Showing papers by "University of Science and Technology of China published in 1993"
TL;DR: In this article, the uplift history of eclogite in the Dabie Mountains can be subdivided into two stages: (1) fast uplift driven by thrust during continental-continental collision and deep subduction (at 221 Ma) of the continental crust; (2) later gentle uplift with rise of the Dabbie Mountains in the late Jurassic and Cretaceous (at 134 Ma).
987 citations
TL;DR: In this paper, a method of preparing coprecipitated powder precursors of ZnO-SnO 2 complex oxide by using oxalic acid and ammonia as precipitants was developed.
Abstract: In this paper, the authors have developed a method of preparing coprecipitated powder precursors of ZnO-SnO 2 complex oxide by using oxalic acid and ammonia as precipitants. The phase constituents, structure and average grain sizes of powder precursors calcined at 500–1000 °C have been studied by means of XRD and TEM, which have an obvious influence on the conductance-temperature (ω- T ) characteristics and gas-sensing properties. It is advantageous for the powder calcined at lower temperatures (500, 600 and 700 °C) to detect combustible gases. The perovskite type of ZnSnO 3 is the dominant phase in the powder calcined at 600 °C; it has a much better sensitivity and selectivity to C 2 H 5 OH gas than anti-spinel type Zn 2 SnO 4 , ZnO and SnO 2 . Therefore, it is reasonable to expect the appearance of a good alcohol sensor by using a ZnSnO 3 -based material with suitable additives.
95 citations
TL;DR: In this article, the formation of cogenetic silica-undersaturated and silica saturated felsic rocks in alkaline igneous complexes has been a long-standing enigma because of constraints imposed by phase equilibrium relationships.
90 citations
TL;DR: It is shown that components of the free energy change can be highly sensitive to the computational details of the simulation leading to the conclusion that free energy calculations cannot currently be used to reliably predict protein stability.
Abstract: The use of free energy simulation techniques in the study of protein stability is critically evaluated. Results from two simulations of the thermostability mutation Asn218 to Ser218 in Subtilisin are presented. It is shown that components of the free energy change can be highly sensitive to the computational details of the simulation leading to the conclusion that free energy calculations cannot currently be used to reliably predict protein stability. The different factors that undermine the reliability are discussed.
83 citations
TL;DR: Results from the power spectrum and Lyapunov exponents quantitatively confirm the transition to chaos through quasiperiodicity in an undriven discharge plasma.
Abstract: The quasiperiodic transition to chaos in an undriven discharge plasma has been investigated. Results from the power spectrum and Lyapunov exponents quantitatively confirm the transition to chaos through quasiperiodicity. A low-dimension strange attractor has been found for this kind of plasma chaos.
77 citations
TL;DR: The kinetic characteristics and reaction conditions of photocross-linking of low-density polyethylene (LDPE) in the melt have been studied using benzophenone and its derivatives such as 4-chlorobenzophenone (4-CBP) as photoinitiator and triallyl cyanurate (TAC) as crosslinker as discussed by the authors.
Abstract: The kinetic characteristics and the reaction conditions of photocross-linking of low-density polyethylene (LDPE) in the melt have been studied using benzophenone (BP) and its derivatives such as 4-chlorobenzophenone (4-CBP) as photoinitiator and triallyl cyanurate (TAC) as cross-linker. The efficiency of the photoinitiated cross-linking system LDPEBP-TAC and various factors affecting the cross-linking process, such as photoinitiator and cross-linker and their concentrations, irradiation time, temperature, and atmosphere, and UV light intensity were examined extensively by determining gel content, IR, and UV spectra. It has been found (i) that LDPE samples of 2–3 mm thickness are easily cross-linked to a gel content of about 70% with a UV-irradiation time of about 15 s under optimum conditions; (ii) that the photoinitiating system of a suitable initiator combined with a multifunctional cross-linker such as 4-CBP–TAC can enhance the efficiency of photocross-linking reactions, especially by increasing the initial rate of cross-linking; (iii) that photocross-linking of LDPE should be carried out in the melt, which increases the penetration of UV light by decreasing the scattering by crystallites, and (iv) that the rate of cross-linking is proportional to the square of the light intensity. An increase in light intensity can decrease the concentration of photoinitiator required to reach a certain rate of cross-linking. The photocross-linking of polyethylene is promising for industrial applications. © 1993 John Wiley & Sons, Inc.
65 citations
TL;DR: The γ-radiation combined with hydrothermal treatment method has been successfully used to prepare pure nanocrystalline silver powders from silver nitrate aqueous solutions Electron microscopy and X-ray powder diffraction techniques show that the average particle size of the prepared silver powder is about 8 nm.
64 citations
TL;DR: In this article, a (2+1)-dimensional breaking soliton equation is constructed via the infinitesimal version of the "dressing" method, which is proved to constitute an infinite-dimensional Lie algebra which contains some Abelian and Virasoro subalgebras.
Abstract: Infinitely many symmetries for a (2+1)-dimensional breaking soliton equation are constructed via the infinitesimal version of the 'dressing' method. These symmetries are proved to constitute an infinite-dimensional Lie algebra which contains some Abelian and Virasoro subalgebras. The hierarchies of equations generated by these symmetries are also considered: these hierarchies of equations are proved to be associated with the isospectral and non-isospectral deformations of the AKNS spectral problem.
53 citations
TL;DR: In this paper, it was shown that the copositivity of a symmetric matrix of order n is equivalent to the coposiability of two symmetric matrices of order 1 if the matrix has a row whose off-diagonal elements are all nonpositive.
47 citations
15 Jun 1993
TL;DR: The problem of scale is solved, and the system is made more practical, so that it can locate unknown human faces spanning a wide range of sizes in a complex black-white picture.
Abstract: A new method to locate human faces in a complex background is proposed. This system utilizes a hierarchical knowledge-based method and consists of three levels. The higher two levels are based on mosaic images at different resolutions. In the lower level, an improved edge detection method is proposed. The problem of scale is solved, and the system is made more practical, so that it can locate unknown human faces spanning a wide range of sizes in a complex black-white picture. >
46 citations
TL;DR: In this article, the infrared spectra of both nano-Al 2 O 3 bulk and nano-al 2 o 3 powders with different original particle diameters were measured after heat treatment at different temperatures for 4 h.
TL;DR: In this paper, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), density, and swelling measurements were used to study the properties of polyethylene photocross-linked in the melt (XLPE).
Abstract: Morphological structure and other properties of polyethylene photocross-linked in the melt (XLPE) have been studied by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), density, and swelling measurements. The WAXD measurements show that the crystallinity of polyethylene decreases with increasing gel content in the XLPE samples and that the regularity and the size of crystals are affected by photocross-linking. DSC data confirm that photocross-linking occurs preferentially in the amorphous and interfacial regions and causes depression of the melting point and decreases the heat of fusion. The density of XLPE apparently decreases with increasing gel content, which is due to decreased crystallinity and lattice expansion. The cross-link density determined by the swelling measurements and evaluated using the Flory–Rehner equation correlates well with the changes in crystallinity and melting point. © 1993 John Wiley & Sons, Inc.
TL;DR: In this paper, the authors search for lepton flavour violation in Z boson decays into lepton pairs using all data collected with the L3 detector during the 1990, 1991 and 1992 runs on an event sample corresponding to 1 500 000 Z's produced.
TL;DR: In this paper, the search for an additional heavy gauge boson Z′ is described, and the models considered are based on either a superstring-motivated E6 or on a left-right symmetry and assume a minimal Higgs sector.
TL;DR: In this article, it was shown that melting incongruency is the main problem encountered in the growth of large and pure-phase single crystals from Bi 2 O 3 -rich melts and that, for x = 0.8, crystals of 2212 phase and 2201 phase coexisting with CuO are obtained from the two segregated parts of the Bi-rich melts.
Abstract: High-quality Bi 2 Sr 2 CaCu 2 O 8 single crystals with dimensions up to 15x4x0.05 mm 3 were grown from the starting composition Bi 2+ x Sr 2 CaCu 2 O y , where x =0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7. Different amounts of Bi 2 O 3 in excess are included in each crystal growth run to act as flux for the growth and the optimum concentrations of the flux amount have been found. Structure characterization of a high-quality 2212 free crystal of 5x1.8x0.02 mm 3 was conducted by the (00 l ), ( h 00) and (0 k 0) X-ray diffractions, using a rotating anode diffractometer, and the back-reflection Laue photograph. It is found that melting incongruency is the main problem encountered in the growth of large and pure-phase single crystals from Bi 2 O 3 -rich melts and we have shown that, for x =0.8, crystals of 2212 phase and crystals of 2201 phase coexisting with CuO are obtained from the two segregated parts of the Bi-rich melts.
01 Nov 1993
TL;DR: In this article, a mixed method consisting of the Pade approximation and the inverse-Pade approximation method is presented for model conversions of a continuous-time (discrete-time) structured uncertain linear system to an equivalent discrete-time structured uncertain model.
Abstract: The paper presents a mixed method consisting of the Pade approximation and the inverse-Pade approximation method for model conversions of a continuous-time (discrete-time) structured uncertain linear system to an equivalent discrete-time (continuous-time) structured uncertain linear model. This allows the use of well-developed theorems and algorithms in the discrete-time (continuous-time) domain to indirectly solve the continuous-time (discrete-time) domain problems. When the ratio of the uncertainties (ΔA, ΔB) to the nominal system parameters (Ao, Bo) and/or the sampling period (T ≤ 2/(∥Ao ∥ + ∥ΔA∥)) are sufficiently small, the linearised uncertain models can be obtained by neglecting the nonlinear uncertain terms, O(T2 ΔA2) and O(T2ΔAΔB), in the state-space models. The comparison of a high-order Pade approximate model with the bilinear approximate model and the Taylor-series approximate model is also presented. Moreover, this paper also presents a method to estimate tighter bounds of discrete-time (continuous-time) structured uncertainties based on the given continuous-time (discrete-time) structured uncertainties.
TL;DR: Measurement of the superconductivity of the Bi 2 Sr 2-x Ba x CuO y samples shows that the appropriate substitution of Ba for Sr can raise the T c of the 2:2:0:1 phase.
Abstract: The microstructure of Bi 2 Sr 2-x Ba x CuO y (0≤x≤0.5) was characterized by transmission-electron microscopy and x-ray diffraction. Electron-diffraction analyses reveal that in the Bi-Sr-Cu-O system there also exists a c=12.5 A insulating phase with commensurate superstructure with the exception of the c=24 A 2:2:0:1 phase. However, with the partial substitution of Ba for Sr in this material, the c∼24 A 2:2:0:1 single phase is obtained, but Ba intercalation reduces the wavelength of modulation of the 2:2:0:1 phase along the b and c directions. Measurement of the superconductivity of the Bi 2 Sr 2-x Ba x CuO y samples shows that the appropriate substitution of Ba for Sr (x≤0.2) can raise the T c of the 2:2:0:1 phase
TL;DR: In this paper, a measurement of R b = Γ b b Γ had from Z → q q events at LEP is reported, which is based on a multidimensional analysis using a neural network approach.
TL;DR: In this article, the authors report on inclusive xc production in Z decays reconstructed via the decay mode Xc → J + γ using 1.1 million hadronic Z events and obtain a branching ratio Br(Z→ Xcl + X) = (7.5±2.9(stat.) ± 0.6(sys.)) × 10−3.
TL;DR: In this paper, the authors studied the antisymmetric resonant vibrational Raman scattering using time-reversal symmetry and showed that for even-electron systems with the ground and the excited vibronic states belonging to real representations, the transition polarizability is strictly zero due to time reversal symmetry.
TL;DR: In this paper, it was shown that the state S(ξ)H p,q (μa 1, μa 2 )|00〉, where H p, q (x, y ) is a two-variable Hermite polynomial, is a minimum uncertainty state for sum squeezing.
TL;DR: An algorithm is derived for determining a set of perturbation polynomials which have the guaranteed minimum norm for all possible such perturbations over a prescribed parameter interval and is applied to the problem of approximately reducing the degree of a rational curve.
Abstract: Two or more randomly chosen polynomials rarely have a common factor. The paper examines how a given set of polynomials can be perturbed so as to induce a linear common factor. An algorithm is derived for determining such a set of perturbation polynomials which have the guaranteed minimum norm for all possible such perturbations over a prescribed parameter interval. This result is applied to the problem of approximately reducing the degree of a rational curve.
TL;DR: In this article, the authors showed that the ductility of epoxy increases with increasing strain rate in the range of 200-600 s -1 under tensile impact, and that the failure envelope of some elastomers is as shown in Fig. 1.
Abstract: where ~ is proportional to the loading speed, U is the activation energy, cr is the strength, V~ is the free volume, A and k are a material constant and Boltzmann's constant, respectively, and T is the absolute temperature. Hence, an increase of ~, means an increase in strength. However, Kawata et al. [1] discovered that woven glass fibre-reinforced epoxy is high-velocity ductile under tensile impact. The strain rate of his tests was <1000 s -1 . Xia et al. [2] pointed out that the ductility of epoxy increases with increasing strain rate in the range of 200-600 s -1 under tensile impact also. Smith and Stedry [3] predicted that the failure envelope of some elastomers is as shown in Fig. 1. Obviously, in Fig. 1 the ductility increases as the strain rate increases under higher rate, however, brittleness occurs when the strain rate keep up the raise. Therefore, a brittle-ductile transition exists from static loading to higher-rate loading, and another ductile-brittle transition exists from higher to very high rate loading. The former was observed by Kawata et al. [1] for woven glass fibre/epoxy and by
TL;DR: In this paper, an accurate dating of recent Ionian Sea sediment cores has been performed by the210Pb radiometric method and by a detailed tephroanalysis, which demonstrates that the sedimentation rate estimated by the 210Pb method is correct and it is constant, at least for the last 2 ky.
Abstract: An accurate dating of recent Ionian Sea sediment cores has been performed by the210Pb radiometric method and by a detailed tephroanalysis. The markers of the historical volcanic eruptions which occurred in the Campanian area (Vesuvius, Phlegrean Fields, Ischia) during the last two millenia have been identified along the cores. Among the others, the famous Plinian Vesuvius eruption of 79 AD, which buried the Roman town of Pompei, has been recognized. Direct210Pb dating is limited to the last two centuries. The tephroanalysis demonstrates that the sedimentation rate estimated by the210Pb method is correct and it is constant, at least for the last 2 ky. The presence of the137Cs peak due to the intense activity of nuclear-weapon testing in the atmosphere in 1963–64 AD assures that the top of the core is present and not disturbed. The high precision of the core dating allows to transform the depth scale into a time scale with an accuracy of ∼1%. The analysis of several cores taken in the same area demonstrates that the results presented here are of general validity, at least in this region. The carbonatic mud deposited in the last millennia in the Gallipoli Terrace can be successfully utilized for investigating the environmental conditions in the recent past.
TL;DR: In this paper, it was found that spherulites could form from the melt by quenching the polyurethanes in the melt state to annealing temperatures between 120°C and 170°C.
Abstract: Small-angle light-scattering (SALS), Polarized light microscopy (PLM), differntial scanning calorimetry (DSC), and small-angle x-ray scattering (SAXS) were used to study morphological changes in segmented polyurethanes with 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) as the hard segment. It was found. for the first time, that spherulites could form from the melt by quenching the polyurethanes in the melt state to annealing temperatures between 120°C and Th, the highest annealing temperature for spherulite formation. Th ranged from 140°C to ca. 170°C and depended upon the hard-and soft-segment compatibility. Within the range 120°C to Th, the radius of the spherulite increased with increasing hard-segment content at each fixed annealing temperature. Annealing at 135–140°C gave rise to the largest spherulites. SAXS was used to investigate the phase-separated structures corresponding to the spherulite formation. The interdomain spacing increased with increasing hard-segment content and with increasing annealing temperature.The degree of phase separation first increased with increasing annealing temperature from room temperatures (ca. 25°C), reached a maximum at ca. 107°C, and then decreased with further increase in the annealing temperature. On the basis of these observations, the mechanisms of phase separation, crystallization, and spherulite formation are discussed. © 1993 John Wiley & Sons, Inc.
TL;DR: The calculated results show that all the clusters have metallic character, and that the clusters with M being Ti, Mn, or Co have closed electronic shells while the others have open electronic shells and are expected to distort further.
Abstract: The stability, electronic and magnetic properties, and reactivity of icosahedral M${\mathrm{Co}}_{12}$ clusters are studied using the discrete variational local-spin-density-functional method, where M=Ti, V, Cr, Mn, Fe, Co, and Ni. By means of the binding-energy calculation, we obtained the M-Co bond length of the clusters and compared their relative stability. We calculated the electronic structure of the clusters in their equilibrium configurations. The calculated results show that all the clusters have metallic character, and that the clusters with M being Ti, Mn, or Co have closed electronic shells while the others have open electronic shells and are expected to distort further. The results also indicate that the cluster moment is reduced by the substitution of the central Co atom with an M atom, and that the average moment per atom of all clusters is larger than that of the bulk Co. Based on the results of electronic structures, we further analyzed the reactivity of the clusters toward ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, and CO molecules and found a strong dependence on the central M atom. Our results compare well with the available experimental results.
TL;DR: In this paper, the rate constants of quenching of CH(A 2 Δ) by CHBr 3 and CH(B 2 Σ − ) by NO, CH 3 ) 2 NH, (C 2 H 5 ) 2 and (CH 3 ) 3 N were measured by using a direct time-resolved technique at 290 K.
TL;DR: In this article, the kinetics of the forward and backward 3 F 4 (Tm)↔ 5 I 7 (Ho) energy transfers in the Gd 3 Ga 5 O 12 (Ca, Zr) garnet are described using the fluorescence "transfer function" method.
TL;DR: In this article, the authors consider ann-dimensional compact minimal submanifolds of a unit sphere and show that if S ≥ 2/3n everywhere on M, then M must be either geodesic or a Veronese surface.
Abstract: LetM be ann-dimensional compact minimal submanifold of a unit sphereS
n+p
(p≥2); and letS be a square of the length of the second fundamental form. IfS≤2/3n everywhere onM, thenM must be totally geodesic or a Veronese surface.
TL;DR: In this article, a non-linear fitting is used to determine AD, from which ESR ages were calculated by both the disequilibria model (DU) and linear uptake model (LU).