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A mould can produce several copies of the same parts in a single "shot". The number of "impressions" in the mould of that part is often incorrectly referred to as cavitation. A tool with one impression is often called a single impression (cavity) mould. A mould with two or more cavities of the same parts is usually called a multiple impression (cavity) mould. (Not to be confused with "Multi-shot moulding" {which is dealt with in the next section.}) Some extremely high production volume moulds (like those for bottle caps) can have over 128 cavities.
In some cases, multiple cavity tooling moulds a series of different parts in the same tool. Some toolmakers call these moulds family moulds, as all the parts are related—e.g., plastic model kits.
Some moulds allow previously moulded parts to be reinserted to allow a new plastic layer to form around the first part. This is often referred to as overmoulding. This system can allow for production of one-piece tires and wheels.
Moulds for highly precise and extremely small parts from micro injection molding requires extra care in the design stage, as material resins react differently compared to their full-sized counterparts where they must quickly fill these incredibly small spaces, which puts them under intense shear strains.
Multi-shot moulding
Two-shot, double-shot or multi-shot moulds are designed to "overmould" within a single moulding cycle and must be processed on specialised injection moulding machines with two or more injection units. This process is actually an injection moulding process performed twice and therefore can allow only for a much smaller margin of error. In the first step, the base colour material is moulded into a basic shape, which contains spaces for the second shot. Then the second material, a different colour, is injection-moulded into those spaces. Pushbuttons and keys, for instance, made by this process have markings that cannot wear off, and remain legible with heavy use.
Mould storage
Manufacturers go to great lengths to protect custom moulds due to their high average costs. The perfect temperature and humidity levels are maintained to ensure the longest possible lifespan for each custom mould. Custom moulds, such as those used for rubber injection moulding, are stored in temperature and humidity controlled environments to prevent warping. | Injection moulding | Wikipedia | 511 | 325831 | https://en.wikipedia.org/wiki/Injection%20moulding | Technology | Materials | null |
Tool materials
Tool steel is often used. Mild steel, aluminium, nickel or epoxy are suitable only for prototype or very short production runs. Modern hard aluminium (7075 and 2024 alloys) with proper mould design, can easily make moulds capable of 100,000 or more part life with proper mould maintenance.
Machining
Moulds are built through two main methods: standard machining and EDM. Standard machining, in its conventional form, has historically been the method of building injection moulds. With technological developments, CNC machining became the predominant means of making more complex moulds with more accurate mould details in less time than traditional methods.
The electrical discharge machining (EDM) or spark erosion process has become widely used in mould making. As well as allowing the formation of shapes that are difficult to machine, the process allows pre-hardened moulds to be shaped so that no heat treatment is required. Changes to a hardened mould by conventional drilling and milling normally require annealing to soften the mould, followed by heat treatment to harden it again. EDM is a simple process in which a shaped electrode, usually made of copper or graphite, is very slowly lowered onto the mould surface over a period of many hours, which is immersed in paraffin oil (kerosene). A voltage applied between tool and mould causes spark erosion of the mould surface in the inverse shape of the electrode.
Cost
The number of cavities incorporated into a mould directly correlate in moulding costs. Fewer cavities require far less tooling work, so limiting the number of cavities lowers initial manufacturing costs to build an injection mould.
As the number of cavities play a vital role in moulding costs, so does the complexity of the part's design. Complexity can be incorporated into many factors such as surface finishing, tolerance requirements, internal or external threads, fine detailing or the number of undercuts that may be incorporated.
Further details, such as undercuts, or any feature that needs additional tooling, increases mould cost. Surface finish of the core and cavity of moulds further influences cost.
Rubber injection moulding process produces a high yield of durable products, making it the most efficient and cost-effective method of moulding. Consistent vulcanisation processes involving precise temperature control significantly reduces all waste material.
Injection process | Injection moulding | Wikipedia | 496 | 325831 | https://en.wikipedia.org/wiki/Injection%20moulding | Technology | Materials | null |
Usually, the plastic materials are formed in the shape of pellets or granules and sent from the raw material manufacturers in paper bags. With injection moulding, pre-dried granular plastic is fed by a forced ram from a hopper into a heated barrel. As the granules are slowly moved forward by a screw-type plunger, the plastic is forced into a heated chamber, where it is melted. As the plunger advances, the melted plastic is forced through a nozzle that rests against the mould, allowing it to enter the mould cavity through a gate and runner system. The mould remains cold so the plastic solidifies almost as soon as the mould is filled.
Injection moulding cycle
The sequence of events during the injection mould of a plastic part is called the injection moulding cycle. The cycle begins when the mould closes, followed by the injection of the polymer into the mould cavity. Once the cavity is filled, a holding pressure is maintained to compensate for material shrinkage. In the next step, the screw turns, feeding the next shot to the front screw. This causes the screw to retract as the next shot is prepared. Once the part is sufficiently cool, the mould opens and the part is ejected.
Scientific versus traditional moulding
Traditionally, the injection portion of the moulding process was done at one constant pressure to fill and pack the cavity. This method, however, allowed for a large variation in dimensions from cycle-to-cycle. More commonly used now is scientific or decoupled moulding, a method pioneered by RJG Inc. In this the injection of the plastic is "decoupled" into stages to allow better control of part dimensions and more cycle-to-cycle (commonly called shot-to-shot in the industry) consistency. First the cavity is filled to approximately 98% full using velocity (speed) control. Although the pressure should be sufficient to allow for the desired speed, pressure limitations during this stage are undesirable. Once the cavity is 98% full, the machine switches from velocity control to pressure control, where the cavity is "packed out" at a constant pressure, where sufficient velocity to reach desired pressures is required. This lets workers control part dimensions to within thousandths of an inch or better.
Different types of injection moulding processes | Injection moulding | Wikipedia | 479 | 325831 | https://en.wikipedia.org/wiki/Injection%20moulding | Technology | Materials | null |
Although most injection moulding processes are covered by the conventional process description above, there are several important moulding variations including, but not limited to:
Die casting
Metal injection moulding
Thin-wall injection moulding
Injection moulding of liquid silicone rubber
Reaction injection moulding
Micro injection moulding
Gas-assisted injection moulding
Cube mold technology
Multi-material injection molding
A more comprehensive list of injection moulding processes may be found here:
Process troubleshooting
Like all industrial processes, injection molding can produce flawed parts, even in toys. In the field of injection moulding, troubleshooting is often performed by examining defective parts for specific defects and addressing these defects with the design of the mould or the characteristics of the process itself. Trials are often performed before full production runs in an effort to predict defects and determine the appropriate specifications to use in the injection process.
When filling a new or unfamiliar mould for the first time, where shot size for that mould is unknown, a technician/tool setter may perform a trial run before a full production run. They start with a small shot weight and fills gradually until the mould is 95 to 99% full. Once they achieve this, they apply a small amount of holding pressure and increase holding time until gate freeze off (solidification time) has occurred. Gate freeze off time can be determined by increasing the hold time, and then weighing the part. When the weight of the part does not change, the gate has frozen and no more material is injected into the part. Gate solidification time is important, as this determines cycle time and the quality and consistency of the product, which itself is an important issue in the economics of the production process. Holding pressure is increased until the parts are free of sinks and part weight has been achieved.
Moulding defects
Injection moulding is a complex technology with possible production problems. They can be caused either by defects in the moulds, or more often by the moulding process itself.
Methods such as industrial CT scanning can help with finding these defects externally as well as internally.
Tolerances
Tolerance depends on the dimensions of the part. An example of a standard tolerance for a 1-inch dimension of an LDPE part with 0.125 inch wall thickness is +/- 0.008 inch (0.2 mm). | Injection moulding | Wikipedia | 479 | 325831 | https://en.wikipedia.org/wiki/Injection%20moulding | Technology | Materials | null |
Power requirements
The power required for this process of injection moulding depends on many things and varies between materials used. Manufacturing Processes Reference Guide states that the power requirements depend on "a material's specific gravity, melting point, thermal conductivity, part size, and molding rate." Below is a table from page 243 of the same reference as previously mentioned that best illustrates the characteristics relevant to the power required for the most commonly used materials.
Robotic moulding
Automation means that the smaller size of parts permits a mobile inspection system to examine multiple parts more quickly. In addition to mounting inspection systems on automatic devices, multiple-axis robots can remove parts from the mould and position them for further processes.
Specific instances include removing of parts from the mould immediately after the parts are created, as well as applying machine vision systems. A robot grips the part after the ejector pins have been extended to free the part from the mould. It then moves them into either a holding location or directly onto an inspection system. The choice depends upon the type of product, as well as the general layout of the manufacturing equipment. Vision systems mounted on robots have greatly enhanced quality control for insert moulded parts. A mobile robot can more precisely determine the placement accuracy of the metal component, and inspect faster than a human can.
Gallery | Injection moulding | Wikipedia | 266 | 325831 | https://en.wikipedia.org/wiki/Injection%20moulding | Technology | Materials | null |
Elephant birds are extinct flightless birds belonging to the order Aepyornithiformes that were native to the island of Madagascar. They are thought to have gone extinct around AD 1000, likely as a result of human activity. Elephant birds comprised three species, one in the genus Mullerornis, and two in Aepyornis. Aepyornis maximus is possibly the largest bird to have ever lived, with their eggs being the largest known for any amniote. Elephant birds are palaeognaths (whose flightless representatives are often known as ratites), and their closest living relatives are kiwi (found only in New Zealand), suggesting that ratites did not diversify by vicariance during the breakup of Gondwana but instead convergently evolved flightlessness from ancestors that dispersed more recently by flying.
Discovery
Elephant birds have been extinct since at least the 17th century. Étienne de Flacourt, a French governor of Madagascar during the 1640s and 1650s, mentioned an ostrich-like bird, said to inhabit unpopulated regions, although it is unclear whether he was repeating folk tales from generations earlier. In 1659, Flacourt wrote of the "vouropatra – a large bird which haunts the Ampatres and lays eggs like the ostriches; so that the people of these places may not take it, it seeks the most lonely places." There has been speculation, especially popular in the latter half of the 19th century, that the legendary roc from the accounts of Marco Polo was ultimately based on elephant birds, but this is disputed.
Between 1830 and 1840, European travelers in Madagascar saw giant eggs and eggshells. British observers were more willing to believe the accounts of giant birds and eggs because they knew of the moa in New Zealand. In 1851 the genus Aepyornis and species A. maximus were scientifically described in a paper presented to the Paris Academy of Sciences by Isidore Geoffroy Saint-Hilaire, based on bones and eggs recently obtained from the island, which resulted in wide coverage in the popular presses of the time, particularly due to their very large eggs. | Elephant bird | Wikipedia | 434 | 325880 | https://en.wikipedia.org/wiki/Elephant%20bird | Biology and health sciences | Palaeognathae | Animals |
Two whole eggs have been found in dune deposits in southern Western Australia, one in the 1930s (the Scott River egg) and one in 1992 (the Cervantes egg); both have been identified as Aepyornis maximus rather than Genyornis newtoni, an extinct giant bird known from the Pleistocene of Australia. It is hypothesized that the eggs floated from Madagascar to Australia on the Antarctic Circumpolar Current. Evidence supporting this is the finding of two fresh penguin eggs that washed ashore on Western Australia but may have originated in the Kerguelen Islands, and an ostrich egg found floating in the Timor Sea in the early 1990s.
Taxonomy and biogeography
Like the ostrich, rhea, cassowary, emu, kiwi and extinct moa, elephant birds were ratites; they could not fly, and their breast bones had no keel. Because Madagascar and Africa separated before the ratite lineage arose, elephant birds has been thought to have dispersed and become flightless and gigantic in situ.
More recently, it has been deduced from DNA sequence comparisons that the closest living relatives of elephant birds are New Zealand kiwi, though the split between the two groups is deep, with the two lineages being estimated to have diverged from each other around 54 million years ago.
Placement of Elephant birds within Palaeognathae, after:
The ancestors of elephant birds are thought to have arrived in Madagascar well after Gondwana broke apart. The existence of possible flying palaeognathae in the Miocene such as Proapteryx further supports the view that ratites did not diversify in response to vicariance. Gondwana broke apart in the Cretaceous and their phylogenetic tree does not match the process of continental drift. Madagascar has a notoriously poor Cenozoic terrestrial fossil record, with essentially no fossils between the end of the Cretaceous (Maevarano Formation) and the Late Pleistocene. Complete mitochondrial genomes obtained from elephant birds eggshells suggest that Aepyornis and Mullerornis are significantly genetically divergent from each other, with a molecular clock analysis estimating the split around 27 million years ago. Molecular dating estimates that the divergence between Aepyornithidae and Mullerornithidae occurred approximately 30 Ma, close to the Eocene-Oligocene boundary, a period of marked global cooling and faunal turnover in the Northern Hemisphere. | Elephant bird | Wikipedia | 486 | 325880 | https://en.wikipedia.org/wiki/Elephant%20bird | Biology and health sciences | Palaeognathae | Animals |
Species
Up to 10 or 11 species in the genus Aepyornis have been described, but the validity of many have been disputed, with numerous authors treating them all in just one species, A. maximus. Up to three species have been described in Mullerornis. Recent work has restricted the number of elephant bird species to three, with two in Aepyornis, one in Mullerornis.
Order Aepyornithiformes Newton 1884 [Aepyornithes Newton 1884]
Genus Aepyornis Geoffroy Saint-Hilaire 1850 (Synonym: Vorombe Hansford & Turvey 2018)
Aepyornis hildebrandti Burckhardt, 1893 (Possibly divided into two subspecies)
Aepyornis maximus Hilaire, 1851
Genus Mullerornis Milne-Edwards & Grandidier 1894
Mullerornis modestus (Milne-Edwards & Grandidier 1869) Hansford & Turvey 2018
All elephant birds are usually placed in the single family Aepyornithidae, but some authors suggest Aepyornis and Mullerornis should be placed in separate families within the Aepyornithiformes, with the latter placed into Mullerornithidae.
Description
Elephant birds were large sized birds (the largest reaching tall in normal standing posture) that had vestigial wings, long legs and necks, with small heads relative to body size, which bore straight, thick conical beaks that were not hooked. The tops of elephant bird skulls display punctuated marks, which may have been attachment sites for fleshy structures or head feathers. Mullerornis is the smallest of the elephant birds, with a body mass of around , with its skeleton much less robustly built than Aepyornis. A. hildebrandti is thought to have had a body mass of around . Estimates of the body mass of Aepyornis maximus span from around to making it one of the largest birds ever, alongside Dromornis stirtoni and Pachystruthio dmanisensis. Females of A. maximus are suggested to have been larger than the males, as is observed in other ratites.
Biology | Elephant bird | Wikipedia | 436 | 325880 | https://en.wikipedia.org/wiki/Elephant%20bird | Biology and health sciences | Palaeognathae | Animals |
Examination of brain endocasts has shown that both A. maximus and A. hildebrandti had greatly reduced optic lobes, similar to those of their closest living relatives, the kiwis, and consistent with a similar nocturnal lifestyle. The optic lobes of Mullerornis were also reduced, but to a lesser degree, suggestive of a nocturnal or crepuscular lifestyle. A. maximus had relatively larger olfactory bulbs than A. hildebrandti, suggesting that the former occupied forested habitats where the sense of smell is more useful while the latter occupied open habitats.
Diet
A 2022 isotope analysis study suggested that some specimens of Aepyornis hildebrandti were mixed feeders that had a large (~48%) grazing component to their diets, similar to that of the living Rhea americana, while the other species (A. maximus, Mullerornis modestus) were probably browsers. It has been suggested that Aepyornis straightened its legs and brought its torso into an erect position in order to browse higher vegetation. Some rainforest fruits with thick, highly sculptured endocarps, such as that of the currently undispersed and highly threatened forest coconut palm (Voanioala gerardii), may have been adapted for passage through ratite guts and consumed by elephant birds, and the fruit of some palm species are indeed dark bluish-purple (e.g., Ravenea louvelii and Satranala decussilvae), just like many cassowary-dispersed fruits, suggesting that they too may have been eaten by elephant birds.
Growth and reproduction
Elephant birds are suggested to have grown in periodic spurts rather than having continuous growth. An embryonic skeleton of Aepyornis is known from an intact egg, around 80–90% of the way through incubation before it died. This skeleton shows that even at this early ontogenetic stage that the skeleton was robust, much more so than comparable hatchling ostriches or rheas, which may suggest that hatchlings were precocial. | Elephant bird | Wikipedia | 421 | 325880 | https://en.wikipedia.org/wiki/Elephant%20bird | Biology and health sciences | Palaeognathae | Animals |
The eggs of Aepyornis are the largest known for any amniote, and have a volume of around , a length of approximately and a width of . The largest Aepyornis eggs are on average thick, with an estimated weight of approximately . Eggs of Mullerornis were much smaller, estimated to be only thick, with a weight of about . The large size of elephant bird eggs means that they would have required substantial amounts of calcium, which is usually taken from a reservoir in the medullary bone in the femurs of female birds. Possible remnants of this tissue have been described from the femurs of A. maximus.
Extinction
It is widely believed that the extinction of elephant birds was a result of human activity. The birds were initially widespread, occurring from the northern to the southern tip of Madagascar. The late Holocene also witnessed the extinction of other Malagasy animals, including several species of Malagasy hippopotamus, two species of giant tortoise (Aldabrachelys abrupta and Aldabrachelys grandidieri), the giant fossa, over a dozen species of giant lemurs, the aardvark-like animal Plesiorycteropus, and the crocodile Voay. Several elephant bird bones with incisions have been dated to approximately 10,000 BC which some authors suggest are cut marks, which have been proposed as evidence of a long history of coexistence between elephant birds and humans; however, these conclusions conflict with more commonly accepted evidence of a much shorter history of human presence on the island and remain controversial. The oldest securely dated evidence for humans on Madagascar dates to the mid-first millennium AD. | Elephant bird | Wikipedia | 343 | 325880 | https://en.wikipedia.org/wiki/Elephant%20bird | Biology and health sciences | Palaeognathae | Animals |
A 2021 study suggested that elephant birds, along with the Malagasy hippopotamus species, became extinct in the interval 800–1050 AD (1150–900 years Before Present), based on the timing of the latest radiocarbon dates. The timing of the youngest radiocarbon dates co-incided with major environmental alteration across Madagascar by humans changing forest into grassland, probably for cattle pastoralism, with the environmental change likely being induced by the use of fire. This reduction of forested area may have had cascade effects, like making elephant birds more likely to be encountered by hunters, though there is little evidence of human hunting of elephant birds. Humans may have utilized elephant bird eggs. Introduced diseases (hyperdisease) have been proposed as a cause of extinction, but the plausibility for this is weakened due to the evidence of centuries of overlap between humans and elephant birds on Madagascar. | Elephant bird | Wikipedia | 178 | 325880 | https://en.wikipedia.org/wiki/Elephant%20bird | Biology and health sciences | Palaeognathae | Animals |
Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on July 22, 2009, and became generally available on October 22, 2009. It is the successor to Windows Vista, released nearly three years earlier. Windows 7's server counterpart, Windows Server 2008 R2, was released at the same time. It was succeeded by Windows 8 in October 2012.
Extended support ended on January 14, 2020, over ten years after the release of Windows 7, after which the operating system ceased receiving further updates. A paid support program was available for enterprises, providing security updates for Windows 7 for up to three years since the official end of life.
Windows 7 was intended to be an incremental upgrade to Windows Vista, addressing the previous OS's poor reception while maintaining hardware and software compatibility as well as fixing some of Vista's inconsistencies (such as Vista's aggressive User Account Control). Windows 7 continued improvements on the Windows Aero user interface with the addition of a redesigned taskbar that allows pinned applications, and new window management features. Other new features were added to the operating system, including libraries, the new file-sharing system HomeGroup, and support for multitouch input. A new "Action Center" was also added to provide an overview of system security and maintenance information, and tweaks were made to the User Account Control system to make it less intrusive. Windows 7 also shipped with updated versions of several stock applications, including Internet Explorer 8, Windows Media Player, and Windows Media Center. | Windows 7 | Wikipedia | 316 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Unlike Windows Vista, Windows 7 received warm reception among reviewers and consumers with critics considering the operating system to be a major improvement over its predecessor because of its improved performance, its more intuitive interface, fewer User Account Control popups, and other improvements made across the platform. Windows 7 was a major success for Microsoft; even before its official release, pre-order sales for the operating system on the online retailer Amazon.com had surpassed previous records. In just six months, over 100 million copies had been sold worldwide, increasing to over 630 million licenses by July 2012. By January 2018, Windows 10 surpassed Windows 7 as the most popular version of Windows worldwide. Windows 11 overtook Windows 7 as the second most popular Windows version on all continents in August 2022. , just 3% of traditional PCs running Windows are running Windows 7, although it remains relatively popular in parts of the world, such as China (where it is tied with Windows 11), and is second most popular in some countries.
It is the final version of Microsoft Windows that supports processors without SSE2 or NX (although an update released in 2018 dropped support for non-SSE2 processors).
Naming
Windows 7 is the successor to Windows Vista, and its version name is Windows NT 6.1, compared to Vista's NT 6.0; its naming caused some confusion when it was announced in 2008. Windows president Steven Sinofsky commented that Windows 95 was the fourth version of Windows, but Windows 7 counts up from Windows NT 4.0 as it is a descendant of NT. | Windows 7 | Wikipedia | 312 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Development history
Originally, a version of Windows codenamed "Blackcomb" was planned as the successor to Windows XP and Windows Server 2003 in 2000. Major features were planned for Blackcomb, including an emphasis on searching and querying data and an advanced storage system named WinFS to enable such scenarios. However, an interim, minor release, codenamed "Longhorn," was announced for 2003, delaying the development of Blackcomb. By the middle of 2003, however, Longhorn had acquired some of the features originally intended for Blackcomb. After three major malware outbreaks—the Blaster, Nachi, and Sobig worms—exploited flaws in Windows operating systems within a short time period in August 2003, Microsoft changed its development priorities, putting some of Longhorn's major development work on hold while developing new service packs for Windows XP and Windows Server 2003. Development of Longhorn (Windows Vista) was also restarted, and thus delayed, in August 2004. A number of features were cut from Longhorn. Blackcomb was renamed Vienna in early 2006, and was later canceled in 2007 due to the scope of the project. | Windows 7 | Wikipedia | 229 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
When released, Windows Vista was criticized for its long development time, performance issues, spotty compatibility with existing hardware and software at launch, changes affecting the compatibility of certain PC games, and unclear assurances by Microsoft that certain computers shipping with XP before launch would be "Vista Capable" (which led to a class-action lawsuit), among other critiques. As such, the adoption of Vista in comparison to XP remained somewhat low. In July 2007, following the shelving of the Vienna project and six months following the public release of Vista, it was reported that the next version of Windows would then be codenamed Windows 7, with plans for a final release within three years. Bill Gates, in an interview with Newsweek, suggested that Windows 7 would be more "user-centric". Gates later said that Windows 7 would also focus on performance improvements. Steven Sinofsky later expanded on this point, explaining in the Engineering Windows 7 blog that the company was using a variety of new tracing tools to measure the performance of many areas of the operating system on an ongoing basis, to help locate inefficient code paths and to help prevent performance regressions. Senior Vice President Bill Veghte stated that Windows Vista users migrating to Windows 7 would not find the kind of device compatibility issues they encountered migrating from Windows XP. An estimated 1,000 developers worked on Windows 7. These were broadly divided into "core operating system" and "Windows client experience", in turn organized into 25 teams of around 40 developers on average.
In October 2008, it was announced that Windows 7 would also be the official name of the operating system. There had been some confusion over naming the product Windows 7, while versioning it as 6.1 to indicate its similar build to Windows Vista and increase compatibility with applications that only check major version numbers, similar to Windows 2000 and Windows XP both having 5.x version numbers. The first external release to select Microsoft partners came in January 2008 with Milestone 1, build 6519. Speaking about Windows 7 on October 16, 2008, Microsoft CEO Steve Ballmer confirmed compatibility between Windows Vista and Windows 7, indicating that Windows 7 would be a refined version of Windows Vista. | Windows 7 | Wikipedia | 441 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
At PDC 2008, Microsoft demonstrated Windows 7 with its reworked taskbar. On December 27, 2008, the Windows 7 Beta was leaked onto the Internet via BitTorrent. According to a performance test by ZDNet, Windows 7 Beta beat both Windows XP and Windows Vista in several key areas, including boot and shutdown time and working with files, such as loading documents. Other areas did not beat XP, including PC Pro benchmarks for typical office activities and video editing, which remain identical to Vista and slower than XP. On January 7, 2009, the x64 version of the Windows 7 Beta (build 7000) was leaked onto the web, with some torrents being infected with a trojan. At CES 2009, Microsoft CEO Steve Ballmer announced the Windows 7 Beta, build 7000, had been made available for download to MSDN and TechNet subscribers in the format of an ISO image. The stock wallpaper of the beta version contained a digital image of the Betta fish.
The release candidate, build 7100, became available for MSDN and TechNet subscribers, and Connect Program participants on April 30, 2009. On May 5, 2009, it became available to the general public, although it had also been leaked onto the Internet via BitTorrent. The release candidate was available in five languages and expired on June 1, 2010, with shutdowns every two hours starting March 1, 2010. Microsoft stated that Windows 7 would be released to the general public on October 22, 2009, less than three years after the launch of its predecessor. Microsoft released Windows 7 to MSDN and Technet subscribers on August 6, 2009. Microsoft announced that Windows 7, along with Windows Server 2008 R2, was released to manufacturing in the United States and Canada on July 22, 2009. Windows 7 build 7600.16385.090713-1255, which was compiled on July 13, 2009, was declared the final RTM build after passing all Microsoft's tests internally.
Features
New and changed | Windows 7 | Wikipedia | 411 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Among Windows 7's new features are advances in touch and handwriting recognition, support for virtual hard disks, improved performance on multi-core processors, improved boot performance, DirectAccess, and kernel improvements. Windows 7 adds support for systems using multiple heterogeneous graphics cards from different vendors (Heterogeneous Multi-adapter), a new version of Windows Media Center, a Gadget for Windows Media Center, improved media features, XPS Essentials Pack, and Windows PowerShell being included, and a redesigned Calculator with multiline capabilities including Programmer and Statistics modes along with unit conversion for length, weight, temperature, and several others. Many new items have been added to the Control Panel, including ClearType Text Tuner, Display Color Calibration Wizard, Gadgets, Recovery, Troubleshooting, Workspaces Center, Location and Other Sensors, Credential Manager, Biometric Devices, System Icons, and Display. Windows Security Center has been renamed to Action Center (Windows Health Center and Windows Solution Center in earlier builds), which encompasses both security and maintenance of the computer. ReadyBoost on 32-bit editions now supports up to 256 gigabytes of extra allocation. Windows 7 also supports images in RAW image format through the addition of Windows Imaging Component-enabled image decoders, which enables raw image thumbnails, previewing and metadata display in Windows Explorer, plus full-size viewing and slideshows in Windows Photo Viewer and Windows Media Center. Windows 7 also has a native TFTP client with the ability to transfer files to or from a TFTP server.
The taskbar has seen the biggest visual changes, where the old Quick Launch toolbar has been replaced with the ability to pin applications to the taskbar. Buttons for pinned applications are integrated with the task buttons. These buttons also enable Jump Lists to allow easy access to common tasks, and files frequently used with specific applications. The revamped taskbar also allows the reordering of taskbar buttons. To the far right of the system clock is a small rectangular button that serves as the Show desktop icon. By default, hovering over this button makes all visible windows transparent for a quick look at the desktop. In touch-enabled displays such as touch screens, tablet PCs, etc., this button is slightly (8 pixels) wider in order to accommodate being pressed by a finger. Clicking this button minimizes all windows, and clicking it a second time restores them. | Windows 7 | Wikipedia | 501 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Window management in Windows 7 has several new features: Aero Snap maximizes a window when it is dragged to the top, left, or right of the screen. Dragging windows to the left or right edges of the screen allows users to snap software windows to either side of the screen, such that the windows take up half the screen. When a user moves windows that were snapped or maximized using Snap, the system restores their previous state. Snap functions can also be triggered with keyboard shortcuts. Aero Shake hides all inactive windows when the active window's title bar is dragged back and forth rapidly. | Windows 7 | Wikipedia | 121 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Windows 7 includes 13 additional sound schemes, titled Afternoon, Calligraphy, Characters, Cityscape, Delta, Festival, Garden, Heritage, Landscape, Quirky, Raga, Savanna, and Sonata. Internet Spades, Internet Backgammon and Internet Checkers, which were removed in Windows Vista, were restored in Windows 7. Users are able to disable or customize many more Windows components than was possible in Windows Vista. New additions to this list of components include Internet Explorer 8, Windows Media Player 12, Windows Media Center, Windows Search, and Windows Gadget Platform. A new version of Microsoft Virtual PC, newly renamed as Windows Virtual PC was made available for Windows 7 Professional, Enterprise, and Ultimate editions. It allows multiple Windows environments, including Windows XP Mode, to run on the same machine. Windows XP Mode runs Windows XP in a virtual machine, and displays applications within separate windows on the Windows 7 desktop. Furthermore, Windows 7 supports the mounting of a virtual hard disk (VHD) as a normal data storage, and the bootloader delivered with Windows 7 can boot the Windows system from a VHD; however, this ability is only available in the Enterprise and Ultimate editions. The Remote Desktop Protocol (RDP) of Windows 7 is also enhanced to support real-time multimedia application including video playback and 3D games, thus allowing use of DirectX 10 in remote desktop environments. The three application limit, previously present in the Windows Vista and Windows XP Starter Editions, has been removed from Windows 7. All editions include some new and improved features, such as Windows Search, Security features, and some features new to Windows 7, that originated within Vista. Optional BitLocker Drive Encryption is included with Windows 7 Ultimate and Enterprise. Windows Defender is included; Microsoft Security Essentials antivirus software is a free download. All editions include Shadow Copy, which—every day or so—System Restore uses to take an automatic "previous version" snapshot of user files that have changed. Backup and restore have also been improved, and the Windows Recovery Environment—installed by default—replaces the optional Recovery Console of Windows XP. | Windows 7 | Wikipedia | 427 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
A new system known as "Libraries" was added for file management; users can aggregate files from multiple folders into a "Library." By default, libraries for categories such as Documents, Pictures, Music, and Video are created, consisting of the user's personal folder and the Public folder for each. The system is also used as part of a new home networking system known as HomeGroup; devices are added to the network with a password, and files and folders can be shared with all other devices in the HomeGroup, or with specific users. The default libraries, along with printers, are shared by default, but the personal folder is set to read-only access by other users, and the Public folder can be accessed by anyone.
Windows 7 includes improved globalization support through a new Extended Linguistic Services API to provide multilingual support (particularly in Ultimate and Enterprise editions). Microsoft also implemented better support for solid-state drives, including the new TRIM command, and Windows 7 is able to identify a solid-state drive uniquely. Native support for USB 3.0 is not included because of delays in the finalization of the standard. At WinHEC 2008 Microsoft announced that color depths of 30-bit and 48-bit would be supported in Windows 7 along with the wide color gamut scRGB (which for HDMI 1.3 can be converted and output as xvYCC). The video modes supported in Windows 7 are 16-bit sRGB, 24-bit sRGB, 30-bit sRGB, 30-bit with extended color gamut sRGB, and 48-bit scRGB.
For developers, Windows 7 includes a new networking API with support for building SOAP-based web services in native code (as opposed to .NET-based WCF web services), new features to simplify development of installation packages and shorten application install times. Windows 7, by default, generates fewer User Account Control (UAC) prompts because it allows digitally signed Windows components to gain elevated privileges without a prompt. Additionally, users can now adjust the level at which UAC operates using a sliding scale.
Removed | Windows 7 | Wikipedia | 431 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Certain capabilities and programs that were a part of Windows Vista are no longer present or have been changed, resulting in the removal of certain functionalities; these include the classic Start Menu user interface, some taskbar features, Windows Explorer features, Windows Media Player features, Windows Ultimate Extras, Search button, and InkBall. Four applications bundled with Windows Vista—Windows Photo Gallery, Windows Movie Maker, Windows Calendar and Windows Mail—are not included with Windows 7 and were replaced by Windows Live-branded versions as part of the Windows Live Essentials suite.
Editions
Windows 7 is available in six different editions, of which the Home Premium, Professional, and Ultimate were available at retail in most countries, and as pre-loaded software on most new computers. Home Premium and Professional were aimed at home users and small businesses respectively, while Ultimate was aimed at enthusiasts. Each edition of Windows 7 includes all of the capabilities and features of the edition below it, and adds additional features oriented towards their market segments; for example, Professional adds additional networking and security features such as Encrypting File System and the ability to join a domain. Ultimate contained a superset of the features from Home Premium and Professional, along with other advanced features oriented towards power users, such as BitLocker drive encryption; unlike Windows Vista, there were no "Ultimate Extras" add-ons created for Windows 7 Ultimate. Retail copies were available in "upgrade" and higher-cost "full" version licenses; "upgrade" licenses require an existing version of Windows to install, while "full" licenses can be installed on computers with no existing operating system.
The remaining three editions were not available at retail, of which two were available exclusively through OEM channels as pre-loaded software. The Starter edition is a stripped-down version of Windows 7 meant for low-cost devices such as netbooks. In comparison to Home Premium, Starter has reduced multimedia functionality, does not allow users to change their desktop wallpaper or theme, disables the "Aero Glass" theme, does not have support for multiple monitors, and can only address 2GB of RAM. Home Basic was sold only in emerging markets, and was positioned in between Home Premium and Starter. The highest edition, Enterprise, is functionally similar to Ultimate, but is only sold through volume licensing via Microsoft's Software Assurance program. | Windows 7 | Wikipedia | 471 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
All editions aside from Starter support both IA-32 and x86-64 architectures, Starter only supports 32-bit systems. Retail copies of Windows 7 are distributed on two DVDs: one for the IA-32 version and the other for x86-64. OEM copies include one DVD, depending on the processor architecture licensed. The installation media for consumer versions of Windows 7 are identical, the product key and corresponding license determines the edition that is installed. The Windows Anytime Upgrade service can be used to purchase an upgrade that unlocks the functionality of a higher edition, such as going from Starter to Home Premium, and Home Premium to Ultimate. Most copies of Windows 7 only contained one license; in certain markets, a "Family Pack" version of Windows 7 Home Premium was also released for a limited time, which allowed upgrades on up to three computers. In certain regions, copies of Windows 7 were only sold in, and could only be activated in a designated region.
Support lifecycle
Support for the original release of Windows 7 (without a service pack) ended on April 9, 2013, requiring users to update to Windows 7 Service Pack 1 in order to continue receiving updates and support. Microsoft ended the sale of new retail copies of Windows 7 in October 2014, and the sale of new OEM licenses for Windows 7 Home Basic, Home Premium, and Ultimate ended on October 31, 2014. OEM sales of PCs with Windows 7 Professional pre-installed ended on October 31, 2016. The sale of non-Professional OEM licenses was stopped on October 31, 2014.
Mainstream support for Windows 7 ended on January 13, 2015. Extended support for Windows 7 ended on January 14, 2020.
Variants of Windows 7 for embedded systems and thin clients have different support policies: Windows Embedded Standard 7 support ended in October 2020. Windows Thin PC and Windows Embedded POSReady 7 had support until October 2021.
In March 2019, Microsoft announced that it would display notifications to users informing users of the upcoming end of support, and direct users to a website urging them to purchase a Windows 10 upgrade or a new computer. | Windows 7 | Wikipedia | 422 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
In August 2019, researchers reported that "all modern versions of Microsoft Windows" may be at risk for "critical" system compromise because of design flaws of hardware device drivers from multiple providers. In the same month, computer experts reported that the BlueKeep security vulnerability, , that potentially affects older unpatched Microsoft Windows versions via the program's Remote Desktop Protocol, allowing for the possibility of remote code execution, may now include related flaws, collectively named DejaBlue, affecting newer Windows versions (i.e., Windows 7 and all recent versions) as well. In addition, experts reported a Microsoft security vulnerability, , based on legacy code involving Microsoft CTF and ctfmon (ctfmon.exe), that affects all Windows versions from the older Windows XP version to the most recent Windows 10 versions; a patch to correct the flaw is currently available.
In September 2019, Microsoft announced that it would provide free security updates for Windows 7 on federally-certified voting machines through the 2020 United States elections.
Extended Security Updates
On September 7, 2018, Microsoft announced a paid "Extended Security Updates" (ESU) service that will offer additional updates for Windows 7 Professional and Enterprise for up to three years after the end of extended support, available via specific volume licensing programs in yearly installments.
Windows 7 Professional for Embedded Systems, Windows Embedded Standard 7, and Windows Embedded POSReady 7 also get Extended Security Updates for up to three years after their end of extended support date, via OEMs. The Extended Security Updates program for Windows Embedded POSReady 7 ended on October 8, 2024, marking the final end of IA-32 updates on the Windows NT 6.1 product line after more than 15 years.
In August 2019, Microsoft announced it would offer a year of 'free' extended security updates to some business users.
Third-party support
In January 2023, version 109 of the Chromium-based Microsoft Edge became the last version of Edge to support Windows 7, Windows 8/8.1, Windows Server 2012, and Windows Server 2012 R2. Alongside this, several other web browsers based on the Chromium codebase also dropped support for these operating systems after version 109, including Google Chrome and Opera. A fork of Chromium named Supermium is maintained for versions of Windows older than Windows 10, including Windows 7. | Windows 7 | Wikipedia | 479 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Mozilla maintains Firefox 115 Extended Support Release (ESR) to support Windows 7, 8 and 8.1. Mozilla has committed to support it until at least March 2025.
Steam ended support for Windows 7, 8, and 8.1 on January 1, 2024.
Upgradability
Several Windows 7 components are upgradable to the latest versions, which include new versions introduced in later versions of Windows, and other major Microsoft applications are available. These latest versions for Windows 7 include:
DirectX 11
Internet Explorer 11
Microsoft Edge (Chromium, version 109)
Windows Virtual PC
.NET Framework 4.8
Visual Studio 2019
Office 2016 was the last version of Microsoft Office to be compatible with Windows 7.
System requirements
Additional requirements to use certain features:
Windows XP Mode (Professional, Ultimate and Enterprise): Requires an additional 1 GB of RAM and additional 15 GB of available hard disk space. As of March 18, 2010, the requirement for a processor capable of hardware virtualization has been lifted.
Windows Media Center (included in Home Premium, Professional, Ultimate and Enterprise), requires a TV tuner to receive and record TV.
Physical memory
The maximum amount of RAM that Windows 7 supports varies depending on the product edition and on the processor architecture, as shown in the following table.
Processor limits
Windows 7 Professional and up support up to 2 physical processors (CPU sockets),
whereas Windows 7 Starter, Home Basic, and Home Premium editions support only 1. Physical processors with either multiple cores, or hyper-threading, or both, implement more than one logical processor per physical processor. The x86 editions of Windows 7 support up to 32 logical processors; x64 editions support up to 256 (4 x 64).
Extent of hardware support | Windows 7 | Wikipedia | 354 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
In January 2016, Microsoft announced that it would no longer support Windows platforms older than Windows 10 on any future Intel-compatible processor lines, citing difficulties in reliably allowing the operating system to operate on newer hardware. Microsoft stated that effective July 17, 2017, devices with Intel Skylake CPUs were only to receive the "most critical" updates for Windows 7 and 8.1, and only if they have been judged not to affect the reliability of Windows 7 on older hardware. For enterprise customers, Microsoft issued a list of Skylake-based devices "certified" for Windows 7 and 8.1 in addition to Windows 10, to assist them in migrating to newer hardware that can eventually be upgraded to 10 once they are ready to transition. Microsoft and their hardware partners provide special testing and support for these devices on 7 and 8.1 until the July 2017 date.
On March 18, 2016, in response to criticism from enterprise customers, Microsoft delayed the end of support and non-critical updates for Skylake systems to July 17, 2018, but stated that they would also continue to receive security updates through the end of extended support. In August 2016, citing a "strong partnership with our OEM partners and Intel", Microsoft retracted the decision and stated that it would continue to support Windows 7 and 8.1 on Skylake hardware through the end of their extended support lifecycle. However, the restrictions on newer CPU microarchitectures remain in force.
In March 2017, a Microsoft knowledge base article announced which implies that devices using Intel Kaby Lake, AMD Bristol Ridge, or AMD Ryzen, would be blocked from using Windows Update entirely. In addition, official Windows 7 device drivers are not available for the Kaby Lake and Ryzen platforms.
Security updates released since March 2018 contained bugs that affect processors that do not support SSE2 extensions, including all Pentium III, Athlon XP, and prior processors. Microsoft initially stated that it would attempt to resolve this issue, and prevented installation of the affected patches on these systems. However, Microsoft retroactively modified its support documents on June 15, 2018 to remove the promise that this bug would be resolved, replacing it with a statement suggesting that users obtain a newer processor. This effectively ends further patch support for Windows 7 on these older systems.
Updates | Windows 7 | Wikipedia | 465 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Service Pack 1
Windows 7 Service Pack 1 (SP1) was announced on March 18, 2010. A beta was released on July 12, 2010. The final version was released to the public on February 22, 2011. At the time of release, it was not made mandatory. It was available via Windows Update, direct download, or by ordering the Windows 7 SP1 DVD. The service pack is on a much smaller scale than those released for previous versions of Windows, particularly Windows Vista.
Windows 7 Service Pack 1 adds support for Advanced Vector Extensions (AVX), a 256-bit instruction set extension for processors, and improves IKEv2 by adding additional identification fields such as E-mail ID to it. In addition, it adds support for Advanced Format 512e as well as additional Identity Federation Services. Windows 7 Service Pack 1 also resolves a bug related to HDMI audio and another related to printing XPS documents.
In Europe, the automatic nature of the BrowserChoice.eu feature was dropped in Windows 7 Service Pack 1 in February 2011 and remained absent for 14 months despite Microsoft reporting that it was still present, subsequently described by Microsoft as a "technical error." As a result, in March 2013, the European Commission fined Microsoft €561 million to deter companies from reneging on settlement promises.
Platform Update
The Platform Update for Windows 7 SP1 and Windows Server 2008 R2 SP1 was released on February 26, 2013 after a pre-release version had been released on November 5, 2012. It is also included with Internet Explorer 10 for Windows 7.
It includes enhancements to Direct2D, DirectWrite, Direct3D, Windows Imaging Component (WIC), Windows Advanced Rasterization Platform (WARP), Windows Animation Manager (WAM), XPS Document API, H.264 Video Decoder and JPEG XR decoder. However support for Direct3D 11.1 is limited as the update does not include DXGI/WDDM 1.2 from Windows 8, making unavailable many related APIs and significant features such as stereoscopic frame buffer, feature level 11_1 and optional features for levels 10_0, 10_1 and 11_0.
Disk Cleanup update
In October 2013, a Disk Cleanup Wizard addon was released that lets users delete outdated Windows updates on Windows 7 SP1, thus reducing the size of the WinSxS directory. This update backports some features found in Windows 8. | Windows 7 | Wikipedia | 495 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Windows Management Framework 5.0
Windows Management Framework 5.0 includes updates to Windows PowerShell 5.0, Windows PowerShell Desired State Configuration (DSC), Windows Remote Management (WinRM), Windows Management Instrumentation (WMI). It was released on February 24, 2016 and was eventually superseded by Windows Management Framework 5.1.
Convenience rollup
In May 2016, Microsoft released a "Convenience rollup update for Windows 7 SP1 and Windows Server 2008 R2 SP1," which contains all patches released between the release of SP1 and April 2016. The rollup is not available via Windows Update, and must be downloaded manually. This package can also be integrated into a Windows 7 installation image.
Since October 2016, all security and reliability updates are cumulative. Downloading and installing updates that address individual problems is no longer possible, but the number of updates that must be downloaded to fully update the OS is significantly reduced.
Monthly update rollups (July 2016 – January 2020)
In June 2018, Microsoft announced that Windows 7 would be moved to a monthly update model beginning with updates released in September 2018, two years after Microsoft switched the rest of their supported operating systems to that model. With the new update model, instead of updates being released as they became available, only two update packages were released on the second Tuesday of every month until Windows 7 reached its end of life—one package containing security and quality updates, and a smaller package that contained only the security updates. Users could choose which package they wanted to install each month. Later in the month, another package would be released which was a preview of the next month's security and quality update rollup.
Microsoft announced in July 2019 that the Microsoft Internet Games services on Windows XP and Windows Me would end on July 31, 2019 (and for Windows 7 on January 22, 2020).
The last non-extended security update rollup packages were released on January 14, 2020, the last day that Windows 7 had extended support.
End of support (after January 14, 2020)
On January 14, 2020, Windows 7 support ended with Microsoft no longer providing security updates or fixes after that date, except for subscribers of the Windows 7 Extended Security Updates (ESU), who were able to receive Windows 7 security updates through January 10, 2023. However, there have been two updates that have been issued to non-ESU subscribers: | Windows 7 | Wikipedia | 482 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
In February 2020, Microsoft released an update via Windows Update to fix a black wallpaper issue caused by the January 2020 update for Windows 7.
In June 2020, Microsoft released an update via Windows Update to roll out the new Chromium-based Microsoft Edge to Windows 7 and 8.1 machines that are not connected to Active Directory. Users, e.g. those on Active Directory, can download Edge from Microsoft's website.
In a support document, Microsoft has stated that a full-screen upgrade warning notification would be displayed on Windows 7 PCs on all editions except the Enterprise edition after January 15, 2020. The notification does not appear on machines connected to Active Directory, machines in kiosk mode, or machines subscribed for Extended Security Updates.
ESU rollups
As part of the September 2022 Extended Security Updates (ESU) rollup, Microsoft quietly added in Secure Boot support, along with partial UEFI support.
Reception | Windows 7 | Wikipedia | 190 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Critical reception
Windows 7 received critical acclaim, with critics noting the increased usability and functionality when compared with its predecessor, Windows Vista. CNET gave Windows 7 Home Premium a rating of 4.5 out of 5 stars, stating that it "is more than what Vista should have been, [and] it's where Microsoft needed to go". PC Magazine rated it a 4 out of 5 saying that Windows 7 is a "big improvement" over Windows Vista, with fewer compatibility problems, a retooled taskbar, simpler home networking and faster start-up. Maximum PC gave Windows 7 a rating of 9 out of 10 and called Windows 7 a "massive leap forward" in usability and security, and praised the new Taskbar as "worth the price of admission alone." PC World called Windows 7 a "worthy successor" to Windows XP and said that speed benchmarks showed Windows 7 to be slightly faster than Windows Vista. PC World also named Windows 7 one of the best products of the year.
In its review of Windows 7, Engadget said that Microsoft had taken a "strong step forward" with Windows 7 and reported that speed is one of Windows 7's major selling points—particularly for the netbook sets. Laptop Magazine gave Windows 7 a rating of 4 out of 5 stars and said that Windows 7 makes computing more intuitive, offered better overall performance including a "modest to dramatic" increase in battery life on laptop computers. TechRadar gave Windows 7 a rating of 5 out of 5 stars, concluding that "it combines the security and architectural improvements of Windows Vista with better performance than XP can deliver on today's hardware. No version of Windows is ever perfect, but Windows 7 really is the best release of Windows yet." USA Today and The Telegraph also gave Windows 7 favorable reviews.
Nick Wingfield of The Wall Street Journal wrote, "Visually arresting," and "A pleasure." Mary Branscombe of Financial Times wrote, "A clear leap forward." Jesus Diaz of Gizmodo wrote, "Windows 7 Kills Snow Leopard." Don Reisinger of CNET wrote, "Delightful." David Pogue of The New York Times wrote, "Faster." J. Peter Bruzzese and Richi Jennings of Computerworld wrote, "Ready." | Windows 7 | Wikipedia | 467 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
Some Windows Vista Ultimate users have expressed concerns over Windows 7 pricing and upgrade options. Windows Vista Ultimate users wanting to upgrade from Windows Vista to Windows 7 had to either pay $219.99 to upgrade to Windows 7 Ultimate or perform a clean install, which requires them to reinstall all of their programs.
The changes to User Account Control on Windows 7 were criticized for being potentially insecure, as an exploit was discovered allowing untrusted software to be launched with elevated privileges by exploiting a trusted component. Peter Bright of Ars Technica argued that "the way that the Windows 7 UAC 'improvements' have been made completely exempts Microsoft's developers from having to do that work themselves. With Windows 7, it's one rule for Redmond, another one for everyone else." Microsoft's Windows kernel engineer Mark Russinovich acknowledged the problem, but noted that malware can also compromise a system when users agree to a prompt.
Sales
In July 2009, in only eight hours, pre-orders of Windows 7 at amazon.co.uk surpassed the demand which Windows Vista had in its first 17 weeks. It became the highest-grossing pre-order in Amazon's history, surpassing sales of the previous record holder, the seventh Harry Potter book. After 36 hours, 64-bit versions of Windows 7 Professional and Ultimate editions sold out in Japan. Two weeks after its release its market share had surpassed that of Snow Leopard, released two months previously as the most recent update to Apple's Mac OS X operating system. According to Net Applications, Windows 7 reached a 4% market share in less than three weeks; in comparison, it took Windows Vista seven months to reach the same mark. As of February 2014, Windows 7 had a market share of 47.49% according to Net Applications; in comparison, Windows XP had a market share of 29.23%. | Windows 7 | Wikipedia | 378 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
On March 4, 2010, Microsoft announced that it had sold more than 90 million licenses.
By April 23, 2010, more than 100 million copies were sold in six months, which made it Microsoft's fastest-selling operating system. As of June 23, 2010, Windows 7 has sold 150 million copies which made it the fastest selling operating system in history with seven copies sold every second. Based on worldwide data taken during June 2010 from Windows Update 46% of Windows 7 PCs run the 64-bit edition of Windows 7. According to Stephen Baker of the NPD Group during April 2010 in the United States 77% of PCs sold at retail were pre-installed with the 64-bit edition of Windows 7. As of July 22, 2010, Windows 7 had sold 175 million copies. On October 21, 2010, Microsoft announced that more than 240 million copies of Windows 7 had been sold. Three months later, on January 27, 2011, Microsoft announced total sales of 300 million copies of Windows 7. On July 12, 2011, the sales figure was refined to over 400 million end-user licenses and business installations. As of July 9, 2012, over 630 million licenses have been sold; this number includes licenses sold to OEMs for new PCs.
Antitrust concerns
As with other Microsoft operating systems, Windows 7 was studied by United States federal regulators who oversee the company's operations following the 2001 United States v. Microsoft Corp. settlement. According to status reports filed, the three-member panel began assessing prototypes of the new operating system in February 2008. Michael Gartenberg, an analyst at Jupiter Research, said, "[Microsoft's] challenge for Windows 7 will be how can they continue to add features that consumers will want that also don't run afoul of regulators."
In order to comply with European antitrust regulations, Microsoft proposed the use of a "ballot" screen containing download links to competing web browsers, thus removing the need for a version of Windows completely without Internet Explorer, as previously planned. Microsoft announced that it would discard the separate version for Europe and ship the standard upgrade and full packages worldwide, in response to criticism involving Windows 7 E and concerns from manufacturers about possible consumer confusion if a version of Windows 7 with Internet Explorer were shipped later, after one without Internet Explorer.
As with the previous version of Windows, an N version, which does not come with Windows Media Player, has been released in Europe, but only for sale directly from Microsoft sales websites and selected others. | Windows 7 | Wikipedia | 505 | 326123 | https://en.wikipedia.org/wiki/Windows%207 | Technology | Operating Systems | null |
The African forest elephant (Loxodonta cyclotis) is one of the two living species of African elephant, along with the African bush elephant. It is native to humid tropical forests in West Africa and the Congo Basin. It is the smallest of the three living elephant species, reaching a shoulder height of . As with other African elephants, both sexes have straight, down-pointing tusks, which begin to grow once the animals reach 1–3 years old. The forest elephant lives in highly sociable family groups of up to 20 individuals. Since they forage primarily on leaves, seeds, fruit, and tree bark, they have often been referred to as the 'megagardener of the forest'; the species is one of many that contributes significantly to maintaining the composition, diversity and structure of the Guinean Forests of West Africa and the Congolese rainforests. Seeds of various plants will go through the elephant's digestive tract and eventually pass through in the animal's droppings (likely in a new location where they will sprout), thus helping to maintain the spread and biodiversity of the forests.
The first scientific description of the species was published in 1900. During the 20th century, overhunting caused a sharp decline in population, and by 2013 it was estimated that fewer than 30,000 individuals remained. It is threatened by habitat loss, fragmentation, and poaching. The conservation status of populations varies across range countries. Since 2021, the species has been listed as Critically Endangered on the IUCN Red List.
Taxonomy
Elephas (Loxodonta) cyclotis was the scientific name proposed by Paul Matschie in 1900 who described the skulls of a female and a male specimen collected by the Sanaga River in southern Cameroon.
Phylogeny and evolution
The African forest elephant was long considered to be a subspecies of the African elephant, together with the African bush elephant. Morphological and DNA analysis showed that they are two distinct species.
The taxonomic status of the African pygmy elephant (Loxodonta pumilio) was uncertain for a long time. Phylogenetic analysis of the mitochondrial genome of nine specimens from museum collections indicates that it is an African forest elephant whose diminutive size or early maturity is due to environmental conditions. | African forest elephant | Wikipedia | 460 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
Phylogenetic analysis of nuclear DNA of African bush and forest elephants, Asian elephants, woolly mammoths and American mastodons revealed that the African forest elephant and African bush elephant are two distinct species that genetically diverged at least 1.9 million years ago. They are therefore considered distinct species. Despite evidence of hybridization between the two species where their ranges overlap, there appears to have been little gene flow between the two species since their initial divergence.
DNA from the extinct European straight-tusked elephant (Palaeoloxodon antiquus) indicates that members of the extinct elephant genus Palaeoloxodon interbred with African forest elephants, with over 1/3 of the nuclear genome as well as the mitochondrial genome of the straight-tusked elephant deriving from that of African forest elephants, with the genomic contribution more closely related to modern West African populations of the forest elephant than to other populations. Palaeoloxodon carried multiple separate mitochondrial lineages derived from forest elephants.
Diagram of the relationships of elephant mitochondrial genomes, after Lin et al. 2023.
Description
The African forest elephant is considerably smaller than the African bush elephant, though the size of the species has been subject to contradictory estimates. A 2000 study suggested that bulls of the species reach a shoulder height of , and weighed , while females were about tall at the shoulder and . However, a 2003 study of forest elephants at a reserve in Gabon did not find any elephants taller than . A 2015 study alternately suggested that fully grown African forest elephant males in optimal condition were only on average tall and in weight, with the largest individuals (representing less than 1 in 100,000 as a proportion of the total population) no bigger than tall and in weight.
The African forest elephant has grey skin, which looks yellow to reddish after wallowing. It is sparsely covered with black coarse hair, which is long around the tip of the tail. The length of the tail varies between individuals from half the height of the rump to almost touching ground. It has five toenails on the fore foot and four on the hind foot. Its back is nearly straight. Its oval-shaped ears have small elliptical-shaped tips. and the tip of the trunk has two finger-like processes. | African forest elephant | Wikipedia | 454 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
The African forest elephant's tusks are straight and point downwards, and are present in both males and females. The African forest elephant has pink tusks, which are thinner and harder than the tusks of the African bush elephant. The length and diameter vary between individuals. Tusks of bulls grow throughout life, tusks of cows cease growing when they are sexually mature. The tusks are used to push through the dense undergrowth of their habitat. The largest tusk recorded for the species is long and in weight. A larger tusk measuring long and weighing has been recorded, but this may belong to a forest-bush elephant hybrid. The average tusk size is uncertain due to measurements historically being lumped in with those of African bush elephants, but based on the sizes of the largest known tusks may be in the region of and .
Distribution and habitat
Populations of the African forest elephant in Central Africa range in large contiguous rainforest tracts from Cameroon to the Democratic Republic of the Congo, with the largest stable population in Gabon, where suitable habitat covers 90% of the country.
Nonetheless, it was estimated that the population of African forest elephants in Central Africa had declined by around 86% (in the 31 years preceding 2021) due to poaching and loss of habitat. In places such as Cameroon, Democratic Republic of the Congo, Republic of the Congo and the Central African Republic, many areas of appropriate forest habitat have been reduced after years of warfare and human conflict. During the first wildlife survey in 30 years (in 2021) by the Wildlife Conservation Society and the National Parks of Gabon, it was reported that an estimated 95,000 forest elephants lived in Gabon. Prior to this the population had been estimated to be as low as 50,000 to 60,000 individuals.
They are also distributed in the evergreen moist deciduous Upper Guinean forests in Ivory Coast and Ghana, in West Africa.
There is a small population of perhaps 10-25 elephants living on the escarpment to the east of Luanda in the Kambondo forest (Hines, pers. comm. 2015) and sightings of these elephants are marked as point records. Which are the southernmost forest elephants in Africa.
Behaviour and ecology | African forest elephant | Wikipedia | 449 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
The African forest elephant lives in family groups. Groups observed in the rain forest of Gabon's Lopé National Park between 1984 and 1991 comprised between three and eight individuals. Groups of up to 20 individuals were observed in the Dzanga-Sangha Complex of Protected Areas, comprising adult cows, their daughters and subadult sons. Family members look after calves together, called allomothering. Once young bulls reach sexual maturity, they separate from the family group and form loose bachelor groups for a few days, but usually stay alone. Adult bulls associate with family groups only during the mating season. Family groups travel about per day and move in a home range of up to .
Their seasonal movement is related to the availability of ripe fruits in Primary Rainforests.
They use a complex network of permanent trails that pass through stands of fruit trees and connect forest clearings with mineral licks. These trails are reused by humans and other animals.
In Odzala-Kokoua National Park, groups were observed to frequently meet at forest clearings indicating a fission–fusion society. They stayed longer when other groups were also present. Smaller groups joined large groups, and bulls joined family units.
Diet
The African forest elephant is an herbivore. Elephants observed in Lopé National Park fed mostly tree bark and leaves, and at least 72 different fruits.
To supplement their diet with minerals, they congregate at mineral-rich waterholes and mineral licks.
Elephant dung piles collected in Kahuzi-Biéga National Park contained seeds and fruit remains of Omphalocarpum mortehanii, junglesop (Anonidium mannii), Antrocaryon nannanii, Klainedoxa gabonensis, Treculia africana, Tetrapleura tetraptera, Uapaca guineensis, Autranella congolensis, Gambeya africana and G. lacourtiana, Mammea africana, Cissus dinklagei, and Grewia midlbrandii. Dung piles collected in a lowland rain forest in the northern Republic of Congo contained seeds of at least 96 plant species, with a minimum of 30 intact seeds and up to 1102 large seeds of more than in a single pile. Based on the analysis of 855 dung piles, it has been estimated that African forest elephants disperse a daily mean of 346 large seeds per of at least 73 tree species; they transport about a third of the large seeds for more than . | African forest elephant | Wikipedia | 503 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
Seeds passed by elephant gut germinate faster. The African forest elephant is one of the most effective seed dispersers in the tropics and has been referred to as the "megagardener of the forest" due to its significant role in maintaining plant diversity. In the Cuvette Centrale, 14 of 18 megafaunal tree species depend on seed dissemination by African forest elephants, including wild mango (Irvingia gabonensis), Parinari excelsa and Tridesmostemon omphalocarpoides. These 14 species are not able to survive without elephants.
African forest elephants provide ecological services that maintain the composition and structure of Central African forests.
Communication
Vocalization is a trait found among L. cyclotis with studies emphasizing significance in acoustic structure and their social dynamics. Vocalization patterns can be classified into three main types: single rumble, single broadband, and combinatorial. Rumbles are tonal, low-frequency calls, while broadband are calls that lack clear harmonic structures, resembling barks and roars. The utilization of rumbles and broadband calls in combinatorial calls may involve distinct acoustic elements, forming multi-element calls, which combine meaningless elements to generate context-specific meaningful calls. L. cyclotis also exhibits a more balanced distribution of combinatorial call types compared to other elephant species. Despite having a simpler social structure, L. cyclotis can display a comparable repertoire of rumble-roar call combinations than L. africana. Communication patterns vary across age and sex, with adult males typically producing more combinatorial calls than adult females. Additionally, certain events may provoke a behavioral change, as evidenced by lowered levels of vocalizations in response to gunfire sounds related to poaching.
For these mammals, hearing and smell are the most important senses they possess because they do not have good eyesight. They can recognize and hear vibrations through the ground and can detect food sources with their sense of smell. Elephants are also an arrhythmic species, meaning they have the ability to see just as well in dim light as they can in the daylight. They are capable of doing so because the retina in their eyes adjusts nearly as quickly as light does.
The elephant's feet are sensitive and can detect vibrations through the ground, whether thunder or elephant calls, from up to 10 miles away. | African forest elephant | Wikipedia | 476 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
Reproduction
Females reach sexual maturity between the age of 8 and 12 years, depending on the population density and nutrition available. On average, they begin breeding at the age of 23 and give birth every 5–6 years. As a result, the birth rate is lower than the bush species, which starts breeding at age 12 and has a calf every 3–4 years.
Baby elephants weigh around at birth. Almost immediately, they can stand up and move around, allowing the mother to roam around and forage, which is also essential to reduce predation. The baby suckles using its mouth while its trunk is held over its head. Their tusks do not come until around 16 months and calves are not weaned until they are roughly 4 or 5 years old. By this time, their tusks are around long and begin to get in the way of suckling.
Forest elephants have a lifespan of about 60 to 70 years and mature slowly, coming to puberty in their early teens. Bulls generally pass puberty within the next year or two of females. Between the ages of 15 and 25, bulls experience "musth", which is a hormonal state they experience marked by increased aggression. The male secretes fluid from the temporal gland between his ear and eye during this time. Younger bulls often experience musth for a shorter period of time, while older bulls do for a longer time. When in musth, bulls have a more erect walk with their head high and tusks inward, they may rub their heads on trees or bushes to spread the musth scent, and they may even flap their ears, accompanied by a musth rumble, so that their smell can be blown toward other elephants. Another behavior affiliated with musth is urination. Bulls allow their urine to slowly come out and spray the insides of their hind legs. All of these behaviors are to advertise to receptive females and competing bulls that they are in the musth state. Bulls only return to the herd to breed or to socialize; they do not provide prenatal care to their offspring but rather play a fatherly role to younger bulls to show dominance. | African forest elephant | Wikipedia | 436 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
Females are polyestrous, meaning they are capable of conceiving multiple times a year, which is a reason why they do not appear to have a breeding season. However, there does appear to be a peak in conceptions during the two rainy seasons of the year. Generally, the female conceives after two or three matings. Though the female has plenty of room in her uterus for twins, twins are rarely conceived. Gestation lasts 22 months. Based on the maturity, fertility, and gestation rates, African forest elephants have the capacity to increase their population by 5% annually under ideal conditions.
Traditional hunting
African forest elephants are hunted by various hunter-gatherer groups in the Congo basin, including by Mbuti pygmies, among others. It is unknown how long the active hunting of elephants in the region has been practised, and it may have only begun as a response for the demand for ivory beginning in the 19th century or earlier.
Elephants are traditionally hunted using spears, typically to stab at the lower abdomen (as is done among the Mbuti) or knees, both of which are effective at rendering the animal immobile. Anthropologist Mitsuo Ichikawa observed the hunting of elephants by Mbuti pygmies in fieldwork during the 1970s and 1980s, when the Mbuti used spears tipped with metal points (though earlier reports suggest that that prior to this they used purely wooden spears, which may have been less effective at breaking the elephants hide). As observed by Ichikawa, elephant hunting by the Mbuti pygmies involved both small and large groups of hunters, which was led by at least one experienced hunter called a mtuma. Before the hunt began, ritual acts of singing and dancing were performed by the community to support the success of the hunt. These hunters often went into the forest without food, living off of wild honey and vegetables, smearing themselves in mud, elephant dung, and charcoal made from certain plants to disguise their scent from the elephants. Once the traces of an elephant are detected, it was carefully tracked, before being approached from downwind and stabbed. It typically took several hours to several days from the first stab to the death of the elephant. | African forest elephant | Wikipedia | 446 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
Many hunts failed due to elephants detecting the hunters before being stabbed and fleeing, with field research by Ichikawa finding that only one out of six Mbuti elephant hunts were successful in a six-month period, corresponding to around 60–70 days of total hunting time, meaning that despite the large quantity of meat provided by each individual elephant, it did not provide reliable subsistence, with the Mbuti instead relying on hunting smaller animals. Following the death of the animal, the Mbuti hunters returned to their homes, with the whole community moving to dismember the elephant carcass. Meat was shared equally among the community with the exception of a few body parts which were reserved for certain community members, with the feast on the animals remains lasting for several days. Elephant hunting was a dangerous activity that was known to result in the deaths of hunters.
Threats
Both African elephant species are threatened foremost by habitat loss and habitat fragmentation following conversion of forests for plantations of non-timber crops, livestock farming, and building urban and industrial areas. As a result, human-elephant conflict has increased. Poaching for ivory and bushmeat is a significant threat in Central Africa. Because of a spike in poaching, the African forest elephant was declared Critically Endangered by the IUCN in 2021 after it was found that the population had decreased by more than 80% over 3 generations.
Civil unrest, human encroachment, and habit fragmentation leaves some elephants confined to small patches of forest without sufficient food. In January 2014, International Fund for Animal Welfare undertook a relocation project at the request of the Ivory Coast government, moving four elephants from Daloa to Assagny National Park.
Poaching | African forest elephant | Wikipedia | 337 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
Genetic analysis of confiscated ivory showed that 328 tusks of African forest elephants seized in the Philippines between 1996 and 2005 originated in the eastern Democratic Republic of the Congo; 2,871 tusks seized in Hong Kong between 2006 and 2013 originated in Tridom, the tri-national Dja-Odzala-Minkébé protected area complex and the adjacent Dzanga Sangha Reserve in the Central African Republic. So did partly worked ivory confiscated between 2013 and 2014 at warehouses in Togo comprising of tusks.
The hard ivory of the African forest elephant makes for more enhanced carving and fetches a higher price on the black market. This preference is evident in Japan, where hard ivory has nearly monopolized the trade for some time. Premium quality bachi, a traditional Japanese plucking tool used for string instruments, is contrived exclusively from African forest elephant tusks. In the impenetrable and often trackless expanses of the rain forests of the Congo Basin, poaching is extremely difficult to detect and track. Levels of off-take, for the most part, are estimated from ivory seizures. The scarcely populated and unprotected forests in Central Africa are most likely becoming increasingly alluring to organized poacher gangs.
Late in the 20th century, conservation workers established a DNA identification system to trace the origin of poached ivory. Due to poaching to meet high demand for ivory, the African forest elephant population approached critical levels in the 1990s and early 2000s. Over several decades, numbers are estimated to have fallen from approximately 700,000 to less than 100,000, with about half of the remaining population in Gabon. In May 2013, Sudanese poachers killed 26 elephants in the Central African Republic's Dzanga Bai World Heritage Site. Communications equipment, video cameras, and additional training of park guards were provided following the massacre to improve protection of the site. From mid-April to mid-June 2014, poachers killed 68 elephants in Garamba National Park, including young ones without tusks.
At the request of President Ali Bongo Ondimba, twelve British soldiers traveled to Gabon in 2015 to assist in training park rangers following the poaching of many elephants in Minkebe National Park. | African forest elephant | Wikipedia | 460 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
On 19 August 2020, Guyvanho, a poacher who killed over 500 African forest elephants in the Nouabalé-Ndoki National Park, was convicted to 30 years in prison for charges of poaching and others. Guyvanho was the first poacher to be tried criminally in the Republic of the Congo, and has the longest prison sentence for a poacher in the Republic of the Congo.
Bushmeat trade
It is not ivory alone that drives African forest elephant poaching. Killing for bushmeat in Central Africa has evolved into an international business in recent decades with markets reaching New York and other major cities of the United States, and the industry is still on the rise. This illegal market poses the greatest threat not only to forest elephants where hunters can target elephants of all ages, including calves, but to all of the larger species in the forests. There are actions that can be taken to lower the incentive for supplying to the bushmeat market. Regional markets, and international trade, require the transporting of extensive amounts of animal meat which, in turn, requires the utilisation of vehicles. Having checkpoints on major roads and railroads can potentially help disrupt commercial networks. In 2006, it was estimated that 410 African forest elephants are killed yearly in the Cross-Sanaga-Bioko coastal forests.
Conservation
In 1986, the African Elephant Database was initiated with the aim to monitor the status of African elephant populations. This database includes results from aerial surveys, dung counts, interviews with local people, and data on poaching.
Both African elephant species have been listed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora on CITES Appendix I since 1989. This listing banned commercial international trade of wild African elephants and their parts and derivatives by countries that signed the CITES agreement. Populations of Botswana, Namibia and Zimbabwe were listed in CITES Appendix II in 1997 as was the population of South Africa in 2000. Hunting elephants is banned in the Central African Republic, Democratic Republic of Congo, Gabon, Côte d'Ivoire, and Senegal. | African forest elephant | Wikipedia | 418 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
African forest elephants are estimated to constitute up to one-third of the continent's elephant population but have been poorly studied because of the difficulty in observing them through the dense vegetation that makes up their habitat. Thermal imaging has facilitated observation of the species, leading to more information on their ecology, numbers, and behavior, including their interactions with elephants and other species. Scientists have learned more about how the elephants, who have poor night vision, negotiate their environment using only their hearing and olfactory senses. They also appeared to be much more active sexually during the night compared to the day, which was unexpected. | African forest elephant | Wikipedia | 120 | 326177 | https://en.wikipedia.org/wiki/African%20forest%20elephant | Biology and health sciences | Proboscidea | Animals |
Solenodons (from , 'channel' or 'pipe' and , 'tooth') are venomous, nocturnal, burrowing, insectivorous mammals belonging to the family Solenodontidae . The two living solenodon species are the Cuban solenodon (Atopogale cubana) and the Hispaniolan solenodon (Solenodon paradoxus). Threats to both species include habitat destruction and predation by non-native cats, dogs, and mongooses, introduced by humans to the solenodons' home islands to control snakes and rodents.
The Hispaniolan solenodon covers a wide range of habitats on the island of Hispaniola from lowland dry forest to highland pine forest. Two other described species became extinct during the Quaternary period. Oligocene North American genera, such as Apternodus, have been suggested as relatives of Solenodon, but the origins of the animal remain obscure.
Taxonomy
Two genera, Atopogale and Solenodon, are known, each with one extant species. Other genera have been erected, but are now regarded as junior synonyms. Solenodontidae show retention of primitive mammal characteristics. In 2016, solenodons were confirmed by genetic analysis as belonging to an evolutionary branch that split from the lineage leading to hedgehogs, moles, and shrews before the Cretaceous-Paleogene extinction event. They are one of two families of Caribbean soricomorphs. The other family, Nesophontidae, became extinct during the Holocene. Molecular data suggest they diverged from solenodons roughly 57 million years ago. The solenodon is estimated to have diverged from other living mammals about 73 million years ago.
Extant species
In addition, 2 extinct species, the giant solenodon (S. arredondoi) and Marcano's solenodon (S. marcanoi) are both thought to have gone extinct during the last 500 years, both presumably due to predation by introduced rats.
Characteristics | Solenodon | Wikipedia | 418 | 326193 | https://en.wikipedia.org/wiki/Solenodon | Biology and health sciences | Eulipotyphla | Animals |
Traditionally, solenodons' closest relatives were considered to be the giant water shrew of Africa and Tenrecidae of Madagascar, though they are now known to be more closely related to true shrews (Eulipotyphla). Solenodons resemble very large shrews, and are often compared to them; with extremely elongated cartilaginous snouts, long, naked, scaly tails, hairless feet, and small eyes. The Cuban solenodon is generally smaller than its Hispaniolan counterpart. It is also a rusty brown with black on its throat and back. The Hispaniolan solenodon is a darker brown with yellowish tint to the face. The snout is flexible and, in the Hispaniolan solenodon, actually has a ball-and-socket joint at the base to increase its mobility. This allows the animal to investigate narrow crevices where potential prey may be hiding.
Solenodons are also noted for the glands in their inguinal and groin areas that secrete what is described as a musky, goat-like odor. Solenodons range from from nose to rump, and weigh between .
Solenodons have a few unusual traits, one of them being the position of the two teats on the female, almost on the buttocks of the animal, and another being the venomous saliva that flows from modified salivary glands in the mandible through grooves on the second lower incisors ("solenodon" derives from the Greek "grooved tooth"). Solenodons are among a handful of venomous mammals. Fossil records show that some other now-extinct mammal groups also had the dental venom delivery system, indicating that the solenodon's most distinct characteristic may have been a more general ancient mammalian characteristic that has been lost in most modern mammals and is only retained in a couple of very ancient lineages. The solenodon has often been called a "living fossil" because it has endured virtually unchanged for the past 76 million years.
It is not known exactly how long solenodons can live in the wild. However, certain individuals of the Cuban species have been recorded to have lived for up to five years in captivity and individuals of the Hispaniolan species for up to eleven years. | Solenodon | Wikipedia | 477 | 326193 | https://en.wikipedia.org/wiki/Solenodon | Biology and health sciences | Eulipotyphla | Animals |
West Indian natives have long known about the venomous character of the solenodon bite. Early studies on the nature of the tiny mammal's saliva suggested that it was very similar to the neurotoxic venom of certain snakes. More recently, the venom has been found to be related to that of the northern short-tailed shrew and it is mostly composed of kallikreins KLK1, serine proteases that prevent blood clotting, cause hypotension and ultimately end up being fatal to the prey. The KLK1 in solenodon venom is very similar to serine protease found in venomous snakes like vipers, and has evolved in parallel in both lineages from an ancient toxin precursor. Solenodons create venom in enlarged submaxillary glands, and only inject venom through their bottom set of teeth. The symptoms of a solenodon bite include general depression, breathing difficulty, paralysis, and convulsions; large enough doses have resulted in death in lab studies on mice.
Their diets consist largely of insects, earthworms, and other invertebrates, but they also eat vertebrate carrion, and perhaps even some living vertebrate prey, such as small reptiles or amphibians. They have also been known to feed on fruits, roots, and vegetables. Based on observation of the solenodon in captivity, they have only been known to drink while bathing. Solenodons have a relatively unspecialised, and almost complete dentition, with a dental formula of: .
Solenodons find food by sniffing the ground until they come upon their prey. If the prey is small enough, the solenodon will consume it immediately. After coming across the prey, the solenodon will bring the forelimbs up to either side of the prey and then move the head forward, opening the jaw and properly catching its prey. While sniffing for food, the solenodon can get through physical barriers with the help of its sharp claws.
There has been research that suggests that males and females of the two species have different eating habits. The female has a habit of scattering the food to make sure that no morsel of food is missed as it is foraging. The male was noted to use its tongue to lap up the food and using the lower jaw as a scoop. However, these specimens were studied in captivity, so these habits may not be found in the wild. | Solenodon | Wikipedia | 503 | 326193 | https://en.wikipedia.org/wiki/Solenodon | Biology and health sciences | Eulipotyphla | Animals |
Reproduction
Solenodons give birth in a nesting burrow to one or two young. The young remain with the mother for several months and initially follow the mother by hanging on to her elongated teats. Once they reach adulthood solenodons are solitary animals and rarely interact except to breed.
The reproductive rate of solenodons is relatively low, producing only two litters per year. Breeding can occur at any time. Males will not aid in the care for the young. The mother will nurse her offspring using her two nipples, which are placed toward the back of the animal. If the litter consists of three offspring, one will become malnourished and die. The nursing period can last for up to seventy-five days.
In their nesting burrows, solenodons give birth to one or two pups, displaying a distinctive reproductive behavior. For several months, the mother tends to them, and the young follow her, clinging on lengthy teats. Breeding can take place at any time, with a comparatively low reproductive rate of two litters annually, and males do not participate in the upbringing of their offspring. Up to 75 days of breastfeeding are dedicated to showcasing the interesting function that mothers play in solenodon reproduction.
Behavior
Solenodons make their homes in bushy areas in forests. During the daytime they seek refuge in caves, burrows, or hollow logs. They are easily provoked and can fly into a frenzy of squealing and biting with no warning. They run and climb quite fast, despite only ever touching the ground with toes. Solenodons are said to give off grunts similar to that of a pig or bird-call when feeling threatened.
Solenodons generate clicking noises similar to those of shews; the sound waves bounce off objects in their vicinity. This form of echolocation helps a solenodon navigate as well as find food. This well developed auditory ability combined with its above average sense of smell helps the solenodon survive despite its extremely small eyes and poor vision.
Solenodons have been described as both omnivorous and insectivorous. Their natural diet largely consists of insects including ants and roaches, grubs, vegetation, and fruit. However, they have also been observed to eat small vertebrates like mice and chicks, meat of large animals, as well as animal products such as eggs and milk, when fed these food items in captivity.
Status | Solenodon | Wikipedia | 493 | 326193 | https://en.wikipedia.org/wiki/Solenodon | Biology and health sciences | Eulipotyphla | Animals |
Cuba
The Cuban solenodon is considered Endangered due to predation by the small Indian mongoose (Urva auropunctata), which was introduced in colonial times to hunt snakes and rats, as well as by feral cats and dogs. The Cuban solenodon was thought to have been extinct until a live specimen was found in 2003.
Haiti
The Hispaniolan solenodon was also once thought to be extinct, more due to its secretive and elusive behavior than to low population numbers. Recent studies have proven that the species is widely distributed through the island of Hispaniola, but it does not tolerate habitat degradation. A 1981 study of the Hispaniolan solenodon in Haiti found that the species was "functionally extinct", with the exception of a small population in the area of Massif de la Hotte. A follow-up study, in 2007, noted that the solenodon was still thriving in the area, even though the region has had an increase in human population density in recent years.
Dominican Republic
The Sierra de Bahoruco, a mountain range in the southwest of the Dominican Republic that straddles the border with Haiti, was examined by conservation teams looking for solenodons. The work occurred during the day when the animals were asleep in burrows so that they could be viewed with an infrared camera. When researchers search for solenodons in daylight, they look for the following clues to their presence:
nearby nose-poke holes that the creatures make in the ground with their long noses to probe the earth, as they look for insects they can hunt and eat. After a relatively long period of time they will be covered in leaves, but a fresh hole will be covered in moist soil.
nearby scratches in logs that were made with their long claws.
a strong musty goat-like smell seeping out of a burrow. The pungent odor indicates that the burrow is active, and a solenodon may be present sleeping. | Solenodon | Wikipedia | 401 | 326193 | https://en.wikipedia.org/wiki/Solenodon | Biology and health sciences | Eulipotyphla | Animals |
A solenodon was captured in 2008 during a month-long expedition in the Dominican Republic, thereby allowing researchers the rare opportunity to examine it in daylight. The Durrell Wildlife Conservation Trust and the Ornithological Society of Hispaniola were able to take measurements and DNA from the creature before it was released. It was the only trapping made from the entire month-long expedition. The new information gathered was significant because little information was known about the solenodon's ecology, behavior, population status, and genetics, and without that knowledge it is difficult for researchers to design effective conservation. In a 2020 assessment from the IUCN, the Hispaniolan solenodon was found to be much more common on Hispaniola than previously thought, warranting its downlisting from "Endangered" to a "Least Concern" species.
Conservation
After the arrival of Europeans to the Caribbean, the existence of both species of solenodon has been threatened by introduced species, like dogs, cats, rats, and mongooses, as well as more dense human settlement. These factors were possibly the catalyst for the relatively recent extinction of two species, the giant solenodon (S. arredondoi) and the Marcano's solenodon (S. marcanoi). Native snakes and birds of prey are also threats. Solenodons have no known negative effects on human populations; in fact, they serve as both pest control, helping ecosystems by keeping down the population of invertebrates, and a means of spreading fruit seeds. Human activity has also had an adverse effect on the solenodon population. Human development on both Cuba and Hispaniola has resulted in fragmentation and habitat loss, further contributing to the reduction of the solenodon's range and numbers. | Solenodon | Wikipedia | 358 | 326193 | https://en.wikipedia.org/wiki/Solenodon | Biology and health sciences | Eulipotyphla | Animals |
Psilocybin mushrooms, commonly known as magic mushrooms, shrooms, or broadly as hallucinogenic mushrooms, are a polyphyletic informal group of fungi that contain psilocybin, which turns into psilocin upon ingestion. The most potent species are members of genus Psilocybe, such as P. azurescens, P. semilanceata, and P. cyanescens, but psilocybin has also been isolated from approximately a dozen other genera, including Panaeolus (including Copelandia), Inocybe, Pluteus, Gymnopilus, and Pholiotina.
Amongst other cultural applications, psilocybin mushrooms are used as recreational drugs. They may be depicted in Stone Age rock art in Africa and Europe, but are more certainly represented in sculptures and glyphs seen throughout the Americas.
History
Psilocybin mushrooms have been and continue to be used in Mexican and Central American cultures in religious, divinatory, or spiritual contexts.
Early
Rock art from from Tassili, Algeria, is believed to depict psychedelic mushrooms and the transformation of the user under their influence. Prehistoric rock art near Villar del Humo in Spain suggests that Psilocybe hispanica was used in religious rituals 6,000 years ago. The hallucinogenic species of the Psilocybe genus have a history of use among the native peoples of Mesoamerica for religious communion, divination, and healing, from pre-Columbian times to the present day. Mushroom stones and motifs have been found in Guatemala. A statuette dating from depicting a mushroom strongly resembling Psilocybe mexicana was found in the west Mexican state of Colima in a shaft and chamber tomb. A Psilocybe species known to the Aztecs as teōnanācatl (literally "divine mushroom": the agglutinative form of teōtl (god, sacred) and nanācatl (mushroom) in Nahuatl language) was reportedly served at the coronation of the Aztec ruler Moctezuma II in 1502. Aztecs and Mazatecs referred to psilocybin mushrooms as genius mushrooms, divinatory mushrooms, and wondrous mushrooms when translated into English. Bernardino de Sahagún reported the ritualistic use of teonanácatl by the Aztecs when he traveled to Central America after the expedition of Hernán Cortés. | Psilocybin mushroom | Wikipedia | 496 | 326201 | https://en.wikipedia.org/wiki/Psilocybin%20mushroom | Biology and health sciences | Edible fungi | Plants |
After the Spanish conquest, Catholic missionaries campaigned against the cultural tradition of the Aztecs, dismissing the Aztecs as idolaters, and the use of hallucinogenic plants and mushrooms, together with other pre-Christian traditions, was quickly suppressed. The Spanish believed the mushroom allowed the Aztecs and others to communicate with demons. Despite this history, the use of teonanácatl has persisted in some remote areas.
Modern
The first mention of hallucinogenic mushrooms in European medicinal literature was in the London Medical and Physical Journal in 1799: A man served Psilocybe semilanceata mushrooms he had picked for breakfast in London's Green Park to his family. The apothecary who treated them later described how the youngest child "was attacked with fits of immoderate laughter, nor could the threats of his father or mother refrain him."
In 1955, Valentina Pavlovna Wasson and R. Gordon Wasson became the first known European Americans to actively participate in an indigenous mushroom ceremony. The Wassons did much to publicize their experience, even publishing an article on their experiences in Life on May 13, 1957. In 1956, Roger Heim identified the psychoactive mushroom the Wassons brought back from Mexico as Psilocybe, and in 1958, Albert Hofmann first identified psilocybin and psilocin as the active compounds in these mushrooms.
Inspired by the Wassons' Life article, Timothy Leary traveled to Mexico to experience psilocybin mushrooms himself. When he returned to Harvard in 1960, he and Richard Alpert started the Harvard Psilocybin Project, promoting psychological and religious studies of psilocybin and other psychedelic drugs. Alpert and Leary sought to conduct research with psilocybin on prisoners in the 1960s, testing its effects on recidivism. This experiment reviewed the subjects six months later, and found that the recidivism rate had decreased beyond their expectation, below 40%. This, and another experiment administering psilocybin to graduate divinity students, showed controversy. Shortly after Leary and Alpert were dismissed from their jobs by Harvard in 1963, they turned their attention toward promoting the psychedelic experience to the nascent hippie counterculture. | Psilocybin mushroom | Wikipedia | 454 | 326201 | https://en.wikipedia.org/wiki/Psilocybin%20mushroom | Biology and health sciences | Edible fungi | Plants |
The popularization of entheogens by the Wassons, Leary, Terence McKenna, Robert Anton Wilson, and many others led to an explosion in the use of psilocybin mushrooms throughout the world. By the early 1970s, many psilocybin mushroom species were described from temperate North America, Europe, and Asia and were widely collected. Books describing methods of cultivating large quantities of Psilocybe cubensis were also published. The availability of psilocybin mushrooms from wild and cultivated sources has made them one of the most widely used psychedelic drugs.
At present, psilocybin mushroom use has been reported among some groups spanning from central Mexico to Oaxaca, including groups of Nahua, Mixtecs, Mixe, Mazatecs, Zapotecs, and others. An important figure of mushroom usage in Mexico was María Sabina, who used native mushrooms, such as Psilocybe mexicana in her practice.
Occurrence
In a 2000 review on the worldwide distribution of psilocybin mushrooms, Gastón Guzmán and colleagues considered these distributed among the following genera: Psilocybe (116 species), Gymnopilus (14), Panaeolus (13), Copelandia (12), Pluteus (6) Inocybe (6), Pholiotina (4) and Galerina (1). Guzmán increased his estimate of the number of psilocybin-containing Psilocybe to 144 species in a 2005 review.
Many of them are found in Mexico (53 species), with the remainder distributed throughout Canada and the US (22), Europe (16), Asia (15), Africa (4), and Australia and associated islands (19). Generally, psilocybin-containing species are dark-spored, gilled mushrooms that grow in meadows and woods in the subtropics and tropics, usually in soils rich in humus and plant debris. Psilocybin mushrooms occur on all continents, but the majority of species are found in subtropical humid forests. P. cubensis is the most common Psilocybe in tropical areas. P. semilanceata, considered the world's most widely distributed psilocybin mushroom, is found in temperate parts of Europe, North America, Asia, South America, Australia and New Zealand, although it is absent from Mexico. | Psilocybin mushroom | Wikipedia | 485 | 326201 | https://en.wikipedia.org/wiki/Psilocybin%20mushroom | Biology and health sciences | Edible fungi | Plants |
Composition
Magic mushroom composition varies from genus to genus and species to species. Its principal component is psilocybin, which is converted into psilocin to produce psychoactive effects. Besides psilocin, norpsilocin, baeocystin, norbaeocystin, and aeruginascin may also be present, which can modify the effects of magic mushrooms. Panaeolus subbalteatus, one species of magic mushroom, had the highest amount of psilocybin compared to the rest of the fruiting body. Certain mushrooms are found to produce beta-carbolines which inhibit monoamine oxidase, an enzyme that breaks down tryptamine alkaloids. They occur in different genera, such as Psilocybe,Cyclocybe, and Hygrophorus. Harmine, harmane, norharmane and a range of other l-tryptophan-derived were discovered in Psilocybe species.
Effects
The effects of psilocybin mushrooms come from psilocybin and psilocin. When psilocybin is ingested, it is broken down by the liver in a process called dephosphorylation. The resulting compound is called psilocin, responsible for the psychedelic effects. Psilocybin and psilocin create short-term increases in tolerance of users, thus making it difficult to misuse them because the more often they are taken within a short period, the weaker the resultant effects are. Psilocybin mushrooms have not been known to cause physical or psychological dependence (addiction). The psychedelic effects appear around 20 minutes after ingestion and can last up to 6 hours. Physical effects may occur, including nausea, vomiting, euphoria, muscle weakness or relaxation, drowsiness, and lack of coordination.
As with many psychedelic substances, the effects of psychedelic mushrooms are subjective and can vary considerably among individual users. The mind-altering effects of psilocybin-containing mushrooms typically last from three to eight hours, depending on dosage, preparation method, and personal metabolism. The first 3–4 hours after ingestion are typically referred to as the 'peak'—in which the user experiences more vivid visuals and distortions in reality. The effects can seem to last much longer for the user because of psilocybin's ability to alter time perception. | Psilocybin mushroom | Wikipedia | 487 | 326201 | https://en.wikipedia.org/wiki/Psilocybin%20mushroom | Biology and health sciences | Edible fungi | Plants |
Sensory
Sensory effects include visual and auditory hallucinations followed by emotional changes and altered perception of time and space. Noticeable changes to the auditory, visual, and tactile senses may become apparent around 30 minutes to an hour after ingestion, although effects may take up to two hours to take place. These shifts in perception visually include enhancement and contrasting of colors, strange light phenomena (such as auras or "halos" around light sources), increased visual acuity, surfaces that seem to ripple, shimmer, or breathe; complex open and closed eye visuals of form constants or images, objects that warp, morph, or change solid colors; a sense of melting into the environment, and trails behind moving objects. Sounds may seem to have increased clarity—music, for example, can take on a profound sense of cadence and depth. Some users experience synesthesia, wherein they perceive, for example, a visualization of color upon hearing a particular sound.
Emotional
As with other psychedelics such as LSD, the experience, or 'trip,' is strongly dependent upon set and setting. Hilarity, lack of concentration, and muscular relaxation (including dilated pupils) are all normal effects, sometimes in the same trip. A negative environment could contribute to a bad trip, whereas a comfortable and familiar environment would set the stage for a pleasant experience. Psychedelics make experiences more intense, so if a person enters a trip in an anxious state of mind, they will likely experience heightened anxiety on their trip. Many users find it preferable to ingest the mushrooms with friends or people familiar with 'tripping.' The psychological consequences of psilocybin use include hallucinations and an inability to discern fantasy from reality. Panic reactions and psychosis also may occur, particularly if a user ingests a large dose.
Dosage
The dosage of mushrooms containing psilocybin depends on the psilocybin and psilocin content, which can vary significantly between and within the same species but is typically around 0.5–2.0% of the dried weight of the mushroom. Usual doses of the common species Psilocybe cubensis range around 1.0 to 2.5 g, while about 2.5 to 5.0 g dried mushroom material is considered a strong dose. Above 5 g is often considered a heavy dose, with 5.0 grams of dried mushroom often being referred to as a "heroic dose". | Psilocybin mushroom | Wikipedia | 497 | 326201 | https://en.wikipedia.org/wiki/Psilocybin%20mushroom | Biology and health sciences | Edible fungi | Plants |
However, microdosing has become a popular technique for many users, which involves taking <1.0g for an experience that is not as intense or powerful, but recreationally enjoyable and even alleviating for symptoms of depression.
The concentration of active psilocybin mushroom compounds varies from species to species but also from mushroom to mushroom within a given species, subspecies or variety. The species Psilocybe azurescens contains the most psilocybin (up to 1.78%).
Toxicology
The species within the most commonly foraged and ingested genus of psilocybin mushrooms, the psilocybe, contains two primary hallucinogenic toxins; psilocybin and psilocin. The median lethal dose, also known as "LD50", of psilocybin is 280 mg/kg.
From a toxicological profile, it would be incredibly difficult to overdose on psilocybin mushrooms, given their primary toxin compounds. To consume such massive amounts of psilocybin, one must ingest more than of dried Psilocybe cubensis given 1-2% of the dried mushroom contains psilocybin.
Posing a more realistic threat than a lethal overdose, significantly elevated levels of psilocin can overstimulate the 5-HT2A receptors in the brain, causing acute serotonin syndrome. A 2015 study observed that a dose of 200 mg/kg psilocin induced symptoms of acute serotonin poisoning in mice.
Neurotoxicity-induced fatal events are uncommon with psilocybin mushroom overdose, as most patients admitted to critical care are released from the department only requiring moderate treatment. However, fatal events related to emotional distress and trip-induced psychosis can occur as a result of over-consumption of psilocybin mushrooms. In 2003, a 27-year-old man was found dead in an irrigation canal due to hypothermia. In his bedroom was found two cultivation pots of psilocybin mushrooms, but no report of toxicology was made.
Clinical research
Due partly to restrictions of the Controlled Substances Act, research in the United States was limited until the early 21st century when psilocybin mushrooms were tested for their potential to treat drug dependence, anxiety and mood disorders. In 2018–19, the Food and Drug Administration (FDA) granted Breakthrough Therapy Designation for studies of psilocybin in depressive disorders.
Legality | Psilocybin mushroom | Wikipedia | 496 | 326201 | https://en.wikipedia.org/wiki/Psilocybin%20mushroom | Biology and health sciences | Edible fungi | Plants |
The legality of the cultivation, possession, and sale of psilocybin mushrooms and psilocybin and psilocin varies from country to country.
After Oregon Measure 109, in 2020, Oregon became the first US state to decriminalize psilocybin and legalize it for therapeutic use. However, selling psilocybin without being licensed may still attract fines or imprisonment. In 2022 Colorado legalized consumption, growing, and sharing for personal use, though sales are prohibited while regulations are being drafted. Other jurisdictions in the United States where psilocybin mushrooms are decriminalized include Ann Arbor and Detroit, Michigan; Oakland and Santa Cruz, California; Easthampton, Somerville, Northampton, and Cambridge, Massachusetts; Seattle, Washington; and Washington, DC.
Furthermore, buying spores of mushroom species containing psilocybin online in the United States is legal in all states except Georgia, Idaho and California. This is because only fruiting mushrooms and mycelium contain psilocybin, a federally banned substance. A technical caveat to consider, however, is that the distributed spores must not be intended to be used for cultivation, but allowed for microscopy purposes.
United Nations
Internationally, mescaline, DMT, and psilocin, are Schedule I drugs under the Convention on Psychotropic Substances. The Commentary on the Convention on Psychotropic Substances notes, however, that the plants containing them are not subject to international control: | Psilocybin mushroom | Wikipedia | 295 | 326201 | https://en.wikipedia.org/wiki/Psilocybin%20mushroom | Biology and health sciences | Edible fungi | Plants |
The dromedary (Camelus dromedarius or ;), also known as the dromedary camel, Arabian camel, or one-humped camel, is a large camel, of the genus Camelus, with one hump on its back.
It is the tallest of the three species of camel; adult males stand at the shoulder, while females are tall. Males typically weigh between , and females weigh between .
The species' distinctive features include its long, curved neck, narrow chest, a single hump (compared with two on the Bactrian camel and wild Bactrian camel), and long hairs on the throat, shoulders and hump. The coat is generally a shade of brown. The hump, tall or more, is made of fat bound together by fibrous tissue.
Dromedaries are mainly active during daylight hours. They form herds of about 20 individuals, which are led by a dominant male. They feed on foliage and desert vegetation; several adaptations, such as the ability to tolerate losing more than 30% of its total water content, allow it to thrive in its desert habitat. Mating occurs annually and peaks in the rainy season; females bear a single calf after a gestation of 15 months.
The dromedary has not occurred naturally in the wild for nearly 2,000 years. It was probably first domesticated in the Arabian Peninsula about 4,000 years ago, or in Somalia where there are paintings in Laas Geel that figure it from 5,000 to 9,000 years ago. In the wild, the dromedary inhabited arid regions, including the Sahara Desert. The domesticated dromedary is generally found in the semi-arid to arid regions of the Old World, mainly in Africa and the Arabian Peninsula, and a significant feral population occurs in Australia. Products of the dromedary, including its meat and milk, support several North African tribes; it is also commonly used for riding and as a pack animal. | Dromedary | Wikipedia | 406 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Etymology
The common name "dromedary" comes from the Old French or the Late Latin . These originated from the Greek word , (GEN (γενική) , ), meaning "running" or "runner", used in Greek in the combination (), literally "running camel", to refer to the dromedary. The first recorded use in English of the name "dromedary" occurred in the 14th century. The dromedary possibly originated in Arabia or Somalia and is therefore sometimes referred to as the Arabian or East African camel. The word "camel" generally refers either to the dromedary or the congeneric Bactrian; the word came into English via Old Norman, from the Latin word , from Ancient Greek (), ultimately from a Semitic source akin to Hebrew () and Arabic ().
Taxonomy and classification
The dromedary shares the genus Camelus with the Bactrian camel (C. bactrianus) and the wild Bactrian camel (C. ferus). The dromedary belongs to the family Camelidae. The ancient Greek philosopher Aristotle (4th century BC) was the first to describe the species of Camelus. He named two species in his History of Animals; the one-humped Arabian camel and the two-humped Bactrian camel. The dromedary was given its current binomial name Camelus dromedarius by Swedish zoologist Carl Linnaeus in his 1758 publication Systema Naturae. In 1927, British veterinarian Arnold Leese classified dromedaries by their basic habitats; the hill camels are small, muscular animals and efficient beasts of burden; the larger plains camels could be further divided into the desert type that can bear light burdens and are apt for riding, and the riverine type – slow animals that can bear heavy burdens; and those intermediate between these two types. | Dromedary | Wikipedia | 397 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
In 2007, Peng Cui of the Chinese Academy of Sciences and colleagues carried out a phylogenetic study of the evolutionary relationships between the two tribes of Camelidae; Camelini – consisting of the three Camelus species (the study considered the wild Bactrian camel as a subspecies of the Bactrian camel) – and Lamini, which consists of the alpaca (Vicugna pacos), the guanaco (Lama guanicoe), the llama (L. glama) and the vicuña (V. vicugna). The study showed the two tribes had diverged 25 million years ago (early Miocene), earlier than previously estimated from North American fossils.
The dromedary and the Bactrian camel often interbreed to produce fertile offspring. Where the ranges of the species overlap, such as in northern Punjab, Persia, and Afghanistan, the phenotypic differences between them tend to decrease as a result of extensive crossbreeding. The fertility of their hybrid has given rise to speculation that the dromedary and the Bactrian camel should be merged into a single species with two varieties. However, a 1994 analysis of the mitochondrial cytochrome b gene showed the species display 10.3% divergence in their sequences.
Genetics and hybrids
The dromedary has 74 diploid chromosomes, the same as other camelids. The autosomes consist of five pairs of small to medium-sized metacentrics and submetacentrics. The X chromosome is the largest in the metacentric and submetacentric group. There are 31 pairs of acrocentrics. The dromedary's karyotype is similar to that of the Bactrian camel.
Camel hybridization began in the first millennium BC. For about a thousand years, Bactrian camels and dromedaries have been successfully bred in regions where they are sympatric to form hybrids with either a long, slightly lopsided hump or two humps – one small and one large. These hybrids are larger and stronger than their parents – they can bear greater loads. A cross between a first generation female hybrid and a male Bactrian camel can also produce a hybrid. Hybrids from other combinations tend to be bad-tempered or runts. | Dromedary | Wikipedia | 469 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Evolution
The extinct Protylopus, which occurred in North America during the upper Eocene, is the oldest and the smallest-known camel. During the transition from Pliocene to Pleistocene, several mammals faced extinction. This period marked the successful radiation of the Camelus species, which migrated over the Bering Strait and dispersed widely into Asia, eastern Europe and Africa. By the Pleistocene, ancestors of the dromedary occurred in the Middle East and northern Africa.
The modern dromedary probably evolved in the hotter, arid regions of western Asia from the Bactrian camel, which in turn was closely related to the earliest Old World camels. It was previously believed that this hypothesis was supported by the dromedary foetus having two humps, but modern studies have shown this to be false. A jawbone of a dromedary that dated from 8,200 BC was found in Saudi Arabia on the southern coast of the Red Sea.
In 1975, Richard Bulliet of Columbia University wrote that the dromedary exists in large numbers in areas from which the Bactrian camel has disappeared; the converse is also true to a great extent. He said this substitution could have taken place because of the heavy dependence on the milk, meat and wool of the dromedary by Syrian and Arabian nomads, while the Asiatic people domesticated the Bactrian camel but did not have to depend upon its products.
Characteristics
The dromedary is the tallest of the three camel species. Adult males range in height between at the shoulder; females range between . Males typically weigh between ; females range between . The distinctive features are its long, curved neck, narrow chest and single hump (the Bactrian camel has two), thick, double-layered eyelashes and bushy eyebrows. They have sharp vision and a good sense of smell. The male has a soft palate ( in Arabic) nearly long, which he inflates to produce a deep pink sac. The palate, which is often mistaken for the tongue, dangles from one side of the mouth and is used to attract females during the mating season. | Dromedary | Wikipedia | 435 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
The coat is generally brown but can range from black to nearly white. Leese reported piebald dromedaries in Kordofan and Darfur in Sudan. Piebald coloration in some camels is thought to be caused by the KITW1 allele of the KIT gene, though there is likely at least one other mutation that also causes white spotting. The hair is long and concentrated on the throat, shoulders and the hump. The large eyes are protected by prominent supraorbital ridges; the ears are small and rounded. The hump is at least high. The dromedary has long, powerful legs with two toes on each foot. The feet resemble flat, leathery pads. Like the giraffe, dromedaries move both legs on one side of the body at the same time.
Compared with the Bactrian camel, the dromedary has a lighter build, longer limbs, shorter hairs, a harder palate and an insignificant or absent ethmoidal fissure. Unlike the camelids of the genus Lama, the dromedary has a hump, and in comparison has a longer tail, smaller ears, squarer feet, and a greater height at the shoulder. The dromedary has four teats instead of the two in the Lama species.
Anatomy
The cranium of the dromedary consists of a postorbital bar, a tympanic bulla filled with spongiosa, a well-defined sagittal crest, a long facial part and an indented nasal bone. Typically, there are eight sternal and four non-sternal pairs of ribs. The spinal cord is nearly long; it terminates in the second and third sacral vertebra. The fibula is reduced to a malleolar bone. The dromedary is a digitigrade animal; it walks on its toes, which are known as digits. It lacks the second and fifth digits. The front feet are wide and long; they are larger than the hind feet, which measure wide and long. | Dromedary | Wikipedia | 426 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
The dromedary has 22 milk teeth, which are eventually replaced by 34 permanent teeth. The dental formula for permanent dentition is , and for milk dentition. In the juvenile, the lower first molars develop by 12 to 15 months and the permanent lower incisors appear at 4.5 to 6.5 years of age. All teeth are in use by 8 years. The lenses of the eyes contain crystallin, which constitutes 8 to 13% of the protein present there.
The skin is black; the epidermis is thick and the dermis is thick. The hump is composed of fat bound together by fibrous tissue. There are no glands on the face; males have glands that appear to be modified apocrine sweat glands that secrete pungent, coffee-coloured fluid during the rut, located on either side of the neck midline. The glands generally grow heavier during the rut, and range from . Each cover hair is associated with an arrector pilli muscle, a hair follicle, a ring of sebaceous glands and a sweat gland. Females have cone-shaped, four-chambered mammary glands that are long with a base diameter of . These glands can produce milk with up to 90% water content even if the mother is at risk of dehydration.
The heart weighs around ; it has two ventricles with the tip curving to the left. The pulse rate is 50 beats per minute. The dromedary is the only mammal with oval red blood corpuscles, which facilitates blood flow during dehydration. The pH of the blood varies from 7.1 to 7.6 (slightly alkaline). The individual's state of hydration and sex and the time of year can influence blood values. The lungs lack lobes. A dehydrated camel has a lower breathing rate. Each kidney has a capacity of , and can produce urine with high chloride concentrations. Like the horse, the dromedary has no gall bladder. The grayish violet, crescent-like spleen weighs less than . The triangular, four-chambered liver weighs ; its dimensions are . | Dromedary | Wikipedia | 443 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Reproductive system
The ovaries are reddish, circular and flattened. They are enclosed in a conical bursa and have the dimensions during anestrus. The oviducts are long. The uterus is bicornuate. The vagina is long and has well-developed Bartholin's glands. The vulva is deep and has a small clitoris. The placenta is diffuse and epitheliochorial, with a crescent-like chorion.
The penis is covered by a triangular penile sheath that opens backwards; it is about long. The scrotum is located high in the perineum with the testicles in separate sacs. Testicles are long, deep and wide. The right testicle is often smaller than the left. The typical mass of either testicle is less than ; during the rut the mass increases from . The Cowper's gland is white, almond-shaped and lacks seminal vesicles; the prostate gland is dark yellow, disc-shaped and divided into two lobes.
The camel epididymis interstitium revealed several blood vessels harboring special regulatory devices such as the spiral arteries, spiral veins, and throttle arterioles.
Health and diseases
The dromedary generally suffers from fewer diseases than other domestic livestock such as goats and cattle. Temperature fluctuations occur throughout the day in a healthy dromedary – the temperature falls to its minimum at dawn, rises until sunset and falls during the night. Nervous camels may vomit if they are carelessly handled; this does not always indicate a disorder. Rutting males may develop nausea. | Dromedary | Wikipedia | 327 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
The dromedary is prone to trypanosomiasis, a disease caused by a parasite transmitted by the tsetse fly. The main symptoms are recurring fever, anaemia and weakness; the disease is typically fatal for the camel. Brucellosis is another prominent malady. In an observational study, the seroprevalence of this disease was generally low (2 to 5%) in nomadic or moderately free dromedaries, but it was higher (8 to 15%) in denser populations. Brucellosis is caused by different biotypes of Brucella abortus and B. melitensis. Other internal parasites include Fasciola gigantica (trematode), two types of cestode (tapeworm) and various nematodes (roundworms). Among external parasites, Sarcoptes species cause sarcoptic mange. In a 2000 study in Jordan, 83% of the 32 camels studied tested positive for sarcoptic mange. In another study, dromedaries were found to have natural antibodies against the rinderpest and ovine rinderpest viruses.
In 2013, a seroepidemiological study (a study investigating the patterns, causes and effects of a disease on a specific population on the basis of serologic tests) in Egypt was the first to show the dromedary might be a host for the Middle East respiratory syndrome coronavirus (MERS-CoV). A 2013–14 study of dromedaries in Saudi Arabia concluded the unusual genetic stability of MERS-CoV coupled with its high seroprevalence in the dromedary makes this camel a highly probable host for the virus. The full genome sequence of MERS-CoV from dromedaries in this study showed a 99.9% match to the genomes of human clade B MERS-CoV. Another study in Saudi Arabia showed the presence of MERS-CoV in 90% of the evaluated dromedaries and suggested that camels could be the animal source of MERS-CoV. | Dromedary | Wikipedia | 434 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Fleas and ticks are common causes of physical irritation. Hyalomma dromedarii is especially adapted to arid conditions, changing its moulting process to complete more or all of its life cycle on a single host if stressed, and having an unusually wide host range. The larvae are not well understood but their questing phase is assumed to occur during the winter, which is also when rain arrives. The nymphs infest the host mostly in January, then the adults May to September. In a study in Egypt, H. dromedarii was dominant in dromedaries, comprising 95.6% of the adult ticks isolated from the camels. In Israel, the number of ticks per camel ranged from 20 to 105. Nine camels in the date palm plantations in Arava Valley were injected with ivermectin, which is not effective against Hyalomma tick infestations. Larvae of the camel nasal fly Cephalopsis titillator can cause possibly fatal brain compression and nervous disorders. Illnesses that can affect dromedary productivity are pyogenic diseases and wound infections caused by Corynebacterium and Streptococcus, pulmonary disorders caused by Pasteurella such as hemorrhagic septicemia and Rickettsia species, camelpox, anthrax, and cutaneous necrosis caused by Streptothrix and deficiency of salt in the diet.
Ecology
The dromedary is diurnal (active mainly during daylight); free-ranging herds feed and roam throughout the day, though they rest during the hottest hours around noon. The night is mainly spent resting. Dromedaries form cohesive groups of about 20 individuals, which consist of several females led by a dominant male. Females may also lead in turns. Some males either form bachelor groups or roam alone. Herds may congregate to form associations of hundreds of camels during migrations at the time of natural disasters. The males of the herd prevent female members from interacting with bachelor males by standing or walking between them and sometimes driving the bachelor males away. In Australia, short-term home ranges of feral dromedaries cover ; annual home ranges can spread over several thousand square kilometres. | Dromedary | Wikipedia | 457 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Special behavioral features of the dromedary include snapping at others without biting them and showing displeasure by stamping their feet. They are generally non-aggressive, with the exception of rutting males. They appear to remember their homes; females, in particular, remember the places they first gave birth or suckled their offspring. Males become aggressive in the mating season, and sometimes wrestle. A 1980 study showed androgen levels in males influences their behavior. Between January and April when these levels are high during the rut, they become difficult to manage, blow out the palate from the mouth, vocalize and throw urine over their backs. Camels scratch parts of their bodies with their legs or with their lower incisors. They may also rub against tree bark and roll in the sand.
Free-ranging dromedaries face large predators typical of their regional distribution, which includes wolves, lions and tigers.
Diet
The dromedary's diet consists mostly of foliage, dry grasses and desert vegetation – mostly thorny plants. A study said the typical diet of the dromedary is dwarf shrubs (47.5%), trees (29.9%), grasses (11.2%), other herbs (0.2%) and vines (11%). The dromedary is primarily a browser; forbs and shrubs comprise 70% of its diet in summer and 90% of its diet in winter. The dromedary may also graze on tall, young, succulent grasses. | Dromedary | Wikipedia | 311 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
In the Sahara, 332 plant species have been recorded as food plants of the dromedary. These include Aristida pungens, Acacia tortilis, Panicum turgidum, Launaea arborescens and Balanites aegyptiaca. The dromedary eats Acacia, Atriplex and Salsola when they are available. Feral dromedaries in Australia prefer Trichodesma zeylanicum and Euphorbia tannensis. In India, dromedaries are fed with forage plants such as Vigna aconitifolia, V. mungo, Cyamopsis tetragonolaba, Melilotus parviflora, Eruca sativa, Trifolium species and Brassica campestris. Dromedaries keep their mouths open while chewing thorny food. They use their lips to grasp the food and chew each bite 40 to 50 times. Its long eyelashes, eyebrows, lockable nostrils, caudal opening of the prepuce and a relatively small vulva help the camel avoid injuries, especially while feeding. They graze for 8–12 hours per day and ruminate for an equal amount of time.
Biology of the Dromedary Camel
Adaptations | Dromedary | Wikipedia | 256 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
The dromedary is specially adapted to its desert habitat; these adaptations are aimed at conserving water and regulating body temperature. The bushy eyebrows and the double row of eyelashes prevent sand and dust from entering the eyes during strong windstorms, and shield them from the sun's glare. The dromedary is able to close its nostrils voluntarily; this assists in water conservation. The dromedary can conserve water by reducing perspiration by fluctuating the body temperature throughout the day from . The kidneys are specialized to minimize water loss through excretion. Groups of camels avoid excess heat from the environment by pressing against each other. The dromedary can tolerate greater than 30% water loss, which is generally impossible for other mammals. In temperatures between , it needs water every 10 to 15 days. In the hottest temperatures, the dromedary takes water every four to seven days. This camel has a quick rate of rehydration and can drink at per minute. The dromedary has a rete mirabile, a complex of arteries and veins lying very close to each other which uses countercurrent blood flow to cool blood flowing to the brain. This effectively controls the temperature of the brain.
The hump stores up to of fat, which the camel can break down into energy to meet its needs when resources are scarce; the hump also helps dissipate body heat. When this tissue is metabolized, through fat metabolization, it releases energy while causing water to evaporate from the lungs during respiration (as oxygen is required for the metabolic process): overall, there is a net decrease in water. If the hump is small, the animal can show signs of starvation. In a 2005 study, the mean volume of adipose tissues (in the external part of the hump that have cells to store lipids) is related to the dromedary's unique mechanism of food and water storage. In case of starvation, they can even eat fish and bones, and drink brackish and salty water. The hair is longer on the throat, hump and shoulders. Though the padded hooves effectively support the camel's weight on the ground, they are not suitable for walking on slippery and muddy surfaces.
Reproduction | Dromedary | Wikipedia | 470 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Camels have a slow growth rate and reach sexual maturity slower than sheep or goat. The age of sexual maturity varies geographically and depends on the individual, as does the reproductive period. Both sexes might mature by three to five years of age, though successful breeding could take longer. Camels are described as atypical seasonal breeders; they exhibit spermatogenesis throughout the whole year with a reduction in spermatogenesis during the nonbreeding season compared to that in the
breeding season (Zayed et al., 1995). The breeding season in Egypt is during spring; the spring months. Mating occurs once a year, and peaks in the rainy season. The mating season lasts three to five months, but may last a year for older animals.
During the reproductive season, males splash their urine on their tails and nether regions. To attract females they extrude their soft palate – a trait unique to the dromedary. As the male gurgles, copious quantities of saliva turns to foam and covers the mouth. Males threaten each other for dominance over the female by trying to stand taller than the other, making low noises and a series of head movements including lowering, lifting and bending their necks backward. Males try to defeat other males by biting the opponent's legs and taking the head between his jaws. Copulation begins with foreplay; the male smells the female's genitalia and often bites her there or around her hump. The male forces the female to sit, then grasps her with his forelegs. Camelmen often aid the male insert his penis into the female's vulva. The male dromedary's ability to penetrate the female on his own is disputed, though feral populations in Australia reproduce naturally. Copulation takes from 7 to 35 minutes, averaging 11 to 15 minutes. Normally, three to four ejaculations occur. The semen of a Bikaneri dromedary is white and viscous, with a pH of around 7.8. | Dromedary | Wikipedia | 409 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
A single calf is born after a gestation period of 15 months. Calves move freely by the end of their first day. Nursing and maternal care continue for one to two years. In a study to find whether young could exist on milk substitutes, two male, month-old camels were separated from their mothers and were fed on milk substitutes prepared commercially for lambs, and they grew to normal weights for male calves after 30 days. Lactational yield can vary with species, breed, individual, region, diet, management conditions and lactating stage. The largest quantity of milk is produced during the early period of lactation. The lactation period can vary between nine and eighteen months.
Dromedaries are induced ovulators. Oestrus may be cued by the nutritional status of the camel and the length of day. If mating does not occur, the follicle, which grows during oestrus, usually regresses within a few days. In one study, 35 complete oestrous cycles were observed in five nonpregnant females over 15 months. The cycles were about 28 days long; follicles matured in six days, maintained their size for 13 days, and returned to their original size in eight days. In another study, ovulation could be best induced when the follicle reaches a size of . In another study, pregnancy in females could be recognized as early as 40 to 45 days of gestation by the swelling of the left uterine horn, where 99.5% of pregnancies were located.
Range
Its range included hot, arid regions of northern Africa, Ethiopia, the Near East, and western and central Asia. The dromedary typically thrives in areas with a long dry season and a short wet season. They are sensitive to cold and humidity, though some breeds can thrive in humid conditions. | Dromedary | Wikipedia | 377 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
The dromedary was first domesticated in the southern Arabian Peninsula around 4000–3000 BC. In the ninth or tenth century BC, the dromedary became popular in the Near East. The Persian invasion of Egypt under Cambyses in 525 BC introduced domesticated camels to the area. The Persian camels were not well-suited to trading or travel over the Sahara; journeys across the desert were made on chariots pulled by horses. The dromedary was introduced into Egypt from south-western Asia (Arabia and Persia). The popularity of dromedaries increased after the Islamic conquest of North Africa. While the invasion was accomplished largely on horseback, new links to the Middle East allowed camels to be imported en masse. These camels were well-suited to long desert journeys and could carry a great deal of cargo, allowing substantial trans-Saharan trade for the first time. In Libya, dromedaries were used for transport and their milk and meat constituted the local diet.
Dromedaries were also shipped from south-western Asia to Spain, Italy, Turkey, France, Canary Islands, the Americas and Australia. Dromedaries were introduced into Spain in 1020 AD and to Sicily in 1059 AD. Camels were exported to the Canary Islands in 1405 during the European colonisation of the area, and are still extant there, especially in Lanzarote and to the south of Fuerteventura. Attempts to introduce dromedaries into the Caribbean, Colombia, Peru, Bolivia and Brazil were made between the 17th and 19th centuries; some were imported to the western United States in the 1850s and some to Namibia in the early 1900s, but presently they exist in small numbers or are absent in these areas.
In 1840, about six camels were shipped from Tenerife to Adelaide, but only one survived the journey to arrive on 12 October that year. The animal, a male called Harry, was owned by the explorer John Ainsworth Horrocks. Harry was ill-tempered but was included in an expedition the following year because he could carry heavy loads. The next major group of camels were imported into Australia in 1860, and between 1860 and 1907 10 to 12 thousand were imported. These were used mainly for riding and transport.
Current distribution of captive animals
In the early 21st century, the domesticated dromedary is found in the semi-arid to arid regions of the Old World. | Dromedary | Wikipedia | 495 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Africa
Africa has more than 80% of the world's total dromedary population; it occurs in almost every desert zone in the northern part of the continent. The Sahel marks the southern extreme of its range, where the annual rainfall is around . The Horn of Africa has nearly 35% of the world's dromedaries; most of the region's stock is in Somalia, followed by Sudan, Eritrea, and Ethiopia (as of the early 2000s). According to the Yearbook of the Food and Agriculture Organization (FAO) for 1984, eastern Africa had about 10 million dromedaries, the largest population of Africa. Western Africa followed with 2.14 million, while northern Africa had nearly 0.76 million. Populations in Africa increased by 16% from 1994 to 2005.
Asia
In Asia, nearly 70% of the population occurs in India and Pakistan. The combined population of the dromedary and the Bactrian camel decreased by around 21% between 1994 and 2004. The dromedary is sympatric with the Bactrian camel in Afghanistan, Pakistan, and central and southwestern Asia. India has a dromedary population of less than one million, with most (0.67 million) in the state of Rajasthan. Populations in Pakistan decreased from 1.1 million in 1994 to 0.8 million in 2005 – a 29% decline. According to the FAO, the dromedary population in six countries of the Persian Gulf was nearly 0.67 million in 2003. In the Persian Gulf region the dromedary is locally classified into breeds including Al-Majahem, Al-Hamrah, Al-Safrah, Al-Zarkah and Al-Shakha, based on coat colour. The UAE has three prominent breeds: Racing camel, Al-Arabiat and Al-Kazmiat.
Feral population
Feral dromedary populations occur in Australia, where they were introduced in 1840. The total dromedary population in Australia was 500,000 in 2005. Nearly 99% of the populations are feral, and they have an annual growth rate of 10%. Most of the Australian feral camels are dromedaries, with only a few Bactrian camels. Most of the dromedaries occur in Western Australia, with smaller populations in the Northern Territory, Western Queensland and northern South Australia. | Dromedary | Wikipedia | 486 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Feral dromedary populations notwithstanding, the wild dromedary camel as opposed to the now domesticated species has been functionally extinct from the wild for the past 2,000 years.
Relationship with humans
The strength and docility of the dromedary make it popular as a domesticated animal. According to Richard Bulliet, they can be used for a wide variety of purposes: riding, transport, ploughing, and trading and as a source of milk, meat, wool and leather. The main attraction of the dromedary for nomadic desert-dwellers is the wide variety of resources they provide, which are crucial for their survival. It is important for several Bedouin pastoralist tribes of northern Arabia, such as the Ruwallah, the Rashaida, the Bani Sakhr and the Mutayr.
Camel urine and camel milk are used for medicinal purposes.
Riding camels
Although the role of the camel is diminishing with the advent of technology and modern means of transport, it is still an efficient mode of communication in remote and less-developed areas. The dromedary has been used in warfare since the 6th century BC. It is particularly prized for its capability to outrun horses in the deserts. Record of its use during the time of Alexander the Great indicate that the animal could cover up to 50 miles per day for a week and they could go for up to a month without water. An account by Aurelian also cited that, in his escape to Euphrates, Zenobia used a dromedary to outrun her pursuers after she was defeated at Palmyra.
The dromedary also remains popular for racing, particularly in the Arab world. Riding camels of Arabia, Egypt and the Sahara are locally known as the Dilool, the Hageen, and the Mehara respectively; several local breeds are included within these groups.
The ideal riding camel is strong, slender and long-legged with thin, supple skin. The special adaptations of the dromedary's feet allow it to walk with ease on sandy and rough terrain and on cold surfaces. The camels of the Bejas of Sudan and the Hedareb, Bilen, and the Tigre people of Eritrea and the Anafi camel bred in Sudan are common breeds used as riding camels. | Dromedary | Wikipedia | 477 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
According to Leese, the dromedary walks with four speeds or gaits: walk, jog, fast run and canter. The first is the typical speed of walking, around . Jog is the most common speed, nearly on level ground. He estimated a speed of during a fast run, by observing northern African and Arabian dromedaries. He gave no speed range to describe the canter, but implied it was a type of gallop that if induced could exhaust the camel and the rider. Canter could be used only for short periods of time, for example in races.
The ideal age to start training dromedaries for riding is three years, although they may be stubborn and unruly. At first the camel's head is controlled, and it is later trained to respond to sitting and standing commands, and to allow mounting. At this stage a camel will often try to escape when a trainer tries to mount it. The next stage involves training it to respond to reins. The animal must be given loads gradually and not forced to carry heavy loads before the age of six. Riding camels should not be struck on their necks, rather they should be struck behind the right leg of the rider. Leese described two types of saddles generally used in camel riding: the Arabian markloofa used by single riders and the Indian pakra used when two riders mount the same camel.
Baggage and draught camels
The baggage camel should be robust and heavy. Studies have recommended the camel should have either a small or a large head with a narrow aquiline nose, prominent eyes and large lips. The neck should be medium to long so the head is held high. The chest should be deep and the hump should be well-developed with sufficient space behind it to accommodate the saddle. The hindlegs should be heavy, muscular and sturdy. The dromedary can be trained to carry baggage from the age of five years, but must not be given heavy loads before the age of six. The hawia is a typical baggage saddle from Sudan. The methods of training the baggage camels are similar to those for riding camels. | Dromedary | Wikipedia | 439 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Draught camels are used for several purposes including ploughing, processing in oil mills and pulling carts. There is no clear description for the ideal draught camel, though its strength, its ability to survive without water and the flatness of its feet could be indicators. It may be used for ploughing in pairs or in groups with buffaloes or bullocks. The draught camel can plough at around , and should not be used for more than six hours a day – four hours in the morning and two in the afternoon. The camel is not easily exhausted unless diseased or undernourished, and has remarkable endurance and hardiness.
Dairy products
Camel milk is a staple food of nomadic tribes living in deserts. It consists of 11.7% solids, 3% protein, 3.6% fat, 0.8% ash, 4.4% lactose and 0.13% acidity (pH 6.5). The quantities of sodium, potassium, zinc, iron, copper, manganese, niacin and vitamin C were relatively higher than the amounts in cow milk. However, the levels of thiamin, riboflavin, folacin, vitamin B12, pantothenic acid, vitamin A, lysine, and tryptophan were lower than those in cow milk. The molar percentages of the fatty acids in milk fat were 26.7% for palmitic acid, 25.5% oleic acid, 11.4% myristic acid and 11% palmitoleic acid. Camel milk has higher thermal stability compared with cow milk, but it does not compare favourably with sheep milk.
Daily milk yield generally varies from and from 1.3% to 7.8% of the body weight. Milk yield varies geographically and depends upon the animals' diet and living conditions. At the peak of lactation, a healthy female would typically provide milk per day. Leese estimated a lactating female would yield besides the amount ingested by the calf. The Pakistani dromedary, which is considered a better milker and bigger, can yield when well-fed. Dromedaries in Somalia may be milked between two and four times a day, while those in Afar, Ethiopia, may be milked up to seven times a day. | Dromedary | Wikipedia | 471 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
The acidity of dromedary milk stored at increases at a slower rate than that of cow milk. Though the preparation of butter from dromedary milk is difficult, it is produced in small amounts by nomads, optimized at 22.5% fat in the cream. In 2001, the ability of dromedary milk to form curd was studied; coagulation did not show curd formation, and had a pH of 4.4. It was much different from curd produced from cow milk, and had a fragile, heterogeneous composition probably composed of casein flakes. Nevertheless, cheese and other dairy products can be made from camel milk. A study found bovine calf rennet could be used to coagulate dromedary milk. A special factory has been set up in Nouakchott to pasteurise and make cheese from camel milk. Mystical beliefs surround the use of camel milk in some places; for example, it may be used as an aphrodisiac in Ethiopia.
Meat | Dromedary | Wikipedia | 216 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
The meat of a five-year-old dromedary has a typical composition of 76% water, 22% protein, 1% fat, and 1% ash. The carcass, weighing for a five-year-old dromedary, is composed of nearly 57% muscle, 26% bone and 17% fat. A seven-to-eight-year-old camel can produce a carcass of . The meat is bright red to a dark brown or maroon, while the fat is white. It has the taste and texture of beef. A study of the meat of Iranian dromedaries showed its high glycogen content, which makes it taste sweet like horse meat. The carcasses of well-fed camels were found to be covered with a thin layer of good quality fat. In a study of the fatty acid composition of raw meat taken from the hind legs of seven one-to-three years old males, 51.5% of the fatty acids were saturated, 29.9% mono-unsaturated, and 18.6% polyunsaturated. The major fatty acids in the meat were palmitic acid (26.0%), oleic acid (18.9%) and linoleic acid (12.1%). In the hump, palmitic acid was dominant (34.4%), followed by oleic acid (28.2%), myristic acid (10.3%) and stearic acid (10%). | Dromedary | Wikipedia | 316 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Dromedary slaughter is more difficult than the slaughter of other domestic livestock such as cattle because of the size of the animal and the significant manual work involved. More males than females are slaughtered. Though less affected by mishandling than other livestock, the pre-slaughter handling of the dromedary plays a crucial role in determining the quality of meat obtained; mishandling can often disfigure the hump. The animal is stunned, seated in a crouching position with the head in a caudal position and slaughtered. The dressing percentage – the percentage of the mass of the animal that forms the carcass – is 55–70%, more than the 45–50% of cattle. Camel meat is often eaten by African camel herders, who use it only during severe food scarcity or for rituals. Camel meat is processed into food items such as burgers, patties, sausages and shawarma. Dromedaries can be slaughtered between four and ten years of age. As the animal ages, the meat grows tougher and deteriorates in taste and quality. In Somalian and Djiboutian culture, the dromedary is a staple food and can be found in many recipes and dishes.
A 2005 report issued jointly by the Ministry of Health (Saudi Arabia) and the United States Centers for Disease Control and Prevention details five cases of bubonic plague in humans resulting from the ingestion of raw camel liver. Four of the five patients had severe pharyngitis and submandibular lymphadenitis. Yersinia pestis was isolated from the camel's bone marrow, from the jird (Meriones libycus) and from fleas (Xenopsylla cheopis) captured at the camel's corral. | Dromedary | Wikipedia | 369 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
Camel hair, wool and hides
Camels in hot climates generally do not develop long coats. Camel hair is light, and has low thermal conductivity and durability, and is thus suitable for manufacturing warm clothes, blankets, tents, and rugs. Hair of highest quality is typically obtained from juvenile or feral camels. In India, camels are clipped usually in spring and around hair is produced per clipping. In colder regions one clipping can yield as much as . A dromedary can produce wool per year, whereas a Bactrian camel has an annual yield of nearly . Dromedaries under the age of two years have a fine undercoat that tends to fall off and should be cropped by hand. Little information about camel hides has been collected but they are usually of inferior quality and are less preferred for manufacturing leather. | Dromedary | Wikipedia | 171 | 326340 | https://en.wikipedia.org/wiki/Dromedary | Biology and health sciences | Artiodactyla | null |
A space rendezvous () is a set of orbital maneuvers during which two spacecraft, one of which is often a space station, arrive at the same orbit and approach to a very close distance (e.g. within visual contact). Rendezvous requires a precise match of the orbital velocities and position vectors of the two spacecraft, allowing them to remain at a constant distance through orbital station-keeping. Rendezvous may or may not be followed by docking or berthing, procedures which bring the spacecraft into physical contact and create a link between them.
The same rendezvous technique can be used for spacecraft "landing" on natural objects with a weak gravitational field, e.g. landing on one of the Martian moons would require the same matching of orbital velocities, followed by a "descent" that shares some similarities with docking.
History
In its first human spaceflight program Vostok, the Soviet Union launched pairs of spacecraft from the same launch pad, one or two days apart (Vostok 3 and 4 in 1962, and Vostok 5 and 6 in 1963). In each case, the launch vehicles' guidance systems inserted the two craft into nearly identical orbits; however, this was not nearly precise enough to achieve rendezvous, as the Vostok lacked maneuvering thrusters to adjust its orbit to match that of its twin. The initial separation distances were in the range of , and slowly diverged to thousands of kilometers (over a thousand miles) over the course of the missions.
In early 1964 the Soviet Union were able to guide two unmanned satellites designated Polyot 1 and Polyot 2 within 5km, and the crafts were able to establish radio communication.
In 1963 Buzz Aldrin submitted his doctoral thesis titled, Line-Of-Sight Guidance Techniques For Manned Orbital Rendezvous. As a NASA astronaut, Aldrin worked to "translate complex orbital mechanics into relatively simple flight plans for my colleagues."
First attempt failed | Space rendezvous | Wikipedia | 387 | 984081 | https://en.wikipedia.org/wiki/Space%20rendezvous | Physical sciences | Orbital mechanics | Astronomy |
NASA's first attempt at rendezvous was made on June 3, 1965, when US astronaut Jim McDivitt tried to maneuver his Gemini 4 craft to meet its spent Titan II launch vehicle's upper stage. McDivitt was unable to get close enough to achieve station-keeping, due to depth-perception problems, and stage propellant venting which kept moving it around.
However, the Gemini 4 attempts at rendezvous were unsuccessful largely because NASA engineers had yet to learn the orbital mechanics involved in the process. Simply pointing the active vehicle's nose at the target and thrusting was unsuccessful. If the target is ahead in the orbit and the tracking vehicle increases speed, its altitude also increases, actually moving it away from the target. The higher altitude then increases orbital period due to Kepler's third law, putting the tracker not only above, but also behind the target. The proper technique requires changing the tracking vehicle's orbit to allow the rendezvous target to either catch up or be caught up with, and then at the correct moment changing to the same orbit as the target with no relative motion between the vehicles (for example, putting the tracker into a lower orbit, which has a shorter orbital period allowing it to catch up, then executing a Hohmann transfer back to the original orbital height).
First successful rendezvous
Rendezvous was first successfully accomplished by US astronaut Wally Schirra on December 15, 1965. Schirra maneuvered the Gemini 6 spacecraft within of its sister craft Gemini 7. The spacecraft were not equipped to dock with each other, but maintained station-keeping for more than 20 minutes. Schirra later commented:
Schirra used another metaphor to describe the difference between the two nations' achievements:
First docking
The first docking of two spacecraft was achieved on March 16, 1966 when Gemini 8, under the command of Neil Armstrong, rendezvoused and docked with an uncrewed Agena Target Vehicle. Gemini 6 was to have been the first docking mission, but had to be cancelled when that mission's Agena vehicle was destroyed during launch.
The Soviets carried out the first automated, uncrewed docking between Cosmos 186 and Cosmos 188 on October 30, 1967.
The first Soviet cosmonaut to attempt a manual docking was Georgy Beregovoy who unsuccessfully tried to dock his Soyuz 3 craft with the uncrewed Soyuz 2 in October 1968. Automated systems brought the craft to within , while Beregovoy brought this closer with manual control. | Space rendezvous | Wikipedia | 496 | 984081 | https://en.wikipedia.org/wiki/Space%20rendezvous | Physical sciences | Orbital mechanics | Astronomy |
The first successful crewed docking occurred on January 16, 1969 when Soyuz 4 and Soyuz 5 docked, collecting the two crew members of Soyuz 5, which had to perform an extravehicular activity to reach Soyuz 4.
In March 1969 Apollo 9 achieved the first internal transfer of crew members between two docked spacecraft.
The first rendezvous of two spacecraft from different countries took place in 1975, when an Apollo spacecraft docked with a Soyuz spacecraft as part of the Apollo–Soyuz mission.
The first multiple space docking took place when both Soyuz 26 and Soyuz 27 were docked to the Salyut 6 space station during January 1978.
Uses
[[File:Mir collision damage STS086-720-091.JPG|right|thumb|Damaged solar arrays on Mir'''s Spektr module following a collision with an uncrewed Progress spacecraft in September 1997 as part of Shuttle-Mir. The Progress spacecraft were used for re-supplying the station. In this space rendezvous gone wrong, the Progress collided with Mir, beginning a depressurization that was halted by closing the hatch to Spektr.|alt=A gold-coloured solar array, bent and twisted out of shape and with several holes. The edge of a module can be seen to the right of the image, and Earth is visible in the background.]]
A rendezvous takes place each time a spacecraft brings crew members or supplies to an orbiting space station. The first spacecraft to do this was Soyuz 11, which successfully docked with the Salyut 1 station on June 7, 1971. Human spaceflight missions have successfully made rendezvous with six Salyut stations, with Skylab, with Mir and with the International Space Station (ISS). Currently Soyuz spacecraft are used at approximately six month intervals to transport crew members to and from ISS. With the introduction of NASA's Commercial Crew Program, the US is able to use their own launch vehicle along with the Soyuz, an updated version of SpaceX's Cargo Dragon; Crew Dragon. | Space rendezvous | Wikipedia | 403 | 984081 | https://en.wikipedia.org/wiki/Space%20rendezvous | Physical sciences | Orbital mechanics | Astronomy |
Robotic spacecraft are also used to rendezvous with and resupply space stations. Soyuz and Progress spacecraft have automatically docked with both Mir and the ISS using the Kurs docking system, Europe's Automated Transfer Vehicle also used this system to dock with the Russian segment of the ISS. Several uncrewed spacecraft use NASA's berthing mechanism rather than a docking port. The Japanese H-II Transfer Vehicle (HTV), SpaceX Dragon, and Orbital Sciences' Cygnus spacecraft all maneuver to a close rendezvous and maintain station-keeping, allowing the ISS Canadarm2 to grapple and move the spacecraft to a berthing port on the US segment. However the updated version of Cargo Dragon will no longer need to berth but instead will autonomously dock directly to the space station. The Russian segment only uses docking ports so it is not possible for HTV, Dragon and Cygnus to find a berth there.
Space rendezvous has been used for a variety of other purposes, including recent service missions to the Hubble Space Telescope. Historically, for the missions of Project Apollo that landed astronauts on the Moon, the ascent stage of the Apollo Lunar Module would rendezvous and dock with the Apollo Command/Service Module in lunar orbit rendezvous maneuvers. Also, the STS-49 crew rendezvoused with and attached a rocket motor to the Intelsat VI F-3 communications satellite to allow it to make an orbital maneuver.
Possible future rendezvous may be made by a yet to be developed automated Hubble Robotic Vehicle (HRV), and by the CX-OLEV, which is being developed for rendezvous with a geosynchronous satellite that has run out of fuel. The CX-OLEV would take over orbital stationkeeping and/or finally bring the satellite to a graveyard orbit, after which the CX-OLEV can possibly be reused for another satellite. Gradual transfer from the geostationary transfer orbit to the geosynchronous orbit will take a number of months, using Hall effect thrusters. | Space rendezvous | Wikipedia | 403 | 984081 | https://en.wikipedia.org/wiki/Space%20rendezvous | Physical sciences | Orbital mechanics | Astronomy |
Alternatively the two spacecraft are already together, and just undock and dock in a different way:
Soyuz spacecraft from one docking point to another on the ISS or Salyut
In the Apollo spacecraft, a maneuver known as transposition, docking, and extraction was performed an hour or so after Trans Lunar Injection of the sequence third stage of the Saturn V rocket / LM inside LM adapter / CSM (in order from bottom to top at launch, also the order from back to front with respect to the current motion), with CSM crewed, LM at this stage uncrewed:
the CSM separated, while the four upper panels of the LM adapter were disposed of
the CSM turned 180 degrees (from engine backward, toward LM, to forward)
the CSM connected to the LM while that was still connected to the third stage
the CSM/LM combination then separated from the third stage
NASA sometimes refers to "Rendezvous, Proximity-Operations, Docking, and Undocking" (RPODU) for the set of all spaceflight procedures that are typically needed around spacecraft operations where two spacecraft work in proximity to one another with intent to connect to one another.
Phases and methods
The standard technique for rendezvous and docking is to dock an active vehicle, the "chaser", with a passive "target". This technique has been used successfully for the Gemini, Apollo, Apollo/Soyuz, Salyut, Skylab, Mir, ISS, and Tiangong programs.
To properly understand spacecraft rendezvous it is essential to understand the relation between spacecraft velocity and orbit. A spacecraft in a certain orbit cannot arbitrarily alter its velocity. Each orbit correlates to a certain orbital velocity. If the spacecraft fires thrusters and increases (or decreases) its velocity it will obtain a different orbit, one with a higher or lower altitude. In circular orbits, higher orbits have a lower orbital velocity. Lower orbits have a higher orbital velocity.
For orbital rendezvous to occur, both spacecraft must be in the same orbital plane, and the phase of the orbit (the position of the spacecraft in the orbit) must be matched. For docking, the speed of the two vehicles must also be matched. The "chaser" is placed in a slightly lower orbit than the target. The lower the orbit, the higher the orbital velocity. The difference in orbital velocities of chaser and target is therefore such that the chaser is faster than the target, and catches up with it. | Space rendezvous | Wikipedia | 506 | 984081 | https://en.wikipedia.org/wiki/Space%20rendezvous | Physical sciences | Orbital mechanics | Astronomy |
Once the two spacecraft are sufficiently close, the chaser's orbit is synchronized with the target's orbit. That is, the chaser will be accelerated. This increase in velocity carries the chaser to a higher orbit. The increase in velocity is chosen such that the chaser approximately assumes the orbit of the target. Stepwise, the chaser closes in on the target, until proximity operations (see below) can be started.
In the very final phase, the closure rate is reduced by use of the active vehicle's reaction control system.
Docking typically occurs at a rate of to .
Rendezvous phases
Space rendezvous of an active, or "chaser", spacecraft with an (assumed) passive spacecraft may be divided into several phases, and typically starts with the two spacecraft in separate orbits, typically separated by more than :
A variety of techniques may be used to effect the translational and rotational maneuvers necessary for proximity operations and docking.
Methods of approach
The two most common methods of approach for proximity operations are in-line with the flight path of the spacecraft (called V-bar, as it is along the velocity vector of the target) and perpendicular to the flight path along the line of the radius of the orbit (called R-bar, as it is along the radial vector, with respect to Earth, of the target).
The chosen method of approach depends on safety, spacecraft / thruster design, mission timeline, and, especially for docking with the ISS, on the location of the assigned docking port.
V-bar approach
The V-bar approach is an approach of the "chaser" horizontally along the passive spacecraft's velocity vector. That is, from behind or from ahead, and in the same direction as the orbital motion of the passive target. The motion is parallel to the target's orbital velocity.
In the V-bar approach from behind, the chaser fires small thrusters to increase its velocity in the direction of the target. This, of course, also drives the chaser to a higher orbit. To keep the chaser on the V-vector, other thrusters are fired in the radial direction. If this is omitted (for example due to a thruster failure), the chaser will be carried to a higher orbit, which is associated with an orbital velocity lower than the target's. Consequently, the target moves faster than the chaser and the distance between them increases. This is called a natural braking effect, and is a natural safeguard in case of a thruster failure. | Space rendezvous | Wikipedia | 508 | 984081 | https://en.wikipedia.org/wiki/Space%20rendezvous | Physical sciences | Orbital mechanics | Astronomy |
STS-104 was the third Space Shuttle mission to conduct a V-bar arrival at the International Space Station. The V-bar, or velocity vector, extends along a line directly ahead of the station. Shuttles approach the ISS along the V-bar when docking at the PMA-2 docking port.
R-bar approach
The R-bar approach consists of the chaser moving below or above the target spacecraft, along its radial vector. The motion is orthogonal to the orbital velocity of the passive spacecraft.
When below the target the chaser fires radial thrusters to close in on the target. By this it increases its altitude. However, the orbital velocity of the chaser remains unchanged (thruster firings in the radial direction have no effect on the orbital velocity). Now in a slightly higher position, but with an orbital velocity that does not correspond to the local circular velocity, the chaser slightly falls behind the target. Small rocket pulses in the orbital velocity direction are necessary to keep the chaser along the radial vector of the target. If these rocket pulses are not executed (for example due to a thruster failure), the chaser will move away from the target. This is a natural braking effect''. For the R-bar approach, this effect is stronger than for the V-bar approach, making the R-bar approach the safer one of the two.
Generally, the R-bar approach from below is preferable, as the chaser is in a lower (faster) orbit than the target, and thus "catches up" with it. For the R-bar approach from above, the chaser is in a higher (slower) orbit than the target, and thus has to wait for the target to approach it.
Astrotech proposed meeting ISS cargo needs with a vehicle which would approach the station, "using a traditional nadir R-bar approach." The nadir R-bar approach is also used for flights to the ISS of H-II Transfer Vehicles, and of SpaceX Dragon vehicles.
Z-bar approach
An approach of the active, or "chaser", spacecraft horizontally from the side and orthogonal to the orbital plane of the passive spacecraft—that is, from the side and out-of-plane of the orbit of the passive spacecraft—is called a Z-bar approach.
Surface rendezvous
Apollo 12, the second crewed lunar landing, performed the first ever rendezvous outside of Low Earth Orbit by landing close to Surveyor 3 and taking parts of it back to Earth. | Space rendezvous | Wikipedia | 507 | 984081 | https://en.wikipedia.org/wiki/Space%20rendezvous | Physical sciences | Orbital mechanics | Astronomy |
A cenote ( or ; ) is a natural pit, or sinkhole, resulting when a collapse of limestone bedrock exposes groundwater. The term originated on the Yucatán Peninsula of Mexico, where the ancient Maya commonly used cenotes for water supplies, and occasionally for sacrificial offerings. The name derives from a word used by the lowland Yucatec Maya——to refer to any location with accessible groundwater.
In Mexico the Yucatán Peninsula alone has an estimated 10,000 cenotes, water-filled sinkholes naturally formed by the collapse of limestone, and located across the peninsula. Some of these cenotes are at risk from the construction of the new tourist Maya Train.
Cenotes are common geological forms in low-altitude regions, particularly on islands (such as Cefalonia, Greece), coastlines, and platforms with young post-Paleozoic limestone with little soil development. The term cenote, originally applying only to the features in Yucatán, has since been applied by researchers to similar karst features in other places such as in Cuba, Australia, Europe, and the United States.
Definition and description
Cenotes are surface connections to subterranean water bodies. While the best-known cenotes are large open-water pools measuring tens of meters in diameter, such as those at Chichen Itza in Mexico, the greatest number of cenotes are smaller sheltered sites and do not necessarily have any surface exposed water. Some cenotes are only found through small <1 m (3 ft) diameter holes created by tree roots, with human access through enlarged holes, such as the cenotes Choo-Ha, Tankach-Ha, and Multum-Ha near Tulum. There are at least 6,000 cenotes in the Yucatán Peninsula of Mexico. Cenote water is often very clear, as the water comes from rain water filtering slowly through the ground, and therefore contains very little suspended particulate matter. The groundwater flow rate within a cenote may be very slow. In many cases, cenotes are areas where sections of the cave roof have collapsed revealing an underlying cave system, and the water flow rates may be much faster: up to per day.
The Yucatan cenotes attract cavern and cave divers who have documented extensive flooded cave systems, some of which have been explored for lengths of or more.
Geology and hydrology | Cenote | Wikipedia | 469 | 985483 | https://en.wikipedia.org/wiki/Cenote | Physical sciences | Caves | Earth science |
Cenotes are formed by the dissolution of rock and the resulting subsurface void, which may or may not be linked to an active cave system, and the subsequent structural collapse. Rock that falls into the water below is slowly removed by further dissolution, creating space for more collapse blocks. Likely, the rate of collapse increases during periods when the water table is below the ceiling of the void since the rock ceiling is no longer buoyantly supported by the water in the void.
Cenotes may be fully collapsed, creating an open water pool, or partially collapsed with some portion of a rock overhanging above the water. The stereotypical cenotes often resemble small circular ponds, measuring some tens of meters in diameter with sheer rock walls. Most cenotes, however, require some degree of stooping or crawling to access the water.
Penetration and extent
In the north and northwest of the Yucatán Peninsula in Mexico, the cenotes generally overlie vertical voids penetrating below the modern water table. However, very few of these cenotes appear to be connected with horizontally extensive underground river systems, with water flow through them being more likely dominated by aquifer matrix and fracture flows.
In contrast, the cenotes along the Caribbean coast of the Yucatán Peninsula (within the state of Quintana Roo) often provide access to extensive underwater cave systems, such as Sistema Ox Bel Ha, Sistema Sac Actun/Sistema Nohoch Nah Chich and Sistema Dos Ojos.
Freshwater/seawater interface
The Yucatán Peninsula contains a vast coastal aquifer system, which is typically density-stratified. The infiltrating meteoric water (i.e., rainwater) floats on top of higher-density saline water intruding from the coastal margins. The whole aquifer is therefore an anchialine system (one that is land-locked but connected to an ocean). Where a cenote, or the flooded cave to which it is an opening, provides deep enough access into the aquifer, the interface between the fresh and saline water may be reached. The density interface between the fresh and saline waters is a halocline, which means a sharp change in salt concentration over a small change in depth. Mixing of the fresh and saline water results in a blurry swirling effect caused by refraction between the different densities of fresh and saline waters. | Cenote | Wikipedia | 484 | 985483 | https://en.wikipedia.org/wiki/Cenote | Physical sciences | Caves | Earth science |
The depth of the halocline is a function of several factors: climate and specifically how much meteoric water recharges the aquifer, hydraulic conductivity of the host rock, distribution and connectivity of existing cave systems, and how effective these are at draining water to the coast, and the distance from the coast. In general, the halocline is deeper further from the coast, and in the Yucatán Peninsula this depth is below the water table at the coast, and below the water table in the middle of the peninsula, with saline water underlying the whole of the peninsula.
Types
In 1936, a simple morphometry-based classification system for cenotes was presented.
Cenotes-cántaro (Jug or pit cenotes) are those with a surface connection narrower than the diameter of the water body;
Cenotes-cilíndricos (Cylinder cenotes) are those with strictly vertical walls;
Cenotes-aguadas (Basin cenotes) are those with shallow water basins; and
Grutas (Cave cenotes) are those having a horizontal entrance with dry sections.
The classification scheme was based on morphometric observations above the water table, and therefore incompletely reflects the processes by which the cenotes formed and the inherent hydrogeochemical relationship with the underlying flooded cave networks, which were only discovered in the 1980s and later with the initiation of cave diving exploration.
Flora and fauna
Flora and fauna are generally scarcer than in the open ocean; however, marine animals do thrive in caves. In caverns, one can spot mojarras, mollies, guppies, catfish, small eels and frogs. In the most secluded and darker cenotes, the fauna has evolved to resemble those of many cave-dwelling species. For example, many animals don't have pigmentation and are often blind, so they are equipped with long feelers to find food and make their way around in the dark.
Chicxulub crater | Cenote | Wikipedia | 397 | 985483 | https://en.wikipedia.org/wiki/Cenote | Physical sciences | Caves | Earth science |
Although cenotes are found widely throughout much of the Yucatán Peninsula, a higher-density circular alignment of cenotes overlies the measured rim of the Chicxulub crater. This crater structure, identified from the alignment of cenotes, but also subsequently mapped using geophysical methods (including gravity mapping) and also drilled into with core recovery, has been dated to the boundary between the Cretaceous and Paleogene geologic periods, 66 million years ago. This meteorite impact at the Cretaceous–Paleogene boundary is therefore associated with the mass extinction of the non-avian dinosaurs and is also known as the Cretaceous–Paleogene extinction event.
Archaeology and anthropology
In 2001–2002 expeditions led by Arturo H. González and Carmen Rojas Sandoval in the Yucatán discovered three human skeletons; one of them, Eve of Naharon, was carbon-dated to be 13,600 years old. In March 2008, three members of the Proyecto Espeleológico de Tulum and Global Underwater Explorers dive team, Alex Alvarez, Franco Attolini, and Alberto Nava, explored a section of Sistema Aktun Hu (part of Sistema Sac Actun) known as the pit Hoyo Negro. At a depth of the divers located the remains of a mastodon and a human skull (at ) that might be the oldest evidence of human habitation in the region.
The Yucatán Peninsula has almost no rivers and only a few lakes, and those are often marshy. The widely distributed cenotes are the only perennial source of potable water and have long been the principal source of water in much of the region. Major Maya settlements required access to adequate water supplies, and therefore cities, including the famous Chichen Itza, were built around these natural wells. Many cenotes like the Sacred Cenote in Chichen Itza played an important role in Maya rites. The Maya believed that cenotes were portals to Xibalba or the afterlife, and home to the rain god, Chaac. The Maya often deposited human remains as well as ceremonial artifacts in these cenotes. | Cenote | Wikipedia | 425 | 985483 | https://en.wikipedia.org/wiki/Cenote | Physical sciences | Caves | Earth science |
The discovery of golden sacrificial artifacts in some cenotes led to the archaeological exploration of most cenotes in the first part of the 20th century. Edward Herbert Thompson (1857–1935), an American diplomat who had bought the Chichen Itza site, began dredging the Sacred Cenote there in 1904. He discovered human skeletons and sacrificial objects confirming a local legend, the Cult of the Cenote, involving human sacrifice to the rain god Chaac by the ritual casting of victims and objects into the cenote. However, not all cenotes were sites of human sacrifice. The cenote at Punta Laguna has been extensively studied and none of the approximately 120 individuals show signs of sacrifice.
The remains of this cultural heritage are protected by the UNESCO Convention on the Protection of the Underwater Cultural Heritage.
Scuba diving
Cenotes have attracted cavern and cave divers, and there are organized efforts to explore and map these underwater systems. They are public or private and sometimes considered "National Natural Parks". Great care should be taken to avoid spoiling this fragile ecosystem when diving. In Mexico, the Quintana Roo Speleological Survey maintains a list of the longest and deepest water-filled and dry caves within the state boundaries. When cavern diving, one must be able to see natural light the entire time that one is exploring the cavern (e.g., Kukulkan cenote near Tulum, Mexico). During a cave dive, one passes the point where daylight can penetrate, and one follows a safety guideline to exit the cave. Things change quite dramatically once moving from a cavern dive into a cave dive.
Contrary to cenote cavern diving, cenote cave diving requires special equipment and training (certification for cave diving). However, both cavern and cave diving require detailed briefings, diving experience, and weight adjustment to freshwater buoyancy. The cenotes are usually filled with rather cool fresh water. Cenote divers must be wary of possible halocline; this produces blurred vision until they reach a more homogeneous area.
Notable cenotes
Australia
Ewens Ponds, near Mount Gambier, South Australia
Kilsby sinkhole, near Mount Gambier, South Australia
Little Blue Lake, near Mount Schank, South Australia
Bahamas
Thunderball Grotto, on Staniel Cay
Belize
Great Blue Hole | Cenote | Wikipedia | 470 | 985483 | https://en.wikipedia.org/wiki/Cenote | Physical sciences | Caves | Earth science |
Canada
Devil's Bath is the largest cenote in Canada at a size of 1178 ft (359m) in diameter and 144 ft (44m) in depth. It is located near the village of Port Alice, British Columbia on the northwest coastline of Vancouver Island. Devil's Bath is continuously fed by an underground spring and is connected by underwater tunnel to the Benson River Cave.
Dominican Republic
Hoyo Azul (Punta Cana)
Los Tres Ojos
Ojos Indigenas (Punta Cana)
Greece
Melissani Cave, Kefalonia
Jamaica
Blue Hole (Ocho Rios)
Mexico
Yucatán Peninsula
Dos Ojos, Municipality of Tulum
Dzibilchaltun, Yucatán
Ik Kil, Yucatan
Gran Cenote, Municipality of Tulum
Hubiku, Yucatan
Sacred Cenote, Chichen Itza
Xtacunbilxunan, Bolonchén
Cenote Azul, Playa del Carmen
Jardin Del Eden, Bacalar
Choo-Ha, Coba
Zaci, Valladolid
El Zapote, the site of the Hells Bells bell-like rock formation
United States
Blue Hole, Santa Rosa, New Mexico
Blue Hole, Castalia, Ohio
Bottomless Lakes, near Roswell, New Mexico
Montezuma Well, Verde Valley, Arizona
Hamilton Pool, Austin, Texas
Zimbabwe
Chinhoyi Caves in Zimbabwe | Cenote | Wikipedia | 275 | 985483 | https://en.wikipedia.org/wiki/Cenote | Physical sciences | Caves | Earth science |
The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components:
a cosmological constant, denoted by lambda (Λ), associated with dark energy;
the postulated cold dark matter, denoted by CDM;
ordinary matter.
It is the current standard model of Big Bang cosmology, as it is the simplest model that provides a reasonably good account of:
the existence and structure of the cosmic microwave background;
the large-scale structure in the distribution of galaxies;
the observed abundances of hydrogen (including deuterium), helium, and lithium;
the accelerating expansion of the universe observed in the light from distant galaxies and supernovae.
The model assumes that general relativity is the correct theory of gravity on cosmological scales. It emerged in the late 1990s as a concordance cosmology, after a period of time when disparate observed properties of the universe appeared mutually inconsistent, and there was no consensus on the makeup of the energy density of the universe.
The ΛCDM model has been successful in modeling broad collection of astronomical observations over decades. Remaining issues have lead to many alternative models and challenges the assumptions of the ΛCDM model.
Overview
The ΛCDM model is based on three postulates on the structure of spacetime:
The cosmological principle, that the universe is the same everywhere and in all directions, and that it is expanding,
A postulate by Hermann Weyl that the lines of spacetime (geodesics) intersect at only one point, where time along each line can be synchronized; the behavior resembles an expanding fluid,
general relativity that relates the geometry of spacetime to the distribution of matter and energy.
This combination greatly simplifies the equations of general relativity in to a form called the Friedmann equations. These equations specify the evolution of the scale factor the universe in terms of the pressure and density of a perfect fluid. The evolving density is composed of different kinds of energy and matter, each with its own role in affecting the scale factor. For example, a model might include baryons, photons, neutrinos, and dark matter. These component densities become parameters extracted when the model constrained to match astrophysical observations. | Lambda-CDM model | Wikipedia | 458 | 985963 | https://en.wikipedia.org/wiki/Lambda-CDM%20model | Physical sciences | Physical cosmology | Astronomy |
The most accurate observations which are sensitive to the component densities are consequences of statistical inhomogeneity called "perturbations" in the early universe. Since the Friedmann equations assume homogeneity, additional theory must be added before comparison to experiments. Inflation is a simple model producing perturbations by postulating an extremely rapid expansion early in the universe that separates quantum fluctuations before they can equilibrate. The perturbations are characterized by additional parameters also determined by matching observations.
Finally, the light which will become astronomical observations must pass through the universe. The latter part of that journey will pass through ionized space, where the electrons can scatter the light, altering the anisotropies. This effect is characterized by one additional parameter.
The ΛCDM model includes an expansion of metric space that is well documented, both as the redshift of prominent spectral absorption or emission lines in the light from distant galaxies, and as the time dilation in the light decay of supernova luminosity curves. Both effects are attributed to a Doppler shift in electromagnetic radiation as it travels across expanding space. Although this expansion increases the distance between objects that are not under shared gravitational influence, it does not increase the size of the objects (e.g. galaxies) in space. Also, since it originates from ordinary general relativity, it, like general relativity, allows for distant galaxies to recede from each other at speeds greater than the speed of light; local expansion is less than the speed of light, but expansion summed across great distances can collectively exceed the speed of light.
The letter Λ (lambda) represents the cosmological constant, which is associated with a vacuum energy or dark energy in empty space that is used to explain the contemporary accelerating expansion of space against the attractive effects of gravity. A cosmological constant has negative pressure, , which contributes to the stress–energy tensor that, according to the general theory of relativity, causes accelerating expansion. The fraction of the total energy density of our (flat or almost flat) universe that is dark energy, , is estimated to be 0.669 ± 0.038 based on the 2018 Dark Energy Survey results using Type Ia supernovae or based on the 2018 release of Planck satellite data, or more than 68.3% (2018 estimate) of the mass–energy density of the universe. | Lambda-CDM model | Wikipedia | 482 | 985963 | https://en.wikipedia.org/wiki/Lambda-CDM%20model | Physical sciences | Physical cosmology | Astronomy |
Dark matter is postulated in order to account for gravitational effects observed in very large-scale structures (the "non-keplerian" rotation curves of galaxies; the gravitational lensing of light by galaxy clusters; and the enhanced clustering of galaxies) that cannot be accounted for by the quantity of observed matter.
The ΛCDM model proposes specifically cold dark matter, hypothesized as:
Non-baryonic: Consists of matter other than protons and neutrons (and electrons, by convention, although electrons are not baryons)
Cold: Its velocity is far less than the speed of light at the epoch of radiation–matter equality (thus neutrinos are excluded, being non-baryonic but not cold)
Dissipationless: Cannot cool by radiating photons
Collisionless: Dark matter particles interact with each other and other particles only through gravity and possibly the weak force
Dark matter constitutes about 26.5% of the mass–energy density of the universe. The remaining 4.9% comprises all ordinary matter observed as atoms, chemical elements, gas and plasma, the stuff of which visible planets, stars and galaxies are made. The great majority of ordinary matter in the universe is unseen, since visible stars and gas inside galaxies and clusters account for less than 10% of the ordinary matter contribution to the mass–energy density of the universe.
The model includes a single originating event, the "Big Bang", which was not an explosion but the abrupt appearance of expanding spacetime containing radiation at temperatures of around 1015 K. This was immediately (within 10−29 seconds) followed by an exponential expansion of space by a scale multiplier of 1027 or more, known as cosmic inflation. The early universe remained hot (above 10 000 K) for several hundred thousand years, a state that is detectable as a residual cosmic microwave background, or CMB, a very low-energy radiation emanating from all parts of the sky. The "Big Bang" scenario, with cosmic inflation and standard particle physics, is the only cosmological model consistent with the observed continuing expansion of space, the observed distribution of lighter elements in the universe (hydrogen, helium, and lithium), and the spatial texture of minute irregularities (anisotropies) in the CMB radiation. Cosmic inflation also addresses the "horizon problem" in the CMB; indeed, it seems likely that the universe is larger than the observable particle horizon. | Lambda-CDM model | Wikipedia | 498 | 985963 | https://en.wikipedia.org/wiki/Lambda-CDM%20model | Physical sciences | Physical cosmology | Astronomy |
The model uses the Friedmann–Lemaître–Robertson–Walker metric, the Friedmann equations, and the cosmological equations of state to describe the observable universe from approximately 0.1 s to the present.
Cosmic expansion history
The expansion of the universe is parameterized by a dimensionless scale factor (with time counted from the birth of the universe), defined relative to the present time, so ; the usual convention in cosmology is that subscript 0 denotes present-day values, so denotes the age of the universe. The scale factor is related to the observed redshift of the light emitted at time by
The expansion rate is described by the time-dependent Hubble parameter, , defined as
where is the time-derivative of the scale factor. The first Friedmann equation gives the expansion rate in terms of the matter+radiation density the curvature and the cosmological constant
where, as usual is the speed of light and is the gravitational constant.
A critical density is the present-day density, which gives zero curvature , assuming the cosmological constant is zero, regardless of its actual value. Substituting these conditions to the Friedmann equation gives
where is the reduced Hubble constant.
If the cosmological constant were actually zero, the critical density would also mark the dividing line between eventual recollapse of the universe to a Big Crunch, or unlimited expansion. For the Lambda-CDM model with a positive cosmological constant (as observed), the universe is predicted to expand forever regardless of whether the total density is slightly above or below the critical density; though other outcomes are possible in extended models where the dark energy is not constant but actually time-dependent.
The present-day density parameter for various species is defined as the dimensionless ratio
where the subscript is one of for baryons, for cold dark matter, for radiation (photons plus relativistic neutrinos), and for dark energy. | Lambda-CDM model | Wikipedia | 398 | 985963 | https://en.wikipedia.org/wiki/Lambda-CDM%20model | Physical sciences | Physical cosmology | Astronomy |
Since the densities of various species scale as different powers of , e.g. for matter etc.,
the Friedmann equation can be conveniently rewritten in terms of the various density parameters as
where is the equation of state parameter of dark energy, and assuming negligible neutrino mass (significant neutrino mass requires a more complex equation). The various parameters add up to by construction. In the general case this is integrated by computer to give the expansion history and also observable distance–redshift relations for any chosen values of the cosmological parameters, which can then be compared with observations such as supernovae and baryon acoustic oscillations.
In the minimal 6-parameter Lambda-CDM model, it is assumed that curvature is zero and , so this simplifies to
Observations show that the radiation density is very small today, ; if this term is neglected
the above has an analytic solution
where
this is fairly accurate for or million years.
Solving for gives the present age of the universe in terms of the other parameters.
It follows that the transition from decelerating to accelerating expansion (the second derivative crossing zero) occurred when
which evaluates to or for the best-fit parameters estimated from the Planck spacecraft.
Parameters
Multiple variants of the ΛCDM model are used with some differences in parameters. One such set is outlined in the table below.
The Planck collaboration version of the ΛCDM model is based on six parameters: baryon density parameter; dark matter density parameter; scalar spectral index; two parameters related to curvature fluctuation amplitude; and the probability that photons from the early universe will be scattered once on route (called reionization optical depth). Six is the smallest number of parameters needed to give an acceptable fit to the observations; other possible parameters are fixed at "natural" values, e.g. total density parameter = 1.00, dark energy equation of state = −1.
The parameter values, and uncertainties, are estimated using computer searches to locate the region of parameter space providing an acceptable match to cosmological observations. From these six parameters, the other model values, such as the Hubble constant and the dark energy density, can be calculated. | Lambda-CDM model | Wikipedia | 451 | 985963 | https://en.wikipedia.org/wiki/Lambda-CDM%20model | Physical sciences | Physical cosmology | Astronomy |
Historical development
The discovery of the cosmic microwave background (CMB) in 1964 confirmed a key prediction of the Big Bang cosmology. From that point on, it was generally accepted that the universe started in a hot, dense state and has been expanding over time. The rate of expansion depends on the types of matter and energy present in the universe, and in particular, whether the total density is above or below the so-called critical density.
During the 1970s, most attention focused on pure-baryonic models, but there were serious challenges explaining the formation of galaxies, given the small anisotropies in the CMB (upper limits at that time). In the early 1980s, it was realized that this could be resolved if cold dark matter dominated over the baryons, and the theory of cosmic inflation motivated models with critical density.
During the 1980s, most research focused on cold dark matter with critical density in matter, around 95% CDM and 5% baryons: these showed success at forming galaxies and clusters of galaxies, but problems remained; notably, the model required a Hubble constant lower than preferred by observations, and observations around 1988–1990 showed more large-scale galaxy clustering than predicted.
These difficulties sharpened with the discovery of CMB anisotropy by the Cosmic Background Explorer in 1992, and several modified CDM models, including ΛCDM and mixed cold and hot dark matter, came under active consideration through the mid-1990s. The ΛCDM model then became the leading model following the observations of accelerating expansion in 1998, and was quickly supported by other observations: in 2000, the BOOMERanG microwave background experiment measured the total (matter–energy) density to be close to 100% of critical, whereas in 2001 the 2dFGRS galaxy redshift survey measured the matter density to be near 25%; the large difference between these values supports a positive Λ or dark energy. Much more precise spacecraft measurements of the microwave background from WMAP in 2003–2010 and Planck in 2013–2015 have continued to support the model and pin down the parameter values, most of which are constrained below 1 percent uncertainty. | Lambda-CDM model | Wikipedia | 434 | 985963 | https://en.wikipedia.org/wiki/Lambda-CDM%20model | Physical sciences | Physical cosmology | Astronomy |
Successes
Among all cosmological models, the ΛCDM model has been the most successful; it describes a wide range of astronomical observations with remarkable accuracy. The notable successes include:
Accurate modeling the high-precision CMB angular distribution measure by the Planck mission and Atacama Cosmology Telescope.
Accurate description of the linear E-mode polarization of the CMB radiation due to fluctuations on the surface of last scattering events.
Prediction of the observed B-mode polarization of the CMB light due to primordial gravitational waves.
Observations of H2O emission spectra from a galaxy 12.8 billion light years away consistent with molecules excited by cosmic background radiation much more energetic – 16-20K – than the CMB we observe now, 3K.
Predictions of the primordial abundance of deuterium as a result of Big bang nucleosynthesis. The observed abundance matches the one derived from the nucleosynthesis model with the value for baryon density derived from CMB measurements.
In addition to explaining many pre-2000 observations, the model has made a number of successful predictions: notably the existence of the baryon acoustic oscillation feature, discovered in 2005 in the predicted location; and the statistics of weak gravitational lensing, first observed in 2000 by several teams. The polarization of the CMB, discovered in 2002 by DASI, has been successfully predicted by the model: in the 2015 Planck data release, there are seven observed peaks in the temperature (TT) power spectrum, six peaks in the temperature–polarization (TE) cross spectrum, and five peaks in the polarization (EE) spectrum. The six free parameters can be well constrained by the TT spectrum alone, and then the TE and EE spectra can be predicted theoretically to few-percent precision with no further adjustments allowed.
Challenges
Despite the widespread success of ΛCDM in matching observations of our universe, cosmologists believe that the model may be an approximation of a more fundamental model.
Lack of detection
Extensive searches for dark matter particles have so far shown no well-agreed detection, while dark energy may be almost impossible to detect in a laboratory, and its value is extremely small compared to vacuum energy theoretical predictions.
Violations of the cosmological principle | Lambda-CDM model | Wikipedia | 453 | 985963 | https://en.wikipedia.org/wiki/Lambda-CDM%20model | Physical sciences | Physical cosmology | Astronomy |
The ΛCDM model, like all models built on the Friedmann–Lemaître–Robertson–Walker metric, assume that the universe looks the same in all directions (isotropy) and from every location (homogeneity) if you look at a large enough scale: "the universe looks the same whoever and wherever you are." This cosmological principle allows a metric, Friedmann–Lemaître–Robertson–Walker metric, to be derived and developed into a theory to compare to experiments. Without the principle, a metric would need to be extracted from astronomical data, which may not be possible. The assumptions were carried over into the ΛCDM model. However, some findings suggested violations of the cosmological principle.
Violations of isotropy
Evidence from galaxy clusters, quasars, and type Ia supernovae suggest that isotropy is violated on large scales.
Data from the Planck Mission shows hemispheric bias in the cosmic microwave background in two respects: one with respect to average temperature (i.e. temperature fluctuations), the second with respect to larger variations in the degree of perturbations (i.e. densities). The European Space Agency (the governing body of the Planck Mission) has concluded that these anisotropies in the CMB are, in fact, statistically significant and can no longer be ignored.
Already in 1967, Dennis Sciama predicted that the cosmic microwave background has a significant dipole anisotropy. In recent years, the CMB dipole has been tested, and the results suggest our motion with respect to distant radio galaxies and quasars differs from our motion with respect to the cosmic microwave background. The same conclusion has been reached in recent studies of the Hubble diagram of Type Ia supernovae and quasars. This contradicts the cosmological principle. | Lambda-CDM model | Wikipedia | 382 | 985963 | https://en.wikipedia.org/wiki/Lambda-CDM%20model | Physical sciences | Physical cosmology | Astronomy |
The CMB dipole is hinted at through a number of other observations. First, even within the cosmic microwave background, there are curious directional alignments and an anomalous parity asymmetry that may have an origin in the CMB dipole. Separately, the CMB dipole direction has emerged as a preferred direction in studies of alignments in quasar polarizations, scaling relations in galaxy clusters, strong lensing time delay, Type Ia supernovae, and quasars and gamma-ray bursts as standard candles. The fact that all these independent observables, based on different physics, are tracking the CMB dipole direction suggests that the Universe is anisotropic in the direction of the CMB dipole.
Nevertheless, some authors have stated that the universe around Earth is isotropic at high significance by studies of the cosmic microwave background temperature maps.
Violations of homogeneity
Based on N-body simulations in ΛCDM, Yadav and his colleagues showed that the spatial distribution of galaxies is statistically homogeneous if averaged over scales 260/h Mpc or more. However, many large-scale structures have been discovered, and some authors have reported some of the structures to be in conflict with the predicted scale of homogeneity for ΛCDM, including
The Clowes–Campusano LQG, discovered in 1991, which has a length of 580 Mpc
The Sloan Great Wall, discovered in 2003, which has a length of 423 Mpc
U1.11, a large quasar group discovered in 2011, which has a length of 780 Mpc
The Huge-LQG, discovered in 2012, which is three times longer than and twice as wide as is predicted possible according to ΛCDM
The Hercules–Corona Borealis Great Wall, discovered in November 2013, which has a length of 2000–3000 Mpc (more than seven times that of the SGW)
The Giant Arc, discovered in June 2021, which has a length of 1000 Mpc
The Big Ring, reported in 2024, which has a diameter of 399 Mpc and is shaped like a ring
Other authors claim that the existence of structures larger than the scale of homogeneity in the ΛCDM model does not necessarily violate the cosmological principle in the ΛCDM model.
El Gordo galaxy cluster collision | Lambda-CDM model | Wikipedia | 479 | 985963 | https://en.wikipedia.org/wiki/Lambda-CDM%20model | Physical sciences | Physical cosmology | Astronomy |
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