Three terminals optoelectronics devices integrated into a silicon on silicon waveguide

In this paper we describe two different kind of optoelectronic devices both based on a three terminals active device and exploit the plasma dispersion effect to achieve the desired working. The first device exploits this effect in order to obtain an optical modulation. The second device is an optoelectronic router based on the mode-mixing principle together with the injection-induced optical phase shift. Both devices are integrated into a Silicon on Silicon optical channel waveguide which can be realized using a standard bipolar process. The possibility of using standard, well-known technology presents several advantages with respect to III–V Optoelectronics. The active three terminal device used is a Bipolar Mode Field Effect Transistor (BMFET). Numerical simulation results are presented on both devices.     

RESOLUTION OF THE INDIVIDUAL TRYPTOPHANYL CONTRIBUTIONS TO THE NEAR-ULTRAVIOLET DICHROIC ACTIVITY OF APOMYOGLOBIN

Abstract –The individual tryptophanyl contributions to the near-ultraviolet dichroic activity of apomyoglobin in its native conformation have been resolved. This was accomplished by comparing the spectra of two classes of apomyoglobin with different aromatic residue contents and observing the effect of a specific modification of indole residues. The circular dichroism (CD) spectra of apomyoglobins containing two tryptophanyl residues, i.e. Trp A-5 and A-12, show the presence of a positive peak centered at 292 nm, attributable to indolic chromophore, which is missing in the CD spectrum of tuna apomyoglobin possessing only Trp A-12. Moreover, the specific modification of Trp A-5 by 2-hydroxy-5-nitrobenzyl bromide is shown by the lack of the 292 nm peak and the appearance of a positive band at longer wavelength. The pH dependence of the position of this band suggests that it arises from the 2-hydroxy-5-nitrobenzyl moiety. The results suggest that Trp A-12 does not substantially contribute to the optical activity in the near ultraviolet.     

Structure and cytotoxicity of phidianidines A and B: first finding of 1,2,4-oxadiazole system in a marine natural product

Two indole alkaloids, phidianidines A (1) and B (2), exhibiting an uncommon 1,2,4-oxadiazole ring linked to the indole system, have been isolated from the marine opisthobranch mollusk Phidiana militaris. The structures of the two metabolites have been elucidated by spectroscopic techniques. Phidianidines exhibit high cytotoxicity against tumor and nontumor mammalian cell lines in in vitro assays.     

Resolution of tryptophan-ANS fluorescence energy transfer in apomyoglobin by site-directed mutagenesis

Resonance energy transfer between tryptophanyl residues and the apolar fluorescent dye 1-anilino-8-naphthalene sulfonate (ANS) occurs when the fluorophore is bound to native folded sperm whale apomyoglobin. The individual transfer contribution of the two tryptophanyl residues (W7 and W14, both located on the A-helix of the protein) was resolved by measuring the tryptophan-ANS transfer efficiency for the ANS-apomyoglobin complexes formed by wild-type protein and protein mutants containing one or no tryptophanyl residues, i.e. W7F, W14F and W7YW14F. The transfer efficiency of W14 residue was found to be higher than that of W7, thus indicating that W14 acts as the main energy donor in the ANS-apomyoglobin complex. This suggests that the plane containing the anilinonaphthalene ring of the extrinsic fluorophore has a spatial orientation similar to that of W14 and, hence, to the heme group in the holoprotein.     

Optical characterization of the recombination process in silicon wafers, epilayers and devices

In this paper we present various approaches to the measurement of recombinative parameters in silicon wafers, epitaxial layers and solar cells. In particular our techniques are able to measure the bulk lifetime and the surface recombination velocity at low injection levels. We also show that the techniques presented are a reliable tool to monitor the fabrication process of a standard crystalline silicon solar cell. In all the methodologies presented there are no stringent requirements concerning the state of wafer surface.     

Design, synthesis and characterisation of guanosine-based amphiphiles

A small library of sugar-modified guanosine derivatives has been prepared, starting from a common intermediate, fully protected on the nucleobase. Insertion of myristoyl chains and of diverse hydrophilic groups, such as an oligoethylene glycol, an amino acid or a disaccharide chain, connected through in vivo reversible ester linkages, or of a charged functional group provided different examples of amphiphilic guanosine analogues, named G1-G7 herein. All of the sugar-modified derivatives were positive in the potassium picrate test, showing an ability to form G-tetrads. CD spectra demonstrated that, as dilute solutions in CHCl(3), distinctive G-quadruplex systems may be formed, with spatial organisations dependent upon the structural modifications. Two compounds, G1 and G2, proved to be good low-molecular-weight organogelators in polar organic solvents, such as methanol, ethanol and acetonitrile. Ion transportation experiments through phospholipid bilayers were carried out to evaluate their ability to mediate H(+) transportation, with G5 showing the highest activity within the investigated series. Moreover, G3 and G5 exhibited a significant cytotoxic profile against human MCF-7 cancer cells in in vitro bioassays.     

Oxygenated cembranoids of the decaryiol type from the Indonesian soft coral Lobophytum sp.

Three novel cembrane diterpenoids, decaryiols B-D (5-7), characterized by a bicyclic skeleton of the decaryiol-type, have been isolated from the Indonesian soft coral Lobophytum sp., along with three known cembranoids. The stereostructures of these metabolites have been established through extensive NMR spectroscopic analysis, application of the modified Mosher method, and chemical conversion. Cembranoids obtained from Lobophytum sp. (2-7) and six semisynthetic derivatives (9-14) prepared from decaryiol were tested for cell growth inhibitory activity against three different cell lines. O-Methyl decaryiol (10) exhibited a significant and selective activity against glioma cell lines.     

Structure and synthesis of a unique isonitrile lipid isolated from the marine mollusk Actinocyclus papillatus

The first chemical study of an Actinocyclidae nudibranch, Actinocyclus papillatus, resulted in the isolation of (-)-actisonitrile (1), a lipid based on a 1,3-propanediol ether skeleton. The structure was established by spectroscopic methods, whereas the absolute configuration of the chiral center was determined by comparing the optical properties of natural actisonitrile with those of (+)- and (-)-synthetic enantiomers, opportunely prepared. Both (-)- and (+)-actisonitrile were tested in preliminary in vitro cytotoxicity bioassays on tumor and nontumor mammalian cells.     

Separation of bulk lifetime and surface recombination velocity obtained by transverse optical probing and multi-wavelength technique

In this paper, a contactless, all-optical and non-destructive technique for simultaneous measurement of minority carrier recombination lifetime and surface recombination velocity is presented. The principle is based upon measurement, at low injection level, of the free carrier optical absorption transient probed by an infrared beam following electron–hole pairs excitation by a pulsed laser beam working at several wavelengths. Being contactless and non-destructive with respect to the surface to be analyzed, the method is appealing for routine lifetime characterization. A brief review of the theory underlying the measurement technique, aimed to emphasize its advantages and limits, and preliminary experimental data proving the applicability of the new scheme are presented.