Apparent Angle Research Articles

Effect of temperature and apparent liquid viscosity on the hydrodynamics of liquid–solid tapered inverse fluidized bed: experimental studies compared with empirical models

In the present work, immersed heater to bed heat transfer coefficient and related hydrodynamics were determined along with different angles (7.85 and 6.8) of the tapered inversed fluidized bed. Carboxyl methylcellulose was used to change the water viscosity by using a power-law model. The hydrodynamics was compared for two different angles of beds. Furthermore, minimum fluidization velocities were carried out for different liquid apparent viscosities and different angles of beds and compared with previous models. The heat transfer coefficient was found to be increasing with liquid velocity and bed voidage, respectively, and it was also found that the bed voidage is high for a high diameter of particles. The correlation was developed between the bed expansion ratio and independent parameters by response surface methodology in design expert software v.9.

Investigation of the effects of nonstationary features on rock joint roughness using the laser scanning technique

Accurately estimating rock joint roughness is crucial for understanding the shear mechanism and permeability behavior of a rock mass. Several influencing factors, including anisotropy, measurement noise, and the scale effect and sampling interval, have been considered. However, little attention is paid to the influences of nonstationary features on the roughness assessment. In this study, a portable laser scanner was employed to collect high-density 3D point clouds of ten natural rock joint specimens. Based on two parameters, namely, the bright area percentage (BAP) and θ*max/(C + 1), where θ*max is the maximum apparent dip angle and C is a dimensionless fitting parameter, the rock joint roughness was determined before and after removing nonstationary features, and a comparison showed that nonstationary features have a considerable influence on the roughness. Subsequently, an approach was proposed to remove nonstationary features through the conversion of spatial coordinates, and an application to a roughness evaluation illustrated that similar trends are observed between the BAP and θ*max/(C + 1) with respect to the point clouds of ten rock joints whose nonstationary features were removed. These findings reveal that nonstationary features should be removed to improve the accuracy and comparability of the roughness assessments.

The perturbative approach for the weak deflection angle

Both null and timelike rays experience trajectory bending in a gravitational field. In this work, we systematically develop a perturbative method to compute the deflection angle of rays with general velocity v in arbitrary static and spherically symmetric spacetimes and in equatorial plane of arbitrary static and axisymmetric spacetimes. We show that the expansion in the large closest approach x_0 limit depends on the asymptotic behavior of the metric functions only, and the generated integrand is always integrable, resulting in a deflection angle in a series form of either x_0 or b, the impact parameter. Using this method, the deflection angles as series of both x_0 and b are found in Schwarzschild, Reissner–Nordström and Kerr–Newman spacetimes to 17-th, 15-th and 6-th orders respectively, for both lightrays and particles with general velocity. The effects of the impact parameter, velocity and other parameters of the spacatimes are briefly analyzed. Moreover, we show that for spacetimes whose metric functions are only asymptotically known, the deflection angle in the weak field limit can also be calculated. Furthermore, it is shown that the deflection angle in general static and spherically symmetric spacetime and equatorial plane of static and axisymmetric spacetime to the lowest non-trivial order, depends only on the impact parameter, velocity of the particle, and the effective ADM mass of the spacetime but not on other parameters such as charge or angular momentum. These deflection angles are used in an exact gravitational lensing equation and the corresponding apparent angles of the images of the source are also solved perturbatively.

Elucidation of the de Vries behavior in terms of the orientational order parameter, apparent tilt angle, and field-induced tilt angle for smectic liquid crystals by polarized infrared spectroscopy.

We report experimental results of the orientational order parameter, the apparent tilt angle, and the field-induced tilt angle for three chiral smectic liquid crystalline materials investigated using infrared (IR) polarized spectroscopy. The common feature in these materials is use of the core 5-methyl-2- pyrimidine benzoate as the central part of the mesogen. This core is terminated by siloxane or carbosilane chains on one of the ends and by the chiral alkoxy chains on the opposite. These compounds exhibit low concomitant layer shrinkage at the smectic A^{*} (SmA^{*}) to smectic C^{*} (SmC^{*}) transition temperature and within the SmC^{*} phase itself. The maximum layer shrinkage in SmC^{*} is observed as ∼1.5%. We calculate the apparent orientational order parameter, S_{app} in the laboratory reference frame from the observed IR absorbance for homeotropic aligned samples, and the true order parameter, S, is calculated using the measured tilt angle and is also interpolated from Iso-SmA^{*} transition temperature closer to SmC^{*} phase. The apparent tilt angle in the SmA^{*} phase calculated from a comparison of order parameters S and S_{app} is found to be significantly large. A low magnitude of S_{app} found for homeotropic aligned samples in the SmA^{*} phase indicates that the order parameter plays a vital role in determining the de Vries characteristics, especially of exhibiting larger apparent tilt angles. Furthermore there is a significant increase in the true order parameter at temperatures close to SmA^{*} to SmC^{*} transition temperature in all three compounds. The planar-aligned samples are used to study the dependence of induced tilt angle on the applied electric field. The generalized Langevin-Debye model given by Shen etal. reasonably fits the experimental data on the field-induced tilt angle. The results show that the dipole moment of the tilt correlated domain in SmA^{*} diverges as temperature is lowered to the SmA^{*}-SmC^{*} transition temperature. The generalized Langevin-Debye model is also found to be extremely effective in confirming some of the conclusions of the de Vries behavior.

Characteristics and triggers of earthquake-induced landslides of pyroclastic fall deposits: An example from Hachinohe during the 1968 M7.9 tokachi-Oki earthquake, Japan

This work characterizes the geomorphological features and describes the factors controlling earthquake-induced landslides of pyroclastic fall deposits. Statistical analysis of the distribution of landslides caused by the 1968 M7.9 Tokachi-Oki earthquake and prior high-magnitude earthquakes was conducted using 0.5-m resolution Light Detection and Ranging data and aerial photographs. Most of the 1968 co-seismic landslides were shallower than 3.5 m and occurred on sliding surfaces with slope angles of less than 34° (average angle of 26.4°). The fitting relationship between the height and length of the 1968 co-seismic landslides was H = 0.226L with a modal apparent friction angle of 12-14°, indicating high mobility. The 1968 co-seismic landslide crowns were primarily located near ridge crests. The hillslope morphology and seismic Arias intensity direction greatly influenced the direction of the earthquake-induced landslides, which were predominantly oriented in a northwest-north-east direction. These earthquake-induced landslides occurred in a cluster where fine marginal portions of Towada-Hachinohe pyroclastic flow deposits, i.e., To-H (pfl), thinly (< 3 m) covered Towada-Hachinohe volcanic ash. Landslide surfaces were formed in the marginal To-H (pfl) layer. Light Detection and Ranging digital elevation model analysis suggests 84.7% of the 1968 co-seismic landslides were undercut by road or river incisions, which form convex slopes that reduce support for the downslope beds. This study supports a correlation between sensitive pyroclastic fall deposit materials and distribution, which can influence potential earthquake-induced landslides with putative seismic intensities of 5 or greater on the Japan Meteorological Agency scale.

A very simple and accurate way to measure the transmission axis of a linear polarizer

A simple and practical method is introduced to obtain the transmission axis of a linear polarizer. The method utilizes non-normal incidence of light through the polarizer whose transmission axis needs to be measured. In the measurement process, a scan of either the vertical or horizontal tilt of the polarizer is performed to impose intentional misalignment on the optical train, and the apparent polarization angles after the polarizer are measured over the scan by a conventional polarimeter. The experimental data is fit based on the mathematical model established by a chain of matrices that characterizes the propagation and interaction of the polarized light to obtain the transmission axis of the polarizer with high precision and accuracy. An example of the practice demonstrates this methodology can infer the transmission axis of the polarizer with an accuracy of a tenth of a degree.

A Quasi-static Hyper-resistive Model of Ultra-high-energy Cosmic-ray Acceleration by Magnetically Collimated Jets Created by Active Galactic Nuclei

This is the fourth in a series of companion papers showing that, when an efficient dynamo can be maintained by accretion disks around supermassive black holes in Active Galactic Nuclei (AGNs), it will lead to the formation of a powerful, magnetically-collimated helix that could explain both the observed jet/radiolobe structures on very large scales and ultimately the enormous power inferred from the observed ultra high energy cosmic rays (UHECRs) with energies > 10^19 eV. Many timescales are involved in this process. Our hyper-resistive magnetohydrodynamic (MHD) model provides a bridge between General Relativistic MHD simulations of dynamo formation, on the short accretion timescale, and observational evidence of magnetic collimation of large-scale jets on astrophysical timescales. Given the final magnetic structure, we apply hyper-resistive kinetic theory to show how instability causes slowly-evolving magnetically-collimated jets to become the most powerful relativistic accelerators in the Universe. The model yields nine observables in reasonable agreement with observations: the jet length, radiolobe radius and apparent opening angle as observed by synchrotron radiation; the synchrotron total power, synchrotron wavelengths and maximum electron energy (TeVs); and the maximum UHECR energy, the cosmic ray energy spectrum and the cosmic ray intensity on Earth.

New algorithm for computation of the Rayleigh-scattering radiance for remote sensing of water color from space.

Rayleigh-scattering radiance (Lr) calculations based on the standard algorithm are often associated with significant uncertainties leading to inconsistent water-leaving radiance retrievals, both spatially and temporally across latitudes and altitudes. The uncertainty could result from the use of Rayleigh lookup tables generated for the standard surface atmospheric pressure and hence the Rayleigh optical thickness (ROT) at the specific atmospheric pressure regardless of its daily and seasonal variations. This study presents a new algorithm (hereafter referred to as the refined algorithm) to compute the Rayleigh-scattering radiance that relies on accurate calculations of the ROT as a function of the composition of air (CO2 volume concentration), surface atmospheric pressure and relative air mass for given sun-sensor geometries. As CO2 is well mixed throughout the atmospheric column, the CO2 volume concentrations derived from this study agree well with measurements in different seasons across studied latitudes. Relative air mass has a significant effect on the ROT and that is calculated as a function of apparent sun-sensor zenith angles with the variations in pressure and thermal characteristics of the atmosphere. Thus, the results indicate significant variations of ROT and air mass with location on the earth's surface and their influence on the Lr, particularly in the UV-Blue region of the spectrum. The refined algorithm for calculating the Lr is tested on several MODIS-Aqua Level 1A data and the relative errors in Rayleigh-scattering radiance and normalized water-leaving radiance (Lwn) retrievals between the refined algorithm and standard (SeaDAS) algorithm are compared using in-situ measurement data collected at MOBY (clear ocean), AERONET (turbid coastal ocean), and NOMAD (clear ocean) sites. The results indicate that the Lr calculated using the SeaDAS algorithm are mostly underestimated and show significant departures with the Lr calculated using the refined algorithm. This departure induced by the SeaDAS algorithm to Lr becomes larger with decreasing wavelength (ΔLr from -2.38% at 412 nm to 1.69% at 678 nm), which causes errors in Lwn retrievals (ΔLwn) of up to 26.48% at 412 nm and 13.34% at 678 nm. The overall improvements in the retrieved Lwn values achieved vary from 56% at 412 nm to 29% at 678nm, which yield similar improvements in Lwn retrievals with lower errors and higher slopes and correlation coefficients when compared with the in-situ Lwn data. These results indicate that the refined algorithm for computation of the Lr can yield more accurate Lwn retrievals and produce spatially and temporally consistent biogeochemical products at different latitudes and altitudes as desired by the scientific community.

Viscous effects on the fundamental solution to ship waves

The fundamental solution to steady ship waves accounting for viscous effects (the viscous-ship-wave Green function) is investigated within the framework of the weakly damped free-surface flow theory. An explicit expression of the viscous-ship-wave Green function is firstly derived, and an accurate and efficient technique is described to evaluate the Green function via decomposing the free-surface term into the local-flow component and wave component. To delve into the physical features of the viscous-ship-wave Green function, the asymptotic approximations in the far field due to Kelvin, Havelock and Peters are presented for the flow-field point located inside, at and outside the Kelvin wedge. In addition, uniform approximations to the wave component based on the Chester–Friedman–Ursell (CFU) approximation and the Kelvin–Havelock–Peters (KHP) approximation are carried out. Both numerical evaluation and asymptotic approximations show that the singular behaviour is eliminated and the divergent waves associated with large wavenumbers leading to rapid oscillations are severely damped when viscous effects are accounted for. In addition, viscous effects also alter the apparent wake angle associated with the wave pattern created by a high-speed translating source, and the apparent wake angle is dependent on both $\mathscr{U}^{-1}$ and $\mathscr{U}^{-2}$, where $\mathscr{U}$ is the translating speed of the source.

Exploring the influence of sphericity on the mechanical behaviors of ballast particles subjected to direct shear

To quantitatively evaluate the influence of shape on the mechanical behaviors of ballast, a series of 2D direct shear simulations were conducted on particles with different sphericities. The particle contours were obtained from the scanning images of 40 ballast particles, based on which the irregular-shaped particles were precisely reconstructed by clumps in the discrete element models. According to the sphericity, five assemblies were prepared for the direct shear simulation. Higher shear strength, vertical relative displacement and apparent angle of shear resistance were observed in assemblies consisting of low-sphericity particles. To explore the mechanism of macro-mechanical behaviors, an in-depth analysis of the mesoscopic responses was conducted. Two parameters were adopted to evaluate the anisotropy of the contact force distribution observed clearly in all samples and stronger anisotropy was found in samples with low-sphericity particles. The translational and rotational displacements of particles were also analyzed. Larger vertical displacements and less rotations were observed in samples with low-sphericity particles. The results suggest that particles with diverse shapes can produce varying particle interlock states and moving behaviors, hence influence the macro-mechanical behaviors.

Tensile creep of asphalt concrete in repeated loading tests and its effect on energy dissipation

ABSTRACT Failure of asphalt concrete in repeated loading tests could be due to fatigue or due to creep of the material. In this study, the effect of creep on the damage of asphalt concrete in these tests was investigated. Stress-controlled repeated loading tests were conducted in uniaxial tension at different frequencies. A different stress amplitude was chosen for each frequency so that the initial average stored energy in a cycle remains constant. Results indicate that the tensile creep of asphalt concrete can have a considerable effect on the damage and failure of specimens. The variations of the apparent dynamic modulus and phase angle, and the total dissipation per cycle with time, when appropriately normalised, were found to be nearly independent of the frequency of the test. In addition, the dissipation of energy in these tests that is related to the damage of the material was further evaluated. Several techniques have been suggested in the literature for the calculation of damage-related dissipation. The suitability of these techniques was analysed using the results of the study. The dissipated creep strain energy (DCSE) was found to provide the most accurate characterisation of damage-related dissipation.

The Moon Illusion as (Partly) an Error in Apparent Visual Angle: A New Possibility.

An illusory exaggeration of the horizon moon’s visual angle (together with an apparently larger physical size) may account for its dramatic appearance.

Aerodynamic interference of yachts sailing upwind on opposite tacks

When two sailing yachts pass each other on opposite tacks, the downwind (or leeward) yacht passes through the wake of its upwind (or windward) counterpart. To date there has been no study that has quantified the changes in drive force, apparent wind, or distance sailed to windward associated with these manoeuvres, although it is of interest to the development of racing yacht tactics.In this study a transient computational fluid dynamics model of yachts passing each other on opposite tacks is developed. Data is presented for a range of separation distances. For close crossing distances the drive force on the windward yacht may be reduced during the encounter, while the leeward yacht experiences a net increase in drive force. The change in drive force is primarily due to the change in the apparent wind angle induced by the other yacht. A leeward yacht changing its course to take advantage of this shift in the apparent wind can achieve a gain of 14 of a boat-length in the distance travelled to windward.

Shear strength of an unsaturated loam soil as affected by vetiver and polyacrylamide

Shear strength is an important soil mechanical property that its improvement is one of the rehabilitation program for the reduction of soil erosion and degradation. The objective of this study was to investigate the effect of polyacrylamide (PAM) and the vetiver system as a cheap and long-term bioengineering method and their combination on unsaturated shear strength parameters (effective cohesion, c' (kPa), angle of effective internal friction, φ' (°) and angle of internal friction related to matric suction, φb (°)) of a loam soil. The experimental treatments included vetiver plant (VP0), two concentrations of PAM dissolved in water [0.2% (V0P2) and 0.4% (V0P4)], and simultaneous presence of vetiver and two concentrations of PAM (VP2 and VP4). Direct shear tests were performed at combinations of three normal stresses of 25, 50 and 100 kPa and four matric suctions of 0, 10, 30 and 50 kPa (12 tests per each treatment) to determine the shear strength parameters. It was found that vetiver and PAM decreased apparent angle of internal friction (φ) and φ', and increased c', total cohesion (c), φb, and as a result increased unsaturated shear strength. However, the positive effect of vetiver on shear strength was greater than that of PAM. It seems that PAM and vetiver enhanced the contact area, inter-particles bonds, aggregation, and inter-aggregate porosity, and as a consequence, increased the soil effective saturation, effective stress, cohesion and shear strength. Also, when matric suction increased the c and shear strength increased although the φ increased slightly. Simultaneous application of vetiver and 0.4% of PAM resulted in maximum shear strength, indicated although vetiver can increase the cohesive strength, it would be more pronounced when PAM was simultaneously applied. Simultaneous application of vetiver and PAM through increasing soil shear strength can be suggested as the rehabilitation program to reduce soil erosion and degradation.

Particle crushing and its influence on a compacted cataclasite under different water content conditions

The shear behavior of cataclasite from Beihetan site in China based on its geological conditions was investigated. Constant water content triaxial tests with large deformation were carried out under high confining pressure and different water contents conditions. The gain-size analysis shows that not only confining pressure but also water content have great effect on the particle crushing, and an empirical expression was established to describe the relationship. The failure envelope is non-linear for cataclasite, and the generalized apparent cohesion and friction angle vary with environmental conditions. The crushing of particles has great effect on this behavior. The friction angle decreases with increasing particle crushing index Br in the form of a power function. Besides, the contractancy enhances with increasing confining pressure and water content, and particle crushing shows a dominating influence on contractancy positively.

Effect of a DC electric field on a meniscus in a square groove

The present study aims at investigating the deformation of a liquid-gas meniscus across a square groove when submitted to an electric field. Two numerical methods are developed: a first one (in-house) consists in solving the strong coupling between the Laplace-Young equation and the Laplace equation for the electric potential; the latter equation being required to get the distribution of the normal electric stress along the meniscus while the first equation is used to calculate the meniscus shape. The Laplace-Young equation is accordingly modified in order to take into account the added contribution of the normal electric stress. A second method based on the phase-field approach is developed for sake of comparison. The results demonstrate a fair agreement between both methods: the electric stress is found to be mostly focused on the top edges of the side walls, which pulls up the interface and yields higher curvatures for a same pressure jump. The in-house method is found to be significantly fast and to accommodate well with realistic boundary conditions, compared to the phase-field method which does not comply with the contact angle. The results, as obtained from the in-house method, are analysed based on non-dimensional numbers whose respective effects on the shape of the interface are properly investigated. A significant impact of the electric field near the triple contact line and at the centre of the groove is made evident. These effects can be described by considering an apparent angle near the triple contact line, or by considering the elevation of the meniscus centre. These results can be used in order to optimise an electro-capillary enhanced structure whose groove geometry is given.

Basal Stress Equations for Granular Debris Masses on Smooth or Discretized Slopes

AbstractKnowledge of basal stresses is essential for analyzing slope stability and modeling the dynamics and erosive potential of debris flows and avalanches. Here we derive and test new algebraic formulas for calculating the shear stress τ and normal stress σ at the base of variable‐thickness granular debris masses in states of static or dynamic equilibrium on slopes. The formulas include a lateral pressure coefficient κ, but use of a fixed value κ = 0.7 yields predictions of σ that on average err by less than 3% and of τ that on average err by less than 13% in matching basal stresses measured in six large‐scale experiments involving wet debris masses with varying geometries and compositions. Much larger prediction errors result from use of infinite‐slope or shallow‐debris approximations. Specialized versions of the new formulas apply if basal topography is discretized and represented by a “staircase” function in a digital elevation model. Use of these formulas to assess static limiting equilibrium conditions shows that the apparent basal Coulomb friction angle ϕtread of debris that engages friction acting on the horizontal surfaces (or “treads”) of a staircase sloping at an angle θ is generally described by tanϕtread = tan (ϕ − θ)+κ tan θ, where ϕ is the true basal friction angle of the same debris in contact with a uniformly sloping bed. Differences between the values of ϕ and ϕtread can greatly influence the results of numerical simulations that use unsmoothed digital elevation model topography to calculate the stability or dynamics of debris masses on slopes.

Myocardial Fiber Mapping of Rat Hearts, Using Apparent Backscatter, with Histologic Validation

Myocardial fiber architecture is a physiologically important regulator of ejection fraction, strain and pressure development. Apparent ultrasonic backscatter has been shown to be a useful method for recreating the myocardial fiber architecture in human-sized sheep hearts because of the dependence of its amplitude on the relative orientation of a myofiber to the angle of ultrasonic insonification. Thus, the anisotropy of the backscatter signal is linked to and provides information about the fiber orientation. In this study, we sought to determine whether apparent backscatter could be used to measure myofiber orientation in rodent hearts. Fixed adult-rat hearts were imaged intact, and both a transmural cylindrical core and transmural wedge of the left ventricular free wall were imaged. Cylindrical core samples confirmed that backscatter anisotropy could be measured in rat hearts. Ultrasound and histologic analysis of transmural myocardial wedge samples confirmed that the apparent backscatter could be reproducibly mapped to fiber orientation (angle of the fiber relative to the direction of insonification). These data provided a quantitative relationship between the apparent backscatter and fiber angle that was applied to whole-heart images. Myocardial fiber architecture was successfully measured in rat hearts. Quantifying myocardial fiber architecture, using apparent backscatter, provides a number of advantages, including its scalable use from rodents to man, its rapid low-cost acquisition and minimal contraindications. The method outlined in this study provides a method for investigators to begin detailed assessments of how the myocardial fiber architecture changes in preclinical disease models, which can be immediately translated into the clinic.

Microencapsulation in foam spray drying

The article presents the results of the experiments of gas-admixing foam spray drying microencapsulation of oil in co-current spray drying tower. The introduction of a foaming gas resulted in a decrease of encapsulation efficiency: for high foaming gas/liquid ratio (GLR) 6.43·10−3 kg/kg and Tair,0=215 °C by over 50% relative to the non-foaming process due to damage of the microcapsule structure and leakage of the oil phase to the particle surface. For moderate drying temperatures and GLR, 80% of microencapsulation efficiency might be achieved with simultaneous control of selected product properties like apparent and bulk density or angle of repose.AbbreviationsGLRgas-to-liquid ratioHRHausner ratioMDXmaltodextrinPSDparticle size distributionSEMscanning electron microscope.

Effect of hybrid-heave motions on the propulsive performance of an oscillating airfoil

Inspiration for a number of unsteady aerodynamics studies has been gathered from biology, mimicking locomotion of birds, insects, and fish. We instead employ a sports-mimetic approach to study unsteady airfoil motions inspired by sail dynamics. Olympic sailors use various unsteady aerodynamic techniques to increase propulsion. One such technique is “sail flicking,” whereby sailors use their bodyweight to roll the boat about its longitudinal axis, flicking the sail periodically. Because sailors do not sail directly into the wind, the boat travels at an angle relative to the wind it experiences, which is generally referred to as the “apparent wind angle.” Due to this angle, the sail oscillates at non-perpendicular angles to the incoming flow, in a motion we call “hybrid-heave”We study these hybrid-heave oscillations with a NACA 0012 airfoil, focusing on its effects on the lift force as well as the driving force, which is aligned in the direction the boat is pointing. The benefits of hybrid-heave are seen across all cases studied here, with the maximum mean lift of up to 6 times the lift of a static airfoil and 2 times the lift of classical heave (heaving perpendicular to the free-stream). We find the existence of a “high-lift mode” close to apparent wind angles (AWA) ≈ +45°, and a “low-lift mode” centered around AWA ≈ -45°. Similar gains are seen in the driving forces with more than three-fold increases compared to the static driving force at optimal conditions. The vortex dynamics of the high-lift case reveal a departure from classical pure heave whereby only one side of the airfoil generates a leading-edge vortex in every cycle, leaving only 3 vortices shed per cycle. High lift is generated for in-phase variation of the airfoil’s instantaneous angle of attack and speed with respect to time. Conversely, out-of-phase variation of these parameters leads to a reduction in lift, compared to the static airfoil case.