165 research outputs found

    Southern African Large Telescope Spectroscopy of BL Lacs for the CTA project

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    In the last two decades, very-high-energy gamma-ray astronomy has reached maturity: over 200 sources have been detected, both Galactic and extragalactic, by ground-based experiments. At present, Active Galactic Nuclei (AGN) make up about 40% of the more than 200 sources detected at very high energies with ground-based telescopes, the majority of which are blazars, i.e. their jets are closely aligned with the line of sight to Earth and three quarters of which are classified as high-frequency peaked BL Lac objects. One challenge to studies of the cosmological evolution of BL Lacs is the difficulty of obtaining redshifts from their nearly featureless, continuum-dominated spectra. It is expected that a significant fraction of the AGN to be detected with the future Cherenkov Telescope Array (CTA) observatory will have no spectroscopic redshifts, compromising the reliability of BL Lac population studies, particularly of their cosmic evolution. We started an effort in 2019 to measure the redshifts of a large fraction of the AGN that are likely to be detected with CTA, using the Southern African Large Telescope (SALT). In this contribution, we present two results from an on-going SALT program focused on the determination of BL Lac object redshifts that will be relevant for the CTA observatory

    Neue B�cher

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    Simulation of ion transport through poly(ethylene oxide) loaded with lithium perchlorate

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    A hierarchical approach is used to simulate lithium ion motion through poly(ethylene oxide) loaded with lithium perchlorate, alone and with a tungsten oxide (WO3) interface to model an electrochromic smart window assembly. The structure of the polymer is simulated using commercial software. Relaxation of the polymer is allowed on a lattice on which the lithium ions move as a lattice gas. Polarization and van der Waals energy changes are calculated for an added lithium ion at each lattice point. The structure and energy are also calculated in the presence of the WO3 interface. Ion transport is simulated in a kinetic Monte Carlo method, with and without an electric field. During runs at 300 K without the WO3 interface, with a field the lithium ions move 35 angstrom along it and 3-7 angstrom across it but without a field they move 2-5 angstrom; these distances vary with temperature as expected for activated hopping. Ions explore their immediate neighbourhood, occasionally jumping to an adjacent neighbourhood along, across or sometimes against the field, thus circumventing regions where transport is hindered. With the WO3, the lithium ions tend to accumulate at the interface, producing a repulsive potential that reduces ion movement

    Comparison of induction of DNA single-strand breaks and initiation of rat hepatocarcinogenesis by different nitrosamines.

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    The capacities of nitrosamines to induce DNA single-strand breaks (SSB) and to initiate carcinogenesis in rat liver were compared. N-Nitrosodiethanolamine (NDELA), N-nitrosoethylhydroxyethylamine (NEHEA) and N-nitrosodiethylamine (NDEA) were equipotent in inducing DNA SSB when administered by gavage at doses of 0.35 mmol/kg, 0.015 mmol/kg and 0.37 mmol/kg, respectively. Male Wistar rats were injected with these nitrosamines and were then submitted to a selection procedure. Ten rats per group were sacrificed one week after the end of the selection to see the effects of the nitrosamines on the development of preneoplastic lesions. The numbers of gamma-glutamyl transferase (GGT)-positive lesions per cm2 were 0.8, 2.1, 5.2 and 40.1 in rats treated with saline, NDELA, NEHEA and NDEA, respectively. N-Nitrosobis(2,2,2-trifluorethyl)amine (6F-NDEA), a nongenotoxic and noncarcinogenic nitrosamine, induced 0.7 GGT-positive lesions per cm2. Ten rats per group also received 0.05% phenobarbital in their drinking-water and were killed six months after initiation in order to see the effect of the different nitrosamines on the incidence and yield of tumours. Two extrahepatic cancers were found after administration of NEHEA, whereas two hepatocellular carcinomas were detected after injection of NDEA. No cancer developed in the other groups. Although other factors may influence the process, these results indicate that no simple correlation can be established between induction of SSB in DNA and initiation of tumours by nitrosamines in rat liver

    2.2 Organische industrielle Produkte

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