筛选条件 共查询到50条结果
排序方式
Macroscopic Relationship between Traffic Condition and Fuel Consumption for an Urban Road Network: Case Study of Beijing

期刊: TRANSPORTATION RESEARCH RECORD, 2019; 2673 (11)

The waste of fuel causing by traffic congestion is a challenge faced by urban traffic management authorities and travelers. At the same time, massive traffic data allows high-resolution understanding of on-road operating conditions. The development of an algorithm to estimate total fuel consumption from primary traffic condition indices, for example, network average speed, will simplify the evaluation of fuel consumption from the management perspective and guide strategy at the local area level. The objective of this study is to develop a macroscopic relationship between total fuel consumption and the network average speed for an urban road network. Floating car data (FCD) covering 13 weekdays was collected in the field in Beijing, China. FCD from 10 ordinary weekdays are used to develop a quantitative model to define the macroscopic relationship between total fuel consumption and network average speed. The model is then validated by the FCD of the other three weekdays when the traffic demand is low. The average of the resultant absolute relative errors from the validation is found to be 4.65%, which indicates a reasonably high reliability of the developed model under various traffic conditions. The facility- and speed-specific distributions of vehicle kilometers traveled (VKT) are analyzed to explain the macroscopic relationship. The result indicates that the link VKT distribution at different speeds varies greatly when the traffic became congested on expressways. The link VKT distributions are similar for different traffic conditions on arterials and collectors.

IF:0.75

Do new bike share stations increase member use: A quasi-experimental study

期刊: TRANSPORTATION RESEARCH PART A-POLICY AND PRACTICE, 2019; 121 ()

As the number of bike share programs across the world has grown, studies of bike programs and operations have proliferated. Most empirical studies of bike share demand have included analyses of station use while a limited number of studies have investigated member behavior. Moreover, a limitation of this research is that the most research designs have been cross-sectional and therefore unable to establish causality. To address this limitation, we employ a quasi-experimental, difference-in-difference modeling approach using a six-year panel data set of members' bike share trips from 2010 to 2015 in Minneapolis-St. Paul, Minnesota. This research design takes advantage of changes in the bike share network over time to establish treatment and control groups and test the significance of effects of changes in accessibility on the frequency of individual member's use of bike share. Improvements in accessibility are measured as a reduction in distance to stations resulting from placement of new stations or relocation of old stations. We find a significant negative impact of distance on the frequency of use and that the effects of increasing bike share accessibility are larger in areas with denser bike share services. Specifically, members for whom access improved (i.e., distance decreased) were significantly more likely to increase the frequency of use than members for whom access remained the same. Moreover, by developing different models, we show the effects of distance are heterogeneous and vary with different built environment contexts. Members who live in areas with higher population density and a higher percentage of retail land use tended to increase their bike share use more. Our results indicate that improvements in physical accessibility may not result in practically meaningful changes in the frequency of use in all cases and imply that multi-faceted strategies for increasing use may be needed.

IF:3.69

Neighborhood socio-demographic characteristics and bike share member patterns of use

期刊: JOURNAL OF TRANSPORT GEOGRAPHY, 2019; 79 ()

Information about factors that affect patterns of use by bike share members is needed to manage systems effectively and equitably. Recent research into the patterns of use by members across heterogeneous neighbor-hoods indicates that neighborhood characteristics as well as built environment characteristics may be associated with use. We use 2017 data on trips taken by 30-day and annual members of the Nice Ride Bike Share System in Minneapolis-St. Paul and examine the associations between user behavior and socio-demographic characteristics at the Census block group (CBG) level where members live. We estimate linear mixed-effects models and multinomial logistic models to analyze the associations of neighborhood socio-demographic characteristics with, respectively, (1) the frequency and duration of weekday and weekend trips by members and (2) the temporal and spatial patterns of their trips. Our results show that, after controlling for station accessibility, nearby bike infrastructure, the built environment, gender, and age, members who reside in minority-concentrated and lower socio-economic status (SES) neighborhoods use bike share more frequently, take trips at more varied times-of-day and across days-of-week, and have more frequently-used origin-destination pairs of stations. A limitation of our analysis is that patterns of use of casual users are not investigated. Our findings have implications for efforts to serve members in neighborhoods with higher concentrations of minorities and residents of lower SES and illustrate the need for more detailed surveys of members to obtain additional information about individual characteristics associated with behaviors of bike share users.

IF:3.56

Effects of Icariin Contents on Properties of Mg/UMAO/CS/IC Coating

期刊: CHINA SURFACE ENGINEERING, 2019; 32 (5)

To study the effects of icariin contents on the characteristics of magnesium/ultrasonic micro-arc oxidation/chitosan/icariin (Mg/UMAO/CS/IC), and enhance the corrosion resistance of pure magnesium, Mg/UMAO/CS/IC coating was prepared using a combined method of UMAO with electrophoretic deposition (EPD) technique on the Mg substrate. The coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. Corrosion resistance was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization in a simulated body fluid (SBF) solution. The results show that the UMAO coating is well sealed by CS/IC coating with a content of 0.4 g/L IC. The coatings with various IC contents all consists of Mg, MgO, CS and Mg2SiO4 phase. The corrosion current density of the coatings with various IC contents are at least one order of magnitude lower compared with that of Mg substrate, which implies that it can provide a more effective protection for Mg substrate. With a content of 0.4 g/L IC, the Mg/UMAO/CS/IC coating has the best corrosion resistance, evidenced by the minimum corrosion current density (1.667x10(-6) A/cm(2)). Mg/UMAO/CS/IC coating effectively solves the problem of high corrosion rate of Mg in clinical bone fixation applications.

Target clamping and cooperative motion control of ant robots

期刊: BIOINSPIRATION & BIOMIMETICS, 2019; 14 (6)

Carpenter ants possess the characteristics of division of labor, communication between individuals, cooperation, and the ability to solve problems. Inspired by the carpenter ant, we designed electromagnetically controlled ant millirobots that can move, clamp, and work cooperatively. The robot can receive power wirelessly to actuate its ionic polymer-metal composite gripper. Further, two robots can be controlled to manipulate small components individually or cooperatively. Dual-robot manipulation is found to take 76.7% of the time required for single-robot manipulation. The results show that complicated manipulation can be performed by robots that are multifunctional and flexible by utilizing electromagnetic actuation, intelligent materials, and wireless power transmission.

IF:3.13

Field Monitoring of Vertical Movement in a Six-Story Wood-Frame Building in Coastal British Columbia

期刊: JOURNAL OF TESTING AND EVALUATION, 2019; 47 (4)

Vertical movement was monitored for 24 months in a six-story wood-frame residential building in the coastal climate of British Columbia, Canada, from construction to service. The work was part of a long-term study to assist in the design of mid-rise wood-frame buildings. Displacement sensors were installed from the first floor to the top floor in a party wall, a hallway wall, and an interior partition wall, plus in the bottom two floors of an exterior wall to measure vertical movement, after the roof sheathing was installed. In addition, sensors were installed in the party wall and the exterior wall on the first floor to measure the moisture content of the wood, together with sensors for measuring environmental conditions in service. It was found that downward vertical movement, i.e., building shortening, occurred from construction to service and leveled off after a period of about 17 months. From the top of sill plates to the underside of roof trusses, the shortening reached approximately 34 mm at the party wall, 35 mm at the hallway wall, and 37 mm at the interior partition wall. The average shortening amount of 35 mm exceeded the predicted shrinkage amount based on a commonly used calculation method by about 25 %. The effects of loads on vertical movement should be taken into account in the design of mid-rise wood-frame construction.

IF:0.71

Peroxide crosslinked butyl rubber composites using TEMPO and sorbates

期刊: COMPOSITES SCIENCE AND TECHNOLOGY, 2019; 183 ()

Peroxide curing can provide rubber products with good thermal aging resistance, low compression set and light color. But butyl rubber (IIR) and bromobutyl rubber (BIIR) will incur severe main chain degradation when using a peroxide as a curing agent. The presence of 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) and in situ formed zinc disorbate (ZDS) in dicumyl peroxide cured BIIR system can inhibit the degradation of BIIR without compromising the curing extent of BIIR vulcanizates. ZDS is grafted on BIIR, while TEMPO functions as a free radical scavenger and nitroxide mediator for the grafting reaction. The in situ formation and grafting reaction of ZDS in BIIR are characterized by FTIR, XRD and NMR spectroscopy. In the presence of TEMPO and ZDS, BIIR does not suffer degradation but exhibits a continuous increase in torque and crosslink density with time during the post-cure period. The presence of TEMPO could effectively improve the thermal stability and aging resistance of BIIR vulcanizates. The study provides an effective route to avoid the degradation and promote the crosslinking of BIIR that can easily incur beta-scission when reacting with peroxides.

IF:6.31

Experimental study on the effect of non-spherical particles on steady combustion in nano-aluminized propellant in air

期刊: MATERIALS RESEARCH EXPRESS, 2019; 6 (11)

To explore the deflagration phenomenon of an aluminized solid propellant during the combustion process, this study conducts an experimental investigation on the effect of non-spherical particles on steady combustion in nano-aluminized propellant in air under various pressure conditions to further validate previous theoretical conclusions. The burning rates of four types of metal raw materials powder column were measured at pressures of 1-5 MPa via the burning rate test system, and the effect of particle morphology, size, and pressure on the steady combustion were discussed in detailed. The experimental results indicate that the particle morphology and size distribution play a significant role in nano-aluminized propellant steady combustion performance, and stable high-pressure has a significant inhibitory effect on it.

IF:1.45

Production Capacity Evaluation of Horizontal Shale Gas Wells in Fuling District

期刊: FDMP-FLUID DYNAMICS & MATERIALS PROCESSING, 2019; 15 (5)

One of the important indicators of shale gas reservoir excavation is capacity evaluation, which directly affects whether large-scale shale gas reservoirs can be excavated. Capacity evaluation is the basis of system analysis and dynamic prediction. Therefore, it is particularly important to conduct capacity evaluation studies on shale gas horizontal wells. In order to accurately evaluate the horizontal well productivity of shale gas staged fracturing, this paper uses a new method to evaluate the productivity of Fuling shale gas. The new method is aimed at the dynamic difference of horizontal wells and effectively analyzes the massive data, which are factors affecting the productivity of shale gas horizontal wells. According to the pressure system, production dynamic characteristics, well trajectory position, fracturing transformation mode and penetration depth, 32 wells were divided into four types. Then, based on the classification, the principal component analysis methods can be used to evaluate the horizontal well productivity of shale gas. The new method of capacity evaluation has improved the accuracy by 10.25% compared with the traditional method, which provides a theoretical basis for guiding the efficient development of the horizontal wells of Fuling shale gas.

Texture-governed electrochemical corrosion behaviour of AA 6082 alloy

期刊: JOURNAL OF MATERIALS SCIENCE, 2019; 54 (8)

The variations of through-thickness corrosion behaviour with the -fibre evolution of hot-rolled AA 6082 alloy at the sub-surface layer (SL), quarter layer and middle layer (ML) in 3.5wt% NaCl solution were mainly investigated by EIS, potentiodynamic polarization, SEM, XRD and 3D-MLM. Results showed that the strong -fibre (rolling) and shear orientation formed at ML and SL, respectively. Compared to ML, charge transfer resistance increased, whereas double-layer capacitance was reduced at SL. From ML to SL, corrosion current density decreased and corrosion potential and pitting potential rose successively. Moreover, the deepened pits occurred at ML. Based on the surface energy of Al in the order (111)<(100)<(110)/high-index planes, the worse corrosion resistance at ML with strong -fibre orientation stemmed from the high surface energy. As a consequence, the available shear textures are beneficial to improving the corrosion resistance. This provides a new design strategy to enhance the corrosion resistance for the commercial Al alloys.

IF:3.44

Fabrication of dispersive alpha-Co(OH)(2) nanosheets on graphene nanoribbons for boosting their oxygen evolution performance

期刊: JOURNAL OF MATERIALS SCIENCE, 2019; 54 (10)

Nanostructured alpha-Co(OH)(2) materials are promising noble-metal-free electro-catalysts for oxygen evolution reaction (OER), but their performance is severally restrained by their poor conductivity. Combination of alpha-Co(OH)(2) and carbon nanotubes (CNTs) can improve their conductivity, but it is difficult to build sufficient interface contact between them due to the mismatched hydrophobicity. Herein, we demonstrate a facile method to in situ grow alpha-Co(OH)(2) nanosheets (NSs) on graphene nanoribbons (GNRs), an intriguing belt-like conductive material after oxidative unzipping of CNTs. Owing to the rich of functional groups, the GNRs can be utilized as substrate in solution to prepare dispersive alpha-Co(OH)(2) nanosheets on their surface. The developed alpha-Co(OH)(2) NSs are well contact with the conductive GNRs substrate and offer sufficient active surface area, showing obviously better OER performance than the alpha-Co(OH)(2) and CNTs/Co(OH)(2) prepared under the same condition. The composite electrocatalysts have been characterized by various apparatuses, and their OER activities are explored in detail.

IF:3.44

Effect of solute content and temperature on the deformation mechanisms and critical resolved shear stress in Mg-Al and Mg-Zn alloys

期刊: ACTA MATERIALIA, 2019; 170 ()

The influence of solute atoms (Al and Zn) on the deformation mechanisms and the critical resolved shear stress for basal slip in Mg alloys at 298 K and 373 K was ascertained by micropillar compression tests in combination with high-throughput processing techniques based on the diffusion couples. It was found that the presence of solute atoms enhances the size effect at 298 K as well as the localization of deformation in slip bands, which is associated with large strain bursts in the resolved shear stress (tau(RSS))-strain (epsilon) curves. Deformation in pure Mg and Mg alloys was more homogeneous at 373 K and the influence of the micropillar size on the critical resolved shear stress was much smaller. In this latter case, it was possible to determine the effect of solute content on the critical resolved shear stress for basal slip in Mg Al and Mg-Zn alloys. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

IF:7.29

Theoretical study on combustion of non-spherical particles in nano-aluminized propellant in air

期刊: MATERIALS RESEARCH EXPRESS, 2019; 6 (6)

To investigate the deflagration phenomenon of an aluminized solid propellant during the combustion process, an improved theoretical combustion model has been developed. The model uses non-spherical particles for predicting the instantaneous mass evaporation rates of droplets as well as the burning time. The burning behavior of individual prolate and oblate spheroidal droplets, including the surface-area ratio, Nusselt numbers, temperature, and size change rate, was theoretically analyzed to elucidate the effect of non-spherical grains on the burning stability. Models for the Al evaporation rates and burnout time of both prolate and oblate spheroids in the diffusion-kinetics controlled regimes were established. According to the results, the particle morphology, size, and Reynolds numbers significantly affect the burning characteristics of nano-aluminized propellants. The proposed model is useful for steady-state combustion-performance assessment of aluminized solid propellants.

IF:1.45

Microstructure and properties of CoCrNi medium-entropy alloy produced by gas atomization and spark plasma sintering

期刊: JOURNAL OF MATERIALS RESEARCH, 2019; 34 (12)

A homogeneous structured CoCrNi medium-entropy alloy was synthesized by gas atomization and spark plasma sintering (SPS). The mechanical properties, corrosion resistance, and magnetic properties were reported in this study. The as-atomized CoCrNi MEA powder, with a spherical morphology in shape and a mean particle diameter of 61 lm, consisted of a single face-centered cubic (FCC) phase with homogeneous distributions of Co, Cr, and Ni elements. Also, the cross-sectional microstructure of powder particles gradually transformed from fully cellular structure into equiaxed-type structure with increasing particle size. After being sintered by SPS, the CoCrNi MEA consisted of a single FCC phase with a mean grain size of 20.8 mu m. Meanwhile, the CoCrNi MEA can capable of offering an ultimate tensile strength of 799 MPa, yield strength of 352 MPa, elongation of 53.6%, and hardness of 195.3 HV. In addition, this MEA showed superior corrosion resistance to that of 304 SS (stainless steel) in both 0.5 mol/L HCl and 1 mol/L NaOH solutions. The magnetization loop indicated that this MEA has good soft magnetic properties.

IF:1.98

Synergistic effects of WC nanoparticles and MC nanoprecipitates on the mechanical and tribological properties of Fe40Mn40Cr10Co10 medium-entropy alloy

期刊: JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 2019; 8 (4)

The synthesis of Fe40Mn40Cr10Co10/WC composites by a combination of ball milling and spark plasma sintering is reported and corresponding mechanical and tribological properties of these composites are investigated. Compared with the Fe40Mn40Cr10Co10 MEA (medium entropy alloy), the addition of 10 vol.% WC nanoparticles led to an increase in the compressive strength and hardness from 1.571 GPa and 320 HV to 2.324 GPa and 788 HV, respectively. Meanwhile, tribological tests demonstrated that the friction coefficient, wear depth and width of the composite decreased in comparison with Fe40Mn40Cr10Co10 MEA. Load transfer effect, thermal mismatch mechanism, Orowan strengthening and grain refinement resulting from synergistic effects between ex-situ WC nanoparticles and in-situ M23C6 nanoprecipitates are responsible for the improvement in mechanical properties, especially thermal mismatch mechanism and grain refinement. In addition, the enhancement in tribological properties is also ascribed to these synergistic effects. (C) 2019 The Authors. Published by Elsevier B.V.

IF:3.33

共50条页码: 1/4页15条/页