An optimal dimension-down iterative algorithm （DDIA） is proposed for solving a mixed （continuous/ discrete） transportation network design problem （MNDP）, which is generally expressed as a mathematical programmin...An optimal dimension-down iterative algorithm （DDIA） is proposed for solving a mixed （continuous/ discrete） transportation network design problem （MNDP）, which is generally expressed as a mathematical programming with equilibrium constraints （MPEC）. The upper level of the MNDP aims to optimize the network performance via both the expansion of existing links and the addition of new candidate links, whereas the lower level is a traditional Wardrop user equilibrium （UE） model. The idea of the proposed DDIA is to reduce the dimensions of the problem. A group of variables （discrete/continuous） are fixed to altemately optimize another group of variables （continuous/discrete）. Some continuous network design problems （CNDPs） and discrete network design problems （DNDPs） are solved repeatedly until the optimal solution is obtained. A numerical example is given to demonstrate the efficiency of the proposed algorithm.展开更多
Research on mixed method has made great development.In order to explore the practical application of mixed method,this article starts from the perspective of language learner cognition and selects The Modern Language ...Research on mixed method has made great development.In order to explore the practical application of mixed method,this article starts from the perspective of language learner cognition and selects The Modern Language Journal and Language Teaching Research as the research journals.It explores some empirical papers that used mixed method to learn the specific research designs of mixed method as well as the main means of its application.The study finds that mixed method has been applied in several fields and is more scientifically reliable than qualitative and quantitative methods especially in language learner cognition,and the different research tools used in the field of language learner cognition demonstrate the flexibility and relevance of mixed method data collection.展开更多
Objective:This study provides a preliminary evaluation of the usability and acceptability of a mobile application(sexual assault care algorithm,SACA).Methods:An explanatory sequential mixed methods research was used.A...Objective:This study provides a preliminary evaluation of the usability and acceptability of a mobile application(sexual assault care algorithm,SACA).Methods:An explanatory sequential mixed methods research was used.A quantitative survey was followed up by a qualitative study.A convenience sample of participants(n=4)was recruited.The research was conducted on a one-on-one basis.In the quantitative phase,a random assignment technique was used to divide four participants into two groups of two participants each.Post-Study System Usability Questionnaire(PSSUQ)and Acceptability e-Scale were used to collect quantitative data.In the qualitative phase,interview,observation,and documentation were used to collect qualitative data.Data were analyzed both quantitative and qualitatively.The qualitative data were linked with the initial quantitative data to determine how the follow-up qualitative data helped explain the initial quantitative results.Results:The quantitative results suggested that SACA has high usability(5.05±1.83)and acceptability(3.81±1.22).The qualitative results further indicate that the participants thought SACA was easy to use and useful,and most of them would recommend it to others.Areas of improvement include adding features that would calculate and validate the elapsed time since the sexual assault,adding explanations to some buttons,and providing training.Conclusions:Our findings highlight the value of using a mixed methods research design to conduct a usability and acceptability test.Nurses are more likely to adopt a new technology for their evidencebased practice when the technology is easy to use and useful and requires less time to find the right piece of guideline evidence.Individualized training needs to be designed based on users'characteristics.展开更多
Durability design of recycled high performance concrete（RHPC） is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate（CRA）. We discussed a frostdurability-based mix propo...Durability design of recycled high performance concrete（RHPC） is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate（CRA）. We discussed a frostdurability-based mix proportion design method for RHPC using 100 % CRA and natural sand. Five groups of RHPC mixes with five strength grades（40, 50, 60, 70 and 80 MPa） were produced using CRA with four quality classes, and their workability, 28 d compressive strengths and frost resistances（measured by the compressive strength loss ratio and the relative dynamic modulus of elasticity） were tested. Relationships between the 28 d compressive strength, the frost resistance and the CRA quality characteristic parameter, water absorption, were then developed. The criterion of a CRA maximum water absorption limit value for RHPC was suggested, independent of its source and quality class. The results show that all RHPC mixes achieve the expected target workability, strength, and frost durability. The research results demonstrate that the application of the proposed method does not require trial testing prior to use.展开更多
Concrete is one of the most consumable construction materials on the earth.The concrete constitutes cement,sand,gravel,water and/or additives in definite proportions.The proportions of raw materials of concrete are de...Concrete is one of the most consumable construction materials on the earth.The concrete constitutes cement,sand,gravel,water and/or additives in definite proportions.The proportions of raw materials of concrete are decided by the concrete mix design.The mix design depends on the various factors.For mix design,most of the countries have their own specifications.In the present study,standard guidelines of India,Britain and America for the concrete mix design have been discussed.The concrete grades of M25,M35 and M45 were designed and compared.Indian Standards were also compared.It was concluded that a new revised version of Indian Standard code has the lowest value of water/cement ratio and highest quantity of cement as compared to other standards.展开更多
Sulpho-aluminate expansive cementitious composite is proved to be one of the most effective ways to prevent concrete cracking too soon. Mix design of sulpho-aluminate expansive cementitious composite completely depend...Sulpho-aluminate expansive cementitious composite is proved to be one of the most effective ways to prevent concrete cracking too soon. Mix design of sulpho-aluminate expansive cementitious composite completely depends on experience and experiments at present. This method ignores the influence of expansion behavior which hinders the application of sulpho-aluminate expansive cementitious composite. The workability,free expansion property,flexural strength and compressive strength of sulpho-aluminate expansive cementitious composite have been investigated by tests. The relationship between expansion ratio and mix design parameters such as curing age,water-cement ratio and cement abundance coefficient is deduced according to the experimental statistics. A new simplified approach to mix design of sulpho-aluminate expansive cementitious composite is proposed as a reference for construction application,which avoids experiments and experience.展开更多
The increasing impact of the greenhouse effect on ecosystems is prompting transportation agencies to seek methods for reducing CO_(2)emissions during pavement construction and maintenance.Additionally,the laboratory m...The increasing impact of the greenhouse effect on ecosystems is prompting transportation agencies to seek methods for reducing CO_(2)emissions during pavement construction and maintenance.Additionally,the laboratory mix design process,which involves selecting aggregate gradation and binder content,is time-consuming and labor-intensive.To accelerate the traditional mix design procedure,this study presented a mix design procedure that can automatically determine gradation and binder content based on machine learning(ML)and a meta-heuristic algorithm.Specifically,ML approaches were employed to model the relationship between volumetric properties(mixture bulk specific gravity(Gmb)and air void(VV))and both mixture component properties and mixture proportion,based on a dataset collected from literature with 660 mixture designs.Integrated with the prediction of ML models and the modified multi-objective grey wolf optimization(MOGWO)algorithm,an automatic asphalt mix design was proposed to pursue three goals,including VV,cost,and CO_(2)emission.The results indicated that least squares support vector regression(LSSVR)and e Xtreme gradient boosting(XGBoost)achieved the highest prediction accuracies(correlation coefficient:0.92 for VV and 0.96 for Gmb).The MOGWO algorithm successfully found the 26 optimal mix designs for the case of VV vs.cost vs.CO_(2)emission.Compared to the traditional laboratory design,the optimal mixture with VV of4%achieves a cost saving of 2.46%and a reduction of 4.03%in carbon emission.The volumetric properties of the mixtures output by the approach also align closely with values measured in a laboratory.展开更多
The mix designs and specimen preparation for the dry process and wet process of sulfur rubber conerete （ SRC ） were investigated. The compressive strength, corrosion-resistance and toughness were studied and discuss...The mix designs and specimen preparation for the dry process and wet process of sulfur rubber conerete （ SRC ） were investigated. The compressive strength, corrosion-resistance and toughness were studied and discussed. The results show that SRC is corrosion-resistanet. Although the compressive strength of SRC decreases with inereasing rubber content, the toughness increases instead . Adding micro-filler will improve the compressive strength of SRC . There is a threshold value for the sulfur content, at which the compressive strength and the workability of SRC reach an optimum balance . The bond between rubber particles and surrounding sulfur is strong due to the vulcanization process that generates cross-link through S-C bonds.展开更多
With the resource shortage in coastal areas,the construction of concrete structures using freshwater and river sand has brought great economic and environmental costs.The use of seawater,sea sand,and coral aggregates ...With the resource shortage in coastal areas,the construction of concrete structures using freshwater and river sand has brought great economic and environmental costs.The use of seawater,sea sand,and coral aggregates in concrete mixes has become an alternative solution for coastal and marine structures,especially for offshore structures and artificial islands.In this study,378 seawater,sea sand,and coral aggregate concrete(Coral-SWSSC)specimens were prepared,and their mechanical properties were investigated comprehensively through compressive tests to explore the optimized mix design at different grades.Results showed that the mechanical properties of Coral-SWSSC were strongly correlated with the water-to-binder ratios,coastal particle gradings,and pretreatment method of coastal particles.Based on the experimental results,mix proportion designs of CoralSWSSC were proposed for concrete from C20 to C50 grades,and the failure mechanism of Coral-SWSSC at different grades was discussed according to their respective failure modes.The findings of the current study provide knowledge on the optimized design of Coral-SWSSC,which can be used to promote the application of Coral-SWSSC in offshore,marine,and ocean engineering.展开更多
A novel soft initiai-rotation control system and an H∞ robust constant rotational speed controller （RCRSC） for a rotational MEMS （micro-electro-mechanical system） gyro are presented. The soft initial-rotation con...A novel soft initiai-rotation control system and an H∞ robust constant rotational speed controller （RCRSC） for a rotational MEMS （micro-electro-mechanical system） gyro are presented. The soft initial-rotation control system can prevent the possible tumbling down of the suspended rotor and ensure a smooth and fast initial-rotation process. After the initial-rotation process, in order to maintain the rotational speed accurately constant, the RCRSC is acquired through the mixed sensitivity design approach. Simulation results show that the actuation voltage disturbances from the internal carrier waves in the gyro is reduced by more than 15.3 dB, and the speed fluctuations due to typical external vibrations ranging from 10 Hz to 200 Hz can also be restricted to 10^-3 rad/s order.展开更多
There is a scarcity of literature discussing nurses’ behaviors toward caring for suspected or confirmed human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) patients. The development of a scal...There is a scarcity of literature discussing nurses’ behaviors toward caring for suspected or confirmed human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) patients. The development of a scale specific to measure nurses’ behaviors will allow health institutions to assess the disposition of their nurses in terms of HIV care. This study aims to present the rigors of developing and validating a reliable instrument to contextualize these nurses’ behaviors. This study utilized a sequential exploratory mixed method design to develop the NB-CSHAP scale. Thematic analysis was done on the qualitative data from the interviews with persons living with HIV/AIDS (PLHA) from which items were selected to be included in the scale. Exploratory factor analysis was utilized to extract the factors and Cronbach’s alpha was used to assess the reliability of the instrument. Four factors were extracted and are categorized as either caring or discriminatory behaviors. These include: (1) service-oriented, (2) openhanded, (3) perceptive, and (4) discriminatory. The scale has an internal consistency of 0.73. The scale shows acceptable psychometric properties, hence can be used to assess the nurses’ behaviors in caring for confirmed or suspected HIV clients. The scale may be used by health institutions to determine the quality of the patient care provided by their nurses to clients with confirmed or suspected HIV .展开更多
The early asphalt pavement in our country severely reduced the road performance due to various external factors during the use process.According to incomplete statistics,there are more asphalt pavements that need to b...The early asphalt pavement in our country severely reduced the road performance due to various external factors during the use process.According to incomplete statistics,there are more asphalt pavements that need to be renovated and repaired every year in China,and the amount of construction waste such as asphalt concrete and other construction waste reaches 1,000.About ten thousand tons.If such a huge amount of construction waste is not used,it will inevitably cause great pollution to the environment.If it can be reused,not only will it be environmentally friendly and energy-saving,it will also save more than one billion yuan in costs.In view of the above problems,this article conducts related Research and Analysis on the Principle in Plant Cold Recycling for Foamed Bitumen and Mixture Performance to provide reference for future projects.展开更多
This research explored the application potential of PUM thin-overlay technology on airport rapid maintenance.The rapid curing process of polyurethane binder determines the limited time window for mixing and constructi...This research explored the application potential of PUM thin-overlay technology on airport rapid maintenance.The rapid curing process of polyurethane binder determines the limited time window for mixing and construction of polyurethane-bonded mixture(PUM),which presents significant difference with hot-mix asphalt(HMA)technology.Therefore,this research investigated and optimized the mix design of PUM for airport thin-overlay technology based on its thermosetting characteristics.First,limestone and basalt were comprehensively compared as an aggregate for PUM.Then,the effects of molding and curing conditions were studied in terms of mixing time,molding method,molding parameters and curing temperature.Statistical analysis was also conducted to evaluate the effects of gradation and particle size on PUM performances based on gray relational analysis(GRA),thus determining the key particle size to control PUM performances.Finally,the internal structural details of PUM were captured by X-ray CT scan test.The results demonstrated that it only took 12 hours to reach 75%of maximum strength at a curing temperature of 50°C,indicating an efficient curing process and in turn allowing short traffic delay.The internal structural details of PUM presented distribution of tiny pores with few connective voids,guaranteeing waterproof property and high strength.展开更多
Pavement and mix design represent one of the key components within the life cycle of a road infrastructure, with links to political, economic, technical, societal and environmental issues. Recent researches related to...Pavement and mix design represent one of the key components within the life cycle of a road infrastructure, with links to political, economic, technical, societal and environmental issues. Recent researches related to the characteristics of materials and associated behavior models both for materials and pavement, made it appropriate to consider updating current pavement design methods, and especially in the USA this has already been in process while in Europe uses of the methods developed in the early 1970s. Thus, this paper firstly presents a brief historical overview of pavement design methods, high- lighting early limitations of old empirical methods. Afterwards, French, UK and Shell methods currently in use in Europe will be presented, undeHining their main components in terms of methodology, traffic, climatic conditions and subgrade. The asphalt mix design and modeling in Europe are presented with their inclusion in the pavement design methods. Finally, the main challenges for the development of a European pavement design method are presented as well as the recent research developments that can be used for that method.展开更多
The clay mineral composition is one of the major factors that governs the physical properties of silty sand subgrade. Therefore, a thorough knowledge of mineral composition is essential to predict the optimum engineer...The clay mineral composition is one of the major factors that governs the physical properties of silty sand subgrade. Therefore, a thorough knowledge of mineral composition is essential to predict the optimum engineering properties of the soil, which is generally characterized by different indices like maximum dry density （MDD）, California bearing ratio （CBR）, unconfined compressive strength （UCS） and free swelling index （FSI）. In this article, a novel multi- attribute decision making （MADM） based approach of mix design has been proposed for silty sand- artificial clay mix to improve the characteristic strength of a soil subgrade. Experimental investigation has been carried out in this study to illustrate the proposed approach of selecting appropriate proportion for the soil mix to optimize all the above mentioned engineering properties simultaneously. The results show that a mix proportion containing approximately 90% silty sand plus 10% bentonite soil is the optimal combination in context to the present study. The proposed methodology for optimal decision making to choose appropriate combination of bentonite and silty sand is general in nature and therefore, it can be extended to other problems of selecting mineral compositions.展开更多
The present study proposes the mix design method of Fly Ash(FA)based geopolymer concrete using Response Surface Methodology(RSM).In this method,different factors,including binder content,alkali/binder ratio,NS/NH rati...The present study proposes the mix design method of Fly Ash(FA)based geopolymer concrete using Response Surface Methodology(RSM).In this method,different factors,including binder content,alkali/binder ratio,NS/NH ratio(sodium silicate/sodium hydroxide),NH molarity,and water/solids ratio were considered for the mix design of geopolymer concrete.The 2D contour plots were used to setup the mix design method to achieve the target compressive strength.The proposed mix design method of geopolymer concrete is divided into three categories based on curing regime,specifically one ambient curing(25°C)and two heat curing(60 and 90°C).The proposed mix design method of geopolymer concrete was validated through experimentation of M30,M50,and M70 concrete mixes at all curing regimes.The observed experimental compressive strength results validate the mix design method by more than 90%of their target strength.Furthermore,the current study concluded that the required compressive strength can be achieved by varying any factor in the mix design.In addition,the factor analysis revealed that the NS/NH ratio significantly affects the compressive strength of geopolymer concrete.展开更多
In order to implement the objective mix design of hot mix asphalt adequately during the construction process, the significance of objective mixing ratio was elaborated, and the variability of materials and its control...In order to implement the objective mix design of hot mix asphalt adequately during the construction process, the significance of objective mixing ratio was elaborated, and the variability of materials and its control method were analyzed. An engineering example is used to illustrate the debugging process of asphalt mixture batching ＆ mixing plant and the dynamic quality management methods. The results show that the set of methods can not only implement the objective mixing ratio of hot mix asphalt adequately, but also control production during the construction process effectively.展开更多
Industrial mixers for powders and granular materials operate with no effective control of mixture quality and lack scientific design. The last twenty years have seen growth in understanding of mixing and mixers. Howev...Industrial mixers for powders and granular materials operate with no effective control of mixture quality and lack scientific design. The last twenty years have seen growth in understanding of mixing and mixers. However, research falls far short of what is needed for on-line characterisation of mixture quality. Secondly, although theoretical descriptions of a few mixer types have been reported, these fall far short of what is needed for equipment design. Two thrusts could revolutionise this situation. One is a scientific characterisation of mixer structure applicable to industrial scale as well as laboratory scale equipment; this is now within our grasp using digital imaging. The other is the development of ideas to overcome the restricted number of particles that can be used in the Distinct Element Method （DEM） for mixers. The goal should be to take the designer through a sequence of steps to the most appropriate mixer size, configuration and operating conditions for a given process duty.展开更多
Many researches have been carried out to study the fresh and hardened properties of concrete containing crumb rubber as replacement to fine aggregate by volume, yet there is no specific guideline has been developed on...Many researches have been carried out to study the fresh and hardened properties of concrete containing crumb rubber as replacement to fine aggregate by volume, yet there is no specific guideline has been developed on the mix design of the rubbercrete. The experimental program, which has been developed and reported in this paper, is designed and executed to provide such mix design guidelines. A total of 45 concrete mixes with three different water to cement ratio （0.41, 0.57 and 0.68） were cast and tested for fresh and mechanical properties of rubbercrete such as slump, air content, unit weight, compressive strength, flexural strength, splitting tensile strength and modulus of elasticity. Influence of mix design parameters such as percentage of crumb rubber replacement, cement content, water content, fine aggregate content, and coarse aggregate content were investigated. Three levels of slump value （for conventional concrete mixes） has been selected; low, medium and high slump. In each slump level, water content was kept constant. Equations for the reduction factors （RFs） for compressive strength, flexural strength, splitting tensile strength and modulus of elasticity have been developed. These RFs can be used to design rubbercrete mixes based on the conventional mix （0% crumb rubber content）展开更多
基金The National Natural Science Foundation of China(No. 50908235 )China Postdoctoral Science Foundation (No.201003520)
文摘An optimal dimension-down iterative algorithm （DDIA） is proposed for solving a mixed （continuous/ discrete） transportation network design problem （MNDP）, which is generally expressed as a mathematical programming with equilibrium constraints （MPEC）. The upper level of the MNDP aims to optimize the network performance via both the expansion of existing links and the addition of new candidate links, whereas the lower level is a traditional Wardrop user equilibrium （UE） model. The idea of the proposed DDIA is to reduce the dimensions of the problem. A group of variables （discrete/continuous） are fixed to altemately optimize another group of variables （continuous/discrete）. Some continuous network design problems （CNDPs） and discrete network design problems （DNDPs） are solved repeatedly until the optimal solution is obtained. A numerical example is given to demonstrate the efficiency of the proposed algorithm.
文摘Research on mixed method has made great development.In order to explore the practical application of mixed method,this article starts from the perspective of language learner cognition and selects The Modern Language Journal and Language Teaching Research as the research journals.It explores some empirical papers that used mixed method to learn the specific research designs of mixed method as well as the main means of its application.The study finds that mixed method has been applied in several fields and is more scientifically reliable than qualitative and quantitative methods especially in language learner cognition,and the different research tools used in the field of language learner cognition demonstrate the flexibility and relevance of mixed method data collection.
基金The development of the application for SACA was partially supported by funding from the Upstate Foundation,a 501(c)3 nonfor-profit corporation (upstatefoundation.org)
文摘Objective:This study provides a preliminary evaluation of the usability and acceptability of a mobile application(sexual assault care algorithm,SACA).Methods:An explanatory sequential mixed methods research was used.A quantitative survey was followed up by a qualitative study.A convenience sample of participants(n=4)was recruited.The research was conducted on a one-on-one basis.In the quantitative phase,a random assignment technique was used to divide four participants into two groups of two participants each.Post-Study System Usability Questionnaire(PSSUQ)and Acceptability e-Scale were used to collect quantitative data.In the qualitative phase,interview,observation,and documentation were used to collect qualitative data.Data were analyzed both quantitative and qualitatively.The qualitative data were linked with the initial quantitative data to determine how the follow-up qualitative data helped explain the initial quantitative results.Results:The quantitative results suggested that SACA has high usability(5.05±1.83)and acceptability(3.81±1.22).The qualitative results further indicate that the participants thought SACA was easy to use and useful,and most of them would recommend it to others.Areas of improvement include adding features that would calculate and validate the elapsed time since the sexual assault,adding explanations to some buttons,and providing training.Conclusions:Our findings highlight the value of using a mixed methods research design to conduct a usability and acceptability test.Nurses are more likely to adopt a new technology for their evidencebased practice when the technology is easy to use and useful and requires less time to find the right piece of guideline evidence.Individualized training needs to be designed based on users'characteristics.
基金Funded by the National Natural Science Foundation of China(No.51278073)Prospective Joint Research Project of Jiangsu Province(No.BY2015027-23)State Key Laboratory for Geo Mechanics and Deep Underground Engineering,China University of Mining&Technology(No.SKLGDUEK1704)
文摘Durability design of recycled high performance concrete（RHPC） is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate（CRA）. We discussed a frostdurability-based mix proportion design method for RHPC using 100 % CRA and natural sand. Five groups of RHPC mixes with five strength grades（40, 50, 60, 70 and 80 MPa） were produced using CRA with four quality classes, and their workability, 28 d compressive strengths and frost resistances（measured by the compressive strength loss ratio and the relative dynamic modulus of elasticity） were tested. Relationships between the 28 d compressive strength, the frost resistance and the CRA quality characteristic parameter, water absorption, were then developed. The criterion of a CRA maximum water absorption limit value for RHPC was suggested, independent of its source and quality class. The results show that all RHPC mixes achieve the expected target workability, strength, and frost durability. The research results demonstrate that the application of the proposed method does not require trial testing prior to use.
文摘Concrete is one of the most consumable construction materials on the earth.The concrete constitutes cement,sand,gravel,water and/or additives in definite proportions.The proportions of raw materials of concrete are decided by the concrete mix design.The mix design depends on the various factors.For mix design,most of the countries have their own specifications.In the present study,standard guidelines of India,Britain and America for the concrete mix design have been discussed.The concrete grades of M25,M35 and M45 were designed and compared.Indian Standards were also compared.It was concluded that a new revised version of Indian Standard code has the lowest value of water/cement ratio and highest quantity of cement as compared to other standards.
基金Supported by Projects of NSFC(No.51108207)Science and Technology Development Planning of Jilin Province(No.201201057)
文摘Sulpho-aluminate expansive cementitious composite is proved to be one of the most effective ways to prevent concrete cracking too soon. Mix design of sulpho-aluminate expansive cementitious composite completely depends on experience and experiments at present. This method ignores the influence of expansion behavior which hinders the application of sulpho-aluminate expansive cementitious composite. The workability,free expansion property,flexural strength and compressive strength of sulpho-aluminate expansive cementitious composite have been investigated by tests. The relationship between expansion ratio and mix design parameters such as curing age,water-cement ratio and cement abundance coefficient is deduced according to the experimental statistics. A new simplified approach to mix design of sulpho-aluminate expansive cementitious composite is proposed as a reference for construction application,which avoids experiments and experience.
基金sponsored by a grant from the Center for Integrated Asset Management for Multimodal Transportation Infrastructure Systems(CIAMTIS),a US Department of Transportation,University Transportation Center,United States,under federal grant number 69A3551847103。
文摘The increasing impact of the greenhouse effect on ecosystems is prompting transportation agencies to seek methods for reducing CO_(2)emissions during pavement construction and maintenance.Additionally,the laboratory mix design process,which involves selecting aggregate gradation and binder content,is time-consuming and labor-intensive.To accelerate the traditional mix design procedure,this study presented a mix design procedure that can automatically determine gradation and binder content based on machine learning(ML)and a meta-heuristic algorithm.Specifically,ML approaches were employed to model the relationship between volumetric properties(mixture bulk specific gravity(Gmb)and air void(VV))and both mixture component properties and mixture proportion,based on a dataset collected from literature with 660 mixture designs.Integrated with the prediction of ML models and the modified multi-objective grey wolf optimization(MOGWO)algorithm,an automatic asphalt mix design was proposed to pursue three goals,including VV,cost,and CO_(2)emission.The results indicated that least squares support vector regression(LSSVR)and e Xtreme gradient boosting(XGBoost)achieved the highest prediction accuracies(correlation coefficient:0.92 for VV and 0.96 for Gmb).The MOGWO algorithm successfully found the 26 optimal mix designs for the case of VV vs.cost vs.CO_(2)emission.Compared to the traditional laboratory design,the optimal mixture with VV of4%achieves a cost saving of 2.46%and a reduction of 4.03%in carbon emission.The volumetric properties of the mixtures output by the approach also align closely with values measured in a laboratory.
基金Funded by the Natural Science Foundation of China ( No.50408004)
文摘The mix designs and specimen preparation for the dry process and wet process of sulfur rubber conerete （ SRC ） were investigated. The compressive strength, corrosion-resistance and toughness were studied and discussed. The results show that SRC is corrosion-resistanet. Although the compressive strength of SRC decreases with inereasing rubber content, the toughness increases instead . Adding micro-filler will improve the compressive strength of SRC . There is a threshold value for the sulfur content, at which the compressive strength and the workability of SRC reach an optimum balance . The bond between rubber particles and surrounding sulfur is strong due to the vulcanization process that generates cross-link through S-C bonds.
基金supported by the National Natural Science Foundation of China (Grant Nos.52078310,51878420)the Ministry of Science and Technology of China (Grant Nos.2018YFC1504303,2017YFC1503103)Xingliao Talent Program of Liaoning Province (Grant No.XLYC1902038)。
文摘With the resource shortage in coastal areas,the construction of concrete structures using freshwater and river sand has brought great economic and environmental costs.The use of seawater,sea sand,and coral aggregates in concrete mixes has become an alternative solution for coastal and marine structures,especially for offshore structures and artificial islands.In this study,378 seawater,sea sand,and coral aggregate concrete(Coral-SWSSC)specimens were prepared,and their mechanical properties were investigated comprehensively through compressive tests to explore the optimized mix design at different grades.Results showed that the mechanical properties of Coral-SWSSC were strongly correlated with the water-to-binder ratios,coastal particle gradings,and pretreatment method of coastal particles.Based on the experimental results,mix proportion designs of CoralSWSSC were proposed for concrete from C20 to C50 grades,and the failure mechanism of Coral-SWSSC at different grades was discussed according to their respective failure modes.The findings of the current study provide knowledge on the optimized design of Coral-SWSSC,which can be used to promote the application of Coral-SWSSC in offshore,marine,and ocean engineering.
基金supported by the National High Technology Research and Development Program of China(863 Program)(2002AA745120)the National Defense Pre-research Foundation(9140A09020706JW314)the National Natural Science Foundationof China(160402003).
文摘A novel soft initiai-rotation control system and an H∞ robust constant rotational speed controller （RCRSC） for a rotational MEMS （micro-electro-mechanical system） gyro are presented. The soft initial-rotation control system can prevent the possible tumbling down of the suspended rotor and ensure a smooth and fast initial-rotation process. After the initial-rotation process, in order to maintain the rotational speed accurately constant, the RCRSC is acquired through the mixed sensitivity design approach. Simulation results show that the actuation voltage disturbances from the internal carrier waves in the gyro is reduced by more than 15.3 dB, and the speed fluctuations due to typical external vibrations ranging from 10 Hz to 200 Hz can also be restricted to 10^-3 rad/s order.
文摘There is a scarcity of literature discussing nurses’ behaviors toward caring for suspected or confirmed human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) patients. The development of a scale specific to measure nurses’ behaviors will allow health institutions to assess the disposition of their nurses in terms of HIV care. This study aims to present the rigors of developing and validating a reliable instrument to contextualize these nurses’ behaviors. This study utilized a sequential exploratory mixed method design to develop the NB-CSHAP scale. Thematic analysis was done on the qualitative data from the interviews with persons living with HIV/AIDS (PLHA) from which items were selected to be included in the scale. Exploratory factor analysis was utilized to extract the factors and Cronbach’s alpha was used to assess the reliability of the instrument. Four factors were extracted and are categorized as either caring or discriminatory behaviors. These include: (1) service-oriented, (2) openhanded, (3) perceptive, and (4) discriminatory. The scale has an internal consistency of 0.73. The scale shows acceptable psychometric properties, hence can be used to assess the nurses’ behaviors in caring for confirmed or suspected HIV clients. The scale may be used by health institutions to determine the quality of the patient care provided by their nurses to clients with confirmed or suspected HIV .
基金the research result of the project"Research and Analysis of the Recycling and Utilization of Waste Concrete Based on Energy-saving and Environmental Protection"PJ20201390519 of the project of"Innovation and Entrepreneurship Training Program for College Students in 2020".Instructor:Congrong Tang。
文摘The early asphalt pavement in our country severely reduced the road performance due to various external factors during the use process.According to incomplete statistics,there are more asphalt pavements that need to be renovated and repaired every year in China,and the amount of construction waste such as asphalt concrete and other construction waste reaches 1,000.About ten thousand tons.If such a huge amount of construction waste is not used,it will inevitably cause great pollution to the environment.If it can be reused,not only will it be environmentally friendly and energy-saving,it will also save more than one billion yuan in costs.In view of the above problems,this article conducts related Research and Analysis on the Principle in Plant Cold Recycling for Foamed Bitumen and Mixture Performance to provide reference for future projects.
基金This study was supported by the National Natural Science Foundation of China under Grant number of 51861145402.
文摘This research explored the application potential of PUM thin-overlay technology on airport rapid maintenance.The rapid curing process of polyurethane binder determines the limited time window for mixing and construction of polyurethane-bonded mixture(PUM),which presents significant difference with hot-mix asphalt(HMA)technology.Therefore,this research investigated and optimized the mix design of PUM for airport thin-overlay technology based on its thermosetting characteristics.First,limestone and basalt were comprehensively compared as an aggregate for PUM.Then,the effects of molding and curing conditions were studied in terms of mixing time,molding method,molding parameters and curing temperature.Statistical analysis was also conducted to evaluate the effects of gradation and particle size on PUM performances based on gray relational analysis(GRA),thus determining the key particle size to control PUM performances.Finally,the internal structural details of PUM were captured by X-ray CT scan test.The results demonstrated that it only took 12 hours to reach 75%of maximum strength at a curing temperature of 50°C,indicating an efficient curing process and in turn allowing short traffic delay.The internal structural details of PUM presented distribution of tiny pores with few connective voids,guaranteeing waterproof property and high strength.
基金the support of Portuguese National Funding Agency for Science, Research and Technology (FCT) through scholarship SFRH/BSAB/114415/ 2016
文摘Pavement and mix design represent one of the key components within the life cycle of a road infrastructure, with links to political, economic, technical, societal and environmental issues. Recent researches related to the characteristics of materials and associated behavior models both for materials and pavement, made it appropriate to consider updating current pavement design methods, and especially in the USA this has already been in process while in Europe uses of the methods developed in the early 1970s. Thus, this paper firstly presents a brief historical overview of pavement design methods, high- lighting early limitations of old empirical methods. Afterwards, French, UK and Shell methods currently in use in Europe will be presented, undeHining their main components in terms of methodology, traffic, climatic conditions and subgrade. The asphalt mix design and modeling in Europe are presented with their inclusion in the pavement design methods. Finally, the main challenges for the development of a European pavement design method are presented as well as the recent research developments that can be used for that method.
文摘The clay mineral composition is one of the major factors that governs the physical properties of silty sand subgrade. Therefore, a thorough knowledge of mineral composition is essential to predict the optimum engineering properties of the soil, which is generally characterized by different indices like maximum dry density （MDD）, California bearing ratio （CBR）, unconfined compressive strength （UCS） and free swelling index （FSI）. In this article, a novel multi- attribute decision making （MADM） based approach of mix design has been proposed for silty sand- artificial clay mix to improve the characteristic strength of a soil subgrade. Experimental investigation has been carried out in this study to illustrate the proposed approach of selecting appropriate proportion for the soil mix to optimize all the above mentioned engineering properties simultaneously. The results show that a mix proportion containing approximately 90% silty sand plus 10% bentonite soil is the optimal combination in context to the present study. The proposed methodology for optimal decision making to choose appropriate combination of bentonite and silty sand is general in nature and therefore, it can be extended to other problems of selecting mineral compositions.
文摘The present study proposes the mix design method of Fly Ash(FA)based geopolymer concrete using Response Surface Methodology(RSM).In this method,different factors,including binder content,alkali/binder ratio,NS/NH ratio(sodium silicate/sodium hydroxide),NH molarity,and water/solids ratio were considered for the mix design of geopolymer concrete.The 2D contour plots were used to setup the mix design method to achieve the target compressive strength.The proposed mix design method of geopolymer concrete is divided into three categories based on curing regime,specifically one ambient curing(25°C)and two heat curing(60 and 90°C).The proposed mix design method of geopolymer concrete was validated through experimentation of M30,M50,and M70 concrete mixes at all curing regimes.The observed experimental compressive strength results validate the mix design method by more than 90%of their target strength.Furthermore,the current study concluded that the required compressive strength can be achieved by varying any factor in the mix design.In addition,the factor analysis revealed that the NS/NH ratio significantly affects the compressive strength of geopolymer concrete.
文摘In order to implement the objective mix design of hot mix asphalt adequately during the construction process, the significance of objective mixing ratio was elaborated, and the variability of materials and its control method were analyzed. An engineering example is used to illustrate the debugging process of asphalt mixture batching ＆ mixing plant and the dynamic quality management methods. The results show that the set of methods can not only implement the objective mixing ratio of hot mix asphalt adequately, but also control production during the construction process effectively.
文摘Industrial mixers for powders and granular materials operate with no effective control of mixture quality and lack scientific design. The last twenty years have seen growth in understanding of mixing and mixers. However, research falls far short of what is needed for on-line characterisation of mixture quality. Secondly, although theoretical descriptions of a few mixer types have been reported, these fall far short of what is needed for equipment design. Two thrusts could revolutionise this situation. One is a scientific characterisation of mixer structure applicable to industrial scale as well as laboratory scale equipment; this is now within our grasp using digital imaging. The other is the development of ideas to overcome the restricted number of particles that can be used in the Distinct Element Method （DEM） for mixers. The goal should be to take the designer through a sequence of steps to the most appropriate mixer size, configuration and operating conditions for a given process duty.
文摘Many researches have been carried out to study the fresh and hardened properties of concrete containing crumb rubber as replacement to fine aggregate by volume, yet there is no specific guideline has been developed on the mix design of the rubbercrete. The experimental program, which has been developed and reported in this paper, is designed and executed to provide such mix design guidelines. A total of 45 concrete mixes with three different water to cement ratio （0.41, 0.57 and 0.68） were cast and tested for fresh and mechanical properties of rubbercrete such as slump, air content, unit weight, compressive strength, flexural strength, splitting tensile strength and modulus of elasticity. Influence of mix design parameters such as percentage of crumb rubber replacement, cement content, water content, fine aggregate content, and coarse aggregate content were investigated. Three levels of slump value （for conventional concrete mixes） has been selected; low, medium and high slump. In each slump level, water content was kept constant. Equations for the reduction factors （RFs） for compressive strength, flexural strength, splitting tensile strength and modulus of elasticity have been developed. These RFs can be used to design rubbercrete mixes based on the conventional mix （0% crumb rubber content）
