Tm3+/Ho3+ codoped tellurite fiber laser

Continuous-wave and Q-switched lasing from a Tm 3+ /Ho 3+ codoped tellurite fiber is reported. An Yb 3+ /Er 3+ -doped silica fiber laser operating at 1.6μm was used as an in-band pump source, exciting the Tm 3+ ions into the F 4 3 level. Energy is then nonradiatively transferred to the upper laser level, the I 7 5 state of Ho 3+ . The laser transition is from the I 7 5 level to the I 8 5 level, and the resulting emission is at 2.1μm . For continuous wave operation, the slope efficiency was 62% and the threshold 0.1W ; the maximum output demonstrated was 0.16W . Mechanical Q switching resulted in a pulse of 0.65μJ energy and 160ns duration at a repetition rate of 19.4kHz

ESTIMATION OF SOME SECONDARY METABOLITES FROM THE IN VITRO CULTURES OF CHLOROPHYTUM BORIVILIANUM SANT. Et. FERN

Objective: To perform phytochemical screening, estimate total saponins and to study the secondary metabolite profiling of Chlorophytum borivilianum by ESI-MS (Electron spray ionisation-mass spectroscopy) and GC-MS (Gas chromatography-mass spectroscopy) techniques.Methods: The powdered samples of leaves and roots (nature grown and freshly harvested and hardened in vitro regenerated) and callus of Chlorophytum borivilianum (2 g) were extracted exhaustively by soxhlet by refluxing with petroleum ether (60-80 °C) and then with ethanol (85%). Alternatively, the methanol extract was prepared for the samples by the cold maceration method and the filtered extract was used. This extract was further analyzed by gas chromatography-mass spectrometry to identify and characterize the chemical compounds present in the crude extracts. Vanillin sulphuric acid assay was done to estimate the total saponin content of extracts.Results: Phytochemical analysis of ethanolic extract showed the presence of major classes of phytochemicals. The spectrophotometric analysis as well as the GC-MS results revealed the remarkably high percentage of saponin content in the in vitro roots. Besides this, many important secondary metabolites viz. β-Sitosterol and Taraxerone were also revealed by GC-MS.Conclusion: Results of this study showed enhanced production of many important secondary metabolites, especially saponins in tubers of in vitro regenerated plantlets vis a vis that of the nature grown plants establishing the fact that micropropagation can pave new vistas for the research in phytopharmaceuticals and bioprospecting of rare and important medicinal plants.Â

A Simple Statistical Model for Analysis of QGP-droplet (Fireball) Formation

We construct the density of states for quarks and gluons using the `Thomas - Fermi model' for atoms and the `Bethe model' for nucleons as templates. With parameters to take care of the plasma (hydrodynamical) features of the QGP with a thermal potential for the interaction, we find a window in the parametric space of the model where observable QGP droplets of $\sim$ 5 fm radius can occur with transition temperature in the range 140 MeV to 250 MeV. By matching with the expectations of Lattice Gauge estimates of the QGP-hadron transitions, we can further narrow the window, thereby restricting the allowed values of the flow-parameters of the model.Comment: LaTex 11 pages, 8 figure

Nonlinear optical properties of stilbene and azobenzene derivatives containing azaphosphane groups

We have studied the nonlinear optical (NLO) properties of some donor-acceptor molecules with stilbene and azobenzene molecules as backbone. We have used the nitro group as the acceptor and azaphosphane (R3P=N-) as the donor group. To study the effect of variation of NLO properties, we have replaced the substituents (Rs) connected to the phosphorus atom by methyl, amine and phenyl groups. We find that both first-order polarizability and hyperpolarizabilities are larger for stilbene derivatives and is maximum for the phenyl substitution. Second-order polarizability is higher for methyl substitution. We have also obtained the two-photon absorption cross-section for these molecules. We find that both one-photon and two-photon absorption cross-sections are maximum for the same excited state (first excited state in the case of stilbene and second excited state in the case of azobenzene derivatives)

Safety-Aware Apprenticeship Learning

Apprenticeship learning (AL) is a kind of Learning from Demonstration techniques where the reward function of a Markov Decision Process (MDP) is unknown to the learning agent and the agent has to derive a good policy by observing an expert's demonstrations. In this paper, we study the problem of how to make AL algorithms inherently safe while still meeting its learning objective. We consider a setting where the unknown reward function is assumed to be a linear combination of a set of state features, and the safety property is specified in Probabilistic Computation Tree Logic (PCTL). By embedding probabilistic model checking inside AL, we propose a novel counterexample-guided approach that can ensure safety while retaining performance of the learnt policy. We demonstrate the effectiveness of our approach on several challenging AL scenarios where safety is essential.Comment: Accepted by International Conference on Computer Aided Verification (CAV) 201

Modes of ejecta emplacement at Martian craters from laboratory experiments of an expanding vortex ring interacting with a particle layer

International audience[1] Ejecta morphologies of many Martian craters indicate fluidized emplacement which differs from ballistic emplacement in dry, airless environments. Double Layered Ejecta craters possess particularly interesting ejecta morphologies: two lobes and radial lineations on their surface, which probably result from gas-dominated radial flow during the emplacement. To examine how a radial flow interacts with surface particles to generate some of the observed morphologies on Mars, we have conducted water tank experiments in which a vortex ring encounters a particle layer. The threshold of particle motion and three interaction modes are described by two dimensionless numbers: particle Shields' parameter and particle Reynolds number. Our results show that gas-dominated flows are possible during cratering and could be used to constrain the ancient Martian environment from observations. Citation: Suzuki, A., I. Kumagai, Y. Nagata, K. Kurita, and O. S. Barnouin-Jha (2007), Modes of ejecta emplacement at Martian craters from laboratory experiments of an expanding vortex ring interacting with a particle layer, Geophys