Special Angle Research Articles

Characterization of excitation beam on second-harmonic generation in fibrillous type I collagen

Following our established theoretical model to deal with the second-harmonic generation (SHG) excited by a linearly polarized focused beam in type I collagen, in this paper, we further quantitatively characterize the differences between SHG emissions in type I collagen excited by collimated and focused beams. The effects of the linear polarization angle (α) and the fibril polarity characterized by the hyperpolarizability ratio ρ on SHG emission has been compared under collimated and focused beam excitation, respectively. In particular, SHG emission components along the i axis [Formula: see text] (i = x,y,z), the induced SHG emission deviation angle γ(ij), and the detected SHG signals (I(2ω,ij)) in the ij plane by rotating the applied polarizer angle φ(ij) have been investigated (i = x, x, y; j = y, z, z). Results show that under our simulation model, SHG emission in the xy plane, such as I(2ω,x) ,I(2ω,y) ,γ(xy) and I(2ω,xy) varying as polarization angle (α) under collimated and focused light, presents no significant difference. The reverse of the fibril polarity has induced great impact on I(2ω,x) ,γ(xy) and I(2ω,xy) in both collimated and focused light. I(2ω,x) and γ(xy) show similarity, but I(2ω,xy) at α = 30° demonstrates a slight difference in focused light to that in collimated light. Under focused light, the reverse of fibril polarity causes obvious changes of the collected SHG intensity I(2ω,xz) and I(2ω,yz) at a special polarization angle α = 60° and γ(xz), γ(yz) along α.

Moveout approximation for horizontal transversely isotropic and vertical transversely isotropic layered medium. Part II: effective model‡

ABSTRACTWe use residual moveouts measured along continuous full azimuth reflection angle gathers, in order to obtain effective horizontal transversely isotropic model parameters. The angle gathers are generated through a special angle domain imaging system, for a wide range of reflection angles and full range of phase velocity azimuths. The estimation of the effective model parameters is performed in two stages. First, the background horizontal transversely isotropic (HTI)/vertical transversely isotropic (VTI) layered model is used, along with the values of reflection angles, for converting the measured residual moveouts (or traveltime errors) into azimuthally dependent normal moveout (NMO) velocities. Then we apply a digital Fourier transform to convert the NMO velocities into azimuthal wavenumber domain, in order to obtain the effective HTI model parameters: vertical time, vertical compression velocity, Thomsen parameter delta and the azimuth of the medium axis of symmetry. The method also provides a reliability criterion of the HTI assumption. The criterion shows whether the medium possesses the HTI type of symmetry, or whether the azimuthal dependence of the residual traveltime indicates to a more complex azimuthal anisotropy. The effective model used in this approach is defined for a 1D structure with a set of HTI, VTI and isotropic layers (with at least one HTI layer). We describe and analyse the reduction of a multi‐layer structure into an equivalent effective HTI model. The equivalent model yields the same NMO velocity and the same offset azimuth on the Earth's surface as the original layered structure, for any azimuth of the phase velocity. The effective model approximates the kinematics of an HTI/VTI layered structure using only a few parameters. Under the hyperbolic approximation, the proposed effective model is exact.

Modulation of Entanglement for Coupled Superconducting Qubits Under Non-Markovian Environment

The evolution of entanglement decoherence is investigated for a coupled superconducting qubit under non-Markovian environment by utilizing a commensal entanglement degree. The results show that, owing to the memory feedback effect of environment, the entanglement degree of the coupled qubits at the thermal equilibrium always monotonously tends to zero so that entanglement sudden death occurs briefly in the non-Markovian process. Different from the Markovian process, stronger the dissipation is, faster the entanglement sudden death is. We find that, furthermore, the interaction between the qubits results generally in reduction of entanglement degree in the quantum system. With some special initial states or initial phase angles, however, the influence of the interaction between qubits on the system entanglement degree can be avoided.

THE AMPLITUDE OF THE DE BROGLIE GRAVITATIONAL WAVES

We calculate the amplitude of the de Broglie gravitational waves using the standard Einstein General Relativity. We find that these waves disappear in the limit ℏ→0 and when their source has a large mass and volume. From the experimental point of view, the knowledge of the amplitude allows to estimate the magnitude of the effect of the wave on a sphere of test particles. We propose also to measure a very special shift angle that does not change with time.

Entropy Minimization for Shadow Removal

Recently, a method for removing shadows from colour images was developed (Finlayson et al. in IEEE Trans. Pattern Anal. Mach. Intell. 28:59–68, 2006) that relies upon finding a special direction in a 2D chromaticity feature space. This “invariant direction” is that for which particular colour features, when projected into 1D, produce a greyscale image which is approximately invariant to intensity and colour of scene illumination. Thus shadows, which are in essence a particular type of lighting, are greatly attenuated. The main approach to finding this special angle is a camera calibration: a colour target is imaged under many different lights, and the direction that best makes colour patch images equal across illuminants is the invariant direction. Here, we take a different approach. In this work, instead of a camera calibration we aim at finding the invariant direction from evidence in the colour image itself. Specifically, we recognize that producing a 1D projection in the correct invariant direction will result in a 1D distribution of pixel values that have smaller entropy than projecting in the wrong direction. The reason is that the correct projection results in a probability distribution spike, for pixels all the same except differing by the lighting that produced their observed RGB values and therefore lying along a line with orientation equal to the invariant direction. Hence we seek that projection which produces a type of intrinsic, independent of lighting reflectance-information only image by minimizing entropy, and from there go on to remove shadows as previously. To be able to develop an effective description of the entropy-minimization task, we go over to the quadratic entropy, rather than Shannon’s definition. Replacing the observed pixels with a kernel density probability distribution, the quadratic entropy can be written as a very simple formulation, and can be evaluated using the efficient Fast Gauss Transform. The entropy, written in this embodiment, has the advantage that it is more insensitive to quantization than is the usual definition. The resulting algorithm is quite reliable, and the shadow removal step produces good shadow-free colour image results whenever strong shadow edges are present in the image. In most cases studied, entropy has a strong minimum for the invariant direction, revealing a new property of image formation.

Coding coarse grained polymer model for LAMMPS and its application to polymer crystallization

We present a patch code for LAMMPS to implement a coarse grained (CG) model of poly(vinyl alcohol) (PVA). LAMMPS is a powerful molecular dynamics (MD) simulator developed at Sandia National Laboratories. Our patch code implements tabulated angular potential and Lennard-Jones-9-6 (LJ96) style interaction for PVA. Benefited from the excellent parallel efficiency of LAMMPS, our patch code is suitable for large-scale simulations. This CG-PVA code is used to study polymer crystallization, which is a long-standing unsolved problem in polymer physics. By using parallel computing, cooling and heating processes for long chains are simulated. The results show that chain-folded structures resembling the lamellae of polymer crystals are formed during the cooling process. The evolution of the static structure factor during the crystallization transition indicates that long-range density order appears before local crystalline packing. This is consistent with some experimental observations by small/wide angle X-ray scattering (SAXS/WAXS). During the heating process, it is found that the crystalline regions are still growing until they are fully melted, which can be confirmed by the evolution both of the static structure factor and average stem length formed by the chains. This two-stage behavior indicates that melting of polymer crystals is far from thermodynamic equilibrium. Our results concur with various experiments. It is the first time that such growth/reorganization behavior is clearly observed by MD simulations. Our code can be easily used to model other type of polymers by providing a file containing the tabulated angle potential data and a set of appropriate parameters. Program summary Program title: lammps-cgpva Catalogue identifier: AEDE_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEDE_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU's GPL No. of lines in distributed program, including test data, etc.: 940 798 No. of bytes in distributed program, including test data, etc.: 12 536 245 Distribution format: tar.gz Programming language: C++/MPI Computer: Tested on Intel-x86 and AMD64 architectures. Should run on any architecture providing a C++ compiler Operating system: Tested under Linux. Any other OS with C++ compiler and MPI library should suffice Has the code been vectorized or parallelized?: Yes RAM: Depends on system size and how many CPUs are used Classification: 7.7 External routines: LAMMPS ( http://lammps.sandia.gov/), FFTW ( http://www.fftw.org/) Nature of problem: Implementing special tabular angle potentials and Lennard-Jones-9-6 style interactions of a coarse grained polymer model for LAMMPS code. Solution method: Cubic spline interpolation of input tabulated angle potential data. Restrictions: The code is based on a former version of LAMMPS. Unusual features.: Any special angular potential can be used if it can be tabulated. Running time: Seconds to weeks, depending on system size, speed of CPU and how many CPUs are used. The test run provided with the package takes about 5 minutes on 4 AMD's opteron (2.6 GHz) CPUs.

A Vision Based Wheel Slip Estimation Technique for Mining Vehicles

Slip plays a vital role in traction control when a mining vehicle traverses over soft soil. This paper presents a vision-based wheel slip estimation technique for mining vehicles. A downward-looking camera is mounted with a special tilted angle to observe both the rotary motion of the wheel and the wheel translatory motion relative to the soil. An optical flow algorithm is developed to estimate the wheel angular velocity and the wheel translatory velocity, by tracking salient features selected from the soil surface and the wheel tire surface separately. The specially orientated camera enables the vision-based algorithm to estimate the wheel slip without wheel odometry information. The proposed technique has been validated on a linear test rig, showing good performance.

Electrical properties of the deformed carbon nanotube field-effect transistors

On the basis of the tight-binding theory, we derive the band structure formula of the deformed carbon nanotube. The results show that the band gap varies with increasing deformation, which shows that the deformation can change the nature of the conductivity of carbon between the metal-type and semiconductor-type. Especially for zigzag nanotubes，there are three different rules goveoning this translation, which is dependent on the remainder of n divided by 3. Furthermore, by using Natori theory on the field-effect transistor we study the current-voltage characteristics of deformed carbon nanotube field-effect transistors. For strain deformation, the conductivity of zigzag nanotube presents different characteristics with the remainder of n by 3. For armchair nanotubes, the conductivity does not change with the strain parameter. However, for torsion deformation, the conductivity rapidly increases, specially for the armchair tube. It has many obviously different conductivity behaviors between zigzag tubes and armchair tubes. At some special torsion angles, the conductivity of zigzag tube and armchair tube has obvious changes, which reveals the translation between metal-type and semiconductor-type conductivities.

Interlayer energy-optimum stacking registry for two curved graphene sheets of nanometre dimensions

The interlayer energy between two circular graphene sheets of nanometre scale, which is curved into cylindrical shape with different curvature radius, is investigated by a molecular force field based on a registry-dependent interlayer interaction potential. It is found that there is a special interlayer stacking angle near which the interlayer energy is significantly lower. This interlayer energy-minimum stacking registry angle shifts away from the original Bernal (AB) stacking orientation when the curvature radius of curved graphene sheets is less than 20 nm, and increases with decreasing curvature radius beyond this point. The stability of interlayer energy-minimum stacking of the curved graphene sheets decreases with decreasing curvature radius.

SU-GG-T-238: Three Dimensional Characterization of the Radiation Isocenter Using a Single Phantom

Purpose: To provide a quality control procedure that characterizes the radiation isocenter of a linear accelerator simultaneously for collimator, couch, and gantry rotations. The primary question addressed is whether the three rotational axes cross each other within an acceptably small sphere. Method and Materials: A film stack phantom was constructed having four films suitably spaced apart. The phantom was placed in a fixed position on the treatment table, and a single reference frame was defined by registration marks. The combined use of Linac jaws and MLC created small spots on the films for each rotation axis. Special angles were chosen for the different axes so that three dimensional information was retrieved. The film spot coordinates were read using commercially available scanning software, and a computer calculation then rendered the data into a three dimensional display of the axes. Results: The procedure has been used nine times with reasonable results on four different accelerators. Comparisons of the minimum tangent circle radius using this method and standard star shots were favorable. In addition, the orthogonality of the axes and their orientations relative to a reference laser system was reported. Conclusion: This procedure is unique in that it provides, using simple commonly found materials,composite information about the radiation isocenter and all three rotational axes in a single measurement. It seems to offer the confidence needed to become a routinely used tool for the Linac annual check.

Exact seismic velocities for transversely isotropic media and extended Thomsen formulas for stronger anisotropies

A different type of approximation to the exact anisotropic wave velocities as a function of incidence angle in transversely isotropic (TI) media is explored. This formulation extends Thomsen’s weak anisotropy approach to stronger deviations from isotropy without significantly affecting the equations’ simplicity. One easily recognized improvement is that the extreme value of the quasi-SV-wave speed [Formula: see text] is located at the correct incidence angle [Formula: see text] rather than always being at the position [Formula: see text]. This holds universally for Thomsen’s approximation, although [Formula: see text] actually is never correct for any TI anisotropic medium. Wave-speed magnitudes are more closely approximated for most values of the incidence angle, although there may be some exceptions depending on actual angular location of the extreme value. Furthermore, a special angle [Formula: see text] (close to theextreme point of the SV-wave speed and also needed by the new formulas) can be deduced from the same data normally used in weak anisotropy data analysis. All the main technical results are independent of the physical source of the anisotropy. Two examples illustrate the use of obtained results based on systems having vertical fractures. The first set of model fractures has axes of symmetry randomly oriented in the horizontal plane. Such a system is then isotropic in the horizontal plane and thus exhibits vertical transversely isotropic (VTI) symmetry. The second set of fractures also has its axes of symmetry in the horizontal plane, but (it is assumed) these axes are aligned so the system exhibits horizontal transverse isotropic (HTI) symmetry. Both VTI and HTI systems, as well as any other TI medium (whether because of fractures, layering, or other physical causes), are easily treated with the new phase-speed formulation.

Stream depletion rate and volume from groundwater pumping in wedge-shape aquifers

In river basins with several tributaries, wells in alluvial valleys are often located near the wedge-shaped confluence of two tributaries. Therefore, stream depletion characteristics, namely stream depletion rate (SDR) and stream depletion volume (SDV), induced by the pumping wells are distributed between two tributaries upstream from the confluence. Existing methods for the evaluation of stream depletion characteristics are applicable only for a wedge-shaped aquifer with special or uncommon wedge angles or for steady-state conditions. In water resources management, temporal stream depletion characteristics are important for the adjudication of water rights. A new and practically important method for analytical evaluation of transient SDR and SDV is developed for a wedge-shaped aquifer with arbitrary wedge angles. Results are obtained for each of two tributaries or the tributary segment lengths. A simple expression for the SDR fraction that originates from each tributary is presented for long period of pumping after which 100% of the pumping rate is supplied by stream depletion. The sensitivity analyses for different parameters are performed to examine their affects on the influence period of the total SDR and the results indicated that the SDR is sensitive to the angles of wedge-shaped aquifer and the pumping well. The results and sensitivity analysis presented in this study may provide useful information in the assessment of water balance or exploitation of river basins.

Microscopic scattering imaging measurement and digital evaluation system of defects for fine optical surface

According to ISO10110-7 and the engineering standards of Inertial Confinement Fusion (ICF), this paper presents a microscopic scattering imaging and analyzing system which allows one to automatically evaluate defects in random distributions and shapes on the surface of fine optical components of large aperture. The annularly disposed multi-beam fiber light sources illuminate the target surface with a special angle. The image, which has bright defects on black background, is suitable for digital image processing. With XY-scanning system, the defect information of full aperture can be obtained by stitching the sub-aperture image array, according to the algorithms of template matching. The full aperture image is divided into N×N sub-apertures, each of which has view field of approximate 3mm×4mm. Image processing software for image recognition has been established using mathematical morphology with high computing efficiency and friendly graphics user interface. A group of standard reticules fabricated by binary optics can scale defects for calibration. As a result the lateral resolution of the system is better than sub-micrometer while the total view field can be hundreds of millimeters. The comparison quantitative data results between the experiment and standard demonstrate the system is competent for the digital evaluation of defect characterization of fine optical surfaces, especially for the ones with large aperture.

Estimating chlorophyll-a concentration in Lake Taihu in summer by irradiance ratio just beneath water surface

Water surface spectra,which can work inadiance ratio just beneath water surface R(O~-)out,is ob- tained by ASD FieldSpec Hand-Held Spectroradiometer.When the in-situ data is collected,a certain special angle has been adopted.After analyzing the relationship between spectral characteristics of R(O~-)and chlorophyll-a concentration,the results showed that the strongest correlations appeared at 762 nm、727 nm and 496 nm,the val- ues separately were 0.85,0.84 and-0.80.The model analysis with single band and band ratio revealed that the quadratic models,of which independent variables were R(O~-)_(762)、R(O~-)_(762)/R(O~-)_(496)、R(O~-)_(727)/R(O~-)_(496), were better than others.R~2 separately reach 0.923、0.919、0.916;std.error of the estimate S separately were 0.012,0.013,0.013;F separately were 101.241,96.576,92.925.Make use of the 10 surplus samples to estimate three quadratic models and carry on the accuracy and error margin examinations.Then find that the quadratic model with the independent variable R(O~-)_(762)/R(O~-)_(496)was the best,and to a certain extent had some functions on chlorophyll-a concentration estimation in Lake Taihu in summer.In addition,try to apply differential calculus to R (O~-)to estimate chlorophyll-a concentration,and can not acquire the better result.

Investigation of the stress singularity of a magnetoelectroelastic bonded antiplane wedge

The order of the stress singularity of a magnetoelectroelastic bonded antiplane wedge is analyzed by complex potential function and eigenfunction expansion method. Contrary to the familiar problem of elastic anisotropic bonded wedges which always produce real values for the order of singularity, the results of the magnetoelectroelastic bonded wedges may be real or complex. Numerical results are presented for problems with different boundary conditions. In particular, special behaviors of the order of the stress singularity for some degenerate composite materials and for some special wedge angles are noted.

Integration of carbon nanotubes with controllable inclination angle into microsystems

The possibility of growing carbon nanotubes in the immediate proximity of microstructures on a surface in a controllable way, with a high degree of control over the inclination angle, is demonstrated. Carbon nanotubes synthesised in a plasma-enhanced chemical vapour deposition process are known to grow in the direction of the electrical field. Geometrical features of the conductive substrate holder are used to distort the electrical field, thereby controlling the inclination angle of the carbon nanotubes locally. It is shown that the geometrical features of the microstructures on the silicon wafer do not interfere substantially with the resulting inclination angle. Finite element simulations show good agreement with the experimental observations, thus this is a route towards integrating carbon nanotubes with a special inclination angle on microstructures.

T2‐weighted balanced SSFP imaging (T2‐TIDE) using variable flip angles

A new technique for acquiring T2-weighted, balanced steady-state free precession (b-SSFP) images is presented. Based on the recently proposed transition into driven equilibrium (TIDE) method, T2-TIDE uses a special flip angle scheme to achieve T2-weighted signal decay during the transient phase. In combination with half-Fourier image acquisition, T2-weighted images can be obtained using T2-TIDE. Numerical simulations were performed to analyze the signal behavior of T2-TIDE in comparison with TSE and b-SSFP. The results indicate identical signal evolution of T2-TIDE and TSE during the transient phase. T2-TIDE was used in phantom experiments, and quantitative ROI analysis shows a linear relationship between TSE and T2-TIDE SNR values. T2-TIDE was also applied to abdominal and head imaging on healthy volunteers. The resulting images were analyzed quantitatively and compared with standard T2-weighted and standard b-SSFP methods. T2-TIDE images clearly revealed T2 contrast and less blurring compared to T2-HASTE images. In combination with a magnetization preparation technique, STIR-weighted images were obtained. T2-TIDE is a robust technique for acquiring T2-weighted images while exploiting the advantages of b-SSFP imaging, such as high signal-to-noise ratio (SNR) and short TRs.

Investigation in Determining the Relative Position between Stator and Rotor of a PMSM in Electromagnetic Field Calculation

When designing a universal finite element software for analyzing a permanent magnet synchronous motor, the relative position of the stator and rotor remains unknown. However, determining the relative position is a precondition for electromagnetic field calculation. Through analyzing the basic relationship of variables in a synchronous machine, the characteristics of an air-gap-resultant electromotive force and an inner power angle under a special inner power factor angle are obtained. A method similar to inverse problem solving is proposed. A series of electromagnetic field calculation under different armature current initial phase angles are carried out, and through searching the field of a special inner power factor angle, the relative position of the rotor and the stator can be determined subsequently.

Realization of an angular filter using one-dimensional photonic crystal containing negative refractive metamaterials

A new kind of one-dimension photonic crystal (PC) which can be used as an angular filter was studied. With the knowledge of resonance tunneling mechanism in zero average index PC, we find such PC must contain negative refractive metamaterials and its structure parameters should satisfy some special conditions. When electromagnetic wave of a given frequency incident on such PC, only those portions with incident angles identical with the special angle (or angles) can pass through such PC, while the others can not. Such filter would have wids applications in microwave and optical communications.

An alternative dispersion equation for water waves over an inclined bed

A classical approach to extending the validity of Airy's dispersion relation for surface gravity waves by Friedrichs (1948) to gentle slopes (of special inclinations) is here re-examined with extended small-slope asymptotics using the full linear harmonic function theory combined with the method of steepest descent. A new dispersion relation emerges that appears to give significantly increased accuracy over sloping beds when tested on the plane beach problem with various forms of the mild-slope equation (MSE) and global error reductions of the order 50% are noted in some 'from deep to shore' computations. Unlike the classical formula, the new formula predicts a discontinuous wavenumber at a place where the bottom slope is discontinuous. Preliminary tests examining the reflection coefficient with the basic (early version) MSE over ramp-type profiles indicate that this is not a major problem and numerical results using wavenumber calculated by the new dispersion relation are qualitatively similar to those of the modified MSE (MMSE) developed in Chamberlain & Porter (1995). When the new formula is applied (with mass conservation) to the MMSE on the ramp, results are almost identical to those of a full linear model for inclines having a gradient up to 8:1. It is also shown that the dominant asymptotic analysis, responsible for the new formula, is valid for all slope angles a < n/2 and not just the special angles considered by Friedrichs.