Ti3AlC2 coated D-shaped fiber saturable absorber for Q-switched pulse generation

In this letter, a titanium aluminum carbide (Ti3AlC2) coated D-shaped fiber is proposed and demonstrated as a new saturable absorber (SA) for Q-switched laser pulse generation. In preparing the SA, the Ti3AlC2 powder is dispersed in liquid polyvinyl alcohol (PVA) before the solution is dropped and left to dry onto a polished surface of D-shape fiber. The SA is added to an erbium-doped fiber laser (EDFL) cavity to modulate the cavity loss for Q-switching. The Q-switched laser is obtained at 1 561 nm. The pulse width of the pulses can be varied between 7.4 µs and 5.1 µs with a corresponding repetition rate range from 41.26 kHz to 54.35 kHz, when the pump power is increased from 42.2 mW to 71.5 mW. At 71.5 mW pump, the pulse energy is obtained at 70.3 nJ. The signal-to-noise ratio (SNR) of the fundamental frequency is recorded at 67 dB, which indicates the stability of the laser.     

A modified Lotka–Volterra model for competition forecasting in Taiwan’s retail industry

The retail industry is an important component of the supply chain of the goods and services that are consumed daily and competition has been increasing among retailers worldwide. Thus, forecasting the degree of retail competition has become an important issue. However, seasonal patterns and cycles in the level of retail activity dramatically reduce forecasting accuracy. This paper attempts to develop an improved forecasting methodology for retail industry competition subject to seasonal patterns and cycles. Using market share data and the moving average method, a modified Lotka–Volterra model with an additional constraint on the summation of market share is proposed. Furthermore, the mean absolute error is used to measure the forecasting accuracy of the market share. Real Taiwanese retail data from 1999 is used to validate the forecasting accuracy of our modified Lotka–Volterra model. Our methodology successfully mitigates errors from seasonal patterns and cycles and outperforms other benchmark models. These benchmarks include the Bass and Lotka–Volterra models for revenue or market share data, with or without using the moving average method. Our methodology assists the retail industry in the development of management strategies and the determination of investment timing. We also demonstrate how the Lotka–Volterra model can be used to forecast the degree of industry competition.     

Wide-band,passively Q-switched Yb- and Tm-doped fibre laser using WSSe saturable absorber

A wide-band, passively Q-switched fibre lasers based on ytterbium- and thulium-doped fibre gain medium are proposed and demonstrated. The lasers employ a transition metal dichalcogenide, tungsten sulphoselenide as a saturable absorber (SA) which is prepared by mechanical exfoliation technique. By integrating the SA in the laser cavities, self-starting Q-switched at 1038 and 1982?nm are obtained. The generated pulses exhibit a microsecond pulse duration with few kilohertz repetition rate. The proposed SA has high potential as a new material to cater to the needs of various scientific, industrial and biomedical applications.     

Optical tomography hardware development for solid gas measurement using mixed projection

The ability to implement fan beam projection in parallel view in an optical tomography setup is one of the novelties of this research. This design involves a sensor jig specifically designed for parallel applications that does not involve a collimator. Therefore, the fan beam projections can also be implemented in the same sensor jig without difficulty. This method is a very practical solution for overcoming the disadvantages of parallel beam projection. Although the fan beam has its own disadvantages, combining the fan beam approach with the parallel beam approach is expected to further enhance the optical tomography image quality. The image quality can be measured using the Peak Signal-to-Noise Ratio (PSNR) and the Normalized Mean-Square Error (NMSE) parameters. The combination of the two approaches also eliminates the unwanted noise that appears when using parallel beam projection alone.     

Magnetic hierarchically porous biomass carbon for realizing broadband and strong absorption of electromagnetic wave

Hierarchically porous carbon materials provide favorable conditions for electromagnetic wave loss enhancement due to the superimposed positive influence of multilevel pores. However, high production costs and complex preparation limit their large-scale production. Biomass carbon with a natural hierarchically porous structure offers an alternative; however, the impedance mismatch and single-loss mechanism prevent biomass carbon from being an ideal absorbent for broadband and strong absorption. In this study, a series of magnetic hierarchically porous biomass carbons were prepared using a facile adsorption-inert calcination method. The natural hierarchical porous structure of the loofah sponge provides numerous adsorption sites for ferric ions, which are transformed in situ into Fe₃O₄ during calcination to regulate the conductivity. The impedance matching and electromagnetic loss properties of the biomass carbon/Fe₃O₄ composites were adjusted by varying the amount of ferric nitrate. Optimal performance occurs when ferric nitrate weighs 0.8 g, and the calcination temperature is 600 °C. Under these conditions, the effective absorption bandwidth reaches 5.28 GHz (11.84–17.12 GHz, 2.5 mm), and the minimum reflection loss (RL_min) is as low as −52.54 dB (4.5 mm), which is achieved by superior impedance matching and strong conduction loss together with polarization loss due heterogeneous interfaces and carbon defects. Our work provides a new perspective and a simple method for the large-scale production of high-efficiency biomass-based electromagnetic wave absorbents.     

High-power wavelength-tunable cladding-pumped rare-earth-doped silica fiber lasers

We describe the design and performance of cladding-pumped silica fiber lasers with high continuous-wave output powers and broad wavelength tunability in the 1, 1.5, and 2 μm spectral ranges. An ytterbium-doped fiber laser was tuned via wavelength dependent feedback provided by an external cavity containing a diffraction grating from 1027 to 1105 nm at multi-watt power levels. Similarly, high output power and wide wavelength tunability from 1540 to 1600 nm and from 1860 to 2090 nm at multi-watt output power levels has been achieved in Er-Yb co-doped and Tm-doped silica fiber lasers, respectively. A neodymium doped fiber laser was tuned from 1057 to 1118 nm at a lower power level. Limiting factors and the prospects for further improvements in performance are considered.     

Dual character of H2S as promoter and inhibitor for hydrodesulfurization of dibenzothiophene

Hydrodesulfurization (HDS) of dibenzothiophene (DBT) over laboratory synthesized bulk MoS₂ catalysts using batch microautoclave reactor was studied. Influence of H₂S (wide range level) on the DBT HDS activity and selectivity was investigated. In general, H₂S was found to inhibit the direct desulfurization route that leads to biphenyl regardless the catalyst applied. However, the hydrogenation pathway which mainly produces phenylcyclohexane inferred to be either uninhibited or even more interestingly highly promoted by the presence of H₂S depending on the catalyst nature. The ultimate sum impact of H₂S on the catalytic activity shows two extremes, inhibition and promotion. Mechanism of H₂S effect is proposed.     

GC–MS metabolomics revealed protocatechuic acid as a cytotoxic and apoptosis-inducing compound from black rice brans

Food Science and Biotechnology - GC–MS metabolomics was used to discriminate the phytochemicals profile of Indonesian white, red, and black rice brans, and Japanese white rice brans. This...