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Blade connectors
A blade connector is a type of single wire, plug-and-socket connection device using a flat conductive blade (plug) that is inserted into a receptacle. Wires are typically attached to male or female blade connector terminals by either crimping or soldering. Insulated and uninsulated varieties are available. In some cases the blade is an integral manufactured part of a component (such as a switch or a speaker unit), and the reciprocal connector terminal is pushed onto the device's connector terminal.
Other connection methods
Alligator and Crocodile clips – conductive clamps used for temporary connections, e.g. jumper cables
Board to board connectors – e.g. card-edge connectors or FPGA mezzanine connectors
Twist-on wire connectors (e.g. wire nuts) – used in low-voltage power circuits for wires up to about 10 AWG
Wire wrapping – used in older circuit boards | Electrical connector | Wikipedia | 234 | 152654 | https://en.wikipedia.org/wiki/Electrical%20connector | Technology | Components | null |
Loop quantum gravity (LQG) is a theory of quantum gravity that incorporates matter of the Standard Model into the framework established for the intrinsic quantum gravity case. It is an attempt to develop a quantum theory of gravity based directly on Albert Einstein's geometric formulation rather than the treatment of gravity as a mysterious mechanism (force). As a theory, LQG postulates that the structure of space and time is composed of finite loops woven into an extremely fine fabric or network. These networks of loops are called spin networks. The evolution of a spin network, or spin foam, has a scale on the order of a Planck length, approximately 10−35 meters, and smaller scales are meaningless. Consequently, not just matter, but space itself, prefers an atomic structure.
The areas of research, which involve about 30 research groups worldwide, share the basic physical assumptions and the mathematical description of quantum space. Research has evolved in two directions: the more traditional canonical loop quantum gravity, and the newer covariant loop quantum gravity, called spin foam theory. The most well-developed theory that has been advanced as a direct result of loop quantum gravity is called loop quantum cosmology (LQC). LQC advances the study of the early universe, incorporating the concept of the Big Bang into the broader theory of the Big Bounce, which envisions the Big Bang as the beginning of a period of expansion, that follows a period of contraction, which has been described as the Big Crunch.
History
In 1986, Abhay Ashtekar reformulated Einstein's general relativity in a language closer to that of the rest of fundamental physics, specifically Yang–Mills theory. Shortly after, Ted Jacobson and Lee Smolin realized that the formal equation of quantum gravity, called the Wheeler–DeWitt equation, admitted solutions labelled by loops when rewritten in the new Ashtekar variables. Carlo Rovelli and Smolin defined a nonperturbative and background-independent quantum theory of gravity in terms of these loop solutions. Jorge Pullin and Jerzy Lewandowski understood that the intersections of the loops are essential for the consistency of the theory, and the theory should be formulated in terms of intersecting loops, or graphs. | Loop quantum gravity | Wikipedia | 448 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
In 1994, Rovelli and Smolin showed that the quantum operators of the theory associated to area and volume have a discrete spectrum. That is, geometry is quantized. This result defines an explicit basis of states of quantum geometry, which turned out to be labelled by Roger Penrose's spin networks, which are graphs labelled by spins.
The canonical version of the dynamics was established by Thomas Thiemann, who defined an anomaly-free Hamiltonian operator and showed the existence of a mathematically consistent background-independent theory. The covariant, or "spin foam", version of the dynamics was developed jointly over several decades by research groups in France, Canada, UK, Poland, and Germany. It was completed in 2008, leading to the definition of a family of transition amplitudes, which in the classical limit can be shown to be related to a family of truncations of general relativity. The finiteness of these amplitudes was proven in 2011. It requires the existence of a positive cosmological constant, which is consistent with observed acceleration in the expansion of the Universe.
Background independence
LQG is formally background independent, meaning the equations of LQG are not embedded in, or dependent on, space and time (except for its invariant topology). Instead, they are expected to give rise to space and time at distances which are 10 times the Planck length. The issue of background independence in LQG still has some unresolved subtleties. For example, some derivations require a fixed choice of the topology, while any consistent quantum theory of gravity should include topology change as a dynamical process.
Spacetime as a "container" over which physics takes place has no objective physical meaning and instead the gravitational interaction is represented as just one of the fields forming the world. This is known as the relationalist interpretation of spacetime. In LQG this aspect of general relativity is taken seriously and this symmetry is preserved by requiring that the physical states remain invariant under the generators of diffeomorphisms. The interpretation of this condition is well understood for purely spatial diffeomorphisms. However, the understanding of diffeomorphisms involving time (the Hamiltonian constraint) is more subtle because it is related to dynamics and the so-called "problem of time" in general relativity. A generally accepted calculational framework to account for this constraint has yet to be found. A plausible candidate for the quantum Hamiltonian constraint is the operator introduced by Thiemann. | Loop quantum gravity | Wikipedia | 506 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Constraints and their Poisson bracket algebra
Dirac observables
The constraints define a constraint surface in the original phase space. The gauge motions of the constraints apply to all phase space but have the feature that they leave the constraint surface where it is, and thus the orbit of a point in the hypersurface under gauge transformations will be an orbit entirely within it. Dirac observables are defined as phase space functions, , that Poisson commute with all the constraints when the constraint equations are imposed,
that is, they are quantities defined on the constraint surface that are invariant under the gauge transformations of the theory.
Then, solving only the constraint and determining the Dirac observables with respect to it leads us back to the Arnowitt–Deser–Misner (ADM) phase space with constraints . The dynamics of general relativity is generated by the constraints, it can be shown that six Einstein equations describing time evolution (really a gauge transformation) can be obtained by calculating the Poisson brackets of the three-metric and its conjugate momentum with a linear combination of the spatial diffeomorphism and Hamiltonian constraint. The vanishing of the constraints, giving the physical phase space, are the four other Einstein equations.
Quantization of the constraints – the equations of quantum general relativity
Pre-history and Ashtekar new variables
Many of the technical problems in canonical quantum gravity revolve around the constraints. Canonical general relativity was originally formulated in terms of metric variables, but there seemed to be insurmountable mathematical difficulties in promoting the constraints to quantum operators because of their highly non-linear dependence on the canonical variables. The equations were much simplified with the introduction of Ashtekar's new variables. Ashtekar variables describe canonical general relativity in terms of a new pair of canonical variables closer to those of gauge theories. The first step consists of using densitized triads (a triad is simply three orthogonal vector fields labeled by and the densitized triad is defined by ) to encode information about the spatial metric, | Loop quantum gravity | Wikipedia | 414 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
(where is the flat space metric, and the above equation expresses that , when written in terms of the basis , is locally flat). (Formulating general relativity with triads instead of metrics was not new.) The densitized triads are not unique, and in fact one can perform a local in space rotation with respect to the internal indices . The canonically conjugate variable is related to the extrinsic curvature by . But problems similar to using the metric formulation arise when one tries to quantize the theory. Ashtekar's new insight was to introduce a new configuration variable,
that behaves as a complex connection where is related to the so-called spin connection via . Here is called the chiral spin connection. It defines a covariant derivative . It turns out that is the conjugate momentum of , and together these form Ashtekar's new variables.
The expressions for the constraints in Ashtekar variables; Gauss's theorem, the spatial diffeomorphism constraint and the (densitized) Hamiltonian constraint then read:
respectively, where is the field strength tensor of the connection and where is referred to as the vector constraint. The above-mentioned local in space rotational invariance is the original of the gauge invariance here expressed by Gauss's theorem. Note that these constraints are polynomial in the fundamental variables, unlike the constraints in the metric formulation. This dramatic simplification seemed to open up the way to quantizing the constraints. (See the article Self-dual Palatini action for a derivation of Ashtekar's formalism).
With Ashtekar's new variables, given the configuration variable , it is natural to consider wavefunctions . This is the connection representation. It is analogous to ordinary quantum mechanics with configuration variable and wavefunctions . The configuration variable gets promoted to a quantum operator via:
(analogous to ) and the triads are (functional) derivatives,
(analogous to ). In passing over to the quantum theory the constraints become operators on a kinematic Hilbert space (the unconstrained Yang–Mills Hilbert space). Note that different ordering of the 's and 's when replacing the 's with derivatives give rise to different operators – the choice made is called the factor ordering and should be chosen via physical reasoning. Formally they read | Loop quantum gravity | Wikipedia | 485 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
There are still problems in properly defining all these equations and solving them. For example, the Hamiltonian constraint Ashtekar worked with was the densitized version instead of the original Hamiltonian, that is, he worked with . There were serious difficulties in promoting this quantity to a quantum operator. Moreover, although Ashtekar variables had the virtue of simplifying the Hamiltonian, they are complex. When one quantizes the theory, it is difficult to ensure that one recovers real general relativity as opposed to complex general relativity.
Quantum constraints as the equations of quantum general relativity
The classical result of the Poisson bracket of the smeared Gauss' law with the connections is
The quantum Gauss' law reads
If one smears the quantum Gauss' law and study its action on the quantum state one finds that the action of the constraint on the quantum state is equivalent to shifting the argument of by an infinitesimal (in the sense of the parameter small) gauge transformation,
and the last identity comes from the fact that the constraint annihilates the state. So the constraint, as a quantum operator, is imposing the same symmetry that its vanishing imposed classically: it is telling us that the functions have to be gauge invariant functions of the connection. The same idea is true for the other constraints.
Therefore, the two step process in the classical theory of solving the constraints (equivalent to solving the admissibility conditions for the initial data) and looking for the gauge orbits (solving the 'evolution' equations) is replaced by a one step process in the quantum theory, namely looking for solutions of the quantum equations . This is because it solves the constraint at the quantum level and it simultaneously looks for states that are gauge invariant because is the quantum generator of gauge transformations (gauge invariant functions are constant along the gauge orbits and thus characterize them). Recall that, at the classical level, solving the admissibility conditions and evolution equations was equivalent to solving all of Einstein's field equations, this underlines the central role of the quantum constraint equations in canonical quantum gravity.
Introduction of the loop representation
It was in particular the inability to have good control over the space of solutions to Gauss's law and spatial diffeomorphism constraints that led Rovelli and Smolin to consider the loop representation in gauge theories and quantum gravity. | Loop quantum gravity | Wikipedia | 472 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
LQG includes the concept of a holonomy. A holonomy is a measure of how much the initial and final values of a spinor or vector differ after parallel transport around a closed loop; it is denoted
.
Knowledge of the holonomies is equivalent to knowledge of the connection, up to gauge equivalence. Holonomies can also be associated with an edge; under a Gauss Law these transform as
For a closed loop and assuming , yields
or
The trace of an holonomy around a closed loop is written
and is called a Wilson loop. Thus Wilson loops are gauge invariant. The explicit form of the Holonomy is
where is the curve along which the holonomy is evaluated, and is a parameter along the curve, denotes path ordering meaning factors for smaller values of appear to the left, and are matrices that satisfy the algebra
The Pauli matrices satisfy the above relation. It turns out that there are infinitely many more examples of sets of matrices that satisfy these relations, where each set comprises matrices with , and where none of these can be thought to 'decompose' into two or more examples of lower dimension. They are called different irreducible representations of the algebra. The most fundamental representation being the Pauli matrices. The holonomy is labelled by a half integer according to the irreducible representation used.
The use of Wilson loops explicitly solves the Gauss gauge constraint. Loop representation is required to handle the spatial diffeomorphism constraint. With Wilson loops as a basis, any Gauss gauge invariant function expands as,
This is called the loop transform and is analogous to the momentum representation in quantum mechanics (see Position and momentum space). The QM representation has a basis of states labelled by a number and expands as
and works with the coefficients of the expansion
The inverse loop transform is defined by
This defines the loop representation. Given an operator in the connection representation,
one should define the corresponding operator on in the loop representation via,
where is defined by the usual inverse loop transform,
A transformation formula giving the action of the operator on in terms of the action of the operator on is then obtained by equating the R.H.S. of with the R.H.S. of with substituted into , namely
or | Loop quantum gravity | Wikipedia | 458 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
where means the operator but with the reverse factor ordering (remember from simple quantum mechanics where the product of operators is reversed under conjugation). The action of this operator on the Wilson loop is evaluated as a calculation in the connection representation and the result is rearranged purely as a manipulation in terms of loops (with regard to the action on the Wilson loop, the chosen transformed operator is the one with the opposite factor ordering compared to the one used for its action on wavefunctions ). This gives the physical meaning of the operator . For example, if corresponded to a spatial diffeomorphism, then this can be thought of as keeping the connection field of where it is while performing a spatial diffeomorphism on instead. Therefore, the meaning of is a spatial diffeomorphism on , the argument of .
In the loop representation, the spatial diffeomorphism constraint is solved by considering functions of loops that are invariant under spatial diffeomorphisms of the loop . That is, knot invariants are used. This opens up an unexpected connection between knot theory and quantum gravity.
Any collection of non-intersecting Wilson loops satisfy Ashtekar's quantum Hamiltonian constraint. Using a particular ordering of terms and replacing by a derivative, the action of the quantum Hamiltonian constraint on a Wilson loop is
When a derivative is taken it brings down the tangent vector, , of the loop, . So,
However, as is anti-symmetric in the indices and this vanishes (this assumes that is not discontinuous anywhere and so the tangent vector is unique).
With regard to loop representation, the wavefunctions vanish when the loop has discontinuities and are knot invariants. Such functions solve the Gauss law, the spatial diffeomorphism constraint and (formally) the Hamiltonian constraint. This yields an infinite set of exact (if only formal) solutions to all the equations of quantum general relativity! This generated a lot of interest in the approach and eventually led to LQG.
Geometric operators, the need for intersecting Wilson loops and spin network states
The easiest geometric quantity is the area. Let us choose coordinates so that the surface is characterized by . The area of small parallelogram of the surface is the product of length of each side times where is the angle between the sides. Say one edge is given by the vector and the other by then, | Loop quantum gravity | Wikipedia | 488 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
In the space spanned by and there is an infinitesimal parallelogram described by and . Using (where the indices and run from 1 to 2), yields the area of the surface given by
where and is the determinant of the metric induced on . The latter can be rewritten where the indices go from 1 to 2. This can be further rewritten as
The standard formula for an inverse matrix is
There is a similarity between this and the expression for . But in Ashtekar variables, . Therefore,
According to the rules of canonical quantization the triads should be promoted to quantum operators,
The area can be promoted to a well defined quantum operator despite the fact that it contains a product of two functional derivatives and a square-root. Putting (-th representation),
This quantity is important in the final formula for the area spectrum. The result is
where the sum is over all edges of the Wilson loop that pierce the surface .
The formula for the volume of a region is given by
The quantization of the volume proceeds the same way as with the area. Each time the derivative is taken, it brings down the tangent vector , and when the volume operator acts on non-intersecting Wilson loops the result vanishes. Quantum states with non-zero volume must therefore involve intersections. Given that the anti-symmetric summation is taken over in the formula for the volume, it needs intersections with at least three non-coplanar lines. At least four-valent vertices are needed for the volume operator to be non-vanishing.
Assuming the real representation where the gauge group is , Wilson loops are an over complete basis as there are identities relating different Wilson loops. These occur because Wilson loops are based on matrices (the holonomy) and these matrices satisfy identities. Given any two matrices and ,
This implies that given two loops and that intersect, | Loop quantum gravity | Wikipedia | 375 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
where by we mean the loop traversed in the opposite direction and means the loop obtained by going around the loop and then along . See figure below. Given that the matrices are unitary one has that . Also given the cyclic property of the matrix traces (i.e. ) one has that . These identities can be combined with each other into further identities of increasing complexity adding more loops. These identities are the so-called Mandelstam identities. Spin networks certain are linear combinations of intersecting Wilson loops designed to address the over-completeness introduced by the Mandelstam identities (for trivalent intersections they eliminate the over-completeness entirely) and actually constitute a basis for all gauge invariant functions.
As mentioned above the holonomy tells one how to propagate test spin half particles. A spin network state assigns an amplitude to a set of spin half particles tracing out a path in space, merging and splitting. These are described by spin networks : the edges are labelled by spins together with 'intertwiners' at the vertices which are prescription for how to sum over different ways the spins are rerouted. The sum over rerouting are chosen as such to make the form of the intertwiner invariant under Gauss gauge transformations.
Hamiltonian constraint of LQG
In the long history of canonical quantum gravity formulating the Hamiltonian constraint as a quantum operator (Wheeler–DeWitt equation) in a mathematically rigorous manner has been a formidable problem. It was in the loop representation that a mathematically well defined Hamiltonian constraint was finally formulated in 1996. We leave more details of its construction to the article Hamiltonian constraint of LQG. This together with the quantum versions of the Gauss law and spatial diffeomorphism constrains written in the loop representation are the central equations of LQG (modern canonical quantum General relativity).
Finding the states that are annihilated by these constraints (the physical states), and finding the corresponding physical inner product, and observables is the main goal of the technical side of LQG. | Loop quantum gravity | Wikipedia | 420 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
An important aspect of the Hamiltonian operator is that it only acts at vertices (a consequence of this is that Thiemann's Hamiltonian operator, like Ashtekar's operator, annihilates non-intersecting loops except now it is not just formal and has rigorous mathematical meaning). More precisely, its action is non-zero on at least vertices of valence three and greater and results in a linear combination of new spin networks where the original graph has been modified by the addition of lines at each vertex together and a change in the labels of the adjacent links of the vertex.
Chiral fermions and the fermion doubling problem
A significant challenge in theoretical physics lies in unifying LQG, a theory of quantum spacetime, with the Standard Model of particle physics, which describes fundamental forces and particles. A major obstacle in this endeavor is the fermion doubling problem, which arises when incorporating chiral fermions into the LQG framework.
Chiral fermions, such as electrons and quarks, are fundamental particles characterized by their "handedness" or chirality. This property dictates that a particle and its mirror image behave differently under weak interactions. This asymmetry is fundamental to the Standard Model's success in explaining numerous physical phenomena.
However, attempts to integrate chiral fermions into LQG often result in the appearance of spurious, mirror-image particles. Instead of a single left-handed fermion, for instance, the theory predicts the existence of both a left-handed and a right-handed version. This "doubling" contradicts the observed chirality of the Standard Model and disrupts its predictive power.
The fermion doubling problem poses a significant hurdle in constructing a consistent theory of quantum gravity. The Standard Model's accuracy in describing the universe at the smallest scales relies heavily on the unique properties of chiral fermions. Without a solution to this problem, incorporating matter and its interactions into a unified framework of quantum gravity remains a significant challenge.
Therefore, resolving the fermion doubling problem is crucial for advancing our understanding of the universe at its most fundamental level and developing a complete theory that unites gravity with the quantum world.
Spin foams | Loop quantum gravity | Wikipedia | 459 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
In loop quantum gravity (LQG), a spin network represents a "quantum state" of the gravitational field on a 3-dimensional hypersurface. The set of all possible spin networks (or, more accurately, "s-knots" – that is, equivalence classes of spin networks under diffeomorphisms) is countable; it constitutes a basis of LQG Hilbert space.
In physics, a spin foam is a topological structure made out of two-dimensional faces that represents one of the configurations that must be summed to obtain a Feynman's path integral (functional integration) description of quantum gravity. It is closely related to loop quantum gravity.
Spin foam derived from the Hamiltonian constraint operator
On this section see and references therein. The Hamiltonian constraint generates 'time' evolution. Solving the Hamiltonian constraint should tell us how quantum states evolve in 'time' from an initial spin network state to a final spin network state. One approach to solving the Hamiltonian constraint starts with what is called the Dirac delta function. The summation of which over different sequences of actions can be visualized as a summation over different histories of 'interaction vertices' in the 'time' evolution sending the initial spin network to the final spin network. Each time a Hamiltonian operator acts it does so by adding a new edge at the vertex.
This then naturally gives rise to the two-complex (a combinatorial set of faces that join along edges, which in turn join on vertices) underlying the spin foam description; we evolve forward an initial spin network sweeping out a surface, the action of the Hamiltonian constraint operator is to produce a new planar surface starting at the vertex. We are able to use the action of the Hamiltonian constraint on the vertex of a spin network state to associate an amplitude to each "interaction" (in analogy to Feynman diagrams). See figure below. This opens a way of trying to directly link canonical LQG to a path integral description. Just as a spin networks describe quantum space, each configuration contributing to these path integrals, or sums over history, describe 'quantum spacetime'. Because of their resemblance to soap foams and the way they are labeled John Baez gave these 'quantum spacetimes' the name 'spin foams'. | Loop quantum gravity | Wikipedia | 470 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
There are however severe difficulties with this particular approach, for example the Hamiltonian operator is not self-adjoint, in fact it is not even a normal operator (i.e. the operator does not commute with its adjoint) and so the spectral theorem cannot be used to define the exponential in general. The most serious problem is that the 's are not mutually commuting, it can then be shown the formal quantity cannot even define a (generalized) projector. The master constraint (see below) does not suffer from these problems and as such offers a way of connecting the canonical theory to the path integral formulation.
Spin foams from BF theory
It turns out there are alternative routes to formulating the path integral, however their connection to the Hamiltonian formalism is less clear. One way is to start with the BF theory. This is a simpler theory than general relativity, it has no local degrees of freedom and as such depends only on topological aspects of the fields. BF theory is what is known as a topological field theory. Surprisingly, it turns out that general relativity can be obtained from BF theory by imposing a constraint, BF theory involves a field and if one chooses the field to be the (anti-symmetric) product of two tetrads
(tetrads are like triads but in four spacetime dimensions), one recovers general relativity. The condition that the field be given by the product of two tetrads is called the simplicity constraint. The spin foam dynamics of the topological field theory is well understood. Given the spin foam 'interaction' amplitudes for this simple theory, one then tries to implement the simplicity conditions to obtain a path integral for general relativity. The non-trivial task of constructing a spin foam model is then reduced to the question of how this simplicity constraint should be imposed in the quantum theory. The first attempt at this was the famous Barrett–Crane model. However this model was shown to be problematic, for example there did not seem to be enough degrees of freedom to ensure the correct classical limit. It has been argued that the simplicity constraint was imposed too strongly at the quantum level and should only be imposed in the sense of expectation values just as with the Lorenz gauge condition in the Gupta–Bleuler formalism of quantum electrodynamics. New models have now been put forward, sometimes motivated by imposing the simplicity conditions in a weaker sense. | Loop quantum gravity | Wikipedia | 486 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Another difficulty here is that spin foams are defined on a discretization of spacetime. While this presents no problems for a topological field theory as it has no local degrees of freedom, it presents problems for GR. This is known as the problem triangularization dependence.
Modern formulation of spin foams
Just as imposing the classical simplicity constraint recovers general relativity from BF theory, it is expected that an appropriate quantum simplicity constraint will recover quantum gravity from quantum BF theory.
Progress has been made with regard to this issue by Engle, Pereira, and Rovelli, Freidel and Krasnov and Livine and Speziale in defining spin foam interaction amplitudes with better behaviour.
An attempt to make contact between EPRL-FK spin foam and the canonical formulation of LQG has been made.
Spin foam derived from the master constraint operator
See below.
The semiclassical limit and loop quantum gravity
The Classical limit is the ability of a physical theory to approximate classical mechanics. It is used with physical theories that predict non-classical behavior. Any candidate theory of quantum gravity must be able to reproduce Einstein's theory of general relativity as a classical limit of a quantum theory. This is not guaranteed because of a feature of quantum field theories which is that they have different sectors, these are analogous to the different phases that come about in the thermodynamical limit of statistical systems. Just as different phases are physically different, so are different sectors of a quantum field theory. It may turn out that LQG belongs to an unphysical sector – one in which one does not recover general relativity in the semiclassical limit or there might not be any physical sector.
Moreover, the physical Hilbert space must contain enough semiclassical states to guarantee that the quantum theory obtained can return to the classical theory when avoiding quantum anomalies; otherwise there will be restrictions on the physical Hilbert space that have no counterpart in the classical theory, implying that the quantum theory has fewer degrees of freedom than the classical theory. | Loop quantum gravity | Wikipedia | 405 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Theorems establishing the uniqueness of the loop representation as defined by Ashtekar et al. (i.e. a certain concrete realization of a Hilbert space and associated operators reproducing the correct loop algebra) have been given by two groups (Lewandowski, Okołów, Sahlmann and Thiemann; and Christian Fleischhack). Before this result was established it was not known whether there could be other examples of Hilbert spaces with operators invoking the same loop algebra – other realizations not equivalent to the one that had been used. These uniqueness theorems imply no others exist, so if LQG does not have the correct semiclassical limit then the theorems would mean the end of the loop representation of quantum gravity. | Loop quantum gravity | Wikipedia | 157 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Difficulties and progress checking the semiclassical limit
There are a number of difficulties in trying to establish LQG gives Einstein's theory of general relativity in the semiclassical limit:
There is no operator corresponding to infinitesimal spatial diffeomorphisms (it is not surprising that the theory has no generator of infinitesimal spatial 'translations' as it predicts spatial geometry has a discrete nature, compare to the situation in condensed matter). Instead it must be approximated by finite spatial diffeomorphisms and so the Poisson bracket structure of the classical theory is not exactly reproduced. This problem can be circumvented with the introduction of the so-called master constraint (see below).
There is the problem of reconciling the discrete combinatorial nature of the quantum states with the continuous nature of the fields of the classical theory.
There are serious difficulties arising from the structure of the Poisson brackets involving the spatial diffeomorphism and Hamiltonian constraints. In particular, the algebra of (smeared) Hamiltonian constraints does not close: It is proportional to a sum over infinitesimal spatial diffeomorphisms (which, as noted above, does not exist in the quantum theory) where the coefficients of proportionality are not constants but have non-trivial phase space dependence – as such it does not form a Lie algebra. However, the situation is improved by the introduction of the master constraint.
The semiclassical machinery developed so far is only appropriate to non-graph-changing operators, however, Thiemann's Hamiltonian constraint is a graph-changing operator – the new graph it generates has degrees of freedom upon which the coherent state does not depend and so their quantum fluctuations are not suppressed. There is also the restriction, so far, that these coherent states are only defined at the Kinematic level, and now one has to lift them to the level of and . It can be shown that Thiemann's Hamiltonian constraint is required to be graph-changing in order to resolve problem 3 in some sense. The master constraint algebra however is trivial and so the requirement that it be graph-changing can be lifted and indeed non-graph-changing master constraint operators have been defined. As far as is currently known, this problem is still out of reach. | Loop quantum gravity | Wikipedia | 472 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Formulating observables for classical general relativity is a formidable problem because of its non-linear nature and spacetime diffeomorphism invariance. A systematic approximation scheme to calculate observables has been recently developed. | Loop quantum gravity | Wikipedia | 48 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Difficulties in trying to examine the semiclassical limit of the theory should not be confused with it having the wrong semiclassical limit.
Concerning issue number 2 above, consider so-called weave states. Ordinary measurements of geometric quantities are macroscopic, and Planckian discreteness is smoothed out. The fabric of a T-shirt is analogous: at a distance it is a smooth curved two-dimensional surface, but on closer inspection we see that it is actually composed of thousands of one-dimensional linked threads. The image of space given in LQG is similar. Consider a large spin network formed by a large number of nodes and links, each of Planck scale. Probed at a macroscopic scale, it appears as a three-dimensional continuous metric geometry.
To make contact with low energy physics it is mandatory to develop approximation schemes both for the physical inner product and for Dirac observables; the spin foam models that have been intensively studied can be viewed as avenues toward approximation schemes for said physical inner product.
Markopoulou, et al. adopted the idea of noiseless subsystems in an attempt to solve the problem of the low energy limit in background independent quantum gravity theories. The idea has led to the possibility of matter of the standard model being identified with emergent degrees of freedom from some versions of LQG (see section below: LQG and related research programs).
As Wightman emphasized in the 1950s, in Minkowski QFTs the point functions
completely determine the theory. In particular, one can calculate the scattering amplitudes from these quantities. As explained below in the section on the Background independent scattering amplitudes, in the background-independent context, the point functions refer to a state and in gravity that state can naturally encode information about a specific geometry which can then appear in the expressions of these quantities. To leading order, LQG calculations have been shown to agree in an appropriate sense with the point functions calculated in the effective low energy quantum general relativity.
Improved dynamics and the master constraint | Loop quantum gravity | Wikipedia | 408 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
The master constraint
Thiemann's Master Constraint Programme for Loop Quantum Gravity (LQG) was proposed as a classically equivalent way to impose the infinite number of Hamiltonian constraint equations in terms of a single master constraint , which involves the square of the constraints in question. An initial objection to the use of the master constraint was that on first sight it did not seem to encode information about the observables; because the Master constraint is quadratic in the constraint, when one computes its Poisson bracket with any quantity, the result is proportional to the constraint, therefore it vanishes when the constraints are imposed and as such does not select out particular phase space functions. However, it was realized that the condition
is where is at least a twice differentiable function on phase space is equivalent to being a weak Dirac observable with respect to the constraints in question. So the master constraint does capture information about the observables. Because of its significance this is known as the master equation.
That the master constraint Poisson algebra is an honest Lie algebra opens the possibility of using a method, known as group averaging, in order to construct solutions of the infinite number of Hamiltonian constraints, a physical inner product thereon and Dirac observables via what is known as refined algebraic quantization, or RAQ.
The quantum master constraint
Define the quantum master constraint (regularisation issues aside) as
Obviously,
for all implies . Conversely, if then
implies
.
First compute the matrix elements of the would-be operator , that is, the quadratic form . is a graph changing, diffeomorphism invariant quadratic form that cannot exist on the kinematic Hilbert space , and must be defined on . Since the master constraint operator is densely defined on , then is a positive and symmetric operator in . Therefore, the quadratic form associated with is closable. The closure of is the quadratic form of a unique self-adjoint operator , called the Friedrichs extension of . We relabel as for simplicity.
Note that the presence of an inner product, viz Eq 4, means there are no superfluous solutions i.e. there are no such that
but for which .
It is also possible to construct a quadratic form for what is called the extended master constraint (discussed below) on which also involves the weighted integral of the square of the spatial diffeomorphism constraint (this is possible because is not graph changing). | Loop quantum gravity | Wikipedia | 502 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
The spectrum of the master constraint may not contain zero due to normal or factor ordering effects which are finite but similar in nature to the infinite vacuum energies of background-dependent quantum field theories. In this case it turns out to be physically correct to replace with provided that the "normal ordering constant" vanishes in the classical limit, that is,
so that is a valid quantisation of .
Testing the master constraint
The constraints in their primitive form are rather singular, this was the reason for integrating them over test functions to obtain smeared constraints. However, it would appear that the equation for the master constraint, given above, is even more singular involving the product of two primitive constraints (although integrated over space). Squaring the constraint is dangerous as it could lead to worsened ultraviolet behaviour of the corresponding operator and hence the master constraint programme must be approached with care.
In doing so the master constraint programme has been satisfactorily tested in a number of model systems with non-trivial constraint algebras, free and interacting field theories. The master constraint for LQG was established as a genuine positive self-adjoint operator and the physical Hilbert space of LQG was shown to be non-empty, a consistency test LQG must pass to be a viable theory of quantum general relativity.
Applications of the master constraint
The master constraint has been employed in attempts to approximate the physical inner product and define more rigorous path integrals.
The Consistent Discretizations approach to LQG, is an application of the master constraint program to construct the physical Hilbert space of the canonical theory.
Spin foam from the master constraint
The master constraint is easily generalized to incorporate the other constraints. It is then referred to as the extended master constraint, denoted . We can define the extended master constraint which imposes both the Hamiltonian constraint and spatial diffeomorphism constraint as a single operator,
.
Setting this single constraint to zero is equivalent to and for all in . This constraint implements the spatial diffeomorphism and Hamiltonian constraint at the same time on the Kinematic Hilbert space. The physical inner product is then defined as
(as ). A spin foam representation of this expression is obtained by splitting the -parameter in discrete steps and writing | Loop quantum gravity | Wikipedia | 449 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
The spin foam description then follows from the application of on a spin network resulting in a linear combination of new spin networks whose graph and labels have been modified. Obviously an approximation is made by truncating the value of to some finite integer. An advantage of the extended master constraint is that we are working at the kinematic level and so far it is only here we have access semiclassical coherent states. Moreover, one can find none graph changing versions of this master constraint operator, which are the only type of operators appropriate for these coherent states.
Algebraic quantum gravity (AQG)
The master constraint programme has evolved into a fully combinatorial treatment of gravity known as algebraic quantum gravity (AQG). The non-graph changing master constraint operator is adapted in the framework of algebraic quantum gravity. While AQG is inspired by LQG, it differs drastically from it because in AQG there is fundamentally no topology or differential structure – it is background independent in a more generalized sense and could possibly have something to say about topology change. In this new formulation of quantum gravity AQG semiclassical states always control the fluctuations of all present degrees of freedom. This makes the AQG semiclassical analysis superior over that of LQG, and progress has been made in establishing it has the correct semiclassical limit and providing contact with familiar low energy physics.
Physical applications of LQG
Black hole entropy
Black hole thermodynamics is the area of study that seeks to reconcile the laws of thermodynamics with the existence of black hole event horizons. The no hair conjecture of general relativity states that a black hole is characterized only by its mass, its charge, and its angular momentum; hence, it has no entropy. It appears, then, that one can violate the second law of thermodynamics by dropping an object with nonzero entropy into a black hole. Work by Stephen Hawking and Jacob Bekenstein showed that the second law of thermodynamics can be preserved by assigning to each black hole a black-hole entropy
where is the area of the hole's event horizon, is the Boltzmann constant, and is the Planck length. The fact that the black hole entropy is also the maximal entropy that can be obtained by the Bekenstein bound (wherein the Bekenstein bound becomes an equality) was the main observation that led to the holographic principle. | Loop quantum gravity | Wikipedia | 494 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
An oversight in the application of the no-hair theorem is the assumption that the relevant degrees of freedom accounting for the entropy of the black hole must be classical in nature; what if they were purely quantum mechanical instead and had non-zero entropy? This is what is realized in the LQG derivation of black hole entropy, and can be seen as a consequence of its background-independence – the classical black hole spacetime comes about from the semiclassical limit of the quantum state of the gravitational field, but there are many quantum states that have the same semiclassical limit. Specifically, in LQG it is possible to associate a quantum geometrical interpretation to the microstates: These are the quantum geometries of the horizon which are consistent with the area, , of the black hole and the topology of the horizon (i.e. spherical). LQG offers a geometric explanation of the finiteness of the entropy and of the proportionality of the area of the horizon. These calculations have been generalized to rotating black holes.
It is possible to derive, from the covariant formulation of full quantum theory (Spinfoam) the correct relation between energy and area (1st law), the Unruh temperature and the distribution that yields Hawking entropy. The calculation makes use of the notion of dynamical horizon and is done for non-extremal black holes.
A recent success of the theory in this direction is the computation of the entropy of all non singular black holes directly from theory and independent of Immirzi parameter. The result is the expected formula , where is the entropy and the area of the black hole, derived by Bekenstein and Hawking on heuristic grounds. This is the only known derivation of this formula from a fundamental theory, for the case of generic non singular black holes. Older attempts at this calculation had difficulties. The problem was that although Loop quantum gravity predicted that the entropy of a black hole is proportional to the area of the event horizon, the result depended on a crucial free parameter in the theory, the above-mentioned Immirzi parameter. However, there is no known computation of the Immirzi parameter, so it was fixed by demanding agreement with Bekenstein and Hawking's calculation of the black hole entropy.
Hawking radiation in loop quantum gravity | Loop quantum gravity | Wikipedia | 469 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
A detailed study of the quantum geometry of a black hole horizon has been made using loop quantum gravity. Loop-quantization does not reproduce the result for black hole entropy originally discovered by Bekenstein and Hawking, unless one chooses the value of the Immirzi parameter to cancel out another constant that arises in the derivation. However, it led to the computation of higher-order corrections to the entropy and radiation of black holes.
Based on the fluctuations of the horizon area, a quantum black hole exhibits deviations from the Hawking spectrum that would be observable were X-rays from Hawking radiation of evaporating primordial black holes to be observed. The quantum effects are centered at a set of discrete and unblended frequencies highly pronounced on top of Hawking radiation spectrum.
Planck star
In 2014 Carlo Rovelli and Francesca Vidotto proposed that there is a Planck star inside every black hole. Based on LQG, the theory states that as stars are collapsing into black holes, the energy density reaches the Planck energy density, causing a repulsive force that creates a star. Furthermore, the existence of such a star would resolve the black hole firewall and black hole information paradox.
Loop quantum cosmology
The popular and technical literature makes extensive references to the LQG-related topic of loop quantum cosmology. LQC was mainly developed by Martin Bojowald. It was popularized in Scientific American for predicting a Big Bounce prior to the Big Bang. Loop quantum cosmology (LQC) is a symmetry-reduced model of classical general relativity quantized using methods that mimic those of loop quantum gravity (LQG) that predicts a "quantum bridge" between contracting and expanding cosmological branches.
Achievements of LQC have been the resolution of the big bang singularity, the prediction of a Big Bounce, and a natural mechanism for inflation.
LQC models share features of LQG and so is a useful toy model. However, the results obtained are subject to the usual restriction that a truncated classical theory, then quantized, might not display the true behaviour of the full theory due to artificial suppression of degrees of freedom that might have large quantum fluctuations in the full theory. It has been argued that singularity avoidance in LQC are by mechanisms only available in these restrictive models and that singularity avoidance in the full theory can still be obtained but by a more subtle feature of LQG. | Loop quantum gravity | Wikipedia | 496 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Loop quantum gravity phenomenology
Quantum gravity effects are difficult to measure because the Planck length is so small. However recently physicists, such as Jack Palmer, have started to consider the possibility of measuring quantum gravity effects mostly from astrophysical observations and gravitational wave detectors. The energy of those fluctuations at scales this small cause space-perturbations which are visible at higher scales.
Background-independent scattering amplitudes
Loop quantum gravity is formulated in a background-independent language. No spacetime is assumed a priori, but rather it is built up by the states of theory themselves – however scattering amplitudes are derived from -point functions (Correlation function) and these, formulated in conventional quantum field theory, are functions of points of a background spacetime. The relation between the background-independent formalism and the conventional formalism of quantum field theory on a given spacetime is not obvious, and it is not obvious how to recover low-energy quantities from the full background-independent theory. One would like to derive the -point functions of the theory from the background-independent formalism, in order to compare them with the standard perturbative expansion of quantum general relativity and therefore check that loop quantum gravity yields the correct low-energy limit.
A strategy for addressing this problem has been suggested; by studying the boundary amplitude, namely a path integral over a finite spacetime region, seen as a function of the boundary value of the field. In conventional quantum field theory, this boundary amplitude is well–defined and codes the physical information of the theory; it does so in quantum gravity as well, but in a fully background–independent manner. A generally covariant definition of -point functions can then be based on the idea that the distance between physical points – arguments of the -point function is determined by the state of the gravitational field on the boundary of the spacetime region considered.
Progress has been made in calculating background-independent scattering amplitudes this way with the use of spin foams. This is a way to extract physical information from the theory. Claims to have reproduced the correct behaviour for graviton scattering amplitudes and to have recovered classical gravity have been made. "We have calculated Newton's law starting from a world with no space and no time." – Carlo Rovelli.
Gravitons, string theory, supersymmetry, extra dimensions in LQG | Loop quantum gravity | Wikipedia | 481 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Some quantum theories of gravity posit a spin-2 quantum field that is quantized, giving rise to gravitons. In string theory, one generally starts with quantized excitations on top of a classically fixed background. This theory is thus described as background dependent. Particles like photons as well as changes in the spacetime geometry (gravitons) are both described as excitations on the string worldsheet. The background dependence of string theory can have physical consequences, such as determining the number of quark generations. In contrast, loop quantum gravity, like general relativity, is manifestly background independent, eliminating the background required in string theory. Loop quantum gravity, like string theory, also aims to overcome the nonrenormalizable divergences of quantum field theories.
LQG does not introduce a background and excitations living on such a background, so LQG does not use gravitons as building blocks. Instead one expects that one may recover a kind of semiclassical limit or weak field limit where something like "gravitons" will show up again. In contrast, gravitons play a key role in string theory where they are among the first (massless) level of excitations of a superstring.
LQG differs from string theory in that it is formulated in 3 and 4 dimensions and without supersymmetry or Kaluza–Klein extra dimensions, while the latter requires both to be true. There is no experimental evidence to date that confirms string theory's predictions of supersymmetry and Kaluza–Klein extra dimensions. In a 2003 paper "A Dialog on Quantum Gravity", Carlo Rovelli regards the fact LQG is formulated in 4 dimensions and without supersymmetry as a strength of the theory as it represents the most parsimonious explanation, consistent with current experimental results, over its rival string/M-theory. Proponents of string theory will often point to the fact that, among other things, it demonstrably reproduces the established theories of general relativity and quantum field theory in the appropriate limits, which loop quantum gravity has struggled to do. In that sense string theory's connection to established physics may be considered more reliable and less speculative, at the mathematical level. Loop quantum gravity has nothing to say about the matter (fermions) in the universe. | Loop quantum gravity | Wikipedia | 488 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Since LQG has been formulated in 4 dimensions (with and without supersymmetry), and M-theory requires supersymmetry and 11 dimensions, a direct comparison between the two has not been possible. It is possible to extend mainstream LQG formalism to higher-dimensional supergravity, general relativity with supersymmetry and Kaluza–Klein extra dimensions should experimental evidence establish their existence. It would therefore be desirable to have higher-dimensional Supergravity loop quantizations at one's disposal in order to compare these approaches. A series of papers have been published attempting this. Most recently, Thiemann (and alumni) have made progress toward calculating black hole entropy for supergravity in higher dimensions. It will be useful to compare these results to the corresponding super string calculations.
LQG and related research programs
Several research groups have attempted to combine LQG with other research programs: Johannes Aastrup, Jesper M. Grimstrup et al. research combines noncommutative geometry with canonical quantum gravity and Ashtekar variables, Laurent Freidel, Simone Speziale, et al., spinors and twistor theory with loop quantum gravity, and Lee Smolin et al. with Verlinde entropic gravity and loop gravity. Stephon Alexander, Antonino Marciano and Lee Smolin have attempted to explain the origins of weak force chirality in terms of Ashketar's variables, which describe gravity as chiral, and LQG with Yang–Mills theory fields in four dimensions. Sundance Bilson-Thompson, Hackett et al., has attempted to introduce the standard model via LQGs degrees of freedom as an emergent property (by employing the idea of noiseless subsystems, a notion introduced in a more general situation for constrained systems by Fotini Markopoulou-Kalamara et al.) | Loop quantum gravity | Wikipedia | 387 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Furthermore, LQG has drawn philosophical comparisons with causal dynamical triangulation and asymptotically safe gravity, and the spinfoam with group field theory and AdS/CFT correspondence. Smolin and Wen have suggested combining LQG with string-net liquid, tensors, and Smolin and Fotini Markopoulou-Kalamara quantum graphity. There is the consistent discretizations approach. Also, Pullin and Gambini provide a framework to connect the path integral and canonical approaches to quantum gravity. They may help reconcile the spin foam and canonical loop representation approaches. Recent research by Chris Duston and Matilde Marcolli introduces topology change via topspin networks.
Problems and comparisons with alternative approaches
Some of the major unsolved problems in physics are theoretical, meaning that existing theories seem incapable of explaining a certain observed phenomenon or experimental result. The others are experimental, meaning that there is a difficulty in creating an experiment to test a proposed theory or investigate a phenomenon in greater detail.
Many of these problems apply to LQG, including:
Can quantum mechanics and general relativity be realized as a fully consistent theory (perhaps as a quantum field theory)?
Is spacetime fundamentally continuous or discrete?
Would a consistent theory involve a force mediated by a hypothetical graviton, or be a product of a discrete structure of spacetime itself (as in loop quantum gravity)?
Are there deviations from the predictions of general relativity at very small or very large scales or in other extreme circumstances that flow from a quantum gravity theory?
The theory of LQG is one possible solution to the problem of quantum gravity, as is string theory. There are substantial differences however. For example, string theory also addresses unification, the understanding of all known forces and particles as manifestations of a single entity, by postulating extra dimensions and so-far unobserved additional particles and symmetries. Contrary to this, LQG is based only on quantum theory and general relativity and its scope is limited to understanding the quantum aspects of the gravitational interaction. On the other hand, the consequences of LQG are radical, because they fundamentally change the nature of space and time and provide a tentative but detailed physical and mathematical picture of quantum spacetime. | Loop quantum gravity | Wikipedia | 454 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
Presently, no semiclassical limit recovering general relativity has been shown to exist. This means it remains unproven that LQG's description of spacetime at the Planck scale has the right continuum limit (described by general relativity with possible quantum corrections). Specifically, the dynamics of the theory are encoded in the Hamiltonian constraint, but there is no candidate Hamiltonian. Other technical problems include finding off-shell closure of the constraint algebra and physical inner product vector space, coupling to matter fields of quantum field theory, fate of the renormalization of the graviton in perturbation theory that lead to ultraviolet divergence beyond 2-loops (see one-loop Feynman diagram in Feynman diagram).
While there has been a proposal relating to observation of naked singularities, and doubly special relativity as a part of a program called loop quantum cosmology, there is no experimental observation for which loop quantum gravity makes a prediction not made by the Standard Model or general relativity (a problem that plagues all current theories of quantum gravity). Because of the above-mentioned lack of a semiclassical limit, LQG has not yet even reproduced the predictions made by general relativity.
An alternative criticism is that general relativity may be an effective field theory, and therefore quantization ignores the fundamental degrees of freedom.
ESA's INTEGRAL satellite measured polarization of photons of different wavelengths and was able to place a limit in the granularity of space that is less than 10−48m or 13 orders of magnitude below the Planck scale. | Loop quantum gravity | Wikipedia | 317 | 152664 | https://en.wikipedia.org/wiki/Loop%20quantum%20gravity | Physical sciences | Quantum mechanics | Physics |
The Z3 was a German electromechanical computer designed by Konrad Zuse in 1938, and completed in 1941. It was the world's first working programmable, fully automatic digital computer. The Z3 was built with 2,600 relays, implementing a 22-bit word length that operated at a clock frequency of about 5–10 Hz. Program code was stored on punched film. Initial values were entered manually.
The Z3 was completed in Berlin in 1941. It was not considered vital, so it was never put into everyday operation. Based on the work of the German aerodynamics engineer Hans Georg Küssner (known for the Küssner effect), a "Program to Compute a Complex Matrix" was written and used to solve wing flutter problems. Zuse asked the German government for funding to replace the relays with fully electronic switches, but funding was denied during World War II since such development was deemed "not war-important".
The original Z3 was destroyed on 21 December 1943 during an Allied bombardment of Berlin. That Z3 was originally called V3 (Versuchsmodell 3 or Experimental Model 3) but was renamed so that it would not be confused with Germany's V-weapons. A fully functioning replica was built in 1961 by Zuse's company, Zuse KG, which is now on permanent display at Deutsches Museum in Munich.
The Z3 was demonstrated in 1998 to be, in principle, Turing-complete. However, because it lacked conditional branching, the Z3 only meets this definition by speculatively computing all possible outcomes of a calculation.
Thanks to this machine and its predecessors, Konrad Zuse has often been suggested as the inventor of the computer.
Design and development | Z3 (computer) | Wikipedia | 348 | 152671 | https://en.wikipedia.org/wiki/Z3%20%28computer%29 | Technology | Early computers | null |
Zuse designed the Z1 in 1935 to 1936 and built it from 1936 to 1938. The Z1 was wholly mechanical and only worked for a few minutes at a time at most. Helmut Schreyer advised Zuse to use a different technology. As a doctoral student at the Technische Hochschule in Charlottenburg (now Technische Universität Berlin) in 1937 he worked on the implementation of Boolean operations and (in today's terminology) flip-flops on the basis of vacuum tubes. In 1938, Schreyer demonstrated a circuit on this basis to a small audience, and explained his vision of an electronic computing machine – but since the largest operational electronic devices contained far fewer tubes this was considered practically infeasible. In that year when presenting the plan for a computer with 2,000 electron tubes, Zuse and Schreyer, who was an assistant at Telecommunication Institute at Technische Universität Berlin, were discouraged by members of the institute who knew about the problems with electron tube technology. Zuse later recalled: "They smiled at us in 1939, when we wanted to build electronic machines ... We said: The electronic machine is great, but first the components have to be developed." In 1940, Zuse and Schreyer managed to arrange a meeting at the Oberkommando der Wehrmacht (OKW) to discuss a potential project for developing an electronic computer, but when they estimated a duration of two or three years, the proposal was rejected.
Zuse decided to implement the next design based on relays. The realization of the Z2 was helped financially by Kurt Pannke, who manufactured small calculating machines. The Z2 was completed and presented to an audience of the ("German Laboratory for Aviation") in 1940 in Berlin-Adlershof. Zuse was lucky – this presentation was one of the few instances where the Z2 actually worked and could convince the DVL to partly finance the next design.
In 1941, improving on the basic Z2 machine, he built the Z3 in a highly secret project of the German government. Joseph Jennissen (1905–1977), member of the "Research-Leadership" (Forschungsführung) in the Reich Air Ministry acted as a government supervisor for orders of the ministry to Zuse's company ZUSE Apparatebau. A further intermediary between Zuse and the Reich Air Ministry was the aerodynamicist Herbert A. Wagner. | Z3 (computer) | Wikipedia | 507 | 152671 | https://en.wikipedia.org/wiki/Z3%20%28computer%29 | Technology | Early computers | null |
The Z3 was completed in 1941 and was faster and far more reliable than the Z1 and Z2. The Z3 floating-point arithmetic was improved over that of the Z1 in that it implemented exception handling "using just a few relays", the exceptional values (plus infinity, minus infinity and undefined) could be generated and passed through operations. It further added a square root instruction.
The Z3, like its predecessors, stored its program on an external punched tape, thus no rewiring was necessary to change programs. However, it did not have conditional branching found in later universal computers.
On 12 May 1941, the Z3 was presented to an audience of scientists including the professors Alfred Teichmann and Curt Schmieden of the ("German Laboratory for Aviation") in Berlin, today known as the German Aerospace Center in Cologne.
Zuse moved on to the Z4 design, which he completed in a bunker in the Harz mountains, alongside Wernher von Braun's ballistic missile development. When World War II ended, Zuse retreated to Hinterstein in the Alps with the Z4, where he remained for several years.
Instruction set
The Z3 operated as a stack machine with a stack of two registers, R1 and R2. The first load operation in a program would load the contents of a memory location into R1; the next load operation would load the contents of a memory location into R2. Arithmetic instructions would operate on the contents of R1 and R2, leaving the result in R1, and clearing R2; the next load operation would load into R2. A store operation would store the contents of R1 into a memory location, and clear R1; the next load operation would load the contents of a memory location into R1.
A read keyboard operation would read a number from the keyboard into R1 and clear R2. A display instruction would display the contents of R1 and clear R2; the next load instruction would load into R2. | Z3 (computer) | Wikipedia | 410 | 152671 | https://en.wikipedia.org/wiki/Z3%20%28computer%29 | Technology | Early computers | null |
Z3 as a universal Turing machine
It was possible to construct loops on the Z3, but there was no conditional branch instruction. Nevertheless, the Z3 was Turing-complete – how to implement a universal Turing machine on the Z3 was shown in 1998 by Raúl Rojas. He proposed that the tape program would have to be long enough to execute every possible path through both sides of every branch. It would compute all possible answers, but the unneeded results would be canceled out (a kind of speculative execution). Rojas concludes, "We can therefore say that, from an abstract theoretical perspective, the computing model of the Z3 is equivalent to the computing model of today's computers. From a practical perspective, and in the way the Z3 was really programmed, it was not equivalent to modern computers."
This seeming limitation belies the fact that the Z3 provided a practical instruction set for the typical engineering applications of the 1940s. Mindful of the existing hardware restrictions, Zuse's main goal at the time was to have a workable device to facilitate his work as a civil engineer.
Relation to other work
The success of Zuse's Z3 is often attributed to its use of the simple binary system. This was invented roughly three centuries earlier by Gottfried Leibniz; Boole later used it to develop his Boolean algebra. Zuse was inspired by Hilbert's and Ackermann's book on elementary mathematical logic Principles of Mathematical Logic. In 1937, Claude Shannon introduced the idea of mapping Boolean algebra onto electronic relays in a seminal work on digital circuit design. Zuse, however, did not know of Shannon's work and developed the groundwork independently for his first computer Z1, which he designed and built from 1935 to 1938.
Zuse's coworker Helmut Schreyer built an electronic digital experimental model of a computer using 100 vacuum tubes in 1942, but it was lost at the end of the war.
An analog computer was built by the rocket scientist Helmut Hölzer in 1942 at the Peenemünde Army Research Center to simulate V-2 rocket trajectories.
The Colossus (1943), built by Tommy Flowers, and the Atanasoff–Berry computer (1942) used thermionic valves (vacuum tubes) and binary representation of numbers. Programming was by means of re-plugging patch panels and setting switches. | Z3 (computer) | Wikipedia | 487 | 152671 | https://en.wikipedia.org/wiki/Z3%20%28computer%29 | Technology | Early computers | null |
The ENIAC computer, completed after the war, used vacuum tubes to implement switches and used decimal representation for numbers. Until 1948 programming was, as with Colossus, by patch leads and switches.
The Manchester Baby of 1948 along with the Manchester Mark 1 and EDSAC both of 1949 were the world's earliest working computers that stored program instructions and data in the same space. In this they implemented the stored-program concept which is frequently (but erroneously) attributed to a 1945 paper by John von Neumann and colleagues. Von Neumann is said to have given due credit to Alan Turing, and the concept had actually been mentioned earlier by Konrad Zuse himself, in a 1936 patent application (that was rejected). Konrad Zuse himself remembered in his memoirs: "During the war it would have barely been possible to build efficient stored program devices anyway." Friedrich L. Bauer later wrote: "His visionary ideas (live programs) which were only to be published years afterwards aimed at the right practical direction but were never implemented by him."
Specifications
Average calculation speed: addition – 0.8 seconds, multiplication – 3 seconds
Arithmetic unit: Binary floating-point, 22-bit, add, subtract, multiply, divide, square root
Data memory: 64 22-bit words
Program memory: Punched celluloid tape
Input: Decimal floating-point numbers
Output: Decimal floating-point numbers
Input and Output was facilitated by a terminal, with a special keyboard for input and a row of lamps to show results
Elements: Around 2,000 relays (1,400 for the memory)
Frequency: 5–10 hertz
Power consumption: Around 4,000 watts
Weight: Around
Modern reconstructions
A modern reconstruction directed by Raúl Rojas and Horst Zuse started in 1997 and finished in 2003. It is now in the Konrad Zuse Museum in Hünfeld, Germany. Memory was halved to 32 words. Power consumption is about 400 W, and weight is about .
In 2008, Horst Zuse started a reconstruction of the Z3 by himself. It was presented in 2010 in the Konrad Zuse Museum in Hünfeld. | Z3 (computer) | Wikipedia | 426 | 152671 | https://en.wikipedia.org/wiki/Z3%20%28computer%29 | Technology | Early computers | null |
A hovercraft (: hovercraft), also known as an air-cushion vehicle or ACV, is an amphibious craft capable of travelling over land, water, mud, ice, and various other surfaces.
Hovercraft use blowers to produce a large volume of air below the hull, or air cushion, that is slightly above atmospheric pressure. The pressure difference between the higher-pressure air below the hull and lower pressure ambient air above it produces lift, which causes the hull to float above the running surface. For stability reasons, the air is typically blown through slots or holes around the outside of a disk- or oval-shaped platform, giving most hovercraft a characteristic rounded-rectangle shape.
The first practical design for hovercraft was derived from a British invention in the 1950s. They are now used throughout the world as specialised transports in disaster relief, coastguard, military and survey applications, as well as for sport or passenger service. Very large versions have been used to transport hundreds of people and vehicles across the English Channel, whilst others have military applications used to transport tanks, soldiers and large equipment in hostile environments and terrain. Decline in public demand meant that , the only year-round public hovercraft service in the world still in operation serves between the Isle of Wight and Southsea in the UK. Oita Hovercraft is planning to resume services in Oita, Japan in 2024.
Although now a generic term for the type of craft, the name Hovercraft itself was a trademark owned by Saunders-Roe (later British Hovercraft Corporation (BHC), then Westland), hence other manufacturers' use of alternative names to describe the vehicles.
History
Early efforts
There have been many attempts to understand the principles of high air pressure below hulls and wings. Hovercraft are unique in that they can lift themselves while still, differing from ground effect vehicles and hydrofoils that require forward motion to create lift.
The first mention, in the historical record of the concepts behind surface-effect vehicles, to use the term hovering was by Swedish scientist Emanuel Swedenborg in 1716.
The shipbuilder John Isaac Thornycroft patented an early design for an air cushion ship / hovercraft in the 1870s, but suitable, powerful, engines were not available until the 20th century. | Hovercraft | Wikipedia | 478 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
In 1915, the Austrian Dagobert Müller von Thomamühl (1880–1956) built the world's first "air cushion" boat (). Shaped like a section of a large aerofoil (this creates a low-pressure area above the wing much like an aircraft), the craft was propelled by four aero engines driving two submerged marine propellers, with a fifth engine that blew air under the front of the craft to increase the air pressure under it. Only when in motion could the craft trap air under the front, increasing lift. The vessel also required a depth of water to operate and could not transition to land or other surfaces. Designed as a fast torpedo boat, the had a top speed of over . It was thoroughly tested and even armed with torpedoes and machine guns for operation in the Adriatic. It never saw actual combat, however, and as the war progressed it was eventually scrapped due to a lack of interest and perceived need, and its engines returned to the air force.
The theoretical grounds for motion over an air layer were constructed by Konstantin Eduardovich Tsiolkovskii in 1926 and 1927.
In 1929, Andrew Kucher of Ford began experimenting with the Levapad concept, metal disks with pressurized air blown through a hole in the centre. Levapads do not offer stability on their own. Several must be used together to support a load above them. Lacking a skirt, the pads had to remain very close to the running surface. He initially imagined these being used in place of casters and wheels in factories and warehouses, where the concrete floors offered the smoothness required for operation. By the 1950s, Ford showed a number of toy models of cars using the system, but mainly proposed its use as a replacement for wheels on trains, with the Levapads running close to the surface of existing rails.
In 1931, Finnish aero engineer Toivo J. Kaario began designing a developed version of a vessel using an air cushion and built a prototype ('Surface Glider'), in 1937. His design included the modern features of a lift engine blowing air into a flexible envelope for lift. Kaario's efforts were followed closely in the Soviet Union by Vladimir Levkov, who returned to the solid-sided design of the . Levkov designed and built a number of similar craft during the 1930s, and his L-5 fast-attack boat reached in testing. However, the start of World War II put an end to his development work. | Hovercraft | Wikipedia | 496 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
During World War II, an American engineer, Charles Fletcher, invented a walled air cushion vehicle, the Glidemobile. Because the project was classified by the U.S. government, Fletcher could not file a patent.
In April 1958, Ford engineers demonstrated the Glide-air, a model of a wheel-less vehicle that speeds on a thin film of air only 76.2 μm ( of an inch) above its tabletop roadbed. An article in Modern Mechanix quoted Andrew A. Kucher, Ford's vice president in charge of Engineering and Research noting "We look upon Glide-air as a new form of high-speed land transportation, probably in the field of rail surface travel, for fast trips of distances of up to about ".
In 1959, Ford displayed a hovercraft concept car, the Ford Levacar Mach I.
In August 1961, Popular Science reported on the Aeromobile 35B, an air-cushion vehicle (ACV) that was invented by William R. Bertelsen and was envisioned to revolutionise the transportation system, with personal hovering self-driving cars that could speed up to .
Christopher Cockerell
The idea of the modern hovercraft is most often associated with Christopher Cockerell, a British mechanical engineer. Cockerell's group was the first to develop the use of a ring of air for maintaining the cushion, the first to develop a successful skirt, and the first to demonstrate a practical vehicle in continued use. A memorial to Cockerell's first design stands in the village of Somerleyton. | Hovercraft | Wikipedia | 320 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
Cockerell came across the key concept in his design when studying the ring of airflow when high-pressure air was blown into the annular area between two concentric tin cans (one coffee and the other from cat food) and a hairdryer. This produced a ring of airflow, as expected, but he noticed an unexpected benefit as well; the sheet of fast-moving air presented a sort of physical barrier to the air on either side of it. This effect, which he called the "momentum curtain", could be used to trap high-pressure air in the area inside the curtain, producing a high-pressure plenum that earlier examples had to build up with considerably more airflow. In theory, only a small amount of active airflow would be needed to create lift and much less than a design that relied only on the momentum of the air to provide lift, like a helicopter. In terms of power, a hovercraft would only need between one quarter to one half of the power required by a helicopter.
Cockerell built and tested several models of his hovercraft design in Somerleyton, Suffolk, during the early 1950s. The design featured an engine mounted to blow from the front of the craft into a space below it, combining both lift and propulsion. He demonstrated the model flying over many Whitehall carpets in front of various government experts and ministers, and the design was subsequently put on the secret list. In spite of tireless efforts to arrange funding, no branch of the military was interested, as he later joked, "The Navy said it was a plane not a boat; the RAF said it was a boat not a plane; and the Army were 'plain not interested'."
SR.N1
This lack of military interest meant that there was no reason to keep the concept secret, and it was declassified. Cockerell was finally able to convince the National Research Development Corporation to fund development of a full-scale model. In 1958, the NRDC placed a contract with Saunders-Roe for the development of what would become the SR.N1, short for "Saunders-Roe, Nautical 1". | Hovercraft | Wikipedia | 436 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
The SR.N1 was powered by a 450 hp Alvis Leonides engine powering a vertical fan in the middle of the craft. In addition to providing the lift air, a portion of the airflow was bled off into two channels on either side of the craft, which could be directed to provide thrust. In normal operation this extra airflow was directed rearward for forward thrust and blew over two large vertical rudders that provided directional control. For low-speed manoeuvrability, the extra thrust could be directed fore or aft, differentially for rotation.
The SR.N1 made its first hover on 11 June 1959, and made its famed successful crossing of the English Channel on 25 July 1959. In December 1959, the Duke of Edinburgh visited Saunders-Roe at East Cowes and persuaded the chief test-pilot, Commander Peter Lamb, to allow him to take over the SR.N1's controls. He flew the SR.N1 so fast that he was asked to slow down a little. On examination of the craft afterwards, it was found that she had been dished in the bow due to excessive speed, damage that was never allowed to be repaired, and was from then on affectionately referred to as the 'Royal Dent'.
Skirts and other improvements
Testing quickly demonstrated that the idea of using a single engine to provide air for both the lift curtain and forward flight required too many trade-offs. A Blackburn Marboré turbojet for forward thrust and two large vertical rudders for directional control were added, producing the SR.N1 Mk II. A further upgrade with the Armstrong Siddeley Viper produced the Mk III. Further modifications, especially the addition of pointed nose and stern areas, produced the Mk IV.
Although the SR.N1 was successful as a testbed, the design hovered too close to the surface to be practical; at even small waves would hit the bow. The solution was offered by Cecil Latimer-Needham, following a suggestion made by his business partner Arthur Ord-Hume. In 1958, he suggested the use of two rings of rubber to produce a double-walled extension of the vents in the lower fuselage. When air was blown into the space between the sheets it exited the bottom of the skirt in the same way it formerly exited the bottom of the fuselage, re-creating the same momentum curtain, but this time at some distance from the bottom of the craft. | Hovercraft | Wikipedia | 491 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
Latimer-Needham and Cockerell devised a high skirt design, which was fitted to the SR.N1 to produce the Mk V, displaying hugely improved performance, with the ability to climb over obstacles almost as high as the skirt. In October 1961, Latimer-Needham sold his skirt patents to Westland, who had recently taken over Saunders Roe's interest in the hovercraft. Experiments with the skirt design demonstrated a problem; it was originally expected that pressure applied to the outside of the skirt would bend it inward, and the now-displaced airflow would cause it to pop back out. What actually happened is that the slight narrowing of the distance between the walls resulted in less airflow, which in turn led to more air loss under that section of the skirt. The fuselage above this area would drop due to the loss of lift at that point, and this led to further pressure on the skirt.
After considerable experimentation, Denys Bliss at Hovercraft Development Ltd. found the solution to this problem. Instead of using two separate rubber sheets to form the skirt, a single sheet of rubber was bent into a U shape to provide both sides, with slots cut into the bottom of the U forming the annular vent. When deforming pressure was applied to the outside of this design, air pressure in the rest of the skirt forced the inner wall to move in as well, keeping the channel open. Although there was some deformation of the curtain, the airflow within the skirt was maintained and the lift remained relatively steady. Over time, this design evolved into individual extensions over the bottom of the slots in the skirt, known as "fingers".
Commercialisation
Through these improvements, the hovercraft became an effective transport system for high-speed service on water and land, leading to widespread developments for military vehicles, search and rescue, and commercial operations. By 1962, many UK aviation and shipbuilding firms were working on hovercraft designs, including Saunders Roe/Westland, Vickers-Armstrong, William Denny, Britten-Norman and Folland. Small-scale ferry service started as early as 1962 with the launch of the Vickers-Armstrong VA-3. With the introduction of the 254 passenger and 30 car carrying SR.N4 cross-channel ferry by Hoverlloyd and Seaspeed in 1968, hovercraft had developed into useful commercial craft. | Hovercraft | Wikipedia | 485 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
Another major pioneering effort of the early hovercraft era was carried out by Jean Bertin's firm in France. Bertin was an advocate of the "multi-skirt" approach, which used a number of smaller cylindrical skirts instead of one large one in order to avoid the problems noted above. During the early 1960s he developed a series of prototype designs, which he called "terraplanes" if they were aimed for land use, and "naviplanes" for water. The best known of these designs was the N500 Naviplane, built for Seaspeed by the Société d'Etude et de Développement des Aéroglisseurs Marins (SEDAM). The N500 could carry 400 passengers, 55 cars and five buses. It set a speed record between Boulogne and Dover of . It was rejected by its operators, who claimed that it was unreliable.
Another discovery was that the total amount of air needed to lift the craft was a function of the roughness of the surface over which it travelled. On flat surfaces, like pavement, the required air pressure was so low that hovercraft were able to compete in energy terms with conventional systems like steel wheels. However, the hovercraft lift system acted as both a lift and a very effective suspension, and thus it naturally lent itself to high-speed use where conventional suspension systems were considered too complex. This led to a variety of "hovertrain" proposals during the 1960s, including England's Tracked Hovercraft and France's Aérotrain. In the U.S., Rohr Inc. and Garrett both took out licences to develop local versions of the Aérotrain. These designs competed with maglev systems in the high-speed arena, where their primary advantage was the very "low tech" tracks they needed. On the downside, the air blowing dirt and trash out from under the trains presented a unique problem in stations, and interest in them waned in the 1970s.
By the early 1970s, the basic concept had been well developed, and the hovercraft had found a number of niche roles where its combination of features were advantageous. Today, they are found primarily in military use for amphibious operations, search-and-rescue vehicles in shallow water, and sporting vehicles.
Design | Hovercraft | Wikipedia | 466 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
Hovercraft can be powered by one or more engines. Smaller craft, such as the SR.N6, usually have one engine with the drive split through a gearbox. On vehicles with several engines, one usually drives the fan (or impeller), which is responsible for lifting the vehicle by forcing high pressure air under the craft. The air inflates the "skirt" under the vehicle, causing it to rise above the surface. Additional engines provide thrust in order to propel the craft. Some hovercraft use ducting to allow one engine to perform both tasks by directing some of the air to the skirt, the rest of the air passing out of the back to push the craft forward.
Uses
Commercial
The British aircraft and marine engineering company Saunders-Roe built the first practical human-carrying hovercraft for the National Research Development Corporation, the SR.N1, which carried out several test programmes in 1959 to 1961 (the first public demonstration was in 1959), including a cross-channel test run in July 1959, piloted by Peter "Sheepy" Lamb, an ex-naval test pilot and the chief test pilot at Saunders Roe. Christopher Cockerell was on board, and the flight took place on the 50th anniversary of Louis Blériot's first aerial crossing.
The SR.N1 was driven by expelled air, powered by a single piston engine. Demonstrated at the Farnborough Airshow in 1960, it was shown that this simple craft can carry a load of up to 12 marines with their equipment as well as the pilot and co-pilot with only a slight reduction in hover height proportional to the load carried. The SR.N1 did not have any skirt, using instead the peripheral air principle that Cockerell had patented. It was later found that the craft's hover height was improved by the addition of a skirt of flexible fabric or rubber around the hovering surface to contain the air. The skirt was an independent invention made by a Royal Navy officer, C.H. Latimer-Needham, who sold his idea to Westland (by then the parent of Saunders-Roe's helicopter and hovercraft interests), and who worked with Cockerell to develop the idea further. | Hovercraft | Wikipedia | 457 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
The first passenger-carrying hovercraft to enter service was the Vickers VA-3, which, in the summer of 1962, carried passengers regularly along the north Wales coast from Moreton, Merseyside, to Rhyl. It was powered by two turboprop aero-engines and driven by propellers.
During the 1960s, Saunders-Roe developed several larger designs that could carry passengers, including the SR.N2, which operated across the Solent, in 1962, and later the SR.N6, which operated across the Solent from Southsea to Ryde on the Isle of Wight for many years. In 1963 the SR.N2 was used in experimental service between Weston-super-Mare and Penarth under the aegis of P & A Campbell, the paddle steamer operators.
Operations by Hovertravel commenced on 24 July 1965, using the SR.N6, which carried 38 passengers. Two 98 seat AP1-88 hovercraft were introduced on this route in 1983, and in 2007, these were joined by the first 130-seat BHT130 craft. The AP1-88 and the BHT130 were notable as they were largely built by Hoverwork using shipbuilding techniques and materials (i.e. welded aluminium structure and diesel engines) rather than the aircraft techniques used to build the earlier craft built by Saunders-Roe-British Hovercraft Corporation. Over 20 million passengers had used the service as of 2004 – the service is still operating () and is by far the longest, continuously-operated hovercraft service.
In 1966, two cross-channel passenger hovercraft services were inaugurated using SR.N6 hovercraft. Hoverlloyd ran services from Ramsgate Harbour, England, to Calais, France, and Townsend Ferries also started a service to Calais from Dover, which was soon superseded by that of Seaspeed. | Hovercraft | Wikipedia | 386 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
As well as Saunders-Roe and Vickers (which combined in 1966 to form the British Hovercraft Corporation (BHC)), other commercial craft were developed during the 1960s in the UK by Cushioncraft (part of the Britten-Norman Group) and Hovermarine based at Woolston (the latter being sidewall hovercraft, where the sides of the hull projected down into the water to trap the cushion of air with normal hovercraft skirts at the bow and stern). One of these models, the HM-2, was used by Red Funnel between Southampton (near the Woolston Floating Bridge) and Cowes.
The world's first car-carrying hovercraft was made in 1968, the BHC Mountbatten class (SR.N4) models, each powered by four Bristol Proteus turboshaft engines. These were both used by rival operators Hoverlloyd and Seaspeed (which joined to form Hoverspeed in 1981) to operate regular car and passenger carrying services across the English Channel. Hoverlloyd operated from Ramsgate, where a special hoverport had been built at Pegwell Bay, to Calais. Seaspeed operated from Dover, England, to Calais and Boulogne in France. The first SR.N4 had a capacity of 254 passengers and 30 cars, and a top speed of . The channel crossing took around 30 minutes and was run like an airline with flight numbers. The later SR.N4 Mk.III had a capacity of 418 passengers and 60 cars. These were later joined by the French-built SEDAM N500 Naviplane with a capacity of 385 passengers and 45 cars; only one entered service and was used intermittently for a few years on the cross-channel service until returned to SNCF in 1983. The service ceased on 1 October 2000 after 32 years, due to competition with traditional ferries, catamarans, the disappearance of duty-free shopping within the EU, the advancing age of the SR.N4 hovercraft, and the opening of the Channel Tunnel. | Hovercraft | Wikipedia | 424 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
The commercial success of hovercraft suffered from rapid rises in fuel prices during the late 1960s and 1970s, following conflict in the Middle East. Alternative over-water vehicles, such as wave-piercing catamarans (marketed as the SeaCat in the UK until 2005), use less fuel and can perform most of the hovercraft's marine tasks. Although developed elsewhere in the world for both civil and military purposes, except for the Solent Ryde-to-Southsea crossing, hovercraft disappeared from the coastline of Britain until a range of Griffon Hoverwork were bought by the Royal National Lifeboat Institution.
Hovercraft used to ply between the Gateway of India in Mumbai and CBD Belapur and Vashi in Navi Mumbai between 1994 and 1999, but the services were subsequently stopped due to the lack of sufficient water transport infrastructure.
Civilian non-commercial
In Finland, small hovercraft are widely used in maritime rescue and during the rasputitsa ("mud season") as archipelago liaison vehicles. In England, hovercraft of the Burnham-on-Sea Area Rescue Boat (BARB) are used to rescue people from thick mud in Bridgwater Bay. Avon Fire and Rescue Service became the first Local Authority fire service in the UK to operate a hovercraft. It is used to rescue people from thick mud in the Weston-super-Mare area and during times of inland flooding. A Griffon rescue hovercraft has been in use for a number of years with the Airport Fire Service at Dundee Airport in Scotland. It is used in the event of an aircraft ditching in the Tay estuary. Numerous fire departments around the US/Canadian Great Lakes operate hovercraft for water and ice rescues, often of ice fisherman stranded when ice breaks off from shore. The Canadian Coast Guard uses hovercraft to break light ice.
In October 2008, The Red Cross commenced a flood-rescue service hovercraft based in Inverness, Scotland. Gloucestershire Fire and Rescue Service received two flood-rescue hovercraft donated by Severn Trent Water following the 2007 UK floods.
Since 2006, hovercraft have been used in aid in Madagascar by HoverAid, an international NGO who use the hovercraft to reach the most remote places on the island. | Hovercraft | Wikipedia | 477 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
The Scandinavian airline SAS used to charter an AP1-88 hovercraft for regular passengers between Copenhagen Airport, Denmark, and the SAS Hovercraft Terminal in Malmö, Sweden.
In 1998, the US Postal Service began using the British built Hoverwork AP1-88 to haul mail, freight, and passengers from Bethel, Alaska, to and from eight small villages along the Kuskokwim River. Bethel is far removed from the Alaska road system, thus making the hovercraft an attractive alternative to the air based delivery methods used prior to introduction of the hovercraft service. Hovercraft service is suspended for several weeks each year while the river is beginning to freeze to minimize damage to the river ice surface. The hovercraft is able to operate during the freeze-up period; however, this could potentially break the ice and create hazards for villagers using their snowmobiles along the river during the early winter.
In 2006, Kvichak Marine Industries of Seattle, US built, under licence, a cargo/passenger version of the Hoverwork BHT130. Designated 'Suna-X', it is used as a high-speed ferry for up to 47 passengers and of freight serving the remote Alaskan villages of King Cove and Cold Bay.
An experimental service was operated in Scotland across the Firth of Forth (between Kirkcaldy and Portobello, Edinburgh), from 16 to 28 July 2007. Marketed as Forthfast, the service used a craft chartered from Hovertravel and achieved an 85% passenger load factor. , the possibility of establishing a permanent service is still under consideration.
Since the Channel routes abandoned hovercraft, and pending any reintroduction on the Scottish route, the United Kingdom's only public hovercraft service is that operated by Hovertravel between Southsea (Portsmouth) and Ryde on the Isle of Wight. | Hovercraft | Wikipedia | 389 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
From the 1960s, several commercial lines were operated in Japan, without much success. In Japan the last commercial line had linked Ōita Airport and central Ōita but was shut down in October 2009. However, the commercial line between Ōita Airport and central Ōita is scheduled to reopen in 2024.
Hovercraft are still manufactured in the UK, near to where they were first conceived and tested, on the Isle of Wight. They can also be chartered for a wide variety of uses including inspections of shallow bed offshore wind farms and VIP or passenger use. A typical vessel would be a Tiger IV or a Griffon. They are light, fast, road transportable and very adaptable with the unique feature of minimising damage to environments.
Military
China
The People's Army Navy of China operates the Jingsah II class LCAC. This troop and equipment carrying hovercraft is roughly the Chinese equivalent of the U.S. Navy LCAC.
Finland
The Finnish Navy designed an experimental missile attack hovercraft class, Tuuli class hovercraft, in the late 1990s. The prototype of the class, Tuuli, was commissioned in 2000. It proved an extremely successful design for a littoral fast attack craft, but due to fiscal reasons and doctrinal change in the Navy, the hovercraft was soon withdrawn.
Iran
The Iranian Navy operates multiple British-made and some Iranian-produced hovercraft. The Tondar or Thunderbolt comes in varieties designed for combat and transportation. Iran has equipped the Tondar with mid-range missiles, machine guns and retrievable reconnaissance drones. Currently they are used for water patrols and combat against drug smugglers.
Russia
The Soviet Union had military hovercraft such as the small Czilim-class hovercraft, comparable to the SR.N6, the large Zubr-class landing craft and the Bora missile launcher surface effect ship (a hybrid between a hovercraft and a catamaran).
United Kingdom | Hovercraft | Wikipedia | 413 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
The first application of the hovercraft for military use was by the British Armed Forces, using hovercraft built by Saunders-Roe. In 1961, the United Kingdom set up the Interservice Hovercraft Trials Unit (IHTU) based at RNAS Lee-on-Solent (HMS Daedalus), now the site of the Hovercraft Museum, near Portsmouth. This unit carried out trials on the SR.N1 from Mk1 through Mk5 as well as testing the SR.N2, SR.N3, SR.N5 and SR.N6 craft. The Hovercraft Trials Unit (Far East) was established by the Royal Navy at Singapore in August 1964 with two armed hovercraft; they were deployed later that year to Tawau in Malaysian Borneo and operated on waterways there during the Indonesia–Malaysia confrontation. The hovercraft's inventor, Sir Christopher Cockerell, claimed late in his life that the Falklands War could have been won far more easily had the British military shown more commitment to the hovercraft; although earlier trials had been conducted in the Falkland Islands with an SRN-6, the hovercraft unit had been disbanded by the time of the conflict. Currently, the Royal Marines use the Griffonhoverwork 2400TD hovercraft, the replacement for the Griffon 2000 TDX Class ACV, which was deployed operationally by the marines in the 2003 invasion of Iraq.
United States | Hovercraft | Wikipedia | 315 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
During the 1960s, Bell licensed and sold the Saunders-Roe SR.N5 as the Bell SK-5. They were deployed on trial to the Vietnam War by the United States Navy as PACV patrol craft in the Mekong Delta where their mobility and speed was unique. This was used in both the UK SR.N5 curved deck configuration and later with modified flat deck, gun turret and grenade launcher designated the 9255 PACV. The United States Army also experimented with the use of SR.N5 hovercraft in Vietnam. Three hovercraft with the flat deck configuration were deployed to Đồng Tâm in the Mekong Delta region and later to Ben Luc. They saw action primarily in the Plain of Reeds. One was destroyed in early 1970 and another in August of that same year, after which the unit was disbanded. The only remaining U.S. Army SR.N5 hovercraft is currently on display in the Army Transport Museum in Virginia.
Experience led to the proposed Bell SK-10, which was the basis for the LCAC-class air-cushioned landing craft now deployed by the U.S. and Japanese Navy. Developed and tested in the mid-1970s, the LACV-30 was used by the US Army to transport military cargo in logistics-over-the-shore operations from the early 1980s until the mid-1990s.
Recreational/sport
Small commercially manufactured, kit or plan-built hovercraft are increasingly being used for recreational purposes, such as inland racing and cruising on inland lakes and rivers, marshy areas, estuaries and inshore coastal waters.
The Hovercraft Cruising Club supports the use of hovercraft for cruising in coastal and inland waterways, lakes and lochs.
The Hovercraft Club of Great Britain, founded in 1966, regularly organizes inland and coastal hovercraft race events at various venues across the United Kingdom. Similar events are also held in Europe and the US.
In August 2010, the Hovercraft Club of Great Britain hosted the World Hovercraft Championships at Towcester Racecourse, followed by the 2016 World Hovercraft Championships at the West Midlands Water Ski Centre in Tamworth. | Hovercraft | Wikipedia | 447 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
The World Hovercraft Championships are run under the auspices of the World Hovercraft Federation. So far the World Hovercraft Championships had been hosted by France: 1993 in Verneuil, 1997 in Lucon, 2006 at the Lac de Tolerme; Germany: 1987 in Bad Karlshafen, 2004 in Berlin, 2012 and 2018 in Saalburg; Portugal: 1995 in Peso de la Regua; Sweden: 2008 and 2022 at Flottbro Ski Centre in Huddinge; UK 1991 and 2000 at Weston Parc; US: 1989 in Troy (Ohio), 2002 in Terre Haute. The 2020 World Hovercraft Championships had to be postponed to 2022 due to restriction caused by the Covid-19 outbreak.
Apart from the craft designed as "racing hovercraft", which are often only suitable for racing, there is another form of small personal hovercraft for leisure use, often referred to as cruising hovercraft, capable of carrying up to four people. Just like their full size counterparts, the ability of these small personal hovercraft to safely cross all types of terrain, (e.g. water, sandbanks, swamps, ice, etc.) and reach places often inaccessible by any other type of craft, makes them suitable for a number of roles, such as survey work and patrol and rescue duties in addition to personal leisure use. Increasingly, these craft are being used as yacht tenders, enabling yacht owners and guests to travel from a waiting yacht to, for example, a secluded beach. In this role, small hovercraft can offer a more entertaining alternative to the usual small boat and can be a rival for the jet-ski. The excitement of a personal hovercraft can now be enjoyed at "experience days", which are popular with families, friends and those in business, who often see them as team building exercises. This level of interest has naturally led to a hovercraft rental sector and numerous manufacturers of small, ready built designs of personal hovercraft to serve the need.
Other uses
Hoverbarge
A real benefit of air cushion vehicles in moving heavy loads over difficult terrain, such as swamps, was overlooked by the excitement of the British Government funding to develop high-speed hovercraft. It was not until the early 1970s that the technology was used for moving a modular marine barge with a dragline on board for use over soft reclaimed land. | Hovercraft | Wikipedia | 502 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
Mackace (Mackley Air Cushion Equipment), now known as Hovertrans, produced a number of successful Hoverbarges, such as the 250 ton payload "Sea Pearl", which operated in Abu Dhabi, and the twin 160 ton payload "Yukon Princesses", which ferried trucks across the Yukon River to aid the pipeline build. Hoverbarges are still in operation today. In 2006, Hovertrans (formed by the original managers of Mackace) launched a 330-ton payload drilling barge in the swamps of Suriname.
The Hoverbarge technology is somewhat different from high-speed hovercraft, which has traditionally been constructed using aircraft technology. The initial concept of the air cushion barge has always been to provide a low-tech amphibious solution for accessing construction sites using typical equipment found in this area, such as diesel engines, ventilating fans, winches and marine equipment. The load to move a 200 ton payload ACV barge at would only be 5 tons. The skirt and air distribution design on high-speed craft again is more complex, as they have to cope with the air cushion being washed out by a wave and wave impact. The slow speed and large mono chamber of the hover barge actually helps reduce the effect of wave action, giving a very smooth ride.
The low pull force enabled a Boeing 107 helicopter to pull a hoverbarge across snow, ice and water in 1982.
Hovertrains
Several attempts have been made to adopt air cushion technology for use in fixed track systems, in order to use the lower frictional forces for delivering high speeds. The most advanced example of this was the Aérotrain, an experimental high speed hovertrain built and operated in France between 1965 and 1977. The project was abandoned in 1977 due to lack of funding, the death of its lead engineer and the adoption of the TGV by the French government as its high-speed ground transport solution. | Hovercraft | Wikipedia | 393 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
A test track for a tracked hovercraft system was built at Earith near Cambridge, England. It ran southwest from Sutton Gault, sandwiched between the Old Bedford River and the smaller Counter Drain to the west. Careful examination of the site will still reveal traces of the concrete piers used to support the structure. The actual vehicle, RTV31, is preserved at Railworld in Peterborough and can be seen from trains, just south west of Peterborough railway station. The vehicle achieved on 7 February 1973 but the project was cancelled a week later. The project was managed by Tracked Hovercraft Ltd., with Denys Bliss as Director in the early 1970s, then axed by the Aerospace Minister, Michael Heseltine. Records of this project are available from the correspondence and papers of Sir Harry Legge-Bourke, MP at Leeds University Library. Heseltine was accused by Airey Neave and others of misleading the House of Commons when he stated that the government was still considering giving financial support to the Hovertrain, when the decision to pull the plug had already been taken by the Cabinet.
After the Cambridge project was abandoned due to financial constraints, parts of the project were picked up by the engineering firm Alfred McAlpine, and abandoned in the mid-1980s. The Tracked Hovercraft project and Professor Laithwaite's Maglev train system were contemporaneous, and there was intense competition between the two prospective British systems for funding and credibility.
At the other end of the speed spectrum, the U-Bahn Serfaus has been in continuous operation since 1985. This is an unusual underground air cushion funicular rapid transit system, situated in the Austrian ski resort of Serfaus. Only long, the line reaches a maximum speed of . A similar system also exists in Narita International Airport near Tokyo, Japan. | Hovercraft | Wikipedia | 374 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
In the late 1960s and early 1970s, the U.S. Department of Transport's Urban Mass Transit Administration (UMTA) funded several hovertrain projects, which were known as Tracked Air Cushion Vehicles or TACVs. They were also known as Aerotrains since one of the builders had a licence from Bertin's Aerotrain company. Three separate projects were funded. Research and development was carried out by Rohr, Inc., Garrett AiResearch and Grumman. UMTA built an extensive test site in Pueblo, Colorado, with different types of tracks for the different technologies used by the prototype contractors. They managed to build prototypes and do a few test runs before the funding was cut.
Heavy haulage
From the 1960s to 1980s, heavy haulers in the UK used an air-cushion system for their hydraulic modular trailers to carry overweight loads over bridges which were not able to bear the weight of the load and the trailer. The Central Electricity Generating Board had to move transformers from one place to another which weighed from 150 tons to 300 tons for which they did not have appropriate equipment; so they hired heavy haulers like Wynns and Pickfords who had specialized equipment like hydraulic modular trailers manufactured by Nicolas and Cometto, and ballast tractors from Scammell which were strong and powerful enough to carry the load. This made the transportation efficient by avoiding bridge reinforcement, in some cases costing .
The transformers were loaded into the girder frame of the hydraulic modular trailer with axle lines in front and behind of the transformer, which made it possible to keep the transformer as low as possible to the ground to negotiate obstacles on the route. Air cushions were mounted under the girder frame's surface and were operated by a compressor vehicle which was a customized Commer 16-ton maxiload provided by CEGB. The vehicle was loaded with 4 air compressors powered by a Rolls-Royce engine producing 235 bhp. While negotiating a bridge the air cushions were inflated and that reduced the stress tremendously on the bridge. Without this technology the government would have had to rebuild the bridges which was not feasible just to carry a small number of loads. | Hovercraft | Wikipedia | 433 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
Non-transportation
The Hoover Constellation was a spherical canister-type vacuum cleaner notable for its lack of wheels. Floating on a cushion of air, it was a domestic hovercraft. They were not especially good as vacuum cleaners as the air escaping from under the cushion blew uncollected dust in all directions, nor as hovercraft as their lack of a skirt meant that they only hovered effectively over a smooth surface. Despite this, original Constellations are sought-after collectibles today.
The Flymo is an air-cushion lawn mower that uses a fan on the cutter blade to provide lift. This allows it to be moved in any direction, and provides double-duty as a mulcher.
The Marylebone Cricket Club owns a "hover cover" that it uses regularly to cover the pitch at Lord's Cricket Ground. This device is easy and quick to move, and has no pressure points, making damage to the pitch less likely.
A power trowel is a hovercraft device used for skimming concrete.
Features
Advantages
Terrain-independence - crossing beachfronts and slopes up to 40 degrees
All-season capability - frozen or flowing rivers no object
Speed
Flexibility, due to low surface friction
Disadvantages
Engine noise emissions
Initial costs
Proneness to contrary winds
Skirt wear and tear
Preservation
The Hovercraft Museum at Lee-on-the-Solent, Hampshire, England, houses the world's largest collection of hovercraft designs, including some of the earliest and largest. Much of the collection is housed within the retired SR.N4 hovercraft Princess Anne. She is the last of her kind in the world.
There are many hovercraft in the museum but all are non-operational.
, Hovercraft continue in use between Ryde on the Isle of Wight and Southsea on the English mainland. The service, operated by Hovertravel, schedules up to three crossings each hour, and provides the fastest way of getting on or off the island. Large passenger-hovercraft are still manufactured on the Isle of Wight.
Records | Hovercraft | Wikipedia | 428 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
World's largest civil hovercraft – The BHC SR.N4 Mk.III, at 56.4 m (185 ft) length and 310 metric tons (305 long tons) weight, can accommodate 418 passengers and 60 cars.
World's largest military hovercraft – The Russian Zubr class LCAC at 57.6 metres (188 feet) length and a maximum displacement of 535 tons. This hovercraft can transport three T-80 main battle tanks (MBT), 140 fully equipped troops, or up to 130 tons of cargo. Four have been purchased by the Greek Navy.
English Channel crossing – 22 minutes by Princess Anne Mountbatten class hovercraft SR.N4 Mk.III on 14 September 1995
World hovercraft speed record – 137.4 km/h (85.38 mph or 74.19 knots). Bob Windt (USA) at World Hovercraft Championships, Rio Douro River, Peso de Regua, Portugal on 18 September 1995.
Hovercraft land speed record – 56.25 mph (90.53 km/h or 48.88 knots). John Alford (USA) at Bonneville Salt Flats, Utah, USA on 21 September 1998.
Longest continuous use – The original prototype SR.N6 Mk.I (009) was in service for over 20 years, and logged 22,000 hours of use. It is currently on display at the Hovercraft Museum in Lee-on-the-Solent, Hampshire, England. | Hovercraft | Wikipedia | 320 | 152690 | https://en.wikipedia.org/wiki/Hovercraft | Technology | Maritime transport | null |
A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most commonly, the term is used to describe a farm vehicle that provides the power and traction to mechanize agricultural tasks, especially (and originally) tillage, and now many more. Agricultural implements may be towed behind or mounted on the tractor, and the tractor may also provide a source of power if the implement is mechanised.
Etymology
The word tractor was taken from Latin, being the agent noun of trahere "to pull". The first recorded use of the word meaning "an engine or vehicle for pulling wagons or plows" occurred in 1896, from the earlier term "traction motor" (1859).
National variations
In the UK, Ireland, Australia, India, Spain, Argentina, Slovenia, Serbia, Croatia, the Netherlands, and Germany, the word "tractor" usually means "farm tractor", and the use of the word "tractor" to mean other types of vehicles is familiar to the vehicle trade, but unfamiliar to much of the general public. In Canada and the US, the word may also refer to the road tractor portion of a tractor trailer truck, but also usually refers to the piece of farm equipment.
History
Traction engines
The first powered farm implements in the early 19th century were portable engines – steam engines on wheels that could be used to drive mechanical farm machinery by way of a flexible belt. Richard Trevithick designed the first 'semi-portable' stationary steam engine for agricultural use, known as a "barn engine" in 1812, and it was used to drive a corn threshing machine. The truly portable engine was invented in 1839 by William Tuxford of Boston, Lincolnshire who started manufacture of an engine built around a locomotive-style boiler with horizontal smoke tubes. A large flywheel was mounted on the crankshaft, and a stout leather belt was used to transfer the drive to the equipment being driven. In the 1850s, John Fowler used a Clayton & Shuttleworth portable engine to drive apparatus in the first public demonstrations of the application of cable haulage to cultivation. | Tractor | Wikipedia | 448 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
In parallel with the early portable engine development, many engineers attempted to make them self-propelled – the fore-runners of the traction engine. In most cases this was achieved by fitting a sprocket on the end of the crankshaft, and running a chain from this to a larger sprocket on the rear axle. These experiments met with mixed success. The first proper traction engine, in the form recognisable today, was developed in 1859 when British engineer Thomas Aveling modified a Clayton & Shuttleworth portable engine, which had to be hauled from job to job by horses, into a self-propelled one. The alteration was made by fitting a long driving chain between the crankshaft and the rear axle.
The first half of the 1860s was a period of great experimentation but by the end of the decade the standard form of the traction engine had evolved and changed little over the next sixty years. It was widely adopted for agricultural use. The first tractors were steam-powered plowing engines. They were used in pairs, placed on either side of a field to haul a plow back and forth between them using a wire cable. In Britain Mann's and Garrett developed steam tractors for direct ploughing, but the heavy, wet soil of England meant that these designs were less economical than a team of horses. In the United States, where soil conditions permitted, steam tractors were used to direct-haul plows. Steam-powered agricultural engines remained in use well into the 20th century until reliable internal combustion engines had been developed.
Fuel
The first gasoline powered tractors were built in Illinois, by John Charter combining single cylinder Otto engines with a Rumley Steam engine chassis, in 1889. In 1892, John Froelich built a gasoline-powered tractor in Clayton County, Iowa, US. A Van Duzen single-cylinder gasoline engine was mounted on a Robinson engine chassis, which could be controlled and propelled by Froelich's gear box. After receiving a patent, Froelich started up the Waterloo Gasoline Engine Company and invested all of his assets. The venture was very unsuccessful, and by 1895 all was lost and he went out of business. | Tractor | Wikipedia | 432 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Richard Hornsby & Sons are credited with producing and selling the first oil-engined tractor in Britain, invented by Herbert Akroyd Stuart. The Hornsby-Akroyd Patent Safety Oil Traction Engine was made in 1896 with a engine. In 1897, it was bought by Mr. Locke-King, the first recorded British tractor sale. That year, it won a Silver Medal from the Royal Agricultural Society of England. It later returned to the factory for a caterpillar track fitting.
The first commercially successful light-weight petrol-powered general purpose tractor was built by Dan Albone, a British inventor in 1901. He filed for a patent on 15 February 1902 for his tractor design and then formed Ivel Agricultural Motors Limited. The other directors were Selwyn Edge, Charles Jarrott, John Hewitt and Lord Willoughby. He called his machine the Ivel Agricultural Motor; the word "tractor" came into common use after Hart-Parr created it. The Ivel Agricultural Motor was light, powerful and compact. It had one front wheel, with a solid rubber tyre, and two large rear wheels like a modern tractor. The engine used water cooling, utilizing the thermo-syphon effect. It had one forward and one reverse gear. A pulley wheel on the left hand side allowed it to be used as a stationary engine, driving a wide range of agricultural machinery. The 1903 sale price was £300. His tractor won a medal at the Royal Agricultural Show, in 1903 and 1904. About 500 were built, and many were exported all over the world. The original engine was made by Payne & Co. of Coventry. After 1906, French Aster engines were used.
The first successful American tractor was built by Charles W. Hart and Charles H. Parr. They developed a two-cylinder gasoline engine and set up their business in Charles City, Iowa. In 1903, the firm built 15 tractors. Their #3 is the oldest surviving internal combustion engine tractor in the United States, and is on display at the Smithsonian National Museum of American History in Washington, D.C. The two-cylinder engine has a unique hit-and-miss firing cycle that produced at the belt and at the drawbar. | Tractor | Wikipedia | 447 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
In 1908, the Saunderson Tractor and Implement Co. of Bedford introduced a four-wheel design, and became the largest tractor manufacturer in Britain at the time. While the earlier, heavier tractors were initially very successful, it became increasingly apparent at this time that the weight of a large supporting frame was less efficient than lighter designs. Henry Ford introduced a light-weight, mass-produced design which largely displaced the heavier designs. Some companies halfheartedly followed suit with mediocre designs, as if to disprove the concept, but they were largely unsuccessful in that endeavor.
While unpopular at first, these gasoline-powered machines began to catch on in the 1910s, when they became smaller and more affordable. Henry Ford introduced the Fordson, a wildly popular mass-produced tractor, in 1917. They were built in the U.S., Ireland, England and Russia, and by 1923, Fordson had 77% of the U.S. market. The Fordson dispensed with a frame, using the strength of the engine block to hold the machine together. By the 1920s, tractors with gasoline-powered internal combustion engines had become the norm.
The first three-point hitches were experimented with in 1917. After Harry Ferguson applied for a British patent for his three-point hitch in 1926, they became popular. A three-point attachment of the implement to the tractor is the simplest and the only statically determinate way of joining two bodies in engineering. The Ferguson-Brown Company produced the Model A Ferguson-Brown tractor with a Ferguson-designed hydraulic hitch. In 1938 Ferguson entered into a collaboration with Henry Ford to produce the Ford-Ferguson 9N tractor. The three-point hitch soon became the favorite hitch attachment system among farmers around the world. This tractor model also included a rear Power Take Off (PTO) shaft that could be used to power three point hitch mounted implements such as sickle-bar mowers.
Electric
In 1969, General Electric introduced the Elec-Trak, the first commercial, electric tractor (electric-powered garden tractor). The Elec-Trak was manufactured by General Electric until 1975.
Electric tractors are manufactured by a German company, Fendt, and by US companies, Solectrac and Monarch Tractor.
John Deere's protoype electric tractor is a plug-in, powered by an electrical cable.
Kubota is prototyping an autonomous electric tractor.
Design, power and transmission | Tractor | Wikipedia | 495 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Configuration
Tractors can be generally classified by number of axles or wheels, with main categories of two-wheel tractors (single-axle tractors) and four-wheel tractors (two-axle tractors); more axles are possible but uncommon. Among four-wheel tractors (two-axle tractors), most are two-wheel drive (usually at the rear); but many are two-wheel drive with front wheel assist, four-wheel drive (often with articulated steering), or track crawler (with steel or rubber tracks).
The classic farm tractor is a simple open vehicle, with two very large driving wheels on an axle below a single seat (the seat and steering wheel consequently are in the center), and the engine in front of the driver, with two steerable wheels below the engine compartment. This basic design has remained unchanged for a number of years after being pioneered by Wallis, but enclosed cabs are fitted on almost all modern models, for operator safety and comfort.
In some localities with heavy or wet soils, notably in the Central Valley of California, the "Caterpillar" or "crawler" type of tracked tractor became popular due to superior traction and flotation. These were usually maneuvered through the use of turning brake pedals and separate track clutches operated by levers rather than a steering wheel.
Four-wheel drive tractors began to appear in the 1960s. Some four-wheel drive tractors have the standard "two large, two small" configuration typical of smaller tractors, while some have four large, powered wheels. The larger tractors are typically an articulated, center-hinged design steered by hydraulic cylinders that move the forward power unit while the trailing unit is not steered separately.
In the early 21st century, articulated or non-articulated, steerable multitrack tractors have largely supplanted the Caterpillar type for farm use. Larger types of modern farm tractors include articulated four-wheel or eight-wheel drive units with one or two power units which are hinged in the middle and steered by hydraulic clutches or pumps. A relatively recent development is the replacement of wheels or steel crawler-type tracks with flexible, steel-reinforced rubber tracks, usually powered by hydrostatic or completely hydraulic driving mechanisms. The configuration of these tractors bears little resemblance to the classic farm tractor design.
Engine and fuels
The predecessors of modern tractors, traction engines, used steam engines for power. | Tractor | Wikipedia | 483 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Gasoline and kerosene
Since the turn of the 20th century, internal combustion engines have been the power source of choice. Between 1900 and 1960, gasoline was the predominant fuel, with kerosene (the Rumely Oil Pull was the most notable of this kind)being a common alternative. Generally, one engine could burn any of those, although cold starting was easiest on gasoline. Often, a small auxiliary fuel tank was available to hold gasoline for cold starting and warm-up, while the main fuel tank held whatever fuel was most convenient or least expensive for the particular farmer. In the United Kingdom, a gasoline-kerosene engine is known as a petrol-paraffin engine.
Diesel
Dieselisation gained momentum starting in the 1960s, and modern farm tractors usually employ diesel engines, which range in power output from 18 to 575 horsepower (15 to 480 kW). Size and output are dependent on application, with smaller tractors used for lawn mowing, landscaping, orchard work, and truck farming, and larger tractors for vast fields of wheat, corn, soy, and other bulk crops.
Liquefied petroleum gas
Liquefied petroleum gas (LPG) or propane also have been used as tractor fuels, but require special pressurized fuel tanks and filling equipment and produced less power, so are less prevalent in most markets. Most are confined for inside work due to their clean burning.
Wood
During the second world war, Petrolium based fuel was scarce in many European nations. So they resorted to using wood gasifires on every vehicle, including tractors.
Biodiesel
In some countries such as Germany, biodiesel is often used. Some other biofuels such as straight vegetable oil are also being used by some farmers.
Electric powered
Prototype battery powered electric tractors are being developed by a German company, Fendt, and by two US companies, Solectrac and Monarch Tractor. John Deere's protoype electric tractor is a plug-in, powered by an electrical cable. Kubota is prototyping an autonomous electric tractor.
Transmission
Most older farm tractors use a manual transmission with several gear ratios, typically three to six, sometimes multiplied into two or three ranges. This arrangement provides a set of discrete ratios that, combined with the varying of the throttle, allow final-drive speeds from less than one up to about 25 miles per hour (40 km/h), with the lower speeds used for working the land and the highest speed used on the road. | Tractor | Wikipedia | 499 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Slow, controllable speeds are necessary for most of the operations performed with a tractor. They help give the farmer a larger degree of control in certain situations, such as field work. When travelling on public roads, the slow operating speeds can cause problems, such as long queues or tailbacks, which can delay or annoy motorists in cars and trucks. These motorists are responsible for being duly careful around farm tractors and sharing the road with them, but many shirk this responsibility, so various ways to minimize the interaction or minimize the speed differential are employed where feasible. Some countries (for example the Netherlands) employ a road sign on some roads that means "no farm tractors". Some modern tractors, such as the JCB Fastrac, are now capable of much higher road speeds of around 50 mph (80 km/h).
Older tractors usually have unsynchronized transmission designs, which often require the operator to engage the clutch to shift between gears. This mode of use is inherently unsuited to some of the work tractors do, and has been circumvented in various ways over the years. For existing unsynchronized tractors, the methods of circumvention are double clutching or power-shifting, both of which require the operator to rely on skill to speed-match the gears while shifting, and are undesirable from a risk-mitigation standpoint because of what can go wrong if the operator makes a mistake – transmission damage is possible, and loss of vehicle control can occur if the tractor is towing a heavy load either uphill or downhill – something that tractors often do. Therefore, operator's manuals for most of these tractors state one must always stop the tractor before shifting. | Tractor | Wikipedia | 354 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
In newer designs, unsynchronized transmission designs were replaced with synchronization or with continuously variable transmissions (CVTs). Either a synchronized manual transmission with enough available gear ratios (often achieved with dual ranges, high and low) or a CVT allow the engine speed to be matched to the desired final-drive speed, while keeping engine speed within the appropriate speed (as measured in rotations per minute or rpm) range for power generation (the working range) (whereas throttling back to achieve the desired final-drive speed is a trade-off that leaves the working range). The problems, solutions, and developments described here also describe the history of transmission evolution in semi-trailer trucks. The biggest difference is fleet turnover; whereas most of the old road tractors have long since been scrapped, many of the old farm tractors are still in use. Therefore, old transmission design and operation is primarily just of historical interest in trucking, whereas in farming it still often affects daily life.
Hitches and power applications
The power produced by the engine must be transmitted to the implement or equipment to do the actual work intended for the equipment. This may be accomplished via a drawbar or hitch system if the implement is to be towed or otherwise pulled through the tractive power of the engine, or via a pulley or power takeoff system if the implement is stationary, or a combination of the two.
Drawbars
Plows and other tillage equipment are most commonly connected to the tractor via a drawbar. The classic drawbar is simply a steel bar attached to the tractor (or in some cases, as in the early Fordsons, cast as part of the rear transmission housing) to which the hitch of the implement was attached with a pin or by a loop and clevis. The implement could be readily attached and removed, allowing the tractor to be used for other purposes on a daily basis. If the tractor was equipped with a swinging drawbar, then it could be set at the center or offset from center to allow the tractor to run outside the path of the implement. | Tractor | Wikipedia | 420 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
The drawbar system necessitated the implement having its own running gear (usually wheels) and in the case of a plow, chisel cultivator or harrow, some sort of lift mechanism to raise it out of the ground at turns or for transport. Drawbars necessarily posed a rollover risk depending on how the tractive torque was applied. The Fordson tractor was prone to roll backward due to an excessively short wheelbase. The linkage between the implement and the tractor usually had some slack which could lead to jerky starts and greater wear and tear on the tractor and the equipment.
Drawbars were appropriate to the dawn of mechanization, because they were very simple in concept and because as the tractor replaced the horse, existing horse-drawn implements usually already had running gear. As the history of mechanization progressed, the advantages of other hitching systems became apparent, leading to new developments (see below). Depending on the function for which a tractor is used, though, the drawbar is still one of the usual means of attaching an implement to a tractor (see photo at left).
Fixed mounts
Some tractor manufacturers produced matching equipment that could be directly mounted on the tractor. Examples included front-end loaders, belly mowers, row crop cultivators, corn pickers and corn planters. In most cases, these fixed mounts were proprietary and unique to each make of tractor, so an implement produced by John Deere, for example, could not be attached to a Minneapolis Moline tractor. Another disadvantage was mounting usually required some time and labor, resulting in the implement being semi-permanently attached with bolts or other mounting hardware. Usually, it was impractical to remove the implement and reinstall it on a day-to-day basis. As a result, the tractor was unavailable for other uses and dedicated to a single use for an appreciable period of time. An implement was generally mounted at the beginning of its season of use (such as tillage, planting or harvesting) and removed when the season ended. | Tractor | Wikipedia | 418 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Three-point and quick
The drawbar system was virtually the exclusive method of attaching implements (other than direct attachment to the tractor) before Harry Ferguson developed the three-point hitch. Equipment attached to the three-point hitch can be raised or lowered hydraulically with a control lever. The equipment attached to the three-point hitch is usually completely supported by the tractor. Another way to attach an implement is via a quick hitch, which is attached to the three-point hitch. This enables a single person to attach an implement quicker and put the person in less danger when attaching the implement.
The three-point hitch revolutionized farm tractors and their implements. While the Ferguson System was still under patent, other manufacturers developed new hitching systems to try to fend off some of Ferguson's competitive advantage. For example, International Harvester's Farmall tractors gained a two-point "Fast Hitch", and John Deere had a power lift that was somewhat similar to the more flexible Ferguson invention. Once the patent protection expired on the three-point hitch, it became an industry standard.
Almost every tractor today features Ferguson's three-point linkage or a derivative of it. This hitch allows for easy attachment and detachment of implements while allowing the implement to function as a part of the tractor, almost as if it were attached by a fixed mount. Previously, when the implement hit an obstacle, the towing link broke or the tractor flipped over. Ferguson's idea was to combine a connection via two lower and one upper lift arms that were connected to a hydraulic lifting ram. The ram was, in turn, connected to the upper of the three links so the increased drag (as when a plough hits a rock) caused the hydraulics to lift the implement until the obstacle was passed.
Recently, Bobcat's patent on its front loader connection (inspired by these earlier systems) has expired, and compact tractors are now being outfitted with quick-connect attachments for their front-end loaders.
Power take-off systems and hydraulics
In addition to towing an implement or supplying tractive power through the wheels, most tractors have a means to transfer power to another machine such as a baler, swather, or mower. Unless it functions solely by pulling it through or over the ground, a towed implement needs its own power source (such as a baler or combine with a separate engine) or else a means of transmitting power from the tractor to the mechanical operations of the equipment. | Tractor | Wikipedia | 505 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Early tractors used belts or cables wrapped around the flywheel or a separate belt pulley to power stationary equipment, such as a threshing machine, buzz saw, silage blower, or stationary baler. In most cases, it was impractical for the tractor and equipment to move with a flexible belt or cable between them, so this system required the tractor to remain in one location, with the work brought to the equipment, or the tractor to be relocated at each turn and the power set-up reapplied (as in cable-drawn plowing systems used in early steam tractor operations).
Modern tractors use a power take-off (PTO) shaft to provide rotary power to machinery that may be stationary or pulled. The PTO shaft generally is at the rear of the tractor, and can be connected to an implement that is either towed by a drawbar or a three-point hitch. This eliminates the need for a separate, implement-mounted power source, which is almost never seen in modern farm equipment. It is also optional to get a front PTO as well when buying a new tractor.
Virtually all modern tractors can also provide external hydraulic fluid and electrical power to the equipment they are towing, either by hoses or wires.
Operation
Modern tractors have many electrical switches and levers in the cab for controlling the multitude of different functions available on the tractor.
Pedals
Some modern farm tractors retain a traditional manual transmission; increasingly they have hydraulically driven powershift transmissions and CVT, which vastly simplify operation.
Those with powershift transmissions have identical pedal arrangements on the floor for the operator to actuate, replacing a clutch pedal on the far left with an inching pedal that cuts off hydraulic flow to the clutches. Twinned brake pedals – one each for left and right side wheels – are placed together on the right side. Some have a pedal for a foot throttle on the far right. Unlike automobiles, throttle speed can also be controlled by a hand-operated lever ("hand throttle"), which may be set to a fixed position. This helps provide a constant speed in field work. It also helps provide continuous power for stationary tractors that are operating an implement by PTO shaft or axle driven belt. The foot throttle gives the operator more automobile-like control over the speed of a mobile tractor in any operation. | Tractor | Wikipedia | 475 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Some modern tractors also have (or offer as optional equipment) a button on the gear stick for controlling the clutch, in addition to the standard pedal, allowing for gear changes and the tractor to be brought to a stop without using the foot pedal to engage the clutch. Others have a button for temporarily increasing throttle speed to improve hydraulic flow to implements, such as a front end loader bucket.
Independent left and right brake pedals are provided to allow improved steering (by engaging the side one wishes to turn to, slowing or stopping its wheel) and improved traction in soft and slippery conditions (by transferring rotation to the wheel with better grip). Some users prefer to lock both pedals together, or utilize a partial lock that allows the left pedal to be depressed independently but engages both when the right is applied. This may be in the form of a swinging or sliding bolt that may be readily engaged or disengaged in the field without tools.
Foot pedal throttle control is mostly a returning feature of newer tractors. In the UK, foot pedal use to control engine speed while travelling on the road is mandatory. Some tractors, especially those designed for row-crop work, have a 'de-accelerator' pedal, which operates in the reverse fashion of an automobile throttle, slowing the engine when applied. This allows control over the speed of a tractor with its throttle set high for work, as when repeatedly slowing to make U-turns at the end of crop rows in fields.
A front-facing foot button is traditionally included just ahead of the driver's seat (designed to be pressed by the operator's heel) to engage the rear differential lock (diff-lock), which prevents wheel slip. The differential normally allows driving wheels to operate at their own speeds, as required, for example, by the different radius each takes in a turn. This allows the outside wheel to travel faster than the inside wheel, thereby traveling further during a turn. In low-traction conditions on a soft surface, the same mechanism can allow one wheel to slip, wasting its torque and further reducing traction. The differential lock overrides this, forcing both wheels to turn at the same speed, reducing wheel slip and improving traction. Care must be taken to unlock the differential before turning, usually by hitting the pedal a second time, since the tractor with good traction cannot perform a turn with the diff-lock engaged. In many modern tractors, this pedal is replaced with an electrical switch. | Tractor | Wikipedia | 495 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Levers and switches
Many functions once controlled with levers have been replaced with some model of electrical switch with the rise of indirect computer controlling of functions in modern tractors.
Until the late of the 1950s, tractors had a single register of gears, hence one gear stick, often with three to five forward gears and one reverse. Then, group gears were introduced, and another gear stick was added. Later, control of the forward-reverse direction was moved to a special stick attached at the side of the steering wheel, which allowed forward or reverse travel in any gear. Now, with CVTs or other gear types, fewer sticks control the transmission, and some are replaced with electrical switches or are totally computer-controlled.
The three-point hitch was controlled with a lever for adjusting the position, or as with the earliest ones, just the function for raising or lowering the hitch. With modern electrical systems, it is often replaced with a potentiometer for the lower bound position and another one for the upper bound, and a switch allowing automatic adjustment of the hitch between these settings.
The external hydraulics also originally had levers, but now are often replaced with some form of electrical switch; the same is true for the power take-off shaft.
Safety
Agriculture in the United States is one of the most hazardous industries, only surpassed
by mining and construction. No other farm machine is so identified with the hazards of production agriculture as the tractor. Tractor-related injuries account for approximately 32% of the fatalities and 6% of the nonfatal injuries in agriculture. Over 50% is attributed to tractor overturns.
The roll-over protection structure (ROPS) and seat belt, when worn, are the most important safety devices to protect operators from death during tractor overturns.
Modern tractors have a ROPS to prevent an operator from being crushed when overturning. This is especially important in open-air tractors, where the ROPS is a steel beam that extends above the operator's seat. For tractors with operator cabs, the ROPS is part
of the frame of the cab. A ROPS with enclosed cab further reduces the likelihood of serious injury because the operator is protected by the sides and windows of the cab. | Tractor | Wikipedia | 446 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
These structures were first required by legislation in Sweden in 1959. Before they were required, some farmers died when their tractors rolled on top of them. Row-crop tractors, before ROPS, were particularly dangerous because of their 'tricycle' design with the two front wheels spaced close together and angled inward toward the ground. Some farmers were killed by rollovers while operating tractors along steep slopes. Others have been killed while attempting to tow or pull an excessive load from above axle height, or when cold weather caused the tires to freeze to the ground, in both cases causing the tractor to pivot around the rear axle. ROPS were first required in the United States in 1986, non-retroactively. ROPS adoption by farmers is thus incomplete. To treat this problem, CROPS (cost-effective roll-over protection structures) have been developed to encourage farmers to retrofit older tractors.
For the ROPS to work as designed, the operator must stay within its protective frame and wear the seat belt.
In addition to ROPS, U.S. manufacturers add instructional seats on tractors with enclosed cabs. The tractors have a ROPS with seatbelts for both the operator and passenger. This instructional seat is intended to be used for training new tractor operators, but can also be used to diagnose machine problems.
The misuse of an instructional seat increases the likelihood of injury, especially when children are transported. The International Organization for Standardization's ISO standard 23205:2014 specifies the minimum design and performance requirements for an instructional seat and states that the instructional seat is neither intended for, nor is it designed for use by children. Despite this, upwards of 40% of farm families give their children rides on tractors, often using these instructional seats.
Applications and variations
Farm
The most common use of the term "tractor" is for the vehicles used on farms. The farm tractor is used for pulling or pushing agricultural machinery or trailers, for plowing, tilling, disking, harrowing, planting, and similar tasks. | Tractor | Wikipedia | 408 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
A variety of specialty farm tractors have been developed for particular uses. These include "row crop" tractors with adjustable tread width to allow the tractor to pass down rows of cereals, maize, tomatoes or other crops without crushing the plants, "wheatland" or "standard" tractors with fixed wheels and a lower center of gravity for plowing and other heavy field work for broadcast crops, and "high crop" tractors with adjustable tread and increased ground clearance, often used in the cultivation of cotton and other high-growing row crop plant operations, and "utility tractors", typically smaller tractors with a low center of gravity and short turning radius, used for general purposes around the farmstead. Many utility tractors are used for nonfarm grading, landscape maintenance and excavation purposes, particularly with loaders, backhoes, pallet forks and similar devices. Small garden or lawn tractors designed for suburban and semirural gardening and landscape maintenance are produced in a variety of configurations, and also find numerous uses on a farmstead.
Some farm-type tractors are found elsewhere than on farms: with large universities' gardening departments, in public parks, or for highway workman use with blowtorch cylinders strapped to the sides and a pneumatic drill air compressor permanently fastened over the power take-off. These are often fitted with grass (turf) tyres which are less damaging to soft surfaces than agricultural tires.
Precision
Space technology has been incorporated into agriculture in the form of GPS devices, and robust on-board computers installed as optional features on farm tractors. These technologies are used in modern, precision farming techniques. The spin-offs from the space race have actually facilitated automation in plowing and the use of autosteer systems (drone on tractors that are manned but only steered at the end of a row), the idea being to neither overlap and use more fuel nor leave streaks when performing jobs such as cultivating. Several tractor companies have also been working on producing a driverless tractor.
Engineering
The durability and engine power of tractors made them very suitable for engineering tasks. Tractors can be fitted with engineering tools such as dozer blades, buckets, hoes, rippers, etc. The most common attachments for the front of a tractor are dozer blades or buckets. When attached to engineering tools, the tractor is called an engineering vehicle. | Tractor | Wikipedia | 471 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
A bulldozer is a track-type tractor with a blade attached in the front and a rope-winch behind. Bulldozers are very powerful tractors and have excellent ground-hold, as their main tasks are to push or drag.
Bulldozers have been further modified over time to evolve into new machines which are capable of working in ways that the original bulldozer can not. One example is that loader tractors were created by removing the blade and substituting a large volume bucket and hydraulic arms which can raise and lower the bucket, thus making it useful for scooping up earth, rock and similar loose material to load it into trucks.
A front-loader or loader is a tractor with an engineering tool which consists of two hydraulic powered arms on either side of the front engine compartment and a tilting implement. This is usually a wide-open box called a bucket, but other common attachments are a pallet fork and a bale grappler.
Other modifications to the original bulldozer include making the machine smaller to let it operate in small work areas where movement is limited. Also, tiny wheeled loaders, officially called skid-steer loaders, but nicknamed "Bobcat" after the original manufacturer, are particularly suited for small excavation projects in confined areas.
Backhoe
The most common variation of the classic farm tractor is the backhoe, also called a backhoe-loader. As the name implies, it has a loader assembly on the front and a backhoe on the back. Backhoes attach to a three-point hitch on farm or industrial tractors. Industrial tractors are often heavier in construction, particularly with regards to the use of a steel grill for protection from rocks and the use of construction tires. When the backhoe is permanently attached, the machine usually has a seat that can swivel to the rear to face the hoe controls. Removable backhoe attachments almost always have a separate seat on the attachment.
Backhoe-loaders are very common and can be used for a wide variety of tasks: construction, small demolitions, light transportation of building materials, powering building equipment, digging holes, loading trucks, breaking asphalt and paving roads. Some buckets have retractable bottoms, enabling them to empty their loads more quickly and efficiently. Buckets with retractable bottoms are also often used for grading and scratching off sand. The front assembly may be a removable attachment or permanently mounted. Often the bucket can be replaced with other devices or tools. | Tractor | Wikipedia | 508 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Their relatively small frames and precise controls make backhoe-loaders very useful and common in urban engineering projects, such as construction and repairs in areas too small for larger equipment. Their versatility and compact size make them one of the most popular urban construction vehicles.
In the UK and Ireland, the word "JCB" is used colloquially as a genericized trademark for any such type of engineering vehicle. The term JCB now appears in the Oxford English Dictionary, although it is still legally a trademark of J. C. Bamford Ltd. The term "digger" is also commonly used.
Compact utility
A compact utility tractor (CUT) is a smaller version of an agricultural tractor, but designed primarily for landscaping and estate management tasks, rather than for planting and harvesting on a commercial scale. Typical CUTs range from with available power take-off (PTO) power ranging from . CUTs are often equipped with both a mid-mounted and a standard rear PTO, especially those below . The mid-mount PTO shaft typically rotates at/near 2000 rpm and is typically used to power mid-mount finish mowers, front-mounted snow blowers or front-mounted rotary brooms. The rear PTO is standardized at 540 rpm for the North American markets, but in some parts of the world, a dual 540/1000 rpm PTO is standard, and implements are available for either standard in those markets.
One of the most common attachments for a CUT is the front-end loader or FEL. Like the larger agricultural tractors, a CUT will have an adjustable, hydraulically controlled three-point hitch. Typically, a CUT will have four-wheel drive, or more correctly four-wheel assist. Modern CUTs often feature hydrostatic transmissions, but many variants of gear-drive transmissions are also offered from low priced, simple gear transmissions to synchronized transmissions to advanced glide-shift transmissions. All modern CUTs feature government-mandated roll over protection structures just like agricultural tractors. The most well-known brands in North America include Kubota, John Deere Tractor, New Holland Ag, Case-Farmall and Massey Ferguson. Although less common, compact backhoes are often attached to compact utility tractors. | Tractor | Wikipedia | 444 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Compact utility tractors require special, smaller implements than full-sized agricultural tractors. Very common implements include the box blade, the grader blade, the landscape rake, the post hole digger (or post hole auger), the rotary cutter (slasher or a brush hog), a mid- or rear-mount finish mower, a broadcast seeder, a subsoiler and the rototiller (rotary tiller). In northern climates, a rear-mounted snow blower is very common; some smaller CUT models are available with front-mounted snow blowers powered by mid-PTO shafts. Implement brands outnumber tractor brands, so CUT owners have a wide selection of implements.
For small-scale farming or large-scale gardening, some planting and harvesting implements are sized for CUTs. One- and two-row planting units are commonly available, as are cultivators, sprayers and different types of seeders (slit, rotary and drop). One of the first CUTs offered for small farms of three to 30 acres and for small jobs on larger farms was a three-wheeled unit, with the rear wheel being the drive wheel, offered by Sears & Roebuck in 1954 and priced at $598 for the basic model.
An even smaller variant of the compact utility tractor is the subcompact utility tractor. Although these tractors are often barely larger than a riding lawn mower, these tractors have all the same features of a compact tractor, such as a three-point hitch, power steering, four-wheel-drive, and front-end loader. These tractors are generally marketed towards homeowners who intend to mostly use them for lawn mowing, with the occasional light landscaping task.
Standard
The earliest tractors were called "standard" tractors, and were intended almost solely for plowing and harrowing before planting, which were difficult tasks for humans and draft animals. They were characterized by a low, rearward seating position, fixed-width tread, and low ground clearance. These early tractors were cumbersome, and ill-suited to enter a field of planted row crops for weed control. The "standard" tractor definition is no longer in current use. However, tractors with fixed wheel spacing and a low center of gravity are well-suited as loaders, forklifts and backhoes, so that the configuration continues in use without the "standard" nomenclature.
Row-crop | Tractor | Wikipedia | 490 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
A general-purpose or row-crop tractor is tailored specifically to the growing of crops grown in rows, and most especially to cultivating these crops. These tractors are universal machines, capable of both primary tillage and cultivation of a crop.
The row-crop tractor category evolved rather than appearing overnight, but the International Harvester (IH) Farmall is often considered the "first" tractor of the category. Some earlier tractors of the 1910s and 1920s approached the form factor from the heavier side, as did motorized cultivators from the lighter side, but the Farmall brought all of the salient features together into one package, with a capable distribution network to ensure its commercial success. In the new form factor that the Farmall popularized, the cultivator was mounted in the front so it was easily visible. Additionally, the tractor had a narrow front end; the front tires were spaced very closely and angled in toward the bottom. The back wheels straddled two rows with their spacing adjustable depending on row spacing, and the unit could cultivate four rows at once. Where wide front wheels were used, they often could be adjusted as well. Tractors with non-adjustable spacing were called "standard" or "wheatland", and were chiefly meant for pulling plows or other towed implements, typically with a lower overall tractor height than row-crop models.
From 1924 until 1963, Farmalls were the largest selling row-crop tractors.
To compete, John Deere designed the Model C, which had a wide front and could cultivate three rows at once. Only 112 prototypes were made, as Deere realized it would lose sales to Farmall if its model did less. In 1928, Deere released the Model C anyway, only as the Model GP (General Purpose) to avoid confusion with the Model D when ordered over the then unclear telephone.
Oliver refined its "Row Crop" model early in 1930. Until 1935, the 18–27 was Oliver–Hart-Parr's only row-crop tractor.
Many Oliver row-crop models are referred to as "Oliver Row Crop 77", "Oliver Row Crop 88", etc. | Tractor | Wikipedia | 437 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Many early row-crop tractors had a tricycle design with two closely spaced front tires, and some even had a single front tire. This made it dangerous to operate on the side of a steep hill; as a result, many farmers died from tractor rollovers. Also, early row-crop tractors had no rollover protection system (ROPS), meaning if the tractor flipped back, the operator could be crushed. Sweden was the first country which passed legislation requiring ROPS, in 1959.
Over 50% of tractor related injuries and deaths are attributed to tractor rollover.
Canadian agricultural equipment manufacturer Versatile makes row-crop tractors that are ; powered by an 8.9 liter Cummins Diesel engine.
Case IH and New Holland of CNH Industrial both produce high horsepower front-wheel-assist row crop tractors with available rear tracks. Case IH also has a four-wheel drive track system called Rowtrac.
John Deere has an extensive line of available row crop tractors ranging from .
Modern row crop tractors have rollover protection systems in the form of a reinforced cab or a roll bar.
Garden
Garden tractors, sometimes called lawn tractors, are small, light tractors designed for use in domestic gardens, lawns, and small estates. Lawn tractors are designed for cutting grass and snow removal, while garden tractors are for small property cultivation. In the U.S., the term riding lawn mower today often is used to refer to mid- or rear-engined machines. Front-engined tractor layout machines designed primarily for cutting grass and light towing are called lawn tractors; heavier-duty tractors of similar size are garden tractors. Garden tractors are capable of mounting a wider array of attachments than lawn tractors. Unlike lawn tractors and rear-engined riding mowers, garden tractors are powered by horizontal-crankshaft engines with a belt-drive to transaxle-type transmissions (usually of four or five speeds, although some may also have two-speed reduction gearboxes, drive-shafts, or hydrostatic or hydraulic drives). Garden tractors from Wheel Horse, Cub Cadet, Economy (Power King), John Deere, Massey Ferguson and Case Ingersoll are built in this manner. The engines are generally one- or two-cylinder petrol (gasoline) engines, although diesel engine models are also available, especially in Europe. Typically, diesel-powered garden tractors are larger and heavier-duty than gasoline-powered units and compare more similarly to compact utility tractors. | Tractor | Wikipedia | 495 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Visually, the distinction between a garden tractor and a lawn tractor is often hard to make – generally, garden tractors are more sturdily built, with stronger frames, 12-inch or larger wheels mounted with multiple lugs (most lawn tractors have a single bolt or clip on the hub), heavier transaxles, and ability to accommodate a wide range of front, belly, and rear mounted attachments.
Two-wheel
Although most people think primarily of four-wheel vehicles when they think of tractors, a tractor may have one or more axles. The key benefit is the power itself, which only takes one axle to provide. Single-axle tractors, more often called two-wheel tractors or walk-behind tractors, have had many users since the introduction of the internal combustion engine tractors. They tend to be small and affordable, this was especially true before the 1960s when a walk-behind tractor could often be more affordable than a two-axle tractor of comparable power. Today's compact utility tractors and advanced garden tractors may negate most of that market advantage, but two-wheel tractors still have a following, especially among those who already own one. Countries where two-wheel tractors are especially prevalent today include Thailand, China, Bangladesh, India, and other Southeast Asia countries. Most two-wheel tractors today are specialty tractors made for one purpose, such as snow blowers, push tillers, and self propelled push mowers.
Orchard
Tractors tailored to use in fruit orchards typically have features suited to passing under tree branches with impunity. These include a lower overall profile; reduced tree-branch-snagging risk (via underslung exhaust pipes rather than smoke-stack-style exhaust, and large sheetmetal cowlings and fairings that allow branches to deflect and slide off rather than catch); spark arrestors on the exhaust tips; and often wire cages to protect the operator from snags.
Automobile conversions and other homemade versions | Tractor | Wikipedia | 395 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
The ingenuity of farm mechanics, coupled in some cases with OEM or aftermarket assistance, has often resulted in the conversion of automobiles for use as farm tractors. In the United States, this trend was especially strong from the 1910s through 1950s. It began early in the development of vehicles powered by internal combustion engines, with blacksmiths and amateur mechanics tinkering in their shops. Especially during the interwar period, dozens of manufacturers (Montgomery Ward among them) marketed aftermarket kits for converting Ford Model Ts for use as tractors. (These were sometimes called 'Hoover wagons' during the Great Depression, although this term was usually reserved for automobiles converted to horse-drawn buggy use when gasoline was unavailable or unaffordable. During the same period, another common name was "Doodlebug", after the popular kit by the same name.) Ford even considered producing an "official" optional kit. Many Model A Fords also were converted for this purpose. In later years, some farm mechanics have been known to convert more modern trucks or cars for use as tractors, more often as curiosities or for recreational purposes (rather than out of the earlier motives of pure necessity or frugality).
During World War II, a shortage of tractors in Sweden led to the development of the so-called "EPA" tractor (EPA was a chain of discount stores and it was often used to signify something lacking in quality). An EPA tractor was simply an automobile, truck or lorry, with the passenger space cut off behind the front seats, equipped with two gearboxes in a row. When done to an older car with a ladder frame, the result was similar to a tractor and could be used as one. After the war it remained popular as a way for young people without a driver's license to own something similar to a car. Since it was legally seen as a tractor, it could be driven from 16 years of age and only required a tractor license. Eventually, the legal loophole was closed and no new EPA tractors were allowed to be made, but the remaining ones were still legal, which led to inflated prices and many protests from people who preferred EPA tractors to ordinary cars.
The Swedish government eventually replaced them with the so called "A-tractor" which now had its speed limited to 30 km/h and allowed people aged 16 and older to drive the cars with a moped license. | Tractor | Wikipedia | 488 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
The German occupation of Italy during World resulted in a severe shortage of mechanized farm equipment. The destruction of tractors was a sort of scorched-earth strategy used to reduce the independence of the conquered. The shortage of tractors in that area of Europe was the origin of Lamborghini. The war was also the inspiration for dual-purpose vehicles such as the Land Rover. Based on the Jeep, the company made a vehicle that combined PTO, tillage, 4wd, and transportation.
In March 1975, a similar type of vehicle was introduced in Sweden, the A tractor [from arbetstraktor (work tractor)]; the main difference is an A tractor has a top speed of 30 km/h. This is usually done by fitting two gearboxes in a row and only using one. The Volvo Duett was, for a long time, the primary choice for conversion to an EPA or A tractor, but since supplies have dried up, other cars have been used, in most cases another Volvo. The SFRO is a Swedish organization advocating homebuilt and modified vehicles.
Another type of homemade tractors are ones that are fabricated from scratch. The "from scratch" description is relative, as often individual components will be repurposed from earlier vehicles or machinery (e.g., engines, gearboxes, axle housings), but the tractor's overall chassis is essentially designed and built by the owner (e.g., a frame is welded from bar stockchannel stock, angle stock, flat stock, etc.). As with automobile conversions, the heyday of this type of tractor, at least in developed economies, lies in the past, when there were large populations of blue-collar workers for whom metalworking and farming were prevalent parts of their lives. (For example, many 19th- and 20th-century New England and Midwestern machinists and factory workers had grown up on farms.) Backyard fabrication was a natural activity to them (whereas it might seem daunting to most people today). | Tractor | Wikipedia | 412 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Nomenclature
The term "tractor" (US and Canada) or "tractor unit" (UK) is also applied to:
Road tractors, tractor units or traction heads, familiar as the front end of an articulated lorry / semi-trailer truck. They are heavy-duty vehicles with large engines and several axles.
The majority of these tractors are designed to pull long semi-trailers, most often to transport freight over a significant distance, and is connected to the trailer with a fifth wheel coupling. In England, this type of "tractor" is often called an "artic cab" (short for "articulated" cab).
A minority is the ballast tractor, whose load is hauled from a drawbar.
Pushback tractors are used on airports to move aircraft on the ground, most commonly pushing aircraft away from their parking stands.
Locomotive tractors (engines) or rail car movers – the amalgamation of machines, electrical generators, controls and devices that comprise the traction component of railway vehicles
Artillery tractors – vehicles used to tow artillery pieces of varying weights.
NASA and other space agencies use very large tractors to move large launch vehicles and Space Shuttles between their hangars and launch pads.
A pipe-tractor is a device used for conveying advanced instruments into pipes for measurement and data logging, and the purging of well holes, sewer pipes and other inaccessible tubes.
Nebraska tests
Nebraska tractor tests are tests mandated by the Nebraska Tractor Test Law and administered by the University of Nebraska, that objectively test the performance of all brands of tractors, 40 horsepower or more, sold in Nebraska. In the 1910s and 1920s, an era of snake oil sales and advertising tactics, the Nebraska tests helped farmers throughout North America to see through marketing claims and make informed buying decisions. The tests continue today, making sure tractors fulfill the manufacturer's advertised claims.
Manufacturers
Some of the many tractor manufacturers and brands worldwide include:
Belarus
Case IH
Caterpillar
Claas
Challenger
Deutz-Fahr
Fendt
ITMCO
Iseki
JCB
John Deere
Lamborghini
Landini
Kubota
Mahindra Tractors
Massey Ferguson
McCormick
Mercedes-Benz
New Holland
SAME
Steyr
TAFE
Ursus
Valtra
Zetor
In addition to commercial manufacturers, the Open Source Ecology group has developed several working prototypes of an open source hardware tractor called the LifeTrac as part of its Global Village Construction Set.
Gallery | Tractor | Wikipedia | 474 | 152692 | https://en.wikipedia.org/wiki/Tractor | Technology | Other | null |
Sculptor is a faint constellation in the southern sky. It represents a sculptor. It was introduced by Nicolas Louis de Lacaille in the 18th century. He originally named it Apparatus Sculptoris (the sculptor's studio), but the name was later shortened.
History
The region to the south of Cetus and Aquarius had been named by Aratus in 270 BC as The Waters – an area of scattered faint stars with two brighter stars standing out. Professor of astronomy Bradley Schaefer has proposed that these stars were most likely Alpha and Delta Sculptoris.
The French astronomer Nicolas-Louis de Lacaille first described the constellation in French as l'Atelier du Sculpteur (the sculptor's studio) in 1751–52, depicting a three-legged table with a carved head on it, and an artist's mallet and two chisels on a block of marble alongside it. Lacaille had observed and catalogued almost 10,000 southern stars during a two-year stay at the Cape of Good Hope, devising fourteen new constellations in uncharted regions of the Southern Celestial Hemisphere not visible from Europe. He named all but one in honour of instruments that symbolised the Age of Enlightenment.
Characteristics
Sculptor is a small constellation bordered by Aquarius and Cetus to the north, Fornax to the east, Phoenix to the south, Grus to the southwest, and Piscis Austrinus to the west. The bright star Fomalhaut is nearby. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Scl". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of 6 segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between and , while the declination coordinates are between −24.80° and −39.37°. The whole constellation is visible to observers south of latitude 50°N.
Notable features
Stars
No stars brighter than 3rd magnitude are located in Sculptor. This is explained by the fact that Sculptor contains the south galactic pole where stellar density is very low. Overall, there are 56 stars within the constellation's borders brighter than or equal to apparent magnitude 6.5.
The brightest star is Alpha Sculptoris, an SX Arietis-type variable star with a spectral type B7IIIp and an apparent magnitude of 4.3. It is 780 ± 30 light-years distant from Earth. | Sculptor (constellation) | Wikipedia | 511 | 152710 | https://en.wikipedia.org/wiki/Sculptor%20%28constellation%29 | Physical sciences | Other | Astronomy |
Eta Sculptoris is a red giant of spectral type M4III that varies between magnitudes 4.8 and 4.9, pulsating with multiple periods of 22.7, 23.5, 24.6, 47.3, 128.7 and 158.7 days. Estimated to be around 1,082 times as luminous as the Sun, it is 460 ± 20 light-years distant from Earth.
R Sculptoris is a red giant that has been found to be surrounded by spirals of matter likely ejected around 1800 years ago. It is 1,440 ± 90 light-years distant from Earth.
The Astronomical Society of Southern Africa in 2003 reported that observations of the Mira variable stars T, U, V and X Sculptoris were very urgently needed as data on their light curves was incomplete.
Deep sky objects
The constellation also contains the Sculptor Dwarf, a dwarf galaxy which is a member of the Local Group, as well as the Sculptor Group, the group of galaxies closest to the Local Group. The Sculptor Galaxy (NGC 253), a barred spiral galaxy and the largest member of the group, lies near the border between Sculptor and Cetus. Another prominent member of the group is the irregular galaxy NGC 55.
One unique galaxy in Sculptor is the Cartwheel Galaxy, at a distance of 500 million light-years. The result of a merger around 300 million years ago, the Cartwheel Galaxy has a core of older, yellow stars, and an outer ring of younger, blue stars, which has a diameter of 100,000 light-years. The smaller galaxy in the collision is now incorporated into the core, after moving from a distance of 250,000 light-years. The shock waves from the collision sparked extensive star formation in the outer ring.
Namesakes
Sculptor (AK-103) was a United States Navy Crater class cargo ship named after the constellation. | Sculptor (constellation) | Wikipedia | 376 | 152710 | https://en.wikipedia.org/wiki/Sculptor%20%28constellation%29 | Physical sciences | Other | Astronomy |
Intensive agriculture, also known as intensive farming (as opposed to extensive farming), conventional, or industrial agriculture, is a type of agriculture, both of crop plants and of animals, with higher levels of input and output per unit of agricultural land area. It is characterized by a low fallow ratio, higher use of inputs such as capital, labour, agrochemicals and water, and higher crop yields per unit land area.
Most commercial agriculture is intensive in one or more ways. Forms that rely heavily on industrial methods are often called industrial agriculture, which is characterized by technologies designed to increase yield. Techniques include planting multiple crops per year, reducing the frequency of fallow years, improving cultivars, mechanised agriculture, controlled by increased and more detailed analysis of growing conditions, including weather, soil, water, weeds, and pests. Modern methods frequently involve increased use of non-biotic inputs, such as fertilizers, plant growth regulators, pesticides, and antibiotics for livestock. Intensive farms are widespread in developed nations and increasingly prevalent worldwide. Most of the meat, dairy products, eggs, fruits, and vegetables available in supermarkets are produced by such farms.
Some intensive farms can use sustainable methods, although this typically necessitates higher inputs of labor or lower yields. Sustainably increasing agricultural productivity, especially on smallholdings, is an important way to decrease the amount of land needed for farming and slow and reverse environmental degradation caused by processes such as deforestation.
Intensive animal farming involves large numbers of animals raised on a relatively small area of land, for example by rotational grazing, or sometimes as concentrated animal feeding operations. These methods increase the yields of food and fiber per unit land area compared to those of extensive animal husbandry; concentrated feed is brought to seldom-moved animals, or, with rotational grazing, the animals are repeatedly moved to fresh forage.
History
Agricultural development in Britain between the 16th century and the mid-19th century saw a massive increase in agricultural productivity and net output. This in turn contributed to unprecedented population growth, freeing up a significant percentage of the workforce, and thereby helped enable the Industrial Revolution. Historians cited enclosure, mechanization, four-field crop rotation, and selective breeding as the most important innovations.
Industrial agriculture arose in the Industrial Revolution. By the early 19th century, agricultural techniques, implements, seed stocks, and cultivars had so improved that yield per land unit was many times that seen in the Middle Ages. | Intensive farming | Wikipedia | 497 | 152772 | https://en.wikipedia.org/wiki/Intensive%20farming | Technology | Forms | null |
The first phase involved a continuing process of mechanization. Horse-drawn machinery such as the McCormick reaper revolutionized harvesting, while inventions such as the cotton gin reduced the cost of processing. During this same period, farmers began to use steam-powered threshers and tractors. In 1892, the first gasoline-powered tractor was successfully developed, and in 1923, the International Harvester Farmall tractor became the first all-purpose tractor, marking an inflection point in the replacement of draft animals with machines. Mechanical harvesters (combines), planters, transplanters, and other equipment were then developed, further revolutionizing agriculture. These inventions increased yields and allowed individual farmers to manage increasingly large farms.
The identification of nitrogen, phosphorus, and potassium (NPK) as critical factors in plant growth led to the manufacture of synthetic fertilizers, further increasing crop yields. In 1909, the Haber-Bosch method to synthesize ammonium nitrate was first demonstrated. NPK fertilizers stimulated the first concerns about industrial agriculture, due to concerns that they came with side effects such as soil compaction, soil erosion, and declines in overall soil fertility, along with health concerns about toxic chemicals entering the food supply.
The discovery of vitamins and their role in nutrition, in the first two decades of the 20th century, led to vitamin supplements, which in the 1920s allowed some livestock to be raised indoors, reducing their exposure to adverse natural elements.
Following World War II synthetic fertilizer use increased rapidly.
The discovery of antibiotics and vaccines facilitated raising livestock by reducing diseases. Developments in logistics and refrigeration as well as processing technology made long-distance distribution feasible. Integrated pest management is the modern method to minimize pesticide use to more sustainable levels.
There are concerns over the sustainability of industrial agriculture, and the environmental effects of fertilizers and pesticides, which has given rise to the organic movement and has built a market for sustainable intensive farming, as well as funding for the development of appropriate technology.
Techniques and technologies
Livestock
Pasture intensification | Intensive farming | Wikipedia | 416 | 152772 | https://en.wikipedia.org/wiki/Intensive%20farming | Technology | Forms | null |
Pasture intensification is the improvement of pasture soils and grasses to increase the food production potential of livestock systems. It is commonly used to reverse pasture degradation, a process characterized by loss of forage and decreased animal carrying capacity which results from overgrazing, poor nutrient management, and lack of soil conservation. This degradation leads to poor pasture soils with decreased fertility and water availability and increased rates of erosion, compaction, and acidification. Degraded pastures have significantly lower productivity and higher carbon footprints compared to intensified pastures.
Management practices which improve soil health and consequently grass productivity include irrigation, soil scarification, and the application of lime, fertilizers, and pesticides. Depending on the productivity goals of the target agricultural system, more involved restoration projects can be undertaken to replace invasive and under-productive grasses with grass species that are better suited to the soil and climate conditions of the region. These intensified grass systems allow higher stocking rates with faster animal weight gain and reduced time to slaughter, resulting in more productive, carbon-efficient livestock systems.
Another technique to optimize yield while maintaining the carbon balance is the use of integrated crop-livestock (ICL) and crop-livestock-forestry (ICLF) systems, which combine several ecosystems into one optimized agricultural framework. Correctly performed, such production systems are able to create synergies potentially providing benefits to pastures through optimal plant usage, improved feed and fattening rates, increased soil fertility and quality, intensified nutrient cycling, integrated pest control, and improved biodiversity. The introduction of certain legume crops to pastures can increase carbon accumulation and nitrogen fixation in soils, while their digestibility helps animal fattening and reduces methane emissions from enteric fermentation. ICLF systems yield beef cattle productivity up to ten times that of degraded pastures; additional crop production from maize, sorghum, and soybean harvests; and greatly reduced greenhouse gas balances due to forest carbon sequestration.
In the Twelve Aprils grazing program for dairy production, developed by the USDA-SARE, forage crops for dairy herds are planted into a perennial pasture.
Rotational grazing | Intensive farming | Wikipedia | 428 | 152772 | https://en.wikipedia.org/wiki/Intensive%20farming | Technology | Forms | null |
Rotational grazing is a variety of foraging in which herds or flocks are regularly and systematically moved to fresh, rested grazing areas (sometimes called paddocks) to maximize the quality and quantity of forage growth. It can be used with cattle, sheep, goats, pigs, chickens, turkeys, ducks, and other animals. The herds graze one portion of pasture, or a paddock, while allowing the others to recover. Resting grazed lands allows the vegetation to renew energy reserves, rebuild shoot systems, and deepen root systems, resulting in long-term maximum biomass production. Pasture systems alone can allow grazers to meet their energy requirements, but rotational grazing is especially effective because grazers thrive on the more tender younger plant stems. Parasites are also left behind to die off, minimizing or eliminating the need for de-wormers. With the increased productivity of rotational systems, the animals may need less supplemental feed than in continuous grazing systems. Farmers can therefore increase stocking rates.
Concentrated animal feeding operations
Intensive livestock farming or "factory farming", is the process of raising livestock in confinement at high stocking density. "Concentrated animal feeding operations" (CAFO), or "intensive livestock operations", can hold large numbers (some up to hundreds of thousands) of cows, hogs, turkeys, or chickens, often indoors. The essence of such farms is the concentration of livestock in a given space. The aim is to provide maximum output at the lowest possible cost and with the greatest level of food safety. The term is often used pejoratively. CAFOs have dramatically increased the production of food from animal husbandry worldwide, both in terms of total food produced and efficiency.
Food and water is delivered to the animals, and therapeutic use of antimicrobial agents, vitamin supplements, and growth hormones are often employed. Growth hormones are not used on chickens nor on any animal in the European Union. Undesirable behaviors often related to the stress of confinement led to a search for docile breeds (e.g., with natural dominant behaviors bred out), physical restraints to stop interaction, such as individual cages for chickens, or physical modification such as the debeaking of chickens to reduce the harm of fighting. | Intensive farming | Wikipedia | 452 | 152772 | https://en.wikipedia.org/wiki/Intensive%20farming | Technology | Forms | null |
The CAFO designation resulted from the 1972 U.S. Federal Clean Water Act, which was enacted to protect and restore lakes and rivers to a "fishable, swimmable" quality. The United States Environmental Protection Agency identified certain animal feeding operations, along with many other types of industry, as "point source" groundwater polluters. These operations were subjected to regulation.
In 17 states in the U.S., isolated cases of groundwater contamination were linked to CAFOs. The U.S. federal government acknowledges the waste disposal issue and requires that animal waste be stored in lagoons. These lagoons can be as large as . Lagoons not protected with an impermeable liner can leak into groundwater under some conditions, as can runoff from manure used as fertilizer. A lagoon that burst in 1995 released 25 million gallons of nitrous sludge in North Carolina's New River. The spill allegedly killed eight to ten million fish.
The large concentration of animals, animal waste, and dead animals in a small space poses ethical issues to some consumers. Animal rights and animal welfare activists have charged that intensive animal rearing is cruel to animals.
Crops
The Green Revolution transformed farming in many developing countries. It spread technologies that had already existed, but had not been widely used outside of industrialized nations. These technologies included "miracle seeds", pesticides, irrigation, and synthetic nitrogen fertilizer.
Seeds
In the 1970s, scientists created high-yielding varieties of maize, wheat, and rice. These have an increased nitrogen-absorbing potential compared to other varieties. Since cereals that absorbed extra nitrogen would typically lodge (fall over) before harvest, semi-dwarfing genes were bred into their genomes. Norin 10 wheat, a variety developed by Orville Vogel from Japanese dwarf wheat varieties, was instrumental in developing wheat cultivars. IR8, the first widely implemented high-yielding rice to be developed by the International Rice Research Institute, was created through a cross between an Indonesian variety named "Peta" and a Chinese variety named "Dee Geo Woo Gen". | Intensive farming | Wikipedia | 420 | 152772 | https://en.wikipedia.org/wiki/Intensive%20farming | Technology | Forms | null |
With the availability of molecular genetics in Arabidopsis and rice the mutant genes responsible (reduced height (rht), gibberellin insensitive (gai1) and slender rice (slr1)) have been cloned and identified as cellular signalling components of gibberellic acid, a phytohormone involved in regulating stem growth via its effect on cell division. Photosynthate investment in the stem is reduced dramatically in shorter plants and nutrients become redirected to grain production, amplifying in particular the yield effect of chemical fertilizers.
High-yielding varieties outperformed traditional varieties several fold and responded better to the addition of irrigation, pesticides, and fertilizers. Hybrid vigour is utilized in many important crops to greatly increase yields for farmers. However, the advantage is lost for the progeny of the F1 hybrids, meaning seeds for annual crops need to be purchased every season, thus increasing costs and profits for farmers.
Crop rotation
Crop rotation or crop sequencing is the practice of growing a series of dissimilar types of crops in the same space in sequential seasons for benefits such as avoiding pathogen and pest buildup that occurs when one species is continuously cropped. Crop rotation also seeks to balance the nutrient demands of various crops to avoid soil nutrient depletion. A traditional component of crop rotation is the replenishment of nitrogen through the use of legumes and green manure in sequence with cereals and other crops. Crop rotation can also improve soil structure and fertility by alternating deep-rooted and shallow-rooted plants. A related technique is to plant multi-species cover crops between commercial crops. This combines the advantages of intensive farming with continuous cover and polyculture.
Irrigation
Crop irrigation accounts for 70% of the world's fresh water use. Flood irrigation, the oldest and most common type, is typically unevenly distributed, as parts of a field may receive excess water in order to deliver sufficient quantities to other parts. Overhead irrigation, using center-pivot or lateral-moving sprinklers, gives a much more equal and controlled distribution pattern. Drip irrigation is the most expensive and least-used type, but delivers water to plant roots with minimal losses. | Intensive farming | Wikipedia | 452 | 152772 | https://en.wikipedia.org/wiki/Intensive%20farming | Technology | Forms | null |
Water catchment management measures include recharge pits, which capture rainwater and runoff and use it to recharge groundwater supplies. This helps in the replenishment of groundwater wells and eventually reduces soil erosion. Dammed rivers creating reservoirs store water for irrigation and other uses over large areas. Smaller areas sometimes use irrigation ponds or groundwater.
Weed control
In agriculture, systematic weed management is usually required, often performed by machines such as cultivators or liquid herbicide sprayers. Herbicides kill specific targets while leaving the crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often based on plant hormones. Weed control through herbicide is made more difficult when the weeds become resistant to the herbicide. Solutions include:
Cover crops (especially those with allelopathic properties) that out-compete weeds or inhibit their regeneration
Multiple herbicides, in combination or in rotation
Strains genetically engineered for herbicide tolerance
Locally adapted strains that tolerate or out-compete weeds
Tilling
Ground cover such as mulch or plastic
Manual removal
Mowing
Grazing
Burning
Terracing
In agriculture, a terrace is a leveled section of a hilly cultivated area, designed as a method of soil conservation to slow or prevent the rapid surface runoff of irrigation water. Often such land is formed into multiple terraces, giving a stepped appearance. The human landscapes of rice cultivation in terraces that follow the natural contours of the escarpments, like contour ploughing, are a classic feature of the island of Bali and the Banaue Rice Terraces in Banaue, Ifugao, Philippines. In Peru, the Inca made use of otherwise unusable slopes by building drystone walls to create terraces known as Andéns.
Rice paddies | Intensive farming | Wikipedia | 346 | 152772 | https://en.wikipedia.org/wiki/Intensive%20farming | Technology | Forms | null |
A paddy field is a flooded parcel of arable land used for growing rice and other semiaquatic crops. Paddy fields are a typical feature of rice-growing countries of east and southeast Asia, including Malaysia, China, Sri Lanka, Myanmar, Thailand, Korea, Japan, Vietnam, Taiwan, Indonesia, India, and the Philippines. They are also found in other rice-growing regions such as Piedmont (Italy), the Camargue (France), and the Artibonite Valley (Haiti). They can occur naturally along rivers or marshes, or can be constructed, even on hillsides. They require large water quantities for irrigation, much of it from flooding. It gives an environment favourable to the strain of rice being grown, and is hostile to many species of weeds. As the only draft animal species which is comfortable in wetlands, the water buffalo is in widespread use in Asian rice paddies.
A recent development in the intensive production of rice is the System of Rice Intensification. Developed in 1983 by the French Jesuit Father Henri de Laulanié in Madagascar, by 2013 the number of smallholder farmers using the system had grown to between 4 and 5 million.
Aquaculture
Aquaculture is the cultivation of the natural products of water (fish, shellfish, algae, seaweed, and other aquatic organisms). Intensive aquaculture takes place on land using tanks, ponds, or other controlled systems, or in the ocean, using cages.
Sustainability
Intensive farming practices which are thought to be sustainable have been developed to slow the deterioration of agricultural land and even regenerate soil health and ecosystem services. These developments may fall in the category of organic farming, or the integration of organic and conventional agriculture.
Pasture cropping involves planting grain crops directly into grassland without first applying herbicides. The perennial grasses form a living mulch understory to the grain crop, eliminating the need to plant cover crops after harvest. The pasture is intensively grazed both before and after grain production. This intensive system yields equivalent farmer profits (partly from increased livestock forage) while building new topsoil and sequestering up to 33 tons of CO2/ha/year.
Biointensive agriculture focuses on maximizing efficiency such as per unit area, energy input and water input.
Agroforestry combines agriculture and orchard/forestry technologies to create more integrated, diverse, productive, profitable, healthy and sustainable land-use systems. | Intensive farming | Wikipedia | 489 | 152772 | https://en.wikipedia.org/wiki/Intensive%20farming | Technology | Forms | null |
Intercropping can increase yields or reduce inputs and thus represents (potentially sustainable) agricultural intensification. However, while total yield per unit land area is often increased, yields of any single crop often decrease. There are also challenges to farmers who rely on farming equipment optimized for monoculture, often resulting in increased labor inputs.
Vertical farming is intensive crop production on a large scale in urban centers, in multi-story, artificially-lit structures, for the production of low-calorie foods like herbs, microgreens, and lettuce.
An integrated farming system is a progressive, sustainable agriculture system such as zero waste agriculture or integrated multi-trophic aquaculture, which involves the interactions of multiple species. Elements of this integration can include:
Intentionally introducing flowering plants into agricultural ecosystems to increase pollen-and nectar-resources required by natural enemies of insect pests
Using crop rotation and cover crops to suppress nematodes in potatoes
Integrated multi-trophic aquaculture is a practice in which the by-products (wastes) from one species are recycled to become inputs (fertilizers, food) for another.
Challenges
Environmental impact
Industrial agriculture uses huge amounts of water, energy, and industrial chemicals, increasing pollution in the arable land, usable water, and atmosphere. Herbicides, insecticides, and fertilizers accumulate in ground and surface waters. Industrial agricultural practices are one of the main drivers of global warming, accounting for 14–28% of net greenhouse gas emissions.
Many of the negative effects of industrial agriculture may emerge at some distance from fields and farms. Nitrogen compounds from the Midwest, for example, travel down the Mississippi to degrade coastal fisheries in the Gulf of Mexico, causing so-called oceanic dead zones.
Many wild plant and animal species have become extinct on a regional or national scale, and the functioning of agro-ecosystems has been profoundly altered. Agricultural intensification includes a variety of factors, including the loss of landscape elements, increased farm and field sizes, and increase usage of insecticides and herbicides. The large scale of insecticides and herbicides lead to the rapid developing resistance among pests renders herbicides and insecticides increasingly ineffective. Agrochemicals have may be involved in colony collapse disorder, in which the individual members of bee colonies disappear. (Agricultural production is highly dependent on bees to pollinate many varieties of fruits and vegetables.) | Intensive farming | Wikipedia | 488 | 152772 | https://en.wikipedia.org/wiki/Intensive%20farming | Technology | Forms | null |
Intensive farming creates conditions for parasite growth and transmission that are vastly different from what parasites encounter in natural host populations, potentially altering selection on a variety of traits such as life-history traits and virulence. Some recent epidemic outbreaks have highlighted the association with intensive agricultural farming practices. For example the infectious salmon anaemia (ISA) virus is causing significant economic loss for salmon farms. The ISA virus is an orthomyxovirus with two distinct clades, one European and one North American, that diverged before 1900 (Krossøy et al. 2001). This divergence suggests that an ancestral form of the virus was present in wild salmonids prior to the introduction of cage-cultured salmonids. As the virus spread from vertical transmission (parent to offspring).
Intensive monoculture increases the risk of failures due to pests, adverse weather and disease.
Social impact
A study for the U.S. Office of Technology Assessment concluded that regarding industrial agriculture, there is a "negative relationship between the trend toward increasing farm size and the social conditions in rural communities" on a "statistical level". Agricultural monoculture can entail social and economic risks. | Intensive farming | Wikipedia | 234 | 152772 | https://en.wikipedia.org/wiki/Intensive%20farming | Technology | Forms | null |
In a multicellular organism, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a function. Tissues of different types combine to form an organ which has a specific function. The intestinal wall for example is formed by epithelial tissue and smooth muscle tissue. Two or more organs working together in the execution of a specific body function form an organ system, also called a biological system or body system.
An organ's tissues can be broadly categorized as parenchyma, the functional tissue, and stroma, the structural tissue with supportive, connective, or ancillary functions. For example, the gland's tissue that makes the hormones is the parenchyma, whereas the stroma includes the nerves that innervate the parenchyma, the blood vessels that oxygenate and nourish it and carry away its metabolic wastes, and the connective tissues that provide a suitable place for it to be situated and anchored. The main tissues that make up an organ tend to have common embryologic origins, such as arising from the same germ layer. Organs exist in most multicellular organisms. In single-celled organisms such as members of the eukaryotes, the functional analogue of an organ is known as an organelle. In plants, there are three main organs.
The number of organs in any organism depends on the definition used. There are approxiamately 79 Organs in the human body,but it is something that is debated as not all scientist agree on what counts as an organ.
Animals | Organ (biology) | Wikipedia | 344 | 152776 | https://en.wikipedia.org/wiki/Organ%20%28biology%29 | Biology and health sciences | Basics_2 | null |
Except for placozoans, multicellular animals including humans have a variety of organ systems. These specific systems are widely studied in human anatomy. The functions of these organ systems often share significant overlap. For instance, the nervous and endocrine system both operate via a shared organ, the hypothalamus. For this reason, the two systems are combined and studied as the neuroendocrine system. The same is true for the musculoskeletal system because of the relationship between the muscular and skeletal systems.
Cardiovascular system: pumping and channeling blood to and from the body and lungs with heart, blood and blood vessels.
Digestive system: digestion and processing food with salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, colon, mesentery, rectum and anus.
Endocrine system: communication within the body using hormones made by endocrine glands such as the hypothalamus, pituitary gland, pineal body or pineal gland, thyroid, parathyroids and adrenals, i.e., adrenal glands.
Excretory system: kidneys, ureters, bladder and urethra involved in fluid balance, electrolyte balance and excretion of urine.
Lymphatic system: structures involved in the transfer of lymph between tissues and the blood stream, the lymph and the nodes and vessels that transport it including the immune system: defending against disease-causing agents with leukocytes, tonsils, adenoids, thymus and spleen.
Integumentary system: skin, hair and nails of mammals. Also scales of fish, reptiles, and birds, and feathers of birds.
Muscular system: movement with muscles.
Nervous system: collecting, transferring and processing information with brain, spinal cord and nerves.
Reproductive system: the sex organs, such as ovaries, oviducts, uterus, vulva, vagina, testicles, vasa deferentia, seminal vesicles, prostate and penis.
Respiratory system: the organs used for breathing, the pharynx, larynx, trachea, bronchi, lungs and diaphragm.
Skeletal system: structural support and protection with bones, cartilage, ligaments and tendons.
Viscera | Organ (biology) | Wikipedia | 486 | 152776 | https://en.wikipedia.org/wiki/Organ%20%28biology%29 | Biology and health sciences | Basics_2 | null |
In the study of anatomy, viscera (: viscus) refers to the internal organs of the abdominal, thoracic, and pelvic cavities. The abdominal organs may be classified as solid organs or hollow organs. The solid organs are the liver, pancreas, spleen, kidneys, and adrenal glands. The hollow organs of the abdomen are the stomach, intestines, gallbladder, bladder, and rectum. In the thoracic cavity, the heart is a hollow, muscular organ. Splanchnology is the study of the viscera. The term "visceral" is contrasted with the term "", meaning "of or relating to the wall of a body part, organ or cavity". The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.
Origin and evolution
The organ level of organisation in animals can be first detected in flatworms and the more derived phyla, i.e. the bilaterians. The less-advanced taxa (i.e. Placozoa, Porifera, Ctenophora and Cnidaria) do not show unification of their tissues into organs.
More complex animals are composed of different organs, which have evolved over time. For example, the liver and heart evolved in the chordates about 550-500 million years ago, while the gut and brain are even more ancient, arising in the ancestor of vertebrates, insects, molluscs, and worms about 700–650 million years ago.
Given the ancient origin of most vertebrate organs, researchers have looked for model systems, where organs have evolved more recently, and ideally have evolved multiple times independently. An outstanding model for this kind of research is the placenta, which has evolved more than 100 times independently in vertebrates, has evolved relatively recently in some lineages, and exists in intermediate forms in extant taxa. Studies on the evolution of the placenta have identified a variety of genetic and physiological processes that contribute to the origin and evolution of organs, these include the re-purposing of existing animal tissues, the acquisition of new functional properties by these tissues, and novel interactions of distinct tissue types.
Plants | Organ (biology) | Wikipedia | 456 | 152776 | https://en.wikipedia.org/wiki/Organ%20%28biology%29 | Biology and health sciences | Basics_2 | null |
The study of plant organs is covered in plant morphology. Organs of plants can be divided into vegetative and reproductive. Vegetative plant organs include roots, stems, and leaves. The reproductive organs are variable. In flowering plants, they are represented by the flower, seed and fruit. In conifers, the organ that bears the reproductive structures is called a cone. In other divisions (phyla) of plants, the reproductive organs are called strobili, in Lycopodiophyta, or simply gametophores in mosses. Common organ system designations in plants include the differentiation of shoot and root. All parts of the plant above ground (in non-epiphytes), including the functionally distinct leaf and flower organs, may be classified together as the shoot organ system.
The vegetative organs are essential for maintaining the life of a plant. While there can be 11 organ systems in animals, there are far fewer in plants, where some perform the vital functions, such as photosynthesis, while the reproductive organs are essential in reproduction. However, if there is asexual vegetative reproduction, the vegetative organs are those that create the new generation of plants (see clonal colony).
Society and culture
Many societies have a system for organ donation, in which a living or deceased donor's organ are transplanted into a person with a failing organ. The transplantation of larger solid organs often requires immunosuppression to prevent organ rejection or graft-versus-host disease.
There is considerable interest throughout the world in creating laboratory-grown or artificial organs.
Organ transplants
Beginning in the 20th century, organ transplants began to take place as scientists knew more about the anatomy of organs. These came later in time as procedures were often dangerous and difficult. Both the source and method of obtaining the organ to transplant are major ethical issues to consider, and because organs as resources for transplant are always more limited than demand for them, various notions of justice, including distributive justice, are developed in the ethical analysis. This situation continues as long as transplantation relies upon organ donors rather than technological innovation, testing, and industrial manufacturing.
History | Organ (biology) | Wikipedia | 447 | 152776 | https://en.wikipedia.org/wiki/Organ%20%28biology%29 | Biology and health sciences | Basics_2 | null |
The English word "organ" dates back to the twelfth century and refers to any musical instrument. By the late 14th century, the musical term's meaning had narrowed to refer specifically to the keyboard-based instrument. At the same time, a second meaning arose, in reference to a "body part adapted to a certain function".
Plant organs are made from tissue composed of different types of tissue. The three tissue types are ground, vascular, and dermal. When three or more organs are present, it is called an organ system.
The adjective visceral, also splanchnic, is used for anything pertaining to the internal organs. Historically, viscera of animals were examined by Roman pagan priests like the haruspices or the augurs in order to divine the future by their shape, dimensions or other factors. This practice remains an important ritual in some remote, tribal societies.
The term "visceral" is contrasted with the term "", meaning "of or relating to the wall of a body part, organ or cavity" The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.
Antiquity
Aristotle used the word frequently in his philosophy, both to describe the organs of plants or animals (e.g. the roots of a tree, the heart or liver of an animal) because, in ancient Greek, the word 'organon' means 'tool', and Aristotle believed that the organs of the body were tools for us by means of which we can do things. For similar reasons, his logical works, taken as a whole, are referred to as the Organon because logic is a tool for philosophical thinking. Earlier thinkers, such as those who wrote texts in the Hippocratic corpus, generally did not believe that there were organs of the body but only different parts of the body.
Some alchemists (e.g. Paracelsus) adopted the Hermetic Qabalah assignment between the seven vital organs and the seven classical planets as follows:
Chinese traditional medicine recognizes eleven organs, associated with the five Chinese traditional elements and with yin and yang, as follows:
The Chinese associated the five elements with the five planets (Jupiter, Mars, Venus, Saturn, and Mercury) similar to the way the classical planets were associated with different metals. The yin and yang distinction approximates the modern notion of solid and hollow organs. | Organ (biology) | Wikipedia | 485 | 152776 | https://en.wikipedia.org/wiki/Organ%20%28biology%29 | Biology and health sciences | Basics_2 | null |
The Portuguese war (Physalia physalis), also known as the man-of-war or bluebottle, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is considered to be the same species as the Pacific man o' war or bluebottle, which is found mainly in the Pacific Ocean. The Portuguese man o' war is the only species in the genus Physalia, which in turn is the only genus in the family Physaliidae.
The Portuguese man o' war is a conspicuous member of the neuston, the community of organisms that live at the surface of the ocean. It has numerous microscopic venomous cnidocytes which deliver a painful sting powerful enough to kill fish, and even, in some cases, humans. Although it superficially resembles a jellyfish, the Portuguese man o' war is in fact a siphonophore. Like all siphonophores, it is a colonial organism, made up of many smaller units called zooids. Although they are morphologically quite different, all of the zooids in a single specimen are genetically identical. These different types of zooids fulfill specialized functions, such as hunting, digestion and reproduction, and together they allow the colony to operate as a single individual.
Etymology
The name man o’ war comes from the man-of-war, a sailing warship, and the animal's resemblance to the Portuguese version (the caravel) at full sail.
Taxonomy
The bluebottle, Pacific man o' war or Indo-Pacific Portuguese man o' war, distinguished by a smaller float and a single long fishing tentacle, was originally considered a separate species in the same genus (P. utriculus). The name was synonymized with P. physalis in 2007, and it is now considered a regional form of the same species. | Portuguese man o' war | Wikipedia | 380 | 152952 | https://en.wikipedia.org/wiki/Portuguese%20man%20o%27%20war | Biology and health sciences | Cnidarians | Animals |
Coloniality
The man o' war is described as a colonial organism because the individual zooids in a colony are evolutionarily derived from either polyps or medusae, i.e. the two basic body plans of cnidarians. Both of these body plans comprise entire individuals in non-colonial cnidarians (for example, a jellyfish is a medusa, while a sea anemone is a polyp). All zooids in a man o' war develop from the same single fertilized egg and are therefore genetically identical. They remain physiologically connected throughout life, and essentially function as organs in a shared body. Hence, a Portuguese man o' war constitutes a single organism from an ecological perspective, but is made up of many individuals from an embryological perspective.
Most species of siphonophores are fragile and difficult to collect intact. However, P. physalis is the most accessible, conspicuous, and robust of the siphonophores, and much has been written about this species. The development, morphology, and colony organization of P. physalis is very different from that of other siphonophores. Its structure, embryological development, and histology have been examined by several authors. These studies provide an important foundation for understanding the morphology, cellular anatomy, and development of this species.
Description
Like all siphonophores, P. physalis is a colonial organism: each animal is composed of many smaller units (zooids) that hang in clusters from under a large, gas-filled structure called the pneumatophore.
Seven different types of zooids have been described in the man o' war, and all of these are interdependent on each other for survival and performing different functions, such as digestion (gastrozooids), reproduction (gonozooids) and hunting (dactylozooids). A fourth type of zooid is the pneumatophore. Three of these types of zooids are of the medusoid type (gonophores, nectophores, and vestigial nectophores), while the remaining four are of the polypoid type (free gastrozooids, tentacle-bearing zooids, gonozooids and gonopalpons). However, naming and categorization of zooids varies between authors, and much of the embryonic and evolutionary relationships of zooids remains unclear. | Portuguese man o' war | Wikipedia | 504 | 152952 | https://en.wikipedia.org/wiki/Portuguese%20man%20o%27%20war | Biology and health sciences | Cnidarians | Animals |
The pneumatophore or bladder is the most conspicuous part of the man o' war. This large, gas-filled, translucent structure is pink, purple or blue in color; it is long and rises as much as above the water. The pneumatophore functions as both a flotation device and a sail, allowing the animal to move with the prevailing wind. The gas in the pneumatophore is mostly air which diffuses in from the surrounding atmosphere, but it also contains as much as 13% carbon monoxide, which is actively produced by the animal. In the event of a surface attack, the pneumatophore can be deflated, allowing the animal to temporarily submerge.
New zooids are added by budding as the colony grows. Long tentacles hang below the float as the animal drifts, fishing for prey to sting and drag up to its digestive zooids.
The colony hunts and feeds through the cooperation of two types of zooids: tentacle-bearing zooids known as dactylozooids (or palpons), and gastrozooids. The palpons are equipped with tentacles, which are typically about in length but can reach over . Each tentacle bears tiny, coiled, thread-like structures called nematocysts. Nematocysts trigger and inject venom on contact, stinging, paralyzing, and killing molluscs and fishes. Large groups of Portuguese man o' war, sometimes over 1,000 individuals, may deplete fisheries. Contraction of tentacles drags the prey upward and into range of the gastrozooids. The gastrozooids surround and digest the food by secreting digestive enzymes. P. physalis typically has multiple stinging tentacles, but a regional form (previously known as a separate species, P. utriculus) has only a single stinging tentacle.
The main reproductive zooids, the gonophores, are situated on branching structures called gonodendra. Gonophores produce sperm or eggs. Besides gonophores, each gonodendron also contains several other types of specialized zooids: gonozooids (which are accessory gastrozooids), nectophores (which have been speculated to allow detached gonodendra to swim), and vestigial nectophores (also called jelly polyps; the function of these is unclear).
Life cycle | Portuguese man o' war | Wikipedia | 502 | 152952 | https://en.wikipedia.org/wiki/Portuguese%20man%20o%27%20war | Biology and health sciences | Cnidarians | Animals |
Man o' war individuals are dioecious, meaning each colony is either male or female. Gonophores producing either sperm or eggs (depending on the sex of the colony) sit on a tree-like structure called a gonodendron, which is believed to drop off from the colony during reproduction. Mating takes place primarily in the autumn, when eggs and sperm are shed from gonophores into the water. As neither fertilization nor early development has been directly observed in the wild, it is not yet known at what depth these occur.
A fertilized man o' war egg develops into a planula that buds off new zooids as it grows, gradually forming a new colony. This development initially occurs under the water, and has been reconstructed by comparing different stages of planulae collected at sea. The first two structures to emerge are the pneumatophore (sail) and a single, early feeding zooid called a protozooid. Later, gastrozooids and tentacle-bearing zooids are added. Eventually, the growing pneumatophore becomes buoyant enough to carry the immature colony on the surface of the water.
Ecology
Predators and prey
The Portuguese man o' war is a carnivore. Using its venomous tentacles, it traps and paralyzes its prey while reeling it inwards to its digestive polyps. It typically feeds on small fish, molluscs, shrimp and other small crustaceans, and zooplankton.
The organism has few predators; one example is the loggerhead sea turtle, which feeds on the Portuguese man o' war as a common part of its diet. The turtle's skin, including that of its tongue and throat, is too thick for the stings to penetrate. Also, the blue sea slug specializes in feeding on the Portuguese man o' war, as does the violet sea snail. The ocean sunfish's diet, once thought to consist mainly of jellyfish, has been found to include many species, including the Portuguese man o' war. | Portuguese man o' war | Wikipedia | 422 | 152952 | https://en.wikipedia.org/wiki/Portuguese%20man%20o%27%20war | Biology and health sciences | Cnidarians | Animals |
The man-of-war fish, Nomeus gronovii, is a driftfish native to the Atlantic, Pacific and Indian Oceans. It is notable for its ability to live within the deadly tentacles of the Portuguese man o' war, upon whose tentacles and gonads it feeds. Rather than using mucus to prevent nematocysts from firing, as is seen in some of the clownfish sheltering among sea anemones, the man-of-war fish appears to use highly agile swimming to physically avoid tentacles. The fish has a very high number of vertebrae (41), which may add to its agility and primarily uses its pectoral fins for swimming—a feature of fish that specialize in maneuvering tight spaces. It also has a complex skin design and at least one antibody to the man o' war's toxins. Although the fish seems to be 10 times more resistant to the toxin than other fish, it can be stung by the dactylozooides (large tentacles), which it actively avoids. The smaller gonozooids do not seem to sting the fish and the fish is reported to frequently nibble on these tentacles.
Commensalism and symbiosis
The Portuguese man o' war is often found with a variety of other marine fish, including yellow jack. These fish benefit from the shelter from predators provided by the stinging tentacles, and for the Portuguese , the presence of these species may attract other fish to eat.
The blanket octopus is immune to the venom of the Portuguese man o' war. Individuals have been observed to carry broken man o' war tentacles, which males and immature females rip off and use for offensive and defensive purposes.
Venom
The stinging, venom-filled nematocysts in the tentacles of the Portuguese man o' war can paralyze small fish and other prey. Detached tentacles and dead specimens (including those that wash up on shore) can sting just as painfully as those of the live organism in the water and may remain potent for hours or even days after the death of the organism or the detachment of the tentacle. | Portuguese man o' war | Wikipedia | 430 | 152952 | https://en.wikipedia.org/wiki/Portuguese%20man%20o%27%20war | Biology and health sciences | Cnidarians | Animals |
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