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41.
Akhtar Munir Tanveer ul Haq Iqtidar Hussain Prof. Ahsanulhaq Qurashi Ubaid Ullah Javed Iqbal Prof. Irshad Hussain 《ChemSusChem》2019,12(23):5117-5125
Metal nanoclusters (NCs, size ≤2 nm) are emerging materials in catalysis owing to their unique catalytic and electronic properties such as high surface/volume ratio, high redox potential, plethora of surface active sites, and dynamic behavior on a suitable support during catalysis. Herein, in situ growth of ultrasmall and robust Co@β-Co(OH)2 NCs (≈2 nm) hosted in a honeycomb-like 3D N-enriched carbon network was developed for water-oxidation catalysis with extremely small onset potential (1.44 V). Overpotentials of 220 and 270 mV were required to achieve a current density of 10 mA cm−2 and 100 mA cm−2, respectively, in alkaline medium (1 m KOH). More promisingly, at η10=240 mV, the prolonged oxygen evolution process (>130 h) with faradaic efficiency >95 % at a reaction rate of 22 s−1 at 1.46 V further substantiated the key role of the ultrasmall supported NCs, which outperformed the benchmark electrocatalysts (RuO2/IrO2) and NCs reported so far. It is anticipated that the high redox potential of NCs with regeneratable active sites and their concerted synergistic effects with the N-enriched porous/flexible carbon network are inherently worth considering to enhance the mass/charge transport owing to the nanoscale interfacial collaboration across the electrode/electrolyte boundary, thereby efficiently energizing the sluggish/challenging oxygen evolution process. 相似文献
42.
Ming‐Hua Zhuge Caofeng Pan Yazhi Zheng Jianbin Tang Salman Ullah Yaoguang Ma Qing Yang 《Advanced Optical Materials》2019,7(17)
Micro/nanolasers (MNLs) emit coherent light on the micro/nanoscale. Research on the application of MNLs has progressed rapidly in the past two decades because of their great potential for optoelectronics with compact sizes, low cost, and low energy consumption. Wavelength‐tunable MNLs are essential for a variety of fields including optical communications, solid‐state lighting, and on‐chip wavelength‐division multiplexing. Thus far, tremendous progress is achieved toward the development of wavelength‐tunable MNLs based on bandgap tuning and cavity design. Lasing wavelength is substantially defined by material bandgap, tuned by changing the geometry of the cavity structures, and can also, to some extent, be influenced by operational environment. This review is focused on the intrinsic merits of wavelength‐tunable MNLs, and the recent progress is examined. Bandgap engineering, materials synthesis, cavity structure design, wavelength‐tuning principles, and lasing performance are explored and systematically discussed. Finally, the current research status and perspectives on possible future applications are summarized. 相似文献
43.
Zain‐ul‐Abdin Li Wang Haojie Yu Rizwan Ullah Khan Raja Summe Ullah Muhammad Haroon 《应用有机金属化学》2018,32(4)
Ferrocene‐based derivatives show potential application as burning rate catalysts (BRCs) for solid composite propellants. However, migration problems of simple ferrocene‐based derivatives limit their application as BRCs in solid composite propellants. To overcome the migration problems of ferrocene‐based BRCs and to enhance the burning rate of ammonium perchlorate (AP)‐based propellants, zero‐ to second‐generation tris(2‐aminoethyl)amine‐based ferrocene‐terminated dendrimers (G0, G1 and G2) were synthesized. The structures of G0, G1 and G2 were confirmed using 1H NMR, Fourier transform infrared and UV–visible spectroscopies. The electrochemical behavior of G0, G1 and G2 was investigated using cyclic voltammetry. It was found that G0, G1 and G2 showed redox behavior due to the presence of ferrocene and this redox behavior was diffusion controlled over the investigated scan range. The burning rate catalytic effect of G0, G1 and G2 on thermal decomposition of AP was investigated using thermogravimetry and differential thermogravimetry. G0, G1 and G2 showed good catalytic effect on the thermal decomposition of AP. Anti‐migration studies showed that migration of G0, G1 and G2 was much slower than that of 2,2‐bis(ethylferrocenyl)propane (catocene) and ferrocene. 相似文献
44.
Saeed Ullah Khattak Zafar Iqbal Irshad Ur Rehman Jamshaid Ahmad Abid Ali Khan 《Natural product research》2018,32(10):1212-1215
In the quest for bioactive natural products of fungal origin, Aspergillus flavus was isolated from rhizosphere of Mentha piperita using Potato Dextrose Agar (PDA) and Czapec Yeast Broth (CYB) nutrient media for metabolites production. In total, three different metabolites were purified using HPLC/LCMS and the structures were established using 500 Varian NMR experiments. Further the isolated metabolites in different concentrations (10, 100, 1000 μg/mL) were tested for herbicidal activity using Completely Randomized design (CRD) against the seeds of Silybum marianum and Avena fatua which are major threats to wheat crop in Pakistan. Among the isolated metabolites, one compound was found active against the test weed species whose activity is reported in the present work. The chemical name of the compound is 2-(1, 4-dihydroxybutan-2-yl)-1, 3-dihydroxy-6, 8-dimethoxyanthracene-9, 10(4aH, 9aH)-dione with mass of 388. Results showed that all seeds germinated in control treatment; however, with the metabolite treated, the growth was retarded to different levels in all parts of the weeds. At a dose of 1000 μg/mL of the pure compound, 100% seeds of S. marianum and 60% seeds of A. fatua were inhibited. Interestingly, the pure compound exhibited less inhibition of 10% towards the seeds of common wheat (Triticum aestivum). 相似文献
45.
The objective of this work is to study the effect of grain orientation on the thermal grooving by surface diffusion. Hackl et al. [1] have presented a finite element model for thermal grooving in three‐dimensions. This variational model involves surface energy, grain boundary energy, external and internal triple line energy. In this study, We use an orientation dependent surface energy. For {1 0 0} grain orientation in the normal direction, we have self‐similar groove profiles for increasing extent of anisotropy of the surface energy. For {1 1 0} and {1 1 1} orientations, there are formation of facets for critical anisotropic cases. These formations are due to so‐called missing orientations concerning the shape of an unconstrained crystal in equilibrium. The rate of grooving varies with change in the extent of surface free energy anisotropy. Flux along the triple line is also important in determining the groove root shape. Triple line energy and its mobility lead to deviate from a typical t1/4 scaling law. For all theses simulations, grain boundary energies are constant, satisfying Herring's relation. Comparisons are made for different values of mobilities for groove shape and its growth rate, using different grain orientations. 相似文献
46.
Munir Ullah KHAN Safir Ullah KHAN CAO Xiaohan Muhammad USMAN Muhammad Naeem SHAH Abdul GHAFFAR Muhammad HASSAN ZHANG Chengjian ZHANG Xinghong 《高等学校化学研究》2023,39(5):790-796
In this study, we report that Berlin Green (FeFe-BG) framework exhibits superior performance in the catalytic coupling of carbon disulfide (CS2) and propylene oxide (PO) to generate a random copolymer containing thioether, propylene monothiocarbonate and ether units. Oxygen and sulfur atom exchange was detected in polymeric and cyclic thiocarbonate byproducts and utilized to modulate the copolymerization of CS2 and propylene oxide. The coupling of PO and CS2 was selective for copolymer formation under various reaction conditions. 1H and 13C NMR spectroscopy determined two distinct polymer linkages and two cyclic byproducts. Copolymer number average molecular weights ranged from 6.4 kg/mol to 10.5 kg/mol, with a comparatively low polydispersity of 1.3-1.7. The CS2/PO molar feed ratio had a significant impact on the O/S exchange process; the ratio of cyclic thiocarbonate byproducts could be efficiently regulated by tuning the CS2 molar feed ratio. 相似文献
47.
Flap deflections of an aircraft wing for active load alleviation within CFD simulations are realized using pure grid deformation due to time saving and low modeling complexity. In this case, spanwise gaps are neglected, which are present in reality during a flap deflection. Another possibility to realize the deflections is the combination of pure grid deformation and Chimera method, which allows the modeling of the gap between flap and wing or consecutive flaps. The overall aim of this work is the analysis of the aerodynamic effects caused by the different modeling approaches realizing leading and trailing edge flap deflections. The comparison of the modeling methods is investigated on the DLR LEISA configuration, which is a generic wing-fuselage configuration. For active gust load alleviation, the leading edge flaps are deflected downward and the trailing edge flaps are deflected upward. Due to the downward deflection of the leading edge flaps, vortices are formed using the combined Chimera method as a result of the gap consideration. These vortices lead to a local drag increase resulting in a difference between both modeling methods in the spanwise as well as global drag coefficient. With the pure grid deformation these vortices do not occur. Due to the upward trailing edge deflection, the combined Chimera method leads to a pressure compensation via the effective gap enlargement, which is not present in the pure grid deformation. Overall, the combined Chimera method offers a good possibility to model the induced drag as well as the pressure compensation at a large flap deflection. 相似文献
48.
Nazakat Ullah 《Pramana》1983,20(2):131-135
An integral which occurs in the new matrix ensembles and the width fluctuation factor is evaluated using a transformation
which changes a Gaussian into an exponential. It is expressed in the form of a series whose terms are found using a simple
recursion relation. It is shown that the series can be summed in closed form for the two-dimensional case. 相似文献
49.
Adam Mohamed Shaker S. Al-Omair Mohammed A. Ullah Farman 《Research on Chemical Intermediates》2019,45(9):4653-4675
Research on Chemical Intermediates - The reactivity of Zn2+ and VO2+ ions towards pyridinyl Schiff bases, in the absence or presence of a p-sodium sulfonate group (HPSNa and HPS, respectively),... 相似文献
50.
Vitex negundo Linn. (Verbenaceae) is used in traditional medical system for respiratory disorders. This study was carried out to investigate its cough-relieving potential. The antitussive effect of the butanolic extract of V. negundo (Vn) on sulphur dioxide (SO(2))-induced cough was examined in mice. Safety profile of Vn was carried out by observing acute neurotoxicity, median lethal dose (LD(50)) and behavioural signs. Vn dose-dependently (250-1000?mg?kg(-1)) inhibited the cough provoked by SO(2) gas in mice and exhibited maximum protection after 60?min of administration. At 1000?mg?kg(-1), Vn caused maximum cough-suppressive effects i.e. cough inhibition at 60?min was 67.4%, as compared to codeine (10?mg?kg(-1)), dextromethorphan (10?mg?kg(-1)) and saline having cough-inhibitory potential 75.7%, 74.7% and 0%, respectively. LD(50) value of V. negundo was found to be greater than 5000?mg?kg(-1). In toxicity tests, no signs of neural impairment and acute behavioural toxicity were observed at antitussive doses and extract has been well tolerated at higher doses. These results indicate that V. negundo exhibits antitussive effect and it was found devoid of toxicity. 相似文献