bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy-preserving methods for guiding center system based on averaged vector field
Authors: Zhu Beibei , Tang Yifa , Liu Jian
Published: March 2022

We propose a family of energy-preserving methods for guiding center dynamics by perceiving its Hamiltonian nature based on the averaged vector field. The energy conservation, symmetric property, and algebraic order of these methods are studied. Furthermore, higher order energy-preserving methods are systematically introduced by using a composition technique. Two second order and two fourth order symmetric energy-preserving methods are constructed and applied to simulate the guiding center motion in both the dipole magnetic field and the tokamak magnetic field. Numerical results show that these methods have significant superiorities in energy conservation compared with the existing canonicalized symplectic methods of the corresponding orders. The numerical case of the guiding center motion in the toroidal acceleration electric field exhibits favorable long-term conservative properties of the new methods to the particle-field system, while the kinetic energy of guiding centers keeps increasing. These energy-preserving methods based on the averaged vector field can be applied to any non-canonical Hamiltonian system.
Subharmonic resonance and antiresonance characteristics for high-frequency confined interface vibration inkjet printing
Authors: Li Dege , Li Haoren , Yang Guodong , Wang Jide , Huang Bingfang , Wu Xinlei , Sun Qiang , Ma Chi , Liu Yonghong , Zhang Yanzhen
Published: March 2022

Confined interface vibration inkjet printing (CIVIJP) in another immiscible liquid phase has been investigated previously as a novel strategy proposed for actively generating ultra-fine droplets, which can be dozens of times smaller than the orifice from which they are ejected. However, the working frequency of this novel CIVIJP technique is much lower than the traditional inkjet printing, and the unique droplet generation mechanism and the interface behavior of CIVIJP are still unapprehended at high working frequency. Here, the CIVIJP working at high frequency was explored to reveal the droplet generation mechanism and improve its printing efficiency. The subharmonic resonance and antiresonance effects which have a final influence on the interface behavior and size of the droplets were found in the case of high working frequency. The droplets' size will fluctuate regularly with the increasing printing frequency induced by the residual vibrations. The subharmonic resonance and antiresonance depend on whether the residual movement of the meniscus is in-phase or out-of-phase with the next droplet formation cycle. The mechanism of this phenomenon was delineated in detail, and the theoretical predicted optimal resonance frequencies were in good agreement with the experimental values. Based on the above mechanisms, a new route was proposed to regulate the size of the droplets facilely. The antiresonance effect was successfully utilized to develop an unprecedented droplet propelling regime after the droplet being dispensed with the same nozzle.
Pseudo-2D RANS: A LiDAR-driven mid-fidelity model for simulations of wind farm flows
Authors: Letizia S. , Iungo G. V.
Published: March 2022

Next-generation models of wind farm flows are increasingly needed to assist the design, operation, and performance diagnostic of modern wind power plants. Accuracy in the descriptions of the wind farm aerodynamics, including the effects of atmospheric stability, coalescing wakes, and the pressure field induced by the turbine rotors are necessary attributes for such tools as well as low computational costs. The Pseudo-2D RANS model is formulated to provide an efficient solution of the Navier–Stokes equations governing wind-farm flows installed in flat terrain and offshore. The turbulence closure and actuator disk model are calibrated based on wind light detection and ranging measurements of wind turbine wakes collected under different operative and atmospheric conditions. A shallow-water formulation is implemented to achieve a converged solution for the velocity and pressure fields across a farm with computational costs comparable to those of mid-fidelity engineering wake models. The theoretical foundations and numerical scheme of the Pseudo-2D RANS model are provided, together with a detailed description of the verification and validation processes. The model is assessed against a large dataset of power production for an onshore wind farm located in North Texas showing a normalized mean absolute error of 5.6% on the 10-min-averaged active power and 3% on the clustered wind farm efficiency, which represent 8% and 24%, respectively, improvements with respect to the best-performing engineering wake model tested in this work.
The strong Gauss–Lucas theorem and analyticity of correlation functions via the Lee–Yang theorem
Authors: Simon Barry
Published: March 2022

We provide a simple mechanism for going from Lee–Yang type theorems to analyticity of correlation functions by exploiting under-appreciated inequalities of Newman. We also describe a Lee–Yang approach that recovers the consequences of a low density cluster expansion for spin S models without any combinatorics.
Penetration height of weak axisymmetric fountain in homogeneous fluid under the combined temperature and salinity effect
Authors: Xia Yaowen , Gao Wenfeng , Liu Tao , Lin W. , Li Qiong , Li Jingjin
Published: March 2022

Fountains under combined temperature and salinity effect are common in environmental and industrial settings. The behavior of weak axisymmetric fountains under combined temperature and salinity effect is studied with two-dimensional direct numerical simulations over 0.25 ≤ FrT ≤ 2.0 and −0.75 ≤ N ≤ 5.0, where FrT is the Froude number based on temperature only and N is the buoyancy ratio quantifying the ratio of salinity to temperature contributed to density. The results show that for each FrT, both the initial and time-average maximum fountain heights decrease when N increases as the combined negative buoyancy due to both temperature and salinity is strengthened, whereas as FrT increases, they increase as the overall negative buoyancy reduces. If the overall Froude number, Fr, which is based on density due to the combined temperature and salinity contributions, is used instead of FrT, the existing scaling relations for weak axisymmetric fountains with density coming from temperature only are also applicable for the weak axisymmetric fountains under the combined temperature and salinity effect when Fr ≲ 2.0, although there are slight differences in their quantified correlations due to the extra effect from the co-existing salinity. It is further shown that the effect from the co-existing salinity shifts the scaling relation for intermediate fountains with 2.0 ≲ Fr ≲ 4.0 with density from only one contributor to the scaling relation for weak fountains with Fr ≲ 2.0 with density coming from both temperature and salinity, further showing the additional effect of salinity.
Toward the core-edge coupling of delta-f and total-f gyrokinetic models
Authors: Trivedi P. , Dominski J. , Chang C. S. , Ku S.
Published: March 2022

The coupling of core reduced delta-f and edge total-f gyrokinetic models could enable a significant speed-up of the whole device modeling simulations. It is thus interesting to compare these models in the core where they will be coupled. The main difference between these models is the presence of the zeroth order term on the right-hand side of the total-f gyrokinetic equation. This term is responsible for driving a radial electric field that is also associated with Geodesic acoustic mode-like oscillations. To investigate the coupling between these models, the subsequent large-scale gyrokinetic 3D turbulence simulations have been performed starting from an already saturated gyrokinetic axisymmetric equilibria (collisions are not included). This work has also been extended to couple different axisymmetric and turbulent models available in XGC. It is shown that the radial electric field and its drive have to be taken care of consistently while coupling different models together.
Influence of high energy electrons on negative ion density in a hot cathode discharge
Authors: Sangma Jocelyn , Sharma Narayan , Chakraborty Monojit , Bandyopadhyay Mainak
Published: March 2022

This study investigates the influence of high energy electrons on the negative ion density along with the effect of filament current, discharge voltage, pressure, and magnetic filter field strength by carrying out measurements of negative ion density in a hot cathode discharge system in the double plasma device using a Langmuir probe technique. In the volume production technique, negative ions are formed by the dissociative attachment of low energy electrons to metastable hydrogen molecules and among the negative ion loss mechanisms; the presence of high energy electrons in the plasma is one of the important factors. Although the magnetic filter could reduce the temperature of the electrons in the target region considerably, high energy electrons were still present in the diffusion region, which could reduce the negative ion density. Negative hydrogen ion density measured by using Langmuir probe in the target region is also compared with the particle balance model considering the set of reactions involved in the production and destruction of negative ions, and a reasonably good match between them has been observed.
Mass transfer from a sheared spherical rigid capsule
Authors: Bielinski Clément , Xia Lumi , Helbecque Guillaume , Kaoui Badr
Published: March 2022

Solute mass transfer from a spherical fluid-filled rigid capsule subjected to shear flow is studied numerically, while considering unsteady, continuous, and nonuniform boundary conditions on its surface. Here, the capsule acts as a reservoir with its initially encapsulated solute concentration decaying over time. This scenario differs from the classical case study of either constant concentration or constant mass flux at the surface of the particle. The flow and the concentration field are computed using fully three-dimensional lattice Boltzmann simulations, where the fluid-structure two-way coupling is achieved by the immersed boundary method. The effects of the flow and the boundary conditions on mass transfer efficacy are quantified by the Sherwood number (the dimensionless mass transfer coefficient), which is found to increase due to the combined effects of forced convection and the rotation of the capsule. Having continuity of both the concentration and the mass flux on the capsule significantly decreases the Sherwood number as compared to the case with constant and uniform boundary condition. All the obtained results can be applied to heat transfer in the case of cooling an initially hot spherical particle, for which the concentration must be replaced by the temperature and the Sherwood number by the Nusselt number.
High speed, antenna-enhanced 10.3
μ
m quantum cascade detector
Authors: Quinchard G. , Mismer C. , Hakl M. , Pereira J. , Lin Q. , Lepillet S. , Trinité V. , Evirgen A. , Peytavit E. , Reverchon J. L. , Lampin J. F. , Barbieri S. , Delga A.
Published: March 2022

The strong potential of intersubband detectors in the field of mid-infrared photodetection places this technology as a relevant alternative to HgCdTe detectors in the race for ultrafast operation. While their extremely short photocarrier's lifetime opens up possibilities of detection beyond 100 GHz, it is also the main reason for their comparatively high dark current. Here, a photovoltaic quantum cascade detector at 10.3 μm, embedded in a metal–metal patch antenna is presented in both direct and heterodyne detection schemes. In DC, a responsivity of 122 mA/W at 77 K and 85 mA/W at 295 K is reached. More strikingly, the device shows temperature independent heterodyne response with a capacitance-limited cutoff frequency of 25 GHz both at 77 K and room temperature. It is modeled quantitatively by means of an equivalent RC-circuit picture stemming from microscopic transport considerations.
A data-driven dynamic nonlocal subgrid-scale model for turbulent flows
Authors: Seyedi S. Hadi , Zayernouri Mohsen
Published: March 2022

We developed a novel autonomously dynamic nonlocal turbulence model for the large and very large eddy simulation (LES, VLES) of homogeneous isotropic turbulent flows. The model is based on a generalized (integer-to-noninteger)-order Laplacian of the filtered velocity field, and a novel dynamic model has been formulated to avoid the need for tuning the model constant. Three data-driven approaches were introduced for the determination of the fractional-order to have a model that is totally free of any tuning parameter. Our analysis includes both the a priori and the a posteriori tests. In the former test, using a high-fidelity and well-resolved dataset from direct numerical simulations (DNSs), we computed the correlation coefficients for the stress components of the subgrid-scale (SGS) stress tensor and the one we get directly from the DNS results. Moreover, we compared the probability density function of the ensemble-averaged SGS forces for different filter sizes. In the latter, we employed our new model along with other conventional models including the static and dynamic Smagorinsky models into our pseudo-spectral solver and tested the final predicted quantities. The results of the newly developed model exhibit an expressive agreement with the ground-truth DNS results in all components of the SGS stress and forces. Also, the model exhibits promising results in the VLES region as well as the LES region, which could be remarkably important for cost-efficient nonlocal turbulence modeling, e.g., in meteorological and environmental applications.
An approach to implement a heat flux limit in a model for fusion relevant plasmas
Authors: Tokar M. Z. , Kobayashi M. , Ohno N.
Published: March 2022

An approach to implement a heat flux limit (HFL) in a plasma model is proposed. The HFL arises if the mean free path length of the heat carrying electrons, λh, significantly exceeds the characteristic length of the temperature variation, LT. For λh≫LT, the heat flux becomes nearly independent of the temperature gradient, in contrast to the case of λh≪LT where it is gradient dependent. As a result, by going from λh≪LT to λh≫LT, the order of the heat balance equation changes and the method proposed allows a reliable integration of this equation in these limits, as well as for λh∼LT. By solving a set of one-dimensional fluid equations for particle, momentum, and heat balance numerically, the importance of the HFL for fusion relevant conditions is demonstrated for plasma parameter profiles at the edge of the heliotron Large Helical Device and detachment conditions in helium plasmas of the linear device NAGDIS-II.
Dynamic mode decomposition analysis of the two-dimensional flow past two transversely in-phase oscillating cylinders in a tandem arrangement
Authors: Zhang Hongfu , Zhou Lei , Liu Tingting , Guo Zijian , Golnary Farshad
Published: March 2022

The flow through tandem square cylinders was investigated at a Reynolds number of 100 for oscillation amplitudes A = 0.1D to 0.7D and gaps L = 2.0D, 5.0D, and 6.0D, where D is the width of the cylinders. A moving reference frame method combined with the spectral/hp element method was employed to simulate the two-dimensional flow in the lock-in regime. Fluid forces, vorticity fields, power spectrum density, and pressure distribution were first investigated. Since surface pressure is directly connected with fluid forces, pressure and velocity field were synchronously analyzed by employing optimal dynamic mode decomposition. An underlying link between fluid forces and coherence modes was then uncovered. The results reveal that the move-induced forces and flow structures strongly depend on gaps and amplitudes in the lock-in regime. With respect to the dynamic mode decomposition analysis, odd-order modes contribute to lift forces, while even-order modes result in drag forces. The flow structures are dominated by at most three modes; as the amplitude increases, the high-order mode energy increases, coinciding with corresponding power spectrum density results of forces. Typical 2S, 2P, and C(2S) wakes were observed for various gaps and two representative amplitudes (A/D = 0 and 0.7), and their dominant modes show distinctive differences that lead to different local pressure shapes on the cylinders. It is the combined effects of local mode shape and global mode energy that account for the change in fluid forces for various gaps and two oscillating amplitudes.
Interfacial charge storage mechanisms of composite electrodes based on poly(ortho-phenylenediamine)/carbon nanotubes via advanced electrogravimetry
Authors: Halim El Mahdi , Demir-Cakan Rezan , Perrot Hubert , El Rhazi Mama , Sel Ozlem
Published: March 2022

To reach a deeper understanding of the charge storage mechanisms of electrode materials is one of the challenges toward improving their energy storage performance. Herein, we investigate the interfacial ion exchange of a composite electrode made of carbon nanotube/poly(ortho-phenylenediamine) (CNT/PoPD) in a 1M NaCl aqueous electrolyte via advanced electrogravimetric analyses based on electrochemical quartz crystal microbalance (EQCM). Classical EQCM at different scan rates of the potential revealed the complex electrogravimetric behavior likely due to multi-species participation at different temporal scales. Thereafter, in order to better understand the behavior of each species (ions, counter ions, and co-ions) in the charge compensation mechanism, the electrogravimetric impedance spectroscopy analysis (also called ac-electrogravimetry) was pursued. Ac-electrogravimetry revealed the role of each species where Na+ cations and Cl− anions as well as protons participate in the charge compensation mechanism of the CNT/PoPD composite with different kinetics and proportions. The water molecules with opposite flux direction with the cations are also detected, suggesting their exclusion during cationic species transfer. Having analyzed ac-electrogravimetry responses in depth, the synergistic interaction between the CNT and PoPD is highlighted, revealing the improved accessibility of species to new sites in the composite.
Mask-less nano-structuring of hydrogen terminated diamond using localized field emission scanning probe lithography (FE-SPL)
Authors: Yianni Steve A. , Hofmann Martin , Schenk Alex K. , Reuter Christoph , Rangelow Ivo W. , Pakes Christopher I.
Published: March 2022

Sensing and manipulating a particle's spin promise the development of more energy efficient and ultra-fast devices. Diamond is a promising candidate for spintronics and quantum systems, where nano-structuring of diamond surfaces on nanometer length scales is required. Here, direct-write modification of a diamond surface at sub-50 nm resolution is demonstrated. This is achieved with an atomic force microscope tip used as a spatially localized field emission source or so-called field-emission scanning probe lithography on a sample in ambient conditions, which are rendered conductive only through the surface conductivity of hydrogen-terminated diamond. Mask-less direct structuring of the diamond surface is observed, creating features of depth in the range of 4–8 nm and linewidths of 70–150 nm, as well as the desorption of hydrogen from the surface achieving minimum linewidths of 40 nm. Both the linewidth and depth of etching appear to depend on the energy of emitted electrons and the resulting electron exposure dose. These findings demonstrate the possibility of controllably nano-structuring diamond surfaces with features over micrometer length scales and with sub-50 nm resolution, while held under ambient conditions.
Ultrafast vibrational excitation transfer on resonant antenna lattices revealed by two-dimensional infrared spectroscopy
Authors: Cohn Bar , Sufrin Shmuel , Chuntonov Lev
Published: March 2022

High-quality lattice resonances in arrays of infrared antennas operating in an open-cavity regime form polariton states by means of strong coupling to molecular vibrations. We studied polaritons formed by carbonyl stretching modes of (poly)methyl methacrylate on resonant antenna arrays using femtosecond 2DIR spectroscopy. At a normal incidence of excitation light, doubly degenerate antenna-lattice resonances (ALRs) form two polariton states: a lower polariton and an upper polariton. At an off-normal incidence geometry of 2DIR experiments, the ALR degeneracy is lifted and, consequently, the polariton energies are split. We spectrally resolved and tracked the time-dependent evolution of a cross-peak signal associated with the excitation of reservoir states and the unidirectional transfer of the excess energy to lower polaritons. Bi-exponential decay of the cross-peak suggests that a reversible energy exchange between the bright and dark lower polaritons occurs with a characteristic transfer time of ∼200 fs. The cross-peak signal further decays within ∼800 fs, which is consistent with the relaxation time of the carbonyl stretching vibration and with the dephasing time of the ALR. An increase in the excitation pulse intensity leads to saturation of the cross-peak amplitude and a modification of the relaxation dynamics. Using quantum-mechanical modeling, we found that the kinetic scheme that captures all the experimental observations implies that only the bright lower polariton accepts the energy from the reservoir, suggesting that transfer occurs via a mechanism involving dipole–dipole interaction. An efficient reservoir-to-polariton transfer can play an important role in developing novel room-temperature quantum optical devices in the mid-infrared wavelength region.
Egg-speriments: Stretch, crack, and spin
Authors: Bertho Yann , Darbois Texier Baptiste , Pauchard Ludovic
Published: March 2022

Eggs are key ingredients in our kitchens because of their nutritional values and functional properties such as foaming, emulsifying, and gelling, offering a wide variety of culinary achievements. They also constitute ideal objects to illustrate a myriad of scientific concepts. In this article, we focus on several experiments (egg-speriments) that involve the singular properties of the liquids contained inside the eggshell, especially the egg white. We first characterize the rheology of an egg white in a rotational rheometer for constant and oscillatory shear stresses revealing its shear-thinning behavior and visco-elastic properties. Then, we measure the tendency of the fluid to generate very long filaments when stretched that we relate to the shear modulus of the material. Second, we explore the anisotropic crack pattern that forms on a thin film of egg white after it is spread on a surface and let dried. The anisotropy results from the long protein chains present in the egg white, which are straightened during film deposition. Finally, we consider the “spin test” that permits to distinguish between raw and hard-boiled eggs. To do so, we measure the residual rotation of a spinning raw egg after a short stop, which reflects the continuation of the internal flow. These observations are interpreted in terms of viscous damping of the internal flow consistently with the measurements deduced from rheology.
Hydrogen induced electronic transition within correlated perovskite nickelates with heavy rare-earth composition
Authors: Bian Yi , Li Haiyan , Yan Fengbo , Li Haifan , Wang Jiaou , Zhang Hao , Jiang Yong , Chen Nuofu , Chen Jikun
Published: March 2022

Although the hydrogen induced electronic transition within the perovskite family of rare-earth nickelate (ReNiO3) beyond conventional semiconductors was recently discovered, the existing research stays at ReNiO3 with light rare-earth compositions. To further extend the cognition toward heavier rare-earth, herein we demonstrate hydrogen induced electronic transitions for quasi-single crystalline ReNiO3/LaAlO3 (001) heterostructures, covering a large variety of the rare-earth composition from Nd to Er. The hydrogen induced elevations in the resistivity of ReNiO3 (RH/R0) show an unexpected non-monotonic tendency with the atomic number of the rare-earth composition, e.g., first increases from Nd to Dy and afterwards decreases from Dy to Er. Although ReNiO3 with heavy rare-earth composition (e.g., DyNiO3) exhibits large RH/R0 up to 107, their hydrogen induced electronic transition is not reversible. Further probing the electronic structures via near edge x-ray absorption fine structure analysis clearly demonstrates the respective transition in electronic structures of ReNiO3 from Ni3+ based electron itinerant orbital configurations toward the Ni2+ based electron localized state. Balancing the hydrogen induced transition reversibility with abruption in the variations of material resistivity, we emphasize that ReNiO3 with middle rare-earth compositions (e.g., Sm) are most suitable in catering to the potential applications in correlated electronic devices.
Simple new methods for deducing lifetimes in recoil distance Doppler-shift measurements
Authors: Petkov P. , Müller-Gatermann C.
Published: March 2022

New approaches for lifetime determination using data from recoil distance Doppler-shift experiments are presented based on the fundamental properties of the functions describing the time evolution of the population of excited nuclear states. To some extent, one of them represents a contraction of the well-known Differential decay-curve method (DDCM) by using the most reliable data point [the maximum of the ni(t) function describing the population of level i in time] and a purely numerical procedure avoiding any fitting of decay curves. The combination with the standard DDCM analysis is promising for improving the reliability and the precision of the results for the lifetimes obtained. The novel part of the approach consists of using a chain of equations at the consecutive maxima of the ni(t) functions, which allow us to precisely determine the ratio of the lifetimes of two consecutive levels and, in the case where one of these lifetimes is known, to determine the unknown one. In addition, a simple integral derivation of the lifetime is presented involving the peak areas measured at different distances, and an application of the first moments (expectation values and centroids in time) of the ni(t) functions for determining lifetimes is also demonstrated to be useful.
Boosting micromachine studies with Stokesian dynamics
Authors: Berdakin Ivan , Marconi V. I. , Banchio Adolfo J.
Published: March 2022

Artificial microswimmers, nano- and microrobots, are essential in many applications from engineering to biology and medicine. We present a Stokesian dynamics study of the dynamical properties and efficiency of one of the simplest artificial swimmers, the three linked spheres swimmer (TLS), extensively shown to be an excellent and model example of a deformable micromachine. Results for two different swimming strokes are compared with an approximate solution based on point force interactions. While this approximation accurately reproduces the solutions for swimmers with long arms and strokes of small amplitude, it fails when the amplitude of the stroke is such that the spheres come close together, a condition where indeed the largest efficiencies are obtained. We find that swimmers with a “square stroke cycle” result more efficient than those with “circular stroke cycle” when the swimmer arms are long compared with the sphere radius, but the differences between the two strokes are smaller when the arms of the swimmers are short. This extended theoretical research of TLS incorporates a much precise description of the swimmer hydrodynamics, demonstrating the relevance of considering the finite size of the constitutive microswimmers spheres. This work expects to trigger future innovative steps contributing to the design of micro- and nanomachines and its applications.
Defect tolerance in halide perovskites: A first-principles perspective
Authors: Zhang Xie , Turiansky Mark E. , Shen Jimmy-Xuan , Van de Walle Chris G.
Published: March 2022

In recent years, the impressive photovoltaic performance of halide perovskites has been commonly attributed to their defect tolerance. This attribution is seemingly intuitive and has been widely promoted in the field, though it has not been rigorously assessed. In this Perspective, we critically discuss the proposition of defect tolerance in halide perovskites based on first-principles calculations. We show that halide perovskites actually do suffer from defect-assisted nonradiative recombination, i.e., they are not defect tolerant. The nonradiative recombination rates in halide perovskites are comparable to or even greater than those in more conventional semiconductors. We note that to obtain accurate defect properties in halide perovskites, the level of theory and computational details are highly important, which was previously not sufficiently recognized. A distinctive feature of halide perovskites is that they can be grown with moderate defect densities using low-cost deposition techniques. But, similar to the case of conventional semiconductors, defect engineering is still key to improving the efficiency of perovskite solar cells.
An investigation of bluff body flow structures in variable velocity flows
Authors: Sarath K. P. , Manu K. V.
Published: March 2022

The present study explores three-dimensional vortex-dynamics past a wall-attached bluff body kept in a variable velocity field with numerical simulations. A trapezoidal pulse of mean velocity, consisting of acceleration phase from rest followed by constant velocity phase and deceleration phase to rest, is imposed at the inlet of the computational domain similar to the experimental study of Das et al. [“Unsteady separation and vortex shedding from a laminar separation bubble over a bluff body,” J. Fluids Struct. 40, 233–245 (2013)]. For a wide range of Reynolds numbers (96≤Reb≤2390), acceleration Reynolds numbers (196≤Rea≤978), and deceleration Reynolds numbers (310≤Red≤1522), different stages of flow evolution are systematically analyzed. The flow evolution starts with the formation of a primary vortex followed by a two-dimensional circular array of spanwise vortex tubes by inflectional shear-layer instability. At a sufficiently high Reynolds number, the shear layer vortices originated from two-dimensional fluctuations deformed by three-dimensional instabilities, giving fragmented streamwise vorticity. In addition, long-wavelength “tongue-like structures” and short-wavelength “rib-like structures” are evident near the top wall and the bluff body, respectively. The streamwise vorticity generation equation indicates that the spanwise vortex tubes initially tilt, resulting in streamwise vorticity, further amplified by the vortex stretching process. The distinct flow features, including mode shape, frequency, and growth rate associated with the shear-layer instability, are identified using the dynamic mode decomposition (DMD) algorithm. Using the maximum growth rate criteria, the DMD technique successfully separates the coherent shear layer modes associated with two-dimensional shear layer instability from the flow field.
Near-wall Lamb vector and its temporal–spatial evolution in the viscous sublayer of wall-bounded flows
Authors: Chen Tao , Liu Tianshu
Published: March 2022

This paper gives the relation between the Lamb vector and fundamental surface quantities in the vicinity of a no-slip flat wall using the Taylor-series expansion solution of the Navier–Stokes equations for incompressible viscous flow. The wall-normal component of the Lamb vector is dominated by the boundary enstrophy at the first order and the boundary enstrophy flux at the second order. The tangential Lamb vector is contributed by the terms related to both the boundary vorticity divergence and the skin friction divergence. Then, the derived relation is validated in the three-dimensional nonorthogonal Hiemenz flow (an attachment line flow) and a single-phase turbulent channel flow simulated using the lattice Boltzmann method. For this Hiemenz flow where the boundary vorticity divergence vanishes, the skin friction divergence-related term dominates the distribution of the near-wall tangential Lamb vector. In the turbulent channel flow, both the skin friction divergence and boundary vorticity divergence-related terms have significant contributions to the streamwise component of the Lamb vector, which are associated with the strong wall-normal velocity events (SWNVEs) in the viscous sublayer. In contrast, the boundary vorticity divergence-related terms have the main contribution to the spanwise component of the Lamb vector. Furthermore, the temporal–spatial evolution of the kinetic energy of the Lamb vector (half of the inner product of the Lamb vector denoted by J) is studied. In the turbulent channel flow, the SWNVEs are the main contributors to the temporal–spatial evolution of J in the viscous sublayer. This evolution is dominated by the viscous dissipation effect due to the gradient of the Lamb vector and the coupling effect between a viscous source term and the Lamb vector. The relations presented in this paper could be useful in understanding the physical mechanisms of the initial formation and evolution of the Lamb vector in the viscous sublayer of wall-bounded turbulence.
Characteristics of a freezing nanosuspension drop in two different schemes
Authors: Miao Yanming , Zhao Yugang , Gao Ming , Yang Liang , Yang Chun
Published: March 2022

Understanding the freezing mechanism of a complex fluid drop is of interest from both fundamental study and application viewpoints. Whereas a water drop is frozen into a peach-like crystal due to the volume expansion upon freezing, the shape of a frozen complex fluid drop is still mysterious. In this work, we investigate the freezing dynamics of a nanosuspension drop in two different schemes, i.e., sessile and deposited. We find that the top of a frozen nanosuspension drop can either be a singular tip or flat plateau depending on the thermal condition onset of icing nucleation. Illustrated using a Hele–Shaw cell experiment, we attribute such intriguing freezing behaviors to the interplay between nanoparticles and two types of ice, i.e., dendritic ice formed in the recalescence stage and planar ice formed in the isothermal stage. Specifically, microcells constructed by dendritic ice lead to the failure of global freezing segregation, which yields the formation of the flat plateau. The fundamental understanding and the ability to control the shape of a frozen complex fluid drop have numerous promising applications in additive manufacturing, microelectronic systems, and others.
Solidification of a hollow sessile droplet under forced convection
Authors: Vu Truong V. , Pham Binh D. , Ho Nang X. , Vu Hung V.
Published: March 2022

This study presents a front-tracking-based numerical analysis of the forced convection solidification of a sessile droplet on a cooling surface. The droplet, a hollow (or compound) droplet with an encapsulated gas core, undergoes a liquid-to-solid phase change in its shell. This phase change starts from the surface. Meanwhile, the surrounding gas, which is characterized by its Reynolds number Re and temperature, moves toward the droplet parallel to the axis of symmetry. When the temperature of the forced flow is below the solidification value (i.e., cold-forced convection), increasing the strength of the forced flow shortens the solidification process. In contrast, increasing the Re number of a hot-forced convection system prolongs solidification. In other words, an increase in the forced flow temperature causes the entire liquid shell to solidify more slowly. Thinner shells require more time to solidify completely than thicker ones. The forced flow does not influence the formation of an apex at the top of the outer droplet surface. The aforementioned apex results from volume expansion. The effects of other parameters, for example, the capillary number and the morphologies of the droplet and cooling surface, are also determined.
Temperature-dependent infrared dielectric functions and hybrid phonon-polaritons in wurtzite GaN: A spectroscopic ellipsometry and multiscale simulation study
Authors: Fei Tianhao , Cheng Tao , Zhang Lei , Zhang Jingyi , Yang Jia-Yue , Liu Linhua
Published: March 2022

Polar wurtzite GaN can host surface phonon-polaritons (SPHPs) along its bulk surface and achieve sub-diffraction confinement with an ultralow optical loss and has emerged as a relevant technological material for infrared nanophotonics. Yet, few studies have reported on the temperature-dependent infrared dielectric functions, lattice vibration's influence on the hybrid phonon-polaritons, and the underlying physics that are largely unexplored. Herein, we perform the infrared spectroscopic ellipsometry (SE) measurements and multiscale simulations including first-principles and finite-difference time-domain (FDTD) to systematically study the infrared dielectric function at varying temperatures, phonon dynamics, and SPHPs in wurtzite GaN. SE experiments identify the reststrahlen band where the amplitude of ordinary dielectric function reduces significantly by a factor of 3.5 and the propagation length of SPHPs decreases by a factor of 4.18 as temperature increases from 250 to 800 K, suggesting the strong influence of lattice vibration on SPHPs. First-principles calculations confirm that the reststrahlen band for the ordinary dielectric function lies between the transverse and longitudinal E1 phonon modes, while that of extraordinary dielectric function lies between the transverse and longitudinal A1 phonon modes. FDTD simulations observe the localized surface phonon resonances in the nano-porous GaN thin films deposited on the sapphire substrate only for the transverse magnetic wave mode, which is consistent with the observation of extra dip in the measured pp-polarized reflection spectroscopy. This work provides a deep insight into lattice vibration influence on phonon dynamics and SPHPs in wurtzite GaN and helps engineer them in nanophotonic devices toward achieving better performance.
Scaling of rough-wall turbulence in a transitionally rough regime
Authors: Ma Guo-Zhen , Xu Chun-Xiao , Sung Hyung Jin , Huang Wei-Xi
Published: March 2022

In this Letter, we propose a roughness scaling method based on the direct numerical simulation of turbulent channel flow over three-dimensional sinusoidal rough walls in a transitionally rough regime. A new coupling scale Reτ/(k¯+S)n is defined by combining the Reynolds number Reτ and the roughness parameter k¯+S, where k¯+ is the mean roughness height, S is the roughness steepness, and n is the scaling exponent—which depends on the roughness type. The relationships between Reτ, k¯+S, the roughness function, the friction factor, and the peak of the streamwise turbulent velocity fluctuation are explored. This approach provides an effective way for collapsing rough-wall turbulence data with different Reτ and k¯+S.
Particle-in-cell model of a relativistic magnetron system driven by a pulse forming network Marx generator
Authors: Lee Kern , Hong Sunghoon , Lee Woosang
Published: March 2022

A three dimensional particle-in-cell (PIC) model of a relativistic magnetron (RM) is established using CST Studio Suite. As we adopted a novel technique to imitate pulse forming action of pulser, simulation domain is now fully extended to include a pulser, a transmission line, and a magnetron tube. This feature enables the model to describe a dynamic power coupling process between the pulser and RM in a self-consistent manner. It is demonstrated that model accuracy is strongly dependent on user-defined parameters for an explosive electron emission model. Particularly, emission rise time for space charge formation influences significantly on an initial mode competition phase. Compared to a previous excitation method using a step voltage pulse, the new model gives more reliable results as the intrinsic impedance of the pulser is now considered. Our model is able to estimate the major RM characteristics over a wide range of an external magnetic field. As a result of dynamic power coupling, the RM impedance, the gap voltage, the excitation frequency, and the output power tend to increase at a higher external magnetic field condition. It is suitable to adopt a proposed modeling technique for the virtual assemble and simulation of the system. Hence, it will suggest a practical way to implement and verify complicated structures or innovative designs that could not be solved by existing PIC codes.
Negatively bias driven enhancement in piezo response for self-powered biomedical and facial expression sensor
Authors: Babu Anand , Gupta Varun , Mandal Dipankar
Published: March 2022

Negatively poled nylon-11 nanofibers with enhanced piezoresponse were prepared using negative bias polarity in the electrospinning setup, thereby achieving a piezoelectric charge coefficient d33 of ∼27 pm/V; this was three times higher than their positively poled counterpart. Polarized Fourier transform infrared spectroscopy indicated that the use of a negative bias increased the degree of molecular dipole alignment and crystallinity content, compared to using a positive bias. In order to assess the piezoelectric performance of these two types of polarized nanofibers, piezoelectric nanogenerators (PNGs) were fabricated. It was observed that the PNG based on negatively biased nanofibers exhibited mechanosensitivity 11 times higher than the PNG based on positively biased nanofibers. As a result, excellent bio-sensing capabilities of negatively poled nylon-11 nanofibers enable tracking of physiological events such as arterial pulse, carotid pulse, and various facial movements for a next generation health care system.
Efficacy of dietary quercetin supplementation with high-energy diet model in broilers: implications on zootechnical parameters, serum biochemistry, antioxidant status, patho-morphology and gene expression studies
Authors: Parmar Abhishek B. , Patel Vipul R. , Patel Jignesh M. , Ramani Umed V. , Desai Dhruv N.
Published: March 2022

Context Currently, fat supplementation is one of the commonest strategies in poultry production for early economic return. However, it might cause various unidentified metabolic alterations in chickens. Flavonoid compound quercetin has potential to modulate oxidative stress and lipid metabolism. Aim The study was designed to evaluate the effect of dietary quercetin supplementation in broilers challenged with high-energy diet (HED). Methods In total, 192 days old Vencobb-400 broiler chicks were randomly allocated to four dietary treatments with four replicates (12 birds/replicate) per treatment. Four treatments included basal diet without any supplementation (T1), basal diet + quercetin (1 g/kg; T2), HED supplemented with vegetable oil [34 g/kg (2–3 weeks), 35 g/kg (4–6 weeks); T3], HED supplemented with vegetable oil [34 g/kg (2–3 weeks), 35 g/kg (4–6 weeks)] + quercetin (1 g/kg; T4) for the age of 2–3 (starter) and 4–6 (finisher) weeks. Key results Improvement was observed in the growth performance and feed conversion ratio in broilers with the dietary treatments (P ≤ 0.05). HED-supplemented group showed increased levels of metabolic stress, which was explained by the elevated concentrations of cortisol and malondialdehyde, and reduced serum/liver superoxide dismutase and glutathione peroxidase activity. Moreover, lipotoxicity was found due to the accumulation of fat, and lipid peroxidation caused various injuries to the vital organs such as liver and kidney, which were manifested by histopathological findings, and also upregulated the hepatic inflammatory interleukin (IL)-1β, IL-6, and tumour necrosis factor-α mRNA expression in the HED group. HED in combination with quercetin attenuates the altered serum metabolic markers, lipid peroxidation with subsequent rising in endogenous enzyme activity. In addition, it exhibited lipolytic action by lysis of accumulated fat and ameliorated the pathomorphic alteration in vital organs and downregulation of hepatic IL-1, IL-6 and TNF-α mRNA expression. Conclusions High dietary energy exhibits metabolic alteration and injuries to the vital organs. It is concluded that quercetin has potential to protect against the adverse effects induced by consumption of high-energy diet in broilers. Implications The supplementation of quercetin as an antioxidant seems to be beneficial for poultry production as an herbal feed additive for better performance, production, and health status.
Artificial nesting hollows for the conservation of Carnaby’s cockatoo Calyptorhynchus latirostris: definitely not a case of erect and forget
Authors: Saunders Denis A. , Dawson Rick , Mawson Peter R.
Published: March 2022

Context Loss of nest hollows in eucalypt woodlands is a major cause of decline for a range of Australian native birds including Carnaby’s cockatoo Calyptorhynchus latirostris, resulting in fewer nest sites for this species. Provision of artificial nesting hollows for Carnaby’s cockatoo is a recent part of approved environmental offsets under Western Australian and Australian government environment approvals processes. Aims We examined the continuing utility of natural and artificial nest hollows over time at Coomallo Creek, WA. Methods Data collected included the location of natural hollows, and their rates of utility and decay. We also installed artificial hollows and measured their use over time, as well as costs associated with their installation and maintenance. Key results Both nest types require repairs on average every 3–4 years. Repairs extend the working life of natural nest hollows and ensure that any artificial nest hollows established for conservation management purposes should continue to fulfil their purpose. Our results demonstrate the importance of regular maintenance to ensure hollows remain available for breeding cockatoos. Conclusions Artificial nest hollows provide a short-term solution to a larger problem of loss of native woodlands, but will only serve that purpose if current and future artificial nest hollows are monitored and repaired on a regular basis, and that adequate funds are provided to ensure that those nest hollows remain serviceable. Implications Provision and maintenance of large numbers of artificial hollows in association with restoration/replanting of woodlands in breeding areas is the only long-term solution to loss of breeding habitat.
SCC behaviour of laser and hybrid laser welded stainless steel weld joints
Authors: Ragavendran M. , Toppo Anita , Vasudevan M.
Published: March 2022

In this study, stress corrosion cracking (SCC) resistance was evaluated for type 316LN stainless steel weld joints fabricated by advanced welding techniques such as Laser, Hybrid Laser – Tungsten inert gas (HLT) and Hybrid Laser – Metal inert gas (HLM) welding. 316 LN stainless steel base metal exhibited significantly better resistance to SCC. The solidification mode, secondary dendritic arm spacing (SDAS) and tensile residual stress distribution in the weld metal was found to strongly influence SCC resistance of 316LN stainless steel weld joints. The weld joint processed by HLM process exhibited the highest time to failure during SCC testing and hence better SCC resistance due to primary ferritic mode of solidification, finer SDAS and lower width of tensile residual stress distribution.
Interferometric sensing of a commercial geophone
Authors: Cooper S J , Collins C J , Prokhorov L , Warner J , Hoyland D , Mow-Lowry C M
Published: March 2022

We present a modified commercial L-4C geophone with interferometric readout that demonstrates a resolution 60 times lower than the included coil-magnet readout at low frequencies. The intended application for the modified sensor is in vibration isolation platforms that require improved performance at frequencies lower than 1 Hz. To illustrate it’s application a controls- and noise-model of an Advanced LIGO ‘HAM-ISI’ vibration isolation system was developed, and shows that our sensor can reduce the residual motion of the platforms by a factor of 70 at 0.1 Hz.