In situ

In situ is a Latin phrase meaning in the place. It is used in many different contexts.

Aerospace
In the aerospace industry equipment on board aircraft must be tested "in situ" or in place to confirm everything functions properly as a system. Individually each piece may work but interference from nearby equipment may create problems not anticipated. Special test equipment is available for this "in situ" testing.

Archaeology
In archaeology, in situ refers to an artifact that has not been moved from its original place of deposition, in other words is stationary meaning "Still". An artifact being in situ is critical to the interpretation of that artifact and, consequently, to the culture which formed it. Once an artifact's 'find–site' has been recorded, the artifact can then be moved for conservation, further interpretation and display. An artifact that is not discovered in situ is considered out of context and will not provide an accurate picture of the associated culture. However, the out of context artifact can provide scientists with an example of types and locations of in situ artifacts yet to be discovered.

An archaeological in–situ–find may be a looted object, an item of "booty". Consequently, the in situ find site may still not reveal its provenance. Further detective work is required. It is also possible for archaeological layers to be reworked (by humans, etc), for example in a tell mound where layers are not typically uniform or horizontal.

Architecture
In architecture and building, in situ means construction which is carried out on the building site using raw materials. Compare that with prefabricated construction, in which building components are made in a factory and then transported to the building site for assembly. For example, concrete slabs may be in situ or prefabricated.

In situ techniques are often more labour-intensive, and take longer, but the materials are cheaper, and the work is versatile and adaptable. Prefabricated techniques are usually much quicker, therefore saving money, but factory-made parts can be expensive. They are also inflexible, and must often be designed on a grid, with all details fully calculated in advance. They may also need special access to the building site for large delivery lorries.

Astronomy
Future space exploration may rely on obtaining supplies in situ, such as previous plans to power the Orion space vehicle with fuel minable on the moon.

Mars Direct mission concept is based primarily on the in situ fuel production using Sabatier reaction.

Biology
In biology, in situ means to examine the phenomenon exactly in place where it occurs (i.e. without moving it to some special medium). This usually means something intermediate between in vivo and in vitro. For example, examining a cell within a whole organ intact and under perfusion may be in situ investigation. This would not be in vivo as the donor is sacrificed before experimentation, but it would not be the same as working with the cell alone (a common scenario in in vitro experiments).

In oncology: for a carcinoma, in situ means that malignant cells are present as a tumor anywhere in the body, but has not metastasized, or invaded, beyond the original site where the tumor was discovered. This can happen anywhere in the body, such as the skin, breast tissue, or lung.

In genetics, in situ can also mean 'in the chromosome.' For example, fluorescent in situ hybridization (FISH) can be done with chromosomes in cells or in a karyotype, such as with spectral karyotyping. In each case, the target sequence is observed in the chromosome.

In conservation of genetic resources, "in-situ conservation" (also "on-site conservation") is the process of protecting an endangered plant or animal species in its natural habitat, as opposed to ex-situ conservation (also "off-site conservation").

Chemistry and chemical engineering
In chemistry, in situ typically means "in the reaction mixture" There are numerous unstable molecules which must be synthesized in situ (i.e. in the reaction mixture but cannot be isolated on their own) for use in various processes. Examples include the Corey-Chaykovsky reagent and adrenochrome.

In chemical engineering, in situ often refers to industrial plant "operations or procedures that are performed in place". For example, aged catalysts in industrial reactors may be regenerated in place (in situ) without being removed from the reactors.

Computer science
In computer science an in situ operation is one that occurs without interrupting the normal state of a system. For example, a file backup may be restored over a running system, without needing to take the system down to perform the restore. In the context of a database, an in situ restore would allow the database system to continue to be available to users while a restore happened. An in situ upgrade would allow an operating system or application to be upgraded while the system was still running, perhaps without the need to reboot it, depending on the sophistication of the system.

An algorithm is said to be an in situ algorithm, or in-place algorithm, if the amount of memory required to execute the algorithm is O(1), that is, does not depend on the size of the input. For example, heapsort is an in situ sorting algorithm.

In designing user interfaces, the term in situ means that a particular user action can be performed without going to another window, for example, if a word processor displays an image and allows you to edit the image without launching a separate image editor, this is called in situ editing.

Earth and atmospheric sciences
In physical geography and the Earth sciences, in situ typically describes natural material or processes prior to transport. For example, in situ is used in relation to the distinction between weathering and erosion, the difference being that erosion requires a transport medium (such as wind, ice, or water), whereas weathering occurs in situ. Geochemical processes are also often described as occurring to material in situ.

In the atmospheric sciences, in situ refers to measurements obtained through direct contact with the respective subject, such as a radiosonde measuring a parcel of air or an anemometer measuring wind, as opposed to remote sensing such as weather radar or satellites.

Environmental engineering
In situ can refer to where a clean up or remediation of a polluted site is performed using and simulating the natural processes in the soil, contrary to ex situ where contaminated soil is excavated and cleaned elsewhere, off site.

Literature
In literature in situ is used to describe a condition. The Rosetta Stone, for example, was originally erected in a courtyard, for public viewing. Most pictures of the famous stone are not "in-situ" pictures of it erected, as it would have been originally. The stone was uncovered as part of building material, within a wall. Its in situ condition today is that it is erected, vertically, on public display at the British Museum.

Linguistics
In linguistics, specifically syntax, an element may be said to be in situ if it is pronounced in the position where it is interpreted. For example, questions in languages such as Chinese have in-situ wh-elements, with structures comparable to "John bought what?" while English wh-elements are not in-situ: "What did John buy?"

Law
In legal context, in situ is often used for its literal meaning. For example, in Hong Kong, in situ land exchange involves the government exchanging the original or expired lease of a piece of land with a new grant or re-grant with the same piece of land or a portion of that.

Petroleum production
In situ means "in place", and refers to recovery techniques which apply heat or solvents to heavy oil or bitumen reservoirs beneath the earth. There are several varieties of in situ technique, but the ones which work best in the oil sands use heat.

RF transmission
In radio frequency (RF) transmission systems, in situ is often used to describe the location of various components while the system is in its standard transmission mode, rather than operation in a test mode. For example, if an in situ wattmeter is used in a commercial broadcast transmission system, the wattmeter can accurately measure power while the station is "on the air".