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Laser-based amorphization on the back surface of a 525-μm thick crystalline silicon sample is studied. To deposit sufficient energy for a local change from a crystalline to an amorphous state, laser irradiation at 2-μm wavelength with 25-ps pulse duration is combined with Bessel beam shaping. Deterministic single-site modifications and homogeneous continuous lines of amorphous silicon are demonstrated. Optical and electron microscopy together with Raman spectroscopy measurements highlight the material transformations featuring the formation of subwavelength periodic surface structures. The investigations open up possibilities for processing in-built microelectronic devices. [ABSTRACT FROM AUTHOR]

Background: Iterative reconstruction for cone-beam computed tomography (CBCT) has been applied to improve image quality and reduce radiation dose. In a case where an object's actual projection is larger than a flat panel detector, CBCT images contain truncated data or incomplete projections, which degrade image quality inside the field of view (FOV). In this work, we propose truncation effect reduction for fast iterative reconstruction in CBCT imaging. Methods: The volume matrix size of the FOV and the height of projection images were extrapolated to a suitable size. These extended projections were reconstructed by fast iterative reconstruction. Moreover, a smoothing parameter for noise regularization in iterative reconstruction was modified to reduce the accumulated error while processing. The proposed work was evaluated by image quality measurements and compared with conventional filtered backprojection (FBP). To validate the proposed method, we used a head phantom for evaluation and preliminarily tested on a human dataset. Results: In the experimental results, the reconstructed images from the head phantom showed enhanced image quality. In addition, fast iterative reconstruction can be run continuously while maintaining a consistent mean-percentage-error value for many iterations. The contrast-to-noise ratio of the soft-tissue images was improved. Visualization of low contrast in the ventricle and soft-tissue images was much improved compared to those from FBP using the same dose index of 5 mGy. Conclusions: Our proposed method showed satisfactory performance to reduce the truncation effect, especially inside the FOV with better image quality for soft-tissue imaging. The convergence of fast iterative reconstruction tends to be stable for many iterations. [ABSTRACT FROM AUTHOR]

Imaging examinations are of remarkable importance for diagnostic support in Dentistry. Imaging techniques allow analysis of dental and maxillofacial tissues (e.g., bone, dentine, and enamel) that are inaccessible through clinical examination, which aids in the diagnosis of diseases as well as treatment planning. The analysis of imaging exams is not trivial; so, it is usually performed by oral and maxillofacial radiologists. The increasing demand for imaging examinations motivates the development of an automatic classification system for diagnostic support, as proposed in this paper, in which we aim to classify teeth as healthy or with endodontic lesion. The classification system was developed based on a Siamese Network combined with the use of convolutional neural networks with transfer learning for VGG-16 and DenseNet-121 networks. For this purpose, a database with 1000 sagittal and coronal sections of cone-beam CT scans was used. The results in terms of accuracy, recall, precision, specificity, and F1-score show that the proposed system has a satisfactory classification performance. The innovative automatic classification system led to an accuracy of about 70%. The work is pioneer since, to the authors knowledge, no other previous work has used a Siamese Network for the purpose of classifying teeth as healthy or with endodontic lesion, based on cone-beam computed tomography images. [ABSTRACT FROM AUTHOR]

The use of deep learning (DL) to improve cone‐beam CT (CBCT) image quality has gained popularity as computational resources and algorithmic sophistication have advanced in tandem. CBCT imaging has the potential to facilitate online adaptive radiation therapy (ART) by utilizing up‐to‐date patient anatomy to modify treatment parameters before irradiation. Poor CBCT image quality has been an impediment to realizing ART due to the increased scatter conditions inherent to cone‐beam acquisitions. Given the recent interest in DL applications in radiation oncology, and specifically DL for CBCT correction, we provide a systematic theoretical and literature review for future stakeholders. The review encompasses DL approaches for synthetic CT generation, as well as projection domain methods employed in the CBCT correction literature. We review trends pertaining to publications from January 2018 to April 2022 and condense their major findings—with emphasis on study design and DL techniques. Clinically relevant endpoints relating to image quality and dosimetric accuracy are summarized, highlighting gaps in the literature. Finally, we make recommendations for both clinicians and DL practitioners based on literature trends and the current DL state‐of‐the‐art methods utilized in radiation oncology. [ABSTRACT FROM AUTHOR]

In stochastic structural mechanics, the treatment of uncertainty is often the main objective of numerical simulations to estimate the responses of a system or physical phenomenon. These predictions can form the basis for decision making, and therefore, a relevant issue to be studied is how reliable they are. Uncertainties, in general, are assessed under two aspects: from the available statistical information and considering the mathematical model that represents the problem numerically. The model identifies a set of relationships based on principles, conservation laws, and metrics of physical magnitude. For the stochastic bending problem of elastic and stationary beams, it is possible to associate randomness to the properties of the material, geometry, and loads on the structure. Thus, the estimates of the responses will be present in the field of stresses and deformations. In the present work, the variational formulation of the stochastic problem of the linear elliptical contour value with random coefficients is studied in light of the stochastic version of the Lax–Milgram lemma. The propagation and uncertainty quantification are investigated based on the recent numerical methodology of asymptotic complexity λ-Neumann–Monte Carlo. The results of the numerical simulation are obtained for the stochastic bending beam problem based on the Levinson–Bickford theory. The theory of high-order elastic bending has the advantage of meeting the condition of zero shears on the lateral surfaces of the beam. Numerical results are presented related to the accuracy, convergence, estimators of statistical moments, error estimate, and the processing time of the approximate solution for the high-order beam. [ABSTRACT FROM AUTHOR]

The finite element method (FEM) is used to investigate the free and forced vibration characteristics of functionally graded graphene-nanoplatelet-reinforced composite (FG-GPLRC) beams. The weight fraction of graphene nanoplatelets (GPLs) is assumed to vary continuously along the beam thickness according to a linear, parabolic, or uniform pattern. For the FG-GPLRC beam, the modified Halpin–Tsai micromechanics model is used to calculate the effective Young's modulus, and the rule of mixture is used to determine the effective Poisson's ratio and mass density. Based on the principle of virtual work under the assumptions of the Euler–Bernoulli beam theory, finite element formulations are derived to analyze the free and forced vibration characteristics of FG-GPLRC beams. A two-node beam element with six degrees of freedom is adopted to discretize the beam, and the corresponding stiffness matrix and mass matrix containing information on the variation of material properties can be derived. On this basis, the natural frequencies and the response amplitudes under external forces are calculated by the FEM. The performance of the proposed FEM is assessed, with some numerical results obtained by layering method and available in published literature. The comparison results show that the proposed FEM is capable of analyzing an FG-GPLRC beam. A detailed parametric investigation is carried out to study the effects of GPL weight fraction, distribution pattern, and dimensions on the free and forced vibration responses of the beam. Numerical results show that the above-mentioned effects play an important role with respect to the vibration behaviors of the beam. [ABSTRACT FROM AUTHOR]

A two-dimensional mixed problem for a thin elastic strip resting on a Winkler foundation is considered within the framework of plane stress setup. The relative stiffness of the foundation is supposed to be small to ensure low-frequency vibrations. Asymptotic analysis at a higher order results in a one-dimensional equation of bending motion refining numerous ad hoc developments starting from Timoshenko-type beam equations. Two-term expansions through the foundation stiffness are presented for phase and group velocities, as well as for the critical velocity of a moving load. In addition, the formula for the longitudinal displacements of the beam due to its transverse compression is derived. [ABSTRACT FROM AUTHOR]

Spectral CT has shown promise for high-sensitivity quantitative imaging and material decomposition. This work presents a new device called a spatial-spectral filter (SSF) which consists of a tiled array of filter materials positioned near the x-ray source that is used to modulate the spectral shape of the x-ray beam. The filter is moved to obtain projection data that is sparse in each spectral channel. To process this sparse data, we employ a one-step direct model-based material decomposition (MBMD) to reconstruct basis material density images directly from the SSF CT data. To evaluate different possible SSF designs, we define a new Fisher-information-based predictive image quality metric called separability index which characterizes the ability of a spectral CT system to distinguish between the signals from two or more materials. This spectral CT performance metric can be used to optimize spectral CT system design. We conducted simulation-based design optimization study to find optimized combinations of filter materials, filter thicknesses, filter widths, and source settings. Finally, we present MBMD results using simulated SSF CT measurements from the optimized designs to demonstrate the ability to reconstruct basis material density images and to show the benefits of the optimized designs. Our results indicate that optimizing SSF CT for separability leads to high-performance at material discrimination tasks. [ABSTRACT FROM AUTHOR]

This work investigates the problem of optimal placement and geometry of piezoelectric sensors and actuators (S/A) to improve active vibration control performance of smart laminated beam. Theoretical formulation is based on efficient layer-wise finite element model along with an optimal control theory. Control theory is implemented in state space format considering a reduced order model. A laminated beam with collocated piezoelectric S/A placed at the top and bottom surfaces has been considered. A series of simulation based on Taguchi design of experiment has been carried out to determine the optimal placement and geometry of the S/A to achieve best control performance that is maximum modal active damping ratio ξ /minimum settling time with minimum actuator voltage. A multi-criteria optimisation has been performed using Proximity Indexed Value (PIV) integrated with entropy methods. Further, the analysis of mean (ANOM) and analysis of variance (ANOVA) are performed to identify the most significant input parameter based on their percentage contribution. For the smart cantilever beam considered in the analysis, the location of the S/A is the most significant having maximum percentage contribution (35.69%) followed by its length (33.04%) and thickness (24.55%). [ABSTRACT FROM AUTHOR]

Based on vector Debye integral, focusing properties of linearly polarized Bessel–Gaussian beam modulated by Bessel gratings combining a radial phase shift modulated spiral zone plate (RSSZP) passing through a large numerical aperture lens system are investigated. The data obtained lead that the intensity and the phase distributions in the focal section are significantly controlled by the order of the beam (m, n), the topological charge p and the shifting parameter β of the RSSZP. Simulations show that by increasing the topological charge, the radius of the ring increases and that the shifting parameter has an effect on the ring size. Also, the linear polarized incident beam lost its polarization after crossing a high-numerical-aperture objective. [ABSTRACT FROM AUTHOR]

The possibility of studying the predicted for ITER effect of anomalous scattering of a microwave beam of ordinary polarization in the plasma of the edge transport barrier at the T-15MD tokamak is shown. [ABSTRACT FROM AUTHOR]

In this paper, we study the well-posedness and the asymptotic behavior of a one-dimensional laminated beam system with a distributed delay term in the first equation, where the heat conduction is given by Fourier's law effective in the rotation angle displacements. We first give the well-posedness of the system by using the semigroup method. Then, we show that the system is exponentially stable under the assumption of equal wave speeds. [ABSTRACT FROM AUTHOR]

The dynamic characteristics of a hub-functionally graded material beam undergoing large overall motions are studied. The deformation field of the flexible beam is described by using the assumed mode method (AMM), the finite element method (FEM) and the point interpolation method (PIM). Assuming that the physical parameters of functionally graded materials follow certain kind of power law gradient distribution and vary along the thickness direction. The longitudinal deformation and transversal deformation of the beam are both considered, and the nonlinear coupling term which is known as the longitudinal shortening caused by transversal deformation is also taken into account. The rigid-flexible coupling dynamics equations of the system described by three different discrete methods which have a uniform form are derived via employing Lagrange's equations of the second kind. The validity of the point interpolation method established in this paper is verified by comparing with the numerical simulation results of the assumed mode method and the finite element method. On this basis, the influence of the functional gradient distribution rules on the dynamic characteristics of flexible beams undergoing large overall motions is discussed. The results show that the assumed mode method cannot deal with large deformation problem. Remaining other physical parameters of functionally graded materials beam unchanged, the maximum displacement of the beam increases with the increase of functionally graded materials index. The natural frequency of transverse bending of beam increases with the increase of rotational speed, when rotational speed is constant, the natural frequency will decrease with the increase of functional gradient index. [ABSTRACT FROM AUTHOR]

An improved non-convex optimized phase recovery algorithm is used to compensate for wavefront aberrations caused by atmospheric turbulence and pointing errors in the vortex beam. The algorithm is divided into two parts: initialization and iteration. To reduce the effect of outliers, truncation rules are formulated in the initialization phase using the robustness of the sample median to obtain an initial value that is close to the global optimum. The relationship between the results of adjacent iterations is used in the iterations to calculate new weight coefficients, which are applied to the gradient descent to ensure the accuracy of the recovery results. Simulation experiments are carried out for different channel environments and different modes, and the results show that the improved phase recovery algorithm can accurately compensate for distorted wave fronts. The improved algorithm recovers the best results at different turbulence intensities and under the influence of different pointing errors. The recovered Strehl ratio can reach 0.9 and the mode purity can reach 0.92. Single-mode and multi-mode simulations were carried out, and the results show that the improved algorithm is effective and robust. [ABSTRACT FROM AUTHOR]

The purpose of this investigation is to examine the properties of finite asymmetric exotic scalar (acoustic) beams with unusual properties using the angular spectrum decomposition in plane waves. Such beams possess intrinsic uncommon characteristics that make them attractive from the standpoint of particle manipulation, handling and rotation, and possibly other applications in particle clearing and separation. Assuming a specific apodization function at the acoustic source, the angular spectrum function is calculated and used to synthesize the radiated pressure field (i.e., excluding evanescent waves that decay away from the source) in the forward direction of wave motion (i.e., away from the source). Moreover, a generalized hybrid method combining the angular spectrum approach with the multipole expansion formalism in spherical coordinates is developed, which is applicable to any finite beam of arbitrary wavefront. The improved approach allows adequate computation of the resonance scattering, radiation force, and spin torque components on an object of arbitrary shape, located on or off the axis of the incident beam in space. Considering the illustrative example of a viscous fluid sphere submerged in a non-viscous liquid and illuminated by finite asymmetric beams such as the Airy and the Bessel vortex beam with fractional order, numerical computations for the scattering, radiation force, and torque components are performed with an emphasis on the distance from the source, the arbitrary location of the particle ,and the asymmetric nature of the incident field. Moreover, beamforming calculations are presented with supplementary animations for the pressure field distribution in space, with an emphasis on the intrinsic properties of the selected beams. The numerical predictions illustrate the scattering, radiation force, and spin torque properties depending on the beam parameters and the distance separating the sphere from the source. This study provides a generalized hybrid method to analyze quantitatively the scattering, radiation force, and spin torque by any finite asymmetric (or symmetric) acoustic beam with potential applications in various fields of applied physics (such as beam-forming, imaging, and mechanical effects of asymmetric sound beams). [ABSTRACT FROM AUTHOR]

The characteristics of high-power vortex Bessel beams in the terahertz range (λ=141 μm) obtained with the use of diffractive axicons (DAs) illuminated by a Gaussian beam of the Novosibirsk free-electron laser were studied. Two of the three possible types of DA recently described in our previous paper, namely, binary spiral silicon axicons (BAs), forming beams with a topological charge l equal to 0–4 and 9, and a diamond “holographic” axicon (HA), forming a beam with l=9, were used in the experiments. These axicons formed beams whose cross sections in the region of inner Bessel rings were close to those of ideal Bessel beams, but their intensities varied in azimuth with a frequency of l and 2l for the BAs and HA, respectively. However, in the case of the BAs, the beams had a pronounced helical structure at the periphery, whereas for the HA, the beam was axisymmetric. By focusing these beams with a lens, we studied the structure of the so-called “perfect” beams (PBs). While an ideal Bessel beam exhibits a PB as a thin ring, in the case of the BAs, we observed a broadened ring structure consisting of 2l short spirals, and for the HA, we observed a narrow ring with 2l maxima in azimuth. A comparison of the numerical calculations and experiments showed that the observed azimuthal intensity variations can be attributed to inaccuracies in the preparation of the axicon relief and/or discrepancies between the calculated and actual wavelengths, within a few percent. The results of this work enable the establishment of quality requirements for axicon manufacture and the appropriate selection of the axicon type in accordance with the requirements for the beam.

Modern cone-beam CT systems are capable of ultra-high-resolution 3D imaging in addition to conventional radiography and fluoroscopy. The combination of various imaging functions in a multi-use setup is particularly appealing for musculoskeletal interventions, such as CBCT arthrography (CBCTA). With this study, we aimed to investigate the feasibility of CBCTA of the wrist in a "one-stop-shop" approach with a gantry-free twin robotic scanner that does not require repositioning of subjects. Additionally, the image quality of CBCTA was compared to subsequent arthrograms on a high-end multidetector CT (MDCTA). Fourteen cadaveric wrists received CBCTA with four acquisition protocols. Specimens were then transferred to the CT suite for additional MDCTA. Dose indices ranged between 14.3 mGy (120 kVp/100 effective mAs; full-dose) and 1.0 mGy (70 kVp/41 effective mAs; ultra-low-dose) for MDCTA and between 17.4 mGy (80 kVp/2.5 mAs per pulse; full-dose) and 1.2 mGy (60 kVp/0.5 mAs per pulse; ultra-low-dose) for CBCTA. Subjective image quality assessment for bone, cartilage and ligamentous tissue was performed by seven radiologists. The interrater reliability was assessed by calculation of the intraclass correlation coefficient (ICC) based on a two-way random effects model. Overall image quality of most CBCTA was deemed suitable for diagnostic use in contrast to a considerable amount of non-diagnostic MDCTA examinations (38.8%). The depiction of bone, cartilage and ligaments in MDCTA with any form of dose reduction was inferior to any CBCTA scan with at least 0.6 mAs per pulse (all p < 0.001). Full-dose MDCTA and low-dose CBCTA were of equal quality for bone tissue visualization (p = 0.326), whereas CBCTA allowed for better depiction of ligaments and cartilage (both p < 0.001), despite merely one third of radiation exposure (MDCTA–14.3 mGy vs. CBCTA–4.5 mGy). Moderate to good interrater reliability was ascertained for the assessment all tissues (ICC 0.689–0.756). Overall median examination time for CBCTA was 5.4 min (4.8–7.2 min). This work demonstrates that substantial dose reduction can be achieved in CT arthrography of the wrist while maintaining diagnostic image quality by employing the cone-beam CT mode of a twin robotic X-ray system. The ability of the multi-use X-ray system to switch between fluoroscopy mode and 3D imaging allows for "one-stop-shop" CBCTA in minimal examination time without the need for repositioning. [ABSTRACT FROM AUTHOR]

Lattice lightsheet microscopy (LLSM) featuring three-dimensional recording is improved to manipulate cellular behavior with subcellular resolution through optogenetic activation (optoLLSM). A position-controllable Bessel beam as a stimulation source is integrated into the LLSM to achieve spatiotemporal photoactivation by changing the spatial light modulator (SLM) patterns. Unlike the point-scanning in a confocal microscope, the lattice beams are capable of wide-field optical sectioning for optogenetic activation along the Bessel beam path.We show that the energy power required for optogenetic activations is lower than 1 nW (or 24 mWcm-2) for time-lapses of CRY2olig clustering proteins, and membrane ruffling can be induced at different locations within a cell with subcellular resolution through light-triggered recruitment of phosphoinositide 3-kinase. Moreover, with the epidermal growth factor receptor (EGFR) fused with CRY2olig, we are able to demonstrate guided cell migration using optogenetic stimulation for up to 6 h, where 463 imaging volumes are collected, without noticeable cellular damages. Using a Bessel beam as a simulation source allows the use of lattice lightsheet microscopy for spatiotemporal control of photoactivation, illustrated by the control of cellular migration behavior. [ABSTRACT FROM AUTHOR]

The capacity of self-healing fields to reconstruct after passing through scattering media may prove useful in reducing speckle formation. Here, we study the speckle response of the space–time (ST) light sheet compared to a Gaussian wave packet, Airy beam, and Bessel Gauss beam. We find that the Pearson's correlation coefficient for the ST light sheet is 50%, 48% and 40% larger than that of the Gaussian, Airy beam and Bessel Gauss beams, respectively, demonstrating a strong correlation to an input beam that has not been speckled. These results suggest that the ST light sheet exhibits considerable resistance to speckle generation. We also investigate the speckle response of the ST light sheet at its second-harmonic frequency and observe a mean Pearson's correlation coefficient close to 0.6, comparable to the second-harmonic Bessel Gauss beam, and 2.8 × the value obtained for the second-harmonic Gaussian beam. Our results lend themselves to a variety of applications including bioimaging, communications, and optical tweezers. [ABSTRACT FROM AUTHOR]

Light detection and ranging systems based on optical phased arrays and integrated silicon photonics have sparked a surge of applications over the recent years. This includes applications in sensing, free-space communications, or autonomous vehicles, to name a few. Herein, we report a design of two-dimensional optical phased arrays, which are arranged in a grid of concentric rings. We numerically investigate two designs composed of 110 and 820 elements, respectively. Both single-wavelength (1550 nm) and broadband multi-wavelength (1535 nm to 1565 nm) operations are studied. The proposed phased arrays enable free-space beam steering, offering improved performance with narrow beam divergences of only 0.5° and 0.22° for the 110-element and 820-element arrays, respectively, with a main-to-sidelobe suppression ratio higher than 10 dB. The circular array topology also allows large element spacing far beyond the sub-wavelength-scaled limits that are present in one-dimensional linear or two-dimensional rectangular arrays. Under a single-wavelength operation, a solid-angle steering between 0.21π sr and 0.51π sr is obtained for 110- and 820-element arrays, respectively, while the beam steering spans the range of 0.24π sr and 0.57π sr for a multi-wavelength operation. This work opens new opportunities for future optical phased arrays in on-chip photonic applications, in which fast, high-resolution, and broadband beam steering is necessary. [ABSTRACT FROM AUTHOR]

In classical thermoelasticity, the bimodular effect of materials is rarely considered. However, all materials will present, in essence, different properties in tension and compression, more or less. The bimodular effect is generally ignored only for simple analysis. In this study, we theoretically analyze a two-dimensional curved beam with a bimodular effect and under mechanical and thermal loads. We first establish a simplified model on a subarea in tension and compression. On the basis of this model, we adopt the Duhamel similarity theorem to change the initial thermoelastic problem as an elasticity problem without the thermal effect. The superposition of the special solution and supplement solution of the Lamé displacement equation enables us to satisfy the boundary conditions and stress continuity conditions of the bimodular curved beam, thus obtaining a two-dimensional thermoelastic solution. The results indicate that the solution obtained can reduce to bimodular curved beam problems without thermal loads and to the classical Golovin solution. In addition, the bimodular effect on thermal stresses is discussed under linear and non-linear temperature rise modes. Specially, when the compressive modulus is far greater than the tensile modulus, a large compressive stress will occur at the inner edge of the curved beam, which should be paid with more attention in the design of the curved beams in a thermal environment. [ABSTRACT FROM AUTHOR]

This paper presents an analytical transfer matrix modeling framework for the forced vibration of a bending-torsional-warping coupling Euler-Bernoulli thin-walled beam carrying an arbitrary number of three degree-of-freedom (DOF) spring-damper-mass (SDM) subsystems. The thin-walled beam is divided into a series of distinct sub-beams whose ends are connected to the SDM subsystems. The transfer matrix for each sub-beam is developed based on the exact shape functions of the bending-torsional-warping coupling Euler-Bernoulli theory. Each SDM system is modelled by a set of effective springs based on the dynamic condensation method. The governing matrix equation is formulated based on the compatibility conditions of the placement and the force at the common interfaces of two adjacent sub-beams. Then, a closed-form expression for the frequency response function of the thin-walled beam system is proposed. The results computed by the proposed method achieve good agreement with those obtained by the conventional finite-element method, which shows the accuracy and reliability of the proposed method. The effects of the system parameters on the vibration transmission and vibration isolation properties of the thin-walled beam system are studied. The presented method can simultaneously consider arbitrary number of SDM subsystems and boundary conditions. Furthermore, none of the associated matrices are larger than 12 × 12, which provides a significant computational advantage. [ABSTRACT FROM AUTHOR]

Various applications of head-tilting techniques in whole-brain radiotherapy (WBRT) have been introduced. However, a study on the setup uncertainties and margins in head-tilting techniques has not been reported. This study evaluated the setup uncertainties and determined the appropriate planning target volume (PTV) margins for patients treated in the head-tilted supine (ht-SP) and conventional supine position (c-SP) in WBRT. Thirty patients who received WBRT at our institution between October 2020 and May 2021 in the c-SP and ht-SP were investigated. The DUON head mask (60124, Orfit Industries, Wijnegem, Belgium) was used in the c-SP, and a thermoplastic U-Frame Mask (R420U, Klarity Medical & Equipment Co. Ltd., Lan Yu, China) was used in the ht-SP. Daily setup verification using planning computed tomography (CT) and cone-beam CT was corrected for translational (lateral, longitudinal, and vertical) and rotational (yaw) errors. In the c-SP, the means of systematic errors were -0.80, 0.79, and 0.37 mm and random errors were 0.27, 0.54, and 0.39 mm in the lateral, longitudinal, and vertical translational dimensions, respectively. Whereas, for the ht-SP, the means of systematic errors were -0.07, 0.73, and -0.63 mm, and random errors were 0.75, 1.39, 1.02 mm in the lateral, longitudinal, and vertical translational dimensions, respectively. The PTV margins were calculated using Stroom et al.'s [2Σ+0.7σ] and van Herk et al.'s recipe [2.5Σ+0.7σ]. Appropriate PTV margins with van Herk et al.'s recipe in WBRT were <2 mm and 1.5° in the c-SP and <3 mm and 2° in the ht-SP in the translational and rotational directions, respectively. Although the head tilt in the supine position requires more margin, it can be applied as a sufficiently stable and effective position in radiotherapy. [ABSTRACT FROM AUTHOR]

Bound states in the continuum (BICs) are resonant modes of open structures that do not suffer damping, despite being compatible with radiation in terms of their momentum. They have been raising significant attention for their intriguing topological features, and their opportunities in photonics to enhance light-matter interactions. In parallel, the coherent excitation of optical devices through the tailored interference of multiple beams has been explored as a way to enhance the degree of real-time control over their response. Here, we leverage the combination of these phenomena, and exploit the topological features of BICs in the presence of multiple input beams to enable full polarization control on the entire Poincaré sphere in a photonic crystal slab only supporting a symmetry-protected BIC, experimentally demonstrating highly efficient polarization conversion controlled in real time through the superposition of coherent excitations. Our findings open exciting opportunities for a variety of photonic and quantum optics applications, benefitting from extreme wave interactions and topological features around BICs combined with optical control through coherent interference of multiple excitations. Polarization control is of paramount importance for various applications. Here, the authors enable extreme control over light polarization spanning the entire Poincaré sphere by combining coherent control of wave phenomena and the physics of bound states in the continuum. [ABSTRACT FROM AUTHOR]

Micro-opto-electro-mechanical systems (MOEMS) based mirrors with a suitable actuation range are often used for optical beam scanning applications. While several MOEMS scanners have been reported, they often have limitations with respect to their range of motion, field of view, mass, size and fabrication cost. In this work, we present a rotary micro-polygon scanner based on an electrostatic variable capacitance micromotor for laser beam steering applications. The miniaturized scanner consists of a hollow micro-polyhedron mirror with a base radius of $200 {\mu }\text{m}$ and a height of $400 {\mu }\text{m}$. It is mounted on the rotor of a variable capacitance micromotor using an epoxy-based adhesive. The rotor has a diameter of $600 {\mu }\text{m}$ and is $2.5 {\mu }\text{m}$ thick. The micromotor was fabricated using a commercial three-layer polysilicon surface micro-machining process (PolyMUMPs) and the micro-polyhedrons were fabricated using a commercial bulk micro-machining process (PiezeoMUMPs). After fabrication of the components, the micro-scanner was assembled and operated under atmospheric conditions using a three-phase square wave excitation ranging from 0 V to 200 V and achieved rotational speeds of up to 2100 rpm. An optical laser beam with a wavelength of 632 nm was reflected off the sidewall of the rotating micro-polyhedron, achieving an experimentally measured scanning angular range of 57.88°, an angular scan rate of 220 radians per second and a scan speed of 25,200 lines per minute or 420 lines per second with a 12 sided micro-mirror. The ratio of the output power over the input optical power is measured over a scanning range of 22°, which is limited by the size of the photo-detector, yielding a ratio spanning from 0.18 to 0.22. This rotary micro-scanner can provide high scanning speeds and a wide scanning field of view with a footprint of 1.25 mm2 and a thickness of 0.83 mm, which is suitable to implement chip-level high-performance micro-beam steering systems for various applications. [2022-0020] [ABSTRACT FROM AUTHOR]

It is difficult for a standing-wave waveguide slot array antenna to generate a complex beam shape in H-plane, such as the cosecant squared pattern. The reason is that a conventional standing-wave waveguide slot array antenna cannot flexibly and independently adjust the amplitude and phase of radiating elements. In this article, a proactive conformal waveguide slot array antenna is designed with the cosecant squared pattern in its H-plane. It is able to control the element phase by proactively curving the array shape. That means the antenna shape is employed as a new parameter to break the limitation in the phase control. Based on this, the proactive conformal waveguide slot array antenna can modulate the element amplitude and phase independently to form the desired complex far-field pattern. The commercial selective laser melting (SLM) technology is applied to print the curved antenna after carefully considering the printing direction and slot shape. A 35 GHz prototype antenna is fabricated and measured. Good performance can be observed in the measured results. [ABSTRACT FROM AUTHOR]

High‐resolution X‐ray microscopy (XRM) is gaining interest for biological investigations of extremely small‐scale structures. XRM imaging of bones in living mice could provide new insights into the emergence and treatment of osteoporosis by observing osteocyte lacunae, which are holes in the bone of few micrometres in size. Imaging living animals at that resolution, however, is extremely challenging and requires very sophisticated data processing converting the raw XRM detector output into reconstructed images. This paper presents an open‐source, differentiable reconstruction pipeline for XRM data which analytically computes the final image from the raw measurements. In contrast to most proprietary reconstruction software, it offers the user full control over each processing step and, additionally, makes the entire pipeline deep learning compatible by ensuring differentiability. This allows fitting trainable modules both before and after the actual reconstruction step in a purely data‐driven way using the gradient‐based optimizers of common deep learning frameworks. The value of such differentiability is demonstrated by calibrating the parameters of a simple cupping correction module operating on the raw projection images using only a self‐supervisory quality metric based on the reconstructed volume and no further calibration measurements. The retrospective calibration directly improves image quality as it avoids cupping artefacts and decreases the difference in grey values between outer and inner bone by 68–94%. Furthermore, it makes the reconstruction process entirely independent of the XRM manufacturer and paves the way to explore modern deep learning reconstruction methods for arbitrary XRM and, potentially, other flat‐panel computed tomography systems. This exemplifies how differentiable reconstruction can be leveraged in the context of XRM and, hence, is an important step towards the goal of reducing the resolution limit of in vivo bone imaging to the single micrometre domain. Lay description: X‐ray microscopy (XRM) is an imaging modality that non‐destructively acquires 3D images of very high resolution. Applied to the bones of living mice, this could yield new insights into the change of small bony structures when the animal is infected with osteoporosis. However, acquiring artifact‐free images of living mice is very challenging. Consequently, powerful data processing is needed to resolve the structures of interest. We present a complete XRM reconstruction algorithm which converts the detector signal into interpretable volumetric images. Our pipeline lets the user adjust and augment the reconstruction to the needs of the given application and even allows to incorporate trainable components such as deep networks. These can flexibly be inserted into the pipeline and learned from data. To demonstrate this, we optimize the few free parameters of a cupping correction module. It reduces prominent intensity differences in the reconstructed bones without the need for any additional measurements. This exemplifies how the proposed pipeline increases the quality of the obtained reconstructions. Overall, our method is a tool enabling flexible, state‐of‐the‐art XRM data processing in order to pave the way toward future in‐vivo experiments. The source code and data are publicly available at https://doi.org/10.24433/CO.2740182.v2. [ABSTRACT FROM AUTHOR]

In this paper, a semi-analytical method for solving circular curved beams is proposed to study the free vibration of in-plane circular curved beams in both undamaged and damaged configurations. The crack damage of the structure is represented by the cross-sectional reduction of the damaged element. Based on the discrete circular curved beam model, the coupling stiffness matrices of shear, compression and bending are derived. Combined with the lumped mass matrix and the dynamic characteristic equation of the multi-degree-of-freedom system, the frequencies and modes of the damaged and undamaged structures are calculated. The results are compared with the finite element method, and the good consistency between them is verified. [ABSTRACT FROM AUTHOR]

A dynamic beam shaping method is proposed for the generation of flat-top beams (FTBs) in the far field. Using the mixed-region amplitude freedom algorithm, this new method is used to design the required phase distribution encoded on a spatial light modulator for the generation of FTB profiles. The characteristics of these new beam shaping methods are used as beam parameters, such as the laser beam size, the beam intensity of square FTBs, and the root-mean-square error (RMSE). Using our proposed method, the theoretical performance of beam intensity shaping is improved to an RMSE < 0.02 with a minimum number of iterations of phase reconstruction. Using the phase hologram of dynamic beam shaping, theoretical and experimental comparisons of edge steepness and plateau uniformity were established for the square FTBs of variable beam sizes. It is shown that the dynamic beam shaping of FTBs can produce high intensity uniformity in the plateau region with steep edges, which makes it an effective tool, especially for laser machining applications. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the role of the damping term μ ⁢ u t in unique determination of unknown spatial load F ⁢ (x) in a damped Euler–Bernoulli beam equation u t ⁢ t + μ ⁢ u t + (r ⁢ (x) ⁢ u x ⁢ x ) x ⁢ x = F ⁢ (x) ⁢ G ⁢ (t) from the measured final time displacement u T ⁢ (x) := u ⁢ (x , T) or velocity ν T ⁢ (x) := u t ⁢ (x , T) . In [A. Hasanov Hasanoğlu and V. G. Romanov, Introduction to Inverse Problems for Differential Equations, Springer, Cham, 2017] it was shown that the unique determination of the spatial load F ⁢ (x) in the undamped wave equation u t ⁢ t - (k ⁢ (x) ⁢ u x) x = F ⁢ (x) ⁢ G ⁢ (t) from final data (displacement or velocity) is not possible. This result is also valid for the undamped beam equation u t ⁢ t + (r ⁢ (x) ⁢ u x ⁢ x ) x ⁢ x = F ⁢ (x) ⁢ G ⁢ (t) . We show that in the presence of the damping term, the spatial load can be uniquely determined from the final time output under some acceptable conditions with respect to the final time T > 0 and the damping coefficient μ > 0 . The cases of pure spatial load G ⁢ (t) ≡ 1 , and the exponentially decaying load G ⁢ (t) = e - η ⁢ t are analyzed separately, leading also to sufficient conditions for the uniqueness of the inverse problem solution. The results presented in this paper clearly demonstrate the key role of the damping term in the unique determination of the unknown spatial load F ⁢ (x) in the damped Euler–Bernoulli beam equation. [ABSTRACT FROM AUTHOR]

The deep neural network has achieved great success in 3D volumetric correspondence. These methods infer the dense displacement or velocity fields directly from the extracted volumetric features without addressing the intrinsic structure correspondence, being prone to shape and pose variations. On the other hand, the spectral maps address the intrinsic structure matching in the low dimensional embedding space, remain less involved in volumetric image correspondence. This paper presents an unsupervised deep volumetric descriptor learning neural network via the low dimensional spectral maps to address the dense volumetric correspondence. The neural network is optimized by a novel criterion on descriptor alignments in the spectral domain regarding the supervoxel graph. Aside from the deep convolved multi-scale features, we explicitly address the supervoxel-wise spatial and cross-channel dependencies to enrich deep descriptors. The dense volumetric correspondence is formulated as the low-dimensional spectral mapping. The proposed approach has been applied to both synthetic and clinically obtained cone-beam computed tomography images to establish dense supervoxel-wise and up-scaled voxel-wise correspondences. Extensive series of experimental results demonstrate the contribution of the proposed approach in volumetric descriptor extraction and consistent correspondence, facilitating attribute transfer for segmentation and landmark location. The proposed approach performs favorably against the state-of-the-art volumetric descriptors and the deep registration models, being resilient to pose or shape variations and independent of the prior transformations. [ABSTRACT FROM AUTHOR]

• The RREF with ACBE is established to solve the numerical simulation problem of radial tire. • According to the dynamic numerical characteristics of the ACBE, a new AACBE is proposed and applied to RREF. • By using the RREF with AACBE, the nonlinear forced transient response characteristics of radial tire are analyzed. Based on the Euler-Bernoulli beam theory, nonlinear axial Lagrangian strain and simplified curvature, the nonlinear differential equations of motion for rotating ring on the elastic foundation (RREF) are established by absolute nodal coordinate formulation curved beam element. In non-rotating state, the double modes at the same frequency are observed. In rotating state, the first-order critical angular speed, the frequency of forward traveling wave and backward traveling wave are obtained. Then, the nonlinear forced transient response (radial deformation rate) of the RRE under the action of concentrated load at bottom point is analyzed. In order to improve computational efficiency, the adaptive ANCF curved beam element is proposed, and reasonable range of two key parameters, i.e., element length and rotation angle of adjacent nodal tangential vector are determined. And it is used to analysis the influences of internal pressure, radial and tangential elastic support stiffness, and Young's modulus on nonlinear transient response characteristics of RREF. In order to study the standing wave phenomenon for a period, the RREF-hub contact model is established and used to analyze the nonlinear transient response of RREF at the first-order critical angular speed. [ABSTRACT FROM AUTHOR]

• FFT-based methods of optical propagation introduce artificial periodicity. • Transverse waves that should leave computational domain are reintroduced. • New sinc method preserves bandwidth and does not have periodicity artefact. • Error of sinc method does not depend on wavelength or propagation distance. We propose a method based on sinc series approximations for computing the Rayleigh-Sommerfeld and Fresnel diffraction integrals of optics. The diffraction integrals are given in terms of a convolution, and our proposed numerical approach is not only super-algebraically convergent, but it also satisfies an important property of the convolution—namely, the preservation of bandwidth. Furthermore, the accuracy of the proposed method depends only on how well the source field is approximated; it is independent of wavelength, propagation distance, and observation plane discretization. In contrast, methods based on the fast Fourier transform (FFT), such as the angular spectrum method (ASM) and its variants, approximate the optical fields in the source and observation planes using Fourier series. We will show that the ASM introduces artificial periodic boundary conditions and violates the preservation of bandwidth property, resulting in limited accuracy which decreases for longer propagation distances. The sinc-based approach avoids both of these problems. Numerical results are presented for Gaussian beam propagation and circular aperture diffraction to demonstrate the high-order accuracy of the sinc method for both short-range and long-range propagation. For comparison, we also present numerical results obtained with the angular spectrum method. [ABSTRACT FROM AUTHOR]

Catheter-directed computed tomography angiography (CDCTA) is an imaging technique where CT images are acquired after selective catheterization of a vessel. Images obtained in this fashion provide several advantages over conventional imaging techniques such as fluoroscopic angiography, digital subtraction angiography, cone-beam CT, and conventional CT angiography. At this point, there is still limited literature on the subject, with prior studies examining a small number of potential uses. The goal of this pictorial essay is to illustrate our single tertiary care center experience using CDCTA. [ABSTRACT FROM AUTHOR]

Interactions between cluster chiral nanoparticles and a high-order Bessel beam (HOBB) with arbitrary illuminations are investigated. The generalized Lorenz–Mie theory (GLMT) is applied to derive the expansions of HOBB. Based on the additional theorem, multiple scattering results of cluster chiral nanoparticles are obtained by taking into account the tangential continuous boundary conditions. The present theory and codes proved to be effective when confronted with the simulations obtained from the Computer Simulation Technology (CST) software. Numerical results concerning the effects of beam order, beam conical angle, incident angles, beam polarization state, the chirality, and the material loss on the scattering of various types of aggregated chiral particles are displayed in detail, including the linearly chiral sphere chain, the chiral cube array, and the complex models composed of aggregated chiral spheres. This study may provide critical support to analytically understand the optical scattering characteristics with aggregated chiral particles of complex shapes, and may find important applications in manipulating collective chiral particles. [ABSTRACT FROM AUTHOR]

Speckle patterns are formed by random interferences of mutually coherent beams. While speckles are often considered as unwanted noise in many areas, they also formed the foundation for the development of numerous speckle-based imaging, holography, and sensing technologies. In the recent years, artificial speckle patterns have been generated with spatially incoherent sources using static and dynamic optical modulators for advanced imaging applications. In this report, a basic study has been carried out with Bessel distribution as the fundamental building block of the speckle pattern (i.e., speckle patterns formed by randomly interfering Bessel beams). In general, Bessel beams have a long focal depth, which in this scenario is counteracted by the increase in randomness enabling tunability of the axial resolution. As a direct imaging method could not be applied when there is more than one Bessel beam, an indirect computational imaging framework has been applied to study the imaging characteristics. This computational imaging process consists of three steps. In the first step, the point spread function (PSF) is calculated, which is the speckle pattern formed by the random interferences of Bessel beams. In the next step, the intensity distribution for an object is obtained by a convolution between the PSF and object function. The object information is reconstructed by processing the PSF and the object intensity distribution using non-linear reconstruction. In the computational imaging framework, the lateral resolution remained a constant, while the axial resolution improved when the randomness in the system was increased. Three-dimensional computational imaging with statistical averaging for different cases of randomness has been synthetically demonstrated for two test objects located at two different distances. The presented study will lead to a new generation of incoherent imaging technologies. [ABSTRACT FROM AUTHOR]

Slippery liquid-infused porous surfaces (SLIPSs) have become an effective method to provide materials with sliding performance and, thus, achieve liquid repellency, through the process of infusing lubricants into the microstructure of the surface. However, the construction of microstructures on high-strength metals is still a significant challenge. Herein, we used a femtosecond laser with a temporally shaped Bessel beam to process NiTi alloy, and created uniform porous structures with a microhole diameter of around 4 µm, in order to store and lock lubricant. In addition, as the lubricant is an important factor that can influence the sliding properties, five different lubricants were selected to prepare the SLIPSs, and were further compared in terms of their sliding behavior. The temperature cycle test and the hydraulic pressure test were implemented to characterize the durability of the samples, and different liquids were used to investigate the possible failure under complex fluid conditions. In general, the prepared SLIPSs exhibited superior liquid repellency. We believe that, in combination with a femtosecond laser, slippery liquid-infused porous surfaces are promising for applications in a wide range of areas. [ABSTRACT FROM AUTHOR]

Bronchoscopic biopsy results for indeterminate pulmonary nodules remain suboptimal. Electromagnetic navigation bronchoscopy (ENB) coupled with cone beam computed tomography (CBCT) for confirmation has the potential to improve diagnostic yield. We present our experience using this multimodal approach to biopsy 17 indeterminate nodules in 14 consecutive patients from April to August 2021. Demographic information, nodule characteristics, and biopsy results were recorded. Procedures were performed in a hybrid operating room equipped with a Siemens Artis Q bi-plane CBCT (Siemens, Munich, Germany). After ENB using the superDimension version 7.1 (Medtronic, Plymouth, MN, USA) to target the lesion, radial endobronchial ultrasound was used as secondary confirmation. Next, transbronchial needle aspiration was performed prior to CBCT to evaluate placement of the biopsy tool in the lesion. The average nodule size was 21.7+/−15 mm with 59% (10/17) < 2 cm in all dimensions and 35% (6/17) showing a radiographic bronchus sign. The diagnostic yield of CBCT-guided ENB was 76% (13/17). No immediate periprocedural or postprocedural complications were identified. Our experience with CBCT-guided ENB further supports the comparable efficacy and safety of this procedure compared to other mature biopsy modalities. Studies designed to optimize the lung nodule biopsy process and to determine the contributions from different procedural aspects are warranted. [ABSTRACT FROM AUTHOR]

Biological probes facilitate optical imaging and disease diagnosis and treatment. However, the large absorption and scattering loss in the tissue highly limit the depth during the application. In the present research, an NIR-I bioprobing system, which utilizes the Bessel beam to excite heavily doping nanocrystals, has been developed for deep tissue applications. On the one hand, the capillary mode selection method generates the Bessel excitation beam, lowering the excitation energy loss. On the other hand, a strong energy harvest of NaYbF4:90%Nd nanocrystals enables effective fluorescence and heat generation upon 800 nm excitation. By considering the advantages of Bessel excitation and heavily doping nanocrystals, up to ∼3 cm penetration depth for ex vivo bioimaging and the potential self-monitored photothermal treatment are demonstrated. The resultant bioprobing system allows deep tissue imaging and photothermal therapy, showcasing broad prospects in medical research and clinical applications. [ABSTRACT FROM AUTHOR]

Objective. Cone-Beam CT (CBCT) often results in severe image artifacts and inaccurate HU values, meaning poor quality CBCT images cannot be directly applied to dose calculation in radiotherapy. To overcome this, we propose a cycle-residual connection with a dilated convolution-consistent generative adversarial network (Cycle-RCDC-GAN). Approach. The cycle-consistent generative adversarial network (Cycle-GAN) was modified using a dilated convolution with different expansion rates to extract richer semantic features from input images. Thirty pelvic patients were used to investigate the effect of synthetic CT (sCT) from CBCT, and 55 head and neck patients were used to explore the generalizability of the model. Three generalizability experiments were performed and compared: the pelvis trained model was applied to the head and neck; the head and neck trained model was applied to the pelvis, and the two datasets were trained together. Main results. The mean absolute error (MAE), the root mean square error (RMSE), peak signal to noise ratio (PSNR), the structural similarity index (SSIM), and spatial nonuniformity (SNU) assessed the quality of the sCT generated from CBCT. Compared with CBCT images, the MAE improved from 28.81 to 18.48, RMSE from 85.66 to 69.50, SNU from 0.34 to 0.30, and PSNR from 31.61 to 33.07, while SSIM improved from 0.981 to 0.989. The sCT objective indicators of Cycle-RCDC-GAN were better than Cycle-GAN’s. The objective metrics for generalizability were also better than Cycle-GAN’s. Significance. Cycle-RCDC-GAN enhances CBCT image quality and has better generalizability than Cycle-GAN, which further promotes the application of CBCT in radiotherapy. [ABSTRACT FROM AUTHOR]

Aim. Using a modified thermal cycling method to establish narrow root fracture models and evaluate the diagnosis efficiency of them using four different cone-beam CT (CBCT) units. Methodology. Fifty-six intact teeth were selected, and the crowns of the teeth were embedded using general purpose acrylic resin. 50 root fracture models were established by soaking these teeth in liquid nitrogen and hot water cyclically; 6 teeth were used as the negative control. All the 56 teeth were scanned with the smallest voxel size of four different CBCT units (NewTom VGi, Planmeca Promax 3D Max, Kavo 3D eXam, and Soredex Scanora3D). 10 teeth were randomly selected, and the roots were sliced using slow-speed saw to obtain horizontal root sections. Scanning electron microscope (SEM) was used to measure the width of the fracture lines (FLs). The CBCT images were evaluated for the presence or absence of fracture lines. Accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated for the diagnosis of FLs using the four CBCT units. Results. Fifty narrow root fracture models were successfully established, and 25 root sections with 45 FLs were acquired. The width of FLs was from 3.43 μm to 143 μm; 32.2% of the points had width under 25 μm, while only 9.6% of them had width over 75 μm. The accuracy was 0.41, 0.54, 0.41, and 0.30 for NewTom VGi, Planmeca Promax 3D Max, Kavo 3D eXam, and Soredex Scanora3D, respectively. Conclusions. The modified temperature cycling method is a simple and effective method to establish narrow root fracture models, and the diagnosis efficiency for these narrow fracture lines was quite poor using all the four different CBCT units. [ABSTRACT FROM AUTHOR]

When performing in vivo imaging of live samples, it is a big challenge to penetrate thick tissues while still maintaining high resolution and a large field of view because of the sample-induced aberrations. These requirements can be met by combining the benefits of two-photon excitation, beam modulation and adaptive optics in an illumination path. However, the relationship between aberrations and the performance of such a microscopy system has never been systematically and comprehensively assessed. Here, two-photon Gaussian and Bessel beams are modulated as illumination beams, and how aberrations affect the thickness of the illumination beams is evaluated. It is found that the thickness variation is highly related to the azimuthal order of Zernike modes. The thickness of the two-photon Gaussian beam is more sensitive to Zernike modes with lower azimuthal order, while the thickness of the two-photon Bessel beam is more sensitive to the higher-azimuthal-order Zernike modes. So, it is necessary to design a new strategy to correct aberrations according to the effects of different Zernike modes in order to maximize the correction capability of correctors and reduce the correction errors for those insensitive Zernike modes. These results may provide important guidance for the design and evaluation of adaptive optical systems in a two-photon excitation microscope. [ABSTRACT FROM AUTHOR]

The investigation of curved structures has attracted more and more attention, and the mainstream research focuses on the characteristics of curved beams subject to transverse loads, while sometimes axial loads are inevitable in engineering practice. Hence, this work aims to investigate the nonlinear vibrations of a curved beam subject to axial loads by developing appropriate modeling and solving methods. In this work, a nonlinear dynamic model of a hinged–hinged slightly curved beam (SCB) with sinusoidal shape subject to axial loads is first established, and the modal hypothesis method is subsequently used to obtain natural frequencies and mode shapes of the SCB subject to axial loads. Thereafter, a procedure to calculate the forced vibration responses of the SCB subject to axial loads is proposed by successively using the Galerkin truncation method, harmonic balance method and pseudo arc-length method. Finally, case studies are carried out to validate the above modeling and solving methods of the SCB subject to axial loads and explore its nonlinear dynamic characteristics. On the one hand, the effectiveness and accuracy of the proposed modeling and solving methods are verified by comparing with the results of finite element analysis. On the other hand, the results of the case studies demonstrate that the initial curvature, axial force, external excitation amplitude and initial configuration of the SCB can significantly affect its nonlinear dynamic characteristics. [ABSTRACT FROM AUTHOR]

A single‐layer reflective metasurface is proposed in this study to generate dual‐mode dual‐polarized high‐order Bessel vortex beams with equal divergence angle in Ka‐band. The metasurface consists of two different subwavelength elements with different polarisations, which are located in the inner disk region and the outer ring region respectively. The inner element, composed of a square ring and a regular octagon, is proposed to achieve a phase response of 360°. The outer element, which consists of a microstrip line and a double W‐shaped line, is designed to achieve the phase compensation and polarization conversion simultaneously. Equal divergence angle of different orbital angular momentum (OAM) modes is achieved by theoretically calculating the radii of the inner and outer regions. The metasurface prototype is fabricated and tested at 29 GHz, and the results show that the high‐order Bessel beams with +1 mode of x‐polarization and +2 mode of y‐polarization are successfully generated. This work provides a simple and practical method to generate dual‐mode dual‐polarized high‐order Bessel vortex beams for high‐capacity OAM communications. [ABSTRACT FROM AUTHOR]

The work was carried out within the context of a competitive ideology of creating the element base of digital optical computers (transphasors, optical switches, memory elements) built on a basis other than the Fabry–Perot interferometer. Mathematical models of stationary (problem I) and non-stationary (problem II) four-beam laser interaction in optically nonlinear media are considered in detail. Problem (I) is the system of ordinary differential equations with specified boundary conditions. Problem (II) is the system of integro-differential equations with boundary conditions. We introduced the original sought-for functions z(x) and u(z, t), υ(z, t) (II). As a result, the problem (I) is reduced to solving a simple transcendental equation (canonical equation of optical hysteresis). The problem (II) is reduced to solving a system of two nonlinear integral equations for the amplitudes of interference patterns (the canonical system of equations of non-stationary optical hysteresis). [ABSTRACT FROM AUTHOR]

In this paper, an analytical expression of the acoustic radiation force (ARF) for a spherical particle with a hemispherically split impedance boundary in a plane wave is deduced. Numerical calculations are carried out by considering the effect of the magnitude and phase of the acoustic impedance on the ARF. Computation results show that the increase in the magnitude of the acoustic impedance results in an overall decrease in the ARF, whereas the phase of the acoustic impedance results in a decrease in the ARF in the low frequency region. As the frequency increases, the positive phase angle leads to a decrease in the ARF, and the negative phase angle causes the ARF to increase rapidly. For a hemispherically split impedance sphere, the values of the ARF range from those of the rigid sphere and uniform impedance sphere. The finite-element models for the calculation of the ARF of a hemispherically split impedance boundary sphere are established and the correctness of the analytical theory is proved by numerical comparison. This work is expected to contribute theoretical support to the acoustic manipulation of particles with a nonuniform hemispherically split structure. [ABSTRACT FROM AUTHOR]

Cold-formed steel (CFS) structural members retain their preferred position in the lightweight construction industry, which is due to their significant advantages. The optimization of these CSF elements will make it possible to construct buildings at very competitive prices, having in addition an increased load capacity, and thus obtaining a stable and economical construction. The main objective of this research being the evaluation of the effectiveness of these new sections in (CSF) and the estimation of the remarkable instabilities as well as the failure modes. This article deals with an experimental study on the behavior of CSF beams of delta and bi-delta shape, solicited by four-point bending loads. These cross section shapes are often used in floors as main and secondary beams. The properties of this type of sections are most often based on the method involving the effective width designated by the Eurocode 3 standard. A nonlinear analysis by finite elements (FE) using the ABAQUS calculation program is carried out, thus making it possible to compare the experimental results with the numerical ones as well as those which are given by the theory proposed by Eurocode 3. Finally, the results obtained essentially showed that the failure modes of the delta and bi-delta beams corresponded to the buckling modes local. [ABSTRACT FROM AUTHOR]

A review on the phenomenon of stimulated Raman scattering of intense laser beams in nonlinear optical media is presented. Emphasis is put on explaining the basic physics of the phenomenon while minimizing the mathematics. As a special case the stimulated Raman scattering (SRS) in fourth state of matter i.e., plasma, is also discussed. [ABSTRACT FROM AUTHOR]