Directions Of Principal Axes Research Articles

Dynamic homogenisation of Maxwell’s equations with applications to photonic crystals and localised waveforms on gratings

A two-scale asymptotic theory is developed to generate continuum equations that model the macroscopic behaviour of electromagnetic waves in periodic photonic structures when the wavelength is not necessarily long relative to the periodic cell dimensions; potentially highly-oscillatory short-scale detail is encapsulated through integrated quantities. The resulting equations include tensors that represent effective refractive indices near band edge frequencies along all principal axes directions, and these govern scalar functions providing long-scale modulation of short-scale Bloch eigenstates, which can be used to predict the propagation of waves at frequencies outside of the long wavelength regime; these results are outside of the remit of typical homogenisation schemes.The theory we develop is applied to two topical examples, the first being the case of aligned dielectric cylinders, which has great importance in modelling photonic crystal fibres. Results of the asymptotic theory are verified against numerical simulations by comparing photonic band diagrams and evanescent decay rates for guided modes. The second example is the propagation of electromagnetic waves localised within a planar array of dielectric spheres; at certain frequencies strongly directional propagation is observed, commonly described as dynamic anisotropy. Computationally this is a challenging three-dimensional calculation, which we perform, and then demonstrate that the asymptotic theory captures the effect, giving highly accurate qualitative and quantitative comparisons as well as providing interpretation for the underlying change from elliptic to hyperbolic behaviour.

A noncontact positioning measuring system based on distributed wireless networks

A new type of distributed wireless network which combines a laser range finder with binocular vision sensors is developed to improve the accuracy of measurement along the direction of optical axis. By obtaining the coordinate of the target by the binocular vision sensor, the laser range finder which is installed at a two-axes rotary table is able to measure the distance between the target and the turntable of the current position. Then, an adaptive weighted fusion algorithm of multi-sensor information fusion is proposed to improve the utilization efficiency of the multi-sensor information and to make the results more accurate. Finally, the parameters of the system are calibrated through the simulations and the experiments show that the system is feasible and effective.

Influence of the antisymmetric part of gyration pseudotensor on the characteristics of transmitted light in biaxial crystals

The influence of the antisymmetric part of gyration pseudotensor on the characteristics of transmitted light have been investigated for biaxial crystals. Analytical expressions for the optical rotation in the direction of optical axis are obtained with allowance for both the symmetric and antisymmetric parts of gyration pseudotensor. The polarization azimuth and transmitted light ellipticity have been calculated at different angles of incidence.

Molecular dynamics study of the behavior of nitromethanes enclosed inside carbon nanotube containers.

We utilized molecular dynamics (MD) to investigate the behavior of nitromethane molecules (NMs) enclosed inside carbon nanotube (CNT) containers sealed with buckybowl caps. Two different sizes of CNT containers, i.e., (10,10) and (20,20), were employed to contain the energetic NMs. After loading the NMs into these containers, MD simulations were carried out at different loading densities. The loading density was changed from 0.4 to 2.0g/cc. At low loading densities, NMs preferentially resided near the surface of the CNT wall (orienting themselves in the cylindrical direction) and near the buckybowl caps (orienting themselves in the principal-axis direction). This behavior suggests the buckybowl caps and the CNT wall have attractive interactions with the NMs. The distribution of the NMs inside the containers did not change upon increasing the temperature from ambient to 100°C. However, the positional preference of the NMs found at ambient temperature to 100°C was not the same as that observed at 1000°C due to the increased thermal motions of the NMs. The size of the CNT container had a significant effect on the fluidity of the NMs. From 25 to 100°C, the NMs inside the (10,10) CNT container were only mobile at low loading densities. On the other hand, in the (20,20) CNT container, the NMs showed good mobility up to a loading density of 1.6g/cc. Graphical Abstract Attractive interactions between the nitromethanes and the buckybowl caps as well as the carbon nanotube wall.

Spectral Solution for Scattering Analysis of Periodic Plasmonic Nano-antennas on Iso/Anisotropic Substrate

A fast solution for the scattering analysis of periodic plasmonic nano-antennas (PPNAs) on iso/anisotropic substrates is presented. This method is based on derivation of the spectral dyadic Green's function with taking into account the plasmonic effects. The obtained dyadic Green's function is then used in an integral equation formulated for computing the induced surface current densities on the PPNAs. The resultant integral equation is solved by means of Galerkin's Method of Moments with entire-domain basis and test functions. With the help of this computational technique, the scattering characteristics of several examples are analyzed. The computed results are validated by means of a full-wave EM solver based on finite element method. For showing the efficiency of this method, the convergence rate and computation time in terms of space harmonic orders are calculated. It is shown that the developed method is an efficient and speedy technique for the analysis of such periodic plasmonic structures. In addition, we study an array of PPNAs on a uniaxial anisotropic substrate where the scattering characteristics are calculated as a function of the optic-axis direction. It is found that using anisotropic materials as the substrate of PPNAs allows additional degrees of freedom for controlling the scattering information.

Research of Multi-Sensor Data Fusion Based on Binocular Vision Sensor and Laser Range Sensor

The system of binocular vision sensor was used in the air-to-air close air target positioning in the paper. Due to the limitation of model itself, the measurement accuracy along the direction of optical axis is far lower than the accuracy of vertical direction. In order to improve the measurement accuracy of the optical axis, the paper put forward to using laser range sensor to cooperate with binocular vision sensor; Then the paper proposed adopts adaptive weighted fusion algorithm of multi-sensor information fusion to improve the utilization efficiency of multi-sensor information and to make the results accurately; Finally, the parameters of the system were calibration respectively and experiment is simulated, experimental results show that the position system is feasibility and effectiveness.

Reducing the influence of direct reflection on return signal detection in a 3D imaging lidar system by rotating the polarizing beam splitter

The direction rule of the laser beam traveling through a deflected polarizing beam splitter (PBS) cube is derived. It reveals that, due to the influence of end-face reflection of the PBS at the detector side, the emergent beam coming from the incident beam parallels the direction of the original case without rotation, with only a very small translation interval between them. The formula of the translation interval is also given. Meanwhile, the emergent beam from the return signal at the detector side deflects at an angle twice that of the PBS rotation angle. The correctness has been verified by an experiment. The intensity transmittance of the emergent beam when propagating in the PBS is changes very little if the rotation angle is less than 35 deg. In a 3D imaging lidar system, by rotating the PBS cube by an angle, the direction of the return signal optical axis is separated from that of the origin, which can decrease or eliminate the influence of direct reflection caused by the prism end face on target return signal detection. This has been checked by experiment.

Masonry structural damage and failure under blasting vibration

Research on structural dynamic response and damage characteristics under blasting vibration is critical in structural safety assessment and blasting design. An orthotropic dynamic damage constitutive model of structural material is proposed in this article to improve the overly simple dynamic damage models of previous studies. A dynamic increase factor is used to assess the strain rate effect, and the dynamic damage stiffness matrix of the unit body is determined using the Sidoroff energy equivalence principle. The Mazars damage evolution model is used to calculate damage variables in the principal axis directions, and the Hoffman yield failure criterion for orthotropic materials is applied. The orthotropic dynamic damage constitutive model is input into dynamic finite element program LS-DYNA as the user subroutine to simulate the dynamic responses of typical masonry structures according to different blasting vibration excitations. The effects of varying particle peak velocity, principal frequency, and duration of blasting vibration on structural dynamic responses and damage are analyzed. The results show that maximal equivalent stress and strain increase positively with the particle peak velocity, structures have a danger frequency band, and structural damage increases with duration.

Affine‐scale invariant feature transform and two‐dimensional principal component analysis: a novel framework for affine and scale invariant face recognition

Face recognition (FR) is one of the most effervescent fields of research with extensive applications that span numerous domains, and it stands resolutely as one of the most challenging problems in computer vision. The accuracy of FR systems is severely affected when two images under consideration for a match, vary in their scale and/or affine angles. The prevalent affine and scale invariant recognition systems have been predominantly developed only for objects, and hence in this study, the authors propose a novel approach for faces based on the affine‐SIFT (ASIFT) and two‐dimensional principal component analysis (2DPCA) techniques, to accomplish the formidable task of facial image recognition, invariant of scale and affine angles, i.e. the ability to simulate with enough accuracy, all the distortions caused by the differences in resolution and the variation of the camera optical axis direction. In the formulation of ASIFT‐2DPCA, they investigate three different variants of 2DPCA: classical 2DPCA, quaternion 2DPCA and sparse 2DPCA to gauge as to which is more effective. The authors'experimentations will demonstrate that the proposed approach can robustly handle affine and scale variations, and hence provide better accuracy and matching performance than the state‐of‐the‐art methodologies.

Performance and optimization research of triple-junction solar cell along the optical axis direction on \text{the HCPV module}

High concentrating photovoltaic (HCPV) technology plays a more and more important role in solar power generation due to its extremely high efficiency. However, the efficiency of the HCPV module can be reduced by many factors. Especially, there are not enough researches and knowledge on the light intensity distribution and non-uniform illumination of different wavelengths of light concentrated by Fresnel lens. It is generally considered that the maximum power of multi-junction solar cell is achieved when the cell is placed on the focal plane of Fresnel lens. But it is proved to be incorrect by our research. When light beams of different wavelengths go through the Fresnel lens, their light spot distributions on the optical axis are not the same as those when they have different refractive indexes in Fresnel lens. At the same time, the triple-junction solar cell consists of three sub-cells which absorb light beams of different wavelengths respectively. Therefore, the performance of triple-junction cells would be influenced by the light distribution along the optical axis, this is exactly what we want to study in this work. The method of simulating the light tracing is used to calculate and analyze the light intensity distribution and non-uniform characteristics of different wavelengths of light concentrated by Fresnel lens. Combined with them from the circuit network model of a triple-junction solar cell, the electrical performances of triple-junction solar cell at different positions along the optical axis are studied. It is found from the simulation that the performance of cell does not reach the best state when cell is placed on the focal plane. The power of cell on the focal plane reaches only 0.41 W while the maximum point arrives at 0.69 W. The high non-uniformity of light on cell surface when cell is placed on the focal plane causes the decline of power. And an outdoor HCPV testing system with the ability to change the distance between Fresnel lens and the cell is conducted. The experimental results and the simulation results match well, therefore our simulation approach is verified. It shows that the module achieves the maximum power on either side of the focal plane, and the output power can increase more than 20% after optimization. It is a result after equilibrium between light intensity and uniformity on cell surface.

Rotation of principal axes and changes of stress due to mine-induced stresses

This research project comprises stress monitoring, primarily of the changes induced by longwall mining or destress blasting, which was realized in a mine of the Ostrava-Karviná Coalfields (Upper Silesian Coal Basin). Verification of the stress field response to stresses induced by different geological or mining factors was the main aim of the research project. Stress change monitoring in the region of the advanced longwall was carried out using seven stress probes. In all, seven boreholes were instrumented with compact conical ended borehole monitoring (CCBM) probes for continuous stress monitoring of the stress–strain changes due to mining and the destress blasting effect. Compact conical-ended borehole overcoring (CCBO) and CCBM probe installation were carried out before the start of the longwall mining. Data of the stress changes in all seven probes were recorded weekly and, after the longwall advanced, daily. Analysis of the stress changes was based on the idea of original stress distribution, which is based on long-term experiences in rock mass behavior in similar geological and mining conditions. For all probes, the magnitude of stress changes and principal axis direction changes were investigated. Analysis results to date indicate that stress changes ahead of the longwall face present not only the changes of stress magnitude, but the rotation of the axes of the stress components as well. Rotations of the principal axes emerged as very important factors of the stress tensor changes and their influence on rock mass deformation and stability of the workings. In addition, results show that the vertical to horizontal stress component ratio converges to 1 and in many cases horizontal stresses are higher than vertical ones. This of course relates to the impact of mine-induced stresses. This knowledge is basic for the purpose of prevention of rock burst because the actual stress state is fundamental to its proper and operative planning.

Fabrication of microchannels in fused silica using femtosecond Bessel beams

Extended birefringent waveguiding microchannels up to 15 mm long were created inside fused silica by single-pulse irradiation with femtosecond Bessel beams. The birefringent refractive index change of 2–4 × 10−4 is attributed to residual mechanical stress. The microchannels were chemically etched in KOH solution to produce 15 mm long microcapillaries with smooth walls and a high aspect ratio of 1:250. Bessel beams provide higher speed of material processing compared to conventional multipulse femtosecond laser micromachining techniques and permit simple control of the optical axis direction of the birefringent waveguides, which is important for practical applications [Corrielli et al., “Rotated waveplates in integrated waveguide optics,” Nat. Commun. 5, 4249 (2014)].

Exemplar-based logo and trademark recognition

Automatic logo recognition facilitates the process of searching and analyzing digital image-based resources. This is due to the simplicity and informativity of logos which can be used as a visual or semantic clue for applications such as content-based image retrieval. For automatic shape recognition, model-based approaches have gained a lot of attention due to their theoretical background and promising results. However, one of the major challenges of these approaches for logo recognition is collecting samples of logos with possible perspective tilts and non-rigid deformations that most likely happen to natural images. Therefore, a robust model cannot be trained due to the lack of sufficient samples. In this paper, we aim to overcome, or at least alleviate, this challenge by introducing an exemplar-based approach. The proposed method synthesizes new images of each logo of interest, so-called exemplars, by simulating two camera axes. This is to produce almost all possible views of a logo that may appear in a given image and guarantee that most of the distortions in the shape of a logo caused by a variation of the camera optical axis direction are covered. Subsequently, an exemplar-based model is derived based on all the exemplars using linear SVMs. Finally, for the detection and recognition, we associate observed logos with the exemplars using our exemplar-based model. Experiments are carried out on two publicly available logo datasets: FlickrLogos-27 and FlickrLogos-32. The results show the superior detection and recognition capabilities of the proposed method over the competitors.

Crystal structure, atomic net charges and electric moments in pyroelectric LiNaSO4 at 296 K.

The crystal structure and electric charge distribution in LiNaSO4 have been studied at 296 K by X-ray diffraction using a spherical crystal. LiNaSO4 is pyroelectric, nonferroelectric and an optically uniaxial insulator which crystallizes in the space group P31c. Least-squares refinement (MOLLY) was based on 13,026 reflections. The asymmetric unit contains Li(+), Na(+) and three SO4(2-) ions, where one O and S lie on a threefold axis about which three O atoms are related with a threefold symmetry in each sulfate ion. Two of the O-S-O groups suffer from disorder. The net charges of the atoms in three independent sulfate ions were determined under ionic charge constraints. The S atoms have positive net electric charges and O atoms are negative. The components of the significant electric multipole moments in the principal axis directions are determined from the distribution of net atomic charges in each sulfate ion. Electric moments in the unit cell generate macroscopic electric moments in the crystal which interact with light. This interaction results in two axial vectors of second rank associated with an optical indicatrix. The ratio of the calculated axial vector components in the principal axis directions originating from the asymmetric unit is 1.0061 (1), which compares well with the ratio of 1.006 for the corresponding optical refractive indices of LiNaSO4 for λ(Na) = 589.29 nm.

Polymer blend effects on fundamental properties of mesogenic phthalocyanine films fabricated by heated spin-coating method

Polymer blending effects on the properties of the mesogenic phthalocyanine thin films fabricated by heated spin-coating method were demonstrated. The spin-coated films of 1,4,8,11,15,18,22,25-octahexylphthalocyanine (C6PcH2) blended with poly(3-hexylthiophene) (P3HT) were prepared by controlling the temperatures of substrates and solutions with the mixed material, and the morphology and optical property of the fabricated film were studied. In the case of the low composite ratio of P3HT, the wide crack lines found in pure C6PcH2 films disappeared while maintaining the uniaxial aligned optic axis direction in the large-area with the diameters of exceeding 1 mm. The polymer blend effects were discussed by taking the anisotropic optical absorption and molecular stacking structure in the films into consideration.

DETECTION OF THE VELOCITY SHEAR EFFECT ON THE SPATIAL DISTRIBUTIONS OF THE GALACTIC SATELLITES IN ISOLATED SYSTEMS

We report a detection of the effect of the large-scale velocity shear on the spatial distributions of the galactic satellites around the isolated hosts. Identifying the isolated galactic systems each of which consists of a single host galaxy and its satellites from the Seventh Data Release of the Sloan Digital Sky Survey and reconstructing linearly the velocity shear field in the local universe, we measure the alignments between the relative positions of the satellites from their isolated hosts and the principal axes of the local velocity shear tensors projected on to the plane of sky. We find a clear signal that the galactic satellites in isolated systems are located preferentially along the directions of the minor principal axes of the large-scale velocity shear field. Those galactic satellites which are spirals, brighter, located at distances larger than the projected virial radii of the hosts and belonging to the spiral hosts yield stronger alignment signals, which implies that the alignment strength depends on the formation and accretion epochs of the galactic satellites. It is also shown that the alignment strength is quite insensitive to the cosmic web environment as well as the size and luminosity of the isolated hosts. Although this result is consistent with the numerical finding of Libeskind et al. based on a N-body experiment, due to the very low significance of the observed signals it remains inconclusive whether or not the velocity shear effect on the satellite distribution is truly universal.

Measurement method for optical retardation based on the phase difference effect of laser feedback fringes.

We present a measurement method for optical phase retardation, which utilizes a phase-difference phenomenon of the feedback fringes in orthogonally polarized directions of a laser with anisotropic weak feedback. This phase difference is dominated by the measured retardation. The measurement principles are given based on the 3-mirror cavity model, and experiments are conducted with quartz waveplates (WPs). A measurement range 0°-180° is achieved, the uncertainty is theoretically better than 0.5°, and the measurement precision can be improved further. This method does not require researchers to know beforehand the principal axes directions of the WPs, and has better anti-disturbance ability than the previous method based on laser feedback.

Internal, combinational and sub-harmonic resonances of a nonlinear asymmetrical rotating shaft

The internal, combinational and sub-harmonic resonances of a simply supported rotating asymmetrical shaft with unequal mass moments of inertia and bending stiffness in the direction of principal axes are simultaneously considered. The excitation terms are due to dynamic imbalances of shaft and shaft asymmetry. The nonlinearities are due to extensionality of shaft and large amplitudes. To analyze the nonlinear equations of motion, the method of harmonic balance is utilized. The influences of inequality between two eccentricities corresponding to the principal axes and external damping on the steady-state responses and bifurcation points of the asymmetrical rotating shaft are investigated. The numerical computations are utilized to verify the harmonic balance method results. The results of harmonic balance method are in accordance with those of numerical computations.

A method for quantitatively analyzing the angle of direction for arbitral c-axis alignment with retardation measurements

c -axis alignment in a polymer or crystal structure has drawn attention in numerous scientific and technological applications, including crystals, thin film growth, electro-optic devices, and phase difference optics. We here demonstrate a new approach based on retardation measurement that can obtain the direction of the c -axis alignment. This is employed to visualize the three-dimensional direction of continuous crystals as a thin optical film utilizing a liquid crystal panel, using retardation analysis equipment with high resolution measurement capability. The direction of the c -axis alignment is shown so as to allow a detailed characterization of the direction perpendicular to the plane. In this analysis, the direction of the c -axis alignment is identified, and differences between molecules at inequivalent sites are quantified. The results suggest that the excellent lubrication properties of the c -axis alignment may be due to a significant localization in lateral directions. • There was no report to analyze c -axis alignment directly. • A new analysis approach is demonstrated with a direction of the c -axis alignment. • We could visualize the three-dimensional direction of optical axes in a thin film.

Axial super-resolution by mirror-reflected stimulated emission depletion microscopy

In stimulated emission depletion (STED) microscopy, the lateral resolution is in the range of tens of nanometers depending on the sample and the instrument. The axial resolution, however, is in standard systems limited by diffraction to about 500 nm. We present an approach to three-dimensional diffraction-unlimited resolution by observing the sample at two optical angles. The system is realized by using an atomic force microscope (AFM) chip as a microreflector to deflect the STED beams near the region-of-interest (ROI), thus allowing observations at an angle ∠. Consequently, the superior lateral resolution can be utilized to resolve details in the axial direction of the main optical axis of the microscope. Here, fluorescent nanoparticles 90 nm apart and biological structures 80 nm apart along axial direction were distinguished by utilizing an off-the-shelf, commercial STED microscope, coupled with an AFM and an AFM chip micro-reflector.