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The effect of an insulated rail joint (IR J) on the contact stress variation near wheel±rail contact zones was simulated by employing three-dimensional ®nite element models. Three linear elastic IR J materials, i.e. epoxy-®breglass, polytetra¯uoroethylene (PTF E) and N ylon-66, were investigated. Contact elements were used to simu late the interaction between the wheel and rail contact points. N umerical results showed that the presence of IR J might signi®cantly affect the wheel±rail contact stress distrib utions. R esults also indicated that the traditional H ertzian contact theory is no longer available to predict the contact stress distribution around the rail joints.

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The effect of neodymium substitution on the lanthanum site in La 0.7−x Nd x Pb 0.3 MnO 3 perovskite polycrystalline has been systematically studied. The substitution of neodymium for lanthanum causes structure change from rhombohedral to orthorhombic. Ferromagnetism is suppressed as neodymium content increases. The magnetic order changes from a ferromagnetic long-range order with x = 0.0 to a spin-glass nature with x = 0.7. Besides, the ferromagnetic-paramagnetic transition temperature values are lower for the neodymium phases than for the lanthanum ones. Therefore, the introduction of neodymium degrades symmetry of the structure, diminishes the spin-coupling exchange interaction, and results in changes of magnetic properties. This fact is in good agreement with increasing the B value in Bloch's T 3/2 law and decreasing the spin-wave stiffness parameter D in quadratic dispersion relation.

The substitution at the Mn site of various transitional metal elements dramatically modifies the magnetic and electronic properties of the La0.7Pb0.3Mn0.8Me0.2O3 (Me=Ni, Co, and Fe) manganites. The powder x-ray diffraction pattern shows a single-phase rhombohedral distorted perovskite structure with space group R3̄c (No. 167) for all samples. The present article is focused on the effects induced by the partial substitution of Ni, Co, and Fe for the Mn site. The field cooled–zero field cooled curves indicate that the magnetic order is modified from a ferromagnetic long-range spin order for La0.7Pb0.3MnO3 to a spin cluster induced short-range spin order for all the doped compositions. The saturation magnetization, transition temperature, and resistance peak temperature decrease significantly from Ni-doped, Co-doped, to Fe-doped composition. In conclusion, the variation of the magnetic and electronic behaviors is due to the dissimilar 3d electron configuration of the substitutions.

This paper investigates the effects of a free rail end on the contact stress distribution near the rail end by employing elastic-plastic finite element methods. The contact elements were used to simulate the interaction between a wheel and a rail. A plane strain model was used in this study. Variations in contact stress fields at various contact points near the rail end were compared. The availability of the Hertz contact theory in the region near the rail end was also investigated. The numerical results indicated that the contact stress distributions around the rail end are sensitive to the contact distance. The location of the maximum von Mises stress was shifted to the contact surface as the contact point moves close to the rail end. Results also show that the plastic zone size and the von Mises stress are increased gradually and extend to the rail end as the contact point moves near the rail end. A higher stress, larger deflection and serious plastic deformation occurring at the rail end may lead to deterioration and delamination at the rail end.

We present studies of the thermal, magnetic, and electrical transport properties of polycrystalline PrBa 2 Cu 4 O 8 prepared at ambient oxygen pressure. Measurements of the low-temperature specific heat C(T) and magnetic susceptibility (T) show similar results as in PrBa 2 Cu 3 O 7 . An anomaly observed at 17 K in C(T) and d/dT may be due to the antiferromagnetic ordering of the Pr sublattice. The upper limit of the entropy associated with the magnetic ordering is estimated to be 6.6 J/mol K. The free magnetic moment from a simple Curie-Weiss fit is 3.11 B . These similarities in magnetic properties of PrBa 2 Cu 3 O 7 and PrBa 2 Cu 4 O 8 suggest that the magnetic coupling mechanism might be mainly associated with the CuO 2 planes. The resistivity (T) is nearly metallic from 1.5 to 300 K. Comparisons of samples prepared by different methods suggest that the anomaly in resistivity around 200 K may be extrinsic. The behavior of (T) is rather puzzling and cannot be explained simply by a dimensional crossover of charge transport arising from the double CuO chains. Other similarities and differences of the mentioned physical properties between PrBa 2 Cu 4 O 8 and PrBa 2 Cu 3 O 7 are stressed as well.