Artículos de revistas: "Viscoelastic respiratory system properties"

1

Jonson, B., L. Beydon, K. Brauer, C. Mansson, S. Valind y H. Grytzell. "Mechanics of respiratory system in healthy anesthetized humans with emphasis on viscoelastic properties". Journal of Applied Physiology 75, n.º 1 (1 de julio de 1993): 132–40. http://dx.doi.org/10.1152/jappl.1993.75.1.132.

Texto completo

Resumen

The classic model of the respiratory system (RS) is comprised of a Newtonian resistor in series with a capacitor and a viscoelastic unit including a resistor and a capacitor. The flow interruption technique has often been used to study the viscoelastic behavior under constant inspiratory flow rate. To study the viscoelastic behavior of the RS during complete respiratory cycles and to quantify viscoelastic resistance (Rve) and compliance (Cve) under unrestrained conditions, we developed an iterative technique based on a differential equation. We, as others, assumed Rve and Cve to be constant, which concords with volume and flow dependency of model behavior. During inspiration Newtonian resistance (R) was independent of flow and volume. During expiration R increased. Static elastic recoil showed no significant hysteresis. The viscoelastic behavior of the RS was in accordance with the model. The magnitude of Rve was 3.7 +/- 0.7 cmH2O.l-1 x s, i.e., two times R. Cve was 0.23 +/- 0.051 l/cmH2O, i.e., four times static compliance. The viscoelastic time constant, i.e., Cve.Rve, was 0.82 +/- 0.11s. The work dissipated against the viscoelastic system was 0.62 +/- 0.13 cmH2O x 1 for a breath of 0.56 liter, corresponding to 32% of the total energy loss within the RS. Viscoelastic recoil contributed as a driving force during the initial part of expiration.

Los estilos APA, Harvard, Vancouver, ISO, etc.

2

Antonaglia, V., A. Grop, P. Demanins, F. Beltrame, U. Lucangelo, A. Peratoner, L. De Simoni, A. Gullo y J. Milic-Emili. "Single-breath method for assessing the viscoelastic properties of the respiratory system". European Respiratory Journal 12, n.º 5 (1 de noviembre de 1998): 1191–96. http://dx.doi.org/10.1183/09031936.98.12051191.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

3

Similowski, T. y JH Bates. "Two-compartment modelling of respiratory system mechanics at low frequencies: gas redistribution or tissue rheology?" European Respiratory Journal 4, n.º 3 (1 de marzo de 1991): 353–58. http://dx.doi.org/10.1183/09031936.93.04030353.

Texto completo

Resumen

The mechanical properties of the respiratory system are generally inferred from measurements of pressure and flow at the airway opening. Traditionally, these measurements have been related through a single-compartment model of the respiratory system. Recently, however, there has been considerable interest in modelling low-frequency respiratory mechanics in terms of two compartments, since this gives a much improved description of experimental data. In this paper we consider two classes of two-compartment models that are compatible with pressure-flow relationships of air measured at the airway opening. One type of model accounts for regional ventilation inhomogeneity in the lung in terms of two alveolar compartments. The other type of model considers pulmonary ventilation to be homogeneous, while the tissues of the respiratory system are modelled as being viscoelastic. In normal dogs, the appropriate two-compartment model has been shown to be the viscoelastic model. In the case of abnormal physiology, however, one must invoke a model having both viscoelastic tissues and ventilation inhomogeneities. Additional experimental data are required in order to identify such a model, and to quantify these two phenomena.

Los estilos APA, Harvard, Vancouver, ISO, etc.

4

Bates, J. H. T. y J. Milic-Emili. "Influence of the viscoelastic properties of the respiratory system on the energetically optimum breathing frequency". Annals of Biomedical Engineering 21, n.º 5 (septiembre de 1993): 489–99. http://dx.doi.org/10.1007/bf02584331.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

5

Clement, M. G. y M. Dimori. "Inhaled Nitric Oxide Counterbalances ET-1 Dependent Pulmonary Hypertension and Bronchoconstriction in the Pig". Mediators of Inflammation 3, n.º 2 (1994): 131–35. http://dx.doi.org/10.1155/s0962935194000165.

Texto completo

Resumen

In anaesthetized, paralysed, ventilated pigs the ability of inhaled nitric oxide (80 ppm in 02) to reduce the haemodynamic and respiratory effects of endothelin-1 administration (200 pmol/kg, i.v.) was evaluated. The mechanical properties of the respiratory system were evaluated by the rapid airway occlusion technique. The overall respiratory resistance, the interrupter resistance and the additional resistance that reflects the viscoelastic properties of tissues and the inequality of the time constant within the system were also evaluated. The results show that inhaled nitric oxide can act as a selective pulmonary vasodilator and as a bronchodilator to counteract the vasoconstrictor and bronchoconstrictor activity of endothelin-1. In the pig, nitric oxide inhaled at 80 ppm for 6 mitt reduced the changes in respiratory-, interrupter- and additional resistance due to endothelin-1 administration without significantly changing the static and dynamic elastance of the respiratory system.

Los estilos APA, Harvard, Vancouver, ISO, etc.

6

Correa, Fatima C. F., Patricia B. Ciminelli, Haroldo Falcão, Bruno J. C. Alcântara, Renata S. Contador, Aline S. Medeiros, Walter A. Zin y Patricia R. M. Rocco. "Respiratory mechanics and lung histology in normal rats anesthetized with sevoflurane". Journal of Applied Physiology 91, n.º 2 (1 de agosto de 2001): 803–10. http://dx.doi.org/10.1152/jappl.2001.91.2.803.

Texto completo

Resumen

Respiratory system, lung, and chest wall mechanical properties were subdivided into their resistive, elastic, and viscoelastic/inhomogeneous components in normal rats, to define the sites of action of sevoflurane. In addition, we aimed to determine the extent to which pretreatment with atropine modified these parameters. Twenty-four rats were divided into four groups of six animals each: in the P group, rats were sedated (diazepam) and anesthetized with pentobarbital sodium; in the S group, sevoflurane was administered; in the AP and AS groups, atropine was injected 20 min before sedation/anesthesia with pentobarbital and sevoflurane, respectively. Sevoflurane increased lung viscoelastic/inhomogeneous pressures and static elastance compared with rats belonging to the P group. In AS rats, lung static elastance increased in relation to the AP group. In conclusion, sevoflurane anesthesia acted not at the airway level but at the lung periphery, stiffening lung tissues and increasing mechanical inhomogeneities. These findings were supported by the histological demonstration of increased areas of alveolar collapse and hyperinflation. The pretreatment with atropine reduced central and peripheral airway secretion, thus lessening lung inhomogeneities.

Los estilos APA, Harvard, Vancouver, ISO, etc.

7

D’Angelo, Edgardo, Edoardo Calderini, Mario Tavola y Matteo Pecchiari. "Standard and viscoelastic mechanical properties of respiratory system compartments in dogs: Effect of volume, posture, and shape". Respiratory Physiology & Neurobiology 261 (marzo de 2019): 31–39. http://dx.doi.org/10.1016/j.resp.2018.12.003.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

8

Freezer, N. J., C. J. Lanteri y P. D. Sly. "Effect of pulmonary blood flow on measurements of respiratory mechanics using the interrupter technique". Journal of Applied Physiology 74, n.º 3 (1 de marzo de 1993): 1083–88. http://dx.doi.org/10.1152/jappl.1993.74.3.1083.

Texto completo

Resumen

The relationship between respiratory mechanics, changes in pulmonary blood flow (PBF), pulmonary arterial pressure, and left atrial pressure is unclear. Conventional methods for the measurement of respiratory mechanics model the respiratory system as a single compartment, which may not adequately represent the respiratory system in a diseased state. The interrupter technique models the respiratory system as two compartments, with the "flow resistance" of the conducting airways and chest wall (Raw) considered separately from Pdif, a measure of the viscoelastic properties of the lung and chest wall, together with any pendelluft present. The respiratory mechanics of 15 infants in the first year of life were studied during cardiac catheterization with the use of conventional methods and the interrupter technique. The infants had a PBF-to-systemic blood flow ratio ranging from 0.6 to 4.0:1. The specific dynamic compliance of the respiratory system was not related to the PBF; however, there was a significant relationship between PBF and the total resistance of the respiratory system (Rrs) [analysis of variance (ANOVA) F = 5.69, P < 0.05], Raw (ANOVA, F = 12.30, P < 0.01), and Pdif (ANOVA, F = 3.79, P < 0.05). Rrs increased significantly with an increase in mean left atrial pressure (ANOVA, F = 6.92, P < 0.05); however, dynamic compliance, Raw, and Pdif did not. These results suggest that the relationship between Rrs and PBF is due an increase in the resistive properties of the conducting airways and tissue components.

Los estilos APA, Harvard, Vancouver, ISO, etc.

9

Pelosi, P., M. Croci, I. Ravagnan, M. Cerisara, P. Vicardi, A. Lissoni y L. Gattinoni. "Respiratory system mechanics in sedated, paralyzed, morbidly obese patients". Journal of Applied Physiology 82, n.º 3 (1 de marzo de 1997): 811–18. http://dx.doi.org/10.1152/jappl.1997.82.3.811.

Texto completo

Resumen

Pelosi, P., M. Croci, I. Ravagnan, M. Cerisara, P. Vicardi, A. Lissoni, and L. Gattinoni. Respiratory system mechanics in sedated, paralyzed, morbidly obese patients J. Appl. Physiol. 82(3): 811–818, 1997.—The effects of inspiratory flow and inflation volume on the mechanical properties of the respiratory system in eight sedated and paralyzed postoperative morbidly obese patients (aged 37.6 ± 11.8 yr who had never smoked and had normal preoperative seated spirometry) were investigated by using the technique of rapid airway occlusion during constant-flow inflation. With the patients in the supine position, we measured the interrupter resistance (Rint,rs), which in humans probably reflects airway resistance, the “additional” resistance (ΔRrs) due to viscoelastic pressure dissipation and time-constant inequalities, and static respiratory elastance (Est,rs). Intra-abdominal pressure (IAP) was measured by using a bladder catheter, and functional residual capacity was measured by the helium-dilution technique. The results were compared with a previous study on 16 normal anesthetized paralyzed humans. Compared with normal persons, we found that in obese subjects: 1) functional residual capacity was markedly lower (0.645 ± 0.208 liter) and IAP was higher (24 ± 2.2 cmH2O); 2) alveolar-arterial oxygenation gradient was increased (178 ± 59 mmHg); 3) the volume-pressure curve of the respiratory system was curvilinear with an “inflection” point; 4) Est,rs, Rint,rs, and ΔRrs were higher than normal (29.3 ± 5.04 cmH2O/l, 5.9 ± 2.4 cmH2O ⋅ l−1 ⋅ s, and 6.4 ± 1.6 cmH2O ⋅ l−1 ⋅ s, respectively); 5) Rint,rs increased with increasing inspiratory flow, Est,rs did not change, and ΔRrs decreased progressively; and 6) with increasing inflation volume, Rint,rs and Est,rs decreased, whereas ΔRrs rose progressively. Overall, our data suggest that obese subjects during sedation and paralysis are characterized by hypoxemia and marked alterations of the mechanical properties of the respiratory system, largely explained by a reduction in lung volume due to the excessive unopposed IAP.

Los estilos APA, Harvard, Vancouver, ISO, etc.

10

Bates, J. H., K. A. Brown y T. Kochi. "Respiratory mechanics in the normal dog determined by expiratory flow interruption". Journal of Applied Physiology 67, n.º 6 (1 de diciembre de 1989): 2276–85. http://dx.doi.org/10.1152/jappl.1989.67.6.2276.

Texto completo

Resumen

We recently proposed an eight-parameter model of the respiratory system to account for its mechanical behavior when flow is interrupted during passive expiration. The model consists of two four-parameter submodels representing the lungs and the chest wall, respectively. The lung submodel consists of an airways resistance together with elements embodying the viscoelastic properties of the lung tissues. The chest wall submodel has similar structure. We estimated the parameters of the model from data obtained in four normal, anesthetized, paralyzed, tracheostomized mongrel dogs. This model explains why lung tissue and chest wall resistances should be markedly frequency dependent at low frequencies and also permits a physiological interpretation of resistance measurements provided by the flow interruption method.

Los estilos APA, Harvard, Vancouver, ISO, etc.

11

Bates, J. H., M. Decramer, D. Chartrand, W. A. Zin, A. Boddener y J. Milic-Emili. "Volume-time profile during relaxed expiration in the normal dog". Journal of Applied Physiology 59, n.º 3 (1 de septiembre de 1985): 732–37. http://dx.doi.org/10.1152/jappl.1985.59.3.732.

Texto completo

Resumen

Airway opening pressure, esophageal pressure, and flow were obtained during relaxed expirations in two normal anesthetized paralyzed dogs. The signal-to-noise ratio in the flow signals was greatly increased by averaging 10 different signals obtained with the same lung inflation volume. Numerical integration of an averaged flow signal then yielded the time course of the volume of the respiratory system above functional residual capacity (the elastic equilibrium volume). Comparison of volume signals obtained with different inflation volumes suggests that the resistance of the respiratory system increases with flow. The flow-volume and semilog volume curves show that expiration is induced by two apparently separate mechanisms: one causes emptying of most of the expired volume over a time interval of much less than 1 s, whereas the other contributes a relatively small amount to the expired volume over a significantly longer time (greater than or equal to 1 s). We postulate the first mechanism to be due to that of the respiratory system behaving like a single unit, with an elastance that is slightly volume dependent, emptying through a single airway which has a resistance that increases with flow. From the nature of airway opening pressure and esophageal pressure measured after occlusion in midexpiration, we conclude that the second mechanism is due to the viscoelastic properties (i.e., creep) of the respiratory system. The properties are manifest mainly in the chest wall.

Los estilos APA, Harvard, Vancouver, ISO, etc.

12

Chelucci, GL, F. Brunet, J. Dall'Ava-Santucci, JF Dhainaut, D. Paccaly, A. Armaganidis, J. Milic-Emili y A. Lockhart. "A single-compartment model cannot describe passive expiration in intubated, paralysed humans". European Respiratory Journal 4, n.º 4 (1 de abril de 1991): 458–64. http://dx.doi.org/10.1183/09031936.93.04040458.

Texto completo

Resumen

The time-course of thoracic volume changes (respiratory inductive plethysmograph) during relaxed expiration was studied in 11 intubated, paralysed, mechanically ventilated subjects. The semilog volume-time curves show that expiration is governed by two apparently separate mechanisms: one causes emptying of most of the expired volume (approximately 80%) with a time constant of 0.50 +/- 0.22 s for a baseline tidal volume of 0.44 +/- 0.12 l (mean +/- SD) and 0.37 +/- 0.14 s when the tidal volume is reduced (VTP); the other contributes a relatively small amount to the expired volume over a significantly longer time, the time constant amounting to 3.27 +/- 1.54 s for baseline VT and 2.95 +/- 1.65 s for VTp. The first mechanism probably reflects the standard elastic and flow resistive properties of the respiratory system, while the second, slower compartment, is probably an expression of the viscoelastic properties of the pulmonary and chest wall tissues.

Los estilos APA, Harvard, Vancouver, ISO, etc.

13

Kaczka, David W., David N. Hager, Monica L. Hawley y Brett A. Simon. "Quantifying Mechanical Heterogeneity in Canine Acute Lung Injury". Anesthesiology 103, n.º 2 (1 de agosto de 2005): 306–12. http://dx.doi.org/10.1097/00000542-200508000-00014.

Texto completo

Resumen

Background The heterogeneous pattern of acute lung injury (ALI) predisposes patients to ventilator-associated lung injury. Currently, there is no simple technique that can reliably quantify lung heterogeneity during the dynamic conditions of mechanical ventilation. Such a technique may be of use in optimizing mechanical ventilatory parameters such as rate, tidal volume, or positive end-expiratory pressure. Methods To determine the impact of heterogeneity on respiratory mechanics, the authors measured respiratory impedance (Zrs), expressed as respiratory resistance (Rrs) and elastance (Ers), in 11 anesthetized dogs from 0.078 to 8.9 Hz using broadband pressure and flow excitations under baseline conditions and after ALI produced by infusion of 0.08 ml/kg oleic acid into the right atrium. Data were obtained at mean airway pressures (Pao) of 5, 10, 15, and 20 cm H2O. The Zrs spectra were fit by various models of the respiratory system incorporating different distributions of parallel viscoelastic tissue properties. Results Under baseline conditions, both Rrs and Ers exhibited dependence on oscillation frequency, reflecting viscoelastic behavior. The Ers demonstrated significant dependence on Pao. After ALI, both the level and frequency dependence of Rrs and Ers increased, as well as the apparent heterogeneity of tissue properties. Both Rrs and Ers as well as heterogeneity decreased with increasing Pao, approaching baseline levels at the highest levels of Pao. Conclusions These data demonstrate that Zrs can provide specific information regarding the mechanical heterogeneity of injured lungs at different levels of Pao. Moderate increases in Pao seem to be beneficial in ALI by reducing heterogeneity and recruiting lung units. These noninvasive measurements of lung heterogeneity may ultimately allow for the development of better ventilation protocols that optimize regional lung mechanics in patients with ALI.

Los estilos APA, Harvard, Vancouver, ISO, etc.

14

Rakhmankulova, Barna, Sayibdjan Mirzaev y Mazhid Yusupov. "Numerical modeling of nonlinear viscoelastic vibrations of vehicles". E3S Web of Conferences 365 (2023): 01006. http://dx.doi.org/10.1051/e3sconf/202336501006.

Texto completo

Resumen

Nonlinear viscoelastic oscillations of a vehicle in a vertical direction excited by static imbalance are considered. When taking into account the rheological properties of the suspension material and spring, the Boltzmann-Volterra principle was used. Mathematical models of the problem under consideration are obtained, which are described by systems of nonlinear integro-differential equations. A solution method based on quadrature formulas has been developed, and a computer program has been compiled on its basis. The results obtained are reflected in graphs. The influence of the material's rheological properties and the nonlinear characteristics of the suspension and spring on the amplitude and frequency of vertical vibrations of vehicles was investigated.

Los estilos APA, Harvard, Vancouver, ISO, etc.

15

Mirzaev, Sayibdjan, Majid Yusupov, Barna Rakhmankulova, Feruza Umarova y Gulnaz Abdikayimova. "Vertical vibrations of traction engine with viscoelastic suspension". E3S Web of Conferences 365 (2023): 01022. http://dx.doi.org/10.1051/e3sconf/202336501022.

Texto completo

Resumen

The tasks of a traction engine with suspension elements and additional devices for converting movement (DCM) are considered. The object of protection, the estimated dynamic state, is solid with mass M and moment of inertia J relative to the center of gravity. To account the suspension material's rheological properties, the Boltzmann-Volterra principle is used. Mathematical models of the problem under consideration are obtained, which are described by the systems of integro-differential equations. A solution method based on quadrature formulas is developed, and a computer program is compiled based on its basis, the results of which are reflected in the graphs. The influence of DCM and rheological properties of the suspension material on the shape of the vertical vibrations of the object is investigated.

Los estilos APA, Harvard, Vancouver, ISO, etc.

16

D'Angelo, E., E. Calderini, G. Torri, F. M. Robatto, D. Bono y J. Milic-Emili. "Respiratory mechanics in anesthetized paralyzed humans: effects of flow, volume, and time". Journal of Applied Physiology 67, n.º 6 (1 de diciembre de 1989): 2556–64. http://dx.doi.org/10.1152/jappl.1989.67.6.2556.

Texto completo

Resumen

The effects of inspiratory flow rate and inflation volume on the resistive properties of the total respiratory system were investigated in 16 anesthetized paralyzed humans by using the technique of rapid airway occlusion during constant flow inflation. This allowed measurement of the intrinsic resistance (Rmin,rs) and of the effective additional resistance (delta Rrs) as the result of viscoelastic pressure dissipations within the pulmonary and chest wall tissues. We observed that 1) at fixed inflation volume, Rmin,rs increased linearly with increasing flow although delta Rrs decreased according to an exponential function; 2) at fixed inflation flow, Rmin,rs decreased with increasing inflation volume although there was a concomitant increase in delta Rrs. This behavior could be explained in terms of a spring-and-dashpot model incorporating 1) the standard resistance and elastance and 2) a spring-and-dashpot in parallel with standard elastance, reflecting the stress adaptation units within the thoracic tissues.

Los estilos APA, Harvard, Vancouver, ISO, etc.

17

Eissa, N. T., V. M. Ranieri, C. Corbeil, M. Chasse, F. M. Robatto, J. Braidy y J. Milic-Emili. "Analysis of behavior of the respiratory system in ARDS patients: effects of flow, volume, and time". Journal of Applied Physiology 70, n.º 6 (1 de junio de 1991): 2719–29. http://dx.doi.org/10.1152/jappl.1991.70.6.2719.

Texto completo

Resumen

The effects of inspiratory flow (V) and inflation volume (delta V) on the mechanical properties of the respiratory system in eight ARDS patients were investigated using the technique of rapid airway occlusion during constant-flow inflation. We measured interrupter resistance (Rint,rs), which in humans represents airway resistance, the additional resistance (delta Rrs) due to viscoelastic pressure dissipations and time constant inequalities, and static (Est,rs) and dynamic (Edyn,rs) elastance. The results were compared with a previous study on 16 normal anesthetized paralyzed humans (D'Angelo et al. J. Appl. Physiol. 67: 2556-2564, 1989). We observed that 1) resistance and elastance were higher in ARDS patients; 2) with increasing V, Rint,rs and Est,rs did not change, delta Rrs decreased progressively, and Edyn,rs increased progressively; 3) with increasing delta V, Rint,rs decreased slightly, delta Rrs increased progressively, and Est,rs and Edyn,rs showed an initial decrease followed by a secondary increase noted only in the ARDS patients. The above findings could be explained in terms of a model incorporating a standard resistance in parallel with a standard elastance and a series spring-and-dashpot body that represents the stress adaptation units within the tissues of the respiratory system.

Los estilos APA, Harvard, Vancouver, ISO, etc.

18

Sullivan, K. J. y J. P. Mortola. "Effect of distortion on the mechanical properties of newborn piglet lung". Journal of Applied Physiology 59, n.º 2 (1 de agosto de 1985): 434–42. http://dx.doi.org/10.1152/jappl.1985.59.2.434.

Texto completo

Resumen

During breathing the relatively high chest wall-to-lung compliance ratio of the newborn favors distortion of the respiratory system. In this study we have examined the effect of lung deformation, generated by a hydrostatic pleural surface pressure gradient, on the static (Cstat) and dynamic (Cdyn) compliance of the isolated newborn piglet lung. Seven lungs from piglets 2–7 days old have been studied in a saline-filled plethysmograph. Static pressure-volume (PV) curves were obtained by changing the volume a known amount and measuring the corresponding changes in transpulmonary pressure. Dynamic PV curves were obtained by ventilating the lung at a fixed pressure and at 20 cycles/min. These experiments were repeated in an air plethysmograph on the undeformed lung. Lung volume history was standardized prior to each maneuver by three inflations to 20–25 cmH2O. Lung collapse was avoided by applying an end-expiratory load equal to the transpulmonary pressure at functional residual capacity. Cstat was not significantly different between the deformed and undeformed lung (P greater than 0.05). Cdyn was less than Cstat in both cases (P less than 0.025) and was reduced further by deformation (P less than 0.05). We conclude that 1) peripheral airway obstruction or the viscoelastic properties of the piglet lung, or both, decrease Cdyn, and 2) deformation increases the external (PV) respiratory work by further decreasing Cdyn.

Los estilos APA, Harvard, Vancouver, ISO, etc.

19

Rakhmankulova, Barna, Sayibdjan Mirzaev y Mazhid Yusupov. "Numerical simulation of tasks of vertical viscoelastic oscillation of suspension systems of frame, engine, cabin and seat". E3S Web of Conferences 365 (2023): 01007. http://dx.doi.org/10.1051/e3sconf/202336501007.

Texto completo

Resumen

The analysis of the structures of the springing systems of modern vehicles showed that polymer composites are used in vehicles for which the decrease in curb weight is a critical indicator. The use of springs (suspensions) from polymer composites makes it possible to reduce the weight of the elastic element and increase durability while improving the smoothness of movement, reducing noise, and increasing traffic safety. When replacing the steel suspension with a polymer composite suspension, the mass of unsprung parts of the car decreases, and the economic performance of wheeled vehicles improves. The article discusses the problem of vertical viscoelastic oscillations of the suspension systems of the skeleton, engine, cabin, and seat. When considering the suspension's rheological properties, the Boltzmann-Volterra integral model is used. The Koltunov-Rzhanitsyn nucleus is used as a nucleus, which has weakly singular features of the Abel type. The system of integro-differential equations describing the studied process is solved by a method based on the use of quadrature formulas. The effect of the parameters of the hereditary-deformable properties of the suspension on the vibration shape is shown.

Los estilos APA, Harvard, Vancouver, ISO, etc.

20

Hernandez, P., P. Navalesi, F. Maltais, A. Gursahaney y S. B. Gottfried. "Comparison of static and dynamic measurements of intrinsic PEEP in anesthetized cats". Journal of Applied Physiology 76, n.º 6 (1 de junio de 1994): 2437–42. http://dx.doi.org/10.1152/jappl.1994.76.6.2437.

Texto completo

Resumen

Dynamic measurements of intrinsic positive end-expiratory pressure (PEEPi,dyn) considerably underestimate values obtained under static conditions (PEEPi,stat) in patients with severe airway obstruction. This may be related to regional differences in respiratory system mechanical properties and/or viscoelastic behavior. To evaluate this concept, PEEPi,stat and PEEPi,dyn were compared in six anesthetized paralyzed cats during dynamic hyperinflation produced by inverse ratio ventilation (IRV) and aerosolized methacholine (MCh). PEEPi,stat did not differ between IRV and MCh, averaging 2.70 +/- 0.33 (SE) and 2.70 +/- 0.25 cmH2O, respectively. PEEPi,dyn was significantly less with MCh (0.25 +/- 0.05 cmH2O) than IRV (2.05 +/- 0.28 cmH2O) (P < 0.0001), resulting in a lower PEEPi,dyn/PEEPi,stat ratio for MCh (0.10 +/- 0.02) than for IRV (0.76 +/- 0.03) (P < 0.0001). Compared with control values (33.5 +/- 3.7 cmH2O.l-1.s), maximum resistance (Rmax) was unchanged during IRV (29.1 +/- 2.1 cmH2O.l-1.s) but increased considerably with MCh (288.8 +/- 18.4 cmH2O.l-1.s) (P < 0.0001). Similar changes in minimum resistance (Rmin) and delta R (Rmax-Rmin) were noted. There was a strong inverse relationship between delta P, an index of time constant inequalities and viscoelastic pressure losses and PEEPi,dyn/PEEPi,stat ratio. No correlation was found between this ratio and Rmax, Rmin, delta R, or compliance. In conclusion, PEEPi,dyn considerably underestimates PEEPi,stat in acute nonhomogeneous airway obstruction with MCh in contrast to IRV, where the magnitude and distribution of mechanical properties remain unaltered. These findings support the concept that the difference between PEEPi,dyn and PEEPi,stat is related to regional time constant inequalities and/or increased viscoelastic pressure losses.

Los estilos APA, Harvard, Vancouver, ISO, etc.

21

Verlan, A. A., B. A. Khudayarov, F. Zh Turaev, N. N. Yuldashev y K. Ruzmetov. "Effect of non-stationary external forces on vibrations of composite pipelines conveying fluid". E3S Web of Conferences 365 (2023): 05014. http://dx.doi.org/10.1051/e3sconf/202336505014.

Texto completo

Resumen

The effect of non-stationary external forces on the vibration of pipelines made of composite materials is investigated in the paper. A mathematical model of composite pipeline vibration is developed, considering the viscosity properties of the structure and pipeline base material, axial forces, internal pressure, resistance forces, and external disturbances. A mathematical model of viscoelastic pipelines conveying fluid under vibrations is constructed based on the Boltzmann-Volterra integral model. The mathematical model to study a pipeline is based on the Euler-Bernoulli beam theory. Considering the physicomechanical properties of the pipeline material, the mathematical model of the problems under consideration presents a system of integro-differential equations (IDE) in partial derivatives with corresponding initial and boundary conditions. The nonlinear partial differential equations, obtained using the Bubnov-Galerkin method under considered boundary conditions, are reduced to solving the system of ordinary integro-differential equations. A computational algorithm is developed based on eliminating features of integro-differential equations with weakly singular kernels, followed by using quadrature formulas.

Los estilos APA, Harvard, Vancouver, ISO, etc.

22

Khudoynazarov, Khayrulla, A. Gadayev y Kh Akhatov. "Torsional vibrations of a rotating viskoelastic rod". E3S Web of Conferences 365 (2023): 02016. http://dx.doi.org/10.1051/e3sconf/202336502016.

Texto completo

Resumen

A homogeneous and isotropic round viscoelastic rod rotating around its axis of symmetry with a constant angular velocity is considered in a cylindrical coordinate system. It is believed that the behavior of the rod is described within the framework of the linear theory of viscoelasticity, where the relationship between stresses and deformations is given in the form of relations Boltzmann-Volterra. In this case, the condition of its reversibility is imposed on the kernel of the integral operator. The equations of motion of the rod concerning non-zero stress components are written, taking into account the centrifugal force caused by the rotation. It is assumed that torsional vibrations are caused by given stress on its surface. A general equation of torsional vibrations of such a rod is obtained, which is an integral-differential equation of infinitely high order for the main part of the torsional displacement. Limiting the general equations to the zero and first approximations, the equations of the second and fourth orders are obtained, which, in the case of the absence of rotation, exactly coincide with the known equations of other authors. The resulting refined equation of the fourth order in its structure considers the angular velocity of rotation, the deformation of the transverse shear, and the inertia of rotation. Based on the derived oscillation equations, a particular problem is solved to study the influence of rotation and viscoelastic properties of the material on the stress-strain state of the rod, according to the results of which graphs of the dependencies of elastic and viscoelastic changes on time at points of three different sections of the rod are constructed. A comparative analysis of the results obtained with the results of other authors is performed.

Los estilos APA, Harvard, Vancouver, ISO, etc.

23

Sly, P. D., K. A. Brown, J. H. Bates, P. T. Macklem, J. Milic-Emili y J. G. Martin. "Effect of lung volume on interrupter resistance in cats challenged with methacholine". Journal of Applied Physiology 64, n.º 1 (1 de enero de 1988): 360–66. http://dx.doi.org/10.1152/jappl.1988.64.1.360.

Texto completo

Resumen

To examine the effects of changes in lung volume on the magnitude of maximal bronchoconstriction, seven anesthetized, paralyzed, tracheostomized cats were challenged with aerosolized methacholine (MCh) and respiratory system resistance (Rss) was measured at different lung volumes using the interrupter technique. Analysis of the pressure changes following end-inspiratory interruptions allowed us to partition Rss into two quantities with the units of resistance, one (Rinit) corresponding to the resistance of the airways and the other (Rdif) reflecting the viscoelastic properties of the tissues of the respiratory system as well as gas redistribution following interruption of flow. Rinit and Rdif were used to construct concentration-response curves to MCh. Lung volume was increased by the application of 5, 10, and 15 cmH2O of positive end-expiratory pressure. The curve for Rinit reached a plateau in all cats, demonstrating a limit to the degree of MCh-induced bronchoconstriction. The mean value of Rinit (cmH2O.ml-1.s) for the group under control conditions was 0.011 and rose to 0.058 after maximal bronchoconstriction; the volume at which the flow was interrupted was 11.5 +/- 0.5 (SE) ml/kg above functional residual capacity (FRC). It then fell progressively to 0.029 at 21.2 +/- 0.8 ml/kg above FRC, 0.007 at 35.9 +/- 1.3 ml/kg above FRC, and 0.005 at 52.0 +/- 1.8 ml/kg above FRC. Cutting either the sympathetic or parasympathetic branches of the vagi had no significant effect on the lung volume-induced changes in MCh-induced bronchoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Los estilos APA, Harvard, Vancouver, ISO, etc.

24

Shardonofsky, F. R., M. Skaburskis, J. Sato, W. A. Zin y J. Milic-Emili. "Effects of volume history and vagotomy on pulmonary and chest wall mechanics in cats". Journal of Applied Physiology 71, n.º 2 (1 de agosto de 1991): 498–508. http://dx.doi.org/10.1152/jappl.1991.71.2.498.

Texto completo

Resumen

Using the technique of rapid airway occlusion during constant-flow inflation, we studied the effects of inflation volume, different baseline tidal volumes (10, 20, and 30 ml/kg), and vagotomy on the resistive and elastic properties of the lungs and chest wall in six anesthetized tracheotomized paralyzed mechanically ventilated cats. Before vagotomy, airway resistance decreased significantly with increasing inflation volume at all baseline tidal volumes. At any given inflation volume, airway resistance decreased with increasing baseline tidal volume. After vagotomy, airway resistance decreased markedly and was no longer affected by baseline tidal volume. Prevagotomy, pulmonary tissue resistance increased progressively with increasing lung volume and was not affected by baseline tidal volume. Pulmonary tissue resistance decreased postvagotomy. Chest wall tissue resistance increased during lung inflation but was not affected by either baseline tidal volume or vagotomy. The static volume-pressure relationships of the lungs and chest wall were not affected by either baseline tidal volume or vagotomy. The data were interpreted in terms of a linear viscoelastic model of the respiratory system (J. Appl. Physiol. 67: 2276–2285, 1989).

Los estilos APA, Harvard, Vancouver, ISO, etc.

25

Similowski, T., P. Levy, C. Corbeil, M. Albala, R. Pariente, J. P. Derenne, J. H. Bates, B. Jonson y J. Milic-Emili. "Viscoelastic behavior of lung and chest wall in dogs determined by flow interruption". Journal of Applied Physiology 67, n.º 6 (1 de diciembre de 1989): 2219–29. http://dx.doi.org/10.1152/jappl.1989.67.6.2219.

Texto completo

Resumen

Pulmonary and chest wall mechanics were studied in six anesthetized paralyzed dogs, by use of the technique of rapid airway occlusion during constant flow inflation. Analysis of the pressure changes after flow interruption allowed us to partition the overall resistance of the lung (Rl) and chest wall (Rw) and total respiratory system (Rrs) into two components, one (Rinit) reflecting in the lung airway resistance (Raw), the other (delta R) reflecting primarily the viscoelastic properties of the pulmonary and chest wall tissues. The effects of varying inspiratory flow and inflation volume were interpreted in terms of frequency dependence of resistance, by using a spring-and-dashpot model previously proposed and substantiated by Bates et al. (Proc. 9th Annu. Conf. IEEE Med. Biol. Soc., 1987, vol. 3, p. 1802-1803). We observed that 1) Raw and Rw,init were nearly equal and small relative to Rl and Rw (both were unaffected by flow); 2) Rrs,init decreased slightly with increasing volume; 3) both delta Rl and delta Rw decreased with increasing flow and increased with increasing lung volume. These changes were manifestations of frequency dependence of delta R, as it is predicted by the model; 4) Rrs, Rl, and Rw followed the same trends as delta R. These results corroborate data previously reported in the literature with the use of different techniques to measure airways and pulmonary tissue resistances and confirm that the use of Rl to assess bronchial reactivity is problematic. The interrupter techniques provides a convenient way to obtain Raw values, as well as analogs of lung and chest wall tissue resistances in intact dogs.

Los estilos APA, Harvard, Vancouver, ISO, etc.

26

Presnyakova, M. V., E. A. Galova, L. N. Sosnina, A. N. Popovicheva, N. A. Lyubavina, O. V. Kostina, V. L. Kuznetsova y N. N. Karyakin. "Disturbances of the hemostasis system and expression of inflammatory reaction in patients with new coronaviral pneumonia". Russian Clinical Laboratory Diagnostics 65, n.º 12 (29 de diciembre de 2020): 744–49. http://dx.doi.org/10.18821/0869-2084-2020-65-12-744-749.

Texto completo

Resumen

Disorders of the hemostatic system and inflammation play a key role in the pathogenesis of new coronavirus pneumonia (NCP), determining its course and outcome. To study the dynamics of the state of the hemostasis system and the severity of the acute phase response in patients with new coronavirus pneumonia. We determined APTT, prothrombin time (PT), fibrinogen (F), D-dimers (D-d), antitrombin III (AT III), C-reactive protein (CRP), platelet count in 22 patients. In 49 patients, the viscoelastic properties of a blood clot were studied by thromboelastography (TEG) with koalin. The age of the patients ranged from 40 to 77 years. According to CT, the severity of 100% cases corresponded to CT2-CT3. Acute respiratory failure (ARF) was diagnosed in 16 patients. A control group included 25 apparently healthy subjects. During hospitalization, patients with NCP were characterized by: an increase in the concentration of D-d, CRP, Fg, lengthening of APTT and PT, ATIII activity and platelet count not differing from the normal range. 10 days after hospitalization and against the background of ongoing therapy, patients with NCP showed positive dynamics in the hemostasiological profile and the severity of the inflammatory response. Thromboelastography indices in patients with LCP did not differ from control values both at hospitalization and on day 10.Thus, in patients with novel coronavirus pneumonia, an increased prothrombotic activity and a pronounced inflammatory response are recorded. Against the background of treatment, there is a positive dynamics in both the coagulation status and the inflammatory response. Additional studies are needed to determine the diagnostic capabilities of thromboelastography in patients with NCP.

Los estilos APA, Harvard, Vancouver, ISO, etc.

27

Rubin, B. K., O. Ramirez y M. King. "Mucus-depleted frog palate as a model for the study of mucociliary clearance". Journal of Applied Physiology 69, n.º 2 (1 de agosto de 1990): 424–29. http://dx.doi.org/10.1152/jappl.1990.69.2.424.

Texto completo

Resumen

To better understand the frog palate model of mucociliary transport, we measured the transport rate of mucus (MTR) from the leopard frog, Rana pipiens, and from the bullfrog, R. catesbeiana, recorded the stability of the MTR over a period of hours and days and over the course of 1 yr, and measured the viscoelasticity, percent solid composition, and spinnability (filance) of mucus from both species. Bullfrog mucus was less rigid than leopard frog mucus (log G* at 1 rad/s 2.09 vs. 2.61; P less than 0.01) and had a higher viscosity-to-elasticity ratio (tan delta at 1 rad/s 0.36 vs. 0.26; P less than 0.05). It also had a lower solids content (8.71 vs. 13.72%; P = 0.02), and there was a trend to lower spinnability for bullfrog mucus (filance 26.7 vs. 33.5 mm). These data suggest that bullfrog mucus has viscoelastic properties similar to normal mammalian respiratory mucus and leopard frog mucus has viscoelasticity similar to sputum samples. MTR was significantly slower in the winter than in the summer months (17 vs. 30 mm/min; P less than 0.0001). Although the leopard frog palate could be used for at least 7 consecutive days without exhaustion, bullfrog palates could be used for only 5 days. Palates of either species could generally be tested for 6 h/day without a significant decrease in MTR. These data clarify some of the sources of variability in the use of this system and suggest methods of standardization.

Los estilos APA, Harvard, Vancouver, ISO, etc.

28

Rancourt, Raymond C., Shusheng Tai, Malcolm King, Sonya L. Heltshe, Churee Penvari, Frank J. Accurso y Carl W. White. "Thioredoxin liquefies and decreases the viscoelasticity of cystic fibrosis sputum". American Journal of Physiology-Lung Cellular and Molecular Physiology 286, n.º 5 (mayo de 2004): L931—L938. http://dx.doi.org/10.1152/ajplung.00352.2003.

Texto completo

Resumen

The persistent and viscous nature of airway secretions in cystic fibrosis (CF) disease leads to airway obstruction, opportunistic infection, and deterioration of lung function. Thioredoxin (Trx) is a protein disulfide reductase that catalyzes numerous thiol-dependent cellular reductive processes. To determine whether Trx can alter the rheological properties of mucus, sputum obtained from CF patients was treated with TRX and its reducing system (0.1 μM thioredoxin reductase + 2 mM NADPH), and liquid phase-gel phase ratio (percent liquid phase) was assessed by compaction assay. Exposure to low Trx concentrations (1 μM) caused significant increases in the percentage of liquid phase of sputum. Maximal increases in percent liquid phase occurred with 30 μM Trx. Additional measurements revealed that sputum liquefaction by the Trx reducing system is dependent on NADPH concentration. The relative potency of the Trx reducing system also was compared with other disulfide-reducing agents. In contrast with Trx, glutathione and N-acetylcysteine were ineffective in liquefying sputum when used at concentrations <1 mM. Sputum viscoelasticity, measured by magnetic microrheometry, also was diminished significantly following 20-min treatment with 3, 10, or 30 μM Trx. Similarly, this reduction in viscoelasticty also was dependent on NADPH concentration. Further investigation has indicated that Trx treatment increases the solubility of high-molecular-weight glycoproteins and causes redistribution of extracellular DNA into the liquid phase of sputum. Recognizing that mucins are the major gel-forming glycoproteins in mucus, we suggest that Trx alters sputum rheology by enzymatic reduction of glycoprotein polymers present in sputum.

Los estilos APA, Harvard, Vancouver, ISO, etc.

29

Antonaglia, V., A. Peratoner, L. De Simoni, A. Gullo, J. Milic-Emili y W. A. Zin. "Bedside assessment of respiratory viscoelastic properties in ventilated patients". European Respiratory Journal 16, n.º 2 (agosto de 2000): 302. http://dx.doi.org/10.1034/j.1399-3003.2000.16b19.x.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

30

Peslin, R., F. Marchal y C. Choné. "Viscoelastic properties of rabbit lung during growth". Respiration Physiology 86, n.º 2 (noviembre de 1991): 189–98. http://dx.doi.org/10.1016/0034-5687(91)90080-3.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

31

Phonthammachai, Nopphawan, Morakot Rumruangwong, Sirirat Jitkanka, Erdogan Gulari, Alexander M. Jamieson y Sujitra Wongkasemjit. "Viscoelastic Properties of Ceria Gel". Materials Science Forum 480-481 (marzo de 2005): 355–60. http://dx.doi.org/10.4028/www.scientific.net/msf.480-481.355.

Texto completo

Resumen

The viscoelastic behavior of different ceria gelling systems prepared through sol-gel transition were investigated by the rheological measurement. The gelation time was observed by the frequency independence of tand, and increased with increasing acid:alkoxide molar ratio. At the gel point, both storage and loss moduli (G’µ wn, G” µ wn)exhibited a power law dependence of applied frequency with n’ = n” = n. The viscoelastic exponents and gel strength parameter were dependent on the composition of system. The increase in HCl:alkoxide molar ratio increased the n value while decreased the S parameter.

Los estilos APA, Harvard, Vancouver, ISO, etc.

32

Pereborova, N. V., A. G. Makarov, S. V. Kiselev y V. I. Wagner. "SYSTEM ANALYSIS OF VISCOELASTIC PROPERTIES OF POLYMER TEXTILE MATERIALS". Вестник Санкт-Петербургского государственного университета технологии и дизайна. Серия 4: Промышленные технологии, n.º 3 (2020): 57–71. http://dx.doi.org/10.46418/2619-0729_2020_3_5.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

33

YAO, Shigeru, Tatsuya SHOJI, Eiichi KAMEI y Masaoki TAKAHASHI. "A Simulation System for Viscoelastic Properties of Polydisperse Polymer Melts". Nihon Reoroji Gakkaishi(Journal of the Society of Rheology, Japan) 21, n.º 3 (1993): 149–55. http://dx.doi.org/10.1678/rheology1973.21.3_149.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

34

Yao, Shigeru. "A Simulation System for Viscoelastic Properties of Polydisperse Polymer Melts." Kobunshi 43, n.º 11 (1994): 800–803. http://dx.doi.org/10.1295/kobunshi.43.800.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

35

Yao, Shigeru, Tatsuya Shoji, Eiichi Kamei y Masaoki Takahashi. "A simulation system for viscoelastic properties of polydisperse polymer melts". Journal of Rheology 38, n.º 3 (mayo de 1994): 757–58. http://dx.doi.org/10.1122/1.550574.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

36

Ci-qun, Liu. "Nonsteady flow of groundwater in aquifer system with viscoelastic properties". Applied Mathematics and Mechanics 7, n.º 11 (noviembre de 1986): 1027–33. http://dx.doi.org/10.1007/bf01897205.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

37

Ramos, E. M., D. Ramos, G. L. Moreira, M. Macchione, E. T. Guimaraes, F. M. M. Rodrigues, A. A. L. de Souza, P. H. Saldiva y J. R. Jardim. "Viscoelastic Properties of Bronchial Mucus After Respiratory Physiotherapy in Subjects With Bronchiectasis". Respiratory Care 60, n.º 5 (3 de febrero de 2015): 724–30. http://dx.doi.org/10.4187/respcare.02429.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

38

Radiom, Milad, Romain Hénault, Salma Mani, Aline Grein Iankovski, Xavier Norel y Jean-François Berret. "Magnetic wire active microrheology of human respiratory mucus". Soft Matter 17, n.º 32 (2021): 7585–95. http://dx.doi.org/10.1039/d1sm00512j.

Texto completo

Resumen

Micrometer-sized magnetic wires are used to study the mechanical properties of human mucus collected after surgery. Our work shows that mucus has the property of a high viscosity gel characterized by large spatial viscoelastic heterogeneities.

Los estilos APA, Harvard, Vancouver, ISO, etc.

39

Lorino, A. M. y A. Harf. "Techniques for measuring respiratory mechanics: an analytic approach with a viscoelastic model". Journal of Applied Physiology 74, n.º 5 (1 de mayo de 1993): 2373–79. http://dx.doi.org/10.1152/jappl.1993.74.5.2373.

Texto completo

Resumen

A homogeneous model with stress relaxation that is described by a pure viscoelastic component was recently proposed to describe the mechanical behavior of the respiratory system during mechanical ventilation (Bates et al. J. Appl. Physiol. 67: 2276–2285, 1989). With the use of this model, analytic expressions of the pressure in response to typical volume inputs are developed, and the recently published studies relating to the influence of the ventilatory pattern on respiratory mechanics are reviewed and analyzed. The analytic expression of pressure responses to rapid airway occlusion following constant-flow inflation and to sinusoidal volume oscillations allows prediction of most of the reported results. The theoretical analysis suggests that in normal subjects the observed flow and volume dependencies of respiratory mechanics are, in fact, illustrations of the dependence of the viscoelastic resistance on inspiratory time and respiratory frequency. Thus the homogeneous viscoelastic model appears suitable to describe respiratory system mechanical behavior under mechanical ventilation.

Los estilos APA, Harvard, Vancouver, ISO, etc.

40

Perez Fontan, J. J. "Effect of lung lavage on the stress relaxation of the respiratory system". Journal of Applied Physiology 75, n.º 4 (1 de octubre de 1993): 1536–44. http://dx.doi.org/10.1152/jappl.1993.75.4.1536.

Texto completo

Resumen

To test the hypothesis that lowering the concentrations of surfactant molecules at the gas-liquid interface increases viscoelastic dissipation in the lungs, the amplitude and time course of stress relaxation were quantified before and after lavage of the lungs with warm saline in five newborn and five 8-wk-old anesthetized piglets. Stress relaxation was separated from other dissipative pressure losses by fitting the pressure decays that follow airway occlusions performed during a period of constant inspiratory flow to a double-exponential regression. The amplitude of stress relaxation (defined by the term of the regression with the longest time constant) related linearly to the changes in respiratory system volume and elastic recoil preceding the occlusions both before and after the lavage. Lung lavage increased the slope of both relationships without altering the time course of the relaxations. In addition to being consistent with the proposed hypothesis, these results suggest that viscoelastic pressure losses remain linked to the elastic stresses generated during lung inflation, as proposed by Fredberg and Stamenovic's structural dumping theory (J. Appl. Physiol. 67: 2408#x2013;2419, 1989).

Los estilos APA, Harvard, Vancouver, ISO, etc.

41

Cederbaum, G. y M. Mond. "Stability Properties of a Viscoelastic Column Under a Periodic Force". Journal of Applied Mechanics 59, n.º 1 (1 de marzo de 1992): 16–19. http://dx.doi.org/10.1115/1.2899424.

Texto completo

Resumen

The dynamic stability of a viscoelastic column subjected to a periodic longitudinal load is investigated. The viscoelastic behavior is given in terms of the Boltzmann superposition principle which yields an integro-differential equation of motion. The stability boundaries of this equation are determined analytically by using the multiplescales method. It is shown that due to the viscoelasticity the stability regions are expanded, relative to the elastic ones, and the time for which a stable system becomes unstable is given. In addition, the stability properties of the viscoelastic column are time dependent and an initially stable system can turn unstable after a finite time, unlike columns that are described by the elastic model.

Los estilos APA, Harvard, Vancouver, ISO, etc.

42

Knapik-Kowalczuk, Justyna, Krzysztof Chmiel, Karolina Jurkiewicz, Natália Correia, Wiesław Sawicki y Marian Paluch. "Physical Stability and Viscoelastic Properties of Co-Amorphous Ezetimibe/Simvastatin System". Pharmaceuticals 12, n.º 1 (19 de marzo de 2019): 40. http://dx.doi.org/10.3390/ph12010040.

Texto completo

Resumen

The purpose of this paper is to examine the physical stability as well as viscoelastic properties of the binary amorphous ezetimibe–simvastatin system. According to our knowledge, this is the first time that such an amorphous composition is prepared and investigated. The tendency toward re-crystallization of the amorphous ezetimibe–simvastatin system, at both standard storage and elevated temperature conditions, have been studied by means of X-ray diffraction (XRD). Our investigations have revealed that simvastatin remarkably improves the physical stability of ezetimibe, despite the fact that it works as a plasticizer. Pure amorphous ezetimibe, when stored at room temperature, begins to re-crystallize after 14 days after amorphization. On the other hand, the ezetimibe-simvastatin binary mixture (at the same storage conditions) is physically stable for at least 1 year. However, the devitrification of the binary amorphous composition was observed at elevated temperature conditions (T = 373 K). Therefore, we used a third compound to hinder the re-crystallization. Finally, both the physical stability as well as viscoelastic properties of the ternary systems containing different concentrations of the latter component have been thoroughly investigated.

Los estilos APA, Harvard, Vancouver, ISO, etc.

43

Amari, Takeshi, Kenji Uesugi y Hiroaki Suzuki. "Viscoelastic properties of carbon black suspension as a flocculated percolation system". Progress in Organic Coatings 31, n.º 1-2 (mayo de 1997): 171–78. http://dx.doi.org/10.1016/s0300-9440(97)00033-7.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

44

Nakamura, Yoshinobu, Manabu Adachi, Yuta Tachibana, Yu Sakai, Shinji Nakano, Syuji Fujii, Mariko Sasaki y Yoshiaki Urahama. "Tack and viscoelastic properties of an acrylic block copolymer/tackifier system". International Journal of Adhesion and Adhesives 29, n.º 8 (diciembre de 2009): 806–11. http://dx.doi.org/10.1016/j.ijadhadh.2009.06.004.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

45

Yatsuyanagi, Fumito, Hiroyuki Kaidou y Masayoshi Ito. "Relationship between Viscoelastic Properties and Characteristics of Filler-Gel in Filled Rubber System". Rubber Chemistry and Technology 72, n.º 4 (1 de septiembre de 1999): 657–72. http://dx.doi.org/10.5254/1.3538824.

Texto completo

Resumen

Abstract The wide-line NMR and viscoelastic measurements were carried out for the filled rubber systems. NMR results revealed that the filler-gel in the filled rubber composites had a multi-component system depending on the mobility of rubber molecules. The fraction and the spin-spin relaxation time of each component were well correlated with the viscoelastic properties such as dynamic storage modulus (E′) and loss-tangent (tan δ) of the filled rubber systems. Such findings turned out to be useful in designing new tread materials with well-balanced wet traction and rolling resistance in tires.

Los estilos APA, Harvard, Vancouver, ISO, etc.

46

Sittikijyothin, Wancheng. "Changes of Dynamic Viscoelastic Properties of Tamarind Gum Aqueous Solutions". Advanced Materials Research 239-242 (mayo de 2011): 477–80. http://dx.doi.org/10.4028/www.scientific.net/amr.239-242.477.

Texto completo

Resumen

Tamarind gum was obtained from the seeds of Tamarindus indica. It was rich in polysaccharide (79.96%) and protein (13.46%) contents. In this work, the dynamic viscoelastic properties of tamarind gum aqueous solutions were investigated with a Haake Rheometer RS75 as a function of gum concentration and temperature. Four types of sample solution systems: a dilute solution, a concentrated solution, a weak gelled system, and a gelled like system were observed. The effect of concentration showed that the typical shape of the mechanical spectra for the dilute solution occurred for 2.30 wt% and the gelled like behaviour arose for the higher concentration (≥7.05 wt%) as measured at 25°C. While the effect of temperature on the dynamic viscoelastic properties of tamarind gum solution (6.91wt%) showed that the gum solution behaved the weak gelled system (25°C) and subsequently gelled like system (≥30°C).

Los estilos APA, Harvard, Vancouver, ISO, etc.

47

Esmaeeli, Roja, Haniph Aliniagerdroudbari, Seyed Reza Hashemi, Chiran JBR y Siamak Farhad. "Designing a New Dynamic Mechanical Analysis (DMA) System for Testing Viscoelastic Materials at High Frequencies". Modelling and Simulation in Engineering 2019 (25 de marzo de 2019): 1–9. http://dx.doi.org/10.1155/2019/7026267.

Texto completo

Resumen

The aim of this study is to design a new dynamic mechanical analysis (DMA) measurement system that can operate for shear tests at frequencies as high as 10 kHz with strain amplitudes sufficient for viscoelastic materials operating in high-frequency deformation applications, such as tire rubbers. The available DMA systems in market cannot effectively operate for accurate and direct measurement of viscoelastic material properties for applications dealing with high-frequency deformation of materials. Due to this, the available DMA systems are used for indirect measurements at low frequencies and low temperatures, followed by using time-temperature superposition principle to predict the properties at high frequencies. The goal of this study is to make the range of the test broad enough to eliminate the use of the time-temperature superposition principle in the determination of properties of viscoelastic materials. Direct measurement of viscoelastic material properties and increasing the accuracy of results are the main motivations to design a new DMA system. For this purpose, the state-of-the-art technologies to achieve high frequencies and strain amplitudes as well as instrumentation and control of the system are studied. The design process is presented in this paper.

Los estilos APA, Harvard, Vancouver, ISO, etc.

48

Rubin, Bruce K., Barry Finegan, Oscar Ramirez y Malcolm King. "General Anesthesia Does Not Alter the Viscoelastic or Transport Properties of Human Respiratory Mucus". Chest 98, n.º 1 (julio de 1990): 101–4. http://dx.doi.org/10.1378/chest.98.1.101.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

49

Lin, J. Y. y R. A. Westmann. "Viscoelastic Winding Mechanics". Journal of Applied Mechanics 56, n.º 4 (1 de diciembre de 1989): 821–27. http://dx.doi.org/10.1115/1.3176177.

Texto completo

Resumen

The viscoelastic analysis of tape systems composed of rate-dependent materials is presented. Histories for winding, winding-pause, and winding-pause-unwinding are considered. The winding problem is reduced to determining the appropriate Green’s function by numerical solution of a Volterra integral equation of the second kind. This Green’s function and integral superposition permits the evaluation of the stress and displacement fields in the tape system for any winding history. Viscoelastic unwinding is treated by the superposition of two-states — one determined from the initial condition of the tape when unwinding begins and the second state given in terms of an arbitrary external pressure evaluated by solving an integral equation. Numerical results are presented for several histories and representative material properties.

Los estilos APA, Harvard, Vancouver, ISO, etc.

50

Gaihede, Michael y Birger Koefoed-Nielsen. "Mechanics of the Middle Ear System: Age-Related Changes in Viscoelastic Properties". Audiology and Neurotology 5, n.º 2 (2000): 53–58. http://dx.doi.org/10.1159/000013867.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

Artículos de revistas sobre el tema "Viscoelastic respiratory system properties"

Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros