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Tsinghua Science and Technology

Issue 4 • Date Dec. 1996

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Displaying Results 1 - 25 of 26
  • [Front cover]

    Publication Year: 1996 , Page(s): c1
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    Freely Available from IEEE
  • Contents

    Publication Year: 1996 , Page(s): 1 - 2
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    Freely Available from IEEE
  • Hypersensitive spectra and coordination structures of trivalent neodynium ion

    Publication Year: 1996 , Page(s): 315 - 322
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    Hypersensitive absorption spectra were used to study the coordination structure of Nd3+ complexes in solutions. The method of theoretical spectroscopic calculation is briefly described. Crystalline complexes with known symmetries: NdCl63Ph3PH, Nd [(C2H5O) 2PO2]3 and Nd(TTA)4 HQ having Oh, Oh and D4d symmetry, respectively, were prepared and the f-f transition spectra of Nd3+ were measured in acetonitrile solution. Spectra calculated for these complexes fit the experimental data quite well. Spectroscopic calculation reveals that the band shape and transition strength of hypersensitive spectra are mainly affected by changes of the donor atom and coordination symmetry. The coordination structure of the TRPO extraction complex of Nd3+ was studied using this method. A D3h symmetric coordination structure is assigned to Nd(NO3)33TRPO complex in dodecane. View full abstract»

    Open Access
  • Numerical simulation and experimental investigation of velocity fields in a rotating disc contactor

    Publication Year: 1996 , Page(s): 323 - 326
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    A tangential velocity field is measured in a rotating disc contactor (RDC) with a column diameter of 300 mm, column height of 360 mm, and rotating speeds ranging from 230 to 600 r/min with no throughput. Numerical simulation is carried out using PHOENICS computational fluid dynamics (CFD) software. Results of the numerical simulation are in fairly good agreement with experimental results. The results obtained in this study are useful for further investigation of fluid behaviour inside an RDC extraction column and for equipment design. View full abstract»

    Open Access
  • Wave behavior of vibrating fluidized beds

    Publication Year: 1996 , Page(s): 327 - 331
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    Experimental data show how vibration energy is imparted to a vibrating fluidized bed (VFB). A new type of sensor was used to measure the wave signals in a VFB. The experimental results show that the vibration energy imparted is through continuous wave propagation in the vibrating fluidized bed. Wave characteristics are affected by the bed properties. A bubble's behavior in the bed is followed by analyzing the wave frequency spectrum. View full abstract»

    Open Access
  • Application of non-equilibrimn stage model to liquid-liquid extraction

    Publication Year: 1996 , Page(s): 332 - 335
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (775 KB)  

    The application of the nor-equilibriun stage model to the multicomponent, non-ideal liquid-liquid extraction process is described in this paper. Pilot plant experinents and a commercial process of aromatic separation by sulfolane in sieve tray extraction colunns were chosen as examples to show the advantages and benefits of the non-equilibriun stage model over the conventional model. View full abstract»

    Open Access
  • Application of hydrophilic polymers in multichannel flow electrophoresis

    Publication Year: 1996 , Page(s): 336 - 340
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    Protein mixtures are separated by multichannel flow electrophoresis (MFE) in a 5-compartment electrolyzer partitioned by membranes. Polyvinyl alcohol (PVA), polyethylene glycol 4000 (PEG 4000) and polyvinylpyroolidone K30 (PVP K30) were applied to the MFE as shielding polymers to prevent protein adsorption on the polysulfone microfiltration membrane during the electrophoresis process. The effects of polymer concentration on the protein transmembrane flux were examined. It was found that PVA, PEG 4000 and PVP K30 greatly reduced protein adsorption on the membrane surface. However, their influences on protein migration in an electric field were different. Continuous separationof bovine serumalbumin and hemoglobin mixture was conducted using PEG 4000 as a shielding polymer and yielded 46. 6 mg BSA and 25. 7 mg HBB per hour. These results show a high potential for scaling MFE up to large scale separation and purification of biomolecules. View full abstract»

    Open Access
  • Combustion kinetics model for HTGR spherical graphite fuel element

    Publication Year: 1996 , Page(s): 341 - 346
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (882 KB)  

    Combustion is the most reliable technique to remove the matrix graphite during reprocessing of spent HTGR (high temperature gas-cooled reactor) 233U nucl ear fuel. The effects of temperature and oxygen concentration on the specific combustion rate of the unirradiated ThO2-UO2 spherical graphite element were studied experimentally. A combustion kinetics model is presented for calculating the specific combustion rate. The combustion process would be controlled by both the reaction and mass transfer for temperature in the range of 750 900 and 750 Reynolds numbers, Re = 56.9 454 9. The Ranz-Marshall correlation was used to predict the apparent mass transfer coefficient and to better fit the experimental data. View full abstract»

    Open Access
  • Water coextraction with tri-n-octylamine(TOA) based on chemical complexation

    Publication Year: 1996 , Page(s): 347 - 350
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    A series of extraction equilibrium experiments were carried out systematically for dilute acetic acid and butyric acid solutions using tri-n-octylamine (TOA) as a camplexing agent and l-octanol or benzene as a diluent. The FT-IR spectra of solvents loaded with organic acids and water were determined. The effects of campositions of mixed solvent, diluent, and solute concentrations on the coextracted water corcentration were discussed The results are beneficial for optimising mixed solvent composition and for enhancing the extraction process. View full abstract»

    Open Access
  • Study on the dehydration of organic solvents by pervaporation and the mass transfer mechanism of pervaporation

    Publication Year: 1996 , Page(s): 351 - 356
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    The dehydration of organic solvents by pervaporation using a PVA/PAN (pdy vinyl alcohol/ polyacrylonitrile) composite membrane is introduced. A theoretical non-equilibrium-solution diffusion model is proposed. Methods are studied to determine solution rate coefficients and diffusion coefficients. Pervaporation separation of an ethanol-water mixture is simulated on the basis of the new mass transfer model. View full abstract»

    Open Access
  • Using artificial neural networks in naphthas RVP modeling

    Publication Year: 1996 , Page(s): 357 - 361
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    Artificial neural networks (ANNs) based on a feedforward architecture and a back-propagation on technique alternately using negative and conjugate gradients, have been used to create a naphtha Reid vapor pressure model of process data from an HYSIM process simulation. The accuracy of the model is to within 1.185×0025; of the target values. Some important measures are proposed to produce simulated operation cases of the stabilizer to provide training and testing data. Procedures were also developed to improve network testing performance and to avoid oscillatories during this network learning procedure in which improved convergence. These measures can be expanded to any chemical engineering process model using ANNs. View full abstract»

    Open Access
  • Fermentation production of poly-β-hydroxybutyrate by recombinant escherichia coli

    Publication Year: 1996 , Page(s): 362 - 366
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (750 KB)  

    Poly-β-hydroxybutyrate (PHB) was produced by recombinant E. coli HMS174 in a glucose-mineral medium. The medium composition and culture conditions were optimized by a series of shake flask experiments. The optimal initial concentrations of glucose and (NH4) 2SO4 were about 20 g/L and 4 g/L, respectively. The optimal temperature, pH, culture and inoculum volume were 37, 7.5, 25% and 10%, respectively. The final cell dry weight, PHB dry weight, PHB content and glucose conversion efficiency reached 8.06 g/L, 6.58 g/L, 81.64% and 98.56%, respectively, at 23.67 g/L initial glucose concentration after 48 h culturing. Different fed-batch cultures were also carried out in the shake flask. View full abstract»

    Open Access
  • Review of computer simulation techniques for thermo-fluid phenomena

    Publication Year: 1996 , Page(s): 367 - 371
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    With the development of modern science and technology, especially the rapid innovation of large-scale computing systems and numerical experimental capabilities, studies of thermo-fluid phenomena of condensed states have become more and more attractive. This paper describes some new developments using molecular dynamics (MD) and Monte Carlo simulation methods to analyze thermo-fluid phenomena. View full abstract»

    Open Access
  • Development of a new column design software using visual basic

    Publication Year: 1996 , Page(s): 372 - 375
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    A new column design software, TCD, was developed using visual basic for windows. The TCD interfaces are very friendly to facilitate communication between the user and the computer. TCD can be used not only to design new columns, but also to check old columns for retray application. TCD can be easily learned and mastered. Several design examples are using TCD to display the advantages of TCD. This paper introduces the interface design process, functions and advantages of TCD. View full abstract»

    Open Access
  • Conduction mechanism in PE-CB composites suitable for low voltages and high currents

    Publication Year: 1996 , Page(s): 376 - 381
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    Carbon black (CB) particles can form conducting passageways or quantum mechanical tunnels only in the boundaries of PE crystal grains or in the amorphous region in HDPE-CB composite PTC materials suitable for low voltages and high currents. The percolation model was modified using considering the effective volume fraction of the conductive component. The effective volume fractions of CB at various temperatures were calculated based on the temperature dependence of the specific volume of polyethylene (PE) and the temperature dependence of the PE unit cell parameters. The temperature dependence of the specimen resistance was then calculated using the modified percolation model. View full abstract»

    Open Access
  • Synthesis and crosslinking mechanism of a polyacrylate/polyurethane composite coating

    Publication Year: 1996 , Page(s): 382 - 385
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    A polyacrylate comprising acetoacetyl group and a polyurethane with vinyl end groups have been prepared. These two polymers could crosslink with each other to form a composite coating in the presence of a basic catalyst at room temperature. A model Michael reaction between ethyl acetoacetate (EAA) and methyl acrylate (MA) was used to investigate the crosslinking mechanism. The results indicate that the two active hydrogen atoms in the acetoacetyl group could both react with vinyl groups to form mono- and bis-adducts in a two step process. View full abstract»

    Open Access
  • Negative-working photosensitive polyimide

    Publication Year: 1996 , Page(s): 386 - 389
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    Photosensitive polyimide precursor containing glycol monocinnamate group was synthesized by a new method. The photoresist, made from the above polyimide precursor, was spin-coated onto silicon wafers, prebaked and then exposed to UV light. The appropriate conditions of the photolithographic procedures were determined. This photosensitive polyimide precursor showed good light sensitivity and the polyimide which was obtained by heating the polyimide precursor had a high thermal stability. View full abstract»

    Open Access
  • Surface modification through gradient morphology control of polymer blends

    Publication Year: 1996 , Page(s): 390 - 394
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    Ethylene-vinyl acetate(EVAc) copolymer was melt-grafted with hydroxy ethylmethacrylate(HEEA) and acrylamide (AAm), then blended with polypropylene(PP) in this study. It was found that both PP/EVAc-g-HEMA and PP/EVAc-g-AAm formed a gradient phase structure during annealing, as same as that of a PP/EVAc blend. The formation of the gradient phase structure resulted in accumulation of the dispersed phase on the sample surface. With the dispersed phase EVAc as a carrier, the grafted polar groups were transported onto the surface of the blend sample while forming an EVAc gradient dispersed phase. Due to the hydrogen bonding between the polyurethane (PU) paints and the polar groups grafted on to the EVAc, the coating adhesion was greatly improved and the peeling strength of the coating reached a high value of 800 g/cm without further treatment of the sample surface. Thus, the gradient phase structure control of blends is an effective way of material surface-modification of materials. View full abstract»

    Open Access
  • Conformations of cytochrome P-450 models by 1D and 2D NMR

    Publication Year: 1996 , Page(s): 395 - 398
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (575 KB)  

    Conformations of organic compounds in solution relate to their physical and chemical properties and biological activities. Two calix[4] arene-porphyrin derivatives were synthesized as models of cytochrome p-450 monooxygenase. The conformations of the models were determined using DQFCOSY (double quantum filter correlation spectroscopy), NOESY (nuclear overhauser effect spectroscopy), etc. The calix[4] arene part showed cone conformation in the compound 1 and showed mainly partial cone conformation in the compound 2. The calix[4] arene and the porphyrin were situated side by side in the compound 1, and above and below each other in the compound 2. View full abstract»

    Open Access
  • Equation of state for electrolyte aqueous solution based on perturbation theory

    Publication Year: 1996 , Page(s): 399 - 405
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    Using perturbation theory, an equation of state was built for electrolyte solution in which a mixture of charged hard spheres and uncharged hard spheres was used as the reference system, and intermolecular forces such as dispersion, dipolar, and induction forces were considered. The densities for 22 single-, 9 binary- and 1 quaternary-electrolyte aqueous solutions at different temperatures were calculated using water parameters and ionic diameters. Also, the densities of NaCl solution at 25 300 and 0.1 100 MPa were calculated. The calculation precision was good. The results show that this equation of state is suitable for calculating densities of single and mixed electrolyte solutions in wide ranges of temperatures and pressures. No empirical parameter is needed when this equation is used for high temperatures and high pressures or for mixed electrolyte solutions. View full abstract»

    Open Access
  • Excess molar enthalpies of binary mixtures of benzyl alcohol with isomers of heptanone

    Publication Year: 1996 , Page(s): 406 - 409
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    Excess molar enthalpies of binary mixtures of benzyl alcohol (BA) with isomers of heptanone have been determined at 298.65 K, 303.65 K and 308.65 K. The \matrix{{\rm E} \cr {\rm M}} values are positive over the entire mole fraction range. The dependence of \matrix{{\rm E} \cr {\rm M}} on the temperature and the structure of the component molecules is discussed. View full abstract»

    Open Access
  • Study on the GE-type mixing rule for cubic equations of state

    Publication Year: 1996 , Page(s): 410 - 415
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (875 KB)  

    Cubic equations of state have been widely used to predict thermodynamic properties of fluids in chemical engineering processes. To determine properties of mixtures, mixing rules for the parameters in equations of state are necessary. In this s paper, the excess Gibbs energy type of mixing rules are systematically studied. In the mixing rule for parameter a, two terms are found can be cancelled when consistent volume parameters are used. The mixing rule for parameter b is also improved to account for mixtures with large size differences. The new mixing rules give obvious improvement for vepor-liquid equilibria of binary alkane systems, especially of methane or ethane + alkane (carbon number from 3 to 44). View full abstract»

    Open Access
  • Kinetics and mechanism studies on the interaction of tetramethoxylbenzoquinone with piperidines

    Publication Year: 1996 , Page(s): 416 - 419
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (683 KB)  

    The kinetics of charge transfer complex (CTC) of 2, 3, 5, 6-tetramethoxyl-l, 4-benzoquinone (TMOQ) with two alicyclic N-donors, piperidine (PD) and morpholine (ML), in methanol, has been investigated by ultraviolet visible spectroscopy. The transformation leads to the formation of substitution products in solution, which have been isolated and characterized as 2, 5-diamino-3, 6-dimethoxyl-l, 4-benzoquinones by 1HNMR, MS, and elemental analysis. The kinetic results of the formation of products indicate that the rate is first order both with the acceptor and the donor. A mechanism of interaction between TMOQ and PD or ML is discussed. View full abstract»

    Open Access
  • Effect of vanadium and bismuth promoters on direct partial oxidation of methane

    Publication Year: 1996 , Page(s): 420 - 424
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (875 KB)  

    Direct oxidation of methane to methanol holds considerable potential for producing liquid fuel from natural gas. A vanadium and bismuth promoted MoO3/Cr2O3/SiO2 catalyst system prepared by coprecipitation was investigated at various temperatures and V and B promoter content. Then homogeneous gas phase oxidation reaction was also studied for comparison. It was found that HCHO and CO2 were the primary products during the non-catalytic homogeneous reaction with CH3OH produced when the reaction temperature increased. However, the primary products in the catalytic reaction were CH3OH and CO. These results suggest that the methane catalytic oxidation mechanism differ somewhat from the non-catalytic one. In-situ FTIR and TPD studies suggest that promoter V promote activation of the C-H bond of CH4 and that Bi be a good promoter to keep the desirable products from deep oxidation as well as enharce the bulk diffusion rate of lattice oxygen that may favor the methanol formation. Adjusting the content of the V and Bi oxides and the preparation conditions, it provided a best Bi-V-Mo-Cr-Ox/SiO2 catalyst system that achieved up to 80% CH3OH+ HCHO selectivity with about 13% CH4 conversion. View full abstract»

    Open Access
  • Determination of inorganic selenium in KSC by electrophoretic capillary ion analysis

    Publication Year: 1996 , Page(s): 425 - 428
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (801 KB)  

    An assay to determine the amount of inorganic selenium in KSC has been developed using electrophoretic capillary ion analysis (CIA). Parameters which influence CIA separation such as the addition of an electroosmotic flow modifier, choice of electrolyte anions and the buffer'S pH are investigated. In the optimized system, selenate and slenite are separated in a buffer containing chromate, triethanolamine, and tetradecyltrimethylammonium bromide at pH 9.2. There is sufficient resolution to allow accurate quantification. 10 mg/L bromide is used as internal standard. Quantification is highly reproducible with a migration time RSD of 0.89% over 6 runs and a peak area RSD of 1.23%. The method is linear over two orders of magnitude. The detection limits of lower than 0.5 mg/L are attainable when the pressure injection (3.5 kPa) time is 10s. The selenite recovery (101%) is acceptable. 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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