Individual and center-of-mass resonances in the motional spectrum of an electron cloud in a Penning trap

We have examined experimentally the motional spectrum of an electron cloud confined in a Penning trap. When the axial oscillation is excited by a radio frequency field the resonance exhibits a double structure. Both components depend differently on the number of trapped electrons and have different shape and width. We conclude that one of them corresponds to the excitation of the individual electrons while the other is the center-of-mass mode of the cloud. The threshold behaviour of the center-of-mass resonance suggests that it is a parametric instability of a Mathieu type equation of motion. Received 11 July 2001 and Received in final form 12 November 2001     

Interactions of xanthines with activated carbon: II. The adsorption equilibrium

In the present work, we have studied the adsorption of xanthine derivatives by activated carbon sorbents in aqueous solutions. The study comprised both kinetic, equilibrium and thermodynamic aspects. The kinetic results were reported in a previous paper; the equilibrium-related results are discussed here. The two types of carbon used exhibit some differences but the equilibrium isotherms obtained are all of the H-3 type in the classification of Giles. This suggests a high affinity of the sorbents for the sorbates. We also found that the overall adsorption process comprises more than one individual adsorption-desorption process of which one leads to the formation of a “monolayer” and the other to the “precipitation” of the sorbate on the sorbent surface (multilayer adsorption); the amount of sorbate adsorbed in monolayer form was seemingly greater in C-A14.     

Stability study of simvastatin under hydrolytic conditions assessed by liquid chromatography

In this work, a liquid chromatography stability-indicating method was developed and applied to study the hydrolytic behavior of simvastatin in different pH values and temperatures. The selected chromatographic conditions were a C18 column; acetonitrile-28 mM phosphate buffer solution, pH 4 (65 + 35) as the mobile phase; 251 degrees C column temperature; and flow rate 1 mL/min. The developed method exhibited an adequate repeatability and reproducibility (coefficient of variation 0.54 and 0.74%, respectively) and a recovery higher than 98%. Furthermore, the detection and quantification limits were 9.1 x 10(-7) and 2.8 x 10(-6) M, respectively. The degradation of simvastatin fitted to pseudo-first order kinetics. The degradation was pH dependent, being much higher at alkaline pH than at acid pH. Activation energy, kinetic rate constants (k) at different temperatures, the half life (t1/2) and the time for 10% degradation to occur (t90) values are also reported.     

A Cyclic and Polymeric Phosphazene as Solid State Template for the Formation of RuO<Subscript>2</Subscript> Nanoparticles

Pyrolysis of the organometallic polymer: {{[N=P(R₁)]_0.8[N=P(OC₆H₄CH₂CN[Ru])₂]_0.15[N=P((OC₆H₅)(OC₆H₄CH₂CN[Ru]]_0.05}{Cl}_0.31} _n , [Ru]=CpRu(PPh₃)₂, R₁ = O₂C₁₂H₈ (1) as well of the cyclic specie {N₃P₃ (OC₆H₅)₅(OC₆H₄CH₂CN[Ru])}{PF₆} (2) under a flow of air at 800°C affords nanostructured RuO₂. Nanoparticles near to 10 nm were observed. The differences in the use of cyclic or polymeric phosphazenes, as solid state template, influence strongly the morphology and slightly the composition of the pyrolytic product. Temperature variable (SQUID) measurements in the range of 5–300 K of the material obtained from the polymer, indicate an antiferromagnetic interaction between the Ru atoms, although lower than that found for the crystalline ruthenium oxide, probably due to some amorphous product present in the pyrolytic material. The possible formation mechanism is discussed and the differences in using the cyclic or the polymeric compound as precursor is analyzed in terms of the relative content of Ru to P, N. A general formation method of nanostructured metal oxides is proposed.     

New polymer-supported catalysts. (Polyvinylchloride-containing redox) catalyst cyclopentadienyl iron moiety: [η5C5H5Feη6C6(CH3)5CH2?]+

New polymer-supported catalysts that contain the redox cyclopentadienyl iron moiety [η⁵C₅H₅Feη⁶C₆(CH₃)₅CH₂? ]⁺ were prepared with polyvinylchloride (PVC) as support. The active center is attached as a pendant organometallic moiety in the side groups of the PVC chain. Metallocenic groups and the supported polymers with various Fe content were analyzed by spectroscopic techniques and by polarographic and cyclic voltammetry. The absorption spectra show a similar profile to that of the nonsupported cation, which indicates that the supported polymer contains side groups in the chain with metallocenic structures. The new polymer-supported catalysts were characterized by viscometric measurements and by differential calorimetry (DSC). A linear relationship between intrinsic viscosity/[η] and the Fe content was observed. The glass transition temperature (T_g) values are higher than those of PVC without modification.     

Osteoarthritis subjects have differentiated lower extremity thermal skin response after the concurrent acute training session

Journal of Thermal Analysis and Calorimetry - This study investigated the thermal skin (Tsk) response of lower limbs in older adults with or without osteoarthritis before and after a concurrent...     

Narrow-line phase-locked quantum cascade laser in the 9.2 microm range

We report the operation of a 50 mW continuous-wave quantum cascade laser (QCL) in the 9.2 microm range, phase locked to a single-mode CO(2) laser with a tunable frequency offset. The wide free-running emission spectrum of the QCL (3-5 MHz) is strongly narrowed down to the kilohertz range, making it suitable for high-resolution molecular spectroscopy.     

Metal complexes of 6-chloropurine

Summary Five Cu(II), Pd(II), Cd(II), Pt(IV), and Au(III) complexes of 6-chloropurine have been obtained. The complexes were characterized by elemental analysis, IR,¹H-NMR and¹³C-NMR spectroscopy. On the basis of these data the structure of the complexes and the coordination of the ligand have been proposed. Thus, the physical and chemical methods supported evidence that in acidic medium, with exception of the Cu(II) complex, 6-chloropurine acts in the monoprotonated form neutralizing the charge of [PdCl₄]^2–, [CdCl₄]^2–, [AuCl₄]^– and [PtCl₆]^2– anions. The thermal behaviour of the complexes has also been studied.

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Metallkomplexe von 6-Chlorpurin

Zusammenfassung Es wurden fünf Komplexe von 6-Chlorpurin mit Cu(II), Pd(II), Cd(II), Pt(IV) und Au(III) erhalten. Die Komplexe wurden mittels Elementaranalysen, IR,¹H-NMR und¹³C-NMR charakterisiert. Auf der Basis dieser Daten wurde eine Komplexstruktur und eine bestimmte Koordination der Liganden vorgeschlagen. Physikalische und chemische Methoden beweisen, daß im sauren Bereich [mit der Ausnahme von Cu(II)] das 6-Chlorpurin in der monoprotonierten Form koordiniert, wobei die Ladung von [PdCl₄]^2–, [CdCl₄]^2–, [AuCl₄]^– und [PtCl₆]^2– jeweils neutralisiert wird. Das thermische Verhalten der Komplexe wurde ebenfalls untersucht.

     

Order and mobility of solid vortex matter in oscillatory driving currents

We study numerically the evolution of the degree order and mobility of the vortex lattice under steady and oscillating applied forces. We show that the oscillatory motion of vortices can favor an ordered structure, even when the motion of the vortices is plastic when the same force is applied in a constant way. Our results relate the spatial order of the vortex lattice with its mobility, and they are in agreement with recent experiments. We predict that, in oscillating applied forces, the lattice orients with a principal axis perpendicular to the direction of motion.