Rapid Pressure Increase Research Articles

New insights into the high-pressure polymorphism of SiO2 cristobalite

Single-crystal X-ray diffraction experiments with SiO2 α-cristobalite reveal that the well-known reversible displacive phase transition to cristobalite-II, which occurs at approximately 1.8 GPa, can be suppressed by rapid pressure increase, leading to an overpressurized metastable state, persisting to pressure as high as 10 GPa. In another, slow pressure increase experiment, the monoclinic high-pressure phase-II was observed to form at ~1.8 GPa, in agreement with earlier in situ studies, and its crystal structure has been unambiguously determined. Single-crystal data have been used to refine the structure models of both phases over the range of pressure up to the threshold of formation of cristobalite X-I at ~12 GPa, providing important constraints on the feasibility of the two competing silica densification models proposed in the literature, based on quantum mechanical calculations. Preliminary diffraction data obtained for cristobalite X-I reveal a monoclinic unit cell that contradicts the currently assumed model.

The role of vasopressin and terlipressin in catecholamine-resistant shock and cardio-circulatory arrest in children: Review of the literature

Arginine-vasopressin (AVP) and terlipressin (TP) are used as rescue drugs for states of shock and cardio-circulatory failure. Review to assess AVP/TP as a rescue therapy in children with catecholamine-resistant shock or cardio-circulatory arrest. A total of 31 reports were included (428 patients); sixteen articles were case series, 10 case reports, 3 clinical evaluation studies, one study was a non-blind RCT while one study was a multicentre double-blind RCT. The most common indication for either drug was catecholamine-refractory septic shock (12 reports). Commonly reported responses following AVP/TP administration were a rapid increase in blood pressure, an increase in urine output, and a decrease in serum lactate. In most reports, AVP and TP led to the reduction of catecholamines. The cumulative mortality rate remained high (188/428; 43.9%) despite the use of AVP/TP. No firm recommendations on the use of AVP/TP in children with severe forms of cardio-circulatory failure can be issued.

Intracanal Pressure in Compressive Spinal Cord Injury: Reduction with Hypothermia

Most cases of human spinal cord injury (SCI) are accompanied by continuing cord compression. Experimentally, compression results in rapid neurological decline over hours, suggesting a rise in intracanal pressure local to the site of injury. The aim of this study was to measure the rise in local intracanal pressure accompanying progressive canal occlusion and to determine the relationship between raised intracanal pressure and neurological outcome. We also aimed to establish whether hypothermia was able to reduce raised intracanal pressure. We demonstrate that, following SCI in F344 rats, local intracanal pressure remains near normal until canal occlusion exceeds 30% of diameter, whereupon a rapid increase in pressure occurs. Intracanal pressure appears to be an important determinant of neurological recovery, with poor long-term behavioural and histological outcomes in animals subject to 8 h of 45% canal occlusion, in which intracanal pressure is significantly elevated. In contrast, good neurological recovery occurs in animals with near normal intracanal pressure (animals undergoing 8 h of 30% canal occlusion or those undergoing immediate decompression). We further demonstrate that hypothermia is an effective therapy to control raised intracanal pressure, rapidly reducing elevated intracanal pressure accompanying critical (45%) canal occlusion to near normal. Overall these data indicate that following SCI only limited canal narrowing is tolerated before local intracanal pressure rapidly rises, inducing a sharp decline in neurological outcome. Raised intracanal pressure can be controlled with hypothermia, which may be a useful therapy to emergently decompress the spinal cord prior to surgical decompression.

Direct numerical simulations of ignition of a lean n-heptane/air mixture with temperature inhomogeneities at constant volume: Parametric study

The effect of thermal stratification on the ignition of a lean homogeneous n-heptane/air mixture at constant volume and high pressure is investigated by direct numerical simulations (DNS) with a new 58-species reduced kinetic mechanism developed for very lean mixtures from the detailed LLNL mechanism (H.J. Curran et al., Combust. Flame 129 (2002) 253–280). Two-dimensional DNS are performed in a fixed volume with a two-dimensional isotropic velocity spectrum and temperature fluctuations superimposed on the initial scalar fields. The influence of variations in the initial temperature field, imposed by changing the mean and variance of temperature, and the ratio of turbulence to ignition delay timescale on multi-stage ignition of a lean n-heptane/air mixture is studied. In general, the mean heat release rate increases more slowly with increasing thermal stratification regardless of the mean initial temperature. Ignition delay decreases with increasing thermal stratification for high mean initial temperature relative to the negative temperature coefficient (NTC) regime. It is, however, increased with increasing thermal fluctuations for relatively low mean initial temperature resulting from a longer overall ignition delay of the mixture. Displacement speed and Damköhler number analyses reveal that the high degree of thermal stratification induces deflagration rather than spontaneous ignition at the reaction fronts, and hence, the mean heat release rate is smoother subsequent to thermal runaway occurring at the highest temperature regions in the domain. Chemical explosive mode analysis (CEMA) also verifies that mixing counterbalances chemical explosion at the reaction fronts for cases with large temperature fluctuation. It is also found that if the ratio of turbulence to ignition delay timescale is short, resultant diminished scalar fluctuations cause the overall ignition to occur by spontaneous ignition. However, the overall effect of turbulence is small compared to the effect of thermal stratification. These results suggest that the critical degree of thermal stratification for smooth operation of homogeneous charge compression-ignition (HCCI) engines depends on both the mean and fluctuations in initial temperature which should be considered in controlling ignition timing and preventing an overly rapid increase in pressure in HCCI combustion.

Analysis of coupled transport phenomena in concrete at elevated temperatures

In this paper, we study a non-linear numerical scheme arising from the implicit time discretization of the Bažant–Thonguthai model for hygro-thermal behavior of concrete at high temperatures. Existence of the time-discrete solution in two dimensions is established using the theory of pseudomonotone operators in Banach spaces. Next, the spatial discretization is accomplished by the conforming finite element method. An illustrative numerical example shows that the model reproduces well the rapid increase of pore pressure in wet concrete due to extreme heating. Such phenomenon is of particular interest for the safety assessment of concrete structures prone to thermally-induced spalling.

Intramural Esophageal Abscess and Dissection due to Retropharygeal Abscess

Intramural esophageal dissection is a rare esophageal disorder characterized by sudden severe retro-sternal pain, hematemesis, odynophagia and dysphagia due to longitudinal separation of submucosa from muscle layer of the esophagus. Even though the etiology of this disorder still remains uncertain, it is usually associated with a rapid increase of intra-esophageal pressure in addition to coagulation disorder. We treated a patient who initially presented with retropharyngeal abscess, but finally progressed to an intramural esophageal dissection, which was successfully treated by endoscopic procedure. This is the first case that recorded disease pro gression and treatment from a retropharyngeal abscess to esophageal dissection. � Korean J Otorhinolaryngol-Head Neck Surg 2011;54:871-4 Key WordsZZRetropharynx ㆍAbscess ㆍEsophagus ㆍDissection.

Reaction of a Phospholipid Monolayer with Gas-Phase Ozone at the Air−Water Interface: Measurement of Surface Excess and Surface Pressure in Real Time

The reaction between gas-phase ozone and monolayers of the unsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, on aqueous solutions has been studied in real time using neutron reflection and surface pressure measurements. The reaction between ozone and lung surfactant, which contains POPC, leads to decreased pulmonary function, but little is known about the changes that occur to the interfacial material as a result of oxidation. The results reveal that the initial reaction of ozone with POPC leads to a rapid increase in surface pressure followed by a slow decrease to very low values. The neutron reflection measurements, performed on an isotopologue of POPC with a selectively deuterated palmitoyl strand, reveal that the reaction leads to loss of this strand from the air-water interface, suggesting either solubilization of the product lipid or degradation of the palmitoyl strand by a reactive species. Reactions of (1)H-POPC on D(2)O reveal that the headgroup region of the lipids in aqueous solution is not dramatically perturbed by the reaction of POPC monolayers with ozone supporting degradation of the palmitoyl strand rather than solubilization. The results are consistent with the reaction of ozone with the oleoyl strand of POPC at the air-water interface leading to the formation of OH radicals. The highly reactive OH radicals produced can then go on to react with the saturated palmitoyl strands leading to the formation of oxidized lipids with shorter alkyl tails.

The pressurization transient analysis for Lungmen advanced boiling water reactor using RETRAN-02

A RETRAN-02 model was devised and benchmarked against the preliminary safety analysis report (PSAR) for the Lungmen nuclear power plant roughly 10 years ago. During these years, the fuel design, some of the reactor vessel designs, and control systems have since been revised. The Lungmen RETRAN-02 model has also been modified with updated information when available. This study uses the analytical results of the final safety analysis report (FSAR) to benchmark the Lungmen RETRAN-02 plant model. Five transients, load rejection (LR), turbine trip (TT), main steam line isolation valves closure (MSIVC), loss of feedwater flow (LOFF), and one turbine control valve closure (OTCVC), were utilized to validate the Lungmen RETRAN-02 model. Moreover, due to the strong coupling effect between neutron dynamics and the thermal-hydraulic response during pressurization of transients, the one-dimensional kinetic model with the cross-section data library is used to simulate the coupling effect. The analytical results show good agreement in trends between the RETRAN-02 calculation and the Lungmen FSAR data. Based on the benchmark of these design-basis transients, the modified Lungmen RETRAN-02 model has been adjusted to a level of confidence for analysis of pressure increase transients. Analytical results indicate that the Lungmen advanced boiling water reactor (ABWR) design satisfied design criteria, i.e., vessel pressure and hot shutdown capability. However, a slight difference exists in the simulation of the water level for cases with changes in water levels. The Lungmen RETRAN-02 model tends to predict the change in water level at a slower rate than that in the Lungmen FSAR. There is also a slight difference in void reactivity response toward vessel pressure change in both simulations, which causes the calculated neutron flux before reactor shutdown to differ to some degree when the reactor experiences a rapid pressure increase. Further studies will be performed in the future using Lungmen startup test data.

Posterior Circulation Stroke after C1–C2 Intraarticular Facet Steroid Injection: Evidence for Diffuse Microvascular Injury

Posterior Circulation Stroke after C1–C2 Intraarticular Facet Steroid Injection: Evidence for Diffuse Microvascular Injury

Right ventricular stiffness constant as a predictor of postoperative hemodynamics in patients with hypoplastic right ventricle: a theoretical analysis

One and a half ventricle repair (1.5VR) is a surgical option for hypoplastic right ventricle (RV). The benefits of this procedure compared to biventricular repair (2VR) or Fontan operation remain unsettled. To compare postoperative hemodynamics, we performed a theoretical analysis using a computational model based on lumped-parameter state-variable equations. We varied the RV stiffness constant (B (RV)) to simulate the various RV hypoplasia, and estimated hemodynamics for a given B (RV). With B (RV) < 150% of normal, cardiac output was the largest in 2VR. With B (RV) > 150%, cardiac output became larger in 1.5VR than in 2VR. With B (RV) > 250%, RV end-diastolic volume was almost the same between 1.5VR and 2VR, and a rapid increase in atrial pressure precluded the use of 1.5VR. These results indicate that the beneficial effect of 1.5VR depends on the RV stiffness constant. Determination of management strategy should not only be based on the morphologic parameters but also on the physiological properties of RV.

Catalyst-free synthesis of onion-like carbon nanoparticles

A one-step process for the synthesis of onion-like carbon nanoparticles is described. The process is based on a thermolysis of a NaN 3-C 6Cl 6 mixture. The effect of buffer gas (Ar or air) on the yield, morphology, and structure of the carbon products was investigated by electron microscopy, X-ray diffraction, and Raman spectroscopy. The products contained carbon-onions, amorphous carbon nanoparticles, and NaCl. The byproducts were completely removed using a simple purification process. The formation of onion-like nanoparticles is likely caused by a shock wave, a rapid increase of pressure, during thermolysis, which induced the coalescence of phenyl radicals.

Hydromechanics of the Koyna–Warna Region, India

Continuous reservoir-induced seismicity has been observed in the Koyna–Warna region in western India following the beginning of impoundment of Koyna and Warna Reservoirs in 1961 and 1985, respectively. This seismicity includes 19 events with M ≥ 5.0 which occurred in 7 episodes (I–VII) between 1967 and 2005 at non-repeating hypocentral locations. In this study, we examined the first six episodes. The seismicity occurs by diffusion of pore pressures from the reservoirs to hypocentral locations along a saturated, critically stressed network of NE trending faults and NW trending fractures. We used the daily lake levels in the two reservoirs, from impoundment to 2000, to calculate the time history of the diffused pore pressures and their daily rate of change at the hypocentral locations. The results of our analysis indicate that Episodes I and IV are primarily associated with the initial filling of the two reservoirs. The diffused pore pressures are generated by the large (20–45 m) annual fluctuations of lake levels. We interpret that critical excess pore pressures >~300 kPa and >~600 kPa were needed to induce Episodes I–III and Episodes IV–VI, respectively, suggesting the presence of stronger faults in the region. The exceedance of the previous water level maxima (stress memory) was found to be the most important, although not determining factor in inducing the episodes. The annual rise of 40 m or more, rapid filling rates and elevated dp/dt values over a filling cycle, contributed to the rapid increase in pore pressure.

Herbig-Haro flows in 3D: the HH 83 jet

Aims. The kinematics of the HH 83 optical outflow, located in the L 1641 molecular cloud, are investigated. Methods. Observations were carried out with the Fabry-Perot scanning interferometer on the 6-m telescope of the Special Astrophysical Observatory. The Hα emission line was scanned with a spectral resolution of R = 8200. Results. The radial velocity along the jet increases with distance from the source, confirming previous results. It also shows lower amplitude variations which are not correlated with intensity. Both the spatial width of the jet as well as the FWHM of the Hα emission line in the jet tend to decrease with distance from the source. The velocity field across the jet demonstrates a decrease from the center to the edges as well as some evidence for a transverse velocity gradient. The blue-shifted bow shock is separated spatially and spectrally into two distinct features, divided by about 2 �� and 250 km s −1 , accordingly. Conclusions. Evidence is provided that these split features correspond to forward and reverse shocks caused by a rapid pressure increase as the jet begins a new oblique impact on the surrounding medium. Radial velocity variations lengthwise and transverse to the jet axis are discussed. Linear extrapolation of the jet velocity up to the location of the terminal shock region yields the radial velocity of the reverse jet shock. The data are consistent with an abrupt outburst about one thousand years ago which ejected material with total speeds of up to 400 km s −1 .

Echocardiographic Evaluation of Diastolic Function Can Be Used to Guide Clinical Care

For normal cardiac performance, the left ventricle (LV) must be able to eject an adequate stroke volume at arterial pressure (systolic function) and fill without requiring an elevated left atrial (LA) pressure (diastolic function). These systolic and diastolic functions must be adequate to meet the needs of the body both at rest and during stress. Response by Tschope and Paulus on p 809 Systolic function is conveniently (although not always accurately) measured as the ejection fraction (EF), calculated as stroke volume divided by end-diastolic volume.1 The LV EF is easily interpreted. The lower limit of normal is ≈50%. The lower the EF is, the greater the reduction in systolic function. Diastolic function has been more difficult to evaluate.2 Traditionally, invasive measures of LV diastolic pressure-volume relations and the rate of LV pressure fall during isovolumetric relaxation have been used. However, these methods are not practical for routine clinical use and do not adequately evaluate all aspects of diastolic filling.3 Comprehensive echocardiographic evaluation of the dynamics of LV filling using blood pool and tissue Doppler has now progressed so that it provides clinically important information that can be used to direct patient care. We present data that support the use of echocardiographic evaluation of diastolic function to recognize cardiac dysfunction in patients with heart failure, especially those with preserved EF; to guide the management of patients by identifying those with and without elevated left filling pressures regardless of underlying EF; and to determine prognosis in a wide variety of patient populations. Although the LV end-diastolic pressure-volume relation describes the passive properties of the LV, LV filling is not a passive or slow process.3 In fact, the peak flow rate across the mitral valve is equal to or greater than the peak flow rate across the aortic valve. …

연속재생 DPF의 재생 성능에 미치는 차량 운행패턴의 영향

This paper is to investigate the influence of driving patterns of slow and high speed vehicles on the performance of continuously regenerating diesel particulate filter(DPF) system matched with operating conditions in field application. The DPF performance test for field application was carried out for two identical DPFs installed to slow and high speed vehicles. A slow speed vehicle was selected among local buses which have driving patterns to repeat running and stop frequently, while a high speed vehicle was prepared to have long route of high speed over 60km/h like inter-city buses. In this test, the regeneration performance on the DPF of slow speed vehicle deteriorated because of high soot load index(SLI) in spite of same balance point temperature(BPT) distribution for high speed vehicle. The DPF of slow speed vehicle melted in the end because the rapid increase of back pressure caused high temperature over 1200℃ in the ceramic wall of DPF. The PM components like ash collected to the filter in the DPF were analyzed in order to investigate the cause of the defect and provide an operation performance of DPF system. In the result of the analysis, high levels of lubrication oil ash(Ca, Mg, P, Zn) were detected.

On the Effects of Subgrade Erosion on the Contact Pressure Distribution under Rigid Surface Structures

The performance of rigid surface structures such as concrete pavements and slabs-on-grade supported by a deteriorated subgrade and experiencing local contact loss is investigated experimentally and numerically in this study. A laboratory setup has been designed to facilitate the simulation of subsurface erosion and measure the changes in contact pressure at selected locations under a slab-on-grade supported on granular material. The presence of erosion voids under a slab-on-grade can lead to rapid increase in the contact pressure in the immediate vicinity of the void in addition to an increase in tensile stresses at the outermost fibers of the slab. This preliminary study suggests that efforts to detect and arrest the growth of erosion voids under slabs-on-grade should be made before the voids reach the size where significant loss of support develops and the tensile strength of the slab material is exceeded.

Transient processes in Stromboli’s shallow basaltic system inferred from dolerite and magmatic breccia blocks erupted during the 5 April 2003 paroxysm

We describe the mineralogy, geochemistry, and mesomicrostructure of fresh subvolcanic blocks erupted during the 5 April 2003 paroxysm of Stromboli (Aeolian Islands, Italy). These blocks represent ∼50 vol.% of the total erupted ejecta and consist of fine- to medium-grained basaltic lithotypes ranging from relatively homogeneous dolerites to strongly or poorly welded magmatic breccias. The breccia components are represented by angular fragments of dolerites entrapped in a matrix of vesiculated (lava-like to scoriae) crystal-rich (CR) basalt. All of the studied blocks are cognates with the CR basalt of the normal Strombolian activity or lavas and they are often coated by a few-centimeter thick layer of crystal-poor (CP) basaltic pumice erupted during the paroxysm. We suggest that they result from the rapid increase of pressure and related subvolcanic rock failure that occurred shortly before the 5 April 2003 explosion, when the uppermost portion of the edifice inflated and suffered brecciation as the result of the sudden rise of the gas-rich CP basalt that triggered the eruption. Dolerites and magmatic matrix of the breccias show major and trace element compositions that match those of the CR basalts erupted during normal Strombolian activity and effusive events at Stromboli volcano. Dolerites consist of (a) phenocrysts normally found in the CR basalts and (b) late-stage magmatic minerals such as sanidine, An60-28 plagioclase, Fe–Mn-rich olivines (Fo68-48), phlogopite, apatite, and opaque mineral pairs (magnetite and ilmenite), most of which are never found both in lava flows and scoriae erupted during the persistent explosive activity that characterizes typical Strombolian behavior. Subvolcanic crystallization of the Stromboli CR magma, leading to slowly cooled equivalents of basalts, could result from transient drainage of the magma from the summit craters to lower levels. Fingering and engulfing of the material that collapsed from the summit crater floor into the shallow basaltic system during the late evening of 28 December 2002 coupled with the short break in the summit persistent explosions between December 2002 and March 2003 permitted the CR magma pockets to solidify as dolerites, which were confined to the uppermost portion of the system and thus not involved in the ongoing flank effusive activity. Crystal size distribution of the basaltic blocks and crystallization of the finer-grained (<0.1 mm) mafic minerals of the dolerites over a time interval of ∼100 days closely agrees with the above interpretation. Vesicle filling (miarolitic cavities) locally found in some dolerites, with minerals deposited as vapor-phase crystallization is a result of continuous gas percolation through the rocks of the uppermost portion of the volcanic system. Poorly welded magmatic breccias formed during syn-eruptive processes of 5 April 2003, when the paroxysm strongly shattered the shallow subvolcanic system and many dolerite fragments were entrapped in the CR magma. In contrast, the high degree of welding between the dolerite clasts and the CR basaltic matrix in the strongly welded magmatic breccias provides a snapshot of subvolcanic intrusions of the CR basalt into the dolerite when, after a 2-month break in activity, CR magmas started to rise again to the summit craters. Blocks similar to these subvolcanic ejecta of 5 April 2003 were also erupted during previous paroxysms (e.g., 1930) suggesting that changes in the usual Strombolian activity (e.g., short breaks in the persistent mild explosions and/or flank effusive activity) lead to transient crystallization of dolerites in the shallow plumbing system.

Potential of phyllosilicate dehydration and dehydroxylation reactions to trigger earthquakes

This study experimentally simulated dehydration‐ and dehydroxylation‐induced weakening of clay‐rich gouges to investigate the potential of phyllosilicate minerals to generate abnormal pore pressure, triggering earthquakes. For the experiment, the gouge samples were subjected to sliding with heating at 9.6°C/min to 500°C under 80 MPa of confining pressure. In the undrained condition in which expulsed water was confined in the gouges, significant frictional strength reductions were found in the Na‐montmorillonite gouge due to dehydration and in the kaolinite gouge due to dehydroxylation. However, frictional strength continued to increase in the fully drained condition that allowed released water to move outside the gouge. Frictional strengths under the two drained conditions were compared during dehydration and dehydroxylation reactions to estimate the pore pressure generated in the gouge zone under the undrained condition. The 6∼8 wt % of dehydroxylated water generated from the kaolinite caused a rapid increase in pore pressure to 68 MPa at 500°C. In contrast, in the Na‐montmorillonite gouge, the pore pressure gradually increased to 72 MPa as the temperature rose to 500°C. Especially on a coseismic stage, these results suggest that dehydration/dehydroxylation could advance the frictional sliding acceleration induced by frictional heating, even if the fault is in a dry condition.

A new miniaturized system for extracorporeal membrane oxygenation in adult respiratory failure

IntroductionMortality of severe acute respiratory distress syndrome in adults is still unacceptably high. Extracorporeal membrane oxygenation (ECMO) could represent an important treatment option, if complications were reduced by new technical developments.MethodsEfficiency, side effects and outcome of treatment with a new miniaturized device for veno-venous extracorporeal gas transfer were analysed in 60 consecutive patients with life-threatening respiratory failure.ResultsA rapid increase of partial pressure of arterial oxygen/fraction of inspired oxygen (PaO2/FiO2) from 64 (48 to 86) mmHg to 120 (84 to 171) mmHg and a decrease of PaCO2 from 63 (50 to 80) mmHg to 33 (29 to 39) mmHg were observed after start of the extracorporeal support (P < 0.001). Gas exchange capacity of the device averaged 155 (116 to 182) mL/min for oxygen and 210 (164 to 251) mL/min for carbon dioxide. Ventilatory parameters were reduced to a highly protective mode, allowing a fast reduction of tidal volume from 495 (401 to 570) mL to 336 (292 to 404) mL (P < 0.001) and of peak inspiratory pressure from 36 (32 to 40) cmH2O to 31 (28 to 35) cmH2O (P < 0.001). Transfusion requirements averaged 0.8 (0.4 to 1.8) units of red blood cells per day. Sixty-two percent of patients were weaned from the extracorporeal system, and 45% survived to discharge.ConclusionsVeno-venous extracorporeal membrane oxygenation with a new miniaturized device supports gas transfer effectively, allows for highly protective ventilation and is very reliable. Modern ECMO technology extends treatment opportunities in severe lung failure.

Exercise Prescription In Diabetes

Exercise Prescription In Diabetes