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Monday, October 3, 2022

Hierarchy

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Hierarchy

A hierarchy (from Greek: ἱεραρχία, hierarkhia, 'rule of a high priest', from hierarkhes, 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an important concept in a wide variety of fields, such as architecture, philosophy, design, mathematics, computer science, organizational theory, systems theory, systematic biology, and the social sciences (especially political philosophy).

A hierarchy can link entities either directly or indirectly, and either vertically or diagonally. The only direct links in a hierarchy, insofar as they are hierarchical, are to one's immediate superior or to one of one's subordinates, although a system that is largely hierarchical can also incorporate alternative hierarchies. Hierarchical links can extend "vertically" upwards or downwards via multiple links in the same direction, following a path. All parts of the hierarchy that are not linked vertically to one another nevertheless can be "horizontally" linked through a path by traveling up the hierarchy to find a common direct or indirect superior, and then down again. This is akin to two co-workers or colleagues; each reports to a common superior, but they have the same relative amount of authority. Organizational forms exist that are both alternative and complementary to hierarchy. Heterarchy is one such form.

Nomenclature

Hierarchies have their own special vocabulary. These terms are easiest to understand when a hierarchy is diagrammed (see below).

In an organizational context, the following terms are often used related to hierarchies:

  • Object: one entity (e.g., a person, department or concept or element of arrangement or member of a set)
  • System: the entire set of objects that are being arranged hierarchically (e.g., an administration)
  • Dimension: another word for "system" from on-line analytical processing (e.g. cubes)
  • Member: an (element or object) at any (level or rank) in a (class-system, taxonomy or dimension)
  • Terms about Positioning
    • Rank: the relative value, worth, complexity, power, importance, authority, level etc. of an object
    • Level or Tier: a set of objects with the same rank OR importance
    • Ordering: the arrangement of the (ranks or levels)
    • Hierarchy: the arrangement of a particular set of members into (ranks or levels). Multiple hierarchies are possible per (dimension taxonomy or Classification-system), in which selected levels of the dimension are omitted to flatten the structure
  • Terms about Placement
    • Hierarch, the apex of the hierarchy, consisting of one single orphan (object or member) in the top level of a dimension. The root of an inverted-tree structure
    • Member, a (member or node) in any level of a hierarchy in a dimension to which (superior and subordinate) members are attached
    • Orphan, a member in any level of a dimension without a parent member. Often the apex of a disconnected branch. Orphans can be grafted back into the hierarchy by creating a relationship (interaction) with a parent in the immediately superior level
    • Leaf, a member in any level of a dimension without subordinates in the hierarchy
    • Neighbour: a member adjacent to another member in the same (level or rank). Always a peer.
    • Superior: a higher level or an object ranked at a higher level (A parent or an ancestor)
    • Subordinate: a lower level or an object ranked at a lower level (A child or a descendant)
    • Collection: all of the objects at one level (i.e. Peers)
    • Peer: an object with the same rank (and therefore at the same level)
    • Interaction: the relationship between an object and its direct superior or subordinate (i.e. a superior/inferior pair)
      • a direct interaction occurs when one object is on a level exactly one higher or one lower than the other (i.e., on a tree, the two objects have a line between them)
    • Distance: the minimum number of connections between two objects, i.e., one less than the number of objects that need to be "crossed" to trace a path from one object to another
    • Span: a qualitative description of the width of a level when diagrammed, i.e., the number of subordinates an object has
  • Terms about Nature
    • Attribute: a heritable characteristic of (members and their subordinates) in a level (e.g. hair-colour)
    • Attribute-value: the specific value of a heritable characteristic (e.g. Auburn)

In a mathematical context (in graph theory), the general terminology used is different.

Most hierarchies use a more specific vocabulary pertaining to their subject, but the idea behind them is the same. For example, with data structures, objects are known as nodes, superiors are called parents and subordinates are called children. In a business setting, a superior is a supervisor/boss and a peer is a colleague.

Degree of branching

Degree of branching refers to the number of direct subordinates or children an object has (in graph theory, equivalent to the number of other vertices connected to via outgoing arcs, in a directed graph) a node has. Hierarchies can be categorized based on the "maximum degree", the highest degree present in the system as a whole. Categorization in this way yields two broad classes: linear and branching.

In a linear hierarchy, the maximum degree is 1. In other words, all of the objects can be visualized in a line-up, and each object (excluding the top and bottom ones) has exactly one direct subordinate and one direct superior. Note that this is referring to the objects and not the levels; every hierarchy has this property with respect to levels, but normally each level can have an infinite number of objects. An example of a linear hierarchy is the hierarchy of life.

In a branching hierarchy, one or more objects has a degree of 2 or more (and therefore the minimum degree is 2 or higher). For many people, the word "hierarchy" automatically evokes an image of a branching hierarchy. Branching hierarchies are present within numerous systems, including organizations and classification schemes. The broad category of branching hierarchies can be further subdivided based on the degree.

A flat hierarchy (also known for companies as flat organization) is a branching hierarchy in which the maximum degree approaches infinity, i.e., that has a wide span. Most often, systems intuitively regarded as hierarchical have at most a moderate span. Therefore, a flat hierarchy is often not viewed as a hierarchy at all. For example, diamonds and graphite are flat hierarchies of numerous carbon atoms that can be further decomposed into subatomic particles.

An overlapping hierarchy is a branching hierarchy in which at least one object has two parent objects. For example, a graduate student can have two co-supervisors to whom the student reports directly and equally, and who have the same level of authority within the university hierarchy (i.e., they have the same position or tenure status).

Etymology

Possibly the first use of the English word hierarchy cited by the Oxford English Dictionary was in 1881, when it was used in reference to the three orders of three angels as depicted by Pseudo-Dionysius the Areopagite (5th–6th centuries). Pseudo-Dionysius used the related Greek word (ἱεραρχία, hierarchia) both in reference to the celestial hierarchy and the ecclesiastical hierarchy. The Greek term hierarchia means 'rule of a high priest', from hierarches (ἱεράρχης, 'president of sacred rites, high-priest') and that from hiereus (ἱερεύς, 'priest') and arche (ἀρχή, 'first place or power, rule'). Dionysius is credited with first use of it as an abstract noun.

Since hierarchical churches, such as the Roman Catholic (see Catholic Church hierarchy) and Eastern Orthodox churches, had tables of organization that were "hierarchical" in the modern sense of the word (traditionally with God as the pinnacle or head of the hierarchy), the term came to refer to similar organizational methods in secular settings.

Representing hierarchies

Maslow's hierarchy of human needs. This is an example of a hierarchy visualized with a triangle diagram. The hierarchical aspect represented here is that needs at lower levels of the pyramid are considered more basic and must be fulfilled before higher ones are met.

A hierarchy is typically depicted as a pyramid, where the height of a level represents that level's status and width of a level represents the quantity of items at that level relative to the whole. For example, the few Directors of a company could be at the apex, and the base could be thousands of people who have no subordinates.

These pyramids are often diagrammed with a triangle diagram which serves to emphasize the size differences between the levels (but note that not all triangle/pyramid diagrams are hierarchical; for example, the 1992 USDA food guide pyramid). An example of a triangle diagram appears to the right.

Another common representation of a hierarchical scheme is as a tree diagram. Phylogenetic trees, charts showing the structure of § organizations, and playoff brackets in sports are often illustrated this way.

More recently, as computers have allowed the storage and navigation of ever larger data sets, various methods have been developed to represent hierarchies in a manner that makes more efficient use of the available space on a computer's screen. Examples include fractal maps, TreeMaps and Radial Trees.

Visual hierarchy

In the design field, mainly graphic design, successful layouts and formatting of the content on documents are heavily dependent on the rules of visual hierarchy. Visual hierarchy is also important for proper organization of files on computers.

An example of visually representing hierarchy is through nested clusters. Nested clusters represent hierarchical relationships using layers of information. The child element is within the parent element, such as in a Venn diagram. This structure is most effective in representing simple hierarchical relationships. For example, when directing someone to open a file on a computer desktop, one may first direct them towards the main folder, then the subfolders within the main folder. They will keep opening files within the folders until the designated file is located.

For more complicated hierarchies, the stair structure represents hierarchical relationships through the use of visual stacking. Visually imagine the top of a downward staircase beginning at the left and descending on the right. Child elements are towards the bottom of the stairs and parent elements are at the top. This structure represents hierarchical relationships through the use of visual stacking.

Informal representation

In plain English, a hierarchy can be thought of as a set in which:

  1. No element is superior to itself, and
  2. One element, the hierarch, is superior to all of the other elements in the set.

The first requirement is also interpreted to mean that a hierarchy can have no circular relationships; the association between two objects is always transitive. The second requirement asserts that a hierarchy must have a leader or root that is common to all of the objects.

Mathematical representation

Mathematically, in its most general form, a hierarchy is a partially ordered set or poset. The system in this case is the entire poset, which is constituted of elements. Within this system, each element shares a particular unambiguous property. Objects with the same property value are grouped together, and each of those resulting levels is referred to as a class.

"Hierarchy" is particularly used to refer to a poset in which the classes are organized in terms of increasing complexity. Operations such as addition, subtraction, multiplication and division are often performed in a certain sequence or order. Usually, addition and subtraction are performed after multiplication and division has already been applied to a problem. The use of parentheses is also a representation of hierarchy, for they show which operation is to be done prior to the following ones. For example: (2 + 5) × (7 - 4). In this problem, typically one would multiply 5 by 7 first, based on the rules of mathematical hierarchy. But when the parentheses are placed, one will know to do the operations within the parentheses first before continuing on with the problem. These rules are largely dominant in algebraic problems, ones that include several steps to solve. The use of hierarchy in mathematics is beneficial to quickly and efficiently solve a problem without having to go through the process of slowly dissecting the problem. Most of these rules are now known as the proper way into solving certain equations.

Subtypes

Nested hierarchy

Matryoshka dolls, also known as nesting dolls or Russian dolls. Each doll is encompassed inside another until the smallest one is reached. This is the concept of nesting. When the concept is applied to sets, the resulting ordering is a nested hierarchy.

A nested hierarchy or inclusion hierarchy is a hierarchical ordering of nested sets. The concept of nesting is exemplified in Russian matryoshka dolls. Each doll is encompassed by another doll, all the way to the outer doll. The outer doll holds all of the inner dolls, the next outer doll holds all the remaining inner dolls, and so on. Matryoshkas represent a nested hierarchy where each level contains only one object, i.e., there is only one of each size of doll; a generalized nested hierarchy allows for multiple objects within levels but with each object having only one parent at each level. The general concept is both demonstrated and mathematically formulated in the following example:

A square can always also be referred to as a quadrilateral, polygon or shape. In this way, it is a hierarchy. However, consider the set of polygons using this classification. A square can only be a quadrilateral; it can never be a triangle, hexagon, etc.

Nested hierarchies are the organizational schemes behind taxonomies and systematic classifications. For example, using the original Linnaean taxonomy (the version he laid out in the 10th edition of Systema Naturae), a human can be formulated as:

Taxonomies may change frequently (as seen in biological taxonomy), but the underlying concept of nested hierarchies is always the same.

In many programming taxonomies and syntax models (as well as fractals in mathematics), nested hierarchies, including Russian dolls, are also used to illustrate the properties of self-similarity and recursion. Recursion itself is included as a subset of hierarchical programming, and recursive thinking can be synonymous with a form of hierarchical thinking and logic.

Containment hierarchy

A containment hierarchy is a direct extrapolation of the nested hierarchy concept. All of the ordered sets are still nested, but every set must be "strict"—no two sets can be identical. The shapes example above can be modified to demonstrate this:

The notation means x is a subset of y but is not equal to y.

A general example of a containment hierarchy is demonstrated in class inheritance in object-oriented programming.

Two types of containment hierarchies are the subsumptive containment hierarchy and the compositional containment hierarchy. A subsumptive hierarchy "subsumes" its children, and a compositional hierarchy is "composed" of its children. A hierarchy can also be both subsumptive and compositional.

Subsumptive containment hierarchy

A subsumptive containment hierarchy is a classification of object classes from the general to the specific. Other names for this type of hierarchy are "taxonomic hierarchy" and "IS-A hierarchy". The last term describes the relationship between each level—a lower-level object "is a" member of the higher class. The taxonomical structure outlined above is a subsumptive containment hierarchy. Using again the example of Linnaean taxonomy, it can be seen that an object that is part of the level Mammalia "is a" member of the level Animalia; more specifically, a human "is a" primate, a primate "is a" mammal, and so on. A subsumptive hierarchy can also be defined abstractly as a hierarchy of "concepts". For example, with the Linnaean hierarchy outlined above, an entity name like Animalia is a way to group all the species that fit the conceptualization of an animal.

Compositional containment hierarchy

A compositional containment hierarchy is an ordering of the parts that make up a system—the system is "composed" of these parts. Most engineered structures, whether natural or artificial, can be broken down in this manner.

The compositional hierarchy that every person encounters at every moment is the hierarchy of life. Every person can be reduced to organ systems, which are composed of organs, which are composed of tissues, which are composed of cells, which are composed of molecules, which are composed of atoms. In fact, the last two levels apply to all matter, at least at the macroscopic scale. Moreover, each of these levels inherit all the properties of their children.

In this particular example, there are also emergent properties—functions that are not seen at the lower level (e.g., cognition is not a property of neurons but is of the brain)—and a scalar quality (molecules are bigger than atoms, cells are bigger than molecules, etc.). Both of these concepts commonly exist in compositional hierarchies, but they are not a required general property. These level hierarchies are characterized by bi-directional causation. Upward causation involves lower-level entities causing some property of a higher level entity; children entities may interact to yield parent entities, and parents are composed at least partly by their children. Downward causation refers to the effect that the incorporation of entity x into a higher-level entity can have on x's properties and interactions. Furthermore, the entities found at each level are autonomous.

Contexts and applications

Kulish (2002) suggests that almost every system of organization which humans apply to the world is arranged hierarchically. Some conventional definitions of the terms "nation" and "government" suggest that every nation has a government and that every government is hierarchical. Sociologists can analyse socioeconomic systems in terms of stratification into a social hierarchy (the social stratification of societies), and all systematic classification schemes (taxonomies) are hierarchical. Most organized religions, regardless of their internal governance structures, operate as a hierarchy under deities and priesthoods. Many Christian denominations have an autocephalous ecclesiastical hierarchy of leadership. Families can be viewed as hierarchical structures in terms of cousinship (e.g., first cousin once removed, second cousin, etc.), ancestry (as depicted in a family tree) and inheritance (succession and heirship). All the requisites of a well-rounded life and lifestyle can be organized using Maslow's hierarchy of human needs - according to Maslow's hierarchy of human needs. Learning steps often follow a hierarchical scheme—to master differential equations one must first learn calculus; to learn calculus one must first learn elementary algebra; and so on. Nature offers hierarchical structures, as numerous schemes such as Linnaean taxonomy, the organization of life, and biomass pyramids attempt to document. Hierarchies are so infused into daily life that they are viewed as trivial.

While the above examples are often clearly depicted in a hierarchical form and are classic examples, hierarchies exist in numerous systems where this branching structure is not immediately apparent. For example, most postal-code systems are hierarchical. Using the Canadian postal code system as an example, the top level's binding concept, the "postal district", consists of 18 objects (letters). The next level down is the "zone", where the objects are the digits 0–9. This is an example of an overlapping hierarchy, because each of these 10 objects has 18 parents. The hierarchy continues downward to generate, in theory, 7,200,000 unique codes of the format A0A 0A0 (the second and third letter positions allow 20 objects each). Most library classification systems are also hierarchical. The Dewey Decimal System is infinitely hierarchical because there is no finite bound on the number of digits can be used after the decimal point.

A simple military organizational hierarchy depicted in the form of a tree. Diagrams like this exemplify organizational charts.

Organizations

Organizations can be structured as a dominance hierarchy. In an organizational hierarchy, there is a single person or group with the most power or authority, and each subsequent level represents a lesser authority. Most organizations are structured in this manner, including governments, companies, armed forces, militia and organized religions. The units or persons within an organization may be depicted hierarchically in an organizational chart.

In a reverse hierarchy, the conceptual pyramid of authority is turned upside-down, so that the apex is at the bottom and the base is at the top. This mode represents the idea that members of the higher rankings are responsible for the members of the lower rankings.

Biology

Empirically, when we observe in nature a large proportion of the (complex) biological systems, they exhibit hierarchic structure. On theoretical grounds we could expect complex systems to be hierarchies in a world in which complexity had to evolve from simplicity. System hierarchies analysis performed in the 1950s, laid the empirical foundations for a field that would become, from the 1980s, hierarchical ecology.

The theoretical foundations are summarized by thermodynamics. When biological systems are modeled as physical systems, in the most general abstraction, they are thermodynamic open systems that exhibit self-organised behavior, and the set/subset relations between dissipative structures can be characterized in a hierarchy.

Other hierarchical representations related to biology include ecological pyramids which illustrate energy flow or trophic levels in ecosystems, and taxonomic hierarchies, including the Linnean classification scheme and phylogenetic trees that reflect inferred patterns of evolutionary relationship among living and extinct species.

Computer-graphic imaging

CGI and computer-animation programs mostly use hierarchies for models. On a 3D model of a human for example, the chest is a parent of the upper left arm, which is a parent of the lower left arm, which is a parent of the hand. This pattern is used in modeling and animation for almost everything built as a 3D digital model.

Linguistics

Many grammatical theories, such as phrase-structure grammar, involve hierarchy.

Direct–inverse languages such as Cree and Mapudungun distinguish subject and object on verbs not by different subject and object markers, but via a hierarchy of persons.

In this system, the three (or four with Algonquian languages) persons occur in a hierarchy of salience. To distinguish which is subject and which object, inverse markers are used if the object outranks the subject.

On the other hand, languages include a variety of phenomena that are not hierarchical. For example, the relationship between a pronoun and a prior noun-phrase to which it refers commonly crosses grammatical boundaries in non-hierarchical ways.

Music

The structure of a musical composition is often understood hierarchically (for example by Heinrich Schenker (1768–1835, see Schenkerian analysis), and in the (1985) Generative Theory of Tonal Music, by composer Fred Lerdahl and linguist Ray Jackendoff). The sum of all notes in a piece is understood to be an all-inclusive surface, which can be reduced to successively more sparse and more fundamental types of motion. The levels of structure that operate in Schenker's theory are the foreground, which is seen in all the details of the musical score; the middle ground, which is roughly a summary of an essential contrapuntal progression and voice-leading; and the background or Ursatz, which is one of only a few basic "long-range counterpoint" structures that are shared in the gamut of tonal music literature.

The pitches and form of tonal music are organized hierarchically, all pitches deriving their importance from their relationship to a tonic key, and secondary themes in other keys are brought back to the tonic in a recapitulation of the primary theme.

Bioenergy with carbon capture and storage

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Bioenergy_with_carbon_capture_and_storage

Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon, thereby removing it from the atmosphere. The carbon in the biomass comes from the greenhouse gas carbon dioxide (CO2) which is extracted from the atmosphere by the biomass when it grows. Energy is extracted in useful forms (electricity, heat, biofuels, etc.) as the biomass is utilized through combustion, fermentation, pyrolysis or other conversion methods. Some of the carbon in the biomass is converted to CO2 or biochar which can then be stored by geologic sequestration or land application, respectively, enabling carbon dioxide removal (CDR) and making BECCS a negative emissions technology (NET).

The IPCC Fifth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC), suggests a potential range of negative emissions from BECCS of 0 to 22 gigatonnes per year. As of 2019, five facilities around the world were actively using BECCS technologies and were capturing approximately 1.5 million tonnes per year of CO2. Wide deployment of BECCS is constrained by cost and availability of biomass.

Negative emission

Carbon flow schematic for different energy systems.

The main appeal of BECCS is in its ability to result in negative emissions of CO2. The capture of carbon dioxide from bioenergy sources effectively removes CO2 from the atmosphere.

Bioenergy is derived from biomass which is a renewable energy source and serves as a carbon sink during its growth. During industrial processes, the biomass combusted or processed re-releases the CO2 into the atmosphere. Carbon capture and storage (CCS) technology serves to intercept the release of CO2 into the atmosphere and redirect it into geological storage locations or concrete. The process thus results in a net zero emission of CO2, though this may be positively or negatively altered depending on the carbon emissions associated with biomass growth, transport and processing, see below under environmental considerations. CO2 with a biomass origin is not only released from biomass fuelled power plants, but also during the production of pulp used to make paper and in the production of biofuels such as biogas and bioethanol. The BECCS technology can also be employed on industrial processes such as these and making cement.

BECCS technologies trap carbon dioxide in geologic formations in a semi-permanent way, whereas a tree stores its carbon only during its lifetime. The IPCC special report on CCS technology projected that more than 99% of carbon dioxide stored through geologic sequestration is likely to stay in place for more than 1000 years. While other types of carbon sinks such as the ocean, trees and soil may involve the risk of adverse feedback loops at increased temperatures, BECCS technology is likely to provide a better permanence by storing CO2 in geological formations.

Industrial processes have released too much CO2 to be absorbed by conventional sinks such as trees and soil to reach low emission targets. In addition to the presently accumulated emissions, there will be significant additional emissions during this century, even in the most ambitious low-emission scenarios. BECCS has therefore been suggested as a technology to reverse the emission trend and create a global system of net negative emissions. This implies that the emissions would not only be zero, but negative, so that not only the emissions, but the absolute amount of CO2 in the atmosphere would be reduced.

Application

Source CO2 Source Sector
Ethanol production Fermentation of biomass such as sugarcane, wheat or corn releases CO2 as a by-product Industry
Pulp and paper mills

Cement production

Industry
Biogas production In the biogas upgrading process, CO2 is separated from the methane to produce a higher quality gas Industry
Electrical power plants Combustion of biomass or biofuel in steam or gas powered generators releases CO2 as a by-product Energy
Heat power plants Combustion of biofuel for heat generation releases CO2 as a by-product. Usually used for district heating Energy

Cost

The IPCC states that estimations for BECCS cost range from $60-$250 per ton of CO2.

Research by Rau et al. (2018) estimates that electrogeochemical methods of combining saline water electrolysis with mineral weathering powered by non-fossil fuel-derived electricity could, on average, increase both energy generation and CO2 removal by more than 50 times relative to BECCS, at equivalent or even lower cost, but further research is needed to develop such methods.

Technology

The main technology for CO2 capture from biotic sources generally employs the same technology as carbon dioxide capture from conventional fossil fuel sources. Broadly, three different types of technologies exist: post-combustion, pre-combustion, and oxy-fuel combustion.

Oxy-combustion

Overview of oxy‐fuel combustion for carbon capture from biomass, showing the key processes and stages; some purification is also likely to be required at the dehydration stage.

Oxy‐fuel combustion has been a common process in the glass, cement and steel industries. It is also a promising technological approach for CCS. In oxy‐fuel combustion, the main difference from conventional air firing is that the fuel is burned in a mixture of O2 and recycled flue gas. The O2 is produced by an air separation unit (ASU), which removes the atmospheric N2 from the oxidizer stream. By removing the N2 upstream of the process, a flue gas with a high concentration of CO2 and water vapor is produced, which eliminates the need for a post‐combustion capture plant. The water vapor can be removed by condensation, leaving a product stream of relatively high‐purity CO2 which, after subsequent purification and dehydration, can be pumped to a geological storage site.

Key challenges of BECCS implementation using oxy-combustion are associated with the combustion process. For the high volatile content biomass, the mill temperature has to be kept at a low temperature to reduce the risk of fire and explosion. In addition, the flame temperature is lower. Therefore, the concentration of oxygen needs to be increased up to 27-30%.

Pre-combustion

"Pre-combustion carbon capture" describes processes that capture CO2 before generating energy. This is often accomplished in five operating stages: oxygen generation, syngas generation, CO2 separation, CO2 compression, and power generation. The fuel first goes through a gasification process by reacting with oxygen to form a stream of CO and H2, which is syngas. The products will then go through a water-gas shift reactor to form CO2 and H2. The CO2 that is produced will then be captured, and the H2, which is a clean source, will be used for combustion to generate energy. The process of gasification combined with syngas production is called Integrated Gasification Combined Cycle (IGCC). An Air Separation Unit (ASU) can serve as the oxygen source, but some research has found that with the same flue gas, oxygen gasification is only slightly better than air gasification. Both have a thermal efficiency of roughly 70% using coal as the fuel source. Thus, the use of an ASU is not really necessary in pre-combustion.

Biomass is considered "sulfur-free" as a fuel for the pre-combustion capture. However, there are other trace elements in biomass combustion such as K and Na that could accumulate in the system and finally cause the degradation of the mechanical parts. Thus, further developments of the separation techniques for those trace elements are needed. And also, after the gasification process, CO2 takes up to 13% - 15.3% by mass in the syngas stream for biomass sources, while it is only 1.7% - 4.4% for coal. This limit the conversion of CO to CO2 in the water gas shift, and the production rate for H2 will decrease accordingly. However, the thermal efficiency of the pre-combustion capture using biomass resembles that of coal which is around 62% - 100%. Some research found that using a dry system instead of a biomass/water slurry fuel feed was more thermally efficient and practical for biomass.

Post-combustion

In addition to pre-combustion and oxy-fuel combustion technologies, post-combustion is a promising technology which can be used to extract CO2 emission from biomass fuel resources. During the process, CO2 is separated from the other gases in the flue gas stream after the biomass fuel is burnt and undergo separation process. Because it has the ability to be retrofitted to some existing power plants such as steam boilers or other newly built power stations, post-combustion technology is considered as a better option than pre-combustion technology. According to the fact sheets U.S. CONSUMPTION OF BIO-ENERGY WITH CARBON CAPTURE AND STORAGE released in March 2018, the efficiency of post-combustion technology is expected to be 95% while pre-combustion and oxy-combustion capture CO2 at an efficient rate of 85% and 87.5% respectively.

Development for current post-combustion technologies has not been entirely done due to several problems. One of the major concerns using this technology to capture carbon dioxide is the parasitic energy consumption. If the capacity of the unit is designed to be small, the heat loss to the surrounding is great enough to cause too many negative consequences. Another challenge of post-combustion carbon capture is how to deal with the mixture's components in the flue gases from initial biomass materials after combustion. The mixture consists of a high amount of alkali metals, halogens, acidic elements, and transition metals which might have negative impacts on the efficiency of the process. Thus, the choice of specific solvents and how to manage the solvent process should be carefully designed and operated.

Biomass feedstocks

Biomass sources used in BECCS include agricultural residues & waste, forestry residue & waste, industrial & municipal wastes, and energy crops specifically grown for use as fuel. Current BECCS projects capture CO2 from ethanol bio-refinery plants and municipal solid waste (MSW) recycling center.

A variety of challenges must be faced to ensure that biomass-based carbon capture is feasible and carbon neutral. Biomass stocks require availability of water and fertilizer inputs, which themselves exist at a nexus of environmental challenges in terms of resource disruption, conflict, and fertilizer runoff. A second major challenge is logistical: bulky biomass products require transportation to geographical features that enable sequestration.

Current projects

To date, there have been 23 BECCS projects around the world, with the majority in North America and Europe. Today, there are only 6 projects in operation, capturing CO2 from ethanol bio-refinery plants and MSW recycling centers.

At ethanol plants

Illinois Industrial Carbon Capture and Storage (IL-CCS) is one of the milestones, being the first industrial-scaled BECCS project, in the early 21st century. Located in Decatur, Illinois, USA, IL-CCS captures CO2 from Archer Daniels Midland (ADM) ethanol plant. The captured CO2 is then injected under the deep saline formation at Mount Simon Sandstone. IL-CCS consists of 2 phases. The first being a pilot project which was implemented from 11/2011 to 11/2014. Phase 1 has a capital cost of around 84 million US dollars. Over the 3-year period, the technology successfully captured and sequestered 1million tonne of CO2 from the ADM plant to the aquifer. No leaking of CO2 from the injection zone was found during this period. The project is still being monitored for future reference. The success of phase 1 motivated the deployment of phase 2, bringing IL-CCS (and BECCS) to industrial scale. Phase 2 has been in operation since 11/2017 and also use the same injection zone at Mount Simon Sandstone as phase 1. The capital cost for second phase is about 208 million US dollars including 141 million US dollar fund from the Department of Energy. Phase 2 has capturing capacity about 3 time larger than the pilot project (phase 1). Annually, IL-CCS can capture more than 1 million tonne of CO2. With the largest of capturing capacity, IL-CCS is currently the largest BECCS project in the world.

In addition to the IL-CCS project, there are about three more projects that capture CO2 from the ethanol plant at smaller scales. For example, Arkalon in Kansas, USA can capture 0.18-0.29 MtCO2/yr, OCAP in the Netherlands can capture about 0.1-0.3 MtCO2/yr, and Husky Energy in Canada can capture 0.09-0.1 MtCO2/yr.

At MSW recycling centers

Beside capturing CO2 from the ethanol plants, currently, there are 2 models in Europe are designed to capture CO2 from the processing of Municipal Solid Waste. The Klemetsrud Plant at Oslo, Norway use biogenic municipal solid waste to generate 175 GWh and capture 315 Ktonne of CO2 each year. It uses absorption technology with Aker Solution Advanced Amine solvent as a CO2 capture unit. Similarly, the ARV Duiven in the Netherlands uses the same technology, but it captures less CO2 than the previous model. ARV Duiven generates around 126 GWh and only capture 50 Ktonne of CO2 each year.

Techno-economics of BECCS and the TESBiC Project

The largest and most detailed techno-economic assessment of BECCS was carried out by cmcl innovations and the TESBiC group (Techno-Economic Study of Biomass to CCS) in 2012. This project recommended the most promising set of biomass fueled power generation technologies coupled with carbon capture and storage (CCS). The project outcomes lead to a detailed “biomass CCS roadmap” for the U.K..

Challenges

Environmental considerations

Some of the environmental considerations and other concerns about the widespread implementation of BECCS are similar to those of CCS. However, much of the critique towards CCS is that it may strengthen the dependency on depletable fossil fuels and environmentally invasive coal mining. This is not the case with BECCS, as it relies on renewable biomass. There are however other considerations which involve BECCS and these concerns are related to the possible increased use of biofuels. Biomass production is subject to a range of sustainability constraints, such as: scarcity of arable land and fresh water, loss of biodiversity, competition with food production, deforestation and scarcity of phosphorus. It is important to make sure that biomass is used in a way that maximizes both energy and climate benefits. There has been criticism to some suggested BECCS deployment scenarios, where there would be a very heavy reliance on increased biomass input.

Large areas of land would be required to operate BECCS on an industrial scale. To remove 10 billion tonnes of CO2, upwards of 300 million hectares of land area (larger than India) would be required. As a result, BECCS risks using land that could be better suited to agriculture and food production, especially in developing countries.

These systems may have other negative side effects. There is however presently no need to expand the use of biofuels in energy or industry applications to allow for BECCS deployment. There is already today considerable emissions from point sources of biomass derived CO2, which could be utilized for BECCS. Though, in possible future bioenergy system upscaling scenarios, this may be an important consideration.

Upscaling BECCS would require a sustainable supply of biomass - one that does not challenge our land, water, and food security. Using bioenergy crops as feedstock will not only cause sustainability concerns but also require the use of more fertilizer leading to soil contamination and water pollution.[citation needed] Moreover, crop yield is generally subjected to climate condition, i.e. the supply of this bio-feedstock can be hard to control. Bioenergy sector must also expand to meet the supply level of biomass. Expanding bioenergy would require technical and economic development accordingly.

Technical challenges

A challenge for applying BECCS technology, as with other carbon capture and storage technologies, is to find suitable geographic locations to build combustion plant and to sequester captured CO2. If biomass sources are not close by the combustion unit, transporting biomass emits CO2 offsetting the amount of CO2 captured by BECCS. BECCS also face technical concerns about efficiency of burning biomass. While each type of biomass has a different heating value, biomass in general is a low-quality fuel. Thermal conversion of biomass typically has an efficiency of 20-27%. For comparison, coal-fired plants have an efficiency of about 37%.

BECCS also faces a question whether the process is actually energy positive. Low energy conversion efficiency, energy-intensive biomass supply, combined with the energy required to power the CO2 capture and storage unit impose energy penalty on the system. This might lead to a low power generation efficiency.

Potential solutions

Alternative biomass sources

Agricultural and forestry residues

Globally, 14 Gt of forestry residue and 4.4 Gt residues from crop production (mainly barley, wheat, corn, sugarcane and rice) are generated every year. This is a significant amount of biomass which can be combusted to generate 26 EJ/year and achieve a 2.8 Gt of negative CO2 emission through BECCS. Utilizing residues for carbon capture will provide social and economic benefits to rural communities. Using waste from crops and forestry is a way to avoid the ecological and social challenges of BECCS.

Municipal solid waste

Municipal solid waste (MSW) is one of the newly developed sources of biomass.Overview waste to energy techniques with CSS Two current BECCS plants are using MSW as feedstocks. Waste collected from daily life is recycled via incineration waste treatment process. Waste goes through high temperature thermal treatment and the heat generated from combusting organic part of waste is used to generate electricity. CO2emitted from this process is captured through absorption using MEA. For every 1 kg of waste combusted, 0.7 kg of negative CO2emission is achieved. Utilizing solid waste also have other environmental benefits.

Co-firing coal with biomass

As of 2017 there were roughly 250 cofiring plants in the world, including 40 in the US. Biomass cofiring with coal has efficiency near those of coal combustion. Instead of co-firing, full conversion from coal to biomass of one or more generating units in a plant may be preferred.

Policy

Based on the Kyoto Protocol agreement, carbon capture and storage projects were not applicable as an emission reduction tool to be used for the Clean Development Mechanism (CDM) or for Joint Implementation (JI) projects. Recognising CCS technologies as an emission reduction tool is vital for the implementation of such plants as there is no other financial motivation for the implementation of such systems. There has been growing support to have fossil CCS and BECCS included in the protocol as well as the current Paris Agreement. Accounting studies on how this can be implemented, including BECCS, have also been done.

European Union

There are some future policies that give incentives to use bioenergy such as Renewable Energy Directive (RED) and Fuel Quality Directive (FQD), which require 20% of total energy consumption to be based on biomass, bioliquids and biogas by 2020.

Sweden

The Swedish Energy Agency has been commissioned by the Swedish government to design a Swedish support system for BECCS to be implemented by 2022.

United Kingdom

In 2018 the Committee on Climate Change recommended that aviation biofuels should provide up to 10% of total aviation fuel demand by 2050, and that all aviation biofuels should be produced with CCS as soon as the technology is available.

United States

In 2018 the US congress significantly increased and extended the section 45Q tax credit for sequestration of carbon oxides. This has been a top priority of carbon capture and sequestration (CCS) supporters for several years. It increased $25.70 to $50 tax credit per tonnes of CO2 for secure geological storage and $15.30 to $35 tax credit per tonne of CO2 used in enhanced oil recovery.

Public perception

Limited studies have investigated public perceptions of BECCS. Of those studies, most originate from developed countries in the northern hemisphere and therefore may not represent a worldwide view.

In a 2018 study involving online panel respondents from the United Kingdom, United States, Australia, and New Zealand, respondents showed little prior awareness of BECCS technologies. Measures of respondents perceptions suggest that the public associate BECCS with a balance of both positive and negative attributes. Across the four countries, 45% of the respondents indicated they would support small scale trials of BECCS, whereas only 21% were opposed. BECCS was moderately preferred among other methods of Carbon dioxide removal like Direct air capture or Enhanced weathering, and greatly preferred over methods of Solar radiation management.

Animal navigation

From Wikipedia, the free encyclopedia
 
Manx shearwaters can fly straight home when released, navigating thousands of miles over land or sea.

Animal navigation is the ability of many animals to find their way accurately without maps or instruments. Birds such as the Arctic tern, insects such as the monarch butterfly and fish such as the salmon regularly migrate thousands of miles to and from their breeding grounds, and many other species navigate effectively over shorter distances.

Dead reckoning, navigating from a known position using only information about one's own speed and direction, was suggested by Charles Darwin in 1873 as a possible mechanism. In the 20th century, Karl von Frisch showed that honey bees can navigate by the sun, by the polarization pattern of the blue sky, and by the earth's magnetic field; of these, they rely on the sun when possible. William Tinsley Keeton showed that homing pigeons could similarly make use of a range of navigational cues, including the sun, earth's magnetic field, olfaction and vision. Ronald Lockley demonstrated that a small seabird, the Manx shearwater, could orient itself and fly home at full speed, when released far from home, provided either the sun or the stars were visible.

Several species of animal can integrate cues of different types to orient themselves and navigate effectively. Insects and birds are able to combine learned landmarks with sensed direction (from the earth's magnetic field or from the sky) to identify where they are and so to navigate. Internal 'maps' are often formed using vision, but other senses including olfaction and echolocation may also be used.

The ability of wild animals to navigate may be adversely affected by products of human activity. For example, there is evidence that pesticides may interfere with bee navigation, and that lights may harm turtle navigation.

Early research

Karl von Frisch (1953) discovered that honey bee workers can navigate, and indicate the range and direction to food to other workers with a waggle dance.

In 1873, Charles Darwin wrote a letter to Nature magazine, arguing that animals including man have the ability to navigate by dead reckoning, even if a magnetic 'compass' sense and the ability to navigate by the stars is present:

With regard to the question of the means by which animals find their way home from a long distance, a striking account, in relation to man, will be found in the English translation of the Expedition to North Siberia, by Von Wrangell. He there describes the wonderful manner in which the natives kept a true course towards a particular spot, whilst passing for a long distance through hummocky ice, with incessant changes of direction, and with no guide in the heavens or on the frozen sea. He states (but I quote only from memory of many years standing) that he, an experienced surveyor, and using a compass, failed to do that which these savages easily effected. Yet no one will suppose that they possessed any special sense which is quite absent in us. We must bear in mind that neither a compass, nor the north star, nor any other such sign, suffices to guide a man to a particular spot through an intricate country, or through hummocky ice, when many deviations from a straight course are inevitable, unless the deviations are allowed for, or a sort of "dead reckoning" is kept. All men are able to do this in a greater or less degree, and the natives of Siberia apparently to a wonderful extent, though probably in an unconscious manner. This is effected chiefly, no doubt, by eyesight, but partly, perhaps, by the sense of muscular movement, in the same manner as a man with his eyes blinded can proceed (and some men much better than others) for a short distance in a nearly straight line, or turn at right angles, or back again. The manner in which the sense of direction is sometimes suddenly disarranged in very old and feeble persons, and the feeling of strong distress which, as I know, has been experienced by persons when they have suddenly found out that they have been proceeding in a wholly unexpected and wrong direction, leads to the suspicion that some part of the brain is specialised for the function of direction.

Later in 1873, Joseph John Murphy replied to Darwin, writing back to Nature with a description of how he, Murphy, believed animals carried out dead reckoning, by what is now called inertial navigation:

If a ball is freely suspended from the roof of a railway carriage it will receive a shock sufficient to move it, when the carriage is set in motion: and the magnitude and direction of the shock … will depend on the magnitude and direction of the force with which the carriage begins to move … [and so] … every change in … the motion of the carriage … will give a shock of corresponding magnitude and direction to the ball. Now, it is conceivably quite possible, though such delicacy of mechanism is not to be hoped for, that a machine should be constructed … for registering the magnitude and direction of all these shocks, with the time at which each occurred … from these data the position of the carriage … might be calculated at any moment.

Karl von Frisch (1886–1982) studied the European honey bee, demonstrating that bees can recognize a desired compass direction in three different ways: by the sun, by the polarization pattern of the blue sky, and by the earth's magnetic field. He showed that the sun is the preferred or main compass; the other mechanisms are used under cloudy skies or inside a dark beehive.

William Tinsley Keeton (1933–1980) studied homing pigeons, showing that they were able to navigate using the earth's magnetic field, the sun, as well as both olfactory and visual cues.

Donald Griffin (1915–2003) studied echolocation in bats, demonstrating that it was possible and that bats used this mechanism to detect and track prey, and to "see" and thus navigate through the world around them.

Ronald Lockley (1903–2000), among many studies of birds in over fifty books, pioneered the science of bird migration. He made a twelve-year study of shearwaters such as the Manx shearwater, living on the remote island of Skokholm. These small seabirds make one of the longest migrations of any bird—10,000 kilometres—but return to the exact nesting burrow on Skokholm year after year. This behaviour led to the question of how they navigated.

Mechanisms

Lockley began his book Animal Navigation with the words:

How do animals find their way over apparently trackless country, through pathless forests, across empty deserts, over and under featureless seas? ... They do so, of course, without any visible compass, sextant, chronometer or chart...

Many mechanisms of spatial cognition have been proposed for animal navigation: there is evidence for a number of them. Investigators have often been forced to discard the simplest hypotheses - for example, some animals can navigate on a dark and cloudy night, when neither landmarks nor celestial cues like sun, moon, or stars are visible. The major mechanisms known or hypothesized are described in turn below.

Remembered landmarks

Animals including mammals, birds and insects such as bees and wasps (Ammophila and Sphex), are capable of learning landmarks in their environment, and of using these in navigation.

Orientation by the sun

The sandhopper, Talitrus saltator, uses the sun and its internal clock to determine direction.

Some animals can navigate using celestial cues such as the position of the sun. Since the sun moves in the sky, navigation by this means also requires an internal clock. Many animals depend on such a clock to maintain their circadian rhythm. Animals that use sun compass orientation are fish, birds, sea-turtles, butterflies, bees, sandhoppers, reptiles, and ants.

When sandhoppers (such as Talitrus saltator) are taken up a beach, they easily find their way back down to the sea. It has been shown that this is not simply by moving downhill or towards the sight or sound of the sea. A group of sandhoppers were acclimatised to a day/night cycle under artificial lighting, whose timing was gradually changed until it was 12 hours out of phase with the natural cycle. Then, the sandhoppers were placed on the beach in natural sunlight. They moved away from the sea, up the beach. The experiment implied that the sandhoppers use the sun and their internal clock to determine their heading, and that they had learnt the actual direction down to the sea on their particular beach.

Experiments with Manx shearwaters showed that when released "under a clear sky" far from their nests, the seabirds first oriented themselves and then flew off in the correct direction. But if the sky was overcast at the time of release, the shearwaters flew around in circles.

Monarch butterflies use the sun as a compass to guide their southwesterly autumn migration from Canada to Mexico.

Orientation by the night sky

In a pioneering experiment, Lockley showed that warblers placed in a planetarium showing the night sky oriented themselves towards the south; when the planetarium sky was then very slowly rotated, the birds maintained their orientation with respect to the displayed stars. Lockley observes that to navigate by the stars, birds would need both a "sextant and chronometer": a built-in ability to read patterns of stars and to navigate by them, which also requires an accurate time-of-day clock.

In 2003, the African dung beetle Scarabaeus zambesianus was shown to navigate using polarization patterns in moonlight, making it the first animal known to use polarized moonlight for orientation. In 2013, it was shown that dung beetles can navigate when only the Milky Way or clusters of bright stars are visible, making dung beetles the only insects known to orient themselves by the galaxy.

Orientation by polarised light

Rayleigh sky model shows how polarization of light can indicate direction to bees.
 

Some animals, notably insects such as the honey bee, are sensitive to the polarisation of light. Honey bees can use polarized light on overcast days to estimate the position of the sun in the sky, relative to the compass direction they intend to travel. Karl von Frisch's work established that bees can accurately identify the direction and range from the hive to a food source (typically a patch of nectar-bearing flowers). A worker bee returns to the hive and signals to other workers the range and direction relative to the sun of the food source by means of a waggle dance. The observing bees are then able to locate the food by flying the implied distance in the given direction, though other biologists have questioned whether they necessarily do so, or are simply stimulated to go and search for food. However, bees are certainly able to remember the location of food, and to navigate back to it accurately, whether the weather is sunny (in which case navigation may be by the sun or remembered visual landmarks) or largely overcast (when polarised light may be used).

Magnetoreception

The homing pigeon can quickly return to its home, using cues such as the earth's magnetic field to orient itself.
 

Some animals, including mammals such as blind mole rats (Spalax) and birds such as pigeons, are sensitive to the earth's magnetic field.

Homing pigeons use magnetic field information with other navigational cues. Pioneering researcher William Keeton showed that time-shifted homing pigeons could not orient themselves correctly on a clear sunny day, but could do so on an overcast day, suggesting that the birds prefer to rely on the direction of the sun, but switch to using a magnetic field cue when the sun is not visible. This was confirmed by experiments with magnets: the pigeons could not orient correctly on an overcast day when the magnetic field was disrupted.

Olfaction

Returning salmon may use olfaction to identify the river in which they developed.

Olfactory navigation has been suggested as a possible mechanism in pigeons. Papi's 'mosaic' model argues that pigeons build and remember a mental map of the odours in their area, recognizing where they are by the local odour. Wallraff's 'gradient' model argues that there is a steady, large-scale gradient of odour which remains stable for long periods. If there were two or more such gradients in different directions, pigeons could locate themselves in two dimensions by the intensities of the odours. However it is not clear that such stable gradients exist. Papi did find evidence that anosmic pigeons (unable to detect odours) were much less able to orient and navigate than normal pigeons, so olfaction does seem to be important in pigeon navigation. However, it is not clear how olfactory cues are used.

Olfactory cues may be important in salmon, which are known to return to the exact river where they hatched. Lockley reports experimental evidence that fish such as minnows can accurately tell the difference between the waters of different rivers. Salmon may use their magnetic sense to navigate to within reach of their river, and then use olfaction to identify the river at close range.

Gravity receptors

GPS tracing studies indicate that gravity anomalies could play a role in homing pigeon navigation.

Other senses

Biologists have considered other senses that may contribute to animal navigation. Many marine animals such as seals are capable of hydrodynamic reception, enabling them to track and catch prey such as fish by sensing the disturbances their passage leaves behind in the water. Marine mammals such as dolphins, and many species of bat, are capable of echolocation, which they use both for detecting prey and for orientation by sensing their environment.

Way-marking

The wood mouse is the first non-human animal to be observed, both in the wild and under laboratory conditions, using movable landmarks to navigate. While foraging, they pick up and distribute visually conspicuous objects, such as leaves and twigs, which they then use as landmarks during exploration, moving the markers when the area has been explored.

Path integration

Path integration sums the vectors of distance and direction travelled from a start point to estimate current position, and so the path back to the start.
 

Dead reckoning, in animals usually known as path integration, means the putting together of cues from different sensory sources within the body, without reference to visual or other external landmarks, to estimate position relative to a known starting point continuously while travelling on a path that is not necessarily straight. Seen as a problem in geometry, the task is to compute the vector to a starting point by adding the vectors for each leg of the journey from that point.

Since Darwin's On the Origins of Certain Instincts (quoted above) in 1873, path integration has been shown to be important to navigation in animals including ants, rodents and birds. When vision (and hence the use of remembered landmarks) is not available, such as when animals are navigating on a cloudy night, in the open ocean, or in relatively featureless areas such as sandy deserts, path integration must rely on idiothetic cues from within the body.

Studies by Wehner in the Sahara desert ant (Cataglyphis bicolor) demonstrate effective path integration to determine directional heading (by polarized light or sun position) and to compute distance (by monitoring leg movement or optical flow).

Path integration in mammals makes use of the vestibular organs, which detect accelerations in the three dimensions, together with motor efference, where the motor system tells the rest of the brain which movements were commanded, and optic flow, where the visual system signals how fast the visual world moves past the eyes. Information from other senses such as echolocation and magnetoreception may also be integrated in certain animals. The hippocampus is the part of the brain that integrates linear and angular motion to encode a mammal's relative position in space.

David Redish states that "The carefully controlled experiments of Mittelstaedt and Mittelstaedt (1980) and Etienne (1987) have demonstrated conclusively that [path integration in mammals] is a consequence of integrating internal cues from vestibular signals and motor efferent copy".

Effects of human activity

Neonicotinoid pesticides may impair the ability of bees to navigate. Bees exposed to low levels of thiamethoxam were less likely to return to their colony, to an extent sufficient to compromise a colony's survival.

Light pollution attracts and disorients photophilic animals, those that follow light. For example, hatchling sea turtles follow bright light, particularly bluish light, altering their navigation. Disrupted navigation in moths can easily be observed around bright lamps on summer nights. Insects gather around these lamps at high densities instead of navigating naturally.

Liquefied petroleum gas

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