bluuebunny/crossref_metadata_2025 huggingface dataset:
C, N, P, S content of the Chlorophyta Chaetomorpha linum (Müller) Kützing in a vast high density mat of a Mediterranean non-tidal lagoon
Authors: Lenzi Mauro , Leporatti-Persiano Marco , Gennaro Paola
Published: September 2020

In a Chaetomorpha linum high density mat extending over 300 hectares, between 2017 and 2019 samples were collected for C, N, P, S tissue content determination, biomass (b) was estimated, sediment samples collected for labile organic matter (LOM) determination, and water chemical-physical variables measured. The latter showed extreme conditions with a wide range of values ​​and with zero oxygen for long periods. N-NO3:SRP atomic ratio showed extreme P-limitation. Tissue macronutrients showed very variable values, highlighting a strong P-limitation and relatively high level of S. With exception of nitrogen, no significant differences were detected for each macronutrient between the months and between the stations, neither was any correlation found between macronutrients and LOM and b data-set. The growth and survival of the mat occurred despite the scarcity of P, which probably reached with very low frequency the surface layer of the mat, the one capable of performing photosynthesis, where it was quickly re-assimilated and utilised.
Use of over-the-scope clips in the colon in clinical practice: results from a German administrative database
Authors: Horenkamp-Sonntag Dirk , Liebentraut Judith , Engel Susanne , Skupnik Christoph , Albers David , Schumacher Brigitte , Koop Herbert
Published: September 2020

Background The efficacy and safety of over-the-scope (OTS) clips in the colon is limited. This study aimed to evaluate OTS clip use in the colon in routine colonoscopy.

Methods Using administrative data from a large health insurance company, patients with OTS clip placement during colonoscopy were identified and analyzed by specific administrative codes. Indication for OTS clipping was analyzed, and follow-up was evaluated for surgical and repeat endoscopic interventions.

Results In 505 patients, indications for OTS clips were iatrogenic perforations (n = 80; Group A), polypectomy (n = 315; Group B), colonic bleeding (n = 51; Group C), and various underlying diseases (n = 59; Group D). In 11 Group A patients (13.8 %), surgical interventions occurred, mostly within 24 hours after clipping (n = 9), predominantly overstitching (n = 8). OTS clipping during polypectomy (Group B) was for complications (e. g. bleeding in 27 %) or was applied prophylactically. Only five patients required early surgery, three of whom had colorectal cancer. In four Group C patients (7.8 %), surgical resections were performed (persistent bleeding n = 1, colorectal cancer n = 2), while six patients underwent early repeat colonoscopy for recurrent bleeding. During further follow-up (days 11–30), 17 patients underwent resection for colonic neoplasms (n = 12) or persistent bleeding (n = 4), but only one case could be directly traced back to local OTS clip complication.

Conclusion Colonic OTS clipping appears safe and effective in selected indications and complications in clinical routine but must be anatomically and technically feasible, avoiding overuse.
Rapid Growth of a Facet Joint Cyst Mimicking an Aggressive Tumor in the Lumbar Spine
Authors: Robins James M. W. , Selvanathan Senthil K. , Ismail Azzam , Derham Chris , Pal Deb
Published: September 2020

A 67-year-old patient with a history of fully treated bowel carcinoma presented with a short history of unilateral lumbosacral radiculopathy. No neurological deficit was found on examination. Magnetic resonance imaging (MRI) demonstrated initially L4/5 foraminal narrowing that was believed to be the cause for the patient’s symptoms; however, a nerve root block led to no improvement in symptoms. MRI was repeated at 5 months and demonstrated a mass causing compression of the S1 nerve. However, the patient declined surgical decompression. MRI at 14 months subsequently showed rapid growth of the lesion suggestive of an aggressive process such as a metastatic lesion or even a nerve sheath tumor such as a Schwannoma. Open biopsy and decompression revealed the lesion to be a facet joint cyst and the patient recovered well and had satisfactory postoperative imaging at 3 months follow-up. There are no reports in the literature of facet joint cysts growing this quickly and thus mimicking other forms of lesion.
An adaptive heuristic clustering algorithm for influence maximization in complex networks
Authors: Yang Ping-Le , Xu Gui-Qiong , Yu Qin , Guo Jia-Wen
Published: September 2020

Influence maximization research in the real world allows us to better understand, accelerate spreading processes for innovations and products, and effectively analyze, predict, and control the spread of diseases, rumors, and computer viruses. In this paper, we first put forward a new path-based node similarity measure, named the dynamic local similarity index, which can be dynamically adjusted to the optimal mode according to network topology characteristics. Compared to the Katz index with high complexity and an LP index with a limited application range, the proposed index achieves an excellent balance between complexity and precision. Second, combining the extended neighborhood coreness with the minimum distance, a novel strategy is presented for selecting initial centers of clusters, which is helpful for speeding up clustering convergence and avoiding local optimum, especially in non-connected networks. Subsequently, we present an adaptive heuristic clustering algorithm, which can find the seed set with maximum collective influence through clustering. The empirical results on four real datasets show the effectiveness and efficiency of the proposed algorithm, which compares favorably to several state-of-the-art algorithms.
Creation and annihilation of point-potentials using Moutard-type transform in spectral variable
Authors: Grinevich P. G. , Novikov R. G.
Published: September 2020

We continue to develop the method for creation and annihilation of contour singularities in the ∂¯-spectral data for the two-dimensional Schrödinger equation at fixed energy. Our method is based on the Moutard-type transforms for generalized analytic functions. In this article, we show that this approach successfully works for point potentials.
Evaluation of core beta effects on pedestal MHD stability in ITER and consequences for energy confinement
Authors: Oosterbeek W. , Weyens T. , Loarte A. , Huijsmans G. T. A. , Artola F. J. , Polevoi A. , Kim S. H.
Published: September 2020

The maximum stable pedestal pressure has been shown to increase with core pressure and, in combination with core transport effects, this can lead to a positive feedback mechanism. However, the effect is shown to saturate for a high β in ASDEX-Upgrade simulations [Wolfrum et al. “Impact of wall materials and seeding gases on the pedestal and on core plasma performance,” Nucl. Mater. Energy 12, 18 (2017)]. In this paper, it is numerically investigated whether this effect appears in ITER plasmas, using ideal MHD numerical codes HELENA and MISHKA for different ITER scenarios, in a range of plasma conditions: two inductive scenarios at 7.5 MA/2.65 T and 15 MA/5.3 T and one steady-state scenario at 10 MA/5.3 T. For all scenarios, reference cases for ITER plasmas were taken as a starting point. No pedestal pressure saturation is found for the inductive scenarios, gradually growing up to the global βN limit, which is determined by the Troyon limit. On the contrary, for the 10 MA/5.3 T steady-state scenario, the maximum stable pedestal pressure does not depend on the total β and it is limited by low-n kink-peeling modes, as opposed to high-n peeling-ballooning modes that limit the maximum attainable pedestal height in the inductive scenarios. This core-edge MHD stability feedback loop has been investigated for two assumptions regarding the scaling of the pedestal width with βp,ped¯, using either a constant pedestal width or when scaling it as ΔψN∝βp,ped¯1/2. A stronger core-edge MHD stability feedback is observed for the varying pedestal width for the inductive plasma scenarios, which is closer to the experimental results from JET [Challis et al. “Improved confinement in JET high plasmas with an ITER-like wall,” Nucl. Fusion 55(5), 053031 (2015)], but not for the steady-state one. Finally, the pressure achieved according to this core-edge feedback stability analysis is compared to the plasma pressure achievable on the basis of the energy confinement IPB98(y,2) scaling for various assumptions regarding the scaling of core plasma confinement with heating power.
The limits of sustained self-excitation and stable periodic pulse trains in the Yamada model with delayed optical feedback
Authors: Ruschel Stefan , Krauskopf Bernd , Broderick Neil G. R.
Published: September 2020

We consider the Yamada model for an excitable or self-pulsating laser with saturable absorber and study the effects of delayed optical self-feedback in the excitable case. More specifically, we are concerned with the generation of stable periodic pulse trains via repeated self-excitation after passage through the delayed feedback loop and their bifurcations. We show that onset and termination of such pulse trains correspond to the simultaneous bifurcation of countably many fold periodic orbits with infinite period in this delay differential equation. We employ numerical continuation and the concept of reappearance of periodic solutions to show that these bifurcations coincide with codimension-two points along families of connecting orbits and fold periodic orbits in a related advanced differential equation. These points include heteroclinic connections between steady states and homoclinic bifurcations with non-hyperbolic equilibria. Tracking these codimension-two points in parameter space reveals the critical parameter values for the existence of periodic pulse trains. We use the recently developed theory of temporal dissipative solitons to infer necessary conditions for the stability of such pulse trains.
Bifurcation analysis of a free boundary model of the atherosclerotic plaque formation associated with the cholesterol ratio
Authors: Hao Wenrui , Zheng Chunyue
Published: September 2020

The low-density lipoprotein (LDL)/high-density lipoprotein (HDL)-cholesterol ratio has been shown to have a high correlation with the cardiovascular risk assessment. Is it possible to quantify the correlation mathematically? In this paper, we develop a bifurcation analysis for a mathematical model of the plaque formation with a free boundary in the early stage of atherosclerosis. This bifurcation analysis, to the ratio of LDL/HDL, is based on explicit formulations of radially symmetric steady-state solutions. By performing the perturbation analysis to these solutions, we establish the existence of bifurcation branches and derive a theoretical condition that a bifurcation occurs for different modes. We also analyze the stability of radially symmetric steady-state solutions and conduct numerical simulations to verify all theoretical results.
Self-organization of multiple anodic double layers in magnetized plasma
Authors: Paul Manash Kumar , Majumder Jayanta , Bose Subhojit
Published: September 2020

We report on the self-organization of multiple double layers (MDLs) and self-organized criticality (SOC) behavior through subsequent layer reduction process around the anode during DC glow discharge in a linear cylindrical vacuum vessel. The present study provides an insight into the characteristic features of self-organized MDLs around the anode itself and the effect of an external magnetic field during its evolution. The MDL formations around the anode initiate through an abrupt jump in the floating potential, ion saturation, and discharge current signals, which suggests an associated sheath—plasma instability of the system. The frequency spectrum of the floating potential exhibits mixed mode oscillations, which later disappears on applying an external magnetic field. The comparative results reveal the complex nature of a simple glow discharge through repeated coupling and decoupling of MDL dynamics during layer reduction process in the presence of an external magnetic field in cusp configuration, while the discharge turns largely oscillatory in the presence of an external magnetic field in mirror configuration. Existence of the SOC behavior in the system is further investigated through nonlinear dynamical analysis of the floating potential fluctuations. The present study on self-organization phenomena in a glow discharge plasma is important for applications regarding utilization or mitigation of self-organization. Self-organized patterns are often formed during plasma interaction with the liquid surface, which play a vital role in diverse applications of plasmas in nanomaterial synthesis and medicine.
Improved fast electron transport through the use of foam guides
Authors: Alraddadi R. A. B. , Robinson A. P. L. , Woolsey N. C.
Published: September 2020

The observation that ultra-intense lasers acting on solid targets results in high absorption is exciting for applications, but the high divergence of the fast electrons carrying this energy remains a key limitation for developing many concepts. We show using three-dimensional simulations how low-density foam filled resistive guide targets lead to fast electron collimation over extended distance. Our analysis shows that long mean free paths of the resistive currents in a foam leads to good collimation. We introduce the use of composite concepts, or hybrid resistive guide target, that couples the advantage of high laser absorption and strong collimation of solid-density guides, with the low-scattering properties and long transport distances of foam-filled guides.
Strain-modulated electrical and optical bandgaps of tetragonal WO3: An HSE06 hybrid functional calculation
Authors: Zhu Feng , Ma Chun-Lan , Gao Bei , Kuai Jia-Jing , Zhang Jia-Yong , Zhang Xiao-Hua
Published: September 2020

The Heyd–Scuseria–Ernzerhof screened hybrid functional is used to investigate the strain-modulated band structure and optical properties of tetragonal WO3. An electronic bandgap of 1.53 eV for the ground state of unstrained WO3 is obtained, which is consistent with the experimental value. Upon in-plane strains of 1.36%, 3.18%, 3.37%, and 4.36% along the directions of lattice vectors a→ and b→, i.e., biaxial strains, as realized by growing WO3 on the (001) surface of LaAlO3, NdGaO3, La0.3Sr0.7Al0.65Ta0.35O3, and SrTiO3, the bandgap decreases down to 1.47 eV, 1.37 eV, 1.36 eV, and 1.30 eV, respectively. The largest change in band structure can induce the downshift of the optical absorption edge, with the optical bandgap decreasing from 2.65 eV to 2.28 eV. Further applying a strain along the direction of lattice vector c→, the bandgap can be additionally tuned very finely. Our research provides a promising tuning method for designing high efficient inorganic photovoltaic materials.
Global gyrokinetic nonlinear simulations of kinetic infernal modes in reversed shear tokamaks
Authors: Ishida Y. , Ishizawa A. , Imadera K. , Kishimoto Y. , Nakamura Y.
Published: September 2020

The nonlinear evolution of electromagnetic instabilities in reversed shear plasmas is investigated by means of global gyrokinetic simulations. It is found that the kinetic infernal mode (KIM), which is a pressure-driven instability with low to intermediate toroidal mode number excited in a region of low magnetic shear, is unstable at high β, while the ion temperature gradient mode is unstable at low β, where β is the ratio of the plasma kinetic pressure to the magnetic pressure. The β threshold of the KIM is much lower than that of the kinetic ballooning mode (KBM) appearing in a normal shear plasma, while both the KIM and KBM are strong at the unfavorable curvature region, and the KIM has the same parity as the KBM. Nonlinear simulations show that the KIM gets saturated by exciting strong zonal flows and fluctuations of low toroidal mode number. The amplitude of the KIM turbulence is similar to that of the KBM turbulence in spite of the fact that the linear growth rate of the KIM is much higher than that of the KBM. This is because the excitation of zonal flows and fluctuations at low toroidal mode number is stronger in the reversed shear plasma than that of the normal shear plasma. On the other hand, the energy flux and particle flux due to the KIM turbulence are about two or three times larger than those by the KBM turbulence.
Flow and stability of a gravity-driven thin film over a locally heated porous wall
Authors: Chand Kumawat Tara , Tiwari Naveen
Published: September 2020

Stability analysis is performed for a gravity-driven thin liquid film flowing down a locally heated porous substrate. Using the lubrication approximation, the governing equations are simplified to derive the evolution equation for the free surface of the liquid film. The Beaver-Joseph condition is employed at the interface of the porous layer and the liquid film. The base profiles are mainly influenced by parameters that appear due to non-uniform heating. Linear stability analysis is performed and reported that both thermocapillary and rivulet instabilities are enhanced with increasing values of the Marangoni number, Biot number, and Beavers–Joseph coefficient and decreasing values of the Darcy number. Dependence of critical Darcy number on the porous layer thickness and the Beavers–Joseph coefficient is presented. It is also shown that the full Darcy model can be replaced with an approximated slip model. The growth rate from nonlinear computations is consistent with the linear stability analysis.
Molecular-scale friction at a water–graphene interface and its relationship with slip behavior
Authors: Zhang Linyang , Wu Keliu , Chen Zhangxin , Li Jing , Yu Xinran , Yang Sheng
Published: September 2020

Understanding molecular-scale friction at a liquid–solid interface in a nanofluidic system is essential, as friction affects slip behavior and flow properties at the nanoscale. In this research, we compute the molecular-scale friction at a water–graphene interface, combined with theoretical analysis and Molecular Dynamics (MD) simulation. A solid–solid friction model is modified, regarding a new method to calculate the work done by the substrate. The reliability of the computations is validated by MD results. It is manifested that liquid–solid friction, solid–solid friction, and viscous friction within liquids have similar mechanisms in terms of energy barriers. Moreover, we analyze the relationship between the slip behavior and the friction process and obtain a theoretical foundation between the slip velocity and the friction force based on a classic molecular kinetic theory. This foundation indicates a hyperbolic-like relation between the friction force and the slip velocity for a single water molecule, which is almost linear under realistic experimental conditions. This foundation provides a new way to determine the boundary condition for water flow between graphene sheets.
Wingtip vortex structure in the near-field of swept-tapered wings
Authors: Skinner S. N. , Green R. B. , Zare-Behtash H.
Published: September 2020

Wingtip vortices are an important phenomenon in fluid dynamics due to their complex and negative impacts. Despite numerous studies, the current understanding of the inner vortex is very limited; thus, a basis for the design of effective wingtip geometry and vortex manipulation is narrow. This work examines the structure of the trailing vortex shed from a swept-tapered wing, analogous to a commercial aircraft topology. Stereoscopic particle imaging velocimetry has been utilized to compare the vortex structure and development through several angles of attack at various downstream stations for a fixed Reynolds number (Re = 1.5 × 106). After correcting for vortex meander through helicity-based spatial localization of the vortex core, relationships between the vortex core velocity/vorticity fields, core shape, and turbulent properties have been examined. Subsequently, the vortex is found to exhibit a layered structure with slow linear rates of dissipation indicative of laminar diffusion mechanisms, despite being a turbulent vortex. The turbulent kinetic energy distribution in the vortex signals that relaminarization of the inner core occurs. Consideration of the streamline curvature around the core, via examination of the local Richardson number, indicated that a laminar core structure had formed within which large-scale turbulent eddies could not contribute to the turbulent diffusion of vorticity away from the core. The normalized circulation within the vortex core has been shown to exhibit self-similar behavior typical of the fully developed axisymmetric vortices.
Bridging inertial and dissipation range statistics in rotating turbulence
Authors: Rathor Shailendra K. , Sharma Manohar Kumar , Ray Samriddhi Sankar , Chakraborty Sagar
Published: September 2020

We investigate the connection between the inertial range and the dissipation range statistics of rotating turbulence through detailed simulations of a helical shell model and a multifractal analysis. In particular, by using the latter, we find an explicit relation between the (anomalous) scaling exponents of equal-time structure functions in the inertial range in terms of the generalized dimensions associated with the energy dissipation rate. This theoretical prediction is validated by detailed simulations of a helical shell model for various strengths of rotation from where the statistics of the dissipation rate and, thus, the generalized dimensions, as well as the inertial range, in particular, the anomalous scaling exponents, are extracted. Our work also underlines a surprisingly good agreement—such as that in the spatial structure of the energy dissipation rates and the decrease in inertial range intermittency with increasing strengths of rotation—between solutions of the Navier–Stokes equation in a rotating frame with those obtained from low-dimensional, dynamical systems such as the shell model, which are not explicitly anisotropic. Finally, we perform direct numerical simulations of the Navier–Stokes equation, with the Coriolis force incorporated, to confirm the robustness of the conclusions drawn from our multifractal and shell model studies.
Interaction of low-level jets with wind turbines: On the basic mechanisms for enhanced performance
Authors: Doosttalab Ali , Siguenza-Alvarado Diego , Pulletikurthi Venkatesh , Jin Yaqing , Bocanegra Evans Humberto , Chamorro Leonardo P. , Castillo Luciano
Published: September 2020

A common, worldwide atmospheric phenomenon known as a low-level jet (LLJ) offers benefits to wind energy production. Despite the fact that this effect may be used to increase the capacity factor of wind farms, the interaction between LLJs and wind power plants is not entirely known. By producing a synthetic LLJ velocity profile under well-controlled laboratory conditions, we show that this phenomenon enhances energy entrainment in the wake of wind turbines. The mechanism is associated with the increased velocity shear around the wind farm canopy height, which leads to higher turbulent mixing and, consequently, more energy flux for inner turbines within wind farms. The new insight from this work offers an opportunity to strategically develop, configure, and operate wind farms by taking into account the particular modulation of LLJs.
Bragg scattering of long waves by an array of floating flexible plates in the presence of multiple submerged trenches
Authors: Kar P. , Sahoo T. , Meylan M. H.
Published: September 2020

Bragg scattering of long gravity waves by an array of floating elastic plates in the presence of a series of rectangular trenches is studied under the assumption of linearized water wave theory and small amplitude structural response. Bragg reflection occurs in the case of an array of multiple floating flexible plates and trenches in isolation or combination, and the number of sub-harmonic peaks between two consecutive peaks is two less than the number of plates/trenches. In the case of long-wave scattering by an array of trenches in the absence of floating plates, wave reflection becomes zero minimum for a certain fixed wavenumber at the end of the first cycle (as referred to 0 < k1h1 < 0.32), irrespective of the even/odd number of trenches. Furthermore, the Bragg resonant reflection pattern of the second cycle is a mirror image of the reflection occurring in the first cycle. Conversely, the symmetric pattern of Bragg reflection exhibited in the case of an array of trenches does not occur for an array of plates in isolation or for plates and trenches in combination. Between consecutive harmonic peaks, the minima/maxima in the wave reflection occur in the case of the even/odd number of trenches/plates in isolation. In contrast, it occurs within the first cycle in the case of trenches and plates in combination. Between consecutive harmonic peaks, maxima/minima of wave reflection coincide for a certain wavenumber, irrespective of the even/odd number of trenches/plates in isolation. In addition, these maxima attained for a certain wavenumber for the even number of trenches/plates are 180° out of phase to that of minima for an odd number of trenches/plates. However, similar phenomena occur within the first cycle of Bragg resonance in the case of trenches and plates in combination. Moreover, the amplitude of oscillation in the wave reflection increases with an increase in plate rigidity. Time-dependent motion due to Bragg scattering by trenches and plates is demonstrated in different cases.
A structural subgrid-scale model for the collision-related statistics of inertial particles in large-eddy simulations of isotropic turbulent flows
Authors: Zhou Zhideng , Wang Shizhao , Yang Xiaolei , Jin Guodong
Published: September 2020

In large-eddy simulations of particle-laden isotropic turbulent flows, the collision of inertial particles is strongly influenced by missing small-scale turbulence. In this paper, we apply the Kinematic Simulation with Approximate Deconvolution (KSAD) model to determine the contribution of small-scale turbulence to the motion of inertial particles and improve the prediction accuracy of the radial distribution function (RDF) and radial relative velocity (RRV), which are closely related to particle collisions. Different values of Stokes numbers (St), which are defined as the ratio of the particle response time to the Kolmogorov time scale, are considered. The KSAD model significantly improves the prediction accuracy of the RRV for all considered St. For the prediction of RDF, good agreement between the KSAD model and direct numerical simulations is only observed for large St, i.e., St ≥ 2.0. To explore the reason for the poor prediction of the KSAD model for small St, we compare the Eulerian statistics of the flow fields and the Lagrangian properties of the particles from different simulations and find the key reason is that the Gaussian turbulence generated in the kinematic simulation model is inadequate in recovering the vortex centrifugal effect of small-scale turbulence on the inertial particle clustering at small St.
Tuning time and energy resolution in time-resolved photoemission spectroscopy with nonlinear crystals
Authors: Gauthier Alexandre , Sobota Jonathan A. , Gauthier Nicolas , Xu Ke-Jun , Pfau Heike , Rotundu Costel R. , Shen Zhi-Xun , Kirchmann Patrick S.
Published: September 2020

Time- and angle-resolved photoemission spectroscopy is a powerful probe of electronic band structures out of equilibrium. Tuning time and energy resolution to suit a particular scientific question has become an increasingly important experimental consideration. Many instruments use cascaded frequency doubling in nonlinear crystals to generate the required ultraviolet probe pulses. We demonstrate how calculations clarify the relationship between laser bandwidth and nonlinear crystal thickness contributing to experimental resolutions and place intrinsic limits on the achievable time-bandwidth product. Experimentally, we tune time and energy resolution by varying the thickness of nonlinear β-BaB2O4 crystals for frequency upconversion, providing a flexible experiment design. We achieve time resolutions of 58–103 fs and corresponding energy resolutions of 55–27 meV. We propose a method to select crystal thickness based on desired experimental resolutions.
Dense gas flow simulations in ultra-tight confinement
Authors: Sheng Qiang , Gibelli Livio , Li Jun , Borg Matthew K. , Zhang Yonghao
Published: September 2020

Modeling dense gas flows inside channels with sections comparable to the diameter of gas molecules is essential in porous medium applications, such as in non-conventional shale reservoir management and nanofluidic separation membranes. In this paper, we perform the first verification study of the Enskog equation by using particle simulation methods based on the same hard-sphere collisions dynamics. Our in-house Event-Driven Molecular Dynamics (EDMD) code and a pseudo-hard-sphere Molecular Dynamics (PHS-MD) solver are used to study force-driven Poiseuille flows in the limit of high gas densities and high confinements. Our results showed (a) very good agreement between EDMD, PHS-MD, and Enskog solutions across density, velocity, and temperature profiles for all the simulation conditions and (b) numerical evidence that deviations exist in the normalized mass flow rate vs Knudsen number curve compared to the standard curve without confinement. While we observe slight deviations in the Enskog density and velocity profiles from the MD when the reduced density is greater than 0.2, this limit is well above practical engineering applications, such as in shale gas. The key advantages of promoting the Enskog equation for upscaling flows in porous media lie in its ability to capture the non-equilibrium physics of tightly confined fluids while being computationally more efficient than fundamental simulation approaches, such as molecular dynamics and derivative solvers.
N-symmetric interaction of N hetons. I. Analysis of the case N = 2
Authors: Sokolovskiy M. A. , Koshel K. V. , Dritschel D. G. , Reinaud J. N.
Published: September 2020

We examine the motion of N symmetric hetons (oppositely signed vertical dipoles) in a two-layer quasi-geostrophic model. We consider the special case of N-fold symmetry in which the original system of 4N ordinary differential equations reduces to just two equations for the so-called “equivalent” heton. We perform a qualitative analysis to classify the possible types of vortex motions for the case N = 2. We identify the regions of the parameter space corresponding to unbounded motion and to different types of bounded, or localized, motions. We focus on the properties of localized, in particular periodic, motion. We identify classes of absolute and relative “choreographies” first introduced by Simó [“New families of solutions to the N-body problems,” in Proceedings of the European 3rd Congress of Mathematics, Progress in Mathematics Vol. 201, edited by C. Casacuberta, R. M. Miró-Roig, J. Verdera, and S. Xambó-Descamps (Birkhäuser, Basel, Barcelona, 2000), pp. 101–115]. We also study the forms of vortex trajectories occurring for unbounded motion, which are of practical interest due to the associated transport of heat and mass over large distances.
Design and optimization of a water jet-based biomimetic antifouling model for marine structures
Authors: Liu Guijie , Jiang Weixiong , Yuan Zichao , Xie Yingchun , Tian Xiaojie , Leng Dingxin , Incecik Atilla , Li Zhixiong
Published: September 2020

Marine structures, such as ship hulls and offshore platforms, are basic elements in marine engineering. Due to the harsh ocean environment, marine structures are prone to adhesion and corrosion by marine biofouling. The biomimetic antifouling technology has been recognized as the most promising solution to marine biofouling, while there is still a long way to go to take this technology outside of research laboratories. In order to develop practical biomimetic antifouling techniques, this work presents a new water jet-based biomimetic antifouling model for marine structures to prevent the enrichment of biofouling. First, a semi-empirical formula is proposed based on the Schlichting self-similar solution to determine the effective width of the water jet. Then, a numerical simulation model is established to investigate the effects of the jet parameters (such as the jet aperture, jet velocity, and jet hole spacing) on the water jet distribution. Subsequently, visualization experiments are carried out to compare and validate the numerical simulation results. Finally, the simulation data are used to train a genetic neural network to predict the effective jet coverage ratio. The optimal parameters of the antifouling model are obtained corresponding to the largest effective jet coverage ratio. The findings of this study deliver a practical biomimetic antifouling technique for marine structures.
Analytical model for predicting maximum spread of droplet impinging on solid surfaces
Authors: Srivastava Tushar , Kondaraju Sasidhar
Published: September 2020

In the present study, we develop a theoretical approach to predict the maximum spread of a liquid droplet on a dry solid surface. By using the dynamics of the gas layer entrapped underneath the droplet during initial stages of spreading, we determine the initial spread velocity of the droplet. The predicted spread velocity is used to model viscous dissipation and spread time of the droplet, post-impact. We also reformulate the surface energy of the droplet at the maximum spread to account for the presence of a rim formed at the periphery of the droplet. Incorporating the renewed terms into an energy conservation equation, the maximum spread of the droplet is predicted. The constructed model is validated with both the in-house experiments and the literature performed for various liquids and surfaces. The study also examines the existing scaling laws available to predict the maximum spread in inertial and viscous regimes and compares them with the model. Results reveal that the proposed model effectively predicts maximum spread values even at a low Weber number, despite variations in wettability values. The scaling laws were found to be inefficient in predicting the maximum spread for water at a low Weber number as they do not account for the effect of the surface wettability.
Anomalous high-infrared reflectance of extruded polyoxymethylene
Authors: Nagai Naoto , Okada Hideki , Amaki Yuko , Okamura Miyuki , Fujii Takuma , Suzuki Takaki , Takayanagi Akihiro , Nakagawa Sumito
Published: September 2020

Polarized infrared (IR) reflectance measurements were performed on polyoxymethylene (POM) prepared by the extrusion method, and an abnormally high reflectance of ∼90% was observed along the extruded direction in the 1000 cm−1–900 cm−1 region. High reflectivity was found in samples made by the conventional injection molding. However, the response of the extrusion sample was higher than that of the injection sample, which can be attributed to the Reststrahlen band. The relative permittivity calculated from the polarized reflection spectrum of the extruded direction shows a notably deep negative region in this high reflectance frequency. Using x rays, by differential scanning calorimetry, and by field emission scanning electron microscopy characterization, the difference in crystallinity and morphology from the extrusion and the injection molding plate was investigated, and the difference in IR optical response was discussed. The conventional IR band assignment of POM was also discussed.
Theoretical foundation of a scheme for the study of dielectrics by analyzing the distortion in fringing field
Authors: Kumar Abhimanyu , Ganguli Souvik
Published: September 2020

This paper presents a scheme for the study of dielectrics. For this purpose, fringing field is employed, which is usually considered an undesired effect. Two non-ideal capacitors are placed one beneath the other, which have a region of interlinking fringing fields. If the fringing fields are canceled out, it is called diminutive physically parallel orientation. This capacitor arrangement is placed in a Wheatstone bridge setup, so whenever a dielectric sample is placed within the main capacitor, then it creates distortion in the interlinking fringing fields. This is canceled out when the circuit is balanced, which happens at an optimum plate separation. Thus, the proposed scheme can be used to study fringing field intensity, sense the movement of a dielectric liquid, measure dielectric properties such as permittivity, study materials and biological substances, etc. This work is expected to find application in industrial sensing. Researchers will also find some interesting ideas to ponder upon.
Photoluminescence intensity change of GaP1−xNx alloys by laser irradiation
Authors: Sultan Md. Zamil , Shiroma Akinori , Yagi Shuhei , Takamiya Kengo , Yaguchi Hiroyuki
Published: September 2020

We report the influence of laser irradiation on photoluminescence (PL) intensity to study the evolution of nonradiative recombination centers in GaP1−xNx alloys. PL mapping measurements confirmed that defects to act as nonradiative recombination centers are permanently generated by laser irradiation, which results in irreversible degradation of the PL intensity. Real-time PL measurements revealed that stronger laser irradiation leads to a larger and faster decrease in the PL intensity with irradiation time. The decay of the PL intensity by laser irradiation is larger and faster for a lower nitrogen concentration, indicating that samples with a lower nitrogen concentration are abound with hidden defects to act as nonradiative recombination centers by laser irradiation. It was demonstrated that PL measurement using high-power density photoexcitation is useful to evaluate the generation or multiplication of irradiation-induced nonradiative defects, which causes the deterioration of optoelectronic devices during operation.
InSbNBi/InSb heterostructures for long wavelength infrared photodetector applications: A 16 band k · p study
Authors: Mal Indranil , Samajdar D. P.
Published: September 2020

The intriguing potential of III-V-N-Bi materials like InSbNBi can lead to pervasive research curiosity in the long wavelength infrared (LWIR) regime. In this article, we have explored numerous prospective possibilities of utilizing InSbNBi for optoelectronic applications using a 16 band k · p Hamiltonian. Considering the lattice-matched condition of InSbNBi with host InSb, we have anticipated the bandgap, spin–orbit coupling splitting energy (ΔSO) and the corresponding operating wavelength of InSb0.9772N0.0028Bi0.02 as 68 meV, 0.824 eV, and around ∼18.23 μm, respectively. At room temperature, a wide range of selective bandgaps and related wavelengths ranging from 160 meV (∼8 μm) to 40 meV (∼30 μm) were obtained for Bi and N concentrations up to 2.5% and 0.35%, respectively. Co-incorporation of N and Bi results in ∼1.5 times reduction in the electron effective mass (0.0091 m0) compared to the host (0.014 m0), which further improves the optical gain of the InSbNBi/InSb quantum well system. The effect of both types of strain (compressive and tensile) on the InSbNBi/InSb system generated due to the deviation from the lattice matched ratio (0.14) of N and Bi offers interesting results. Along with a red shift in optical spectra, compressive strain (∼0.1%) offers a reduction in bandgap, electron effective mass, and enhancement in ΔSO by 44.7 meV, 0.0024 m0, and 12 meV, respectively. On the contrary, tensile strain (∼1.14%) increases the bandgap and the electron effective mass by 26.7 meV and 0.0066 m0, respectively, and reduces ΔSO by 219 meV. Nevertheless, tensile strain beyond 0.25% for a N concentration of 1.3% and fixed Bi concentration (1%) convert the InSbNBi/InSb heterostructure from a type I structure to a type II broken gap structure, which enables the possibility of realizing InSbNBi/InSb material for tunnel junction devices and the intermediate band solar cell along with the LWIR detector.
Numerical characterization of under-expanded cryogenic hydrogen gas jets
Authors: Ren Zhaoxin , Wen Jennifer X.
Published: September 2020

High-resolution direct numerical simulations are conducted for under-expanded cryogenic hydrogen gas jets to characterize the nearfield flow physics. The basic flow features and jet dynamics are analyzed in detail, revealing the existence of four stages during early jet development, namely, (a) initial penetration, (b) establishment of near-nozzle expansion, (c) formation of downstream compression, and (d) wave propagation. Complex acoustic waves are formed around the under-expanded jets. The jet expansion can also lead to conditions for local liquefaction from the pressurized cryogenic hydrogen gas release. A series of simulations are conducted with systematically varied nozzle pressure ratios and systematically changed exit diameters. The acoustic waves around the jets are found to waken with the decrease in the nozzle pressure ratio. The increase in the nozzle pressure ratio is found to accelerate hydrogen dispersion and widen the regions with hydrogen liquefaction potential. The increase in the nozzle exit diameter also widens the region with hydrogen liquefaction potential but slows down the evolution of the flow structures.
A simplified discrete unified gas kinetic scheme for incompressible flow
Authors: Zhong Mingliang , Zou Sen , Pan Dongxin , Zhuo Congshan , Zhong Chengwen
Published: September 2020

The discrete unified gas kinetic scheme (DUGKS) is a new finite volume (FV) scheme for continuum and rarefied flows, which combines the benefits of both the lattice Boltzmann method and UGKS. By the reconstruction of the gas distribution function using particle velocity characteristic lines, the flux contains more detailed information of fluid flow and more concrete physical nature. In this work, a simplified DUGKS is proposed with the reconstruction stage on a whole time step instead of a half time step in the original DUGKS. Using the temporal/spatial integral Boltzmann Bhatnagar–Gross–Krook equation, the auxiliary distribution function with the inclusion of the collision effect is adopted. The macroscopic and mesoscopic fluxes of the cell on the next time step are predicted by the reconstruction of the auxiliary distribution function at interfaces along particle velocity characteristic lines. According to the conservation law, the macroscopic variables of the cell on the next time step can be updated through its flux, which is a moment of the predicted mesoscopic flux at cell interfaces. The equilibrium distribution function on the next time step can also be updated. The gas distribution function is updated by the FV scheme through its predicted mesoscopic flux in a time step. Compared with the original DUGKS, the computational process of the proposed method is more concise because of the omission of half time step flux calculation. The numerical time step is only limited by the Courant–Friedrichs–Lewy condition, and a relatively good stability has been preserved. Several test cases, including the Couette flow, lid-driven cavity flow, laminar flows over a flat plate, a circular cylinder, and an airfoil, and microcavity flow cases, are conducted to validate the present scheme. The observed numerical simulation results reasonably agree with the reported results.
Selective mask formation and gallium nitride template fabrication on patterned sapphire substrates for light-emitting diodes
Authors: Cho Seunghee , Jeong Woo Seop , Ahn Min Joo , Shim Kyu-Yeon , Kang Seong Ho , Byun Dongjin
Published: September 2020

Patterned sapphire substrates are composed of multiple planes, leading to the undesirable polycrystalline growth of gallium nitride (GaN) during template deposition. However, patterned sapphire substrates and templates with good crystalline quality would be useful for increasing the light extraction efficiency in light-emitting diodes. In this study, a silicon dioxide (SiO2) mask was selectively introduced onto the lenses of a patterned sapphire substrate to suppress the growth of polycrystalline GaN. The SiO2 mask prevented the negative influence of the patterned sapphire substrate on GaN growth under various conditions. High-resolution x-ray diffraction analysis revealed that the GaN template grew as a single crystal in the presence of the SiO2 mask. Furthermore, the compressive stress generated in the GaN template was relieved due to the suppression of polycrystalline growth.
On the use of the Lambert function in solving non-Newtonian flow problems
Authors: Pitsillou Rafaella , Georgiou Georgios C. , Huilgol Raja R.
Published: September 2020

We consider unidirectional flows of ideal or regularized Bingham fluids as well as viscoelastic fluids for which analytical solutions can be derived in terms of the Lambert W function. Explicit expressions are derived for the radius of the yielded region in partially yielded circular and axial Couette flows. Analytical solutions are also derived for the velocity and the volumetric flow rate in the plane and axisymmetric Poiseuille flows of a Windhab fluid, which is a combination of the Bingham and Papanastasiou models, and for the shear stress in the plane Couette flow of an exponential Phan–Thien–Tanner fluid. Finally, the Lambert function is used to solve the Poiseuille flow of a power-law fluid and the Newtonian circular Couette flow with wall slip and non-zero slip yield stress by means of a regularized slip equation, which is valid for any value of the wall shear stress.
Enhancing oil recovery using an immiscible slug: Lattice Boltzmann simulation by three-phase pseudopotential model
Authors: Wei Bei , Hou Jian , Sukop Michael C. , Du Qingjun
Published: September 2020

In the oil development process, an immiscible third-phase slug can be injected to the formation temporarily to assist the water flooding, resulting in a three-phase flow underground. In this work, we study slug-assisted water flooding at the pore scale using the three-phase pseudopotential lattice Boltzmann model. We first briefly describe the three-phase pseudopotential model and propose a concise scheme to set the contact angles of the Janus droplet on the solid wall. Then, we simulate the slug-assisted water flooding process in different porous media structures, i.e., a single pore-throat channel, parallel throats, and a heterogeneous porous medium. The simulation results show that oil recovery can be improved effectively with the addition of the third-phase slug. The addition of the third phase results in much more interfacial interaction between different phases, which helps recover trapped oil in pore corners, narrow throats, and the high permeability zone in the porous medium. Moreover, the injection volume, injection timing, contact angle, and viscosity of the third phase influence the oil recovery in different ways. The injected slug can also be trapped in the porous medium, which may result in formation damage. The study explains the enhanced oil recovery mechanisms of slug-assisted water flooding at the pore scale and provides an effective way to design the injection scheme during industrial production.
The effect of a variable coupling parameter on the tunneling properties from graphene to α-T3 model
Authors: Yang C. H. , Wieser R. , Wang L.
Published: September 2020

The transmission properties for square potential barriers have been investigated and compared from graphene to a dice lattice via a variable coupling parameter. There are two limiting cases of pseudospin 1/2 and 1, respectively. The perfect Klein tunneling has been obtained for all parameter conditions. With the increase of the coupling parameter, the tunneling probability increases at oblique incidence. The tunneling shows little dependence on the number of barriers for the dice model. However, the barrier number is an effective factor to tune the transmission feature in graphene. The tunneling peaks can be analyzed from the energy band structure in the expanded periodic potential system and the wave function distribution in the well/barrier regions. The present findings are useful in the development of electronic devices based on quantum transport property with massless pseudospin particles.