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Pressure Differential (pressure + differential)
Selected AbstractsAutomated diffusion chambers to monitor diurnal and seasonal dynamics of the soil CO2 concentration profileEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2009F. Albanito Summary To better understand the factors controlling carbon dioxide (CO2) production and transport in soil, we developed a new method to continuously monitor soil CO2 concentration at multiple depths, by using diffusion chambers. The soil diffusion chambers are constructed from a high-density polyethylene cylindrical frame enclosed by a micro-polyvinylidene difluoride flat membrane (PVDF). All chambers are linked to an infrared gas analyser positioned above-ground through a multi-port valve system. We set up two experimental sites for long-term measurements of soil CO2 concentration, soil temperature and soil water content at depths of 0, 10, 20, 40 and 80 cm. The system provides the following advantages : (i) the use of the PVDF combined with the small dimensions of the diffusion chambers allows rapid diffusion of soil gas into the chambers and therefore a short equilibration time of the gas phase with the surrounding soil atmosphere, (ii) the equilibrating closed loop system allows the semi-continuous measurement of soil profile CO2 concentrations without creating a pressure differential within the chambers, thus reducing gas concentration distortions in the soil, (iii) the small size of the closed diffusion chambers reduces the initial soil disturbance during installation, (iv) it allows sampling in wet, humid soils, including ones that are waterlogged or temporarily saturated, and (v) the chambers do not require removal for maintenance purposes and are inexpensive. [source] Novel Poly(vinyl alcohol)-tetraethoxysilane hybrid matrix membranes as oxygen barriers,JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Mallikarjunagouda B. Patil Abstract Novel type of membranes based on poly(vinyl alcohol) crosslinked with tetraethoxysilane have been prepared by solution casting and solvent-evaporation method. The membranes thus formed were characterized by Fourier transform infrared spectroscopy (FTIR) to study the chemical interactions, X-ray diffraction (XRD), and thermogravimetry (TGA) to investigate morphological and thermal properties. Membranes were prepared in two different thicknesses (30 and 55 ,m) and used for measuring the oxygen permeability under varying feed pressures (maintaining the desired pressure differential across the membrane) in the range from 1 to 50 kg/cm2 pressure. Oxygen permeability of the membranes ranged from 0.0091 to 1.6165 Barrer for 30 ,m and 0.0305 to 0.1409 Barrer for 55-,m thick membranes by increasing the feed pressures on the feed side. Except at 50 kg/cm2 pressure, the observed oxygen permeability values are almost close to total permeability. Membranes of this study could be useful as oxygen barriers for applications in food packaging industries. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 273,278, 2007 [source] Estimation of the differential pressure at renal artery stenoses,MAGNETIC RESONANCE IN MEDICINE, Issue 5 2004Peter J. Yim Abstract Atherosclerotic disease of the renal artery can lead to reduction in arterial caliber and ultimately to conditions including renovascular hypertension. Renal artery stenosis is conventionally assessed, using angiography, according to the severity of the stenosis. However, the severity of a stenosis is not a reliable indicator of functional significance, or associated differential pressure, of a stenosis. A methodology is proposed for estimation of the renal artery differential pressure (RADP) from MR imaging. Realistic computational fluid dynamics (CFD) models are constructed from MR angiography (MRA) and phase-contrast (PC) MR. The CFD model is constructed in a semiautomated manner from the MR images using the Isosurface Deformable Model (IDM) for surface reconstruction and a Marching Front algorithm for construction of the volumetric CFD mesh. Validation of RADP estimation was performed in a realistic physical flow-through model. Under steady flow, the CFD estimate of the differential pressure across a stenosis in the physical flow-through model differed by an average of 5.5 mmHg from transducer measurements of the pressure differential, for differential pressures less than 60 mmHg. These results demonstrate that accurate estimates of differential pressure at stenoses may be possible based only on structural and flow images. Magn Reson Med 51:969,977, 2004. Published 2004 Wiley-Liss, Inc. [source] Physical Model-Based Indirect Measurements of Blood Pressure and Flow Using a Centrifugal PumpARTIFICIAL ORGANS, Issue 8 2000Tadashi Kitamura Abstract: This article describes a technique offering indirect measurements of pump pressure differential and flow with certain accuracy independent of changes in blood viscosity. This technique is based on noninvasive measurements of the motor current and rotation speed using the physical model equations of the centrifugal pump system. Blood viscosity included in the coefficients of the dynamic equations is first estimated, and then substitution of the estimated viscosity into the steady equations of the model provides pump flow and pressure differential. In vitro tests using a Capiox pump showed a sufficient linear correlation between actual values and their estimates for pressure differential and pump flow. An in vivo test using a 45 kg sheep showed that the proposed algorithm needs robustness for the convergence of estimates of viscosity. An overall evaluation, however, of the developed algorithm/model showed indications of success in terms of efficient computation and modeling. [source] A porcine model of bladder outlet obstruction incorporating radio-telemetered cystometryBJU INTERNATIONAL, Issue 1 2007Matthew B. Shaw OBJECTIVE To present a novel porcine model of bladder outlet obstruction (BOO) with a standardized bladder outlet resistance and real-time ambulatory radio-telemetered cystometry, as BOO is a common condition with many causes in both adults and children, with significant morbidity and occasional mortality, but attempts to model this condition in many animal models have the fundamental problem of standardising the degree of outlet resistance. MATERIALS AND METHODS BOO was created in nine castrated male pigs by dividing the mid-urethra; outflow was allowed through an implanted bladder drainage catheter containing a resistance valve, allowing urine to flow across the valve only when a set pressure differential was generated across the valve. An implantable radio-telemetered pressure sensor monitored the pressure within the bladder and abdominal cavity, and relayed this information to a remote computer. Four control pigs had an occluded bladder drainage catheter and pressure sensor placed, but were allowed to void normally through the native urethra. Intra-vesical pressure was monitored by telemetry, while the resistance valve was increased weekly, beginning with 2 cmH2O and ultimately reaching 10 cmH2O. The pigs were assessed using conventional cystometry under anaesthesia before death, and samples conserved in formalin for haematoxylin and eosin staining. RESULTS The pigs had radio-telemetered cystometry for a median of 26 days. All telemetry implants functioned well for the duration of the experiment, but one pig developed a urethral fistula and was excluded from the study. With BOO the bladder mass index (bladder mass/body mass × 10 000) increased from 9.7 to 20 (P = 0.004), with a significant degree of hypertrophy of the detrusor smooth muscle bundles. Obstructed bladders were significantly less compliant than control bladders (8.3 vs 22.1 mL/cmH2O, P = 0.03). Telemetric cystometry showed that there was no statistically significance difference in mean bladder pressure between obstructed and control pigs (4.8 vs 6.7 cmH2O, P = 0.7), but that each void was longer in the pigs with BOO. CONCLUSION This new model of BOO provides a method of reliably and precisely defining the bladder outlet resistance; it induces the changes classically seen with BOO, including increased bladder mass, increased smooth muscle bundle size and decreased compliance. [source] Histological and ultrastructural aspects of the nasal complex in the harbour porpoise, Phocoena phocoenaJOURNAL OF MORPHOLOGY, Issue 11 2009Susanne Prahl Abstract During the evolution of odontocetes, the nasal complex was modified into a complicated system of passages and diverticulae. It is generally accepted that these are essential structures for nasal sound production. However, the mechanism of sound generation and the functional significance of the epicranial nasal complex are not fully understood. We have studied the epicranial structures of harbor porpoises (Phocoena phocoena) using light and electron microscopy with special consideration of the nasal diverticulae, the phonic lips and dorsal bursae, the proposed center of nasal sound generation. The lining of the epicranial respiratory tract with associated diverticulae is consistently composed of a stratified squamous epithelium with incomplete keratinization and irregular pigmentation. It consists of a stratum basale and a stratum spinosum that transforms apically into a stratum externum. The epithelium of the phonic lips comprises 70,80 layers of extremely flattened cells, i.e., four times more layers than in the remaining epicranial air spaces. This alignment and the increased number of desmosomes surrounding each cell indicate a conspicuous rigid quality of the epithelium. The area surrounding the phonic lips and adjacent fat bodies exhibits a high density of mechanoreceptors, possibly perceiving pressure differentials and vibrations. Mechanoreceptors with few layers and with perineural capsules directly subepithelial of the phonic lips can be distinguished from larger, multi-layered mechanoreceptors without perineural capsules in the periphery of the dorsal bursae. A blade-like elastin body at the caudal wall of the epicranial respiratory tract may act as antagonist of the musculature that moves the blowhole ligament. Bursal cartilages exist in the developmental stages from fetus through juvenile and could not be verified in adults. These histological results support the hypothesis of nasal sound generation for the harbor porpoise and display specific adaptations of the echolocating system in this species. J. Morphol. 2009. © 2009 Wiley-Liss, Inc. [source] | ||||||||||