The waste of coal resources, a complicated production process and slow mining speed seriously restrict the rapid development of longwall mining. To achieve effective mining, an innovative noncoal ...pillar mining approach (i.e., Gob-side Entry Retaining by Roof Cutting (GERRC)) was introduced. The mechanism of the GERRC approach and its three key technologies (i.e., roof support technology, directional presplit cumulative blasting technology and surrounding rock control technology) were studied by theoretical analysis, numerical simulation, laboratory and field experiments. The new approach was finally tested under medium-thick coal seam and compound roof conditions. The results show that the directional presplit cumulative blasting technology can effectively control the damage evolution in the roof rock, maintain the integrity of the entry roof and contribute the gob roof to the cave in time. The support technologies in different roof movement stages can control the entry surroundings, and the final section of the retained entry met the safety production requirements. The test results suggested that the proposed approach for coal effective mining is feasible, and the introduced key technologies and design methods potentially produce reasonable values for applications of pillarless mining in similar projects.
Virus filtration is a downstream unit operation in the manufacturing of biotherapeutics to remove potential viral contaminations based on size exclusion. While even very small viruses are effectively ...retained under normal flow conditions, process interruptions can compromise the virus-reduction capacity of a filter. Yet, direct insights into the underlying flow-dependent retention and breakthrough mechanisms of relevant parvoviruses are still lacking. To study the retention of parvoviruses inside the polymeric structures of four commonly used filter types, minute virus of mice (MVM) was fluorescently labeled and visualized in membrane cross-sections post-filtration by laser scanning microscopy. The virus retention profiles revealed a membrane structure-specific accumulation of viral particles at a distinct depth in the separation-active layers. Pressure release experiments showed that flow interruption-induced virus breakthrough is associated with the mobilization and deeper migration of viruses into denser membrane layers. Moreover, we discovered that local clusters of breakthrough foci in a particular filter type are responsible for the substantial transmission of viruses to the filtrate. Taken together, the membrane-specific phenomena visualized herein contribute to a better understanding of the underlying virus retention mechanisms and provide cues for a specific optimization of virus filtration processes.
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•First comparative visualization of a relevant parvovirus in different filters.•Viruses are retained in characteristic membrane structure-related patterns.•Flow interruptions lead to mobilization and deeper migration of viruses.•Clusters of breakthrough foci cause substantial virus penetration through filters.
•The critical burst pressure for ignition decreases with tube length increase.•Higher release pressure reduces ignition delay time.•The speed of flame front in the air has a sharp increase.•A strong ...deflagration is observed and leads to the pressure increase.•The jet flame shows different morphologies at different release stages.
Spontaneous ignition and subsequent flame propagation of high-pressure hydrogen release via a tube into air are experimentally investigated using pressure records, flame detection and direct high-speed photographs. The study shows that as the burst pressure increases the likelihood of spontaneous ignition increases and the initial ignition is closer to the burst disk. With the increase of tube length, the possibility of spontaneous ignition increases, while the critical release pressure for spontaneous ignition decreases. It is also found that a strong shock wave generated to trigger the ignition and a long tube to promote the growth of the flame are two key factors for the transition from spontaneous ignition inside the tube to jet flame in the air. After the flame exits from the tube, a flame envelope is formed in the front of the hydrogen jet, which gradually splits into upstream and downstream combustion regions. The upstream flame region propagates forward. However, the downstream flame region moves back toward the tube exit. The flame is then stabilized at the tube exit and gradually grows. Noticeable deflagration events were observed to occur successively in the semi-enclosed space. The deflagration leads to a significant increase of pressure in the chamber. And the overpressure of the deflagration is higher than that of the leading shock wave. Both the overpressures of the leading shock wave and the deflagration increase with the release pressure. A stable jet flame is formed outside the tube subsequent to the deflagration. And different jet flame configurations are observed at different controlling mechanisms of flow.
Purpose
Experimental animal models of acute respiratory distress syndrome (ARDS) have shown that the updated airway pressure release ventilation (APRV) methodologies may significantly improve ...oxygenation, maximize lung recruitment, and attenuate lung injury, without circulatory depression. This led us to hypothesize that early application of APRV in patients with ARDS would allow pulmonary function to recover faster and would reduce the duration of mechanical ventilation as compared with low tidal volume lung protective ventilation (LTV).
Methods
A total of 138 patients with ARDS who received mechanical ventilation for <48 h between May 2015 to October 2016 while in the critical care medicine unit (ICU) of the West China Hospital of Sichuan University were enrolled in the study. Patients were randomly assigned to receive APRV (
n
= 71) or LTV (
n
= 67). The settings for APRV were: high airway pressure (P
high
) set at the last plateau airway pressure (P
plat
), not to exceed 30 cmH
2
O) and low airway pressure ( P
low
) set at 5 cmH
2
O; the release phase (T
low
) setting adjusted to terminate the peak expiratory flow rate to ≥ 50%; release frequency of 10–14 cycles/min. The settings for LTV were: target tidal volume of 6 mL/kg of predicted body weight; P
plat
not exceeding 30 cmH
2
O; positive end-expiratory pressure (PEEP) guided by the PEEP–FiO
2
table according to the ARDSnet protocol. The primary outcome was the number of days without mechanical ventilation from enrollment to day 28. The secondary endpoints included oxygenation, P
plat
, respiratory system compliance, and patient outcomes.
Results
Compared with the LTV group, patients in the APRV group had a higher median number of ventilator-free days {19 interquartile range (IQR) 8–22 vs. 2 (IQR 0–15);
P
< 0.001}. This finding was independent of the coexisting differences in chronic disease. The APRV group had a shorter stay in the ICU (
P
= 0.003). The ICU mortality rate was 19.7% in the APRV group versus 34.3% in the LTV group (
P
= 0.053) and was associated with better oxygenation and respiratory system compliance, lower P
plat
, and less sedation requirement during the first week following enrollment (
P
< 0.05, repeated-measures analysis of variance).
Conclusions
Compared with LTV, early application of APRV in patients with ARDS improved oxygenation and respiratory system compliance, decreased P
plat
and reduced the duration of both mechanical ventilation and ICU stay.
Assisted mechanical ventilation may alter the pressure profile in the thorax compared to normal breathing, which can affect the blood flow to and from the heart. Studies suggest that in patients with ...severe lung disease, airway pressure release ventilation (APRV) may be haemodynamically beneficial compared to other ventilator settings. The primary aim of this study was to investigate if APRV affects cardiac index in intubated intensive care patients without severe lung disease when compared to pressure support ventilation (PSV). The secondary aim comprised potential changes in other haemodynamic and ventilatory parameters.
Twenty patients were enrolled in the intensive care unit (ICU) at Sahlgrenska University Hospital. Eligible patients met the inclusion criteria; 18 years of age or above, intubated and mechanically ventilated, triggering and stable on PSV mode, with indwelling haemodynamic monitoring via a pulse-induced continuous cardiac output (PiCCO) catheter. The study protocol started with a 30-min interval on PSV mode, followed by a 30-min interval on APRV mode, and finally a 30-min interval back on PSV mode. At the end of each interval, PiCCO outputs, ventilator outputs, arterial and venous blood gas analyses, heart rate and central venous pressure were recorded and compared between modes.
There was no significant difference in cardiac index (3.42 vs. 3.39 L/min/m
) between PSV and APRV, but a significant increase in central venous pressure (+1.0 mmHg, p = .027). Furthermore, we found a significant reduction in peak airway pressure (-3.16 cmH
O, p < .01) and an increase in mean airway pressure (+2.1 cmH
O, p < .01). No statistically significant change was found in oxygenation index (partial pressure of O
pO
/fraction of inspired oxygen) nor in other secondary outcomes when comparing PSV and APRV. There was no significant association between global end-diastolic volume index and cardiac index (R
= 0.0089) or central venous pressure (R
= 0.278). All parameters returned to baseline after switching the ventilator mode back to PSV.
We could not detect any changes in cardiac index in ICU patients without severe lung disease during APRV compared to PSV mode, despite lower peak airway pressure and increased mean airway pressure.
In the pursuit of science, competitive ideas and debate are necessary means to attain knowledge and expose our ignorance. To quote Murray Gell-Mann (1969 Nobel Prize laureate in Physics): “Scientific ...orthodoxy kills truth”. In mechanical ventilation, the goal is to provide the best approach to support patients with respiratory failure until the underlying disease resolves, while minimizing iatrogenic damage. This compromise characterizes the philosophy behind the concept of “lung protective” ventilation. Unfortunately, inadequacies of the current conceptual model–that focuses exclusively on a nominal value of low tidal volume and promotes shrinking of the “baby lung” - is reflected in the high mortality rate of patients with moderate and severe acute respiratory distress syndrome. These data call for exploration and investigation of competitive models evaluated thoroughly through a scientific process. Airway Pressure Release Ventilation (APRV) is one of the most studied yet controversial modes of mechanical ventilation that shows promise in experimental and clinical data. Over the last 3 decades APRV has evolved from a rescue strategy to a preemptive lung injury prevention approach with potential to stabilize the lung and restore alveolar homogeneity. However, several obstacles have so far impeded the evaluation of APRV’s clinical efficacy in large, randomized trials. For instance, there is no universally accepted standardized method of setting APRV and thus, it is not established whether its effects on clinical outcomes are due to the ventilator mode
per se
or the method applied. In addition, one distinctive issue that hinders proper scientific evaluation of APRV is the ubiquitous presence of myths and misconceptions repeatedly presented in the literature. In this review we discuss some of these misleading notions and present data to advance scientific discourse around the uses and misuses of APRV in the current literature.
Airway pressure release ventilation is a ventilatory mode characterized by a mandatory inverse inspiratory:expiratory ratio with a very short expiratory phase, aimed to avoid derecruitment and allow ...spontaneous breathing. Recent basic and clinical evidence suggests that this mode could be associated with improved outcomes in patients with acute respiratory distress syndrome. The aim of this study was to compare the outcomes between airway pressure release ventilation and traditional ventilation targeting low tidal volume, in patients with severe coronavirus disease 2019.
Single-center randomized controlled trial.
ICU of a Mexican referral center dedicated to care of patients with confirmed diagnosis of coronavirus disease 2019.
Ninety adult intubated patients with acute respiratory distress syndrome associated with severe coronavirus disease 2019.
Within 48 hours after intubation, patients were randomized to either receive ventilatory management with airway pressure release ventilation or continue low tidal volume ventilation.
Forty-five patients in airway pressure release ventilation group and 45 in the low tidal volume group were included. Ventilator-free days were 3.7 (0-15) and 5.2 (0-19) in the airway pressure release ventilation and low tidal volume groups, respectively (p = 0.28). During the first 7 days, patients in airway pressure release ventilation had a higher Pao2/Fio2 (mean difference, 26 95%CI, 13-38; p < 0.001) and static compliance (mean difference, 3.7 mL/cm H2O 95% CI, 0.2-7.2; p = 0.03), higher mean airway pressure (mean difference, 3.1 cm H2O 95% CI, 2.1-4.1; p < 0.001), and higher tidal volume (mean difference, 0.76 mL/kg/predicted body weight 95% CI, 0.5-1.0; p < 0.001). More patients in airway pressure release ventilation had transient severe hypercapnia, defined as an elevation of Pco2 at greater than or equal to 55 along with a pH less than 7.15 (42% vs 15%; p = 0.009); other outcomes were similar. Overall mortality was 69%, with no difference between the groups (78% in airway pressure release ventilation vs 60% in low tidal volume; p = 0.07).
In conclusion, when compared with low tidal volume, airway pressure release ventilation was not associated with more ventilator-free days or improvement in other relevant outcomes in patients with severe coronavirus disease 2019.
In the Oil & Gas sector, the use of flammable substances stored and transported in gaseous form and under pressure conditions is quite common. In the field of industrial safety, high-pressure gaseous ...releases of a flammable material impacting an obstacle are of paramount importance, as possible accidental scenarios, due to their catastrophic consequences. Although hot release (i.e., jet fire scenarios) is a topic that has been largely covered in literature, cold releases (i.e., unignited flammable releases) did not. This gap increases when considering high-pressure cold releases interacting with an obstacle. Being a probable situation when an accidental high-pressure loss of containment occurs, the need of reliable as well as quick tools for prompt safety evaluations of the hazardous area of this kind of scenario is of primary importance. To this aim, the present work proposes such a consequences assessment tool derived from an extensive CFD analysis of several possible situations of a cylindrical obstacle impinged by an unignited high-pressure gaseous methane jet.
•a high-pressure methane jet outflowing from a loss of containment is simulated.•The influence of cylindrical tanks on the LFL extension is investigated by CFD.•a simple procedure that allow to estimate the hazardous distance is proposed.
Nowadays methane is a fossil fuel widely used both in industries and in civil appliances. From the safety point of view, due to its flammability, its use implies hazards for people and assets. The ...hazardous area related to a high-pressure jet of methane arising from an accidental loss of containment requires the estimation of the distance at which the methane concentration falls below the Lower Flammability limit. Such a topic is well covered in the literature when considering free jet conditions, i.e., jets that do not interact with any equipment or surface. The same cannot be said for high pressure jets impacting an obstacle. In this context, the present work focuses on studying high pressure methane jets impacting spherical obstacles by means of Computational Fluid Dynamics with the aim of giving some insights about such a jet-obstacle interaction, possibly providing a brief by-hand procedure that, only based on known scenario information, allows to estimate the maximum extent of the unignited high-pressure jet when interacting with a spherical obstacle.
•A high-pressure methane jet outflowing from a loss of containment is simulated.•The influence of a spherical obstacle on the LFL extension is investigated.•A simple procedure that permits to estimate the hazardous distance is proposed.
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