Now showing items 1-20 of 10527

• #### TRIP: An Interactive Retrieving-Inferring Data Imputation Approach

(Institute of Electrical and Electronics Engineers (IEEE), 2015-03-09)
Data imputation aims at filling in missing attribute values in databases. Most existing imputation methods to string attribute values are inferring-based approaches, which usually fail to reach a high imputation recall by just inferring missing values from the complete part of the data set. Recently, some retrieving-based methods are proposed to retrieve missing values from external resources such as the World Wide Web, which tend to reach a much higher imputation recall, but inevitably bring a large overhead by issuing a large number of search queries. In this paper, we investigate the interaction between the inferring-based methods and the retrieving-based methods. We show that retrieving a small number of selected missing values can greatly improve the imputation recall of the inferring-based methods. With this intuition, we propose an inTeractive Retrieving-Inferring data imPutation approach (TRIP), which performs retrieving and inferring alternately in filling in missing attribute values in a data set. To ensure the high recall at the minimum cost, TRIP faces a challenge of selecting the least number of missing values for retrieving to maximize the number of inferable values. Our proposed solution is able to identify an optimal retrieving-inferring scheduling scheme in deterministic data imputation, and the optimality of the generated scheme is theoretically analyzed with proofs. We also analyze with an example that the optimal scheme is not feasible to be achieved in τ-constrained stochastic data imputation (τ-SDI), but still, our proposed solution identifies an expected-optimal scheme in τ-SDI. Extensive experiments on four data collections show that TRIP retrieves on average 20 percent missing values and achieves the same high recall that was reached by the retrieving-based approach.
• #### Selective Separation of Similarly Sized Proteins with Tunable Nanoporous Block Copolymer Membranes

(American Chemical Society (ACS), 2012-12-19)
An integral asymmetric membrane was fabricated in a fast and one-step process by combining the self-assembly of an amphiphilic block copolymer (PS-b-P4VP) with nonsolvent-induced phase separation. The structure was found to be composed of a thin layer of densely packed highly ordered cylindrical channels with uniform pore sizes perpendicular to the surface on top of a nonordered sponge-like layer. The as-assembled membrane obtained a water flux of more than 3200 L m h bar, which was at least an order of magnitude higher than the water fluxes of commercially available membranes with comparable pore sizes, making this membrane particularly well suited to size-selective and charge-based separation of biomolecules. To test the performance of the membrane, we conducted diffusion experiments at the physiological pH of 7.4 using bovine serum albumin (BSA) and globulin-γ, two proteins with different diameters but too close in size (2-fold difference in molecular mass) to be efficiently separated via conventional dialysis membrane processes. The diffusion rate differed by a factor of 87, the highest value reported to date. We also analyzed charge-based diffusive transport and separation of two proteins of similar molecular weight (BSA and bovine hemoglobin (BHb)) through the membrane as a function of external pH. The membrane achieved a selectivity of about 10 at pH 4.7, the isoelectric point (pI) of BSA. We then positively charged the membrane to improve the separation selectivity. With the modified membrane BSA was completely blocked when the pH was 7.0, the pI of BHb, while BHb was completely blocked at pH 4.7. Our results demonstrate the potential of our asymmetric membrane to efficiently separate biological substances/pharmaceuticals in bioscience, biotechnology, and biomedicine applications. © 2012 American Chemical Society.
• #### Modeling a typical winter-time dust event over the Arabian Peninsula and the Red Sea

(Copernicus GmbH, 2013-02-20)
We used WRF-Chem, a regional meteorological model coupled with an aerosol-chemistry component, to simulate various aspects of the dust phenomena over the Arabian Peninsula and Red Sea during a typical winter-time dust event that occurred in January 2009. The model predicted that the total amount of emitted dust was 18.3 Tg for the entire dust outburst period and that the two maximum daily rates were ?2.4 Tg day-1 and ?1.5 Tg day-1, corresponding to two periods with the highest aerosol optical depth that were well captured by ground-and satellite-based observations. The model predicted that the dust plume was thick, extensive, and mixed in a deep boundary layer at an altitude of 3-4 km. Its spatial distribution was modeled to be consistent with typical spatial patterns of dust emissions. We utilized MODIS-Aqua and Solar Village AERONET measurements of the aerosol optical depth (AOD) to evaluate the radiative impact of aerosols. Our results clearly indicated that the presence of dust particles in the atmosphere caused a significant reduction in the amount of solar radiation reaching the surface during the dust event. We also found that dust aerosols have significant impact on the energy and nutrient balances of the Red Sea. Our results showed that the simulated cooling under the dust plume reached 100 W m-2, which could have profound effects on both the sea surface temperature and circulation. Further analysis of dust generation and its spatial and temporal variability is extremely important for future projections and for better understanding of the climate and ecological history of the Red Sea.
• #### A new traveltime approximation for TI media

(Society of Exploration Geophysicists, 2012-07)
In a transversely isotropic (TI) medium, the trade-off between inhomogeneity and anisotropy can dramatically reduce our capability to estimate anisotropy parameters. By expanding the TI eikonal equation in power series in terms of the aneliptic parameter η, we derive an efficient tool to estimate (scan) for η in a generally inhomogeneous, elliptically anisotropic background medium. For a homogeneous-tilted transversely isotropic medium, we obtain an analytic nonhyperbolic moveout equation that is accurate for large offsets. In the common case where we do not have well information and it is necessary to resolve the vertical velocity, the background medium can be assumed isotropic, and the traveltime equations becomes simpler. In all cases, the accuracy of this new TI traveltime equation exceeds previously published formulations and demonstrates how η is better resolved at small offsets when the tilt is large.
• #### Photo-responsive suspended micro-membranes

(Royal Society of Chemistry (RSC), 2018-09-26)
Light-responsive devices are becoming increasingly relevant in many applications ranging from soft-robotics, energy harvesting, regenerative medicine and tissue engineering. Here we present a two-photon fabrication process based on a photocurable azopolymeric compound that we successfully employed to manufacture suspended micro-membranes. Thanks to the incorporation of azobenzene units, the membranes are shown to exhibit a remarkable mechanical photo-responsivity despite the disordered, amorphous structure of the crosslinked network. When irradiated with a focused laser beam at 532 nm wavelength, a reversible shape modification is observed, with a linear expansion coefficient as large as 28%. This effect is accompanied by a refractive index decrease of about 0.16, as measured interferometrically. The initial state of the membrane is fully recovered when the irradiation is switched off, as the cyclic photoisomerization process is stopped. The presented approach can be extended to light-induce complex modifications of the mechanical features in 3D printed objects by remotely providing arbitrary illumination patterns.
• #### Role of Planetary Boundary Layer Processes in the Simulation of Tropical Cyclones Over the Bay of Bengal

(Springer Nature America, Inc, 2018-10-15)
The behaviour of planetary boundary layer (PBL) schemes initialized at different life stages of a tropical cyclone (TC) is studied by considering seven Bay of Bengal TC cases. In each TC case, the Advanced Research Weather Research and Forecasting (WRF-ARW) model is initialized at four life stages (depression to very severe cyclone storm) with National Center for Environmental Prediction (NCEP) Global analysis and integrated up to 96 h. A set of six PBL sensitivity experiments are conducted at four stages for all seven TC cases to analyse the impact of the model boundary layer in simulating the TC track and intensity parameters. The model-produced track, intensity and rainfall patterns are evaluated with the best track, intensity and gridded rainfall estimates obtained from the India Meteorological Department (IMD). The spatial and radius/height section simulated fields are evaluated with satellite retrievals. Results depict that the six PBL schemes during model initialization at different stages of a TC have produced sizable differences in the simulation of track and intensity parameters. The local and nonlocal schemes produced different results based on the TC stage at which the model is initialized. The results also suggest that if the model is initialized with a non-organized cyclonic vortex such as depression stage of the storm, PBL schemes exhibit high sensitivity and spread in terms of both track and intensity. While the spread between PBL schemes was significantly reduced and found close to the observed estimates when the model was initialized at the advanced stages of the TC. In addition, the local 1.5-order closure scheme simulated the storm parameters relatively better when the cyclone vortex was not well organized in the model's initial conditions, while the non-local and first-order closure schemes perform better with initial model conditions of a well-defined cyclonic vortex.
• #### Precise Control of Pt Particle Size for Surface Structure–Reaction Activity Relationship

(American Chemical Society (ACS), 2018-09-27)
The use of surface organometallic chemistry on metal (SOMC/M) allows the controlled and stepwise variation of the platinum particle size in Pt/SiO catalysts. This SOMC/M method is possible thanks to the better affinity of most organometallic compounds with the surface of zerovalent metal particles covered with hydrogen than their support. In this paper, Pt(acac) was used as the organometallic precursor, silica as a support, and then hydrogen to reduce the adsorbed organometallic layer on top of the starting Pt nanoparticle. We partially succeeded in adding one Pt layer with a stepwise particle size increase of around 0.6 nm when going from the first (1G) to the second (2G) refilling run, as obtained from TEM and H chemisorption analysis and then confirmed by DFT calculations. The metal loading could be kept at a very low level (<1-2 wt %), which is relevant for catalytic applications. The particle size distribution remained relatively narrow even after two refilling runs, allowing more precise relationships between particle size and catalytic properties to be established. The TOR (for hydrogenolysis) dramatically decreased, while TOR (for skeletal isomerization) slightly increased with increasing the particles size. It is therefore suggested that hydrogenolysis might preferentially occur on low coordination surface platinum atoms (corners and edges), while isomerization occurs mostly on the facets.
• #### Rician K-Factor-Based Analysis of XLOS Service Probability in 5G Outdoor Ultra-Dense Networks

(Institute of Electrical and Electronics Engineers (IEEE), 2018-10-09)
In this letter, we introduce the concept of Rician K-factor-based radio resource and mobility management for fifth generation (5G) ultra-dense networks (UDN), where the information on the gradual visibility between the new radio node B (gNB) and the user equipment (UE)—dubbed X-line-of-sight (XLOS)—would be required. We therefore start by presenting the XLOS service probability as a new performance indicator; taking into account both the UE serving and neighbor cells. By relying on a lognormal K-factor model, a parametric expression of the XLOS service probability in a 5G outdoor UDN is derived, where the link between network parameters and the availability of a XLOS condition is established. The obtained formula is given in terms of the multivariate Fox H-function, wherefore we develop a fast graphical processing unit (GPU)-enebled MATLAB code. Residue theory is then applied to infer the relevant asymptotic behavior and show its practical implications. Finally, numerical results are provided for various network configurations, and underpinned by extensive Monte-Carlo simulations.
• #### Ocean Solutions to Address Climate Change and Its Effects on Marine Ecosystems

(Frontiers Media SA, 2018-10-04)
The Paris Agreement target of limiting global surface warming to 1.5-2°C compared to pre-industrial levels by 2100 will still heavily impact the ocean. While ambitious mitigation and adaptation are both needed, the ocean provides major opportunities for action to reduce climate change globally and its impacts on vital ecosystems and ecosystem services. A comprehensive and systematic assessment of 13 global- and local-scale, ocean-based measures was performed to help steer the development and implementation of technologies and actions toward a sustainable outcome. We show that (1) all measures have tradeoffs and multiple criteria must be used for a comprehensive assessment of their potential, (2) greatest benefit is derived by combining global and local solutions, some of which could be implemented or scaled-up immediately, (3) some measures are too uncertain to be recommended yet, (4) political consistency must be achieved through effective cross-scale governance mechanisms, (5) scientific effort must focus on effectiveness, co-benefits, disbenefits, and costs of poorly tested as well as new and emerging measures.
• #### Effect of air gap membrane distillation parameters on the removal of fluoride from synthetic water

(Desalination Publications, 2018-10-07)
As freshly available water around the world becomes scarcer, schemes to reuse and rectify contaminated water sources are becoming a necessity. The implementation of conventional treatment processes increases stress on existing infrastructure resources, requiring significant quantities of energy and/or chemicals, including pre-treatment processes and ongoing maintenance. An unconventional alternative to these processes is air-gap membrane distillation (AGMD), an emerging technology delivering excellent rejection of contaminants over a broad range of operating conditions. While showing great promise, the size of membrane distillation systems in existing literature is not readily scaled to industrial levels. In this paper, we present the results of our research in terms of permeate quality, rejection efficiency and scalability of a large laboratory scale AGMD system, with effective area of approximately 25 times larger than those presented in previous studies. This study found a large discrepancy in flux production when compared with small scale results, with experimental data analysed using normality and residual analysis tests. Statistical analysis of the AGMD process data provides insight into the key driving forces and interactions of feedwater temperature, concentration and flowrate on flux production. Results showed excellent rejection of contaminants (>98%) along with some fouling evident after approximately 25 h of operation.
• #### Mach number effect on the instability of a planar interface subjected to a rippled shock

(American Physical Society (APS), 2018-10-15)
The Richtmyer-Meshkov (RM) instability of a planar interface (N2-SF6) subjected to a sinusoidal rippled shock, as the variant of a sinusoidal interface impinged by a planar shock, is investigated through high-order compressible multicomponent hydrodynamic simulations. The rippled shock is generated by a planar shock penetrating through a single-mode interface (He-N2), and its propagation characteristic agrees reasonably with Bates' analytical solution. Evolution of the flat contact surface impacted by the rippled shock is found to be heavily dependent on the rippled shock phase, and it can be well explained by the impulsive perturbation and continuous perturbation regimes. Various rippled shocks with different Mach numbers ranging from 1.15 to 1.80 are considered. It is found that the influence of the shock strength on the instability growth behaves differently for rippled shocks at different phases. In the case that the shock-interface collision happens when the rippled shock amplitude vanishes for the first time, as the shock strength increases, the impulsive perturbation (i.e., amplitude growth caused by the impulsive shock impact) plays an increasingly more important role in the instability growth than the continuous perturbation (i.e., amplitude growth induced by the disturbed postshock pressure field). In contrast, in the case that the impingement occurs when the rippled shock amplitude becomes zero for the second time, the instability development contributed by the impulsive perturbation is a certain percentage of the total instability growth regardless of the shock strength. The role of the impulsive perturbation in the present nonstandard RM instability within the single-mode framework can be reasonably predicted by an empirical formula combined with the model of Ishizaki et al. [Phys. Rev. E 53, R5592 (1996)1063-651X10.1103/PhysRevE.53.R5592].
• #### Temperature study of the giant spin Hall effect in the bulk limit of \nβ−W

(American Physical Society (APS), 2018-10-15)
Giant spin Hall effect (GSHE) in heavy metals can convert charge current into spin current with a high efficiency characterized by a spin Hall angle. In this paper, we prepare a set of multilayer systems of β-W/CoFeB/MgO/Ta with the different β-W thickness up to 18 nm. Using a direct-current magneto-transport method and relying on the anomalous Hall effect of CoFeB, we observed a large spin Hall angle of 64% in the bulk limit of β-W solid at room temperature and a weak temperature dependence of the spin Hall angle. Additionally, we also studied the crystal structure, magnetization, magnetic anisotropy, electrical transport, spin diffusion, and interfacial spin current transmission in this exemplary GSHE system over a broad temperature range of 10 to 300 K, which would benefit fundamental studies and potential spintronics applications of β-W.
• #### The dynamics of weather-band sea level variations in the Red Sea

(Elsevier BV, 2018-09-27)
The variations of sea level over the Red Sea may be divided into three broad categories: tidal, seasonal and weather-band. Our study employs a variety of in situ and satellite-derived data in the first comprehensive examination of the Red Sea water level variations in the weather-band (covering periods of [Formula presented] 4–30 days). In the central Red Sea, the range of the weather-band sea level signal is of order 0.7 m, which exceeds the tidal and seasonal sea level ranges. From EOF and correlation analysis, we find that a large fraction of the weather-band sea level variation is due to a single mode of motion that extends over the entire Red Sea. In this mode, the water level rises and falls in unison with an amplitude that declines going southward over the southern Red Sea. The temporal signal of this mode is highly correlated with the along-axis surface wind stress over the southern Red Sea, and is closely reproduced by a simple one-dimensional barotropic model with forcing by the along-axis wind stress. Although this model does not account for the full suite of dynamics affecting weather-band sea level variations in the Red Sea, it may serve as a useful predictive tool. Sea level changes associated with the development and movement of sub-mesoscale features (e.g., eddies and boundary currents) are also shown to contribute to weather-band sea level motions in the Red Sea.
• #### A three-way association causing coral injuries in the Red Sea

(Bulletin of Marine Science, 2018-03-28)
• #### Self-Organized Scheduling Request for Uplink 5G Networks: A D2D Clustering Approach

(Institute of Electrical and Electronics Engineers (IEEE), 2018-10-16)
In one of the several manifestations, the future cellular networks are required to accommodate a massive number of devices; several orders of magnitude compared to today’s networks. At the same time, the future cellular networks will have to fulfill stringent latency constraints. To that end, one problem that is posed as a potential showstopper is extreme congestion for requesting uplink scheduling over the physical random access channel (PRACH). Indeed, such congestion drags along scheduling delay problems. In this paper, the use of self-organized device-to-device (D2D) clustering is advocated for mitigating PRACH congestion. To this end, the paper proposes two D2D clustering schemes, namely; Random-Based Clustering (RBC) and Channel-Gain-Based Clustering (CGBC). Accordingly, this paper sheds light on random access within the proposed D2D clustering schemes and presents a case study based on a stochastic geometry framework. For the sake of objective evaluation, the D2D clustering is benchmarked by the conventional scheduling request procedure. Accordingly, the paper offers insights into useful scenarios that minimize the scheduling delay for each clustering scheme. Finally, the paper discusses the implementation algorithm and some potential implementation issues and remedies.
• #### Monitoring Influent Measurements at Water Resource Recovery Facility Using Data-Driven Soft Sensor Approach

(Institute of Electrical and Electronics Engineers (IEEE), 2018-10-16)
Monitoring inflow measurements of water resource recovery facilities (WRRFs) is essential to promptly detect abnormalities and helpful in the decision making of the operators to better optimize, take corrective actions, and maintain downstream processes. In this paper, we introduced a flexible and reliable monitoring soft sensor approach to detect and identify abnormal influent measurements of WRRFs to enhance their efficiency and safety. The proposed data-driven soft sensor approach merges the desirable characteristics of principal component analysis (PCA) with k-nearest neighbor (KNN) scheme. PCA performed effective dimension reduction and revealed interrelationships between inflow measurements, while KNN distances demonstrated superior detection capacity, robustness to underlying data distribution, and efficiency in handling high-dimensional dataset. Furthermore, nonparametric thresholds derived from kernel density estimation further enhanced detection results of PCA-KNN approach when compared with parametric counterparts. Moreover, the radial visualization plot is innovatively employed for fault analysis and diagnosis in combination with PCA and delineated interpretable visualization of anomalies and detector performances. The effectiveness of these soft sensor schemes is evaluated by using real data from a coastal municipal WRRF located in Saudi Arabia. Also, we compared the proposed soft sensor scheme with the conventional PCA-based approaches, including standard prediction error, Hotelling’s T2, and joint univariate methods. Results demonstrate that this soft sensor-based monitoring approach outperforms conventional PCA-based methods.
• #### Performance Analysis of FD MIMO DF Cooperative Relaying Networks Using ZFBF

(Institute of Electrical and Electronics Engineers (IEEE), 2018-10-17)
In this paper, we statistically analyze the performance of full-duplex (FD) MIMO decode-&-forward (DF) cooperative relaying networks.More specifically, we evaluate the endto- end (e2e) statistics under assumed system and channel models. Then, based on these results, we derive accurate closed-form expressions of the outage probability and the average bit error rate (BER) for both the transmit and the receive zero-forcing beamforming (ZFBF) schemes in Rayleigh fading environments. Some selected results are presented to illustrate some interesting observations useful for system designers. For instance, we find that the increased hardware complexity of DF relays is generally worth the high cost in FD relay scenarios, but not in half-duplex cases.
• #### Mixed Finite Element Simulation with Stability Analysis for Gas Transport in Low-Permeability Reservoirs

(MDPI AG, 2018-01-15)
Natural gas exists in considerable quantities in tight reservoirs. Tight formations are rocks with very tiny or poorly connected pors that make flow through them very difficult, i.e., the permeability is very low. The mixed finite element method (MFEM), which is locally conservative, is suitable to simulate the flow in porous media. This paper is devoted to developing a mixed finite element (MFE) technique to simulate the gas transport in low permeability reservoirs. The mathematical model, which describes gas transport in low permeability formations, contains slippage effect, as well as adsorption and diffusion mechanisms. The apparent permeability is employed to represent the slippage effect in low-permeability formations. The gas adsorption on the pore surface has been described by Langmuir isotherm model, while the Peng-Robinson equation of state is used in the thermodynamic calculations. Important compatibility conditions must hold to guarantee the stability of the mixed method by adding additional constraints to the numerical discretization. The stability conditions of the MFE scheme has been provided. A theorem and three lemmas on the stability analysis of the mixed finite element method (MFEM) have been established and proven. A semi-implicit scheme is developed to solve the governing equations. Numerical experiments are carried out under various values of the physical parameters.
• #### Monitoring robotic swarm systems under noisy conditions using an effective fault detection strategy

(Institute of Electrical and Electronics Engineers (IEEE), 2018-10-22)
Fault detection in robotic swarm systems is imperative to guarantee their reliability, safety, and to maximize operating efficiency and avoid expensive maintenance. However, data from these systems are generally contaminated with noise, which masks important features in the data and degrades the fault detection capability. This paper introduces an effective fault detection approach against noise and uncertainties in data, which integrates the multiresolution representation of data using wavelets with the sensitivity to small changes of an exponentially weighted moving average scheme. Specifically, to monitor swarm robotics systems performing a virtual viscoelastic control model for circle formation task, the proposed scheme has been applied to the uncorrelated residuals form principal component analysis model. A simulated data from ARGoS simulator is used to evaluate the effectiveness of the proposed method. Also, we compared the performance of the proposed approach to that of the conventional principal component-based approach and found improved sensitivity to faults and robustness to noises. For all the fault types tested–abrupt faults, random walks, and complete stop faults–our approach resulted in a significant enhancement in fault detection compared with the conventional approach.
• #### Physical-Layer Security for Mixed <formula>\n <tex>$\eta-\mu$</tex>\n </formula> and <formula>\n <tex>$\mathcal{M}$</tex>\n </formula>-Distribution Dual-Hop RF/FSO Systems

(Institute of Electrical and Electronics Engineers (IEEE), 2018-11-16)
In this correspondence, we investigate the physical-layer security of a mixed radio frequency/free space optical (RF/FSO) dual-hop communication system for both fixed and variable gain relaying schemes. More specifically, we only assume that the eavesdropping happens at the RF link because the optical link has high security. We assume that all RF channels suffer from <formula><tex>$\eta-\mu$</tex></formula> fading, while the FSO link experiences <formula><tex>$\mathcal{M}$</tex></formula>-distributed fading. Then, we derive some analytical results for the average secrecy rate (ASR) and secrecy outage probability (SOP).