Where does gain collide?

The factor by which a circuit or system multiplies its input to produce its output: an amplifier with a gain of ten returns an output ten times the size of the input, and the same idea describes loop gain, which sets how strongly a feedback path acts. Black's 1934 Stabilized Feedback Amplifiers showed how deliberately giving away raw gain through negative feedback buys stability, low distortion, and predictable behaviour, and it made gain the central quantity traded against stability, with the gain margin measuring how much more gain a loop can take before it oscillates. The referent is a multiplying factor in an engineered system, and it is not the amplification of light in a laser, a mutation that adds an activity to a gene, or a profit made on a sold asset.[1]

Unit

A dimensionless output-to-input ratio, often quoted in decibels

Recovery means

Not applicable

Measured by

Measured as the ratio of output to input amplitude across frequency, read from a Bode plot with its gain and phase margins

The growth in the strength of a light beam as it passes through a material in which more atoms sit in an excited state than in a lower one, so that stimulated emission adds more light than absorption removes: this optical gain is what lets a laser or an optical amplifier build a weak beam into a strong, coherent one. Schawlow and Townes's 1958 Infrared and Optical Masers set out the conditions under which a gain medium placed between mirrors can oscillate and emit coherent light, founding the laser. The referent is the amplification of light inside a physical medium, counted per unit of length travelled, and it differs from a circuit's output-to-input ratio, a gene that acquires a new activity, or money earned on a sale.[2]

Unit

A gain coefficient per unit length in the medium

Recovery means

Not applicable

Measured by

Measured as the fractional increase in beam power per unit length, or as the threshold gain that just balances the losses of a laser cavity

A change to a gene that gives its product a new activity or increases an existing one, so the altered gene does more rather than less: a gain-of-function mutation is set against a loss-of-function change, which removes or weakens activity, and gain-of-function variants are often dominant because a single altered copy can drive the new effect. Wilkie's 1994 review The molecular basis of genetic dominance laid out how gain-of-function and loss-of-function mutations come to produce dominant traits by different routes. The referent is a property of a mutated gene in a living organism, judged against its normal function, not a ratio in a circuit, the amplification of light, or a financial profit.[3]

Unit

A single mutation classified by its effect on gene product activity

Recovery means

Not applicable

Measured by

Established by comparing variant and normal alleles in functional assays, patterns of dominance, and molecular study of the gene product

The profit taken when an asset is sold for more than it was bought for: the capital gain is the difference between the sale price and the purchase cost, or basis, and in most tax systems it is recognised and taxed only when the asset is actually sold rather than as its value rises. Feldstein, Slemrod, and Yitzhaki's 1980 study The Effects of Taxation on the Selling of Corporate Stock and the Realization of Capital Gains showed how the tax owed at sale leads investors to hold assets longer to put off the bill, locking in their gains. The referent is a sum of money earned on a transaction, measured in currency, and it has nothing in common with a circuit's gain, a laser's gain, or a mutation that adds an activity to a gene.[4]

Unit

A monetary amount: sale price minus purchase cost (basis)

Recovery means

Not applicable

Measured by

Computed as realised sale proceeds minus the asset's cost basis, reported and taxed at the time of the sale