Temperature effects on supercontinuum generation using a continuous-wave Raman fiber laser

We describe the effect of temperature variations on supercontinuum (SC) generation in optical fibers using a continuous-wave (CW) Raman fiber laser as a pump. We achieve supercontinuum generation by pumping only ∼2 W of power into a 7 km-long nonzero dispersion-shifted fiber (NZDSF) in the region of small anomalous dispersion. In these conditions, the supercontinuum builds up basically on modulational instability and Raman. At room temperature, the supercontinuum covers effectively the S, C and L transmission bands defined by the International Telecommunication Union (ITU). Temperature tuning of the fiber environment provides a means of tuning the fiber dispersion, and thus a means of changing the width and shape of the supercontinuum spectrum. We demonstrate a 27% increase in the 10-dB SC width. We believe that the application of this new tuning mechanism to other experimental configurations using pulsed sources might be used to produce extremely broad supercontinuums.     

Implementation of recycling routes for scanning probe microscopy tips.

In this work, effective, yet simple, recycling mechanisms for used scanning probe microscopy (SPM) tips were implemented. Comprising a tip profile characterization methodology and specific cleaning procedures, which decontaminate SPM tips whether the contamination nature is known or not, such routes were optimized during numerous tests with brand new, previously used, and already discarded categories of SPM tips. The results show that if the used tip suffered contamination only, but no physical damages, during its scanning lifetime, it becomes readily available for reutilization after the cleansing process, characterizing a recycling route. On the other hand, if the tip went through wear and breakages during its utilization, it still can be decontaminated, but may not be directly reutilized due to its inadequate physical profile. Nevertheless, the methodology developed in this work may yet be applied as part of a more complex recycling route.     

QSAR modeling with the electrotopological state indices: Corticosteroids

A structure-activity analysis of a series of steroids binding to corticosteroid-binding globulin was made using the electrotopological state index for each atom in the molecule. Two indices were found to correlate well with the binding affinity. The indices encode structural characteristics in the A and the D rings of the steroids in the study. One of the indices was formulated as the difference between two indices in the A ring. The two were not intercorrelated, suggesting that the composite index signals the influence of structure changes in or near the A ring that can be monitored by the composite index. This is a new observation using this structure-activity method. It is suggested that this model makes some contributions towards detection of the pharmacophore.     

Reaction of allylsilanes and allylstannanes with alkynes catalyzed by electrophilic late transition metal chlorides

The intramolecular reaction of allylsilanes and allylstannanes with alkynes proceeds catalytically in the presence of Pt(II), Pd(II), Ru(II), and Au(III) chlorides. Although more limited, AgOTf also catalyzes the cyclization. Usually, PtCl2 as the catalyst in methanol or acetone gives the best results. The reaction proceeds by exo attack of the allyl nucleophile on the alkyne to form five- or six-membered ring carbocycles. The reaction generally proceeds with anti stereoselectivity. However, a terminally substituted trimethylsilyl derivative reacts by a syn-type addition. The intermediate alkenylpalladium complex has been trapped with allyl chloride to form an allylated derivative with an additional carbon-carbon bond.     

Substituent effects on the photophysical properties of pterin derivatives in acidic and alkaline aqueous solutions

Pterins are heterocyclic compounds with important biological functions, and most of them may exist in two acid-base forms in the pH range between 3 and 13 in aqueous solution. In this work, the photophysical properties of acid and basic forms of six compounds of the pterin family (6-hydroxymethylpterin [HPT], 6-methylpterin [MPT], 6,7-dimethylpterin [DPT], rhamnopterin [RPT], N-methylfolic acid [MFA], and pteroic acid [PA]) have been studied. The effects of the chemical nature of the substituents at position 6 of the pterin moiety and the effects of the pH on the absorption and emission properties are analyzed. The fluorescence characteristics (spectra, quantum yields, lifetimes) of these compounds have been investigated using the single-photon-counting technique. Results obtained for pterin derivatives containing small substituents with 1 carbon atom (HPT, MPT, DPT) and short hydrocarbon chain (4 carbon atoms) (RPT) are different from those found for pterin derivatives containing a p-aminobenzoic acid (PABA) moiety in the substituent (MFA and PA). Fluorescence quantum yields (Phi(F)) of the first group of compounds are relatively high (>/=0.4), whereas MFA and PA exhibit very small Phi(F) values (相似文献   

Aza-analogues of extended tetrathiafulvalenes

The phosphoramidate-like reaction of 1,3-dithiole derived N-(diethoxyphosphinyl)hydrazones with formyl derivatives of 1,3-dithiole affords the longest aza-analogues of extended tetrathiafulvalenes with a polyenic spacer reported to date. Their structural and electrochemical properties are discussed.     

On the convergence of isolated neutral oxygen vacancy and divacancy properties in metal oxides using supercell models

The properties of isolated neutral oxygen vacancies and divacancies of metal oxides of increasing complexity (MgO, CaO, alpha-Al2O3, and ZnO) have been studied by means of density-functional theory within a supercell periodic approach. Vacancy formation energies, vacancy-vacancy interactions, and geometry rearrangements around these point defects have been investigated in detail. The characterization of the electronic structure of these point defects has been established by analysis of the density of states and of the topology of the electron density and of electron localization function. It is found that the chemical character of the oxide determines the properties of the oxygen vacancies. For the covalent ZnO oxide, a more complex scheme arises in which the relaxation around the oxygen vacancy is much larger leading to the formation of Zn4-like almost metallic particles in the crystal. The relationship of these structures with the crystal shear planes is discussed. The present study shows that supercells containing approximately 200-300 atoms provide converged values for the geometric and electronic structure of oxygen vacancies of these metal oxides in the point defect low concentration limit.     

Selection of thermotolerant yeasts for simultaneous saccharification and fermentation (SSF) of cellulose to ethanol

A total of 27 yeast strains belonging to the groupsCandida, Saccharomyces, andKluyveromyces were screened for their ability to grow and ferment glucose at temperatures ranging 32-45°C. K. marxianus andK. fragilis were found to be the best ethanol producing organisms at the higher temperature tested and, so, were selected for subsequent simultaneous saccharification and fermentation (SSF) studies.