Gallium nitride with wurtzite crystal structure is a chemically stable semiconductor with high internal spontaneous and piezoelectric polarization, which make it highly suitable materials to create very sensitive and robust sensors for the detection of ions, gases and liquids. Sensing characteristics of an open-gate liquid-phase sensor fabricated on undoped-AlGaN/GaN high-electron-mobility-transistor (HEMT) structure in aqueous solution was investigated. In ambient atmosphere, the open-gate undoped AlGaN/GaN HEMT clearly showed only the presence of linear region of currents while Si-doped AlGaN/GaN showed the linear and saturation regions of currents, very similar to those of gated devices. This seems to show that very low Fermi level pinning by surface states exists in undoped AlGaN/GaN sample. In aqueous solution, the typical current-voltage (I-V) characteristics of HEMTs with good gate controllability were observed. The potential of the AlGaN surface at the open-gate area is effectively controlled via aqueous solution by Ag/AgCl reference gate electrode. The open-gate undoped AlGaN/GaN HEMT structure is capable of stable operation in aqueous electrolytes and exhibit linear sensitivity, and high sensitivity of 1.9 mA/pH or 3.88 mA/mm/pH at drain-source voltage, VDS = 5 V was obtained. Due to large leakage current where it increases with the negative reference gate voltage, the Nernstian’s like sensitivity cannot be determined. Suppression of current leakage is likely to improve the device performance. The open-gate undoped-AlGaN/GaN structure is expected to be suitable for pH sensing application.
The CMOS standard process with advantage of simplicity in term of design and fabrication process compatibility has triggered the invention of MEMS very low capacitive pressure sensor, (MEMS-VLCPS). In this paper the development of the whole structure of MEMS-VLCPS that involves the design simulation, fabrication and testing is described. The novelty of this work lies in the design and fabrication process itself. A new technique in fabricating thin sensor membrane of VLCPS using seal-off techniques is also presented. The physical structure of the membrane consists of parallel plate. The top plate acts as the flexible electrode membrane and the bottom plate acts as the counter electrode membrane. Both plates are separated by absolute air gap with fixed end at both sides. As a result, it was found that the etch-opening holes of 0.8 μm and seal-off thickness of 4000 Å gave the optimum sealing surface. The percentage of relative capacitance change is extracted from the reference capacitance measurement. Air gap thickness of 0.3 μm gives the highest percentage of PRCC showing that smaller air gap thickness provides a larger change in capacitance value.
This paper reports on structural, optical transmittance and electrical properties of fluorine-doped tin oxide (FTO) thin films deposited using an inkjet printer. The FTO ink was synthesized from a mixture of tin chloride pentahydrate (SnCl4.5H2O) and ammonium fluoride (NH4F) solutions. The thin films were deposited on glass substrates at ambient temperature or heated at 40oC and 60oC. The surface electronic state and the elemental composition of the thin films were analyzed using XPS spectroscopy. The spectra of the FTO thin films revealed that tin, oxygen, fluoride and carbon were present in the samples. The signals corresponding to Sn 3d5/2, O1s, and F1s were found at 486.6 eV, 530.5 eV and 684.5 eV, respectively. XRD analysis showed that the FTO films were in the form of crystalline with cassiterite shape. The optical and electrical properties of the films were affected by the deposition temperatures. It was observed the film deposited at 40oC has the optimum optical transmittance and sheet resistivity which were 91%T and 16 Ω/, respectively.
Sn doped zinc oxide polycrystalline thin films were prepared by sol-gel process. The sol was prepared from zinc acetate dehydrate and tin chloride were used. 2-methoxyethanol and monoethanolamine were used as the solvent and stabilizer, respectively. The quantity of tin in the sol was 0, 15, and 25 at.% Sn with annealing temperature 400, 500 and 600°C. Structural investigation including surface morphology and microstructure was carried out by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The films give a hexagonal wurtzite structure with diffraction peaks at (100), (002) and (101). Changes in particle size with an increase in annealing temperature were observed in the SEM micrograph. The optical properties were determined by photoluminescence (PL) and UV-Visible (UV-VIS-NIR) spectrometer. The band gaps increased (2.78 eV to 4.10 eV) as the concentration of Sn was increased and the increasing of annealing temperature. Annealing temperature plays a key role in the formation of defects which is strongly related to the nonradiative recombination centers. The increment of the band gap is acceptable as a requirement for good anti-reflecting coating element. Therefore, these films can be applied on silicon solar cells.
Atomic force microscopy (AFM) has a wide range of applications and is rapidly growing in research and development. This powerful technique has been used to visualize surfaces both in liquid or gas media. It has been considered as an effective tool to investigate the surface structure for its ability to generate high-resolution 3D images at a subnanometer range without sample pretreatment. In this paper, the use of AFM to characterize the membrane roughness is presented for commercial and self-prepared membranes for specific applications. Surface roughness has been regarded as one of the most important surface properties, and has significant effect in membrane permeability and fouling behaviour. Several scan areas were used to compare surface roughness for different membrane samples. Characterization of the surfaces was achieved by measuring the average roughness (Ra) and root mean square roughness (Rrms) of the membrane. AFM image shows that the membrane surface was composed entirely of peaks and valleys. Surface roughness is substantially greater for commercial available hydrophobic membranes, in contrast to self-prepared membranes. This study also shows that foulants deposited on membrane surface would increase the membrane roughness.
This paper reports on the detection of several organic vapors using the unique characteristic of localized surface plasmon resonance (LSPR) gold nanoparticles. Gold nanoparticles on quartz substrate were prepared using seed mediated growth method. In a typical process, gold nanoparticles with average size ca. 36 nm were obtained to densely grown on the substrate. Detection of gas was based on the change in the LSPR of the gold nanoparticles film upon the exposure to the gas sample. It was found that gold nanoparticles were sensitive to the presence of volatile organic compound (VOC) gas from the change in the surface plasmon resonance (SPR) intensity. The mechanism for the detection of VOC’s gas will be discussed.
Solvolysis liquefaction of soda lignin in the presence of various transition metal sulfide catalysts was studied to investigate the catalyst effects on the oil and gas yields, conversion rate and higher heating value (HHV) of oil. Nanosized copper sulfide, iron sulfide and molybdenum sulfide were successfully synthesized via a simple hydrothermal method under reaction temperature 200°C for 90 min. The addition of transition metal sulfide based catalysts (CuS, MoS2 and FeS2) enhanced both production of the oils and gas and the higher heating value (HHV) of oil products. A high oil and gas yields of 82.1% and 2890 cm3 was obtained with MoS2 at 250°C for 60 min. Elemental analyses for the oils revealed that the liquid products have much higher heating values than the crude soda lignin powder.
Polyaniline montmorillonite nanocomposite was prepared using H2O2 as the oxidant. The catalytic environment of montmorillonite favours polymerization. Intercalation and composite formation was proven from various techniques such as XRD, FTIR, DRS and thermal analysis. XRD patterns give the dimension of the intercalated PANI, from the shift of 2θ values, which is in the nano range. FTIR showed that PANI composite formation occured without affecting the basic clay layer structure. Thus the successful development of an alternative cheap route for polyaniline–montmorillonite nanocomposite was well established.
The effects of annealing parameters on crystallinity and surface morphology of RF sputtered zinc oxide nano films were investigated. The structure and morphology of the nano films were dependent on temperature, gas flow rate and time of annealing. The results from atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) showed smooth and uniform growth of c-axis orientation films with an average grain sizes from 10 to 30 nm. Increments of the annealing temperature from 400 to 800°C led to bigger grain size, better crystallinity and also increase of the surface roughness. Moreover, the results showed that the crystallinity was independent of the annealing time up to 40 min after starting the annealing process. Increase in the percentage of oxygen in the O/Ar (mixture of annealing gases) from 50% to 100% results in no changes in AFM results, but XRD revealed that the (100) peak intensity was decreased, the position of (002) peak was slightly shifted towards higher angle and FWHM of (002) peak was improved.
The influence of PANI additions on methanol sensing properties of ZnO thin films at room temperature had been investigated. Commercial polyaniline powder (PANI) was mixed into 3 mL ZnO solution in five different weight percentages namely 1.25, 2.50, 3.75, 5.00 and 6.25% to obtain ZnO/PANI composite solutions. These solutions were spin coated onto glass substrate to form thin films. Microstructural studies by FESEM indicated that ZnO/PANI films showed porous structures with nanosize grains. The thickness of the film increased from 55 to 256 nm, proportionate to increment of PANI. The presence of 2 adsorption peaks at ~310 nm and ~610 nm in UV-Vis spectrum proved that addition of PANI has modified the adsorption peak of ZnO film. Methanol vapour detection showed that addition of PANI into ZnO dramatically improved the sensing properties of the sensor. The sensors also exhibited good repeatability and reversibility. Sensor with the amount of PANI of 3.75 wt% exhibited the highest sensitivity with response and recovery time was about 10 and 80 s, respectively. The possible sensing mechanism of the sensor was also discussed in this article.
Single-walled carbon nanotubes (SWCNTs) were synthesized by catalytic chemical vapor deposition (CCVD) of ethanol (C2H5OH) over Fe-Mo-MgO catalyst by using argon as a carrier gas. The reaction conditions are important factors that influence the yield and quality of carbon nanotubes. The effects of temperature and flow rate of carrier gas were investigated to increase the yield of carbon nanotubes. The synthesized carbon nanotubes were characterized by scanning electron microscopy, transmission electron microscopy, X-Ray diffraction and thermo-gravimetric analysis. The results showed that the growth of carbon nanotubes was effectively influenced by the reaction ambience and the synthesis condition. The temperature and flow rate of carrier gas played a key role in the yield and quality of synthesized CNTs. The estimated yield of synthesized carbon nanotubes was almost over 70%.
Many sampling methods have been suggested for estimating the population median. In the situation when the sampling units in a study can be easily ranked than quantified, the ranked set sampling methods are found to be more efficient and cost effective as compared to the simple random sampling. In this paper, the superiority of several ranked set sampling methods over the simple random sampling are illustrated through some simulation study. In addition, some new research topics under ranked set sampling are suggested.
MeSH terms: Cost-Benefit Analysis; Research Design
The effect of radiation on magnetohydrodynamic (MHD) boundary layer flow of a viscous fluid over an exponentially stretching sheet was studied. The governing system of partial differential equations was transformed into ordinary differential equations before being solved numerically by an implicit finite-difference method. The effects of the governing parameters on the flow field and heat transfer characteristics were obtained and discussed. It was found that the local heat transfer rate at the surface decreases with increasing values of the magnetic and radiation parameters.
MeSH terms: Government; Hot Temperature; Convection; Physical Phenomena
In this paper, we discuss a well known class studied by many authors including Ramesha et al. and Janteng, few to mention. Next, we extend the class to a wider class of functions f denoted by uab, which are normalized and univalent, in the open unit disk D={z:|z|<1} satisfying the condition:
where g ∈ S* (b),g(z) ≠ 0 is a normalized starlike function of order b, for 0 ≤ b < 1. For f ∈ uab we shall obtain sharp upper bounds for the Fekete-Szegö functional |a3 – μa22| when μ is real.
The effect of adding aluminum hydroxide (ATH) in the palm-based polyurethane hybrid composite was studied. The compression stress and modulus, thermal conductivity and acoustic property were determined. The hybrid composite was prepared by adding 10 wt% of oil palm empty fruit bunch fibre (EFB) followed by ATH at varying amount of 2, 4 and 6 wt% of the overall mass of the resin. The compression stress and modulus gave the highest values of 575 kPa and 2301 kPa, respectively at 2 wt% ATH. At 4 wt% ATH, the compression stress and modulus decreased to 431 kPa and 1659 kPa, respectively and further decreased at 6 wt% ATH to 339 kPa and 1468 kPa respectively. The k-value increased with the increment of the ATH loading exhibited a poor thermal conductivity. Sound absorption analysis indicated that the absorption coefficient was higher at higher frequency (4000 Hz) for all samples with PU-EFB/ATH with 4% ATH showed the highest absorption coefficient.
In-situ polymerization method was used to prepare palm-based polyurethane (PU) composites loading with 15 wt% magnetite (Fe3O4), polyaniline (PANI) and Fe3O4 coated with PANI labeled as PU15, PP and PPM, respectively. FTIR spectroscopy analysis indicated a shift in the carbonyl, C=O and NH in PP. The shift of the peak indicated that there was hydrogen bonding between the C=O (proton acceptor) of urethane with NH (proton-donator) of PANI. PPM gave the highest impact and flexural strengths at 4875 kJ/ m2 and 42 MPa, respectively but with the lowest flexural modulus (1050 MPa). Two-stage degradation behavior was observed in the TGA thermogram.
This study was aimed to determine the effects of pink guava (Psidium guajava) puree supplementation on enzyme activities, kidney and liver function tests of Spontaneous Hypertensive Rats (SHR). Twenty-four male SHR were divided into four groups (control, CG (distilled water); low dosage group, LDG (0.5 g/kg body weight); medium dosage group, MDG (1.0 g/kg body weight); high dosage group, HDG (2.0g/kg body weight)). The rats were given pink guava puree via force-feeding and fed rat pellets ad libitum for 28 days in individual cages at 25±2°C. At the end of experiment, the rats were fast overnight (12 to14 h) and euthanized under an anesthetic condition with ether, and blood was collected from the portal vein or posterior vena cava. The specific activities of glutathione peroxidase (GPx) was significantly higher in LDG (2332.5±81.8 U/L), MDG (2424.8±97.1 U/L) and HDG (2594.6±82.8 U/L) respectively, as compared to CG (2171.8±65.9 U/L). Significant differences were also seen in glutathione reductase (GR) activities among all treated groups (LDG (132.5±11.8 U/L), MDG (141.5±16.4 U/L), HDG (148.8±13.2 U/L) compared to CG (126.1±14.2 U/L)). Liver function tests for total antioxidant status (TAS), alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH) and γ-glutamyl transpeptidase (GGT) showed significant differences in the treated group compared to control group. In conclusion, this study shows pink guava puree supplementation increase antioxidant enzyme activity in SHR’s blood concentration.
This study was carried out to determine the effect of super olein (POo) and sunflower oil (SFO) on the rheological properties of chocolate syrup. The formulation of chocolate syrup was modified from that used in a preliminary study consisting of 49.1% water, 30% sugar, 15% cocoa powder, 5% vegetable fats (POo and SFO), 0.5% lecithin and 0.4% vanilla flavour. The rheology of chocolate syrup was measured at a shear rate of 0.01-60 s-1 using a rotational rheometer equipped with a parallel plate at 4°C and 25°C. The shear stress and shear rate data were entered into the Power Law model to determine the apparent viscosity, flow behaviour index (n) and consistency index (K) of the chocolate syrup. In this study, the apparent viscosity of the chocolate syrup was determined at a shear rate of 30 s-1. The apparent viscosity of POo chocolate syrup was the highest at 14.62 ± 1.97 Pa.s (4°C) and 3.91 ± 0.21 Pa.s (25°C), followed by SFO chocolate syrup, with apparent viscosities of 5.42 ± 0.40 Pa.s (4°C) and 1.203 ± 0.076 Pa.s (25°C). The apparent viscosity of Hershey’s chocolate syrup was the lowest, at 2.15 ± 0.070 Pa.s (4°C) and 0.6734 ± 0.027 Pa.s (25°C). All of the chocolate syrups exhibited shear-thinning behaviours with n<1 at 4°C and 25°C. The consistency index of chocolate syrup increased in the order of KHershey
The aim of this study was to determine the effect of Fe3+ concentration (0.35, 4.89, 9.44 and 13.99 mg/L) on the growth, protein content and total phenolic content of Chlorella sp. The Chlorella sp. cells were grown at 51% relative humidity, 25°C ± 2 under continuous illumination at 36 W irradiance supplied by day-light fluorescent lamp, and agitated by bubbling at a flow rate 2.7 m/s2. Samples were collected every 2 days over 21 days of the cultivation period to estimate the growth of Chlorella sp. Protein and total phenolic content of samples were determined on phase 7th, 14th, and 21st day of cultivation. Statistical analysis showed that there were significant differences (p<0.05) on growth, protein content and total phenolic content of Chlorella sp. at different iron concentrations. These differences could be related to specific differences in the cell metabolism. Protein content (8.34 mg/g dry weight), total phenolic content (8.70 mgGAE/g dry weight), cell number (1.03 × 107 cell/mL) and the specific growth rate (μ) of Chlorella sp. (1.85/day) were highest at the lowest Fe3+ concentration (0.35 mg/L).
This study was carried out to detect and identify the presence of Enterobacteriaceae, and Cronobacter sakazakii, and determine the microbial population of infant formula products obtained from hypermarkets and a private hospital in Malaysia. Sixteen infant formulas and 14 special infant formulas from eight manufacturers were tested. Enterobacter cloacae, E. asburiae, Klebsiella pneumoniae spp. pneumoniae, K. planticola and Pantoea sp., 3 were confirmed present in five samples using ID 32E biochemical test (Biomerieux). C. sakazakii was not detected in any of the infant formulas tested. Five samples failed to comply with the microbiological criterion for aerobic plate count. The infant formula and special infant formula samples with different ingredients and nutrient composition did not show any significant difference in terms of aerobic plate count. Although one of the samples contained probiotic, the high microbial count for the other samples could have been contributed by the above identified Enterobacteriaceae since the infant formula samples non-sterile and contamination could have occurred during milk production and/ or milk preparation. It is imperative to prepare the infant formula milk samples according to the manufacturer’s instruction and in an aseptic condition.