19672 research outputs found
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Generation of sub-nanosecond pulse in dual-wavelength praseodymium fluoride fibre laser
No full textIn this paper, we demonstrate a stable dual-wavelength pulsed output from a praseodymium doped fluoride fiber laser. These dual functions are induced by intensity-dependent transmission and loss due to the cavity birefringence. The two lasing wavelengths centered at 1298.26 nm and 1299.91 nm with a spacing of 1.65 nm and a 3 dB bandwidth of 0.11 nm and 0.13 nm respectively are obtained. The pulse width induced by the dual-wavelength laser falls within the picosecond region, with a repetition rate of 389 KHz and a maximum average pulse energy of 5.4 nJ. © 2019 Astro Ltd
Dual characteristics of molybdenum disulfide based PN heterojunction photodetector prepared via drop-cast technique
No full textA p-silicon/molybdenum disulfide (p-Si/MoS2) p-n heterojunction photodetector (PD) is proposed and fabricated using the drop-casting technique. The composition of elements in the localized surface morphology enables for excellent photoconduction under 380 nm illumination at various ultraviolet (UV) powers. The uneven and even distribution of the current-voltage I-V curve in the negative and positive bias regions indicate substantial dual characteristics in the fabricated device. A high responsivity of about 9.6 and 0.388 AW−1 is measured at the negative and positive bias regions respectively, allowing the p-Si/MoS2 p-n heterojunction PD to operate at UV powers lower than 830 μW. © 2019 Elsevier Gmb
Mode-locking in Er-doped fiber laser with reduced graphene oxide on a side-polished fiber as saturable absorber
No full textIn this work, the generation of highly stable mode-locked pulses from a side-polished fiber (SPF) embedded with graphene oxide (rGO) nanoparticles (NPs) is proposed and demonstrated. The rGO NPs are obtained from a graphene oxide solution prepared using Hummer's technique, before being reduced by a hydrothermal route. The rGO NPs, suspended in the form of a solution, are then drop-casted onto the SPF. The SPF is fabricated by polishing away the cladding layer of a single-mode fiber section, leaving the core exposed and allowing the evanescent field of the signal propagating through the fiber to interact directly with the NPs. The SPF is integrated into an erbium doped fiber laser (EDFL) cavity, and the strong nonlinear optical response and spectral filtering by the rGO NPs as well as total anomalous dispersion of the laser cavity generates highly stable soliton mode-locked pulses with visible Kelly's sidebands at 1544.02 nm. The output pulses have a pulse repetition rate of 16.79 MHz and pulse duration of 1.17 ps throughout the mode-locking operation range of 64.44–280.5 mW. The rGO NP coated SPF in this work demonstrates the viability and performance of the SPF for mode-locked pulse generation via evanescent field interactions. © 201
100 GHz free spectral range-tunable multi-wavelength fiber laser using single–multi–single mode fiber interferometer
No full textSix single–multi–single (SMS) mode fiber-based Mach–Zehnder Interferometers (MZI) with different spooling radii are demonstrated as spatial mode filtering elements for multi-wavelength laser generation. Free spectral range (FSR) tuning of the multi-wavelength output generated is realized by alternating between the six MZIs, which have different macro-bending losses. Additional FSR tuning is also realized by changing the spooling radius of the two-mode step index fiber section within the MZI setups from 80 mm to 30 mm, giving an FSR tuning range of 0.89–0.99 nm. All generated multi-wavelength outputs show high stability over a test period of 100 min. The proposed multi-wavelength lasers are highly suitable for various microwave photonics applications the field of such as microwave signal source generation and microwave photonic filtering. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature
Optically Modulated Tunable O-Band Praseodymium-Doped Fluoride Fiber Laser Utilizing Multi-Walled Carbon Nanotube Saturable Absorber*
No full textA tunable and optically modulated fiber laser utilizing a multi-walled carbon nanotube based saturable absorber is demonstrated for operation in the O-band region. A praseodymium-doped fluoride fiber is used as the gain medium and the system is capable of generating modulated outputs at 1300 nm. Pulsed output is observed at pump powers of 511 mW and above, with repetition rates and pulse widths that can be tuned from 41 kHz and 3.4 μs to 48 kHz and 2.4 μs, respectively, at the maximum pump power available. A maximum average output power of 100 μW with a corresponding single pulse energy of 2.1 nJ is measured, while the tunability of the proposed laser is from 1290 nm to 1308 nm. The output is stable, with peak power fluctuations of ∼4 dB from the average value. © 2019 Chinese Physical Society and IOP Publishing Ltd
The Determinants of Bank Capital for East Asian Countries
No full textThis study identifies the determinants of bank capital ratios in eight East Asian countries using unbalanced panel data of 278 banks from 2004 to 2014. The results indicate that bank capital decisions are significantly driven by management quality, liquidity, leverage and bank size, as well as bank regulations, indicating that the determinants of bank capital are consistent with past findings for US and European banks. The capital adequacy ratios in East Asia are not linked with banks’ risk appetite. Given that our results show that bank managers generally react negatively to capital requirements, capital regulations should be followed with more rigorous supervisory oversight, to reduce the adverse effects of high capital requirements on bank safety. © 2019 International Management Institute, New Delhi
Optimization of see do il extraction process parameters from Brucea javanica using Design of Experiment (DoE)
Get PDFThe project was done to improve Soxhlet process for extraction of oil for seeds of Brucea javanica and explore its various applications. The optimization was done by RSM (response surface methodology) using Box Behnken design of experiment (DoE). Properties of the Brucea javanica oil (BJO) was determined using Gas/Mass Spectrometric approach and Fourier Transform Infrared Spectroscopy (FT-IR) analysis. GCMS analysis indicated that important fatty acid are presence in BJO and FTIR suggested the presence of core functional groups in BJO. Quadratic model was used to analyse the results obtained from the optimised experimental design. ANOVA of developed model showed good presentation of model with R 2 value of 0.9078. Similarly, it was discovered that model were significant because their probability values (p-values) were discovered to be less than 0.05. The design of experiment showed a highest yield of 44.89 % at 75°C, 6hour extraction time and hexane 425ml
Ammonia flux tailoring on the quality of AlN epilayers grown by pulsed atomic-layer epitaxy techniques on (0 0 0 1)-oriented sapphire substrates via MOCVD
No full textA smooth and dense surface of single-crystalline aluminium nitride thin films has been epitaxially grown on (0 0 0 1)-sapphire substrates by tailoring and optimizing the ammonia flux density during deposition. The aluminium nitride films were deposited by metal organic chemical vapour deposition using the pulsed atomic-layer epitaxy technique at a relatively low growth temperature for ammonia flux densities between 2.2 and 0.2 standard litres per minute (SLM). It is found that the ammonia flux of 0.6 SLM produced the best quality of aluminium nitride films. Field emission scanning electron microscopy as well as atomic force microscopy images revealed a smooth, crack-free and dense surface of aluminium nitride films with the lowest root mean square roughness of 1.61 nm. The in-plane compressive strain inside aluminium nitride films, induced by the hetero-epitaxial growth on sapphire, was examined by focusing on the transition of the E2 (high) peak frequency obtained from the Raman spectra. The lowest threading and mixed-edge dislocation densities were estimated to be 1.50 × 107 and 3.7 × 109 cm−2, respectively, which are comparable to those of state-of-the-art aluminium nitride thin films. © The Royal Society of Chemistry
Ficus deltoidea: Effects of solvent polarity on antioxidant and anti-proliferative activities in breast and colon cancer cells
No full textIntroduction: Ficus deltoiea (FD) is traditionally used to treat hyperlipidaemia, hypertension and diabetes. Limited studies are available on their anti-proliferative effects. The aim of this study was to evaluate the antioxidant activities of the hexane, ethyl acetate, methanol and water extracts of three varieties of FD and to evaluate their anti-proliferative effects on breast and colon cancer cells. Methods: The plant extracts were analysed for polyphenolic and flavonoid content. Antioxidant activities were determined using DPPH, ABTS and O2 ·− radical scavenging assays, FRAP, Fe2+ chelating, and cellular antioxidant assays. The anti-proliferative activity and apoptotic effects of the extracts was analysed using breast (MCF-7, MDA-MB 231, HCC 1937) and colon cancer (HCT 116) cell lines. Gene expression analysis of selected extracts was investigated against HCT 116 cells. Results: Methanol was the best solvent for extraction of antioxidants and had the highest polyphenolic content (70–100 mg GAE/g), FRAP (6.0–9.0 mmol Fe2+/g), ABTS (2.0–3.0 mmol TE/g) and DPPH (EC50:200-410 μg/mL) activities. The ethyl acetate extracts of FD variety A (FDA-EA) and B (FDB-EA) demonstrated anti-proliferative activities in MCF-7, MDA-MB 231, and HCT 116 (IC50<100 μg/mL) and moderate activities in HCC 1937 (IC50:150-200 μg/mL) cells. The extracts also increased caspase 3/7 activities in HCT 116 and HCC 1937 cells. HCT 116 cells treated with FDA-EA showed upregulation of Fas1, Bax, Cdk-1, TNF-α and Cdk-2 and downregulation of Bcl-2 and Tp53 genes, implying the induction of apoptosis. Conclusion: FD especially FDA-EA is a promising source of antioxidants and anti-proliferative agents, especially against colon cancer. © 2019 Elsevier Gmb
Service Management for IoT: Requirements, Taxonomy, Recent Advances and Open Research Challenges
No full textThe exponential growth in the number of smart devices connected to the Internet of Things (IoT), and associated with various IoT-based smart applications and services, raises interoperability challenges which could affect the sustainability of IoT services. IoT software applications are built using different software platforms and embedded in diverse types of terminals and sensing devices. Aiming to offer smart services over a range of network technologies that use different communication protocols. The concept of Web service with service-oriented solutions was introduced to cope with the heterogeneity of hardware and software, and to tackle issues of interoperability, flexibility and scalability. The main step of this solution was the integration of Web of Things technologies into smart device networks, with the utilization of IoT gateways. Service management is a crucial factor in sustaining service-oriented solutions in dynamic and highly scalable IoT systems, and is concerned with several issues associated with service provisioning, orchestration, composition and adaption. This work was motivated by the need for robust and flexible service management systems that can meet the requirements for the rapid scalability and heterogeneity associated with the exponential growth of IoT systems. In the literature there is no survey of service management issues and associated research efforts in the field of IoT. In this article, we identify the key requirements for managing IoT services as well as common service management platforms for IoT. We provide a thematic taxonomy based on the important factors, and investigate recent advances in service management for IoT systems. Finally, the major challenges that remain open are presented as a guide for future research directions. © 2013 IEEE