Average Pressure Difference Research Articles

An Evaluation of GNSS Radio Occultation Technology for Australian Meteorology

Earth atmospheric information has been primarily observed by a global network of radiosonde weather observation stations for global weather forecasting and climatologic studies for many years. However, the main disadvantage of this method is that it can not sufficiently capture the complex dynamics of the Earth’s atmosphere since its limited and heterogeneous geographic distribution of launching stations. Since the first low earth orbit (LEO) satellite equipped with a GPS receiver was launched in early 1990s, there are more than a dozen of GPS receivers onboard LEO satellites used for Earth atmospheric observation. Recent research has shown that the Global Navigation Satellite System (GNSS) radio occultation (RO) derived atmospheric profiles have great potentials to overcome many limitations of existing atmospheric observation methods. Constellation Observing Systems for Meteorology, Ionosphere, and Climate (COSMIC) retrieved atmospheric profiles are investigated using radiosonde measurements at 42 collocated stations in the Australian region. Statistical results show that the difference in average temperature is about 0.05 ?C with a standard deviation of 1.52?C and the difference in average pressure is -1.06 hPa with a standard deviation of 0.91 hPa. This research has also demonstrated that the GNSS RO derived atmospheric profiles have good agreement with the radiosonde observations.

Hammocking: The effect of cushion covers on interface pressure measurements

Purpose. To investigate the effects of the cushion covers on interface pressure measurements using pressure mapping technology.Methods. Sixty-one healthy participants were recruited for a laboratory-based study using a single group design. Participants were pressure mapped on a visco-elastic foam cushion and a foam and fluid pack cushion with their covers on and with their covers removed. An air-filled cushion was tested with two different types of covers, an incontinence cover and a ‘Comfair’ cover. Average and maximum pressures recorded at 6 mins by the Force Sensing Array pressure mapping system were used for statistical analysis.Results. There were no significant differences in maximum pressures for the three cushions tested with their covers on or with their covers removed. The cushion with the foam base and fluid pack did not demonstrate any significant differences in average pressure with the cover on or with the cover removed. However, the visco-elastic foam cushion showed significantly lower average pressures with the cover on (p = 0.019). The air-filled cushion showed lower average pressures with the incontinence cover on, when compared to the Comfair cover (p = 0.029).Conclusion. Contrary to the belief that the process of hammocking may create surface tension within the cushion covers, which in turn may adversely affect the cushions ability to reduce interface pressure, the cushions tested in the current study did not show significantly lower interface pressure measurements with the covers removed. Therefore the covers did not adversely affect the cushion's ability to reduce interface pressure. The findings of this study require verification with disabled clients.

4228 液滴の振動周波数に及ぼす振幅と回転の影響(G05-13 気泡・液滴(2),G05 流体工学)

Three-dimensional oscillations and rotations of a liquid droplet are simulated numerically using the level set method. It is found that the oscillation frequency decreases as the initial amplitude increases, while it increases as the rotation frequency increases. It is found that the oscillation frequency depends on the average pressure difference between the pole and the equator of the droplet.

防排煙時の室間圧力差予測のための中間的開放扉の基本特性

The basic properties of intermediate open doors necessary for predicting pressure differences between rooms in a smoke control plan were determined. These were determined in the following manner. (1) An experimental system was proposed for determining the flow rate coefficient relative to the opening angle of an intermediate open door. (2) The relationship of door closing force, door shape and pressure difference between rooms with respect to the opening angle of a free-swinging door was proposed by introducing a pressure difference distribution coefficient. (3) The relationship between the opening angle of an arbitrary free-swinging door and the average pressure difference between rooms can be estimated from the door width and height by determining this relationship for a specific door. (4) The pressure difference between rooms immediately before opening a door can be estimated from the door surface area on which pressure is acting and the door closing force regardless of the magnitude of the door closing force.

Roles of large and small arteries in vascular disease

Roles of large and small arteries in vascular disease

Physiologic Control of Rotary Blood Pumps: An In Vitro Study

Rotary blood pumps (RBPs) are currently being used as a bridge to transplantation as well as for myocardial recovery and destination therapy for patients with heart failure. Physiologic control systems for RBPs that can automatically and autonomously adjust the pump flow to match the physiologic requirement of the patient are needed to reduce human intervention and error, while improving the quality of life. Physiologic control systems for RBPs should ensure adequate perfusion while avoiding inflow occlusion via left ventricular (LV) suction for varying clinical and physical activity conditions. For RBPs used as left ventricular assist devices (LVADs), we hypothesize that maintaining a constant average pressure difference between the pulmonary vein and the aorta (deltaPa) would give rise to a physiologically adequate perfusion while avoiding LV suction. Using a mock circulatory system, we tested the performance of the control strategy of maintaining a constant average deltaPa and compared it with the results obtained when a constant average pump pressure head (deltaP) and constant rpm are maintained. The comparison was made for normal, failing, and asystolic left heart during rest and at light exercise. The deltaPa was maintained at 95 +/- 1 mm Hg for all the scenarios. The results indicate that the deltaPa control strategy maintained or restored the total flow rate to that of the physiologically normal heart during rest (3.8 L/m) and light exercise (5.4 L/m) conditions. The deltaPa approach adapted to changing exercise and clinical conditions better than the constant rpm and constant deltaP control strategies. The deltaPa control strategy requires the implantation of two pressure sensors, which may not be clinically feasible. Sensorless RBP control using the deltaPa algorithm, which can eliminate the failure prone pressure sensors, is being currently investigated.

Crossflow microfiltration of mineral dispersions using ceramic membranes

Crossflow microflltration experiments were performed on aqueous dispersions of titanium dioxide through a 0.1 Urn pore size ceramic membrane at various operating parameters. The initial transient flux decline follows dead-end filtration theory, with the membrane resistance determined from the initial flux and the cake resistance determined from the rate of flux decline due to cake build-up. For long times, the observed fluxes reached steady- or nearly steady-state values, presumably as a result of the cake growth being arrested by the shear exerted at its surface. The steady-state fluxes increased with increasing inlet crossflow velocity and decreasing feed concentration. Rheological work has shown that the titania dispersions exhibit shear-thinning behaviour. Extreme sensitivity with pH was observed, whereby the dispersion viscosity can be changed by as much as an order of magnitude with pH variation at constant volume fraction. The steady-state permeate flux values were determined from the steady-state model based on the Kozeny—Carman equation for cake resistance and Darcy's law applied over the filter area to relate filtration rate to average pressure difference between the feed and permeate sides of the filter. The model includes a cake resistance of the cake layer, which was determined for the titanium dioxide dispersions by fitting the experimental flux data to the model. The resulting fluxes obtained from the model using simple values for the membrane resistance, cake resistance, and rheological parameters for each data set are in good agreement with the measured fluxes.

Static filling pressure in patients during induced ventricular fibrillation.

The static pressure resulting after the cessation of flow is thought to reflect the filling of the cardiovascular system. In the past, static filling pressures or mean circulatory filling pressures have only been reported in experimental animals and in human corpses, respectively. We investigated arterial and central venous pressures in supine, anesthetized humans with longer fibrillation/defibrillation sequences (FDSs) during cardioverter/defibrillator implantation. In 82 patients, the average number of FDSs was 4 +/- 2 (mean +/- SD), and their duration was 13 +/- 2 s. In a total of 323 FDSs, arterial blood pressure decreased with a time constant of 2.9 +/- 1.0 s from 77.5 +/- 34.4 to 24.2 +/- 5.3 mmHg. Central venous pressure increased with a time constant of 3.6 +/- 1.3 s from 7.5 +/- 5.2 to 11.0 +/- 5.4 mmHg (36 points, 141 FDS). The average arteriocentral venous blood pressure difference remained at 13.2 +/- 6.2 mmHg. Although it slowly decreased, the pressure difference persisted even with FDSs lasting 20 s. Lack of true equilibrium pressure could possibly be due to a waterfall mechanism. However, waterfalls were identified neither between the left ventricle and large arteries nor at the level of the diaphragm in supine patients. We therefore suggest that static filling pressures/mean circulatory pressures can only be directly assessed if the time after termination of cardiac pumping is adequate, i.e., >20 s. For humans, such times are beyond ethical options.

Control strategy for maintaining physiological perfusion with rotary blood pumps.

We present arguments and simulation results in favor of a novel strategy for control of rotary blood pumps. We suggest that physiological perfusion is achieved when the blood pump is controlled to maintain an average reference differential pressure. In the case of rotary left ventricular assist devices, our simulations show that maintaining a constant average pressure difference between the left ventricle and aorta results in physiological perfusion over a wide range of physical activities and clinical cardiac conditions. We simulated rest, light, and strenuous exercise conditions, corresponding to cardiac demands of 4.92, 7.98, and 14.62 L/min, respectively. For different exercise levels, the clinical conditions ranged from normal to failing to asystolic heart. By maintaining a constant pressure difference of 75 mm Hg between the left ventricle and aorta, with either an axial or a centrifugal blood pump, a total cardiac output close to the physiological cardiac demand was achieved, irrespective of the heart condition. The simulations of the transitions between different levels of exercise indicate that with the same reference differential pressure, the proposed approach leads to rapid adaptation of the total cardiac output to physiological levels, while avoiding suction. Comparison with the traditional control strategy of maintaining a reference rotational speed (rpm) of the pump indicates that though the traditional approach has some degree of adaptability, it is only adequate over a narrow range of cardiac demand and clinical conditions of the patient. Our results indicate that the proposed approach is superior to the alternatives in providing an adequate and autonomous adaptation of the total cardiac output over a broad range of exercise conditions (expected when an assist device is used as a destination therapy) and clinical statuses of the native heart (such as further deterioration or recovery of cardiac function), while having the potential to improve the quality of life of patients by reducing the need for monitoring and frequent human intervention. The proposed approach can be clinically implemented using simple controllers, and requires the implantation of two pressure sensors, or estimation of the pressure difference based on other available measurements.

PHYSIOLOGIC CONTROL OF ROTARY BLOOD PUMPS

Rotary blood pumps (RBP) are currently being used as a bridge to transplantation as well as for myocardial recovery and destination therapy for patients with heart failure. Control systems for RBP should ensure adequate perfusion while avoiding inflow occlusion via left ventricular (LV) suction for varying clinical and physical activity conditions. We present mock circulatory system test results which indicate that maintaining a constant average pressure difference between the pulmonary vein and the aorta (APa), gives rise to a physiologically adequate perfusion and is effective at avoiding LV suction, for RBP used as left ventricular assist devices (LVAD). The mock system was run at the following clinical test conditions: normal, failing, and asystolic left heart during rest and at light exercise. The ΔPa was maintained at 96±2 mmHg for all the scenarios. The ΔPa control strategy maintained a total flow rate that was closer to the flow rate obtained with a normal heart without LVAD assistance during rest (3.8 Ipm) and light exercise (5.6 Ipm) conditions, in comparison to the traditional strategies of maintaining a constant pump rpm and maintaining a constant pump pressure difference. The ΔPa control strategy is simple to implement but requires the implantation of two pressure sensors. Sensorless RBP control, which can eliminate the failure prone pressure sensors, is being pursued as a follow-on investigation.

Nonlinear Controller for Ventricular Assist Devices

This paper presents the design of a gain-scheduled proportional integral (PI) feedback controller for ventricular assist devices to maintain physiologically motivated perfusion. The selected control objective is to maintain an average differential pressure deltaP between the left ventricle and the aorta. Computer simulations for different pathological conditions, ranging from the normal heart to left heart asystole, and a wide range of physiological scenarios, ranging from rest to strenuous exercise, were used to validate the performance of the controller and the effectiveness of the selected control objective in ensuring physiologically adequate perfusion under different clinical and cardiac demand conditions.

附室加圧煙制御システムにおける給気量の手計算方法

While vestibule pressurization smoke control systems are now popularly used in Japan in place of the smoke extraction methods prescribed in the Building Standards Law, it cannot be said that a rational method for determining the air supply rates required for achieving the smoke control goals has been well-established. As a result, computer simulation models are usually used as the means to estimate the air supply rates. It may not be inappropriate but it causes some difficulties for ordinary designers to try this smoke control system. This paper proposes a practical design method of vestibule pressurization smoke control systems. This method comprehensively covers the fire scenarios corresponding to every stage of evacuation, namely fire room evacuation, fire floor evacuation and whole building evacuation. The required rates of air supply are determined to meet all the criteria imposed to verify the safety requirements at these three stages of evacuation. The calculation procedure in this method consists of a set of simple formulas for pressure and opening flow rates developed based on the average pressure difference concept so it can only be followed by the use of a hand calculator. This method is expected to help designers and engineers easily understand what and how to do to rationally and effectively design the smoke control system and to help building officials or whoever may concern with approval of the system know how to check its compliance.

Tidal pumping of fluids within and from the oceanic crust: new observations and opportunities for sampling the crustal hydrosphere

Seven boreholes established by the Ocean Drilling Program in sedimented ridge-crest and ridge-flank environments have been sealed to stop the exchange of formation water and seawater via the holes after drilling, and instrumented to allow long-term hydrologic monitoring. Records of seafloor and basement-fluid pressures in these holes document tidal-frequency formation-pressure variations that are attenuated and phase-shifted relative to variations at the seafloor. Spatial variations in the response to seafloor tidal loading create oscillatory pressure gradients which drive fluid flow within the crust, and tidal pressure differentials between the crust and the water column modulate flow through the seafloor. Both may have significant geochemical and biological consequences. The magnitude of the tidal pressure differential observed across sediment sections is in many instances larger than the average differential pressure created by hydrothermal buoyancy forces, and this causes the pressure difference across fluid sampling ports incorporated in the borehole seals to reverse sign periodically. This can create a problem for obtaining undiluted crustal fluid samples at the seafloor from moderately overpressured holes, but it also provides an opportunity for fluids to be pumped passively from moderately underpressured holes through the use of uni-directional valves. Potential production rates, estimated using pre- and post-seal thermal, fluid-flow, and pressure data, indicate that significant fluid fluxes can be established, of the order of 10 m 3 (typically one hole-volume) per month.

Twenty-Year Follow-up of Visual Field Defects in Primary Glaucoma Eyes

Purpose: The time course of visual field defects in patients with primary glaucoma was investigated for 20 or more years. Methods: The subjects were 51 eyes of 29 patients (open angle glaucoma, 40 eyes of 21 patients angle closure glaucoma, 11 eyes of 8 patients). The mean intraocular pressure of these subjects was within 21 mm Hg during the follow-up periods. All the eyes were monitored with Goldmann's perimetry, and the visual field was graded using Kozaki's classification. Results: At the 20-year follow-up, 68% of the open angle cases and 45% of the angle closure cases had significant progression of visual field defects. There was no significant difference in average intraocular pressure during the follow-up period between the progression group and the stable group. Conclusion: These results suggested that, in a follow-up of twenty years, visual field defects both in primary open angle glaucoma and chronic angle closure glaucoma can progress frequently, even if the intraocular pressure of these patients was well controlled.

Evidence for a Dose-Response Relationship between Occupational Noise and Blood Pressure

In this study, we investigated the role of occupational noise exposure and blood pressure among workers at 2 plants. A noise-exposed plant (plant 1, > or = 89 dBA) and a less-noise-exposed plant (plant 2, < or = 83 dBA) were chosen. Exposure was based on department-wide average noise measures; on the basis of job location and adjusting for layoffs during their employment at the plant, a cumulative time-weighted average noise level was calculated for each worker. The study population comprised 329 males in plant 1 and 314 males in plant 2. Their ages ranged from 40 to 63 y (mean ages = 49.6 and 48.7, respectively), and they had worked at least 15 y at the plant. The clinical examination was administered prior to the workday and measured height, weight, pulse, and blood pressure. In addition, we noted medical and personal-habits histories, including alcohol intake and cigarette smoking patterns. We used a questionnaire to determine in-depth occupation, military history, noisy hobbies, and family history of hypertension. When individuals who took blood-pressure medication were removed from the analysis, t tests for differences in average blood pressure between plants showed a mean systolic blood pressure of 123.3 mm Hg in plant 1 versus 120.8 mm Hg in plant 2 (p = .06) and a mean diastolic blood pressure of 80.3 mm Hg versus 77.8 mm Hg in Plant 1 and 2, respectively (p = .014). On the basis of data from the combined plants, multivariate analysis revealed that age, body mass index, cumulative noise exposure, current use of blood pressure medications, and alcohol intake were significant predictors for systolic blood pressure. Cumulative noise exposure was a significant predictor of diastolic blood pressure in plant 1 but not in plant 2, possibly reflecting a threshold effect.

Relative Permeability Analysis of Tube Bundle Models

The analytical solution for calculating two-phase immiscible flow through a bundle of parallel capillary tubes of uniform diametral probability distribution is developed and employed to calculate the relative permeabilities of both phases. Also, expressions for calculating two-phase flow through bundles of serial tubes (tubes in which the diameter varies along the direction of flow) are obtained and utilized to study relative permeability characteristics using a lognormal tube diameter distribution. The effect of viscosity ratio on conventional relative permeability was investigated and it was found to have a significant effect for both the parallel and serial tube models. General agreement was observed between trends of relative permeability ratios found in this work and those from experimental results of Singhal et al. (1976) using porous media consisting of mixtures of Teflon powder and glass beads. It was concluded that neglecting the difference between the average pressure of the non-wetting phase and the average pressure of the wetting phase (the macro-scale capillary pressure) – a necessary assumption underlying the popular analysis methods of Johnson et al. (1959) and Jones and Roszelle (1978) – was responsible for the disparity in the relative permeability curves for various viscosity ratios. The methods therefore do not account for non-local viscous effects when applied to tube bundle models. It was contended that average pressure differences between two immiscible phases can arise from either capillary interfaces (micro-scale capillary pressures) or due to disparate pressure gradients that are maintained for a flow of two fluids of viscosity ratio that is different from unity.

Difference between clinic and daytime blood pressure is not a measure of the white coat effect.

The purpose of the present study was to evaluate whether the difference between blood pressure measured in the clinic or physician's office and the average daytime blood pressure accurately reflects the blood pressure response of the patient to the physician ("white coat effect" or "white coat hypertension"). We studied 28 hypertensive outpatients (mean age, 41.8+/-11.2 years; age range, 21 to 64 years) of 35 consecutive patients attending our hypertension clinic, in whom (1) continuous noninvasive finger blood pressure was recorded before and during the visit, (2) blood pressure was measured according to the Riva-Rocci-Korotkoff method (mercury sphygmomanometer) with the patient in the supine position, and (3) daytime ambulatory blood pressure was monitored with a SpaceLabs 90207 device. The peak blood pressure increase recorded directly during the visit was compared with the difference between clinic and daytime average ambulatory blood pressures. Compared with previsit values, peak increases in finger systolic and diastolic blood pressures during the visit to the clinic were 38.2+/-3.1 and 20.7+/-1.6 mm Hg, respectively (mean+/-SEM, P<.01 for both). Daytime average systolic and diastolic blood pressures were 135.5+/-2.5 and 89.2+/-1.9 mm Hg, with both lower than the corresponding clinic blood pressure values (146.6+/-3.6 and 94.9+/-2.2 mm Hg, P<.01). These differences, however, were <30% of the peak finger blood pressure increases during the physician's visit, to which these increases showed no relation. Although the visit to the physician's office was associated with tachycardia (9.0+/-1.6 bpm, P<.01), there was no difference between clinic and daytime average heart rates. These data indicate that the clinic-daytime average blood pressure difference does not reflect the alerting reaction and the pressure response elicited by the physician's visit and thus is not a reliable measure of the white coat effect.

Patient noncompliance in the managed care setting. The case of medical therapy for glaucoma.

The authors identify demographic and clinical characteristics associated with noncompliance in patients beginning medical therapy for the treatment of glaucoma in a managed care setting. The authors describe a retrospective cohort study in a group-model health maintenance organization in Massachusetts. Patients were members of the health maintenance organization who were newly initiated on topical drug therapy to treat open-angle glaucoma during the period January 1, 1987 through December 31, 1990, who met eligibility requirements, and who had evidence of health services utilization for a 12-month follow-up period. For all study subjects, we determined the number of days without available therapy for glaucoma during the 12-month period. Study subjects who did not fill prescriptions adequate to provide medication to cover at least 80% of days during the study period were considered noncompliant. Logistic regression analysis was used to assess demographic and clinical factors independently associated with noncompliance among patients initiated on medical therapy for the treatment of glaucoma. Of 616 subjects who met inclusion criteria, 152 (24.7%; 95% confidence interval, 21.3%-28.1%) met the study definition for noncompliance. These patients had an average number of days without therapy during the 12-month study period of 103.9 +/- 70.0 days compared with 6.8 +/- 19.5 days for those categorized as compliant. Of a variety of selected demographic and clinical characteristics, having fewer visits with an ophthalmologist during the study period (< 2) was most strongly related to noncompliance (odds ratio 2.99; 95% confidence interval 2.03, 4.40). There were no differences in average intraocular pressure between the compliant and noncompliant groups during the study period. Noncompliance with prescribed medical therapy for glaucoma was found to be common in a managed care setting characterized by essentially unrestricted access to health care and medications. It remains difficult to identify noncompliant patients based on demographic and clinical characteristics. The use of automated prescription data to identify noncompliant patients is feasible in large managed health care insurance programs where such data are collected routinely for administrative purposes.

Crossflow microfiltration of shear-thinning aqueous titanium dioxide dispersions

Crossflow microfiltration experiments were performed on aqueous dispersions of rutile (titanium dioxide) through a 0.1 μm pore size ceramic membrane at various operating parameters. The initial transient flux decline follows deadend filtration theory, with the membrane resistance determined from the initial flux and the cake resistance determined from the rate of flux decline due to cake build-up. For a long time, the observed fluxes reached steady or nearly steady-state values, presumably as a result of the cake growth being arrested by the shear exerted at its surface. The steady-state fluxes increase with increasing inlet crossflow velocity and decreasing feed concentration. The steady-state permeate flux values were determined from the steady-state model based on the Kozeny-Carman equation for cake resistance and Darcy's law applied over the filter area to relate filtration rate to average pressure difference between the feed and permeate sides of the filter. The model includes a cake resistance of the cake layer, which was determined for the titanium dioxide dispersions by fitting the experimental flux data to the model. The apparent viscosity of the dispersion, which is an input parameter in the flux model, is also adjusted to account for a model of the Herschel-Bulkley type. The resulting fluxes obtained from the model using simple values for the membrane resistance, cake resistance, and rheological parameters for each data set are in good agreement with the measured fluxes.

An improved method for estimating surface humidity from daily minimum temperature

Minimum daily air temperature ( T n) is often used as a surrogate for mean daily dew point (TI,day) to estimate near-surface humidity. This method is unreliable under arid conditions where nightly minimum temperatures may remain well above the dew point. Daily meteorological data from 52 weather stations within the continental US and Alaska were evaluated. Daily differences between T d,day and T n were large in arid climates, with corresponding vapor pressure differences averaging between 0.8 and 1.2 kPa on an annual basis. Sites with semi-arid characteristics showed a large degree of seasonality in the results with average vapor pressure differences ranging from 0.1 to 0.6 kPa between winter and summer months. Sites in other climate regimes generally showed small differences between T n and T d,day over the entire year, corresponding to average vapor pressure differences of less than 0.3 kPa. An empirical model was developed to improve the accuracy of T n based humidity estimates using daily air temperature, annual precipitation and estimated daily potential evapotranspiration. The model reduced humidity estimation errors by up to 80% at semi-arid and arid sites and had minimal effects when T n based humidity estimates were relatively accurate. The ratio of annual precipitation to estimated annual evapotranspiration was useful for distinguishing sites where T n based humidity estimates were relatively accurate from sites where estimation errors were large. The results of this investigation provide a simple, more accurate method than T n for estimating humidity in arid and semi-arid regions using general weather station data.