Intermediate Angles Research Articles

Proper orthogonal decomposition analysis for two-dimensional wake transition behind a NACA 0012 airfoil in a soap film

Abstract An experimental study has been conducted to analyze the flow characteristics around a NACA 0012 airfoil in a horizontal soap film tunnel. The investigation involves both the qualitative observations and the quantitative measurements at various angles of attack (0° to 20°) for Reynolds numbers ∼ 3000 and 5000. Flow visualizations were carried out using the interference technique, while particle image velocimetry (PIV) was used for velocity field measurements. The study examines the two-dimensional wake transition of the NACA 0012 airfoil under different Reynolds numbers and angles of attack in a soap film tunnel. Results indicate that changes in the trailing flow within the soap film are primarily influenced by the Reynolds number and angle of attack. The visualization of the flow exposes different states of wakes and their corresponding flow structures. At lower angles of attack α ≤ 6°, vortex shedding occurs in an alternating mode, while at intermediate angles (8° to 16°), the wake widens. The vortices exhibit more chaotic and turbulent behavior at higher angles of attack, i.e., α ≥ 16°. Furthermore, the study indicates that the same wake transition takes place at lower angles of attack as Reynolds numbers rise.

Damage of thin target plates impacted by conical projectiles with varying apex angles in ballistic application: experimental, FEA and ANN integrated approach

In the current study, an experimental setup consisting of smoothbore 30-caliber powder gun was employed to launch spherical projectiles (3 g/ϕ9) in the ballistic range of velocities from 500 to 1700 m/s and obliquity (0, 33 and 65°), impacting 2 mm thin Steel 1006 target plates. Crater dimensions (major and minor dia.) obtained from series of FE simulations run for the above configuaration was validated by corresponding experimental data. Subsequently, a fullscale 3D FE model considering 8-noded hexahedral elements was used to discretize SS304 conical projectiles (replacing spherical projectile) with various apex angles viz. 40°, 60°, 80° and 100° impacting on single (3 mm) and double layer (1.5 mm each) steel 1006 targets (replacing 2 mm target) in LS dyna. The material behavior was characterized using J–C strength and damage models, along with Gruneisen Equation of State. An erosion algorithm was used in the explicit FE code LS-DYNA to remove undesirable elements. In the next stage, Adam and Nadam optimizers have been employed in ANN models developed using Python code within the Tensor-Flow framework. The Keras Tuner library in the Tensor-Flow framework was used for hyper parameter tuning. The ANN models trained using simulation data successfully predicted the residual KE of conical projectiles with intermediate apex angles of 90°, 70°, and 50° across twelve different impact scenarios. The models with Adam and Nadam optimizers achieved mean squared error (MSE)/coefficient of determination (R2)/mean absolute percentage error (MAPE) values of 109.44/0.998/6.72 and 91.19/0.998/7.76, respectively.

First Detailed Study of the Quantum Decoherence of Entangled Gamma Photons.

Constraints on the quantum decoherence of entangled γ quanta at the mega-electron-volt scale, such as those produced following positron annihilation, have remained elusive for many decades. We present the first statistically and kinematically precise experimental data for triple Compton scattering of such entangled γ. An entanglement witness (R), relating to the enhancement of the azimuthal correlation between the final scattering planes, is obtained where one of the γ underwent intermediate Compton scattering. The measured R, deconvolved from multiple scattering backgrounds, are found to exceed the classical limit for intermediate scatter angles up to ∼60° and diminish at larger angles. The data are consistent with predictions from a first quantum theory of entangled triple Compton scattering as well as a simple model based approach. The results are crucial to future study and utilization of entangled mega-electron-volt γ in fundamental physics and positron emission tomography imaging.

Numerical analysis of the impact of winding angles on the mechanical performance of filament wound type 4 composite pressure vessels for compressed hydrogen gas storage

Transportation relies heavily on petroleum products, forcing the adoption of alternative energy sources like hydrogen. Hydrogen is considered the cleanest fuel for the twenty-first century due to its water-based combustion and no CO2 emissions. However, challenges persist in production, utilization, and storage; employing composite material-based high-pressure storage vessels is increasing in the hydrogen storage sector. The paper analyzes the impact of the winding angles on the mechanical performance of the filament wound Type 4 composite pressure vessels (CPVs) for compressed hydrogen gas storage at 70 MPa. This work examines the individual winding angles and combined angles winding patterns to promote the efficiency of Type 4 CPVs by achieving maximum burst pressure, ensuring safe burst mode, and reducing CPV weight by applying maximum principal stress theory with the aid of the Ansys ACP Prep/Post and static modules. The weight and burst pressure of CPVs are significantly influenced by fiber orientation; a combination of positive and negative helical winding angles promotes higher burst pressure at a lower weight. A hoop angle and intermediate helical angles can be combined to create high-efficiency CPVs that provide mechanical performance comparable to that of a combination of high and low helical angles. Finally, a one-factor-at-a-time (OAT) sensitivity analysis was performed to determine how the winding angle and the thicknesses of layers affect the CPVs' performance. It was found that the performance of the CPVs is significantly influenced by the thicknesses of the wound layers.

Theory of phonon sidebands in the absorption spectra of moiré exciton–polaritons

Excitons in twisted bilayers of transition metal dichalcogenides have strongly modified dispersion relations due to the formation of periodic moiré potentials. The strong coupling to a light field in an optical cavity leads to the appearance of moiré polaritons. In this paper, we derive a theoretical model for the linear absorption spectrum of the coupled moiré polariton–phonon system based on the time-convolutionless (TCL) approach. Results obtained by numerically solving the TCL equation are compared to those obtained in the Markovian limit and from a perturbative treatment of non-Markovian corrections. A key quantity for the interpretation of the findings is the generalized phonon spectral density. We discuss the phonon impact on the spectrum for realistic moiré exciton dispersions by varying twist angle and temperature. Key features introduced by the coupling to phonons are broadenings and energy shifts of the upper and lower polariton peak and the appearance of phonon sidebands between them. We analyze these features with respect to the role of Markovian and non-Markovian effects and find that they strongly depend on the twist angle. We can distinguish between the regimes of large, small, and intermediate twist angles. In the latter phonon effects are particularly pronounced due to dominating phonon transitions into regions which are characterized by van Hove singularities in the density of states.

The Dolan Fire of Central Coastal California: Burn Severity Estimates from Remote Sensing and Associations with Environmental Factors

In 2020, wildfires scarred over 4,000,000 hectares in the western United States, devastating urban populations and ecosystems alike. The significant impact that wildfires have on plants, animals, and human environments makes wildfire adaptation, management, and mitigation strategies a critical task. This study uses satellite imagery from Landsat to calculate burn severity and map the fire progression for the Dolan Fire of central Coastal California which occurred in August 2020. Several environmental factors, such as temperature, humidity, fuel type, topography, surface conditions, and wind velocity, are known to affect wildfire spread and burn severity. The aim of this study is the investigation of the relationship between these environmental factors, estimates of burn severity, and fire spread patterns. Burn severity is calculated and classified using the Difference in Normalized Burn Ratio (dNBR) before being displayed as a time series of maps. The Dolan Fire had a moderate severity burn with an average dNBR of 0.292. The ignition site location, when paired with the patterns of fire spread, is consistent with wind speed and direction data, suggesting fire movement to the southeast of the fire ignition site. Patterns of increased burn severity are compared with both topography (slope and aspect) and fuel type. Locations that were found to be more susceptible to high burn severity featured Long Needle Timber Litter and Mature Timber fuels, intermediate slope angles between 15 and 35°, and north- and east-facing slopes. This study has implications for the future predictive modeling of wildfires that may serve to develop wildfire mitigation strategies, manage climate change impacts, and protect human lives.

Controls on the Leeside Angle of Dunes in Shallow Unidirectional Flows

AbstractDunes are ubiquitous features in alluvial channels, serve as major agents of sediment transport and contribute significantly to flow resistance. Research in the past decade has illustrated the complexity of dune geometry and widespread occurrence of dunes that have a low leeside angle. However, there is a debate concerning the occurrence of such dunes and their formative processes. This paper seeks to further our understanding of low‐angle dunes by utilizing data from a robust set of shallow flow laboratory experiments detailing equilibrium bedform morphology across a range of sediment transport conditions. Analysis of bedform morphology demonstrates that dunes with low‐angle leesides are generated in shallow laboratory flows and are not restricted to deep rivers. Of the possible processes that have been proposed to explain the formation of low‐angle dunes, this finding unequivocally shows that liquefied leeside avalanches, which rely on deep flows for their generation, are not a controlling mechanism. In addition, dunes formed under suspension‐dominated conditions possess lower leeside angles compared with those formed under bedload‐dominated conditions. However, where bedload transport dominates and sediment suspension is likely of lesser importance, low‐angle dunes are still present, and preliminary analysis shows that bedform superimposition can result in lowering of the dune leeside angle. Low and intermediate angle dunes formed under these various conditions also have a lower potential for large‐scale, permanent, leeside flow separation compared with angle‐of‐repose dunes, confirming the need to account for these differences in predictions of flow resistance associated with dune form roughness.

Dynamics of a two-layer immiscible fluid system exposed to ultrasound.

The relocation dynamics of a two-layer immiscible fluid system exposed to bulk acoustic waves using simulations and experiments are reported. A theoretical formulation of the acoustic radiation pressure (ARP) acting on the interface reveals that ARP is a nonlinear function of the impedance contrast. It has been shown that the force acting on the interface is the simple sum of the ARP and the interfacial tension, which is dependent on the angle of the interface. It was discovered that although the acoustic radiation force is directed from high-impedance fluid (HIF) to low-impedance fluid (LIF), the final steady-state configuration depends on the wall-fluid contact angle (CA). Our study reveals that the HIF and LIF would relocate to the channel center for CA>110°, and CA<70°, respectively, while complete flipping of the fluids is observed for intermediate angles. The forces relocate the fluids in the channel, generally, by a clockwise or anticlockwise rotation. Here, it is demonstrated that the direction of this twist can be determined by the relative densities and wettabilities of the two fluids.

Silahlı İnsansız Hava Araçları İçin Namlu Mekanizması Analizi

Silahlı insansız hava araçlarının ve bu araçların gelecekteki farklı nesillerinin tasarım ve imalatına vizyonlu bir bakış açısı sunacak bu çalışmada; özel kuvvetler ve askeri taktik kullanım alanına uygun, mini insansız hava aracı konsept tasarımı yapılmıştır. Söz konusu araç; yatay, dikey ve ara açılarda atış yapabilen, hedefi hareket halinde takip eden, nişan alıp ateşleme yapabilen bir silah sistemine sahip taktik silahlı insansız hava aracıdır (SİHA). Tasarımın, silah sistemine ait matematiksel modellemesi karmaşık sayılar kullanılarak oluşturulmuştur. Yapılan matematiksel modelleme bilgisayar ortamına aktarılmıştır. Elde edilen parametrik veriler, bilgisayar ortamında yapılan simülasyonlar ile doğrulanmıştır.

Measurement of ultrashort laser pulses with a time-dependent polarization state using the d-scan technique

The dispersion scan (d-scan) technique is extended to measurement of the time-dependent polarization state of ultrashort laser pulses. In the simplest implementation for linearly polarized ultrashort pulses, the d-scan technique records the second harmonic generation spectrum as a function of a known spectral phase manipulation. By applying this method to two orthogonally polarized projections of an arbitrary polarized electric field and by measuring the spectrum at an intermediate angle, we can reconstruct the evolution over time of the polarization state. We demonstrate the method by measuring a polarization gate generated from 6fs pulses with a combination of waveplates. The measurements are compared to simulations, showing an excellent agreement.

New Chorus Diffusion Coefficients for Radiation Belt Modeling

AbstractWhistler mode chorus is an important magnetospheric wave emission playing a major role in radiation belt dynamics, where it contributes to both the acceleration and loss of relativistic electrons. In this study we compute bounce and drift averaged chorus diffusion coefficients for 3.0 &lt; L* &lt; 6.0, using the TS04 external magnetic field model, taking into account co‐located near‐equatorial measurements of the wave intensity and fpe/fce, by combining the Van Allen probes measurements with data from a multi‐satellite VLF wave database. The variation of chorus wave normal angle (WNA) with spatial location and fpe/fce is also taken into account. We find that chorus propagating at small WNAs has the dominant contribution to the diffusion rates in most MLT sectors. However, in the region 4 ≤ MLT &lt; 11 high WNAs dominate at intermediate pitch angles. In the region 3 &lt; L* &lt; 4, the bounce and drift averaged pitch angle and energy diffusion rates during active conditions are primarily larger than those in our earlier models by up to a factor of 10 depending on energy and pitch angle. Further out, the results are similar. We find that the bounce and drift averaged energy and pitch angle diffusion rates can be significantly larger than the new model in regions of low , where the differences can be up to a factor of 10 depending on energy and pitch angle.

Electron impact triple differential cross sections of Xe atoms for coplanar to perpendicular plane single ionisation at 60 eV, 80 eV and 100 eV above ionisation

The evolution of the triple differential cross section (TDCS) for the electron impact ionisation of xenon atoms is reported for the variation of momentum of the projectile electron from a coplanar geometry to a perpendicular plane through intermediate angles with the detection plane. The TDCSs have been calculated for the Xe atoms at 60 eV, 80 eV and 100 eV above the ionisation potential. We have calculated the TDCS using distorted wave Born approximation, utilising both the first and second Born terms. Effects of target polarisation and post-collision interaction have also been included in the complete description of the collision dynamics. The TDCS results are compared with recent measurements by Patel et al (2022 Phys. Rev. A 105 032818) showing a dependence between the TDCS and the scattering geometry and kinematics of the collision. Second-order effects have been found significant, particularly in the description of perpendicular plane ionisation at a low energy and the effect of target polarisation has been found important in describing the coplanar ionisation of the xenon target. With an overall good agreement with the recent measurements, there are points of disagreement which are the motivation for further theoretical effort in the near future, as the present attempt is the first of its kind to analyse these measurements.

Electron impact electronic excitation of benzene: Theory and experiment.

We report experimental differential cross sections (DCSs) for electron impact excitation of bands I to V of benzene at incident energies of 10, 12.5, 15, and 20eV. They are compared to calculations using the Schwinger multichannel method while accounting for up to 437 open channels. For intermediate scattering angles, the calculations reveal that the most intense band (V) emerges from surprisingly similar contributions from all its underlying states (despite some preference for the dipole-allowed transitions). They further shed light on intricate multichannel couplings between the states of bands I to V and higher-lying Rydberg states. In turn, the measurements support a vibronic coupling mechanism for excitation of bands II and IV and also show an unexpected forward peak in the spin-forbidden transition accounting for band III. Overall, there is decent agreement between theory and experiment at intermediate angles and at lower energies and in terms of the relative DCSs of the five bands. Discrepancies between the present and previous experiment regarding bands IV and V draw attention to the need of additional experimental investigations. We also report measured DCSs for vibrational excitation of combined C-H stretching modes.

Formation of Electron Butterfly Pitch Angle Distributions in Saturn's Magnetosphere Due To Scattering by Equatorial ECH Waves

AbstractThe features of electron pitch angle distributions (PADs) often imply different physical mechanisms in planetary magnetospheres. We report a simultaneous equatorial electrostatic electron cyclotron harmonic (ECH) wave event with butterfly PADs of electrons at L ∼ 7.6–9 observed by the Cassini spacecraft. Via calculating the bounce‐averaged electron diffusion rates, we found that Saturnian ECH waves can resonate with ∼10 eV to several keV electrons at &lt;60° pitch angles at time scales from ∼10−8 to 10−4 s−1. Simulations show that the formation of ∼100 eV to ∼1 keV electron butterfly PADs are mainly caused by the pitch angle scattering of electrons at low pitch angles (&lt;30°) and the momentum scattering at intermediate pitch angles of ∼30°–45°, though previous studies suggested the adiabatic transport is the dominated mechanism. Additionally, our results successfully reproduce the variation of peak pitch angles (αp) and phase space density ratios between α90° and αp with L‐shell.

The Role of Magnetic Shear in Reconnection-driven Flare Energy Release

Using observations from the Solar Dynamics Observatory’s Atmosphere Imaging Assembly and the Ramaty High Energy Solar Spectroscopic Imager, we present novel measurements of the shear of post-reconnection flare loops (PRFLs) in SOL20141218T21:40 and study its evolution with respect to magnetic reconnection and flare emission. Two quasi-parallel ribbons form adjacent to the magnetic polarity inversion line (PIL), spreading in time first parallel to the PIL and then mostly in a perpendicular direction. We measure the magnetic reconnection rate from the ribbon evolution, and also the shear angle of a large number of PRFLs observed in extreme ultraviolet passbands (≲1 MK). For the first time, the shear angle measurements are conducted using several complementary techniques allowing for cross validation of the results. In this flare, the total reconnection rate is much enhanced before a sharp increase in the hard X-ray emission, and the median shear decreases from 60°–70° to 20°, on a timescale of 10 minutes. We find a correlation between the shear-modulated total reconnection rate and the nonthermal electron flux. These results confirm the strong-to-weak shear evolution suggested in previous observational studies and reproduced in numerical models, and also confirm that, in this flare, reconnection is not an efficient producer of energetic nonthermal electrons during the first 10 minutes when the strongly sheared PRFLs are formed. We conclude that an intermediate shear angle, ≤40°, is needed for efficient particle acceleration via reconnection, and we propose a theoretical interpretation.

Coherent Phonons in van der Waals MoSe2/WSe2 Heterobilayers.

The increasing role of two-dimensional (2D) devices requires the development of new techniques for ultrafast control of physical properties in 2D van der Waals (vdW) nanolayers. A special feature of heterobilayers assembled from vdW monolayers is femtosecond separation of photoexcited electrons and holes between the neighboring layers, resulting in the formation of Coulomb force. Using laser pulses, we generate a 0.8 THz coherent breathing mode in MoSe2/WSe2 heterobilayers, which modulates the thickness of the heterobilayer and should modulate the photogenerated electric field in the vdW gap. While the phonon frequency and decay time are independent of the stacking angle between the MoSe2 and WSe2 monolayers, the amplitude decreases at intermediate angles, which is explained by a decrease in the photogenerated electric field between the layers. The modulation of the vdW gap by coherent phonons enables a new technology for the generation of THz radiation in 2D nanodevices with vdW heterobilayers.

Effect of misorientation of grain boundaries on the discontinuous precipitates of Cu–Ni–Si alloy

In this study, the effects of differences in grain size, grain boundary type and misorientation on the initiation of discontinuous precipitates are investigated for the Cu–5Ni–1.25Si alloy. Samples with different grain sizes are obtained by thermomechanical treatment, and the smaller the grain size, the higher the percentage of discontinuous precipitate at the same aging time, while there is no significant difference in the growth rate of the reaction front of discontinuous precipitates. EBSD is used to study the effect of grain boundary misorientation on discontinuous precipitates, the characteristics of discontinuous precipitates initiation on different grain boundaries are investigated by multivariate statistical analysis. It is found that discontinuous precipitates only initiate from random grain boundaries instead of coincident site lattice boundaries, where random grain boundaries with misorientation angles of 30–50° are more prone to discontinuous precipitates. And the initiation of DPs at different misorientation axes is different. There is a clear borderline for the axes such as <102>, <103>, and <203>. The grain boundaries below this borderline do not initiate DP, while all grain boundaries below this angle initiate DPs. The cases for axes such as <112>, <114>, and <214> are more complicated. On these misorientation axes, grain boundaries with lower or higher misorientation angles do not initiate DPs, while grain boundaries at intermediate range misorientation angles do initiate DPs.

Layer-Dependent Interaction Effects in the Electronic Structure of Twisted Bilayer Graphene Devices.

Near the magic angle, strong correlations drive many intriguing phases in twisted bilayer graphene (tBG) including unconventional superconductivity and chern insulation. Whether correlations can tune symmetry breaking phases in tBG at intermediate (≳ 2°) twist angles remains an open fundamental question. Here, using ARPES, we study the effects of many-body interactions and displacement field on the band structure of tBG devices at an intermediate (3°) twist angle. We observe a layer- and doping-dependent renormalization of bands at the K points that is qualitatively consistent with moiré models of the Hartree-Fock interaction. We provide evidence of correlation-enhanced inversion symmetry-breaking, manifested by gaps at the Dirac points that are tunable with doping. These results suggest that electronic interactions play a significant role in the physics of tBG even at intermediate twist angles and present a new pathway toward engineering band structure and symmetry-breaking phases in moiré heterostructures.

Bent-Linear Isomerism and a Caveat on Bond Angle Distortion Anomalies in CpMo(NO)(η3-Methallyl)NCO

The displacement of the iodide ligand in (+)-(Cp)Mo(NO)(η3-methallyl)I, (+)-1, by treatment with silver(I) isocyanate yields (+)-(Cp)Mo(NO)(η3-methallyl)(NCO), (+)-2, with retention of configuration at the metal and was found to have the SMo configuration by X-ray crystallography. The X-ray data also showed the presence of two structure types in the unit cell of (+)-2, one bent and one linear with ∠MoNC bond angles of 154.4(4)° and 173.4(4)° respectively. In contrast, crystals of rac-2 show only one structure in the solid with an intermediate angle of 165.7(4). If (+)-2 is prepared via conversion of (+)-1 first to the carbonyl, by abstraction of iodide and treatment with CO, and subsequently sodium azide, yielded crystals of (+)-2 which showed varying angles ∠MoNC that appeared to be distortion isomers. Closer inspection of these products revealed an admixture of the intermediate azide compound, (+)-(Cp)Mo(NO)(η3-methallyl)N3, (+)-3, in the sample that was predominantly (+)-2. Mixtures of (+)-3 and (+)-2 or (-)-3 and (-)-2-co-crystallize and the results of X-ray structures of such mixtures appear to show 2 with varying bond angles ∠MoNC depending on the percentage of 3 in them. For example crystals with 85% of (-)-2 show ∠MoNC bond angles of 148.9(5)° and 171.9(5)°. This compares with the ∠MoNN in pure azide (+)-3 of 123.7(6)°

Effects of Multi-Directional Seismic Input on Non-Linear Static Analysis of Existing Reinforced Concrete Structures

Recent studies have shown the importance of including the seismic input directionality in nonlinear analyses for an accurate prediction of the structural demand on frame structures. This paper proposes a new method that includes the multi-directionality of the input seismic forces in Nonlinear Static Analyses (NSAs). Conventionally, the pushover (PO) analyses apply monotonically increasing lateral loads in two directions that typically correspond with the building X and Y directions, that in the case of a rectangular plan are parallel to the building sides. Since in general the direction of the seismic input is a priori unknown, the effects of applying the PO load patterns along varying angles are studied in this paper. Two non-code-conforming reinforced concrete buildings are used as a case study. They have identical structural design but the first one is doubly symmetric while the second one has a significant plan asymmetry due to the translation of the center of mass. PO loads are applied to both structures at angles between 0° and 360° with 15° increments. The results of the NSAs are compared with those of multi-directional NHAs applied at the same angles. The structural demands show that the multi-directional NSAs are more conservative than the conventional NSAs, especially at the corners of the asymmetric- plan building where they can yield significantly higher demands. The base shear capacities in the X and Y directions decrease for intermediate angles due to the interaction between the responses in the X and Y directions that can be captured thanks to the columns’ fiber section discretization. On average the results of the multi-directional NSAs are closer to those of the NHAs, even though they are generally lower.