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The debate is complicated because sea otters have sometimes been held responsible for declines of shellfish stocks that were more likely caused by overfishing, disease, pollution, and seismic activity. Shellfish declines have also occurred in many parts of the North American Pacific coast that do not have sea otters, and conservationists sometimes note the existence of large concentrations of shellfish on the coast is a recent development resulting from the fur trade's near-extirpation of the sea otter. Although many factors affect shellfish stocks, sea otter predation can deplete a fishery to the point where it is no longer commercially viable. Scientists agree that sea otters and abalone fisheries cannot exist in the same area, and the same is likely true for certain other types of shellfish, as well.
Many facets of the interaction between sea otters and the human economy are not as immediately felt. Sea otters have been credited with contributing to the kelp harvesting industry via their well-known role in controlling sea urchin populations; kelp is used in the production of diverse food and pharmaceutical products. Although human divers harvest red sea urchins both for food and to protect the kelp, sea otters hunt more sea urchin species and are more consistently effective in controlling these populations. E. lutris is a controlling predator of the red king crab (Paralithodes camtschaticus) in the Bering Sea, which would otherwise be out of control as it is in its invasive range, the Barents Sea. (Berents otters, Lutra lutra, occupy the same ecological niche and so are believed to help to control them in the Berents but this has not been studied.) The health of the kelp forest ecosystem is significant in nurturing populations of fish, including commercially important fish species. In some areas, sea otters are popular tourist attractions, bringing visitors to local hotels, restaurants, and sea otter-watching expeditions.
Roles in human cultures | Sea otter | Wikipedia | 403 | 567471 | https://en.wikipedia.org/wiki/Sea%20otter | Biology and health sciences | Carnivora | null |
For many maritime indigenous cultures throughout the North Pacific, especially the Ainu in the Kuril Islands, the Koryaks and Itelmen of Kamchatka, the Aleut in the Aleutian Islands, the Haida of Haida Gwaii and a host of tribes on the Pacific coast of North America, the sea otter has played an important role as a cultural, as well as material, resource. These cultures, many of which have strongly animist traditions full of legends and stories in which many aspects of the natural world are associated with spirits, regarded the sea otter as particularly kin to humans. The Nuu-chah-nulth, Haida, and other First Nations of coastal British Columbia used the warm and luxurious pelts as chiefs' regalia. Sea-otter pelts were given in potlatches to mark coming-of-age ceremonies, weddings, and funerals. The Aleuts carved sea otter bones for use as ornaments and in games, and used powdered sea-otter baculum as a medicine for fever.
Some Ainu folk-tales portray the sea-otter as an occasional messenger between humans and the creator. The sea otter is a recurring figure in Ainu folklore. A major Ainu epic, the Kutune Shirka, tells the tale of wars and struggles over a golden sea-otter. Versions of a widespread Aleut legend tell of lovers or despairing women who plunge into the sea and become otters. These stories have been associated with the many human-like behavioral features of the sea otter, including apparent playfulness, strong mother-pup bonds and tool use, yielding to ready anthropomorphism. The beginning of commercial exploitation had a great impact on the human, as well as animal, populations. The Ainu and Aleuts have been displaced or their numbers are dwindling, while the coastal tribes of North America, where the otter is in any case greatly depleted, no longer rely as intimately on sea mammals for survival.
Since the mid-1970s, the beauty and charisma of the species have gained wide appreciation, and the sea otter has become an icon of environmental conservation. The round, expressive face and soft, furry body of the sea otter are depicted in a wide variety of souvenirs, postcards, clothing, and stuffed toys. | Sea otter | Wikipedia | 474 | 567471 | https://en.wikipedia.org/wiki/Sea%20otter | Biology and health sciences | Carnivora | null |
Aquariums and zoos
Sea otters can do well in captivity, and are featured in over 40 public aquariums and zoos. The Seattle Aquarium became the first institution to raise sea otters from conception to adulthood with the birth of Tichuk in 1979, followed by three more pups in the early 1980s. In 2007, a YouTube video of two sea otters holding paws drew 1.5 million viewers in two weeks, and had over 22 million views . Filmed five years previously at the Vancouver Aquarium, it was YouTube's most popular animal video at the time, although it has since been surpassed. The lighter-colored otter in the video is Nyac, a survivor of the 1989 Exxon Valdez oil spill. Nyac died in September 2008, at the age of 20. Milo, the darker one, died of lymphoma in January 2012.
Other sea otters at the Vancouver Aquarium have also gone viral. During the 2020 COVID-19 pandemic, the livestream of Joey, a rescued sea otter pup at the Marine Mammal Rescue Center, attracted millions of viewers from across the world on YouTube and Twitch. Many viewers said the stream helped them cope with the anxiety and depression caused by the pandemic lockdowns. In June 2024, a video of another rescued sea otter pup, Tofino, received over 120,000,000 views and 5,000,000 likes on Instagram.
Beginning in 2019, the streamer Douglas Wreden, popularly known as DougDoug, has held charity streams for the Monterey Bay Aquarium to celebrate the birthday of Rosa the sea otter. As of 2024, DougDoug and his community have raised over $1,000,000 in Rosa's name.
Current conservation
Sea otters, being a known keystone species, need a humanitarian effort to be protected from endangerment through "unregulated human exploitation". This species has increasingly been impacted by the large oil spills and environmental degradation caused by overfishing and entanglement in fishing gear. Current efforts have been made in legislation: the international Fur Seal Treaty, The Endangered Species Act, IUCN/The World Conservation Union, Convention on international Trade in Endangered Species of Wild Fauna and Flora, and the Marine Mammal Protection Act of 1972. Other conservation efforts are done through reintroduction and zoological parks. | Sea otter | Wikipedia | 476 | 567471 | https://en.wikipedia.org/wiki/Sea%20otter | Biology and health sciences | Carnivora | null |
Sea Otter Awareness Week is held every year during the last full week of September. Zoos, aquariums, and other educational institutions hold events highlighting sea otters, their ecological importance, and the challenges facing their conservation. It is organized and sponsored by Defenders of Wildlife, the Monterey Bay Aquarium, the California Department of Parks and Recreation, Sea Otter Savvy, and the Elakha Alliance. | Sea otter | Wikipedia | 80 | 567471 | https://en.wikipedia.org/wiki/Sea%20otter | Biology and health sciences | Carnivora | null |
Pliers are a hand tool used to hold objects firmly, possibly developed from tongs used to handle hot metal in Bronze Age Europe. They are also useful for bending and physically compressing a wide range of materials. Generally, pliers consist of a pair of metal first-class levers joined at a fulcrum positioned closer to one end of the levers, creating short jaws on one side of the fulcrum, and longer handles on the other side. This arrangement creates a mechanical advantage, allowing the force of the grip strength to be amplified and focused on an object with precision. The jaws can also be used to manipulate objects too small or unwieldy to be manipulated with the fingers.
Diagonal pliers, also called side cutters, are a similarly shaped tool used for cutting rather than holding, having a pair of stout blades, similar to scissors except that the cutting surfaces meet parallel to each other rather than overlapping. Ordinary (holding/squeezing) pliers may incorporate a small pair of such cutting blades. Pincers are a similar tool with a different type of head used for cutting and pulling, rather than squeezing. Tools designed for safely handling hot objects are usually called tongs. Special tools for making crimp connections in electrical and electronic applications are often called crimping pliers or crimpers; each type of connection uses its own dedicated tool.
Parallel pliers have jaws that close in parallel to each other, as opposed to the scissor-type action of traditional pliers. They use a box joint system to do this, and it allows them to generate more grip from friction on square and hexagonal fastenings.
There are many kinds of pliers made for various general and specific purposes.
History
As pliers in the general sense are an ancient and simple invention, no single inventor can be credited. Early metal working processes from several millennia BCE would have required plier-like devices to handle hot materials in the process of smithing or casting. Development from wooden to bronze pliers would have probably happened sometime prior to 3000 BCE. Among the oldest illustrations of pliers are those showing the Greek god Hephaestus in his forge. The number of different designs of pliers grew with the invention of the different objects which they were used to handle: horseshoes, fasteners, wire, pipes, electrical, and electronic components. | Pliers | Wikipedia | 480 | 567489 | https://en.wikipedia.org/wiki/Pliers | Technology | Hand tools | null |
Design
The basic design of pliers has changed little since their origins, with the pair of handles, the pivot (often formed by a rivet), and the head section with the gripping jaws or cutting edges forming the three elements.
The materials used to make pliers consist mainly of steel alloys with additives such as vanadium or chromium, to improve strength and prevent corrosion. The metal handles of pliers are often fitted with grips of other materials to ensure better handling; grips are usually insulated and additionally protect against electric shock. The jaws vary widely in size, from delicate needle-nose pliers to heavy jaws capable of exerting much pressure, and shape, from basic flat jaws to various specialized and often asymmetrical jaw configurations for specific manipulations. The surfaces are typically textured rather than smooth, to minimize slipping.
A plier-like tool designed for cutting wires is often called diagonal pliers. Some pliers for electrical work are fitted with wire-cutter blades either built into the jaws or on the handles just below the pivot.
Where it is necessary to avoid scratching or damaging the workpiece, as for example in jewellery and musical instrument repair, pliers with a layer of softer material such as aluminium, brass, or plastic over the jaws are used.
Ergonomics
Much research has been undertaken to improve the design of pliers, to make them easier to use in often difficult circumstances (such as restricted spaces). The handles can be bent, for example, so that the load applied by the hand is aligned with the arm, rather than at an angle, thus reducing muscle fatigue. It is especially important for factory workers who use pliers continuously and helps prevent carpal tunnel syndrome.
Types | Pliers | Wikipedia | 351 | 567489 | https://en.wikipedia.org/wiki/Pliers | Technology | Hand tools | null |
Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a coordinated system of preparing goods for transport, warehousing, logistics, sale, and end use. Packaging contains, protects, preserves, transports, informs, and sells. In many countries it is fully integrated into government, business, institutional, industrial, and for personal use.
Package labeling (American English) or labelling (British English) is any written, electronic, or graphic communication on the package or on a separate but associated label. Many countries or regions have regulations governing the content of package labels. Merchandising, branding, and persuasive graphics are not covered in this article.
History of packaging
Ancient era
The first packages used the natural materials available at the time: baskets of reeds, wineskins (bota bags), wooden boxes, pottery vases, ceramic amphorae, wooden barrels, woven bags, etc. Processed materials were used to form packages as they were developed: first glass and bronze vessels. The study of old packages is an essential aspect of archaeology.
The first usage of paper for packaging was sheets of treated mulberry bark used by the Chinese to wrap foods as early as the first or second century BC.
The usage of paper-like material in Europe was when the Romans used low grade and recycled papyrus for the packaging of incense.
The earliest recorded use of paper for packaging dates back to 1035, when a Persian traveller visiting markets in Cairo, Arab Egypt, noted that vegetables, spices and hardware were wrapped in paper for the customers after they were sold.
Modern era
Tinplate
The use of tinplate for packaging dates back to the 18th century. The manufacturing of tinplate was the monopoly of Bohemia for a long time; in 1667 Andrew Yarranton, an English engineer, and Ambrose Crowley brought the method to England where it was improved by ironmasters including Philip Foley. By 1697, John Hanbury had a rolling mill at Pontypool for making "Pontypoole Plates". The method pioneered there of rolling iron plates by means of cylinders enabled more uniform black plates to be produced than was possible with the former practice of hammering. | Packaging | Wikipedia | 466 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
Tinplate boxes first began to be sold from ports in the Bristol Channel in 1725. The tinplate was shipped from Newport, Monmouthshire. By 1805, 80,000 boxes were made and 50,000 exported. Tobacconists in London began packaging snuff in metal-plated canisters from the 1760s onwards.
Canning
With the discovery of the importance of airtight containers for food preservation by French inventor Nicholas Appert, the tin canning process was patented by British merchant Peter Durand in 1810. After receiving the patent, Durand did not himself follow up with canning food. He sold his patent in 1812 to two other Englishmen, Bryan Donkin and John Hall, who refined the process and product and set up the world's first commercial canning factory on Southwark Park Road, London. By 1813, they were producing the first canned goods for the Royal Navy.
The progressive improvement in canning stimulated the 1855 invention of the can opener. Robert Yeates, a cutlery and surgical instrument maker of Trafalgar Place West, Hackney Road, Middlesex, UK, devised a claw-ended can opener with a hand-operated tool that haggled its way around the top of metal cans. In 1858, another lever-type opener of a more complex shape was patented in the United States by Ezra Warner of Waterbury, Connecticut.
Paper-based packaging
Set-up boxes were first used in the 16th century and modern folding cartons date back to 1839. The first corrugated box was produced commercially in 1817 in England. Corrugated (also called pleated) paper received a British patent in 1856 and was used as a liner for tall hats. Scottish-born Robert Gair invented the pre-cut paperboard box in 1890—flat pieces manufactured in bulk that folded into boxes. Gair's invention came about as a result of an accident: as a Brooklyn printer and paper-bag maker during the 1870s, he was once printing an order of seed bags, and the metal ruler, commonly used to crease bags, shifted in position and cut them. Gair discovered that by cutting and creasing in one operation he could make prefabricated paperboard boxes.
Commercial paper bags were first manufactured in Bristol, England, in 1844, and the American Francis Wolle patented a machine for automated bag-making in 1852.
20th century | Packaging | Wikipedia | 473 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
Packaging advancements in the early 20th century included Bakelite closures on bottles, transparent cellophane overwraps and panels on cartons. These innovations increased processing efficiency and improved food safety. As additional materials such as aluminum and several types of plastic were developed, they were incorporated into packages to improve performance and functionality.
In 1952, Michigan State University became the first university in the world to offer a degree in Packaging Engineering.
In-plant recycling has long been typical for producing packaging materials. Post-consumer recycling of aluminum and paper-based products has been economical for many years: since the 1980s, post-consumer recycling has increased due to curbside recycling, consumer awareness, and regulatory pressure.
Many prominent innovations in the packaging industry were developed first for military use. Some military supplies are packaged in the same commercial packaging used for general industry. Other military packaging must transport materiel, supplies, foods, etc. under severe distribution and storage conditions. Packaging problems encountered in World War II led to Military Standard or "mil spec" regulations being applied to packaging, which was then designated "military specification packaging". As a prominent concept in the military, mil spec packaging officially came into being around 1941, due to operations in Iceland experiencing critical losses, ultimately attributed to bad packaging. In most cases, mil spec packaging solutions (such as barrier materials, field rations, antistatic bags, and various shipping crates) are similar to commercial grade packaging materials, but subject to more stringent performance and quality requirements.
, the packaging sector accounted for about two percent of the gross national product in developed countries. About half of this market was related to food packaging.
In 2019 the global food packaging market size was estimated at USD 303.26 billion, exhibiting a CAGR of 5.2% over the forecast period. Growing demand for packaged food by consumers owing to quickening pace of life and changing eating habits is expected to have a major impact on the market.
The purposes of packaging and package labels | Packaging | Wikipedia | 397 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
Packaging and package labeling have several objectives
Physical protection – The objects enclosed in the package may require protection from, among other things, mechanical shock, vibration, electrostatic discharge, abrasion, compression, temperature, etc.
Barrier protection – A barrier to oxygen, water vapor, sunlight, dust, etc., is often required. Permeation is a critical factor in design. Some packages contain desiccants or oxygen absorbers to help extend shelf life. Modified atmospheres or controlled atmospheres are also maintained in some food packages. Keeping the contents clean, fresh, sterile and safe for the duration of the intended shelf life is a primary function. A barrier is also implemented in cases where segregation of two materials prior to end use is required, as in the case of special paints, glues, medical fluids, etc.
Containment or agglomeration – liquids and powders need to be contained for shipment and sale. Small objects are typically grouped together in one package for reasons of storage and selling efficiency. For example, a single box of 1000 marbles requires less physical handling than 1000 single marbles. Liquids, powders, and granular materials need containment.
Information transmission – Packages and labels communicate how to use, transport, recycle, or dispose of the package or product. With pharmaceuticals, food, medical, and chemical products, some types of information are required by government legislation. Some packages and labels also are used for track and trace purposes. Most items include their serial and lot numbers on the packaging, and in the case of food products, medicine, and some chemicals the packaging often contains an expiry/best-before date, usually in a shorthand form. Packages may indicate their construction material with a symbol.
Marketing – Packaging and labels can be used by marketers to encourage potential buyers to purchase a product. Package graphic design and physical design have been important and constantly evolving phenomena for several decades. Marketing communications and graphic design are applied to the surface of the package and often to the point of sale display. Most packaging is designed to reflect the brand's message and identity on the one hand while highlighting the respective product concept on the other hand. | Packaging | Wikipedia | 437 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
Security – Packaging can play an important role in reducing the security risks of shipment. Packages can be made with improved tamper resistance to deter manipulation and they can also have tamper-evident features indicating that tampering has taken place. Packages can be engineered to help reduce the risks of package pilferage or the theft and resale of products: Some package constructions are more resistant to pilferage than other types, and some have pilfer-indicating seals. Counterfeit consumer goods, unauthorized sales (diversion), material substitution and tampering can all be minimized or prevented with such anti-counterfeiting technologies. Packages may include authentication seals and use security printing to help indicate that the package and contents are not counterfeit. Packages also can include anti-theft devices such as dye-packs, RFID tags, or electronic article surveillance tags that can be activated or detected by devices at exit points and require specialized tools to deactivate. Using packaging in this way is a means of retail loss prevention.
Convenience – Packages can have features that add convenience in distribution, handling, stacking, display, sale, opening, reclosing, using, dispensing, reusing, recycling, and ease of disposal
Portion control – Single serving or single dosage packaging has a precise amount of contents to control usage. Bulk commodities (such as salt) can be divided into packages that are a more suitable size for individual households. It also aids the control of inventory: selling sealed one-liter bottles of milk, rather than having people bring their own bottles to fill themselves.
Branding/Positioning – Packaging and labels are increasingly used to go beyond marketing to brand positioning, with the materials used and design chosen key to the storytelling element of brand development. Due to the increasingly fragmented media landscape in the digital age this aspect of packaging is of growing importance.
Packaging types
Packaging may be of several different types. For example, a transport package or distribution package can be the shipping container used to ship, store, and handle the product or inner packages. Some identify a consumer package as one which is directed toward a consumer or household.
Packaging may be described in relation to the type of product being packaged: medical device packaging, bulk chemical packaging, over-the-counter drug packaging, retail food packaging, military materiel packaging, pharmaceutical packaging, etc. | Packaging | Wikipedia | 473 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
It is sometimes convenient to categorize packages by layer or function: primary, secondary, tertiary,etc.
Primary packaging is the material that first envelops the product and holds it. This usually is the smallest unit of distribution or use and is the package which is in direct contact with the contents.
Secondary packaging is outside the primary packaging, and may be used to prevent pilferage or to group primary packages together.
Tertiary or transit packaging is used for bulk handling, warehouse storage and transport shipping. The most common form is a palletized unit load that packs tightly into containers.
These broad categories can be somewhat arbitrary. For example, depending on the use, a shrink wrap can be primary packaging when applied directly to the product, secondary packaging when used to combine smaller packages, or tertiary packaging when used to facilitate some types of distribution, such as to affix a number of cartons on a pallet.
Packaging can also have categories based on the package form. For example, thermoform packaging and flexible packaging describe broad usage areas.
Labels and symbols used on packages
Many types of symbols for package labeling are nationally and internationally standardized. For consumer packaging, symbols exist for product certifications (such as the FCC and TÜV marks), trademarks, proof of purchase, etc. Some requirements and symbols exist to communicate aspects of consumer rights and safety, for example the CE marking or the estimated sign that notes conformance to EU weights and measures accuracy regulations. Examples of environmental and recycling symbols include the recycling symbol, the recycling code (which could be a resin identification code), and the "Green Dot". Food packaging may show food contact material symbols. In the European Union, products of animal origin which are intended to be consumed by humans have to carry standard, oval-shaped EC identification and health marks for food safety and quality insurance reasons.
Bar codes, Universal Product Codes, and RFID labels are common to allow automated information management in logistics and retailing. Country-of-origin labeling is often used. Some products might use QR codes or similar matrix barcodes. Packaging may have visible registration marks and other printing calibration and troubleshooting cues.
The labelling of medical devices includes many symbols, many of them covered by international standards, foremost ISO 15223-1. | Packaging | Wikipedia | 466 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
Consumer package contents
Several aspects of consumer package labeling are subject to regulation. One of the most important is to accurately state the quantity (weight, volume, count) of the package contents. Consumers expect that the label accurately reflects the actual contents. Manufacturers and packagers must have effective quality assurance procedures and accurate equipment; even so, there is inherent variability in all processes.
Regulations attempt to handle both sides of this. In the US, the Fair Packaging and Labeling Act provides requirements for many types of products. Also, NIST has Handbook 133, Checking the Net Contents of Packaged Goods. This is a procedural guide for compliance testing of net contents and is referenced by several other regulatory agencies.
Other regions and countries have their own regulatory requirements. For example, the UK has its Weights and Measures (Packaged Goods) Regulations as well as several other regulations. In the EEA, products with hazardous formulas need to have a UFI.
Shipping container labeling
Technologies related to shipping containers are identification codes, bar codes, and electronic data interchange (EDI). These three core technologies serve to enable the business functions in the process of shipping containers throughout the distribution channel. Each has an essential function: identification codes either relate product information or serve as keys to other data, bar codes allow for the automated input of identification codes and other data, and EDI moves data between trading partners within the distribution channel.
Elements of these core technologies include UPC and EAN item identification codes, the SCC-14 (UPC shipping container code), the SSCC-18 (Serial Shipping Container Codes), Interleaved 2-of-5 and UCC/EAN-128 (newly designated GS1-128) bar code symbologies, and ANSI ASC X12 and UN/EDIFACT EDI standards.
Small parcel carriers often have their own formats. For example, United Parcel Service has a MaxiCode 2-D code for parcel tracking.
RFID labels for shipping containers are also increasingly used. A Wal-Mart division, Sam's Club, has also moved in this direction and is putting pressure on its suppliers to comply. | Packaging | Wikipedia | 428 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
Shipments of hazardous materials or dangerous goods have special information and symbols (labels, placards, etc.) as required by UN, country, and specific carrier requirements. On transport packages, standardized symbols are also used to communicate handling needs. Some are defined in the ASTM D5445 "Standard Practice for Pictorial Markings for Handling of Goods", ISO 780 "Pictorial marking for handling of goods", and GHS hazard pictograms.
Package development considerations
Package design and development are often thought of as an integral part of the new product development process. Alternatively, the development of a package (or component) can be a separate process but must be linked closely with the product to be packaged.
Package design starts with the identification of all the requirements: structural design, marketing, shelf life, quality assurance, logistics, legal, regulatory, graphic design, end-use, environmental, etc. The design criteria, performance (specified by package testing), completion time targets, resources, and cost constraints need to be established and agreed upon. Package design processes often employ rapid prototyping, computer-aided design, computer-aided manufacturing and document automation.
An example of how package design is affected by other factors is its relationship to logistics. When the distribution system includes individual shipments by a small parcel carrier, the sorting, handling, and mixed stacking make severe demands on the strength and protective ability of the transport package. If the logistics system consists of uniform palletized unit loads, the structural design of the package can be designed to meet those specific needs, such as vertical stacking for a longer time frame. A package designed for one mode of shipment may not be suited to another.
With some types of products, the design process involves detailed regulatory requirements for the packaging. For example, any package components that may contact foods are designated food contact materials.
Toxicologists and food scientists need to verify that such packaging materials are allowed by applicable regulations. Packaging engineers need to verify that the completed package will keep the product safe for its intended shelf life with normal usage. Packaging processes, labeling, distribution, and sale need to be validated to assure that they comply with regulations that have the well being of the consumer in mind. | Packaging | Wikipedia | 444 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
Sometimes the objectives of package development seem contradictory. For example, regulations for an over-the-counter drug might require the package to be tamper-evident and child resistant: These intentionally make the package difficult to open. The intended consumer, however, might be disabled or elderly and unable to readily open the package. Meeting all goals is a challenge.
Package design may take place within a company or with various degrees of external packaging engineering: independent contractors, consultants, vendor evaluations, independent laboratories, contract packagers, total outsourcing, etc. Some sort of formal project planning and project management methodology is required for all but the simplest package design and development programs. An effective quality management system and Verification and Validation protocols are mandatory for some types of packaging and recommended for all.
Environmental considerations
Package development involves considerations of sustainability, environmental responsibility, and applicable environmental and recycling regulations. It may involve a life cycle assessment
which considers the material and energy inputs and outputs to the package, the packaged product (contents), the packaging process, the logistics system, waste management, etc. It is necessary to know the relevant regulatory requirements for point of manufacture, sale, and use. | Packaging | Wikipedia | 233 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
The traditional "three R's" of reduce, reuse, and recycle are part of a waste hierarchy which may be considered in product and package development.
Prevention – Waste prevention is a primary goal. Packaging should be used only where needed. Proper packaging can also help prevent waste. Packaging plays an important part in preventing loss or damage to the packaged product (contents). Usually, the energy content and material usage of the product being packaged are much greater than that of the package. A vital function of the package is to protect the product for its intended use: if the product is damaged or degraded, its entire energy and material content may be lost.
Minimization (also "source reduction") – Eliminate overpackaging. The mass and volume of packaging (per unit of contents) can be measured and used as criteria for minimizing the package in the design process. Usually "reduced" packaging also helps minimize costs. Packaging engineers continue to work toward reduced packaging.
Reuse – Reusable packaging is encouraged. Returnable packaging has long been useful (and economically viable) for closed-loop logistics systems. Inspection, cleaning, repair, and recouperage are often needed. Some manufacturers re-use the packaging of the incoming parts for a product, either as packaging for the outgoing product or as part of the product itself.
Recycling – Recycling is the reprocessing of materials (pre- and post-consumer) into new products. Emphasis is focused on recycling the largest primary components of a package: steel, aluminum, papers, plastics, etc. Small components can be chosen which are not difficult to separate and do not contaminate recycling operations. Packages can sometimes be designed to separate components to better facilitate recycling.
Energy recovery – Waste-to-energy and refuse-derived fuel in approved facilities make use of the heat available from incinerating the packaging components.
Disposal – Incineration, and placement in a sanitary landfill are undertaken for some materials. Certain US states regulate packages for toxic contents, which have the potential to contaminate emissions and ash from incineration and leachate from landfill. Packages should not be littered.
Development of sustainable packaging is an area of considerable interest to standards organizations, governments, consumers, packagers, and retailers.
Sustainability is the fastest-growing driver for packaging development, particularly for packaging manufacturers that work with the world's leading brands, as their CSR (Corporate Social Responsibility) targets often exceed those of the EU Directive.
Packaging machinery | Packaging | Wikipedia | 504 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
Choosing packaging machinery includes an assessment of technical capabilities, labor requirements, worker safety, maintainability, serviceability, reliability, ability to integrate into the packaging line, capital cost, floorspace, flexibility (change-over, materials, multiple products, etc.), energy requirements, quality of outgoing packages, qualifications (for food, pharmaceuticals, etc.), throughput, efficiency, productivity, ergonomics, return on investment, etc.
Packaging machinery can be:
purchased as standard, off-the-shelf equipment
purchased custom-made or custom-tailored to specific operations
manufactured or modified by in-house engineers and maintenance staff
Efforts at packaging line automation increasingly use programmable logic controllers and robotics.
Packaging machines may be of the following general types:
Accumulating and collating machines
Blister packs, skin packs and vacuum packaging machines
Bottle caps equipment, over-capping, lidding, closing, seaming and sealing machines
Box, case, tray, and carrier forming, packing, unpacking, closing, and sealing machines
Cartoning machines
Cleaning, sterilizing, cooling and drying machines
Coding, printing, marking, stamping, and imprinting machines
Converting machines
Conveyor belts, accumulating and related machines
Feeding, orienting, placing and related machines
Filling machines: handling dry, powdered, solid, liquid, gas, or viscous products
Inspecting: visual, sound, metal detecting, etc.
Label dispenser
Orienting, unscrambling machines
Package filling and closing machines
Palletizing, depalletizing, unit load assembly
Product identification: labeling, marking, etc.
Sealing machines: heat sealer or glue units
Slitting machines
Weighing machines: check weigher, multihead weigher
Wrapping machines: stretch wrapping, shrink wrap, banding
Form, fill and seal machines
Other specialty machinery: slitters, perforating, laser cutters, parts attachment, etc. | Packaging | Wikipedia | 384 | 568715 | https://en.wikipedia.org/wiki/Packaging | Technology | Containers | null |
A giant star has a substantially larger radius and luminosity than a main-sequence (or dwarf) star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsprung–Russell diagram and correspond to luminosity classes II and III. The terms giant and dwarf were coined for stars of quite different luminosity despite similar temperature or spectral type (namely K and M) by Ejnar Hertzsprung in 1905 or 1906.
Giant stars have radii up to a few hundred times the Sun and luminosities between 10 and a few thousand times that of the Sun. Stars still more luminous than giants are referred to as supergiants and hypergiants.
A hot, luminous main-sequence star may also be referred to as a giant, but any main-sequence star is properly called a dwarf, regardless of how large and luminous it is.
Formation
A star becomes a giant after all the hydrogen available for fusion at its core has been depleted and, as a result, leaves the main sequence. The behaviour of a post-main-sequence star depends largely on its mass. | Giant star | Wikipedia | 242 | 568726 | https://en.wikipedia.org/wiki/Giant%20star | Physical sciences | Stellar astronomy | null |
Intermediate-mass stars
For a star with a mass above about 0.25 solar masses (), once the core is depleted of hydrogen it contracts and heats up so that hydrogen starts to fuse in a shell around the core. The portion of the star outside the shell expands and cools, but with only a small increase in luminosity, and the star becomes a subgiant. The inert helium core continues to grow and increase in temperature as it accretes helium from the shell, but in stars up to about it does not become hot enough to start helium burning (higher-mass stars are supergiants and evolve differently). Instead, after just a few million years the core reaches the Schönberg–Chandrasekhar limit, rapidly collapses, and may become degenerate. This causes the outer layers to expand even further and generates a strong convective zone that brings heavy elements to the surface in a process called the first dredge-up. This strong convection also increases the transport of energy to the surface, the luminosity increases dramatically, and the star moves onto the red-giant branch where it will stably burn hydrogen in a shell for a substantial fraction of its entire life (roughly 10% for a Sun-like star). The core continues to gain mass, contract, and increase in temperature, whereas there is some mass loss in the outer layers., § 5.9.
If the star's mass, when on the main sequence, was below approximately , it will never reach the central temperatures necessary to fuse helium., p. 169. It will therefore remain a hydrogen-fusing red giant until it runs out of hydrogen, at which point it will become a helium white dwarf., § 4.1, 6.1. According to stellar evolution theory, no star of such low mass can have evolved to that stage within the age of the Universe. | Giant star | Wikipedia | 385 | 568726 | https://en.wikipedia.org/wiki/Giant%20star | Physical sciences | Stellar astronomy | null |
In stars above about the core temperature eventually reaches 108 K and helium will begin to fuse to carbon and oxygen in the core by the triple-alpha process.,§ 5.9, chapter 6. When the core is degenerate helium fusion begins explosively, but most of the energy goes into lifting the degeneracy and the core becomes convective. The energy generated by helium fusion reduces the pressure in the surrounding hydrogen-burning shell, which reduces its energy-generation rate. The overall luminosity of the star decreases, its outer envelope contracts again, and the star moves from the red-giant branch to the horizontal branch., chapter 6.
When the core helium is exhausted, a star with up to about has a carbon–oxygen core that becomes degenerate and starts helium burning in a shell. As with the earlier collapse of the helium core, this starts convection in the outer layers, triggers a second dredge-up, and causes a dramatic increase in size and luminosity. This is the asymptotic giant branch (AGB) analogous to the red-giant branch but more luminous, with a hydrogen-burning shell contributing most of the energy. Stars only remain on the AGB for around a million years, becoming increasingly unstable until they exhaust their fuel, go through a planetary nebula phase, and then become a carbon–oxygen white dwarf., § 7.1–7.4.
High-mass stars
Main-sequence stars with masses above about are already very luminous and they move horizontally across the HR diagram when they leave the main sequence, briefly becoming blue giants before they expand further into blue supergiants. They start core-helium burning before the core becomes degenerate and develop smoothly into red supergiants without a strong increase in luminosity. At this stage they have comparable luminosities to bright AGB stars although they have much higher masses, but will further increase in luminosity as they burn heavier elements and eventually become a supernova.
Stars in the range have somewhat intermediate properties and have been called super-AGB stars. They largely follow the tracks of lighter stars through RGB, HB, and AGB phases, but are massive enough to initiate core carbon burning and even some neon burning. They form oxygen–magnesium–neon cores, which may collapse in an electron-capture supernova, or they may leave behind an oxygen–neon white dwarf. | Giant star | Wikipedia | 491 | 568726 | https://en.wikipedia.org/wiki/Giant%20star | Physical sciences | Stellar astronomy | null |
O class main sequence stars are already highly luminous. The giant phase for such stars is a brief phase of slightly increased size and luminosity before developing a supergiant spectral luminosity class. Type O giants may be more than a hundred thousand times as luminous as the sun, brighter than many supergiants. Classification is complex and difficult with small differences between luminosity classes and a continuous range of intermediate forms. The most massive stars develop giant or supergiant spectral features while still burning hydrogen in their cores, due to mixing of heavy elements to the surface and high luminosity which produces a powerful stellar wind and causes the star's atmosphere to expand.
Low-mass stars
A star whose initial mass is less than approximately will not become a giant star at all. For most of their lifetimes, such stars have their interior thoroughly mixed by convection and so they can continue fusing hydrogen for a time in excess of years, much longer than the current age of the Universe. They steadily become hotter and more luminous throughout this time. Eventually they do develop a radiative core, subsequently exhausting hydrogen in the core and burning hydrogen in a shell surrounding the core. (Stars with a mass in excess of may expand at this point, but will never become very large.) Shortly thereafter, the star's supply of hydrogen will be completely exhausted and it is expected to become a helium white dwarf, although the universe is too young for any such star to exist yet, so no star with that history has ever been observed.
Subclasses
There are a wide range of giant-class stars and several subdivisions are commonly used to identify smaller groups of stars.
Subgiants
Subgiants are an entirely separate spectroscopic luminosity class (IV) from giants, but share many features with them. Although some subgiants are simply over-luminous main-sequence stars due to chemical variation or age, others are a distinct evolutionary track towards true giants.
Examples:
Gamma Geminorum (γ Gem), an A-type subgiant;
Eta Bootis (η Boo), a G-type subgiant.
Delta Scorpii (δ Sco), a B-type subgiant.
Bright giants
Bright giants are stars of luminosity class II in the Yerkes spectral classification. These are stars which straddle the boundary between ordinary giants and supergiants, based on the appearance of their spectra. The bright giant luminosity class was first defined in 1943. | Giant star | Wikipedia | 507 | 568726 | https://en.wikipedia.org/wiki/Giant%20star | Physical sciences | Stellar astronomy | null |
Well known stars which are classified as bright giants include:
Canopus
Albireo
Epsilon Canis Majoris
Theta Scorpii
Beta Draconis
Alpha Herculis
Gamma Canis Majoris
Red giants
Within any giant luminosity class, the cooler stars of spectral class K, M, S, and C, (and sometimes some G-type stars) are called red giants. Red giants include stars in a number of distinct evolutionary phases of their lives: a main red-giant branch (RGB); a red horizontal branch or red clump; the asymptotic giant branch (AGB), although AGB stars are often large enough and luminous enough to get classified as supergiants; and sometimes other large cool stars such as immediate post-AGB stars. The RGB stars are by far the most common type of giant star due to their moderate mass, relatively long stable lives, and luminosity. They are the most obvious grouping of stars after the main sequence on most HR diagrams, although white dwarfs are more numerous but far less luminous.
Examples:
Pollux, a K-type giant.
Epsilon Ophiuchi, a G-type red giant.
Arcturus (α Boötis), a K-type giant.
R Doradus, a M-type giant.
Mira (ο Ceti), an M-type giant and prototype Mira variable.
Aldebaran, a K-type giant | Giant star | Wikipedia | 292 | 568726 | https://en.wikipedia.org/wiki/Giant%20star | Physical sciences | Stellar astronomy | null |
Yellow giants
Giant stars with intermediate temperatures (spectral class G, F, and at least some A) are called yellow giants. They are far less numerous than red giants, partly because they only form from stars with somewhat higher masses, and partly because they spend less time in that phase of their lives. However, they include a number of important classes of variable stars. High-luminosity yellow stars are generally unstable, leading to the instability strip on the HR diagram where the majority of stars are pulsating variables. The instability strip reaches from the main sequence up to hypergiant luminosities, but at the luminosities of giants there are several classes of pulsating variable stars:
RR Lyrae variables, pulsating horizontal-branch class A (sometimes F) stars with periods less than a day and amplitudes of a magnitude of less;
W Virginis variables, more-luminous pulsating variables also known as type II Cepheids, with periods of 10–20 days;
Type I Cepheid variables, more luminous still and mostly supergiants, with even longer periods;
Delta Scuti variables, includes subgiant and main-sequence stars.
Yellow giants may be moderate-mass stars evolving for the first time towards the red-giant branch, or they may be more evolved stars on the horizontal branch. Evolution towards the red-giant branch for the first time is very rapid, whereas stars can spend much longer on the horizontal branch. Horizontal-branch stars, with more heavy elements and lower mass, are more unstable.
Examples:
Sigma Octantis (σ Octantis), an F-type giant and a Delta Scuti variable;
Capella Aa (α Aurigae Aa), a G-type giant.
Beta Corvi (β Corvi), a G-type bright giant.
Blue (and sometimes white) giants
The hottest giants, of spectral classes O, B, and sometimes early A, are called blue giants. Sometimes A- and late-B-type stars may be referred to as white giants. | Giant star | Wikipedia | 425 | 568726 | https://en.wikipedia.org/wiki/Giant%20star | Physical sciences | Stellar astronomy | null |
The blue giants are a very heterogeneous grouping, ranging from high-mass, high-luminosity stars just leaving the main sequence to low-mass, horizontal-branch stars. Higher-mass stars leave the main sequence to become blue giants, then bright blue giants, and then blue supergiants, before expanding into red supergiants, although at the very highest masses the giant stage is so brief and narrow that it can hardly be distinguished from a blue supergiant.
Lower-mass, core-helium-burning stars evolve from red giants along the horizontal branch and then back again to the asymptotic giant branch, and depending on mass and metallicity they can become blue giants. It is thought that some post-AGB stars experiencing a late thermal pulse can become peculiar blue giants.
Examples:
Meissa (λ Orionis A), an O-type giant.
Alcyone (η Tauri), a B-type giant, the brightest star in the Pleiades;
Thuban (α Draconis), an A-type giant. | Giant star | Wikipedia | 221 | 568726 | https://en.wikipedia.org/wiki/Giant%20star | Physical sciences | Stellar astronomy | null |
Gmail is the email service provided by Google. it had 1.5 billion active users worldwide, making it the largest email service in the world. It also provides a webmail interface, accessible through a web browser, and is also accessible through the official mobile application. Google also supports the use of third-party email clients via the POP and IMAP protocols.
At its launch in 2004, Gmail (or Google Mail at the time) provided a storage capacity of one gigabyte per user, which was significantly higher than its competitors offered at the time. Today, the service comes with 15 gigabytes of storage for free for individual users, which is divided among other Google services, such as Google Drive, and Google Photos. Users in need of more storage can purchase Google One to increase this 15 GB limit across most Google services. Users can receive emails up to 50 megabytes in size, including attachments, and can send emails up to 25 megabytes. Gmail supports integration with Google Drive, allowing for larger attachments. Gmail has a search-oriented interface and supports a "conversation view" similar to an Internet forum. The service is notable among website developers for its early adoption of Ajax.
Google's mail servers automatically scan emails for multiple purposes, including to filter spam and malware and, prior to June 2017, to add context-sensitive advertisements next to emails. This advertising practice has been significantly criticized by privacy advocates with concerns over unlimited data retention, ease of monitoring by third parties, users of other email providers not having agreed to the policy upon sending emails to Gmail addresses, and the potential for Google to change its policies to further decrease privacy by combining information with other Google data usage. The company has been the subject of lawsuits concerning the issues. Google has stated that email users must "necessarily expect" their emails to be subject to automated processing and claims that the service refrains from displaying ads next to potentially sensitive messages, such as those mentioning race, religion, sexual orientation, health, or financial statements. In June 2017, Google announced the end of the use of contextual Gmail content for advertising purposes, relying instead on data gathered from the use of its other services.
Features
Storage | Gmail | Wikipedia | 448 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
On April 1, 2004, Gmail was launched with one gigabyte (GB) of storage space, a significantly higher amount than competitors offered at the time.
The limit was doubled to two gigabytes of storage on April 1, 2005, the first anniversary of Gmail. Georges Harik, the product management director for Gmail, stated that Google would "keep giving people more space forever."
In October 2007, Gmail increased storage to 4 gigabytes, after recent changes from competitors Yahoo and Microsoft.
On April 24, 2012, Google announced the increase of storage included in Gmail from 7.5 to 10 gigabytes ("and counting") as part of the launch of Google Drive.
On May 13, 2013, Google announced the overall merge of storage across Gmail, Google Drive, and Google+ Photos, allowing users 15 gigabytes of included storage among three services.
On August 15, 2018, Google launched Google One, a service where users can pay for additional storage, shared among Gmail, Google Drive and Google Photos, through a monthly subscription plan. , storage of up to 15 gigabytes is included, and paid plans are available for up to 2 terabytes for personal use.
There are also storage limits to individual Gmail messages. Initially, one message, including all attachments, could not be larger than 25 megabytes. This was changed in March 2017 to allow receiving an email of up to 50 megabytes, while the limit for sending an email stayed at 25 megabytes. In order to send larger files, users can insert files from Google Drive into the message.
Interface
The Gmail user interface initially differed from other web-mail systems with its focus on search and conversation threading of emails, grouping several messages between two or more people onto a single page, an approach that was later copied by its competitors. Gmail's user interface designer, Kevin Fox, intended users to feel as if they were always on one page and just changing things on that page, rather than having to navigate to other places.
Gmail's interface also makes use of 'labels' (tags) – that replace the conventional folders and provide a more flexible method of organizing emails; filters for automatically organizing, deleting or forwarding incoming emails to other addresses; and importance markers for automatically marking messages as 'important'. | Gmail | Wikipedia | 481 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
In November 2011, Google began rolling out a redesign of its interface that "simplified" the look of Gmail into a more minimalist design to provide a more consistent look throughout its products and services as part of an overall Google design change. Majorly redesigned elements included a streamlined conversation view, configurable density of information, new higher-quality themes, a resizable navigation bar with always-visible labels and contacts, and better search. Users were able to preview the new interface design for months prior to the official release, as well as revert to the old interface, until March 2012, when Google discontinued the ability to revert and completed the transition to the new design for all users.
In May 2013, Google updated the Gmail inbox with tabs which allow the application to categorize the user's emails. The five tabs are: Primary, Social, Promotions, Updates, and Forums. In addition to customization options, the entire update can be disabled, allowing users to return to the traditional inbox structure.
In April 2018, Google introduced a new web UI for Gmail. The new redesign follows Google's Material Design, and changes in the user interface include the use of Google's Product Sans font. Other updates include a Confidential mode, which allows the sender to set an expiration date for a sensitive message or to revoke it entirely, integrated rights management and two-factor authentication.
On 16 November 2020, Google announced new settings for smart features and personalization in Gmail. Under the new settings users were given control of their data in Gmail, Chat, and Meet, offering smart features like Smart Compose and Smart Reply.
On 6 April 2021, Google rolled out Google Chat and Room (early access) feature to all Gmail users.
On 28 July 2022, Google rolled out Material You to all Gmail users.
Spam filter
Gmail's spam filtering features a community-driven system: when any user marks an email as spam, this provides information to help the system identify similar future messages for all Gmail users.
In the April 2018 update, the spam filtering banners got a redesign, with bigger and bolder lettering.
Gmail Labs | Gmail | Wikipedia | 448 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
The Gmail Labs feature, introduced on June 5, 2008, allows users to test new or experimental features of Gmail. Users can enable or disable Labs features selectively and provide feedback about each of them. This allows Gmail engineers to obtain user input about new features to improve them and also to assess their popularity.
Popular features, like the "Undo Send" option, often "graduate" from Gmail Labs to become a formal setting in Gmail.
All Labs features are experimental and are subject to termination at any time.
Search
Gmail incorporates a search bar for searching emails. The search bar can also search contacts, files stored in Google Drive, events from Google Calendar, and Google Sites.
In May 2012, Gmail improved the search functionality to include auto-complete predictions from the user's emails.
Gmail's search functionality does not support searching for word fragments (also known as 'substring search' or partial word search). Workarounds exist.
Language support
, the Gmail interface supports 72 languages, including: Arabic, Basque, Bulgarian, Catalan, Chinese (simplified), Chinese (traditional), Croatian, Czech, Danish, Dutch, English (UK), English (US), Estonian, Finnish, French, German, Greek, Gujarati, Hebrew, Hindi, Hungarian, Icelandic, Indonesian, Italian, Japanese, Kannada, Korean, Latvian, Lithuanian, Malay, Malayalam, Marathi, Norwegian (Bokmål), Odia, Persian, Polish, Punjabi, Portuguese (Brazil), Portuguese (Portugal), Romanian, Russian, Serbian, Sinhala, Slovak, Slovenian, Spanish, Swedish, Tagalog (Filipino), Tamil, Telugu, Thai, Turkish, Ukrainian, Urdu, Vietnamese, Welsh and Zulu.
Language input styles
In October 2012, Google added over 100 virtual keyboards, transliterations, and input method editors to Gmail, enabling users different types of input styles for different languages in an effort to help users write in languages that are not "limited by the language of your keyboard."
In October 2013, Google added handwriting input support to Gmail.
In August 2014, Gmail became the first major email provider to let users send and receive emails from addresses with accent marks and letters from outside the Latin alphabet.
Platforms
Web browsers
The modern AJAX version is officially supported in the current and previous major releases of Google Chrome, Firefox, Microsoft Edge and Safari web browsers on a rolling basis. | Gmail | Wikipedia | 496 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
Gmail's "basic HTML" version works on almost all browsers. This version of Gmail has been discontinued from January 2024.
In August 2011, Google introduced Gmail Offline, an HTML5-powered app for providing access to the service while offline. Gmail Offline runs on the Google Chrome browser and can be downloaded from the Chrome Web Store.
In addition to the native apps on iOS and Android, users can access Gmail through the web browser on a mobile device.
Mobile
Gmail has native applications for iOS devices (including iPhone, iPad, and iPod Touch) and for Android devices.
In November 2014, Google introduced functionality in the Gmail Android app that enabled sending and receiving emails from non-Gmail addresses (such as Yahoo! Mail and Outlook.com) through POP or IMAP.
In November 2016, Google redesigned the Gmail app for the iOS platform, bringing the first complete visual overhaul in "nearly four years". The update added much more use of colors, sleeker transitions, and the addition of several "highly-requested" features, including Undo Send, faster search with instant results and spelling suggestions, and Swipe to Archive/Delete.
In May 2017, Google updated Gmail on Android to feature protection from phishing attacks. Media outlets noticed that the new protection was announced amid a widespread phishing attack on a combination of Gmail and Google's Docs document service that occurred on the same day.
Later in May, Google announced the addition of "Smart Reply" to Gmail on Android and iOS. "Smart Reply", a feature originally launched for Google's Inbox by Gmail service, scans a message for information and uses machine intelligence to offer three responses the user can optionally edit and send. The feature is limited to the English language at launch, with additional support for Spanish, followed by other languages arriving later.
Inbox by Gmail, another app from the Gmail team, was also available for iOS and Android devices. It was discontinued in April 2019.
Third-party programs can be used to access Gmail, using the POP or IMAP protocols. In 2019, Google rolled out dark mode for its mobile apps in Android and iOS.
Inbox by Gmail | Gmail | Wikipedia | 455 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
In October 2014, Google introduced Inbox by Gmail on an invitation-only basis. Developed by the Gmail team, but serving as a "completely different type of inbox", the service is made to help users deal with the challenges of an active email. Citing issues such as distractions, difficulty in finding important information buried in messages, and receiving more emails than ever, Inbox by Gmail has several important differences from Gmail, including bundles that automatically sort emails of the same topic together, highlights that surface key information from messages, and reminders, assists, and snooze, that help the user in handling incoming emails at appropriate times.
Inbox by Gmail became publicly available in May 2015. In September 2018, Google announced it would end the service at the end of March 2019, most of its key features having been incorporated into the standard Gmail service. The service was discontinued on April 2, 2019.
Integration with Google products
In August 2010, Google released a plugin that provides integrated telephone service within Gmail's Google Chat interface. The feature initially lacked an official name, with Google referring to it as both "Google Voice in Gmail chat" and "Call Phones in Gmail". The service logged over one million calls in 24 hours. In March 2014, Google Voice was discontinued, and replaced with functionality from Google Hangouts, another communication platform from Google.
On February 9, 2010, Google commenced its new social networking tool, Google Buzz, which integrated with Gmail, allowing users to share links and media, as well as status updates. Google Buzz was discontinued in October 2011, replaced with new functionality in Google+, Google's then-new social networking platform.
Gmail was integrated with Google+ in December 2011, as part of an effort to have all Google information across one Google account, with a centralized Google+ user profile. Backlash from the move caused Google to step back and remove the requirement of a Google+ user account, keeping only a private Google account without a public-facing profile, starting in July 2015. | Gmail | Wikipedia | 418 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
In May 2013, Google announced the integration between Google Wallet and Gmail, which would allow Gmail users to send money as email attachments. Although the sender must use a Gmail account, the recipient does not need to be using a Gmail address. The feature has no transaction fees, but there are limits to the amount of money that can be sent. Initially only available on the web, the feature was expanded to the Android app in March 2017, for people living in the United States.
In September 2016, Google released Google Trips, an app that, based on information from a user's Gmail messages, automatically generates travel cards. A travel card contains itinerary details, such as plane tickets and car rentals, and recommends activities, food and drinks, and attractions based on location, time, and interests. The app also has offline functionality. In April 2017, Google Trips received an update adding several significant features. The app now also scans Gmail for bus and train tickets, and allows users to manually input trip reservations. Users can send trip details to other users' email, and if the recipient also has Google Trips, the information will be automatically available in their apps as well.
Security
History
Google has supported the secure HTTPS since the day it launched. In the beginning, it was only default on the login page, a reason that Google engineer Ariel Rideout stated was because HTTPS made "your mail slower". However, users could manually switch to secure HTTPS mode inside the inbox after logging in. In July 2008, Google simplified the ability to manually enable secure mode, with a toggle in the settings menu.
In 2007, Google fixed a cross-site scripting security issue that could let attackers collect information from Gmail contact lists.
In January 2010, Google began rolling out HTTPS as the default for all users.
In June 2012, a new security feature was introduced to protect users from state-sponsored attacks. A banner will appear at the top of the page that warns users of an unauthorized account compromise.
In March 2014, Google announced that an encrypted HTTPS connection would be used for the sending and receiving of all Gmail emails, and "every single email message you send or receive —100% of them —is encrypted while moving internally" through the company's systems. | Gmail | Wikipedia | 471 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
Whenever possible, Gmail uses transport layer security (TLS) to automatically encrypt emails sent and received. On the web and on Android devices, users can check if a message is encrypted by checking if the message has a closed or open red padlock.
Gmail automatically scans all incoming and outgoing e-mails for viruses in email attachments. For security reasons, some file types, including executables, are not allowed to be sent in emails.
At the end of May 2017, Google announced that it had applied machine learning technology to identify emails with phishing and spam, having a 99.9% detection accuracy. The company also announced that Gmail would selectively delay some messages, approximately 0.05% of all, to perform more detailed analysis and aggregate details to improve its algorithms.
In November 2020, Google started adding click-time link protection by redirecting clicked links to Google in official Gmail clients.
Third-party encryption in transit
In Google's Transparency Report under the Safer email section, it provides information on the percentage of emails encrypted in transit between Gmail and third-party email providers.
Two-step verification
Gmail supports two-step verification, an optional additional measure for users to protect their accounts when logging in.
Once enabled, users are required to verify their identity using a second method after entering their username and password when logging in on a new device. Common methods include entering a code sent to a user's mobile phone through a text message, entering a code using the Google Authenticator smartphone app, responding to a prompt on an Android/iOS device or by inserting a physical security key into the computer's USB port.
Using a security key for two-step verification was made available as an option in October 2014.
24-hour lockdowns
If an algorithm detects what Google calls "abnormal usage that may indicate that your account has been compromised", the account can be automatically locked down for between one minute and 24 hours, depending on the type of activity detected. Listed reasons for a lock-down include:
Receiving, deleting, or downloading large amounts of mail from POP/IMAP client within a short period of time.
Sending a large number of messages which fail to deliver.
Using software which automatically logs into one's account.
Leaving multiple instances of Gmail open. | Gmail | Wikipedia | 483 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
Anti-child pornography policy
Google combats child pornography through Gmail's servers in conjunction with the National Center for Missing & Exploited Children (NCMEC) to find children suffering abuse around the world. In collaboration with the NCMEC, Google creates a database of child pornography pictures. Each one of the images is given a unique numerical number known as a hash. Google then scans Gmail looking for the unique hashes. When suspicious images are located Google reports the incident to the appropriate national authorities.
History
The idea for Gmail was developed by Paul Buchheit several years before it was announced to the public. The project was known by the code name Caribou. During early development, the project was kept secret from most of Google's own engineers. This changed once the project improved, and by early 2004, most employees were using it to access the company's internal email system.
Gmail was announced to the public by Google on April 1, 2004, as a limited beta release.
In November 2006, Google began offering a Java-based application of Gmail for mobile phones.
In October 2007, Google began a process of rewriting parts of the code that Gmail used, which would make the service faster and add new features, such as custom keyboard shortcuts and the ability to bookmark specific messages and email searches. Gmail also added IMAP support in October 2007.
An update around January 2008 changed elements of Gmail's use of JavaScript, and resulted in the failure of a third-party script some users had been using. Google acknowledged the issue and helped users with workarounds.
Gmail exited the beta status on July 7, 2009.
Prior to December 2013, users had to approve to see images in emails, which acted as a security measure. This changed in December 2013, when Google, citing improved image handling, enabled images to be visible without user approval. Images are now routed through Google's secure proxy servers rather than the original external host servers. MarketingLand noted that the change to image handling means email marketers will no longer be able to track the recipient's IP address or information about what kind of device the recipient is using. However, Wired stated that the new change means senders can track the time when an email is first opened, as the initial loading of the images requires the system to make a "callback" to the original server.
Growth | Gmail | Wikipedia | 488 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
In June 2012, Google announced that Gmail had 425 million active users globally. In May 2015, Google announced that Gmail had 900 million active users, 75% of whom were using the service on mobile devices. In February 2016, Google announced that Gmail had passed 1 billion active users. In July 2017, Google announced that Gmail had passed 1.2 billion active users.
In the business sector, Quartz reported in August 2014 that, among 150 companies checked in three major categories in the United States (Fortune 50 largest companies, mid-size tech and media companies, and startup companies from the last Y Combinator incubator class), only one Fortune 50 company used Gmail – Google itself – while 60% of mid-sized companies and 92% of startup companies were using Gmail.
In May 2014, Gmail became the first app on the Google Play Store to hit one billion installations on Android devices.
Gamil Design company and misspellings
Before the introduction of Gmail, the website of product and graphic design from Gamil Design in Raleigh, North Carolina, received 3,000 hits per month. In May 2004, a Google engineer who had accidentally gone to the Gamil site a number of times contacted the company and asked if the site had experienced an increase in traffic. In fact, the site's activity had doubled. Two years later, with 600,000 hits per month, the Internet service provider wanted to charge more, and Gamil posted the message on its site "You may have arrived here by misspelling Gmail. We understand. Typing fast is not our strongest skill. But since you've typed your way here, let's share."
Google Workspace
As part of Google Workspace (formerly G Suite), Google's business-focused offering, Gmail comes with additional features, including:
Email addresses with the customer's domain name (@yourcompany.com)
99.9% guaranteed uptime with zero scheduled downtime for maintenance
Either 30 GB or unlimited storage shared with Google Drive, depending on the plan
24/7 phone and email support
Synchronization compatibility with Microsoft Outlook and other email providers
Support for add-ons that integrate third-party apps purchased from the Google Workspace Marketplace with Gmail
Reception
Gmail is noted by web developers for its early adoption of Ajax.
Awards | Gmail | Wikipedia | 481 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
Gmail was ranked second in PC World'''s "100 Best Products of 2005", behind Firefox. Gmail also won 'Honorable Mention' in the Bottom Line Design Awards 2005. In September 2006, Forbes declared Gmail to be the best webmail application for small businesses. In November 2006, Gmail received PC World's 4-star rating.
Criticism
Privacy
Google has one privacy policy that covers all of its services.
Google claims that they "will not target ads based on sensitive information, such as race, religion, sexual orientation, health, or sensitive financial categories."
Automated scanning of email content
Google's mail servers automatically scan emails for multiple purposes, including filtering spam and malware, and (until 2017) adding context-sensitive advertisements next to emails.
Privacy advocates raised concerns about this practice; concerns included that allowing email content to be read by a machine (as opposed to a person) can allow Google to keep unlimited amounts of information forever; the automated background scanning of data raises the risk that the expectation of privacy in email usage will be reduced or eroded; information collected from emails could be retained by Google for years after its current relevancy to build complete profiles on users; emails sent by users from other email providers get scanned despite never having agreed to Google's privacy policy or terms of service; Google can change its privacy policy unilaterally, and for minor changes to the policy it can do so without informing users; in court cases, governments and organizations can potentially find it easier to legally monitor email communications; at any time, Google can change its current company policies to allow combining information from emails with data gathered from use of its other services; and any internal security problem on Google's systems can potentially expose many – or all – of its users.
In 2004, thirty-one privacy and civil liberties organizations wrote a letter calling upon Google to suspend its Gmail service until the privacy issues were adequately addressed. The letter also called upon Google to clarify its written information policies regarding data retention and data sharing among its business units. The organizations also voiced their concerns about Google's plan to scan the text of all incoming messages for the purposes of ad placement, noting that the scanning of confidential email for inserting third-party ad content violates the implicit trust of an email service provider. | Gmail | Wikipedia | 469 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
On June 23, 2017, Google announced that, later in 2017, it would phase out the scanning of email content to generate contextual advertising, relying on personal data collected through other Google services instead. The company stated that this change was meant to clarify its practices and quell concerns among enterprise G Suite (now Google Workspace) customers who felt an ambiguous distinction between the free consumer and paid professional variants, the latter being advertising-free.
Lawsuits
In March 2011, a former Gmail user in Texas sued Google, claiming that its Gmail service violates users' privacy by scanning e-mail messages to serve relevant ads.
In July 2012, some California residents filed two class action lawsuits against Google and Yahoo!, claiming that they illegally intercept emails sent by individual non-Gmail or non-Yahoo! email users to Gmail and Yahoo! recipients without the senders' knowledge, consent or permission. A motion filed by Google's attorneys in the case concedes that Gmail users have "no expectation of privacy".
A court filing uncovered by advocacy group Consumer Watchdog in August 2013 revealed that Google stated in a court filing that no "reasonable expectation" exists among Gmail users in regard to the assured confidentiality of their emails. In response to a lawsuit filed in May 2013, Google explained:"... all users of email must necessarily expect that their emails will be subject to automated processing ... Just as a sender of a letter to a business colleague cannot be surprised that the recipient's assistant opens the letter, people who use web-based email today cannot be surprised if their communications are processed by the recipient's ECS [electronic communications service] provider in the course of delivery.A Google spokesperson stated to the media on August 15, 2013, that the corporation takes the privacy and security concerns of Gmail users "very seriously".
April 2014 Terms of service update
Google updated its terms of service for Gmail in April 2014 to create full transparency for its users in regard to the scanning of email content. The relevant revision states: "Our automated systems analyze your content (including emails) to provide you personally relevant product features, such as customized search results, tailored advertising, and spam and malware detection. This analysis occurs as the content is sent, received, and when it is stored." A Google spokesperson explained that the corporation wishes for its policies "to be simple and easy for users to understand." | Gmail | Wikipedia | 493 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
In response to the update, Jim Killock, executive director of the Open Rights Group, stated: "The really dangerous things that Google is doing are things like the information held in Analytics, cookies in advertising and the profiling that it is able to do on individual accounts".
Microsoft ad campaign against Google
In 2013, Microsoft launched an advertising campaign to attack Google for scanning email messages, arguing that most consumers are not aware that Google monitors their personal messages to deliver targeted ads. Microsoft claims that its email service Outlook does not scan the contents of messages and a Microsoft spokesperson called the issue of privacy "Google's kryptonite". In response, Google stated; "We work hard to make sure that ads are safe, unobtrusive and relevant ... No humans read your e-mail or Google Account information in order to show you advertisements or related information. An automated algorithm — similar to that used for features like Priority Inbox or spam filtering — determines which ads are shown." The New York Times cites "Google supporters", who say that "Microsoft's ads are distasteful, the last resort of a company that has been unsuccessful at competing against Google on the more noble battleground of products".
Other privacy issues
2010 attack from China
In January 2010, Google detected a "highly sophisticated" cyberattack on its infrastructure that originated from China. The targets of the attack were Chinese human rights activists, but Google discovered that accounts belonging to European, American and Chinese activists for human rights in China had been "routinely accessed by third parties". Additionally, Google stated that their investigation revealed that "at least" 20 other large companies from a "wide range of businesses" - including the Internet, finance, technology, media and chemical sectors – had been similarly targeted. Google was in the process of notifying those companies and it had also worked with relevant US authorities. In light of the attacks, Google enhanced the security and architecture of its infrastructure, and advised individual users to install anti-virus and anti-spyware on their computers, update their operating systems and web browsers, and be cautious when clicking on Internet links or when sharing personal information in instant messages and emails. | Gmail | Wikipedia | 444 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
Social network integration
The February 2010 launch of Google Buzz, a now defunct social network linked to Gmail, immediately drew criticism for publicly sharing details of users' contacts unless the default settings were changed. A new Gmail feature was launched in January 2014, whereby users could email people with Google+ accounts even though they do not know the email address of the recipient. Marc Rotenberg, President of the Electronic Privacy Information Center, called the feature "troubling", and compared it to the initial privacy flaw of Google Buzz's launch.
Update to DoubleClick privacy policy
In June 2016, Julia Angwin of ProPublica wrote about Google's updated privacy policy, which deleted a clause that had stated Google would not combine DoubleClick web browsing cookie information with personally identifiable information from its other services. This change has allowed Google to merge users' personally identifiable information from different Google services to create one unified ad profile for each user. After publication of the article, Google reached out to ProPublica to say that the merge would not include Gmail keywords in ad targeting.
Outages
Gmail suffered at least seven outages in 2009, causing doubts about the reliability of its service. It suffered a new outage on February 28, 2011, in which a bug caused Gmail accounts to seem empty. Google stated in a blog post that "email was never lost" and restoration was in progress. Other outages occurred on April 17, 2012, September 24, 2013, January 24, 2014, January 29, 2019 and August 20, 2020.
Google has stated that "Gmail remains more than 99.9% available to all users, and we're committed to keeping events like [the 2009 outage] notable for their rarity." | Gmail | Wikipedia | 354 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
"On behalf of" tag
In May 2009, Farhad Manjoo wrote on The New York Times blog about Gmail's "on behalf of" tag. Manjoo explained: "The problems [sic]'' is, when you try to send outbound mail from your Gmail universal inbox, Gmail adds a tag telling your recipients that you're actually using Gmail and not your office e-mail. If your recipient is using Microsoft Outlook, he'll see a message like, 'From youroffice@domain.com on behalf of yourgmail@gmail.com. Manjoo further wrote that "Google explains that it adds the tag in order to prevent your e-mail from being considered spam by your recipient; the theory is that if the e-mail is honest about its origins, it shouldn't arouse suspicion by spam checking software". The following July, Google announced a new option that would remove the "On behalf of" tag, by sending the email from the server of the other email address instead of using Gmail's servers. | Gmail | Wikipedia | 227 | 569005 | https://en.wikipedia.org/wiki/Gmail | Technology | Communication | null |
Plant propagation is the process by which new plants grow from various sources, including seeds, cuttings, and other plant parts. Plant propagation can refer to both man-made and natural processes.
Propagation typically occurs as a step in the overall cycle of plant growth. For seeds, it happens after ripening and dispersal; for vegetative parts, it happens after detachment or pruning; for asexually-reproducing plants, such as strawberry, it happens as the new plant develops from existing parts.
Countless plants are propagated each day in horticulture and agriculture.
Plant propagation is vital to agriculture and horticulture, not just for human food production but also for forest and fibre crops, as well as traditional and herbal medicine. It is also important for plant breeding.
Sexual propagation
Seeds and spores can be used for reproduction (e.g. sowing). Seeds are typically produced from sexual reproduction within a species because genetic recombination has occurred. A plant grown from seeds may have different characteristics from its parents. Some species produce seeds that require special conditions to germinate, such as cold treatment. The seeds of many Australian plants and plants from southern Africa and the American west require smoke or fire to germinate. Some plant species, including many trees, do not produce seeds until they reach maturity, which may take many years. Seeds can be difficult to acquire, and some plants do not produce seed at all. Some plants (like certain plants modified using genetic use restriction technology) may produce seed, but not a fertile seed. In certain cases, this is done to prevent the accidental spreading of these plants, for example by birds and other animals.
Asexual propagation
Plant roots, stems, and leaves have a number of mechanisms for asexual or vegetative reproduction, which horticulturists employ to multiply or clone plants rapidly, such as in tissue culture and grafting. Plants are produced using material from a single parent and as such, there is no exchange of genetic material, therefore vegetative propagation methods almost always produce plants that are identical to the parent.
In some plants, seeds can be produced without fertilization and the seeds contain only the genetic material of the parent plant. Therefore, propagation via asexual seeds or apomixis is asexual reproduction but not vegetative propagation. | Plant propagation | Wikipedia | 479 | 569180 | https://en.wikipedia.org/wiki/Plant%20propagation | Technology | Horticulture | null |
Techniques for vegetative propagation include:
Air or ground layering
Division
Grafting and bud grafting, widely used in fruit tree propagation
Micropropagation
Offsets
Stolons (runners)
Storage organs such as bulbs, corms, tubers, and rhizomes
Striking or cuttings
Twin-scaling
Heated propagator
A heated propagator is a horticultural device to maintain a warm and damp environment for seeds and cuttings to grow in. They generally provide bottom heat (maintained at a particular temperature) and high humidity, which is essential in successful seed germination and in helping cuttings to take root. In colder climates they are sometimes used for plants like peppers and sweet peas which need warmer environments (about 15°C, for the plants listed) in order to germinate. If excessive condensation forms on the inside of the lid, the gardener can open the ventilating holes to regulate the temperature a little.
Non-electric propagators (mainly a seed tray and a clear plastic lid) are a lot cheaper to purchase than a heated propagator, but without the constant regulated warmth and bottom heat provided by a heated propagator, growth of seedlings tends to be slower and less consistent (with increased risk of seeds failing to germinate).
Seed propagation mat
An electric seed-propagation mat is a heated rubber mat covered by a metal cage that is used in gardening. The mats are made so that planters containing seedlings can be placed on top of the metal cage without the risk of starting a fire. Another example is a seedling heat mat, multiple layers of durable, water resistant plastic material with insulated heating coils embedded inside (similar to underfloor heating systems, but with rubber mat instead of flooring). In extreme cold, gardeners place a loose plastic cover over the planters/mats which creates a sort of miniature greenhouse. The constant and predictable heat allows people to raise seedlings in the winter months when the weather is generally too cold for seedlings to survive naturally outside. When combined with a lighting system, many plants can be grown indoors using these mats. This can increase the variety of plants that a gardener can use. | Plant propagation | Wikipedia | 446 | 569180 | https://en.wikipedia.org/wiki/Plant%20propagation | Technology | Horticulture | null |
Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula (CH3)2. This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water. It has a relatively high boiling point. DMSO is metabolised to compounds that leave a garlic-like taste in the mouth after DMSO is absorbed by skin.
In terms of chemical structure, the molecule has idealized Cs symmetry. It has a trigonal pyramidal molecular geometry consistent with other three-coordinate S(IV) compounds, with a nonbonded electron pair on the approximately tetrahedral sulfur atom.
Synthesis and production
Dimethyl sulfoxide was first synthesized in 1866 by the Russian scientist Alexander Zaytsev, who reported his findings in 1867. Its modern use as an industrial solvent began through popularization by Thor Smedslund at the Stepan Chemical Company. Dimethyl sulfoxide is produced industrially from dimethyl sulfide, a by-product of the Kraft process, by oxidation with oxygen or nitrogen dioxide.
Reactions
Reactions with electrophiles
The sulfur center in DMSO is nucleophilic toward soft electrophiles and the oxygen is nucleophilic toward hard electrophiles. With methyl iodide it forms trimethylsulfoxonium iodide, [(CH3)3SO]I:
(CH3)2SO + CH3I → [(CH3)3SO]I
This salt can be deprotonated with sodium hydride to form the sulfur ylide:
[(CH3)3SO]I + NaH → (CH3)2S(CH2)O + NaI + H2
Acidity
The methyl groups of DMSO are only weakly acidic, with a . For this reason, the basicities of many weakly basic organic compounds have been examined in this solvent. | Dimethyl sulfoxide | Wikipedia | 426 | 569213 | https://en.wikipedia.org/wiki/Dimethyl%20sulfoxide | Physical sciences | Concepts: General | Chemistry |
Deprotonation of DMSO requires strong bases like lithium diisopropylamide and sodium hydride. Stabilization of the resultant carbanion is provided by the S(O)R group. The sodium derivative of DMSO formed in this way is referred to as dimsyl sodium. It is a base, e.g., for the deprotonation of ketones to form sodium enolates, phosphonium salts to form Wittig reagents, and formamidinium salts to form diaminocarbenes. It is also a potent nucleophile.
Oxidant
In organic synthesis, DMSO is used as a mild oxidant. It forms the basis of several selective sulfonium-based oxidation reactions including the Pfitzner–Moffatt oxidation, Corey–Kim oxidation and the Swern oxidation. The Kornblum oxidation is conceptually similar. These all involve formation of an intermediate sulfonium species (R2S+X where X is a heteroatom)
Ligand and Lewis base
Related to its ability to dissolve many salts, DMSO is a common ligand in coordination chemistry. Illustrative is the complex dichlorotetrakis(dimethyl sulfoxide)ruthenium(II) (RuCl2(dmso)4). In this complex, three DMSO ligands are bonded to ruthenium through sulfur. The fourth DMSO is bonded through oxygen. In general, the oxygen-bonded mode is more common.
In carbon tetrachloride solutions DMSO functions as a Lewis base with a variety of Lewis acids such as I2, phenols, trimethyltin chloride, metalloporphyrins, and the dimer Rh2Cl2(CO)4. The donor properties are discussed in the ECW model. The relative donor strength of DMSO toward a series of acids, versus other Lewis bases, can be illustrated by C-B plots.
Applications
Solvent | Dimethyl sulfoxide | Wikipedia | 421 | 569213 | https://en.wikipedia.org/wiki/Dimethyl%20sulfoxide | Physical sciences | Concepts: General | Chemistry |
DMSO is a polar aprotic solvent and is less toxic than other members of this class, such as dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, and hexamethylphosphoramide (HMPA). DMSO is frequently used as a solvent for chemical reactions involving salts, most notably Finkelstein reactions and other nucleophilic substitutions. It is also extensively used as an extractant in biochemistry and cell biology. Because DMSO is only weakly acidic, it tolerates relatively strong bases and as such has been extensively used in the study of carbanions. A set of non-aqueous pKa values (C-H, O-H, S-H and N-H acidities) for thousands of organic compounds have been determined in DMSO solution.
Because of its high boiling point, , DMSO evaporates slowly at normal atmospheric pressure. Samples dissolved in DMSO cannot as easily be recovered compared to other solvents, as it is very difficult to remove all traces of DMSO by conventional rotary evaporation. One technique to fully recover samples is removal of the organic solvent by evaporation followed by addition of water (to dissolve DMSO) and cryodesiccation to remove both DMSO and water. Reactions conducted in DMSO are often diluted with water to precipitate or phase-separate products. The relatively high freezing point of DMSO, , means that at, or just below, room temperature it is a solid, which can limit its utility in some chemical processes (e.g. crystallization with cooling).
In its deuterated form (DMSO-d6), it is a useful solvent for NMR spectroscopy, again due to its ability to dissolve a wide range of analytes, the simplicity of its own spectrum, and its suitability for high-temperature NMR spectroscopic studies. Disadvantages to the use of DMSO-d6 are its high viscosity, which broadens signals, and its hygroscopicity, which leads to an overwhelming H2O resonance in the 1H-NMR spectrum. It is often mixed with CDCl3 or CD2Cl2 for lower viscosity and melting points. | Dimethyl sulfoxide | Wikipedia | 485 | 569213 | https://en.wikipedia.org/wiki/Dimethyl%20sulfoxide | Physical sciences | Concepts: General | Chemistry |
DMSO is used to dissolve test compounds in in vitro drug discovery and drug design screening programs, including high-throughput screening programs. This is because it is able to dissolve both polar and nonpolar compounds, can be used to maintain stock solutions of test compounds (important when working with a large chemical library), is readily miscible with water and cell culture media, and has a high boiling point (this improves the accuracy of test compound concentrations by reducing room temperature evaporation). One limitation with DMSO is that it can affect cell line growth and viability, with low DMSO concentrations sometimes stimulating cell growth, and high DMSO concentrations sometimes inhibiting or killing cells.
DMSO is used as a vehicle in in vivo studies of test compounds. It has, for example, been employed as a co-solvent to assist absorption of the flavonol glycoside Icariin in the nematode worm Caenorhabditis elegans. As with its use in in vitro studies, DMSO has some limitations in animal models. Pleiotropic effects can occur and, if DMSO control groups are not carefully planned, then solvent effects can falsely be attributed to the prospective drug. For example, even a very low dose of DMSO has a powerful protective effect against paracetamol (acetaminophen)-induced liver injury in mice.
DMSO is finding increased use in manufacturing processes to produce microelectronic devices. It is widely used to strip photoresist in TFT-LCD 'flat panel' displays and advanced packaging applications (such as wafer-level packaging / solder bump patterning). DMSO is an effective paint stripper, being safer than many of the others such as nitromethane and dichloromethane.
Biology
DMSO is used in polymerase chain reaction (PCR) to inhibit secondary structures in the DNA template or the DNA primers. It is added to the PCR mix before reacting, where it interferes with the self-complementarity of the DNA, minimizing interfering reactions. | Dimethyl sulfoxide | Wikipedia | 442 | 569213 | https://en.wikipedia.org/wiki/Dimethyl%20sulfoxide | Physical sciences | Concepts: General | Chemistry |
DMSO in a PCR is applicable for supercoiled plasmids (to relax before amplification) or DNA templates with high GC-content (to decrease thermostability). For example, 10% final concentration of DMSO in the PCR mixture with Phusion decreases primer annealing temperature (i.e. primer melting temperature) by .
It is well known as a reversible cell cycle arrester at phase G1 of human lymphoid cells.
DMSO may also be used as a cryoprotectant, added to cell media to reduce ice formation and thereby prevent cell death during the freezing process. Approximately 10% may be used with a slow-freeze method, and the cells may be frozen at or stored in liquid nitrogen safely.
In cell culture, DMSO is used to induce differentiation of P19 embryonic carcinoma cells into cardiomyocytes and skeletal muscle cells.
Medicine
Use of DMSO in medicine dates from around 1963, when an Oregon Health & Science University Medical School team, headed by Stanley Jacob, discovered it could penetrate the skin and other membranes without damaging them and could carry other compounds into a biological system. In medicine, DMSO is predominantly used as a topical analgesic, a vehicle for topical application of pharmaceuticals, as an anti-inflammatory, and an antioxidant. Because DMSO increases the rate of absorption of some compounds through biological tissues, including skin, it is used in some transdermal drug delivery systems. Its effect may be enhanced with the addition of EDTA. It is frequently compounded with antifungal medications, enabling them to penetrate not just skin but also toenails and fingernails.
DMSO has been examined for the treatment of numerous conditions and ailments, but the U.S. Food and Drug Administration (FDA) has approved its use only for the symptomatic relief of patients with interstitial cystitis. A 1978 study concluded that DMSO brought significant relief to the majority of the 213 patients with inflammatory genitourinary disorders that were studied. The authors recommended DMSO for genitourinary inflammatory conditions not caused by infection or tumor in which symptoms were severe or patients failed to respond to conventional therapy. | Dimethyl sulfoxide | Wikipedia | 469 | 569213 | https://en.wikipedia.org/wiki/Dimethyl%20sulfoxide | Physical sciences | Concepts: General | Chemistry |
In interventional radiology, DMSO is used as a solvent for ethylene vinyl alcohol in the Onyx liquid embolic agent, which is used in embolization, the therapeutic occlusion of blood vessels.
In cryobiology DMSO has been used as a cryoprotectant and is still an important constituent of cryoprotectant vitrification mixtures used to preserve organs, tissues, and cell suspensions. Without it, up to 90% of frozen cells will become inactive. It is particularly important in the freezing and long-term storage of embryonic stem cells and hematopoietic stem cells, which are often frozen in a mixture of 10% DMSO, a freezing medium, and 30% fetal bovine serum. In the cryogenic freezing of heteroploid cell lines (MDCK, VERO, etc.) a mixture of 10% DMSO with 90% EMEM (70% EMEM + 30% fetal bovine serum + antibiotic mixture) is used. As part of an autologous bone marrow transplant the DMSO is re-infused along with the patient's own hematopoietic stem cells.
DMSO is metabolized by disproportionation to dimethyl sulfide and dimethyl sulfone. It is subject to renal and pulmonary excretion. A possible side effect of DMSO is therefore elevated blood dimethyl sulfide, which may cause a blood borne halitosis symptom.
Alternative medicine
DMSO's popularity as an alternative medicine is stated to stem from a March 1980 60 Minutes documentary "The Riddle of DMSO" and April 1980 Time magazine article covering the treatments of ardent DMSO advocate Dr. Stanley Jacob beginning in the 1960s. | Dimethyl sulfoxide | Wikipedia | 371 | 569213 | https://en.wikipedia.org/wiki/Dimethyl%20sulfoxide | Physical sciences | Concepts: General | Chemistry |
The use of DMSO as an alternative treatment for cancer is of particular concern, as it has been shown to interfere with a variety of chemotherapy drugs, including cisplatin, carboplatin, and oxaliplatin. There is insufficient evidence to support the hypothesis that DMSO has any effect, and most sources agree that its history of side effects when tested warrants caution when using it as a dietary supplement, for which it is marketed heavily with the usual disclaimer. DMSO is an ingredient in some products listed by the U.S. FDA as fake cancer cures and the FDA has had a running battle with distributors. One such distributor is Mildred Miller, who promoted DMSO for a variety of disorders and was consequently convicted of Medicare fraud.
Veterinary medicine
DMSO is commonly used in veterinary medicine as a liniment for horses, alone or in combination with other ingredients. In the latter case, often, the intended function of the DMSO is as a solvent, to carry the other ingredients across the skin. Also in horses, DMSO is used intravenously, again alone or in combination with other drugs. It is used alone for the treatment of increased intracranial pressure and/or cerebral edema in horses.
Taste
The perceived garlic taste upon skin contact with DMSO may be due to nonolfactory activation of TRPA1 receptors in trigeminal ganglia. Unlike dimethyl and diallyl disulfides (which have odors resembling garlic), mono- and tri- sulfides (which typically have foul odors), and similar odiferous sulfur compounds, the pure chemical DMSO is odorless.
Safety
Toxicity
DMSO is a non-toxic solvent with a median lethal dose higher than ethanol (DMSO: LD50, oral, rat, 14,500 mg/kg; ethanol: LD50, oral, rat, 7,060 mg/kg).
DMSO can cause contaminants, toxins, and medicines to be absorbed through the skin, which may cause unexpected effects. DMSO is thought to increase the effects of blood thinners, steroids, heart medicines, sedatives, and other drugs. In some cases this could be harmful or dangerous. | Dimethyl sulfoxide | Wikipedia | 470 | 569213 | https://en.wikipedia.org/wiki/Dimethyl%20sulfoxide | Physical sciences | Concepts: General | Chemistry |
Because DMSO easily penetrates the skin, substances dissolved in DMSO may quickly be absorbed. Glove selection is important when working with DMSO. Butyl rubber, fluoroelastomer, neoprene, or thick (15mil / 0.4mm) latex gloves are recommended. Nitrile gloves, which are very commonly used in chemical laboratories, may protect from brief contact but have been found to degrade rapidly with exposure to DMSO.
Regulation
In Australia, it is listed as a Schedule 4 (S4) Drug, and a company has been prosecuted for adding it to products as a preservative.
Clinical safety
Early clinical trials with DMSO were stopped because of questions about its safety, especially its ability to harm the eye. The most commonly reported side effects include headaches and burning and itching on contact with the skin. Strong allergic reactions have been reported.
On September 9, 1965, The Wall Street Journal reported that a manufacturer of the chemical warned that the death of an Irish woman after undergoing DMSO treatment for a sprained wrist may have been due to the treatment, although no autopsy was done, nor was a causal relationship established. Clinical research using DMSO was halted and did not begin again until the National Academy of Sciences (NAS) published findings in favor of DMSO in 1972. In 1978, the US FDA approved DMSO for treating interstitial cystitis. In 1980, the US Congress held hearings on claims that the FDA was slow in approving DMSO for other medical uses. In 2007, the US FDA granted "fast track" designation on clinical studies of DMSO's use in reducing brain tissue swelling following traumatic brain injury.
DMSO exposure to developing mouse brains can produce brain degeneration. This neurotoxicity could be detected at doses as low as 0.3mL/kg, a level exceeded in children exposed to DMSO during bone marrow transplant. | Dimethyl sulfoxide | Wikipedia | 404 | 569213 | https://en.wikipedia.org/wiki/Dimethyl%20sulfoxide | Physical sciences | Concepts: General | Chemistry |
Odor problem
DMSO disposed into sewers can cause odor problems in municipal effluents: waste water bacteria transform DMSO under hypoxic (anoxic) conditions into dimethyl sulfide (DMS) that has a strong disagreeable odor, similar to rotten cabbage. However, chemically pure DMSO is odorless because of the lack of C-S-C (sulfide) and C-S-H (mercaptan) linkages. Deodorization of DMSO is achieved by removing the odorous impurities it contains.
Explosion hazard
Dimethyl sulfoxide can produce an explosive reaction when exposed to acyl chlorides; at a low temperature, this reaction produces the oxidant for Swern oxidation.
DMSO can decompose at the boiling temperature of 189 °C at normal pressure, possibly leading to an explosion. The decomposition is catalyzed by acids and bases and therefore can be relevant at even lower temperatures. A strong to explosive reaction also takes place in combination with halogen compounds, metal nitrides, metal perchlorates, sodium hydride, periodic acid and fluorinating agents. | Dimethyl sulfoxide | Wikipedia | 240 | 569213 | https://en.wikipedia.org/wiki/Dimethyl%20sulfoxide | Physical sciences | Concepts: General | Chemistry |
Dimethyl ether (DME; also known as methoxymethane) is the organic compound with the formula CH3OCH3,
(sometimes ambiguously simplified to C2H6O as it is an isomer of ethanol). The simplest ether, it is a colorless gas that is a useful precursor to other organic compounds and an aerosol propellant that is currently being demonstrated for use in a variety of fuel applications.
Dimethyl ether was first synthesised by Jean-Baptiste Dumas and Eugene Péligot in 1835 by distillation of methanol and sulfuric acid.
Production
Approximately 50,000 tons were produced in 1985 in Western Europe by dehydration of methanol:
The required methanol is obtained from synthesis gas (syngas). Other possible improvements call for a dual catalyst system that permits both methanol synthesis and dehydration in the same process unit, with no methanol isolation and purification.
Both the one-step and two-step processes above are commercially available. The two-step process is relatively simple and start-up costs are relatively low. A one-step liquid-phase process is in development.
From biomass
Dimethyl ether is a synthetic second generation biofuel (BioDME), which can be produced from lignocellulosic biomass. The EU is considering BioDME in its potential biofuel mix in 2030; It can also be made from biogas or methane from animal, food, and agricultural waste, or even from shale gas or natural gas.
The Volvo Group is the coordinator for the European Community Seventh Framework Programme project BioDME where Chemrec's BioDME pilot plant is based on black liquor gasification in Piteå, Sweden.
Applications
The largest use of dimethyl ether is as the feedstock for the production of the methylating agent, dimethyl sulfate, which entails its reaction with sulfur trioxide:
Dimethyl ether can also be converted into acetic acid using carbonylation technology related to the Monsanto acetic acid process:
Laboratory reagent and solvent
Dimethyl ether is a low-temperature solvent and extraction agent, applicable to specialised laboratory procedures. Its usefulness is limited by its low boiling point (), but the same property facilitates its removal from reaction mixtures. Dimethyl ether is the precursor to the useful alkylating agent, trimethyloxonium tetrafluoroborate. | Dimethyl ether | Wikipedia | 507 | 569315 | https://en.wikipedia.org/wiki/Dimethyl%20ether | Physical sciences | Esters and ethers | Chemistry |
Niche applications
A mixture of dimethyl ether and propane is used in some over-the-counter "freeze spray" products to treat warts by freezing them. In this role, it has supplanted halocarbon compounds (Freon).
Dimethyl ether is also a component of certain high temperature "Map-Pro" blowtorch gas blends, supplanting the use of methyl acetylene and propadiene mixtures.
Dimethyl ether is also used as a propellant in aerosol products. Such products include hair spray, bug spray and some aerosol glue products.
Research
Fuel
A potentially major use of dimethyl ether is as substitute for propane in LPG used as fuel in household and industry. Dimethyl ether can also be used as a blendstock in propane autogas.
It is also a promising fuel in diesel engines, and gas turbines. For diesel engines, an advantage is the high cetane number of 55, compared to that of diesel fuel from petroleum, which is 40–53. Only moderate modifications are needed to convert a diesel engine to burn dimethyl ether. The simplicity of this short carbon chain compound leads to very low emissions of particulate matter during combustion. For these reasons as well as being sulfur-free, dimethyl ether meets even the most stringent emission regulations in Europe (EURO5), U.S. (U.S. 2010), and Japan (2009 Japan).
At the European Shell Eco Marathon, an unofficial World Championship for mileage, vehicle running on 100 % dimethyl ether drove 589 km/L (169.8 cm3/100 km), fuel equivalent to gasoline with a 50 cm3 displacement 2-stroke engine. As well as winning they beat the old standing record of 306 km/liter (326.8 cm3/100 km), set by the same team in 2007.
To study the dimethyl ether for the combustion process a chemical kinetic mechanism is required which can be used for Computational fluid dynamics calculation. | Dimethyl ether | Wikipedia | 419 | 569315 | https://en.wikipedia.org/wiki/Dimethyl%20ether | Physical sciences | Esters and ethers | Chemistry |
Refrigerant
Dimethyl ether is a refrigerant with ASHRAE refrigerant designation R-E170. It is also used in refrigerant blends with e.g. ammonia, carbon dioxide, butane and propene.
Dimethyl ether was the first refrigerant. In 1876, the French engineer Charles Tellier bought the ex-Elder-Dempster a 690 tons cargo ship Eboe and fitted a methyl-ether refrigerating plant of his design. The ship was renamed Le Frigorifique and successfully imported a cargo of refrigerated meat from Argentina. However the machinery could be improved and in 1877 another refrigerated ship called Paraguay with a refrigerating plant improved by Ferdinand Carré was put into service on the South American run.
Safety
Unlike other alkyl ethers, dimethyl ether resists autoxidation. Dimethyl ether is also relatively non-toxic, although it is highly flammable. On July 28, 1948, a BASF factory in Ludwigshafen suffered an explosion after 30 tonnes of dimethyl ether leaked from a tank and ignited in the air. 200 people died, and a third of the industrial plant was destroyed.
Data sheet
Routes to produce dimethyl ether
Vapor pressure | Dimethyl ether | Wikipedia | 269 | 569315 | https://en.wikipedia.org/wiki/Dimethyl%20ether | Physical sciences | Esters and ethers | Chemistry |
The white-tailed deer (Odocoileus virginianus), also known commonly as the whitetail and the Virginia deer, is a medium-sized species of deer native to North America, Central America, and South America as far south as Peru and Bolivia, where it predominately inhabits high mountain terrains of the Andes. It has also been introduced to New Zealand, all the Greater Antilles in the Caribbean (Cuba, Jamaica, Hispaniola, and Puerto Rico), and some countries in Europe, such as the Czech Republic, Finland, France, Germany, Romania and Serbia. In the Americas, it is the most widely distributed wild ungulate.
In North America, the species is widely distributed east of the Rocky Mountains as well as in southwestern Arizona and most of Mexico, except Lower California. It is mostly displaced by the black-tailed or mule deer (Odocoileus hemionus) from that point west except for mixed deciduous riparian corridors, river valley bottomlands, and lower foothills of the northern Rocky Mountain region from Wyoming west to eastern Washington and eastern Oregon and north to northeastern British Columbia and southern Yukon, including in the Montana valley and foothill grasslands. The westernmost population of the species, known as the Columbian white-tailed deer, was once widespread in the mixed forests along the Willamette and Cowlitz River valleys of western Oregon and southwestern Washington, but current numbers are considerably reduced, and it is classified as near-threatened. This population is separated from other white-tailed deer populations.
Texas is home to the most white-tailed deer of any U.S. state or Canadian province, with an estimated population of 5.3 million. High populations of white-tailed deer exist in the Edwards Plateau of central Texas. Michigan, Minnesota, Iowa, Mississippi, Missouri, New Jersey, Illinois, Wisconsin, Maryland, New York, North Dakota, Ohio, and Indiana also boast high deer densities. The conversion of land adjacent to the Canadian Rockies to agriculture use and partial clear-cutting of coniferous trees, resulting in widespread deciduous vegetation, has been favorable to the white-tailed deer and has pushed its distribution to as far north as Yukon. Populations of deer around the Great Lakes have expanded their range northwards, also due to conversion of land to agricultural use, with local caribou, elk, and moose populations declining. White-tailed deer are crepuscular, meaning they are most active during the dawn and dusk hours.
Taxonomy | White-tailed deer | Wikipedia | 504 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Some taxonomists have attempted to separate white-tailed deer into a host of subspecies, based largely on morphological differences. Genetic studies, however, suggest fewer subspecies within the animal's range, as compared to the 30 to 40 subspecies that some scientists have described in the last century. The Florida Key deer, O. v. clavium, and the Columbian white-tailed deer, O. v. leucurus, are both listed as endangered under the U.S. Endangered Species Act. In the United States, the Virginia white-tail, O. v. virginianus, is among the most widespread subspecies. Several local deer populations, especially in the Southern United States, are descended from white-tailed deer transplanted from various localities east of the Continental Divide. Some of these deer populations may have been from as far north as the Great Lakes region to as far west as Texas, yet are also quite at home in the Appalachian and Piedmont regions of the south. These deer, over time, have intermixed with the local indigenous deer (O. v. virginianus and/or O. v. macrourus) populations.
Central and South America have a complex number of white-tailed deer subspecies that range from Guatemala to as far south as Peru. This list of subspecies of deer is more exhaustive than the list of North American subspecies, and the number of subspecies is also questionable. However, the white-tailed deer populations in these areas are difficult to study, due to overhunting in many parts and a lack of protection. Some areas no longer carry deer, so assessing the genetic difference of these animals is difficult.
Subspecies
There are 26 subspecies; seventeen of these occur in North America, ordered alphabetically. (Numbers in parentheses are range map locations.) | White-tailed deer | Wikipedia | 358 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
North and Central America
O. v. acapulcensis (1)– (Southern coastal Mexico)
O. v. borealis (2)– northern white-tailed deer (the largest and darkest of the white-tailed deer)
O. v. carminis (4)– Carmen Mountains white-tailed deer (Texas-Mexico border)
O. v. chiriquensis (5)– (Panama)
O. v. clavium (6)– Key deer or Florida Keys white-tailed deer
O. v. couesi (7)– Coues' white-tailed deer, Arizona white-tailed deer, or fantail deer
O. v. dacotensis (9)– Dakota white-tailed deer or northern plains white-tailed deer (most northerly distribution, rivals the northern white-tailed deer in size)
O. v. hiltonensis (12)– Hilton Head Island white-tailed deer
O. v. leucurus (13)– Columbian white-tailed deer (Oregon and western coastal area)
O. v. macrourus (14)– Kansas white-tailed deer
O. v. mcilhennyi (15)– Avery Island white-tailed deer
O. v. mexicanus (17)– (central Mexico)
O. v. miquihuanensis (18)– (northern central Mexico)
O. v. nelsoni (19)– (southern Mexico to Nicaragua)
O. v. nemoralis (20)– Nicaraguan white-tailed deer (Gulf of Mexico to Suriname in South America; further restricted from Honduras to Panama)
O. v. nigribarbis (21)– Blackbeard Island white-tailed deer
O. v. oaxacensis (22)– (southern Mexico)
O. v. ochrourus (23)– northwestern white-tailed deer or northern Rocky Mountains white-tailed deer
O. v. osceola (24)– Florida coastal white-tailed deer
O. v. rothschildi (26)– (Coiba Island, Panama)
O. v. seminolus (27)– Florida white-tailed deer
O. v. sinaloae (28)– (southern Mexico)
O. v. taurinsulae (29)– Bulls Island white-tailed deer (Bulls Island, South Carolina)
O. v. texanus (30)– Texas white-tailed deer
O. v. thomasi (31)– (southern Mexico) | White-tailed deer | Wikipedia | 510 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
O. v. toltecu (32)– (southern Mexico to El Salvador)
O. v. venatorius (35)– Hunting Island white-tailed deer (Hunting Island, South Carolina)
O. v. veraecrucis (36)– (eastern coastal Mexico)
O. v. virginianus (37)– Virginia white-tailed deer or southern white-tailed deer
O. v. yucatanesis (38)– (northern Yucatán, Mexico) | White-tailed deer | Wikipedia | 97 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
South America
O. v. cariacou (3)– (French Guiana and northern Brazil)
O. v. curassavicus (8)– (Curaçao)
O. v. goudotii (10)– (Colombia (Andes) and western Venezuela)
O. v. gymnotis (11)– South American white-tailed deer (northern half of Venezuela, including Venezuela's Llanos region)
O. v. margaritae (16)– (Margarita Island)
O. v. nemoralis (20)– Nicaraguan white-tailed deer (Gulf of Mexico to Suriname in South America; further restricted from Honduras to Panama)
O. v. peruvianus (25)– South American white-tailed deer or Andean white-tailed deer (most southerly distribution in Peru and possibly Bolivia)
O. v. tropicalis (33)– Peru and Ecuador (possibly Colombia)
O. v. ustus (34)– Ecuador (possibly southern Colombia and northern Peru)
Description
The white-tailed deer's coat is a reddish-brown in the spring and summer, and turns to a grey-brown throughout the fall and winter. The white-tailed deer can be recognized by the characteristic white underside to its tail. It raises its tail when it is alarmed to warn the predator that it has been detected.
An indication of a deer's age is the length of the snout and the color of the coat, with older deer tending to have longer snouts and grayer coats.
A population of white-tailed deer in New York is entirely white except for the nose and hooves – not albino – in color. The former Seneca Army Depot in Romulus, New York, has the largest known concentration of white deer. Strong conservation efforts have allowed white deer to thrive within the confines of the depot.
The white-tailed deer's horizontally slit pupil allows for good night vision and color vision during the day. Whitetails process visual images at a much more rapid rate than humans and are better at detecting motion in low-light conditions.
Size and weight | White-tailed deer | Wikipedia | 426 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
The white-tailed deer is highly variable in size, generally following both Allen's rule and Bergmann's rule that the average size is larger farther away from the equator. North American male deer (also known as a buck) usually weigh , but mature bucks over have been recorded in the northernmost reaches of their native range, namely Minnesota, Ontario, and Manitoba. In 1926, Carl J. Lenander Jr. took a white-tailed buck near Tofte, Minnesota, that weighed after it was field-dressed (internal organs and blood removed) and was estimated at when alive. The female (doe) in North America usually weighs from . White-tailed deer from the tropics and the Florida Keys are markedly smaller-bodied than temperate populations, averaging , with an occasional adult female as small as . White-tailed deer from the Andes are larger than other tropical deer of this species and have thick, slightly woolly-looking fur. Length ranges from , including a tail of , and the shoulder height is . Including all races, the average summer weight of adult males is and is in adult females. It is among the largest deer species in North America, and is also one of the largest in South America, behind only the marsh deer.
Deer have dichromatic (two-color) vision with blue and yellow primaries; humans normally have trichromatic vision. Thus, deer poorly distinguish the oranges and reds that stand out so well to humans. This makes it very convenient to use deer-hunter orange as a safety color on caps and clothing to avoid accidental shootings during hunting seasons.
Antlers | White-tailed deer | Wikipedia | 325 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Males regrow their antlers every year. About one in 10,000 females also has antlers, although this is usually associated with freemartinism. Bucks without branching antlers are often termed "spikehorn", "spiked bucks", "spike bucks", or simply "spikes/spikers". The spikes can be quite long or very short. Length and branching of antlers are determined by nutrition, age, and genetics. Rack growth tends to be very important from late spring until about a month before velvet sheds. Healthy deer in some areas that are well-fed can have eight-point branching antlers as yearlings (1.5 years old). Although antler size typically increases with age, antler characteristics (e.g., number of points, length, or thickness of the antlers) are not good indicators of buck age, in general, because antler development is influenced by the local environment. The individual deer's nutritional needs for antler growth is dependent on the diet of the deer, particularly protein intake. Good antler-growth nutritional needs (calcium) and good genetics combine to produce wall trophies in some of their range. Spiked bucks are different from "button bucks" or "nubbin' bucks", that are male fawns and are generally about six to nine months of age during their first winter. They have skin-covered nobs on their heads. They can have bony protrusions up to in length, but that is very rare, and they are not the same as spikes.
Antlers begin to grow in late spring, covered with a highly vascularised tissue known as velvet. Bucks either have a typical or atypical antler arrangement. Typical antlers are symmetrical and the points grow straight up off the main beam. Atypical antlers are asymmetrical and the points may project at any angle from the main beam. These descriptions are not the only limitations for typical and atypical antler arrangement. The Boone and Crockett or Pope and Young scoring systems also define relative degrees of typicality and atypicality by procedures to measure what proportion of the antlers is asymmetrical. Therefore, bucks with only slight asymmetry are scored as "typical". A buck's inside spread can be from . Bucks shed their antlers when all females have been bred, from late December to February. | White-tailed deer | Wikipedia | 488 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Ecology
White-tailed deer are generalists and can adapt to a wide variety of habitats. The largest deer occur in the temperate regions of North America. The northern white-tailed deer (O. v. borealis), Dakota white-tailed deer (O. v. dacotensis), and northwest white-tailed deer (O. v. ochrourus) are some of the largest animals, with large antlers. The smallest deer occur in the Florida Keys and in partially wooded lowlands in the Neotropics.
Although most often thought of as forest animals depending on relatively small openings and edges, white-tailed deer can equally adapt themselves to life in more open prairie, savanna woodlands, and sage communities as in the Southwestern United States and northern Mexico. These savanna-adapted deer have relatively large antlers in proportion to their body size and large tails. Also, a noticeable difference exists in size between male and female deer of the savannas. The Texas white-tailed deer (O. v. texanus), of the prairies and oak savannas of Texas and parts of Mexico, are the largest savanna-adapted deer in the Southwest, with impressive antlers that might rival deer found in Canada and the northern United States. Populations of Arizona (O. v. couesi) and Carmen Mountains (O. v. carminis) white-tailed deer inhabit montane mixed oak and pine woodland communities. The Arizona and Carmen Mountains deer are smaller, but may also have impressive antlers, considering their size. The white-tailed deer of the Llanos region of Colombia and Venezuela (O. v. apurensis and O. v. gymnotis) have antler dimensions similar to the Arizona white-tailed deer. | White-tailed deer | Wikipedia | 353 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
In some western regions of North America, the white-tailed deer range overlaps with those of the mule deer. White-tail incursions in the Trans-Pecos region of Texas have resulted in some hybrids. In the extreme north of the range, their habitat is also used by moose in some areas. White-tailed deer may occur in areas that are also exploited by elk (wapiti) such as in mixed deciduous river valley bottomlands and formerly in the mixed deciduous forest of eastern United States. In places such as Glacier National Park in Montana and several national parks in the Columbian Mountains (Mount Revelstoke National Park) and Canadian Rocky Mountains, as well as in the Yukon Territory (Yoho National Park and Kootenay National Park), white-tailed deer are shy and more reclusive than the coexisting mule deer, elk, and moose.
Central American white-tailed deer prefer tropical and subtropical dry broadleaf forests, seasonal mixed deciduous forests, savanna, and adjacent wetland habitats over dense tropical and subtropical moist broadleaf forests. South American subspecies of white-tailed deer live in two types of environments. The first type, similar to the Central American deer, consists of savannas, dry deciduous forests, and riparian corridors that cover much of Venezuela and eastern Colombia. The other type is the higher elevation mountain grassland/mixed forest ecozones in the Andes Mountains, from Venezuela to Peru. The Andean white-tailed deer seem to retain gray coats due to the colder weather at high altitudes, whereas the lowland savanna forms retain the reddish brown coats. South American white-tailed deer, like those in Central America, also generally avoid dense moist broadleaf forests.
Since the second half of the 19th century, white-tailed deer have been introduced to Europe. A population in the Brdy area remains stable today. In 1935, white-tailed deer were introduced to Finland. The introduction was successful, and the deer began spreading through northern Scandinavia and southern Karelia, competing with, and sometimes displacing, native species. The 2020 population of some 109,000 deer originated from four animals provided by Finnish Americans from Minnesota. | White-tailed deer | Wikipedia | 435 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Diet
White-tailed deer eat large amounts of food, commonly eating legumes and foraging on other plants, including shoots, leaves, cacti (in deserts), prairie forbs, and grasses. They also eat acorns, fruit, and corn. Their multi-chambered stomachs allow them to eat some foods humans cannot, such as mushrooms (even those that are toxic to humans) and poison ivy. Their diets vary by season according to the availability of food sources. They also eat hay, grass, white clover, and other foods they can find in a farmyard. Though almost entirely herbivorous, white-tailed deer have been known to opportunistically feed on nesting songbirds, field mice, and birds trapped in mist nets, if the need arises. When additional amounts of minerals such as calcium are needed in their diet, they can resort to osteophagy, chewing on bones of dead animals. A grown deer can eat around of vegetable matter annually. A population of around can start to destroy the forest environment in their foraging area.
Their diet consists mostly of woody shoots, stems, and leaves of woody plants as well as grasses, cultivated crops, nuts, berries, and wildflowers. The items they feed on are not generally abundant in mature forests and are mostly found at "edges". Edges are described as a "mosaic of vegetation types that create numerous interwoven 'edges' where their respective boundaries intersect" and provide optimum cover for browsers such as the white-tailed deer. White-tailed deer can easily thrive in suburban areas, as a combination of increased safety from some predators (including human hunting), high quality and abundance of foods in home gardens, city parks, open farmland, and other factors all create landscapes with an abundance of edge habitat. | White-tailed deer | Wikipedia | 369 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
The white-tailed deer is a ruminant, which means it has a four-chambered stomach. Each chamber has a different and specific function that allows the deer to eat a variety of different foods, digesting it at a later time in a safe area of cover. The stomach hosts a complex set of microbes that change as the deer's diet changes through the seasons. If the microbes necessary for digestion of a particular food (e.g., hay) are absent, it will not be digested. Utilizing foregut fermentation, the fermented ingesta (known as cud) is regurgitated and chewed again, to mix it with saliva and reduce the particle size. Smaller particle size allows for increased nutrient absorption and the saliva is important because it provides liquid for the microbial population, recirculates nitrogen and minerals, and acts as a buffer for the rumen pH.
Predators
There are several natural predators of white-tailed deer, with wolves, cougars, American alligators, jaguars (in the American southwest, Mexico, and Central and South America) and humans being the most effective natural predators. Aside from humans, these predators frequently pick out easily caught young or infirm deer (which is believed to improve the genetic stock of a population), but can and do take healthy adults of any size. Bobcats, Canada lynx, grizzly and American black bears, wolverines, and packs of coyotes usually prey mainly on fawns. Bears may sometimes attack adult deer, while lynxes, coyotes, and wolverines are most likely to take adult deer when the ungulates are weakened by harsh winter weather. Many scavengers rely on deer as carrion, including New World vultures, raptors, red and gray foxes, and corvids. Few wild predators can afford to be picky and any will readily consume deer as carrion. Records exist of American crows and common ravens attempting to prey on white-tailed deer fawns by pecking around their face and eyes, though no accounts of success are given. Occasionally, both golden and bald eagles may capture deer fawns with their talons. In one case, a golden eagle was filmed in Illinois unsuccessfully trying to prey on a large mature white-tailed deer. | White-tailed deer | Wikipedia | 467 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
White-tailed deer typically respond to the presence of potential predators by breathing very heavily (also called blowing) and fleeing. When they blow, the sound alerts other deer in the area. As they run, the flash of their white tails warns other deer. This especially serves to warn fawns when their mother is alarmed. Most natural predators of white-tailed deer hunt by ambush, although canids may engage in an extended chase, hoping to exhaust the prey. Felids typically try to suffocate the deer by biting the throat. Cougars and jaguars will initially knock the deer off balance with their powerful forelegs, whereas the smaller bobcats and lynxes will jump astride the deer to deliver a killing bite. In the case of canids and wolverines, the predators bite at the limbs and flanks, hobbling the deer, until they can reach vital organs and kill it through loss of blood. Bears, which usually target fawns, often simply knock down the prey and then start eating it while it is still alive. Alligators snatch deer as they try to drink from or cross bodies of water, grabbing them with their powerful jaws and dragging them into the water to drown. | White-tailed deer | Wikipedia | 243 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Most primary natural predators of white-tailed deer have been essentially extirpated in eastern North America, with a very small number of reintroduced critically endangered red wolves, around North Carolina and a small remnant population of Florida panthers, a subspecies of the cougar. Gray wolves, the leading cause of deer mortality where they overlap, co-occur with whitetails in northern Minnesota, Wisconsin, Michigan, and most of Canada. This almost certainly plays a role in the overpopulation issues with this species. Coyotes, widespread and with a rapidly expanding population, are often the only major nonhuman predator of the species in the Eastern U.S., besides an occasional domestic dog. In some areas, American black bears are also significant predators. In north-central Pennsylvania, black bears were found to be nearly as common predators of fawns as coyotes. Bobcats, still fairly widespread, usually only exploit deer as prey when smaller prey is scarce. Discussions have occurred regarding the possible reintroduction of gray wolves and cougars to sections of the eastern United States, largely because of the apparent controlling effect they have through deer predation on local ecosystems, as has been illustrated in the reintroduction of wolves to Yellowstone National Park and their controlling effect on previously overpopulated elk. However, due to the heavy urban development in much of the Eastern U.S., and fear for livestock and human lives, such ideas have ultimately been rejected by local communities and/or by government services and have not been carried through.
In areas where they are heavily hunted by humans, deer run almost immediately from people and are quite wary even where not heavily hunted.
White-tailed deer can run faster than their predators and have been recorded sprinting at speeds of per hour and sustaining speeds of per hour over distances of ; this ranks them amongst the fastest of all deer, alongside the Eurasian roe deer. They can also jump high and up to forward. When shot at, a white-tailed deer will run at high speeds with its tail down. If frightened, the deer will hop in a zig-zag with its tail straight up. If the deer feels extremely threatened, however, it may choose to attack, charging the person or predator posing the threat, using its antlers or, if none are present, its head to fight off its target. | White-tailed deer | Wikipedia | 469 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Forest alteration
In certain parts of eastern North America, high deer densities have caused large reductions in plant biomass, including the density and heights of certain forest wildflowers, tree seedlings, and shrubs. Although they can be seen as a nuisance species, white-tailed deer also play an important role in biodiversity. At the same time, increases in browse-tolerant grasses and sedges and unpalatable ferns have often accompanied intensive deer herbivory. Changes to the structure of forest understories have, in turn, altered the composition and abundance of forest bird communities in some areas. In regions of intermediate density, deer activity has also been shown to increase herbaceous plant diversity, particularly in disturbed areas, by reducing competitively dominant plants; and to increase the growth rates of important canopy trees, perhaps by increased nutrient inputs into the soil.
In northeastern hardwood forests, high-density deer populations affect plant succession, particularly following clear-cuts and patch cuts. In succession without deer, annual herbs and woody plants are followed by commercially valuable, shade-tolerant oak and maple. The shade-tolerant trees prevent the invasion of less commercial cherry and American beech, which are stronger nutrient competitors, but not as shade tolerant. Although deer eat shade-tolerant plants and acorns, this is not the only way deer can shift the balance in favor of nutrient competitors. Deer consuming earlier-succession plants allows in enough light for nutrient competitors to invade. Since slow-growing oaks need several decades to develop root systems sufficient to compete with faster-growing species, removal of the canopy prior to that point amplifies the effect of deer on succession. High-density deer populations possibly could browse eastern hemlock seedlings out of existence in northern hardwood forests; however, this scenario seems unlikely, given that deer browsing is not considered the critical factor preventing hemlock re-establishment at large scales.
Ecologists have also expressed concern over the facilitative effect high deer populations have on invasions of exotic plant species. In a study of eastern hemlock forests, browsing by white-tailed deer caused populations of three exotic plants to rise faster than they do in the areas which are absent of deer. Seedlings of the three invading species rose exponentially with deer density, while the most common native species fell exponentially with deer density, because deer were preferentially eating the native species. The effects of deer on the invasive and native plants were magnified in cases of canopy disturbance. | White-tailed deer | Wikipedia | 498 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Population and controls
The white-tailed deer population in North America has declined by several million since 2000, but as of 2017 is considered healthy and is approximately equal to the historical pre-colonization white-tailed population on the continent. The species has rebounded considerably after being overhunted nearly to extinction in the late 1800s and very early 1900s. By contrast, the species' closest cousins (blacktail deer and mule deer) have seen their populations cut by more than half in North America after peaking in 1960 and have never regained their pre-colonization numbers. In the 21st century, the loss of natural predators has been more than offset by the ongoing loss of natural habitat to human development, and changes to logging operations.
Several methods have been developed to curb the population of white-tailed deer in suburban areas where they are perceived as overabundant, and these can be separated into lethal and nonlethal strategies. Most common in the U.S. is the use of extended hunting as population control, as well as a way to provide meat for humans. In Maryland and many other states, a state agency sets regulations on bag limits and hunting in the area depending on the deer population levels assessed. Hunting seasons may fluctuate in duration, or restrictions may be set to affect how many deer or what type of deer can be hunted in certain regions. For the 2015–2016 white-tailed deer-hunting season, some areas allowed only the hunting of antlerless white-tailed deer. These included young bucks and females, which encouraged the culling of does, aiding in population control.
A more targeted yet more expensive removal strategy than public hunting is a method referred to as sharpshooting. Sharpshooting can be an option when the area inhabited by the deer is unfit for public hunting. This strategy may work in areas close to human populations, since it is done by professional marksmen, and requires a submitted plan of action to the city with details of the time and location of the action, as well as number of deer to be culled. Another controversial method involves trapping the deer in a net or other trap, and then administering a chemical euthanizing agent or extermination by firearm. A main issue in questioning the humaneness of this method is the stress that the deer endure while trapped and awaiting extermination. | White-tailed deer | Wikipedia | 469 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Nonlethal methods include contraceptive injections, sterilization, and translocation of deer. While lethal methods have municipal support as being the most effective in the short term, some opponents of this view suggest that extermination has no significant impact on deer populations. Opponents of contraceptive methods point out that fertility control cannot provide meat and proves ineffective over time as populations in open-field systems move about. Concerns are voiced that the contraceptives have not been adequately researched for the effect they could have on humans. Fertility control also does nothing to affect the current population and the effects their grazing may be having on the forest plant make-up.
Translocation has been considered overly costly for the little benefit it provides. Deer experience high stress and are at high risk of dying in the process, putting into question its humaneness. Another concern regarding translocation is the possible spreading of chronic wasting disease to unaffected deer populations and concerns about exposure to human populations.
In addition to the danger of deer-vehicle collisions the National Agricultural Statistics Service (NASS) reported that the estimated loss in field crops, nuts, fruits, and vegetables in 2001 was near $765 million, (equivalent to $ in ).
Behavior
Males compete for the opportunity of breeding females. Sparring among males determines a dominance hierarchy. Bucks attempt to copulate with as many females as possible, losing physical condition, since they rarely eat or rest during the rut. The general geographical trend is for the rut to be shorter in duration at increased latitude. Many factors determine how intense the "rutting season" will be; air temperature is a major one. Any time the temperature rises above , the males do much less traveling looking for females, else they will be subject to overheating or dehydrating. Another factor for the strength of rutting activity is competition. If numerous males are in a particular area, then they compete more with the females. If fewer males or more females are present, then the selection process will not need to be as competitive.
Reproduction
Females enter estrus, colloquially called the rut, in the autumn, normally in late October or early November, triggered mainly by the declining photoperiod. Sexual maturation of females depends on population density, as well as the availability of food. Young females often flee from an area heavily populated with males. Some does may be as young as six months when they reach sexual maturity, but the average age of maturity is 18 months. Copulation consists of a brief copulatory jump. | White-tailed deer | Wikipedia | 512 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Females give birth to one to three spotted young, known as fawns, in mid-to-late spring, generally in May or June. Fawns lose their spots during the first summer and weigh from by the first winter. Male fawns tend to be slightly larger and heavier than females. For the first four weeks, fawns are hidden in vegetation by their mothers, who nurse them four to five times a day. This strategy keeps scent levels low to avoid predators. After about a month, the fawns are then able to follow their mothers on foraging trips. They are usually weaned after 8–10 weeks, but cases have been seen where mothers have continued to allow nursing long after the fawns have lost their spots (for several months, or until the end of fall) as seen by rehabilitators and other studies. Males leave their mothers after a year and females leave after two.
Bucks are generally sexually mature at 1.5 years old and begin to breed even in populations stacked with older bucks.
Communication
White-tailed deer have many forms of communication involving sounds, scent, body language, and marking. In addition to the blowing as mentioned above in the presence of danger, all white-tailed deer can produce audible noises unique to each animal. Fawns release a high-pitched squeal, known as a bleat, to call out to their mothers. This bleat deepens as the fawn grows until it becomes the grunt of the mature deer, a guttural sound that attracts the attention of any other deer in the area. A doe makes maternal grunts when searching for her bedded fawns. Bucks also grunt, at a pitch lower than that of the doe; this grunt deepens as the buck matures. In addition to grunting, both does and bucks also snort, a sound that often signals an imminent threat. Mature bucks also produce a grunt-snort-wheeze pattern, unique to each animal, that asserts its dominance, aggression, and hostility. White-tailed deer also use "tail-flagging," a behavior where the tail is raised when they detect a threat. However, the function of this behavior is disputed, and it appears to be a signal to predators more than an intraspecific communication warning other deer. | White-tailed deer | Wikipedia | 473 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Marking
White-tailed deer possess many glands that allow them to produce scents, some of which are so potent they can be detected by the human nose. Four major glands are the preorbital, forehead, tarsal, and metatarsal glands. Secretions from the preorbital glands (in front of the eye) were thought to be rubbed on tree branches, but research suggests this is not so. Scent from the forehead or sudoriferous glands (found on the head, between the antlers and eyes) is used to deposit scent on branches that overhang scrapes (areas scraped by the deer's front hooves before rub-urination). The tarsal glands are found on the upper inside of the hock (middle joint) on each hind leg. The scent is deposited from these glands when deer walk through and rub against vegetation. These scrapes are used by bucks as a sort of "sign-post" by which bucks know which other bucks are in the area, and to let does know a buck is regularly passing through the area—for breeding purposes. The scent from the metatarsal glands, found on the outside of each hind leg, between the ankle and hooves, may be used as an alarm scent. The scent from the interdigital glands, which are located between the hooves of each foot, emit a yellow waxy substance with an offensive odor. Deer can be seen stomping their hooves if they sense danger through sight, sound, or smell; this action leaves an excessive amount of odor for warning other deer of possible danger.
Throughout the year, deer rub-urinate, a process during which a deer squats while urinating so the urine will run down the insides of the deer's legs, over the tarsal glands, and onto the hair covering these glands. Bucks rub-urinate more frequently during the breeding season. Secretions from the preputial glands and tarsal glands mix with the urine and bacteria to produce a strong-smelling odor. During the breeding season, does release hormones and pheromones that tell bucks a doe is in heat and able to breed. Bucks also rub trees and shrubs with their antlers and heads during the breeding season, possibly transferring scent from the forehead glands to the tree, leaving a scent other deer can detect. | White-tailed deer | Wikipedia | 472 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Sign-post marking (scrapes and rubs) is a very obvious way white-tailed deer communicate. Although bucks do most of the marking, does visit these locations often. To make a rub, a buck uses his antlers to strip the bark off small-diameter trees, helping to mark his territory and polish his antlers. To mark areas they regularly pass through, bucks make scrapes. Often occurring in patterns known as scrape lines, scrapes are areas where a buck has used his front hooves to expose bare earth. They often rub-urinate into these scrapes, which are often found under twigs that have been marked with scent from the forehead glands.
Hunting
White-tailed deer have long been hunted as game, for pure sport and for their commodities, and is probably the most hunted native big game species in the Americas. In Mesoamerica, white-tailed deer (Odocoileus virginianus) were hunted from very early times. Rites and rituals in preparation for deer hunting and celebration for an auspicious hunt are still practiced in the area today. Ancient hunters ask their gods for permission to hunt, and some deer rites take place in caves.
Venison, or deer meat, is a nutritious form of lean animal protein. In some areas where their populations are very high, white-tailed deer are considered a pest, and hunting is used as a method to control them.
In 1884, one of the first hunts of white-tailed deer in Europe was conducted in Opočno and Dobříš (Brdy Mountains area), in what is now the Czech Republic. In the same era, white-tailed deer were hunted to near extinction in North America, but numbers have since rebounded to approximate pre-colonization levels. In the United States, whitetail hunting is far more popular in some states than others. The top five states for whitetail hunter concentrations are all in the Northeast and Midwest (Pennsylvania, Rhode Island, New York, Wisconsin, and Ohio). The Northeast in particular has twice the hunter density of the Midwest and Southeast and ten times that of the West. | White-tailed deer | Wikipedia | 428 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Since whitetail deer are very adaptable, inhabiting diverse regions ranging from tropical rain forests to high-altitude mountain chains of the Andes Mountains at more than 13,000 feet, different hunting methods as well as types of guns and ammo may be used. Most common cartridges used include the .243 Winchester, .308 Winchester, .25-06 Remington, 6.5mm Creedmoor, .270 Winchester, 7mm Remington Magnum, .30-06 Springfield, .30-30 Winchester (.30 WCF), .300 Winchester Magnum and 12 gauge shotshells. Due to the whitetail deer's frame and weight, cup and core bullets are the most recommended for taking clean, ethical shots.
Sport hunting for whitetail deer is a way of conservation of natural habitats as well as a population management.
Human interactions
By the early 20th century, commercial exploitation and unregulated hunting had severely depressed deer populations in much of their range. For example, by about 1930, the U.S. population was thought to number about 300,000. After an outcry by hunters and conservation ecologists, commercial exploitation of deer became illegal and conservation programs along with regulated hunting were introduced. In 2005, estimates put the deer population in the United States at around 30 million. Conservation practices have proved so successful, in parts of their range, the white-tailed deer populations currently far exceed their cultural carrying capacity and the animal may be considered a nuisance. A reduction in non-human predators (which normally cull young, sick, or infirm specimens) has also contributed to locally abundant populations. | White-tailed deer | Wikipedia | 324 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
At high population densities, farmers can suffer economic damage from deer feeding on cash crops, especially in corn and orchards. It has become nearly impossible to grow some crops in some areas unless very burdensome deer-deterring measures are taken. Deer can easily jump fences, and their fear of motion and sounds meant to scare them away is soon dulled. Timber harvesting and forest clearance have historically resulted in increased deer population densities, which in turn have slowed the rate of reforestation following logging in some areas. High densities of deer can have severe impacts on native plants and animals in parks and natural areas; however, deer browsing can also promote plant and animal diversity in some areas. Deer can also cause substantial damage to landscape plants in suburban areas, leading to limited hunting or trapping to relocate or sterilize them. In parts of the Eastern US with high deer populations and fragmented woodlands, deer often wander into suburban and urban habitats that are less than ideal for the species.
Farming
In New Zealand, the United States, and Canada, white-tailed deer are kept as livestock, and are extensively as well as intensively farmed for their meat, antlers, and pelts. The industry for farming white-tailed deer has grown significantly in the past two decades. In recent years, sales of white-tailed deer have generated up to $44 million in revenue. They are a good business venture because they have a high fertility rate and long reproductive life, can tolerate all weather, can be raised on land that is not suitable for agriculture and offer many by-products that can be sold. The North American white-tailed deer industry is split between breeding farms and hunting ranches. While some people care about the by-products produced by the deer, some people just care for the pursuit of a hunt. In the United States alone, around 13-14 million hunting licenses are sold every year. This could be a very profitable industry, especially considering the invasiveness of this species and the rate they have shown they are able to reproduce. However, this industry could have great repercussions on the ecosystem the farms are placed in because overpopulation of deer causes damage to local fauna.
Deer–vehicle collisions | White-tailed deer | Wikipedia | 444 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Motor vehicle collisions with deer are a significant issue in many parts of their range, especially at night and during rutting season, causing injuries and fatalities among both deer and humans. Vehicular damage can be substantial in some cases. In the United States, such collisions increased from 200,000 in 1980 to 500,000 in 1991. By 2009, the insurance industry estimated 2.4 million deer–vehicle collisions had occurred over the past two years, estimating damage cost to be over 7 billion dollars and 300 human deaths. Despite the high rate of these accidents, the effect on deer density is still quite low. Vehicle collisions of deer were monitored for two years in Virginia, and the collective annual mortality did not surpass 20% of the estimated deer population.
Many techniques have been investigated to prevent roadside mortality. Fences or road under- or over- passes have been shown to decrease deer-vehicle collisions, but are expensive and difficult to implement on a large scale. Roadside habitat modifications could also successfully decrease the number of collisions along roadways. An essential procedure in understanding factors resulting in accidents is to quantify risks, which involves the driver's behavior in terms of safe speed and ability to observe the deer. Some have suggested that reducing speed limits during the winter months when deer density is exceptionally high would likely reduce deer-vehicle collisions, but this may be an impractical solution.
Diseases
Another issue that exists with high deer density is the spreading of infectious diseases. Increased deer populations lead to increased transmission of tick-borne diseases, which pose a threat to human health, to livestock, and to other deer. Deer are the primary host and vector for the adult black-legged tick, which transmits the Lyme disease bacterium to humans. Lyme disease is the most common vector-borne disease in the country with confirmed cases, according to 2019 CDC data, in virtually every state in the U.S. with the highest incidence levels in the states from Maine to Virginia, Minnesota, and Wisconsin. In 2019 the number of confirmed and probable cases totaled about 35,000. Furthermore, the incidence of Lyme disease seems to reflect deer density in the eastern United States, which suggests a strong correlation. White-tailed deer also serve as intermediate hosts for many diseases that infect humans through ticks, such as Rocky Mountain spotted fever.
Newer evidence suggests the white-footed mouse is the most significant vector.
SARS-CoV-2 | White-tailed deer | Wikipedia | 488 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Blood samples gathered by USDA researchers in 2021 also showed that 40% of sampled white-tailed deer demonstrated evidence of SARS-CoV-2 antibodies, with the highest percentages in Michigan, at 67%, and Pennsylvania, at 44%. A later study by Penn State University and wildlife officials in Iowa showed that up to 80 percent of Iowa deer sampled from April 2020 through January 2021 had tested positive for active SARS-CoV-2 infection, rather than solely antibodies from prior infection. This data, confirmed by the National Veterinary Services Laboratory, alerted scientists to the possibility that white-tailed deer had become a natural reservoir for the coronavirus, serving as a potential "variant factory" for eventual retransmission back into humans. An Ohio State University study further showed that humans had transmitted SARS-CoV-2 to white-tailed deer on at least six separate occasions and that deer possessed six mutations that were uncommon in humans at the time of the study. Infected deer can shed virus via nasal secretions and feces for five to six days and frequently engage in activities conductive to viral spread, such as sniffing food intermingled with waste, nuzzling noses, polygamy, and the sharing of salt licks. Canadian researchers uncovered an entirely new SARS-CoV-2 variant within a November–December 2021 study of Ontario white-tailed deer. The new COVID variant had also infected a person who had close contact with local deer, potentially marking the first instance of deer-to-human transmission.
Cultural significance
In the U.S., the species is the state animal of Arkansas, Georgia, Illinois, Michigan, Mississippi, Nebraska, New Hampshire, Ohio, Pennsylvania, and South Carolina, the game animal of Oklahoma, and the wildlife symbol of Wisconsin. The white-tailed deer is also the inspiration of the professional basketball team the Milwaukee Bucks. The profile of a white-tailed deer buck caps the coat of arms of Vermont, is on the flag of Vermont, and is in stained glass at the Vermont State House. It is the national animal of Honduras and Costa Rica and the provincial animal of Canadian Saskatchewan and Finnish Pirkanmaa. It appears on the reverse side of the Costa Rican 1,000 colón note. The 1942 Disney film adaptation of Bambi, famously changed Bambi's species from the novel's roe deer into a white-tailed deer.
Climate change | White-tailed deer | Wikipedia | 488 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
Migration patterns
Climate change is affecting the white-tailed deer by changing their migration patterns and increasing their population size. This species of deer is restricted from moving northward due to cold harsh winters. Consequently, as climate change warms up Earth, these deer are allowed to migrate further north which will result in the populations of the white-tailed deer increasing. Between 1980 and 2000 in a study by Dawe and Boutin, presence of white-tailed deer in Alberta, Canada was driven primarily by changes in the climate. Populations of white-tailed deer have also moved anywhere from 50 to 250 km north of the eastern Alberta study site. Another study by Kennedy-Slaney, Bowman, Walpole, and Pond found that if current CO2 emissions remained the same, global warming resulting from the increased greenhouse gases in the atmosphere will allow white-tailed deer to survive further and further north by 2100.
Food web
When species are introduced to foreign ecosystems, they could potentially wreak havoc on the existing food web. For example, when the deer moved north in Alberta, gray wolf populations increased. This butterfly effect was also demonstrated in Yellowstone National Park when the rivers changed because wolves were re-introduced to the ecosystem. It is also possible that the increasing white-tailed deer populations could result in them becoming an invasive species for various plants in Alberta, Canada.
Disease
The species is vulnerable to diseases that are more prevalent in the summer. Insects carrying these diseases are usually killed during the first snowfall. However, as time goes on, they will be able to live longer than they used to meaning the deer are at higher risk of getting sick. It is possible that this will increase the deers' mortality rate from disease. Examples of these diseases are hemorrhagic disease (HD), epizootic hemorrhagic disease and bluetongue viruses, which are transmitted by biting midges. The hotter summers, longer droughts, and more intense rains create the perfect environment for the midges to thrive in. Ticks also thrive in warmer weather heat results in faster development in all of their life stages. 18 different species of tick infest white-tailed deer in the United States alone. Ticks are parasitic to white-tailed deer transmit diseases causing irritation, anemia, and infections. | White-tailed deer | Wikipedia | 460 | 569459 | https://en.wikipedia.org/wiki/White-tailed%20deer | Biology and health sciences | Deer | Animals |
In biochemistry and pharmacology, receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems. These signals are typically chemical messengers which bind to a receptor and produce physiological responses such as change in the electrical activity of a cell. For example, GABA, an inhibitory neurotransmitter, inhibits electrical activity of neurons by binding to GABA receptors. There are three main ways the action of the receptor can be classified: relay of signal, amplification, or integration. Relaying sends the signal onward, amplification increases the effect of a single ligand, and integration allows the signal to be incorporated into another biochemical pathway.
Receptor proteins can be classified by their location. Cell surface receptors, also known as transmembrane receptors, include ligand-gated ion channels, G protein-coupled receptors, and enzyme-linked hormone receptors. Intracellular receptors are those found inside the cell, and include cytoplasmic receptors and nuclear receptors. A molecule that binds to a receptor is called a ligand and can be a protein, peptide (short protein), or another small molecule, such as a neurotransmitter, hormone, pharmaceutical drug, toxin, calcium ion or parts of the outside of a virus or microbe. An endogenously produced substance that binds to a particular receptor is referred to as its endogenous ligand. E.g. the endogenous ligand for the nicotinic acetylcholine receptor is acetylcholine, but it can also be activated by nicotine and blocked by curare. Receptors of a particular type are linked to specific cellular biochemical pathways that correspond to the signal. While numerous receptors are found in most cells, each receptor will only bind with ligands of a particular structure. This has been analogously compared to how locks will only accept specifically shaped keys. When a ligand binds to a corresponding receptor, it activates or inhibits the receptor's associated biochemical pathway, which may also be highly specialised.
Receptor proteins can be also classified by the property of the ligands. Such classifications include chemoreceptors, mechanoreceptors, gravitropic receptors, photoreceptors, magnetoreceptors and gasoreceptors.
Structure | Receptor (biochemistry) | Wikipedia | 475 | 569480 | https://en.wikipedia.org/wiki/Receptor%20%28biochemistry%29 | Biology and health sciences | Cell processes | Biology |
The structures of receptors are very diverse and include the following major categories, among others:
Type 1: Ligand-gated ion channels (ionotropic receptors) – These receptors are typically the targets of fast neurotransmitters such as acetylcholine (nicotinic) and GABA; activation of these receptors results in changes in ion movement across a membrane. They have a heteromeric structure in that each subunit consists of the extracellular ligand-binding domain and a transmembrane domain which includes four transmembrane alpha helices. The ligand-binding cavities are located at the interface between the subunits.
Type 2: G protein-coupled receptors (metabotropic receptors) – This is the largest family of receptors and includes the receptors for several hormones and slow transmitters e.g. dopamine, metabotropic glutamate. They are composed of seven transmembrane alpha helices. The loops connecting the alpha helices form extracellular and intracellular domains. The binding-site for larger peptide ligands is usually located in the extracellular domain whereas the binding site for smaller non-peptide ligands is often located between the seven alpha helices and one extracellular loop. The aforementioned receptors are coupled to different intracellular effector systems via G proteins. G proteins are heterotrimers made up of 3 subunits: α (alpha), β (beta), and γ (gamma). In the inactive state, the three subunits associate together and the α-subunit binds GDP. G protein activation causes a conformational change, which leads to the exchange of GDP for GTP. GTP-binding to the α-subunit causes dissociation of the β- and γ-subunits. Furthermore, the three subunits, α, β, and γ have additional four main classes based on their primary sequence. These include Gs, Gi, Gq and G12.
Type 3: Kinase-linked and related receptors (see "Receptor tyrosine kinase" and "Enzyme-linked receptor") – They are composed of an extracellular domain containing the ligand binding site and an intracellular domain, often with enzymatic-function, linked by a single transmembrane alpha helix. The insulin receptor is an example. | Receptor (biochemistry) | Wikipedia | 471 | 569480 | https://en.wikipedia.org/wiki/Receptor%20%28biochemistry%29 | Biology and health sciences | Cell processes | Biology |
Type 4: Nuclear receptors – While they are called nuclear receptors, they are actually located in the cytoplasm and migrate to the nucleus after binding with their ligands. They are composed of a C-terminal ligand-binding region, a core DNA-binding domain (DBD) and an N-terminal domain that contains the AF1(activation function 1) region. The core region has two zinc fingers that are responsible for recognizing the DNA sequences specific to this receptor. The N terminus interacts with other cellular transcription factors in a ligand-independent manner; and, depending on these interactions, it can modify the binding/activity of the receptor. Steroid and thyroid-hormone receptors are examples of such receptors. | Receptor (biochemistry) | Wikipedia | 144 | 569480 | https://en.wikipedia.org/wiki/Receptor%20%28biochemistry%29 | Biology and health sciences | Cell processes | Biology |
Membrane receptors may be isolated from cell membranes by complex extraction procedures using solvents, detergents, and/or affinity purification.
The structures and actions of receptors may be studied by using biophysical methods such as X-ray crystallography, NMR, circular dichroism, and dual polarisation interferometry. Computer simulations of the dynamic behavior of receptors have been used to gain understanding of their mechanisms of action.
Binding and activation
Ligand binding is an equilibrium process. Ligands bind to receptors and dissociate from them according to the law of mass action in the following equation, for a ligand L and receptor, R. The brackets around chemical species denote their concentrations.
One measure of how well a molecule fits a receptor is its binding affinity, which is inversely related to the dissociation constant Kd. A good fit corresponds with high affinity and low Kd. The final biological response (e.g. second messenger cascade, muscle-contraction), is only achieved after a significant number of receptors are activated.
Affinity is a measure of the tendency of a ligand to bind to its receptor. Efficacy is the measure of the bound ligand to activate its receptor.
Agonists versus antagonists
Not every ligand that binds to a receptor also activates that receptor. The following classes of ligands exist: | Receptor (biochemistry) | Wikipedia | 267 | 569480 | https://en.wikipedia.org/wiki/Receptor%20%28biochemistry%29 | Biology and health sciences | Cell processes | Biology |
(Full) agonists are able to activate the receptor and result in a strong biological response. The natural endogenous ligand with the greatest efficacy for a given receptor is by definition a full agonist (100% efficacy).
Partial agonists do not activate receptors with maximal efficacy, even with maximal binding, causing partial responses compared to those of full agonists (efficacy between 0 and 100%).
Antagonists bind to receptors but do not activate them. This results in a receptor blockade, inhibiting the binding of agonists and inverse agonists. Receptor antagonists can be competitive (or reversible), and compete with the agonist for the receptor, or they can be irreversible antagonists that form covalent bonds (or extremely high affinity non-covalent bonds) with the receptor and completely block it. The proton pump inhibitor omeprazole is an example of an irreversible antagonist. The effects of irreversible antagonism can only be reversed by synthesis of new receptors.
Inverse agonists reduce the activity of receptors by inhibiting their constitutive activity (negative efficacy).
Allosteric modulators: They do not bind to the agonist-binding site of the receptor but instead on specific allosteric binding sites, through which they modify the effect of the agonist. For example, benzodiazepines (BZDs) bind to the BZD site on the GABAA receptor and potentiate the effect of endogenous GABA.
Note that the idea of receptor agonism and antagonism only refers to the interaction between receptors and ligands and not to their biological effects.
Constitutive activity
A receptor which is capable of producing a biological response in the absence of a bound ligand is said to display "constitutive activity". The constitutive activity of a receptor may be blocked by an inverse agonist. The anti-obesity drugs rimonabant and taranabant are inverse agonists at the cannabinoid CB1 receptor and though they produced significant weight loss, both were withdrawn owing to a high incidence of depression and anxiety, which are believed to relate to the inhibition of the constitutive activity of the cannabinoid receptor.
The GABAA receptor has constitutive activity and conducts some basal current in the absence of an agonist. This allows beta carboline to act as an inverse agonist and reduce the current below basal levels. | Receptor (biochemistry) | Wikipedia | 511 | 569480 | https://en.wikipedia.org/wiki/Receptor%20%28biochemistry%29 | Biology and health sciences | Cell processes | Biology |
Mutations in receptors that result in increased constitutive activity underlie some inherited diseases, such as precocious puberty (due to mutations in luteinizing hormone receptors) and hyperthyroidism (due to mutations in thyroid-stimulating hormone receptors).
Theories of drug-receptor interaction
Occupation
Early forms of the receptor theory of pharmacology stated that a drug's effect is directly proportional to the number of receptors that are occupied. Furthermore, a drug effect ceases as a drug-receptor complex dissociates.
Ariëns & Stephenson introduced the terms "affinity" & "efficacy" to describe the action of ligands bound to receptors.
Affinity: The ability of a drug to combine with a receptor to create a drug-receptor complex.
Efficacy: The ability of drug to initiate a response after the formation of drug-receptor complex.
Rate
In contrast to the accepted Occupation Theory, Rate Theory proposes that the activation of receptors is directly proportional to the total number of encounters of a drug with its receptors per unit time. Pharmacological activity is directly proportional to the rates of dissociation and association, not the number of receptors occupied:
Agonist: A drug with a fast association and a fast dissociation.
Partial-agonist: A drug with an intermediate association and an intermediate dissociation.
Antagonist: A drug with a fast association & slow dissociation
Induced-fit
As a drug approaches a receptor, the receptor alters the conformation of its binding site to produce drug—receptor complex.
Spare Receptors
In some receptor systems (e.g. acetylcholine at the neuromuscular junction in smooth muscle), agonists are able to elicit maximal response at very low levels of receptor occupancy (<1%). Thus, that system has spare receptors or a receptor reserve. This arrangement produces an economy of neurotransmitter production and release.
Receptor regulation
Cells can increase (upregulate) or decrease (downregulate) the number of receptors to a given hormone or neurotransmitter to alter their sensitivity to different molecules. This is a locally acting feedback mechanism.
Change in the receptor conformation such that binding of the agonist does not activate the receptor. This is seen with ion channel receptors.
Uncoupling of the receptor effector molecules is seen with G protein-coupled receptors.
Receptor sequestration (internalization), e.g. in the case of hormone receptors.
Examples and ligands | Receptor (biochemistry) | Wikipedia | 510 | 569480 | https://en.wikipedia.org/wiki/Receptor%20%28biochemistry%29 | Biology and health sciences | Cell processes | Biology |
The ligands for receptors are as diverse as their receptors. GPCRs (7TMs) are a particularly vast family, with at least 810 members. There are also LGICs for at least a dozen endogenous ligands, and many more receptors possible through different subunit compositions. Some common examples of ligands and receptors include:
Ion channels and G protein coupled receptors
Some example ionotropic (LGIC) and metabotropic (specifically, GPCRs) receptors are shown in the table below. The chief neurotransmitters are glutamate and GABA; other neurotransmitters are neuromodulatory. This list is by no means exhaustive.
Enzyme linked receptors
Enzyme linked receptors include Receptor tyrosine kinases (RTKs), serine/threonine-specific protein kinase, as in bone morphogenetic protein and guanylate cyclase, as in atrial natriuretic factor receptor. Of the RTKs, 20 classes have been identified, with 58 different RTKs as members. Some examples are shown below:
Intracellular Receptors
Receptors may be classed based on their mechanism or on their position in the cell. 4 examples of intracellular LGIC are shown below:
Role in health and disease
In genetic disorders
Many genetic disorders involve hereditary defects in receptor genes. Often, it is hard to determine whether the receptor is nonfunctional or the hormone is produced at decreased level; this gives rise to the "pseudo-hypo-" group of endocrine disorders, where there appears to be a decreased hormonal level while in fact it is the receptor that is not responding sufficiently to the hormone.
In the immune system
The main receptors in the immune system are pattern recognition receptors (PRRs), toll-like receptors (TLRs), killer activated and killer inhibitor receptors (KARs and KIRs), complement receptors, Fc receptors, B cell receptors and T cell receptors. | Receptor (biochemistry) | Wikipedia | 407 | 569480 | https://en.wikipedia.org/wiki/Receptor%20%28biochemistry%29 | Biology and health sciences | Cell processes | Biology |
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas, the main characteristic being that the optical path folds back onto itself, relative to the optical system's primary mirror entrance aperture. This design puts the focal point at a convenient location behind the primary mirror and the convex secondary adds a telephoto effect creating a much longer focal length in a mechanically short system.
In a symmetrical Cassegrain both mirrors are aligned about the optical axis, and the primary mirror usually contains a hole in the center, thus permitting the light to reach an eyepiece, a camera, or an image sensor. Alternatively, as in many radio telescopes, the final focus may be in front of the primary. In an asymmetrical Cassegrain, the mirror(s) may be tilted to avoid obscuration of the primary or to avoid the need for a hole in the primary mirror (or both).
The classic Cassegrain configuration uses a parabolic reflector as the primary while the secondary mirror is hyperbolic. Modern variants may have a hyperbolic primary for increased performance (for example, the Ritchey–Chrétien design); and either or both mirrors may be spherical or elliptical for ease of manufacturing.
The Cassegrain reflector is named after a published reflecting telescope design that appeared in the April 25, 1672 Journal des sçavans which has been attributed to Laurent Cassegrain. Similar designs using convex secondary mirrors have been found in the Bonaventura Cavalieri's 1632 writings describing burning mirrors and Marin Mersenne's 1636 writings describing telescope designs. James Gregory's 1662 attempts to create a reflecting telescope included a Cassegrain configuration, judging by a convex secondary mirror found among his experiments.
The Cassegrain design is also used in catadioptric systems.
Cassegrain designs
"Classic" Cassegrain telescopes
The "classic" Cassegrain has a parabolic primary mirror and a hyperbolic secondary mirror that reflects the light back down through a hole in the primary. Folding the optics makes this a compact design. On smaller telescopes, and camera lenses, the secondary is often mounted on an optically flat, optically clear glass plate that closes the telescope tube. This support eliminates the "star-shaped" diffraction effects caused by a straight-vaned support spider. The closed tube stays clean, and the primary is protected, at the cost of some loss of light-gathering power. | Cassegrain reflector | Wikipedia | 512 | 2151693 | https://en.wikipedia.org/wiki/Cassegrain%20reflector | Technology | Telescope | null |
It makes use of the special properties of parabolic and hyperbolic reflectors. A concave parabolic reflector will reflect all incoming light rays parallel to its axis of symmetry to a single point, the focus. A convex hyperbolic reflector has two foci and will reflect all light rays directed at one of its two foci towards its other focus. The mirrors in this type of telescope are designed and positioned so that they share one focus and so that the second focus of the hyperbolic mirror will be at the same point at which the image is to be observed, usually just outside the eyepiece.
In most Cassegrain systems, the secondary mirror blocks a central portion of the aperture. This ring-shaped entrance aperture significantly reduces a portion of the modulation transfer function (MTF) over a range of low spatial frequencies, compared to a full-aperture design such as a refractor or an offset Cassegrain. This MTF notch has the effect of lowering image contrast when imaging broad features. In addition, the support for the secondary (the spider) may introduce diffraction spikes in images.
The radii of curvature of the primary and secondary mirrors, respectively, in the classic configuration are
and
where
is the effective focal length of the system,
is the back focal length (the distance from the secondary to the focus),
is the distance between the two mirrors and
is the secondary magnification.
If, instead of and , the known quantities are the focal length of the primary mirror, , and the distance to the focus behind the primary mirror, , then and .
The conic constant of the primary mirror is that of a parabola, . Thanks to that there is no spherical aberration introduced by the primary mirror. The secondary mirror, however, is of a hyperbolic shape with one focus coinciding with that of the primary mirror and the other focus being at the back focal length . Thus, the classical Cassegrain has ideal focus for the chief ray (the center spot diagram is one point). We have,
,
where
.
Actually, as the conic constants should not depend on scaling, the formulae for both and can be greatly simplified and presented only as functions of the secondary magnification. Finally,
and
.
Ritchey-Chrétien | Cassegrain reflector | Wikipedia | 466 | 2151693 | https://en.wikipedia.org/wiki/Cassegrain%20reflector | Technology | Telescope | null |
The Ritchey-Chrétien is a specialized Cassegrain reflector which has two hyperbolic mirrors (instead of a parabolic primary). It is free of coma and spherical aberration at a flat focal plane, making it well suited for wide field and photographic observations. It was invented by George Willis Ritchey and Henri Chrétien in the early 1910s. This design is very common in large professional research telescopes, including the Hubble Space Telescope, the Keck Telescopes, and the Very Large Telescope (VLT); it is also found in high-grade amateur telescopes.
Dall-Kirkham
The Dall-Kirkham Cassegrain telescope design was created by Horace Dall in 1928 and took on the name in an article published in Scientific American in 1930 following discussion between amateur astronomer Allan Kirkham and Albert G. Ingalls, the magazine's astronomy editor at the time. It uses a concave elliptical primary mirror and a convex spherical secondary. While this system is easier to polish than a classic Cassegrain or Ritchey-Chretien system, the off-axis coma is significantly worse, so the image degrades quickly off-axis. Because this is less noticeable at longer focal ratios, Dall-Kirkhams are seldom faster than f/15.
Off-axis configurations
An unusual variant of the Cassegrain is the Schiefspiegler telescope ("skewed" or "oblique reflector"; also known as the "Kutter telescope" after its inventor, Anton Kutter) which uses tilted mirrors to avoid the secondary mirror casting a shadow on the primary. However, while eliminating diffraction patterns this leads to several other aberrations that must be corrected.
Several different off-axis configurations are used for radio antennas.
Another off-axis, unobstructed design and variant of the Cassegrain is the 'Yolo' reflector invented by Arthur Leonard. This design uses a spherical or parabolic primary and a mechanically warped spherical secondary to correct for off-axis induced astigmatism. When set up correctly the Yolo can give uncompromising unobstructed views of planetary objects and non-wide field targets, with no lack of contrast or image quality caused by spherical aberration. The lack of obstruction also eliminates the diffraction associated with Cassegrain and Newtonian reflector astrophotography.
Catadioptric Cassegrains | Cassegrain reflector | Wikipedia | 500 | 2151693 | https://en.wikipedia.org/wiki/Cassegrain%20reflector | Technology | Telescope | null |
Catadioptric Cassegrains use two mirrors, often with a spherical primary mirror to reduce cost, combined with refractive corrector element(s) to correct the resulting aberrations.
Schmidt-Cassegrain
The Schmidt-Cassegrain was developed from the wide-field Schmidt camera, although the Cassegrain configuration gives it a much narrower field of view. The first optical element is a Schmidt corrector plate. The plate is figured by placing a vacuum on one side, and grinding the exact correction required to correct the spherical aberration caused by the spherical primary mirror. Schmidt-Cassegrains are popular with amateur astronomers. An early Schmidt-Cassegrain camera was patented in 1946 by artist/architect/physicist Roger Hayward, with the film holder placed outside the telescope.
Maksutov-Cassegrain
The Maksutov-Cassegrain is a variation of the Maksutov telescope named after the Soviet optician and astronomer Dmitri Dmitrievich Maksutov. It starts with an optically transparent corrector lens that is a section of a hollow sphere. It has a spherical primary mirror, and a spherical secondary that is usually a mirrored section of the corrector lens.
Argunov-Cassegrain
In the Argunov-Cassegrain telescope all optics are spherical, and the classical Cassegrain secondary mirror is replaced by a sub-aperture corrector consisting of three air spaced lens elements. The element farthest from the primary mirror is a Mangin mirror, which acts as a secondary mirror.
Klevtsov-Cassegrain
The Klevtsov-Cassegrain, like the Argunov-Cassegrain, uses a sub-aperture corrector consisting of a small meniscus lens and a Mangin mirror as its "secondary mirror".
Cassegrain radio antennas
Cassegrain designs are also utilized in satellite telecommunication earth station antennas and radio telescopes, ranging in size from 2.4 metres to 70 metres. The centrally located sub-reflector serves to focus radio frequency signals in a similar fashion to optical telescopes.
An example of a cassegrain radio antenna is the 70-meter dish at JPL's Goldstone antenna complex. For this antenna, the final focus is in front of the primary, at the top of the pedestal protruding from the mirror. | Cassegrain reflector | Wikipedia | 474 | 2151693 | https://en.wikipedia.org/wiki/Cassegrain%20reflector | Technology | Telescope | null |
Thin-layer chromatography (TLC) is a chromatography technique that separates components in non-volatile mixtures.
It is performed on a TLC plate made up of a non-reactive solid coated with a thin layer of adsorbent material. This is called the stationary phase. The sample is deposited on the plate, which is eluted with a solvent or solvent mixture known as the mobile phase (or eluent). This solvent then moves up the plate via capillary action. As with all chromatography, some compounds are more attracted to the mobile phase, while others are more attracted to the stationary phase. Therefore, different compounds move up the TLC plate at different speeds and become separated. To visualize colourless compounds, the plate is viewed under UV light or is stained. Testing different stationary and mobile phases is often necessary to obtain well-defined and separated spots.
TLC is quick, simple, and gives high sensitivity for a relatively low cost. It can monitor reaction progress, identify compounds in a mixture, determine purity, or purify small amounts of compound.
Procedure
The process for TLC is similar to paper chromatography but provides faster runs, better separations, and the choice between different stationary phases. Plates can be labelled before or after the chromatography process with a pencil or other implement that will not interfere with the process.
There are four main stages to running a thin-layer chromatography plate:
Plate preparation: Using a capillary tube, a small amount of a concentrated solution of the sample is deposited near the bottom edge of a TLC plate. The solvent is allowed to completely evaporate before the next step. A vacuum chamber may be necessary for non-volatile solvents. To make sure there is sufficient compound to obtain a visible result, the spotting procedure can be repeated. Depending on the application, multiple different samples may be placed in a row the same distance from the bottom edge; each sample will move up the plate in its own "lane." | Thin-layer chromatography | Wikipedia | 418 | 2152225 | https://en.wikipedia.org/wiki/Thin-layer%20chromatography | Physical sciences | Chromatography | Chemistry |
Development chamber preparation: The development solvent or solvent mixture is placed into a transparent container (separation/development chamber) to a depth of less than 1 centimetre. A strip of filter paper (aka "wick") is also placed along the container wall. This filter paper should touch the solvent and almost reach the top of the container. The container is covered with a lid and the solvent vapors are allowed to saturate the atmosphere of the container. Failure to do so results in poor separation and non-reproducible results.
Development: The TLC plate is placed in the container such that the sample spot(s) are not submerged into the mobile phase. The container is covered to prevent solvent evaporation. The solvent migrates up the plate by capillary action, meets the sample mixture, and carries it up the plate (elutes the sample). The plate is removed from the container before the solvent reaches the top of the plate; otherwise, the results will be misleading. The solvent front, the highest mark the solvent has travelled along the plate, is marked.
Visualization: The solvent evaporates from the plate. Visualization methods include UV light, staining, and many more.
Separation process and principle
The separation of compounds is due to the differences in their attraction to the stationary phase and because of differences in solubility in the solvent. As a result, the compounds and the mobile phase compete for binding sites on the stationary phase. Different compounds in the sample mixture travel at different rates due to the differences in their partition coefficients. Different solvents, or different solvent mixtures, gives different separation. The retardation factor (Rf), or retention factor, quantifies the results. It is the distance traveled by a given substance divided by the distance traveled by the mobile phase. | Thin-layer chromatography | Wikipedia | 370 | 2152225 | https://en.wikipedia.org/wiki/Thin-layer%20chromatography | Physical sciences | Chromatography | Chemistry |
In normal-phase TLC, the stationary phase is polar. Silica gel is very common in normal-phase TLC. More polar compounds in a sample mixture interact more strongly with the polar stationary phase. As a result, more-polar compounds move less (resulting in smaller Rf) while less-polar compounds move higher up the plate (higher Rf). A more-polar mobile phase also binds more strongly to the plate, competing more with the compound for binding sites; a more-polar mobile phase also dissolves polar compounds more. As such, all compounds on the TLC plate move higher up the plate in polar solvent mixtures. "Strong" solvents move compounds higher up the plate, whereas "weak" solvents move them less.
If the stationary phase is non-polar, like C18-functionalized silica plates, it is called reverse-phase TLC. In this case, non-polar compounds move less and polar compounds move more. The solvent mixture will also be much more polar than in normal-phase TLC.
Solvent choice
An eluotropic series, which orders solvents by how much they move compounds, can help in selecting a mobile phase. Solvents are also divided into solvent selectivity groups. Using solvents with different elution strengths or different selectivity groups can often give very different results. While single-solvent mobile phases can sometimes give good separation, some cases may require solvent mixtures.
In normal-phase TLC, the most common solvent mixtures include ethyl acetate/hexanes (EtOAc/Hex) for less-polar compounds and methanol/dichloromethane (MeOH/DCM) for more polar compounds. Different solvent mixtures and solvent ratios can help give better separation. In reverse-phase TLC, solvent mixtures are typically water with a less-polar solvent: Typical choices are water with tetrahydrofuran (THF), acetonitrile (ACN), or methanol.
Analysis
As the chemicals being separated may be colourless, several methods exist to visualise the spots: | Thin-layer chromatography | Wikipedia | 434 | 2152225 | https://en.wikipedia.org/wiki/Thin-layer%20chromatography | Physical sciences | Chromatography | Chemistry |
Placing the plate under blacklight (366 nm light) makes fluorescent compounds glow
TLC plates containing a small amount of fluorescent compound (usually manganese-activated zinc silicate) in the adsorbent layer allow for visualisation of some compounds under UV-C light (254 nm). The adsorbent layer will fluoresce light-green, while spots containing compounds that absorb UV-C light will not.
Placing the plate in a container filled with iodine vapours temporarily stains the spots. They typically become a yellow or brown colour.
The TLC plate can either be dipped in or sprayed with a stain and sometimes heated depending on the stain used. Many stains exist for a large range of chemical moieties but some examples include:
Potassium permanganate (no heating, for oxidisable groups)
Ninhydrin (heating, amines and amino-acids)
Acidic vanillin (heating, general reagent)
Phosphomolybdic acid (no heating, general reagent)
In the case of lipids, the chromatogram may be transferred to a polyvinylidene fluoride membrane and then subjected to further analysis, for example, mass spectrometry. This technique is known as far-eastern blot.
Plate production
TLC plates are usually commercially available, with standard particle size ranges to improve reproducibility. They are prepared by mixing the adsorbent, such as silica gel, with a small amount of inert binder like calcium sulfate (gypsum) and water. This mixture is spread as a thick slurry on an unreactive carrier sheet, usually glass, thick aluminum foil, or plastic. The resultant plate is dried and activated by heating in an oven for thirty minutes at 110 °C. The thickness of the absorbent layer is typically around 0.1–0.25 mm for analytical purposes and around 0.5–2.0 mm for preparative TLC. Other adsorbent coatings include aluminium oxide (alumina), or cellulose.
Applications | Thin-layer chromatography | Wikipedia | 432 | 2152225 | https://en.wikipedia.org/wiki/Thin-layer%20chromatography | Physical sciences | Chromatography | Chemistry |
Reaction monitoring and characterization
TLC is a useful tool for reaction monitoring. For this, the plate normally contains a spot of starting material, a spot from the reaction mixture, and a co-spot (or cross-spot) containing both. The analysis will show if the starting material disappeared and if any new products appeared. This provides a quick and easy way to estimate how far a reaction has proceeded. In one study, TLC has been applied in the screening of organic reactions. The researchers react an alcohol and a catalyst directly in the co-spot of a TLC plate before developing it. This provides quick and easy small-scale testing of different reagents.
Compound characterization with TLC is also possible and is similar to reaction monitoring. However, rather than spotting with starting material and reaction mixture, it is with an unknown and a known compound. They may be the same compound if both spots have the same Rf and look the same under the chosen visualization method. However, co-elution complicates both reaction monitoring and characterization. This is because different compounds will move to the same spot on the plate. In such cases, different solvent mixtures may provide better separation.
Purity and purification
TLC helps show the purity of a sample. A pure sample should only contain one spot by TLC. TLC is also useful for small-scale purification. Because the separated compounds will be on different areas of the plate, a scientist can scrape off the stationary phase particles containing the desired compound and dissolve them into an appropriate solvent. Once all the compound dissolves in the solvent, they filter out the silica particles, then evaporate the solvent to isolate the product. Big preparative TLC plates with thick silica gel coatings can separate more than 100 mg of material.
For larger-scale purification and isolation, TLC is useful to quickly test solvent mixtures before running flash column chromatography on a large batch of impure material. A compound elutes from a column when the amount of solvent collected is equal to 1/Rf. The eluent from flash column chromatography gets collected across several containers (for example, test tubes) called fractions. TLC helps show which fractions contain impurities and which contain pure compound. | Thin-layer chromatography | Wikipedia | 460 | 2152225 | https://en.wikipedia.org/wiki/Thin-layer%20chromatography | Physical sciences | Chromatography | Chemistry |
Furthermore, two-dimensional TLC can help check if a compound is stable on a particular stationary phase. This test requires two runs on a square-shaped TLC plate. The plate is rotated by 90º before the second run. If the target compound appears on the diagonal of the square, it is stable on the chosen stationary phase. Otherwise, it is decomposing on the plate. If this is the case, an alternative stationary phase may prevent this decomposition.
TLC is also an analytical method for the direct separation of enantiomers and the control of enantiomeric purity, e.g. active pharmaceutical ingredients (APIs) that are chiral. | Thin-layer chromatography | Wikipedia | 136 | 2152225 | https://en.wikipedia.org/wiki/Thin-layer%20chromatography | Physical sciences | Chromatography | Chemistry |
The Archaeognatha are an order of apterygotes, known by various common names such as jumping bristletails. Among extant insect taxa they are some of the most evolutionarily primitive; they appeared in the Middle Devonian period at about the same time as the arachnids. Specimens that closely resemble extant species have been found as both body and trace fossils (the latter including body imprints and trackways) in strata from the remainder of the Paleozoic Era and more recent periods. For historical reasons an alternative name for the order is Microcoryphia.
Until the late 20th century the suborders Zygentoma and Archaeognatha comprised the order Thysanura; both orders possess three-pronged tails comprising two lateral cerci and a medial epiproct or appendix dorsalis. Of the three organs, the appendix dorsalis is considerably longer than the two cerci; in this the Archaeognatha differ from the Zygentoma, in which the three organs are subequal in length. In the late 20th century, it was recognized that the order Thysanura was paraphyletic, thus the two suborders were each raised to the status of an independent monophyletic order, with Archaeognatha sister taxon to the Dicondylia, including the Zygentoma.
The order Archaeognatha is cosmopolitan; it includes roughly 500 species in two families. No species is currently evaluated as being at conservation risk.
Description
Archaeognatha are small insects with elongated bodies and backs that are arched, especially over the thorax. Their abdomen ends in three long tail-like structures, of which the lateral two are cerci, while the medial filament, which is longest, is an epiproct. The tenth abdominal segment is reduced. The antennae are flexible. The two large compound eyes meet at the top of the head, and there are three ocelli. The mouthparts are partly retractable, with simple chewing mandibles and seven-segmented maxillary palps which are commonly longer than the legs.
Unlike other insect orders, they do not have olfactory receptor-coreceptors (Orco), which have either been lost or were never present in the first place. | Archaeognatha | Wikipedia | 476 | 2152928 | https://en.wikipedia.org/wiki/Archaeognatha | Biology and health sciences | Insects: General | Animals |
Archaeognatha differ from Zygentoma in various ways, such as their relatively small head, their bodies being compressed laterally (from side to side) instead of flattened dorsiventrally, and in their being able to use their tails to spring up to into the air if disturbed. They have eight pairs of short appendages called styli on abdominal segments 2 to 9. Family Machilidae is also unique among insects in possessing small muscleless styli on the second and third thoracic legs, but are absent on the second pair of thoracic legs in some genera. Similar stylets on the legs are absent in family Meinertellidae. They have one or two pairs of eversible membranous vesicles on the underside of abdominal segments 1 to 7, which are used to absorb water and assisting with molting. There are nine pairs of spiracles; two pairs on the thorax, and seven pairs on abdominal segments 2 to 8. The pair of spiracles on the first abdominal segment has been lost.
Further unusual features are that the abdominal sternites are each composed of three sclerites, and they cement themselves to the substrate before molting, often using their own feces as glue. The body is covered with readily detached scales, that make the animals difficult to grip and also may protect the exoskeleton from abrasion. The thin exoskeleton offers little protection against dehydration, and they accordingly must remain in moist air, such as in cool, damp situations under stones or bark.
Etymology
The name Archaeognatha is derived from the Greek , meaning 'ancient', and , meaning 'jaw'. This refers to the articulation of the mandibles, which are different from those of other insects. It was originally believed that Archaeognatha possessed a single phylogenetically primitive condyle each (thus the name "Monocondylia"), where all more derived insects have two, but this has since been shown to be incorrect; all insects, including Archaeognatha, have dicondylic mandibles, but archaeognaths possess two articulations that are homologous to those in other insects, though slightly different.
An alternative name, Microcoryphia, comes from the Greek , and , which in context means 'head'.
Taxonomy | Archaeognatha | Wikipedia | 497 | 2152928 | https://en.wikipedia.org/wiki/Archaeognatha | Biology and health sciences | Insects: General | Animals |
Biology
Archaeognatha occur in a wide range of habitats. While most species live in moist soil, others have adapted to chaparral, and even sandy deserts. They feed primarily on algae, but also lichens, mosses, or decaying organic detritus.
Three types of mating behavior are known. In some species the male spins a silk thread (carrier thread) stretched out on the ground. On the thread there are droplets of sperm which the female will take up when her ovipositor makes contact. In others a packet of sperm (spermatophore) is deposited on the top of a short stalk. If a female takes up the sperm or not is often random, but in many species the male will try to lead the female's genitals over the sperm during courtship. A more direct way of fertilization occurs in species of the genus Petrobius, where the male place a droplet of sperm directly on the female's ovipositor. One hypothesis is that the external genitals of insects started as structures specialized for water-uptake, which could reach deeper crevices than the coxal vesicles, and over time the female would use it to take up sperm from the ground instead of water. After fertilization she lays a batch of around 30 eggs in a suitable crevice. The young resemble the adults, and take up to two years to reach sexual maturity, depending on the species and conditions such as temperature and available food.
Unlike most insects, the adults continue to moult after reaching adulthood, and typically mate once at each instar. Archaeognaths may have a total lifespan of up to four years, longer than most larger insects. | Archaeognatha | Wikipedia | 353 | 2152928 | https://en.wikipedia.org/wiki/Archaeognatha | Biology and health sciences | Insects: General | Animals |
Psocoptera () are a paraphyletic group of insects that are commonly known as booklice, barklice or barkflies. The name Psocoptera has been replaced with Psocodea in recent literature, with the inclusion of the former order Phthiraptera into Psocodea (as part of the suborder Troctomorpha).
These insects first appeared in the Permian period, 295–248 million years ago. They are often regarded as the most primitive of the hemipteroids. Their name originates from the Greek word ψῶχος (psokhos), meaning "gnawed" or "rubbed" and πτερά (ptera), meaning "wings". There are more than 5,500 species in 41 families in three suborders. Many of these species have only been described in the early twenty-first century. They range in size from in length.
The species known as booklice received their common name because they are commonly found amongst old books—they feed upon the paste used in binding. The barklice are found on trees, feeding on algae and lichen.
Anatomy and biology
Psocids are small, scavenging insects with a relatively generalized body plan. They feed primarily on fungi, algae, lichen, and organic detritus in nature but are also known to feed on starch-based household items like grains, wallpaper glue and book bindings. They have chewing mandibles, and the central lobe of the maxilla is modified into a slender rod. This rod is used to brace the insect while it scrapes up detritus with its mandibles. They also have a swollen forehead, large compound eyes, and three ocelli. Their bodies are soft with a segmented abdomen. Some species can spin silk from glands in their mouth. They may festoon large sections of trunk and branches in dense swathes of silk.
Some psocids have small ovipositors that are up to 1.5 times as long as the hindwings, and all four wings have a relatively simple venation pattern, with few cross-veins. The wings, if present, are held tent-like over the body. The legs are slender and adapted for jumping, rather than gripping, as in the true lice. The abdomen has nine segments, and no cerci. | Psocoptera | Wikipedia | 489 | 2154225 | https://en.wikipedia.org/wiki/Psocoptera | Biology and health sciences | Insects: General | Animals |
There is often considerable variation in the appearance of individuals within the same species. Many have no wings or ovipositors, and may have a different shape to the thorax. Other, more subtle, variations are also known, such as changes to the development of the setae. The significance of such changes is uncertain, but their function appears to be different from similar variations in, for example, aphids. Like aphids, however, many psocids are parthenogenic, and the presence of males may even vary between different races of the same species.
Psocids lay their eggs in minute crevices or on foliage, although a few species are known to be viviparous. The young are born as miniature, wingless versions of the adult. These nymphs typically molt six times before reaching full adulthood. The total lifespan of a psocid is rarely more than a few months.
Booklice range from approximately . Some species are wingless and they are easily mistaken for bedbug nymphs and vice versa. Booklouse eggs take two to four weeks to hatch and can reach adulthood approximately two months later. Adult booklice can live for six months. Besides damaging books, they also sometimes infest food storage areas, where they feed on dry, starchy materials. Although some psocids feed on starchy household products, the majority of psocids are woodland insects with little to no contact with humans, therefore they are of little economic importance. They are scavengers and do not bite humans.
Psocids can affect the ecosystems in which they reside. Many psocids can affect decomposition by feeding on detritus, especially in environments with lower densities of predacious micro arthropods that may eat psocids. The nymph of a psocid species, Psilopsocus mimulus, is the first known wood-boring psocopteran. These nymphs make their own burrows in woody material, rather than inhabiting vacated, existing burrows. This boring activity can create habitats that other organisms may use. | Psocoptera | Wikipedia | 431 | 2154225 | https://en.wikipedia.org/wiki/Psocoptera | Biology and health sciences | Insects: General | Animals |
Interaction with humans
Some species of psocids, such as Liposcelis bostrychophila, are common pests of stored products. Psocids, among other arthropods, have been studied to develop new pest control techniques in food manufacturing. One study found that modified atmospheres during packing (MAP) helped to control the reoccurrence of pests during the manufacturing process and prevented further infestation in the final products that go to consumers.
Classification
In the 2000s, morphological and molecular phylogenetic evidence has shown that the parasitic lice (Phthiraptera) evolved from within the psocopteran suborder Troctomorpha, thus making Psocoptera paraphyletic with respect to Phthiraptera. In modern systematics, Psocoptera and Phthiraptera are therefore treated together in the order Psocodea.
Here is a cladogram showing the relationships within Psocodea, with the former grouping Psocoptera highlighted: | Psocoptera | Wikipedia | 209 | 2154225 | https://en.wikipedia.org/wiki/Psocoptera | Biology and health sciences | Insects: General | Animals |
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