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The following outline is provided as an overview of and topical guide to computing:
Computing – activity of using and improving computer hardware and computer software .
Computer science – ( outline )
See information processor for a high-level block diagram.
After the commoditization of memory , attention turned to optimizing CPU performance at the instruction level. Various methods of speeding up the fetch-execute cycle include:
The main goal of CbWN is to optimize the system performance of the flexible wireless network.
There are several terms which describe classes , or categories, of computers:
See also Open standard
Major figures associated with making personal computers popular. | https://en.wikipedia.org/wiki/Outline_of_computing |
The following outline is provided as an overview of and topical guide to construction:
Construction – process of building or assembling infrastructure. A complex activity, large scale construction involves extensive multitasking. Normally, a job is managed by a project manager, and supervised by a construction manager, design engineer, construction engineer or project architect.
History of construction
List of construction trades
List of construction methods
List of building materials | https://en.wikipedia.org/wiki/Outline_of_construction |
The following outline is provided as an overview of and topical guide to control engineering:
Control engineering – engineering discipline that applies control theory to design systems with desired behaviors. The practice uses sensors to measure the output performance of the device being controlled and those measurements can be used to give feedback to the input actuators that can make corrections toward desired performance. When a device is designed to perform without the need of human inputs for correction it is called automatic control (such as cruise control for regulating a car's speed). | https://en.wikipedia.org/wiki/Outline_of_control_engineering |
The following outline is provided as an overview of a topical guide to design:
Design (as a verb: designing, or, to design) is the intentional creation of a plan or specification for the construction or manufacturing of an object or system or for the implementation of an activity or process.
Design (as a noun: a design) can refer to such a plan or specification (e.g. a drawing or other document) or to the created object, etc., and features of it such as aesthetic, functional, economic or socio-political. [ 1 ] | https://en.wikipedia.org/wiki/Outline_of_design |
Discrete mathematics is the study of mathematical structures that are fundamentally discrete rather than continuous . In contrast to real numbers that have the property of varying "smoothly", the objects studied in discrete mathematics – such as integers , graphs , and statements in logic [ 1 ] – do not vary smoothly in this way, but have distinct, separated values. [ 2 ] Discrete mathematics, therefore, excludes topics in "continuous mathematics" such as calculus and analysis .
Included below are many of the standard terms used routinely in university-level courses and in research papers. This is not, however, intended as a complete list of mathematical terms; just a selection of typical terms of art that may be encountered.
For further reading in discrete mathematics, beyond a basic level, see these pages. Many of these disciplines are closely related to computer science .
Elementary algebra – Basic concepts of algebra
Combinatorics – Branch of discrete mathematics
Probability – Branch of mathematics concerning chance and uncertainty | https://en.wikipedia.org/wiki/Outline_of_discrete_mathematics |
The following outline is provided as an overview of and topical guide to ecology:
Ecology – scientific study of the distribution and abundance of living organisms and how the distribution and abundance are affected by interactions between the organisms and their environment . The environment of an organism includes both physical properties, which can be described as the sum of local abiotic factors such as solar insolation , climate and geology , as well as the other organisms that share its habitat . Also called ecological science .
Ecology can also be classified on the basis of:
Ecology is a broad discipline comprising many subdisciplines. The field of ecology can be subdivided according to several classification schemes:
Arranged from lowest to highest level of organisation : [ 1 ]
Ecology has also inspired (and lent its name to) other non-biological disciplines such as:
Biogeographic realm – Broadest biogeographic division of Earth's land surface. The World Wildlife Fund (WWF) developed a system of eight biogeographic realms (ecozones):
Ecoregion – Ecological and geographic area
The World has over 800 terrestrial ecoregions . See Lists of ecoregions by country .
History of ecology | https://en.wikipedia.org/wiki/Outline_of_ecology |
The following outline is provided as an overview of and topical guide to fluid dynamics:
In physics , physical chemistry and engineering , fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases . It has several subdisciplines, including aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of water and other liquids in motion). Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft , determining the mass flow rate of petroleum through pipelines , predicting weather patterns , understanding nebulae in interstellar space , understanding large scale geophysical flows involving oceans/atmosphere and modelling fission weapon detonation .
Below is a structured list of topics in fluid dynamics.
Fluid dynamics can be described as all of the following:
History of fluid dynamics
Contributors to the field of fluid dynamics in turn come from a wide array of fields, and in addition to their other titles, each is also a fluid dynamicist. Following is a list of notable fluid dynamicists: | https://en.wikipedia.org/wiki/Outline_of_fluid_dynamics |
The following outline is provided as an overview of and topical guide to forensic science:
Forensic science – application of a broad spectrum of sciences to answer questions of interest to a legal system. This may be in matters relating to criminal law, civil law and regulatory laws. it may also relate to non-litigious matters. The term is often shortened to forensics .
General forensics topics include:
18. # P.Chandra Sekharan, 'LIP FORENSICS' (2011), ISBN 978-81-8465-769-2 ; Anand Publications, 143, SFS407, Yelahanka New Town, Bangalore 560 106; India
19. P.Chandra Sekharan, " The First Human Bomb; ISBN 81-8395-035-3 ALT Publications, Hyderabad -2 | https://en.wikipedia.org/wiki/Outline_of_forensic_science |
The following outline is provided as an overview of and topical guide to fungi and mycology :
Fungi – "Fungi" is plural for "fungus". A fungus is any member of the group of eukaryotic organisms that includes unicellular microorganisms such as yeasts and molds , as well as multicellular fungi that produce familiar fruiting forms known as mushrooms . Biologists classify these organisms as a kingdom , Fungi , the second highest taxonomic rank of living organism beneath the Eukaryota domain; other kingdoms include plants, animals, protists, and bacteria. One difference that places fungi in a different kingdom is that their cell walls contain chitin , unlike the cell walls of plants, bacteria and some protists. Similar to animals, fungi are heterotrophs , that is, they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment. Growth is their means of mobility, except for spores (a few of which are flagellated ), which may travel through air or water. Fungi function as the principal decomposers in ecological systems .
Mycology | https://en.wikipedia.org/wiki/Outline_of_fungi |
This article provides an outline of terminology and topics that are important to know in genetics.
The following outline is provided as an overview of and topical guide to genetics:
Genetics – science of genes , heredity , and variation in living organisms . [ 1 ] [ 2 ] Genetics deals with the molecular structure and function of genes, and gene behavior in context of a cell or organism (e.g. dominance and epigenetics ), patterns of inheritance from parent to offspring, and gene distribution, variation and change in populations .
History of genetics
History of genetics | https://en.wikipedia.org/wiki/Outline_of_genetics |
Geometry is a branch of mathematics concerned with questions of shape, size, relative position of figures, and the properties of space. Geometry is one of the oldest mathematical sciences.
History of geometry | https://en.wikipedia.org/wiki/Outline_of_geometry |
The following outline is provided as an overview of and topical guide to human–computer interaction:
Human–Computer Interaction (HCI) – the intersection of computer science and behavioral sciences — this field involves the study, planning, and design of the interaction between people (users) and computers. Attention to human-machine interaction is important, because poorly designed human-machine interfaces can lead to many unexpected problems. A classic example of this is the Three Mile Island accident where investigations concluded that the design of the human-machine interface was at least partially responsible for the disaster.
Human–Computer Interaction can be described as all of the following:
Human–computer interaction draws from the following fields:
History of human–computer interaction
Hardware input/output devices and peripherals :
Motion pictures featuring interesting user interfaces:
Industrial labs and companies known for innovation and research in HCI: | https://en.wikipedia.org/wiki/Outline_of_human–computer_interaction |
The following outline is provided as an overview of and topical guide to hydrology:
Hydrology – study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle , water resources and environmental watershed sustainability.
Hydrology can be described as all of the following:
History of hydrology
Water cycle (aka "hydrological cycle")
Source: [ 1 ]
Source: [ 1 ]
Source: [ 1 ]
Source: [ 1 ]
Basin
Catchment
Evaporation
Infiltration/Soil Movement
Streamflow/Open channel
Erosion
Groundwater
Hydrological transport model
Some examples of applications of hydrology: | https://en.wikipedia.org/wiki/Outline_of_hydrology |
The following outline is provided as an overview of and topical guide to immunology:
Immunology – study of all aspects of the immune system in all organisms . [ 1 ] It deals with the physiological functioning of the immune system in states of both health and disease; malfunctions of the immune system in immunological disorders ( autoimmune diseases , hypersensitivities , immune deficiency , transplant rejection ); the physical, chemical and physiological characteristics of the components of the immune system in vitro , in situ , and in vivo .
Immunology
1. General Immunology
2. Basic Immunology
3. Advanced Immunology
4. Medical Immunology
5. Pharmaceutical Immunology
9. Clinical Immunology
6. Environmental Immunology
8. Cellular and Molecular Immunology
9. Food and Agricultural Immunology
History of immunology
Immune system
Adaptive immune system
Innate immune system
Lymphatic system
Primary lymphoid organs
Secondary lymphoid organs
White blood cells
Lymphoid cells
Pattern recognition receptor
Complement receptor
Fc receptor
Cytokine receptor
Natural killer cell receptors
Antibodies
Cytokine
Major histocompatibility complex
Antimicrobial peptides
Cell adhesion molecules
Immune disorder
Immunodeficiency
peripheral: Purine nucleoside phosphorylase deficiency
aggressive: Sézary disease
Immunoproliferative immunoglobulin disorders
List of immunologists | https://en.wikipedia.org/wiki/Outline_of_immunology |
The following outline is provided as an overview of and topical guide to industrial machinery: | https://en.wikipedia.org/wiki/Outline_of_industrial_machinery |
The following outline is provided as an overview of and topical guide to life forms:
A life form (also spelled life-form or lifeform ) is an entity that is living , [ 1 ] [ 2 ] such as plants ( flora ), animals ( fauna ), and fungi ( funga ). It is estimated that more than 99% of all species that ever existed on Earth, amounting to over five billion species, [ 3 ] are extinct . [ 4 ] [ 5 ]
Earth is the only celestial body known to harbor life forms. No form of extraterrestrial life has yet been discovered. [ 6 ] | https://en.wikipedia.org/wiki/Outline_of_life_forms |
This is an outline of topics related to linear algebra, the branch of mathematics concerning linear equations and linear maps and their representations in vector spaces and through matrices.
Linear equation
Matrix
Matrix decomposition
Vector space
Multilinear algebra
Affine space
Projective space | https://en.wikipedia.org/wiki/Outline_of_linear_algebra |
Logic is the formal science of using reason and is considered a branch of both philosophy and mathematics and to a lesser extent computer science . Logic investigates and classifies the structure of statements and arguments, both through the study of formal systems of inference and the study of arguments in natural language . The scope of logic can therefore be very large, ranging from core topics such as the study of fallacies and paradoxes , to specialized analyses of reasoning such as probability , correct reasoning, and arguments involving causality . One of the aims of logic is to identify the correct (or valid ) and incorrect (or fallacious ) inferences . Logicians study the criteria for the evaluation of arguments .
Philosophy of logic
Informal logic Critical thinking Argumentation theory
Logical connective
Proposition
Rule of inference ( list )
Metalanguage
Propositional logic
Predicate logic
Mathematical relation
Mathematical logic
Set theory ( list )
Metalogic – The study of the metatheory of logic.
Proof theory – The study of deductive apparatus .
Model theory – The study of interpretation of formal systems.
Computability theory – branch of mathematical logic that originated in the 1930s with the study of computable functions and Turing degrees . The field has grown to include the study of generalized computability and definability. The basic questions addressed by recursion theory are "What does it mean for a function from the natural numbers to themselves to be computable?" and "How can noncomputable functions be classified into a hierarchy based on their level of noncomputability?". The answers to these questions have led to a rich theory that is still being actively researched.
Formal semantics (natural language)
Classical logic
Modal logic
Non-classical logic
Mathematical logic
History of logic | https://en.wikipedia.org/wiki/Outline_of_logic |
The following outline is provided as an overview of, and topical guide to, machine learning:
Machine learning ( ML ) is a subfield of artificial intelligence within computer science that evolved from the study of pattern recognition and computational learning theory . [ 1 ] In 1959, Arthur Samuel defined machine learning as a "field of study that gives computers the ability to learn without being explicitly programmed". [ 2 ] ML involves the study and construction of algorithms that can learn from and make predictions on data . [ 3 ] These algorithms operate by building a model from a training set of example observations to make data-driven predictions or decisions expressed as outputs, rather than following strictly static program instructions.
Dimensionality reduction
Ensemble learning
Meta-learning
Reinforcement learning
Supervised learning
Bayesian statistics
Decision tree algorithm
Linear classifier
Unsupervised learning
Artificial neural network
Association rule learning
Hierarchical clustering
Cluster analysis
Anomaly detection
Semi-supervised learning
Deep learning
History of machine learning
Machine learning projects: | https://en.wikipedia.org/wiki/Outline_of_machine_learning |
The following outline is provided as an overview of and topical guide to medicine:
Medicine – science of healing . It encompasses a variety of health care practices evolved to maintain health by the prevention and treatment of illness .
Medical biology
Practice of medicine
Drugs
Medical equipment
Medical education – education related to the practice of being a medical practitioner; either the initial training to become a physician , additional training thereafter, and fellowship.
Medical research
Medical terminology | https://en.wikipedia.org/wiki/Outline_of_medicine |
The following outline is provided as an overview of and topical guide to nanotechnology:
Nanotechnology is science , engineering , and technology conducted at the nanoscale , which is about 1 to 100 nanometers.
Implications of nanotechnology
Fullerene – any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Fullerene spheres and tubes have applications in nanotechnology.
Nanoparticle –
Nanomedicine –
Molecular self-assembly –
Nanoelectronics –
Molecular electronics –
Nanolithography –
Molecular nanotechnology –
Microscopy –
List of nanotechnology organizations | https://en.wikipedia.org/wiki/Outline_of_nanotechnology |
The following outline is provided as an overview of and topical guide to neuroscience:
Neuroscience is the scientific study of the structure and function of the nervous system. [ 1 ] [ 2 ] It encompasses the branch of biology [ 3 ] that deals with the anatomy , biochemistry , molecular biology , and physiology of neurons and neural circuits . It also encompasses cognition, and human behavior. [ 2 ] Neuroscience has multiple concepts that each relate to learning abilities and memory functions. Additionally, the brain is able to transmit signals that cause conscious/unconscious behaviors that are responses verbal or non-verbal. This allows people to communicate with one another. [ 4 ]
Neurophysiology is the study of the function (as opposed to structure) of the nervous system .
Neuroanatomy is the study of the anatomy of nervous tissue and neural structures of the nervous system.
Neuropharmacology is the study of how drugs affect cellular function in the nervous system.
Behavioral neuroscience , also known as biological psychology, biopsychology, or psychobiology, is the application of the principles of biology to the study of mental processes and behavior in human and non-human animals.
Developmental neuroscience aims to describe the cellular basis of brain development and to address the underlying mechanisms. The field draws on both neuroscience and developmental biology to provide insight into the cellular and molecular mechanisms by which complex nervous systems develop.
( see also Child development - Mechanisms )
Cognitive neuroscience is concerned with the scientific study of biological substrates underlying cognition, with a focus on the neural substrates of mental processes.
Systems neuroscience is a subdiscipline of neuroscience which studies the function of neural circuits and systems. It is an umbrella term, encompassing a number of areas of study concerned with how nerve cells behave when connected together to form neural networks.
Molecular neuroscience is a branch of neuroscience that examines the biology of the nervous system with molecular biology, molecular genetics, protein chemistry and related methodologies ( ie. concerning neurotransmitters moving via physiology of synapses etc )
[ also see Neuropharmacology above]
Computational neuroscience includes both the study of the information processing functions of the nervous system, and the use of digital computers to study the nervous system. It is an interdisciplinary science that links the diverse fields of neuroscience, cognitive science and psychology, electrical engineering, computer science, physics and mathematics.
Neurophilosophy or "philosophy of neuroscience" is the interdisciplinary study of neuroscience and philosophy. Work in this field is often separated into two distinct approaches. The first approach attempts to solve problems in philosophy of mind with empirical information from the neurosciences. The second approach attempts to clarify neuroscientific results using the conceptual rigor and methods of philosophy of science.
Neurology is the medical specialty dealing with disorders of the nervous system. It deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems.
Neuropsychology studies the structure and function of the brain related to psychological processes and behaviors. The term is used most frequently with reference to studies of the effects of brain damage in humans and animals.
Outline of the human nervous system | https://en.wikipedia.org/wiki/Outline_of_neuroscience |
The following outline is provided as an overview of and topical guide to organic chemistry:
Organic chemistry is the scientific study of the structure, properties, composition, reactions , and preparation (by synthesis or by other means) of carbon -based compounds, hydrocarbons , and their derivatives. These compounds may contain any number of other elements, including hydrogen , nitrogen , oxygen , the halogens as well as phosphorus , silicon , and sulfur . [ 1 ] [ 2 ] [ 3 ]
Current trends in organic chemistry include (as of 2020): | https://en.wikipedia.org/wiki/Outline_of_organic_chemistry |
The following outline is provided as an overview of and topical guide to physiology:
Physiology – scientific study of the normal function in living systems. [ 1 ] A branch of biology, its focus is in how organisms, organ systems, organs, cells, and biomolecules carry out the chemical or physical functions that exist in a living system. [ 2 ]
Physiology can be described as all of the following:
By approach
By organism
By process
By subsystem
History of physiology | https://en.wikipedia.org/wiki/Outline_of_physiology |
Probability is a measure of the likeliness that an event will occur. Probability is used to quantify an attitude of mind towards some proposition whose truth is not certain. The proposition of interest is usually of the form "A specific event will occur." The attitude of mind is of the form "How certain is it that the event will occur?" The certainty that is adopted can be described in terms of a numerical measure, and this number, between 0 and 1 (where 0 indicates impossibility and 1 indicates certainty) is called the probability. Probability theory is used extensively in statistics , mathematics , science and philosophy to draw conclusions about the likelihood of potential events and the underlying mechanics of complex systems.
(Related topics: set theory , simple theorems in the algebra of sets )
(Related topics: measure theory )
(Related topics: integral transforms )
(Related topics: convergence ) | https://en.wikipedia.org/wiki/Outline_of_probability |
The following outline is provided as an overview of and topical guide to regression analysis:
Regression analysis – use of statistical techniques for learning about the relationship between one or more dependent variables ( Y ) and one or more independent variables ( X ). | https://en.wikipedia.org/wiki/Outline_of_regression_analysis |
The following outline is provided as an overview of and topical guide to the Solar System:
Solar System – gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets (including Earth), with the remainder being significantly smaller objects, such as dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury.
From largest to smallest structure:
Discovery and exploration of the Solar System –
Formation and evolution of the Solar System –
The number of currently known, or observed, objects of the Solar System are in the hundreds of thousands. Many of them are listed in the following articles:
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Outline_of_the_Solar_System |
The following outline is provided as an overview of and topical guide to transport:
Transport or transportation – movement of people and goods from one place to another.
Aviation
Animal-powered transport
Cable transport
Conveyor transport
Convoy
Human-powered transport
Ground transportation
Road transport
Off-road transport
Rail transport
Pipeline transport
Ship transport
Space transport
Transmission
Transportation : | https://en.wikipedia.org/wiki/Outline_of_transport |
The following outline is provided as an overview of and topical guide to trigonometry:
Trigonometry – branch of mathematics that studies the relationships between the sides and the angles in triangles . Trigonometry defines the trigonometric functions , which describe those relationships and have applicability to cyclical phenomena, such as waves .
Uses of trigonometry
Trigonometric identity ( list )
Solution of triangles
Trigonometric tables
Spherical trigonometry
mnemonics in trigonometry | https://en.wikipedia.org/wiki/Outline_of_trigonometry |
The following outline is provided as an overview of and topical guide to zoology:
Zoology – study of animals . Zoology, or "animal biology", is the branch of biology that relates to the animal kingdom, including the identification, structure, embryology , evolution , classification , habits , and distribution of all animals , both living and extinct , and how they interact with their ecosystems. The term is derived from Ancient Greek word ζῷον ( zōon ), i.e. "animal" and λόγος, ( logos ), i.e. "knowledge, study". [ 1 ] To study the variety of animals that exist (or have existed), see list of animals by common name and lists of animals .
Animals
Kingdom: Animalia
In alphabetical order by surname: | https://en.wikipedia.org/wiki/Outline_of_zoology |
ORFS stands for Output RF Spectrum , where 'RF' stands for Radio Frequency .
The acronym ORFS is used in the context of mobile communication systems, e.g., GSM . It stands for the relationship between (a) the frequency offset from the carrier and (b) the power, measured in a specific bandwidth and time, produced by the mobile station due to effects in modulation and power ramping and switching. [ 1 ] ORFS measurements are defined and required in order to prove conformance by various institutions, e.g., the U.S. Federal Communications Commission (FCC) or ETSI .
This science article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Output_Radio_Frequency_Spectrum |
In computing, output padding is the insertion of non-printing characters into the device output stream to allow for a preceding control operation to take effect.
Output padding was necessary on many printing devices, notably Teletype and other mechanical terminals, after the issuance of a carriage return . [ 1 ] Without the padding, following characters might print in the middle of the output line.
Output padding was also necessary on many display terminals after cursor positioning, scrolling, and other commands. [ 2 ] [ 3 ]
Typically the null character was used; the delete character was occasionally used. The number of padding characters depended on the particular device, but also sometimes on the horizontal position of the printing carriage .
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Output_padding |
An output signal switching device ( OSSD ) is an electronic device used as part of the safety system of a machine. It provides a coded signal which, when interrupted due to a safety event, signals the machine to shut down. It works by converting the standard direct current supply, usually 24 volts, into two pulsed and out-of-phase signals. The benefit of this is to avoid the possibility of a stray signal keeping the machine operating while actually in an unsafe condition.
The device usually acts as the interface of a sensor (such as a light curtain ), designed to signal a safety-related event, typically when the light curtain beam's being "broken". OSSD signals are the outputs from the protective device (light curtain or scanner) to a safety relay . OSSD outputs are typically semiconductor or transistor outputs, as opposed to relay or contact type outputs. There are usually two independent channels, so-called OSSD1 and OSSD2.
The non-tripped state is typically 24 VDC, and the tripped state (when the safety barrier has been violated) 0 VDC. If a wire were to break between the light curtain and the safety relay, the safety relay would trip to the safe state.
The OSSD outputs are self-checked. In the non-tripped state, the outputs periodically pulse low. The protective device checks the output, to make sure it does indeed go low when commanded. If not, the output may have failed or has shorted to 24V somewhere else. Between OSSD1 and OSSD2 the pulse intervals are staggered to check for crisscrossed wiring between the two. [ 1 ]
The technology relies on two independent channels carrying the same information output by the device:
The OSSD technology and a classification of timing and other properties are described in the "Position Paper CB24I" [ 2 ] issued by ZVEI - German Electrical and Electronic Manufacturer's Association.
OSSD signals are typically of Interface type C as described in CB24I.
Some related terms:
This engineering-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Output_signal_switching_device |
An outrigger is a projecting structure on a boat, with specific meaning depending on types of vessel. Outriggers may also refer to legs on a wheeled vehicle that are folded out when it needs stabilization, for example on a crane that lifts heavy loads.
An outrigger describes any contraposing float rigging beyond the side ( gunwale ) of a boat to improve the vessel's stability. If a single outrigger is used it is usually but not always windward . [ 1 ] [ why? ] The technology was originally developed by the Austronesian people . There are two main types of boats with outriggers: double outriggers (prevalent in maritime Southeast Asia ) and single outriggers (prevalent in Madagascar , Melanesia , Micronesia and Polynesia ). Multihull ships are also derived from outrigger boats. [ 2 ]
In an outrigger canoe and in sailboats such as the proa , an outrigger is a thin, long, solid, hull used to stabilise an inherently unstable main hull. The outrigger is positioned rigidly and parallel to the main hull so that the main hull is less likely to capsize . If only one outrigger is used on a vessel, its weight reduces the tendency to capsize in one direction and its buoyancy reduces the tendency in the other direction.
On a keelboat , "outrigger" refers to a variety of structures by which the running rigging (such as a sheet ) may be attached outboard (outside the lateral limits) of the boat's hull. The Racing Rules of Sailing generally prohibit [ 3 ] such outriggers, though they are explicitly permitted on specific classes, such as the IMOCA Open 60 [ 4 ] used in several major offshore races.
In fishing from vessels, an outrigger is a pole or series of poles that allow boats to trawl more lines in the water without tangling and simulates a school of fish.
In a rowing boat or galley , an outrigger (or rigger) is a triangular frame that holds the rowlock (into which the oar is slotted) away from the saxboard (or gunwale in gig rowing ) to optimize leverage. Wooden outriggers appear on the new trireme around the 7th or 6th centuries BC and later on Italian galleys around AD 1300 , while Harry Clasper (1812–1870), a British professional rower, popularised the use of the modern tubular-metal version and the top rowing events accepted the physiological and ergonomic advantages so acceded to its use in competitions. In recent decades, some manufacturers of racing shells have developed wing-riggers which are reinforced arcs or flattened tubular projections akin to aircraft wings, instead of conventional triangular structures. | https://en.wikipedia.org/wiki/Outrigger |
An outron is a nucleotide sequence at the 5' end of the primary transcript of a gene that is removed by a special form of RNA splicing during maturation of the final RNA product. [ 1 ] Whereas intron sequences are located inside the gene, outron sequences lie outside the gene. [ 2 ]
The outron is an intron-like sequence possessing similar characteristics such as the G+C content [ 3 ] and a splice acceptor site that is the signal for trans -splicing . [ 4 ] [ 5 ] Such a trans -splice site is essentially defined as an acceptor (3') splice site without an upstream donor (5') splice site.
In eukaryotes such as euglenozoans , dinoflagellates , sponges , nematodes , cnidarians , ctenophores , flatworms , crustaceans , chaetognaths , rotifers , and tunicates , the length of spliced leader (SL) outrons range from 30 to 102 nucleotides (nt) , with the SL exon length ranging from 16 to 51 nt, and the full SL RNA length ranging from 46 to 141 nt. [ 3 ]
In standard cis-splicing , the donor splice site in upstream position is required together with an acceptor site located on downstream position on the same pre-RNA molecule.
By contrast, the SL trans -splicing relies on a 3' acceptor splice site on the outron, and a 5' donor splice site (GU dinucleotide) located on a separate RNA molecule, the SL RNA. [ 3 ] Moreover, the outron of the premature mRNA contains a branchpoint adenosine — followed by a downstream polypyrimidine tract — which interacts with the intron-like portion of the SL RNA to form a 'Y' branched byproduct, reminiscent of the lasso structure formed during intron splicing. Nuclear machinery then resolves this 'Y' branching structure by trans -splicing the SL RNA sequence to the 3′ trans -splice acceptor site (AG dinucleotide) of the pre-mRNA. [ 2 ]
When outrons are processed, the SL exon is trans -spliced to distinct, unpaired, downstream acceptor sites adjacent to each open reading frame of the polycistronic pre-mRNA, leading to distinct mature capped transcripts. [ 6 ] [ 7 ] [ 8 ] | https://en.wikipedia.org/wiki/Outron |
Outsourcing is a business practice in which companies use external providers to carry out business processes that would otherwise be handled internally. [ 1 ] [ 2 ] [ 3 ] Outsourcing sometimes involves transferring employees and assets from one firm to another.
The term outsourcing , which came from the phrase outside resourcing , originated no later than 1981 at a time when industrial jobs in the United States were being moved overseas, contributing to the economic and cultural collapse of small, industrial towns. [ 4 ] [ 5 ] [ 6 ] In some contexts, the term smartsourcing is also used. [ 7 ]
The concept, which The Economist says has "made its presence felt since the time of the Second World War ", [ 8 ] often involves the contracting out of a business process (e.g., payroll processing, claims processing), operational, and/or non-core functions, such as manufacturing, facility management , call center /call center support.
The practice of handing over control of public services to private enterprises ( privatization ), even if conducted on a limited, short-term basis, [ 9 ] may also be described as outsourcing. [ 10 ]
Outsourcing includes both foreign and domestic contracting, [ 11 ] and therefore should not be confused with offshoring which is relocating a business process to another country but does not imply or preclude another company. [ 12 ] In practice, the concepts can be intertwined, i.e. offshore outsourcing , and can be individually or jointly, partially or completely reversed, [ 13 ] as described by terms such as reshoring , inshoring , and insourcing .
Global labor arbitrage can provide major financial savings from lower international labor rates, which could be a major motivation for offshoring. Cost savings from economies of scale and specialization can also motivate outsourcing, even if not offshoring. Since about 2015 indirect revenue benefits have increasingly become additional motivators. [ 14 ] [ 15 ]
Another motivation is speed to market. To make this work, a new process was developed: "outsource the outsourcing process". [ 16 ] Details of managing DuPont 's chief information officer Cinda Hallman 's $4 billion 10-year outsourcing contract with Computer Sciences Corporation and Accenture were outsourced, thus avoiding "inventing a process if we'd done it in-house". A term subsequently developed to describe this is midsourcing . [ 17 ] [ 18 ] [ 19 ]
Outsourcing can offer greater budget flexibility and control by allowing organizations to pay for the services and business functions they need, when they need them. It is often perceived to reduce hiring and training specialized staff, to make available specialized expertise, and to decrease capital, operating expenses, [ 20 ] and risk.
"Do what you do best and outsource the rest" has become an internationally recognized business tagline first "coined and developed" [ 21 ] in the 1990s by management consultant Peter Drucker . The slogan was primarily used to advocate outsourcing as a viable business strategy. Drucker began explaining the concept of "outsourcing" as early as 1989 in his Wall Street Journal article entitled "Sell the Mailroom". [ 22 ]
From Drucker's perspective, a company should only seek to subcontract in those areas in which it demonstrated no special ability. [ 23 ] The business strategy outlined by his slogan recommended that companies should take advantage of a specialist provider's knowledge and economies of scale to improve performance and achieve the service needed. [ 24 ]
In 2009, by way of recognition, Peter Drucker posthumously received a significant honor when he was inducted into the Outsourcing Hall of Fame for his outstanding work in the field. [ 23 ]
The biggest difference between outsourcing and in-house provision is with regards to the difference in ownership: outsourcing usually presupposes the integration of business processes under a different ownership, over which the client business has minimal or no control. This requires the use of outsourcing relationship management . [ 25 ]
Sometimes the effect of what looks like outsourcing from one side and insourcing from the other side can be unexpected; The New York Times reported in 2001 that "6.4 million Americans .. worked for foreign companies as of 2001, [but] more jobs are being outsourced than" [the reverse]. [ 26 ]
While U.S. companies do not outsource to reduce high top level executive or managerial costs, [ 27 ] they primarily outsource to reduce peripheral and "non-core" business expenses. [ 28 ] Further reasons are higher taxes, high energy costs, and excessive government regulation or mandates.
Mandated benefits like social security , Medicare , and safety protection (e.g. Occupational Safety and Health Administration regulations) are also motivators. [ 29 ] By contrast, executive pay in the U.S. in 2007, which could exceed 400 times more than average workers—a gap 20 times bigger than it was in 1965, [ 27 ] is not a factor. [ 30 ]
Other reasons include reducing and controlling operating costs, [ 31 ] improving company focus, gaining access to world-class capabilities, tax credits, [ 32 ] freeing internal resources for other purposes, streamlining or increasing efficiency for time-consuming functions, and maximizing use of external resources. For small businesses, contracting/subcontracting/"outsourcing" might be done to improve work-life balance . [ 33 ]
Two organizations may enter into a contractual agreement involving an exchange of services , expertise, and payments . Outsourcing is said to help firms to perform well in their core competencies, fuel innovation , and mitigate a shortage of skill or expertise in the areas where they want to outsource. [ 34 ] Established good practices include covering exit arrangements within an outsourcing agreement, with an exit period and a mutual commitment to maintaining continuity until the exit phase is completed. [ 35 ]
Following the adding of management layers in the 1950s and 1960s to support expansion for the sake of economy of scale, corporations found that agility and added profits could be obtained by focusing on core strengths; the 1970s and 1980s were the beginnings of what later was named outsourcing. [ 36 ] Kodak 's 1989 "outsourcing most of its information technology systems" [ 37 ] was followed by others during the 1990s. [ 37 ]
In 2013, the International Association of Outsourcing Professionals gave recognition to Electronic Data Systems Corporation's Morton H. Meyerson [ 38 ] who, in 1967, proposed the business model that eventually became known as outsourcing. [ 39 ]
The growth of offshoring of IT-enabled services, although not universally accepted, [ 40 ] [ 41 ] both to subsidiaries and to outside companies (offshore outsourcing) is linked to the availability of large amounts of reliable and affordable communication infrastructure following the telecommunication and Internet expansion of the late 1990s. [ 42 ] Services making use of low-cost countries included:
In the early 21st century, businesses increasingly outsourced to suppliers outside their own country, sometimes referred to as offshoring or offshore outsourcing . Other options subsequently emerged including: nearshoring, crowdsourcing , multisourcing , [ 44 ] [ 45 ] strategic alliances / strategic partnerships , strategic outsourcing. [ 46 ]
Forbes considered the 2016 U.S. presidential election "the most disruptive change agent for the outsourcing industry", [ 47 ] especially the renewed "invest in America" goal highlighted in campaigning, but the magazine tepidly reversed direction in 2019 as to the outcome for employment. [ 48 ] In the case of armament acquisition , section 323 of the National Defense Authorization Act for 2014 requires military personnel "to solicit information from all U.S.-owned arsenals regarding the capability of that arsenal to fulfill the manufacturing requirement" when undertaking a make-or-buy analysis. [ 49 ]
Furthermore, there are growing legal requirements for data protection , where obligations and implementation details must be understood by both sides. [ 50 ] [ 51 ] This includes dealing with customer rights. [ 52 ]
UK government policy notes that certain services must remain in-house, citing the development of policy , stewardship of tax spend and retention of certain critical knowledge as examples. Guidance states that specific criteria must govern the identification of such services, and that "everything else" could potentially be outsourced. [ 53 ]
Inflation, high domestic interest rates, and economic growth pushed India's IT salaries 10–15%, making some jobs relatively "too" expensive, compared to other offshoring destinations. Areas for advancing within the value chain included research and development, equity analysis, tax-return processing, radiological analysis, and medical transcription .
Although offshoring initially focused on manufacturing, white-collar offshoring/outsourcing has grown rapidly since the early 21st century. The digital workforce of countries like India and China are only paid a fraction of what would be minimum wage in the United States. On average, software engineers are getting paid between 250,000 and 1,500,000 rupees (US$4,000 to US$23,000) in India as opposed to $40,000–$100,000 in countries such as the U.S. and Canada . [ 54 ] Closer to the U.S., Costa Rica has become a major source for the advantages of a highly educated labor force, a large bilingual population, stable democratic government, and similar time zones as the U.S. It takes only a few hours to travel between Costa Rica and U.S. Companies such as Intel , Procter & Gamble , HP, Gensler , Amazon and Bank of America have big operations in Costa Rica. [ 55 ]
Unlike outsourced manufacturing, outsourced white collar workers have flextime and can choose their working hours, and for which companies to work. Clients benefit from remote work , reduced office space, management salary, and employee benefits as these individuals are independent contractors . [ 56 ]
Ending a government outsourcing arrangement poses difficulties. [ 57 ]
There are many outsourcing models, with variations [ 58 ] by country, [ 59 ] year [ 60 ] [ 61 ] and industry. [ 62 ] Japanese companies often outsource to China, particularly to formerly Japanese-occupied cities. [ 63 ] German companies have outsourced to Eastern European countries with German-language affiliation, such as Poland and Romania . [ 64 ] French companies outsource to North Africa for similar reasons. For Australian IT companies, Indonesia is one of the major choice of offshoring destination. Near-shore location, common time zone and adequate IT work force are the reasons for offshoring IT services to Indonesia. [ citation needed ]
Another approach is to differentiate between tactical and strategic outsourcing models. Tactical models include:
Strategic consultancy includes for business process improvement . [ 65 ]
When offshore outsourcing knowledge work, firms heavily rely on the availability of technical personnel at offshore locations. One of the challenges in offshoring engineering innovation is a reduction in quality. [ 66 ]
Co-sourcing is a hybrid of internal staff supplemented by an external service provider. [ 67 ] [ 68 ] Co-sourcing can minimize sourcing risks, increase transparency, clarity and lend toward better control than fully outsourced. [ 69 ]
Co-sourcing services can supplement internal audit staff with specialized skills such as information risk management or integrity services, or help during peak periods, or similarly for other areas such as software development or human resources.
Identity management co-sourcing is when on-site hardware [ 70 ] [ 71 ] interacts with outside identity services.
This contrasts with an "all in-the-cloud" service scenario, where the identity service is built, hosted and operated by the service provider in an externally hosted, cloud computing infrastructure.
Offshore software R&D is the provision of software development services by a supplier (whether external or internal) located in a different country from the one where the software will be used. The global software R&D services market, as contrasted to information technology outsourcing (ITO) and business process outsourcing (BPO), is rather young and currently is at a relatively early stage of development. [ 72 ]
Canada, India, Ireland , and Israel were the four leading countries as of 2003. [ 72 ] Although many countries have participated in the offshore outsourcing of software development, their involvement in co-sourced and outsourced Research & Development (R&D) was somewhat limited. Canada, the second largest by 2009, had 21%. [ 73 ]
As of 2018, the top three were deemed by one "research-based policy analysis and commentary from leading economists" as China, India and Israel." [ 74 ]
Gartner Group adds in Russia , but does not make clear whether this is pure R&D or run-of-the-mill IT outsourcing. [ 75 ]
Focusing on software quality metrics is a good way to maintain track of how well a project is performing. [ 76 ] [ better source needed ]
Globalization and complex supply chains , along with greater physical distance between higher management and the production-floor employees often requires a change in management methodologies, as inspection and feedback may not be as direct and frequent as in internal processes. This often requires the assimilation of new communication methods such as voice over IP , instant messaging , and issue tracking systems , new time management methods such as time tracking software , and new cost- and schedule-assessment tools such as cost estimation software . [ 77 ] [ 78 ] [ 79 ]
The term "transition methodology" [ 80 ] describes the process of migrating knowledge, systems, and operating capabilities between the two sides. [ 81 ]
In the area of call-center outsourcing, especially when combined with offshoring, [ 82 ] agents may speak with different linguistic features such as accents , word use and phraseology, which may impede comprehension. [ 83 ] [ 84 ] [ 85 ] [ 86 ]
In 1979, Nobel laureate Oliver E. Williamson wrote that the governance structure is the "framework within which the integrity of a transaction is decided", and that "because contracts are varied and complex, governance structures vary with the nature of the transaction". [ 87 ] University of Tennessee researchers have been studying complex outsourcing relationships since 2003. Emerging thinking regarding strategic outsourcing is focusing on creating a contract structure in which the parties have a vested interest in managing what are often highly complex business arrangements in a more collaborative, aligned, flexible, and credible way. [ 88 ] [ 89 ]
Reduced security, sometimes related to lower loyalty [ 90 ] may occur, even when 'outsourced' staff change their legal status but not their desk. While security and compliance issues are supposed to be addressed through the contract between the client and the suppliers, fraud cases have been reported.
In April 2005, a high-profile case involved the theft of $350,000 from four Citibank customers when call-center workers acquired the passwords to customer accounts and transferred the money to their own accounts opened under fictitious names. Citibank did not find out about the problem until the American customers noticed discrepancies with their accounts and notified the bank. [ 91 ]
Richard Baldwin 's 2006 The Great Unbundling work was followed in 2012 by Globalization's Second Acceleration (the Second Unbundling) and in 2016 by The Great Convergence: Information Technology and the New Globalization . [ 92 ] It is here, rather than in manufacturing, that the bits economy can advance in ways that the economy of atoms and things cannot: an early 1990s Newsweek ran a half page cartoon showing someone who had just ordered a pizza online, and was seeking help to download it. [ citation needed ]
Step-in rights allow the client or a nominated third party the right to step-in and intervene, in particular to directly operate the outsourced services or to appoint a new operator. Circumstances where step-in rights may be contractually invoked may include supplier insolvency , a force majeure event which prevents or impedes the outsourced service provision, where the client believes that there is a substantial risk to the provision of the services, or where performance fails to meet a defined critical level of service. [ 93 ] Suitable clauses in a contract may provide for the outsourced service provider to pay any additional costs which are faced by the client and specify that the provider's obligation to provide the services is annulled or suspended. [ 94 ]
If a contract has a clause granting step-in rights, [ 95 ] then there is a right, though not an obligation, [ 96 ] to take over a task that is not going well, or even the entire project. When and How are important: "What is the process for stepping-in" must be clearly defined in the collateral warranty . [ 97 ]
An example of when there is sometimes hesitancy about exercising this right was reported by the BBC in 2018, when Wealden District Council in East Sussex was "considering exercising 'step in rights' on its waste collection contract with Kier " due to issues of poor service. [ 98 ] After some discussion in this case, a "recovery plan" was agreed with the contractor so that the step in rights were not actually exercised. [ 99 ]
Stabler notes that in the event that step-in rights are taken up, it is important to establish which elements of a process are business-critical and ensure these are made top priority when implementing the step-in. [ 93 ]
A number of outsourcings and offshorings that were deemed failures [ 100 ] [ 101 ] [ 66 ] led to reversals [ 102 ] [ 103 ] signaled by use of terms such as insourcing and reshoring . The New York Times reported in 2017 that IBM "plans to hire 25,000 more workers in the United States over the next four years," overlapping India-based Infosys 's "10,000 workers in the United States over the next two years." [ 103 ] A clue to a tipping point having been reached was a short essay titled "Maybe You Shouldn't Outsource Everything After All" [ 104 ] and the longer "That Job Sent to India May Now Go to Indiana."
Among problems encountered were supply-and-demand induced raises in salaries and lost benefits of similar-time-zone. Other issues were differences in language and culture. [ 103 ] [ 84 ] Another reason for a decrease in outsourcing is that many jobs that were subcontracted abroad have been replaced by technological advances. [ 105 ]
According to a 2005 Deloitte Consulting survey, a quarter of the companies which had outsourced tasks reversed their strategy. [ 105 ]
These reversals, however, did not undo the damage. New factories often:
Public opinion in the U.S. and other Western powers opposing outsourcing was particularly strengthened by the drastic increase in unemployment as a result of the 2007–2008 financial crisis. From 2000 to 2010, the U.S. experienced a net loss of 687,000 jobs due to outsourcing, primarily in the computers and electronics sector. Public disenchantment with outsourcing has not only stirred political responses, as seen in the 2012 U.S. presidential campaigns , but it has also made companies more reluctant to outsource or offshore jobs. [ 105 ]
A counterswing depicted by a 2016 Deloitte survey suggested that companies are no longer reluctant to outsource. [ 107 ] Deloitte's survey identified three trends:
Insourcing is the process of reversing an outsourcing, possibly using help from those not currently part of the in-house staff. [ 108 ] [ 109 ] [ 110 ] Some authors call this backsourcing, [ 111 ] reserving the term insourcing to refer simply to conducting certain activities in-house.
Outsourcing has gone through many iterations and reinventions, and some outsourcing contracts have been partially or fully reversed. Often the reason is to maintain control of critical production or competencies, and insourcing is used to reduce costs of taxes, labor and transportation. [ 112 ] Sometimes there are problems with the outsourcing agreements, because of the pressure to bring jobs back to their home country, or simply because it has stopped being efficient to outsource particular tasks. [ 113 ]
Studies conducted at companies confirm the positive impact of using insourcing on financial performance. [ 114 ]
Regional insourcing, a related term, takes place when a company assigns work to a subsidiary that is within the same country. This differs from onshoring and reshoring , which may be either inside or outside the company. For this process, a company establishes satellite locations for specific entities of their business, making use of advantages one state may have over another, such as taxes, education, or workforce skill sets, [ 115 ] This concept focuses on the delegating or reassigning of procedures, functions, or jobs from production within a business in one location to another internal entity that specializes in that operation. This allows companies to streamline production, boost competency, and increase their bottom line.
This competitive strategy applies the classical argument of Adam Smith , which posits that two nations would benefit more from one another by trading the goods that they are more proficient at manufacturing. [ 116 ] [ 117 ]
To those who are concerned that nations may be losing a net number of jobs due to outsourcing, some [ 118 ] point out that insourcing also occurs. A 2004 study [ 119 ] in the U.S., the UK, and many other industrialized countries more jobs are insourced than outsourced. The New York Times disagreed, and wrote that free trade with low-wage countries is win-lose for many employees who find their jobs offshored or with stagnating wages. [ 120 ]
The impact of offshore outsourcing, according to two estimates published by The Economist , showed unequal effect during the period studied 2004 to 2015, ranging from 150,000 to as high as 300,000 jobs lost per year. [ 121 ]
In 2010, a group of manufacturers started the Reshoring Initiative, focusing on bringing manufacturing jobs for American companies back to the country. Their data indicated that
140,000 American jobs were lost in 2003 due to offshoring. Eleven years later in 2014, the U.S. recovered 10,000 of those offshored positions; this marked the highest net gain in 20 years. [ 122 ] More than 90% of the jobs that American companies "offshored" and outsourced manufacturing to low cost countries such as China, Malaysia and Vietnam did not return. [ 122 ]
The fluctuation of prefixes and names give rise to many more "cross-breeds" of insourcing. For example, "offshore insourcing" is "when companies set up their own " captive " process centers overseas, sometimes called a Captive Service , [ 123 ] taking advantage of their cheaper surroundings while maintaining control of their back-office work and business processes." [ 124 ] " Remote insourcing " refers to hiring developers to work in-house from virtual (remote) facilities. [ 125 ]
A 2012 series of articles in The Atlantic [ 126 ] [ 127 ] [ 128 ] [ 129 ] highlighted a turning of the tide for parts of the U.S.'s manufacturing industry. Specific causes identified include rising third-world wages, recognition of hidden off-shoring costs, innovations in design/manufacture/assembly/time-to-market, increasing fuel and transportation costs, falling energy costs in the U.S., increasing U.S. labor productivity, and union flexibility. Hiring at GE's giant Appliance Park in Louisville, Kentucky , increased 90% during 2012.
More than one company uses a "100% U. Based" phrase, whether within or outside their envelopes. "100% US-based customer service available 24/7" is how, in 2024, Business Insider described the expectations of some customers. [ 130 ]
From the standpoint of labor, outsourcing may represent a new threat, contributing to worker insecurity, and is reflective of the general process of globalization and economic polarization . [ 131 ]
Western governments may attempt to compensate workers affected by outsourcing through various forms of legislation. In Europe, the Acquired Rights Directive attempts to address the issue. The directive is implemented differently in different nations. In the U.S., the Trade Adjustment Assistance Act is meant to provide compensation for workers directly affected by international trade agreements. Whether or not these policies provide the security and fair compensation they promise is debatable.
In response to the recession, U.S. president Barack Obama launched the SelectUSA program in 2011. In January 2012, Obama issued a Call to Action to Invest in America at the White House "Insourcing American Jobs" Forum. [ 136 ] Obama met with representatives of Otis Elevator , Apple , DuPont, Master Lock , and others which had recently brought jobs back or made significant investments in the U.S.
Governments may legislate to authorise the outsourcing of specific functions or the work of specific government agencies, for example in the United Kingdom, the Social Security Administration Act 1992 (as amended) authorises the contracting-out of work-focussed interviews and documentary work, [ 137 ] and the Contracting Out of Functions (Tribunal Staff) Order 2009 authorises the contracting-out of tribunals ' administrative work. [ 138 ]
A main feature of outsourcing influencing policy-making is the unpredictability it generates, including its defense/military ramifications, [ 139 ] regarding the future of any particular sector or skill-group. The uncertainty of future conditions influences governance approaches to different aspects of long-term policies.
In particular, distinction is needed between
A governance that attempts adapting to the changing environment will facilitate growth and a stable transition to new economic structures [ 140 ] until the economic structures become detrimental to the social, political and cultural structures.
Automation increases output and allows for reduced cost per item. When these changes are not well synchronized, unemployment or underemployment is a likely result. When transportation costs remain unchanged, the negative effect may be permanent; [ 106 ] jobs in protected sectors may no longer exist. [ 141 ]
Studies suggest that the effect of U.S. outsourcing on Mexico is that for every 10% increase in U.S. wages, north Mexico cities along the border experienced wage rises of 2.5%, about 0.69% higher than in inner cities. [ 142 ]
By contrast, higher rates of saving and investment in Asian countries, along with rising levels of education, studies suggest, fueled the 'Asian miracle' rather than improvements in productivity and industrial efficiency. There was also an increase in patenting and research and development expenditures. [ 143 ]
Outsourcing results from an internationalization of labor markets as more tasks become tradable. According to leading economist Greg Mankiw , the labour market functions under the same forces as the market of goods, with the underlying implication that the greater the number of tasks available to being moved, the better for efficiency under the gains from trade. With technological progress, more tasks can be offshored at different stages of the overall corporate process. [ 144 ]
The tradeoffs are not always balanced, and a 2004 viewer of the situation said "the total number of jobs realized in the United States from insourcing is far less than those lost through outsourcing." [ 145 ]
Import competition has caused a de facto 'race-to-the-bottom' where countries lower environmental regulations to secure a competitive edge for their industries relative to other countries.
As Mexico competes with China over Canadian and American markets, its national Commission for Environmental Cooperation has not been active in enacting or enforcing regulations to prevent environmental damage from increasingly industrialized Export Processing Zones. Similarly, since the signing of the North American Free Trade Agreement , heavy industries have increasingly moved to the U.S., which has a comparative advantage due to its abundant presence of capital and well-developed technology. A further example of environmental de-regulation with the objective of protecting trade incentives have been the numerous exemptions to carbon taxes in European countries during the 1990s.
Although outsourcing can influence environmental de-regulatory trends, the added cost of preventing pollution does not majorly determine trade flows or industrialization. [ 146 ]
Companies such as ET Water Systems (now a Jain Irrigation Systems company), [ 147 ] GE Appliances and Caterpillar found that with the increase of labor costs in Japan and China, the cost of shipping and custom fees, it cost only about 10% more to manufacture in America. [ 105 ] Advances in technology and automation such as 3D printing technologies [ 148 ] have made bringing manufacturing back to the U.S., both cost effective and possible. Adidas , for example, plans to produce highly customized shoes with 3D printers in the U.S. [ 149 ]
Outsourcing has contributed to further levelling of global inequalities as it has led to general trends of industrialization in the Global South and deindustrialization in the Global North. [ 150 ]
Not all manufacturing should return to the U.S. [ 151 ] The rise of the middle class in China, India and other countries has created markets for the products made in those countries. Just as the U.S. has a Made in USA program, other countries support products being made domestically. Localization, the process of manufacturing products for the local market, is an approach to keeping some manufacturing offshore and bringing some of it back. Besides the cost savings of manufacturing closer to the market, the lead time for adapting to changes in the market is faster.
The rise in industrial efficiency which characterized development in developed countries has occurred as a result of labor-saving technological improvements. Although these improvements do not directly reduce employment levels but rather increase output per unit of work, they can indirectly diminish the amount of labor required for fixed levels of output. [ 152 ]
It has been suggested that "workers require more education and different skills, working with software rather than drill presses" rather than rely on limited growth labor requirements for non-tradable services. [ 106 ]
The main driver for offshoring development work has been the greater availability of developers at a lower cost than in the home country. However, the rise in offshore development has taken place in parallel with an increased awareness of the importance of usability, and the user experience, in software. Outsourced development poses special problems for development, i.e. the more formal, contractual relationship between the supplier and client, and geographical separation place greater distance between the developers and users, which makes it harder to reflect the users' needs in the final product. This problem is exacerbated if the development is offshore. Further complications arise from cultural differences, which apply even if the development is carried out by an in-house offshore team. [ 153 ]
Historically offshore development concentrated on back office functions but, as offshoring has grown, a wider range of applications have been developed. Offshore suppliers have had to respond to the commercial pressures arising from usability issues by building up their usability expertise. Indeed, this problem has presented an attractive opportunity to some suppliers to move up market and offer higher value services. [ 154 ] [ 155 ] [ 156 ]
Offshore Software R&D means that company A turns over responsibility, in whole or in part, of an in-house software development to company B whose location is outside of company A's national jurisdiction. Maximizing the economic value of an offshore software development asset critically depends on understanding how best to use the available forms of legal regulations to protect intellectual rights. If the vendor cannot be trusted to protect trade secrets, then the risks of an offshoring software development may outweigh its potential benefits. Hence, it is critical to review the intellectual property policy of the potential offshoring supplier. The intellectual property protection policy of an offshore software development company must be reflected in these crucial documents: General Agreement, Non-Disclosure Agreement, and Employee Confidentiality Contract. [ 157 ]
As forecast in 2003, [ 158 ] R&D is outsourced. Ownership of intellectual property by the outsourcing company, despite outside development, was the goal. To defend against tax-motivated cost-shifting, the U.S. government passed regulations in 2006 to make outsourcing research harder. [ 159 ] Despite many R&D contracts given to Indian universities and labs, only some research solutions were patented. [ 160 ]
While Pfizer moved some of its R&D from the UK to India, [ 161 ] a Forbes article suggested that it is increasingly more dangerous to offshore IP-sensitive projects to India, because of India's continued ignorance of patent regulations. [ 162 ] In turn, companies such as Pfizer and Novartis, have lost rights to sell many of their cancer medications in India because of lack of IP protection .
A 2018 University of Chicago Law School article titled "The Future of Outsourcing" begins with "The future of outsourcing is digital." [ 50 ] According to other sources, the "Do what you do best and outsource the rest" [ 21 ] approach means that "integration with retained systems" [ 50 ] is the new transition challenge; people training still exists, but is merely an "also".
There is more complexity than before, especially when the outside company may be an integrator. [ 50 ]
While the number of technically skilled labor grows in India, Indian offshore companies are increasingly tapping into the skilled labor already available in Eastern Europe to better address the needs of the Western European R&D market. [ 163 ] [ citation needed ]
Protection of some data involved in outsourcing, such as about patients ( HIPAA ) is one of the few federal protections.
"Outsourcing" is a continuing political issue in the U.S., having been conflated with offshoring during the 2004 U.S. presidential election . The political debate centered on outsourcing's consequences for the domestic U.S. workforce. Democratic U.S. presidential candidate John Kerry called U.S. firms that outsource jobs abroad or that incorporate overseas in tax havens to avoid paying their "fair share" of U.S. taxes " Benedict Arnold corporations".
A Zogby International August 2004 poll found that 71% of American voters believed "outsourcing jobs overseas" hurt the economy while another 62% believed that the U.S. government should impose some legislative action against these companies, possibly in the form of increased taxes. [ 164 ] [ 165 ] President Obama promoted the Bring Jobs Home Act to help reshore jobs by using tax cuts and credits for moving operations back to the U.S. [ 166 ] [ 167 ] The same bill was reintroduced in the 113th U.S. Congress . [ 168 ] [ 169 ]
While labor advocates claim union busting as one possible cause of outsourcing, [ 170 ] another claim is high corporate income tax rate in the U.S. relative to other OECD nations, [ 171 ] [ 172 ] [ needs update ] and the practice of taxing revenues earned outside of U.S. jurisdiction, a very uncommon practice. Some counterclaim that the actual taxes paid by U.S. corporations may be considerably lower than "official" rates due to the use of tax loopholes, tax havens, and "gaming the system". [ 173 ] [ 174 ]
Sarbanes-Oxley has also been cited as a factor. [ citation needed ]
The U.S. has a special visa , the H-1B, which enables American companies to temporarily (up to three years, or by extension, six) hire foreign workers to supplement their employees or replace those holding existing positions. In hearings on this matter, a U.S. senator called these "their outsourcing visa". [ 175 ]
The European Council 's Directive 77/187 of 14 February 1977 protects employees' rights in the event of transfers of undertakings, businesses or parts of businesses (as amended 29 June 1998, Directive 98/50/EC and 12 March 2001's Directive 2001/23). Rights acquired by employees with the former employer are to be safeguarded when they, together with the undertaking in which they are employed, are transferred to another employer, i.e., the contractor.
Case subsequent to the European Court of Justice 's Christel Schmidt v. Spar- und Leihkasse der früheren Ämter Bordesholm, Kiel und Cronshagen , Case C-392/92 [1994] have disputed whether a particular contracting-out exercise constituted a transfer of an undertaking (see, for example, Ayse Süzen v. Zehnacker Gebäudereinigung GmbH Krankenhausservice , Case C-13/95 [1997]). In principle, employees may benefit from the protection offered by the directive.
Countries which have been the focus of outsourcing include India and the Philippines for American and European companies, and China and Vietnam for Japanese companies .
The Asian IT service market is still in its infancy, but in 2008 industry think tank Nasscom-McKinsey predicted a $17 billion IT service industry in India alone. [ 176 ]
A China-based company, Lenovo , outsourced/reshored manufacturing of some time-critical customized PCs to the U.S. since "If it made them in China they would spend six weeks on a ship." [ 105 ]
Article 44 of Japan's Employment Security Act implicitly bans the domestic/foreign workers supplied by unauthorized companies regardless of their operating locations. The law will apply if at least one party of suppliers, clients, labors reside in Japan, and if the labors are the integral part of the chain of command by the client company, or the supplier.
Victims can lodge a criminal complaint against the CEO of the suppliers and clients. The CEO risks arrest, and the Japanese company may face a private settlement with financial package in the range between 20 and 100 million JPY ($200,000 – US$1 million).
Print and mail outsourcing is the outsourcing of document printing and distribution.
The Print Services & Distribution Association was formed in 1946, and its members provide services that today might involve the word outsource. Similarly, members of the Direct Mail Marketing Association (established 1917) were the "outsourcers" for advertising agencies and others doing mailings.
The term "outsourcing" became very common in the print and mail business during the 1990s, and later expanded to be very broad and inclusive of most any process by 2000. Today, there are web based print to mail solutions for small to mid-size companies which allow the user to send one to thousands of documents into the mail stream, directly from a desktop or web interface. [ 179 ]
The term outsource marketing has been used in Britain to mean the outsourcing of the marketing function. [ 180 ] The motivation for this has been:
While much of this work is the "bread and butter" of specialized departments within advertising agencies, sometimes specialist are used, such as when The Guardian outsourced most of its marketing design in May 2010. [ 185 ]
Business process outsourcing ( BPO ) is a subset of outsourcing that involves the contracting of the operations and responsibilities of a specific business process to a third-party service provider . Originally, this was associated with manufacturing firms, such as Coca-Cola that outsourced large segments of its supply chain . [ 186 ]
BPO is typically categorized into back office and front office outsourcing. [ 187 ] BPO can help your business remain competitive and efficient by leveraging the expertise of other companies that are more specialized in certain functions. [ 188 ]
BPO can be offshore outsourcing, near-shore outsourcing to a nearby country, or onshore outsourcing to the same country. Information technology -enabled service (ITES-BPO), [ 189 ] knowledge process outsourcing (KPO) and legal process outsourcing (LPO), a.k.a. legal outsourcing, are some of the sub-segments of BPO.
Although BPO began as a cost-reducer, changes (specifically the move to more service-based rather than product-based contracts), companies now choose to outsource their back-office increasingly for time flexibility and direct quality control. [ 190 ] Business process outsourcing enhances the flexibility of an organization in different ways:
BPO vendor charges are project-based or fee-for-service, using business models such as remote in-sourcing or similar software development and outsourcing models. [ 191 ] [ 192 ] This can help a company to become more flexible by transforming fixed into variable costs . [ 193 ] A variable cost structure helps a company responding to changes in required capacity and does not require a company to invest in assets, thereby making the company more flexible. [ 194 ]
BPO also permits focusing on a company's core competencies . [ 195 ]
Supply chain management with effective use of supply chain partners and business process outsourcing can increase the speed of several business processes. [ 186 ]
Even various contractual compensation strategies may leave the company as having a new "single point of failure" (where even an after the fact payment is not enough to offset "complete failure of the customer's business"). [ 196 ] Unclear contractual issues are not the only risks; there's also changing requirements and unforeseen charges, failure to meet service levels, and a dependence on the BPO which reduces flexibility. The latter is called lock-in ; flexibility may be lost due to penalty clauses and other contract terms. [ 197 ] Also, the selection criteria may seem vague and undifferentiated. [ 198 ]
Security risks can arise regarding both from physical communication and from a privacy perspective. Employee attitude may change, and the company risks losing independence. [ 199 ] [ 200 ]
Risks and threats of outsourcing must therefore be managed, to achieve any benefits. In order to manage outsourcing in a structured way, maximizing positive outcome, minimizing risks and avoiding any threats, a business continuity management (BCM) model is set up. BCM consists of a set of steps, to successfully identify, manage and control the business processes that are, or can be outsourced. [ 201 ]
Analytic hierarchy process (AHP) is a framework of BPO focused on identifying potential outsourceable information systems. [ 202 ] L. Willcocks, M. Lacity and G. Fitzgerald identify several contracting problems companies face, ranging from unclear contract formatting, to a lack of understanding of technical IT processes. [ 203 ]
Industry analysts have identified robotic process automation (RPA) software and in particular the enhanced self-guided RPAAI based on artificial intelligence as a potential threat to the industry [ 204 ] [ 205 ] and speculate as to the likely long-term impact. [ 206 ] In the short term, however, there is likely to be little impact as existing contracts run their course: it is only reasonable to expect demand for cost efficiency and innovation to result in transformative changes at the point of contract renewals. With the average length of a BPO contract being 5 years or more [ 207 ] – and many contracts being longer – this hypothesis will take some time to play out.
On the other hand, an academic study by the London School of Economics was at pains to counter the so-called 'myth' that RPA will bring back many jobs from offshore. [ 208 ] One possible argument behind such an assertion is that new technology provides new opportunities for increased quality, reliability, scalability and cost control, thus enabling BPO providers to increasingly compete on an outcomes-based model rather than competing on cost alone. With the core offering potentially changing from a "lift and shift" approach based on fixed costs to a more qualitative, service based and outcomes-based model, there is perhaps a new opportunity to grow the BPO industry with a new offering.
One estimate of the worldwide BPO market from the BPO Services Global Industry Almanac 2017, puts the size of the industry in 2016 at about US$140 billion. [ 209 ]
India, China and the Philippines are major powerhouses in the industry. In 2017, in India, the BPO industry generated US$30 billion in revenue according to the national industry association. [ 210 ] The BPO industry is a small segment of the total outsourcing industry in India. The BPO industry workforce in India is expected to shrink by 14% in 2021. [ 211 ]
The BPO industry and IT services industry in combination are worth a total of US$154 billion in revenue in 2017. [ 212 ] The BPO industry in the Philippines generated $26.7 billion in revenues in 2020, [ 213 ] while around 700 thousand medium and high skill jobs would be created by 2022. [ 214 ]
In 2015, official statistics put the size of the total outsourcing industry in China, including not only the BPO industry but also IT outsourcing services, at $130.9 billion. [ 215 ] | https://en.wikipedia.org/wiki/Outsourcing |
The Outstanding Structure Award is an award presented by the International Association for Bridge and Structural Engineering to the Engineer, Architect, Contractor, and the Owner in recognition of the most remarkable, innovative, creative or otherwise stimulating structure completed within the last few years .
The Award consists of a Plaque that can be fixed to the winning structure. One or more structures are awarded annually since 2000. | https://en.wikipedia.org/wiki/Outstanding_Structure_Award |
The ouzo effect ( / ˈ uː z oʊ / OO -zoh ), also known as the louche effect ( / l uː ʃ / LOOSH ) and spontaneous emulsification , is the phenomenon of formation of a milky oil-in-water emulsion when water is added to ouzo and other anise-flavored liqueurs and spirits , such as pastis , rakı , arak , sambuca and absinthe . Such emulsions occur with only minimal mixing and are highly stable. [ 1 ]
First a strongly hydrophobic essential oil such as trans -anethole is dissolved in a water- miscible solvent , such as ethanol , and the ethanol itself forms a solution (a homogeneous mixture ) with water.
If then the concentration of ethanol is lowered by addition of more water the hydrophobic substance precipitates from the solution and forms an emulsion with the remaining ethanol-water-mixture. The tiny droplets of the substance in the emulsion scatter light and thus make the mixture appear white.
Oil-in-water emulsions are not normally stable. Oil droplets coalesce until complete phase separation is achieved at macroscopic levels. Addition of a small amount of surfactant or the application of high shear rates (strong stirring) can stabilize the oil droplets.
In a water-rich ouzo mixture the droplet coalescence is dramatically slowed without mechanical agitation, dispersing agents, or surfactants. It forms a stable homogeneous fluid dispersion by liquid–liquid nucleation . [ 2 ] The size of the droplets when measured by small-angle neutron scattering was found to be on the order of a micron . [ 3 ]
Using dynamic light scattering , Sitnikova et al. [ 1 ] showed that the droplets of oil in the emulsion grow by Ostwald ripening , and that droplets do not coalesce. The Ostwald ripening rate is observed to diminish with increasing ethanol concentrations until the droplets stabilize in size with an average diameter of 3 microns .
Based on thermodynamic considerations of the multi-component mixture, the emulsion derives its stability from trapping between the binodal and spinodal curves in the phase diagram . [ 3 ] However, the microscopic mechanisms responsible for the observed slowing of Ostwald ripening rates at increasing ethanol concentrations appear not fully understood.
Emulsions have many commercial uses. A large range of prepared food products, detergents , and body-care products take the form of emulsions that are required to be stable over a long period of time. The ouzo effect is seen as a potential mechanism for generating surfactant -free emulsions without the need for high-shear stabilisation techniques that are costly in large-scale production processes. The creation of a variety of dispersions such as pseudolatexes, silicone emulsions, and biodegradable polymeric nanocapsules, have been synthesized using the ouzo effect, though as stated previously, the exact mechanism of this effect remains unclear. [ 4 ] Nanoparticles formed using the ouzo effect are thought to be kinetically stabilized as opposed to thermodynamically stabilized micelles formed using a surfactant due to the fast solidification of the polymer during the preparation process. [ 5 ]
Media related to Ouzo effect at Wikimedia Commons | https://en.wikipedia.org/wiki/Ouzo_effect |
An ova bank , or cryobank , or egg cell bank is a facility that collects and stores human ova , mainly from ova donors , primarily for the purpose of achieving pregnancies of either the donor, at a later time (i.e. to overcome issues of infertility), or through third party reproduction , notably by artificial insemination . Ova donated in this way are known as donor ova .
There are currently very few ova banks in existence. [ 1 ] [ 2 ] [ 3 ]
Generally, the main purpose of storing ova, at present, is to overcome infertility which may arise at a later age, or due to a disease. The ova are generally collected between 31 and 35 years of age. [ 4 ]
The procedure of collecting ova may or may not [ 5 ] include ovarian hyperstimulation . [ 6 ]
It can be expected however that ova collection will become more important in the future, i.e. for third party reproduction , and/or for producing stem cells , i.e. from unfertilized eggs (oocytes). [ 7 ] | https://en.wikipedia.org/wiki/Ova_bank |
Ovarian culture is an in-vitro process that allows for the investigation of the development, toxicology and pathology of the ovary . [ 1 ] This technique can also be used to study possible applications of fertility treatments e.g. isolating oocytes from primordial ovarian follicles that could be used for fertilisation. [ 1 ]
There are several culture systems which can be employed to investigate ovarian and follicular growth and development. [ citation needed ]
The culture of intact ovaries supports the formation and development of primordial follicles. Ovaries are dissected from neonatal mouse pups and placed into ovarian culture medium containing Bovine Serum Albumen (BSA) dissolved in α-Minimal Essential Media (αMEM). The cultures are maintained in a 37°C, 5% CO 2 incubator and then the ovaries are frozen or fixed to facilitate further study. [ 1 ]
This method of culturing supports the growth of individual follicles from late pre-antral to pre-ovulatory stage. This system allows follicle growth and hormone production to be studied. The ovaries of young mice (19–23 days) are removed and halved, and follicles are identified under a microscope. Late pre-antral follicles are identified as having a diameter of 180-200 μm and containing 2-3 layers of granulosa cells . Follicles are manually dissected and then examined for suitability to culture. Follicles are chosen for culture only if they are healthy (diameter of 190 ± 10 μm; translucent; without dark atretic areas; intact basal lamina .) Wells containing follicle culture medium (α-Minimal Essential Media, recombinant human follicle stimulating hormone, ascorbic acid and adult female mouse serum) is overlaid with sterilised silicon oil, which prevents medium evaporation. A follicle is placed at the bottom of each well and maintained in a 37°C, 5% CO 2 incubator, being moved into a well containing fresh medium for up to 6 days. If growth measurements are being taken visually the distortion due to the oil layer must be accounted for. Follicles are frozen or fixed so further analysis can be performed. [ 1 ]
By culturing 2 follicles in close proximity, follicle-follicle interactions can be examined. The follicles may grow together to form a two-follicle unit. The follicles are dissected from the ovaries as above, then placed in contact with each other in pairs, in a well with follicle culture medium and sterilised silicon oil. Follicles from different genetic sources can be co-cultured so that tissue origins can be differentiated within the co-culture. The medium is replaced every 2 days and after 6 days the culture is fixed or frozen for further processing. [ 1 ]
This method allows follicle-ovary interactions to be studied. The ovaries and follicles are dissected as above and then one follicle is placed in contact with one pole of a neonatal ovary on a plate. The follicle-ovary plate is cultured in follicle culture medium at 37 °C, 5% CO 2 for up to 5 days. At this point the co-culture is frozen or fixed before further processing. To facilitate differentiation between tissue origins the ovary and the follicle should be from different genetic sources. [ 1 ]
At present research within the field of reproductive toxicology is principally carried out in vivo , however new culture methods have been developed with the aim of allowing ovarian follicles to be grown in vitro . [ 3 ] These new methods allow us to culture isolated ovarian follicles, embryos, ovaries (whole organ or only part of the tissue), and embryonic stem cells. [ 1 ] Ovarian cultures are useful to research as they can allow us to replicate systematic follicle development, periodical ovulation, and follicle atresia in an environment with modulated culture conditions. [ 1 ] The ability of in vitro ovarian cultures to detect damage to the ovary and its specialised structures of the follicles and oocytes, allows for faster screening of potential developmental and/or reproductive toxicants. [ 3 ] Therefore, ovarian culture systems have become increasingly widely used in reproductive biology and toxicology. [ 3 ]
Culture of the whole ovary or ovarian fragments allows evaluation of various parameters in a controlled way and, therefore, has the potential for more complete reproductive toxicity studies. [ 3 ] A big advantage of ovarian culture is the ability to evaluate the effect of drugs on the pool of primordial follicles that make up the ovarian reserve. However, this strategy is restricted regarding the duration of culture time, as short periods may not be sufficient to ensure follicular development. [ 4 ] On the contrary, cells may be negatively affected by longer periods of culture. [ 1 ]
Most in vitro toxicology studies use female mice and rat models. These species have been selected to assess the adverse effects of drugs on reproductive function and fertility, due to ease of handling and small size. [ 5 ] Additionally, these species have been well characterised; anatomically, physiologically, and genetically. Their short life cycles make it convenient to assess gestation, breastfeeding, and puberty. [ 5 ] The relevance of animal studies for toxicological risk assessment in heterogeneous human populations remains undetermined as it is unknown if the results obtained can be extrapolated to humans. [ 2 ]
The use of in vivo maturation in ovarian culture would eliminate the risk of Ovarian Hyperstimulation Syndrome during IVF in patients with polycystic ovary syndrome (PCOS). [ 1 ] For those without PCOS, in vitro maturation still has advantages as the process is less intense as superovulation is not required. [ 6 ] Principles of ovarian culture can be applied to women who are resistant to FSH or oestrogen sensitive tumours. [ 6 ] In comparison to IVF, cells used in vitro maturation are harvested at a smaller size, immature and arrested at Metaphase I stage of meiosis. [ 6 ] Once in the lab they undergo maturation to Metaphase II. [ 6 ]
Ovarian tissue can be harvested before ovarian damaging treatments and re-implanted at a later stage using cryopreservation. [ 5 ] However, this method is associated with the recurrence of malignancy in those with ovarian cancer and leukaemia. [ 5 ] In theory, ovarian tissue culture is a safer method to produce mature oocytes for fertilisation in these patients. [ 5 ] | https://en.wikipedia.org/wiki/Ovarian_culture |
Ovarian drilling , also known as multiperforation or laparoscopic ovarian diathermy, is a surgical technique of puncturing the membranes surrounding the ovary with a laser beam or a surgical needle using minimally invasive laparoscopic procedures. [ 1 ] It differs from ovarian wedge resection, which involves the cutting of tissue. Minimally invasive ovarian drilling procedures have replaced wedge resections. [ 2 ] Ovarian drilling is favored over wedge resection because cutting into the ovary might result in adhesions, potentially complicating postoperative outcomes. [ 3 ] Ovarian drilling and ovarian wedge resection are treatment options to reduce the amount of androgen producing tissue in women with polycystic ovarian syndrome (PCOS). [ 4 ] PCOS is the primary cause of anovulation, which results in female infertility. [ 5 ] The induction of mono-ovulatory cycles can restore fertility. [ 6 ]
The oral drug clomiphene citrate (CC) is the first-line treatment for PCOS-related infertility, yet one-fifth of women are resistant to the drug and fail to ovulate. [ 7 ] Patients are considered resistant if the treatment fails for six months at the appropriate dosage. [ 1 ] Women who are resistant to the medication clomiphene citrate are commonly treated with medications that induce ovulation such as gonadotrophins. [ 8 ] Medications that induce ovulation such as CC can also be associated with multiple pregnancies and problems with the women's cycle and this therapy is very expensive due to the route of administration (daily by injection) and the requirement for regular ultrasounds, laparoscopic ovarian drilling is sometimes considered by medical professionals for treating anovulation. [ 8 ] Known side effects and risks include the need for anesthesia , the risk of infection, and a risk of adhesions forming. [ 8 ] There may sometimes be a smaller risk of the person losing ovarian function. [ 8 ]
Ovarian drilling is a surgical alternative to CC treatment or recommended for women with WHO Group II ovulation disorders . [ 6 ] Other non-surgical medical options in the treatment of PCOS include the oestrogen receptor modulator tamoxifen , aromatase inhibitors , insulin sensitising drugs, and hormonal ovarian stimulation. [ 9 ] The effectiveness of the surgical procedure is similar to CC or gonadotropin treatment for induced ovulation for PCOS patients, but results in fewer multiple pregnancies per ongoing pregnancy regardless if the technique is unilaterally or bilaterally performed. [ 10 ]
If patients do not become pregnant six months after ovulation has been reestablished from ovarian drilling treatment, drug treatments may be reintroduced or in vitro fertilisation (IVF) may be considered. [ 1 ]
Part of the criteria of PCOS diagnosis includes elevated levels of androgens in the bloodstream or other signs of androgen excess ( hyperandrogenism ). [ 1 ] The procedure causes a drop in serum androgen levels and possibly in estrogen levels. [ 5 ] After ovarian follicles and stroma are destroyed, there is a reduction in these hormone levels. [ 11 ] The procedure results in a decrease in plasma luteinizing hormone (LH) and in pulsations as well as a periodic drop in inhibin B levels. [ 1 ] The most plausible theory states that the reduction of these hormone concentrations leads to an increase in the secretion of follicle-stimulating hormone (FSH) and sex hormone-binding globulin , leading to effective follicular maturation and ovulation. [ 5 ] [ 1 ] Low serum oestradiol concentrations are associated with decreased aromatase activity. [ 1 ] Inflammatory growth factors such as insulin-like growth factor-1 are produced due to injury and aid the effects of FSH through greater blood flow and gonadotropin delivery. [ 11 ] Circulating and intrafollicular levels of anti-Müllerian hormone (AMH), which can help quantify recruitable ovarian follicle activity, are reduced after laparoscopic ovarian drilling in women with PCOS. [ 12 ]
When the clinician determines that ovarian drilling is appropriate and the woman decides to undergo this treatment, consent is obtained. The risks are communicated to the woman. [ 13 ]
The most commonly performed method is with a monopolar needle or hook because of the equipment's availability and simple installation. [ 6 ] Other common instrumentation consists of the use of a bipolar electrical surgical electrodes or a CO 2 , argon, or ND-YAG laser . [ 14 ] This instrumentation has the ability to produce the intended results with a very focal approach. Typically, a 100 W electrical cautery dissector is first used to cross the ovarian cortex, then electrocoagulation is performed at 40 W, however rates range from 30 to 400 W. [ 1 ] The surgical punctures are performed on the ovarian cortex and are usually 4–10 mm deep and 3 mm wide. [ 10 ] [ 11 ] The number of punctures is related to subsequent ability to conceive—it has been found that five to ten punctures are more likely to produce the intended conception. [ 13 ] Ovarian drilling is performed laparoscopically and either transumbilical ( culdoscopy ) or transvaginal ( fertiloscopy ). [ 1 ]
Though preferable to creating incisions on the ovary, ovarian drilling does have some risks. These are: pelvic adhesion formation, hemorrhage , gas embolism , pneumothorax , premature ovarian failure , long-term ovarian function, developing hyperstimulation syndrome , adhesion formation, infertility and multiple births . [ 2 ] [ 13 ] [ 6 ] [ 15 ] Transvaginal hydrolaparoscopy (THL) ovarian drilling may minimize the risk of iatrogenic adhesion formation and decreased ovarian reserve (DOR), which can impinge upon fertility. [ 16 ] LOD does not contribute to the risk of decreased ovarian reserve. [ 12 ] There is risk of electrical accidents with monopoly current. [ 1 ] A rare complication of LOD is major vascular injury, mostly on the small vessels in the anterior abdominal wall when the Veress needle and trocar are inserted at the beginning of the procedure. [ 15 ]
Ovarian drilling has lower rates of ovarian hyperstimulation syndrome and of multi-fetal gestation . [ 17 ] [ 8 ] The advantages of the procedure also include its singular treatment, as opposed to several trials of ovulation inductions. [ 2 ] Other benefits of this technique include cost-effectiveness and that it can be performed as an outpatient procedure . [ 6 ]
Ovarian drilling was first used in the treatment of PCOS in 1984 and has evolved as a safe and effective surgery. [ 11 ] After performing laparoscopic electrosurgical ovarian drilling in CC-resistant patients in 1984, Gjönnaess found that this technique increased ovulation rates to 45 percent and pregnancy rates to 42 percent. [ 18 ] In 1988, laparoscopic multiple punch resection of ovaries on the hypothalamo-pituitary axis, slightly modified from Gjönnaess's operation, caused a reduction in LH pulsation and pituitary responsiveness in the treatment of PCOS. [ 19 ] In 1989, ovarian drilling was conducted with argon, carbon dioxide (CO 2 ) or potassium-titanyl-phosphate (KTP) laser vaporization causing spontaneous ovulation in 71 percent of those treated. [ 14 ] The procedure has been modified and popularized in the treatment of patients with CC-resistance. [ 11 ] | https://en.wikipedia.org/wiki/Ovarian_drilling |
Ovarian follicle activation can be defined as primordial follicles in the ovary moving from a quiescent (inactive) to a growing phase. The primordial follicle in the ovary is what makes up the “pool” of follicles that will be induced to enter growth and developmental changes that change them into pre-ovulatory follicles, ready to be released during ovulation . The process of development from a primordial follicle to a pre-ovulatory follicle is called folliculogenesis .
Activation of the primordial follicle involves the following: a morphological change from flattened to cuboidal granulosa cells , proliferation of granulosa cells, formation of the protective zona pellucida layer, and growth of the oocyte. [ 1 ]
It is widely understood that androgens act primarily on preantral follicles and that this activity is important for preantral follicle growth. Additionally, it is thought that androgens are involved in primordial follicle activation. However, the influence of androgens on primordial follicle recruitment and whether this response is primary or secondary is still uncertain.
Primordial follicles are activated to grow into antral follicles . Communication between the oocytes and the surrounding somatic cells, such as the granulosa cells and the theca cells , is involved in the control of primordial follicle activation. There are various activator signalling pathways that are involved in the control of ovarian follicle activation, including: Neurotropin , nerve growth factor (NGF) and its tyrosine receptor kinase (NTRK1), neurotrophin 4 (NT4), brain-derived neurotrophic factor (BDNF) and their receptor NTRK2. Additional ligands have a role in facilitating primordial follicle activation such as transforming growth factor-beta (TGF-B), growth differentiation factor 9 (GDF9) and bone morphogenic protein 15 (BMP15).
The follicular activation rate is increased in experiments where recombinant GDF9 is added. Additionally, the in vitro addition of GDF9 to human ovarian cortical tissue causes enhanced activation and follicular survival. Removing GDF9 from mice, through knock-out experiments, halts follicle progression beyond the first stage, and prevents granulosa cell proliferation. However, these GDF9 null mice have accelerated oocyte growth, suggesting that GDF9 is partially responsible for granulosa cell recruitment, as well as inhibiting oocyte growth. GDF9 promotes follicular survival and growth as a result of dampened granulosa apoptosis and follicular atresia. [ 2 ]
As discussed above TGF-β ligands, for example BMP4 and 7 have a role in follicular activation. SMADS are downstream molecules of the TGF-β signalling pathway, hence rely on TGF-β for activation. In the absence of SMADs, mice have decreased folliculogenesis, with decreased quantities of primordial follicles, as well as developed adult follicles at both developmental stages. BMP15 has been shown to stimulate granulosa cell growth by encouraging the proliferation of undifferentiated granulosa cells. This is not dependent on FSH. It was shown that two proliferation markers, Ki-67 and proliferating cell nuclear antigen (PCNA), are regulated by these factors. Additionally, PCNA has been suggested to act as a key regulator of ovarian follicle development. The temporal expression of PCNA in oocytes is coincident with the start of primordial follicle formation. PCNA promotes apoptosis of oocytes, which regulates primordial follicle assembly. [ citation needed ]
Another molecule that has been implicated in the activation of oocyte follicles is Forkhead boxL2 (Foxl2). In knock out studies, it has been shown that Foxl2 may be responsible for the cuboidal transition of the pre-granulosa cells. Hence, when Foxl2 is removed, the primordial follicles are unable to develop into secondary follicles. [ 2 ]
Spermatogenesis-and-oogenesis-specific basic helix-loop-helix containing protein 1 (Sohlh1) is expressed within germ cell clusters and in new primordial follicles. Knock out studies of this protein in mice show a reduced number of oocytes present at 7 weeks post birth and a malfunction in the transition from primordial to primary follicle. [ 2 ]
Phosphatase and tensin homolog ( PTEN ) is a tumour suppressor gene whose actions directly affect the activation of primordial follicles. It does this by negatively controlling the PI3K/AKT/mTOR pathway . [ 2 ] This particular action of PTEN was initially discovered in an experiment using PTEN knockout mice. [ 2 ] The absence of PTEN within the primordial follicles lead to an increase in AKT phosphorylation. This then creates a subsequent rise in FOXO3 export, as AKT is no longer inhibiting its production. [ 3 ] This led to over-activation of the primordial follicles, which resulted in a premature decline of the primordial follicle pool. [ 2 ]
When Foxo3 is KO in mice models a huge uncontrolled activation of follicles is seen thus the mouse ovaries are deficient of the entire pool of primordial follicles because they have been prematurely activated. [ 2 ] This action is regulated by phosphorylation, the unphosphorylated form is transcriptionally active in the nucleus. However, when phosphorylation occurs the protein is transported to the cytoplasm and loses its transcriptional activity. Pelosi et al. noted that the timing and level of the Foxo3 expression is very important to regulate ovarian follicle activation. [ 4 ]
AKt- PTEN-AKt and Foxo3 are all involved in the same pathway. PTEN is situated upstream of AKt. Therefore, if PTEN is deleted specifically from an oocyte this causes an increase in AKt activity resulting in large numbers of dormant ovarian follicles resuming their growth and differentiation. The TSC complex also plays an important role in this pathways by suppressing the activity of mTOR which has been proven to be essential for maintaining dormancy. [ 5 ]
Tuberin/tuberous sclerosis complex is also thought to be important in the regulation of primordial follicle activation. TSC negatively controls the function of mTOR (mammalian target of rapamycin). TSC knockout mice have a raised level of mTORC1 activity. [ 6 ] Suppressing mTORC1 is a necessary process to prevent primordial follicles from being prematurely activated and therefore premature ovarian insufficiency. [ 7 ]
AMH ( anti-Müllerian hormone ) is a member of the transforming growth factor beta (TGF-b), that has a very important role in regulating both testicular and ovarian function. In the first instance AMH inhibits the initial enrollment of the resting primordial follicles. Secondly AMH prevents the regulation of preantral/small antral follicle growth by reducing their responsiveness to FSH. [ 8 ]
P27 inhibits cell cycle progression at the G1 phase [ 9 ] by preventing the action of cyclin E-Cdk2. [ 3 ] Due to its important role in the cell cycle, it is found within the nucleus of mice oocytes in primordial and primary follicles. During puberty of p27 knock out mice, all primordial follicles are activated and leads to POF. This indicates that p27 is a vital regulator in maintaining a quiescent state in primordial follicles. [ 6 ]
Premature ovarian failure (POF), or premature ovarian insufficiency (POI), is a female reproductive disorder characterised by at least 4 months of primary or secondary amenorrhea , before the age of 40. [ 10 ] It is caused by either a decrease in the primordial follicle pool, accelerated atresia of follicles or altered maturation or recruitment of primordial follicles and is associated with menopausal levels of follicle stimulating hormones, exceeding 40 Ul/L. [ 10 ] , [ 11 ] Specific activator and suppressor genes are implicated in ovarian follicle activation and recent research suggests that POF may be the consequence of a genetic mutation in one or more of these genes.
FOXL2 - FOXL2 knockout mouse models showed failure of granulosa cell differentiation, which led to the premature activation and depletion of primordial follicles, characteristic of POF. Two different variations of mutations in the FOXL2 gene, which cause different forms of POF, one with earlier onset and the other with later onset and incomplete penetrance, have been identified. [ 12 ] Additionally, mutations in the FOXL2 gene have been found in approximately 5% of nonsyndromic POF patients, which suggests that FOXL2 mutations are also associated with idiopathic POF. [ 10 ]
BMP15 and GDF9 - Mutations in BMP15 and GDF9 genes can be involved in POF, but are not major causes of the disease. For example, low GDF9 mutation frequency has been found in a large cohort of Indian cases of POF. [ 13 ]
SOHLH1 - Little is known about the causative association of SOHLH1 and POF, however three novel SOHLH1 variants have been found to potentially cause the disease and when studied, they were absent in controls. [ 12 ]
AMH - A decrease in AMH expression in POF antral follicles leads to defective antral development. [ 14 ]
mTORC1 and PI3K - Deregulation of mTORC1 and PI3K signaling pathways in oocytes results in ovarian pathological conditions, including POF and subsequent infertility. [ 15 ]
PTEN - Studies of mice with a deletion in PTEN in the oocytes showed early activation of the entire pool of primordial follicles, leading to a lack of primordial follicles in adulthood, resulting in a POF phenotype. [ 16 ]
Foxo3a - Studies into mice with complete and partial Foxo3a deletions also showed premature activation of the entire primordial follicle pool, destroying the ovarian reserve and leading to oocyte death. This led to a POF phenotype, seen in studies in a range of countries. [ 17 ] , [ 18 ]
TSC - In the oocytes of Tsc2 knockout mice, elevated mTORC1 activity causes the pool of primordial follicles to become activated prematurely. This results in follicle depletion in early adulthood, causing POF. [ 7 ]
As well as having many genetic causes, premature ovarian failure has been shown to be a side effect of many chemotherapeutic agents. [ 19 ] The damage suffered by ovaries appears to be dose-dependent , and a class of chemotherapy drugs known as alkylating agents , seem to cause the most damage to the ovary and follicles. There are two ways in which this damage occurs:
Chemotherapeutic agents, such as Cyclophosphamide, have been shown to activate the PI3K/PTEN/Akr pathway, which is the main pathway involved in keeping the follicles dormant and permitting them to grow - activation of this pathway encourages more primordial follicles to grow and develop. [ 19 ] These growing follicles may then be destroyed in subsequent rounds of chemotherapy, which often target growing cells, which will then cause more primordial follicles to differentiate and grow to replace the destroyed cells. This concept, known as burnout, leads to a depletion of the ovarian reserve and results in premature ovarian failure. [ citation needed ]
Oocyte cryopreservation is a preservative process which can be used as a way of preserving fertility in children treated for childhood or adolescent cancer, and to avoid the damage caused to the ovaries caused by cytotoxic drugs often used in chemotherapy. [ 20 ] There are several methods of cryopreservation , each with different levels of effectiveness. After cryopreservation, the ovarian tissue must be placed back into the patient, in order to allow the ovary to function normally again and regain fertility.
Restoration of the ovarian function occurs in almost all cases of cryopreservation, but it takes a while for the ovarian follicles to regain full function. In all cases of successful function restoration, it took 3.5-6.5 months after reimplantation before a rise in oestrogen , a key hormone produced by the ovary, and a decrease in follicle stimulating hormone (FSH) were detected. The variation in time difference may be due to differences in the follicular reserves in the women at the time of cryopreservation. [ 20 ]
In vitro follicle activation describes the process by which primordial follicles are deliberately activated. Oocytes from these activated follicles can be used to establish a pregnancy. [ 21 ] This has potential for widespread use in restoring fertility in women suffering with fertility issues such as early or medically induced menopause . [ 22 ]
Conventional IVA or drug free IVA can be used to preserve fertility in patients with Diminished Ovarian Reserve (see Poor Ovarian Reserve ) or Premature Ovarian Insufficiency (POI). [ 23 ]
Drug free IVA is more beneficial in patients with DOR or POI with recent menses cessation than conventional IVA. This is because it reduces the invasiveness of surgical approaches and circumvents adverse effects of tissue culture on follicles. [ 24 ] Traditional IVA is recommended in patients with low ovarian reserve like in patients with POI with prolonged menopause or patients looking for immediate outcomes. [ 23 ]
Using drug free IVA, at least a total of 18 healthy live births and three more ongoing pregnancies in POI and DOR patients charted in papers, with additional unpublished deliveries and ongoing pregnancies reported in scientific conferences. [ 23 ]
Patients with resistant ovary syndrome (ROS) are a subgroup of patients with POI who have multiple antral follicles present in the ovary as shown by ultrasound monitoring. These follicles secrete low levels of oestrogen but are resistant to exogenous follicle stimulating hormone treatment so cannot develop to maturity. [ 24 ]
Like patients with POI, ROS patients can respond to incision of the ovarian cortex to cause Hippo signalling disruption. Additionally, laparoscopic ovarian incision (LOI) can be performed in vivo to successfully promote follicle growth without removing tissue outside of the body. [ 24 ]
Oocyte cryopreservation is widely used to protect primordial follicles from gonadotoxic treatment but some patients are not eligible for this, IVA could be a beneficial option for fertility preservation in cancer patients. The IVA approach could maximise the number of secondary oocytes in infertile woman since transplanting ovarian tissue successfully activates the dormant follicle pool. [ 23 ]
The IVA method focuses on the short-term goal of generating a large number of activated follicles immediately following transplantation of tissue back into the body. [ 24 ] This means that the IVA method has a reduced graft lifespan compared to the 4–5 years that can be offered in the cryopreservation method. The graft lifespan relates to the length of time following transplantation back into the body that pregnancies can occur within. [ 25 ] This is because IVA promotes loss of dormant follicles to activation so fewer dormant follicles will remain in the graft. This, as a result, reduces graft lifespan. [ 25 ] However, this can be beneficial in patients looking for immediate outcomes or to improve her chance of conceiving as fast as possible due to advancing age. [ 23 ]
So far, there have been no reported live births but progress is being made in in-vitro research. [ 23 ]
Patients are usually treated with synthetic oestrogen and progesterone for at least a month in order to suppress their gonadotrophin levels which has been shown to promote ovulation . [ 26 ] A laparoscopic approach is used to remove the ovary. The outer part of the ovary (the cortex) is removed using scissors as this minimises any damage to the sensitive inner ovarian tissue. This tissue is then analysed to assess the presence of existing follicles before further manipulation. [ 27 ]
Artificial ovaries can be used to provide follicles for artificial activation. [ 2 ] Follicles from these synthetic ovaries have been shown to support successful pregnancies in mouse models and show promise for potential for future treatments in humans. [ 2 ]
The Hippo signalling pathway is an essential pathway involving several components that regulate cell growth, survival and stem cell renewal. [ 28 ] For this reason, the Hippo signalling pathway has been implicated in the maintenance and control of organ size in organisms.
In recent years, ovarian fragmentation has surfaced as an effective strategy to promote ovarian follicular activation and growth. [ 2 ] Studies undertaken on cultured human ovarian cortical fragments have demonstrated that the mechanical damage resulting from ovarian tissue fragmentation disrupts the Hippo signalling pathway. This has been found to accelerate follicle activation. Mechanical damage to the ovaries through fragmentation have been found to induce a transient elevation in actin polymerisation - a process where small actin molecules (proteins) combine to form a large, chain-like structure with repeating actin units. [ 2 ] Mechanical damage to the ovaries has also decreased phosphorylation of Yes-associated protein (YAP), an essential compound in the Hippo Signalling pathway. [ 29 ] Phosphorylation refers to the addition of phosphate groups to molecules. Consequently, this leads to an increase in the levels of YAP in the nucleus. This in turn triggers a downstream ripple effect to increase the expression of growth factors and apoptosis inhibitors, therefore promoting cell growth and survival.
Another key pathway in ovarian follicle activation is the PI3K-PTEN-AKT-FOXO3 pathway .
The PI3K-PTEN-AKT-FOXO3 pathway is a complex signal transduction pathway involving a cascade of several molecules. This pathway is involved in promoting growth, survival and proliferation of cells in response to certain factors. [ 30 ] The pathway is therefore implicated in the activation of ovarian primordial follicles. In in vitro activation of ovarian follicles, drugs such as inhibitors of PTEN or activators of PI3K can be administered to stimulate follicle activation. [ citation needed ]
Stimulation of the Atk pathway activates dormant primordial follicles. The hippo signalling pathway regulates growth by inhibiting cell proliferation and promoting apoptosis, disrupting this pathway stimulates cell growth and proliferation. [ 2 ] In vitro activation (IVA) consists of the combination of disrupting the hippo signalling pathway and stimulation of Akt signalling to activate ovarian follicle growth and maturation. [ 2 ] [ 3 ] Atk pathway activation can be artificially induced by Atk stimulating drugs such as PTEN inhibitors and PI3K activators and hippo signalling disruption is achieved through fragmentation of ovarian cortex via various methods. [ 2 ] Growth of follicles can be seen in subsequent autografts, mature eggs can be retrieved and IVF carried out making it a good candidate for fertility preservation. Drug free IVA may alternatively be used. This is the same as IVA however no drugs are used to stimulate the Atk pathway, only ovarian cortex fragmentation is used. [ 3 ] | https://en.wikipedia.org/wiki/Ovarian_follicle_activation |
Ove Christiansen (born November 13, 1969, in Holstebro , Denmark) is professor of chemistry at the Department of Chemistry, Aarhus University (AU), [ 1 ] Denmark. He is contributor to the DALTON program package [ 2 ] and initiated the MidasCpp (Molecular Interactions Dynamics and Simulations in C++ ) program [ 3 ] for the accurate description of nuclear dynamics with means of Coupled Cluster Theory.
Ove Christiansen made important contributions to electronic structure theory by introducing the CC2 and CC3 method and by establishing a hierarchy of Coupled cluster electronic structure models: CCS, CC2, CCSD, CC3, etc.. [ 4 ] He introduced contributions to response theory for the purpose of describing electronic excited states. [ 5 ] Later he changed the emphasis of his main research interest towards vibrational structure theory and defined a variant of vibrational Coupled cluster (VCC) and developed the theoretical machinery for automatic derivation and implementation of VCC. [ 6 ] Moreover, he defined vibrational response theory for various wave function types. All these progress is assembled in the publicly available MidasCpp program suite [1] .
Ove Christiansen received his PhD in Theoretical Chemistry under the supervision of Prof. Poul Jørgensen at Aarhus University Denmark in 1997. Afterwards he joined from 1997 to 1999 as Alexander von Humboldt fellow the group of Prof. Jürgen Gauß in Mainz Germany and later went to the University of Lund in Sweden, where he became a Docent in 2000. In 2002 he returned to Aarhus University as Associate Professor, became Professor MSO (Professor with special obligations) in 2013 and was promoted to a full Professor in 2018. [ 7 ] | https://en.wikipedia.org/wiki/Ove_Christiansen |
An over-the-air update (or OTA update ), also known as over-the-air programming (or OTA programming ), [ 1 ] is an update to an embedded system that is delivered through a wireless network , such as Wi-Fi or a cellular network . [ 2 ] [ 3 ] [ 4 ] These embedded systems include mobile phones , tablets , set-top boxes , cars and telecommunications equipment .
OTA updates for cars and internet of things devices can also be called firmware over-the-air ( FOTA ). [ 5 ] [ 6 ] Various components may be updated OTA, including the device's operating system, applications, configuration settings, or parameters like encryption keys .
The term over-the-air update applies specifically to embedded systems , [ 4 ] rather than non-embedded systems like computers. Before OTA updates, embedded devices could only be flashed through direct physical access (with a JTAG ) or wired connections (usually through USB or a serial port ).
Over-the-air delivery may allow updates to be distributed at larger scales, reduce the cost of delivering updates, [ 7 ] or increase the rate of adoption of these updates.
The distributor of these updates can decide whether users are allowed to decline these updates, and may choose to disable certain features on end-user devices until an update is applied. Users may be unable to revert an update after it is installed.
OTA updates are designed to be as small as possible in order to minimize energy consumption, network usage, and storage space. This is achieved by only transferring the differences between the old firmware and the new firmware, rather than transmitting the entire firmware. A delta of the old and new firmware is produced through a process called diffing ; then, the delta file is distributed to the end-device, which uses the delta file to update itself. [ 8 ]
On smartphones , tablets, and other devices, an over-the-air update is a firmware or operating system update that is downloaded by the device over the internet . Previously, users had to connect these devices to a computer over USB to perform an update. These updates may add features, patch security vulnerabilities , or fix software bugs . The two main mobile operating systems are iOS and Android .
iOS gained support for over-the-air updates in iOS 5 . [ 9 ] iOS updates are distributed exclusively by Apple, resulting in wide availability and relatively high adoption rates. Major iOS releases are usually installed on 60%–70% of iPhones within a few months of the update's release. [ 10 ] [ 11 ] [ 12 ]
Android OTA updates are not distributed directly by Google, but by OEMs (like Samsung) and wireless carriers . [ 13 ] This has led to inconsistent availability of updates, and to Android fragmentation . [ 11 ] [ 12 ] In the past, fragmentation increased the complexity of developing third-party apps for Android (due to inconsistent availability of the latest software frameworks on users' phones), [ 14 ] and led to security concerns due to delays in the distribution of security updates. [ 15 ] Google has reduced Android fragmentation through the 2017 Project Treble , which allows OEMs to release OS updates without needing to re-test hardware drivers for each version, [ 13 ] [ 16 ] and the 2019 Project Mainline, which allows Google to update Android components [ 16 ] and deliver security patches [ 17 ] through its Play Store , without requiring a full OS update. [ 16 ] Project Mainline significantly lowers the role of middlemen in delivering OTA updates. [ 18 ] [ 17 ] Since Android 8.0 , Android OTA updates follow an A/B partition scheme, in which an update is installed to a second ("B") partition in the background, and the phone switches to that partition the next time it is rebooted; this reduces the time taken to install updates. [ 19 ]
Cars can support OTA updates to their in-car entertainment system, navigation map, telematic control unit , or their electronic control units (the onboard computers responsible for most of the car's operation). [ 20 ] In cars, the telematic control unit is in charge of downloading and installing updates, [ 4 ] and OTA updates are downloaded through cellular networks, like smartphones. Cars cannot be driven while an OTA update is being installed. Before an update, the car checks that the update is genuine, and after the update completes, it verifies the integrity of all affected systems. [ 20 ]
OTA updates provide several benefits. In the past, Volkswagen had to recall 11 million vehicles to fix an issue with its cars' emissions control software, and other manufacturers have instituted recalls due to software bugs affecting the brakes, or the airbags, requiring all affected customers to travel to dealership to receive updates. OTA updates would have removed the need to go through dealerships, leading to lower warranty costs for manufacturers and lower downtime for customers. OTA updates also allow manufacturers to deploy potential new features and bug fixes more quickly, making their cars more competitive in the market, and resulting in an increased pace of product improvements for consumers. For example, OTA updates can deliver improvements to a car's driver assistance systems and improve the car's safety. [ 5 ] : 138–139 [ 20 ]
However, OTA updates can also present a new attack vector for hackers, since security vulnerabilities in the update process could be used by hackers to remotely take control of cars. Hackers have discovered such vulnerabilities in the past, and many car manufacturers have responded by instituting vulnerability disclosure programs ( a.k.a. bug bounty programs ). [ 20 ] [ 21 ] Attack vectors specific to OTA updates include " spoofing , tampering, repudiation [attacks], information leakage , denial-of-service ," replay attacks , and privilege escalation attacks. Example scenarios include a hacker successfully interrupting an ongoing update (deemed a "flashing fail"), which may corrupt the car's computer systems and make the car malfunction later on; another scenario is "arbitrary flashings", in which hackers trick the car into installing a malicious OTA update. [ 5 ] : 141–142
More recently, with the new concepts of Wireless Sensor Networks and the Internet of Things (IoT), where the networks consist of hundreds or thousands of nodes, OTA is taken to a new direction: for the first time OTA is applied using unlicensed frequency bands (868 MHz, 900 MHz, 2400 MHz) and with low consumption and low data rate transmission using protocols such as 802.15.4 and Zigbee . [ 22 ]
Sensor nodes are often located in places that are either remote or difficult to access. As an example, Libelium has implemented an OTA programming system for Zigbee WSN devices. This system enables firmware upgrades without the need of physical access, saving time and money if the nodes must be re-programmed. [ 23 ]
OTA is similar to firmware distribution methods used by other mass-produced consumer electronics , such as cable modems , which use TFTP as a way to remotely receive new programming, thus reducing the amount of time spent by both the owner and the user of the device on maintenance.
Over-the-air provisioning (OTAP) is also available in wireless environments (though it is disabled by default for security reasons). It allows an access point (AP) to discover the IP address of its controller. When enabled, the controller tells the other APs to include additional information in the Radio Resource Management Packets (RRM) that would assist a new access point in learning of the controller. It is sent in plain text however, which would make it vulnerable to sniffing. That is why it is disabled by default.
Over-the-air provisioning (OTAP) is a form of OTA update by which cellular network operators can remotely provision a mobile phone (termed a client or mobile station in industry parlance) and update the cellular network settings stored on its SIM card . This can occur at any time while a phone is turned on. The term over-the-air parameter administration (OTAPA) is synonymous. [ 24 ] [ 25 ] OTA provisioning allows mobile phones to remain properly configured when cellular network operators make changes to their networks. It also configures phones with the settings required to access certain features, like WAP (an early incarnation of the mobile web ), MMS messaging, and cellular data (which requires the configuration of an Access Point Name ).
The similar term over-the-air service provisioning (OTASP) specifically refers to the wireless initial provisioning ("activation") of a phone. During activation, a mobile phone is provisioned with parameters like its phone number, mobile identification number , and system ID , granting it initial access to the cellular network. OTASP is sometimes called over-the-air activation or over-the-air bootstrapping . The alternative to OTA bootstrapping is SIM bootstrapping, where the phone reads the network settings stored on a SIM card . SIM bootstrapping has limitations: settings stored on a SIM card may become stale between the time the SIM is manufactured and the time it is used; also, some phones (and other cellular client equipment) do not use SIM cards. [ 25 ] [ 26 ]
Various standards bodies have issued OTA provisioning standards. In 2001, the WAP Forum published the WAP Client Provisioning standard. After the Open Mobile Alliance subsumed the WAP Forum, this standard became known as OMA Client Provisioning (OMA CP). In OMA CP, phones are provisioned by "invisible" SMS messages sent by the cellular network, which contain the requisite settings. OMA CP was followed by a newer standard, OMA Device Management (OMA DM), which use a different form of SMS-based provisioning (called "OMA Push"). OMA DM sessions are always client-initiated. The "invisible" SMS does not contain configuration settings; instead, it tells the phone (the "DM Client") to connect to a DM Server (operated by the cellular network provider); once connected, the DM Server sends configuration commands to the client. [ 26 ]
There are a number of standards that describe OTA functions. One of the first was the GSM 03.48 series. The Zigbee suite of standards includes the Zigbee Over-the-Air Upgrading Cluster which is part of the Zigbee Smart Energy Profile and provides an interoperable (vendor-independent) way of updating device firmware. | https://en.wikipedia.org/wiki/Over-the-air_update |
Over-the-counter ( OTC ) drugs are medicines sold directly to a consumer without a requirement for a prescription from a healthcare professional, [ 1 ] as opposed to prescription drugs , which may be supplied only to consumers possessing a valid prescription. In many countries, OTC drugs are selected by a regulatory agency to ensure that they contain ingredients that are safe and effective when used without a physician 's care. OTC drugs are usually regulated according to their active pharmaceutical ingredient (API) and strengths of final products. [ 2 ]
The term over-the-counter ( OTC ) refers to a medication that can be purchased without a medical prescription. [ 3 ] In contrast, prescription drugs require a prescription from a doctor or other health care professional and should only be used by the prescribed individual. [ 4 ] Some drugs may be legally classified as over-the-counter (i.e. no prescription is required), but may only be dispensed by a pharmacist after an assessment of the patient's needs or the provision of patient education . Regulations detailing the establishments where drugs may be sold, who is authorized to dispense them, and whether a prescription is required vary considerably from country to country.
As of 2011, around a third of older adults in the US reportedly used OTC drugs, and this number is increasing. [ 5 ] [ 6 ] [ 7 ] [ 8 ] By 2018, the prevalence of use by adults in the U.S. as first-line treatment for minor illnesses had reached 81%: however, there is some debate as to whether this figure relates to an actual improvement of health. [ 9 ] [ 1 ] [ 10 ]
In Canada , there are four drug schedules: [ 11 ]
All medications other than Schedule 1 may be considered an OTC drug, as they do not require prescriptions for sale. While the National Association of Pharmacy Regulatory Authorities provides recommendations on the scheduling of drugs for sale in Canada, each province may determine its own scheduling. [ 12 ] The drugs found in each schedule may vary from province to province. [ citation needed ]
In November 2016, India's Drug Consultative Committee announced it was embarking on establishing a definition of drugs which could be dispensed without a prescription. [ 1 ] Prior to this, the general assumption was that any drug which did not fall into a prescription schedule could be purchased without a prescription. [ 1 ] However, the needed definition had not been enacted by early 2018. The lack of a legal definition for OTC drugs has led to this US$4 billion market segment being effectively unregulated. [ 1 ]
In the Netherlands , there are four categories: [ 13 ]
A drug that is UA may be sold OTC but only by pharmacists. The drug can be on the shelves like any other product. Examples are domperidone , 400 mg ibuprofen up to 50 tablets and dextromethorphan . A drug that is UAD can also be sold at drugstores which are stores where no prescription can be filled. The drugs are usually on the shelves, and the store also sells items like toys, gadgets, perfumes and homeopathic products. The drugs in this category have limited risk and addiction potential. Examples are naproxen and diclofenac in small amounts, cinnarizine , 400 mg ibuprofen up to 20 tablets and also 500 mg paracetamol up to 50 tablets. Drugs in the AV category can be sold at supermarkets , gas stations, etc. and include only drugs with minimal risk to the public, like paracetamol up to 20 tablets, 200 mg ibuprofen up to 10 tablets, cetirizine and loperamide .
In the United States , the manufacture and sale of OTC substances are regulated by the Food and Drug Administration . The FDA requires that all "new drugs" obtain a New Drug Application (NDA) before entering interstate commerce, but the act exempts any drugs generally recognized as safe and effective (GRAS/E). [ 14 ] To deal with the vast number of OTC drugs that were already on the market before the requirement that all drugs obtain an NDA, the FDA created the OTC monograph system to review classes of drugs and to categorize them as GRAS/E after review by expert panels. Certain classes of OTC drugs would not be required to obtain an NDA and could remain on the market if they conformed to the monograph guidelines for doses, labeling, and warnings finalized in the Code of Federal Regulations [ 15 ]
Thus, an OTC drug product is allowed to be marketed either (1) pursuant to an FDA monograph or (2) pursuant to an NDA for products that do not fit within a specific monograph. [ 16 ] There is also the possibility that certain OTC drug products are marketed under the grandfathering provisions of the Federal Food, Drug, and Cosmetic Act , but the FDA has never formally acknowledged that any legitimate grandfathered OTC drug exists.
Examples of OTC substances approved in the United States are sunscreens, anti-microbial and anti-fungal products, external and internal analgesics such as lidocaine and aspirin , psoriasis and eczema topical treatments, anti- dandruff shampoos containing coal tar , and other topical products with a therapeutic effect.
The Federal Trade Commission regulates advertising of OTC products, in contrast to prescription drug advertising, which is regulated by the FDA. [ 17 ]
The FDA requires OTC products to be labeled with an approved "Drug Facts" label to educate consumers about their medications. The labels comply to a standard format and are intended to be easy for typical consumers to understand. Drug Facts labels include information on the product's active ingredient(s) , indications and purpose, safety warnings, directions for use, and inactive ingredients . [ 18 ]
The 2020 Coronavirus Aid, Relief, and Economic Security Act (CARES Act) includes reforms that modernize the way certain OTC drugs are regulated in the United States. [ 19 ] [ 20 ] Many OTC monographs need to be updated but updating or changing an OTC monograph requires the slow and burdensome notice-and-comment rulemaking process. [ 19 ] The CARES Act includes OTC monograph reform provisions that replace the rulemaking process with an administrative order process. [ 19 ]
In the United Kingdom, medication is governed by the Human Medicines Regulations, 2012 . Medication falls into one of three categories: [ 1 ] [ 21 ]
If it is not appropriate to sell a 'P' medication – i.e. the condition is not suitable for self-management and requires referral to a medical prescriber – then a sale should not occur and the pharmacist has a legal and professional obligation to refer this on to an appropriate service.
Examples of these include some sleep aid tablets such as diphenhydramine , human deworming tablets such as mebendazole , painkillers with small amounts of codeine (up to 12.8 mg per tablet), and pseudoephedrine . Medication available only with a prescription is marked somewhere on the box/container with [POM]. Pharmacy-only products are marked with [P]. A prescription is not required for [P] medicines, and pharmacy sales assistants are required by Royal Pharmaceutical Society codes to ask certain questions, which varies for what the customer says. If they ask for a specific product, the pharmacy assistant must ask "Who is it for?", "How long have you had the symptoms?", "Are you allergic to any medication?", "Are you taking any medication?" ('WHAM' questions). If a customer asks for a remedy, e.g., hay fever, then the '2WHAM questions' must be asked "Who is it for?", "What are the symptoms?", "How long have you had the symptoms?", "Have you taken any action towards your symptoms?", and "Are you taking any other medication?". It is with this information that the pharmacist can halt the sale, if need be. No [POM], [P] or [GSL] products that are stocked in a pharmacy can be sold, dispensed, or pre-made until a responsible pharmacist is signed in and on the premises. Some medication available in supermarkets and petrol stations is sold only in smaller packet sizes. Often, larger packs will be marked as [P] and available only from a pharmacy. Frequently, customers buying larger-than-usual doses of [P] medicines (such as DXM , promethazine, codeine or Gee's Linctus ) will be queried, due to the possibility of abuse. [ 22 ]
As a general rule, over-the-counter drugs have to be used primarily to treat a condition that does not require the direct supervision of a doctor and must be proven to be reasonably safe and well tolerated. [ 23 ] OTC drugs are usually also required to have little or no abuse potential, although in some areas drugs such as codeine are available OTC (usually in strictly limited formulations or requiring paperwork or identification to be submitted during purchase). [ 24 ]
Over time, often 3–6 years, drugs that prove themselves safe and appropriate as prescription medicines may be switched from prescription to OTC. [ citation needed ] An example of this is diphenhydramine (Benadryl), an anti-histamine which once required a prescription but now is available OTC nearly everywhere. [ citation needed ] More recent [ when? ] examples are cimetidine and loratadine in the United States, and ibuprofen in Australia. [ citation needed ]
It is somewhat unusual for an OTC drug to be withdrawn from the market as a result of safety concerns, rather than market forces, though it does happen occasionally. For example, phenylpropanolamine was removed from sale in the United States over concern regarding strokes in young women. [ 25 ] A study has been done examining consumer's perceptions about the risk of and access to nonprescription medication. The study concluded that a small percentage of consumers prefer having access to medication over potential risks of taking non-prescribed medication. [ 26 ] Ranitidine was suspended in multiple markets due to concerns over the presence of the carcinogen N -nitrosodimethylamine (NDMA). [ 27 ] [ 28 ] [ 29 ] [ 30 ]
In the United Kingdom, it was announced in February 2007 that Boots the Chemist would try over-the-counter sales of Viagra in stores in Manchester , England (previous available as prescription only). Men aged between 30 and 65 could buy four tablets after a consultation with a pharmacist . [ 31 ] [ needs update ] | https://en.wikipedia.org/wiki/Over-the-counter_drug |
Over the Air was an annual mobile technology-focused overnight hack day event held in London from 2008 to 2016. [ 1 ] The two-day event would include practical and educational talks and a hacking competition. [ 2 ] Sponsors of the event have included the BBC , [ 3 ] Bluevia, [ 4 ] Nokia , [ 5 ] PayPal , [ 6 ] and Vodafone . [ 7 ] Some of the ideas developed at Over the Air have been turned into commercial services. [ 8 ]
Over the Air developed from previous hack day events in 2007 and 2008.
From 2008 to 2010, the event was held at Imperial College in South Kensington . [ 9 ] [ 3 ] [ 10 ] [ 11 ] The 2011 version of Over the Air was part of the 2011 London Mobile Week. [ 12 ] [ 13 ] From 2011 to 2013, it was held at Bletchley Park . [ 8 ] There was no Over the Air event in 2014.
In 2015, the event was held at St John the Baptist, Hoxton ; on 25 and 26 September. It featured one of the first workshop sessions [ 14 ] for the Micro Bit ; along with the usual hackathon and lightning talks. The 8th (and final) event was also St. John's, on 25 and 26 November 2016. | https://en.wikipedia.org/wiki/Over_the_Air |
In biology , overabundant species refers to an excessive number of individuals [ 1 ] and occurs when the normal population density has been exceeded. Increase in animal populations is influenced by a variety of factors, some of which include habitat destruction or augmentation by human activity, the introduction of invasive species and the reintroduction of threatened species to protected reserves.
Population overabundance can have a negative impact on the environment, and in some cases on the public as well. There are various methods through which populations can be controlled such as hunting , contraception, chemical controls, disease and genetic modification. Overabundant species is an important area of research as it can potentially impact the biodiversity of ecosystems.
Most research studies have examined negative impacts of overabundant species, whereas very few have documented or performed an in-depth examination on positive impacts. As a result, this article focuses on the negative impact of overabundant species.
When referring to animals as “overabundant”, various definitions apply. The following classes [ 2 ] explore the different associations with overabundance:
Out of all these classifications, class 4 is considered the most significant due to consequent ecological impacts.
Overabundance may occur naturally, for example after weather events such as a period of high rainfall [ 3 ] in which habitat conditions become optimal. However, other contributing factors include:
Natural habitats are altered by human activity resulting in habitat fragmentation , decrease in forest densities and wild fires. [ 4 ] Other human disturbances include restrictions on hunting, agricultural land modification [ 5 ] and predator removal or control within a region or area. [ 3 ] [ 6 ] The consequent change in land use and the presence or withdrawal of human influence can trigger a rapid increase in both native and non-native species populations. [ 4 ]
Invasive species are often overabundant as they outcompete native species for resources such as food and shelter which allows their population to thrive. [ 7 ] Other factors influencing population growth include the lack of native predators [ 8 ] or the less common presence of the introduced species within native predator habitat. [ 7 ]
Some methods in managing threatened species involve reintroducing species to enclosed reserves or island areas. Once these species are introduced, their populations can become overabundant as these areas serve to protect the targeted species against predators and competitors. This occurred for the Bettongia lesueur , the burrowing bettong, which was reintroduced to the Arid Recovery reserve in Australia: their population has increased from 30 to approximately 1532 individuals. Due to the damage within this reserve their population is considered overabundant. [ 3 ]
Overabundant species can have an adverse impact on ecosystems. Within ecosystems food resources and availability, competitors, and species composition can be negatively impacted on. [ 2 ]
A common impact from overabundant herbivores is vegetative damage by overgrazing , where overgrazing refers to the effect of grazing having reached a level where other biodiversity within the ecosystem becomes threatened. Overgrazing can occur in both terrestrial and marine environments and can alter vegetation as well as the composition of vegetation. Population densities and the composition of fauna can also be negatively impacted on. [ 3 ] Additionally, permanent ecological damage can be caused by overgrazing before maximum carrying capacity has been reached. [ 3 ]
Trophic relationships (i.e. feeding relationships in the ecosystem) can be altered by overabundant species, potentially causing a trophic cascade . Trophic cascades impact vegetation as well as invertebrates (including microorganisms) and birds. [ 6 ] Furthermore, predator behaviour and populations may be indirectly affected. [ 9 ]
Overabundant predators are considered harmful to local biodiversity as they prey on native species, compete for resources and can introduce disease. They can decrease native mammal populations and, in some cases, can cause species to become extinct which results in a cascading ecological impact. Examples of invasive species include: “cats ( Felis catus ), rats ( Rattus rattus ), mongoose ( Urva auropunctata ), stoats ( Mustela erminea )” [ 8 ] and red foxes ( Vulpes vulpes ). Such species have contributed to the extinction of approximately 58% of modern-day mammals, birds and reptiles. [ 8 ]
In Australia, red foxes and feral cats have contributed to many native mammals becoming threatened or extinct which has led to diminished vegetation as foraging mammals have an important ecological role in maintaining a healthy landscape. A particular example is where grassland vegetation diminished to shrub land as a result of seabirds being preyed on by Arctic foxes. Seabirds have an essential ecological role which consists of helping to maintain nutrient levels and soil fertility.
“Invasive predators also threaten 596 species classed as "vulnerable" (217 species), "endangered" (223), or "critically endangered" (156), of which 23 are classed as “possibly extinct.” [ 8 ]
It can be very costly to control or eradicate overabundant species. For example, fencing regions as a protective measure against red foxes can cost approximately $10, 000 per kilometre while baiting an area of 35,000 2 kilometres can cost about $1.3 million. [ 10 ]
According to biology, invasive species are non-native animals that are introduced to a region or area outside of their usual habitat. [ 11 ] Invasive species can either be introduced intentionally (if they have a beneficial purpose) or non-intentionally. [ 12 ]
In general, invasive species that become overabundant most commonly have a negative impact on local biodiversity [ 12 ] with little research having found positive effects. Furthermore, an invasive species may have an initial positive benefit that fades as the species become overabundant and the cost of damage control increases. [ 13 ]
Invasive species can negatively impact food web structures. In terms of trophic levels, the initial introduction of a non-native species results in a higher species richness whereby the trophic relationships are altered by the additional resource (if an animal is not a predator at the top of the food chain) and consumer. However, the consequent degree of the impact on the local ecosystem once a species becomes overabundant is case dependent as some invasive species, like the brown tree snake in Guam, have caused numerous extinctions of native fauna, while others have had fewer damaging impacts on the environment. [ 12 ]
Costs of invasive species are estimated at millions and billions each year. [ 14 ]
The red fox , Vulpes Vulpes, was introduced to Australia during the 1870s. The established population has thrived in previous years due to the following factors: adaptability to climate conditions, the ability to live in a wide range of habitats including deserts and forests, and lastly human modification of Australian landscapes which are suitable environments for red foxes to thrive in. Red foxes have mainly had a negative impact on Australian fauna, with the exception of regulated rabbit populations. [ 13 ] The diet of red foxes include a number of threatened native fauna which has contributed to their population declines and extinctions. [ 10 ] [ 13 ] Furthermore, populations of native fauna, mammals in particular, have increased through fox population control techniques.
Rabbits were initially introduced to Australia as pets during colonisation. Rabbits pose a threat to native herbivores as they compete for shared resources. Additionally, overgrazing and modification of habitat vegetation by rabbits allow introduced predators to thrive when hunting. [ 15 ]
Rabbits have thrived in Australia as they reproduce rapidly, have few predators to regulate their population and the climatic conditions is preferable, especially as the environmental conditions limit diseases that regulate rabbit populations on other continents. [ 16 ]
There are various methods for controlling overabundant populations. Some methods have been used over many years, for example culling, while others such as immunocontraception are still being researched.
Culling refers to selective elimination of animals to decrease a population. Two ways of culling involve killing animals by hunting and translocation of animals. Culling of animals may also be an option in reserves established for specific animal conservation as a way of managing their population density, examples include: elephants and hippos. [ 2 ]
Target animals can be hunted on the ground or culled by aerial pursuit, with the aim to eliminate the animal in one accurate hit to reduce or limit suffering before death. This method allows a large number of animals to be eliminated within a relatively short amount of time, however shots are not always accurate which can lead to the escape and suffering of individuals. [ 17 ]
Baiting is a common method of controlling overabundant populations, it involves the placement of lethal chemicals in food (the bait) that eliminates the animal. It is cost-effective and helps remove a large number of animals from a population, [ 17 ] however if ingested by non-target animals it could potentially cause death depending on the type of bait the chemical is administered in, as well as the areas of bait placement. [ 18 ]
1080 is a common chemical used in bait. 1080 once ingested causes death by inhibiting the animal's neurological functioning. [ 19 ] It consists of an enzyme that native Australian fauna is tolerant to, however it can still be lethal if ingested.
Fumigation, which involves the spreading of poisonous gas, helps to selectively kill a large number of animals. It is a method used to control rabbit and fox populations in Australia by spraying a lethal chemical into warrens and dens. Chemicals used include phosphine for rabbits and carbon monoxide for foxes, both of which induce suffering prior to death. [ 17 ]
Difficulties with fumigation include pinpointing individual dens and warrens, which can be both time-consuming and hard work, as well as the restricted time period during which animals regularly inhabit their dens, for example during spring when offspring are born. [ 13 ]
This method is used on select animals and is species specific, such as to control the rabbit population in Australia. It involves spreading a disease, for example "rabbit calicivirus disease", [ 20 ] through bait or through capture and release programs. The aim is to have the disease spread through the targeted species population to reduce their numbers. Death may take up to 1 or 2 weeks in which the animal suffers from symptoms such as fever, loss of appetite and lethargy. [ 17 ]
Two methods for managing fertility in overabundant wildlife include the employment of biotechnology such as immunocontraception, and surgery to neuter males or spay females. There are various factors that impact the effectiveness of contraceptive methods, some of which include: expense, longevity of the treatment effect, level of difficulty in administering the treatment, and whether or not the method has a negative impact on the individual or other species in the environment. [ 21 ]
An example of an immune-contraceptive is gonadotropin releasing hormone (GnRH). Studies have been conducted on various animals, for example white-tailed deer and cats, of which have shown that GnRH can be effective in reducing short term fertility. [ 22 ] [ 23 ]
Immunocontraception causes animals to become infertile which helps to control and reduce overabundant populations. Two methods of administration include vaccines and chemical implants. In some studies immunocontraception has shown to effectively reduce pregnancy rates, however this method is both time-consuming and expensive due to further research required to overcome challenges such as longevity of the contraceptive effect. [ 24 ]
This method can be effective in small populations as it is fairly accessible, however the procedure is costly, invasive as well as the individual being at risk of infection after surgery. Surgical sterilisation is permanent, as a result it may not be appropriate for use in native populations due to the risk of potentially losing genetic variation. [ 21 ] | https://en.wikipedia.org/wiki/Overabundant_species |
Overall equipment effectiveness [ 1 ] ( OEE ) is a measure of how well a manufacturing equipment is utilized compared to its full potential, during the periods when it is scheduled to run.
It identifies the percentage of manufacturing time that is truly productive as well as the time it is losing effectiveness. An OEE of 100% means that only good parts are produced (100% quality ), at the maximum speed (100% performance ), and without interruption (100% availability ).
Measuring OEE is a manufacturing best practice . By measuring OEE and the underlying losses, important insights can be gained on how to systematically improve the manufacturing process.
Technically, OEE is an effective metric for identifying and visualizing losses, and steering the improvement of the effectiveness of manufacturing equipment by eliminating 'waste'.
Socially, OEE can provide a common language for groups speaking in different 'languages' such as shop floor (units), managers (money) or planners (time).
The term OEE was first mentioned in Seiichi Nakajima 's book 'TPM Tenkai' in 1982. OEE was described as a central part of the Total Productive Maintenance methodology. [ 2 ] It is based on the Harrington Emerson way of thinking [ citation needed ] regarding labor efficiency. [ citation needed ]
100% OEE is considered to be a theoretical reference point where a machine would be permanenty running, at its theoretical maximal speed, producing only good products. Anything hindering this is considered to be a 'loss'. To gain insight which losses occure on the equipment and to target the areas that should be improved to increase the value-creating conversion (effectiveness), three questions are asked: [ 3 ]
The first question leads to the 'availabilty rate' of the equipment, the second one to the 'performance rate' and the third one to the 'quality rate'.
in this way, a cascade of effectiveness and effectiveness losses arisess.
The quality rate refers to a PART of the performance (the part that there was 'speed', the other part is lost in the performance rate). The Performance rate refers to part of the availability (the time there was output - the other part is lost in the availability rate)
The OEE can now be calculated as the product of the three separate components: [ 4 ]
Each of the three components of the OEE points to an aspect of the process that can be targeted for improvement.
OEE may be applied to any individual equipment or line. This tool also allows for drilling down for very specific analysis, such as a particular Time frame, Shift, Team or any of several other parameters.
Although the performance of a particular product can be determined from OEE data, OEE cannot be calculated for that product because this would require that all downtime (availability losses) should be correlated to specific products.
OEE focusses on the 'if not' in the equations: Where did potential effectiveness got lost? These 'losses' of effectiveness are being subdivided further into what is known as the 'Six Big Losses' [ 5 ] to OEE.
In order to make this more universally applicable and also to better reflect the financial impact of the losses, the original six big losses were later adjusted slightly. [ 6 ]
The reason for identifying the losses in these categories is so that specific countermeasures can be applied to reduce the loss and improve the overall OEE.
Multiplying the three undeluing grades AxPxQ results in a percentage value that indicates the proportion of the scheduled machine running time during which production actually met the quality criteria.
This value is always well below 100%, as 100% is a theoretical value. Even if a system runs continuously at maximum speed without causing a single defect, it will for example still need to be serviced at some point.
OEE is calculated with the formula: O E E = A v a i l a b i l i t y ∗ P e r f o r m a n c e ∗ Q u a l i t y {\displaystyle OEE=Availability*Performance*Quality}
Example: (Availability= 86.6%)*(Performance=93%)*(Quality=91.3%)= (OEE=73.6%)
Alternatively, the OEE as a number could be calculated by dividing the minimum time needed to produce the parts under optimal conditions by the actual time needed to produce the parts.
However, in this way the losses are no longer known, meaning the most important part of OEE is missing.
The value range for OEE is between 0% and 100%. If an effectiveness level of more than 100% is displayed, this indicates an error in the definition.
100% time for OEE is the time when the machine is scheduled to be in operation: This is usually the “shift time.”
The Availability portion of the OEE Metric represents the percentage of scheduled time (also referred to as 'loading time') that the equipment is available to operate.
A given machine is scheduled to run for an 8-hour (480-minute) shift with a 30-minute break, during which the machine is being stopped, and there is a breakdown of 60 minutes.
During the scheduled operating time of 480 minutes, the machine was waiting 30 min. because of the break and 60 minutes because it broke down.
It was actually operating 480 - 30 - 60 = 390 Minutes
Method 1: A v a i l a b i l i t y = o p e r a t i n g t i m e / s c h e d u l e d t i m e {\displaystyle Availability=operating\ time/scheduled\ time}
Method 2: A v a i l a b i l i t y = ( l o a d i n g t i m e − d o w n t i m e ) / l o a d i n g t i m e {\displaystyle Availability=(loading\ time-downtime)/loading\ time}
The performance rate represents the ratio between the theoretical maximum speed of the machine and its actual speed.
Performance can only be calculated when there is output; thus during actual running time.
While the actual performance can be measured, it is often difficult in operational practice to obtain the theoretical maximum speed as a reference value. [ 7 ] The technical data provided by the machine manufacturer does not usually correspond to the theoretically possible maximum values, e.g. to avoid complaints or for other reasons.
Defining a too low maximum speed will become visible when the performance goes above 100%, which is undesirable. Ultimately, the goal of OEE is to reveal all potential.
It is a good practice to calculate the maximum value based on physical limits, e.g., a calculation of heat transfer, the power of a motor, or the fall speed of a product. If that fails, the concept of “best demonstrated cycle time” has proven itself. This involves determining the production speeds of products from the past and increasing the highest production speed by a margin of 20%. Defining this as 100% performance may lead to a structurally too low OEE, however it will visualize any potential loss on the performance.
The factor 1 (100%) now represents a peak value that is never exceeded, even for a short time.
For systems that only manufacture one or a few products, calculating the performance factor is simple. If a large number of different products with different maximum speeds are run on one system (multi-product companies), the effort required to determine the maximum speed can be high and the performance should be calculated correctly using a weighted average.
The Performance is calculated with formula: [ 8 ]
P e r f o r m a n c e = P a r t s p r o d u c e d ∗ I d e a l c y c l e t i m e O p e r a t i n g t i m e {\displaystyle Performance={\frac {Parts\ produced*Ideal\ cycle\ time}{Operating\ time}}}
A given equipment is scheduled to run for an 8-hour (480-minute) and has 90 min downtime.
The Standard Rate for the part being produced is 40 Units/Hour or 1.5 Minutes/Unit
The equipment produces 242 Total Units during the shift. Note: The basis is Total Units, not Good Units. The Performance metric does not penalizes for Quality.
Time to Produce Parts = 242 Units * 1.5 Minutes/Unit = 363 Minutes
The Quality portion of the OEE Metric represents the Good Units produced as a percentage of the Total Units produced. The Quality Metric is a pure measurement of Process Yield that is designed to exclude the effects of Availability and Performance. The losses due to defects and rework are called quality losses .
Calculation: The Quality is calculated with the formula: [ 9 ]
Q u a l i t y = U n i t s p r o d u c e d − D e f e c t i v e u n i t s U n i t s p r o d u c e d {\displaystyle Quality={\frac {Units\ produced-Defective\ units}{Units\ produced}}}
Example:
242 Units are produced. 21 are defective.
The calculations of OEE may not seem to be particularly complicated, but care must be taken as to standards that are used as the basis. In order to visualize all losses, it is crucial to use the right 'configuration' of the metric.
Definitions — for parts — of the OEE can be found in ISO 22400-2:2014. [ 10 ] and VDI 3423:2011-08 (2011) [ 11 ] These definitions are not standardized for all industries and are individually tailored to the respective company in its application.
This to OEE dedicated standard aims for the visualisation of all effectiveness losses on any manufacturing equipment, being unabigiously clear to production personnel. The standard uses the same logic and uniform terminology for any type of equipment. [ 12 ]
In order to calculatie OEE, operational data needs to be aquiered from the production process. [ 13 ] This needs to reflect 'what happened' on one hand, and 'what did not happen' (the losses) on the other hand. When this data is not present to the level required to make a meaningful OEE calculation, roughly two strategies can be followed:
Depending on the systems or products, it can be difficult to collect the basic data required to determine the key figure. Many companies therefore rely on special software for data collection.
Although manual recording by the operator can be considered to be time-consuming and inaccurate, it has some significant advantages
The goal of TPM ( Total Productive Maintenance ) as set out by Seiichi Nakajima, is "The continuous improvement of OEE by engaging all those that impact on it in small group activities". To achieve this, the TPM toolbox sets out a Focused improvement tactic to reduce each of the six types of OEE loss. For example, the Focused improvement tactic to systematically reduce breakdown risk sets out how to improve asset condition and standardise working methods to reduce human error and accelerated wear. Zero Failure Management [ 14 ] provides a profound structure to achieve this.
Combining OEE with Focused improvement converts OEE from a lagging to a leading indicator. [ 15 ] [ 16 ]
The first Focused improvement stage of OEE improvement is to achieve a stable OEE. One which varies at around 5% from the mean for a representative production sample. The asset is stable and not impacted by variability in equipment wear rates and working methods.
The second stage of OEE improvement (optimisation) can be carried out to remove chronic losses. Combining OEE and TPM Focused improvement tactics creates a leading indicator that can be used to guide performance management priorities.
As the TPM process delivers these gains through small cross functional improvement teams, the process of OEE improvement raises front line team engagement/problem ownership, collaboration and skill levels.
It is this combination of OEE as a KPI, TPM Focused improvement tactics and front line team engagement that locks in the gains and delivers the TPM goal of year on year improvement in OEE.
Zero Failure Management [ 17 ] offers a profound structure to achieve this.
OEE measurement is also commonly used as a key performance indicator (KPI) in conjunction with lean manufacturing efforts. To achieve te main goal of Lean, creating flow, individual pieces of equipment need to be fully reliable and in tune.
Total effective equipment performance (TEEP) is a closely to OEE related measure. TEEP quantifies OEE against calendar hours rather than only against scheduled operating hours. A TEEP of 100% means that the operations have run with an OEE of 100% 24 hours a day and 365 days a year (100% loading ). [ 18 ]
TEEP, therefore, reports the 'bottom line' effectiveness of manufacturing equipment.
To calculate the Total Effective Equipment Performance(TEEP), the OEE is multiplied by a fourth component: Loading.
T E E P = L o a d i n g r a t e ∗ O E E {\displaystyle TEEP=Loading\ rate*OEE\ }
The Loading rate of the TEEP Metric represents the percentage of time that the equipment is scheduled to operate compared to the total Calendar Time that is available. The Loading Metric is a pure measurement of Schedule effectiveness and is designed to exclude the effects how well that equipment may perform.
L o a d i n g = S c h e d u l e d t i m e / C a l e n d a r t i m e {\displaystyle Loading=Scheduled\ time/Calendar\ time} Example:
A given equipment is scheduled to run 5 Days per Week, 24 Hours per Day.
For a given week, the Total Calendar Time is 7 Days at 24 Hours.
Where TEEP includes ALL time (so also time the machine was never scheduled to run), OOE includes time that initially had been scheduled, but where the equipment was un-scheduled later on; usually for reasons outside the span of control of the shop floor team:
Where in OEE availabilty is calculated based on the scheduled (shift) time, in OOE the availability is calculated based on the scheduled PLUS the un-sheduled time (not to be confused with the NOT scheduled time as in TEEP)
Availability in OOE:
A v a i l a b i l i t y O O E = R u n n i n g T i m e + W a i t i n g T i m e + B r e a k d o w n T i m e + U n s c h e d u l e d T i m e S c h e d u l e d T i m e {\displaystyle AvailabilityOOE={\frac {RunningTime+WaitingTime+BreakdownTime+UnscheduledTime}{ScheduledTime}}}
The advantage of OEE lies in the transparency of the value added share and the associated losses of the equipment.
The term ,,Overall Equipment Efficiency” is often wrongly used as a synonym for ,,Overall Equipment Effectiveness”. Measures that increase production output but incur disproportionately high costs may well be effective, but at the same time they may be inefficient and therefore economically unviable and thus unproductive.
To assume that 85% OEE is a “world Class” target value is in many cases incorrect:
Often, insufficient quality is not detected at the equipment that caused it. In this case, it has proven effective to apply the “discovery principle,” [ citation needed ] i.e., to apply an OEE reduction to the equipment where the error was discovered. This removes the OEE from being purely equipment-related and turns it into a process indicator.
However, the OEE of a piece of equipment can of course also be optimized by making improvements to other equipment. The OEE should also be a key figure that is as up-to-date as possible. In this respect, the OK quantity should be determined at the latest at the end of the shift and the OEE calculated.
From the perspective of Process Control, the question rises how an operator can be responsible for manufacturing correct products if he cannot see whether the products are correct.
To highlight this problem, it is worth considering blocked products as a quality issue: after all, they were not right the first time around.
Valuable activities such as setup or maintenance will also reduce overall equipment effectiveness (OEE) at the beginning. If setup activities reduce overall equipment effectiveness, there is an incentive to reduce setup times using SMED (Single Minute Exchange of Die). On the other hand, this also means that OEE can be increased by reducing the number of changeovers, i.e. by increasing batch sizes. This would contradict the principles of lean production. This highlights the importance of a clear explanation of OEE: the goal is not to be as high as possible, but to identify obstacles and then eliminate them.
A convention must be agreed within the company to define when downtime occurs. Recording and justifying every second of equipment downtime is too time-consuming for most companies. In practice, a recording limit of 1 to 5 minutes of equipment downtime has proven to be a pragmatic approach. All downtimes of less than one minute are therefore included in the performance rate.
The collected data must be processed in order to obtain meaningful information. This information is aimed at various target groups, such as.
Meaningful analyses prove to be the key to good decisions. Theoretically, this is only possible with very precise figures. In practice, it has been shown that correctly selected data has a greater effect in this respect than high precision.
Although tempting, OEE (as a number) is NOT suitable for comparing machines or benchmarking.
Consider this situation:
Are they the same?
For similar reasons, OEE may not be applied to aggregate to Department or Plant levels.
Where multiple machines are linked together, each individual piece of equipment will display the waiting categories “No Input” (Starved) and “No output” (Blocked) in addition to the standard standstill reasons. This allows upstream or downstream faults in production equipment to be identified.
Without profound knowledge of manufacturing environments and certainly while lacking insight and understanding of the underlying data that lead to a specific OEE number, the number as such is of little to no value.
OEE cannot be used to measure employee performance. It is used to identify and measure equipment losses, which can then be eliminated through appropriate root cause analysis and measures.
Using OEE as a heuristic is not recommended. | https://en.wikipedia.org/wiki/Overall_equipment_effectiveness |
Overall labor effectiveness ( OLE ) is a key performance indicator (KPI) that measures the utilization, performance, and quality of the workforce and its impact on productivity.
Similar to overall equipment effectiveness (OEE), OLE measures availability, performance, and quality.
OLE allows manufacturers to make operational decisions by giving them the ability to analyze the cumulative effect of these three workforce factors on productive output, while considering the impact of both direct and indirect labor. OLE supports Lean and Six Sigma methodologies and applies them to workforce processes, allowing manufacturers to make labor-related activities more efficient, repeatable and impactful. [ 1 ]
There are many factors that influence workforce availability and therefore the potential output of equipment and the manufacturing plant. OLE can help manufacturers be sure that they have the person with the right skills available at the right time by enabling manufacturers to locate areas where providing and scheduling the right mix of employees can increase the number of productive hours. OLE also accounts for labor utilization. Understanding where downtime losses are coming from and the impact they have on production can reveal root causes—which can include machine downtime, material delays, or absenteeism —that delay a line startup. Calculation: Availability = Time operators are working productively / Time scheduled Example: Two employees (workforce) are scheduled to work 8 hour (480 minutes) shifts. The normal shift includes a scheduled 30 minute break. The employees experience 60 minutes of unscheduled downtime. Scheduled Time = 960 min − 60 min break = 900 Min Available Time = 900 min Scheduled − 120 min Unscheduled Downtime = 780 Min Availability = 780 Avail Min / 900 Scheduled Min = 86.67%
When employees cannot perform their work within standard times, performance can suffer. Effective training can increase performance by improving the skills that directly impact the quality of output. A skilled operator knows how to measure work, understands the impacts of variability, and knows to stop production for corrective actions when quality falls below specified limits. Accurately measuring this metric with OLE can pinpoint performance improvement opportunities down to the individual level. Calculation: Performance = Actual output of the operators / the expected output (or labor standard) Example: Two employees (workforce) are scheduled to work an 8-hour (480 minute) shift with a 30-minute scheduled break. Available Time = 960 min − 60 min break − 120 min Unscheduled Downtime = 780 Min
The Standard Rate for the part being produced is 60 Units/Hour or 1 Minute/Unit The Workforce produces 700 Total Units during the shift. Time to Produce Parts = 700 Units * 1 Minutes/Unit = 700 Minutes Performance = 700 minutes / 780 minutes = 89.74 %
A number of drivers contribute to quality, but the effort to improve quality can result in a lowering of labor performance. When making the correlation between the workforce and quality it is important to consider factors such as the training and skills of employees, whether they have access to the right tools to follow procedures, and their understanding of how their roles drive and impact quality. OLE can help manufacturers analyze shift productivity down to a single-shift level, and determine which individual workers are most productive, and then identify corrective actions to bring operations up to standards. Calculation: Quality = Saleable parts / Total parts produced Example: Two employees (workforce) produce 670 Good Units during a shift. 700 Units were started in order to produce the 670 Good Units. Quality = 670 Good Units / 700 Units Started = 95.71%
Effective use of OLE uncovers the data that fuels root-cause analysis and points to corrective actions. Likewise, OLE exposes trends that can be used to diagnose more subtle problems. It also helps managers understand whether corrective actions did, in fact, solve problems and improve overall productivity. Example: Calculation: OLE = Availability x Performance x Quality Example: A workforce experiences... Availability of 87% The Work Center Performance is 89.74%. Work Center Quality is 96%. OLE = 86.67% Availability x 89.74% Performance x 95.71% Quality = 74.44%
The following table provides examples of the labor information tracked by overall labor effectiveness organized by its major categories. Using this labor information, manufacturers can make operational decisions to improve the cumulative effect of labor availability, performance, and quality. [ 5 ] [ 6 ] | https://en.wikipedia.org/wiki/Overall_labor_effectiveness |
In aeronautical engineering , overall pressure ratio , or overall compression ratio , is the amount of times the pressure increases due to ram compression and the work done by the compressor stages.
The compressor pressure ratio is the ratio of the stagnation pressures at the front and rear of the compressor of a gas turbine .
Overall pressure ratio in a high-bypass turbofan is a function of inlet pressure ratio and compressor pressure ratio: O P R = I P R × C P R {\displaystyle OPR=IPR\times CPR}
The terms compression ratio and pressure ratio are used interchangeably. [ 1 ]
As can be seen in the formula for maximum theoretical thermal efficiency in an ideal Brayton cycle engine, a high pressure ratio leads to higher thermal efficiency: η = 1 − ( 1 P R γ − 1 γ ) {\displaystyle \eta =1-\left({\frac {1}{PR^{\frac {\gamma -1}{\gamma }}}}\right)} where PR is the pressure ratio and gamma the heat capacity ratio of the fluid, 1.4 for air.
Keep in mind that pressure ratio scales exponentially with the number of compressor stages. Imagine a gas turbine with n {\displaystyle n} compressor stages, each one of which compresses the air by a factor x {\displaystyle x} . The pressure ratio would therefore equal x {\displaystyle x} n {\displaystyle n} .
Listed below are the theoretical thermal efficiencies (as calculated using the formula above) associated with various pressure ratios, ignoring all losses due to compression not happening isentropically, viscous drag, as well as the process not taking place perfectly adiabatically.
for each additional stage
A high overall pressure ratio permits a larger area ratio nozzle to be fitted on the jet engine [ citation needed ] . This means that more of the heat energy is converted to jet speed, and energetic efficiency improves. This is reflected in improvements in the engine's specific fuel consumption .
The GE Catalyst has a 16:1 OPR and its thermal efficiency is 40%, the 32:1 Pratt & Whitney GTF has a thermal efficiency of 50% and the 58:1 GEnx has a thermal efficiency of 58%. [ disputed – discuss ] [ 2 ]
One of the primary limiting factors on pressure ratio in modern designs is that the air heats up as it is compressed. As the air travels through the compressor stages it can reach temperatures that pose a material failure risk for the compressor blades. This is especially true for the last compressor stage, and the outlet temperature from this stage is a common figure of merit for engine designs. [ citation needed ]
Military engines are often forced to work under conditions that maximize the heating load. For instance, the General Dynamics F-111 Aardvark was required to operate at speeds of Mach 1.1 at sea level . As a side-effect of these wide operating conditions, and generally older technology in most cases, military engines typically have lower overall pressure ratios. The Pratt & Whitney TF30 used on the F-111 had a pressure ratio of about 20:1, while newer engines like the General Electric F110 and Pratt & Whitney F135 have improved this to about 30:1.
An additional concern is weight. A higher compression ratio implies a heavier engine, which in turn costs fuel to carry around. Thus, for a particular construction technology and set of flight plans an optimal overall pressure ratio can be determined.
Early jet engines had limited pressure ratios due to construction inaccuracies of the compressors and various material limits. For instance, the Junkers Jumo 004 from World War II had an overall pressure ratio 3.14:1. The immediate post-war Snecma Atar improved this marginally to 5.2:1. Improvements in materials, compressor blades, and especially the introduction of multi-spool engines with several different rotational speeds, led to the much higher pressure ratios common today.
Modern civilian engines generally operate between 40 and 55:1. The highest in-service is the General Electric GEnx -1B/75 with an OPR of 58 at the end of the climb to cruise altitude (Top of Climb) and 47 for takeoff at sea level . [ 3 ]
The term should not be confused with the more familiar term compression ratio applied to reciprocating engines . Compression ratio is a ratio of volumes. In the case of the Otto cycle reciprocating engine, the maximum expansion of the charge is limited by the mechanical movement of the pistons (or rotor), and so the compression can be measured by simply comparing the volume of the cylinder with the piston at the top and bottom of its motion. The same is not true of the "open ended" gas turbine, where operational and structural considerations are the limiting factors. Nevertheless, the two terms are similar in that they both offer a quick way of determining overall efficiency relative to other engines of the same class.
Engine pressure ratio (EPR) differs from OPR in that OPR compares the intake pressure to the pressure of the air as it exits the compressor, and is always greater than 1 (often very much so), whereas EPR compares the intake pressure to the pressure at the engine's tailpipe (i.e., after the air has been used for combustion and given up energy to the engine's turbine wheel(s)), and is often less than 1 at low power settings.
The broadly equivalent measure of rocket engine efficiency is chamber pressure/exit pressure, and this ratio can be over 2000 for the Space Shuttle Main Engine . | https://en.wikipedia.org/wiki/Overall_pressure_ratio |
F60 is the series designation of five overburden conveyor bridges used in brown coal (lignite) opencast mining in the Lusatian coalfields in Germany . They were built by the former Volkseigener Betrieb TAKRAF in Lauchhammer and are the largest movable technical industrial machines in the world. As overburden conveyor bridges, they transport the overburden which lies over the coal seam . The cutting height is 60 m (200 ft), hence the name F60. In total, the F60 is up to 80 m (260 ft) high and 240 m (790 ft) wide; with a length of 502 m (1,647 ft), it is described as the lying Eiffel Tower , [ 2 ] making these behemoths not only the longest vehicle ever made—beating Prelude FLNG , the longest ship—but the largest vehicle by physical dimensions ever made by mankind. In operating condition, it weighs 13,600 metric tons making the F60 also one of the heaviest land vehicles ever made, beaten only by Bagger 293 , which is a giant bucket-wheel excavator . Nevertheless, despite its immense size, it is operated by only a crew of 14. [ 1 ] The first conveyor bridge was built from 1969 to 1972, being equipped with a feeder bridge in 1977. The second was built from 1972 to 1974, having been equipped with a feeder bridge during construction. The third conveyor bridge was built from 1976 to 1978, being provided with a feeder bridge in 1985. The fourth and fifth conveyor bridges were built 1986–1988 and 1988–1991 respectively.
There are still four F60s in operation in the Lusatian coalfields today: [ when? ] in the brown coal opencast mines in Jänschwalde (Brandenburg, near Jänschwalde Power Station ), Welzow -Süd (Brandenburg, near Schwarze Pumpe Power Station ), Nochten and Reichwalde (Saxony, both near Boxberg Power Station ). The fifth F60, the last one built, is in Lichterfeld-Schacksdorf and is accessible to visitors.
The F60 has two bogies , one on the dumping side (front) and one on the excavating side (back), which each run on two rails ( 1,435 mm or 4 ft 8 + 1 ⁄ 2 in standard gauge ). In addition to the two rails on the excavating side, there are another two rails for the transformer and cable cars. There are a total of 760 wheels on the bogies, of which 380 are powered. The maximum speed of the F60 is 13 m/min (0.78 km/h) and the operating speed is 9 m/min (0.54 km/h). All in all, the F60 is powered by two large Siemens Type 1DM6536-4AA14-Z electric motors which supply more than 1,800 horsepower of electricity, the motors themselves are connected to 6,000 meters of cable capable of supplying up to 30,000 volts. [ 1 ] [ 2 ] However, like the majority of ultraheavy mining machines, the F60 gets the majority of its power from a nearby external coal power plant. [ 1 ] Because of the physical limitations of the cable, the F60 only has a operational range of 6km. [ 1 ] The F60 has two bucket chain excavators of Type Es 3750 on the sides to do preparatory work (see the panoramic photograph from the Jänschwalde mine), one each on the northern and southern crosswise conveyor. They each have an output of 29,000 m 3 /h (38,000 cuyd/h) (26,448 t/h or 26,030 long ton/h or 29,154 short ton/h), which corresponds to a volume the size of a soccer field with a depth of 7–8 m (23–26 ft). There are nine various overburden conveyor belts with a speed of 10 m/min (0.60 km/h).
The F60, including the two excavators, requires 27,000 kW (36,000 hp ) of power. The bridge needs 1.2 kWh (4.3 MJ ; 4,100 BTU ) of electricity to convey one cubic metre (35 cu ft) of overburden, from the crosswise conveyors up to the dumping at a height of 75 m (246 ft).
The overburden conveyor bridge of Lichterfeld-Schacksdorf , now shut down, was used from 1991 until 1992 in the brown coal mine Klettwitz-Nord near Klettwitz . It is open for visitors today as a project of the Internationale Bauausstellung Fürst-Pückler-Land (International Mining Exhibition Fürst-Pückler-Land) and is an anchor of the European Route of Industrial Heritage (ERIH).
This F60 is the last of five F60s. The installation was carried out between 1988 and 1991 in the Klettwitz-Nord opencast mine. The F60 began operation in March 1991. Between its commission and its shutting down in June 1992, it moved around 27,000 km 3 (6,500 cu mi) [ citation needed ] of overburden. After the German reunification , the mine became the responsibility of the Lausitzer und Mitteldeutsche Bergbau-Verwaltungsgesellschaft (Lusatian and Middle-German Mining Administrative Society, LMBV), which closed the mine on the orders of the German federal government and renovated it economically and in a way not harmful to the environment.
Between 2000 and 2010, the Internationale Bauausstellung Fürst-Pückler-Land is pursuing the goal of giving new momentum to the region and the former opencast mine of Klettwitz-Nord has also been integrated into that concept. The mine has been converted into a 'visitors' mine' and the conveyor bridge has been accessible since 1998. Various sound and light installations help make the facility an attraction for visitors. | https://en.wikipedia.org/wiki/Overburden_Conveyor_Bridge_F60 |
[Overchoice takes place when] the advantages of diversity and individualization are canceled by the complexity of buyer's decision-making process.
Overchoice or choice overload [ 1 ] is the paradoxical phenomenon that choosing between a large variety of options can be detrimental to decision making processes. The term was first introduced by Alvin Toffler in his 1970 book, Future Shock . [ 2 ]
The phenomenon of overchoice occurs when many equivalent choices are available. [ 3 ] Making a decision becomes overwhelming due to the many potential outcomes and risks that may result from making the wrong choice. Having too many approximately equally good options is mentally draining because each option must be weighed against alternatives to select the best one. The satisfaction of choices by number of options available can be described by an inverted U model. [ 4 ] In this model, having no choice results in very low satisfaction. Initially more choices lead to more satisfaction, but as the number of choices increases it then peaks and people tend to feel more pressure, confusion, and potentially dissatisfaction with their choice. Although larger choice sets can be initially appealing, smaller choice sets lead to increased satisfaction and reduced regret. Another component of overchoice is the perception of time. Extensive choice sets can seem even more difficult with a limited time constraint. [ 5 ]
Choice overload is not a problem in all cases, there are some preconditions that must be met before the effect can take place. [ 6 ] First, people making the choice must not have a clear prior preference for an item type or category. When the choice-maker has a preference, the number of options has little impact on the final decision and satisfaction. [ 6 ] Second, there must not be a clearly dominant option in the choice set, meaning that all options must be perceived of equivalent quality. One option cannot stand out as being better from the rest. The presence of a superior option and many less desirable options will result in a more satisfied decision. [ 6 ] Third, there is a negative correlation between choice assortment (quantity) and satisfaction only in people less familiar with the choice set. This means that if the person making a choice has expertise in the subject matter, they can more easily sort through the options and not be overwhelmed by the variety. [ 6 ]
Decision-makers in large choice situations enjoy the decision process more than those with smaller choice sets, but feel more responsible for their decisions. [ 3 ] Despite this, more choices result with more dissatisfaction and regret in decisions. [ 3 ] The feeling of responsibility causes cognitive dissonance when presented with large array situations. [ 5 ] In this situation, cognitive dissonance results when there is a mental difference between the choice made and the choice that should have been made. More choices lead to more cognitive dissonance because it increases the chance that the decision-maker made the wrong decision. These large array situations cause the chooser to feel both enjoyment as well as feel overwhelmed with their choices. These opposing emotions contribute to cognitive dissonance , and causes the chooser to feel less motivated to make a decision. This also disables them from using psychological processes to enhance the attractiveness of their own choices. [ 5 ] The amount of time allotted to make a decision also has an effect on an individual's perception of their choice. Larger choice sets with a small amount of time results in more regret with the decision. When more time is provided, the process of choosing is more enjoyable in large array situations and results in less regret after the decision has been made. [ 3 ]
Choice overload is reversed when people choose for another person. Polman has found that overload is context dependent: choosing from many alternatives by itself is not demotivating. [ 7 ] Polman found that it is not always a case of whether choices differ for the self and others at risk, but rather “according to a selective focus on positive and negative information."
Evidence shows there is a different regulatory focus for others compared to the self in decision-making. Therefore, there may be substantial implications for a variety of psychological processes in relation to self-other decision-making. [ 7 ]
Among personal decision-makers, a prevention focus is activated and people are more satisfied with their choices after choosing among few options compared to many options, i.e. choice overload. However, individuals experience a reverse choice overload effect when acting as proxy decision-makers. [ 7 ]
The psychological phenomenon of overchoice can most often be seen in economic applications. There are limitless products currently on the market. Having more choices, such as a vast amount of goods and services available, appears to be appealing initially, but too many choices can make decisions more difficult. According to Miller (1956), a consumer can only process seven items at a time. After that the consumer would have to create a coping strategy to make an informed decision. [ 8 ] This can lead to consumers being indecisive, unhappy, and even refrain from making the choice (purchase) at all. [ 9 ] [ 10 ] [ 11 ] [ 3 ] Alvin Toffler noted that as the choice turns to overchoice, "freedom of more choices" becomes the opposite—the "unfreedom". Often, a customer makes a decision without sufficiently researching his choices, which may often require days. [ 11 ] When confronted with too many choices especially under a time constraint, many people prefer to make no choice at all, even if making a choice would lead to a better outcome.
The existence of over choice, both perceived and real, is supported by studies as early as the mid-1970s. [ 9 ] [ 11 ] Numbers of various brands , from soaps to cars, have been steadily rising for over half a century. [ 11 ] In just one example—different brands of soap and detergents—the numbers of choices offered by an average US supermarket went from 65 in 1950, through 200 in 1963, to over 360 in 2004. The more choices tend to increase the time it requires to make a decision. [ 11 ]
There are two steps involved in making a choice to purchase. First, the consumer selects an assortment. Second, the consumer chooses an option within the assortment. Variety and complexity vary in their importance in carrying out these steps successfully, resulting in the consumer deciding to make a purchase. [ 12 ]
Variety is the positive aspect of assortment. When selecting an assortment during the perception stage, the first stage of deciding, consumers want more variety.
Complexity is the negative aspect of assortment. Complexity is important for the second step in making a choice—when a consumer needs to choose an option from an assortment. When making a choice for an individual item within an assortment, too much variety increases complexity. This can cause a consumer to delay or opt out of making a decision. [ 12 ]
Images are processed as a whole when making a purchasing decision. This means they require less mental effort to be processed which gives the consumer a sense that the information is being processed faster. [ 12 ] Consumers prefer this visual shortcut to processing, termed "visual heuristic " by Townsend, no matter how big the choice set size. Images increase our perceived variety of options. As previously stated, variety is good when making the first step of choosing an assortment. On the other hand, verbal descriptions are processed in a way that the words that make up a sentence are perceived individually. That is, our minds string words along to develop our understanding. In larger choice sets where there is more variety, perceived complexity decreases when verbal descriptions are used. [ 12 ] | https://en.wikipedia.org/wiki/Overchoice |
Overcompleteness is a concept from linear algebra that is widely used in mathematics, computer science, engineering, and statistics (usually in the form of overcomplete frames ). It was introduced by R. J. Duffin and A. C. Schaeffer in 1952. [ 1 ]
Formally, a subset of the vectors { ϕ i } i ∈ J {\displaystyle \{\phi _{i}\}_{i\in J}} of a Banach space X {\displaystyle X} , sometimes called a "system", is complete if every element in X {\displaystyle X} can be approximated arbitrarily well in norm by finite linear combinations of elements in { ϕ i } i ∈ J {\displaystyle \{\phi _{i}\}_{i\in J}} . [ 2 ] A system is called overcomplete if it contains more vectors than necessary to be complete, i.e., there exist ϕ j ∈ { ϕ i } i ∈ J {\displaystyle \phi _{j}\in \{\phi _{i}\}_{i\in J}} that can be removed from the system such that { ϕ i } i ∈ J ∖ { ϕ j } {\displaystyle \{\phi _{i}\}_{i\in J}\setminus \{\phi _{j}\}} remains complete. In research areas such as signal processing and function approximation , overcompleteness can help researchers to achieve a more stable, more robust, or more compact decomposition than using a basis . [ 3 ]
The theory of frames originates in a paper by Duffin and Schaeffer on non-harmonic Fourier series . [ 1 ] A frame is defined to be a set of non-zero vectors { ϕ i } i ∈ J {\displaystyle \{\phi _{i}\}_{i\in J}} such that for an arbitrary f ∈ H {\displaystyle f\in {\mathcal {H}}} ,
where ⟨ ⋅ , ⋅ ⟩ {\displaystyle \langle \cdot ,\cdot \rangle } denotes the inner product, A {\displaystyle A} and B {\displaystyle B} are positive constants called bounds of the frame. When A {\displaystyle A} and B {\displaystyle B} can be chosen such that A = B {\displaystyle A=B} , the frame is called a tight frame. [ 4 ]
It can be seen that H = span { ϕ i } {\displaystyle {\mathcal {H}}=\operatorname {span} \{\phi _{i}\}} .
An example of frame can be given as follows.
Let each of { α i } i = 1 ∞ {\displaystyle \{\alpha _{i}\}_{i=1}^{\infty }} and { β i } i = 1 ∞ {\displaystyle \{\beta _{i}\}_{i=1}^{\infty }} be an orthonormal basis of H {\displaystyle {\mathcal {H}}} , then
is a frame of H {\displaystyle {\mathcal {H}}} with bounds A = B = 2 {\displaystyle A=B=2} .
Let S {\displaystyle S} be the frame operator,
A frame that is not a Riesz basis , in which case it consists of a set of functions more than a basis, is said to be overcomplete or redundant . [ 5 ] In this case, given f ∈ H {\displaystyle f\in {\mathcal {H}}} , it can have different decompositions based on the frame. The frame given in the example above is an overcomplete frame.
When frames are used for function estimation, one may want to compare the performance of different frames. The parsimony of the approximating functions by different frames may be considered as one way to compare their performances. [ 6 ]
Given a tolerance ϵ {\displaystyle \epsilon } and a frame F = { ϕ i } i ∈ J {\displaystyle F=\{\phi _{i}\}_{i\in J}} in L 2 ( R ) {\displaystyle L^{2}(\mathbb {R} )} , for any function f ∈ L 2 ( R ) {\displaystyle f\in L^{2}(\mathbb {R} )} , define the set of all approximating functions that satisfy ‖ f − f ^ ‖ < ϵ {\displaystyle \|f-{\hat {f}}\|<\epsilon }
Then let
k ( f , ϵ ) {\displaystyle k(f,\epsilon )} indicates the parsimony of utilizing frame F {\displaystyle F} to approximate f {\displaystyle f} . Different f {\displaystyle f} may have different k {\displaystyle k} based on the hardness to be approximated with elements in the frame. The worst case to estimate a function in L 2 ( R ) {\displaystyle L^{2}(\mathbb {R} )} is defined as
For another frame G {\displaystyle G} , if k F ( ϵ ) < k G ( ϵ ) {\displaystyle k_{F}(\epsilon )<k_{G}(\epsilon )} , then frame F {\displaystyle F} is better than frame G {\displaystyle G} at level ϵ {\displaystyle \epsilon } . And if there exists a γ {\displaystyle \gamma } that for each ϵ < γ {\displaystyle \epsilon <\gamma } , we have k F ( ϵ ) < k G ( ϵ ) {\displaystyle k_{F}(\epsilon )<k_{G}(\epsilon )} , then F {\displaystyle F} is better than G {\displaystyle G} broadly.
Overcomplete frames are usually constructed in three ways.
An example of an overcomplete frame is shown below. The collected data is in a two-dimensional space, and in this case a basis with two elements should be able to explain all the data. However, when noise is included in the data, a basis may not be able to express the properties of the data. If an overcomplete frame with four elements corresponding to the four axes in the figure is used to express the data, each point would be able to have a good expression by the overcomplete frame.
The flexibility of the overcomplete frame is one of its key advantages when used in expressing a signal or approximating a function. However, because of this redundancy, a function can have multiple expressions under an overcomplete frame. [ 7 ] When the frame is finite, the decomposition can be expressed as
where f {\displaystyle f} is the function one wants to approximate, A {\displaystyle A} is the matrix containing all the elements in the frame, and x {\displaystyle x} is the coefficients of f {\displaystyle f} under the representation of A {\displaystyle A} . Without any other constraint, the frame will choose to give x {\displaystyle x} with minimal norm in L 2 ( R ) {\displaystyle L^{2}(\mathbb {R} )} . Based on this, some other properties may also be considered when solving the equation, such as sparsity. So different researchers have been working on solving this equation by adding other constraints in the objective function. For example, a constraint minimizing x {\displaystyle x} 's norm in L 1 ( R ) {\displaystyle L^{1}(\mathbb {R} )} may be used in solving this equation. This should be equivalent to the Lasso regression in statistics community. Bayesian approach is also used to eliminate the redundancy in an overcomplete frame. Lweicki and Sejnowski proposed an algorithm for overcomplete frame by viewing it as a probabilistic model of the observed data. [ 7 ] Recently, the overcomplete Gabor frame has been combined with bayesian variable selection method to achieve both small norm expansion coefficients in L 2 ( R ) {\displaystyle L^{2}(\mathbb {R} )} and sparsity in elements. [ 8 ]
In modern analysis in signal processing and other engineering field, various overcomplete frames are proposed and used. Here two common used frames, Gabor frames and wavelet frames, are introduced and discussed.
In usual Fourier transformation, the function in time domain is transformed to the frequency domain. However, the
transformation only shows the frequency property of this function and loses its information in the time domain. If a
window function g {\displaystyle g} , which only has nonzero value in a small interval, is multiplied with the original
function before operating the Fourier transformation, both the information in time and frequency domains may remain
at the chosen interval. When a sequence of translation of g {\displaystyle g} is used in the transformation, the
information of the function in time domain are kept after the transformation.
Let operators
A Gabor frame (named after Dennis Gabor and also called Weyl - Heisenberg frame) in L 2 ( R ) {\displaystyle L^{2}(R)} is defined as the form { E m b T n a g } m , n ∈ Z {\displaystyle \{E_{mb}T_{na}g\}_{m,n\in Z}} , where a , b > 0 {\displaystyle a,b>0} and g ∈ L 2 ( R ) {\displaystyle g\in L^{2}(R)} is a fixed function. [ 5 ] However, not for every a {\displaystyle a} and b {\displaystyle b} { E m b T n a g } m , n ∈ Z {\displaystyle \{E_{mb}T_{na}g\}_{m,n\in Z}} forms a frame on L 2 ( R ) {\displaystyle L^{2}(R)} . For example, when a b > 1 {\displaystyle ab>1} , it is not a frame for L 2 ( R ) {\displaystyle L^{2}(R)} . When a b = 1 {\displaystyle ab=1} , { E m b T n a g } m , n ∈ Z {\displaystyle \{E_{mb}T_{na}g\}_{m,n\in Z}} is possible to be a frame, in which case it is a Riesz basis. So the possible situation for { E m b T n a g } m , n ∈ Z {\displaystyle \{E_{mb}T_{na}g\}_{m,n\in Z}} being an overcomplete frame is a b < 1 {\displaystyle ab<1} .
The Gabor family { E m b / c T n a c g c } m , n ∈ Z {\displaystyle \{E_{mb/c}T_{nac}g_{c}\}_{m,n\in Z}} is also a frame and sharing the same frame bounds as { E m b T n a g } m , n ∈ Z . {\displaystyle \{E_{mb}T_{na}g\}_{m,n\in Z}.}
Different kinds of window function g {\displaystyle g} may be used in Gabor frame. Here examples of three window functions are shown, and the condition for the corresponding Gabor system being a frame is shown as
follows.
(1) g ( x ) = e − x 2 {\displaystyle g(x)=e^{-x^{2}}} , { E m b T n a g } m , n ∈ Z {\displaystyle \{E_{mb}T_{na}g\}_{m,n\in Z}} is a frame when a b < 0.994 {\displaystyle ab<0.994}
(2) g ( x ) = 1 c o s h ( π x ) {\displaystyle g(x)={\frac {1}{cosh(\pi x)}}} , { E m b T n a g } m , n ∈ Z {\displaystyle \{E_{mb}T_{na}g\}_{m,n\in Z}} is a frame when a b < 1 {\displaystyle ab<1}
(3) g ( x ) = I [ 0 , c ) ( x ) {\displaystyle g(x)=I_{[0,c)}(x)} , where I ( x ) {\displaystyle I(x)} is the indicator function. The situation for { E m b T n a g } m , n ∈ Z {\displaystyle \{E_{mb}T_{na}g\}_{m,n\in Z}} to be a frame stands as follows.
1) a > c {\displaystyle a>c} or a > 1 {\displaystyle a>1} , not a frame
2) c > 1 {\displaystyle c>1} and a = 1 {\displaystyle a=1} , not a frame
3) a ≤ c ≤ 1 {\displaystyle a\leq c\leq 1} , is a frame
4) a < 1 {\displaystyle a<1} and is an irrational, and c ∈ ( 1 , 2 ) {\displaystyle c\in (1,2)} , is a frame
5) a = p q < 1 {\displaystyle a={\frac {p}{q}}<1} , p {\displaystyle p} and q {\displaystyle q} are relatively primes, 2 − 1 q < c < 2 {\displaystyle 2-{\frac {1}{q}}<c<2} , not a frame
6) 3 4 < a < 1 {\displaystyle {\frac {3}{4}}<a<1} and c = L − 1 + L ( 1 − a ) {\displaystyle c=L-1+L(1-a)} , where L ≥ 3 {\displaystyle L\geq 3} and be a natural number ,
not a frame
7) a < 1 {\displaystyle a<1} , c > 1 {\displaystyle c>1} , | c − [ c ] − 1 2 | < 1 2 − a {\displaystyle |c-[c]-{\frac {1}{2}}|<{\frac {1}{2}}-a} , where [ c ] {\displaystyle [c]} is the biggest integer not exceeding c {\displaystyle c} , is a frame.
The above discussion is a summary of chapter 8 in. [ 5 ]
A collection of wavelet usually refers to a set of functions based on ψ {\displaystyle \psi }
This forms an orthonormal basis for L 2 ( R ) {\displaystyle L^{2}(R)} . However, when j , k {\displaystyle j,k} can take values in R {\displaystyle R} , the set represents an overcomplete frame and called undecimated wavelet basis. In general case, a
wavelet frame is defined as a frame for L 2 ( R ) {\displaystyle L^{2}(R)} of the form
where a > 1 {\displaystyle a>1} , b > 0 {\displaystyle b>0} , and ψ ∈ L 2 ( R ) {\displaystyle \psi \in L^{2}(R)} .
The upper and lower bound of this frame can be computed as follows.
Let ψ ^ ( γ ) {\displaystyle {\hat {\psi }}(\gamma )} be the Fourier transform for ψ ∈ L 1 ( R ) {\displaystyle \psi \in L^{1}(R)}
When a , b {\displaystyle a,b} are fixed, define
Then
Furthermore, when
the generated frame { ψ j , k } j , k ∈ Z {\displaystyle \{\psi _{j,k}\}_{j,k\in Z}} is a tight frame.
The discussion in this section is based on chapter 11 in. [ 5 ]
Overcomplete Gabor frames and Wavelet frames have been used in various research area including signal detection, image representation, object recognition, noise reduction , sampling theory, operator theory , harmonic analysis , nonlinear sparse approximation , pseudodifferential operators , wireless communications, geophysics, quantum computing, and filter banks . [ 3 ] [ 5 ] | https://en.wikipedia.org/wiki/Overcompleteness |
In an electric power system , overcurrent or excess current is a situation where a larger than intended electric current exists through a conductor , leading to excessive generation of heat, and the risk of fire or damage to equipment. Possible causes for overcurrent include short circuits , excessive load, incorrect design, an arc fault , or a ground fault . Fuses , circuit breakers , and current limiters are commonly used overcurrent protection (OCP) mechanisms to control the risks .
Circuit breakers, relays, and fuses protect circuit wiring from damage caused by overcurrent. [ 1 ]
Overcurrent capabilities of electrical generators are essential for the power system operations . Lack of overcurrent capability (low short circuit ratio ) of a weak grid creates a multitude of problems, including: [ 2 ]
This article about electric power is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Overcurrent |
In mathematics , a system of equations is considered overdetermined if there are more equations than unknowns. [ 1 ] [ citation needed ] An overdetermined system is almost always inconsistent (it has no solution) when constructed with random coefficients. However, an overdetermined system will have solutions in some cases, for example if some equation occurs several times in the system, or if some equations are linear combinations of the others.
The terminology can be described in terms of the concept of constraint counting . Each unknown can be seen as an available degree of freedom. Each equation introduced into the system can be viewed as a constraint that restricts one degree of freedom .
Therefore, the critical case occurs when the number of equations and the number of free variables are equal. For every variable giving a degree of freedom, there exists a corresponding constraint. The overdetermined case occurs when the system has been overconstrained — that is, when the equations outnumber the unknowns. In contrast, the underdetermined case occurs when the system has been underconstrained — that is, when the number of equations is fewer than the number of unknowns. Such systems usually have an infinite number of solutions.
Consider the system of 3 equations and 2 unknowns ( X and Y ), which is overdetermined because 3 > 2, and which corresponds to Diagram #1: Y = − 2 X − 1 Y = 3 X − 2 Y = X + 1. {\displaystyle {\begin{aligned}Y&=-2X-1\\Y&=3X-2\\Y&=X+1.\end{aligned}}}
There is one solution for each pair of linear equations: for the first and second equations (0.2, −1.4), for the first and third (−2/3, 1/3), and for the second and third (1.5, 2.5). However, there is no solution that satisfies all three simultaneously. Diagrams #2 and 3 show other configurations that are inconsistent because no point is on all of the lines. Systems of this variety are deemed inconsistent .
The only cases where the overdetermined system does in fact have a solution are demonstrated in Diagrams #4, 5, and 6. These exceptions can occur only when the overdetermined system contains enough linearly dependent equations that the number of independent equations does not exceed the number of unknowns. Linear dependence means that some equations can be obtained from linearly combining other equations. For example, Y = X + 1 and 2 Y = 2 X + 2 are linearly dependent equations because the second one can be obtained by taking twice the first one.
Any system of linear equations can be written as a matrix equation.
The previous system of equations (in Diagram #1) can be written as follows: [ 2 1 − 3 1 − 1 1 ] [ X Y ] = [ − 1 − 2 1 ] {\displaystyle {\begin{bmatrix}2&1\\-3&1\\-1&1\\\end{bmatrix}}{\begin{bmatrix}X\\Y\end{bmatrix}}={\begin{bmatrix}-1\\-2\\1\end{bmatrix}}} Notice that the rows of the coefficient matrix (corresponding to equations) outnumber the columns (corresponding to unknowns), meaning that the system is overdetermined. The rank of this matrix is 2, which corresponds to the number of dependent variables in the system. [ 2 ] A linear system is consistent if and only if the coefficient matrix has the same rank as its augmented matrix (the coefficient matrix with an extra column added, that column being the column vector of constants). The augmented matrix has rank 3, so the system is inconsistent. The nullity is 0, which means that the null space contains only the zero vector and thus has no basis .
In linear algebra the concepts of row space , column space and null space are important for determining the properties of matrices. The informal discussion of constraints and degrees of freedom above relates directly to these more formal concepts.
The homogeneous case (in which all constant terms are zero) is always consistent (because there is a trivial, all-zero solution). There are two cases, depending on the number of linearly dependent equations: either there is just the trivial solution, or there is the trivial solution plus an infinite set of other solutions.
Consider the system of linear equations: L i = 0 for 1 ≤ i ≤ M , and variables X 1 , X 2 , ..., X N , where each L i is a weighted sum of the X i s. Then X 1 = X 2 = ⋯ = X N = 0 is always a solution. When M < N the system is underdetermined and there are always an infinitude of further solutions. In fact the dimension of the space of solutions is always at least N − M .
For M ≥ N , there may be no solution other than all values being 0. There will be an infinitude of other solutions only when the system of equations has enough dependencies (linearly dependent equations) that the number of independent equations is at most N − 1. But with M ≥ N the number of independent equations could be as high as N , in which case the trivial solution is the only one.
In systems of linear equations, L i = c i for 1 ≤ i ≤ M , in variables X 1 , X 2 , ..., X N the equations are sometimes linearly dependent; in fact the number of linearly independent equations cannot exceed N +1. We have the following possible cases for an overdetermined system with N unknowns and M equations ( M > N ).
These results may be easier to understand by putting the augmented matrix of the coefficients of the system in row echelon form by using Gaussian elimination . This row echelon form is the augmented matrix of a system of equations that is equivalent to the given system (it has exactly the same solutions). The number of independent equations in the original system is the number of non-zero rows in the echelon form. The system is inconsistent (no solution) if and only if the last non-zero row in echelon form has only one non-zero entry that is in the last column (giving an equation 0 = c where c is a non-zero constant). Otherwise, there is exactly one solution when the number of non-zero rows in echelon form is equal to the number of unknowns, and there are infinitely many solutions when the number of non-zero rows is lower than the number of variables.
Putting it another way, according to the Rouché–Capelli theorem , any system of equations (overdetermined or otherwise) is inconsistent if the rank of the augmented matrix is greater than the rank of the coefficient matrix . If, on the other hand, the ranks of these two matrices are equal, the system must have at least one solution. The solution is unique if and only if the rank equals the number of variables. Otherwise the general solution has k free parameters where k is the difference between the number of variables and the rank; hence in such a case there are an infinitude of solutions.
All exact solutions can be obtained, or it can be shown that none exist, using matrix algebra . See System of linear equations#Matrix solution .
The method of ordinary least squares can be used to find an approximate solution to overdetermined systems. For the system A x = b , {\displaystyle A\mathbf {x} =\mathbf {b} ,} the least squares formula is obtained from the problem min x ‖ A x − b ‖ , {\displaystyle \min _{\mathbf {x} }\lVert A\mathbf {x} -\mathbf {b} \rVert ,} the solution of which can be written with the normal equations , [ 3 ] x = ( A T A ) − 1 A T b , {\displaystyle \mathbf {x} =\left(A^{\mathsf {T}}A\right)^{-1}A^{\mathsf {T}}\mathbf {b} ,} where T {\displaystyle {\mathsf {T}}} indicates a matrix transpose , provided ( A T A ) − 1 {\displaystyle \left(A^{\mathsf {T}}A\right)^{-1}} exists (that is, provided A has full column rank ). With this formula an approximate solution is found when no exact solution exists, and it gives an exact solution when one does exist. However, to achieve good numerical accuracy, using the QR factorization of A to solve the least squares problem is preferred. [ 4 ]
The QR decomposition of a (tall) matrix A {\displaystyle A} is the representation of the matrix in the product form,
where Q {\displaystyle Q} is a (tall) semi-orthonormal matrix that spans the range of the matrix A {\displaystyle A} , and where R {\displaystyle R} is a (small) square right-triangular matrix.
The solution to the problem of minimizing the norm ‖ A x − b ‖ 2 {\displaystyle \|Ax-b\|^{2}} is then given as
where in practice instead of calculating R − 1 {\displaystyle R^{-1}} one should do a run of backsubstitution on the right-triangular system
The Singular Value Decomposition (SVD) of a (tall) matrix A {\displaystyle A} is the representation of the matrix in the product form,
where U {\displaystyle U} is a (tall) semi-orthonormal matrix that spans the range of the matrix A {\displaystyle A} , S {\displaystyle S} is a (small) square diagonal matrix with non-negative singular values along the diagonal, and where V {\displaystyle V} is a (small) square orthonormal matrix.
The solution to the problem of minimizing the norm ‖ A x − b ‖ 2 {\displaystyle \|Ax-b\|^{2}} is then given as
In finite dimensional spaces, a system of equations can be written or represented in the form of
{ f 1 ( x 1 , … , x n ) = 0 ⋮ ⋮ ⋮ f m ( x 1 , … , x n ) = 0 {\displaystyle \left\{{\begin{array}{ccc}f_{1}(x_{1},\ldots ,x_{n})&=&0\\\vdots &\vdots &\vdots \\f_{m}(x_{1},\ldots ,x_{n})&=&0\end{array}}\right.}
or in the form of f ( x ) = 0 {\displaystyle \mathbf {f} (\mathbf {x} )=\mathbf {0} } with
f ( x ) = [ f 1 ( x 1 , … , x n ) ⋮ f m ( x 1 , … , x n ) ] and 0 = [ 0 ⋮ 0 ] {\displaystyle \mathbf {f} (\mathbf {x} )=\left[{\begin{array}{c}f_{1}(x_{1},\ldots ,x_{n})\\\vdots \\f_{m}(x_{1},\ldots ,x_{n})\end{array}}\right]\;\;\;{\mbox{and}}\;\;\;\mathbf {0} =\left[{\begin{array}{c}0\\\vdots \\0\end{array}}\right]}
where x = ( x 1 , … , x n ) {\displaystyle \mathbf {x} =(x_{1},\ldots ,x_{n})} is a point in R n {\displaystyle R^{n}} or C n {\displaystyle C^{n}} and f 1 , … , f m {\displaystyle f_{1},\ldots ,f_{m}} are real or complex functions. The system is overdetermined if m > n {\displaystyle m>n} . In contrast, the system is an underdetermined system if m < n {\displaystyle m<n} . [ 5 ] [ 6 ]
As an effective method for solving overdetermined systems, the Gauss-Newton iteration locally quadratically converges to solutions at which the Jacobian matrices of f ( x ) {\displaystyle \mathbf {f} (\mathbf {x} )} are injective.
The concept can also be applied to more general systems of equations, such as systems of polynomial equations or partial differential equations . In the case of the systems of polynomial equations, it may happen that an overdetermined system has a solution, but that no one equation is a consequence of the others and that, when removing any equation, the new system has more solutions. For example, ( x − 1 ) ( x − 2 ) = 0 , ( x − 1 ) ( x − 3 ) = 0 {\displaystyle (x-1)(x-2)=0,(x-1)(x-3)=0} has the single solution x = 1 , {\displaystyle x=1,} but each equation by itself has two solutions. | https://en.wikipedia.org/wiki/Overdetermined_system |
Overdominance is a phenomenon in genetics where the phenotype of the heterozygote lies outside the phenotypical range of both homozygous parents. Overdominance can also be described as heterozygote advantage regulated by a single genomic locus , wherein heterozygous individuals have a higher fitness than homozygous individuals. However, not all cases of the heterozygote advantage are considered overdominance, as they may be regulated by multiple genomic regions. [ 1 ] Overdominance has been hypothesized as an underlying cause for heterosis (increased fitness of hybrid offspring). [ 2 ] [ 3 ]
An example of overdominance in humans is that of the sickle cell anemia . This condition is determined by a single polymorphism . Possessors of the deleterious allele have lower life expectancy, with homozygotes rarely reaching 50 years of age. However, this allele also yields some resistance to malaria . Thus in regions where malaria exerts or has exerted a strong selective pressure, sickle cell anemia has been selected for its conferred partial resistance to the disease. While homozygotes will have either no protection from malaria or a dramatic propensity to sickle cell anemia, heterozygotes have fewer physiological effects and a partial resistance to malaria. [ 4 ]
Major histocompatibility complex (MHC) genes exhibit extensive variation, generally attributed to the notion of heterozygous individuals identifying a wider range of peptides than homozygous individuals. In arctic char population in Finland , fish heterozygous for MHC alleles had fewer cysts, grew larger, and had a better chance at survival, all indicating a higher fitness of the heterozygotes. [ 5 ]
In Gymnadenia rhellicani , flower pigmentation is controlled by changes to amino acids 612 and 663 in GrMYB1, which plays a role in anthocyanin pigment production. Red flowers, heterozygous with black and white alleles, maintain a reproductive fitness advantage over white and black varieties presumably because they attract both bee and fly pollinator populations. Since the emergence of the white allele, the frequency of the red phenotype has been increasing in wild populations in multiple regions of the alps. [ 6 ]
Polar overdominance is a type of overdominance where either only the paternal or maternal allele is being synthesized in the offspring. An example of this was illustrated by a famous ram named Solid Gold and his offspring. This ram was known for its callipyge phenotype (pronounced muscular features and hindquarters) caused by a mutated allele, but only 15% of its offspring received these same traits. Solid Gold’s offspring only expressed the same callipyge phenotype if they inherited the mutated allele from Solid Gold and a wildtype allele from their mother, which would result in a C pat /N mat genotype. Offspring with genotypes such as: C pat /C mat , N pat /N mat , and N pat /C mat did not express the callipyge phenotype. [ 7 ]
Population Geneticist John H. Gillespie established the following convention: [ 8 ]
Where h is the heterozygote effect and s is the recessive allele effect.
Thus given a value for s (i.e.: 0<s<1), h can yield the following information:
For the case of sickle cell anemia the situation corresponds to the case h<0 in the Gillespie Model. | https://en.wikipedia.org/wiki/Overdominance |
Overeating occurs when an individual consumes more calories than the energy that is expended via physical activity or expelled via excretion , or when they consume food past the point of satiation, often leading to weight gain and often obesity . Overeating is the defining characteristic of binge eating disorder , [ 1 ] and it can be a symptom of bulimia nervosa . [ 2 ] [ 1 ]
In a broader sense, hyperalimentation includes excessive food administration through other means than eating, e.g. through parenteral nutrition .
Cognitive behavioural therapy , individual therapy, and group therapy are often beneficial in helping people keep track of their eating habits and changing the way they cope with difficult situations. Often overeating and the related binge eating are related to dieting, body image issues, as well as social pressures. [ 3 ]
There are several 12-step programs that helps overeaters, such as Overeaters Anonymous or Food Addicts in Recovery Anonymous and others.
It is quite clear through research, and various studies that overeating causes addictive behaviors.
In some instances, overeating has been linked to the use of medications known as dopamine agonists , such as pramipexole . [ 4 ] | https://en.wikipedia.org/wiki/Overeating |
Overengineering , or over-engineering , [ 1 ] is the act of designing a product or providing a solution to a problem that is complicated in a way that provides no value or could have been designed to be simpler. [ 2 ] It has been employed intentionally in situations where an exceptionally wide margin of error is desired, but is otherwise considered an error of design due to the disproportionate time and resources needed to manufacture and maintain such products, as well as the introduction of unneeded single points of failure . As a design philosophy , it is a violation of the practice of value engineering and the minimalist ethos of " less is more " or " worse is better ", as well as the related KISS principle .
NASA listed excessive features as one of the top 10 risks of failure for development projects, [ 3 ] and Mercedes-Benz developed and removed 600 non-essential features from their cars due to malfunctions, lack of usability and customer complaints. [ 4 ]
Overengineering is often identified with design choices that increase safety , add functionality, or overcome a perceived design flaw that most users would not notice or would accept. It can be hard to avoid when safety or performance is critical (e.g. in aerospace vehicles and luxury road vehicles ), or when extremely broad functionality is required (e.g. diagnostic and medical tools, power users of products). Overengineering often occurs in high-end products and specialized markets. A product may be overbuilt – with performance far in excess of expected normal operation such as a city car with top speed of 300 km/h, or a home video recorder with a lifespan of 100 years. Such products may be more expensive, bulkier, and heavier than necessary. A product may be overcomplicated – with functions that are not necessary, and reduce the usability of the product by overwhelming users which is sometimes called feature fatigue.
Sometimes overengineering occurs over time in the form of feature creep . Overengineering can decrease the productivity of a development team because even though the team produces product, the value realized might be less than if the team was producing only what the user needs and wants. Overengineering can consist of premature optimization , potentially to the detriment of the project due to diminishing returns on time and effort invested in the design process.
A story about very precise engineering is given in the 1858 story The Deacon's Masterpiece or, the Wonderful "One-hoss Shay": A Logical Story by Oliver Wendell Holmes Sr. , which tells of a carriage ( one-horse shay )
That was built in such a logical way It ran a hundred years to a day, And then, ... went to pieces all at once, -- All at once, and nothing first, -- Just as bubbles do when they burst.
Because it had been engineered so that no single piece failed first – no piece was over-engineered relative to the others, and they thus all collapsed at the same time. A similar quote by Ferdinand Porsche claimed "the perfect race car crosses the finish line in first place and immediately falls into pieces." [ 5 ]
German Second World War weapons, like the famous Tiger I tank or Panther tank , have been listed as examples of over-engineering, [ 6 ] in comparison to their Soviet rivals such as the T-34 . German arms allegedly used expensive materials and excessively labour-intensive production processes, limiting production and making them hard to repair when they broke down in the field. Another example is Juicero , a wi-fi "smart" juicing press with an initial market price of $699. [ 7 ] After its release, Bloomberg News published a story that showed that the juice packs could be squeezed by hand faster than the press, and that hand-squeezing produced juice that was near-indistinguishable in quality and quantity from the output of the machine, which cost $400 even after a price reduction. [ 8 ]
In 2024, former technical director and chair of Network Rail High Speed Andrew McNaughton stated to the Transport Committee that HS2 was overengineered in respect of bridge foundations and masts. [ 9 ] | https://en.wikipedia.org/wiki/Overengineering |
Overexploitation , also called overharvesting or ecological overshoot , refers to harvesting a renewable resource to the point of diminishing returns . [ 2 ] Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term applies to natural resources such as water aquifers , grazing pastures and forests , wild medicinal plants , fish stocks and other wildlife .
In ecology , overexploitation describes one of the five main activities threatening global biodiversity . [ 3 ] Ecologists use the term to describe populations that are harvested at an unsustainable rate, given their natural rates of mortality and capacities for reproduction. This can result in extinction at the population level and even extinction of whole species. In conservation biology , the term is usually used in the context of human economic activity that involves the taking of biological resources, or organisms, in larger numbers than their populations can withstand. [ 4 ] The term is also used and defined somewhat differently in fisheries , hydrology and natural resource management .
Overexploitation can lead to resource destruction, including extinctions . However, it is also possible for overexploitation to be sustainable, as discussed below in the section on fisheries. In the context of fishing, the term overfishing can be used instead of overexploitation, as can overgrazing in stock management , overlogging in forest management , overdrafting in aquifer management, and endangered species in species monitoring. Overexploitation is not an activity limited to humans. Introduced predators and herbivores, for example, can overexploit native flora and fauna .
The concern about overexploitation, while relatively recent in the annals of modern environmental awareness, traces back to ancient practices embedded in human history. Contrary to the notion that overexploitation is an exclusively contemporary issue, the phenomenon has been documented for millennia and is not limited to human activities alone. Historical evidence reveals that various cultures and societies have engaged in practices leading to the overuse of natural resources, sometimes with drastic consequences.
One poignant example can be found in the ceremonial cloaks of Hawaiian kings , which were adorned with the feathers of the now-extinct mamo bird. Crafting a single cloak required the feathers of approximately 70,000 adult mamo birds, illustrating a staggering scale of resource extraction that ultimately contributed to its extinction. This instance underscores how cultural traditions and their associated demands can sometimes precipitate the overexploitation of a species to the brink of extinction. [ 7 ] [ 8 ]
Similarly, the story of the dodo bird from Mauritius provides another clear example of overexploitation. The dodo, a flightless bird, exhibited a lack of fear toward predators, including humans, making it exceptionally vulnerable to hunting. The dodo's naivety and the absence of natural defenses against human hunters and introduced species led to its rapid extinction. This case offers insight into how certain species, particularly those isolated on islands, can be disproportionately affected by human activities due to their evolutionary adaptations. [ 9 ]
Hunting has long been a vital human activity for survival, providing food, clothing, and tools. However, the history of hunting also includes episodes of overexploitation, particularly in the form of overhunting. The overkill hypothesis , which addresses the Quaternary extinction events, explains the relatively rapid extinction of megafauna . This hypothesis suggests that these extinctions were closely linked to human migration and population growth. One of the most compelling pieces of evidence supporting this theory is that approximately 80% of North American large mammal species disappeared within just approximately a thousand years of humans arriving in the Western Hemisphere . This rapid disappearance indicates a significant impact of human activity on these species, underscoring the profound influence humans have had on their environment throughout history. [ 10 ]
The fastest-ever recorded extinction of megafauna occurred in New Zealand . By 1500 AD, a mere 200 years after the first human settlements, ten species of the giant moa birds were driven to extinction by the Māori . This rapid extinction underscores the significant impact humans can have on native wildlife, especially in isolated ecosystems like New Zealand. The Māori, relying on the moa as a primary food source and for resources such as feathers and bones, hunted these birds extensively. The moa's inability to fly and their size, which made them easier targets, contributed to their rapid decline. This event serves as a cautionary tale about the delicate balance between human activity and biodiversity and highlights the potential consequences of over-hunting and habitat destruction. [ 5 ] A second wave of extinctions occurred later with European settlement. This period marked significant ecological disruption, largely due to the introduction of new species and land-use changes. European settlers brought with them animals such as rats, cats, and stoats, which preyed upon native birds and other wildlife. Additionally, deforestation for agriculture significantly altered the habitats of many endemic species. These combined factors accelerated the decline of New Zealand's unique biodiversity, leading to the extinction of several more species. The European settlement period serves as a poignant example of how human activities can drastically impact natural ecosystems.
In more recent times, overexploitation has resulted in the gradual emergence of the concepts of sustainability and sustainable development , which has built on other concepts, such as sustainable yield , [ 11 ] eco-development , [ 12 ] [ 13 ] and deep ecology . [ 14 ] [ 15 ]
Overexploitation does not necessarily lead to the destruction of the resource, nor is it necessarily unsustainable. However, depleting the numbers or amount of the resource can change its quality. For example, footstool palm is a wild palm tree found in Southeast Asia. Its leaves are used for thatching and food wrapping, and overharvesting has resulted in its leaf size becoming smaller.
In 1968, the journal Science published an article by Garrett Hardin entitled "The Tragedy of the Commons". [ 16 ] It was based on a parable that William Forster Lloyd published in 1833 to explain how individuals innocently acting in their own self-interest can overexploit, and destroy, a resource that they all share. [ 17 ] [ pages needed ] Lloyd described a simplified hypothetical situation based on medieval land tenure in Europe. Herders share common land on which they are each entitled to graze their cows. In Hardin's article, it is in each herder's individual interest to graze each new cow that the herder acquires on the common land, even if the carrying capacity of the common is exceeded, which damages the common for all the herders. The self-interested herder receives all of the benefits of having the additional cow, while all the herders share the damage to the common. However, all herders reach the same rational decision to buy additional cows and graze them on the common, which eventually destroys the common. Hardin concludes:
Therein is the tragedy. Each man is locked into a system that compels him to increase his herd without limit—in a world that is limited. Ruin is the destination toward which all men rush, each pursuing his own interest in a society that believes in the freedom of the commons. Freedom in a commons brings ruin to all. [ 16 ] : 1244
In the course of his essay, Hardin develops the theme, drawing in many examples of latter day commons, such as national parks , the atmosphere, oceans, rivers and fish stocks . The example of fish stocks had led some to call this the "tragedy of the fishers". [ 18 ] A major theme running through the essay is the growth of human populations , with the Earth 's finite resources being the general common.
The tragedy of the commons has intellectual roots tracing back to Aristotle , who noted that "what is common to the greatest number has the least care bestowed upon it", [ 19 ] as well as to Hobbes and his Leviathan . [ 20 ] The opposite situation to a tragedy of the commons is sometimes referred to as a tragedy of the anticommons : a situation in which rational individuals, acting separately, collectively waste a given resource by underutilizing it.
The tragedy of the commons can be avoided if it is appropriately regulated. Hardin's use of "commons" has frequently been misunderstood, leading Hardin to later remark that he should have titled his work "The tragedy of the unregulated commons". [ 21 ]
In wild fisheries , overexploitation or overfishing occurs when a fish stock has been fished down "below the size that, on average, would support the long-term maximum sustainable yield of the fishery". [ 22 ] However, overexploitation can be sustainable. [ 23 ]
When a fishery starts harvesting fish from a previously unexploited stock, the biomass of the fish stock will decrease, since harvesting means fish are being removed. For sustainability, the rate at which the fish replenish biomass through reproduction must balance the rate at which the fish are being harvested. If the harvest rate is increased, then the stock biomass will further decrease. At a certain point, the maximum harvest yield that can be sustained will be reached, and further attempts to increase the harvest rate will result in the collapse of the fishery. This point is called the maximum sustainable yield , and in practice, usually occurs when the fishery has been fished down to about 30% of the biomass it had before harvesting started. [ 24 ]
It is possible to fish the stock down further to, say, 15% of the pre-harvest biomass, and then adjust the harvest rate so the biomass remains at that level. In this case, the fishery is sustainable, but is now overexploited, because the stock has been run down to the point where the sustainable yield is less than it could be.
Fish stocks are said to "collapse" if their biomass declines by more than 95 percent of their maximum historical biomass. Atlantic cod stocks were severely overexploited in the 1970s and 1980s, leading to their abrupt collapse in 1992. [ 1 ] Even though fishing has ceased, the cod stocks have failed to recover. [ 1 ] The absence of cod as the apex predator in many areas has led to trophic cascades . [ 1 ]
About 25% of world fisheries are now overexploited to the point where their current biomass is less than the level that maximizes their sustainable yield. [ 25 ] These depleted fisheries can often recover if fishing pressure is reduced until the stock biomass returns to the optimal biomass. At this point, harvesting can be resumed near the maximum sustainable yield. [ 26 ]
The tragedy of the commons can be avoided within the context of fisheries if fishing effort and practices are regulated appropriately by fisheries management . One effective approach may be assigning some measure of ownership in the form of individual transferable quotas (ITQs) to fishermen. In 2008, a large scale study of fisheries that used ITQs, and ones that did not, provided strong evidence that ITQs help prevent collapses and restore fisheries that appear to be in decline. [ 27 ] [ 28 ]
Water resources, such as lakes and aquifers , are usually renewable resources which naturally recharge (the term fossil water is sometimes used to describe aquifers which do not recharge). Overexploitation occurs if a water resource, such as the Ogallala Aquifer , is mined or extracted at a rate that exceeds the recharge rate, that is, at a rate that exceeds the practical sustained yield. Recharge usually comes from area streams, rivers and lakes. An aquifer which has been overexploited is said to be overdrafted or depleted. Forests enhance the recharge of aquifers in some locales, although generally forests are a major source of aquifer depletion. [ 29 ] [ 30 ] Depleted aquifers can become polluted with contaminants such as nitrates , or permanently damaged through subsidence or through saline intrusion from the ocean.
This turns much of the world's underground water and lakes into finite resources with peak usage debates similar to oil . [ 31 ] [ 32 ] These debates usually centre around agriculture and suburban water usage but generation of electricity from nuclear energy or coal and tar sands mining is also water resource intensive. [ 33 ] A modified Hubbert curve applies to any resource that can be harvested faster than it can be replaced. [ 34 ] Though Hubbert's original analysis did not apply to renewable resources, their overexploitation can result in a Hubbert-like peak . This has led to the concept of peak water .
Forests are overexploited when they are logged at a rate faster than reforestation takes place. Reforestation competes with other land uses such as food production, livestock grazing, and living space for further economic growth. Historically utilization of forest products, including timber and fuel wood, have played a key role in human societies, comparable to the roles of water and cultivable land. Today, developed countries continue to utilize timber for building houses, and wood pulp for paper . In developing countries almost three billion people rely on wood for heating and cooking. [ 35 ] Short-term economic gains made by conversion of forest to agriculture, or overexploitation of wood products, typically leads to loss of long-term income and long term biological productivity. West Africa , Madagascar , Southeast Asia and many other regions have experienced lower revenue because of overexploitation and the consequent declining timber harvests. [ 36 ]
Overexploitation is one of the main threats to global biodiversity . [ 3 ] Other threats include pollution , introduced and invasive species, habitat fragmentation , habitat destruction , [ 3 ] uncontrolled hybridization , [ 37 ] climate change , [ 38 ] ocean acidification [ 39 ] and the driver behind many of these, human overpopulation . [ 40 ]
One of the key health issues associated with biodiversity is drug discovery and the availability of medicinal resources. [ 41 ] A significant proportion of drugs are natural products derived, directly or indirectly, from biological sources. Marine ecosystems are of particular interest in this regard. [ 42 ] However, unregulated and inappropriate bioprospecting could potentially lead to overexploitation, ecosystem degradation and loss of biodiversity . [ 43 ] [ 44 ] [ 45 ]
Species from all groups of fauna and flora are affected by overexploitation. This phenomenon is not bound by taxonomy; it spans across mammals, birds, fish, insects, and plants alike. Animals are hunted for their fur, tusks, or meat, while plants are harvested for medicinal purposes, timber, or ornamental uses. This unsustainable practice disrupts ecosystems, threatening biodiversity and leading to the potential extinction of vulnerable species.
All living organisms require resources to survive. Overexploitation of these resources for protracted periods can deplete natural stocks to the point where they are unable to recover within a short time frame. Humans have always harvested food and other resources they need to survive. Human populations, historically, were small, and methods of collection were limited to small quantities. With an exponential increase in human population , expanding markets and increasing demand, combined with improved access and techniques for capture, are causing the exploitation of many species beyond sustainable levels. [ 46 ] In practical terms, if continued, it reduces valuable resources to such low levels that their exploitation is no longer sustainable and can lead to the extinction of a species, in addition to having dramatic, unforeseen effects , on the ecosystem . [ 47 ] Overexploitation often occurs rapidly as markets open, utilising previously untapped resources, or locally used species.
Today, overexploitation and misuse of natural resources is an ever-present threat for species richness . This is more prevalent when looking at island ecology and the species that inhabit them, as islands can be viewed as the world in miniature. Island endemic populations are more prone to extinction from overexploitation, as they often exist at low densities with reduced reproductive rates. [ 48 ] A good example of this are island snails, such as the Hawaiian Achatinella and the French Polynesian Partula . Achatinelline snails have 15 species listed as extinct and 24 critically endangered [ 49 ] while 60 species of partulidae are considered extinct with 14 listed as critically endangered. [ 50 ] The WCMC have attributed over-collecting and very low lifetime fecundity for the extreme vulnerability exhibited among these species. [ 51 ]
As another example, when the humble hedgehog was introduced to the Scottish island of Uist , the population greatly expanded and took to consuming and overexploiting shorebird eggs, with drastic consequences for their breeding success. Twelve species of avifauna are affected, with some species numbers being reduced by 39%. [ 52 ]
Where there is substantial human migration, civil unrest, or war, controls may no longer exist. With civil unrest, for example in the Congo and Rwanda , firearms have become common and the breakdown of food distribution networks in such countries leaves the resources of the natural environment vulnerable. [ 53 ] Animals are even killed as target practice, or simply to spite the government. Populations of large primates, such as gorillas and chimpanzees , ungulates and other mammals, may be reduced by 80% or more by hunting, and certain species may be eliminated. [ 54 ] This decline has been called the bushmeat crisis .
Overexploitation threatens one-third of endangered vertebrates , as well as other groups. Excluding edible fish, the illegal trade in wildlife is valued at $10 billion per year. Industries responsible for this include the trade in bushmeat , the trade in Chinese medicine , and the fur trade . [ 55 ] The Convention for International Trade in Endangered Species of Wild Fauna and Flora, or CITES was set up in order to control and regulate the trade in endangered animals. It currently protects, to a varying degree, some 33,000 species of animals and plants. It is estimated that a quarter of the endangered vertebrates in the United States of America and half of the endangered mammals is attributed to overexploitation. [ 3 ] [ 56 ]
Overall, 50 bird species that have become extinct since 1500 (approximately 40% of the total) have been subject to overexploitation, [ 57 ] including:
Overexploitation of species can result in knock-on or cascade effects . This can particularly apply if, through overexploitation, a habitat loses its apex predator . Because of the loss of the top predator, a dramatic increase in their prey species can occur. In turn, the unchecked prey can then overexploit their own food resources until population numbers dwindle, possibly to the point of extinction.
A classic example of cascade effects occurred with sea otters . Starting before the 17th century and not phased out until 1911, sea otters were hunted aggressively for their exceptionally warm and valuable pelts, which could fetch up to $2500 US. This caused cascade effects through the kelp forest ecosystems along the Pacific Coast of North America. [ 60 ]
One of the sea otters’ primary food sources is the sea urchin . When hunters caused sea otter populations to decline, an ecological release of sea urchin populations occurred. The sea urchins then overexploited their main food source, kelp , creating urchin barrens, areas of seabed denuded of kelp, but carpeted with urchins. No longer having food to eat, the sea urchin became locally extinct as well. Also, since kelp forest ecosystems are homes to many other species, the loss of the kelp caused other cascade effects of secondary extinctions. [ 61 ]
In 1911, when only one small group of 32 sea otters survived in a remote cove, an international treaty was signed to prevent further exploitation of the sea otters. Under heavy protection, the otters multiplied and repopulated the depleted areas, which slowly recovered. More recently, with declining numbers of fish stocks, again due to overexploitation, killer whales have experienced a food shortage and have been observed feeding on sea otters, again reducing their numbers. [ 62 ] | https://en.wikipedia.org/wiki/Overexploitation |
OVERFLOW - the OVERset grid FLOW solver - is a software package for simulating fluid flow around solid bodies using computational fluid dynamics (CFD). It is a compressible 3-D flow solver that solves the time-dependent, Reynolds-averaged, Navier–Stokes equations using multiple overset structured grids.
OVERFLOW was developed as part of a collaborative effort between NASA 's Johnson Space Center in Houston, Texas and NASA Ames Research Center (ARC) in Moffett Field , California . The driving force behind this work was the need for evaluating the flow about the Space Shuttle launch vehicle. Originally developed in the early 1990s by NASA's Pieter Buning , Dennis Jespersen and others, the code is an outgrowth of earlier codes F3D and ARC3D, and a result of ARC's long history of flow-solver development. [ 1 ]
Scientists use OVERFLOW to better understand the aerodynamic forces on a vehicle by evaluating the flowfield surrounding the vehicle. While wind tunnel testing provides limited data at many flow conditions, CFD simulations provide detailed information about selected conditions, and also provide a distribution of forces on the vehicle, aiding in structural design.
OVERFLOW has also been used to simulate the effect of debris on the space shuttle launch vehicle. [ 2 ] | https://en.wikipedia.org/wiki/Overflow_(software) |
In computer processors, the overflow flag (sometimes called the V flag ) is usually a single bit in a system status register used to indicate when an arithmetic overflow has occurred in an operation, indicating that the signed two's-complement result would not fit in the number of bits used for the result. Some architectures may be configured to automatically generate an exception on an operation resulting in overflow.
An example, suppose we add 127 and 127 using 8-bit registers. 127+127 is 254, but using 8-bit arithmetic the result would be 1111 1110 binary, which is the two's complement encoding of −2, a negative number. A negative sum of positive operands (or vice versa) is an overflow. The overflow flag would then be set so the program can be aware of the problem and mitigate this or signal an error. The overflow flag is thus set when the most significant bit (here considered the sign bit) is changed by adding two numbers with the same sign (or subtracting two numbers with opposite signs). Overflow cannot occur when the sign of two addition operands are different (or the sign of two subtraction operands are the same). [ 1 ]
When binary values are interpreted as unsigned numbers , the overflow flag is meaningless and normally ignored. One of the advantages of two's complement arithmetic is that the addition and subtraction operations do not need to distinguish between signed and unsigned operands. For this reason, most computer instruction sets do not distinguish between signed and unsigned operands, generating both (signed) overflow and (unsigned) carry flags on every operation, and leaving it to following instructions to pay attention to whichever one is of interest. [ 2 ]
Internally, the overflow flag is usually generated by an exclusive or of the internal carry into and out of the sign bit.
Bitwise operations (and, or, xor, not, rotate) do not have a notion of signed overflow, so the defined value varies on different processor architectures. Some processors clear the bit unconditionally (which is useful because bitwise operations set the sign flag, and the clear overflow flag then indicates that the sign flag is valid), others leave it unchanged, and some set it to an undefined value. Shifts and multiplies do permit a well-defined value, but it is not consistently implemented. For example, the x86 instruction set only defines the overflow flag for multiplies and 1-bit shifts; multi-bit shifts leave it undefined. | https://en.wikipedia.org/wiki/Overflow_flag |
Overflow metabolism refers to the seemingly wasteful strategy in which cells incompletely oxidize their growth substrate (e.g. glucose ) instead of using the respiratory pathway, even in the presence of oxygen. [ 1 ] As a result of employing this metabolic strategy, cells excrete (or "overflow") metabolites like lactate , acetate and ethanol . Incomplete oxidation of growth substrates yields less energy (e.g. ATP ) than complete oxidation through respiration , and yet overflow metabolism—known as the Warburg effect in the context of cancer [ 2 ] and the Crabtree effect in the context of yeast—occurs ubiquitously among fast-growing cells, including bacteria, fungi and mammalian cells.
Based on experimental studies of acetate overflow in Escherichia coli , recent research has offered a general explanation for the association of overflow metabolism with fast growth. According to this theory, the enzymes required for respiration are more costly than those required for partial oxidation of glucose. [ 3 ] [ 4 ] That is, if the cell were to produce enough of these enzymes to support fast growth with respiratory metabolism , it would consume much more energy, carbon and nitrogen (per unit time) than supporting fast growth with an incompletely oxidative metabolism (e.g. fermentation). Given that cells have limited energy resources and fixed physical volume for proteins, there is thought to be a trade-off between efficient energy capture through central metabolism (i.e. respiration) and fast growth achieved through high central-metabolic fluxes (e.g. through fermentation as in yeast ).
As an alternative explanation, it was suggested that cells could be limited by the rate with which they can dissipate Gibbs energy to the environment. [ 5 ] Using combined thermodynamic and stoichiometric metabolic models in flux balance analyses with (i) growth maximization as objective function and (ii) an identified limit in the cellular Gibbs energy dissipation rate, correct predictions of physiological parameters, intracellular metabolic fluxes and metabolite concentrations were achieved. [ 5 ] | https://en.wikipedia.org/wiki/Overflow_metabolism |
In engineering , some methods or components make special demands on the system. The extra design features necessary to meet these demands are called overhead . For instance, in electrical engineering , a particular integrated circuit might draw large current , requiring a robust power delivery circuit and a heat-dissipation mechanism.
An example from software engineering is the encoding of information and data. The date and time "2011-07-12 07:18:47" can be expressed as Unix time with the 32-bit signed integer 1310447927 , consuming only 4 bytes . Represented as ISO 8601 formatted UTF-8 encoded string 2011-07-12 07:18:47 the date would consume 19 bytes, a size overhead of 375% over the binary integer representation. As XML this date can be written as follows with an overhead of 218 characters, while adding the semantic context that it is a CHANGEDATE with index 1.
The 349 bytes resulting from the UTF-8 encoded XML correspond to a size overhead of 8725% over the original integer representation.
This engineering-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Overhead_(engineering) |
Overheating is a phenomenon of rising temperatures in an electrical circuit . Overheating causes damage to the circuit components and can cause fire, explosion, and injury. Damage caused by overheating is usually irreversible; the only way to repair it is to replace some components.
When overheating, the temperature of the part rises above the operating temperature . Overheating can take place:
Overheating may be caused from any accidental fault of the circuit (such as short-circuit or spark-gap), or may be caused from a wrong design or manufacture (such as the lack of a proper heat dissipation system).
Due to accumulation of heat, the system reaches an equilibrium of heat accumulation vs. dissipation at a much higher temperature than expected.
Circuit-breakers can be placed at portions of a circuit in series to the path of current it will affect. If more current than expected goes through the circuit-breaker, the circuit breaker "opens" the circuit and stops all current. A fuse is a common type of circuit breaker that involves direct effect of Joule-overheating. A fuse is always placed in series with the path of current it will affect. Fuses usually consist of a thin strand of wire of definite-material. When more that the rated current flows through the fuse, the wire melts and breaks the circuit.
Many systems use ventilation holes or slits kept on the box of equipment to dissipate heat. Heat sinks are often attached to portions of the circuit that produce most heat or are vulnerable to heat. Fans are also often used. Some high-voltage instruments are kept immersed in oil. In some cases, to remove unwanted heat, a cooling system like air conditioning or refrigerating heat-pumps may be required.
Sometimes, special circuits are built for the purpose of sensing and controlling the temperature or voltage status. Devices such as thermistors , voltage-dependent resistors , thermostats and sensors such as infrared thermometers are used to modify the current upon different conditions such as circuit-temperature and input voltage.
For certain purposes in an item of electrical equipment or a portion of it, definite type and size of materials with proper rating for voltage, current and temperature, are used. The circuit resistance never kept too low. Sometimes some parts placed inside the board and box, maintaining a proper distance from each other, to avoid heat damage and short-circuit damage. To prevent short circuit, appropriate types of electrical connectors and mechanical fasteners are used. | https://en.wikipedia.org/wiki/Overheating_(electricity) |
The overlap extension polymerase chain reaction (or OE-PCR ) is a variant of PCR . It is also referred to as Splicing by overlap extension / Splicing by overhang extension (SOE) PCR . It is used to assemble multiple smaller double stranded DNA fragments into a larger DNA sequence. OE-PCR is widely used to insert mutations at specific points in a sequence or to assemble custom DNA sequence from smaller DNA fragments into a larger polynucleotide . [ 1 ]
As in most PCR reactions, two primers—one for each end—are used per sequence. To splice two DNA molecules, special primers are used at the ends that are to be joined. For each molecule, the primer at the end to be joined is constructed such that it has a 5' overhang complementary to the end of the other molecule. Following annealing when replication occurs, the DNA is extended by a new sequence that is complementary to the molecule it is to be joined to. Once both DNA molecules are extended in such a manner, they are mixed and a PCR is carried out with only the primers for the far ends. The overlapping complementary sequences introduced will serve as primers and the two sequences will be fused. This method has an advantage over other gene splicing techniques in not requiring restriction sites.
To get higher yields, some primers are used in excess as in asymmetric PCR .
To insert a mutation into a DNA sequence, a specific primer is designed. The primer may contain a single substitution or contain a new sequence at its 5' end. If a deletion is required, a sequence that is 5' of the deletion is added, because the 3' end of the primer must have complementarity to the template strand so that the primer can sufficiently anneal to the template DNA.
Following annealing of the primer to the template, DNA replication proceeds to the end of the template. The duplex is denatured and the second primer anneals to the newly formed DNA strand, containing sequence from the first primer. Replication proceeds to produce a strand of the required sequence, containing the mutation.
The duplex is denatured again and the first primer can now bind to the latest DNA strand. The replication reaction continues to produce a fully dimerised DNA fragment. After further PCR cycles, to amplify the DNA, the sample can be separated by agarose gel electrophoresis , followed by electroelution for collection.
Efficiently generating oligonucleotides beyond ~110 nucleotides in length is very difficult, so to insert a mutation further into a sequence than a 110 nt primer will allow, it is necessary to employ overlap extension PCR. In OE-PCR the sequence being modified is used to make two modified strands with the mutation at opposite ends, using the technique described above. After mixing and denaturation, the strands are allowed to anneal to produce three different combinations as detailed in the diagram. Only the duplex without overlap at the 5' end will allow extension by DNA polymerase in 3' to 5' direction.
Following the extension of the OE-PCR reaction, the PCR mix or the eluted fragments of appropriate size are subject to normal PCR, using the outermost primers used in the initial, mutagenic PCR reactions.
In addition, the combination of OE-PCR and asymmetric PCR could be used to improved the efficiency of site-directed mutagenesis . [ 2 ]
Besides the introduction of mutations, Overlap Extension PCR is widely used to assemble complex DNA sequences without the introduction of undesired nucleotides at any position. This is possible since OE-PCR relies on the utilization of complementary overhangs to guide the scarless splicing of custom DNA fragments in a desired order. This is the main advantage of OE-PCR and other long-homology based cloning methods such as Gibson assembly , which overcome the limitations of traditional restriction enzyme digestion and ligation cloning methods. [ 3 ]
Assembly of custom DNA sequences with OE-PCR consists on three main steps. First, individual DNA sequences are amplified by PCR from different templates and flanked with the required complementary overhangs. Second, the formerly obtained PCR products are combined together into the overlap extension PCR reaction, where the complementary overhangs bind pair-wise allowing the polymerase to extend the DNA strand. Eventually, outer primers targeting the external overhangs are used and the desired DNA product is amplified in the final PCR reaction.
The overall success of OE-PCR based DNA assemblies relies on several factors, being the most relevant ones the instrinsic features of the DNA sequence to assemble, the sequence and length of the overlapping overhangs, the design of outer primers for the final amplification and the conditions of the PCR reaction. Normally, from 2 to 6 fragments can be spliced simultaneously into a single OE-PCR reaction. [ 4 ] Overhangs should be at least 40 nucleotides long to ensure adequate interaction between fragments. Final amplification primers are commonly designed following general guidelines for PCR, however they are used in 2 to 5 times lower concentration than in standard PCR reactions, as it this has been shown to reduce undesired amplifications. [ 5 ] Additionally the utilization of proofreading DNA polymerases is highly recommended. | https://en.wikipedia.org/wiki/Overlap_extension_polymerase_chain_reaction |
Overlapped I/O is a name used for asynchronous I/O in the Windows API . [ 1 ] [ 2 ] [ 3 ] It was introduced as an extension to the API in Windows NT .
Utilizing overlapped I/O requires passing an OVERLAPPED structure to API functions that normally block, including ReadFile() , WriteFile() , and Winsock 's WSASend() and WSARecv() . The requested operation is initiated by a function call which returns immediately, and is completed by the OS in the background. The caller may optionally specify a Win32 event handle to be signalled when the operation completes. Alternatively, a program may receive notification of an event via an I/O completion port , which is the preferred method of receiving notification when used in symmetric multiprocessing environments or when handling I/O on numerous files or sockets . The third and the last method to get the I/O completion notification with overlapped IO is to use ReadFileEx() and WriteFileEx() , which allow the User APC routine to be provided, which will be fired on the same thread on completion (User APC is the thing very similar to Unix/POSIX signal , with the main difference being that the signals are using signal numbers from the historically predefined enumeration, while the User APC can be any function declared as " void f(void* context) "). The so-called overlapped API presents some differences depending on the Windows version used. [ 4 ]
Asynchronous I/O is particularly useful for sockets and pipes .
Unix and Linux implement the POSIX asynchronous I/O API (AIO).
This Microsoft Windows article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Overlapped_I/O |
The Overlapping distribution method was introduced by Charles H. Bennett [ 1 ] for estimating chemical potential .
For two N particle systems 0 and 1 with partition function Q 0 {\displaystyle Q_{0}} and Q 1 {\displaystyle Q_{1}} ,
from F ( N , V , T ) = − k B T ln Q {\displaystyle F(N,V,T)=-k_{B}T\ln Q}
get the thermodynamic free energy difference is Δ F = − k B T ln ( Q 1 / Q 0 ) = − k B T ln ( ∫ d s N exp [ − β U 1 ( s N ) ] ∫ d s N exp [ − β U 0 ( s N ) ] ) {\displaystyle \Delta F=-k_{B}T\ln(Q_{1}/Q_{0})=-k_{B}T\ln({\frac {\int ds^{N}\exp[-\beta U_{1}(s^{N})]}{\int ds^{N}\exp[-\beta U_{0}(s^{N})]}})}
For every configuration visited during this sampling of system 1 we can compute the potential energy U as a function of the configuration space, and the potential energy difference is
Δ U = U 1 ( s N ) − U 0 ( s N ) {\displaystyle \Delta U=U_{1}(s^{N})-U_{0}(s^{N})}
Now construct a probability density of the potential energy from the above equation:
p 1 ( Δ U ) = ∫ d s N exp ( − β U 1 ) δ ( U 1 − U 0 − Δ U ) Q 1 {\displaystyle p_{1}(\Delta U)={\frac {\int ds^{N}\exp(-\beta U_{1})\delta (U_{1}-U_{0}-\Delta U)}{Q_{1}}}}
where in p 1 {\displaystyle p_{1}} is a configurational part of a partition function
p 1 ( Δ U ) = ∫ d s N exp ( − β U 1 ) δ ( U 1 − U 0 − Δ U ) Q 1 = ∫ d s N exp [ − β ( U 0 + Δ U ) ] δ ( U 1 − U 0 − Δ U ) Q 1 {\displaystyle p_{1}(\Delta U)={\frac {\int ds^{N}\exp(-\beta U_{1})\delta (U_{1}-U_{0}-\Delta U)}{Q_{1}}}={\frac {\int ds^{N}\exp[-\beta (U_{0}+\Delta U)]\delta (U_{1}-U_{0}-\Delta U)}{Q_{1}}}} = Q 0 Q 1 exp ( − β Δ U ) ∫ d s N exp ( − β U 0 ) δ ( U 1 − U 0 − Δ U ) Q 0 = Q 0 Q 1 exp ( − β Δ U ) p 0 ( Δ U ) {\displaystyle ={\frac {Q_{0}}{Q_{1}}}\exp(-\beta \Delta U){\frac {\int ds^{N}\exp(-\beta U_{0})\delta (U_{1}-U_{0}-\Delta U)}{Q_{0}}}={\frac {Q_{0}}{Q_{1}}}\exp(-\beta \Delta U)p_{0}(\Delta U)}
since
Δ F = − k B T ln ( Q 1 / Q 0 ) {\displaystyle \Delta F=-k_{B}T\ln(Q_{1}/Q_{0})}
ln p 1 ( Δ U ) = β ( Δ F − Δ U ) + ln p 0 ( Δ U ) {\displaystyle \ln p_{1}(\Delta U)=\beta (\Delta F-\Delta U)+\ln p_{0}(\Delta U)}
now define two functions:
f 0 ( Δ U ) = ln p 0 ( Δ U ) − β Δ U 2 f 1 ( Δ U ) = ln p 1 ( Δ U ) + β Δ U 2 {\displaystyle f_{0}(\Delta U)=\ln p_{0}(\Delta U)-{\frac {\beta \Delta U}{2}}f_{1}(\Delta U)=\ln p_{1}(\Delta U)+{\frac {\beta \Delta U}{2}}}
thus that
f 1 ( Δ U ) = f 0 ( Δ U ) + β Δ F {\displaystyle f_{1}(\Delta U)=f_{0}(\Delta U)+\beta \Delta F}
and Δ F {\displaystyle \Delta F} can be obtained by fitting f 1 {\displaystyle f_{1}} and f 0 {\displaystyle f_{0}} | https://en.wikipedia.org/wiki/Overlapping_distribution_method |
Overlay architecture , or Overlay , is "event architecture ", such as the temporary elements that are added to more permanent buildings to enable the operation of major sporting events or festivals . These elements provide additional facilities for the duration of an event and are generally of a lightweight construction, as they are often removed afterwards.
The role of overlay is extensive and can cover all aspects of a major event, starting with the "back of house" user groups, including staff, operations, officials, broadcast , media , hospitality, VIPs and the athletes themselves. These groups all require physical facilities to provide accreditation , accommodation, segregation and wayfinding , which need to be separated from, but connected to, the spectators at the "front of house", to preserve the magic and mystery of the event experience.
It is important that the overlay design is integrated into the masterplan of major events at an early stage, in order that the flow of people through the site can be effectively managed and sufficient space provided for the various overlay facilities.
The overlay design also has a significant role in helping to define the overall environment of a major event. By taking a design-inclusive approach and considering the cultural and design aspects alongside the commercial and functional requirements, memorable places and spaces can be created out of simple components and hired commodities.
Overlay can be categorised in three main ways:
This architecture -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Overlay_architecture |
An overlayer is a layer of adatoms adsorbed onto a surface, for instance onto the surface of a single crystal . [ 1 ]
Adsorbed species on single crystal surfaces are frequently found to exhibit long-range ordering; that is to say that the adsorbed species form a well-defined overlayer structure. Each particular structure may only exist over a limited coverage range of the adsorbate, and in some adsorbate/substrate systems a whole progression of adsorbate structure are formed as the surface coverage is gradually increased. [ 2 ]
The periodicity of the overlayer (which often is larger than that of the substrate unit cell) can be determined by low-energy electron diffraction (LEED), because there will be additional diffraction beams associated with the overlayer. [ 3 ]
There are two types of overlayers: commensurate and incommensurate . In the former the substrate-adsorbate interaction tends to dominate over any lateral adsorbate-adsorbate interaction, while in the latter the adsorbate-adsorbate interactions are of similar magnitude to those between adsorbate and substrate. [ 4 ]
An overlayer on a substrate can be notated in either Wood's notation or matrix notation . [ 5 ]
Wood's notation takes the form
where M is the chemical symbol of the substrate, A is the chemical symbol of the overlayer, ( h k ℓ ) {\displaystyle (hk\ell )} are the Miller indices of the surface plane, R and α {\displaystyle \alpha } correspond to the rotational difference between the substrate and overlayer vectors, and the vector magnitudes shown are those of the substrate ( s {\displaystyle s} subscripts) and of the overlayer ( 0 {\displaystyle 0} subscripts). This notation can only describe commensurate overlayers however, while matrix notation can describe both.
Matrix notation differs from Wood's notation in the second term, which is replaced by the G {\displaystyle G} matrix that describes the overlayer primitive vectors in terms of the substrate primitive vectors:
and so hence matrix notation has the form
This chemistry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Overlayer |
The Overman rearrangement is a chemical reaction that can be described as a Claisen rearrangement of allylic alcohols to give allylic trichloroacetamides through an imidate intermediate. [ 1 ] [ 2 ] [ 3 ] The Overman rearrangement was discovered in 1974 by Larry Overman . [ 4 ]
The [3,3]-sigmatropic rearrangement is diastereoselective and requires heating or the use of Hg(II) or Pd(II) salts as catalysts. [ 5 ] The resulting allylamine structures can be transformed into many chemically and biologically important natural and un-natural amino acids (like (1- adamantyl )glycine). [ 6 ]
The Overman rearrangement may also be used for asymmetric synthesis . [ 7 ] [ 8 ] | https://en.wikipedia.org/wiki/Overman_rearrangement |
Overpopulation or overabundance is a state in which the population of a species is larger than the carrying capacity of its environment . This may be caused by increased birth rates, lowered mortality rates , reduced predation or large scale migration , leading to an overabundant species and other animals in the ecosystem competing for food, space, and resources. The animals in an overpopulated area may then be forced to migrate to areas not typically inhabited, or die off without access to necessary resources.
Judgements regarding overpopulation always involve both facts and values. Animals are often judged overpopulated when their numbers cause impacts that people find dangerous, damaging, expensive, or otherwise harmful. Societies may be judged overpopulated when their human numbers cause impacts that degrade ecosystem services , decrease human health and well-being, or crowd other species out of existence.
In ecology , overpopulation is a concept used primarily in wildlife management . [ 1 ] [ 2 ] Typically, an overpopulation causes the entire population of the species in question to become weaker, as no single individual is able to find enough food or shelter. As such, overpopulation is thus characterized by an increase in the diseases and parasite-load which live upon the species in question, as the entire population is weaker. Other characteristics of overpopulation are lower fecundity, adverse effects on the environment (soil, vegetation or fauna) and lower average body weights. [ 2 ] Especially the worldwide increase of deer populations, which usually show irruptive growth , is proving to be of ecological concern. Ironically, where ecologists were preoccupied with conserving or augmenting deer populations only a century ago, the focus has now shifted in the direct opposite, and ecologists are now more concerned with limiting the populations of such animals. [ 3 ] [ 4 ]
Supplemental feeding of charismatic species or interesting game species is a major problem in causing overpopulation, [ 2 ] [ 5 ] [ 6 ] as is too little hunting or trapping of such species. Management solutions are increasing hunting by making it easier or cheaper for (foreign) hunters to hunt, [ 2 ] [ 5 ] banning supplemental feeding, [ 2 ] awarding bounties, [ 7 ] forcing landowners to hunt or contract professional hunters, [ 5 ] [ 8 ] using immunocontraception , [ 9 ] promoting the harvest of venison or other wild meats, [ 10 ] introducing large predators ( rewilding ), [ 11 ] [ 12 ] poisonings or introducing diseases.
A useful tool in wildlife culling is the use of mobile freezer trailers in which to store carcasses. [ 13 ] The harvest of meat from wild animals is a sustainable method of creating a circular economy . [ 10 ]
Immunocontraception is a non-lethal method of regulating wild-animal population growth. Immunocontraception has been successfully used or tested in a variety of wild-animal populations including those of bison , [ 14 ] deer , [ 15 ] elephants , [ 16 ] gray squirrels , [ 17 ] pigeons , [ 16 ] rats and wild horses . [ 18 ] [ 16 ] Among the limitations of injectable immunocontraceptives are a relatively long time between vaccine administration and a reduction in population size (although stabilization of population size occurs faster) [ 19 ] [ 20 ] and the need to be in close proximity with animals for injection. [ 21 ] Oral vaccines do not have the latter limitation, but they are still not as well developed as injectable vaccines. [ 22 ] [ 21 ]
Judgements about overpopulation of wildlife or domestic animals typically are made in terms of human purposes and interests; since these vary, such judgements may vary, too. Judgements about human overpopulation are even more contentious, since the purposes and interests involved may be very important, even rising to the level of existence itself. [ 23 ] [ 24 ] Nevertheless, all people and every society have an interest in preserving a habitable biosphere, which may be compromised or degraded by too may people. [ 25 ] [ 26 ] In the context of rapid climate change, mass species extinction and other global environmental problems, discussions regarding human overpopulation are inevitable. [ 27 ] [ 28 ]
Recent scientific evidence from many sources suggests Earth may be overpopulated currently. Evidence of rapidly declining ecosystem services was presented in detail in the Millennium Ecosystem Assessment of 2005, a collaborative effort involving more than 1,360 experts worldwide. [ 29 ] More recent scientific accounts are provided by ecological footprint accounting [ 30 ] and interdisciplinary research on planetary boundaries for safe human use of biosphere. [ 31 ] The Sixth Assessment Report on Climate Change from the IPCC and the First Assessment Report on Biodiversity and Ecosystem Services by the IPBES , large international summaries of the state of scientific knowledge regarding climate disruption and biodiversity loss , also support the view that unprecedented human numbers are contributing to global ecological decline. [ 32 ] [ 33 ] Recent estimates of a sustainable global human population run between two and four billion people. [ 26 ] [ 34 ]
Judgements about human or animal overpopulation hinge partly on whether people feel a moral obligation to leave sufficient habitat and resources to preserve viable populations of other species. [ 35 ] Recent biodiversity losses show that humanity's success in supporting larger human populations over the past century has depended on reducing the populations of many of Earth's other species. [ 33 ] [ 36 ] This is a special example of the competitive exclusion principle in ecology, which states that two species which compete for the same limited resource cannot coexist at constant population values. [ 37 ] Today humanity essentially competes with other species everywhere on Earth. [ 33 ] [ 38 ] We thus face choices regarding whether to preserve populations of other species and limit our own, or not. [ 39 ] [ 40 ] These essentially ethical choices [ 41 ] [ 42 ] will make a difference in future judgements about overpopulation. [ 36 ] [ 43 ]
In the Scottish Highlands , the arrangement in which landowners privately cull the overpopulation of red deer has proved an abject failure. [ 8 ] [ 44 ] Scotland's deer are stunted, emaciated, and frequently starve in the Spring. [ 44 ] As of 2016, the population is now so high that 100,000 deer would need to be culled each year just to maintain the current population. [ 8 ] A number of landowners have proven unwilling to accede to the law, requiring government intervention anyway. It has been necessary to contract professional hunters in order to satisfy landowner legislation regarding the annual cull. [ 5 ] Millions of pounds of taxpayers' cash is spent on the annual cull. [ 12 ] As of 2020, 100,000 deer are shot each year. [ 10 ] Compounding the problem, some landowners have used supplemental feeding at certain shooting blinds in order to facilitate sport hunting. [ 5 ] [ 44 ]
Overpopulation can affect forage plants, eventually causing a species to alter the greater environment. [ 45 ] Natural ecosystems are extremely complex. The overpopulation of deer in Britain has been caused by legislation making hunting more difficult, [ 46 ] [ 47 ] but another reason may be the proliferation of forests, used by different deer species to breed and shelter. Forests and parks have caused Britain to be much more forested than it was in recent history, [ 47 ] and may thus perversely be causing biodiversity loss , [ 45 ] [ 48 ] conversion of heath habitat to grassland, [ 8 ] extirpation of grassland and woodland plants due to overgrazing and the changing of the habitat structure. [ 3 ] [ 48 ] Examples are bluebells and primroses . Deer open up the forest and reduce the amount of brambles, which then has knock-on effects on dormice and certain birds which nest near the ground, [ 45 ] [ 48 ] such as the capercaillie , dunnock , nightingale , song thrush , willow warbler , marsh tit , willow tit and bullfinch . [ 45 ] Populations of the nightingale and the European turtle dove are believed to be primarily impacted by muntjac . [ 46 ] Grouse populations suffer due to smashing into the fencing needed to protect against deer. [ citation needed ]
A significant amount of the environmental destruction in Britain is caused by an overabundance of deer. Besides ecological effects, overpopulation of deer causes economic effects due to browsing on crops, expensive fencing needed to combat this and protect new afforestation planting and coppice growth, and increasing numbers of road traffic incidents . [ 3 ] [ 45 ] [ 46 ] High populations cause stripping of the bark of trees, eventually destroying forests. Protecting forests from deer costs on average three times [ clarification needed ] [ over what period? ] as much as planting the forest in the first place. [ 45 ] The NGO Trees for Life spent weeks planting native trees in Scotland, aiming to rebuild the ancient Caledonian Forest . After winter snowdrifts in 2014/2015 flattened the deer fences, more than a decade's growth was lost in a matter of weeks. [ 5 ] In 2009 – 2010 the cost of forest protection in Scotland ran to £10.5m. [ 12 ]
Some animals, such as muntjac , are too small and boring for most hunters to shoot, which poses additional management problems. [ 45 ]
In the United States the exact same problem is seen with white-tailed deer , where populations have exploded and become invasive species in some areas. The state of Wisconsin has an estimated population of 1.9 million White tail deer, measured in 2020. [ 49 ] In continental Europe roe deer pose a similar problem: although the populations were formerly much less, they have swelled in the 20th century so that although two and a half million are shot each year by hunters in Western Europe alone, as of 1998, the population still appears to be increasing, causing problems for forestry and traffic. In an experiment where roe deer on a Norwegian island were freed from human harvest and predators, the deer doubled in population each year or two. [ 4 ] In the Netherlands and southern England roe deer were extirpated from the entirety of the country except for a few small areas around 1875. In the 1970s the species was still completely absent from Wales, but as of 2013, it has colonized the entire country. [ 48 ] [ 50 ] [ 51 ] As new forests were planted in the Netherlands in the 20th century, the population began to expand rapidly. As of 2016 there are some 110,000 deer in the country. [ 51 ]
Aquaculture operations, recreation angling and populations of endangered fish such as the schelly are impacted by cormorant populations. Open aquaculture ponds provide winter or year-round homes and food for cormorants. Cormorants' effect on the aquaculture industry is significant, with a dense flock capable of consuming an entire harvest. [ 7 ] [ 52 ] [ 53 ] [ 54 ] [ 55 ] [ 56 ] Cormorants are estimated to cost the catfish industry in Mississippi alone between $10 million and $25 million annually. [ 55 ] Cormorant culling is commonly achieved by sharp-shooting, nest destruction, roost dispersal and oiling the eggs . [ 53 ] [ 55 ]
Geese numbers have also been called overpopulated. In the Canadian Arctic region, snow geese , Ross's geese , greater white-fronted geese and some populations of Canada geese have been increasing significantly over the past decades. Lesser snow geese populations have increased to over three million, and continue to increase by some 5% per year. Giant Canada geese have grown from near extinction to nuisance levels, in some areas. Average body sizes have decreased and parasite loads are higher. Before the 1980s, Arctic geese populations had boom and bust cycles (see above) thought to be based on food availability, although there are still some bust years, this no longer seems the case. [ 57 ]
It is difficult to know what the numbers of geese were before the 20th century, before human impact presumably altered them. There are a few anecdotal claims from that time of two or three million, but these are likely exaggerations, as that would imply a massive die-off or vast amounts harvested, for which there is no evidence. More likely estimates from the period of 1500 to 1900 are a few hundred thousand animals, which implies that with the exception of Ross's geese, modern populations of geese are many millions more than in pre-industrial levels. [ 57 ]
Humans are blamed as the ultimate cause for the increase, directly and indirectly, due to management legislation limiting hunting introduced specifically in order to protect bird populations, but most importantly due to the increase in agriculture and large parks, which has had the effect of creating vast amounts of unintentional sanctuaries filled with food. [ 57 ] Urban geese flocks have increased enormously. City ordinances generally prohibit discharging firearms, keeping such flocks safe, and there is abundant food. [ 58 ] Geese profit from agricultural grain crops, and seem to be shifting their habitat preferences to such farmlands. Reduction of goose hunting in the US since the 1970s seems to have further had the effect of protecting populations. In Canada hunting has also decreased dramatically, from 43.384% harvest rates in the 1960s to 8% in the 1990s. Nonetheless, when kill rates were compared to populations, hunting alone does not seems to be solely responsible for the increase -weather or a not yet completed shift in habitat preference to agricultural land may also be factors. Although hunting may have formerly been the main factor in maintaining stable populations, ecologists no longer consider it a practical management solution, as public interest in the practice has continued to wane, and the population is now so large that the massive culls needed are unrealistic to ask from the public. Climate change in the Arctic would appear to be an obvious cause for the increase, but when subpopulations are correlated with local climatic increases, this does not seem to hold true, and furthermore, breeding regions seem to be shifting southwards anyway, irrespective of climate change. [ 57 ]
The nutrient subsidy provided by foraging in agricultural land may have made the overall landscape use by geese unsustainable. Where such geese congregate local plant communities have been substantially altered; these chronic effects are cumulative, and have been considered a threat to the Arctic ecosystems, due to knock-on effects on native ducks, shorebirds and passerines. Grubbing and overgrazing by geese completely denudes the tundra and marshland, in combination with abiotic processes, this creates large desert expanses of hypersaline, anoxic mud which continue to increase each year. Biodiversity drops to only one or two species which are inedible for geese, such as Senecio congestus , Salicornia borealis and Atriplex hastata . Because grazing occurs in serial stages, with biodiversity decreasing at each stage, floral composition may be used as an indicator of the degree of goose foraging at a site. Other effects are destruction of the vegetation holding dunes in place, the shift from sedge meadows and grassy swards with herbaceous plants to moss fields, which can eventually give way to bare ground called 'peat barrens', and the erosion of this bare peat until glacial gravel and till is bared. In the High Arctic research is less developed: Eriophorum scheuchzeri and E. angustifolium fens appear to be affected, and are being replaced by carpets of moss, whereas meadows covered in Dupontia fisheri appear to be escaping destruction. There does not appear to be the damage found at lower latitudes in the Arctic. There is little proper research in effects on other birds. The yellow rail ( Coturnicops noveboracensis ) appears to be extirpated from areas of Manitoba due habitat loss caused by the geese, whereas on the other hand the semipalmated plover ( Charadrius semipalmatus ) appears to be taking advantage of the large areas of dead willows as a breeding ground. [ 57 ]
In the wintering grounds in continental USA, effects are much less pronounced. Experimentally excluding geese by means of fencing in North Carolina has found heavily affected areas can regenerate after only two years. Bulrush stands ( Schoenoplectus americanus ) are still an important component of the diet, but there are indications the bulrush is being impacted, with soft mudflats gradually replacing areas where it grows. [ 57 ]
Damage to agriculture is primarily to seedlings, winter wheat and hay production. Changing the species composition to species less palatable to geese, such as Lotus may alleviate losses in hay operations. Geese also feed on agricultural land without causing economic loss, gleaning seeds from corn, soya or other grains and feeding on wheat, potato and corn stubble. In Québec crop damage insurance for the hay industry began in 1992 and claims increased yearly; actual compensation paid by the government, including administrative costs, amount to some half a million dollars a year. [ 57 ]
Arctic regions are remote, there is little public understanding for combatting the problem, and ecologists as yet do not have any effective solutions for combatting the problem anyway. In Canada, the most important hunters of geese are the Cree people around Hudson Bay, members of the Mushkegowuk Harvesters Association, with an average kill rate of up to 60.75 birds per species per hunter in the 1970s. Kill rates have dropped, with hunters taking only half as much in the 1990s. However, total numbers of kills have increased, i.e. there are more hunters, but they are killing less per person. Nonetheless, per household the kills are approximately the same, at 100 birds. This indicates that stimulating an increase in native hunting might be difficult to achieve. The Cree population has increased. Elders say the taste of the birds has gotten worse, and they are thinner: both possibly due to the overpopulation. Elders also say that hunting has gotten more difficult, because there are fewer young and goslings, which are more likely to fall for decoys . Inuit and other people in the north do much less hunting of geese, with kill rates of 1 to 24 per species per hunter. Hunters can save some $8.14 to $11.40 per kilogram compared to buying poultry at stores. Total kill numbers from hunters elsewhere in the US and southern Canada have been falling steadily. This is blamed on a decline in people interested in hunting, more feeding areas for the birds, and larger flocks with more experienced adult birds which makes decoying difficult. Individual hunters are bagging higher numbers, compensating for lower hunter numbers. [ 57 ]
Management strategies in the USA include increasing the bag limit and the number of open hunting days, goose egg addling , trapping and relocation, and egg and nest destruction, managing habitat to make it less attractive to geese, harassment and direct culling. [ 58 ] In Denver, Colorado , during moulting season biologists rounded up 300 Canada geese (of 5,000 in the city), ironically on Canada Day , killing them and distributing the meat to needy families (as opposed to sending it to a landfill), to try to curb the number of geese, following such programs in New York, Pennsylvania, Oregon and Maryland. Complaints about the birds were that they had taken over the golf courses, pooped all over the place, devoured native plants and scared citizens. Such culls have proven socially controversial, with intense backlash by some citizens. Park officials had tried dipping eggs in oil, using noise-makers and planting tall plants, but this was not sufficient. [ 59 ]
In Russia, the problem does not seem to exist, likely due to human harvest and local long-term cooling climate trends in the Russian Far East and Wrangel Island . [ 57 ]
It is also possible that the population growth is completely natural, and that when the carrying capacity of the environment is reached the population will stop growing. [ 57 ] For organisations such as Ducks Unlimited , the resurgence of goose populations in North America can be called one of the greatest success stories in wildlife management. By 2003 the US goose harvest was approaching 4 million, three times the numbers 30 years previously. [ 60 ]
In the United States, over half of the households own a dog or a cat. Even with so much pet ownership there is still an issue with pet overpopulation, especially seen in shelters. [ 64 ] Because of this problem it is estimated that between 10 and 25 percent of dogs and cats are killed yearly. The animals are killed humanely, but the goal is to greatly lower and eventually completely avoid this. [ 64 ] Estimating the overpopulation of pets, especially cats and dogs, is a difficult task, but it has been a continuous problem. It has been hard to determine the number of shelters and animals in each shelter around even just the US. [ 65 ] Animals are constantly being moved around or euthanized, so it is difficult to keep track of those numbers across the country. It is becoming universally agreed upon that sterilization is a tool that can help reduce population size so that less offspring are produced in the future [ 66 ] With less offspring, pet populations can start to decrease which reduces the amount that get killed each year. [ 66 ]
In the wild, rampant population growth of prey species often causes growth in the populations of predators . [ 1 ] Such predator-prey relationships can form cycles, which are usually mathematically modelled as Lotka–Volterra equations . [ 67 ] [ 68 ]
In natural ecosystems , predator population growth lags just behind the prey populations. After the prey population crashes, the overpopulation of predators causes the entire population to be subjected to mass starvation. The population of the predator drops, as less young are able to survive into adulthood. This could be considered a perfect time for wildlife managers to allow hunters or trappers to harvest as much of these animals as necessary, for example lynx in Canada, although on the other hand this may impact the ability of the predator to rebound when the prey population begins to exponentially increase again. [ 1 ] Such mathematical models are also crucial in determining the amount of fish which may be sustainably harvested in fisheries , [ 69 ] this is known as the maximum sustainable yield . [ 70 ]
Predator population growth has the effect of controlling the prey population, and can result in the evolution of prey species in favour of genetic characteristics that render it less vulnerable to predation (and the predator may co-evolve , in response). [ 71 ]
In the absence of predators, species are bound by the resources they can find in their environment, but this does not necessarily control overpopulation, at least in the short term. An abundant supply of resources can produce a population boom followed by a population crash. Rodents such as lemmings and voles have such population cycles of rapid growth and subsequent decrease. [ 72 ] [ 73 ] Snowshoe hares populations similarly cycle dramatically, as did those of one of their predators, the lynx . [ 1 ] Another example is the cycles among populations of grey wolves and moose in Isle Royale National Park . [ 74 ] For some still unexplained reason, such patterns in mammal population dynamics are more prevalent in ecosystems found at more arctic latitudes. [ 72 ]
Some species such as locusts experience large natural cyclic variations, experienced by farmers as plagues . [ 75 ]
When determining whether a species is overpopulated, a variety of factors must be looked at. Given the complexity of the issue, scientists and wildlife managers often differ in judging such claims. In many cases scientists will look to food sources and living space to gauge the abundance of a species in a particular area. National parks collect extensive data on the activities and quality of the environment in which they are established. This data can be used to track whether a specific species is consuming larger amounts of their desired food source over time. [ 76 ]
This is done typically in four ways:
Similar methods can be used to determine the population of fish; however some key differences arise in the extrapolation of data. Unlike many land animals in-land fish populations are divided into smaller population sizes. Factors such as migration may not be relevant when determining population in a specific locales while more important for others such as the many species of salmon or trout. [ 78 ] Monitoring of waterways and isolated bodies of water provide more frequently updated information on the populations in specific areas. This is done using similar methods to the mark-recapture methods of many land animals.
The introduction of a foreign species has often caused ecological disturbance, such as when deer and trout were introduced into Argentina, [ 79 ] or when rabbits were introduced to Australia and predators were introduced in turn to attempt to control the rabbits. [ 80 ]
When an introduced species is so successful that its population begins to increase exponentially and causes deleterious effects to farmers, fisheries, or the natural environment, these introduced species are called invasive species .
In the case of the Mute swan, Cygnus olor , their population has rapidly spread across much of North America as well as parts of Canada and western Europe. [ 81 ] This species of swan has caused much concern for wildlife management as they damage aquatic vegetation, and harass other waterfowl, displacing them. The population of the Mute swan has seen an average increase of around 10-18% per year which further threatens to impact the areas they inhabit. [ 82 ] Management of the species comes in a variety of ways. Similar to overpopulated or invasive species, hunting is one of the most effective methods of population control. Other methods may involve trapping, relocation, or euthanasia . [ 83 ]
In natural ecosystems, populations naturally expand until they reach the carrying capacity of the environment; if the resources on which they depend are exhausted, they naturally collapse. According to the animal rights movement, calling this an 'overpopulation' is more an ethics question than a scientific fact. Animal rights organisations are commonly critics of ecological systems and wildlife management. [ 84 ] Animal rights activists and locals earning income from commercial hunts counter that scientists are outsiders who do not know wildlife issues, and that any slaughter of animals is evil. [ 5 ]
Various case studies indicate that use of cattle as ' natural grazers ' in many European nature parks due to absence of hunting, culling or natural predators (such as wolves), may cause an overpopulation because the cattle do not migrate. [ citation needed ] This has the effect of reducing plant biodiversity , as the cattle consume native plants. Because such cattle populations begin to starve and die in the winter as available forage drops, this has caused animal rights activists to advocate supplemental feeding, which has the effect of exacerbating the ecological effects, causing nitrification and eutrophication due to excess faeces, deforestation as trees are destroyed, and biodiversity loss . [ 85 ] [ 86 ]
Despite the ecological effects of overpopulation, wildlife managers may want such high populations in order to satisfy public enjoyment of seeing wild animals. [ 45 ] Others contend that introducing large predators such as lynx and wolves may have similar economic benefits, even if tourists rarely actually catch glimpses of such creatures. [ 11 ]
In regards to population size, most of the methods used give estimates that vary in accuracy to the actual size and density of the population. Criticisms of theses methods generally fall onto the efficacy of methods used. [ 87 ]
Overpopulation can result from an increase in births, a decline in mortality rates against the background of high fertility rates. [ 88 ] [ 89 ] It is possible for very sparsely populated areas to be overpopulated if the area has a meagre or non-existent capability to sustain life (e.g. a desert ). Advocates of population moderation cite issues like quality of life and risk of starvation and disease and human pressures on the environment as a basis to argue against continuing high human population growth and for population decline . [ 26 ] [ 90 ] | https://en.wikipedia.org/wiki/Overpopulation |
An overpressure protection system is one designed to protect an individual or group of individuals in a chemical, biological, radiological and nuclear ( CBRN ) environment. The two parts of the system are a safe area which as far as possible is sealed from possible contaminated air and an air filtration system which will filter out all possible toxins. Air pumps force clean air through the filters into the safe area such that the air pressure within the safe area will always be higher than that outside of the safe area. This pressure differential means that any flows of air will always be from the safe area to the outside, preventing the ingress of toxins.
The safe area may be as small as a protective hood for an individual, to a full body hazmat suit , to a fallout shelter or warship. Most modern armoured fighting vehicles will have such a system with the safe area being the crew and passenger compartments, these systems being first adopted to protect against poison gas attack. On a larger scale an overpressure system may be designed into the structure of a building or mobile prefabricated military structures to provide collective protection .
In a civilian context the same principles of filtration and positive pressure is used in positive pressure personnel suits .
This technology-related article is a stub . You can help Wikipedia by expanding it .
This article related to nuclear weaponry is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Overpressure_(CBRN_protection) |
Overprovisioning is the technique of committing more of some resource than strictly necessary, in order to improve the performance or reliability of an engineered system. In specific contexts, overprovisioning can describe:
Computer networks can be designed to allocate additional bandwidth in Network planning and design § Dimensioning .
Storage devices may contain more physical storage space than their advertised capacity, reserving the additional capacity to improve the device's performance or endurance characteristics. [ 1 ] For example, solid-state drives allocate a reserve for wear leveling to mitigate write amplification .
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Overprovisioning |
In signal processing , oversampling is the process of sampling a signal at a sampling frequency significantly higher than the Nyquist rate . Theoretically, a bandwidth-limited signal can be perfectly reconstructed if sampled at the Nyquist rate or above it. The Nyquist rate is defined as twice the bandwidth of the signal. Oversampling is capable of improving resolution and signal-to-noise ratio , and can be helpful in avoiding aliasing and phase distortion by relaxing anti-aliasing filter performance requirements.
A signal is said to be oversampled by a factor of N if it is sampled at N times the Nyquist rate.
There are three main reasons for performing oversampling: to improve anti-aliasing performance, to increase resolution and to reduce noise.
Oversampling can make it easier to realize analog anti-aliasing filters . [ 1 ] Without oversampling, it is very difficult to implement filters with the sharp cutoff necessary to maximize use of the available bandwidth without exceeding the Nyquist limit . By increasing the bandwidth of the sampling system, design constraints for the anti-aliasing filter may be relaxed. [ 2 ] Once sampled, the signal can be digitally filtered and downsampled to the desired sampling frequency. In modern integrated circuit technology, the digital filter associated with this downsampling is easier to implement than a comparable analog filter required by a non-oversampled system.
In practice, oversampling is implemented in order to reduce cost and improve performance of an analog-to-digital converter (ADC) or digital-to-analog converter (DAC). [ 1 ] When oversampling by a factor of N, the dynamic range also increases a factor of N because there are N times as many possible values for the sum. However, the signal-to-noise ratio (SNR) increases by N {\displaystyle {\sqrt {N}}} , because summing up uncorrelated noise increases its amplitude by N {\displaystyle {\sqrt {N}}} , while summing up a coherent signal increases its average by N. As a result, the SNR increases by N {\displaystyle {\sqrt {N}}} .
For instance, to implement a 24-bit converter, it is sufficient to use a 20-bit converter that can run at 256 times the target sampling rate. Combining 256 consecutive 20-bit samples can increase the SNR by a factor of 16, effectively adding 4 bits to the resolution and producing a single sample with 24-bit resolution. [ 3 ] [ a ]
The number of samples required to get n {\displaystyle n} bits of additional data precision is
To get the mean sample scaled up to an integer with n {\displaystyle n} additional bits, the sum of 2 2 n {\displaystyle 2^{2n}} samples is divided by 2 n {\displaystyle 2^{n}} :
This averaging is only effective if the signal contains sufficient uncorrelated noise to be recorded by the ADC. [ 3 ] If not, in the case of a stationary input signal, all 2 n {\displaystyle 2^{n}} samples would have the same value and the resulting average would be identical to this value; so in this case, oversampling would have made no improvement. In similar cases where the ADC records no noise and the input signal is changing over time, oversampling improves the result, but to an inconsistent and unpredictable extent.
Adding some dithering noise to the input signal can actually improve the final result because the dither noise allows oversampling to work to improve resolution. In many practical applications, a small increase in noise is well worth a substantial increase in measurement resolution. In practice, the dithering noise can often be placed outside the frequency range of interest to the measurement, so that this noise can be subsequently filtered out in the digital domain—resulting in a final measurement, in the frequency range of interest, with both higher resolution and lower noise. [ 4 ]
If multiple samples are taken of the same quantity with uncorrelated noise [ b ] added to each sample, then because, as discussed above, uncorrelated signals combine more weakly than correlated ones, averaging N samples reduces the noise power by a factor of N . If, for example, we oversample by a factor of 4, the signal-to-noise ratio in terms of power improves by factor of four which corresponds to a factor of two improvement in terms of voltage.
Certain kinds of ADCs known as delta-sigma converters produce disproportionately more quantization noise at higher frequencies. By running these converters at some multiple of the target sampling rate, and low-pass filtering the oversampled signal down to half the target sampling rate, a final result with less noise (over the entire band of the converter) can be obtained. Delta-sigma converters use a technique called noise shaping to move the quantization noise to the higher frequencies.
Consider a signal with a bandwidth or highest frequency of B = 100 Hz . The sampling theorem states that sampling frequency would have to be greater than 200 Hz. Sampling at four times that rate requires a sampling frequency of 800 Hz. This gives the anti-aliasing filter a transition band of 300 Hz (( f s /2) − B = (800 Hz/2) − 100 Hz = 300 Hz) instead of 0 Hz if the sampling frequency was 200 Hz. Achieving an anti-aliasing filter with 0 Hz transition band is unrealistic whereas an anti-aliasing filter with a transition band of 300 Hz is not difficult.
The term oversampling is also used to denote a process used in the reconstruction phase of digital-to-analog conversion, in which an intermediate high sampling rate is used between the digital input and the analog output. Here, digital interpolation is used to add additional samples between recorded samples, thereby converting the data to a higher sample rate, a form of upsampling . When the resulting higher-rate samples are converted to analog, a less complex and less expensive analog reconstruction filter is required. Essentially, this is a way to shift some of the complexity of reconstruction from analog to the digital domain. Oversampling in the ADC can achieve some of the same benefits as using a higher sample rate at the DAC. | https://en.wikipedia.org/wiki/Oversampling |
In environmental science , a population "overshoots" its local carrying capacity — the capacity of the biome to feed and sustain that population — when that population has not only begun to outstrip its food supply in excess of regeneration, but actually shot past that point, setting up a potentially catastrophic crash of that feeder population once its food populations have been consumed completely. Overshoot can apply to human overpopulation as well as other animal populations: any life-form that consumes others to sustain itself.
Environmental science studies to what extent human populations through their resource consumption have risen above the sustainable use of resources. For people, "overshoot" is that portion of their demand or ecological footprint which must be eliminated to be sustainable, or the delta between a sustainable population and what we currently have. [ 1 ] [ 2 ] Excessive demand leading to overshoot is driven by both consumption and population . [ 3 ]
Population decline due to overshoot is known as 'collapse'. The path taken by such a population is referred to as 'overshoot-and-collapse'. Collapse, like overshoot, can occur due to various factors, with the Malthusian catastrophe being a specific but not identical case. [ citation needed ]
Overshoot can happen as a result of delayed impacts, where reproduction rates persistently surpass the death rate . [ 4 ] This can lead to significant consequences, with entire ecosystems being profoundly impacted and sometimes simplified due to prolonged overshoot. [ 5 ] An instance of this phenomenon took place in the Horn of Africa when smallpox was eradicated, causing a sudden increase in the population that exceeded the region's carrying capacity. For centuries, the land had sustained approximately 1 million pastoralists , but with the elimination of the disease, the population suddenly grew to 14 million people. Consequently, overgrazing occurred, leading to soil erosion. [ 6 ]
The most famous example of an overshoot-and-crash may be from St. Matthew Island . In 1944, 29 reindeer were introduced to the island, which by 1963 had grown to a peak population of roughly 6000 individuals — well past the estimated carrying capacity . At next count, in 1965, the population had plummeted and only 42 reindeer were left alive.
Thomas Malthus (1766-1864) is perhaps the most well-known writer to have articulated the roots of the modern concept of human overshoot, with The Population Bomb (1967) by Paul Ehrlich reigniting the hotly-debated topic in more recent history. Daniel Quinn claims to have modernized the concept of human overpopulation in what are likely the most well-read volumes to have given it extensive treatment as a subject of ecology : The Story of B (1996) and My Ishmael (1997).
The 1972 book The Limits to Growth discussed the limits to growth of society as a whole. This book included a computer-based model which predicted that the Earth would reach a carrying capacity of ten to fourteen billion people after some two hundred years, after which the human population would collapse. [ 7 ] The model was based on five variables: " population , food production, industrialization, pollution, and consumption of non-renewable natural resources ". [ 8 ] : 25 This simulation modelled human populations after the overshoot and collapse seen in all unmoderated species. It was controversial and generally dismissed by economists. [ 9 ]
Sociologist William R. Catton, Jr. explored the connections between human societies and the natural environment in his book Overshoot published in 1980. Catton expressed his concerns about the global population exceeding Earth's sustainable limits, advocating that a reduction in population through natural means, such as mortality, was necessary. He argued that the predicament stemmed from both overpopulation , where the number of people surpassed what the planet could support, and overconsumption , referring to the excessive utilization of resources. Catton predicted that unless these issues were addressed, humanity would surpass the Earth's optimal carrying capacity, leading to potentially dire consequences. [ 10 ] [ 11 ] [ 12 ]
The Global Footprint Network purports to be able to measure how much the human economy demands against what the Earth can renew. [ 13 ] [ 14 ] The Optimum Population Trust (now called Population Matters ) has listed what they believe is the overshoot (overpopulation) of a number of countries, based on the above. [ 15 ]
In one study [ 16 ] published in January 2021 in Frontiers in Conservation Science , the significance of overshoot is discussed. It says that alongside the growth of the global population, humanity's consumption relative to Earth's regenerative capacity has surged by 73% in 1960 to 170% in 2016, particularly in countries with higher incomes . [ 17 ] These findings are based on recent ecological footprint studies. [ 18 ]
An article in Frontiers in Conservation Science also says ecological overshoot has been facilitated by the increasing reliance on fossil fuels. The widespread use of convenient energy sources has allowed human demand to detach from the limits of biological regeneration . Notably, fossil fuels account for 85% of commercial energy production, 65% of fiber production, and serve as the primary raw material for most plastics. [ 17 ]
As a possible cause for societal collapse , overshoot has been scholarly discussed, but has not been found having been the cause for historic cases of collapse. [ 19 ]
British scholar Thomas Malthus , in his seminal work published in 1798 titled An Essay on the Principle of Population , forecast the potential depletion of the world's food resources due to the growth of human population. Malthus composed this essay with the intention of refuting the impractical utopian concepts advocated by William Godwin and Marquis de Condorcet in their respective works, namely Political Justice and The Future Progress of the Human Mind . In 1968, Paul R. Ehrlich revived Malthus' argument in his book The Population Bomb , wherein he anticipated an impending global famine of catastrophic proportions. [ 21 ]
The predictions of Ehrlich and other neo-Malthusians were challenged by a number of economists, notably Julian Lincoln Simon , who said advances in agriculture, collectively known as the Green Revolution , forestalled any potential global famine in the late 20th century. Notably, between 1950 and 1984, the Green Revolution transformed agriculture around the world and grain production increased by over 250%. [ 22 ] The world population has grown by over four billion since the beginning of the Green Revolution, but food production has so far kept pace with population growth. Most scholars believe that, without the Green Revolution, there would be greater levels of famine and malnutrition than the UN presently documents. [ 23 ] However, neo-Malthusians point out that fossil fuels provided the energy for the Green Revolution, in the form of natural gas-derived fertilizers , oil-derived pesticides , and hydrocarbon -fueled irrigation , and that many crops have become so genetically uniform that a crop failure in any one country could potentially have global repercussions. [ 24 ]
In May 2008, the price of grain rose because of the increased cultivation of biofuels , the increase of world oil prices to over $140 per barrel ($880/m 3 ), [ 25 ] global population growth, [ 26 ] the effects of climate change , [ 27 ] the loss of agricultural land to residential and industrial development, [ 28 ] [ 29 ] and growing consumer demand in the population centres of China and India. [ 30 ] [ 31 ] Food riots subsequently occurred in some countries. [ 32 ] [ 33 ] However, oil prices then fell sharply. Resource demands are expected to ease as population growth declines, but it is unclear whether mass food wastage and rising living standards in developing countries will once again create resource shortages. [ 34 ] [ 35 ]
David Pimentel , professor of ecology and agriculture at Cornell University , estimates that the sustainable agricultural carrying capacity for the United States is about 200 million people; its population as of 2015 is over 300 million. [ 36 ] In 2009, the UK government's chief scientific advisor, Professor John Beddington , warned that growing populations, falling energy reserves and food shortages would create a "perfect storm" of shortages of food, water, and energy by 2030. [ 20 ] [ 37 ] According to a 2009 report by the United Nations Food and Agriculture Organization (FAO), the world will have to produce 70% more food by 2050 to feed a projected extra 2.3 billion people. [ 38 ]
The figures for 2007 showed an actual increase in absolute numbers of undernourished people in the world, with 923 million undernourished in 2007, versus 832 million in 1995. [ 39 ] The 2009 FAO estimates showed an even more dramatic increase, to 1.02 billion. [ 40 ]
A number of scientists have argued that the looming human impact on the environment and accompanying increase in resource consumption threatens the world's ecosystem and the survival of human civilization. [ 41 ] [ 42 ] [ 43 ] [ 17 ] Scientists contend that continued human population growth and overconsumption , particularly by the wealthy, are the primary drivers of mass species extinction [ 44 ] [ 45 ] [ 46 ] and some suggesting human overpopulation as a driver. [ 47 ] [ 48 ]
Human population planning is the practice of intervening to alter the rate of population growth. Historically, human population control has been implemented by limiting a region's birth rate , by voluntary contraception or by government mandate. It has been undertaken as a response to factors including high or increasing levels of poverty, environmental concerns , and religious reasons . The use of abortion in some population control strategies has caused controversy, [ 49 ] with religious organizations such as the Roman Catholic Church explicitly opposing any intervention in the human reproductive process. [ 50 ]
The University of Nebraska publication Green Illusions argues that population control to alleviate environmental pressures need not be coercive. It states that "Women who are educated, economically engaged, and in control of their own bodies can enjoy the freedom of bearing children at their own pace, which happens to be a rate that is appropriate for the aggregate ecological endowment of our planet." [ 51 ] The book Fatal Misconception by Matthew Connelly similarly points to the importance of supporting the rights of women in bringing population levels down over time. [ 52 ] Paul Ehrlich also advocates making "modern contraception and back-up abortion available to all and give women full equal rights, pay and opportunities with men," noting that it could possibly "lead to a low enough total fertility rate that the needed shrinkage of population would follow. [But] it will take a very long time to humanely reduce total population to a size that is sustainable." Ehrlich places the optimum global population size at 1.5 to 2 billion people. [ 53 ]
Other academicians and public figures have pointed to the role of agriculture and agricultural productivity of increasing human carrying capacity , which results in population overshoot, as with any other species when their food supply experiences an increase, which in turn results in resource depletion and mass poverty and starvation in the case of humans. [ 54 ] [ 55 ] [ 56 ] [ 57 ] | https://en.wikipedia.org/wiki/Overshoot_(population) |
In road transport , an oversize load (or overweight load ) is a load that exceeds the standard or ordinary legal size and/or weight limits for a truck to convey on a specified portion of road , highway , or other transport infrastructure, such as air freight or water freight. In Europe, it may be referred to as special transport or heavy and oversized transportation . There may also be load-per- axle limits. However, a load that exceeds the per-axle limits but not the overall weight limits is considered overweight. [ 1 ] Examples of oversize/overweight loads include construction machines (cranes, front loaders, backhoes, etc.), pre-built homes, containers, and construction elements (bridge beams, generators, windmill propellers, rocket stages , and industrial equipment).
The legal dimensions and weights vary between countries and regions within a country. [ 2 ] A vehicle which exceeds the legal dimensions usually requires a special permit which requires extra fees to be paid in order for the oversize/overweight vehicle to legally travel on the roadways. [ 3 ] The permit usually specifies a route the load must follow as well as the dates and times during which the load may travel.
When a load cannot be dismantled into units that can be transported without exceeding the limitations in terms of the dimensions and/or mass, it is classified as an abnormal load. Another definition can be summarized as follows: an abnormal indivisible load ('AIL') is one which cannot be divided into two or more loads for transporting (on roads). [ 4 ] Also, break bulk is used to define the freight that cannot be loaded into any ocean container or too large for air cargo .
Any road transport is framed by the CMR Convention (Convention on the Contract for the International Carriage of Goods by Road), [ 5 ] which relates to various legal issues concerning transportation of cargo, predominantly by lorries , by road.
According to the Federal Motor Carrier Safety Administration, National Highway Traffic Safety Administration, Large Truck Crash Causation Study [ 6 ] 7% of U.S. trucking accidents are caused by improper cargo securement or cargo shifts. Shifting cargo can cause the truck to destabilize or the load can fall off completely leading to serious public safety issues.
Load shifting is prohibited by law and it is the responsibility of the shipper, motor carrier, driver, receiver, and the securing device manufacturer to ensure the cargo is completely secured. [ 7 ]
In a specific country, the roads are built in a way that allows a vehicle with dimensions within the standard legal limits to safely (though not necessarily easily) drive and turn. Roads that do not allow large vehicles may be marked with the traffic signs. [ 8 ] These may include per-axle load, height, width, or overall length limits.
Trucks must have special signs of "convoi exceptionnel" and lights that warn the oversized cargo. The escort car has also special signs, depending the country within it operates. Special permits are issued by local authorities to allow a transporter to operate on a public road for a limited period and for a certain and given route. [ 9 ]
Heavy transport companies tend to focus on renewables, civil and infrastructure, offshore, oil and gas, heavy engineering and power generation industries. Other companies across Europe have also collaborated to form the Route To Space Alliance. [ 10 ]
Due to its strategic location, there are many Dutch-based special transport companies, but due to the relatively small size of the country, these companies, such as Van der Vlist have often started to spread further afield to increase their market and take advantage of the freedom of movement offered through the EU. [ 11 ]
In Romania, if the total dimensions (truck+load) exceed 16.5 by 2.5 by 4 metres (54.1 ft × 8.2 ft × 13.1 ft) × 40 tonnes (39 long tons; 44 short tons) (or if it does not fit into a tilt truck), then a transport is considered out of gauge. A table of maximum dimensions and weight as well as best practices is available for European countries on the following industry resource site. [ 12 ]
Romania has an active market for special transporters where, as mentioned above, companies such as Schnell Trans, deal with international transportation projects. Trailers suitable for special loads have different characteristics depending on the number of axles , height from the ground to the platform, extensions or load capacity. Each of these trucks can carry loads such as trams, energy transformers, construction machines, metallic structures or wooden boxes/crates. [ 13 ]
An abnormal load is defined as
Anyone wishing to transport an abnormal load must notify the police, highway authorities and any on-route bridge and structure owners such as Network Rail . [ 14 ] National Highways operates a system known as "Electronic Service Delivery for Abnormal Loads" (ESDAL) for the purpose of supporting notifications. [ 15 ]
In New Zealand, an oversize load is a vehicle and/or load that is wider than 2.55 m (8 ft 4 in) or higher than 4.3 m (14 ft 1 in). Overlength limits vary depending on the type and the configuration of vehicle, but the overall maximum forward distance (i.e. the length from the front of the vehicle to the centre axis of the rear axle set) is 9.5 m (31 ft 2 in), the overall maximum single vehicle length is 12.6 m (41 ft 4 in) (some buses can be longer), and the overall maximum combination length is 22.0 m (72 ft 2 in). Loads must be indivisible, except when the vehicle is oversize itself where it can carry divisible loads as long as the divisible load fits within the standard load limits. Permits are not required for oversize vehicles which are under 25.0 m (82 ft 0 in) long, under 5.00 m (16 ft 5 in) high, and fit within a set combination of width and forward distance; but they must comply with certain rules regarding piloting, travel times and obstructions. [ 16 ] [ 17 ]
In the United States, an oversize load is a vehicle and/or load that is wider than 8 ft 6 in (2.59 m). Each individual state has different requirements regarding height and length (most states are 13 ft 6 in or 4.11 m tall), and a driver must purchase a permit for each state he/she will be traveling through. In many states, a load must be considered "nondivisible" to qualify for a permit (i.e. an object which cannot be broken down into smaller pieces), although some states allow divisible loads to be granted permits. [ 18 ]
In India, any load which protrudes the platform of the vehicle which is defined in CMVR 1989 is considered ODC (Over Dimensional Cargo). Dimensions of a load with the height of 4 mtr or width of 2.6 mtr or length of 12mtr in case of rigid vehicle and 18 mtr in case of tractor trailer combination [ 19 ] needs to obtain state specific permissions, but no load can exceed the GVW of the vehicle. Loads above 55 tons can only be moved on HMT (hydraulic modular trailer) and puller tractor combination, for which a nationalized permission must be obtained via MORTH (Ministry of Road Transport and Highways of India) portal with HMT payload of 18 ton per axle excluding the weight of the puller tractor. [ 20 ] Loads not complying with rules are fined by the RTO (Regional Transport Office) officers individually, three for each dimension and one for weight. [ 21 ]
A pilot car driver may temporarily block traffic at intersections to ensure the safe passage of the truck. [ 22 ]
Oversize loads present a hazard to roadway structures as well as to road traffic. Because they exceed design clearances , there is a risk that such vehicles can hit bridges and other overhead structures. Over-height vehicle impacts are a frequent cause of damage to bridges, and truss bridges are particularly vulnerable, due to having critical support members over the roadway. An over-height load struck the overhead beams on the I-5 Skagit River bridge in 2013, which caused the bridge to collapse . [ 23 ]
Different countries have different approaches to licensing oversize/overweight loads. Licenses may be issued for a specific load, for a period of time, or to a specific company. In most jurisdictions, the permit specifies the exact route a vehicle must take, and includes clearance warnings. However, in some places, such as Washington state , drivers are responsible for choosing their own route. The carrier can choose to obtain the required permits themselves or go through a permit service . [ 23 ] | https://en.wikipedia.org/wiki/Oversize_load |
Overspeed is a condition in which an engine is allowed or forced to turn beyond its design limit. The consequences of running an engine too fast vary by engine type and model and depend upon several factors, the most important of which are the duration of the overspeed and the speed attained. With some engines, a momentary overspeed can result in greatly reduced engine life or catastrophic failure. [ 1 ] The speed of an engine is typically measured in revolutions per minute (rpm). [ 2 ] [ citation needed ]
Sometimes a regulator or governor is fitted to make engine overspeed impossible or less likely. For example:
An excerpt presented by the San Francisco Maritime National Park Association illustrates the types of overspeed systems with governor and engine control. [ 4 ] Overspeed governors are either centrifugal or hydraulic. [ 4 ] Centrifugal governors depend on the revolving force created by its own weight. [ 4 ] Hydraulic governors use the centrifugal force but drive a medium to accomplish the same task. [ 4 ] The overspeed governor is implemented on most marine diesel engines. [ 4 ] The governor is a safety measure that acts when the engine is approaching overspeed and will trip the engine off if the regulator governor fails. [ 4 ] It trips off the engine by cutting off fuel injection by having the centrifugal force act on levers linked to the governor collar. [ 4 ]
Overspeeds for power plant turbines can be catastrophic, resulting in failure due to the turbines' shafts and blades being off balance and potentially throwing their blades and other metal parts at very high speeds. [ 5 ] Different safeguards exist, which include a mechanical and electrical protection system. [ 6 ]
Mechanical overspeed protection is in the form of sensors. [ 6 ] The system relies on the centripetal force of the shaft, a spring, and a weight. [ 6 ] At the designed point of overspeed, the balance point of the weight is shifted, causing the lever to release a valve that makes the trip oil header to lose pressure due to draining. [ 6 ] This loss of oil affects the pressure, and moves a trip mechanism to then trip the system off. [ 6 ]
An electrical overspeed detection system involves a gear with teeth and probes. [ 6 ] These probes detect how fast the teeth are moving, and if they are moving beyond the designated rpm , it relays that to the logic solver (overspeed detection). The logic solver trips the system by sending the overspeed to the trip relay, which is connected to a solenoid -operated valve. [ 6 ]
In turbines and many other mechanical devices used for power generation, it is critical that the response times for overspeed prevention systems be as precise as possible. [ 7 ] If the response is off by even a fraction of a second, it can lead to turbines and its driven load (i.e. compressor, generator, pump, etc..) suffering catastrophic damage, and can put people at risk. [ 7 ]
Mechanical overspeed systems on turbines rely on an equilibrium between the centripetal force of the rotating shaft imparted on a weight attached to the end of a turbine blade. [ 7 ] At the specified trip point, this weight makes physical contact with a lever that releases the trip oil header, which directly moves a trip bolt and/or a hydraulic circuit to activate stop valves to close. [ 7 ] Because the contact with the lever occurs over a relatively limited angle, there is a maximum trip response time of 15 ms (i.e. 0.015 sec). [ 7 ] The issue with these devices has less to do with response time as it does with response latency and variability in the trip point due to systems sticking. [ 7 ] Some systems add two trip bolts for redundancy, which enables response latency to be reduced by half. [ 7 ]
Electrical overspeed systems on turbines rely on a multitude of probes that sense speed through measuring the passages of the teeth of a spur gear. [ 7 ] Using a digital logic solver, the overspeed system determines the propeller shaft rpm given the ratio of the gear to the shaft. [ 7 ] If the shaft rpm is too high, it outputs a trip command which de-energizes a trip relay. [ 7 ] Overspeed response varies from system to system, so it is key to check the original equipment manufacturer's specification to set the Overspeed trip time accordingly. [ 7 ] Typically, unless specified otherwise, the response time to change the output relay will be 40 ms. [ 7 ] This time includes the time required for the probes to detect speed, compare it to an overspeed set-point, calculate results, and finally output the trip command. [ 7 ]
When configuring, testing, and running any overspeed systems on turbines or diesel engines, one factor considered is timing. [ 4 ] This is because the response to overspeed is usually too fast for people to notice.
There is a strong argument to instrument the trip systems in such a way that the total system response can be measured. This way during a test a change in the response could indicate a degradation that might compromise system protection or point out a failing component.
The responsibility of calibrating the correct overspeed response for a specific system falls on the manufacturer. However, variability is always present, and it is important for the owner/operator to understand the system in the event of maintenance, replacement, or retrofitting of outdated or worn out parts. [ 6 ] After overspeed has occurred, it is essential to check all machinery parts for stress. [ 8 ] The first place to start for impulse turbines is the rotor. [ 8 ] At the rotor, there are balance holes [ 9 ] that equalise the pressure difference between turbines, and if warped, would require the replacement of the entire rotor. [ 8 ] | https://en.wikipedia.org/wiki/Overspeed |
The ISCB Overton Prize is a computational biology prize awarded annually for outstanding accomplishment by a scientist in the early to mid stage of his or her career. Laureates have made significant contribution to the field of computational biology either through research, education, service, or a combination of the three. [ 1 ]
The prize was established by the International Society for Computational Biology (ISCB) in memory of G. Christian Overton [ Wikidata ] [ 2 ] a major contributor to the field of bioinformatics and member of the ISCB Board of Directors who died unexpectedly in 2000. [ 1 ]
The Overton Prize is traditionally awarded at the Intelligent Systems for Molecular Biology (ISMB) conference.
Laureates include [ 1 ] | https://en.wikipedia.org/wiki/Overton_Prize |
Overwintering is the process by which some organisms pass through or wait out the winter season , or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures , ice , snow , limited food supplies) make normal activity or even survival difficult or near impossible. In some cases "winter" is characterized not necessarily by cold but by dry conditions; passing through such periods could likewise be called overwintering.
Hibernation and migration are the two major ways in which overwintering is accomplished. Animals may also go into a state of reduced physiological activity known as torpor . [ 1 ]
Overwintering occurs in several classes of lifeform.
In entomology , overwintering is how an insect passes the winter season. Many insects overwinter as adults, pupae , or eggs. This can be done inside buildings, under tree bark, or beneath fallen leaves or other plant matter on the ground, among other places. All such overwintering sites shield the insect from adverse conditions associated with winter. Activity almost completely ceases until conditions become more favourable. One example is the mourning cloak butterfly , which experiences advantages to overwintering in its desired locations by being one of the first butterflies to emerge after a cold winter. [ 2 ] Another example are the eggs of the forest tent caterpillar moth which overwinter tightly packed on tree branches. [ 3 ] Other insects, such as the monarch butterfly , migrate and overwinter in warmer areas. Additionally, the ghost moth overwinters as a larva. The common brimstone , found across a broad geographic range, overwinters for 7 months to wait for the development of their larval host plants. [ 4 ] Another unique butterfly, the large white , will only overwinter in southern Eurasia; they are not seen overwintering elsewhere. [ 5 ] Some species of parasitic conopid flies, such as P. tibialis , are known to overwinter inside of the corpse of their bee/wasp hosts before emerging in the spring. [ 6 ] The queens of the yellow-faced bumblebee ( Bombus vosnesenskii ) will over-winter, and then emerge early in the flight season to obtain the best available subterranean nests. [ 7 ] Lastly, many species of Lasioglossum , including L. hemichalceum (which is a common sweat bee ), will overwinter in underground nests before emerging in the spring to start new colonies. [ 8 ]
Many birds migrate and then overwinter in regions where temperatures are warmer or food is more readily available, in Europe for example common crane and white storks . Some birds, however, such as black-capped chickadees , Golden-crowned kinglets , woodpeckers , and corvids , instead remain in colder areas throughout the winter, often remaining in groups for warmth. [ 9 ]
Plants are sometimes said to overwinter. At such times, growth of vegetative tissues and reproductive structures becomes minimal or ceases completely. For plants, overwintering often involves restricted water supplies and reduced light exposure. In the spring following overwintering many plants will enter their flowering stage. Farmers and gardeners use a process of "overwintering" [ 10 ] to achieve early spring harvests of some crops by planting annual or biennial species in fall, often under the protection of high or low tunnels. [ 11 ] In plant pathology , overwintering is where a plant pathogen survives the winter, during which its normal crop host species is not growing, by transferring to an alternative host, living freely in the soil or surviving on plant refuse such as discarded potatoes.
People are also described from time to time as overwintering. This was especially true in the past during the exploration of the planet when people had to pass the winter in places not ideally suited for winter survival, and even today in the polar regions . Today people may be said to overwinter when they temporarily move to warmer areas during the months of prevailing cold weather in northern latitudes, such as people from various parts of North America staying in Florida , Arizona, or New Mexico (among other places) for parts of November to March. | https://en.wikipedia.org/wiki/Overwintering |
Ovine forestomach matrix (OFM), marketed as AROA ECM , is a layer of decellularized extracellular matrix (ECM) biomaterial isolated from the propria submucosa of the rumen of sheep. [ 1 ] [ 2 ] OFM is used in tissue engineering and as a tissue scaffold for wound healing and surgical applications. [ 3 ] [ 4 ]
OFM was developed and is manufactured by Aroa Biosurgery Limited (New Zealand, formerly Mesynthes Limited, New Zealand) [ 5 ] and was first patented in 2008 [ 6 ] and described in the scientific literature in 2010. [ 7 ] OFM is manufactured from sheep rumen tissue, using a process of decellularization to selectively remove the unwanted sheep cells and cell components to leave an intact and functional extracellular matrix. [ 8 ] OFM comprises a special layer of tissue found in rumen, the propria submucosa, which is structurally and functionally distinct from the submucosa of other gastrointestinal tissues. [ 9 ] [ 10 ]
OFM was first cleared by the FDA in 2009 for the treatment of wounds . [ 11 ] [ 12 ] Since 2008 there have been >70 publications describing OFM and its clinical applications, and over 6 million clinical applications of OFM-based devices. [ 13 ] [ 14 ]
OFM comprises more than 24 collagens (most notably types I and III ), but also contains many growth factors , polysaccharides and proteoglycans that naturally exist as part of the extracellular matrix and play important roles in wound healing and soft tissue repair. [ 15 ] [ 16 ] The composition includes more than 150 different proteins, [ 17 ] including elastin , fibronectin , glycosaminoglycans , basement membrane components , and various growth factors, such as vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF) and platelet derived growth factor (PDGF). [ 18 ] OFM has been shown to recruit mesenchymal stem cells , [ 19 ] [ 20 ] stimulate cell proliferation , angiogenesis and vascularogenesis, [ 21 ] and modulate matrix metalloproteinase and neutrophil elastase . [ 22 ] The porous structure of OFM has been characterized by differential scanning calorimetry (DSC), [ 23 ] scanning electron microscopy (SEM), [ 24 ] [ 25 ] atomic force microscopy (AFM), [ 26 ] histology , [ 27 ] Sirius Red staining, [ 28 ] small-angle x-ray scattering (SAXS), [ 29 ] [ 30 ] and micro computerized topography (MicroCT) . [ 31 ] [ 32 ] OFM has been shown to contain residual vascular channels that facilitate blood vessel formation through angioconduction. [ 33 ] [ 34 ]
OFM can be fabricated into a range of different product presentations for tissue engineering applications, and can be functionalized with therapeutic agents including silver, [ 35 ] doxycycline [ 36 ] and hyaluronic acid . [ 37 ] OFM has been commercialized as single and multi-layered sheets, reinforced biologics and powders. [ 38 ] [ 39 ]
When placed in the body OFM does not elicit a negative inflammatory response and is absorbed into the regenerating tissues via a process called tissue remodeling . [ 40 ] [ 41 ] [ 42 ]
Aroa Biosurgery Limited first distributed OFM commercially in 2012 as Endoform™ Dermal Template (later Endoform™ Natural) through a distribution partnership with Hollister Incorporated (IL, USA). [ 43 ] Endoform™ Natural and Endoform™ Antimicrobial (0.3% ionic silver w/w), are single layers of OFM used in the treatment of acute and chronic wounds, including diabetic foot ulcers (DFU) [ 44 ] and venous leg ulcers (VLU). [ 45 ] Endoform™ Natural has been shown to accelerate wound healing of DFU. [ 46 ] [ 47 ] The wound product Symphony™ combines OFM and hyaluronic acid and is designed to support healing during the proliferative phase particularly in patients whose healing is severely impaired or compromised due to disease [ 48 ] [ 49 ]
OFM was cleared by the FDA in 2016 and 2021 for surgical applications in plastics and reconstructive surgery as a multi-layered product (Myriad Matrix™) [ 50 ] [ 51 ] [ 52 ] and powdered format (Myriad Morcells™). [ 53 ] [ 54 ] OFM-based surgical devices are routinely used in complex lower extremity reconstruction, [ 55 ] pilonidal sinus reconstruction, [ 56 ] hidradenitis suppurativa [ 57 ] and complex traumatic wounds.
OFM-based surgical devices are routinely used in plastics and reconstructive surgery for the regeneration of soft tissues when used as an artificial skin [ 58 ] [ 59 ] [ 60 ]
Multi-layered OFM devices, reinforced with synthetic polymer were first described in 2008 [ 61 ] and in the scientific literature in 2010. [ 62 ] These devices, termed ‘reinforced biologics’ have been designed for applications in the surgical repair of hernia as an alternative to synthetic surgical mesh (a mesh prosthesis ). OFM reinforced biologics are distributed in the US by Tela Bio Inc. [ 63 ] [ 64 ] Clinical studies have shown that OFM reinforced biologics have lower hernia recurrence rates versus synthetic hernia meshes [ 65 ] [ 66 ] [ 67 ] or biologics [ 68 ] such as acellular dermis . | https://en.wikipedia.org/wiki/Ovine_forestomach_matrix |
Ovomucin is a glycoprotein found mainly in egg whites , as well as in the chalaza and vitelline membrane . The protein makes up around 2-4% of the protein content of egg whites; like other members of the mucin protein family , ovomucin confers gel -like properties. It is composed of two subunits, alpha-ovomucin (MUC5B) and beta-ovomucin (MUC6), of which the beta subunit is much more heavily glycosylated. [ 1 ] [ 2 ] The alpha subunit has a high number of acidic amino acids, while the beta subunit has more hydroxyl amino acids. The protein has a carbohydrate content of around 33%, featuring at least three unique types of carbohydrate side chains. [ 3 ] It is known to possess a wide range of biological activities, including regulating cell functions and promoting the production of macrophages, lymphocytes, and cytokines, suggesting that it plays a role in the immune system. [ 4 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ovomucin |
Owl's eye appearance , also known as owl's eye sign , is a pattern used in the medical field to describe cells (or cell attributes) that resemble the shape of an actual owl's eye. Using the techniques of histology and radiology , microscopes and other medical imaging are used to locate this pattern of "owl's eye" shaped cells. The term may be applied to the appearance of the cells themselves, or to aspects of their morphology , such as reference to an "owl eye nucleus ". The presence of "owl's eye" cells has been linked to a variety of conditions, such as in the pathology of Hodgkin's lymphoma , a form of cancer. In particular, owl's eye appearance has been used to indicate the presence of cytomegalovirus (CMV) , a genus of virus found in humans and other primates.
The description "owl's eye" may refer to:
The owl's eye appearance has a relationship with Reed–Sternberg cells in regard to cytomegalovirus infection . [ 3 ] Owl's eye appearance was used as an indication of the presence of the cytomegalovirus for the following case studies.
In 1982, a textbook wrote a chapter on cytomegalovirus and elaborated on its further relevance to owl's eye appearances. [ 4 ] It was stated that the owl's eye had a characteristic of a clear halo that extended towards the cell membrane's nucleus. The cellular structure was found to be relevant to pneumonia which was caused by cytomegalovirus.
In a 1986 case study, a journal wrote that an owl's eye appearance was found in a total of 10 out of 10 patients. [ 5 ] This was apparently due to the cytomegalovirus found in the patients that were also found to be diagnosed with AIDS. [ 5 ] This case study involved CT scans that were used as a proposal as a way to detect the cytomegalovirus; however, the case study found that the cytomegalovirus had little relevance to the ability of CT scans. [ 5 ]
In 1987, a 33-year-old man diagnosed with AIDS was discovered with the cytomegalovirus in his eyes. [ 6 ] The presence of an owl's eye appearance indicated the hospital that this patient was infected with the cytomegalovirus.
In 1990, a case study journal found that the owl's eye appearance correlated with the appearance of HIV infection . [ 7 ] This was where the case study involved the study of hospital cases and concluding that HIV plays a role in certain symptoms such as diarrhea. [ 7 ] In another case study journal, the owl's eye appearances were found within the four patients that were observed. [ 8 ] These patients were diagnosed with AIDS, and the presence of the owl's eye appearances proved the presence of cytomegalovirus. The confirmation of this virus was by the use of immunohistochemistry . [ 8 ]
In a 2000 case study, it was discovered that the owl's eye appearance as a cell body was key for the histopathological understanding of the cytomegalovirus. [ 2 ] The study found a strong relationship with a positive CMV PCR (p < 0.001). [ 2 ] The discovery led to a result that owl's eye appearances were a strong sign for finding cytomegalovirus inside organs. [ 2 ]
In 2006, a case study journal wrote that owls' eye signs were found in patients with compromised immune system . [ 9 ] The purpose of this case study was to identify the features of the cytomegalovirus itself and the appearance of owl's eyes in relevance.
In 2009, a case study journal found a 44-year-old male patient to be infected with the cytomegalovirus. [ 10 ] The presence of an eye's owl appearance found within the infected area, gave the necessary clues to confirm cytomegalovirus infection. [ 10 ] A different case study found the appearance of an owl's eye in eighteen patients who were induced with drugs with a syndrome. [ 11 ] The case study concluded that the cytomegalovirus disease was present, as the syndrome caused these patients to compromise their immune system. The case also found that the significant decrease of white blood cells was a factor in the preliminary stage of cytomegalovirus infection.
In 2011, a second edition textbook found that an owl's eye appearance was found inside a dead retina . [ 12 ] It was found due to the cause of the cytomegalovirus [ 12 ] that had been residing inside an eye causing it to transition from healthy to dead.
In 2012, a journal was written on patients with cytomegalovirus infection and was used in mapping out the owl's eye cells using their microscopic technology. [ 13 ] The patients were two elderly men at ages 75 and 77 years old. The image of the owl's eye appearance was created using the microscope via lasers, and two-dimensional images were created using computer software. The conclusion made by the journal was that the owl's eye had relevance to cytomegalovirus infection.
In 2019, a four-year-old boy was found with acute flaccid paralysis and was found to have an owl's eye appearance. [ 14 ] The case also spoke on the presence of enterovirus . [ 14 ] The boy was also found to have a compromised immune system, which the enterovirus came through in infection. This case is unique due to the owl's eye appearance in relevance to the enterovirus.
Owl's eye appearances were also found within tissues and organs and are tied with histopathological cases. Most of these cases are also relevant to the pathology cases. However, these cases focused more on the specifics of a singular organ or tissue where the owl's eye appeared. These cases also have moderate relevance to the cytomegalovirus .
In 1983, a journal wrote on a case study that found owl's eye appearance within the human eyes with the presence of potential cytomegalovirus with a deficient immune system. [ 15 ] This was from the symptoms of inflammation that gave the diagnosis of an immune system to be deficient.
In 1985, a journal wrote that the appearance of owl's eye signs was due to the presence of inflammatory bowel disease . [ 16 ] This finding created a suspicion that the patient, in this case, was, infected with the cytomegalovirus infection . However, further investigations showed that the patient was leading to a weak immune system. The patient was also identified as an 80-year-old man with a short-term case of diarrhea of blood and mucus, [ 16 ] which was not contained and resulted in his death. The autopsy found the presence of cytomegalovirus this way.
In 2002, a rare case study journal wrote that a range of cytomegalovirus could infect patients diagnosed with AIDS and compromised immune systems. However, it was rare to involve the patient's skin. [ 17 ] The skin at the cellular level was found to have owl's eye appearance and was concluded after several tests to be the cytomegalovirus infection.
In 2007, a journal wrote about the presence of owls' eye appearance as cells found in a transplant to a patient. [ 18 ] The owl's eye appearance was considered rare for cytomegalovirus infection in the transplant, but was considered concerning. [ 18 ] The cytomegalovirus infection was found of relevance towards compromised immune patients, as previous cases show that immune problems for patients have a similar case of cytomegalovirus infection.
In 2015, a review journal wrote on herpes infection . It made a finding that owl's eye appearance was found in most organs [ 19 ] through the investigation of a liver transplant. This provides evidence that the appearance of an owl's eye allowed the doctors to diagnose that cytomegalovirus infection from the liver transplant can be detected through detection tools.
In 2019, a case study was conducted on a series of patients that were infected with cytomegalovirus, [ 20 ] and found the presence of the owl's eye appearance due to the presence of the virus. These owl's eye appearances were able to conclude that high-risk patients had a higher risk of cytomegalovirus.
Another particular case in 1957 found that an owl's eye appearance was found by two cells mirroring each other, producing the pattern inside the histological case study of tumors . [ 21 ] This is essentially what an owl's eye appearance is, however, the symptom did not occur from the presence of cytomegalovirus but from a unique case.
In another particular case in 1999, a case study was conducted by investigating a series of babies and found a baby with the presence of an owl's sign which was also found to be known as an eye mask . This had to do with the presence of a rash, not the reality of cytomegalovirus. [ 22 ]
In a particular case in 2011, the owl's eye appearance was found within the cellular structure of the spinal ganglia . [ 23 ]
Owl's eye appearance is also found within radiology images from X-rays and CT scans . [ 24 ] They appear as an indication of a clue to be used for analyzing the problem. These scans so far do not indicate that the owl's eye appearance found within radiology has any relevance towards the cytomegalovirus infection within patients. [ 25 ] An example of the appearance of an owl's eye appearing within an image is of a skeleton within the bone structure, especially in the spinal cord .
In 2009, a journal wrote on the presence of an owl's eye appearance that was found within the skeletal structure from the magnetic resonance imaging (MRI) scan in regards to compression of the spinal cord . [ 26 ] The owl's eye sign indicated that the spinal issues may be similar to other spinal cord cases and can be used to identify future cases.
In 2012, a case study journal article was written on a 10-year-old boy and discovered the owl's eye appeared inside the brain from an MRI scan. [ 27 ] In the findings, it was found that the owl eye's sign was seen when doing neuroradiology images. The owl's eye sign was also detected from the spinal cord in spine MRI scans conducted post-treatment for the boy.
In 2015, a case study on owl's eye sign was found in a neuroimaging via MRI, which was rare due to the patient's diagnosis. [ 28 ] The patient was found with Flailing Arm Syndrome .
In June 2016, a journal article was written on a central pontine myelinolysis presence. [ 29 ] And from doing radiology scans within the brain, they were able to find observations of owl's eye signs that also resembled similar to monkey signs . [ 29 ] The owl's eye appearance was also used as a sign in the MRI scans conducted in the scanning of the brain to show its relevance to the patient's diagnosed profile. In September 2016, a journal article examined MRI scans relevant to spinal cord conditions. [ 30 ] These tests found owls' eye appearance as they were relevant to spinal cords in past cases. The journal concluded that the owl's eyes were not a main characteristic of tissue death.
A textbook has stated that within radiology, the appearance of an owl's eye can be seen from the cells and neurological disorders . [ 31 ] This textbook is a clinical review textbook and has provided relevance between owl's eye signs and neurological imaging .
It was found that a 1986 case study found that CT scans [ 5 ] were of little effect when trying to find cytomegalovirus in the presence of owl's eye appearance. | https://en.wikipedia.org/wiki/Owl's_eye_appearance |
The OxFA process is a process to produce formic acid from biomass by catalytic oxidation using molecular oxygen or air. Polyoxometalates of the Keggin-type are used as catalysts.
Formic acid is obtained by aqueous catalytic partial oxidation of wet biomass. [ 1 ] [ 2 ] [ 3 ] A Keggin-type polyoxometalate (H 5 PV 2 Mo 10 O 40 ) is used as the homogeneous catalyst to convert sugars, wood, waste paper or cyanobacteria to formic acid and CO 2 as the sole byproduct. Yields of up to 53% formic acid can be achieved.
It is possible to convert water-insoluble biomass in a suspension with the catalyst. After the reaction, formic acid is separated from the reaction mixture. Depending on the separation process, the formic acid can be further purified or used as it is. The remaining solution of the catalyst, residual formic acid and additives are recycled to the reaction. In this step, solids (e.g. soil from dirty biomass) or unreactive inorganics (e.g. inorganic salts from the natural salt content of the biomass) may be separated from the catalyst solution.
The general reaction for a simple sugar like glucose can be summarized as follows:
C 6 H 12 O 6 + wO 2 → xHCOOH + yCO 2 + zH 2 O
Water-insoluble biomass must be shredded to an appropriate size to enhance the surface area at which the reaction takes place. Water-soluble biomass needs no special pretreatment.
The reaction is carried out at 363 K and 30 bar oxygen partial pressure , either as pure oxygen or air. Since hot formic acid is corrosive, suitable autoclaves (e.g. Hastelloy ) must be used. Reaction times depend on the reactivity of the feed. For example, microcrystalline cellulose is converted to 15 and 22% after 24 h and 66 h, respectively, whereas the more reactive xylan is converted to 88% and 94% respectively.
The use of additives more than doubles the reaction rates, especially for the refractory compound cellulose. If p-toluenesulfonic acid is used as the additive, conversion of cellulose rises from 22% to 68% after 66 h.
Under the reaction conditions, overoxidation of the produced formic acid does not occur. In another recent example, formic acid was produced from biomass-derived sugars using hydrogen peroxide as the oxidant over heterogeneous catalysts. [ 4 ] [ 5 ]
Formic acid can be separated from the reaction mixture by means of distillation or extraction .
Distillation of the reaction mixture yields a condensate that is high in water content, since water and formic acid form a high boiling azeotrope . Formic acid is concentrated in the still bottom. If all the volatile compound are distilled, the concentration of the received formic acid is that of the original reaction mixture.
Extraction of formic acid can be effected with several solvents.
The solvents listed in the table were found to be stable against oxidation by the catalyst.
Only the solvent dibutyl ether leaves the catalyst in the aqueous phase, whereas with dibutylformamide the catalyst is completely extracted into the organic phase.
After most or all of the formic acid is separated from the reaction mixture, the remaining solution contains water, the catalyst, additives and residual formic acid. This solution can be directly recycled to the reaction without loss of performance.
Formic acid has been considered as a material for hydrogen storage . [ 6 ] This process would allow to use bio-based instead of fossil-based formic acid. | https://en.wikipedia.org/wiki/OxFA_process |
Oxacillin (trade name Bactocill ) is a narrow-spectrum second-generation beta-lactam antibiotic of the penicillin class developed by Beecham . [ 1 ]
It was patented in 1960 and approved for medical use in 1962. [ 2 ]
Oxacillin is a penicillinase-resistant β-lactam . It is similar to methicillin , and has replaced methicillin in clinical use. Other related compounds are nafcillin , cloxacillin , dicloxacillin , and flucloxacillin . Since it is resistant to penicillinase enzymes, such as that produced by Staphylococcus aureus , it is widely used clinically in the US to treat penicillin-resistant Staphylococcus aureus . However, with the introduction and widespread use of both oxacillin and methicillin, antibiotic-resistant strains called methicillin-resistant and oxacillin-resistant Staphylococcus aureus (MRSA/ORSA) have become increasingly prevalent worldwide. MRSA/ORSA can be treated with vancomycin or other new antibiotics. [ citation needed ]
The use of oxacillin is contraindicated in individuals that have experienced a hypersensitivity reaction to any medication in the penicillin family of antibiotics. [ 3 ] Cross-allergenicity has been documented in individuals taking oxacillin that experienced a previous hypersensitivity reaction when given cephalosporins and cephamycins . [ 4 ] [ 5 ]
Commonly reported adverse effects associated with the use of oxacillin include skin rash, diarrhea, nausea, vomiting, hematuria, agranulocytosis, eosinophilia, leukopenia, neutropenia, thrombocytopenia, hepatotoxicity, acute interstitial nephritis, and fever. High doses of oxacillin have been reported to cause renal, hepatic, and nervous system toxicity. Common to all members of the penicillin class of drugs, oxacillin may cause acute or delayed hypersensitivity reactions. As an injection, oxacillin may cause injection site reactions, which may be characterized by redness, swelling, and itching. [ 3 ]
Oxacillin, through its β-lactam ring, covalently binds to penicillin-binding proteins, which are enzymes involved in the synthesis of the bacterial cell wall. This binding interaction interferes with the transpeptidation reaction and inhibits the synthesis of peptidoglycan, a prominent component of the cell wall. By decreasing the integrity of the bacterial cell wall, it is thought that oxacillin and other penicillins kill actively growing bacteria through cell autolysis. [ 6 ]
As with other members of the penicillin family, the chemical structure of oxacillin features a 6-aminopenicillanic acid nucleus with a substituent attached to the amino group. The 6-aminopenicillanic acid nucleus consists of a thiazolidine ring attached to a β-lactam ring, which is the active moiety responsible for the antibacterial activity of the penicillin family. The substituent present on oxacillin is thought to impart resistance to degradation via bacterial β-lactamases. [ 6 ]
Oxacillin, a derivative of methicillin , was first synthesized in the early 1960s as part of a research initiative led by Peter Doyle and John Naylor of Beecham , in consort with Bristol-Myers . Members of the isoxazolyl penicillin family, which includes cloxacillin , dicloxacillin , and oxacillin, were synthesized to counter the increasing prevalence of infections caused by penicillin-resistant Staphylococcus aureus . While methicillin could only be administered via injection, the isoxazolyl penicillins, including oxacillin, could be given orally or by injection. Following the synthesis of cloxacillin and oxacillin, Beecham retained the right to commercially develop cloxacillin in the United Kingdom while Bristol-Myers was given the marketing rights for oxacillin in the United States. [ 1 ]
Source: [ 3 ]
The average wholesale price (AWP) for oxacillin products are provided as follows. The prices listed below are intended to serve as reference values and do not represent the pricing determined by any single manufacturer or entity. [ 3 ] | https://en.wikipedia.org/wiki/Oxacillin |
Oxalic anhydride or ethanedioic anhydride , also called oxiranedione , is a hypothetical organic compound , one of several isomers having the formula C 2 O 3 that have been studied computationally . It can be viewed as the anhydride of oxalic acid or the two-fold ketone of ethylene oxide . It is an oxide of carbon (an oxocarbon ).
The simple compound apparently has yet to be observed (as of 2009). In 1998, however, Paolo Strazzolini and others have claimed the synthesis of dioxane tetraketone (C 4 O 6 ), which can be viewed as the cyclic dimer of oxalic anhydride. [ 1 ]
It has been conjectured to be a fleeting intermediate in the thermal decomposition of certain oxalates [ 2 ] and certain chemoluminescent reactions of oxalyl chloride . [ 3 ]
This article about an organic compound is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Oxalic_anhydride |
Oxaloacetic acid (also known as oxalacetic acid or OAA ) is a crystalline organic compound with the chemical formula HO 2 CC(O)CH 2 CO 2 H. Oxaloacetic acid, in the form of its conjugate base oxaloacetate , is a metabolic intermediate in many processes that occur in animals. It takes part in gluconeogenesis , the urea cycle , the glyoxylate cycle , amino acid synthesis , fatty acid synthesis and the citric acid cycle . [ 1 ]
Oxaloacetic acid undergoes successive deprotonations to give the dianion :
At high pH , the enolizable proton is ionized:
The enol forms of oxaloacetic acid are particularly stable. Keto-enol tautomerization is catalyzed by the enzyme oxaloacetate tautomerase . trans -Enol-oxaloacetate also appears when tartrate is the substrate for fumarase . [ 2 ]
Oxaloacetate forms in several ways in nature. A principal route is upon oxidation of L -malate , catalyzed by malate dehydrogenase , in the citric acid cycle. Malate is also oxidized by succinate dehydrogenase in a slow reaction with the initial product being enol-oxaloacetate. [ 3 ] It also arises from the condensation of pyruvate with carbonic acid, driven by the hydrolysis of ATP :
Occurring in the mesophyll of plants, this process proceeds via phosphoenolpyruvate , catalysed by phosphoenolpyruvate carboxylase . Oxaloacetate can also arise from trans- or de- amination of aspartic acid .
Oxaloacetate is an intermediate of the citric acid cycle , where it reacts with acetyl-CoA to form citrate , catalyzed by citrate synthase . It is also involved in gluconeogenesis , the urea cycle , the glyoxylate cycle , amino acid synthesis , and fatty acid synthesis . Oxaloacetate is also a potent inhibitor of complex II .
Gluconeogenesis [ 1 ] is a metabolic pathway consisting of a series of eleven enzyme-catalyzed reactions, resulting in the generation of glucose from non-carbohydrates substrates. The beginning of this process takes place in the mitochondrial matrix , where pyruvate molecules are found. A pyruvate molecule is carboxylated by a pyruvate carboxylase enzyme, activated by a molecule each of ATP and water. This reaction results in the formation of oxaloacetate. NADH reduces oxaloacetate to malate . This transformation is needed to transport the molecule out of the mitochondria . Once in the cytosol , malate is oxidized to oxaloacetate again using NAD+. Then oxaloacetate remains in the cytosol, where the rest of reactions will take place. Oxaloacetate is later decarboxylated and phosphorylated by phosphoenolpyruvate carboxykinase and becomes 2-phosphoenolpyruvate using guanosine triphosphate (GTP) as phosphate source. Glucose is obtained after further downstream processing.
The urea cycle is a metabolic pathway that results in the formation of urea using one ammonium molecule from degraded amino acids, another ammonium group from aspartate and one bicarbonate molecule. [ 1 ] This route commonly occurs in hepatocytes . The reactions related to the urea cycle produce NADH , and NADH can be produced in two different ways. One of these uses oxaloacetate . In the cytosol there are fumarate molecules. Fumarate can be transformed into malate by the actions of the enzyme fumarase . Malate is acted on by malate dehydrogenase to become oxaloacetate, producing a molecule of NADH. After that, oxaloacetate will be recycled to aspartate , as transaminases prefer these keto acids over the others. This recycling maintains the flow of nitrogen into the cell.
The glyoxylate cycle is a variant of the citric acid cycle. [ 4 ] It is an anabolic pathway occurring in plants and bacteria utilizing the enzymes isocitrate lyase and malate synthase . Some intermediate steps of the cycle are slightly different from the citric acid cycle; nevertheless oxaloacetate has the same function in both processes. [ 1 ] This means that oxaloacetate in this cycle also acts as the primary reactant and final product. In fact the oxaloacetate is a net product of the glyoxylate cycle because its loop of the cycle incorporates two molecules of acetyl-CoA.
In previous stages acetyl-CoA is transferred from the mitochondria to the cytoplasm where fatty acid synthase resides. The acetyl-CoA is transported as a citrate, which has been previously formed in the mitochondrial matrix from acetyl-CoA and oxaloacetate. This reaction usually initiates the citric acid cycle, but when there is no need of energy it is transported to the cytoplasm where it is broken down to cytoplasmic acetyl-CoA and oxaloacetate.
Another part of the cycle requires NADPH for the synthesis of fatty acids. [ 5 ] Part of this reducing power is generated when the cytosolic oxaloacetate is returned to the mitochondria as long as the internal mitochondrial layer is non-permeable for oxaloacetate. Firstly the oxaloacetate is reduced to malate using NADH. Then the malate is decarboxylated to pyruvate. Now this pyruvate can easily enter the mitochondria, where it is carboxylated again to oxaloacetate by pyruvate carboxylase. In this way, the transfer of acetyl-CoA that is from the mitochondria into the cytoplasm produces a molecule of NADH. The overall reaction, which is spontaneous, may be summarized as:
Six essential amino acids and three nonessential are synthesized from oxaloacetate and pyruvate . [ 6 ] Aspartate and alanine are formed from oxaloacetate and pyruvate, respectively, by transamination from glutamate . Asparagine is synthesized by amidation of aspartate, with glutamine donating the NH4.
These are nonessential amino acids, and their simple biosynthetic pathways occur in all organisms. Methionine, threonine, lysine, isoleucine, valine, and leucine are essential amino acids in humans and most vertebrates. Their biosynthetic pathways in bacteria are complex and interconnected.
Oxaloacetate produces oxalate by hydrolysis. [ 7 ]
This process is catalyzed by the enzyme oxaloacetase . This enzyme is seen in plants, but is not known in the animal kingdom. [ 8 ]
Acetyl-CoA
Oxaloacetate
Malate
Fumarate
Succinate
Succinyl-CoA
Citrate
cis- Aconitate
Isocitrate
Oxalosuccinate
2-oxoglutarate | https://en.wikipedia.org/wiki/Oxaloacetic_acid |
Oxalosuccinic acid is a substrate of the citric acid cycle . It is acted upon by isocitrate dehydrogenase . Salts and esters of oxalosuccinic acid are known as oxalosuccinates .
Oxalosuccinic acid/oxalosuccinate is an unstable 6-carbon intermediate in the tricarboxylic acid cycle . It's a keto acid , formed during the oxidative decarboxylation of isocitrate to alpha-ketoglutarate , which is catalyzed by the enzyme isocitrate dehydrogenase. Isocitrate is first oxidized by coenzyme NAD+ to form oxalosuccinic acid/oxalosuccinate. [ 1 ] Oxalosuccinic acid is both an alpha-keto and a beta-keto acid (an unstable compound) and it is the beta-ketoic property that allows the loss of carbon dioxide in the enzymatic reaction in conversion to the five-carbon molecule 2-oxoglutarate . [ 2 ]
Acetyl-CoA
Oxaloacetate
Malate
Fumarate
Succinate
Succinyl-CoA
Citrate
cis- Aconitate
Isocitrate
Oxalosuccinate
2-oxoglutarate
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Oxalosuccinic_acid |
Oxalotrophic bacteria are bacteria capable of using oxalate as their sole source of carbon and energy . [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] Oxalate is the anion of a salt of oxalic acid ; oxalotrophs often consume calcium oxalate . Oxalotrophic bacteria are often facultative methylotrophs . [ 7 ]
This Betaproteobacteria -related article is a stub . You can help Wikipedia by expanding it .
This bacteria -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Oxalotrophic |
Oxamic acid is an organic compound with the formula NH 2 C(O)COOH . It is a white, water-soluble solid. It is the mono amide of oxalic acid . [ 3 ] Oxamic acid inhibits lactate dehydrogenase A . [ 4 ] The active site of lactate dehydrogenase (LDH) is closed off once oxamic acid attaches to the LDH - NADH complex, effectively inhibiting it. [ 5 ]
Oxamic acid also has applications in polymer chemistry. It increases the water solubility of certain polymers, including polyester , epoxide , and acrylic upon binding with them. [ 6 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Oxamic_acid |
Oxamyl is a chemical used as a pesticide that comes in two forms: granulated and liquid. The granulated form has been banned in the United States . [ 2 ] It is commonly sold under the trade name Vydate .
It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities. [ 3 ]
Oxamyl is a carbamate pesticide. According to the WHO Food and Agriculture Organization , "Oxamyl is a colourless crystalline solid with a melting point of 100-102 °C changing to a dimorphic form with a melting point of 108-110 °C. It has a slightly sulfurous odour. Oxamyl is non-corrosive. It has a specific gravity of 0.97 (25°/4°)." [ 1 ]
According to the United Nations Environment Programme , "This product is efficient in controlling most nematode species in addition to a large number of sucking and chewing insects such as aphids and thrips ." Oxamyl is extremely toxic to humans whether ingested, inhaled, or contact with the skin. Its overuse can also lead to residue accumulation in food , [ 2 ] though its chemical composition—once coming into contact with the soil—rapidly degrades. [ 4 ] Signs of Oxamyl poisoning include: Malaise, muscle weakness, dizziness, sweating, Headache, salivation, nausea, vomiting, abdominal pain, Miosis with blurred vision, incoordination, muscle twitching and slurred speech—though symptoms can worsen with severe poisoning. According to the Food and Agriculture Organization, "Contact with the skin, inhalation of dust or spray, or swallowing may be fatal." [ 1 ]
Because of its toxicity, its use is restricted in the EU with maximum residue limits for apples and oranges being 0.001 mg/kg since 2024. [ 5 ] This is after a 2023 review by the European Food Safety Authority identified areas of concern and chronic consumer exposure concerns. [ 6 ] [ 7 ] | https://en.wikipedia.org/wiki/Oxamyl |
CID 9255 from PubChem | https://en.wikipedia.org/wiki/Oxazole_(data_page) |
Oxcarbazepine , sold under the brand name Trileptal among others, is a medication used to treat epilepsy . [ 3 ] [ 5 ] For epilepsy it is used for both focal seizures and generalized seizures . [ 6 ] It has been used both alone and as add-on therapy in people with bipolar disorder who have had no success with other treatments. [ 7 ] [ 5 ] It is taken by mouth . [ 3 ] [ 5 ]
Common side effects include nausea, vomiting, dizziness, drowsiness, double vision and trouble with walking . [ 3 ] Serious side effects may include anaphylaxis , liver problems, pancreatitis , suicide ideation , and an abnormal heart beat . [ 3 ] [ 6 ] While use during pregnancy may harm the baby, use may be less risky than having a seizure. [ 1 ] [ 8 ] Use is not recommended during breastfeeding . [ 1 ] In those with an allergy to carbamazepine there is a 25% risk of problems with oxcarbazepine. [ 3 ] How it works is not entirely clear. [ 5 ]
Oxcarbazepine was patented in 1969 and came into medical use in 1990. [ 9 ] It is available as a generic medication . [ 6 ] In 2022, it was the 167th most commonly prescribed medication in the United States, with more than 3 million prescriptions. [ 10 ] [ 11 ]
Oxcarbazepine is an anticonvulsant used to reduce the occurrence of epileptic episodes, and is not intended to cure epilepsy. [ 12 ] Oxcarbazepine is used alone or in combination with other medications for the treatment of focal (partial) seizures in adults. [ 3 ] In pediatric populations, it can be used by itself for the treatment of partial seizures for children 4 years and older, or in combination with other medications for children 2 years and older. [ 3 ] There is some evidence to support its effectiveness in reducing seizure frequency when used as an add-on therapy for drug-resistant focal epilepsy but there are concerns over tolerability. [ 13 ]
Oxcarbazepine (brand name Trileptal), has been historically used off-label by psychiatrists as a mood stabilizer . However, due to the limited data supporting efficacy it is typically reserved for patients for whom other medications have not worked or are contraindicated . [ 14 ] [ 15 ]
Side effects are dose-dependent. The most common include dizziness, blurred or double vision, nystagmus , ataxia , fatigue , headaches, nausea, vomiting, sleepiness, difficulty in concentration, and mental sluggishness. [ 3 ] The incidence of movement disorders appears to be lower compared to carbamazepine . [ 16 ]
Other, rare, side effects of oxcarbazepine include severe low blood sodium (hyponatremia) , anaphylaxis / angioedema , hypersensitivity (especially if experienced with carbamazepine), toxic epidermal necrolysis , Stevens–Johnson syndrome , and thoughts of suicide. [ 3 ]
Measurement of serum sodium levels should be considered in maintenance treatment or if symptoms of hyponatremia develop. [ 3 ] Low blood sodium is seen in 20–30% of people taking oxcarbazepine, and 8–12% of those experience severe hyponatremia. Some side effects, such as headaches, are more pronounced shortly after a dose is taken and tend to fade with time (60 to 90 minutes). Other side effects include stomach pain, tremor , rash, diarrhea, constipation, decreased appetite, and dry mouth. Photosensitivity is a potential side-effect and people could experience severe sunburns as a result of sun exposure. [ 3 ]
Oxcarbazepine may lead to hypothyroxinemia. The well-known reduction in free and total thyroxine concentration may be due to both peripheral and central mechanisms. [ 17 ]
Oxcarbazepine is pregnancy category C in the US. [ 18 ] There is limited data supporting its safety in pregnancy. Several alternative medications with similar efficacy profiles provide significantly more robust data to support safety during pregnancy. [ 19 ] However limited recent research shows similar rates of fetal malformations in exposed pregnancies to the general non- teratogen exposed population. [ 20 ] Careful consideration of the risks, benefits, alternatives, and expert advise is needed when considering Oxcarbazepine use during pregnancy. [ citation needed ]
Historically Oxcarbazepine was considered to be teratogenic in humans due to animal studies which have shown increased fetal abnormalities in pregnant rats and rabbits exposed to oxcarbazepine during pregnancy. Additionally it's similar structure of to carbamazepine, raised concern as it is teratogenic in humans (pregnancy category D). [ 21 ] [ 22 ]
Oxcarbazepine and its metabolite licarbazepine are both present in human breast milk and thus, some of the active drug can be transferred to a nursing infant. [ 3 ] When considering whether to continue this medication in nursing mothers, the impact of the drug's side effect profile on the infant should be weighed against its anti-epileptic benefit for the mother. [ 3 ]
Oxcarbazepine, licarbazepine and many other common drugs influence each other through interaction with the cytochrome P450 family of enzymes. This leads to a cluster of dozens of common drugs interacting with one another to varying degrees, some of which are especially noteworthy. [ citation needed ]
Oxcarbazepine and licarbazepine are potent inhibitors of CYP2C19 and thus have the potential to increase plasma concentration of drugs, which are metabolized through this pathway. [ 3 ] Other antiepileptics, which are CYP2C19 substrates and thus may be metabolised at a reduced rate when combined with oxcarbazepine, include diazepam , [ 23 ] [ 24 ] hexobarbital , [ 23 ] mephenytoin , [ 23 ] [ 24 ] methylphenobarbital , [ 23 ] nordazepam , [ 24 ] phenobarbital , [ 23 ] phenytoin , [ 24 ] and primidone . [ 23 ]
In addition, oxcarbazepine and licarbazepine are CYP3A4 and CYP3A5 inducers and thus have the potential to decrease the plasma concentration of CYP3A4 and CYP3A5 substrates, [ 3 ] including calcium channel antagonists against high blood pressure and oral contraceptives . [ 3 ] [ 12 ] However, whether the extent of CYP3A4/5 induction at therapeutic doses reaches clinical significance is unclear. [ 3 ]
Oxcarbazepine is a prodrug , which is largely metabolized to its pharmacologically active 10-monohydroxy derivative licarbazepine (sometimes abbreviated MHD ). [ 3 ] [ 25 ] Oxcarbazepine and MHD exert their action by blocking voltage-sensitive sodium channels, thus leading to the stabilization of hyper-excited neural membranes, suppression of repetitive neuronal firing and diminishment propagation of synaptic impulses. [ 3 ] Furthermore, anticonvulsant effects of these compounds could be attributed to enhanced potassium conductance and modulation of high-voltage activated calcium channels. [ 3 ]
Oxcarbazepine has high bioavailability upon oral administration. [ 3 ] In a study in humans, only 2% of oxcarbazepine remained unchanged, 70% were reduced to licarbazepine; the rest were minor metabolites. [ 3 ] The half-life of oxcarbazepine is considered to be about 2 hours, whereas licarbazepine has a half-life of nine hours. Through its chemical difference to carbamazepine metabolic epoxidation is avoided, reducing hepatic risks. [ 26 ] Licarbazepine is metabolised by conjugation with Glucuronic acid . Approximately 4% are oxidised to the inactive 10,11-dihydroxy derivative. Elimination is almost completely renal, with faeces accounting to less than 4%. 80% of the excreted substances are to be attributed to licarbazepine or its glucuronides. [ citation needed ]
Both oxcarbazepine and licarbazepine were found to show anticonvulsant properties in seizure models done on animals. [ 3 ] These compounds had protective functions whenever tonic extension seizures were induced electrically, but such protection was less apparent whenever seizures were induced chemically. [ 3 ] There was no observable tolerance during a four weeks course of treatment with daily administration of oxcarbazepine or licarbazepine in electroshock test on mice and rats. [ 3 ] Most of the antiepileptic activity can be attributed to licarbazepine. [ 3 ] Aside from its reduction in side effects, it is presumed to have the same main mechanism as carbamazepine, sodium channel inhibition, and is generally used to treat the same conditions. [ citation needed ]
The human leukocyte antigen (HLA) allele B*1502 has been associated with an increased incidence of Stevens–Johnson syndrome and toxic epidermal necrolysis in people treated with carbamazepine, and thus those treated with oxcarbazepine might have similar risks. [ 3 ] People of Asian descent are more likely to carry this genetic variant, especially some Malaysian populations, Koreans (2%), Han Chinese (2–12%), Indians (6%), Thai (8%), and Philippines (15%). [ 3 ] Therefore, it has been suggested to consider genetic testing in these people prior to initiation of treatment. [ 3 ]
Oxcarbazepine is a structural derivative of carbamazepine , with a ketone in place of the carbon–carbon double bond on the dibenzazepine ring at the 10 position (10-keto). This difference helps reduce the impact on the liver of metabolizing the drug, and also prevents the serious forms of anemia or agranulocytosis occasionally associated with carbamazepine . [ citation needed ] Aside from this reduction in side effects, it is thought to have the same mechanism as carbamazepine — sodium channel inhibition (presumed to be the main mechanism of action) – and is generally used to treat the same conditions. [ citation needed ]
Oxcarbazepine is a prodrug which is activated to licarbazepine in the liver. [ 25 ]
First made in 1966, [ 26 ] it was patent -protected by Geigy in 1969 through DE 2011087 . It was approved for use as an anticonvulsant in Denmark in 1990, Spain in 1993, Portugal in 1997, and eventually for all other EU countries in 1999. It was approved in the US in 2000. [ 5 ] In September 2010, Novartis , of which Geigy are part of its corporate roots, pleaded guilty to marketing Trileptal for the unapproved uses of neuropathic pain and bipolar disorder. [ 27 ]
Antiepileptics are a key pharmacological therapy used in the treatment of bipolar disorder. [ 28 ] Research has investigated the use of oxcarbazepine as a mood stabilizer in bipolar disorder, with further evidence needed to fully assess its suitability. [ 7 ] [ 29 ] [ 30 ] [ 31 ] Oxcarbazepine used in conjunction with lithium has been shown to be effective in the maintenance phase. [ 32 ]
It may be beneficial in trigeminal neuralgia . [ 33 ] | https://en.wikipedia.org/wiki/Oxcarbazepine |
The Oxford Concordance Program (OCP) [ 1 ] [ 2 ] was first released in 1981 and was a result of a project started
in 1978 by Oxford University Computing Services (OUCS) to create a machine independent text analysis program for producing word lists, indexes and concordances in a variety of languages and alphabets.
In the 1980s it was claimed to have been licensed to around 240 institutions in 23 countries.
OCP was designed and written in FORTRAN by Susan Hockey and Ian Marriott of Oxford University Computing Services in the period 1979–1980 and its authors acknowledged that it owed much to the earlier COCOA and CLOC (University of Birmingham) concordance systems. [ 3 ] [ 4 ]
During 1985–86 OCP was completely rewritten as version 2 to increase the efficiency of the program, a version was also produced for the IBM PC called Micro-OCP. [ 5 ] | https://en.wikipedia.org/wiki/Oxford_Concordance_Program |
Oxford Dictionary of Biology (often abbreviated to ODB ) is a multiple editions dictionary published by the English Oxford University Press . With more than 5,500 entries, [ 1 ] [ 2 ] it contains comprehensive information in English on topics relating to biology , biophysics , and biochemistry . [ 3 ] The first edition was published in 1985 as A Concise Dictionary of Biology . [ 4 ] The seventh edition, A Dictionary of Biology , was published in 2015 and it was edited by Robert Hine and Elizabeth Martin. [ 3 ]
Robert Hine studied at King's College London and University of Aberdeen and since 1984 he has contributed to numerous journals and books. [ 3 ]
The sixth and seventh editions of the ODB are available online for members of subscribed institutions and for subscribed individuals via Oxford Reference .
The first edition of Oxford Dictionary of Biology was first published in 1985 and the seventh edition in 2015. [ 4 ]
This article about a dictionary is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Oxford_Dictionary_of_Biology |
Helix (also known as Helix Oxford or Maped Helix ) is a United Kingdom -based manufacturer of stationery . It exports to over 65 countries, with offices in Hong Kong and US, and has its UK headquarters in Kingswinford in the West Midlands .
Helix was established in 1887 under the name 'The Universal Woodworking Company Ltd.'; it manufactured wooden rulers and metal laboratory apparatus. In 1894, it patented the drawing compass and, with it, launched the Helix brand, following on from the initial success of the compass and rule. In 1912, the company's first mathematical set was created; and, in 1935, the brand "Helix Oxford" was launched. In 1955 the company was renamed the Helix Universal Company, and moved its headquarters to Lye, West Midlands . In the 1960s, the name was changed to Helix International Ltd.
In 2004, the company's factory in Lye ceased production. [ 1 ] In January 2012, the company entered administration. On 8 February 2012 the company stated, "The joint administrators from Grant Thornton UK LLP are currently speaking to a number of interested parties and have received offers for the sale of the business as a going concern." [ 2 ] One week later, the company was bought by the French Maped group. [ 3 ]
When Helix joined the Maped Helix Group the company changed its name to Helix Trading Ltd and moved its UK headquarters from Lye, West Midlands to nearby Kingswinford , where it has its showroom. In 2014 it reported sales of £8.5 million. [ 4 ] [ 5 ]
The Oxford Set of Mathematical Instruments is a set of instruments used by generations of school children in the United Kingdom and around the world in mathematics and geometry lessons. The set is marketed in over 100 countries by Helix.
It consists of a metal tin embossed on the front with a drawing of Balliol College and the words 'THE HELIX OXFORD SET OF MATHEMATICAL INSTRUMENTS COMPLETE & ACCURATE' in white against a blue background.
Inside the tin there are two set squares , a 180° protractor , a 15 cm ruler , a metal compass , a 9 cm pencil , a pencil sharpener , and an eraser . (In the 1970s a stencil for drawing chemical apparatus was included.) There is also a fact sheet and glossary of mathematical terms with a school timetable printed on the back. The export version also includes dividers . | https://en.wikipedia.org/wiki/Oxford_Set_of_Mathematical_Instruments |
The Oxford–Liverpool Inventory of Feelings and Experiences (O-LIFE) is a questionnaire for measuring psychosis-proneness, principally schizotypy . [ 1 ] It was introduced in 1995 and has since been used in a variety of experimental and clinical studies. The O-LIFE is a tool with 104 items in the Yes/No response format, although a shorter version (sO-LIFE) can be used as well with only 43 items. [ 2 ] It has been used, for instance, in several studies assessing schizotypy in relation to Kamin blocking . [ 3 ] [ 4 ]
This neuroscience article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Oxford–Liverpool_Inventory_of_Feelings_and_Experiences |
Oxhide ingots are heavy (20–30 kg) metal slabs, usually of copper but sometimes of tin , produced and widely distributed during the Mediterranean Late Bronze Age (LBA). Their shape resembles the hide of an ox with a protruding handle in each of the ingot's four corners. Early thought was that each ingot was equivalent to the value of one ox. [ 1 ] : 138 However, the similarity in shape is simply a coincidence. The ingots' producers probably designed these protrusions to make the ingots easily transportable overland on the backs of pack animals . [ 1 ] : 140 Complete or partial oxhide ingots have been discovered in Sardinia , Crete , Peloponnese , Cyprus , Cannatello in Sicily , Boğazköy in Turkey (ancient Hattusa , the Hittite capital), Qantir in Egypt (ancient Pi-Ramesses ), and Sozopol in Bulgaria . [ 2 ] [ 3 ] Archaeologists have recovered many oxhide ingots from two shipwrecks off the coast of Turkey (one off Uluburun and one in Cape Gelidonya).
The appearance of oxhide ingots in the archaeological record corresponds with the beginning of the bulk copper trade in the Mediterranean—approximately 1600 BC. [ 4 ] : 281 The earliest oxhide ingots found come from Crete and date to the Late Minoan IB , approximately 1500 BC to 1450 BC. [ 5 ] : 322 The latest oxhide ingots date to approximately 1000 BC, and were found on Sardinia. [ 4 ] : 283 The copper trade was largely maritime: the principal sites where oxhide ingots are found are at sea, on the coast, and on islands. [ 1 ] : 138
It is uncertain whether the oxhide ingots served as a form of currency. Ingots found in excavations at Mycenae are now part of the exhibits of the Numismatic Museum of Athens . Cemal Pulak argues that the weights of the Uluburun ingots are similar enough to have allowed "a rough but quick reckoning of a given quantity of raw metal prior to weighing". [ 1 ] : 138 But George Bass proposes, via the Gelidonya ingots, whose weights are approximately the same if somewhat lower than the Uluburun ingot weights, that the weights were not standard and thus the ingots were not a currency. [ 6 ] : 70 Another theory is that the oxhide shape, as well as the bun shape that some ingots took, was a visual statement that the ingot at hand is part of a legitimate trade. [ 1 ] : 138 In Sardinia, oxhide ingot fragments have been found in hoards with bun ingots and scrap metal and, in some cases, in a metallurgical workshop. [ 7 ] Citing this evidence, Vasiliki Kassianidou argues that the oxhide ingots "were meant to be used rather than to be kept as prestige goods". [ 7 ]
In 1982, a diver discovered a shipwreck off the shore of Uluburun, Turkey. [ 8 ] The ship contained 317 copper ingots in the normal oxhide shape, 36 with only two corner protrusions, 121 shaped like buns, and five shaped like pillows. [ 9 ] : 276 [ 1 ] : 141 [ 10 ] : 2 The oxhide ingots (ingots with two or four protrusions) range in weight from 20.1 to 29.5 kilograms (44 to 65 lb) after being cleaned of their corrosion. [ 1 ] : 141 These ingots were found stacked in four rows following a herringbone pattern. [ 1 ] : 140 The smooth sides of the ingots faced downwards, and the lowest layer rested on brushwood. [ 1 ] : 140–141 There are three whole tin oxhide ingots, and there are many tin ingots cut into quarters or halves, with their corner protrusion(s) still intact. [ 1 ] : 150–151 Besides metal ingots, the cargo included ivory, metal jewelry, and Mycenaean , Cypriot, and Canaanite pottery. [ 9 ] : 274 Tree-ring dating of firewood from the ship gives an approximate date of 1300 BC. [ 1 ] : 137 More than 160 copper oxhide ingots, 62 bun ingots, and some of the tin oxhide ingots have incised marks typically on their rough sides. [ 1 ] : 146 Some of these marks—resembling fish, oars, and boats—relate to the sea, and they were probably incised after casting, when the ingot was received or exported. [ 1 ] : 146
Recently Yuval Goren proposed that the ten tons of copper ingots, one ton of tin ingots, and the resin stored in the Canaanite jars aboard the ship were one complete package. The recipients of the copper, tin, and resin would have used these materials for bronze casting through the lost-wax technique . [ 11 ]
In the early 1950s, divers found the remains of a shipwreck in Cape Gelidonya , off the coast of Turkey. [ 6 ] : 14 The remains included a substantial amount of copper oxhide ingot material: 34 in full, five in half, 12 corners, and 75 kilograms (165 lb) of random fragments. [ 6 ] : 52 Twenty-four full copper oxhide ingots have stamps on their centers—usually of a circle containing intersecting lines. [ 6 ] : 52 These stamps were likely made when the metal was soft. [ 6 ] : 52 In addition, the ship contained numerous complete and incomplete copper bun-shaped ingots, rectangular tin bars, and Cypriot agricultural tools made of scrap bronze. [ 12 ] [ 6 ] : 78 Radiocarbon dating of brushwood from the ship gives an approximate date of 1200 BC. [ 6 ] : 168
Typically the copper oxhide ingots are highly pure (approximately 99 weight percent copper) with trace element content of less than one weight percent. [ 10 ] : 13 The few tin oxhide ingots that have been available to study are also exceptionally pure. [ 10 ] : 16 Microscopic analysis of the Uluburun copper oxhide ingots reveals that they are highly porous. [ 10 ] : 4 This feature results from the effervescence of gases as the molten metal cooled. [ 10 ] : 4 Slag inclusions are also present. [ 10 ] : 6–7 Their existence implies that slag was not fully removed from the smelted metal and thus that the ingots were made from remelted copper. [ 10 ] : 12
Macroscopic observation of the Uluburun copper ingots indicates that they were cast through multiple pours; there are distinct layers of metal in each ingot. [ 1 ] : 141 Furthermore, the relatively high weight and high purity of the ingots would be difficult to achieve even today in only one pour. [ 13 ] [ 4 ] : 287–288
The porosity of the copper ingots and the natural brittleness of tin suggest that both metal ingots were easy to break. [ 10 ] : 19 As Bass et al. proposes, a metalsmith could simply break off a piece of the ingot whenever he liked for a new casting. [ 6 ] : 71
Controversy has swirled around the provenance of the copper oxhide ingots. Lead isotope analysis (LIA) suggests that the late LBA ingots (that is, after 1250 BC) are composed of Cypriot copper, specifically copper from the Apilki mine and its surrounding area. [ 14 ] The Gelidonya ingots' ratios are consistent with Cypriot ores while the Uluburun ingots fall on the periphery of the Cypriot isotopic field. [ 15 ] On the other hand, Late Minoan I ingots found on Crete have Paleozoic lead isotope ratios and are more consistent with ore sources in Afghanistan , Iran , or Central Asia . [ 14 ] The controversy settles on the validity of LIA. Paul Budd argues that LBA copper is the product of such extensive mixing and recycling that LIA, which works best for metals from a single ore deposit, is unfeasible. [ 16 ]
Some scholars worry that the 1250 BC date is too limiting. They note that Cyprus was smelting copper on a large scale in the early LBA and had the potential to export the metal to Crete and other places at this time. [ 7 ] : 334 [ 4 ] : 292 Furthermore, copper ore is more plentiful on Cyprus than on Sardinia and far more plentiful than on Crete. [ 5 ] : 320–321 Archaeologists have discovered numerous Cypriot exports to Sardinia including metalworking tools and prestige metal objects. [ 17 ]
Due to the heavy corrosion of tin oxhide ingots and the limited data for lead isotopic studies of tin, the provenance of the tin ingots has been uncertain. [ 18 ] The fact that scholars have been unable to pinpoint Bronze Age tin ore deposits compounds this problem. [ 19 ]
A mold for casting an oxhide ingot was discovered in the LBA north palace at Ras Ibn Hani in Syria . [ 20 ] : 4 It is made of fine-grained "ramleh", a shelly limestone . [ 20 ] : 4 Archaeologists found burnt copper droplets around the mold. [ 20 ] : 4 In spite of the questionable durability of limestone, Paul Craddock et al. concluded that limestone can be used for casting “large simple shapes” such as oxhide ingots. [ 20 ] : 7 Evolution of carbon dioxide from the limestone would damage the metal surface that touched the mold. [ 20 ] : 6 Thus, metal objects requiring surface detail could not be produced successfully. [ 20 ] : 6
This is not to say that oxhide ingots were normally cast in limestone molds. Using an experimental clay mold, Bass et al. argue that the ingot's smooth side was in contact with the mold while its rough side was exposed to the atmosphere. [ 6 ] : 70 The roughness results from the interaction of the atmosphere and the cooling metal. [ 6 ] : 70
In the Late Bronze Age, Cyprus produced numerous bronze stands that depicted a man carrying an oxhide ingot. The stands were designed to hold vases, and they were cast through the lost-wax process. [ 21 ] : 341, 344 The ingots show the familiar shape of four protruding handles, and the men carry them over their shoulders. These Cypriot stands were exported to Crete and Sardinia, and both islands created similar stands in local bronze workshops. [ 21 ] : 351
While only one oxhide ingot fragment has been recovered from Egypt (in the context of a LBA smelting workshop), there is a wide array of painted scenes in Egypt that show oxhide ingots. The earliest scene dates to the 15th century BC and the latest scene to the 12th century BC. [ 6 ] : 62, 67 The ingots display their typical four protrusions, and red paint (which suggests they are copper) is preserved on them. [ 6 ] : 62–67 The captions accompanying the scenes explain that the men who bring the ingots come from the north, specifically Retnu (Syria) and Keftiu (unidentified). [ 6 ] : 62–67 They are shown being carried on the shoulders of men, sitting with other goods in storage, or as part of scenes in smelting workshops. [ 6 ] : 62–67 In a relief from Karnak , the pharaoh Amenhotep II is seen riding a chariot and spearing an oxhide ingot with five arrows. A laudatory caption emphasizing the pharaoh's strength accompanies the scene. [ 6 ] : 65
Several of the “ Amarna letters ” dating to the mid-14th century BC refer to hundreds of copper talents—in addition to goods such as elephant tusks and glass ingots—sent from the kingdom of Alashiya to Egypt. [ 4 ] : 293 [ 1 ] : 140 Some scholars identify Cyprus with Alashiya. [ 4 ] : 293 In particular, the Uluburun cargo is similar to the goods that, according to the letters, Alashiya sent to Egypt. [ 1 ] : 140 | https://en.wikipedia.org/wiki/Oxhide_ingot |
The oxhydroelectric effect consists in the generation of voltage and electric current in pure liquid water , without any electrolyte, upon exposure to electromagnetic radiation in the infrared range, after creating a physical (not chemical) asymmetry in liquid water e.g. thanks to a strongly hydrophile polymer, such as Nafion . [ 1 ] [ 2 ] [ 3 ]
Since the publication of the first seminal research, other independent research has been published, which refer to this effect, in scientific peer reviewed, reputable journals (with impact factors higher than the median in the respective fields). [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ]
The system can be described as a photovoltaic cell operating in the infrared electromagnetic range, based on liquid water instead of a semiconductor .
The model proposed by Roberto Germano and his collaborators, who have first observed the effect [ 1 ] [ 2 ] [ 3 ] is based on the known concept of the exclusion zone .
The first observations of a different behaviour of water molecules close to the walls of its container date back to late ‘60s and early ‘70s, when Drost-Hansen, upon reviewing many experimental articles, came to the conclusion that interfacial water shows structural difference with respect to the bulk liquid water. [ 9 ] [ 10 ]
In 2006 Gerald Pollack published a seminal work on the exclusion zone [ 11 ] and those observations were subsequently reported by several other groups, [ 12 ] [ 13 ] which all report observations of a coherent water region created at the boundary between the surface of a hydrophilic material and the bulk water.
Further elaborating on the work of Pollack, the model describes liquid water as a system made of two phases: a matrix of non-coherent water molecules hosting many “Coherence Domains” (CDs), about 0.1 um in size, found in the exclusion zone, but also in the bulk volume.
In this model the behaviour of the coherence domains is also considered as the cause for the formation of xerosydryle.
The two phases, are characterized by different thermodynamic parameters, and are in a stable non-equilibrium state.
The coherent phase should be described by a quantum state , and in particular a state oscillating between a fundamental state, where electrons are firmly bound (ionization energy of 12.60 eV), and an excited state characterized by a quasi-free electron configuration. The energy of the excited state is 12.06 eV, which means that only a small amount of energy as small as (12.60 - 12.06) eV = 0.54 eV (Infrared range) is sufficient to extract an electron.
Then, at a fixed temperature and for molecules density exceeding a threshold, the transition of the non-coherent water molecules to the coherence state is spontaneous because it is driving the system to a lower energy configuration.
More exactly, the almost free electrons have to cross an energy barrier of (0.54 - Χ) eV, where Χ ~ 0.1 eV is the electric potential difference at the CD boundary with the non-coherent water.
This small amount of energy, ~ 0.44 eV, necessary for the electron extraction, makes the coherent water a reservoir of quasi-free electrons that can be easily released by Infrared stimulation, or quantum tunnel effect or by small external perturbation.
The two water phases, with their different potentials behave as the two components of a photovoltaic cell based on semiconductors.
Then, in the cell described in the patent, [ 3 ] one of the two sectors has sheets of hydrophilic material, which create (more) coherent domains in that sector, with respect to the other sector.
The research on the effect has started as a side project in Germano's "technology transfer company" Promete s.r.l. [ 14 ] and since 2023 it is conducted in Oxhy s.r.l., [ 15 ] a startup created with the purpose to further develop this line of research. | https://en.wikipedia.org/wiki/Oxhydroelectric_effect |
The oxidase test is used to determine whether an organism possesses the cytochrome c oxidase enzyme. The test is used as an aid for the differentiation of Neisseria , Moraxella , Campylobacter and Pasteurella species (oxidase positive). It is also used to differentiate pseudomonads from related species. [ 1 ]
Strains may be either oxidase-positive (OX+) or oxidase-negative (OX-).
OX+ normally means the bacterium contains cytochrome c oxidase (also known as Complex IV) and can therefore use oxygen for energy production by converting O 2 to H 2 O 2 or H 2 O with an electron transfer chain .
The Pseudomonadaceae are typically OX+. [ 1 ]
The Gram-negative diplococci Neisseria and Moraxella are oxidase-positive. [ 2 ]
Many Gram-negative, spiral curved rods are also oxidase-positive, which includes Helicobacter pylori , Vibrio cholerae , and Campylobacter jejuni .
Legionella pneumophila may be oxidase-positive. [ 3 ]
OX− normally means the bacterium does not contain cytochrome c oxidase and, therefore, either cannot use oxygen for energy production with an electron transfer chain or employs a different cytochrome for transferring electrons to oxygen.
Enterobacteriaceae are typically OX−. [ 4 ]
The test uses disks impregnated with reagents such as N,N,N′,N′ -tetramethyl- p -phenylenediamine , TMPD (or N,N -dimethyl- p -phenylenediamine , DMPD, which is another redox indicator). The reagent is a dark-blue to maroon color when oxidized, and colorless when reduced. Oxidase-positive bacteria possess cytochrome oxidase or indophenol oxidase (an iron-containing hemoprotein). [ 5 ] These both catalyze the transport of electrons from donor compounds ( NADH ) to electron acceptors (usually oxygen). The test reagent TMPD acts as an artificial electron donor for the enzyme oxidase. The oxidized reagent forms the colored compound indophenol blue . The cytochrome system is usually only present in aerobic organisms that are capable of using oxygen as the terminal electron acceptor. The end-product of this metabolism is either water or hydrogen peroxide (broken down by catalase ). [ 1 ]
In alternative manner, live bacteria cultivated on trypticase soy agar plates may be prepared using sterile technique with a single-line streak inoculation. The inoculated plates are incubated at 37 °C for 24–48 hours to establish colonies. Fresh bacterial preparations should be used. After colonies have grown on the medium, 2-3 drops of the reagent DMPD are added to the surface of each organism to be tested. | https://en.wikipedia.org/wiki/Oxidase_test |
Oxidation response is stimulated by a disturbance in the balance between the production of reactive oxygen species and antioxidant responses, known as oxidative stress . Active species of oxygen naturally occur in aerobic cells and have both intracellular and extracellular sources. These species, if not controlled, damage all components of the cell, including proteins, lipids and DNA. Hence cells need to maintain a strong defense against the damage.
The following table gives an idea of the antioxidant defense system in bacterial system.
protein repair system
Small changes in cellular oxidant status can be sensed by specific proteins which regulate a set of genes encoding antioxidant enzymes. Such a global response induces an adaptive metabolism including ROS elimination, the bypass of injured pathways, reparation of oxidative damages and maintenance of reducing power.
Peroxide and superoxide are the two major active oxygen species. It is found that the peroxide and superoxide stress responses are distinct in bacteria. The exposure of microorganisms to low sublethal concentrations of oxidants leads to the acquisition of cellular resistance to a subsequent lethal oxidative stress.
In response to an increased flux of hydrogen peroxide and other organic peroxides such as tert-butyl hydroperoxide and cumene hydroperoxide , peroxide stimulon gets activated. Studies of E. coli response to H 2 O 2 have shown that exposure to H 2 O 2 elevated mRNA levels of 140 genes, of which 30 genes are members of the OxyR regulon . The genes include many genes coding for metabolic enzymes and antioxidant enzymes demonstrating the role of these enzymes in reorganization of metabolism under stress conditions. [ 1 ]
When stressed under elevated levels of the superoxide radical anion O 2 − , bacteria respond by invoking the superoxide stimulon. Superoxide-generating compounds activate SoxR regulator by the one-electron oxidation of the 2Fe-2S clusters. Oxidized SoxR then induces the expression of SoxS protein, which in turn activates the transcription of structural genes of the SoxRS regulon. [ 2 ]
The transcriptional factor OxyR regulates the expression of OxyR regulon. H 2 O 2 oxidizes the transcriptional factor by forming an intramolecular disulfide bond. The oxidized form of this factor specifically binds to the promoters of constituent genes of OxyR regulon, including katG (hydroperoxidase- catalase HPІ), gorA ( glutathione reductase ), grxA ( glutaredoxin 1), trxC ( thioredoxin 2), ahpCF ( alkyl hydroperoxide reductase ), dps (nonspecific DNA binding protein) and oxyS (a small regulatory RNA). Reduced OxyR provides autorepression by binding only to the oxyR promoter. [ 1 ]
Regulation of the soxRS regulon occurs by a two-stage process: the SoxR protein is first converted to an oxidized form that enhances soxS transcription, and the increased level of SoxS protein in turn activates the expression of the regulon. The structural genes under this regulon include sodA (Mn- superoxide dismutase (SOD)), zwf ( glucose-6-phosphate dehydrogenase ( G6PDH )), acnA ( aconitase A), nfsA ( nitrate reductase A), fumC ( fumarase C) and nfo ( endonuclease IV) among others. In E.coli, negative autoregulation of SoxS protein serves as a dampening mechanism for the soxRS redox stress response. [ 3 ]
SoxRS regulon genes can be regulated by additional factors. [ 2 ]
At least three known genes including xthA and katE are regulated by a sigma factor, KatF( RpoS ), whose synthesis is turned on during the stationary phase . XthA (exonuclease III, a DNA repair enzyme) and KatE (catalase) are known to play important roles in the defense against oxidative stress but KatF regulon genes are not induced by oxidative stress. [ 2 ]
There is an overlap between oxidative stress response and other regulatory networks like heat shock response, SOS response .
The defenses against deleterious effects of active oxygen can be logically divided into two broad classes, preventive and reparative.
Cellular defenses against the damaging effects of oxidative stress involve both enzymatic and nonenzymatic components.
The enzymatic components may directly scavenge active oxygen species or may act by producing the nonenzymatic antioxidants. There are four enzymes that provide the bulk of protection against deleterious reactions involving active oxygen in bacteria: SODs (superoxide dismutases encoded by sodA and sodB ), catalases ( katE and katG ), glutathione synthetase ( gshAB ) and glutathione reductase ( gor ). Some bacteria have NADH-dependent peroxidases specific for H 2 O 2 .
The main nonenzymatic antioxidants in E. coli are GSH and thioredoxin (encoded by trxA ). Ubiquinone and menaquinone may also serve as membrane-associated antioxidants.
Secondary defenses include DNA-repair systems, proteolytic and lipolytic enzymes . DNA repair enzymes include endonuclease IV, induced by oxidative stress, and exonuclease III, induced in the stationary phase and in starving cells. These enzymes act on duplex DNA and clean up DNA 3' terminal ends.
Prokaryotic cells contain catalysts that modify the primary structure of proteins frequently by reducing disulfide bonds. This occurs in the following steps:
(i) thioredoxin reductase transfers electrons from NADPH to thioredoxin via a flavin carrier
(ii) glutaredoxin is also able to reduce disulfide bonds, but using GSH as an electron donor
(iii) protein disulfide isomerase facilitates disulfide exchange reactions with large inactive protein substrates, besides having chaperone activity
Oxidation of surface exposed methionine residues surrounding the entrance to the active site could function as a “last-chance” antioxidant defense system for proteins. [ 4 ]
The complexity in bacterial responses appears to be in the number of proteins induced by oxidative stress. In mammalian cells, the number of proteins induced is small but the regulatory pathways are highly complex.
The inducers of oxidative stress responses in bacteria appear to be either the oxidant itself or interaction of the oxidant with a cell component. Most mammalian cells exist in an environment where the oxygen concentration is constant, thus responses are not directly stimulated by oxidants. Rather, cytokines such as tumor necrosis factor , interleukin-1 or bacterial polysaccharides induce SOD synthesis and multigene responses. Recent work shows that superoxide is a strong tumor promoter that works by activation and induction growth-competence related gene products. Other factors involved in the antioxidant gene expression include an induction of calmodulin kinase by increase in Ca 2+ concentrations.
E. coli cells have revealed similarities to the aging process of higher organisms. The similarities include increased oxidation of cellular constituents and its target specificity, the role of antioxidants and oxygen tension in determining life span, and an apparent trade-off
between activities related to reproduction and survival. [ 5 ] | https://en.wikipedia.org/wiki/Oxidation_response |
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