Spectroscopic characterization of red perylimide/surfactant nanocomposites

Novel photoluminescent materials formed by some selected surfactants, metal derivatives of bis(2-ethylhexyl) sulfosuccinate (M(AOT) _n ; M = Na⁺, Co²⁺, Er³⁺ and Yb³⁺), bis(2-ethylhexyl) amine (BEEA), bis(2-ethylhexy1) phosphoric acid (HDEHP) and a 1:1 BEEA/HDEHP mixture, doped with the red perylimide (ROT-300) have been prepared, and their optical properties have been tested by absorption spectroscopy and steady state and time-resolved fluorescence. Experimental results show spectral shifts of the typical ROT-300 absorption and fluorescence bands with respect to that in apolar solvent medium. Data analysis leads consistently to attribute this feature mainly to the freezing of the diffusive movement of the dye molecules confined in the nanodomains of the surfactant liquid crystals, whilst minor effects can be due to interaction with the surfactant polar groups. Potentialities of these novel luminescent nanostructured composites as dye lasers, optical amplifiers and solar concentrators have been highlighted. In particular, under optical pumping using a pulse laser, amplified spontaneous fluorescence emission of the ROT-300/HDEHP system above an excitation energy threshold value of about 725 mJ cm⁻² was observed.     

Structural study of CH3S self-assembled monolayers on Au(111)

We present preliminary results of an experimental investigation of ordered phases of CH₃S chemisorbed on Au(111). The self-assembled monolayer has been grown by dosing dimethyl disulfide in ultrahigh vacuum at different substrate temperatures between 200 K and 320 K and following different protocols. The monolayers have been characterized by means of low-energy He atom scattering with time-of-flight detection in a temperature range between 150 K and 300 K. The observed diffraction patterns show that the main periodicity is well-described by the (3 × 4) overlayer of the Au(111) lattice, coexisting with the (√3 × √3) periodicity, in agreement with previous results obtained by means of low-energy electron diffraction.     

Imaging the Electric‐Field Distribution in Organic Devices by Confocal Electroreflectance Microscopy

Space resolved Stark spectroscopy is introduced as a non invasive optical technique for imaging electric field distribution in organic semiconductors. Stark spectroscopy relies on the electric field induced change in the absorption/reflection. It is shown that local monitoring of Stark shift with confocal spatial resolution provides quantitative information on the strength of the local field as well as charge distribution within the transport channel.     

Conformationally constrained CCK8 analogues obtained from a rationally designed peptide library as ligands for cholecystokinin type B receptor

A library of 14 cyclic peptide analogues derived from the octapeptide C-terminal sequence of the human cholecystokinin hormone (CCK(26-33), or CCK8) was designed, synthesized, and characterized. The 14 peptide analogues were rationally designed to specifically interact with the CCK type B receptor (CCK(B)-R) on the basis of the structure of the bimolecular complex between CCK8 and the third extracellular loop of CCK(B)-R, namely CCK(B)-R(352-379). The rational design of new ligands for CCK(B)-R has relied on stabilization by cyclic constraints of the structural motifs that bring the key residues of the ligand (especially Trp 30, Met 31, and Phe 33) in the proper spatial orientation for optimal interaction with the receptor. The binding affinity of the new ligands for CCK(B)-R was assessed by displacement experiments of (111)In-radiolabeled CCK8 in cells that overexpress the CCK(B) receptor. The new ligands generally showed binding affinities lower than that of parent CCK8, with the best compounds having IC50 values around 10 microM. Structure-activity relationship data show that preservation of the Trp 30-Met 31 motif is essential and that the Phe 33 side chain must be present. NMR conformational studies of the compound with maximal binding affinity (cyclo-B11, IC50=11 microM) in DPC micelles shows that this compound presents a turn-like conformation centered at the Trp 30-Met 31 segment, as planned by rational design. Such a conformation is stabilized by its interaction with the micelle rather than by the cyclic constraint.     

An eddy current integral formulation on parallel computer systems

In this paper, we show how an eddy current volume integral formulation can be used to analyse complex 3D conducting structures, achieving a substantial benefit from the use of a parallel computer system. To this purpose, the different steps of the numerical algorithms in view of their parallelization are outlined to enlighten the merits and the limitations of the proposed approach. Numerical examples are developed in a parallel environment to show the effectiveness of the method. Copyright © 2004 John Wiley & Sons, Ltd.     

A GRASP metaheuristic for microarray data analysis

The Weighted Gene Regulatory Network (WGRN) problem consists in pruning a regulatory network obtained from DNA microarray gene expression data, in order to identify a reduced set of candidate elements which can explain the expression of all other genes. Since the problem appears to be particularly hard for general-purpose solvers, we develop a Greedy Randomized Adaptive Search Procedure (GRASP) and refine it with three alternative Path Relinking procedures. For comparison purposes, we also develop a Tabu Search algorithm with a self-adapting tabu tenure. The experimental results show that GRASP performs better than Tabu Search and that Path Relinking significantly contributes to its effectiveness.     

Focusing of 915 MHz Electromagnetic Power on Deep Human Tissues: A Mathematical Model Study

The distribution of ohmic power in a CAT scan section of a human chest irradiated with 915 MHz peripheral sources is calculated using the moment method. In the simulation, the chest section (assumed to be uniformally developed along the cranio-caudal axis for a height equivalent to the field penetration) is subdivided in 235 subvolumes of known electric constants. The focusing of power on a selected region of the chest is obtained by properly exciting the sources. An optimization method allows selecting the amplitudes and phases in such a way that the power level in all subvolumes outside the focal region is kept below a given threshold.