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Capillary wicking in a thicker gel blot microfluidics paper has been investigated through a combination of an analytical framework, experiments, and numerical simulations. The primary objectives of this work are to investigate the concentration-dependent wicking process inside thicker microfluidic paper and to estimate the concentration-dependent permeability using both theoretical models and experimental data. An additional goal is to estimate the parameters for saturation-dependent flow modeling in thicker microfluidic paper. To comprehend the wicking phenomenon on thicker gel blot paper, a series of experiments employing aqueous food dye solutions at varying concentrations has been conducted. In order to calculate the temporal wicking length analytically, the Brinkman-extended Darcy equation is implemented. By modifying the permeability expression for a simple rectangular unidirectional fiber cell and pure liquid, the expression of effective permeability for the analytical framework has also been introduced. The concentrations of the food dye solutions appear to have a substantial influence on the wicking phenomenon. Effective permeability and wicking length have been found to follow a decreasing pattern at lower concentrations while both increase at higher values. Intriguingly, employing a microfluidics paper with a relatively greater thickness facilitates the visualization of the fluid front. This phenomenon is identified by the formation of an acute angle at intermediate time instants, while the fluid front angle assumes an angle nearly ∼90° during smaller and higher time instants. In order to evaluate the saturation-dependent capillary pressure and permeability, the empirical correlation of concentration-dependent Brooks and Corey parameters is additionally determined experimentally. These parameters are subsequently employed in numerical simulations to illustrate the saturation-dependent flow field using Richards' equation. Furthermore, numerical simulations based on these estimated model parameters have been conducted, and it turns out that the saturation field has an excellent agreement with the experimental results. The results of the current study can be used to design low-cost paper-based diagnostic devices for usage in healthcare and environmental applications. [ABSTRACT FROM AUTHOR]

The paper referred to in the title, in J. Chem. Phys. 84, 1788 (1986), presented results of computer simulations of non-Markovian barrier crossing dynamics, and compared these results with various theoretical predictions. One comment made here is that the observed limited applicability of the Grote–Hynes theory can be explained by singular perturbation theory. The other comment concerns the importance of a second constant of the motion when the non-Markovian friction has a very long relaxation time. [ABSTRACT FROM AUTHOR]

Paper spray (PS) ionization is a recently developed ion source that has been used to analyze samples in their native environments at ambient pressure without requiring sample preparation or pre-separation. The design of an ion mobility spectrometer (IMS) coupled with PS ionization can help expand IMS applications to on-site detection of complex liquid samples. We report a paper spray ionization ion mobility spectrometer prototype that consists of a PS source and an ion mobility spectrometer optimized using a numerical simulation. The performance of the design was evaluated by measuring 2, 6-di-tert-butylpyridine (2, 6-DtBP). The mobility spectra of the 2, 6-DtBP exhibited a single-product ion peak with reduced mobility calculated at 1.42 cm2/(V s) and a linear response of 0.1-10 μg/ml, with an estimated detection limit of 0.05 μg/ml. The Relative Standard Deviation for 1 μg/ml was 5.7% over 11 measurements. The highest resolving power (47) was measured for 2, 6-DtBP. Based on these preliminary results, the present PSIMS design is expected to become a tool of choice for the rapid analysis of complex liquid samples. [ABSTRACT FROM AUTHOR]

Alternating current (ac) losses in conductor-on-rounded-core (CORC) cables of YBCO high-temperature superconducting (HTS) tapes are a significant challenge in HTS power applications. This study employs two finite element analysis (FEA) models to investigate the contributions from different ac loss components and provide approaches for reducing ac losses in cables. An FEA model based on the T-A formulation treats the cross section of thin superconducting layers as 1D lines and, therefore, only can predict the ac loss generated by the perpendicular magnetic field. In contrast, the model based on H-formulation can be performed on the actual 2D rectangular cross section HTS tapes to provide the total ac losses generated by magnetic fluxes penetrating from both the edges and surfaces of HTS tapes, although this model requires more computing time and memory. The 1D and 2D simulation models were validated by cross comparing the results from both models and by comparing sub-section and full cross section models. Subsequently, two models relate cable design and operational parameters to the surface and edge losses of a two-layer CORC cable by considering the (1) relative contributions of edge and surface losses to the overall ac losses; (2) effect of the current distribution between inner and outer HTS layers on ac losses; (3) impact of the tape alignment on ac losses in each HTS layer; (4) influence of the thickness of HTS layers on ac losses; (5) effect of size and number of inter-tape gaps on ac losses; and (6) contribution frequency on the ac losses. The research results given in this paper are therefore not only valuable to suggest strategies for reducing ac loss in multi-layer cables but also for developing more accurate and effective methods to calculate ac loss in CORC HTS cables. [ABSTRACT FROM AUTHOR]

As in the preceding paper (Paper I) we study here a model of chains with excluded volume enclosed in a ‘‘box’’ on a square lattice. The system is simulated by the Metropolis Monte Carlo method and the entropy is extracted from the samples by using the ‘‘hypothetical scanning method.’’ With this method each system configuration is treated as if it has been generated step by step with the scanning method (studied in Paper I). The transition probabilities are reconstructed and three approximations of the entropy are obtained. Thus the pressure and the chemical potential are calculated directly from the results of the entropy as in Paper I using standard thermodynamic relations. These results are found to be in a very good agreement with those obtained in Paper I, which are considered to be exact within the statistical error. [ABSTRACT FROM AUTHOR]

This document is a retraction notice from AIP Advances regarding four manuscripts that have been retracted due to evidence of manipulation in the publication and peer review processes. The editors of AIP Advances have determined that critical steps in the peer review process were manipulated, including the return of identical reviewer reports and author-suggested reviewers requesting revisions to add citations to unrelated works by the authors. As a result, the validity of these papers has been called into question and they are considered potentially unreliable. The authors maintain that the data support the validity of the papers, but the editors believe that the issues with the peer review process undermine confidence in their validity. [Extracted from the article]

In this paper, a frequency domain simulation method of magneto-acousto-electrical tomography (MAET) was proposed. This method is based on discrete Fourier transform. With this approach, the solving degrees of freedom of the simulation model can be significantly reduced. It can greatly reduce the requirements of computer hardware and improve efficiency. At the same time, the interaction between fluid and biological tissues was considered, which makes the simulation model closer to the real model. In this paper, an MAET simulation model of acoustic–solid–electromagnetic multi-physical field coupling corresponding to the actual physical world was established. It is more reasonable to adopt the fully coupled method. However, the fully coupled method needs more computational memory. To further study the memory and time required for calculation, the segregated method was used to calculate the simulation model without affecting the accuracy and tolerance in this paper. The results show that using the segregated method can significantly reduce the memory requirement of the MAET model, but the solution time will increase accordingly. Therefore, the appropriate solution method can be selected according to the simulation computer configuration and the desired solution time. We, finally, built an experimental platform to conduct MAET experiments and verified the theoretical and simulation analyses. [ABSTRACT FROM AUTHOR]

In order to accurately predict the motion trajectory of ice shedding and ensure the safe flight of aircraft, the motion characteristics of ice shedding under two-dimensional (2D) and three-dimensional (3D) conditions are simulated and analyzed. Considering the influence of any possible shape of shedding ice and its rotation and the magnitude and direction of acceleration with time under aerodynamic force, a six degree-of-freedom analysis method is introduced in this paper. This paper proposes a theoretical model, which can be used to calculate the 3D trajectory of ice shedding with arbitrary shape. The dynamic analysis of real 3D shedding ice is carried out, and the motion behavior of shedding ice with different positions and shapes is calculated. The results show that the movement mode of the shedding ice after leaving the aircraft is translation and rotation. The shape of the low-speed region on the leeward side of the shedding ice will first increase, then decrease, and then increase with the rotation of the ice body. The influence of ice shape on ice shedding trajectory is mainly that the shedding ice continues to flip during the downstream movement of the flow field, and the projected area of the effective windward area in the lift and the drag direction changes with time. The average deviation of the shedding ice at position 5 along the spanwise is only 22.9% of that at position 1. Finally, the closer the initial position of ice shedding is to the airfoil root, the greater the probability of ice shedding hitting the aircraft fuselage. In this paper, the probability of ice shedding hitting the aircraft fuselage is 8%, which all occurred in the case with position 1 as the initial position of ice shedding. [ABSTRACT FROM AUTHOR]

Contrast ultrasound (CUS) has received much interest because of its sensitivity enhancement for blood flow imaging. However, there is still a lack of nonlinear simulation method for CUS, as conventional simulators cannot deal with the microbubble acoustic nonlinearity. In this paper, a nonlinear simulation method of CUS is developed based on a combination strategy of the k-space pseudospectral method and Rayleigh-Plesset Marmottant model. Different contrast pulse sequence strategies as well as the radial modulation imaging are simulated and compared using the proposed method. For blood flow imaging, simulations under different scenarios such as power Doppler and ultrasound localization microscopy are also carried out. Furthermore, a face-to-face comparison is performed between simulations and phantom experiments to validate the proposed method., (© 2024 Acoustical Society of America.)

In this work, we determine the dissociation line of the nitrogen (N2) hydrate by computer simulation using the TIP4P/Ice model for water and the TraPPE force field for N2. This work is the natural extension of Paper I, in which the dissociation temperature of the N2 hydrate has been obtained at 500, 1000, and 1500 bar [Algaba et al., J. Chem. Phys. 159, 224707 (2023)] using the solubility method and assuming single occupancy. We extend our previous study and determine the dissociation temperature of the N2 hydrate at different pressures, from 500 to 4500 bar, taking into account the single and double occupancy of the N2 molecules in the hydrate structure. We calculate the solubility of N2 in the aqueous solution as a function of temperature when it is in contact with a N2-rich liquid phase and when in contact with the hydrate phase with single and double occupancy via planar interfaces. Both curves intersect at a certain temperature that determines the dissociation temperature at a given pressure. We observe a negligible effect of occupancy on the dissociation temperature. Our findings are in very good agreement with the experimental data taken from the literature. We have also obtained the driving force for the nucleation of the hydrate as a function of temperature and occupancy at several pressures. As in the case of the dissociation line, the effect of occupancy on the driving force for nucleation is negligible. To the best of our knowledge, this is the first time that the effect of the occupancy on the driving force for nucleation of a hydrate that exhibits sII crystallographic structure is studied from computer simulation. [ABSTRACT FROM AUTHOR]

The flow around a cylinder near a free surface contains many physical phenomena and mechanisms, especially when the cylinder is moving. In this paper, the two-dimensional flow of a rotating cylinder near the free surface is simulated. The dynamic behavior of the rotating cylinder and the flow characteristics such as force coefficient, vortex structure, and air entrainment under different depth ratios, Fr numbers, and rotation ratios are discussed. In such problems, the rotational motion is rarely mentioned. The two-phase model is the sharp volume of the fluid method based on the two-dimensional incompressible Navier–Stokes equation. Combined with the spatially adaptive four-octree grid, the gas–liquid interface is reconstructed with the high-density ratio (ρwater/ρair = 816). The results show that, at α ≤ 2.0, the combined effect of the free surface and the rotation causes the wake vortex to produce a positive upper and negative lower distribution, which is contrary to the single condition. For the rotating cylinder, the existence of a free surface leads to the stable vortex layer at a low rotation ratio (α = 1.0), which only occurs at the high rotation ratio (2 < α < 4.2) without free surface. For the force coefficients, the simultaneous existence of the free surface and the rotation obviously changes the value and periodicity of the coefficients, which is different from the single condition. As for the air entrainment, it can be divided into two categories within the selected parameters: vortex entrainment caused by the parallel free surface and wake jet entrainment. In the latter model, the entailed bubbles have a wider distribution in space due to the influence of shedding vortices. [ABSTRACT FROM AUTHOR]

Performing full-resolution atomistic simulations of nucleic acid folding has remained a challenge for biomolecular modeling. Understanding how nucleic acids fold and how they transition between different folded structures as they unfold and refold has important implications for biology. This paper reports a theoretical model and computer simulation of the ab initio folding of DNA inverted repeat sequences. The formulation is based on an all-atom conformational model of the sugar-phosphate backbone via chain closure, and it incorporates three major molecular-level driving forces—base stacking, counterion-induced backbone self-interactions, and base pairing—via separate analytical theories designed to capture and reproduce the effects of the solvent without requiring explicit water and ions in the simulation. To accelerate computational throughput, a mixed numerical/analytical algorithm for the calculation of the backbone conformational volume is incorporated into the Monte Carlo simulation, and special stochastic sampling techniques were employed to achieve the computational efficiency needed to fold nucleic acids from scratch. This paper describes implementation details, benchmark results, and the advantages and technical challenges with this approach. [ABSTRACT FROM AUTHOR]

Optoelectronic oscillators (OEOs), which have attracted extensive studies in the past decades, are high quality-factor optoelectronic feedback loops for generating various ultra-pure microwave signals. In essence, OEOs are also dissipative nonlinear systems with multiple timescale characteristics and abundant nonlinearities, which open the possibilities for exploring localized dissipative solitary waves. In this paper, we demonstrate a new-class temporal dissipative soliton, i.e., dissipative microwave photonic soliton molecule (DMPSM), in a dual-bandpass OEO. Both the numerical simulation and experiment are conducted to reveal the physical mechanism of DMPSM generation and to evaluate the characteristics of the generated DMPSM sequences. Unlike optical soliton molecules in mode-locked lasers, the formation of DMPSMs arises from the combined action of multiple timescale coupling, nonlinear bistability, and time-delayed feedback in the OEO cavity, where the soliton interval and number in a DMPSM can be well-controlled through varying the multiple timescale variables in the OEO cavity, and the repetition frequency of the DMPSMs can be tuned through changing that of the initially injected perturbation signal. Meanwhile, the generated DMPSM sequence performs with high stability and excellent coherence, which shows enormous application potentials in pulse radar detection, dense microwave comb generation, and neuromorphology. [ABSTRACT FROM AUTHOR]

In this paper, we devise a pentamode metamaterial plate exhibiting topological characteristics. By organizing pentamode metamaterial structural elements, topological boundary states are attained, effectively safeguarding propagation of elastic waves. Moreover, based on the numerical simulation model, we employ a polymer to fabricate a macro-scale specimen via additive manufacturing. Through assessing the vibrational response of the sample, we corroborate its topological attributes in governing elastic wave transmission. This discovery paves the way for a novel approach to manipulating acoustic/elastic waves employing pentamode metamaterials. [ABSTRACT FROM AUTHOR]

When a shock wave impacts a roughened metal/gas interface, metal ejecta particles emit and transport in the gas. The exchanges of momentum and energy between ejecta particles and the gas occur. If active metal particles transport in the reactive gas, the heat released by a chemical reaction could change these exchanges. In this paper, we use numerical simulations to study solid cerium ejecta transporting in a vacuum, and in non-reactive and reactive gases. In vacuum, the emitted ejecta could self-similarly expand neglecting the particle interaction. In the non-reactive gas (He), ejecta particles slow down by the gas resistance and have the exchanges of momentum and energy with the gas. In the reactive gas ( D 2 ), the ejecta particles also slow down. The exothermic reaction could induce the temperature rise of the ejecta and the gas, which could induce changes in physical property values of the gas after the shock wave and the velocity of the shock wave. The numerical result shows that the maximum temperature of the ejecta may appear in the middle of the mixture zone, which may result from the ejecta temperature being controlled by two competitive effects. Furthermore, the maximum ejecta temperature increases rapidly in the beginning and then becomes steady. Finally, the ejecta with a different initial size distribution is investigated. The ejecta with a smaller maximum size has a larger maximum particle temperature, a larger gas temperature after the shock wave, and a larger chemical reaction function of the ejecta at the same moment. [ABSTRACT FROM AUTHOR]

In the original paper [Yasui and Izu, J. Acoust. Soc. Am. 141(6), 4398–4407 (2017)], the temperature gradient in Rott equations was assumed as zero by mistake as an author error, although temperature gradient was adequately taken into account in the numerical simulations of thermal conduction between a fluid parcel and the wall of a stack. In the present erratum, the results of the corrected numerical simulations are shown. The results show that the pV work done by a fluid parcel is larger in a wet stack compared to that in a dry stack not only in a traveling-wave thermoacoustic engine but also in a standing-wave thermoacoustic engine. The pV work is determined not only by the volume oscillation amplitude of a fluid parcel but also by the change in the mean volume of a fluid parcel. [ABSTRACT FROM AUTHOR]

Multiple-gated junctionless transistors (JLTs) with an extremely simple structure and bulk-conduction-based operation could overcome fundamental problems with respect to short-channel effects for sub-3-nm technology nodes. In this paper, the performance of a tri-gate JLT with an electrostatically highly doped channel is demonstrated through numerical simulation. Unique characteristics previously reported in fabricated JLTs were exhibited by the tri-gate transistors with an additional bottom-gate bias (Vgb = 50 V), which induced an effectively highly doped state of the channel. The results of this study show the feasibility of producing impurity scattering-free JLTs for next-generation technology nodes. [ABSTRACT FROM AUTHOR]

The process of quasi-isothermal dehydration of thin films of pure water and aqueous sugar solutions is investigated with a dual experimental and theoretical approach. A nanoporous paper disk with a homogeneous internal structure was used as a substrate. This experimental set-up makes it possible to gather thermodynamic data under well-defined conditions, develop a numerical model, and extract needed information about the dehydration process, in particular the water activity. It is found that the temperature evolution of the pure water film is not strictly isothermal during the drying process, possibly due to the influence of water diffusion through the cellulose web of the substrate. The role of sugar is clearly detectable and its influence on the dehydration process can be identified. At the end of the drying process, trehalose molecules slow down the diffusion of water molecules through the substrate in a more pronounced way than do the glucose molecules. [ABSTRACT FROM AUTHOR]

Inspired by the emerging field of twistronics, moiré photonic structures have attracted great interest. In this paper, we introduce the concept of the moiré Kagome lattice (MKL), which arises from the overlapping of a Kagome lattice at a commensurable angle of 38.211°. MKL exhibits a significantly broader main photonic bandgap (PBG) when compared to the traditional Kagome lattice. Through numerical simulations, we delved into the adjustable properties of the PBG of MKL by varying lattice parameters, including filling factors and materials. Meanwhile, we also observed the presence of photonic flatbands within the MKL structure. Specifically, the emergence of a super flat isolated flatband aids in achieving single-mode omnidirectional lasers and enhancing the omnidirectional electromagnetic interaction of materials, thereby expanding the applications of moiré photonic crystals. [ABSTRACT FROM AUTHOR]

Adding carbon nanoparticles into organic phase change materials (PCMs) such as paraffin is a common way to enhance their thermal conductivity and to improve the efficiency of heat storage devices. However, the sedimentation stability of such blends can be low due to aggregation of aromatic carbon nanoparticles in the aliphatic paraffin environment. In this paper, we explore whether this important issue can be resolved by the introduction of a polymer agent such as poly(3-hexylthiophene) (P3HT) into the paraffin–nanoparticle blends: P3HT could ensure the compatibility of aromatic carbon nanoparticles with aliphatic paraffin chains. We employed a combination of experimental and computational approaches to determine the impact of P3HT addition on the properties of organic PCMs composed of paraffin and carbon nanoparticles (asphaltenes). Our findings clearly show an increase in the sedimentation stability of paraffin–asphaltene blends, when P3HT is added, through a decrease in average size of asphaltene aggregates as well as in an increase of the blends' viscosity. We also witness the appearance of the yield strength and gel-like behavior of the mixtures. At the same time, the presence of P3HT in the blends has almost no effect on their thermophysical properties. This implies that all properties of the blends, which are critical for heat storage applications, are well preserved. Thus, we demonstrated that adding polyalkylthiophenes to paraffin–asphaltene mixtures led to significant improvement in the performance characteristics of these systems. Therefore, the polymer additives can serve as promising compatibilizers for organic PCMs composed of paraffins and asphaltenes and other types of carbon nanoparticles. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a dual-broadband dual-function polarization conversion metasurface, which can convert a linearly polarized (LP) incident electromagnetic wave into a cross-polarized LP wave and a circularly polarized wave, effectively, in different bands. The numerical simulations and experiments show that the metasurface can be used as a high-efficiency cross-polarization converter from 5.50 to 12.4 GHz, where the polarization conversion ratio is greater than 0.9 with a fractional bandwidth of 77.1%. Simultaneously, it can convert the LP incident wave into a right-handed circularly polarized wave from 13.50 to 19.75 GHz, where the axis ratio is lower than 3 dB and the fractional bandwidth is 37.4%. A honeycomb is used as a support layer instead of air gaps, which improves the efficiency of cross-polarization conversion and broadens the bandwidth of linear to circular conversion. To reveal the conversion mechanism of the proposed polarization converter, the surface current is analyzed. Finally, we fabricated and tested it, and the experimental results are in line with the simulation results. [ABSTRACT FROM AUTHOR]

The control of the excitation force of pump-jets is of great significance for the stealth performance of submarines. In a previous study, the authors found that the sinusoidal unevenly spaced rotor blades (SUSR) can control the excitation force of the rotor, but the suppression effect is limited by the low degree of freedom. This paper proposes random unevenly spaced rotor blades (RUSR) with higher degrees of freedom, achieving twice the suppression effect of the SUSR. A method for batch generation of RUSRs is proposed in this paper, and a large number of RUSRs are generated. The numerical simulation study was carried out by selecting the RUSRs with better suppression effects through theoretical methods, and the numerical simulation method used was improved based on the previous study. The RUSR also has an impact on the excitation force of the duct. The conclusion of this paper has guiding significance for the low excitation design of pump-jets and has the potential to promote the use of unevenly spaced rotor blades in the field of pump-jets. [ABSTRACT FROM AUTHOR]

The thermal counterflow of superfluid helium past a cylinder has been found to generate two pairs of symmetrical vortexes upstream and downstream of the cylinder in experiments. This is a unique physical phenomenon that differs from classical fluids. In this paper, we have developed a new solver on the OpenFOAM® platform based on the simplified two-fluid model proposed by Kitamura et al. and use it to simulate the thermal counterflow phenomenon. The numerical simulation results obtained by the simplified two-fluid model agree well with the experimental results. Based on this numerical simulation, an investigation has been carried out into the evolution of the four-vortex structure of the superfluid helium thermal counterflow. This paper supports the conjecture of many researchers that large scale quantum turbulence in superfluid helium can be explained using classical mechanics. Details of the theoretical basis, the solver computational procedure, the numerical simulation results, and the discussion based on the results are presented in this paper. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the influence of small disturbance on the statistical behaviors of fluid particles of the three-dimensional divergence-free hexagonal Beltrami flow from a Lagrangian point of view. Due to the butterfly-effect, numerical noise increases exponentially for chaotic dynamic systems. Thus, a powerful strategy, namely, the clean numerical simulation, is used to gain reliable/convergent trajectory in a long enough interval of time. It is found that the statistics of chaotic trajectory of fluid particles are stable in some cases, corresponding to the so-called "normal-chaos," but unstable in some cases, i.e., rather sensitive to small disturbances, corresponding to the so-called "ultra-chaos," which is a new concept proposed currently. Obviously, an ultra-chaotic trajectory of fluid particles is at a higher disorder than a normal chaotic trajectory. In theory, it is impossible to repeat any experimental/numerical results of an ultra-chaotic system even by means of statistics, but reproducibility is a corner-stone of our modern science paradigm. Hence, the wide existence or non-existence of ultra-chaos has a very important meaning. In this paper, we illustrate that the ultra-chaotic trajectories of fluid particles indeed widely exist in a hexagonal Beltrami flow field. This fact is important for deepening our understanding of chaotic dynamic systems and revealing the limitations of our paradigm of modern science. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of sloshing loads acting on liquid cargo tanks based on classification rules and numerical simulations. For the design of liquid cargo tanks, sloshing load is one of the key factors that should be considered. To reduce the sloshing load and motion of the contained liquid, internal structures such as bulkheads and baffles are commonly installed in the tanks. In classification rules, methodologies to estimate the sloshing loads are proposed considering the design parameters related to these internal structure members. In this paper, we carefully investigate the limitation of classification rules through smoothed particle hydrodynamics. Our investigations focus on the impact of the design parameters on sloshing loads, the patterns of the free surface, and the characteristics of velocity distribution in the tank. Through the obtained results, it is identified that the existing classification rules lack consideration for the design parameters that affect the sloshing loads and fluid characteristics in the tank. This result provides a better understanding of the existing classification rules and their limitations. It can contribute to foundational data for the future revision of classification rules. [ABSTRACT FROM AUTHOR]

In the field of fluid mechanics, dimensionality reduction (DR) is widely used for feature extraction and information simplification of high-dimensional spatiotemporal data. It is well known that nonlinear DR techniques outperform linear methods, and this conclusion may have reached a consensus in the field of fluid mechanics. However, this conclusion is derived from an incomplete evaluation of the DR techniques. In this paper, we propose a more comprehensive evaluation system for DR methods and compare and evaluate the performance differences of three DR methods: principal component analysis (PCA), isometric mapping (isomap), and independent component analysis (ICA), when applied to cavitation flow fields. The numerical results of the cavitation flow are obtained by solving the compressible homogeneous mixture model. First, three different error metrics are used to comprehensively evaluate reconstruction errors. Isomap significantly improves the preservation of nonlinear information and retains the most information with the fewest modes. Second, Pearson correlation can be used to measure the overall structural characteristics of the data, while dynamic time warping cannot. PCA performs the best in preserving the overall data characteristics. In addition, based on the uniform sampling-based K-means clustering proposed in this paper, it becomes possible to evaluate the local structural characteristics of the data using clustering similarity. PCA still demonstrates better capability in preserving local data structures. Finally, flow patterns are used to evaluate the recognition performance of flow features. PCA focuses more on identifying the major information in the flow field, while isomap emphasizes identifying more nonlinear information. ICA can mathematically obtain more meaningful independent patterns. In conclusion, each DR algorithm has its own strengths and limitations. Improving evaluation methods to help select the most suitable DR algorithm is more meaningful. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy experiments are able to reveal the fundamental charge transport properties of a wide variety of complex disordered and nano-structured materials provided that appropriate modeling tools are used. In this paper, we present a numerical simulation-based approach to model the dynamical conductivity of networks formed by self-assembled metal nanoparticles. Inter-particle nano-resistance and nano-capacitance are implemented at the nano-scale assuming inter-particle charge transfer and accumulation mechanisms that can be adapted depending on the nature of the nano-particles and the surrounding medium. The actual positions and spatial arrangements of the nanoparticles within the network are taken into consideration, allowing the attributes of percolating conducting routes to be extracted, classified, and compared in terms of path conductance and statistical distribution of path lengths. Our findings are contrasted to those obtained using analytic models, which are commonly used, but rely on strong assumptions about the electric properties of the conducting paths. We address these assumptions and show that in the case of weakly disordered systems, there is a general agreement between numerical simulations and analytic modeling-based approaches. In the case of disordered networks where the nano-particle size and position fluctuations are included, we show that the path length distribution is frequency-dependent and can differ significantly from the lognormal distribution usually assumed in the analytic models. The impedance of individual pathways may be extracted from the numerical simulations; we discovered that the conductance and susceptance of a specific path are frequency-dependent and inversely proportional to the path length only in ordered networks. Strong scattering of conductance values is caused by disorder effects. The developed numerical approach is generic and applies to most nano-devices where charge transport relies on percolation; it allows to bridge the gap between the nano-scale and micro-scale electric characteristics and, thus, permits a deeper understanding of the charge transport properties of nano-structured materials. [ABSTRACT FROM AUTHOR]

In this paper, circularly polarized metasurface radiators (meta-radiator) are elaborately designed with low-profile, small footprint, and highly efficient specifications. The proposed array consists of single-feed dense radiating meta-atoms that overall occupies a small area of 1.57 λ 0 × 1.57 λ 0 at f = 5.8 GHz. The inter-element coupling is involved by analyzing the contributing meta-atoms with Floquet boundary conditions. For demonstration purposes, an 8 × 8 sample of meta-radiators excited by an isolated network beneath the ground plane is fabricated. Both numerical and experimental results demonstrate that the meta-radiator exposes a pure left-hand circularly polarized radiation with a peak broadside directivity, a realized gain, and an axial ratio of 14.9 dBi, 14.2 dB, and 1.28 dB, respectively. Numerical simulations indicate that the aperture, radiation, and total efficiencies are as high as 99%, 97.5%, and 84.3%, respectively. In comparison with the conventional array antennas with similar performances, the proposed meta-radiator provides a higher aperture efficiency, in a simpler manner to achieve circular polarization, and more compact size as discussed throughout the paper. This new class of radiating architectures may find great potential applications in target detection systems and wireless communications. [ABSTRACT FROM AUTHOR]

The lifetime of deep-ultraviolet light-emitting diodes (LEDs) is still limited by a number of factors, which are mainly related to semiconductor defects, and still need to be clarified. This paper improves the understanding of UV LED degradation, by presenting an analysis based on combined deep-level transient spectroscopy (C-DLTS), electro-optical characterization, and simulations, carried out before and during a constant current stress test. The original results of this paper are (i) C-DLTS measurements allowed us to identify three traps, two associated with Mg-related defects, also detected in the unaged device, and one related to point defects that were generated by the ageing procedure. (ii) Based on these results and on TCAD simulations, we explain the variation in the forward I–V by the degradation of the p-contact, due to Mg passivation. (iii) On the other hand, optical degradation is ascribed to an increase in defectiveness of the active region and surrounding areas, which led to a decrease in injection efficiency, to an increase in non-radiative recombination, and to an increase in trap-assisted tunneling processes. [ABSTRACT FROM AUTHOR]

This paper discusses the terahertz electromagnetic response of metallic gratings on anisotropic dielectric substrates. The metallic gratings consist of parallel gold stripes. Utilizing numerical simulations, we observe that it is possible to excite a series of resonant modes in these structures. These modes are affected differently by the different indices on the anisotropic substrate. An analytical model is discussed to show that modes associated with transmission peaks are due to the excitation of (a) Fabry–Pérot modes with polarization along the grating and/or (b) waveguide modes with polarization perpendicular to the grating. It is observed that the resonance associated with the TM1,1 mode is a narrow linewidth resonance which, in some particular circumstances, becomes nearly independent of substrate thickness. Therefore, from the spectral position of this resonance, it is possible to extract the out-of-plane component of the substrate refractive index with very small uncertainty. Based on this observation, we demonstrate the refractive index characterization of several lossless semiconductor substrates through frequency-domain polarized terahertz transmission measurements in the frequency range of 0.2–0.6 THz at normal incidence. The reliability of the technique is demonstrated on well-known materials, such as high-resistivity silicon and sapphire substrates. This technique is also applied for the characterization of a Fe-doped β-Ga2O3 single-crystal substrate. [ABSTRACT FROM AUTHOR]

Can active forces be exploited to drive the consistent collapse of an active polymer into a folded structure? In this paper, we introduce and perform numerical simulations of a simple model of active colloidal folders and show that a judicious inclusion of active forces into a stiff colloidal chain can generate designable and reconfigurable two-dimensional folded structures. The key feature is to organize the forces perpendicular to the chain backbone according to specific patterns (sequences). We characterize the physical properties of this model and perform, using a number of numerical techniques, an in-depth statistical analysis of structure and dynamics of the emerging conformations. We discovered a number of interesting features, including the existence of a direct correspondence between the sequence of the active forces and the structure of folded conformations, and we discover the existence of an ensemble of highly mobile compact structures capable of moving from conformation to conformation. Finally, akin to protein design problems, we discuss a method that is capable of designing specific target folds by sampling over sequences of active forces. [ABSTRACT FROM AUTHOR]

Personal Sound Zone (PSZ) allows listeners to enjoy their individual sound without being disturbed by sound from other zones. Acoustic contrast, signal distortion, and array effort are the most frequently used metrics for measuring the performance of a PSZ system. However, usually, the three metrics cannot be optimized at the same time. A trade-off between the three metrics has to be made when designing a PSZ system. In this paper, two generalized methods based on multi-objective optimization are proposed for dealing with all possible trade-off problems between the three metrics in PSZ. Optimality analysis of the two proposed methods is taken, and the relationship between the two proposed methods is investigated. Numerical simulations are presented to validate the efficacy and flexibility of the two proposed methods. [ABSTRACT FROM AUTHOR]