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991.
A. H. H. Al-Masoodi M. H. M. Ahmed A. A. Latiff H. Arof 《Journal of Modern Optics》2018,65(15):1801-1808
A passive Q-switched and mode-locked ytterbium-doped fibre laser (YDFL) pulse generation using a nickel oxide thin film as a saturable absorber is reported. The nickel oxide nanoparticle thin film was fabricated by a simple processing technique, and it has a modulation depth of 39% and saturation intensity of 0.04 MW/cm2. The saturable absorber was constructed by inserting a small piece of the film between two fibre ferrules. Then it was integrated in a YDFL cavity. The Q-switching operation started at a threshold pump power of 117.73 mW with an initial wavelength of 1073.5 nm. When the pump power was raised from 117.73 to 133 mW, the repetition rate grew from 9.5 to 15.8 kHz. The pulses had a maximum pulse energy of 478 nJ. Furthermore, a stable self-started mode-locked pulse was also succesfully generated at the threshold pump power of 97.3 mW. The central wavelength and repetition rate of the laser were 1037.72 nm and 23 MHz, respectively. The maximum pulse energy of 0.56 nJ and a peak power of 26.4 W were recorded at a pump power of 137.5 mW. 相似文献
992.
Md. A. Ahmed S. K. Neogi N. Midya A. Banerjee S. Bandyopadhyay 《Journal of Materials Science: Materials in Electronics》2018,29(19):16178-16187
Present work aims to study the impact of 50 MeV Li3+ ion irradiation on magnetic properties and their correlation with the substitutional incorporation of Mn at Zn site (MnZn) and defects in Mn:ZnO (Mn doped ZnO). 2 at% Mn:ZnO has been synthesized by solid-state reaction method and irradiated with fluences 1012, 1013 and 1014 ions/cm2. The concomitant changes have been probed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetization measurements. XRD patterns indicate single-phase nature of the samples and MnZn nicely varied with fluence of irradiation. Temperature dependent dc and ac magnetization (M-T) measurement reveals a minor presence of spin glass nature or superparamagnetism (SPM) though all of the samples are strongly intrinsically ferromagnetic and field dependent magnetization (M-H) measurement actually confirms this observation. It is noteworthy to observe that the ordering of spins and the magnetic parameters viz. saturation magnetization (MS), remnant magnetization (MR) and coercivity (HC) can be tuned by fluences of irradiation. Finally, proportion of defect [particularly zinc vacancy (VZn)] and MnZn seems to dictate the trend of variation of magnetization (MS and MR). Temperature dependent ac magnetization measurement and magnetic relaxation measurement actually detect a weak spin glass nature of the samples and eliminate the possibility of SPM. 相似文献
993.
Hussain Ali Badran Ahmed Al-Maliki R. K. Fakher Alfahed Bahjat Ali Saeed A. Y. Al-Ahmad F. A. Al-Saymari Rita S. Elias 《Journal of Materials Science: Materials in Electronics》2018,29(13):10890-10903
Curcumin and other three curcuminoids (bisdemethoxycurcumin, α-chlorocurcumin and α-methylcurcumin) were synthesized. Fourier transform infrared spectroscopy, Fluorescence quantum yields, AFM analysis and image surface profiles were characterized. All compounds possessed electron donor moieties at both ends of the conjugated π-system and an electron acceptor moiety in the middle of the molecules (D-A-D system) and should exhibit different optical properties depending on substituents on the benzene rings. The third order nonlinear optical properties of the curcuminoids have been investigated by z-scan technique. The optical response was characterized by measuring the refractive index (n2) of the derivatives of curcumin using the Z-scan technique. The compounds showed negative and large nonlinear refractive index values of the order of 10?7 cm2/W and reverse saturable absorption with high values of the nonlinear absorption coefficient of the order of 10?4 cm/W. The nonlinear refractive index was found to vary with the different compound. The optical constants of the different compound films were studied and the dispersion of the refractive index was discussed in terms of the Wemple-DiDomenico single oscillator model. The photo-physical properties of these compounds are compared to those of native curcumin, in order to provide a rationale to the design of samples with molecular structures optimized for a photosensitizer. These types of materials may be considering new photonic applications. 相似文献
994.
Marek E. Schmidt Manoharan Muruganathan Teruhisa Kanzaki Takuya Iwasaki Ahmed M. M. Hammam Shunei Suzuki Shinichi Ogawa Hiroshi Mizuta 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(46)
The predicted quasiparticle energy gap of more than 1 eV in sub‐6 nm graphene nanoribbons (GNRs) is elusive, as it is strongly suppressed by the substrate dielectric screening. The number of techniques that can produce suspended high‐quality and electrically contacted GNRs is small. The helium ion beam milling technique is capable of achieving sub‐5 nm patterning; however, the functional device fabrication and the electrical characteristics are not yet reported. Here, the electrical transport measurement of suspended ≈6 nm wide mono‐ and bilayer GNR functional devices is reported, which are obtained through sub‐nanometer resolution helium ion beam milling with controlled total helium ion budget. The transport gap opening of 0.16–0.8 eV is observed at room temperature. The measured transport gap of the different edge orientated GNRs is in good agreement with first‐principles simulation results. The enhanced electron–electron interaction and reduced dielectric screening in the suspended quasi‐1D GNRs and anti‐ferromagnetic coupling between opposite edges in the zigzag GNRs substantiate the observed large transport gap. 相似文献
995.
Baron Rubahamya K. Suresh Kumar Reddy Ahmed Al Shoaibi 《Fullerenes, Nanotubes and Carbon Nanostructures》2018,26(1):16-22
Benzene is one of the aromatic hydrocarbons co-absorbed with acid gases during amine scrubbing that contribute to deactivation of catalyst in the Claus process. The present work attempts to modify the porous carbon surface through nitrogen group functionalization utilizing melamine as the nitrogen source, adopting Design of Experiments (DOE) with concentration of melamine, duration of impregnation and temperature of impregnation being the process variables, while BET surface area was the response variable. The surface modified samples were subjected to benzene adsorption. The optimal nitrogen content that had minimal pore damage was found to be less than 4.3%, with concentration of melamine being the most significant variable. Surface nitrogen functionalization reduced the surface area whereas the benzene adsorption capacity increased. Benzene adsorption capacity as high as 14.72 mmol/g was recorded at 45°C at a pressure of 235 mbar. Such high adsorption capacities have not been reported in open literature and the nitrogen functionalization augmented the adsorption to the tune of 20 to 30% at a pressure of 100 mbar, and only up to 10 to 15% at higher pressures. The adsorption isotherms as well as the kinetics of adsorption were modelled using the well-known popular models. Further, successful regeneration of the surface modified adsorbents were ensured through adsorption/desorption cycle experiments. 相似文献
996.
Ateyya A. Aboul-Enein Ahmed E. Awadallah Adel A.-H. Abdel-Rahman Ahmed M. Haggar 《Fullerenes, Nanotubes and Carbon Nanostructures》2018,26(7):443-450
The pyrolysis of different plastic waste types such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET) and polystyrene (PS) for producing multi-walled carbon nanotubes (MWCNTs) using a two-stage process has been investigated. Firstly, the cracking of plastic wastes was carried out at a temperature of 700°C to produce hydrocarbon gases. In the second stage, the produced hydrocarbon gases were decomposed at 650°C on the surface of the Ni-Mo/Al2O3 catalyst to form CNTs. Various analytical tools such as XRD, TPR, TGA, Raman spectroscopy and TEM were used to describe both the fresh catalyst and the obtained CNTs. The results showed that the amount of the hydrocarbon gases was related to the type of plastic waste and hence the CNT yield. Accordingly, LDPE or PP was decomposed to produce the largest gases yield of 72.5 or 70.7 wt%, respectively. As a result, a large CNTs yield of 5.8 and 5 g/gcat can be achieved by pyrolysis of PP and LDPE waste, respectively. However, a small yield of CNTs with little quality and low purity was obtained by using PS or PET waste as the carbon feedstock. 相似文献
997.
998.
Adnan A. Ahmed Luca Susmel 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(4):883-904
A novel approach based on the equivalent homogenised material concept and the theory of critical distances is formulated to perform static assessment of plain/notched objects of polylactide (PLA) when this polymer is additively manufactured with different infill levels. The key idea is that the internal net structure resulting from the 3D‐printing process can be modelled by keeping treating the material as linear elastic, continuum, homogenous, and isotropic, with the effect of the internal voids being taken into account in terms of change in mechanical/strength properties. This idea is initially used to assess the detrimental effect of the manufacturing voids on the static strength of the plain (ie, unnotched) material. This is done by addressing this problem in a Kitagawa‐Takahashi setting via the Theory of Critical Distances. Subsequently, this approach is extended to the static assessment of notched components of 3D‐printed PLA; ie, it is used to take into account simultaneously the effect of both manufacturing voids and macroscopic geometrical features. The accuracy and reliability of this design methodology were checked against a large number of experimental data generated by testing, under axial loading, plain specimens, as well as notched samples (including open notches) of PLA. These specimens were manufactured by making the infill level vary in the rage 10% to 90%. This validation exercise allowed us to demonstrate that the proposed approach is highly accurate, returning estimates falling within an error interval of ±20%. This remarkable level of accuracy strongly supports the idea that static assessment of 3D‐printed materials with complex geometries and manufactured with different infill levels can be performed by simply post‐processing conventional linear elastic finite element (FE) solid models, ie, without the need for modelling explicitly the detrimental effect of the manufacturing voids. 相似文献
999.
Huifang Pang Ahmed M. Abdalla Rakesh P. Sahu Yuping Duan Ishwar K. Puri 《Journal of Materials Science》2018,53(24):16288-16302
Noting that the dielectric properties of manganese oxide make it a promising microwave-absorbing material, a low-temperature method to deposit crystalline MnO2 over carbon nanotubes (CNTs) is developed. Adjusting the pH of the precursor solution allows control over the phases and morphologies of the synthesized manganese oxides MnO2 and Mn3O4 that have minimum reflection losses of ??11 dB and ??6 dB, respectively. The synthesized CNT–MnO2 and CNT–Mn3O4 nanocomposites are superior microwave absorbers than simpler physical mixtures of CNTs and manganese oxides, with reflection losses as high as ??19 dB at 9.5 GHz and ??34 dB at 4 GHz, and have wider absorption bands than pure manganese oxides. Coating CNTs with manganese oxide not only increases dielectric and magnetic losses, but also improves the impedance match between free space and the absorber. The addition of CNTs to pure MnO2 and Mn3O4 improves impedance matching by enhancing the relaxation polarization and conductivity losses, magnetic loss, including contributions form eddy current and natural resonance. This facile, low-cost, scalable, high-yield method produces an enhanced microwave-absorbing nanocomposite. 相似文献
1000.
Shenghua Wu Haifang Wen Weiguang Zhang Shihui Shen Louay N. Mohammad Ahmed Faheem 《International Journal of Pavement Engineering》2019,20(1):33-43
As a result of repeated rehabilitation efforts over the past few decades, often asphalt pavements have become deep-strength pavements. Consequently, top-down cracking has become a primary distress type. In particular, the top-down cracking performance of warm mix asphalt (WMA) pavements, i.e. how does it compare with similar hot mix asphalt (HMA) pavements is largely unclear mainly due to the lack of field performance data. This paper presents an effort of monitoring the top-down cracking performance of 28 pavement projects including WMA pavements and their corresponding HMA control pavements with service lives ranging between 4 and 10 years. These pavements cover different climate zones, WMA technologies, service years, pavement structures and traffic volume levels. Two rounds of distress surveys were conducted at a two-year interval, and the material (asphalt binder and mixture) properties of the pavements were determined using field cores. The top-down cracking performance of the HMA and WMA pavements was compared based on the first and second round distress surveys. It was found that the HMA and WMA pavement in general exhibited comparable performance. The significant determinants (material properties) for top-down cracking were determined, which were vertical failure deformation of mixes measured at 20 °C from indirect tension test. 相似文献