The influence of doping on the laser performance

We report a comparison, at low inversion population density, between two Yb:YAG ceramics lasers with different doping levels (10 and 20 at %) emitting at 1030 and 1050 nm. At the shorter lasing wavelength, the efficiency and the maximum output power of both samples are almost independent on the concentration of dopants. Conversely, at 1050 nm the two samples show a sizeable difference in the performances for higher values of the pump power. The results are compared with numerical simulations accounting for the pump beam and the laser radiation in order to map the temperature distribution experienced by the samples. We studied the effects of the reinjection of the pump inside the active medium. We obtained an output power of 10 W with a slope efficiency of 59% in respect of the pump power on the 20 at % sample. Finally, we report the tuning range for the heavier-doped sample (20 at %), which, to the best of our knowledge, is the first measurement on an heavily doped sample even reported in literature.     

Scaling Limits for Multi-species Statistical Mechanics Mean-Field Models

We study the limiting thermodynamic behavior of the normalized sums of spins in multi-species Curie-Weiss models. We find sufficient conditions for the limiting random vector to be Gaussian (or to have an exponential distribution of higher order) and compute the covariance matrix in terms of model parameters.     

Characterization of weld (Reseda luteola L.) and spurge flax (Daphne gnidium L.) by high-performance liquid chromatography–diode array detection–mass spectrometry in Arraiolos historical textiles

The natural dyes, and dye sources, in two seventeenth century Arraiolos carpets from the National Museum of Machado de Castro were analysed by high-performance liquid chromatography with UV–vis diode array detection (HPLC–DAD) and HPLC–mass spectrometry (LC–MS). Weld (Reseda luteola L.), indigo and spurge flax (Daphne gnidium L.) were found to be the dye sources, in agreement with original dyeing recipes collected during the nineteenth century. In order to fully characterize the plant sources, LC–MS conditions were optimized with plant extracts and the chromatographic separation and mass detection were enhanced. Extraction of the dyes, in the Arraiolos carpet samples, was performed using mild conditions that avoid glycoside decomposition. For the blues a dimethylformamide solution proved to be efficient for indigotin recovery. For all the other colours, an improved mild extraction method (with oxalic acid, methanol, acetone and water) was used, enabling to obtain the full dye source fingerprint, namely the flavonoid glycosides in the yellow dyes.     

New stereoselective beta-glycosylation via a vinyl oxirane derived from D-glucal

[reaction: see text] The reaction of the vinyl oxirane 1 derived from D-glucal with a series of O-nucleophiles (alcohols, phenol, and diacetone D-glucose) affords the corresponding 2-unsaturated beta-O-glycosides in a completely stereoselective way (syn 1,4-addition pathway). Epoxide 1 is generated in situ by treatment of the corresponding hydroxy mesylate 2 with t-BuOK in anhydrous benzene.     

The low energy 2H(α, αp)n reaction

An investigation of the breakup reaction ²H(α, αp)n with incident energies of α-particles between 9.847 and 13.991 MeV has been performed. Results from kinematically complete measurements at 21 different kinematical configurations are presented. Final-state interaction enhancements have been experimentally observed. The energy is sufficiently low that the A = 6 system should be reasonably well described as a three-body system. The experimental data were compared with predictions based on Faddeev equations. Taking into account that no adjustable parameter is used, the quality of agreement is in general acceptable.     

Computational titration analysis of a multiprotic HIV-1 protease-ligand complex

A new computational method for analyzing the protonation states of protein-ligand complexes with multiple ionizable groups is applied to the structurally characterized complex between the peptide Glu-Asp-Leu and HIV-1 protease. This complex has eight ionizable groups at the active site: four from the ligand and four Asp residues on the protein. Correlation, with an error of ca. 0.6 kcal mol-1, is made between the calculated titration curve and the experimental titration curve. The analysis suggests that between four and five of the eight ionizable groups are protonated at the pH of crystallization.     

Nuclear temperature measurements with the double isotope ratio technique: Influence of the experimental conditions

The dependence of the nuclear temperatures of highly excited systems, extracted by means of the double ratios of the emitted isotopes, on the experimental conditions is investigated. Experimental data obtained in the Xe+Cu 30 MeV/nucleon reaction are used to study the sensitivity of the method and the effects of the energy thresholds on the obtained temperature values. We find that the temperatures extracted using the He/Li ratios can be strongly influenced by the experimental energy thresholds which are different for different elements. These distortions depend on the velocity of the emitting system and on the detection angle and therefore particular care is needed in the choice of the detectors in those experiments in which velocities are low and angles are large. The use of four isotopes of the same element make negligible such effects. Received: 6 October 1999 / Accepted: 28 May 2000     

Ferula L. Plant Extracts and Dose-Dependent Activity of Natural Sesquiterpene Ferutinin: From Antioxidant Potential to Cytotoxic Effects

The employment studies of natural extracts in the prevention and treatment of several diseases highlighted the role of different species of genus Ferula L., belonging to the Apiaceae family, dicotyledonous plants present in many temperate zones of our planet. Ferula communis L. is the main source of sesquiterpene ferutinin, a bioactive compound studied both in vitro and in vivo, because of different effects, such as phytoestrogenic, antioxidant, anti-inflammatory, but also antiproliferative and cytotoxic activity, performed in a dose-dependent and cell-dependent way. The present review will focus on the molecular mechanisms involved in the different activities of Ferutinin, starting from its antioxidant potential at low doses until its ionophoric property and the subsequent mitochondrial dysfunction induced through administration of high doses, which represent the key point of its anticancer action. Furthermore, we will summarize the data acquired from some experimental studies on different cell types and on several diseases. The results obtained showed an important antioxidant and phytoestrogenic regulation with lack of typical side effects related to estrogenic therapy. The preferential cell death induction for tumor cell lines suggests that ferutinin may have anti-neoplastic properties, and may be used as an antiproliferative and cytotoxic agent in an estrogen dependent and independent manner. Nevertheless, more data are needed to clearly understand the effect of ferutinin in animals before using it as a phytoestrogen or anticancer drug.     

Lifetime measurements with the pinhole method in presence of radiation trapping: II—application to Yb<Superscript>3+</Superscript> doped ceramics and crystals

In this paper, we present an experimental verification of a theoretical model for the evaluation of the results of the so-called pinhole method for the measurement of the upper level lifetime in doped optical materials where the resonant reabsorption of the emitted fluorescence determines significant radiation trapping effects. As an experimental verification of the model, we measured the lifetime of the upper laser level of Yb³⁺ in various crystals and ceramic samples usually employed for the realization of solid state laser sources.