|\epsilon|-Near-zero materials in the near-infrared

We consider a mixture of metal-coated quantum dots dispersed in a polymer matrix and, using a modified version of the standard Maxwell-Garnett mixing rule, we prove that the mixture parameters (particles radius, quantum dots gain, etc.) can be chosen so that the effective medium permittivity has an absolute value very close to zero in the near-infrared, i.e. $|{\rm Re}(\epsilon)| \ll 1$ and $|{\rm Im}(\epsilon)| \ll 1$ at the same near-infrared wavelength. Resorting to full-wave simulations, we investigate the accuracy of the effective medium predictions and we relate their discrepancy with rigorous numerical results to the fact that $|\epsilon| \ll 1$ is a critical requirement. We show that a simple method for reducing this discrepancy, and hence for achieving a prescribed and very small value of $|\epsilon|, $ consists in a subsequent fine-tuning of the nanoparticles volume filling fraction.     

Self-Assembly of Supramolecular Architectures Using Chlorotetra(Pyrrole-2-Carboxylato)Diruthenium Molecules as Building Blocks

Two new complexes, based on the unit Ru₂Cl(μ-O₂CC₄H₄N)₄ (1) (O₂CC₄H₄N = pyrrole-2-carboxylate), Ru₂Cl(μ-O₂CC₄H₄N)₄(H₂O)·4H₂O [1(H ₂ O)·4H ₂ O], and Ru₂Cl(μ-O₂CC₄H₄N)₄(Me₂CO) [1(Me ₂ CO)], are synthesized and structurally characterized. The physical properties of these complexes are studied and compared with those previously reported for Ru₂Cl(μ-O₂CC₄H₄N)₄(thf)·thf·H₂O [1(thf)·thf·H ₂ O]. The nature of the solvent molecule bonded to the axial position of the dimetallic unit determines the supramolecular interactions leading to different arrangements in the solid state. The presence of NH groups in the pyrrolic rings favours the existence of hydrogen bond interactions that are present in the three complexes. In addition, complex 1(Me ₂ CO) shows π–π stacking interactions through pyrrolic rings of different dimetallic units. Dedicated to the memory of Prof. F. Albert Cotton.     

Molecular recognition: A thermodynamic study of non bonded interactions in aqueous solutions of iminoacids. Effects of steric and geometric isomerism

Enthalpies of dilution of binary and ternary aqueous solutions containing L-and D-proline, cis-L- and cis-D-4-hydroxy proline, trans-L-4-hydroxy proline, have been determined by flow calorimetry at 25°C. Pairwise self-and cross-interaction coefficients of the virial expansion of the excess enthalpies were evaluated. They are positive for solutions of unsubstituted prolines. On the contrary, upon the introduction of a hydroxy group, they become negative, reaching the largest value for the cis-L-lcis-D-4-hydroxy proline system. The results are interpreted in terms of preferential configurations, stabilized by interactions between the hydrophilic groups.     

ISOLATION,CHARACTERIZATION AND RECONSTITUTION OF PHYCOBILIPROTEIN ROD-CORE LINKER POLYPEPTIDE COMPLEXES FROM THE PHYCOBILISOME OF Mastigocladus laminosus*

A rod-core complex, (αβ)₆^PC. L_RC^29.5,(αβ)₃^APC.L_C^8.9, composed of hexameric phycocyanin (PC) and trimeric allophycocyanin (APC) subcomplexes associated to the CpcG2 gene product, has been isolated from the phycobilisome of Mastigocladus laminosus. Exactly the same complex was obtained by reconstitution using the subcomplexes(αβ)₃^PC. L_RC 29.5 and (aβ)₃^APC.L_C^8.9 as educts. Spectroscopic analysis of the isolated PC-L_R and PC-L_RC complexes from M. laminosus shows that the L_RC cause the largest red-shift in the absorbance and fluorescence emission maxima of PC. These results indicate that L_RC mediate PC-APC interactions in vitro. Only the CpcG2 polypeptide was able to promote this specific interaction, as neither CpcG3-PC nor, as a negative control, CpcC-PC complexes showed any reconstitution products with the core subcomplex (αβ)₃^APC.L_c^8.9. This is an indication that each of the four L_RC in the phycobilisomes of M. laminosus and Anabaena sp. PCC 7120 attaches two peripheral rods specifically to one of four different core binding sites.     

Thermodynamics of alcohols and monosaccharides in aqueous solutions of biuret at 25°C

The excess enthalpies of ternary aqueous solutions of biuret with four aliphatic alcohols or four isomeric pentoses have been determined by flow microcalorimetry at 25°C. The coefficients of the virial expansion of the excess enthalpies have been evaluated and compared with those already reported for urea and thiourea with the same alcohols and pentoses used here. For biuret-alcohol systems, the cross coefficients are positive and depend on the length and branching of the alkyl chain of the alcohols. On the contrary, they are negative for biuret-pentose systems. Hence, biuret, as urea and thioura, is able to differentiate the behavior of families of solutes characterized by the same functional groups. The results are interpreted in terms of the relative stabilities of the hydration cospheres of predominantly hydrophobic or predominantly hydrophilic cosolutes. However, hypotheses about the hydration cospheres of the saccharides, which are more complex than those used previously, seem to be necessary to rationalize their complete behavior in water.     

Physico-chemical properties of aqueous extremely diluted solutions in relation to ageing

An extensive study has been carried out on aqueous ‘extremely diluted solutions’ (EDS). The employed experimental methodologies were well established physico-chemical techniques: flux calorimetry, conductometry, pH-metry, e.m.f. of suitable galvanic cell. The obtained results show that the preparation procedure significantly alters the physico-chemical behaviour of such solutions. Moreover, the analysis of the experimental data vs. the ‘arrow of time’ turned out to be astonishingly important. In fact some measured physico-chemical parameters evolve with time. Some experimentally measurable physico-chemical properties of the solvent water were largely affected by both time and the ‘life path’ of the samples. In particular, we evidenced two new experimental phenomena characterizing the EDS: the presence of a series of maximums in the measured electrical conductivity vs. the sample age; the dependence of said maximums on the volume of the EDS during its ageing. All of these new experimental results clearly suggest the presence of an extended and ‘ordered’ dynamics involving the whole of the water molecules in the liquid. A temporal evolution, featuring three maximums in the course of four years of ageing and the dependence on the ageing volumes do not fit the framework of classical thermodynamics. It therefore seems appropriate to interpret these phenomena on the basis of the thermodynamics of dissipative structures, which are far from equilibrium systems.     

Optimizing ICA in fMRI using information on spatial regularities of the sources

Spatial independent component analysis (ICA) is a well-established technique for multivariate analysis of functional magnetic resonance imaging (fMRI) data. It blindly extracts spatiotemporal patterns of neural activity from functional measurements by seeking for sources that are maximally independent. Additional information on one or more sources (e.g., spatial regularity) is often available; however, it is not considered while looking for independent components. In the present work, we propose a new ICA algorithm based on the optimization of an objective function that accounts for both independence and other information on the sources or on the mixing model in a very general fashion. In particular, we apply this approach to fMRI data analysis and illustrate, by means of simulations, how inclusion of a spatial regularity term helps to recover the sources more effectively than with conventional ICA. The improvement is especially evident in high noise situations. Furthermore we employ the same approach on data sets from a complex mental imagery experiment, showing that consistency and physiological plausibility of relatively weak components are improved.