Small Tilt Angles Research Articles

Critical Roles of Impurities and Imperfections in Various Phases of Materials.

In many materials, impurities and imperfections play a critical role on the physical and chemical properties. In the present review, some examples of such materials are discussed. A bulk nanobubble (an ultrafine bubble) is stabilized against dissolution by hydrophobic impurities attached to the bubble surface. An acoustic cavitation threshold in various liquids decreases significantly by the presence of impurities such as solid particles, etc. The strength of brittle ceramics is determined by the size and number of pre-existing microcracks (imperfections) in the specimen. The size effect of a BaTiO3 nanocrystal is influenced by the amount and species of adsorbates (impurities) on its surface as adsorbate-induced charge-screening changes the free energy. The dielectric constant of an assembly of BaTiO3 nanocubes is influenced by a small tilt angle (imperfection) between two attached nanocubes, which induces strain inside a nanocube, and is also influenced by the spatial strain-relaxation due to defects and dislocations (imperfections), resulting in flexoelectric polarization.

CRACK INTERACTION WITH TILT GRAIN BOUNDARIES IN BRITTLE FRACTURE OF ALUMINUM

This paper presents a molecular dynamics study of crack propagation in aluminum bicrystals with tilt grain boundaries under uniaxial tension. The simulations showed that crack propagation is always preceded by an abrupt increase in the atomic volume at the crack tip as a result of nanopore formation. The beginning of crack growth or crack initiation after arrest is always accompanied by a rapid decrease in the atomic volume at the crack tip. The results obtained in this study show that the crack can cause significant grain boundary migration. The amount of grain boundary migration increases with decreasing grain misorientation angle. Tilt grain boundaries with misorientation angles above 20° fully prevent crack propagation into a neighboring grain. At smaller tilt angles, the crack is temporarily arrested by the grain boundary, and the arrest time increases with increasing tilt angle.

Analysis of Edge Method Accuracy and Practical Multidirectional Modulation Transfer Function Measurement

The modulation transfer function (MTF) is commonly used as an imaging quality criterion reflecting the spatial resolution capability of imaging systems. The modified edge methods based on ISO Standard 12233 are widely used in MTF measurement for various imaging fields with high confidence. However, there are two problems in the existing edge methods which limit the application in remote sensing (RS) field with complicated image quality and usually uncontrollable edge angle: a near-horizontal or near-vertical “small tilt angle straight (STAS)” edge is required, and the MTF measurement results show low robustness and non-uniqueness. In this study, the influence of edge angle, oversampling rate (OSR), region of interest (ROI), edge contrast, and random noise on the edge method accuracy is quantitatively analyzed, and a practical multidirectional MTF measurement edge method is proposed based on the above analysis results. The modified edge method adaptively determines the optimal OSR according to edge angle and combines multiple measurement states, such as multi-ROI extraction and multi-phase binning, to improve the robustness, accuracy, and practicality of the edge method.

Design, Heat Transfer, and Visualization of the Milli-Reactor by CFD and ANN

This paper proposes a milli-reactor design method incorporating reactor runaway criteria. Based on Computational Fluid Dynamic (CFD) simulation, neural networks are applied to obtain the optimal reactor structure according to the target reaction requirements. Varma’s theory, the critical Nusselt number for stable operation of the flow reactor, is derived. Inserts of the multi-blade structure are designed and investigated to enhance mixing and heat transfer performance. The flow field and heat transfer capacities are obtained by CFD calculations in the range of Re 50–1800. The internal components increase the heat transfer performance up to 21 times, and the pressure drop up to 16 times. The inclined angle of the blade is recommended to be 45°, which can effectively improve heat transfer without generating excessive pressure drop. By partial least squares regression (PLS) analysis, Re and the number of blades are the most critical factors affecting heat transfer, and the five blades and smaller tilt angles are recommended. The CFD calculation results are in good agreement with the Particle Image Velocimetry (PIV) experimental results.

Influence of microstructure on fatigue crack propagation behaviors of Al-xCu-1.5Li-X alloys

The fatigue crack propagation (FCP) behaviors of Al-Cu-Li cold-rolled sheets with different Cu contents were assessed systematically. The increase of Cu contents significantly reduces the threshold value of fatigue crack growth as secondary particles induce the initiation of microcracks, and provides more opportunities for crack deflection due to finer recrystallized grains. Moreover, Brass-orientated grains with low Schmid factor force the crack to change the direction of propagation, which prevents further crack propagation. Compared to Goss-orientated grains with small tilt and twist angle, cracks prone to deflect at its boundaries with large tilt angles difference between the adjacent grains.

Numerical calculation and finite element analysis for anisotropic elastic properties of carbon fibers: dependence of integration subinterval and mesh size on indentation-derived elastic modulus

The elastic modulus measured by indentation of carbon fibers with various anisotropic elasticity is calculated by two numerical approaches, the Vlassak–Nix model and finite element analysis, to reveal the acceptable calculation condition for highly anisotropic materials. Five commercially available carbon fibers that varied in anisotropy index in the range of 0.5–7.9 are used (either polyacrylonitrile- or pitch-based). The numerical error in the calculated modulus increases with the decrease in fiber angle and with the increase in the anisotropy index under the same mesh condition, indicating finer mesh is required for a highly anisotropic material. The acceptable mesh size linearly increases with anisotropic index. The Vlassak–Nix model overestimates the elastic modulus at a small tilt angle if few integration subintervals are used. Conversely, finite element analysis of the Hertz contact problem with coarse mesh underestimates the modulus at a small tilt angle, and a maximum modulus is observed when the fiber is tilted a few degrees against the indentation axis. These findings are expected to assist the future determination of ideal calculation conditions for materials with large anisotropic elasticity including fibers and composites.

Influence of the Anatomical Structure on the Hemodynamics of Iliac Vein Stenosis.

Few reports study the effects of the anatomical structure of the iliac vein on hemodynamics and the methods to reduce and delay in-stent thrombosis. The anatomical structure of iliac vein stenosis was used to establish vascular models with different stenosis rates, taper angle, and left branch tilt angle in the work. The influence of anatomical structure on hemodynamics was revealed through theoretical research and in vitro experimental verification. A real iliac vein model was built based on computed tomography angiography (CTA) images, and hemorheological parameters including time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI) and relative residence time (RRT) were analyzed by computational fluid dynamics (CFD). The results showed that iliac vein stenosis could significantly increase the wall shear stress (WSS) of the blood vessels at the stenosis site and outside the intersection area, which was easy to produce eddy currents in the distal blood vessels. With the increased taper angle, the proportion of low-wall shear stress areas and the risk of thrombosis increased. A small tilt angle could aggravate the influence of narrow blood vessels on the blood flow characteristics and vascular wall. The numerical simulation results were consistent with the theoretical research results, and the experimental study verified the correctness of the simulation. The work is helpful to further understand the hemodynamic characteristics of the iliac vein, providing a scientific reference for clinical treatment and diagnosis.

What does a Barkhausen surface coil actually measure ?

The surface coil, which measures the magnetic flux rate from the sample surface, is the most used sensor for Magnetic Barkhausen signal measurement. However, there is little knowledge about how the magnetic flux corresponding to Barkhausen events is leaked from the sample surface and which components of the magnetic flux density contributes to the induced signal. The present work shows an effort to answer these questions by measuring the normal and tangential components of the signals induced in the surface coil and analyzing these measurements using a micro-mesoscopic model of Barkhausen effect. The results show that the presence of even a small tilt angles of the surface coil induces not only components of the applied field in the coil, as thought so far, but also induces tangential components of the Barkhausen signal. The presence of both components of the Barkhausen effect in the induced signal due to the tilt of the surface coil could be a result of the sample surface irregularities or due to the non-uniformity of the coil winding. Finally, the outcomes also reveal that magnetic flux contributing to the induced signal comes from a ring of the material surface surrounding the surface coil. These findings have important implications for Barkhausen setup and applications.

Vibrations Affecting Stability and Edge Control of Snowboards

Background: During a carving turn, vibrations are induced at the heel of the snowboard through edge friction when the heel slips sideways and subsequently travel through and along the board to the shovel, which vibrates and affects the edge control. The purpose of this study was to find a method for assessing the edge grip with a laser vibrometer. Method: Two boards, loaded and tilted at four different angles, were placed on a soft surface, with a shaker connected to the heel at the hindmost edge point. The shovel and particularly the frontmost edge point were scanned with a Polytec laser vibrometer. The frequency response functions of coherence, average shovel displacement, and displacement of the foremost edge point were recorded, and the latter was integrated for obtaining an edge mobility measure (EMM) to quantify the edge control. Results: Of the two boards compared, the shovel of board A was stiffer in the 1st and in the 3rd torsional mode, and the one of board B was stiffer in bending modes. The 2nd torsional mode was responsible for large edge vibrations and therefore for a diminished edge control. Shovel B had a smaller EMM at greater tilt angles, that is, less amplitude of the vibrations at the frontmost edge point, and therefore a better edge control. Shovel A, however, had a smaller EMM at smaller tilt angles. Conclusion: The method developed in this study provides a reliable test for assessment of edge control of a snowboard under standardized test conditions.

Deciphering the structure-photoluminescence correlation at small-tilt-angle grain boundaries in monolayer WS2

Grain boundaries (GBs) frequently emerge in a CVD-grown large-scale transition metal dichalcogenides monolayer thin film, which affect the electronic and optical properties of the material. Photoluminescence (PL) can be easily quenched/enhanced at GBs, which are, however, merely investigated in relatively large tilt angles (θ>14°) in previous research. Here, we experimentally examine the PL properties of monolayer WS2 GBs with tilt angles as small as a few degrees. Contrary to conventional wisdom, we find that PL intensity remains intact by the GBs when their tilt angles θ≤8°. The abnormal PL behavior is elucidated by a detailed structure analysis on the dislocation cores. For a small tilt angle, the strain fields introduced by the defective cores are sparsely distributed without mutual coupling, and the chemical stoichiometry along the GBs preserves very well. These two key structural features of the small-tilt-angle GBs allow excitons to diffuse transparently across the GB, leading to a neglectable influence on the optical and electronic properties, as verified by our first-principle simulations. The PL invariant of the small-tilt-angle GBs sheds light on the future development of CVD-grown wafer-scale techniques and their optical applications.

Diffraction characteristics of radiated tilted fiber grating and its spectrometer application.

We have numerically and experimentally presented the diffraction characteristics of radiated tilted fiber grating (RTFG) in terms of the spectrum, bandwidth, degree of polarization, angular dispersion, and temperature crosstalk. The theoretical and experimental results have shown that the polarization property, bandwidth, and dispersion of RTFG highly depended on the tilt angle of RTFG, and the RTFG has ultra-low temperature crosstalk. We have simulated the transmission spectrum of the RTFG with different tilt angles (25°, 31°, 38°, 45°, and 54°), in which the results show that the larger tilt angle has the wider bandwidth. The RTFGs with the tilt angle of 25°, 31°, 38°, 45°, and 54° have the 3dB bandwidth of 110 nm, 144 nm, 182 nm, 242 nm, and 301 nm, respectively. Besides, the degree of polarization (DOP) of the radiated light from RTFG with the different tilt angles are 0.876, 0.944, 0.967, 0.998, and 0.970, respectively, and the RTFG has the maximum DOP at the tilt angle of 45°, which could be used as single-polarization diffraction device. The experimental results show that with further increase or decrease of the tilt angle, the DOP of radiated light of RTFG would decrease. Both the theoretical and experimental results show that the smaller tilt angle could greatly improve the diffraction angular dispersion of RTFG, in which the 25°, 31°, 38°, and 45° RTFG have the angular dispersion of 0.2288 °/nm, 0.1026 °/nm, 0.0714 °/nm, and 0.0528 °/nm, respectively. Due to the broad working bandwidth, the diffraction angles of RTFG have ultra-low temperature crosstalk, where -0.00042, -0.00054, -0.00064, and -0.00099 degree / °C at the tilt angle of 25°, 31°, 38°, and 45°. Finally, we have demonstrated a miniaturized spectrometer integrated by a 25° RTFG, which has a high spectral resolution of 0.08 nm. The proposed RTFG would be an ideal in-fiber diffraction device and widely applied in spectral analysis, space optical communication, and Lidar areas.

Numerical Simulation of Tiltrotor Flow Field during Shipboard Take-Off and Landing Based on CFD-CSD Coupling

Due to the small tilt angle, a tiltrotor operates in non-axial flow conditions during shipboard take-off and landing. The non-uniformity of the blade’s air-load is high, resulting in structural deformation with high fluctuation frequency, affecting the rotor’s aerodynamic characteristics. A new computational fluid-dynamic computational structural dynamics (CFD-CSD) solver is proposed to analyze the effects of the blade’s elastic deformation on the aerodynamic characteristics. This method is suitable for the aeroelastic simulation of shipboard tiltrotor take-offs and landings. The CFD method uses the Reynolds-averaged Navier-Stokes (RANS) equations as the control equation, while the CSD solver is based on the Timoshenko beam model. The solvers are combined with a two-way loose coupling strategy to improve the solution efficiency. The reverse overset assembly technique (ROAT) is utilized to eliminate the effects of orphan mesh points after deformation. The simulation is conducted during take-off and landing at different heights and different tilt angles, using the XV-15 tiltrotor as an example. An analysis of the rotor’s air-load and the mutual interference of the vortex and wake indicates that when the tiltrotor takes off or lands with a small tilt angle, the wing shedding vortex causes the rotor’s wake to roll upward before it reaches the ship’s deck, producing strong thrust fluctuations. The elastic deformation of the blade reduces the fluctuations in the thrust amplitude. This phenomenon is more pronounced in areas of high fluctuations in the blade’s air-load.

A Dynamo Simulation Generating Saturn‐Like Small Magnetic Dipole Tilts

AbstractAmong planetary dynamos, the magnetic field of Saturn stands out in its exceptional level of axisymmetry. One of its peculiar features is that the magnetic dipole mode is tilted with respect to the planetary rotation axis by only ≈0.007° or less. Numerical dynamo simulations performed in this context have had great difficulty in producing such small dipole tilt angles without introducing ad hoc ingredients such as a latitudinally varying heat flux pattern in the outer layers or stably stratified layers (SSLs). Here we present a numerical dynamo simulation that generates a highly axisymmetric dynamo with a dipole tilt of about ≈0.0008° on average. The model consists of a deep dynamo layer and an overlying low‐conductivity layer but without any SSLs. We highlight a novel mechanism where strong differential rotation generated in the atmospheric layer penetrates into the dynamo region, helping to maintain a very small magnetic dipole tilt.

Wind load characteristics of photovoltaic panel arrays mounted on flat roof

To quantify design wind load of photovoltaic panel array mounted on flat roof, wind tunnel tests were conducted in this study. Results show that the first and the last two rows on the roof are the most unfavorable ones regarding to the wind load. Influences of array spacing, panels’ tilt angle and parapet height on wind load of the panels are studied. Most unfavorable lift force of panels decreases with increase of array spacing for middle located panels. The aerodynamics are similar to flow over repeated hills. Middle located unit got greater turbulence, which leading to unfavorable C fp_min. While the changing amplitude of most unfavorable wind pressure is small increase with array spacing. C fp_max and C fp_min of panel units shows quite strong dependence on tilt angle. There is significant pressure equalization for small tilt angle cases. The local flow separation is responsible for C fp_min of larger tilt angle cases. Parapet height of 2 h (h is the panel height projected on the vertical plane) is the critical height for C fp_max and C fp_min. Increasing parapet height can significantly reduce the wind load of panel units. Design pressure coefficient of the basic working condition with different area sizes at different location are proposed.

Calculation of Voltages Ensuring Trouble-Free Operation of an Electrostatic Meter of the Direction of Small Angle Tilts

Introduction. Periodic geodetic observations are used to control the position of building structures and soil massifs. Since tilt is considered to be one of the most dangerous types of building deformations, this paper considers existing methods for its determination. When a horizontal displacement (tilt) is detected, it is of particular importance to assess not so much its angle but its direction. This allows preventive measures to be timely enforced. Therefore, determination of the direction of horizontal displacements at small tilt angles presents a relevant research problem. In order to increase the sensitivity of the considered measuring device, it is proposed to use the action of electric field.Aim. Calculation of electrical voltages that ensure reliable operation of the device under consideration, depending on its geometric dimensions and characteristics of the materials used.Materials and methods. The device was made of conductive, semiconductive and dielectric materials. Calculations were based on an analysis of forces acting on a vertically suspended load in the presence of electric field. The conditions of equilibrium and instability of the position of the load arising due to strong positive feedback in electric field were considered.Results. Calculations were performed to support a reasonable choice of geometric and electrophysical characteristics of the developed device. A formula was obtained for the values of electrical voltages that could ensure troublefree operation of the device. The calculated values of operating voltages were found to be acceptable for practical application. The main structural elements of the device and one of the possible methods for registering information signals were proposed.Conclusion. Due to the instable position of the load in a sufficiently strong electric field, the developed device allows the direction of displacements to be measured even when their values tend to zero. This makes the developed device promising for practical application. However, it should be noted that, under such small displacements, the accuracy of the device depends on the manufacturing conditions and random factors.

Optimization of the Sowing Unit of a Piezoelectrical Sensor Chamber with the Use of Grain Motion Modeling by Means of the Discrete Element Method. Case Study: Rape Seed

Nowadays, in the face of continuous technological progress and environmental requirements, all manufacturing processes and machines need to be optimized in order to achieve the highest possible efficiency. Agricultural machines such as seed drills and cultivation units are no exception. Their efficiency depends on the amount of sowing material to be used and the patency of seed transport tubes or colters. Most available control systems for seed drills are optical ones whose operation is not effective when working close to the ground due to large dusting. Thus, there is still a need to provide seed drills with sensors to be equipped with control systems suitable for use under conditions of massive dusting that would shorten the time of reaction to clogging and be affordable for every farmer. This study presents an analysis of grain motion in the sowing system and an analysis of the operation efficiency of an original piezoelectric sensor with patent application. The novelty of this work is reflected in the new design of a specially designed piezoelectric sensor in the sowing unit, for which an analysis of indication errors was carried out. A seed arrangement of this type has not been described so far. An analysis of the influence of the seed tube tilt angle and the type of its exit hole end on the coordinates of the grain point of collision with the sensor surface and erroneous indications of the amount of sown grains identified by the piezoelectric sensor is presented. Low values of the sensor indication errors (up to 10%), particularly for small tilt angles (0° and 5°) confirm its high grain detection efficiency, comparable with other sensors used in sowing systems, e.g., photoelectric, fiber or infrared sensors and confirm its suitability for commercial application. The results presented in this work broaden the knowledge on the use of sensors in seeding systems and provide the basis for the development of precise systems with piezoelectric sensors.

Phase-field study on an array of tilted columnar dendrites during the directional solidification of a binary alloy

An array of columnar dendrites is important to the microsegregation and permeability of interdendritic liquid flow. In this study, an array of tilted columnar dendrites growing during the directional solidification of a binary alloy was investigated via large-scale phase-field simulation. The main conclusion is that the hexagonal array is the dominant array for reasonably tilted dendrites as well as dendrites that grow along the temperature gradient. It is also concluded that the array ordering gradually improves with growth for all tilt angles, and the ordering rate is faster for a small tilt angle.

Manifestations of Aging in Virtual Reality Implementation of Rod and Frame Test

Senior adults’ reliance on the visual frame of reference for spatial orientation is a manifestation of an age-related shift in cognitive style from field independence to field dependence. We implemented a virtual reality rod and frame test (VR-RFT) to assess visual field dependence (VFD) in n=39 young adults (20-30 years old) and n=43 seniors (60 years old and above). The subjects were asked to determine subjective visual vertical (SVV) for 19 angles of frame tilt (running from -45 degrees to 45 degrees in steps of 5 degrees). The strong VFD of seniors was manifested not only by the increased error in the determination of SVV (SVVE) but also in its distribution. For small and large frame tilt angles, seniors’ SVVE skewness and kurtosis were greater than those of young adults. The SVVE median dependence on frame tilt may be accounted for with a phenomenological model whose two parameters describe the strengths of primary (P) and secondary (S) visual attractors which subjects use to infer SVV: the edges of the frame and its imaginary diagonals. For young adults, these parameters were: PY=14.91 and SY=12.51. For seniors, we observed an over 50% increase in the strength of the primary attractor PS=26.31 while the strength of the secondary one was only weakly affected by aging: SS=13.74. We demonstrate that the asymmetry between the strength of attractors significantly contributes to SVVE made by seniors at large frame tilts. We hypothesize that a variant VR-RFT may be used in rehabilitation to reduce excessive VFD.

The landslides mechanism on the slopes of mount rinjani due to the july 2018 Lombok earthquake

The Lombok earthquake that occurred in succession, which began at the end of July 2018, triggered landslides on several slopes on Mount Rinjani. The vibrations caused by the earthquake make the slopes unstable due to a decrease in the normal force as a component of the frictional force that binds the deposited material on the mountain slopes. The standard power is one factor that influences the friction force as a material binding to resist landslides. Under ordinary conditions, the average pressure depends on mass, gravity, and the slope's slope. During an earthquake, the normal force can be significantly reduced, causing landslides to occur. The slope stability angle shows the maximum slope angle susceptible to landslides due to an earthquake shock. The greater the peak ground acceleration (PGA) due to an earthquake, will have a landslide effect at a smaller tilt angle. The means that a significant shock due to an earthquake on a slope will be able to launch a landslide on a gentle slope, whereas a small shock can only slide a steep slope with a large angle. From the calculation of slope stability, which depends on the static friction coefficient, and PGA, which depends on the earthquake magnitude and the distance of the earthquake source from the slopes of Mount Rinjani, it gives a maximum value of 61.9o and a minimum value of 45.76o.

Hydrophobicity of Self-Assembled Monolayers of Alkanes: Fluorination, Density, Roughness, and Lennard-Jones Cutoffs.

The interplay of fluorination and structure of alkane self-assembled monolayers and how these affect hydrophobicity are explored via molecular dynamics simulations, contact angle goniometry, and surface-enhanced infrared absorption spectroscopy. Wetting coefficients are found to grow linearly in the monolayer density for both alkane and perfluoroalkane monolayers. The larger contact angles of monolayers of perfluorinated alkanes are shown to be primarily caused by their larger molecular volume, which leads to a larger nearest-neighbor grafting distance and smaller tilt angle. Increasing the Lennard-Jones force cutoff in simulations is found to increase hydrophilicity. Specifically, wetting coefficients scale like the inverse square of the cutoff, and when extrapolated to the infinite cutoff limit, they yield contact angles that compare favorably to experimental values. Nanoscale roughness is also found to reliably increase monolayer hydrophobicity, mostly via the reduction of the entropic part of the work of adhesion. Analysis of depletion lengths shows that droplets on nanorough surfaces partially penetrate the surface, intermediate between Wenzel and Cassie-Baxter states.