Poly-vinyl-pyrrolidone (PVP)/polyaniline based surface acoustic wave (SAW) sensors were fabricated and characterized and their performances towards hydrogen gas were investigated. The PVP/polyaniline fibers composite were prepared by electrospinning of the composite aqueous solution deposited directly onto the active area of SAW transducers. Via scanning electron microscopy (SEM), the morphology of the deposited nanostructure material was observed. From the dynamic response, frequency shifts of 6.243 kHz (1% H2) and 8.051 kHz (1% H2) were recorded for the sensors deposited with PVP/ES and PVP/EB, respectively.
Spin field-effect transistors (SpinFETs) are promising candidates for future integrated microelectronic circuits. A SpinFET is composed of two ferromagnetic contacts (source and drain), which sandwich a semiconductor channel. Current modulation is achieved by electrically tuning the gate voltage dependent strength of the spin-orbit interaction in the semiconductor region. We investigated the properties of SpinFETs for various parameters - the band mismatch, the barrier height between the contacts and the channel and the strength of the spin-orbit coupling, for various temperatures. We demonstrated that the creation of Schottky barriers between the channel and the contacts guarantees a pronounced modulation of the magnetoresistance sufficient to open a possibility to operate SpinFETs at room temperature. We also demonstrated that silicon fins with [100] orientation exhibit a stronger dependence on the value of the spin-orbit interaction and are thus preferable for practical realization of silicon-based SpinFETs.
Gallium nitride is considered as the most promising material for liquid-phase sensor applications due to its chemical stability and high internal piezoelectric polarization. In this work, the sensing responses of undoped-AlGaN/GaN two terminal devices upon exposure to various pH levels in aqueous solution (a mixture of HCl and NaOH) as well as their possible sensing mechanism have been investigated. No reference voltage or gate voltage is applied. The changes in drain-source current, IDS as a function of pH level were evaluated. In the acidic region, there was an almost linear change in IDS where IDS decreased with the increase in pH level. Hence, the translated channel resistance increases with the pH level. High H+ ion concentration at low pH level which corresponds to the large net positive potential on the surface leads to the enhancement of the flow of electrons in 2DEG channel. As the pH level was increased towards neutral point in the acidic region which corresponds to the increase of OH- ion concentration, the net surface potential on the surface starts to be dominated by negative potential. As a result, the 2DEG channel starts to deplete which resulted in the increase of channel resistance. The estimated current and resistance change for sensing area of 1 mm2 and drain-source voltage, VDS of 1- 6 V are in the range of 2.16-80.1 mA/pH and 154.6-500.5 kΩ/pH, respectively. However, the linear decreases of IDS were not continuously observed in the basic region where OH- ions were dominant. The IDS levels were high, showing that the flows of carriers in 2DEG channel were enhanced again. The resistance was low and almost constant in the basic region. It seems to be resulted by the formation of thin Ga(x)O(y) layer on the AlGaN surface contributed by the interaction of OH- with the Ga-face surface. Hence, the net potential on the AlGaN surface seems to be dominated again by the net positive surface potential.
A graphene-based three-branch nanojunction (TBJ) device having nanowire width of 200 nm was successfully fabricated. The layer number of graphene prepared by mechanical exfoliation was determined using a simple optical contrast method which showed good agreement with theoretical value. n-type doping by Polyethylene imines (PEI) was done to control the position of Dirac point. Baking and PEI doping was found to decrease contact resistance and increase the carrier mobility. The chemically-doped TBJ graphene showed carrier mobility of 20000 cm2/Vs, which gave related mean free path of 175 nm.
Silicon nanowires (SiNWs) with diameter of about a few nanometers and length of 3 μm on silicon wafers were synthesized by very high frequency plasma enhanced chemical vapor deposition. Scanning electron microscopy (SEM) observations showed that the silicon nanowires were grown randomly and energy-dispersive X-ray spectroscopy analysis indicates that the nanowires have the composition of Si, Au and O elements. The SiNWs were characterized by high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. SEM micrographs displayed SiNWs that are needle-like with a diameter ranged from 30 nm at the top to 100 nm at the bottom of the wire and have length a few of micrometers. In addition, HRTEM showed that SiNWs consist of crystalline silicon core and amorphous silica layer.
Cu-doped TiO2 nanopowders were prepared by sonochemical-assisted process via a precursor solution of titanium isopropoxide, copper nitrate trihydrate and sodium hydroxide in the presence of polyvinyl alcohol in combination with calcinations process. The as-synthesized products were calcined at various temperatures ranging from 500-1000°C. The physical microstructures, morphologies and chemical bonding of as-calcined nanopowders were characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. It was noted that the crystallization, structure and size of the powders were strongly dependent on calcinations temperature. Their optical absorption properties were investigated and the results suggested that Cu dopant could significantly improve the optical absorption properties of TiO2.
Combination of magnetic and biocompatible materials to form core-shell nanomaterials has been widely used in medical fields. These core-shell magnetic biomaterials have a great potential for magnetic fluid hyperthermia (MFH) treatment to remedy cancer. The aims of this study were to investigate the production of core-shell cobalt ferrite/polycaprolactone (CoFe2O4/PCL) nanomaterials with different ratios of cobalt ferrite to caprolactone, to study the effects of using polymer in reducing the agglomerations between particles and to determine the structure, morphology, thermal and magnetic properties of these core-shell nanomaterials. The core-shell nanomaterials were produced by in situ polymerization method. The formation of the CoFe2O4/PCL was investigated by means of Fourier transform infrared spectroscopy (FTIR), x-ray diffractometer (XRD) and transmission electron microscopy (TEM). Its thermal properties were determined by using thermogravimetric analyzer (TGA). The vibrating sample magnetometer (VSM) was used to reveal the magnetic properties. The results for the XRD and FTIR spectra demonstrated the formation of cobalt ferrite and polycaprolactone in core-shell nanomaterials. From the TEM results, it was seen that the core-shell CoFe2O4/PCL nanomaterials were best formed at a ratio of CoFe2O4 to monomer caprolactone mixtures of 1:4.
This study was aimed to characterize the rejection of oil emulsion by two tubular surface filters, namely 13 μm slots and 4 μm circular pores. A 17 mm helix was incorporated inside the filters to increase the wall shear stress. Rejection of oil, throughputs and flux decay were measured at varying shear stresses (Rw) and transmembrane pressures (TMP). The results showed that the13 μm slots produced a fairly good oil rejection of 22 μm at Rw=0.26 Pa and TMP=6.9 kPa, while the circular pores gave the rejection of 14.4 μm at Rw=0.21 Pa and TMP=34.5 kPa. The results suggested that the circular pores filter could achieve a better oil retention under lower TMP, while the slots filter could be satisfactorily operated under moderate shear stress and low TMP. The increase of TMP offered poor oil rejection by both filters and this was also true for slots-helix configuration.
A simple and rapid sample preparation method based on dispersive liquid-liquid microextraction-solidification of floating organic drop (DLLME-SFO) combined with gas chromatography-mass spectrometry (GC-MS) method was developed for the analysis of antidepressant drugs in water samples. This method uses organic solvent with low density and less toxicity. In the method, the disperser solvent (0.5 mL acetonitrile) containing 30 μL of n-hexadecane was rapidly injected using a syringe into 5.0 mL of water sample in a glass tube. After centrifugation for 7 min at 3500 rpm, the mixture was cooled in ice bath for 5 min. The solidified n-hexadecane was transferred into a conical vial, where it melted rapidly at room temperature and 2 μL of it was injected into a gas chromatograph for analysis. Under optimized conditions, the method showed good linearity in the range of 0.04 - 0.12 μg mL-1 for amitriptyline and chlorpromazine with correlation of determination (r2) in the range of 0.992 - 0.995. The limits of detections (LODs) were in the range 0.0085 - 0.0285 μg mL-1. The extraction recoveries of amitriptyline and chlorpromazine from water samples at spiking level of 0.08 μg mL-1 were 71.34 - 73.52% and 73.83 - 91.09%, respectively, with relative standard deviations (RSDs) in the range of 4.97 - 6.85% for amitriptyline and 4.84 - 7.49% for chlorpromazine. The method was successfully applied to the determination of the analytes in drinking water, lake water and tap water samples.
Pathogenic bacterial infections have become a major health problem worldwide. New antimicrobial agents are urgently needed to overcome this problem. In this study, antibacterial activity of Nigella sativa seed extract against some pathogenic bacterial strains (Streptococcus pyogene, Pseudomonas aeruginosa, Klebseilla pneumoniae and Proteus vulgaris) was evaluated. Methanol extract at the concentration of 100 mg/mL had a remarkable sensitivity towards all tested bacteria in this study. Klebseila pneumonia and Proteus vulgaris showed resistance against aqueous extract at 20 mg/mL. Methanol extract of Nigella sativa exhibited significant antibacterial activity at the concentration of 50 mg/mL (p ≤ 0.01) against Streptococcus pyogenes with a greater inhibition zone of 19 mm, while a 15 mm zone of inhibition was observed in Pseudomonas aeruginosa, Klebseilla pneumonia and Proteus vulgaris. Kruskal Wallis analysis showed that both aqueous and methanol extract of black seed exhibited a greater inhibition on Gram positive bacteria (Streptococcus pyogenes) compared with Gram negative bacteria (Pseudomonas aeruginosa, Klebseilla pneumoniae and Proteus vulgaris). Our study also showed that species, strains and concentrations of Nigella sativa extract are some of the factors that may influence the sensitivity of the tested bacteria. A significant correlation was observed between zone of inhibition and concentration of extract.
An efficient analytical technique capable of analyzing three most common phosphodiesterase-5 (PDE5) inhibitors (vardenafil, sildenafil and tadalafil) simultaneously in premix coffee was developed. Sample extractions using either acetonitrile or methanol with two different extraction techniques (with and without evaporation steps) were evaluated. Identification and quantitation was conducted by high performance liquid chromatography with photo-diode-array (HPLC-DAD) at different wavelengths; 230 nm, 245 nm and 290 nm; and by time of flight mass spectrometry (LC-MS-TOF). Extraction with acetonitrile (without evaporation with nitrogen) showed recovery ranging from 105% to 113% (± <10%) for HPLC-DAD at 245 nm and 93% to 102% (± <2.5%) for LC-MS-TOF. Chromatogram separation was best achieved with mobile phase consisted of water (0.1% formic acid) and acetonitrile (0.1% formic acid) with gradient elution within 20 min. Thus, the results indicated that extraction using acetonitrile without evaporation step was the most efficient technique for determination of PDE5 inhibitors in premix coffee.
Baccaurea angulata or locally known as ‘belimbing dayak’ or ‘belimbing hutan’ is an underutilized fruit indigenous to Borneo with its proximate analysis and antioxidant values are yet to be explored. Proximate analysis and antioxidative properties of oven-dried B. angulata fruits of three fractions; whole fruit, skins and berries were evaluated. From the analysis conducted, whole fruit, berries and skins fraction of B. angulata contained 2.83%, 5.15% and 0.28% of total fat; 3.11%, 3.43% and 3.89% of protein; 16.66%, 19.09% and 11.37% of moisture; 4.57%, 3.68% and 7.28% of total ash and water activity (Aw) of 0.41, 0.44 and 0.44, respectively. Evaluation of antioxidant activities using ferric reducing ability of plasma (FRAP), 1,1-diphenyl-2-pycrylhydrazyl (DPPH) and Trolox/ABTS equivalent antioxidant capacity (TEAC) revealed that the skins fraction exhibits highest antioxidant activities (p<0.05) followed by whole fruit and berries fractions. The antioxidant activities were significantly correlated (p<0.05) with total phenolic and total flavonoid content but not to anthocyanins. Considering the nutritional values it contained, B. angulata is another good source of natural antioxidants with significant health benefits and high value for commercialization.
This study aimed to evaluate the total phenolics and antioxidant capacities of the seeds, pulp and peel of Pouteria campechiana fruit using three extraction solvents (water, 70% methanol and 70% ethanol). Among them, 70% ethanol exhibited the best solvent for yielding highest total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activities. The result showed that 70% ethanol extract from the peel contained the highest TPC (2304.7 mg gallic acid equivalent/100 g dw) while the pulp has the highest TFC (6414.03 mg rutin equivalent/100 g dw). The antioxidant activities of the pulp and peel ethanolic extracts were high as determined using 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation assay (49.60 and 49.56 mmoL TE/100 g dw) and ferric reducing antioxidant power assay (43.88 and 42.94 Fe2+/100 g dw) but not for seeds. However, their diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities were ~88%. Thus, the pulp and peel of P. campechiana fruit can be utilized as natural source for antioxidant components.
We studied the clusters of GaAs by using the density functional theory simulation to optimize the structure. We determined the binding energy, bond lengths, Fermi energy and vibrational frequencies for all of the clusters. We use the Raman data of nanowires of GaAs to compare our calculated values with the experimental values of the vibrational frequencies. The nanowire of GaAs gives a Raman line at 256 cm-1 whereas in the bipyramidal Ga2As3 the calculated value is 256.33 cm-1. Similarly 285 cm-1 found in the experimental Raman data agrees with 286.21 cm-1 found in the values calculated for Ga2As2 (linear) showing that linear bonds occur in the nanowire. The GaAs is found in two structures zinc-blend as well as wurtzite structures. In the nanowire mixed structures as well as clusters are formed.
Recently we have reported on standard MAP and generalized Jacobi Elliptic monopole-antimonopole pair (MAP) solutions of the SU(2) Yang-Mills-Higgs model. Here we apply Cho Abelian decomposition to the gauge potential of these MAP solutions. It is shown that the point singularities at the locations of the monopole (antimonopole), that comes from the restricted part, are removed by the unrestricted valence potential. We also consider the effect of decomposition upon energy and magnetic charge density for the cases of standard MAP and generalized Jacobi elliptic MAP solutions, under the conditions of vanishing (λ = 0) and non vanishing (λ = 1) Higgs potential.
Aluminum foams were fabricated by sintering dissolution process (SDP) using sodium chloride (NaCl) as space holder. The compositions of space holder, used in this study were 40 and 60 wt. % with different dissolution times; 1, 2 and 3 h. The effect of different dissolution times on compressive behavior and energy absorption of foams were evaluated. The result showed that by increasing space holder and dissolution times, energy absorption capability increases. For aluminum foam contains 60 wt. % NaCl, longer dissolution times resulted in thinner cell wall and cell structure become more unstable which lead to lower plateau region.
In this research we investigated the in situ formation mechanism of NbC in mechanically alloyed Fe-Nb-C mixture. Powders of iron, niobium and graphite with a composition Fe-20 %Nb was milled in a planetary mill for various milling times (i.e. 5, 10, 15 and 20 h) to investigate the influence of this variable on phase formation and properties of composite. The mixture was cold pressed and sintered at 1300°C for 1 h. Only phase of the initial raw materials was observed after milling, whilst NbC phase was detected after sintering. Increasing the milling time resulted in an increase in crystallite size and strain energy, which is beneficial for hardness and density improvement.
Kajian ini dijalankan untuk mengesahkan kemampuan teknologi DNA mikroaturan cip gen OliproTM FoodPATH bagi mengesan bakteria patogen makanan. Sebanyak 9 jenis DNA bakteria patogen makanan telah digunakan iaitu Bacillus cereus, Escherichia coli O157:H7, Staphylococcus aureus, Vibrio cholerae, Vibrio parahaemolyticus, Listeria monocytogenes, Salmonella spp., Shigella spp. dan Campylobacter spp. Sebanyak 36 kombinasi templat DNA bakteria patogen makanan telah digunakan. Pengesahan bagi mengesan bakteria patogen makanan dilakukan dengan menggunakan kaedah reaksi berantai polimerase (PCR) dan penghibridan Southern-blotting di atas cip gen untuk mengesahkan kemampuannya. Keputusan daripada analisis hibridasi di atas cip gen telah dibandingkan dengan hasil gel elektroforesis 2.0% (w/v). Lima saringan diperlukan untuk menghabiskan 36 kombinasi templat DNA bakteria patogen makanan. Setiap saringan, satu cip gen telah digunakan sebagai kawalan negatif tidak diinokulasikan dengan sebarang kombinasi DNA bakteria patogen makanan. Daripada hasil kajian, didapati bahawa semua kombinasi templat DNA bakteria patogen makanan telah dapat dikesan. Cip yang digunakan sebagai kawalan negatif tidak menunjukkan kehadiran DNA. Oleh itu, daripada kajian ini cip gen OliproTM FoodPATH didapati memberikan keputusan yang lebih baik berbanding dengan 2.0% (w/v) gel elektroforesis.
Kajian ini dijalankan untuk menentukan isoterma dan kinetik penjerapan bahan pencemar boron daripada air sisa sintetik menggunakan batu kapur sebagai bahan penjerap berkos rendah. Penjerapan boron berlaku secara optimum pada julat pH6-8, masa sentuhan pada 90 min dan dos batu kapur 240 g/L yang penyingkirannya mencapai 40%. Isoterma penjerapan lebih diwakili oleh model Freundlich (R2 = 0.91) berbanding model Langmuir (R2 = 0.78) yang menunjukkan penjerapan secara multilapisan adalah dominan. Kajian kinetik penjerapan menunjukkan penjerapan boron ke atas batu kapur mematuhi dengan baik model penjerapan pseudo-tertib pertama (R2 = 0.93), pseudo-tertib kedua (R2 = 0.987), Elovich (R2 = 0.931) dan Intrapartikel (R2 = 0.960). Mekanisme penjerapan secara kimia adalah dominan berdasarkan nilai R2 yang paling tinggi bagi model pseudo-tertib kedua.
Filem nipis ZnO terdop Ga (ZnO:Ga) disediakan menggunakan teknik sol-gel dan salutan berputar. Ga didopkan kepada ZnO dengan peratusan berat (wt. %) yang berbeza iaitu 0, 2, 4, 6 dan 8 wt. %. Kesan pengedopan Ga ke atas struktur dan sifat optik filem nipis ZnO dikaji. Pencirian struktur filem nipis ini dilakukan menggunakan kaedah pembelauan sinar-X (XRD), mikroskop imbasan elektron pancaran medan (FESEM) dan mikroskop daya atom (AFM). Pencirian sifat optik filem nipis pula dilakukan menggunakan spektroskopi ultraungu cahaya nampak (UV-VIS) dan fotoluminesen (PL). Ujian XRD mengesahkan kesemua sampel berstruktur wurtzit. Saiz kristalit ZnO mengecil dengan peningkatan peratusan berat Ga seterusnya mengurangkan kekasaran permukaan filem. Pengedopan Ga menunjukkan peratus transmisi cahaya pada panjang gelombang 300 - 380 nm bertambah berbanding filem nipis ZnO tanpa dop. Nilai jurang tenaga optik, Eg dan keamatan PL filem nipis ZnO meningkat apabila pengedopan Ga dilakukan. Hasil kajian ini menunjukkan saiz kristalit yang lebih kecil memberi kesan ke atas sifat optik sampel pada peratus pengedopan Ga 0-6%. Pada peratus pengedopan Ga yang lebih tinggi, kesan transformasi struktur menjadi lebih dominan dalam mempengaruhi nilai Eg.