In this work, we propose a reduced dimension and low complexity algorithm to estimate the direction-of-arrival (DOA), direction-of-departure (DOD) and the Doppler shift of a moving target for a multiple-input-multiple-output (MIMO) radar. We derive two cost functions based on two different objective functions. We solve each of the derived cost function with a low complexity fast-Fourier-transform (FFT)-based solution in three dimensions. We further carry out a derivation to reduce the three-dimensional search to two-dimensional (2D) search and solve it with a 2D-FFT. Another reduced dimension algorithm is derived using the generalized eigenvalue method which finds the estimate of unknown parameters in one dimension with less memory constraints. This way, we propose three algorithms based on the first cost function and another three algorithms based on the second. Simulation results are used to validate the proposed algorithms. We compare the mean-square-error (MSE) performance and computational complexity of our proposed algorithms with existing ones as well. We show that our proposed algorithms have better MSE performance than existing ones and achieves the Cramér-Rao lower bound (CRLB) for all unknown target parameters. The proposed algorithms exhibit lower computational complexity than the existing ones and also provide an estimate for the Doppler shift.
Alkali-metal ions, particularly sodium (Na+) and potassium (K+), are the messengers of living cells, governing a cascade of physiological processes through the action of ion channels. Devices that can monitor, in real time, the concentrations of these cations in aqueous media are in demand not only for the study of cellular machinery, but also to detect conditions in the human body that lead to electrolyte imbalance. In this work, conducting polymers are developed that respond rapidly and selectively to varying concentrations of Na+ and K+ in aqueous media. These polymer films, bearing crown-ether-functionalized thiophene units specific to either Na+ or K+, generate an electrical output proportional to the cation type and concentration. Using electropolymerization, the ion-selective polymers are integrated as the gate electrode of an organic electrochemical transistor (OECT). The OECT current changes with respect to the concentration of the ion to which the polymer electrode is selective. Designed as a single, miniaturized chip, the OECT enables the selective detection of the cations within a physiologically relevant range. These electrochemical ion sensors require neither ion-selective membranes nor a reference electrode to operate and have the potential to surpass existing technologies for the detection of alkali-metal ions in aqueous media.
Wang, Kai; Tang, Ming-Chun; Dang, Hoang X; Munir, Rahim; Barrit, Dounya; de Bastiani, Michele; Aydin, Erkan; Smilgies, Detlef-M; De Wolf, Stefaan; Amassian, Aram(Advanced materials (Deerfield Beach, Fla.), Wiley, 2019-06-18)[Article]
Perovskite solar cells increasingly feature mixed-halide mixed-cation compounds (FA1- x - y MAx Csy PbI3- z Brz ) as photovoltaic absorbers, as they enable easier processing and improved stability. Here, the underlying reasons for ease of processing are revealed. It is found that halide and cation engineering leads to a systematic widening of the anti-solvent processing window for the fabrication of high-quality films and efficient solar cells. This window widens from seconds, in the case of single cation/halide systems (e.g., MAPbI3 , FAPbI3 , and FAPbBr3 ), to several minutes for mixed systems. In situ X-ray diffraction studies reveal that the processing window is closely related to the crystallization of the disordered sol-gel and to the number of crystalline byproducts; the processing window therefore depends directly on the precise cation/halide composition. Moreover, anti-solvent dripping is shown to promote the desired perovskite phase with careful formulation. The processing window of perovskite solar cells, as defined by the latest time the anti-solvent drip yields efficient solar cells, broadened with the increasing complexity of cation/halide content. This behavior is ascribed to kinetic stabilization of sol-gel state through cation/halide engineering. This provides guidelines for designing new formulations, aimed at formation of the perovskite phase, ultimately resulting in high-efficiency perovskite solar cells produced with ease and with high reproducibility.
Sequeira, A M M; Heupel, M R; Lea, M-A; Eguíluz, V M; Duarte, Carlos M.; Meekan, M G; Thums, M; Calich, H J; Carmichael, R H; Costa, D P; Ferreira, L C; Fernandéz-Gracia, J; Harcourt, R; Harrison, A-L; Jonsen, I; McMahon, C R; Sims, D W; Wilson, R P; Hays, G C(Ecological applications : a publication of the Ecological Society of America, Wiley, 2019-06-12)[Article]
Telemetry is a key, widely used tool to understand marine megafauna distribution, habitat use, behavior, and physiology; however, a critical question remains:
Mixed lead halide perovskite solar cells have been demonstrated to benefit tremendously from the addition of Cs+ and Rb+, but its root cause is yet to be understood. This hinders further improvement, and processing approaches remain largely empirical. We address the challenge by tracking the solidification of precursors in situ and linking the evolutions of different crystalline phases to the presence of Cs+ and Rb+. In their absence, the perovskite film is inherently unstable, segregating into MA-I- and FA-Br-rich phases. Adding either Cs+ or Rb+ is shown to alter the solidification process of the perovskite films. The optimal addition of both Cs+ and Rb+ drastically suppress phase segregation and promotes the spontaneous formation of the desired α phase. We propose that the synergistic effect is due to the collective benefits of Cs+ and Rb+ on the formation kinetics of the α phase and on the halide distribution throughout the film.
Aggregation is a vital behavior when performing complex tasks in most of the swarm systems such as swarm robotics systems. In this paper, three new aggregation methods, namely the Distance-Angular, the Distance-Cosine, and the Distance-Minkowski k-nearest neighbor (k-NN) have been introduced. These aggregation methods are mainly built on well-known metrics: the Cosine, Angular and Minkowski distance functions, which are used here to compute distances among robots neighbors. Relying on these methods, each robot identifies its k nearest neighborhood set that will interact with. Then in order to achieve the aggregation, the interactions sensing capabilities among the set members are modeled using a virtual viscoelastic mesh. Analysis of the results obtained from the ARGoS simulator shows a significant improvement in the swarm aggregation performance while compared to the conventional distance-weighted k-NN aggregation method. Also, the aggregation performance of the methods is reported to be robust to partially faulty robots and accurate under noisy sensors.
Zincir, Burak; Shukla, Pravesh; Shamun, Sam; Tuner, Martin; Deniz, Cengiz; Johansson, Bengt(Energy & Fuels, American Chemical Society (ACS), 2019-05-24)[Article]
Methanol has unique properties as a fuel, and partially premixed combustion has promising results with high engine efficiency and low emissions. Low load studies with methanol partially premixed combustion are scarce, and the effect of intake temperature on low load methanol partially premixed combustion still remains an intriguing question. This study aims to investigate the effect of intake temperature on low load limitations of methanol partially premixed combustion by an experimental study. The engine was operated at 800 rpm under two different loads. The low load condition was performed at 3 bar Indicated mean effective pressure (IMEP), and the idle condition was commenced at 1 bar IMEP. From the results, it was seen that the intake temperature affected engine stability, engine performance, and engine emissions. The combustion stability decreased with the decrease of intake temperature. The ignition delay became longer and the peak cylinder pressure became smaller with lower intake temperature. The combustion efficiency reduced with the decrease of intake temperature from 0.99 to 0.96 at 3 bar IMEP, whereas it decreased from 0.99 to 0.98 at 1 bar IMEP for the single injection case and the split injection case. The thermodynamic efficiency remained constant at 0.43 at 3 bar IMEP, decreased from 0.30 to 0.28 at 1 bar IMEP for the single injection case, and reduced from 0.26 to 0.24 at 1 bar IMEP for the split injection case. The gross indicated efficiency increased from 0.41 to 0.42 at 3 bar IMEP, whereas it reduced from 0.29 to 0.28 and 0.26–0.24 at 1 bar IMEP at single injection and split injection, respectively. Total hydrocarbon emission increased, NOX emission decreased or remained constant, and CO emission remained constant with the decrease in intake temperature. Finally, the combustion phasing study was performed at 1 bar IMEP at constant intake temperature to determine the effect of the start of injection timing on the engine’s performance and the emissions under the idle condition.
A pronounced enhancement of the power conversion efficiency (PCE) by 38% is achieved in one-step doctor-blade printing organic solar cells (OSCs) via a simple solvent vapor annealing (SVA) step. The organic blend composed of a donor polymer, a nonfullerene acceptor, and an interfacial layer (IL) molecular component is found to phase-separate vertically when exposed to a solvent vapor-saturated atmosphere. Remarkably, the spontaneous formation of a fine, self-organized IL between the bulk heterojunction (BHJ) layer and the indium tin oxide (ITO) electrode facilitated by SVA yields solar cells with a significantly higher PCE (11.14%) than in control devices (8.05%) without SVA and in devices (10.06%) made with the more complex two-step doctor-blade printing method. The stratified nature of the ITO/IL/BHJ/cathode is corroborated by a range of complementary characterization techniques including surface energy, cross-sectional scanning electron microscopy, grazing incidence wide angle X-ray scattering, and X-ray photoelectron spectroscopy. This study demonstrates that a spontaneously formed IL with SVA treatment combines simplicity and precision with high device performance, thus making it attractive for large-area manufacturing of next-generation OSCs.
In our first paper (Part 1) about the square-root variable metric (SRVM) method we presented the basic theory and validation of the inverse algorithm applicable to large-scale seismic data inversions. In this second paper (Part 2) about the SRVM method, the objective is to estimate the resolution and uncertainty of the inverted resulting geophysical model. Bayesian inference allows estimating the posterior model distribution from its prior distribution and likelihood function. These distributions, when being linear and Gaussian, can be mathematically characterized by their covariance matrices. However, it is prohibitive to explicitly construct and store the covariance in large-scale practical problems. In Part 1, we applied the SRVM method to elastic full-waveform inversion in a matrix-free vector version. This new algorithm allows accessing the posterior covariance by reconstructing the inverseHessian with memory-Affordable vector series. The focus of this paper is on extracting quantitative and statistical information from the inverse Hessian for quality assessment of the inverted seismic model by FWI. To operate on the inverse Hessian more efficiently, we compute its eigenvalues and eigenvectors with randomized singular value decomposition. Furthermore, we collect point-spread functions from the Hessian in an efficient way. The posterior standard deviation quantitatively measures the uncertainties of the posterior model. 2-D Gaussian random samplers will help to visually compare both the prior and posterior distributions. We highlight our method on several numerical examples and demonstrate an uncertainty estimation analysis applicable to large-scale inversions.
Li, Wenjie; Kerr, Emily; Goulet, Marc Antoni; Fu, Hui-Chun; Zhao, Yuzhou; Yang, Ying; Veyssal, Atilla; He, Jr-Hau; Gordon, Roy G.; Aziz, Michael J.; Jin, Song(Advanced Energy Materials, Wiley, 2019-01-01)[Article]
Monolithically integrated solar flow batteries (SFBs) hold promise as compact stand-alone energy systems for off-grid solar electrification. Although considerable research is devoted to studying and improving the round-trip efficiency of SFBs, little attention is paid to the device lifetime. Herein, a neutral pH aqueous electrolyte SFB with robust organic redox couples and inexpensive silicon-based photoelectrodes is demonstrated. Enabled by the excellent stability of both electrolytes and protected photoelectrodes, this SFB device exhibits not only unprecedented stable continuous cycling performance over 200 h but also a capacity utilization rate higher than 80%. Moreover, through comprehensive study on the working mechanisms of SFBs, a new theory based on instantaneous solar-to-output electricity efficiency toward more optimized device design is developed and a significantly improved solar-to-output electricity efficiency of 5.4% from single-junction silicon photoelectrodes is realized. The design principles presented in this work for extending device lifetime and boosting round trip energy efficiency will make SFBs more competitive for off-grid applications.
The export option will allow you to export the current search results of the entered query to a file. Different
formats are available for download. To export the items, click on the button corresponding with the preferred download format.
By default, clicking on the export buttons will result in a download of the allowed maximum amount of items.
For anonymous users the allowed maximum amount is 50 search results.
To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export.
The amount of items that can be exported at once is similarly restricted as the full export.
After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.