Commonly,the standards for the geometric design of roads refer to a given set of values for the friction coefficient(longitudinal and transverse friction).These"reference"values imply corresponding visibilit...Commonly,the standards for the geometric design of roads refer to a given set of values for the friction coefficient(longitudinal and transverse friction).These"reference"values imply corresponding visibility sights,curvature radii,and speed limits.Unfortunately,not only do these reference values not correspond to a given standard to measure them,but nothing is said about the decrease of the posted speed limit(variable speed limits)when roads become slippery and lanes for autonomous vehicle(AV)are concerned.Furthermore,the same assessment of the friction coefficient has plenty of uncertainties due to measurement device,temperature,location,time passed from the construction,alignment-related variables(e.g.,curve,tangent,transition curve,convexity/crests or concavity/sags,longitudinal slope,superelevation,and ruling gradient),and supplementary singularities such as joints and bridge approaches.All the issues above may harm road safety and the complexity of forensic investigations of pavements.Consequently,this study's objectives were confined to(1)carrying out friction measurements and analyzing the problem of friction decay over time;(2)setting up a method to lower the speed limits where friction decays are detected;(3)setting up a method to handle friction decays for autonomous vehicles.Results demonstrate that:(1)a power law describes how the speed limits are affected by friction;(2)for speeds up to 170 km/h,due to the lower reaction time,AV reaction distance is lower,which benefits AV traffic(lower stopping distance);(3)on the contrary,for higher values of friction and higher speeds,under the hypothesis of having the same reaction time law for non-AV(NAV)(i.e.,decreasing with the initial speed),AV speed limits become lower than NAV speed limits;(4)not only do comfort-based speed profiles for AVs bring higher braking distances,but also,in the median part(of the deceleration process),this could pose safety issues and reduce the distance between the available and the needed friction.展开更多
A mathematically rigorous framework for singular limits of the magnetohydrodynamic rotating shallow water equations with ill-prepared data is developed when the Rossby and Froude numbers tend to zero at different rate...A mathematically rigorous framework for singular limits of the magnetohydrodynamic rotating shallow water equations with ill-prepared data is developed when the Rossby and Froude numbers tend to zero at different rates.The reduced systems are derived,respectively,for the stratification-dominant and the rotation-dominant cases by means of the developed three-scale fast averaging method.展开更多
In this paper,we compute sub-Riemannian limits of some important curvature variants associated with the connection with torsion for four dimensional twisted BCV spaces and derive a Gauss-Bonnet theorem for four dimens...In this paper,we compute sub-Riemannian limits of some important curvature variants associated with the connection with torsion for four dimensional twisted BCV spaces and derive a Gauss-Bonnet theorem for four dimensional twisted BCV spaces.展开更多
In chemical flooding,emulsification and interfacial tension(IFT)reduction are crucial for enhanced oil recovery(EOR).However,the dominant performance parameter and technical limits of surfactants for oil displacement ...In chemical flooding,emulsification and interfacial tension(IFT)reduction are crucial for enhanced oil recovery(EOR).However,the dominant performance parameter and technical limits of surfactants for oil displacement remain underexplored.This study investigated the relationship between the emulsification capability and IFT.Accordingly,the dominant performance parameter and the technical limits of surfactants were determined using oil displacement experiments.Specifically,an analysis of 74 sets of experimental results revealed a shift in the significant correlation between EI(a quantitative measure of emulsification capability)andσat anσvalue of 8.5×10^(-2)mN/m(i.e.,critical valueσ_(c)).Forσ<σ_(c),emulsification capability and IFT function as independent performance parameters.The oil displacement experiments using two surfactants with contrasting EI andσvalues demonstrate that emulsification capability,rather than ultra-low IFT,is the dominant performance parameter.This study determined the technical limit of EI using oil displacement experiments via in-situ emulsification.The experimental results indicate strong correlations of EI with oil displacement and recovery efficiencies.The incremental displacement and recovery efficiencies were employed to quantify the potential of surfactants to enhance oil displacement and recovery efficiencies,respectively.The incremental displacement and recovery efficiencies versus EI curves revealed a critical EI(EI_(c))value of 0.53.When EIEI_(c),their increasing rates slowed down markedly.Therefore,the technical limits of the emulsification capability and IFT of surfactants used in this study are determined at EI≥0.53 andσ≤8.5×10^(-2)mN/m,respectively.展开更多
Purpose–This study aimed to facilitate a rapid evaluation of track service status and vehicle ride comfort based on car body acceleration.Consequently,a low-cost,data-driven approach was proposed for analyzing speed-...Purpose–This study aimed to facilitate a rapid evaluation of track service status and vehicle ride comfort based on car body acceleration.Consequently,a low-cost,data-driven approach was proposed for analyzing speed-related acceleration limits in metro systems.Design/methodology/approach–A portable sensing terminal was developed to realize easy and efficient detection of car body acceleration.Further,field measurements were performed on a 51.95-km metro line.Data from 272 metro sections were tested as a case study,and a quantile regression method was proposed to fit the control limits of the car body acceleration at different speeds using the measured data.Findings–First,the frequency statistics of the measured data in the speed-acceleration dimension indicated that the car body acceleration was primarily concentrated within the constant speed stage,particularly at speeds of 15.4,18.3,and 20.9 m/s.Second,resampling was performed according to the probability density distribution of car body acceleration for different speed domains to achieve data balance.Finally,combined with the traditional linear relationship between speed and acceleration,the statistical relationships between the speed and car body acceleration under different quantiles were determined.We concluded the lateral/vertical quantiles of 0.8989/0.9895,0.9942/0.997,and 0.9998/0.993 as being excellent,good,and qualified control limits,respectively,for the lateral and vertical acceleration of the car body.In addition,regression lines for the speedrelated acceleration limits at other quantiles(0.5,0.75,2s,and 3s)were obtained.Originality/value–The proposed method is expected to serve as a reference for further studies on speedrelated acceleration limits in rail transit systems.展开更多
Two-dimensional(2D)transition metal dichalcogenides(TMDs)allow for atomic-scale manipulation,challenging the conventional limitations of semiconductor materials.This capability may overcome the short-channel effect,sp...Two-dimensional(2D)transition metal dichalcogenides(TMDs)allow for atomic-scale manipulation,challenging the conventional limitations of semiconductor materials.This capability may overcome the short-channel effect,sparking significant advancements in electronic devices that utilize 2D TMDs.Exploring the dimension and performance limits of transistors based on 2D TMDs has gained substantial importance.This review provides a comprehensive investigation into these limits of the single 2D-TMD transistor.It delves into the impacts of miniaturization,including the reduction of channel length,gate length,source/drain contact length,and dielectric thickness on transistor operation and performance.In addition,this review provides a detailed analysis of performance parameters such as source/drain contact resistance,subthreshold swing,hysteresis loop,carrier mobility,on/off ratio,and the development of p-type and single logic transistors.This review details the two logical expressions of the single 2D-TMD logic transistor,including current and voltage.It also emphasizes the role of 2D TMD-based transistors as memory devices,focusing on enhancing memory operation speed,endurance,data retention,and extinction ratio,as well as reducing energy consumption in memory devices functioning as artificial synapses.This review demonstrates the two calculating methods for dynamic energy consumption of 2D synaptic devices.This review not only summarizes the current state of the art in this field but also highlights potential future research directions and applications.It underscores the anticipated challenges,opportunities,and potential solutions in navigating the dimension and performance boundaries of 2D transistors.展开更多
In September 2018,we proposed the cutting-edge concept of“Beyond Limits Manufacturing”(BLM).BLM technology is based on the three-dimensional inner engraving or precise outer engraving of ultra-fast laser,to invent m...In September 2018,we proposed the cutting-edge concept of“Beyond Limits Manufacturing”(BLM).BLM technology is based on the three-dimensional inner engraving or precise outer engraving of ultra-fast laser,to invent micro/nano scale flow chips or devices,which makes it possible for the microform,integration,economy,safety,high efficiency,green and intelligence of research,development and manufacturing process,so as to realize transformational manufacturing in the era of Industry 4.0.In this paper,we reviewed the representative results we made in the field of micro/nano flow chemistry during the implementation of the BLM major project(December 2019 to August 2023),and discussed its application prospects in micro/nano flow chemistry.展开更多
A hypothetical photon mass m_(γ) can produce a frequency-dependent vacuum dispersion of light, which leads to an additional time delay between photons with different frequencies when they propagate through a fixed di...A hypothetical photon mass m_(γ) can produce a frequency-dependent vacuum dispersion of light, which leads to an additional time delay between photons with different frequencies when they propagate through a fixed distance. The dispersion measure and redshift measurements of fast radio bursts(FRBs) have been widely used to constrain the rest mass of the photon. However, all current studies analyzed the effect of the frequency-dependent dispersion for massive photons in the standard ΛCDM cosmological context. In order to alleviate the circularity problem induced by the presumption of a specific cosmological model based on the fundamental postulate of the masslessness of photons, here we employ a new model-independent smoothing technique, artificial neural network(ANN), to reconstruct the Hubble parameter H(z) function from 34 cosmic-chronometer measurements.By combining observations of 32 well-localized FRBs and the H(z) function reconstructed by ANN, we obtain an upper limit of m_(γ) ≤ 3.5 × 10^(-51)kg, or equivalently m_(γ) ≤ 2.0 × 10^(-15)eV/c^(2)(m_(γ) ≤ 6.5 × 10^(-51)kg, or equivalently m_(γ) ≤ 3.6 × 10^(-15)eV/c_(2)) at the 1σ(2σ) confidence level. This is the first cosmology-independent photon mass limit derived from extragalactic sources.展开更多
This review explores the concept of life-on-a-chip,which involves the creation of miniaturized biological systems,such as organs,tissues,and model organisms,on microscale platforms called microfluidic chips.These chip...This review explores the concept of life-on-a-chip,which involves the creation of miniaturized biological systems,such as organs,tissues,and model organisms,on microscale platforms called microfluidic chips.These chips consist of intricately etched channels,wells,and chambers that enable precise control and observation of fluids,cells,and biochemical reactions,facilitating the simulation of various aspects of human or animal physiology and the study of responses to different stimuli,drugs,or disease conditions.The review highlights the application of a novel technology,“Beyond Limit Manufacturing”(BLM),in the development of sophisticated three-dimensional cell models and model organism microchips.Modelorganism-on-a-chip and organ-on-a-chip(OoC)are among the thriving developments in the field of microfluidics,allowing for the reconstruction of living microenvironments and implementation of multiple stimuli.The review discusses the latest advancements in life-on-a-chip technology using BLM and outlines potential future research directions,emphasizing the significant role of these chips in studying complex biological processes in a controlled and scalable manner.展开更多
Microscopic pore structure in continental shale oil reservoirs is characterized by small pore throats and complex micro-structures.The adsorption behavior of hydrocarbons on the pore walls exhibits unique physical and...Microscopic pore structure in continental shale oil reservoirs is characterized by small pore throats and complex micro-structures.The adsorption behavior of hydrocarbons on the pore walls exhibits unique physical and chemical properties.Therefore,studying the adsorption morphology of hydrocarbon components in nanometer-sized pores and clarifying the exploitation limits of shale oil at the microscopic level are of great practical significance for the efficient development of continental shale oil.In this study,molecular dynamics simulations were employed to investigate the adsorption characteristics of various single-component shale oils in inorganic quartz fissures,and the influence of pore size and shale oil hydrocarbon composition on the adsorption properties in the pores was analyzed.The results show that different molecules have different adsorption capacities in shale oil pores,with lighter hydrocarbon components(C6H14)exhibiting stronger adsorption abilities.For the same adsorbed molecule,the adsorption amount linearly increases with the increase in pore diameter,but larger pores contribute more to shale oil adsorption.In shale pores,the thickness of the adsorption layer formed by shale oil molecules ranges from 0.4 to 0.5 nm,which is similar to the width of alkane molecules.Shale oil in the adsorbed state that is difficult to be exploited is mainly concentrated in the first adsorption layer.Among them,the volume fraction of adsorbed shale oil in 6 nm shale pores is 40.8%,while the volume fraction of shale oil that is difficult to be exploited is 16.2%.展开更多
Introduction: Convulsions are a frequent cause of admission to paediatric wards in countries with limited resources, and a major cause of neurological and cognitive sequelae. In sub-Saharan Africa, the aetiology of fe...Introduction: Convulsions are a frequent cause of admission to paediatric wards in countries with limited resources, and a major cause of neurological and cognitive sequelae. In sub-Saharan Africa, the aetiology of febrile convulsions is dominated by infections of the central nervous system. A detailed clinical examination and laboratory and imaging tests are carried out to identify the cause of the disease. Computed tomography is reserved for emergency situations or as a second line of defence, after Magnetic Resonance Imaging (MRI) to look for calcifications. Imaging thus helps to establish the nature of the epileptogenic lesion, specify its extent and guide its therapeutic management. The aim of this study is to clarify the contribution of MRI in the etiological investigation of convulsions in children at the paediatric university hospital, in addition to the usual means of exploration. Patient and Method: This was a cross-sectional, descriptive study from January 2022 to December 2023. We carried out an exhaustive sampling of all children aged between 1 and 59 months admitted for convulsion with fever or not who had undergone complementary examinations for aetiological purposes in relation to our technical platform during the study period. Results: Thirty patients were recruited. Children aged 12 to 59 months were the most represented (69.7%). The sex ratio was 1.30. The mean age was 36 months (range 30 days to 59 months). Of the 30 patients, 21.8% had a history of febrile convulsions. Most of our patients were from Bangui (73.3%). On admission, the majority of patients presented with an elevated temperature ranging from 38.5 degrees Celsius to 39.4 degrees Celsius in 33.1% of cases. The dominant clinical manifestations were tonic-clonic convulsions (53.2%), tonic convulsions (35.3%) and clonic convulsions (11.5%). According to their characteristics, convulsions were complex in 53.7% of cases and simple in 46.3%. Examinations for infectious diseases, tumors or malformation has been ruled out. The anticonvulsants most commonly used were diazepam, phenobarbital and phenytoin. We recorded a 73.3% cure rate and 4 (13.3%) cases of death. Conclusion: The investigation of seizures in search of aetiology outside the usual means in our context still presents difficulties. MRI is the examination of choice for exploring the posterior fossa and midline lesions. Combined with CT, it is better for exploring hemispheric tumours.展开更多
The aspiration of all wind turbine designers is to attain Betz’s upper limit, which represents the highest efficiency in wind energy extraction. Majority of working turbines operate slightly below this limit with an ...The aspiration of all wind turbine designers is to attain Betz’s upper limit, which represents the highest efficiency in wind energy extraction. Majority of working turbines operate slightly below this limit with an exception of a few operating in wind tunnels. This study proposes for a comprehensive reevaluation of Betz’s derivation, aiming to establish the gap between a theoretical power limit and a practical limit for realization. There are two common expressions for power coefficient giving the same optimal value of 59%, but they generate different power-coefficient curves when plotted against velocity ratios. This paper presents a new method being referred as “Direct Multiplication Fractional Change” (DMFC) for deriving power-coefficient curves in wind energy, and compares its generated curve with established models. Discrepancies in power-coefficient expressions are identified and harmonized. Three approaches, namely EVAM, LVM, and DMFCM, were used for the numerical derivation of cp in the study, with their evaluation summarized in a table. The study collaborates its findings with a formulated velocity-distance curve, commonly presented as a hypothetical velocity profile in some publications. The results from DMFCM indicate two distinct maxima for the power coefficient. On the front side of the disc, a maximum of 0.5 is achievable in practice, although it is not the highest theoretically. On the rear side, a theoretical maximum of 0.59 is observed, but this value is not attainable in practice. These maxima are separated by their positions along the line of flow relative to the disc. However, this approximation is limited to a streamlined flow model of the rotor disc.展开更多
Because of the various elements that come into play in natural soil formation, the impact of varied proportions of mineral composition and fines amount on Atterberg limits and compaction characteristics of soils is no...Because of the various elements that come into play in natural soil formation, the impact of varied proportions of mineral composition and fines amount on Atterberg limits and compaction characteristics of soils is not well known. Three distinct soil samples were used in this investigation. The findings indicated the effect of varied mineral composition proportions and fines amount on the liquid limit, plastic limit, and plasticity index as assessed by the Casagrande test and hand-rolling method. The fluctuation of maximum dry density and optimal moisture content with these three soils has also been studied. Furthermore, correlations were established to indicate the compaction parameters and the amount of minerals and particles in the soil. The data show that the mineral content of the soil has a direct impact on the Atterberg limits and compaction characteristics. Soils containing larger percentages of expansive minerals, such as montmorillonite, have more flexibility and volume change capability. Mineral composition influences compaction parameters such as maximum dry density, ideal water content, axial strain, and axial stress. Soils with a larger proportion of fines, such as Soil 2 and Soil 3, have stronger flexibility and lower compaction qualities, with higher ideal water content and lower maximum dry density. Soil 1 has moderate flexibility and intermediate compaction qualities due to its low fines percentage. The effect of different mineral compositions and fines on the Atterberg limits and compaction characteristics of soils can be used to predict the behavior of compacted soils encountered in engineering practices, reducing the time and effort required to assess soil suitability for engineering use.展开更多
Based on archetype analysis of system dynamics,the limits-to-growth archetype of Peter Senge(one of his eight archetypes) was borrowed,and various influence factors of rural tourism development combined to construct t...Based on archetype analysis of system dynamics,the limits-to-growth archetype of Peter Senge(one of his eight archetypes) was borrowed,and various influence factors of rural tourism development combined to construct the limits-to-growth archetype which consists of limits-to-growth archetype of scientific planning balance,and limits-to-growth archetype of infrastructure input balance,and limits-to-growth archetype of high-quality staff balance.Through the join of limits-to-growth sub-archetypes,limits-to-growth archetype of rural tourism development in overseas countries were obtained,on the basis of which further researches were carried out to analyze management countermeasures to eliminate limits to growth via rural tourism development.It was stressed that government should play the guiding role,unified planning,scientific management and policy support further enhanced;more efforts should be devoted to the infrastructure construction,and more financial support given by the government;more professional talents should be introduced in multiple ways,and training for present rural tourism staff enhanced.展开更多
The problem of collision avoidance for non-cooperative targets has received significant attention from researchers in recent years.Non-cooperative targets exhibit uncertain states and unpredictable behaviors,making co...The problem of collision avoidance for non-cooperative targets has received significant attention from researchers in recent years.Non-cooperative targets exhibit uncertain states and unpredictable behaviors,making collision avoidance significantly more challenging than that for space debris.Much existing research focuses on the continuous thrust model,whereas the impulsive maneuver model is more appropriate for long-duration and long-distance avoidance missions.Additionally,it is important to minimize the impact on the original mission while avoiding noncooperative targets.On the other hand,the existing avoidance algorithms are computationally complex and time-consuming especially with the limited computing capability of the on-board computer,posing challenges for practical engineering applications.To conquer these difficulties,this paper makes the following key contributions:(A)a turn-based(sequential decision-making)limited-area impulsive collision avoidance model considering the time delay of precision orbit determination is established for the first time;(B)a novel Selection Probability Learning Adaptive Search-depth Search Tree(SPL-ASST)algorithm is proposed for non-cooperative target avoidance,which improves the decision-making efficiency by introducing an adaptive-search-depth mechanism and a neural network into the traditional Monte Carlo Tree Search(MCTS).Numerical simulations confirm the effectiveness and efficiency of the proposed method.展开更多
This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the pre...This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the prepared surfaces are placed on top of each other and by rolling with reduction more than 50%,the bonding between layers is established.In this research,the roll bonding process was done at room temperature,without the use of lubricants and with a 70%thickness reduction.Then,the final thickness of the Ag/Al bilayer sheet reached 350μm by several stages of cold rolling.Before cold rolling,it should be noted that to decrease the hardness created due to plastic deformation,the roll-bonded samples were subjected to annealing heat treatment at 400℃for 90 min.Thus,the final samples were annealed at 200,300 and 400℃for 90 min and cooled in a furnace to examine the annealing temperature effects.The uniaxial tensile and microhardness tests measured mechanical properties.Also,to investigate the fracture mechanism,the fractography of the cross-section was examined by scanning electron microscope(SEM).To evaluate the formability of Ag/Al bilayer sheets,forming limit curves were obtained experimentally through the Nakazima test.The resistance of composites to failure due to cracking was also investigated by fracture toughness.The results showed that annealing increases the elongation and formability of the Ag/Al bilayer sheet while reduces the ultimate tensile strength and fracture toughness.However,the changing trend is not the same at different temperatures,and according to the results,the most significant effect is obtained at 300℃and aluminum layers.It was also determined that by increasing annealing temperature,the fracture mechanism from shear ductile with small and shallow dimples becomes ductile with deep cavities.展开更多
This letter critically evaluates Jiang et al's article on the differentiation of benign and malignant liver lesions using Emax and platelet count.Despite notable findings,significant methodological and interpretat...This letter critically evaluates Jiang et al's article on the differentiation of benign and malignant liver lesions using Emax and platelet count.Despite notable findings,significant methodological and interpretative limitations are identified.The study lacks detailed assay conditions for Emax measurement,employs inadequate statistical methods without robust multivariate analysis,and does not provide clinically relevant threshold values.The nomogram's reliance on Emax as a major diagnostic contributor is questionable due to attenuation in hepatocellular carcinoma patients with cirrhosis.Moreover,the study's limitations,such as selection bias and confounding factors,are not adequately addressed.Future research should adopt more rigorous methodologies,including prospective studies with larger cohorts and standardized protocols for biomarker measurement,to enhance validity and clinical applicability.展开更多
Foot reflexology is a non-invasive and safe complementary therapy that works by massaging the reflex zones of the feet and exerts systemic or whole-body regulation through meridian nerve conduction.This therapy is com...Foot reflexology is a non-invasive and safe complementary therapy that works by massaging the reflex zones of the feet and exerts systemic or whole-body regulation through meridian nerve conduction.This therapy is commonly used in the treatment of various conditions such as autism and Parkinson's disease.However,there is limited reporting on the use of foot reflexology therapy for infants with sensorineural hearing loss(SNHL).Currently,there is no definitive conclusion on how foot reflexology therapy can influence hearing.This editorial holds some guiding significance regarding this clinical issue.The aim is to present physiological evidence of how foot reflexology therapy can impact infants with SNHL,thereby enhancing clinician’s awareness of foot reflexology in treating infants with SNHL.展开更多
A theoretical analysis on the perforation of Weldox 460E steel plates struck by flat-nosed projectiles is presented using a previously developed model within a unified framework.This model contains a dimensionless emp...A theoretical analysis on the perforation of Weldox 460E steel plates struck by flat-nosed projectiles is presented using a previously developed model within a unified framework.This model contains a dimensionless empirical equation to describe the variation of energy absorbed through global deformation as a function of impact velocity.The study further investigates the energy absorption mechanisms of Weldox 460E steel plates,with particular focus on the“plateau”phenomenon,i.e.,limited increase in ballistic limit with increasing plate thickness.This phenomenon is explained and compared with results from previously studied 2024-T351 aluminium plates.The model predictions agree well with experimental data for Weldox 460E steel plates impacted by flat-nosed projectiles,including:relationship between global deformation and impact velocity,ballistic limit,residual velocity,and critical conditions for the transition of failure modes.Moreover,the model effectively predicts the“plateau”phenomenon observed in intermediate plate thickness range.It is also found that the indentation absorption energy contributes a significantly larger fraction of the total absorption energy in Weldox 460E steel plates perforated by flat-nosed projectiles than in 2024-T351 aluminium plates,due to the differences in material properties.展开更多
In order to study the preferred skin color for printing images,two CMYK images from ISO 400 and one from iStock,including five skin color images of East Asian females was selected in this study.The images were adjuste...In order to study the preferred skin color for printing images,two CMYK images from ISO 400 and one from iStock,including five skin color images of East Asian females was selected in this study.The images were adjusted with the CMYK printing ink volume variation of the single,double and triple channels in the given 280%total ink limit conditions.A larger number of color vision normal observers were organized to carry out the color preference evaluation experiment,and the selected preferred skin colors were analyzed.The distribution range of the chromaticity values for skin color images were obtained and the results indicated that there are three regions for printing skin color preferences,and the observers have a memory preference for brighter,fairer skin colors in young female and a reddish skin colors in girl,which can provide the guidance for color adjustment of printed skin color images.展开更多
文摘Commonly,the standards for the geometric design of roads refer to a given set of values for the friction coefficient(longitudinal and transverse friction).These"reference"values imply corresponding visibility sights,curvature radii,and speed limits.Unfortunately,not only do these reference values not correspond to a given standard to measure them,but nothing is said about the decrease of the posted speed limit(variable speed limits)when roads become slippery and lanes for autonomous vehicle(AV)are concerned.Furthermore,the same assessment of the friction coefficient has plenty of uncertainties due to measurement device,temperature,location,time passed from the construction,alignment-related variables(e.g.,curve,tangent,transition curve,convexity/crests or concavity/sags,longitudinal slope,superelevation,and ruling gradient),and supplementary singularities such as joints and bridge approaches.All the issues above may harm road safety and the complexity of forensic investigations of pavements.Consequently,this study's objectives were confined to(1)carrying out friction measurements and analyzing the problem of friction decay over time;(2)setting up a method to lower the speed limits where friction decays are detected;(3)setting up a method to handle friction decays for autonomous vehicles.Results demonstrate that:(1)a power law describes how the speed limits are affected by friction;(2)for speeds up to 170 km/h,due to the lower reaction time,AV reaction distance is lower,which benefits AV traffic(lower stopping distance);(3)on the contrary,for higher values of friction and higher speeds,under the hypothesis of having the same reaction time law for non-AV(NAV)(i.e.,decreasing with the initial speed),AV speed limits become lower than NAV speed limits;(4)not only do comfort-based speed profiles for AVs bring higher braking distances,but also,in the median part(of the deceleration process),this could pose safety issues and reduce the distance between the available and the needed friction.
基金supported by Natural Science Foundation of China(12001506)the Natural Science Foundation of Shandong Province(ZR2020QA014).
文摘A mathematically rigorous framework for singular limits of the magnetohydrodynamic rotating shallow water equations with ill-prepared data is developed when the Rossby and Froude numbers tend to zero at different rates.The reduced systems are derived,respectively,for the stratification-dominant and the rotation-dominant cases by means of the developed three-scale fast averaging method.
基金Supported by National Natural Science Foundation of China(Grant No.11771070).
文摘In this paper,we compute sub-Riemannian limits of some important curvature variants associated with the connection with torsion for four dimensional twisted BCV spaces and derive a Gauss-Bonnet theorem for four dimensional twisted BCV spaces.
基金funded by a basic research project of SINOPEC(KL22023)。
文摘In chemical flooding,emulsification and interfacial tension(IFT)reduction are crucial for enhanced oil recovery(EOR).However,the dominant performance parameter and technical limits of surfactants for oil displacement remain underexplored.This study investigated the relationship between the emulsification capability and IFT.Accordingly,the dominant performance parameter and the technical limits of surfactants were determined using oil displacement experiments.Specifically,an analysis of 74 sets of experimental results revealed a shift in the significant correlation between EI(a quantitative measure of emulsification capability)andσat anσvalue of 8.5×10^(-2)mN/m(i.e.,critical valueσ_(c)).Forσ<σ_(c),emulsification capability and IFT function as independent performance parameters.The oil displacement experiments using two surfactants with contrasting EI andσvalues demonstrate that emulsification capability,rather than ultra-low IFT,is the dominant performance parameter.This study determined the technical limit of EI using oil displacement experiments via in-situ emulsification.The experimental results indicate strong correlations of EI with oil displacement and recovery efficiencies.The incremental displacement and recovery efficiencies were employed to quantify the potential of surfactants to enhance oil displacement and recovery efficiencies,respectively.The incremental displacement and recovery efficiencies versus EI curves revealed a critical EI(EI_(c))value of 0.53.When EIEI_(c),their increasing rates slowed down markedly.Therefore,the technical limits of the emulsification capability and IFT of surfactants used in this study are determined at EI≥0.53 andσ≤8.5×10^(-2)mN/m,respectively.
基金the National Natural Science Foundation of China(NSFC)under No.52308473the National KeyR&DProgram under No.2022YFB2603301the China Postdoctoral Science Foundation funded project(Certificate Number:2023M743895).
文摘Purpose–This study aimed to facilitate a rapid evaluation of track service status and vehicle ride comfort based on car body acceleration.Consequently,a low-cost,data-driven approach was proposed for analyzing speed-related acceleration limits in metro systems.Design/methodology/approach–A portable sensing terminal was developed to realize easy and efficient detection of car body acceleration.Further,field measurements were performed on a 51.95-km metro line.Data from 272 metro sections were tested as a case study,and a quantile regression method was proposed to fit the control limits of the car body acceleration at different speeds using the measured data.Findings–First,the frequency statistics of the measured data in the speed-acceleration dimension indicated that the car body acceleration was primarily concentrated within the constant speed stage,particularly at speeds of 15.4,18.3,and 20.9 m/s.Second,resampling was performed according to the probability density distribution of car body acceleration for different speed domains to achieve data balance.Finally,combined with the traditional linear relationship between speed and acceleration,the statistical relationships between the speed and car body acceleration under different quantiles were determined.We concluded the lateral/vertical quantiles of 0.8989/0.9895,0.9942/0.997,and 0.9998/0.993 as being excellent,good,and qualified control limits,respectively,for the lateral and vertical acceleration of the car body.In addition,regression lines for the speedrelated acceleration limits at other quantiles(0.5,0.75,2s,and 3s)were obtained.Originality/value–The proposed method is expected to serve as a reference for further studies on speedrelated acceleration limits in rail transit systems.
基金supported by the National Key R&D Plan of China(Grant 2021YFB3600703)the National Natural Science Foundation(Grant 62204137)of China for Youth,the Open Research Fund Program of Beijing National Research Centre for Information Science and Technology(BR2023KF02009)+1 种基金the National Natural Science Foundation of china(U20A20168,61874065,and 51861145202)the Research Fund from Tsinghua University Initiative Scientific Research Program,the Center for Flexible Electronics Technology of Tsinghua University,and a grant from the Guoqiang Institute,Tsinghua University.
文摘Two-dimensional(2D)transition metal dichalcogenides(TMDs)allow for atomic-scale manipulation,challenging the conventional limitations of semiconductor materials.This capability may overcome the short-channel effect,sparking significant advancements in electronic devices that utilize 2D TMDs.Exploring the dimension and performance limits of transistors based on 2D TMDs has gained substantial importance.This review provides a comprehensive investigation into these limits of the single 2D-TMD transistor.It delves into the impacts of miniaturization,including the reduction of channel length,gate length,source/drain contact length,and dielectric thickness on transistor operation and performance.In addition,this review provides a detailed analysis of performance parameters such as source/drain contact resistance,subthreshold swing,hysteresis loop,carrier mobility,on/off ratio,and the development of p-type and single logic transistors.This review details the two logical expressions of the single 2D-TMD logic transistor,including current and voltage.It also emphasizes the role of 2D TMD-based transistors as memory devices,focusing on enhancing memory operation speed,endurance,data retention,and extinction ratio,as well as reducing energy consumption in memory devices functioning as artificial synapses.This review demonstrates the two calculating methods for dynamic energy consumption of 2D synaptic devices.This review not only summarizes the current state of the art in this field but also highlights potential future research directions and applications.It underscores the anticipated challenges,opportunities,and potential solutions in navigating the dimension and performance boundaries of 2D transistors.
文摘In September 2018,we proposed the cutting-edge concept of“Beyond Limits Manufacturing”(BLM).BLM technology is based on the three-dimensional inner engraving or precise outer engraving of ultra-fast laser,to invent micro/nano scale flow chips or devices,which makes it possible for the microform,integration,economy,safety,high efficiency,green and intelligence of research,development and manufacturing process,so as to realize transformational manufacturing in the era of Industry 4.0.In this paper,we reviewed the representative results we made in the field of micro/nano flow chemistry during the implementation of the BLM major project(December 2019 to August 2023),and discussed its application prospects in micro/nano flow chemistry.
基金supported by the National SKA Program of China (2022SKA0130100)the National Natural Science Foundation of China (Grant Nos. 12373053, 12321003, and 12041306)+4 种基金the Key Research Program of Frontier Sciences of Chinese Academy of Sciences (Grant No. ZDBSLY-7014)the International Partnership Program of Chinese Academy of Sciences for Grand Challenges (Grant No. 114332KYSB20210018)the CAS Project for Young Scientists in Basic Research (Grant No. YSBR-063)the CAS Organizational Scientific Research Platform for National Major Scientific and Technological Infrastructure: Cosmic Transients with FASTthe Natural Science Foundation of Jiangsu Province (Grant No. BK20221562)。
文摘A hypothetical photon mass m_(γ) can produce a frequency-dependent vacuum dispersion of light, which leads to an additional time delay between photons with different frequencies when they propagate through a fixed distance. The dispersion measure and redshift measurements of fast radio bursts(FRBs) have been widely used to constrain the rest mass of the photon. However, all current studies analyzed the effect of the frequency-dependent dispersion for massive photons in the standard ΛCDM cosmological context. In order to alleviate the circularity problem induced by the presumption of a specific cosmological model based on the fundamental postulate of the masslessness of photons, here we employ a new model-independent smoothing technique, artificial neural network(ANN), to reconstruct the Hubble parameter H(z) function from 34 cosmic-chronometer measurements.By combining observations of 32 well-localized FRBs and the H(z) function reconstructed by ANN, we obtain an upper limit of m_(γ) ≤ 3.5 × 10^(-51)kg, or equivalently m_(γ) ≤ 2.0 × 10^(-15)eV/c^(2)(m_(γ) ≤ 6.5 × 10^(-51)kg, or equivalently m_(γ) ≤ 3.6 × 10^(-15)eV/c_(2)) at the 1σ(2σ) confidence level. This is the first cosmology-independent photon mass limit derived from extragalactic sources.
基金the “Shanghai Beyond Limits Manufacturing Project” for supporting the realization of the BLM concept for microchip products.
文摘This review explores the concept of life-on-a-chip,which involves the creation of miniaturized biological systems,such as organs,tissues,and model organisms,on microscale platforms called microfluidic chips.These chips consist of intricately etched channels,wells,and chambers that enable precise control and observation of fluids,cells,and biochemical reactions,facilitating the simulation of various aspects of human or animal physiology and the study of responses to different stimuli,drugs,or disease conditions.The review highlights the application of a novel technology,“Beyond Limit Manufacturing”(BLM),in the development of sophisticated three-dimensional cell models and model organism microchips.Modelorganism-on-a-chip and organ-on-a-chip(OoC)are among the thriving developments in the field of microfluidics,allowing for the reconstruction of living microenvironments and implementation of multiple stimuli.The review discusses the latest advancements in life-on-a-chip technology using BLM and outlines potential future research directions,emphasizing the significant role of these chips in studying complex biological processes in a controlled and scalable manner.
文摘Microscopic pore structure in continental shale oil reservoirs is characterized by small pore throats and complex micro-structures.The adsorption behavior of hydrocarbons on the pore walls exhibits unique physical and chemical properties.Therefore,studying the adsorption morphology of hydrocarbon components in nanometer-sized pores and clarifying the exploitation limits of shale oil at the microscopic level are of great practical significance for the efficient development of continental shale oil.In this study,molecular dynamics simulations were employed to investigate the adsorption characteristics of various single-component shale oils in inorganic quartz fissures,and the influence of pore size and shale oil hydrocarbon composition on the adsorption properties in the pores was analyzed.The results show that different molecules have different adsorption capacities in shale oil pores,with lighter hydrocarbon components(C6H14)exhibiting stronger adsorption abilities.For the same adsorbed molecule,the adsorption amount linearly increases with the increase in pore diameter,but larger pores contribute more to shale oil adsorption.In shale pores,the thickness of the adsorption layer formed by shale oil molecules ranges from 0.4 to 0.5 nm,which is similar to the width of alkane molecules.Shale oil in the adsorbed state that is difficult to be exploited is mainly concentrated in the first adsorption layer.Among them,the volume fraction of adsorbed shale oil in 6 nm shale pores is 40.8%,while the volume fraction of shale oil that is difficult to be exploited is 16.2%.
文摘Introduction: Convulsions are a frequent cause of admission to paediatric wards in countries with limited resources, and a major cause of neurological and cognitive sequelae. In sub-Saharan Africa, the aetiology of febrile convulsions is dominated by infections of the central nervous system. A detailed clinical examination and laboratory and imaging tests are carried out to identify the cause of the disease. Computed tomography is reserved for emergency situations or as a second line of defence, after Magnetic Resonance Imaging (MRI) to look for calcifications. Imaging thus helps to establish the nature of the epileptogenic lesion, specify its extent and guide its therapeutic management. The aim of this study is to clarify the contribution of MRI in the etiological investigation of convulsions in children at the paediatric university hospital, in addition to the usual means of exploration. Patient and Method: This was a cross-sectional, descriptive study from January 2022 to December 2023. We carried out an exhaustive sampling of all children aged between 1 and 59 months admitted for convulsion with fever or not who had undergone complementary examinations for aetiological purposes in relation to our technical platform during the study period. Results: Thirty patients were recruited. Children aged 12 to 59 months were the most represented (69.7%). The sex ratio was 1.30. The mean age was 36 months (range 30 days to 59 months). Of the 30 patients, 21.8% had a history of febrile convulsions. Most of our patients were from Bangui (73.3%). On admission, the majority of patients presented with an elevated temperature ranging from 38.5 degrees Celsius to 39.4 degrees Celsius in 33.1% of cases. The dominant clinical manifestations were tonic-clonic convulsions (53.2%), tonic convulsions (35.3%) and clonic convulsions (11.5%). According to their characteristics, convulsions were complex in 53.7% of cases and simple in 46.3%. Examinations for infectious diseases, tumors or malformation has been ruled out. The anticonvulsants most commonly used were diazepam, phenobarbital and phenytoin. We recorded a 73.3% cure rate and 4 (13.3%) cases of death. Conclusion: The investigation of seizures in search of aetiology outside the usual means in our context still presents difficulties. MRI is the examination of choice for exploring the posterior fossa and midline lesions. Combined with CT, it is better for exploring hemispheric tumours.
文摘The aspiration of all wind turbine designers is to attain Betz’s upper limit, which represents the highest efficiency in wind energy extraction. Majority of working turbines operate slightly below this limit with an exception of a few operating in wind tunnels. This study proposes for a comprehensive reevaluation of Betz’s derivation, aiming to establish the gap between a theoretical power limit and a practical limit for realization. There are two common expressions for power coefficient giving the same optimal value of 59%, but they generate different power-coefficient curves when plotted against velocity ratios. This paper presents a new method being referred as “Direct Multiplication Fractional Change” (DMFC) for deriving power-coefficient curves in wind energy, and compares its generated curve with established models. Discrepancies in power-coefficient expressions are identified and harmonized. Three approaches, namely EVAM, LVM, and DMFCM, were used for the numerical derivation of cp in the study, with their evaluation summarized in a table. The study collaborates its findings with a formulated velocity-distance curve, commonly presented as a hypothetical velocity profile in some publications. The results from DMFCM indicate two distinct maxima for the power coefficient. On the front side of the disc, a maximum of 0.5 is achievable in practice, although it is not the highest theoretically. On the rear side, a theoretical maximum of 0.59 is observed, but this value is not attainable in practice. These maxima are separated by their positions along the line of flow relative to the disc. However, this approximation is limited to a streamlined flow model of the rotor disc.
文摘Because of the various elements that come into play in natural soil formation, the impact of varied proportions of mineral composition and fines amount on Atterberg limits and compaction characteristics of soils is not well known. Three distinct soil samples were used in this investigation. The findings indicated the effect of varied mineral composition proportions and fines amount on the liquid limit, plastic limit, and plasticity index as assessed by the Casagrande test and hand-rolling method. The fluctuation of maximum dry density and optimal moisture content with these three soils has also been studied. Furthermore, correlations were established to indicate the compaction parameters and the amount of minerals and particles in the soil. The data show that the mineral content of the soil has a direct impact on the Atterberg limits and compaction characteristics. Soils containing larger percentages of expansive minerals, such as montmorillonite, have more flexibility and volume change capability. Mineral composition influences compaction parameters such as maximum dry density, ideal water content, axial strain, and axial stress. Soils with a larger proportion of fines, such as Soil 2 and Soil 3, have stronger flexibility and lower compaction qualities, with higher ideal water content and lower maximum dry density. Soil 1 has moderate flexibility and intermediate compaction qualities due to its low fines percentage. The effect of different mineral compositions and fines on the Atterberg limits and compaction characteristics of soils can be used to predict the behavior of compacted soils encountered in engineering practices, reducing the time and effort required to assess soil suitability for engineering use.
基金Supported by Scientific and Technological Program of Jiangxi Provincial Department of Education: Limits to Growth Archetype Analysis ofRural Tourism with Restricted Resources and Countermeasure Research(GJJ1622)~~
文摘Based on archetype analysis of system dynamics,the limits-to-growth archetype of Peter Senge(one of his eight archetypes) was borrowed,and various influence factors of rural tourism development combined to construct the limits-to-growth archetype which consists of limits-to-growth archetype of scientific planning balance,and limits-to-growth archetype of infrastructure input balance,and limits-to-growth archetype of high-quality staff balance.Through the join of limits-to-growth sub-archetypes,limits-to-growth archetype of rural tourism development in overseas countries were obtained,on the basis of which further researches were carried out to analyze management countermeasures to eliminate limits to growth via rural tourism development.It was stressed that government should play the guiding role,unified planning,scientific management and policy support further enhanced;more efforts should be devoted to the infrastructure construction,and more financial support given by the government;more professional talents should be introduced in multiple ways,and training for present rural tourism staff enhanced.
基金co-supported by the Foundation of Shanghai Astronautics Science and Technology Innovation,China(No.SAST2022-114)the National Natural Science Foundation of China(No.62303378),the National Natural Science Foundation of China(Nos.124B2031,12202281)the Foundation of China National Key Laboratory of Science and Technology on Test Physics&Numerical Mathematics,China(No.08-YY-2023-R11)。
文摘The problem of collision avoidance for non-cooperative targets has received significant attention from researchers in recent years.Non-cooperative targets exhibit uncertain states and unpredictable behaviors,making collision avoidance significantly more challenging than that for space debris.Much existing research focuses on the continuous thrust model,whereas the impulsive maneuver model is more appropriate for long-duration and long-distance avoidance missions.Additionally,it is important to minimize the impact on the original mission while avoiding noncooperative targets.On the other hand,the existing avoidance algorithms are computationally complex and time-consuming especially with the limited computing capability of the on-board computer,posing challenges for practical engineering applications.To conquer these difficulties,this paper makes the following key contributions:(A)a turn-based(sequential decision-making)limited-area impulsive collision avoidance model considering the time delay of precision orbit determination is established for the first time;(B)a novel Selection Probability Learning Adaptive Search-depth Search Tree(SPL-ASST)algorithm is proposed for non-cooperative target avoidance,which improves the decision-making efficiency by introducing an adaptive-search-depth mechanism and a neural network into the traditional Monte Carlo Tree Search(MCTS).Numerical simulations confirm the effectiveness and efficiency of the proposed method.
基金Project(4013311)supported by the National Science Foundation of Iran(INSF)。
文摘This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the prepared surfaces are placed on top of each other and by rolling with reduction more than 50%,the bonding between layers is established.In this research,the roll bonding process was done at room temperature,without the use of lubricants and with a 70%thickness reduction.Then,the final thickness of the Ag/Al bilayer sheet reached 350μm by several stages of cold rolling.Before cold rolling,it should be noted that to decrease the hardness created due to plastic deformation,the roll-bonded samples were subjected to annealing heat treatment at 400℃for 90 min.Thus,the final samples were annealed at 200,300 and 400℃for 90 min and cooled in a furnace to examine the annealing temperature effects.The uniaxial tensile and microhardness tests measured mechanical properties.Also,to investigate the fracture mechanism,the fractography of the cross-section was examined by scanning electron microscope(SEM).To evaluate the formability of Ag/Al bilayer sheets,forming limit curves were obtained experimentally through the Nakazima test.The resistance of composites to failure due to cracking was also investigated by fracture toughness.The results showed that annealing increases the elongation and formability of the Ag/Al bilayer sheet while reduces the ultimate tensile strength and fracture toughness.However,the changing trend is not the same at different temperatures,and according to the results,the most significant effect is obtained at 300℃and aluminum layers.It was also determined that by increasing annealing temperature,the fracture mechanism from shear ductile with small and shallow dimples becomes ductile with deep cavities.
文摘This letter critically evaluates Jiang et al's article on the differentiation of benign and malignant liver lesions using Emax and platelet count.Despite notable findings,significant methodological and interpretative limitations are identified.The study lacks detailed assay conditions for Emax measurement,employs inadequate statistical methods without robust multivariate analysis,and does not provide clinically relevant threshold values.The nomogram's reliance on Emax as a major diagnostic contributor is questionable due to attenuation in hepatocellular carcinoma patients with cirrhosis.Moreover,the study's limitations,such as selection bias and confounding factors,are not adequately addressed.Future research should adopt more rigorous methodologies,including prospective studies with larger cohorts and standardized protocols for biomarker measurement,to enhance validity and clinical applicability.
基金Supported by the Fundamental Research Funds for the Central Universities,No.2022CDJYGRH-004.
文摘Foot reflexology is a non-invasive and safe complementary therapy that works by massaging the reflex zones of the feet and exerts systemic or whole-body regulation through meridian nerve conduction.This therapy is commonly used in the treatment of various conditions such as autism and Parkinson's disease.However,there is limited reporting on the use of foot reflexology therapy for infants with sensorineural hearing loss(SNHL).Currently,there is no definitive conclusion on how foot reflexology therapy can influence hearing.This editorial holds some guiding significance regarding this clinical issue.The aim is to present physiological evidence of how foot reflexology therapy can impact infants with SNHL,thereby enhancing clinician’s awareness of foot reflexology in treating infants with SNHL.
文摘A theoretical analysis on the perforation of Weldox 460E steel plates struck by flat-nosed projectiles is presented using a previously developed model within a unified framework.This model contains a dimensionless empirical equation to describe the variation of energy absorbed through global deformation as a function of impact velocity.The study further investigates the energy absorption mechanisms of Weldox 460E steel plates,with particular focus on the“plateau”phenomenon,i.e.,limited increase in ballistic limit with increasing plate thickness.This phenomenon is explained and compared with results from previously studied 2024-T351 aluminium plates.The model predictions agree well with experimental data for Weldox 460E steel plates impacted by flat-nosed projectiles,including:relationship between global deformation and impact velocity,ballistic limit,residual velocity,and critical conditions for the transition of failure modes.Moreover,the model effectively predicts the“plateau”phenomenon observed in intermediate plate thickness range.It is also found that the indentation absorption energy contributes a significantly larger fraction of the total absorption energy in Weldox 460E steel plates perforated by flat-nosed projectiles than in 2024-T351 aluminium plates,due to the differences in material properties.
文摘In order to study the preferred skin color for printing images,two CMYK images from ISO 400 and one from iStock,including five skin color images of East Asian females was selected in this study.The images were adjusted with the CMYK printing ink volume variation of the single,double and triple channels in the given 280%total ink limit conditions.A larger number of color vision normal observers were organized to carry out the color preference evaluation experiment,and the selected preferred skin colors were analyzed.The distribution range of the chromaticity values for skin color images were obtained and the results indicated that there are three regions for printing skin color preferences,and the observers have a memory preference for brighter,fairer skin colors in young female and a reddish skin colors in girl,which can provide the guidance for color adjustment of printed skin color images.
