National University of Malaysia

About: National University of Malaysia is a education organization based out in Kuala Lumpur, Malaysia. It is known for research contribution in the topics: Population & Heat transfer. The organization has 26593 authors who have published 41270 publications receiving 552683 citations. The organization is also known as: NUM & Universiti Kebangsaan Malaysia.

Effect of ethanol concentration, extraction time and extraction temperature on the recovery of phenolic compounds and antioxidant capacity of Centella asiatica extracts

Abstract: The present study was to optimize the phenolic recovery from Centella asiatica by investigating the effects of ethanol concentration (0-100%, v/v), extraction time (60-300 min) and extraction temperature (25- 65°C) on phenolic extraction using single-factor experiments. Total phenolic content (TPC), total flavonoid content (TFC) and condensed tannin content (CTC) were used for determination of phenolic content while 2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical-scavenging capacity and 2,2'-diphenyl- 1-picrylhydrazyl (DPPH) radical-scavenging capacity were used for measuring the antioxidant capacity of C. asiatica extract. All extraction conditions had significant effect (p<0.05) on the phenolic contents and antioxidant capacities of C. asiatica extract. The optimal conditions for phenolic recovery were 40% ethanol for 60 min at 65 o C, with values of 1203.49 mg GAE/ 100 g DW for TPC, 561.92 mg CE/ 100 g DW for TFC, 181.25 mg CE/ 100 g DW for CTC, 730.37 µmol TEAC/ 100 g DW for ABTS and 1948.30 µmol TEAC/ 100 g DW for DPPH. TFC was found to be positive correlated significantly (0.902, p<0.05) with DPPH under influence of ethanol concentration. However, all antioxidant compound assays (TPC, TFC and CTC) were negatively correlated significantly with ABTS under the effect of extraction temperature.

Heavy metal contamination in water and sediment of the Port Klang coastal area, Selangor, Malaysia

Abstract: This investigation presents the temporal and spatial distribution of heavy metals (As, Cd, Cr, Cu, Ni, Pb, Hg, and Zn), in water and in sediments of Port Klang, Malaysia. Water and sediment samples were collected from 21 stations at 3-month intervals, and contamination factor \( (C_{\text{f}} ) \) and contamination degree \( (C_{\text{d}} ) \) were calculated to estimate the contamination status at the sampling stations. Cluster analysis was used to classify the stations based on the contamination sources. Results show that concentrations of As, Cd, Hg, and Pb in sediment and As, Cd, Hg, Pb, Cr, and Zn in water were significantly higher than the background values at which these metals are considered hazardous. The main sources of heavy metal contamination in Port Klang were industrial wastewater and port activities.

Effects of flow field design on water management and reactant distribution in PEMFC: a review

Abstract: The performance of a proton exchange membrane fuel cell (PEMFC) stack is affected by many factors, including the operating conditions, flow field and manifold design, and membrane performance. To achieve the desired PEMFC performance, the reactant must be uniformly distributed and effectively diffused into the catalyst layer for the electrochemical reaction. Water management and reactant distribution in fuel cells are crucial because they affect the distribution and diffusion rate of the reactant. This paper reviews the important research results reported in recent years related to the effects of water and reactant distribution on the performance and life span of PEMFC stacks.