2025-04-25 2016, Volume 23 Issue 7

  • Select all
  • Feng He , Zi-jun He , Jun-lin Xie , Shu-xia Mei , Ming-fang Jin

    Glasses based on ZnO−Bi2O3−B2O3 system are expected to be a new kind of sealing glasses because of their low melting temperature and other properties. In order to reveal the effect of B2O3 on the rheological behavior of ZnO−Bi2O3−B2O3 system glass melt, the properties of viscosity, thermal expansion, fluxion property and wetting process between cylinder samples and stainless steel were investigated with the rotating crucible viscometer, dilatometer and high-temperature microscope. The structure of sintered glass samples was investigated with scanning electron microscope. The results show that the B2O3 content increasing in B1−B3 at the given temperature between 400 °C and 500 °C leads to the increasing of the sample viscosity. When the amount of B2O3 increases from 5.24% to 9.24% (mass fraction), the coefficients of thermal expansion of glass samples decrease smoothly from 10.94×10−6 to 10.71×10−6 and 10.38×10−6 °C−1 respectively. In the case of sealing temperature, its value increases from 453 °C to 494 °C. ZnO−Bi2O3−B2O3 system low-melting glass powder sintering was with viscous liquid to participate, which could make the densification of glass sample more effective and more efficient. With the content of B2O3 increasing, the wetting angle between the glasses samples and stainless steel could also increase, and the resulting appropriate sealing temperature range is 460−490 °C.

  • Yan-zhong Zhao , Min Yang , Hai-bin Zhang , Jun Zhu , Ke-chao Zhou

    The control synthesis of nanoparticles was the implementation process of material ideal design. Nano-hydroxyapatite (HAP) was prepared by a hydrothermal method with calcium nitrate and diammonium hydrogen phosphate as raw material, to study its characteristics for morphology modification by arginine-functionalization and doping with rare earth such as Tb3+. The crystallization, grain size and dispersibility of the sample HAP were analyzed and discussed. The results show that the surface Zeta potential of arginine-functionalized HAP is changed, and the growth rate of HAP is inhibited to a certain extent during the synthesis. The structure of HAP/Arg is not affected during the synthesis by a small amount of rare earth ions doped such as Tb3+, and has a single phase of HAP with good dispersibility. The synthesized HAP is also of nano-sized level. Nano-hydroxyapatite argininefunctionalized and doped with rare earth such as Tb3+, is suitable for the application of gene delivery as a gene carrier.

  • Meng-han Wang , Rui Wang , Lie Meng , Gen-tian Wang

    The hot working mechanism of 2Cr11Mo1VNbN steel was investigated by means of compression tests at temperatures of 900–1150 °C and strain rates of 0.005–5 s−1. At strains of 0.2, 0.3, 0.5 and 0.7, the relationship among strain rate sensitivity, power dissipation efficiency and instability parameter under different conditions were studied. Power dissipation maps and instability maps at different strains were established. The optimal and the instable deformation regimes were established by the processing maps based on the dynamic material model. The processing maps were developed for the typical strains of 0.2, 0.3, 0.5 and 0.7, predicting the instability regions occurring at high strain rate more than 0.05 s−1, which should be avoided during hot deformation. The optimized processing parameters for hot working of 2Cr11Mo1VNbN supercritical stainless steel were temperatures of 1080−1120 °C and strain rates of 0.005−0.01 s−1.

  • Tao Jin , Meng-xi Wu , Jia-le Huang , Ke Tang , Li-xin Chen

    The hydrogenation reaction characteristics and the properties of its hydrides for the magnetic regenerative material HoCu2 (CeCu2-type) of a cryocooler were investigated. The XRD testing reveals that the hydrides of HoCu2 were a mixture of Cu, unknown hydride I, and unknown hydride II. Based on the PCT (pressure−concentration−temperature) curves under different reaction temperatures, the relationships among reaction temperature, equilibrium pressure, and maximum hydrogen absorption capacity were analyzed and discussed. The enthalpy change ΔH and entropy change ΔS as a result of the whole hydrogenation process were also calculated from the PCT curves. The magnetization and volumetric specific heat capacity of the hydride were also measured by SQUID magnetometer and PPMS, respectively.

  • Gui-hua Liu , Wen Zhang , Tian-gui Qi , Zhi-hong Peng , Qiu-sheng Zhou , Xiao-bin Li

    The structural changes of silicate anions in the desilication process with the addition of calcium hydrate alumino-carbonate were studied by measuring Raman spectra, infrared spectra and corresponding second derivative spectra. The results show that the desilication ratio in the solution prepared by the addition of sodium silicate (solution-SS) is much greater than that in the solution by the addition of green liquor (solution-GL), and low alumina concentration in the sodium aluminate solutions facilitates the desilication process. It is also shown that alumino-silicate anions in the solution-GL, and Q3 polymeric silicate anions in solution-SS are predominant, respectively. In addition, increasing the concentration of silica favors respectively the formation of the alumino-silicate or the Q3 silicate anions in the solution-GL or the solution-SS. Therefore, it can be inferred that the low desilication ratio in the silicate-bearing aluminate solution is mainly attributed to the existence of alumino-silicate anions.

  • Li-mei Hao , Xiao-le Yan , You Xie , Tao Zhang , Zhi Chen

    This work presents a method to solve the weak solubility of zinc chloride (ZnCl2) in the ethanol by adding some reasonable water into an ethanol electrolyte containing ZnCl2 and myristic acid (CH3(CH2)12COOH). A rapid one-step electrodeposition process was developed to fabricate anodic (2.5 min) and cathodic (40 s) superhydrophobic surfaces of copper substrate (contact angle more than 150°) in an aqueous ethanol electrolyte. Morphology, composition, chemical structure and superhydrophobicity of these superhydrophobic surfaces were investigated by SEM, FTIR, XRD, and contact angle measurement, respectively. The results indicate that water ratio of the electrolyte can reduce the required deposition time, superhydrophobic surface needs over 30 min with anhydrous electrolyte, while it needs only 2.5 min with electrolyte including 10 mL water, and the maximum contact angle of anodic surface is 166° and that of the cathodic surface is 168°. Two copper electrode surfaces have different reactions in the process of electrodeposition time, and the anodic copper surface covers copper myristate (Cu[CH3(CH2)12COO]2) and cupric chloride (CuCl); while, zinc myristate (Zn[CH3(CH2)12COO]2) and pure zinc (Zn) appear on the cathodic surface.

  • Du-chao Zhang , Qing-kai Xiao , Wei-feng Liu , Lin Chen , Tian-zu Yang , You-nian Liu

    Carbonate decomposition of carbonic refractory gold ore and the following pressure oxidation were studied. In the carbonate decomposition procedure, the effects of liquid-to-solid ratio and reaction time on decomposition ratio of carbonate were investigated. The experimental result shows that the decomposition ratio of carbonate is 98.24% under the conditions of liquid-to-solid ratio of 5:1, Fe3+ concentration of 20 g/L, sulfuric acid concentration of 20 g/L, reaction temperature of 80 °C and reaction time of 2 h. Then, the slurry obtained from carbonate decomposition was put into the titanium autoclave for pressure oxidation leaching. Effects of liquid-to-solid ratio, temperature, time and oxygen partial pressure on sulfur oxidation ratio were studied during pressure oxidation. With the prolonged time, pyrite and arsenopyrite are oxidized to ferric subsulfate, hydrated ferric sulfate and jarosite, resulting in the increasing residue ratio. The residue ratio and the sulfur content in the residue can be decreased by ferric subsulfate dissolution. The oxidation ratio of the sulfur is 99.35% under the conditions of oxidation time of 4 h, temperature of 210 °C, oxygen partial pressure of 0.8 MPa and stirring speed of 600 r/min.

  • Meng Wang , Hui-ping Hu , Jin-wei Liu , Qi-yuan Chen

    Hydration grossular and hematite monominerals were synthesized. The effects of dissolved organic compounds (including sodium formate, sodium acetate, sodium oxalate, sodium salicylate or disodium phthalate) on the settling performance of hydration grossular or hematite slurries were studied. The settling of the slurries was also investigated with the addition of sodium polyacrylate (PAAS) or hydroxamated polyacrylamide flocculant (HCPAM). The adsorption mechanism of organic compounds on monominerals surfaces was studied by FT-IR and XPS, respectively. A deterioration in settling is observed in order of disodium phthalate>sodium salicylate>sodium oxalate>sodium formate (or sodium acetate). Moreover, PAAS can efficiently eliminate the negative effects of organic compounds on the settling performance of the hydration grossular slurry. HCPAM can efficiently eliminate the negative effects of sodium formate, sodium acetate and sodium oxalate on the settling performance of the hematite slurry, but it only partially improves the settling performance of hematite slurry containing sodium salicylate or disodium phthalate. FT-IR and XPS results show that organic compounds are physically adsorbed on hydration grossular surface, and chemisorptions of organic compounds occur on hematite surface with a bidentate chelating complex.

  • Yun-jing Huang , Wei-jun Yang , Ming-gao Qin , Hao-liang Zhao

    Rubidium phosphate can be more conveniently obtained by extracting trace Rb+ from the salt lake brine. Rb3PO4 was found to be an excellent heterogeneous catalyst for transfer hydrogenation. Rb3PO4 lost 70% of its active sites after adsorbing water, but the remaining was not affected. The reductions of aldehydes and ketones, when promoted by Rb3PO4, were allowed at room temperature. The activities of substrates at room temperature followed a descending order of 2,6-dichlorobenzaldehyde>4-bromobenzaldehyde>benzaldehyde>acetophenone>anisaldehyde>butanone. A new catalytic cycle postulating a six-membered cyclic transition state for the reductions of aldehydes and ketones was proposed. These results exploited the catalytic usage of Rb3PO4 and worth in industrial application.

  • Chen-lu Long , Zhao-guang Yang , Yuan Yang , Hai-pu Li , Qiang Wang

    A reliable method for detecting nanoparticles is necessary for the wide application of nanomaterials. Single particle-inductively coupled plasma mass spectrometry (SP-ICP-MS) was investigated to detect the size of gold nanoparticles (AuNPs) in this work. Discrimination of particle signal and iterative algorithm were used to calculate the baseline of particle signal. Influence of dwell time was discussed and 3 ms was selected as dwell time for size detection. Different AuNPs standards (30, 60, 80 and 100 nm) and mixed samples (60 and 100 nm) were determined by SP-ICP-MS and the accuracy was confirmed with reference values. The particle size detection limit was 19 nm in ultrapure water (UP water) and 31 nm in 0.1 μg/L Au3+ solution. Stability of AuNPs in ultrapure water and natural water samples was investigated by detecting size variation of AuNPs. The result shows that AuNPs are stable in aqueous environment for 6 d but degraded after 30 d.

  • Reza Behnood , Bagher Anvaripour , Nematollah Jaafarzadeh , Masoome Farasati

    In the recent decades oil spills in the aquatic environments are one of the major sources of environmental pollutions, which are steadily growing with the increase in oil consumption. Adsorption is a rapid and cost effective process to minimize the environmental impacts of oil spills and cleanup these pollutants. In this work, the crude oil sorption capacity was examined with raw sugarcane bagasse and acetylated sugarcane bagasse. Results show that the acetylated bagasse was significantly more oleophilic than the raw bagasse and acetylation reaction can increase bagasse oil sorption ability by about 90%. The maximum sorption capacities of acetylated bagasse were obtained about 11.3 g and 9.1 g in dry system (crude oil sorption) and oil layer sorption, respectively. The physicochemical characteristics of the sorbents such as composition, water solubility, moisture content and density were measured according to ASTM standard methods. Also Fourier transform infrared spectroscopy (FTIR) of raw and acetylated bagasse was performed to investigate the effect of acetylation on sugarcane bagasse structure.

  • Yi-min Pan , Rui-xue Jiang , Ji-li Yang , Hao Zheng , Er-qin Yin

    The adsorption capacity of Pb(II) on litchi pericarps was investigated as a function of temperature, pH, and adsorbent dose using batch experiments. The experimental data obtained were evaluated using adsorption equilibrium isotherms and a kinetic model. Additionally, the removal of Pb(II) in leachate of litchi pericarps was also evaluated. The results show that litchi pericarps exhibit a high adsorption capacity to Pb(II), with the maximum removal efficiency occurring at a temperature of 25 °C, a pH of 6.0−7.0 and an adsorbent dosage of 10 g/L. Langmuir and Freundlich isotherms and the pseudo-second-order kinetic model can all fit the equilibrium adsorption satisfactorily, with correlation coefficients (R2) of 0.9935, 0.9918 and 1.0, respectively. An average removal efficiency of 66.65% is found for Pb(II) in leachate of litchi pericarps.

  • Nachimani Charde

    A high current, AC waveform controller with C-type body frame of spot welder (75 kVA), was examined for the electrode actuating system whose pneumatically driven system has been redesigned and refitted for the servo based system without any vertical spring assistance in the 50 mm movable distance. Moreover, the pressing mechanism was carefully handled during the entire pressing tasks as to ensure that no catastrophic reaction happens for the electrodes’ caps, electrodes’ holders as well as the other part of mechanical assembly. With the mechanically originated-pneumatic and also the converted-servo systems, the stainless steels are welded for both systems to characterize the improvements. While the welding processes were carried out, the electrical signals have been captured to compute the signals’ representation of entire sequences. Later, the welded samples were underwent the tensile shear test, metallurgical observation and hardness test. The analytical results show distinct changes in the force profiles which has led to profound changes in mechanical properties of welded specimens.

  • Wahyu Kunto Wibowo , Seok-Kwon Jeong

    This work proposes a new strategy to improve the rotor position estimation of a permanent magnet synchronous motor (PMSM) over wide speed range. Rotor position estimation of a PMSM is performed by using sliding mode observer (SMO). An adaptive observer gain was designed based on Lyapunov function and applied to solve the chattering problem caused by the discontinuous function of the SMO in the wide speed range. The cascade low-pass filter (LPF) with variable cut-off frequency was proposed to reduce the chattering problem and to attenuate the filtering capability of the SMO. In addition, the phase shift caused by the filter was counterbalanced by applying the variable phase delay compensation for the whole speed area. High accuracy estimation result of the rotor position was obtained in the experiment by applying the proposed estimation strategy.

  • Wei Shen , Jian Zhang , Yi Sun , Di-jia Zhang , Ji-hai Jiang

    Cavitation bubble collapse has a great influence on the temperature of hydraulic oil. Herein, cone-type throttle valve experiments are carried out to study the thermodynamic processes of cavitation. First, the processes of growth and collapse are analysed, and the relationships between the hydraulic oil temperature and bubble growth and collapse are deduced. The effect of temperature is then considered on the hydraulic oil viscosity and saturated vapour pressure. Additionally, an improved form of the Rayleigh–Plesset equation is developed. The effect of cavitation on the hydraulic oil temperature is experimentally studied and the effects of cavitation bubble collapse in the hydraulic system are summarised. Using the cone-type throttle valve as an example, a method to suppress cavitation is proposed.

  • E. Prabhu , H. Mangalam , S. Karthick

    In this work, power efficient butterfly unit based FFT architecture is presented. The butterfly unit is designed using floating-point fused arithmetic units. The fused arithmetic units include two-term dot product unit and add-subtract unit. In these arithmetic units, operations are performed over complex data values. A modified fused floating-point two-term dot product and an enhanced model for the Radix-4 FFT butterfly unit are proposed. The modified fused two-term dot product is designed using Radix-16 booth multiplier. Radix-16 booth multiplier will reduce the switching activities compared to Radix-8 booth multiplier in existing system and also will reduce the area required. The proposed architecture is implemented efficiently for Radix-4 decimation in time (DIT) FFT butterfly with the two floating-point fused arithmetic units. The proposed enhanced architecture is synthesized, implemented, placed and routed on a FPGA device using Xilinx ISE tool. It is observed that the Radix-4 DIT fused floating-point FFT butterfly requires 50.17% less space and 12.16% reduced power compared to the existing methods and the proposed enhanced model requires 49.82% less space on the FPGA device compared to the proposed design. Also, reduced power consumption is addressed by utilizing the reusability technique, which results in 11.42% of power reduction of the enhanced model compared to the proposed design.

  • De-zun Zhao , Jian-yong Li , Wei-dong Cheng , Tian-yang Wang , Wei-gang Wen

    The accurate estimation of the rolling element bearing instantaneous rotational frequency (IRF) is the key capability of the order tracking method based on time-frequency analysis. The rolling element bearing IRF can be accurately estimated according to the instantaneous fault characteristic frequency(IFCF). However, in an environment with a low signal-to-noise ratio (SNR), e.g., an incipient fault or function at a low speed, the signal contains strong background noise that seriously affects the effectiveness of the aforementioned method. An algorithm of signal preprocessing based on empirical mode decomposition (EMD) and wavelet shrinkage was proposed in this work. Compared with EMD denoising by the cross-correlation coefficient and kurtosis(CCK) criterion, the method of EMD soft-thresholding (ST) denoising can ensure the integrity of the signal, improve the SNR, and highlight fault features. The effectiveness of the algorithm for rolling element bearing IRF estimation by EMD ST denoising and the IFCF was validated by both simulated and experimental bearing vibration signals at a low SNR.

  • Fang Li , Pei-qing Ye , Hui Zhang

    Permanent magnet tubular linear motors (TLMs) arranged in multiple rows and multiple columns used for a radiotherapy machine were studied. Due to severe volumetric and thermal constraints, the TLMs were at high risk of overheating. To predict the performance of the TLMs accurately, a multi-physics analysis approach was proposed. Specifically, it considered the coupling effects amongst the electromagnetic and the thermal models of the TLMs, as well as the fluid model of the surrounding air. To reduce computation cost, both the electromagnetic and the thermal models were based on lumped-parameter methods. Only a minimum set of numerical computation (computational fluid dynamics, CFD) was performed to model the complex fluid behavior. With the proposed approach, both steady state and transient state temperature distributions, thermal rating and permissible load can be predicted. The validity of this approach is verified through the experiment.

  • Zhong-jie Zhang , Jian Huang , Ying Wei

    A novel binary particle swarm optimization for frequent item sets mining from high-dimensional dataset (BPSO-HD) was proposed, where two improvements were joined. Firstly, the dimensionality reduction of initial particles was designed to ensure the reasonable initial fitness, and then, the dynamically dimensionality cutting of dataset was built to decrease the search space. Based on four high-dimensional datasets, BPSO-HD was compared with Apriori to test its reliability, and was compared with the ordinary BPSO and quantum swarm evolutionary (QSE) to prove its advantages. The experiments show that the results given by BPSO-HD is reliable and better than the results generated by BPSO and QSE.

  • Xin Liu , Kun-qi Chen , Jun-hua Yan

    In cognitive radio network (CRN), a secondary user (SU) may utilize the spectrum resource of the primary user (PU) and avoid causing harmful interference to the primary network (PN) via spectrum sensing. In the traditional time spectrum sensing, the SU cannot detect the PU’s presence during its transmission, thus increasing interference to the PN. In this work, a novel weighed cooperative bandwidth spectrum sensing method is proposed, which allows multiple SUs to use part of the bandwidth to perform cooperative spectrum sensing throughout the whole frame in order to detect the PU’s reappearance in time. The SU’s spectrum efficiency is maximized by jointly optimizing sensing bandwidth proportion, number of cooperative SUs and detection probability, subject to the constraints on the SU’s interference and the false alarm probability. Simulation results show significant decrease on the interference and improvement on the spectrum efficiency using the proposed weighed cooperative bandwidth spectrum sensing method.

  • Ling Shen , Jian-jun He , Shou-yi Yu , Wei-hua Gui

    The temperature control of the large-scale vertical quench furnace is very difficult due to its huge volume and complex thermal exchanges. To meet the technical requirement of the quenching process, a temperature control system which integrates temperature calibration and temperature uniformity control is developed for the thermal treatment of aluminum alloy workpieces in the large-scale vertical quench furnace. To obtain the aluminum alloy workpiece temperature, an air heat transfer model is newly established to describe the temperature gradient distribution so that the immeasurable workpiece temperature can be calibrated from the available thermocouple temperature. To satisfy the uniformity control of the furnace temperature, a second order partial differential equation (PDE) is derived to describe the thermal dynamics inside the vertical quench furnace. Based on the PDE, a decoupling matrix is constructed to solve the coupling issue and decouple the heating process into multiple independent heating subsystems. Then, using the expert control rule to find a compromise of temperature rising time and overshoot during the quenching process. The developed temperature control system has been successfully applied to a 31 m large-scale vertical quench furnace, and the industrial running results show the significant improvement of the temperature uniformity, lower overshoot and shortened processing time.

  • Jin-hui Li , Jie Li

    This work proposes a practical nonlinear controller for the MIMO levitation system. Firstly, the mathematical model of levitation modules is developed and the advantages of the control scheme with magnetic flux feedback are analyzed when compared with the current feedback. Then, a backstepping controller with magnetic flux feedback based on the mathematical model of levitation module is developed. To obtain magnetic flux signals for full-size maglev system, a physical method with induction coils installed to winding of the electromagnet is developed. Furthermore, to avoid its hardware addition, a novel conception of virtual magnetic flux feedback is proposed. To demonstrate the feasibility of the proposed controller, the nonlinear dynamic model of full-size maglev train with quintessential details is developed. Based on the nonlinear model, the numerical comparisons and related experimental validations are carried out. Finally, results illustrating closed-loop performance are provided.

  • A. H. Mazinan

    A novel hybrid robust three-axis attitude control approach, namely HRTAC, is considered along with the well-known developments in the area of space systems, since there is a consensus among the related experts that the new insights may be taken into account as decision points to outperform the available materials. It is to note that the traditional control approaches may generally be upgraded, as long as a number of modifications are made with respect to state-of-the-art, in order to propose high-precision outcomes. Regarding the investigated issues, the robust sliding mode finite-time control approach is first designed to handle three-axis angular rates in the inner control loop, which consists of the pulse width pulse frequency modulations in line with the control allocation scheme and the system dynamics. The main subject to employ these modulations that is realizing in association with the control allocation scheme is to be able to handle a class of overactuated systems, in particular. The proportional derivative based linear quadratic regulator approach is then designed to handle three-axis rotational angles in the outer control loop, which consists of the system kinematics that is correspondingly concentrated to deal with the quaternion based model. The utilization of the linear and its nonlinear terms, simultaneously, are taken into real consideration as the research motivation, while the performance results are of the significance as the improved version in comparison with the recent investigated outcomes. Subsequently, there is a stability analysis to verify and guarantee the closed loop system performance in coping with the whole of nominal referenced commands. At the end, the effectiveness of the approach considered here is highlighted in line with a number of potential recent benchmarks.

  • Tiao-yu Lei , Wei-ping Peng , Jin Lei , Yuan-hua Zhong , Qiu-hua Zhang , Jun-hao Dou

    Modular technology can effectively support the rapid design of products, and it is one of the key technologies to realize mass customization design. With the application of product lifecycle management (PLM) system in enterprises, the product lifecycle data have been effectively managed. However, these data have not been fully utilized in module division, especially for complex machinery products. To solve this problem, a product module mining method for the PLM database is proposed to improve the effect of module division. Firstly, product data are extracted from the PLM database by data extraction algorithm. Then, data normalization and structure logical inspection are used to preprocess the extracted defective data. The preprocessed product data are analyzed and expressed in a matrix for module mining. Finally, the fuzzy c-means clustering (FCM) algorithm is used to generate product modules, which are stored in product module library after module marking and post-processing. The feasibility and effectiveness of the proposed method are verified by a case study of high pressure valve.

  • Guang-yin Lu , Shu-jin Cao , Zi-qiang Zhu

    Geological structures often exhibit smooth characteristics away from sharp discontinuities. One aim of geophysical inversion is to recover information about the smooth structures as well as about the sharp discontinuities. Because no specific operator can provide a perfect sparse representation of complicated geological models, hyper-parameter regularization inversion based on the iterative split Bregman method was used to recover the features of both smooth and sharp geological structures. A novel preconditioned matrix was proposed, which counteracted the natural decay of the sensitivity matrix and its inverse matrix was calculated easily. Application of the algorithm to synthetic data produces density models that are good representations of the designed models. The results show that the algorithm proposed is feasible and effective.

  • Ali Alzuhairi , Mustafa Aldhaheri , Zhan-bo Sun , Jun-Seok Oh , Valerian Kwigizile

    Recent research has revealed that human exposure to air pollutants such as CO, NOX, and particulates can lead to respiratory diseases, especially among school-age children. Towards understanding such health impacts, this work estimates local-scale vehicular emissions and concentrations near a highway traffic network, where a school zone is located in. In the case study, VISSIM traffic micro-simulation is used to estimate the source of vehicular emissions at each roadway segment. The local-scale emission sources are then used as inputs to the California line source dispersion model (CALINE4) to estimate concentrations across the study area. To justify the local-scale emissions modeling approach, the simulation experiment is conducted under various traffic conditions. Different meteorological conditions are considered for emission dispersion. The work reveals that emission concentrations are usually higher at locations closer to the congested segments, freeway ramps and major arterial intersections. Compared to the macroscopic estimation (i.e. using network-average emission factors), the results show significantly different emission patterns when the local-scale emission modeling approach is used. In particular, it is found that the macroscopic approach over-estimates emission concentrations at freeways and under-estimations are observed at arterials and local streets. The results of the study can be used to compare to the US environmental protection agency (EPA) standards or any other air quality standard to further identify health risk in a fine-grained manner.

  • He-zhou Qu , Steven I. -Jy. Chien , Xiao-bo Liu , Pei-tong Zhang , Athanassios Bladikas

    As a major mode choice of commuters for daily travel, bus transit plays an important role in many urban and metropolitan areas. This work proposes a mathematical model to optimize bus service by minimizing total cost and considering a temporally and directionally variable demand. An integrated bus service, consisting of all-stop and stop-skipping services is proposed and optimized subject to directional frequency conservation, capacity and operable fleet size constraints. Since the research problem is a combinatorial optimization problem, a genetic algorithm is developed to search for the optimal result in a large solution space. The model was successfully implemented on a bus transit route in the City of Chengdu, China, and the optimal solution was proved to be better than the original operation in terms of total cost. The sensitivity of model parameters to some key attributes/variables is analyzed and discussed to explore further the potential of accruing additional benefits or avoiding some of the drawbacks of stop-skipping services.

  • Shuo-feng Wang , Zhi-heng Li , Shan Jiang , Na Xie

    City regions often have great diversity in form and function. To better understand the role of each region, the relations between city regions need to be carefully studied. In this work, the human mobility relations between regions of Shanghai based on mobile phone data is explored. By formulating the regions as nodes in a network and the commuting between each pair of regions as link weights, the distribution of nodes degree, and spatial structures of communities in this relation network are studied. Statistics show that regions locate in urban centers and traffic hubs have significantly larger degrees. Moreover, two kinds of spatial structures of communities are found. In most communities, nodes are spatially neighboring. However, in the communities that cover traffic hubs, nodes often locate along corridors.

  • Li-hua Luo , Ying-en Ge , Ji-hong Chen , Fang-wei Zhang

    This work considers those road networks in which there are multi-route choices for bifurcation-destination (or origin-destination) pairs, and designs a real-time variable message sign (VMS)-based routing control strategy in the model predictive control (MPC) framework. The VMS route recommendation provided by the traffic management authority is directly considered as the control variable, and the routing control model is established, in which a multi-dimensional control vector is introduced to describe the influence of route recommendations on flow distribution. In the MPC framework, a system optimum routing strategy with the constraints regarding drivers’ acceptability with recommended routes is designed, which can not only meet the traffic management authority’s control requirement but also improve drivers’ satisfaction with the route guidance system. The simulation carried out shows that the proposed routing control can effectively mitigate traffic congestion, reduces followers’ time delay, and improves drivers’ satisfaction with routing control in road networks.

  • Da-peng Zhang , Xiao-kun Wang

    Fostering the use of transit has been broadly accepted as an effective way to improve social equity and reduce the externalities caused by transportation. In the great body of transit literature, many have focused on the improvement of transfer efficiency. However, investigation on transit transfer efficiency is still lacking for medium sized cities or suburban areas that have sprawled from city centers. The special features associated with such an urban form lead to unique travel patterns and bus operations. This work develops a process to improve bus transfer efficiency for small conurbations considering their special characteristics. A case study of New York’s Capital District is used to illustrate the proposed method. Results show that the transfer waiting time can be remarkably shortened. The proposed method can be widely adapted to other transit systems in small conurbations.