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Engineering Engineering Physics ANKARA 06100 BESEVL TURKEY Temperature and field dependence of the magnetic behavior of magnetic moments of the rare earth and Mn sublattices of RMn2Ge2, where R is a rare earth element, leads to a variety of interesting magnetic properties. These compounds crytallise in the tetragonal ThCr2Si2 type crystal structure with space group I4/mmm which consist of layers along the c-axis with sequence RGe-Mn-Ge-R. When light rare-earth elements ( Pr, La, Ce or Nd) use in title compounds, the interlayer magnetic coupling in the Mn sublattice is ferromagnetic, whereas it is antiferromagnetic in the case of Gd, Tb or Dy. At low temperatures, the rare earth sublattice also orders and reconfigures the ordering in the Mn sublattice. In this study, crystal structure and magnetic properties of Pr1-xTbxMn2Ge2 compounds were investigated by X-ray diffraction and magnetic measurements. The results of earlier neutron diffraction and Mössbauer studies on samples with x = 0 and x = 1 are also used for interpreting the magnetization data and to give an account on the competing effects between various magnetic structures in the Mn and rare earth sublattices. In low field, we have observed that, temperature dependence of zero field cooled and field cooled magnetizations shows large difference at the Curie temperature of Mn sublattices (TC). This behavior is related to pinnnig of the ferromagnetic components of Mn sublattices and proved that there is an antiferromagnetic ordering of Mn sublattices with Neel temperature TN > TC,which has been observed only by using neutron diffraction techniques. Ingots of several compositions of the Cu(In1-xGax) ~Te5 semiconducting system were prepared by the Bridgman technique in a multi-zone vertical furnace. Xray powder diffraction and optical studies allowed to characterize the fundamental structural aspects and determine the energy band gap Eg. of these materials. The structural study carried out using powder diffraction data collected with a SIEMENS D-5005 diffractomer indicates that a solid solution is formed over the entire range of composition. The parameters a and c of the tetragonal chalcopyrite-related unit cell obtained vary from 6.1639(3) and 12.346(2) Å for x = 0 to 5.9321(8) Å and 11.825(4) Å for x =1, respectively. The variation of the energy band gap with composition is linear, contrary to the quadratic relation of the form Eg = a + bx + cx 2 observed in the Cu(In1-xGax) ~Se5 semiconducting system. This work was supported by grants from CONICIT and CDCHT-ULA. Crystal structure of Sr2YCu2FeO6+δ and Sr2YCu2CoO6+δ has been analyzed using neutron powder diffraction. These compounds consist of nanometer-scale sequence of alternating double CuO2 sheets as those in high-Tc superconductors, and (Fe,Co)Oδ sheet similar to that in the Sr(Fe,Co)O3-δ magnetic compound with brownmillerite-type structure. Sr2YCu2FeO6+δ exhibits superconductivity around 50 K when it is annealed under N2 atmosphere and subsequently under O2 atmosphere, while Sr2YCu2CoO6+δ with the same ...

This paper reports on an extensive tank test program performed on a modal representative of a typical modern semisubmersible drilling vessel. Specific response values obtained in this study apply only to the configuration_and mass c~ar acteristics of the model tested. However, the general conclusion of the study is that wave steepness effects can be important, and this finding is of significance for all sucn configurations to be certified for operation in severe seas. Distinct nonlinearities were found at drafts of 70, 60, and 50 ft. There were test conditions where the heave response ratio was substantially linear, but at other conditions the nonlinearity ranged from moderate to severe. In general, the nonlinearities were more severe at the shallower draft.References and illustrations at end of paper.

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