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In this paper, an ultra-wide-angle and broadband metamaterial absorber with a monopole top loading structure (MA-MTLS) was proposed. The resistive films printed on the dielectric are on the top layer. The dielectric square cylindrical shells with resistive films on the outside are in the middle, and a metal plate is on the bottom layer. The whole structure can be regarded as a top loading monopole antenna that has a good omnidirectional radiation capability. According to reciprocity, when a composite structure is used as an absorber, it will have a good absorption performance. The impedance matching characteristics were demonstrated by Smith chart and equivalent circuit, and then, the absorption performance was optimized. The simulated results show that the absorption of the MA-MTLS is more than 90% under TM polarized waves of 3.6–13.8 GHz as the incident angle changes from 0° to 80°. When the incident angle increases to 83°, the absorption is higher than 80% in the frequency band of 3.7–14.5 GHz. At the stage of experiment, the dielectric substrate was made by three-dimensional printing technology, the resistive films on the top layer were printed using screen printing techniques, and the resistive films on the outside of the square cylindrical shells were completed by pasting. The consistency between the experimental results and simulation data indicates that the design method is feasible and has good application prospects. [ABSTRACT FROM AUTHOR]

Heat exchangers have a very wide range of applications in many industrial fields, so the rational design and the performance are to improve the heat exchanger energy efficiency and reduce the production cost of an important means. In this paper, the heat transfer mechanism of pulsation is revealed by simulating and analyzing the effects of three pulsation parameters: volumetric flow rate, pulsation frequency, and pulsation amplitude on the flow and heat transfer of a wavy-walled tube heat exchanger, with the study focusing on the instability behavior that affects the heat transfer mechanism. The results reveal that the combined heat transfer performance of the wavy-walled tube heat exchanger is about 8.2% higher than that of the straight-walled tube heat exchanger. The flow field of the heat exchanger is more fully developed under the pulsating flow field, and its performance evaluation coefficients (PECs) are all greater than 1. It is also found that with the increase in the volume flow rate Qv, the heat transfer enhancement coefficient and PEC first increase and then decrease, and reach the maximum value near Qv = 2.0 m3/h; with the increase in the amplitude A, the vortex and heat transfer enhancement coefficient inside the heat exchanger increase, but the integrated heat transfer performance of the heat exchanger is gradually weakened; with the increase in the frequency fT, the heat transfer enhancement coefficient and PEC first increase gradually, but the increase gradually decreases and levels off in the later stages, reaching a maximum value near fT = 0.5 Hz. Meanwhile, the field coefficients of the wavy-walled tube heat exchanger were analyzed and found to be much smaller than 1, with an order of magnitude of 10−4, and the results also showed that the field coefficients were inversely proportional to the volume flow rate and directly proportional to the amplitude of pulsation and that the field coefficients showed a tendency of increasing and then decreasing with the change of pulsation frequency and reached a maximum value near fT = 0.5 Hz. This work provides an important reference for current manufacturing industries to optimize heat exchanger sizing and develop efficient thermal management systems. [ABSTRACT FROM AUTHOR]

The extensive applications of double-suction centrifugal pumps consume a considerable amount of energy. It is urgent to reveal the detailed energy dissipation generation and find the critical factor for pump performance enhancement. In this investigation, the internal flow field of a double-suction centrifugal pump was obtained by solving the Reynolds averaged Navier–Stokes equations. The entropy production method was utilized to calculate and visualize irreversible energy dissipation. The Omega vortex method was utilized to identify vortical structures and determine the temporal and spatial relationship between entropy production and vortices. The results indicate that the entropy production in the main flow regions was critical in hydraulic loss, accounting for 54%–71% of the loss, and turbulent dissipation in the main flow regions of the impeller and volute casing dominated the variation of pump efficiency. The near-wall entropy production in the impeller positively correlated with the flow rate, but the impact was insignificant in volute casing. Although the suction chamber contributed minimally to the hydraulic loss, the backflows at the impeller inlet were relieved near the ribs, and the dissipation at the impeller inlet was reduced when the blade leading edges passed the ribs. By adopting Omega vortex identification, wake vortices, separation vortices, and their interactions were determined to correlate strongly with hydraulic loss in volute channels and near cutwaters. Furthermore, these vortices were influenced by the back flows from the impeller sidewall gaps. Additionally, this study can also provide the foundational principles for the optimal design of this type of pump. [ABSTRACT FROM AUTHOR]

The Coulomb interaction effect in disordered conductors has long been a topic of fundamental importance and intense attention. Here, we systematically study the influence of this effect on the electrical transport of a series of ∼ 1 μ m thick Sn-doped indium oxide (ITO) films grown at different oxygen partial pressures. We find that both the electrical conductivity σ and Hall coefficient R H vary linearly with T from ∼ 35 K down to ∼ 4 K. The extracted electron screening factor F ~ σ of each film is nearly in agreement with the corresponding theoretical value. Moreover, the F ~ σ values increase with decreasing carrier concentration in the ITO films, which originates from less screening effect of electrons and enhanced Coulomb interaction. These features are consistent with conventional three-dimensional Coulomb interaction theories. We explore the long-standing puzzle of the carrier concentration dependence of F ~ σ. Our results provide the fundamental physics to modulate the intensity of the Coulomb interaction effect, which may be useful to optimize the performance of electron transport for nanoscale electronic devices. [ABSTRACT FROM AUTHOR]

Plasmonic structure (PS) has recently been demonstrated to provide full control of dispersion characteristics by virtue of spoof surface plasmonic polariton (SSPP). In this paper, a comprehensive scheme is proposed, which develops the non-planar PS as a covering on the absorber to enhance the k-vector matching absorption in a wider frequency band. Owing to the dispersion engineering of SSPP, our theoretical investigation shows that the PS covering based on a straight wire array can not only enhance the k-vector matching absorption of the ground absorber at low frequency, but also achieve the broadband absorption at high frequency. As a proof, two hybrid plasmonic metamaterial absorbers (PMAs) based on the combinations of PS covering and various absorbers are proposed here. Simulations and experimental measurements demonstrate that two kinds of hybrid PMAs can simultaneously achieve broadband absorption enhancement, especially for the lower-frequency absorption. Our proposed strategy succeeds in the comprehensive utilization of dispersion engineering for broadband absorption enhancement, and a wide range of applications is expected to emerge from our design concept ranging from microwave to optical frequencies. [ABSTRACT FROM AUTHOR]

Inclined semiconductor Bi2O2Se nanoplates of a high crystal quality were prepared via chemical vapor deposition, and a circular photogalvanic effect (CPGE) current was detected in them. The CPGE current in the Bi2O2Se nanoplate reached 100 nA/W, which is far beyond what has been found in other two-dimensional (2D) materials, e.g., Bi2Se3, WSe2, and Sb2Te3, as well as some 2D electron systems such as AlxGa1-xN/GaN heterostructures, indicating the large spin–orbit coupling (SOC) in inclined Bi2O2Se. To tune the strength of the SOC, an ionic liquid gate was applied to the Bi2O2Se nanoplate. The significant increase in the CPGE current that appeared with the application of the positive gate voltage indicates that the gate can further break spatial inversion symmetry, leading to enhanced SOC. Unlike the in-plane Bi2O2Se, the bottom surface of which has electrostatic interactions with the mica substrate and hence is naturally asymmetric with the top surface, the inclined-grown nanoplate has two Bi2O2Se-air interfaces. Therefore, the large CPGE current in the inclined Bi2O2Se shows that strong SOC is intrinsic to the Bi2O2Se lattice instead of the interfaces, and Bi2O2Se is a prospective material in the application of spintronic devices. [ABSTRACT FROM AUTHOR]

During laser-induced exit-surface damage of fused silica components, strain and stress are generated and accompanied by cracks in the substrate, further deteriorating the component. The authors studied the behaviors of surface and shear waves quantitatively using a time-resolved multipolariscopic imaging system, showing their potential to affect the development of circumferential and longitudinal cracks. When the material received a cumulative shot, a greater stress intensity was observed, and the stress wave had a greater impact on the laser-induced damage. The results indicate that the two stress waves from the cumulated shots dominated the developmental characteristics of the damage morphology. [ABSTRACT FROM AUTHOR]

The traditional aeromagnetic compensation model does not consider the negative effects of the gradient of the geomagnetic background field. Especially in emergency aeromagnetic surveys, this gradient effect is obvious and can reduce the performance of magnetic compensation. To solve this problem, we propose a method of reducing the gradient effect of the magnetic sensor for aeromagnetic compensation. A magnetic gradient model of the Earth's background field is established for the aeromagnetic compensation, and the gradient effect is then suppressed using altitude data. An experimental platform was built, and flight tests were conducted. Comparison results show that the adoption of the proposed method increased the improvement ratio (IR) of our compensator on two flights from 20.4 and 21.3 to 25.9 and 26.0, with the growth rates of the IR, respectively, reaching 27% and 22%. [ABSTRACT FROM AUTHOR]

The structural disorder-induced localized effect is an essential topic of nanophysics in graphene-like layered materials. Here, we investigate the conductivity behavior and angle-magnetresistance (MR) properties of a 1.4 nm-thick ultrathin PtSe 2 film. The observed insulating behavior is dominated by nearest-neighbor hopping and variable-range hopping (VRH) of the localized carriers throughout the measured temperature. At low temperatures, a crossover from the Mott-VRH to Efros-Shklovskii (ES)-VRH conducting process is observed in the conductivity data, suggesting the existence of the Coulomb gap around the Fermi level. In this strong localized regime, the observed negative MR under a perpendicular magnetic field is ascribed to the quantum interference among random hopping paths between hopping sites. When the field aligns with current, the appearance of positive MR can be considered as a consequence of the reduction in hopping probability due to field-induced modification of the charger wavefunction at impurity or defect centers. The charge transport research of ultrathin PtSe 2 is of great significance for both fundamental physics and nanoscale electronic applications. [ABSTRACT FROM AUTHOR]

The effective g factors (g*) of the lowest three subbands of Al0.25Ga0.75N/GaN-based quantum point contacts (QPCs) are obtained in various magnetic field orientations. The g factors show an anisotropic enhancement compared to those in the two-dimensional electron gas, among which an in-plane anisotropy becomes manifested, when the QPC is depleted from the third to the first subband and the channel width shrinks from the order of 10−7 m–10−8 m. In the one-dimensional (1D) regime with only one subband in the QPC, the in-plane g* perpendicular to the current is evidently larger than the parallel one. The in-plane anisotropy can be attributed to the Rashba spin–orbit coupling (SOC) in the narrow confinement. The reason that the anisotropy can be observed in this work, but not in conventional III–V semiconductors studied previously, is due to the fact that the Al0.25Ga0.75N/GaN-based QPCs have larger polarization-field-induced Rashba SOC and much stronger 1D constriction. [ABSTRACT FROM AUTHOR]

Estimating acoustic wave dispersion in pipelines filled with water is studied using theoretical analysis and laboratory experiments. Previous methods for experimentally estimating the dispersion of the propagating modes require multiple spatial measurements, making it difficult to measure. In this work the authors propose a method that utilizes only one spatial measurement using a singular value decomposition based approach. Experimental results of a cylindrical high-density polyethylene pipeline are used to demonstrate the usefulness of the approach. The approach could be useful in estimating the size and material properties of pipelines. [ABSTRACT FROM AUTHOR]

A magnetic sensor of the optically pumped magnetometer may enter a dead zone during an aeromagnetic survey, resulting in unavoidable abnormal data and seriously affecting the effect of aeromagnetic compensation. We propose a fast discrimination and culling method based on the Hough transform to prevent abnormal data from participating in the coefficient estimation. In the proposed method, the parameter space is partitioned into small buckets and the most frequently passed region of sinusoidal curves is detected to eliminate abnormal data. Although the conventional method performs similarly to the proposed method when there is only 1% abnormal data, it is theoretically shown that the proposed method has a better goodness of fit of 0.9518, compared with a value of 0.1956 for the conventional method, in the presence of 45% abnormal data. Furthermore, we construct an experimental platform and conduct a flight test in which the proposed method has an improvement ratio of 4.11 compared with a value of 0.34 for the conventional method. [ABSTRACT FROM AUTHOR]

Light-induced domain reversals of Mg-doped, Zr-doped, and nominally pure LiNbO3 crystals were investigated with focused 514.5 nm laser beams. It was found the light-reduced values of electric field for domain reversal are almost the same, about 3 kV/mm. Inverted domains always first nucleate on the -c surface within the illuminated region but appear at the edge of the spot on the +c surface. The light-induced inverted domains are hard to be reversed by application of a reverse electric field or by heating to temperatures as high as 600 °C. According to these experimental results, we present a qualitative model on the light-induced domain reversal process in LiNbO3. [ABSTRACT FROM AUTHOR]

The influence of pipeline thickness and radius on the attenuation of guided waves in water-filled steel pipelines is investigated using theoretical analysis and experimental measurement. Attenuations of individual axisymmetric modes in unburied water-filled steel pipelines are predicted by an analytical model under different pipeline radius-thickness ratios. Model predictions indicate that attenuation of the fundamental mode increases as the ratio rises. This effect is investigated by finding the displacement variations under different ratios. Laboratory experiments were also carried out in four unburied steel pipelines with three distinctly different radius-thickness ratios using acoustic transducers to acquire signals uniformly spaced along the axis of the pipe. By applying the iterative quadratic maximum likelihood algorithm, the attenuations could be accurately estimated from the measurement data for individual modes. Experimental results show that attenuation of the fundamental axisymmetric mode is sensitive to radius-thickness ratio, but high-order modes are barely affected, agreeing with the model predictions mentioned in this paper. The characteristics of water-filled buried pipelines are also investigated using an analytical model to understand the relation between wave attenuation and the radius-thickness ratio. [ABSTRACT FROM AUTHOR]

A straightforward explicit expression is derived for estimating the size and position of leaks in a water pipeline using the acoustic transient response. Experimental results are provided for a water pipeline with multiple leaks to demonstrate the usefulness and performance of the proposed approach. The form of the leak estimation expression can be further combined with an existing explicit expression derived for blockage detection. Using this combined expression it is also demonstrated that the proposed approach can detect and estimate leaks and blockages when they are simultaneously present in pipelines. [ABSTRACT FROM AUTHOR]

The interactions of guided acoustic waves with pipelines and associated components has become a topic of interest due to their application in water pipeline condition assessment. In this paper, guided acoustic wave interactions with flanged junctions in a water-filled pipeline are investigated by an analytical model and experimental measurements. In the model, axial wavenumbers, displacement, and stress profiles of the main pipeline and flange junction components are calculated by an existing cylindrical waveguide analytical model. These components are then concatenated together using mode matching to determine the overall theoretical characteristics. Experiments with a flanged water-filled steel pipeline are carried out to verify model predictions. Transmitted signals are acquired using acoustic transducers uniformly spaced along the pipeline axis to separate individual modes and extract mode amplitudes. Transmission losses are estimated by comparing the extracted amplitudes in a pipeline with and without the flanged junction. Both theoretical predictions and experimental results indicate that the flanged junction interacts with pipeline wall dominant modes by transforming them into waterborne modes and as a result guides acoustic power into the water medium. The flange is shown to cause a small transmission loss in waterborne modes as compared to the pipeline without flanges. [ABSTRACT FROM AUTHOR]

As an important part of All-Time star sensor design, the generation of the short-wave infrared (SWIR) guide star catalog is crucial to the system performance. The generation process needs estimation of the instrument magnitude and the guide star selection. Different from the commonly used star sensors, since the SWIR band is far away from the visual band and the detectable magnitude limit of the All-Time star sensor is dynamically changing as the observation conditions vary, the current methods of estimating the instrument magnitude cannot be directly applied and the catalog obtained through the current reduction methods that mainly aimed at improving the distribution uniformity cannot ensure enough stars measured in the field of view under strong sky background radiation. To solve the problems, we propose a method for guide star catalog generation for the All-Time star sensor. First, through the specific analysis of the spectral response curves of the SWIR detector and 2MASS detection bandpasses, the method of estimating instrument magnitudes for the All-Time sensor is determined. Subsequently, dynamic detectable magnitude limits are determined through the signal-to-noise model and the atmospheric background radiation intensity analysis. Based on the dynamic detectable magnitude limits, a reduction method is proposed. The simulation experiment results indicate that the RMS error of the estimation of instrument magnitude is 0.075. Compared to the magnitude filtering method, the guide star catalog obtained through our method can guarantee the completeness, besides, the global distribution uniformity increases by 2.2 times and the local distribution uniformity increases by 10.7 times. [ABSTRACT FROM AUTHOR]

An approximate inverse scattering technique is proposed for reconstructing cross-sectional area variation along water pipelines to deduce the size and position of blockages. The technique allows the reconstructed blockage profile to be written explicitly in terms of the measured acoustic reflectivity. It is based upon the Born approximation and provides good accuracy, low computational complexity, and insight into the reconstruction process. Numerical simulations and experimental results are provided for long pipelines with mild and severe blockages of different lengths. Good agreement is found between the inverse result and the actual pipe condition for mild blockages. [ABSTRACT FROM AUTHOR]

We report on the observation of Cˇerenkov emission of a third-harmonic frequency in a two-dimensional nonlinear photonic crystal, where the second-order nonlinearity χ(2) is spatially modulated by the reversal of ferroelectric domains. We analyze both spatial and polarization properties of the emitted radiation and find the results in agreement with our theoretical predictions. [ABSTRACT FROM AUTHOR]

In this paper we study the bubble dynamics driven by an aspherical acoustic field, based on the theory of hydrodynamics. Evolution equations for an aspherical bubble are derived under the aspherical acoustic driving. The numerical calculations show that the aspherical bubble can oscillate stably and periodically under suitable conditions, which is out of the explanation of spherical perturbation theory. Furthermore, under some controlling parameters, the aspherical distortion can either grow rapidly, leading to the bubble's breakdown, or decay gradually making the bubble spherical, which is similar to the result of the perturbation theory driven by a spherical ultrasound.