Interlaminar stress analysis for carbon/epoxy composite space rotors.

This paper extends the previous works that appears in the International Journal of Multiphysics, Varatharajoo, Salit and Goh (2010). An approach incorporating cohesive zone modelling technique is incorporated into an optimized flywheel to properly simulate the stresses at the layer interfaces. Investigation on several fiber stacking sequences are also conducted to demonstrate the effect of fiber orientations on the overall rotor stress as well as the interface stress behaviour. The results demonstrated that the rotor interlaminar stresses are within the rotor materials' ultimate strength and that the fiber direction with a combination of 45°/-45°/0° offers the best triple layer rotor among the few combinations selected for this analysis. It was shown that the present approach can facilitate also further investigation on the interface stress behaviour of rotating rotors

The relationship between perceived parenting styles and stress levels among Malaysian secondary school students

This research aimed to investigate the relationship between parenting styles and stress level among Malaysian adolescents. A final sample of 140 participants with equal number of males and females, with ages ranging from 13 to 16 years old were recruited. Data collection was conducted in two public secondary schools in Pahang. This survey included three instruments: Parental Authority Questionnaire (PAQ), Adolescent Stress Questionnaire (ASQ) and demographic questionnaire. The results showed mothers prefer authoritative parenting compared to fathers and that parenting styles are not related to adolescents? stress level. There was also no gender difference in adolescents? stress level in home-life, peer pressure and school performance. Recommendations for future studies and implications of study are discussed

Effects of family functioning and family hardiness on self-efficacy among college students

Family functioning has been related to numerous developmental problems. Although there are other factors affecting a student?s self-efficacy, this research focused on the effects of family functioning and family hardiness. The implications that family functioning plays a great role in shaping one?s self belief systems will help to emphasize the need to resolve a growing cycle of social issues. The objectives of this study is to find out whether family functioning and family hardiness will have an influence on students? self-efficacy and also to determine the level of difference in self-efficacy of male and female students. Participants involved in this study were made up of a random sample of 120 students from a few colleges in the state of Selangor. Results obtained from this research study showed that there is a correlation amongst all three variables used, namely, family functioning, family hardiness and self-efficacy are interrelated. In addition, the results also showed that more males than females have been categorized in the category of clinical group for family functioning and selfefficacy

Secondary metabolites from two garcinia species and their biological activities.

Detail chemical studies on Garcinia maingayi have yielded one xanthone, 1,3,7-trihydroxy-2-(3-methylbut-2-enyl)xanthone, one benzophenone, isoxanthochymol, one benzoic acid derivative 3,4-dihydroxy-methylbenzoate and two triterpenoids, stigmasterol and sitosterol. Meanwhile, investigations on Garcinia parvifolia have afforded one triterpenoid, α-amyrin and two xanthones, cowanin and rubraxanthone. Their structures were derived based on spectroscopic evidence, mainly 1D and 2D NMR spectroscopy. Acetylation reaction was carried out on rubraxanthone to yield triacetate rubraxanthone. It was found that the pure rubraxanthone was strongly active against the larvae of Aedes aegypti with LC50 value of 15.49 μg/mL and HL-60 cell line with an IC50 value of 7.5 μg/mL

Mechanical, thermal and flame retardant properties of poly (lactic acid) / poly (methyl methacrylate) blends / Teoh, Ee Lian

Poly(lactic acid)/poly(methyl methacrylate) (PLA/PMMA) blends were prepared by melt compounding technique. Phosphorus-based flame retardant (FR) was used together with β-cyclodextrin (CD) to improve the flame resistant and thermal properties of PLA/PMMA blends. In the first stage, study was focus on the evaluation on the miscibility of PLA/PMMA blends at various blending ratio (i.e., 80/20, 60/40, 40/60, and 20/80). The evaluation was performed through thermal properties measurement [i.e., differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA)] and solvent uptake experiment. Single glass transition temperature (Tg) was detected on PLA/PMMA blends over entire composition range during DMA measurement. The solvent uptake experiment showed that PLA/PMMA20 blend exhibited smallest interaction parameter (χ12 = −0.03) according to the calculation of Flory-Huggins interaction parameter (χ12). In the second stage, phosphorus-based flame retardant (FR; 20 part per hundred resin) was added to improve the flame resistant and thermal properties of PLA/PMMA blends at blending ratio of 80/20 and 60/40.UL-94 vertical burning test and limiting oxygen index (LOI) were conducted to characterize the flame resistant properties of the blends, while thermogravimetric analyzer (TGA) was used to determine the thermal stability of the blends. Both of the PLA/PMMA20/FR and PLA/PMMA40/FR successfully achieved V-0 rating in the burning test, regardless of the PLA/PMMA blending ratio. TGA results showed that addition of FR had accelerated the thermal decomposition of PLA/PMMA20/FR and PLA/PMMA40/FR blends at low temperature, but improved the thermal stability of blends at high temperature. Higher LOI value was attained by PLA/PMMA20/FR (i.e., 31.3%) than PLA/PMMA40/FR (i.e., 28.0%), indicating PLA/PMMA20/FR having higher flame resistant properties than PLA/PMMA40/FR. In the third stage, half of the FR was replaced by CD and the efficiency of the combination in improving flame resistant and thermal properties of PLA/PMMA blend was investigated. During flammability tests, dripping behavior of the PLA/PMMA20/FR/CD was improved while maintaining its flame retardancy (i.e., UL-94 V-0; LOI = 29.3%). Higher maximum degradation temperature (Tmax) was obtained for PLA/PMMA20/FR/CD during TGA measurement, suggested the thermal degradation was delayed in the presence of CD. Scanning electron microscope (SEM) showed an extensive and compact char layer was formed on the burning surface of PLA/PMMA20/FR/CD, proving that CD could be an effective adjuvant for FR in improving flame retardancy of PLA/PMMA20/FR/CD

Natural products from Malaysian rainforests

Plants have played an important role in the ancient culture of India, China and Egypt as medicine. Plants have been and always will be an important source of new drugs and new drug leads. Drug discovery based on plants have resulted in the development of anticancer agents and continues to contribute to new leads in clinical trials. The discovery of Cinchona in the 17th century, followed by Digitalis, morphine and then the introduction of synthetic aspirin, a derivative of a plant-based drug, have led human beings to believe in the many wonders of the wealth of the forests. Natural products have provided challenging synthetic targets and their biological activity has given leads for the development of valuable medicines. Screening programmes exist for bioactive compounds and these have led to new drugs, example: taxol - which is used for the treatment of various cancers. Natural products also play a role in ecology by regulating the interactions between plants, microorganisms, insects, and animals. These can be defensive substances, anti feedants, attractants, and pheromones. Chemotaxonomy is another reason for scientists to study natural products. Chemotaxonomy involves the use of natural products in the classification of species, e.g. alkaloids are typically present in the Annonaceae family especially in Kopsiaspecies, or xanthones are typically present in Garciniaspecies while coumarins are typical of Calophyllumspecies. Phytochemical surveys can also reveal natural products that are markers for botanical and evolutionary relationships. The study of natural products have resulted in modern techniques for separation, structural elucidation, screening and combinatorial synthesis have led to increased interest in plant natural products as sources of new drugs. The introduction of herbal products in the form of nutraceuticals and dietary supplements are also changing the plant-based drug market

Alpha-mangostin and beta-mangostin from Cratoxylum laucum.

Our continuing interest in xanthones and anthraquinones from the Cratoxylum genus has led us to look at Cratoxylum glaucum. This resulted in the isolation of alpha-mangostin (1), beta-mangostin (2), fuscaxanthone C (3), 3-geranyloxy-6-methyl-1,8-dihydroxyanthraquinone (4), beta-sitosterol (5), 1,8-dihydroxy-3-methoxy-6-methylanthraquinone (6), stigmasterol (7), friedelin (8) and betulinic acid (9). Structural elucidations of these compounds were achieved by using ID and 2D NMR spectroscopic experiments. Cytotoxic assays indicated that the hexane and ethyl acetate extracts demonstrated cytotoxicity against the MCF7 cancer cell line. Meanwhile, the ethyl acetate and methanol extracts of C. glaucum inhibited the HL-60 cancer cell line activity

Anthraquinones and Xanthones from Cratoxylum glaucum (Guttiferae)

In a continuing search for xanthones and quinones from the Guttifere family, we decided to look at the genus Crotoxylum. A detailed chemical study on Cratoxylum glaucum has led to the isolation of two triterpenoids, friedelin (1) and stigmasterol 9(2), two anthraquinones 1,8-dihydroxy-6-menthoxyanthraquinone (3) and vismiaquinone (4) and one xanthone dimenthymangostin (5). These compounds were identified using the 1D and 2D NMR spectroscopy. This is the first report done on the chemistry of Cratoxylum glaucum

Chemistry and cytotoxic activity of essential oil from the stem bark of Calophyllum soulattri

GCMS analysis of the essential oil from the stem bark of Calophyllum soulattri detected twenty components. Allo-aromadendrene was present as the most abundant component. Two other major constituents are α-gurjunene and β-eudesmene. The volatile oil exhibited moderate cytotoxicity against SNU-1, Hep G2, NCI-H23, K562, Raji, IMR-32 and SK-MEL-28 cells

Garcinia mangostana: a source of potential anti-cancer lead compounds against CEM-SS cell line

Our current interest in searching for natural anti-cancer lead compounds from plants has led us to the discovery that the stem and roots of Garcinia mangostana can be a source of such compounds. The stem furnished 2,8-dihydroxy-6-methoxy-5-(3-methylbut-2-enyl)-xanthone (1), which is a new xanthone. Meanwhile, the root bark of the plant furnished six xanthones, namely -mangostin (2), β-mangostin (3), γ-mangostin (4), garcinone D (5), mangostanol (6), and gartanin (7). The hexane and chloroform extracts of the root bark of G. mangostana as well as the hexane extract of the stem bark were found to be active against the CEM-SS cell line. γ-Mangostin (4) showed good activity with a very low IC50 value of 4.7 μg/ml, while -mangostin (2), mangostanol (6), and garcinone D (5) showed significant activities with IC50 values of 5.5, 9.6, and 3.2 μg/ml, respectively. This is the first report on the cytotoxicity of the extracts of the stem and root bark of G. mangostana and of -mangostin, mangostanol, and garcinone D against the CEM-SS cell line