Critical Pressure Value Research Articles

Laboratory tests and analysis of CIPP epoxy resin internal liners used in pipelines – part II: comparative analysis with the use of the FEM and engineering algorithms

Abstract In the case of underground network infrastructure it can be seen that objects functioning in the second technical condition, according to DWA-ATV 143-2, and subjected to rehabilitation with the use of close-fit trenchless technologies are capable of withstanding external loads. The main external load that is taken into account in engineering calculations in the case of conduits in the second technical condition is external groundwater pressure. In order to compare design parameters obtained with the use of various calculation methods, a comparative analysis was conducted in order to determine the values of critical pressure. The calculations were carried out using popular engineering algorithms. In addition, analyses using the Finite Element Method and Abaqus software as a computational tool were carried out for the purpose of verifying laboratory tests. This paper aims to broaden knowledge concerning the possibility of performing control numerical analyses for close-fit liners installed in pipelines that are in the second technical condition according to DWA-ATV 143-2. The analyses were carried out on ten 3D models. The models were parameterized in order to reflect the CIPP samples in the most accurate way. The computational models were built based on assumptions, which are commonly used in this type of scientific analysis, regarding material parameters and their interactions. The direct value of the performed engineering calculations and numerical analyses is the extension of knowledge in the field of strength parameters that are obtained by various material groups of close-fit liners. Comparative analysis of the results of laboratory tests and numerical analyses, and the conclusions that result from them, constitute the basis for the optimization of the design process and the individual approach to issues related to the use of liners that strengthen underground pipelines.

Mechanical criterion for coal and gas outburst: a perspective from multiphysics coupling

Although a series of hypotheses have been proposed, the mechanism underlying coal and gas outburst remains unclear. Given the low-index outbursts encountered in mining practice, we attempt to explore this mechanism using a multiphysics coupling model considering the effects of coal strength and gas mass transfer on failure. Based on force analysis of coal ahead of the heading face, a risk identification index Cm and a critical criterion (Cm ≥ 1) of coal instability are proposed. According to this criterion, the driving force of an outburst consists of stress and gas pressure gradients along the heading direction of the roadway, whereas resistance depends on the shear and tensile strengths of the coal. The results show that outburst risk decreases slightly, followed by a rapid increase, with increasing vertical stress, whereas it decreases with increasing coal strength and increases with gas pressure monotonically. Using the response surface method, a coupled multi-factor model for the risk identification index is developed. The results indicate strong interactions among the controlling factors. Moreover, the critical values of the factors corresponding to outburst change depending on the environment of the coal seams, rather than being constants. As the buried depth of a coal seam increases, the critical values of gas pressure and coal strength decrease slightly, followed by a rapid increase. According to its controlling factors, outburst can be divided into stress-dominated, coal-strength-dominated, gas-pressure-dominated, and multi-factor compound types. Based on this classification, a classified control method is proposed to enable more targeted outburst prevention.

Determination of barometric criteria for rupture of atherosclerotic plaques in the brachiocephalic arteries

The sequence of determining determination of the critical value of blood pressure for the occurrence of dissection of atherosclerotic intima of the internal carotid artery according to the experimental study. Atherosclerotic lesion of the brachiocephalic arteries was modeled on a vascular silicone phantom of the carotid arteries, in which the surgical material (intact annular area of atherosclerotic intima with plaque), obtained after eversion endarterectomy in a patient with atherosclerotic lesions, was placed and fixed in the region of the mouth of the internal carotid artery. A total of 30 models were created. To determine the critical values of the pressure on the intima with the plaque, at which it ruptures, balloon catheters were used, controlling the pressure with a manometer. The results were compared with the preoperative data of ultrasound and computed tomography examinations of patients. Dissection of the intima in the area of the plaque occurred in 6 cases at a pressure of 150180 mm Hg; in 9 cases at 180200 mm Hg, in 3 cases at a pressure of more than 200 mmHg, in 12 when exposed to more than 300 mm Hg. All patients, whose intima ruptured at a pressure of less than 200 mm Hg, had a fluid component of the plaque on preoperative examination, and in 6 patients, the critical pressure on the plaque was 150 mm Hg., there was also a thinned "cover" of the plaque. In the rest of the cases, the plaques were stable without a liquid component. Dissection of the intima in these cases did not occur when the exposure value was more than 300 mm Hg. The presence of a fluid component in an atherosclerotic plaque of the carotid artery in combination with a thinned cover of the plaque indicates the extreme danger of its destruction and embolism during a hypertensive crisis. The degree of stenosis of the carotid artery was found to be a less significant risk factor for unstable plaque rupture than the presence of a fluid component.

Natural vibrations and stability of loaded cylindrical shells partially filled with fluid, taking into account gravitational effects

The paper presents the results of studying circular cylindrical shells partially filled with an ideal liquid and subjected to uniform external and internal hydrostatic pressure. The behavior of an elastic structure and a compressible fluid is described in the framework of the classical nonlinear theory of shells, based on the Kirchhoff – Love hypotheses, and the Euler equations. The problem is solved using a semi-analytical version of the finite element method. The influence of the level of fluid in the shell on the critical values of external pressure is analyzed with and without consideration of gravitational effects on the free and lateral surfaces of the fluid. Shells with different boundary conditions and linear dimensions are considered. It has been shown that for certain geometrical parameters the gravitational field can significantly affect the dynamic characteristics of the structure.

Water Adsorption Behavior on a Highly Dense Single-Walled Carbon Nanotube Film with an Enhanced Interstitial Space.

In this study, we describe the adsorption behavior of water (H2O) in the interstitial space of single-walled carbon nanotubes (SWCNTs). A highly dense SWCNT (HD-SWCNT) film with a remarkably enhanced interstitial space was fabricated through mild HNO3/H2SO4 treatment. The N2, CO2, and H2 adsorption isotherm results indicated remarkably developed micropore volumes (from 0.10 to 0.40 mL g–1) and narrower micropore widths (from 1.5 to 0.9 nm) following mild HNO3/H2SO4 treatment, suggesting that the interstitial space was increased from the initial densely-packed network assembly structure of the SWCNTs. The H2O adsorption isotherm of the HD-SWCNT film at 303 K showed an increase in H2O adsorption (i.e., by ∼170%), which increased rapidly from the critical value of relative pressure (i.e., 0.3). Despite the remarkably enhanced adsorption capacity of H2O, the rates of H2O adsorption and desorption in the interstitial space did not change. This result shows an adsorption behavior different from that of the fast transport of H2O molecules in the internal space of the SWCNTs. In addition, the adsorption capacities of N2, CO2, H2, and H2O molecules in the interstitial space of the HD-SWCNT film showed a linear relationship with the kinetic diameter, indicating an adsorption behavior that is highly dependent on the kinetic diameter.

Involvement of purinergic system and electron transport chain in two species of cichlids from the Amazon basin exposed to hypoxia

The Amazonian aquatic ecosystem undergoes seasonal variations and daily changes that directly affect the availability of oxygen. During the day the levels of oxygen can reach supersaturation, and at night can drop to zero. In this way, aquatic organisms are exposed daily to physiological challenges regarding the availability of oxygen. The present study revealed significant differences in the physiology and performance of two cichlids: Geophagus proximus (black water cichlid – from Negro River) and Chaetobranchopsis orbicularis (white water cichlid – from Amazon River), exposed to hypoxia. The white water cichlid showed lower value (1.99 ± 0.79 pKa) of critical pressure of oxygen (Pcrit) and a longer time (68.00 ± 14.11 min) for total loss of balance (LOE); however, this species showed 50% mortality during exposure to hypoxia, while the black water cichlid did not show mortality. Both cichlids presented a decrease in O2 consumption rate (OCR) during hypoxia.. In this sense, it was observed that the black water cichlid presented several physiological strategies during hypoxia, such as, a significant increase in plasma cortisol levels, nucleoside triphosphate diphosphohydrolase activity (for adenosine diphosphate (ADP) as a substrate) in the gills, and the activity of adenosine deaminase (ADA) in gills and liver, in addition to a significant increase in the activity of complexes (II-III) in the transporter chain of electrons in both analyzed tissues and succinate dehydrogenase activity of gills' mitochondria. On the other hand, the only physiological change observed in the white water cichlid was a significant reduction in the activity of complexes II-III in gills and liver. Based on our findings, we can hypothesize that the white water cichlid specie has less tolerant to hypoxia when compared to the black water cichlid.

Comprehensive model toward optimization of SAG In-rich InGaN nanorods by hydride vapor phase epitaxy

Controlled growth of In-rich InGaN nanowires/nanorods (NRs) has long been considered as a very challenging task. Here, we present the first attempt to fabricate InGaN NRs by selective area growth using hydride vapor phase epitaxy. It is shown that InGaN NRs with different indium contents up to 90% can be grown by varying the In/Ga flow ratio. Furthermore, nanowires are observed on the surface of the grown NRs with a density that is proportional to the Ga content. The impact of varying the NH3 partial pressure is investigated to suppress the growth of these nanowires. It is shown that the nanowire density is considerably reduced by increasing the NH3 content in the vapor phase. We attribute the emergence of the nanowires to the final step of growth occurring after stopping the NH3 flow and cooling down the substrate. This is supported by a theoretical model based on the calculation of the supersaturation of the ternary InGaN alloy in interaction with the vapor phase as a function of different parameters assessed at the end of growth. It is shown that the decomposition of the InGaN solid alloy indeed becomes favorable below a critical value of the NH3 partial pressure. The time needed to reach this value increases with increasing the input flow of NH3, and therefore the alloy decomposition leading to the formation of nanowires becomes less effective. These results should be useful for fundamental understanding of the growth of InGaN nanostructures and may help to control their morphology and chemical composition required for device applications.

INVESTIGATION OF HYPERELASTIC SOFT SHELLS NONSTATIONARY DYNAMICS PROBLEMS SOLUTION FEATURES

Results of hyperelastic soft shells nonlinear axisymmetric dynamic deforming problems solution algorithm testing are represented in the work. Equations of motion are given in vector-matrix form. For the nonlinear initial-boundary value problem solution an algorithm which lies in reduction of the system of partial differential equations of motion to the system of ordinary differential equations with the help of lines method is developed. At this finite-difference approximation of partial time derivatives is used. The system of ordinary differential equations obtained as a result of this approximation is solved using parameter differentiation method at each time step. The algorithm testing results are represented for the case of pressure uniformly distributed along the meridian of the shell and linearly increasing in time. Three types of elastic potential characterizing shell material are considered: Neo-hookean, Mooney – Rivlin and Yeoh. Features of numerical realization of the algorithm used are pointed out. These features are connected both with the properties of soft shells deforming equations system and with the features of the algorithm itself. The results are compared with analytical solution of the problem considered. Solution behavior at critical pressure value is investigated. Formulations and conclusions given in analytical studies of the problem are clarified. Applicability of the used algorithm to solution of the problems of soft shells dynamic deforming in the range of displacements several times greater than initial dimensions of the shell and deformations much greater than unity is shown. The numerical solution of the initial boundary value problem of nonstationary dynamic deformation of the soft shell is obtained without assumptions about the limitation of displacements and deformations. The results of the calculations are in good agreement with the results of analytical studies of the test problem.

Динамічна втрата стійкості складеною нанокомпозитною оболонкою

Free oscillations and dynamic instability due to supersonic airflow pressure are investigated in a functional-gradient compound composite conical-cylindrical shell made of a carbon nanotubes-reinforced material. Nanocomposite materials with a linear distribution of the volumetric fraction of nanotubes over the thickness are considered. Extended mixture rule is used to estimate nanocomposite’s mechanical characteristics. A high-order shear deformation theory is used to represent the shell deformation. The assumed-mode technique, along with a Rayleigh-Ritz method, is applied to obtain the equations of the structure motion. To analyze the compound structure dynamics, a new system of piecewise basic functions is suggested. The pressure of a supersonic flow on the shell is obtained by using the piston theory. An example of the dynamic analysis of a nanocomposite conical-cylindrical shell in the supersonic gas flow is considered. The results of its modal analysis using the Rayleigh-Ritz technique are close to the natural frequencies of the shell obtained by finite element analysis. In this case, finite element analysis can only be used for shells made of material with a uniform distribution of nanotubes over the thickness. The dependence of the natural frequencies of a compound shell on the ratio of the lengths of the conical and cylindrical parts is studied. The dependence of the critical pressure of a supersonic flow on the Mach numbers and the type of carbon nanotubes reinforcement is investigated. Shells with a concentration of nanotubes predominantly near the outer and inner surfaces are characterized by higher values of natural frequencies and critical pressure than the shells with a uniform distribution of nanotubes or with a predominant concentration of nanotubes inside the shell.

Improvement of Technological Approaches to the Use of a Combined Method for Eliminating Sinkholes over Mining Workings

Analysis of projects for the elimination of open-pit mine workings in Russia has shown that most accidents associated with damage to the earth's surface are caused by critical values of rock pressure in empty spaces, a decrease in the bearing capacity of supports or their absence, as well as loss of stability of support structures. Rapid removal of the generated sinkholes does not always provide positive results, since often the material for filling them is burnt rock, and it was used without studying the properties of the earth's surface, where it is laid. This circumstance leads to the fact that the dips are re-activated. In this regard, the justification of the parameters of the method of eliminating sinkholes is an urgent scientific and practical task. The problem of stability of the abandoned mine workings, as well as geomechanical and environmental safety in the places where they are located, can only be solved using a systematic approach, which involves solving a set of issues to minimize the impact of each factor in the formation of sinkholes both in space and in time. The article describes the approaches to determining the technological parameters of the combined method of eliminating the sinkholes of mine workings, applied taking into account the geological characteristics of rocks and the mining and technical conditions of their location, the use of which will provide a reasonable calculation of the complex of engineering indicators for guaranteed removal.

ОЦЕНКА УСТОЙЧИВОСТИ ЦИЛИНДРИЧЕСКОЙ ОБОЛОЧКИ КОТЛА ЦИСТЕРНЫ C УЧЕТОМ ЗАПОЛНЕНИЯ ЕЕ ЖИДКИМ ГРУЗОМ

The paper considers an approach to justification of parameters for a cylindrical part of a tank shell in terms of construction stability loss at influence of external excessive pressure. A feature of the proposed approach is in the fact that it considers a level of filling of a tank shell with a liquid freight. The considered approach is based on a differential equation of gently sloping cylindrical shell. The authors use radial loads that are conditioned by external excessive and internal hydrostatic pressure as applied external forces. The differential equation is solved by the Bubnov - Galerkin method with the use of double trigonometric series. As a result, the authors have gained an algebraic expression that allows determining a level of critical excessive external pressure that can influence on tank shell at freight discharge, in case of failure of pressure relief valves, after flush and steam-curing and premature closure of tank hatches. On the basis of the algebraic expression the authors have determined values of critical pressure at various levels of filling with liquid freight for different types of railway tank-cars. Moreover, they have compared results of the study with data calculated with the use of the finite element method.

Buckling of the cylindrical shell joint with annular plates under external pressure

By means of an asymptotic method the buckling under the uniform external pressure of the thin cylindrical shell supported by identical annular plates is analyzed. Boundary conditions on an internal parallel of the shell joined to a thin plate are obtained. At the edges of the shell the free support conditions are introduced. We seek the approximate solutions of the eigenvalue problem as a sum of slowly varying functions and edge effect integrals. On a parallel, where the plate joint with the shell, the main boundary conditions for the formulation of an eigenvalue problem of zero approximation are obtained. This problem describes also vibrations of a simply supported beam stiffened by springs. Its solution we seek as linear combinations of Krylov’s functions. It is shown, that in zero approximation it is possible to replace a narrow plate with a circular beam. At increase in width of a plate stiffness of the corresponding spring tend to a constant. It occurs because of localization plate deformations near to the internal edge of a plate. As an example the dimensionless critical pressure for the case when the shell is supported by one plate is found. The replacement of a narrow plate with a circular beam does not lead to appreciable change of the critical pressure, however for a wide plate the beam model gives the overestimated value of critical pressure.

New modified PC-SAFT pure component parameters for accurate VLE and critical phenomena description

The theory of Perturbed Chain Statistical Associating Fluid (PC-SAFT) is largely applied in many industrial fields. It requires three parameters: the segment number (m), the hard-core segment diameter (σ), and the segment-segment interaction energy parameter (ε/k) for every pure non-associating fluid. By convention, they are determined by fitting vapor pressure and liquid density data. However, the shortage behind these parameters adopted by their respective authors is that they give excessive values of critical temperatures and critical pressures, which are crucial to forecasting vapor-liquid critical pressure and composition of the mixture at high pressures and temperatures.In this paper, a new approach is proposed to evaluate PC-SAFT parameters of different substances from diverse chemical families. Good fits of saturation pressure and vapor densities values of 94 pure substances are obtained, with an overall AARD of 0.89% and 1.50% respectively.The proposed method requires as input the critical pressure (Pc), the critical temperature (Tc), and the acentric factor (ω). By using these parameters, PC-SAFT estimates with accuracy the critical properties of pure compounds as well as the successful prediction of vapor-liquid equilibria for many non-associating binary systems at critical regions including mixtures containing ammonia, comparing with other literature values. But the limitation of this method is reflected in underestimated liquid densities.

Benchmark Investigation of Band-Gap Tunability of Monolayer Semiconductors under Hydrostatic Pressure with Focus-On Antimony.

In this paper, the band-gap tunability of three monolayer semiconductors under hydrostatic pressure was intensively investigated based on first-principle simulations with a focus on monolayer antimony (Sb) as a semiconductor nanomaterial. As the benchmark study, monolayer black phosphorus (BP) and monolayer molybdenum disulfide (MoS2) were also investigated for comparison. Our calculations showed that the band-gap tunability of the monolayer Sb was much more sensitive to hydrostatic pressure than that of the monolayer BP and MoS2. Furthermore, the monolayer Sb was predicted to change from an indirect band-gap semiconductor to a conductor and to transform into a double-layer nanostructure above a critical pressure value ranging from 3 to 5 GPa. This finding opens an opportunity for nanoelectronic, flexible electronics and optoelectronic devices as well as sensors with the capabilities of deep band-gap tunability and semiconductor-to-metal transition by applying mechanical pressure.

How Does Chronic Intermittent Hypoxia Influence Upper Airway Stability in Rats?

BackgroundObstructive sleep apnea (OSA) is characterized by repetitive episodes of upper airway collapse during sleep. The contraction of upper airway dilator muscles plays a crucial role in maintaining UA patency. Chronic intermittent hypoxia (CIH) is the most important pathophysiological process of OSA. Exposure to CIH induced not only the damage of dilator muscles but also the plasticity of the muscles. This study aimed to dynamically assess the influence of CIH on the upper airway.MethodsThe experiments were performed on 44 rats. They were randomly divided into a normoxia (NO) group (n=22) and CIH group (n=22). In each group (n=6, respectively), EMG, transcranial magnetic stimulation (TMS) response, and critical pressure (Pcrit) value were recorded on day 0 (the day before exposure), and the 7th, 14th, 21st, and 28th day of air/CIH exposure. For each group, 16 rats were used for transmission electron microscopy observations on day 0, and the 7th, 14th and 28th day of air/CIH exposure (n=4 for every time point).ResultsCompared to the NO group at the same point, the CIH group showed a damaged ultrastructure of genioglossus, increased activity of genioglossus corticomotor area, and increased Pcrit of the upper airway from the 7th to the 28th day of CIH. Increased EMG activity occurred at the 14th day of CIH and lasted for 2 weeks.ConclusionThe elevated genioglossus corticomotor excitability in response to the CIH could not counterbalance the damage effect of CIH on upper airway dilator muscles, which ultimately increased the collapsibility of the upper airway.

Numerical investigation of debonding extent development of cementing interfaces during hydraulic fracturing through perforation cluster

The perforation will damage the sealing integrity of cement sheath/cementing interfaces around the hole more or less, especially the debonding of cementing interfaces may lead to the fluid channeling during hydraulic fracturing. In this work, a laboratory experiment were used to verify the cohesive zone method (CZM) for simulating the debonding extent of casing/cement interface from a single hole during hydraulic fracturing. Then the debonding degree of cementing interfaces through perforation cluster during fracturing was investigated by using CZM. The numerical analysis results showed that the axial debonding length of the cement/formation interface is longer than which of casing/cement interface under the same working conditions. When the debonding zone around the perforation holes connected to each other, the cement/formation interface debonded faster than that of the casing/cement interface under the pressure of fracturing. The parameter sensitivity analysis shows that it is beneficial to diminish the debonding extent of cementing interfaces by reducing the viscosity of fracturing fluid and the pump pressure. The reliability of CZM method was validated by means of the peak values of critical failure pressure and casing displacement during lab scale fracturing experiment. Improving interfacial bonding strength and reducing the elastic modulus of the cement sheath can effectively promote wellbore integrity during hydraulic fracturing. This work can be used to evaluate the sealing performance of the cement sheath under the hydraulic fracturing and to provide guidance for fracturing planning.

The critical threshold value of systolic blood pressure for aortic occlusion in trauma patients in profound hemorrhagic shock.

This study aimed to determine the critical threshold of systolic blood pressure (SBP) for aortic occlusion (AO) in severely injured patients with profound hemorrhagic shock. All adult patients (>15 years) undergoing AO via resuscitative endovascular balloon occlusion of the aorta (REBOA) or thoracotomy with aortic cross clamping (TACC) between 2014 and 2018 at level I trauma center were included. Patients who required cardiopulmonary resuscitation in the prehospital setting were excluded. A logistic regression analysis based on mechanism of injury, age, Injury Severity Score, REBOA/TACC, and SBP on admission was done. A total of 107 patients underwent AO. In 57, TACC was performed, and in 50, REBOA was performed. Sixty patients who underwent AO developed traumatic cardiac arrest (TCA), and 47 did not (no TCA). Penetrating trauma was more prevalent in the TCA group (TCA, 90% vs. no TCA, 74%; p < 0.05) but did not modify 24-hour mortality (odds ratio, 0.51; 95% confidence interval, 0.13-2.00; p = 0.337). Overall, 24-hour mortality was 47% (50) and 52% (56) for 28-day mortality. When the SBP reached 60 mm Hg, the predicted mortality at 24 hours was more than 50% and a SBP lower than 70 mm Hg was also associated with an increased of probability of cardiac arrest. Systolic blood pressure of 60 mm Hg appears to be the optimal value upon which AO must be performed immediately to prevent the probability of death (>50%). However, values of SBP less than 70 mm Hg also increase the probability of cardiac arrest. Therapeutic study, level IV.

A study on the correlation between remnant cholesterol and urinary albumin to creatinine ratio in Chinese community adults: A report from the REACTION study.

The correlation between remnant cholesterol (RC) and urinary albumin to creatinine ratio (UACR) has not been illustrated. The present study aims to explore the correlation between RC levels and UACR in Chinese community adults. This study included 35 848 participants from a cohort study (REACTION). The UACR data were divided into three groups: UACR <10 mg/g, 10 ≤UACR<30 mg/g, and UACR ≥30 mg/g groups. RC was divided into two groups, according to the 75th percentile: <75% group and ≥75% group. Multiple logistic regression analysis was used to evaluate the correlation between RC and UACR. The RC exhibited an adjusted odds ratio that was significant in models 1-5. Although all confounders were corrected in model 5, RC and UACR were still significantly correlated， and the correlation was more significant in females，when compared to males (odds ratio [OR]: 1.117, 95% CI: 1.063-1.176, P < 0.001 for all subjects; OR: 1.092, 95% CI: 1.128-1.161, P = 0.004 for females; and OR: 1.085, 95% CI: 0.998-1.194, P = 0.088 for males). The RC was significantly correlated with UACR for subjects with 5.6 ≤ fasting blood glucose < 7.0 or 7.8 ≤ post-load blood glucose < 11.1 mmol/L, 24 ≤ body mass index (BMI) < 28 kg/m2 , 120 ≤ systolic blood pressure < 140 and/or 80 ≤ diastolic blood pressure < 90 mm Hg. In the Chinese community, RC is highly correlated with UACR, and the correlation is more significant in females compared with males. At higher RC levels, patients with critical values of blood pressure, BMI and blood glucose have a more significant correlation between RC and UACR.

Mechanisms of cell damage due to mechanical impact: an in vitro investigation

The dynamic response of cells when subjected to mechanical impact has become increasingly relevant for accurate assessment of potential blunt injuries and elucidating underlying injury mechanisms. When exposed to mechanical impact, a biological system such as the human skin, brain, or liver is rapidly accelerated, which could result in blunt injuries. For this reason, an acceleration of greater than > 150 g is the most commonly used criteria for head injury. To understand the main mechanism(s) of blunt injury under such extreme dynamic threats, we have developed an innovative experimental method that applies a well-characterized and -controlled mechanical impact to live cells cultured in a custom-built in vitro setup compatible with live cell microscopy. Our studies using fibroblast cells as a model indicate that input acceleration ({a}_{in}) alone, even when it is much greater than the typical injury criteria, e.g., {a}_{in}>1{,}000 g, does not result in cell damage. On the contrary, we have observed a material-dependent critical pressure value above which a sudden decrease in cell population and cell membrane damage have been observed. We have unambiguously shown that (1) this critical pressure is associated with the onset of cavitation bubbles in a cell culture chamber and (2) the dynamics of cavitation bubbles in the chamber induces localized compressive/tensile pressure cycles, with an amplitude that is considerably greater than the acceleration-induced pressure, to cells. More importantly, the rate of pressure change with time for cavitation-induced pressure is significantly faster (more than ten times) than acceleration-induced pressure. Our in vitro study on the dynamic response of biological systems due to mechanical impact is a crucial step towards understanding potential mechanism(s) of blunt injury and implementing novel therapeutic strategies post-trauma.

An investigation of flammability limits of gaseous mixtures at reduced pressures

An experimental investigation of flammability limits of hydrogen, methane and propane in air and oxygen at reduced pressures was carried out. A slow influence of sizes of an experimental vessel of a diameter higher than 125 mm on the flammability limits was revealed, but an influence of a type of an oxidizer (air or oxygen) and an ignition energy is significant. Critical values of an initial pressure for a possibility of a flame propagation were determined. The limiting values of the ignition energy were determined, for which an elevation of this parameter does not influence the critical pressure and the flammability region. A qualitative interpretation of obtained experimental results is given, which is based on a peculiarities of a flame initiation.