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 (10 cm) 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 cm 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.
The Collaborative International Dictionary
Serf \Serf\, n. [F., fr. L. serus servant, slave; akin to servare to protect, preserve, observe, and perhaps originally, a client, a man under one's protection. Cf. Serve, v. t.] A servant or slave employed in husbandry, and in some countries attached to the soil and transferred with it, as formerly in Russia.
In England, at least from the reign of Henry II, one
only, and that the inferior species [of villeins],
existed . . . But by the customs of France and Germany,
persons in this abject state seem to have been called
serfs, and distinguished from villeins, who were only
bound to fixed payments and duties in respect of their
lord, though, as it seems, without any legal redress if
injured by him.
Syn: Serf, Slave.
Usage: A slave is the absolute property of his master, and may be sold in any way. A serf, according to the strict sense of the term, is one bound to work on a certain estate, and thus attached to the soil, and sold with it into the service of whoever purchases the land.
Longman Dictionary of Contemporary English
Douglas Harper's Etymology Dictionary
late 15c., "servant, serving-man, slave," from Old French serf "vassal, servant, slave" (12c.), from Latin servum (nominative servus) "slave" (see serve). Fallen from use in original sense by 18c. Meaning "lowest class of cultivators of the soil in continental European countries" is from 1610s. Use by modern writers with reference to medieval Europeans first recorded 1761 (contemporary Anglo-Latin records used nativus, villanus, or servus).
n. 1 A partially free peasant of a low hereditary class, slavishly attached to the land owned by a feudal lord and required to perform labour, enjoying minimal legal or customary rights. 2 A similar agricultural labourer in 18th and 19th century Europe. 3 (context strategy games English) A worker unit.
Usage examples of "serf".
For his services the nobleman was given land and serfs, but not as outright or allodial property, as in the West, and only on condition that he served the Tsar.
So you can paste it in your tall silk hat, Mayn, that the Planetsmen are free men, not brainless stupid serfs.
My hold on this castle and the des mesne must be absolute, and my ville ins and serfs made to be aware that I will brook no trace of indisci-pline.
After a hard day of toiling in the wheat fields of some equally brain-damaged noble, there was nothing the average serf would rather do than down a couple pints of ale and go have some cross-eyed microcephalic with a wooden leg give him a blow job.
For three months Repin lived among the former serfs of Shiriayevo, a village overlooking the Volga near Samara.
After Russian country dances and chorus dances, Pelageya Danilovna made the serfs and gentry join in one large circle: a ring, a string, and a silver ruble were fetched and they all played games together.
An enormous crowd of factory hands, house serfs, and peasants, with whom some officials, seminarists, and gentry were mingled, had gone early that morning to the Three Hills.
He blew on his fingers to warm them, then sauntered out from behind the crates and melted into a small crowd of serfs haggling with each other over a brace of squawking chickens held upside down by their feet.
Ivan, the Squinter, ruled over his serfs with Oriental despotism: he was ignorant, coarse, and profligate.
And so many crops were being cultivated because the food had to feed all the serfs, not just the freaky threesome in the castle.
The serfs have been seeing a monstrously deformed shape in the marshes around Lake Venne for centuries now.
Though aware of the dissatisfaction of the frontiersmen those serfs wanted to become part of the Military Frontier because villeinage service and the constantly growing taxes were becoming increasingly difficult for them to bear.
The heavy wood door, carried on the backs of serfs from faraway Bhutan centuries ago, was closed.
Instantly the yellow-haired serfs in waiting, the Calmucks at the hall-door, and the half-witted dwarf who crawled around the table in his tow shirt, began laughing in chorus, as violently as they could.
Yolande laughed and held up her arms for the serf to slide the Moorish-style striped djellaba over her head.