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81.
Coplanar waveguides (CPW) used in microwave integrated circuits are significantly dispersive. An analytical approximation to the frequency dependence of both eff and c of CPW with finite metallisation thickness and conductivity is discussed. The effect of increasing loss tangent on dielectric constant is also presented. 相似文献
82.
The body of knowledge necessary to observe holographic-moiré patterns in real time is introduced. The basic factors influencing fringe visibility in holographic moiré are analyzed and expressions to evaluate fringe visibility for any given displacement and deformation are given. The application of the introduced theory in the case of real-time observation is discussed. It is shown that the maximum benefits of this technique are achieved by combining it with closed-circuit TV. Several examples of application are given. 相似文献
83.
An integral approach to phase measurement is presented. First, the use of a high-resolution technique for the pixelwise detection of phase steps is proposed. Next, the robustness of the algorithm that is developed is improved by incorporation of a denoising procedure during spectral estimation. The pixelwise knowledge of phase steps is then applied to the Vandermonde system of equations for retrieval of phase values at each pixel point. Conceptually, our proposal involves the design of an annihilating filter that has zeros at the frequencies associated with the polynomial that describes the fringe intensity. The parametric estimation of this annihilating filter yields the desired spectral information embedded in the signal, which in our case represents the phase steps. The proposed method offers the advantage of extracting the interference phase of nonsinusoidal waveforms in the presence of miscalibration error of the piezoelectric transducer. In addition, in contrast to previously reported methods, this method does not require the application of selective phase steps between data frames for nonsinusoidal waveforms. 相似文献
84.
A maximum-likelihood (ML) method based on spectral estimation theory for the extraction of dual phase distributions in holographic moire in the presence of nonsinusoidal waveforms, noise, and the miscalibration of piezoelectric (PZT) devices is proposed. The extraction of these phases requires incorporating two PZTs into the moire setup. ML estimators are asymptotically efficient for sufficient data samples. The approach presented uses a direct stochastic algorithm called probabilistic global search Lausanne for minimizing the ML function. 相似文献
85.
Metal-oxide-semiconductor (MOS) storage capacitors based on electron beam deposited Y2O3 extrinsic dielectric on Si show changes in capacitance density depending on the amorphous and crystalline phases. Bias stress
cycle-dependent changes in capacitance density occur due to the non-equilibrium nature of defect states at the Y2O3/Si interface after O2 annealing as a result of the emergence of a 4–8 nm thick SiO2 film at the interface. Leakage currents show instability under repeated dc bias stress, the nature and extent of which depend
upon the structure of the Y2O3 gate dielectric and the polarity of dc bias. With amorphous Y2O3, leakage currents drift to lower values under gate injection due to electron trapping, and to higher values under Si-injection
due to the generation of holes. Though leakage current drift is minimal for crystalline Y2O3, its magnitude increases as the energy of injected electrons from mid-gap states is low and the local field due to asperity
is high. The emergence of interfacial SiO2 reduces the magnitude of Si-injection leakage current substantially, but causes transient changes resulting in switching
to higher values at a threshold dc bias. Thermal detrapping of holes and reverse bias stress studies confirm that the instability
of current is caused by an increase in the cathodic field from hole trapping at interface states. Leakage current instability
limits the application of extrinsic high dielectric constant dielectrics in a high density DRAM storage capacitor, unless
a new interface layer scheme other than SiO2 and a method to form a defect-free dielectric layer can be implemented.
Received: 29 October 2001 / Accepted: 22 April 2002 / Published online: 4 December 2002
RID="*"
ID="*"Corresponding author. Fax: +1-413/545-4611, E-mail: rastogi@ecs.umass.edu 相似文献
86.
Menon S Vaidya H Pillai S Vidya R Mitscher LA 《Combinatorial chemistry & high throughput screening》2003,6(5):471-480
A solution phase strategy for the multiple parallel synthesis of a demonstration library of indazoles is described by which regio-selectivity problems inherent to previous syntheses of this nucleus are largely overcome. Synthesis of selected components proceeded satisfactorily indicating that a fully realized library of indazole analogs could readily be produced using this methodology. Simple modifications of the basic nucleophilic aromatic substitution route unambiguously produce a range of N-1 substitutions (alkyl, aryl and aralkyl) in 50-75% yields. Next a range of substituents was introduced at the C-3 position in 50-80% yields by O-alkylation. Careful choice of reagents and reaction conditions were required to prevent by-product formation due to competing alkylation at N-2 (trace to 15% yields). When present, these contaminants were readily removed by chromofiltration. A third diversity site was sketched in at C-5 in 75-90% yield by reductive alkylation or acylation. Screening of some of the demonstration library members in vitro revealed highly active antioxidants suggesting that producing a full library would be worthwhile. 相似文献
87.
Propagation characteristics of a segmented cladding fiber 总被引:3,自引:0,他引:3
We propose a novel optical fiber design that consists of a uniform core and a segmented cladding formed by alternate regions of high and low refractive indices in the azimuthal direction. The structure is analyzed by use of the radial effective-index method, and the propagation characteristics of the structure are studied. The fiber has a highly dispersive cladding and shows characteristics similar to those of photonic-crystal fibers and holey fibers. The novel fiber offers the possibility of single-mode operation over a wide range of wavelengths with a large core diameter. 相似文献
88.
Himadri R. Soni Venu Mankad Sanjay D. Gupta Sanjeev K. Gupta Prafulla K. Jha 《Journal of Thermal Analysis and Calorimetry》2012,107(1):39-44
In the present paper, we report an ab initio calculation of the ground state, electronic and thermodynamical properties like
constant volume lattice specific heat, vibrational energy, internal energy, and entropy for GaP and Ga2P is presented. These properties are obtained after calculating the phonon spectrum over the entire Brillouin zone. The calculations
were performed using the ABINIT program package, which is based on density functional theory (DFT) method and the use of pseudopotentials
and plane wave expansion. Difference in the ground state properties such as electronic structure and thermodynamical properties
are discussed. The thermodynamical properties follow the expected trend. There is a good agreement between present theoretical
and limited available experimental data in the case of ground state such as lattice constant and bulk modulus and electronic
properties. With the increase of Ga atoms in the unit cell the semiconducting nature of Ga2P turns to metallic. There is a noticeable difference in the thermodynamical properties in the case of both gallium compounds. 相似文献
89.
Treatment of [PtCl2(Ptolyl3)2] (tolyl = 4-MeC6H4) with Na2S in benzene gave [Pt2(μ2-S)2(Ptolyl3)4] (1), which is soluble in common organic solvents. Reactions of (1) with various metal complexes have been studied and several polynuclear metal aggregates isolated. These new complexes were
characterized by elemental analysis and n.m.r. spectroscopy.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
90.
Low‐temperature sol–gel transformation of methyl silicon precursors to silica‐based hybrid materials
Veena Dhayal Rakesh Bohra Meena Nagar Ajay Kaushik Sanjay Mathur Sven Barth 《应用有机金属化学》2008,22(11):629-636
Six new methyl silicon (IV) precursors of the type [MeSi{ON?C(R)Ar}3] [when R = Me, Ar = 2‐C5H4N ( 1 ), 2‐C4H3O ( 2 ) or 2‐C4H3S ( 3 ); and when R = H, Ar = 2‐C5H4N ( 4 ), 2‐C4H3O ( 5 ) or 2‐C4H3S ( 6 )] were prepared and structurally characterized by various spectroscopic techniques. Molecular weight measurements and FAB (Fast Atomic Bombardment) mass spectral studies indicated their monomeric nature. 1H and 13C{1H} NMR spectral studies suggested the oximate ligands to be monodentate in solution, which was confirmed by 29Si{1H} NMR signals in the region expected for tetra‐coordinated methylsilicon (IV) derivatives. Thermogravimetric analysis of 1 revealed the complex to be thermally labile, decomposing to a hybrid material of definite composition. Two representative compounds ( 2 and 4 ) were studied as single source molecular precursor for low‐temperature transformation to silica‐based hybrid materials using sol–gel technique. Formation of homogenous methyl‐bonded silica materials (MeSiO3/2) at low sintering temperature was observed. The thermogravimetric analysis of the methylsilica material indicated that silicon‐methyl bond is thermally stable up to a temperature of 400 °C. Reaction of 2 and Al(OPri)3 in equimolar ratio in anhydrous toluene yielded a brown‐colored viscous liquid of the composition [MeSi{ON?C(CH3)C4H3O}3.Al(OPri)3]. Spectroscopic techniques 1H, 13C{1H}, 27Al{1H} and 29Si{1H} NMR spectra of the viscous product indicated the presence of tetracoordination around both silicon and aluminum atoms. On hydrolysis it yielded methylated aluminosilicate material with high specific surface area (464 m2/g). Scanning electron micrography confirmed a regular porous structure with porosity in the nanometric range. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献