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Search Results: 1 - 10 of 264960 matches for " K. H. Yeap "
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Design and Development of Automated Digital Circuit Structure Base on Evolutionary Algorithm Method
K.H. Chong,S.P. Koh,S.K. Tiong,K.H. Yeap
International Journal of Electronics, Computer and Communications Technologies , 2011,
Abstract: Evolutionary Algorithms (EAs) covers all the applications involving the use of Evolutionary Computation in electronic system’s design. It is largely applied to complex optimization problems. EAs introduces a new idea for automatic design of electronic systems; instead of imagine model, abstractions, and conventional techniques, it uses search algorithm to design a circuit. In this paper, a method for automatic optimization of digital circuit design method has been introduced. This method is based on randomized search techniques mimicking natural genetic evolution. The proposed method is an iterative procedure that consists of a constant-size population of individuals, each one encoding a possible solution in a given problem space. The structure of the circuit is encoded into one-dimensional genotype as represented by a finite string of bits. A number of bit string used to represent the wires connection between the level and 7 types of possible logic gates; XOR, XNOR, NAND, NOR, AND, OR, NOT 1 and NOT 2,. The structure of gates are arranged in a m * n matrix form which m is the number of input variables.
Wave Propagation in Lossy and Superconducting Circular Waveguides
K. H. Yeap,C. Y. Tham,K. C. Yeong,H. J. Woo
Radioengineering , 2010,
Abstract: We present an accurate approach to compute the attenuation of waves, propagating in circular waveguides with lossy and superconducting walls. A set of transcendental equation is developed by matching the fields at the surface of the wall with the electrical properties of the wall material. The propagation constant kz is found by numerically solving for the root of the equation. The complex conductivity of the superconductor is obtained from the Mattis-Bardeen equations. We have compared the loss of TE11 mode computed using our technique with that using the perturbation and Stratton’s methods. The results from the three methods agree very well at a reasonable range of frequencies above the cutoff. The curves, however, deviate below cutoff and at millimeter wave frequencies. We attribute the discrepancies to the dispersive effect and the presence of the longitudinal fields in a lossy waveguide. At frequencies below the gap, the superconducting waveguide exhibits lossless transmission behavior. Above the gap frequency, Cooper-pair breaking becomes dominant and the loss increases significantly.
Attenuation in Rectangular Waveguides with Finite Conductivity Walls
K. H. Yeap,C. Y. Tham,G. Yassin,K. C. Yeong
Radioengineering , 2011,
Abstract: We present a fundamental and accurate approach to compute the attenuation of electromagnetic waves propagating in rectangular waveguides with finite conductivity walls. The wavenumbers kx and ky in the x and y directions respectively, are obtained as roots of a set of transcendental equations derived by matching the tangential component of the electric field (E) and the magnetic field (H) at the surface of the waveguide walls. The electrical properties of the wall material are determined by the complex permittivity ε, permeability μ, and conductivity σ. We have examined the validity of our model by carrying out measurements on the loss arising from the fundamental TE10 mode near the cutoff frequency. We also found good agreement between our results and those obtained by others including Papadopoulos’ perturbation method across a wide range of frequencies, in particular in the vicinity of cutoff. In the presence of degenerate modes however, our method gives higher losses, which we attribute to the coupling between modes as a result of dispersion.
(E)-N′-(2,4,5-Trifluorobenzylidene)isonicotinohydrazide monohydrate
H. S. Naveenkumar,Amirin Sadikun,Pazilah Ibrahim,Chin Sing Yeap
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810004514
Abstract: In the Schiff base molecule of the title compound, C13H8F3N3O·H2O, the benzene ring and the pyridine ring are nearly coplanar, making a dihedral angle of 6.64 (7)°. The molecule exists in an E configuration with respect to the C=N double bond. In the crystal structure, molecules are linked via the water molecules into two-dimensional planes parallel to the ab plane through intermolecular N—H...O, O—H...O O—H...N and C—H...O hydrogen bonds.
Bis{(E)-N′-[2,4-bis(trifluoromethyl)benzylidene]isonicotinohydrazide} monohydrate
H. S. Naveenkumar,Amirin Sadikun,Pazilah Ibrahim,Chin Sing Yeap
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810025493
Abstract: The asymmetric unit of the title compound, 2C15H9F6N3O·H2O, contains two independent Schiff base molecules and one water molecule. Both Schiff base molecules exist in an E configuration with respect to the C=N double bonds and the dihedral angles between the benzene and the pyridine rings in the two molecules are 17.53 (12) and 20.62 (12)°. In the crystal structure, molecules are linked by intermolecular N—H...O and C—H...O hydrogen bonds into infinite one-dimensional chains along the a axis. In addition, intermolecular O—H...N, O—H...F, C—H...F and C—H...O hydrogen bonds further link these chains into a three-dimensional network. Weak π–π interactions with centroid–centroid distances in the range 3.6495 (17)–3.7092 (16) are also observed.
N′-(Cyclohexylcarbonyl)isonicotinohydrazide
H. S. Naveenkumar,Amirin Sadikun,Pazilah Ibrahim,Chin Sing Yeap
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809027469
Abstract: In the title compound, C13H17N3O2, the mean plane of the cyclohexane ring forms a dihedral angle of 33.12 (5)° with the pyridine ring. The two O atoms are twisted away from each other, as indicated by the C—N—N—C torsion angle of 74.97 (9)°. In the crystal structure, molecules are linked into a three-dimensional network by intermolecular N—H...N, N—H...O and C—H...O hydrogen bonds. The structure is also stabilized by C—H...π interactions.
(E)-N′-(2,4,5-Trimethoxybenzylidene)isonicotinohydrazide dihydrate
H. S. Naveenkumar,Amirin Sadikun,Pazilah Ibrahim,Chin Sing Yeap
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810015254
Abstract: The asymmetric unit of the title compound, C16H17N3O4·2H2O, contains one Schiff base molecule and two water molecules. The Schiff base molecule exists in an E configuration with respect to the C=N double bond and is essentially planar, the dihedral angle between the benzene and pyridine rings being 5.48 (8)°. The three methoxy groups are also coplanar with the benzene ring [C—O—C—C torsion angles = 3.9 (2), 178.51 (15) and 0.8 (2) ]. In the crystal structure, the water molecules link the molecules into a three-dimensional network via intermolecular N—H...O, O—H...O, O—H...N and C—H...O hydrogen bonds.
(E)-N'-(2,3,4-Trimethoxybenzylidene)isonicotinohydrazide
H. S. Naveenkumar,Amirin Sadikun,Pazilah Ibrahim,Chin Sing Yeap
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810015266
Abstract: In the title compound, C16H17N3O4, the molecule exists in an E configuration with respect to the C=N double bond. The molecule is not planar, the dihedral angle between the pyridine and benzene rings being 71.67 (8)°. In the crystal structure, molecules are linked into chains along the b axis by bifurcated N—H...O and C—H...O hydrogen bonds. These chains are linked into a three-dimensional network by C—H...O and C—H...π interactions.
Ethyl 4-(5-chloro-3-methyl-1-phenyl-1H-pyrazol-4-yl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate
Hoong-Kun Fun,Chin Sing Yeap,K. V. Sujith,B. Kalluraya
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809016365
Abstract: In the title compound, C18H19ClN4O3, the dihydropyrimidinone ring adopts a flattened boat conformation. The dihedral angle between the phenyl and pyrazole rings is 43.39 (6)°. An intramolecular C—H...O contact generates an S(8) ring motif that stabilizes the molecular conformation and precludes the carbonyl O atom of the ester group from forming intermolecular interactions. Molecules are linked into centrosymmetric dimers by pairs of N—H...O hydrogen bonds and the dimers are linked into infinite chains along [101] by N—H...N hydrogen bonds.
N′-[(E)-4-Chlorobenzylidene]-2-(4-isobutylphenyl)propanohydrazide
Hoong-Kun Fun,Chin Sing Yeap,K. V. Sujith,B. Kalluraya
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809015906
Abstract: The asymmetric unit of title compound, C20H23ClN2O, consists of two crystallographically independent molecules (A and B) in which the orientations of the 4-isobutylphenyl units are different. The isobutyl group of molecule B is disordered over two positions with occupancies of 0.850 (5) and 0.150 (5). The dihedral angle between the two benzene rings is 88.70 (9)° in molecule A and 89.38 (9)° in molecule B. The independent molecules are linked together into chains along [100] by N—H...O and C—H...O hydrogen bonds, and by C—H...π interactions. In the chain, N—H...O and C—H...O hydrogen bonds generate R21(6) ring motifs. In addition, C—H...N hydrogen bonds are observed. The presence of pseudosymmetry in the structure suggests the higher symmetry space group Pbca but attempts to refine the structure in this space group resulted in high R (0.119) and wR (0.296) values.
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