Column

A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member. The term column applies especially to a large round support (the shaft of the column) with a capital and a base or pedestal[1] which is made of stone, or appearing to be so. A small wooden or metal support is typically called a post, and supports with a rectangular or other non-round section are usually called piers. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces. Other compression members are often termed "columns" because of the similar stress conditions. Columns are frequently used to support beams or arches on which the upper parts of walls or ceilings rest. In architecture, "column" refers to such a structural element that also has certain proportional and decorative features. A column might also be a decorative element not needed for structural purposes; many columns are "engaged", that is to say form part of a wall.

National Capitol Columns - Washington, D.C.
National Capitol Columns at the United States National Arboretum in Washington, D.C.

History

Antiquity

All significant Iron Age civilizations of the Near East and Mediterranean made some use of columns.

Egyptian

In Ancient Egyptian architecture as early as 2600 BC the architect Imhotep made use of stone columns whose surface was carved to reflect the organic form of bundled reeds, like papyrus, lotus and palm; in later Egyptian architecture faceted cylinders were also common. Their form is thought to derive from archaic reed-built shrines. Carved from stone, the columns were highly decorated with carved and painted hieroglyphs, texts, ritual imagery and natural motifs. Egyptian columns are famously present in the Great Hypostyle Hall of Karnak (circa 1224 BC), where 134 columns are lined up in 16 rows, with some columns reaching heights of 24 metres.

One of the most important type are the papyriform columns. The origin of these columns goes back to the 5th Dynasty. They are composed of lotus (papyrus) stems which are drawn together into a bundle decorated with bands: the capital, instead of opening out into the shape of a bellflower, swells out and then narrows again like a flower in bud. The base, which tapers to take the shape of a half-sphere like the stem of the lotus, has a continuously recurring decoration of stipules.

The grammar of ornament (1868) (14587326250)

Illustration of papyriform capitals, in The Grammar of Ornament

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Illustration of various types of capitals, drawn by the egyptologist Karl Richard Lepsius

Mammisi Philae2

Columns with Hathoric capitals

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Papyriform columns in the Luxor Temple

Persian

Persepolis Colonne flandin
Plan, front view and side view of a typical Persepolis column, of Persia (Iran)

Some of the most elaborate columns in the ancient world were those of the Persians, especially the massive stone columns erected in Persepolis. They included double-bull structures in their capitals. The Hall of Hundred Columns at Persepolis, measuring 70 × 70 metres, was built by the Achaemenid king Darius I (524–486 BC). Many of the ancient Persian columns are standing, some being more than 30 metres tall. Tall columns with bull's head capitals were used for porticoes and to support the roofs of the hypostylehall, partly inspired by the ancient Egyptian precedent. Since the columns carried timber beams rather than stine, they could be taller, slimmer and more widerly spaced than Egyptian ones.

Greek & Roman

Schema Saeulenordnungen
Illustration of Doric (left three), Ionic (middle three) and Corinthian (right two) columns
Table of architecture, Cyclopaedia, 1728, volume 1
Very detailed llustrations of the Tuscan, Doric, Ionic, Corinthian and Composite orders

The Minoans used whole tree-trunks, usually turned upside down in order to prevent re-growth, stood on a base set in the stylobate (floor base) and topped by a simple round capital. These were then painted as in the most famous Minoan palace of Knossos. The Minoans employed columns to create large open-plan spaces, light-wells and as a focal point for religious rituals. These traditions were continued by the later Mycenaean civilization, particularly in the megaron or hall at the heart of their palaces. The importance of columns and their reference to palaces and therefore authority is evidenced in their use in heraldic motifs such as the famous lion-gate of Mycenae where two lions stand each side of a column. Being made of wood these early columns have not survived, but their stone bases have and through these we may see their use and arrangement in these palace buildings.

The Egyptians, Persians and other civilizations mostly used columns for the practical purpose of holding up the roof inside a building, preferring outside walls to be decorated with reliefs or painting, but the Ancient Greeks, followed by the Romans, loved to use them on the outside as well, and the extensive use of columns on the interior and exterior of buildings is one of the most characteristic features of classical architecture, in buildings like the Parthenon. The Greeks developed the classical orders of architecture, which are most easily distinguished by the form of the column and its various elements. Their Doric, Ionic, and Corinthian orders were expanded by the Romans to include the Tuscan and Composite orders (see below).

Knossos 03

Minoan columns at the West Bastion of the Palace of Knossos

EB1911 Capital Fig. 5 Early Greek Capital from the Tomb of Agamemnon, Mycenae

Illustration of the end of a Mycenaean column, from the Tomb of Agamemnon

Fotothek df tg 0001022 Architektur ^ Säule ^ dorische Ordnung ^ Brücke

Illustration of the Tuscan order

DoricParthenon

Illustration of the Doric order

Ionic order J.L.Leroy

Illustration of the Ionic order

Evolution of the Corinthian Capital 138

Evolution of the Corinthian order

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Illustration of the Composite order

Middle Ages

Columns, or at least large structural exterior ones, became much less significant in the architecture of the Middle Ages. The classical forms were abandoned in both Byzantine architecture and the Romanesque and Gothic architecture of Europe in favour of more flexible forms, with capitals often using various types of foliage decoration, and in the West scenes with figures carved in relief.

Furing the Romanesque period, builders continued to reuse and imitate ancient Roman columns wherever possible. Where new, the emphasis was on elegance and beauty, as illustrated by twisted columns. Often they were decorated with mosaics.

Empress loge Hagia Sophia 2007 002

Byzantine columns in Hagia Sophia (Istanbul, Turkey)

Igreja de São Tiago, Coimbra. Capiteis y colunelos

Romanesque columns from the 12th century

Neuwiller StPierre-Paul 117

Gothic columns of a church from Neuwiller-lès-Saverne (France)

Renaissance and later styles

Renaissance architecture was keen to revive the classical vocabulary and styles, and the informed use and variation of the classical orders remained fundamental to the training of architects throughout Baroque, Rococo and Neo-classical architecture.

Structure

Early columns were constructed of stone, some out of a single piece of stone. Monolithic columns are among the heaviest stones used in architecture. Other stone columns are created out of multiple sections of stone, mortared or dry-fit together. In many classical sites, sectioned columns were carved with a centre hole or depression so that they could be pegged together, using stone or metal pins. The design of most classical columns incorporates entasis (the inclusion of a slight outward curve in the sides) plus a reduction in diameter along the height of the column, so that the top is as little as 83% of the bottom diameter. This reduction mimics the parallax effects which the eye expects to see, and tends to make columns look taller and straighter than they are while entasis adds to that effect. There are fillets and flutes that run up the shaft of columns. The flute is the part of the column that is indented in with a semi circular shape. The fillet of the column is the part between each of the flutes on the ionic order columns. The flute width changes on all tapered columns as it goes up the shaft and stays the same on all non tapered columns. This was done to the columns to add visual interest to them. The ionic order and the corinthian orders are the only column styles that have fillets and flutes. The doric style has flutes but not fillets. Doric flutes are connected at a sharp point where the fillets are located on ionic and corinthian order columns.

Nomenclature

Most classical columns arise from a basis, or base, that rests on the stylobate, or foundation, except for those of the Doric order, which usually rest directly on the stylobate. The basis may consist of several elements, beginning with a wide, square slab known as a plinth. The simplest bases consist of the plinth alone, sometimes separated from the column by a convex circular cushion known as a torus. More elaborate bases include two toruses, separated by a concave section or channel known as a scotia or trochilus. Scotiae could also occur in pairs, separated by a convex section called an astragal, or bead, narrower than a torus. Sometimes these sections were accompanied by still narrower convex sections, known as annulets or fillets.[2][3]

At the top of the shaft is a capital, upon which the roof or other architectural elements rest. In the case of Doric columns, the capital usually consists of a round, tapering cushion, or echinus, supporting a square slab, known as an abax or abacus. Ionic capitals feature a pair of volutes, or scrolls, while Corinthian capitals are decorated with reliefs in the form of acanthus leaves. Either type of capital could be accompanied by the same moldings as the base.[2][3] In the case of free-standing columns, the decorative elements atop the shaft are known as a finial.

Modern columns may be constructed out of steel, poured or precast concrete, or brick, left bare or clad in an architectural covering, or veneer. Used to support an arch, an impost, or pier, is the topmost member of a column. The bottom-most part of the arch, called the springing, rests on the impost.

Equilibrium, instability, and loads

ColumnEffectiveLength
Table showing values of K for structural columns of various end conditions (adapted from Manual of Steel Construction, 8th edition, American Institute of Steel Construction, Table C1.8.1)

As the axial load on a perfectly straight slender column with elastic material properties is increased in magnitude, this ideal column passes through three states: stable equilibrium, neutral equilibrium, and instability. The straight column under load is in stable equilibrium if a lateral force, applied between the two ends of the column, produces a small lateral deflection which disappears and the column returns to its straight form when the lateral force is removed. If the column load is gradually increased, a condition is reached in which the straight form of equilibrium becomes so-called neutral equilibrium, and a small lateral force will produce a deflection that does not disappear and the column remains in this slightly bent form when the lateral force is removed. The load at which neutral equilibrium of a column is reached is called the critical or buckling load. The state of instability is reached when a slight increase of the column load causes uncontrollably growing lateral deflections leading to complete collapse.

For an axially loaded straight column with any end support conditions, the equation of static equilibrium, in the form of a differential equation, can be solved for the deflected shape and critical load of the column. With hinged, fixed or free end support conditions the deflected shape in neutral equilibrium of an initially straight column with uniform cross section throughout its length always follows a partial or composite sinusoidal curve shape, and the critical load is given by

where E = elastic modulus of the material, Imin = the minimal moment of inertia of the cross section, and L = actual length of the column between its two end supports. A variant of (1) is given by

where r = radius of gyration of [column]cross-section which is equal to the square root of (I/A), K = ratio of the longest half sine wave to the actual column length, Et = tangent modulus at the stress Fcr, and KL = effective length (length of an equivalent hinged-hinged column). From Equation (2) it can be noted that the buckling strength of a column is inversely proportional to the square of its length.

When the critical stress, Fcr (Fcr =Pcr/A, where A = cross-sectional area of the column), is greater than the proportional limit of the material, the column is experiencing inelastic buckling. Since at this stress the slope of the material's stress-strain curve, Et (called the tangent modulus), is smaller than that below the proportional limit, the critical load at inelastic buckling is reduced. More complex formulas and procedures apply for such cases, but in its simplest form the critical buckling load formula is given as Equation (3),

A column with a cross section that lacks symmetry may suffer torsional buckling (sudden twisting) before, or in combination with, lateral buckling. The presence of the twisting deformations renders both theoretical analyses and practical designs rather complex.

Eccentricity of the load, or imperfections such as initial crookedness, decreases column strength. If the axial load on the column is not concentric, that is, its line of action is not precisely coincident with the centroidal axis of the column, the column is characterized as eccentrically loaded. The eccentricity of the load, or an initial curvature, subjects the column to immediate bending. The increased stresses due to the combined axial-plus-flexural stresses result in a reduced load-carrying ability.

Column elements are considered to be massive if their smallest side dimension is equal to or more than 400 mm. Massive columns have the ability to increase in carrying strength over long time periods (even during periods of heavy load). Taking into account the fact, that possible structural loads may increase over time as well (and also the threat of progressive failure), massive columns have an advantage compared to non-massive ones.

Extensions

When a column is too long to be built or transported in one piece, it has to be extended or spliced at the construction site. A reinforced concrete column is extended by having the steel reinforcing bars protrude a few inches or feet above the top of the concrete, then placing the next level of reinforcing bars to overlap, and pouring the concrete of the next level. A steel column is extended by welding or bolting splice plates on the flanges and webs or walls of the columns to provide a few inches or feet of load transfer from the upper to the lower column section. A timber column is usually extended by the use of a steel tube or wrapped-around sheet-metal plate bolted onto the two connecting timber sections.

Foundations

A column that carries the load down to a foundation must have means to transfer the load without overstressing the foundation material. Reinforced concrete and masonry columns are generally built directly on top of concrete foundations. When seated on a concrete foundation, a steel column must have a base plate to spread the load over a larger area, and thereby reduce the bearing pressure. The base plate is a thick, rectangular steel plate usually welded to the bottom end of the column.

Orders of Columns

The Roman author Vitruvius, relying on the writings (now lost) of Greek authors, tells us that the ancient Greeks believed that their Doric order developed from techniques for building in wood. The earlier smoothed tree-trunk was replaced by a stone cylinder.

Doric order

The Doric order is the oldest and simplest of the classical orders. It is composed of a vertical cylinder that is wider at the bottom. It generally has neither a base nor a detailed capital. It is instead often topped with an inverted frustum of a shallow cone or a cylindrical band of carvings. It is often referred to as the masculine order because it is represented in the bottom level of the Colosseum and the Parthenon, and was therefore considered to be able to hold more weight. The height-to-thickness ratio is about 8:1. The shaft of a Doric Column is almost always fluted.

The Greek Doric, developed in the western Dorian region of Greece, is the heaviest and most massive of the orders. It rises from the stylobate without any base; it is from four to six times as tall as its diameter; it has twenty broad flutes; the capital consists simply of a banded necking swelling out into a smooth echinus, which carries a flat square abacus; the Doric entablature is also the heaviest, being about one-fourth the height column. The Greek Doric order was not used after c. 100 B.C. until its “rediscovery” in the mid-eighteenth century.

Tuscan order

The Tuscan order, also known as Roman Doric, is also a simple design, the base and capital both being series of cylindrical disks of alternating diameter. The shaft is almost never fluted. The proportions vary, but are generally similar to Doric columns. Height to width ratio is about 7:1.

Ionic order

The Ionic column is considerably more complex than the Doric or Tuscan. It usually has a base and the shaft is often fluted (it has grooves carved up its length). The capital features a volute, an ornament shaped like a scroll, at the four corners. The height-to-thickness ratio is around 9:1. Due to the more refined proportions and scroll capitals, the Ionic column is sometimes associated with academic buildings. Ionic style columns were used on the second level of the Colosseum.

Corinthian order

The Corinthian order is named for the Greek city-state of Corinth, to which it was connected in the period. However, according to the architectural historian Vitruvius, the column was created by the sculptor Callimachus, probably an Athenian, who drew acanthus leaves growing around a votive basket. In fact, the oldest known Corinthian capital was found in Bassae, dated at 427 BC. It is sometimes called the feminine order because it is on the top level of the Colosseum and holding up the least weight, and also has the slenderest ratio of thickness to height. Height to width ratio is about 10:1.

Composite order

The Composite order draws its name from the capital being a composite of the Ionic and Corinthian capitals. The acanthus of the Corinthian column already has a scroll-like element, so the distinction is sometimes subtle. Generally the Composite is similar to the Corinthian in proportion and employment, often in the upper tiers of colonnades. Height to width ratio is about 11:1 or 12:1.

Solomonic

A Solomonic column, sometimes called "barley sugar", begins on a base and ends in a capital, which may be of any order, but the shaft twists in a tight spiral, producing a dramatic, serpentine effect of movement. Solomonic columns were developed in the ancient world, but remained rare there. A famous marble set, probably 2nd century, was brought to St Peter's, Rome by Constantine I, and placed round the saint's shrine, and was thus familiar throughout the Middle Ages, by which time they were thought to have been removed from the Temple of Jerusalem.[4] The style was used in bronze by Bernini for his spectacular St. Peter's baldachin, actually a ciborium (which displaced Constantine's columns), and thereafter became very popular with Baroque and Rococo church architects, above all in Latin America, where they were very often used, especially on a small scale, as they are easy to produce in wood by turning on a lathe (hence also the style's popularity for spindles on furniture and stairs).

Caryatid

A Caryatid is a sculpted female figure serving as an architectural support taking the place of a column or a pillar supporting an entablature on her head. The Greek term karyatides literally means "maidens of Karyai", an ancient town of Peloponnese.

Engaged Columns

Engaged columns embedded in the side walls of the cella of the Maison Carrée at Nîmes (left side of the image) In architecture, an engaged column is a column embedded in a wall and partly projecting from the surface of the wall, sometimes defined as semi or three-quarter detached.[1] Engaged columns are rarely found in classical Greek architecture, and then only in exceptional cases, but in Roman architecture they exist in abundance, most commonly embedded in the cella walls[1] of pseudoperipteral buildings.

Pillar tombs

Pillar tombs are monumental graves, which typically feature a single, prominent pillar or column, often made of stone. A number of world cultures incorporated pillars into tomb structures. In the Ancient Greek colony of Lycia in Anatolia, one of these edifices is located at the tomb of Xanthos. In the town of Hannassa in southern Somalia, ruins of houses with archways and courtyards have also been found along with other pillar tombs, including a rare octagonal tomb.[5]

Gallery

Great Hypostyle Hall

Great Hypostyle Hall, Karnak, Egypt

Columns of the Temple of Apollo at Delphi, Greece.jpeg

Columns found at the Temple of Apollo in Delphi

Carpark Cinema Undercroft Albany II

Modern column grid in a car park or parking garage

Solomonic columns at St Peters Vatican (cropped)

At right, two of the Solomonic columns brought to Rome by Constantine, in their present-day location on a pier in St. Peter's Basilica, Rome. In the foreground at left is part of Bernini's Baldachin, inspired by the original columns.

Colonne-p1040009

Ionic capital

Western colonnade at courtyard, UVa 2004

Tuscan columns can be seen at the University of Virginia

Construction of Sigismund Column

Construction of Sigismund's Column in Warsaw, detail of the 1646 engraving.

Columns in the inner court of the Bel Temple Palmyra Syria

These are composed of stacked segments and finished in the Corinthian style (Temple of Bel, Syria)

Bankstownreservoir

The pillars of Bankstown Reservoir, Sydney

MosqueeKairouan 6bis

Reused Roman columns and capitals in the Great Mosque of Kairouan

See also

References

Chisholm, Hugh, ed. (1911). "Engaged Column". Encyclopædia Britannica. 9 (11th ed.). Cambridge University Press. pp. 404–405.

Stierlin, Henri The Roman Empire: From the Etruscans to the Decline of the Roman Empire, TASCHEN, 2002

Alderman, Liz (7 July 2014). "Acropolis Maidens Glow Anew". The New York Times. Retrieved 9 July 2014.

Stokstad, Marilyn; Cothren, Michael (2014). Art History (Volume 1 ed.). New Jersey: Pearson Education, Inc. p. 110.

  1. ^ "Column - Definition and More from the Free Merriam-Webster Dictionary". Merriam-webster.com. 2012-08-31. Archived from the original on 2013-10-04. Retrieved 2013-07-04.
  2. ^ a b Hewson Clarke and John Dougall, The Cabinet of Arts, T. Kinnersley, London (1817), pp. 271, 272.
  3. ^ a b "Architectural Glossary", in The Universal Decorator, Francis Benjamin Thompson, Ed., vol. III (1859).
  4. ^ J. Ward-Perkins, "The shrine of St. Peter's and its twelve spiral columns" Journal of Roman Studies 42 (1952) p 21ff.
  5. ^ Sanseverino, Hilary Costa (1983). "Archaeological Remains on the Southern Somali Coast". Azania: Archaeological Research in Africa. 18 (1): 151–164. doi:10.1080/00672708309511319.
Bar chart

A bar chart or bar graph is a chart or graph that presents categorical data with rectangular bars with heights or lengths proportional to the values that they represent. The bars can be plotted vertically or horizontally. A vertical bar chart is sometimes called a line graph.

A bar graph shows comparisons among discrete categories. One axis of the chart shows the specific categories being compared, and the other axis represents a measured value. Some bar graphs present bars clustered in groups of more than one, showing the values of more than one measured variable.

Chromatography

Chromatography is a laboratory technique for the separation of a mixture.

The mixture is dissolved in a fluid called the mobile phase, which carries it through a structure holding another material called the stationary phase. The various constituents of the mixture travel at different speeds, causing them to separate. The separation is based on differential partitioning between the mobile and stationary phases. Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase and thus affect the separation.Chromatography may be preparative or analytical. The purpose of preparative chromatography is to separate the components of a mixture for later use, and is thus a form of purification. Analytical chromatography is done normally with smaller amounts of material and is for establishing the presence or measuring the relative proportions of analytes in a mixture. The two are not mutually exclusive.

Columnist

A columnist is a person who writes for publication in a series, creating an article that usually offers commentary and opinions.

Columns appear in newspapers, magazines and other publications, including blogs. They take the form of a short essay by a specific writer who offers a personal point of view. In some instances, a column has been written by a composite or a team, appearing under a pseudonym, or (in effect) a brand name. Some columnists appear on a daily or weekly basis and later reprint the same material in book collections.

Corinthian order

The Corinthian order is the last developed of the three principal classical orders of ancient Greek and Roman architecture. The other two are the Doric order which was the earliest, followed by the Ionic order. When classical architecture was revived during the Renaissance, two more orders were added to the canon, the Tuscan order and the Composite order. The Corinthian, with its offshoot the Composite, is the most ornate of the orders. This architectural style is characterized by slender fluted columns and elaborate capitals decorated with acanthus leaves and scrolls. There are many variations.The name Corinthian is derived from the ancient Greek city of Corinth, although the style had its own model in Roman practice, following precedents set by the Temple of Mars Ultor in the Forum of Augustus (c. 2 AD). It was employed in southern Gaul at the Maison Carrée, Nîmes (illustration, below) and at the comparable podium temple at Vienne. Other prime examples noted by Mark Wilson Jones are the lower order of the Basilica Ulpia and the arch at Ancona (both of the reign of Trajan, 98–117 AD) the "column of Phocas" (re-erected in Late Antiquity but 2nd century in origin), and the "Temple of Bacchus" at Baalbek (c. 150 AD).

Doric order

The Doric order was one of the three orders of ancient Greek and later Roman architecture; the other two canonical orders were the Ionic and the Corinthian. The Doric is most easily recognized by the simple circular capitals at the top of columns. Originating in the western Dorian region of Greece, it is the earliest and in its essence the simplest of the orders, though still with complex details in the entablature above.

The Greek Doric column was fluted or smooth-surfaced, and had no base, dropping straight into the stylobate or platform on which the temple or other building stood. The capital was a simple circular form, with some mouldings, under a square cushion that is very wide in early versions, but later more restrained. Above a plain architrave, the complexity comes in the frieze, where the two features originally unique to the Doric, the triglyph and guttae, are skeuomorphic memories of the beams and retaining pegs of the wooden constructions that preceded stone Doric temples. In stone they are purely ornamental.

The relatively uncommon Roman and Renaissance Doric retained these, and often introduced thin layers of moulding or further ornament, as well as often using plain columns. More often they used versions of the Tuscan order, elaborated for nationalistic reasons by Italian Renaissance writers, which is in effect a simplified Doric, with un-fluted columns and a simpler entablature with no triglyphs or guttae. The Doric order was much used in Greek Revival architecture from the 18th century onwards; often earlier Greek versions were used, with wider columns and no bases to them.

Since at least Vitruvius it has been customary for writers to associate the Doric with masculine virtues (the Ionic representing the feminine). It is also normally the cheapest of the orders to use. When the three orders are used one above the other, it is usual for the Doric to be at the bottom, with the Ionic and then the Corinthian above, and the Doric, as "strongest", is often used on the ground floor below another order in the storey above.

Fifth column

A fifth column is any group of people who undermine a larger group from within, usually in favour of an enemy group or nation. The activities of a fifth column can be overt or clandestine. Forces gathered in secret can mobilize openly to assist an external attack. This term is also extended to organised actions by military personnel. Clandestine fifth column activities can involve acts of sabotage, disinformation, or espionage executed within defense lines by secret sympathizers with an external force.

Financial Times

The Financial Times (FT) is an English-language international daily newspaper owned by Nikkei Inc, headquartered in London, with a special emphasis on business and economic news.

The paper was founded in 1888 by James Sheridan and Horatio Bottomley, and merged in 1945 with its closest rival, the Financial News (which had been founded in 1884).

The Financial Times has a record paying readership of one million, three-quarters of which are digital subscriptions (as of April 2019). On 23 July 2015, Nikkei Inc. agreed to buy the Financial Times from Pearson for £844m ($1.32 billion) and the acquisition was completed on 30 November 2015.

Gas chromatography

Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture (the relative amounts of such components can also be determined). In some situations, GC may help in identifying a compound. In preparative chromatography, GC can be used to prepare pure compounds from a mixture.In gas chromatography, the mobile phase (or "moving phase") is a carrier gas, usually an inert gas such as helium or an unreactive gas such as nitrogen. Helium remains the most commonly used carrier gas in about 90% of instruments although hydrogen is preferred for improved separations. The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, inside a piece of glass or metal tubing called a column (an homage to the fractionating column used in distillation). The instrument used to perform gas chromatography is called a gas chromatograph (or "aerograph", "gas separator").

The gaseous compounds being analyzed interact with the walls of the column, which is coated with a stationary phase. This causes each compound to elute at a different time, known as the retention time of the compound. The comparison of retention times is what gives GC its analytical usefulness.

Gas chromatography is in principle similar to column chromatography (as well as other forms of chromatography, such as HPLC, TLC), but has several notable differences. First, the process of separating the compounds in a mixture is carried out between a liquid stationary phase and a gas mobile phase, whereas in column chromatography the stationary phase is a solid and the mobile phase is a liquid. (Hence the full name of the procedure is "Gas–liquid chromatography", referring to the mobile and stationary phases, respectively.) Second, the column through which the gas phase passes is located in an oven where the temperature of the gas can be controlled, whereas column chromatography (typically) has no such temperature control. Finally, the concentration of a compound in the gas phase is solely a function of the vapor pressure of the gas.Gas chromatography is also similar to fractional distillation, since both processes separate the components of a mixture primarily based on boiling point (or vapor pressure) differences. However, fractional distillation is typically used to separate components of a mixture on a large scale, whereas GC can be used on a much smaller scale (i.e. microscale).Gas chromatography is also sometimes known as vapor-phase chromatography (VPC), or gas–liquid partition chromatography (GLPC). These alternative names, as well as their respective abbreviations, are frequently used in scientific literature. Strictly speaking, GLPC is the most correct terminology, and is thus preferred by many authors.

Geologic time scale

The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history. The table of geologic time spans, presented here, agree with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS).

High-performance liquid chromatography

High-performance liquid chromatography (HPLC; formerly referred to as high-pressure liquid chromatography) is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to pass a pressurized liquid solvent containing the sample mixture through a column filled with a solid adsorbent material. Each component in the sample interacts slightly differently with the adsorbent material, causing different flow rates for the different components and leading to the separation of the components as they flow out of the column.

HPLC has been used for manufacturing (e.g., during the production process of pharmaceutical and biological products), legal (e.g., detecting performance enhancement drugs in urine), research (e.g., separating the components of a complex biological sample, or of similar synthetic chemicals from each other), and medical (e.g., detecting vitamin D levels in blood serum) purposes.Chromatography can be described as a mass transfer process involving adsorption. HPLC relies on pumps to pass a pressurized liquid and a sample mixture through a column filled with adsorbent, leading to the separation of the sample components. The active component of the column, the adsorbent, is typically a granular material made of solid particles (e.g., silica, polymers, etc.), 2–50 μm in size. The components of the sample mixture are separated from each other due to their different degrees of interaction with the adsorbent particles. The pressurized liquid is typically a mixture of solvents (e.g., water, acetonitrile and/or methanol) and is referred to as a "mobile phase". Its composition and temperature play a major role in the separation process by influencing the interactions taking place between sample components and adsorbent. These interactions are physical in nature, such as hydrophobic (dispersive), dipole–dipole and ionic, most often a combination.

HPLC is distinguished from traditional ("low pressure") liquid chromatography because operational pressures are significantly higher (50–350 bar), while ordinary liquid chromatography typically relies on the force of gravity to pass the mobile phase through the column. Due to the small sample amount separated in analytical HPLC, typical column dimensions are 2.1–4.6 mm diameter, and 30–250 mm length. Also HPLC columns are made with smaller adsorbent particles (2–50 μm in average particle size). This gives HPLC superior resolving power (the ability to distinguish between compounds) when separating mixtures, which makes it a popular chromatographic technique.

The schematic of a HPLC instrument typically includes a degasser, sampler, pumps, and a detector. The sampler brings the sample mixture into the mobile phase stream which carries it into the column. The pumps deliver the desired flow and composition of the mobile phase through the column. The detector generates a signal proportional to the amount of sample component emerging from the column, hence allowing for quantitative analysis of the sample components. A digital microprocessor and user software control the HPLC instrument and provide data analysis. Some models of mechanical pumps in a HPLC instrument can mix multiple solvents together in ratios changing in time, generating a composition gradient in the mobile phase. Various detectors are in common use, such as UV/Vis, photodiode array (PDA) or based on mass spectrometry. Most HPLC instruments also have a column oven that allows for adjusting the temperature at which the separation is performed.

Ionic order

The Ionic order forms one of the three classical orders of classical architecture, the other two canonic orders being the Doric and the Corinthian. There are two lesser orders: the Tuscan (a plainer Doric), and the rich variant of Corinthian called the composite order, both added by 16th-century Italian architectural writers, based on Roman practice. Of the three canonic orders, the Ionic order has the narrowest columns.

The Ionic capital is characterized by the use of volutes. The Ionic columns normally stand on a base which separates the shaft of the column from the stylobate or platform; the cap is usually enriched with egg-and-dart.

Since Vitruvius, a female character has been ascribed to the Ionic (in contrast to the masculine Doric).

Nelson's Column

Nelson's Column is a monument in Trafalgar Square in the City of Westminster, Central London built to commemorate Admiral Horatio Nelson, who died at the Battle of Trafalgar in 1805. The monument was constructed between 1840 and 1843 to a design by William Railton at a cost of £47,000 (equivalent to £4,532,261 in 2018). It is a column of the Corinthian order built from Dartmoor granite. The Craigleith sandstone statue of Nelson is by E.H. Baily, and the four bronze lions on the base, added in 1867, were designed by Sir Edwin Landseer.The pedestal is decorated with four bronze relief panels, each 18 feet (5.5 m) square, cast from captured French guns. They depict the Battle of Cape St Vincent, the Battle of the Nile, the Battle of Copenhagen and the death of Nelson at Trafalgar. The sculptors were Musgrave Watson, William F. Woodington, John Ternouth and John Edward Carew, respectively.

It was refurbished in 2006 at a cost of £420,000 (equivalent to £596,901 in 2018), at which time it was surveyed and found to be 14 feet 6 inches (4.42 m) shorter than previously supposed. The whole monument is 169 feet 3 inches (51.59 m) tall from the bottom of the pedestal to the top of Nelson's hat.

Op-ed

An op-ed, short for "opposite the editorial page", is a written prose piece typically published by a newspaper or magazine which expresses the opinion of an author usually not affiliated with the publication's editorial board. Op-eds are different from both editorials (opinion pieces submitted by editorial board members) and letters to the editor (opinion pieces submitted by readers).

Pilaster

The pilaster is an architectural element in classical architecture used to give the appearance of a supporting column and to articulate an extent of wall, with only an ornamental function. It consists of a flat surface raised from the main wall surface, usually treated as though it were a column, with a capital at the top, plinth (base) at the bottom, and the various other elements. In contrast to a pilaster, an engaged column or buttress can support the structure of a wall and roof above.

Spinal cord

The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord, which contains cerebrospinal fluid. The brain and spinal cord together make up the central nervous system (CNS). In humans, the spinal cord begins at the occipital bone, passing through the foramen magnum and entering the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae, where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) in men and around 43 cm (17 in) long in women. The diameter of the spinal cord ranges from 13 mm (1⁄2 in) in the cervical and lumbar regions to 6.4 mm (1⁄4 in) in the thoracic area.

The spinal cord functions primarily in the transmission of nerve signals from the motor cortex to the body, and from the afferent fibers of the sensory neurons to the sensory cortex. It is also a center for coordinating many reflexes and contains reflex arcs that can independently control reflexes. It is also the location of groups of spinal interneurons that make up the neural circuits known as central pattern generators. These circuits are responsible for controlling motor instructions for rhythmic movements such as walking.

Stamen

The stamen (plural stamina or stamens) is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium.

The Sydney Morning Herald

The Sydney Morning Herald (SMH) is a daily compact newspaper in Sydney, New South Wales, Australia owned by Nine. Founded in 1831 as the Sydney Herald, the SMH is the oldest continuously published newspaper in Australia and a national online news brand. The print version of the newspaper is published six days a week.

Trajan's Column

Trajan's Column (Italian: Colonna Traiana, Latin: COLVMNA·TRAIANI) is a Roman triumphal column in Rome, Italy, that commemorates Roman emperor Trajan's victory in the Dacian Wars. It was probably constructed under the supervision of the architect Apollodorus of Damascus at the order of the Roman Senate. It is located in Trajan's Forum, built near the Quirinal Hill, north of the Roman Forum. Completed in AD 113, the freestanding column is most famous for its spiral bas relief, which artistically represents the wars between the Romans and Dacians (101–102 and 105–106). Its design has inspired numerous victory columns, both ancient and modern.

The structure is about 30 metres (98 feet) in height, 35 metres (115 feet) including its large pedestal. The shaft is made from a series of 20 colossal Carrara marble drums, each weighing about 32 tons, with a diameter of 3.7 metres (12.1 feet). The 190-metre (620-foot) frieze winds around the shaft 23 times. Inside the shaft, a spiral staircase of 185 steps provides access to a viewing platform at the top. The capital block of Trajan's Column weighs 53.3 tons, which had to be lifted to a height of c. 34 metres (112 feet).Ancient coins indicate preliminary plans to top the column with a statue of a bird, probably an eagle, but after construction, a statue of Trajan was put in place; this statue disappeared in the Middle Ages. On December 4, 1587, the top was crowned by Pope Sixtus V with a bronze figure of St. Peter, which remains to this day.

The column was originally flanked by two libraries, which may have contained Trajan's scroll-written despatches from his Roman-Dacian Wars. Filippo Coarelli suggests that such scrolls are the basis both of the column's design and its spiraling, sculpted narrative. The column shows 2,662 figures, and 155 scenes; Trajan himself appears on the column 58 times.

Vertebral column

The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates has been replaced by a segmented series of bone: vertebrae separated by intervertebral discs. The vertebral column houses the spinal canal, a cavity that encloses and protects the spinal cord.

There are about 50,000 species of animals that have a vertebral column. The human vertebral column is one of the most-studied examples.

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