查看更多>>摘要：The available studies in the literature on physical and mathematical modeling of the argon-oxygen decarburization (AOD) process of stainless steel have briefly been reviewed. The latest advances made by the author with his research group have been summarized. Water modeling was used to investigate the fluid flow and mixing characteristics in the bath- of an 18 t AOD vessel, as well as the "back-attack" action of gas jets and its effects on the erosion and wear of the refractory lining, with sufficiently full kinematic similarity. The non- rotating and rotating gas jets blown through two annular tuyeres, respectively of straight- tube and spiral-flat tube type, were employed in the experiments. The geometric similarity ratio between the model and its prototype (including the straight-tube type tuyeres) was 1:3. The influences of the gas flow rate, the angle included between the two tuyeres and other operating parameters, and the suitability of the spiral tuyere as a practical application, were examined. These latest studies have clearly and successfully brought to light the fluid flow and mixing characteristics in the bath and the overall features of the back-attack phenomena of gas jets during the blowing, and haye offered a better understanding of the refining process. Besides, mathematical modeling for the refining process of stainless steel was carried but and a new mathematical model of the process was proposed and developed. The model performs the rate calculations of the refining and the mass and heat balances of the system. Also, the effects of the operating factors, including adding the slag materials, crop ends, and -scrap, and alloy agents; the non-isothermal conditions; the changes in the amounts of metal and slag during the refining; and other factors were all considered. The model was used to deal with and analyze the austenitic stainless steel making (including ultra-low carbon steel) and was tested on data of 32 heats obtained in producing 304 grade steel in an 18 t AOD vessel. The changes in the bath composition and temperature during the refining process with time can be accurately predicted using this model. The model can provide some very useful information and a reliable basis for optimizing the process practice of the refining of stainless steel and control of the process in real-time and online.
查看更多>>摘要：The mechanism and criterion of crack initiation and propagation of rocks were investigated by many researchers. And the creep behaviour of rocks was also theoretically and experimentally studied by some scientists and engineers. The characteristics of crack initiation and propagation of rocks under creep condition, however, are very important for rock engineering and still not paid enough attention by researchers. In this paper, the criterion and mechanism of crack initiation and propagation under creep condition were investigated using specimens collected from sandstone rock formations outcropping in the Emei Mountain, the Sichuan Province of China. Cuboid specimens under three point bending were used in this investigation. All specimens were classified into four sorts and used for Mode-Ⅰ fracture or creep fracture tests. The experimental result shows that due to creep deformation, rock crack will inevitably initiate and propagate under a load of K_I, which is less than fracture toughness K_(IC) but not less than a constant (marked as K_(IC2)). K_(IC2) indicates the ability of rock to resist crack initiation and propagation under creep conditions and is less than fracture toughness K_(IC), defined as creep fracture toughness in this paper. K_(IC2) should be considered as an important parameter on design and computation of rock engineering. The microstructural mechanism for crack initiation and propagation of rock materials under creep condition was introduced based on competitive model between softening effect and hardening effect, and the validity of test result was explained. The test result was also verified in rheological theory. When K_I is more than K_(IC2) but less than K_(IC), rock crack will initiate and propagate after a time interval of sustained loading under creep condition. In order to find the relation between duration of sustained loading, which can lead to crack initiation and propagation, and the initial stress intensity factor K_I, an unequal-interval time sequence forecasting and predicting model was introduced, and the relation was obtained for homogeneous and isotropic fine-grained red sandstone. Finally a modified fracture toughness formula was given, in which the influence of fracture process zone(FPZ) was fully considered.
查看更多>>摘要：This paper concentrated on the effect of azimuthal variation of section shape on the instability of a cylindrical jet. A single fluid model under certain assumptions was constructed. The characteristic relation between frequency and wave number is obtained using the normal-mode method. The effect of some parameters on the stability was examined and some phenomena in experiments were explained.
查看更多>>摘要：In this paper, the intrinsic behavior of rotating Euler-Benoulli flexible shafts was studied due to coupled bending and tor-sional vibrations. The equations of motion of the shaft with unbalanced eccentricity and viscous material damping were derived by the Hamilton principle. The numerical solution was obtained using the perturbation approach and mode-assuming method. The influences of the coupled vibrations between the bending and torsion, the rotating speed, material damping and the slenderness ratio of the shaft were analyzed. It is clearly shown that the beating phenomena can occur when the interaction of torsion and flexure is considered.
查看更多>>摘要：Up-conversion processes for the blue, green and red emissions were found two-photon phenomenon, known as the cooperative phenomenon. This phenomenon was assisted by Nd~(3+) → Yb~(3+) → Ho~(3+) energy transfer. The strong green emission due to the Ho~(3+) : (~5F_4, ~5S_2) → ~5I_8 transitions was observed in Nd~(3+) - Ho~(3+) co-doped ZrF_4-based fluoride glasses under 800 nm excitation. As an attempt to enhance Ho~(3+) up-conversion luminescences in the Nd~(3+) - Ho~(3+) co-doped ZrF_4-based glasses, Yb~(3+) ions were added to the glasses. As a result it was found that, in 800 nm excitation of 60ZrF_4. 30BaF2. (8-x)LaF_3. 1NdF_3. xYbF_3. 1HoF_3 glasses (x = 0 to 7), sensitized up-conversion luminescences are observed at around 490 nm (blue), 545 nm (green), and 650 nm (red), which correspond to the Ho~(3+) : ~5F_3 → ~5I_8, ( ~5F_4, ~5S_2) → ~5I_8 and ~5F_5 → ~5I_8 transitions respectively. The intensities of the green and red emissions in a 3 mol% YbF_3-containing glass were about 50 times stronger than those glasses without YbF_3. This is based on sensitization due to Yb~(3+) ions. In particular, the green emission was extremely strong and the Nd~(3+) - Yb~(3+) - Ho~(3+) co-doped ZrF_4-based glasses have a high possibility of realizing a green up-conversion laser glass. In this paper the up-conversion mechanism in the glasses is discussed in detail.
查看更多>>摘要：Oscillations of the spin-polarized conductance controlled by a uniform magnetic field in a modified Aharonov-Bohm ring is studied with use of one-dimensional quantum wave guide. Its expression at zero temperature is obtained as a function of the flux penetrating the ring and the magnetic field. It has been found that there are two kinds of polarized conductance extremas for a given Fermi energy. As Zeemann energy of spin-polarized electron in the stub is varied, one kind of extrema exhibits continuous phase shift. However, another is locked at particular values of phase shift and it can only change abruptly from a maxima to a minima when Zeemann crosses the level of the bound state of isolated stub. This is a different mehanism for abrupt change phase of conductance osillations.
查看更多>>摘要：This paper proposes a modified shape coding algorithm called modified vertex-based shape coding (MVBSC) to encode the boundary of a visual object compactly by using a modified polygonal approximation approach which uses modified curvature scale space (CSS) theory to extract feature-points.
查看更多>>摘要：The effect of queuing delay of output buffer on the crosstalk property in optical packet switching nodes is investigated. The relationship between crosstalk and buffer length is obtained. From the calculation and simulation results, it is concluded that the crosstalk power penalty predominantly depends on the buffer length, the longer the buffer, the greater the penalty, as well as the random range of the penalty. While comparing with the effect of queuing delay, the effect of random routing path delay takes very little proportion in the total power penalty.
查看更多>>摘要：This paper introduces a family of error-correcting codes called zigzag codes. A zigzag code is described by a highly structured zigzag graph. Due to the structural properties of the graph, very low-complexity soft-in, soft-out decoding rules can be implemented. We present a decoding rule, based on the Max-Log-APP(MLA) formulation, which requires a total of only 20 addition-equivalent-operations per information bit per iteration. Simulation of a rate-1/2 concatenated zigzag code with four constituent encoders with interleaver length 65536 yields a bit error rate (BER) and of 10~(-5) at 0.9 dB and 1.4 dB away from the Shannon limit by optimal (APP) and low-cost sub-optimal (MLA) decoders, respectively.
查看更多>>摘要：A realization of three phase to three phase matrix electric power converter (33MC) with practicality is depicted, which is characteristic of modular configuration, simple and safe semi-natural semi-forced two-step commutation strategy, general over-current protection circuit, flexible generalized switching functions, combined bilateral power switches, and so on. A new approach to manufacturing-oriented 33MC comes forth, which is composed of 3 modular three phase to single phase non-square matrix electric power converters (31MC).
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