The influence of ramps on the transient rolling contact characteristics and damage mechanisms of switch rails remains unclear,presenting substantial challenges to the safety of railway operations.To this end,this pape...The influence of ramps on the transient rolling contact characteristics and damage mechanisms of switch rails remains unclear,presenting substantial challenges to the safety of railway operations.To this end,this paper constructs a transient rolling contact finite element model of the wheel-rail in switch under different ramps using ANSYS/LSDYNA method,and analyzes the tribology and damage characteristics when the wheel passes through the switch at a uniform speed.Our research findings reveal that the vibration induced in the switch rail during the wheel load transfer process leads to a step-like increase in the contact force.Moreover,the interaction between the wheel and the rail primarily involves slip contact,which may significantly contribute to the formation of corrugations on the switch rail.Additionally,the presence of large ramps exacerbates switch rail wear and rolling contact fatigue,resulting in a notable 13.2%increase in switch rail damage under 40‰ramp conditions compared to flat(0‰ramp)conditions.Furthermore,the large ramps can alter the direction of crack propagation,ultimately causing surface spalling of the rail.Therefore,large ramps intensify the dynamic interactions during the wheel load transfer process,further aggravating the crack and spalling damage to the switch rails.展开更多
A numerical investigation and experimental validation is performed to address deeper insights into the combined effect of shaped holes and Sand-Dune-shaped upstream Ramp(SDR)on enhancing the film cooling effectiveness...A numerical investigation and experimental validation is performed to address deeper insights into the combined effect of shaped holes and Sand-Dune-shaped upstream Ramp(SDR)on enhancing the film cooling effectiveness,under a wide blowing ratio range(M=0.25–1.5).Three kinds of holes(Cylindrical Hole(CH),Fan-Shaped Hole(FSH),and Crater-Shaped Hole(CSH))are taken into consideration.The SDR shows an inherent affecting mechanism on the mutual interaction of jet-in-crossflow.It aggravates the lateral spreading of cooling jet and thus improves the film cooling uniformity significantly,regardless of film-hole shape and blowing ratio.When the blowing ratio is beyond 1.0,the combined effect of shaped holes and SDR on improving film cooling effectiveness behaves more significantly.It is suggested that FSH-SDR is a most favorable film cooling scheme.For FSH-SDR case,the spatially-averaged film cooling effectiveness is increased monotonously with the increase of blowing ratio,among the present bowing ratio range.展开更多
In this paper, we present a new macro model for traffic flow on a highway with ramps based on the existing models. We use the new model to study the effects of on-off-ramp on the main road traffic during the morning r...In this paper, we present a new macro model for traffic flow on a highway with ramps based on the existing models. We use the new model to study the effects of on-off-ramp on the main road traffic during the morning rush period and the evening rush period. Numerical tests show that, during the two rush periods, these effects are often different and related to the status of the main road traffic. If the main road traffic flow is uniform, then ramps always produce stop-and-go traffic when the main road density is between two critical values, and ramps have little effect on the main road traffic when the main road density is less than the smaller critical value or greater than the larger critical value. If a small perturbation appears on the main road, ramp may lead to stop-and-go traffic, or relieve or even eliminate the stop-and-go traffic, under different circumstances. These results are consistent with real traffic, which shows that the new model is reasonable.展开更多
Although there are many studies involving influence of runaway truck entry speed and longitudinal grade on stopping distance,focusing on aggregate properties is scarce.This paper investigates the influence of the aggr...Although there are many studies involving influence of runaway truck entry speed and longitudinal grade on stopping distance,focusing on aggregate properties is scarce.This paper investigates the influence of the aggregate properties such as types of aggregate and river gravel radius on stopping distance through numerical analysis of particle flow code in two dimensions(PFC2D).The software is used to generate stopping distance data for two aggregate types and four group gravel radii under various approaching speeds and grades.The generated data are compared with the testing results of full-scale arrester bed.The simulated finding of this paper implies that types of aggregates and river gravel radii have a significant impact on the stopping distance for runaway truck on escape ramps.展开更多
In this paper, we develop a cellular automaton model to describe the phase transition of traffic flow on urban expressway systems with on-off-ramps and accessory roads. The lane changing rules are given in detailed, t...In this paper, we develop a cellular automaton model to describe the phase transition of traffic flow on urban expressway systems with on-off-ramps and accessory roads. The lane changing rules are given in detailed, the numerical results show that the main road and the accessory road both produce phase transitions. These phase transitions will omen be influenced by the number of lanes, lane changing, the ramp flow, the input flow rate, and the geometry structure.展开更多
This study introduces a multi-area cooperative merging control strategy to enhance the safety and efficiency of connected and autonomous vehicles(CAVs)at freeway merging areas with multiple mainline lanes and a dual-l...This study introduces a multi-area cooperative merging control strategy to enhance the safety and efficiency of connected and autonomous vehicles(CAVs)at freeway merging areas with multiple mainline lanes and a dual-lane ramp.The strategy integrateslane changing in advance tactics for upstream mainline vehicles and speed regulation for ramp vehicles into a structured control framework.This framework comprises distinct areas for proactive mainline lane changing in advance,ramp speed regulation and cooperative merging.For the mainline lane-changing area,we propose a strategy that relies on maintaining a minimum safety distance and optimizing speed benefits,thereby enhancing merging opportunities for ramp vehicles and balancing downstream traffic flows.In the ramp speed regulation area,a vehicular speed control model is established,utilizing a'FIFO rule'based on the vehicles'arrival times at the acceleration lane start,coupled with a virtual platoon concept to synchronize and optimize platoon speeds for efficient travel on ramps.In the cooperative merging area,vehicle trajectories on the mainline and ramp are optimized in a rolling horizon manner,facilitating seamless integration of ramp vehicles into the mainline.Simulation results indicate that our proposed cooperative control method significantly surpasses uncontrol led and trajectory-only optimization approaches in control efficiency across varying traffic demands.This method demonstrates notable advancements in average speed,delay reduction and fewer stops,with minimized fluctuations and increased control stability.Additionally,the cooperative control approach demonstrates superior adaptability across different numbers of ramp lanes,with scenarios involving dual-lane ramps exhibiting a more pronounced advantage.展开更多
[目的]比较关节镜下缝合钩和Fast-fix缝合Ⅳ型半月板Ramp区损伤的临床疗效。[方法]回顾性分析2016年1月—2020年10月45例前交叉韧带(anterior cruciate ligament, ACL)损伤合并Ⅳ型半月板Ramp损伤患者的临床资料。所有患者均取自体腘绳...[目的]比较关节镜下缝合钩和Fast-fix缝合Ⅳ型半月板Ramp区损伤的临床疗效。[方法]回顾性分析2016年1月—2020年10月45例前交叉韧带(anterior cruciate ligament, ACL)损伤合并Ⅳ型半月板Ramp损伤患者的临床资料。所有患者均取自体腘绳肌腱行ACL重建,依据术前医患沟通结果,21例应用缝合钩缝合Ramp损伤,24例应用Fast-fix缝合。对比患者围手术期、随访及影像学结果。[结果]所有患者均顺利完成手术,术中未出现血管、神经损伤等并发症。缝合钩组手术时间[(91.2±10.6) min vs (62.5±8.4) min, P<0.001]、切口总长度[(5.9±0.5) cm vs (5.1±0.6) cm, P<0.001]均显著长于Fast-fix组,但前者住院费用显著少于后者[(3.4±0.3)万元vs (4.3±0.7)万元, P<0.001]。两组Ramp撕裂长度、缝合针数、下地行走时间、切口愈合、住院时间比较差异均无统计学意义(P>0.05)。所有患者均获36~72个月随访。两组完全负重活动时间的差异无统计学意义(P>0.05)。术后1年及末次随访时,两组膝间隙压痛、麦氏征,轴移征、膝关节屈伸ROM、IKDC评分及Lysholm评分较术前均显著改善(P<0.05)。同一时间点,两组上述指标的差异均无统计学意义(P>0.05)。影像方面,与术前相比,术后1年,两组半月板损伤分级及胫骨平台后侧骨髓水肿均显著改善(P<0.05),相应时间点,两组上述指标的差异均无统计学意义(P>0.05)。术后1年MRI显示缝合钩组愈合率为90.5%、Fast-fix组为87.5%,差异无统计学意义(P>0.05)。[结论]关节镜下缝合钩和Fast-fix缝合半月板Ramp区Ⅳ型损伤均可获得满意疗效。展开更多
胰腺癌是公认的最具侵袭性和致命性的恶性肿瘤之一,其中约20%的病例为胰体尾部癌症。由于该类型癌症生长迅速且早期缺乏明显症状,许多患者在诊断时已经错过了最佳治疗时机。手术是唯一可能治愈的手段,但传统的远端胰腺切除术和脾切除术...胰腺癌是公认的最具侵袭性和致命性的恶性肿瘤之一,其中约20%的病例为胰体尾部癌症。由于该类型癌症生长迅速且早期缺乏明显症状,许多患者在诊断时已经错过了最佳治疗时机。手术是唯一可能治愈的手段,但传统的远端胰腺切除术和脾切除术存在较高的阳性切缘率、较低的淋巴结清扫率和较差的总体生存率,已发表的证据表明经过传统手术治疗的病人,其五年生存率介于8%至22%之间。2003年,Strasberg等人提出了一种新的手术方法——根治性顺行模块化胰脾切除术(Radical Antegrade Modular Pancreatosplenectomy, RAMPS),旨在提供更好的肿瘤切除效果、提高R0切除率并改善患者的长期预后。RAMPS的五年总体生存率可高达30%~40%。随着腹腔镜技术的不断进步,腹腔镜下根治性顺行模块化胰脾切除术(Laparoscopic Radical Antegrade Modular Pancreatosplenectomy, L-RAMPS)作为一种微创手术,具有术后恢复快等优势,逐渐获得越来越多外科医师的关注。文章总结了这种手术的现状,并展望其未来发展。Pancreatic cancer is widely recognized as one of the most aggressive and lethal malignant tumors, with approximately 20% of cases occurring in the body and tail of the pancreas. Due to the rapid growth of this cancer and the lack of obvious symptoms in its early stages, many patients miss the opportunity for optimal treatment by the time of diagnosis. Surgery remains the only potentially curative option;however, traditional distal pancreatectomy and splenectomy are associated with high positive margin rates, low lymph node dissection rates, and poor overall survival. Published evidence shows that the five-year survival rate for patients treated with traditional surgery ranges from 8% to 22%. In 2003, Strasberg et al. proposed a new surgical technique—Radical Antegrade Modular Pancreatosplenectomy (RAMPS)—designed to improve tumor resection, increase the R0 resection rate, and enhance long-term prognosis. The five-year overall survival rate for RAMPS can reach 30%~40%. With the continuous advancement of laparoscopic technology, Laparoscopic Radical Antegrade Modular Pancreatosplenectomy (L-RAMPS), as a minimally invasive procedure, offers advantages such as faster postoperative recovery and is gradually gaining more attention from surgeons. This article provides an overview of the current status of this surgery and discusses its potential future development.展开更多
Traditional in situ biogeochemical transformation suffers from competition among crucial microorganisms and inadequate formation of reactive minerals,thus leading to the accumulation of toxic intermediates.In this stu...Traditional in situ biogeochemical transformation suffers from competition among crucial microorganisms and inadequate formation of reactive minerals,thus leading to the accumulation of toxic intermediates.In this study,three regulation schemes were proposed to solve these problems from the perspective of engineering mode.Results showed intermittent injection mode effectively reduced the accumulation of toxic intermediates but the reduction rate of tetrachloroethylene was decreased.And periodical supplementation of carbon and sulfur sources accelerated the removal of tetrachloroethylene but failed to reduce the accumulation of toxic products.While,regular supplementation of sulfate effectively weakened the competition of methanogens and increased the iron sulfide proportion on the surface of the minerals,thus reducing the accumulation of toxicity.Based on the results,this study obtained an effective engineering approach for practical site application.In addition,the main forms of active minerals capable ofβ-eliminating contaminants during biogeochemical transformation were identified in this study,including FeS,FeS_(2),and Fe_(3)S_(4).Furthermore,the engineered regulatory mechanism of this study was summarized through the analysis of microbial community structure and mineral morphology.The amendment promotes the production of minerals and thus controls the transformation pathway of contaminants by altering the abundance of sulfate-reducing bacteria and dissimilatory iron reducing bacteria.This mechanism can provide a basis for subsequent theoretical studies.展开更多
Purpose–On-ramp merging areas are typical bottlenecks in the freeway network since merging on-ramp vehicles may cause intensive disturbances on the mainline traffic flow and lead to various negative impacts on traffi...Purpose–On-ramp merging areas are typical bottlenecks in the freeway network since merging on-ramp vehicles may cause intensive disturbances on the mainline traffic flow and lead to various negative impacts on traffic efficiency and safety.The connected and autonomous vehicles(CAVs),with their capabilities of real-time communication and precise motion control,hold a great potential to facilitate ramp merging operation through enhanced coordination strategies.This paper aims to present a comprehensive review of the existing ramp merging strategies leveraging CAVs,focusing on the latest trends and developments in the research field.Design/methodology/approach–The review comprehensively covers 44 papers recently published in leading transportation journals.Based on the application context,control strategies are categorized into three categories:merging into sing-lane freeways with total CAVs,merging into singlane freeways with mixed traffic flows and merging into multilane freeways.Findings–Relevant literature is reviewed regarding the required technologies,control decision level,applied methods and impacts on traffic performance.More importantly,the authors identify the existing research gaps and provide insightful discussions on the potential and promising directions for future research based on the review,which facilitates further advancement in this research topic.Originality/value–Many strategies based on the communication and automation capabilities of CAVs have been developed over the past decades,devoted to facilitating the merging/lane-changing maneuvers at freeway on-ramps.Despite the significant progress made,an up-to-date review covering these latest developments is missing to the authors’best knowledge.This paper conducts a thorough review of the cooperation/coordination strategies that facilitate freeway on-ramp merging using CAVs,focusing on the latest developments in this field.Based on the review,the authors identify the existing research gaps in CAV ramp merging and discuss the potential and promising future research directions to address the gaps.展开更多
Poor early adaptation in aviaries has adverse effects on welfare and the later production.Effects of system modification by ramps and ladders on early adaptation of birds were investigated.A total of 240 pullets and 2...Poor early adaptation in aviaries has adverse effects on welfare and the later production.Effects of system modification by ramps and ladders on early adaptation of birds were investigated.A total of 240 pullets and 24 cockerels of Yukou Jing Pink II parent stock were allocated into six perchery compartments at the age of 83 days from conventional cages.Three compartments were modified with ramps of different angles,30°,40°and 30°&50°combination.The other compartments were fitted with 2 ladders,with 22 cm steps and 33 cm steps.Spatial distribution of birds and eggs,as well as the data of ramps and ladders utilization were used to assess birds’adaptation and the effectiveness of modification facilities.A higher proportion of hens got onto the tiered platforms in ramp group(p<0.001)and engaged in feeding(p=0.002).Inversely more than 85.0%of hens dwelled on the system floor in the ladder group for the whole observation period.The proportion of birds feeding increased over time(p<0.001),with the proportion of birds lying decreasing(p<0.001).A higher frequency of utilization of ramps was found compared with ladders(4.5-25.8 vs.2.8-14.7 times/40 birds per hour).For ramp use,79.3%of hens negotiated level change by using 30°ramp and behavioral process was also found related with the type of ramps.On the contrary,very few successful level changes were observed via ladders and 60%of ladder use was ended with birds backing to the system floor.Besides,a higher proportion of non-nest eggs was recorded in ladder group in the early laying period.These results indicated that modification of ramps is more applicable for improving birds’early adaptation and later production in perchery system of multi-tier,especially for pullets reared in conventional cages.展开更多
Queue storage at a metered freeway on-ramp is an essential design element for metered on-ramps to prevent on-ramp queue from extending beyond on-ramps.In this paper,various existing methodologies that are used to size...Queue storage at a metered freeway on-ramp is an essential design element for metered on-ramps to prevent on-ramp queue from extending beyond on-ramps.In this paper,various existing methodologies that are used to size the queue storage at metered on-ramps were first reviewed.It was found that queue storage sized using 7%of peak hour on-ramp demand is widely accepted in practice.A limited dataset collected in California helps provide some reality check for this method.It is recommended that queue storage be recognized as an indispensable design element at metered on-ramps,and detailed sizing guidance be developed in the highway geometric design policy of the American Association of State Highway and Transportation Officials(AASHTO).展开更多
In Section 4I.02 of the newly published Manual on Uniform Traffic Control Devices(MUTCD),standards were specified for the placement of signal heads for traffic control signals at freeway entrance ramps,or ramp meters....In Section 4I.02 of the newly published Manual on Uniform Traffic Control Devices(MUTCD),standards were specified for the placement of signal heads for traffic control signals at freeway entrance ramps,or ramp meters.For simultaneous operations,i.e.when ramp control signals are operated such that green signal indications are always displayed simultaneously to all of the lanes on the ramp,a minimum of two signal faces per ramp shall face entering traffic.For staggered operations,i.e.the ramp control signal are operated such that green signal indications are not always displayed simultaneously to all of the lanes on the ramp,one signal face shall be provided over the approximate center of each separately-controlled lane.Based on a nation-wide survey,it was realized that the two standards did not fully reflect the state-of-the-practice with respect to ramp metering operations.Due to the lack of significant conflicting movements at ramp meters,for any on-ramp lane,a minimum of one overhead mounted,or one upper and one lower roadside-mounted signal face is sufficient to control the metering operations.The minimum necessary number of signal faces changes according to the total number of lanes,how the signal faces are mounted(overhead or roadside mounting),and how the meters are operated(simultaneous or staggered).Suggestions are made to revise the two standards to better reflect the current nation-wide practices,and better consider the specific operational needs for ramp meters.展开更多
Ensuring adequate access to truck parking is critical to the safe and efficient movement of freight traffic. There are strict federal guidelines for commercial truck driver rest periods. Rest areas and private truck s...Ensuring adequate access to truck parking is critical to the safe and efficient movement of freight traffic. There are strict federal guidelines for commercial truck driver rest periods. Rest areas and private truck stops are the only places for the trucks to stop legally and safely. In locations without sufficient parking areas, trucks often park on interstate ramps, which create safety risks for other interstate motorists. Historically, agencies have employed costly and time intensive manual counting methods, camera surveillance, and driver surveys to assess truck parking. Connected truck data, available in near real-time, offers an efficient alternative to practitioners to assess truck parking patterns and identify areas where there may be insufficient safe parking spaces. This paper presents a case study of interstate I-70 in east central Indiana and documents the observed spatiotemporal impacts of a rest area closure on truck parking on nearby interstate ramps. Results showed that there was a 28% increase in parking on ramps during the rest area closure. Analysis also found that ramps closest to the rest area were most impacted by the closure, seeing a rise in truck parking sessions as high as 2.7 times. Parking duration on the ramps during rest area closure also increased drastically. Although it was expected that this would result in increased parking by trucks on adjacent ramps, this before, during, after scenario provided an ideal scenario to evaluate the robustness of these techniques to assess changing parking characteristics of long-haul commercial trucks. The data analytics and visualization tools presented in this study are scalable nationwide and will aid stakeholders in informed data-driven decision making when allocating resources towards improving the nations commercial vehicle parking infrastructure.展开更多
目的评价屈膝90°MRI对内侧半月板Ramp损伤的临床诊断价值。方法以2021年9月—2023年9月以膝关节疼痛为主诉收治的228例患者作为研究对象,其中51例患者符合选择标准纳入研究。男31例,女20例;年龄15~67岁,平均38.6岁。身体质量指数17...目的评价屈膝90°MRI对内侧半月板Ramp损伤的临床诊断价值。方法以2021年9月—2023年9月以膝关节疼痛为主诉收治的228例患者作为研究对象,其中51例患者符合选择标准纳入研究。男31例,女20例;年龄15~67岁,平均38.6岁。身体质量指数17.2~28.7 kg/m^(2),平均23.9 kg/m^(2)。左膝25例,右膝36例。受伤至入院时间0.1~14.3周,平均2.1周。术前均行伸膝0°(伸膝位)、屈膝90°(屈膝位)MRI检查,判断是否存在内侧半月板后缘不规则以及PHMM液体高信号[即内侧半月板后角(posterior horn of the medial meniscus,PHMM)与后囊之间充盈液体]征象。以关节镜探查结果为“金标准”,分别评估伸膝、屈膝位MRI对Ramp损伤两种特异征象的敏感度、特异度、准确度、阳性预测值及阴性预测值。结果经关节镜检查,21例(41.2%)确诊Ramp损伤,其中ThaunatⅠ型1例、Ⅱ型2例、Ⅲ型6例、Ⅳ型7例、Ⅴ型5例。伸膝位、屈膝位MRI示内侧半月板后缘不规则征象阳性率与关节镜下诊断Ramp损伤结果比较,差异均有统计学意义(P<0.05)。伸膝位MRI检查敏感度76.1%、特异度60.0%、准确度66.7%、阳性预测值57.1%、阴性预测值78.3%,屈膝位分别为85.7%、73.3%、78.4%、69.2%、88.0%。伸膝位、屈膝位MRI示PHMM液体高信号征象阳性率与关节镜下诊断Ramp损伤结果比较,差异亦有统计学意义(P<0.05);伸膝位MRI检查敏感度38.1%、特异度100%、准确度74.5%、阳性预测值100%、阴性预测值69.8%,屈膝位分别为85.7%、100%、94.1%、100%、90.9%。结论与传统伸膝0°MRI相比,基于屈膝90°MRI诊断内侧半月板Ramp损伤的敏感度、特异度和准确度均更高。展开更多
基金Project(2023YFB2604304)supported by the National Key R&D Program of ChinaProjects(52122810,51978586,51778542,U23A20666,52472458)supported by the National Natural Science Foundation of China+1 种基金Project(K2022G034)supported by the Technology Research and Development Program of China National Railway Group Co.Ltd.Projects(2020JDJQ0033,2023NSFSC0884)supported by Sichuan Province Science and Technology Support Program,China。
文摘The influence of ramps on the transient rolling contact characteristics and damage mechanisms of switch rails remains unclear,presenting substantial challenges to the safety of railway operations.To this end,this paper constructs a transient rolling contact finite element model of the wheel-rail in switch under different ramps using ANSYS/LSDYNA method,and analyzes the tribology and damage characteristics when the wheel passes through the switch at a uniform speed.Our research findings reveal that the vibration induced in the switch rail during the wheel load transfer process leads to a step-like increase in the contact force.Moreover,the interaction between the wheel and the rail primarily involves slip contact,which may significantly contribute to the formation of corrugations on the switch rail.Additionally,the presence of large ramps exacerbates switch rail wear and rolling contact fatigue,resulting in a notable 13.2%increase in switch rail damage under 40‰ramp conditions compared to flat(0‰ramp)conditions.Furthermore,the large ramps can alter the direction of crack propagation,ultimately causing surface spalling of the rail.Therefore,large ramps intensify the dynamic interactions during the wheel load transfer process,further aggravating the crack and spalling damage to the switch rails.
基金financial support for this project from the National Natural Science Foundation of China(No.U1508212)National Science and Technology Major Projects(Nos.2017-Ⅲ-0011-0025 and 2017-Ⅲ0011-0037)。
文摘A numerical investigation and experimental validation is performed to address deeper insights into the combined effect of shaped holes and Sand-Dune-shaped upstream Ramp(SDR)on enhancing the film cooling effectiveness,under a wide blowing ratio range(M=0.25–1.5).Three kinds of holes(Cylindrical Hole(CH),Fan-Shaped Hole(FSH),and Crater-Shaped Hole(CSH))are taken into consideration.The SDR shows an inherent affecting mechanism on the mutual interaction of jet-in-crossflow.It aggravates the lateral spreading of cooling jet and thus improves the film cooling uniformity significantly,regardless of film-hole shape and blowing ratio.When the blowing ratio is beyond 1.0,the combined effect of shaped holes and SDR on improving film cooling effectiveness behaves more significantly.It is suggested that FSH-SDR is a most favorable film cooling scheme.For FSH-SDR case,the spatially-averaged film cooling effectiveness is increased monotonously with the increase of blowing ratio,among the present bowing ratio range.
基金supported by National Natural Science Foundation of China under Grant Nos. 70701002 and 70521001the State Key Basic Research Program of China under Grant No. 2006CB705503the Research Grants Council of the Hong Kong Special Administrative Region under Grant No. HKU7187/05E
文摘In this paper, we present a new macro model for traffic flow on a highway with ramps based on the existing models. We use the new model to study the effects of on-off-ramp on the main road traffic during the morning rush period and the evening rush period. Numerical tests show that, during the two rush periods, these effects are often different and related to the status of the main road traffic. If the main road traffic flow is uniform, then ramps always produce stop-and-go traffic when the main road density is between two critical values, and ramps have little effect on the main road traffic when the main road density is less than the smaller critical value or greater than the larger critical value. If a small perturbation appears on the main road, ramp may lead to stop-and-go traffic, or relieve or even eliminate the stop-and-go traffic, under different circumstances. These results are consistent with real traffic, which shows that the new model is reasonable.
文摘Although there are many studies involving influence of runaway truck entry speed and longitudinal grade on stopping distance,focusing on aggregate properties is scarce.This paper investigates the influence of the aggregate properties such as types of aggregate and river gravel radius on stopping distance through numerical analysis of particle flow code in two dimensions(PFC2D).The software is used to generate stopping distance data for two aggregate types and four group gravel radii under various approaching speeds and grades.The generated data are compared with the testing results of full-scale arrester bed.The simulated finding of this paper implies that types of aggregates and river gravel radii have a significant impact on the stopping distance for runaway truck on escape ramps.
基金Supported by grants from the Humanities and Social Sciences Foundation of Ministry of Education of China under Grant No. 09YJC790193Funding Project for Academic Human Resources Development in Institutions of Higher Learning Under the Jurisdiction of Beijing Municipality the Research Funds of Capital University of Economics and Business under Grant No. 00591056721621the National Natural Science Foundation of China under Grant No. 70971007
文摘In this paper, we develop a cellular automaton model to describe the phase transition of traffic flow on urban expressway systems with on-off-ramps and accessory roads. The lane changing rules are given in detailed, the numerical results show that the main road and the accessory road both produce phase transitions. These phase transitions will omen be influenced by the number of lanes, lane changing, the ramp flow, the input flow rate, and the geometry structure.
基金funded by the Natural Science Foundation of Hunan Province(Grant No.2023JJ30039)the National National Natural Science Foundation of China(Grant No.52372296)+1 种基金the Postgraduate Scientific Research Innovation Project of Hunan Province(Grant No.CX20220862)the Chang Sha Science andTechnology Major Special Project(Grant No.kh2301004)。
文摘This study introduces a multi-area cooperative merging control strategy to enhance the safety and efficiency of connected and autonomous vehicles(CAVs)at freeway merging areas with multiple mainline lanes and a dual-lane ramp.The strategy integrateslane changing in advance tactics for upstream mainline vehicles and speed regulation for ramp vehicles into a structured control framework.This framework comprises distinct areas for proactive mainline lane changing in advance,ramp speed regulation and cooperative merging.For the mainline lane-changing area,we propose a strategy that relies on maintaining a minimum safety distance and optimizing speed benefits,thereby enhancing merging opportunities for ramp vehicles and balancing downstream traffic flows.In the ramp speed regulation area,a vehicular speed control model is established,utilizing a'FIFO rule'based on the vehicles'arrival times at the acceleration lane start,coupled with a virtual platoon concept to synchronize and optimize platoon speeds for efficient travel on ramps.In the cooperative merging area,vehicle trajectories on the mainline and ramp are optimized in a rolling horizon manner,facilitating seamless integration of ramp vehicles into the mainline.Simulation results indicate that our proposed cooperative control method significantly surpasses uncontrol led and trajectory-only optimization approaches in control efficiency across varying traffic demands.This method demonstrates notable advancements in average speed,delay reduction and fewer stops,with minimized fluctuations and increased control stability.Additionally,the cooperative control approach demonstrates superior adaptability across different numbers of ramp lanes,with scenarios involving dual-lane ramps exhibiting a more pronounced advantage.
文摘[目的]比较关节镜下缝合钩和Fast-fix缝合Ⅳ型半月板Ramp区损伤的临床疗效。[方法]回顾性分析2016年1月—2020年10月45例前交叉韧带(anterior cruciate ligament, ACL)损伤合并Ⅳ型半月板Ramp损伤患者的临床资料。所有患者均取自体腘绳肌腱行ACL重建,依据术前医患沟通结果,21例应用缝合钩缝合Ramp损伤,24例应用Fast-fix缝合。对比患者围手术期、随访及影像学结果。[结果]所有患者均顺利完成手术,术中未出现血管、神经损伤等并发症。缝合钩组手术时间[(91.2±10.6) min vs (62.5±8.4) min, P<0.001]、切口总长度[(5.9±0.5) cm vs (5.1±0.6) cm, P<0.001]均显著长于Fast-fix组,但前者住院费用显著少于后者[(3.4±0.3)万元vs (4.3±0.7)万元, P<0.001]。两组Ramp撕裂长度、缝合针数、下地行走时间、切口愈合、住院时间比较差异均无统计学意义(P>0.05)。所有患者均获36~72个月随访。两组完全负重活动时间的差异无统计学意义(P>0.05)。术后1年及末次随访时,两组膝间隙压痛、麦氏征,轴移征、膝关节屈伸ROM、IKDC评分及Lysholm评分较术前均显著改善(P<0.05)。同一时间点,两组上述指标的差异均无统计学意义(P>0.05)。影像方面,与术前相比,术后1年,两组半月板损伤分级及胫骨平台后侧骨髓水肿均显著改善(P<0.05),相应时间点,两组上述指标的差异均无统计学意义(P>0.05)。术后1年MRI显示缝合钩组愈合率为90.5%、Fast-fix组为87.5%,差异无统计学意义(P>0.05)。[结论]关节镜下缝合钩和Fast-fix缝合半月板Ramp区Ⅳ型损伤均可获得满意疗效。
文摘胰腺癌是公认的最具侵袭性和致命性的恶性肿瘤之一,其中约20%的病例为胰体尾部癌症。由于该类型癌症生长迅速且早期缺乏明显症状,许多患者在诊断时已经错过了最佳治疗时机。手术是唯一可能治愈的手段,但传统的远端胰腺切除术和脾切除术存在较高的阳性切缘率、较低的淋巴结清扫率和较差的总体生存率,已发表的证据表明经过传统手术治疗的病人,其五年生存率介于8%至22%之间。2003年,Strasberg等人提出了一种新的手术方法——根治性顺行模块化胰脾切除术(Radical Antegrade Modular Pancreatosplenectomy, RAMPS),旨在提供更好的肿瘤切除效果、提高R0切除率并改善患者的长期预后。RAMPS的五年总体生存率可高达30%~40%。随着腹腔镜技术的不断进步,腹腔镜下根治性顺行模块化胰脾切除术(Laparoscopic Radical Antegrade Modular Pancreatosplenectomy, L-RAMPS)作为一种微创手术,具有术后恢复快等优势,逐渐获得越来越多外科医师的关注。文章总结了这种手术的现状,并展望其未来发展。Pancreatic cancer is widely recognized as one of the most aggressive and lethal malignant tumors, with approximately 20% of cases occurring in the body and tail of the pancreas. Due to the rapid growth of this cancer and the lack of obvious symptoms in its early stages, many patients miss the opportunity for optimal treatment by the time of diagnosis. Surgery remains the only potentially curative option;however, traditional distal pancreatectomy and splenectomy are associated with high positive margin rates, low lymph node dissection rates, and poor overall survival. Published evidence shows that the five-year survival rate for patients treated with traditional surgery ranges from 8% to 22%. In 2003, Strasberg et al. proposed a new surgical technique—Radical Antegrade Modular Pancreatosplenectomy (RAMPS)—designed to improve tumor resection, increase the R0 resection rate, and enhance long-term prognosis. The five-year overall survival rate for RAMPS can reach 30%~40%. With the continuous advancement of laparoscopic technology, Laparoscopic Radical Antegrade Modular Pancreatosplenectomy (L-RAMPS), as a minimally invasive procedure, offers advantages such as faster postoperative recovery and is gradually gaining more attention from surgeons. This article provides an overview of the current status of this surgery and discusses its potential future development.
基金supported by the National Natural Science Foundation of China(No.42277057).
文摘Traditional in situ biogeochemical transformation suffers from competition among crucial microorganisms and inadequate formation of reactive minerals,thus leading to the accumulation of toxic intermediates.In this study,three regulation schemes were proposed to solve these problems from the perspective of engineering mode.Results showed intermittent injection mode effectively reduced the accumulation of toxic intermediates but the reduction rate of tetrachloroethylene was decreased.And periodical supplementation of carbon and sulfur sources accelerated the removal of tetrachloroethylene but failed to reduce the accumulation of toxic products.While,regular supplementation of sulfate effectively weakened the competition of methanogens and increased the iron sulfide proportion on the surface of the minerals,thus reducing the accumulation of toxicity.Based on the results,this study obtained an effective engineering approach for practical site application.In addition,the main forms of active minerals capable ofβ-eliminating contaminants during biogeochemical transformation were identified in this study,including FeS,FeS_(2),and Fe_(3)S_(4).Furthermore,the engineered regulatory mechanism of this study was summarized through the analysis of microbial community structure and mineral morphology.The amendment promotes the production of minerals and thus controls the transformation pathway of contaminants by altering the abundance of sulfate-reducing bacteria and dissimilatory iron reducing bacteria.This mechanism can provide a basis for subsequent theoretical studies.
基金grateful to VINNOVA(ICV-Safe,2019–03418),Area of Advance Transport and AI Center(CHAIR)at the Chalmers University of Technology for funding this research.
文摘Purpose–On-ramp merging areas are typical bottlenecks in the freeway network since merging on-ramp vehicles may cause intensive disturbances on the mainline traffic flow and lead to various negative impacts on traffic efficiency and safety.The connected and autonomous vehicles(CAVs),with their capabilities of real-time communication and precise motion control,hold a great potential to facilitate ramp merging operation through enhanced coordination strategies.This paper aims to present a comprehensive review of the existing ramp merging strategies leveraging CAVs,focusing on the latest trends and developments in the research field.Design/methodology/approach–The review comprehensively covers 44 papers recently published in leading transportation journals.Based on the application context,control strategies are categorized into three categories:merging into sing-lane freeways with total CAVs,merging into singlane freeways with mixed traffic flows and merging into multilane freeways.Findings–Relevant literature is reviewed regarding the required technologies,control decision level,applied methods and impacts on traffic performance.More importantly,the authors identify the existing research gaps and provide insightful discussions on the potential and promising directions for future research based on the review,which facilitates further advancement in this research topic.Originality/value–Many strategies based on the communication and automation capabilities of CAVs have been developed over the past decades,devoted to facilitating the merging/lane-changing maneuvers at freeway on-ramps.Despite the significant progress made,an up-to-date review covering these latest developments is missing to the authors’best knowledge.This paper conducts a thorough review of the cooperation/coordination strategies that facilitate freeway on-ramp merging using CAVs,focusing on the latest developments in this field.Based on the review,the authors identify the existing research gaps in CAV ramp merging and discuss the potential and promising future research directions to address the gaps.
基金This study was funded by China Agricultural Research System-National Technology System for Layer Industry(CARS-40-19K)National Natural Science Foundation of China(31601981).
文摘Poor early adaptation in aviaries has adverse effects on welfare and the later production.Effects of system modification by ramps and ladders on early adaptation of birds were investigated.A total of 240 pullets and 24 cockerels of Yukou Jing Pink II parent stock were allocated into six perchery compartments at the age of 83 days from conventional cages.Three compartments were modified with ramps of different angles,30°,40°and 30°&50°combination.The other compartments were fitted with 2 ladders,with 22 cm steps and 33 cm steps.Spatial distribution of birds and eggs,as well as the data of ramps and ladders utilization were used to assess birds’adaptation and the effectiveness of modification facilities.A higher proportion of hens got onto the tiered platforms in ramp group(p<0.001)and engaged in feeding(p=0.002).Inversely more than 85.0%of hens dwelled on the system floor in the ladder group for the whole observation period.The proportion of birds feeding increased over time(p<0.001),with the proportion of birds lying decreasing(p<0.001).A higher frequency of utilization of ramps was found compared with ladders(4.5-25.8 vs.2.8-14.7 times/40 birds per hour).For ramp use,79.3%of hens negotiated level change by using 30°ramp and behavioral process was also found related with the type of ramps.On the contrary,very few successful level changes were observed via ladders and 60%of ladder use was ended with birds backing to the system floor.Besides,a higher proportion of non-nest eggs was recorded in ladder group in the early laying period.These results indicated that modification of ramps is more applicable for improving birds’early adaptation and later production in perchery system of multi-tier,especially for pullets reared in conventional cages.
文摘Queue storage at a metered freeway on-ramp is an essential design element for metered on-ramps to prevent on-ramp queue from extending beyond on-ramps.In this paper,various existing methodologies that are used to size the queue storage at metered on-ramps were first reviewed.It was found that queue storage sized using 7%of peak hour on-ramp demand is widely accepted in practice.A limited dataset collected in California helps provide some reality check for this method.It is recommended that queue storage be recognized as an indispensable design element at metered on-ramps,and detailed sizing guidance be developed in the highway geometric design policy of the American Association of State Highway and Transportation Officials(AASHTO).
文摘In Section 4I.02 of the newly published Manual on Uniform Traffic Control Devices(MUTCD),standards were specified for the placement of signal heads for traffic control signals at freeway entrance ramps,or ramp meters.For simultaneous operations,i.e.when ramp control signals are operated such that green signal indications are always displayed simultaneously to all of the lanes on the ramp,a minimum of two signal faces per ramp shall face entering traffic.For staggered operations,i.e.the ramp control signal are operated such that green signal indications are not always displayed simultaneously to all of the lanes on the ramp,one signal face shall be provided over the approximate center of each separately-controlled lane.Based on a nation-wide survey,it was realized that the two standards did not fully reflect the state-of-the-practice with respect to ramp metering operations.Due to the lack of significant conflicting movements at ramp meters,for any on-ramp lane,a minimum of one overhead mounted,or one upper and one lower roadside-mounted signal face is sufficient to control the metering operations.The minimum necessary number of signal faces changes according to the total number of lanes,how the signal faces are mounted(overhead or roadside mounting),and how the meters are operated(simultaneous or staggered).Suggestions are made to revise the two standards to better reflect the current nation-wide practices,and better consider the specific operational needs for ramp meters.
文摘Ensuring adequate access to truck parking is critical to the safe and efficient movement of freight traffic. There are strict federal guidelines for commercial truck driver rest periods. Rest areas and private truck stops are the only places for the trucks to stop legally and safely. In locations without sufficient parking areas, trucks often park on interstate ramps, which create safety risks for other interstate motorists. Historically, agencies have employed costly and time intensive manual counting methods, camera surveillance, and driver surveys to assess truck parking. Connected truck data, available in near real-time, offers an efficient alternative to practitioners to assess truck parking patterns and identify areas where there may be insufficient safe parking spaces. This paper presents a case study of interstate I-70 in east central Indiana and documents the observed spatiotemporal impacts of a rest area closure on truck parking on nearby interstate ramps. Results showed that there was a 28% increase in parking on ramps during the rest area closure. Analysis also found that ramps closest to the rest area were most impacted by the closure, seeing a rise in truck parking sessions as high as 2.7 times. Parking duration on the ramps during rest area closure also increased drastically. Although it was expected that this would result in increased parking by trucks on adjacent ramps, this before, during, after scenario provided an ideal scenario to evaluate the robustness of these techniques to assess changing parking characteristics of long-haul commercial trucks. The data analytics and visualization tools presented in this study are scalable nationwide and will aid stakeholders in informed data-driven decision making when allocating resources towards improving the nations commercial vehicle parking infrastructure.
文摘目的评价屈膝90°MRI对内侧半月板Ramp损伤的临床诊断价值。方法以2021年9月—2023年9月以膝关节疼痛为主诉收治的228例患者作为研究对象,其中51例患者符合选择标准纳入研究。男31例,女20例;年龄15~67岁,平均38.6岁。身体质量指数17.2~28.7 kg/m^(2),平均23.9 kg/m^(2)。左膝25例,右膝36例。受伤至入院时间0.1~14.3周,平均2.1周。术前均行伸膝0°(伸膝位)、屈膝90°(屈膝位)MRI检查,判断是否存在内侧半月板后缘不规则以及PHMM液体高信号[即内侧半月板后角(posterior horn of the medial meniscus,PHMM)与后囊之间充盈液体]征象。以关节镜探查结果为“金标准”,分别评估伸膝、屈膝位MRI对Ramp损伤两种特异征象的敏感度、特异度、准确度、阳性预测值及阴性预测值。结果经关节镜检查,21例(41.2%)确诊Ramp损伤,其中ThaunatⅠ型1例、Ⅱ型2例、Ⅲ型6例、Ⅳ型7例、Ⅴ型5例。伸膝位、屈膝位MRI示内侧半月板后缘不规则征象阳性率与关节镜下诊断Ramp损伤结果比较,差异均有统计学意义(P<0.05)。伸膝位MRI检查敏感度76.1%、特异度60.0%、准确度66.7%、阳性预测值57.1%、阴性预测值78.3%,屈膝位分别为85.7%、73.3%、78.4%、69.2%、88.0%。伸膝位、屈膝位MRI示PHMM液体高信号征象阳性率与关节镜下诊断Ramp损伤结果比较,差异亦有统计学意义(P<0.05);伸膝位MRI检查敏感度38.1%、特异度100%、准确度74.5%、阳性预测值100%、阴性预测值69.8%,屈膝位分别为85.7%、100%、94.1%、100%、90.9%。结论与传统伸膝0°MRI相比,基于屈膝90°MRI诊断内侧半月板Ramp损伤的敏感度、特异度和准确度均更高。
