Microstructured cladding elements to enhance performance and flexibility of large mode area leakage channel fibers

Large mode area fibers are imperative for scaling up the average power of fiber lasers. Single-mode behavior and low FM loss are the crucial functionalities for these fibers. However, for key applications such as picosecond pulsed lasers, the device length needs to at least a few meters. This makes a certain degree of bend tolerance a prerequisite in the fiber design. While rod-type PCFs have been very successful in offering large mode areas, their rigid configuration limits their application domain. Alternatively, leakage channel fibers (LCFs) have shown a great potential for offering substantial bend tolerance along with large mode areas. However, the proposed use of Fluorine-doped rods in the all-solid version limits their practical design space. Here, we propose a novel design concept to attain single-material, large mode area fibers (mode area >~ 1000µm2) with effectively single mode operation coupled with bending characteristics comparable to all-solid LCFs and greater design flexibility and easier splicing that is comparable to rod-type PCFs

The simulated cooling of the hot-rolled structural steel sections

AbstractTemperature models based on the finite difference, ADI and Runge-Kutta methods have been written in order to establish the most efficient algorithm when simulating the cooling of newly hot-rolled steel sections under a variety of cooling conditions. For air-cooling, the most efficient results were obtained using extended-stability Runge-Kutta methods, together with adaptive step-size control procedures. CPU time-savings of around 85% were achieved when an existing finite difference based section air-cooling model was modified to run using a specially developed, highly stable, second-order Runge-Kutta formula with the method of lines. The ADI approach gave the most efficient results for water spray cooling, producing accurate results in approximately half the CPU time required by the finite difference method

Predicting Structural and Optical Properties of Hollow-Core Photonic Bandgap Fibers from Second Stage Preforms

We propose a simple theory based on mass conservation that allows accurate prediction of guidance properties in hollow-core photonic bandgap fibers (HC-PBGF) from knowledge of the second stage preforms from which the fibers are drawn

Effects of resonant single-particle states on pairing correlations

Effects of resonant single-particle (s.p.) states on the pairing correlations are investigated by an exact treatment of the pairing Hamiltonian on the Gamow shell model basis. We introduce the s.p. states with complex energies into the Richardson equations. The solution shows the property that the resonant s.p. states with large widths are less occupied. The importance of many-body correlations between bound and resonant prticle pairs is shown.Comment: 4 pages, 3 figures, to be published in Phys. Rev.

Quons Restricted to the Antisymmetric Subspace: Formalism and Applications

In this work we develop a formalism to treat quons restricted to the antisymmetric part of their many-body space. A model in which a system of identical quons interact through a pairing force is then solved within this restriction and the differences between our solution and the usual fermionic model solution are then presented and discussed in detail. Possible connections to physical systems are also considered.Comment: 12 pages, 3 figure

Impacts of Federal Tax Laws and Economic Developments on the Texas Cattle Industry.

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Manufacturing of high performance hollow core microstructured optical fibres

Although fabrication technologies of Microstructured Optical Fibres (MOFs) fibres have matured at an impressive rate over the past ten years, these fibres are widely perceived as "challenging" and some key issues are still outstanding in order to improve their manufacturability. One such issue revolves around methods to improve structural control during the fibre draw. Structural control is of particular importance for certain types of microstructured fibres, such as hollow core Photonic Bandgap Fibres (PBGFs) and Anti-resonant (AR) fibres (also known as Kagome fibres). These fibres exploit resonant and/or anti-resonant guidance mechanisms and thus their transmission properties depend on the structure to a much greater extent as compared to conventional fibres. Hollow core MOFs have been identified as promising media for applications such as low latency (speed-of-light-in-air) communications, fibre sensing (chemical sensing, gyroscopes, sensors based on distributed scattering), laser power delivery (both high-peak and high average). However the successful implementation of these fibres in advanced demonstrators leading to commercial devices has been hindered by high cost, poor consistency and, in some instances, by lack of fibres with sufficiently good properties. We are actively investigating methods to improve structural control during the fibre draw and methods for scaling up the current manufacturing yields. Here we present recent progress in the fabrication hollow core MOFs at the Optoelectronics Research Centre; in particular, we report the fabrication of ultra-low loss (~few dB/km), wide bandwidth (>150nm) Photonic Bandgap Fibres and anti-resonant Hexagram Fibres with broadband low loss transmission suitable for the delivery of extremely high peak optical powers

Understanding wavelength scaling in 19-cell core hollow-core photonic bandgap fibers

First experimental wavelength scaling in 19-cell core HC-PBGF indicates that the minimum loss waveband occurs at longer wavelengths than previously predicted. Record low loss (2.5dB/km) fibers operating around 2µm and gas-purging experiments are also reported

No Evidence Supporting Flare Driven High-Frequency Global Oscillations

The underlying physics that generates the excitations in the global low-frequency, < 5.3 mHz, solar acoustic power spectrum is a well known process that is attributed to solar convection; However, a definitive explanation as to what causes excitations in the high-frequency regime, > 5.3 mHz, has yet to be found. Karoff and Kjeldsen (Astrophys. J. 678, 73-76, 2008) concluded that there is a correlation between solar flares and the global high-frequency solar acoustic waves. We have used the Global Oscillations Network Group (GONG) helioseismic data in an attempt to verify Karoff and Kjeldsen (2008) results as well as compare the post-flare acoustic power spectrum to the pre-flare acoustic power spectrum for 31 solar flares. Among the 31 flares analyzed, we observe that a decrease in acoustic power after the solar flare is just as likely as an increase. Furthermore, while we do observe variations in acoustic power that are most likely associated with the usual p-modes associated with solar convection, these variations do not show any significant temporal association with flares. We find no evidence that consistently supports flare driven high-frequency waves.Comment: 20 pages, 9 figures, Accepted for publication in Solar Physic