bluuebunny/crossref_metadata_2025 huggingface dataset:
Systematic search for lensed X-ray sources in the CLASH fields
Authors: Liu Ang , Tozzi Paolo , Rosati Piero , Bergamini Pietro , Caminha Gabriel Bartosch , Gilli Roberto , Grillo Claudio , Meneghetti Massimo , Mercurio Amata , Nonino Mario , Vanzella Eros
Published: February 2021

Aims. We exploit the high angular resolution of Chandra to search for unresolved X-ray emission from lensed sources in the field of view of 11 CLASH clusters, whose critical lines and amplification maps were previously obtained with accurate strong-lensing models. We consider a solid angle in the lens plane corresponding to a magnification μ > 1.5, which amounts to a total of ∼100 arcmin2, of which only 10% corresponds to μ > 10. Our main goal is to assess the efficiency of massive clusters as cosmic telescopes to explore the faint end of the X-ray extragalactic source population.

Methods. The main obstacle to this study is the overwhelming diffuse X-ray emission from the intracluster medium that encompasses the region with the strongest magnification power. To overcome this aspect, we first searched for X-ray emission from strongly lensed sources that were previously identified in the optical and then performed an untargeted detection of lensed X-ray sources.

Results. We detect X-ray emission in either in the soft (0.5−2 keV) or hard (2−7 keV) band in only 9 out of 849 lensed or background optical sources. The stacked emission of the sources without detection does not reveal any signal in any band. Based on the untargeted detection in the soft, hard, and total band images, we find 66 additional X-ray sources without spectroscopic confirmation that are consistent with being lensed (background) sources. Assuming an average redshift distribution consistent with the Chandra Deep Field South survey (CDFS), we estimate their magnification, and after accounting for completeness and sky coverage, measure the soft- and hard-band number counts of lensed X-ray sources for the first time. The results are consistent with current modeling of the population distribution of active galactic nuclei (AGN). The distribution of delensed fluxes of the sources identified in moderately deep CLASH fields reaches a flux limit of ∼10−16 and ∼10−15 erg s−1 cm−2 in the soft and hard bands, respectively, therefore approximately 1.5 orders of magnitude above the flux limit of the CDFS.

Conclusions. We conclude that in order to match the depth of the CDFS in exploiting massive clusters as cosmic telescopes, the required number of cluster fields is about two orders of magnitude larger than is offered by the 20 year Chandra archive. At the same time, the discovery of strongly lensed sources close to the critical lines remains an attractive if rare occurrence because the source density in the X-ray sky is low. A significant step forward in this field will be made when future X-ray facilities an angular resolution of ∼1 arcsec and a large effective area will allow the serendipitous discovery of rare, strongly lensed high-z X-ray sources. This will enable studying faint AGN activity in the early Universe and measuring gravitational time delays in the X-ray variability of multiply imaged AGN.
Astrophotonics: Processing starlight
Authors: Dinkelaker Aline N. , Rahman Aashia
Published: February 2021

The field of astrophotonics has been fostering photonic innovations critical and unique to astronomical applications for several years. As we are about to embark on the new era of extremely large telescopes, astrophotonics is poised to become an integral part of the next generation astronomical instruments.
‘Uncertainty’ principle in two fluid–mechanics
Authors: Gavrilyuk Sergey
Published: February 2021

Hamilton’s principle (or principle of stationary action) is one of the basic modelling tools in finite-degree-of-freedom mechanics. It states that the reversible motion of mechanical systems is completely determined by the corresponding Lagrangian which is the difference between kinetic and potential energy of our system. The governing equations are the Euler-Lagrange equations for Hamil- ton’s action.

Hamilton’s principle can be naturally extended to both one-velocity and multi-velocity continuum mechanics (infinite-degree-of-freedom systems). In particular, the motion of multi–velocity continuum is described by a coupled system of ‘Newton’s laws’ (Euler-Lagrange equations) for each component. The introduction of dissipative terms compatible with the second law of thermodynamics and a natural restriction on the behaviour of potential energy (convexity) allows us to derive physically reasonable and mathematically well posed governing equations.

I will consider a simplest example of two-velocity fluids where one of the phases is incompressible (for example, flow of dusty air, or flow of compressible bubbles in an incompressible fluid). A very surprising fact is that one can obtain different governing equations from the same Lagrangian. Different types of the governing equations are due to the choice of independent variables and the corresponding virtual motions. Even if the total momentum and total energy equations are the same, the equations for individual components differ from each other by the presence or absence of gyroscopic forces (also called ‘lift’ forces). These forces have no influence on the hyperbolicity of the governing equations, but can drastically change the distribution of density and velocity of components.

To the best of my knowledge, such an uncertainty in obtaining the governing equations of multi- phase flows has never been the subject of discussion in a ‘multi-fluid’ community.
A combined virtual impactor and field-effect transistor microsystem for particulate matter separation and detection
Authors: Li Yanna , Fu Muqing , Pang Wei , Chang Ye , Duan Xuexin
Published: February 2021

Ambient suspended particulate matter (PM) (primarily with particle diameter 2.5 µm or less, i.e., PM2.5) can adversely affect ecosystems and human health. Currently, optical particle sensors based on light scattering dominate the portable PM sensing market. However, the light scattering method has poor adaptability to different-sized PM and adverse environmental conditions. Here, we design and develop a portable PM sensing microsystem that consists of a micromachined virtual impactor (VI) for particle separation, a thermophoretic deposition chip for particle collection, and an extended-gate field-effect transistor (FET) for particle analysis. This system can realize on-site separation, collection, and analysis of aerosol particles without being influenced by environmental factors. In this study, the design of the VI is thoroughly analyzed by numerical simulation, and mixtures of different-sized silicon dioxide (SiO2) particles are used in an experimental verification of the performance of the VI and FET. Considering the low cost and compact design of the whole system, the proposed PM analysis microsystem has potential for PM detection under a wide range of conditions, such as heavily polluted industrial environments and for point-of-need outdoor and indoor air quality monitoring.
A comparative study of heat transfer characteristics of wall jet with boundary layer transition using six low-Reynolds number k–ε models
Authors: Nie Xin , Zhu Zehui , Liao Haibo , Lü Ming , Xu Jiangrong
Published: February 2021

A Low-Reynolds Number (LRN) k–ε model can well simulate the transition characteristics of the momentum boundary layer, but so far, there are few studies on the influence of boundary layer transition on heat transfer characteristics by using the LRN k–ε model. Due to the larger degree of flexibility and controllability of flow parameters than the conventional boundary layer, a wall jet is an ideal flow configuration to research the transition of the boundary layer. To investigate the performance of the LRN k–ε model in simulating the heat transfer characteristics of the wall jet with boundary layer transition, six versions of LRN k–ε models are used to simulate a three-dimensional wall jet with boundary layer transition and the computational results were compared with experimental data. It is found that the Abe–Kondoh–Nagano (AKN) and Yang–Shih (YS) models can accurately simulate the flow field and heat transfer of the laminar boundary layer due to the use of the Kolmogorov scale in the developing region. Compared with the YS model, the AKN model is capable of predicting the influence of boundary layer transition on the heat transfer process in good agreement with experimental results over the whole domain. From the calculation results, it is found that Abid and Change and Hsieh and Chen models are more appropriate for simulating the heat transfer in the fully turbulent region of the wall jet. The damping function fµ of the Lam–Bremhorst and Launder–Sharma models approaches a constant value near the wall, which does not meet the wall limiting conditions and leads to a negative impact on the simulation of heat transfer near the wall.
Landau damping in one dimensional periodic inhomogeneous collisionless plasmas
Authors: Pandey Sanjeev Kumar , Ganesh Rajaraman
Published: February 2021

Landau damping in a collisionless plasma is a well-known example of wave particle interaction. In the past, this phenomenon was addressed for homogeneous equilibria in the linear and non-linear limit of the perturbation amplitude. However, in reality, equilibria are almost always inhomogeneous or non-uniform in space. Considering a one dimensional, collisionless, unmagnetized, electrostatic plasma with stationary ions and kinetic electrons in a periodic inhomogeneous exact equilibrium of scale k0−1 as the starting point, the fate of a small amplitude (linear) perturbation of scale k−1 is investigated using a Vlasov–Poisson solver. Three different spatial regimes, namely, k0 > k, k0 ∼ k, and k0 < k, are addressed. In the k0 > k regime, long wavelength perturbation k is found to generate (k ± Nk0) modes (where N is an integer), which allows damping of long wavelength perturbation in an inhomogeneous plasma and formation of phase-space vortices at phase velocities vϕ = ω/(k ± Nk0). Perhaps for the first time, novel phenomena such as “inhomogeneity induced Landau damping arrest” and “inhomogeneity induced plasma echo” are observed in k0 ∼ k and k0 < k regimes, respectively. New scaling laws as a function of inhomogeneity amplitude are also reported.
The development of an on-chip microinitiator with a built-in safety-and-arming device
Authors: Hu Tengjiang , Zhao Yulong , Wang Kexin , Fang Kuang , Ren Wei
Published: February 2021

With the development of small size and high energy output of initiators, how to improve the safety of the system becomes an urgent problem. Therefore, a novel Micro-electro-mechanical System (MEMS) initiator with a built-in safety-and-arming (S&A) device is introduced in this paper. The MEMS initiator is composed of the MEMS ignitor and the MEMS S&A device. A movable barrier with a fire hole is controlled by the MEMS S&A device. Driven by the electro-thermal principle, the barrier can be moved backward or forward to open or close the fire channel, and the status conversion between the armed mode and the safe mode can be realized. The test results show that under specific control signals, the MEMS S&A device can generate 1 mm output displacement. Under the armed mode, the flame can burst out from the fire channel when stimulated by 64 V pulse voltage. Under the safe mode, the barrier hit by the flame can stay intact, and the explosion energy is blocked in the fire channel successfully. The silicon wafer and silicon-on-insulator wafer are used to fabricate the MEMS S&A device. Integrated with the MEMS ignitor, the total chip size is 11 × 12 × 1.2 mm3.
Oversampled filter bank channelizer for cryogenic detectors
Authors: Arnaldi L. H. , Dellavale H. D.
Published: February 2021

We present the field-programmable gate array (FPGA) implementation of an oversampled generalized discrete Fourier transform (GDFT) filter bank (FB), optimized for its usage in the readout of cryogenic detectors, such as microwave kinetic inductance detectors. A polyphase structure is derived underlining the efficiency of complex-valued subband processing, raised by a GDFT modulation. For the latter, a fast Fourier algorithm realization may be used, yielding a highly efficient polyphase implementation for arbitrary integer decimation ratios. The FB is tested through a 16-channel GDFT channelizer. The implementation is based on the Xilinx Zynq family of FPGAs and aims to show the data reuse and flexibility offered by the GDFT channelizer structure. General design criteria are summarized for the 16-channel polyphase FB channelizer. The performance in hardware resource usage is also presented, taking into account one of the main objectives of the current physics experiments, aiming to have an extremely large readout format.
Apparatus for simultaneous dynamic light scattering–small angle neutron scattering investigations of dynamics and structure in soft matter
Authors: Nigro V. , Angelini R. , King S. , Franco S. , Buratti E. , Bomboi F. , Mahmoudi N. , Corvasce F. , Scaccia R. , Church A. , Charleston T. , Ruzicka B.
Published: February 2021

Dynamic Light Scattering (DLS) and Small-Angle Neutron Scattering (SANS) are two key tools to probe the dynamic and static structure factors, respectively, in soft matter. Usually, DLS and SANS measurements are performed separately, in different laboratories, on different samples, and at different times. However, this methodology has particular disadvantages for a large variety of soft materials, which exhibit a high sensitivity to small changes in fundamental parameters, such as waiting times, concentration, pH, and ionic strength. Here, we report on a new portable DLS-SANS apparatus that allows one to simultaneously measure both the microscopic dynamics (through DLS) and the static structure (through SANS) on the same sample. The apparatus has been constructed as a collaboration between two laboratories, each an expert in one of the scattering methods, and was commissioned on the LOQ and ZOOM SANS instruments at the ISIS Pulsed Neutron and Muon Source, U.K.
Study on the time-varying characteristics of AC local arc over the contaminated insulation surface
Authors: Yang H. , Ren Y. , Wen R. , Zhang L. , Chen Y.
Published: February 2021

From laboratory experiments it was shown that the flashover voltage of the wet contaminated insulator was significantly influenced by the parameters of the local arc. An integrated optical and electrical diagnostic platform was designed in this paper, which was used to acquire the emission spectrum and electrical parameters of the AC local arc over the wet contaminated surface. The analysis of thermodynamic and electric results showed that AC local arc had a “static time-varying” feature. Hence, a new characterization method of volt–ampere characteristics of the AC local arc was proposed, and a time constant was introduced to describe the time required for the AC local arc to reach the stable state from the beginning. The relationship between the voltage gradient of the AC local arc and the leakage current amplitude was obtained for flashover voltage calculation. Special attention was also paid to the influence of environmental factors, such as air pressure and ambient temperature, on the arc characteristic. This work can enrich the investigation of the parameters of the local arc over the wet contaminated insulation surface and may provide useful parameters for flashover voltage calculation of insulators in service.
Interface-dependent tunable elastic interface states in soft metamaterials
Authors: Niu Hao , Li Shuaifeng , Zang Jianfeng
Published: February 2021

Elastic interface states, which are usually generated at the interface of two connected domains with opposite topological invariant, have been successfully demonstrated in periodic structures. Therefore, the interface states determined by the position of interface between two domain walls in one-dimensional elastic systems are rarely reported, which were mainly restricted by the mirror-symmetric geometry of the unit cell. Jointing interface-dependent interface states were mostly implemented with analogs of quantum valley Hall effects in two-dimensional systems. Herein, we first observe two types of elastic interface states simultaneously occurred in one-dimensional combined metamaterials, where two interface modes separately located at two connected domain walls and they can be actively tuned simply through deforming two components on two sides. Flexible and versatile frequency shift and switch on–off characteristics of combination of two interface modes are demonstrated, which may be employed in the multifunctional elastic wave filters, tunable energy harvesting, and elastography devices. Our primitive cell of the soft metamaterial, which breaks the inversion symmetry along the horizontal direction, may be generalized to realize tunable elastic valley Hall edge states.
Analytic evaluation of energy first derivatives for spin–orbit coupled-cluster singles and doubles augmented with noniterative triples method: General formulation and an implementation for first-order properties
Authors: Liu Junzi , Zheng Xuechen , Asthana Ayush , Zhang Chaoqun , Cheng Lan
Published: February 2021

A formulation of analytic energy first derivatives for the coupled-cluster singles and doubles augmented with noniterative triples [CCSD(T)] method with spin–orbit coupling included at the orbital level and an implementation for evaluation of first-order properties are reported. The standard density-matrix formulation for analytic CC gradient theory adapted to complex algebra has been used. The orbital-relaxation contributions from frozen core, occupied, virtual, and frozen virtual orbitals to analytic spin-orbit CCSD(T) gradients are fully taken into account and treated efficiently, which is of importance to calculations of heavy elements. Benchmark calculations of first-order properties including dipole moments and electric-field gradients using the corresponding exact two-component property integrals are presented for heavy-element containing molecules to demonstrate the applicability and usefulness of the present analytic scheme.
Scattering of slow electron from hydrogen atom in non-ideal classical plasmas: Zero-energy resonances
Authors: Das Biswajit , Ghoshal Arijit
Published: February 2021

The scattering of slow electrons from the hydrogen atom embedded in non-ideal classical plasma has been investigated by using the effective range theory. A pseudopotential, which has been derived from a solution of Bogolyubov's hierarchy equations, is used to represent the interactions among the charged particles in plasma. A detailed study is made on the effects of non-ideality of plasma on the scattering dynamics for a wide range of the non-ideality parameter. In particular, the zero-energy resonance phenomenon has been studied in detail by evaluating the singlet scattering length. It is found that the scattering length suffers significant changes when the non-ideality parameter approaches its critical value.
High thermoelectrical figure of merit in chiral topological superconductor junctions
Authors: Chen Xiao-Feng , Wang Xing , Song Juntao , Li Yu-Xian
Published: February 2021

Performing the non-equilibrium Green’s function method, we calculate the Seebeck coefficient (S) and the thermoelectrical figure of merit (ZT) in the quantum anomalous Hall insulator-topological superconductor-quantum anomalous Hall insulator hybrid structure with temperature gradient. It is found that a high thermoelectrical figure of merit can be achieved with the helical topological superconductor phase. The S and the ZT are mainly affected by the temperature and the device size. At a certain temperature and the right device size, the Seebeck coefficient and the figure of merit can reach very high values.
Metamaterial beam for flexural wave resonance rainbow trapping and piezoelectric energy harvesting
Authors: Wang Biao , Huang Yang , Zhou Weijian , Yang Zhengbao
Published: February 2021

The rainbow trapping effect demonstrates great potential in multiple-band energy harvesting. However, the existing finite-size devices with the rainbow trapping phenomenon hardly harvest energy efficiently due to the mismatch between rainbow trapping frequencies and resonance frequencies of the devices. In this study, for the first time, we report a periodically perforated metamaterial beam, which achieves both the flexural wave rainbow trapping and resonance simultaneously for the multiple-band and multiple-position energy harvesting. The band structure of the unit cell in the metamaterial beam is analyzed to illustrate its ability to realize strong dispersion and energy concentration. The study first indicates that the rainbow trapping effect activated by resonance frequencies causes much more intense spatial separation and localization of flexural waves compared with that by cutoff frequencies for the periodically perforated bare beam. We, then, demonstrate that the resonance rainbow trapping phenomenon allows the proposed design to show superiority in piezoelectric energy harvesting compared with the counterpart with off-resonance rainbow trapping. Simulations indicate that the optimal resistance and the highest output power vary much for different pairs of piezoelectric patches at the corresponding resonance rainbow frequencies; by contrast, the positions of piezoelectric patches have little influence on the performance of the device. The design concept of on-resonance rainbow trapping in metamaterials in this study will help engineers to open a new venue for high-performance piezoelectric energy harvesters.
Recurrent canards producing relaxation oscillations
Authors: Abdulwahed C. , Verhulst F.
Published: February 2021

For three three-dimensional chaotic systems (Sprott NE1, NE8, and NE9) with only linear and quadratic terms and one parameter, but without equilibria, we consider the second order asymptotic approximations in the case that the parameter is small and near the origin of phase-space. The calculation leads to the existence and approximation of periodic solutions with neutral stability for systems NE1, NE9, and asymptotic stability for system NE8. Extending to a larger neighborhood in phase-space, we find a new type of relaxation oscillations with pulse behavior that can be understood by identifying hidden canards. The relaxation dynamics coexists with invariant tori and chaos in the systems.
Extending correlation functions of molecular dynamics simulation by Kovalenko–Hirata and Kobryn–Gusarov–Kovalenko closures for monatomic Lennard-Jones solvent and its application to a calculation of solvation
Authors: Miyata Tatsuhiko , Nishida Shunsuke , Ogasawara Yu
Published: February 2021

We have tried to extend the short-ranged radial distribution function of the molecular dynamics (MD) simulation for a monatomic Lennard-Jones solvent by applying the Ornstein–Zernike theory with two hybrid closures. One was the hybrid with the Kovalenko–Hirata or the KH closure (hybrid MD–KH closure), whereas the other was the hybrid with the Kobryn–Gusarov–Kovalenko or the KGK closure (hybrid MD–KGK closure). As long as the switching distance between the MD and the KH (or the KGK) is chosen appropriately, the direct correlation functions obtained by these hybrid closures were almost identical to each other, which also agree with those of the hybrid closure with the hypernetted chain or the HNC (hybrid MD–HNC closure). The calculations on the solute–solvent correlation function and the solvation free energy also supported the practical equivalence among the hybrid MD–KH, hybrid MD–KGK, and hybrid MD–HNC closures.
Network hubs cease to be influential in the presence of low levels of advertising
Authors: Rossman Gabriel , Fisher Jacob C.
Published: February 2021

Significance

A major focus of social network analysis is attempting to find central “influencers” or “opinion leaders” who can hasten or slow the spread of a social contagion. Using a simulation, we demonstrate that the most central node is important only under conventional but implausible scope conditions. We model the introduction of mass media or advertising and show that this allows social contagions to spread equally fast whether or not the seed node is highly central to the network. The most central node loses its relative importance even if mass media or advertising influence is extremely weak. This implies that, rather than targeting a node with a highly central position, marketers and public health officials should advertise broadly.
Design of genetically encoded sensors to detect nucleosome ubiquitination in live cells
Authors: dos Santos Passos Carolina , Choi Yun-Seok , Snow Christopher D. , Yao Tingting , Cohen Robert E.
Published: February 2021

Histone posttranslational modifications (PTMs) are dynamic, context-dependent signals that modulate chromatin structure and function. Ubiquitin (Ub) conjugation to different lysines of histones H2A and H2B is used to regulate diverse processes such as gene silencing, transcriptional elongation, and DNA repair. Despite considerable progress made to elucidate the players and mechanisms involved in histone ubiquitination, there remains a lack of tools to monitor these PTMs, especially in live cells. To address this, we combined an avidity-based strategy with in silico approaches to design sensors for specifically ubiquitinated nucleosomes. By linking Ub-binding domains to nucleosome-binding peptides, we engineered proteins that target H2AK13/15Ub and H2BK120Ub with Kd values from 10−8 to 10−6 M; when fused to fluorescent proteins, they work as PTM sensors in cells. The H2AK13/15Ub-specific sensor, employed to monitor signaling from endogenous DNA damage through the cell cycle, identified and differentiated roles for 53BP1 and BARD1 as mediators of this histone PTM.
A novel dual Ca2+ sensor system regulates Ca2+-dependent neurotransmitter release
Authors: Li Lei , Liu Haowen , Krout Mia , Richmond Janet E. , Wang Yu , Bai Jihong , Weeratunga Saroja , Collins Brett M. , Ventimiglia Donovan , Yu Yi , Xia Jingyao , Tang Jing , Liu Jie , Hu Zhitao
Published: February 2021

Ca2+-dependent neurotransmitter release requires synaptotagmins as Ca2+ sensors to trigger synaptic vesicle (SV) exocytosis via binding of their tandem C2 domains—C2A and C2B—to Ca2+. We have previously demonstrated that SNT-1, a mouse synaptotagmin-1 (Syt1) homologue, functions as the fast Ca2+ sensor in Caenorhabditis elegans. Here, we report a new Ca2+ sensor, SNT-3, which triggers delayed Ca2+-dependent neurotransmitter release. snt-1;snt-3 double mutants abolish evoked synaptic transmission, demonstrating that C. elegans NMJs use a dual Ca2+ sensor system. SNT-3 possesses canonical aspartate residues in both C2 domains, but lacks an N-terminal transmembrane (TM) domain. Biochemical evidence demonstrates that SNT-3 binds both Ca2+ and the plasma membrane. Functional analysis shows that SNT-3 is activated when SNT-1 function is impaired, triggering SV release that is loosely coupled to Ca2+ entry. Compared with SNT-1, which is tethered to SVs, SNT-3 is not associated with SV. Eliminating the SV tethering of SNT-1 by removing the TM domain or the whole N terminus rescues fast release kinetics, demonstrating that cytoplasmic SNT-1 is still functional and triggers fast neurotransmitter release, but also exhibits decreased evoked amplitude and release probability. These results suggest that the fast and slow properties of SV release are determined by the intrinsically different C2 domains in SNT-1 and SNT-3, rather than their N-termini–mediated membrane tethering. Our findings therefore reveal a novel dual Ca2+ sensor system in C. elegans and provide significant insights into Ca2+-regulated exocytosis.
Multimode unidirectional spin-wave coupling in an array of non-identical magnonic crystals near band gap frequencies
Authors: Gubanov V A , Sheshukova S E , Nikitov S A , Sadovnikov A V
Published: February 2021

Using Brillouin light spectroscopy and micromagnetic simulation methods, we show how the intermodal coupling between two magnonic crystals (MCs) affects signals spatial selection with frequency separation during spin-wave transport. We have experimentally demonstrated control of the intermodal coupling of spin waves (SWs) propagating in non-identical magnonic-crystal microwaveguides near the band gap frequency. We show that the spin-wave propagation direction within the MCs of different width can be controlled by the lateral coupling between SWs. Our findings provide an alternative method for signal filtering and separation within magnonic networks for the implementation of magnonic demultiplexers, power dividers, couplers and microwave signal processing devices. based on the lateral array of non-identical MCs.
Exciton-plasmon coupling and giant photoluminescence enhancement in monolayer MoS2 through hierarchically designed TiO2/Au/MoS2 ternary core−shell heterostructure
Authors: Mawlong Larionette P L , Paul Kamal Kumar , Giri P K
Published: February 2021

Enhancing the light coupling efficiency of large-area monolayer molybdenum disulfide (1L-MoS2) is one of the major challenges for its successful applications in optoelectronics and photonics. Herein, we demonstrate a dramatically enhanced photoluminescence (PL) emission from direct chemical vapor deposited monolayer MoS2 on a fluorine-doped TiO2/Au nanoparticle plasmonic substrate, where the PL intensity is enhanced by nearly three orders of magnitude, highest among the reported values. The formation of TiO2/Au/1L-MoS2 ternary core–shell heterojunction is evidenced by the high-resolution transmission electron microscopy and Raman analyses. Localized surface plasmon resonance induced enhanced absorption and improved light coupling in the system was revealed from the UV–vis absorption and Raman spectroscopy analyzes. Our studies reveal that the observed giant PL enhancement in 1L-MoS2 results from two major aspects: firstly, the heavy p-doping of the MoS2 lattice is caused by the transfer of the excess electrons from the MoS2 to TiO2 at the interface, which enhances the neutral exciton emissions and restrains the trion formation. Secondly, the localized surface plasmon in Au NPs underneath the 1L-MoS2 film initiates exciton-plasmon coupling between excitons of the 1L-MoS2 and surface plasmons of the Au NPs at the MoS2/Au interface. The PL and Raman analyses further confirm the p-doping effect. We isolate the contributions of plasmon enhancement from the theoretical calculation of the field enhancement factor using the effective medium approximation of plasmonic heterostructure, which is in excellent agreement with the experimental data. This work paves a way for the rational design of the plasmonic heterostructure for the effective improvement in the light emission efficiency of 1L-MoS2, and may enable engineering the different contributions to enhance the optoelectronic performance of 2D heterostructures.
A chip-sized piezoelectric receiver for low-frequency, near-field wireless power transfer: design, modeling and experimental validation
Authors: Halim Miah A , Rendon-Hernandez Adrian A , Smith Spencer E , Arnold David P
Published: February 2021

This work presents the design, modeling and characterization of a chip-sized piezoelectric receiver for low-frequency, near-field wireless power transmission. Utilizing a laser micro-machined titanium suspension, one NdFeB magnet, and two PZT-5A piezo-ceramic patches, the receiver operates at its torsion mode mechanical resonance. Two unimorph piezo-ceramic transducers are designed to maximize the power density of the receiver while maintaining a low mechanical resonant frequency for low-frequency electrodynamic wireless power transmission. An equivalent lumped-element circuit model is used to model the system performance. A prototype device is fabricated, assembled and tested, and the experimental results are compared with the system model. The 0.08 cm3 device generates a maximum of 360 μW average power at 1 cm distance from a transmitter coil operating at 724 Hz and below human head and torso exposure limits. This data corresponds to 4.2 mW cm−3 power density. Overall, this volume-efficient design offers a low-profile and compact footprint for potentially wirelessly charging wearable and bio-implantable devices.
Multi-level stochastic refinement for complex time series and fields: a data-driven approach
Authors: Sinhuber M , Friedrich J , Grauer R , Wilczek M
Published: February 2021

Spatio-temporally extended nonlinear systems often exhibit a remarkable complexity in space and time. In many cases, extensive datasets of such systems are difficult to obtain, yet needed for a range of applications. Here, we present a method to generate synthetic time series or fields that reproduce statistical multi-scale features of complex systems. The method is based on a hierarchical refinement employing transition probability density functions (PDFs) from one scale to another. We address the case in which such PDFs can be obtained from experimental measurements or simulations and then used to generate arbitrarily large synthetic datasets. The validity of our approach is demonstrated at the example of an experimental dataset of high Reynolds number turbulence.
Enhancing the optical absorption, conductivity, and nonlinear parameters of PVOH films by Bi-doping
Authors: Ali H Elhosiny , Yahia I S , Algarni H , Khairy Yasmin
Published: February 2021

New polymeric nanocomposite films of PVOH (polyvinyl alcohol) embedded with Bi-nanoparticles have been described by scanning electron microscopy and x-ray diffractometer. From UV-visible spectroscopy, the absorption edge shifts to the higher wavelengths direction (redshift). Tauc’s model for optical bandgap transitions demonstrates that the direct and indirect values are reduced with the increase of Bi percentage in the PVOH matrix. In contrast, Urbach energy (tail bandwidth), extinction coefficient, refractive index, and optical conductivity are increased. These indicate the rise of the charge transfer among the Bi nanoparticles and the macromolecules of the matrix. Using Wemple–Di Domenico model for single-oscillator, we calculated the nonlinear optical refractive index and susceptibility. The optical limiting characteristic has been tested via a green laser source of wavelength 533 nm. The present results offer new materials for optical Cut-Off and nonlinear optical applications.
Platinum dissolution and tissue response following long-term electrical stimulation at high charge densities
Authors: Shepherd Robert K , Carter Paul M , Dalrymple Ashley N , Enke Ya Lang , Wise Andrew K , Nguyen Trung , Firth James , Thompson Alex , Fallon James B
Published: February 2021

Objective. Established guidelines for safe levels of electrical stimulation for neural prostheses are based on a limited range of the stimulus parameters used clinically. Recent studies have reported particulate platinum (Pt) associated with long-term clinical use of these devices, highlighting the need for more carefully defined safety limits. We previously reported no adverse effects of Pt corrosion products in the cochleae of guinea pigs following 4 weeks of electrical stimulation using charge densities far greater than the published safe limits for cochlear implants. The present study examines the histopathological effects of Pt within the cochlea following continuous stimulation at a charge density well above the defined safe limits for periods up to 6 months. Approach. Six cats were bilaterally implanted with Pt electrode arrays and unilaterally stimulated using charge balanced current pulses at a charge density of 267 μC cm−2 phase−1 using a tripolar electrode configuration. Electrochemical measurements were made throughout the implant duration and evoked potentials recorded at the outset and on completion of the stimulation program. Cochleae were examined histologically for particulate Pt, tissue response, and auditory nerve survival; electrodes were examined for surface corrosion; and cochlea, brain, kidney, and liver tissue analysed for trace levels of Pt. Main results. Chronic stimulation resulted in both a significant increase in tissue response and particulate Pt within the tissue capsule surrounding the electrode array compared with implanted, unstimulated control cochleae. Importantly, there was no stimulus-induced loss of auditory neurons (ANs) or increase in evoked potential thresholds. Stimulated electrodes were significantly more corroded compared with unstimulated electrodes. Trace analysis revealed Pt in both stimulated and control cochleae although significantly greater levels were detected within stimulated cochleae. There was no evidence of Pt in brain or liver; however, trace levels of Pt were recorded in the kidneys of two animals. Finally, increased charge storage capacity and charge injection limit reflected the more extensive electrode corrosion associated with stimulated electrodes. Significance. Long-term electrical stimulation of Pt electrodes at a charge density well above existing safety limits and nearly an order of magnitude higher than levels used clinically, does not adversely affect the AN population or reduce neural function, despite a stimulus-induced tissue response and the accumulation of Pt corrosion product. The mechanism resulting in Pt within the unstimulated cochlea is unclear, while the level of Pt observed systemically following stimulation at these very high charge densities does not appear to be of clinical significance.
Coupled explicit-damping simulation of laser shock peening on x12Cr steam turbine blades
Authors: Fameso Festus , Desai Dawood , Kok Schalk , Newby Mark , Glaser Daniel
Published: February 2021

Timeous prevention of, and recovery from, downtimes due to in-service failure of crucial power plant components, like turbine blades, portends huge consequences in the form of operational and financial viability concerns. Intensive research and development in manufacturing, re-manufacturing and condition-based maintenance of these components have birthed a novel technique, which deploys high intensity lasers to induce compressive residual stresses to the surface of the blades. This paper presents the application of an alternate computational modelling technique in simulating this surface treatment technique on X12Cr steel, an exotic steam turbine blades material, while also investigating the economic parameters of the induced residual stresses. A numerical model is developed in this work using the commercial finite elements software ABAQUS©. The results show this computational modelling technique as being time efficient. The parametric outcomes of the simulation agreed with experimental results, lending credence to its validity. Induced compressive stresses as high as 700 MPa and depths close to 1 mm from the surface of the blade were obtained. This by indication can prospectively quell crack initiation, growth and unplanned failure of the blade while in service, with the introduced simulation technique offering a solution for timely, non-destructive mechanical integrity enhancement of engineered components.
A pragmatic controller for a gantry crane
Authors: Abduljabbar Bilal , Billingsley John , Wen Paul
Published: February 2021

A gantry crane presents a control problem with ten state variables. The undamped swinging of the load has led earlier researchers to apply cumbersome control strategies. The essence of pragmatic control is gleaned from autopilot designs of half a century ago. The control is designed as a set of ‘nested loops’, where the innermost loop takes the form of a velocity loop wrapped around a motor to give crisp velocity control. Target values are derived from states in the outer loops, to be applied to a succession of inner loops. These target values are subjected to constraints. Thus in the case of the crane, the horizontal position of the load can be considered to be the two outermost variables. In this study, from the load position error, two target velocity components are calculated and subjected to limits. The velocity error leads in turn to a target acceleration of the load and subsequently, to the target displacement that takes place between the horizontal coordinates of the hoist and the load. In this paper, the pragmatic control technique is demonstrated with the aid of a JavaScript and MATLAB software programs using a state-space model.
A thorough investigation of the sawdust’s angle of repose subjected to a spectrum of stimulating vibration frequencies, using a specially developed testing device.
Authors: Zalimidis Pavlos
Published: February 2021

The transportation and storage of powdered bulk materials is an important part of the manufacturing process of many products and requires equally important productive resources such as time, space and capital. Accurate estimation of these materials’ mechanical properties, especially those related to the above processes, such as the angle of repose provides information necessary for the design of optimized mechanical systems that minimize production costs. In the context of the present study, a mechanical device has been developed at the Machine Design Laboratory of the School of Pedagogical & Technological Education (ASPETE) for the determination of the angle of repose of bulk materials, a dimension necessary for many calculations related to machinery, such as maximum capacity e.g. of conveyor bolts, straps and lifts. This device allows studying this property very accurately under various vibration conditions, thus giving more realistic and much more useful results. Measurements were conducted on dry and wet sawdust, a raw material of many important product, and angle-of-repose diagrams were generated with respect to stimulating vibration frequency.
Equilibrium solutions of axially moving Timoshenko beam with a supercritical speed
Authors: Wang Ze , Ren Jianting
Published: February 2021

Analytical solution of the equilibrium configuration of an axially moving Timoshenko beam in supercritical regime is studied. Three kinds of classical boundary conditions are considered. An analytical solution of the equilibrium configuration in terms of the axial velocity in supercritical regime is determined. But most of all, for an axially moving Timoshenko beam with the fixed ends in supercritical regime, an anti-symmetric configuration is firstly detected. And, its analytical solution is solved. Besides, numerical example shows that the solution of the equilibrium configuration bifurcates with axially velocity. And the critical velocity derived from the Timoshenko beam theory is smaller than that derived from Euler-Bernoulli beam theory. The amplitude of the solution of equilibrium configuration derived from Timoshenko beam is larger.
SSA-LSTM neural network for hourly PM2.5 concentration prediction in Shenyang, China
Authors: Zhang Ye , Li Weide
Published: February 2021

Atmospheric environment has become the focus of global attention. Fine particulate matter has posed a serious threat to human respiratory system. In order to effectively control atmospheric environment and protect human health, pollutant prediction has become a necessary work for human survival and development. In order to improve the accuracy of PM2.5 prediction, this paper developed a new combined prediction model — SSA-LSTM. Firstly, the observed time series are decomposed into periodic component and noise component by SSA (Singular spectrum analysis). Then, LSTM (Long short-term memory) neural network was used to forecast the decomposed components. Finally, the predicted results of different components are integrated to generate the final predicted results. The results show that the proposed model has a significant improvement in the accuracy of prediction.
Parameter tuning of active disturbance rejection control in quad tilt rotor based on particle swarm optimization
Authors: Wang Zhigang , Lyu Zhichao , Li Jianbo
Published: February 2021

The quad tilt rotor (QTR) has complex dynamics characteristics, especially in transition mode. It is difficult to model the QTR dynamics and the environmental factors have a great influence on it. To solve the problem of control in transition mode of QTR, this paper carries out the design of the controller based on active disturbance rejection control (ADRC). ADRC has many parameters to be tuned, and the coupling effect is more serious, so it is very difficult to tune parameters. Particle swarm optimization (PSO) algorithm has faster computing speed and better global search ability in dynamic and multi-objective optimization. So, using PSO algorithm to realize self-tuning of ADRC parameters in ADRC parameters tuning. By comparing the control performance of ADRC before and after optimization, the rationality and effectiveness of ADRC parameters tuning algorithm in QTR are verified in both time domain and frequency domain.
Arbitrary polynomial chaos expansion and its application to power flow analysis-Fast approximation of probability distribution by arbitrary polynomial expansion
Authors: Katagiri Yuki , Iwamura Kazuaki , Nakanishi Yosuke , Takano Sachio , Suzuki Ryohei
Published: February 2021

This paper introduces an arbitrary polynomial chaos expansion method for performing probabilistic power flow analysis in power systems. The proposed method is used for uncertainty analysis, expressing the uncertainty of a system as random variables with an arbitrary output distribution based on orthogonal polynomial expansion. This method is advantageous because of its calculation speed and accuracy. This study expresses probabilistic power flow in a power system with many uncertain power sources using linear combination polynomial expansion. The orthogonal polynomial system employed is generated by moment analysis from renewable energy output data, with the polynomial coefficients derived from a collocation method. Simulation of probabilistic power flow using the proposed method is applied to a 29-bus transmission network model including three renewable energies, and the calculation speed and accuracy are evaluated by changing the expansion order of the polynomial. In addition, the influence on the polynomial coefficient is assessed when the system topology is changed due to a line fault. Therefore, since the arbitrary polynomial chaos expansion method can represent complex networks by linear combination of orthogonal polynomial sets, calculation based on it is several hundred times faster than the conventional Monte Carlo method. The results demonstrate that the proposed method is very useful for analyzing the probabilistic power distribution and that third-order expansion is practically appropriate.
Pedestrian identification in infrared and visible images based on pose keypoints matching
Authors: Brehar Raluca , Marita Tiberiu , Negru Mihai , Nedevschi Sergiu
Published: February 2021

The identification of persons in multi-spectral images that are not spatially aligned is a challenging process. A correct identification can improve the pedestrian detection task for machine vision applications. In this context we propose a person identification mechanism able to correctly find the same person in infrared and visible images. The main contribution of the paper is the keypoint based matcher that uses a deep learning based solution for finding relevant human pose keypoints and a local neighbour search for extracting the best candidates for person identification. For each of the two images, infrared and color we first perform pedestrian detection. Next, on each detected instance we extract the relevant keypoints for shoulders, hands and legs. A matching algorithm between the extracted keypoints is proposed in order to perform the identification of persons in the two images. We obtain an identification accuracy of 76% for pedestrians that have a medium height with respect to the image dimensions, and have a small occlusion degree.