Stress evolution and support mechanism of a bolt anchored in a rock mass with a weak interlayer

By applying experimental method, the bolt stress and supporting mechanism is studied during the deformation process of a rock mass containing a weak interlayer. The force measuring bolt is installed manually and instrumented five pairs of symmetrical strain gauges. The experimental results show that the fully grouted bolt suffers tensile, compressive, bending and shear stress at the same time. The bolt stress evolution is closely related to the deformation stages of the rock mass which are very gradually varying stage, gradually varying stage at the pre-peak and suddenly varying stage at the post peak stage.The axial compressive stress in the bolt is mainly induced by the moment. Thus, in most cases the axial compressive stress is distributed on one side of the bolt. For axial stresses, induced by the axial force and the bending moment at the post-peak stage, three types of changing are observed, viz. increasingincreasing type, decreasing-increasing type and increasing-decreasing type. The stress characteristics of the bolt section in the weak interlayer are significantly different from those in the hard rock. The failure models of the anchored bolt are tensile failure and shear failure, respectively. The bolt not only provides constraints on the free surface of the rock mass, but also resists the axial and lateral loading by the bending moment. This study provides valuable guidelines for bolting support design and its safety assessment.

Support and Positioning Mechanism of a Detection Robot inside a Spherical Tank

Large pressure equipment needs to be tested regularly to ensure safe operation;wall-climbing robots can carry the necessary tools to inspect spherical tanks,such as cameras and non-destructive testing equipment.However,a wall-climbing robot inside a spherical tank cannot be accurately positioned owing to the particularity of the spherical tank structure.This paper proposes a passive support and positioning mechanism fixed in a spherical tank to improve the adsorption capacity and positioning accuracy of the inspection robot.The main body of the mechanism was designed as a truss composed of carbon fiber telescopic rods and can work in spherical tanks with diameters of 4.6-15.7 m.The structural strength,stiffness,and stability of the mechanism are analyzed via force and deformation simulations.By constructing a mathematical model of the support and positioning mechanism,the influence of structural deformation on the supporting capacity is analyzed and calculated.The robot positioning method based on the support and positioning mechanism can effectively locate the robot inside a spherical tank.Experiments verified the support performance and robot positioning accuracy of the mechanism.This research proposes an auxiliary support and positioning mechanism for a detection robot inside a spherical tank,which can effectively improve the positioning accuracy of the robot and meet the robotic inspection requirements.

A study of support strategies in deep soft rock:The horsehead crossing roadway in Daqiang Coal Mine

Geomechanics in deep mines becomes more complex and structural support in soft rock can be very difficult.Highly stressed soft rock subject to expansion deformation is particularly difficult to control.The Tiefa Coal Industry Group Daqiang Coal Mine is used as an example.A ventilation shaft,à550 horsehead,is located in tertiary soft rock.Analysis of the reasons for deformation shows an intumescent rock,which is easily damaged.Field observations and theoretical analysis led to a design capable of stabilizing the rock.A combination of spray,anchors,anchor bolts,and soft corner coupled truss supports allowed the deformation to be controlled.This provides a model for similar designs when support of a horsehead roadway is required.

Optimization of construction scheme and supporting technology for HJS soft rock tunnel

For a soft rock tunnel under high stress in jointed and swell soft rock （HJS）, two construction schemes pilot-tunneling enlarging excavation and step-by-step excavation were optimized using FLAC20, and the deformation effects of the two construction schemes were verified by field tests. Based on engineer- ing geological investigation and mechanical analysis of large deformations, the complex deformation mechanisms of stress expansion and structural deformation of the soft rock tunnel were confirmed, and support countermeasures from the complex deformation mechanism converted to a single type were proposed, and the support parameters were optimized by field tests. These technologies were proved by engineering practice, which produced significant technical and economic benefits.

The research of the evaluation system for the sealability of hydraulic supports and jacks＇ seals

In order to enhance the sealing quality and assemble efficiency of hydraulic supports, the evaluation system for the sealability of the hydraulic support and jack＇s seals was established through the testing and experimenting technology in respects, such as seals＇ dimensions, reasonable amounts of compression, sealability, life, resistance to pressure, etc. Through life detecting test of the seal, found the longest life seal ring under the same conditions, and through the reciprocating test of the hydraulic support, found the most appropriate amount of interference between the groove and the seal ring, thus, to decrease the leakage and extend the life span of the hydraulic support.

Rock roadway complementary support technology in Fengfeng mining district

This paper takes No.52 return uphill roadway of Yangquhe coal mine as a research project. Based on the research, especially its geological condition, indoor experiments, numerical simulation and theoretical analysis were employed to determine the difficult coefficients of Yangquhe project. By using these means,the difficult coefficients of the deep rock engineering were determined. From a study of the effects of crustal stress and the roof mechanism on roadway stability, the transformation mechanism in Yangquhe coal mine has been determined. As a result of this research, the interactive support technology of prestressed cable mesh was developed and the technology tested in mining engineering, which proved to be feasible.

High-resistance controlled yielding supporting technique in deep-well oil shale roadways

In order to avoid the deep-well oil shale roadway being deformed, damaged, or difficult to maintain after excavating and supporting in Haishiwan coal mine, this paper has analyzed the characteristics of the deformed roadway and revealed its failure mechanism by taking comprehensively the methods of field geological investigation, displacement monitoring of surrounding rock, rock properties and hydration properties experiments and field application tests. Based on this work, the high-resistance controlled yielding supporting principle is proposed, which is： to ＂resist＂ by high pre-tightening force and high stiff- ness in the early stage, to ＂yield＂ by making use of the controlled deformation of a yielding tube in the middle stage, and to ＂fix＂ by applying total-section Gunite in the later stage. A high-resistance controlled yielding supporting technique of ＂high pre-tightening force yielding anchor bolt ＋ small-bore pre-tight- ening force anchor cable ＋ rebar ladder beam ＋ rhombic metal mesh ＋ lagging gunite＂ has been estab- lished, and industrial on site testing implemented. The practical results show that the high-resistance controlled yielding supporting technique can effectively control the large deformation and long-time rheology of deep-well oil shale roadways and can provide beneficial references for the maintenance of other con-generic roadways.Deep-well Oil shale

Research on coal roadway truss and numerical simulation of bolting support effect

According to the research results in world, the paper comprehensively analyzed and gave a demonstration of mechanism of single-truss and its stressing advantage. Comparison and analysis effect were given to single-truss and bolting supporting. By the way of element simulation. The paper shows that single truss supporting have better effect to bolting supporting to improving the stress condition of surrounding rocks, controlling the surrounding rocks plastic failure development zone and deformation effect of surrounding rocks, which provided the elementary theory basis to the research, experiment and expanding the single-truss bolting technology in colliery.

Study on support mechanism of pre-stressed truss cable and its application

The truss cable support technology was put forward to control the large mining height and composite mudstone strata roadway. This technique makes the steady rock in roadway slantwise top be anchor points, makes the truss cable be steady support structure through special implement, and supplied rock in anchor area with horizontal and vertical pressure which strengthens the surrounding rock＇s anti-strain capability, so it can solve the support problem in roadway with the large cross section and large mining height with mudstone strata. The support mechanism of truss cable about how to make the soft strata stabilize is analyzed by use of the mechanical method. Based on the mechanism and numerical simulation method, the truss cable support project was designed and used to the large mining setting room in eleventh mining area of Bailong Mine successfully.

Symptomatic and optimal supportive care of critical COVID-19:A case report and literature review

BACKGROUND Coronavirus disease 2019(COVID-19)severity is classified as asymptomatic,mild,moderate,severe,and critical.Mild cases account for a large percentage of cases in the epidemic and typically exhibit a favorable prognosis.However,a 49%-67%mortality is noted in critical cases.No COVID-19-specific drug has been reported to date,and symptomatic and optimal supportive care,including oxygenation,anti-coinfection treatments,and ventilation,represent the mainstay of treatment for this disease,especially in critical patients.CASE SUMMARY In the above-mentioned context,we share our experience with the treatment of one critical COVID-19 case and review the relevant literature.CONCLUSION Timely tracheal intubation,reasonable mechanical ventilation support,appropriate anti-infection treatment,and early anticoagulation and immunity support are key factors in the successful treatment of this case.

Management of ventricular tachycardia storm in patients with structural heart disease

Electrical storm(ES) is a medical emergency characterized by repetitive episodes of sustained ventriculararrhythmias(VAs) in a limited amount of time(at least 3 within a 24-h period) leading to repeated appropriate implantable cardioverter defibrillator therapies. The occurrence of ES represents a major turning point in the natural history of patients with structural heart disease being associated with poor short-and longterm survival particularly in those with compromised left ventricular ejection fraction(LVEF) that can develop hemodynamic decompensation and multi-organ failure. Management of ES is challenging with limited available evidence coming from small retrospective series and a substantial lack of randomized-controlled trials. In general, a multidisciplinary approach including medical therapies such as anti-arrhythmic drugs, sedation, as well as interventional approaches like catheter ablation, may be required. Accurate patient risk stratification at admission for ES is pivotal and should take into account hemodynamic tolerability of VAs as well as comorbidities like low LVEF, advanced NYHA class and chronic pulmonary disease. In high risk patients, prophylactic mechanical circulatory support with left ventricular assistance devices or extracorporeal membrane oxygenation should be considered as bridge to ablation and recovery. In the present manuscript we review the available strategies for management of ES and the evidence supporting them.

Optimal timing of same-admission orthotopic heart transplantation after left ventricular assist device implantation

AIM To investigate the impact of timing of same-admission orthotopic heart transplant(OHT) after left ventricular assist device(LVAD) implantation on in-hospital mortality and post-transplant length of stay.METHODS Using data from the Nationwide Inpatient Sample from 1998 to 2011, we identified patients 18 years of age or older who underwent implantation of a LVAD and for whom the procedure date was available. We calculated in-hospital mortality for those patients who underwent OHT during the same admission as a function of time from LVAD to OHT, adjusting for age, sex, race, household income, and number of comorbid diagnoses. Finally, we analyzed the effect of time to OHT after LVAD implantation on the length of hospital stay post-transplant.RESULTS Two thousand and two hundred patients underwent implantation of a LVAD in this cohort. One hundred and sixty-four(7.5%) patients also underwent OHT duringthe same admission, which occurred on average 32 d(IQR 7.75-66 d) after LVAD implantation. Of patients who underwent OHT, patients who underwent transplantation within 7 d of LVAD implantation("early") experienced increased in-hospital mortality(26.8% vs 12.2%, P = 0.0483) compared to patients who underwent transplant after 8 d("late"). There was no statistically significant difference in age, sex, race, household income, or number of comorbid diagnoses between the early and late groups. Post-transplant length of stay after LVAD implantation was also not significantly different between patients who underwent early vs late OHT. CONCLUSION In this cohort of patients who received LVADs, the rate of in-hospital mortality after OHT was lower for patients who underwent late OHT(at least 8 d after LVAD implantation) compared to patients who underwent early OHT. Delayed timing of OHT after LVAD implantation did not correlate with longer hospital stays post-transplant.

Ground pressure and overlying strata structure for a repeated mining face of residual coal after room and pillar mining

To investigate the abnormal ground pressures and roof control problem in fully mechanized repeated mining of residual coal after room and pillar mining, the roof fracture structural model and mechanical model were developed using numerical simulation and theoretical analysis. The roof fracture characteristics of a repeated mining face were revealed and the ground pressure law and roof supporting condi- tions of the repeated mining face were obtained. The results indicate that when the repeated mining face passes the residual pillars, the sudden instability causes fracturing in the main roof above the old goal and forms an extra-large rock block above the mining face. A relatively stable ＂Voussoir beam＂ structure is formed after the advance fracturing of the main roof. When the repeated mining face passes the old goaf, as the large rock block revolves and touches gangue, the rock block will break secondarily under overburden rock loads. An example calculation was performed involving an integrated mine in Shanxi province, results showed that minimum working resistance values of support determined to be reason- able were respectively 11,412 kN and 10,743 kN when repeated mining face passed through residual pillar and goaf. On-site ground pressure monitoring results indicated that the mechanical model and support resistance calculation were reasonable.

Extra-corporeal membrane oxygenation in aortic surgery and dissection: A systematic review

BACKGROUND Very little is known about the role of extracorporeal membrane oxygenation(ECMO)for the management of patients undergoing major aortic surgery with particular reference to aortic dissection.AIM To review the available literature to determine if there was any evidence.METHODS A systematic literature search through PubMed and EMBASE was undertaken according to specific key words.RESULTS The search resulted in 29 publications relevant to the subject:1 brief communication,1 surgical technique report,1 invited commentary,1 retrospective case review,1 observational study,4 retrospective reviews,13 case reports and 7 conference abstracts.A total of 194 patients were included in these publications of whom 77 survived.CONCLUSION Although there is no compelling evidence for or against the use of ECMO in major aortic surgery or dissection,it is enough to justify its use in this patient population despite current adverse attitude.

The role of temporary mechanical circulatory support in de novo heart failure syndromes with cardiogenic shock:A contemporary review

Cardiogenic shock(CS)is a complex clinical syndrome with a high mortality rate.It can occur to due to multiple etiologies of cardiovascular disease and is phenotypically heterogeneous.Acute myocardial infarction-related CS(AMI-CS)has historically been the most prevalent cause,and thus,research and guidance have focused primarily on this.Recent data suggest that the burden of non-ischemic CS is increasing in the population of patents requiring intensive care admission.There is,however,a paucity of data and guidelines to inform the management of these patients who fall into two broad groups:those with existing heart failure and CS and those with no known history of heart failure who present with"de novo"CS.The use of temporary mechanical circulatory support(MCS)has expanded across all etiologies,despite its high cost,resource intensity,complication rates,and lack of high-quality outcome data.Herein,we discuss the currently available evidence on the role of MCS in the management of patients with de novo CS to include fulminant myocarditis,right ventricular(RV)failure,Takotsubo syndrome,post-partum cardiomyopathy,and CS due to valve lesions and other cardiomyopathies.

To ventricular assist devices or not:When is implantation of a ventricular assist device appropriate in advanced ambulatory heart failure?

Advanced heart failure has been traditionally treated via either heart transplantation,continuous inotropes,consideration for hospice and more recently via left ventricular assist devices(LVAD).Heart transplantation has been limited by organ availability and the futility of other options has thrust LVAD therapy into the mainstream of therapy for end stage heart failure.Improvements in technology and survival combined with improvements in the quality of life have made LVADs a viable option for many patients suffering from heart failure.The question of when to implant these devices in those patients with advanced,yet still ambulatory heart failure remains a controversial topic.We discuss the current state of LVAD therapy and the risk vs benefit of these devices in the treatment of heart failure.

Auctions to reveal consumers’willingness to pay for low-carbon hydrogen projects:combining lessons from renewables and natural-gas industries

Low-carbon hydrogen is expected to play a key role in realizing net-zero and sustainable development plans.Nonetheless,there is a gap between the cost of producing low-carbon hydrogen and its potential users’willingness to pay for such hydrogen.To implement support for the development of the industry,we propose using low-carbon hydrogen long-term agreements allocated through auction mechanisms.The objectives are 2-fold:(i)matching supply and demand volumes considering the time horizon and geographical delivery point specification and(ii)allocating the subsidy.This perspective article innovates by proposing a reference price indexed to liquid to natural-gas prices,which is the main product that low-carbon hydrogen aims to substitute.The premium and the production cost are defined through a double-sided auction.This aims to minimize the public policy funds required to incentivize the low-carbon hydrogen market while facilitating long-term agreements and mitigating price risks that may hinder investment.

A Mechanism Supporting the Client/Server Relationship in the Operating System of Distributed System “THUDS”

This paper presents a distributed operating system modeled as an abstract machine that provides all the distributed processes with the same set of services.The kernel of our operating system supports ser- vices which are achieved by a remote procedure call on requests by parallel processes.Therefore,a scheme for solving the client-server relationship is required.In our system there are more than one cli- ents and,at least,a receive would he required for each.Similarly,there are more than one servers such that the send in a client should produce a message that can he received by every server. Consequently,a mechanism well suited for programming multiple-clients/single-server and sin- gle client/multiple-servers interactions is proposed.

CLINICAL OUTCOMES OF 22 PEDIATRIC PATIENTS WITH CONGENITAL HEART DISEASE MANAGED WITH MECHANICAL CIRCULATORY SUPPORT AFTER CARDIAC SURGERY

Objective To investigate the clinical outcomes of children with congenital heart disease （CHD） requiring extracorporeal membrane oxygenation （ECMO） and left ventricular assist device （LVAD） support after cardiac surgery. Methods A total of 22 patients with CHD who required postcardiotomy mechanical circulatory support between March 2004 and March 2011 （85 months ） were analyzed retrospectively. Median age of the patients was 420 d （ 15 d - 4 years） and median weight was 3.4 kg （ 2 - 14. 5 kg ）. Eight patients were put on ECMO, while 14 patients were placed on LVAD. Results Thirteen （59%） patients died and 9 （41% ） survived to discharge. In survivals, the duration of LVAD and the duration of ECMO were both shorter than those of nonsurvivals （P 〈 O. 05）. The main complication was bleeding. Conclusion The earlier treatment and application of more advanced cardiac support devices for CHD patients are key factors for reducing complications.

Pharmacological strategies in extracorporeal membrane oxygenation weaning failure: a call to action

Extracorporeal membrane oxygenation has emerged as a viable alternative for stabilizing and improving critically ill patients in acute cardiovascular diseases.However,the weaning stage has been associated with a high morbidity and mortality rate.This makes searching for strategies that reduce failure in this final process necessary.Implementing a new approach must be tried and included in our protocols,seeking the patient’s well-being at all times.In this article,the authors discuss their point of view regarding potential pharmacological alternatives and the mechanism of action involved,which could decrease the mortality associated with this therapeutic.