Application of extended criteria donor grafts in liver transplantation for acute-on-chronic liver failure:A retrospective cohort study

BACKGROUND There is no consensus on the usage of extended criteria donor(ECD)grafts in liver transplantation(LT)for acute-on-chronic liver failure(ACLF)patients.AIM To summarize the experience of using ECD livers in ACLF-LT.METHODS A retrospective cohort study was conducted,enrolling patients who underwent LT at the First Affiliated Hospital of Sun Yat-Sen University from January 2015 to November 2021.The patients were divided into ECD and non-ECD groups for analysis.RESULTS A total of 145 recipients were enrolled in this study,of which ECD and non-ECD recipients accounted for 53.8%and 46.2%,respectively.Donation after cardiac death(DCD)recipients accounted for the minority compared with donation after brain death(DBD)recipients(16.6%vs 83.4%).Neither overall survival nor graft survival significantly differed between ECD and non-ECD and DCD and DBD recipients.ECD grafts were associated with a significantly higher incidence of early allograft dysfunction(EAD)than non-ECD grafts(67.9%vs 41.8%,P=0.002).Postoperative outcomes between DCD and DBD recipients were comparable(P>0.05).ECD graft(P=0.009),anhepatic phase(P=0.034)and recipient gamma glutamyltransferase(P=0.016)were independent risk factors for EAD.Recipient preoperative number of extrahepatic organ failures>2(P=0.015)and intraoperative blood loss(P=0.000)were independent predictors of poor post-LT survival.CONCLUSION Although related to a higher risk of EAD,ECD grafts can be safely used in ACLF-LT.The main factors affecting post-LT survival in ACLF patients are their own severe preoperative disease and intraoperative blood loss.

Energy evolution mechanism and failure criteria of jointed surrounding rock under uniaxial compression

The object of this article is to investigate the energy evolution mechanism and failure criteria of cross-jointed samples containing an opening during deformation and failure based on the uniaxial compression test and rock energy principle.The results show that the energy evolution characteristics of the samples correspond to a typical progressive damage mode.The peak total energy,peak elastic energy,and total input energy of the samples all first decrease and then increase with an increase of half of the included angle,reaching their minimum values when this angle is 45°,while the dissipated energy generally increases with this angle.The existence of the opening and cross joints can obviously weaken the energy storage capacity of the rock,and the change in the included angle of the cross joint has a great influence on the elastic energy ratio of the sample before the peak stress,which leads to some differences in the distribution laws of the input energy.The continuous change and the subsequent sharp change in the rate of change in the energy consumption ratio can be used as the criteria of the crack initiation and propagation and the unstable failure of the sample,respectively.

Initial support distance of a non-circular tunnel based on convergence constraint method and integral failure criteria of rock

For deep tunnel projects,selecting an appropriate initial support distance is critical to improving the self-supporting capacity of surrounding rock.In this work,an intuitive method for determining the tunnel’s initial support distance was proposed.First,based on the convergence-confinement method,a three-dimensional analytical model was constructed by combining an analytical solution of a non-circular tunnel with the Tecplot software.Then,according to the integral failure criteria of rock,the failure tendency coefficients of hard surrounding rock were computed and the spatial distribution plots of that were constructed.On this basis,the tunnel’s key failure positions were identified,and the relationship between the failure tendency coefficient at key failure positions and their distances from the working face was established.Finally,the distance from the working face that corresponds to the critical failure tendency coefficient was taken as the optimal support distance.A practical project was used as an example,and a reasonable initial support distance was successfully determined by applying the developed method.Moreover,it is found that the stability of hard surrounding rock decreases rapidly within the range of 1.0D(D is the tunnel diameter)from the working face,and tends to be stable outside the range of 1.0D.

Upper bound analysis of ultimate pullout capacity of shallow 3-D circular plate anchors based on nonlinear Mohr-Coulomb failure criterion

Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultimate pullout capacity(UPC)is determined.A derivative function of the projection function for projecting the 3-D axisymmetric failure surface on plane is deduced using the variation theory.By using difference principle,the primitive function of failure surface satisfying boundary condition and numerical solution to its corresponding ultimate pullout capacity function are obtained.The influences of nonlinear Mohr-Coulomb parameters on UPC and failure mechanism are studied.The result shows that UPC decreases with dimensionless parameter m and uniaxial tensile strength increases but increases when depth and radius of plate anchor,surface overload,initial cohesion,geomaterial density and friction angle increase.The failure surface is similar to a symmetrical spatial funnel,and its shape is mainly determined by dimensionless parameter m;the surface damage range expands with the increase of radius and depth of the plate anchor as well as initial cohesion but decreases with the increase of dimensionless parameter m and uniaxial tensile strength as well as geomaterial density.As the dimensionless parameter m=2.0,the numerical solution of UPC based on the difference principle is proved to be feasible and effective through the comparison with the exact solution.In addition,the comparison between solutions of UPC computed by variation method and those computed by upper bound method indicate that variation method outperforms upper bound method.

Evaluation of the Reliability Performance of Failure Criteria for Composite Structures

Evolution of materials, following the design requirements of special structures, has shifted interest towards development of composite members able to meet strength requirements “tailored” to specific applications. These members can provide appropriate, more cost effective structures, however absence of generic design guidelines raise constraints towards derivation of optimized structures. Reliability-based assessment can overcome this limitation by ensuring that acceptable levels of target reliability are achieved throughout their service life. This paper presents a methodology for reliability assessment of composite members based on appropriate limit state functions derived according to fundamental failure criteria, Tsai-Hill and Tsai-Wu, applicable to composite materials. The methodology that is proposed employs a Stochastic Response Surface Method (SRSM) which combines in discrete steps FEA modelling, numerical simulations and analytical probabilistic assessment techniques, allowing use of commercial and custom developed specialized numerical tools. Application of the proposed methodology on a complex composite structural geometry will illustrate its efficiency and evaluate the reliability performance of the limit states derived and examined.

Failure criteria of unreinforced masonry walls of rural buildings under the impact of flash floods in mountainous regions

Damage to rural buildings in mountainous regions caused by flash floods accounts for a significant proportion of economic losses from disasters.The unreinforced masonry(URM)wall is the most vulnerable structural element of rural buildings exposed to flash floods.The failure of a URM wall indicates damage to rural buildings in flash floods.Based on the yield line theory of out-of-plane damage of URM walls and the virtual work method,brittle failure criteria for URM walls under the impact of flash floods were established.According to the field investigation data of the 26 June 2020 flash flood event in Damawu Gully and the corresponding simulation results of FLO-2D,the disaster-causing process was analysed,and the failure criteria were validated.Three building parameters were identified to influence the flood-resistance of URM walls,including the mortar grade,the span-to-height ratio of the wall,and the number of floors of the rural building.The results showed that the cause of the 26June disaster was the diversion of a 50-year flash flood into the residential community on the alluvial fan.The affected buildings were constructed with hollow blocks and lacked flood-resistance reinforcement.The critical failure depth of a URM wall restrained at the top by ring beams(RBs)under hydrostatic load conditions is 1.17 to 1.20 times greater than that of a URM wall without RBs,and the difference is even more pronounced when lowerstrength mortar is used.The flood-resistance of a URM wall constructed with Mb 7.5 mortar and restrained by RBs is almost as strong as that of a URM wall constructed with Mb 20 mortar and without RBs.The span-to-height ratio of a URM wall should not be greater than 1.875 in this case.However,the flood-resistance of a URM wall with RB restraint is almost independent of the span-to-height ratio.The brittle fracture energy of masonry mortar is more crucial to the flood-resistance of 4-edge restrained URM walls if L/Z>1.875.The flood-resistance of the URM wall of the first storey increases linearly with the number of floors.Single-storey rural buildings should be given priority to the use of high-grade masonry mortar and high-density blocks to improve flood-resistance.The failure criteria and the influence laws of building parameters on the flood-resistance of URM walls can provide references for flash flood mitigation and flood-resistance reinforcement of rural buildings in mountainous regions of Southwest China.

Predicting Virological Failure with Immunological Criteria in First Line ART Patients in a Resource Poor Setting

Indroduction: National Aids control Organisation in India implementing National AIDS control?program uses WHO’s immunological criteria to screen virological failure. Using immunological criteria to detect virological failure has to be assessed. Predicting virological failure with immunological criteria in resource limited settings had low sensitivity. Factors that influence the outcome are studied. Methods: Retrospective study in tertiary care centre for HIV and TB, Chennai, India. Out of 35,044 on ART between January 2008 and September 2009, 452 suspected immunological failures were referred. 273 screened for virological failure.?Frequency, sensitivity/specificity, positive/negative predictive values, chi-square test, odds-ratio, independent sample t test for viral load greater than 10,000 and 1000 of each immunological criterion using Epi-Info and SPSS version 19. Results: 172 had virological failure (62.09%). Average age of failed was 37.33. Single criteria’s sensitivity was 60 to 84 for detecting virolological failure. Two or more criteria had specificity 55 to 79. Combination of two or more criteria increased odds ratio for virological failure. Positive predictive value was above 63 for all criteria. PPV was above 80 to the criterion all three positive. Conclusions: ART naive patients with >95% adherence the sensitivity of immunological criteria to detect virological failure is three times than earlier studies. Combination of criteria is more significantly associated with virological failure. Odds ratio doubled for two or more combination of criteria. Immunological criteria is affordable/acceptable for screening virological failure, with adherence > 95% and longer the duration of ART.

Modified EASL-CLIF criteria that is easier to use and perform better to prognosticate acute-on-chronic liver failure

BACKGROUND We have recently shown that the European Association for the Study of the Liver-Chronic Liver Failure Consortium(EASL-CLIF)criteria showed a better sensitivity to detect acute-on-chronic liver failure(ACLF)with a better prognostic capability than the North American Consortium for the Study of End-Stage Liver Disease criteria.AIM To simplify EASL-CLIF criteria for ease of use without sacrificing its sensitivity and prognostic capability.METHODS Using the United Network for Organ Sharing data(January 11,2016,to August 31,2020),we modified EASL-CLIF(mEACLF)criteria;the modified mEACLF criteria included six organ failures(OF)as in the original EASL-CLIF,but renal failure was defined as creatinine≥2.35 mg/dL and coagulation failure was defined as international normalized ratio(INR)≥2.0.The mEACLF grades(0,1,2,and≥3)directly reflected the number of OF.RESULTS Of the 40357 patients,14044 had one or more OF,and 9644 had ACLF grades 1-3 by EASL-CLIF criteria.By the mEACLF criteria,15574 patients had one or more OF.The area under the receiver operating characteristic(AUROC)for 30-d allcause mortality by OF was 0.842(95%CI:0.831-0.853)for mEACLF and 0.835(95%CI:0.824-0.846)for EASL-CLIF(P=0.006),and AUROC for 30-d transplantfree mortality by OF was 0.859(95%CI:0.849-0.869)for mEACLF and 0.851(95%CI:0.840-0.861)for EASL-CLIF(P=0.001).The AUROC of 30-d all-cause mortality by ACLF grades was 0.842(95%CI:0.831-0.853)for mEACLF and 0.793(95%CI:0.781-0.806)for EASL-CLIF(P<0.0001).The AUROC of 30-d transplant-free mortality by ACLF was 0.859(95%CI:0.848-0.869)for mEACLF and 0.805(95%CI:0.793-0.817)for EASL-CLIF(P<0.0001).CONCLUSION Our study showed that EASL-CLIF criteria for ACLF grades could be simplified for ease of use without losing its prognostication capability and sensitivity.

Mechanical model for failure modes of rock and soil under compression

The failure modes of rock and soil under compression are complex phenomena that have not been explained in a mechanical perspective. However, large amounts of studies indicate that the failure modes of rock and soil samples can be categorized into eight types. In this work, the inner tensile stress and the dissipation and conversion of energy of rock and soil under compression are analyzed, then the effective conversion coefficient of energy is deduced, thus the tensile failure criterion of rock and soil under compression is established. Combined with the shear strength criterion of Mohr–Coulomb, a tensile joint shear strength criterion for rock and soil under compression is built. Therefore, a mechanical criterion model concerning the failure modes of rock and soil under compression is established and verified by tests. This model easily explains the test results in the existing literature and many natural phenomena, such as collapse.

Prognostic models for acute liver failure

BACKGROUND: Acute liver failure (ALF) remains a dramatic and unpredictable disease with high morbidity and mortality. Early and accurate prognostic assessment of patients with ALF is critically important for optimum clinical pathway. DATA SOURCES: Five English-language medical databases, MEDLINE, Science Direct, OVID, Springer Link and Wiley Interscience were searched for articles on 'acute liver failure', 'prognosis', and related topics. RESULTS: Multi-variable prognostic models including the King's College Hospital criteria and the model for end-stage liver disease score have been widely used in determination of the prognosis of ALF, but the results are far from satisfactory. Other prognostic indicators including serum Gc-globulin, arterial blood lactate, serum phosphate, arterial blood ammonia, and serum alpha-fetoprotein are promising but await further assessement. CONCLUSIONS: A reliable prognostic model to be developed in the future should not only have predictive value for poor outcome but also help to predict the survival of patients without a liver transplantation. Further studies are necessary to assess the prognostic accuracy of any new models. (Hepatobiliary Pancreat Dis Int 2010; 9: 122-128)

Diagnosis and treatment of heart failure with preserved left ventricular ejection fraction

Nearly six million people in United States have heart failure.Fifty percent of these people have normal left ventricular(LV)systolic heart function but abnormal diastolic function due to increased LV myocardial stiffness.Most commonly,these patients are elderly women with hypertension,ischemic heart disease,atrial fibrillation,obesity,diabetes mellitus,renal disease,or obstructive lung disease.The annual mortality rate of these patients is 8%-12%per year.The diagnosis is based on the history,physical examination,laboratory data,echocardiography,and,when necessary,by cardiac catheterization.Patients with obesity,hypertension,atrial fibrillation,and volume overload require weight reduction,an exercise program,aggressive control of blood pressure and heart rate,and diuretics.Miniature devices inserted into patients for pulmonary artery pressure monitoring provide early warning of increased pulmonary pressure and congestion.If significant coronary heart disease is present,coronary revascularization should be considered.

Peridynamic modeling and simulation of thermo-mechanical de-icing process with modified ice failure criterion

De-icing technology has become an increasingly important subject in numerous applications in recent years.However,the direct numerical modeling and simulation the physical process of thermomechanical deicing is limited.This work is focusing on developing a numerical model and tool to direct simulate the de-icing process in the framework of the coupled thermo-mechanical peridynamics theory.Here,we adopted the fully coupled thermo-mechanical bond-based peridynamics(TM-BB-PD)method for modeling and simulation of de-icing.Within the framework of TM-BB-PD,the ice constitutive model is established by considering the influence of the temperature difference between two material points,and a modified failure criteria is proposed,which takes into account temperature effect to predict the damage of quasi-brittle ice material.Moreover,thermal boundary condition is used to simulate the thermal load in the de-icing process.By comparing with the experimental results and the previous reported finite element modeling,our numerical model shows good agreement with the previous predictions.Based on the numerical results,we find that the developed method can not only predict crack initiation and propagation in the ice,but also predict the temperature distribution and heat conduction during the de-icing process.Furthermore,the influence of the temperature for the ice crack growth pattern is discussed accordingly.In conclusion,the coupled thermal-mechanical peridynamics formulation with modified failure criterion is capable of providing a modeling tool for engineering applications of de-icing technology.

Failure Pressure Analysis of Corroded Moderate-to-High Strength Pipelines

Based on the elastic-plastic, large-deformation finite element method, burst capacity of steel pipeline with longitudinal corrosion defect subjected to internal pressure is studied. The appropriate stress-based criterion is used to predict the failure pressure of finite element model of corroded pipeline under internal pressure. By considering the pipe steel grades and geometries of corrosion defects, a series of finite element analyses is conducted. The effects of corrosion depth, length and width on burst capacity are also discussed. A specific failure pressure solution for the assessment of corrosion defects in moderate-to-high strength pipeline is proposed on the base of numerical results. The failure pressures predicted by the proposed method are in better agreement with the experimental results than the results by the other methods.

Validation of Hoek-Brown failure criterion charts for rock slopes

Although stability charts suggested by Hoek and Bray on the basis of Mohr-Coulomb criterion are used for rock slopes,but complete and precise recognition is required for distinguishing cohesive strength and Mohr-Coulomb equivalent internal friction angle for rock mass.The paper by Lia et al.[6]is the only one that introduced rock slope charts according to Hoek-Brown failure criterion.In this paper,at first,this type of charts is introduced.Then,Mohr-Coulomb failure criterion charts[2]are compared and validated with Hoek-Brown failure criterion ones[6].Next,Bishop method utilizing Slide software is compared with Hoek-Brown failure criterion stability charts.Average standard deviation(ASD),root mean square error(RMSE)and variance account for(VAF)were used for the comparison.According to the results,because of high distribution and very low correlation among the comparisons,Hoek-Brown failure criterion charts are not efficient.

Progressive failure analysis of composite structure based on micro- and macro-mechanics models

Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stress distribution of the composite structure is calculated by commercial finite element software. According to the macro-stress, the damaged point is found and the micro-stress distribution of representative volume element is calculated by finite-volume direct averaging micromechanics(FVDAM). Compared with the results calculated by failure criterion based on macro-stress field(the maximum stress criteria and Hashin criteria) and micro-stress field(Huang model), it is proven that the failure analysis based on macro- and micro-mechanics model is feasible and efficient.

Liver transplantation in acute liver failure:Dilemmas and challenges

Acute liver failure(ALF)refers to a state of severe hepatic injury that leads to altered coagulation and sensorium in the absence of pre-existing liver disease.ALF has different causes,but the clinical characteristics are strikingly similar.In clinical practice,however,inconsistency in the definition of ALF worldwide and confusion regarding the existence of pre-existing liver disease raise diagnostic dilemmas.ALF mortality rates used to be over 80%in the past;however,survival rates on medical treatment have significantly improved in recent years due to a greater understanding of pathophysiology and advances in critical care management.The survival rates in acetaminophen-associated ALF have become close to the post-transplant survival rates.Given that liver transplantation(LT)is an expensive treatment that involves a major surgical operation in critically ill patients and lifelong immunosuppression,it is very important to select accurate patients who may benefit from it.Still,emergency LT remains a lifesaving procedure for many ALF patients.However,there is a lack of consistency in current prognostic models that hampers the selection of transplant candidates in a timely and precise manner.The other problems associated with LT in ALF are the shortage of graft,development of contraindications on the waiting list,vaguely defined delisting criteria,time constraints for pre-transplant evaluation,ethical concerns,and comparatively poor post-transplant outcomes in ALF.Therefore,there is a desperate need to establish accurate prognostic models and explore the roles of evolving adjunctive and alternative therapies,such as liver support systems,plasma exchange,stem cells,auxiliary LT,and so on,to enhance transplant-free survival and to fill the void created by the graft shortage.

Prediction of the Biaxial Failure Strength of Composite Laminates with Unit Cell Analytic Model

A new method to predict the ultimate strength of fiber reinforced composites under arbitrary load condition is introduced. The micromechanics strength theory is used to perform the final failure prediction of composite laminates. The theory is based on unit cell analytic model which can provide the ply composite material properties by only using the constituent fiber and matrix properties and the laminate geometric parameters without knowing any experimental information of the laminates. To show that this method is suitable for predicting the strength of composite laminates, the micromechanics strength theory is ranked by comparing it with all the micro-level and the best two macro-level theories chosen from the World Wide Failure Exercise. The results show that this method can be used for predicting strength of any composite laminates and provide a direct reference for composite optimum design.

Establishment of tensile failure induced sanding onset prediction model for cased-perforated gas wells

Sand production is a challenging issue in upstream oil and gas industry,causing operational and safety problems.Therefore,before drilling the wells,it is essential to predict and evaluate sanding onset of the wells.In this paper,new poroelastoplastic stress solutions around the perforation tunnel and tip based on the Mohr-Coulomb criterion are presented firstly.Based on the stress models,a tensile failure induced sanding onset prediction model for cased-perforated gas wells is derived.Then the analytical model is applied to field data to verify its applicability.The results from the perforation tip tensile failure induced sanding model are very close to field data.Therefore,this model is recommended for forecasting the critical conditions of sand production analysis.Such predictions are necessary for providing technical support for sand control decision-making and predicting the production condition at which sanding onset occurs.

砌体结构地震风险控制决策方法研究

地震等自然灾害作用下生命安全风险的相关决策会对社会公共安全产生重大的影响,因此,工程结构应将风险限制在合理可接受水平,在经济投资、使用效益和生命安全保护方面达到综合最佳。为了解决“多安全才足够安全”这个问题,首先,根据我国2018年基本国情和经济水平确定生活质量指数(life quality index,LQI),并建立基于LQI的风险可接受准则;其次,对新建砌体结构和加固既有砌体结构进行可靠度分析,采用蒙特卡罗法计算地震作用下砌体结构的失效概率;最后,建立砌体结构的地震风险控制决策方法,并通过实例应用提出新建砌体结构的最优设计方案和加固既有砌体结构的最佳加固策略。结果表明:文中提出的方法对新建砌体结构可靠度指标的要求与规范要求基本吻合;地震作用下多层砌体结构的可接受失效概率为0.001~0.010。

基于HRR场的疲劳裂纹扩展模型研究

针对实际工程中安全性与经济性的需求,基于Hutchinson-Rice-Rosengren(HRR)应力-应变场提出一种Ⅰ型疲劳裂纹扩展速率预测模型。采用HRR应力-应变场描述裂纹尖端区域的应力应变分布状态,在考虑循环载荷及应变能密度理论的前提下,定义一个裂纹尖端损伤区域;同时,为消除裂纹尖端的应力奇异值问题,建立考虑裂纹尖端钝化效应的钝化半径计算方法;结合RICE的塑性叠加法与塑性应变能失效准则,发展一种Ⅰ型疲劳裂纹扩展速率模型。利用所提LIUX(HRR)预测模型对9种金属材料裂纹扩展速率进行计算,与Pandey(HRR)与CHEN-CAI Rice-Kujawski-Ellyin(RKE)两种裂纹扩展预测模型计算结果进行对比分析。同时,基于R2拟合效果及疲劳裂纹扩展三阶段的不同需求,给出三种预测模型的预测结果,并从安全性、精确性及经济性三方面给出相应的评分。最终结果表明,LIUX(HRR)预测模型适用范围更广,拟合效果更佳,能够更好地满足实际工程中的经济性与安全性的需求。