Combined High Pressure Research Articles

Investigation of the orifice flow of over-the-rotor liner and its interaction with the rotor flow field

The emergence of ultra-high bypass ratio engines calls for advanced noise control technology. A promising technology is installing the acoustic liner at the casing over the rotor (OTR), forming the so-called OTR liner. Experiments have shown that this treatment could compensate for the reduced noise absorption due to the shortened intake length. Compared with the conventional liner receiving a pure acoustic pressure excitation, the OTR liner is exposed to the combined aerodynamic pressure perturbance and high acoustic pressure excitation, leading to complex flow mechanisms in the liner orifices. In this work, the large-eddy simulation method is used to investigate the flow phenomenon of OTR liner where each liner orifice is explicitly modeled to capture the flow behaviors at the blade tip proximity. Interesting findings are as follows: first, OTR liner orifices have an asynchronous dynamic response with a phase lag corresponding to the blade traversing speed; second, oscillating flow, resembling that in a classical Helmholtz resonator, is formed in the upstream liner orifices, while a bias flow appears in the downstream liner orifices. The dramatically different flow behaviors lead to non-uniform energy dissipation among orifices, implying the uniform impedance assumption in conventional acoustic liner definition fails when installing the liner near the rotor blade. Results also show that the orifice flow interacts with the blade tip leakage flow, affecting the development of the tip leakage vortex that may impact the rotor–stator interaction noise.

Inactivation of Saccharomyces cerevisiae by combined high pressure carbon dioxide and high pressure homogenization

A combined treatment of high pressure carbon dioxide (HPCD) and high pressure homogenization (HPH) was investigated to inactivate Saccharomyces cerevisiae in a phosphate buffered solution. The inactivation kinetics, protein leakage, particle size distribution, SEM images, and TEM images of Saccharomyces cerevisiae exposed to HPH alone, HPCD alone, and the combined treatment of HPCD and HPH (HPCD+HPH) were studied. Results showed that HPCD+HPH was superior to HPH alone and HPCD alone in the inactivation of Saccharomyces cerevisiae. The inactivation kinetics of the combined treatment exhibited a fast-slow biphasic curve. The synergic bactericidal ability of HPCD+HPH could be attributed to the enhancing effect of HPH on CO2 germicidal capability. The possibility of the combination of HPH and HPCD for microbial inactivation of Saccharomyces cerevisiae was validated, and the combined treatment has the potential to be a viable approach for microbial inactivation.

Combining high pressure homogenization with free nitrous acid pretreatment to improve anaerobic digestion of sewage sludge.

Single pretreatment of sewage sludge, either physical, chemical or biological, has its own drawbacks in term of poor sanitization, energy intensity and high operational and capital cost. To tackle these drawbacks, combined high pressure homogenization (HPH) and free nitrous acid (FNA) pretreatment for sludge solubilization and further biodegradation in anaerobic digestion was investigated. Synergistic effect of combined HPH (40MPa) and FNA (2.49mg/L) pretreatment (HPH-FNA) for improving anaerobic digestion was evaluated, and its effect on archaeal and bacterial community structure was analyzed. Compared with single HPH and FNA pretreatments, HPH-FNA pretreatment efficiently solubilized wasted activated sludge (WAS), subsequently improved anaerobic digestion. Cumulative biogas production from sewage sludge pretreated with HPH-FNA was 154%, 108% and 284% more than that with single pretreatment of FNA, HPH and raw sludge, respectively. In addition, volumetric biogas production of combined pretreatment system (815ml) was more than the sum from single pretreatment (710ml). Methane content in biogas for raw sludge, FNA, HPH and HPH-FNA pretreated sludge was 45%, 51%, 55% and 65%, respectively. Illumina MiSeq sequencing analysis revealed that HPH-FNA pretreatment promoted bacterial growth of phyla Bacteroidetes, Firmicutes and Synergistetes and archaeal genera Methanospirillum and Methanosaeta. Overall, combined HPH-FNA pretreatment of sewage sludge, prior to anaerobic digestion, is an environmentally-friendly and potentially economic technology.

Usefulness of low tidal volume ventilation strategy for patients with acute respiratory distress syndrome: a systematic review and meta-analysis

The effects of lower tidal volume ventilation (LTV) were controversial for patients with acute respiratory distress syndrome (ARDS). This systematic review and meta-analysis aimed to evaluate the use of LTV strategy in patients with ARDS. We performed a literature search on MEDLINE, CENTRAL, EMBASE, CINAHL, “Igaku-Chuo-Zasshi”, clinical trial registration sites, and the reference of recent guidelines. We included randomized controlled trials (RCTs) to compare the LTV strategy with the higher tidal volume ventilation (HTV) strategy in patients with ARDS. Two authors independently evaluated the eligibility of studies and extracted the data. The primary outcomes were 28-day mortality. We used the GRADE methodology to assess the certainty of evidence. Among the 19,864 records screened, 13 RCTs that recruited 1874 patients were included in our meta-analysis. When comparing LTV (4–8 ml/kg) versus HTV (> 8 ml/kg), the pooled risk ratio for 28-day mortality was 0.79 (11 studies, 95% confidence interval [CI] 0.66–0.94, I2 = 43%, n = 1795, moderate certainty of evidence). Subgroup-analysis by combined high positive end-expiratory pressure with LTV showed interaction (P = 0.01). Our study indicated that ventilation with LTV was associated with reduced risk of mortality in patients with ARDS when compared with HTV.Trial registration: UMIN-CTR (UMIN000041071).

Effects of combined high pressure and temperature on solubility, foaming, and rheological properties of soy 11S globulin

AbstractThis study examines the effects of combined high pressure (0.1, 200, and 400 MPa) and temperature (25 and 50°C) on the solubility, aggregation, conformation, foaming, emulsifying capacity, and rheological properties of soy 11S globulin. The foaming stability, particle size, free sulfhydryl groups content, emulsifying activity, emulsifying stability, and shear stress of soy 11S globulin were decreased significantly (p ≤ .05) compared with that of 0.1 MPa‐treated sample, but the solubility, surface hydrophobicity, foaming capacity, and apparent viscosity were increased significantly (p ≤ .05), except the sample treated at 400 MPa and 50 ± 2°C. The solubility, surface hydrophobicity and free sulfhydryl groups content of soy 11S globulin decreased significantly (p ≤ .05) with increasing pressure and temperature, which caused the decrease of the foaming capacity, emulsifying activity, emulsifying stability, shear stress, and apparent viscosity. Overall, the use of high‐pressure and thermal treatments combined could change the foaming, emulsifying, and rheological properties of soy 11S globulin through the increase/decrease of protein solubility, aggregation, surface hydrophobicity, and free sulfhydryl groups content.Practical applicationsThis study provides a method of high‐pressure and thermal treatments combined, which can change the solubility, foaming, and rheological properties soy 11S globulin, and its use should be expanded in food processing.

Immuno-Electron and Confocal Laser Scanning Microscopy of the Glycocalyx.

Simple SummaryThe glycocalyx (GCX) is a hydrated, gel-like layer of biological macromolecules attached to the cell membrane. The GCX acts as a barrier and regulates the entry of external substances into the cell. The function of the GCX is highly dependent on its structure and composition. Pathogenic factors can affect the protective structure of the GCX. We know very little about the three-dimensional organization of the GXC. The tiny and delicate structures of the GCX are difficult to study by microscopic techniques. In this study, we evaluated a method to preserve and label sensitive GCX components with antibodies for high-resolution microscopy analysis. High-resolution microscopy is a powerful tool because it allows visualization of ultra-small components and biological interactions. Our method can be used as a tool to better understand the role of the GCX during the development and progression of diseases, such as viral infections, tumor invasion, and the development of atherosclerosis.The glycocalyx (GCX), a pericellular carbohydrate rich hydrogel, forms a selective barrier that shields the cellular membrane, provides mechanical support, and regulates the transport and diffusion of molecules. The GCX is a fragile structure, making it difficult to study by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). Sample preparation by conventional chemical fixation destroys the GCX, giving a false impression of its organization. An additional challenge is to process the GCX in a way that preserves its morphology and enhanced antigenicity to study its cell-specific composition. The aim of this study was to provide a protocol to preserve both antigen accessibility and the unique morphology of the GCX. We established a combined high pressure freezing (HPF), osmium-free freeze substitution (FS), rehydration, and pre-embedding immunogold labeling method for TEM. Our results showed specific immunogold labeling of GCX components expressed in human monocytic THP-1 cells, hyaluronic acid receptor (CD44) and chondroitin sulfate (CS), and maintained a well-preserved GCX morphology. We adapted the protocol for antigen localization by CLSM and confirmed the specific distribution pattern of GCX components. The presented combination of HPF, FS, rehydration, and immunolabeling for both TEM and CLSM offers the possibility for analyzing the morphology and composition of the unique GCX structure.

Effects of combined high hydrostatic pressure and pH-shifting pretreatment on the structure and emulsifying properties of soy protein isolates

The effects of high hydrostatic pressure (HHP) combined with pH-shifting treatment, on the structural and emulsifying properties of soy protein isolate (SPI) were investigated. SPI was subject to different pH solutions (pH 7, pH 3, and pH 11) with pressure levels ranging from 0.1 MPa to 400 MPa before being neutralized to pH 7. The combination of HHP and the pH-shifting process increased the protein solubility and the surface charge of the protein molecule, and induced the formation of smaller re-aggregated protein particles. Structural changes were characterized by free sulfhydryl groups, surface hydrophobicity, ultraviolet–visible spectroscopy, and circular dichroism spectra. Emulsions fabricated with SPI treated by the combined treatment were characterized by mean droplet size, zeta potential, emulsifying activity, emulsifying stability, and fluorescence microstructure. The results suggested that the increasing pressure enhanced the effect of pH shifting, and the protein structure could be significantly unfolded by the synergistic effect of HHP and pH-shifting, further improving the emulsifying performance of SPI. • Structural changes of soy protein isolate were induced by high pressure and pH shifting. • Enhanced unfolding in pH shifted SPI were observed after pressurization. • High pressure aided pH shifting improved the emulsifying properties of SPI.

Effect of combined pulsed electric energy and high pressure homogenization on selective and energy efficient extraction of bio-molecules from microalga Parachlorella kessleri

This work investigates the potential of pulsed electric energy (pulsed electric fields (PEF) and high-voltage electrical discharges (HVED)) and high pressure homogenization (HPH) for extraction of bio-molecules from Parachlorealla kessleri. The applied procedures included individual pulsed electric energy (PEF, HVED), HPH treatments, and their combination. The cell concentrations of suspension applied in PEF or HVED treatment were 5–25 g/L, while 5 g/L suspension was always applied for HPH treatment. The effects of applied procedures on the extraction of ionic components, carbohydrates, proteins, and pigments were evaluated. The data evidenced that HVED treatment allowed selective extraction of ionic components and carbohydrates, while HPH treatment was most efficient for simultaneous release all the bio-molecules. HPH treatment (120 MPa, 10 passes) gave 4-fold higher content for pigments, 1.2-fold higher content for carbohydrates and 6.5-fold higher content for proteins than HVED treatment (40 kV/cm, 8 ms). For combined procedure, application of preliminary PEF or HVED treatment with 5 g/L suspension allowed increasing the extraction of carbohydrates at high energy consumption. By contrast, application of preliminary HVED treatment with 15 g/L or 25 g/L suspensions allowed enhancing extraction efficiencies of carbohydrates and proteins, and reducing total energy consumption.

Combined high pressure and heat treatment effectively disintegrates spore membranes and inactivates Alicyclobacillus acidoterrestris spores in acidic fruit juice beverage

The commercial potential of high pressure and thermal processing (HPTP) was investigated against Alicyclobacillus acidoterrestris spores in commercial acidic apple juice beverage and in acidified and neutral potassium buffers. With starting spore counts prior to treatments being 6.5 and 7.2 log10 respectively for strains AJA 66 (D90°C 15.4 min) and ATCC 49025 (D90°C 8.5 min), HPTP at 600 MPa at 80 °C for 3 min provided an optimal treatment with spore viability reduced below the detection limit for both strains. HPTP at 80 °C for 1 min and HPTP at 70 °C for 3 min achieved 4.1–4.5 log10 CFU/mL reduction. HPTP at 70 °C for 1 min reduced the number of viable spores by 2.0–2.5-log10 CFU/mL. Flow cytometry revealed the presence of membrane-compromised spores among culturable spores following HPTP and heat alone treatments at different temperatures. Electron microscopy clearly showed the efficiency of HPTP with crushed or hollow spores predominating after treatments. No correlation between HPTP susceptibility and genetic diversity was observed for two genotypes of A. acidoterrestris spores. The treatment combination provides a promising option for industrial utility since it requires lower heat and processing time.

Destabilization of hidden order in URu2Si2 under magnetic field and pressure

The mystery of the hidden-order phase in the correlated electron paramagnet URu2Si2 is still unsolved. To address this problem, one strategy is to search for clues in the subtle competition between this state and neighbouring magnetically ordered states. It is now well established that long-range antiferromagnetic order can be stabilized in this metal when it is under pressure and that a spin-density wave manifests when a magnetic field is applied along the easy magnetic axis c. However, the full boundaries of the hidden-order phase in the pressure–magnetic-field plane have not been determined so far. Here we present a systematic investigation of URu2Si2 under combined high pressures and intense magnetic fields. The boundaries of the hidden-order, antiferromagnetic and spin-density-wave phases are mapped out, indicating an intricate three-dimensional phase diagram. We show that the field-induced spin-density-wave and hidden-order phases disappear in favour of antiferromagnetism at high pressure. Interestingly, a large number of phase boundaries are controlled by the field and pressure dependences of a single parameter. This gives new constraints for theories that model the electronic correlations and ordered phases in URu2Si2. The nature of the hidden order in URu2Si2 is still unknown. Here detailed measurements of the phase diagram of this material produce constraints for theories that aim to describe that phase.

Outcomes and potential mechanism of a protocol to optimize foot orthoses in patients with rheumatoid arthritis

BackgroundFoot problems are highly prevalent in patients with rheumatoid arthritis. Treatment of foot problems related to rheumatoid arthritis often consists of custom made foot orthoses. One of the assumed working mechanisms of foot orthoses is redistribution of plantar pressure by creating a larger weight bearing area. Overall, the reported treatment effect of foot orthoses on foot pain in rheumatoid arthritis is small to medium. Therefore, we developed a foot orthoses optimization protocol for evaluation and adaptation of foot orthoses by using the feedback of in-shoe plantar pressure measurements. The objectives of the present study were: 1) to evaluate the 3-months outcomes of foot orthoses developed according to the protocol on pain, physical functioning and forefoot plantar pressure in patients with foot problems related to rheumatoid arthritis, and 2) to determine the relationship between change in forefoot plantar pressure and change in pain and physical functioning.MethodsForty-five patients with foot problems related to rheumatoid arthritis were included and received foot orthoses developed according to the protocol. Outcome measures were assessed at baseline and after three months of wearing foot orthoses in 38 patients. Change scores and effect sizes (ES) were calculated for pain, physical functioning and plantar pressure. In a subgroup of patients with combined forefoot pain and high plantar pressure, the relationship between change in plantar pressure and change in pain and physical functioning was analyzed.ResultsIn the total group of 38 patients, statistically significant changes in pain (ES 0.69), physical functioning (ES 0.82) and forefoot plantar pressure (ES 0.35) were found. In the subgroup (n = 23) no statistically significant relationships were found between change in plantar pressure and change in pain or physical functioning.ConclusionFoot orthoses developed according to a protocol for improving the plantar pressure redistribution properties lead to medium to large improvements in pain and physical functioning. The hypothesis that more pressure reduction would lead to better clinical outcomes could not be proven.

Design and parametric study of macro-structure of foams for combined high absorption and low pressure drop

Porous materials with high flow-resistivity could provide significant sound absorption. However, the pressure drop across such materials may be unacceptable for applications involving mean flow, such as in heat sinks. The goal of this study is to design a foam macro-structure that minimizes pressure drop while retaining optimal acoustic performance. Corrugated macro-geometries have been studied previously for heat sinking applications with a focus on increasing heat transfer coefficient and reducing pumping power. In this study, a corrugated macro-geometry is proposed as a potential shape for flow-acoustic applications. Foam macro-structures are fabricated in the proposed corrugated shape and compared against the well-known wedge and block shapes for combined flow-acoustic performance. Both stochastic and periodic foams are used for this study. The acoustic performance of these foam samples is characterized by measuring the absorption coefficient and transmission loss. The flow performance is characterized by measuring the pressure drop across these foam samples using a custom-designed flow resistivity setup. Numerical studies are also performed to predict the transmission loss, absorption coefficient, and pressure drop. The experimental results are in close agreement with numerical predictions. Evaluation of the tested foam samples by combined flow-acoustic indices reveal that corrugated macro-geometry is significantly better for acoustic absorption in applications involving mean flow. Furthermore, a parametric study is performed on the geometrical attributes of the corrugated macro-structure, which gives a guideline to design an optimal geometry.

Decompression-Induced Diamond Formation from Graphite Sheared under Pressure.

Graphite is known to transform into diamond under dynamic compression or under combined high pressure and high temperature, either by a concerted mechanism or by a nucleation mechanism. However, these mechanisms fail to explain the recently reported discovery of diamond formation during ambient temperature compression combined with shear stress. Here we report a new transition pathway for graphite to diamond under compression combined with shear, based on results from both theoretical simulations and advanced experiments. In contrast to the known model for thermally activated diamond formation under pressure, the shear-induced diamond formation takes place during the decompression process via structural transitions. At a high pressure with large shear, graphite transforms into ultrastrong sp^{3} phases whose structures depend on the degree of shear stress. These metastable sp^{3} phases transform into either diamond or graphite upon decompression. Our results explain several recent experimental observations of low-temperature diamond formation. They also emphasize the importance of shear stress for diamond formation, providing new insight into the graphite-diamond transformation mechanism.

Understanding Olive Oil Stability Using Filtration and High Hydrostatic Pressure.

Veiled extra virgin olive oil (VEVOO) is very attractive on the global market. A study was performed to highlight the role of different amounts of water and microorganisms on the evolution of VEVOO quality during storage, using the selective effects of the application of individual or combined filtration and high hydrostatic pressure (HHP) treatments. Four oil processing trials were carried out in four replicates, resulting in a full factorial design with two independent fixed factors: filtration and HPP treatments. The turbidity of all the olive oil samples was characterized. Furthermore, all the olive oil samples were analysed for legal parameters, volatile organic compounds and phenolic compounds during the storage tests. The microbial contamination in the presence of a high level of water activity (>0.6 Aw) was related to the formation of volatile aroma compounds, which were responsible for the “fusty” sensory defect. Furthermore, high water activity values were related to an increase in the hydrolytic degradation rate of the phenolic compounds. The oil turbidity has to be planned and controlled, starting from adjustment of the water content and application of good manufacturing practices.

Effects of high pressure in combination with the type of aging on the eating quality and biochemical changes in pork loin

This study investigated the effects of high pressure (0.1, 150 and 400 MPa) and the aging method (wet- and dry-aging) on the quality characteristics of pork loin. Pork pressurized at the target pressure levels was aged at 1 °C for 3 weeks in vacuum packaging (wet-aging) or a moisture/vapor permeable bag (dry-aging). The water binding properties, shear force, color, volatile compounds and microbial counts were estimated as the quality characteristics of aged pork. Despite dry-aged pork having distinctive flavor characteristics, high moisture loss during aging was estimated as the most important factor that affected the quality of aged pork. Alternately, wet aging showed advantages of producing tender and juicy pork, and moderate pressurization (150 MPa) modified or improved the qualities of wet-aged pork. Consequently, this study indicated that pressurization followed by wet-aging had potential application as a meat tenderizing technique.

High-risk Fontan completion patients achieve low perioperative risk and benefit from cavopulmonary connection 7 years out†.

Our unit has pursued Fontan completion in all patients except those with immobility or combined poor ventricular function and high pulmonary artery pressures. We assessed retrospectively whether conventional high-risk criteria would predict patients with a poorer outcome. One hundred and thirty-three consecutive children who underwent extracardiac Fontan completion (2004-2012) had their outcomes recorded (mean follow-up of 7 years). Three groups were analysed: those with 1 of 6 historical risk factors (outside 6 commandments), those with 1 of reduced systemic ventricular function or pulmonary artery pressure >15 mmHg (outside 2 commandments) versus those with no contraindications. The Fischer's exact test examined frequency differences, with the χ2 test to look for outcome associations. There were no differences in postoperative complication rates between the outside 6 commandments (n = 105) or outside 2 commandments (n = 49) versus the low-risk no-contraindication group (n = 28): arrhythmias [18% (P = 0.3) or 18% (P = 0.3) vs 25%], infection [22% (P = 0.6) or 33% (P = 0.2) vs 21%], cerebrovascular accident [6% (P = 0.5) or 10% (P = 0.3) vs 4%], length of stay [20 days (P = 0.4) or 23 days (P = 0.2) vs 21 days] and duration of chest drainage (P = 0.5). There was 1 predischarge mortality in each group. Long term, the majority of patients in each group had suitable haemodynamics for fenestration closure [95% (P = 0.7) or 95% (P = 0.7) vs 92%]. Long term, there was no difference in the rate of arrhythmias [11% (P = 0.5) or 12.5% (P = 0.3) vs 7%], protein-losing enteropathy [1% (P = 0.1) or 2% (P = 0.3) vs 7%] or moderate or more ventricular dysfunction on echocardiography [2% (P = 0.7) or 4% (P = 0.7) vs 4%]. Notably, there was a higher rate of catheter reinterventions in the high-risk groups [22% (P < 0.05) or 24% (P < 0.05) vs 7%]. The medium-term benefits of Fontan completion can be achieved for high-risk patients, suggesting that historical selection criteria should be re-examined.

Effects of combined high pressure and enzymatic treatments on physicochemical and antioxidant properties of peanut proteins.

Isolated peanut protein (PPI) dispersions were pretreated by high pressure at 100, 300, and 500 MPa prior to enzymatic hydrolysis with alkaline protease (Alcalase). The degree of hydrolysis (DH) was determined by the pH‐stat method, the hydrolysates profiles were analyzed by high‐performance liquid chromatography (HPLC), the molecular weight distribution (MWD) was analyzed by gel filtration chromatogram (GFC), and content of SH/S‐S and antioxidant activity of hydrolysates were evaluated. Results showed that HP pretreatment improved effectively the enzymatic hydrolysis of PPI, with an effective sequence of 300 > 100 > 500 MPa. However, no significant differences were observed in the peak pattern of HPLC profiles, but the peak times were earlier in HPLC profiles of the HP‐treated protein. GFC analysis showed that more peptide fractions with low molecular weight appeared in the hydrolysates of the HP‐treated PPI with increasing pressure. Moreover, the level of free SH of hydrolysates of the HP‐treated PPI was relatively higher than non‐HP‐treated PPI. The hydrolysates of the HP‐treated PPI exerted higher antioxidant activity (reducing power and DPPH radical scavenging) than the hydrolysates of non‐HP‐treated PPI. The results indicated that high pressure treatment affected the enzymatic hydrolysis of peanut protein and some protein structure properties and improved antioxidant activity of PPI hydrolysates.

Tuning of the magnetic properties of Hf2Co11B alloys through a combined high pressure torsion and annealing treatment

The evolution of crystalline structure induced by heat treatment and high pressure torsion (HPT) deformation and its influence on the magnetic properties of amorphous and partially crystalline Hf2Co11B ribbons were investigated. Slight improvement in thermal stability of the as-quenched sample after deformation was observed as indicated by the shift of the first crystallization peak from 592 to 598 °C. Plastic deformation of the initially annealed partially crystalline alloy led to its amorphization, as confirmed by X-ray diffraction (XRD). However, the presence of small volume fraction of needle-like nanocrystals was indicated by transmission electron microscopy (TEM). The annealed sample subjected to high pressure torsion was characterized by the reduced coercive field, from 0.7 to 0.2 kOe, while the subsequent reannealing of the deformed sample enhanced the coercivity up to 1.3 kOe. Transmission electron microscopy analysis revealed the existence of nanocrystals with large lattice constant of 8 Å characteristic of Hf2Co11 phase. Magnetic measurements also confirmed that some nanocrystals of the hard magnetic phase were present in the sample after deformation, indicating their importance for maximization of coercivity. The isolation of this quite elusive phase is clearly linked to magnetic performance and the method combining severe plastic deformation (SPD) and heat treatment was found to allow tuning of the structure and improving the hard magnetic properties.

Comprehensive characterization of pore and throat system for tight sandstone reservoirs and associated permeability determination method using SEM, rate-controlled mercury and high pressure mercury

Unconventional resource formations like tight sandstone reservoirs have complex pore and throat structure that are hard to characterize in micro scale. In this research, the pore and throat system of tight sandstones was characterized comprehensively, analysed qualitatively using scanning electron microscopy (SEM) techniques and quantitatively through combined high pressure mercury (HPM) and rate-controlled mercury (RCM) methods. First, the throat, distinguished from the pore, was divided in several types for tight sandstones and visualized through SEM imaging. Then, an integrated approach was proposed to combine the results from both HPM and RCM measurements, resulting in overall size distributions of the pore and the throat with scales from nanometer to micrometer. Both overall size distribution using the new combining method represented the pore and the throat more accurately in wider ranges. The results also showed that for tight sandstone core samples with different permeability, the difference of pore size distribution was less obvious than that of the throat. Therefore, the quantitative characterization of the throat size distribution was ultimately employed in developing a new permeability model together with physical considerations. The results demonstrated that the permeability of tight sandstones was in general depend on the size distribution of relatively larger throat, denoted as the macrothroat. However, for extreme low permeability (<0.1mD) formation, the small throats like microthroats and mesothroats mainly contributed to the permeability since the contents of macrothroats are really low.

Interaction of calmodulin with poly(acrylic acid) brushes: Effects of high pressure, pH-value and ligand binding.

Poly(acrylic acid) (PAA) brushes are well-known to interact with proteins in an ionic strength-dependent way. Moreover, they provide a native-like environment that largely maintains the secondary structure and biological activity of adsorbed proteins. Recently, it has been shown that the application of high pressure can lead to a reduced protein adsorption at a PAA brush in the case of a positively charged protein. Here, we analyze the effect of pressure on the interactions between a protein and a PAA brush in more detail. We use calmodulin as model protein that has a negative net charge at neutral pH-value and determine the degree of adsorption at a planar PAA brush applying total internal reflection fluorescence (TIRF) spectroscopy. Remarkably, the degree of calmodulin adsorption at a PAA brush is increasing with increasing pressure, when the protein is negatively charged. However, at low pH-value, where calmodulin is positively charged, high pressure leads to a partial desorption of the protein. Moreover, in the presence of trifluoperazine, which binds to calmodulin as a ligand, the pressure effect is diminished. The results of this study indicate that protein adsorption at a PAA brush at the "wrong" side of the isoelectric point, i.e. under net electrostatic repulsion, can involve a volume reduction that is favored under high pressure. It is suggested that this volume reduction is related to a hydration of counterions that are released from the PAA chains and the protein surface. In contrast, at pH-values close to the isoelectric point, the obtained data are consistent with a charge regulation mechanism that involves a volume increase. Thus, the application of high pressure in combination with pH-variation, as carried out in this study, provides the volume changes of adsorption that need to be consistent with any proposed mechanism of protein interaction with a PAA brush.