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Different types of protective equipment for human lower limb, such as boots and gaiters, have been developed in order to reduce the injury caused by blast antipersonnel-mines. Damage is mainly studied by the energy transmitted to the extremity that has stepped on the mine; nonetheless, side effects that may affect adjacent limbs cannot be left aside. This study is divided into three stages due to the complexity in modeling the different phenomena related to the problem. The first stage is the study of the energy transmitted when a mine is activated. Different results are gathered according to the variation of parameters such as: deep of burial, standoff between ground and protective equipment, explosive mass, energy absorbing material placed between the ground and the protected limb, and computational issues like the distance of the boundary conditions and the discretization level. The second stage is the base and first approximation to the modeling and evaluation of lower limb behavior. It includes the interaction of the detonation products and a lower limb that is placed in a mechanical measuring device. The energy transferred to the mechanical device is correlated to the damage caused by the explosion products in an attempt to validate previously experimental data. Finally, in the third stage, the side effect on the lower contiguous leg is assessed: pressure and temperature measures are taken at different distances according to the human pace in order to evaluate the worst-case scenario. The first and third stages propose different material arrangements or configurations to reduce the energy transmitted to the mechanical device and to mitigate damage caused to the contiguous limb respectively. All the three stages are simulated using two-dimensional (2D) hydrocode Ansys AUTODYN ® and material previously reported in literature.

Oxygen-stoichiometric La0.5Sr0.5M0.5Ti0.5O3 (M = Mn, Fe) perovskites and the corresponding reduced specimens, of La0.5Sr0.5M0.5Ti0.5O3-δ composition, have been prepared and characterized by x-ray diffraction and neutron powder diffraction (NPD), in complement with thermal analysis, electrical conductivity, and thermal expansion measurements. NPD data show that these perovskites are all orthorhombic, space group Pbnm (No. 62). The total reduction of M3+ to M2+ in the reduced phases is accompanied with the occurrence of oxygen vacancies, which was confirmed by thermogravimetric analysis (TGA). Above room-temperature, these phases undergo two structural phase transitions studied in situ from NPD data; the former to a tetragonal (I4/mcm) structure, and the second one to a cubic (Pm-3m) phase. All the oxides display a semiconductor-like behavior with a maximum conductivity value of 15 S·cm-1 for the oxidized La0.5Sr0.5Mn0.5Ti0.5O3 phase at 850 °C. The measured thermal expansion coefficients perfectly match with the values usually displayed by solid-oxide fuel cell (SOFC) electrolytes. The obtained results present these perovskites as alternative electrodes for SOFCs. [ABSTRACT FROM AUTHOR]

The oxygen-deficient Sr2CoMoO6-δ double perovskite has been proposed as an anode material in solid-oxide fuel cells (SOFC). The evolution of its crystal structure has been followed by 'in situ' temperature-dependent neutron powder diffraction from 23 °C (RT) to 867 °C in the heating and cooling runs in ultrahigh vacuum (PO2≈10-6 Torr) in order to simulate the reducing atmosphere corresponding to the working conditions of an anode in a SOFC. At RT the sample is described as tetragonal in the I4/m space group. When this oxide is heated above Tt=262 °C it undergoes a tetragonal I4/m to cubic Fm-3m phase transition. This phase transition takes place at a temperature around 25 °C lower than that previously described for the oxidized sample, and it is affected by a significant hysteresis (Tt=174 °C in the cooling run). The absence of tilting of the CoO6 and MoO6 octahedra in the high-temperature cubic phase favors the orbital overlap and the electronic conductivity; a high mobility of the oxygen atoms is derived from the elevated displacement parameters, for instance 3.2 Å2 at 867 °C. Both factors contribute to the excellent performance described for this mixed ionic-electronic conductor (MIEC) oxide as anode in single fuel cells. The dilatometric analysis shows a change of slope at around 270 °C that can be correlated with this tetragonal-to-cubic phase transition. The obtained thermal expansion coefficient (TEC) in the tetragonal region, between 50 and 270 °C is 14.5×10-6 K-1 whereas in the cubic region, between 270 and 850 °C, the TEC is 11.2×10-6 K-1. These figures are comparable to those obtained from the mentioned structural analysis; moreover the TEC for the cubic phase perfectly matches those of the usual electrolytes in a SOFC. [ABSTRACT FROM AUTHOR]

A pyrochlore-like phase of composition Ho2MnRuO7 has been synthesized by a soft-chemistry procedure followed by thermal treatments at moderate temperatures up to 900 °C for 12 h in air. It has been characterized by x-ray diffraction and neutron powder diffraction (NPD), as well as dc and ac susceptibilities. As in the parent Ho2Mn2O7 oxide, the magnetic Mn and Ru ions statistically occupy the 16c sites in a cubic unit cell with space group Fd3m, which define a potentially frustrated three-dimensional array of corner sharing (Mn,Ru)4 tetrahedra. The dc and ac magnetic susceptibilities of Ho2MnRuO7 display a sharp increase near 60 K. In addition, the field-cooled and zero-field-cooled curves diverge below 30 K. The ac data present frequency variability below 60 K and broad frequency dependent maxima at lower temperatures (∼30 K), suggesting a spin-glass like behavior similar to Ho2Mn2O7. However, a low-temperature NPD study of the magnetic structure unveils an antiferromagnetic coupling of two subsets of Mn4+ /Ru4+ spins, indicating that the magnetic frustration is partially relieved by the random distribution of Mn and Ru over the 16c sites; at lower temperatures there is a polarization of the Ho3+ magnetic moments, which also participate in the magnetic structure. Under an external magnetic field the Ho moments become totally polarized, giving a saturation magnetization at 2 K of 10.8 μB/ f.u. at 5 T. [ABSTRACT FROM AUTHOR]