Serfdom

Serfdom is the status of many peasants under feudalism, specifically relating to manorialism. It was a condition of bondage, which developed primarily during the High Middle Ages in Europe and lasted in some countries until the mid-19th century.

Serfs who occupied a plot of land were required to work for the Lord of the Manor who owned that land, and in return were entitled to protection, justice and the right to exploit certain fields within the manor to maintain their own subsistence. Serfs were often required not only to work on the lord's fields, but also his mines, forests and roads. The manor formed the basic unit of feudal society, and the Lord of the manor and his serfs were bound legally, economically, and socially. Serfs formed the lowest social class of feudal society.

The decline of serfdom in Western Europe has sometimes been attributed to the Black Death, which reached Europe in 1347, although the decline had begun before that date. Serfdom became increasingly rare in most of Western Europe after the Renaissance, but conversely, it grew strong in Central and Eastern Europe, where it had previously been less common (this phenomenon was known as "later serfdom").

SERF

A spin exchange relaxation-free (SERF) magnetometer is a type of magnetometer developed at Princeton University in the early 2000s. SERF magnetometers measure magnetic fields by using lasers to detect the interaction between alkali metal atoms in a vapor and the magnetic field.

The name for the technique comes from the fact that spin exchange relaxation, a mechanism which usually scrambles the orientation of atomic spins, is avoided in these magnetometers. This is done by using a high (10¹⁴ cm⁻³) density of Potassium atoms and a very low magnetic field. Under these conditions, the atoms exchange spin quickly compared to their magnetic precession frequency so that the average spin interacts with the field and is not destroyed by decoherence.

A SERF magnetometer achieves very high magnetic field sensitivity by monitoring a high density vapor of alkali metal atoms precessing in a near-zero magnetic field. The sensitivity of SERF magnetometers improves upon traditional atomic magnetometers by eliminating the dominant cause of atomic spin decoherence caused by spin-exchange collisions among the alkali metal atoms. SERF magnetometers are among the most sensitive magnetic field sensors and in some cases exceed the performance of SQUID detectors of equivalent size. A small 1 cm³ volume glass cell containing potassium vapor has reported 1 fT/√Hz sensitivity and can theoretically become even more sensitive with larger volumes. They are vector magnetometers capable of measuring all three components of the magnetic field simultaneously.

SERF2

Small EDRK-rich factor 2 is a protein that in humans is encoded by the SERF2 gene.

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