Large Angle Research Articles

Improving large angle flow measurement accuracy of five-hole probe using novel calibration coefficient and accuracy progressive neural network

Novel calibration coefficients and data-fitting techniques based on a two-stage accuracy progressive neural network were developed to improve the accuracy of a five-hole probe in measuring large-angle flows. By modifying the denominator and numerator of traditional calibration coefficients, the novel coefficients can solve the singularity and multi-value problems of large-angle flow measurement. By training the neural network using both global calibration data and the calibration data of large measurement error points, the two-stage accuracy progressive neural network can effectively improve the measurement accuracy of a five-hole probe when flow separation occurs around the probe head at large flow angles. The experimental results demonstrate that applying the novel calibration coefficients and accuracy progressive neural network ensures that the calibration error of the flow angle is less than 0.8°, and the flow pressure error is less than 0.1 % when the flow angle reaches 50° at low subsonic speeds.

Benzimidazole based electron-transport hosts for efficient pure blue narrowband OLED device

Two electron-transport host materials are synthesized by linking anthracene with benzimidazole derivatives through a unit of methyl substituted phenyl. The methyl substitution generates a large dihedral angle between the benzimidazole plane and bridging phenyl, keeping the excited state distribution and energy levels of T1 and S1 unchanged. The electron-only devices reveal that the two hosts have obviously enhanced electron transport ability than that of Ph-AN-MBP without benzimidazole. As a result, the devices with Ph-AN-BIZ and N1-AN-BIZ as hosts and a blue multiple resonance material of tBuCz-DABNA as emitter exhibit high external quantum efficiency of 10.1 % and 9.1 %, respectively, and low turn-on voltage of 2.7 V, which is better than those of Ph-AN-MBP based device (7.9 %, 3.4 V). And their electroluminescence spectra have a very small full-width at half-maximum of 16.2 nm and pure blue color with CIE coordinates of (0.12, 0.11).

Suppressing torsional buckling in auxetic meta-shells

Take a thin cylindrical shell and twist it; it will buckle immediately. Such unavoidable torsional buckling can lead to systemic failure, for example by disrupting the blood flow through arteries. In this study, we prevent this torsional buckling instability using a combination of auxeticity and orthotropy in cylindrical metamaterial shells with a holey pattern. When the principal axes of the orthotropic meta-shell are relatively aligned with that of the compressive component of the applied stress during twisting, the meta-shell uniformly shrinks in the radial direction as a result of a local buckling instability. This shrinkage coincides with a softening-stiffening transition that leads to ordered stacking of unit cells along the compressive component of the applied stress. These transitions due to local instabilities circumvent the usual torsional instability even under a large twist angle. This study highlights the potential of tailoring anisotropy and programming instabilities in metamaterials, with potential applications in designing mechanical elements for soft robotics, biomechanics or fluidics. As an example of such applications, we demonstrate soft torsional compressor for generating pulsatile flows through a torsion release mechanism.

A new seismic wave input method for canyon sites based on the finite element method-indirect boundary integral equation method

The seismic input is the basis for the seismic safety analysis of dams, but current seismic input methods have not reasonably considered the influence of canyon scattering effects on the dynamic response of dams. In this paper, the total motion field of the canyon is deconstructed into the free field of a uniform half space and the scattering field of the canyon and they are obtained separately. The indirect boundary integral equation method (IBIEM) is used to determine the scattering field of the canyon, which is superimposed with the free field to obtain the seismic ground motion field (total motion field) of the canyon. The accuracy of the total motion field of the canyon is verified through reference solutions. In the finite element analysis of seismic ground motion field in the canyon, the total motion field at the truncation boundary of the canyon foundation is transformed into the equivalent seismic input loads and the interior of the canyon are simulated using the finite element method (FEM). Then, based on the wave input for the free field combined with the viscoelastic artificial boundary, a new wave input method for the total motion field combined with the viscoelastic artificial boundary is established. The seismic wave input method based on the finite element-indirect boundary integral equation method is applied to numerically determine the seismic response of a trapezoidal canyon. The differences in the seismic response of the canyon under free-field input and total motion field input are discussed. The results show that there is a certain deviation between the displacement and waveform obtained from the free-field input and the solutions obtained from the indirect boundary integral equation method. There is a large error for a large angle of incidence, and the errors increase with increasing seismic wave frequency. When the incident angle is 60°, the maximum error in the frequency domain reaches 92.3 %, and the maximum error in the time domain reaches 250 %. The displacement amplitude and waveform of the canyon obtained from the total motion field input showed agreement with the results of the indirect boundary integral equation method. The wave input method established in this paper has high calculation accuracy and reasonably considers the scattering effect of canyons, which provides a basis for more accurate predictions of the seismic response of dams on canyon foundations.

Research on multi-resonance mechanism to achieve ultra-wideband high absorption of a metamaterial absorber in the UV to MIR range

Wideband metamaterial perfect absorbers have been extensively researched due to their excellent properties. A four-layer ultra-broadband metamaterial perfect absorber engraved with a square cavity is proposed. A clever combination of grating and square cavity allows the absorber to manifests an overall absorption of over 92 % and an average absorption rate of 97.27 % within the operational band from 280 to 5400 nm. Through analysis, it can be concluded that the coupling effects of Rayleigh anomaly (RA), magnetic resonance (MR), cavity resonance (CR), propagating surface plasmon resonance (PSPR) and local surface plasmon resonance (LSPR) result in perfect absorption. The absorber is insensitive to polarization and large angle incidence. It is worth mentioning that the average absorption rate of our structure reaches 93.32 % at a large incidence angle of 60° in TE mode, which is much higher than that of other absorbers. At 1000 K, the total photothermal conversion efficiency of our absorber is still above 90 %. The designed structure has the following advantages: high absorption, ultra-wide bandwidth, high tolerance to fabrication errors and insensitivity to large angle incidence. Thus, the absorber can be used in the solar energy harvesting and perfect stealth. Additionally, it also can be served as a reference in thermophotovoltaics, thermal imaging and infrared detection.

Modeling Ocean Swell and Overtopping Waves: Understanding Wave Shoaling with Varying Seafloor Topographies

One risk posed by hurricanes and typhoons is local inundation as ocean swell and storm surge bring a tremendous amount of energy and water flux to the shore. Numerical wave tanks are developed to understand the dynamics computationally. The three-dimensional equations of motion are solved by the software ‘Open Field Operation And Manipulation’ v2206. The ‘Large Eddy Simulation’ scheme is adopted as the turbulence model. A fifth-order Stokes wave is taken as the inlet condition. Breaking, ‘run-up’, and overtopping waves are studied for concave, convex, and straight-line seafloors for a fixed ocean depth. For small angles of inclination (<10°), a convex seafloor displays wave breaking sooner than a straight-line one and thus actually delivers a smaller volume flux to the shore. Physically, a convex floor exhibits a greater rate of depth reduction (on first encounter with the sloping seafloor) than a straight-line one. Long waves with a speed proportional to the square root of the depth thus experience a larger deceleration. Nonlinear (or ‘piling up’) effects occur earlier than in the straight-line case. All these scenarios and reasoning are reversed for a concave seafloor. For large angles of inclination (>30°), impingement, reflection, and deflection are the relevant processes. Empirical dependence for the setup and swash values for a convex seafloor is established. The reflection coefficient for waves reflected from the seafloor is explored through Fourier analysis, and a set of empirical formulas is developed for various seafloor topographies. Understanding these dynamical factors will help facilitate the more efficient designing and construction of coastal defense mechanisms against severe weather.

Measurement and advanced data post-processing of proton resonance frequency shift in 7 T MRI to obtain local temperature in a tissue-mimicking phantom

Abstract The radio-frequency (RF) transmit power deposition in tissue during magnetic resonance imaging (MRI) at ultra-high fields, i.e. B 0 ≥ 7 T, is a major challenge for pulse sequences requesting large flip angles. The absorbed RF energy can pose safety risk to patients as it is rising temperature in the tissue. The temperature can be accessed using MRI itself via the proton-resonance frequency (PRF) shift technique, which at low B 0 has been shown a valid MR thermometry method. In this paper, we explore the applicability of the PRF method to the assessment of local temperature in 7 T MRI procedures. To this end, we built a phantom filled with a material presenting electrical conductivity and permittivity close to muscle tissue. Tubes filled with oil were placed nearby the phantom to observe the time dependent B 0 drift. MRI phase images were acquired by gradient-echo (GRE) sequences at time points between spin-echo sequences with large flip angle allowing for a continuous assessment of the temperature during a 114 min RF-heating experiment. All acquired phase images were post-processed with attention to the time dependent instability of B 0, and, in addition, to potential spatial and temporal phase discontinuities, known as wraps. In this paper, we present a strategy to analyze and to unfold these phase wraps for large measurement fields and long acquisition times. It is shown that the PRF shift method is beneficial for the assessment of temperature at 7 T MRI. The temperature maps for axial and coronal planes display a temperature increase of approximately 3.5 °C during the time of the RF-heating experiment. Overall it is shown that B 0-drift correction and, importantly, the spatio-temporal unwrapping are an indispensable part of post-processing.

Bridging the small and large in twisted transition metal dichalcogenide homobilayers: A tight binding model capturing orbital interference and topology across a wide range of twist angles

Many of the important phases observed in twisted transition metal dichalcogenide homobilayers are driven by short-range interactions, which should be captured by a local tight binding description since no Wannier obstruction exists for these systems. Yet, published theoretical descriptions have been mutually inconsistent, with honeycomb lattice tight binding models adopted for some twist angles, triangular lattice models adopted for others, and with tight binding models forsaken in favor of band projected continuum models in many numerical simulations. Here, we derive and study a minimal model containing both honeycomb orbitals and a triangular site that represents the band physics across a wide range of twist angles. The model provides a natural basis to study the interplay of interaction and topology in these heterostructures. It elucidates from generic features of the bilayer the sequence of Chern numbers occurring as twist angle is varied, and the microscopic origin of the magic angle at which flat-band physics occurs. At integer filling, the model successfully captures the Chern ferromagnetic and van Hove-driven antiferromagnetic insulators experimentally observed for small and large angles, respectively, and allows a straightforward calculation of the magnetoelectric properties of the system. Published by the American Physical Society 2024

A study on a physical based manoeuvring mathematical model for submarines

The manoeuvrability of submarines is one of the important factors from mission and safety points of view. In particular, manoeuvring motions with a large drift angle and/or angle of attack in both the horizontal and the vertical planes have different motion parameters compared to the normal manoeuvring motions. To evaluate the manoeuvrability during these types of particular motions of submarines, especially at the initial design stage, the manoeuvring hydrodynamic derivatives that are related to various manoeuvring motions must be identified.Karasuno model, which is termed a physical based model, has the advantages that it needs only model experiments for drift motion and it can provide greater accuracy under motion with large angles. Despite these advantages, this model has not been applied to other vessels excluding fishing vessels. The applicability of this method to submarines therefore should be examined. The applicability of Karasuno model for submarines is validated through a computational fluid dynamics (CFD) analysis and comparisons with experimental data in this work. The findings contribute to identifying the manoeuvring hydrodynamic forces for submarines and evaluating their manoeuvring performance. Through rigorous validation, the potential of the proposed model as a reliable tool for predicting and analyzing submarine maneuvering motions is demonstrated.

Interplanetary Type IV Solar Radio Bursts: A Comprehensive Catalog and Statistical Results

Decameter hectometric (DH; 1–14 MHz) type IV radio bursts are produced by flare-accelerated electrons trapped in postflare loops or the moving magnetic structures associated with the coronal mass ejections (CMEs). From a space weather perspective, it is important to systematically compile these bursts, explore their spectrotemporal characteristics, and study the associated CMEs. We present a comprehensive catalog of DH type IV bursts observed by the Radio and Plasma Wave Investigation instruments on board the Wind and Solar TErrestrial RElations Observatory spacecraft covering the period of white-light CME observations by the Large Angle and Spectrometric Coronagraph on board the Solar and Heliospheric Observatory mission between 1996 November and 2023 May. The catalog has 139 bursts, of which 73% are associated with a fast (>900 km s−1) and wide (>60°) CME, with a mean CME speed of 1301 km s−1. All DH type IV bursts are white-light CME-associated, with 78% of the events associated with halo CMEs. The CME source latitudes are within ±45°. Seventy-seven events had multiple-vantage-point observations from different spacecraft, letting us explore the impact of the line of sight on the dynamic spectra. For 48 of the 77 events, there were good data from at least two spacecraft. We find that, unless occulted by nearby plasma structures, a type IV burst is best viewed when observed within a ±60° line of sight. Also, bursts with a duration above 120 minutes have source longitudes within ±60°. Our inferences confirm the inherent directivity in the type IV emission. Additionally, the catalog forms a Sun-as-a-star DH type IV burst database.

Particle Acceleration in Relativistic Alfvénic Turbulence

Strong magnetically dominated Alfvénic turbulence is an efficient engine of nonthermal particle acceleration in a relativistic collisionless plasma. We argue that in the limit of strong magnetization, the type of energy distribution attained by accelerated particles depends on the relative strengths of turbulent fluctuations δ B 0 and the guide field B 0. If δ B 0 ≪ B 0, the particle magnetic moments are conserved, and the acceleration is provided by magnetic curvature drifts. Curvature acceleration energizes particles in the direction parallel to the magnetic field lines, resulting in log-normal tails of particle energy distribution functions. Conversely, if δ B 0 ≳ B 0, interactions of energetic particles with intense turbulent structures can scatter particles, creating a population with large pitch angles. In this case, magnetic mirror effects become important, and turbulent acceleration leads to power-law tails of the energy distribution functions.

Experimental research on the flow flied of the nacelle and inlet of a civil aircraft with wind-mounted engines at low speed

Abstract Modern civil transport aircraft with wing-mounted engines are exposed to the upwash induced by the wing, resulting in the local angle of attack at the nacelle leading edge, notably greater than that of aircraft. Large local angles of attack can be combined with different engine airflow conditions, causing adversary aerodynamic phenomena to occur at different locations. Total and static pressures obtained in a wind tunnel test using a full-span aircraft model and simulating required engine airflow with an ejector indicate that during the around with landing configuration, the high suction peak will form on the bottom of the inlet with local air flow being supersonic and could lead to inlet distortion. In contrast, the engine that fails during takeoff climb will have a significant suction peak form on the top of the nacelle and might experience external separation and additional drag. Test results also demonstrate that well-designed nacelles can postpone these adversary phenomena until the aircraft stalls first.

Large angle attitude control of cubesat based on multi-objective optimization

Abstract The rigid body motion of CubeSat is strongly coupled with the elastic vibration of the flexible structure during the large angle attitude maneuver of the CubeSat. The drastic change of attitude will aggravate the jitter of the solar panel, which will then disrupt its stability. To deal with the contradictions between the rapidity and high-precision stability of large angle attitude maneuver of CubeSats and ensure the higher attitude pointing accuracy of the satellite after the attitude maneuver, this paper presents a multi-objective optimization algorithm based on the quintic polynomial path. This optimization algorithm can reduce the angular velocity as much as possible and obtain the optimal solution of maneuvering time. Then, a terminal sliding mode finite-time controller developed from a nonlinear disturbance observer is proposed. The nonlinear disturbance observer can calculate the disturbance, and the terminal sliding mode finite-time controller can perform feedforward compensation to improve the anti-interference ability of the control system, to achieve the desired finite-time attitude tracking control. Finally, a digital simulation platform based on the momentum wheel and magnetic torque is built. Experimental results show that the quintic polynomial path based on the multi-objective optimization algorithm can effectively reduce the angular velocity during attitude maneuver, and achieve the optimal time solution. The finite-time controller can effectively track the optimal path and ensure the rapidity and stability of attitude maneuvers.

Multiple Satellite Observations of the High‐Latitude Cusp Aurora During Northward IMF Conditions

AbstractCusp auroras poleward of the typical auroral oval are ascribed to high‐latitude lobe reconnection when the Interplanetary Magnetic Field (IMF) Bz is predominantly northward. In this study, we further investigate the ionospheric characteristics of a unique high‐latitude cusp region employing multiple satellite observations. A cusp aurora event with wide spatial spread was observed in the postnoon polar cap region. It was found to be associated with northward IMF Bz and positive By components. The cusp aurora was located from 68° to 86° in magnetic latitude and within 15–17 hr in magnetic local time. This broad coverage in the polar cap indicates direct precipitating particles from the magnetosheath. Particle energy is different between the equatorward and poleward edges of the cusp aurora. The precipitating ions at the equatorward side maintain magnetosheath particle characteristics as expected, while ions with higher energies occurred in the poleward side. Further, the poleward edge of the cusp aurora was nearly situated in the center of a convection shear and was associated with an upward field‐aligned current. These observations suggest a lobe cell circulation, hence we attribute the formation of the cusp aurora to the high‐latitude lobe reconnection. Simultaneous observations in the southern hemisphere indicate the absence of cusp aurora. The auroral presence only in the northern hemisphere is probably due to the combination of large dipole tilt angle and positive IMF Bz, which facilitates the lobe reconnection.

ФИЗИКАНЫ ЖАНА АСТРОНОМИЯНЫ ОКУТУУДА ЖАНА ИЗИЛДӨӨДӨ МАТЕМАТИКАНЫН ОРДУ

This scientific article is devoted to the ways of using mathematics in teaching and researching the subjects of physics and astronomy. Newton's first polynomial was used in mathematical modeling of the emission of electron and hole color centers in solid state physics. Shannon's formula was used to determine information entropy, and the logarithmic function of Boltzmann's formula was used to determine statistical entropy. In astronomy, trigonometric functions and stereographic transformations are used to determine celestial coordinates and transform very large angles. This research paper will help students in their study of these disciplines. Particular attention is paid to the close connection between mathematics and astronomy and physics.

Effect of βSn grain orientations on the electromigration-induced evolution of voids in SAC305 BGA solder joints

The electromigration (EM) failure of solder joints is closely related to the development of voids during EM. In this paper, an integrated approach combining experimentation and finite element simulation was employed to reveal the evolution of voids in solder joints under current stress. The results indicate that the quantity and volume of voids near the cathode consistently increase, while those close to the anode decrease. These asymmetric evolutions of voids are mainly due to the Sn flux, which is controlled by both current density and βSn grain orientation. The magnitude of Sn flux increases with higher current densities and larger angles γ between the c-axis of βSn and the current direction. The direction of Sn flux is more significantly influenced by the current direction rather than the βSn orientation, due to the weak anisotropic self-diffusion of Sn. Voids near the anode tend to shrink while those close to the cathode expand, parallel to the substrate, due to higher Sn flux distributions at the waists of voids, where current crowding is seen. Void splitting related to rapid Cu diffusion has been observed, leading to an abnormal increase in the number of voids near the cathode. This study enhances the understanding of the electromigration failure mechanisms involving void evolution in solder joints.

Regulation of Dihedral Angle on Molecular Engineering for Enhancing Triboelectric Performance

AbstractThe performance of triboelectric polymers relies on their molecular structure. Therefore, investigating how to construct high‐performance molecular structures of triboelectric polymers becomes imperative, yet the relationship between microscopic structural parameters and triboelectric performance remains unclear. In this study, the relationship is studied between dihedral angles of adjacent conjugated planes and triboelectric performance. Various polyimide monomers are synthesized to manipulate the conjugated dihedral angles within the molecular chains. Introducing larger dihedral angles in polyimides (PIs) reduces the conjugation between molecular chains, suppressing the formation of charge transfer complexes (CTCs), and widening the energy gap between molecular orbitals. With the increase in dihedral angles, the output performance improved by 100%. The surface charge density of 335 µC·m−2 is achieved through the synergistic effect of the high charge retention capability of the PI film and the high triboelectric properties of the corona‐polarized fluorinated ethylene propylene (FEP). A large dihedral angle can form numerous deep traps and effectively prevent charge escaping while ensuring stable output. This study provides a feasible strategy for investigating the construction of high triboelectric performance molecular structures, enriching the understanding of how molecular structures influence the triboelectric properties of polymer materials and promote high‐performance fluorine‐free and environmentally friendly polymers.

A Highly Efficient Plasmonic Polarization Conversion Metasurface Supporting a Large Angle of Incidence

The angle of incidence of the compact polarization conversion device is crucial for practical use in integrated miniaturized optical systems. However, this index is often ignored in the design of quarter-wave plate based on metasurface. Herein, it is shown that a thick metallic cross-shaped hole array supports extraordinary optical transmission peaks controlled by a Fabry–Pérot (FP) resonator mode. The positions of these peaks have been proven to be independent over a large range of incidence angles. We numerically design a miniatured quarter-wave plate (QWP) with an 80 nm bandwidth (840~920 nm) and approximately 80% average efficiency capable of effectively functioning as a linear-to-circular (LTC) polarization converter at an incidence inclination angle of less than 30°. This angle-insensitive compact polarization conversion device may be significant in a new generation of integrated metasurface-based photonics devices.

Preparation and thermal properties of biomimetic polymer-based flexible ultra-thin flat heat pipe

Inspired by the structure of the human spine, a flexible ultra-thin flat heat pipe featuring a biomimetic human spine design has been devised. This flat heat pipe, equipped with a biomimetic human spine structure, is capable of undergoing repeated bending at large angles. An experimental study was conducted to investigate the primary influencing factors. The results revealed that the optimal liquid filling ratio for the flexible ultra-thin flat heat pipe is 0.3. The dip angle is positively correlated with the heat transfer performance of the flexible ultra-thin flat heat pipe, and the bending angle is negatively correlated with the heat transfer performance of the flexible ultra-thin flat heat pipe. The maximum thermal conductivity of the flexible ultra-thin flat heat pipe can reach 1457.68 W/(m·K). The flexible ultra-thin flat heat pipe with liquid filling rate of 0.3 and bending angle of 0 degree has the fastest start-up speed. A visualized experimental platform was further designed to observe the internal flow of the working fluid within the flexible ultra-thin heat pipe in various bending states. The visual experimental results demonstrate that bending initiates the premature condensation of steam within the flexible section, and the condensed working medium subsequently generates resistance to the flow of subsequent steam, leading to an inability for the latter to be smoothly transported to the condensing section, thereby creating a vicious cycle.

Patient-Centered Neurosurgery: Improved Outcomes after Subtotal Surgical Resection and Nonframe-Based Fractionated Stereotactic Radiotherapy for Large Cerebellopontine Angle Vestibular Schwannoma

Abstract Background The novel paradigm in neurosurgery for large vestibular schwannomas (VSs) involves a combination of planned subtotal resection (STR) and scheduled postoperative fractionated stereotactic radiotherapy (FSRT). Methods This retrospective observational study aimed to evaluate and compare the outcomes of patients who underwent either near-total resection (NTR) or were treated with STR and scheduled FSRT over 6 years. We systematically coded and analyzed the data to obtain comprehensive insights into the results. Results Our study included 65 patients diagnosed with large VS, who underwent retrosigmoid craniotomy and NTR or STR for tumor removal. The mean age of the cohort was 42.6 (standard deviation: 16.2) years, with 40 (61.5%) female patients. All patients presented with asymmetrical sensory neural hearing loss and other prevalent symptoms such as headache (58) and tinnitus (58). Cerebellar signs, speech abnormalities, and pyramidal signs were also observed. Ten patients underwent NTR, and 55 underwent STR followed by an FSRT at 3 months or later based on the physical and radiological findings. Facial nerve palsy was noted in all cases of those who underwent NTR, while no instances of facial nerve palsy, lower cranial nerve palsy, posterior fossa, or brain stem injury were noted in the STR group. One patient undergoing STR experienced meningitis and died despite best possible medical management. The majority of patients showed symptom improvement, and none of the patients reported recurrence at 3-year follow-up. Conclusion The combined approach of STR and FSRT ensures safety, high tumor control rates, and favorable outcomes. It provides a sensible alternative to NTR for managing large tumors, emphasizing tumor debulking while preserving neurological function for overall benefit.