Pressure Accumulation Research Articles

Spatial Measurements of Perfusion, Interstitial Fluid Pressure and Liposomes Accumulation in Solid Tumors.

The heterogeneous intra-tumoral accumulation of liposomes is a critical determinant of their efficacy. Both the chaotic tumor microcirculation and elevated IFP are linked to the heterogeneous intra-tumoral distribution of nanotechnology-based drug delivery systems such as liposomes. In the present study, the relationship between tumor microcirculation, elevated IFP, and accumulation of nanoparticles was investigated through in vivo experimentation. This was accomplished by evaluation of the tumor microcirculation using dynamic contrast enhanced computed tomography (DCE-CT) and measurement of tumor IFP using a novel image-guided robotic needle placement system connected to the micro-CT scanner. The intra-tumoral accumulation of liposomes was determined by CT image-based assessment of a nanoparticle liposomal formulation that stably encapsulate the contrast agent iohexol (CT-liposomes). CT imaging allowed for co-localization of the spatial distribution of tumor hemodynamics, IFP and CT-liposome accumulation in an individual subcutaneous xenograft mouse model of breast cancer. Measurements led to the discovery that perfusion and plasma volume fraction are strong mediators of the intra-tumoral distribution of liposomes. Furthermore, the results suggest that IFP plays an indirect role in mediating liposome distribution through modulating blood flow.

Evaluation of thermal spike due to exothermic reaction in curing process of carbon fiber-reinforced plastic pressure accumulators for hydrogen stations

In the curing process of fiber-reinforced plastic accumulators, a thermal spike appears due to the exothermic reaction of the resin. It is necessary to accurately evaluate this thermal spike to guarantee quality and avoid using a trial and error approach to control the temperature. Thus, we developed a curing process simulator that is able to accurately evaluate the thermal spike of the thermosetting resin. A simplified mesoscale finite element model with the definite separation of fiber and resin is used in the simulation. In this study, the newly developed simulation system was examined by comparing its results with the experimental results from the curing process of fiber-reinforced plastic accumulators.

Investigating the cyclic behaviour of clays using a kinematic hardening soil model

The stability of geotechnical structures under repeated loading depends to a large extent on the induced cyclic shearing stresses. The design of these structures usually requires engineers to employ advanced soil models in their analyses. While a number of such models do exist, their validation against cyclic laboratory tests is still very limited. In particular, the influence of the initial structure of the clay and its subsequent degradation under cyclic loading appears to be insufficiently investigated from both experimental and constitutive modelling standpoint.The work outlined in this paper adds a new contribution to the theoretical understanding of cyclic response of clayey materials, presenting the extensive validation of an advanced kinematic hardening model against laboratory data on a number of natural and compacted clays found in literature. In order to analyse in detail the evolution of shear and hysteretic soil behaviour over a wide strain range, further modelling accounting for the effects of overconsolidation ratio and structure degradation is undertaken. The modelling results of shear stiffness degradation, hysteretic dissipation and pore pressure accumulation are presented and compared with experimental data. The results show that the enhanced kinematic hardening model gives very satisfactory predictions of clay response during cyclic loading.

Role of Microvascular Tone and Extracellular Matrix Contraction in the Regulation of Interstitial Fluid

The pathophysiology of aortic dissection is poorly understood, and its risk is resistant to medical treatment. Most studies have focused on a proposed pathogenic role of transforming growth factor-β in Marfan disease and related thoracic aortic aneurysms and aortic dissections. However, clinical testing of this concept using angiotensin II type 1 receptor antagonists to block transforming growth factor-β signaling fell short of promise. Genetic mutations that predispose to thoracic aortic aneurysms and aortic dissections affect components of the extracellular matrix and proteins involved in cellular force generation. Thus, a role for dysfunctional mechanosensing in abnormal aortic wall remodeling is emerging. However, how abnormal mechanosensing leads to aortic dissection remains a mystery. Here, we review current knowledge about the regulation of interstitial fluid dynamics and myogenic tone and propose that alteration in contractile force reduces vascular tone in the microcirculation (here, aortic vasa vasorum) and leads to elevations of blood flow, transmural pressure, and fluid flux into the surrounding aortic media. Furthermore, reduced contractile force in medial smooth muscle cells coupled with alteration of structural components of the extracellular matrix limits extracellular matrix contraction, further promoting the formation of intramural edema, a critical step in the initiation of aortic dissection. The concept is supported by several pathophysiological and clinical observations. A direct implication of this concept is that drugs that lower blood pressure and limit interstitial fluid accumulation while preserving or increasing microvascular tone would limit the risk of dissection. In contrast, drugs that substantially lower microvascular tone would be ineffective or may accelerate the disease and precipitate aortic dissection.

Assessing the likelihood and magnitude of volcanic explosions based on seismic quiescence

Volcanic eruptions are generally forecast based on strong increases in monitoring parameters such as seismicity or gas emissions above a relatively low background level (e.g., Voight, 1988; Sparks, 2003). Because of this, forecasting individual explosions during an ongoing eruption, or at persistently restless volcanoes, is difficult as seismicity, gas emissions, and other indicators of unrest are already in a heightened state. Therefore, identification of short-term precursors to individual explosions at volcanoes already in heightened states of unrest, and an understanding of explosion trigger mechanisms, is important for the reduction of volcanic risk worldwide. Seismic and visual observations at Telica Volcano, Nicaragua, demonstrate that a) episodes of seismic quiescence reliably preceded explosions during an eruption in May 2011 and b) the duration of precursory quiescence and the energy released in the ensuing explosion were strongly correlated. Precursory seismic quiescence is interpreted as the result of sealing of shallow gas pathways, leading to pressure accumulation and eventual catastrophic failure of the system, culminating in an explosion. Longer periods of sealing and pressurization lead to greater energy release in the ensuing explosion. Near-real-time observations of seismic quiescence at restless or erupting volcanoes can thus be useful for both timely eruption warnings and for forecasting the energy of impending explosions.

A method to calculate the annular liquid volume of an immobile string

Immobile string technology is often used to develop the production of multi-layer and thin low-permeability gas reservoirs. This type of reservoir is characterized by low productivities and high pressure drop rates. Simplified ground facilities and control choke technologies are often adopted to effectively reduce the investment. Because gas wells in low permeability gas reservoirs often have low productivities (for instance, the individual well production rates in the Sulige Gas Field range from only 3000 m3/d to 5000 m3/d), a large number of adopted down-hole sensors will result in gas fields that are unable to run properly. The water production data and the bottom pressure become difficult to measure. The casing pressure is controlled by both reservoir pressure and liquid accumulation. To predict liquid volume correctly, the superposed effects of the reservoir pressure and liquid accumulation should be stripped as a priority. Taking the dynamic reserve, production proration and production rate into consideration, we analyzed the casing pressures of dry gas wells. In addition, we quoted a parameter (the production rate in the unit casing pressure drop) to remove the influence of reservoir pressure drop and the output fluctuation “noise” on casing pressure. To strip out the effects of liquid accumulation, we discussed the casing pressure under different liquid accumulation rates. Through the above research, we created a method to calculate the annular liquid volume of an immobile string. This method applied to the Sulige Gas Field very well, and it can also be introduced to other similar gas reservoirs.

An integrated model for pore pressure accumulations in marine sediment under combined wave and current loading

In this paper, an integrated model for the wave (current)-induced seabed response is presented. The present model consists of two parts: hydrodynamic model for wave-current interactions and poro-elastic seabed model for pore accumulations. In the wave-current model, based on the fifth-order wave theory, ocean waves were generated by adding a source function into the mass conservation equation. Then, currents were simulated through imposing a steady inlet velocity on one domain and pressure outlet on the other side. In addition, both of the Reynolds-Averaged Navier-Stokers (RANS) Equations and <TEX>$k-{\varepsilon}$</TEX> turbulence model would be applied in the fluid field. Once the wave pressures on the seabed calculated through the wave-current interaction model, it would be applied to be boundary conditions on the seabed model. In the seabed model, the poro-elastic theory would be imposed to simulate the seabed soil response. After comparing with the experimental data, the effect of currents on the seabed response would be examined by emphasize on the residual mechanisms of the pore pressure inside the soil. The build-up of the pore water pressure and the resulted liquefaction phenomenon will be fully investigated. A parametric study will also be conducted to examine the effects of waves and currents as well as soil properties on the pore pressure accumulation.

Development of an automatically deployable roll over protective structure for agricultural tractors based on hydraulic power: Prototype and first tests

An inadequate use of the deployable Roll Over Protective Structure (ROPS) in agricultural tractors contributes to fatalities in rollover events. To help to resolve this problem, an automatically deployable ROPS was designed, constructed and tested. The prototype, called HydraROPS, established two assistance levels for the elevation of the foldable ROPS. In the first level, the driver decides to change the ROPS’ position and this change is made using the manual activation on the board. In the second level, an automatic change to the operative position occurs in situations of impending rollover, without the intervention of the driver. In this level, it automatically sends a phone message with the GPS location to contact emergency response personnel. The tractor’s hydraulic power was used to move the protective structure. In order to increase the deployment speed of ROPS, a pressure accumulator was included in the hydraulic circuit. The deployment time of the ROPS without the pressure accumulator was 2.599s and with the pressure accumulator 0.743s. The results of the research show that the pressure accumulator assembled in the hydraulic circuit reduced the deployment time of ROPS by 71%; and that the electronic control system can correctly predict overturn. HydraROPS has the advantage compared to other automatic deployment devices of protective structures that can be installed on tractors equipped with a certified rollover protective structure. The installation in marketable tractor models does not modify the protection structure; therefore a new certification of the protection structure is not necessary.

Effect of permeability on the cyclic generation and dissipation of pore pressures in saturated gravel layers

A dramatic consequence of the Christchurch, New Zealand, earthquakes of 2010 and 2011 was the widespread liquefaction in the city. Part of the central business district (CBD) was badly affected by liquefaction but elsewhere large volumes of ejecta were not evident for those parts of the CBD where the upper layers in the soil profile are sandy gravel and gravelly sand. The purpose of the paper is to investigate the effect of the gravel permeability on the rise and dissipation of excess pore water pressure during cyclic loading of a soil profile idealised from Christchurch data. The Cyclic1D software, which performs one-dimensional non-linear effective stress site response analysis, was used. Permeability values associated with gravel were found to suppress the cyclic accumulation of excess pore water pressure in gravel layers. Given that there has not been any systematic measurement of the in situ permeability of the gravels in Christchurch, the modelling in the paper suggests that likely values for the bulk permeability of the gravel layers are within the range suggested in the geotechnical literature. However, the work reported is of wider application than Christchurch and emphasises the controlling influence of permeability on the accumulation and dissipation of cyclic pore pressures.

The effect of the downstream pressure accumulation on the time-lag accuracy for membranes with non-linear isotherms

The time-lag method based on downstream measurements is one of the most popular methods for gas membrane characterization. This method is commonly used to characterize all types of membranes, either glassy or rubbery, and regardless of the type of isotherm for a gas molecule/membrane system. The time-lag method has originally been derived for a linear isotherm system (Henry's relation) under the assumption of vacuum at the downstream side of the membrane. This zero-pressure assumption is obviously violated as a finite downstream volume is required to record a pressure change necessary to estimate the time lag. The objective of this investigation is therefore to critically assess the degree of validity of the downstream time-lag method under more realistic boundary conditions and for systems characterized with nonlinear isotherms such as dual-mode sorption. To achieve this objective, the mass diffusion equation was solved numerically by finite differences and numerical results were compared with known analytical solutions. This study provides a deeper understanding on the behavior of adsorption and the transport of molecules inside a membrane for the cases of linear isotherm and dual-mode sorption with complete immobilization and instantaneous equilibrium. Results clearly show that the sorption parameters have a major impact on the time required to achieve steady state as well as on the transient behavior before reaching steady state under ideal boundary conditions. Under the realistic boundary conditions, steady state can never be achieved and can only be approached due to gas accumulation in the downstream compartment. Conditions under which higher accuracy is obtained in the determination of the diffusion coefficient are discussed.

Hypertension and decreased aortic compliance due to reduced elastin amounts do not increase atherosclerotic plaque accumulation in Ldlr−/− mice

Background and aimsHigh blood pressure and reduced aortic compliance are associated with increased atherosclerotic plaque accumulation in humans. Animal studies support these associations, but additional factors, such as fragmented elastic fibers, are present in most previous animal studies. Elastin heterozygous (Eln+/−) mice have high blood pressure and reduced aortic compliance, with no evidence of elastic fiber fragmentation and represent an appropriate model to directly investigate the effects of these factors on atherosclerosis. Methods and resultsEln+/− and Eln+/+ mice were crossed with low density lipoprotein receptor knockout (Ldlr−/−) and wild-type (Ldlr+/+) mice and fed normal or Western diet (WD) for 16 weeks. We hypothesized that on WD, Eln+/−Ldlr−/− mice with high blood pressure and reduced aortic compliance would have increased atherosclerotic plaque accumulation compared to Eln+/+Ldlr−/− mice. We measured serum cholesterol and cytokine levels, blood pressure, aortic compliance, and plaque accumulation. Contrary to our hypothesis, we found that on WD, Eln+/−Ldlr−/− mice do not have increased plaque accumulation compared to Eln+/+Ldlr−/− mice. At the aortic root, there are no significant differences in plaque area between Eln+/−Ldlr−/− and Eln+/+Ldlr−/− mice on WD (p = 0.89), while in the ascending aorta, Eln+/−Ldlr−/− mice on WD have 29% less normalized plaque area than Eln+/+Ldlr−/− mice on WD (p = 0.009). ConclusionUsing an atherogenic mouse model, we conclude that increased blood pressure and reduced aortic compliance are not direct causes of increased aortic plaque accumulation. We propose that additional insults, such as fragmentation of elastic fibers, are necessary to alter plaque accumulation.

Degradation of soft subgrade soil from slow, large, cyclic heavy-haul road loads: a review

Extraction of resources in remote locations can require temporary haul roads to transport extremely large, slow-moving, indivisible loads (e.g., plant, oil–gas production modules, and reactors, weighing in excess of 1000 t) without interruptions. Poor subgrade soils may experience larger cyclic strains and greater cyclic degradation under these conditions than under conventional roads, yet the short engineering life precludes many foundation-strengthening options due to cost. As there is little research into this unique situation, this paper synthesizes research from a broad range of applications to discuss implications on expected soil response. Reference is made to critical state theory and discrete element method (DEM) modelling to develop fundamental concepts considering particle-scale interactions. Cyclic failure is proposed to be a kinematically unstable process, triggered by shear banding on the Hvorslev surface, tensile liquefaction or fabric-governed meta-stable liquefaction; the latter is particularly influenced by stress history and anisotropy. This paper finds pore-water pressure accumulation under load and dissipation between loads are key to cyclic degradation and furthermore to be dependent upon load duration, principal stress rotation, and repetition frequency. For meta-stable, liquefiable soils in particular, inclination of principal stresses is at least as important in assessing failure risk as magnitude of stresses.

Numerical modelling of transient cyclic vertical loading of suction caissons in sand

This paper presents numerical investigations of the monotonic and cyclic behaviours of suction caissons upon vertical transient loading. Both drained and partially drained conditions are investigated. Monotonic compression and traction simulations are carried out to qualitatively compare results with the literature and validate the model. They highlight the different modes of reaction of the caisson to both compression and traction loading. A sensitivity analysis points out the strong influence of some parameters on the resistance of the caisson but also on the failure mechanism. The transient behaviour of the caisson upon different kinds of cyclic load signals is analysed. Results reproduce the settlement and pore water pressure accumulations observed during experiments. The influence of the key design parameters on the settlement accumulation is also assessed. Finally a cyclic diagram is proposed to describe the evolution of the final settlement upon different magnitudes of loading.

Numerical Modeling of Cyclone Machine for Cleaning Gas Generator Gases

Analysis of contemporary cyclone gas purification apparatus was carried out in this article Calculation of the characteristics of the counterflow cyclone in application of pressurization system of the LV fuel tanks with gas pressure accumulator has been executed. 3D-model of the counter-flow cyclone was built. Numerical modeling of soot-cleaning process in countercurrent cyclone has been performed using ANSYS Fluent.

Laboratory investigation of liquefaction mitigation in silty sand using nanoparticles

Nanomaterials are presented in this paper as a novel method of liquefaction mitigation that overcomes the limitations of traditional mitigation methods. The proposed method is different from traditional densification and chemical grouting methods: no ground disturbance occurs and an entire site can be treated. In this study, laponite, synthetic silicate nanoparticles that are nontoxic, pure, highly plastic, and smaller in size than natural clay particles, has been selected as a representative nanomaterial that can be used in conjunction with liquefiable silty sand. Little research has been undertaken on the mixing of such materials. The cyclic behavior and liquefaction resistance of mixtures of laponite and silty sand have been studied by means of dynamic triaxial tests. The pore pressure accumulation process and deformation properties are compared between pure silty sand and laponite–silty sand samples to verify the effect of laponite on the liquefaction mitigation of the silty sand. Additionally, the viscosity of laponite suspensions is measured to determine the appropriate gel time for curing the laponite–silty sand samples. Microstructural imaging with a scanning electron microscope is analyzed in conjunction with liquefaction mitigation mechanisms. Then the effects of laponite concentration and curing time on the liquefaction resistance of the treated samples are discussed. This work provides experimental data to support the beneficial effects of laponite mixing on the reduction of liquefaction susceptibility in saturated silty sand. It also assesses the mechanisms and effects of nanoparticles on liquefaction potential.

Experimental studies on natural convection of water in a closed-loop vertical annulus

Experimental studies on heat transfer and fluid flow of water in a vertical annulus, circulating through a cold leg forming a closed loop thermo-siphon, have been carried out in this article. The annulus has a radius ratio (outer radius to inner radius) of 1.184 and aspect ratio (length to annular gap) equal to 352. The experiments were conducted for constant heat fluxes of 1, 2.5, 5, 7.5, 10, 12.5, and 15 kW/m2. Transient behavior during the heat-up period of the system until the steady-state condition is attained and discussed. Variation in the heat transfer coefficient and Nusselt number along the annulus height represent the developing boundary layer at the entrance and fully developed flow in the remaining length. A large drop in the differential pressure is experienced when the liquid is circulated through the flow meters, which restrict the flow due to their very small passages. Flow restriction causes mass accumulation and rise of pressure at the exit of the annulus. It also causes a decrease in liquid head in the cooling leg. An increase in the heat flux leads to an increase in the heat transfer coefficient and Nusselt number. As a result of the data analysis correlations for the average Nusselt number, Reynolds number and circulation rate have been developed in terms of the heat flux.

Influence of relative permeability on injection pressure and plume configuration during CO2 injections in a mafic reservoir

Carbon capture and sequestration projects have traditionally targeted deep sedimentary basins; however, mafic reservoirs may also be attractive targets for CO2 disposal on the basis of permanent mineral trapping over relatively short time scales (101 to 102yr). Nevertheless, CCS development in mafic reservoirs is hampered by substantial uncertainty in fracture-controlled reservoir characteristics, particularly with respect to the effects of multi-phase fluid flow, e.g., relative permeability and capillary pressure. The present study quantifies uncertainty surrounding relative permeability effects in a basalt reservoir by developing a numerical modeling experiment on the basis of site characterization data from the Slack Canyon #2 flow top, which is one of three flow tops comprising the injection zone at the Wallula Basalt Sequestration Pilot Project in southeast Washington State. This numerical modeling experiment controls for the effects of curvature in the relative permeability models by performing an ensemble of 399 CO2 injection simulations with constant geometry and reservoir properties, while systematically varying the phase interference parameter (λ) and residual CO2 saturation (Sgr), which govern wetting and non-wetting phase relative permeability, respectively. The relative permeability parameter space is defined by selecting combinations of λ and Sgr that cover a wide range of experimental laboratory measurements. For each simulation, CO2 is injected into the reservoir for 10 years at a constant rate of 2.78kgs−1 (87,856metrictons(MT)yr−1), which is 10% of the annual injection rate proposed for one injection scenario at the Wallula Site. Results from the ensemble of simulations show that relative permeability alone can account for >50MPa of variability in the injection pressure and a two-fold difference in lateral CO2 plume migration. Additionally, this work shows that curvature in the wetting phase relative permeability model is the stronger influence on reservoir pressure accumulation, while curvature in the non-wetting phase relative permeability model strongly governs CO2 plume geometry.

Calcific tendinitis of the rotator cuff.

Calcific tendinitis within the rotator cuff tendon is a common shoulder disorder that should be differentiated from dystrophic calcification as the pathogenesis and natural history of both is totally different. Calcific tendinitis usually occurs in the fifth and sixth decades of life among sedentary workers. It is classified into formative and resorptive phases. The chronic formative phase results from transient hypoxia that is commonly associated with repeated microtrauma causing calcium deposition into the matrix vesicles within the chondrocytes forming bone foci that later coalesce. This phase may extend from 1 to 6 years, and is usually asymptomatic. The resorptive phase extends from 3 wk up to 6 mo with vascularization at the periphery of the calcium deposits causing macrophage and mononuclear giant cell infiltration, together with fibroblast formation leading to an aggressive inflammatory reaction with inflammatory cell accumulation, excessive edema and rise of the intra-tendineous pressure. This results in a severely painful shoulder. Radiological investigations confirm the diagnosis and suggest the phase of the condition and are used to follow its progression. Although routine conventional X-ray allows detection of the deposits, magnetic resonance imaging studies allow better evaluation of any coexisting pathology. Various methods of treatment have been suggested. The appropriate method should be individualized for each patient. Conservative treatment includes pain killers and physiotherapy, or "minimally invasive" techniques as needling or puncture and aspiration. It is almost always successful since the natural history of the condition ends with resorption of the deposits and complete relief of pain. Due to the intolerable pain of the acute and severely painful resorptive stage, the patient often demands any sort of operative intervention. In such case arthroscopic removal is the best option as complete removal of the deposits is unnecessary.

Numerical Investigations on Track-substructure System Considering the Effect of Different Train Speeds

Quasi-static and dynamic loads from train-traffic are applied to the entire track system: super-structure, substructure and subsoil. Due to lack of maintenance of the track bed, the dynamic loads on the track system causes an accumulation of excess pore water pressure within the sub-structure. Furthermore, a pumping effect exerted on the track system, which depends on the axle load and velocity of the vehicle, may cause in mud hole formation, rising of the underlying soil, ballast contamination and the clogging of gravel bed pores. Consequently, the subgrade resistance is reduced and hence the system loading capacity. The main objective is to detect mud holes as early as possible by non-invasive, non-destructive measurements to avoid costly interim or long term treatments. The present publication focuses on the comparison of vertical velocities due to a moving train load in the absence of water, thus eliminating any complexities arising from any variation in the pore pressure. Due to the large velocity of the trains, elastic and plastic deformations might develop in the vicinity of the track-subgrade system. In the current publication, a simplified numerical simulation of one axle of an ICE train traversing along the rail track with various speeds have been simulated.

Precise epileptogenic zone location with stereotactic electroencephalography navigated by ROSA in patients with focal cortical dyplasia in children

High blood pressure and reduced aortic compliance are associated with increased atherosclerotic plaque accumulation in humans. Animal studies support these associations, but additional factors, such as fragmented elastic fibers, are present in most previous animal studies. Elastin heterozygous (Eln+/−) mice have high blood pressure and reduced aortic compliance, with no evidence of elastic fiber fragmentation and represent an appropriate model to directly investigate the effects of these factors on atherosclerosis.Eln+/− and Eln+/+ mice were crossed with low density lipoprotein receptor knockout (Ldlr−/−) and wild-type (Ldlr+/+) mice and fed normal or Western diet (WD) for 16 weeks. We hypothesized that on WD, Eln+/−Ldlr−/− mice with high blood pressure and reduced aortic compliance would have increased atherosclerotic plaque accumulation compared to Eln+/+Ldlr−/− mice. We measured serum cholesterol and cytokine levels, blood pressure, aortic compliance, and plaque accumulation. Contrary to our hypothesis, we found that on WD, Eln+/−Ldlr−/− mice do not have increased plaque accumulation compared to Eln+/+Ldlr−/− mice. At the aortic root, there are no significant differences in plaque area between Eln+/−Ldlr−/− and Eln+/+Ldlr−/− mice on WD (p = 0.89), while in the ascending aorta, Eln+/−Ldlr−/− mice on WD have 29% less normalized plaque area than Eln+/+Ldlr−/− mice on WD (p = 0.009).Using an atherogenic mouse model, we conclude that increased blood pressure and reduced aortic compliance are not direct causes of increased aortic plaque accumulation. We propose that additional insults, such as fragmentation of elastic fibers, are necessary to alter plaque accumulation.