Electron Spectroscopy and Density-Functional Study of "Ferric Wheel" Molecules

The Li-centered "ferric wheel" molecules with six oxo-bridged iron atoms form molecular crystals. We probed their electronic structure by X-ray photoelectron (XPS) and soft X-ray emission spectroscopy (XES), having calculated in parallel the electronic structure of a single "ferric wheel" molecule from first-principles by tools of the density-functional theory, using, specifically, the Siesta method. The Fe local moments were found to be 4 mu_B, irrespective of their mutual orientation. Neighbouring atoms, primarily oxygen, exhibit a noticeable magnetic polarization, yielding effective spin S=5/2 per iron atom, that can get inverted as a "rigid" one in magnetic transitions. Corresponding energy preferences can be mapped onto the Heisenberg model with effective exchange parameter J of about -80 K.Comment: 8 pages with 3 embedded postscript figures; uses elsart.cls; contribution at the E-MRS 2003 Spring Meeting (Strasbourg, June 2003

The Energetics of Li Off-Centering in K1−x_{1-x}Lix_xTaO3_3; First Principles Calculations

K$_{1-x}$Li$_{x}$TaO$_3$ (KLT) solid solutions exhibit a variety of interesting physical phenomena related to large displacements of Li-ions from ideal perovskite A-site positions. First-principles calculations for KLT supercells were used to investigate these phenomena. Lattice dynamics calculations for KLT exhibit a Li off-centering instability. The energetics of Li-displacements for isolated Li-ions and for Li-Li pairs up to 4th neighbors were calculated. Interactions between nearest neighbor Li-ions, in a Li-Li pair, strongly favor ferroelectric alignment along the pair axis. Such Li-Li pairs can be considered "seeds" for polar nanoclusters in KLT. Electrostriction, local oxygen relaxation, coupling to the KT soft-mode, and interactions with neighboring Li-ions all enhance the polarization from Li off-centering. Calculated hopping barriers for isolated Li-ions and for nearest neighbor Li-Li pairs are in good agreement with Arrhenius fits to experimental dielectric data.Comment: 14 pages including 10 figures. To Physical Review B. Replaced after corrections due to referees' remark

Observation of spontaneous combustion of hydrogen and oxygen in microbubbles

Experimental evidence is presented that combustion can ignite at room temperature spontaneously inside microbubbles filled with mixture of hydrogen and oxygen. We perform water electrolysis in a closed microchamber by voltage pulses of alternating polarity at repetition frequencies 100 kHz to pump the gases rapidly into the electrolyte and produce extreme supersaturation with both gases. After a delay of 300 600 ls, we observe stroboscopically microbubbles of 5 20 lm in diameter that appear in between the electrodes for several microseconds. Each event is accompanied by a pressure jump of 0:1 1 bar that is measured interferometrically. The pressure jumps are attributed to combustion of the gases in the microbubbles

Exchange interactions and magnetic anisotropy in the ``Ni<span class='mathrm'>₄</span>'' magnetic molecule

Postnikov A, Brüger M, Schnack J. Exchange interactions and magnetic anisotropy in the ``Ni&lt;sub&gt;4&lt;/sub&gt;'' magnetic molecule. Phase Transitions. 2005;78(1-3):47-59

Clinical Observation of a Child with Astrocytoma

The article deals with the result of clinical observation of a child with astrocytoma and lesion of subependymal zones of lateral ventricles of the brain and gray tuber

Primary Hemophagocytic Lymphohistiocytosis in a Newborn Child

The article presents the data of clinical observation of hemophagocytic lymphohistiocytosis in newborn child, complicated with spontaneous splenic rupture. Issues of diagnosis according to the recommendations of the International society for the study of histiocytic diseases (Histiocyte Society, 2004)