Teoria di Galois,fibrazioni proiettive e geometrie non desarguesiane

Dedicato al Prof. L. J. Mordell in occasione del suo 75^o compleanno     

Structural analysis of sonochemically prepared PtRu versus Johnson Matthey PtRu in operating direct methanol fuel cells

Sonochemically prepared PtRu (3 : 1) and Johnson Matthey PtRu (1 : 1) were analyzed by X-ray absorption spectroscopy in operating liquid feed direct methanol fuel cells. The total metal loadings were 4 mg cm(-2) unsupported catalysts at the anode and cathode of the membrane electrode assembly. Ex situ XRD lattice parameter analysis indicates partial segregation of the Ru from the PtRu fcc alloy in both catalysts. A comparison of the in situ DMFC EXAFS to that of the as-received catalyst shows that catalyst restructuring during DMFC operation increases the total metal coordination numbers. A combined analysis of XRD determined grain sizes and lattice parameters, ex situ and in situ EXAFS analysis, and XRF of the as-received catalysts enables determination of the catalyst shell composition. The multi-spectrum analysis shows that the core size increases during DMFC operation by reduction of Pt oxides and incorporation of Pt into the core. This increases the mole fraction of Ru in the catalyst shell structure.     

Spinodal decomposition in a model colloid-polymer mixture in microgravity

We study phase separation in a deeply quenched colloid-polymer mixture in microgravity on the International Space Station using small-angle light scattering and direct imaging. We observe a clear crossover from early-stage spinodal decomposition to late-stage, interfacial-tension-driven coarsening. Data acquired over 5 orders of magnitude in time show more than 3 orders of magnitude increase in domain size, following nearly the same evolution as that in binary liquid mixtures. The late-stage growth approaches the expected linear growth rate quite slowly.     

Quantitative performance measurements of bent crystal Laue analyzers for X‐ray fluorescence spectroscopy

Third‐generation synchrotron radiation sources pose difficult challenges for energy‐dispersive detectors for XAFS because of their count rate limitations. One solution to this problem is the bent crystal Laue analyzer (BCLA), which removes most of the undesired scatter and fluorescence before it reaches the detector, effectively eliminating detector saturation due to background. In this paper experimental measurements of BCLA performance in conjunction with a 13‐element germanium detector, and a quantitative analysis of the signal‐to‐noise improvement of BCLAs are presented. The performance of BCLAs are compared with filters and slits.     

NMR structural study of hydrogels based on partially deacetylated hyaluronan

Hydrogels have been prepared using two partially deacetylated hyaluronan (deHA) samples having a molar ratio of free amino groups to total initial N-acetamido groups equal to 23 and 33%, respectively. Taking advantage of such primary amino functionalities, polymeric networks could be easily obtained in aqueous media by means of two different crosslinking procedures, namely: a) Ugi multicomponent reactions and, more simply, b) glutaraldehyde reticulation. In this paper, we wish to report on the synthesis of deHA based hydrogels and, in particular, on their structural elucidation as obtained by NMR studies.

Structure of HA (R = COCH₃) and de-HA (R = H) repeat units.     

Radioimmunoassay for parathyroid hormone (PTH): Characterization of commercially available antigens and antisera

Ohne ZusammenfassungSupported by Deutsche Forschungsgemeinschaft.     

EPR spectroscopy of a bidimensional distribution of N-alkyl-pyridinium TCNQ microcrystals: A model for langmuir-blodgett films

We have studied the EPR spectra of a bidimensionally ordered collection of platelike crystallites formed by Tetracyanoquinodimethane (TCNQ) ion salts. We have examinedS=1/2 andS=1 systems which exhibit g tensor and Zero-Field Splitting (ZFS) tensor anisotropy, respectively. EPR spectra change when the magnetic field is rotated with respect to the plane of the teflon support on which the ordered powder adheres. Simulation of such spectra has been exploited to get structural information on the arrangement of the TCNQ molecules stacked inside the crystallite.     

Measurement of non-maxwellian electron distribution functions in hot plasma and the importance for Thomson scattering diagnostics

Thomson scattering measurements show that non-Maxwellian electron distribution functions can occur in Tokamak plasma when the ratio of electron drift velocity to thermal velocity, $\text{ν}{}_{\mathrm{<mtext>D</mtext>}}\text{ν}{}_{\mathrm{<mtext>th</mtext>}}$, is $\text{ν}{}_{\mathrm{<mtext>D</mtext>}}\text{ν}{}_{\mathrm{<mtext>th</mtext>}}\text{? 0.1}$. Consequences for Thomson scattering diagnostics are discussed.     

Multilamellar liposomes formed by phosphatidyl nucleosides: an NMR-HR-MAS characterization

We present an NMR investigation of multilamellar vesicles (MLVs) obtained from phosphatidyl nucleosides, 5'-(1-palmitoyl-2-oleoyl-sn-glycero(3)phospho)cytidine (1), 5'-(1-palmitoyl-2-oleoyl-sn-glycero(3)phospho)inosine (2), and their mixtures. Because of the lower stability of liposomes obtained from 2, studies have been preferentially performed in this case with mixed liposomes 2/POPC (4:1). The investigation is conducted mostly via the HR-MAS technique and the general observation is that the resolution achieved in this way is superior to that obtained in the past with small unilamellar vesicles (SUVs). A full assignment is now possible, which includes the spectral region of the ribose ring and part of the glycerol moiety. Also in the case of MLVs, both for 1 and 2, a stacking between the aromatic bases of the same liposome layer seems to be ruled out, although in both cases the nucleobases appear to be exposed to the aqueous phase. The splitting of both aromatic H-5cyt and H-6cyt is ascribed to the presence of two aggregate populations that may correspond to the two syn and anti conformations observed for cytidine monophosphate in aqueous solution. On the basis of NOESY cross-peaks, it is not always possible to discriminate between inter- and intramolecular interactions; however, the distances found for 1 appear to be compatible with the intramolecular contacts in the anti conformation of the cytidine and also with intermolecular interactions between neighboring molecules of 1. We also find that the glycerol moiety does not seem to interact with the cytidine; however, part of the ribose ring seems to be close to the glycerol moiety. More generally, the interaction of one base with the sugar moiety of a neighboring base, previously observed for SUVs, still appears to be true for MLVs. Studies have been performed also for mixed liposomes obtained from the mixture of 1 and 2, where it is observed that the HR-MAS spectra of the corresponding MLVs are not simply the sum of the spectra of the two isolated components. In particular, there is the presence of a NOESY cross-peak between the aromatic protons H-6cyt and H-2ino, and this permits us to rule out large patchwork domains containing only one nucleoside components in the mixed liposomes. Finally, a study is performed on the time evolution of the system obtained by mixing the previously prepared liposomes of 1 and 2. No interaction is obtained in this case, i.e., the spectra are constitutive, which is consistent with the general picture of liposomes as kinetic traps that are not fusing with each other.