Nanocrystalline lanthanide nitride materials synthesised by thermal treatment of amido and ammine metallocenes: X-ray studies and DFT calculations

The decomposition process of ammine lanthanide metallocenes was studied by X-ray diffractometry, spectroscopy and theoretical investigations. A series of ammine-tris(eta(5)-cyclopentadienyl)lanthanide(III) complexes 1-Ln (Lanthanide (Ln)=Sm, Gd, Dy, Ho, Er, Yb) was synthesised by the reaction of [Cp(3)Ln] complexes (Cp=cyclopentadienyl) with liquid ammonia at -78 degrees C and structurally characterised by X-ray diffraction methods, mass spectrometry and vibrational (IR, Raman) spectroscopy. Furthermore, amido-bis(eta(5)-cyclopentadienyl)lanthanide(III) complexes 2-Ln (Ln=Dy, Ho, Er, Yb) were synthesised by heating the respective ammine adduct 1-Ln in an inert gas atmosphere at temperatures of between 240 and 290 degrees C. X-ray diffraction studies, mass spectrometry and vibrational (IR, Raman) spectroscopy were carried out for several 2-Ln species and proved the formation of dimeric mu(2)-bridged compounds. Species 1-Ln are highly reactive coordination compounds and showed different behaviour regarding the decomposition to 2-Ln. The reaction of 1-Ln and 2-Ln with inorganic bases yielded lanthanide nitride LnN powders with an estimated crystallite size of between 40 and 90 nm at unprecedented low temperatures of 240 to 300 degrees C. Temperature-dependent X-ray powder diffraction and transmission electron microscopy (TEM) investigations were performed and showed that the decomposition reaction yielded nanocrystalline material. Structural optimisations were carried out for 1-Ln and 2-Ln by employing density functional (DFT) calculations. A good agreement was found between the observed and calculated structural parameters. Also, Gibbs free energies were calculated for 1-Ln, 2-Ln and the pyrolysis reaction to the nitride material, and were found to fit well with the expected ranges.     

Chitosan and a modified chitosan as agents to improve performances of mucoadhesive vaginal gels

New mucoadhesive formulations were designed and studied in order to improve local vaginal therapy by increasing formulation retention prolonging thus drug-mucosa contact time. Some gels were prepared using hydroxyethylcellulose (HEC) alone or mixed with chitosan (CS) or its derivative 5-methyl-pyrrolidinone-chitosan (MPCS) and were loaded with the antibacterial metronidazole (MET) (0.75%). All formulations showed pseudoplastic flow and viscosity increase was observed proportionally to chitosan content (CS>MPCS). Prepared gels showed better extrusion properties (yield stress) than market formulation Zidoval. Mucoadhesion force studies permitted to point out that: (i) CS decreases mucoadhesion force; (ii) MPCS addition increases the mucoadhesion force at high percentage; (iii) all gels containing chitosan showed better mucoadhesive performances than Zidoval. Gels containing MPCS showed higher and faster drug release than those containing CS. All the preparations were able to release higher drug amounts if compared to market formulation. In conclusion MPCS improved gel characteristics in terms of mucoadhesion force, rheological behaviour and drug release pointing out that this modified chitosan is very suitable to obtain manageable and more acceptable vaginal formulation.     

Co-Administration of Fendiline Hydrochloride Enhances Chemotherapeutic Efficacy of Cisplatin in Neuroblastoma Treatment

Despite significant improvement of neuroblastoma (NB) patients’ survival due to recent treatment advancements in recent years, NB is still associated with high mortality rate. In search of novel strategies to increase NB’s susceptibility to pharmacological treatments, we investigated the in vitro and in vivo effects of fendiline hydrochloride as an enhancer of cisplatin antitumor activity. To assess the modulation of fendiline treatment on cisplatin responses, we used in vitro (evaluating NB cell proliferation by XCELLigence technology and colony formation, and gene expression by RT-PCR) and in vivo (NB cell grafts in NOD-SCID mice) models of NB. NB cell treatment with fendiline induced the expression of the ncRNA NDM29, leading to cell differentiation and to the reduction of the expression of MDRs/ABC transporters linked to multidrug resistance. These events were correlated to higher NB cell susceptibility to cisplatin and, consequently, increased its cytotoxic potency. In vivo, this drug interaction causes an enhanced ability of cisplatin to induce apoptosis in NB masses, resulting in tumor growth reduction and prolonged animal survival rate. Thus, the administration of fendiline might be a possible novel therapeutic approach to increase cisplatin efficacy in aggressive and poorly responsive NB cases.     

The ablation stage in the fast abrasion model

In order to verify the effect of the ablation stage on the fast abrasion mechanism, detailed evaporative calculations have been performed on the primary projectile and target-like fragments issued from the reactions⁴⁰Ar+²⁷Al and⁴⁰Ca+²⁷Al. The results account for many of the experimental features observed in the projectile and target-like fragments produced at intermediate energies. However it is pointed out that, in order to get a better agreement between theory and experimental data, the primary projectile and target-like fragments should carry a more substantial excitation energy than predicted by a purely geometric abrasion model.     

YBCO step-edge SQUIDs by magnetron sputtering technique

Summary YBCO step-edge junction d.c. SQUIDs have been realized by using the Inverted Cylindrical Magnetron Sputtering (ICMS) technique. This last represents a novel technology for high-T _c Josephson junctions (HTSC). Steps are obtained by standard ion milling procedure on LaAlO₃ (100) substrates using Nb-masks patterned by reactive ion etching. Measurements of currentvs. voltage, maximum d.c. Josephson currentvs. magnetic field and SQUID voltage response measurements have been performed, also as a function of the temperature. Operating temperature as high as 77K has been achieved. At 4.2K the SQUIDs show a maximum voltage of flux transfer function (∂V/∂ϕ)_max=870 μV/Ф₀ and a good periodicity of theV-ϕ modulation up to 20Ф₀ without any sign of hysteresis. The ratio between the step height (h) and the film thickness (d) seems to play a fundamental role in determining Josephson properties of the bridges, these conditions being more severe with respect to most of the data available in literature. Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994.     

DC Solutions of Postbuckling Problems

In this paper we present an approach to determine the local minima of a specific class of minimization problems. Attention is focused on the inextensibility condition of flexible rods expressed as a non convex constraint. Two algorithms are derived from a special splitting of the Lagrangian into the difference of two convex functions (DC). They are compared to the classical augmented Lagrangian method used in this context. These DC formulations are easily extended to contact problems and applied to the determination of confined postbuckling shapes and to microbuckling in a cellular structure.     

Controlling natural convection in a closed thermosyphon using neural networks

The aim of this paper is to present a neural network-based approach to identification and control of a rectangular natural circulation loop. The first part of the paper defines a NARMAX model for the prediction of the experimental oscillating behavior characterizing the fluid temperature. The model has been generalized and implemented by means of a Multilayer Perceptron Neural Network that has been trained to simulate the system experimental dynamics. In the second part of the paper, the NARMAX model has been used to simulate the plant during the training of another neural network aiming to suppress the undesired oscillating behavior of the system. In order to define the neural controller, a cascade of several couples of neural networks representing both the system and the controller has been used, the number of couples coinciding with the number of steps in which the control action is exerted.     

Identification of elastic parameters by displacement field measurementIdentification de paramètres mécaniques par mesure de champ de déplacement

In this Note we study a parameter identification problem associated with a two-dimensional mechanical problem. In a first part, the experimental technique of determining the displacement field is presented. The variational method proposed herein is based on the minimization of a separate convex functional which leads to the reconstruction of the elastic tensor and the stress field. These two reconstructed fields are continuous and piecewise linear on a triangulation of the two-dimensional problem. Some numerical and experimental examples are presented to test the performance of the algorithm. To cite this article: G. Geymonat et al., C. R. Mecanique 330 (2002) 403–408.     

Direct surface-transfer reaction to the continuum states induced by a 1760 MeV 40Ar beam on 27Al and natTi target nuclei

The inclusive energy spectra of few-nucleon transfer reactions obtained by bombarding ²⁷Al and ^natTi target nuclei with the GANIL 1760 MeV ⁴⁰Ar beam have been analysed in terms of direct surface-transfer reactions populating the continuum states. The shape at forward angles of the various energy spectra and the corresponding angular distributions are well reproduced by a diffractional model calculation based on mutual excitation of the two residual partners. It turns out that one of the essential ingredients of the calculations is the Williams partial level density either of the target or of the projectile constructed only with the transferred nucleons or residual holes coupled to the ground state.