High temperature stability of natural maghemite: a magnetic and spectroscopic study

A combined magneto-mineralogical approach is used to diagnose maghemitization in magnetic grains of basaltic rock fragments from sand dunes in the Namibian desert in SW Africa. Data were obtained from static magnetic analysis, ferromagnetic resonance (FMR) spectroscopy, micro-Raman spectroscopy and electron microscopy. Micro-Raman spectroscopy showed that the magnetic grains in the lithic fragments form oxidative solid solution series with magnetite and maghemite as end-members. The five active Raman modes at 712, 665, 507, 380 and 344 cm−1 indicate that maghemite in the magnetic grains has well-defined structural properties. The FMR spectral analysis provides evidence for long-range dipolar coupling, which suggests intergrowth of the magnetic phases of the oxidative solid solution series. Thermomagnetic experiments and hysteresis measurements reveal a Curie temperature of about 890 K for this maghemite. Upon heating to 970 K part of the maghemite is altered to thermodynamically more stable hematite. After selective thermal decomposition of the maghemite in a protected atmosphere, the remaining magnetic phase has a Curie temperature of 850 K, characteristic for magnetite. The unique thermal stability of this natural maghemite above its Curie temperature is explained by the well-defined mineral structure, which formed during slow oxidative alteration of magnetite under arid climate condition

Signals for a Transition from Surface to Bulk Emission in Thermal Multifragmentation

Excitation-energy-gated two-fragment correlation functions have been studied between 2 to 9A MeV of excitation energy for equilibrium-like sources formed in $\pi^-$ and p + $^{197}$Au reactions at beam momenta of 8,9.2 and 10.2 GeV/c. Comparison of the data to an N-body Coulomb-trajectory code shows a decrease of one order of magnitude in the fragment emission time in the excitation energy interval 2-5A MeV, followed by a nearly constant breakup time at higher excitation energy. The observed decrease in emission time is shown to be strongly correlated with the increase of the fragment emission probability, and the onset of thermally-induced radial expansion. This result is interpreted as evidence consistent with a transition from surface-dominated to bulk emission expected for spinodal decomposition.Comment: 11 pages including 3 postscript figures (1 color

Nucleon-induced reactions at intermediate energies: New data at 96 MeV and theoretical status

Double-differential cross sections for light charged particle production (up to A=4) were measured in 96 MeV neutron-induced reactions, at TSL laboratory cyclotron in Uppsala (Sweden). Measurements for three targets, Fe, Pb, and U, were performed using two independent devices, SCANDAL and MEDLEY. The data were recorded with low energy thresholds and for a wide angular range (20-160 degrees). The normalization procedure used to extract the cross sections is based on the np elastic scattering reaction that we measured and for which we present experimental results. A good control of the systematic uncertainties affecting the results is achieved. Calculations using the exciton model are reported. Two different theoretical approches proposed to improve its predictive power regarding the complex particle emission are tested. The capabilities of each approach is illustrated by comparison with the 96 MeV data that we measured, and with other experimental results available in the literature.Comment: 21 pages, 28 figure

Measurements of sideward flow around the balance energy

Sideward flow values have been determined with the INDRA multidetector for Ar+Ni, Ni+Ni and Xe+Sn systems studied at GANIL in the 30 to 100 A.MeV incident energy range. The balance energies found for Ar+Ni and Ni+Ni systems are in agreement with previous experimental results and theoretical calculations. Negative sideward flow values have been measured. The possible origins of such negative values are discussed. They could result from a more important contribution of evaporated particles with respect to the contribution of promptly emitted particles at mid-rapidity. But effects induced by the methods used to reconstruct the reaction plane cannot be totally excluded. Complete tests of these methods are presented and the origins of the ``auto-correlation'' effect have been traced back. For heavy fragments, the observed negative flow values seem to be mainly due to the reaction plane reconstruction methods. For light charged particles, these negative values could result from the dynamics of the collisions and from the reaction plane reconstruction methods as well. These effects have to be taken into account when comparisons with theoretical calculations are done.Comment: 27 pages, 15 figure

Evidence for Spinodal Decomposition in Nuclear Multifragmentation

Multifragmentation of a ``fused system'' was observed for central collisions between 32 MeV/nucleon 129Xe and natSn. Most of the resulting charged products were well identified thanks to the high performances of the INDRA 4pi array. Experimental higher-order charge correlations for fragments show a weak but non ambiguous enhancement of events with nearly equal-sized fragments. Supported by dynamical calculations in which spinodal decomposition is simulated, this observed enhancement is interpreted as a ``fossil'' signal of spinodal instabilities in finite nuclear systems.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Letter

Synthesis of Nitrogenated Heterocycles by Asymmetric Transfer Hydrogenation of N-(tert-Butylsulfinyl)haloimines

Highly optically enriched, protected, nitrogenated heterocycles with different ring sizes have been synthesized by a very efficient methodology consisting of the asymmetric transfer hydrogenation of N-(tert-butylsulfinyl)haloimines followed by treatment with a base to promote an intramolecular nucleophilic substitution process. N-Protected aziridines, pyrrolidines, piperidines, and azepanes bearing aromatic, heteroaromatic, and aliphatic substituents have been obtained in very high yields and diastereomeric ratios up to >99:1. The free heterocycles can be easily obtained by a simple and mild desulfinylation procedure. Both enantiomers of the free heterocycles can be prepared with the same good results by changing the absolute configuration of the sulfur atom of the sulfinyl group.This work was generously supported by the Spanish Ministerio de Ciencia e Innovación (MICINN; grant no. CONSOLIDER INGENIO 2010, CSD2007-00006, CTQ2007-65218 and CTQ2011-24151) and the Generalitat Valenciana (PROMETEO/2009/039 and FEDER). O.P. thanks the Spanish Ministerio de Educación for a predoctoral fellowship (grant no. AP-2008-00989)

Engineering Semantic Self-composition of Services Through Tuple-Based Coordination

Service self-composition is a well-understood research area focusing on service-based applications providing new services by automatically combining pre-existing ones. In this paper we focus on tuple-based coordination, and propose a solution leveraging logic tuples and tuple spaces to support semantic self-composition for services. A full-stack description of the solution is provided, ranging from a theoretical formalisation to a technologically valuable design and implementation

Arterial stiffness and stroke in sickle cell disease

BACKGROUND AND PURPOSE: Large vessels are also affected in sickle cell disease. The aim of this study was to assess several parameters in adult patients with sickle cell disease compared with control subjects and in patients with sickle cell disease with stroke. METHODS: Carotid arterial stiffness, intima-media thickness, and transcranial Doppler ultrasonography were measured. RESULTS: Arterial stiffness and transcranial Doppler velocity were significantly increased in 49 patients with sickle cell disease compared with 47 control subjects (P<0.05) and especially in patients with stroke (P<0.05). CONCLUSIONS: These data suggest that transcranial Doppler and arterial stiffness might be associated to stroke in adult patients with sickle cell disease