Critical Angle Of Incidence Research Articles

Optimally Suppressed Phonon Tunneling in van der Waals Graphene-WS2 Heterostructure with Ultralow Thermal Conductivity.

Van der Waals heterostructures have great potential for realizing ultimately low thermal conductivity because defectless interfaces can be constructed at a length scale smaller than the phonon wavelength, allowing modulation of coherent phonon transport. In this Letter, we demonstrate the mechanism for thermal conductivity reduction at a mode-resolved level. The graphene-WS2 heterostructure with the lowest cross-plane thermal conductivity of 0.048 W/(m·K) is identified from 16,384 candidates by combining Bayesian optimization and molecular dynamics simulations. Then, the angle-resolved phonon transmission is calculated using the mode-resolved atomistic Green's function. The results reveal that the optimal heterostructure nearly completely terminates phonon transport with finite incident angles, owing to the reduced critical incident angle and suppression of phonon tunneling.

Life-cycle seismic performance of bridges with thin-walled steel piers under bi-directional excitations

In corrosive environments, steel bridges demonstrate time-dependent seismic performance and varied directional responses to bi-directional excitation at different life-cycle stages. However, current seismic assessment methods for bridges have not adequately addressed the time-dependent effects of bi-directional excitation directionality on seismic responses throughout their entire life cycle. Thus, this study aims to investigate the time-varying directional effects of bi-directional seismic excitations on steel bridges with multiple parameters and to propose a method for predicting the range of critical incident angles while considering the aging effects of bridges. Initially, time-dependent functions that characterize steel corrosion are integrated into multiscale finite element models of the steel bridges to simulate corrosion progression across their life-cycle stages. Subsequently, a quantitative analysis of the bi-directional seismic response of steel bridges is conducted throughout their life cycle, accounting for the directionality of seismic excitation. Finally, a method and process for predicting the range of time-varying bi-directional critical incident angles with 95 % probability are derived by fitting the statistical probability distribution boundary values of the critical incident angle deviation index. The study's findings indicate that the aging effects of steel bridges amplify the displacement response under bi-directional seismic excitation, with the maximum displacement response difference exceeds 40 %. The service time may increase the sensitivity of steel bridges to changes in incident angles, potentially amplifying the displacement response by a factor of 1.69. The study's findings highlight the importance of considering aging effects and bi-directional excitation directionality in bridge seismic assessments.

Observation of micropolar modes in the transmission of acoustic waves at oblique incidence by polystyrene plates.

This study investigates micropolar plates through the analysis of transmitted acoustic waves at various incident angles. Using a combined theoretical and experimental approach, we explore the non-classical elasto-dynamic behavior of these materials. Theoretical transmission coefficients are tailored to highlight generalized Lamb modes and a new type of vibration mode called micropolar modes, considering the constant thickness of the plate and the effects of material micropolarity on linear elasticity. Overlaying diverse transmission coefficients for different angles provides insight into micropolar behavior, aiding in the understanding of mode evolution in the frequency domain and the estimation of the critical angle. We employ two types of low-density closed-cell foams made from polystyrene (expanded in one case, extruded in the other), covering a frequency range from 4 to 60 kHz using a tweeter loudspeaker and a microphone integrated with a National Instruments acquisition system. Identification of the first vibration mode of the plates is facilitated by the frequency range rich in low frequencies. Additionally, all responses exhibit supersonic velocities with substantial attenuations. The originality of this paper is twofold: it provides theoretical predictions of micropolar modes, along with their experimental observations above a critical angle of incidence. Consequently, this research enriches our understanding of micropolar materials and their potential contribution to effective noise reduction strategies in acoustic engineering.

Seismic performance of skewed bridges with uniform and non-uniform scour

Seismic safety of highway bridges is one of the critical issues for the functionality of transportation lifelines after severe earthquakes. Skewed highway bridges are found to be more vulnerable due to the irregular distribution of seismic demands on the bridge components. Moreover, scour induced loss of soil material and hence reduction in lateral support around the foundation piles can amplify the seismic effects on the structural components of water crossing bridges. A numerical study was conducted to investigate the seismic performance of skewed and straight highway bridges with varying scour depths and two different scouring types around the bridge piles. Analytical models of straight (0°) and 45° skewed bridges were created using the OpenSees program and a series of nonlinear response history analysis was carried out under the effect of recorded strong ground motions. In the first scouring type which was called as Case-1, scour depth was assumed the same around all piles and varied uniformly. In Case 2, two different non-uniform scouring types with linearly varying scour depth around the piles were investigated. The uncertainty in the earthquake ground motion excitation direction of the two horizontal components was also studied by considering the variable incidence angle of ground motion pairs. The maximum seismic demands of the members at different ground motion incidence angles were evaluated and compared to the demands obtained for the critical ground motion incidence angles suggested by Caltrans. Superstructure displacement, curvature demands of bridge column and shear force demands of pile elements are the seismic demand parameters examined within the scope of the study and were compared for each scour condition for both straight (0°) and 45° skewed bridge.

Solar radiation on naturally ventilated double skin facade in real climates: The impact of solar incidence angle

Although the angular dependence of optical properties has long been recognised in transparent glazing facades, the impact of such dependence on natural ventilation between glazing has not been widely studied, especially in building facades with high solar incident angles. To better cope with such properties with the prevailing implementation of transparent building envelopes, this study investigated the effects of high solar incidence angles for vertical building facades through theoretical and numerical methods. The theoretical model validates the features of the optical properties simulated by the numerical model, supporting the numerical model's capability of revealing the radiation reflection, absorption, and transmission when multi-reflection is present. Then, such angular impact is studied with typical seasonal data in three cities, namely Shanghai, Melbourne and Chicago. Results firstly revealed the discrepancies between considering or ignoring multi-reflection between two glazing facades at varying incidence angles. Due to the opposite variation trend in reflectivity and transmissivity over angles, there is a critical solar incidence angle at 75° when multi-reflection's impact on natural ventilation reaches its highest. After that, the influence is reduced to its minimum. Identifying this angle helped highlight the enhanced natural flow due to realistic angular-dependent reflections between transparent panes, namely, under-estimation occurs if the angular dependence is not considered in the setting of optical properties. The analysis in three cities also revealed the climatic and locational impact of the angular impacts on ventilation rates. By addressing the impact on the optical and thermal performance of transparent facades, the dynamic variation of solar conditions can be more accurately integrated into passive building designs.

Weak measurement of the Goos–Hänchen shift for a Hermite–Gaussian laser beam

We report on an experimental investigation of the Goos–Hänchen (GH) optical beam shift in the vicinity of the critical angle of incidence at an air–glass interface using a weak value amplification (WVA) technique for two mutually orthogonal first order Hermite–Gaussian (HG) modes (HG10 and HG01) of a light beam at 633 nm generated by a phase-only reflective spatial light modulator. We have developed a mathematical approach to visualize the beam shaping due to the WVA scheme of beam shifts for the HG modes. The study reveals the angle of incidence dependency of the GH shift in the total internal reflection condition. For both modes, a detailed study of the horizontal and transverse beam shift values with varied post-selection angles is also reported. In addition, a comparison of the beam shift values for both of the selected modes with the fundamental mode (HG00) has been demonstrated. We found a significant enhancement (about two to three times) in the beam shifts for the first order HG10 and HG01 modes compared to the fundamental mode (HG00). Our results clearly demonstrate the advantages of the HG modes of the light beam-exploiting WVA technique and thus may contribute significantly to this field and open up important applications in photonic manipulation and future technologies.

Effects of curved vanes on aerodynamic performance and flow structures in highly loaded tandem cascades

Combining tandem cascades and curved vanes can mitigate the separation in highly loaded compressor cascades. Flow loss mechanisms in curved tandem cascades are crucial for fundamental design and optimization. This study investigates the flow losses and vortex structures in curved tandem cascades with different curved angles and an original straight tandem cascade. Numerical simulations are conducted at variable incidence angles. The results indicate no consistent effect of curved angles on the aerodynamic performance of curved tandem cascades. The tandem cascade with a curved angle of 5° effectively reduces losses at all incidence angles, while the tandem cascade with a curved angle of 15° extends the critical incidence angle to 3°. The comparative analyses reveal that curved vanes increase spanwise pressure gradients, causing low-energy fluid near endwalls to move toward the midspan. The weighting coefficient of losses quantitatively describes that curved vanes weaken the trailing edge shedding vortices of both vanes and passage vortex while enhancing the end wall spanwise vortex of the front vane, thus affecting the loss distribution. Finally, this study innovatively applies topological analysis methods to curved tandem cascades, establishing the relationship between topological structures and vortex structures in corner regions of tandem cascades, which provides a valid research approach to reveal the vortex dynamics mechanisms of the loss distribution in tandem cascades influenced by curved vanes.

Flow control over a circular cylinder using a slot and axially arranged holes

Circular cylinder flow is controlled using a slot and axially arranged holes (AAH) at a Reynolds number of 32000. When the slot and AAH are placed at small incidence angles from the free-stream direction, the passive jet generated on the leeward cylinder side pushes the wake vortex downstream, reducing the drag compared to the baseline cylinder. If the incidence angle is larger than the critical angle, the alternate blowing and suction induced by the slot and AAH promote a boundary-layer transition on one side and a shear-layer transition on the other. The earlier transition to turbulent flow substantially shortens the separated shear layers on both sides, shifting the wake formation region toward the base and leading to an increase in drag. The AAH has a higher critical incidence angle than the same-size slot, as the passive jet developed from the AAH undergoes a transition to alternate blowing and suction at a higher incidence angle than the slot. Just before the incidence angle of the AAH reaches the critical angle, the weak jet flow induced on the windward cylinder side delays the boundary-layer separation through early separation and laminar reattachment without shortening the separated shear layer, thereby allowing additional drag reduction.

Deposition of nanometer-thick amorphous carbon films by filtered cathodic vacuum arc under oblique ion incidence conditions

Filtered cathodic vacuum arc (FCVA) is a promising technique for synthesizing extremely thin carbon films exhibiting highly tetrahedral (sp3) carbon atom hybridization. However, most FCVA studies are for incident ions impinging perpendicular to the substrate surface. In this study, the effects of the ion incidence angle on the thickness, structure, and surface roughness of amorphous carbon (a-C) films deposited under different substrate bias voltages were examined in the light of computational and experimental results. Dynamic simulations and film thickness measurements showed a decrease in film thickness with increasing ion incidence angle, attributed to the decrease in carbon ion fluence on the film surface. Carbon atom hybridization analysis revealed a critical ion incidence angle for a given substrate bias voltage. Simulation and experimental results demonstrated that the enhancement of sp3 hybridization resulted from carbon-carbon collision cascades on the growing film surface and densification induced by direct and recoil implantation processes controlled by the ion incidence angle and substrate bias voltage. The strong dependence of a-C film growth on the carbon ion incidence angle exemplified by the results of this study has direct implications in the oblique deposition of ultrathin a-C films with predominant tetrahedral carbon atom hybridization. The present study provides a framework for optimizing the ion incidence angle to achieve the deposition of a-C ultrathin films with high sp3 contents.

Flexural gravity wave interaction with an articulated heterogeneous plate within the paradigm of blocking dynamics

Surface gravity waves interact with the flexural waves to generate the flexural gravity waves whose characteristics are triggered for higher values of lateral compressive stress to generate multiple propagating wave modes. This investigation examines the scattering of obliquely incident flexural gravity waves due to articulation in two semi-infinite heterogeneous floating elastic plates in finite water depth within a blocking dynamics regime. The dispersion curve demonstrates the existence of three propagating wave modes within the blocking limits. The canonical eigenfunction expansion method used for a single propagating mode is generalized to account for multiple propagating wave modes within the limits of blocking periods. The energy relation is established using the conservation of wave energy flux and Snell's law of refraction, which depends upon the angles and amplitude of the scattered waves along with the wave energy transfer rates. The amplitude of scattering coefficients (energy transfer rate) goes beyond the unit, where the corresponding energy transfer rate (scattering coefficients) diminishes for specific wave periods. Subsequently, complete wave reflection occurs for oblique waves beyond a critical angle of incidence for a fixed period and prior to a critical angle of incidence at a higher angle of incidence. Removable discontinuities occur at the blocking and saddle points, while a jump discontinuity appears due to a change in the incident wave mode in the scattering coefficients. Surface plots reveal the irregular pattern of plate deflection for the period within the blocking limits. Linear time-dependent plate displacement is simulated in two and three dimensions.

Quasi-soliton control in optical lattices with longitudinal exponentially modulation

The dynamical evolution of one-dimensional quasi-soliton in Kerr-type linear-nonlinear optical lattices with the exponential asymptotically longitudinal modulation is investigated. The optical lattice features both the transverse linear refractive index modulation and the nonlinear coefficient periodically modulation. The analytical solutions of the integral beam center, the mean square of the beam width, and the critical incident angle are obtained by adopting the effective particle approach. The dynamical trapping and switching phenomena have been observed. Moreover, the introduction of the longitudinal modulation improves greatly the mobility of the soliton. The propagation states of the quasi-soliton can be controlled by varying a variety of parameters, such as the depths of the linear nonlinear lattices, the form factor and the incident angle of soliton, as well as the asymptotic rate of longitudinal modulation. Thus our results offer a new opportunity for the all optical manipulation of light beam.

Numeric Study on the Critical Angle of Seismic Incidence for High-Speed Railway Bridges with Round-Ended Piers Based on the Fragility Method

Considering the difference of seismic capacity in different cross-sectional directions of round-ended piers, the effects of the critical angle of seismic incidence on high-speed railway bridges is analyzed by the fragility method. The detailed three-dimensional finite element (FE) model of a typical three-span high-speed continuous girder railway bridge is developed in OpenSees. The fragility curves with respect to cross-sectional direction under different angles of seismic incidence are obtained. The critical angle of seismic incidence is determined by comparing the median value of the fragility function in the critical cross-sectional directions at different angles of seismic incidence. Results show that the difference between the critical angle of seismic incidence determined by the longitudinal direction and that determined by the critical cross-sectional direction is small, but the fragility curves are significantly different. The seismic capacity difference of round-ended piers in all cross-sectional directions is significant, which must be considered in seismic analysis, otherwise the probability of damage to the bridge will be seriously underestimated.

Oblique impact of a buckling table-tennis ball on a rigid surface.

We report on the rebound of a table-tennis ball impinging without any initial spin in oblique incidence on a rigid surface. We show that, below a critical incidence angle, the ball rolls without sliding when bouncing back from the surface. In that case, the reflected angular velocity acquired by the ball can be predicted without any knowledge of the properties of the contact between the ball and the solid surface. Beyond the critical incidence angle, the condition of rolling without sliding is not reached within the time of contact with the surface. In this second case, one can predict the reflected angular and linear velocities, as well as the rebound angle, provided the supplementary knowledge of the friction coefficient associated with the ball-substrate contact.

Generalized total internal reflection at dynamic interfaces

Recent research developments in the area of spacetime metamaterial structures and systems have raised new questions as to how the physics of fundamental phenomena is altered in the presence of spacetime modulation. In this context, we present a generalized and comparative description of the phenomenon of total internal reflection (TIR) at different dynamic interfaces. Such interfaces include, beyond the classical interfaces corresponding to the boundaries of moving bodies (moving interface--moving matter systems), interfaces formed by a traveling-wave step modulation of an electromagnetic parameter (e.g., refractive index) (moving interface--stationary matter systems) and fixed interfaces between moving-matter media (stationary interface--moving matter systems). We first resolve the problem using the evanescence of the transmitted wave as the criterion for TIR and applying the conventional technique of relative frame hopping (between the laboratory and rest frames), which results in closed-form formulas for the relevant critical (incidence, reflection, phase refraction, and power refraction) angles. We then introduce the concept of catch-up limit between the dynamic interface and the transmitted wave as an alternative criterion for the critical angle. We use this approach both to analytically verify the critical angle formulas, further validated by full-wave (FDTD) analysis, and to explain the related physics, using Fresnel-Fizeau drag and spacetime frequency transition considerations. These results might find various applications in ultrafast optics, gravity analogs, and quantum processing.

NEA surface AlGaN heterojunction tilted nanowire array photocathode for vacuum electron sources

As the core component of the electron accelerator, the electron source is responsible for providing high-quality electron beams. GaN has a wide bandgap and must be driven by an ultraviolet laser, making it a strong candidate for photocathode electron source research. We established a theoretical model of photoemission for field-assisted negative electron affinity (NEA) AlGaN heterojunction tilted nanowire array photocathodes. The top-down built-in electric field facilitated the transport of photogenerated carriers within the nanowire. The inclination of the nanowires effectively improved the quantum efficiency of the photocathode. With the critical angle of incidence of ultraviolet, the quantum efficiency was up to 81.2%, and the collection efficiency was up to 51%. This work could provide theoretical support for the design and fabrication of high-quality photocathode electron sources.

Перенос электронов через границу полупроводник-вакуум с отрицательным и положительным электронным сродством: влияние скачка массы

The effect of jump in electron mass at the crystal-vacuum interface on photoemission from semiconductors is considered. In the effective mass approximation, the angular and energy dependences of the electron transmission coefficient through interfaces with a jump in mass and potential steps of different signs, corresponding to negative and positive electron affinities, are considered. It is shown that due to the jump in mass, there are a critical energy and a critical angle of incidence of electrons, which separate qualitatively different angular and energy dependences of the transmission coefficient, respectively. The jump in mass makes it possible for electrons to transfer (up to complete transmission) through a positive potential step with a normal component of kinetic energy below the height of the step. The calculated dependences of the emission quantum yield of thermalized electrons on the affinity value are compared with the experimental data on photoemission from p-GaAs(Cs,O). Possible reasons for the significant differences between the experiment and the calculation are analyzed: a complex potential profile, including the near-surface band bending in the semiconductor and the image charge potential in vacuum, scattering in the (Cs,O) layer, and the need to go beyond the effective mass approximation and to take into account full Bloch nature of electron wave functions in semiconductors.

Near Field Evolution of Blade Wakes Under the Influence of Upstream Transitional Flow in a Compressor Cascade at Moderate Reynolds Numbers

Abstract The variation of blade wake characteristics under the influence of upstream transitional flow has not been thoroughly studied, since few control volumes in experimental investigations capture both the blade surface transitional flow and the downstream wake. In this study, instantaneous flow fields in the near-blade and the near-wake region of a compressor cascade at various incidences (i = 0 deg, 2.5 deg, 5 deg, 7.5 deg, and 10 deg) were investigated using particle image velocimetry (PIV). The mean and fluctuating near-wake fields of the compressor blade at Rec = 24,000 were analyzed considering the upstream blade surface laminar separation bubble (LSB) types. The suction-side flow topology shifts at a critical incidence angle of 5 deg from laminar separation without reattachment (i < 5 deg) into a LSB near the trailing edge (i = 5 deg) and an LSB which is advancing to the leading edge (i > 5 deg). The laminar separation vortices retain sufficient strength and coherence to interact with the wake at the low incidence angles (LIA cases, i ≤ 5 deg) but lose coherence beyond the reattachment point at the high incidence angles (HIA cases, i > 5 deg). Self-similarity of the asymmetrical wakes under the influence of various LSB types was established. Near field evolution of wake width, wake decay rate, and flow fluctuations are directly correlated with the LSB type. An optimal incidence exists for the minimum overall flow fluctuation with a delayed separation and alleviated vortical interactions when the LSB locates at the trailing edge.

Use of critical response spectrum for design of multi-story steel buildings under multi-component seismic excitation

During an earthquake, buildings are simultaneously excited by three-components of ground motion (two horizontal and one vertical) orientations of which are not known apriori. To take account for the uncertainty in the direction of incidence of earthquake waves, a structure is required to be designed such that it is safe for all directions of incidence. For this purpose, the combined effects of two horizontal components of motion are commonly determined using simplified methods such as the percentage rules (e.g. 100%+30%, 100%+40%), square root of the sum of squares (SRSS) and Complete Quadratic Combination (CQC-3) rules. The modern building codes recommend to estimate the orthogonal response quantities for the individual horizontal component of motion using response spectrum superposition methods with design spectrum in the principal direction of motion. In the present paper, a new method is proposed to evaluate the maximum response of multi-story buildings under the simultaneous action of two horizontal components of ground motion using the concept of critical response spectrum. The critical response spectrum is computed using the resultant response of a bidirectional single degree of freedom system at each time step under the simultaneous action of the two horizontal components of motion. For an illustration of the proposed method, steel building asymmetric in the plan is analysed using critical response spectra of the three different pairs of recorded ground motion and the results obtained are validated by comparison with the exact time-history solutions. The exact response is taken as the maximum of the responses estimated by applying the two horizontal time-histories of ground acceleration at different angles from 0 to 180 degree with respect to the structural x-axis. On the other hand, in the response spectrum method, two values of the desired response quantity are obtained by applying the critical response spectrum along the x- and y-directions of the structure and are combined using SRSS method. It has been found that the use of the critical spectrum provides a very convenient method for estimating the maximum response under multi-component excitation without the need for computation of critical incident angle of incidence.

Blocked electron transmission/reflection by coupled Rashba–Zeeman effects for forward and backward spin filtering

We present a theory for studying the quantum dynamics of both the transmission and reflection behavior of a two-dimensional electron gas across a planar potential step within a quantum well. In our model, we introduce the combined effect of the Rashba–Zeeman coupling on the conduction electrons. Our results demonstrate that as the energy of an incident or a transmitted electron stays within the Zeeman energy gap, both Klein reflection and Klein tunneling occur in this Rashba–Zeeman coupled electronic system, where the former corresponds to a backward spin filter while the latter to a forward spin filter. Meanwhile, our system also predicts a critical incident angle beyond which the electron tunneling will be fully suppressed. Such distinctive spin-filtering features are expected to give rise to a variety of applications in both spintronics and quantum-computation devices.

Hydrodynamic analysis of floating tunnel with submerged rubble mound breakwater

The wave interaction with a Submerged Floating Tunnel (SFT) of two different shapes (rectangular and circular) in the presence of a submerged rubble mound breakwater (SRMB) is analyzed using Multi-Domain Boundary Element Method (MDBEM). Furthermore, three typical SFT cross-sections (rectangular, trapezoidal, and circular) of equal area and structural height in the presence of SRMB under similar operating conditions are investigated as comparative study to analyse the influence of SFT shape on hydrodynamic performance. The performance of the tunnel configurations is analyzed as a (a) measurement in terms of hydrodynamic efficiency and (b) criterion for tunnel structure safety. In both shallow and intermediate water depth regions, the critical wave number and the critical angle of incidence followed by resonant wave reflection are identified, and suitable structural parameters of SRMB such as structural porosity in the armour layer, relative crest width, relative gap width between the SFT and the SRMB, structural width and position (relative draft of tunnel structure measured from the free water surface) of SFT are investigated. The present parametric investigation of SFT with SRMB reveals an improved wave transformation properties for a specific range of water depth. The coupling of SRMB has resulted not only in a reduction of wave-induced force acting on SFTs, but also in improved performance in wave transformation characteristics as a coastal protection structure, which is substantially determined by SRMB structural properties. Due to the presence of SRMB, the SFT's safety is improved, which may also add stability to the SFT. A comparative study of different distinct cross-sections of SFTs indicates that, due to its shape, the circular SFT has a reduced reflection capability and lower wave-induced force with nearly the same wave transmission as the rectangular and trapezoidal SFT. The study performed on the coupled SFT and rubble mound breakwater may be useful in determining the suitability of breakwaters not only for maintaining shore dynamics but also for protecting important floating structures for underwater transit.