bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact analysis of time‐varying voltage‐dependent load models on hybrid DG planning in a radial distribution system using analytical approach
Authors: M.L. Merlin Sajini , S. Suja , S. Merlin Gilbert Raj
Published: January 2021

This paper investigates the impact of time‐varying voltage‐dependent load models on hybrid distributed generation planning studies. Firstly, a multi‐objective index is constructed with indices namely real and reactive power loss index, voltage deviation index, and mega‐volt‐ampere capacity index with an objective of reduction of real and reactive power loss, voltage profile improvement, and decreased line loading. The multi‐objective index derived is minimised to locate the distributed generation. Secondly, the analytical expression is obtained to size the distributed generation units with the time‐varying voltage‐dependent load models and probabilistic nature of solar and wind generation. Finally, the impact of load models with the generation effects is separately analysed for PV/wind (hybrid) distributed generation planning. The proposed perspective was validated on the IEEE 33‐bus, IEEE 69‐bus radial distribution network, and a real 16‐bus distribution substation for its effectiveness because the distributed generators are placed in the distribution side of an electrical network. The outcomes reveal that the distributed generation allocation for time‐varying voltage‐dependent load model and probabilistic nature of solar and wind has significant impacts on the distribution system by reducing real and reactive power loss, improving voltage deviation and reduced mega‐volt‐ampere intake.
Effects of motor–generator pair system on improving inertial response and primary frequency regulation capability of renewable energy
Authors: Gu Yujun , Huang Yongzhang , Li Chenyang , Guan Fei , Fu Wenqi , Zhan Yang , Zhao Haisen
Published: January 2021

The increasing penetration of renewable energy leads to the decrease of inertia and damping for replacing conventional power plants. The motor–generator pair (MGP) is proposed to improve inertial response and frequency regulation capability for the renewable energy. First, the mathematical model of the MGP and the control method of DC‐link voltage are given. Then, the inertial characteristics of the MGP are analysed, and a mass block is designed by analysing the key factor affecting the moment of inertia. The transient processes in two machines are discussed by comparing the variations of the voltage and current vectors. It turns out that the electromagnetic–mechanical coupling is the key to realise the primary frequency regulation without frequency acquisition. The photovoltaic (PV) is chosen to illustrate the mechanism of achieving a better primary frequency response with DC‐link voltage control methods based on the de‐loading and additional frequency deviation strategies. A grid‐scale simulation model is built to verify the effectiveness of the proposed scheme. Furthermore, six groups of experiments are designed and performed on an experimental bench. The simulation and experimental results demonstrate that the inertial response and primary frequency response of PV can be improved effectively by adopting MGP for grid connection.
Contingency‐constrained operation optimization of microgrid with wind and solar generations: A decision‐driven stochastic adaptive‐robust approach
Authors: Ebrahimi Mohammad Reza , Amjady Nima
Published: January 2021

This paper presents a decision‐driven stochastic adaptive‐robust microgrid operation optimization model considering the uncertainties of wind and solar generations, electricity price, and demand as well as the availability uncertainties of microgrid's components. Unlike previous works, this paper utilizes stochastic adaptive‐robust optimization approach to model both continuous and binary uncertainties simultaneously. To do so, adaptive‐robust optimization is used to model the continuous uncertainties, while the binary uncertainties are modelled by means of stochastic programming. An operating dispatchable unit usually exhibits a higher forced outage rate than a de‐committed one. Hence, due to the effect of the optimization decisions on the availability uncertainties, this research work proposes an intrinsic scenario production technique to model these binary uncertainties. In addition, a tri‐level decomposition method is introduced to solve the proposed microgrid operation optimization problem. In this decomposition method, the worst‐case realization of continuous uncertain parameters and unit commitment decisions are determined at each iteration considering the produced scenarios in the previous iteration. Case studies on the IEEE 69‐bus test system exhibit the effectiveness of the proposed decision‐driven stochastic adaptive‐robust model and the proposed solution method.
A state of charge‐based linearised frequency–voltage droop for interlinking converters in an isolated hybrid microgrid
Authors: Malik Sarmad Majeed , Sun Yingyun
Published: January 2021

A battery‐dominated hybrid microgrid architecture where various battery modules are linked to the ac bus via converters is presented. A novel frequency–voltage droop scheme is proposed for the interlinking converter connecting the dc and ac grids. The ac grid frequency and dc grid voltage are linked together in outer controller loop through two factors, the ratio of which defines the frequency–voltage droop. This enables autonomous bidirectional power flow and regulation where each grid is supporting the other grid through its surplus power. A state of charge (SOC)‐based control scheme is also proposed for the battery units linked to ac bus which ensures power sharing based on the SOC of individual storage units. The system small‐signal model is developed and a stable range of operation is defined. The impact of number of battery units and SOC of an individual battery on the system performance is also analysed. In addition, the proposed strategy is compared with normalised SOC‐based control to evaluate its feasibility. Simulations in PSCAD/EMTDC show that the proposed SOC‐based scheme helps maintain charge balance while regulating the voltage and frequency and ensuring power flow among battery units and grids.
A full sequence impedance modelling and stability analysis of the virtual synchronous generator with inner loops
Authors: Peng Yang , Wang Yue , Liu Yonghui , Yu Peng , Shu Sirui , Lei Wanjun
Published: January 2021

Virtual synchronous generator (VSG) has been widely studied owing to its inertia support to the grid. However, the stability of VSG is not analysed accurately for actual applications in previous studies that overlook voltage and current inner loops of VSG. Since inner loops are essential to control output voltage and current accurately in practical engineering, this study focuses on stability analysis of the interconnection system of VSG and the grid by sequence impedance modelling of VSG with inner loops. The complete sequence impedance model for VSG with inner loops is built and compared with that of the VSG‐ignoring inner loops, and then the stability is analysed based on that. It shows that inner loops bring the risk of instability and oscillation for VSG, which was not predicted in previous studies. Then, the influence of each parameter of inner loops on the impedance and oscillation is analysed, showing that the oscillation can hardly be eliminated by tuning the parameters of inner loops. Therefore, corresponding virtual resistor with proper value is studied and adopted in VSG with inner loops to avoid oscillation. Finally, the correctness of theoretical analysis and the effectiveness of the adopted virtual resistance are verified by the hardware‐in‐the‐loop experiments.
Islanding detection in distributed energy resources based on gradient boosting algorithm
Authors: Azizi Resul , Noroozian Reza
Published: January 2021

This paper proposes a novel passive‐based intelligent method for anti‐islanding. Passive methods generally suffer from the improper tuning of threshold values for measured variables and false detection when the active or reactive power mismatch is small. Conversely, intelligence‐based methods highly depend on the choice of an appropriate model, the universality of data and selected features. In addition, the risk of overfitting and underfitting for a single model due to an improper selected feature or insufficient data is always possible. This condition makes a single classification model unreliable for practical purposes. The method used in this work is a sequential ensemble of intelligence‐based models called gradient boosting. The sequential form of an ensemble is substantially designed to solve the underfitting problem. In addition, by selecting the best combination of features and ensembles, algorithm overfitting can be prevented and the attribute data space can be constructed with maximum discrimination. Furthermore, this condition yields a model with a zero non‐detection zone. As a result, a multi‐objective optimisation method called the non‐dominated sorting genetic algorithm‐III is used to tune the model. The reliability and economy of this method for distribution networks with various types of inverter‐based and synchronous distributed energy resources are demonstrated.
Reference voltage vector based model predictive control for semicontrolled open‐winding flux‐switching permanent magnet generator system with a novel zero‐sequence current suppression strategy
Authors: Zhao Shuangshuang , Yu Feng , Liu Xing , Hua Wei
Published: January 2021

This paper studies a reference voltage vector (RVV) based model predictive control (MPC) for semicontrolled open‐winding flux‐switching permanent magnet generator (SOW‐FSPMG). Common dc bus is adopted in this configuration, thereby leading to zero‐sequence current (ZSC). The first concern of this work is put into proposing a novel ZSC suppression strategy, which is on the basis of the redundant vector pre‐selection. Secondly, a deadbeat flux control (DBFC) is adopted to calculate the RVV. Then, only 4, 3 or 2 vectors adjacent to the RVV are of interest during each sampling period, thereby decreasing the computation burden; meanwhile, a simplified cost function that evaluates the error between the RVV and the prediction voltage vectors is defined. Thirdly, the side effect of dead‐time inherent to voltage source converter (VSC) on the system's steady‐state performance is analysed and discussed. In order to properly leverage the dead‐time, a solution to regulate duty‐cycles of the dead‐time voltage vector and the selected one is studied, by which means, steady‐state performance of the system can be highly improved. Finally, experimental results are presented to verify the correctness and effectiveness of the proposed method.
Feasibility study of a renewable system (PV/HKT/GB) for hybrid tramway based on fuel cell and super capacitor
Authors: Arévalo Paul , Cano Antonio , Benavides Javier , Jurado Francisco
Published: January 2021

The configuration, modelling and control of several possible hybrid systems for the propulsion of the existing tramway in Cuenca‐Ecuador are analysed. The system consists of novel renewable sources: Photovoltaic energy, hydrokinetic turbines and a biomass gasifier, which increases the reliability of the system and reduces CO2 emissions. In addition, a proton exchange fuel cell and a super capacitor thatsupply the necessary power for the tramway, as well as, a hydrogen tank that stores the excess energy. Energy management is done through renewable sources that recharge the super capacitor and the fuel cell at the charging stations along the tramway route. Different renewable hybrid systems have been analysed, which indicates that the most favourable case from a technical, environmental and economic point of view using data analysis and machine learning techniques is S4. Sensitivity analyses allow the study of variables such as CO2, net present cost and COE for different demand variations, as well as, for the minimum state of charge in the super capacitor. The results indicate the optimal net present cost is M$ 1.46 and 0.12 $ kWh−1 in cost of energy, validity of the proposed system in the round trip of the tramway.
Artificial ecosystem‐based optimiser to electrically characterise PV generating systems under various operating conditions reinforced by experimental validations
Authors: Elkholy Mahmoud M. , El‐Hameed Mohamed A. , El‐Fergany Attia A.
Published: January 2021

Efficient modelling of photovoltaic (PV) generating units' characteristics to investigate their steady‐state and dynamic impacts on the performances of power systems and electric drives is essential. The current work aims at developing an effective tool based on artificial ecosystem optimiser (AEO) to define (optimally) the uncertain parameters of PV generating units. The root mean squared deviations (RMSDs) along with the predefined inequality constraints formulate the optimization problem to be solved by the AEO. Initially, two test cases with different PV technologies are demonstrated complete with their relevant discussions and necessary validations. At a later stage, real measurements (followed the procedures of IEC 60904) of a commercial PV module namely Ultra 85‐P of Shell PowerMax are made for further experimental validations of the AEO results. Various operating temperatures and sun irradiance levels are investigated among the simulated scenarios. The statistical validations along with predefined indices plus comparisons to other competing methods appraise the results obtained by the AEO. It can be confirmed that the AEO is able to produce best values of unidentified parameters of the PV units with different solar technologies under study with lesser values of RMSDs among other optimisers.
Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices
Authors: Basalgète R. , Dupuy R. , Féraud G. , Romanzin C. , Philippe L. , Michaut X. , Michoud J. , Amiaud L. , Lafosse A. , Fillion J.-H. , Bertin M.
Published: January 2021

Context.Astrophysical observations show complex organic molecules (COMs) in the gas phase of protoplanetary disks. X-rays emitted from the central young stellar object that irradiate interstellar ices in the disk, followed by the ejection of molecules in the gas phase, are a possible route to explain the abundances observed in the cold regions. This process, known as X-ray photodesorption, needs to be quantified for methanol-containing ices. This Paper I focuses on the case of X-ray photodesorption from pure methanol ices.

Aims.We aim at experimentally measuring X-ray photodesorption yields (in molecule desorbed per incident photon, displayed as molecule/photon for more simplicity) of methanol and its photo-products from pure CH3OH ices, and to shed light on the mechanisms responsible for the desorption process.

Methods.We irradiated methanol ices at 15 K with X-rays in the 525–570 eV range from the SEXTANTS beam line of the SOLEIL synchrotron facility. The release of species in the gas phase was monitored by quadrupole mass spectrometry, and photodesorption yields were derived.

Results.Under our experimental conditions, the CH3OH X-ray photodesorption yield from pure methanol ice is ~10−2molecule/photon at 564 eV. Photo-products such as CH4, H2CO, H2O, CO2, and CO also desorb at increasing efficiency. X-ray photodesorption of larger COMs, which can be attributed to either ethanol, dimethyl ether, and/or formic acid, is also detected. The physical mechanisms at play are discussed and must likely involve the thermalization of Auger electrons in the ice, thus indicating that its composition plays an important role. Finally, we provide desorption yields applicable to protoplanetary disk environments for astrochemical models.

Conclusions.The X-rays are shown to be a potential candidate to explain gas-phase abundances of methanol in disks. However, more relevant desorption yields derived from experiments on mixed ices are mandatory to properly support the role played by X-rays in nonthermal desorption of methanol (see Paper II).
Use of program and target planning for increase in level of traffic safety
Authors: Korchagin Viktor , Pogodaev Anatoly , Ljapin Sergej , Konovalova Viktorija
Published: January 2021

In work it is offered to minimize damage from the happened road accidents due to application of program and target planning for all socially-naturally-economic transport system, the providing merging of the services and organizations participating in mitigation of consequences of road accident in a subsystem of mitigation of consequences of road accident and increase in effective management of this subsystem due to rationalization of the offered “tree of the purposes”.
Endothelial β1 Integrin-Mediated Adaptation to Myocardial Ischemia
Authors: Henning Carina , Branopolski Anna , Follert Paula , Lewandowska Oksana , Ayhan Aysel , Benkhoff Marcel , Flögel Ulrich , Kelm Malte , Heiss Christian , Lammert Eckhard
Published: January 2021

Background Short episodes of myocardial ischemia can protect from myocardial infarction. However, the role of endothelial β1 integrin in these cardioprotective ischemic events is largely unknown.

Objective In this study we investigated whether endothelial β1 integrin is required for cardiac adaptation to ischemia and protection from myocardial infarction.

Methods Here we introduced transient and permanent left anterior descending artery (LAD) occlusions in mice. We inhibited β1 integrin by intravenous injection of function-blocking antibodies and tamoxifen-induced endothelial cell (EC)-specific deletion of Itgb1. Furthermore, human ITGB1 was silenced in primary human coronary artery ECs using small interfering RNA. We analyzed the numbers of proliferating ECs and arterioles by immunohistochemistry, determined infarct size by magnetic resonance imaging (MRI) and triphenyl tetrazolium chloride staining, and analyzed cardiac function by MRI and echocardiography.

Results Transient LAD occlusions were found to increase EC proliferation and arteriole formation in the entire myocardium. These effects required β1 integrin on ECs, except for arteriole formation in the ischemic part of the myocardium. Furthermore, this integrin subunit was also relevant for basal and mechanically induced proliferation of human coronary artery ECs. Notably, β1 integrin was needed for cardioprotection induced by transient LAD occlusions, and the absence of endothelial β1 integrin resulted in impaired growth of blood vessels into the infarcted myocardium and reduced cardiac function after permanent LAD occlusion.

Conclusion We showed that endothelial β1 integrin is required for adaptation of the heart to cardiac ischemia and protection from myocardial infarction.
Asymptotic properties of solutions for impulsive neutral stochastic functional integro-differential equations
Authors: Huang Hai , Fu Xianlong
Published: January 2021

In this work, we are concerned with the asymptotic properties of solutions for an impulsive neutral stochastic functional integro-differential equation. By applying the theory of resolvent operators, the Banach fixed point principle theorem, and results on stochastic analysis, we study respectively the existence, uniqueness, and global attracting and quasi-invariant sets of mild solutions for the considered equation. We also derive some sufficient conditions of pth moment exponential stability and almost surely exponential stability of the mild solutions. An example is provided in the end to illustrate the applications of the obtained results.
Interpreting Kelvin probe force microscopy on semiconductors by Fourier analysis
Authors: Xu Jie , Chen Deyuan
Published: January 2021

Kelvin probe force microscopy (KPFM) has become a popular surface scanning tool for functional materials and devices, and it has been widely interpreted by the contact potential difference (CPD) theory as the precedent Kelvin probe method. In this article, we developed a Fourier analysis framework for KPFM on the basis that the probe in KPFM is excited by a sinusoidal ac voltage, which is different from the classical Kelvin method. As a result, it was found that the KPFM signal will deviate from the CPD value if the sample charge quantity is not an odd function of the external bias, i.e., the CPD interpretation is invalid on those samples such as doped semiconductors. In order to further estimate the signal deviation from the CPD in the KPFM measurement on semiconductors, the tip–sample system was simulated as a one-dimensional metal–insulator–semiconductor capacitor using Fermi–Dirac statistics. The simulation results showed that the KPFM signals on doped semiconductors behave like those on an intrinsic one when the ac voltage is large, and therefore, the KPFM signal contrast on a pn junction could be flattened even if the sample surface has a clear CPD contrast without any Fermi level pinning due to surface states. Finally, possible ways for tuning KPFM operation parameters to suppress the signal deviation effect were also discussed.
Current reflux from an electron beam transmitted in a plasma ion channel
Authors: Xia Yuxi , Yang Shengpeng , Chen Shaoyong , Tang Changjian
Published: January 2021

In this paper, the mechanism by which current reflux forms from a plasma-focused electron beam is studied theoretically and numerically by considering nonlinear interactions between the beam and plasma. We demonstrate that a moving virtual cathode can be generated at the end of a plasma ion channel due to the influence of the boundary plasma electrons on the beam, and that this accounts for reflux formation. In addition, the reflux formation condition is derived and analyzed via the beam envelope and space-charge-limited current theories. The results indicate that the virtual cathode tends to form at defocusing positions of the beam. Particle-in-cell simulations are used to verify the theoretical results and to show that the beam divergence and energy spread increase during current reflux formation.
Using quantum annealers to calculate ground state properties of molecules
Authors: Copenhaver Justin , Wasserman Adam , Wehefritz-Kaufmann Birgit
Published: January 2021

Quantum annealers are an alternative approach to quantum computing, which make use of the adiabatic theorem to efficiently find the ground state of a physically realizable Hamiltonian. Such devices are currently commercially available and have been successfully applied to several combinatorial and discrete optimization problems. However, the application of quantum annealers to problems in chemistry remains a relatively sparse area of research due to the difficulty in mapping molecular systems to the Ising model Hamiltonian. In this paper, we review two different methods for finding the ground state of molecular Hamiltonians using Ising model-based quantum annealers. In addition, we compare the relative effectiveness of each method by calculating the binding energies, bond lengths, and bond angles of the H3+ and H2O molecules and mapping their potential energy curves. We also assess the resource requirements of each method by determining the number of qubits and computation time required to simulate each molecule using various parameter values. While each of these methods is capable of accurately predicting the ground state properties of small molecules, we find that they are still outperformed by modern classical algorithms and that the scaling of the resource requirements remains a challenge.
Excited states in variational Monte Carlo using a penalty method
Authors: Pathak Shivesh , Busemeyer Brian , Rodrigues João N. B. , Wagner Lucas K.
Published: January 2021

In this article, the authors present a technique using variational Monte Carlo to solve for excited states of electronic systems. This technique is based on enforcing orthogonality to lower energy states, which results in a simple variational principle for the excited states. Energy optimization is then used to solve for the excited states. This technique is applied to the well-characterized benzene molecule, in which ∼10 000 parameters are optimized for the first 12 excited states. Agreement within ∼0.2 eV is obtained with higher scaling coupled cluster methods; small disagreements with experiment are likely due to vibrational effects.
Semiconductor nanocrystal photocatalysis for the production of solar fuels
Authors: Burke Rebeckah , Bren Kara L. , Krauss Todd D.
Published: January 2021

Colloidal semiconducting nanocrystals (NCs) are powerful elements of a photocatalytic system useful for enabling a variety of chemical transformations owing to their strong light-absorbing properties and high degree of size-, shape-, and composition-tunability. Key to their utility is our understanding of the photoinduced charge transfer processes required for these photochemical transformations. This Perspective will focus on the implementation of semiconductor NCs for photochemical fuel formation. Three general system designs for photocatalytic proton reduction using semiconductor NCs will be reviewed: metal–semiconductor heterostructures, NC photosensitizers with molecular catalysts, and hydrogenase-based systems. Other relevant reactions toward solar fuel targets, such as CO2 and N2 reductions with NCs, will also be highlighted. Illustrating the versatile roles that NCs can play in light-driven chemical reactions, advances made toward NC-catalyzed organic transformations will be discussed. Finally, we will share a few concluding thoughts and perspectives on the future of the field, with a focus on goals toward improving and implementing NC-based technologies for solar fuel development.
Efficient mm-wave photomodulation via coupled Fabry–Perot cavities
Authors: Barr L. E. , Hooper I. R. , Hornett S. M. , Lawrence C. R. , Hendry E.
Published: January 2021

An efficient mm-wave photomodulator is designed based on coupled Fabry–Perot modes in a low-lifetime silicon wafer and an adjacent cavity formed from a transparent reflector, such as indium tin oxide. The modulation of a reflected beam using this coupled-cavity design is increased by a factor of 7 compared with that from an isolated silicon wafer, while also introducing a degree of tunability and maintaining low angular dispersion. For the particular design built and tested, a modulation of 32% is achieved for an extremely low optical illumination of just 0.006W/cm2 and with a maximum operation rate of more than 3 kHz. The large increase in modulation, coupled with the flexibility of the design and the fact that all components can be industrially manufactured, makes this photomodulator a promising candidate for many communication, imaging, and sensing applications.
A PEGDA hydrogel nanocomposite to improve gold nanoparticles stability for novel plasmonic sensing platforms
Authors: Miranda B. , Moretta R. , De Martino S. , Dardano P. , Rea I. , Forestiere C. , De Stefano L.
Published: January 2021

A 3D plasmonic sensing platform that combines the properties of citrate gold nanoparticles (AuNPs) and poly-(ethylene glycol) diacrylate (PEGDA) hydrogels is proposed as a nanocomposite hybrid material for biosensing applications, whose optical properties and sensitivity can be tuned by varying the particle mean diameter as also predicted by the Mie theory. It is found that AuNPs embedded in the hydrogel network are more stable when compared to the colloidal aqueous solutions. PEGDA hydrogel physically retains the gold nanoparticles even after a full swelling process during immersion in liquids. Such a property is confirmed by exposing the AuNPs-containing PEGDA hydrogels to organic solvents and buffers that would usually cause the aggregation of the nanoparticles in solution. Moreover, biotin, as a small molecule model, has been captured, and optically detected with a transmission mode customized setup, by a cysteamine modified AuNPs-containing PEGDA hydrogel layer to achieve a biorecognition hybrid device.
Meshfree method based on discrete gas-kinetic scheme to simulate incompressible/compressible flows
Authors: Zhan Ningyu , Chen Rongqian , You Yancheng
Published: January 2021

A meshfree method based on the discrete gas-kinetic scheme (DGKS) (called the meshfree-DGKS) for simulation of incompressible/compressible flows is proposed in this work. In this approach, the governing equations are discretized using the meshfree method based on the least squares-based finite difference approach. To simulate compressible problems with discontinuities, the virtual mid-points between adjacent nodes, which are regarded as Riemann discontinuities, are established. Then, the concept of numerical flux is introduced, which enables computing both compressible and incompressible problems. The fluxes at the mid-points are calculated using the DGKS based on the discrete particle velocity model. The corresponding particle velocity components and distribution functions are integrated based on moment relations to obtain the flux. The meshfree-DGKS maintains the advantages of the meshless method as it is implemented at arbitrarily distributed nodes. This breaks through the limitations of the grid topology and is suitable to handle complex geometries. More importantly, the fluxes at the mid-point are reconstructed with the DGKS using the local solution of the Boltzmann equation, which can describe its physical properties well, thus easily and stably capturing the shock wave. In addition, the DGKS can simultaneously calculate inviscid and viscous fluxes when simulating viscous flow problems, which gives an improved algorithm consistency. Several representative examples, such as shock tube problems, implosion problem, couette flow, lid-driven cavity flow, flow in a channel with a backward-facing step, supersonic flow around a ramp segment, and flow around staggered NACA0012 biplane configuration, are simulated to validate the proposed meshfree-DGKS.
Solvent effect for an effective attraction between like-charged macroions immersed in an electrolyte solution: The intensification mechanism of the effective attraction caused by the translational motion of solvent particles
Authors: Suematsu Ayumi , Akiyama Ryo
Published: January 2021

The effective interaction between macroanions immersed in an electrolyte solution was calculated using an integral equation theory of liquids to study the solvent granularity effect on the effective attraction mediated by cations. Explicit and implicit solvent models were examined. The effective attraction for the explicit solvent model was found to be stronger than that for the implicit solvent model. This solvent effect was remarkably enhanced only when the effective attraction between macroanions was strong; this means that the solvent effect is not a usual excluded volume effect. The intensification mechanism of the attraction by the solvent granularity is analyzed in the present study, and an indirect mechanism is proposed.
Influence of trapped energetic ions on low-frequency magnetohydrodynamic instabilities with reversed shear profile
Authors: Gao Baofeng , Cai Huishan , Wang Feng , Gao Xiang , Wan Yuanxi
Published: January 2021

The influence of trapped energetic ions (TEIs) on m/n=2/1 low-frequency magnetohydrodynamic (MHD) instabilities with reversed shear profile is investigated by a global kinetic–MHD hybrid simulation. For low energetic-ion beta, TEIs have a stabilizing effect on the double tearing mode (DTM). When the energetic-ion beta is larger than a threshold, an energetic-particle-driven mode, the fishbone-like mode (FLM), is excited; that is, a mode transition from the DTM to the FLM occurs. The threshold increases with increasing resistivity, and the growth rate of the FLM is reduced by the presence of resistivity. In addition, the dependences on energetic-ion beta, gyroradius, and injection velocity of the effects of TEIs are studied systematically.
Plasmon-enhanced coherent anti-stokes Raman scattering vs plasmon-enhanced stimulated Raman scattering: Comparison of line shape and enhancement factor
Authors: Zong Cheng , Xie Yurun , Zhang Meng , Huang Yimin , Yang Chen , Cheng Ji-Xin
Published: January 2021

Plasmon-enhanced coherent Raman scattering microscopy has reached single-molecule detection sensitivity. Due to the different driven fields, there are significant differences between a coherent Raman scattering process and its plasmon-enhanced derivative. The commonly accepted line shapes for coherent anti-Stokes Raman scattering and stimulated Raman scattering do not hold for the plasmon-enhanced condition. Here, we present a theoretical model that describes the spectral line shapes in plasmon-enhanced coherent anti-Stokes Raman scattering (PECARS). Experimentally, we measured PECARS and plasmon-enhanced stimulated Raman scattering (PESRS) spectra of 4-mercaptopyridine adsorbed on the self-assembled Au nanoparticle (NP) substrate and aggregated Au NP colloids. The PECARS spectra show a nondispersive line shape, while the PESRS spectra exhibit a dispersive line shape. PECARS shows a higher signal to noise ratio and a larger enhancement factor than PESRS from the same specimen. It is verified that the nonresonant background in PECARS originates from the photoluminescence of nanostructures. The decoupling of background and the vibrational resonance component results in the nondispersive line shape in PECARS. More local electric field enhancements are involved in the PECARS process than in PESRS, which results in a higher enhancement factor in PECARS. The current work provides new insight into the mechanism of plasmon-enhanced coherent Raman scattering and helps to optimize the experimental design for ultrasensitive chemical imaging.
Engineered magnetization and exchange stiffness in direct-write Co–Fe nanoelements
Authors: Bunyaev S. A. , Budinska B. , Sachser R. , Wang Q. , Levchenko K. , Knauer S. , Bondarenko A. V. , Urbánek M. , Guslienko K. Y. , Chumak A. V. , Huth M. , Kakazei G. N. , Dobrovolskiy O. V.
Published: January 2021

Media with engineered magnetization are essential building blocks in magnonics, spintronics, and superconductivity. However, the established thin film and lithographic techniques insufficiently suit the realization of planar components with on-demand-tailored magnetization in the lateral dimension. Here, we demonstrate the engineering of the magnetic properties of CoFe-based nanodisks fabricated by the mask-less technique of focused electron beam-induced deposition (FEBID). The material composition in the nanodisks is tuned in situ via the e-beam waiting time in the FEBID process and their post-growth irradiation with Ga ions. The saturation magnetization Ms and exchange stiffness A of the disks are deduced from perpendicular spin-wave resonance measurements. The achieved Ms variation in the broad range from 720 emu/cm3 to 1430 emu/cm3 continuously bridges the gap between the Ms values of widely used magnonic materials such as Permalloy and CoFeB. The presented approach paves the way toward nanoscale 2D and 3D systems with controllable space-varied magnetic properties.
Fine-structure resolved rovibrational transitions for SO + H2 collisions
Authors: Price Teri J. , Forrey Robert C. , Yang Benhui , Stancil Phillip C.
Published: January 2021

Cross sections and rate coefficients for sulfur monoxide (SO) + H2 collisions are calculated using a full six-dimensional (6D) potential energy surface (PES). The coupled states (CS) approximation is used to compute fine-structure resolved cross sections for rovibrational transitions between states with v = 0–2, where v is the vibrational quantum number of the SO molecule. The CS calculations for Δv = 1 are benchmarked against close-coupling (CC) results for spin-free interactions. For Δv = 0, the present fine-structure resolved CS results are benchmarked against existing CC results obtained with a rigid rotor approximation. In both cases, the agreement is found to be satisfactory, which suggests that the present results may provide reliable estimates for fine-structure resolved rovibrational transitions. These estimates are the first of their kind based on a full 6D PES. Rate coefficients are reported for temperatures between 10 K and 3000 K for both para- and ortho-H2 colliders. A comparison of the para-H2 rates with mass-scaled results for He shows substantial differences that may be important in astrophysical models.
Comparing flow characteristics of viscoelastic liquids in long and short capillaries (entrance effects)
Authors: Malkin A. Ya. , Kulichikhin V. G. , Gumennyi I. V.
Published: January 2021

This study is devoted to the analysis of the physical meaning of the difference in the results of the viscosity measurements obtained by using the two-capillary method—carrying on the same flow rate through two circular parallel capillaries of different lengths but the same diameter. Furthermore, there is the other approach for using short capillaries for determination of a value, known as “elongational viscosity,” based on the concept of domination extension at the convergent flow along the inlet of a capillary. The theory of this method dates back to the publication of Cogswell. However, it was shown that this approach is inadequate for polymeric liquids that demonstrate time-dependence effects. In this study, we present experimental data for melts of two polyethylenes of different molecular weights and their mixtures. The data of capillary viscometry are accompanied by measuring their viscoelastic properties. The obtained data showed that the two-capillary method cannot give a chance to estimate “elongational viscosity” for elastic liquids. The difference between the losses in flow through long and short capillaries is treated in the terms of “end correction,” which is determined by the Weissenberg number. Hence, elasticity is the main physical parameter responsible for additional losses in the flow through a short capillary.
Appearance of the instability from the inhomogeneity in two-phase flow with gas-producing reaction in fractured porous medium
Authors: Konyukhov A. , Pankratov L. , Voloshin A.
Published: January 2021

A homogenized model of incompressible two-phase flow accompanied by a gas-producing reaction in a double porosity medium with a chemically active skeleton is derived. The equations of the homogenized model contain non-local in time source terms corresponding to the contribution of the gas-producing chemical reaction in the matrix blocks. The time non-locality, which manifests itself as the appearance of a time delay between the change in reactant concentrations and the reaction rate, is shown to stimulate the instability of the one-dimensional two-phase flow initiated by injection of the acid solution into the double porosity medium with chemically active matrix blocks. The instability results in the development of the self-oscillating mode of the reaction wave propagation.
Birational types of algebraic orbifolds
Authors: Kresch A. , Tschinkel Yu.
Published: January 2021

We introduce a variant of the birational symbols group of Kontsevich, Pestun and the second author, and use this to define birational invariants of algebraic orbifolds.

Bibliography: 20 titles.
Hermitian-Yang-Mills approach to the conjecture of Griffiths on the positivity of ample vector bundles
Authors: Demailly J.-P.
Published: January 2021

Given a vector bundle of arbitrary rank with ample determinant line bundle on a projective manifold, we propose a new elliptic system of differential equations of Hermitian-Yang-Mills type for the curvature tensor. The system is designed so that solutions provide Hermitian metrics with positive curvature in the sense of Griffiths — and even in the dual Nakano sense. As a consequence, if an existence result could be obtained for every ample vector bundle, the Griffiths conjecture on the equivalence between ampleness and positivity of vector bundles would be settled.

Bibliography: 15 titles.
Impact of elevated CO2 and heat stress on wheat pollen viability and grain production
Authors: Bokshi Anowarul I. , Tan Daniel K. Y. , Thistlethwaite Rebecca J. , Trethowan Richard , Kunz Karolin
Published: January 2021

Periods of high temperature and an expected increase in atmospheric CO2 concentration as a result of global climate change are major threats to wheat (Triticum aestivum L.) production. Developing heat-tolerant wheat cultivars demands improved understanding of the impacts of high temperature and elevated CO2 on plant growth and development. This research investigated the interactive effects of heat stress and CO2 concentration on pollen viability and its relationship to grain formation and yield of wheat in greenhouse conditions. Nineteen wheat genotypes and a current cultivar, Suntop, were heat stressed at either meiosis or anthesis at ambient (400 µL L–1) or elevated (800 µL L–1) CO2. Elevated CO2 and heat stress at meiosis reduced pollen viability, spikelet number and grain yield per spike; however, increased tillering at the elevated CO2 level helped to minimise yield loss. Both heat-tolerant genotypes (e.g. genotype 1, 2, 10 or 12) and heat-sensitive genotypes (e.g. genotype 6 or 9) were identified and response related to pollen sensitivity and subsequent impacts on grain yield and yield components were characterised. A high-throughput protocol for screening wheat for heat stress response at elevated CO2 was established and meiosis was the most sensitive stage, affecting pollen viability, grain formation and yield.
Effective electrical resistivity in a square array of oriented square inclusions
Authors: Guralnik Benny , Hansen Ole , Henrichsen Henrik H , Caridad José M , Wei Wilson , Hansen Mikkel F , Nielsen Peter F , Petersen Dirch H
Published: January 2021

The continuing miniaturization of optoelectronic devices, alongside the rise of electromagnetic metamaterials, poses an ongoing challenge to nanofabrication. With the increasing impracticality of quality control at a single-feature (-device) resolution, there is an increasing demand for array-based metrologies, where compliance to specifications can be monitored via signals arising from a multitude of features (devices). To this end, a square grid with quadratic sub-features is amongst the more common designs in nanotechnology (e.g. nanofishnets, nanoholes, nanopyramids, μLED arrays etc). The electrical resistivity of such a quadratic grid may be essential to its functionality; it can also be used to characterize the critical dimensions of the periodic features. While the problem of the effective electrical resistivity ρ
eff of a thin sheet with resistivity ρ
1, hosting a doubly-periodic array of oriented square inclusions with resistivity ρ
2, has been treated before (Obnosov 1999 SIAM J. Appl. Math.
59 1267–87), a closed-form solution has been found for only one case, where the inclusion occupies c = 1/4 of the unit cell. Here we combine first-principle approximations, numerical modeling, and mathematical analysis to generalize ρ
eff for an arbitrary inclusion size (0 < c < 1). We find that in the range 0.01 ≤ c ≤ 0.99, ρ
eff may be approximated (to within <0.3% error with respect to finite element simulations) by:

ρ

e
f
f

=

ρ

1

α

(
c
)

−

1
−

ρ

2

/

ρ

1

1
+

ρ

2

/

ρ

1

α

(
c
)

+

1
−

ρ

2

/

ρ

1

1
+

ρ

2

/

ρ

1

c
·
α

(
c
)

,

α

(
c
)

=
1
+

0.9707

0.9193
+

c

1
−
c

2.1261

0.4671

.

whereby at the limiting cases of c → 0 and c → 1, α approaches asymptotic values of α = 2.039 and α = 1/c − 1, respectively. The applicability of the approximation to considerably more complex structures, such as recursively-nested inclusions and/or nonplanar topologies, is demonstrated and discussed. While certainly not limited to, the theory is examined from within the scope of micro four-point probe (M4PP) metrology, which currently lacks data reduction schemes for periodic materials whose cell is smaller than the typical μm-scale M4PP footprint.
Micromechanical modeling approach with simplified boundary conditions to compute electromechanical properties of architected piezoelectric composites
Authors: Khan Kamran A , Al Hajeri Falah , Khan Muhammad Ali
Published: January 2021

Architected piezoelectric composites (PCs) have recently gained interest in designing transducers and nondestructive testing devices. The current analytical modeling approach cannot be readily applied to design architected periodic PCs exhibiting elastic anisotropy and piezoelectric activity. This study presents a micromechanical (MM)-model based finite element (FE) modeling framework to predict the electromechanical properties (EMPs) of the architected PCs. As an example, the microstructure with one-dimensional (1–3 PCs) connectivity is considered with different cross-sections of fibers. 3D FE models are developed. The intrinsic symmetry of architected composite is used to derive boundary conditions (BCs) equivalent to periodic BCs (PBCs). The proposed approach is simple and eliminates the need for a tedious mesh generation process on opposite boundary faces on the MM model of architected PCs. The EMPs of 1–3 PCs calculated from the proposed micromechanics-FE models were compared with those obtained from analytical solutions (i.e. based on micromechanics theories), and FE homogenization (i.e. obtained by employing the PBCs available in the literature). A quite good agreement between the proposed modeling approach and the ones obtained using the analytical model was observed. However, an excellent agreement is observed with the MM results that employed PBCs. Hence, we have concluded that the proposed MM modeling approach is equivalent to MM models that employed PBCs. The computed enhanced effective elastic, piezoelectric, and dielectric properties and corresponding figure of merit revealed that 1–3 PCs are suitable in transducer applications.
Fabrication, characterization and analytical modeling of gradient auxetic closed cell foams
Authors: Duncan Olly , Alderson Andrew , Allen Tom
Published: January 2021

Auxetic (negative Poisson’s ratio) and gradient open cell foams have shown promise for their conformability and high impact energy absorption—useful in applications like protective equipment, footwear and prosthetics. Recent methods fabricated auxetic closed cell foam by steaming conventional closed cell foam. Methods developed herein control the cell structure of auxetic closed cell foam, to produce novel intentionally anisotropic and gradient auxetic closed cell foam. Pins passed through the foam constrained or stretched regions during steaming to further modify cell structure, and impart gradients in cell structure, Young’s modulus and Poisson’s ratios. Fabricated foams had Poisson’s ratios between 1 and −1. Imparted Young’s moduli of 1–12 MPa were similar to foams used in footwear, prosthesis, helmets and other impact protection. The effect of changes to cell structure on Young’s moduli and Poisson’s ratio are explained by combining analytical models of auxetic open cell and conventional closed cell foam.
Timber moisture detection using wavelet packet decomposition and convolutional neural network
Authors: Yuan Cheng , Zhang Jicheng , Chen Lin , Xu Jia , Kong Qingzhao
Published: January 2021

As timber structures are vulnerable to degradation due to the tendency to trap moisture, the present study proposed a new percussion-based method to replace the existing constant contact between structures and sensors. A total of two approaches have been proposed to automated detect the moisture content (MC) of timber: (a) the random forest classifier (machine learning-based) was employed to classify the wavelet packet decomposition (WPD) features extracted from excitation-induced sound signals (WPD + RF); and (b) the 2D-CNN framework (deep learning-based) was employed to classify the Mel frequency cepstral coefficient (MFCC) features extracted from excitation-induced sound signals (MFCC + 2DCNN). The proposed automatic detection methods are covered from 1D time-domain signal classification to 2D image classification. To verify the effectiveness of both two approaches, an experimental study was conducted. The MC of two types of timber specimens (i.e. softwood and hardwood) was gradually increased from 0% to 60% with 10% increments. The change of MC of timber material caused different material properties, resulting in a measurable differential in forced vibration among the various specimens used. The results demonstrated that MFCC + 2DCC outperformed the RF + WPD in MC classification of timber material. Overall, the percussion-based method proposed in this study can provide an outstanding classification performance.