Showing papers by "Tsinghua University published in 1992"

On the precise formulation of the equivalence theorem.

Abstract: A systematic analysis of renormalization schemes and a general proof of the precise formulation of the equivalence theorem are given in the {ital R}{sub {xi}} gauge for both the SU(2){sub {ital L}} and the SU(2){times}U(1) theories. The precise formula for the modification factor {ital C}{sub mod} is obtained, and a convenient particular scheme in which {ital C}{sub mod} is exactly unity is proposed. {ital C}{sub mod} in other schemes are discussed up to one loop in the heavy Higgs boson limit.

Analysis of the effects of quantization in multilayer neural networks using a statistical model

Abstract: A statistical quantization model is used to analyze the effects of quantization when digital techniques are used to implement a real-valued feedforward multilayer neural network. In this process, a parameter called the effective nonlinearity coefficient, which is important in the studying of quantization effects, is introduced. General statistical formulations of the performance degradation of the neural network caused by quantization are developed as functions of the quantization parameters. The formulations predict that the network's performance degradation gets worse when the number of bits is decreased; that a change of the number of hidden units in a layer has no effect on the degradation; that for a constant effective nonlinearity coefficient and number of bits, an increase in the number of layers leads to worse performance degradation; and the number of bits in successive layers can be reduced if the neurons of the lower layer are nonlinear. >

Improved QCD-motivated heavy-quark potentials with explicit Λ MS̄ dependence

Abstract: We propose two models for a heavy-quark potential with possible natural QCD interpretations. The potentials approach the two-loop perturbative QCD formula at short distance and a linear confining potential at large distance, and their predicted $c\overline{c}$ and $b\overline{b}$ spectra all fit the data very well for ${\ensuremath{\Lambda}}_{\stackrel{-}{\mathrm{MS}}}$ in the range 100-500 MeV, where $\stackrel{-}{\mathrm{MS}}$ denotes the modified minimal subtraction scheme. Furthermore, the potentials are described directly in coordinate space with explicit ${\ensuremath{\Lambda}}_{\stackrel{-}{\mathrm{MS}}}$ dependence so that they are convenient for practical calculations. Some of their phenomenological predictions are given, especially, in the picture regarding a confining potential as a scalar exchange. The predicted masses of $\ensuremath{\psi}(1^{1}P_{1})$ and $\ensuremath{\Upsilon}(1^{1}P_{1})$ are higher than the center-of-gravity values of the $1^{3}P_{J}$ states by 0.9-1.8 MeV and 0.4-0.7 MeV, respectively, for ${\ensuremath{\Lambda}}_{\stackrel{-}{\mathrm{MS}}}$ in the range 100-200 MeV.

Prevention of tissue calcification on bioprosthetic heart valve by using epoxy compounds: a study of calcification tests in vitro and in vivo.

Abstract: Calcification is the principal cause of the clinical failures of the bioprosthetic heart valves fabricated from glutaraldehyde pretreated porcine aortic valves or bovine pericardium. In this paper, we compared the calcification on various types of bovine pericardiums pretreated with two hydrophilic epoxy compounds adding GA post-treatment (EP 1 and EP 2), glutaraldehyde (GA)- and nontreated pericardium (Fresh), respectively, by in vitro and in vivo tests. Significant decrease of calcification was found by pretreatment with both epoxy compounds rather than with glutaraldehyde : 0.250 ± 0.001 (Fresh), 0.276 ± 0.058 (EP l), 0.302 ± 0.071 (EP 2), and 0.478 ± 0.172 (GA) μg (Ca)/mg (dried tissue), respectively, after 20 days dipping in a simulating serum solution in vitro; 115.13 ± 60.11 (Fresh), 129.84 ± 51.08 (EP 1), 167.39 ± 20.81 (EP 2), and 205.19 ± 16.86 (GA) pg/mg, respectively, after 3 months subcutaneous implantation i n rabbits. The in uifro method for evaluating calcification designed by us gave the similar order among four samples with that obtained by in uiuo test. Because the bovine pericardium pretreated with the epoxy compounds adding GA post treatment possesses the greater tenacity than that pretreated only with epoxy compounds or GA, meanwhile the calcification is also significantly decreased with this pretreatment, it may be expected that the bovine pericardium with this pretreatment will have the greater anticalcification and durability in dynamic stress. © 1992 John Wiley & Sons, Inc.

Unbalanced bidding on contracts with variation trends in client-provided quantities

Abstract: This paper examines unbalanced contract bidding, a strategy for the allocation of rates to unit quantities for the benefit of the bidder. A mathematical model is proposed which attempts to objectively exploit variation trends in client-provided quantities. It is shown that the model can be solved by two methods - linear programming and the maximum–minimum method. The maximum–minimum method is preferred for most real-world situations.

An augmented UD identification algorithm

Abstract: An augmented UD identification (AUDI) algorithm for system identification is developed by rearranging the data vectors and augmenting the covariance matrix of Bierman's UD factorization algorithm. The structure of the augmented information (covariance) matrix is particularly easy to interpret and it is shown that the AUDI algorithm is a direct extension of the familiar recursive least squares (RLS) algorithm. The proposed algorithm permits simultaneous identification of the model parameters plus loss functions for all orders from 1 to n at each time step with approximately the same calculation effort as «th order RLS. This provides a basis for simultaneous model order and parameter identification so that problems due to over- and under-estimation of model can be avoided. Based on its least-squares properties, numerical robustness, theoretical basis and the fact that it simultaneously estimates multiple models, the proposed AUDI algorithm is recommended for use in place of RLS and Bierman's UD factorizatio...

D- centers in spherical quantum dots.

Abstract: A negatively charged donor center ${\mathit{D}}^{\mathrm{\ensuremath{-}}}$ (i.e., a neutral shallow donor ${\mathit{D}}^{0}$ that binds a second electron) in a spherical quantum dot is studied by use of a variational approach. A trial function which includes electron-correlation effects and approaches the Chandrasekhar-type function in the limit of zero barrier height is used. The well-radius and barrier-height dependence of the ``binding energy'' of the ${\mathit{D}}^{\mathrm{\ensuremath{-}}}$ center is obtained. The dimensional characteristics are clearly demonstrated not only for the ``binding energy'' and its maximum of the ${\mathit{D}}^{\mathrm{\ensuremath{-}}}$ center but also for the ratio of ${\mathit{D}}^{\mathrm{\ensuremath{-}}}$ to ${\mathit{D}}^{0}$ ``binding energy'' and the electron-correlation effect.

ELM-a fast addition algorithm discovered by a program

Abstract: A new addition algorithm, ELM, is presented. This algorithm makes use of a tree of simple processors and requires O(log n) time, where n is the number of bits in the augend and addend. The sum itself is computed in one pass through the tree. This algorithm was discovered by a VLSI CAD tool, FACTOR, developed for use in synthesizing CMOS VLSI circuits. >

A two-dimensional resistance simulator using the boundary element method

Abstract: A resistance simulator for extraction of the parasitic parameters from VLSI layout is presented. The calculation of the resistor network is based on the boundary element method (BEM). The computational results indicate that the BEM has an advantage over the finite difference method (FDM) and the finite element method (FEM). Since only discretized equations on the boundary of solved domain need to be solved, the grid number on the boundary is much smaller and mesh generation is greatly simplified. Hence the execution CPU time is reduced drastically. In order to treat the corners on the boundary, the concept of multiple normal derivatives at a corner is proposed. The concept is used in both continuous and partially discontinuous linear elements to increase the accuracy and reduce the number of unknowns. It is shown that a nonuniform mesh scheme is useful for problems with some stronger singularities. >

Effect of pretreatment with epoxy compounds on the mechanical properties of bovine pericardial bioprosthetic materials.

Abstract: Early failures of bovine pericardial heart valves are due to leaflet perforation, tearing and calcification. Since glutaraldehyde fixation has been shown to produce marked changes in leaflet mechanics and has been linked to development of calcification, bovine pericardium fixed with the four hydrophilic epoxy formulations and their mechanical properties are studied in this paper. We measured the thicknesses, shrinkage temperatures, stress relaxations and stress-strain curves of bovine pericardiums after different treatments with (1) non-treatment (fresh), (2) glutaraldehyde (GA), (3) epoxy compounds followed by the posttreatment with GA (EP 1#, EP 2#), and (4) epoxy compounds (EP 3# and EP 4#). Results of this study showed that the hydrophilic epoxy compounds are good crosslinking agents. There are no significant differences of shrinkage temperature and ultimate tensile stress among all tissue samples pretreated with GA, EP 1# and EP 2#. However, the stress relaxations of tissue-samples pretreated with epoxy compounds followed by the posttreatment with GA (EP 1# and EP 2#) are significantly slower than that pretreated with GA, and the strains at fracture of EP 1# and EP 2# are also significantly larger than that of GA or epoxy compounds. These facts show that the bovine pericardium pretreated with the epoxy compound followed by the posttreatment with GA (EP 1# and EP 2#) possesses greater tenacity and potential durability in dynamic stress.

Stable adaptive control of backlash nonlinear system with bounded disturbances

Abstract: An adaptive control algorithm for backlash nonlinear systems with bounded disturbances is presented. Its closed-loop stability is proved, and the upper bound of the control error is given, even for nonminimum-phase systems. Simulation results show the effectiveness of the algorithm. >

Kinetics of the course of inactivation of aminoacylase by 1,10-phenanthroline.

Abstract: The kinetic theory of the substrate reaction during modification of enzyme activity previously described [Tsou (1988) Adv. Enzymol. Relat. Areas Mol. Biol. 61, 381-436] has been applied to a study on the kinetics of the course of inactivation of aminoacylase by 1,10-phenanthroline. Upon dilution of the enzyme that had been incubated with 1,10-phenanthroline into the reaction mixture, the activity of the inhibited enzyme gradually increased, indicating dissociation of a reversible enzyme--1,10-phenanthroline complex. The kinetics of the substrate reaction with different concentrations of the substrate chloroacetyl-L-alanine and the inactivator suggest a complexing mechanism for inactivation by, and substrate competition with, 1,10-phenanthroline at the active site. The inactivation kinetics are single phasic, showing that the initial formation of an enzyme-Zn(2+)-1,10-phenanthroline complex is a relatively rapid reaction, followed by a slow inactivation step that probably involves a conformational change of the enzyme. The presence of Zn2+ apparently stabilizes an active-site conformation required for enzyme activity.

Structure of the alloy (GaAs)1-xGe2x and its electronic properties.

Abstract: An improved model for the structure of the alloy (GaAs${)}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{2\mathit{x}}$ is proposed. The phase diagram is calculated using the Kikuchi approximation, with the interaction energies of nearest-neighbor atom pairs computed by a universal-parameter tight-binding method. The Ge atoms are taken to be randomly distributed in order to avoid phase segregation in the computation of the metastable phase diagram of (GaAs${)}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{2\mathit{x}}$. There is a metastable order-disorder transition point at ${\mathit{x}}_{\mathit{c}}$=0.36, which agrees well with experiment. The contribution of the order-disorder transition to band-gap bowing is also calculated.

Cardiovascular responses to external counterpulsation: a computer simulation.

Abstract: A mathematical model of the human cardiovascular system is presented which includes a simulation of cardiac assistance by external counterpulsation. The model was established to study the effects of external counterpulsation on cardiovascular haemodynamics. The closed simulation includes both the left and the right heart and the pulmonary circulation. The model is able to provide data for the behaviour of the system under varying modes of assistance. Our results suggest that control of external counterpulsation is more difficult than control of the intra-aortic balloon pump and requires regulation of a larger number of variables. The results also suggest that a tradeoff exists between improved oxygen delivery to the heart and reduction in the oxygen consumption of the myocardium, an observation similar to that reported for the intra-aortic balloon pump.

Heterodyne interferometric optical fiber displacement sensor for measuring displacement of an object

Abstract: A heterodyne interferometric optical fiber displacement sensor using a laser diode. The frequency and the intensity of the laser diode beam are periodically modulated by an injection current. The laser diode beam is routed to a rod lens via a first optical fiber, an optical fiber coupler, and a second optical fiber. The interference light resulting from the interference between the light reflected from the exit surface of the rod lens and the light reflected from an object surface is routed to a third optical fiber via the optical fiber coupler, which is then detected by a photodiode attached to the end of the third optical fiber. From the output of the photodiode, a given frequency component is extracted using a bandpass-filter. The extracted signal is converted into a pulse signal. The frequency change of the pulse signal (equivalent to a doppler frequency shift caused by the movement of the object surface) is accumulated using an electronic circuit. Then, the accumulated value is used to calculate the displacement of the object surface.

Time-varying potential field based 'perception-action' behaviors of mobile robot

Abstract: An efficient method is presented for implementing mobile robot perception-action behaviors, based on the time-varying potential field. The concept of dynamic potential is proposed to achieve the control scheme. The scheme was successfully implemented on the THMR-II mobile robot for a variety of applications. The drawbacks of known potential field methods are solved by the composition of the behavior controls. Experimental results based on sonar and vision signals are given to show that the method had good real-time response and adaptability, and was robust in dynamic environments. >