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61.
A novel current-mode active-only universal filter based on and employing three DO-CCCIIs and two OAs is introduced. The circuit is fully integrable and programmable, and implements all the five generic filtering functions. The three basic filtering responses LP, BP and HP are implemented simultaneously by the circuit, while AP and notch signals can be realized simply by connecting appropriate node currents. The currents are available at high output impedances, so the synthesized filter can be cascaded without additional buffers to realize higher order filters. The filter performance factors ω 0 and Q are electronically tunable in an orthogonal manner through separate bias currents of the CCCII. The PSPICE simulation was carried out to realize the proposed circuit. 相似文献
62.
Abdul Ghafar Shah Tahir Mahmood Muhammad N. Naeem Zafar Iqbal Shahid H. Arshad 《Acta Mechanica》2010,211(3-4):293-307
In this paper, a study on the vibrations of functionally graded cylindrical shells based on the Winkler and Pasternak foundations is presented. The shell equations are amended by inducting the moduli of the Winkler and Pasternak foundations. The wave propagation method is employed to solve the shell dynamical equations. The method is based on the approximate eigenvalues of characteristic beam functions. The validity and accuracy of the present approach are verified by a number of comparisons. 相似文献
63.
A highly accurate method of optical path-length measurement is introduced by use of a scanning heterodyne optical interferometer with no moving parts. The instrument has demonstrated the potential to measure optical path length at angstrom resolution over continuous thickness in the micrometer range. This optical path length can be used to calculate the thickness of any material if the refractive index is known or to measure the refractive index of the material if the thickness is known. The instrument uses a single acousto-optic device in an in-line ultra-stable reflective geometry to implement rapid scanning in the microsecond domain for thickness measurements of the test medium. 相似文献
64.
Tungsten inert gas (TIG) welded joints between Zircaloy-4 and stainless steel 304L have been studied by scanning electron
microscope (SEM) having energy dispersive system (EDS) as an attachment. Intermetallic compound Zr(Cr, Fe)2 and Zr2Fe–Zr2Ni eutectic phase have been observed in the molten zone. The surface area occupied by intermetallic compound Zr(Cr, Fe)2 is about twice compared to Zr2Fe–Zr2Ni eutectic phase. The shape of the intermetallic compound is rod like. The phases were also identified by using X-ray diffraction
(XRD) technique. EDS and XRD results are quite in agreement. 相似文献
65.
Novel polystyrene microsphere (PSMS)-based PSMS/Si and polystyrene/silica nanoparticle/multi-walled carbon nanotube (PS/Si/MWCNT) nanocomposite has been prepared using in situ sol-gel and chemical amalgamation methods. Aniline monomer was introduced by in situ route to form PSMS/PANI, PSMS/PANI/Si and PSMS/PANI/Si/MWCNT nanocomposite. FESEM of nanocomposite indicated core-shell spherical and tubular morphology. Glass transition temperature (Tg) and maximum decomposition temperature (Tmax) of PSMS/PANI/Si/MWCNT nanocomposite were found as 295°C and 524°C, respectively, which were higher than the PSMS/PANI (Tg = 245°C; Tmax = 387°C) and PSMS/PANI/Si (Tg = 257°C; Tmax = 388°C) nanocomposite. For nanocomposite dispersion, tetrahydrofuran was studied as fine solvent. XRD depicted amorphous nature of PSMS/Si and PSMS/PANI/Si; however MWCNT reduced amorphous character of PSMS/PANI/Si/MWCNT. Electromagnetic interference (EMI) shielding effectiveness improved from 0.1 dB (PSMS) to 12.3 dB (PSMS/PANI/Si) to 24.5 dB (PSMS/PANI/Si/MWCNT). The increase in EMI shielding effectiveness was also observed with variation in log of conductivity from ?14 mho m?1 (PSMA) to 1.17 mho m?1 (PSMS/PANI/Si/MWCNT). 相似文献
66.
Cigdem Gencel Kai Petersen Aftab Ahmad Mughal Muhammad Imran Iqbal 《Journal of Systems and Software》2013
Software organizations face challenges in managing and sustaining their measurement programs over time. The complexity of measurement programs increase with exploding number of goals and metrics to collect. At the same time, organizations usually have limited budget and resources for metrics collection. It has been recognized for quite a while that there is the need for prioritizing goals, which then ought to drive the selection of metrics. On the other hand, the dynamic nature of the organizations requires measurement programs to adapt to the changes in the stakeholders, their goals, information needs and priorities. Therefore, it is crucial for organizations to use structured approaches that provide transparency, traceability and guidance in choosing an optimum set of metrics that would address the highest priority information needs considering limited resources. This paper proposes a decision support framework for metrics selection (DSFMS) which is built upon the widely used Goal Question Metric (GQM) approach. The core of the framework includes an iterative goal-based metrics selection process incorporating decision making mechanisms in metrics selection, a pre-defined Attributes/Metrics Repository, and a Traceability Model among GQM elements. We also discuss alternative prioritization and optimization techniques for organizations to tailor the framework according to their needs. The evaluation of the GQM-DSFMS framework was done through a case study in a CMMI Level 3 software company. 相似文献
67.
We investigated the effect of surface hardening and micro-structural modifications in Mild steel (MS) with the addition of Boron Carbide, melted by thermionic electron beam. Boron Carbide in the form of powder was added by making grooves in MS samples to trap the molten solution for interaction with solid particles. These samples were irradiated by 10 KeV electron beam with variable beam current (50-100 mA). XRD confirmed the addition of Boron Carbide in the matrix and SEM indicated micro-structural changes introduced by the electron beam. Micro-structural modification further revealed that ferrites have been transformed into dendrites and pearlites have been refined as a result of re-solidified melt. This significantly has enhanced the surface hardness greater than 6-times compared to as received Mild steal. 相似文献
68.
Vodhanel R.S. Elrefaie A.F. Iqbal M.Z. Wagner R.E. Gimlett J.L. Tsuji S. 《Lightwave Technology, Journal of》1990,8(9):1379-1386
A comparison is presented of the performance of amplitude-shift-keying (ASK), frequency-shift keying (FSK), and differential-phase-shift-keying (DPSK) lightwave systems which operate at 10 Gb/s with directly modulated 1550-nm distributed feedback (DFB) laser transmitters and conventional 1310-nm dispersion-optimized fiber. Computer modeling techniques were used to accurately simulate the amplitude modulation response and the frequency modulation response of DBF lasers. The system performance is evaluated from simulated eye patterns for both direct and heterodyne detection. With the narrow-optical spectral widths of these signal formats, fiber chromatic dispersion limits up to 70 km were obtained for transmission at 1550-nm using conventional 1310-nm optimized fiber 相似文献
69.
Iqbal M.Z. Ma K.B. Zah C.E. Lee T.P. Cheung N.K. 《Photonics Technology Letters, IEEE》1990,2(1):48-50
An experimental and theoretical study of the effects of gain ripples in semiconductor optical amplifiers on lightwave systems at data rates in excess of 10 Gb/s is discussed. Significant system degradations, or even complete eye closure, occurred in an 11 Gb/s system due to the effect of large amplifier gain variations on the signals from a directly modulated distributed-feedback laser 相似文献
70.
The static and dynamic coefficient of friction between two flat surfaces at elevated temperature is under investigation. The equipment used in this study was originally designed for the precision glass molding (PGM) process and was then modified for friction measurement. The ultimate aim of this research is to study and characterize the frictional behavior between glass and a mold surface at elevated temperatures typical of the PGM process and under conditions similar to those for this process. This paper describes the design of the apparatus, and validation experiments using a steel-steel material pair at room temperature for comparison with values reported in the literature. The average friction coefficient between the steel-steel pair was found to be 0.17. Subsequent experiments using steel against steel and BK-7 glass against steel, found the stick-slip phenomena is happening at 577 °C. 相似文献