A solvated complex of alpha-H(4)SiW(12)O(40).4HMPA.2H(2)O composed the heteropolytungstate alpha-H(4)SiW(12)O(40) and the organic substrate hexamethylphosphoramide (HMPA) has been synthesised, purified, and characterized. The electronic spectra (lambda = 220-500 nm) as well as the (1)H NMR spectra for the title compound dissolved in CD(3)CN establish that this complex dissociates into free SiW(12)O(40)(4)(-) and HMPA moieties in solution unless the organic substrate HMPA is present in very high concentrations. The solid reflectance electronic spectra and IR spectra indicate that there is interaction between the alpha-H(4)SiW(12)O(40) and the organic substrate. The complex has no photosensitivity under irradiation of sunlight, but under the near-UV light result in a charge transfer by oxidation of the HMPA and the reduction of the polyoxometalate. Light yellow polyhedrons of the title compound crystallize from the aqueous solvent of acetonitrile and aqueous solution as the formula of alpha-H(4)SiW(12)O(40).4HMPA.2H(2)O in the monoclinic, space group P2(1). The unit cell has a = 12.791(3) Å, b = 22.103(6) Å, c = 15.532(4) Å, beta = 102.860(10) degrees, and Z = 2. From the bond-valence parameters, it was found that the four hydrogen atoms of the polyoxometalate were combined with the N atoms of the four HMPA respectively. The title compound shows a certain second-order and third-order nonlinear optical response of I(2)(omega) = 0.7I(2)(omega)(KDP) and chi((3)) = 2.63 x 10(-)(11) esu, respectively.
The aim of the study was to determine the depth of cure of a new nanocomposite when exposed to different curing times and also when different shades were polymerized. The nanocomposite, Filtek Supreme (3M ESPE), was packed into 96 plastic cylindrical moulds measuring 4 mm in internal diameter and 8 mm in length and then polymerized using a conventional quartz-tungsten-halogen light curing unit. The first part of the study involved curing 16 samples each of A2 shade of the nanocomposite at exposure times of 20s, 40s, 60s and 120s. For the second part, a similar number of samples of the dentinal opacity shades of A2, B3 and A4 of the nanocomposite were polymerized at a constant exposure time of 40s. The depth of polymerization of the nanocomposite in each sample was measured using a digimatic indicator. Curing depths were found to increase significantly (P < 0.05) with longer exposure time (20s < 40s < 60s < 120s) and decrease significantly with darker shades (A2 > B3 > A4).
Oleic acid (OA) capped wolfram (VI) oxide, WO3 nanoparticles were chemically synthesized and characterized by means of Fourier Transform-Infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The tribological properties of the capped WO3 nanoparticles as an additive in base oils were investigated using a four-ball machine. Results show that OA-capped WO3 nanoparticles are able to prevent water adsorption and capable of being dispersed stable in organic solvents which is base oils. The as-prepared capped WO3 nanoparticles have an average size of 15 nm. In addition, OA-capped WO3 nanoparticles as an additive in base oils perform good anti-wear (AW) and anti-friction (AF) properties owing to the formation of a boundary film.
Welding process is most widely used in joining components or structures in industry. Although welding is part of a larger category called metals joining, the weld itself still gives significant problems to engineers, researchers and manufacturers until today. Several widely used welding processes, such as the Metal Inert Gas (MIG), Tungsten Inert Gas (TIG), and Manual Metal Arc (MMA), were studied. In the present paper, the characterization of the macrostructure, microstructure, hardness and residual stress distribution are highlighted and discussed to achieve a better understanding of the welded quality which is crucial in determining the welded products.
Tungsten-loaded TiO(2) photocatalyst has been successfully prepared and characterized. TEM analysis showed that the photocatalysts were nanosize with the tungsten species forming layers of coverage on the surface of TiO(2), but not in clustered form. This was confirmed by XRD and FT-Raman analyses where tungsten species were well dispersed at lower loading (<6.5 mol%), but were in crystalline WO(3) at higher loadings (>12 mol%). In addition, loading with tungsten could stabilize the anatase phase from transforming into inactive rutile phase and did not shift the optical absorption to the visible region as shown by DRUV-vis analysis. PZC value of TiO(2) was found at 6.4, but the presence of tungsten at 6.5 mol% WO(3), decreased the PZC value to 3. Tungsten-loaded TiO(2) was superior to unmodified TiO(2) with 2-fold increase in degradation rate of methylene blue, and equally effective for the degradation of different class of dyes such as methyl violet and methyl orange at 1 mol% WO(3) loading.
BACKGROUND: The clinical success of relining depends on the ability of reline resin to bond to denture base. Surface preparations may influence reline bond strength of urethane-based dimethacrylate denture base resin.
AIM: To investigate the effect of bur preparation on the surface roughness (R a ) of eclipse denture base resin and its shear bond strength (SBS) to an intra-oral self-curing reline material. The mode of reline bonding failure was also examined.
MATERIALS AND METHODS: Twenty-four cylindrical Eclipse™ specimens were prepared and separated into three groups of eight specimens each. Two groups were subjected to mechanical preparation using standard and fine tungsten carbide (TC) burs and the third group (control) was left unprepared. The R a of all specimens was measured using a contact stylus profilometer. Subsequently, relining was done on the prepared surface and SBS testing was carried out a day later using a universal testing machine.
RESULTS: One-way ANOVA revealed significant differences (P<0.05) in R a and SBS values for all the groups. Post-hoc Tukey's HSD test showed significant differences (P<0.05) between all the groups in the R a values. For SBS also there were significant differences (P<0.05), except between standard bur and control.
CONCLUSIONS: 1) There was a statistically significant difference in the R a of Eclipse™ specimens prepared using different carbide burs (P<0.05). 2) There was a statistically significant difference in the relined SBS (P<0.05) when prepared using different burs, but the difference between the standard bur and the control group was not statistically significant.
We report on a process for fabricating self-aligned tungsten (W) nanowires with polycrystalline silicon core. Tungsten nanowires as thin as 10 nm were formed by utilizing polysilicon sidewall transfer technology followed by selective deposition of tungsten by chemical vapor deposition (CVD) using WF6 as the precursor. With selective CVD, the process is self-limiting whereby the tungsten formation is confined to the polysilicon regions; hence, the nanowires are formed without the need for lithography or for additional processing. The fabricated tungsten nanowires were observed to be perfectly aligned, showing 100% selectivity to polysilicon and can be made to be electrically isolated from one another. The electrical conductivity of the nanowires was characterized to determine the effect of its physical dimensions. The conductivity for the tungsten nanowires were found to be 40% higher when compared to doped polysilicon nanowires of similar dimensions.
The aim of this study was to assess the wear of tungsten carbide burs and round rotary diamond instruments through measurements of rake angle and visual observations respectively under a field emission scanning electron microscope. Sixty short and long head pear-shaped tungsten carbide burs and 18 round rotary diamond instruments that had been used to complete < 5, > 5 and > 10 cavity preparations (n=10/group) were selected from the 3rd and 4th year dental students, Faculty of Dentistry, University of Malaya. There were two control groups consisting of long and short tungsten carbide burs of ten each. Two-way ANOVA was used to analyse the rake angle data. The data from the two control groups were collectively analysed following multiple paired t-test (p>.05) which showed no significant difference between the two types of tungsten carbide bur (short and long head). The mean rake angle of the control group was significantly higher (p < .05) compared to the < 5, > 5 and > 10 cavity preparation groups. The rake angle of the > 10 cavity preparation group was significantly lower than the other two test groups (p < .05). Round rotary diamond instruments in the < 5 cavity preparation group showed intact diamond particles with distinct cutting facets comparable to the control group. However, diamonds instruments in the > 5 and > 10 cavity preparation groups showed blunt diamond particles. In conclusion, wear of tungsten carbide burs and round rotary diamond instruments were evident after repeated use. Wear was more pronounced when instruments were used to prepare more than ten cavities.
Mamografi adalah cara paling efektif untuk mengesan keabnormalan payudara di kalangan wanita. Namun, mamografi dipercayai boleh menyebabkan karsinogenesis aruhan sinaran. Justeru pengukuran dos adalah penting untuk menganggar risiko dan mengawal kualiti imej. Kajian ini dijalankan untuk membandingkan dos glandular purata (AGD) yang diperolehi fantom payudara berdasarkan dua kombinasi anod/penuras yang berbeza iaitu tungsten/rhodium (W/Rh) dan tungsten/argentum (W/Ag). Fantom payudara CIRS 012A didedahkan pada projeksi kraniokaudal (CC) menggunakan sistem mamografi digital Hologic Selenia. Kerma udara kemasukan permukaan (ESAK) diukur menggunakan dosimeter pendar cahaya terma (TLD). AGD diperolehi daripada pengiraan asas ESAK dengan faktor penukaran berdasarkan formula Euref. Ujian t tak bersandar menunjukkan perbezaan bererti dalam purata AGD yang diperolehi. Purata AGD W/Rh adalah lebih tinggi berbanding purata AGD W/Ag (p = 0.002, 95% CI: 0.22, 0.53). Kesimpulannya, penggunaan W/Ag menyumbang kepada pengurangan dos semasa pemeriksaan mamografi.
Characteristics of X-ray transmissions were investigated for epoxy composites filled with 2-10 vol% WO3 loadings using synchrotron X-ray absorption spectroscopy (XAS) at 10-40 keV. The results obtained were used to determine the equivalent X-ray energies for the operating X-ray tube voltages of mammography and radiology machines. The results confirmed the superior attenuation ability of nano-sized WO3-epoxy composites in the energy range of 10-25 keV when compared to their micro-sized counterparts. However, at higher synchrotron radiation energies (i.e., 30-40 keV), the X-ray transmission characteristics were similar with no apparent size effect for both nano-sized and micro-sized WO3-epoxy composites. The equivalent X-ray energies for the operating X-ray tube voltages of the mammography unit (25-49 kV) were in the range of 15-25 keV. Similarly, for a radiology unit operating at 40-60 kV, the equivalent energy range was 25-40 keV, and for operating voltages greater than 60 kV (i.e., 70-100 kV), the equivalent energy was in excess of 40 keV. The mechanical properties of epoxy composites increased initially with an increase in the filler loading but a further increase in the WO3 loading resulted in deterioration of flexural strength, modulus and hardness.
Bis(dithiolene) tungsten carbonyl complex, W(S2C2Ph2)2(CO)2 was successfully synthesized and the structure, frontier molecular orbital and optical properties of the complex were investigated theoretically using density functional theory calculations. The investigation started with a molecular structure construction, followed by an optimization of the structural geometry using generalized-gradient approximation (GGA) in a double numeric plus polarization (DNP) basis set at three different functional calculation approaches. Vibrational frequency analysis was used to confirm the optimized geometry of two possible conformations of [W(S2C2Ph2)2(CO)2], which showed distorted octahedral geometry. Electronic structure and optical characterization were done on the ground states. Metal to ligand and ligand to metal charge transfer were dominant in this system.
The recent developments of nanostructured WO3 thin films synthesized through the electrochemical route of electrochemical anodization and cathodic electrodeposition for the application in photoelectrochemical (PEC) water splitting are reviewed. The key fundamental reaction mechanisms of electrochemical anodization and cathodic electrodeposition methods for synthesizing nanostructured WO3 thin films are explained. In addition, the effects of metal oxide precursors, electrode substrates, applied potentials and current densities, and annealing temperatures on size, composition, and thickness of the electrochemically synthesized nanostructured WO3 thin films are elucidated in detail. Finally, a summary is given for the general evaluation practices used to calculate the energy conversion efficiency of nanostructured WO3 thin films and a recommendation is provided to standardize the presentation of research results in the field to allow for easy comparison of reported PEC efficiencies in the near future.
Tungsten trioxide (WO₃) possesses a small band gap energy of 2.4-2.8 eV and is responsive to both ultraviolet and visible light irradiation including strong absorption of the solar spectrum and stable physicochemical properties. Thus, controlled growth of one-dimensional (1D) WO₃ nanotubular structures with desired length, diameter, and wall thickness has gained significant interest. In the present study, 1D WO₃ nanotubes were successfully synthesized via electrochemical anodization of tungsten (W) foil in an electrolyte composed of 1 M of sodium sulphate (Na₂SO₄) and ammonium fluoride (NH₄F). The influence of NH₄F content on the formation mechanism of anodic WO₃ nanotubular structure was investigated in detail. An optimization of fluoride ions played a critical role in controlling the chemical dissolution reaction in the interface of W/WO₃. Based on the results obtained, a minimum of 0.7 wt% of NH₄F content was required for completing transformation from W foil to WO₃ nanotubular structure with an average diameter of 85 nm and length of 250 nm within 15 min of anodization time. In this case, high aspect ratio of WO₃ nanotubular structure is preferred because larger active surface area will be provided for better photocatalytic and photoelectrochemical (PEC) reactions.
A new homoleptic dithiolene tungsten complex, tris-{1,2-bis(3,5-dimethoxyphenyl)-1,2-ethylenodithiolene-S,S'}tungsten, was successfully synthesized via a reaction of the thiophosphate ester and sodium tungstate. The thiophosphate ester was prepared from 3,5-dimethoxybenzaldehyde via benzoin condensation to produce the intermediate 1,2-bis-(3,5-dimethoxyphenyl)-2-hydroxy-ethanone compound, followed by a reaction of the intermediate with phosphorus pentasulfide. FTIR, UV-Vis spectroscopy, 1H NMR and 13C NMR and elemental analysis confirmed the product as tris{1,2-bis-(3,5-dimethoxyphenyl)-1,2-ethylenodithiolene-S,S'}tungsten with the molecular formula of C54H54O12S6W. Crystals of the product adopted a monoclinic system with space group of P2(1)/n, where a=12.756(2) Å, b=21.560(3) Å, c=24.980(4) Å and β=103.998(3)°. Three thioester ligands were attached to the tungsten as bidentate chelates to form a distorted octahedral geometry. Density functional theory calculations were performed to investigate the molecular properties in a generalized-gradient approximation framework system using Perdew-Burke-Ernzerhof functions and a double numeric plus polarization basis set. The HOMO was concentrated on the phenyl ligands, while the LUMO was found along the W(S2C2)3 rings. The theoretical optical properties showed a slight blue shift in several low dielectric solvents. The solvatochromism effect was insignificant for high polar solvents.
In current work, the nutritional composition, bioactive compounds, total phenolic contents and anti-oxidant activity of young Malaysian ginger rhizome were investigated. Proximate analysis and high performance liquid chromatography (HPLC) recruited to determine nutritional composition and bioactive compounds. The total flavonoid (TF) and total phenolic contents (TPC) of ginger rhizome were determined by aluminium chloride calorimetric assay and Folin-Ciocalteau reagent, respectively. 2,2’-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging method were used to measure antioxidant capacity. The rhizome contained high moisture content and low level of carbohydrate and energy. 6-gingerol was the most abundant component in the selected ginger, and total flavonoid and phenolic content were reported to be 3.66±0.45 mg gallic acid/g and 10.22±0.87 mg quercetin/g of dry weight of rhizome, respectively. The rhizome also showed lower antioxidant activity than controls, with the IC 50 value of 46.5 vs. 15.5 for α-tocopherol and 22 for BHT. The results of this study predicted that the young ginger rhizome originated from Malaysia may exhibit anti-oxidative and anti-inflammatory potentials due to high levels of gingerols, total flavonoid and phenolic compounds and antioxidant capacity.
Light intensity output is one of the determinants for adequate curing of visible light-cured materials. The aim of this survey was to evaluate the light intensity outputs (LIOs) of light curing units (LCUs) in dental clinics of Hospital Universiti Sains Malaysia (HUSM) and School of Dental Sciences, Universiti Sains Malaysia (USM). The respective LIOs of all functioning Quartz Tungsten Halogen (QTH) and Light Emitting Diode (LED) LCUs were tested using two light radiometers. For cordless LED LCUs, the testing procedure was done in situ and after being fully charged. Statistical analysis using Kruskal Wallis and Wilcoxon signed ranks tests were performed to compare the LIOs between groups and between the LIOs of in situ and post-charged cordless LED LCUs, respectively. The level of significance was set at 0.05 (p
Feedstock preparation, as well as its characterization, is crucial in the production of highly sintered parts with minimal defect. The hard metal powder - particularly, cemented carbide (wc-co) used in this study was investigated both physically and thermally to determine its properties before the mixing and injection molding stage. Several analyses were conducted, such as scanning electron microscopy, energy dispersive X-ray diffraction, pycnometer density, critical powder volume percentage (cPvP), as well as thermal tests, such as thermogravimetric analysis and differential scanning calorimetry. On the basis of the CPVP value, the feedstock, consisting of wc-co powder, was mixed with 60% palm stearin and 40% polyethylene at an optimal powder loading, within 2 to 5% lower than the CPVP value. The CPVP spotted value was 65%. The feedstock optimal value at 61% showed good rheological properties (pseudoplastic behavior) with an n value lower than 1, considerably low activation energy and high moldability index. These preliminary properties of the feedstock serve as a benchmark in designing the schedule for the next whole steps (i.e. injection, debinding and sintering processes).
A novel bimetallic double thiocyanate-bridged ruthenium and tungsten metal complex containing bipyridyl and dithiolene co-ligands was synthesized and the behavior of the complex as a dye-sensitizer for a photoelectrochemical (PEG) cell for a direct water splitting reaction was investigated. The ligands and metal complexes were characterized on the basis of elemental analysis as well as uv-Vis, Fourier transform infrared ( Pim) and nuclear magnetic resonance (11I and 13C NMR) spectroscopy. Cyclic voltammetry of the bimetallic complex showed multiple redox couples, in which half potentials E 112 at 0 .625 , 0.05 and 0.61 V were assigned as the formal redox processes of Ru(III)IRu(II) reduction, W(IV)IW(V) and W(V)IW(VI) oxidations, respectively. Photocurrent measurements were performed in homogeneous system and TiO2 was used as the photoanode for photocurrent measurements. Current density generated by the bimetallic complex was higher than that of N3 commercial dye which suggested that the bimetallic complex donated more electrons to the semiconductor.
WO₃-decorated TiO₂ nanotube arrays were successfully synthesized using an in situ anodization method in ethylene glycol electrolyte with dissolved H₂O₂ and ammonium fluoride in amounts ranging from 0 to 0.5 wt %. Anodization was carried out at a voltage of 40 V for a duration of 60 min. By using the less stable tungsten as the cathode material instead of the conventionally used platinum electrode, tungsten will form dissolved ions (W(6+)) in the electrolyte which will then move toward the titanium foil and form a coherent deposit on the titanium foil. The fluoride ion content was controlled to determine the optimum chemical dissolution rate of TiO₂ during anodization to produce a uniform nanotubular structure of TiO₂ film. Nanotube arrays were then characterized using FESEM, EDAX, XRD, as well as Raman spectroscopy. Based on the FESEM images obtained, nanotube arrays with an average pore diameter of up to 65 nm and a length of 1.8 µm were produced. The tungsten element in the samples was confirmed by EDAX results which showed varying tungsten content from 0.22 to 2.30 at%. XRD and Raman results showed the anatase phase of TiO₂ after calcination at 400 °C for 4 h in air atmosphere. The mercury removal efficiency of the nanotube arrays was investigated by photoirradiating samples dipped in mercury chloride solution with TUV (Tube ultraviolet) 96W UV-B Germicidal light. The nanotubes with the highest aspect ratio (15.9) and geometric surface area factor (92.0) exhibited the best mercury removal performance due to a larger active surface area, which enables more Hg(2+) to adsorb onto the catalyst surface to undergo reduction to Hg⁰. The incorporation of WO₃ species onto TiO₂ nanotubes also improved the mercury removal performance due to improved charge separation and decreased charge carrier recombination because of the charge transfer from the conduction band of TiO₂ to the conduction band of WO₃.
BACKGROUND: The Jatropha curcas plant or locally known as "Pokok Jarak" has been widely used in traditional medical applications. This plant is used to treat various conditions such as arthritis, gout, jaundice, wound and inflammation. However, the nature of compounds involved has not been well documented. Hence, this study was conducted to investigate the anti-inflammatory activity of different parts of J. curcas plant and to identify the active compounds involved.
METHODS: In this study, methanol (80%) extraction of four different parts (leaves, fruits, stem and root) of J. curcas plant was carried out. Phenolic content of each part was determined by using Folin-Ciocalteau reagent. Gallic acid was used as the phenol standard. Each plant part was screened for anti-inflammatory activity using cultured macrophage RAW 264.7 cells. The active plant part was then partitioned with hexane, chloroform, ethyl acetate and water. Each partition was again screened for anti-inflammatory activity. The active partition was then fractionated using an open column chromatography system. Single spots isolated from column chromatography were assayed for anti-inflammatory and cytotoxicity activities. Spots that showed activity were subjected to gas chromatography mass spectrophotometry (GC-MS) analysis for identification of active metabolites.
RESULTS: The hexane partition from root extract showed the highest anti-inflammatory activity. However, it also showed high cytotoxicity towards RAW 264.7 cells at 1 mg/mL. Fractionation process using column chromatography showed five spots. Two spots labeled as H-4 and H-5 possessed anti-inflammatory activity, without cytotoxicity activity. Analysis of both spots by GC-MS showed the presence of hexadecanoic acid methyl ester, octadecanoic acid methyl ester and octadecanoic acid.
CONCLUSION: This finding suggests that hexadecanoic acid methyl ester, octadecanoic acid methyl ester and octadecanoic acid could be responsible for the anti-inflammatory activity of the J. curcas root extract.