Showing papers by "Nanjing University published in 1995"

A Conducting Polymer Film Stronger Than Aluminum

Abstract: Polythiophene (Pth) was electrochemically deposited onto stainless steel substrate from freshly distilled boron fluoride-ethyl ether containing 10 millimoles of thiophene per liter. The free-standing Pth film obtained at an applied potential of 1.3 volts (versus Ag/AgCl) had a conductivity of 48.7 siemens per centimeter. Its tensile strength (1200 to 1300 kilograms per square centimeter) was greater than that of aluminium (1000 to 1100 kilograms per square centimeter). This Pth film behaves like a metal sheet and can be easily cut into various structures with a knife or a pair of scissors.

Partition of nonpolar organic pollutants from water to soil and sediment organic matters.

Abstract: The partition coefficients (K oc ) of carbon tetrachloride and,1,2-dichlorobenzene between normal soil/sediment organic matter and water have been determined for a large set of soils, bed sediments, and suspended solids from the United States and the People's Republic of China. The K oc values for both solutes are quite invariant either for the soils or for the bed sediments; the values on bed sediments are about twice those on soils. The similarity of K oc values between normal soils and between normal bed sediments suggests that natural organic matters in soils (or sediments) of different geographic origins exhibit comparable polarities and possibly comparable compositions. The results also suggest that the process that converts eroded soils into bed sediments brings about a change in the organic matter property. The difference between soil and sediment K oc values provides a basis for identifying the source of suspended solids in river waters. The very high K oc values observed for some special soils and sediments are diagnostic of severe anthropogenic contamination

A broadband spectrometer for decimeter and microwave radio bursts

Abstract: Observations of solar microwave bursts with high temporal and spectral resolution have shown interesting fine structures (FSs) of short duration and small bandwidth which are usually superimposed on the smooth continuum. These FSs are very intense (up to 1015 K) and show sometimes a high degree of circular polarization (up to 100%). They are believed to be generated by electron cyclotron maser emission (ECME) in magnetic loops. Another type are the microwave type III bursts, which are drifting microwave FSs, and are probably the signatures of travelling electron beams in the solar atmosphere. The exact emission mechanisms for these phenomena, in particular the source configuration, the plasma parameters and the distribution of radiating electrons are not clear. For a detailed study of these problems new observations of intensity and polarization with high resolution in time and in frequency in decimeter and microwave wavebands are essential. In order to investigate these features in greater detail, spectrometers with high temporal and spectral resolution are being developed by the solar radio astronomy community of China (Beijing Astronomical Observatory (BAO), Purple Mountain Observatory (PMO), Yunnan Astronomical Observatory (YAO), and Nanjing University (NJU)). The frequency range from 0.7 to about 12 GHz is covered by about five spectrometers in frequency ranges of 0.7–1.4 GHz, 1–2 GHz, 2.4–3.6 GHz, 4.9–7.3 GHz, and 8–12 GHz, respectively. The radiospectrometers will form a combined type of swept-frequency and multi-channel receivers. The main characteristics of the solar radio spectrometers are: frequency resolution: 1–10 MHz; temporal resolution: 1–10 ms; sensitivity: better than 2% of the quiet-Sun level. We pay special attention to the sensitivity and the accuracy of polarization. Now, the 1–2 GHz radiospectrometer is being set up. The full system will be set up in 3–4 years.

Geologic and geochemical characteristics of the Yichun Ta-Nb-Li deposit, Jiangxi Province, South China

Abstract: The Yichun Ta-Nb-Li mine is situated within a small, sheetlike body of topaz-lepidolite granite which is the most fractionated phase of the Yashan batholith. Volumetrically, the most important phase in the batholith is a coarse-grained, protolithionite-muscovite granite which has a finer grained, muscovite granite margin. The protolithionite-muscovite granite is intruded by small bodies of muscovite granite which form the locus of a tungsten vein system at the Xin Fang tungsten mine. Two sheetlike bodies, a lower Li mica granite and an upper topaz-lepidolite granite intrude the upper contact between the protolithionite-muscovite granite and the host metasediments. The granites are crosscut by unmineralized porphyry dikes that are exploited as a source of kaolin. The topaz-lepidolite granite is a major, low-grade Ta-Nb-Li deposit which is exploited via open-pit mining. The topaz-lepidolite granite is composed dominantly of albite, lepidolite. and quartz, with topaz. K feldspar, amblygonite, and accessory zircon, monazite, pollucite, columbite-tantalite, microlite, and Ta-rich cassiterite. Phenocrysts of quartz, topaz, and K feldspar contain abundant inclusions of albite laths and occasional lepidolite crystals along growth zones ("snowball" texture), indicating simultaneous crystallization of these minerals from a subsolvus, residual magma. The topaz-lepidolite granite is characterized by high F, Li, P, Al 2 O 3 , and Na 2 O contents (with Na 2 O > K 2 O), and by very low SiO 2 , TiO 2 , MgO, CaO, and K 2 O contents. It is strongly enriched in Rb, Nb, and Ta, and strongly depleted in Sr and Zr compared with the earlier granite phases. Chemical trends are consistent with an origin via fractionation involving especially the removal of plagioclase, K feldspar, quartz, Fe-Mg silicates, and zircon. Most of this fractionation appears to have taken place within a deeper level magma chamber, with successive magma batches emplaced into the present level of exposure. Mineralization at Yichun consists of columbite-tantalite, microlite, and Ta-rich cassiterite which occur throughout the topaz-lepidolite granite closely associated with, and as inclusions, in lepidolite. The ore minerals also occur as interstitial crystals between the major silicate phases. Crystallization of the Nb-Ta-Sn minerals is an integral part of the cystallization of the topaz-lepidolite granite, and the effects of postmagmatic alteration in the formation of mineralization are absent or minor.

Modified Berenger PML absorbing boundary condition for FD-TD meshes

Abstract: A new modified, perfectly matched layer absorbing boundary condition (MPML ABC) is presented. In the MPML, the introducing of extra degrees of freedom provides the possibility of adjusting the parameters of nonphysical material absorber (PML) for the purpose of enhancing the attenuation rate of the evanescent modes. Compared to Berenger PML, the MPML is more efficient in absorbing the evanescent energy and keeps the same performance for propagation modes. The sophisticated properties of MPML ABC result in the reduction of the thickness of the matched tapers and their closer allocation, leading to better accuracy simulations and less computer burdens in FD-TD modeling. >

The electrochemical behavior of methylene blue at a microcylinder carbon fiber electrode

Abstract: The electrochemical behavior of methylene blue (MB) at a carbon fiber microcylinder electrode, was studied by cyclic voltammetry. The charge transfer coefficient α of the electrode reaction with two-electron transfer is 0.5, and the number of H+ participating in the electrode process is 3 at pH 2.2–5.4, 2 at pH 5.4–6.0 and 1 at pH 6.0–10.7, respectively. The standard electron transfer rate constant ko′, and standard formal potential Eo′ of MB at various pH were determined by using the carbon fiber microcylinder electrode. The electrode reaction mechanism of methylene blue at various pH is proposed. The adsorbability of MB at the electrode is discussed and explored by cyclic voltammetry and chronocoulometric technique.

Eigenmode sequence for an elliptical waveguide with arbitrary ellipticity

Abstract: Eigenmode sequence for an elliptical waveguide with arbitrary ellipticity is studied by directly calculating the parametric zeros of the modified Mathieu functions of the first kind and their derivatives. The normalized cutoff wavelength of the lowest 100 successive modes are presented, and the curvefitting expressions for the determination of the cutoff wavelength of the lowest 10 order modes are given, which are valid for the ellipticities ranging from 0.0 to 0.99. >

Ultrasound characterization of normal ocular tissue in the frequency range from 50 MHz to 100 MHz

Abstract: The ultrasonic properties of ocular tissues including sclera, cornea, ciliary body and iris have been quantitatively evaluated over the frequency range from 50 MHz to 100 MHz at 37/spl deg/C. Measurements were made with a wideband 60 MHz PVDF copolymer transducer in conjunction with a C-scan microscopy system developed in the authors' laboratory. Using this system, high resolution overview images were produced to identify homogeneous tissue regions for detailed quantitative analysis. The speed of sound for the four eye tissues ranged from 1542 m/s for iris to 1622 m/s for sclera. At 50 MHz the attenuation coefficient ranged from 1.3 dB/mm for cornea to 4.3 dB/mm for sclera. Scleral tissue also had the highest backscatter coefficient (0.0157 Sr/sup -1/ mm/sup -1/), while iris had the lowest (0.00184 Sr/sup -1/ mm/sup -1/). The measured ultrasonic properties are qualitatively related to their histological structure and imaging characteristics. >

Quark delocalization, color screening, and dibaryons

Abstract: The quark delocalization and color screening model, a quark potential model, is used for a systematic search of dibaryon candidates in the {ital u}, {ital d}, and {ital s} three flavor world. Color screening, which appears in unquenched lattice gauge calculations, and quark delocalization (which is similar to electron delocalization in molecular physics) are both included. Flavor symmetry breaking and channel coupling effects are studied. The model is constrained not only by baryon ground state properties but also by the {ital N}-{ital N} scattering phase shifts. The deuteron and zero energy dinucleon resonance are both reproduced qualitatively. The model predicts two extreme types of dibaryonic systems: ``molecular`` like the deuteron, and highly delocalized six-quark systems among which only a few narrow dibaryon resonances occur in the {ital u}, {ital d}, and {ital s} three flavor world. Possible high spin dibaryon resonances are emphasized.

Neural network for solving linear programming problems with bounded variables

Abstract: A new neural network for solving linear programming problems with bounded variables is presented. The network is shown to be completely stable and globally convergent to the solutions to the linear programming problems. The proposed new network is capable of achieving the exact solutions, in contrast to existing optimization neural networks which need a suitable choice of the network parameters and thus can obtain only approximate solutions. Furthermore, both the primal problems and their dual problems are solved simultaneously by the new network. >

Transport theory in metallic films: Crossover from the classical to the quantum regime.

Abstract: Using the quantum-statistical approach, we have developed a unified transport theory of metallic films. A general description for the conductivity in metallic films has been rigorously formulated in the presence of both impurity scattering and surface roughness. An explicit connection between the quasiclassical and present quantum approaches is also presented. We show that the quasiclassical theory by Fuchs [Proc. Cambridge Philos. Soc. 34, 100 (1938)] and Sondheimer [Adv. PHys. 1, 1 (1952)] can be reformed to be applicable to ultrathin metallic films by introducing a treatment of the surface via angle-dependent specularity parameters and including the quantum size effect. Moreover, to the lowest-order approximation in the theory, the previous quantum-approach results and discussions have naturally been recovered.

The synthesis and characterization of HgBa2Ca2Cu3O8+δ superconductors with substitution of Hg by Pb

Abstract: We have successfully fabricated ceramic superconductors of Hg-1223 with substitution of Pb for Hg, i.e. Hg1−xPbxBa2Ca2Cu3Oy, by using encapsulation and short time annealing techniques. Samples fabricated in this manner may have nearly single phase structure and some enhancement of Tc can be achieved through this method. The materials of this ceramic with x ranging from 0 to 0.5 exhibit high-temperature superconductivity at temperatures falling in the range from 103 to 135 K. The sample with optimum doping of Pb of x = 0.34 and ° = 0.40 has a highest Tc of 135 K, and its diamagnetic onset temperature Tcdia = 143 K. The composition of this sample has been found experimentally and is specified by a formula of Hg0.66Pb0.34Ba2Ca1.98O8.4. The valence number for the copper constituent is given by V Cu = 2.30 . X-ray diffraction (XRD), transmission electron microscope (TEM) and electron probe microanalyzer (EPMA) analyses have been carried out for detailed investigation. Results indicate that the critical temperature for samples which were post-annealed with either oxygen flow or in high pressure of oxygen gas was increased, while that for those annealed in argon flow was decreased. Furthermore, the as-prepared samples were slightly in the under-doped state with respect to the vacancy. It was shown that Tc parabolically depends on the valence state of copper.

The ionic conductive property of sulfonated polyethylene oxide polyurethane ionomers

Abstract: A series of lithium and sodium salts of sulfonated polyethylene oxide (PEO) polyurethane ionomers in different levels of ionization were prepared. It has been found that this material is a new type of ionic conductive polymer, characterized by a single-ion transport mechanism and good mechanical properties. The ionization level significantly influences the ionic conductivity of the samples. When the mole ratio of the metal ion and ether oxygen atom is about 0.05, the ionomers exhibit maximum cationic conductivity. An optimal cationic conductivity of 1.0 × 10−5 S/cm is obtained at about 70°C without any addition of organic plasticizer. The conductivity increases apparently when propylene carbonate and low MW PEO are added to the polyurethane ionomer. © 1995 John Wiley & Sons, Inc.

Effect of solution concentration on the gelation of aqueous polyvinyl alcohol solution

Abstract: The concentration dependence of cryogenic gelation for aqueous solution of poly(vinyl alcohol) was studied by measuring the apparent gel fraction G and the swelling ratio Q of the gel formed by freezing and thawing. It was found that for the gelation process there were three distinct regions of solution concentration bounded by two concentrations C gel and C * gel . The gel started to form at C = C gel , while no visible gel could be detected even upon repeated freezing and thawing of the extremely dilute solutions of C C * gel . In the intermediate concentration region, C gel < C < C * gel , which covers three orders of magnitude in concentration, gel and sol phases coexist. Both concentration dependencies of G and Q show two branches jointed at a concentration very close to the overlap concentration C * . The curve of G.Q versus C shows a sharp cusp. In case the sharp cusp concentration is really the value of C * , gelation offers a precise method to determine the overlap concentration.

Analysis of 2-d flare spectra: Velocity fields derived from Hα line asymmetries

Abstract: We derive a time series of two-dimensional velocity fields for a flare region on 1992 December 16, based on the asymmetries of the Hα line. The Hα spectra were obtained by an imaging spectrograph at the Solar Tower Telescope of Nanjing University. Four sites with evident chromospheric downflows are found to appear and decay consecutively in the studied region. The value of maximum velocities is 30–40 km s−1 and the lifetime of downflows is 2–3 min at these sites. It is also shown that the asymmetries only exist at the line wing, while the line center has nearly no shifts for this flare. Finally, we make a discussion on the characteristics of the velocity distribution and its correlations with the intensity distribution, as well as with the hard X-ray emission.

Isolated word recognition using Markov chain models

Abstract: The paper describes how Markov chains may be applied to speech recognition. In this application, a spectral vector is modeled by a state of the Markov chain, and an utterance is represented by a sequence of states. The Markov chain model (MCM) offers a substantial reduction in computation, but at the expense of a significant increase in memory requirement when compared to the hidden Markov model (HMM). Experiments on isolated word recognition show that the MCM achieved results that are comparable to those of the HMMs tested for comparison.

Magnetic relaxation and the flux diffusion barrier for TlSr2Ca2Cu3Oy doped with Pb and Ba determined by complex ac susceptibility measurements

Abstract: Complex ac susceptibility has been measured on the ${\mathrm{TlSr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ superconductor doped with Pb and Ba, which was prepared by the partial melt processing. The flux creep barriers U(J,B,T)\ensuremath{\propto}${\mathit{J}}^{\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\mu}}}$${\mathit{B}}^{\mathrm{\ensuremath{-}}0.75}$(1-${\mathit{T}}^{2}$/${\mathit{T}}_{\mathit{c}}^{2}$${)}^{1.5}$ with \ensuremath{\mu}=0.64 and current decay S=-d lnJ/d ln[t/${\mathit{t}}_{0}$] =1/(\ensuremath{\mu} ln[t/${\mathit{t}}_{0}$]) with ${\mathit{t}}_{0}$=2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$ s have been determined at various temperatures, ac frequencies f, dc fields B, and current densities J in a time window ${10}^{\mathrm{\ensuremath{-}}5}$ s\char21{}${10}^{\mathrm{\ensuremath{-}}3}$ s, which extends considerably the very limited one (typically 1 s\char21{}${10}^{4}$ s) used by the conventional dc magnetometer. The result that U(J)\ensuremath{\propto}${\mathit{J}}^{\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\mu}}}$ is an evidence of the vortex-glass phase or collective-creep mechanism predicted by theories from the ac susceptibility measurements.

Structural and Electronic Similarity but Functional Difference in Methylmalonyl-CoA Mutase between Coenzyme B12 and the Analog 2’,5'-Dideoxyadenosylcobalamin

Abstract: The cofactor analog 2',5'-dideoxyadenosylcobalamin (ddAdoCbl) differs from the natural cofactor coenzyme B12 [5'-deoxyadenosylcobalamin (dAdoCbl)] by lacking only one oxygen atom. The 1H and 13C NMR spectra of ddAdoCbl have been assigned unambiguously by homonuclear and heteronuclear 2D NMR techniques. The 1H, 13C, and 31P chemical shift values for ddAdoCbl were compared with those of another organocobalamin, namely dAdoCbl. This assessment shows that the analog is very similar both electronically and structurally to the natural cofactor. The effectiveness of ddAdoCbl as a cofactor for both the human and Propionibacterium shermanii methylmalonyl-CoA mutases was compared with that of the natural cofactor. ddAdoCbl was found to be a competitive inhibitor with respect to dAdoCbl. Similar binding affinities to both enzymes were found for both the ddAdoCbl analog and the natural cofactor. However, in the presence of ddAdoCbl, the rate of conversion of methylmalonyl-CoA to succinyl-CoA was only 1-2% of that seen with the natural cofactor. There were no changes with time in the visible absorption spectrum of the bound cofactor analog in the presence of substrate, suggesting that the Co-C bond was not cleaved. The CD (circular dichroism) spectra of dAdoCbl and ddAdoCbl are very similar, consistent with the NMR results. The CD spectral changes upon binding to P. shermanii methylmalonyl-CoA mutase are large compared to those reported on the binding of dAdoCbl to ethanolamine ammonia lyase. Furthermore, the CD spectra of both enzyme-bound cobalamins are very similar, suggesting that similar changes in the conformation or structure in these cobalamins occur on binding to the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison between β and L zeolites supported platinum for n-hexane aromatization

Abstract: The performance of zeolite Kβ supported platinum as a bifunctional catalyst for the reforming of n-hexane has been examined using pulse and continuous flow microreaction methods. A comparison under the same conditions with zeolite KL supported platinum was carried out. It is found that due to the stronger acidity of zeolite β, Pt Kβ exhibits more skeletal isomerization and cracking than does Pt KL zeolite, while the latter shows superior aromatization activity. Ion exchange of β zeolite with alkali cations as Cs+ can reduce the acidity and increase benzene selectivity. Ba2+ exchange also can lead to better dispersion of platinum and so can improve the aromatization activity. In contrast to the high sensitivity to sulphur poisoning of Pt KL , Pt Kβ is relatively stable to sulphur poisoning and regains to some extent its initial activity. All these observations are explained in terms of support acidity, the electron state and the dispersion of platinum.

Geostrophic Adjustment: Frontogenesis and Energy Conversion

Abstract: Nonlinear geostrophic adjustment is examined with a Boussinesq model. The motion is restricted to a two-dimensional channel in the horizontal and vertical (x, z) plane; the fluid is in uniform rotation, is stably stratified, inviscid, and incompressible. The flows considered fall under two classes: zero and uniform potential vorticity flows. Steady geostrophic flow fields are determined from initial man imbalances, represented by both symmetric and antisymmetric density anomalies that vary along the x axis. The distinguishing characteristic of these solutions is the development of a front, defined as a zero-order discontinuity in both density and geostrophic velocity at one or both vertical boundaries. Frontal formation occurs, as previously discovered by Ou for zero potential vorticity flow, when the initial horizontal density gradient is sufficiently large. The critical values are displayed for different cases in terms of the initial amplitude and initial scale of the density anomaly. The conve...