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During critical illness, a state of adrenal insufficiency and tissue resistance to corticosteroids may occur. This has been termed critical illness–related corticosteroid insufficiency. Treatment with corticosteroids might be most beneficial in those with septic shock and early severe ARDS, whereas its role in others such as those with pancreatitis or severe pneumonia is unclear. However, the exact way of determining corticosteroid insufficiency remains problematic. It should be suspected in those poorly responding to resuscitation with fluids and vasopressors. Neither ACTH stimulation testing nor random cortisol levels are recommended to confirm the diagnosis. The method of stopping glucocorticoid drugs is variable, and it is unclear whether they should be slowly decreased or simply abruptly stopped. However, the 2016 Surviving Sepsis Campaign recommended to taper steroids when vasopressors are no longer needed.
Anesthesia
A target tidal volume of 6 mL/kg of predicted body weight (PBW) and a plateau pressure less than 30 cm H2O is recommended for those who require ventilation due to sepsis-induced severe ARDS. High positive end expiratory pressure (PEEP) is recommended for moderate to severe ARDS in sepsis as it opens more lung units for oxygen exchange. Predicted body weight is calculated based on sex and height, and tools for this are available. Recruitment maneuvers may be necessary for severe ARDS by briefly raising the transpulmonary pressure. It is recommended that the head of the bed be raised if possible to improve ventilation. However, β2 adrenergic receptor agonists are not recommended to treat ARDS because it may reduce survival rates and precipitate abnormal heart rhythms. A spontaneous breathing trial using continuous positive airway pressure (CPAP), T piece, or inspiratory pressure augmentation can help reduce the duration of ventilation. Minimizing intermittent or continuous sedation helps reduce the duration of mechanical ventilation. | Sepsis | Wikipedia | 418 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
General anesthesia is recommended for people with sepsis who require surgical procedures to remove the infective source. Usually, inhalational and intravenous anesthetics are used. Requirements for anesthetics may be reduced in sepsis. Inhalational anesthetics can reduce the level of proinflammatory cytokines, altering leukocyte adhesion and proliferation, inducing apoptosis (cell death) of the lymphocytes, possibly with a toxic effect on mitochondrial function. Although etomidate has a minimal effect on the cardiovascular system, it is often not recommended as a medication to help with intubation in this situation due to concerns it may lead to poor adrenal function and an increased risk of death. The small amount of evidence there is, however, has not found a change in the risk of death with etomidate.
Paralytic agents are not suggested for use in sepsis cases in the absence of ARDS, as a growing body of evidence points to reduced durations of mechanical ventilation, ICU and hospital stays. However, paralytic use in ARDS cases remains controversial. When appropriately used, paralytics may aid successful mechanical ventilation, however, evidence has also suggested that mechanical ventilation in severe sepsis does not improve oxygen consumption and delivery.
Source control
Source control refers to physical interventions to control a focus of infection and reduce conditions favorable to microorganism growth or host defense impairment, such as drainage of pus from an abscess. It is one of the oldest procedures for the control of infections, giving rise to the Latin phrase Ubi pus, ibi evacua, and remains important despite the emergence of more modern treatments. | Sepsis | Wikipedia | 353 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Early goal directed therapy
Early goal directed therapy (EGDT) is an approach to the management of severe sepsis during the initial 6 hours after diagnosis. It is a step-wise approach, with the physiologic goal of optimizing cardiac preload, afterload, and contractility. It includes giving early antibiotics. EGDT also involves monitoring of hemodynamic parameters and specific interventions to achieve key resuscitation targets which include maintaining a central venous pressure between 8–12 mmHg, a mean arterial pressure of between 65 and 90 mmHg, a central venous oxygen saturation (ScvO2) greater than 70% and a urine output of greater than 0.5 mL/kg/hour. The goal is to optimize oxygen delivery to tissues and achieve a balance between systemic oxygen delivery and demand. An appropriate decrease in serum lactate may be equivalent to ScvO2 and easier to obtain.
In the original trial, early goal-directed therapy was found to reduce mortality from 46.5% to 30.5% in those with sepsis, and the Surviving Sepsis Campaign has been recommending its use. However, three more recent large randomized control trials (ProCESS, ARISE, and ProMISe), did not demonstrate a 90-day mortality benefit of early goal-directed therapy when compared to standard therapy in severe sepsis. It is likely that some parts of EGDT are more important than others. Following these trials the use of EGDT is still considered reasonable.
Newborns
Neonatal sepsis can be difficult to diagnose as newborns may be asymptomatic. If a newborn shows signs and symptoms suggestive of sepsis, antibiotics are immediately started and are either changed to target a specific organism identified by diagnostic testing or discontinued after an infectious cause for the symptoms has been ruled out. Despite early intervention, death occurs in 13% of children who develop septic shock, with the risk partly based on other health problems. For those without multiple organ system failures or who require only one inotropic agent, mortality is low.
Other
Treating fever in sepsis, including people in septic shock, has not been associated with any improvement in mortality over a period of 28 days. Treatment of fever still occurs for other reasons.
A 2012 Cochrane review concluded that N-acetylcysteine does not reduce mortality in those with SIRS or sepsis and may even be harmful. | Sepsis | Wikipedia | 497 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Recombinant activated protein C (drotrecogin alpha) was originally introduced for severe sepsis (as identified by a high APACHE II score), where it was thought to confer a survival benefit. However, subsequent studies showed that it increased adverse events—bleeding risk in particular—and did not decrease mortality. It was removed from sale in 2011. Another medication known as eritoran also has not shown benefit.
In those with high blood sugar levels, insulin to bring it down to 7.8–10 mmol/L (140–180 mg/dL) is recommended with lower levels potentially worsening outcomes. Glucose levels taken from capillary blood should be interpreted with care because such measurements may not be accurate. If a person has an arterial catheter, arterial blood is recommended for blood glucose testing. | Sepsis | Wikipedia | 168 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Intermittent or continuous renal replacement therapy may be used if indicated. However, sodium bicarbonate is not recommended for a person with lactic acidosis secondary to hypoperfusion. Low-molecular-weight heparin (LMWH), unfractionated heparin (UFH), and mechanical prophylaxis with intermittent pneumatic compression devices are recommended for any person with sepsis at moderate to high risk of venous thromboembolism. Stress ulcer prevention with proton-pump inhibitor (PPI) and H2 antagonist are useful in a person with risk factors of developing upper gastrointestinal bleeding (UGIB) such as on mechanical ventilation for more than 48 hours, coagulation disorders, liver disease, and renal replacement therapy. Achieving partial or full enteral feeding (delivery of nutrients through a feeding tube) is chosen as the best approach to provide nutrition for a person who is contraindicated for oral intake or unable to tolerate orally in the first seven days of sepsis when compared to intravenous nutrition. However, omega-3 fatty acids are not recommended as immune supplements for a person with sepsis or septic shock. The usage of prokinetic agents such as metoclopramide, domperidone, and erythromycin are recommended for those who are septic and unable to tolerate enteral feeding. However, these agents may precipitate prolongation of the QT interval and consequently provoke a ventricular arrhythmia such as torsades de pointes. The usage of prokinetic agents should be reassessed daily and stopped if no longer indicated.
People in sepsis may have micronutrient deficiencies, including low levels of vitamin C. Reviews mention that an intake of 3.0 g/day, which requires intravenous administration, may be needed to maintain normal plasma concentrations in people with sepsis or severe burn injury.
Prognosis
Sepsis will prove fatal in approximately 24.4% of people, and septic shock will prove fatal in 34.7% of people within 30 days (32.2% and 38.5% after 90 days).
Lactate is a useful method of determining prognosis, with those who have a level greater than 4 mmol/L having a mortality of 40% and those with a level of less than 2 mmol/L having a mortality of less than 15%. | Sepsis | Wikipedia | 505 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
There are a number of prognostic stratification systems, such as APACHE II and Mortality in Emergency Department Sepsis. APACHE II factors in the person's age, underlying condition, and various physiologic variables to yield estimates of the risk of dying of severe sepsis. Of the individual covariates, the severity of the underlying disease most strongly influences the risk of death. Septic shock is also a strong predictor of short- and long-term mortality. Case-fatality rates are similar for culture-positive and culture-negative severe sepsis. The Mortality in Emergency Department Sepsis (MEDS) score is simpler and useful in the emergency department environment.
Some people may experience severe long-term cognitive decline following an episode of severe sepsis, but the absence of baseline neuropsychological data in most people with sepsis makes the incidence of this difficult to quantify or study.
Epidemiology
Sepsis causes millions of deaths globally each year and is the most common cause of death in people who have been hospitalized. The number of new cases worldwide of sepsis is estimated to be 18 million cases per year. In the United States sepsis affects approximately 3 in 1,000 people, and severe sepsis contributes to more than 200,000 deaths per year.
Sepsis occurs in 1–2% of all hospitalizations and accounts for as much as 25% of ICU bed utilization. Due to it rarely being reported as a primary diagnosis (often being a complication of cancer or other illness), the incidence, mortality, and morbidity rates of sepsis are likely underestimated. A study of U.S. states found approximately 651 hospital stays per 100,000 population with a sepsis diagnosis in 2010. It is the second-leading cause of death in non-coronary intensive care unit (ICU) and the tenth-most-common cause of death overall (the first being heart disease). Children under 12 months of age and elderly people have the highest incidence of severe sepsis. Among people from the U.S. who had multiple sepsis hospital admissions in 2010, those who were discharged to a skilled nursing facility or long-term care following the initial hospitalization were more likely to be readmitted than those discharged to another form of care. A study of 18 U.S. states found that amongst people with Medicare in 2011, sepsis was the second most common principal reason for readmission within 30 days. | Sepsis | Wikipedia | 505 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Several medical conditions increase a person's susceptibility to infection and developing sepsis. Common sepsis risk factors include age (especially the very young and old); conditions that weaken the immune system such as cancer, diabetes, or the absence of a spleen; and major trauma and burns.
From 1979 to 2000, data from the United States National Hospital Discharge Survey showed that the incidence of sepsis increased fourfold, to 240 cases per 100,000 population, with a higher incidence in men when compared to women. However, the global prevalence of sepsis has been estimated to be higher in women. During the same time frame, the in-hospital case fatality rate was reduced from 28% to 18%. However, according to the nationwide inpatient sample from the United States, the incidence of severe sepsis increased from 200 per 10,000 population in 2003 to 300 cases in 2007 for a population aged more than 18 years. The incidence rate is particularly high among infants, with an incidence of 500 cases per 100,000 population. Mortality related to sepsis increases with age, from less than 10% in the age group of 3 to 5 years to 60% by sixth decade of life. The increase in the average age of the population, alongside the presence of more people with chronic diseases or on immunosuppressive medications, and also the increase in the number of invasive procedures being performed, has led to an increased rate of sepsis.
History
The term "σήψις" (sepsis) was introduced by Hippocrates in the fourth century BC, and it meant the process of decay or decomposition of organic matter. In the eleventh century, Avicenna used the term "blood rot" for diseases linked to severe purulent process. Though severe systemic toxicity had already been observed, it was only in the 19th century that the specific term – sepsis – was used for this condition. | Sepsis | Wikipedia | 389 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
The terms "septicemia", also spelled "septicaemia", and "blood poisoning" referred to the microorganisms or their toxins in the blood. The International Statistical Classification of Diseases and Related Health Problems (ICD) version 9, which was in use in the US until 2013, used the term septicemia with numerous modifiers for different diagnoses, such as "Streptococcal septicemia". All those diagnoses have been converted to sepsis, again with modifiers, in ICD-10, such as "Sepsis due to streptococcus".
The current terms are dependent on the microorganism that is present: bacteremia if bacteria are present in the blood at abnormal levels and are the causative issue, viremia for viruses, and fungemia for a fungus.
By the end of the 19th century, it was widely believed that microbes produced substances that could injure the mammalian host and that soluble toxins released during infection caused the fever and shock that were commonplace during severe infections. Pfeiffer coined the term endotoxin at the beginning of the 20th century to denote the pyrogenic principle associated with Vibrio cholerae. It was soon realized that endotoxins were expressed by most and perhaps all gram-negative bacteria. The lipopolysaccharide character of enteric endotoxins was elucidated in 1944 by Shear. The molecular character of this material was determined by Luderitz et al. in 1973.
It was discovered in 1965 that a strain of C3H/HeJ mouse was immune to the endotoxin-induced shock. The genetic locus for this effect was dubbed Lps. These mice were also found to be hyper-susceptible to infection by gram-negative bacteria. These observations were finally linked in 1998 by the discovery of the toll-like receptor gene 4 (TLR 4). Genetic mapping work, performed over five years, showed that TLR4 was the sole candidate locus within the Lps critical region; this strongly implied that a mutation within TLR4 must account for the lipopolysaccharide resistance phenotype. The defect in the TLR4 gene that led to the endotoxin-resistant phenotype was discovered to be due to a mutation in the cytoplasm. | Sepsis | Wikipedia | 488 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Controversy occurred in the scientific community over the use of mouse models in research into sepsis in 2013 when scientists published a review of the mouse immune system compared to the human immune system and showed that on a systems level, the two worked very differently; the authors noted that as of the date of their article over 150 clinical trials of sepsis had been conducted in humans, almost all of them supported by promising data in mice and that all of them had failed. The authors called for abandoning the use of mouse models in sepsis research; others rejected that but called for more caution in interpreting the results of mouse studies, and more careful design of preclinical studies. One approach is to rely more on studying biopsies and clinical data from people who have had sepsis, to try to identify biomarkers and drug targets for intervention.
Society and culture
Economics
Sepsis was the most expensive condition treated in United States' hospital stays in 2013, at an aggregate cost of $23.6 billion for nearly 1.3 million hospitalizations. Costs for sepsis hospital stays more than quadrupled since 1997 with an 11.5 percent annual increase. By payer, it was the most costly condition billed to Medicare and the uninsured, the second-most costly billed to Medicaid, and the fourth-most costly billed to private insurance.
Education
A large international collaboration entitled the "Surviving Sepsis Campaign" was established in 2002 to educate people about sepsis and to improve outcomes with sepsis. The Campaign has published an evidence-based review of management strategies for severe sepsis, with the aim to publish a complete set of guidelines in subsequent years. The guidelines were updated in 2016 and again in 2021.
Sepsis Alliance is a charitable organization based in the United States that was created to raise sepsis awareness among both the general public and healthcare professionals.
Research | Sepsis | Wikipedia | 374 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Some authors suggest that initiating sepsis by the normally mutualistic (or neutral) members of the microbiome may not always be an accidental side effect of the deteriorating host immune system. Rather it is often an adaptive microbial response to a sudden decline of host survival chances. Under this scenario, the microbe species provoking sepsis benefit from monopolizing the future cadaver, utilizing its biomass as decomposers, and then transmitting through soil or water to establish mutualistic relations with new individuals. The bacteria Streptococcus pneumoniae, Escherichia coli, Proteus spp., Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella spp., Clostridium spp., Lactobacillus spp., Bacteroides spp. and the fungi Candida spp. are all capable of such a high level of phenotypic plasticity. Not all cases of sepsis arise through such adaptive microbial strategy switches.
Paul E. Marik's "Marik protocol", also known as the "HAT" protocol, proposed a combination of hydrocortisone, vitamin C, and thiamine as a treatment for preventing sepsis for people in intensive care. Marik's initial research, published in 2017, showed dramatic evidence of benefit, leading to the protocol becoming popular among intensive care physicians, especially after the protocol received attention on social media and National Public Radio, leading to criticism of science by press conference from the wider medical community. Subsequent independent research failed to replicate Marik's positive results, indicating the possibility that they had been compromised by bias. A systematic review of trials in 2021 found that the claimed benefits of the protocol could not be confirmed.
Overall, the evidence for any role of vitamin C in the treatment of sepsis remains unclear . | Sepsis | Wikipedia | 375 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula FeSO4·xH2O. These compounds exist most commonly as the heptahydrate (x = 7) but several values for x are known. The hydrated form is used medically to treat or prevent iron deficiency, and also for industrial applications. Known since ancient times as copperas and as green vitriol (vitriol is an archaic name for hydrated sulfate minerals), the blue-green heptahydrate (hydrate with 7 molecules of water) is the most common form of this material. All the iron(II) sulfates dissolve in water to give the same aquo complex [Fe(H2O)6]2+, which has octahedral molecular geometry and is paramagnetic. The name copperas dates from times when the copper(II) sulfate was known as blue copperas, and perhaps in analogy, iron(II) and zinc sulfate were known respectively as green and white copperas.
It is on the World Health Organization's List of Essential Medicines. In 2022, it was the 107th most commonly prescribed medication in the United States, with more than 6million prescriptions.
Uses
Industrially, ferrous sulfate is mainly used as a precursor to other iron compounds. It is a reducing agent, and as such is useful for the reduction of chromate in cement to less toxic Cr(III) compounds. Historically ferrous sulfate was used in the textile industry for centuries as a dye fixative. It is used historically to blacken leather and as a constituent of iron gall ink. The preparation of sulfuric acid ('oil of vitriol') by the distillation of green vitriol (iron(II) sulfate) has been known for at least 700 years.
Medical use
Plant growth
Iron(II) sulfate is sold as ferrous sulfate, a soil amendment for lowering the pH of a high alkaline soil so that plants can access the soil's nutrients. | Iron(II) sulfate | Wikipedia | 436 | 158405 | https://en.wikipedia.org/wiki/Iron%28II%29%20sulfate | Physical sciences | Sulfuric oxyanions | Chemistry |
In horticulture it is used for treating iron chlorosis. Although not as rapid-acting as ferric EDTA, its effects are longer-lasting. It can be mixed with compost and dug into the soil to create a store which can last for years. Ferrous sulfate can be used as a lawn conditioner. It can also be used to eliminate silvery thread moss in golf course putting greens.
Pigment and craft
Ferrous sulfate can be used to stain concrete and some limestones and sandstones a yellowish rust color.
Woodworkers use ferrous sulfate solutions to color maple wood a silvery hue.
Green vitriol is also a useful reagent in the identification of mushrooms.
Historical uses
Ferrous sulfate was used in the manufacture of inks, most notably iron gall ink, which was used from the Middle Ages until the end of the 18th century. Chemical tests made on the Lachish letters () showed the possible presence of iron. It is thought that oak galls and copperas may have been used in making the ink on those letters. It also finds use in wool dyeing as a mordant. Harewood, a material used in marquetry and parquetry since the 17th century, is also made using ferrous sulfate.
Two different methods for the direct application of indigo dye were developed in England in the 18th century and remained in use well into the 19th century. One of these, known as china blue, involved iron(II) sulfate. After printing an insoluble form of indigo onto the fabric, the indigo was reduced to leuco-indigo in a sequence of baths of ferrous sulfate (with reoxidation to indigo in air between immersions). The china blue process could make sharp designs, but it could not produce the dark hues of other methods.
In the second half of the 1850s ferrous sulfate was used as a photographic developer for collodion process images. | Iron(II) sulfate | Wikipedia | 400 | 158405 | https://en.wikipedia.org/wiki/Iron%28II%29%20sulfate | Physical sciences | Sulfuric oxyanions | Chemistry |
Hydrates
Iron(II) sulfate can be found in various states of hydration, and several of these forms exist in nature or were created synthetically.
FeSO4·H2O (mineral: szomolnokite, relatively rare, monoclinic)
FeSO4·H2O (synthetic compound stable at pressures exceeding 6.2 GPa, triclinic)
FeSO4·4H2O (mineral: rozenite, white, relatively common, may be dehydration product of melanterite, monoclinic)
FeSO4·5H2O (mineral: siderotil, relatively rare, triclinic)
FeSO4·6H2O (mineral: ferrohexahydrite, very rare, monoclinic)
FeSO4·7H2O (mineral: melanterite, blue-green, relatively common, monoclinic)
The tetrahydrate is stabilized when the temperature of aqueous solutions reaches . At these solutions form both the tetrahydrate and monohydrate.
Mineral forms are found in oxidation zones of iron-bearing ore beds, e.g. pyrite, marcasite, chalcopyrite, etc. They are also found in related environments, like coal fire sites. Many rapidly dehydrate and sometimes oxidize. Numerous other, more complex (either basic, hydrated, and/or containing additional cations) Fe(II)-bearing sulfates exist in such environments, with copiapite being a common example.
Production and reactions
In the finishing of steel prior to plating or coating, the steel sheet or rod is passed through pickling baths of sulfuric acid. This treatment produces large quantities of iron(II) sulfate as a by-product.
Another source of large amounts results from the production of titanium dioxide from ilmenite via the sulfate process.
Ferrous sulfate is also prepared commercially by oxidation of pyrite:
It can be produced by displacement of metals less reactive than Iron from solutions of their sulfate:
Reactions
Upon dissolving in water, ferrous sulfates form the metal aquo complex [Fe(H2O)6]2+, which is an almost colorless, paramagnetic ion. | Iron(II) sulfate | Wikipedia | 478 | 158405 | https://en.wikipedia.org/wiki/Iron%28II%29%20sulfate | Physical sciences | Sulfuric oxyanions | Chemistry |
On heating, iron(II) sulfate first loses its water of crystallization and the original green crystals are converted into a white anhydrous solid. When further heated, the anhydrous material decomposes into sulfur dioxide and sulfur trioxide, leaving a reddish-brown iron(III) oxide. Thermolysis of iron(II) sulfate begins at about .
->[\Delta]
Like other iron(II) salts, iron(II) sulfate is a reducing agent. For example, it reduces nitric acid to nitrogen monoxide and chlorine to chloride:
Its mild reducing power is of value in organic synthesis. It is used as the iron catalyst component of Fenton's reagent.
Ferrous sulfate can be detected by the cerimetric method, which is the official method of the Indian Pharmacopoeia. This method includes the use of ferroin solution showing a red to light green colour change during titration. | Iron(II) sulfate | Wikipedia | 199 | 158405 | https://en.wikipedia.org/wiki/Iron%28II%29%20sulfate | Physical sciences | Sulfuric oxyanions | Chemistry |
A Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period and amplitude. Cepheids are important cosmic benchmarks for scaling galactic and extragalactic distances; a strong direct relationship exists between a Cepheid variable's luminosity and its pulsation period.
This characteristic of classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt after studying thousands of variable stars in the Magellanic Clouds. The discovery establishes the true luminosity of a Cepheid by observing its pulsation period. This in turn gives the distance to the star by comparing its known luminosity to its observed brightness, calibrated by directly observing the parallax distance to the closest Cepheids such as RS Puppis and Polaris.
Cepheids change brightness due to the κ–mechanism, which occurs when opacity in a star increases with temperature rather than decreasing. The main gas involved is thought to be helium. The cycle is driven by the fact doubly ionized helium, the form adopted at high temperatures, is more opaque than singly ionized helium. As a result, the outer layer of the star cycles between being compressed, which heats the helium until it becomes doubly ionized and (due to opacity) absorbs enough heat to expand; and expanded, which cools the helium until it becomes singly ionized and (due to transparency) cools and collapses again. Cepheid variables become dimmest during the part of the cycle when the helium is doubly ionized.
Etymology
The term Cepheid originates from the star Delta Cephei in the constellation Cepheus, which was one of the early discoveries.
History | Cepheid variable | Wikipedia | 379 | 158530 | https://en.wikipedia.org/wiki/Cepheid%20variable | Physical sciences | Stellar astronomy | null |
On September 10, 1784, Edward Pigott detected the variability of Eta Aquilae, the first known representative of the class of classical Cepheid variables. The eponymous star for classical Cepheids, Delta Cephei, was discovered to be variable by John Goodricke a few months later. The number of similar variables grew to several dozen by the end of the 19th century, and they were referred to as a class as Cepheids. Most of the Cepheids were known from the distinctive light curve shapes with the rapid increase in brightness and a hump, but some with more symmetrical light curves were known as Geminids after the prototype ζ Geminorum.
A relationship between the period and luminosity for classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt in an investigation of thousands of variable stars in the Magellanic Clouds. She published it in 1912 with further evidence. Cepheid variables were found to show radial velocity variation with the same period as the luminosity variation, and initially this was interpreted as evidence that these stars were part of a binary system. However, in 1914, Harlow Shapley demonstrated that this idea should be abandoned. Two years later, Shapley and others had discovered that Cepheid variables changed their spectral types over the course of a cycle.
In 1913, Ejnar Hertzsprung attempted to find distances to 13 Cepheids using their motion through the sky. (His results would later require revision.) In 1918, Harlow Shapley used Cepheids to place initial constraints on the size and shape of the Milky Way and of the placement of the Sun within it. In 1924, Edwin Hubble established the distance to classical Cepheid variables in the Andromeda Galaxy, until then known as the "Andromeda Nebula" and showed that those variables were not members of the Milky Way. Hubble's finding settled the question raised in the "Great Debate" of whether the Milky Way represented the entire Universe or was merely one of many galaxies in the Universe.
In 1929, Hubble and Milton L. Humason formulated what is now known as Hubble's law by combining Cepheid distances to several galaxies with Vesto Slipher's measurements of the speed at which those galaxies recede from us. They discovered that the Universe is expanding, confirming the theories of Georges Lemaître. | Cepheid variable | Wikipedia | 498 | 158530 | https://en.wikipedia.org/wiki/Cepheid%20variable | Physical sciences | Stellar astronomy | null |
In the mid 20th century, significant problems with the astronomical distance scale were resolved by dividing the Cepheids into different classes with very different properties. In the 1940s, Walter Baade recognized two separate populations of Cepheids (classical and type II). Classical Cepheids are younger and more massive population I stars, whereas type II Cepheids are older, fainter Population II stars. Classical Cepheids and type II Cepheids follow different period-luminosity relationships. The luminosity of type II Cepheids is, on average, less than classical Cepheids by about 1.5 magnitudes (but still brighter than RR Lyrae stars). Baade's seminal discovery led to a twofold increase in the distance to M31, and the extragalactic distance scale. RR Lyrae stars, then known as Cluster Variables, were recognized fairly early as being a separate class of variable, due in part to their short periods.
The mechanics of stellar pulsation as a heat-engine was proposed in 1917 by Arthur Stanley Eddington (who wrote at length on the dynamics of Cepheids), but it was not until 1953 that S. A. Zhevakin identified ionized helium as a likely valve for the engine.
Classes
Cepheid variables are divided into two subclasses which exhibit markedly different masses, ages, and evolutionary histories: classical Cepheids and type II Cepheids. Delta Scuti variables are A-type stars on or near the main sequence at the lower end of the instability strip and were originally referred to as dwarf Cepheids. RR Lyrae variables have short periods and lie on the instability strip where it crosses the horizontal branch. Delta Scuti variables and RR Lyrae variables are not generally treated with Cepheid variables although their pulsations originate with the same helium ionisation kappa mechanism.
Classical Cepheids | Cepheid variable | Wikipedia | 402 | 158530 | https://en.wikipedia.org/wiki/Cepheid%20variable | Physical sciences | Stellar astronomy | null |
Classical Cepheids (also known as Population I Cepheids, type I Cepheids, or Delta Cepheid variables) undergo pulsations with very regular periods on the order of days to months. Classical Cepheids are Population I variable stars which are 4–20 times more massive than the Sun, and up to 100,000 times more luminous. These Cepheids are yellow bright giants and supergiants of spectral class F6 – K2 and their radii change by (~25% for the longer-period I Carinae) millions of kilometers during a pulsation cycle.
Classical Cepheids are used to determine distances to galaxies within the Local Group and beyond, and are a means by which the Hubble constant can be established. Classical Cepheids have also been used to clarify many characteristics of the Milky Way galaxy, such as the Sun's height above the galactic plane and the Galaxy's local spiral structure.
A group of classical Cepheids with small amplitudes and sinusoidal light curves are often separated out as Small Amplitude Cepheids or s-Cepheids, many of them pulsating in the first overtone.
Type II Cepheids
Type II Cepheids (also termed Population II Cepheids) are population II variable stars which pulsate with periods typically between 1 and 50 days. Type II Cepheids are typically metal-poor, old (~10 Gyr), low mass objects (~half the mass of the Sun). Type II Cepheids are divided into several subgroups by period. Stars with periods between 1 and 4 days are of the BL Her subclass, 10–20 days belong to the W Virginis subclass, and stars with periods greater than 20 days belong to the RV Tauri subclass.
Type II Cepheids are used to establish the distance to the Galactic Center, globular clusters, and galaxies. | Cepheid variable | Wikipedia | 411 | 158530 | https://en.wikipedia.org/wiki/Cepheid%20variable | Physical sciences | Stellar astronomy | null |
Anomalous Cepheids
A group of pulsating stars on the instability strip have periods of less than 2 days, similar to RR Lyrae variables but with higher luminosities. Anomalous Cepheid variables have masses higher than type II Cepheids, RR Lyrae variables, and the Sun. It is unclear whether they are young stars on a "turned-back" horizontal branch, blue stragglers formed through mass transfer in binary systems, or a mix of both.
Double-mode Cepheids
A small proportion of Cepheid variables have been observed to pulsate in two modes at the same time, usually the fundamental and first overtone, occasionally the second overtone. A very small number pulsate in three modes, or an unusual combination of modes including higher overtones.
Uncertain distances
Chief among the uncertainties tied to the classical and type II Cepheid distance scale are: the nature of the period-luminosity relation in various passbands, the impact of metallicity on both the zero-point and slope of those relations, and the effects of photometric contamination (blending with other stars) and a changing (typically unknown) extinction law on Cepheid distances. All these topics are actively debated in the literature.
These unresolved matters have resulted in cited values for the Hubble constant (established from Classical Cepheids) ranging between 60 km/s/Mpc and 80 km/s/Mpc. Resolving this discrepancy is one of the foremost problems in astronomy since the cosmological parameters of the Universe may be constrained by supplying a precise value of the Hubble constant. Uncertainties have diminished over the years, due in part to discoveries such as RS Puppis. | Cepheid variable | Wikipedia | 365 | 158530 | https://en.wikipedia.org/wiki/Cepheid%20variable | Physical sciences | Stellar astronomy | null |
Delta Cephei is also of particular importance as a calibrator of the Cepheid period-luminosity relation since its distance is among the most precisely established for a Cepheid, partly because it is a member of a star cluster and the availability of precise parallaxes observed by the Hubble, Hipparcos, and Gaia space telescopes. The accuracy of parallax distance measurements to Cepheid variables and other bodies within 7,500 light-years is vastly improved by comparing images from Hubble taken six months apart, from opposite points in the Earth's orbit. (Between two such observations 2 AU apart, a star at a distance of 7500 light-years = 2300 parsecs would appear to move an angle of 2/2300 arc-seconds = 2 x 10−7 degrees, the resolution limit of the available telescopes.)
Pulsation model
The accepted explanation for the pulsation of Cepheids is called the Eddington valve, or "κ-mechanism", where the Greek letter κ (kappa) is the usual symbol for the gas opacity.
Helium is the gas thought to be most active in the process. Doubly ionized helium (helium whose atoms are missing both electrons) is more opaque than singly ionized helium. As helium is heated, its temperature rises until it reaches the point at which double ionisation spontaneously occurs and is sustained throughout the layer in much the same way a fluorescent tube 'strikes'. At the dimmest part of a Cepheid's cycle, this ionized gas in the outer layers of the star is relatively opaque, and so is heated by the star's radiation, and due to the increasing temperature, begins to expand. As it expands, it cools, but remains ionised until another threshold is reached at which point double ionization cannot be sustained and the layer becomes singly ionized hence more transparent, which allows radiation to escape. The expansion then stops, and reverses due to the star's gravitational attraction. The star's states are held to be either expanding or contracting by the hysteresis generated by the doubly ionized helium and indefinitely flip-flops between the two states reversing every time the upper or lower threshold is crossed. This process is rather analogous to the relaxation oscillator found in electronics. | Cepheid variable | Wikipedia | 488 | 158530 | https://en.wikipedia.org/wiki/Cepheid%20variable | Physical sciences | Stellar astronomy | null |
In 1879, August Ritter (1826–1908) demonstrated that the adiabatic radial pulsation period for a homogeneous sphere is related to its surface gravity and radius through the relation:
where k is a proportionality constant. Now, since the surface gravity is related to the sphere mass and radius through the relation:
one finally obtains:
where Q is a constant, called the pulsation constant.
Examples
Classical Cepheids include: Eta Aquilae, Zeta Geminorum, Beta Doradus, RT Aurigae, Polaris, as well as Delta Cephei.
Type II Cepheids include: W Virginis, Kappa Pavonis and BL Herculis.
Anomalous Cepheids include: XZ Ceti (overtone pulsation mode) and BL Boötis. | Cepheid variable | Wikipedia | 170 | 158530 | https://en.wikipedia.org/wiki/Cepheid%20variable | Physical sciences | Stellar astronomy | null |
An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Aircraft using power components are referred to as powered flight. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many small UAVs have used electric motors.
Manufacturing industry
In commercial aviation the major Western manufacturers of turbofan engines are Pratt & Whitney (a subsidiary of Raytheon Technologies), General Electric, Rolls-Royce, and CFM International (a joint venture of Safran Aircraft Engines and General Electric). Russian manufacturers include the United Engine Corporation, Aviadvigatel and Klimov. Aeroengine Corporation of China was formed in 2016 with the merger of several smaller companies.
The largest manufacturer of turboprop engines for general aviation is Pratt & Whitney. General Electric announced in 2015 entrance into the market.
Development history | Aircraft engine | Wikipedia | 181 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
1848: John Stringfellow made a steam engine for a 10-foot wingspan model aircraft which achieved the first powered flight, albeit with negligible payload.
1903: Charlie Taylor built an inline engine, mostly of aluminum, for the Wright Flyer (12 horsepower).
1903: Manly-Balzer engine sets standards for later radial engines.
1906: Léon Levavasseur produces a successful water-cooled V8 engine for aircraft use.
1908: René Lorin patents a design for the ramjet engine.
1908: Louis Seguin designed the Gnome Omega, the world's first rotary engine to be produced in quantity. In 1909 a Gnome powered Farman III aircraft won the prize for the greatest non-stop distance flown at the Reims Grande Semaine d'Aviation setting a world record for endurance of .
1910: Coandă-1910, an unsuccessful ducted fan aircraft exhibited at Paris Aero Salon, powered by a piston engine. The aircraft never flew, but a patent was filed for routing exhaust gases into the duct to augment thrust.
1914: Auguste Rateau suggests using exhaust-powered compressor – a turbocharger – to improve high-altitude performance; not accepted after the tests
1915: The Mercedes D.VI - an eighteen-cylinder liquid-cooled W-18 type aircraft engine - (517 hp/380 kW) was the most powerful engine during WW1.
1917–18: The Idflieg-numbered R.30/16 example of the Imperial German Luftstreitkräfte's Zeppelin-Staaken R.VI heavy bomber becomes the earliest known supercharger-equipped aircraft to fly, with a Mercedes D.II straight-six engine in the central fuselage driving a Brown-Boveri mechanical supercharger for the R.30/16's four Mercedes D.IVa engines.
1918: Sanford Alexander Moss picks up Rateau's idea and creates the first successful turbocharger
1926: Armstrong Siddeley Jaguar IV (S), the first series-produced supercharged engine for aircraft use; two-row radial with a gear-driven centrifugal supercharger.
1930: Frank Whittle submitted his first patent for a turbojet engine.
June 1939: Heinkel He 176 is the first successful aircraft to fly powered solely by a liquid-fueled rocket engine.
August 1939: Heinkel HeS 3 turbojet propels the pioneering German Heinkel He 178 aircraft. | Aircraft engine | Wikipedia | 500 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
1940: Jendrassik Cs-1, the world's first run of a turboprop engine. It is not put into service.
1943 Daimler-Benz DB 670, first turbofan runs
1944: Messerschmitt Me 163B Komet, the world's first rocket-propelled combat aircraft deployed.
1945: First turboprop-powered aircraft flies, a modified Gloster Meteor with two Rolls-Royce Trent engines.
1947: Bell X-1 rocket-propelled aircraft exceeds the speed of sound.
1948: 100 shp 782, the first turboshaft engine to be applied to aircraft use; in 1950 used to develop the larger Turbomeca Artouste.
1949: Leduc 010, the world's first ramjet-powered aircraft flight.
1950: Rolls-Royce Conway, the world's first production turbofan, enters service.
1968: General Electric TF39 high bypass turbofan enters service delivering greater thrust and much better efficiency.
2002: HyShot scramjet flew in dive.
2004: NASA X-43, the first scramjet to maintain altitude.
2020: Pipistrel E-811 is the first electric aircraft engine to be awarded a type certificate by EASA. It powers the Pipistrel Velis Electro, the first fully electric EASA type-certified aeroplane. | Aircraft engine | Wikipedia | 276 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
Shaft engines
Reciprocating (piston) engines
In-line engine
In this section, for clarity, the term "inline engine" refers only to engines with a single row of cylinders, as used in automotive language, but in aviation terms, the phrase "inline engine" also covers V-type and opposed engines (as described below), and is not limited to engines with a single row of cylinders. This is typically to differentiate them from radial engines.
A straight engine typically has an even number of cylinders, but there are instances of three- and five-cylinder engines. The greatest advantage of an inline engine is that it allows the aircraft to be designed with a low frontal area to minimize drag. If the engine crankshaft is located above the cylinders, it is called an inverted inline engine: this allows the propeller to be mounted high up to increase ground clearance, enabling shorter landing gear. The disadvantages of an inline engine include a poor power-to-weight ratio, because the crankcase and crankshaft are long and thus heavy. An in-line engine may be either air-cooled or liquid-cooled, but liquid-cooling is more common because it is difficult to get enough air-flow to cool the rear cylinders directly.
Inline engines were common in early aircraft; one was used in the Wright Flyer, the aircraft that made the first controlled powered flight. However, the inherent disadvantages of the design soon became apparent, and the inline design was abandoned, becoming a rarity in modern aviation.
For other configurations of aviation inline engine, such as X-engines, U-engines, H-engines, etc., see Inline engine (aeronautics).
V-type engine
Cylinders in this engine are arranged in two in-line banks, typically tilted 60–90 degrees apart from each other and driving a common crankshaft. The vast majority of V engines are water-cooled. The V design provides a higher power-to-weight ratio than an inline engine, while still providing a small frontal area. Perhaps the most famous example of this design is the legendary Rolls-Royce Merlin engine, a 27-litre (1649 in3) 60° V12 engine used in, among others, the Spitfires that played a major role in the Battle of Britain.
Horizontally opposed engine | Aircraft engine | Wikipedia | 459 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
A horizontally opposed engine, also called a flat or boxer engine, has two banks of cylinders on opposite sides of a centrally located crankcase. The engine is either air-cooled or liquid-cooled, but air-cooled versions predominate. Opposed engines are mounted with the crankshaft horizontal in airplanes, but may be mounted with the crankshaft vertical in helicopters. Due to the cylinder layout, reciprocating forces tend to cancel, resulting in a smooth running engine. Opposed-type engines have high power-to-weight ratios because they have a comparatively small, lightweight crankcase. In addition, the compact cylinder arrangement reduces the engine's frontal area and allows a streamlined installation that minimizes aerodynamic drag. These engines always have an even number of cylinders, since a cylinder on one side of the crankcase "opposes" a cylinder on the other side.
Opposed, air-cooled four- and six-cylinder piston engines are by far the most common engines used in small general aviation aircraft requiring up to per engine. Aircraft that require more than per engine tend to be powered by turbine engines.
H configuration engine
An H configuration engine is essentially a pair of horizontally opposed engines placed together, with the two crankshafts geared together.
Radial engine
This type of engine has one or more rows of cylinders arranged around a centrally located crankcase. Each row generally has an odd number of cylinders to produce smooth operation. A radial engine has only one crank throw per row and a relatively small crankcase, resulting in a favorable power-to-weight ratio. Because the cylinder arrangement exposes a large amount of the engine's heat-radiating surfaces to the air and tends to cancel reciprocating forces, radials tend to cool evenly and run smoothly. The lower cylinders, which are under the crankcase, may collect oil when the engine has been stopped for an extended period. If this oil is not cleared from the cylinders prior to starting the engine, serious damage due to hydrostatic lock may occur.
Most radial engines have the cylinders arranged evenly around the crankshaft, although some early engines, sometimes called semi-radials or fan configuration engines, had an uneven arrangement. The best known engine of this type is the Anzani engine, which was fitted to the Bleriot XI used for the first flight across the English Channel in 1909. This arrangement had the drawback of needing a heavy counterbalance for the crankshaft, but was used to avoid the spark plugs oiling up. | Aircraft engine | Wikipedia | 500 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
In military aircraft designs, the large frontal area of the engine acted as an extra layer of armor for the pilot. Also air-cooled engines, without vulnerable radiators, are slightly less prone to battle damage, and on occasion would continue running even with one or more cylinders shot away. However, the large frontal area also resulted in an aircraft with an aerodynamically inefficient increased frontal area.
Rotary engine
Rotary engines have the cylinders in a circle around the crankcase, as in a radial engine, (see above), but the crankshaft is fixed to the airframe and the propeller is fixed to the engine case, so that the crankcase and cylinders rotate. The advantage of this arrangement is that a satisfactory flow of cooling air is maintained even at low airspeeds, retaining the weight advantage and simplicity of a conventional air-cooled engine without one of their major drawbacks.
The first practical rotary engine was the Gnome Omega designed by the Seguin brothers and first flown in 1909. Its relative reliability and good power to weight ratio changed aviation dramatically. Before the first World War most speed records were gained using Gnome-engined aircraft, and in the early years of the war rotary engines were dominant in aircraft types for which speed and agility were paramount. To increase power, engines with two rows of cylinders were built.
However, the gyroscopic effects of the heavy rotating engine produced handling problems in aircraft and the engines also consumed large amounts of oil since they used total loss lubrication, the oil being mixed with the fuel and ejected with the exhaust gases. Castor oil was used for lubrication, since it is not soluble in petrol, and the resultant fumes were nauseating to the pilots. Engine designers had always been aware of the many limitations of the rotary engine so when the static style engines became more reliable and gave better specific weights and fuel consumption, the days of the rotary engine were numbered.
Wankel engine | Aircraft engine | Wikipedia | 392 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
The Wankel is a type of rotary engine. The Wankel engine is about one half the weight and size of a traditional four-stroke cycle piston engine of equal power output, and much lower in complexity. In an aircraft application, the power-to-weight ratio is very important, making the Wankel engine a good choice. Because the engine is typically constructed with an aluminium housing and a steel rotor, and aluminium expands more than steel when heated, a Wankel engine does not seize when overheated, unlike a piston engine. This is an important safety factor for aeronautical use. Considerable development of these designs started after World War II, but at the time the aircraft industry favored the use of turbine engines. It was believed that turbojet or turboprop engines could power all aircraft, from the largest to smallest designs. The Wankel engine did not find many applications in aircraft, but was used by Mazda in a popular line of sports cars. The French company Citroën had developed Wankel powered helicopter in 1970's.
In modern times the Wankel engine has been used in motor gliders where the compactness, light weight, and smoothness are crucially important.
The now-defunct Staverton-based firm MidWest designed and produced single- and twin-rotor aero engines, the MidWest AE series. These engines were developed from the motor in the Norton Classic motorcycle. The twin-rotor version was fitted into ARV Super2s and the Rutan Quickie. The single-rotor engine was put into a Chevvron motor glider and into the Schleicher ASH motor-gliders. After the demise of MidWest, all rights were sold to Diamond of Austria, who have since developed a MkII version of the engine.
As a cost-effective alternative to certified aircraft engines some Wankel engines, removed from automobiles and converted to aviation use, have been fitted in homebuilt experimental aircraft. Mazda units with outputs ranging from to can be a fraction of the cost of traditional engines. Such conversions first took place in the early 1970s; and as of 10 December 2006 the National Transportation Safety Board has only seven reports of incidents involving aircraft with Mazda engines, and none of these is of a failure due to design or manufacturing flaws.
Combustion cycles
The most common combustion cycle for aero engines is the four-stroke with spark ignition. Two-stroke spark ignition has also been used for small engines, while the compression-ignition diesel engine is seldom used. | Aircraft engine | Wikipedia | 497 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
Starting in the 1930s attempts were made to produce a practical aircraft diesel engine. In general, Diesel engines are more reliable and much better suited to running for long periods of time at medium power settings. The lightweight alloys of the 1930s were not up to the task of handling the much higher compression ratios of diesel engines, so they generally had poor power-to-weight ratios and were uncommon for that reason, although the Clerget 14F Diesel radial engine (1939) has the same power to weight ratio as a gasoline radial. Improvements in Diesel technology in automobiles (leading to much better power-weight ratios), the Diesel's much better fuel efficiency and the high relative taxation of AVGAS compared to Jet A1 in Europe have all seen a revival of interest in the use of diesels for aircraft. Thielert Aircraft Engines converted Mercedes Diesel automotive engines, certified them for aircraft use, and became an OEM provider to Diamond Aviation for their light twin. Financial problems have plagued Thielert, so Diamond's affiliate — Austro Engine — developed the new AE300 turbodiesel, also based on a Mercedes engine. Competing new Diesel engines may bring fuel efficiency and lead-free emissions to small aircraft, representing the biggest change in light aircraft engines in decades.
Power turbines
Turboprop
While military fighters require very high speeds, many civil airplanes do not. Yet, civil aircraft designers wanted to benefit from the high power and low maintenance that a gas turbine engine offered. Thus was born the idea to mate a turbine engine to a traditional propeller. Because gas turbines optimally spin at high speed, a turboprop features a gearbox to lower the speed of the shaft so that the propeller tips don't reach supersonic speeds. Often the turbines that drive the propeller are separate from the rest of the rotating components so that they can rotate at their own best speed (referred to as a free-turbine engine). A turboprop is very efficient when operated within the realm of cruise speeds it was designed for, which is typically .
Turboshaft | Aircraft engine | Wikipedia | 409 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
Turboshaft engines are used primarily for helicopters and auxiliary power units. A turboshaft engine is similar to a turboprop in principle, but in a turboprop the propeller is supported by the engine and the engine is bolted to the airframe: in a turboshaft, the engine does not provide any direct physical support to the helicopter's rotors. The rotor is connected to a transmission which is bolted to the airframe, and the turboshaft engine drives the transmission. The distinction is seen by some as slim, as in some cases aircraft companies make both turboprop and turboshaft engines based on the same design.
Electric power
A number of electrically powered aircraft, such as the QinetiQ Zephyr, have been designed since the 1960s. Some are used as military drones. In France in late 2007, a conventional light aircraft powered by an 18 kW electric motor using lithium polymer batteries was flown, covering more than , the first electric airplane to receive a certificate of airworthiness.
On 18 May 2020, the Pipistrel E-811 was the first electric aircraft engine to be awarded a type certificate by EASA for use in general aviation. The E-811 powers the Pipistrel Velis Electro.
Limited experiments with solar electric propulsion have been performed, notably the manned Solar Challenger and Solar Impulse and the unmanned NASA Pathfinder aircraft.
Many big companies, such as Siemens, are developing high performance electric engines for aircraft use, also, SAE shows new developments in elements as pure Copper core electric motors with a better efficiency. A hybrid system as emergency back-up and for added power in take-off is offered for sale by Axter Aerospace, Madrid, Spain.
Small multicopter UAVs are almost always powered by electric motors.
Reaction engines
Reaction engines generate the thrust to propel an aircraft by ejecting the exhaust gases at high velocity from the engine, the resultant reaction of forces driving the aircraft forwards. The most common reaction propulsion engines flown are turbojets, turbofans and rockets. Other types such as pulsejets, ramjets, scramjets and pulse detonation engines have also flown. In jet engines the oxygen necessary for fuel combustion comes from the air, while rockets carry an oxidizer (usually oxygen in some form) as part of the fuel load, permitting their use in space.
Jet turbines
Turbojet | Aircraft engine | Wikipedia | 481 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
A turbojet is a type of gas turbine engine that was originally developed for military fighters during World War II. A turbojet is the simplest of all aircraft gas turbines. It consists of a compressor to draw air in and compress it, a combustion section where fuel is added and ignited, one or more turbines that extract power from the expanding exhaust gases to drive the compressor, and an exhaust nozzle that accelerates the exhaust gases out the back of the engine to create thrust. When turbojets were introduced, the top speed of fighter aircraft equipped with them was at least 100 miles per hour faster than competing piston-driven aircraft. In the years after the war, the drawbacks of the turbojet gradually became apparent. Below about Mach 2, turbojets are very fuel inefficient and create tremendous amounts of noise. Early designs also respond very slowly to power changes, a fact that killed many experienced pilots when they attempted the transition to jets. These drawbacks eventually led to the downfall of the pure turbojet, and only a handful of types are still in production. The last airliner that used turbojets was the Concorde, whose Mach 2 airspeed permitted the engine to be highly efficient.
Turbofan | Aircraft engine | Wikipedia | 247 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
A turbofan engine is much the same as a turbojet, but with an enlarged fan at the front that provides thrust in much the same way as a ducted propeller, resulting in improved fuel efficiency. Though the fan creates thrust like a propeller, the surrounding duct frees it from many of the restrictions that limit propeller performance. This operation is a more efficient way to provide thrust than simply using the jet nozzle alone, and turbofans are more efficient than propellers in the transsonic range of aircraft speeds and can operate in the supersonic realm. A turbofan typically has extra turbine stages to turn the fan. Turbofans were among the first engines to use multiple spools—concentric shafts that are free to rotate at their own speed—to let the engine react more quickly to changing power requirements. Turbofans are coarsely split into low-bypass and high-bypass categories. Bypass air flows through the fan, but around the jet core, not mixing with fuel and burning. The ratio of this air to the amount of air flowing through the engine core is the bypass ratio. Low-bypass engines are preferred for military applications such as fighters due to high thrust-to-weight ratio, while high-bypass engines are preferred for civil use for good fuel efficiency and low noise. High-bypass turbofans are usually most efficient when the aircraft is traveling at , the cruise speed of most large airliners. Low-bypass turbofans can reach supersonic speeds, though normally only when fitted with afterburners.
Advanced technology engine
The term advanced technology engine refers to the modern generation of jet engines. The principle is that a turbine engine will function more efficiently if the various sets of turbines can revolve at their individual optimum speeds, instead of at the same speed. The true advanced technology engine has a triple spool, meaning that instead of having a single drive shaft, there are three, in order that the three sets of blades may revolve at different speeds. An interim state is a twin-spool engine, allowing only two different speeds for the turbines.
Pulsejets | Aircraft engine | Wikipedia | 425 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
Pulsejets are mechanically simple devices that—in a repeating cycle—draw air through a no-return valve at the front of the engine into a combustion chamber and ignite it. The combustion forces the exhaust gases out the back of the engine. It produces power as a series of pulses rather than as a steady output, hence the name. The only application of this type of engine was the German unmanned V1 flying bomb of World War II. Though the same engines were also used experimentally for ersatz fighter aircraft, the extremely loud noise generated by the engines caused mechanical damage to the airframe that was sufficient to make the idea unworkable.
Gluhareff Pressure Jet
The Gluhareff Pressure Jet (or tip jet) is a type of jet engine that, like a valveless pulsejet, has no moving parts. Having no moving parts, the engine works by having a coiled pipe in the combustion chamber that superheats the fuel (propane) before being injected into the air-fuel inlet. In the combustion chamber, the fuel/air mixture ignites and burns, creating thrust as it leaves through the exhaust pipe. Induction and compression of the fuel/air mixture is done both by the pressure of propane as it is injected, along with the sound waves created by combustion acting on the intake stacks. It was intended as a power plant for personal helicopters and compact aircraft such as Microlights.
Rocket
A few aircraft have used rocket engines for main thrust or attitude control, notably the Bell X-1 and North American X-15.
Rocket engines are not used for most aircraft as the energy and propellant efficiency is very poor, but have been employed for short bursts of speed and takeoff. Where fuel/propellant efficiency is of lesser concern, rocket engines can be useful because they produce very large amounts of thrust and weigh very little.
Rocket turbine engine
A rocket turbine engine is a combination of two types of propulsion engines: a liquid-propellant rocket and a turbine jet engine. Its power-to-weight ratio is a little higher than a regular jet engine, and works at higher altitudes.
Precooled jet engines
For very high supersonic/low hypersonic flight speeds, inserting a cooling system into the air duct of a hydrogen jet engine permits greater fuel injection at high speed and obviates the need for the duct to be made of refractory or actively cooled materials. This greatly improves the thrust/weight ratio of the engine at high speed. | Aircraft engine | Wikipedia | 504 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
It is thought that this design of engine could permit sufficient performance for antipodal flight at Mach 5, or even permit a single stage to orbit vehicle to be practical. The hybrid air-breathing SABRE rocket engine is a pre-cooled engine under development.
Piston-turbofan hybrid
At the April 2018 ILA Berlin Air Show, Munich-based research institute :de:Bauhaus Luftfahrt presented a high-efficiency composite cycle engine for 2050, combining a geared turbofan with a piston engine core.
The 2.87 m diameter, 16-blade fan gives a 33.7 ultra-high bypass ratio, driven by a geared low-pressure turbine but the high-pressure compressor drive comes from a piston-engine with two 10 piston banks without a high-pressure turbine, increasing efficiency with non-stationary isochoric-isobaric combustion for higher peak pressures and temperatures.
The 11,200 lb (49.7 kN) engine could power a 50-seat regional jet.
Its cruise TSFC would be 11.5 g/kN/s (0.406 lb/lbf/hr) for an overall engine efficiency of 48.2%, for a burner temperature of , an overall pressure ratio of 38 and a peak pressure of .
Although engine weight increases by 30%, aircraft fuel consumption is reduced by 15%.
Sponsored by the European Commission under Framework 7 project , Bauhaus Luftfahrt, MTU Aero Engines and GKN Aerospace presented the concept in 2015, raising the overall engine pressure ratio to over 100 for a 15.2% fuel burn reduction compared to 2025 engines.
Engine position numbering
On multi-engine aircraft, engine positions are numbered from left to right from the point of view of the pilot looking forward, so for example on a four-engine aircraft such as the Boeing 747, engine No. 1 is on the left side, farthest from the fuselage, while engine No. 3 is on the right side nearest to the fuselage.
In the case of the twin-engine English Electric Lightning, which has two fuselage-mounted jet engines one above the other, engine No. 1 is below and to the front of engine No. 2, which is above and behind.
In the Cessna 337 Skymaster, a push-pull twin-engine airplane, engine No. 1 is the one at the front of the fuselage, while engine No. 2 is aft of the cabin. | Aircraft engine | Wikipedia | 494 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
Fuel
Aircraft reciprocating (piston) engines are typically designed to run on aviation gasoline. Avgas has a higher octane rating than automotive gasoline to allow higher compression ratios, power output, and efficiency at higher altitudes. Currently the most common Avgas is 100LL. This refers to the octane rating (100 octane) and the lead content (LL = low lead, relative to the historic levels of lead in pre-regulation Avgas).
Refineries blend Avgas with tetraethyllead (TEL) to achieve these high octane ratings, a practice that governments no longer permit for gasoline intended for road vehicles. The shrinking supply of TEL and the possibility of environmental legislation banning its use have made a search for replacement fuels for general aviation aircraft a priority for pilots’ organizations.
Turbine engines and aircraft diesel engines burn various grades of jet fuel. Jet fuel is a relatively less volatile petroleum derivative based on kerosene, but certified to strict aviation standards, with additional additives.
Model aircraft typically use nitro engines (also known as "glow engines" due to the use of a glow plug) powered by glow fuel, a mixture of methanol, nitromethane, and lubricant. Electrically powered model airplanes and helicopters are also commercially available. Small multicopter UAVs are almost always powered by electricity, but larger gasoline-powered designs are under development. | Aircraft engine | Wikipedia | 284 | 158681 | https://en.wikipedia.org/wiki/Aircraft%20engine | Technology | Aviation | null |
For organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such as aldehydes, ketones and carboxylic acids), as part of many larger functional groups. A compound containing a carbonyl group is often referred to as a carbonyl compound.
The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (a metal carbonyl, e.g. nickel carbonyl).
The remainder of this article concerns itself with the organic chemistry definition of carbonyl, such that carbon and oxygen share a double bond.
Carbonyl compounds
In organic chemistry, a carbonyl group characterizes the following types of compounds:
Other organic carbonyls are urea and the carbamates, the derivatives of acyl chlorides chloroformates and phosgene, carbonate esters, thioesters, lactones, lactams, hydroxamates, and isocyanates. Examples of inorganic carbonyl compounds are carbon dioxide and carbonyl sulfide.
A special group of carbonyl compounds are dicarbonyl compounds, which can exhibit special properties.
Structure and reactivity
For organic compounds, the length of the C-O bond does not vary widely from 120 picometers. Inorganic carbonyls have shorter C-O distances: CO, 113; CO2, 116; and COCl2, 116 pm.
The carbonyl carbon is typically electrophilic. A qualitative order of electrophilicity is RCHO (aldehydes) > R2CO (ketones) > RCO2R' (esters) > RCONH2 (amides). A variety of nucleophiles attack, breaking the carbon-oxygen double bond.
Interactions between carbonyl groups and other substituents were found in a study of collagen. Substituents can affect carbonyl groups by addition or subtraction of electron density by means of a sigma bond. ΔHσ values are much greater when the substituents on the carbonyl group are more electronegative than carbon. | Carbonyl group | Wikipedia | 467 | 158788 | https://en.wikipedia.org/wiki/Carbonyl%20group | Physical sciences | Concepts: General | Chemistry |
The polarity of C=O bond also enhances the acidity of any adjacent C-H bonds. Due to the positive charge on carbon and the negative charge on oxygen, carbonyl groups are subject to additions and/or nucleophilic attacks. A variety of nucleophiles attack, breaking the carbon-oxygen double bond, and leading to addition-elimination reactions. Nucleophilic reactivity is often proportional to the basicity of the nucleophile and as nucleophilicity increases, the stability within a carbonyl compound decreases. The pKa values of acetaldehyde and acetone are 16.7 and 19 respectively,
Spectroscopy
Infrared spectroscopy: the C=O double bond absorbs infrared light at wavenumbers between approximately 1600–1900 cm−1(5263 nm to 6250 nm). The exact location of the absorption is well understood with respect to the geometry of the molecule. This absorption is known as the "carbonyl stretch" when displayed on an infrared absorption spectrum. In addition, the ultraviolet-visible spectra of propanone in water gives an absorption of carbonyl at 257 nm.
Nuclear magnetic resonance: the C=O double-bond exhibits different resonances depending on surrounding atoms, generally a downfield shift. The 13C NMR of a carbonyl carbon is in the range of 160–220 ppm. | Carbonyl group | Wikipedia | 283 | 158788 | https://en.wikipedia.org/wiki/Carbonyl%20group | Physical sciences | Concepts: General | Chemistry |
A protocarnivorous plant (sometimes also paracarnivorous, subcarnivorous, or borderline carnivore), according to some definitions, traps and kills insects or other animals but lacks the ability to either directly digest or absorb nutrients from its prey like a carnivorous plant. The morphological adaptations such as sticky trichomes or pitfall traps of protocarnivorous plants parallel the trap structures of confirmed carnivorous plants.
Some authors prefer the term "protocarnivorous" because it implies that these plants are on the evolutionary path to true carnivory, whereas others oppose the term for the same reason. The same problem arises with "subcarnivorous". Donald Schnell, author of the book Carnivorous Plants of the United States and Canada, prefers the term "paracarnivorous" for a less rigid definition of carnivory that can include many of the possible carnivorous plants.
The demarcation between carnivorous and protocarnivorous is blurred by the lack of a strict definition of botanical carnivory and ambiguous academic literature on the subject. Many examples of protocarnivorous plants exist, some of which are counted among the ranks of true carnivorous plants as a matter of historical preference. Further research into these plants' carnivorous adaptations may reveal that a few protocarnivorous plants do meet the more rigid definition of a carnivorous plant.
Historical observations | Protocarnivorous plant | Wikipedia | 277 | 9270823 | https://en.wikipedia.org/wiki/Protocarnivorous%20plant | Biology and health sciences | Botany | Biology |
Historical observations of the carnivorous syndrome in plant species have been restricted to the more obvious examples of carnivory, such as the active trapping mechanisms of Drosera (the sundews) and Dionaea (Venus flytrap), though authors have often noted speculation about other species that may not be so obviously carnivorous. In one of the earlier publications on carnivorous plants, Charles Darwin had suggested many plants that have developed adhesive glands, such as Erica tetralix, Mirabilis longifolia, Pelargonium zonale, Primula sinesis, and Saxifraga umbrosa, may indeed be carnivorous but little research has been done on them. Darwin himself only mentioned these species in passing and did not follow through with any investigation. Adding to the small but growing list, Francis Lloyd provided his own list of species suspected of carnivory in his 1942 book on carnivorous plants, though these species and their potential were only mentioned in the introduction. Later, in a 1981 review of the literature, Paul Simons rediscovered Italian journal articles from the early 1900s that identified several additional sticky species that digested insect prey. Simons was surprised to find these articles lacking in the literature cited sections of many modern books and articles on carnivorous plants, suggesting that academic research has treated Lloyd's 1942 book as the authoritative and comprehensive source on pre-1942 research on the carnivorous syndrome.
Defining carnivory
Debate about what criteria a plant must meet to be considered carnivorous has yielded two proposed definitions: one with strict requirements and the other less restrictive.
The strict definition requires that a plant must possess morphological adaptations that attract prey through scent or visual cues, capture and retain prey (e.g., the waxy scales of Brocchinia reducta or downward facing hairs of Heliamphora prevent escape), digest the dead prey through enzymes produced by the plant, and absorb the products of digestion through specialized structures. The presence of commensals is also listed as strong evidence of a long evolutionary history of carnivory. By this definition, many sun pitcher plants (Heliamphora) and the cobra lily (Darlingtonia californica) would not be included on a roster of carnivorous plants because they rely on symbiotic bacteria and other organisms to produce the necessary proteolytic enzymes. | Protocarnivorous plant | Wikipedia | 480 | 9270823 | https://en.wikipedia.org/wiki/Protocarnivorous%20plant | Biology and health sciences | Botany | Biology |
The broader definition differs mainly in including plants that do not produce their own digestive enzymes but rely on internal food webs or microbes to digest prey, such as Darlingtonia and some species of Heliamphora. The original definition of botanical carnivory, set out in Givnish et al. (1984), required a plant to exhibit an adaptation of some trait specifically for the attraction, capture, or digestion of prey while gaining a fitness advantage through the absorption of nutrients derived from said prey. Upon further analysis of genera currently considered carnivorous, botanists widened the original definition to include species that use mutualistic interactions for digestion.
Both the strict and broad definitions require absorption of the digested nutrients. The plant must receive some benefit from the carnivorous syndrome; that is, the plant must display some increase in fitness because of the nutrients obtained from its carnivorous adaptations. Increased fitness might mean improved growth rate, increased chance of survival, higher pollen production or seed set.
Degrees of carnivory
One prevailing idea is that carnivory in plants is not a black and white duality, but rather a spectrum from strict non-carnivorous photoautotrophs (a rose, for example) to fully carnivorous plants with active trapping mechanisms like those of Dionaea or Aldrovanda. However, passive traps are still considered fully carnivorous. Plants that fall between the definitions in the strict carnivorous/non-carnivorous demarcation can be defined as being protocarnivorous. | Protocarnivorous plant | Wikipedia | 307 | 9270823 | https://en.wikipedia.org/wiki/Protocarnivorous%20plant | Biology and health sciences | Botany | Biology |
It is thought that these plants that have evolved protocarnivorous habits typically reside in habitats where there is a significant nutrient deficiency, but not the severe deficiency in nitrogen and phosphorus seen where true carnivorous plants grow. The function of the protocarnivorous habit, however, need not be directly related to lack of nutrient access. Some classic protocarnivorous plants represent convergent evolution in form but not necessarily in function. Plumbago, for example, possesses glandular trichomes on its calyces that structurally resemble the tentacles of Drosera and Drosophyllum. The function of the Plumbago tentacles is, however, disputed. Some contend that their function is to aid in pollination, adhering seeds to visiting pollinators. Others note that on some species (Plumbago auriculata), small, crawling insects have been trapped in the Plumbago's mucilage, which supports the conclusion that these tentacles could have evolved to exclude crawling insects and favor flying pollinators for greater seed dispersal or perhaps for protection against crawling insect predators.
Trapping mechanisms
There are visible parallels between the trapping mechanisms of carnivorous plants and protocarnivorous plants. Plumbago and other species with glandular trichomes resemble the flypaper traps of Drosera and Drosophyllum. The pitfall traps of protocarnivorous plants, such as some Heliamphora species and Darlingtonia californica, are so similar to those of true carnivorous plants that the only reason they may be considered protocarnivorous instead of carnivorous is that they do not produce their own digestive enzymes. There are also protocarnivorous bromeliads that form a pitfall trap in an "urn" of rosetted leaves that are held together tightly. There are also other plants that produce a sticky mucilage not necessarily associated with a tentacle or glandular trichome, but instead can be described more like a slime capable of trapping and killing insects.
Flypaper traps | Protocarnivorous plant | Wikipedia | 404 | 9270823 | https://en.wikipedia.org/wiki/Protocarnivorous%20plant | Biology and health sciences | Botany | Biology |
Dr. George Spomer of the University of Idaho has discovered protocarnivorous activity and function in several glandular plant species, including Cerastium arvense, Ipomopsis aggregata, Heuchera cylindrica, Mimulus lewisii, Penstemon attenuata, Penstemon diphyllus, Potentilla glandulosa var. intermedia, Ribes cereum, Rosa nutkana var. hispida, Rosa woodsii var. ultramontana, Solanum tuberosum, Stellaria americana, and Stellaria jamesiana. These species tested positive for protease activity, though it is unclear whether the protease is produced by the plant or by surface microbes. Two other species evaluated by Dr. Spomer, Geranium viscosissimum and Potentilla arguta, exhibited protease activity and were further examined with 14C-labeled algal protein for nutrient absorption activity. Both of these latter species displayed an ability to digest and absorb the labeled protein.
Other plants that are considered to be protocarnivorous have sticky trichomes on some surface, such as the flower scape and bud of Stylidium and Plumbago, the bracts of Passiflora, and leaves of Roridula. The trichomes of Stylidium, which appear below the flower, have been known to trap and kill small insects since their discovery several centuries ago, but their purpose remained ambiguous. In November 2006, Dr. Douglas Darnowski published a paper describing the active digestion of proteins when they come in contact with a trichome of a Stylidium species grown in aseptic tissue culture, proving that the plant, rather than the surface microbes, was the source of protease production. Darnowski asserts in that paper that given this evidence, Stylidium species are properly called carnivorous, though in order to fulfill the strict definition of carnivory it needs to be proven that they are capable of absorbing nutrients derived from prey and that this adaptation gives the plants some competitive advantage. | Protocarnivorous plant | Wikipedia | 428 | 9270823 | https://en.wikipedia.org/wiki/Protocarnivorous%20plant | Biology and health sciences | Botany | Biology |
The glandular hairs on the calyx of plants of the genus Plumbago have been proposed as a potential carnivorous adaptation. While these calyxes have long been considered as a seed dispersal mechanism, many researchers have noted the entrapment of numerous ants and other small insects on the species Plumbago auriculata, Plumbago europa, Plumbago indica, and Plumbago zeylanica. Studies on P. auriculata and P. indica detected potential protease activity from these glands, but were inconsistent in detecting it. Energy-dispersive X-ray spectroscopy spectra of the glands on P. auriculata and P. zeylanica found that the glandular secretions were composed mainly of the elements C, O, Si, Mg, and Al. One such species, P. europaea, has also been noted to kill small birds by covering them in sticky calyxes, causing them to be unable to fly and subsequently die. A similar sticky-seed killing mechanism has been studied Pisonia grandis, but was concluded to not be a carnivorous adaptation.
Roridula has a more complex relationship with its prey. The plants in this genus produce sticky leaves with resin-tipped glands that look similar to those of larger Drosera. However, the resin, unlike mucilage, is unable to carry digestive enzymes. Therefore, Roridula species do not directly benefit from the insects they catch. Instead, they form a mutualistic symbiosis with species of assassin bugs that eat the trapped insects. The plant benefits from the nutrients in the bugs' feces.
Likewise, the sticky, modified bracts of passion flowers of the section Dysosmia have notable glandular bracts that surround flowers and forming fruit. While this has long been discussed as a defense mechanism, studies of Passiflora foetida have investigated them for potential carnivorous abilities. A 1995 paper published in the Journal of Biosciences detailed the evidence that the glandular bracts played a distinct role in defense of the flower and were also capable of digesting captured prey and absorbing the nutrients. Various authors have questioned the methods and conclusions of this paper. Further studies using on the glandular bracts using histochemical tests have confirmed the presence of enzymes in both Passiflora foetida and Passiflora sublanceolata. | Protocarnivorous plant | Wikipedia | 487 | 9270823 | https://en.wikipedia.org/wiki/Protocarnivorous%20plant | Biology and health sciences | Botany | Biology |
Various plants of the Martyniaceae family have been considered crude flypaper protocarnivores. Early publications identified the entrapment of numerous insects on the glandular hairs covering the stems and leaves of Martynia annua, Proboscidea louisiana, Proboscidea parviflora, and Ibicella lutea. Early, rudimentary studies showed that placed bits of food—beef and hard-boiled egg white broke down when placed on the leaf surface ofP. louisiana and I. lutea, respectively. Despite this, more recent studies have suggested that there are no detectable proteases on the leaves of I. lutea and P. louisiana and no detectable phosphatases or uptake of N, P, K, Mg from dried flies places on I. lutea and P. parviflora. Observations have suggested that there may be a digestive mutualism between carnivorous insects and the sticky plant surface similar to Roridula. A similar relationship has been identified in many other sticky desert plants and concluded to be a passive defense mechanism.
Pitfall traps
The pitfall traps of protocarnivorous plants are identical to those of carnivorous plants in every way except in the plant's mode of digestion. The rigid definition of carnivory in plants requires digestion of prey by enzymes produced by the plant. Given this criterion, many of the pitfall trap plants commonly considered to be carnivorous would instead be classified as protocarnivorous. However, this is highly contentious and generally not reflected in current carnivorous plant phylogenies or literature. Darlingtonia californica and several Heliamphora species do not produce their own enzymes, relying instead on an internal food web to break down the prey into absorbable nutrients. | Protocarnivorous plant | Wikipedia | 363 | 9270823 | https://en.wikipedia.org/wiki/Protocarnivorous%20plant | Biology and health sciences | Botany | Biology |
Another pitfall trap form unrelated to the Sarraceniaceae family are the urns of bromeliad leaves that are formed when leaves are tightly packed together in a rosette, collecting water and trapping insects. Unlike Brocchinia reducta, which has been proven to produce at least one digestive enzyme and can therefore be considered carnivorous, the epiphytic Catopsis berteroniana has little evidence supporting the claims that it is carnivorous. It is able to attract and kill prey and the trichomes on the surface of the leaves can absorb nutrients, but so far no enzyme activity has been detected. It may be that this plant also relies on an internal food web for soft tissue digestion. The same could be said for Paepalanthus bromelioides, though it is a member of Eriocaulaceae and not a bromeliad. It also forms a central water reservoir that has adaptations to attract insects. It, like C. berteroniana, produces no digestive enzymes.
Another potential protocarnivorous pitfall trap is a species of teasel, Dipsacus fullonum, which has been only suggested as a possible carnivore. Only one major study has examined D. fullonum for carnivory and no evidence of digestive enzymes or foliar nutrient absorption was revealed.
Other
Capsella bursa-pastoris, Shepherd's purse, is another plant where the claim of carnivory is contested. This unique protocarnivorous plant is only capable of capturing and digesting prey during one stage of its life cycle. The seeds of the plant, when moistened, secrete a Mucilage that attracts and kills prey. There is also evidence of protease activity and absorption of nutrients. More recent studies have suggested that the plants may benefit from the feeding of Nematodes to the seeds of the plants, but due to a small sample size such conclusions cannot be made. Other plants such as Descurainia pinnata, Descurainia sophia, Hirschfeldia incana, and Lepidium flavum were also noted to entrap small insects. Mucilage production by seeds is fairly common in the plant kingdom and is typically associated with root and shoot penetration. Further work to identify the nutrient fluxes in this seed-insect system in-situ are required to understand any carnivorous aspects of this system. | Protocarnivorous plant | Wikipedia | 491 | 9270823 | https://en.wikipedia.org/wiki/Protocarnivorous%20plant | Biology and health sciences | Botany | Biology |
Puya raimondii and Puya chilensis are two large arid bromeliads that have been suspected of being proto-carnivorous plants due to their entrapment of small animals in their spiny leaves. Puya raimondii was noted to have associated with numerous birds, some of which would become ensnared in the spiky foliage and die. It is hypothesized that this, as well as dropping from the birds who lived amongst the leaves, are a source of nutrients upon decomposition and subsequent foliage absorption by the plant. Similarly, Puya chilensis was noted to ensnare livestock such as sheep who, unless rescued would degrade and feed the plant. Despite this, the adaptations seen in Puya that lead to ensnarement of animals seems most likely to be a defense mechanism.
Loss of carnivory
A few plants that could be considered protocarnivorous or paracarnivorous are those that once had carnivorous adaptations but appear to be evolving or have evolved away from a direct prey relationship with arthropods and rely on other sources for obtaining nutrients. One example of such a phenomenon is the pitfall trap of Nepenthes ampullaria, a tropical pitcher plant. Although it retains its ability to attract, capture, kill, and digest insect prey, this species has acquired adaptations that appear to favor digestion of leaf litter. It could potentially be referred to as a detritivore. Another tropical pitcher plant, Nepenthes lowii, is known to catch very few prey items compared to other Nepenthes. Preliminary observations suggest that this particular species may have moved away from a solely (or even primarily) carnivorous nature and be adapted to "catching" the droppings of birds feeding at its nectaries. A 2009 study found that mature N. lowii plants derived 57–100% of their foliar nitrogen from treeshrew droppings.
Utricularia purpurea, a bladderwort, comes from another genus of carnivorous plants and may have lost its appetite for carnivory, at least in part. This species can still trap and digest arthropod prey in its specialized bladder traps, but does so sparingly. Instead, it harbors a community of algae, zooplankton, and debris in the bladders, giving rise to the hypothesis that the bladders of U. purpurea favor a mutualistic interaction in place of a predator-prey relationship.
Evolution | Protocarnivorous plant | Wikipedia | 507 | 9270823 | https://en.wikipedia.org/wiki/Protocarnivorous%20plant | Biology and health sciences | Botany | Biology |
The disciplines of ecology and evolutionary biology have presented several hypotheses on the evolution of carnivorous plants that may also apply to protocarnivorous plants. The name "protocarnivorous plant" itself suggests that these species are on their way to carnivory, though others may simply be an example of a defense-related adaptation, such as that found in Plumbago. Still others (Utricularia purpurea, Nepenthes ampullaria, and Nepenthes lowii) may be examples of carnivorous plants moving away from the carnivorous syndrome.
In his 1998 book, Interrelationship Between Insects and Plants, Pierre Jolivet only considered four species of plants to be protocarnivorous: Catopsis berteroniana, Brocchinia reducta, B. hectioides, and Paepalanthus bromeloides. Jolivet writes, "It is important to remember that all carnivorous plants are dicots and all protocarnivorous plants are monocots," though he does not explain why nor does he describe his reasons for excluding other dicotyledonous plants that are protocarnivorous. | Protocarnivorous plant | Wikipedia | 237 | 9270823 | https://en.wikipedia.org/wiki/Protocarnivorous%20plant | Biology and health sciences | Botany | Biology |
Street photography is photography conducted for art or inquiry that features unmediated chance encounters and random incidents within public places. It usually has the aim of capturing images at a decisive or poignant moment by careful framing and timing. Street photography overlaps widely with candid photography, although the latter can also be used in other settings, such as portrait photography and event photography.
Street photography does not necessitate the presence of a street or even the urban environment. Though people usually feature directly, street photography might be absent of people and can be of an object or environment where the image projects a decidedly human character in facsimile or aesthetic.
Street photography can focus on people and their behavior in public. In this respect, the street photographer is similar to social documentary photographers or photojournalists who also work in public places, but with the aim of capturing newsworthy events. Any of these photographers' images may capture people and property visible within or from public places, which often entails navigating ethical issues and laws of privacy, security, and property.
Much of what is regarded, stylistically and subjectively, as definitive street photography was made in the era spanning the end of the 19th century through to the late 1970s, a period which saw the emergence of portable cameras that enabled candid photography in public places.
History
Depictions of everyday public life form a genre in almost every period of world art, beginning in the pre-historic, Sumerian, Egyptian and early Buddhist art periods. Art dealing with the life of the street, whether within views of cityscapes, or as the dominant motif, appears in the West in the canon of the Northern Renaissance, Baroque, Rococo, of Romanticism, Realism, Impressionism and Post-Impressionism. With the type having been so long established in other media, it followed that photographers would also pursue the subject as soon as technology enabled them.
Nineteenth-century precursors | Street photography | Wikipedia | 385 | 975495 | https://en.wikipedia.org/wiki/Street%20photography | Technology | Photography | null |
In 1838 or 1839 the first photograph of figures in the street was recorded by Louis-Jacques-Mandé Daguerre in one of a pair of daguerreotype views taken from his studio window of the Boulevard du Temple in Paris. The second, made at the height of the day, shows an unpopulated stretch of street, while the other was taken at about 8:00 am, and as Beaumont Newhall reports, "The Boulevard, so constantly filled with a moving throng of pedestrians and carriages was perfectly solitary, except an individual who was having his boots brushed. His feet were compelled, of course, to be stationary for some time, one being on the box of the boot black, and the other on the ground. Consequently his boots and legs were well defined, but he is without body or head, because these were in motion."
Charles Nègre was the first photographer to attain the technical sophistication required to register people in movement on the street in Paris in 1851. Photographer John Thomson, a Scotsman working with journalist and social activist Adolphe Smith, published Street Life in London in twelve monthly installments starting in February 1877. Thomson played a key role in making everyday life on the streets a significant subject for the medium.
Eugene Atget is regarded as a progenitor, not because he was the first of his kind, but as a result of the popularisation in the late 1920s of his record of Parisian streets by Berenice Abbott, who was inspired to undertake a similar documentation of New York City. As the city developed, Atget helped to promote Parisian streets as a worthy subject for photography. From the 1890s to the 1920s he mainly photographed its architecture, stairs, gardens, and windows. He did photograph some workers, but people were not his main interest.
First sold in 1925, the Leica was the first commercially successful camera to use 35 mm film. Its compactness and bright viewfinder, matched to lenses of quality (changeable on Leicas sold from 1930) helped photographers move through busy streets and capture fleeting moments.
Twentieth-century practitioners
United Kingdom
Paul Martin is considered a pioneer, making candid unposed photographs of people in London and at the seaside in the late 19th and early 20th century in order to record life. Martin is the first recorded photographer to do so in London with a disguised camera. | Street photography | Wikipedia | 474 | 975495 | https://en.wikipedia.org/wiki/Street%20photography | Technology | Photography | null |
Mass-Observation was a social research organisation founded in 1937 which aimed to record everyday life in Britain and to record the reactions of the 'man-in-the-street' to King Edward VIII's abdication in 1936 to marry divorcée Wallis Simpson, and the succession of George VI. Humphrey Spender made photographs on the streets of the northern English industrial town of Bolton, identified for the project's publications as "Yorktown", while filmmaker Humphrey Jennings made a cinematic record in London for a parallel branch of investigation. The chief Mass-Observationists were anthropologist Tom Harrisson in Bolton and poet Charles Madge in London, and their first report was produced as the book "May the Twelfth: Mass-Observation Day-Surveys 1937 by over two hundred observers"
France
The post-war French Humanist School photographers found their subjects on the street or in the bistro. They worked primarily in black‐and‐white in available light with the popular small cameras of the day, discovering what the writer Pierre Mac Orlan (1882–1970) called the "fantastique social de la rue" (social fantastic of the street) and their style of image-making rendered romantic and poetic the way of life of ordinary European people, particularly in Paris. Between 1946 and 1957 Le Groupe des XV annually exhibited work of this kind.
Street photography formed the major content of two exhibitions at the Museum of Modern Art (MoMA) in New York curated by Edward Steichen, Five French Photographers: Brassai; Cartier-Bresson, Doisneau, Ronis, Izis in 1951 to 1952, and Post-war European Photography in 1953, which exported the concept of street photography internationally. Steichen drew on large numbers of European humanist and American humanistic photographs for his 1955 exhibition The Family of Man, proclaimed as a compassionate portrayal of a global family, which toured the world, inspiring photographers in the depiction of everyday life.
Henri Cartier-Bresson's widely admired Images à la Sauvette (1952) (the English-language edition was titled The Decisive Moment) promoted the idea of taking a picture at what he termed the "decisive moment"; "when form and content, vision and composition merged into a transcendent whole". His book inspired successive generations of photographers to make candid photographs in public places before this approach per se came to be considered déclassé in the aesthetics of postmodernism. | Street photography | Wikipedia | 495 | 975495 | https://en.wikipedia.org/wiki/Street%20photography | Technology | Photography | null |
America
Walker Evans worked from 1938 to 1941 on a series in the New York City Subway in order to practice a pure 'record method' of photography; candid portraits of people who would unconsciously come 'into range before an impersonal fixed recording machine during a certain time period'. The recording machine was 'a hidden camera', a 35 mm Contax concealed beneath his coat, that was 'strapped to the chest and connected to a long wire strung down the right sleeve'. However, his work had little contemporary impact as due to Evans' sensitivities about the originality of his project and the privacy of his subjects, it was not published until 1966, in the book Many Are Called, with an introduction written by James Agee in 1940. The work was exhibited as Walker Evans Subway Photographs and Other Recent Acquisitions held at the National Gallery of Art, 1991–1992, accompanied by the catalogue Walker Evans: Subways and Streets.
Helen Levitt, then a teacher of young children, associated with Evans in 1938–39. She documented the transitory chalk drawings that were part of children's street culture in New York at the time, as well as the children who made them. In July 1939, MoMA's new photography section included Levitt's work in its inaugural exhibition. In 1943, Nancy Newhall curated her first solo exhibition Helen Levitt: Photographs of Children there. The photographs were ultimately published in 1987 as In The Street: chalk drawings and messages, New York City 1938–1948.
The beginnings of street photography in the United States can also be linked to those of jazz, both emerging as outspoken depictions of everyday life. This connection is visible in the work of the New York school of photography (not to be confused with the New York School). The New York school of photography was not a formal institution, but rather comprised groups of photographers in the mid-20th century based in New York City. | Street photography | Wikipedia | 392 | 975495 | https://en.wikipedia.org/wiki/Street%20photography | Technology | Photography | null |
Robert Frank's 1958 book, The Americans, was significant; raw and often out of focus, Frank's images questioned mainstream photography of the time, "challenged all the formal rules laid down by Henri Cartier-Bresson and Walker Evans" and "flew in the face of the wholesome pictorialism and heartfelt photojournalism of American magazines like LIFE and Time". Although the photo-essay format was formative in his early years in Switzerland, Frank rejected it: "I wanted to follow my own intuition and do it my way, and not make any concession – not make a Life story'. Even the work of Cartier-Bresson he regarded as insufficiently subjective: "I've always thought it was terribly important to have a point of view, and I was also sort of disappointed in him [Cartier-Bresson] that that was never in his pictures'.
Frank's work thus epitomises the subjectivity of postwar American photography, as John Szarkowski prominently argued; "Minor White's magazine Aperture and Robert Frank's book The Americans were characteristic of the new work of their time in the sense that they were both uncompromisingly committed to a highly personal vision of the world". His claim for subjectivism is widely accepted, resulting more recently in Patricia Vettel-Becker's perspective on postwar street photography as highly masculine and centred on the male body, and Lili Corbus Benzer positioning Robert Frank's book as negatively prioritising 'personal vision' over social activism. Mainstream photographers in America fiercely rejected Frank's work, but the book later "changed the nature of photography, what it could say and how it could say it". It was a stepping stone for fresh photographers looking to break away from the restrictions of the old style and "remains perhaps the most influential photography book of the 20th century". Szarkowski's recognition of Frank's subjectivity led him to promote more street photography in America, such as his curation of the 1967 New Documents exhibition featuring Diane Arbus, Lee Friedlander and Garry Winogrand or of Mark Cohen's work in 1973. Both at the Museum of Modern Art (MoMA). | Street photography | Wikipedia | 455 | 975495 | https://en.wikipedia.org/wiki/Street%20photography | Technology | Photography | null |
Individual approaches in the later twentieth and early twenty-first centuries
Inspired by Frank, in the 1960s Garry Winogrand, Lee Friedlander and Joel Meyerowitz began photographing on the streets of New York. Phil Coomes, writing for BBC News in 2013, said "For those of us interested in street photography there are a few names that stand out and one of those is Garry Winogrand"; critic Sean O'Hagan, writing in The Guardian in 2014, said "In the 1960s and 70s, he defined street photography as an attitude as well as a style – and it has laboured in his shadow ever since, so definitive are his photographs of New York."
Returning to the UK in 1965 from the US where he had met Winogrand and adopted street photography, Tony Ray-Jones turned a wry eye on often surreal groupings of British people on their holidays or participating in festivals. The acerbic comic vein of Ray-Jones' high-contrast monochromes, which before his premature death were popularized by Creative Camera (for which he conducted an interview with Brassaï), is mined more recently by Martin Parr in hyper-saturated colour.
Characteristics and Distinctions
Street photography is a vast genre that can be defined in many ways, but it is often characterized by the spontaneous capturing of an unrepeatable, fleeting moment, often of the everyday going-ons of strangers. It is classically shot with wider angle lenses (e.g. 35mm) and usually features urban environments.
Street photography versus documentary photography
Street photography and documentary photography are similar genres of photography that often overlap while having distinct individual qualities.
Documentary photographers typically have a defined, premeditated message and an intention to record particular events in history. The gamut of the documentary approach encompasses aspects of journalism, art, education, sociology and history. In social investigation, documentary images are often intended to provoke, or to highlight the need for, societal change. Conversely, street photography is reactive and disinterested by nature and motivated by curiosity or creative inquiry, allowing it to deliver a relatively neutral depiction of the world that mirrors society, "unmanipulated" and with usually unaware subjects.
Candid street photography versus street portraits
Street photography is generally seen as unposed and candid, but there are a few street photographers who interact with strangers on the streets and take their portraits. Street portraits are unplanned portraits taken of strangers while out doing street photography, however they are seen as posed because there is interaction with the subject. | Street photography | Wikipedia | 512 | 975495 | https://en.wikipedia.org/wiki/Street%20photography | Technology | Photography | null |
Legal concerns
The issue of street photographers taking photographs of strangers in public places without their consent (i.e. 'candid photography' by definition) for fine art purposes has been controversial. Photographing people and places in public is legal in most countries protecting freedom of expression and journalistic freedom. There are usually limits on how photos of people may be used and most countries have specific laws regarding people's privacy.
Street photography may also conflict with laws that were originally established to protect against paparazzi, defamation, or harassment and special laws will sometimes apply when taking pictures of minors.
Canada
While the common-law provinces follow the United Kingdom, with respect to the freedom to take pictures in a public place, Quebec law provides that, in most circumstances, their publication can take place only with the consent of the subjects therein.
European Union
The European Union's Human Rights Act 1998, which all EU countries have to uphold in their domestic law, establishes in a right to privacy. This can result in restrictions on the publication of photography. The right to privacy is protected by Article 8 of the convention. In the context of photography, it stands at odds to the Article 10 right of freedom of expression. As such, courts will usually consider the public interest in balancing the rights through the legal test of proportionality.
France
While also limiting photography in order to protect privacy rights, street photography can still be legal in France when pursued as an art form under certain circumstances. While in one prominent case the freedom of artistic expression trumped the individual's right to privacy, the legality will much depend on the individual case.
Germany
Germany protects the right to take photos in public, but also recognizes a "right to one's own picture". That means that even though pictures can often be taken without someones consent, they must not be published without the permission of the person in the picture. The law also protects specifically against defamation".
This right to one's picture, however, does not extend to people who are not the main focus of the picture (e.g. who just wandered into a scene), or who are not even recognizable in the photo. It also does not usually extend to people who are public figures (e.g. politicians or celebrities).
If a picture is considered art, the courts will also consider the photographer's freedom of artistic expression; meaning that "artful" street photography can still be legally published in certain cases. | Street photography | Wikipedia | 495 | 975495 | https://en.wikipedia.org/wiki/Street%20photography | Technology | Photography | null |
Greece
Production, publication and non-commercial sale of street photography is legal in Greece, without the need to have the consent of the shown person or persons. In Greece the right to take photographs and publish them or sell licensing rights over them as fine art or editorial content is protected by the Constitution of Greece (Article 14 and other articles) and free speech laws as well as by case law and legal cases. Photographing the police and publishing the photographs is also legal.
Photography and video-taking is also permitted across the whole Athens Metro transport network, which is very popular among Greek street photographers.
Hungary
In Hungary, from 15 March 2014 anyone taking photographs is technically breaking the law if someone wanders into shot, under a new civil code that outlaws taking pictures without the permission of everyone in the photograph. This expands the law on consent to include the taking of photographs, in addition to their publication.
Japan
In Japan permission, or at least signification of intent to photo and the absence of refusal, is needed both for photography and for publication of photos of recognisable people even in public places. 'Hidden photography' (kakushidori hidden, surreptitious photography) 'stolen photography' (tōsatsu with no intention of getting permission) and "fast photography' (hayayori before permission and refusal can be given) are forbidden unless in the former permission is obtained from the subject immediately after taking the photo. People have rights to their images (shōzōken, droit de image). The law is especially strict when that which is taken, or the taking, is in any sense shameful. Exception is made for photos of famous people in public places and news photography by registered news media outlets where favour is given to the public right to know.
South Africa
In South Africa, photographing people in public is legal. Reproducing and selling photographs of people is legal for editorial and limited fair use commercial purposes. There exists no case law to define what the limits on commercial use are. Civil law requires the consent of any identifiable persons for advertorial and promotional purposes. Property, including animals, do not enjoy any special consideration.
South Korea
In South Korea, taking pictures of women without their consent, even in public, is considered to be criminal sexual assault, punishable by a fine of up to 10 million won and up to 5 years imprisonment. In July 2017 an amendment to the law was voted on in favour of allowing for chemical castration of people taking such photographs. | Street photography | Wikipedia | 504 | 975495 | https://en.wikipedia.org/wiki/Street%20photography | Technology | Photography | null |
United Kingdom
The United Kingdom has enacted domestic law in accordance with the Human Rights Act, which limits the publication of certain photographs in the context of the news media. However, as a general rule, the taking of photographs of other people, including children, in a public place is legal, whether or not the person consents.
In terms of photographing property, in general under UK law one cannot prevent photography of private property from a public place, and in general the right to take photographs on private land upon which permission has been obtained is similarly unrestricted. However, landowners are permitted to impose any conditions they wish upon entry to a property, such as forbidding or restricting photography. There are however nuances to these broad principles, and even where photography is restricted as a condition of entry, the landowner's remedies for a breach will usually be limited to asking the photographer to leave the premises. They cannot confiscate cameras or memory cards nor can they require photographs be deleted.
United States
In the US, the protection of free speech is generally interpreted widely, and encompasses art speech, including photography. As such, street photography is exempt from right to privacy claims.
For example, the case Nussenzweig v. DiCorcia established that taking, publishing and selling street photography (including street portraits) is legal, even without the consent of the person being portrayed, because photography is protected as free speech and art by the First Amendment. However, the Court of Appeals for the State of New York upheld the Nussenzweig decision solely on the basis of the statute of limitations expiring and did not address the free speech and First Amendment arguments.
Street photography is additionally protected by court precedent. As courts regularly uphold that individuals have no right to privacy in public places, there is little, if any, legal action that can be taken against a street photographer.
Ethical concerns
Street photography's nonconsensual nature can raise concerns about privacy and autonomy. | Street photography | Wikipedia | 396 | 975495 | https://en.wikipedia.org/wiki/Street%20photography | Technology | Photography | null |
Privacy
An invasion of privacy occurs when an individual's right to privacy is infringed upon by unwelcome intrusion into their private life, including public disclosure of private information. While a person may lose their reasonable expectation of privacy when going out in public according to court precedent, some feel that individuals should be able to control their information (such as their image) even in public. These critics would contend that it cannot be said that every person in public accepts the possibility of being photographed because assumption of risk is based on conscious consent, and might also argue that a photograph's ability to accentuate details means that it does more than just record what the public sees.
Autonomy
As the right to privacy can be seen as protecting representations of oneself and since nonconsensual use of an individual's image in street photography denies the subject control of the final image, some view street photography as taking away autonomy. When a person is not asked for consent to use their picture, they do not get to decide whether or where the picture is published or how it is viewed. | Street photography | Wikipedia | 217 | 975495 | https://en.wikipedia.org/wiki/Street%20photography | Technology | Photography | null |
In geology, a dike or dyke is a sheet of rock that is formed in a fracture of a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma flows into a crack then solidifies as a sheet intrusion, either cutting across layers of rock or through a contiguous mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack.
Magmatic dikes
A magmatic dike is a sheet of igneous rock that cuts across older rock beds. It is formed when magma fills a fracture in the older beds and then cools and solidifies. The dike rock is usually more resistant to weathering than the surrounding rock, so that erosion exposes the dike as a natural wall or ridge. It is from these natural walls that dikes get their name.
Dikes preserve a record of the fissures through which most mafic magma (fluid magma low in silica) reaches the surface. They are studied by geologists for the clues they provide on volcanic plumbing systems. They also record ancient episodes of extension of the Earth's crust, since large numbers of dikes (dike swarms) are formed when the crust is pulled apart by tectonic forces. The dikes show the direction of extension, since they form at right angles to the direction of maximum extension.
Description
The thickness of a dike is much smaller than its other two dimensions, and the opposite walls are roughly parallel, so that a dike is more or less constant in thickness. The thickness of different dikes can range from a few millimeters to hundreds of meters, but is most typically from about a meter to a few tens of meters. The lateral extent can be tens of kilometers, and dikes with a thickness of a few tens of meters or more commonly extend for over 100 km. Most dikes are steeply dipping; in other words, they are oriented nearly vertically. Subsequent tectonic deformation may rotate the sequence of strata through which the dike propagates so that the dike becomes horizontal. | Dike (geology) | Wikipedia | 426 | 975686 | https://en.wikipedia.org/wiki/Dike%20%28geology%29 | Physical sciences | Geologic features | Earth science |
It is common for a set of dikes, each a few kilometers long, to form en echelon. This pattern is seen in the Higganum dike set of New England. This dike set consists of individual dikes that are typically four kilometers in length at the surface and up to 60 meters wide. These short segments form longer groups extending for around 10 km. The entire set of dikes forms a line extending for 250 km. Individual segments overlap, with the overlapping portions thinner, so that the combined thickness of the two overlapped portions is about the same as the thickness of a single segment. Other examples of en echelon dikes are the Inyo dike of Long Valley, California, US; the Jagged Rocks complex, Arizona, US; and the dikes of oceanic spreading centers.
Dikes range in composition from basaltic to rhyolitic, but most are basaltic. The texture is typically slightly coarser than basalt erupted at the surface, forming a rock type called diabase. The grain size varies systematically across the dike, with the coarsest grains normally at the center of the dike. Dikes formed at shallow depth commonly have a glassy or fine-grained chilled margin 1 to 5 cm thick, formed where the magma was rapidly cooled by contact with the cold surrounding rock. Shallow dikes also typically show columnar jointing perpendicular to the margins. Here the dike rock fractures into columns as it cools and contracts. These are usually 5- to 6-sided, but 3- to 4-sided columns are also common. These are fairly uniform in size within a single dike, but range from a few centimeters to over 0.3 meters across in different dikes, tending to be thicker in wider dikes. Larger columns are likely a consequence of slower cooling.
Dike rock is usually dense, with almost no vesicles (frozen bubbles), but vesicles may be seen in the shallowest part of a dike. When vesicles are present, they tend to form bands parallel to walls and are elongated in direction of flow. Likewise, phenocrysts (larger crystals) on the margins of the dike show an alignment in the direction of flow.
In contrast to dikes, which cut across the bedding of layered rock, a sill is a sheet intrusion that forms within and parallel to the bedding. | Dike (geology) | Wikipedia | 489 | 975686 | https://en.wikipedia.org/wiki/Dike%20%28geology%29 | Physical sciences | Geologic features | Earth science |
Formation
Mafic magma (fluid magma low in silica) usually reaches the surface through fissures, forming dikes.
At the shallowest depths, dikes form when magma rises into an existing fissure. In the young, shallow dikes of the Hawaiian Islands, there is no indication of forceful intrusion of magma. For example, there is little penetration of magma into the walls of dikes even when the walls consist of highly porous volcanic clinker, and little wall material breaks off into the molten magma. These fissures likely open as a result of bulging of the rock beds above a magma chamber that is being filled with magma from deeper in the crust.
However, open fractures can exist only near the surface. Magma deeper in the crust must force its way through the rock, always opening a path along a plane normal to the minimum principal stress. This is the direction in which the crust is under the weakest compression and so requires the least work to fracture. At shallow depths, where the rock is brittle, the pressurized magma progressively fractures the rock as it advances upwards. Even if the magma is only slightly pressurized compared with the surrounding rock, tremendous stress is concentrated on the tip of the propagating fracture. In effect, the magma wedges apart the brittle rock in a process called hydraulic fracture. At greater depths, where the rock is hotter and less brittle, the magma forces the rock aside along brittle shear planes oriented 35 degrees to the sides of the dock. This bulldozer-like action produces a blunter dike tip. At the greatest depths, the shear planes become ductile faults, angled 45 degree from the sides of the dike. At depths where the rock is completely plastic, a diapir (a rising plug of magma) forms instead of a dike.
The walls of dikes often fit closely back together, providing strong evidence that the dike formed by dilatation of a fissure. However, a few large dikes, such as the 120-meter-thick Medford dike in Maine, US, or the 500-meter-thick Gardar dike in Greenland, show no dilatation. These may have formed by stoping, in which the magma fractured and disintegrated the rock at its advancing tip rather than prying the rock apart. Other dikes may have formed by metasomatism, in which fluids moving along a narrow fissure changed the chemical composition of the rock closest to the fissure. | Dike (geology) | Wikipedia | 508 | 975686 | https://en.wikipedia.org/wiki/Dike%20%28geology%29 | Physical sciences | Geologic features | Earth science |
There is an approximate relationship between the width of a dike and its maximum extent, expressed by the formula:
Here is the thickness of the dike; is its lateral extent; is the excess pressure in the magma relative to the host rock; is the density of the host rock; and is the P-wave velocity of the host rock (essentially, the speed of sound in the rock). This formula predicts that dikes will be longer and narrower at greater depths below the surface. The ratio of thickness to length is around 0.01 to 0.001 near the surface, but at depth it ranges from 0.001 to 0.0001. A surface dike 10 meters in thickness will extend about 3 km, while a dike of similar thickness at depth will extend about 30 km. This tendency of intruding magma to form shorter fissures at shallower depths has been put forward as an explanation of en echelon dikes. However, en echelon dikes have also been explained as a consequence of the direction of minimum principal stress changing as the magma ascends from deep to shallow levels in the crust.
An en echelon dike set may evolve into single dike with bridges connecting the formerly separate segments and horns showing former segment overlaps. In ancient dikes in deformed rock, the bridges and horns are used by geologists to determine the direction of magma flow.
Where there is rapid flow of molten magma through a fissure, the magma tends to erode the walls, either by melting the wall rock or by tearing off fragments of wall rock. This widens the fissure and increases flow. Where flow is less rapid, the magma may solidify next to the wall, narrowing the fissure and decreasing flow. This causes flow to become concentrated at a few points. At Hawaii, eruptions often begin with a curtain of fire where lava erupts along the entire length of a fissure several kilometers long. However, the length of erupting fissure diminishes over time, becoming focused on a short segment of less than half a kilometer. The minimum possible width of a dike is determined by the balance between magma movement and cooling.
Multiple and composite dikes | Dike (geology) | Wikipedia | 452 | 975686 | https://en.wikipedia.org/wiki/Dike%20%28geology%29 | Physical sciences | Geologic features | Earth science |
There may be more than one injection of magma along a given fissure. When multiple injections are all of similar composition, the dike is described as a multiple dike. However, subsequent injections are sometimes quite different in composition, and then the dike is described as a composite dike. The range of compositions in a composite dike can go all the way from diabase to granite, as is observed in some dikes of Scotland and northern Ireland.
After the initial formation of a dike, subsequent injections of magma are most likely to take place along the center of the dike. If the previous dike rock has cooled significantly, the subsequent injection can be characterized by fracturing of the old dike rock and the formation of chilled margins on the new injection.
Dike swarms
Sometimes dikes appear in swarms, consisting of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event. Dike swarms are almost always composed of diabase and most often are associated with flood basalts of large igneous provinces. They are characteristic of divergent plate boundaries. For example, Jurassic dike swarms in New England and Paleogene swarms in the west of Scotland and running into northern England record the early opening of the Atlantic Ocean. Dike swarms are forming in the present day along the divergent plate boundary running through Iceland. Dike swarms often have a great cumulative thickness: Dikes in Iceland average 3 to 5 meters in width, but one 53-kilometer stretch of coast has about 1000 dikes with total thickness of 3 kilometers. The world's largest dike swarm is the Mackenzie dike swarm in the Northwest Territories, Canada. | Dike (geology) | Wikipedia | 351 | 975686 | https://en.wikipedia.org/wiki/Dike%20%28geology%29 | Physical sciences | Geologic features | Earth science |
Dike swarms (also called dike complexes) are exposed in the eroded rift zones of Hawaiian volcanoes. As with most other magmatic dikes, these were fissures through which lava reached the surface. The swarms are typically 2.5 to 5 km in width, with individual dikes about a meter in width. The dike swarms extend radially out from volcano summits and parallel to the long axis of the volcanic shield. Sills and stocks are occasionally present in the complexes. They are abruptly truncated at the margins of summit calderas. Typically, there are about 50 to 100 dikes per kilometer at the center of the rift zone, though the density can be as high as 500 per kilometer and the dikes then make up half the volume of the rock. The density drops to 5 to 50 per kilometer away from the center of the rift zone before abruptly dropping to very few dikes. It is likely that the number of dikes must increase with depth, reaching a typical value of 300 to 350 per kilometer at the level of the ocean floor. In some respects, these dike swarms resemble those of western Scotland associated with the flood eruptions that preceded the opening of the Atlantic Ocean.
Dikes often form as radial swarms from a central volcano or intrusion. Though they appear to originate in the central intrusion, the dikes often have a different age and composition from the intrusion. These radial swarms may have formed over the intrusion and were later cut by the rising body of magma, or the crust was already experiencing regional tension and the intrusion triggered formation of the fissures.
Sheeted dike complexes
In rock of the oceanic crust, pillow lava erupted onto the sea floor is underlain by sheeted dike complexes that preserve the conduits through which magma reached the ocean floor at mid-ocean ridges. These sheeted dikes characteristically show a chilled margin on only one side, indicating that each dike was split in half by a subsequent eruption of magma.
Ring dikes and cone sheets | Dike (geology) | Wikipedia | 409 | 975686 | https://en.wikipedia.org/wiki/Dike%20%28geology%29 | Physical sciences | Geologic features | Earth science |
Ring dikes and cone sheets are special types of dikes associated with caldera volcanism. These are distributed around a shallow magma chamber. Cone sheets form when magma is injected into a shallow magma chamber, which lifts and fractures the rock beds above it. The fractures take the form of a set of concentric cones dipping at a relatively shallow angle into the magma chamber. When the caldera is subsequently emptied by explosive volcanic activity, the roof of the magma chamber collapses as a plug of rock surrounded by a ring fracture. Magma rising into the ring fracture produces a ring dike. Good examples of ring dikes and cone sheets are found in the Ardnamurchan peninsula of Scotland.
Other special types
A feeder dike is a dike that acted as a conduit for magma moving from a magma chamber to a localized intrusion. For example, the Muskox intrusion in arctic Canada was fed by a large dike, with a thickness of 150 meters.
A sole injection is a dike injected along a thrust fault plane, where rock beds were fractured and thrust up over younger beds.
Clastic dikes
Clastic dikes (also known as sedimentary dikes) are vertical bodies of sedimentary rock that cut off other rock layers. They can form in two ways:
When shallow unconsolidated sediment is composed of alternating coarse-grained and impermeable clay layers the fluid pressure inside the coarser layers may reach a critical value due to lithostatic overburden. Driven by the fluid pressure the sediment breaks through overlying layers and forms a dike.
When a soil is under permafrost conditions the pore water is totally frozen. When cracks are formed in such rocks, they may fill up with sediments that fall in from above. The result is a vertical body of sediment that cuts through horizontal layers, a dike.
Gallery | Dike (geology) | Wikipedia | 377 | 975686 | https://en.wikipedia.org/wiki/Dike%20%28geology%29 | Physical sciences | Geologic features | Earth science |
The fire-bellied toads are a group of six species of small frogs (most species typically no longer than ) belonging to the genus Bombina.
The name "fire-bellied" is derived from the brightly colored red- or yellow-and-black patterns on the toads' ventral regions, which act as aposematic coloration, a warning to predators of the toads' reputedly foul taste. The other parts of the toads' skins are green or dark brown. When confronted with a potential predator, these toads commonly engage in an unkenreflex, Unken- being the combining form of Unke, German for fire-bellied toad. In the unkenreflex, the toad arches its back, raising its front and back legs to display the aposematic coloration of its ventral side.
Species
The currently recognized species are:
Biology
The female of the species typically lays 80–300 eggs that can be found hanging off plant stems. The offspring develop in pools or puddles. Their metamorphosis is complete within a few weeks, peaking in July–August. The toadlets attain a length of 12–15 mm. The eggs, laid in August, metamorphose only after the winter, with the toadlets attaining a length of 3–5 cm. These toadlets still have white bellies.
Tadpoles eat mainly algae and higher plants. The young toads and the adult toads consume insects, such as flies and beetles, shrimp and larvae; but also annelid worms and terrestrial arthropods. Fire-bellied toads are sometimes active during the day, but are more so during the night. The mating call of the male sounds like a dog's bark, rather than the typical drawn out croaking groan.
Distribution and habitat
The species can be found both in Europe and in areas in Asia with a moderate climate.
All kinds of toads prefer habitats of stagnant water, which they are reluctant to leave. The fire-bellied toad lives primarily in a continental climate in standing water or calmer backwaters of rivers or ponds. The species can also be found in flood pools and in floodplains. The yellow-bellied species typically live at higher altitude, where they are primarily found in small bodies of water like ponds or water-filled ruts, often near small mountain streams. The Asian species also live in small bodies of water and can live at altitudes of over 3000 meters. | Fire-bellied toad | Wikipedia | 505 | 976931 | https://en.wikipedia.org/wiki/Fire-bellied%20toad | Biology and health sciences | Frogs and toads | Animals |
Captivity
Several species in the genus Bombina, particularly B. orientalis, B bombina, and B. variegata, are commonly kept as exotic pets and are readily available in pet stores. In captivity, they are easily maintained in vivaria, and when provided with proper food and environmental conditions, often prove to be robust, flamboyant, and long-lived amphibians. Captive fire-bellied toads can live from 3–10 years and some captive specimens have reached over 20 years.
In captivity, they eat a wide variety of food, including crickets, moths, minnows, blood worms and pinkie mice, though some frogs cannot handle certain foods, due to their size. They can sometimes act very aggressively against each other, particularly males. They have a ferocious appetite. Due to this, its best to monitor their food intake to ensure they're not over eating.
Fire-bellied toads breed extremely easily in captivity. Pet owners can expect to hear their mating calls largely starting in May and continuing to mid-August. Breeding will happen unprovoked by the owner. Younger females will have smaller clutches of around 60 to 80 eggs where older females can lay around 200. Fire-bellied toads bred in captivity will often have darker and less vibrant coloration having a more orange underside. Wild caught specimens tend to be brighter and have deeper red stomachs.
Fire-bellied toads are easy to raise and handle in solitude. This makes them advantageous to study in various sciences.
Toxicity
Fire-bellied toads secrete bombesin and 5-hydroxytryptamine, which cause irritation to the skin and eyes. Most reported exposures are of young children, did not result in major clinical effects, and were treated by rinsing. | Fire-bellied toad | Wikipedia | 365 | 976931 | https://en.wikipedia.org/wiki/Fire-bellied%20toad | Biology and health sciences | Frogs and toads | Animals |
Halocarbon compounds are chemical compounds in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms (fluorine, chlorine, bromine or iodine – ) resulting in the formation of organofluorine compounds, organochlorine compounds, organobromine compounds, and organoiodine compounds. Chlorine halocarbons are the most common and are called organochlorides.
Many synthetic organic compounds such as plastic polymers, and a few natural ones, contain halogen atoms; they are known as halogenated compounds or organohalogens. Organochlorides are the most common industrially used organohalides, although the other organohalides are used commonly in organic synthesis. Except for extremely rare cases, organohalides are not produced biologically, but many pharmaceuticals are organohalides. Notably, many pharmaceuticals such as Prozac have trifluoromethyl groups.
For information on inorganic halide chemistry, see halide.
Chemical families
Halocarbons are typically classified in the same ways as the similarly structured organic compounds that have hydrogen atoms occupying the molecular sites of the halogen atoms in halocarbons. Among the chemical families are:
haloalkanes—compounds with carbon atoms linked by single bonds
haloalkenes—compounds with one or more double bonds between carbon atoms
haloaromatics—compounds with carbons linked in one or more aromatic rings with a delocalised donut shaped pi cloud.
The halogen atoms in halocarbon molecules are often called "substituents," as though those atoms had been substituted for hydrogen atoms. However halocarbons are prepared in many ways that do not involve direct substitution of halogens for hydrogens.
History and context
A few halocarbons are produced in massive amounts by microorganisms. For example, several million tons of methyl bromide are estimated to be produced by marine organisms annually. Most of the halocarbons encountered in everyday life – solvents, medicines, plastics – are man-made. The first synthesis of halocarbons was achieved in the early 1800s. Production began accelerating when their useful properties as solvents and anesthetics were discovered. Development of plastics and synthetic elastomers has led to greatly expanded scale of production. A substantial percentage of drugs are halocarbons. | Halocarbon | Wikipedia | 481 | 977193 | https://en.wikipedia.org/wiki/Halocarbon | Physical sciences | Halocarbons | Chemistry |
Natural halocarbons
A large amount of the naturally occurring halocarbons, such as dioxine, are created by wood fire and volcanic activity. A third major source is marine algae, which produce several chlorinated methane and ethane containing compounds. Several thousand complex halocarbons are known to be produced mainly by marine species. Although chlorine compounds are the majority of the discovered compounds, bromides, iodides and fluorides have also been found in nature. Tyrian purple is a bromide and is produced by certain sea snails. Thyroxine is secreted by the thyroid gland and is an iodide. The highly toxic fluoroacetate is one of the rare natural organofluorides and is produced by certain plants.
Organoiodine compounds, including biological derivatives
Organoiodine compounds, called organic iodides, are similar in structure to organochlorine and organobromine compounds, but the C-I bond is weaker. Many organic iodides are known, but few are of major industrial importance. Iodide compounds are mainly produced as nutritional supplements.
The thyroxin hormones are essential for human health, hence the usefulness of iodized salt.
Six mg of iodide a day can be used to treat patients with hyperthyroidism due to its ability to inhibit the organification process in thyroid hormone synthesis, the so-called Wolff–Chaikoff effect. Prior to 1940, iodides were the predominant antithyroid agents. In large doses, iodides inhibit proteolysis of thyroglobulin, which permits TH to be synthesized and stored in colloid, but not released into the bloodstream. This mechanism is referred to as Plummer effect.
This treatment is seldom used today as a stand-alone therapy despite the rapid improvement of patients immediately following administration. The major disadvantage of iodide treatment lies in the fact that excessive stores of TH accumulate, slowing the onset of action of thioamides (TH synthesis blockers). In addition, the functionality of iodides fades after the initial treatment period. An "escape from block" is also a concern, as extra stored TH may spike following discontinuation of treatment.
Uses
The first halocarbon commercially used was Tyrian purple, a natural organobromide of the Murex brandaris marine snail. | Halocarbon | Wikipedia | 486 | 977193 | https://en.wikipedia.org/wiki/Halocarbon | Physical sciences | Halocarbons | Chemistry |
Common uses for halocarbons have been as solvents, pesticides, refrigerants, fire-resistant oils, ingredients of elastomers, adhesives and sealants, electrically insulating coatings, plasticizers, and plastics. Many halocarbons have specialized uses in industry. One halocarbon, sucralose, is a sweetener.
Before they became strictly regulated, the general public often encountered haloalkanes as paint and cleaning solvents such as trichloroethane (1,1,1-trichloroethane) and carbon tetrachloride (tetrachloromethane), pesticides like 1,2-dibromoethane (EDB, ethylene dibromide), and refrigerants like Freon-22 (duPont trademark for chlorodifluoromethane). Some haloalkanes are still widely used for industrial cleaning, such as methylene chloride (dichloromethane), and as refrigerants, such as R-134a (1,1,1,2-tetrafluoroethane).
Haloalkenes have also been used as solvents, including perchloroethylene (Perc, tetrachloroethene), widespread in dry cleaning, and trichloroethylene (TCE, 1,1,2-trichloroethene). Other haloalkenes have been chemical building blocks of plastics such as polyvinyl chloride ("vinyl" or PVC, polymerized chloroethene) and Teflon (duPont trademark for polymerized tetrafluoroethene, PTFE). | Halocarbon | Wikipedia | 359 | 977193 | https://en.wikipedia.org/wiki/Halocarbon | Physical sciences | Halocarbons | Chemistry |
Haloaromatics include the former Aroclors (Monsanto Company trademark for polychlorinated biphenyls, PCBs), once widely used in power transformers and capacitors and in building caulk, the former Halowaxes (Union Carbide trademark for polychlorinated naphthalenes, PCNs), once used for electrical insulation, and the chlorobenzenes and their derivatives, used for disinfectants, pesticides such as dichloro-diphenyl-trichloroethane (DDT, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), herbicides such as 2,4-D (2,4-dichlorophenoxyacetic acid), askarel dielectrics (mixed with PCBs, no longer used in most countries), and chemical feedstocks.
A few halocarbons, including acid halides like acetyl chloride, are highly reactive; these are rarely found outside chemical processing. The widespread uses of halocarbons were often driven by observations that most of them were more stable than other substances. They may be less affected by acids or alkalis; they may not burn as readily; they may not be attacked by bacteria or molds; or they may not be affected as much by sun exposure.
Hazards
The stability of halocarbons tended to encourage beliefs that they were mostly harmless, although in the mid-1920s physicians reported workers in polychlorinated naphthalene (PCN) manufacturing suffering from chloracne , and by the late 1930s it was known that workers exposed to PCNs could die from liver disease and that DDT would kill mosquitos and other insects . By the 1950s, there had been several reports and investigations of workplace hazards. In 1956, for example, after testing hydraulic oils containing polychlorinated biphenyl (PCB)s, the U.S. Navy found that skin contact caused fatal liver disease in animals and rejected them as "too toxic for use in a submarine" . | Halocarbon | Wikipedia | 443 | 977193 | https://en.wikipedia.org/wiki/Halocarbon | Physical sciences | Halocarbons | Chemistry |
In 1962 a book by U.S. biologist Rachel Carson started a storm of concerns about environmental pollution, first focused on DDT and other pesticides, some of them also halocarbons. These concerns were amplified when in 1966 Danish chemist Soren Jensen reported widespread residues of PCBs among Arctic and sub-Arctic fish and birds . In 1974, Mexican chemist Mario Molina and U.S. chemist Sherwood Rowland predicted that common halocarbon refrigerants, the chlorofluorocarbons (CFCs), would accumulate in the upper atmosphere and destroy protective ozone . Within a few years, ozone depletion was being observed above Antarctica, leading to bans on production and use of chlorofluorocarbons in many countries. In 2007, the Intergovernmental Panel on Climate Change (IPCC) said halocarbons were a direct cause of global warming.
Since the 1970s there have been longstanding, unresolved controversies over potential health hazards of trichloroethylene (TCE) and other halocarbon solvents that had been widely used for industrial cleaning . More recently perfluorooctanoic acid (PFOA), a precursor in the most common manufacturing process for Teflon and also used to make coatings for fabrics and food packaging, became a health and environmental concern starting in 2006 , suggesting that halocarbons, though thought to be among the most inert, may also present hazards.
Halocarbons, including those that might not be hazards in themselves, can present waste disposal issues. Because they do not readily degrade in natural environments, halocarbons tend to accumulate. Incineration and accidental fires can create corrosive byproducts such as hydrochloric acid and hydrofluoric acid, and poisons like halogenated dioxins and furans. Species of Desulfitobacterium are being investigated for their potential in the bioremediation of halogenic organic compounds. | Halocarbon | Wikipedia | 401 | 977193 | https://en.wikipedia.org/wiki/Halocarbon | Physical sciences | Halocarbons | Chemistry |
In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms substituent and functional group, as well as side chain and pendant group, are used almost interchangeably to describe those branches from the parent structure, though certain distinctions are made in polymer chemistry. In polymers, side chains extend from the backbone structure. In proteins, side chains are attached to the alpha carbon atoms of the amino acid backbone.)
The suffix -yl is used when naming organic compounds that contain a single bond replacing one hydrogen; -ylidene and -ylidyne are used with double bonds and triple bonds, respectively. In addition, when naming hydrocarbons that contain a substituent, positional numbers are used to indicate which carbon atom the substituent attaches to when such information is needed to distinguish between isomers. Substituents can be a combination of the inductive effect and the mesomeric effect. Such effects are also described as electron-rich and electron withdrawing. Additional steric effects result from the volume occupied by a substituent.
The phrases most-substituted and least-substituted are frequently used to describe or compare molecules that are products of a chemical reaction. In this terminology, methane is used as a reference of comparison. Using methane as a reference, for each hydrogen atom that is replaced or "substituted" by something else, the molecule can be said to be more highly substituted. For example:
Markovnikov's rule predicts that the hydrogen atom is added to the carbon of the alkene functional group which has the greater number of hydrogen atoms (fewer alkyl substituents).
Zaitsev's rule predicts that the major reaction product is the alkene with the more highly substituted (more stable) double bond.
Nomenclature
The suffix -yl is used in organic chemistry to form names of radicals, either separate species (called free radicals) or chemically bonded parts of molecules (called moieties). It can be traced back to the old name of methanol, "methylene" (from , 'wine' and , 'wood', 'forest'), which became shortened to "methyl" in compound names, from which -yl was extracted. Several reforms of chemical nomenclature eventually generalized the use of the suffix to other organic substituents. | Substituent | Wikipedia | 512 | 977244 | https://en.wikipedia.org/wiki/Substituent | Physical sciences | Concepts_2 | Chemistry |
The use of the suffix is determined by the number of hydrogen atoms that the substituent replaces on a parent compound (and also, usually, on the substituent). According to the 1993 IUPAC recommendations:
-yl means that one hydrogen is replaced.
-ylidene means that two hydrogens are replaced by a double bond between parent and substituent.
-ylidyne means that three hydrogens are replaced by a triple bond between parent and substituent.
The suffix -ylidine is encountered sporadically, and appears to be a variant spelling of "-ylidene"; it is not mentioned in the IUPAC guidelines.
For multiple bonds of the same type, which link the substituent to the parent group, the infixes -di-, -tri-, -tetra-, etc., are used: -diyl (two single bonds), -triyl (three single bonds), -tetrayl (four single bonds), -diylidene (two double bonds).
For multiple bonds of different types, multiple suffixes are concatenated: -ylylidene (one single and one double), -ylylidyne (one single and one triple), -diylylidene (two single and one double).
The parent compound name can be altered in two ways: | Substituent | Wikipedia | 288 | 977244 | https://en.wikipedia.org/wiki/Substituent | Physical sciences | Concepts_2 | Chemistry |
For many common compounds the substituent is linked at one end (the 1 position) and historically not numbered in the name. The IUPAC 2013 Rules however do require an explicit locant for most substituents in a preferred IUPAC name. The substituent name is modified by stripping -ane (see alkane) and adding the appropriate suffix. This is "recommended only for saturated acyclic and monocyclic hydrocarbon substituent groups and for the mononuclear parent hydrides of silicon, germanium, tin, lead, and boron". Thus, if there is a carboxylic acid called "X-ic acid", an alcohol ending "X-anol" (or "X-yl alcohol"), or an alkane called "X-ane", then "X-yl" typically denotes the same carbon chain lacking these groups but modified by attachment to some other parent molecule.
The more general method omits only the terminal "e" of the substituent name, but requires explicit numbering of each yl prefix, even at position 1 (except for -ylidyne, which as a triple bond must terminate the substituent carbon chain). Pentan-1-yl is an example of a name by this method, and is synonymous with pentyl from the previous guideline.
Note that some popular terms such as "vinyl" (when used to mean "polyvinyl") represent only a portion of the full chemical name.
Methane substituents
According to the above rules, a carbon atom in a molecule, considered as a substituent, has the following names depending on the number of hydrogens bound to it, and the type of bonds formed with the remainder of the molecule:
Notation
In a chemical structural formula, an organic substituent such as methyl, ethyl, or aryl can be written as R (or R1, R2, etc.) It is a generic placeholder, the R derived from radical or rest, which may replace any portion of the formula as the author finds convenient. The first to use this symbol was Charles Frédéric Gerhardt in 1844.
The symbol X is often used to denote electronegative substituents such as the halides. | Substituent | Wikipedia | 484 | 977244 | https://en.wikipedia.org/wiki/Substituent | Physical sciences | Concepts_2 | Chemistry |
Statistical distribution
One cheminformatics study identified 849,574 unique substituents up to 12 non-hydrogen atoms large and containing only carbon, hydrogen, nitrogen, oxygen, sulfur, phosphorus, selenium, and the halogens in a set of 3,043,941 molecules. Fifty substituents can be considered common as they are found in more than 1% of this set, and 438 are found in more than 0.1%. 64% of the substituents are found in only one molecule. The top 5 most common are the methyl, phenyl, chlorine, methoxy, and hydroxyl substituents. The total number of organic substituents in organic chemistry is estimated at 3.1 million, creating a total of 6.7×1023 molecules. An infinite number of substituents can be obtained simply by increasing carbon chain length. For instance, the substituents methyl (-CH3) and pentyl (-C5H11). | Substituent | Wikipedia | 219 | 977244 | https://en.wikipedia.org/wiki/Substituent | Physical sciences | Concepts_2 | Chemistry |
The Santiago Metro () is a rapid transit system serving the city of Santiago, the capital of Chile. It currently consists of seven lines (numbered 1-6 and 4A), 143 stations, and of revenue route. The system is managed by the state-owned Metro S.A. and is the first rapid transit system in the country.
The Santiago Metro carries around 2.5 million passengers daily. This figure represents an increase of more than a million passengers per day compared to 2007, when the ambitious Transantiago project was launched, in which the metro plays an important role in the public transport system serving the city. Its highest passenger peak was reached on 2 May 2019, reaching 2,951,962 passengers.
In June 2017 the government announced plans for the construction of Line 7, connecting Renca in the northwest of Santiago with Vitacura in the northeast. The new line will add and 19 new stations to the Metro network, running along the municipalities of Renca, Cerro Navia, Quinta Normal, Santiago, Providencia, Las Condes and Vitacura. Its cost has been initially estimated at US$2.53 bn, and it is projected to open in 2027.
In March 2012, the Santiago Metro was chosen as the best underground system in the Americas, after being honoured at the annual reception held by Metro Rail in London.
History and development
Early projections and construction of Line 1
The idea of constructing an underground railway network in Santiago dates back to 1944 when efforts to improve the chaotic transport system were initiated due to the rapid population growth the city had been experiencing since the early 1930s.
However, concrete plans began to materialize in the 1960s when Juan Parrochia was appointed as Chief Architect of the Intercommunal Plan of Santiago and began working on an urban master plan featuring a Metro network.
Consequently, the government issued an international tender for the development of an urban transport system. On 24 October 1968, the government of Eduardo Frei Montalva approved the draft submitted by the Franco-Chilean consortium BCEOM SOFRETU CADE, in which the construction of five lines with an extension of approximately by 1990 was proposed.
On 29 May 1969, works finally began for the construction of the first line, which would link the Civil District and the area of Barrancas (current-day Lo Prado). | Santiago Metro | Wikipedia | 473 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
On 15 September 1975, the first line of the metro was opened by Augusto Pinochet during the military dictatorship. Line 1, during its opening stage, was mostly underground from San Pablo to La Moneda, running below the Alameda. In 1977, the line was extended towards Providencia and by 1980, the line reached as far as Escuela Militar in Las Condes.
In March 1978, Line 2 was opened. Its initial section ran at ground level from Los Héroes to Franklin. By December, the second segment of the line was opened, running underground towards the south along the Gran Avenida up to Lo Ovalle.
Project changes
Despite the fast growth of the network, the severe economic crisis that affected the country in 1982 halted the original plans. Furthermore, studies showed that southeast Santiago was becoming more populated than the north end of the capital, area that was then covered by the planned extensions of the service.
In order to supply future demand, the layout for Line 2 was changed and the extension would start at Los Héroes and go around the Civic District, crossing Line 1 again at Baquedano to head south through Vicuña Mackenna. Meanwhile, Line 3 was projected through Independencia and Irarrázaval to supply the northern area that Line 2 was supposed to run.
However, these plans were affected once again when an earthquake struck the Chilean Central Valley on 3 March 1985. Most of the funds destined for the construction of the Line 2 extension and Line 3 were used to rebuild the city. The opening of two new stations towards the north in 1986 (Santa Ana) and 1987 (Puente Cal y Canto) were the only finalised works from these plans: Santa Ana and Mapocho stations on Line 2. The latter would change its name later, as remains of the old Calicanto Bridge –emblem of the city for over a century– were discovered during the excavation process. That same year, the Metrobús service was launched with services operating from Escuela Militar, Lo Ovalle and Las Rejas.
Institutionally, the management of Metro de Santiago was changed at the end of the decade. The former General Directorate of Metro, a branch of the Ministry of Public Works, became a state-funded public company, Metro S.A., with the provisions of Law 18,772 published on 28 January 1989. | Santiago Metro | Wikipedia | 479 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
Following the economic recovery after the second miracle, the metro's expansion plans resurged. Population growth in the southeastern area of the capital became unstoppable during the 1980s, and La Florida became the most populous commune in the country, thus the construction of a new line to supply that area was paramount. The first plans were drawn in 1989 and it was officially announced in 1991 by President Patricio Aylwin. This new line would start from Baquedano and head southwards to Américo Vespucio Avenue, crossing through Vicuña Mackenna.
Line 5 was opened on 5 April 1997 by President Eduardo Frei Ruiz-Tagle. This new line would have a length of initially running underground from Baquedano to Irarrázaval, emerging as a viaduct on Vicuña Mackenna and going underground before reaching its southeastern terminus, Bellavista de la Florida.
In March 2000, a new section of Line 5 crossing the historic centre of the capital was opened to the public. The new connection between Baquedano and Santa Ana through Plaza de Armas and Bellas Artes meant that all three at-the-time existing lines would be connected.
New lines 4 and 4A and line 2 extension
With the election of Ricardo Lagos as President of Chile in 2000, one of his main objectives was an overhaul of the transport system serving the capital. To achieve this, a new extension for Line 5 was designed, heading westwards to Quinta Normal, following Catedral street, and an extension for Line 2 from both ends of the line to reach the northern and southern ends of the Américo Vespucio ring road.
Despite this, the biggest announcement was made in 2002 when Lagos disclosed the construction of a fourth line for the metro, serving the southeastern communes of Santiago to reach the heart of Puente Alto, which had taken over La Florida as the most populous commune of the country. With these new projects, the Metro network would double its extension by 2010, year in which the country would celebrate its bicentennial. | Santiago Metro | Wikipedia | 417 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
These new projects were designed to make Metro the key element of the new transport reform plan for the city, Transantiago. Along with the new extensions, exchange stations were designed to allow for a better interaction between the urban railways and other means of transport, mainly buses. The first exchange station would open in Quinta Normal after the Line 5 extension was finalised on 31 March 2004. However, the original plan to host a railway station would be discarded following the failure of the Melitrén construction.
On September 8, 2004, the Metro would make another breakthrough when the Mapocho river was crossed underground, with the opening of Patronato and Cerro Blanco stations on Line 2. On 22 December 2004, the southern extension of the same line opened its new stations, El Parrón and La Cisterna. A second stretch of Line 2 towards the north would open on 25 November 2005, and the last in the series of extensions opened on 22 December 2005, with a total cost of US$170 million and a 27-million passenger increase annually.
On November 30, 2005, the first underground leg of Line 4 from Tobalaba to Grecia, and the viaduct between Vicente Valdés and Plaza de Puente Alto opened to the public. The unfinished track from Grecia and Vicente Valdés was covered by a rail replacement bus service operated by Transantiago until March 2, 2006, when the remaining stations and track were finished. Line 4 at this time was the longest of the network, with an extension of and 22 stations serving Providencia, Las Condes, Ñuñoa, La Reina, Peñalolén, Macul, La Florida and Puente Alto. This new line also saw the introduction of new rolling stock, the AS-2002, manufactured by Alstom in Brazil, featuring more interior space than those running other lines. Finally, Line 4 would be complemented with the opening of a branch service on August 16, 2006, Line 4A, which connected Line 2 from La Cisterna with Line 4 at Vicuña Mackenna, running through the Américo Vespucio ring road.
Extensions to Las Condes and Maipú
On November 15, 2005, President Ricardo Lagos announced the extension of Line 1 to the east, from Escuela Militar to Los Dominicos station, in the commune of Las Condes. To achieve this, three new stations were built, adding 4 kilometers to the railway network, which were inaugurated on January 7, 2010, during the presidency of Michelle Bachelet. | Santiago Metro | Wikipedia | 512 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
Along with the extension to Las Condes, one of the most important projects of the service was announced: the extension of the metro to the west, connecting the communes of Maipú, Pudahuel, Lo Prado and Quinta Normal to the Metro Network. In this way, the Metro approached the western sector of the city for the first time, reaching Maipú, the most populated commune in the country after surpassing Puente Alto in 2008.
On October 31, 2009, the final layout of the extension of Line 5 was approved, starting from the Quinta Normal station along Avenida San Pablo underground, turning south to come to the surface and travel along Avenida Teniente Cruz and later Avenida Pajaritos before becoming underground again and reaching the terminal station, in the Plaza de Armas of Maipú. The first section to the Pudahuel station was delivered on January 12, 2010, while the remaining section Until Maipú was opened to the public on February 3, 2011.
Along with the construction of the new extensions, important works were carried out that allowed the Pajaritos station on Line 1 to be renovated to convert it into the terminal of a loop, allowing greater efficiency to the most loaded section of said line and the postponed San José de la Estrella station was inaugurated on Line 4. The Del Sol station was also built in the extension to Maipú, which serves as a transfer to intercity buses.
In March 2012, the Santiago Metro was chosen as the best metro system in America, a distinction received at the annual Metro Rail dinner held in London, United Kingdom.
Line 2 and 3 extensions
On May 26, 2016, Metro announced the extension of Lines 2 and 3, adding 8.9 kilometers and 7 new stations to the Metro network. Both extensions are expected to begin operations during the second half of 2021. The extension of Line 2 to the south will add 5.1 kilometers and 4 new stations connecting the current terminal station in La Cisterna with San Bernardo locality. The new terminal station will be located next to a hospital called Hospital El Pino in San Bernardo. Meanwhile, the extension of Line 3 to the west will add 3.8 kilometers and 3 new stations to the Metro network, connecting future station Los Libertadores with Quilicura. | Santiago Metro | Wikipedia | 461 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
On November 2, 2017, Line 6 was inaugurated from Cerrillos to Los Leones adding 10 new stations. This new line does not have staffed ticket offices; instead there are automatic machines for ticket sales and loading money onto bip! cards. It has platform-edge doors to protect passengers, and traction power is supplied by overhead line equipment, not by conductor rails as on the other lines. It has new entrance and exit turnstiles at stations. The trains on Line 6 only have steel wheels, and are driverless.
On January 22, 2019, Line 3 was inaugurated, after 9 years of prospecting and construction and being delayed since the 1980s after the 1985 Algarrobo earthquake and the changing demographics of the city during the '80s and '90s. Its rolling stock material is identical to the Line 6 and were built simultaneously, so they're considered "twin lines".
On September 25, 2023, Line 3 was extended 3.8 km west from its northern terminus to Plaza Quilicura.
On November 27, 2023, Line 2 was extended 5.2 km south from its southern terminus to Hospital El Pino.
2019 protests
During the month of October 2019, the Santiago metro network was affected by social protests due to the increase in the fare of the entire Metropolitan Mobility Network. Initially, secondary students staged massive acts of evasion between 6 and 11 October. The protests quickly escalated to several metro stations, resulting in train service being repeatedly interrupted.
On Friday the 18th, the situation escalated and the entire network had to be closed due to attacks on stations and workers. At night, after the declaration of a state of emergency by President Sebastián Piñera, several stations of the Metro were destroyed and burned, some of which were attacked again the next day, even though a curfew had been established. Meanwhile, the Instituto Nacional de Derechos Humanos investigated accusations that the Baquedano station was used as a detention and torture center by police and military. On the morning of the same day, the site was reviewed by staff from the INDH, PDI and guarantee judges. The judges found no evidence of torture or illegal detentions at the site, but an investigation was launched to rule out any irregular situation. However, investigations conducted by the National Institute of Human Rights and the Public Prosecutor's Office found no evidence in this regard; in 2020, the allegations were dismissed, and the case was closed. | Santiago Metro | Wikipedia | 493 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
The Metro network had been partially reactivated as of Monday, October 21; however, due to the damage of some stations, the network will only be available in its entirety within a period of up to 7 months. Damage costs are estimated at more than $300 million. Metro de Santiago indicated that it does not have insurance contracted for the infrastructure of the stations and trains. Lines 3 and 6, meanwhile, opened on 23 October, Lines 2 and 5 on the 25th, Line 4 on the 28th, and line 4A on November 25, in all cases partially and on a shortened schedule.
On October 23, it was reported that 79 stations had been damaged in all, with lines 4, 4A, and 5 having the highest number of stations destroyed or vandalized. There were also damage to 6 trains, 5 on line 4 and one on line 1 - the latter set on fire at the San Pablo station. Upon the reopening of the last two stations (Trinidad and Protectora de la Infancia) on September 25, 2020, the metro system was back to 100% operation.
Lines 7, 8 and 9
On June 1, 2017, President Michelle Bachelet announced in her last public account the construction of Metro Line 7. The plan initially included 21 stations along a 25 km extension, between the commune of Renca in the northwestern sector, and Vitacura in the northeastern sector. The route, estimated to open around 2027, was designed with a line parallel to the Mapocho River and Line 1 in mind, which would allow it to be decongested by approximately 10 000 daily passengers. Line 7 would allow the incorporation of the communes of Renca, Cerro Navia and Vitacura into the Network, also connecting popular neighborhoods with part of the financial and commercial district of the city.
At the end of 2017, the newspaper El Mercurio published a report that indicated that the route of the line was modified, so that in the Providencia sector it would not circulate under Andrés Bello Avenue (as originally thought), but would go parallel to Line 1 along Providencia Avenue, eliminating the combination in Salvador and moving it to Pedro de Valdivia. In addition, Metro announced that it would extend Line 6 to Isidora Goyenechea of the future Line 7. | Santiago Metro | Wikipedia | 466 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
One year after the announcement of Line 7, President Sebastián Piñera announced in his 2018 annual account that studies would begin for the construction of two new metro lines in a north–south direction: Line 8, which will connect the communes of La Florida and Puente Alto with Providencia, while Line 9 would reach from the center to the commune of La Pintana, one of the last in the city to receive the Metro. In addition, he announced that Line 4 would be extended by three stations in the southern sector to reach Bajos de Mena in Puente Alto. It was projected at that time that lines 8 and 9 would be inaugurated in 2028.
The impact of the social outbreak of 2019 delayed the planning work for the extension of the three lines, being resumed in September 2021, so it is estimated that lines 7, 8 and 9 would be inaugurated from 2030. In August 2023, a modification to the layout of Line 9 was announced, expanding it in the north to the Puente Cal y Canto station — which will become the first station with four concurrent lines — and in the south to Plaza de Puente Alto, combining with Line 4 and absorbing the proposed extension to Bajos de Mena.
Future plans
Various proposals have been presented to expand the Santiago Metro once lines 7, 8 and 9 are built.
Two communes in Greater Santiago will not have a direct connection to the Metro Network: Lo Espejo and Lo Barnechea, while other three only have in theirs limits; San Bernardo, Peñalolén and Huechuraba. In the case of Lo Espejo, the municipality has proposed expanding Line 4A through Américo Vespucio towards the west, in order to connect the commune to the network, while Lo Barnechea has expressed its interest in building two additional stations on Line 7 to reach La Dehesa. Meanwhile, the municipality of Maipú —one of the most populated in the city— launched a campaign to request the government to extend Line 6 to the western sector. Other proposals include reach the International Airport, for example, through a branch of Line 7. | Santiago Metro | Wikipedia | 428 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
During the inauguration of Line 3 in 2019, President Sebastián Piñera declared that Line 10 was going to be built. Although Metro indicated that a tenth line was not officially in its project portfolio, the government indicated that the initiative attempted to connect the Avenida Mapocho sector with Avenida Tobalaba, following the so-called "central ring" along Las Rejas, Suiza and Departamental avenues.
Other alternatives for new lines have been analyzed in the media in recent years and have been momentarily discarded; a line in the eastern sector through Tobalaba-Vespucio or Manquehue, another parallel to Line 1 through 5 de Abril-Blanco Encalada-Santa Isabel-Bilbao and Manquehue, and the northern section of "Line 10" through Dorsal, Lo Espinoza and Radal.
Timeline
Rolling stock
The Santiago Metro currently operates 9 models of rolling stock: two models (the AS-2002 and the AS-2014) are steel-wheeled, while the others are all rubber-tyred. The NS 74 and NS 93 stock are based on the MP 73 and MP 89 stock of the Paris Metro respectively, while the NS-88 and NS-2007 stock are based on the FM-86 and NM-02 stock of the Mexico City Metro respectively. All rubber-tyred stock is preceded with the acronym NS (for Neumático Santiago); likewise, all steel-wheeled stock is preceded with the acronym AS (for Acero Santiago). The number representing each type of rubber-tyred and steel-wheeled rolling stock is the year of design of a particular rolling stock, not year of first use, similar to the practice in the Mexico City Metro and Paris Métro.
Currently, all the NS-2007 stock and a number of the NS-93 stock units are retrofitted with air conditioning, whereas the NS-2012, AS-2014 and NS-2016 were all built with air conditioning.
In September 2012, the NS 2012 trains went into service on Line 1. These trains are the first to be built with air conditioning. | Santiago Metro | Wikipedia | 423 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
On November 2, 2017, the line 6 entered revenue service. This line utilizes the AS-2014 (Acero Santiago 2014) which are the most modern stock of the system , being the first model in the system that are driverless. However, in the first and last car there is a control panel meant to control the train when necessary. It is also the first with security cameras, energy obtainment via overhead rigid catenary, and evacuation doors at the front of the first and last car (with an evacuation ramp for people on wheelchairs) as well as on the sides of each convoy. They are also the second to be built with air conditioning, and the third with LED lights. The line that they operate in is also the first in revenue service with platform safety barriers, followed by Line 3 opened in January 2019.
Stations
In bold are transfer stations. In grey are stations projected or currently under construction.
MetroArte
The Santiago Metro incorporates 73 public artworks in its stations through the MetroArte fundation. Universidad de Chile features Memoria visual de una nación ("Visual Memory of a Nation"), a 1,200 square-meters mural created by Chilean painter Mario Toral and represents the history of the country. Other pieces of art are in Baquedano (featuring modern art and a concert space), Bellas Artes (multimedia art), Santa Lucía (Portuguese azulejos, a gift made by the Lisbon Metro), La Moneda (with realistic painting representing typical landscape), and various other stations.
Station amenities
A diverse array of services are provided within each Metro station. Ticket offices, public telephones and metro-network information panels exist in every station; Redbanc, Cirrus and Plus-enabled ATMs, typically provided by either the Banco de Chile company or the BancoEstado national bank, are common. Automatic recharge machines are also common, with all such machines charging a customer's Bip! card with either cash deposits or a Redbanc-enabled card. In higher-traffic stations, there are screens that display MetroTV, featuring additional system information as well as music videos and short news segments.
Some 21 of the busiest stations contain a branch of Bibliometro, a system of lending libraries supported by the national Department of Libraries, Archives and Museums (Dibam). A Chilean ID or foreign passport allows any Metro customer to freely borrow from a reserve of books and other literature, but a registration is needed first. | Santiago Metro | Wikipedia | 504 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
Customers may rent a parking space for their bicycles through the Bicimetro network, which opened in 2008 at six stations and is slowly expanding, for a starting cost of $300 (approximately US$0.50) a day. There are weekly and monthly rental services too, that guarantee a fixed space for the bike (contrary to the daily rent which relies on random free-space).
Most underground Metro stations contain at least one shop or convenience store, with large line-transfer stations such as Baquedano featuring several food vendors and retailers, and even a small underground "shopping center" in Universidad de Chile.
Security and safety
Various private security agencies have day-to-day responsibility for maintaining order in the metro and deterring petty crime or attempts to board without paying. The largest transfer stations, such as Tobalaba, also feature depots of the Carabineros de Chile, the national military police force. Metro staff man the ticket counters in closed box offices and distribute tickets and money through small transaction windows.
Signage to advise customers of safety hazards is extensive, and each platform has a painted yellow line which customers are advised to not cross except to board a train. During rush hour, Metro staff line the platform edge to keep people from being crowded off the platform and to support disabled customers. There is no physical barrier between the edge and the tracks (with the exception of recently opened Lines 3 and 6), including the hazardous, electrified third rail. However, lines 3 and 6 use overhead lines as the powersource of the trains.
Metro travelers are advised to keep a close guard on their belongings, as petty or opportunistic theft is somewhat of a problem in lines that connect some districts to the center of Santiago. This is most apparent with passengers who reverse their backpacks so that the bag is across the stomach, to ensure that no one can pilfer the pockets out of sight. | Santiago Metro | Wikipedia | 385 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
Pricing and working hours
Metro is part of Red Metropolitana de Movilidad, the integrated public transport system that serves the capital using also feeder and main bus routes. Red works with an integrated fare system, which allows passengers to make bus-bus or bus-metro transfers on a two-hour time limit from the first trip (maximum of two changes) using a contactless smart card called "Bip! card". Bus-to-bus, metro-to-bus and metro-to-train transfers do not cost extra. Bus-to-metro transfers costs $20 (approx. US$0.03) during Horario Valle (low-use hours) and $80 (approx. US$0.12) during Horario Punta (rush hour).
Bip! cards are available in all the ticketing offices in every station at a cost of $1,550 (approx. US$2.23), with a minimum first charge of $1000 worth of credit (approx. US$1.41). Tickets are sold from 6:00 to 23:00 Monday to Friday, 6:30 to 23:00 on Saturdays, and 8:00 to 22:30 on Sundays and holidays. Cards can be topped up to $20000, and the credit only expires if the card it is not used in two years.
Metro also used to sell single-trip, Metro-use only tickets, but they went out of circulation in early 2017. Fares depended on the time of the use of the system. The cost of a ticket in the Horario Punta (rush hour, 7:00–8:59 and 18:00–19:59) was $700 (approx. US$1.01); in the Horario Valle (off-peak hours, 6:30–6:59, 9:00–18:00, 20:00–20:44, and all day on weekends and holidays) was $640 (approximately US$0.90); and in the Horario Bajo (low-use hours, 6:00–6:29 and 20:45–23:00) was $590 (approximately US0.85).
Senior citizens (65 and older) and students holding concession cards pay $200 (US$0.28). Senior concession fare does not apply during rush hours. | Santiago Metro | Wikipedia | 490 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
On weekdays, the metro operates from 5.35 am until 12.08 am, while on Saturdays it operates from 6.30 am until 12.08 am and on Sundays and public holidays the metro operates from 8 am (Line 1 from 9 am) until 11.48 pm. However, due to the COVID-19 Pandemic, operating hours have varied in accordance with national curfew.
(warning: stations close earlier - see timetable) | Santiago Metro | Wikipedia | 92 | 977418 | https://en.wikipedia.org/wiki/Santiago%20Metro | Technology | Americas | null |
The rings of Saturn are the most extensive and complex ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometers to meters, that orbit around Saturn. The ring particles are made almost entirely of water ice, with a trace component of rocky material. There is still no consensus as to their mechanism of formation. Although theoretical models indicated that the rings were likely to have formed early in the Solar System's history, newer data from Cassini suggested they formed relatively late.
Although reflection from the rings increases Saturn's brightness, they are not visible from Earth with unaided vision. In 1610, the year after Galileo Galilei turned a telescope to the sky, he became the first person to observe Saturn's rings, though he could not see them well enough to discern their true nature. In 1655, Christiaan Huygens was the first person to describe them as a disk surrounding Saturn. The concept that Saturn's rings are made up of a series of tiny ringlets can be traced to Pierre-Simon Laplace, although true gaps are few – it is more correct to think of the rings as an annular disk with concentric local maxima and minima in density and brightness. On the scale of the clumps within the rings there is much empty space.
The rings have numerous gaps where particle density drops sharply: two opened by known moons embedded within them, and many others at locations of known destabilizing orbital resonances with the moons of Saturn. Other gaps remain unexplained. Stabilizing resonances, on the other hand, are responsible for the longevity of several rings, such as the Titan Ringlet and the G Ring.
Well beyond the main rings is the Phoebe ring, which is presumed to originate from Phoebe and thus share its retrograde orbital motion. It is aligned with the plane of Saturn's orbit. Saturn has an axial tilt of 27 degrees, so this ring is tilted at an angle of 27 degrees to the more visible rings orbiting above Saturn's equator.
In September 2023, astronomers reported studies suggesting that the rings of Saturn may have resulted from the collision of two moons "a few hundred million years ago".
History
Early observations | Rings of Saturn | Wikipedia | 455 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
Galileo Galilei was the first to observe the rings of Saturn in 1610 using his telescope, but was unable to identify them as such. He wrote to the Duke of Tuscany that "The planet Saturn is not alone, but is composed of three, which almost touch one another and never move nor change with respect to one another. They are arranged in a line parallel to the zodiac, and the middle one (Saturn itself) is about three times the size of the lateral ones." He also described the rings as Saturn's "ears". In 1612 the Earth passed through the plane of the rings and they became invisible. Mystified, Galileo remarked "I do not know what to say in a case so surprising, so unlooked for and so novel." He mused, "Has Saturn swallowed his children?" — referring to the myth of the Titan Saturn devouring his offspring to forestall the prophecy of them overthrowing him. He was further confused when the rings again became visible in 1613.
Early astronomers used anagrams as a form of commitment scheme to lay claim to new discoveries before their results were ready for publication. Galileo used the anagram "" for Altissimum planetam tergeminum observavi ("I have observed the most distant planet to have a triple form") for discovering the rings of Saturn.
In 1657 Christopher Wren became Professor of Astronomy at Gresham College, London. He had been making observations of the planet Saturn from around 1652 with the aim of explaining its appearance. His hypothesis was written up in De corpore saturni, in which he came close to suggesting the planet had a ring. However, Wren was unsure whether the ring was independent of the planet, or physically attached to it. Before Wren's hypothesis was published Christiaan Huygens presented his hypothesis of the rings of Saturn. Immediately Wren recognised this as a better hypothesis than his own and De corpore saturni was never published. Robert Hooke was another early observer of the rings of Saturn, and noted the casting of shadows on the rings.
Huygens' ring hypothesis and later developments | Rings of Saturn | Wikipedia | 431 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
Huygens began grinding lenses with his father Constantijn in 1655 and was able to observe Saturn with greater detail using a 43× power refracting telescope that he designed himself. He was the first to suggest that Saturn was surrounded by a ring detached from the planet, and famously published the letter string "". Three years later, he revealed it to mean Annulo cingitur, tenui, plano, nusquam coherente, ad eclipticam inclinato ("[Saturn] is surrounded by a thin, flat, ring, nowhere touching [the body of the planet], inclined to the ecliptic"). He published his ring hypothesis in Systema Saturnium (1659) which also included his discovery of Saturn's moon, Titan, as well as the first clear outline of the dimensions of the Solar System.
In 1675, Giovanni Domenico Cassini determined that Saturn's ring was composed of multiple smaller rings with gaps between them; the largest of these gaps was later named the Cassini Division. This division is a region between the A ring and B Ring.
In 1787, Pierre-Simon Laplace proved that a uniform solid ring would be unstable and suggested that the rings were composed of a large number of solid ringlets.
In 1859, James Clerk Maxwell demonstrated that a nonuniform solid ring, solid ringlets or a continuous fluid ring would also not be stable, indicating that the ring must be composed of numerous small particles, all independently orbiting Saturn. Later, Sofia Kovalevskaya also found that Saturn's rings cannot be liquid ring-shaped bodies. Spectroscopic studies of the rings which were carried out independently in 1895 by James Keeler of the Allegheny Observatory and by Aristarkh Belopolsky of the Pulkovo Observatory showed that Maxwell's analysis was correct. | Rings of Saturn | Wikipedia | 373 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
Four robotic spacecraft have observed Saturn's rings from the vicinity of the planet. Pioneer 11s closest approach to Saturn occurred in September 1979 at a distance of . Pioneer 11 was responsible for the discovery of the F ring. Voyager 1s closest approach occurred in November 1980 at a distance of . A failed photopolarimeter prevented Voyager 1 from observing Saturn's rings at the planned resolution; nevertheless, images from the spacecraft provided unprecedented detail of the ring system and revealed the existence of the G ring. Voyager 2s closest approach occurred in August 1981 at a distance of . Voyager 2s working photopolarimeter allowed it to observe the ring system at higher resolution than Voyager 1, and to thereby discover many previously unseen ringlets. Cassini spacecraft entered into orbit around Saturn in July 2004. Cassini images of the rings are the most detailed to-date, and are responsible for the discovery of yet more ringlets.
The rings are named alphabetically in the order they were discovered: A and B in 1675 by Giovanni Domenico Cassini, C in 1850 by William Cranch Bond and his son George Phillips Bond, D in 1933 by Nikolai P. Barabachov and B. Semejkin, E in 1967 by Walter A. Feibelman, F in 1979 by Pioneer 11, and G in 1980 by Voyager 1. The main rings are, working outward from the planet, C, B and A, with the Cassini Division, the largest gap, separating Rings B and A. Several fainter rings were discovered more recently. The D Ring is exceedingly faint and closest to the planet. The narrow F Ring is just outside the A Ring. Beyond that are two far fainter rings named G and E. The rings show a tremendous amount of structure on all scales, some related to perturbations by Saturn's moons, but much unexplained.
In September 2023, astronomers reported studies suggesting that the rings of Saturn may have resulted from the collision of two moons "a few hundred million years ago". | Rings of Saturn | Wikipedia | 413 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
Saturn's axial inclination
Saturn's axial tilt is 26.7°, meaning that widely varying views of the rings, of which the visible ones occupy its equatorial plane, are obtained from Earth at different times. Earth makes passes through the ring plane every 13 to 15 years, about every half Saturn year, and there are about equal chances of either a single or three crossings occurring in each such occasion. The most recent ring plane crossings were on 22 May 1995, 10 August 1995, 11 February 1996 and 4 September 2009; upcoming events will occur on 23 March 2025, 15 October 2038, 1 April 2039 and 9 July 2039. Favorable ring plane crossing viewing opportunities (with Saturn not close to the Sun) only come during triple crossings.
Saturn's equinoxes, when the Sun passes through the ring plane, are not evenly spaced. The sun passes south to north through the ring plane when Saturn's heliocentric longitude is 173.6 degrees (e.g. 11 August 2009), about the time Saturn crosses from Leo to Virgo. 15.7 years later Saturn's longitude reaches 353.6 degrees and the sun passes to the south side of the ring plane. On each orbit the Sun is north of the ring plane for 15.7 Earth years, then south of the plane for 13.7 years. Dates for north-to-south crossings include 19 November 1995 and 6 May 2025, with south-to-north crossings on 11 August 2009 and 23 January 2039. During the period around an equinox the illumination of most of the rings is greatly reduced, making possible unique observations highlighting features that depart from the ring plane.
Physical characteristics
The dense main rings extend from to away from Saturn's equator, whose radius is (see Major subdivisions). With an estimated local thickness of as little as 10 meters (32' 10") and as much as 1 km (1093 yards), they are composed of 99.9% pure water ice with a smattering of impurities that may include tholins or silicates. The main rings are primarily composed of particles smaller than 10 m. | Rings of Saturn | Wikipedia | 437 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
Cassini directly measured the mass of the ring system via their gravitational effect during its final set of orbits that passed between the rings and the cloud tops, yielding a value of 1.54 (± 0.49) × 1019 kg, or 0.41 ± 0.13 Mimas masses. This is around two-thirds the mass of the Earth's entire Antarctic ice sheet, spread across a surface area 80 times larger than that of Earth. The estimate is close to the value of 0.40 Mimas masses derived from Cassini observations of density waves in the A, B and C rings. It is a small fraction of the total mass of Saturn (about 0.25 ppb). Earlier Voyager observations of density waves in the A and B rings and an optical depth profile had yielded a mass of about 0.75 Mimas masses, with later observations and computer modeling suggesting that was an underestimate. | Rings of Saturn | Wikipedia | 186 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
Although the largest gaps in the rings, such as the Cassini Division and Encke Gap, can be seen from Earth, the Voyager spacecraft discovered that the rings have an intricate structure of thousands of thin gaps and ringlets. This structure is thought to arise, in several different ways, from the gravitational pull of Saturn's many moons. Some gaps are cleared out by the passage of tiny moonlets such as Pan, many more of which may yet be discovered, and some ringlets seem to be maintained by the gravitational effects of small shepherd satellites (similar to Prometheus and Pandora's maintenance of the F ring). Other gaps arise from resonances between the orbital period of particles in the gap and that of a more massive moon further out; Mimas maintains the Cassini Division in this manner. Still more structure in the rings consists of spiral waves raised by the inner moons' periodic gravitational perturbations at less disruptive resonances.
Data from the Cassini space probe indicate that the rings of Saturn possess their own atmosphere, independent of that of the planet itself. The atmosphere is composed of molecular oxygen gas (O2) produced when ultraviolet light from the Sun interacts with water ice in the rings. Chemical reactions between water molecule fragments and further ultraviolet stimulation create and eject, among other things, O2. According to models of this atmosphere, H2 is also present. The O2 and H2 atmospheres are so sparse that if the entire atmosphere were somehow condensed onto the rings, it would be about one atom thick. The rings also have a similarly sparse OH (hydroxide) atmosphere. Like the O2, this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic ions that bombard water molecules ejected by Saturn's moon Enceladus. This atmosphere, despite being extremely sparse, was detected from Earth by the Hubble Space Telescope.
Saturn shows complex patterns in its brightness. Most of the variability is due to the changing aspect of the rings, and this goes through two cycles every orbit. However, superimposed on this is variability due to the eccentricity of the planet's orbit that causes the planet to display brighter oppositions in the northern hemisphere than it does in the southern. | Rings of Saturn | Wikipedia | 464 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
In 1980, Voyager 1 made a fly-by of Saturn that showed the F ring to be composed of three narrow rings that appeared to be braided in a complex structure; it is now known that the outer two rings consist of knobs, kinks and lumps that give the illusion of braiding, with the less bright third ring lying inside them.
New images of the rings taken around the 11 August 2009 equinox of Saturn by NASA's Cassini spacecraft have shown that the rings extend significantly out of the nominal ring plane in a few places. This displacement reaches as much as at the border of the Keeler Gap, due to the out-of-plane orbit of Daphnis, the moon that creates the gap.
Formation and evolution of main rings
Estimates of the age of Saturn's rings vary widely, depending on the approach used. They have been considered to possibly be very old, dating to the formation of Saturn itself. However, data from Cassini suggest they are much younger, having most likely formed within the last 100 million years, and may thus be between 10 million and 100 million years old. This recent origin scenario is based on a new, low mass estimate modeling of the rings' dynamical evolution, and measurements of the flux of interplanetary dust, which feed into an estimate of the rate of ring darkening over time. Since the rings are continually losing material, they would have been more massive in the past than at present. The mass estimate alone is not very diagnostic, since high mass rings that formed early in the Solar System's history would have evolved by now to a mass close to that measured. Based on current depletion rates, they may disappear in 300 million years. | Rings of Saturn | Wikipedia | 347 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
There are two main hypotheses regarding the origin of Saturn's inner rings. A hypothesis originally proposed by Édouard Roche in the 19th century is that the rings were once a moon of Saturn (named Veritas, after a Roman goddess who hid in a well). According to the hypothesis, the moon's orbit decayed until it was close enough to be ripped apart by tidal forces (see Roche limit). Numerical simulations carried out in 2022 support this hypothesis; the authors of that study proposed the name "Chrysalis" for the destroyed moon. A variation on this hypothesis is that this moon disintegrated after being struck by a large comet or asteroid. The second hypothesis is that the rings were never part of a moon, but are instead left over from the original nebular material from which Saturn formed.
A more traditional version of the disrupted-moon hypothesis is that the rings are composed of debris from a moon 400 to 600 km (200 to 400 miles) in diameter, slightly larger than Mimas. The last time there were collisions large enough to be likely to disrupt a moon that large was during the Late Heavy Bombardment some four billion years ago.
A more recent variant of this type of hypothesis by R. M. Canup is that the rings could represent part of the remains of the icy mantle of a much larger, Titan-sized, differentiated moon that was stripped of its outer layer as it spiraled into the planet during the formative period when Saturn was still surrounded by a gaseous nebula. This would explain the scarcity of rocky material within the rings. The rings would initially have been much more massive (≈1,000 times) and broader than at present; material in the outer portions of the rings would have coalesced into the innermost moons of Saturn (those closest to Saturn), out to Tethys, also explaining the lack of rocky material in the composition of most of these moons. Subsequent collisional or cryovolcanic evolution of Enceladus, which is another of these moons, might then have caused selective loss of ice from this moon, raising its density to its current value of 1.61 g/cm3, compared to values of 1.15 for Mimas and 0.97 for Tethys. | Rings of Saturn | Wikipedia | 463 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
The idea of massive early rings was subsequently extended to explain the formation of Saturn's moons out to Rhea. If the initial massive rings contained chunks of rocky material (>100 km; 60 miles across) as well as ice, these silicate bodies would have accreted more ice and been expelled from the rings, due to gravitational interactions with the rings and tidal interaction with Saturn, into progressively wider orbits. Within the Roche limit, bodies of rocky material are dense enough to accrete additional material, whereas less-dense bodies of ice are not. Once outside the rings, the newly formed moons could have continued to evolve through random mergers. This process may explain the variation in silicate content of Saturn's moons out to Rhea, as well as the trend towards less silicate content closer to Saturn. Rhea would then be the oldest of the moons formed from the primordial rings, with moons closer to Saturn being progressively younger.
The brightness and purity of the water ice in Saturn's rings have also been cited as evidence that the rings are much younger than Saturn, as the infall of meteoric dust would have led to a darkening of the rings. However, new research indicates that the B Ring may be massive enough to have diluted infalling material and thus avoided substantial darkening over the age of the Solar System. Ring material may be recycled as clumps form within the rings and are then disrupted by impacts. This would explain the apparent youth of some of the material within the rings. Evidence suggesting a recent origin of the C ring has been gathered by researchers analyzing data from the Cassini Titan Radar Mapper, which focused on analyzing the proportion of rocky silicates within this ring. If much of this material was contributed by a recently disrupted centaur or moon, the age of this ring could be on the order of 100 million years or less. On the other hand, if the material came primarily from micrometeoroid influx, the age would be closer to a billion years.
The Cassini UVIS team, led by Larry Esposito, used stellar occultation to discover 13 objects, ranging from 27 meters (89') to 10 km (6 miles) across, within the F ring. They are translucent, suggesting they are temporary aggregates of ice boulders a few meters across. Esposito believes this to be the basic structure of the Saturnian rings, particles clumping together, then being blasted apart. | Rings of Saturn | Wikipedia | 498 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
Research based on rates of infall into Saturn favors a younger ring system age of hundreds of millions of years. Ring material is continually spiraling down into Saturn; the faster this infall, the shorter the lifetime of the ring system. One mechanism involves gravity pulling electrically charged water ice grains down from the rings along planetary magnetic field lines, a process termed 'ring rain'. This flow rate was inferred to be 432–2870 kg/s using ground-based Keck telescope observations; as a consequence of this process alone, the rings will be gone in ~ million years. While traversing the gap between the rings and planet in September 2017, the Cassini spacecraft detected an equatorial flow of charge-neutral material from the rings to the planet of 4,800–44,000 kg/s. Assuming this influx rate is stable, adding it to the continuous 'ring rain' process implies the rings may be gone in under 100 million years.
Subdivisions and structures within the rings
The densest parts of the Saturnian ring system are the A and B Rings, which are separated by the Cassini Division (discovered in 1675 by Giovanni Domenico Cassini). Along with the C Ring, which was discovered in 1850 and is similar in character to the Cassini Division, these regions constitute the main rings. The main rings are denser and contain larger particles than the tenuous dusty rings. The latter include the D Ring, extending inward to Saturn's cloud tops, the G and E Rings and others beyond the main ring system. These diffuse rings are characterised as "dusty" because of the small size of their particles (often about a μm); their chemical composition is, like the main rings, almost entirely water ice. The narrow F Ring, just off the outer edge of the A Ring, is more difficult to categorize; parts of it are very dense, but it also contains a great deal of dust-size particles.
Physical parameters of the rings
Major subdivisions
C Ring structures
Cassini Division structures
Source:
A Ring structures
D Ring
The D Ring is the innermost ring, and is very faint. In 1980, Voyager 1 detected within this ring three ringlets designated D73, D72 and D68, with D68 being the discrete ringlet nearest to Saturn. Some 25 years later, Cassini images showed that D72 had become significantly broader and more diffuse, and had moved planetward by 200 km (100 miles). | Rings of Saturn | Wikipedia | 500 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
Present in the D Ring is a finescale structure with waves 30 km (20 miles) apart. First seen in the gap between the C Ring and D73, the structure was found during Saturn's 2009 equinox to extend a radial distance of 19,000 km (12,000 miles) from the D Ring to the inner edge of the B Ring. The waves are interpreted as a spiral pattern of vertical corrugations of 2 to 20 m amplitude; the fact that the period of the waves is decreasing over time (from 60 km; 40 miles in 1995 to 30 km; 20 miles by 2006) allows a deduction that the pattern may have originated in late 1983 with the impact of a cloud of debris (with a mass of ≈1012 kg) from a disrupted comet that tilted the rings out of the equatorial plane. A similar spiral pattern in Jupiter's main ring has been attributed to a perturbation caused by impact of material from Comet Shoemaker-Levy 9 in 1994.
C Ring
The C Ring is a wide but faint ring located inward of the B Ring. It was discovered in 1850 by William and George Bond, though William R. Dawes and Johann Galle also saw it independently. William Lassell termed it the "Crepe Ring" because it seemed to be composed of darker material than the brighter A and B Rings.
Its vertical thickness is estimated at 5 meters (16'), its mass at around 1.1 kg, and its optical depth varies from 0.05 to 0.12. That is, between 5 and 12 percent of light shining perpendicularly through the ring is blocked, so that when seen from above, the ring is close to transparent. The 30-km wavelength spiral corrugations first seen in the D Ring were observed during Saturn's equinox of 2009 to extend throughout the C Ring (see above).
Colombo Gap and Titan Ringlet
The Colombo Gap lies in the inner C Ring. Within the gap lies the bright but narrow Colombo Ringlet, centered at 77,883 km (48,394 miles) from Saturn's center, which is slightly elliptical rather than circular. This ringlet is also called the Titan Ringlet as it is governed by an orbital resonance with the moon Titan. At this location within the rings, the length of a ring particle's apsidal precession is equal to the length of Titan's orbital motion, so that the outer end of this eccentric ringlet always points towards Titan. | Rings of Saturn | Wikipedia | 512 | 977592 | https://en.wikipedia.org/wiki/Rings%20of%20Saturn | Physical sciences | Solar System | Astronomy |
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