Propagation Distance Research Articles

Accurate Range Modeling for High-Resolution Spaceborne Synthetic Aperture Radar.

Spaceborne synthetic aperture radar (SAR) is an advanced microwave imaging technology that provides all-weather and all-day target information. However, as spaceborne SAR resolution improves, traditional echo signal models based on airborne SAR design become inadequate due to the curved orbit, Earth rotation, and increased propagation distance. In this study, we propose an accurate range model for high-resolution spaceborne SAR by analyzing motion trajectory and Doppler parameters from the perspective of the space geometry of spaceborne SAR. We evaluate the accuracy of existing range models and propose an advanced equivalent squint range model (AESRM) that accurately fits the actual range history and compensates for high-order term errors by introducing third-order and fourth-order error terms while maintaining the simplicity of the traditional model. The proposed AESRM's concise two-dimensional frequency spectrum form facilitates the design of imaging algorithms. Point target simulations confirm the effectiveness of the proposed AESRM, demonstrating significant improvements in fitting accuracy for range histories characterized by nonlinear trajectories. The developed AESRM provides a robust foundation for designing imaging algorithms and enables higher resolution and more accurate radar imaging.

Phase-contrast neutron imaging compared with wave propagation and McStas simulations

Propagation-based phase contrast, for example in the form of edge enhancement contrast, is well established within X-ray imaging but is not widely used in neutron imaging. This technique can help increase the contrast of low-attenuation samples but may confuse quantitative absorption measurements. Therefore, it is important to understand the experimental parameters that cause and amplify or dampen this effect in order to optimize future experiments properly. Two simulation approaches have been investigated, a wave-based simulation and a particle-based simulation conducted in McStas [Willendrup & Lefmann (2020). J. Neutron Res. 22, 1–16], and they are compared with experimental data. The experiment was done on a sample of metal foils with weakly and strongly neutron absorbing layers, which were measured while varying the rotation angle and propagation distance from the sample. The experimental data show multiple signals: attenuation, phase contrast and reflection. The wave model reproduces the sample attenuation and the phase peaks but it does not reproduce the behavior of these peaks as a function of rotation angle. The McStas simulation agrees better with the experimental data, as it reproduces attenuation, phase peaks and reflection, as well as the change in these signals as a function of rotation angle and distance. This suggests that the McStas simulation approach, where the particle description of the neutron facilitates the incorporation of multiple effects, is the most convenient way of modeling edge enhancement in neutron imaging.

Amplification and excitation of surface plasmon polaritons via four-wave mixing process

We suggest a scheme for the excitation and amplification of surface plasmon polaritons (SPPs) along the interface between metal and semiconductor quantum well (SQW), employing a four-wave mixing (FWM) process. The SQW consists of four-level asymmetric double quantum wells that exhibit quantum interference effects, which leads to the coupler-free excitation of SPPs. In our proposed system, the inherent losses of SPPs are compensated by introducing gain through the FWM process, resulting in a significant enhancement in the propagation length and penetration depth of SPPs. We further analyze the effect of gain on the long-range and short-range SPPs and observe that the propagation distance and lifetime of both types of SPPs are increased.

Intensity distribution of the partially coherent Gaussian Schell vortex beam diffracted by classical axicon

Based on the mathematical framework of the partially coherent Gaussian Schell model vortex (PCGSMV) beam and the Huygens-Fresnel integral, we conducted a study to analyze the intensity distribution and depth of focus (DOF) of the PCGSMV beam as it propagates through a classical axicon. Our numerical results indicate the influence of factors such as the beam width, spatial degree of coherence, topological charge, and axicon base angle on the intensity distribution and DOF. In addition, we investigated the relationship between the beam spot size and propagation distance, as well as the effects of the spatial degree of coherence and propagation distance on the intensity profile. Our findings highlight the importance of the intensity values along the DOF for various applications, including the optical trapping and manipulation of micro-particles.

A novel method for holdup measurement of three phases by an ultrasonic device with the flexible substrate

The precise measurement of multiphase flow holds significant importance across diverse industrial contexts. However, rigid probes struggle with the variable dimensions of curved surfaces, while flexible probes are hindered by fragility, susceptibility, and challenges in large-scale production. Herein, we propose an ultrasonic device featuring a flexible substrate that seamlessly amalgamates flexibility and rigidity to enable precise measurement of three-phase flow. Through simulation, we determine the optimal ultrasonic frequency (1 MHz) and flexible substrate thickness (3 mm) for a specified probe and pipe size (20 mm). A novel concept, the specific attenuation coefficient (SAC), derived from the voltage-amplitude of transmitted and received signals and propagation distance, is introduced to differentiate between oil and water. The discrepancy between measured and actual three-phase holdups are 0.55 %, 0.36 %, and 0.59 % for water, gas and oil, respectively, with a variance of measurement results 0.027.

The Cause of the Difference in the Propagation Distances between Compact and Transient Jets in Black Hole X-Ray Binaries

Accreting black hole binaries change their properties during evolution, passing through two main luminous states, dominated by either hard or soft X-rays. In the hard state, steady compact jets emitting multiwavelength radiation are present. Those jets are usually observed in radio, and when resolved, their extent is ≲1015 cm. Then, during hard-to-soft transitions, powerful ejecta in the form of blobs appear. They are observed up to distances of ∼1018 cm, which are ≳1000 times larger than the extent of hard-state jets. On the other hand, estimates of the accretion rates during most luminous hard states and the hard-to-soft transitions are very similar, implying that maximum achievable powers of both types of jets are similar and cannot cause a huge difference in their propagation. Instead, we explain the difference in the propagation length by postulating that the ejecta consist of electron-ion plasmas, whereas the hard-state jets consist mostly of electron–positron pairs. The inertia of the ejecta are then much higher than those of compact jets, and the former are not readily stopped by ambient media. A related result is that the accretion flow during the hard state is of standard and normal evolution, while it is a magnetically arrested disk during transient ejections. The pairs in hard-state jets can be produced by collisions of photons of the hard spectrum emitted by hot accretion flows within the jet base. On the other hand, the X-ray spectra during the state transitions are relatively soft, and the same process produces much fewer pairs.

Simulations of non-integer upconversion in resonant six-wave scattering

Resonant upconversion through a sixth order relativistic nonlinearity resulting in a unique resonance was recently proposed [Malkin and Fisch, Phys. Rev. E 108, 045208 (2023)]. The high order resonance is a unique non-integer multiple of a driving pump frequency resulting in a frequency upshift by a factor of ≈3.73. We demonstrate the presence, unique requirements, and growth of this mode numerically. Through tuning waves to high amplitude, in a mildly underdense plasma, the six-photon process may grow more than other non-resonant but lower order processes. The growth of the high frequency mode remains below the nonlinear growth regime. However, extending current numerical results to more strongly coupled resonances with longer pulse propagation distances suggests a pathway to significant upconversion.

Theoretical and numerical study on transient acoustic wave propagation across ice layers in the Arctic Ocean.

The study of transient acoustic wave propagation across the Arctic Ocean ice layer provides theoretical guidance for the design of trans-ice acoustic communication systems. In this study, the Arctic Ocean was modeled as an ice-water composite structure, where the ice and water are regarded as an elastic solid and liquid, respectively. An analytical transient solution for acoustic wave propagation in this structure was derived using the eigenfunction expansion method. Further, the numerical procedures were presented and used to analyze the acoustic wave propagation characteristics across the ice layer. The results show that waveforms corresponding to the radial displacements are more severely distorted than the axial displacements. The amplitudes of the radial and axial displacements decreased rapidly with increasing propagation distance. The ice thickness had a greater impact on the radial displacement than axial displacement; the thicker the ice, the greater the distortion for both radial and axial displacements.

Orbital angular momentum spectrum of model partially coherent beams in turbulence

The use of partial coherence has been extensively studied as a potential solution to mitigate the destructive effects of atmospheric turbulence in optical applications involving the free space propagation of light. However, in OAM-based optical systems, reducing coherence leads to the broadening of the orbital angular momentum (OAM) spectrum, consequently increasing the cross-talk between adjacent modes. In this paper, we have investigated three fundamental classes of partially coherent OAM beams under the influence of turbulence. The aim is to identify a distinct type of partially coherent beam (PCB) in which the reduction in coherence results in higher resistance of the OAM spectrum against atmospheric disturbances. It is demonstrated that, for a specific propagation distance, we can prepare a PCB in which the benefits of reducing coherence outweigh its drawbacks.

Laser protection by using vortex wavefront coding imaging system

Laser blindness can reduce or disable the information acquisition ability of photoelectric imaging systems. In this paper, numerical simulation and experimental verification are both performed to systematically study the laser protection performance of the vortex phase mask. First, the imaging model and laser transmission model of the vortex wavefront coding imaging system are introduced in detail. Then, the experimental setup of the imaging system is built, and the imaging result of the imaging system is obtained. Finally, the influence of propagation distance on the maximum single-pixel receiving power and suppression ratio of the imaging system is measured experimentally. The simulation and experimental results both show that the energy suppression ratio of this method can reach more than two orders of magnitude compared with the conventional imaging system, and the probability of laser blindness can be effectively reduced.

Prediction method for the tension force of support ropes in flexible rockfall barriers based on full-scale experiments and numerical analysis

This paper proposes a prediction method for the tension force of support ropes in flexible rockfall barriers. The method is based on two full-scale model tests with an impact energy of 3000 kJ, as well as 36 set numerical models featuring varying lengths and impact energies. From the results of full scale tests and numerical models, it is inferred that the tension force at the end of the support rope is significantly less than that at the point of impact, exhibiting an approximate Gaussian attenuation distribution with propagation distance. To account for the attenuation of tensile forces in support ropes, a tensile attenuation coefficient is defined. Through comparative analysis of data obtained from 36 models with varying impact energies and propagation distances, the average attenuation coefficient for the upper support rope is determined to be approximately 0.7, while the average coefficient for the lower support rope is around 0.8. Utilizing the least squares method, a prediction method for the tension force of support ropes in flexible rockfall barriers is established. This method takes into account both the propagation distance and impact energy, enabling accurate predictions of the tensile behavior of the ropes under different conditions. This prediction model provides valuable insights for engineers in the design and optimization of these flexible barriers for rockfall mitigation.

Extra-cavity modulation of a chirped Gaussian bisoliton

Optical solitons can find important applications in optical fiber communication systems. Here, we simulate extra-cavity modulation of a chirped Gaussian bisoliton in a 1 μm wavelength band. Several different soliton parameters are varied (including the amplitude ratio and time delay of orthogonal components, the projection angle, phase difference, pulse chirps and propagation distances), to effectively change the optical spectra and pulse shapes of the initial input chirped Gaussian bisoliton. For example, when the two branches in the optical fiber modulation system have the same or different fiber lengths, the modulated chirped Gaussian bisoliton will show obviously different properties in the time domain for orthogonally polarized components, while the corresponding optical spectra have no obvious differences. The simulation results reveal the effects of extra-cavity modulation of the chirped Gaussian bisoliton, which further explores the field of soliton shaping out of a fiber laser cavity.

Engineering Waveguide Nonlinear Effective Length via Low Index Thin Films

AbstractNovel photonic nanowires are fabricated using low‐index materials and tested in the near‐infrared spectrum to assess their nonlinear optical properties. In this work, the need to redefine the standard nonlinear figure of merit in terms of nonlinear phase shift and optical transmission for a given propagation distance is argued. According to this new metric, the devices largely outperform all established platforms for optical modules with a linear footprint in the range of 50–500 µm, which is demonstrated to be an outstanding technological gap. For 85 fs pulses, with carrier wavelength at 1480 nm and sub‐µW power levels, a spectral broadening exceeding 80% of the initial bandwidth was recorded over a propagation length of just 50 µm. Leveraging on CMOS‐compatible processes and well‐established materials such as silicon, silica, and indium tin oxide, the devices bring great promise for developing alternative all‐optical devices with unparalleled nonlinear performances within the aforementioned range.

Phase-shifted counterpropagating atmospheric pressure plasma jets: Characterization and interaction with materials

This study investigates the interaction between two counterpropagating atmospheric pressure plasma jets when their respective streamer ignition times are varied by introducing a phase difference between the AC waveforms used to generate them. When the plasma jets are driven in phase, the streamers form at approximately the same time, resulting in a dark region between the two jets. As the phase difference increases, this dark region shifts toward one of the electrodes. With a sufficiently large phase difference, this region vanishes, giving rise to a uniform plasma channel spanning the distance between the electrodes. High-speed imaging reveals that the interaction between the streamers within the channel reduces the streamer propagation length at intermediate phase differences. At large phase differences, the propagation distance of each streamer is enhanced due to the absence of the opposing streamer. Increasing the phase from 0° to 160° reduced the power consumption of the two jets by about 10%, while there was no significant change in the electron density or the N2 vibrational/rotational temperature. Finally, we show how phase-shifting enhances the interaction with three-dimensional objects located between the opposing jets, enabling the treatment of 3D substrates.

Labor linkages and flow paths of industry in China

As economic power increases and market patterns adapt, labor becomes an increasingly significant factor of production. However, there is a dearth of discourse regarding the structural changes that have occurred in the correlation of the labor force across industries, as well as a visual representation of the labor force's movement across industries. To quantify and analyze the correlation effect with greater precision, it is necessary to establish an input-output model as the foundation of analysis, comparing the changes in the total output of the economic system prior to and subsequent to the exclusion using the vertical integration algorithm. By decomposing the path structure, the average propagation distance of the labor force population's demand for each industry can be determined. By employing labor force population data from the corresponding years and China's input-output tables published by the National Bureau of Statistics of China (NBS) from 2005 to 2020, this study conducts a quantitative analysis of the correlation effect between labor force population and the trend of its transfer across 19 industries. The findings indicate that the correlation effect between labor force and population is most pronounced in the manufacturing sector. Furthermore, the construction sector faces an especially critical requirement for labor force personnel from other industries. The article culminates with a recommendation that the government enhance its macro-control endeavors to address labor market risk shocks and take an active stance in response to labor market fluctuations.

Influence of component parameters on propagation characteristics of foaming polyurethane grout in rock fractures

Polyurethane grouting is an important technical solution used for seepage prevention and mechanical reinforcement of fractured rock. Various components of polyurethane grout significantly affect the grout properties and propagation behavior. The present study focuses on the crucial role of component parameters in controlling the propagation process and designing grouting parameters for foaming polyurethane grout. A coupled modeling approach combining chemical reactions and flow field analysis is developed to investigate the polyurethane foaming process. The proposed modeling approach is validated by comparing simulation results with experimental data from the literature. The influence of key component parameters: isocyanate index, initial water concentration and physical blowing agent, on the propagation characteristics (including propagation distance, maximum pressure, final density, reaction time and maximum temperature) of foaming polyurethane grout in rock fractures are further analyzed. The results reveal two distinct types of effects caused by the components, i.e., a monotonic relationship and a parabolic trend. Critical values are identified for the impact of isocyanate index on maximum propagation distance, final density and characteristic time, as well as for the influence of physical blowing agent on maximum propagation distance, final density and maximum pressure. Other parameters demonstrated a monotonic relationship. Additionally, a quantitative assessment is conducted to evaluate the impact of multiple components on propagation characteristics. The finding indicates that the initial water concentration has a significant effect on all properties, while isocyanate index exerts a more pronounced impact on reaction time and maximum temperature. The effect of the physical blowing agent is relatively minor compared to other factors. This study is helpful for material selection and proportioning of polyurethane grout in practical engineering applications.

Band-amplified angle spectrum method for the phase hologram design to achieve high-quality holographic imaging in long distance

The angular spectrum method (ASM) is widely used in the design of computer-generated holograms (CGH) due to its strict adherence to the Helmholtz equations and the potential for accelerated computation using fast Fourier transform (FFT). However, when dealing with long distance propagation conditions, the reduction of effective spectral components and spectral aliasing will introduce significant computation errors, leading to a substantial degradation in holographic imaging quality. To achieve high-quality holographic imaging design in long distance, we introduce a novel angular spectrum computation method, the calculation process is divided into two steps: (1) First propagate a longer distance from the CGH plane to an intermediate plane. (2) Then continue to propagate to the observation plane after incorporating a spread spectrum phase factor to amplify the effective non-aliased bandwidth in the intermediate plane and eliminating the aliasing artifacts. Furthermore, the non-uniform fast Fourier transform (NUFFT) algorithm is adopted which allows for the flexible adjustments of the sampling interval and quantity in the spatial frequency domain, all while maintaining compliance with the Nyquist sampling theorem even in the context of bandwidth amplification. Both simulations and optical experiments are conducted to validate the feasibility and effectiveness of our proposed method.

Overtaking Effects on Spherical Shock Wave Propagation in Metallic Mediums

The propagation of spherical shock waves through metallic mediums have been considered in this paper. The effect of overtaking disturbances in the propagation of spherical shock waves through solids, especially metals such as Aluminium and Copper, has been analysed by employing Chisnell-Chester-Whitham method. Under the influence of spherical shock waves flow variables have been obtained analytically as well as estimated numerically. Expressions for the pressure and the particle velocity behind the shock wave have also been obtained. It is found that shock strength in both the metals decreases as shock propagates through them. Shock velocity and modified shock velocity depict a decreasing pattern with increasing propagation distance. These observations suggest many industrial and medical applications of shock waves.

How good are collimated Gaussian beams produced with engineered diffusers?

Collimating a Gaussian beam from an uncollimated laser source has been achieved via the deployment of engineered diffusers (EDs)—also referred to as light shaping diffusers. When compared to conventional pinhole-based optical collimation systems, this method of beam collimation ensures high optical transmission efficiency at the expense of the introduction of additional speckle and a resulting reduction in spatial coherence. Despite a lower collimation quality, these ED-produced collimated beams are attractive and promising in terms of their deployment in various benchtop or tabletop systems that involve shorter beam propagation distances of up to a few meters while requiring a high optical power throughput. This paper aims to further the understanding of collimation quality and propagation properties of ED-produced Gaussian collimated beams via carefully designed experiments and accompanying analysis. We measure and document the beam divergence, Rayleigh distance, and M2 factor, as well as evolution of the wavefront radius of curvature (RoC), of these ED-generated beams over a few meters of propagation—a propagation distance which encapsulates a vast majority of optical systems. We further investigate the changes in the beam profile with the addition of a laser speckle reducer (SR) and compare the ED-produced beams with a near-ideal collimated beam produced with spatial filtering systems.

Characteristics of shock wave in 355 nm laser-induced damage growth in fused silica

During the 355 nm laser-induced damage growth in fused silica, the distance of shock wave propagation decreases as the irradiation number increases. The dynamic image of the damage reveals that the growth of the damage cavity region is one of the primary reasons for the variation in shock wave propagation distance and structure. The growth coefficient and the depth-to-diameter ratio of the cavity are closely related to the decrease in shock wave propagation distance. Based on the Taylor–Sedov theory, this work presents a modified scaling that couples the growth coefficient with the depth-to-diameter ratio. The calculated results are in agreement with the experiment. It is a valuable complement to the study of shockwave propagation characteristics of damage growth.