Showing papers by "Nanjing University of Science and Technology published in 2002"

Convective heat transfer and flow characteristics of Cu-water nanofluid

Abstract: An experimental system is built to investigate convective heat transfer and flow characteristics of the nanofluid in a tube. Both the convective heat transfer coefficient and friction factor of Cu-water nanofluid for the laminar and turbulent flow are measured. The effects of such factors as the volume fraction of suspended nanoparticles and the Reynolds number on the heat transfer and flow characteristics are discussed in detail. The experimental results show that the suspended nanoparticles remarkably increase the convective heat transfer coefficient of the base fluid and show that the friction factor of the sample nanofluid with the low volume fraction of nanoparticles is almost not changed. Compared with the base fluid, for example, the convective heat transfer coefficient is increased about 60% for the nanofluid with 2.0 vol% Cu nanoparticles at the same Reynolds number. Considering the factors affecting the convective heat transfer coefficient of the nanofluid, a new convective heat transfer correlation for nanofluid under single-phase flows in tubes is established. Comparison between the experimental data and the calculated results indicate that the correlation describes correctly the energy transport of the nanofluid.

Application of the fractional Fourier transform to moving target detection in airborne SAR

Abstract: As a useful signal processing technique, the fractional Fourier transform (FrFT) is largely unknown to the radar signal processing community. In this correspondence, the FrFT is applied to airborne synthetic aperture radar (SAR) slow-moving target detection. For airborne SAR, the echo from a ground moving target can be regarded approximately as a chirp signal, and the FrFT is a way to concentrate the energy of a chirp signal. Therefore, the FrFT presents a potentially effective technique for ground moving target detection in airborne SAR. Compared with the common Wigner-Ville distribution (WVD) algorithm, the FrFT is a linear operator, and will not be influenced by cross-terms even if multiple moving targets exist. Moreover, to solve the problem whereby weak targets are shadowed by the sidelobes of strong ones, a new implementation of the CLEAN technique is proposed based on filtering in the fractional Fourier domain. In this way strong moving targets and weak ones can be detected iteratively. This combined method is demonstrated by using raw clutter data combined with simulated moving targets.

Characterization of a bioflocculant produced by the marine myxobacterium Nannocystis sp. NU-2.

Abstract: The marine myxobacterium strain NU-2, which can grow on high concentrations (up to 7%) of NaCl, was isolated from a salt soil sample collected from the coast of the Huanghai Sea, China. Morphological properties and 16S rDNA sequence analysis indicated that the isolate is a novel species related to the genus Nannocystis. Nannocystis sp. NU-2 produced a new kind of flocculating substance in a starch medium with a yield of 14.8 g l–1. The NU-2 flocculant was composed of 40.3% proteins and 56.5% polysaccharides, of which glucose, mannose and glucuronic acid were the principal constituents in the relative proportions of 5:4:1. The flocculation activity of the NU-2 flocculant depends strongly on cations such as Fe3+ and Al3+. When a 30 mg l–1 FeCl3 solution is present in kaolin clay suspension, 30 mg l–1of the flocculant produced a high flocculating activity value of 90%, which remained unchanged over an extensive pH range (pH 2.0–13.0). The flocculant was tested for its ability to bleach dyeing liquors, and the bleaching activities were 98.2% for acid red in 100 mg l–1of the flocculant and 99.0% for direct emerald blue in 50 mg l–1of the flocculant under test conditions. Use of the flocculant to bleach basic pink and cation emerald blue liquors was not effective.

Application of the SSOR preconditioned CG algorithm to the vector FEM for 3D full-wave analysis of electromagnetic-field boundary-value problems

Abstract: The symmetric successive overrelaxation (SSOR) preconditioning scheme is applied to the conjugate-gradient (CG) method for solving a large system of linear equations resulting from the use of edge-based finite-element method (FEM). For this scheme, there is no additional computing time required to construct the preconditioning matrix and it contains more global information of the coefficient matrix when compared with those of the banded-matrix preconditioning scheme. The efficient implementation of this preconditioned CG (PCG) algorithm is described in details for complex coefficient matrix. With SSOR as the preconditioner and its efficient implementation in the CG algorithm, this PCG approach can reach convergence in five times CPU time shorter than CG for several typical structures. By comparison with other preconditioned techniques, these results demonstrate that SSOR preconditioning strategy is especially effective for CG iterative method when an edge FEM is applied to solve large-scale time-harmonic electromagnetic-field problems.

CAD/CAM integrated system in collaborative development environment

Abstract: For virtual enterprises to realize efficient operation in the 21st century, it is necessary to develop an environment that can support collaborative work of multi-disciplinary groups distributed in different places. CAD/CAM integrated system is an important subsystem in this environment. In this paper, the structure of CAD/CAM integrated system is presented, then, key technologies related to realize CAD/CAM integration are discussed in detail and finally main functions and an application case of CAD/CAM integrated system is introduced.

Robust H∞ control for uncertain linear neutral delay systems

Abstract: This paper deals with the problem of robust H∞ control for uncertain linear neutral delay systems. The parameter uncertainty under consideration is assumed to be norm-bounded time-invariant and appears in all the matrices of the state-space model. The problem we address is the design of memoryless state feedback controllers such that the closed-loop system is asymptotically stable and the H∞ norm of the closed-loop transfer function from disturbance to the controlled output is strictly less than a prescribed positive scalar for all admissible uncertainties. In terms of a linear matrix inequality (LMI), a sufficient condition for the solvability of the above problem is proposed. When this matrix inequality is feasible, an explicit expression for the desired state feedback controller is given. Furthermore, a numerical example is provided to demonstrate the effectiveness of the proposed approach. Copyright © 2002 John Wiley & Sons, Ltd.

Transient Plane-Strain Response of Multilayered Elastic Cylinders to Axisymmetric Impulse

Abstract: This paper presents an exact solution and an approximate solution, using the expansion of transient wave functions in a series of eigenfunctions, for the transient response of an infinitely long and multilayered circular cylinder subjected to uniformly distributed dynamic pressures at the boundaries. Numerical results are given to illustrate the effects of the layer properties on the interfacial stresses and the spatial and temporal variations of the displacement and stresses. In particular, the exact solution is used to examine the applicability of the thin shell theories to the transient response of multilayered cylinders. ©2002 ASME

Comments on discrete chirp-Fourier transform and its application to chirp rate estimation [with reply]

Abstract: This comment points out that the sample rate of the discrete chirp-Fourier transform (DCFT) proposed by Xia (see ibid., vol.48, p. 3122-33, 2000) is not sufficient to avoid severe "picket-fence" effect and causes some restrictions for its practical applications. By increasing the sample rate and modifying the DCFT definition, a new robust DCFT is proposed. Xia (see ibid., vol.50, no.12, p.3116, 2002) replies by first correcting an error on the analog-to-discrete parameter conversions of a chirp signal. Xia also add that when the chirp rate detection resolution is increased, it is more robust to the chirp rate error. On the other- hand, what is sacrificed by doing so is that the magnitudes of the sidelobes of the transform are increased, which may limit its capability of detecting chirps in a multicomponent or low SNR signal. Therefore, which DCFT needs to be used has to depend on the practical application.

Comparative studies on the structures, infrared spectrum, and thermodynamic properties of phthalocyanine using ab initio Hartree-Fock and density functional theory methods

Abstract: The molecular structure, vibrational spectrum, standard thermodynamic functions, and enthalpy of formation of free base phthalocyanine (Pc) have been studied using the density functional theory B3LYP procedure, as well as the ab initio Hartree–Fock method. Various basis sets 3-21G, 6-31G*, and LANL2DZ have been employed. The results obtained at various levels are discussed and compared with each other and with the available experimental data. It is shown that calculations performed at the Hartree–Fock level cannot produce a reliable geometry and related properties such as the dipole moment of Pc and similar porphyrin-based systems. Electron correlation must be included in the calculations. The basis set has comparatively less effect on the calculated results. The results derived at the B3LYP level using the smaller 3-21G and LANL2DZ basis sets are very close to those produced using the medium 6-31G* basis set. The geometry of Pc obtained at the B3LYP level has D2h symmetry and the diameter of the central macrocycle is about 4 A. The enthalpy of formation of Pc in the gas phase has been predicted to be 1518.50 kJ/mol at the B3LYP/6-311G(2d,2p)//B3LYP/6-31G* level via an isodesmic reaction. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

Production of an exopolysaccharide bioflocculant by Sorangium cellulosum.

Abstract: Aims: To isolate a new exopolysaccharide bioflocculant produced by the myxobacterium Sorangium cellulosum NUST06, and to characterize its chemical composition and expolysaccharide production relative to carbon source. Methods and Results: Exopolysaccharide levels and biomass production by S. cellulosum NUST06 were analysed relative to carbon source. Glucose in the medium at a level of 3 g l−1 completely inhibited cell growth and exopolysaccharide production, but low concentrations of glucose (1–2 g l−1) could stimulate cell utilization of starch. The chemical composition and flocculating activity of the NUST06 exopolysaccharide was investigated. The flocculant comprised 38·3% proteins and 58·5% carbohydrates, of which glucose, mannose and glucuronic acid were present at 51·3%, 39·2% and 10·5%, respectively. The flocculating activity of the NUST06 flocculant depended strongly on cations. Conclusions: It is feasible to produce an exopolysaccharide bioflocculant by the strain NUST06 in a mineral salts medium using starch as a carbon source. Significance and Impact of the Study: This strain may be advantageous for commercial bioflocculant production and may enrich existing knowledge of myxobacteria.

The detectability and observer design of 2-D singular systems

Abstract: This paper discusses the detectability and asymptotic reconstructability of the state of two-dimensional (2-D) singular systems. The sufficient conditions of the detectability of 2-D singular systems are discussed and a constructive procedure for designing general asymptotic observers is provided. The sufficient conditions and an algorithm of designing a class of a full-order asymptotic observer are given. Meanwhile, the properties of the state feedback systems that contain observers are obtained. Two corresponding examples of designing observer are given.

Theoretical studies on heats of formation for cubylnitrates using density functional theory B3LYP method and semiempirical MO methods

Abstract: The heats of formation (HOF) have been calculated for all the 21 cubylnitrate compounds using the semiemprical molecular orbital (MO) methods (MINDO/3, MNDO, AM1, and PM3) and for 8 of 21 cubylnitrates containing 1–4 ONO2 groups using the density functional theory (DFT) method at the B3LYP/6-31G* level by means of designed isodesmic reactions. The cubane cage skeletons in cubylnitrate molecules have been kept in setting up isodesmic reactions to produce more accurate and reliable results. It is found that there are good linear relationships between the HOFs of the 8 cubylnitrates calculated using B3LYP/6-31G* and two semiempirical MO (PM3 and AM1) methods, and the linear correlation coefficients of PM3 and AM1 methods are 0.9901 and 0.9826, respectively. Subsequently, the accurate HOFs at B3LYP/6-31G* level of other 13 cubylnitrates containing 4–8 ONO2 groups are obtained by systematically correcting their PM3-calculated HOFs. Compared with noncaged nitrates, all the 21 cubylnitrates have high heats of formation implying that they may be very powerful energetic materials and have highly exploitable value. The relationship between the HOFs and the molecular structures of cubylnitrates has been discussed. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

Intermolecular interaction of hydrazine dimers: a comparative theoretical study

Abstract: Ab initio HF, MPn (n=2,4) and DFT(B3LYP) levels of theory with different basis sets in combination with counterpoise procedure (CP) for basis set superposition error correction have been applied to hydrazine and its dimers. Five optimized stable dimers were found on the potential energy surface. The structures obtained at different computational levels are in agreement with each other except for systems with much ‘overlap’ of submolecules. The corrected binding energy for the most stable dimer is predicted to be −18.00 kJ/mol at the MP4/aug-cc-pVDZ//MP2/aug-cc-pVDZ level. The energy barriers of the Walden conversion for amino group are 9.2 and 29.1 kJ/mol, and the smaller energy barriers for the internal rotation around the N–N bond are 3.6 and 36.1 kJ/mol at the HF/6-311G∗ level, for monomer and the most stable dimer, respectively. The molecular interaction slightly hinders both the internal rotation and Walden conversion. Binding energies obtained from the MP2 and B3LYP optimized structures are more sensitive to basis sets than those from the HF method. Larger basis functions generally tend to produce slightly longer intermolecular distances, and the B3LYP and MP2 methods generate shorter intermolecular distances though they usually produce longer bond lengths compared with those at the HF level. Both the frequencies of the NH2 wag mode and their blue shifts relative to those of monomer at the B3LYP/aug-cc-pVDZ level are in good agreement with the experiment.

Theoretical prediction on heats of formation for polyisocyanocubanes : - Looking for typical high energetic density material (HEDM) ()

Abstract: The heats of formation (HOF) for all the 21 polyisocyanocubanes are calculated systematically with density functional theory (DFT) B3LYP and semiempirical MO(MINDO/3, MNDO, AM1 and PM3) methods. First, the accurate HOFs for the 8 title compounds are obtained by means of designed isodesmic reactions at DFT-B3LYP/6-31G* level, and the cubane cage skeleton has not been broken (i.e. choosing cubane as a reference compound) to produce more accurate and reliable results. It is found that there are good linear relationships between the HOFs calculated using the B3LYP/6-31G* and four semiempirical MO methods, respectively, and all of the linear correlation coefficients are more than 0.9971. The HOFs obtained from PM3 calculation are the best among the four semiempirical MO methods. Then, the accurate HOFs at B3LYP/6-31G* level of other 13 polyisocyanocubanes are obtained by systematically correcting their PM3-calculated HOFs. Polyisocyanocubanes have very high HOFs, and the HOFs increase linearly with the increasing of the number of isocyano groups in a molecule. The results show that polyisocyanocubanes are the new generation explosives with highly potential and exploitable value.

Synthesis and intercalation properties of nanoscale layered tetratitanate

Abstract: Nanoscale layered tetratitanate K2Ti4O9 powders were prepared at relatively low temperature by a stearic acid method. The structures of the titanates and the products which had undergone H+, Ag+ exchange and intercalated by propylamine and NH2(CH2)3Si(OC2H5)3 (APS) were investigated by XRD, TEM, TG and BET analysis. Compared with the larger-size products prepared by a conventional solid state reaction, the nanoscale K2Ti4O9 takes in more intercalating molecules and leads to larger interlayer distances in the intercalated products, which may facilitate the exfoliation of the layered compound.

Synthesis, Crystal Structure and Stability Studies of Dithiocarbamate Complexes of Some Transition Elements (M=Co, Ni, Pd)

Abstract: Single-crystal x-ray structure determinations have been recorded at 295 K for the dithiocarbamate metal compounds • [Co(Et2dtc)3], [Co(nPr2dtc)3], [Pd(iPr2dtc)2] and [Pd(Et2dtc)2]. The stability constants(K) in EtOH of dialkyldithiocarbamate metal complexes [M(R2dtc)n] (M=Co, Ni, Pd. R=Me, Et, iPr, nPr. n=2, 3. dtc=dithiocarbamate) are determined by UV-vis data. The stability of the metal complexes increases in the order: Co iPr>nPr>Me. The results obtained from this study confirm that the stability due to alkyl groups may be partly attributed to changes in the residual positive charge and also partly to steric hindrance of branched alkyl-groups. The comparison between the solid and solution states shows that the [M(R2dtc)2] (M=Pd, Ni) complexes have similar changes in M-S distance and stability with change in alkyl group. [M(iPr2dtc)2] has the s...

Three-dimensional vibration analysis of a torus with circular cross section

Abstract: The free vibration characteristics of a torus with a circular cross section are studied by using the three-dimensional, small-strain, elasticity theory A set of three-dimensional orthogonal coordinates system, comprising the polar coordinate (r, theta) at each circular cross section and the circumferential coordinate phi around the ring, is developed Each of the displacement components u(r), v(theta), and w(phi) in the r, theta, and phi directions, respectively, is taken as a product of the Chebyshev polynomials in the r direction and the trigonometric functions in the theta and phi directions Eigenfrequencies and vibration mode shapes have been obtained via a three-dimensional displacement-based extremum energy principle Upper bound convergence of the first seven eigenfrequencies accurate to at least six significant figures is obtained by using only a few terms of the admissible functions The eigenfrequency responses due to variation of the ratio of the radius of the ring centroidal axis to the cross-sectional radius are investigated in detail Very accurate eigenfrequencies and deformed mode shapes of the three-dimensional vibration are presented All major modes such as flexural thickness-shear modes, in-plane stretching modes, and torsional modes are included in the analysis The results may serve as a benchmark reference for validating other computational techniques for the problem