Zero Flow Rate Research Articles

Effects of pressure-controlled ventilation targeting end-inspiratory flow rate on pulmonary complications and inflammation levels in patients undergoing spinal surgery in the prone position: a randomized clinical trial

BackgroundThis study assessed the impact of pressure-controlled ventilation (PCV) focusing on end-inspiratory flow rate on the incidence of postoperative pulmonary complications (PPCs) and inflammation levels in patients undergoing spinal surgery in the prone position.MethodsA total of 187 patients who underwent posterior spinal surgery were enrolled and randomly divided into 3 groups: 61 in the volume-controlled ventilation (VCV) group (group V), 62 in the PCV-volume-guaranteed (VG) group (group P1), and 64 in the PCV-VG end-expiratory zero flow rate group (group P2). Indicators including tidal volume (VT), peak airway pressure (Ppeak), and dynamic lung compliance (Cdyn) were recorded. The Ppeak, Cdyn, PETCO2, and oxygenation index (PaO2/FiO2) after intubation (T0), after prone position (T1), 60 min after prone position (T2), and after supine position at the end of surgery (T3) of the three groups were collected.ResultsIn the within-group comparison, compared with T0, Ppeak increased at T1 − 2 in groups V and P1 (P < 0.01), whereas it decreased at T1 − 3 in group P2 (P < 0.01). Cdyn decreased at T1 − 2 and PaO2/FiO2 increased at T1 − 3 in all three groups (P < 0.01), and PaO2/FiO2 increased at T1 − 3 (P < 0.01). Compared with group V, Ppeak decreased at T0 − 3 in group P1 (P < 0.01) and at T1 − 3 in group P2 (P < 0.01), while Cdyn increased at T0 − 3 in groups P1 and P2 (P < 0.01). Compared with group P1, Ppeak was elevated at T0 (P < 0.01) and decreased at T1 − 3 (P < 0.05), and Cdyn was elevated at T0 − 3 in group P2 (P < 0.01). The total incidence of PPCs in group P2 was lower than that in group V (P < 0.01). Compared with the preoperative period, serum interleukin 6 (IL-6) and C-reactive protein (CRP) levels were increased at 24 and 72 h after surgery in group V (P < 0.01), whereas that was increased at 24 h after surgery in group P1 and group P2 (P < 0.01). Compared with group V, serum IL-6 and CRP levels were reduced at 24 h after surgery in groups P1 and P2 (P < 0.01 or < 0.05).ConclusionIn patients undergoing spinal surgery in the prone position, PCV-VG targeting an end-inspiratory zero flow rate lowers the incidence of PPCs and inflammation levels.

Effect of condensate flow rate, surface tension, density and vapor velocity on condensate retention of wire wrapped tubes

Simulated condensation has been conducted on three wire wrapped tubes having same root diameter but different fin spacing of 1.5 mm, 2 mm, and 2.5 mm. Different fluids (ethanol, ethylene-glycol, and water) are used for condensation by providing them to the tubes through tiny holes in inter-fin spacing on the top of the surface of tubes. The major parameters are to be controlled in this research are fin spacing, vapor velocity, condensate flow rate and ratio of surface tension density of the fluid. Obtained results show that flooding angle (calculated from the top of the tube to the level where fluid fills the fin) rises by increasing fin spacing. Also, retention angles increase by reducing ratio of surface tension density of fluid. Acute flooding angles at zero air velocity and zero flow rate, elevates by increasing air velocity. However, obtuse flooding angles at static conditions drop by reducing air velocity. An interesting result is obtained regarding retention angle which remains almost even for the higher condensation flow rates until the tube gets inundated with condensation. Moreover, critical flow rates for all the tubes against using different working fluids are measured. Results obtained for static conditions have good correspondence with already available authentic data for flooding angle. Pictures showing condensate retention angles have been included in this paper.

Zero Flow Rate Detection of Ultrasonic Water Meter Using Machine Learning Techniques

This paper presents a classification-based method to detect false-positive ultrasonic sensor measurements when the flow rate is zero while the pipeline is full of water caused by the physical disturbances in flow metering. Due to the outlined disturbances, these false-positive readings of the meters may cause the wrong billing. To overcome this problem, ultrasonic sensor measurements are collected as timeseries data at variously different water flow rates. Numerical and statistical measures of the timerseries are computed to construct an input-output relation. Hence, the feature extraction process is performed. For the modeling phase, both zero flow rate and non-zero flow rate parts of the dataset, and its corresponding features are labeled. Logistic Regression (LR), Support Vector Machine (SVM), and Linear Discriminant Analysis (LDA) algorithms are employed to classify the flow status in the MATLAB environment. Model performances are compared in terms of accuracy, sensitivity, specificity, and precision. For the investigation of the availability of the implementation of an embedded system, model complexities are discussed. Selected model parameters are embedded in a water meter, and consumption values are compared to a water meter without the detection algorithm in the same test bench underfilled pipeline with zero flow rate condition. To simulate the physical disturbance conditions, and observe the effect of the false-positive detection algorithm on flow metering, the flow pipeline is vibrated periodically. Consumption loggings of the water meters are tabled, model performance results are discussed, and test results are shared. According to the results, the radial basis kernel SVM algorithm performs better in terms of all metrics. LR algorithm is employed for the real plant experiment when its model complexity is considered.

Improving Output Performance of a Resonant Piezoelectric Pump by Adding Proof Masses to a U-Shaped Piezoelectric Resonator.

This study proposes the improvement of the output performance of a resonant piezoelectric pump by adding proof masses to the free ends of the prongs of a U-shaped piezoelectric resonator. Simulation analyses show that the out-of-phase resonant frequency of the developed resonator can be tuned more efficiently within a more compact structure to the optimal operating frequency of the check valves by adjusting the thickness of the proof masses, which ensures that both the resonator and the check valves can operate at the best condition in a piezoelectric pump. A separable prototype piezoelectric pump composed of the proposed resonator and two diaphragm pumps was designed and fabricated with outline dimensions of 30 mm × 37 mm × 54 mm. Experimental results demonstrate remarkable improvements in the output performance and working efficiency of the piezoelectric pump. With the working fluid of liquid water and under a sinusoidal driving voltage of 298.5 Vpp, the miniature pump can achieve the maximum flow rate of 2258.9 mL/min with the highest volume efficiency of 77.1% and power consumption of 2.12 W under zero backpressure at 311/312 Hz, and the highest backpressure of 157.3 kPa under zero flow rate at 383 Hz.

ТЕЧЕНИЕ ТИПА КУЭТТА С УЧЕТОМ ИДЕАЛЬНОГО СКОЛЬЖЕНИЯ НА КОНТАКТЕ С ТВЕРДОЙ ПОВЕРХНОСТЬЮ

On the basis of a system of hydrodynamic equations, the unidirectional steady flow of a viscous incompressible fluid in a horizontal extended layer is studied. The solution to the governing equations is discovered in a distinguished class of functions that are linear in coordinates. The contact of the fluid with a lower hydrophobic solid boundary is described by the Navierslip condition. At the upper boundary of the layer, the temperature and pressure fields are assumed to be given, and a zero shear stress is specified. The system of boundary conditions is redefined due to the fact that all conditions for velocities are assigned as their derivatives. Zero flow rate is taken as an additional condition. The obtained exact solution to the boundary value problem is the only possible polynomial solution. The highest (eighth) degree of polynomials corresponds to a solution for background pressure. Analysis of the solution shows that it can describe a multiple stratification of kinetic-force fields. Since the analysis is carried out in a general form (without specifying physical constants that uniquely identify the fluid under study), the obtained results are applicable to viscous fluids of different nature.

Collecting antibodies and large molecule biomarkers in mouse interstitial brain fluid: a comparison of microdialysis and cerebral open flow microperfusion

ABSTRACT The determination of concentrations of large therapeutic molecules, like monoclonal antibodies (mAbs), in the interstitial brain fluid (ISF) is one of the cornerstones for the translation from preclinical species to humans of treatments for neurodegenerative diseases. Microdialysis (MD) and cerebral open flow microperfusion (cOFM) are the only currently available methods for extracting ISF, and their use and characterization for the collection of large molecules in rodents have barely started. For the first time, we compared both methods at a technical and performance level for measuring ISF concentrations of a non-target-binding mAb, trastuzumab, in awake and freely moving mice. Without correction of the data for recovery, concentrations of samples are over 10-fold higher through cOFM compared to MD. The overall similar pharmacokinetic profile and ISF exposure between MD (corrected for recovery) and cOFM indicate an underestimation of the absolute concentrations calculated with in vitro recovery. In vivo recovery (zero-flow rate method) revealed an increased extraction of trastuzumab at low flow rates and a 6-fold higher absolute concentration at steady state than initially calculated with the in vitro recovery. Technical optimizations have significantly increased the performance of both systems, resulting in the possibility of sampling up to 12 mice simultaneously. Moreover, strict aseptic conditions have played an important role in improving data quality. The standardization of these complex methods makes the unraveling of ISF concentrations attainable for various diseases and modalities, starting in this study with mAbs, but extending further in the future to RNA therapeutics, antibody-drug conjugates, and even cell therapies.

Measurement and numerical simulation of a small centrifugal compressor characteristics at small or negative flow rate

For centrifugal compressors used in automotive turbochargers, the extension of the surge margin is demanded because of lower engine speed. In order to estimate the surge line exactly, it is required to acquire the compressor characteristics at small or negative flow rate. In this paper, measurement and numerical simulation of the characteristics at small or negative flow rate are carried out. In the measurement, an experimental facility with a valve immediately downstream of the compressor is used to suppress the surge. In the numerical work, a new boundary condition that specifies mass flow rate at the outlet boundary is used to simulate the characteristics around the zero flow rate region. Furthermore, flow field analyses at small or negative flow rate are performed with the numerical results. The separated and re-circulated flow fields are investigated by visualization to identify the origin of losses.

鰭ポンプの性能特性に関する実験的研究

A fin pump utilizing a forced vibration of a flexible sheet in the same way as a caudal fin motion was developed for a treatment of fetal hydrocephalus. This study conducted an experiment to investigate the performance characteristics of the fin pump. A link system was designed to generate a pitching motion of a silicon rubber sheet and to control a vibration frequency and an amplitude. The vibration modes were analyzed by visualization. The pressure rise of the fin pump was derived from the flexible sheet deformation equation. The relative pressure coefficients for all experimental results were distributed on a line. This implies that the relative pressure coefficient is determined by the frequency ratio. The pressure rise was almost constant when the flexible sheet vibrated in the standing modes. On the other hands, the pressure rise increased with an increase of the frequency ratio when the flexible sheet vibrated in the travelling modes. This means that the pressure rise of the fin pump is closely related with the vibration modes determined by the frequency ratio. The pressure performance curve, the flow rate versus the pressure rise, was obtained by controlling a booster pump and a valve. At lower flow rates, the performance characteristics were similar to the results at the zero flow rate.

A U-shaped piezoelectric resonator for a compact and high-performance pump system

A resonantly driven piezoelectric pump system with outstanding characteristics is developed in this paper. The system consists of two diaphragm displacement pumps and a U-shaped resonator. The diaphragm pump is comprised of a pump chamber, two arrays of polydimethylsiloxane check valves and two compressible spaces near the inlet and outlet. The U-shaped resonator is designed to obtain uniform strain distribution under the out-of-phase vibration mode. This system utilizes a symmetric structure and flexible link fixture to enhance the overall performance with prominent features such as good reliability, low energy loss, high working efficiency, automatic adjustment of working conditions and ease of holding. Dynamic characteristics of the resonator are investigated. A prototype pump system with the outline dimensions of 30 mm × 37 mm × 72.5 mm is fabricated and tested. Experimental results show that the system can pump tap water at a flow rate of over 1660 ml min−1 under zero backpressure or at a backpressure of approximately 85 kPa under zero flow rate, when driven by sinusoidal voltages of 300 Vpp and resonant frequencies of 312 and 345 Hz.

Combined Microdialysis-Tumor Homogenate Method for the Study of the Steady State Compartmental Distribution of a Hydrophobic Anticancer Drug in Patient-Derived Xenografts.

To develop a reproducible microdialysis-tumor homogenate method for the study of the intratumor distribution of a highly hydrophobic anticancer drug (SN-38; 7-ethyl-10-hydroxycamptothecin) in neuroblastoma patient-derived xenografts. We studied the nonspecific binding of SN-38 to the microdialysis tubing in the presence of 2-hydroxypropyl-beta-cyclodextrin (HPBCD) in the perfusate. We calibrated the microdialysis probes by the zero flow rate (ZFR) method and calculated the enhancement factor (f = extrapolated SN-38 concentration at the ZFR / SN-38 concentration in the dialysed solution) of HPBCD. We characterized the extravasation of HPBCD to tumors engrafted in mice. In vivo microdialysis and terminal homogenate data at the steady state (subcutaneous pump infusions) were used to calculate the volume of distribution of unbound SN-38 (Vu,tumor) in neuroblastoma. HPBCD (10% w/v) in the perfusate prevented the nonspecific binding of SN-38 to the microdialysis probe and enhanced SN-38 recovery (f = 1.86). The extravasation of HPBCD in the tumor during microdialysis was lower than 1%. Vu,tumor values were above 3 mL/g tumor for both neuroblastoma models and suggested efficient cellular penetration of SN-38. The method contributes to overcome the limitations of the microdialysis technique in hydrophobic drugs and provides a powerful tool to characterize compartmental anticancer drug distribution in xenografts.

Estimation of human leptin concentration in the subcutaneous adipose and skeletal muscle tissues.

Interstitial leptin concentrations in subcutaneous adipose and skeletal muscle tissues were determined by open-flow microperfusion. In 12 lean male subjects (age: 25.6 ± 1.1 years), a zero flow rate experiment using different flow rates was applied. Recovery was determined by urea as an internal reference. In the no-net-flux experiments, catheters were perfused with five solutions containing different concentrations of leptin. Concentrations of interstitial leptin were calculated by applying linear regression analysis to perfusate as opposed to sampled leptin concentrations. The zero flow rate protocol showed significantly higher concentrations of leptin in the interstitial fluid of subcutaneous adipose compared to skeletal muscle tissue [36.8 ± 10.32 vs. 7.1 ± 2.5% of the corresponding plasma level (P = 0.018)]. The recovery of urea in the samples was comparable for all catheters [79.4 ± 6.8 vs. 83.0 ± 5.8 of the corresponding plasma level, flow rate of 0.3 μL/min; (P = ns)] and was higher when compared to leptin. In the no-net-flux protocol, the concentration of leptin in subcutaneous adipose tissue was almost identical to plasma [90. 5 ± 7.0%] and the skeletal muscle tissue concentration of leptin was 23.7 ± 2.5% of the corresponding plasma level. Open-flow microperfusion enables the estimation of leptin concentrations in subcutaneous adipose and skeletal muscle tissues in humans in vivo. This is the first documentation on the use of open-flow microperfusion to demonstrate that relevant amounts of leptin are also found in skeletal muscle tissue.

Wall polymer depletion effects on electrokinetic diffusioosmosis of power-law liquids in cylindrical capillaries

We investigate electrokinetic diffusioosmotic flows of power-law liquids including the effects of a polymer-depleted Newtonian liquid layer near the wall boundaries in circular cylindrical capillaries. Semi-analytical solutions to the flow velocity distribution and volume flow rate are obtained for conditions involving finite double layer effects on the induced electric field of the electrokinetic diffusioosmosis. Results show that the flow behavior and responses of the electrokinetic diffusioosmotic flow depend not only on the wall zeta potential, diffusivity difference parameter, and flow behavior index, but also on the depletion layer thickness to Debye thickness ratio, the ratio of the flow consistency parameter of the power-law liquid core to the viscosity of the Newtonian depletion layer, as well as the exact numeric values of the flow consistency parameter and the Newtonian viscosity. Including the Newtonian depletion layer gives rise to wiggled-shaped zero flow rate border curves on the zeta potential versus diffusivity difference parameter map when the depletion layer thickness to Debye thickness ratio and the ratio of the flow consistency parameter of the power-law liquid core to the viscosity of the Newtonian depletion layer are close to one. These results are not identified in previous Newtonian or non-Newtonian electrokinetic diffusioosmosis literature and may likely open new possibilities and suggest new ideas in the analysis and design of diffusiophoretic separation and diffusioosmotic flow operations.

Experimental Study of a Centrifugal Conductive MHD Pump

Results of experiments performed on disk models of a centrifugal conductive magnetohydrodynamic (MHD) pump, which can be considered as prototypes of pumps in casting of ferrous and nonferrous metals, are presented. Low-temperature Wood and Rose alloys are used as working fluids. Dependence values of the output pressure and flow rate on parameter IB (where I is the electric current and B is the magnetic field) in various pump operation modes are determined for a model centrifugal conductive MHD pump with an axisymmetric supply of current (the side surface of the MHD cell is electrically conductive). Similar experiments on the model with an insulated surface of the MHD cell and external electrodes in the zero flow rate regime show that the output pressure generated by the pump is appreciably greater than that in the case with an axisymmetric current supply.

Abstract 2742: Cerebral microdialysis for simultaneous sampling of crenolanib (PDGFR inhibitor) and erlotinib (EGFR inhibitor) in mouse models of glioma

Abstract Cerebral microdialysis, a technique used to monitor anticancer drug disposition in the central nervous system (CNS), is commonly used to sample extracellular fluid (ECF) for analysis of a single anticancer agent. However, combining anticancer drugs represents a promising strategy to overcome the highly resistant nature of some CNS tumors, such as malignant glioma. To date, the feasibility of simultaneous sampling multiple anti-cancer agents via cerebral microdialysis has not been reported. Given the role of PDGFRα and EGFR in providing multiple inputs for sustaining PI3K signaling, critical for glioma cell survival and proliferation, combining PDGFRα and EGFR inhibitors represents a valid treatment strategy for these tumors. The goals of the current study are to 1) to optimize microdialysis conditions to sample crenolanib and erlotinib as single agents or in combination from brain ECF (CbECF) and tumor ECF (CtECF) and 2) to characterize CNS penetration of crenolanib as a single agent and in combination with erlotinib. In vitro microdialysis experiments to sample crenolanib and erlotinib from aCSF determined that addition of 10% hydroxylpropyl betacyclodextrin increased the recovery of crenolanib and erlotinib by 16.1 and 2.6 fold, respectively. Zero-flow rate recovery method estimated stock concentrations with &amp;gt;85% accuracy. Sensitive LC-MS/MS methods will allow us to detect very low concentrations in the CNS (LLOQ for crenolanib and erlotinib is 0.1 and 0.5ng/mL, respectively). Unbound crenolanib concentrations in brain and tumor ECF were determined in a spontaneous glioma model under steady-state conditions achieved by using a miniosmotic pump loaded with crenolanib which administered a dose of 300 mg/kg/day. Plasma steady-state levels (Cpss) were 516.8±92.9ng/mL, mean ± SD. Crenolanib penetration into tumors [PTumor = CtECF/Cpss] was 3-fold higher than in normal brain [PBrain = CbECF/Cpss] (1.0±0.5 and 0.3±0.02, respectively). In a murine orthotopic xenograft model bearing SJG2 pediatric glioma tumors, crenolanib (300 mg/kg/day via miniosmotic pumps) inhibited PDGFRα phosphorylation (in vitro IC50 =8.1ng/mL) in 75% (3/4) of SJG2 tumors but failed to inhibit AKT phosphorylation or to induce apoptosis. We subsequently treated these animals with an EGFR inhibitor, erlotinib, and tried to determine whether co-administration of erlotinib affected the CNS penetration of crenolanib. Administration of 200 mg/kg/day crenolanib and erlotinib simultaneously via a miniosmotic pump resulted in a crenolanib Cpss of 210.1± 57 ng/mL and an erlotinib Cpss of 634±208 ng/mL. To conclude, optimizing microdialysis technique enhances the ability to simultaneously dialyze crenolanib and erlotinib in vitro. Studies to determine the effect of co-administration of erlotinib on crenolanib CNS penetration are ongoing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2742. doi:1538-7445.AM2012-2742

Abstract 5474: Optimization of a microdialysis method for evaluation of CP-868,596 penetration in glioblastoma murine models using a sensitive liquid chromatography mass spectrometry (LC-MS/MS) method

Abstract Focal amplification and gene rearrangement of the platelet derived growth factor receptor alpha (PDGFRA) gene, resulting in constitutively active signaling, has been identified in a subset of cases of glioblastoma multiforme (GBM). Thus, inhibiting PDGFR signaling represents a valid treatment strategy for these tumors. CP-868,596, a potent inhibitor of the PDGFR kinase, is currently undergoing preclinical testing for the treatment of GBM. CP-868,596 inhibits the intracellular ATP-binding site of PDGFR, thereby attenuating downstream signaling events. To characterize CP-868,596 penetration in murine high grade glioma, we used a cerebral microdialysis approach. This approach would allow us to measure unbound CP-868,596 concentrations in the tumor extracellular fluid (ECF) using microdialysis under steady-state conditions. To accurately measure the potentially low concentrations of CP-868,596 in the dialysates, we developed and validated a highly sensitive LC-MS/MS method for analysis of CP-868,596. The parent drug CP-868,596 and its deuterated form as an internal standard (ISTD) were separated on a Pursuit 3µ C18 column (50 × 2.0 mm) with mobile phase consisting of 85% acetonitrile and 15% 10mM HCOONH4. The ion transitions at m/z 444.4→301.1 for CP-868,596 and at m/z 448.2→374.2 for the ISTD were selected. Samples were processed using liquid-liquid extraction (LLE) with t-butyl methyl ether. The extracted samples were dried by nitrogen gas and reconstituted with 40% acetonitrile. 10 µLs were injected for analysis. Both within-day and between-day precision (%CV) were ≤ 7% and accuracy ranged from 93.7% to 102.5%. Next, we optimized the microdialysis conditions for CP-868,596. Initial in vitro microdialysis experiments using artificial cerebrospinal-fluid (aCSF) as a perfusate demonstrated low CP-868,596 recovery (8.24 ± 1.26, mean ± SD). Addition of 10% hydroxyl-propyl beta cyclodextrin to the perfusate increased recovery to 91.2% ± 4.6%. Several approaches to estimate probe recovery were tested including retrodialysis and Zero-Flow Rate (ZFR) methods. The ZFR method estimated stock concentrations with &amp;gt; 85% accuracy; hence, this method will be used to estimate recovery under in vivo steady-state conditions. To achieve steady-state plasma concentrations, CP-868,596-loaded miniosmotic pump (Alzet model 2001D) was s.c. implanted in wild-type FVB mice (n=6). Analysis showed that steady-state plasma levels of CP-868,596 were maintained for 30 hours (516.8 ± 92.9 ng/ml, mean ± SD). We predict that our sensitive analytical method (LLOQ 0.1 ng/mL) will allow us to measure the low CP-868,596 concentrations expected during in vivo cerebral microdialysis experiments. Studies measuring CP-868,596 tumor concentrations using the cerebral microdialysis approach in several murine GBM models are ongoing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5474. doi:10.1158/1538-7445.AM2011-5474

Comparison of constant-volume sampler and bag mini-diluter emissions measurements of a plug-in hybrid electric vehicle

The impending introduction of dual-fuel plug-in hybrid vehicles (PHEVs) will impose significant challenges on current vehicle emissions testing equipment and protocols. One reason is the all-electric range and random start of the combustion engine. A second reason is the period of low or zero flow rate of exhaust volume. The present paper systematically evaluates these challenges by testing a Toyota prototype with an industry-standard, constant-volume sampler system in parallel with bag mini diluter equipment. Both systems exhibit technical difficulties when testing the PHEV. Discrepancies between the two methods can be corrected with software manipulations for a charge-sustaining operation. However, there are clear mechanisms of possible error in CO2 emissions collected during charge-depleting operation for both technologies. These findings indicate that alternative methods, including continuous sampling methods, may be required for accurate vehicle certification.

Analysis of electroosmotic flow in a microchannel packed with microspheres

The electroosmotic flow in a microchannel packed with microspheres under both direct and alternating electric fields is analyzed. In the case of the steady DC electroosmosis in a packed microchannel, the so-called “capillary model” is used, in which it is assumed that a porous medium is equivalent to a series of intertwined tubules. The interstitial tubular velocity is obtained by analytically solving the Navier–Stokes equation and the complete Poisson–Boltzmann equation. Then, using the volume-averaging method, the solution for the electroosmotic flow in a single charged cylindrical tubule is applied to estimate the electroosmosis in the overall porous media by introducing the porosity and tortuosity. Assuming uniform porosity, an exact solution accounting for the electrokinetic wall effect is obtained by solving the modified Brinkman momentum equation. For the electroosmotic flow under alternating electric fields in a cylindrical microchannel packed with microspheres of uniform size, two different conditions regarding the openness of the channel ends are considered. Based on the capillary model, the time-periodic oscillating electroosmotic flow in an open-ended microchannel in response to the application of an alternating electric field is obtained using the Green’s function approach to the Navier–Stokes equation. When the two ends of the channel are closed, a backpressure is induced to generate a counter flow, resulting in a new zero flow rate. Such induced backpressure associated with the counter flow in a closed-end microchannel is obtained analytically by solving the transient modified Brinkman momentum equation.

A cyclic hydraulic jacking test to determine the in situ stress normal to a fracture

Hydraulic fracturing and cyclic hydraulic jacking (step-pressure) tests were used to determine the virgin stress normal to six natural joints in grantic rocks. A numerical model was used to analyse the coupled problem of fluid flow and rock/fracture deformation during the field tests. Fracture closure and virgin normal stress was determined from the zero-flow pressure in a well pressure-well flow diagram. The cyclic hydraulic jacking tests gave a zero-flow pressure in close agreement with both the shut-in pressure and the weight of the overburden rock for four out of six tested joints. For the two remaining joints the virgin normal stress could be estimated by a linear extrapolation to zero-flow rate. The zero-flow pressure is clearly defined and is insensitive to the transmissivity and non-linear normal stiffness of the fracture near the wellbore. Cyclic hydraulic jacking is therefore an alternative to traditional shut-in analysis when shut-in pressure is difficult to determine.

The permeability of the secretin stimulated exocrine pancreas to non-electrolytes.

1. A method of measuring the permeability of the pancreas by determining the apparent reflexion coefficient (sigmaA) is described, in the isolated pancreas secreting maximally under the influence of secretin. The principle is to add a non-electrolyte to the perfusate which will create an osmotic gradient (RTsigmadeltaC) counter to that of active transport and reduce the secretion rate. This is compared with the effect of an equal concentration (0.1 M) of sucrose (RTdeltaC; sigma = 1). The apparent reflection coefficient is obtained by dividing the percentage reduction in the secretion rate due to the test molecule with that due to sucrose. 2. Sucrose when added to the perfusate inhibits pancreatic secretion. For every 10 mM increase in sucrose concentration, the secretion rate was inhibited by 7.1%. It has been estimated that an osmotic gradient of 131 m-osmole/kg water will cause zero flow rate. This is a measure of the pressure required to counteract the local osmotic gradient set up by active transport, it is equivalent to about 3.4 atm. 3. Non-electrolytes with molecular volumes greater than about 85 cm3 mole-1 are relatively impermeable, below this value they enter the pancreatic juice with increasing ease as the molecular volume decreases. 4. SigmaA for a number of compounds has been measured: urea 0.17; ethanediol 0.27; thiourea 0.51; glycerol 0.69; creatinine 0.81; erythritol 0.91; arabinose 0.96; xylose 0.98; sorbitol 0.98. 5. The addition of non-electrolytes to the perfusate had effects on pancreatic secretion which were a function of sigmaA. For molecules with sigmaA lying between 0.81 and 1.0 an osmotic load of 0.1 M increased both the concentration of sodium plus potassium and the concentration of chloride plus bicarbonate by about 50 m-mole/l. Whereas the cation change is almost exclusively one of sodium that of the anions was preferentially an increase in chloride. For compounds with sigmaA lying between 0 and 0.81 the concentration of sodium plus potassium was proportional to sigmaA. 6. A number of compounds have been described which inhibit pancreatic secretion, other than by an osmotic effect. These include acetaldehyde, thioglycerol, nicotinamide, ribose, dihydroxyacetone, and glyceraldehyde. 7. It is concluded that the pancreas is more permeable than the gall-bladder of rabbit, fish and bullfrog, the proximal tubule of the kidney of rat and the small intestine of bullfrog, but is probably similar to that of small intestine of guinea-pig and man.

A Research on Electro-Hydraulic Pressure Control Servovalve

Most of the servo valves taken up for research previously were pressure control valves which control a hydraulic pressure linear to input current and allow a vent flow. No research exists on the servo valves which are able to control hydraulic pressure linear to input current at near zero flow rate without a vent flow. This report describes thet establishment of a design method by theory and experiments utilizing pressure control servo valves experimentally manufactured which are able to obtain hydraulic pressure linear to input current independently of flow rate.