Design of 3D Imaging Lidar Optical System for Large Field of View Scanning

3D lidar has been widely used in various fields. The MEMS scanning system is one of its most important components, while the limitation of scanning angle is the main obstacle for its application in various fields to improve the demerit. In this paper, a folded large field of view scanning optical system is proposed. The structure and parameters of the system are determined by theoretical derivation of ray tracing. The optical design software Zemax is used to design the system. After optimization, the final structure performs well in collimation and beam expansion. The results show that the scan angle can be expanded from ±5° to ±26.5°, and finally parallel light scanning is realized. The spot diagram at a distance of 100 mm from the exit surface shows that the maximum radius of the spot is 0.506 mm with a uniformly distributed spot. The maximum radius of the spot at 100 m is 19 cm, and the diffusion angle is less than 2 mrad. The energy concentration in the spot range is greater than 90% with a high system energy concentration, and the parallelism is good. This design overcomes the shortcoming of the small mechanical scanning angle of the MEMS lidar, and has good performance in collimation and beam expansion. It provides a design method for large-scale application of MEMS lidar.

Dynamics of a Laser-Induced Bubble above the Flat Top of a Solid Cylinder—Mushroom-Shaped Bubbles and the Fast Jet

The dynamics of a laser-induced bubble on top of a solid cylinder is studied both experimentally and numerically. When the bubble is generated close to the flat top along the axis of the cylinder and its maximum radius exceeds the one of the flat top surface, it collapses in the form of a mushroom with a footing on the cylinder, a long stem and a hat-like cap typical for a mushroom head. The head may collapse forming a thin, fast liquid jet into the stem, depending on bubble size and bubble distance to the top of the cylinder. Several experimental and numerical examples are given. The results represent a contribution to understand the behavior of bubbles collapsing close to structured surfaces and in particular, how thin, fast jets are generated.

Static cylindrical symmetric solutions in the Einstein-Aether theory

In this work, we present all the possible solutions for a static cylindrical symmetric spacetime in the Einstein-Aether (EA) theory. As far as we know, this is the first work in the literature that considers cylindrically symmetric solutions in the theory of EA. One of these solutions is the generalization in EA theory of the Levi-Civita (LC) spacetime in General Relativity (GR) theory. We have shown that this generalized LC solution has unusual geodesic properties, depending on the parameter [Formula: see text] of the aether field. The circular geodesics are the same of the GR theory, no matter the values of [Formula: see text]. However, the radial and [Formula: see text]-direction geodesics are allowed only for certain values of [Formula: see text] and [Formula: see text]. The [Formula: see text]-direction geodesics are restricted to an interval of [Formula: see text] different from those predicted by the GR and the radial geodesics show that the motion is confined between the origin and a maximum radius. The latter is not affected by the aether field but the velocity and acceleration of the test particles are besides, for [Formula: see text], when the cylindrical symmetry is preserved, this spacetime is singular at the axis [Formula: see text], although for [Formula: see text] exists interval of [Formula: see text] where the spacetime is not singular, which is completely different from that one obtained with the GR theory, where the axis [Formula: see text] is always singular.

Surrounding Rock Failure Characteristics and Water Inrush Mechanism of Roadway above the Aquifer in Nonuniform Stress Field

The expansion of the roadway surrounding rock failure zone may connect the floor aquifer and cause the roadway water inrush. In order to reveal the mechanism of the roadway water inrush above confined water, we established the force model of the roadway surrounding rock above confined water in nonuniform stress field and studied the shape characteristics and expansion law of the roadway surrounding rock plastic zone. The results show that the roadway surrounding rock will form three kinds of plastic zone under different lateral pressure coefficients: circular, elliptical, and butterfly; when the shape of plastic zone is circular or elliptic, the maximum radius increases linearly with the increase of regional stress; when the shape is butterfly, the maximum radius increases exponentially with the increase of stress. Under the condition of a larger bidirectional stress ratio, the surrounding rock of the roadway will show butterfly-shaped failure, and small stress change will cause malignant expansion of the plastic zone; when the plastic zone is connected with the underlying aquifer, confined water of floor will enter the rock mass from the water diversion point and eventually flood into the roadway, causing floor water inrush.

Implementasi Automatic Waypoint untuk Return Trip pada Autonomous Robot dengan Titik Acuan Potensi Korban Bencana

ABSTRAK Langkah utama dan mendasar yang diperlukan untuk navigasi pada robot secara autonomous pada medan yang tak beraturan dan tidak diketahui keadaannya secara dinamis, setidaknya adalah identifikasi koordinat titik jalan (waypoint), tindakan yang harus dilakukan di titik jalan, identifikasi dimensi kerja, dan hambatan yang diketahui. Penelitian ini bertujuan untuk mengimplementasikan titik jalan otomatis (automatic waypoint) pada robot pencari potensi keberadaan korban pasca bencana, dilengkapi dengan kemampuan robot untuk navigasi dari titik awal berjalan mencari potensi keberadaan korban sebagai titik acuan hingga kembali ke titik awal (return trip) secara autonomous. Metode yang digunakan pada perancangan sistem merupakan pengembangan dari metode waypoint menjadi automatic waypoint untuk navigasi secara autonomous. Hasil yang didapat, robot mampu mendeteksi keberadaan korban maksimal dalam radius 3 meter di dalam simulasi reruntuhan. Ketercapaian rata-rata akurasi pembacaan posisi robot terhadap korban dan titik awal sebesar 6,76 meter. Kata kunci: robot, autonomous, automatic waypoint, korban, return trip. ABSTRACT There are necessary steps required for a robot to navigate autonomously on an unknown and uncertain environment. Those steps consist of the identification of the waypoint coordinates, the actions to be conducted, the identification of the environment’s dimension, and the known obstacles. This study aims to implement an automatic waypoint on a robot for searching the potential existence of post-disaster victims. The robot is equipped with the ability to navigate from the starting point to search for potential victims and then return to the starting point autonomously. We modified the existing waypoint method into an automatic waypoint for autonomous navigation. Results show that the robot is able to detect the presence of the victim within the maximum radius of 3 meters in the simulation of rubble (tables, chairs, wood and iron poles). The accuracy of robot in reading the position of the victim and the starting point is 6,76 meters. Keywords: robot, autonomous, automatical waypoint, victims, return trip.

Scientific and technical aspects of grouting of marginal rocks of mine workings

The goal of the paper is to justify ways to achieve maximum radius of extent of grouting mortar in a rock massif and to maximize filling of cavities and cracks with minimal openings. Filling of cavities and cracks directly influences a “massif – roadway – safety structure” system. Some scientific and technical aspects of grouting and injecting inorganic binders into marginal rocks are considered. Advantages of usage of triple plunger pumps in injecting units are determined. The influence of pulsation on a condition and process of grouting mortar extension is justified. It is established that under equal operating conditions, pulsations created by a triple plunger pump reduce mortar viscosity by 15 %, and a radius of extent of mortar based on grouting cements is increased by an average of 12 %, and with usage of very finely dispersed substances – up to 20 %. Suggested recommendations significantly improve the technology of grouting of marginal rocks and concrete structures.

Gravitoviscous protoplanetary disks with a dust component

Aims. Spatial distribution and growth of dust in a clumpy protoplanetary disk subject to vigorous gravitational instability and fragmentation is studied numerically with sub-au resolution using the FEOSAD code. Methods. Hydrodynamics equations describing the evolution of self-gravitating and viscous protoplanetary disks in the thin-disk limit were modified to include a dust component consisting of two parts: sub-micron-sized dust and grown dust with a variable maximum radius. The conversion of small to grown dust, dust growth, friction of dust with gas, and dust self-gravity were also considered. Results. We found that the disk appearance is notably time-variable with spiral arms, dusty rings, and clumps, constantly forming, evolving, and decaying. As a consequence, the total dust-to-gas mass ratio is highly non-homogeneous throughout the disk extent, showing order-of-magnitude local deviations from the canonical 1:100 value. Gravitationally bound clumps formed through gravitational fragmentation have a velocity pattern that deviates notably from the Keplerian rotation. Small dust is efficiently converted into grown dust in the clump interiors, reaching a maximum radius of several decimeters. Concurrently, grown dust drifts towards the clump center forming a massive compact central condensation (70–100 M⊕). We argue that protoplanets may form in the interiors of inward-migrating clumps before they disperse through the action of tidal torques. We foresee the formation of protoplanets at orbital distances of several tens of au with initial masses of gas and dust in the protoplanetary seed in the (0.25–1.6) MJup and (1.0–5.5) M⊕ limits, respectively. The final masses of gas and dust in the protoplanets may however be much higher due to accretion from surrounding massive metal-rich disks/envelopes. Conclusions. Dusty rings formed through tidal dispersal of inward-migrating clumps may have a connection to ring-like structures found in youngest and massive protoplanetary disks. Numerical disk models with a dust component that can follow the evolution of gravitationally bound clumps through their collapse phase to the formation of protoplanets are needed to make firm conclusions on the characteristics of planets forming through gravitational fragmentation.

Influence of Scanner Position and Plot Size on the Accuracy of Tree Detection and Diameter Estimation Using Terrestrial Laser Scanning on Forest Inventory Plots

This research tested how different scanner positions and sample plot sizes affect the tree detection and diameter measurement in forest inventories. For this, a multistage density-based clustering approach was further developed for the automatic mapping of tree positions and simultaneously applied with automatic measurements of tree diameters. This further development of the algorithm reduced the proportion of falsely detected tree locations by about 64%. The algorithms were tested in different settings with respect to the number and spatial alignment of scanner positions and under manifold forest conditions, covering different age classes and a mixture of scenarios, and representing a broad gradient of structural complexity. For circular sample plots with a maximum radius of 20 m, the tree mapping algorithm showed a detection rate of 82.4% with seven scanner positions at the vertices of a hexagon plus the center coordinates, and 68.3% with four scanner positions aligned in a triangle plus the center. Detection rates were significantly increased with smaller maximum radii. Thus, with a maximum radius of 10 m, the hexagon setting yielded a detection rate of 90.5% and the triangle 92%. Other alignments of scanner positions were also tested, but proved to be either unfavorable or too labor-intensive. The commission rates were on average less than 3%. The root mean square error (RMSE) of the dbh (diameter at breast height) measurement was between 2.66 cm and 4.18 cm for the hexagon and between 3.0 cm and 4.7 cm for the triangle design. The robustness of the algorithm was also demonstrated via tests by means of an international benchmark dataset. It has been shown that the number of stems per hectare had a significant impact on the detection rate.

KONSEP DESAIN MITIGASI BENCANA KEBAKARAN PADA BANGUNAN PURA BERATAP IJUK

The use of Palm-Fiber roof on sacred buildings in Balinese Temples still preserved well, however case of fire disasters becoming a threat in temple existence nowadays. Fire disasters could start with some sparks on roof section. Palm fiber and thatched roof are building materials that very vulnerable to fire disasters and when fire disaster happens because of this materials,it could easily spread out the fire on other building next to it. This article was an article created by purposed to give an idea or innovation in fire disasters mitigation especially in temples or “palinggih” with palm-fiber roof. Content explanation using concept design model and system scenarios related to extinguished fire with conventional fire extinguisher tool. Automatic fire extinguisher concept design which installed on roof section of building or “palinggih” with palm fiber roof only had two alternative models. First model for building with roof sized not more than 3x3m, and second model for roof sized more than 3x3m. The Consideration is head sprinkler that only could served on 3 m maximum radius. This article still a concept design and still need some testing on the field on next research. Keywords: mitigations, fire disasters, palm-fiber roof Abstrak: Penggunaan atap ijuk pada bangunan-bangunan suci di pura-pura di Bali masih tetap terjaga dengan baik. Namun, beberapa permasalahan yang terjadi belakangan ini adalah banyaknya kebakaran yang terjadi di pura-pura dan diawali dari percikan api pada bagian atap. Atap ijuk dan atap alang-alang adalah material yang sangat mudah terbakar dan mudah menjalar ke bangunan lain. Hal itu juga terjadi disaat terjadi kebakaran di atap ijuk bangunan pura yang memiliki lebih dari satu bangunan beratap ijuk dengan posisi yang berdekatan. Tulisan ini merupakan sebuah tulisan yang bertujuan untuk memberikan gagasan dan inovasi dalam mitigasi bencana kebakaran khususya di pura atau palinggih dengan atap ijuk. Penjelasan materi dengan menggunakan model desain konsep dan skenario sistem-sistem pemadam kebakaran dengan perlengkapan yang digunakan pada sistem pemadam pada umumnya. Konsep desain pemadam kebakaran otomatis yang dipasang pada bagian atap dari bangunan atau palinggih dengan atap ijuk untuk saat ini hanya mempunyai dua alternatif model. Model pertama diperuntukkan untuk bangunan dengan atap berukuran tidak lebih dari 3x3m, dan model kedua untuk atap yang berukuran lebih dari 3x3 m. Pertimbangannya adalah head sprinkler yang hanya mampu melayani radius maksimum 3 m.Tulisan ini masih berupa desain konsep dan masih perlu uji coba di tahap berikutnya.Kata Kunci: mitigasi, kebakaran, atap ijuk