264 research outputs found
Polarization-maintaining ytterbium-doped fibre with an aluminosilicate inner-cladding fabricated using in-situ doping technique
No full textThe ytterbium-doped fibre laser (YDFL) has become the forerunner for high-power fibre lasers and amplifiers largely owing to the broad emission of Yb3+ ions (lambda = 975 to 1200 nm) and their ability to be incorporated in a silica host in relatively high concentrations. Achieving multi-kilowatts of output power from a fibre has been made possible through improved fibre design and fabrication. In this paper we report on a robust polarization-maintaining (PM) YDFL with a unique aluminosilicate pedestal structure
Single-molecule fluorescence analysis of opening and closing of the RNA polymerase clamp
No full textCrystal structures of RNA polymerase (RNAP) indicate that the RNAP β’ pincer (“clamp”) can exist in conformational states, ranging from a fully open conformation that permits entry and exit of DNA, to a fully closed conformation that prevents entry and exit of DNA. It has been hypothesized that the clamp also adopts multiple conformational states in solution and conformational changes in the clamp are important for function. In this work, a single-molecule fluorescence resonance energy transfer (smFRET) approach was developed that enables determination of RNAPclamp conformation in solution. smFRET was measured between a probe at the tip of the RNAP clamp and a probe at a fixed reference point in RNAP. A computational framework was then employed to interpret measured FRET efficiencies in terms of structural changes. Using this approach, RNAP clamp conformation was defined in each step of 70-dependent transcription initiation and elongation and in each step in σ54-dependent transcription initiation. Additionally, effects of four RNAP inhibitors, myxopyronin, corallopyronin, ripostatin and Gp2 on RNAP clamp conformation were assessed. It was observed that the clamp is predominantly open in free RNAP and in all steps leading up to the formation of a catalytically-competent-transcription-initiation complex. Upon formation of a catalytically-competent-transcription-initiation complex, the clamp closes, and continues to remain closed during transcription elongation. It was further observed that myxopyronin, corallopyronin, ripostatin and Gp2, prevent opening of the RNAP clamp. The results lead to the proposal that, the open clamp state is important for entry of DNA into, and unwinding of DNA in, the RNAP active center cleft during formation of a catalytically-competent-transcription initiation complex. The results lead to the proposal that, after entry of DNA into the RNAP active-center cleft upon formation of the catalytically competent transcription initiation complex, electrostatic interactions between the negatively charged DNA and the positively charged inner facet of the clamp, induce and/or stabilize clamp closure. The results are in agreement with the proposal that, clamp closure is important for stability of the catalytically competent transcription initiation complex and for stability and processivity of the transcription elongation complex.Ph. D.Includes bibliographical referencesby Anirban Chakrabort
Recent developments in rare-earths doped nano-engineered glass based optical fibers for high power fiber lasers
No full textRecent advances of development of rare-earth (RE) doped optical fibers have become increasingly important due to their applications in various optoelectronic devices such as high power optical fiber amplifiers, fiber lasers, etc. We present a review of recent progress on development of RE-doped glass host based optical fiber materials with special emphasis on large mode area fibers for efficient laser and amplifier. The challenging task is to manage high power inside the active core otherwise output power instability would affect the beam quality. Best solution is to use suitable dopants in addition to active elements during the process of fabrication. Modified chemical vapour deposition (MCVD) process combined with solution doping technique is deployed to develop RE-doped nano-engineered glass based optical fibers through suitable thermal annealing of optical preforms. The developed doped fibers are characterized by DTA, TEM, XRD, XAS, EPMA and EXAFS to assess the structural parameters. This new class of optical fiber materials will open up new possibilities for extended functionality and greater optoelectronic integration
Saltwater intrusion management of coastal aquifers. II: operation uncertainty and monitoring
No full textManagement of saltwater intrusion in coastal aquifers should be based on robust management strategies and monitoring of their impacts. A robust optimal management strategy is less sensitive to deviations from prescribed strategies at the field level. Development of robust management framework is an important issue that needs attention especially when it results in near optimal strategies even when deviations from prescribed strategies occur in the field implementation stage. Implementation of a strategy requires field scale monitoring to determine the impact in terms of compliance with management goals due to possible deviation from an optimal prescribed strategy. Design of such an optimal monitoring network for compliance also requires robust optimal design due to the uncertainties involved. Deviations from prescribed strategies in the field are often more sensitive to uncertainties in the implementation phase. A multiple objective management model for robust optimal management of saltwater intrusion in coastal aquifers is proposed. Both risk neutral and risk-based management model formulations are presented. A robust monitoring network design methodology is also proposed for compliance monitoring of proposed robust management strategies. Performances of the developed methodology are tested for an illustrative coastal aquifer study area, as presented by Dhar and Datta. Performance evaluations show potential applicability of the developed methodologies and some of the relative advantages
Thulium-doped silica fibers with enhanced<sup>3</sup>H 4 level lifetime: modelling the devices for 800-820 nm band
No full textSilica-based thulium-doped fiber devices operating around 810 nm would extend the spectral range covered by highpower fiber devices. Using a comprehensive numerical model of the fiber we have shown that efficient lasing at 810 nm can be achieved for specific ranges of the laser cavity parameters in silica-based thulium-doped fibers with enhanced 3H4 lifetime up to 58 µs as measured in our highly alumina-codoped fibers. We present optimization of the thulium-doped fiber and laser cavity parameters and also potential applications of the developed host material in amplifiers and broadband sources
Visualizing WSPDs and Their Applications (Media Exposition)
No full textIntroduced by Callahan and Kosaraju back in 1995, the concept of well-separated pair decomposition (WSPD) has occupied a special significance in computational geometry when it comes to solving distance problems in d-space. We present an in-browser tool that can be used to visualize WSPDs and several of their applications in 2-space. Apart from research, it can also be used by instructors for introducing WSPDs in a classroom setting. The tool will be permanently maintained by the third author at https://wisno33.github.io/VisualizingWSPDsAndTheirApplications/
Germanium microsphere high-Q resonator
No full textIn this Letter, the fabrication and characterization of a microsphere resonator from the semiconductor germanium is demonstrated. Whispering gallery modes are excited in a 46 µm diameter germanium microsphere resonator using evanescent coupling from a tapered silica optical fiber with a waist diameter of 2 µm. Resonances with Q factors as high as 3.8 x 104 at wavelengths near 2 µm are observed. Because of their ultrahigh optical nonlinearities and extremely broad transparency window, germanium microsphere resonators offer the potential for optical processing devices, in particular at long wavelengths, such as around 2 µm
Hyperaeschra innotata
No full textHyperaeschra innotata (Hampson, 1896) Phalera innotata * Hampson, 1896; 4: 455. Hyperaeschra innotata; Schintlmeister, 2013; 11: 222. TL: Khasis [Meghalaya, India]; TD: unknown type depository. Distribution: India: Meghalaya. Note: Endemic to NE India. *Hampson mentioned “Swinh. MS.” against the species in volume 4 of Fauna of British India, Moths. Since the species was described there for the first time, the credit as the main author is given to Hampson.Published as part of Chandra, Kailash, Mazumder, Arna, Sanyal, Abesh Kumar, Ash, Anirban, Bandyopadhyay, Uttaran, Mallick, Kaushik & Raha, Angshuman, 2018, Catalogue of Indian Notodontidae Stephens, 1829 (Lepidoptera: Noctuoidea), pp. 1-84 in Zootaxa 4505 (1) on page 37, DOI: 10.11646/zootaxa.4505.1.1, http://zenodo.org/record/260670
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