'Ultracentrifuge' is an ill-defined term applied to centrifuges with rated speeds greater than about 25 000 rpm, regardless of the medium or rotor design. While speed was historically used to designate ultracentrifugation, some manufactures now reserve this term for centrifuges that operate at sufficient speeds to require a vacuum to reduce frictional drag and/or rotor heating. Most such units are also equipped with refrigerant capability for the same purpose.

Ultracentrifuges are classified as preparative or analytical. Preparative ultracentrifuges are used to separate and recover purified sample components at speeds ranging up to 150 000 rpm and forces to 900 000g. The rotor configuration may be any of the types described in this section - bottle, zonal, or continuous - with fixed-angle and vertical-bottle centrifuges providing the highest speeds and titanium being the most common material of construction.

Analytical ultracentrifuges, originally developed by Svedberg, are used to study the behaviour of particles during sedimentation. While analytical rotors are available in various shapes and sizes, their defining feature is a transparent window, typically constructed of quartz or sapphire, that permits the sedimenting particles to be monitored optically during the run. UV absorption and/or refractive index measurements are the most common monitoring techniques. The required sample volume is low, ranging down to 5 |L, making this a useful technique when sample availability may otherwise be a limiting factor. Sample recovery is generally a secondary consideration, if conducted at all. Analytical ultracentrifuges are available at speeds up to 70 000 rpm and centrifugal forces in excess of 350 000g.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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