bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced light harvesting and charge separation over wormhole mesoporous TiO2−X nanocrystallites towards efficient hydrogen generation
Authors: Negi Sanjay Singh
Published: March 2019

Improved visible light absorption by meso-TiO2−X materials compared to TiO2 for enhanced solar light harvesting.
Monitoring the hydrogen bond net configuration and the dimensionality of aniline and phenyloxamate by adding 1H-pyrazole and isoxazole as substituents for molecular self-recognition
Authors: Oliveira Willian X. C. , do Pim Walace D. , Pinheiro Carlos B. , Journaux Yves , Julve Miguel , Pereira Cynthia L. M.
Published: March 2019

Monitoring the hydrogen bond and dimensionality of aniline and phenyloxamate by adding 1H-pyrazole/isoxazole for molecular self-recognition.
In situ encapsulation of Co3O4 polyhedra in graphene sheets for high-capacitance supercapacitors
Authors: Lin Guanyu , Jiang Yulin , He Chengen , Huang Zhiyong , Zhang Xiaofang , Yang Yingkui
Published: March 2019

The graphene encapsulated Co3O4 polyhedra (rGO/Co3O4) exhibited large capacitance, high energy density, and excellent cycling stability, due to the 3D double conductive network from graphene sheets and porous channels of Co3O4 polyhedra/N-doped carbon hybrid.
Diastereodivergent synthesis of cyclopropanes via on-water [2 + 1] annulations of diazo compounds with electron-deficient alkenes
Authors: Li Qing-Zhu , Zhang Xiang , Xie Ke , Dai Qing-Song , Zeng Rong , Liu Yan-Qing , Jia Zhi-Qiang , Feng Xin , Li Jun-Long
Published: March 2019

An efficient on-water [2 + 1] annulation of diazo compounds and electron-deficient alkenes under catalyst-free conditions was developed, which allows the synthesis of cyclopropanes in a diastereodivergent manner.
Conversion of CO2to value-added products mediated by ionic liquids
Authors: Chen Yu , Mu Tiancheng
Published: March 2019

The thermal, electrochemical and photochemical conversion of CO2mediated by ionic liquids is systematically reviewed.
Responsive capsules that enable hermetic encapsulation of contents and their thermally triggered burst-release
Authors: Goertz John P. , DeMella Kerry C. , Thompson Benjamin R. , White Ian M. , Raghavan Srinivasa R.
Published: March 2019

Capsules with an aqueous core and a wax shell perfectly encapsulate their contents at room temperature, while the contents are released above the melting temperature of the wax.
The supramolecular structure and van der Waals interactions affect the electronic structure of ferrocenyl-alkanethiolate SAMs on gold and silver electrodes
Authors: Cao Liang , Yuan Li , Yang Ming , Nerngchamnong Nisachol , Thompson Damien , Yu Xiaojiang , Qi Dong-Chen , Nijhuis Christian A.
Published: March 2019

Understanding the influence of structural properties on the electronic structure will pave the way for optimization of charge transport properties of SAM devices.
Transition state analysis of an enantioselective Michael addition by a bifunctional thiourea organocatalyst
Authors: Izzo Joseph A. , Myshchuk Yaroslaw , Hirschi Jennifer S. , Vetticatt Mathew J.
Published: March 2019

Transition structure for the bifunctional thiourea catalyzed Michael addition using 13C KIEs and DFT calculations.
Self-organization of gel networks formed by block copolymer stars
Authors: Gârlea Ioana C. , Jaramillo-Cano Diego , Likos Christos N.
Published: March 2019

Block copolymers stars can self-assemble to form a variety of equilibrium network architectures, due to their reconfigurability.
Bis[di(4-methoxyphenyl)amino]carbazole-capped indacenodithiophenes as hole transport materials for highly efficient perovskite solar cells: the pronounced positioning effect of a donor group on the cell performance
Authors: Hua Yong , Chen Song , Zhang Dongyang , Xu Peng , Sun Anxin , Ou Yangmei , Wu Tai , Sun Hanwen , Cui Bo , Zhu Xunjin
Published: March 2019

Two indacenodithiophene-based HTMs have been designed and applied in PSCs. The PSC device based on YK1 displays a very impressive PCE of 20.13%.
Experimental design and theoretical calculation for sulfur-doped carbon nanofibers as a high performance sodium-ion battery anode
Authors: Jin Qianzheng , Li Wei , Wang Kangli , Feng Pingyuan , Li Haomiao , Gu Tiantian , Zhou Min , Wang Wei , Cheng Shijie , Jiang Kai
Published: March 2019

S-doped carbon nanofibers derived from bacterial cellulose with interlinked networks and pores were facilely prepared in a sustainable approach. This product presents a high Na-ion storage capacity and excellent rate performances.
CH3NH3PbI3 perovskite thin films as a saturable absorber for a passively Q-switched Nd:YAG laser
Authors: Wang Jiang , Wang Yonggang , Chen Zhendong , Yang Xiguang , Lv Ruidong
Published: March 2019

We experimentally demonstrated a passively Q-switched Nd:YAG laser based on CH3NH3PbI3 perovskite as a saturable absorber.
3D-Printed alternating current electroluminescent devices
Authors: Brubaker Cole D. , Newcome Kailey N. , Jennings G. Kane , Adams Douglas E.
Published: March 2019

Phosphor-based alternating current electroluminescent (ACEL) devices are fabricated using a fused deposition modeling (FDM) type 3D printing approach.
Novel sky blue heteroleptic iridium(iii) complexes with finely-optimized emission spectra for highly efficient organic light-emitting diodes
Authors: Du Mingxu , Wang Yu , Wang Jiujiu , Chen Shuonan , Wang Zhen , Wang Shiping , Bai Fuquan , Liu Yu , Wang Yue
Published: March 2019

Two novel highly efficient sky blue phosphorescent iridium complexes possessing single-peak & narrow-FWHM emission spectra have been constructed by a rare four-membered Ir–N–C–N backbone.
Q‐RTS: a real‐time swarm intelligence based on multi‐agent Q‐learning
Authors: Matta M. , Cardarilli G.C. , Di Nunzio L. , Fazzolari R. , Giardino D. , Re M. , Silvestri F. , Spanò S.
Published: March 2019

The authors introduce a novel approach for swarm reinforcement learning that extends the standard Q‐learning to multi‐agent systems. State‐of‐the‐art methods implement a knowledge sharing mechanism between the agents that is triggered by the episodes succession. This causes an intrinsic limit in the convergence speed of the algorithms. They overcame this issue by developing a Q‐learning real‐time swarm algorithm (Q‐RTS), which is iteration‐based and suitable for real‐time systems. Q‐RTS was tested in different environments and compared to other related methods in the literature. They obtained positive results in terms of learning time and scalability, i.e. achieving a speed‐up factor of at least 1.49 with respect to standard Q‐learning. Moreover, Q‐RTS shows enhanced learning performance as the environments complexity increases.
Fixed point iteration‐based subspace identification of Hammerstein state‐space models
Authors: Hou Jie , Chen Fengwei , Li Penghua , Zhu Zhiqin
Published: March 2019

In this study, a fixed point iteration‐based subspace identification method is proposed for Hammerstein state‐space systems. The original system is decomposed into two subsystems with fewer parameters based on the hierarchical identification principle. Each subsystem is related directly to either the linear dynamics or the static non‐linearity. A two‐stage least‐squares‐based iterative method is then implemented to separately estimate the coefficients of the non‐linear subsystem and the extended Markov parameters of the linear subsystem. The linear subsystem parameters are extracted from the identified extended Markov parameters using a singular value decomposition based method. Convergence analysis of the proposed method is established using fixed point theory, which shows that the proposed method gives consistent estimates under arbitrary non‐zero initial conditions. Simulation results are included to show the performance of the proposed method.
New MPC‐5LUC with reduced PSD count for MVHP direct‐drive WECS with PMSG: a cost‐effective solution
Authors: Yalla Naveen , Agarwal Pramod
Published: March 2019

In this study, a new multi‐point clamped (MPC), three‐phase two‐leg, five‐level unidirectional front end high‐power‐factor converter is proposed for directly connected wind energy conversion system with a permanent magnet synchronous generator. The proposed topology can be modelled and modulated similarly to other existing MPC structured converters with the omission of clamping diodes and bidirectional switches. The proposed converter has an advantage of reduced power semiconductor device count and maximum device stress. A factor (normalised index) is introduced and comprehensive comparative analysis with N level existing topologies is carried out. The minimum value of the normalised index makes the proposed topology as a suitable option for medium‐voltage and high‐power applications. Also, the fault ride through capability is one of the key performance indicators is also investigated on proposed topology under voltage sag condition. Further, steady state and transient performance of topology during load as well as dc‐link voltage change are presented. Minimum distorted and balanced line currents with unity power factor are drawn from supply by implementing negative sequence elimination control algorithm. The validation of proposed topology is verified with simulation and a down‐scaled experimental setup.
Automatic geometry calibration for multi‐projector display systems with arbitrary continuous curved surfaces
Authors: Wang Xiuhui , Yan Ke , Liu Yanqiu
Published: March 2019

A large‐scale multi‐projector display system offers high‐resolution, high‐brightness and immersive visualisation for realistic experience to end users. It has been demonstrated to be effective tackling the conflict between the increasing demands of super‐resolution display and the resolution limitation of a single display system. However, there is still no standardisation method for curved‐surface projection screen. In this study, we propose a novel approach for calibrating multi‐projector display systems, which have curved surfaces. First, based on a detailed analysis on arbitrarily curved surfaces, we present a three‐dimensional reconstruction algorithm based on Bezier surface models. Then, for fully utilising the projection area of each projector, we propose a novel curved‐surface stitching algorithm to achieve geometry seamlessness of multi‐projector display systems. Experimental results show that by constructing local Bessel models for the curved screen, the proposed method performs better than traditional approaches, i.e. the new method achieves geometric calibration with higher accuracy. The proposed method of modelling projection screen and the corresponding automatic geometric correction scheme effectively increase the utilisation ratio of the original projection area of each projector and improve the calibration accuracy of multi‐projector system with continuous curved surface.
Modification of metasurface‐based CP array antenna by using cascade feed network
Authors: Karamzadeh Saeid , Rafiei Vahid
Published: March 2019

In this work, a unique compact size high gain circularly polarised (CP) array antenna is proposed. The array is considered as a 2 × 2 metasurface‐based CP patch antennas which fed by a cascade network. The single element consists of two different layers of substrate that metasurface layer excited by aperture slot on metallic ground layer in middle layer between metasurface cells and microstrip line, meanwhile this layer isolates destructive effects of feed lines on radiation layer. For achieving high gain at a compact size several techniques such as (i) use of broadband feed network, (ii) utilising of adjacent cells with unique structure as mutual coupling reducer, and etc. have been simultaneously applied. In order to validation of simulated parameters the proposed array has been fabricated and measured. The measurement results for the proposed compact size array antenna are the impedance bandwidth (|S11| < −10 dB) of 4.22–7 GHz (49.55%), a 3‐dB axial ratio bandwidth of 4.71 to 6.28 GHz (28.5%), and a peak gain of 16.57 dBic at 5.5 GHz.
Machine‐learning‐based prediction methods for path loss and delay spread in air‐to‐ground millimetre‐wave channels
Authors: Yang Guanshu , Zhang Yan , He Zunwen , Wen Jinxiao , Ji Zijie , Li Yue
Published: March 2019

The unmanned aerial vehicles (UAVs) have been widely applied in various fields due to their advantages like high mobility and low cost. Reliable communication is the premise to ensure the connectivity between UAV nodes. To provide reasonable references for the design, deployment, and operation of UAV communication systems, the precise prediction of radio channel parameters are required. In this study, the authors propose prediction methods for path loss and delay spread in air‐to‐ground millimetre‐wave channels based on machine learning. Random forest and K‐nearest‐neighbours are the algorithms employed in the methods. Then, a feature selection scheme is proposed to further improve the prediction accuracy and generalisation performance of the machine‐learning‐based methods. Generally, machine learning algorithms require massive data for training purpose. However, measuring data is time‐consuming and costly, especially when the scenario or frequency changes. Therefore, transfer learning methods are introduced to predict path loss with limited data. The proposed methods for path loss prediction are compared to Okumura–Hata and COST‐231 Hata models. The lognormal distribution is the contrast model in delay spread prediction. Based on the data generated by ray‐tracing software, the new methods have a smaller root mean square errors than contrast models.
Design of a wideband terahertz absorber composed of graphene patches
Authors: Karimi Parisa , Maddahali Mohsen , Bakhtafrouz Ahmad , Shahabadi Mahmoud
Published: March 2019

Here, the design of a wideband absorber operating at terahertz frequencies is presented. The design is based on an analytical circuit model of graphene arrays of rectangular patches obtained from the presented circuit model of graphene arrays of disks. A recently proposed method is generalised for the design of wideband absorbers at higher frequencies. The bandwidth is increased by correct tuning of the input impedance for a structure composed of two layers of graphene arrays and a metal‐backed dielectric layer. Using two‐layer graphene arrays, the authors decrease the slope of the imaginary part of the input impedance to increase the bandwidth. The designed absorber works at a frequency of 4THz and has a higher bandwidth of about 30% with respect to the predicted bandwidth by the recently proposed method. The structure is analysed by a transmission‐line formulation method. Consequently, it is demonstrated that the 90% ‐absorption bandwidth can be increased up to 80% of the central frequency.
Research and application of the FETD method for the EM transient response of MTLs excited by HEMP
Authors: Gong Yanfei , Hao Jianhong , Jiang Luhang , Liu Qiang , Zhou Haijing
Published: March 2019

An efficient field‐to‐line coupling model in the time domain is developed combining the second‐order decoupled multiconductor transmission lines (MTLs) equations and the finite‐element time‐domain (FETD) method for evaluating the electromagnetic (EM) transient response of MTLs over a lossy ground excited by a high‐altitude EM pulse (HEMP). First, the incident HEMP electric fields on the lines are calculated as equivalent distributed sources introduced into the MTLs equations. Then, the discrete FETD equations for the lines against the HEMP, in which the effect of frequency‐dependent parameters caused by the ground impedance is considered, are derived using the FETD method with current as the single iteration variable. Finally, the transient currents induced on the lines are obtained by assembling all the discrete FETD equations into the global FETD equation, and the transient induced voltages on the lines are calculated by discretising the coupled equations with respect to current and voltage. The proposed model is successfully compared with the finite‐difference time‐domain method via several examples. It is then employed to analyse the effect of various parameters on the transient currents including the polarisation and the incident angles of the HEMP, the conductivity, and the relative permittivity of the soil.
Diagnostic challenges in dielectric loss assessment and interpretation: a review
Authors: Morsalin Sayidul , Phung Toan Bao , Danikas Michael , Mawad Damia
Published: March 2019

In any sustainable electrical systems, various high‐voltage (HV) power apparatuses such as electrical cable, transformer etc. play a pivotal role to transfer electrical energy from the generation end to the consumer end. The degradation due to electrical stress is very unlikely to avoid in operation. Prominently, the insulation system is mostly expected to be strong enough, and its degradation always provides a constant threat to the reliable operation. Moreover, the continual deterioration can gradually lead to the complete breakdown of HV equipment. To assess the overall dielectric properties, the regular monitoring/diagnosing of electrical insulation has a paramount importance in power systems. One of the potential tools for diagnostic assessment is the tan‐delta (tan δ) measurement. Considering different aspects at various frequencies, this study elucidates a comprehensive review of tan δ measurement. First, a detailed review and explanation of multiple challenges associated with dielectric loss measurement are presented. Various dielectric losses, their contribution to tan δ, measurement techniques and their comparisons are also discussed. This study further reviews the analogy of different physical dipolar theories, modelling and a brief analysis of commercially available measurement instruments.
Resolving the distance controversy for Sharpless 269
Authors: Quiroga-Nuñez L. H. , Immer K. , van Langevelde H. J. , Reid M. J. , Burns R. A.
Published: March 2019

Context. Sharpless 269 (S 269) is one of a few HII regions in the outer spiral arm of the Milky Way with strong water maser emission. Based on data from the Very Long Baseline Interferometry (VLBI) Exploration of Radio Astrometry (VERA) array, two parallax measurements have been published, which differ by nearly 2σ. Each distance estimate supports a different structure for the outer arm. Moreover, given its large Galactocentric radii, S 269 has special relevance as its proper motion and parallax have been used to constrain the Galactic rotation curve at large radii.

Aims. Using recent Very Long Baseline Array (VLBA) observations, we accurately measure the parallax and proper motion of the water masers in S 269. We interpret the position and motion of S 269 in the context of Galactic structure, and possible optical counterparts.

Methods. S 269’s 22 GHz water masers and two close by quasars were observed at 16 epochs between 2015 and 2016 using the VLBA. We calibrated the data by inverse phase referencing using the strongest maser spot. The parallax and proper motion were fitted using the standard protocols of the Bar and Spiral Structure Legacy survey.

Results. We measure an annual parallax for S 269 of 0.241 ± 0.012 mas corresponding to a distance from the Sun of 4.15+0.22−0.20kpc by fitting four maser spots. The mean proper motion for S 269 was estimated as 0.16 ± 0.26 mas yr−1and −0.51 ± 0.26 mas yr−1forμαcosδandμδrespectively, which corresponds to the motion expected for a flat Galactic rotation curve at large radius. This distance estimate, Galactic kinematic simulations and observations of other massive young stars in the outer region support the existence of a kink in the outer arm atl ≈ 140°. Additionally, we find more than 2000 optical sources in the Gaia DR2 catalog within 125 pc radius around the 3D position of the water maser emission; from those only three sources are likely members of the same stellar association that contains the young massive star responsible for the maser emission (S 269 IRS 2w).
Diagnostic potential of the Ca II 8542 Å line for solar filaments
Authors: Díaz Baso C. J. , Martínez González M. J. , Asensio Ramos A. , de la Cruz Rodríguez J.
Published: March 2019

Aims. In this study we explore the diagnostic potential of the chromospheric Ca II line at 8542 Å for studying the magnetic and dynamic properties of solar filaments. We have acquired high spatial resolution spectropolarimetric observations in the Ca II 8542 Å line using the CRISP instrument at the Swedish 1 m Solar Telescope.

Methods. We used the NICOLE inversion code to infer physical properties from observations of a solar filament. We discuss the validity of the results due to the assumption of hydrostatic equilibrium. We have used observations from other telescopes such as CHROTEL and SDO, in order to study large scale dynamics and the long term evolution of the filament.

Results. We show that the Ca II 8542 Å line encodes information of the temperature, line-of-sight velocity and magnetic field vector from the region where the filament is located. The current noise levels only allow us to estimate an upper limit of 260 G for the total magnetic field of the filament. Our study also reveals that if we consider information from the aforementioned spectral line alone, the geometric height, the temperature and the density could be degenerated parameters outside the hydrostatic equilibrium approach.
X-ray analysis of the accreting supermassive black hole in the radio galaxy PKS 2251+11
Authors: Ronchini S. , Tombesi F. , Vagnetti F. , Panessa F. , Bruni G.
Published: March 2019

Context. We have investigated the dichotomy between jetted and non-jetted active galactic nuclei (AGNs), focusing on the fundamental differences of these two classes in the accretion physics onto the central supermassive black hole (SMBH). We tested the validity of the unification model of AGNs through the characterization of the mutual interaction between accreting and outflowing matter in radio galaxies.

Aims. Our aim is to study and constrain the structure, kinematics and physical state of the nuclear environment in the broad line radio galaxy (BLRG) PKS 2251+11. The high X-ray luminosity and the relative proximity make such AGN an ideal candidate for a detailed analysis of the accretion regions in radio galaxies. The investigation will help to shed light on the analogies and differences between the BLRGs and the larger class of radio-quiet Seyfert galaxies and hence on the processes that trigger the launch of a relativistic jet.

Methods. We performed a spectral and timing analysis of a ∼64 ks observation of PKS 2251+11 in the X-ray band with XMM-Newton. We modeled the spectrum considering an absorbed power law superimposed to a reflection component. We performed a time-resolved spectral analysis to search for variability of the X-ray flux and of the individual spectral components.

Results. We find that the power law has a photon index Γ = 1.8 ± 0.1, absorbed by an ionized partial covering medium with a column density NH = (10.1 ± 0.8) × 1023 cm−2, a ionization parameter log ξ = 1.3 ± 0.1 erg s−1 cm and a covering factor f ≃ 90%. Considering a density of the absorber typical of the broad line region (BLR), its distance from the central SMBH is of the order of r ∼ 0.1 pc. An Fe Kα emission line is found at 6.4 keV, whose intensity shows variability on timescales of hours. We derive that the reflecting material is located at a distance r ≳ 600rs, where rs is the Schwarzschild radius.

Conclusions. Concerning the X-ray properties, we found that PKS 2251+11 does not differ significantly from the non-jetted AGNs, confirming the validity of the unified model in describing the inner regions around the central SMBH, but the lack of information regarding the state of the very innermost disk and SMBH spin still leaves unconstrained the origin of the jet.
Effects of ions on the characteristics of monolayer at brine/oil interfaces
Authors: Alotaibi Mohammed B. , Cha Dongkyu , Chand Karam , Yousef Ali A.
Published: March 2019

The advanced waterflooding technologies through salinity and ionic content adjustment can make favorable impacts on rock wettability and oil recovery. In carbonate reservoirs, SmartWater at low ionic strength showed strong chemical interactions with carbonate minerals and oil components. As a result, several hypotheses are proposed in literature as ionic exchange, rock dissolution, surface charges and others. The applied macroscopic and microscopic technologies have certain limitations in identifying the structures at interfaces especially at monolayers. In this paper, advanced Sum Frequency Generation (SFG) spectroscopy is utilized for the first time to characterize the chemical structures of molecules at the brine/oil interfaces. Different brines recipes and model oil are tested to determine the effects of individual and combined ions on the monolayer structures. Stearic acid is also mixed with hydrocarbons to mimic the acidity condition of fluids in the reservoir. The change in the chemical structure is mo nitored with time at a broad wavenumber range from 1,000 to 3,800 cm-1. Distinct spectral signatures of oil components and water ions are detected at different pH conditions. The SFG data is compared with the previous macroscopic wettability results to predict the components that are highly affected during waterflooding and enhanced oil recovery (EOR) processes. This study brings new insights on understanding the chemical structures at the thin monolayers of flat and curved geometric at different aqueous interfaces. The measured spectra, coupled with a wide range of laser polarization settings, and signal intensity trends are discussed in terms of composition, and structure of organic and inorganic components. For example, the intensity for SmartWater at certain wavenumber is three folds higher when compared to high salinity water. This indicates that the interactions at oil/water interfaces are enhanced at lower ionic strengths. In addition, these findings are also confirmed with similar behaviors at a higher salinity brine as connate formation brine. The novelty of this interfacial study can provide better understanding of the reaction mechanisms altering the ionic strength and salinity of injection water and its impact due to the changes in geometric interfaces. Such understanding is also crucial to optimize the chemistry of injection water and its interaction with oil components and carbonate rock, to ultimately alter wettability toward water-wet.
Uniformly accurate time-splitting methods for the semiclassical linear Schrödinger equation
Authors: Chartier Philippe , Le Treust Loïc , Méhats Florian
Published: March 2019

This article is devoted to the construction of numerical methods which remain insensitive to the smallness of the semiclassical parameter for the linear Schrödinger equation in the semiclassical limit. We specifically analyse the convergence behavior of the first-order splitting. Our main result is a proof of uniform accuracy. We illustrate the properties of our methods with simulations.
An Eulerian finite element method for PDEs in time-dependent domains
Authors: Lehrenfeld Christoph , Olshanskii Maxim
Published: March 2019

The paper introduces a new finite element numerical method for the solution of partial differential equations on evolving domains. The approach uses a completely Eulerian description of the domain motion. The physical domain is embedded in a triangulated computational domain and can overlap the time-independent background mesh in an arbitrary way. The numerical method is based on finite difference discretizations of time derivatives and a standard geometrically unfitted finite element method with an additional stabilization term in the spatial domain. The performance and analysis of the method rely on the fundamental extension result in Sobolev spaces for functions defined on bounded domains. This paper includes a complete stability and error analysis, which accounts for discretization errors resulting from finite difference and finite element approximations as well as for geometric errors coming from a possible approximate recovery of the physical domain. Several numerical examples illustrate the theory and demonstrate the practical efficiency of the method.
Stability analysis and best approximation error estimates of discontinuous time-stepping schemes for the Allen–Cahn equation
Authors: Chrysafinos Konstantinos
Published: March 2019

Fully-discrete approximations of the Allen–Cahn equation are considered. In particular, we consider schemes of arbitrary order based on a discontinuous Galerkin (in time) approach combined with standard conforming finite elements (in space). We prove that these schemes are unconditionally stable under minimal regularity assumptions on the given data. We also prove best approximation a-priori error estimates, with constants depending polynomially upon (1/ε) by circumventing Gronwall Lemma arguments. The key feature of our approach is a carefully constructed duality argument, combined with a boot-strap technique.
Path-conservative central-upwind schemes for nonconservative hyperbolic systems
Authors: Castro Díaz Manuel Jesús , Kurganov Alexander , Morales de Luna Tomás
Published: March 2019

We develop path-conservative central-upwind schemes for nonconservative one-dimensional hyperbolic systems of nonlinear partial differential equations. Such systems arise in a variety of applications and the most challenging part of their numerical discretization is a robust treatment of nonconservative product terms. Godunov-type central-upwind schemes were developed as an efficient, highly accurate and robust ``black-box’’ solver for hyperbolic systems of conservation and balance laws. They were successfully applied to a large number of hyperbolic systems including several nonconservative ones. To overcome the difficulties related to the presence of nonconservative product terms, several special techniques were proposed. However, none of these techniques was sufficiently robust and thus the applicability of the original central-upwind schemes was rather limited. In this paper, we rewrite the central-upwind schemes in the form of path-conservative schemes. This helps us (i) to show that the main drawback of the original central-upwind approach was the fact that the jump of the nonconservative product terms across cell interfaces has never been taken into account and (ii) to understand how the nonconservative products should be discretized so that their influence on the numerical solution is accurately taken into account. The resulting path-conservative central-upwind scheme is a new robust tool for both conservative and nonconservative hyperbolic systems. We apply the new scheme to the Saint-Venant system with discontinuous bottom topography and two-layer shallow water system. Our numerical results illustrate the good performance of the new path-conservative central-upwind scheme, its robustness and ability to achieve very high resolution.
A positivity-preserving central-upwind scheme for isentropic two-phase flows through deviated pipes
Authors: Hernandez-Duenas Gerardo , Velasco-García Ulises , Velasco-Hernández Jorge X.
Published: March 2019

Directional drilling in oil and gas extraction can encounter difficulties such as accumulation of solids in deviated pipes. Motivated by such phenomenon, we consider a model for isentropic two-phase flows through deviated pipes. The system of partial differential equations is aimed at simulating the dynamics between a particle bed and a gas phase. The pipe can be either horizontal or vertically deviated where the effects of gravity are incorporated. Furthermore, the acceleration or deceleration due to friction between phases is investigated and spectral properties of the hyperbolic system of balance laws are described. The existence and characterization of steady states under appropriate conditions is analyzed. A new type of steady states arises when a balance between gas and solid phases results in a non-uniform solid particle bed and vanishing solid velocity. This state corresponds to an accumulation of sedimented solids. A central-upwind scheme that preserves the positivity of the gas and solid densities and volume fractions is presented. Including an application of the model to an analysis of accumulation of solids, a variety of numerical tests is presented to show the merits of the scheme.
Analysis of electromagnetic scattering from plasmonic inclusions beyond the quasi-static approximation and applications
Authors: Li Hongjie , Li Shanqiang , Liu Hongyu , Wang Xianchao
Published: March 2019

This paper is concerned with the analysis of time-harmonic electromagnetic scattering from plasmonic inclusions in the finite frequency regime beyond the quasi-static approximation. The electric permittivity and magnetic permeability in the inclusions are allowed to be negative-valued. Using layer potential techniques for the full Maxwell system, the scattering problem is reformulated into a system of integral equations. We derive the complete eigensystem of the involved matrix-valued integral operator within spherical geometry. As applications, we construct two types of plasmonic structures such that one can induce surface plasmon resonances within finite frequencies and the other one can produce invisibility cloaking. It is particularly noted that the cloaking effect is a newly found phenomenon and is of different nature from those existing ones for plasmonic structures in the literature. The surface plasmon resonance result may find applications in electromagnetic imaging.
Algebraic flux correction schemes preserving the eigenvalue range of symmetric tensor fields
Authors: Lohmann Christoph
Published: March 2019

This work extends the algebraic flux correction (AFC) paradigm to finite element discretizations of conservation laws for symmetric tensor fields. The proposed algorithms are designed to enforce discrete maximum principles and preserve the eigenvalue range of evolving tensors. To that end, a continuous Galerkin approximation is modified by adding a linear artificial diffusion operator and a nonlinear antidiffusive correction. The latter is decomposed into edge-based fluxes and constrained to prevent violations of local bounds for the minimal and maximal eigenvalues. In contrast to the flux-corrected transport (FCT) algorithm developed previously by the author and existing slope limiting techniques for stress tensors, the admissible eigenvalue range is defined implicitly and the limited antidiffusive terms are incorporated into the residual of the nonlinear system. In addition to scalar limiters that use a common correction factor for all components of a tensor-valued antidiffusive flux, tensor limiters are designed using spectral decompositions. The new limiter functions are analyzed using tensorial extensions of the existing AFC theory for scalar convection-diffusion equations. The proposed methodology is backed by rigorous proofs of eigenvalue range preservation and Lipschitz continuity. Convergence of pseudo time-stepping methods to stationary solutions is demonstrated in numerical studies.
Analysis of a hybridizable discontinuous Galerkin method for the Maxwell operator
Authors: Chen Gang , Cui Jintao , Xu Liwei
Published: March 2019

In this paper, we study a hybridizable discontinuous Galerkin (HDG) method for the Maxwell operator. The only global unknowns are defined on the inter-element boundaries, and the numerical solutions are obtained by using discontinuous polynomial approximations. The error analysis is based on a mixed curl-curl formulation for the Maxwell equations. Theoretical results are obtained under a more general regularity requirement. In particular for the low regularity case, special treatment is applied to approximate data on the boundary. The HDG method is shown to be stable and convergence in an optimal order for both high and low regularity cases. Numerical experiments with both smooth and singular analytical solutions are performed to verify the theoretical results.
Analysis of the error in an iterative algorithm for asymptotic regulation of linear distributed parameter control systems
Authors: Aulisa Eugenio , Gilliam David S. , Pathiranage Thanuka W.
Published: March 2019

Applications of regulator theory are ubiquitous in control theory, encompassing almost all areas of systems and control engineering. Examples include active noise suppression [Banks et al., Decision and Control, Active Noise Control: Piezoceramic Actuators in Fluid/structure Interaction Models, IEEE, Los Alamitos, CA (1991) 2328–2333], design and control of energy efficient buildings [Borggaard et al., Control, Estimation and Optimization of Energy Efficient Buildings. Riverfront, St. Louis, MO (2009) 837–841.] and control of heat exchangers [Aulisa et al., IFAC-PapersOnLine 49 (2016) 104–109.]. Numerous other examples can be found in [Aulisa and Gilliam, A Practical Guide to Geometric Regulation for Distributed Parameter Systems. Chapman and Hall/CRC, Boca Raton (2015).]. In the geometric approach to asymptotic regulation the main object of interest is a pair of operator equations called the regulator equations, whose solution provides a control solving the tracking/disturbance rejection regulation problem. In this paper we present an iterative algorithm, called the β-iteration method, which is based on the geometric methodology, and delivers accurate control laws for approximate asymptotic regulation. This iterative scheme has been successfully applied to a wide range of linear and nonlinear multi-physics examples and in practice only one or two iterations are usually required to deliver sufficiently accurate results. One drawback to these research efforts is that no proof was given of the convergence of the method. This work contains a detailed analysis of the error in the iterative scheme for a large class of linear distributed parameter systems. In particular we show that the iterative errors converge at a geometric rate. We demonstrate our estimates on three control problems in multi-physics applications.
Finite element method with local damage of the mesh
Authors: Duprez Michel , Lleras Vanessa , Lozinski Alexei
Published: March 2019

We consider the finite element method on locally damaged meshes allowing for some distorted cells which are isolated from one another. In the case of the Poisson equation and piecewise linear Lagrange finite elements, we show that the usual a priori error estimates remain valid on such meshes. We also propose an alternative finite element scheme which is optimally convergent and, moreover, well conditioned, i.e. the conditioning number of the associated finite element matrix is of the same order as that of a standard finite element method on a regular mesh of comparable size.
Damage-driven fracture with low-order potentials: asymptotic behavior, existence and applications
Authors: Caroccia Marco , Van Goethem Nicolas
Published: March 2019

We study the Γ-convergence of damage to fracture energy functionals in the presence of low-order nonlinear potentials that allows us to model physical phenomena such as fluid-driven fracturing, plastic slip, and the satisfaction of kinematical constraints such as crack non-interpenetration. Existence results are also addressed.
Numerical approximation of stochastic time-fractional diffusion
Authors: Jin Bangti , Yan Yubin , Zhou Zhi
Published: March 2019

We develop and analyze a numerical method for stochastic time-fractional diffusion driven by additive fractionally integrated Gaussian noise. The model involves two nonlocal terms in time,i.e.,a Caputo fractional derivative of orderα ∈ (0,1), and fractionally integrated Gaussian noise (with a Riemann-Liouville fractional integral of orderγ ∈ [0,1] in the front). The numerical scheme approximates the model in space by the standard Galerkin method with continuous piecewise linear finite elements and in time by the classical Grünwald-Letnikov method (for both Caputo fractional derivative and Riemann-Liouville fractional integral), and the noise by theL2-projection. Sharp strong and weak convergence rates are established, using suitable nonsmooth data error estimates for the discrete solution operators for the deterministic inhomogeneous problem. One- and two-dimensional numerical results are presented to support the theoretical findings.
Error analysis of PML-FEM approximations for the Helmholtz equation in waveguides
Authors: Kim Seungil
Published: March 2019

In this paper, we study finite element approximate solutions to the Helmholtz equation in waveguides by using a perfectly matched layer (PML). The PML is defined in terms of a piecewise linear coordinate stretching function with two parameters for absorbing propagating and evanescent components respectively, and truncated with a Neumann condition on an artificial boundary rather than a Dirichlet condition for cutoff modes that waveguides may allow. In the finite element analysis for the PML problem, we have to deal with two difficulties arising from the lack of full regularity of PML solutions and the anisotropic nature of the PML problem with, in particular, large PML damping parameters. Anisotropic finite element meshes in the PML regions depending on the damping parameters are used to handle anisotropy of the PML problem. As a main goal, we establish quasi-optimal a priori error estimates, that does not depend on anisotropy of the PML problem (when no cutoff mode is involved), including the exponentially convergent PML error with respect to the width and the strength of PML. The numerical experiments that confirm the convergence analysis will be presented.
Les facteurs influençant le rendement oléicole : cas de la région de Jijel du Nord-Est algérien
Authors: Lachibi Moussa , Chehat Fouèd , Belhouadjeb Fathi Abdellatif
Published: March 2019

La région de Jijel, dans le Nord-Est algérien, possède un important potentiel naturel oléicole favorisant une activité économique importante autour de ce produit, notamment dans le milieu rural. Néanmoins, la production des exploitations de la région demeure faible et instable dans le temps, malgré les efforts de plantations entrepris depuis 2001. La recherche des causes de cette faiblesse nous a conduits à repérer les principaux facteurs spécifiques ayant un impact significatif sur les rendements. À cet effet, quatre facteurs ont été identifiés comme ayant des effets significatifs sur les rendements des exploitations oléicoles locales : deux s’avèrent liés à la variété et les deux autres à l’environnement. Les facteurs intrinsèques sont l’origine de la variété (locales et hors région) et l’âge des plants. Les deux autres facteurs extrinsèques (liés à l’environnement) sont l’altitude et la pente des terrains ; les exploitations se situant à des altitudes supérieures à 600 mètres, avec des pentes modérées enregistraient des rendements plus importants. Cette étude nous a permis de connaître les exigences agro-écologiques et les principaux facteurs spécifiques à prendre en considération pour une bonne affectation de la ressource oléicole au niveau local.
A heuristic for the minimum cost chromatic partition problem
Authors: Ribeiro Celso C. , dos Santos Philippe L. F.
Published: March 2019

The graph coloring problem consists in coloring the vertices of a graphG=(V, E)with a minimum number of colors, such as that any two adjacent vertices receive different colors. The minimum cost chromatic partition problem (MCCPP) is an extension of the graph coloring problem in which there are costs associated with the colors and one seeks a vertex coloring minimizing the sum of the costs of the colors used in each vertex. The problem finds applications in VLSI design and in some scheduling problems modeled on interval graphs. We propose a trajectory search heuristic using local search, path-relinking, and perturbations for solving MCCPP and discuss computational results.
Decision policies on players’ different risk combination under supplier encroachment
Authors: Chen Ping , Li Bo , Huang Huafei
Published: March 2019

Literature concerning about the supply chain management problem is usually based on perfect rationality. However, risk preferences have been proved to be an important role which influences managers’ decisions significantly. This paper investigates a risk combination problem under supplier encroachment with different risk preferences players. Assuming that the supply chain players may be risk-averse, risk-neutral and risk-taking, we build a Stackelberg game model to explore the optimal decisions and the impact of different risk combinations, respectively. We focus on two scenarios: the consumers perceive uniform quality between the two channels and perceive differentiated quality between the two channels. We find that the retailer always prefers a risk-averse supplier, while the supplier always prefers a risk-taking retailer. But the combination of a risk-averse supplier and a risk-taking retailer is not always beneficial to the whole supply chain. Further, we conduct numerical experiments to explore the risk combinations and the impacts of players’ selfish, aggressive and altruistic behaviors on optimal decisions.
Current Methods for the Discovery of New Active Ingredients from Natural Products for Cosmeceutical Applications
Authors: Espinosa-Leal Claudia , Garcia-Lara Silverio
Published: March 2019

Cosmeceuticals are designed to serve a dual purpose: to provide desired esthetical effects and to treat dermatological conditions. Natural products derived from plants and marine organisms are a novel source of potential cosmeceutical active ingredients for incorporation into new formulations due to consumer demands. Contrary to common perceptions, most regulatory agencies do not view cosmeceuticals as being a separate category from cosmetics; thus, these products are not regulated accordingly, thereby forcing the consumer to rely on the self-regulatory policies of the cosmetics industry. Cosmeceuticals are advertised as having capabilities that include anti-aging, anti-acne, solar-protective, wound healing, and skin whitening. Such traits normally comprise several biological activities. In order to ensure the safety and efficacy of these products, active ingredients employed in the formulations must undergo a series of tests. In this review, in vitro (enzymatic and cellular) and in vivo tests employed to evaluate the potential of new cosmeceutical active ingredients are discussed, and new trends that are being explored by the cosmeceutical industry are described.
Imaging of Total Ankle Arthroplasty: Normal Imaging Findings and Hardware Complications
Authors: Omar Imran , Abboud Samir , Youngner Jonathan
Published: March 2019

End-stage ankle osteoarthritis often significantly impacts patients' quality of life. This can be managed surgically either by ankle arthrodesis or total ankle arthroplasty (TAA). Although ankle arthrodesis is considered by some as the standard-of-care surgical option for this condition, it restricts range of motion and may lead to accelerated osteoarthritis of neighboring joints. Better understanding of ankle biomechanics, the biological effects of orthopaedic devices, and new surgical techniques have led to significant improvements in the designs of TAAs, and over the last several decades TAA has been used increasingly to treat patients with end-stage tibiotalar osteoarthritis. However, complication and ultimate failure rates remain greater than those seen with total knee and hip arthroplasty, and imaging is often critical in determining whether a prosthesis is beginning to fail. As a result, imagers should be familiar with the basic types of TAAs in clinical use, the normal radiographic appearances, as well as the common complications seen with this procedure.