Autonomous wind turbine inspection using a quadrotor

There has been explosive growth of wind farm installations in recent years due to the fact that wind energy is gaining worldwide popularity. However, the maintenance of these offshore or onshore wind turbines, especially in remote areas, remains a challenging task. In this work, vision-based autonomous wind turbine inspection using a quadrotor is designed based on realistic assumptions. Both simulation and Hardware-In-the-Loop (HIL) testing results have shown the effectiveness of the proposed approach

Efficient nitrogen-vacancy centers' fluorescence excitation and collection from micrometer-sized diamond by a tapered optical fiber

Efficiently excite nitrogen-vacancy (NV) centers in diamond and collect their fluorescence significantly benefit the fiber-optic-based NV sensors. Here, using a tapered optical fiber (TOF) tip, we significantly improve the efficiency of the laser excitation and fluorescence collection of the NV, thus enhance the sensitivity of the fiber-optic based micron-sized diamond magnetic sensor. Numerical calculation shows that the TOF tip delivers a high numerical aperture (NA) and has a high fluorescence excitation and collection efficiency. Experiments demonstrate that using such TOF tip can obtain up to over 7-fold the fluorescence excitation efficiency and over15-fold the fluorescence collection efficiency of a flat-ended (non-TOF) fiber. Such fluorescence collection enhances the sensitivity of the optical fiber-based diamond NV magnetometer, thus extending its potential application region.Comment: 11 pages, 13 figure

Seismic response of a mid-story-isolated structure considering soil–Structure interaction in sloping ground under three-dimensional earthquakes

A mid-story-isolated structure is developed from a base-isolated structure. Mid-story-isolated structures located in sloping ground have become a research hotspot in recent years. It is important to consider the soil–structure interaction (SSI) effects and multi-dimensional earthquakes on these structures. This paper established a model of the mid-story-isolated structure considering SSI in sloping ground. An elastic–plastic time history analysis was carried out under the one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) earthquakes. Under 3D earthquakes, the traditional 2D isolated bearing has limited damping capacity. Therefore, two kinds of 3D isolated bearings were designed. Results show that the seismic response of the mid-story-isolated structure considering SSI in sloping ground can be amplified compared with that of the mid-story-isolated structure without considering SSI. The seismic response of the structure under 3D earthquakes is more significant than that under 2D earthquakes and 1D earthquakes. For the two kinds of 3D isolated bearings, the minimum reduction rate of tensile and compressive stress is about 46% compared with that of the traditional 2D isolated bearings. When the 3D isolated bearings are used, the stress of the soil foundation decreases, which is more conducive to the stability of the soil foundation

Enhancing fluorescence excitation and collection from the nitrogen-vacancy center in diamond through a micro-concave mirror

We experimentally demonstrate a simple and robust optical fibers based method to achieve simultaneously efficient excitation and fluorescence collection from Nitrogen-Vacancy (NV) defects containing micro-crystalline diamond. We fabricate a suitable micro-concave (MC) mirror that focuses scattered excitation laser light into the diamond located at the focal point of the mirror. At the same instance, the mirror also couples the fluorescence light exiting out of the diamond crystal in the opposite direction of the optical fiber back into the optical fiber within its light acceptance cone. This part of fluorescence would have been otherwise lost from reaching the detector. Our proof-of-principle demonstration achieves a 25 times improvement in fluorescence collection compared to the case of not using any mirrors. The increase in light collection favors getting high signal-to-noise ratio (SNR) optically detected magnetic resonance (ODMR) signals hence offers a practical advantage in fiber-based NV quantum sensors. Additionally, we compacted the NV sensor system by replacing some bulky optical elements in the optical path with a 1x2 fiber optical coupler in our optical system. This reduces the complexity of the system and provides portability and robustness needed for applications like magnetic endoscopy and remote-magnetic sensing.Comment: 6 pages, 8 figure

The Sihailongwan Maar Lake, northeastern China as a candidate Global Boundary Stratotype Section and Point for the Anthropocene Series

Sihailongwan Maar Lake, located in Northeast China, is a candidate Global boundary Stratotype Section and Point (GSSP) for demarcation of the Anthropocene. The lake’s varved sediments are formed by alternating allogenic atmospheric inputs and authigenic lake processes and store a record of environmental and human impacts at a continental-global scale. Varve counting and radiometric dating provided a precise annual-resolution sediment chronology for the site. Time series records of radioactive (239,240Pu, 129I and soot 14C), chemical (spheroidal carbonaceous particles, polycyclic aromatic hydrocarbons, soot, heavy metals, δ13C, etc), physical (magnetic susceptibility and grayscale) and biological (environmental DNA) indicators all show rapid changes in the mid-20th century, coincident with clear lithological changes of the sediments. Statistical analyses of these proxies show a tipping point in 1954 CE. 239,240Pu activities follow a typical unimodal globally-distributed profile, and are proposed as the primary marker for the Anthropocene. A rapid increase in 239,240Pu activities at 88 mm depth in core SHLW21-Fr-13 (1953 CE) is synchronous with rapid changes of other anthropogenic proxies and the Great Acceleration, marking the onset of the Anthropocene. The results indicate that Sihailongwan Maar Lake is an ideal site for the Anthropocene GSSP

An optical see-through head mounted display with addressable focal planes

Figure 1. Move clip (VariFocalPlane.wmv) of a virtual torus rendered by the see-through HMD moving along the z-axis in the augmented space. The three subset clips were captured by a camcorder which was manually focused at (a) 16cm, (b) 33cm, and (c) 100cm, respectively. Most existing stereoscopic head mounted displays (HMDs), presenting a pair of stereoscopic images at a fixed focal distance, lack the ability to correctly render the naturally coupled accommodation and convergence cues. Psychophysical studies have shown that such displays may cause many adverse consequences such as visual fatigue, diplopic vision, degraded oculomotor response, and depth perception errors. In this paper, we present a see-through HMD with addressable focal planes utilizing a novel active optical element—a liquid lens. The element, with a varying optical power from-5 to 20 diopters, is able to address the focal distance of the HMD from infinity to the near point of the eye. A monocular prototype was built from off-the-shelf elements and experimental results are presented to validate the proposed designs. We also describe both subjective and objective measurements of the accommodation responses of the viewer to the focal distances presented by the prototype

Influencing factors analyses and matching design of ultimate bearing capacity of external pressure tank

ObjectivesThis paper aims to discuss the relationship between the ultimate bearing capacity of a pressure hull and pressure tank under the same strength margin, and obtain a matching design with the equivalent ultimate bearing capacity and strength margins accordingly. MethodsTo this end, a typical external pressure tank is taken as the research object. On the basis of evaluating the stability and ultimate bearing capacity of the initial structural scheme, the influences of the thicknesses of the pressure tank shell, solid floor and transverse bulkhead on the ultimate bearing capacity are studied. The initial scheme is then adjusted to obtain a scheme with the equivalent strength margins of the pressure hull and pressure tank. In this context, the relationship between the ultimate bearing capacity of the pressure hull and pressure tank is discussed. By strengthening the pressure hull to match the ultimate bearing capacities of the pressure tank and pressure hull, the corresponding strength margins are obtained. ResultsThe results show that thinning the pressure tank shell by 30%, solid floor shell by 33.3% and transverse bulkhead shell by 30% reduces the ultimate bearing capacity of the tank by 16.5%, 36.4% and 0.17% respectively. ConclusionsAs further analyses show, under the condition of the same strength margin, the ultimate bearing capacity of the pressure hull is much lower than that of the pressure tank. When the strength margin of the pressure tank is about 25% and that of the pressure hull is about 40%, the ultimate bearing capacities of the pressure hull and pressure tank are roughly the same

Thin and Large Depth-Of-Field Compound-Eye Imaging for Close-Up Photography

Large depth of field (DOF) and stereo photography are challenging yet rewarding areas of research in close-up photography. In this study, a compound-eye imaging system based on a discrete microlens array (MLA) was implemented for close-range thin imaging. A compact imaging system with a total length of 3.5 mm and a DOF of 7 mm was realized using two planar aspherical MLAs in a hexagonal arrangement. A new three-layer structure and discrete arrangement of sublenses were proposed to suppress stray light and enable the spatial refocusing method, which restores image information at different object depths. The system is successfully fabricated, and the system performance is carefully investigated. Our system offers a large depth of field, high resolution, and portability, making it ideal for close-up photography applications requiring a short conjugate distance and small device volume, while also addressing the issue of crosstalk between adjacent channels