AbstractThe interfacial bond parameters are quantified and modeled in this work through experimental and analytical studies. A database comprising 628 shear tests of externally-bonded fiber ...reinforced polymer (FRP) joints is built for model development. A newly derived closed-form solution is used for identification of bond parameters by matching the analytical solution with test results. Factors that affect the bond parameters are identified and configurations of the models are determined through analytical reasoning. Coefficients of the models are subsequently derived by regression analyses. It is found that the FRP-to-concrete width factor, which has been modeled as a function of FRP-to-concrete width ratio only in all existing bond strength models, should also be a function of concrete strength. A new model for the width factor as a function of both the width ratio and concrete strength is developed, which leads to more accurate and rational bond strength and fracture energy models.
Life is an out-of-equilibrium system sustained by a continuous supply of energy. In extant biology, the generation of the primary energy currency, adenosine 5'-triphosphate and its use in the ...synthesis of biomolecules require enzymes. Before their emergence, alternative energy sources, perhaps assisted by simple catalysts, must have mediated the activation of carboxylates and phosphates for condensation reactions. Here, we show that the chemical energy inherent to isonitriles can be harnessed to activate nucleoside phosphates and carboxylic acids through catalysis by acid and 4,5-dicyanoimidazole under mild aqueous conditions. Simultaneous activation of carboxylates and phosphates provides multiple pathways for the generation of reactive intermediates, including mixed carboxylic acid-phosphoric acid anhydrides, for the synthesis of peptidyl-RNAs, peptides, RNA oligomers and primordial phospholipids. Our results indicate that unified prebiotic activation chemistry could have enabled the joining of building blocks in aqueous solution from a common pool and enabled the progression of a system towards higher complexity, foreshadowing today's encapsulated peptide-nucleic acid system.
Recycling of construction and demolition waste in the concrete is considered a sustainable way However, recycled aggregates (RA) with inferior properties are produced after recycling as compared to ...natural aggregates. This study aims to improve the performance of RA by utilizing different treatment methods and to evaluate the properties of the resulting recycled aggregate concrete (RAC). For this purpose, five different treatment techniques of RA, such as carbonation, acetic acid immersion, acetic acid immersion with mechanical rubbing, acetic acid immersion with carbonation and lime immersion with carbonation are adopted during the study. Different mechanical tests are performed to investigate the effect of different RA treatment techniques on the mechanical properties of RAC with treated and untreated RA. Increase in split tensile strength and flexural strength along with improved stress-strain behavior of RAC is observed for treated RA as compared to untreated RA. The stress-strain behavior of RAC having RA treated through acetic acid immersion with mechanical rubbing and lime immersion with carbonation is observed very close to the stress-strain curves of natural aggregate concrete reflecting the positive impact of these RA treatment techniques on the performance of RAC. Moreover, empirical relations to predict different mechanical properties and stress-strain model of RAC with both treated and untreated RA are also developed in this work. A comparative study of the existing and proposed models with the test results indicates that the proposed relations and model can effectively predict the mechanical behavior of RAC with both treated and untreated RA.
Recovering sparse signals from compressed measurements has received much attention in recent years. Considering that measurement errors always exist, an improved orthogonal matching pursuit (OMP) ...method which is called Searching Forward OMP (SFOMP), is proposed in this letter. The proposed SFOMP method is designed for compressive sensing and sparse signal recovery in the noisy environment. To improve the recovery performance, the SFOMP method incorporates a searching forward strategy to find the column leading to a minimum norm of residual error among the added candidates in each iteration. Numerical results show that, compared with other commonly used methods, this method provides a higher recovery signal‐to‐noise ratio, more accurate reconstruction of support set, and a competitive computational complexity with noisy measurements.
•New test method for shear resistance of RC beams.•Distribution of strain in shear reinforcement.•Principal compression strain and correlation with principal compression stress.•Variation of shear ...strength components.
This paper presents an experimental work and analysis of test results on diagonal cracking behavior of reinforced concrete (RC) beams that failed in shear. The strain distributions of transverse reinforcement, obtained by closely spaced strain gauges mounted inside transverse reinforcement without disturbing bond, are presented in a form of contour lines at different load levels. The diagonal crack width, average principal and shear strain fields of the shear span were obtained by using the digital image correlation (DIC). Based on the strains of transverse reinforcement along the path of the critical diagonal crack, the shear strength contribution of the transverse reinforcement (Vs) is isolated from the shear strength contribution of concrete (Vc). The value of Vs calculated in this way is generally larger than that obtained from the strains measured at mid-height of stirrups in the case of strong bond, while the difference is insignificant in the case of weak bond. With the full and detailed pictures of internal and external strain fields of the beams, important shear characteristics such as inclination of the principal compression strain and its correlation with principal compression stress, variation of Vc and Vs with respect to crack width and member deflection, relationships between crack width, shear force, principal tensile strain of concrete, and strain of transverse reinforcement, etc. are studied in this work. These relationships shed light on further study of the shear behavior of RC beams.
•Variation of bond workmanship is studied experimentally.•Bond quality affect debonding failure mode.•Offset of FRP strip does not cause significant variation of bond.•Existing cracks in RC beams do ...not have significant influence on FRP strengthening efficiency.
In practical engineering works, external bonding (EB) of fiber reinforced polymer (FRP) composite materials to concrete cannot be as perfect as in laboratory. Defects in bonding, therefore, cannot be avoided. An experimental program including single shear pull-out tests on EB-FRP concrete joints and three-point bending tests on reinforced concrete (RC) beams with/without EB-FRP was conducted. The effects of existing cracks in concrete with different spacing and widths, as well as FRP location relative to the centerline of specimen, were studied. Most of the specimens in the experimental program were prepared by unskilled personnel to simulate the “imperfect” workmanship. Test results show that EB-FRP joints with more than 10% concrete pulled off on the bond surface could have stable strength and ductility. Transverse offset of FRP from longitudinal center line does not have a significant effect on bond behavior. Existing cracks have a two-sided effect on bond-slip relationship. Cracking of concrete causes degradation of the bond slip relationship when crack width is large. However, cracking with smaller crack width could enhance the bond behavior to a certain degree. Existing cracks have limited influence on the load-deflection curves of FRP strengthened RC beams.
Predicting the number of new suspected or confirmed cases of novel coronavirus disease 2019 (COVID-19) is crucial in the prevention and control of the COVID-19 outbreak. Social media search indexes ...(SMSI) for dry cough, fever, chest distress, coronavirus, and pneumonia were collected from 31 December 2019 to 9 February 2020. The new suspected cases of COVID-19 data were collected from 20 January 2020 to 9 February 2020. We used the lagged series of SMSI to predict new suspected COVID-19 case numbers during this period. To avoid overfitting, five methods, namely subset selection, forward selection, lasso regression, ridge regression, and elastic net, were used to estimate coefficients. We selected the optimal method to predict new suspected COVID-19 case numbers from 20 January 2020 to 9 February 2020. We further validated the optimal method for new confirmed cases of COVID-19 from 31 December 2019 to 17 February 2020. The new suspected COVID-19 case numbers correlated significantly with the lagged series of SMSI. SMSI could be detected 6-9 days earlier than new suspected cases of COVID-19. The optimal method was the subset selection method, which had the lowest estimation error and a moderate number of predictors. The subset selection method also significantly correlated with the new confirmed COVID-19 cases after validation. SMSI findings on lag day 10 were significantly correlated with new confirmed COVID-19 cases. SMSI could be a significant predictor of the number of COVID-19 infections. SMSI could be an effective early predictor, which would enable governments' health departments to locate potential and high-risk outbreak areas.
Display omitted
•Z-scheme MnIn2S4/g-C3N4 catalysts were synthesized by hydrothermal route.•Composites were highly efficient photocatalysts for TCH degradation and H2 evolution.•The obviously improved ...catalytic activity was ascribed to smart structure design.•Composites possess excellent photostability.
Semiconductor photocatalysis has been regarded as an environmentally friendly technology in wastewater treatment and energy production. Here, a series of direct Z-scheme MnIn2S4/g-C3N4 (MnISCN) photocatalysts without electron mediators were fabricated by a simple hydrothermal route on the basis of in-situ loading of MnIn2S4 (MnIS) nanoflakes on the surface of g-C3N4 (CN) nanosheets. Photocatalytic performances evaluated under visible light irradiation revealed these Z-scheme heterostructured photocatalysts exhibited higher photocatalytic activities than single-component samples. The effect of weight ratio between MnIn2S4 nanoflakes and mesoporous CN nanosheets on photocatalytic activity towards treatment of pharmaceutical wastewater was optimized to achieve highly efficient photocatalytic activities for both degradation of pharmaceutical wastewater and hydrogen generation compared with alone MnIS nanoflakes and isolated mesoporous CN nanosheets. The significant enhancement in photocatalytic activity could be primarily ascribed to the construction of Z-scheme MnISCN architectures, which effectively accelerated the transfer and separation of photogenerated charge carriers via tight interface contacts built among these two components. The recycling experiments for pharmaceutical wastewater treatment revealed the excellent stability of MnISCN nanocomposites. The advantages of highly efficient photocatalytic activity and excellent stability endowed a promising potential for MnISCN nanocomposites to apply in photocatalytic fields.
PDF
