Superconductivity in CoSr2(Y1-xCax)Cu2O7+d

The roles of aliovalent Ca(II)-for-Y(III) substitution and high-pressure-oxygen annealing in the process of "superconducterizing" the Co-based layered copper oxide, CoSr2(Y1-xCax)Cu2O7+d (Co-1212), were investigated. The as-air-synthesized samples up to x = 0.4 were found essentially oxygen stoichiometric (-0.03 <= d <= 0.00). These samples, however, were not superconductive, suggesting that the holes created by the divalent-for-trivalent cation substitution are trapped on Co in the charge reservoir. Ultra-high-pressure heat treatment carried out at 5 GPa and 500C for 30 min in the presence of Ag2O2 as an excess oxygen source induced bulk superconductivity in these samples. The highest Tc was obtained for the high-oxygen-pressure treated x = 0.3 sample at ~40 K.Comment: 16 pages, 6 figures, submitted to Solid State Communication

Atomic structure and vibrational properties of icosahedral B4_4C boron carbide

The atomic structure of icosahedral B$_4$C boron carbide is determined by comparing existing infra-red absorption and Raman diffusion measurements with the predictions of accurate {\it ab initio} lattice-dynamical calculations performed for different structural models. This allows us to unambiguously determine the location of the carbon atom within the boron icosahedron, a task presently beyond X-ray and neutron diffraction ability. By examining the inter- and intra-icosahedral contributions to the stiffness we show that, contrary to recent conjectures, intra-icosahedral bonds are harder.Comment: 9 pages including 3 figures, accepted in Physical Review Letter

First-principles study on the intermediate compounds of LiBH4_4

We report the results of the first-principles calculation on the intermediate compounds of LiBH$_4$. The stability of LiB$_3$H$_8$ and Li$_2$B$_n$H$_n (n=5-12)$ has been examined with the ultrasoft pseudopotential method based on the density functional theory. Theoretical prediction has suggested that monoclinic Li$_2$B$_{12}$H$_{12}$ is the most stable among the candidate materials. We propose the following hydriding/dehydriding process of LiBH$_4$ via this intermediate compound : LiBH$_4 \leftrightarrow {1/12}$Li$_{2}$B$_{12}$H$_{12} + {5/6}$ LiH $+ {13/12}$H$_2 \leftrightarrow$LiH $+$ B $+ {3/2}$H$_2$. The hydrogen content and enthalpy of the first reaction are estimated to be 10 mass% and 56 kJ/mol H$_2$, respectively, and those of the second reaction are 4 mass% and 125 kJ/mol H$_2$. They are in good agreement with experimental results of the thermal desorption spectra of LiBH$_4$. Our calculation has predicted that the bending modes for the $\Gamma$-phonon frequencies of monoclinic Li$_2$B$_{12}$H$_{12}$ are lower than that of LiBH$_4$, while stretching modes are higher. These results are very useful for the experimental search and identification of possible intermediate compounds.Comment: 7 pages, 5 figures, submitted to PR

X-ray diffraction measurements of the c-axis Debye-Waller factors of YBa2Cu3O7 and HgBa2CaCu2O6

We report the first application of x-rays to the measurement of the temperature dependent Bragg peak intensities to obtain Debye-Waller factors on high-temperature superconductors. Intensities of (0,0,l) peaks of YBa2Cu3O7 and HgBa2CaCu2O6 thin films are measured to obtain the c-axis Debye-Waller factors. While lattice constant and some Debye-Waller factor measurements on high Tc superconductors show anomalies at the transition temperature, our measurements by x-ray diffraction show a smooth transition of the c-axis Debye-Waller factors through T$_c$. This suggests that the dynamic displacements of the heavy elements along the c-axis direction in these compounds do not have anomalies at Tc. This method in combination with measurements by other techniques will give more details concerning dynamics of the lattice.Comment: 4 pages, 2 figures. To be published in Physical Review B (Brief Report

Structure of MnO nanoparticles embedded into channel-type matrices

X-ray diffraction experiments were performed on MnO confined in mesoporous silica SBA-15 and MCM-41 matrices with different channel diameters. The measured patterns were analyzed by profile analysis and compared to numerical simulations of the diffraction from confined nanoparticles. From the lineshape and the specific shift of the diffraction reflections it was shown that the embedded objects form ribbon-like structures in the SBA-15 matrices with channels diameters of 47-87 {\AA}, and nanowire-like structures in the MCM-41 matrices with channels diameters of 24-35 {\AA}. In the latter case the confined nanoparticles appear to be narrower than the channel diameters. The physical reasons for the two different shapes of the confined nanoparticles are discussed.Comment: 8 pages, including 9 postscript figures, uses revtex4.cl

Duality theorems and Kolyvagin systems for elliptic curves

After developing the theory of arithmetic duality for Galois cohomology with a particular focus on the cohomology of an elliptic curve over a local field or a number field, we use these results to define Kolyvagin systems and show how they provide bounds for the Selmer groups of the elliptic curve.ope

Acute coating transfer from commercial drug-coated balloons: in vivo evidence and controlled ex vivo experiments demonstrating the impact of contact pressure on drug-coating delivery

LAUREA MAGISTRALEI drug-coated balloon (DCB) sono dispositivi medici ampiamente utilizzati per il trattamento delle malattie cardiovascolari, ma la loro efficacia è spesso limitata da un insufficiente trasferimento del rivestimento farmacologico dal palloncino al sito bersaglio. Comprendere e migliorare questo processo di trasferimento è fondamentale per migliorare i risultati terapeutici. Una delle sfide fondamentali è capire come i parametri fisici, come la pressione di contatto, influenzino l'efficienza del trasferimento del rivestimento farmacologico. Attualmente, inoltre, mancano metodi non distruttivi per analizzare la quantità di farmaco trasferita al tessuto, rendendo difficile studiare questo processo e ottimizzarlo senza distruggere i campioni. Questa tesi si propone di affrontare questi problemi studiando i meccanismi alla base del trasferimento del farmaco dai DCB al tessuto arterioso, concentrandosi in particolare su come la pressione di contatto influisca su questo processo. Il lavoro mira anche a sviluppare tecniche avanzate di elaborazione delle immagini per confrontare il rivestimento di farmaco trasferito con il farmaco sfuso dopo il trattamento in vivo ed esplorare il potenziale di metodi non distruttivi come la tomografia a coerenza ottica (OCT) per valutare l'efficacia del trasferimento del rivestimento. Per raggiungere questi obiettivi sono state utilizzate metodologie in vivo, ex vivo e in silico. Negli studi in vivo, le arterie suine trattate con DCB sono state analizzate con OCT e microscopia elettronica a scansione (SEM) per creare mappe della distribuzione del rivestimento del farmaco. Per gli esperimenti ex vivo, i palloncini rivestiti di farmaco sono stati gonfiati e sottoposti a prove di stamping con una macchina monoassiale, che simulava la compressione applicata durante l'angioplastica con DCB. I tessuti sono stati analizzati con l'elaborazione di immagini per quantificare la quantità di farmaco trasferita a diversi livelli di pressione di contatto; per convalidare i nostri risultati, li abbiamo confrontati con il metodo standard HPLC. Inoltre, sono state eseguite simulazioni computazionali per capire come fattori quali la rigidità e lo spessore dell'arteria possano influenzare il trasferimento del farmaco. I risultati hanno dimostrato che l'aumento della pressione di contatto aumenta significativamente il trasferimento del rivestimento di farmaco, ma questa correlazione non è lineare, infatti si osserva che fino a un certo valore di pressione di contatto si ha un trend e dopo tale valore si ha lo stesso trend ma con una pendenza inferiore. Confrontando le mappe OCT e SEM possiamo affermare che l'imaging basato sull'OCT ha prodotto risultati simili a quelli del SEM, indicando che l'OCT potrebbe essere un'alternativa più rapida e meno invasiva per studi futuri per valutare l'efficacia del trasferimento. In conclusione, il trasferimento del rivestimento acuto è correlato con il farmaco sfuso sia nello studio in vivo che in quello ex vivo, suggerendo che l'analisi delle immagini è uno strumento affidabile per valutare l'efficacia del trasferimento del farmaco. Inoltre, la segmentazione 2D e l'analisi basata sull'OCT si sono rivelate promettenti, offrendo potenzialmente un nuovo modo per ottimizzare i trattamenti con DCBs senza distruggere i campioni di tessuto. Le mappe di distribuzione del rivestimento OCT sono qualitativamente correlate alle mappe SEM e, per la loro minore invasività, la prima può essere eseguita nell'uomo mentre la SEM no.Drug-coated balloons (DCBs) are medical devices widely used to treat cardiovascular diseases, but their effectiveness is often limited by Insufficient transfer of the drug coating from the balloon to the targeted site. Understanding and improving this transfer process is crucial for enhancing therapeutic outcomes. One of the fundamental challenges is understanding how physical parameters, such as contact pressure, influence the efficiency of drug coating transfer. Currently, there is also a lack of non-destructive methods for analyzing how much drug is transferred to the tissue, making it difficult to study this process and optimize it without destroying the samples. This thesis aimed to address these issues by investigating the mechanisms behind drug transfer from DCBs to arterial tissue, focusing specifically on how contact pressure affects this process. The work also aims to develop advanced image processing techniques to compare the transferred drug coating with the bulk drug post in vivo treatment and explore the potential of non-destructive methods like Optical Coherence Tomography (OCT) to assess coating transfer efficacy. To achieve these goals in vivo, ex vivo, and in silico methodologies were used. In the in vivo studies, porcine arteries treated with DCBs were analyzed using OCT and Scanning Electron Microscopy (SEM) to create maps of drug coating distribution. For the ex vivo experiments, drug-coated balloons were inflated and subjected to stamping tests using a uniaxial machine, which simulated the compression applied during DCB angioplasty. The tissues were analyzed with image processing to quantify the amount of drug transferred at different levels of contact pressure, to validate our results we compare them with goal standard method HPLC. Additionally, computational simulations were performed to understand how factors like arterial stiffness and thickness might influence drug transfer. The results demonstrated that increased contact pressure significantly increased drug coating transfer, but this correlation is not linear in fact we observe that until a certain value of contact pressure we have trend and after that value we have the same trend but with a lower slope. Comparing OCT and SEM maps we can afferm that OCT-based imaging produced results similar to SEM, indicating that OCT could be a faster and less invasive alternative for future studies to assess transfer efficacy. In conclusion acute coating transfer are correlated with bulk drug both in the vivo and in the ex vivo study, suggesting that image analysis is a reliable tool to assess the drug transfer efficacy. Moreover, 2D segmentation and OCT-based analysis proved to be promising potentially offering a new way to optimize DCBs treatments without destroying tissue samples. OCT coating distribution maps are qualitative correlated with SEM maps and for their less invasive solution the first one can be performed in humans while SEM not

Nuclear Inelastic X-Ray Scattering of FeO to 48 GPa

The partial density of vibrational states has been measured for Fe in compressed FeO (w\"ustite) using nuclear resonant inelastic x-ray scattering. Substantial changes have been observed in the overall shape of the density of states close to the magnetic transiton around 20 GPa from the paramagnetic (low pressure) to the antiferromagnetic (high pressure) state. Our data indicate a substantial softening of the aggregate sound velocities far below the transition, starting between 5 and 10 GPa. This is consistent with recent radial x-ray diffraction measurements of the elastic constants in FeO. The results indicate that strong magnetoelastic coupling in FeO is the driving force behind the changes in the phonon spectrum of FeO.Comment: 4 pages, 4 figure

Generalized calculation of magnetic coupling constants for Mott-Hubbard insulators: Application to ferromagnetic Cr compounds

Using a Rayleigh-Schr\"odinger perturbation expansion of multi-band Hubbard models, we present analytic expressions for the super-exchange coupling constants between magnetic transition metal ions of arbitrary separation in Mott-Hubbard insulators. The only restrictions are i) all ligand ions are closed shell anions and ii) all contributing interaction paths are of equal length. For short paths, our results essentially confirm the Goodenough-Kanamori-Anderson rules, yet in general there does not exist any simple rule to predict the sign of the magnetic coupling constants. The most favorable situation for ferromagnetic coupling is found for ions with less than half filled d shells, the (relative) tendency to ferromagnetic coupling increases with increasing path length. As an application, the magnetic interactions of the Cr compounds Rb$_2$CrCl$_4$, CrCl$_3$, CrBr$_3$ and CrI$_3$ are investigated, all of which except CrCl$_3$ are ferromagnets.Comment: 13 pages, 6 eps figures, submitted to Phys Rev

A neutron scattering study of two-magnon states in the quantum magnet copper nitrate

We report measurements of the two-magnon states in a dimerized antiferromagnetic chain material, copper nitrate (Cu(NO3)2*2.5D2O). Using inelastic neutron scattering we have measured the one and two magnon excitation spectra in a large single crystal. The data are in excellent agreement with a perturbative expansion of the alternating Heisenberg Hamiltonian from the strongly dimerized limit. The expansion predicts a two-magnon bound state for q ~ (2n+1)pi*d which is consistent with the neutron scattering data.Comment: 11 pages of revtex style with 6 figures include