A new non-pillar mining technology, gob-side entry retaining by roof cutting (GERRC), different from the conventional gob-side entry retaining formed by a roadside filling support, is introduced in ...this study. In the new technology, roof cutting is conducted so that the roof plate forms a short cantilever beam structure within a certain range above the retained entry, thus changing the stress boundary condition of the roof structure. To explore the deformation characteristics of the roof under this special condition, a short cantilever beam mechanical model was established and solved using energy theory and displacement variational methods. Meanwhile, a theoretical and analytical control solution for roof deformation was obtained and verified via field-measured results. Based on the aforementioned calculation, the relationship between the roof deformation and main influence parameters was explored. It was concluded that the rotation of the upper main roof and width of the retained entry had the most significant impacts on roof deformation. Bolt and cable support and temporary support in the entry had a non-obvious influence on the roof deformation and could not prevent the given deformation that was caused by the rotation of the upper main roof. Based on comprehensive theoretical analysis and calculation results, ideas and countermeasures to control short cantilever roof deformation—that is, designing a reasonable height of roof cutting and a controlled width of retaining entry—were proposed and tested. Field monitoring shows that the entry control effects were satisfactory.
Postoperative pulmonary complications and cardiovascular complications are major causes of morbidity, mortality, and resource utilization in cardiac surgery patients.
To investigate the effects of ...airway pressure release ventilation (APRV) on respiration and hemodynamics in post cardiac surgery patients.
A single-center randomized control trial was performed. In total, 138 patients undergoing cardiopulmonary bypass were prospectively screened. Ultimately 39 patients met the inclusion criteria and were randomized into two groups: 19 patients were managed with pressure control ventilation (PCV) and 20 patients were managed with APRV. Respiratory mechanics after 4 h, hemodynamics within the first day, and Chest radiograph score (CRS) and blood gasses within the first three days were recorded and compared.
A higher cardiac index (3.1 ± 0.7 vs. 2.8 ± 0.8 L⋅min
⋅m
;
< 0.05), and shock volume index (35.4 ± 9.2 vs. 33.1 ± 9.7 ml m
;
< 0.05) were also observed in the APRV group after 4 h as well as within the first day (
< 0.05). Compared to the PCV group, the PaO2/FiO
was significantly higher after 4 h in patients of APRV group (340 ± 97 vs. 301 ± 82,
< 0.05) and within the first three days (
< 0.05) in the APRV group. CRS revealed less overall lung injury in the APRV group (
< 0.001). The duration of mechanical ventilation and ICU length of stay were not significantly (
= 0.248 and 0.424, respectively).
Compared to PCV, APRV may be associated with increased cardiac output improved oxygenation, and decreased lung injury in postoperative cardiac surgery patients.
Although the diffusion of its storage and transport under liquefied conditions, nowadays it is common to have methane in gaseous form in several industrial applications. This leads to safety ...implications to be considered: hazards are linked to both the high-pressure at which the gas is kept and to its flammability. Scenarios where flammable jets impact an obstacle are of paramount importance because of their possible occurrence. Following a numerical approach, literature shows up that their assessment can be reliably performed by means of only Computational Fluid Dynamics tools. However, despite the improvements of computing power, Computational Fluid Dynamics costs still limit its use in daily risk analysts’ activities. Therefore, considering an accidental jet-obstacle scenario of industrial interest, the present work investigates how a pipe rack can influence the development of a high-pressure methane jet. Based on a Computational Fluid Dynamics analysis, main achievements of this work are a simple criterion able to identify the situations where the pipe rack does not influence the high-pressure methane jet behavior, therefore allowing to identify the scenarios where simpler models can be used (i.e., analytical correlations known for the free jet situation), and, if present, a simple analytical relationship that roughly predicts the influence of the pipe rack without the need of performing complex Computational Fluid Dynamics simulations.
•A high-pressure methane jet outflowing from a loss of containment is simulated.•The influence of a pipe rack on the LFL extension is investigated.•A simple procedure that allow to estimate the hazardous distance is proposed.
The use of computational fluid dynamics (CFD) in process safety to estimate the risk of a given incidental scenario has become ever more present in common industry practice. The simulation of ...high-pressure, compressible natural gas jets is often performed by modelling its source with a simpler notional diameter approach, such that the highly computationally expensive nearfield zone need not to be simulated; this is particularly determining when simulating a gas release in complex scenario like liquid natural gas (LNG) regasification plants. In this study, we analysed the structure of compressible and incompressible jets, using Birch 1984 (B84) and Birch 1987 (B87) models. In this work, a study on the positioning of the notional diameter with respect to the real orifice of the released gas is performed, along with a statistical analysis to assess the limits of the simpler model approaches.
It was found that no spacing is needed between the virtual and real sources, as the potential core generated by the simpler model is as large as the fully simulated nearfield zone by the compressible model. Additionally, an end-of-transition zone position correlation is reported. The incompressible models can be used instead of the fully compressible model for a wide range of release conditions, with both models providing accurate predictions of axisymmetrical mole fraction, temperature, and velocity profiles between 2.5 and 130 bar of storage pressure at a 1-inch orifice diameter. However, as the diameter increases, B84 is not a viable model for a “full bore” (10-inch diameter size) release at 65 bar. While B84 is reliable, B87 is the superior model for its ability to account for the compressible effects of the expansion. Therefore, B87 should be used when simulating cases where temperature is of particular interest to the user.
•Three high-pressure natural gas jet models were compared through CFD simulations.•The positioning of the equivalent diameter used in notional diameter models was assessed.•A correlation for the location of the end of the transition zone is presented.•Limits of the studied notional diameter models were determined.
Objective:
The aim of the study was to compare the effects of APRV and LTV ventilation on pulmonary permeability in severe ARDS.
Methods:
Mini Bama adult pigs were randomized into the APRV group (
n
...= 5) and LTV group (
n
= 5). A severe ARDS animal model was induced by the whole lung saline lavage. Pigs were ventilated and monitored continuously for 48 h.
Results:
Compared with the LTV group, CStat was significantly better (
p
< 0.05), and the PaO
2
/FiO
2
ratio showed a trend to be higher throughout the period of the experiment in the APRV group. The extravascular lung water index and pulmonary vascular permeability index showed a trend to be lower in the APRV group. APRV also significantly mitigates lung histopathologic injury determined by the lung histopathological injury score (
p
< 0.05) and gross pathological changes of lung tissues. The protein contents of occludin (
p
< 0.05), claudin-5 (
p
< 0.05), E-cadherin (
p
< 0.05), and VE-cadherin (
p
< 0.05) in the middle lobe of the right lung were higher in the APRV group than in the LTV group; among them, the contents of occludin (
p
< 0.05) and E-cadherin (
p
< 0.05) of the whole lung were higher in the APRV group. Transmission electron microscopy showed that alveolar–capillary barrier damage was more severe in the middle lobe of lungs in the LTV group.
Conclusion:
In comparison with LTV, APRV could preserve the alveolar–capillary barrier architecture, mitigate lung histopathologic injury, increase the expression of cell junction protein, improve respiratory system compliance, and showed a trend to reduce extravascular lung water and improve oxygenation. These findings indicated that APRV might lead to more profound beneficial effects on the integrity of the alveolar–capillary barrier architecture and on the expression of biomarkers related to pulmonary permeability.
OBJECTIVES:To evaluate the efficacy and safety of airway pressure release ventilation in critically ill adults with acute hypoxemic respiratory failure.
DATA SOURCES:A systematic literature search of ...MEDLINE via PUBMED, EMBASE, the Cochrane Library, published conference proceedings and abstracts, reference lists of eligible studies and review articles, and hand searches of relevant journals and trial registers.
STUDY SELECTION:Eligible studies included randomized controlled trials published between years 2000 and 2018, comparing airway pressure release ventilation to any ventilation mode, in critically ill adults with acute hypoxemic respiratory failure and reporting at least one mortality outcome.
DATA EXTRACTION:Screened citations were reviewed and extracted independently by two investigators onto a prespecified proforma.
DATA SYNTHESIS:There were 412 patients from seven randomized controlled trials included in the qualitative and quantitative data synthesis. Airway pressure release ventilation was associated with a significant mortality benefit (relative risk, 0.67; 95% CI, 0.48–0.94; I < 0.1%; p = 0.97) and improvement in day 3 PaO2/FIO2 ratio (weighted mean difference, 60.4; 95% CI, 10.3–110.5). There was no significant difference in requirement to initiate rescue treatments including inhaled pulmonary vasodilators, prone positioning, or extracorporeal membrane oxygenation (relative risk, 0.51; 95% CI, 0.22–1.21; I = 64.7%; p = 0.04). The risk of barotrauma was only reported in three studies and did not differ between groups (relative risk, 0.39; 95% CI, 0.12–1.19; I < 0.1%; p = 0.99).
CONCLUSIONS:In adult patients requiring mechanical ventilation for acute hypoxic respiratory failure, airway pressure release ventilation is associated with a mortality benefit and improved oxygenation when compared with conventional ventilation strategies. Given the limited number of patients enrolled in the available studies, larger multicenter studies are required to validate these findings.
High-pressure gaseous methane release is a relevant safety-related problem mainly in the Oil and Gas industry. As well documented, the reason for these safety concerns is connected with the severe ...consequences of the domino effect subsequent to the possible ignition. In risk assessment activities, estimation of the damage area is of primary importance in order to draw up proper safety guidelines. To do this, loss prevention specialists use quick and well-established numerical tools (i.e., integral models) in their daily activities. However, the presence of an obstacle in the flow field of the jet (e.g., the ground) is a more probable situation to deal with. It is known that integral models fail in this kind of scenario, leading to unreliable predictions. Hence, the present work investigates how an industrial ground surface influences the LFL cloud size of a horizontal high-pressure methane jet. An innovative quick procedure is proposed allowing to determine the height below which the ground begins to influence the LFL cloud size and the extent of such influence. Therefore, this procedure allows practitioners to establish when integral models can be used and when not to use them, and also provides a simple and reliable alternative to their use. These analytical instruments are derived from an extensive computational fluid dynamics analysis performed with Ansys Fluent 19.0.
•A high-pressure methane jet outflowing from a loss of containment is simulated.•The influence of the ground on the LFL extension is investigated.•A simple procedure that allow to estimate the hazardous distance is proposed.
OBJECTIVES:Low tidal volume (= tidal volume ≤ 6 mL/kg, predicted body weight) ventilation using volume control benefits patients with acute respiratory distress syndrome. Airway pressure release ...ventilation is an alternative to low tidal volume-volume control ventilation, but the release breaths generated are variable and can exceed tidal volume breaths of low tidal volume-volume control. We evaluate the application of a low tidal volume-compatible airway pressure release ventilation protocol that manages release volumes on both clinical and feasibility endpoints.
DESIGN:We designed a prospective randomized trial in patients with acute hypoxemic respiratory failure. We randomized patients to low tidal volume-volume control, low tidal volume-airway pressure release ventilation, and traditional airway pressure release ventilation with a planned enrollment of 246 patients. The study was stopped early because of low enrollment and inability to consistently achieve tidal volumes less than 6.5 mL/kg in the low tidal volume-airway pressure release ventilation arm. Although the primary clinical study endpoint was PaO2/FIO2 on study day 3, we highlight the feasibility outcomes related to tidal volumes in both arms.
SETTING:Four Intermountain Healthcare tertiary ICUs.
PATIENTS:Adult ICU patients with hypoxemic respiratory failure anticipated to require prolonged mechanical ventilation.
INTERVENTIONS:Low tidal volume-volume control, airway pressure release ventilation, and low tidal volume-airway pressure release ventilation.
MEASUREMENTS AND MAIN RESULTS:We observed wide variability and higher tidal (release for airway pressure release ventilation) volumes in both airway pressure release ventilation (8.6 mL/kg; 95% CI, 7.8–9.6) and low tidal volume-airway pressure release ventilation (8.0; 95% CI, 7.3–8.9) than volume control (6.8; 95% CI, 6.2–7.5; p = 0.005) with no difference between airway pressure release ventilation and low tidal volume-airway pressure release ventilation (p = 0.58). Recognizing the limitations of small sample size, we observed no difference in 52 patients in day 3 PaO2/ FIO2 (p = 0.92). We also observed no significant difference between arms in sedation, vasoactive medications, or occurrence of pneumothorax.
CONCLUSIONS:Airway pressure release ventilation resulted in release volumes often exceeding 12 mL/kg despite a protocol designed to target low tidal volume ventilation. Current airway pressure release ventilation protocols are unable to achieve consistent and reproducible delivery of low tidal volume ventilation goals. A large-scale efficacy trial of low tidal volume-airway pressure release ventilation is not feasible at this time in the absence of an explicit, generalizable, and reproducible low tidal volume-airway pressure release ventilation protocol.
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