Set Of Angles Research Articles

Multitone reconstruction visual cryptography based on phase periodicity

The current no-computation grayscale image visual cryptography (VC) can only achieve halftone reconstruction but cannot truly achieve multitone. To solve this problem, we propose the concept of phase periodicity of the λ/2 retarder film and calculate the optical axis angle set with phase periodicity. According to the phase periodicity, we propose a λ/2 retarder film phase periodicity visual cryptography (RPP-VC). In RPP-VC, the secret pixels are encoded as the optical axis angles of nλ/2 retarder films and distributed to n shares. The decoding process does not require computation. The reconstructed image has no pixel expansion and can reach up to 23 tones. The quality of the reconstructed images has been greatly improved and the evaluation indicators of perceived quality are nearly doubled compared with other grayscale image VC schemes. The experimental results verify the feasibility of RPP-VC.

Polynomial Shaping-based Field-of-View Constrained Impact Time Guidance against Non-maneuvering Targets

This paper proposes polynomial shaping-based guidance strategies that assure interception of non-maneuvering targets at a pre-defined time without violating the seeker's field-of-view constraint. One of the proposed guidance strategies is obtained after expressing relative distance between the interceptor and the target as a nonlinear polynomial function of time-to-go. In contrast, the other guidance scheme shapes the line-of-sight angle as a polynomial function of the relative range between the two vehicles. The coefficients of both of these polynomials are obtained using the necessary boundary conditions that are consistent with required terminal and in-flight constraints. Using these coefficients, the desired set of look angles of the interceptor to achieve the mission objectives are first computed and then a nonlinear dynamic inversion-based controller is designed to track these reference values for achieving the guidance objectives. The performances of the proposed guidance strategies are validated and compared with each other using numerical simulations.

Quaternion Constrained Structured Adaptive Attitude Control

In this paper, a novel, attitude-constrained, structured adaptive control strategy is proposed for a spacecraft in the presence of parametric uncertainties. A set of cone angles are defined as a way to quantify the relative orientation error between two reference frames. While tracking the desired attitude, the corresponding cone angles are driven to zero while being constrained to lie within a maximum value. Using an error transformation, the restriction on the cone angles is converted into quaternion constraints that are subsequently used in barrier Lyapunov function (BLF) based controller synthesis. Attitude error constraints are satisfied by ensuring the boundedness of BLFs in the closed-loop Lyapunov stability analysis. Eventually, an adaptive control law is synthesized that drives the spacecraft to the desired attitude with the help of approximate and nominal spacecraft dynamics. While doing so, a function approximation strategy is used to obtain a stable weight update rule to estimate the disturbance term. Finally, the effectiveness of the proposed adaptive control law is demonstrated via numerical simulations.

Combined effect of upstream ramp and effusion cooling in combustion chamber liners of gas turbine

Effusion cooling technique is a highly efficient cooling method used to reduce the thermal stresses of combustion chamber liners in a gas turbine engine. The present study focuses on enhancing the adiabatic effectiveness of effusion cooling. The computational investigations are carried out using COMSOL Multiphysics 5.4 with the standard k- ε turbulence model. Detailed computations for 20 rows of effusion holes on the flat plate are examined for blowing ratios 0.25, 0.5, 1.0, 3.2, and 5.0 for each set of injection angles 30 o and 60o . To enhance the effusion cooling performance, an upstream ramp (ramp angles 14o , 24o, and 34o ) is introduced before the upstream of effusion holes. The results show that the adiabatic effectiveness increases with an increase of bl owing r a tio and r amp angles. By pl acing an upstream ramp, the low blowing ratios can greatly increase the adiabatic effectiveness by 29%, 31%, and 35% for ramp angles of 14o , 24o , and 34o, respectively. For high blowing ratios, an increase in the angles of the ramp shows less impact on adiabatic effectiveness throughout the effusion surface. However, adiabatic effectiveness has increased by 26% compared to the baseline model. It is also observed that injection angle of 30o provides more effectiveness than 60o . This study concludes that placing an upstream ramp increases the effusion cooling performance in the combustion chamber liners of a gas turbine engine.

A Task Allocation Method for Multi-AUV Search and Rescue with Possible Target Area

Task allocation is crucial for autonomous underwater vehicle (AUV) collaboration in multi-AUV maritime search and rescue missions. In real projects, there are possible target areas existing in task areas, which are not expected to be divided. Motivated by such a special situation, this paper proposes an area partitioning method to allocate the task to multiple AUVs and maintain the possible target area as a whole. First, the spatial structure of the task area is defined by the spiked Morse decomposition, which divides the task area according to a set of angles. Then, we perform a variational transformation to determine the optimal angles using the AUV order. Next, a customized backtracking method is introduced to determine the optimal AUV order which divides the task area among the multiple AUVs without disturbing the possible target areas. The proposed methodology is validated under various challenging scenarios using a different number of AUVs. The empirical results show that the divided possible target areas and workload variance were superior to the comparison methods. This indicates that the proposed method can generate stable solutions that effectively reduce the segmentation of possible target areas and keep the workload of the multiple AUVs balanced.

A sweeping algorithm of unstructured elements in discontinuous spectral element method for thermal radiation in irregular multidimensional geometries

The discontinuous spectral element method (DSEM) coupled with an element-by-element sweeping strategy is proposed as a solution to the radiative transfer equation (RTE) for participating media in irregular geometries. In the solving processing, a spatial domain of RTE is discretized by unstructured meshes; an angular direction of RTE is discretized as a set of contrast angles by structured quadrilateral meshes. Then, both spatial domain and angular direction are coupling solved by DSEM. However, this coupling solution leads to a large-scale matrix problem. To address this, the element-by-element sweeping strategy optimizes the ordering of unstructured spatial elements. Several examples are provided to demonstrate the effectiveness of DSEM with the element-by-element sweeping strategy. Compared to the original sweep strategy, the element-by-element approach significantly improves calculation efficiency and reduces computational time.

Effect of variable conduction angle on the losses of switched reluctance machine

Switched Reluctance Machine (SRM) is the advanced version of the stepper motor and since last decade, it is of high interest among researchers and industrial applications. Modelling an SRM relies on accurate data and proper selection of parameters. The next step is the performance analysis of the machine for which losses determination is indispensable. Previous studies have shown losses calculation only at a particular instant of switching of the machine (i.e., conduction angle). Therefore, the impact of losses in a motoring region cannot be justified. This paper investigates the impact of varying conduction angle on the performance of machines for a set of switch-on angle. Losses are calculated and predicted through simulating motor operating parameters carried out in MATLAB environment and accuracy of results are compared with experimental results.

Inverse Kinematics for Serial Robot Manipulators by Particle Swarm Optimization and POSIX Threads Implementation

Inverse kinematics is a fundamental problem in manipulator robotics: a set of joint angles must be calculated so that the robot arm can be manipulated to the corresponding desired end effector position and orientation (also known as “pose”). Traditional solution techniques include analytical kinematics solvers, which provide the closed-form expressions for the joint positions as functions of the end-effector pose. When analytical inverse kinematics solvers are not possible due to the manipulator structure, numerical methods such as Newton–Raphson or Jacobian inverse can be used to achieve the task, but at a much slower speed due, to the iterative nature of the computation. Recent swarm intelligence technology has also contributed to manipulator inverse kinematics solutions. In this paper, the use of the Particle Swarm Optimization (PSO) approach in solving the inverse kinematics problem is investigated for the general serial robotic manipulators. Many of the reviewed robotic manipulator inverse kinematics solvers using swarm intelligence only deal with end effector position and not its orientation. Our PSO approach provides the convergence of a complete end-effector pose and will be demonstrated using the Baxter Research Robot, which has two seven-joint arms, although the method is applicable to any general serial robotic manipulator. For computational efficiency, the inverse kinematic calculations were implemented in parallel using Portable Operating Interface (POSIX) threads to take advantage of the independent swarm particle dynamics.

The Polarimetric Radar Scattering Properties of Oriented Aggregates

Abstract The scattering properties of aggregates are studied herein. Early aggregates (<7 monomers) of branched planar crystals and mature aggregates (up to 100 monomers) of columns are randomly generated with varying assumptions about the monomer attachment processes and the orientation behavior during collection. The resulting physical properties of the aggregates correspond well with prior in situ and retrieved sizes and shapes. Assumed azimuthally uniform orientations during collection and monomer pivoting upon attachment resulted in flatter and denser aggregates. The column aggregates had lower density and more spherical shapes than the branched planar crystal aggregates. The scattering properties were calculated using the discrete dipole approximation for a set of orientation angles and transformed to spectral coefficients representing modes of orientation angle variability. The zeroth- and second-order coefficients dominate this variability, with the zeroth-order coefficients representing the scattering properties for randomly oriented particles. The second-order coefficients for backscatter showed differences between horizontal and vertical polarization increasing with density, and these coefficients for specific differential phase increase with both mass and density. Similarly, coefficients for the copolar covariance decreased with density. Rapid changes in the contributions to the radar moments from the second-order coefficients from low to moderate density were observed, likely due to the increasing presence of horizontally aligned monomers in the aggregate structure. Differences in how differential reflectivity and correlation coefficient evolve with the orientation distribution parameters suggest that these measurements, along with specific differential phase and reflectivity, provide complementary information about aggregate sizes, shapes, and orientation distributions.

Error Analysis for Shipborne-based-based Single Band LiDAR Point Cloud Data

A new measuring technique called a ship-based single band LiDAR system is utilized to swiftly capture underwater terrain to employ dense and precise point cloud data on a vast region for bathymetry. The accuracy of point clouds is strongly impacted by the ease with which numerous error sources might affect shipborne single-band lidar measurement systems. Shipborne-based single-band LiDAR point cloud errors are mostly caused by GPS, attitude angle, range, and integration errors. This research explores and examines the impact of the scanning angle and attitude angle on bathymetry because they can fluctuate significantly throughout the actual measurement process. The point cloud errors resulting from numerous sets of scanning angle and attitude-angle data sets are calculated. The linear relationship and positioning accuracy between the three are intuitively depicted by comparable curves, presuming that other error causes are quantifiable. Analysis reveals that the error will also rise as the scanning angle increases.Additionally, the roll angle inaccuracy in the attitude angle has a minimal impact on the accuracy of the plane but a substantial impact on the accuracy of the elevation. Elevation error significantly impacts plane positioning accuracy but less on elevation accuracy. Positioning is only minimally affected by yaw angle inaccuracy.

Manufacturing, burst test and modeling of high pressure thermoplastic composite overwrap pressure vessel

This article presents the design, the prototyping and the burst test of a thermoplastic composite overwrapped pressure vessel. New models for composite stacking in the dome area are proposed and compared to state of the art solution. The complex pattern of tapes following geodesic path around the dome is synthetized in a 2D axisymmetric model. An adapted set of thickness and angle is chosen for each element to correctly model the geometry and the stiffness of the winded composite. A tomography of the whole tank is done to check the geometrical reliability of the model. The behavior of the tank during the burst test is monitored by strain gages to evaluate the stiffness prediction of the built finite element model. A time-dependent behavior is noticed during a pressure plateau at 700Bars. The burst occurs at 1586 Bars in the dome area, where the model predicts the maximum fiber stress.

Darfix - data analysis for dark-field X-ray microscopy.

A Python package for the analysis of dark-field X-ray microscopy (DFXM) and rocking curve imaging (RCI) data is presented. DFXM is a non-destructive diffraction imaging technique that provides three-dimensional maps of lattice strain and orientation. The darfix package enables fast processing and visualization of these data, providing the user with the essential tools to extract information from the acquired images in a fast and intuitive manner. These data processing and visualization tools can be either imported as library components or accessed through a graphical user interface as an Orange add-on. In the latter case, the different analysis modules can be easily chained to define computational workflows. Operations on larger-than-memory image sets are supported through the implementation of online versions of the data processing algorithms, effectively trading performance for feasibility when the computing resources are limited. The software can automatically extract the relevant instrument angle settings from the input files' metadata. The currently available input file format is EDF and in future releases HDF5 will be incorporated.

Rational 𝜃-parallelogram envelopes via 𝜃-congruent elliptic curves

We introduce a new generalization of [Formula: see text]-congruent numbers by defining a rational [Formula: see text]-parallelogram envelope. It turns out that the existence of a rational [Formula: see text]-parallelogram envelope associated to an [Formula: see text] is connected to the property of [Formula: see text] being a [Formula: see text]-congruent number. Then, we study some problems related to the rational [Formula: see text]-parallelogram envelopes, using the arithmetic of algebraic curves. Our results generalize the recent work of Ochiai, where only the case [Formula: see text] was considered. Moreover, we answer open questions raised by Ochiai in the more general setting of an arbitrary Pythagorean angle.

Optimization of Setting Angle Distribution to Suppress Hump Characteristic in Pump Turbine

Pump turbines play a quite important role of peak-valley shifting in the grid, and the hump margin is a critical criterion related to the safety and stability of operation in pump mode. Aiming at investigating the influence of runner outlet setting angle distribution on hump performance of a pump turbine, three runners with different linear distributions of setting angle at outlet were proposed, and the corresponding hump performance comparison was analyzed numerically through the SST k-ω turbulent model. The numerical result shows that, compared to the experiment, the relative errors of all simulated performances (energy characteristic, torque characteristic, and efficiency) were within 3%. Moreover, it was found that setting angle distribution modes could lead to a remarkably different performance in the hump region and, for the runner whose setting angle at shroud was 10° larger than that at hub, the hump safety margin could be increased from 4% to 4.5%. Thereafter, the corresponding mechanisms including energy input and hydraulic loss were investigated through the Euler head theory and the entropy method, respectively. It was found that hydraulic loss distribution played a more important role than the input energy on controlling hump performance. Moreover, for the runner with the largest hump margin, the hydraulic loss was distributed more evenly in the decreasing discharge direction, contributing to the elimination of hump performance. In addition, hydraulic loss distribution was calculated through local entropy production rate (LEPR) method. For all proposed runners, when the pump turbine entered the hump region from a normal operation point, the hydraulic loss was mainly concentrated in vaneless areas and guide/stay vane channels, while the runner with a large setting angle at shroud could better control the hydraulic loss distribution in both the spatial location and the discharge varying direction, increasing the hump margin. The design method presented in our paper is more likely to be applied in engineering applications.

Antenna tracking profile generation using mixed-integer linear programming

The increasing demand for the improved quantitative and qualitative performance of Earth observation images requires an increase in image data sizes and satellite agility, and that requires an increased effectiveness of antenna operations transmitting data to a ground station. Here, a mixed-integer linear programming (MILP)-based algorithm generating a tracking profile for an antenna subjected to operational constraints was utilized to maximize data transmission time. The constraints included angle and angular velocity limits. This algorithm considers a transition between two sets of angles for the elevation-over-azimuth mechanism to avoid rapid movement. Data transmission angle ranges are depicted as polygons representing the mission environment as mathematical equations in the MILP model. To reduce computation time, two assumptions were applied to simplify the algorithm, which extracts sampling points that can represent interior points. The proposed algorithm was verified by general imaging mission scenarios from a high-mobility satellite with special mission scenarios (i.e., worst-case scenarios for antenna maneuvers). The results were then compared with the preliminary tracking profile from the ground station searching method, which is a heuristic method. The MILP-based algorithm created solutions where data could be transmitted for 97.87% of the entire contact duration; total maneuvers of azimuth and elevation angles averaged at below 45.49% and 60.88% than of those constantly directed at the ground station, respectively. Operational constraints were satisfied in all scenarios, confirming that the algorithm is well suited to both general and worst-case scenario missions.

Influence of inflow directions and setting angle of inlet guide vane on hydraulic performance of an axial-flow pump

Inlet flow direction significantly affects the hydraulic performance of an axial-flow pump. Usually, the research papers ignore this phenomenon, resulting in discrepancies between simulation and experimental results. This study examines the influence of inflow direction in five cases (0%, 5%, 10%, 15%, and 30% pre-swirl intensities) to determine the relationship between the pre-swirl intensity and the hydraulic performance of the axial-flow pump. Based on this, changing the setting angle of the inlet guide vane (IGV) is proposed and thoroughly investigated to reduce the effect of inflow direction. In this study, the influence of clearances in IGV blades on hydraulic performance is also investigated in detail. Numerical simulations are performed using ANSYS–CFX and a shear stress transport reattachment modification (SST k-omega) turbulence model with small y+ values at all walls. Specifically, the hydraulic performance curves and internal flow characteristics, including contours and streamlines, are assessed and analyzed. The inflow direction significantly impacts the hydraulic efficiency of the axial-flow pump. Increased pre-swirl intensity causes more loss in the IGV passage. The internal flow field and performance are not affected by the clearance at the hub and shroud of the IGV. However, the tip clearance of the impeller causes a decrease in hydraulic efficiency due to the tip leakage vortex. By adjusting the setting angle of the IGV, the efficiency and head gradually increase from a negative to a positive setting angle. Additionally, 30° is considered the critical setting angle for IGV.

Effect of blade chord length on startup performance of H-type tidal current turbine rotor

This study aims to reveal the effect of the blade chord length on the startup performance of the lift rotor that converts the kinetic energy of tidal currents. The computational fluid dynamics technique was used to simulate unsteady flows around the rotor. The six degrees of freedom method was adopted to model the correlation between the rotational speed of the rotor and influential torques acting on the rotor. A comparative analysis of transient flows, rotational speed, and output torque was implemented at different initial azimuthal angles. The results show that as the rotor starts up at the minimum torque, the time required to attain the maximum rotational speed is longer than that associated with the maximum torque. As the maximum rotational speed is reached, low-pressure elements are produced in the area enclosed by the rotor blades, which is insensitive to the initial setting angle. A large area of low pressure is responsible for low output torque. During the startup process, the rotational speed experiences stages of sharp increase, fluctuating decrease, and moderate fluctuation, as is common at different blade chord lengths. As the chord length increases from 0.16 to 0.24 m, the startup process is extended by 0.63 s, and the average rotational speed in the stabilization stage decreases.

Pilot Search for Axion-Like Particles by a Three-Beam Stimulated Resonant Photon Collider with Short Pulse Lasers

Toward the systematic search for axion-like particles in the eV mass range, we proposed the concept of a stimulated resonant photon collider by focusing three short pulse lasers into a vacuum. In order to realize such a collider, we have performed a proof-of-principle experiment with a set of large incident angles between three beams to overcome the expected difficulty to ensure the space–time overlap between short pulse lasers and also established a method to evaluate the bias on the polarization states, which is useful for a future variable–incident–angle collision system. In this paper, we present a result from the pilot search with the developed system and the method. The search result was consistent with null. We thus have set the upper limit on the minimum ALP-photon coupling down to 1.5×10−4 GeV−1 at the ALP mass of 1.53 eV with a confidence level of 95%.

Uniqueness in Inverse Diffraction Grating Problems With Infinitely Many Plane Waves at a Fixed Frequency

This paper is concerned with uniqueness of solution of the inverse diffraction by problems by a periodic curve with Dirichlet boundary condition in two dimensions. It is proved that the periodic curve can be uniquely determined by the near-field measurement data corresponding to infinitely many incident plane waves with distinct directions at a fixed frequency. Our proof is based on Schiffer’s idea which consists of two ingredients: (i) the total fields for incident plane waves with distinct directions are linearly independent, and (ii) for a fixed wave number there exist only finitely many linearly independent Dirichlet eigenfunctions in a bounded domain or in a closed waveguide under additional assumptions on the waveguide boundary. Based on the Rayleigh expansion, we prove that the phased near-field data can be uniquely determined by the phaseless near-field data in a bounded domain, with the exception of a finite set of incident angles. Such a phase retrieval result leads to a new uniqueness result for the inverse grating diffraction problem with phaseless near-field data at a fixed frequency. Since the incident direction determines the quasi-periodicity of the boundary value problem, our inverse issues are different from the existing results of [F. Hettlich and A. Kirsch, Inverse Problems, 13 (1997), pp. 351–361], where fixed-direction plane waves at multiple frequencies were considered.

Diamane-like Films Based on Twisted G/BN Bilayers: DFT Modelling of Atomic Structures and Electronic Properties.

Diamanes are unique 2D carbon materials that can be obtained by the adsorption of light atoms or molecular groups onto the surfaces of bilayer graphene. Modification of the parent bilayers, such as through twisting of the layers and the substitution of one of the layers with BN, leads to drastic changes in the structure and properties of diamane-like materials. Here, we present the results of the DFT modelling of new stable diamane-like films based on twisted Moiré G/BN bilayers. The set of angles at which this structure becomes commensurate was found. We used two commensurate structures with twisted angles of θ = 10.9° and θ = 25.3° with the smallest period as the base for the formation of the diamane-like material. Previous theoretical investigations did not take into account the incommensurability of graphene and boron nitride monolayers when considering diamane-like films. The double-sided hydrogenation or fluorination of Moiré G/BN bilayers and the following interlayer covalent bonding led to the opening of a gap up to 3.1 eV, which was lower than the corresponding values of h-BN and c-BN. The considered G/BN diamane-like films offer great potential in the future for a variety of engineering applications.