[en] In this paper, sufficient conditions have been obtained for oscillation and non-oscillation of solutions of first order differential equations with piecewise constant deviating arguments. These equations occur in mathematical models of certain biomedical problems. (author)

[en] In this study, intermetallic TiAl and steel are diffusion bonded successfully by using composite barrier layers of titanium/vanadium/copper. The relationship of the bond parameters and tensile strength of the joints is discussed, and the optimum bond parameters were obtained. The reaction products and the interface structures of the joints were investigated by SEM, EPMA, and XRD. In this case, a dual phase Ti₃Al+TiAl layer and a Ti solid solution, which enhances the strength of the joint, are obtained at the TiAl/Ti interface. A formation mechanism at the interface of TiAl/Ti was proposed. The whole reaction process can be divided into three stages. In the first stage, Ti (Al_ss) layer is formed at the interface TiAl/titanium. In the second stage, the continuous diffusion of Al atoms from TiAl to titanium leads to the formation of Ti₃Al, a TiAl+Ti₃Al layer is formed adjacent to TiAl. In the last stage, the thickness of each reaction layer increases with bonding time according to a parabolic law. The interface of TiAl/titanium/vanadium/copper/steel was free from intermetallic compounds and other brittle phases, and the strength of the joint was as high as 420 MPa, very close to that of the TiAl base. This method provides a reliable bonding method of intermetallic TiAl and steel

[en] Diffusion bonding of TiAl-based alloy to steel was carried out at 850-1100 deg. C for 1-60 min under a pressure of 5-40 MPa in this paper. The relationship of the bond parameters and tensile strength of the joints was discussed, and the optimum bond parameters were obtained. When products are diffusion-bonded, the optimum bond parameters are as follows: bonding temperature is 930-960 deg. C, bonding pressure is 20-25 MPa, bonding time is 5-6 min. The maximum tensile strength of the joint is 170-185 MPa. The reaction products and the interface structures of the joints were investigated by scanning electron microscopy (SEM), electron probe X-ray microanalysis (EPMA) and X-ray diffraction (XRD). Three kinds of reaction products were observed to have formed during the diffusion bonding of TiAl-based alloy to steel, namely Ti₃Al+FeAl+FeAl₂ intermetallic compounds formed close to the TiAl-based alloy. A decarbonised layer formed close to the steel and a face-centered cubic TiC formed in the middle. The interface structure of diffusion-bonded TiAl/steel joints is TiAl/Ti₃Al+FeAl+FeAl₂/TiC/decarbonised layer/steel, and this structure will not change with bond time once it forms. The formation of the intermetallic compounds results in the embrittlement of the joint and poor joint properties. The thickness of each reaction layer increases with bonding time according to a parabolic law. The activation energy Q and the growth velocity K₀ of the reacting layer Ti₃Al+FeAl+FeAl₂+TiC in the diffusion-bonded joints of TiAl base alloy to steel are 203 kJ/mol and 6.07 mm²/s, respectively. Careful control of the growth of the reacting layer Ti₃Al+FeAl+FeAl₂+TiC can influence the final joint strength

[en] The author presents the threefold massive events produced in 25-A-MeV ⁴⁰Ar + ¹¹⁵In, ¹⁰³Rh and ⁹³Nb reactions. In these massive events the fragments emitted with angles larger than 36 degree were detected by ten parallel-plate, position-sensitive avalanche counters, each with a detection area of 25 x 20 cm². For these events total kinetic energies (TKE), a yield ratio of threefold fragmentation (3-F) to fission P₃₂, several distributions in fragment mass, velocity, relative angle among them, and so on, were obtained. From the ratio of each fragment mass to the mass of the compound nucleus in the threefold massive events, a simple empirical expression could roughly reproduce it. Using a simple space-time model to fit the relative angular correlations, the time difference between the two scission points in the threefold mass splitting process for the Ar + In system was derived. A systematics of P₃₂ versus Z²/A for hot nuclei was performed

[en] Results of three- and four-fold fragmentation of hot nuclei produced in 25 MeV/nucleon ⁴⁰Ar + ²⁰⁹Bi, ¹⁹⁷Au and ¹⁵⁹Tb reactions are presented. The events with 3 or 4 massive fragments emitted with angles larger than 36 deg were detected by eight PPACs. For these events the total kinetic energy, ratio of 3-fold over fission P₃₂, distributions of mass, velocity, relative angle and so on were obtained. From the relative angular distributions of 3-fold fragmentation events by analyzing their angular correlation function with in a simple model, the time difference between the two scission times were derived. (authors). 14 refs., 12 figs., 5 tabs

[en] The first three-fold and four-fold fragmentation measurements in hot compound nuclei produced in the reactions of a 25 MeV/u ⁴⁰Ar beam with targets of ²⁰⁹Bi, ¹⁹⁷Au, ¹⁵⁹Tb, ¹¹⁵In, ¹⁰³Rh, and ⁹³Nb are presented. Various distributions are measured for these fragments, including distributions of velocities, relative velocities, angles, relative angles, masses, fragment mass ratios, total kinetic energies (TKE), as well as the yield ratios of three-fold fragmentation to fission P₃₂ and the time difference Δt between two scissions after the formation of one compound nucleus

[en] Highlights: •The NbSi₂ coatings were treated by electron beam remelting process. •After EB treatment, the amount of porosity and cracks of the coatings were reduced, and the grain was finer. •With the EB voltage increasing, the residual stress state of the coatings is first tensile and then turns to be compressive. •The increase for hardness of the coatings mainly comes from the presence of residual stress and Nb₅Si₃ phase. -- Abstract: NbSi₂ coatings were prepared on niobium alloy surface by a fused slurry method. Electron beam remelting process is explored to modify the morphology and the phase composition of the coated layer. After electron beam treatment, the amount of porosity and cracks of the coatings are reduced, and the grain is finer. With accelerating voltage of the electron beam increasing, Nb₅Si₃ phase can be detected in the NbSi₂ coatings. The results of residual stress and surface hardness provide a good evidence to explain the microstructure evolution and surface modification of the coatings

[en] The paper presents the 4-fold fission or fragmentation of hot nuclei produced in 25MeV/u ⁴⁰Ar+²⁰⁹Bi, ¹⁹⁷Au and ¹⁵⁹Tb reactions. The events with 4 massive fragments emitted with angles larger than 36 were detected by 8 PPACs with area of 25x20cm². The TKE, distributions of mass and velocity for the four fragments have been obtained. ((orig.))

[en] The inclusive reduced velocity correlation functions of the intermediate mass fragments were measured in the reactions of ³⁶Ar + ^112,124Sn at 35 MeV/u. The anti-correlation is observed to be stronger in ³⁶Ar + ¹²⁴Sn system than that in ³⁶Ar + ¹¹²Sn. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three body Coulomb repulsive trajectory model is employed to calculate the emission time scale of the IMFs for the two systems. The time scale is 150 fm/c in ³⁶Ar + ¹¹²Sn and 120 fm/c in the ³⁶Ar + ¹²⁴Sn, respectively