Minimum Radius Research Articles

Room-temperature fabrication of flexible oxide TFTs by co-sputtering of IGZO and ITO

Amorphous oxide semiconductors, especially indium gallium zinc oxide (IGZO), have been widely studied and obtained significant progress in flexible thin-film transistors (TFTs) due to the high carrier mobility and low deposition temperature. However, a further annealing step is generally required to activate electrical properties and improve the device performance, which limited their applications in flexible electronics. In this study, we achieved flexible TFTs and arrays using co-sputtered IGZO and indium tin oxide (ITO) as channels deposited at room temperature without post-annealing. It was found that better transistor switching properties could be effectively achieved by regulating the sputtering power of ITO in the co-sputtered deposition. The device performance is comparable to that of the conventional oxide TFTs with high annealing temperatures (⩾300 °C), exhibiting a high saturation mobility (μ sat) of 15.3 cm2 V−1s−1, a small subthreshold swing (SS) of 0.21 V dec−1, and a very high on–off ratio (I on/off) of 1011. In addition, a 12 × 12 flexible TFT array was achieved with uniform performance owing to the low-temperature processing advantage of this technique. The flexible TFTs exhibited robust mechanical flexibility with a minimum bending radius of 5 mm and bending cycles up to 1000. Furthermore, an inverter based on co-sputtered IGZO and ITO was demonstrated with the maximum gain of 22. All these achievements based on the proposed TFTs without post-annealing process are expected to promote the applications in advanced flexible displays and large-area integrated circuits.

Massive parametric study for prospective design space of a compact tokamak fusion reactor

Using a novel computational algorithm that integrates tokamak systems analysis with neutron transport calculations, the minimum major radius (R0) and resulting maximum magnetic field at the plasma center (BT) can be determined uniquely for a given plasma performance. Plasma performance was varied extensively using a supercomputer (KAIROS) and scanning over a wide range of physics, technology, and system parameters to derive the optimal design space for a compact tokamak fusion reactor. Given the design goals of fusion gain Q > 20.0, net electric power > 100 MW, neutron wall loading < 2.0 MW/m2, indicator of divertor power handling PSOL/R0 < 25 MW/m, direct capital cost < $4.0 billion, and steady-state operation, a prospective design space was determined depending on the levels of physics and technology. Advanced engineering features, such as maximum allowable magnetic field at the toroidal field coil (Bmax = 23 T), were implemented by adopting high-temperature superconducting magnet technology, using an advanced shield material such as tungsten carbide (WC), and a plug-bucked magnet support structure. It was found that by exceeding the energy confinement scaling laws of IPB98y2, a design space of R0 < 4.0 m could be accessed under the following conditions for a conventional tokamak: confinement enhancement factor H > 1.7, bootstrap current fraction fBS > 0.55, magnetic field at the magnetic axis BT > 4.0 T, fusion power Pfusion > 600 MW, and thermodynamic efficiency ηth > 0.33. For a spherical tokamak, these conditions were H > 1.3, fBS > 0.6, BT 〈 6.0 T, and Pfusion 〉 500 MW. Sensitivity studies on the energy confinement scaling laws showed that stricter conditions on the physics parameters were required with the ITPA20 scaling law, whereas the conditions were mitigated with the β-independent scaling law.

Disproof of a conjecture on the minimum spectral radius and the domination number

Let Gn,γ be the set of all connected graphs on n vertices with domination number γ. A graph is called a minimizer graph if it attains the minimum spectral radius among Gn,γ. Very recently, Liu, Li and Xie (2023) [17] proved that the minimizer graph over all graphs in Gn,γ must be a tree. Moreover, they determined the minimizer graph among Gn,⌊n2⌋ for even n, and posed the conjecture on the minimizer graph among Gn,⌊n2⌋ for odd n. In this paper, we disprove the conjecture and completely determine the unique minimizer graph among Gn,⌊n2⌋ for odd n.

Review of calibration strategies for discrete element model in quasi-static elastic deformation

This study first reviewed theories of the mechanical response of structures under loading, and the discrete element method provides a route for studying mechanical response including elastic deformation and structure failure. However, the direct acquisition of the microscopic parameters from the governing equations of the discrete element method via experiments encounters challenges. One possible strategy to obtain these microscopic parameters is parameter calibration that are widely used by researchers. Secondly, the governing equations and failure criterion of the discrete element method are summarized, and the microscopic parameters that would be calibrated are pinpointed. Next, the principles of classical calibration methods of discrete element method are explicated in detail, alongside the validation and discussion of their properties. Lastly, this study examined the applicability of calibrated parameters and points out that the size ratio, porosity, maximum radius, and minimum radius of particles should be identical in both the geometric calibration model and that for applications.

Corner flow effect on the relative permeability of two-phase flow in nano-confined porous media

Relative permeability is a critical factor clarifying the multiphase flow behavior in nano-porous media. However, most studies have focus on the circle flow, neglecting the corner flow effect. Therefore, in this work, a comprehensive relative permeability model considering the corner flow effect is proposed. We integrated the corner flow with the immiscible flow model and the confined liquid-gas phase equilibrium with the near-miscible flow model. Then it was validated against the experimental measured data, indicating the proposed model can well describe the two-phase flow in the confined space. Subsequently, sensitivity analysis of corner number, fractal dimension, minimum radius, and viscosity ratio were conducted. Results show that the corner flow effect is noticeable when corner number is less than 8. Under the optimal pore radius of 2 × 10−5 m, the gas relative permeability increases from 0.4909 to 0.9274 with corner number raising from 4 to 10. Under critical oil phase saturation of 0.175, increase of fraction dimension, minimum radius, and viscosity ratio leads to the significant decrease of oil relative permeability and increase of gas relative permeability. In addition, nano-confinement effect and CO2 injection will reduce the interfacial tension and increase the near-miscible relative permeability. When CO2 injection increase to 100% under oil saturation of 0.4084, the increment of oil relative permeability is nearly 67.2%. Interfacial intension-based interpolation method indicates that the confined fluid is more likely to be miscible than the bulk fluid. This relative permeability model provides deeper understandings of two-phase flow in the nano-porous media, which is benefit for the better development of unconventional reservoirs.

Isentropic Swirling Flow Through Supersonic Nozzles - Part I (free Vortex Flow)

An analytical model has been developed and an approximate solution for the free vortex swirling supersonic flow through nozzles. Earlier work by Mager, is potential flow based. In the present model swirl number has been redefined to confine the flow properties within the valid range. Flow properties are always determined by the total conditions (P0 and a0), nozzle profile and swirl intensity as in the case of one-dimensional flow. Integral form of the continuity equation has been used in order to satisfy the boundary conditions, since radial velocity component is ignored. For free vortex case, it has been shown that there exists a minimum radius along the length of the nozzle at which the density is zero and flow seems to be void causing reasonable blockage to the flow at throat. In defining the non-dimensional swirl number (β), axial velocity at each section was employed for non-dimensionalization as compared to Mager’s definition of using a global constant to find swirl number (α). The variations of performance parameters of the nozzle such as co-efficient of discharge (Cd) thrust efficiency (ηs) and impulse efficiency (ηI) and flow field parameters such as density, pressure, velocity etc. are presented as a function of swirl numbers (α, β) and compared with the available experimental data. The swirl numbers (α, β) are also correlated.

Multiple designs with broad applicability for enhancing birefringence in low-loss terahertz HC-ARF

The use of hollow-core anti-resonant fiber (HC-ARF) as a transmission medium for the terahertz (THz) frequency range is attracting increasing attention from researchers. This paper introduces a low-loss, high birefringence anti-resonant fiber. The proposed structure achieves a maximum birefringence of 2.72 × 10−3 around 1 THz and maintains a birefringence above the 10−3 level over a wide frequency band (0.7∼1.12 THz). It has a minimum loss of 0.2 dB/m and a minimum bend radius of 0.3 m, and the paper validates that this structure has good manufacturing error tolerance. Furthermore, three methods for introducing high birefringence into low-loss ARFs are proposed and three structures are selected for verification. These findings contribute to the development of more efficient and reliable THz transmission systems.

The minimal radius of Galerkin information for the problem of numerical differentiation

The problem of numerical differentiation for periodic functions with finite smoothness is investigated. For multivariate functions, different variants of the truncation method are constructed and their approximation properties are obtained. Based on these results, sharp bounds (in the power scale) of the minimal radius of Galerkin information for the problem under study are found.

A New Insect-Scale Piezoelectric Robot With Asymmetric Structure

To realize the switching of the multiple locomotion modes, a new insect-scale piezoelectric robot with asymmetric structure is proposed, fabricated, and tested. The robot prototype has a weight of 32.8 g and size of 55 mm×50 mm×20 mm. Driven by two pieces of piezoelectric ceramics, working at six vibration modes, the piezoelectric robot can realize two kinds of linear motion and four kinds of circular motion by contact friction. Performance assessments show that the robot has a maximum velocity of 155 mm/s and a minimum motion radius of 45 mm. In addition, the robot can move at a speed up to 97 mm/s (100 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-p</sub> ) with integrated drive device (45.7 g). The insect-scale piezoelectric robot has simple structure, but has multiple motion modes, large speed range, good output characteristics and fast response time, which provides a new idea for the design and driving of micro robot.

Quantitative characterization of critical reservoir physical properties of tight oil charging in the third member of the Shahejie Formation in the Gaobei Slope of Nanpu Sag, Bohai Bay Basin

Unconventional petroleum occupies an important position in the world energy structure. Tight oil is an important field of unconventional oil and gas exploration and development, and the physical property condition of a tight oil reservoir is an important determinant of its commercial production. The application of different geological and engineering strategies to quantitative characterization of the aspect of hydrocarbon charge vis-à-vis reservoir physical properties is critical and essential to thoroughly understand the formation and accumulation mechanism and help in achieving the optimum producibility of tight oil resources. This study focuses on the tight oil of the third member of the Shahejie Formation (Es3) region in the Gaobei Slope of the Nanpu Sag. The upper and lower physical limits of charging were quantitatively deduced and explained characterized by a combination of geological analysis, analytical testing, and numerical simulation of force balance; the formation mechanism of the tight oil reservoir is primarily constrained by its permeability. The inversion phenomenon of oil and water in the tight oil Es3 reservoir occurs at a burial depth of 3900 m. The pore type of the reservoir is mainly primary in nature, with a positive correlation between the porosity and the permeability. The upper limit of tight oil charging is quantitatively characterized by porosity approximately equal to 10%, the corresponding permeability being 1 × 10−3 μm2. When the reservoir's physical properties exceed the upper limit of tight oil charging, the reservoir mainly develops a water layer. This is mainly caused by the boundary effect of tight reservoirs, where the pore throat radius corresponding to the critical physical property is equivalent to the boundary layer thickness of oil in the reservoir pore, making it difficult for boundary fluids to flow in the pore space at this time. On the other hand, based on comprehensive analysis of the minimum flow hole roar radius, the irreducible water saturation, and drilling result statistical methods, the lower limit of the tight oil charging in Es3 reservoir is characterized quantitatively by the porosity of about 2%–4%, wherein the pore throat radius is approximately equal to 0.04 μm. The lower limit of tight oil charging varies from one place to another, mainly attributed to factors such as interfacial tension, hydrocarbon generation dynamics, kerogen type, and basin temperature. The charging process of tight oil complies with the principle of force balance, whereas the pressure exerted the generated hydrocarbon is counterbalanced by the capillary force of the pore space.

Dynamics of a Laser-Induced Cavitation Bubble near a Cone: An Experimental and Numerical Study

A bubble’s motion is strongly influenced by the boundaries of tip structures, which correspond to the bubble’s size. In the present study, the dynamic behaviors of a cavitation bubble near a conical tip structure are investigated experimentally and numerically. A series of experiments were carried out to analyze the bubble’s shape at different relative cone distances quantitatively. Due to the crucial influence of the phase change on the cavitation bubble’s dynamics over multiple cycles, a compressible two-phase model taking into account the phase change and heat transfer implemented in OpenFOAM was employed in this study. The simulation results regarding the bubble’s radius and shape were validated with corresponding experimental photos, and a good agreement was achieved. The bubble’s primary physical features (e.g., shock waves, liquid jets, high-pressure zones) were well reproduced, which helps us understand the underlying mechanisms. Meanwhile, the latent damage was quantified by the pressure load at the cone apex. The effects of the relative distance γ and cone angle θ on the maximum temperature, pressure peaks, and bubble position are discussed and summarized. The results show that the pressure peaks during the bubble’s collapse increase with the decrease in γ. For a larger γ, the first minimum bubble radius increases while the maximum temperature decreases as θ increases; the pressure peak at the second final collapse is first less than that at the first final collapse and then much greater than that one. For a smaller γ, the pressure peaks at different θ values do not vary very much.

On the Improvement of the Heuristic Algorithm for Packing Circles into a Circle of Minimum Radius

The article is devoted to investigation of a heuristic algorithm for solving the competitive problem "Circles Dense packing into a circle of minimum radius" and development of its improved version using Shor's r-algorithm with step dichotomy. The heuristic algorithm was developed by Bohdan Zadorozhnyi, a third-year student of Uzhhorod National University. The program implemented on its basis took second place in the competition and used less time than the maximum time, which, according to the competition, was allocated for a one-time launch of the program for 50 competitive tasks. The article describes the research results of how the Shor r-algorithm can be used to improve efficiency of the heuristic algorithm. The algorithm for improving the heuristic solution is implemented according to the following scheme. We start from the best arrangement of circles found by the heuristic algorithm. Then, we perform the following four stages of the algorithm: Stage 1. We set a rather large value of the initial step (we determine it depending on the input data or simply choose it as a large step); Stage 2. We run the r-algorithm from the starting point and find the local minimum of the corresponding nonlinear programming problem; Stage 3. If the local minimum found guarantees a smaller radius of the outer circle, then the local minimum point becomes the starting point; the local minimum found does not guarantee a smaller radius of the outer circle, then the size of the step h is reduced by half. Stage 4. If the step value is greater than the specified value, then we proceed to Stage 2. Otherwise, we finish work of the algorithm with solution improvement. Python 3.9.5 programming language and NumPy 1.24.2 library were used for software implementation of both algorithms. For 50 competitive tests and different number of iterations of the heuristic algorithm (10, 20, 30, 40 and 50 iterations), the analysis of the obtained results was conducted according to three parameters: the number of points obtained, program execution time and the number of exchanges of circles in one iteration of the heuristic algorithm. For most of the competitive tests, the refined algorithm allows you to get better results in points, in particular, in most cases the improvement is up to 2 points, and in some cases – from 3 to 6 points. The biggest improvements (6 points) are seen in tests, where the circles have the same or close radii. Here, the heuristic algorithm works not so effectively, therefore, for such tests, due to the algorithm with refinement, it is possible to significantly improve the results of competitive tasks in terms of points. Keywords: circle packing, heuristics, r-algorithm, Python 3.9.5, NumPy 1.24.2.

Probabilistic analysis of the longitudinal performance of shield tunnels based on a simplified finite element procedure and its surrogate model considering spatial soil variability

This paper presents a probabilistic analysis framework for the longitudinal performance of a shield tunnel considering spatial soil variability. Within this framework, a finite element procedure of a Timoshenko beam-based soil-shield tunnel interaction model is developed as the deterministic model to capture tunnel responses. Winkler elastic supports with varying stiffnesses configured in the analytical model are utilized to account for the spatial variation in the subgrade stiffness along the longitudinal direction of the tunnel. The random field discretized by the Karhunen-Loève expansion technique is introduced to simulate the spatial variation in the subgrade stiffness. The Kriging metamodel-based Monte Carlo simulation method is employed to perform probabilistic analysis to improve the computational efficiency. Based on this framework, the probabilistic analysis for surcharge load-induced longitudinal responses of a shield tunnel is performed considering the variability of the ground stiffness under the tunnel. The probabilistic analysis results show that the spatial soil variability leads to a nonnegligible impact on the longitudinal performance of the shield tunnel. As the variability of the subgrade stiffness increases, the failure probability of the shield tunnel rises significantly. The coefficient of variation of the subgrade stiffness has a remarkable influence on the probabilistic characteristics of the tunnel longitudinal performance, while the influence of the autocorrelation distance is slight. The maximal settlement and minimum curvature radius of the tunnel can provide a more conservative evaluation of the tunnel performance than the joint deformations.

Design of single-mode single-circularly polarized chiral anti-resonant fiber for the communication band

We propose a design of anti-resonant fiber (ARF) involving the introduction of chiral material into the inner regions of six germanium-doped silica glass cladding tubes, which can support the operation of single-mode single left-handed circular polarization in the communication band from 1.540 to 1.605 µm. In particular, the loss reaches a minimum value of 0.009 dB m−1 at 1.550 µm. The sign of the chiral parameter can control the handedness of polarization in the operation of single-mode single-circular polarization. In addition, the ARF possesses a good bending resistance performance. The minimum bending radius of the ARF is 10 to maintain the single-mode single left-handed circular polarization for 1.550 µm. We believe the novel ARF can find applications in optical communication, polarization imaging and chiral sensing.

Fluctuating hydrodynamics and the Rayleigh–Plateau instability

The Rayleigh-Plateau instability occurs when surface tension makes a fluid column become unstable to small perturbations. At nanometer scales, thermal fluctuations are comparable to interfacial energy densities. Consequently, at these scales, thermal fluctuations play a significant role in the dynamics of the instability. These microscopic effects have previously been investigated numerically using particle-based simulations, such as molecular dynamics (MD), and stochastic partial differential equation-based hydrodynamic models, such as stochastic lubrication theory. In this paper, we present an incompressible fluctuating hydrodynamics model with a diffuse-interface formulation for binary fluid mixtures designed for the study of stochastic interfacial phenomena. An efficient numerical algorithm is outlined and validated in numerical simulations of stable equilibrium interfaces. We present results from simulations of the Rayleigh-Plateau instability for long cylinders pinching into droplets for Ohnesorge numbers of Oh = 0.5 and 5.0. Both stochastic and perturbed deterministic simulations are analyzed and ensemble results show significant differences in the temporal evolution of the minimum radius near pinching. Short cylinders, with lengths less than their circumference, were also investigated. As previously observed in MD simulations, we find that thermal fluctuations cause these to pinch in cases where a perturbed cylinder would be stable deterministically. Finally, we show that the fluctuating hydrodynamics model can be applied to study a broader range of surface tension-driven phenomena.

T Tauri stars in the SuperWASP and NSVS surveys II. Spectral modelling

ABSTRACT We present results from long-term spectroscopic monitoring of 21 T-Tauri stars located in the Taurus–Auriga star-forming region (SFR). We combine medium and high-dispersion Echelle spectroscopy obtained at the Stará Lesná, Skalnaté Pleso (both in Slovakia), and Tautenburg (Germany) observatories with low-resolution flux-calibrated spectra from Asiago (Italy) observatory all taken between 2015 and 2018. We extend the coverage by additional medium-resolution spectra from Stará Lesná obtained in 2022. In the previous paper, we measured photometric periods of these targets in a range of 0.7–3.1 d, which could be due to the rotation of a spotted surface or binarity. Here, we use the broadening-function technique to determine the radial and projected rotational velocities to reveal any close binary companion. Our analysis concludes that no such companion is present with an orbital period equal to the photometric period. We focus our analysis primarily on determining atmospheric parameters such as surface gravity log g, effective temperature Teff, and metallicity [Fe/H]. Additionally, we measure the equivalent width of H α, Li i, and interstellar Na i lines. We also investigate the effect of possible reddening on individual targets and construct the HR diagram of our sample. Using pre-main-sequence evolutionary models, we determine the age of our targets. This analysis hints at ages younger than 50 Myr with mean age 5 ± 3 Myr, masses between 0.75 and 2.10 M⊙, and minimum radii in the range 0.60–3.17 R⊙. Altogether, the results are consistent with expected young stars with larger radii than those of main-sequence stars.

Dynamical Stability of Polar Circumbinary Orbits and Planet Formation in the Planetary Disk of 99 Herculis

A possible polar-ring debris disk, the dynamics of which can be described by the outer hierarchical restricted three-body problem, has been detected in 99 Herculis. An empirical formula for the minimum radius beyond which test particles in polar orbits can keep stable within 107 binary periods is provided through numerical fitting, applying to the binary eccentricity and the mass ratio of the binary , where λ = m 0/m 1 (m 0 and m 1 represent the masses of the two binary stars). The polar planetary disk has the lowest statistical accretion efficiency and a moderate impact frequency of collisions among planetesimals (with radii of 1–10 km) compared to those in a circumbinary coplanar disk and a standard disk around the single host star. The collision timescale in the circumbinary disk (both polar and coplanar configurations) is longer than 107 yr, exceeding the dissipation timescale of the gas disk. Stochastic simulations show that successive collisions cannot make planetesimals grow, which may explain the formation of the debris disk observed in 99 Herculis.

Dynamics of a surfactant-laden viscoelastic thread in the presence of surface viscosity

As is known, the presence of surfactants can profoundly influence the dynamics of Newtonian viscous threads. Also, it is known that non-Newtonian viscoelastic threads behave differently from Newtonian ones, particularly in the nonlinear regime. A naturally arising question is how surfactants affect the dynamic behaviour of non-Newtonian viscoelastic threads. To gain some insights into it, we build a one-dimensional model for an Oldroyd-B/finitely extensible nonlinear elastic-Peterlin approximation (FENE-P) viscoelastic liquid thread covered with an insoluble surfactant monolayer based on the slender body theory. A parametric study is performed to examine the effects of the dimensionless numbers related to the surfactant, including the initial concentration, the Marangoni number, the surface Péclet number, the shear Boussinesq number and the dilatational Boussinesq number. It is found that the formation of the beads-on-a-string structure can be greatly delayed by the surfactant. At large values of the surface Péclet number, the exponential thinning of the Oldroyd-B viscoelastic thread is little influenced, but the surfactant may lead to the disappearance of secondary droplets. At moderate values of the surface Péclet number, the surfactant induces the formation of secondary droplets. The primary droplets are axially stretched by the Marangoni or surface viscous stresses and evolve into a prolate or a more singular shape eventually. The surfactant can delay the pinch-off of the FENE-P viscoelastic thread to a great extent, but it affects little the decrease in the minimum thread radius prior to pinch-off when the surface Péclet number is large.

Design exploration of additively manufactured chiral auxetic structure using explainable machine learning

A design exploration of hexachiral structures using explainable machine learning (ML) is performed in this work. The hexachiral structures are fabricated using resin via vat photopolymerization (VPP). The ML model is used to build the function that explains the association between Poisson’s ratio and the hexachiral design parameters. The data set for ML model construction is first collected by using the Halton sequence and simulated using the finite element method (FEM). To validate the data set, the results obtained from the FEM simulation are compared with those obtained from the compression test. The Gaussian Process Regression (GPR) models for Poisson’s ratio and porosity are constructed to extract important design insight. A Global Sensitivity Analysis (GSA) and Shapley Additive Explanations (SHAP) are used to analyze the sensitivity of the porosity and Poisson’s ratio to the hexachiral design parameters. GSA result shows that the strut’s thickness is the most decisive parameter that affects the Poisson’s ratio. The application of SHAP also reveals that the relationship between the strut thickness and Poisson’s ratio is nonlinear. Finally, the minimum Poisson’s ratio value is achieved by design with minimum strut thickness, minimum node radius, and maximum strut length.

Study on the effect of bubble number on the collapse of a multi-bubble system near the rigid wall

The mechanism of multi-bubble collapse is one of the key technologies that need to be overcome in the development of large submersibles, which is urgently needed to study and explore. The VOF method is used to study the collapse process of a multi-bubble system near the rigid wall. The bubble collapse process is analyzed under three different bubble numbers and four different initial bubble wall distances. The influence of the number of bubbles and initial bubble wall distance on the bubble collapse process is obtained, and the mechanism of multi-bubble collapsing near the rigid wall is revealed. The results indicate that in a multi-bubble system, as the number of bubbles increases, the duration of bubble collapse increases, the minimum bubble radius decreases, and the maximum central pressure increases. The closer the bubble is to the rigid wall, the longer the duration of bubble collapse, which also lead to fluctuations in the maximum center pressure and maximum interface velocity of a multi-bubble system. The results of this study are expected to provide a theoretical basis and technical support for the design and performance optimization of deep submersible mechanical seals.