New perovskite materials of the La(2-x)Sr(x)CoTiO6 series

Substitution of La(3+) by Sr(2+) in the double perovskite La(2)CoTiO(6) yields materials of the La(2-x)Sr(x)CoTiO(6) series showing a significant amount of trivalent cobalt ions when prepared at ambient atmosphere. The as-prepared compounds can be reduced in severe conditions retaining the perovskite structure while inducing the formation of a large amount of oxygen vacancies. The limit of aliovalent substitution in this series was found to extend up to x = 1. For substitution of La(3+) up to 15% cobalt and titanium are ordered, though the order is progressively lost as x increases; for x≥ 0.30 no ordering is observed as evidenced by magnetic measurements. The ability of these materials to present either cobalt ions in a mixed oxidation state or large amounts of anion vacancies depending on the atmosphere makes them interesting to be further investigated regarding their electrical and electrochemical properties, and hence, their usefulness in some electrochemical devices.     

Lower bounds of the life span of classical solutions to a system of semilinear wave equations in two space dimensions

In this paper we consider a system of semilinear wave equations in two space dimensions and with propagation speeds possibly different from one. Under smallness assumptions on the data, we show lower bounds for the life span of classical solutions.     

Activation Energies for the Longitudinal Relaxation Rates of the Water in Normal and Neoplastic Lung

Variable temperature water T₁ relaxation times have been measured on some normal and neoplastic human lung tissues. The corresponding activation energies have been derived and a short discussion of the experimental results is given.     

Melnikov theory for nonlinear implicit ODEs

We apply dynamical system methods and Melnikov theory to study small amplitude perturbation of some implicit differential equations. In particular we show persistence of such orbits connecting singularities in finite time provided a Melnikov like condition holds.     

A Comparative Study of Water T1 and T2 Nmr Relaxation Times in Healthy and Pathological Blood Fluid

Water protons T₁ and T₂ relaxation times in samples of whole blood, obtained from healthy people and from patients affected by Macrocytic Anemia on one side and Lymphatic and Myeloid Leukemia on the other, have been measured with the FT NMR technique at 80 Mhz and at 25 °C. No significant difference with respect to the value of the spin lattice relaxation time parameter measured for the healthy control group is experimentally evident in the case of the Macrocytic Anaemia while the spin spin relaxation time increases in magnitude. On the reverse both the leukemic cases present a significant (p < 0.001) increase in the relaxation times with respect to the control group. The experimental relaxation data belonging to the anaemic case show a linear correlation with the red cells volume while that obtained for the two leukaemic cases appear linearly correlated with the total white cell numbers. From the relaxation data an estimate of the amount of water tightly bound to the white cells membrane can be determined which results roughly thirty times lower than that bound to the red cells membrane. In this work is also presented a step by step outline of the water relaxation behavior which starts with the pure water and ends with the water in the whole blood supported by relaxation experiments done on the isolated blood main components.     

Reactions of nitrogen compounds with ruthenium tetroxide. Determination of the absolute configuration of 3-ethylpiperidine

(-)-3-Kthylpiperidine and (R)-(-)-2-ethylglutarie acid have been chemically correlated through N-subslituted α-ethylglutarimides obtained from the oxidation of optically active N-ethyl- and N-benzyl-3-ethylpiperidine with ruthenium tetroxide. The (R)-(-) configuration of (-)-3-ethylpiperidine was confirmed by CD measurements. The selective oxidation of endocyclic methylenes linked to the nitrogen atom was explained in term of different conformational freedom of endo- and exocyclic methylene groups.     

Singular Perturbations, Transversality, and Sil'nikov Saddle-Focus Homoclinic Orbits

We consider the singularly perturbed system $\dot x$ =εf(x,y,ε,λ), $\dot y$ =g(x,y,ε,λ). We assume that for small (ε,λ), (0,0) is a hyperbolic equilibrium on the normally hyperbolic centre manifold y=0 and that y ₀(t) is a homoclinic solution of $\dot y$ =g(0,y,0,0). Under an additional condition, we show that there is a curve in the (ε,λ) parameter space on which the perturbed system has a homoclinic orbit also. We investigate the transversality properties of this orbit and use our results to give examples of 4 dimensional systems with Sil'nikov saddle-focus homoclinic orbits.     

Homoclinic Trajectories in Discontinuous Systems

We study bifurcations of bounded solutions from homoclinic orbits for time-perturbed discontinuous systems. Functional analytic method is used. An illustrative example of a periodically perturbed piecewise linear differential equation in is presented.      

Research on potentially bioactive aza and thiaza polycyclic compounds containing a bridgehead nitrogen atom. III. Synthesis and antimicrobial activity of some 1,4‐benzothiazines and pyrrolobenzothiazines

Cyclization reactions of N‐(2,2‐dialkoxyethyl)‐1,4‐benzothiazine lactams 2 and 1,4‐benzothiazine‐sulfones 10 lead to the corresponding pyrrolo[1,2,3‐de]‐1,4‐benzothiazines 4 and 12, respectively, by using the dioxane/p‐toluenesulfonic acid or polyphosphoric acid/chloroform systems. In contrast, in the same reaction conditions, 1,4‐benzothiazines 5a‐h do not provide the expected pyrrolobenzothiazines 7, and as for 5c‐h considerable amount of the 2‐amino‐phenyl‐sulfide 8 was obtained. The results of microbiological assays are reported.     

Mesoporous materials incorporating a zinc(II) complex: Synthesis and direct luminescence quantum yield determination

New luminescent inorganic–organic hybrid materials incorporating the luminescent zinc(II) complex ZnL₂ (λ_em = 457 nm and Φ_em = 4.4% reference values for ZnL₂; HL = chelating ligand resulting from the reaction between salicylaldehyde and 3-aminopropyltriethoxysilane), covalently bonded to different types of mesoporous silica hosts (namely MCM-41, MCM-48 and SBA-15), were prepared via both the methods of grafting post-synthesis (GPS) and one-pot synthesis (OPS). The products obtained, which form the GPS [(GPS)(Zn/MCM-41), (GPS)(Zn/MCM-48), (GPS)(Zn/SBA-15)] and the OPS [(OPS)(Zn/MCM-41), (OPS)(Zn/MCM-48), (OPS)(Zn/SBA-15)] series, contain the ZnL₂ guest covalently bonded to the silica framework through silicon–oxygen bonds formed when the silane group is placed at the periphery of the Zn(II) coordination sphere. GPS and OPS materials were characterized by powder X-ray diffraction, N₂ adsorption/desorption, thermogravimetric analysis (TGA) and UV/vis spectroscopy. For the new mesoporous materials the emission quantum yield (EQY) was measured by means of an integrating sphere combined with a spectrofluorimeter. The ZnL₂ loading (measured by the ZnL₂/SiO₂ ratio calculated from TGA data) for MCM-41 appears to be independent of the synthesis procedure, whereas, for both MCM-48 and SBA-15, the ZnL₂/SiO₂ ratio of the materials obtained via OPS is about four times higher than products obtained from GPS. The ZnL₂ loaded GPS and OPS series show λ_em maxima at about 485 and 455 nm, respectively. Moreover, with reference to EQY (GPS)(Zn/SBA-15) and (OPS)(Zn/SBA-15), although featuring ZnL₂/SiO₂ ratios of 0.13 and 0.45, respectively, they showed similar EQY values: 2% and 5%. On the contrary, (GPS)(Zn/MCM-41) and (OPS)(Zn/MCM-41) which give similar ZnL₂/SiO₂ ratios (0.09 and 0.14) exhibit very different EQY, i.e. 2% and 22%, respectively.