tm decreases in both specimens. A specimen of width to length ratio 1:10, i.e. easy glide, seems to be more sensitive to gamma irradiation than one of aspect ratio 1.3:1. The peak height and its temperature in the former specimen was found to be always higher than in the latter when both were irradiated with a similar dosage. The relation between [Formula: see text] and the gamma irradiation dose is of the form [Formula: see text] where y equals 1.4 or 1.5 depending on the mechanical treatment. Moreover, the study suggests that Q−1 is proportional to the dislocation loop length L in the form [Formula: see text] where n has values of 1.4 and 1.5 which agrees with the pair-kink generation model first proposed by Seeger.

Relaxation of the diaphragm muscle: influence of ryanodine and fatigue

Relaxation of rat diaphragm was shown to be sensitive to load, as previously described for adult mammalian ventricular muscle, because the time course of isotonic relaxation could be changed by changing the load: the lighter the load, the greater the shortening, the quicker the relaxation. Maximum velocity of isotonic relaxation was linearly related to the extent of shortening (r = 0.90). To quantify the degree of load sensitivity, we measured the tRi, i.e., the ratio of time at which the isometric relaxation of the twitch afterloaded at 50% of the isometric peak active tension began to time at which the isometric twitch was relaxed to 50% of the isometric peak active twitch tension. tRi was 0.76 +/- 0.03 (SE) in control conditions but significantly increased to 0.91 +/- 0.02 after ryanodine, which is an inhibitor of the sarcoplasmic reticulum (SR) function, and to 0.89 +/- 0.03 after fatigue. These results suggest that in adult rat diaphragm, as in cardiac muscle, the load sensitivity of relaxation requires a well-functioning SR and that the relaxation abnormalities observed in fatigued diaphragm are related to a dysfunction of the SR.

Tetrodotoxin-resistant relaxation to transmural nerve stimulation in canine saphenous veins: a possible neural origin

Transmural nerve stimulation following sympathetic (guanethidine 10−4 mol/L, phenoxybenzamine 2 × 10−5 mol/L, propranolol 2 × 10−6 mol/L) and muscarinic blockade (atropine 5 × 10−5 mol/L) produces a relaxatory response in canine saphenous veins contracted with prostaglandin F2α. This relaxatory response was shown previously to be resistant to tetrodotoxin. Transmural nerve stimulation (10 V, 1.0 ms) was applied as intermittent trains of stimuli of 30 s duration at frequencies of 1–32 Hz. The veins showed a frequency dependent relaxation (maximum 2.65 ± 0.20 g). The stimulations were repeated in the presence of lignocaine (10−3 mol/L), apamin (10−8 mol/L), ascorbic acid (10−4 mol/L), or catalase (50 μg/mL). The relaxatory response was unaffected by apamin, scorpion toxin, superoxide dismutase, ascorbic acid, and catalase (p > 0.05). However, lignocaine (10−3 mol/L) reduced significantly the relaxatory response to transmural nerve stimulation in this preparation (p < 0.05). In a separate group of veins, lignocaine (10−3 mol/L)l abolished the contractile response to transmural nerve stimulation with little effect upon the contractile response to exogenous noradrenaline and the relaxatory responses to isoprenaline and sodium nitrite. These findings support the proposition that the nonadrenergic, noncholinergic tetrodotoxin-resistant relaxatory response observed with transmural nerve stimulation in the canine saphenous vein is mediated by a neural mechanism.