THE KAUST Repository is an initiative of the University Library to expand the impact of conference papers, technical reports, peer-reviewed articles, preprints, theses, images, data sets, and other research-related works of King Abdullah University of Science and Technology (KAUST).
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Aerial Data Aggregation in IoT Networks: Hovering & Traveling Time Dilemma(IEEE, 2018-12-13)The next era of information revolution will rely on aggregating big data from massive numbers of devices that are widely scattered in our environment. The majority of these devices are expected to be of low-complexity, low-cost, and limited power supply, which imposes stringent constraints on the network operation. In this regards, this paper proposes an aerial data aggregation from a finite spatial field via an unmanned aerial vehicle (UAV). Instead of fusing, relaying, and routing the data across the wireless nodes to fixed locations access points, a UAV flies over the field and collects the required data. Particularly, the field is divided into several subregions where the UAV hover over each subregion to collect samples from the underlying nodes. To this end, an optimization problem is formulated and solved to find the optimal number of subregions, the area of each subregion, the hovering locations, the hovering time at each location, and the trajectory between hovering locations such that an average number of samples are collected from the field in minimal time. The proposed the formulation is shown to be np-hard mixed integer problem, and hence, a decoupled heuristic solution is proposed. The results show that there exists an optimal number of subregions that balance the tradeoff between the hovering and traveling times such that the total time for collecting the required samples is minimized.
Observation of piezotronic and piezo-phototronic effects in n-InGaN nanowires/Ti grown by molecular beam epitaxy(Elsevier, 2018-10-17)Group-III nitride nano-dimensional materials with noncentrosymmetric crystal structure offer an exciting area of piezotronics for energy conversion applications. We experimentally report the piezotronic and piezo-phototronic effects of n-InGaN nanowires (NWs) having an emission wavelength in the visible region (≈ 510 nm). The n-type InGaN NWs, exhibiting high structural and optical quality, were grown by plasma-assisted molecular beam epitaxy (PAMBE) on Ti/TaN/Si substrates to facilitate the direct bottom electrical contact to the NWs. Further, we use Pt/Ir conductive atomic force microscopy (c-AFM) tip as a top electrical contact to the NW. Applying compressive strain on the NWs using a c-AFM tip, the Schottky barrier height (SBH) formed at the metal-semiconductor NW interface was tuned by means of strain induced piezo-potential. Thus, we study the two-way coupling of mechanical and electrical energy results in piezotronics of n-InGaN NWs. Such measurements were further carried out under optical excitation with 405 nm laser to understand its effect on change in SBH. Thereby, we demonstrate the three-way coupling of the piezo-phototronics of n-InGaN NWs by exploiting their excellent visible optoelectronic properties. The photogenerated carriers reduce the SBH while they play a lesser role at higher tip deflection force on NWs. This revealed that at the higher strain on NW, the piezo fields screen the photoexcited carriers hence resulting in a negligible change in I-V characteristics for ≥ 6 nN tip force with and without illumination. Thus, the investigation of nanoscale piezotronic and piezo-phototronic effects of n-InGaN NWs provides an opportunity to enable piezoelectric functional devices to be used as strain-tunable, self-powered electronics and optoelectronics applications.
The Curious Case of Ketene in Zeolite Chemistry and Catalysis(Wiley, 2018-10-17)Ketenes in the limelight: The influential role of ketenes has never been adequately acknowledged in zeolite chemistry and catalysis; unlike other first generation highly reactive intermediates, such as carbocations, carbanions, radicals, and carbenes. In fact, the role that ketenes play during catalysis-whether beneficial or detrimental-is a contentious subject that requires further consideration.
Approximation Methods for Inhomogeneous Geometric Brownian Motion(World Scientific Pub Co Pte Lt, 2018-10-16)We present an accurate and easy-to-compute approximation of the transition probabilities and the associated Arrow-Debreu (AD) prices for the inhomogeneous geometric Brownian motion (IGBM) model for interest rates, default intensities or volatilities. Through this procedure, dubbed exponent expansion, transition probabilities and AD prices are obtained as a power series in time to maturity. This provides remarkably accurate results—for time horizons up to several years—even when truncated after the first few terms. For farther time horizons, the exponent expansion can be combined with a fast numerical convolution to obtain high-precision results.
Ethanolic gasoline, a lignocellulosic advanced biofuel(Royal Society of Chemistry (RSC), 2018-10-16)In line with society's growing need for a more sustainable fuel economy, various biofuels and alternative fuel formulations are being proposed. In this work, the ignition quality of a novel tricomponent advanced biofuel is examined. Ethyl levulinate, diethyl ether and ethanol (EL/DEE/EtOH) result from the acid hydrolysis of lignocellulosic biomass in ethanol. In this paper, derived cetane numbers are established for a wide variety of blend fractions, using Ignition Quality Tester measurements. EL/DEE/EtOH mixtures of ignition quality equivalent to market diesel and gasoline are identified. One mixture of Motor Octane Number (MON) 88.3 and Research Octane Number (RON) 95 is selected for detailed analysis in comparison to a FACE (Fuels for Advanced Combustion Engines) gasoline, as a representative of petroleum-derived gasoline, with a similar MON of 88.8 and RON of 94.4. Ignition delay times for the EL/DEE/EtOH gasoline fuel are measured using a rapid compression machine at equivalence ratios of 0.5 and 1.0, at 20 and 40 bar over a temperature range of 600–900 K. The data shows that at temperatures >800 K, the EL/DEE/EtOH fuel behaves quite similar to the petroleum derived gasoline, FACE-F. However, the tri-component biofuel shows a dramatically truncated extent of ignition reactivity at lower temperatures, with a total absence of low-temperature chemistry or negative temperature coefficient (NTC) region; in this respect this biofuel blend is very different to conventional gasoline. To understand this differing behaviour, a detailed chemical kinetic model is developed. Analysis of this model shows that ignition of the EL/DEE/EtOH blend is inhibited by the dominance of alkyl radical elimination pathways, which leads to a heightened rate of production of HO2 radicals. At high temperatures, while both fuels maintain a similar ignition delay time, the sensitivity analysis and the radical pool population shows that a different combustion mechanism is occurring for the EL/DEE/EtOH fuel, where ethyl and methyl radicals play a much more prominent role in the ignition process.