Facet Planes Research Articles

A binocular reconstruction based on perspective projection constraints and its application on robot eye‐hand coordination

Stereo matching algorithms have been developed for many years but basically focus only on the implementation of existing datasets and are rarely applied to real scenarios, such as industrial robot scenarios. Traditional stereo matching algorithms have a high error rate, and deep learning algorithms are difficult to obtain good results in real scenarios because of their weak generalisation ability and difficult access to training data. In order to use stereo matching algorithms for industrial robot guidance, it is better to design a new traditional algorithm with low time complexity for the characteristics of industrial robot scenarios dominated by planar facets. This paper proposes a new matching method based on subrows of pixels, instead of individual pixels, in order to improve robustness of matching and reduce running time. First, the pixel strings from the same row of the left and right images are divided into several colour-identical or colour-gradient segments. Then, the colour and length of the two left and right pixel segment are used as clues to determine a matching relation and obtain the matching type. Then, all match types can be determined according to non-crossing mapping. Each match type can reason backward to the corresponding spatial state of the stimulus source so that the disparity of pixels in pixel segments representing the spatial state can be calculated. This new matching method makes full use of the stimulus homology constraints and projective geometric constraints of row-aligned images. The method can obtain good results in industrial robot scenarios and be applied for industrial robot guidance.

A Stereo Matching Algorithm for High‐Precision Guidance in a Weakly Textured Industrial Robot Environment Dominated by Planar Facets

AbstractAlthough many algorithms perform very well on certain datasets, existing stereo matching algorithms still fail to obtain ideal disparity images with high precision in practical robotic applications with weak or untextured objects. This greatly limits the application of binocular vision for robotic arm guidance. Traditional stereo matching algorithms suffer from disparity loss, dilation and other problems, and deep learning algorithms have weakly generalization ability, making high‐accuracy results impossible with non‐training images. We propose an algorithm that uses segments and edges as matching units. We find the mapping relationship between two‐dimensional images and three‐dimensional scenes using segments. The algorithm obtains highly accurate results in industrial robotic applications with mainly planar facets. We combine it with a deep learning algorithm to obtain very good high‐accuracy results in both general scenes and applications of industrial robots. The algorithm effectively improves the non‐linear optimization ability of traditional algorithms and generalization ability of deep learning, and provides an effective method for the binocular vision guidance of industrial robotic scenes. We used the algorithm to guide the robot arm for threading with a success rate of 70%.

Use of Weight-Bearing Computed Tomography in the Evaluation of Abnormal Hindfoot Morphology in Charcot-Marie-Tooth Patients

Category:Hindfoot; OtherIntroduction/Purpose:The hindfoot deformity seen in Charcot-Marie-Tooth disease (CMT) is poorly understood, and the contribution of abnormal bone morphology has never been conclusively demonstrated. The purpose of this study was to compare the three-dimensional (3D) bone morphology of the talus, calcaneus and navicular in a cohort of CMT patients versus a control population. We used the data obtained from weight-bearing computed tomography (WBCT) to reconstruct the geometric shape of each bone using 3D surface meshing techniques. Surface mesh analysis of this type is commonly used in engineering to evaluate and optimize 3D geometries and structures.Methods:A total of 17 WBCTs from 15 patients (average age 24) with CMT who underwent WBCT without previous surgeries, degenerative changes or open physes were included. These were compared to 20 healthy control WBCTs. Calcaneal measurements included the radius of curvature and the angle between the posterior tuberosity and posterior facet in the sagittal plane. Talar measurements include axial and sagittal declination between the body and neck as well as coronal rotation of the talar head relative to the body. Surface-mesh model analysis was performed comparing the average of the CMT cohort to the controls using CT analysis software (Disior Bonelogic). Means were compared with a t test (p<0.05).Results:CMT patients had significantly less sagittal declination (plantarflexion) versus controls (14.9 versus 25.1 degrees respectively) (p<0.01). Similarly, CMT patients had less talar head coronal rotation versus controls (30.2 versus 42.5 degrees respectively) (p<0.001). There was no difference in axial rotation of the talar neck versus body between the groups (p=0.88). The calcaneal radius of curvature in CMT patients was significantly smaller than the control population (716.6 versus 2143.5 mm respectively) (p<0.05). Angular differences were also significant between the posterior tuberosity and posterior facet of the subtalar joint in the sagittal plane (CMT 57.7 degrees, control 67.9 degrees) (p<0.001). Additionally, surface-mesh model analysis demonstrated the largest differences in morphology at the navicular tuberosity, medial talar head, sustentaculum tali and anterior process of the calcaneus (Figure 1).Conclusion:This is the first study to quantify the morphologic differences in osteology seen in CMT patients. The decreased sagittal declination of the talar neck is seen with a reciprocal decreased slope of the posterior facet of the calcaneus. The coronal rotation of the talar head and abnormal navicular tuberosity morphology shows changes seen in patients with CMT and may be attributed to unbalanced pull of the posterior tibial tendon during development. These findings will help refine, and potentially revolutionize the surgical reconstruction of cavovarus deformity in CMT patients.

Twin boundary formation at a grain-boundary groove during the directional solidification of InSb

We investigated twin boundary formation during directional solidification of the compound semiconductor InSb. We directly observed a groove formed at the junction of a solid–liquid interface and a Σ9 grain-boundary by optical microscopy. When the depth of the grain-boundary groove reached about 100 μm, rapid growth occurred to fill the groove. We found that two facet planes of the grain-boundary groove became twin boundary planes. Calculations of the change in free energy associated with nucleation at the grain-boundary groove indicates that the preferential twin nucleation occurs at the bottom of the groove, consistent with the direct observations in this study.

(Invited) Selective Epitaxy of Submicron Ge Wire Structures for Photodetectors and Optical Modulators in Si Photonics

Ge epitaxial layer on a Si-on-insulator substrate has been applied to waveguide photodetectors (PDs) in Si photonics, which operate at the optical communication wavelengths (1.3–1.6 µm). For enhancing the operating frequency over 50 GHz with keeping a high photodetection efficiency, a sub-micron-wide Ge wire structure with a lateral pin junction is effective because of the RC delay smaller than that for conventional vertical pin PDs. Such a Ge wire structure allows a single-mode light propagation, being also applicable to electro-absorption optical modulators (EA-MODs) based on the Franz-Keldysh effect. Here, in terms of higher-performance PDs and EA-MODs, sub-micron Ge wire structures by selective epitaxial growth on Si are presented. Bandgap engineering is discussed utilizing a control of grown-in tensile strain in sub-micron Ge.Figure 1(a) shows a typical cross-sectional scanning electron microscope image of a Ge wire structure with the width as narrow as 0.6 µm. The Ge wire in the [110] direction was selectively grown on an exposed Si (001) surface in a SiO2-covered Si substrate by ultrahigh-vacuum chemical vapor deposition at 700°C. The wire surface was surrounded mainly with inclined {113} and {111} facet planes, remaining a narrow (001) top plane. For protecting the fragile Ge surface, a Si cap layer was subsequently grown at 600°C, whereas a surface roughening was unfavorably induced on the {113} planes near the boundary with the {111} plane, as in Fig. 1(b). Raman spectra show that a SiGe alloy was accompanied on the wire surfaces, although no such SiGe was detected on the (001) plane of wide mesa top [1]. Based on theoretical analyses, a mass transport together with a Si-Ge interdiffusion would be induced by a stress concentration at the {113}/{111} facet boundaries. It is important that the roughening and alloying were significantly suppressed by decreasing the growth temperature for the Si cap layer to 530°C, as in Fig. 1(c).Typical photoluminescence (PL) spectra are shown in Fig. 1(d). For the Ge wire structure, the PL peak due to the direct transitions was located at the wavelength of 1.55 µm, which is shorter than 1.57 µm for the blanket Ge film on Si. The peak position is similar to that for a bulk Ge wafer. The blue shift for the wire corresponds to a widening of direct bandgap, which results from an elastic relaxation [2] of grown-in tensile strain generated by the thermal expansion mismatch with the Si substrate. The blue shift plays a significant role for Ge EA-MODs. As reported recently [3], in contrast to the operating wavelength range of > 1.60 µm in previous studies, EA-MODs of a sub-micron Ge wire favorably operates in the 1.55 µm range of C band (1.530–1.565 µm).[1] Y. Ishikawa et al., Proc. SPIE 11193, 1119309 (2019).[2] M. Nishimura et al., ECS Trans. 86, 3 (2018).[3] J. Fujikata et al., Opt. Express 28, 33123 (2020). Figure 1

Few-Molecule Strong Coupling with Dimers of Plasmonic Nanoparticles Assembled on DNA.

Hybrid nanostructures, in which a known number of quantum emitters are strongly coupled to a plasmonic resonator, should feature optical properties at room temperature such as few-photon nonlinearities or coherent superradiant emission. We demonstrate here that this coupling regime can only be reached with dimers of gold nanoparticles in stringent experimental conditions, when the interparticle spacing falls below 2 nm. Using a short transverse DNA double-strand, we introduce five dye molecules in the gap between two 40 nm gold particles and actively decrease its length down to sub-2 nm values by screening electrostatic repulsion between the particles at high ionic strengths. Single-nanostructure scattering spectroscopy then evidence the observation of a strong-coupling regime in excellent agreement with electrodynamic simulations. Furthermore, we highlight the influence of the planar facets of polycrystalline gold nanoparticles on the probability of observing strongly coupled hybrid nanostructures.

Effect of texture characteristics on the high-cycle fatigue properties of a Ti-6Al-4V alloy

A Ti-6Al-4V alloy was rolled at different temperatures and subsequently annealed to obtain fatigue samples with different texture characteristics. The samples were then subjected to tension-tension high-cycle fatigue (HCF) tests and the fracture morphology was observed to correlate the texture characteristics with the HCF properties. The results show that the texture intensity significantly affects the HCF strength for the equiaxed microstructure of Ti-6Al-4V alloys with an equivalent grain size and the same texture type; also, the HCF strength decreases with increasing texture intensity. The fracture morphology observation and Schmid factor calculation show that planar facets, which are a characteristic feature of crack initiation sites, are formed due to the strength mismatch caused by the inhomogeneous slip distribution favored either for prismatic or basal slip. The effect of the texture intensity on the HCF properties can be explained by the influence of the number of pile-up locations of ‘soft’ grains neighboring ‘hard’ grains in the typical Stroh model that elucidates the planar facet formation mechanism.

Si-capping-induced surface roughening on the strip structures of Ge selectively grown on an Si substrate

Si-capping-induced surface roughening, accompanying Si–Ge alloying, is reported for strip structures of Ge selectively grown on Si via ultrahigh vacuum chemical vapor deposition. A 0.7-μm-wide strip structure of Ge running in the [110] direction, as well as a 100-μm-wide mesa structure, is selectively grown on an Si (001) surface exposed in an SiO2-masked Si substrate. In contrast to a wide mesa structure with a Ge thickness of 0.5 μm, composed of a (001) plane at the top and {113} facet planes at the sidewalls, the (001) top plane almost disappears for the narrow strip structure. The strip is mainly surrounded with inclined {113} planes near the top and adjacent {111} planes at the side, while the structure near the bottom edges depends on the growth temperature (600/700 °C). An Si cap layer with a thickness of 10 nm or larger is subsequently grown at 600 °C to protect the fragile Ge surface. The scanning electron microscopy observations reveal a roughened surface on the {113} planes, with depressions specifically induced near the boundary with the {111} planes. The Raman spectra indicate that an SiGe alloy is formed on the strip and the wide mesa sidewalls due to the Si–Ge interdiffusion. There is no such SiGe alloy on the (001) plane of the wide mesa top. The Si cap layer with a misfit strain probably works as a stressor for the underlying Ge, applying stress concentrated around the facet boundaries and inducing a mass transport alongside the Si–Ge interdiffusion for strain relaxation. In terms of the fabrication of practical devices, it is important to suppress the roughening and alloying significantly by decreasing the growth temperature for the Si cap layer from 600 to 530 °C.

Tropism of Sub-Axial Cervical Facet Joints Is Not Related to Segmental Movement during Active Movement or Therapist-Perceived Symptomatic Locations

Tropism, or asymmetry, of facet joints in the cervical spine has been found to be related to degenerative changes of the joints and discs. Clinicians often assume that differences in segmental mobility are related to tropism. The aims of this study were to determine the relationship between asymmetry of facet joints in the sub-axial cervical spine and (1) segmental mobility and (2) spinal levels perceived by therapists to have limited mobility. Eighteen participants with idiopathic neck pain had MRIs of their cervical spine in neutral and at the end of active rotation. Angular movement and translational movement of each motion segment was calculated from 3D segmentations of the vertebrae. A plane was fitted to the facet on each side. Tropism was considered to be the difference in the orientation of the facet planes and ranged from 1 to 30° with a median of 7.7°. No relationships were found between the extent of tropism and either segmental movement or locations deemed to be symptomatic. Tropism in the sub-axial cervical spine does not appear to be related to segmental mobility in rotation or to levels deemed to be symptomatic.

Relaxing the Small Facet Size Requirement for the Far-Field Calculation of Large Reflector Antennas

The accurate calculation of the far-field of a large reflector antenna based on the set of discrete reflector points resulting from a structural analysis of the antenna is one of the key problems in the integrated structural-electromagnetic optimization of such antennas. In this study, the classical method that extends the discrete set of points into flat triangular facets on the basis of which the far-field is calculated is considerably upgraded. The innovation is that the proposed method makes full use of the exact knowledge of the systematic error between the ideal reflector surface and its faceted counterpart, and uses this known systematic error to upgrade the calculation of the mechanically deformed reflector, whose surface is composed of corresponding planar facets. Two versions are introduced, the single-grid version and the double-grid version. The double-grid version makes use of a double grid to even further refine the description of the systematic error. Based on this, the dichotomy method is used to quickly obtain the maximum size of the facets that still results in the required precision of the far-field calculation. In the examples given, concerning 50 m standard and 33 m offset reflector antennas operated at 60 GHz, the size of the small facets can be relaxed considerably, yielding much larger facets (such as more than 200 times the operating wavelength for the 50-m standard antenna) for a required far-field accuracy of -60 dB with respect to the main lobe level.

Design of an illumination system for high numerical aperture anamorphic extreme ultraviolet projection lithography.

The illumination system design for high numerical aperture (NA) anamorphic objectives is a key challenge for extreme ultraviolet lithography. In this paper, a reverse design method of the off-axis mixed-conic-surface-type relay system and an automatic arrangement method of field facets are proposed to design a high NA anamorphic illumination system. The two off-axis relay mirrors are fitted into different conic surfaces based on the conjugation of the mask plane and field facet and that of the illumination exit pupil and pupil facet. To eliminate ray obscuration between neighboring field facets, the field facets are automatically arranged according to the distances that are determined by the relative tilt angles of neighboring field facets under the current illumination mode. The proposed methods are applied in the design of an illumination system matching the NA0.60 anamorphic objective. Simulation results show that the uniformity of the scanning energy distribution can reach 99% on the mask plane under different illumination modes.

In-situ TEM investigation of nano-scale helium bubble evolution in tantalum-doped tungsten at 800°C

The aim of this work is to probe the helium-induced defect production and accumulation in 40 keV He+ irradiated polycrystalline W and its alternative alloy W-5wt.%Ta using transmission electron microscopy (TEM) combined with in-situ helium irradiation at 800°С. A maximum damage level of 1 dpa with a maximum He-to-dpa ratio of 5.5 at%/dpa has been reached in this work for both materials, which corresponds to an ion fluence of 7.33 × 1016 He+/cm2. The presence of radiation-induced dislocation loops was not observed at this temperature. The low density of the incipient bubbles in W has been already detected at 0.004 dpa, which corresponds to a fluence of 3.3 × 1014He+/cm2. The experiments conducted at 800°C have shown that the addition of 5wt.% of tantalum into tungsten may diminish the binding of He ions with vacancies into complexes, which serve as the core of the bubble, thus hindering helium bubble formation below 0.02 dpa and their further growth and population at higher damage levels. By exceeding the damage dose ≥0.3 dpa, a progressive transition from a spherical to a faceted shape of the bubbles has been observed in W but not in the W-5Ta alloy. At 1 dpa, >80% of the bubbles in W were of the faceted type with the facet planes of {110}.

Active facet determination of layered double hydroxide for oxygen evolution reaction

Correlation of edge area ratio and OER activity, cyanate inhibiting-probe and DFT calculation demonstrate that edge facet of LDHs is the real active facet in comparison with plane facet. Oxygen evolution reaction (OER) plays an indispensable role in developing renewable clean energy resources. One of the critical bottlenecks for the reaction is the development of highly efficient electrocatalyst to decrease the high overpotentials of four-electron transfer process of OER. Recently, layered double hydroxides (LDHs) have been widely investigated among the most promising electrocatalysts for OER due to their high intrinsic activity, excellent stability as well as low-cost. However, it remains unclear how the exposed facet of the LDHs affects their electrocatalytic activity. Here we elucidate the active edge facet of LDHs towards OER by combining the finely control of edge facet ratio coupled with molecular probe method and computational calculation. The LDHs with higher edge facet area ratio show superior activity with low onset potential as well as decreased Tafel slope. The active edge site is further proved by blocking the unsaturated edge sites with cyanate probe anion, of which the adsorption largely inhibits OER activity. Furthermore, based on density functional theory (DFT) calculation, two-dimensional map of theoretical overpotentials as a function of Gibbs free energy reveals that the edge (100) facet exhibits a much higher OER activity than basal plane (001) facet.

Technical Note: Evaluating automatic tube current modulation in CT using the standard CTDI dosimetry phantom.

To assess the utility of the standard body CTDI phantom in characterizing the operation scheme of tube current modulation (TCM) systems in CT. The body CDTI phantom was used to characterize two TCM systems: TCM1 and TCM2 , implemented in scanners from different vendors. The phantom was aligned at the gantry isocenter in two configurations. In configuration A, the facet planes of the phantom were parallel to the patient table, while in configuration B they were vertical to the patient table and parallel to the patient's long axis. Acquisitions were performed using the routine abdominal examination protocol. mA(z) profiles were recorded from images' DICOM header. The water equivalent diameter (dw ) and oval ratio (OR) were calculated as a function of z-axis location. Image noise was defined as the standard deviation (SD) of the mean Hounsfield unit value measured in a region of interest at the center of the phantom's image. Regression analysis was performed to modulated mA and SD vs dw and OR. The spatial concordance between the change in phantom size and change in mA (SCmA ) was calculated as the percent difference in the slope of mA(z) change between the 1st and 2nd half of the phantom. The corresponding spatial concordance between the change in phantom size and change in image noise (SCnoise ) was calculated. Modulated mA(z) along the z-axis did not substantially differentiate between configurations A and B. Correlation between ln(mA) and OR was found to be higher compared to correlation between ln(mA) and dw . SCmA was 48% for TCM1 and 33% for TCM2 . The corresponding SCnoise was 29% for TCM1 and 16% for TCM2 . Apart from routine CT dosimetry evaluations, the standard CTDI phantom positioned in configuration A or B may additionally be used by medical physicists to evaluate the performance of TCM operational characteristics.

Stabilization of cold-field-emission current from a CeB6 single-crystal emitter by using a faceted (100) plane

A cerium hexaboride (CeB6) single crystal grown by the floating-zone method has a low work function of about 2.6 eV, and along with lanthanum hexaboride (LaB6), it is one of the most popular cathode materials. It has been widely used as the thermionic emitter of electron microscopes, such as SEMs and TEMs. However, cold-field emitters (CFEs) based on CeB6 and LaB6 have not been put to practical use due to their insufficient emission stability compared to that of conventional tungsten (W)-CFEs. In consideration of that background, in the present study, the stability of the emission current from a CeB6 single-crystal CFE was improved by using the (100) plane at the faceted tip of the single crystal. The CeB6⟨100⟩ single crystal was processed by electrochemical etching and successive high-temperature field evaporation and faceting under an appropriate electric field to make a (100) plane at the apex of the crystal. The improved CeB6(100)-CFE emitted a monochromatic electron beam, which has about three-quarters of the energy width of that of W(310)-CFEs. Emission current from the (100) plane maintained low emission noise, and emission decay in the electron-gun chamber of the SEM was suppressed. The resulting current noise is low enough to produce SEM images without image deterioration, and the relatively small decay makes it possible to use the CeB6(100) emitter for one flashing process per day.

Determination of Facet Plane and Cleavage Fracture Plane of the Top Dross Formed in a Molten Zinc Bath

Determination of Facet Plane and Cleavage Fracture Plane of the Top Dross Formed in a Molten Zinc Bath

Shuffling mode competition leads to directionally anisotropic mobility of faceted Σ11 boundaries in fcc metals

Faceted grain boundaries can migrate in interesting and unexpected ways. For example, faceted {\Sigma}11 <110> tilt grain boundaries were observed to exhibit mobility values that could be strongly dependent on the direction of migration. In order to understand whether this directionally-anisotropic mobility is a general phenomenon and to isolate mechanistic explanations for this behavior, molecular dynamics simulations of bicrystals evolved under an artificial driving force are used to study interface migration for a range of boundary plane inclination angles and temperatures in multiple face centered cubic metals (Al, Ni, and Cu). We find that directionally-anisotropic mobility is active in a large fraction of these boundaries in Ni and Cu and should therefore impact the coarsening of polycrystalline materials. On the other hand, no such anisotropy is observed in any of the Al boundaries, showing that this behavior is material-dependent. Migration of the faceted boundaries is accomplished through transformation events at facet nodes and incommensurate boundary plane facets, which are termed shuffling modes. Three major shuffling modes have been identified, namely Shockley shuffling, slip plane shuffling, and disordered shuffling. A shift from the first two ordered modes to the third disordered mode is found to be responsible for reducing or removing directionally-anisotropic mobility, especially at the highest temperatures studied.

Interplay of intrinsic and extrinsic states in pinning and passivation of m-plane facets of GaN n-p-n junctions

Intrinsic and extrinsic pinning and passivation of m-plane cleavage facets of GaN n-p-n junctions were investigated by cross-sectional scanning tunneling microscopy and spectroscopy. On freshly cleaved and clean p-type GaN(101¯0) surfaces, the Fermi level is found to be extrinsically pinned by defect states, whereas n-type surfaces are intrinsically pinned by the empty surface state. For both types of doping, air exposure reduces the density of pinning states and shifts the pinning levels toward the band edges. These effects are assigned to water adsorption and dissociation, passivating intrinsic and extrinsic gap states. The revealed delicate interplay of intrinsic and extrinsic surface states at GaN(101¯0) surfaces is a critical factor for realizing flatband conditions at sidewall facets of nanowires exhibiting complex doping structures.

Cavity etching evolution on the A-plane of sapphire crystal in molten KOH etchant

Chemical wet etching technology is widely applied in semiconductor device fabrication such as the patterned sapphire substrates. However, the etching of pre-formed structure is still lack of investigations, which has potential applications in the preparation of particular devices. By using molten KOH etchant, the present work studied the wet etching behaviors of cavity on the A-plane of sapphire crystal in three-dimensional space and revealed the etching kinetics. It was demonstrated that the cavity will evolve into a complicate symmetric shape with multiple facet planes during etching. The width of the cavity is gradually expanded however the depth of the cavity is stable during etching, where the Arrhenius model was held, indicating that the etching process is realized by step flow removal of atoms. The present results improve the understanding of the morphology evolution and relevant kinetics of a pre-formed structure on sapphire crystal during wet etching, which shed further light on the single crystal wet etching technology for device fabrication.

Equilibrium shapes of facetted 3D metal nanoclusters intercalated near the surface of layered materials

Experimental studies indicate that 3D crystalline metal nanoclusters (NCs) intercalated under the surface of graphite have flat-topped equilibrated shapes. We characterize the shapes of these facetted NCs sandwiched between a blanketing graphene layer and the underlying graphite substrate. Specifically, we focus on the cases of fcc Cu and hcp Fe NCs. The analysis involves numerical minimization of the system energy for a specified NC volume and NC height, the latter corresponding to the separation between parallel top and bottom facets. Our numerical analysis quantifies how the distance of the side facet planes from center of the nanocluster varies linearly with a natural characteristic linear dimension of the nanocluster. Calculated shapes of fcc Cu and hcp Fe NCs are consistent with the hexagonal footprints observed in scanning tunneling microscopy studies.