Search

Electron paramagnetic resonance (EPR) and static magnetic susceptibility data have been collected on a set of powder samples of and , Mn analogues of one-layer BSCCO superconductors. EPR spectra, analysed in a crystal field approach, indicate that typically 40 - 50% of ions are substituted by species in the lead-free compound and that strong deviations of the average Mn oxidation state can be introduced by reduced thermal cycles during the preparation procedure, as supported by XPS analysis. Susceptibility data, compared with the EPR response, suggest that Mn mixed valence may be a crucial factor, together with structural modulations or local anisotropy, in determining the variety of magnetic behaviours (mainly antiferromagnetic and metamagnetic) observed in these compounds.

The structure and the oxygen stoichiometry of the layered oxide BiPbSr2MnO6 has been examined by profile analysis from powder neutron diffraction data. The structure was refined in the space group Amaa (n°). The material has orthorhombic symmetry with lattice parameters a=5.3204(3), b=5.3796(3) and c=23.714(1) A . Its structure is analogue to that of superconducting cuprate Bi2Sr2CuO6+δ, but without modulation. An important structural feature of BiPbSr2MnO6 is that the oxygens in the (Bi,Pb)O layer are disordered over two positions along the a-axis. The calculated effective valence of manganese is 3.2. The MnO6 octahedra are elongated along the c-axis, characteristics of the Jahn-Teller distortion of octahedra with Mn3+ ions.

The role of silver in catalysing and promoting the textured growth of 2223 phase in Ag-sheathed (Powder In Tube) tapes, starting from a precursor «bi-component» powder, constituted by Bi-2212 and other mixed oxides, was investigated in detail by means of DTA and X-ray analyses at the different stages of the annealing of the tapes. By monitoring the reaction it was possible to show how the presence of silver modifies the thermal behaviour of the reactants. The reduction of the temperature at which a liquid phase is formed is believed to be the key mechanism through which the presence of silver enhances the overall conversion to 2223 phase. This temperature decrease was shown (for the first time, to our knowledge) to be active only as long as some precursor (unreacted) powder was present, and not on fully reacted 2223 phase. Further investigation on 2212 phase and the other mixed oxides, separately analysed by DTA, clarified that only the thermal behaviour of the former was modified by the presence of silver. An explanation based on oxygen unbalancing in the material possibly induced, at the annealing temperature, by the presence of silver, is suggested: as a consequence of the very high solubility of oxygen in silver at high temperature, O2 would be «pumped off» the superconducting 2212 phase, with the result of lowering its melting point.

Bi{sub 2}Sr{sub 2}MnO{sub 6+x} and BiPbSr{sub 2}MnO{sub 6}, isotypic with the 2201 BSCCO superconductor, were investigated by X-ray powder diffraction and X-ray absorption spectroscopy (synchrotron radiation). The unit-cell constants are a = 21.796(3), b = 5.4268(7), c = 23.612(2) {Angstrom}, and a = 5.3186(8), b = 5.3892(8), c = 23.765(3) {Angstrom}, respectively. Superlattice modulation peaks (h {ne} 4n) are evident in the diffractogram of the first phase. XAFS spectra at the K edge of manganese were recorded for the two compounds and for metallic Mn, MnO, and Mn{sub 2}O{sub 3}. An energy shift of about 1.5 eV is observed between the profiles of the two phases. By comparison of spectral features with those of the simple oxides, the oxidation state of Mn is inferred to be +2.6(1) and +2.9(1) in Bi{sub 2}Sr{sub 2}MnO{sub 6+x} and BiPbSr{sub 2}MnO{sub 6}, respectively.

La chirurgia mininvasiva, che comprende la laparoscopia, la retroperitoneoscopia e la toracoscopia, e diventata, nel corso degli ultimi due decenni, un mezzo sicuro e affidabile per ridurre l’onere della chirurgia senza compromettere il risultato oncologico nella popolazione di adulti affetti da tumore.

A differenza di altre aree in chirurgia pediatrica, la resezione epatica mininvasiva non ha ottenuto ampia popolarita. Le ragioni di cio sono presumibilmente correlate al timore di complicanze intraoperatorie quali sanguinamento o embolismo gassoso. Comunque, i miglioramenti in tecnologia laparoscopica e l’incrementata esperienza nella chirurgia degli adulti a partire dalla prima descrizione nel 1992 ora autorizza le resezioni laparoscopiche epatiche e la ricostruzione del tratto biliare in pazienti pediatrici selezionati.

The ground-state crystal energies of cubic MgAl2O4 (spinel) and MgO (periclase) and of rhombohedral alpha-Al2O3 (corundum) have been calculated at different volumes, relaxing the corresponding structures, by all-electron periodic Hartree-Fock methods (CRYSTAL program). Basis sets of contracted Gaussian-type functions are employed for the 18 atomic (including d) orbitals representing each of the Mg, Al, and O atoms. Mulliken net atomic charges z(Mg)=1.86\e\ (MgO), z(Al)=2.30\e\ (alpha-Al2O3), z(Mg)=1.74\e\, and z(Al) = 2.24\e\ (spinel) are obtained. The elastic bulk modulus, the Murnaghan equation of state p(V) at the athermal limit, the Mg-O and Al-O bond compressibilities, and the binding energy have been derived for each phase (and the elastic constants C-11 and C-12 for spinel only). Comparison with existing experimental data is discussed. The enthalpy change for spinel decomposition into the simple oxides has been computed as a function of pressure, including a correction for the electron correlation energy based on local-density-functional theory. A decomposition pressure of 11 GPa at T=0 K is predicted, against values of 8 and 13 GPa derived from experimental thermodynamic data and from direct compression experiments, respectively.

In the experience of other authors, double kidney transplant have a higher complication rate (30%) if compared with single renal graft. In personal experience the use of small calibre ureteral stents with antireflux valve can reduce this complication rate.From November 1999 to April 2001, at the A.S.O. S. Giovanni Battista in Turin, we performed 29 double kidney transplantations with the application of small calibre stents in 20 male and 9 female patients, aged 50-74 years. The uretero-neocystostomies were carried out according to Lich-Gregoire technique, and the JJ stents used were pediatric ones, 12 cm long and 4.8 Ch, with antireflux valve.We complained only 2 urological complications out of 58 anastomoses (distal unilateral ureteral necrosis in 1 case and total ureteral necrosis in the other).Complication rate is lower than in the literature: the authors suggest that the use of small calibre JJ stents can keep the complication rate low in double kidney transplant.

A periodic ab initio Hartree-Fock method (the program CRYSTAL) has been used to evaluate the total-electron-energy surface of MgF2 (rutile-type tetragonal structure) as a function of crystal strain. Mg and F atoms are represented by 13 atomic orbitals in the form of contracted Gaussian-type functions. The equilibrium unit-cell edges and fluorine coordinates, the binding energy, and the six elastic constants C-11, C-12, C-13, C33, C44, and C66 have been calculated. Inner strain was accounted for by relaxing the F-atom position for each lattice deformation applied, and contributed significantly to the C44, C66, and C33 components. An average deviation of 8.0% is observed with respect to experimental elastic data Classical two-body empirical calculations have been performed for the purpose of comparison. Energy bands, Mulliken electron populations, and charge-density maps are analyzed, and the chemical bonding is discussed, showing significant deviations from ionicity (z(Mg) = 1.80(e)).

To evaluate survival rate, follow-up and renal function in patients treated with "nephron-sparing" approach due to cancer in a transplanted kidney.During the 18 years' activity of our Transplantation Centre 3 renal carcinomas in transplanted kidneys (0.24%) have been found. Diagnoses were made in one case during transplantation procedures and, in the remaining two, 1 month and 10 years after. All tumours were unifocal, small (10, 12 and 18 mm of diameter), capsulated and low stage (T1). The resection of the mass ("nephron-sparing" surgery) and of a layer (1 cm thick) of the tissue surrounding the tumour was performed. The histological exam showed in all cases low grade (G2) renal cell carcinoma and negative surgical margins.138, 94 and 15 months after transplant all patients are alive, without disease recurrence and with good renal function. In all cases the doses of immune-suppressive therapy were reduced.Renal cancer in transplanted kidneys is generally treated with nephrectomy. On the contrary, we decided to apply the same criteria which are accepted for the treatment of renal neoplasms in general and then to perform a "nephron-sparing" surgery when the tumour is small, capsulated and with negative surgical margins at the intraoperative histological exam. In personal experience good results from the oncologic and nephrologic point of view have been accomplished.

We report our experience in transplantation proceedings with the use of small caliber JJ ureteral stent with antireflux valve during uretero-vesical anastomosis.During renal transplantations we usually perform an uretero-cystoneostomy with antireflux technique according to Lich Gregoir. In the past we used to intubate the uretero-vesical anastomosis only in particular cases; since April 1998 we performed 112 single and 8 double transplants and in all cases we positioned a 12 cm long paediatric 4.8 Ch JJ ureteral stent with antireflux valve, in order to reduce urologic complications. The vesical catheter was usually removed in 6o-7o day and the ureteral stent 40-60 days after transplantation.We have performed 129 uretero-vesical anastomoses and we complained only one case of early dehiscence of the anastomosis (unilateral in a double transplant) and two cases of late stents' displacement. We noticed no stenosis of the anastomosis and no dysfunction in urine outflow from the upper urinary ways.The routinary use of paediatric JJ ureteral stents with antireflux valve was decisive in drastically reducing early urologic complications after renal transplantation. Furthermore, the risk of vesico-ureteral reflux is almost completely reduced, thanks to the technique adopted for the anastomosis which allows a physiologic-like antireflux mechanism, to the presence of the antireflux valve and to the early recovery of the physiologic ureteral peristalsis, which is promoted by the small calibre of the stent. These factors lead to a faster recovery of the renal function, with excellent results from the nephrologic and urologic points of view.

cited By 7; International audience; Ab initio calculations of static structure factors of fluorite (CaF2) are performed by a linear combination of atomic orbitals Hartree-Fock method as implemented in the CRYSTAL program. The effect of thermal motion is then introduced by taking into account the atomic mean square displacements given in the literature at different temperatures and leads to dynamic structure factors. Finally, a very slight displacement of fluorine ions with respect to their ideal position is considered, to simulate an anharmonic vibration or disordered structure so as to improve the agreement with experimental data.

Some locally ordered arrangements of the lithium-lanthanum-vacancy distribution were devised, within the disordered perovskite superstructure of the LixLa2/3−x/3 1/3−2x/3TiO3 ion conductors. By consideration of the Li1/8La5/8 1/4TiO3 composition, two ordered superstructures are built up on the basis of 8 formula units/primitive cell (with monoclinic Pm space group symmetry). Periodic quantum-mechanical calculations were carried out at the B3LYP level by the CRYSTAL06 code, using ECP for lanthanum and all-electron basis sets for all other atoms. For each ordered model the complete structure was fully relaxed by energy minimization, finding that the 4La/1La+1Li+2 arrangement is more stable than 3La+1 /2La+1Li+1. Hence the average disordered Cmmm structures of Li0.16La0.613TiO3 and Li0.18La0.607TiO3 (neutron diffraction data) can be rationalized. The optimized Li positions were found to lie in peripheral sites within the A-type cavities, close to separating windows and in flattened square-pyramidal coordination. Some ambiguous aspects of the corresponding results of diffraction experiments can then be clarified.

Introduction La chirurgie reconstructive des formes proximales d’hypospadias represente toujours un challenge. Les procedures les plus utilisees sont la greffe de muqueuse buccale, la technique d’Onlay, de Bracka et de Koyanagi avec ses variantes. On presente notre experience avec la technique de Koyanagi. Materiels et methodes 21 patients avec hypospadias proximal et un age moyen de 23 mois (9-40 mois), ont ete operes par le meme chirurgien selon la technique originelle de Koyanagi. Le recul moyen du suivi est de 13 mois (6-21 mois). Tous les malades ont eu de la stimulation hormonale pre-operatoire avec testosterone. Les resultats fonctionnels ont ete evalues et un questionnaire a ete realise pur evaluer la satisfaction des parents et du chirurgien sur le plan esthetique. Resultats Le redressement de la verge est obtenu chez tous les patients sauf un par dissection des l’ensemble des tissus ventraux. Les complications observees ont ete : dehiscence partielle de l’uretre (47,6 %), fistule (19 %), uretrocele (19 %), stenose du meat (14,3 %). Ces complications ont amene a 15 reprises chirurgicales dans 12 cas et trois patients sont actuellement porteurs d’une uretrostomie perineale. Parmi les 9 patients restants, 3 sont en attente d’un geste chirurgical complementaire. Le questionnaire a ete complete pour 8 malades : la reconstruction de la verge et du scrotum ainsi que le redressement de la verge etaient bien juges par le chirurgien et les parents, qui etaient moins satisfaits de l’aspect du meat. Conclusion La technique originelle de Koyanagi est une alternative acceptable pour des formes d’hypospadias avec une division proximale du corps spongieux a la jonction peno-scrotale, une coudure majeure et quand la gouttiere uretrale n’est pas utilisable pour la reconstruction.Le redressement correct de la verge est obtenu sans autres procedures additionnelles et le resultat esthetique est satisfaisant. Le taux de complications est considerable et les parents doivent etre prevenus du risque des reprises. La technique modifiee de Koyanagi, en permettant une meilleure vascularisation distale des lambeaux cutanes, pourrait reduire le risque de complications.

The new triclinic phase Ca5(HAsO4)2(AsO4)2 · 5 H2O, polymorph of monoclinic vladimirite, was obtained by dehydration of Ca5(HAsO4)2(AsO4)2 · 9H2O (ferrarisite) at 60°C. Unit-cell data are: a = 8.286(4), b = 6.673(3), c = 9.743(4) Å, α = 86.58(3), β = 111.10(3), γ = 99.74(3)°; Z = 1, space group P[unk]. The structure was solved by direct methods and least-squares refined to R = 0.088, using 1200 observed counter reflections (MoKα radiation). One Ca atom and three water molecules are disordered over centrosymmetrically-related positions. Isostructural (001) layers of Ca and As coordination polyhedra are observed in the structures of both nona- and penta-hydrated phases; however, they differ by a relative shift and sandwich ordered and disordered Ca octahedra, respectively, in the two cases. Dehydration of ferrarisite involves the loss of inter-layer water molecules alternatively from either set of centrosymmetrically-related positions, while layers slide and approach one another. The sandwiched Ca atoms are left attached alternatively to either side of facing layers, and replace their broken coordination bonds by new ones on the side of the shifted layer. This random character of the dehydration reaction is the cause of disorder in the penta-hydrated phase. Crystal-chemical properties of the M5(HAsO4)2(AsO4)2 · n H2O phases are analyzed.

Sodium dihydrogen phosphate dihydrate (NaH2PO4.2H20) is orthorhombic, space group P212121, with a=7.275 (9), b=11-384 (6) and c=6-606 (4) A; Z=4. The structure was solved from X-ray measurements by direct methods and refined anisotropically with X-ray (R = 0.032 over 898 reflexions) and neutron data (R=0.059 over 751 reflexions); both sets of intensities were collected on singlecrystal diffractometers (Mo Ks radiation and 2= 1-035 A respectively). A correction for secondary extinction was applied to the neutron data. While the two acidic hydrogens form strong hydrogen bonds (2.577 and 2.536 ,&), one of those of the water molecules is involved in a very weak O H . . . O contact of 3-106 ,&. The P tetrahedra are linked by hydrogen bonds in a distorted diamond-type framework. Six systems of pseudo-hexagonal channels are present; the largest of them, along [001], accommodates a chain of Na octahedra. The configuration of the hydrogen-bonded groups is described. Bond-strength/bond-length correlations are discussed and their weakness for the case of strongly hydrogen-bonded atoms is pointed out. A comparison of X-ray and neutron results by Z 2 tests and half-normal probability plots shows significant differences for the thermal parameters only.

The transition between the monoclinic fl and orthorhombic a' phases of strontium orthosilicate was investigated by single-crystal diffractometry and polarizing microscopy at variable temperatures, on the basis of the disappearance or appearance of twin domains of the fl form. The phase change occurred sharply with thermal hysteresis in both experiments, at 364 and 355 K (X-rays) and at 369 and 359 K (light, best values out of a number of samples) for fl --, a' and a' --, fl, respectively; the optical study showed that transition temperatures are influenced by the size and habit of crystals. The orientations of fl and a' lattices are related by a simple rotation of the x axis. A first-order character is suggested by thermal results for the phase change, though it relates ordered and disordered structures. Crystals of fl-Sr2SiO 4 prove to be ferroelastic (Aizu's species mmmF2/m) with a spontaneous strain of 0.033. The mechanisms of the phase transition and of the transformation between mirrorrelated orientation states are discussed in relation to structural disorder of the paraelastic a' form.

The Born-Mayer model in the alkaline-earth oxides is reconsidered, using new compressibility data. All four oxides cannot share a unique hardness parameter ϱ. An exact solution is found by assuming that ϱ (MgO) = ϱ (CaO) and ϱ (SrO) = ϱ (BaO); another solution is proposed, which involves three distinct ϱ values in the family of salts. Results are tested by calculating the electron affinity of O 2- from each salt.

Elastic neutron diffraction data were collected from a single crystal of synthetic newberyite (λ=1.269 A). The anisotropic least-squares refinement of 146 parameters against 1008 observations yieldedR=1.9%. The environment of water molecules, hydrogen bonding, especially of bifurcated geometry, and the thermal motion of hydrogen atoms are discussed.

Equations relating the first and second partial derivatives of the lattice energy (with respect to the unit-cell constants) to the components of the elastic stiffness tensor have been obtained for orthorhombic crystals. By assuming a Born-Mayer model for the lattice energy, and using Ewald's method for calculating the electrostatic term, formulas are derived for the computation of the lattice-energy derivatives. In these expressions, the repulsive coefficients and the atomic charges appear as unknown parameters which can be determined by solving the above equations, provided that experimental data about elasticity and thermal-expansion tensors are available.

The pyrochlore-type compound KTaWO/sub 6/ . H/sub 2/O has been characterized by X-ray diffraction technique, thermogravimetric analysis and differential scanning calorimetry. Electrical conductivity measurements have been carried out in the temperature range 25-500/sup 0/C by complex admittance method.

Mg3(P04h' 22 H20-II crystallizes in space group P f, with a 6.937(3),b = 6.932(3), c = 16.132(5)A, a = 82.15(3), f3 = 89.72(3), y 119.49(3) , Z = 1. The structure was solved (direct methods) and refined anisotropically (least squares) to R = 0.042, using 1826 observed reflections measured on a single-crystal diffractometer (MoKa radiation). All hydrogen atoms were located from difference maps and included in the refinement. (001)layers formed by Mg(H20)6 and P04 polyhedra and by lattice water moleculesare linked by hydrogen bonds and stacked with the. . . A BB' A. . . scheme.A structure previously studied by other authors has been recognized as a polytype, Mg3(P04h . 22 H20-I, where the pair of layers AB is nearly identical as in II, but the B' layer is oriented differently with respect to B. The two orientations are related by a mirror pseudo-symmetry of the B layer. Differencesof the hydrogen bonding scheme in the two cases are pointed out.

The contribution of homogeneous lattice deformations (neglecting internal strains) to elastic properties of crystals with triclinic or higher symmetry is examined. The deformed lattice constants are expressed as functions of the components of the finite Lagrangian strain tensor, and their derivatives are calculated. Thus equations are obtained that relate the second-order elastic constants to first and second partial derivatives of the static crystal energy with respect to unit-cell parameters. With the assumption of a two-body Born-type interatomic potential, the energy derivatives were calculated analytically, and a rigid-body approximation was introduced to account for molecular groups in the crystal structure. Test computations of elastic constants were performed for MgF2 (rutile-type), benzene and naphthalene, using literature potential parameters optimized on structural data; results are discussed with respect to adequacy of the potentials and of the approximations of the model used.

Ewald's method is reconsidered to express the dependence of Madelung energy on the ionic charges explicitly, also taking into account the space-group symmetry of the structure. Upper bounds for the residues of the two partial series have been calculated by integral approximation; that relative to the direct-lattice series is shown to depend on the cube root of the unit-cell volume. The optimum value of the parameter A, which equalizes the rates of convergence of the two sums and minimizes the total number of terms, has been determined numerically for a given termination error and for a range of unit-cell dimensions. Theoretical results are tested by calculations on some specific crystal structures.