Effects of biochar-amended alkali-activated slag on the stabilization of coral sand in coastal areas

Coral sand is widely encountered in coastal areas of tropical and subtropical regions.Compared with silica sand,it usually exhibits weaker performance from the perspective of engineering geology.To improve the geomechanical performance of coral sand and meet the requirement of foundation construction in coastal areas,a novel alkali activation-based sustainable binder was developed.The alkaliactivated slag(AAS)binder material was composed of ground granulated blast-furnace slag(GGBS)and hydrated lime with the amendment of biochar,an agricultural waste-derived material.The biocharamended AAS stabilized coral sand was subjected to a series of laboratory tests to determine its mechanical,physicochemical,and microstructural characteristics.Results show that adding a moderate amount of biochar in AAS could improve soil strength,elastic modulus,and water holding capacity by up to 20%,70%,and 30%,respectively.Moreover,the addition of biochar in AAS had a marginal effect on the sulfate resistance of the stabilized sand,especially at high biochar content.However,the resistance of the AAS stabilized sand to wet-dry cycles slightly deteriorated with the addition of biochar.Based on these observations,a conceptual model showing biochar-AAS-sand interactions was proposed,in which biochar served as an internal curing agent,micro-reinforcer,and mechanically weak point.

Compressibility characteristics of bio-cemented calcareous sand treated through the bio-stimulation approach

Calcareous sand is widely present in coastal areas around the world and is usually considered as a weak and unstable material due to its high compressibility and low strength.Microbial-induced calcium carbonate precipitation(MICP)is a promising technique for soil improvement.However,the commonly adopted bio-augmented MICP approach is in general less compatible with the natural soil environment.Thus,this study focuses on the bio-stimulated MICP approach,which is likely to enhance the dominance of ureolytic bacteria for longer period and thus is deemed more efficient.The main objective of this paper is to investigate the compressibility of calcareous sand treated by bio-stimulated MICP approach.In the current study,a series of one-dimension compression tests was conducted on bio-cemented sand pre-pared via bio-stimulation with different initial relative densities(D r).Based on the obtained compression curves and particle size distribution(PSD)curves,the parameters including cementation content,the coefficient of compressibility(a v),PSD,relative breakage(B r),and relative agglomeration(A r)were discussed.The results showed that a v decreased with the increasing cementation content.The bio-cemented sand prepared with higher initial D r had smaller(approximately 20%e70%)a v values than that with lower initial D r.The specimen with higher initial D r and higher cementation content resulted in smaller B r but larger A r.Finally,a conceptual framework featuring multiple contact and damage modes was proposed.

Magnetocardiograph as a noninvasive and radiation-free diagnostic device for myocardial infarction:a systematic review and meta-analysis

Background:This study aimed to evaluate the diagnostic accuracy of magnetocardiograph,a relatively new noninvasive device,in patients with myocardial infarction(MI).Methods:To identify studies assessing the diagnostic accuracy of magnetocardiography for MI,we searched four databases on November 7,2022,the Cochrane Central Register of Controlled Trials,MEDLINE,EMBASE,and Web of Science,plus ClinicalTrials.gov.Three reviewers screened the studies independently and emailed the authors for more precise data when necessary.The Quality Assessment of Diagnostic Accuracy Studies 2 tool was used to evaluate the quality of the included studies.STATA(version 17;Stata Corporation,College Station,TX,USA)was used for meta-analysis of 2
2 contingency table data.Results:A total of 6 articles were included in this study.The diagnostic parameters of all included studies were summarized as follows:the pooled sensitivity was 0.91(95%confidence intervals[95%CIs]:0.81–0.96;I 2=88.54);specificity was 0.83(95%CI:0.75–0.89;I 2=83);positive likelihood ratio was 5.3(95%CI:3.5–8.2);negative likelihood ratio was 0.1(95%CI:0.04–0.24);and diagnostic odds ratio was 51(95%CI:16–161).The area under the curve for the receiver operating characteristic curve was 0.92(95%CI:0.89–0.94).After metaregression analysis,we found that the number of channels and the way of environmental magnetic noise elimination were heterogeneous sources.Conclusion:In summary,our meta-analysis shows that magnetocardiography holds a high accuracy in diagnosing MI and takes the advantages of noninvasive,radiation-free,and noncontact.However,further high-quality studies to confirm its usefulness in diagnosing MI are warranted.

A CASCADIC MULTIGRID METHOD FOR EIGENVALUE PROBLEM

一个 cascadic multigrid 方法基于 multilevel 修正计划为特征值问题被建议。与这个新计划，在最好的空间的一个特征值问题能被线性变光滑的步在一系列 multilevel 上解决在特殊最粗糙的空格的有限元素空格和非线性的改正步。一旦有限元素空格的顺序和弄平步的数字适当地被选择，有最佳的计算工作的最佳的集中率能被获得。一些数字实验被介绍验证我们的理论分析。