Rotational Configuration Research Articles

Design of a Low Scattering Metasurface for Stealth Applications.

The design of a metasurface with low radar cross section (RCS) property is presented in this paper. The low scattering of the metasurface is achieved by applying the artificial magnetic conductor (AMC) unit cells in three different configurations. Two different AMC unit cells with an effective phase difference of 180 ± 37° are first designed to analyze the out of phase reflection in a wideband frequency range from 5.9 to 12.2 GHz. Then, the unit cells are placed in a chessboard-like configuration, newly constructed rotated rectangular-shaped configuration, and optimized configuration to study and compare the RCS reduction performance. All designs of the metasurface with different configurations show obvious RCS reduction as compared with the metallic plate of the same size. However, the relative bandwidth of the optimized metasurface is larger than the chessboard-like configuration and rotated rectangular-shaped configuration. To certify the results of the simulations, the metasurface with the optimized configuration is fabricated further to measure the RCS reduction bandwidth. The measured results are in good accordance with the simulated results. Therefore, the proposed metasurface can be a good option for applications where low RCS is desirable.

Tilting‐Sensitive Triboelectric Nanogenerators for Energy Harvesting from Unstable/Fluctuating Surfaces

AbstractThe invention of triboelectric nanogenerators provides an opportunity to utilize previously wasted mechanical energy. The sway energy of ships that affects navigation and comfort on board has been considered negative in the past. Here, a tilting‐sensitive triboelectric nanogenerator (TS‐TENG) that can effectively harvest energy from unstable/fluctuating surfaces is demonstrated by using the sway energy of ships. The device adopts integrated blade structures on sliders, which make it sensitive to tilts and guarantee its power output. The response of the device to tilt agitations of different slopes and frequencies is systematically investigated. Rotational symmetry configuration is used to improve the motion stability of the device by excluding extra torque on the sliders. The peak power density and average power density of the TS‐TENG can reach 1.41 and 0.1 W m−3, respectively, in low‐frequency and low‐amplitude fluctuating conditions. By the excellent performance of harvesting energy from unstable/fluctuating surfaces, the TS‐TENG is considered promising for powering various distributed sensor devices on the ship for smart ships.

Rotational design of BP/XY2 (X = Mo, W; Y = S, Se) composites for overall photocatalytic water-splitting

Photocatalytic water-splitting for hydrogen generation is a promising way to solve the energy crisis, yet the design of efficient photocatalysts is still a challenge. By utilization of first principles calculations, we predict the photocatalytic properties of monolayer boron phosphide (BP) based BP/XY2 (X = Mo, W; Y = S, Se) composites of different rotated configurations. Our results suggest that the BP/XY2 composites can be stably formed, and the narrowed bandgaps ensure these composites are suitable for absorbing visible light. The bandgaps and band edge positions are slightly affected by the rotation angles. The BP/MoS2, BP/MoSe2, and BP/WSe2 are type II heterostructures. Furthermore, the transferred charge from BP to XY2 layers leads to the formation of electric fields, which efficiently separate the photoinduced carriers. The band alignments of BP/MoS2, BP/MoS2, BP/MoSe2, and BP/WSe2 satisfy the requirements of overall water-splitting within the pH scope of 3.6–7.9, 6.8–7.9, 4.0–8.0, and 8.7–8.8. This work will provide valuable insight for designing efficient water-splitting photocatalysts.

Geometric Kinematic Control of a Spherical Rolling Robot

We give a geometric account of kinematic control of a spherical rolling robot controlled by two internal wheels just like the toy robot Sphero. Particularly, we introduce the notion of shape space and fibers to the system by exploiting its symmetry and the principal bundle structure of its configuration space; the shape space encodes the rotational angles of the wheels, whereas each fiber encodes the translational and rotational configurations of the robot for a particular shape. We show that the system is fiber controllable—meaning any translational and rotational configuration modulo shapes is reachable—as well as find exact expressions of the geometric phase or holonomy under some particular controls. We also solve an optimal control problem of the spherical robot, show that it is completely integrable, and find an explicit solution of the problem.

Planar Self-Balanced Magnetic Dipole Antenna With Wide Beamwidth Characteristic

A design approach to a novel planar self-balanced magnetic dipole antenna with wide beamwidth is proposed. By incorporating a parasitic rectangular strip to a circular sector magnetic dipole at its angular bisector on the bottom layer, a virtual magnetic wall boundary condition is partly introduced within the horizontal plane. In this way, the unbalanced current can be utilized to generate unidirectional radiation behavior, leading to the formulation of a self-balanced antenna with widened beamwidth. As numerically demonstrated and experimentally validated at the 2.45 GHz band, the half-power beamwidth (HPBW) of a planar, air-substrate magnetic dipole antenna can be effectively broadened up to 100° without increasing antenna profile, inquiring symmetrically rotational configurations, utilizing multilayered substrates or periodic loadings. The proposed approach not only provides a clear physical insight but also works out a set of closed-form formulas. As exhibited, the planar wide beamwidth antennas have a simple configuration and wide impedance bandwidth up to 20%.

Robust Superlubricity of Gold–Graphite Heterointerfaces

AbstractNoncommensurate 2D interfaces hold great promise toward low friction and nanoelectromechanical applications. For identical constituents, the crystals interlock at specific rotational configurations leading to high barriers for slide. In contrast, nonidentical constituents comprising different lattice parameters should enable robust superlubricity for all rotational configurations. This is however not the case for gold–graphite interfaces, as both theory and experiments show scaling behavior of the sliding force as a function of the interface contact area. By simulating the sliding force for gold–graphite interfaces, this work shows that the origin for high force barriers at special angular configurations is a result of commensurability between the moiré structure and the contact geometry. Consequently, this paper suggests new geometries that can potentially overcome such commensurability effects to enable robust superlubricity.

Assessing Disk Galaxy Stability through Time

Abstract N-body simulations have shown that a bar in a galaxy can be triggered by two processes: (1) by its own instabilities in the disk, or (2) by interactions with other galaxies. Both mechanisms have been widely studied. However, the literature has not shown measurements of the critical limits of the disk stability parameters (DSPs). We show measurements of those parameters through the whole evolution in isolated disk models and find that the initial rotation configuration of those models stays in the stable or unstable regime from the initial to the final evolution. Then we perturbed the isolated models to study the evolution of DSPs under perturbation. We find that the critical limits of DSPs are not much affected in barred models, but when the bar is triggered by a perturbation, the disk falls into the unstable regimen. We show in our models that a bar triggered by a light perturbation grows in two phases: first, the bar appears as a slow rotator, and then it evolves to be a fast rotator; second, when the perturbation is far from the target galaxy, the bar evolves from fast to slow rotator. When the bar is triggered by a heavy perturbation, it appears as a fast rotator and evolves to be a slow rotator, similar to classical bar models.

Multiband circular dichroism from bilayer rotational F4 nanostructure arrays.

A chiral nanostructure array is designed, which is composed of a bilayer rotational F4-shaped nanoarray configuration. The surface plasmon resonance and circular dichroism are studied by changing the parameters of the structure. The results show that the structure has strong multiband circular dichroism, which is attributed to the coupling of the layers. In theory, based on the Born-Kuhn model, the upper and lower nanostructures are equivalent to electric dipoles. By analyzing the coupling mode of electric dipoles in the upper and lower layer, the mechanism of circular dichroism and the shift of the circular dichroism resonance are revealed. Besides, there are several specific modes that are fault tolerant of fabrication issues. This feature unveils the bright prospect of spectral anti-interference. So, the suggested chiral nanostructure can be used in biologically targeted molecular detection and spectral sensing.

The real-time determination of d- and l-lactate based on optical weak measurement

A simple transmission optical rotation (OR) configuration based on weak measurement was developed for the real-time determination of d- and l-lactate.

Flow-induced oscillations of three tandem rotating cylinders

The oscillation responses and the associated wake structures of three rotating tandem cylinders, mounted on elastic supports in both the streamwise (x-) and transverse (y-) directions, are numerically studied. Finite element computations are carried out at Reynolds number Re = 150, where the flow is two-dimensional (2-D), and at Re = 2000 (3-D flow), varying the reduced velocity (U*) in the range U* = 2–14. Each cylinder is placed at a distance of 5 diameters (5D) from its immediate neighbor. In the two-dimensional flow, the upstream and the second downstream cylinders are rotated at the rotation rate (α) of 1, while for the first downstream cylinder, α = 0, 0.5, and 1 are employed. In the 3-D computations, α = 1 is considered for the three bodies. It is observed that at Re = 150, all the cylinders exhibit three distinct lock-in modes, namely, modes I, II, and III. Depending on the rotation configuration, 2S, P + S, and 2P shedding patterns appear in the wake of upstream cylinder, while the downstream cylinders shed 2S, P, P + S, 2P, and T + P modes of primary vortices. In the 3-D flow (at Re = 2000), the upstream cylinder exhibits a bell-shaped profile in the variation of amplitude response as a function of U*. Oscillation responses of the two downstream bodies appear in three distinct regions. During high amplitude oscillations, the upstream cylinder sheds the 2P mode of primary vortices, while in the near wakes of the two downstream bodies, small and incoherent primary vortical structures form due to the presence of three-dimensional instability. Low and high amplitude responses are associated with weak and strong 3-D flow instabilities, respectively.

A projection-based approach for the derivation of the floating frame of reference formulation for multibody systems

The reduction in the number of coordinates for flexible multibody systems is necessary in order to achieve acceptable simulation times of real-life structures and machines. The conventional model order reduction technique for flexible multibody systems is based on the floating frame of reference formulation (FFRF), using a rigid body frame and superimposed small flexible deformations. The FFRF leads to strongly coupled terms in rigid body and flexible coordinates as well as to a non-constant mass matrix. As an alternative to the FFRF, a formulation based on absolute coordinates has been proposed which uses a co-rotational strain. In this way, a constant mass matrix and a co-rotational stiffness matrix are obtained. In order to perform a reduction in the number of coordinates, by means of the component mode synthesis, e.g., the number of modes needs to be increased, such that all modes are represented in every possible rotated configuration. This approach leads to the method of generalized component mode synthesis (GCMS). The present paper shows in detail how the equations of motion of the FFRF evolve from the ones of the GCMS by considering rigid body constraint conditions and subsequently eliminating them via an appropriate null-space projection. This approach allows a straightforward, term-by-term interpretation of the FFRF mass matrix and of the generalized gyroscopic forces, which, to the same extent, cannot be deduced from former publications on the FFRF. From a practical point of view, the resulting expressions allow to calculate all inertia coefficients from the constant finite element mass matrix together with standard input data of the finite element model in the course of a preprocessing step. Then, the repeated updates of the FFRF mass matrix and of the gyroscopic forces in the course of time integration involve only simple vector matrix operations of low dimensions. In contrast to previous implementations of the FFRF, no evaluations of extra inertia integrals are required. Consequently, the present formulation can be implemented entirely independent of the related finite element code.

An inertial device biases on-line monitoring method in the applications of two rotational inertial navigation systems redundant configuration

Rotation modulation technology can enhance the autonomous navigation accuracy of inertial navigation system significantly, which has contributed to the wide applications of rotational inertial navigation system (RINS). To ensure the reliability and safety of high-precision autonomous navigation for the long endurance navigation in vehicle or marine applications, two or more RINSs are usually equipped. In this condition, the RINSs fault detection and isolation can be realized by comparing the differences of navigation information from different RINSs. In this paper, an on-line monitoring method for inertial device biases in the applications of two RINSs redundant configuration is proposed. The method takes advantages that the rotation modulation technology could improve the observable degrees of inertial device biases to achieve on-line optimal estimation of the gyro drifts and accelerometer biases for all the six gyros and accelerometers of the two RINSs. Two RINSs redundant configuration was presented and the inertial device biases estimation models were deduced. Based on the system model, simulations and experiments were both conducted. Simulation and experimental results showed that the proposed method could detect and isolate the faulty inertial devices of two RINSs effectively in autonomous navigation. Furthermore, gyro drifts monitoring accuracy could be better than 0.001°/h and accelerometer biases monitoring accuracy could be better than 1 μg in cases where the random constant gyro drifts are 0.02°/h (1σ) and random constant accelerometer biases are 50 μg (1σ), which demonstrates the effectiveness of the proposed inertial device biases on-line monitoring method.

Oscillation responses and wake modes of three staggered rotating cylinders in two- and three-dimensional flows

Oscillation responses and wake modes of three staggered rotating cylinders, free to move in streamwise and transverse directions, are numerically studied in two- (2-D) and three-dimensional (3-D) flows. 2-D computations are carried out for Reynolds number Re = 60–150, employing the following rotation rates (α), respectively, for the upstream, upper, and lower downstream cylinders: 1, 1, 0; 1, 1, 1; 1, 1, −1. Here, the clockwise rotation is positive. 3-D simulations are performed at Re = 2000 and reduced velocity, U* = 2–11, with the three cylinders being rotated at α = 1. Bell-shaped amplitude profiles are observed for all the rotating cylinders, indicating that the bodies undergo vortex-induced vibrations. In 2-D flow, the considered Re regime can be categorized into three distinct regions, based on the oscillation and frequency responses. Cylinders exhibit negligible amplitudes in the first region, whereas the second region is characterized by high amplitude lock-in oscillations for all three cylinders. In the third region, the downstream cylinders exhibit lock-in response in certain rotation configurations. The oscillation responses and wake modes appear sensitive to the direction of rotation of the lower downstream cylinder for the streamwise and transverse gaps of 5 diameters (5D) and 3D, respectively, between the cylinders. Depending on the rotation configuration, 2S, P, and P + S modes of primary shedding are observed. In 3-D flow also, the cylinders exhibit bell-shaped amplitude profiles, contrary to the galloping response noticed for isolated rotating cylinders in few previous studies. Higher and lower amplitude oscillations induce stronger and weaker 3-D flow instabilities, respectively, in the wake region.

Collision Risk Mitigation of Varian TrueBeam Linear Accelerator With Supplemental Live-View Cameras

BackgroundNoncoplanar radiation therapy techniques such as 4π have potential dosimetric advantages but introduce complexities in treatment delivery that increase the risk for collision. Direct or remote visual confirmation of clearance is a safeguard against collisions of the gantry, couch, and patient. With our institution’s Varian TrueBeam system, we identified configurations that cannot be visualized with the included closed-circuit television cameras. At our practice, electronic, portal imaging device (EPID) collision risk also exists because of the routine deployment to capture exit-dose images for treatment quality assurance. We propose a simple, cost-effective solution using network cameras to help eliminate blind spots that permits safe, noncoplanar arrangements with an EPID-acquired exit dose. Methods and materialsTwo Panasonic cameras were installed overhead while a third Panasonic camera was mounted onto the pedestal to monitor the couch undersurface. Live views from each camera were accessed with a web-based client. The EPID and gantry were visually assessed at 52 couch and gantry rotational angle configurations at 6 couch translational positions. Visibility was compared for the standard and supplemental camera setups at each configuration (χ2 test). ResultsOf the 294 assessable couch-gantry configurations, the standard camera setup had limited visibility of either gantry or EPID for 146 configurations compared with 72 configurations with additional cameras (51% blind-spot reduction; P < .01). An 87% blind-spot reduction was observed for our laterally centered, cranial-based, couch translational position (P < .01). ConclusionsThe supplemental cameras were simple, effective additions for collision detection, especially for noncoplanar radiation therapy with EPID-acquired, exit-dose imaging. Over half of the assessable noncoplanar configurations had blind spots using standard cameras, which was reduced to <25% with additional cameras. In practice, there were almost no blind spots for patients with brain tumors who were treated with our templated beam arrangements. Using live-view camera feeds, vault re-entry to visually confirm clearance was reduced approximately 10-fold, which increased the treatment efficiency. In the most recent 12 months, no collision or near-collision events have been reported.

Predicting the pressure losses while the drillstring is buckled and rotating using artificial intelligence methods

The prediction of equivalent circulating density in realistic conditions is complex due to many parameters in effect. Drillstring configuration and motion can play a significant role on the pressure profile in the annulus. Eccentricity, rotation and axial position of the drillstring can cause distinct pressure losses. If an accurate prediction is desired, these effects need to be accounted for.In this study, the pressure losses of Yield Power Law fluids with various drillstring rotation speeds and configurations are analyzed. These configurations include eccentricity and various buckling configurations and rotation speeds of the drillstring. Neural networks are used to predict the pressure losses and the results are compared with the experimental results and existing models from the literature.The input to the neural networks is optimized by comparing using direct measurements and using dimensionless parameters derived from the measurements. The comparison shows that using direct measurements as input yield better results instead of using dimensionless parameters, considering the experimental data used in this study.The results of this study showed that using neural networks to predict the pressure losses in complex geometries and motion showed a better precision compared to the existing models from the literature. The results analysis show that predicting with neural networks can yield as low as 5% absolute average percent error while predicting using existing models can yield as high as 115% absolute average percent error. Using neural networks shows a strong potential to accurately predict the pressure losses especially considering complex fluids and geometries.

Effect of process parameters on mechanical properties of friction stir welded dissimilar 7075-T651 and 5083-H111 aluminum alloys

In this paper, the influence of process parameters (tool rotational speed, pin design, and configuration of joined alloys) on the macrostructure and mechanical properties of friction stir welded aluminum alloys 7075-T651 and 5083-H111 was characterized. The tool rotational speed and the alloy placement significantly influenced the formation of the weld (especially the stir zone). Superior mixing of materials was obtained at higher rotational speeds and in the configuration with 5083 on the advancing side and 7075 on the retreating side. However, under these conditions, more defects, such as porosity, voids, or wormholes, were found in the stir zone. Regardless of the pin design and weld configuration, with an increasing tool rotational speed, the mechanical properties decrease. Using the Triflute pin, however, guarantees higher tensile strength and weld efficiency (above 100%). The weld configuration did not influence the mechanical properties. The highest tensile strength (371 MPa) defect-free joint was obtained with 5083 on the advancing side, 7075 on the retreating side, a tool rotational speed of 280 rpm, and the Triflute pin.

Strongly anisotropic RKKY interaction in monolayer black phosphorus

We theoretically study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in two-dimensional black phosphorus, phosphorene. The RKKY interaction enhances significantly for the low levels of hole doping owing to the nearly valence flat band. Remarkably, for the hole-doped phosphorene, the highest RKKY interaction occurs when two impurities located along the zigzag direction and it tends to a minimum value with changing the direction from the zigzag to the armchair direction. We show that the interaction is highly anisotropic and the magnetic ground-state of two magnetic adatoms can be tuned by changing the rotational configuration of impurities. Owing to the anisotropic band dispersion, the oscillatory behavior with respect to the angle of the rotation and the distance of two magnetic impurities, R is well-described by sin(2kFR), where the Fermi wavelength kF changes in different directions. We also find that the tail of the RKKY oscillations falls off as 1/R2 at large distances.

Minimum Resistance Anisotropy of Epitaxial Graphene on SiC.

We report on electronic transport measurements in rotational square probe configuration in combination with scanning tunneling potentiometry of epitaxial graphene monolayers which were fabricated by polymer-assisted sublimation growth on SiC substrates. The absence of bilayer graphene on the ultralow step edges of below 0.75 nm scrutinized by atomic force microscopy and scanning tunneling microscopy result in a not yet observed resistance isotropy of graphene on 4H- and 6H-SiC(0001) substrates as low as 2%. We combine microscopic electronic properties with nanoscale transport experiments and thereby disentangle the underlying microscopic scattering mechanism to explain the remaining resistance anisotropy. Eventually, this can be entirely attributed to the resistance and the number of substrate steps which induce local scattering. Thereby, our data represent the ultimate limit for resistance isotropy of epitaxial graphene on SiC for the given miscut of the substrate.

Rotational-guided growth

Background: Rotational deformities of the femur and tibia are some of the most common orthopedic alignment problems in the lower extremity. In-toeing and out-toeing are common complaints seen by pediatric orthopedic surgeons as well. The idea of guided growth to correct axial rotation deformities in children is appealing. The purpose of this study was to investigate this concept and to test it in a large animal model taking advantage of the human like dimensions and biomechanics. Method: To generate axial-rotational growth we tether the growth plate on both sides at a fixed inclined angle on each side a cable with two screws. This construct was called the Percutaneous Progressive Derotator (PPD). Eight calves, two-month old, four male (50%) and the other four female, were used as models. The PPD device was implanted at the distal physis of the right metacarpal in an external rotation configuration, leaving the left side as control. The PPD device was left in for 3 months and was then removed. The total followed up was 2 years and 3 months. Results: The hypothesis that guided growth was possible in large animals has been confirmed. Rotation of 24° average were achieved in the right metacarpus of the growing cattle (P < 0.001), using the torque generated in the growth plate by the PPD.

A decoupled flexure-based rotary micropositioning stage with compact size

This paper presents the design and analysis of a novel compact flexure-based rotary micropositioning stage driven by piezoelectric actuator. The developed stage possesses a double four-bar rotary mechanism with rotational symmetric configuration and totally kinematic decoupling, which can convert the linear motion of the piezoelectric actuator into the pure rotational motion, significantly minimizing the parasitic error at the rotation center. Based on the configuration, a single piezoelectric actuator is employed to drive the stage, avoiding actuator redundancy and large configuration size. Meanwhile, we introduce a compliant rotational guiding mechanism to enhance the rotational stiffness and dynamics of the stage. Analytical modeling and finite element analysis are adopted to facilitate the design of dimension. Finally, a prototype of the stage is manufactured and tested, which is capable of a rotational angle of [Formula: see text] with the first natural frequency of 430 Hz, whilst the well-constrained maximum center shift along the X- and Y-axis are 0.29 µm and 0.12 µm, respectively, indicating good decoupling capability. Furthermore, the compact size of [Formula: see text] is beneficial for limited working space.