Cosine Of Angle Research Articles

Probing the optical characteristics of MoS2 under external electrical fields using polarized Raman spectroscopy

Raman spectroscopy effectively revealed a strain-induced electronic structure change during polarization-dependent studies on molybdenum disulfide (MoS2). Initially, we used a polarized Raman system to obtain the polarization-dependent Raman spectra of single-, bi-, and tri-layer MoS2 and analyzed their vibration modes. We determined that the in-plane () mode of vibration was double-degenerate whereas the out-of-plane (A1g) mode of vibration was not. We also observed the mode to be independent of polarization, and the A1g mode to be quadratically dependent on the cosine of the polarization angle. The experimental data agreed strongly with the theoretical models. We present the Raman spectra collected with applied top gate voltages and operational frequencies for an MoS2 transistor. The Raman signal intensities, peak positions, and linewidths of two active modes were calculated under different applied top gate voltages and operational frequencies. The broadening of linewidth for the out-of-plane mode was a result of the strengthening of electron–phonon coupling with increasing gate voltage. Owing to the electric potential across the metal-MoS2 interface, a dramatic frequency shift can be observed. For the AC operational mode, the Raman signals can be regarded as constant in the proper operational frequency region.

Estimating the leaf area of an individual tree in urban areas using terrestrial laser scanner and path length distribution model

Urban leaf area measurement is crucial to properly determining the effect of urban trees on micro-climate regulation, heat island effect, building cooling, air quality improvement, and ozone formation. Previous works on the leaf area measurement have mainly focused on the stand level, although the presence of individual trees is more common than forests in urban areas. The only feasible ways for an operational non-destructive leaf area measurement, namely, optical indirect methods, are mostly limited in urban areas because light path is constantly intercepted by surrounding buildings or other objects. A terrestrial laser scanner (TLS), which can extract an individual tree by using its unique distance information, provides a possibility for indirectly measuring the leaf area index (LAI) in urban areas. However, indirect LAI measurement theory, which uses the cosine of an observation zenith angle for path-length correction, is incompatible for an individual tree because the representative projected area of LAI changes while the observation zenith angle changes, thus making the results incomparable and ambiguous. Therefore, we modified a path length distribution model for the leaf area measurement of an individual tree by replacing the traditional cosine path length correction for a continuous canopy with real path length distribution. We reconstructed the tree crown envelope from a TLS point cloud and calculated a real path length distribution through laser pulse-envelope intersections. Consequently, leaf area density was separated from the path length distribution model for leaf area calculation. Comparisons with reference measurement for an individual tree showed that the TLS-derived leaf area using the path length distribution is insensitive to the scanning resolution and agrees well with an allometric measurement with an overestimation from 5 m2 to 18 m2 (3–10%, respectively). Results from different stations are globally consistent, and using a weighted mean for different stations by sample numbers further improves the universality and efficiency of the proposed method. Further automation of the proposed method can facilitate a rapid and operational leaf area extraction of an individual tree for urban climate modeling.

A shadow- eliminated vegetation index (SEVI) for removal of self and cast shadow effects on vegetation in rugged terrains

ABSTRACTThe effect of terrain shadow, including the self and cast shadows, is one of the main obstacles for accurate retrieval of vegetation parameters by remote sensing in rugged terrains. A shadow- eliminated vegetation index (SEVI) was developed, which was computed from only red and near-infrared top-of-atmosphere reflectance without other heterogeneous data and topographic correction. After introduction of the conceptual model and feature analysis of conventional wavebands, the SEVI was constructed by ratio vegetation index (RVI), shadow vegetation index (SVI) and adjustment factor (f (Δ)). Then three methods were used to validate the SEVI accuracy in elimination of terrain shadow effects, including relative error analysis, correlation analysis between the cosine of solar incidence angle (cosi) and vegetation indices, and comparison analysis between SEVI and conventional vegetation indices with topographic correction. The validation results based on 532 samples showed that the SEVI relative errors for self and cast shadows were 4.32% and 1.51% respectively. The coefficient of determination between cosi and SEVI was only 0.032 and the coefficient of variation (std/mean) for SEVI was 12.59%. The results indicate that the proposed SEVI effectively eliminated the effect of terrain shadows and achieved similar or better results than conventional vegetation indices with topographic correction.

A critical assessment of the line tension determined by the modified Young’s equation

Although the modified Young’s equation is frequently applied to evaluate the line tension of droplets, debate concerning the value and even the sign of the line tension is ongoing. The reason for this is that the line tension defined in the modified Young’s equation is not a pure line tension but an apparent line tension, which includes the effects of the Tolman length and the stiffness coefficients. In this paper, we employ molecular dynamics (MD) to simulate three-dimensional water nanodroplets on platinum surfaces and determine their apparent line tensions by applying a linear fit to the relation of the cosine of the contact angle to the curvature of the contact line. The effects of the Tolman length and the position of the solid-liquid dividing interface on the measured line tension are investigated. On the one hand, our results elucidate the reason why MD results for line tensions are so scattered and also lend numerical support to Schimmele et al.’s theoretical predictions [“Conceptual aspects of line tensions,” J. Chem. Phys. 127, 164715 (2007)]. On the other hand, our MD simulation results demonstrate that the modified Young’s equation is a useful tool to predict the macroscopic contact angle based on a linear fit of the measured contact angles at the nanoscale. The apparent line tension is, however, sensitive to the chosen position of the solid-liquid dividing interface.

The effect of perturbations of frames and fusion frames on their redundancies

Abstract An interesting question about the perturbed sequences is: when do they inherit the properties of the original one? An elegant relation between frames (fusion frames) and their perturbations is the relation of their redundancies. In this paper, we investigate these relationships. Also, we express the redundancy of frames (fusion frames) in terms of the cosine angle between some subspaces.

Enhanced Parameter-Free Diversity Discriminant Preserving Projections for Face Recognition

The manifold-based learning methods have recently drawn more and more attention in dimension reduction. In this paper, a novel manifold-based learning method named enhanced parameter-free diversity discriminant preserving projections (EPFDDPP) is presented, which effectively avoids the neighborhood parameter selection and characterizes the manifold structure well. EPFDDPP redefines the weighted matrices, the discriminating similarity matrix and the discriminating diversity matrix, respectively. The weighted matrices are computed by the cosine angle distance between two data points and take special consideration of both the local information and the class label information, which are parameterless and favorable for face recognition. After characterizing the discriminating similarity scatter matrix and the discriminating diversity scatter matrix, the novel feature extraction criterion is derived based on maximum margin criterion. Experimental results on the Wine data set, Olivetti Research Laboratory (ORL); AR (face database created by Aleix Martinez and Robert Benavente); and Pose, Illumination, and Expression (PIE) face databases show the effectiveness of the proposed method.

Fast and reliable flux map on cylindrical receivers

The thermal design of external solar receivers is a complex problem, in which the main input is the flux caused by the entire heliostat field on the cylindrical receiver surface. In this work, a fast and reliable model of flux distribution on the cylindrical receiver is proposed. This new cylinder flux map is based on the HFLCAL model for the analytic flux density sent by a heliostat on its image plane and the projection, in the direction of the central reflected ray, of any point in the plane image onto the cylindrical surface. The heliostat flux density includes shading and blocking, cosine of the incidence angle, atmospheric attenuation and effective reflectivity. A differential energy balance supports the coherence of the new model, i.e. the power contained in a differential of area in the image plane has to be equal to the power contained in the projected differential of area onto the cylinder. As an application of this new flux distribution on cylindrical receivers, we present the receiver sizing for a Noor III-like 150 MWe plant, with 7400 heliostats, in which the minimum LCOE gives the receiver diameter and a preliminary receiver height. With the help of the new flux map, this height is analysed to verify the maximum allowable flux. A multi-aiming strategy suggested by Vant-Hull (2002) and put into practice by Sanchez-Gonzalez and Santana (2015) is used to spread the hot spots along the receiver height. The PC CPU time to produce a coherent flux map on the cylinder is around six seconds.

A Semiempirical Approach to the Determination of Daily Erythemal Doses.

The maintenance of ground-based instruments to measure the incidence of ultraviolet radiation (UVR) from the Sun demands strict and well-developed procedures. A piece of equipment can be out of service for a couple of weeks or months for calibration, repair or even the improvement of the facilities where it has been set up. However, the replacement of an instrument in such circumstances can be logistically and financially prohibitive. On the other hand, the lack of data can jeopardize a long-term experiment. In this study, we introduce a semiempirical approach to the determination of the theoretical daily erythemal dose (DEDt ) for periods of instrumental absence in a tropical site. The approach is based on 5 years of ground-based measurements of daily erythemal dose (DED) linearly correlated with parameters of total ozone column (TOC) and reflectivity (RPC ) from the Ozone Monitoring Instrument (OMI) and the cosine of solar zenith angle at noon (SZAn ). Seventeen months of missing ground-based data were replaced with DEDt , leading to a complete 5-year series of data. The lowest and the highest values of typical DED were 2411 ± 322 J m-2 (1σ) (winter) and 5263 ± 997 J m-2 (summer). The monthly integrated erythemal dose (mED) varied from 59 kJ m-2 (winter) to 162 kJ m-2 (summer). Both of them depended mainly on cos(SZAn ) and RPC . The 12-month integrated erythemal dose (12-ED) ranged from 1350 kJ m-2 to 1546 kJ m-2 , but it can depend significantly on other atmospheric parameter (maybe aerosols) not explicitly considered here.

Model independent new physics analysis in Lambda _brightarrow Lambda mu ^+mu ^- decay

We study the rare Lambda _brightarrow Lambda mu ^+mu ^- decay in the Standard Model and beyond. Beyond the Standard Model we include new vector and axial-vector operators, scalar and pseudo-scalar operators, and tensor operators in the effective Hamiltonian. Working in the helicity basis and using appropriate parametrization of the Lambda _b rightarrow Lambda hadronic matrix elements, we give expressions of hadronic and leptonic helicity amplitudes and derive expression of double differential branching ratio with respect to dilepton invariant mass squared and cosine of lepton angle. Appropriately integrating the differential branching ratio over the lepton angle, we obtain the longitudinal polarization fraction and the leptonic forward-backward asymmetry and sequentially study the observables in the presence of the new couplings. To analyze the implications of the new vector and axial-vector couplings, we follow the current global fits to brightarrow smu ^+mu ^- data. While the impacts of scalar couplings can be significant, exclusive bar{B}rightarrow X_smu ^+mu ^- data imply stringent constraints on the tensor couplings and hence the effects on Lambda _brightarrow Lambda mu ^+mu ^- are negligible.

Water vapor radiative effects on short-wave radiation in Spain

In this work, water vapor radiative effect (WVRE) is studied by means of the Santa Barbara's Disort Radiative Transfer (SBDART) model, fed with integrated water vapor (IWV) data from 20 ground-based GPS stations in Spain. Only IWV data recorded during cloud-free days (selected using daily insolation data) were used in this study. Typically, for SZA = 60.0 ± 0.5° WVRE values are around − 82 and − 66 Wm−2 (first and third quartile), although it can reach up − 100 Wm−2 or decrease to − 39 Wm−2. A power dependence of WVRE on IWV and cosine of solar zenith angle (SZA) was found by an empirical fit. This relation is used to determine the water vapor radiative efficiency (WVEFF = ∂WVRE/∂IWV). Obtained WVEFF values range from − 9 and 0 Wm−2 mm−1 (− 2.2 and 0% mm−1 in relative terms). It is observed that WVEFF decreases as IWV increases, but also as SZA increases. On the other hand, when relative WVEFF is calculated from normalized WVRE, an increase of SZA results in an increase of relative WVEFF. Heating rates were also calculated, ranging from 0.2 Kday−1 to 1.7 Kday−1. WVRE was also calculated at top of atmosphere, where values ranged from 4 Wm−2 to 37 Wm−2.

Wetting properties of aqueous short-chain alcohols’ solutions

The article presents results of research on the wetting ability of aqueous solutions of short-chain alcohols in relation to selected hydrophobic materials. Polyethylene and Teflon were used as standard hydrophobic smooth materials. Dried peat with granulation d < 0.5 mm was used as the porous hydrophobic material. Physical properties of alcohols and their solutions having a direct influence on the rate of saturation of capillary layers have been discussed. The wettability of smooth surfaces was characterized by the advancing and receding contact angles and wetting tension, defined as the product of the liquid surface tension and cosine of contact angle. The contact angles were determined by Wilhelmy’s method using the Krüss K-100 tensiometer. Wettability of peat was determined by measuring the mass rate of liquid imbibition by capillary forces. For comparison, analogous tests of wettability and capillary imbibition rates were carried out using sodium dodecyl sulfate solutions and solutions of typical wetting agent used in firefighting activities. The solutions of surfactants, in the range of concentrations used in extinguishing operations, showed much better wetting properties in relation to a smooth hydrophobic surface (polyethylene) than solutions of alcohols in the entire range of concentrations (up to 100%). The imbibition capacity of the hydrophobic peat layers of alcohol solutions with concentrations above 10% was higher than the solutions of surfactants.

Interactions Between Stratigraphy and Interfacial Properties on Flow and Trapping in Geologic Carbon Storage

AbstractGas leakage from geologic carbon storage sites could undermine the long‐term goal of reducing emissions to the atmosphere and negatively impact groundwater resources. Despite this, there remain uncertainties associated with the transport processes that would govern this leakage. These stem from the complex interaction between governing forces (e.g., gravitational, viscous, and capillary), the heterogeneous nature of the porous media, and the characteristic length scales of these leakage events, all of which impact the CO2 fluid flow processes. Here we assessed how sub‐basin‐scale horizons in porous media could impact the migration and trapping of a CO2 plume. A high‐pressure column packed with two layers of sand with different properties (e.g., grain size and wettability) was used to create a low‐contrast stratigraphic horizon. CO2 in supercritical or liquid phase was injected into the bottom of the column under various conditions (e.g., temperature, pressure, and capillary number) and the transport of the resulting plume was recorded using electrical resistivity. The results show that CO2 trapping was most strongly impacted by shifting the wettability balance to mixed‐wet conditions, particularly for residual saturation. A 16% increase in the cosine of the contact angle for a mixed‐wet sand resulted in nearly twice as much residual trapping. Permeability contrast, pressure, and temperature also impacted the residual saturation but to a lesser extent. Flow rate affected the dynamics of saturation profile development, but the effect is transient, suggesting that the other effects observed here could apply to a broad range of leakage conditions.

Development of phase-shifting device for implementation of three-step interferometric method with arbitrary phase shifts of reference wave

Two basic approaches to the implementation of procedures of a wavefront stepwise and smooth phase shifts in a two-beam optical interferometer are considered. Advantages and lacks of both procedures are analyzed. It is noted that the smooth phase shift procedure removes the oscillations of a phase shifting element (PSE) that occur during the stepwise procedure. A phase-shifting device that is used to realize the three-step phase shifting interferometry (PSI) method with two arbitrary phase shifts of the reference wave within the angular interval (0, π) is developed. This device does not need the calibration procedure, because the three step PSI method allows defining any phase shift angle by calculating the correlation coefficient between two recorded interferograms. The correlation coefficient can be considered as a normalized scalar product of two interferograms that can be represented by centered multidimensional vectors or as a cosine of a phase shift angle between these vectors. Therefore, the developed device is much simpler and cheaper than its calibrated prototypes. It contains a PSE consisting of a piezoelectric transducer (PZT) and a mirror attached to the PZT, and an electronic unit for smooth linear motion of the mirror in the reference beam of the interferometer. Basic characteristics of the developed electronic unit are considered. The operating principle of the phase-shifting device electronic unit is to provide the smooth rising voltage supply initiated a smooth change of the PZT size. Therefore, the mirror attached to the PZT also moves smoothly. The PSE is located in the reference beam of the two-beam interferometer. If the reference beam in the interferometer enters the mirror in the direction perpendicular to the plane of the mirror, the beam wavefront moves to a distance twice that of the mirror. To verify the reliability of the developed phase-shifting device, we have elaborated the experimental setup dedicated for formation, registration and processing of interferograms of test surfaces and based on the Twyman-Green interferometer architecture. In this setup, the three-step PSI method with arbitrary phase shifts of a reference wave is fulfilled by recording of three interferograms during smooth phase shift of the mirror attached to the PZT. Comparative analysis of stepwise and smooth phase shift procedures for interferograms recording in the experimental setup has shown that their modulation transfer functions (MTFs) are similar for small exposures of interferograms. In particular, it is shown that for interferogram’s small exposure times, whose ratio to the voltage increase time in the angular interval (0, π) does not exceed 0.06, the MTF of the interferogram recorded with the smooth phase shift of the reference beam does not differ from the interferogram MTF obtained by stepwise phase shift. Key words: phase shifting interferometry, phase shift, phase shifting element, interferogram, modulation transfer function

6R Robot Inverse Solution Algorithm Based on Quaternion Matrix and Groebner Base

This article proposes a new algorithm of quaternion and dual quaternion in matrix form. It applies quaternion in special cases of rotated plane, transforming the sine and cosine of the rotation angle into matrix form, then exporting flat quaternions base in two matrix form. It establishes serial 6R manipulator kinematic equations in the form of quaternion matrix. Then five variables are eliminated through linear elimination and application of lexicographic Groebner base. Thus, upper bound of the degree of the equation is determined, which is 16. In this way, a 16-degree equation with single variable is obtained without any extraneous root. This is the first time that quaternion matrix modeling has been used in 6R robot inverse kinematics analysis.

Pore-level determination of spectral reflection behaviors of high-porosity metal foam sheets

Open cell metal foams are currently attracting attention and their radiative behaviors are of primary importance in high temperature applications. The spectral reflection behaviors of high-porosity metal foam sheets, bidirectional reflectance distribution function (BRDF) and directional-hemispherical reflectivity were numerically investigated. A set of realistic nickel foams with porosity from 0.87 to 0.97 and pore density from 10 to 40 pores per inch were tomographied to obtain their 3-D digital cell network. A Monte Carlo ray-tracing method was employed in order to compute the pore-level radiative transfer inside the network within the limit of geometrical optics. The apparent reflection behaviors and their dependency on the textural parameters and strut optical properties were comprehensively computed and analysed. The results show a backward scattering of the reflected energy at the foam sheet surface. Except in the cases of large incident angles, an energy peak is located almost along the incident direction and increases with increasing incident angles. Through an analytical relation established, the directional-hemispherical reflectivity can be related directly to the porosity of the foam sheet and to the complex refractive index of the solid phase as well as the specularity parameter which characterizes the local reflection model. The computations show that a linear decrease in normal-hemispherical reflectivity occurs with increasing porosity. The rate of this decrease is directly proportional to the strut normal reflectivity. In addition, the hemispherical reflectivity increases as a power function of the incident angle cosine.

Crystallization of Lennard-Jones liquids under dynamic compression: Heterogeneous and homogeneous nucleation.

We investigate crystallization of Lennard-Jones liquids on substrates under dynamic compression with large-scale molecular dynamics simulations. The substrates examined include single crystals and bicrystals with different crystallographic orientations, and the loading paths include shock and quasi-isentropic loading. Microstructure is characterized with simulated x-ray diffraction and orientation mapping. For shock loading, only heterogeneous nucleation occurs at the simulation scales. Quasi-isentropic loading induces less heating and larger supercooling; as a result, heterogeneous nucleation occurs at low loading strengths, and both heterogeneous and homogeneous nucleation occur at high loading strengths, despite the crystalline substrates. Crystallization depends on the substrate structure (crystal orientation and grain boundary) and loading characteristics. Deformation may induce grain structure change (e.g., reorientation and twinning) of substrates and affect subsequent crystallization. Crystallization rate is anisotropic, inversely proportional to the cosine of the dihedral angle between the substrate plane and a main {111} growth plane.

A drop penetration method to measure powder blend wettability

Water wettability of pharmaceutical blends affects important quality attributes of final products. We investigate the wetting properties of a pharmaceutical blend lubricated with Magnesium Stearate (MgSt) as a function of the mechanical shear strain applied to the blend. We measure the penetration dynamics of sessile drops deposited on slightly compressed powder beds. We consider a blend composed of 9% Acetaminophen 90% Lactose and 1% MgSt by weight. Comparing the penetration time of water and a reference liquid Polydimethylsiloxane (silicon oil) we obtain an effective cosine of the contact angle with water, based on a recently developed drop penetration method. We repeat the experiments for blends exposed to increasing levels of shear strain and demonstrate a significant decrease in water wettability (decrease in the cosine of the contact angle). The results are consistent with the development of a hydrophobic film coating the powder particles as a result of the increased shear strain. Finally, we show that, as expected dissolution times increase with the level of shear strain. Therefore, the proposed drop penetration method could be used to directly assess the state of lubrication of a pharmaceutical blend and act as a quality control on powder blend attributes before the blend is tableted.

Relationship between contact angle and contact line radius for micro to atto [10− 6 to 10− 18] liter size oil droplets

Contact angles of liquids on surfaces characterize wettability and have been studied extensively, especially for sessile droplets on flat surfaces. Continuum models that incorporate the contact line energy into Young's equation predict a linear dependence between the cosine of the contact angle and the inverse line radius. Experimental evidence for non-volatile nanodroplets suggests a non-linear relationship. At these dimensions (femto and atto liter sized droplets), experimental evidence suggests a flattening of the curve which can be explained by the addition of internal Laplace pressures. This, in turn, indicates that the contact angle for ultra small droplets is less than that measured for macro droplets.

Hybrid self-optimized clustering model based on citation links and textual features to detect research topics.

The challenge of detecting research topics in a specific research field has attracted attention from researchers in the bibliometrics community. In this study, to solve two problems of clustering papers, i.e., the influence of different distributions of citation links and involved textual features on similarity computation, the authors propose a hybrid self-optimized clustering model to detect research topics by extending the hybrid clustering model to identify “core documents”. First, the Amsler network, consisting of bibliographic coupling and co-citation links, is created to calculate the citation-based similarity based on the cosine angle of papers. Second, the cosine similarity is also used to compute the text-based similarity, which consists of the textual statistical and topological features. Then, the cosine angle of the linear combination of citation- and text-based similarity is considered as the hybrid similarity. Finally, the Louvain method is applied to cluster papers, and the terms based on term frequency are used to label clusters. To test the performance of the proposed model, a dataset related to the data envelopment analysis field is used for comparison and analysis of clustering results. Based on the benchmark built, different clustering methods with different citation links or textual features are compared according to evaluation measures. The results show that the proposed model can obtain reasonable and effective clustering results, and the research topics of data envelopment analysis field are also analyzed based on the proposed model. As different features are considered in the proposed model compared with previous hybrid clustering models, the proposed clustering model can provide inspiration for further studies on topic identification by other researchers.

A semi-empirical model for estimating diffuse solar near infrared radiation in Thailand using ground- and satellite-based data for mapping applications

This work has developed a semi-empirical model for estimating monthly average hourly diffuse solar near infrared (NIR) radiation in Thailand. Diffuse NIR radiation data were recorded at four stations in Thailand namely, Chiang Mai (18.78oN, 98.98oE), Ubon Ratchathani (15.25oN, 104.87oE), Nakhon Pathom (13.82oN, 100.04oE) and Songkhla (7.20oN, 100.60oE). Our analysis has shown that diffuse NIR radiation is related to cloud, precipitable water and cosine of solar zenith angle in terms of an exponential function. Therefore, the model was formulated with these parameters and validated with independent diffuse NIR measurements. The result showed that diffuse NIR radiation from the model and that from the measurements were in reasonable agreement with root mean square difference and mean bias difference of 16.7% and 1.5%, respectively. The semi-empirical model was used to generate diffuse maps of NIR for the country which displayed both diurnal and seasonal variations.