Rapid Pressure Changes Research Articles

Accelerated Protein Folding Using Greedy-Proximal A.

The protein folding problem has been studied in the field of molecular biophysics and biochemistry for many years. Even small changes in folding patterns may lead to serious diseases such as Alzheimer's or Parkinson's where proteins are folded either too quickly or too slowly. Molecular dynamics (MD) is one of the tools used to understand how proteins fold into native conformations. While it captures sequences of conformations that lead over time to the folded state, limitations in simulation timescales remain problematic. Although many approaches have been suggested to speed up the simulation process using rapid changes in temperature or pressure, we propose a rational approach, Greedy-proximal A* (GPA*), derived from path finding algorithms to explore the supposed shortest path folding pathway from the unfolded to a given folded conformation. We introduce several new protein structure comparison metrics based on the contact map distance to help mitigate the challenges faced by "standard" metrics. We test our approach on proteins which represent the two main types of secondary structure: (a) the Trp-cage miniprotein construct TC5b (1L2Y) which is a short, fast-folding protein that represents an α-helical secondary structure formed because of a locked tryptophan in the middle, (b) the immunoglobulin binding domain of the streptococcal protein G (1GB1), containing an α-helix and several β-sheets, and (c) the chicken villin subdomain HP-35, N68H protein (1YRF)-one of the fastest folding proteins which forms three α-helices. We compare our algorithm to replica-exchange MD and steered MD methods which represent the main algorithms used for accelerating folding proteins with MD. We find that GPA* not only reduces the computational time needed to obtain the folded conformation without adding artificial energy bias but also makes it possible to generate trajectories which contain minimal motions needed for the folding transition.

Arterial Baroreflex Function in Patients with Parkinson’s Disease: a Pharmacological Approach

Parkinson’s disease (PD) is a neurodegenerative disorder that is known for its motor dysfunction. Moreover, PD also causes non‐motor impairments, and approximately 40% of the patients experience coexistent abnormalities, like orthostatic hypotension (OH). The OH induces incapacitating symptoms that can contribute to an increased risk of falls, which have a great impact on patients’ quality of life. The arterial baroreflex system plays a pivotal role in counteracting transient falls in blood pressure during the execution of activities of daily living. Although a plethora of studies have indicated that an impaired baroreflex function is a clinical feature in patients with PD, none of the human studies have used the modified oxford method, which is considered the gold standard approach for assessing arterial baroreflex sensitivity (BRS). Additionally, since the OH and arterial BRS have an age‐dependent effect, studies with younger patients with PD is lacking. In this sense, the aim of the present study was to test the arterial baroreflex function in patients with PD with and without OH and aged‐matched control during rapid changes in blood pressure induced by sequential boluses of vasoactive drugs (Modified‐Oxford Technique). Beat‐to‐beat HR (electrocardiography) and BP (finger photoplethysmography) were obtained during 10‐min of supine rest preceding a modified‐Oxford [bolus injection of 65–100μg sodium nitroprusside (NTP) followed by 65–100μg phenylephrine hydrochloride (PHE) 1 min afterwards] in five patients with PD (50±6yr; Hohen and Yhar: <3a.u.; diagnose time: 8.8±3.7yr) and seven age‐matched controls (48±7yr). Arterial BRS was analyzed using the slopes of the linear portions of the R‐R interval‐systolic BP relationship. Patients with PD had lower BP at rest compared to controls (82±7 vs. 94±5mmHg, P=0.01) and a trend for higher HR (72±13 vs. 59±8bpm, P=0.06). The average of falling (ΔSBP: −37±0.65 vs. −31±0.43, P=0.26) and rising systolic BP (ΔSBP: −27±0.76 vs. −20±0.58, P=0.38) was similar between patients with PD and controls. Our preliminary results showed that arterial BRS was lower in patients with PD compared to controls for falling pressure (NTP trial: 4.52±0.34 vs. 9.81±0.23ms/mmHg, P=0.01) and for rising pressure (PHE trial: 5.08±0.27 vs. 13.60±0.55ms/mmHg, P=0.03). Of note, only one of the patients presented OH, and the baroreflex function was characterized by a marked blunted arterial BRS for failing pressure (NTP trial: 1.83ms/mmHg) and an averaged BRS for rising in pressure. Our preliminary results indicated that the ups and downs of baroreflex function are impaired in patients with PD, and the downs appear to be further impaired in patients with OH. These findings provide a better understanding of the neural control of blood pressure in patients with PD, and future studies should focus on OH.Support or Funding InformationCNPq, FAPDF and CAPES.

Measurement and Evaluation for Interbedded Pore Water Pressure of Saturated Asphalt Pavement under Vehicle Loading

Dynamic water scouring damage is the main cause of pavement structure damage, and the main reason for dynamic water scouring damage is the rapid change of pore water pressure caused by vehicle load. Numerical simulation is a commonly used pore water pressure test technology, but its accuracy is not high, and the test data are very different to actual values. In this study, a pore water pressure test method is designed, which has the advantages of less disturbance to the pavement structure and the measured data are closer to the true pore water pressure value of the pavement structure. Measurement data show that the pore water pressure gradually increases with increasing vehicle speed, and the pore water pressure response time becomes shorter. The pore water pressure response time is greater than vehicle loading time. Moreover, the phenomenon of periodic decay of pore water pressure with time is analyzed based on hydrodynamic water hammer theory. The empirical formula of maximum positive pressure with speed and the empirical formula of Abp at different speeds were obtained.

Effect of effective saturation and ceramic cup properties on the response time of tensiometers

In recent years, more studies have been focusing on the transient behaviors of the movement of soil water and changes in matric potential, which require the measurement of the rapid changes in matric potential or capillary pressure. Because of the delayed response, the value of the matric potential measured using a tensiometer may not precisely reflect the actual matric potential during a transient condition. We performed a series of experiments to analyze the effect of grain size, effective saturation, and the hydraulic conductivities of ceramic cup and porous media on the response time of a tensiometer. The outcomes suggested that a decrease of hydraulic conductivity of the ceramic cup significantly increases the response time. Moreover, the response time measured under unsaturated conditions did not follow an ideal exponential decay. This finding was consistent with the existing theories, based on which, we proposed three models to describe the time-varied response function. These models were applied to correct the measured matric potential for dynamic water retention curve (WRC), and the findings were compared with those of other existing methods used for measuring the matric potential. We found that the incorporation of the theory of response time significantly reduced the discrepancy between the matric potential measured using two ceramic cups with different response times during dynamic drainage. We concluded that the delayed response of a tensiometer can have a significant effect on the measurement of the transient matric potential or capillary pressure and can be corrected using response time equations.

Discovery of an Electron Gyroradius Scale Current Layer: Its Relevance to Magnetic Fusion Energy, Earth's Magnetosphere, and Sunspots

In the Earth’s magnetosphere, sunspots and magnetic cusp fusion devices, the boundary between the plasma and the magnetic field is marked by a diamagnetic current layer with a rapid change in plasma pressure and magnetic field strength. First principles numerical simulations were conducted to investigate this boundary layer with a spatial resolution beyond electron gyroradius while incorporating a global equilibrium structure. The boundary layer thickness is discovered to be on the order of electron gyroradius scale due to a self-consistent electric field suppressing ion gyromotion at the boundary. Formed at the scale of the electron gyroradius, the electric field plays a critical role in determining equilibrium structure and plasma transport. The discovery highlights the necessity to incorporate electron gyroradius scale physics in studies aimed at advancing our understanding of fusion devices, the magnetosphere and sunspots.

The amplification mechanism of a meteo-tsunami originating off the western coast of Kyushu Island of Japan in the winter of 2010

A meteo-tsunami is a tsunami-like phenomenon excited by a traveling atmospheric disturbance. In Japan, meteo-tsunamis are frequently observed along the western coast of Kyushu Island during winter–spring. One of the largest meteo-tsunamis occurred on March 3, 2010, where the maximum amplitude of water level oscillations exceeded 1 m in various bays on the western coast of Kyushu Island including Nagasaki Bay and Makurazaki Bay. Simultaneously, a sequence of rapid atmospheric pressure changes with amplitudes of ~ 1 hPa was recorded at various meteorological stations along the western coast of Kyushu Island. We numerically reproduce large sea level oscillations in both bays assuming that a simple atmospheric pressure disturbance consisting of a sequence of triangular-shaped pressure changes in 10–20 min propagates east-southeastward at a speed of ~ 30 m/s over the East China Sea. Over a wide area of the shallow continental shelf in the East China Sea, oceanic waves are amplified through a resonant coupling (Proudman resonance) to the traveling atmospheric disturbance. Oceanic waves propagate eastward while being further amplified through reflection and refraction owing to the complicated topographic and configuration constraints in the coastal area and excite meteo-tsunamis along the western coast of Kyushu Island. In particular, the reflection of oceanic waves (edge waves) from the end of the elongated continental shelf running east–west off Makurazaki Bay plays a key role in amplifying water level oscillations; the eigen-oscillations are excited on the continental shelf, which continue to supply water waves that are resonant with eigen-oscillations in Makurazaki Bay.

Turbulent Flow Measurements near the Discharge Port of a Screw Compressor

Mean flow and turbulence characteristics have been measured within the male and female rotors close to the discharge port of a double screw compressor at different radial positions, two axial positions from the exit port, Hp, and two radial planes, αp. Cycle-resolved axial and tangential mean flow measurements and their corresponding turbulent velocity fluctuations were made over a time window of 1° using a laser Doppler velocimetry, LDV, system. Measurements were performed through two transparent windows near the inlet of the discharge port inside the male and female working chambers. The results revealed a highly complex 3-D flow within the male and female working chambers, in particular, near the discharge port with two distinct flow zones 1 and 2 before and after the opening of the port, respectively. The flow in zone 1 was controlled by the rotor motion while in zone 2 was greatly influenced by the discharge process. In zone 2, both components of mean velocities were subjected to a sudden increase in velocity forming strong axial and tangential jet flows due to rapid change in pressure across the port as the flow is exposed into the discharge port. It was found that the flow structures have been affected considerably by the position of the discharge port, radial planes and radial positions. Axial and tangential RMS velocity distributions within both rotors were found to be relatively high and less affected by the flow changes of zones 1 and 2 with almost uniform distribution. The measured magnitudes of axial and tangential RMS velocities suggest it would be reasonable to assume the local turbulence to be isotropic for the modelling purposes. To authors’ knowledge, the results are unique, original and in great details not only to describe the flow structure, but also, they can be used in CFD codes to establish a reliable model of the flow and pressure distribution within twin screw machines.

Implications of habitual endurance and resistance exercise for dynamic cerebral autoregulation.

What is the central question of this study? Does habitual resistance and endurance exercise modify dynamic cerebral autoregulation? What is the main finding and its importance? To the authors' knowledge, this is the first study to directly assess dynamic cerebral autoregulation in resistance-trained individuals, and potential differences between exercise training modalities. Forced oscillations in blood pressure were induced by repeated squat-stands, from which dynamic cerebral autoregulation was assessed using transfer function analysis. These data indicate that dynamic cerebral autoregulatory function is largely unaffected by habitual exercise type, and further document the systemic circulatory effects of regular exercise. Regular endurance and resistance exercise produce differential but desirable physiological adaptations in both healthy and clinical populations. The chronic effect of these different exercise modalities on cerebral vessels' ability to respond to rapid changes in blood pressure (BP) had not been examined. We examined dynamic cerebral autoregulation (dCA) in 12 resistance-trained (mean±SD, 25±6years), 12 endurance-trained (28±9years) and 12 sedentary (26±6years) volunteers. The dCA was assessed using transfer function analysis of forced oscillations in BP vs. middle cerebral artery blood velocity (MCAv), induced via repeated squat-stands at 0.05 and 0.10Hz. Resting BP and MCAv were similar between groups (interaction: both P≥0.544). The partial pressure of end-tidal carbon dioxide ( ) was unchanged (P=0.561) across squat-stand manoeuvres (grouped mean for absolute change +0.6±2.3mmHg). Gain and normalized gain were similar between groups across all frequencies (both P≥0.261). Phase showed a frequency-specific effect between groups (P=0.043), tending to be lower in resistance-trained (0.63±0.21 radians) than in endurance-trained (0.90±0.41, P=0.052) and -untrained (0.85±0.38, P=0.081) groups at slower frequency (0.05Hz) oscillations. Squat-stands induced mean arterial pressure perturbations differed between groups (interaction: P=0.031), with greater changes in the resistance (P<0.001) and endurance (P=0.001) groups compared with the sedentary group at 0.05Hz (56±13 and 49±11vs. 35±11mmHg, respectively). The differences persisted at 0.1Hz between resistance and sedentary groups (49±12vs. 33±7mmHg, P<0.001). These results indicate that dCA remains largely unaltered by habitual endurance and resistance exercise with a trend for phase to be lower in the resistance exercise group at lower fequencies.

Two-phase pressurized thermal shock analysis with CFD including the effects of free-surface condensation

Pressurized thermal shock (PTS) is the stress experienced by a reactor pressure vessel (RPV) due to a rapid temperature and pressure change, or large spatial variations in temperature because of plumes and stripes of cold water surrounded by hotter water. PTS resulting from a loss-of-coolant accident was investigated for the nuclear Power Plant Gösgen-Däniken, which is a German-type three-loop pressurized-water reactor. The most critical regions in the RPV during such PTS transients are the most irradiated regions in the downcomer wall under the cold leg in the vicinity of the first weld of the first ring of the RPV. Cooling plumes or stripes develop at the RPV wall or core barrel wall depending on parameters like the water level in the downcomer, the mass flow rate of the injected cooling water and condensation effects.For fracture-mechanics analysis of the RPV, temperature profiles and heat-transfer coefficients corresponding to either cooling plumes or stripes at the wall (here mainly at the inner RPV wall) are needed. Various methodologies can be followed for generating the temperature profiles and heat-transfer coefficients resulting from the mixing of cold injection water with the hot RPV water. One is the calculation of these data by analytical fluid-mixing codes validated with experiments, such as KWU-MIX. Alternatively, computational fluid dynamics (CFD) tools can be used after suitable validation. One advantage of CFD is the possibility to show attachment of plumes and stripes to the inner wall of the RPV or detachment towards the core barrel.A free-surface condensation model was implemented in ANSYS CFX for simulating two-phase transients when the water level is below the cold-leg nozzle. For the purpose of validating free-surface condensation and the maximum mass flow rate for the stripe of liquid water before detachment from the RPV wall, experimental data from the full-scale Upper Plenum Test Facility (UPTF) were used.The comparison of CFD and KWU-MIX analyses of the limiting transient for the core weld obtained from the selection process with KWU-MIX shows that the inherent conservatism in the standard KWU-MIX approach leads to higher thermal loading than the best-estimate CFD approach and demonstrates the benefits of a CFD tool to quantify potential margins.

Improving Peaceman well flow modelling with 1D radial simulation

In reservoir simulation, Peaceman’s method is the most popular solution for simulating the flow from the reservoir to the well. It is easy to implement and works well if there are no phase changes in the well block. However, it will give inaccurate results when there is rapid pressure change near the wellbore. There are various methods for obtaining a detailed pressure profile around wells. But these methods either require dedicated gridding technique or perform poorly. In the present work, Peaceman’s method has been improved by conducting an extra 1D radial simulation from the equivalent well block radius to the wellbore radius. A series of virtual coaxial cylindrical nodes are introduced which can be mapped from the existing blocks that come from either the local grid refinement or inactive blocks. Features such as relative permeability and pressure–volume–temperature can be retained in the 1D radial simulation. The new method can be easily adapted by most reservoir simulators that have implemented Peaceman’s method. The new method can accurately mimic the local physics around a well and provides insight into the flow behaviour around the well with little extra computational effort.

Occurrence of Hazardous Meteotsunamis Coupled with Pressure Disturbance Traveling in the Yellow Sea, Korea

Kim, M.-S.; Kim, H.; Eom, H.-M.; Yoo, S.-H., and Woo, S.-B., 2019. Occurrence of hazardous meteotsunamis coupled with pressure disturbance traveling in the Yellow Sea, Korea. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 71-75. Coconut Creek (Florida), ISSN 0749-0208.Several unexpected abnormal waves occurred near the west coast of Korea on March 31, 2007, May 4, 2008, April 26, 2011, and caused enormous damage to property and human lives. None of the events reported at the time were noticeably large, such as earthquakes or typhoons. However, in all reported events, it was observed that sea-level pressure disturbances combined with clusters of the atmospheric instability were propagated from China to the west coast of Korea. After these atmospheric disturbances were observed along the coast, significant meteorological tsunamis were also observed at tidal stations near the accident site. On the hazardous meteotsunami dates, arrival time and duration of the high-frequency sea-level oscillations were correlated with the pressure disturbance and high rain rate. To analyze the interaction between the pressure disturbance and the following sea-level oscillations, their propagation characteristics were also compared. As a result, they traveled to the eastward crossing over the Yellow Sea with coupled propagation on the dates of the accident. This process made the sea-level fluctuated by rapid pressure changes and amplified by Proudman resonance in a specific range of depth.

The relationship between biomechanics of pharyngoesophageal segment and tracheoesophageal phonation

This study examined the relationship between biomechanical features of the pharyngoesophageal (PE) segment, acoustic characteristics of tracheoesophageal (TE) phonation, and patients’ satisfaction with TE phonation. Fifteen patients using TE phonation after total laryngectomy completed the Voice Symptom Scale (VoiSS) and underwent acoustic voice analysis for cepstral peak prominence (CPP) and relative intensity. High resolution manometry (HRM) combined with videofluoroscopy was used to evaluate PE segment pressure and calculate the pressure gradient (ΔP), which was the pressure difference between the upper oesophagus and a point two centimetres above the vibrating PE segment. The upper oesophageal sphincter (UOS) minimal diameters were measured by Endolumenal Functional Lumen Imaging Probe (EndoFLIP). HRM detected rapid pressure changes at the level of the 4th – 6th cervical vertebra. CPP, relative intensity, and ΔP were significant predictors of satisfactory TE phonation. ΔP was a significant predictor of CPP and intensity. Minimal UOS diameter was a significant predictor of relative intensity of TE phonation. In two patients with unsuccessful TE phonation, endoscopic dilatation subsequently restored TE phonation. These findings suggest that sufficient ΔP and large UOS diameter are required for satisfactory TE phonation. Endoscopic dilatation increasing UOS diameter may provide a new approach to treat unsuccessful TE phonation.

Pore water pressure and total horizontal stress response to EPBM tunnelling in London Clay

The ground response, in terms of surface and subsurface displacements, to twin-bore Crossrail tunnel construction beneath a research monitoring site in Hyde Park, London, using earth-pressure-balance machines (EPBMs) in London Clay, has recently been reported in two companion papers by the authors. This third paper presents and discusses corresponding changes in pore water pressure and total horizontal stress measured using multi-level piezometers and pushed-in spade cells. The three papers together provide a comprehensive and completely unique field monitoring case history of the short-term ground response to EPBM tunnelling in London Clay, making them invaluable for validating future numerical analyses. The fully grouted vibrating-wire piezometers were able to measure the rapid pore water pressure changes around the tunnels as they were constructed. Five distinct immediate pore water pressure responses are identified, induced by different stages of the tunnel drives as the EPBMs approached and passed the instruments. The responses are correlated with tunnel-boring machine operation variables and a postulated arching mechanism, identified for the first time through field measurements. The sense and magnitude of changes in horizontal total stress were reasonable and are correlated with overall pore water pressure changes. Both responses are linked where possible with measured subsurface displacements and generally correlate well, at least qualitatively. Limitations to the measurements and influencing factors are also discussed.

EET Analogs and the Dual‐Inhibition of sEH/COX‐2 for the Treatment of Focal Segmental Glomerular Sclerosis

Focal segmental glomerulosclerosis (FSGS) is the single most common form of kidney disease. This devastating disorder can lead to end stage renal disease (ESRD), a terminal diagnosis in the absence of a kidney transplant. The progression of FSGS is defined by sclerotic damage to the glomerulus, the filtering unit of blood in the kidney. Epoxyeicosatrienoic acids (EETs) are a family of arachidonic acid metabolites important to glomerular function. EETs are metabolized by enzymes such as soluble epoxide hydrolase (sEH) and cyclooxygenase (COX), and we have developed a novel dual‐ligand drug (PTUPB) that inhibits both sEH and COX‐2. We hypothesize that EET analogs and the dual‐inhibition of sEH and COX‐2 will mitigate glomerular damage caused by FSGS. The long‐term goal of this research is to better understand the role of 8,9‐EET and its metabolites on glomerular function so that we can develop new therapies to treat FSGS and other nephropathies.MethodsGlomerular Permeability Assay: Glomeruli were pre‐incubated in 5% albumin (50kDa dialyzed BSA), followed by a bath exchange to 1% albumin. Under normal conditions the glomeruli are non‐permeable to albumin, and as a result, when the 5% albumin bath is exchanged for 1% albumin, water is taken up into the intra‐glomerular space due to the rapid change in oncotic pressure. Glomerular permeability was tested using our non‐hydrolyzable 8,9‐EET analog (1μM), our non‐hydrolyzable 14,15‐EET analog (EET‐A, 1μM) or PTUPB (1μM) with isolated SD rat glomeruli in the presence or absence of angiotensin II (AngII, 10μM), a known glomerular permeabilizing agent. 3D‐Confocal imaging (72μm z‐depth, 27‐layer z‐stack) was utilized to measure the relative changes in glomerular volume.ResultsGlomerular permeability to albumin (Palb) is derived from the albumin reflection coefficient (σalb), where a value of 1 indicates high permeability to albumin, and 0 indicates low permeability (relative to control). A baseline response to a 5% to 1% albumin exchange resulted in very low albumin permeability (Palb = −0.21 ± 0.21, n=6). Conversely, the presence of AngII resulted high albumin permeability (Palb = 1.21 ± 0.12, n=15). Our 8,9‐EET analog, in the presence of AngII, mitigated the effects of AngII‐induced permeability (Palb = 0.13 ± 0.18, n=7), as did our dual sEH/COX2 inhibitor, PTUPB, under the same Ang‐II stimulation (Palb = 0.71% ± 0.35, n=7), but not the 14,15‐EET analog (Palb = 0.99% ± 0.21, n=4) . All values are mean ± SEM.ConclusionFSGS is complex multi‐model disease, and glomerular damage/dysfunction are at the core of this condition. The ability of our 8,9‐EET analog and PUTPB to decrease AngII‐associated glomerular permeability suggest and important role for EETs and their metabolism. Future work will investigate not only the effects of 8,9‐EET analogs and PTUPB on glomerular health, but also the consequences of EET metabolites and other EET‐analogs, on both glomerular and mesangial function using cell and animal models.Support or Funding InformationR01 DK103616‐01 (John D. Imig). Dr. Ralph and Marian Falk Medical Research Trust ‐ Phase II (John D. Imig)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Arterial lines: why, when, how?

Arterial lines are a useful tool in the emergency and intensive care patient. Invasive blood pressure measurement is considered the gold standard in patient care and has become commonplace in veterinary practice, especially in veterinary anaesthesia. Arterial catheters are catheters placed within the arterial lumen by a skilled veterinary surgeon or veterinary nurse. This catheter is attached to a monitor which provides information such as systolic, mean and diastolic arterial pressure, heart rate and an arterial waveform. Having an invasive arterial catheter gives the advantage of a constant measurement of arterial blood pressure, meaning the effects on patients of drugs, fluids and environment can be seen. Arterial lines are useful in patients where rapid changes in blood pressure are anticipated, and abnormal measurements can be detected quickly. This article discusses the different aspects of arterial lines from what they are, to waveform analysis and complications.

Methane spikes, background seasonality and non-detections on Mars: A geological perspective

The story of methane (CH4) on Mars continues to grow. A long series of CH4 detections (spikes, plumes, seasonal variations) and non-detections in the martian atmosphere suggest that CH4 is occasionally released from subsurface rocks, but also that an unknown process of rapid CH4 removal in the atmosphere must exist. The observations can be interpreted integrating concepts of subsurface geological gas source variability (CH4 seepage flux patterns), atmospheric chemistry (CH4 removal processes), and atmospheric circulation (CH4 transport and dilution). While the last two are widely studied, potential gas seepage patterns on Mars have never been discussed. In this work, we use the factors controlling gas seepage flux patterns observed on Earth to address key questions about the significance of the martian detections and non-detections. As on Earth, CH4 seepage on Mars must occur mainly through advection (non-diffusion) mechanisms, driven by pressure gradients and permeability, typically related to faults and fracture networks, which control release patterns, in terms of intensity, duration and variability. CH4 release may occur, therefore, whenever gas pressure and/or rock permeability increase (e.g., via destabilization of storage bodies such as clathrates or zeolites; breaching of seals such as permafrost; planetary stresses, impacts, or gas pressure build-up along faults). Rapid atmospheric pressure changes, due to storms and winds, may also play a role. All these forcings can lead to local, episodic, irregular or seasonal gas releases, which may explain the observations acquired so far if relatively rapid (month or day time-scales) mechanisms of CH4 removal exist in the lower atmosphere or near-surface. The release patterns cannot reveal whether CH4 is biologic or abiotic. If CH4 sensors operate discontinuously and only in one site or over limited regions, then, non-detections will be the rule and detections will be relatively rare. The chances of CH4 detection may increase if the observations are focused and repeated on specific, potential areas of gas release determined by geological analysis.

Response of collagen matrices under pressure and hydraulic resistance in hydrogels.

Extracellular matrices in animal tissue are hydrogels mostly made of collagen. In these matrices, collagen fibers are hierarchically assembled and cross-linked to form a porous and elastic material, through which migrating cells can move by either pushing through open matrix pores, or by actively digesting collagen fibers. The influence of matrix mechanical properties on cell behavior is well studied. Less attention has been focused on hydraulic properties of extracellular matrices, and how hydrodynamic flows in these porous hydrogels are influenced by matrix composition and architecture. Here we study the response of collagen hydrogels using rapid changes in the hydraulic pressure within a microfluidic device, and analyze the data using a poroelastic theory. Major poroelastic parameters can be obtained in a single experiment. Results show that depending on the density, porosity, and the degree of geometric confinement, moving micron-sized objects such as cells can experience substantially increased hydraulic resistance (by as much as 106 times) when compared to 2D environments. Therefore, in addition to properties such as mechanical stiffness, the fluidic environment of the cell is also likely to impact cell behavior.

Modelling of fine fragmentation and fission gas release of UO2 fuel in accident conditions

In reactor accidents that involve rapid overheating of oxide fuel, overpressurization of gas-filled bubbles and pores may lead to rupture of these cavities, fine fragmentation of the fuel material, and burst-type release of the cavity gas. Analytical rupture criteria for various types of cavities exist, but application of these criteria requires that microstructural characteristics of the fuel, such as cavity size, shape and number density, are known together with the gas content of the cavities. In this paper, we integrate rupture criteria for two kinds of cavities with models that calculate the aforementioned parameters in UO2 LWR fuel for a given operating history. The models are intended for implementation in engineering type computer programs for thermal-mechanical analyses of LWR fuel rods. Here, they have been implemented in the FRAPCON and FRAPTRAN programs and validated against experiments that simulate LOCA and RIA conditions. The capabilities and shortcomings of the proposed models are discussed in light of selected results from this validation. Calculated results suggest that the extent of fuel fragmentation and transient fission gas release depends strongly on the pre-accident fuel microstructure and fission gas distribution, but also on rapid changes in the external pressure exerted on the fuel pellets during the accident.

Dynamic cerebral autoregulation is attenuated in young fit women.

Young women exhibit higher prevalence of orthostatic hypotension with presyncopal symptoms compared to men. These symptoms could be influenced by an attenuated ability of the cerebrovasculature to respond to rapid blood pressure (BP) changes [dynamic cerebral autoregulation (dCA)]. The influence of sex on dCA remains unclear. dCA in 11 fit women (25 ± 2 years) and 11 age‐matched men (24 ± 1 years) was compared using a multimodal approach including a sit‐to‐stand (STS) and forced BP oscillations (repeated squat‐stand performed at 0.05 and 0.10 Hz). Prevalence of initial orthostatic hypotension (IOH; decrease in systolic ≥ 40 mmHg and/or diastolic BP ≥ 20 mmHg) during the first 15 sec of STS was determined as a functional outcome. In women, the decrease in mean middle cerebral artery blood velocity (MCAvmean) following the STS was greater (−20 ± 8 vs. −11 ± 7 cm sec−1; P = 0.018) and the onset of the regulatory change (time lapse between the beginning of the STS and the increase in the conductance index (MCAvmean/mean arterial pressure) was delayed (P = 0.007). Transfer function analysis gain during 0.05 Hz squat‐stand was ~48% higher in women (6.4 ± 1.3 vs. 3.8 ± 2.3 cm sec−1 mmHg−1; P = 0.017). Prevalence of IOH was comparable between groups (women: 4/9 vs. men: 5/9, P = 0.637). These results indicate the cerebrovasculature of fit women has an attenuated ability to react to rapid changes in BP in the face of preserved orthostasis, which could be related to higher resting cerebral blood flow allowing women to better face transient hypotension.

Experimental characterization of RDE combustor flowfield using linear channel

An experimental study was conducted to characterize fundamental behavior of detonation waves propagating across an array of reactant jets inside a narrow channel, which simulated an unwrapped rotating detonation engine (RDE) configuration. Several key flow features in an ethylene-oxygen combustor were explored by sending detonation waves across reactant jets entering into cold bounding gas as well as hot combustion products. In this setup, ethylene and oxygen were injected separately into each recessed injector tube, while a total of 15 injectors were used to establish a partially premixed reactant jet array. The results revealed various details of transient flowfield, including a complex detonation wave front leading a curved oblique shock wave, the unsteady production of transverse waves at the edge of the reactant jets, and the onset of suppressed reactant jets re-entering the combustor following a detonation wave passage. The visualization images showed a complex, multidimensional, and highly irregular detonation wave front. It appeared non-uniform mixing of reactant jets lead to dynamic transverse wave structure. The refreshed reactant jets evolving in the wake of the detonation wave were severely distorted, indicating the effect of dynamic flowfield and rapid pressure change. The results suggest that the mixing between the fuel and oxidizer, as well as the mixing between the fresh reactants and the background products, should affect the stability of the RDE combustor processes.