Showing papers by "Shanghai University published in 1997"

Reliability analysis of M/G/1 queueing systems with server breakdowns and vacations

Abstract: This note introduces reliability issues to the analysis of queueing systems. We consider an M/G/1 queue with Bernoulli vacations and server breakdowns. The server uptimes are assumed to be exponential, and the server repair times are arbitrarily distributed. Using a supplementary variable method we obtain a transient solution for both queueing and reliability measures of interest. These results provide insight into the effect of server breakdowns and repairs on system performance.

Gibbs free energy evaluation of the FCC(γ) and HCP(ε) phases in Fe-MN-Si alloys

Abstract: The Gibbs free energy as a function of temperature of the fcc(γ) and hcp(e) phases in the Fe-Mn-Si system is evaluated by the application of the general model for predicting thermodynamic properties for ternary systems from binary ones, suggested by Chou and by the utilization of the available data from binary Fe-Mn, Fe-Si and Mn-Si systems and the SGTE DATA given by Dinsdale. The calculated result seems reasonable as compared with the experimental data.

Gauge transformation and A-B effect

Abstract: The aim of this paper is to show that the vector potential in the so-called Aharonov-Bohm (A-B) effect is not a gauge transformation of the vacuum, even when α = integer(≠0) (where α = Φ / Φ 0 represents the magnetic flux in the long cylindrical solenoid and Φ 0 = h / e ). To this end, it is discussed that the wave function of the electron and the gauge function in a gauge transformation are required to be single-valued so that the Schrodinger wave mechanics and the Maxwell electromagnetic theory are well-formulated. It is also discussed that the gauge transformation of wave functions and the representation change of operators of Kobe's meaning are the same thing.

Analysis and evaluation of the transverse flux circumferential current machine

Abstract: With the evolution of novel high power density machines, it becomes important to compare the power potential of such machines with vastly different topologies having a variety of different waveforms of back EMF and current. The approach of this paper is based on general-purpose sizing and power density equations, which will permit a comparison of the main dimensions and power of such machines. In this paper, the comparison method of machine power densities is extended to include the transverse flux circumferential current type permanent magnet (TFCCPM) machine, and furthermore to compare the power production capability between the TFCCPM machine and the well-known squirrel cage induction machine.

Mg effects on the eutectic structure and tensile properties of Al-Si-Mg alloys

Abstract: The tensile behaviour of two commercial Al 7% Si casting alloys, with magnesium contents 0.4% and 0.66% have been studied. Different microstructures were produced by varying the solidification rate and by modification with strontium. An extraction technique was used to study the three dimensional features of the Si flakes and particles.

Classification of stress modes in assumed stress fields of hybrid finite elements

Abstract: A classification method is presented to classify stress modes in assumed stress fields of hybrid finite element based on the eigenvalue examination and the concept of natural deformation modes. It is assumed that there only exist m (=n−r) natural deformation modes in a hybrid finite element which has n degrees of freedom and r rigid-body modes. For a hybrid element, stress modes in various assumed stress fields proposed by different researchers can be classified into m stress mode groups corresponding to m natural deformation modes and a zero-energy stress mode group corresponding to rigid-body modes by the m natural deformation modes. It is proved that if the flexibility matrix [H] is a diagonal matrix, the classification of stress modes is unique. Each stress mode group, except the zero-energy stress mode group, contains many stress modes that are interchangeable in an assumed stress field and do not cause any kinematic deformation modes in the element. A necessary and sufficient condition for avoiding kinematic deformation modes in a hybrid element is also presented. By means of the m classified stress mode groups and the necessary and sufficient condition, assumed stress fields with the minimum number of stress modes can be constructed and the resulting elements are free from kinematic deformation modes. Moreover, an assumed stress field can be constructed according to the problem to be solved. As examples, 2-D, 4-node plane element and 3-D, 8-node solid element are discussed. © 1997 John Wiley & Sons, Ltd.

Preparation and structure of bulk nanostructured WC-Co alloy by high energy ball-milling

Abstract: Abstracts are not published in this journal

Compression of ECG data by vector quantization

Abstract: The authors first estimate the ECG rate-distortion bound, which is the theoretical limit in the compression of the ECG data. They then present ECG data-compression schemes based on codebook quantizer and finite-state VQ (FSVQ), which are suitable for coding a correlative signal. Then, the authors' modified FSVQ-based scheme is presented.

Optimal efficiency control of PM hybrid motor drives for electrical vehicles

Abstract: The paper deals with the control of a novel brushless PM hybrid motor to optimize its efficiency. The approach is to adaptively adjust the field current to minimize the total loss based on its potential for a high efficiency over a wide torque speed region. The optimal controller has good performance for electrical vehicles.

[Actions of salvianolic acid A on CCl4-poisoned liver injury and fibrosis in rats].

Abstract: AIM: To study the actions of salvianolic acid A (SA-A) on liver injury and liver fibrosis METHODS: The liver fibrotic rat was made by ip injection of CCl4 The model rats were divided into 3 groups treated with SA-A, colchicine (Col), and Salvia miltiorrhiza Bunge (SMB), respectively Six wk later the rat liver pathology was examined, type I and III collagen in the liver were examined by immunohistochemistical method Also hydroxyproline (Hyd) and malondialdehyde (MDA) in the liver, alanine aminotransferase (AlaAT), aspartate aminotransferase (AspAT), and albumin (Alb) levels in the serum were measured RESULTS: SA-A inhibited serum AlaAT and AspAT activities, decreased MDA and Hyd contents, alleviated liver fibrogenesis, protected deposition of type I and III collagen in liver matrix The actions of SA-A on liver fibrosis were similar to those of Col and SMB, action of SA-A decreasing MDA was better than that of Col CONCLUSION: SA-A has marked effects against liver injury and fibrosis, associated with its anti-lipid peroxidation actions

Effect of annealing on phase structure and degradation of a zinc oxide varistor with Si-additive

Abstract: The effect of annealing on phase structure and degradation of the current-voltage characteristics for a ZnO varistor with Si-additive has been investigated. By means of X-ray diffraction, analytical electron microscopy and thermal analysis, it is found that a phase transition from δ-Bi2O3 (with dissolved Si), to Bi24Si2O40 (bismuth silicate) took place in the ZnO varistor after annealing at 470 °C. This transition is associated with a volume contraction, no notable thermal effect, a high transition rate and reversibility. It is calculated by crystallography that the volume contraction of the phase transition is 6.02%. The transition of the Bi-rich phase results in decreased levels of degradation and improved stability of the ZnO varistor.

Analytical prediction of armature-reaction field in disc-type permanent magnet generators

Abstract: A two dimensional (2D) analytical method to predict the armature-reaction field in the slotted opening airgap/magnet region of a permanent magnet (PM) disc-type generator is presented. The currents in the slot are modeled by a uniform distributed current sheet along an arc at the slot opening. The analysis takes into account the harmonics in the armature current waveforms which are calculated from the voltage equations. The effects of the stator slot openings are being accounted for by the introduction of a 2D relative permeance function which is calculated directly from the nonlinear equation described by conformal transformation. A more refined permeance distribution can then be obtained easily.

Dielectric and piezoelectric properties of Pb(Ni1/3Nb2/3)O3-PbTiO3-PbZrO3 ceramics modified with bismuth and zinc substitutions

Abstract: The dielectric and piezoelectric properties of the (Pb0.985Bi0.01)(Ni1/4Zn1/12Nb2/3)x- (ZrσTi1-σ)1-xO3 piezoelectric ceramic system (0.2 ≤ x ≤ 0.7, 0.1 ≤ σ ≤ 0.9) were systematically investigated. The results showed that, after poling, the dielectric constant, e 33 T , increased for the tetragonal compositions but decreased for the rhombohedral compositions. Furthermore, high values of e 33 T and piezoelectric modulus, d 31 were found for the compositions along the extension of the morphotropic phase boundary. The highest values of the planar electromechanical coupling factor, K p, and the piezoelectric modulus, d 31, were found to be 0.70 and − 274 × 10-12 C N-1, respectively. The Curie temperature, remanent polarization, coercive field and the lattice constants of the a and c axes in relation to the Pb(Ni1/3Nb2/3)O3 content and the Zr/Zr + Ti ratio were also determined.

Effects of 24 Chinese medicinal herbs on nucleic acid, protein and cell cycle of human lung adenocarcinoma cells

Abstract: Objective: To study the effects of 24 Chinese medicinal herbs on nucleic acid, protein and cell cycle of human lung adenocarcinoma cells.Methods: Using flow cytometry the authors analysed the effects of 24 Chinese medicinal herbs (CMH) in compound recipe on proliferation index (PI), DNA index, protein index and ratio of various phases in cell cycle of human lung adenocarcinoma cells (SPC-A-1).Results: The PI was more than 20%, in 4 CMH, while 3 CMH, Gynostemma Pentaphylla, Radix Glehnia, and Radix Ginseng could strengthen the body resistance. That suggested using CMH of strengthening body resistance could not only serve as conventional tonic but also as tumor cell inhibitor. Meanwhile the action points of 24 CMH on cell cycle were different from one another.Conclusions: According to these results, Chinese recipes were more effective in clinical practice.

Gel formation in mullite precursors obtained via tetraethylorthosilicate (TEOS) pre-hydrolysis

Abstract: Tetraethylorthosilicate (TEOS) and aluminium chloride were taken as sources of SiO2 and Al2O3 to prepare precursors of mullite by pre-hydrolysis of TEOS under refluxing conditions. Gelation was carried out at different pH values and the effect of the pH of gelation on the subsequent temperature-induced phase transformations was characterized by differential thermal analysis, powder X-ray diffraction and 29Si and 27Al solid-state nuclear magnetic resonance spectroscopy. A pH-dependent exothermic peak was observed at ∼980°C. Strong acidic conditions (pH=1.5) were found to be beneficial for improving the mixing scale of the Al–Si components, leading to a mullitization temperature of ∼1200° and a sharp 980°C exothermic peak. In strong basic conditions (pH=11.5), no evident ∼980°C exothermic peak was detected, and the mullitization temperature was as high as 1350°C, probably due to heterogeneity in the mixing scale of the Al–Si components in the precursor system. A gel formation process has been proposed.

Reagentless amperometric biosensor highly sensitive to hydrogen peroxide based on the incorporation of Meldola Blue, fumed-silica and horseradish peroxidase into carbon paste

Abstract: A reagentless amperometric sensor highly sensitive to H2O2 has been prepared by incorporating fumed silica, horseradish peroxidase (HRP) and Meldola Blue into carbon paste. The efficient mediating ability to shift electrons between HRP and the carbon paste electrode via Meldola Blue was investigated by cyclic voltammetric and amperometric measurements. Reproducibility, response time, detection limit, selectivity and effects of applied potential, temperature and pH on the response of the sensor are reported. The high sensitivity of the sensor with a detection limit of 0.1 μmol/1 arose from the high efficiency of the bioelectrocatalytic reduction of hydrogen peroxide via HRP and Meldola Blue. The dependence of the Michaelis-Menten constant on the applied potential and the mediator concentration has been investigated and the results are presented.

Electronic and hydrogenic impurity states in a corner under an applied electric field

Abstract: With the use of a variational method to solve the effective-mass equation, we have studied the electronic and hydrogenic impurity states in a corner under an applied electric field. The electron energy levels and the impurity binding energies are calculated. Our results show that, with the increasing strength of the electric field, the electron energy levels increase, and the impurity binding energy in the ground state increases at first, to a peak value, then decreases to a value which is determined by the impurity position in the corner. The dependence of the impurity binding energy on the applied electric field and impurity position is discussed in detail.