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Category: Instrumentation

Signal Processing: Aliasing and Filtering

Signal Processing: Aliasing and Filtering

Aliasing describes the production of an artificially long wavelength due to slow periodic sampling of a periodic signal. To reproduce the signal accurately, the sampling frequency should be at least slightly larger than twice the highest frequency contained in the signal (a.k.a. the Nyquist frequency). For example, if the sampling rate is 2b then all frequencies less than b will not be aliased. Band Pass Filters will filter out certain wavelengths to allow the user to focus on different parts of…

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X-Ray Powder Diffraction

X-Ray Powder Diffraction

X-RAY POWDER DIFFRACTION is a process of identifying the crystal structure (i.e. atomic spacing) of a powder sample using x-rays. It can tell you both what elements are present as well as differentiating between polymorphs. PRODUCING X-RAYS Electrons are freed from a tungsten filament (aka cathode) by heating, where the valence electrons are free to move with very little energy input. Normally the electrons would stay within the metal because it becomes (+) charged when the electrons leave, drawing them…

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Gas Chromatography

Gas Chromatography

Gas Chromatography is a method of analyzing an unknown liquid mixture by separating the components by boiling point 1. A liquid mixture of unknown compounds A and B is injected into a column with an inert gas (usually Helium) which pushes the liquid through the column into an oven (brown) where it vaporizes 2. The column is coated with a liquid with a high boiling point (green). The gas with the higher boiling point (B) will form stronger bonds with…

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