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Recarte V.,Public University of Navarra | Perez-Landazabal J.I.,Public University of Navarra | Sanchez-Alarcos V.,Public University of Navarra | Cesari E.,University of the Balearic Islands | And 4 more authors.
Applied Physics Letters | Year: 2013

The martensitic transformation in stoichiometric Ni2MnGa alloys is preceded by a weakly first order transformation from a high temperature cubic phase to a near-cubic modulated intermediate phase related to the presence of a soft phonon mode. This transformation has been proposed to appear as a consequence of the magnetoelastic coupling. Inelastic neutron scattering experiment performed under external magnetic field shows a temperature shift of the characteristic energy dip at ζ ≈ 0.33. Furthermore, an enhancement of the long-wavelength limit (C ′) of this branch with the applied magnetic field has been observed. Both results evidence a strong magnetoelastic interaction at the intermediate transition. © 2013 AIP Publishing LLC.

Chua Y.Z.,University of Rostock | Schulz G.,University of Rostock | Shoifet E.,University of Rostock | Huth H.,University of Rostock | And 3 more authors.
Colloid and Polymer Science | Year: 2014

Molecular dynamics is often studied by broad band dielectric spectroscopy (BDS) because of the wide dynamic range available and the large number of processes resulting in electrical dipole fluctuations and with that in a dielectrically detectable relaxation process. Calorimetry on the other hand is an effective analytical tool to characterize phase and glass transitions by its signatures in heat capacity. In the linear response scheme, heat capacity is considered as entropy compliance. Consequently, only processes significantly contributing to entropy fluctuations appear in calorimetric curves. The glass relaxation is a prominent example for such a process. Here, we present complex heat capacity at the dynamic glass transition (segmental relaxation) of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in a dynamic range of 11 orders of magnitude, which is comparable to BDS. As one of the results, we determined the characteristic length scale of the corresponding fluctuations. The dynamic glass transition measured by calorimetry is finally compared to the cooling rate dependence of fictive temperature and BDS data. For PS, dielectric and calorimetric data are similar but for PMMA with its very strong secondary relaxation process some peculiarities are observed. © 2014 Springer-Verlag.

Accardo A.,University of Naples Federico II | Morisco A.,University of Naples Federico II | Gianolio E.,University of Turin | Tesauro D.,University of Naples Federico II | And 4 more authors.
Journal of Peptide Science | Year: 2011

New mixed nanoparticles were obtained by self-aggregation of two amphiplic monomers. The first monomer (C18)2L5-Oct contains two C18 hydrophobic moieties bound to the N-terminus of the cyclic peptide octreotide, and spaced from the bioactive peptide by five units of dioxoethylene linkers. The second monomer, (C18)2DTPAGlu, (C18)2DTPA or (C18)2DOTA, and the corresponding Gd(III) complexes, contains two C18 hydrophobic moieties bound through a lysine residue to different polyamino-polycarboxy ligands: DTPAGlu, DTPA or DOTA. Mixed aggregates have been obtained and structurally characterized by small angle neutron scattering (SANS) techniques and for their relaxometric behavior. According to a decrease of negative charges in the surfactant head-group, a total or a partial micelle-to-vesicle transition is observed by passing from (C18)2DTPAGlu to (C18)2DOTA. The thicknesses of the bilayers are substantially constant, around 50 Å, in the analyzed systems. Moreover, the mixed aggregates, in which a small amount of amphiphilic octreotide monomer (C18)2L5-Oct (10% mol/mol) was inserted, do not differ significantly from the respective self-assembled systems. Fluorescence emission of tryptophan residue at 340 nm indicates low mobility of water molecules at the peptide surface. The proton relaxivity of mixed aggregates based on (C18)2DTPAGlu(Gd), (C18)2DTPA(Gd) and (C18)2DOTA(Gd) resulted to be 17.6, 15.2 and 10.0 mM-1 s-1 (at 20 MHz and 298K), respectively. The decrease in the relaxivity values can be ascribed to the increase in τM (81, 205 and 750 ns). The presence of amphiphilic octreotide monomer exposed on mixed aggregate surface gives the entire nanoparticles a potential binding selectivity toward somatostatin sstr2 receptor subtype, and these systems could act as MRI target-specific contrast agent. Mixed nanoparticles (micelles and liposomes) are obtained by co-aggregation of lipophilic octreotide with gadolinium complex containing amphiphilic monomers for MRI applications. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.

Leu L.-C.,Boise State University | Bian J.,Shanghai University | Gout D.,Oak Ridge National Laboratory | Gout D.,Juelich Center for Neutron Science | And 2 more authors.
RSC Advances | Year: 2012

The order-disorder phase transition of magnesium lithium titanate solid-solution (1-x)Li 2TiO 3-xMgO (0 ≤ x ≤ 0.5) ceramics prepared by conventional solid-state processing has been examined. The phase and structural analysis was carried out using electron diffraction, neutron diffraction and high-resolution transmission electron microscopy. Both electron and neutron diffraction results revealed the onset of an order-to-disorder transition at 0.3 < x < 0.4. Superlattice reflections found in certain regions of x = 0.2 samples and most areas of x = 0.3 samples were caused by a twin structure stabilized by Mg incorporation. Rietveld refinements of neutron diffraction data suggested a random distribution of Mg on the Li 4e sites and equal distribution of Mg on the two Ti 4e sites for x ≤ 0.3. As the Mg content continues to increase, the crystal symmetry transforms from monoclinic to cubic rocksalt. Consequently, the cation ordering on the 8f and 4d sites of the C2/c structure became corrupted and turned into short-range ordering on the 4a sites of a cubic structure with symmetry, resulting in diffuse scattering in electron diffraction patterns. © 2012 The Royal Society of Chemistry.

Baum M.,University of Cologne | Leist J.,University of Gottingen | Finger T.,University of Cologne | Schmalzl K.,Juelich Center for Neutron Science | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

The time dependence of switching multiferroic domains in MnWO4 has been studied by time-resolved polarized neutron diffraction. Inverting an external electric field inverts the chiral magnetic component within rise times ranging between a few and some tens of milliseconds in perfect agreement with macroscopic techniques. There is no evidence for any faster process in the inversion of the chiral magnetic structure. The time dependence is well described by a temperature-dependent rise time suggesting a well-defined process of domain reversion. As expected, the rise times decrease when heating towards the upper boundary of the ferroelectric phase. However, switching also becomes faster upon cooling towards the lower boundary, which is associated with a first-order phase transition. © 2014 American Physical Society.

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