Debris flows are among the fatal geological hazards in Malaysia, with 23 incidents recorded in the last two decades. To date, very few studies have been carried out to understand the debris flow processes, causes, and runouts nationwide. This study simulated the debris flow at the Mesilau watershed of Kundasang Sabah caused by the prolonged rainfall after the 2015 Ranau earthquake. Several interrelated processing platforms, such as ArcGIS, HEC-HMS, and HyperKANAKO, were used to extract the parameters, model the debris flow, and perform a sensitivity analysis to achieve the best-fit debris flow runout. The debris flow travelled at least 18.6 km to the Liwagu Dam. The best-fit runout suggested that the average velocity was 12.5 m/s and the lead time to arrive at the Mesilau village was 4.5 min. This high debris flow velocity was probably due to the high-water content from the watershed baseflow with a discharge rate of 563.8 m³/s. The flow depth and depositional thickness were both lower than 5.0 m. This study could provide crucial inputs for designing an early warning system, improving risk communication, and strengthening the local disaster risk reduction and resilience strategy in a tectonically active area in Malaysia.

In this work, we demonstrate an optical fibre tip sensor coated with chitosan for lead ion (Pb²⁺) detection. The sensor was fabricated using a tip of standard single mode optical fibre. The fibre tip region was cleaved and dipped into chitosan solution to form a sensitive layer. The coated sensor was exposed to different Pb²⁺ concentration ranging from 0 to 70 ppm. In order to compare the sensor’s performance, the uncoated optical fibre tip sensor was firstly used to perform the measurement. The chitosan-coated tip sensor has greatly enhanced the sensor’s sensitivity 7 times higher compared to uncoated the sensor with high linearity up to 97%. As the proposed sensor shows a promising potential in detecting Pb²⁺, we believe the application of the sensor can be extended for environmental and wastewater monitoring.

Sodium chloride (NaCl) is an essential compound that human needs mainly to regulate the amount of water in body. However, the level intake of NaCl daily consumption should wisely be regulated. Previously, various techniques have been employed to measure NaCl concentrations but high cost and complex fabrication become one of the limitations that need to be overcome. Thus, this paper demonstrates a sodium chloride (NaCl) concentration measurement using an optical fiber tip sensor. The flat end facet of single – mode fiber was used to emit the broadband light at near infrared wavelength region to detect NaCl at different concentration ranging from 0% – 4%. The optical power reading was recorded at every increment of 0.5% of NaCl concentration. When the aqueous NaCl was dropped onto the sensing region, the optical power decreases as the NaCl concentration increases. This experiment has shown that the sensitivity achieved by this sensor was 0.1239 dBm/% with regression value up to 0.999.

We demonstrate a generation of three lasing wavelengths with the assistance of Rayleigh backscattering as the stabilizer of peak power variations. The proposed laser consists of a combination of the semiconductor optical amplifier (SOA) and erbium-doped fiber amplifier (EDFA) as the amplifying media. Three fiber Bragg gratings are employed as the selective wavelength selectors at 1544, 1547 and 1550 nm. At 110 mA SOA current and 18 dBm EDFA output power, a flattened output spectrum with 0.9 dB peak power variation is attained. In terms of stability, the maximum peak power fluctuation for the individual laser is 0.24 dB within 120 minutes observation period. Without the Rayleigh backscattering effect, the peak power flatness is severely degraded. This shows that the weakly distributed photons can be utilized as peak power stabilizers in fiber laser systems.

The fiber Bragg grating sensor is often demonstrated as a bend sensor. However, the demonstrated sensor in previous studies was limited to low sensitivity, thus reducing the sensing performance. Hence, this work demonstrated the polydimethylsiloxane-coated fiber Bragg grating sensor for sensitivity enhancement. The proposed sensor with a diameter of 5 cm was bent by adjusting the translation stage from 0.1 cm to 0.9 cm distance in forward and backward direction. The results showed that the Bragg wavelength shifted towards the longer wavelength region when the distance decreased. The polydimethylsiloxane-coated fiber Bragg grating sensor shows a sensitivity of 1743000 A.U, 8 times higher than the uncoated fiber Bragg sensor with a sensitivity of 284000 A.U. The presence of the polydimethylsiloxane layer has successfully improved the sensor performance.