Home About us Contact
|
Home About us Contact | ||
|
|
||
Pressure Waves (pressure + wave)
Selected AbstractsMotor patterns and propulsion in the rat intestine in vivo recorded by spatio-temporal mapsNEUROGASTROENTEROLOGY & MOTILITY, Issue 5 2005D. M. Ferens Abstract, We have used spatio-temporal maps derived from video images to investigate propagated contractions of the rat small intestine in vivo. The abdomen, including an exteriorized segment of jejunum, was housed in a humid chamber with a viewing window. Video records were converted to spatio-temporal maps of jejunal diameter changes. Intraluminal pressure and fluid outflow were measured. Contractions occupied 3.8 ± 0.2 cm of intestine and propagated anally at 3.1 ± 0.2 mm s,1 when baseline pressure was 4 mmHg. Contractions at any one point lasted 8.7 ± 0.6 s. Contractions often occurred in clusters; within cluster frequencies were 2.28 ± 0.04 min,1. Pressure waves, with amplitudes greater than about 9 mmHg, expelled fluid when the baseline pressure was 4 mmHg. In the presence ofl -NAME, circular muscle contractions occurred at a high frequency, but they were not propagated. We conclude that video recording methods give good spatio-temporal resolution of intestinal movement when applied in vivo. They reveal neurally-mediated propulsive contractions, similar to those previously recorded from intestinal segments in vitro. The propagated contractions had speeds of propagation that were slower and frequencies of occurrence that were less than speeds and frequencies of slow waves in the rat small intestine. [source] Numerical aspects of improvement of the unsteady pipe flow equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2007Romuald Szymkiewicz Abstract The paper presents an analysis of some recently proposed improvements of the water hammer equations, which concern the friction term in the momentum equation. A comparison of the experimental data and numerical results shows that the required damping and smoothing of the pressure wave cannot be obtained by modification of the friction factor only. In order to evaluate the significance of the introduced improvements into the momentum equation, the accuracy of the numerical solution has been analysed using the modified equation approach. The analysis shows why the physical dissipation process observed in the water hammer phenomenon cannot be reproduced with the commonly used source term in Darcy,Weisbach form, representing friction force in the momentum equation. Therefore, regardless of the proposed form of the friction factor for unsteady flow, the model of water hammer improved in such a way keeps its hyperbolic character. Consequently, it cannot ensure the expected effects of damping and smoothing of the calculation head oscillations. Copyright © 2007 John Wiley & Sons, Ltd. [source] Human duodenal phase III migrating motor complex activity is predominantly antegrade, as revealed by high-resolution manometry and colour pressure plotsNEUROGASTROENTEROLOGY & MOTILITY, Issue 4 2002J. M. Andrews Abstract,Late phase III migrating motor complex activity has been said to be primarily retroperistaltic but has not been assessed with high resolution manometry or three-dimensional colour pressure plots (pressure/time/distance). Duodenal phase III was examined in healthy young volunteers (seven male, two female) with a 20-lumen assembly. With the most proximal sidehole in the distal antrum, after a 4.5-cm interval 18 sideholes at 1.5-cm intervals spanned the duodenum with a final sidehole 3 cm beyond. Fasting pressures were recorded until phase III occurred. Comparisons were made between proximal (P) and distal (D) duodenum during early (E) (first 0.5,1 min) and late (L) (last 0.5,1 min) phase III. With colour pressure analysis, 121 of 180 pressure wave (PW) sequences were purely antegrade, two purely retrograde and 57 bidirectional. Ten of fifty-seven bidirectional PW sequences were complex, branching to become two separate sequences. Bidirectional sequences occurred more frequently in late than early phase III (L 43 vs. E 14 of 57), but their occurrence did not differ between proximal and distal duodenum (P31 vs. D 24 of 57). Antegrade propagation velocity was faster in late compared with early phase III (L 28.50 vs. E 17.05 mm s,1; P = 0.006), but did not differ between proximal and distal duodenum. Colour pressure analysis also indicated an intermittent segmental pattern to phase III, with each subject exhibiting a change in velocity or direction, or a relative failure of peristalsis somewhere along the duodenum during part of phase III. Duodenal phase III is not homogenous and, in contrast with previous studies, does not primarily constitute a retroperistaltic pump. Colour pressure analysis is useful in interpreting intraluminal pressure profiles and may improve the sensitivity and specificity of clinical studies. [source] A study of departures from the inverse-barometer response of sea level to air-pressure forcing at a period of 5 daysTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 597 2004E. L. Mathers Abstract The response of the sea level to atmospheric forcing is investigated through the cross-spectral analysis of tide-gauge data from around 100 island and deep-ocean stations and atmospheric pressure records. The focus is at a period of 5 days, coinciding with an atmospheric pressure oscillation (Madden,Julian wave) of the same frequency. Outside the Tropics the energy in synoptic weather systems masks the small amplitude of the pressure wave, resulting in a response indistinguishable from that of an inverse barometer (IB). Within the Tropics, variability of air pressure is smaller in comparison with the amplitude of the pressure wave and departures from the IB model are found. Analysis of several sub-surface pressure records in the tropical Atlantic also yields departures at this time-scale, and indicates the barotropic nature of the response. Findings from a near-global barotropic numerical model forced with realistic air pressure and wind-stress fields show reasonable agreement with results at tide-gauge locations, and provide a more complete view of the sea-level response. These results indicate the possibility of providing an improved simulation of sea-level response to atmospheric-pressure forcing at this time-scale than is currently provided by the IB model, for example in the field of satellite altimetry. Copyright © 2004 Royal Meteorological Society [source] Water pipeline failure due to water hammer effectsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2006C. SCHMITT ABSTRACT A numerical model has been established in order to simulate the propagation of pressure waves in water networks. The present model formulation is based on a system of partial hyperbolic differential equations. This system has been solved via the characteristics method. The current model provides the necessary data and the necessary damping of water hammer waves, taking into account the structure of the pipe network and the pressure loss. The numerical algorithm estimates the maximum pressure values resulting from the water hammer when closing valves in the network and consequently, the maximum stresses in the pipes have been calculated. In the case of simultaneous closing of several valves, the over pressure can exceed the admissible pressure. In this case, the severity of a defect such as a corrosion crater (pit) has been estimated by computing a safety factor for the stress distribution at the defect tip. This allows the applied notch stress intensity factor to be obtained. To investigate the defect geometry effects, semi-spherical and semi-elliptical defects are deemed to exist in up to one-half of the thickness of the pipe wall. The outcomes have been introduced into the structural integrity assessment procedure (SINTAP) failure diagram assessment (FAD) in order to obtain the safety factor value. Conventionally, it is considered that a failure hazard exists if this safety factor is less than two. [source] A New Scenario in Probe Local Oxidation: Transient Pressure-Wave-Assisted Ionic Spreading and Oxide Pattern Formation,ADVANCED MATERIALS, Issue 18 2007N. Xie A new mechanism based on transient shock-wave-assisted lateral ionic spreading and oxide growth is reported for atomic force microscopy probe local oxidation (see figure). Transitory high pressure waves generated in the nanoscopic tip,sample junction significantly extend the distribution of hydroxyl oxidants to facilitate micrometer-scale disk-oxide growth on a silicon substrate. The results show that shock propagation may be a general phenomenon in AFM nanolithography. [source] Divergence of mucosal and motor effects of insulin-like growth factor (IGF)-I and LR3IGF-I on rat isolated ileum following abdominal irradiationJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 10 2000R Fraser Abstract Background and Aims: In addition to its beneficial effects on small intestinal mucosal development and repair, insulin-like growth factor (IGF)-I has also been reported to improve neural function in toxic neuropathies. It has recently been recognized that enteric neural abnormalities contribute to the small intestinal dysmotility observed during and after abdominal radiotherapy for gynecological and pelvic malignancy. The aim of the present study was to evaluate the effects of IGF-I (5 mg/kg per day) and the more potent analog LR3IGF-I (5 mg/kg per day) on neurally mediated ileal dysmotility following irradiation. Methods: Intestinal motor activity was recorded from 6,8 cm segments of explanted rat ileum using a miniaturized manometric technique during arterial perfusion with oxygenated fluorocarbon solution. Studies were performed 4 days after treatment with 10 Gy abdominal irradiation. At the time of irradiation, all rats underwent implantation of an osmotic mini-pump that contained 100 mmol/L acetic acid vehicle (n = 8), IGF-I (n = 8) or LR3IGF-I (n = 7). For each experiment, the total number of pressure waves, high-amplitude long-duration (defined as > 20 mmHg, > 6 s; HALD) pressure waves and long bursts (> 20) of pressure waves were determined. Ileal segments from 12 non-irradiated rats were used as controls for manometric studies. In radiotherapy treated animals, the degree of mucosal damage was determined using a standardized histologic scoring system. Results: The HALD pressure waves were infrequent in non-irradiated rats but occurred in all irradiated animals. Insulin-like growth factor-I and LR3IGF-I had no effect on the frequency, amplitude or migration characteristics of HALD pressure waves compared with vehicle. Histologic damage was reduced in animals that received IGF-I and LR3IGF-I compared with vehicle-treated animals. Conclusions: In radiation enteritis, IGF-I has no effect on neurally mediated small intestinal dysmotility while improving mucosal histology. The disparity between these results suggests that parallel but separate pathologic processes underlie mucosal and motor abnormalities in radiation enteritis. [source] Fully automated analysis of colonic manometry recordingsNEUROGASTROENTEROLOGY & MOTILITY, Issue 6 2002A. M. P. De Schryver AbstractThe purpose of this study was to develop a computer program for fully automated analysis of all presently known motor patterns in human colonic motility recordings. Colonic pressure recordings obtained from 24 healthy volunteers were used. Algorithms were developed for the detection and numerical analysis of five types of pressure waves: antegrade, retrograde, simultaneous, high-amplitude and isolated pressure waves. Furthermore, periodical motor activity was quantified. Validation was performed by comparison with visual analysis by two experienced observers. Patterns recorded during day- and night-time were compared using multiple-factor analysis of variance with Bonferroni correction. Automated analysis correlated well with visual peak detection (r = 0.98, P <0.01) and detection of antegrade pressure waves (r = 0.98, P <0.01). Most motor patterns showed a diurnal variation. During the night, prevalences of antegrade (938 vs 455; P <0.05), retrograde (112 vs 81; P <0.05), high-amplitude (12.9 vs 1.3; P <0.05), isolated pressure waves (1114 vs 765; P <0.05), and periodic motor activity were decreased (7.33 vs 4.47%; P <0.05). However, when expressed as percentage of absolute numbers of pressure waves, prevalences remained constant. In conclusion, fully automated analysis of all hitherto described colonic motility patterns is feasible. During the night, overall wave prevalences markedly decreased, but the distribution over the various motor patterns was preserved. [source] Low antroduodenal pressure gradients are responsible for gastric emptying of a low-caloric liquid meal in humansNEUROGASTROENTEROLOGY & MOTILITY, Issue 1 2002T. HAUSKEN The motor mechanisms responsible for transpyloric flow of gastric contents are still poorly understood. The aim of our study was to investigate the relationship between luminal pressures and gastric wall motion and between gastroduodenal pressure gradients and pressure waves, and ante- and retro-grade transpyloric flow. In eight healthy volunteers, intraluminal pressures were recorded from the antrum and proximal duodenum. Transpyloric flow was monitored simultaneously using duplex ultrasonography, before, during and after ingestion of 300 mL meat soup. Transpyloric emptying occurred as sequences of alternating periods of emptying,reflux,emptying. Approximately one-third of the sequences were not associated with peristalsis. The antroduodenal pressure gradients were significantly lower during nonperistaltic-related emptying than during peristaltic-related emptying (0.15 (0,0.3) kPa, and 1.7 (0.2,2.0) kPa, respectively [mean ± (range)], P < 0.005). The duration of emptying episodes not associated with peristalsis were significantly longer than those associated with peristalsis at (6.5 (3,8.7) s and 4.4 (2,6) s, respectively, P=0.059). Manometry detected only 56% of the antral contractions seen on ultrasound. We concluded that gastric emptying of a low-calorie liquid meal occurs both during peristaltic and nonperistaltic antral activity. In spite of lower antroduodenal pressure gradients, the emptying episodes were longer for nonperistaltic emptying, which is likely to be caused by low pyloric resistance. Considerable flow seems to occur without peristalsis during gastric emptying of a low-calorie, liquid meal in humans. [source] Effect of endotoxin on opossum oesophageal motor functionNEUROGASTROENTEROLOGY & MOTILITY, Issue 3 2000H. Park Endotoxin induces nitric oxide (NO,) synthase and alters gastrointestinal functions. We explored the effect of lipopolysaccharide (LPS) on oesophageal motor function at 6, 12, 24, and 48 h. The effects of inhibiting inducible NO, synthase (iNOS) were studied 12 h after administration of LPS with/without aminoguanidine (AG). Oesophageal manometry was performed and tissue bath studies were performed with muscle strips from the oesophagus and lower oesophageal sphincter (LOS). Plasma nitrite/nitrate concentrations were determined. The amplitudes of peristaltic pressure waves, resting LOS pressure and the percentage LOS relaxations were diminished by LPS. AG attenuated the decrease in amplitude of oesophageal pressure waves, LOS pressure, and percentage relaxation of LOS brought about by LPS. LPS decreased electrical field stimulation (EFS)-induced relaxation of LOS muscle. AG attenuated this decrease in LOS relaxation. The off-response of transverse oesophageal muscle strips was decreased, and AG antagonized this effect. Plasma concentrations of nitrite/nitrate were increased. The increase in plasma nitrite/nitrate was attenuated by AG. These studies support the hypothesis that endotoxin modulates oesophageal motor function by increasing NO production and suggest that this results from the induction of iNOS. [source] Negative mass sound shielding structures: Early resultsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2009Emilio P. Calius Abstract Elastic meta-materials or meta-composites can be designed to have a negative effective mass density at certain vibration frequencies, thus blocking wave propagation through the material within that frequency band. The negative mass behaviour is generated by resonant structures within the material that oscillate 180° out of phase with the acoustic pressure waves applied to the surface. As this research is in its initial stages this paper describes work in progress in both the experimental and numerical domains, and some early results from solids containing geometrically simple spring,mass resonant structures. Behaviour is characterized experimentally by dynamic tests of individual resonators as well as impedance tube measurements of panel-like structures containing multiple resonant elements. The experimental results exhibit clear evidence of the expected resonances, and partial band gap behaviour. Finite element models of both single resonant elements and impedance tube specimens are being developed, and the current status of these models is described. Their results to date show good agreement with the mass law and qualitative agreement with the experimental results. [source] Polymer,nanofiller prepared by high-energy ball milling and high velocity cold compactionPOLYMER COMPOSITES, Issue 3 2008Bruska Azhdar High-energy ball milling using comilling in a solid state by low-temperature mechanical alloying to prepare nickel-ferrite (NiFe2O4) nanopowders and ultrafine poly(methyl methacrylate) (PMMA), dispersing nanoparticles in a polymer matrix, and a uniaxial high-velocity cold compaction process using a cylindrical, hardened steel die and a new technique with relaxation assists have been studied. The focus has been on the particle size distributions of the nanocomposite powder during the milling and on the surface morphology of the nanocomposite-compacted materials after compaction with and without relaxation assists. Experimental results for different milling systems are presented showing the effects of milling time and material ratio. It was found that a longer mixing time give a higher degree of dispersion of the nanopowder on the PMMA particle surfaces. Furthermore, with increasing content of NiFe2O4 nanopowder, the reduction of the particle size was more effective. Different postcompacting profiles, i.e. different energy distributions between the upper and lower parts of the compacted powder bed, lead to different movements of the various particles and particle layers. Uniformity, homogeneity, and densification on the surfaces in the compacted powder are influenced by the postcompacting magnitude and direction. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by reducing the expansion of the compacted volume and by reducing the different opposite velocities, giving the compacted composite bed a more homogeneous opposite velocity during the decompacting stage and reducing the delay time between the successive pressure waves. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers [source] | |||||||||||||