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Circadian rhythm

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A circadian rhythm is any biological process that displays an endogenous, entrainable oscillation of about 24 hours. [1]

159 relations: Actigraphy, Acute kidney injury, Adenosine triphosphate, Advanced sleep phase disorder, Alexander the Great, Androsthenes of Thasos, Animal, ARNTL, ARNTL2, Auguste Forel, Autophagy, Azotemia, Bacterial circadian rhythm, Biphasic and polyphasic sleep, Bipolar disorder, Cell (biology), Charles Czeisler, Chemical kinetics, Chronobiology, Chronotherapy (treatment scheduling), Chronotype, Circa, Circadian clock, Circadian rhythm sleep disorder, Circasemidian rhythm, Circaseptan, Cocaine, Colin Pittendrigh, Cone cell, Conifer cone, Cortisol, Cryptochrome, Cyanobacteria, Delayed sleep phase disorder, Derk-Jan Dijk, Diabetes mellitus, Diurnal cycle, Diurnality, Drosophila, Drosophila pseudoobscura, Endogeny (biology), Entrainment (chronobiology), Epigenetics, Epithalamus, Esophagus, Fatigue, Franz Halberg, Free-running sleep, Fungus, Gene D. Block, ..., Great Oxygenation Event, Ground squirrel, Harvard University, Heart rate, Hormone, Human body temperature, Human eye, Human spaceflight, Hyperoxia, Hypothalamus, Hypoxia (medical), Illuminance, Ingeborg Beling, Insomnia, Intrinsically photosensitive retinal ganglion cells, Irradiance, Jean-Jacques d'Ortous de Mairan, Jeffrey C. Hall, Jet lag, Joseph Takahashi, KaiA, KaiB, KaiC, Latin, Light effects on circadian rhythm, Light in school buildings, Liver, Lung, Mammal, Mars, Melanopsin, Melatonin, Metabolism, Metabolite, Metal-halide lamp, Michael Rosbash, Michael W. Young, Mimosa pudica, Monarch butterfly, Nathaniel Kleitman, National Transportation Safety Board, Neural oscillation, Nobel Prize in Physiology or Medicine, Nocturnality, Non-24-hour sleep–wake disorder, Obesity, Optic lobe (arthropods), Oscillation, Oxidative stress, Pancreas, PER1, PER2, PER3, Period (gene), Phase response curve, Pheromone, Photoperiodism, Photoreceptor cell, Pineal gland, Plant, Polyphagia, Porcupine, Power nap, Prokaryote, Pupa, Q10 (temperature coefficient), Quail, Reactive oxygen species, Redox, Reindeer, Repressilator, Reticular formation, Retina, Retinohypothalamic tract, Rev-ErbA alpha, Rock ptarmigan, Rod cell, Ronald J. Konopka, Seymour Benzer, Shift work, Sleep, Sleep disorder, Sleep in non-human animals, Sleep onset latency, Sodium-vapor lamp, Solar time, Spalax, Spleen, Spodoptera littoralis, Stefania Follini, Stem cell, Suprachiasmatic nucleus, Svalbard, Tamarind, The Washington Post, Thymus, Tide, Time zone, TOC1 (gene), Traditional Chinese medicine, Ultradian rhythm, Ultraviolet, Unfolded protein response, University of Tromsø, Uremia, Zeitgeber, 13th century, 70th parallel north, 78th parallel north. Expand index (109 more) »


Actigraphy is a non-invasive method of monitoring human rest/activity cycles.

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Acute kidney injury

Acute kidney injury (AKI), previously called acute renal failure (ARF), is an abrupt loss of kidney function that develops within 7 days.

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Adenosine triphosphate

Adenosine triphosphate (ATP) is a complex organic chemical that participates in many processes.

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Advanced sleep phase disorder

Advanced sleep phase disorder (ASPD), also known as the advanced sleep-phase type (ASPT) of circadian rhythm sleep disorder or advanced sleep phase syndrome (ASPS), is a condition in which patients feel very sleepy and go to bed early in the evening (e.g. 6:00–8:00 p.m.) and wake up very early in the morning (e.g. around 3:00 a.m.).

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Alexander the Great

Alexander III of Macedon (20/21 July 356 BC – 10/11 June 323 BC), commonly known as Alexander the Great (Aléxandros ho Mégas), was a king (basileus) of the ancient Greek kingdom of Macedon and a member of the Argead dynasty.

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Androsthenes of Thasos

Androsthenes (Ἀνδροσθένης) of Thasos, son of Callistratus, was one of the admirals of Alexander the Great.

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Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia.

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Aryl hydrocarbon receptor nuclear translocator-like protein 1 is protein that in humans is encoded by the ARNTL gene, also known as BMAL1, MOP3, and, less commonly, BHLHE5, BMAL, BMAL1C, JAP3, PASD3, and TIC.

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Aryl hydrocarbon receptor nuclear translocator-like 2, also known as Mop9, Bmal2, Clif, or Arntl2, is a gene.

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Auguste Forel

Auguste-Henri Forel (1 September 1848 – 27 July 1931) was a Swiss myrmecologist, neuroanatomist, psychiatrist and eugenicist, notable for his investigations into the structure of the human brain and that of ants.

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Autophagy (or autophagocytosis) (from the Ancient Greek αὐτόφαγος autóphagos, meaning "self-devouring" and κύτος kýtos, meaning "hollow") is the natural, regulated, destructive mechanism of the cell that disassembles unnecessary or dysfunctional components.

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Azotemia (azot, "nitrogen" + -emia, "blood condition") is a medical condition characterized by abnormally high levels of nitrogen-containing compounds (such as urea, creatinine, various body waste compounds, and other nitrogen-rich compounds) in the blood.

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Bacterial circadian rhythm

Bacterial circadian rhythms, like other circadian rhythms, are endogenous "biological clocks" that have the following three characteristics: (a) in constant conditions (i.e. constant temperature and either constant light or constant darkness) they oscillate with a period that is close to, but not exactly, 24 hours in duration, (b) this "free-running" rhythm is temperature compensated, and (c) the rhythm will entrain to an appropriate environmental cycle.

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Biphasic and polyphasic sleep

Biphasic sleep (or diphasic, bimodal or bifurcated sleep) is the practice of sleeping during two periods over 24 hours, while polyphasic sleep refers to sleeping multiple times – usually more than two.

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Bipolar disorder

Bipolar disorder, previously known as manic depression, is a mental disorder that causes periods of depression and periods of abnormally elevated mood.

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Cell (biology)

The cell (from Latin cella, meaning "small room") is the basic structural, functional, and biological unit of all known living organisms.

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Charles Czeisler

Charles A. Czeisler (born 1952) is an American physician and sleep researcher.

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Chemical kinetics

Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes.

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Chronobiology is a field of biology that examines periodic (cyclic) phenomena in living organisms and their adaptation to solar- and lunar-related rhythms.

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Chronotherapy (treatment scheduling)

Chronotherapy, also called chronotherapeutics or chronotherapeutic drug delivery, refers to the use of circadian or other rhythmic cycles of a condition's symptoms and/or of the individual being treated in the application of therapy.

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Chronotype refers to the behavioral manifestation of underlying circadian rhythms of myriad physical processes.

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Circa, usually abbreviated c., ca. or ca (also circ. or cca.), means "approximately" in several European languages (and as a loanword in English), usually in reference to a date.

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Circadian clock

A circadian clock, or circadian oscillator, is a biochemical oscillator that cycles with a stable phase and is synchronized with solar time.

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Circadian rhythm sleep disorder

Circadian rhythm sleep disorders (CRSD) are a family of sleep disorders affecting (among other bodily processes) the timing of sleep.

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Circasemidian rhythm

In chronobiology, a circasemidian rhythm is a physiological arousal cycle that peaks twice in a 24-hour day.

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A circaseptan rhythm is a cycle consisting of 7 days in which many biological processes of life resolve.

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Cocaine, also known as coke, is a strong stimulant mostly used as a recreational drug.

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Colin Pittendrigh

Colin Pittendrigh (October 13, 1918 – March 19, 1996) "Colin Pittendrigh, 'Father of biological clock,' dies at 77", March 25, 1996, accessed April 9, 2011.

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Cone cell

Cone cells, or cones, are one of three types of photoreceptor cells in the retina of mammalian eyes (e.g. the human eye).

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Conifer cone

A cone (in formal botanical usage: strobilus, plural strobili) is an organ on plants in the division Pinophyta (conifers) that contains the reproductive structures.

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Cortisol is a steroid hormone, in the glucocorticoid class of hormones.

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Cryptochromes (from the Greek κρυπτός χρώμα, "hidden colour") are a class of flavoproteins that are sensitive to blue light.

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Cyanobacteria, also known as Cyanophyta, are a phylum of bacteria that obtain their energy through photosynthesis, and are the only photosynthetic prokaryotes able to produce oxygen.

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Delayed sleep phase disorder

Delayed sleep phase disorder (DSPD), more often known as delayed sleep phase syndrome and also as delayed sleep-wake phase disorder, is a chronic dysregulation of a person's circadian rhythm (biological clock), compared to those of the general population and societal norms.

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Derk-Jan Dijk

Derk-Jan Dijk (born 1958 in Zwollerkerspel, Netherlands) is a researcher of sleep and circadian rhythms.

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Diabetes mellitus

Diabetes mellitus (DM), commonly referred to as diabetes, is a group of metabolic disorders in which there are high blood sugar levels over a prolonged period.

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Diurnal cycle

A diurnal cycle is any pattern that recurs every 24 hours as a result of one full rotation of the Earth around its own axis.

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Diurnality is a form of plant or animal behavior characterized by activity during the day, with a period of sleeping, or other inactivity, at night.

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Drosophila is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit.

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Drosophila pseudoobscura

Drosophila pseudoobscura is a species of fruit fly, used extensively in lab studies of speciation.

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Endogeny (biology)

Endogenous substances and processes are those that originate from within an organism, tissue, or cell.

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Entrainment (chronobiology)

Entrainment, within the study of chronobiology, occurs when rhythmic physiological or behavioral events match their period to that of an environmental oscillation.

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Epigenetics is the study of heritable changes in gene function that do not involve changes in the DNA sequence.

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The epithalamus is a (dorsal) posterior segment of the diencephalon.

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The esophagus (American English) or oesophagus (British English), commonly known as the food pipe or gullet (gut), is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the stomach.

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Fatigue is a subjective feeling of tiredness that has a gradual onset.

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Franz Halberg

Franz Halberg (July 5, 1919 – June 9, 2013) was a scientist and one of the founders of modern chronobiology.

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Free-running sleep

Free-running sleep is a sleep pattern that is not adjusted (entrained) to the 24-hour cycle in nature nor to any artificial cycle.

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A fungus (plural: fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms.

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Gene D. Block

Gene D. Block (born August 17, 1948) is an American biologist, academic, inventor, and chancellor of the University of California, Los Angeles.

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Great Oxygenation Event

The Great Oxygenation Event, the beginning of which is commonly known in scientific media as the Great Oxidation Event (GOE, also called the Oxygen Catastrophe, Oxygen Crisis, Oxygen Holocaust, Oxygen Revolution, or Great Oxidation) was the biologically induced appearance of dioxygen (O2) in Earth's atmosphere.

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Ground squirrel

The ground squirrels are members of the squirrel family of rodents (Sciuridae) which generally live on or in the ground, rather than trees.

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Harvard University

Harvard University is a private Ivy League research university in Cambridge, Massachusetts.

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Heart rate

Heart rate is the speed of the heartbeat measured by the number of contractions of the heart per minute (bpm).

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A hormone (from the Greek participle “ὁρμῶ”, "to set in motion, urge on") is any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour.

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Human body temperature

Normal human body temperature, also known as normothermia or euthermia, is the typical temperature range found in humans.

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Human eye

The human eye is an organ which reacts to light and pressure.

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Human spaceflight

Human spaceflight (also referred to as crewed spaceflight or manned spaceflight) is space travel with a crew or passengers aboard the spacecraft.

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Hyperoxia occurs when cells, tissues and organs are exposed to an excess supply of oxygen (O2) or higher than normal partial pressure of oxygen.

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The hypothalamus(from Greek ὑπό, "under" and θάλαμος, thalamus) is a portion of the brain that contains a number of small nuclei with a variety of functions.

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Hypoxia (medical)

Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level.

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In photometry, illuminance is the total luminous flux incident on a surface, per unit area.

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Ingeborg Beling

Ingeborg Beling was a German ethologist from the early 20th century who worked in the field of chronobiology.

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Insomnia, also known as sleeplessness, is a sleep disorder where people have trouble sleeping.

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Intrinsically photosensitive retinal ganglion cells

Intrinsically photosensitive retinal ganglion cells (ipRGCs), also called photosensitive retinal ganglion cells (pRGC), or melanopsin-containing retinal ganglion cells (mRGCs), are a type of neuron in the retina of the mammalian eye.

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In radiometry, irradiance is the radiant flux (power) received by a surface per unit area.

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Jean-Jacques d'Ortous de Mairan

Jean-Jacques d'Ortous de Mairan (26 November 1678 – 20 February 1771) was a French geophysicist, astronomer and most notably, chronobiologist, was born in the town of Béziers on 26 November 1678.

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Jeffrey C. Hall

Jeffrey Connor Hall (born May 3, 1945) is an American geneticist and chronobiologist.

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Jet lag

Jet lag is a physiological condition which results from alterations to the body's circadian rhythms caused by rapid long-distance trans-meridian (east–west or west–east) travel.

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Joseph Takahashi

Joseph S. Takahashi is a Japanese American neurobiologist and geneticist.

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kaiA is a gene in the "kaiABC" gene cluster that plays a crucial role in the regulation of bacterial circadian rhythms, such as in the cyanobacterium Synechococcus elongatus.

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KaiB is a gene located in the highly-conserved kaiABC gene cluster of various cyanobacterial species.

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KaiC is a gene belonging to the KaiABC gene cluster (with KaiB, and KaiC) that, together, regulate bacterial circadian rhythms, specifically in cyanobacteria.

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Latin (Latin: lingua latīna) is a classical language belonging to the Italic branch of the Indo-European languages.

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Light effects on circadian rhythm

Most animals and other organisms have "built in clocks" in their brains that regulate the timing of biological processes and daily behavior.

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Light in school buildings

Light in school buildings traditionally is from a combination of daylight and electric light to illuminate learning spaces (e.g. classrooms, labs, studios, etc.), hallways, cafeterias, offices and other interior areas.

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The liver, an organ only found in vertebrates, detoxifies various metabolites, synthesizes proteins, and produces biochemicals necessary for digestion.

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The lungs are the primary organs of the respiratory system in humans and many other animals including a few fish and some snails.

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Mammals are the vertebrates within the class Mammalia (from Latin mamma "breast"), a clade of endothermic amniotes distinguished from reptiles (including birds) by the possession of a neocortex (a region of the brain), hair, three middle ear bones, and mammary glands.

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Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury.

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Melanopsin is a type of photopigment belonging to a larger family of light-sensitive retinal proteins called opsins and encoded by the gene Opn4.

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Melatonin, also known as N-acetyl-5-methoxy tryptamine, is a hormone that is produced by the pineal gland in animals and regulates sleep and wakefulness.

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Metabolism (from μεταβολή metabolē, "change") is the set of life-sustaining chemical transformations within the cells of organisms.

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A metabolite is the intermediate end product of metabolism.

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Metal-halide lamp

A metal-halide lamp is an electrical lamp that produces light by an electric arc through a gaseous mixture of vaporized mercury and metal halides (compounds of metals with bromine or iodine).

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Michael Rosbash

Michael Morris Rosbash (born March 7, 1944) is an American geneticist and chronobiologist.

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Michael W. Young

Michael Warren Young (born March 28, 1949) is an American biologist and geneticist.

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Mimosa pudica

Mimosa pudica (from pudica "shy, bashful or shrinking"; also called sensitive plant, sleepy plant, action plant, Dormilones, touch-me-not, shameplant, or shy plant) is a creeping annual or perennial flowering plant of the pea/legume family Fabaceae and Magnoliopsida taxon, often grown for its curiosity value: the compound leaves fold inward and droop when touched or shaken, defending themselves from harm, and re-open a few minutes later.

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Monarch butterfly

The monarch butterfly or simply monarch (Danaus plexippus) is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae.

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Nathaniel Kleitman

Nathaniel Kleitman (April 26, 1895 Kishinev – August 13, 1999 Los Angeles) was a physiologist and sleep researcher who served as Professor Emeritus in Physiology at the University of Chicago.

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National Transportation Safety Board

The National Transportation Safety Board (NTSB) is an independent U.S. government investigative agency responsible for civil transportation accident investigation.

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Neural oscillation

Neural oscillations, or brainwaves, are rhythmic or repetitive patterns of neural activity in the central nervous system.

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Nobel Prize in Physiology or Medicine

The Nobel Prize in Physiology or Medicine (Nobelpriset i fysiologi eller medicin), administered by the Nobel Foundation, is awarded once a year for outstanding discoveries in the fields of life sciences and medicine.

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Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day.

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Non-24-hour sleep–wake disorder

Non-24-hour sleep–wake disorder (non-24), is one of several chronic circadian rhythm sleep disorders (CRSDs).

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Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have a negative effect on health.

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Optic lobe (arthropods)

The optic(al) lobe of arthropods is a structure of the protocerebrum that sits behind the arthropod eye (mostly compound eyes) and is responsible for the processing of the visual information.

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Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states.

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Oxidative stress

Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage.

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The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates.

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The PER1 gene encodes the period circadian protein homolog 1 protein in humans.

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PER2 is a protein in mammals encoded by the PER2 gene.

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The PER3 gene encodes the period circadian protein homolog 3 protein in humans.

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Period (gene)

Period (per) is a gene located on the X chromosome of Drosophila melanogaster.

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Phase response curve

A phase response curve (PRC) illustrates the transient change in the cycle period of an oscillation induced by a perturbation as a function of the phase at which it is received.

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A pheromone (from Ancient Greek φέρω phero "to bear" and hormone, from Ancient Greek ὁρμή "impetus") is a secreted or excreted chemical factor that triggers a social response in members of the same species.

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Photoperiodism is the physiological reaction of organisms to the length of day or night.

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Photoreceptor cell

A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction.

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Pineal gland

The pineal gland, also known as the conarium, kônarion or epiphysis cerebri, is a small endocrine gland in the vertebrate brain.

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Plants are mainly multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae.

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Polyphagia or hyperphagia is excessive hunger or increased appetite.

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Porcupines are rodents with a coat of sharp spines, or quills, that protect against predators.

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Power nap

A power nap is a short sleep which terminates prior the occurrence of deep sleep (slow-wave sleep (SWS)), intended to quickly revitalize the subject.

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A prokaryote is a unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle.

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A pupa (pūpa, "doll"; plural: pūpae) is the life stage of some insects undergoing transformation between immature and mature stages.

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Q10 (temperature coefficient)

The Q10 temperature coefficient is a measure of the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10 °C.

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Quail is a collective name for several genera of mid-sized birds generally placed in the order Galliformes.

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Reactive oxygen species

Reactive oxygen species (ROS) are chemically reactive chemical species containing oxygen.

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Redox (short for reduction–oxidation reaction) (pronunciation: or) is a chemical reaction in which the oxidation states of atoms are changed.

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The reindeer (Rangifer tarandus), also known as the caribou in North America, is a species of deer with circumpolar distribution, native to Arctic, sub-Arctic, tundra, boreal and mountainous regions of northern Europe, Siberia and North America.

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The repressilator is a synthetic genetic regulatory network consisting of a ring-oscillator with three genes, each expressing a protein that represses the next gene in the loop.

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Reticular formation

The reticular formation is a set of interconnected nuclei that are located throughout the brainstem.

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The retina is the innermost, light-sensitive "coat", or layer, of shell tissue of the eye of most vertebrates and some molluscs.

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Retinohypothalamic tract

The retinohypothalamic tract (RHT) is a photic neural input pathway involved in the circadian rhythms of mammals.

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Rev-ErbA alpha

Rev-ErbA alpha also known as NR1D1 (nuclear receptor subfamily 1, group D, member 1), is a protein that in humans is encoded by the NR1D1 gene.

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Rock ptarmigan

The rock ptarmigan (Lagopus muta) is a medium-sized gamebird in the grouse family.

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Rod cell

Rod cells are photoreceptor cells in the retina of the eye that can function in less intense light than the other type of visual photoreceptor, cone cells.

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Ronald J. Konopka

Ronald J. Konopka (1947-2015) was an American geneticist who studied chronobiology.

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Seymour Benzer

Seymour Benzer (October 15, 1921 – November 30, 2007) was an American physicist, molecular biologist and behavioral geneticist.

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Shift work

Shift work is an employment practice designed to make use of, or provide service across, all 24 hours of the clock each day of the week (often abbreviated as 24/7).

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Sleep is a naturally recurring state of mind and body, characterized by altered consciousness, relatively inhibited sensory activity, inhibition of nearly all voluntary muscles, and reduced interactions with surroundings.

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Sleep disorder

A sleep disorder, or somnipathy, is a medical disorder of the sleep patterns of a person or animal.

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Sleep in non-human animals

Sleep in non-human animals refers to a behavioral and physiological state characterized by altered consciousness, reduced responsiveness to external stimuli, and homeostatic regulation.

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Sleep onset latency

In sleep science, sleep onset latency (SOL) is the length of time that it takes to accomplish the transition from full wakefulness to sleep, normally to the lightest of the non-REM sleep stages.

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Sodium-vapor lamp

A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nm.

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Solar time

Solar time is a calculation of the passage of time based on the position of the Sun in the sky.

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The genus Spalax contains the blind, fossorial, or subterranean mole rats, which are one of several types of rodents that are called "mole rats".

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The spleen is an organ found in virtually all vertebrates.

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Spodoptera littoralis

Spodoptera littoralis, also referred to as the African cotton leafworm or Egyptian cotton leafworm or Mediterranean Brocade, is a species of moth in the family Noctuidae.

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Stefania Follini

Stefania Follini (born 16 August 1961) is an Italian interior designer.

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Stem cell

Stem cells are biological cells that can differentiate into other types of cells and can divide to produce more of the same type of stem cells.

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Suprachiasmatic nucleus

The suprachiasmatic nucleus or nuclei (SCN) is a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm.

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Svalbard (prior to 1925 known by its Dutch name Spitsbergen, still the name of its largest island) is a Norwegian archipelago in the Arctic Ocean.

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Tamarind (Tamarindus indica) is a leguminous tree in the family Fabaceae indigenous to tropical Africa.

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The Washington Post

The Washington Post is a major American daily newspaper founded on December 6, 1877.

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The thymus is a specialized primary lymphoid organ of the immune system.

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Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of Earth.

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Time zone

A time zone is a region of the globe that observes a uniform standard time for legal, commercial, and social purposes.

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TOC1 (gene)

Timing of CAB expression 1 is a protein that in Arabidopsis thaliana is encoded by the TOC1 gene.

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Traditional Chinese medicine

Traditional Chinese medicine (TCM) is a style of traditional medicine built on a foundation of more than 2,500 years of Chinese medical practice that includes various forms of herbal medicine, acupuncture, massage (tui na), exercise (qigong), and dietary therapy, but recently also influenced by modern Western medicine.

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Ultradian rhythm

In chronobiology, an ultradian rhythm is a recurrent period or cycle repeated throughout a 24-hour day.

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Ultraviolet (UV) is electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays.

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Unfolded protein response

The unfolded protein response (UPR) is a cellular stress response related to the endoplasmic reticulum (ER) stress.

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University of Tromsø

The University of Tromsø - The Arctic University of Norway (Universitetet i Tromsø – Norges arktiske universitet; is the world's northernmost university. Located in the city of Tromsø, Norway, it was established in 1968, and opened in 1972. It is one of eight universities in Norway. The University of Tromsø is the largest research and educational institution in northern Norway. The University's location makes it a natural venue for the development of studies of the region's natural environment, culture, and society. The main focus of the University's activities is on the Auroral light research, Space science, Fishery science, Biotechnology, Linguistics, Multicultural societies, Saami culture, Telemedicine, epidemiology and a wide spectrum of Arctic research projects. The close vicinity of the Norwegian Polar Institute, the Norwegian Institute of Marine Research and the Polar Environmental Centre gives Tromsø added weight and importance as an international centre for Arctic research. Research activities, however, are not limited to Arctic studies. The University researchers work within a broad range of subjects and are recognised both nationally and internationally. On 1 January 2009, the University of Tromsø merged with Tromsø University College. On 1 August 2013, the university merged with Finnmark University College to form Universitetet i Tromsø – Norges arktiske universitet (The University of Tromsø – The Arctic University of Norway), thereby adding campuses in Alta, Hammerfest and Kirkenes. On 1 January 2016, Narvik University College and Harstad University College merged with UiT - The Arctic University of Norway. As of January 2016 the university now has six campus locations in northern Norway, the main campus being Tromsø.

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Uremia is the condition of having "urea in the blood".

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A zeitgeber is any external or environmental cue that entrains or synchronizes an organism's biological rhythms to the Earth's 24-hour light/dark cycle and 12-month cycle.

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13th century

As a means of recording the passage of time, the 13th century was the century which lasted from January 1, 1201 through December 31, 1300 in accordance with the Julian calendar in the Common Era.

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70th parallel north

The 70th parallel north is a circle of latitude that is 70 degrees north of the Earth's equatorial plane, in the Arctic.

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78th parallel north

The 78th parallel north is a circle of latitude that is 78 degrees north of the Earth's equatorial plane, in the Arctic.

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[1] https://en.wikipedia.org/wiki/Circadian_rhythm

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