Definitions

Cutoff

Cutoff

[kuht-awf, -of]

In theoretical physics, cutoff is the maximal or minimal value of energy, momentum, or length, so that the objects with even larger or smaller values than these physical quantities are ignored. It is usually represented within a particular energy or length scale, such as Planck units.

An infrared cutoff (long-distance cutoff) is the minimal value of energy - or, equivalently, the maximal wavelength (usually a very large distance) - that the human eye takes into account. On the contrary, an ultraviolet cutoff is the maximal allowed energy or the shortest allowed distance (usually a very short length scale). If some quantities are computed as integrals over energy or another physical quantity, these cutoffs determine the limits of integration. The exact physics is reproduced when the appropriate cutoffs are sent to zero or infinity. However, these integrals are often divergent - see IR divergence and UV divergence - and a cutoff is needed. The dependence of physical quantities on the chosen cutoffs (especially the ultraviolet cutoffs) is the main focus of the theory of renormalization group.

UV Cutoff

Burdick & Jackson solvents are arranged in order of increasing UV cutoff, the wavelength at which the solvent absorbance in a 1 cm path length cell is equal to 1 AU (absorbance unit) using water in the reference cell.

Acetonitrile UV 190 Pentane 190 Water 190 Hexane UV 195 Cyclopentane 198 Cyclohexane 200 Heptane 200 Isopropyl Alcohol 205 Methanol 205 Ethyl Alcohol 210 2-Methoxyethanol 210 Methyl t-Butyl Ether 210 n-Propyl Alcohol 210 Trifluoroacetic Acid 210 Tetrahydrofuran UV 212 n-Butyl Alcohol 215 1,4-Dioxane 215 Ethyl Ether 215 Iso-Octane 215 n-Butyl Chloride 220 Glyme 220 Isobutyl Alcohol 220 Propylene Carbonate 220 Ethylene Dichloride 228 1,1,2-Trichlorotrifluoroethane 231 Dichloromethane 233 Chloroform 245 n-Butyl Acetate 254 Ethyl Acetate 256 Dimethyl Acetamide 268 N,N-Dimethylformamide 268 Dimethyl Sulfoxide 268 Toluene 284 N-Methylpyrrolidone 285 Chlorobenzene 287 o-Xylene 288 o-Dichlorobenzene 295 1,2,4-Trichlorobenzene 308 Methyl Ethyl Ketone 329 Acetone 330 Methyl Isoamyl Ketone 330 Methyl n-Propyl Ketone 331 Methyl Isobutyl Ketone 334

Not included: Isopropyl Myristate Petroleum Ether Pyridine Triethylamine

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