13474 research outputs found
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Dispersion stability of graphene in bio-based lubricant and its effect on tribological properties / Muhammad Harith Hasnul
No full textThe upsurge in the usage of petroleum-based product nowadays have caused huge alarming concern to the society as they are non-renewable and harmful to the environment. Therefore, it is important to hunt for a suitable alternative such as bio-based lubricant. However, bio-based lubricant cannot perform well on its own, hence there is need for suitable additives to be introduced. Graphene is a promising additive due to its unique two-dimensional structure and remarkable properties. However, several reports have stated that graphene is unable to form a stable suspension in the lubricant. Hence this study was carried out to study the dispersibility of graphene in bio-based lubricant and how it will affect to its tribological performance as well as choosing a suitable surfactant to counter this low dispersibility. To achieve this, three bio-based polyol esters i.e., neopentyl glycol dioleate (NPG), trimethylol propane trioleate (TMP) and pentaerythritol tetraoleate (PE) were selected as base oil for graphene to be dispersed in. The graphene nanoparticles were added at various concentration (0.01 wt.%, 0.03 wt.%, 0.05 wt.%, 0.07 wt.% and 0.10 wt.%) into the base oils via magnetic stirrer. Three surfactant (ionic liquid, oleic acid and Triton X-100) were used to improve the dispersion stability of graphene. The dispersion stability of graphene was observed using sedimentation method and UV-Vis spectroscopy for over one month. Tribological behaviour of base oil with graphene before and after one month were tested using fourball tribotester whereas samples with surfactant were tested using high frequency reciprocating rig (HFRR). Worn surface from HFRR testing were observed under scanning electron microscope, energy-dispersive X-ray spectroscopy. Raman spectroscopy and optical surface analyser. In term of physical properties, no significant change is observed after the addition of graphene and surfactant. Varying suspension
stability were observed in different base oil which indicated there is a matter of compatibility when selecting the base oil for graphene additive. Based on the tribological tests, graphene is more promising as an antiwear additive compared to its performance as a friction modifier. After one month, graphene sedimentation reduced its tribological performance and the more stable suspension retained its performance. Out of all surfactant, ionic liquid is the most promising surfactant as stable suspension is observed for over one-month. Synergistic behaviour of graphene and ionic liquid have been confirmed as this combination significantly improved its tribological performance
Biomechanical determinants of shuttlecock speed in the forehand jumping smash by elite male Malaysian badminton players / Yuvaraj Ramasamy
No full textBadminton is the fastest racket sport in the world with smash speeds reaching over 111 m/s (400 kph). This study examined the forehand jump smash in badminton using synchronised force plates and full-body motion capture to quantify contributions to shuttlecock speed through correlations. Nineteen elite male Malaysian badminton players were recorded performing forehand jump smashes with the fastest, most accurate jump smash from each player analysed. The fastest smash by each participant was on average 97 m/s with a peak of 105 m/s. A correlational analysis revealed that a faster smash speed was characterised by a more internally rotated shoulder, a less elevated shoulder, and less extended elbow at contact. The positioning of the arm at contact appears to be critical in developing greater shuttlecock smash speeds. Vertical ground reaction force and rate of force development were not correlated with shuttlecock speed, and further investigation is required as to their importance for performance of the jump smash e.g. greater jump height and shuttle angle. It is recommended that players/coaches focus on not over-extending the elbow or excessively elevating the upper arm at contact when trying to maximise smash speed
Torsional behaviours and crack localization in palm oil clinker concrete / Safdar Khan
No full textThe utilization of a Palm oil clinker for the production of sustainable lightweight concrete has environmental, economic, and social benefits. This study presents the investigation of the torsional behavior and localization of cracks in concrete at different substitution levels of POC coarse aggregate with granite. The DOE method was used for the design of the control mix, and all other mixes were prepared with the substitution of granite with the increasing amounts of POC at replacement levels of 20%, 40%, 60%, 80%, and 100%. The maximum reduction in the hard density, compression strength, splitting tensile strength, and flexural strength was 18.80%, 37.25%, 30.94%, and 15%, but an increment in water absorption of 1.78 times higher than the POC0 mix at the full substitution of POC with granite. The impact energies (first and failure cracks) at 60% and 100% incorporation of POC were approximately 4 and 1.60 times higher than control mix. The torque at initial and ultimate cracks were decreased by increasing the substitution levels of POC coarse aggregate. The POC100 had 1.64, and 2 times lower initial torsional stiffness, and torsional toughness as compared to NWC. The initial crack has happened almost in the range of 14-25% of the ultimate crack. The rise in the AE activities, when the initial, and ultimate cracks have developed accompanied by a dropped in the torque-twist curve, after the ultimate torque. The initial crack, ultimate crack, initial, and ultimate torque have been investigated by using the acoustic emission parameters such as absolute energy, and cumulative signal strengt
Design of an isolated bidirectional resonant DC-DC converter with wide input voltage range for medium power applications / Asif Mustafa
No full textIsolated Bidirectional DC-DC converters (IBDCs) are mainly used to provide reliable and good quality power in various electrical applications such as uninterrupted power supply (UPS), DC micro-grid with energy storage systems (ESSs), electric vehicles, vehicle-to-grid (V2G), grid-to-vehicle (G2V) and many more. Among several IBDCs, the single-phase resonant converter is mostly preferred owing to its minimized switching losses, high reliability, high power density, reduced electromagnetic interference, and ability to operate at high frequency. Nevertheless, it has the limitations of circulating power flow and limited soft-switching range for wide input voltage and load range variations. This research provides a novel topology for dual-phase LLC resonant converter with an improved variable frequency based zero circulating current phase shift modulation (VFPSM-ZCC). The topology is based on H6 inverter topology able to generate two square voltage waveforms and provide a dual-phase for two symmetrical resonant tanks and its high-frequency transformers, which are connected in series. The arrangement leads to a reduction of voltage stress across upper and lower switches to half of the input voltage that can be useful at high voltage input conditions. On the secondary side of the high-frequency transformer, an identical six-switch arrangement as an active rectifier is employed that becomes the critical component in energy storage systems (i.e., batteries, super-capacitors) for the purpose of bidirectional power flow. The converter is capable of achieving ZVS for primary as well as secondary switches for a wide variation of input voltage and output load. The proposed modulation scheme is a 3-variable control that enables the converter to operate with increased voltage gain range under all input voltage and loading conditions. Variable frequency control leads to the soft-switching operation of the switches connected to the primary side for all load ranges. The phase shift control is used as power transfer control along with maintaining a constant output voltage under changing input voltage. Moreover, the duty cycle calculation based on load
conditions helps in eliminating the reverse power flow (RPF) due to circulating current, especially under light-load conditions, thereby increasing the conversion efficiency in comparison to the conventional dual active bridge converter. The inherent ability of frequency selection based on the loading conditions also minimizes the RMS resonant current that reduces the conduction losses while operation, especially under light-load conditions. To verify the performance of the proposed converter and employed modulation scheme, a 1.5kW prototype with 210V-400V input and 80V output is built, and the experimental results have been presented. The measured efficiency of the built PCB prototype of the converter at full load is 96.7% and 94.2% under maximum and minimum input voltage conditions, respectively
Assessment of bacterial community structure and characterisation of novel bacterial species in weaver ants Oecophylla Smaragdina / Chua Kah Ooi
No full textThe Asian weaver ant, Oecophylla smaragdina has major workers that exhibit strong territorial behaviour and are aggressive predator of other arthropods. This makes them an effective biocontrol agent against many agricultural-important insect pests. Despite its importance in pest management, microbiome information of O. smaragdina is limited. In this study, the bacterial microbiome of O. smaragdina was characterized using 16S rRNA gene amplicon sequencing. Across all 12 samples, 97.8% of the sequences constituted 16 major operational taxonomic units (OTUs) that were assigned to eight bacterial families. The core bacterial microbiome was dominated by families Acetobacteraceae and Lactobacillaceae. Spatial variation attributed to predominance of Acetobacteraceae in ant samples obtained from forest area but reduced abundance in those from urban areas was observed. This suggested influences of the ant’s living environments especially in term of food resources. Notably, two Acetobacteraceae taxa were identified in every O. smaragdina colony. Subsequently, two groups of bacterial isolates were cultivated and identified as the persistent Acetobacteraceae taxa. Selected bacterial strains from each group were taxonomically studied through a polyphasic approach. Based on morphological, physiological and biochemical characterizations, bacterial strains in MALDI-TOF cluster 3 and strain F3b2T of MALDI-TOF cluster 2 exhibited discernible phenotypic features from closely related Acetobacteraceae type members. The genomes of strains Ha5T, Ta1 and Jb2 from MALDI-TOF cluster 3 and strain F3b2T were sequenced. A 16S rRNA gene-based phylogenetic and core genome-based phylogenomic analyses revealed that these strains formed two monophyletic lineages distinctive from all current Acetobacteraceae taxa. In terms of genome-relatedness, these strains showed lower than species-level thresholds average nucleotide identity (ANI), in-silico DNADNA hybridization (DDH) and average amino acid identity (AAI) values with all current Acetobacteraceae taxa. Strains Ha5T, Ta1 and Jb2 constituted a species that exhibited high phenotypic and genomic coherences and were placed in a monophyletic lineage. These strains and strain F3b2T were differentiated from current taxa of family Acetobacteraceae based on their phenotypic differences, low genome relatedness and distant placements on distinctive lineages in phylogenetic analyses. Genomic analysis revealed that these strains possessed a plasmid-borne sole rrn operon. Further analysis of these strains revealed reduced genes for motility, mobile elements, membrane transport and central metabolic pathways. However, they retained genes for basic cellular processes, biosynthesis of most essential amino acids, cofactors and vitamins as compared to closely related type members. Despite genome reduction, genomic analysis indicated capability of these strains in nutritional provision of multiple essential amino
acids, cofactors and vitamins to the host O. smaragdina as bacterial symbionts. Taken
together, bacterial strains Ha5T, Ta1 and Jb2 and strain F3b2T represent novel species of two novel genera in family Acetobacteraceae. The name Oecophyllibacter saccharovorans gen. nov. sp. nov. was proposed for strains Ha5T, Ta1 and Jb2 of which strain Ha5T (= DSM106907T = LMG30589T = NBRC 113643T = KCTC62952T) was selected as the type strain. On the other hand, the name Formicincola oecophyllae gen. nov. sp. nov. was proposed for strain F3b2T (= LMG30590T = DSM106908T =
NBRC113640T = KCTC62951T) and it represented the type strain of this new taxon.
Keywords
Association of Palb2 variants with risk to breast cancer and molecular characterisation of PALB2 tumours / Ng Pei Sze
No full textPurpose: Germline rare protein truncating variants (PTVs) in PALB2 are associated with
an increased risk to breast cancer. At present, most of the available data on genetic
predisposition to breast cancer are derived from studies in women of European descent,
and it is unclear the extent to which population-specific differences in genetic and lifestyle
factors may contribute to differences in lifetime risk to breast cancer in women of other
ancestries. This study sought to determine the prevalence of, mutation spectrum in and
the risk estimates associated with PALB2 in a multiethnic cohort of 7840 breast cancer
cases and 7928 healthy individuals from Malaysia and Singapore. In addition, this study
sought to describe the pathological and molecular characteristics associated with cancers
arising in carriers of PTV of PALB2. Methods: Mutation testing was performed on
genomic DNA from peripheral blood using targeted panel sequencing of 35 known or
suspected breast cancer susceptibility genes. Library preparation was conducted using the
Fluidigm Access Array or Fluidigm Juno system and the final pooled products were
sequenced on the Illumina Hiseq platform. Sanger sequencing was conducted to confirm
all variants identified in the bioinformatics analysis. For somatic mutational analyses,
DNA from fresh frozen tumour sections and matched normal DNA from peripheral blood
were subjected for whole exome sequencing (WES). For tumour gene expression
analyses, RNA from fresh frozen tumour sections were analysed using whole
transcriptomic RNA sequencing (RNA-seq). Results: The case-control analysis revealed
that germline PTV in PALB2 were rare but associated with significant increased risk of
breast cancer [OR=5.18, 95% CI 2.71 to 9.90, p<0.0001]. However, rare missense
variants in PALB2 [when analyzed as a group] were not associated with increased risk of
breast cancer. We found that tumours with PTV in PALB2 have characteristics that were
iv
similar to BRCA1 and BRCA2 tumours, having significantly more somatic alterations, and
a high proportion of mutational signature and genomic scar scores characteristic of
deficiencies in homologous recombination (HR), compared to tumours arising in patients
with no alterations. In addition, we report that unlike BRCA1 and BRCA2 tumours, PALB2
tumours did not have high prevalence of TP53 somatic alterations or an enriched immune
microenvironment. Conclusion: In this multi-ethnic cohort, which is unselected based on
age or family history, germline PTVs were identified in 0.73% of breast cancer cases and
0.14% healthy individuals. Based on the molecular profiling of PALB2 tumours, the
findings from this study suggest that breast cancer patients with PALB2 PTVs have
similar molecular characteristics to BRCA1 and BRCA2 tumours and are therefore likely
to benefit from the emerging targeted therapies for BRCA carriers such as platinum-based
chemotherapy and/or PARP inhibitors. These results confirm that PALB2 is the most
clinically significant breast cancer susceptibility gene after BRCA1 and BRCA2, thus
justifying the inclusion of PALB2 into the mainstream genetic testing to improve the
management of cancer risk for affected and unaffected carriers.
Key words: PALB2, breast cancer, germline, tumour genomics, transcriptomic
A microservice-based architecture for an online product review analysis system / Mehdi Mohammadi
No full textSince the emergence of Web 2.0 in late 1999, online product reviews have played a significant role in the e-commerce channels, social media, online forums, and online communities. The majority of studies in the area of product review analysis (PRA) systems have focused on evaluating and improving the techniques for review analysis to increase efficiency, accuracy, effectiveness, usefulness, ranking, spam detection, and feature extraction. The architecture of PRA systems is not the primary concern of research in this field. In this study, some of the implicit and explicit architectures of scientifically reported PRA systems were extracted to examine how the architectures have been evolving. One of the recently employed architectures in this area is the microservice architecture, aimed at achieving high flexibility and maintainability by developing loosely-coupled microservices. Current PRA systems do not fully utilise microservice architecture to achieve low-coupling in design. This research focuses on evaluating existing PRA architectures and proposing improvements on a microservice-based PRA architecture (Viscovery) in terms of reducing coupling. To evaluate the proposed architecture, two different methods, one of them is a quality model (MM4S model) and the other one involving descriptive techniques, were adopted. A prototype PRA system was developed based on the proposed architecture. The prototype system can retrieve reviews from multiple e-commerce websites and analyse the review text. The evaluation shows that the prototype system achieves lower coupling, as compared to a benchmarked microservice-based PRA system
Optimized biodiesel production by using ultrasound assisted transesterification / Omar Saifuddin Aasimudin
No full textIn order to combat the world crisis of consuming fossil fuel energy, biodiesel has
been an alternative to fossil fuel as the clean burning fuel. Despite the effort to make a
more environmentally friendly biofuel, there are challenges that comes with it. The
current commercial biodiesel in Malaysia utilizes only palm oil as the feedstock in which
the feedstock is used in food industry as well, so there is a stiff competition in obtaining
it. Waste cooking oil and jatropha oil are added to the palm oil feedstock to lessen the use
of palm oil. Since jatropha oil is a promising aspect in Malaysia and also a nonedible oil
there will not be a competition from the food industry. Moreover, to fully utilize the waste
cooking oil from being disposed and gone to waste, the three feedstocks are being mixed
together as a feedstock. The feedstock will be converted into biodiesel through an
ultrasonic assisted transesterification. Due to its efficiency, time and energy saving
method compared to the conventional method. The physicochemical properties of
viscosity, density, acid value, higher heating value, flash point, oxidation stability, and
fatty acid methyl ester content of the biodiesel were being studied and compared to
commercial biodiesel and biodiesel standard EN14214. The results proved that compared
to the palm oil biodiesl, the density at 15°C of WC50J15P35 biodiesel has improved by
0.9%, the acid value improved by 13.6%, the higher heating value improved by 0.3%, the
oxidation stability improved by 24%, and lastly, the flash point has improved by 1.6%.
Meanwhile the obtained kinematic viscosity at 40°C is 4.504 mm2/s, The FFA content is
0.22, and the percentage yield is 91%
Biomechanical mechanical and clinical analysis on the improvement of prosthetic liner using polyurethane on anterior distal part of the residual limb / Mohamed Afifuddeen Mohamed Nizam
No full textMost transtibial prosthesis users experience pain sensation at the distal side of the residual limb due to bony prominences and nerve endings. Many initiatives have been taken to resolve this problem, including using softer material such as silicone or gel liner and designing a distal off-load prosthetic socket. This study aims to conduct a survey among the users on the effect of the prosthetic liner on their daily living activities, to design a new prosthetic liner using polyurethane at the anterior-distal part of the residual limb to replace Pelite as a prosthetic liner and to compare the biomechanical gait analysis of the new modified liner using polyurethane with common Pelite as liner. A total of four left unilateral transtibial amputees were recruited and two transtibial prosthesis with different liners were fabricated for each subject. One was the Patellar Tendon Bearing socket with Pelite liner transtibial prosthesis and the other was the Patellar Tendon Bearing socket with modified liner using polyurethane foam transtibial prosthesis. The modified liner using polyurethane foam consists of ethylene-vinyl acetate�polyurethane�ethylene-vinyl acetate sandwich placed at the anterior-distal part of the residual limb. The function of the ethylene-vinyl acetate�polyurethane�ethylene-vinyl acetate sandwich is to improve the walking gait and compensate for pain sensation experienced by the user when wearing Pelite liner. Biomechanical analysis is done using the Vicon Motion Analysis System on the prosthesis user when using three types of liners which are Pelite (new) liner, modified liner using polyurethane foam that were fabricated for this study and the Pelite (original) liner from the subject. During the loading response phase, the Pelite (original) liner exerted a slightly higher force than Pelite (new) and modified liner. Meanwhile, at 30 % and 50 % of the gait cycle, the Pelite (original) liner exerted low force compared to the Pelite (new) liner and modified liner for Ground Reaction Force at the amputated side. However, for Ground Reaction Force (Non-Amputated), no difference was shown between all prosthetic liners. The biomechanical analysis shows
that the modified liner using polyurethane foam improves the walking gait cycle of the prosthesis user
Biomechanical analysis of distal stent-graft-induced new entry (SINE) formation in aortic dissection patients / Tan Wei Ting
No full textDistal stent graft-induced new entry (dSINE) is a post-treatment complication with a mortality rate of 26.1-28.6% in patients with aortic dissection (AD). dSINE creates a new path for blood flow, leading to the formation of false lumen, aneurysmal expansion, and aortic rupture. These complications necessitate re-intervention in 30-60% patients. In this study, computational approach was used to investigate potential risk factors for dSINE in aortic dissection patients. Patient-specific simulations were performed based on post thoracic endovascular aortic repair (TEVAR) computed tomography images acquired from six patients (3 dSINE and 3 non-dSINE) to analyse the correlation between anatomical characteristics and stress/strain distribution. Patient geometries were reconstructed for structural simulation. Internal pressure was applied on the inner wall of all models with restrictions of movement at all ends. Hyperelastic material models were applied. Sensitivity analysis was carried out using idealised models to independently assess the effect of stent graft length (50, 80, 100, 130, 160 and 180 mm), stent tortuosity (5˚, 10˚, 20˚ and 30˚) and wedge apposition angle (-25˚, 0˚ and 25˚) at the landing zone on key biomechanical variables. Mismatch in biomechanical properties between the stented and nonstented regions led to high stress at the distal stent graft-vessel interface in all patients, as well as shear strain in the neighboring region, which coincides with the location of tear formation. Increase in von Mises stress was observed with an increase in stent graft tortuosity (from 263 kPa at a tortuosity angle of 50 to 313 kPa at 300). Stress was further amplified by stent graft landing at the inflection point of a curve. Malapposition of the stent graft created an asymmetrical segment within the aorta, thus varying the location and magnitude of the maximum von Mises stress substantially (up to +25.9% with a +25o change in the distal wedge apposition angle). A large increase in stress occurred when the position of the maximum stress fell on the concave surface of the aorta at the distal stent graft-vessel interface. In conclusion, severe dSINE patient has high stent tortuosity with high tortuosity angle at the distal stent-graft landing zone. The mismatch at the stent aortic wall interface induced higher stress with an increase in the tortuosity angle. Stent tortuosity and wedge apposition angle served as important risk predictors for dSINE formation