Abstract:

Degradable cardiovascular interventional devices have become a hot topic in medical device development. Biomedical materials are the core of degradable cardiovascular interventional devices. This paper summarizes the chemical and physical properties as well as the degradation characteristics of related degradable polymeric materials， and discusses the relationship between the expected functions of degradable cardiovascular interventional devices and the properties of degradable polymeric materials. Finally， it points the challenges and future development directions of biodegradable polymeric materials to provide reference for relevant practitioners.

Abstract:

Polyhydroxyalkanoates （PHA） are a series of natural polymers synthesized by microorganisms， with more than 150 monomers and various properties. Since PHA has an excellent biocompatibility and biodegradability， and the degradation product 3HB， the most common and widely studied type of PHA， i.e.， poly （3-hydroxybutyrate） or PHB， has potential therapeutic functions for a variety of diseases， PHA-related materials have received extensive attentions in the field of tissue repair and regeneration. This paper summarizes the application of PHA consisting of different monomers in different tissue engineering fields， including repairing bone defects， healing skin wounds， nerve reconstruction and drug delivery. It also summarizes the relevant preparation methods of materials and mechanisms of tissue repair， which provides a new idea for the future biomedical application of PHA.

Abstract:

A new generation of non-metallic catalysts was adopted by adding the third monomer phthalic anhydride and the fourth monomer epoxycyclohexane for copolymerization to created a new type of carbon dioxide copolymer with good mechanical properties， high glass transition temperature， water and oxygen resistance， full biodegradation， simple production process， no three wastes in the production process， minimal investment， ultra-low raw material cost and other outstanding advantages， whose application is promising.

Abstract:

In recent years， the large-scale production and application of petroleum-based polyester materials have brought a series of problems to resource， energy， and environment. The preparation of bio-based polyethylene furandicarboxylate （PEF） from biomass resources has become a hot topic in the chemical industry. Compared with widely used petroleum-based plastics such as polyethylene terephthalate （PET）， PEF not only has similar physical properties， but also has more obvious advantages in gas barrier properties， which is considered as a perfect substitute for PET. This paper， focusing on the synthesis of PEF， summarizes the influence of catalysts， polymerization conditions， and raw material sources on the color and molecular weight of PEF， and anticipates the future development trend and application prospects of PEF.

Abstract:

In order to improve the water vapor barrier and weather resistance of poly （butylene adipate-co-terephthalate） （PBAT）， PBAT/poly（propylene carbonate） （PPC） films were prepared by extrusion blending and blowing film. The effects of composition ratios on water vapor barrier properties， mechanical properties， thermal properties， microstructure， and light transmittance of the films were investigated， and all blend films were subjected to natural weathering test. The results show that the addition of PPC improves the water vapor barrier of PBAT-based films， and reduces the mechanical properties and thermal stability of films. Adding 20% PPC could reduce the water vapor permeability of the films by 54.5%. The natural weathering test indicates that PPC can improve the weather resistance of PBAT-based films.

Abstract:

Polylactic acid （PLA） is widely considered to be one of the most promising biodegradable polymers. The promulgation of the national “banning plastic bags” has led to an unprecedented expansion of PLA production and application areas. The chemical purity， optical purity， and production cost of lactide （LD）， a key intermediate of bioplastic PLA， directly determine the quality and economic value of PLA. The two-step synthesis technology is standard in the industry nowadays， and the pre-polymerization-depolymerization approach ensures the conversion rate of lactic acid. Still， its main problems are LD racemization， low selectivity， and high energy cost. The one-step method as an alternative strategy is well suited to overcome some disadvantages of the two-step LD synthesis. Therefore， this review focuses on the one-step synthesis of LD and describes and compares the different methods technically.

Abstract:

Manual dataset labeling is always at the expense of low efficiency and high cost in the deep learning model training of crack detection. The adaptability of existing automatic labeling algorithms to complex environment is weak as well. Aiming at these problems， the concept of fast labeling with low supervision is proposed based on computer vision and the probability statistics theory. In addition， a novel fast labeling algorithm for crack dataset is formed， composed of computer labeling and manual labeling. Compared with manual pixel-by-pixel labeling， the labeling accuracy of the proposed automatic method is more than 84%， and can save at least 85% of the time. Compared with traditional computer labeling， complex background can be better dealt with by labeling interference and simple manual labeling. Validated by U-Net deep learning model， the average intersection ratio of test sets can reach 0.90.

Abstract:

The intelligent counting method of steel based on the deep learning target detection technology is studied in this paper. First， many pictures of steel bars， round steel pipe， and square steel pipe at the construction site are obtained and marked， and a data set containing nearly 400 000 counting points is constructed. Based on the YOLOv4 object detection algorithm， an intelligent steel counting model is established， and the counting accuracy of the steel model is improved by improving its network structure， loss function， and adopting appropriate training strategies. The maximum average precision of the model is 91.41%， with a mean absolute error of 4.07. Based on the above achievements， an APP software is developed， and the real-time counting is completed by taking photos and uploading them.

Abstract:

This paper developed a 3D printing system which could continuously and stably print concrete with an aggregate size up to 10 mm. Then， it tested and compared the mechanical properties of 3D printed concrete and cast concrete. It is found that the compressive strength of 3D printed concrete is slightly anisotropic with a difference of 5%. The flexural strength shows significant anisotropy with a difference of 20%~25%. Compared with the cast concrete， the compressive strength of 3D printed concrete is reduced by 10%~15%， the flexural strength perpendicular to the printing direction （F_y and F_z） is reduced by 10%~15%， and the flexural strength parallel to the printing direction （F_x） is reduced by 30%~35%. The microstructure analysis indicates that there is little difference between the total porosity of 3D printed concrete and the total porosity of cast one， but there are obvious interlayers in 3D printed concrete， where the gray value is about 25% lower than the average gray value， indicating that the pore distribution of the interlayer is denser. Therefore， the proportion of pores with a volume bigger than 10 mm³ in 3D printed concrete is 10.6% higher than that of cast specimen， which explains the reduction of the compressive strength and flexural strength of 3D printed concrete. It is concluded that the cement content of 3D printing coarse aggregate concrete is 17.8%~49.6% lower than that of 3D printing mortar in the previous study.

Abstract:

The strain-controlled biaxial compression experiments in bi-disperse granular system are conducted by using a homemade photo-elastic apparatus， which can provide soft boundary pressure to the granular sample. The Hough transform is used to locate each particle position based on the experimental images. The particle tracking velocimetry （PTV） is applied to track the particle in the time scale. Hence， each particle is marked in both time and space scales. The affine motion of each particle is taken out based on the shear strain and space position of corresponding particle. The non-affine displacement field shows that the main displacements happen close to the compression sides and very small displacement in the center of the sample. Meanwhile， the photo-elastic responds of the granular systems also reveal the cage effect clearly， and some of the particles do not have any force even the sample has been compressed a lot. The anisotropy of the force chain network can be seen at the center of the sample with relatively low packing fraction， which is just the place where the shear band passes through.

Abstract:

Truck platooning has proposed high bearing capacity and fine design requirement for pavement structure. In combination with the topology optimization theory， this paper proposes a topology optimization method of cement concrete pavement structure based on the solid isotropic microstructure with penalization （SIMP） method， the topology gradient method， and the method of moving asymptotes （MMA）. A prototype structure of cement concrete pavement is designed based on the numerical calculation， considering the analyzed wheel track characteristic of truck platooning. Finally， the scale experiment is employed to verify the mechanical property of the prototype structure. The results show that the maximum fatigue stress of the prototype is reduced to 45.0% and 37.5% of the traditional concrete pavement structure at a channelized traffic load and the traffic load with an offset of 15 cm respectively， and the weight is reduced to 34.3% and 30.5% of the traditional structure. The bearing capacity of the prototype structure measured by the experiment is 18.3% higher than the traditional structure， which proves the effectiveness of the design method.

Abstract:

Autonomous vehicle （AV） testing data is characterized by containing both continuous and discrete variables， and indirect information including timestamps， latitude and longitude， etc.， for which the traditional information entropy method should be adapted to AV testing data analyses. This paper proposes a driving mode-weighted information entropy method to determine the amount of AV testing data information by adapting the traditional entropy method using data feature mining and filtering， continuous variable discretization， driving mode-weighting， etc. Then， it establishes an AV testing data pricing model based on an evolved Stackelberg game with constraints of both information amount and data trading-platform profit rate， by integrating the information amount into the utility function of data consumers. It conducts a typical case analysis based on the actual test data of AV road testing in Shanghai. The results show that the evolved Stackelberg game-based pricing model can effectively evaluate the information amount of AV testing data， and reasonably allocate the profits among the three stakeholders of data providers， data trading platform， and data consumers. The data trading volume and the total utility of the system could be increased significantly， which contributes substantially to the booming of the AV testing data trading market.

Abstract:

There is a lack of comprehensive characterization of waste exhaust catalysts， resulting in an incomplete understanding of their physicochemical properties and causes of failures， which affects the recovery of platinum group metals from them. To this end， in this paper， a series of properties such as chemical composition and phases， surface elements， microscopic morphology， particle size， specific surface area and thermal stability were characterized and analyzed for waste exhaust catalysts. It is concluded that the failure causes mainly include sulfide and phosphide poisoning of platinum group metals， carbon adsorption on the catalyst surface， oxidation of platinum group metals， sintering agglomeration and packaging of platinum group metals in the substrate， reduction of specific surface area and total pore volume， etc.

Abstract:

Ferrous iron （Fe²⁺） combined with three oxidants， sodium hypochlorite （NaClO）， sodium persulfate （Na?S?O₈） and hydrogen peroxide （H₂O₂） were used to treat thermal desorption wastewater from the crude oil-contaminated soil. The influences of pH， Fe²⁺ dosage， oxidant dosage and reaction time on the treatment efficiency were investigated. The results show that PHCs （typical pollutants in thermal desorption wastewater） can be effectively removed by Fe²⁺/H₂O₂ and Fe²⁺/Na?S?O₈， with a removal efficiency of 100.0% and 97.8%， respectively. However， the chemical oxygen demand （COD） removal efficiency of Fe²⁺/H₂O₂ system is significantly higher than that of Fe²⁺/Na?S?O₈. Fe²⁺/H₂O₂ can oxidize and decompose organic matters completely， while Fe²⁺/NaClO and Fe²⁺/Na?S?O₈ can only convert organic matters into intermediate substances. The multivariate analysis results indicate that pH and oxidant dosage are the main factors affecting the removal efficiency. The cost of Fe²⁺/H₂O₂ in the treatment of thermal desorption wastewater is higher， but it has the best removal efficiency. The cost of Fe²⁺/Na?S?O₈ is lower than that of Fe²⁺/H₂O₂. However， COD cannot be degraded completely. Fe²⁺/NaClO has the lowest cost but the worst removal efficiency. Hence， considering the removal effect and economic factors， the Fe²⁺/H₂O₂ system is more suitable for the treatment of thermal desorption wastewater.

Abstract:

In this paper， operating conditions containing more “irreversible degradation” information are filtered based on the method of the information theory. The sequential quadratic programming method is used to integrate operating conditions and the output power into the integrated state of health（SOH） indicator. Compared to the indicator with output power as SOH， the integrated SOH indicator improves by 22.83%， 91.96% ，and 55.60% in the monotonicity， consistency of aging， and comprehensive performance， respectively.

Abstract:

After studying the risk indicators that affect the design development， the risk indicators are identified comprehensively and systematically， and the hierarchical structure model is established by applying fuzzy analytic hierarchy process（FAHP） to calculate and comprehensively evaluate the weight of the indicators and the membership matrix of the evaluation indicators， so as to provide a quantitative basis for the risk response of car styling design projects. The method can effectively and accurately evaluate and control the risk of the styling project contracted for the car design company.

Abstract:

Based on a two-cylinder diesel engine and a self-designed pure oxygen intake system，the effect of different intake oxygen volume fractions on the combustion process and stability of homogeneous charge compression ignition of n-heptane were investigated.The experimental results show that， with the decreasing volume fraction of oxygen and increasing volume fraction of carbon dioxide in the mixture， the average specific heat capacity in the cylinder is increased， which leads to the maximum combustion temperature in the cylinder is decreased， the corresponding peak phase is delayed， the combustion start point is delayed， the peak heat release rate is decreased， and the thermal efficiency is reduced.Meanwhile， it was found that with the increasing of carbon dioxide volume fraction， the temperature in the cylinder decreased， which led to the strengthening of the combustion cycle instability. The above phenomena indicate that the higher volume fraction of carbon dioxide can effectively inhibit the homogeneous charge compression ignition of n-heptane under pure oxygen atmosphere.Moreover， the interval duration of negative temperature coefficient of n-heptane homogeneous charge compression ignition is significantly shortened in pure oxygen atmosphere.

Abstract:

Based on the Heston model， a credit rating migration model with random volatility variance is established by means of bond pricing to evaluate credit risk. Corporation bonds are divided into high and low credit ratings based on predefined asset threshold.The volatility variance of corporate assets has different volatility at different credit ratings， i.e.， the volatility variance satisfies different CIR（cox-ingersoll-ross） processes. According to the no arbitrage principle， etc.， the partial differential equations is derived for bond values at high and low ratings and the conditions satisfied at the coupling boundary. Finally， the implicit scheme difference method is used to get the numerical solution of bond value.