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61.
In this paper an experimental investigation is performed to describe the fracture behavior and failure mechanisms of woven fabrics composites, under static loading, using a compact tension test (CT). We studied the development of the different damage phases using the digital image correlation and the compliance method. The crack length was estimated at in the front of the notch tip. The approach of the effective crack length via the compliance procedure was compared to the measures of the damage in the epoxy/glass fiber composite obtained by the digital image correlation (DIC). 相似文献
62.
Structural, elastic, electronic and optical properties ofzinc-chalcogenides (viz. ZnX, X = S, Se and Te) are studied in zinc-blende structure under hydrostatic pressure using the full-potential linearized augmented plane wave method. Generalized gradient approximation is used for exchange correlation potentials. Pressure-dependent lattice constants and bulk moduli are obtained using the optimization method. Young's modulus, Poisson's ratio, internal strain parameter and anisotropy are also calculated. The higher values of Young's modulus in comparison to the bulk modulus show that these materials are hard to break. Poisson's ratio is computed for the first time for these materials to the best of our knowledge and its values show higher ionic contribution in these materials. Modified Becke and Johnson (mBJ) method is used to study band gaps, density of states, dielectric function and refractive index. Electronic study shows direct band gaps convert to indirect band gaps with increasing pressure in the case of ZnS and ZnTe. We compared our results with other theoretical and experimental results. Our results are far better than other theoretical results because mBJ is the best technique to treat Ⅱ-Ⅵ semiconductors. 相似文献
63.
Nader Mohamed Jameela Al-Jaroodi Imad Jawhar Sanja Lazarova-Molnar 《Journal of Intelligent and Robotic Systems》2014,74(1-2):309-321
For a while, Unmanned Arial Vehicles (UAVs) use was limited to military applications, however recently UAVs are also used for a wide range of civilian applications. Some of these UAV applications may involve multiple UAVs that must cooperate to achieve a common goal. This kind of applications is termed collaborative UAV applications. This paper investigates the collaborative aspects and challenges of multiple UAV systems. One of the main issues for multiple UAV systems is developing an effective framework to enable the development of software systems for collaborative UAV operations. One possible approach is to rely on service-oriented computing and service-oriented middleware technologies to simplify the development and operations of such applications. This paper discusses how the service-oriented middleware approach can help resolve some of the challenges of developing collaborative UAVs. The paper also proposes a service-oriented middleware architecture that can satisfy the development and operations of such applications. 相似文献
64.
We have recently proposed in [1] a blind frame synchronization method based on a Maximum A Posteriori (MAP) approach. In this letter, we study the properties of this method and show that this synchronization technique is well suitable for codes having a sparse parity check matrix, such as Low-Density Parity-Check (LDPC) codes. We also find the probability distributions involved in our synchronization criterion and expand the analytical expression of the probability of false synchronization. Through computer simulations we validate our theoretical results and show that this synchronization technique has excellent performance when applied to LDPC codes. We also show that this method outperforms another approach of blind frame synchronization that computes hard values of the syndrome instead of its Log-Likelihood Ratios (LLR). 相似文献
65.
Salahddine Krit Hassan Qjid Imad El Affar Yafrah Khadij Ziani Messghati Yassir El-Ghzizal 《半导体学报》2010,31(4):045001-5
This paper presents a novel organization of switch capacitor charge pump circuits based on voltage doubler structures. Each voltage doubler takes a dc input and outputs a doubled dc voltage. By cascading voltage doublers the output voltage increases up to 2 times. A two-phase voltage doubler and a multiphase voltage doubler structures are discussed and design considerations are presented. A simulator working in the Q-V realm was used for simplified circuit level simulation. In order to evaluate the power delivered by a charge pump, a resistive load is attached to the output of the charge pump and an equivalent capacitance is evaluated. To avoid the short circuit during switching, a clock pairs generator is used to achieve multi-phase non-overlapping clock pairs.
This paper also identifies optimum loading conditions for different configurations of the charge pumps. The proposed charge-pump circuit is designed and simulated by spice with TSMC 0.35-μm CMOS technology and operates with a 2.7 V to 3.6 V supply voltage. It has an area of 0.4 mm2; it was designed with a frequency regulation of 1 MHz and internal current mode to reduce power consumption. 相似文献
66.
Mark M. Hytros Imad M. Jureidini Jung-Hoon Chun Richard C. Lanza Nannaji Saka 《Metallurgical and Materials Transactions A》1999,30(5):1403-1409
An X-ray computed tomography (CT) system was developed for monitoring the solidification front in metal casting. The X-ray
source was a 6 MeV linear accelerator (linac) emitting photons in 5 μs pulses at a rate of 180 Hz. The source intensity was 300 R/min at 1 m. The X-ray beam was collimated in a 30 deg fan shape
with a 10-mm height. A detector array comprising 128 elements was located 845 mm from the source. Pure aluminum in a clay-graphite
crucible (178-mm o.d., 146-mm i.d.) was melted in a resistance heater furnace, and a cooling tube at the center of the crucible
solidified the molten aluminum to simulate the casting process. A solidification front formed around the tube and progressed
outward over an hour until the aluminum was completely solidified. X-ray attenuation measurements were taken every minute
during this time. Density images were later reconstructed from these measurements using CT. From these images, the progression
of the solidification front was determined with a planar resolution of 1.3 mm and a sensitivity of 3.7 pct. The density maps
agree with expected values and correlate well with temperature measurements obtained independently by thermocouples. 相似文献
67.
Ali Abu-Lathou Imad I. Hamdan Ahmed Tahraoui 《Drug development and industrial pharmacy》2013,39(6):577-588
Effective isocratic separations of decongestants and antihistamines is a challenging analytical task due to wild differences in their lipohilicities (hydrophilic decongestants and hydrophobic antihistamines). In this paper a new approach for resolving such a problem is described taking pseudoephedrine sulfate and loratadine as an example. The chromatographic behavior of pseudoephedrine sulfate and loratadine on RP C18 and C8 columns were studied in presence and absence of sodium lauryl sulfate (SLS). The effect of combining two different types of stationary phases (cyano and C18 or C8) on the relative retention of the two compounds was investigated. In conclusion, it was found that the combination of a C18 column followed by a standard cyano column provides a stationary phase that separates both compounds effectively and within a reasonable time. This approach was compared to a literature method and demonstrated to have superior selectivity. 相似文献
68.
Songsu Son Imad L. Al-Qadi Tom Zehr 《International Journal of Pavement Engineering》2016,17(9):799-809
This paper presents the design of stone matrix asphalt (SMA) with 4.75-mm nominal maximum aggregate size (NMAS) and alternative surfacing cross-section for an asphalt wearing course that may improve pavement performances while controlling costs by using locally available aggregates. The 4.75 -mm NMAS dense-graded mix was previously used in several states to reduce layer thickness and cost. Because of its poor friction and limited performance, however, it was generally used as levelling binder and placed on low-volume roads. The 4.75-mm SMA is proposed for thinner asphalt overlays in this study to improve its performance as well as surface texture. The ultimate goal of this study is to develop the 4.75-mm SMA and evaluate its performance and engineering benefits as a wearing course under laboratory and field conditions. Test pavement sections were constructed in Northern Illinois and on-site performance tests were conducted to evaluate its performance under actual traffic loading. The engineering cost-benefit analysis with respect to performances from both laboratory and field studies suggests the proper application of 4.75-mm SMA as an efficient and cost-effective wearing course for asphalt thin overlays. 相似文献
69.
Maryam Shakiba Hasan Ozer Mojtaba Ziyadi Imad L. Al-Qadi 《Mechanics of Time-Dependent Materials》2016,20(4):579-600
The structure-induced rolling resistance of pavements, and its impact on vehicle fuel consumption, is investigated in this study. The structural response of pavement causes additional rolling resistance and fuel consumption of vehicles through deformation of pavement and various dissipation mechanisms associated with inelastic material properties and damping. Accurate and computationally efficient models are required to capture these mechanisms and obtain realistic estimates of changes in vehicle fuel consumption. Two mechanistic-based approaches are currently used to calculate vehicle fuel consumption as related to structural rolling resistance: dissipation-induced and deflection-induced methods. The deflection-induced approach is adopted in this study, and realistic representation of pavement–vehicle interactions (PVIs) is incorporated. In addition to considering viscoelastic behavior of asphalt concrete layers, the realistic representation of PVIs in this study includes non-uniform three-dimensional tire contact stresses and dynamic analysis in pavement simulations. The effects of analysis type, tire contact stresses, pavement viscoelastic properties, pavement damping coefficients, vehicle speed, and pavement temperature are then investigated. 相似文献
70.
Hasan?OzerEmail author Ziad?G.?Ghauch Heena?Dhasmana Imad?L.?Al-Qadi 《Mechanics of Time-Dependent Materials》2016,20(3):441-453
Micromechanical computational modeling is used in this study to determine the smallest domain, or Representative Volume Element (RVE), that can be used to characterize the effective properties of composite materials such as Asphalt Concrete (AC). Computational Finite Element (FE) micromechanical modeling was coupled with digital image analysis of surface scans of AC specimens. Three mixtures with varying Nominal Maximum Aggregate Size (NMAS) of 4.75 mm, 12.5 mm, and 25 mm, were prepared for digital image analysis and computational micromechanical modeling. The effects of window size and phase modulus mismatch on the apparent viscoelastic response of the composite were numerically examined. A good agreement was observed in the RVE size predictions based on micromechanical computational modeling and image analysis. Micromechanical results indicated that a degradation in the matrix stiffness increases the corresponding RVE size. Statistical homogeneity was observed for window sizes equal to two to three times the NMAS. A model was presented for relating the degree of statistical homogeneity associated with each window size for materials with varying inclusion dimensions. 相似文献