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Springs have been used for a variety of human needs - including drinking water, domestic water supply, irrigation, mills, navigation, and electricity generation. Modern uses include recreational activities such as fishing, swimming, and floating; therapy; water for livestock; fish hatcheries; and supply for bottled mineral water or bottled spring water. Springs have taken on a kind of mythic quality in that some people falsely believe that springs are always healthy sources of drinking water. They may or may not be. One must take a comprehensive water quality test to know how to use a spring appropriately, whether for a mineral bath or drinking water. Springs that are managed as spas will already have such a test.
Drinking water
Springs are often used as sources for bottled water. When purchasing bottled water labeled as spring water one can often find the water test for that spring on the website of the company selling it.
Irrigation
Springs have been used as sources of water for gravity-fed irrigation of crops. Indigenous people of the American Southwest built spring-fed acequias that directed water to fields through canals. The Spanish missionaries later used this method.
Sacred springs
A sacred spring, or holy well, is a small body of water emerging from underground and revered in some religious context: Christian and/or pagan and/or other. The lore and mythology of ancient Greece was replete with sacred and storied springs—notably, the Corycian, Pierian and Castalian springs. In medieval Europe, pagan sacred sites frequently became Christianized as holy wells. The term "holy well" is commonly employed to refer to any water source of limited size (i.e., not a lake or river, but including pools and natural springs and seeps), which has some significance in local folklore. This can take the form of a particular name, an associated legend, the attribution of healing qualities to the water through the numinous presence of its guardian spirit or of a Christian saint, or a ceremony or ritual centered on the well site. Christian legends often recount how the action of a saint caused a spring's water to flow - a familiar theme, especially in the hagiography of Celtic saints.
Thermal springs
The geothermally heated groundwater that flows from thermal springs is greater than human body temperature, usually in the range of , but they can be hotter. Those springs with water cooler than body temperature but warmer than air temperature are sometimes referred to as warm springs. | Spring (hydrology) | Wikipedia | 492 | 316612 | https://en.wikipedia.org/wiki/Spring%20%28hydrology%29 | Physical sciences | Hydrology | null |
Bathing and balneotherapy
Hot springs or geothermal springs have been used for balneotherapy, bathing, and relaxation for thousands of years. Because of the folklore surrounding hot springs and their claimed medical value, some have become tourist destinations and locations of physical rehabilitation centers.
Geothermal energy
Hot springs have been used as a heat source for thousands of years. In the 20th century, they became a renewable resource of geothermal energy for heating homes and buildings. The city of Beppu, Japan contains 2,217 hot spring well heads that provide the city with hot water. Hot springs have also been used as a source of sustainable energy for greenhouse cultivation and the growing of crops and flowers.
Terminology
Spring boil
Spring pool
Spring runs also called rheocrene springs
Spring vent
Cultural representations
Springs have been represented in culture through art, mythology, and folklore throughout history. The Fountain of Youth is a mythical spring which was said to restore youth to anyone who drank from it. It has been claimed that the fountain is located in St. Augustine, Florida, and was discovered by Juan Ponce de León in 1513. However, it has not demonstrated the power to restore youth, and most historians dispute the veracity of Ponce de León's discovery.
Pythia, also known as the Oracle at Delphi was the high priestess of the Temple of Apollo. She delivered prophesies in a frenzied state of divine possession that were "induced by vapours rising from a chasm in the rock". It is believed that the vapors were emitted from the Kerna spring at Delphi.
The Greek myth of Narcissus describes a young man who fell in love with his reflection in the still pool of a spring. Narcissus gazed into "an unmuddied spring, silvery from its glittering waters, which neither shepherds nor she-goats grazing on the mountain nor any other cattle had touched, which neither bird nor beast nor branch fallen from a tree had disturbed." (Ovid)
The early 20th century American photographer, James Reuel Smith created a comprehensive series of photographs documenting the historical springs of New York City before they were capped by the city after the advent of the municipal water system. Smith later photographed springs in Europe leading to his book, Springs and Wells in Greek and Roman Literature, Their Legends and Locations (1922). | Spring (hydrology) | Wikipedia | 475 | 316612 | https://en.wikipedia.org/wiki/Spring%20%28hydrology%29 | Physical sciences | Hydrology | null |
The 19th century Japanese artists Utagawa Hiroshige and Utagawa Toyokuni III created a series of wood-block prints, Two Artists Tour the Seven Hot Springs (Sōhitsu shichitō meguri) in 1854.
The Chinese city Jinan is known as "a City of Springs" (Chinese: 泉城), because of its 72 spring attractions and numerous micro spring holes spread over the city centre. | Spring (hydrology) | Wikipedia | 83 | 316612 | https://en.wikipedia.org/wiki/Spring%20%28hydrology%29 | Physical sciences | Hydrology | null |
A spring is a device consisting of an elastic but largely rigid material (typically metal) bent or molded into a form (especially a coil) that can return into shape after being compressed or extended. Springs can store energy when compressed. In everyday use, the term most often refers to coil springs, but there are many different spring designs. Modern springs are typically manufactured from spring steel. An example of a non-metallic spring is the bow, made traditionally of flexible yew wood, which when drawn stores energy to propel an arrow.
When a conventional spring, without stiffness variability features, is compressed or stretched from its resting position, it exerts an opposing force approximately proportional to its change in length (this approximation breaks down for larger deflections). The rate or spring constant of a spring is the change in the force it exerts, divided by the change in deflection of the spring. That is, it is the gradient of the force versus deflection curve. An extension or compression spring's rate is expressed in units of force divided by distance, for example or N/m or lbf/in. A torsion spring is a spring that works by twisting; when it is twisted about its axis by an angle, it produces a torque proportional to the angle. A torsion spring's rate is in units of torque divided by angle, such as N·m/rad or ft·lbf/degree. The inverse of spring rate is compliance, that is: if a spring has a rate of 10 N/mm, it has a compliance of 0.1 mm/N. The stiffness (or rate) of springs in parallel is additive, as is the compliance of springs in series.
Springs are made from a variety of elastic materials, the most common being spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after manufacture. Some non-ferrous metals are also used, including phosphor bronze and titanium for parts requiring corrosion resistance, and low-resistance beryllium copper for springs carrying electric current. | Spring (device) | Wikipedia | 434 | 316617 | https://en.wikipedia.org/wiki/Spring%20%28device%29 | Technology | Components_2 | null |
History
Simple non-coiled springs have been used throughout human history, e.g. the bow (and arrow). In the Bronze Age more sophisticated spring devices were used, as shown by the spread of tweezers in many cultures. Ctesibius of Alexandria developed a method for making springs out of an alloy of bronze with an increased proportion of tin, hardened by hammering after it was cast.
Coiled springs appeared early in the 15th century, in door locks. The first spring powered-clocks appeared in that century and evolved into the first large watches by the 16th century.
In 1676 British physicist Robert Hooke postulated Hooke's law, which states that the force a spring exerts is proportional to its extension.
On March 8, 1850, John Evans, Founder of John Evans' Sons, Incorporated, opened his business in New Haven, Connecticut, manufacturing flat springs for carriages and other vehicles, as well as the machinery to manufacture the springs. Evans was a Welsh blacksmith and springmaker who emigrated to the United States in 1847, John Evans' Sons became "America's oldest springmaker" which continues to operate today.
Types
Classification
Springs can be classified depending on how the load force is applied to them:
Tension/extension spring The spring is designed to operate with a tension load, so the spring stretches as the load is applied to it.
Compression spring Designed to operate with a compression load, so the spring gets shorter as the load is applied to it.
Torsion spring Unlike the above types in which the load is an axial force, the load applied to a torsion spring is a torque or twisting force, and the end of the spring rotates through an angle as the load is applied.
Constant spring Supported load remains the same throughout deflection cycle
Variable spring Resistance of the coil to load varies during compression
Variable stiffness spring Resistance of the coil to load can be dynamically varied for example by the control system, some types of these springs also vary their length thereby providing actuation capability as well
They can also be classified based on their shape: | Spring (device) | Wikipedia | 416 | 316617 | https://en.wikipedia.org/wiki/Spring%20%28device%29 | Technology | Components_2 | null |
Flat spring Made of a flat spring steel.
Machined spring Manufactured by machining bar stock with a lathe and/or milling operation rather than a coiling operation. Since it is machined, the spring may incorporate features in addition to the elastic element. Machined springs can be made in the typical load cases of compression/extension, torsion, etc.
Serpentine spring A zig-zag of thick wire, often used in modern upholstery/furniture.
Garter spring A coiled steel spring that is connected at each end to create a circular shape.
Common types
The most common types of spring are: | Spring (device) | Wikipedia | 126 | 316617 | https://en.wikipedia.org/wiki/Spring%20%28device%29 | Technology | Components_2 | null |
Cantilever spring A flat spring fixed only at one end like a cantilever, while the free-hanging end takes the load.
Coil spring Also known as a helical spring. A spring (made by winding a wire around a cylinder) is of two types:
Tension or extension springs are designed to become longer under load. Their turns (loops) are normally touching in the unloaded position, and they have a hook, eye or some other means of attachment at each end.
Compression springs are designed to become shorter when loaded. Their turns (loops) are not touching in the unloaded position, and they need no attachment points.
Hollow tubing springs can be either extension springs or compression springs. Hollow tubing is filled with oil and the means of changing hydrostatic pressure inside the tubing such as a membrane or miniature piston etc. to harden or relax the spring, much like it happens with water pressure inside a garden hose. Alternatively tubing's cross-section is chosen of a shape that it changes its area when tubing is subjected to torsional deformation: change of the cross-section area translates into change of tubing's inside volume and the flow of oil in/out of the spring that can be controlled by valve thereby controlling stiffness. There are many other designs of springs of hollow tubing which can change stiffness with any desired frequency, change stiffness by a multiple or move like a linear actuator in addition to its spring qualities.
Arc spring A pre-curved or arc-shaped helical compression spring, which is able to transmit a torque around an axis.
Volute spring A compression coil spring in the form of a cone so that under compression the coils are not forced against each other, thus permitting longer travel.
Balance spring Also known as a hairspring. A delicate spiral spring used in watches, galvanometers, and places where electricity must be carried to partially rotating devices such as steering wheels without hindering the rotation.
Leaf spring A flat spring used in vehicle suspensions, electrical switches, and bows.
V-spring Used in antique firearm mechanisms such as the wheellock, flintlock and percussion cap locks. Also door-lock spring, as used in antique door latch mechanisms.
Other types
Other types include: | Spring (device) | Wikipedia | 461 | 316617 | https://en.wikipedia.org/wiki/Spring%20%28device%29 | Technology | Components_2 | null |
Belleville washer A disc shaped spring commonly used to apply tension to a bolt (and also in the initiation mechanism of pressure-activated landmines)
Constant-force spring A tightly rolled ribbon that exerts a nearly constant force as it is unrolled
Gas spring A volume of compressed gas.
Ideal spring An idealised perfect spring with no weight, mass, damping losses, or limits, a concept used in physics. The force an ideal spring would exert is exactly proportional to its extension or compression.
Mainspring A spiral ribbon-shaped spring used as a power store of clockwork mechanisms: watches, clocks, music boxes, windup toys, and mechanically powered flashlights
Negator spring A thin metal band slightly concave in cross-section. When coiled it adopts a flat cross-section but when unrolled it returns to its former curve, thus producing a constant force throughout the displacement and negating any tendency to re-wind. The most common application is the retracting steel tape rule.
Progressive rate coil springs A coil spring with a variable rate, usually achieved by having unequal distance between turns so that as the spring is compressed one or more coils rests against its neighbour.
Rubber band A tension spring where energy is stored by stretching the material.
Spring washer Used to apply a constant tensile force along the axis of a fastener.
Torsion spring Any spring designed to be twisted rather than compressed or extended. Used in torsion bar vehicle suspension systems.
Wave spring various types of spring made compact by using waves to give a spring effect.
Physics
Hooke's law
An ideal spring acts in accordance with Hooke's law, which states that the force with which the spring pushes back is linearly proportional to the distance from its equilibrium length:
,
where
is the displacement vector – the distance from its equilibrium length.
is the resulting force vector – the magnitude and direction of the restoring force the spring exerts
is the rate, spring constant or force constant of the spring, a constant that depends on the spring's material and construction. The negative sign indicates that the force the spring exerts is in the opposite direction from its displacement
Most real springs approximately follow Hooke's law if not stretched or compressed beyond their elastic limit.
Coil springs and other common springs typically obey Hooke's law. There are useful springs that don't: springs based on beam bending can for example produce forces that vary nonlinearly with displacement. | Spring (device) | Wikipedia | 501 | 316617 | https://en.wikipedia.org/wiki/Spring%20%28device%29 | Technology | Components_2 | null |
If made with constant pitch (wire thickness), conical springs have a variable rate. However, a conical spring can be made to have a constant rate by creating the spring with a variable pitch. A larger pitch in the larger-diameter coils and a smaller pitch in the smaller-diameter coils forces the spring to collapse or extend all the coils at the same rate when deformed.
Simple harmonic motion
Since force is equal to mass, m, times acceleration, a, the force equation for a spring obeying Hooke's law looks like:
The mass of the spring is small in comparison to the mass of the attached mass and is ignored. Since acceleration is simply the second derivative of x with respect to time,
This is a second order linear differential equation for the displacement as a function of time. Rearranging:
the solution of which is the sum of a sine and cosine:
and are arbitrary constants that may be found by considering the initial displacement and velocity of the mass. The graph of this function with (zero initial position with some positive initial velocity) is displayed in the image on the right.
Energy dynamics
In simple harmonic motion of a spring-mass system, energy will fluctuate between kinetic energy and potential energy, but the total energy of the system remains the same. A spring that obeys Hooke's Law with spring constant k will have a total system energy E of:
Here, A is the amplitude of the wave-like motion that is produced by the oscillating behavior of the spring.
The potential energy U of such a system can be determined through the spring constant k and its displacement x:
The kinetic energy K of an object in simple harmonic motion can be found using the mass of the attached object m and the velocity at which the object oscillates v:
Since there is no energy loss in such a system, energy is always conserved and thus:
Frequency & period
The angular frequency ω of an object in simple harmonic motion, given in radians per second, is found using the spring constant k and the mass of the oscillating object m:
The period T, the amount of time for the spring-mass system to complete one full cycle, of such harmonic motion is given by:
The frequency f, the number of oscillations per unit time, of something in simple harmonic motion is found by taking the inverse of the period: | Spring (device) | Wikipedia | 489 | 316617 | https://en.wikipedia.org/wiki/Spring%20%28device%29 | Technology | Components_2 | null |
Theory
In classical physics, a spring can be seen as a device that stores potential energy, specifically elastic potential energy, by straining the bonds between the atoms of an elastic material.
Hooke's law of elasticity states that the extension of an elastic rod (its distended length minus its relaxed length) is linearly proportional to its tension, the force used to stretch it. Similarly, the contraction (negative extension) is proportional to the compression (negative tension).
This law actually holds only approximately, and only when the deformation (extension or contraction) is small compared to the rod's overall length. For deformations beyond the elastic limit, atomic bonds get broken or rearranged, and a spring may snap, buckle, or permanently deform. Many materials have no clearly defined elastic limit, and Hooke's law can not be meaningfully applied to these materials. Moreover, for the superelastic materials, the linear relationship between force and displacement is appropriate only in the low-strain region.
Hooke's law is a mathematical consequence of the fact that the potential energy of the rod is a minimum when it has its relaxed length. Any smooth function of one variable approximates a quadratic function when examined near enough to its minimum point as can be seen by examining the Taylor series. Therefore, the force – which is the derivative of energy with respect to displacement – approximates a linear function.
Force of fully compressed spring
where
E – Young's modulus
d – spring wire diameter
L – free length of spring
n – number of active windings
– Poisson ratio
D – spring outer diameter
Zero-length springs
Zero-length spring is a term for a specially designed coil spring that would exert zero force if it had zero length. That is, in a line graph of the spring's force versus its length, the line passes through the origin. A real coil spring will not contract to zero length because at some point the coils touch each other. "Length" here is defined as the distance between the axes of the pivots at each end of the spring, regardless of any inelastic portion in-between. | Spring (device) | Wikipedia | 435 | 316617 | https://en.wikipedia.org/wiki/Spring%20%28device%29 | Technology | Components_2 | null |
Zero-length springs are made by manufacturing a coil spring with built-in tension (A twist is introduced into the wire as it is coiled during manufacture; this works because a coiled spring unwinds as it stretches), so if it could contract further, the equilibrium point of the spring, the point at which its restoring force is zero, occurs at a length of zero. In practice, the manufacture of springs is typically not accurate enough to produce springs with tension consistent enough for applications that use zero length springs, so they are made by combining a negative length spring, made with even more tension so its equilibrium point would be at a negative length, with a piece of inelastic material of the proper length so the zero force point would occur at zero length.
A zero-length spring can be attached to a mass on a hinged boom in such a way that the force on the mass is almost exactly balanced by the vertical component of the force from the spring, whatever the position of the boom. This creates a horizontal pendulum with very long oscillation period. Long-period pendulums enable seismometers to sense the slowest waves from earthquakes. The LaCoste suspension with zero-length springs is also used in gravimeters because it is very sensitive to changes in gravity. Springs for closing doors are often made to have roughly zero length, so that they exert force even when the door is almost closed, so they can hold it closed firmly.
Uses
Airsoft gun
Aerospace
Retractable ballpoint pens
Buckling spring keyboards
Clockwork clocks, watches, and other things
Firearms
Forward or aft spring, a method of mooring a vessel to a shore fixture
Gravimeters
Industrial Equipment
Jewelry: Clasp mechanisms
Most folding knives, and switchblades
Lock mechanisms: Key-recognition and for coordinating the movements of various parts of the lock.
Spring mattresses
Medical Devices
Pogo Stick
Pop-open devices: CD players, tape recorders, toasters, etc.
Spring reverb
Toys; the Slinky toy is just a spring
Trampoline
Upholstery coil springs
Vehicle suspension, Leaf springs | Spring (device) | Wikipedia | 427 | 316617 | https://en.wikipedia.org/wiki/Spring%20%28device%29 | Technology | Components_2 | null |
In polymer chemistry, emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water, monomers, and surfactants. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer (the oil) are emulsified (with surfactants) in a continuous phase of water. Water-soluble polymers, such as certain polyvinyl alcohols or hydroxyethyl celluloses, can also be used to act as emulsifiers/stabilizers. The name "emulsion polymerization" is a misnomer that arises from a historical misconception. Rather than occurring in emulsion droplets, polymerization takes place in the latex/colloid particles that form spontaneously in the first few minutes of the process. These latex particles are typically 100 nm in size, and are made of many individual polymer chains. The particles are prevented from coagulating with each other because each particle is surrounded by the surfactant ('soap'); the charge on the surfactant repels other particles electrostatically. When water-soluble polymers are used as stabilizers instead of soap, the repulsion between particles arises because these water-soluble polymers form a 'hairy layer' around a particle that repels other particles, because pushing particles together would involve compressing these chains.
Emulsion polymerization is used to make several commercially important polymers. Many of these polymers are used as solid materials and must be isolated from the aqueous dispersion after polymerization. In other cases the dispersion itself is the end product. A dispersion resulting from emulsion polymerization is often called a latex (especially if derived from a synthetic rubber) or an emulsion (even though "emulsion" strictly speaking refers to a dispersion of an immiscible liquid in water). These emulsions find applications in adhesives, paints, paper coating and textile coatings. They are often preferred over solvent-based products in these applications due to the absence of volatile organic compounds (VOCs) in them. | Emulsion polymerization | Wikipedia | 436 | 316993 | https://en.wikipedia.org/wiki/Emulsion%20polymerization | Physical sciences | Organic reactions | Chemistry |
Advantages of emulsion polymerization include:
High molecular weight polymers can be made at fast polymerization rates. By contrast, in bulk and solution free-radical polymerization, there is a tradeoff between molecular weight and polymerization rate.
The continuous water phase is an excellent conductor of heat, enabling fast polymerization rates without loss of temperature control.
Since polymer molecules are contained within the particles, the viscosity of the reaction medium remains close to that of water and is not dependent on molecular weight.
The final product can be used as is and does not generally need to be altered or processed.
Disadvantages of emulsion polymerization include:
Surfactants and other polymerization adjuvants remain in the polymer or are difficult to remove
For dry (isolated) polymers, water removal is an energy-intensive process
Emulsion polymerizations are usually designed to operate at high conversion of monomer to polymer. This can result in significant chain transfer to polymer.
Can not be used for condensation, ionic, or Ziegler-Natta polymerization, although some exceptions are known.
History
The early history of emulsion polymerization is connected with the field of synthetic rubber. The idea of using an emulsified monomer in an aqueous suspension or emulsion was first conceived at Bayer, before World War I, in an attempt to prepare synthetic rubber. The impetus for this development was the observation that natural rubber is produced at room temperature in dispersed particles stabilized by colloidal polymers, so the industrial chemists tried to duplicate these conditions. The Bayer workers used naturally occurring polymers such as gelatin, ovalbumin, and starch to stabilize their dispersion. By today's definition these were not true emulsion polymerizations, but suspension polymerizations.
The first "true" emulsion polymerizations, which used a surfactant and polymerization initiator, were conducted in the 1920s to polymerize isoprene. Over the next twenty years, through the end of World War II, efficient methods for production of several forms of synthetic rubber by emulsion polymerization were developed, but relatively few publications in the scientific literature appeared: most disclosures were confined to patents or were kept secret due to wartime needs. | Emulsion polymerization | Wikipedia | 449 | 316993 | https://en.wikipedia.org/wiki/Emulsion%20polymerization | Physical sciences | Organic reactions | Chemistry |
After World War II, emulsion polymerization was extended to production of plastics. Manufacture of dispersions to be used in latex paints and other products sold as liquid dispersions commenced. Ever more sophisticated processes were devised to prepare products that replaced solvent-based materials. Ironically, synthetic rubber manufacture turned more and more away from emulsion polymerization as new organometallic catalysts were developed that allowed much better control of polymer architecture.
Theoretical overview
The first successful theory to explain the distinct features of emulsion polymerization was developed by Smith and Ewart, and Harkins in the 1940s, based on their studies of polystyrene. Smith and Ewart arbitrarily divided the mechanism of emulsion polymerization into three stages or intervals. Subsequently, it has been recognized that not all monomers or systems undergo these particular three intervals. Nevertheless, the Smith-Ewart description is a useful starting point to analyze emulsion polymerizations. | Emulsion polymerization | Wikipedia | 192 | 316993 | https://en.wikipedia.org/wiki/Emulsion%20polymerization | Physical sciences | Organic reactions | Chemistry |
The Smith-Ewart-Harkins theory for the mechanism of free-radical emulsion polymerization is summarized by the following steps:
A monomer is dispersed or emulsified in a solution of surfactant and water, forming relatively large droplets in water.
Excess surfactant creates micelles in the water.
Small amounts of monomer diffuse through the water to the micelle.
A water-soluble initiator is introduced into the water phase where it reacts with monomer in the micelles. (This characteristic differs from suspension polymerization where an oil-soluble initiator dissolves in the monomer, followed by polymer formation in the monomer droplets themselves.) This is considered Smith-Ewart interval 1.
The total surface area of the micelles is much greater than the total surface area of the fewer, larger monomer droplets; therefore the initiator typically reacts in the micelle and not the monomer droplet.
Monomer in the micelle quickly polymerizes and the growing chain terminates. At this point the monomer-swollen micelle has turned into a polymer particle. When both monomer droplets and polymer particles are present in the system, this is considered Smith-Ewart interval 2.
More monomer from the droplets diffuses to the growing particle, where more initiators will eventually react.
Eventually the free monomer droplets disappear and all remaining monomer is located in the particles. This is considered Smith-Ewart interval 3.
Depending on the particular product and monomer, additional monomer and initiator may be continuously and slowly added to maintain their levels in the system as the particles grow.
The final product is a dispersion of polymer particles in water. It can also be known as a polymer colloid, a latex, or commonly and inaccurately as an 'emulsion'.
Smith-Ewart theory does not predict the specific polymerization behavior when the monomer is somewhat water-soluble, like methyl methacrylate or vinyl acetate. In these cases homogeneous nucleation occurs: particles are formed without the presence or need for surfactant micelles. | Emulsion polymerization | Wikipedia | 432 | 316993 | https://en.wikipedia.org/wiki/Emulsion%20polymerization | Physical sciences | Organic reactions | Chemistry |
High molecular weights are developed in emulsion polymerization because the concentration of growing chains within each polymer particle is very low. In conventional radical polymerization, the concentration of growing chains is higher, which leads to termination by coupling, which ultimately results in shorter polymer chains. The original Smith-Ewart-Hawkins mechanism required each particle to contain either zero or one growing chain. Improved understanding of emulsion polymerization has relaxed that criterion to include more than one growing chain per particle, however, the number of growing chains per particle is still considered to be very low.
Because of the complex chemistry that occurs during an emulsion polymerization, including polymerization kinetics and particle formation kinetics, quantitative understanding of the mechanism of emulsion polymerization has required extensive computer simulation. Robert Gilbert has summarized a recent theory.
More detailed treatment of Smith-Ewart theory
Interval 1
When radicals generated in the aqueous phase encounter the monomer within the micelle, they initiate polymerization. The conversion of monomer to polymer within the micelle lowers the monomer concentration and generates a monomer concentration gradient. Consequently, the monomer from monomer droplets and uninitiated micelles begin to diffuse to the growing, polymer-containing, particles. Those micelles that did not encounter a radical during the earlier stage of conversion begin to disappear, losing their monomer and surfactant to the growing particles. The theory predicts that after the end of this interval, the number of growing polymer particles remains constant. | Emulsion polymerization | Wikipedia | 301 | 316993 | https://en.wikipedia.org/wiki/Emulsion%20polymerization | Physical sciences | Organic reactions | Chemistry |
Interval 2
This interval is also known as steady state reaction stage. Throughout this stage, monomer droplets act as reservoirs supplying monomer to the growing polymer particles by diffusion through the water. While at steady state, the ratio of free radicals per particle can be divided into three cases. When the number of free radicals per particle is less than , this is called Case 1. When the number of free radicals per particle equals , this is called Case 2. And when there is greater than radical per particle, this is called Case 3. Smith-Ewart theory predicts that Case 2 is the predominant scenario for the following reasons. A monomer-swollen particle that has been struck by a radical contains one growing chain. Because only one radical (at the end of the growing polymer chain) is present, the chain cannot terminate, and it will continue to grow until a second initiator radical enters the particle. As the rate of termination is much greater than the rate of propagation, and because the polymer particles are extremely small, chain growth is terminated immediately after the entrance of the second initiator radical. The particle then remains dormant until a third initiator radical enters, initiating the growth of a second chain. Consequently, the polymer particles in this case either have zero radicals (dormant state), or 1 radical (polymer growing state) and a very short period of 2 radicals (terminating state) which can be ignored for the free radicals per particle calculation. At any given time, a micelle contains either one growing chain or no growing chains (assumed to be equally probable). Thus, on average, there is around 1/2 radical per particle, leading to the Case 2 scenario. The polymerization rate in this stage can be expressed by
where is the homogeneous propagation rate constant for polymerization within the particles and is the equilibrium monomer concentration within a particle. represents the overall concentration of polymerizing radicals in the reaction. For Case 2, where the average number of free radicals per micelle are , can be calculated in following expression:
where is number concentration of micelles (number of micelles per unit volume), and is the Avogadro constant (). Consequently, the rate of polymerization is then
Interval 3
Separate monomer droplets disappear as the reaction continues. Polymer particles in this stage may be sufficiently large enough that they contain more than 1 radical per particle. | Emulsion polymerization | Wikipedia | 477 | 316993 | https://en.wikipedia.org/wiki/Emulsion%20polymerization | Physical sciences | Organic reactions | Chemistry |
Process considerations
Emulsion polymerizations have been used in batch, semi-batch, and continuous processes. The choice depends on the properties desired in the final polymer or dispersion and on the economics of the product. Modern process control schemes have enabled the development of complex reaction processes, with ingredients such as initiator, monomer, and surfactant added at the beginning, during, or at the end of the reaction.
Early styrene-butadiene rubber (SBR) recipes are examples of true batch processes: all ingredients added at the same time to the reactor. Semi-batch recipes usually include a programmed feed of monomer to the reactor. This enables a starve-fed reaction to ensure a good distribution of monomers into the polymer backbone chain. Continuous processes have been used to manufacture various grades of synthetic rubber.
Some polymerizations are stopped before all the monomer has reacted. This minimizes chain transfer to polymer. In such cases the monomer must be removed or stripped from the dispersion.
Colloidal stability is a factor in design of an emulsion polymerization process. For dry or isolated products, the polymer dispersion must be isolated, or converted into solid form. This can be accomplished by simple heating of the dispersion until all water evaporates. More commonly, the dispersion is destabilized (sometimes called "broken") by addition of a multivalent cation. Alternatively, acidification will destabilize a dispersion with a carboxylic acid surfactant. These techniques may be employed in combination with application of shear to increase the rate of destabilization. After isolation of the polymer, it is usually washed, dried, and packaged.
By contrast, products sold as a dispersion are designed with a high degree of colloidal stability. Colloidal properties such as particle size, particle size distribution, and viscosity are of critical importance to the performance of these dispersions.
Living polymerization processes that are carried out via emulsion polymerization such as iodine-transfer polymerization and RAFT have been developed.
Controlled coagulation techniques can enable better control of the particle size and distribution.
Components | Emulsion polymerization | Wikipedia | 449 | 316993 | https://en.wikipedia.org/wiki/Emulsion%20polymerization | Physical sciences | Organic reactions | Chemistry |
Monomers
Typical monomers are those that undergo radical polymerization, are liquid or gaseous at reaction conditions, and are poorly soluble in water. Solid monomers are difficult to disperse in water. If monomer solubility is too high, particle formation may not occur and the reaction kinetics reduce to that of solution polymerization.
Ethene and other simple olefins must be polymerized at very high pressures (up to 800 bar).
Comonomers
Copolymerization is common in emulsion polymerization. The same rules and comonomer pairs that exist in radical polymerization operate in emulsion polymerization. However, copolymerization kinetics are greatly influenced by the aqueous solubility of the monomers. Monomers with greater aqueous solubility will tend to partition in the aqueous phase and not in the polymer particle. They will not get incorporated as readily in the polymer chain as monomers with lower aqueous solubility. This can be avoided by a programmed addition of monomer using a semi-batch process.
Ethene and other alkenes are used as minor comonomers in emulsion polymerization, notably in vinyl acetate copolymers.
Small amounts of acrylic acid or other ionizable monomers are sometimes used to confer colloidal stability to a dispersion.
Initiators
Both thermal and redox generation of free radicals have been used in emulsion polymerization. Persulfate salts are commonly used in both initiation modes. The persulfate ion readily breaks up into sulfate radical ions above about 50 °C, providing a thermal source of initiation. Redox initiation takes place when an oxidant such as a persulfate salt, a reducing agent such as glucose, Rongalite, or sulfite, and a redox catalyst such as an iron compound are all included in the polymerization recipe. Redox recipes are not limited by temperature and are used for polymerizations that take place below 50 °C.
Although organic peroxides and hydroperoxides are used in emulsion polymerization, initiators are usually water soluble and partition into the water phase. This enables the particle generation behavior described in the theory section. In redox initiation, either the oxidant or the reducing agent (or both) must be water-soluble, but one component can be water-insoluble. | Emulsion polymerization | Wikipedia | 494 | 316993 | https://en.wikipedia.org/wiki/Emulsion%20polymerization | Physical sciences | Organic reactions | Chemistry |
Surfactants
Selection of the correct surfactant is critical to the development of any emulsion polymerization process. The surfactant must enable a fast rate of polymerization, minimize coagulum or fouling in the reactor and other process equipment, prevent an unacceptably high viscosity during polymerization (which leads to poor heat transfer), and maintain or even improve properties in the final product such as tensile strength, gloss, and water absorption.
Anionic, nonionic, and cationic surfactants have been used, although anionic surfactants are by far most prevalent. Surfactants with a low critical micelle concentration (CMC) are favored; the polymerization rate shows a dramatic increase when the surfactant level is above the CMC, and minimization of the surfactant is preferred for economic reasons and the (usually) adverse effect of surfactant on the physical properties of the resulting polymer. Mixtures of surfactants are often used, including mixtures of anionic with nonionic surfactants. Mixtures of cationic and anionic surfactants form insoluble salts and are not useful.
Examples of surfactants commonly used in emulsion polymerization include fatty acids, sodium lauryl sulfate, and alpha-olefin sulfonate.
Non-surfactant stabilizers
Some grades of polyvinyl alcohol and other water-soluble polymers can promote emulsion polymerization even though they do not typically form micelles and do not act as surfactants (for example, they do not lower surface tension). It is believed that growing polymer chains graft onto these water-soluble polymers, which stabilize the resulting particles.
Dispersions prepared with such stabilizers typically exhibit excellent colloidal stability (for example, dry powders may be mixed into the dispersion without causing coagulation). However, they often result in products that are very water sensitive due to the presence of the water-soluble polymer.
Other ingredients
Other ingredients found in emulsion polymerization include chain transfer agents, buffering agents, and inert salts. Preservatives are added to products sold as liquid dispersions to retard bacterial growth. These are usually added after polymerization, however.
Applications
Polymers produced by emulsion polymerization can roughly be divided into three categories. | Emulsion polymerization | Wikipedia | 485 | 316993 | https://en.wikipedia.org/wiki/Emulsion%20polymerization | Physical sciences | Organic reactions | Chemistry |
Synthetic rubber
Some grades of styrene-butadiene (SBR)
Some grades of Polybutadiene
Polychloroprene (Neoprene)
Nitrile rubber
Acrylic rubber
Fluoroelastomer (FKM)
Plastics
Some grades of PVC
Some grades of polystyrene
Some grades of PMMA
Acrylonitrile-butadiene-styrene terpolymer (ABS)
Polyvinylidene fluoride
Polyvinyl fluoride
PTFE
Dispersions (i.e. polymers sold as aqueous dispersions)
polyvinyl acetate
polyvinyl acetate copolymers
polyacrylates
Styrene-butadiene
VAE (vinyl acetate – ethylene copolymers) | Emulsion polymerization | Wikipedia | 164 | 316993 | https://en.wikipedia.org/wiki/Emulsion%20polymerization | Physical sciences | Organic reactions | Chemistry |
El Niño–Southern Oscillation (ENSO) is a global climate phenomenon that emerges from variations in winds and sea surface temperatures over the tropical Pacific Ocean. Those variations have an irregular pattern but do have some semblance of cycles. The occurrence of ENSO is not predictable. It affects the climate of much of the tropics and subtropics, and has links (teleconnections) to higher-latitude regions of the world. The warming phase of the sea surface temperature is known as "El Niño" and the cooling phase as "La Niña". The Southern Oscillation is the accompanying atmospheric oscillation, which is coupled with the sea temperature change.
El Niño is associated with higher than normal air sea level pressure over Indonesia, Australia and across the Indian Ocean to the Atlantic. La Niña has roughly the reverse pattern: high pressure over the central and eastern Pacific and lower pressure through much of the rest of the tropics and subtropics. The two phenomena last a year or so each and typically occur every two to seven years with varying intensity, with neutral periods of lower intensity interspersed. El Niño events can be more intense but La Niña events may repeat and last longer.
A key mechanism of ENSO is the Bjerknes feedback (named after Jacob Bjerknes in 1969) in which the atmospheric changes alter the sea temperatures that in turn alter the atmospheric winds in a positive feedback. Weaker easterly trade winds result in a surge of warm surface waters to the east and reduced ocean upwelling on the equator. In turn, this leads to warmer sea surface temperatures (called El Niño), a weaker Walker circulation (an east-west overturning circulation in the atmosphere) and even weaker trade winds. Ultimately the warm waters in the western tropical Pacific are depleted enough so that conditions return to normal. The exact mechanisms that cause the oscillation are unclear and are being studied.
Each country that monitors the ENSO has a different threshold for what constitutes an El Niño or La Niña event, which is tailored to their specific interests. | El Niño–Southern Oscillation | Wikipedia | 420 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
El Niño and La Niña affect the global climate and disrupt normal weather patterns, which as a result can lead to intense storms in some places and droughts in others. El Niño events cause short-term (approximately 1 year in length) spikes in global average surface temperature while La Niña events cause short term surface cooling. Therefore, the relative frequency of El Niño compared to La Niña events can affect global temperature trends on timescales of around ten years. The countries most affected by ENSO are developing countries that are bordering the Pacific Ocean and are dependent on agriculture and fishing.
In climate change science, ENSO is known as one of the internal climate variability phenomena. Future trends in ENSO due to climate change are uncertain, although climate change exacerbates the effects of droughts and floods. The IPCC Sixth Assessment Report summarized the scientific knowledge in 2021 for the future of ENSO as follows: "In the long term, it is very likely that the precipitation variance related to El Niño–Southern Oscillation will increase". The scientific consensus is also that "it is very likely that rainfall variability related to changes in the strength and spatial extent of ENSO teleconnections will lead to significant changes at regional scale".
Definition and terminology
The El Niño–Southern Oscillation is a single climate phenomenon that periodically fluctuates between three phases: Neutral, La Niña or El Niño. La Niña and El Niño are opposite phases in the oscillation which are deemed to occur when specific ocean and atmospheric conditions are reached or exceeded.
An early recorded mention of the term "El Niño" ("The Boy" in Spanish) to refer to climate occurred in 1892, when Captain Camilo Carrillo told the geographical society congress in Lima that Peruvian sailors named the warm south-flowing current "El Niño" because it was most noticeable around Christmas. Although pre-Columbian societies were certainly aware of the phenomenon, the indigenous names for it have been lost to history.
The capitalized term El Niño refers to the Christ Child, Jesus, because periodic warming in the Pacific near South America is usually noticed around Christmas.
Originally, the term El Niño applied to an annual weak warm ocean current that ran southwards along the coast of Peru and Ecuador at about Christmas time. However, over time the term has evolved and now refers to the warm and negative phase of the El Niño–Southern Oscillation (ENSO). The original phrase, El Niño de Navidad, arose centuries ago, when Peruvian fishermen named the weather phenomenon after the newborn Christ. | El Niño–Southern Oscillation | Wikipedia | 512 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
La Niña ("The Girl" in Spanish) is the colder counterpart of El Niño, as part of the broader ENSO climate pattern. In the past, it was also called an anti-El Niño and El Viejo, meaning "the old man."
A negative phase exists when atmospheric pressure over Indonesia and the west Pacific is abnormally high and pressure over the east Pacific is abnormally low, during El Niño episodes, and a positive phase is when the opposite occurs during La Niña episodes, and pressure over Indonesia is low and over the west Pacific is high.
Fundamentals
On average, the temperature of the ocean surface in the tropical East Pacific is roughly cooler than in the tropical West Pacific. The sea surface temperature (SST) of the West Pacific northeast of Australia averages around . SSTs in the East Pacific off the western coast of South America are closer to . Strong trade winds near the equator push water away from the East Pacific and towards the West Pacific. This water is slowly warmed by the Sun as it moves west along the equator. The ocean surface near Indonesia is typically around higher than near Peru because of the buildup of water in the West Pacific. The thermocline, or the transitional zone between the warmer waters near the ocean surface and the cooler waters of the deep ocean, is pushed downwards in the West Pacific due to this water accumulation.
The total weight of a column of ocean water is almost the same in the western and east Pacific. Because the warmer waters of the upper ocean are slightly less dense than the cooler deep ocean, the thicker layer of warmer water in the western Pacific means the thermocline there must be deeper. The difference in weight must be enough to drive any deep water return flow. Consequently, the thermocline is tilted across the tropical Pacific, rising from an average depth of about in the West Pacific to a depth of about in the East Pacific. | El Niño–Southern Oscillation | Wikipedia | 383 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Cooler deep ocean water takes the place of the outgoing surface waters in the East Pacific, rising to the ocean surface in a process called upwelling. Along the western coast of South America, water near the ocean surface is pushed westward due to the combination of the trade winds and the Coriolis effect. This process is known as Ekman transport. Colder water from deeper in the ocean rises along the continental margin to replace the near-surface water. This process cools the East Pacific because the thermocline is closer to the ocean surface, leaving relatively little separation between the deeper cold water and the ocean surface. Additionally, the northward-flowing Humboldt Current carries colder water from the Southern Ocean to the tropics in the East Pacific. The combination of the Humboldt Current and upwelling maintains an area of cooler ocean waters off the coast of Peru. The West Pacific lacks a cold ocean current and has less upwelling as the trade winds are usually weaker than in the East Pacific, allowing the West Pacific to reach warmer temperatures. These warmer waters provide energy for the upward movement of air. As a result, the warm West Pacific has on average more cloudiness and rainfall than the cool East Pacific.
ENSO describes a quasi-periodic change of both oceanic and atmospheric conditions over the tropical Pacific Ocean. These changes affect weather patterns across much of the Earth. The tropical Pacific is said to be in one of three states of ENSO (also called "phases") depending on the atmospheric and oceanic conditions. When the tropical Pacific roughly reflects the average conditions, the state of ENSO is said to be in the neutral phase. However, the tropical Pacific experiences occasional shifts away from these average conditions. If trade winds are weaker than average, the effect of upwelling in the East Pacific and the flow of warmer ocean surface waters towards the West Pacific lessen. This results in a cooler West Pacific and a warmer East Pacific, leading to a shift of cloudiness and rainfall towards the East Pacific. This situation is called El Niño. The opposite occurs if trade winds are stronger than average, leading to a warmer West Pacific and a cooler East Pacific. This situation is called La Niña and is associated with increased cloudiness and rainfall over the West Pacific. | El Niño–Southern Oscillation | Wikipedia | 451 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Bjerknes feedback
The close relationship between ocean temperatures and the strength of the trade winds was first identified by Jacob Bjerknes in 1969. Bjerknes also hypothesized that ENSO was a positive feedback system where the associated changes in one component of the climate system (the ocean or atmosphere) tend to reinforce changes in the other. For example, during El Niño, the reduced contrast in ocean temperatures across the Pacific results in weaker trade winds, further reinforcing the El Niño state. This process is known as Bjerknes feedback. Although these associated changes in the ocean and atmosphere often occur together, the state of the atmosphere may resemble a different ENSO phase than the state of the ocean or vice versa. Because their states are closely linked, the variations of ENSO may arise from changes in both the ocean and atmosphere and not necessarily from an initial change of exclusively one or the other. Conceptual models explaining how ENSO operates generally accept the Bjerknes feedback hypothesis. However, ENSO would perpetually remain in one phase if Bjerknes feedback were the only process occurring. Several theories have been proposed to explain how ENSO can change from one state to the next, despite the positive feedback. These explanations broadly fall under two categories. In one view, the Bjerknes feedback naturally triggers negative feedbacks that end and reverse the abnormal state of the tropical Pacific. This perspective implies that the processes that lead to El Niño and La Niña also eventually bring about their end, making ENSO a self-sustaining process. Other theories view the state of ENSO as being changed by irregular and external phenomena such as the Madden–Julian oscillation, tropical instability waves, and westerly wind bursts.
Walker circulation
The three phases of ENSO relate to the Walker circulation, which was named after Gilbert Walker who discovered the Southern Oscillation during the early twentieth century. The Walker circulation is an east-west overturning circulation in the vicinity of the equator in the Pacific. Upward air is associated with high sea temperatures, convection and rainfall, while the downward branch occurs over cooler sea surface temperatures in the east. During El Niño, as the sea surface temperatures change so does the Walker Circulation. Warming in the eastern tropical Pacific weakens or reverses the downward branch, while cooler conditions in the west lead to less rain and downward air, so the Walker Circulation first weakens and may reverse.
Southern Oscillation | El Niño–Southern Oscillation | Wikipedia | 493 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
The Southern Oscillation is the atmospheric component of ENSO. This component is an oscillation in surface air pressure between the tropical eastern and the western Pacific Ocean waters. The strength of the Southern Oscillation is measured by the Southern Oscillation Index (SOI). The SOI is computed from fluctuations in the surface air pressure difference between Tahiti (in the Pacific) and Darwin, Australia (on the Indian Ocean).
El Niño episodes have negative SOI, meaning there is lower pressure over Tahiti and higher pressure in Darwin. La Niña episodes on the other hand have positive SOI, meaning there is higher pressure in Tahiti and lower in Darwin.
Low atmospheric pressure tends to occur over warm water and high pressure occurs over cold water, in part because of deep convection over the warm water. El Niño episodes are defined as sustained warming of the central and eastern tropical Pacific Ocean, thus resulting in a decrease in the strength of the Pacific trade winds, and a reduction in rainfall over eastern and northern Australia. La Niña episodes are defined as sustained cooling of the central and eastern tropical Pacific Ocean, thus resulting in an increase in the strength of the Pacific trade winds, and the opposite effects in Australia when compared to El Niño.
Although the Southern Oscillation Index has a long station record going back to the 1800s, its reliability is limited due to the latitudes of both Darwin and Tahiti being well south of the Equator, so that the surface air pressure at both locations is less directly related to ENSO. To overcome this effect, a new index was created, named the Equatorial Southern Oscillation Index (EQSOI). To generate this index, two new regions, centered on the Equator, were defined. The western region is located over Indonesia and the eastern one over the equatorial Pacific, close to the South American coast. However, data on EQSOI goes back only to 1949.
Sea surface height (SSH) changes up or down by several centimeters in Pacific equatorial region with the ESNO: El Niño causes a positive SSH anomaly (raised sea level) because of thermal expansion while La Niña causes a negative SSH anomaly (lowered sea level) via contraction. | El Niño–Southern Oscillation | Wikipedia | 443 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Three phases of sea surface temperature
The El Niño–Southern Oscillation is a single climate phenomenon that quasi-periodically fluctuates between three phases: Neutral, La Niña or El Niño. La Niña and El Niño are opposite phases which require certain changes to take place in both the ocean and the atmosphere before an event is declared. The cool phase of ENSO is La Niña, with SST in the eastern Pacific below average, and air pressure high in the eastern Pacific and low in the western Pacific. The ENSO cycle, including both El Niño and La Niña, causes global changes in temperature and rainfall.
Neutral phase
If the temperature variation from climatology is within 0.5 °C (0.9 °F), ENSO conditions are described as neutral. Neutral conditions are the transition between warm and cold phases of ENSO. Sea surface temperatures (by definition), tropical precipitation, and wind patterns are near average conditions during this phase. Close to half of all years are within neutral periods. During the neutral ENSO phase, other climate anomalies/patterns such as the sign of the North Atlantic Oscillation or the Pacific–North American teleconnection pattern exert more influence.
El Niño phase
El Niño conditions are established when the Walker circulation weakens or reverses and the Hadley circulation strengthens, leading to the development of a band of warm ocean water in the central and east-central equatorial Pacific (approximately between the International Date Line and 120°W), including the area off the west coast of South America, as upwelling of cold water occurs less or not at all offshore.
This warming causes a shift in the atmospheric circulation, leading to higher air pressure in the western Pacific and lower in the eastern Pacific, with rainfall reducing over Indonesia, India and northern Australia, while rainfall and tropical cyclone formation increases over the tropical Pacific Ocean. The low-level surface trade winds, which normally blow from east to west along the equator, either weaken or start blowing from the other direction.
El Niño phases are known to happen at irregular intervals of two to seven years, and lasts nine months to two years. The average period length is five years. When this warming occurs for seven to nine months, it is classified as El Niño "conditions"; when its duration is longer, it is classified as an El Niño "episode". | El Niño–Southern Oscillation | Wikipedia | 473 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
It is thought that there have been at least 30 El Niño events between 1900 and 2024, with the 1982–83, 1997–98 and 2014–16 events among the strongest on record. Since 2000, El Niño events have been observed in 2002–03, 2004–05, 2006–07, 2009–10, 2014–16, 2018–19, and 2023–24.
Major ENSO events were recorded in the years 1790–93, 1828, 1876–78, 1891, 1925–26, 1972–73, 1982–83, 1997–98, 2014–16, and 2023–24. During strong El Niño episodes, a secondary peak in sea surface temperature across the far eastern equatorial Pacific Ocean sometimes follows the initial peak.
La Niña phase
An especially strong Walker circulation causes La Niña, which is considered to be the cold oceanic and positive atmospheric phase of the broader El Niño–Southern Oscillation (ENSO) weather phenomenon, as well as the opposite of weather pattern, where sea surface temperature across the eastern equatorial part of the central Pacific Ocean will be lower than normal by 3–5 °C (5.4–9 °F). The phenomenon occurs as strong winds blow warm water at the ocean's surface away from South America, across the Pacific Ocean towards Indonesia. As this warm water moves west, cold water from the deep sea rises to the surface near South America.
The movement of so much heat across a quarter of the planet, and particularly in the form of temperature at the ocean surface, can have a significant effect on weather across the entire planet. Tropical instability waves visible on sea surface temperature maps, showing a tongue of colder water, are often present during neutral or La Niña conditions.
La Niña is a complex weather pattern that occurs every few years, often persisting for longer than five months. El Niño and La Niña can be indicators of weather changes across the globe. Atlantic and Pacific hurricanes can have different characteristics due to lower or higher wind shear and cooler or warmer sea surface temperatures.
A timeline of all La Niña episodes between 1900 and 2023. Note that each forecast agency has a different criteria for what constitutes a La Niña event, which is tailored to their specific interests.
La Niña events have been observed for hundreds of years, and occurred on a regular basis during the early parts of both the 17th and 19th centuries. Since the start of the 20th century, La Niña events have occurred during the following years: | El Niño–Southern Oscillation | Wikipedia | 492 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Transitional phases
Transitional phases at the onset or departure of El Niño or La Niña can also be important factors on global weather by affecting teleconnections. Significant episodes, known as Trans-Niño, are measured by the Trans-Niño index (TNI). Examples of affected short-time climate in North America include precipitation in the Northwest US and intense tornado activity in the contiguous US.
Variations
ENSO Modoki
The first ENSO pattern to be recognised, called Eastern Pacific (EP) ENSO, to distinguish if from others, involves temperature anomalies in the eastern Pacific. However, in the 1990s and 2000s, variations of ENSO conditions were observed, in which the usual place of the temperature anomaly (Niño 1 and 2) is not affected, but an anomaly also arises in the central Pacific (Niño 3.4). The phenomenon is called Central Pacific (CP) ENSO, "dateline" ENSO (because the anomaly arises near the dateline), or ENSO "Modoki" (Modoki is Japanese for "similar, but different"). There are variations of ENSO additional to the EP and CP types, and some scientists argue that ENSO exists as a continuum, often with hybrid types.
The effects of the CP ENSO are different from those of the EP ENSO. The El Niño Modoki is associated with more hurricanes more frequently making landfall in the Atlantic. La Niña Modoki leads to a rainfall increase over northwestern Australia and northern Murray–Darling basin, rather than over the eastern portion of the country as in a conventional EP La Niña. Also, La Niña Modoki increases the frequency of cyclonic storms over Bay of Bengal, but decreases the occurrence of severe storms in the Indian Ocean overall.
The first recorded El Niño that originated in the central Pacific and moved toward the east was in 1986. Recent Central Pacific El Niños happened in 1986–87, 1991–92, 1994–95, 2002–03, 2004–05 and 2009–10. Furthermore, there were "Modoki" events in 1957–59, 1963–64, 1965–66, 1968–70, 1977–78 and 1979–80. Some sources say that the El Niños of 2006-07 and 2014-16 were also Central Pacific El Niños. Recent years when La Niña Modoki events occurred include 1973–1974, 1975–1976, 1983–1984, 1988–1989, 1998–1999, 2000–2001, 2008–2009, 2010–2011, and 2016–2017. | El Niño–Southern Oscillation | Wikipedia | 508 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
The recent discovery of ENSO Modoki has some scientists believing it to be linked to global warming. However, comprehensive satellite data go back only to 1979. More research must be done to find the correlation and study past El Niño episodes. More generally, there is no scientific consensus on how/if climate change might affect ENSO.
There is also a scientific debate on the very existence of this "new" ENSO. A number of studies dispute the reality of this statistical distinction or its increasing occurrence, or both, either arguing the reliable record is too short to detect such a distinction, finding no distinction or trend using other statistical approaches, or that other types should be distinguished, such as standard and extreme ENSO.
Likewise, following the asymmetric nature of the warm and cold phases of ENSO, some studies could not identify similar variations for La Niña, both in observations and in the climate models, but some sources could identify variations on La Niña with cooler waters on central Pacific and average or warmer water temperatures on both eastern and western Pacific, also showing eastern Pacific Ocean currents going to the opposite direction compared to the currents in traditional La Niñas.
ENSO Costero
Coined by the Peruvian (ENFEN), ENSO Costero, or ENSO Oriental, is the name given to the phenomenon where the sea-surface temperature anomalies are mostly focused on the South American coastline, especially from Peru and Ecuador. Studies point many factors that can lead to its occurrence, sometimes accompanying, or being accompanied, by a larger EP ENSO occurrence, or even displaying opposite conditions from the observed ones in the other Niño regions when accompanied by Modoki variations.
ENSO Costero events usually present more localized effects, with warm phases leading to increased rainfall over the coast of Ecuador, northern Peru and the Amazon rainforest, and increased temperatures over the northern Chilean coast, and cold phases leading to droughts on the peruvian coast, and increased rainfall and decreased temperatures on its mountainous and jungle regions.
Because they don't influence the global climate as much as the other types, these events present lesser and weaker correlations to other significant ENSO features, neither always being triggered by Kelvin waves, nor always being accompanied by proportional Southern Oscillation responses. According to the Coastal Niño Index (ICEN), strong El Niño Costero events include 1957, 1982–83, 1997–98 and 2015–16, and La Niña Costera ones include 1950, 1954–56, 1962, 1964, 1966, 1967–68, 1970–71, 1975–76 and 2013. | El Niño–Southern Oscillation | Wikipedia | 512 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Monitoring and declaration of conditions
Currently, each country has a different threshold for what constitutes an El Niño event, which is tailored to their specific interests, for example:
In the United States, an El Niño is declared when the Climate Prediction Center, which monitors the sea surface temperatures in the Niño 3.4 region and the tropical Pacific, forecasts that the sea surface temperature will be above average or more for the next several seasons. The Niño 3.4 region stretches from the 120th to 170th meridians west longitude astride the equator five degrees of latitude on either side, are monitored. It is approximately to the southeast of Hawaii. The most recent three-month average for the area is computed, and if the region is more than 0.5 °C (0.9 °F) above (or below) normal for that period, then an El Niño (or La Niña) is considered in progress.
The Australian Bureau of Meteorology looks at the trade winds, Southern Oscillation Index, weather models and sea surface temperatures in the Niño 3 and 3.4 regions, before declaring an ENSO event.
The Japan Meteorological Agency declares that an ENSO event has started when the average five month sea surface temperature deviation for the Niño 3 region is over for six consecutive months or longer.
The Peruvian government declares that an ENSO Costero is under way if the sea surface temperature deviation in the Niño 1+2 regions equal or exceed for at least three months.
The United Kingdom's Met Office also uses a several month period to determine ENSO state. When this warming or cooling occurs for only seven to nine months, it is classified as El Niño/La Niña "conditions"; when it occurs for more than that period, it is classified as El Niño/La Niña "episodes".
Effects of ENSO on global climate
In climate change science, ENSO is known as one of the internal climate variability phenomena. The other two main ones are Pacific decadal oscillation and Atlantic multidecadal oscillation.
La Niña impacts the global climate and disrupts normal weather patterns, which can lead to intense storms in some places and droughts in others. El Niño events cause short-term (approximately 1 year in length) spikes in global average surface temperature while La Niña events cause short term cooling. Therefore, the relative frequency of El Niño compared to La Niña events can affect global temperature trends on decadal timescales. | El Niño–Southern Oscillation | Wikipedia | 490 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Climate change
There is no sign that there are actual changes in the ENSO physical phenomenon due to climate change. Climate models do not simulate ENSO well enough to make reliable predictions. Future trends in ENSO are uncertain as different models make different predictions. It may be that the observed phenomenon of more frequent and stronger El Niño events occurs only in the initial phase of the global warming, and then (e.g., after the lower layers of the ocean get warmer, as well), El Niño will become weaker. It may also be that the stabilizing and destabilizing forces influencing the phenomenon will eventually compensate for each other.
The consequences of ENSO in terms of the temperature anomalies and precipitation and weather extremes around the world are clearly increasing and associated with climate change. For example, recent scholarship (since about 2019) has found that climate change is increasing the frequency of extreme El Niño events. Previously there was no consensus on whether climate change will have any influence on the strength or duration of El Niño events, as research alternately supported El Niño events becoming stronger and weaker, longer and shorter.
Over the last several decades, the number of El Niño events increased, and the number of La Niña events decreased, although observation of ENSO for much longer is needed to detect robust changes.
Studies of historical data show the recent El Niño variation is most likely linked to global warming. For example, some results, even after subtracting the positive influence of decadal variation, are shown to be possibly present in the ENSO trend, the amplitude of the ENSO variability in the observed data still increases, by as much as 60% in the last 50 years. A study published in 2023 by CSIRO researchers found that climate change may have increased by two times the likelihood of strong El Niño events and nine times the likelihood of strong La Niña events. The study stated it found a consensus between different models and experiments.
The IPCC Sixth Assessment Report summarized the state of the art of research in 2021 into the future of ENSO as follows:
"In the long term, it is very likely that the precipitation variance related to El Niño–Southern Oscillation will increase" and
"It is very likely that rainfall variability related to changes in the strength and spatial extent of ENSO teleconnections will lead to significant changes at regional scale". and
"There is medium confidence that both ENSO amplitude and the frequency of high-magnitude events since 1950 are higher than over the period from 1850 and possibly as far back as 1400". | El Niño–Southern Oscillation | Wikipedia | 512 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Investigations regarding tipping points
The ENSO is considered to be a potential tipping element in Earth's climate. Global warming can strengthen the ENSO teleconnection and resulting extreme weather events. For example, an increase in the frequency and magnitude of El Niño events have triggered warmer than usual temperatures over the Indian Ocean, by modulating the Walker circulation. This has resulted in a rapid warming of the Indian Ocean, and consequently a weakening of the Asian Monsoon.
Effects of ENSO on weather patterns
El Niño affects the global climate and disrupts normal weather patterns, which can lead to intense storms in some places and droughts in others.
Tropical cyclones
Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies. Areas west of Japan and Korea tend to experience many fewer September–November tropical cyclone impacts during El Niño and neutral years. During El Niño years, the break in the subtropical ridge tends to lie near 130°E, which would favor the Japanese archipelago.
Based on modeled and observed accumulated cyclone energy (ACE), El Niño years usually result in less active hurricane seasons in the Atlantic Ocean, but instead favor a shift to tropical cyclone activity in the Pacific Ocean, compared to La Niña years favoring above average hurricane development in the Atlantic and less so in the Pacific basin. | El Niño–Southern Oscillation | Wikipedia | 279 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Over the Atlantic Ocean, vertical wind shear is increased, which inhibits tropical cyclone genesis and intensification, by causing the westerly winds to be stronger. The atmosphere over the Atlantic Ocean can also be drier and more stable during El Niño events, which can inhibit tropical cyclone genesis and intensification. Within the Eastern Pacific basin: El Niño events contribute to decreased easterly vertical wind shear and favor above-normal hurricane activity. However, the impacts of the ENSO state in this region can vary and are strongly influenced by background climate patterns. The Western Pacific basin experiences a change in the location of where tropical cyclones form during El Niño events, with tropical cyclone formation shifting eastward, without a major change in how many develop each year. As a result of this change, Micronesia is more likely, and China less likely, to be affected by tropical cyclones. A change in the location of where tropical cyclones form also occurs within the Southern Pacific Ocean between 135°E and 120°W, with tropical cyclones more likely to occur within the Southern Pacific basin than the Australian region. As a result of this change tropical cyclones are 50% less likely to make landfall on Queensland, while the risk of a tropical cyclone is elevated for island nations like Niue, French Polynesia, Tonga, Tuvalu, and the Cook Islands.
Remote influence on tropical Atlantic Ocean
A study of climate records has shown that El Niño events in the equatorial Pacific are generally associated with a warm tropical North Atlantic in the following spring and summer. About half of El Niño events persist sufficiently into the spring months for the Western Hemisphere Warm Pool to become unusually large in summer. Occasionally, El Niño's effect on the Atlantic Walker circulation over South America strengthens the easterly trade winds in the western equatorial Atlantic region. As a result, an unusual cooling may occur in the eastern equatorial Atlantic in spring and summer following El Niño peaks in winter. Cases of El Niño-type events in both oceans simultaneously have been linked to severe famines related to the extended failure of monsoon rains.
Impacts on humans and ecosystems
Economic impacts | El Niño–Southern Oscillation | Wikipedia | 416 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
When El Niño conditions last for many months, extensive ocean warming and the reduction in easterly trade winds limits upwelling of cold nutrient-rich deep water, and its economic effect on local fishing for an international market can be serious. Developing countries that depend on their own agriculture and fishing, particularly those bordering the Pacific Ocean, are usually most affected by El Niño conditions. In this phase of the Oscillation, the pool of warm water in the Pacific near South America is often at its warmest in late December.
More generally, El Niño can affect commodity prices and the macroeconomy of different countries. It can constrain the supply of rain-driven agricultural commodities; reduce agricultural output, construction, and services activities; increase food prices; and may trigger social unrest in commodity-dependent poor countries that primarily rely on imported food. A University of Cambridge Working Paper shows that while Australia, Chile, Indonesia, India, Japan, New Zealand and South Africa face a short-lived fall in economic activity in response to an El Niño shock, other countries may actually benefit from an El Niño weather shock (either directly or indirectly through positive spillovers from major trading partners), for instance, Argentina, Canada, Mexico and the United States. Furthermore, most countries experience short-run inflationary pressures following an El Niño shock, while global energy and non-fuel commodity prices increase. The IMF estimates a significant El Niño can boost the GDP of the United States by about 0.5% (due largely to lower heating bills) and reduce the GDP of Indonesia by about 1.0%.
Health and social impacts
Extreme weather conditions related to the El Niño cycle correlate with changes in the incidence of epidemic diseases. For example, the El Niño cycle is associated with increased risks of some of the diseases transmitted by mosquitoes, such as malaria, dengue fever, and Rift Valley fever. Cycles of malaria in India, Venezuela, Brazil, and Colombia have now been linked to El Niño. Outbreaks of another mosquito-transmitted disease, Australian encephalitis (Murray Valley encephalitis—MVE), occur in temperate south-east Australia after heavy rainfall and flooding, which are associated with La Niña events. A severe outbreak of Rift Valley fever occurred after extreme rainfall in north-eastern Kenya and southern Somalia during the 1997–98 El Niño. | El Niño–Southern Oscillation | Wikipedia | 476 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
ENSO conditions have also been related to Kawasaki disease incidence in Japan and the west coast of the United States, via the linkage to tropospheric winds across the north Pacific Ocean.
ENSO may be linked to civil conflicts. Scientists at The Earth Institute of Columbia University, having analyzed data from 1950 to 2004, suggest ENSO may have had a role in 21% of all civil conflicts since 1950, with the risk of annual civil conflict doubling from 3% to 6% in countries affected by ENSO during El Niño years relative to La Niña years.
Ecological consequences
During the 1982–83, 1997–98 and 2015–16 ENSO events, large extensions of tropical forests experienced a prolonged dry period that resulted in widespread fires, and drastic changes in forest structure and tree species composition in Amazonian and Bornean forests. Their impacts do not restrict only vegetation, since declines in insect populations were observed after extreme drought and terrible fires during El Niño 2015–16. Declines in habitat-specialist and disturbance-sensitive bird species and in large-frugivorous mammals were also observed in Amazonian burned forests, while temporary extirpation of more than 100 lowland butterfly species occurred at a burned forest site in Borneo.
In seasonally dry tropical forests, which are more drought tolerant, researchers found that El Niño induced drought increased seedling mortality. In a research published in October 2022, researchers studied seasonally dry tropical forests in a national park in Chiang Mai in Thailand for 7 years and observed that El Niño increased seedling mortality even in seasonally dry tropical forests and may impact entire forests in long run.
Coral bleaching
Following the El Nino event in 1997 – 1998, the Pacific Marine Environmental Laboratory attributes the first large-scale coral bleaching event to the warming waters. | El Niño–Southern Oscillation | Wikipedia | 358 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Most critically, global mass bleaching events were recorded in 1997-98 and 2015–16, when around 75-99% losses of live coral were registered across the world. Considerable attention was also given to the collapse of Peruvian and Chilean anchovy populations that led to a severe fishery crisis following the ENSO events in 1972–73, 1982–83, 1997–98 and, more recently, in 2015–16. In particular, increased surface seawater temperatures in 1982-83 also lead to the probable extinction of two hydrocoral species in Panamá, and to a massive mortality of kelp beds along 600 km of coastline in Chile, from which kelps and associated biodiversity slowly recovered in the most affected areas even after 20 years. All these findings enlarge the role of ENSO events as a strong climatic force driving ecological changes all around the world – particularly in tropical forests and coral reefs.
Impacts by region
Observations of ENSO events since 1950 show that impacts associated with such events depend on the time of year. While certain events and impacts are expected to occur, it is not certain that they will happen. The impacts that generally do occur during most El Niño events include below-average rainfall over Indonesia and northern South America, and above average rainfall in southeastern South America, eastern equatorial Africa, and the southern United States.
Africa
La Niña results in wetter-than-normal conditions in southern Africa from December to February, and drier-than-normal conditions over equatorial east Africa over the same period.
The effects of El Niño on rainfall in southern Africa differ between the summer and winter rainfall areas. Winter rainfall areas tend to get higher rainfall than normal and summer rainfall areas tend to get less rain. The effect on the summer rainfall areas is stronger and has led to severe drought in strong El Niño events.
Sea surface temperatures off the west and south coasts of South Africa are affected by ENSO via changes in surface wind strength. During El Niño the south-easterly winds driving upwelling are weaker which results in warmer coastal waters than normal, while during La Niña the same winds are stronger and cause colder coastal waters. These effects on the winds are part of large scale influences on the tropical Atlantic and the South Atlantic High-pressure system, and changes to the pattern of westerly winds further south. There are other influences not known to be related to ENSO of similar importance. Some ENSO events do not lead to the expected changes. | El Niño–Southern Oscillation | Wikipedia | 492 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Antarctica
Many ENSO linkages exist in the high southern latitudes around Antarctica. Specifically, El Niño conditions result in high-pressure anomalies over the Amundsen and Bellingshausen Seas, causing reduced sea ice and increased poleward heat fluxes in these sectors, as well as the Ross Sea. The Weddell Sea, conversely, tends to become colder with more sea ice during El Niño. The exact opposite heating and atmospheric pressure anomalies occur during La Niña. This pattern of variability is known as the Antarctic dipole mode, although the Antarctic response to ENSO forcing is not ubiquitous.
Asia
In Western Asia, during the region's November–April rainy season, there is increased precipitation in the El Niño phase and reduced precipitation in the La Niña phase on average.
During El Niño years: As warm water spreads from the west Pacific and the Indian Ocean to the east Pacific, it takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific. Singapore experienced the driest February in 2010 since records began in 1869, with only 6.3 mm of rain falling in the month. The years 1968 and 2005 had the next driest Februaries, when 8.4 mm of rain fell.
During La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific Ocean, which increases the landfall threat in China. In March 2008, La Niña caused a drop in sea surface temperatures over Southeast Asia by . It also caused heavy rains over the Philippines, Indonesia, and Malaysia.
Australia
Across most of the continent, El Niño and La Niña have more impact on climate variability than any other factor. There is a strong correlation between the strength of La Niña and rainfall: the greater the sea surface temperature and Southern Oscillation difference from normal, the larger the rainfall change.
During El Niño events, the shift in rainfall away from the Western Pacific may mean that rainfall across Australia is reduced. Over the southern part of the continent, warmer than average temperatures can be recorded as weather systems are more mobile and fewer blocking areas of high pressure occur. The onset of the Indo-Australian Monsoon in tropical Australia is delayed by two to six weeks, which as a consequence means that rainfall is reduced over the northern tropics. The risk of a significant bushfire season in south-eastern Australia is higher following an El Niño event, especially when it is combined with a positive Indian Ocean Dipole event. | El Niño–Southern Oscillation | Wikipedia | 499 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Europe
El Niño's effects on Europe are controversial, complex and difficult to analyze, as it is one of several factors that influence the weather over the continent and other factors can overwhelm the signal.
North America
La Niña causes mostly the opposite effects of El Niño: above-average precipitation across the northern Midwest, the northern Rockies, Northern California, and the Pacific Northwest's southern and eastern regions. Meanwhile, precipitation in the southwestern and southeastern states, as well as southern California, is below average. This also allows for the development of many stronger-than-average hurricanes in the Atlantic and fewer in the Pacific.
ENSO is linked to rainfall over Puerto Rico. During an El Niño, snowfall is greater than average across the southern Rockies and Sierra Nevada mountain range, and is well-below normal across the Upper Midwest and Great Lakes states. During a La Niña, snowfall is above normal across the Pacific Northwest and western Great Lakes.
In Canada, La Niña will, in general, cause a cooler, snowier winter, such as the near-record-breaking amounts of snow recorded in the La Niña winter of 2007–2008 in eastern Canada.
In the spring of 2022, La Niña caused above-average precipitation and below-average temperatures in the state of Oregon. April was one of the wettest months on record, and La Niña effects, while less severe, were expected to continue into the summer.
Over North America, the main temperature and precipitation impacts of El Niño generally occur in the six months between October and March. In particular, the majority of Canada generally has milder than normal winters and springs, with the exception of eastern Canada where no significant impacts occur. Within the United States, the impacts generally observed during the six-month period include wetter-than-average conditions along the Gulf Coast between Texas and Florida, while drier conditions are observed in Hawaii, the Ohio Valley, Pacific Northwest and the Rocky Mountains.
Study of more recent weather events over California and the southwestern United States indicate that there is a variable relationship between El Niño and above-average precipitation, as it strongly depends on the strength of the El Niño event and other factors. Though it has been historically associated with high rainfall in California, the effects of El Niño depend more strongly on the "flavor" of El Niño than its presence or absence, as only "persistent El Niño" events lead to consistently high rainfall. | El Niño–Southern Oscillation | Wikipedia | 481 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
To the north across Alaska, La Niña events lead to drier than normal conditions, while El Niño events do not have a correlation towards dry or wet conditions. During El Niño events, increased precipitation is expected in California due to a more southerly, zonal, storm track. During La Niña, increased precipitation is diverted into the Pacific Northwest due to a more northerly storm track. During La Niña events, the storm track shifts far enough northward to bring wetter than normal winter conditions (in the form of increased snowfall) to the Midwestern states, as well as hot and dry summers. During the El Niño portion of ENSO, increased precipitation falls along the Gulf coast and Southeast due to a stronger than normal, and more southerly, polar jet stream.
Isthmus of Tehuantepec
The synoptic condition for the Tehuantepecer, a violent mountain-gap wind in between the mountains of Mexico and Guatemala, is associated with high-pressure system forming in Sierra Madre of Mexico in the wake of an advancing cold front, which causes winds to accelerate through the Isthmus of Tehuantepec. Tehuantepecers primarily occur during the cold season months for the region in the wake of cold fronts, between October and February, with a summer maximum in July caused by the westward extension of the Azores-Bermuda high pressure system. Wind magnitude is greater during El Niño years than during La Niña years, due to the more frequent cold frontal incursions during El Niño winters. Tehuantepec winds reach to , and on rare occasions . The wind's direction is from the north to north-northeast. It leads to a localized acceleration of the trade winds in the region, and can enhance thunderstorm activity when it interacts with the Intertropical Convergence Zone. The effects can last from a few hours to six days. Between 1942 and 1957, La Niña had an impact that caused isotope changes in the plants of Baja California, and that had helped scientists to study his impact.
Pacific islands
During an El Niño event, New Zealand tends to experience stronger or more frequent westerly winds during their summer, which leads to an elevated risk of drier than normal conditions along the east coast. There is more rain than usual though on New Zealand's West Coast, because of the barrier effect of the North Island mountain ranges and the Southern Alps. | El Niño–Southern Oscillation | Wikipedia | 481 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Fiji generally experiences drier than normal conditions during an El Niño, which can lead to drought becoming established over the Islands. However, the main impacts on the island nation is felt about a year after the event becomes established. Within the Samoan Islands, below average rainfall and higher than normal temperatures are recorded during El Niño events, which can lead to droughts and forest fires on the islands. Other impacts include a decrease in the sea level, possibility of coral bleaching in the marine environment and an increased risk of a tropical cyclone affecting Samoa.
In the late winter and spring during El Niño events, drier than average conditions can be expected in Hawaii. On Guam during El Niño years, dry season precipitation averages below normal, but the probability of a tropical cyclone is more than triple what is normal, so extreme short duration rainfall events are possible. On American Samoa during El Niño events, precipitation averages about 10 percent above normal, while La Niña events are associated with precipitation averaging about 10 percent below normal.
South America
The effects of El Niño in South America are direct and strong. An El Niño is associated with warm and very wet weather months in April–October along the coasts of northern Peru and Ecuador, causing major flooding whenever the event is strong or extreme.
Because El Niño's warm pool feeds thunderstorms above, it creates increased rainfall across the east-central and eastern Pacific Ocean, including several portions of the South American west coast. The effects of El Niño in South America are direct and stronger than in North America. An El Niño is associated with warm and very wet weather months in April–October along the coasts of northern Peru and Ecuador, causing major flooding whenever the event is strong or extreme. The effects during the months of February, March, and April may become critical along the west coast of South America, El Niño reduces the upwelling of cold, nutrient-rich water that sustains large fish populations, which in turn sustain abundant sea birds, whose droppings support the fertilizer industry. The reduction in upwelling leads to fish kills off the shore of Peru. | El Niño–Southern Oscillation | Wikipedia | 419 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
The local fishing industry along the affected coastline can suffer during long-lasting El Niño events. Peruvian fisheries collapsed during the 1970s due to overfishing following the 1972 El Niño Peruvian anchoveta reduction. The fisheries were previously the world's largest, however, this collapse led to the decline of these fisheries. During the 1982–83 event, jack mackerel and anchoveta populations were reduced, scallops increased in warmer water, but hake followed cooler water down the continental slope, while shrimp and sardines moved southward, so some catches decreased while others increased. Horse mackerel have increased in the region during warm events. Shifting locations and types of fish due to changing conditions create challenges for the fishing industry. Peruvian sardines have moved during El Niño events to Chilean areas. Other conditions provide further complications, such as the government of Chile in 1991 creating restrictions on the fishing areas for self-employed fishermen and industrial fleets.
Southern Brazil and northern Argentina also experience wetter than normal conditions during El Niño years, but mainly during the spring and early summer. Central Chile receives a mild winter with large rainfall, and the Peruvian-Bolivian Altiplano is sometimes exposed to unusual winter snowfall events. Drier and hotter weather occurs in parts of the Amazon River Basin, Colombia, and Central America.
During a time of La Niña, drought affects the coastal regions of Peru and Chile. From December to February, northern Brazil is wetter than normal. La Niña causes higher than normal rainfall in the central Andes, which in turn causes catastrophic flooding on the Llanos de Mojos of Beni Department, Bolivia. Such flooding is documented from 1853, 1865, 1872, 1873, 1886, 1895, 1896, 1907, 1921, 1928, 1929 and 1931. | El Niño–Southern Oscillation | Wikipedia | 358 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
Galápagos Islands
The Galápagos Islands are a chain of volcanic islands, nearly 600 miles west of Ecuador, South America. in the Eastern Pacific Ocean. These islands support a wide diversity of terrestrial and marine species. The ecosystem is based on the normal trade winds which influence upwelling of cold, nutrient rich waters to the islands. During an El Niño event the trade winds weaken and sometimes blow from west to east, which causes the Equatorial current to weaken, raising surface water temperatures and decreasing nutrients in waters surrounding the Galápagos. El Niño causes a trophic cascade which impacts entire ecosystems starting with primary producers and ending with critical animals such as sharks, penguins, and seals. The effects of El Niño can become detrimental to populations that often starve and die back during these years. Rapid evolutionary adaptations are displayed amongst animal groups during El Niño years to mitigate El Niño conditions.
History
In geologic timescales
Evidence is also strong for El Niño events during the early Holocene epoch 10,000 years ago.
Different modes of ENSO-like events have been registered in paleoclimatic archives, showing different triggering methods, feedbacks and environmental responses to the geological, atmospheric and oceanographic characteristics of the time. These paleorecords can be used to provide a qualitative basis for conservation practices.
Scientists have also found chemical signatures of warmer sea surface temperatures and increased rainfall caused by El Niño in coral specimens that are around 13,000 years old.
In a paleoclimate study published in 2024, the authors suggest that El Niños had a strong influence on Earth's hothouse climate during the Permian-Triassic extinction event. The increasing intensity and duration of El Niño events were associated with active volcanism, which resulted in the dieback of vegetation, an increase in the amount of carbon dioxide in the atmosphere, a significant warming and disturbances in the circulation of air masses.
During human history
ENSO conditions have occurred at two- to seven-year intervals for at least the past 300 years, but most of them have been weak.
El Niño may have led to the demise of the Moche and other pre-Columbian Peruvian cultures. A recent study suggests a strong El Niño effect between 1789 and 1793 caused poor crop yields in Europe, which in turn helped touch off the French Revolution. The extreme weather produced by El Niño in 1876–77 gave rise to the most deadly famines of the 19th century. The 1876 famine alone in northern China killed up to 13 million people. | El Niño–Southern Oscillation | Wikipedia | 504 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
The phenomenon had long been of interest because of its effects on the guano industry and other enterprises that depend on biological productivity of the sea. It is recorded that as early as 1822, cartographer Joseph Lartigue, of the French frigate La Clorinde under Baron Mackau, noted the "counter-current" and its usefulness for traveling southward along the Peruvian coast.
Charles Todd, in 1888, suggested droughts in India and Australia tended to occur at the same time; Norman Lockyer noted the same in 1904. An El Niño connection with flooding was reported in 1894 by Victor Eguiguren (1852–1919) and in 1895 by Federico Alfonso Pezet (1859–1929). In 1924, Gilbert Walker (for whom the Walker circulation is named) coined the term "Southern Oscillation". He and others (including Norwegian-American meteorologist Jacob Bjerknes) are generally credited with identifying the El Niño effect.
The major 1982–83 El Niño led to an upsurge of interest from the scientific community. The period 1990–95 was unusual in that El Niños have rarely occurred in such rapid succession. An especially intense El Niño event in 1998 caused an estimated 16% of the world's reef systems to die. The event temporarily warmed air temperature by 1.5 °C, compared to the usual increase of 0.25 °C associated with El Niño events. Since then, mass coral bleaching has become common worldwide, with all regions having suffered "severe bleaching".
Around 1525, when Francisco Pizarro made landfall in Peru, he noted rainfall in the deserts, the first written record of the impacts of El Niño.
Related patterns
Madden–Julian oscillation
Link to the El Niño-Southern oscillation
Pacific decadal oscillation
Mechanisms
Pacific Meridional Mode | El Niño–Southern Oscillation | Wikipedia | 371 | 317311 | https://en.wikipedia.org/wiki/El%20Ni%C3%B1o%E2%80%93Southern%20Oscillation | Physical sciences | Climatology | null |
In an automobile, ball joints are spherical bearings that connect the control arms to the steering knuckles, and are used on virtually every automobile made. They bionically resemble the ball-and-socket joints found in most tetrapod animals.
A ball joint consists of a bearing stud and socket enclosed in a casing; all these parts are made of steel. The bearing stud is tapered and threaded, and fits into a tapered hole in the steering knuckle. A protective encasing prevents dirt from getting into the joint assembly. Usually, this is a rubber-like boot that allows movement and expansion of lubricant. Motion-control ball joints tend to be retained with an internal spring, which helps to prevent vibration problems in the linkage.
The "offset" ball joint provides means of movement in systems where thermal expansion and contraction, shock, seismic motion, and torsional motions, and forces are present.
Theory
A ball joint is used for allowing free rotation in two planes at the same time while preventing translation in any direction, including rotating in those planes. Combining two such joints with control arms enables motion in all three planes, allowing the front end of an automobile to be steered and a spring and shock (damper) suspension to make the ride comfortable.
A simple kingpin suspension requires that the upper and lower control arms (wishbones) have pivot axes that are parallel, and in strict geometric relationship to the kingpin, or the top and bottom trunnions, which connect the kingpin to the control arms, would be severely stressed and the bearings would suffer severe wear. In practice, many vehicles had elastomeric bearings in the horizontal pivots of the trunnions, which allowed some small amount of flexibility, however this was insufficient to allow much adjustment of caster to be made, and also introduced compliance where the suspension designer may not have desired it in his quest for optimum handling. Camber angle could generally be adjusted by moving both inner pivots of either the upper or lower control arm inwards or outwards by an exactly equal amount. But compliance of the control arm inner pivots, typically due to the use of elastomeric bearings, would again cause the trunnions to be stressed. The suspension designer's freedom was limited, it was necessary to have some compliance where it might not be wanted, and very little where more would have been useful in absorbing the fore and aft impact loading from bumps. | Ball joint | Wikipedia | 505 | 4069796 | https://en.wikipedia.org/wiki/Ball%20joint | Technology | Mechanisms | null |
The introduction of ball joints top and bottom allowed 3-axis articulation and so removed all the constraints on the control arm axes being exactly parallel, so caster could be freely adjusted, typically by asymmetric adjustment of the position of the control arm inner pivots, while camber was adjusted by the symmetric adjustment of these same pivots.
The arrangements for adjusting the toe angle are not changed by introducing ball joints in the suspension, although the steering linkage itself must use 4 or more pivots, also usually ball joints, and in almost every vehicle ever made, some of these have been adjustable by having a threaded end and locknut, to enable the toe to be set precisely.
This ability to fine-tune ball-jointed suspension allows manufacturers to make the automobile more stable and easier to steer, compared to the older kingpin style suspension. It may also be quieter and more comfortable, because lateral and fore and aft compliance in the suspension can be introduced in controlled amounts at the control arm inner pivots without compromising the integrity of the steering axis pivots, which are now ball joints instead of a king pin and trunnions. The smoother ride may also increase tire tread life, since the ball-joint suspension allows better control of suspension geometry and so can provide better tire-to-road contact.
Purpose
On modern vehicles, joints are the pivot between the wheels and the suspension of an automobile. They are today almost universally used in the front suspension, having replaced the kingpin/link pin or kingpin/trunnion arrangement, but can also be found in the rear suspension of a few higher-performance autos. Ball joints play a critical role in the safe operation of an automobile's steering and suspension.
Many currently manufactured automobiles worldwide use MacPherson strut suspension, which utilises one ball joint per side, between the lower end of the strut and the control arm, with the necessary small amount of articulation at the top of the strut being usually provided by an elastomeric bearing, within which is a ball bearing to allow free rotation about the steering axis. So, there are commonly only two ball joints in the suspension, however there will be at least four (track rod ends and rack ends) in the steering linkage. | Ball joint | Wikipedia | 470 | 4069796 | https://en.wikipedia.org/wiki/Ball%20joint | Technology | Mechanisms | null |
In non-MacPherson strut automobile suspension, the two ball joints are called the "upper ball joint" and "lower ball joint". Lower ball joints are sometimes larger and may wear out faster, because the fore and aft loads, primarily due to braking, are higher at the bottom ball joint. (Torque reaction and drag add at the bottom joint, and partly cancel at the top joint.) Also, lateral cornering loads are higher at the bottom joint. Depending on the suspension design, the vertical load from the suspension spring may be handled entirely by the top ball joint, or entirely by the bottom ball joint. The damper load, (which is low in normal conditions, zero when stationary, but in peak bump or rebound rate may be almost as large as the spring load) is usually, but not always, taken on the same ball joint as the spring load. The anti-roll bar loading is often, but not always, taken on the bottom ball joint. It may be taken by the top ball joint, or directly from the steering knuckle by ball-jointed drop links.
If one of the ball joints does not carry spring load, it may be fitted with an internal anti-rattle spring to keep the ball preferentially in contact with one seat. This was the case in the BMC Mini of 1959 and its many derivatives, where the lower control arm carried no vertical loading, so the joint needed an anti-rattle spring, while the top joint, comprising identical parts, was always in compression due to spring (rubber cone) and damper loads, and so was not fitted with a spring.
Other vehicles of the 1960s era, including some Vauxhalls, had lower ball joints with considerable end float, because the joint was always in tension as the spring and damper loads were applied via the lower control arm and were always non-zero.
Another example is the Ford Focus, which uses MacPherson struts, and the anti-roll bar is connected directly to the strut, so the lower ball joint is only carrying fore and aft traction/braking and lateral cornering loads. | Ball joint | Wikipedia | 431 | 4069796 | https://en.wikipedia.org/wiki/Ball%20joint | Technology | Mechanisms | null |
Front-wheel drive
Unlike a kingpin, which requires an assembly in the center of the wheel in order to pivot, joints connect to the upper and lower end of the spindle (steering knuckle), to the control arms. This leaves the center section open to allow the use of front-wheel drive. Older kingpin designs can only be used in a rear-wheel-drive configuration.
Lubrication
Sealed ball joints do not require lubrication as they are "lubed for life". Formerly most ball joints had grease fitting (sometimes called a grease zerk) and were designed for periodic addition of a lubricant, however almost all modern cars use sealed ball joints to minimise maintenance requirements. The lubricant was usually a very high-viscosity lubricant. It is commonly believed that standard ball joints will outlive sealed ones because eventually the seal will break, causing the joint to dry out and rust. Additionally, the act of adding new lubricant pushes out old and dry lubricant, extending the life of the joint. This was supposed to be done at intervals of 1000 to 2000 miles on many vehicles, which is incompatible with the service interval on modern cars, often 12000 miles or more, and in any case was rarely attended to by owners, resulting in severe wear and possible ball joint failure, which can result in serious accidents. For this reason, almost all ball joints on modern European or Far Eastern cars are the sealed for life type. New technology especially applied to the internal bearing design has allowed ball joints to meet these longer service intervals. The special designs incorporate sintered metal bearings which replace OEM sealed polymer/plastic version and improved dust boot seals that work much better at retaining the grease.
Spherical rolling joint
A spherical rolling joint is a high-precision ball joint consisting of a spherical outer and inner race separated by ball bearings. The ball bearings are housed in a spherical retainer and roll along both the inner and outer surfaces. This design allows the joint to have very low friction while maintaining a large range of motion and backlash as low as 1 μm. SRJs are often used in parallel robotics applications like a Stewart platform, where high rigidity and low backlash are essential.
Most SRJs are designed with an offset housing, allowing for higher compressive loads in a smaller space. Alternatively, the joint can be assembled backwards for higher tensile load capability but less range of motion. | Ball joint | Wikipedia | 498 | 4069796 | https://en.wikipedia.org/wiki/Ball%20joint | Technology | Mechanisms | null |
An alternative to the SRJ is the universal joint, which consists of two revolute joints. By using spherical rolling joints instead of universal, designers can reduce the number of joints to achieve the same result. Using a spherical joint as opposed to a universal joint also eliminates the problematic possibility of a kinematic singularity. Plain spherical bearings can be used in place of SRJs at the cost of increased friction, but offer an opportunity to preload the joint further.
Failure
While there is no exact lifespan that can be put on sealed ball joints, they can fail as early as in modern vehicles, and much sooner in older vehicles. Signs of a failing ball joint may start with a sudden burst sound as a result of ball joint dismantling. Then it keeps on with clicking, popping or snapping sound when the wheel is turned and eventually turn into a squeaking sound at the end of a stop, when the gas pedal is used and/or also when hitting bumps. Another symptom could be 'thud' noises coming from front suspension when going over bumps. Dry ball joints have dramatically increased friction and can cause the steering to stick or be more difficult.
If a ball joint fails, the results can be dangerous as the wheel's angle becomes unconstrained, causing loss of control. Because the tire will be at an unintended angle, the vehicle will come to an abrupt halt, damaging the tires. Also, during failure, debris can damage other parts of the vehicle.
Other uses
While in automotive parlance the term "ball joint" usually refers to the primary ball joint connections at the ends of the control arms, this type of joint is used in other parts as well, including tie rod ends. In these other applications, they are typically called tie rod ends or, when they are an inner tie rod end on a rack-and-pinion steering system, they are called inner socket assemblies. These joints are also used in a number of other non-automotive applications, from the joints of dolls to other mechanical linkages for a variety of devices, or any place where a degree of rotation in movement is desired. | Ball joint | Wikipedia | 431 | 4069796 | https://en.wikipedia.org/wiki/Ball%20joint | Technology | Mechanisms | null |
A conveyor system is a common piece of mechanical handling equipment that moves materials from one location to another. Conveyors are especially useful in applications involving the transport of heavy or bulky materials. Conveyor systems allow quick and efficient transport for a wide variety of materials, which make them very popular in the material handling and packaging industries. They also have popular consumer applications, as they are often found in supermarkets and airports, constituting the final leg of item/ bag delivery to customers. Many kinds of conveying systems are available and are used according to the various needs of different industries. There are chain conveyors (floor and overhead) as well. Chain conveyors consist of enclosed tracks, I-Beam, towline, power & free, and hand pushed trolleys.
Industries where used
Conveyor systems are used widespread across a range of industries due to the numerous benefits they provide.
Conveyors are able to safely transport materials from one level to another, which when done by human labor would be strenuous and expensive.
They can be installed almost anywhere, and are much safer than using a forklift or other machine to move materials.
They can move loads of all shapes, sizes and weights. Also, many have advanced safety features that help prevent accidents.
There are a variety of options available for running conveying systems, including the hydraulic, mechanical and fully automated systems, which are equipped to fit individual needs.
Conveyor systems are commonly used in many industries, including the Mining, automotive, agricultural, computer, electronic, food processing, aerospace, pharmaceutical, chemical, bottling and canning, print finishing and packaging. Although a wide variety of materials can be conveyed, some of the most common include food items such as beans and nuts, bottles and cans, automotive components, scrap metal, pills and powders, wood and furniture and grain and animal feed. Many factors are important in the accurate selection of a conveyor system. It is important to know how the conveyor system will be used beforehand. Some individual areas that are helpful to consider are the required conveyor operations, such as transport, accumulation and sorting, the material sizes, weights and shapes and where the loading and pickup points need to be.
Care and maintenance
A conveyor system is often the lifeline to a company's ability to effectively move its product in a timely fashion. The steps that a company can take to ensure that it performs at peak capacity, include regular inspections and system audits, close monitoring of motors and reducers, keeping key parts in stock, and proper training of personnel. | Conveyor system | Wikipedia | 512 | 13215001 | https://en.wikipedia.org/wiki/Conveyor%20system | Technology | Industry: General | null |
Increasing the service life of a conveyor system involves: choosing the right conveyor type, the right system design and paying attention to regular maintenance practices.
A conveyor system that is designed properly will last a long time with proper maintenance. Overhead conveyor systems have been used in numerous applications from shop displays, assembly lines to paint finishing plants and more.
Impact and wear-resistant materials used in manufacturing
Conveyor systems require materials suited to the displacement of heavy loads and the wear-resistance to hold-up over time without seizing due to deformation. Where static control is a factor, special materials designed to either dissipate or conduct electrical charges are used. Examples of conveyor handling materials include UHMW, nylon, Nylatron NSM, HDPE, Tivar, Tivar ESd, and polyurethane.
Growth in various industries
As far as growth is concerned the material handling and conveyor system makers are getting utmost exposure in the industries like automotive, pharmaceutical, packaging and different production plants. The portable conveyors are likewise growing fast in the construction sector and by the year 2014 the purchase rate for conveyor systems in North America, Europe and Asia is likely to grow even further. The most commonly purchased types of conveyors are line-shaft roller conveyors, chain conveyors and conveyor belts at packaging factories and industrial plants where usually product finishing and monitoring are carried. Commercial and civil sectors are increasingly implementing conveyors at airports, shopping malls, etc.
Types
Aero-mechanical conveyor
Automotive conveyor
Belt conveyor
Belt-driven live roller conveyor
Bucket conveyor
Chain conveyor
Chain-driven live roller conveyor
Drag conveyor
Dust-proof conveyor
Electric track vehicle system
Flexible conveyor
Gravity conveyor
Gravity skate-wheel conveyor
Lineshaft roller conveyor
Motorized-drive roller conveyor
Overhead I-beam conveyor
Overland conveyor
Pharmaceutical conveyor
Plastic belt conveyor
Pneumatic conveyor
Screw or auger conveyor
Spiral conveyor
Tube chain conveyor
Tubular Gallery conveyor
Vacuum conveyor
Vertical conveyor
Vibrating conveyor
Walking Beam
Wire mesh conveyor | Conveyor system | Wikipedia | 416 | 13215001 | https://en.wikipedia.org/wiki/Conveyor%20system | Technology | Industry: General | null |
Pneumatic
Every pneumatic system uses pipes or ducts called transport lines that carry a mixture of materials and a stream of air. These materials are free flowing powdery materials like cement and fly ash. Products are moved through tubes by air pressure. Pneumatic conveyors are either carrier systems or dilute-phase systems; carrier systems simply push items from one entry point to one exit point, such as the money-exchanging pneumatic tubes used at a bank drive-through window. Dilute-phase systems use push-pull pressure to guide materials through various entry and exit points. Air compressors or blowers can be used to generate the air flow.
Three systems used to generate high-velocity air stream:
Suction or vacuum systems, utilizing a vacuum created in the pipeline to draw the material with the surrounding air. The system operated at a low pressure, which is practically 0.4–0.5 atm below atmosphere, and is utilized mainly in conveying light free flowing materials.
Pressure-type systems, in which a positive pressure is used to push material from one point to the next. The system is ideal for conveying material from one loading point to a number of unloading points. It operates at a pressure of 6 atm and upwards.
Combination systems, in which a suction system is used to convey material from a number of loading points and a pressure system is employed to deliver it to a number of unloading points.
Vibrating
A vibrating conveyor is a machine with a solid conveying surface which is turned up on the side to form a trough. They are used extensively in food-grade applications to convey dry bulk solids where sanitation, washdown, and low maintenance are essential. Vibrating conveyors are also suitable for harsh, very hot, dirty, or corrosive environments. They can be used to convey newly-cast metal parts which may reach upwards of . Due to the fixed nature of the conveying pans vibrating conveyors can also perform tasks such as sorting, screening, classifying and orienting parts. Vibrating conveyors have been built to convey material at angles exceeding 45° from horizontal using special pan shapes. Flat pans will convey most materials at a 5° incline from horizontal line. | Conveyor system | Wikipedia | 449 | 13215001 | https://en.wikipedia.org/wiki/Conveyor%20system | Technology | Industry: General | null |
Flexible
The flexible conveyor is based on a conveyor beam in aluminum or stainless steel, with low-friction slide rails guiding a plastic multi-flexing chain. Products to be conveyed travel directly on the conveyor, or on pallets/carriers. These conveyors can be worked around obstacles and keep production lines flowing. They are made at varying levels and can work in multiple environments. They are used in food packaging, case packing, and pharmaceutical industries and also in large retail stores such as Wal-Mart and Kmart.
Spiral
Like vertical conveyors, spiral conveyors raise and lower materials to different levels of a facility. In contrast, spiral conveyors are able to transport material loads in a continuous flow. A helical spiral or screw rotates within a sealed tube and the speed makes the product in the conveyor rotate with the screw. The tumbling effect provides a homogeneous mix of particles in the conveyor, which is essential when feeding pre-mixed ingredients and maintaining mixing integrity. Industries that require a higher output of materials - food and beverage, retail case packaging, pharmaceuticals - typically incorporate these conveyors into their systems over standard vertical conveyors due to their ability to facilitate high throughput. Most spiral conveyors also have a lower angle of incline or decline (11 degrees or less) to prevent sliding and tumbling during operation.
Vertical
Vertical conveyors, also commonly referred to as freight lifts and material lifts, are conveyor systems used to raise or lower materials to different levels of a facility during the handling process. Examples of these conveyors applied in the industrial assembly process include transporting materials to different floors. While similar in look to freight elevators, vertical conveyors are not equipped to transport people, only materials.
Vertical lift conveyors contain two adjacent, parallel conveyors for simultaneous upward movement of adjacent surfaces of the parallel conveyors. One of the conveyors normally has spaced apart flights (pans) for transporting bulk food items. The dual conveyors rotate in opposite directions, but are operated from one gear box to ensure equal belt speed. One of the conveyors is pivotally hinged to the other conveyor for swinging the attached conveyor away from the remaining conveyor for access to the facing surfaces of the parallel conveyors. Vertical lift conveyors can be manually or automatically loaded and controlled. Almost all vertical conveyors can be systematically integrated with horizontal conveyors, since both of these conveyor systems work in tandem to create a cohesive material handling assembly line. | Conveyor system | Wikipedia | 496 | 13215001 | https://en.wikipedia.org/wiki/Conveyor%20system | Technology | Industry: General | null |
Like spiral conveyors, vertical conveyors that use forks can transport material loads in a continuous flow. With these forks the load can be taken from one horizontal conveyor and put down on another horizontal conveyor on a different level. By adding more forks, more products can be lifted at the same time. Conventional vertical conveyors must have input and output of material loads moving in the same direction. By using forks many combinations of different input- and output- levels in different directions are possible. A vertical conveyor with forks can even be used as a vertical sorter. Compared to a spiral conveyor a vertical conveyor - with or without forks - takes up less space.
Vertical reciprocating conveyors (or VRC) are another type of unit handling system. Typical applications include moving unit loads between floor levels, working with multiple accumulation conveyors, and interfacing overhead conveyors line. Common material to be conveyed includes pallets, sacks, custom fixtures or product racks and more.
Motorized Drive Roller (MDR)
Motorized Drive Roller (MDR) conveyor utilize drive rollers that have a Brushless DC (BLDC) motor embedded within a conveyor roller tube. A single motorized roller tube is then mechanically linked to a small number of non-powered rollers to create a controllable zone of powered conveyor. A linear collection of these individually powered zones are arranged end to end to form a line of contiguous conveyor. The mechanical performance (torque, speed, efficiency, etc.) of drive rollers equipped with BLDC motors is right in the range of that needed for roller conveyor zones when they need to convey general use carton boxes of the size and weight seen in typical modern warehouse and distribution applications. A typical motorized roller conveyor zone can handle carton items weighing up to approximately 35 kg (75 lbs.).
Heavy-duty roller
Heavy-duty roller conveyors are used for moving items that weigh at least . This type of conveyor makes the handling of such heavy equipment/products easier and more time effective. Many of the heavy duty roller conveyors can move as fast as .
Other types of heavy-duty roller conveyors are gravity roller conveyors, chain-driven live roller conveyors, pallet accumulation conveyors, multi-strand chain conveyors, and chain and roller transfers.
Gravity roller conveyors are easy to use and are used in many different types of industries such as automotive and retail. | Conveyor system | Wikipedia | 496 | 13215001 | https://en.wikipedia.org/wiki/Conveyor%20system | Technology | Industry: General | null |
Chain-driven live roller conveyors are used for single or bi-directional material handling. Large, heavy loads are moved by chain driven live roller conveyors.
Pallet accumulation conveyors are powered through a mechanical clutch. This is used instead of individually powered and controlled sections of conveyors.
Multi-strand chain conveyors are used for double-pitch roller chains. Products that cannot be moved on traditional roller conveyors can be moved by a multi-strand chain conveyor.
Chain and roller conveyors are short runs of two or more strands of double-pitch chain conveyors built into a chain-driven line roller conveyor. These pop up under the load and move the load off of the conveyor.
Walking Beam
It usually consists of two fluid power cylinders or also can use a motor driven cam. For the cylinder driven fluid power type, one axis is for vertical motion and the other for horizontal. Both cam and fluid power types require nests at each station to retain the part that is being moved. The beam is raised, raising the part from its station nest and holding the part in a nest on the walking beam, then moved horizontally, transporting the part to the next nest, then lowered vertically, placing the part in the next station's nest. The beam is then returned to its home position while it is in the lowered position out of the way of the parts. This type of conveying system is useful for parts that need to be accurately physically located or relatively heavy parts. All stations are equidistance and require a nest to retain the part. | Conveyor system | Wikipedia | 314 | 13215001 | https://en.wikipedia.org/wiki/Conveyor%20system | Technology | Industry: General | null |
Roman concrete, also called , was used in construction in ancient Rome. Like its modern equivalent, Roman concrete was based on a hydraulic-setting cement added to an aggregate.
Many buildings and structures still standing today, such as bridges, reservoirs and aqueducts, were built with this material, which attests to both its versatility and its durability. Its strength was sometimes enhanced by the incorporation of pozzolanic ash where available (particularly in the Bay of Naples). The addition of ash prevented cracks from spreading. Recent research has shown that the incorporation of mixtures of different types of lime, forming conglomerate "clasts" allowed the concrete to self-repair cracks.
Roman concrete was in widespread use from about 150 BC; some scholars believe it was developed a century before that.
It was often used in combination with facings and other supports, and interiors were further decorated by stucco, fresco paintings, or coloured marble. Further innovative developments in the material, part of the so-called concrete revolution, contributed to structurally complicated forms. The most prominent example of these is the Pantheon dome, the world's largest and oldest unreinforced concrete dome.
Roman concrete differs from modern concrete in that the aggregates often included larger components; hence, it was laid rather than poured. Roman concretes, like any hydraulic concrete, were usually able to set underwater, which was useful for bridges and other waterside construction.
Historic references
Vitruvius, writing around 25 BC in his Ten Books on Architecture, distinguished types of materials appropriate for the preparation of lime mortars. For structural mortars, he recommended pozzolana ( in Latin), the volcanic sand from the beds of Pozzuoli, which are brownish-yellow-gray in colour in that area around Naples, and reddish-brown near Rome. Vitruvius specifies a ratio of 1 part lime to 3 parts pozzolana for mortar used in buildings and a 1:2 ratio for underwater work.
The Romans first used hydraulic concrete in coastal underwater structures, probably in the harbours around Baiae before the end of the 2nd century BC. The harbour of Caesarea is an example (22-15 BC) of the use of underwater Roman concrete technology on a large scale, for which enormous quantities of pozzolana were imported from Puteoli. | Roman concrete | Wikipedia | 470 | 13222289 | https://en.wikipedia.org/wiki/Roman%20concrete | Technology | Building materials | null |
For rebuilding Rome after the fire in 64 AD which destroyed large portions of the city, Nero's new building code largely called for brick-faced concrete. This appears to have encouraged the development of the brick and concrete industries.
Material properties
Roman concrete, like any concrete, consists of an aggregate and hydraulic mortar, a binder mixed with water that hardens over time. The composition of the aggregate varied, and included pieces of rock, ceramic tile, lime clasts, and brick rubble from the remains of previously demolished buildings. In Rome, readily available tuff was often used as an aggregate.
Gypsum and quicklime were used as binders. Volcanic dusts, called pozzolana or "pit sand", were favoured where they could be obtained. Pozzolana makes the concrete more resistant to salt water than modern-day concrete. Pozzolanic mortar had a high content of alumina and silica.
Research in 2023 found that lime clasts, previously considered a sign of poor aggregation technique, react with water seeping into any cracks. This produces reactive calcium, which allows new calcium carbonate crystals to form and reseal the cracks. These lime clasts have a brittle structure that was most likely created in a "hot-mixing" technique with quicklime rather than traditional slaked lime, causing cracks to preferentially move through the lime clasts, thus potentially playing a critical role in the self-healing mechanism.
Concrete and, in particular, the hydraulic mortar responsible for its cohesion, was a type of structural ceramic whose utility derived largely from its rheological plasticity in the paste state. The setting and hardening of hydraulic cements derived from hydration of materials and the subsequent chemical and physical interaction of these hydration products. This differed from the setting of slaked lime mortars, the most common cements of the pre-Roman world. Once set, Roman concrete exhibited little plasticity, although it retained some resistance to tensile stresses.The setting of pozzolanic cements has much in common with setting of their modern counterpart, Portland cement. The high silica composition of Roman pozzolana cements is very close to that of modern cement to which blast furnace slag, fly ash, or silica fume have been added. | Roman concrete | Wikipedia | 470 | 13222289 | https://en.wikipedia.org/wiki/Roman%20concrete | Technology | Building materials | null |
The strength and longevity of Roman 'marine' concrete is understood to benefit from a reaction of seawater with a mixture of volcanic ash and quicklime to create a rare crystal called tobermorite, which may resist fracturing. As seawater percolated within the tiny cracks in the Roman concrete, it reacted with phillipsite naturally found in the volcanic rock and created aluminous tobermorite crystals. The result is a candidate for "the most durable building material in human history". In contrast, modern concrete exposed to saltwater deteriorates within decades.
The Roman concrete at the Tomb of Caecilia Metella is another variation higher in potassium that triggered changes that "reinforce interfacial zones and potentially contribute to improved mechanical performance".
Seismic technology
For an environment as prone to earthquakes as the Italian peninsula, interruptions and internal constructions within walls and domes created discontinuities in the concrete mass. Portions of the building could then shift slightly when there was movement of the earth to accommodate such stresses, enhancing the overall strength of the structure. It was in this sense that bricks and concrete were flexible. It may have been precisely for this reason that, although many buildings sustained serious cracking from a variety of causes, they continue to stand to this day.
Another technology used to improve the strength and stability of concrete was its gradation in domes. One example is the Pantheon, where the aggregate of the upper dome region consists of alternating layers of light tuff and pumice, giving the concrete a density of . The foundation of the structure used travertine as an aggregate, having a much higher density of . | Roman concrete | Wikipedia | 329 | 13222289 | https://en.wikipedia.org/wiki/Roman%20concrete | Technology | Building materials | null |
Modern use
Scientific studies of Roman concrete since 2010 have attracted both media and industry attention. Because of its unusual durability, longevity, and lessened environmental footprint, corporations and municipalities are starting to explore the use of Roman-style concrete in North America. This involves replacing the volcanic ash with coal fly ash that has similar properties. Proponents say that concrete made with fly ash can cost up to 60% less, because it requires less cement. It also has a reduced environmental footprint, due to its lower cooking temperature and much longer lifespan. Usable examples of Roman concrete exposed to harsh marine environments have been found to be 2000 years old with little or no wear.
In 2013, the University of California Berkeley published an article that described for the first time the mechanism by which the suprastable calcium-aluminium-silicate-hydrate compound binds the material together. During its production, less carbon dioxide is released into the atmosphere than any modern concrete production process. It is no coincidence that the walls of Roman buildings are thicker than those of modern buildings. However, Roman concrete was still gaining its strength for several decades after construction had been completed. | Roman concrete | Wikipedia | 228 | 13222289 | https://en.wikipedia.org/wiki/Roman%20concrete | Technology | Building materials | null |
Pastoralism is a form of animal husbandry where domesticated animals (known as "livestock") are released onto large vegetated outdoor lands (pastures) for grazing, historically by nomadic people who moved around with their herds. The animal species involved include cattle, camels, goats, yaks, llamas, reindeer, horses, and sheep.
Pastoralism occurs in many variations throughout the world, generally where environmentally effected characteristics such as aridity, poor soils, cold or hot temperatures, and lack of water make crop-growing difficult or impossible. Operating in more extreme environments with more marginal lands means that pastoral communities are very vulnerable to the effects of global warming.
Pastoralism remains a way of life in many geographic areas, including Africa, the Tibetan plateau, the Eurasian steppes, the Andes, Patagonia, the Pampas, Australia and many other places. , between 200 million and 500 million people globally practiced pastoralism, and 75% of all countries had pastoral communities.
Pastoral communities have different levels of mobility. The enclosure of common lands has led to Sedentary pastoralism becoming more common as the hardening of political borders, land tenures, expansion of crop farming, and construction of fences and dedicated agricultural buildings all reduce the ability to move livestock around freely, leading to the rise of pastoral farming on established grazing-zones (sometimes called "ranches"). Sedentary pastoralists may also raise crops and livestock together in the form of mixed farming, for the purpose of diversifying productivity, obtaining manure for organic farming, and improving pasture conditions for their livestock. Mobile pastoralism includes moving herds locally across short distances in search of fresh forage and water (something that can occur daily or even within a few hours); as well as transhumance, where herders routinely move animals between different seasonal pastures across regions; and nomadism, where nomadic pastoralists and their families move with the animals in search for any available grazing-grounds—without much long-term planning. Grazing in woodlands and forests may be referred to as silvopastoralism.
Those who practice pastoralism are called "pastoralists". | Pastoralism | Wikipedia | 436 | 966760 | https://en.wikipedia.org/wiki/Pastoralism | Technology | Agriculture_2 | null |
Pastoralist herds interact with their environment, and mediate human relations with the environment as a way of turning uncultivated plants (like wild grass) into food. In many places, grazing herds on savannas and in woodlands can help maintain the biodiversity of such landscapes and prevent them from evolving into dense shrublands or forests. Grazing and browsing at the appropriate levels often can increase biodiversity in Mediterranean climate regions. Pastoralists shape ecosystems in different ways: some communities use fire to make ecosystems more suitable for grazing and browsing animals.
Origins
One theory suggests that pastoralism developed from mixed farming. Bates and Lees proposed that the incorporation of irrigation into farming resulted in specialization. Advantages of mixed farming include reducing risk of failure, spreading labour, and re-utilizing resources. The importance of these advantages and disadvantages to different farmers or farming societies differs according to the sociocultural preferences of the farmers and the biophysical conditions as determined by rainfall, radiation, soil type, and disease. The increased productivity of irrigation agriculture led to an increase in population and an added impact on resources. Bordering areas of land remained in use for animal breeding. This meant that large distances had to be covered by herds to collect sufficient forage. Specialization occurred as a result of the increasing importance of both intensive agriculture and pastoralism. Both agriculture and pastoralism developed alongside each other, with continuous interactions.
A different theory suggests that pastoralism evolved from the hunting and gathering. Hunters of wild goats and sheep were knowledgeable about herd mobility and the needs of the animals. Such hunters were mobile and followed the herds on their seasonal rounds. Undomesticated herds were chosen to become more controllable for the proto-pastoralist nomadic hunter and gatherer groups by taming and domesticating them. Hunter-gatherers' strategies in the past have been very diverse and contingent upon the local environmental conditions, like those of mixed farmers. Foraging strategies have included hunting or trapping big game and smaller animals, fishing, collecting shellfish or insects, and gathering wild-plant foods such as fruits, seeds, and nuts.
These diverse strategies for survival amongst the migratory herds could also provide an evolutionary route towards nomadic pastoralism.
Resources
Pastoralism occurs in uncultivated areas. Wild animals eat the forage from the marginal lands and humans survive from milk, blood, and often meat of the herds and often trade by-products like wool and milk for money and food. | Pastoralism | Wikipedia | 486 | 966760 | https://en.wikipedia.org/wiki/Pastoralism | Technology | Agriculture_2 | null |
Pastoralists do not exist at basic subsistence. Pastoralists often compile wealth and participate in international trade. Pastoralists have trade relations with agriculturalists, horticulturalists, and other groups. Pastoralists are not extensively dependent on milk, blood, and meat of their herd. McCabe noted that when common property institutions are created, in long-lived communities, resource sustainability is much higher, which is evident in the East African grasslands of pastoralist populations. However, the property rights structure is only one of the many different parameters that affect the sustainability of resources, and common or private property per se, does not necessarily lead to sustainability.
Some pastoralists supplement herding with hunting and gathering, fishing and/or small-scale farming or pastoral farming.
Mobility
Mobility allows pastoralists to adapt to the environment, which opens up the possibility for both fertile and infertile regions to support human existence. Important components of pastoralism include low population density, mobility, vitality, and intricate information systems. The system is transformed to fit the environment rather than adjusting the environment to support the "food production system." Mobile pastoralists can often cover a radius of a hundred to five hundred kilometers.
Pastoralists and their livestock have impacted the environment. Lands long used for pastoralism have transformed under the forces of grazing livestock and anthropogenic fire. Fire was a method of revitalizing pastureland and preventing forest regrowth. The collective environmental weights of fire and livestock browsing have transformed landscapes in many parts of the world. Fire has permitted pastoralists to tend the land for their livestock. Political boundaries are based on environmental boundaries. The Maquis shrublands of the Mediterranean region are dominated by pyrophytic plants that thrive under conditions of anthropogenic fire and livestock grazing.
Nomadic pastoralists have a global food-producing strategy depending on the management of herd animals for meat, skin, wool, milk, blood, manure, and transport. Nomadic pastoralism is practiced in different climates and environments with daily movement and seasonal migration. Pastoralists are among the most flexible populations. Pastoralist societies have had field armed men protect their livestock and their people and then to return into a disorganized pattern of foraging. The products of the herd animals are the most important resources, although the use of other resources, including domesticated and wild plants, hunted animals, and goods accessible in a market economy are not excluded. The boundaries between states impact the viability of subsistence and trade relations with cultivators. | Pastoralism | Wikipedia | 504 | 966760 | https://en.wikipedia.org/wiki/Pastoralism | Technology | Agriculture_2 | null |
Pastoralist strategies typify effective adaptation to the environment. Precipitation differences are evaluated by pastoralists. In East Africa, different animals are taken to specific regions throughout the year that corresponds to the seasonal patterns of precipitation. Transhumance is the migration of livestock and pastoralists between seasonal pastures.
In the Himalayas, pastoralists have often historically and traditionally depended on rangelands lying across international borders. The Himalayas contain several international borders, such as those between India and China, India and Nepal, Bhutan and China, India and Pakistan, and Pakistan and China. With the growth of nation states in Asia since the mid-twentieth century, mobility across the international borders in these countries have tended to be more and more restricted and regulated. As a consequence, the old, customary arrangements of trans-border pastoralism have generally tended to disintegrate, and trans-border pastoralism has declined. Within these countries, pastoralism is often at conflict these days with new modes of community forestry, such as Van Panchayats (Uttarakhand) and Community Forest User Groups (Nepal), which tend to benefit settled agricultural communities more. Frictions have also tended to arise between pastoralists and development projects such as dam-building and the creation of protected areas.
Some pastoralists are constantly moving, which may put them at odds with sedentary people of towns and cities. The resulting conflicts can result in war for disputed lands. These disputes are recorded in ancient times in the Middle East, as well as for East Asia. Other pastoralists are able to remain in the same location which results in longer-standing housing.
Different mobility patterns can be observed: Somali pastoralists keep their animals in one of the harshest environments but they have evolved over the centuries. Somalis have well-developed pastoral culture where complete system of life and governance has been refined. Somali poetry depicts humans interactions, pastoral animals, beasts on the prowl, and other natural things such the rain, celestial events and historic events of significance. Wise sage Guled Haji coined a proverb that encapsulates the centrality of water in pastoral life:
Mobility was an important strategy for the Ariaal; however with the loss of grazing land impacted by the growth in population, severe drought, the expansion of agriculture, and the expansion of commercial ranches and game parks, mobility was lost. The poorest families were driven out of pastoralism and into towns to take jobs. Few Ariaal families benefited from education, healthcare, and income earning. | Pastoralism | Wikipedia | 500 | 966760 | https://en.wikipedia.org/wiki/Pastoralism | Technology | Agriculture_2 | null |
The flexibility of pastoralists to respond to environmental change was reduced by colonization. For example, mobility was limited in the Sahel region of Africa with settlement being encouraged. The population tripled and sanitation and medical treatment were improved.
Environment knowledge
Pastoralists have mental maps of the value of specific environments at different times of year. Pastoralists have an understanding of ecological processes and the environment. Information sharing is vital for creating knowledge through the networks of linked societies.
Pastoralists produce food in the world's harshest environments, and pastoral production supports the livelihoods of rural populations on almost half of the world's land. Several hundred million people are pastoralists, mostly in Africa and Asia. ReliefWeb reported that "Several hundred million people practice pastoralism—the use of extensive grazing on rangelands for livestock production, in over 100 countries worldwide. The African Union estimated that Africa has about 268 million pastoralists—over a quarter of the total population—living on about 43 percent of the continent's total land mass." Pastoralists manage rangelands covering about a third of the Earth's terrestrial surface and are able to produce food where crop production is not possible.
Pastoralism has been shown, "based on a review of many studies, to be between 2 and 10 times more productive per unit of land than the capital intensive alternatives that have been put forward". However, many of these benefits go unmeasured and are frequently squandered by policies and investments that seek to replace pastoralism with more capital intensive modes of production. They have traditionally suffered from poor understanding, marginalization and exclusion from dialogue. The Pastoralist Knowledge Hub, managed by the Food and Agriculture Organization of the UN serves as a knowledge repository on technical excellence on pastoralism as well as "a neutral forum for exchange and alliance building among pastoralists and stakeholders working on pastoralist issues".
The Afar pastoralists in Ethiopia uses an indigenous communication method called dagu for information. This helps them in getting crucial information about climate and availability of pastures at various locations.
Farm animal genetic resource | Pastoralism | Wikipedia | 414 | 966760 | https://en.wikipedia.org/wiki/Pastoralism | Technology | Agriculture_2 | null |
There is a variation in genetic makeup of the farm animals driven mainly by natural and human based selection. For example, pastoralists in large parts of Sub Saharan Africa are preferring livestock breeds which are adapted to their environment and able to tolerate drought and diseases. However, in other animal production systems these breeds are discouraged and more productive exotic ones are favored. This situation could not be left unaddressed due to the changes in market preferences and climate all over the world, which could lead to changes in livestock diseases occurrence and decline forage quality and availability. Hence pastoralists can maintain farm animal genetic resources by conserving local livestock breeds. Generally conserving farm animal genetic resources under pastoralism is advantageous in terms of reliability and associated cost.
Tragedy of the commons
Hardin's Tragedy of the Commons (1968) described how common property resources, such as the land shared by pastoralists, eventually become overused and ruined. According to Hardin's paper, the pastoralist land use strategy was unstable and a cause of environmental degradation.
One of Hardin's conditions for a "tragedy of the commons" is that people cannot communicate with each other or make agreements and contracts. Many scholars have pointed out that this is implausible, and yet it is applied in development projects around the globe, motivating the destruction of community and other governance systems that have managed sustainable pastoral systems for thousands of years. The outcomes have often been disastrous. In her book Governing the Commons, Elinor Ostrom showed that communities were not trapped and helpless amid diminishing commons. She argued that a common-pool resource, such as grazing lands used for pastoralism, can be managed more sustainably through community groups and cooperatives than through privatization or total governmental control. Ostrom was awarded a Nobel Memorial Prize in Economic Sciences for her work.
Pastoralists in the Sahel zone in Africa were held responsible for the depletion of resources. The depletion of resources was actually triggered by a prior interference and punitive climate conditions. Hardin's paper suggested a solution to the problems, offering a coherent basis for privatization of land, which stimulates the transfer of land from tribal peoples to the state or to individuals. The privatized programs impact the livelihood of the pastoralist societies while weakening the environment. Settlement programs often serve the needs of the state in reducing the autonomy and livelihoods of pastoral people. | Pastoralism | Wikipedia | 479 | 966760 | https://en.wikipedia.org/wiki/Pastoralism | Technology | Agriculture_2 | null |
The violent herder–farmer conflicts in Nigeria, Mali, Sudan, Ethiopia and other countries in the Sahel and Horn of Africa regions have been exacerbated by climate change, land degradation, and population growth.
It has also been shown that pastoralism supports human existence in harsh environments and often represents a sustainable approach to land use. | Pastoralism | Wikipedia | 68 | 966760 | https://en.wikipedia.org/wiki/Pastoralism | Technology | Agriculture_2 | null |
Messier 77 (M77), also known as NGC 1068 or the Squid Galaxy, is a barred spiral galaxy in the constellation Cetus. It is about away from Earth, and was discovered by Pierre Méchain in 1780, who originally described it as a nebula. Méchain then communicated his discovery to Charles Messier, who subsequently listed the object in his catalog. Both Messier and William Herschel described this galaxy as a star cluster. Today, however, the object is known to be a galaxy. It is one of the brightest Seyfert galaxies visible from Earth and has a D25 isophotal diameter of about .
The morphological classification of NGC 1068 in the De Vaucouleurs system is (R)SA(rs)b, where the '(R)' indicates an outer ring-like structure, 'SA' denotes a non-barred spiral, '(rs)' means a transitional inner ring/spiral structure, and 'b' says the spiral arms are moderately wound. Ann et al. (2015) gave it a class of SAa, suggesting tightly wound arms. However, infrared images of the inner part of the galaxy reveal a prominent bar not seen in visual light, and for this reason it is now considered a barred spiral.
Messier 77 is an active galaxy with an active galactic nucleus (AGN), which is obscured from view by astronomical dust at visible wavelengths. The diameter of the molecular disk and hot plasma associated with the obscuring material was first measured at radio wavelengths by the VLBA and VLA. The hot dust around the nucleus was subsequently measured in the mid-infrared by the MIDI instrument at the VLTI. It is the brightest and one of the closest and best-studied type 2 Seyfert galaxies, forming a prototype of this class.
X-ray source 1H 0244+001 in Cetus has been identified as Messier 77. Only one supernova has been detected in Messier 77. The supernova, named SN 2018ivc, was discovered on 24 November 2018 by the DLT40 Survey. It is a type II supernova, and at discovery it was 15th magnitude and brightening.
It has a radio jet consisting of a northeast and a southwest region, caused by interactions with the interstellar medium. | Messier 77 | Wikipedia | 474 | 967488 | https://en.wikipedia.org/wiki/Messier%2077 | Physical sciences | Notable galaxies | Astronomy |
In February 2022 astronomers reported a cloud of cosmic dust, detected through infrared interferometry observations, located at the centre of Messier 77 that is hiding a supermassive black hole.
In November 2022, the IceCube collaboration announced the detection of a neutrino source emitted by the active galactic nucleus of Messier 77. It is the second detection by IceCube after TXS 0506+056, and only the fourth known source including SN1987A and solar neutrinos. | Messier 77 | Wikipedia | 107 | 967488 | https://en.wikipedia.org/wiki/Messier%2077 | Physical sciences | Notable galaxies | Astronomy |
The pumpkinseed (Lepomis gibbosus), also referred to as sun perch, pond perch, common sunfish, punkie, sunfish, sunny, and kivver, is a small to medium–sized freshwater fish of the genus Lepomis (true sunfishes), from the sunfish family (Centrarchidae) in the order Centrarchiformes. It is endemic to eastern North America.
Distribution and habitat
The pumpkinseed's natural range in North America is from New Brunswick down the east coast to South Carolina. It then runs inland to the middle of North America, and extends through Iowa and back through Pennsylvania.
Pumpkinseed sunfish have however been introduced throughout most of North America. They can now be found from Washington and Oregon on the Pacific Coast to Georgia on the Atlantic Coast. Yet they are primarily found in the northeastern United States and more rarely in the south-central or southwestern region of the continent.
In Europe, the pumpkinseed is considered an invasive species. They were introduced to European waters, and could outcompete native fish. This species is included since 2019 in the list of Invasive Alien Species of Union concern (the Union list). It cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union.
The pumpkinseed has also been introduced to the United Kingdom, having arrived in the country around the same time as the populations in Continental Europe. Its range is believed to be restricted to Southern England and the West Country, with stable populations found in East Sussex, West Sussex and Somerset, though the species may potentially be present in the vicinity of London as well.
Description | Pumpkinseed | Wikipedia | 347 | 967508 | https://en.wikipedia.org/wiki/Pumpkinseed | Biology and health sciences | Acanthomorpha | Animals |
Pumpkinseeds have a body shaped much like a pumpkin seed (thus the common name), typically about but up to in length. They typically weigh less than , with the world record being caught by Robert Warne while fishing Honeoye Lake, Upstate New York in 2016. They are orange, green, yellow or blue in color, with speckles over their sides and back and a yellow-orange breast and belly, and the coloration of the ctenoid scales of the pumpkinseed is one of the most vibrant of any freshwater fish and can range from an olive-green or brown to bright orange and blue. The sides are covered with vertical bars that are a faint green or blue, which are typically more prevalent in female pumpkinseeds. Orange spots may cover the dorsal, anal, and caudal fins and the cheeks have blue lines across them. The pumpkinseed is noted for the orange-red spot on the margin of its black gill cover. The pectoral fins of a pumpkinseed can be amber or clear, while the dorsal spines are black. They have a small mouth with an upper jaw stopping right under the eye.
Pumpkinseeds are very similar to the larger bluegill, and are often found in the same habitats. One difference between the two species is their opercular flap, which is black in both species but the pumpkinseed has a crimson spot in the shape of a half moon on the back portion. Pumpkinseeds have seven or eight vertical, irregular bands on their sides that are duller in color compared to the bluegill.
Habitat
Pumpkinseeds typically live in warm, calm lakes, ponds, and pools of creeks and small rivers with plenty of vegetation. They prefer clear water where they can find shelter to hide. They tend to stay near the shore and can be found in numbers within shallow and protected areas. They will feed at all water levels from the surface to the bottom in the daylight, and their heaviest feeding will be in the afternoon. Pumpkinseed sunfish usually travel together in schools that can also include bluegills and other sunfish.
Pumpkinseeds are more tolerant of low oxygen levels than bluegills are, but less tolerant of warm water. Groups of young fish school close to shore, but adults tend to travel in groups of two to four in slightly deeper yet still covered waters. Pumpkinseeds are active throughout the day, but they rest at night near the bottom or in shelter areas in rocks or near submerged logs. | Pumpkinseed | Wikipedia | 506 | 967508 | https://en.wikipedia.org/wiki/Pumpkinseed | Biology and health sciences | Acanthomorpha | Animals |
Dietary habits
Pumpkinseeds are carnivorous and feed on a variety of small prey both at the water surface and at the bottom. Among their favorites are insects, small molluscs and crustaceans (such as small crawfish), worms, minnow fry, small frogs or tadpoles, and even cannibalizing other smaller pumpkinseeds. They are effective at destroying mosquito larvae and even occasionally consume small pieces of aquatic vegetation and detritus. They also will readily consume human food scraps, most notably bread which is commonly used for bait.
The pumpkinseed sunfish has a terminal mouth, allowing it to open at the anterior end of the snout. Pumpkinseed sunfish that live in waters with larger gastropods have larger mouths and associated jaw muscles to crack the shells.
Sport fishing
The pumpkinseed sunfish are typically very likely to bite on a worm bait, which makes them easy to catch while angling. Many fishermen consider the pumpkinseed to be a nuisance fish, as it bites so easily and frequently when the fisherman is attempting to catch something else. The pumpkinseeds are very popular with young fishermen due to their willingness to bite, their abundance and close locations to the shore. Although many people consider the meat of a pumpkinseed to be good-tasting, it is typically not a popular sport fish due to its small size.
Because pumpkinseeds tend to remain in the shallows and feed all day, pumpkinseeds are relatively easy to catch via bank fishing. They will bite at most bait – including garden worms, insects, leeches, or bits of fish meat. They will also take small lures and can be fished for with a fly rod with wet or dry flies. They will also hit at grubs early in the winter, but are less active from mid- to late winter. They may be easy to catch and popular with the youngest anglers, but pumpkinseeds are often sought by adults as well. The fish do put up an aggressive fight on line, and they have an excellent flavor and are low in fat and high in protein.
The IGFA world record for the species stands at , caught near Honeoye, New York, in 2016. | Pumpkinseed | Wikipedia | 453 | 967508 | https://en.wikipedia.org/wiki/Pumpkinseed | Biology and health sciences | Acanthomorpha | Animals |
Conservation status
The pumpkinseed sunfish is very common and is not listed by CITES. It is considered Least Concern (not threatened) by the IUCN. Spawning grounds of the pumpkinseeds can be disturbed by shoreline development and shoreline erosion from heavy lake use. Their susceptibility to silt and pollution makes the pumpkinseed a good indicator of the cleanliness and health of water.
Reproduction and life cycle
Once water temperatures reach in the late spring or early summer, the male pumpkinseeds will begin to build nests. Nesting sites are typically in shallow water on sand or gravel lake bottoms. The males will use their caudal fins to sweep out shallow, oval-shaped nesting holes that stretch about twice the length of the pumpkinseed itself. The fish will remove debris and large rocks from their nests with their mouths.
Nests are arranged in colonies consisting of about three to 15 nests each. Often, pumpkinseeds build their nests near bluegill colonies, and the two species interbreed. Male pumpkinseeds are vigorous and aggressive, and defend their nests by spreading their opercula. Because of this aggressive behavior, pumpkinseeds tend to maintain larger territories than bluegills.
Females arrive after the nests are completed, coming in from deeper waters. The male then releases milt and the female releases eggs. Females may spawn in more than one nest, and more than one female may use the same nest. Also, more than one female will spawn with a male in one nest simultaneously. Females are able produce 1,500 to 1,700 eggs, depending on their size and age.
Once released, the eggs stick to gravel, sand, or other debris in the nest, and they hatch in as few as three days. Females leave the nest immediately after spawning, but males remain and guard their offspring. The male guards them for about the first 11 days, returning them to the nest in his mouth if they stray from the nesting site.
The young fish stay on or near the shallow breeding area and grow to about in their first year. Sexual maturity is usually achieved by age two. Pumpkinseeds have lived to be 12 years old in captivity, but in nature most do not exceed six to eight years old.
Adaptations
The pumpkinseed sunfish has adapted in many ways to the surroundings where it lives. Its skin reflects camouflage for its habitat. The pattern that appears on the pumpkinseed resembles that of the sunlight patterns that reflect on the shallow water of bays and river beds. | Pumpkinseed | Wikipedia | 503 | 967508 | https://en.wikipedia.org/wiki/Pumpkinseed | Biology and health sciences | Acanthomorpha | Animals |
The pumpkinseed sunfish has developed a specific method of protection. Along the dorsal fin are 10 to 11 spines, and three additional spines on the anal fin. These spines are very sharp, which aid the fish in defense. The pumpkinseed has the ability to anticipate approaching predators (or prey) via a lateral line system, allowing it to detect changes or movements in the water using different mechanical receptors.
The brightly colored gill plates of the pumpkinseed sunfish also serve as a method of protection and dominance. Also known as an eye spot, the dark patch at the posterior of the gill plate provides the illusion that the eye of the fish is larger and positioned further back on the body, thus making the fish seem up to four times larger than it actually is. When a pumpkinseed feels threatened by a predator, it flares its gills to make it seem larger in size, and shows off the flashy red coloration. Males of the species also flare their gills in the spring spawning season in a show of dominance and territoriality.
In the southernmost regions of its distribution, the pumpkinseed has developed a larger mouth opening and abnormally large jaw muscles to aid in feeding; its forage is small crustaceans and mollusks. The larger bite radius and enhanced jaw muscles allow the pumpkinseed to crack the shells of their prey to attain the soft flesh within, thus providing one common name of 'shellcracker'.
Etymology
Lepomis, in Greek, means 'scaled gill cover' and gibbosus means 'humped'. The defining characteristic of a pumpkinseed sunfish is the bright red spot at the tip of the ear flap. The pumpkinseed sunfish is widely recognized by its shape of a pumpkin seed, from which its common name comes. | Pumpkinseed | Wikipedia | 364 | 967508 | https://en.wikipedia.org/wiki/Pumpkinseed | Biology and health sciences | Acanthomorpha | Animals |
The cookiecutter shark (Isistius brasiliensis), also called the cigar shark, is a species of small squaliform shark in the family Dalatiidae. This shark lives in warm, oceanic waters worldwide, particularly near islands, and has been recorded as deep as . It migrates vertically up to every day, approaching the surface at dusk and descending with the dawn. Reaching only in length, the cookiecutter shark has a long, cylindrical body with a short, blunt snout, large eyes, two tiny spineless dorsal fins, and a large caudal fin. It is dark brown, with light-emitting photophores covering its underside except for a dark "collar" around its throat and gill slits.
The name "cookiecutter shark" refers to its feeding method of gouging round plugs, as if cut out with a cookie cutter, out of larger animals. Marks made by cookiecutter sharks have been found on a wide variety of marine mammals and fishes, and on submarines, undersea cables, and human bodies. It also consumes whole smaller prey, such as squid. Cookiecutter sharks have adaptations for hovering in the water column, and likely rely on stealth and subterfuge to capture more active prey. Its dark collar seems to mimic the silhouette of a small fish, while the rest of its body blends into the downwelling light via its ventral photophores. When a would-be predator approaches the lure, the shark attaches itself using its suctorial lips and specialized pharynx and neatly excises a chunk of the flesh using its bandsaw-like set of lower teeth. This species has been known to travel in schools.
Though rarely encountered because of its oceanic habitat, a handful of documented attacks on humans were apparently caused by cookiecutter sharks. Nevertheless, this diminutive shark is not regarded as dangerous to humans. The International Union for Conservation of Nature has listed the cookiecutter shark under least concern, as it is widely distributed, has no commercial value, and is not particularly susceptible to fisheries. | Cookiecutter shark | Wikipedia | 423 | 969122 | https://en.wikipedia.org/wiki/Cookiecutter%20shark | Biology and health sciences | Sharks | Animals |
Taxonomy
French naturalists Jean René Constant Quoy and Joseph Paul Gaimard originally described the cookiecutter shark during the 1817–1820 exploratory voyage of the corvette Uranie under Louis de Freycinet, giving it the name Scymnus brasiliensis because the type specimen was caught off Brazil. In 1824, their account was published as part of Voyage autour du monde...sur les corvettes de S.M. l'Uranie et la Physicienne, Louis de Freycinet's 13 volume report on the voyage. In 1865, American ichthyologist Theodore Nicholas Gill coined the new genus Isistius for this species, after Isis, the Egyptian goddess of light.
One of the earliest accounts of the wounds left by the cookiecutter shark on various animals is in ancient Samoan legend, which held that atu (skipjack tuna) entering Palauli Bay would leave behind pieces of their flesh as a sacrifice to Tautunu, the community chief. In later centuries, various other explanations for the wounds were advanced, including lampreys, bacteria, and invertebrate parasites. In 1971, Everet Jones of the U.S. Bureau of Commercial Fisheries (a predecessor of the National Marine Fisheries Service) discovered the cigar shark, as the cookiecutter shark was then generally known, was responsible. Shark expert Stewart Springer thus popularized the name "cookiecutter shark" for this species (though he originally called them "demon whale-biters"). Other common names used for this shark include luminous shark, smalltooth cookiecutter shark, and smooth cookiecutter shark.
Description
The cookiecutter shark has an elongated, cigar-shaped body with a short, bulbously rounded snout. The nostrils have a very short flap of skin in front. The large, oval, green eyes are placed forward on the head, though not so that binocular vision is extensive. Behind the eyes are large spiracles, positioned on the upper surface of the head. | Cookiecutter shark | Wikipedia | 411 | 969122 | https://en.wikipedia.org/wiki/Cookiecutter%20shark | Biology and health sciences | Sharks | Animals |
The mouth is short, forming a nearly transverse line, and is surrounded by enlarged, fleshy, suctorial lips. The upper jaw has 30–37 rows of teeth, and the lower jaw has 25–31, increasing with body size. The upper and lower teeth are extremely different; the upper teeth are small, narrow, and upright, tapering to a single, smooth-edged cusp. The lower teeth are also smooth-edged, but much larger, broader, and knife-like, with their bases interlocking to form a single saw-like cutting edge. The five pairs of gill slits are small.
The pectoral fins are short and roughly trapezoidal in shape. Two spineless dorsal fins are placed far back on the body, the first originating just ahead of the pelvic fins and the second located just behind. The second dorsal fin is slightly larger than the first, and the pelvic fins are larger than either. The anal fin is absent. The caudal fin is broad, with the lower lobe almost as large as the upper, which has a prominent ventral notch. The dermal denticles are squarish and flattened, with a slight central concavity and raised corners. The cookiecutter shark is chocolate brown in color, becoming subtly lighter below, and a dark "collar" wraps around the gill region.
The fins have translucent margins, except for the caudal fin, which has a darker margin. Complex, light-producing organs called photophores densely cover the entire underside, except for the collar, and produce a vivid green glow. The maximum recorded length for this species is for males and for females. | Cookiecutter shark | Wikipedia | 341 | 969122 | https://en.wikipedia.org/wiki/Cookiecutter%20shark | Biology and health sciences | Sharks | Animals |
Distribution and habitat
Inhabiting all of the world's major tropical and warm-temperate oceanic basins, the cookiecutter shark is most common between the latitudes of 20°N and 20°S, where the surface water temperature is . In the Atlantic, it has been reported off the Bahamas and southern Brazil in the west, Cape Verde, Guinea to Sierra Leone, southern Angola, and South Africa in the east, and Ascension Island in the south. In the Indo-Pacific region, it has been caught from Mauritius to New Guinea, Australia, and New Zealand, including Tasmania and Lord Howe Island, as well as off Japan. In the central and eastern Pacific, it occurs from Fiji north to the Hawaiian Islands, and east to the Galápagos, Easter, and Guadalupe Islands. Fresh wounds observed on marine mammals suggest this shark may range as far as California in warm years.
Based on catch records, the cookiecutter shark appears to conduct a diel vertical migration up to each way. It spends the day at a depth of , and at night it rises into the upper water column, usually remaining below , but on rare occasions venturing to the surface. This species may be more tolerant of low dissolved oxygen levels than sharks in the related genera Euprotomicrus and Squaliolus. It is frequently found near islands, perhaps for reproductive purposes or because they hold congregations of large prey animals. In the northeastern Atlantic, most adults are found between 11°N and 16°N, with the smallest and largest individuals being found in lower and higher latitudes, respectively. There is no evidence of sex segregation.
Biology and ecology | Cookiecutter shark | Wikipedia | 329 | 969122 | https://en.wikipedia.org/wiki/Cookiecutter%20shark | Biology and health sciences | Sharks | Animals |
Best known for biting neat round chunks of tissue from marine mammals and large fish, the cookiecutter shark is considered a facultative ectoparasite, as it also wholly ingests smaller prey. It has a wide gape and a very strong bite, by virtue of heavily calcified cranial and labial cartilages. With small fins and weak muscles, this ambush predator spends much of its time hovering in the water column. Its liver, which can comprise some 35% of its weight, is rich in low-density lipids, which enables it to maintain neutral buoyancy. This species has higher skeletal density than Euprotomicrus or Squaliolus, and its body cavity and liver are proportionately much larger, with much higher oil content. Its large caudal fin allows it to make a quick burst of speed to catch larger, faster prey that come in range.
The cookiecutter shark regularly replaces its teeth like other sharks, but sheds its lower teeth in entire rows rather than one at a time. A cookiecutter shark has been calculated to have shed 15 sets of lower teeth, totaling 435–465 teeth, from when it was long to when it reached , a significant investment of resources. The shark swallows its old sets of teeth, enabling it to recycle the calcium content.
Unlike other sharks, the retina of the cookiecutter shark has ganglion cells concentrated in a concentric area rather than in a horizontal streak across the visual field; this may help to focus on prey in front of the shark.
This shark has been known to travel in schools, which may increase the effectiveness of its lure (see below), and discourage attacks by much larger predators.
Bioluminescence
The intrinsic green luminescence of the cookiecutter shark is the strongest known of any shark, and has been reported to persist for three hours after it has been taken out of water. The ventrally positioned photophores serve to disrupt its silhouette from below by matching the downwelling light, a strategy known as counter-illumination, that is common among bioluminescent organisms of the mesopelagic zone. The individual photophores are set around the denticles and are small enough that they cannot be discerned by the naked eye, suggesting they have evolved to fool animals with high visual acuity and/or at close distances. | Cookiecutter shark | Wikipedia | 488 | 969122 | https://en.wikipedia.org/wiki/Cookiecutter%20shark | Biology and health sciences | Sharks | Animals |
Set apart from the glowing underside, the darker, nonluminescent collar tapers at both sides of the throat, and has been hypothesized to serve as a lure by mimicking the silhouette of a small fish from below. The appeal of the lure would be multiplied in a school of sharks. If the collar does function in this way, the cookiecutter shark would be the only known case of bioluminescence in which the absence of light attracts prey, while its photophores serve to inhibit detection by predators. As the shark can only match a limited range of light intensities, it has been suggested that its vertical movements might serve to preserve the effectiveness of its disguise across various times of day and weather conditions.
Feeding
Virtually every type of medium- to large-sized oceanic animal sharing the habitat of the cookiecutter shark is open to attack; bite scars have been found on cetaceans (including porpoises, orcas, dolphins, beaked whales, sperm whales and baleen whales), pinnipeds (including fur seals, leopard seals and elephant seals), dugongs, larger sharks (including blue sharks, goblin sharks, basking sharks, great white sharks, megamouth sharks and smalltooth sand tiger sharks), stingrays (including deepwater stingrays, pelagic stingrays and sixgill stingrays), and bony fishes (including billfishes, tunas, dolphinfishes, jacks, escolars, opahs, and pomfrets). The cookiecutter shark also regularly hunts and eats entire squid with a mantle length of , comparable in size to the shark itself, as well as bristlemouths, copepods, and other smaller prey.
Parasitic attacks by the cookiecutter shark leave a round "crater wound", averaging across and deep. The prevalence of these attacks can be high: off Hawaii, nearly every adult spinner dolphin bears scars from this species. Diseased or otherwise weakened animals appear to be more susceptible, and in the western Atlantic observations have been made of emaciated beached melon-headed whales with dozens to hundreds of recent and healing cookiecutter shark wounds, while such wounds are rare on non-emaciated beached whales. The impact of parasitism on prey species, in terms of resources diverted from growth or reproduction, is uncertain. | Cookiecutter shark | Wikipedia | 489 | 969122 | https://en.wikipedia.org/wiki/Cookiecutter%20shark | Biology and health sciences | Sharks | Animals |
The cookiecutter shark exhibits a number of specializations to its mouth and pharynx for its parasitic lifestyle. The shark first secures itself to the body surface of its prey by closing its spiracles and retracting its basihyal (tongue) to create pressure lower than that of the surroundings; its suctorial lips ensure a tight seal. It then bites, using its narrow upper teeth as anchors while its razor sharp lower teeth slice into the prey. Finally, the shark twists and rotates its body to complete a circular cut, quite possibly aided by the initial forward momentum and subsequent struggles of its prey. The action of the lower teeth may also be assisted by back-and-forth vibrations of the jaw, a mechanism akin to that of an electric carving knife. This shark's ability to create strong suction into its mouth probably also helps in capturing smaller prey such as squid.
Life history
Like other dogfish sharks, the cookiecutter shark is aplacental viviparous, with the developing embryos being sustained by yolk until birth. Females have two functional uteri and give birth to litters of 6 to 12 pups. A case has been recorded of a female carrying 9 embryos long; though they were close to the birth size, they still had well-developed yolk sacs, suggesting a slow rate of yolk absorption and a long gestation period. The embryos had developed brown pigmentation, but not the dark collar or differentiated dentition. Newborn cookiecutter sharks are long. Males attain sexual maturity at a length of , and females at a length of .
Human interactions | Cookiecutter shark | Wikipedia | 330 | 969122 | https://en.wikipedia.org/wiki/Cookiecutter%20shark | Biology and health sciences | Sharks | Animals |
Favoring offshore waters and thus seldom encountered by humans, the cookiecutter shark is not considered dangerous because of its small size. However, it has been implicated in a few attacks on humans; in one case, a school of 30-cm (12 in) long fish with blunt snouts attacked an underwater photographer on an open-ocean dive. Similar reports have come from shipwreck survivors, of suffering small, clean, deep bites during the night. In March 2009, Maui resident Mike Spalding was bitten by a cookiecutter shark while swimming across Alenuihaha Channel. Swimmer Eric Schall was bitten by a cookiecutter shark on March 31, 2019 while crossing the Kaiwi Channel, and suffered a large laceration to his stomach. A second cookiecutter attack occurred in the same spot three weeks later: Isaiah Mojica was attempting the channel swim on April 6, 2019 as part of the Oceans Seven challenge when he was bitten on the left shoulder. A third person attempting to complete the swim was bitten in nearly the same area of the channel: Adherbal Treidler de Oliveira was attempting the swim on July 29, 2019, when he was bitten on the stomach and on the left thigh. Two of the three swimmers were using electrical shark deterrents, but they did not deter the sharks. In 2017, a seven-year-old boy, Jack Tolley, was bitten in the leg while wading in Alma Bay in North Queensland with his family. The shark caused a 7.3 cm wound that was nearly down to the bone. On February 9, 2022, a deep-water swimmer off Kailua-Kona, Hawaii was bitten on the right foot and calf. In March 2023, Andy Walberer was attacked by two cookiecutter sharks while swimming the Molokai channel. He was able to grab and throw both sharks before serious injury was inflicted.
There are several records of human bodies recovered from the water with post-mortem cookiecutter shark bites. | Cookiecutter shark | Wikipedia | 410 | 969122 | https://en.wikipedia.org/wiki/Cookiecutter%20shark | Biology and health sciences | Sharks | Animals |
During the 1970s, several U.S. Navy submarines were forced back to base to repair damage caused by cookiecutter shark bites to the neoprene boots of their AN/BQR-19 sonar domes, which caused the sound-transmitting oil inside to leak and impaired navigation. An unknown enemy weapon was initially feared, before this shark was identified as the culprit; the problem was solved by installing fiberglass covers around the domes. In the 1980s, some 30 U.S. Navy submarines were damaged by cookiecutter shark bites, mostly to the rubber-sheathed electric cable leading to the sounding probe used to ensure safety when surfacing in shipping zones. Again, the solution was to apply a fiberglass coating. Oceanographic equipment and telecommunications cables have also been damaged by this species.
The harm inflicted by cookiecutter sharks on fishing nets and economically important species may have a minor detrimental effect on commercial fisheries. The shark itself is too small to be of value, and is only infrequently taken, as bycatch, on pelagic longlines and in midwater trawls and plankton nets. The lack of significant population threats, coupled with a worldwide distribution, has led the IUCN to assess the cookiecutter shark as of least concern. In June 2018 the New Zealand Department of Conservation classified the cookiecutter shark as "Not Threatened" with the qualifier "Secure Overseas" under the New Zealand Threat Classification System. | Cookiecutter shark | Wikipedia | 295 | 969122 | https://en.wikipedia.org/wiki/Cookiecutter%20shark | Biology and health sciences | Sharks | Animals |
Protein structure is the three-dimensional arrangement of atoms in an amino acid-chain molecule. Proteins are polymers specifically polypeptides formed from sequences of amino acids, which are the monomers of the polymer. A single amino acid monomer may also be called a residue, which indicates a repeating unit of a polymer. Proteins form by amino acids undergoing condensation reactions, in which the amino acids lose one water molecule per reaction in order to attach to one another with a peptide bond. By convention, a chain under 30 amino acids is often identified as a peptide, rather than a protein. To be able to perform their biological function, proteins fold into one or more specific spatial conformations driven by a number of non-covalent interactions, such as hydrogen bonding, ionic interactions, Van der Waals forces, and hydrophobic packing. To understand the functions of proteins at a molecular level, it is often necessary to determine their three-dimensional structure. This is the topic of the scientific field of structural biology, which employs techniques such as X-ray crystallography, NMR spectroscopy, cryo-electron microscopy (cryo-EM) and dual polarisation interferometry, to determine the structure of proteins.
Protein structures range in size from tens to several thousand amino acids. By physical size, proteins are classified as nanoparticles, between 1–100 nm. Very large protein complexes can be formed from protein subunits. For example, many thousands of actin molecules assemble into a microfilament.
A protein usually undergoes reversible structural changes in performing its biological function. The alternative structures of the same protein are referred to as different conformations, and transitions between them are called conformational changes.
Levels of protein structure
There are four distinct levels of protein structure.
Primary structure | Protein structure | Wikipedia | 363 | 969126 | https://en.wikipedia.org/wiki/Protein%20structure | Biology and health sciences | Proteins | Biology |
The primary structure of a protein refers to the sequence of amino acids in the polypeptide chain. The primary structure is held together by peptide bonds that are made during the process of protein biosynthesis. The two ends of the polypeptide chain are referred to as the carboxyl terminus (C-terminus) and the amino terminus (N-terminus) based on the nature of the free group on each extremity. Counting of residues always starts at the N-terminal end (NH2-group), which is the end where the amino group is not involved in a peptide bond. The primary structure of a protein is determined by the gene corresponding to the protein. A specific sequence of nucleotides in DNA is transcribed into mRNA, which is read by the ribosome in a process called translation. The sequence of amino acids in insulin was discovered by Frederick Sanger, establishing that proteins have defining amino acid sequences. The sequence of a protein is unique to that protein, and defines the structure and function of the protein. The sequence of a protein can be determined by methods such as Edman degradation or tandem mass spectrometry. Often, however, it is read directly from the sequence of the gene using the genetic code. It is strictly recommended to use the words "amino acid residues" when discussing proteins because when a peptide bond is formed, a water molecule is lost, and therefore proteins are made up of amino acid residues. Post-translational modifications such as phosphorylations and glycosylations are usually also considered a part of the primary structure, and cannot be read from the gene. For example, insulin is composed of 51 amino acids in 2 chains. One chain has 31 amino acids, and the other has 20 amino acids.
Secondary structure | Protein structure | Wikipedia | 365 | 969126 | https://en.wikipedia.org/wiki/Protein%20structure | Biology and health sciences | Proteins | Biology |
Secondary structure refers to highly regular local sub-structures on the actual polypeptide backbone chain. Two main types of secondary structure, the α-helix and the β-strand or β-sheets, were suggested in 1951 by Linus Pauling. These secondary structures are defined by patterns of hydrogen bonds between the main-chain peptide groups. They have a regular geometry, being constrained to specific values of the dihedral angles ψ and φ on the Ramachandran plot. Both the α-helix and the β-sheet represent a way of saturating all the hydrogen bond donors and acceptors in the peptide backbone. Some parts of the protein are ordered but do not form any regular structures. They should not be confused with random coil, an unfolded polypeptide chain lacking any fixed three-dimensional structure. Several sequential secondary structures may form a "supersecondary unit".
Tertiary structure
Tertiary structure refers to the three-dimensional structure created by a single protein molecule (a single polypeptide chain). It may include one or several domains. The α-helices and β-pleated-sheets are folded into a compact globular structure. The folding is driven by the non-specific hydrophobic interactions, the burial of hydrophobic residues from water, but the structure is stable only when the parts of a protein domain are locked into place by specific tertiary interactions, such as salt bridges, hydrogen bonds, and the tight packing of side chains and disulfide bonds. The disulfide bonds are extremely rare in cytosolic proteins, since the cytosol (intracellular fluid) is generally a reducing environment.
Quaternary structure | Protein structure | Wikipedia | 336 | 969126 | https://en.wikipedia.org/wiki/Protein%20structure | Biology and health sciences | Proteins | Biology |
Quaternary structure is the three-dimensional structure consisting of the aggregation of two or more individual polypeptide chains (subunits) that operate as a single functional unit (multimer). The resulting multimer is stabilized by the same non-covalent interactions and disulfide bonds as in tertiary structure. There are many possible quaternary structure organisations. Complexes of two or more polypeptides (i.e. multiple subunits) are called multimers. Specifically it would be called a dimer if it contains two subunits, a trimer if it contains three subunits, a tetramer if it contains four subunits, and a pentamer if it contains five subunits, and so forth. The subunits are frequently related to one another by symmetry operations, such as a 2-fold axis in a dimer. Multimers made up of identical subunits are referred to with a prefix of "homo-" and those made up of different subunits are referred to with a prefix of "hetero-", for example, a heterotetramer, such as the two alpha and two beta chains of hemoglobin.
Homomers
An assemblage of multiple copies of a particular polypeptide chain can be described as a homomer, multimer or oligomer. Bertolini et al. in 2021 presented evidence that homomer formation may be driven by interaction between nascent polypeptide chains as they are translated from mRNA by nearby adjacent ribosomes. Hundreds of proteins have been identified as being assembled into homomers in human cells. The process of assembly is often initiated by the interaction of the N-terminal region of polypeptide chains. Evidence that numerous gene products form homomers (multimers) in a variety of organisms based on intragenic complementation evidence was reviewed in 1965.
Domains, motifs, and folds in protein structure
Proteins are frequently described as consisting of several structural units. These units include domains, motifs, and folds. Despite the fact that there are about 100,000 different proteins expressed in eukaryotic systems, there are many fewer different domains, structural motifs and folds. | Protein structure | Wikipedia | 442 | 969126 | https://en.wikipedia.org/wiki/Protein%20structure | Biology and health sciences | Proteins | Biology |
Structural domain
A structural domain is an element of the protein's overall structure that is self-stabilizing and often folds independently of the rest of the protein chain. Many domains are not unique to the protein products of one gene or one gene family but instead appear in a variety of proteins. Domains often are named and singled out because they figure prominently in the biological function of the protein they belong to; for example, the "calcium-binding domain of calmodulin". Because they are independently stable, domains can be "swapped" by genetic engineering between one protein and another to make chimera proteins. A conservative combination of several domains that occur in different proteins, such as protein tyrosine phosphatase domain and C2 domain pair, was called "a superdomain" that may evolve as a single unit.
Structural and sequence motifs
The structural and sequence motifs refer to short segments of protein three-dimensional structure or amino acid sequence that were found in a large number of different proteins
Supersecondary structure
Tertiary protein structures can have multiple secondary elements on the same polypeptide chain. The supersecondary structure refers to a specific combination of secondary structure elements, such as β-α-β units or a helix-turn-helix motif. Some of them may be also referred to as structural motifs.
Protein fold
A protein fold refers to the general protein architecture, like a helix bundle, β-barrel, Rossmann fold or different "folds" provided in the Structural Classification of Proteins database. A related concept is protein topology.
Protein dynamics and conformational ensembles | Protein structure | Wikipedia | 321 | 969126 | https://en.wikipedia.org/wiki/Protein%20structure | Biology and health sciences | Proteins | Biology |
Proteins are not static objects, but rather populate ensembles of conformational states. Transitions between these states typically occur on nanoscales, and have been linked to functionally relevant phenomena such as allosteric signaling and enzyme catalysis. Protein dynamics and conformational changes allow proteins to function as nanoscale biological machines within cells, often in the form of multi-protein complexes. Examples include motor proteins, such as myosin, which is responsible for muscle contraction, kinesin, which moves cargo inside cells away from the nucleus along microtubules, and dynein, which moves cargo inside cells towards the nucleus and produces the axonemal beating of motile cilia and flagella. "[I]n effect, the [motile cilium] is a nanomachine composed of perhaps over 600 proteins in molecular complexes, many of which also function independently as nanomachines...Flexible linkers allow the mobile protein domains connected by them to recruit their binding partners and induce long-range allostery via protein domain dynamics. "
Proteins are often thought of as relatively stable tertiary structures that experience conformational changes after being affected by interactions with other proteins or as a part of enzymatic activity. However, proteins may have varying degrees of stability, and some of the less stable variants are intrinsically disordered proteins. These proteins exist and function in a relatively 'disordered' state lacking a stable tertiary structure. As a result, they are difficult to describe by a single fixed tertiary structure. Conformational ensembles have been devised as a way to provide a more accurate and 'dynamic' representation of the conformational state of intrinsically disordered proteins. | Protein structure | Wikipedia | 343 | 969126 | https://en.wikipedia.org/wiki/Protein%20structure | Biology and health sciences | Proteins | Biology |
Protein ensemble files are a representation of a protein that can be considered to have a flexible structure. Creating these files requires determining which of the various theoretically possible protein conformations actually exist. One approach is to apply computational algorithms to the protein data in order to try to determine the most likely set of conformations for an ensemble file. There are multiple methods for preparing data for the Protein Ensemble Database that fall into two general methodologies – pool and molecular dynamics (MD) approaches (diagrammed in the figure). The pool based approach uses the protein's amino acid sequence to create a massive pool of random conformations. This pool is then subjected to more computational processing that creates a set of theoretical parameters for each conformation based on the structure. Conformational subsets from this pool whose average theoretical parameters closely match known experimental data for this protein are selected. The alternative molecular dynamics approach takes multiple random conformations at a time and subjects all of them to experimental data. Here the experimental data is serving as limitations to be placed on the conformations (e.g. known distances between atoms). Only conformations that manage to remain within the limits set by the experimental data are accepted. This approach often applies large amounts of experimental data to the conformations which is a very computationally demanding task.
The conformational ensembles were generated for a number of highly dynamic and partially unfolded proteins, such as Sic1/Cdc4, p15 PAF, MKK7, Beta-synuclein and P27
Protein folding
As it is translated, polypeptides exit the ribosome mostly as a random coil and folds into its native state. The final structure of the protein chain is generally assumed to be determined by its amino acid sequence (Anfinsen's dogma).
Protein stability
Thermodynamic stability of proteins represents the free energy difference between the folded and unfolded protein states. This free energy difference is very sensitive to temperature, hence a change in temperature may result in unfolding or denaturation. Protein denaturation may result in loss of function, and loss of native state. The free energy of stabilization of soluble globular proteins typically does not exceed 50 kJ/mol. Taking into consideration the large number of hydrogen bonds that take place for the stabilization of secondary structures, and the stabilization of the inner core through hydrophobic interactions, the free energy of stabilization emerges as small difference between large numbers.
Protein structure determination | Protein structure | Wikipedia | 492 | 969126 | https://en.wikipedia.org/wiki/Protein%20structure | Biology and health sciences | Proteins | Biology |
Around 90% of the protein structures available in the Protein Data Bank have been determined by X-ray crystallography. This method allows one to measure the three-dimensional (3-D) density distribution of electrons in the protein, in the crystallized state, and thereby infer the 3-D coordinates of all the atoms to be determined to a certain resolution. Roughly 7% of the known protein structures have been obtained by nuclear magnetic resonance (NMR) techniques. For larger protein complexes, cryo-electron microscopy can determine protein structures. The resolution is typically lower than that of X-ray crystallography, or NMR, but the maximum resolution is steadily increasing. This technique is still a particularly valuable for very large protein complexes such as virus coat proteins and amyloid fibers.
General secondary structure composition can be determined via circular dichroism. Vibrational spectroscopy can also be used to characterize the conformation of peptides, polypeptides, and proteins. Two-dimensional infrared spectroscopy has become a valuable method to investigate the structures of flexible peptides and proteins that cannot be studied with other methods. A more qualitative picture of protein structure is often obtained by proteolysis, which is also useful to screen for more crystallizable protein samples. Novel implementations of this approach, including fast parallel proteolysis (FASTpp), can probe the structured fraction and its stability without the need for purification. Once a protein's structure has been experimentally determined, further detailed studies can be done computationally, using molecular dynamic simulations of that structure. | Protein structure | Wikipedia | 320 | 969126 | https://en.wikipedia.org/wiki/Protein%20structure | Biology and health sciences | Proteins | Biology |
Protein structure databases
A protein structure database is a database that is modeled around the various experimentally determined protein structures. The aim of most protein structure databases is to organize and annotate the protein structures, providing the biological community access to the experimental data in a useful way. Data included in protein structure databases often includes 3D coordinates as well as experimental information, such as unit cell dimensions and angles for x-ray crystallography determined structures. Though most instances, in this case either proteins or a specific structure determinations of a protein, also contain sequence information and some databases even provide means for performing sequence based queries, the primary attribute of a structure database is structural information, whereas sequence databases focus on sequence information, and contain no structural information for the majority of entries. Protein structure databases are critical for many efforts in computational biology such as structure based drug design, both in developing the computational methods used and in providing a large experimental dataset used by some methods to provide insights about the function of a protein.
Structural classifications of proteins
Protein structures can be grouped based on their structural similarity, topological class or a common evolutionary origin. The Structural Classification of Proteins database and CATH database provide two different structural classifications of proteins. When the structural similarity is large the two proteins have possibly diverged from a common ancestor, and shared structure between proteins is considered evidence of homology. Structure similarity can then be used to group proteins together into protein superfamilies. If shared structure is significant but the fraction shared is small, the fragment shared may be the consequence of a more dramatic evolutionary event such as horizontal gene transfer, and joining proteins sharing these fragments into protein superfamilies is no longer justified. Topology of a protein can be used to classify proteins as well. Knot theory and circuit topology are two topology frameworks developed for classification of protein folds based on chain crossing and intrachain contacts respectively.
Computational prediction of protein structure
The generation of a protein sequence is much easier than the determination of a protein structure. However, the structure of a protein gives much more insight in the function of the protein than its sequence. Therefore, a number of methods for the computational prediction of protein structure from its sequence have been developed. Ab initio prediction methods use just the sequence of the protein. Threading and homology modeling methods can build a 3-D model for a protein of unknown structure from experimental structures of evolutionarily-related proteins, called a protein family. | Protein structure | Wikipedia | 489 | 969126 | https://en.wikipedia.org/wiki/Protein%20structure | Biology and health sciences | Proteins | Biology |
A herd is a social group of certain animals of the same species, either wild or domestic. The form of collective animal behavior associated with this is called herding. These animals are known as gregarious animals.
The term herd is generally applied to mammals, and most particularly to the grazing ungulates that classically display this behaviour. Different terms are used for similar groupings in other species; in the case of birds, for example, the word is flocking, but flock may also be used for mammals, particularly sheep or goats. Large groups of carnivores are usually called packs, and in nature a herd is classically subject to predation from pack hunters.
Special collective nouns may be used for particular taxa (for example a flock of geese, if not in flight, is sometimes called a gaggle) but for theoretical discussions of behavioural ecology, the generic term herd can be used for all such kinds of assemblage.
The word herd, as a noun, can also refer to one who controls, possesses and has care for such groups of animals when they are domesticated. Examples of herds in this sense include shepherds (who tend to sheep), goatherds (who tend to goats), and cowherds (who tend to cattle).
The structure and size of herds
When an association of animals (or, by extension, people) is described as a herd, the implication is that the group tends to act together (for example, all moving in the same direction at a given time), but that this does not occur as a result of planning or coordination. Rather, each individual is choosing behaviour in correspondence with most other members, possibly through imitation or possibly because all are responding to the same external circumstances. A herd can be contrasted with a coordinated group where individuals have distinct roles. Many human groupings, such as army detachments or sports teams, show such coordination and differentiation of roles, but so do some animal groupings such as those of eusocial insects, which are coordinated through pheromones and other forms of animal communication. | Herd | Wikipedia | 421 | 969684 | https://en.wikipedia.org/wiki/Herd | Biology and health sciences | Ethology | Biology |
A herd is, by definition, relatively unstructured. However, there may be two or a few animals which tend to be imitated by the bulk of the herd more than others. An animal in this role is called a "control animal", since its behaviour will predict that of the herd as a whole. It cannot be assumed, however, that the control animal is deliberately taking a leadership role; control animals are not necessarily socially dominant in conflict situations, though they often are. Group size is an important characteristic of the social environment of gregarious species.
Costs and benefits of animals in groups
The reason why animals form herds can not always be stated easily, since the underlying mechanisms are diverse and complex. Understanding the social behaviour of animals and the formation of groups has been a fundamental goal in the field of sociobiology and behavioural ecology. Theoretical framework is focused on the costs and benefits associated with living in groups in terms of the fitness of each individual compared to living solitarily. Living in groups evolved independently multiple times in various taxa and can only occur if its benefits outweigh the costs within an evolutionary timescale. Thus, animals form groups whenever this increases their fitness compared to living in solitary.
The following includes an outline about some of the major effects determining the trade-offs for living in groups.
Dilution effect
Perhaps the most studied effect of herds is the so-called dilution effect. The key argument is that the risk of being preyed upon for any particular individual is smaller within a larger group, strictly because a predator has to decide which individual to attack. Although the dilution effect is influenced by so-called selfish herding, it is primarily a direct effect of group size instead of the position within a herd. Greater group sizes result in higher visibility and detection rates for predators, but this relation is not directly proportional and saturates at some point, while the risk of being attacked for an individual is directly proportional to group size. Thus, the net effect for an individual in a group concerning its predation risk is beneficial.
Whenever groups, such as shoals of fish, synchronize their movements, it becomes harder for predators to focus on particular individuals. However, animals that are weak and slower or on the periphery are preferred by predators, so that certain positions within the group are better than others (see selfish herd theory). For fit animals, being in a group with such vulnerable individuals may thus decrease the chance of being preyed upon even further.
Collective vigilance | Herd | Wikipedia | 506 | 969684 | https://en.wikipedia.org/wiki/Herd | Biology and health sciences | Ethology | Biology |
The effect of collective vigilance in social groups has been widely studied within the framework of optimal foraging theory and animal decision making. While animals under the risk of predation are feeding or resting, they have to stay vigilant and watch for predators. It could be shown in many studies (especially for birds) that with increase in group size individual animals are less attentive, while the overall vigilance suffers little (many eyes effect). This means food intake and other activities related to fitness are optimized in terms of time allocation when animals stay in groups.
However, some details about this concepts remain unclear. Being the first to detect predators and react accordingly can be advantageous, implying individuals may not fully be able to rely only on the group. Moreover, the competition for food can lead to the misuse of warning calls, as was observed for great tits: If food is scarce or monopolized by dominant birds, other birds (mainly subordinates) use antipredatory warning calls to induce an interruption of feeding and gain access to resources.
Another study concerning a flock of geese suggested that the benefits of lower vigilance concerned only those in central positions, due to the fact that the possibly more vulnerable individuals in the flock's periphery have a greater need to stay attentive. This implies that the decrease in overall vigilance arises simply because the geese on the edge of the flock comprise a smaller group when groups get large.
A special case of collective vigilance in groups is that of sentinels. Individuals take turn in keeping guard, while all others participate in other activities. Thus, the strength of social bonds and trust within these groups have to be much higher than in the former cases. | Herd | Wikipedia | 348 | 969684 | https://en.wikipedia.org/wiki/Herd | Biology and health sciences | Ethology | Biology |
Foraging
Hunting together enables group-living predators, such as wolves and wild dogs, to catch large prey, which they are unable to achieve when hunting alone. Working together significantly improves foraging efficiency, meaning the net energy gain of each individual is increased when animals are feeding collectively. As an example, a group of Spinner dolphins is able to corral fish into a smaller volume, which makes catching them easier, as there is less opportunity for the fish to escape. Furthermore, large groups are able to monopolize resources and defend them against solitary animals or smaller groups of the same or different species. It has been shown that larger groups of lions tend to be more successful in protecting prey from hyenas than smaller ones. Being able to communicate the location and type of food to other group members may increase the chance for each individual to find profitable food sources, a mechanism which is known to be used by both bees (via a Waggle dance) and several species of birds (using specific vocalisations to indicate food).
In terms of Optimal foraging theory, animals always try to maximize their net energy gain when feeding, because this is positively correlated to their fitness. If their energy requirement is fixed and additional energy is not increasing fitness, they will use as little time for foraging as possible (time minimizers). If on the other hand time allocated to foraging is fixed, an animal's gain in fitness is related to the quantity and quality of resources it feeds on (Energy maximizers).
Since foraging may be energetically costly (searching, hunting, handling, etc.) and may induce risk of predation, animals in groups may have an advantage, since their combined effort in locating and handling food will reduce time needed to forage sufficiently. Thus, animals in groups may have shorter searching and handling times as well as an increased chance of finding (or monopolizing) highly profitable food, which makes foraging in groups beneficial for time minimizers and energy maximizers alike.
The obvious disadvantage of foraging in groups is (scramble or direct) competition with other group members. In general, it is clear that the amount of resources available for each individual decreases with group size. If the resource availability is critical, competition within the group may get so intense, that animals no longer experience benefits from living in groups. However, only the relative importance of within- and between-group competition determines the optimal group size and ultimately the decision of each individual whether or not to stay in the group. | Herd | Wikipedia | 498 | 969684 | https://en.wikipedia.org/wiki/Herd | Biology and health sciences | Ethology | Biology |
Diseases and parasites
Since animals in groups stay near each other and interact frequently, infectious diseases and parasites spread much easier between them compared to solitary animals. Studies have shown a positive correlation between herd size and intensity of infections, but the extent to which this sometimes drastic reduction in fitness governs group size and structure is still unclear. However, some animals have found countermeasures such as propolis in beehives or grooming in social animals.
Energetic advantages
Staying together in groups often brings energetic advantages. Birds flying together in a flock use aerodynamic effects to reduce energetic costs, e.g. by positioning themselves in a V-shaped formation. A similar effect can be observed when fish swim together in fixed formations.
Another benefit of group living occurs when climate is harsh and cold: By staying close together animals experience better thermoregulation, because their overall surface to volume ratio is reduced. Consequently, maintaining adequate body temperatures becomes less energetically costly.
Antipredatory behaviour
The collective force of a group mobbing predators can reduce risk of predation significantly. Flocks of raven are able to actively defend themselves against eagles and baboons collectively mob lions, which is impossible for individuals alone. This behaviour may be based on reciprocal altruism, meaning animals are more likely to help each other if their conspecifics did so earlier.
Mating
Animals living in groups are more likely to find mates than those living in solitary and are also able to compare potential partners in order to optimize genetic quality for their offspring.
Domestic herds
Domestic animal herds are assembled by humans for practicality in raising them and controlling them. Their behaviour may be quite different from that of wild herds of the same or related species, since both their composition (in terms of the distribution of age and sex within the herd) and their history (in terms of when and how the individuals joined the herd) are likely to be very different.
Human parallels
The term herd is also applied metaphorically to human beings in social psychology, with the concept of herd behaviour. However both the term and concepts that underlie its use are controversial. | Herd | Wikipedia | 422 | 969684 | https://en.wikipedia.org/wiki/Herd | Biology and health sciences | Ethology | Biology |
The term has acquired a semi-technical usage in behavioral finance to describe the largest group of market investors or market speculators who tend to "move with the market", or "follow the general market trend". This is at least a plausible example of genuine herding, though according to some researchers it results from rational decisions through processes such as information cascade and rational expectations. Other researchers, however, ascribe it to non-rational process such as mimicry, fear and greed contagion. "Contrarians" or contrarian investors are those who deliberately choose to invest or speculate counter to the "herd". | Herd | Wikipedia | 127 | 969684 | https://en.wikipedia.org/wiki/Herd | Biology and health sciences | Ethology | Biology |
The common toad, European toad, or in Anglophone parts of Europe, simply the toad (Bufo bufo, from Latin bufo "toad"), is a toad found throughout most of Europe (with the exception of Ireland, Iceland, parts of Scandinavia, and some Mediterranean islands), in the western part of North Asia, and in a small portion of Northwest Africa. It is one of a group of closely related animals that are descended from a common ancestral line of toads and which form a species complex. The toad is an inconspicuous animal as it usually lies hidden during the day. It becomes active at dusk and spends the night hunting for the invertebrates on which it feeds. It moves with a slow, ungainly walk or short jumps, and has greyish-brown skin covered with wart-like lumps.
Although toads are usually solitary animals, in the breeding season, large numbers of toads converge on certain breeding ponds, where the males compete to mate with the females. Eggs are laid in gelatinous strings in the water and later hatch out into tadpoles. After several months of growth and development, these sprout limbs and undergo metamorphosis into tiny toads. The juveniles emerge from the water and remain largely terrestrial for the rest of their lives.
The common toad seems to be in decline in part of its range, but overall is listed as being of "least concern" in the IUCN Red List of Threatened Species. It is threatened by habitat loss, especially by drainage of its breeding sites, and some toads get killed on the roads as they make their annual migrations. It has long been associated in popular culture and literature with witchcraft.
Taxonomy
The common toad was first given the name Rana bufo by the Swedish biologist Carl Linnaeus in the 10th edition of Systema Naturae in 1758. In this work, he placed all the frogs and toads in the single genus Rana. It later became apparent that this genus should be divided, and in 1768, the Austrian naturalist Josephus Nicolaus Laurenti placed the common toad in the genus Bufo, naming it Bufo bufo. The toads in this genus are included in the family Bufonidae, the true toads. | Common toad | Wikipedia | 455 | 969943 | https://en.wikipedia.org/wiki/Common%20toad | Biology and health sciences | Frogs and toads | Animals |
Various subspecies of B. bufo have been recognized over the years. The Caucasian toad is found in the mountainous regions of the Caucasus and was at one time classified as B. b. verrucosissima. It has a larger genome and differs from B. bufo morphologically and is now accepted as Bufo verrucosissimus. The spiny toad was classified as B. b. spinosus. It is found in France, the Iberian Peninsula and the Maghreb and grows to a larger size and has a spinier skin than its more northern counterparts with which it intergrades. It is now accepted as Bufo spinosus. The Gredos toad, B. b. gredosicola, is restricted to the Sierra de Gredos, a mountain range in central Spain. It has exceptionally large paratoid glands and its colour tends to be blotched rather than uniform. It is now considered to be a synonym of Bufo spinosus.
B. bufo is part of a species complex, a group of closely related species which cannot be clearly demarcated. Several modern species are believed to form an ancient group of related taxa from preglacial times. These are the spiny toad (B. spinosus), the Caucasian toad (B. verrucosissimus) and the Japanese common toad (B. japonicus). The European common toad (Bufo bufo) seems to have arisen more recently. It is believed that the range of the ancestral form extended into Asia but that isolation between the eastern and western species complexes occurred as a result of the development of the Central Asian Deserts during the Middle Miocene. The exact taxonomic relationships between these species remains unclear. A serological investigation into toad populations in Turkey undertaken in 2001 examined the blood serum proteins of Bufo verrucosissimus and Bufo spinosus. It found that the differences between the two were not significant and that therefore the former should be synonymized with the latter. | Common toad | Wikipedia | 414 | 969943 | https://en.wikipedia.org/wiki/Common%20toad | Biology and health sciences | Frogs and toads | Animals |
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