Low temperature magnetic transition in RuSr2EuCeCu2O10 ruthenocuprate

A new magnetic transition in the ruthenocuprate parent compound RuSr2EuCeCu2O10 has been observed below 10 K. It shows up only as a kink in the imaginary part of the ac susceptibility and exhibits a pronounced frequency dependence. At the same time, the real part of the ac susceptibility and the dc magnetization study show very little change in the same temperature window suggesting only a minor fraction of the material to be involved in the transition. Frequency dependence shows excellent agreement with the predictions of the Arrhenius law known to describe well the dynamics of the superparamagnetic particles. The same type of the investigation on the RuSr2Eu1.1Ce0.9Cu2O10 composition showed no evidence of the similar transition, which points to a possible intrinsic behavior.Comment: to be published in Physica

Ni3TeO6 - a collinear antiferromagnet with ferromagnetic honeycomb planes

We report a comprehensive study of magnetic properties of Ni3TeO6. The system crystallizes in a noncentrosymmetric rhombohedral lattice, space group R3. There are three differently coordinated Ni atoms in the unit cell. Two of them form an almost planar honeycomb lattice, while the third one is placed between the layers. Magnetization and specific heat measurements revealed a single magnetic ordering at TN = 52 K. Below TN the susceptibility with the magnetic field parallel to the c-axis drops towards zero while the perpendicular susceptibility remains constant, a characteristic of antiferromagnetic materials. Neutron diffraction confirmed that the system is antiferromagnet below TN with ferromagnetic ab-planes stacked antiferromagnetically along the c-axis. All Ni moments are in the S = 1 spin state and point along the c-axis.Comment: accepted for publication in Journal of Physics Condensed Matte

Thermodynamics of a model for RNA folding

We analyze the thermodynamic properties of a simplified model for folded RNA molecules recently studied by G. Vernizzi, H. Orland, A. Zee (in {\it Phys. Rev. Lett.} {\bf 94} (2005) 168103). The model consists of a chain of one-flavor base molecules with a flexible backbone and all possible pairing interactions equally allowed. The spatial pseudoknot structure of the model can be efficiently studied by introducing a $N \times N$ hermitian random matrix model at each chain site, and associating Feynman diagrams of these models to spatial configurations of the molecules. We obtain an exact expression for the topological expansion of the partition function of the system. We calculate exact and asymptotic expressions for the free energy, specific heat, entanglement and chemical potential and study their behavior as a function of temperature. Our results are consistent with the interpretation of $1/N$ as being a measure of the concentration of $\rm{Mg}^{++}$ in solution.Comment: 11 pages, 4 figure

Patofiziološki aspekti poremećaja metabolizma purina u reumatoidnom artritisu

The aim of the paper is testing the activity of purine metabolism enzyme at patients with rheumatoid arthritis, as well as testing the connection between the severity of clinical manifestation of rheumatoid arthritis and inflammation degree, and the activity of the enzyme which takes part in purine metabolism. The research included 160 patients diagnosed with rheumatoid arthritis (RA), 100 of which had late and 60 early RA, as well as 60 control group patients. Activity of 5’-nucleotidase showed significant connection with late RA. Disease activity in late RA showed mild, but significant negative correlation with AMP deaminase. Early rheumatoid arthritis showed strong and significant inverse correlation between RF values and activities of AMP deaminase (C=-0.89, p<0.05). There was no correlation between sedimentation rate, fibrinogen concentration and number of leucocytes, and RA stage. DАS28 score demonstrated connection with all inflammation markers at patients with late RA. VAS scale of pain showed significant correlation with CRP, while HAQ score showed correlation with CRP and RF. As for patients with early RA, sedimentation rate and CRP values correlated with DАS28 score. Binary regression analysis proved the presence of significant correlation between ADA activity and RA occurrence, as well as between sedimentation rate and RA occurrence. ADA activity was significantly higher at patients who were not treated with methotrexate, as compared to patients who were treated with methotrexate. We recorded increased activity of xanthine oxidase at patients who were not treated with methotrexate and thus concluded that patients with rheumatoid arthritis had significant changes in the activity of enzymes included in purine metabolism, which pointed to their important role in the occurrence and development of rheumatoid arthritis. Purine metabolism disorder and inflammation represent independent factors which have a significant role in pathogenesis and clinical manifestation of rheumatoid arthritis. Methotrexate has a favorable therapeutic effect as it reduces the number of granulocytes, activities of adenosine deaminase and xanthine oxidase at rheumatoid arthritis

Organization of the magnetosphere during substorms

The change in degree of organization of the magnetosphere during substorms is investigated by analyzing various geomagnetic indices, as well as interplanetary magnetic field z-component and solar wind flow speed. We conclude that the magnetosphere self-organizes globally during substorms, but neither the magnetosphere nor the solar wind become more predictable in the course of a substorm. This conclusion is based on analysis of five hundred substorms in the period from 2000 to 2002. A minimal dynamic-stochastic model of the driven magnetosphere that reproduces many statistical features of substorm indices is discussed

Site-selective quantum correlations revealed by magnetic anisotropy in the tetramer system SeCuO3

We present the investigation of a monoclinic compound SeCuO3 using x-ray powder diffraction, magnetization, torque and electron-spin-resonance (ESR). Structurally based analysis suggests that SeCuO3 can be considered as a 3D network of tetramers. The values of intra-tetramer exchange interactions are extracted from the temperature dependence of the susceptibility and amount to ~200 K. The inter-tetramer coupling leads to the development of long-range antiferromagnetic order at TN = 8 K. An unusual temperature dependence of the effective g-tensors is observed, accompanied with a rotation of macroscopic magnetic axes. We explain this unique observation as due to site-selective quantum correlations

Friction stir welding of aluminium alloys - T joints

The paper presents results of research on the possibility of producing T-joints of aluminium alloys without defect by friction stir welding process. Friction stir welding process is applied in welding T-joints of aluminium alloys 5052-H32 and 5754-H111. These relatively new welding tech-nologies produce high quality welded joints, where strength of the joint can reach the strength of the base material. Visual and macrostructural examination and microhard-ness measuring of the welded T-joints are processed

Friction stir welding of aluminium alloys - T joints

The paper presents results of research on the possibility of producing T-joints of aluminium alloys without defect by friction stir welding process. Friction stir welding process is applied in welding T-joints of aluminium alloys 5052-H32 and 5754-H111. These relatively new welding tech-nologies produce high quality welded joints, where strength of the joint can reach the strength of the base material. Visual and macrostructural examination and microhard-ness measuring of the welded T-joints are processed

Ground state order and spin-lattice coupling in tetrahedral spin systems Cu2Te2O5X2

High-resolution ac susceptibility and thermal conductivity measurement on Cu2Te2O5X2(X=Br,Cl) single crystals are reported. For Br-sample, sample dependence prevents to distinguish between possibilities of magnetically ordered and spin-singlet ground states. In Cl-sample a three-dimensional transition at 18.5 K is accompanied by almost isotropic behavior of susceptibility and almost switching behavior of thermal conductivity. Thermal conductivity studies suggest the presence of a tremendous spin-lattice coupling characterizing Cl- but not Br-sample. Below the transition Cl-sample is in a complex magnetic state involving AF order but also the elements consistent with the presence of a gap in the excitation spectrum.Comment: version accepted for publication in Phys.Rev.B-Rapid Communicatio