Constant Incidence Angle Research Articles

Numerical simulation of the interaction between a planar shock wave and a backward-facing triangular bubble containing gases with different Atwood numbers

The interaction between a shock wave and an interface delineating two gases engenders intricate flow physics, with particular attention drawn to the hydrodynamic instability due to its practical significance. Previous studies have primarily focused on elucidating different wave patterns and instabilities evolution at the interface during the initial phase of shock interaction with cylindrical or spherical bubbles. However, scant literature has shifted its focus toward exploring the long-term morphology of bubbles, especially those characterized by polygonal interfaces. Notably, the detailed examination of shock interaction with a polygonal interface, such as a triangular one with a constant incident angle, remains largely unexplored in existing literature. Recently, the longtime evolution of detailed flow structures across the interface of shock-forward-facing triangular bubbles was captured by Kundu et al. [“A study on dynamics of shock-accelerated forward-facing triangular bubbles at different Atwood numbers,” Phys. Fluids 36, 016110 (2024)] through numerical simulation. In this study, the dynamics of a shock-accelerated backward-facing triangular interface containing various gases, namely, Sulfur Hexafluoride, Refrigerant-22, Argon, Neon, and Helium, is studied for a shock Mach number of 1.21. Simulations were performed by solving the two-dimensional Euler equation using low-dissipative advection upwind splitting methods (AUSMD), in conjunction with a derived ninth-order upwind scheme and a four-stage third-order Runge–Kutta scheme for temporal integration. The development of Richtmyer–Meshkov (RM) and Kelvin–Helmholtz (K–H) instabilities at the interface, mixing, and normalized movements of backward-facing triangular bubbles is captured at different Atwood (At) numbers.

Strong shock solutions in symmetric wedge flows: Unphysical or unstable?

This paper investigates the strong shock solutions in a supersonic wedge experimentally, analytically, and numerically. Experiments and computations are conducted on scaled-down models for the two types of shock reflection to be possible. The time-resolved schlieren observation of the flow evolution revealed that the shock formation is a highly dynamic transition of the starting shock from a strong Mach reflection (MR) to a weak regular reflection (RR) via a strong RR reflection over a constant shock wave angle for a wedge angle less than the detachment criterion angle for the shock transition. However, when the wedge angle is greater than the detachment criterion angle, the shock moves over the wedge with the MR structures of diminishing Mach stem height at a constant incident shock wave angle. These intermediate shock reflections are found to be unstable and oscillate at high amplitude and low frequencies to upstream pressure fluctuations. The nature of the intermediate shock reflection during the shock transition over the wedge has also been studied using an unsteady second-order two-dimensional compressible Navier–Stokes solver code with shear stress transport k-ω turbulence modeling. The computed flow parameters around the intermediate shock reflections confirmed that these are indeed strong shock reflections believed to be unphysical in steady wedge flows.

A new method to measure spectral reflectance and film thickness using a modified chromatic confocal sensor

A chromatic confocal sensor is modified to measure the spectral reflectance of nontransparent surfaces or transparent thin films. According to the Fresnel formula, specular reflectance depends on the wavelength, refractive indexes of the media around the reflecting interface, angle of incidence, and also the thickness of (thin) films. To provide a constant angle of incidence, a suitably designed annular aperture is installed in the dispersion probe. In this way, it is possible to generate a conic incident beam onto the reflecting interface. Furthermore, a self-reference method is used to acquire the reflected spectrum using a continuous scan across the dispersion range. Then, the spectral reflectance is calculated based on a comparison with a standard mirror with known spectral reflectance. The experimental results show a reflectance measurement error of about ±0.05 within the spectral range from 445 nm to 645 nm. Furthermore, the thicknesses of several silicon-dioxide films on silicon substrates were determined by fitting the measured spectral reflectance with the theoretical spectral reflectance. The repeatability of the measurement is within about 0.6 nm, and the results agree with the ellipsometry and commercial film thickness gauge. When the scan speed is set to 0.05 mm/s, 0.1 mm/s, 0.2 mm/s, and 0.4 mm/s, the measured thicknesses change slightly (<0.22 nm), which means there is still a significant potential to enhance the measurement efficiency. Finally, the film thickness topography is obtained to determine the uniformity of the film. Overall, the proposed method has a big potential for the measurement of spectral reflectance and film thickness.

OPTICAL PROPERTIES OF LASER-COLOURING MARKED STAINLESS STEEL

Laser colour-marking method often displace conventional marking techniques. Complicated technology of laser-induced periodic surface structure creation on stainless steel samples allows changing their surface morphology and optical properties, which were studied in this work by atomic force microscopy (AFM), laser scanning microscopy, reflectance spectroscopy and ellipsometry. Reflectance spectra of the samples demonstrate reflectance maxima correlate with the visible colours of the samples and with the extrema in the non-monotonic spectral dependences of the derivative of real part of complex dielectric permittivity extracted from the ellipsometric data. Thus, the most intensive light scattering takes place when the real part of complex dielectric permittivity falls down quickly with changing wavelength. We did not observe any “azimuth anisotropy” in our optical measurements at constant incidence angle: the spectra were the same independently of the light incidence plane orientation (parallel or perpendicular to the previous laser light spot scanning direction). We suppose that this selective resonance-like light scattering is due to the sample surface inhomogeneity, which is the result of previous laser treatment. This assumption agrees with estimations based on laser microscope and AFM images as well as with predictions of Mie theory. Thus, the colours of the samples under study are due to the light scattering by randomly distributed surface species with different sizes.

The MIRS Microwave Radiometer–Spectrometer as the Basis for the Convergence Space Experiment

The MIRS microwave radiometer–spectrometer is described. The instrument is being developed using a conceptual design that was the first stage of ground preparations for the Convergence Space Experiment (SE). At the next stage of SE implementation, it is planned to use the proposed technical solutions as design documentation for manufacturing test and flight prototypes. MIRS is a multi-frequency scanner and sounder intended to record the characteristic radiothermal radiation emitted by the system of the Earth’s surface and atmosphere. The set of frequencies of the received radiation is in the range of 10 to 200 GHz. The device is to be installed on the Russian Orbital Segment (ROS) of the International Space Station (ISS). Conical scanning of the Earth’s surface is done by rotating an antenna unit mounted on a fixed base. With a 1.3 s period of rotation and a constant Earth incidence angle of 53.1 deg, continuous coverage of the Earth’s surface is ensured in a swath 800 km wide with spatial resolution of 10 km for the highest-frequency channels. Nine radiometer–polarimeters laid out as a full-power radiometer are used as radiation receivers. The MIRS antenna system is an offset parabolic antenna with separated irradiators. The optimum design solutions allowing the main problems of the SE to be solved and the MIRS parameters to be maintained under operating conditions on board the ISS are chosen for the conceptual design.

Spurious Signal in SMAP Fourth Stokes Parameter

The radiometer on the NASA Soil Moisture Active/Passive (SMAP) mission is a fully polarimetric instrument that operates at L-band in the spectrum window at 1400–1427 MHz protected for passive use only. A unique feature of the radiometer is the fully digital back-end which permits direct computation of the third and fourth Stokes parameters: the real and imaginary part of the correlation of signal at horizontal and vertical polarizations, respectively. In particular, the SMAP conical scanning geometry provides the opportunity to look at the global distribution of the fourth Stokes parameter, TA4, at constant incidence angle (40°). A striking feature of TA4 is the existence of a strong (±10 K) spurious signal at coastlines. This article provides examples of the spikes and an explanation of the cause. Simulations have shown that the spurious signal is associated with antenna imperfections, such as cross polarization coupling and phase mismatch between polarizations.

Factors of photovoltaic system cost affect in Ecuador

A photovoltaic system is a set of devices that take advantage of the energy produced by the sun and convert it into electrical energy. The impact produced by the possibility of using solar energy in a controlled manner for different uses and purposes has allowed the development of complete systems of transformation, storage and distribution of the energy produced with photovoltaic systems as appropriate. The production of electricity from solar radiation using solar cells and photovoltaic panels is an application that has yet fully disseminated in Third World countries, such as Ecuador. The generation of electric power will depend on the hours that the sun shines and affects the solar panel, the type and quantity of modules installed, orientation, inclination, solar radiation that reaches them, quality of the installation and the power that can be delivered to the user. Ecuador is in a privileged location in terms of solar radiation, because the equatorial line that divides the planet into two hemispheres passes through it, being almost perpendicular to the radiation it receives. In addition, this does not change during the year and there a constant angle of incidence, characteristics that give photovoltaic solar energy a great potential for use. In the investigation, an analysis of how the prices of photovoltaic systems affect the Province of Manabí, the methodology used has been the bibliographic review to know as much as possible about what replenishes the costs of photovoltaic systems.

Electrically tunable harmonics in time-modulated metasurfaces for wavefront engineering

Modulation of metasurfaces in time gives rise to several exotic space–time scattering phenomena by breaking the reciprocity constraint and generation of higher-order frequency harmonics. We introduce a new design paradigm for time-modulated metasurfaces, enabling tunable engineering of the generated frequency harmonics and their emerging wavefronts by electrically controlling the phase delay in modulation. It is demonstrated that the light acquires a dispersionless phase shift regardless of incident angle and polarization, upon undergoing frequency conversion in a time-modulated metasurface which is linearly proportional to the modulation phase delay and the order of generated frequency harmonic. The conversion efficiency to the frequency harmonics is independent of modulation phase delay and only depends on the modulation depth and resonant characteristics of the metasurface, with the highest efficiency occurring in the vicinity of resonance, and decreasing away from the resonant regime. The modulation-induced phase shift allows for creating tunable spatially varying phase discontinuities with 2π span in the wavefronts of generated frequency harmonics for a wide range of frequencies and incident angles. Specifically, we apply this approach to a time-modulated metasurface in the Teraherz regime consisted of graphene-wrapped silicon microwires. For this purpose, we use an accurate and efficient semi-analytical framework based on multipole scattering. We demonstrate the utility of the design rule for tunable beam steering and focusing of generated frequency harmonics giving rise to several intriguing effects such as spatial decomposition of harmonics, anomalous bending with full coverage of angles and dual-polarity lensing. Furthermore, we investigate the angular and spectral performance of the time-modulated metasurface in manipulation of generated frequency harmonics to verify its constant phase response versus incident wavelength and angle. The nonreciprocal response of the metasurface in wavefront engineering is also studied by establishing nonreciprocal links with large isolations via modulation-induced phase shift. The proposed design approach enables a new class of high-efficiency tunable metasurfaces with wide angular and frequency bandwidth, wavefront engineering capabilities, nonreciprocal response and multi-functionality.

Performance of a flat-field grating spectrometer for tender x-ray emission spectroscopy.

A flat-field grating spectrometer for tender x-ray emission spectroscopy has been developed. The grating has been coated with an aperiodic Ni/C multilayer that improves the diffraction efficiency in the range 1-3.5keV at a constant angle of incidence. The aperiodic layer structure originates from the topmost bilayer with a larger thickness compared to other Ni/C bilayers. The performance of the spectrometer has been evaluated by measuring characteristic x rays such as the L series emitted from a Cu(In,Ga)Se2-based thin-film solar cell specimen. It is shown that the Lα1,2 x-ray emission spectra of Cu, In, Ga, and Se can be clearly simultaneously observed in the range from 0.9 to 3.3keV, and the linewidths are 4.9, 26.1, 4.6, and 6.1eV, respectively, corresponding to a spectral resolution of 100-300.

Non-conventional scans in high-resolution X-ray diffraction analysis of epitaxial systems

High resolution X-ray diffraction is commonly used for the analysis of single crystalline epitaxial layers exhibiting high degree of crystal perfection. The method enables to resolve fine variations of the measured intensities and therefore is very efficient in the investigation of the structural parameters of single or multilayered epitaxial systems. In this article the method combining the standard HR technique with grazing incidence set-up is outlined. It is shown that in non-coplanar geometry the intensity distribution within the section of reciprocal space perpendicular to the sample surface, standardly scanned in coplanar geometry, can be measured at constant angle of incidence α. For asymmetric diffractions that are not accessible in coplanar geometry the value of α can be decreased to extremely low values close to zero making the method depth-sensitive. The effect of non-coplanar geometry on the angular resolution is analyzed and the possible application of φ scans in asymmetric non-coplanar geometry is discussed. The proposed scans are illustrated by measurements on selected GaN based epitaxial layers and they can be applied also to other types of epitaxial systems with medium crystal quality.

Association Between Lumbar Spinal Degeneration and Anatomic Pelvic Parameters.

Retrospective cohort study. The objective was to prove the association between anatomic pelvis parameters and specific types of lumbar spinal degeneration. Different spinopelvic sagittal profile types are suggested to be associated with specific degenerative lumbar spine pathologies. Because pelvic morphology plays a key role defining the spinal shape as well as its load and function it thereby potentially predisposes the development of spinal degeneration. Patients with symptomatic lumbar spinal degeneration who were surgically treated in 2 spine departments from March 2011 until August 2016 were included in this retrospective analysis. Single-level degenerative pathologies were classified as lumbar disc herniation (LDH), degenerative disc disease (DDD), lumbar spinal stenosis (LSS), and degenerative spondylolisthesis (DSPL). The constant anatomic pelvic parameters pelvic incidence (PI), pelvic radius (PR), and sacral table angle (STA) were assessed in lateral radiographs of the lumbar spine and compared between the pathologies. In total, 249 patients were assigned to the LDH (n=73), DDD (n=67), LSS (n=42), and DSPL (n=67) groups. Group comparisons revealed significant differences in the anatomic pelvic parameters PR (LDH, 139.5±10.8 mm; DDD, 135.9±14.0 mm; LSS, 127.8±14.3 mm; DSPL, 135.8±12.7 mm; P<0.001), PI (LDH, 53.1±10.0 degrees; DDD, 50.0±9.9 degrees; LSS, 54.5±9.6 degrees; DSPL, 57.1±10.8 degrees; P=0.001), and STA (LDH, 95.3±12.7 degrees; DDD, 105.4±9.0 degrees; LSS, 105.9±11.5 degrees; DSPL, 98.6±9.5 degrees; P<0.001). Post hoc tests indicated significant differences between the PR of the LSS group and that of all other subgroups (P<0.012), the PI of the DDD group and that of DSPL (P<0.001), and the STA of the LDH/DSPL groups and that of the LSS/DDD group (P<0.005). We found all the constant anatomic parameters to be specific for distinct types of degeneration, suggesting pelvis shape is a predisposing factor for their development. Level III.

Inferring Water Table Depth Dynamics from ENVISAT-ASAR C-Band Backscatter over a Range of Peatlands from Deeply-Drained to Natural Conditions

Water table depth (WTD) is one of the key variables controlling many processes in peatlands. Reliable WTD estimates based on remote sensing data would advance peatland research from global-scale climate monitoring to field-scale ecosystem management. Here, we evaluate the relationship between ENVISAT Advanced Synthetic Aperture Radar (ASAR) C-band backscatter (σ°) and in situ observed WTD dynamics over 17 peatlands in Germany covering deeply-drained to natural conditions, excluding peatlands dominated by forest or inundation periods. The results show increasing σ° with shallower WTD (=wetter conditions), with average temporal Pearson correlation coefficients of 0.38 and 0.54 (-) for natural (also including disturbed and rewetted/restored states) and agriculturally-used drained peatlands, respectively. The anomaly correlation further highlights the potential of ASAR backscatter to capture interannual variations with values of 0.33 and 0.43 (-), for natural and drained peatlands. The skill metrics, which are similar to those for evaluations of top soil moisture from C-band over mineral soils, indicate a strong capillary connection between WTD and the ‘C-band-sensitive’ top 1–2 cm of peat soils, even during dry periods with WTD at around −1 m. Various backscatter processing algorithms were tested without significant differences. The cross-over angle concept for correcting dynamical vegetation effects was tested, but not superior, to constant incidence angle correction.

Omega–Phi compensated GID in side inclination mode for measurement of residual stress in polycrystalline thin films

The grazing incidence diffraction (GID) method in side inclination mode, described by Ma et al. in 2002, of polycrystalline thin-film residual stress was revisited and explained using simple geometric relations. To overcome the issue of decreasing peak intensity of this method, which is induced by the decreasing incident angle because of the Eulerian cradle Chi-tilt, an improvement of Omega (ω)–Phi (φ) compensation was devised and applied to a NiFe thin-film sample. The geometry of this improved ω–φ compensated GID method in side inclination mode is detailed in this paper. This improvement guarantees a constant incident angle on the sample surface and a fixed sample illumination volume during measurement. The measured data were analysed using parametric refinement in DIFFRAC.TOPAS v6 software in Launch Mode, and details of the input file (.INP) are explained in this paper. The tensile stress of the NiFe thin-film sample was measured to be 1181 ± 85 MPa using this improved method.

Efficient tight focusing of laser beams optimally matched to their thin-film linear-to-radial polarization conversion: Method, implementation, and field near focus

A method is proposed for efficient, rotationally symmetric, tight mirror focusing of laser beams that is optimally matched to their thin-film linear-to-radial polarization conversion by a constant near-Brewster angle of incidence of the beams onto a polarizing element. Two optical systems and their modifications are considered that are based on this method and on the use of Toraldo filters. If focusing components of these systems operate in media with refractive indices equal to that of the focal region, they take the form of an axicon and an annular reflector generated by the revolution of an inclined parabola around the optical axis. Vectorial formulas for calculating the diffracted field near the focus of these systems are derived. Also presented are the results of designing a thin-film obliquely illuminated polarizer and a numerical simulation of deep UV laser beams generated by one of the systems and focused in an immersion liquid. The transverse and axial sizes of a needle longitudinally polarized field generated by the system with a simplest phase Toraldo filter were found to be 0.39 λ and 10.5 λ, with λ being the wavelength in the immersion liquid.

A detailed study on the effects of sunshape and incident angle on the optical performance of parabolic trough solar collectors

The influences of sunshape and incident angle on the optical performance of the parabolic trough solar collector (PTC) are investigated comprehensively based on Monte Carlo Ray Tracing (MCRT) method and theoretical analysis. This study adopts the acceptance-rejection sampling method, instead of the direct sampling method, for random variable sampling to reduce computing complexity. Both the energy proportion bounded by any angle span in the optical cone and the end loss caused by any incident angle are derived theoretically. It is revealed that the sunshape has great effects on the optical performance of a PTC, which should be taken into consideration in practice. The geometrical configuration of the PTC, especially the absorber tube diameter, should be determined to meet the energy requirement based on local sunshape (circumsolar ratio) conditions. It is also found that the end loss, caused by the incident angle, weakens the optical efficiency. Larger aperture width and smaller absorber diameter will cause greater end loss for constant incident angle. When the absorber length is long enough, the effect of incident angle will be negligible. In a range of small focal lengths, the optical efficiency increases with the increase of focal length, and then decreases constantly with further increasing focal length. Findings in this paper can be used as reference or guidance for designing and optimizing PTC’s structure in practice.

L-band vegetation optical depth and effective scattering albedo estimation from SMAP

Over land the vegetation canopy affects the microwave brightness temperature by emission, scattering and attenuation of surface soil emission. Attenuation, as represented by vegetation optical depth (VOD), is a potentially useful ecological indicator. The NASA Soil Moisture Active Passive (SMAP) mission carries significant potential for VOD estimates because of its radio frequency interference mitigation efforts and because the L-band signal penetrates deeper into the vegetation canopy than the higher frequency bands used for many previous VOD retrievals. In this study, we apply the multi-temporal dual-channel retrieval algorithm (MT-DCA) to derive global VOD, soil moisture, and effective scattering albedo estimates from SMAP Backus-Gilbert enhanced brightness temperatures posted on a 9km grid and with three day revisit time. SMAP VOD values from the MT-DCA follow expected global distributions and are shown to be highly correlated with canopy height. They are also broadly similar in magnitude (though not always in seasonal amplitude) to European Space Agency Soil Moisture and Ocean Salinity (SMOS) VOD. The SMOS VOD values are based on angular brightness temperature information while the SMAP measurements are at a constant incidence angle, requiring an alternate approach to VOD retrieval presented in this study.Globally, albedo values tend to be high over regions with heterogeneous land cover types. The estimated effective scattering albedo values are generally higher than those used in previous soil moisture estimation algorithms and linked to biome classifications. MT-DCA retrievals of soil moisture show only small random differences with soil moisture retrievals from the Baseline SMAP algorithm, which uses a prior estimate of VOD based on land cover and optical data. However, significant biases exist between the two datasets. The soil moisture biases follow the pattern of differences between the MT-DCA retrieved and Baseline-assigned VOD values.

Regional-scale probabilistic shoreline evolution modelling for flood-risk assessment

Rapid deterministic modelling of shoreline evolution at regional and coastal-scheme scale enables Monte-Carlo simulations by which long-term shoreline statistics can be estimated. This paper describes UnaLinea, a fast, accurate finite difference solver of the one-line sediment continuity equation. The model is verified for the evolution of an initially straight shoreline of a plane beach subject to regular breaking waves at constant angle of incidence in the presence of either a groyne or a continuous single-point feed of sediment. Grid convergence and stability tests are used to obtain accurate, stable results, with satisfactory computational efficiency. Influences of wave input filtering and event-based sediment loading are considered. The rapid deterministic model is applied to Monte-Carlo simulations of the evolution of the west coast of Calabria, Italy for different scenarios including increased sediment load from a river and selected beach nourishment. The potential role of probabilistic shoreline evolution in regional coastal flood-risk assessment is explored through application to an idealised stretch of the Holderness coastline, U.K., where flood depths and expected damage are estimated for a 1000 year return period event.

X-ray diffraction grazing-incidence methods applied for gradient-free residual stress profile measurements in electrodeposited Ni coatings

The present work investigates the possibility of bias introduced in grazing-incidence-angle X-ray diffraction techniques applied to residual stress measurements. In these studies, monotextured nanocrystalline nickel coatings obtained by electrodeposition were examined as the model reference samples. Selected Ni coatings exhibited well developed and simple gradient-free residual stress states that were visible using conventional sin2ψ measurements with varying X-ray penetration depths. These results were verified against the stress state picture obtained by two variants of grazing-incidence X-ray methods: multi-reflection (differenthkl) and constant angle of incidence (singlehkl). The outcome of both grazing techniques consistently excluded stress gradients in the samples, which agreed with conventional sin2ψ measurement results. However, only the results of the constant angle of incidence technique agreed with those obtained by the sin2ψ method in terms of calculated residual stress level, suggesting this approach could be applied in further studies of graded material coatings. All analysed coatings yielded uniformly distributed tensile residual stress related to gradual structure development in electrodeposited Ni coatings studied by electron microscopy techniques.

Plasma-Fabricated Surface Plasmon Resonance Chip for Biosensing

This work reports the fabrication of a biosensing chip surface designed for plasmonic detection, and features a layer of noble metal nanoparticles encapsulated as a sandwich within amine-functionalized polysiloxane layers formed by plasma-enhanced chemical vapour deposition. The collective surface plasmon resonance (CSPR) phenomenon characteristic of a dense particle layer is demonstrated for encapsulated gold nanoparticles of different diameters. Biomolecular immobilization is carried out through the amine functional groups that are part of the encapsulating layer. The detection of biomolecular binding events at the sensor surface is demonstrated both by a shift in resonance wavelength at constant angle of incidence using SPR-enhanced spectroscopic ellipsometry and by detecting the angular shift in resonance in a commercial SPR instrument (Biacore®). Taken with other results, this work shows how a complete SPR chip can be assembled by a rapid sequence of operations in a single plasma chamber.

Surface Plasmon Resonance Sensor Based on an Angled Optical Fiber

Optical fiber-based surface plasmon resonance (SPR) sensors show great promise in applications for biochemistry detection. In this paper, a SPR sensor employing the angled optical fiber tip with a constant incident angle is reported. The incident angle and light interaction have been theoretical analyzed. The sensing probe has been fabricated via polishing the fiber tip to a specific angle. The process to achieve the smooth polished surface is also presented. The SPR spectra of solutions with different refractive indexes are obtained by collecting the light reflected by the angled fiber with metal coating. There is a red shift with the increase of analytes' refractive index. Slightly different from the theoretical value 8300 nm/RIU, the sensitivity obtained in the experiment is 7650 nm/RIU.