Needle Beam Method Of Tunneling Pdf 11
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By special monitoring the NATM method is flexible, even at surprising changes of the geomechanical rock consistency during the tunneling work. The measured rock properties lead to appropriate tools for tunnel strengthening. In the last decades also soft ground excavations up to 10 kilometres (6.2 mi) became usual.
Soft-ground tunneling methods are commonly used for urban services (subways, sewers, and other utilities). The tunnel structure in soft ground is generally designed to support the entire load of the ground above it, partly because the ground arch in soil deteriorates with time and as an allowance for load changes resulting from future construction of buildings or tunnels.
This method is suitable for soils where the roof could be depended upon to stand for some minutes without support. This method could be advanced by 10' to 12' length per day. The needle beam consists of a stout timber beam or a composite flitched beam and forms the temporary primary support during the excavation.
Only a few compounds have been reported to deviate from this trend. While a material with a complex or low-symmetry crystal structure does not necessarily possess a glassy thermal conductivity, most materials exhibiting the trend are structurally complex. Examples include NaNbO321 with a low-symmetry monoclinic or orthorhombic crystal structure at room temperature25, orthorhombic CsBiNb2O7 with 22 atoms per primitive cell26, polydiacetylene single crystals27, Yb-based zintls28, and clathrates5,6,29. The glassy thermal conductivity of clathrates, in particular, have been extensively investigated30,31,32. However, unambiguously identifying the origin of the glassy trend has proved challenging. For instance, while early works on clathrates hypothesized that two-level systems were responsible29,30, later works suggested that charge carrier scattering could play a role33 as the samples were electrically conducting. Further, direct detection of tunneling of heavy structural atoms is generally not possible with scattering methods as the tunneling splitting energies are expected to be sub GHz34, which is too low to affect thermal conduction except at temperatures less than around 1 K. As a result, the mechanism underlying the glassy thermal conductivity of single crystals remains unclear.
Single-crystal needles were grown using chemical vapor transport, similar to methods employed for other perovskite sulfides reported elsewhere35,36. The precursors, barium sulfide (Sigma-Aldrich, 99.9%), titanium (Alfa Aesar, 99.9%), and sulfur (Alfa Aesar, 99.999%) were mixed stoichiometrically and loaded in a quartz ampoule with the transporting agent iodine (Alfa Aesar 99.99%) in an argon-filled glove box. The tube was then evacuated and flame sealed using a blowtorch. The sealed ampoule was about 12 cm in length and 2 cm in diameter. The samples were heated to 1000 C with a 0.3 C/min ramp rate, held at 1000 C for 60 h, and then quenched to room temperature using a sliding furnace setup with a cooling rate of 100 C/min.
The c-axis direction of the needle-like crystal was confirmed by rotating the BaTiS3 crystal along an in-plane direction to identify the six-fold rotational axis of the crystal (see Supplementary Fig. S1). The XRD map with sample tilt and the rocking curve measurements were carried out in a Bruker D8 Advance X-ray diffractometer with parallel beam configuration and a Ge (440) 2-bounce monochromator for Cu Kα1 radiation.
A method is described to design a microstructure comprised of multi-Fresnel zone plate (FZP) fragments for shaping an optical needle with arbitrary length. Thus, a microstructure comprised of three planar FZP fragments with different focal lengths f1, f2, and f3 is designed to form a long optical needle by delicate interference of coherent light beams diffracted from these three FZP fragments. For a 74.34-μm-diameter microstructure illuminated with a linearly x-polarized beam, a 7.87-λ-long optical needle is produced at a distance of 12.31 λ away from the mask surface. The sizes of transverse beam are 0.97 and 0.4 λ in x and y directions, respectively. For this work, the vectorial angular spectrum (VAS) theory is employed to describe the electric field of light behind the microstructure, as well as the three-dimensional finite-difference time-domain (3D FDTD) method is adopted to further verify the results obtained.
As shown in the figure below, the needle beam is placed horizontally, whose front end rests on the drift itself and the rear end is supported on the vertical stout post, resting on the lining of the tunnel. 153554b96e