[en] A simple method for detection of melting event in laser-heated diamond anvil cells (DACs) is introduced. The melting is registered optically by the formation of spherical drops of the investigated material as heated in an inert pressure transmitting medium. Feasibility of the method is demonstrated on the examples of metal (iron and gold) and iron oxide (Fe₂O₃), materials molten at pressures over 40 GPa employing a portable laser heating system. (Author) 25 refs.

[en] Pb₂(AsO₂OH)Cl₂, M_r=609.21, monoclinic, P2₁/m, a=6.410(2), b=5.525(1), c=9.293(3) A, β=90.69(2)deg, V=329.1(2) A³, Z=2, D_x=6.15 Mg m^-3, Mo Kα, λ=0.71073 A, μ=54.9 mm^-1, F(000)=512, room temperature, R(F)=0.044 for 1410 independent reflections with F₀>3 σ F₀ and 47 variables. The As atom is trigonal-pyramidally coordinated by two O atoms and one OH group. From consideration of the nearest neighbours around the Pb atoms, Pb(1)O₄ and Pb(2)O₂Cl pyramids are combined into rows along [010]. The AsO₂OH anion and the hydrogen bridge O-H...Cl are within the same row. These rows are interconnected by additional Pb-O and Pb-Cl bonds. Crystals of the title compound were synthesized under hydrothermal conditions. (orig.)

[en] Melt-powder melt-grown YBa₂Cu₃O₇ samples with different amounts of artificially introduced non-superconducting 211 particles were exposed to fast neutron irradiation up to a fluence of 4 x 10²¹m^-2 (E > 0.1 MeV). The influence of the irradiation on the critical current characteristics and on the irreversibility lines is investigated. Shifts of the irreversibility lines and enhanced critical current densities are observed. The results are compared with similar experiments on high quality single crystals. (author)

[en] Melt-powder melt-grown samples of YBa₂Cu₃O₇ superconductors with different amounts of artificially introduced 211 particles were exposed to fast neutron irradiation up to a fluence of 4 x 10²¹ m^-2 (E> 0.1 MeV). The influence of the irradiation on the critical current characteristics and on the irreversibility lines is investigated. Shifts of the irreversibility lines and enhanced critical current densities are observed. The results are compared with similar experiments on high quality single crystals. (author)

[en] The neuronal uptake and metabolism of 2-fluorodopamine (2F-dopamine), 6-fluorodopamine (6F-dopamine) and tritium-labeled dopamine were compared in heart, submaxillary gland and spleen of rats to assess the utility of 18F-labeled 2F- or 6F-dopamine for positron emission tomographic imaging of sympathetically innervated tissues. Tritiated dopamine with and without 2F- or 6F-dopamine, or tritiated 2F-dopamine alone, were injected i.v. into rats that were or were not pretreated with desipramine to block catecholamine neuronal uptake or with reserpine to block vesicular translocation of catecholamines. Tissue and plasma samples were obtained at intervals up to 1 hr after injections. At 1 hr after injection of tritiated dopamine, tritium-labeled norepinephrine, dopamine, dihydroxyphenylacetic acid and dihydroxyphenylglucol accounted for less than 2% of the tritium in plasma but up to 92% of that in tissues; tritiated norepinephrine accounted for 70% or more of the tritium in tissues. In contrast, at 1 hr after injection of tritiated 2F-dopamine, tritiated 2F-norepinephrine accounted for 30 to 46% of the tritium in tissues. Desipramine and reserpine pretreatment blocked the tissue accumulation of tritiated and fluorinated dopamine as well as their dihydroxy-metabolites, indicating that accumulation of exogenous norepinephrine and dopamine analogs was within sympathetic storage vesicles. Relative to the doses of dopamine precursors, less 2F- and 6F-norepinephrine accumulated in tissues than tritiated norepinephrine, due largely to inefficient beta-hydroxylation of fluorinated dopamine

[en] Sites of uptake, storage, and metabolism of [¹⁸F]fluorodopamine and excretion of [¹⁸F]fluorodopamine and its metabolites were visualized using positron emission tomographic (PET) scanning after intravenous injection of the tracer into anesthetized dogs. Radioactivity was concentrated in the renal pelvis, heart, liver, spleen, salivary glands, and gall bladder. Uptake of 18F by the heart resulted in striking delineation of the left ventricular myocardium. Pretreatment with desipramine markedly decreased cardiac positron emission, consistent with dependence of the heart on neuronal uptake (uptake-1) for removal of circulating catecholamines. In reserpinized animals, cardiac positron emission was absent within 30 minutes after injection of [¹⁸F]-6-fluorodopamine, demonstrating that the emission in untreated animals was from radioactive labeling of the sympathetic storage vesicles. Decreased positron emission from denervated salivary glands confirmed that the tracer was concentrated in sympathetic neurons. Radioactivity in the gall bladder and urinary system depicted the hepatic and renal excretion of the tracer and its metabolites. Administration of tyramine or nitroprusside increased and ganglionic blockade with trimethaphan decreased the rate of loss of myocardial radioactivity. The results show that PET scanning after administration of [¹⁸F]fluorodopamine can be used to visualize sites of sympathetic innervation, follow the metabolism and renal and hepatic excretion of catecholamines, and examine cardiac sympathetic function

[en] Highlights: • Experimental high-pressure investigations on synthetic single crystal material. • X-ray diffraction with complementary vibrational spectroscopy data up to 9 GPa. • Polymorphism of kieserite-type α- and β-forms of FeSO₄∙H₂O. • second order structural phase transition and isothermal equations of state. -- Abstract: The kieserite-type ferrous sulfate FeSO₄∙H₂O has been studied up to pressures of 9.2 GPa by means of X-ray diffraction, Fourier-transform infrared spectroscopy and Raman spectroscopy. The monoclinic phase undergoes a ferroelastic pressure-induced phase transitions at P_c = 6.154(1) GPa with the thermodynamic character being second order. The structure solution of the high-pressure polymorph revealed a purely displacive transition with the SO₄ and FeO₆ units remaining unchanged in their topology. Birch-Murnaghan equations of state were fitted to the unit-cell volume data thus yielding V₀ = 365.23(30) ų, K₀ = 45.2(2) GPa, K′ = 6.7(1) for the C2/c phase and V₀ = 369.86(46) ų, K₀ = 38.5(6) GPa for the high-pressure P$\overline{1}$ polymorph with K′ fixed to 5.4 as derived from normalized pressure-strain analysis. The analyses of the high-pressure spectra and the structure refinements reveal changes in the hydrogen-bonding system to be the responsible driving mechanism for the phase transition.

[en] The properties of materials near structural phase transitions are often successfully described in the framework of Landau theory. While the focus is usually on phase transitions, which are induced by temperature changes approaching a critical temperature T_c, here we will discuss structural phase transformations driven by high hydrostatic pressure, as they are of major importance for understanding processes in the interior of the earth. Since at very high pressures the deformations of a material are generally very large, one needs to apply a fully nonlinear description taking physical as well as geometrical nonlinearities (finite strains) into account. In particular it is necessary to retune conventional Landau theory to describe such phase transitions. In Troester et al (2002 Phys. Rev. Lett. 88 55503) we constructed a Landau-type free energy based on an order parameter part, an order parameter-(finite)strain coupling and a nonlinear elastic term. This model provides an excellent and efficient framework for the systematic study of phase transformations for a wide range of materials up to ultrahigh pressures. We illustrate the model with the specific example of BaCr(Si₄O₁₀), showing that it fully accounts for the elastic softening which is observed near the pressure induced phase transformation

[en] Durango apatite was irradiated with energetic U ions of 2.64 GeV and Kr ions of 2.1 GeV, with and without simultaneous exposure to a pressure of 10.5 GPa. Analysis by confocal Raman spectroscopy gives evidence of vibrational changes being marginal for fluences below 5 x 10¹¹ ions/cm² but becoming dominant when increasing the fluence to 8 x 10¹² ions/cm². Samples irradiated with U ions experience severe strain resulting in crystal cracking and finally breakage at high fluences. These radiation effects are directly linked to the formation of amorphous tracks and the fraction of amorphized material increasing with fluence. Raman spectroscopy of pressurized irradiated samples shows small shifts of the band positions with decreasing pressure but without a significant change of the Grueneisen parameter. Compared to irradiations at ambient conditions, the Raman spectra of apatite irradiated at 10.5 GPa exhibit fewer modifications, suggesting a higher radiation stability of the lattice by the pressure applied. (orig.)

[en] This study tackles the question if ruby crystals, irradiated with energetic heavy ions, can still be used as reliable pressure sensors. The problem is linked to novel irradiation experiments, exposing pressurized samples to swift heavy-ion beams. In order to test and quantify a possible influence of radiation damage on the laser-induced fluorescence lines of ruby (Al₂O₃:Cr³⁺), small crystals were exposed to different heavy ions (Xe, Au, and U) with kinetic energies of several giga-electron volt at ambient as well as high-pressure conditions. With increasing fluence (ions/cm²), the R₁ and R₂ lines shift both to lower wavelengths which leads to an underestimation of the pressure. An empirical correction term ε is proposed to include the irradiation damage effect into the commonly employed ruby calibration scale.