Sometimes, output from an electronic source affects future input. This can form what is called a "feedback loop". In some cases the output reinforces the input, making it stronger; this is called "self-reinforcing", "positive", "runaway" or "amplifying". In other cases, the output blocks or stops some of the input; this is called a negative feedback loop.
Think about a sound system with input from a microphone and output to a loudspeaker. If the sound coming out of the loudspeaker is heard by the microphone, a loop is created, from speaker, to the microphone, through the cord, and back into the speaker. The loop is made up of sound and the electrical energy that the microphone and loudspeaker use to create that sound. If nothing stops the sound and electricity in the loop, it will travel faster and faster, which is why feedback starts out as a low hum and turns into a high squeal very quickly
This is an example of a positive feedback loop: the output reinforces the input; it makes the input stronger.
Think about two mirrors that face each other. The mirrors reflect each other infinitely, or forever, but in each reflection, the image in the mirror is slightly smaller than the image it reflects. The images get smaller and smaller until they are no longer visible. This is an example of a negative feedback loop: the output (the reflection) reduces the input; it makes the input smaller.
Warm temperature caused a glacier to melt. As the glacier melts, areas that were at one time covered by snow and ice are now water or land. Because snow and ice reflect heat but water and land absorb heat, this causes the glacier to melt faster as more snow and ice is melted. This type of positive feedback is an example of thermal runaway.
American mathematician Norbert Wiener made feedback loops more well known in 1948 in his book "Cybernetics". Cybernetics is the study of feedback loops and their role in communication and control.
Phosphate
A phosphate is a salt of phosphoric acid. Phosphates are important in biochemistry.
Phosphates have the formula PO and a molar mass of 94.973 g/mol. An example of a phosphate is sodium phosphate. Three different types of phosphates are known. They are orthophosphate, PO; metaphosphate, PO; and pyrophosphate, PO. They have a combining power of 3.
Phosphates are made of one phosphorus atom surrounded by four oxygen atoms.
Many phosphates do not dissolve in water.
Cerebrum
The cerebrum is the largest part of the brain. It is in the front part of the brain. It contains about 15 billion cells, and is the latest brain structure to have evolved.
The cerebrum takes in data from sight and other sense organs, and 'makes sense' of it (interprets it). It controls consciousness and action (voluntary muscular activity). It plans, thinks, judges, and organises speech and information. These are the so-called 'higher mental functions'.
The cerebrum is divided into two "cerebral hemispheres". These two cerebral hemispheres are connected by three bands of nerve fibres, or commissures, which connect the two halves. The outer layers of the cerebrum are made up of the grey matter, and is called the cerebral cortex. The inner layers are made up of the white matter (nerve fibres), and the basal ganglia.
In the cerebrum, there are specific regions for each kind of stimulus and its response. For example, occipital lobe is the region for visual reception, temporal lobe for auditory reception, and parietal lobe for touch, smell, temperature and conscious association. The frontal lobe takes action, based on sensory input and other factors.
Karelia
Karelia is an area in eastern Fennoscandia. It is to the east from where Finnish people live. There are many opinions about what places exactly belong to Karelia.
Most of Karelia belongs to Russia today. Small parts of Karelia belong to Finland. On the Russian side of Karelia is the Republic of Karelia. On the Finnish side are the provinces of North Karelia and South Karelia.
The original people of Karelia are Karelians. Karelian people speak Karelian, a Finnic language very close to Finnish. Karelians knew many old poems. Many poems of the Finnish book Kalevala are from the Karelians. Today in the Republic of Karelia, Karelians are a minority and Russians are a majority. Some people fear Karelian culture and language will die out.
Most of Karelia was part of Finland until the Soviet Union took it in the Winter War. East Karelia was not. To make peace after World War II, Finland had to give most of Karelia to the Soviet Union. After peace, many people from the Soviet Union went to live in Karelia.
Kalevala
Kalevala is the Finnish national epic. This means it is a book that is very important to Finnish people.
Kalevala has many stories and folklores in it. The stories of Kalevala are poems that are very old. Long ago, people sang these poems. The poems have a unique metre that is not known outside Finnic languages. There are many themes in these stories from different times in the past. The oldest themes are from the stone age. Many of the poems are collected from Karelia and areas nearby.
Heroes have adventures in these stories. The most important heroes are Väinämöinen, Ilmarinen, Lemminkäinen and Kullervo. The enemies of heroes are Louhi and Joukahainen. Many stories in Kalevala are about two countries fighting each other. These countries are the land of Kalevala and land of Pohjola. The Land of Kalevala is the land of Heroes. Pohjola is the land of enemies. Pohjola is an evil and cold place somewhere far north.
Elias Lönnrot was a man who collected these poems and made a book of them. Kalevala has been translated into many languages. There is also an English Kalevala.
Edred of England
King Edred or "Eadred" (c. 923 – November 23 955) was King of England from 946 until his death. He was a son of King Edward the Elder and Edgiva of Kent. He was king after his brother, King Edmund I. Like both his older brothers, Edred was successful against the Vikings. Edred was a very religious man, but had very poor health (he could barely eat his food). He died on November 23 955, in Frome, Somerset, and was buried in the Old Minster at Winchester. His nephew, King Edwy, became king after him.
Plant pathology
Plant pathology, or phytopathology, is the study of plant diseases. Like animals, plants can get infected and damaged by viruses, bacteria and fungi.
It includes not only the harm done by pathogens (infectious organisms), but also harm done by environmental conditions.
Organisms which cause infectious disease include fungi, oomycetes, bacteria, plant viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants.
Not included are ectoparasites like insects, mites, vertebrate, or other pests that affect plant health by eating plant tissues. Plant pathology involves the study of pathogen identification, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, and how to manage plant diseases.
Plant pathology is of fundamental importance to agriculture.
Chytridiomycota
Chytridiomycota is a phylum of the Fungi kingdom. The name comes from chytridium (from the Greek "chytridion", meaning "little pot"): the structure containing unreleased spores.
The chytrids are the most primitive of the fungi. Many chytrids are found in fresh water. There are approximately 1,000 chytrid species, in 127 genera, distributed among 5 orders.
Chytrids get their energy mostly from non-living organic matter.
Both zoospores and gametes of the chytrids are mobile by their flagella, one whiplash per individual.
Some chytrid species are known to kill amphibians in large numbers. The actual process, however, is unknown.
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