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A core sample is a cylindrical section of (usually) a naturally-occurring substance. Most core samples are obtained by drilling with special drills into the substance, such as sediment or rock, with a hollow steel tube, called a core drill. The hole made for the core sample is called the "core hole".
Truck-mounted core drill. A modern core drill is a drill specifically designed to remove a cylinder of material, much like a hole saw. The material left inside the drill bit is referred to as the core. Core drills used in metal are called annular cutters. Core drills used for concrete and hard rock generally use industrial diamond grit as the ...
Instead, it was discovered in 2009 that the density of the old stars peaks at a distance of roughly 0.5 parsec from Sgr A*, then falls inward: instead of a dense cluster, there is a "hole", or core, around the black hole. [52] Several suggestions have been put forward to explain this puzzling observation, but none is completely satisfactory.
An annular cutter (also called a core drill, core cutter, broach cutter, trepanning drill, hole saw, or cup-type cutter) is a form of core drill used to create holes in metal. An annular cutter, named after the annulus shape , cuts only a groove at the periphery of the hole and leaves a solid core or slug at the center.
An added benefit is that hollow core can be formed if the gas is introduced via holes in the core surface which cause only the surface of the core to harden; the remaining sand is then just dumped out to be used again. [4] For example, a cold-box sand casting core binder is sodium silicate which hardens on exposure to carbon dioxide. [5]
Core plugs are usually thin metal cups press fitted into the casting holes, but may be made of rubber or other materials. The most common metal plugs used in automotive engines are made from plated mild steels, stainless steels, brass or bronze. In some high-performance engines the core plugs are large diameter cast metal threaded pipe plugs. [3]
The Kola Superdeep Borehole SG-3 (Russian: Кольская сверхглубокая скважина СГ-3, romanized: Kol'skaya sverkhglubokaya skvazhina SG-3) is the deepest human-made hole on Earth (since 1979), which attained maximum true vertical depth of 12,262 metres (40,230 ft; 7.619 mi) in 1989. [1]
A core electron can be removed from its core-level upon absorption of electromagnetic radiation. This will either excite the electron to an empty valence shell or cause it to be emitted as a photoelectron due to the photoelectric effect. The resulting atom will have an empty space in the core electron shell, often referred to as a core-hole.
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