Small Oblique Angles Research Articles

Modeling the electron cyclotron emission radiation signature from suprathermal electrons in a tokamak.

An Electron Cyclotron Emission (ECE) modeling code has been developed to model ECE radiation with an arbitrary electron momentum distribution, a small oblique angle, both ordinary (O-mode) and extraordinary polarizations (X-mode), and multiple cyclotron frequency harmonics. The emission and absorption coefficients are calculated using the Poynting theorem from the cold plasma dispersion and the electron-microwave interaction from the full anti-Hermitian tensor. The modeling shows several ECE radiation signatures that can be used to diagnose the population of suprathermal electrons in a tokamak. First, in an n = 2 X-mode (X2) optically thick plasma and oblique ECE view, the modeling shows that only suprathermal electrons, which reside in a finite region of the velocity and space domains, can effectively generate cyclotron emissions to the ECE receiver. The code also finds that the O1 mode is sensitive to suprathermal electrons of both a high v⊥ and v‖, while the X2 mode is dominantly sensitive to suprathermal electrons of a high v⊥. The modeling shows that an oblique ECE system with both X/O polarization and a broad frequency coverage can be used to effectively yield information of the suprathermal electron population in a tokamak.

Magnetic Properties Regulation of FeGa and FeGaNi Films with Oblique Magnetron Sputtering

Magnetic FeGa and FeGaNi films with an in-plane anisotropy were deposited by employing oblique magnetron sputtering. With the increase in oblique angle, the crystallite size of FeGa decreases, which indicates that oblique sputtering can refine the crystallite size. The remanence ratio of FeGa films increases from 0.5 to 0.92 for an easy axis, and the coercivity increases with the decrease in the crystallite size. The calculated static anisotropic field shows that the in-plane magnetic anisotropy can be induced by oblique sputtering and the strength increases with the oblique sputtering angle. After doping Ni by co-sputtering, FeGaNi films exhibit a stable remanence ratio at 0.8, low coercivity and good anisotropy. With the low sputtering power of the Ni target, there is a competitive relationship between the effect of crystallite size and Ni doping which causes the coercivity of FeGaNi films to first increase and then decrease with the increase in the oblique angle. The FeGaNi film also shows high anisotropy in a small oblique angle. The variation of coercivity and anisotropy of FeGaNi films can be explained by the crystalline size effect and increase in Ni content. For the increasing intensity of collisions between FeGa and Ni atoms in the co-sputtering, the in-plane magnetic anisotropy increases first and then decreases. As a result, the magnetic properties of FeGa films were examined to tailor their magnetic softness and magnetic anisotropy by controlling the oblique sputtering angle and Ni doping.

Magnetic anisotropy and electrical property of CoZrTaB thin films deposited by oblique sputtering

Soft magnetic materials have been studied extensively in recent years due to their applications in micro-transformers, micro-inductors, spin dependent memories etc. Achieving high uniaxial anisotropy is one of the most important properties for these materials. Oblique angle sputtering without the presence of the magnetic field enables the ease thus lower cost of the adoption of magnetic materials in applications. With a highly soft magnetic material, one can operate the devices made out of these films at giga hertz regions without significant loss of efficiency thus desirable for applications such as power conversion and radio frequency (RF) devices. This work focuses on analyzing different growth conditions of thin films of CoZrTaB and the resulting magnetic and electrical properties of the films. Thin films are grown by oblique-angle sputtering, where the sputtering gun forms an angle with respect to the sample substrate normal, ranging from 0 to 75 degrees. External magnetic field normally applied in order to form magnetic anisotropy is not used during film sputtering process. Using vibrating sample magnetometer, it was observed that films resulting from small oblique angles have no clear magnetic anisotropy developed; whereas in samples deposited at large angles close to 60°, there is clear magnetic anisotropy observed. Scanning electron microscopy imaging of the cross-section of film suggests the formation of tilted columns, which is likely to be the reason for magnetic anisotropy. Resistivity of the films was measured systematically and found to increase as the magnitude of oblique angle during sputtering increased.

Hydraulic performance of circular crested oblique weirs

Abstract The present study attempted to improve the discharge capacity of oblique weirs by rounding their crests. Twenty-four oblique weir models have been tested in which oblique angle (α), weir height (P) and crest diameter (D) were changed. Analysis of the results shows that the discharge (QOC) increases with the increase of effective head above crest (He). Values of discharge coefficient (CD) are found decreasing slightly with the increase of (He/P) and (He/D) values and weirs of small oblique angles give lower values of CD. An empirical expression is presented to determine CD in terms of He/P, He/D and α (in radian) with a correlation coefficient of 0.90 and a standard error of 0.01. The highest discharge capacity is obtained from a weir having α = 20°, P = 20 cm, D = 4 cm and D/P ratio = 0.2 in which the percentage increase in discharge is ranging between 147% and 175% compared to sharp crested normal weir. Comparison of the present study results with those of other investigations shows that circular crested oblique weirs offer higher discharge capacity compared with some other weir shapes. A simple design method is recommended through which the lasting dimensions and the head-discharge relationship of the weir can be predicted.

Theoretical Investigation on Microcavity Coupler for Terahertz Quantum-Well Infrared Photodetectors

Resonant behaviors and absorption enhancement of metallic grating-dielectric-metal (GDM) microcavity are theoretically investigated. The GDM structure is treated as periodic unit cells of two serially-connected metal-dielectric-metal (MDM) and air-dielectric-metal (ADM) waveguide resonators. The resonant modes can be divided into three types: the LC mode, the TEM modes supported by the MDM waveguide resonator, and the TEM-TM hybrid modes supported by the whole GDM structure. The resonant frequencies of LC and TEM modes are independent on a small incident oblique angle. However, for the TEM-TM hybrid modes, each mode splits into two branches with non-zero incident angles. Based on the temporal coupled-mode theory, the intersubband absorption efficiency of multi quantum wells inserted into the GDM microcavity is calculated and discussed qualitatively. We point out that the condition of critical coupling is not the optimal condition for intersubband absorption efficiency when the metallic loss cannot be neglected. An optimization procedure is given for the design of high performance GDM-microcavity-coupled terahertz quantum-well infrared photodetectors.

Illusion and cloaking using dielectric conformal metasurfaces.

Decoration of curved topological objects with an ultrathin layer of meta-atoms, which creates a conformal metasurface, allows the scattering wavefront to be modulated willingly. Here, we demonstrate adaptive conformal metasurfaces, which are composed of subwavelength dielectric TiO2 nano-posts on curved surfaces. Further, these surfaces support novel phenomena, such as focusing, tunable anomalous refraction, cloaking, and illusion (curved holography) in the visible range. The polarization-independent cloaking is demonstrated successfully by using these high-efficiency dielectric conformal metasurfaces. Besides, the metasurfaces's performance under small oblique angles of incidence angles was similar to its performance under normal angles of incidence. Conformal metasurfaces loaded on curved objects are promising platforms for applications in miniaturized optical systems, such as medical devices, wearable electronics, and communication devices.

Analysis of the quality of slope surface in selective laser melting process by simulation and experiments

Slope surface is unavoidable and has an important effect on the quality of final fabricated product in the selective laser melting (SLM) process. In this paper, finite element simulation and experimental research on the effect of slope surface with different oblique angles are performed. In the finite element model, the difference in thermal physical properties between the fabricated part and powder material are taken into account. The temperature distribution, melt pool shape, slope surface morphology, roughness and dimensional accuracy are investigated. It shows that the melt pool depth and length are significantly influenced by the oblique angle and the tail of melt pool trends to one side as the oblique angle becomes small. The quality of slope surface increases and the dimensional deviation decreases with the increasing oblique angle. Based on the results, large oblique angle is recommended when designing part, and rotation in the vertical direction is prompted for obtaining large oblique angle when fabricating product. In addition, large dimension compensation and intensified post processing are suggested for slope surface with small oblique angle.

Pattern‐forming fronts in a Swift–Hohenberg equation with directional quenching — parallel and oblique stripes

We study the effect of domain growth on the orientation of striped phases in a Swift-Hohenberg equation. Domain growth is encoded in a step-like parameter dependence that allows stripe formation in a half plane, and suppresses patterns in the complement, while the boundary of the pattern-forming region is propagating with fixed normal velocity. We construct front solutions that leave behind stripes in the pattern-forming region that are parallel to or at a small oblique angle to the boundary. Technically, the construction of stripe formation parallel to the boundary relies on ill-posed, infinite-dimensional spatial dynamics. Stripes forming at a small oblique angle are constructed using a functional-analytic, perturbative approach. Here, the main difficulties are the presence of continuous spectrum and the fact that small oblique angles appear as a singular perturbation in a traveling-wave problem. We resolve the former difficulty using a farfield-core decomposition and Fredholm theory in weighted spaces. The singular perturbation problem is resolved using preconditioners and boot-strapping.

High-accuracy biaxial optical extensometer based on 2D digital image correlation

In two-dimensional digital image correlation (2D-DIC), the optical axis of the camera must be exactly perpendicular to the object surface to avoid the generation of out-of-plane displacement, which leads to low strain accuracy. In this work, we first studied the strain accuracy of a common optical extensometer when the optical axis of the camera is not perpendicular to the specimen surface. Derivation reveals that even a very small oblique angle θ will introduce a considerable strain error and that an opposite oblique angle θ generates an opposite strain error of the same magnitude. Therefore, taking the strain average of these two optical extensometers can almost entirely eliminate such effect of non-perpendicularity, which has the same form as the optical extensometer realized by dual-reflector imaging. Because the transverse strain of a specimen is less than its axial strain, the measurement of transverse strain requires higher strain-measurement accuracy. With the aid of a self-designed right-angled apparatus, we conveniently extend this 1D extensometer to a 2D situation, which is called the biaxial optical extensometer. Uniaxial tensile tests of a stainless-steel specimen are conducted to evaluate the strain accuracy of the biaxial optical extensometer quantitatively. Experimental results show that the transverse and axial strains obtained using the proposed biaxial extensometer are in good agreement with those obtained using strain gauges and that the proposed extensometer achieves higher strain accuracy compared to the 3D-DIC extensometer.

Transverse vortex-induced vibrations of a near-wall cylinder under oblique flows

Transverse vortex-induced vibrations (VIVs) of a near-wall cylinder under oblique flows are studied experimentally in a water flume for both increasing and decreasing velocities. The VIV responses and the wake flow patterns around the cylinder are measured with a synchronous measurement system and a PIV. The validity of the Independence Principle (IP) for a cylinder in proximity to a wall is examined in terms of the vibration amplitude, frequency and critical normal reduced velocity. The results show that the combinations of the gap ratio and oblique angle have significant effect on the VIV response of a circular cylinder. The IP is found to be valid in predicting the VIV response for small oblique angles (θ≤30°) and large gap ratios (e/D≥0.8) whereas for large oblique angles (θ>30°) or small gap ratios (e/D<0.8), the deviations from the IP are pronounced. The upper and lower critical normal reduced velocities for the onset of VIV are obtained for both increasing and decreasing velocities. Empirical relationships between the correction factor of the critical normal reduced velocity and gap ratio and the oblique angles (θ≤45°) are established. Based on the analyses of the wake flow patterns obtained by PIV, it is found that the difference in the onset of VIV for increasing and decreasing velocities corresponds to different vortex shedding modes at the initial branch: the 2S vortex shedding mode for increasing velocity and the C(2S) mode for decreasing velocity.

CFD based investigation on the impact acceleration when a gannet impacts with water during plunge diving

Plunge diving is the most commonly used feeding method of a gannet, which can make the gannet transit from air to water rapidly and successfully. A large impact acceleration can be generated due to the air-to-water transition. However, the impact acceleration experienced by the gannet during plunge diving has not been studied. In this paper, this issue is investigated by using the CFD method. The effect of the dropping height and the water-entry inclination angle on the impact acceleration is considered. The results reveal that the impact acceleration along the longitudinal body axis increases with either of the two parameters. The peak time decreases with the dropping height. A quadratic relation is found between the peak impact acceleration and the initial water-entry velocity. According to the computation, when the dropping height is 30 m (most of gannets plunge from about this height), the peak impact acceleration can reach about 23 times the gravitational acceleration, which will exert a considerable force on the gannet body. Furthermore, the pressure distribution of different water-entry inclination angles indicates that the large pressure asymmetry caused by a small oblique angle may lead to a large impact acceleration in the direction perpendicular to the longitudinal body axis and cause damage to the neck of the gannet, which partly explains the reason why a gannet performing a high plunge diving in nature enters water with a large oblique angle from the perspective of impact mechanics. The investigation on the plunge-diving behavior in this paper will inspire and promote the development of a biomimetic amphibious robot that transits from air to water with the plunge-diving mode.

Qualitative shape from shading, highlights, and mirror reflections

The human visual system has a remarkable ability to perceive three-dimensional (3-D) surface shape from shading and specular reflections. This paper presents two experiments that examined the perception of local qualitative shape under various conditions. Surfaces were rendered using standard computer graphics models of matte, glossy, and mirror reflectance and were viewed from a small oblique angle to avoid occluding contour shape cues. The subjects' task was to judge whether a marked point on each surface lay on a local hill or valley. In the first experiment, performance was lower for glossy surfaces than matte surfaces, which is contrary to findings in previous studies of quantitative shape. For mirror surfaces, performance was high despite the absence of occluding contours, and performance was increased when the environment map was brighter in the upper hemisphere as in a natural environment. The second experiment examined how subjects resolve a depth-reversal shape ambiguity where surfaces can be either upward or downward facing. An upward-facing surface prior that is known to exist for matte surfaces was also found to exist for glossy and mirror surfaces. Subjects relied entirely on this prior to resolve the depth-reversal ambiguity for matte and glossy surfaces, but relied on perspective cues as well for mirror surfaces.

Small Oblique Angle Technique for Principal-Strain Separation in Luminescent Photoelastic Coating

To determine the individual values of the two strain components by separate principal strains, a theoretical model of strain separation by oblique incidence with a new luminescent photoelastic coating configuration is presented. Considering the non-strain related refraction effect included in the total optical response at oblique incidence, the small incidence angle technique for simplifying the post-processing complexity is given. To affirm the validity of this strain separation method based on small oblique angles, the signal-to-noise ratio for providing sufficient signal intensity has been theoretically analyzed.

Numerical study on the localized surface plasmon resonance of cone-shaped nanoparticles

The effect of oblique angle on the localized surface plasmon resonance of cone-shaped nanoparticles is explored. The finite difference time domain method is applied to analyze the extinction spectra and the electric field intensity. The simulation results show that cone nanoparticles with a small oblique angle exhibit a larger resonant wavelength than those with a large oblique angle. The full width at half maximum initially decreases and then increases as the oblique angle increases, with a turning point of 17.5°. The refractive index sensitivity and the sensing sensitivity both decrease when the oblique angle of the cone nanoparticles increases, achieving a maximum figure of merit (FOM) of 14.6 RIU−1. For cone-shaped nanoparticles, the shape can be described by the power exponent m of the curve in the cross-section. The larger the power exponent m, the larger the oblique angle. Cone-shaped nanoparticles with power exponent m < 1 (concave conical surface) exhibit larger FOM than those with m > 1 (convex conical surface). The largest FOM is achieved when m = 1/3.

Relationships of Barge Bow Force–Deformation for Bridge Design

Loads generated during vessel collisions with bridges are inherently dependent on force–deformation characteristics of the impacting vessel. Currently in the United States, barge impact forces used in bridge design are computed with a force–deformation (crush–curve) model proposed by AASHTO. A recent study uncovered important limitations in the AASHTO barge-crushing model, and a revised procedure for developing barge force–deformation relationships was developed. However, relationships developed in this previous study were based on the assumption that impact occurred directly head on to the impacted pier; the scenario was unlikely. Impact more likely occurs at some oblique angle. This paper shows that barge impact forces on flat-faced pier surfaces (i.e., rectangular columns or waterline pile caps) are typically less severe when collisions occur at even small oblique angles. Thus, the current study focused on updating the prior crushing model to account probabilistically for reduced forces associated with oblique impact. In this paper, oblique impact forces were quantified by means of a series of high-resolution simulations of finite element barge bow crushing. Results obtained from these simulations were used in a probabilistic study to develop a force prediction model that implicitly accounted for the relative likelihood of impact occurring at particular angles. Findings from the current study were then integrated into the previously developed barge-crushing model to produce a design-oriented calculation framework that would permit bridge designers to account easily for force reductions that arise in oblique impact scenarios.

Pattern-forming instability induced by light in pure and dye-doped nematic liquid crystals.

We study theoretically the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle on a thin layer of homeotropically oriented nematic liquid crystal with special emphasis on the dye-doped case. The spatially periodic Hopf bifurcation that occurs as the secondary instability after the stationary Freedericksz transition is analyzed.

MERT vs tangential photon beams vs IMRT for breast cancer: a comparative dosimetry study

Purpose: Recently, energy- and intensity-modulated electron radiotherapy (MERT) has garnered growing interest for the treatment of superficial targets. In MERT, small electron beams (beamlets) of different angles, energies and intensities are optimized to achieve dose conformity both laterally and in the depth direction. The potential of MERT for breast cancer is to improve dose uniformity in the treatment volume while reducing dose to normal tissues such as the lung, heart and contralateral breast. In this work, we carried out a comparative dosimetry study to evaluate MERT, photon beam intensity-modulated radiation therapy (IMRT) and conventional tangential photon beams for the treatment of breast cancer. We also included the effects of respiration (organ motion) on each treatment modality. Materials and methods: A MERT system has been investigated, which consists of a set of software tools to perform accurate dose calculation, treatment optimization, leaf sequencing and plan analysis. A prototype electron multileaf collimator (eMLC) for accurate MERT beam delivery has also been developed. For this study, we have compared breast treatment plans (with and without nodal involvement) generated using MERT, IMRT and conventional tangential photon beams. The MERT plans were derived using our own treatment optimization software with up to 3 gantry angles and 5 nominal energies (6, 9, 12, 16, 20 MeV beams from a Varian Clinac 2100C accelerator). The tangential photon treatment plans were derived using the CMS FOCUS 3D treatment planning system with 6 MV wedged photon beams. A 6 MV anterior-posterior field was also used if there was nodal involvement. The IMRT plans were derived using the NOMOS CORVUS treatment optimization system with the same tangential beam angles of 6 MV x-rays. To remove any inconsistencies between the dose calculation algorithms used in the treatment planning system, all the plans were recalculated using the Monte Carlo method. Our Monte Carlo code system also took into account the effects of organ motion due to respiration and the effects of photon and electron leakage through the MLC and scattering off the MLC leaves. Results: In general, MERT provides better or similar target dose coverage compared with conventional wedged tangential photon beams and intensity-modulated tangential beams. Our results confirmed the findings of previous investigators that IMRT could reduce the dose to the lung, heart and contralateral breast compared to conventional tangential wedged beams (up to 5 Gy in the maximum dose). However, MERT reduces the maximum dose to the lung by up to 20 Gy and to the heart by up to 35 Gy compared to conventional tangential wedged beams. When respiration motion was considered with a 1 cm chest wall movement significant dose heterogeneities were found in regions where the tangential photon beams abut the anterior-posterior supraclav photon beams. The effect of respiratory motion on MERT dose distributions was very small since the modulated electron beams were incident normally or at relatively small oblique angles. Conclusion: Because of its superior capabilities to achieve dose conformity both laterally and in the depth direction, MERT can be developed into a useful modality for superficial targets, especially for the treatment of breast cancer. The advantages of MERT over the currently used treatment techniques include uniform target coverage and significantly reduced normal tissue toxicity. Software and hardware development is ongoing with the hope for clinical testing of this new beam modality in early 2002. Further investigations are being carried out for other treatment sites such as head and neck, lung (mesothelioma), and palliative spine cases. This work was supported in part by NIH: CA78331 and by DOD US Army Breast Cancer Research Program: BC971292.

前面斜交すみ肉溶接継目の実験 : すみ肉溶接による柱・梁仕口に関する研究(その2)

In this paper, tensile tests were carried out to investigate strength of oblique crossing joint by fillet weld. The results of macro tests explain that inadequate penetration of fillet weld occurred at the acute side of welds because of the small oblique angle. The results of tensile tests explain as follows ; 1) The failure of joint often occurred at the obtuse side of welds. 2) Failure angle of welds disagrees with the angles of those minimum throat thicknesses. 3) The strength of fillet weld decreases with smaller oblique angle.

Electron cyclotron heating and current drive in the TJ-II stellarator

Electron cyclotron resonance heating (ECRH) has become an attractive technique in today's fusion experiments not only as a heating mechanism but also as a diagnostic tool and a way to induce controllable currents through electron cyclotron current drive (ECCD). In this paper we show, using ray tracing simulations, how one can address all these issues with the ECRH system designed for the TJ-II stellarator. This ECRH set up consists of two 500 kW gyrotrons at f = 53.2 Ghz coupled to the plasma through two quasi-optical transmission lines, placed at two stellarator symmetric positions, and equipped with an internal steerable mirror. Using the three-dimensional (3D) Hamiltonian ray tracing code, TRECE, almost full single-pass absorption with localized power deposition is found for both on- and off-axis heating for any magnetic configuration. The simulations also show that it is possible to induce an appreciable ECCD despite the small oblique incidence angles attainable with the movable mirrors because of the rapid variation of the magnetic field direction and strength with the toroidal angle in TJ-II.

Wave Reflection from Breakwater

A new method is presented for estimating the reflection of a random, multidirectional sea from a coastal structure. The technique is applicable to an array of wave gauges of arbitrary geometry deployed seaward of the reflector. An expansion for small oblique wave-incidence angles is used to derive an approximate relationship between measured array cross-spectra and a small number of parameters that describe the incident-wave properties and the reflectivity of the structure. Model tests with simulated array data demonstrate that the gross properties of incident and reflected waves can be accurately estimated for wave-incidence angles less than about 30°. The new method is applied to array data acquired offshore of a permeable, rubble-mound breakwater in Monterey Bay, California. The estimated reflection coefficients decrease approximately linearly with increasing frequency. Whereas the observed reflections depend only weakly on the incident-wave energy, the fraction of the incident-wave energy flux transmitted through the breakwater decreases with encreasing wave energy, suggesting that dissipation is enhanced with large-amplitude waves.