Loop antenna over a conducting cone with a spherical cap

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163889/1/mia2bf01314.pd

Effect of metal matrix and foam porosity on thermal performance of latent heat thermal storage for solar thermal power plant

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.In this paper, the thermal performance of latent heat thermal storage system using metal matrix and foam is investigated for the medium temperature (~ 200 ⁰C) and medium power (~1 MW) ORC-based solar thermal power plant. The latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy and has the advantage of high-energy storage density which makes the storage system compact. The main drawback of PCMs like molten salts is its low thermal conductivity (~0.2-0.5 W/m.K) which inhibits heat transfer to/from PCM. To overcome this, metal matrix and foam are introduced in PCM as thermal conductivity enhancers (TCE) to improve the heat transfer rate. The volume averaging technique for porous medium is adopted to model the metal foam and matrix embedded in PCM. The fluid flow and phase change in porous medium is modelled using single domain enthalpy–porosity technique. A parametric study is performed to show the effect of porosity of the metal matrix and foam on the outlet temperature of heat transfer (HTF) during charging/ discharging period. It is found that the TES with 0.7 metal matrix and foam porosity performs better than TES with PCM and any other porosity.dc201

Mode-locked thulium ytterbium co-doped fiber laser with graphene oxide paper saturable absorber

A mode-locked thulium ytterbium co-doped fiber laser (TYDFL) is proposed and demonstrated by using a commercial graphene oxide (GO) paper as saturable absorber (SA). The GO paper is sandwiched between two fiber ferrules and incorporates a ring laser cavity to generate soliton pulse train operating at 1942.0 nm at a threshold multimode pump power as low as 1.8 W. The mode-locked TYDFL has a repetition rate of 22.32 MHz and the calculated pulse width of 1.1 ns. Even though the SA has a low damage threshold, the easy fabrication of GO paper should promote its potential application in ultrafast photonics

Design of supramolecular beta-sheet forming beta-turns containing aromatic rings and non-coded alpha-aminoisobutyric acid and the formation of flat fibrillar structures through self-assembly

Single crystal X-ray diffraction studies show that the three designed tripeptides Boc-Leu-Aib-m-NA-NO2 (I), Boc-Phe-Aib-m-NA-NO2 (II) and Boc-Pro-Aib-m-ABA-OMe (III) (Aib, -aminoisobutyric acid; m-NA, m-nitroaniline; m-ABA, m-aminobenzoic acid; Boc, t-butyloxycarbonyl) containing aromatic rings in the backbones adopt -turn structures that are self-assembled through intermolecular hydrogen bonds and van der Waals interactions to create layers of -sheets. Solvent-dependent NMR titration and CD studies show that the -turn structures of the peptides also exist in the solution phase. The field emission scanning electron microscopic and transmission electron microscopic images of the peptides in the solid state reveal fibrillar structures of flat morphology that are formed through -sheet mediated self-assembly of the preorganised -turn building blocks

Development of CW and pulsed thulium ytterbium co-doped fiber lasers using nano-engineered yttria-alimina-silica based gain medium in conjunction with cladding pumping technique

Background: Pulsed fiber lasers operating near 1900 nm are becoming emerging laser sources for scientific and industrial applications, because of their unique advantages in terms of eye-safe wavelength, and high absorption in greenhouse gases, liquid water, and most polycarbonate materials. We develop new nanoengineering double-clad Thulium-Ytterbium co-doped fiber (TYDF) to provide an efficient lasing at 1950 nm region based on energy transfer from Ytterbium to Thulium ion. The performance of the TYDF is investigated for both continuous wave (CW) and pulse laser operations. Methods: The TYDF is fabricated using a Modified Chemical Vapor Deposition (MCVD) process in conjunction with solution doping technique. The lasing characteristic of the TYDF laser (TYDFL) is investigated for both linear and ring configurations. The pulse generations are demonstrated using various passive saturable absorbers (SAs) such multiwalled carbon nanotubes (MWCNTs) and graphene oxide. Results: With a linear configuration, the TYDFL operates at center wavelength of 1936.4 nm, 1958.6 nm and 1967.5 nm at gain medium lengths of 5 m, 10 m and 15 m, respectively. The proposed laser produces the highest efficiency of 9 .9 % at 10 m long TYDF and the lowest threshold pump power of 400 mW at a longer TYDF length of 15 m. The Q-switched laser operates at 1960 nm region is achieved by exploiting a MWCNTs embedded in polymer composite film as a SA. The proposed TYDFL generates a stable pulse train with repetition rates and pulse widths ranging from 18.9 to 35.1 kHz and 7.94 to 1.52 μs, respectively by varying the multimode 980 nm pump power from 440 mW to 528 mW. The maximum pulse energy of 11.2 nJ is obtained at the pump power of 512 mW. A higher performance Q switching is expected to be achieved with the optimization of the laser cavity and SA. A mode-locked TYDFL is also demonstrated using a graphene oxide (GO) based SA. The laser operates at 1942.0 nm with a threshold pump power as low as 1.8 W, a repetition rate of 22.32 MHz and calculated pulse duration of 1.1 ns. Conclusion: The developed TYDF is capable for use in developing both CW and pulsed fiber laser in conjunction with cladding pumping technique

A Q-switched fibre laser operating in the 2 mu m region based on nonlinear polarization rotation technique

We demonstrate a Q-switched fibre laser operating at 1949.0 nm, which is based on a nonlinear polarization rotation (NPR) technique. It uses a 2 m long commercial thulium-doped fibre and a 15 m long homemade thulium-ytterbium co-doped fibre as active media. They are pumped respectively by 800 nm single-mode and 905 nm multimode radiations. A stable Q-switched pulse train with the repetition rate 13.49 kHz and the pulse width 3.089 mu s is obtained when the 905 nm and 800 nm pump powers are fixed at 2.3 W and 110.4 mW, respectively. The maximum pulse energy, 11 nJ, is obtained at the 800 nm and 905 nm pump powers equal respectively to 110.4 mW and 2.5 W. To the best of our knowledge, this is the first reported Q-switched fibre laser using the NPR technique