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Tsinghua Science and Technology

Issue 4 • Date Aug. 2010

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Displaying Results 1 - 18 of 18
  • [Front cover]

    Page(s): c1
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    Freely Available from IEEE
  • Contents

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    Freely Available from IEEE
  • Hydrogen adsorption on metal-organic framework MOF-177

    Page(s): 363 - 376
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    This review summarizes the recent literature on the synthesis, characterization, and adsorption properties of meal-organic framework MOF-177. MOF-177 is a porous crystalline material that consists of Zn4O tetrahedrons connected with benzene tribenzoate (BTB) ligands. It is an ideal adsorbent with an exceptionally high specific surface area (BET>4500 m/g) a uniform micropore size distribution with a median pore diameter of 12.7 A, a large pore volume (2.65 cm 3/g), and very promising adsorption properties for hydrogen storage and other gas separation and purification applications. A hydrogen adsorption amount of 19.6 wt.% on MOF-177 at 77 K and 100 bar was observed, and a CO2 uptake of 35 mmol/g on MOF-177 was measured at 45 bar and an ambient temperature. Other hydrogen properties (kinetics and heat of adsorption) along with adsorption of other gases including CO2, CO, CH4, and N2O on MOF-177 were also be discussed. It was observed in experiments that MOF-177 adsorbent tends to degrade or decompose when it is exposed to moisture. Thermogravimetric analysis showed that the structure of MOF-177 remains intact at temperatures below 330°C under a flow of oxygen, but decomposes to zinc oxide at 420°C. View full abstract»

    Open Access
  • Synthesis and characterization of ordered meso-macro-porous silica membranes on a porous alumina support

    Page(s): 377 - 384
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    Macroporous silica materials with ordered three-dimensional pore structure can be easily prepared by the template-directed sol-gel process. However, it is still a challenge to prepare them in membrane form on a porous support, which limits their applications. In this work, we have demonstrated the feasibility of obtaining a three-dimensional ordered macroporous silica membrane on macroporous alumina support using poly-methyl methacrylate (PMMA) spheres as the template. PMMA spheres were packed on the top of an Anopore-alumina support by filtration of a PMMA aqueous suspension. Silica sol obtained by an acid-catalyzed sol-gel process was infiltrated into the voids among the spheres. Drying induced stress caused the membrane to crack or peel off from the top of the support. This can be minimized by annealing the PMMA template layer before the introduction of silica sol which increases the mechanical strength of the template. Calcination or solvent extraction to remove the template produced a highly ordered three-dimensional macroporous silica membrane with spherical pores connected by windows in the mesoporous range. The results show that the PMMA-templated infiltration method is effective in preparing three-dimensional ordered macroporous silica membranes on a porous support. View full abstract»

    Open Access
  • Osmotic Pressure of Water in Nafion®

    Page(s): 385 - 390
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    Mechanical failure modes leading to cracks or breeches in proton exchange membrane fuel cells are driven by mechanical forces associated with swelling from water uptake and shrinkage from dehumidification. To determine the magnitude of compressive mechanical stress imposed by water swelling in a proton exchange fuel-cell membrane, the osmotic pressure of water in a perfluorosulfonic acid ionomer (Nafion® N 117) membrane was measured using a hydrostatic piston-cylinder device with an in-situ hydrophilic frit. Experiments indicate that hydrostatic stresses greater than 103.5 MPa are created in a membrane when swollen with water at 23°C suggesting that pressure from water swelling can distort Nafion N 117-based structures as the osmotic pressure is of the same order of magnitude as the flow stress of Nafion N 117. View full abstract»

    Open Access
  • Removal of ammonia from wastewater effluent by chlorella vulgaris

    Page(s): 391 - 396
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (309 KB)  

    The capability of Chiarella vulgaristo remove nitrogen in the form of ammonia and/or ammonium ions from wastewater effluent in a local wastewater treatment plant (i.e., the Mill Creek Plant in Cincinnati, Ohio, U.S.A.) was studied. The wastewater effluent leaving the plant was found to include high concentrations of nitrogen (7.7±0.19 mg/L) (ammonia (NH3) and/or ammonium ion (NH4+)) and total inorganic carbon (58.6±0.28 mg/L) at pH 7, and to be suitable for growing Chiarella vulgaris. When Chiarella vulgariswas cultivated in a batch mode under a closed system, half of the nitrogen concentration was dramatically removed in 48 h after a 24-h lag-phase period. Total inorganic carbon concentration also concomitantly decreased during the rapid growth-phase. The total biomass weight gained during the entire cultivation period balanced out well with the total amount of inorganic carbon and nitrogen removed from the culture medium. These results indicate that wastewater can be synergistically used to polish residual nutrients in wastewater as well as to cultivate microalgae for biofuel production. View full abstract»

    Open Access
  • Preferential oxidation of CO in a hydrogen-rich gas through Au/NaY catalytic membranes

    Page(s): 397 - 403
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    This paper describes novel Au/NaY catalytic membranes for preferential oxidation of CO (CO-PROX) in an H2-rich gas. NaY zeolite membranes with a high C02/N2 separation factor were loaded with nanosized Au particles using an ion-exchanged method. X-ray diffraction analyses showed that the structure of the NaY zeolite was not damaged by the ion exchange process. CO-PROX experiments showed that the catalytic membranes had excellent catalytic performance for selective oxidation of CO. The CO/H2 molar ratio on the permeate side decreased with increasing operating temperature in the range of 80–200°C. At 200°C, almost no CO was detected from the permeate stream of a catalytic membrane with the feed containing 0.67% CO, 1.33% O2, 32.67% H2, and He in balance. Thus, these Au/NaY catalytic membranes show a promise for CO removal from hydrogen fuels. View full abstract»

    Open Access
  • Heat transfer in the microlayer under a bubble during nucleate boiling

    Page(s): 404 - 413
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (650 KB)  

    Many studies have shown that a very thin liquid microlayer forms under vapor bubbles during nucleate boiling. The heat transfer from the surface to the bubble is then significantly affected by this microlayer and the curved region leading into the microlayer. Various models have been developed to predict the microlayer shape and the heat transfer along the curved interfacial region, but they tend to have inconsistent boundary conditions or unrealistic results. This paper presents a theoretical model to predict the microlayer thickness and the heat transfer rates for a variety of conditions. The results show how the wall superheat, the Hamaker constant, the bubble radius, and the accommodation coefficient at the interface affect the evaporation heat transfer rates and the microlayer shape for a large range of conditions for water and FC 72. The microlayer results are then shown to compare well with predictions made by solving the Navier-Stokes equations in the microlayer. View full abstract»

    Open Access
  • Experimental losses and optimum conditions for phenanthrene extraction

    Page(s): 414 - 417
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    Polycyclic aromatic hydrocarbons (PAHs) are a class of pollutants that are widespread in the environment. Their hydrophobic properties make accurate analyses very difficult. In addition, the experimental losses during extraction of PAHs are inevitable and of great concern. In this study, dichloromethane (DCM), chloroform (CF), and carbon disulfide (CDS) were used as solvents to extract phenanthrene (PHN), a typical PAH, at various temperature and pressure reduction conditions. The extraction was improved using a multiple microtube extraction methodology. The results indicate that the CDS had the best performance followed by CF and DCM at 25°C and standard pressure. This was ascribed to the intensity of the molecular interactions between the solvent, the water, and the PHN due to their different molecular structures leading to different stereo and hydrogen bonding effects. The optimum conditions for extraction of PHN by CDS were determined by correlating the experimental results. The regression shows that the experimental loss rate is linearly proportional to the pressure reduction and exponentially related to the temperature. The correlation can be used to improve extraction efficiencies. View full abstract»

    Open Access
  • Impact of flue gas species and temperature on mercury oxidation

    Page(s): 418 - 425
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    Systematic experimental research has been conducted in a fix-bed reactor system to determine the impact of coal-fired flue gas species and temperature on mercury oxidation. This work focuses on the temperatures range of 200°C to 800°C to demonstrate that temperature is a critical factor for the effect of the gas components on the mercury oxidation process. Among the investigated gases, hydrogen chloride is essential for oxidizing the elemental mercury. Nitrogen oxide was also found to have a positive correlation with the mercury oxidation when hydrogen chloride was present. Sulfur dioxide can either promote or inhibit the oxidation depending on the conditions; however, when nitrogen oxide is also present, sulfur dioxide has a negative impact. Ammonia exhibits an strong inhibitory effect. Several plausible mercury oxidation pathways are suggested in this paper. View full abstract»

    Open Access
  • Numerical simulations of a micro-channel wall-tube condenser for domestic refrigerators

    Page(s): 426 - 433
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    In recent years, microchannel heat exchangers have begun to be used in refrigeration and air conditioning systems. This paper introduces a microchannel condenser for domestic refrigerators with a theoretical model to evaluate its performance. The model was used to obtain the optimal design parameters for different numbers of tubes and tube lengths. The results show that the needed tube height of the downward section decreases with the number of tubes and the tube diameter. Compared with the original condenser, the present optimal design parameters can reduce the total metal mass by 48.60/0 for the two wall two side design and by 26% for the two wall one side design. Thus, the present condenser is much better than the condensers usually used in actual domestic refrigerators. View full abstract»

    Open Access
  • Modeling and experimental investigation of a variable speed drive water source heat pump

    Page(s): 434 - 440
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    Accurate variable speed characteristics are needed for water source heat pumps (WSHP) to design variable speed controls to adjust refrigerant flow rates in heat pumps and air conditioners. The system capacity can then be regulated to match the compressor loads to the heating or cooling needs to improve the energy efficiency and lower energy costs. The motor and compression characteristics of WSHP were modeled to include the coupling between the motor speed and the torque characteristics and compression characteristics. An analytical model is given for a variable speed hermetic scroll compressor that describes various factors, such as the drive frequency, suction pressure, and discharge pressure as a function of the compressor speed. The model was validated experimentally using R22 and R134a in an experimental WSHP with variable speed control using frequency conversion. The results show that the analytical model properly describes the variable speed characteristics and provides a control strategy for adjusting the capacity of scroll compressors to match the heat pump or air conditioner operating conditions. View full abstract»

    Open Access
  • Onset of nucleate boiling in natural circulation systems predicted using the second stir theory

    Page(s): 441 - 446
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    Experimental data and calculated results for the onset of nucleate boiling (ONB) in natural circulation systems show that for the same operating conditions, the equilibrium vapor quality for ONB in natural circulation is lower than for forced convections. The differences can be explained using second stir theory. The weak vortices and small stir energy in natural circulation systems result in nucleate boiling occurring earlier than in forced convection systems. In natural circulation systems high mass flow rates are accompanied by large kinetic energies and large stir energies, which enables changes in the directions of flow eddies and energy transport. The equilibrium vapor qualities at ONB are then higher at higher mass flow rates. The influence of other flow parameters on ONB can be evaluated by the relationships between these flow parameters and the mass flow rate. The same values can lead to different results due to different eddy directions. This indicates that the quantitative comparability in mathematics cannot be considered as only scientific standard. The second stir theory offers a new visual angle for researches on natural circulation. View full abstract»

    Open Access
  • Characterization of antibody responses against the 2F5 epitope ELDKWA using HIV-1 Env-mediated membrane fusion and neutralization assays

    Page(s): 447 - 451
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (334 KB)  

    The epitope ELDKWA, which is located in the membrane-proximal external region (MPER) of HIV-1 gp41, is an important neutralizing epitope. The human monoclonal antibody (mAb) 2F5 against this epitope shows broad neutralizing activity toward many HIV strains. However, several reports have shown that the epitope-specific mAbs induced by peptides containing MPER did not exhibit the same neutralizing activities as human mAb 2F5. In this study, four ELDKWA epitope specific mAbs (9E7, 7E10, 6B5, and 2B4) induced by immunization with the ELDKWA epitope in varied molecular contexts, all showed inhibitory activities with different potencies in HIV-1 Env-mediated membrane fusion assays and pseudovirus neutralization assays. This result indicates that though these antibodies recognize the epitope ELDKWA, their characterizations differ from that of neutralizing antibodies, implying that the neutralizing mAbs can be induced but also need to be screened, and the protective ability of a related vaccine antigen depends on the concentration of the neutralizing mAbs in the induced polyclonal antibodies. View full abstract»

    Open Access
  • Acid hydrolytic method for determination of ginkgo biloba total flavonoids in rat plasma by HPLC for pharmacokinetic studies

    Page(s): 452 - 459
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    A simple, reliable, economical method was developed using HPLC with a diode-array detector for determination of total flavonoids in plasma after introvenous administration of ginkgo bilobaextract. The method simultaneously detects quercetin, kaempferol, and isorhamnetin after acid hydrolysis and recalculation. The hydrolysis and extraction conditions were optimized in an orthogonal test. The specificity was tested by comparing the retention time, UV spectra, and peak purity indices with standards. The detection limits were 20 ng/mL was quercetin, 20 ng/mL for kaempferol, and 50 ng/mL for isorhamnetin. The calibration curve ranges were 75–2400, 71–2280, and 70–2240 ng/mL. The pharmacokinetic characteristics of ginkgo bilobaflavonoids after venous administration of 50 mg/kg ginkgo bilobaextract to rats were analyzed using a two-compartment model. The initial plasma concentration was 171.22 μg/mL. The half-life of flavonoids in the first compartment (distribution) was 0.07 h and at the second compartment (elimination) was 4.51 h, while the AUC(o-∞) was 1711.06 μg·min/mL. The apparent volume of distribution was 0.11 L/kg. The total body clearance is 10.52 mL/(min;kg). The result shows the method is suitable for pharmacokinetic studies. View full abstract»

    Open Access
  • Effect of flavonoids in scutellariae radix on depression-like behavior and Brain Rewards: Possible in dopamine system

    Page(s): 460 - 466
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (397 KB)  

    A series of animal models are used to investigate the anti-depression mechanism of flavonoids in scutellariae radix (SR) in vivo. Depression-like behavior in mice was studied after intraperitoneal administration of SR. The results showed that SR administered to mice by the intraperitoneal route obviously shortened the duration in the tail suspension test and the forced swimming test, aggravated the symptoms of eyelid ptosis, akinesia, and mortality caused by reserpine, prolonged climbing times, affected the conditioned place preference, and increased sugar consumption in mice. However the SR did not affect the head twitches induced by 5-HTP, locomotor activity in mice, the toxicity of yohimbine, and the body temperature decrease caused by high dosage of apomorphine. The tests show that SR has some anti-depression effect related to the dopamine system. Furthermore another anti-depression mechanism was possible that could affect the mechanism of brain reward, bring positive reinforcement, and increase the sensitivity to euphoria in mice. View full abstract»

    Open Access
  • Integrated quay crane and yard truck schedule problem in container terminals

    Page(s): 467 - 474
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    Quay crane and yard truck scheduling are two important subproblems in container terminal operations which have been studied separately in previous research. This paper proposes a new problem for the integrated quay crane and yard truck scheduling for inbound containers. The problem is formulated as a mixed integer programming (MIP) model. Due to the intractability, a genetic algorithm (GA) and a modified Johnson's Rule-based heuristic algorithm (MJRHA) are used for the problem solution. In addition, two closed form lower bounds are given to evaluate the solution accuracy. Computational experiments show that the solution algorithm can efficiently handle the scheduling problem and that the integrated methods are very useful. View full abstract»

    Open Access
  • Location specific cell transmission model for freeway traffic

    Page(s): 475 - 480
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    This paper describes a location specific cell transmission model of freeway traffic based on the observed variability of fundamental diagrams both along and across freeway segments. This model extends the original cell transmission model (CTM) mechanism by defining various shapes of fundamental diagrams to reproduce more complex traffic phenomena, including capacity drops, lane-by-lane variations, nonhomogeneous wave propagation velocities, and temporal lags. A field test on a Canadian freeway was used to demonstrate the validity of the location specific CTM. The simulated spatio-temporal evolutions of traffic flow show that the model can be used to describe the traffic dynamics near bottlenecks more precisely than the original model. View full abstract»

    Open Access

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Tsinghua Science and Technology (Tsinghua Sci Technol) aims to highlight scientific achievements in computer science, electronic engineering, and other IT fields. Contributions all over the world are welcome.

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