Double Scattering Research Articles

Determination of equivalent crack length for voids in metallic alloys based on continuum damage mechanics modeling

Metals contain different kinds of spatial defects significantly reducing the fatigue performance. Accurate defect-based life prediction methods are required to improve structural integrity analysis and life design reliability. The present work developed a method to determine the equivalent crack length for defects based on continuum damage mechanics. The spatial effects of defects in the calculation of the equivalent crack were quantified and verified by fatigue tests. It is confirmed that the equivalent crack length of both slit and elliptic defects is affected not only by the defect geometry but also by the applied load. Based on the equivalent crack and combined with Paris’ law, the predicted fatigue lives of various slit holes under different loading orientations are within the double scatter band and are much more accurate than the conventional projection method.

Secured Performance Analysis of Double Scattering MIMO Network

Secured Performance Analysis of Double Scattering MIMO Network

Total and Double Differential Scattering Cross-Section Measurements of Isotropic Graphite

Total and Double Differential Scattering Cross-Section Measurements of Isotropic Graphite

Orthogonal Space-Time Block Coding for Double Scattering V2V Links with LOS and Ground Reflections

This work presents the performance analysis of space-time block codes (STBCs) for vehicle-to-vehicle (V2V) fast-fading channels in scenarios with modified line-of-sight (LOS). The objective is to investigate how the V2V MIMO (multiple-input multiple-output) system performance is influenced by two important impairments: deterministic ground reflections and an increased Doppler frequency (time-variant channels). STBCs of various coding rates (using an approximation model) are evaluated by assuming antenna elements distributed over the surface of two contiguous vehicles. A multi-ray model is used to study the multiple constructive/destructive interference patterns of the transmitted/received signals by all pairs of Tx–Rx antenna links considering ground reflections. A double scattering model is used to include the effects of stochastic channel components that depend on the Doppler frequency. The results show that STBCs are capable of counteracting fades produced by destructive self-interference components across a range of inter-vehicle distances and for a range of Doppler frequency values. Notably, the effectiveness of STBCs in deep fades is shown to outperform schemes with exclusive receive diversity, despite the interference created by the loss of orthogonality in time-varying channels with a moderate increase of Doppler frequency (mainly due to higher vehicle speeds, higher frequency or shorter time slots). Higher-order STBCs with rate losses are also evaluated using an approximation model, showing interesting gains even for low coding rate performance, particularly when accompanied by a multiple antenna receiver. Overall, these results can shed light on how to exploit transmit diversity in time-varying vehicular channels with modified LOS.

Increased flexibility and efficiency of a double-scattering FLASH proton beamline configuration for in vivo SOBP radiotherapy treatments

Objective. To commission a proton, double-scattering FLASH beamline by maximizing efficiency and field size, enabling higher-linear energy transfer FLASH radiotherapy to cells and small animals using a spread-out Bragg peak (SOBP) treatment configuration. We further aim to provide a configuration guide for the design of future FLASH proton double-scattering (DS) beamlines. Approach. Beam spot size and spread were measured with film and implemented into TOol for PArticle Simulation (TOPAS). Monte Carlo simulations were optimized to verify the ideal positioning, dimensions, and material of scattering foils, secondary scatterers, ridge filters, range compensators, and apertures. A ridge filter with three discrete heights was used to create a spread-out Bragg peak (SOBP) and was experimentally verified using our in-house experimental FLASH beamline. The increase in dose rate was compared to nominal shoot-through techniques. Results. The configuration and scatterer distance producing the largest field size of acceptable flatness, without drastically compromising dose rate was determined to be an elliptical field of 2 cm × 1.5 cm (25% larger than a previous configuration). SOBP testing yielded three distinct but connected spikes in dose with flatness under 5%. Reducing the thickness of the (first) scattering foil by a factor of two was found to increase efficiency by 50%. The new settings increased the field size, provided a Bragg peak treatment option, and increased the maximum available dose rate by 85%, as compared to the previous, shoot through method. Significance. Beam line updates established FLASH dose rates of over 135 Gy s−1 (potentially higher) at our double-scattering beamline, increased the efficiency and field size, and enabled SOBP treatments by incorporating an optimized ridge filter. Based on our simulations we provide parametric suggestions when commissioning a new proton DS beamline. This enhanced FLASH beamline for SOBP irradiations with higher dose rates and larger field sizes will enable a wider variety of experimentation in future studies.

Complete mode conversion between longitudinal and transverse waves by an elastic metamaterial slab with a double-scatterer structure

In this work, we propose a design of a double-scatterer structure to achieve complete conversion for elastic bulk waves. Every unit of the elastic metamaterial slab contains a pair of scatterers with a relatively oblique direction. When the slab attaches on a semi-infinite solid background, it can completely convert the normal incident longitudinal wave into the reflected shear wave, or vice versa. The conversion can be attributed to the in-phase coupling of the double scatterers’ quadrupolar resonances. The coupled two quadrupoles could interact with the background and bring oblique displacements. Consequently, the oblique displacements generate horizontal displacements for reflected waves.

Secondary radiation dose modeling in passive scattering and pencil beam scanning very high energy electron (VHEE) radiation therapy.

Electrons with kinetic energy up to a few hundred MeV, also called very high energy electrons (VHEE), are currently considered a promising technique for the future of radiation therapy (RT) and in particular ultra-high dose rate (UHDR) therapy. However, the feasibility of a clinical application is still being debated and VHEE therapy remains an active area of research for which the optimal conformal technique is also yet to be determined. In this work, we will apply two existing formalisms based on analytical Gaussian multiple-Coulomb scattering theory and Monte Carlo (MC) simulations to study and compare the electron and bremsstrahlung photon dose distributions arising from two beam delivery systems (passive scattering with or without a collimator or active scanning). We therefore tested the application of analytical and MC models to VHEE beams and assessed their performance and parameterization in the energy range of 6-200MeV. The optimized electron beam fluence, the bremsstrahlung, an estimation of central-axis and off-axis x-ray dose at the practical range and neutron contributions to the total dose, along with an extended parameterization for the photon dose model were developed, together with a comparison between double scattering (DS) and pencil beam scanning (PBS) techniques. MC simulations were performed with the TOPAS/Geant4 toolkit to verify the dose distributions predicted by the analytical calculations. The results for the clinical energy range (between 6 and 20MeV) as well as for higher energies (VHEE range between 20 and 200MeV) and for two treatment field sizes (5×5 and 10×10 cm2 ) are reported, showing a reasonable agreement with MC simulations with mean differences below 2.1%. The relative contributions of photons generated in the medium or by the scattering system along the central-axis (up to 50% of the total dose) are also illustrated, along with their relative variations with electron energy. The fast analytical models parametrized in this study allow an estimation of the amount of photons produced behind the practical range by a DS system with an accuracy lower than 3%, providing important information for the eventual design of a VHEE system. The results of this work could support future research on VHEE radiotherapy.

Investigation the Performance Accuracy of Contoured Dual Ring Double Scatterer System for Flat Beam Generation at Proton Therapy

At proton radiotherapy, the extracted beam from accelerator is not initially suitable for tumor treatment and a modification is needed for beam shape and energy due to tumor dimension and site. One clinical strategy is the use of double scattering systems known as passive dose delivery technique to generate proper flattening, transversely. This work aims to design and simulate a new version of double scattering system and compare its performance with another available scatterer system, quantitatively. In this analytical study, Monte Carlo FLUKA code is utilized to simulate the performance of proposed system in generating lateral flat beam. The simulation process is very close to real experimental condition, performed at proton beam irradiation room at Tohoku University in Japan. Moreover, the presence of secondary neutrons, produced due to protons collision with proposed scattering system, is considered as main issue. Final results represent that the proposed scattering system is robust to generate 40 mm flat region with an acceptable uniformity degree. Energy loss caused by current dual scatterer is more than simple ring technique, while the secondary neutrons produced by proposed system are larger than other system. This study simulates the performance of a new dual ring double scattering system. Final results show that there is a close correlation between proposed system and current scattering system. The only concern is about the presence of secondary neutrons mainly at high energy proton particles.

Toward improved urban flood detection using Sentinel-1: dependence of the ratio of post- to preflood double scattering cross sections on building orientation

High-resolution synthetic aperture radar (SAR) sensors are now commonly used for flood detection. Automated detection tends to be limited to rural areas owing to the complicated backscattering mechanisms occurring in urban areas. Flooding can be identified in urban areas by searching for increased SAR backscatter in a postflood image due to double scattering between water and adjacent buildings, compared with a preflood image where double scattering is between unflooded ground and buildings. For co-polarized data, if φ is the angle between the building wall and the satellite direction of travel, double scattering is strongest for φ = 0 deg and falls off as φ increases. Theoretical studies estimating the ratio of flooded-to-unflooded double scatterer (DS) radar cross section (RCS) using X-band SAR data, found that the ratio was high at φ = 0 deg but only small at φ > 10 deg. Ostensibly, this implies that few DSs might be detected in an urban area. However, experiments on real images have called into question the veracity of the modeling. We describe an empirical study to examine the relationship between the flooded-to-unflooded DS RCS ratio and φ in Sentinel-1 (S-1) C-band data. We use high-resolution light detection and ranging and aerial photographs so that φ can be measured accurately and is based on S-1 images from flood events that occurred in the United Kingdom during the storms of winter 2019 to 2020. Results indicate that vertical–vertical polarization is better than vertical–horizontal at distinguishing flooded from unflooded DS; that the theoretical model used underestimates the number of DS with high RCS ratios in the φ range 10 deg to 30 deg; and that sufficient DS ground heights can be determined to estimate an accurate local average flood level, although in high density housing there are less of these due to the presence of adjacent buildings.

Automatic Ship Detection Using PolSAR Imagery and the Double Scatterer Model

In ship detection by means of Polarimetric SAR imagery, a very promising feature is the characterization of the pixels of the ship based on the elementary scattering mechanisms that can be extracted using different decomposition algorithms. Elementary scattering mechanisms provide information regarding the physical, electrical and geometrical properties of the scatterers in each Polarimetric SAR pixel. In this work, the newly established algorithm of the Double Scatterer Model is applied to interpret each pixel of the Polarimetric SAR image with the contributions of two elementary scattering mechanisms, namely, primary and secondary. The main idea is to construct a binary image while preserving the rich information content in order to proceed in simple and fast image processing for target detection. The present algorithm is applied to datasets with different inherent characteristics acquired by Radarsat-2 and ALOS-PALSAR. The results presented by this new perspective on ship monitoring are remarkable.

Double Coherent Scatter Radars Observations of the Daytime F‐Region Irregularities in Low‐Latitudes on 29 May 2017

AbstractIn the morning on 29 May 2017, the Sanya very‐high‐frequency Radar and the Hainan COherent Scatter Phased Array Radar (HCOPAR) at Fuke were cooperated with similar operating frequencies to investigate the dissipation of the daytime F‐region Field‐Aligned Irregularities (FAIs). The two radars are located on south and north sides of the Hainan island of China, and the distance between them is about 140 km. The Sanya VHF radar recorded the FAIs between 00:12 and 02:42 UT (07:12 and 09:42 LT), and the FAIs observed by the HCOPAR appeared more than 10 min later at lower altitudes and suffered severe dissipation. The echoes emerged in all the beams simultaneously, and their Doppler velocities were close to zero, implying that the daytime FAIs were traveling along the magnetic field lines downward and northward with almost no zonal velocity. The front and bottom edges of the irregularities decayed earlier, and the parts in the FAIs with steeper density gradient lasted longer. The dissipation mechanism is attributed primarily to the photoionization and diffusing across the geomagnetic field in different period and gradient of the irregularities.

Pencil Beam Scanning (PBS) Proton Therapy for Children Requiring Radiotherapy with Anesthesia (GA) for Pelvic Rhabdomyosarcoma (RMS)

<h3>Purpose/Objective(s)</h3> Radiotherapy (RT) for pediatric pelvic RMS presents unique challenges, particularly for young children who require GA during RT, for whom bladder/rectal filling can be particularly variable. PBS may reduce dose to OARs and risk of second malignancy vs. double scatter (DS) protons; however, the precision of PBS requires highly reproducible daily setup. This study was undertaken to describe use of PBS in patients requiring RT for pelvic RMS with daily GA. <h3>Materials/Methods</h3> Pts with RMS of pelvic soft tissues treated with PBS from 1/2013-6/2020 with GA were included in this IRB-approved retrospective analysis. PBS proton plans were developed for all. DS plans were generated for all, and photon (VMAT) backup plans for 9/11 pts. Statistical analyses used 2-sided Student's t-tests. <h3>Results</h3> 11 total pts, median age 2.4 y (R 9 m – 5.9 y), 6 male patients, all had fusion-negative RMS (10 group 3 disease; 1 recurrent bladder/vaginal wall). Primary site included bladder (1), prostate (6), uterus (2), and vagina (1). During simulation/daily treatments under GA, Foley catheter with bladder filling to 75% expected capacity was used for 10. Rectal balloon was used for 2; aggressive management of constipation to promote empty rectum was used for all. All pts had IGRT (daily kV +/- CT [6]). RT dose was 41.4 Gy after delayed primary excision (DPE) (3) and 50.4 Gy without (8). Of 10 pts with FU data, all were without evidence of disease at median FU 1.3 y (range 0.3 – 5.6 y). Acute G3 toxicities included anorexia (3), diarrhea (1), and dermatitis (1), with no G4+ toxicities. One pt developed late RT cystitis. Among pts treated to 50.4 Gy, mean bladder dose (p<0.05) and body V5 (p<0.001) were significantly lower for PBS vs. photons. Max bladder, rectum, and body doses were significantly lower for PBS vs. DS (p<0.05 for each). <h3>Conclusion</h3> PBS proton therapy for very young children with pelvic RMS demonstrates acceptable rates of local control and toxicity when delivered under GA with deliberate management of bladder/rectal filling. Integral dose is reduced with PBS vs. VMAT, and OAR doses are reduced with PBS vs. DS. PBS should be considered in future trials as a standard RT approach for pediatric pelvic RMS.

Land Cover Classification Based on Double Scatterer Model and Neural Networks

In this paper, a supervised land cover classification is presented based on the extracted information from polarimetric synthetic aperture radar (PolSAR) images. The analysis of the polarimetric scattering matrix is accomplished according to the Double Scatterer Model which interprets each PolSAR cell by a pair of elementary scattering mechanisms. Subsequently, by utilizing the contribution rate of the two fundamental scatterers, a novel data representation is accomplished, providing great informational content. The main component of the research is to highlight the robust new feature-tool and afterwards to present a classification scheme exploiting a fully connected artificial neural network (ANN). The PolSAR images used to verify the proposed method were acquired by RADARSAT-2 and the experimental results confirm the effectiveness of the presented methodology with an overall classification accuracy of 93%, which is considered satisfactory since only four feature-vectors are used.

Critical plane-based fatigue life model under multiaxial random loading

PurposeEngineering components/structures are usually subjected to complex and variable loads, which result in random multiaxial stress/strain states. However, fatigue analysis methods under constant loads cannot be directly applied to fatigue life prediction analysis under random loads. Therefore, the purpose of this study is how to effectively evaluate fatigue life under multiaxial random loading.Design/methodology/approachFirst, the average phase difference is characterized as the ratio of the number of shear strain cycles to the number of normal strain cycles, and the new non-proportional additional hardening factor is proposed. Then, the determined random typical load spectrum is processed into a simple variable amplitude load spectrum, and the damage in each plane is calculated according to the multiaxial fatigue life prediction model and Miner theory. Meanwhile, the cumulative damage can be calculated separately by projection method. Finally, the maximum projected cumulative damage plane is defined as the critical plane of multiaxial random fatigue.FindingsThe fatigue life prediction capability of the method is verified based on test data of TC4 titanium alloy under random multiaxial loading. Most of the predicting results are within double scatter bands.Originality/valueThe objective of this study is to provide a reference for the determination of critical plane and non-proportional additional hardening factor under multiaxial random loading, and to promote the development of multiaxial fatigue from experimental studies to practical engineering applications.

Front-End Design for SiPM-Based Monolithic Neutron Double Scatter Imagers.

Neutron double scatter imaging exploits the kinematics of neutron elastic scattering to enable emission imaging of neutron sources. Due to the relatively low coincidence detection efficiency of fast neutrons in organic scintillator arrays, imaging efficiency for double scatter cameras can also be low. One method to realize significant gains in neutron coincidence detection efficiency is to develop neutron double scatter detectors which employ monolithic blocks of organic scintillator, instrumented with photosensor arrays on multiple faces to enable 3D position and multi-interaction time pickoff. Silicon photomultipliers (SiPMs) have several advantageous characteristics for this approach, including high photon detection efficiency (PDE), good single photon time resolution (SPTR), high gain that translates to single photon counting capabilities, and ability to be tiled into large arrays with high packing fraction and photosensitive area fill factor. However, they also have a tradeoff in high uncorrelated and correlated noise rates (dark counts from thermionic emissions and optical photon crosstalk generated during avalanche) which may complicate event positioning algorithms. We have evaluated the noise characteristics and SPTR of Hamamatsu S13360-6075 SiPMs with low noise, fast electronic readout for integration into a monolithic neutron scatter camera prototype. The sensors and electronic readout were implemented in a small-scale prototype detector in order to estimate expected noise performance for a monolithic neutron scatter camera and perform proof-of-concept measurements for scintillation photon counting and three-dimensional event positioning.

Uplink Power Control in Massive MIMO With Double Scattering Channels

Massive multiple-input multiple-output (MIMO) is a key technology for improving the spectral and energy efficiency in 5G-and-beyond wireless networks. For a tractable analysis, most of the previous works on Massive MIMO have been focused on the system performance with complex Gaussian channel impulse responses under rich-scattering environments. In contrast, this paper investigates the uplink ergodic spectral efficiency (SE) of each user under the double scattering channel model. We derive a closed-form expression of the uplink ergodic SE by exploiting the maximum ratio (MR) combining technique based on imperfect channel state information. We further study the asymptotic SE behaviors as a function of the number of antennas at each base station (BS) and the number of scatterers available at each radio channel. We then formulate and solve a total energy optimization problem for the uplink data transmission that aims at simultaneously satisfying the required SEs from all the users with limited data power resource. Notably, our proposed algorithms can cope with the congestion issue appearing when at least one user is served by lower SE than requested. Numerical results illustrate the effectiveness of the closed-form ergodic SE over Monte-Carlo simulations. Besides, the system can still provide the required SEs to many users even under congestion.

Proceedings to the 7th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA)

Proceedings to the 7th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA)

γ-Net: Superresolving SAR Tomographic Inversion via Deep Learning

Synthetic aperture radar tomography (TomoSAR) has been extensively employed in 3-D reconstruction in dense urban areas using high-resolution SAR acquisitions. Compressive sensing (CS)-based algorithms are generally considered as the state-of-the art in super-resolving TomoSAR, in particular in the single look case. This superior performance comes at the cost of extra computational burdens, because of the sparse reconstruction, which cannot be solved analytically, and we need to employ computationally expensive iterative solvers. In this article, we propose a novel deep learning-based super-resolving TomoSAR inversion approach, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\gamma }$ </tex-math></inline-formula> -Net, to tackle this challenge. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\gamma }$ </tex-math></inline-formula> -Net adopts advanced complex-valued learned iterative shrinkage thresholding algorithm (CV-LISTA) to mimic the iterative optimization step in sparse reconstruction. Simulations show the height estimate from a well-trained <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\gamma }$ </tex-math></inline-formula> -Net approaches the Cramér-Rao lower bound (CRLB) while improving the computational efficiency by one to two orders of magnitude comparing to the first-order CS-based methods. It also shows no degradation in the super-resolution power comparing to the state-of-the-art second-order TomoSAR solvers, which are much more computationally expensive than the first-order methods. Specifically, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\gamma }$ </tex-math></inline-formula> -Net reaches more than 90% detection rate in moderate super-resolving cases at 25 measurements at 6 dB SNR. Moreover, simulation at limited baselines demonstrates that the proposed algorithm outperforms the second-order CS-based method by a fair margin. Test on real TanDEM-X data with just six interferograms also shows high-quality 3-D reconstruction with high-density detected double scatterers.

Sum-Rate Analysis of a Multi-Cell Multi-User MISO System Under Double Scattering Channels

This paper aims to derive expressions of the downlink ergodic user rates in a multi-cell large-scale multi-user multiple-input single-output (MISO) system under the assumption that each base station (BS) employs maximum ratio transmission (MRT) precoding and that single-antenna users in each cell are divided into groups, where channels of users in the same group share common covariance matrices and follow the double scattering channel model. Moreover, both channel estimation errors and pilot contamination effects caused by re-use of pilot sequences in neighboring cells are taken into consideration in this work. The analysis is carried out using statistical tools under the exact and asymptotic regimes in which the number of antennas at BS N, the number of users in each cell K, and the number of scatterers S grow large at the same pace. Furthermore, the obtained exact expressions and deterministic approximations of the ergodic rates are expressed in simplified closed-forms under the special case of multi-keyhole channels to yield useful insights. They reveal that signal-to-noise plus interference ratio (SINR) without user grouping in a multi-keyhole channel is similar to that under standard Rayleigh channel in the asymptotic regime. However, under user grouping, we show that the massive multiple-input multiple-output (MIMO) gains promised by deploying large-scale antenna arrays in multi-cell settings are limited by the number of scatterers even if the number of antennas grows large. Simulation results illustrate the close match provided by the asymptotic analysis for moderate system dimensions and confirm the insights drawn from the theoretical findings.

Basis Pursuit Denoising via Recurrent Neural Network Applied to Super-Resolving SAR Tomography

Finding sparse solutions of underdetermined linear systems commonly requires the solving of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> regularized least squares minimization problem, which is also known as the basis pursuit denoising (BPDN). They are computationally expensive since they cannot be solved analytically. An emerging technique known as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deep unrolling</i> provided a good combination of the descriptive ability of neural networks, explainable, and computational efficiency for BPDN. Many unrolled neural networks for BPDN, e.g. learned iterative shrinkage thresholding algorithm and its variants, employ shrinkage functions to prune elements with small magnitude. Through experiments on synthetic aperture radar tomography (TomoSAR), we discover the shrinkage step leads to unavoidable information loss in the dynamics of networks and degrades the performance of the model. We propose a recurrent neural network (RNN) with novel sparse minimal gated units (SMGUs) to solve the information loss issue. The proposed RNN architecture with SMGUs benefits from incorporating historical information into optimization, and thus effectively preserves full information to the final output. Taking TomoSAR inversion as an example, extensive simulations demonstrated that the proposed RNN outperforms the state-of-the-art deep learning-based algorithm in terms of super-resolution power as well as generalization ability. It achieved 10% to 20% higher double scatterers detection rate and is less sensitive to phase and amplitude ratio difference between scatterers. Test on real TerraSAR-X spotlight images also shows high-quality 3-D reconstruction of test site.