Showing papers by "Tsinghua University published in 1986"

Multiple Bad Data Identification for State Estimation by Combinatorial Optimization

Abstract: The problem of multiple bad data in state estimation is thoroughly analyzed and a new approach to bad data identification is proposed. The method supersedes the largest normalized residual method as a special case for single or multiple noninteracting bad data. The approach borrows the framework from Decision Theory. The bad data identification is formulated as a combinatorial optimization problem. The optimization takes into account the reliability of the measurements. An efficient branch-and-bound algorithm fully exploiting the knowledge of the problem is developed. The method is reliable, efficient, and does not require separate testing of network observability.

Heat Transfer from a Rarefied Plasma Flow to a Metallic or Nonmetallic Particle

Abstract: Heat transfer from a plasma flow to a metallic or nonmetallic spherical particle is studied in this paper for the extreme case of free-molecule flow regime. Analytical expressions are derived for the heat flux due to, respectively, atoms, ions, and electrons and for the floating potential on the sphere exposed to a two-temperature plasma flow. It has been shown that the local or average heat flux density over the whole sphere is independent of the sphere radius and approximately in direct proportion to the gas pressure. The presence of a macroscopic relative velocity between the plasma and the sphere causes substantially nonuniform distributions of the local heat flux and enhances the total heat flux to the sphere. The heat flux is also enhanced by the gas ionization. Appreciable difference between metallic and nonmetallic spheres is found in the distributions along the oncoming flow direction of the floating potential and of the local heat flux densities due to ions and electrons. The total heat flux to the whole sphere is, however, almost the same for these different spheres. For a fixed value of the electron temperature, the heat flux decreases with increasing temperature ratio Te/Th.

Corona Modelling for the Calculation of Transients on Transmission Lines

Abstract: The paper presents a mathematical corona model and its use for transmission line modelling with corona and, if desired, with frequency dependence of its parameters. The corona model has been developed from macroscopical physical laws, reflecting relations between charge, electric field intensity and voltage. Space charges, their development and their displacement are taken into account. The parameters of the model are determined so that the simulated qv curves closely fit those available from measurements. The corona model is then used as an element of the discretized transmission line model. This consists either of longitudinal inductances or of travel delay modules. Modelling of frequency dependence is optional. The line equations are integrated using the trapezoidal rule, so that Norton equivalents are obtained for the two line ends for the purpose of interfacing with the external system. Thus the model is fully compatible with an Electro-Magnetic Transients Program (EMTP).

Observing non-linear time-variable systems through a canonical form observer

Abstract: Bestle and Zeitz have introduced a non-linear time-variable observer canonical form which permits, through a non-linear state transformation, the use of the eigenvalue assignment method to design observers for non-linear time-variable dynamic systems. In this paper, a necessary and sufficient condition under which the transformation exists is given. It is also proved that the transformation could be determined by integrating single variable functions instead of solving a set of partial differential equations as shown by Bestle and Zeitz. Examples are included to show how to do the transformation.

Reconstruction of 3D objects form orthographic projections

Abstract: An algorithm for automatic reconstruction of 3D objects from their orthographic projections is presented in this paper. It makes some improvements to, and complements the, Wesley-Markowsky algorithm, which is a typical hierarchical reconstruction algorithm limited to polyhedral objects, and extracts the idea of pattern recognition expressed in the Aldefeld algorithm. It is shown in theory by analysis and in practice by implementation that the proposed algorithm successfully rejected pathological cases and found all solutions with the same set of orthographic views. Compared with the existing algorithms presented in references, this algorithm covers some more complex cases of objects incorporating cylinders.

Multifunctional ceramic sensor

Abstract: There is provided a multifunctional ceramic sensor and technology which is capable of detecting temperature, humidity and gas with a single sensing element made of p-type metal-oxide porous ceramic semiconductor Ba(Ti 1-x Sn x )O 3 (x=0.05-0.5). The sensing element is prepared by special ceramic technique which is formed on porosity and sintered on green pack that form a kind of network of capillary pipe with tree-like structure in three dimensions. The present invention posses advantages are as follows: high sensitivity, fast response time, small hysteresis, good separability, high reproducibility and long durability. The multifunctional ceramic sensor not only use for air conditioners, driers, cookers and microwave ovens but also use to detect or control the temperature-humidity-gases for food stuff, tobacco, leather, textile, print, dye and petrochemical industry.

Stabilizabiltty of certain stochastic systems

Abstract: In this paper, we present certain sufficient conditions for (feedback) stabilizability of controlled stochastic systems. Theoretical results are illustrated by three examples applied to electrically suspended gyros.

An Autoregressive Model of the BAEP Signal for Hearng-Threshold Testing

Abstract: A new objective method for hearing threshold testing, parametric modeling, is proposed in this paper. The fifth-order autoregressive models are estimated for the averaged BAEP records at a series of stimulus levels. The normalized prediction error enor is chosen as the hearing threshold measure. For normal hearing subjects, the values of enor are very different between the control condition and the click stimulus. For abnormal patients with different hearing loss problems, the estimated hearing thresholds in terms of enor show a good agreement with the physicians' assessment.

A two-stage output feedback design

Abstract: The problem of output feedback control design for discrete systems with fast and slow modes is considered. It is shown that, when the effect of the slow mode on the fast mode is linearly related to the slow output vector, the control design can be implemented in two stages by using separate gain matrices. The new output feedback design yields first-order perturbations in the behaviour of the discrete system. A ninth-order boiler model is used to illustrate the design procedure.

Waveform Sampler CAMAC Module

Abstract: A Waveform Sampler Module (WSM) for the measurement of signal shapes coming from the multi-hit drift chambers of the SLAC SLD detector is described. The module uses a high speed, high resolution analog storage device (AMU) developed in collaboration between SLAC and Stanford University. The AMU devices together with high speed TTL clocking circuitry are packaged in a hybrid which is also suitable for mounting on the detector. The module is in CAMAC format and provides eight signal channels, each recording signal amplitude versus time in 512 cells at a sampling rate of up to 360 MHz. Data are digitized by a 12-bit ADC with a 1 ?s conversion time and stored in an on-board memory accessible through CAMAC.

The microscopic features of ion-induced metastable Fe−Cu phases

Abstract: Ion beam mixing was employed as an unique method to study the microscopic features of ion induced Fe−Cu phase dependence on increasing ion doses. The multiple metastable phases were observed by transmission electron microscopy. The phase identification was carried out by selected area electron diffraction and the corresponding compositions of the observed phases were determined by energy dispersive spectroscopy.

Application of the Riccati Method to Rotor Dynamic Analysis of Long Shafts on a Flexible Foundation

Abstract: A method is described for calculating critical speeds, unbalance response and damped natural frequencies of long rotors on a flexible foundation. The shaft and the foundation are calculated separately and coupled at the bearings through impedance matching. Included in the analysis is also a method for representing the shaft response by an expansion in its free-free modes.

Multiple bad data identification for state estimation by combinatorial optimization

Abstract: The problem of multiple bad data in state estimation is thoroughly analyzed and a new approach to bad data identification is proposed. The method supersedes the largest normalized residual method as a special case for single or multiple noninteracting bad data. The approach borrows the framework from Decision Theory. The bad data identification is formulated as a combinatorial optimization problem. The optimization takes into account the reliability of the measurements. An efficient branch-and-bound algorithm fully exploiting the knowledge of the problem is developed. The method is reliable, efficient, and does not require separate testing of network observability.

Internal separator for circulating fluidized bed combustion boiler

Abstract: A new type of internal separator for a CFB boiler system is introduced in this paper The main advantages of the separator are its high separation efficiency and low pressure drop It can be used with or without a special circulating passage Experimental results of 18 models installed in two bench scale facilities in cold condition are presented The cross sections of the bed and the freeboard of one facility are 360 × 360 mm2 and 500 × 500 mm2 respectively Another facility with a cylindrical combustion chamber is of inside diameter 300 mm When the bed material used is fly ash, the separation efficiency may reach up to 92-97%, while the pressure drop is usually lower than 4 mm H2O Recently, a full scale internal separator has been used in a test in a fluidized bed boiler It is found to improve the combustion efficiency A typical set of axial, tangential and radial velocity profiles of the air flow measured by a probe and the fields of particle contentrations determined by a light-guided fibre device above this separator in the freeboard are presented The critical particle diameter is estimated by solving the differential equations of motion with the help of a computer

Optimization of linear-quadratic regulator systems in the presence of parameter perturbations

Abstract: The problem of LQ optimality under parameter perturbations is discussed and a sufficient condition is given for insensitivity of the optimality of a closed-loop system to parameter variations. The permitted region (PR) of parameter perturbations is further introduced so that a perturbed closed-loop system will still be optimal to the parameter variations within PR and an algorithm is given for its construction. The possible ways are then suggested for expanding the size of PR.

Ion mixing to form amorphous alloys in the CoCd system

Abstract: Amorphous Co–Gd alloy films are formed by 300 keV Xe ion mixing of multilayered samples with alloy compositions of Co10Gd90, Co35Gd65, Co45Gd55, and Co50Gd50. Subsequent ion irradiation of the ion mixed amorphous alloys is made and a demixing effect is observed in some cases. Besides, the diffraction factors S = 2π sin (θ/λ) of the amorphous films so obtained are found similar to those of the amorphous Co–Gd alloys manufactured by rf sputter deposition. Amorphe dunne Schichten werden durch 300 keV Xe-Ionen-Bestrahlung aus Vielfachschichten der Legierungen von Co10Gd90, Co35Gd65, Co45Gd55 und Co50Gd50 hergestellt. Bei weiterer Bestrahlung einiger amorpher Legierungen werden Entmischungsvorgange beobachtet. Auserdem ergibt sich, das die Beugungsparameter S = 2π sin (θ/λ) der durch Ionenmischung entstandenen Schichten denjenigen amorpher Legierungen, die durch andere Techniken hergestellt werden, ahnlich sind.

A further study of superconducting critical temperature of L12 type superconductors

Abstract: A further study is made of Tc of L12 type superconductors on the basis of the crystal constants of L12 type compounds given by the author, and yields the predicted values of Tc of L12 type La- and Pb-radical superconductors by comparison. It it found that a prudent attitude must be maintained in studying lattice constant a and superconducting critical temperature Tc of the Al compounds. Es wird eine weitere Untersuchung von Tc der Supraleiter mit L12-Struktur auf der Grundlage von fruher vom Autor angegebenen Kristallkonstanten der L12-Verbindungen durchgefuhrt, sie liefert durch Vergleich die vorhergesagten Werte von Tc fur La- und Pb-Radikalsupraleiter mit L12-Struktur. Es wird gefunden, das man bei der Untersuchung der Gitterkonstante a und der kritischen Supraleitungstemperatur Tc der A1-Verbindungen vorgichtig sein mus.

Fluidized bed boiler and high temperature separators used therein

Abstract: A fluidized bed boiler and a high temperature separator used therein. Each separator consists of a horizontal S-shaped passage formed in a casted block and having an inlet for receiving flue gases from the boiler. A divider wall divides a portion of the passage into a dense-phase gas bypass and a vertical-flow ash collecting chamber. As a result flyash of a diameter (50 μm) can be separated, and the combustion cycle efficiency can reach over 98%.

Two component LDV system with dual-differential acousto-optical frequency shift and its applications

Abstract: This paper describes the main properties of the two component LDV system developed with the dual-differential frequency shift technique. It has the advantages of multiple functions, better SNR and high utilization of information. So it offers as a complete technique and method for measuring 2-D complex flows. By applying this system, 2-D turbulent separated flow measurements have been made in a duct with an asymmetrical sudden expansion and in a wind tunnel flow over a 2-D rib. The Reynolds numbers were at 5900 and 4500 respectively.

Temperature-humidity-gas multifunctional ceramic sensor and technology

Abstract: @ There is provided a multifunctional ceramic sensor and technology which is capable of detecting temperature, humidity and gas with a single sensing element made of p-type metal-oxide porous ceramic semiconductor Ba (Ti1-xSnx) O3 (x = 0.05-0.5). The sensing element is prepared by special ceramic technique which is formed on porosity and sintered on green pack that forms a kind of network of capillary pipe with tree-like structure in three dimensions. The advantages of the present invention are as follows: high sensitivity, fast response time, small hysteresis, good separability, high reproducibility and long durability. The multifunctional ceramic sensor not only used for air conditioners, driers, cookers and microwave ovens but also used to detect or control the temperature-humidity-gases for food stuff, tobacco, leather, textile, print, dye and petrochemical industry.

Boundary Element Technique in Infinite and Semi-infinite Plane Domain

Abstract: A modified Kelvin weighting function and infinite boundary element formulations are presented to solve semi-infinite plane domain problems having geometrically irregular boundaries. Results show that much fewer elements need to be prescribed and excellent accuracy can be obtained.

Discrete signal reconstruction from its spectral magnitude and some samples

Abstract: Discrete signal reconstruction from its spectral magnitude and some samples has a variety of potential applications. In this paper, a discrete signal is shown to be uniquely reconstructed by its spectral magnitude and some saples under mild restriction on its original sequence. Three theorems are provided. Several numerical algorithms have been discussed and a new algorithm called three domains iteration method in which the convergence is guaranteed is developed.

Avalanche GaAlAs/GaAs heterojunction phototransistor with optoelectronic bistability

Abstract: Optoelectronic bistability in an avalanche GaAlAs/GaAs HPT which operates in the negative resistance region is reported for the first time. Theoretical and experimental results are presented. This device can be used in regulation, differential amplification and optical memory signals.