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Potential energy surfaces
The concept of potential energy surface was very important in the development of TST. The foundation of this concept was laid by René Marcelin in 1913. He theorized that the progress of a chemical reaction could be described as a point in a potential energy surface with coordinates in atomic ... | Transition state theory | Wikipedia | 431 | 9217017 | https://en.wikipedia.org/wiki/Transition%20state%20theory | Physical sciences | Kinetics | Chemistry |
Justification for the Eyring equation
One of the most important features introduced by Eyring, Polanyi and Evans was the notion that activated complexes are in quasi-equilibrium with the reactants. The rate is then directly proportional to the concentration of these complexes multiplied by the frequency (kBT/h) with w... | Transition state theory | Wikipedia | 506 | 9217017 | https://en.wikipedia.org/wiki/Transition%20state%20theory | Physical sciences | Kinetics | Chemistry |
Here, k‡ is directly proportional to the frequency of the vibrational mode responsible for converting the activated complex to the product; the frequency of this vibrational mode is . Every vibration does not necessarily lead to the formation of product, so a proportionality constant , referred to as the transmission c... | Transition state theory | Wikipedia | 370 | 9217017 | https://en.wikipedia.org/wiki/Transition%20state%20theory | Physical sciences | Kinetics | Chemistry |
Because the functional form of the Eyring and Arrhenius equations are similar, it is tempting to relate the activation parameters with the activation energy and pre-exponential factors of the Arrhenius treatment. However, the Arrhenius equation was derived from experimental data and models the macroscopic rate using o... | Transition state theory | Wikipedia | 238 | 9217017 | https://en.wikipedia.org/wiki/Transition%20state%20theory | Physical sciences | Kinetics | Chemistry |
The entropy of activation, ΔS‡, gives the extent to which transition state (including any solvent molecules involved in or perturbed by the reaction) is more disordered compared to the starting materials. It offers a concrete interpretation of the pre-exponential factor A in the Arrhenius equation; for a unimolecular,... | Transition state theory | Wikipedia | 494 | 9217017 | https://en.wikipedia.org/wiki/Transition%20state%20theory | Physical sciences | Kinetics | Chemistry |
For a thermodynamically-controlled reaction, every difference of RT ln 10 ≈ (1.987 × 10−3 kcal/mol K)(298 K)(2.303) ≈ 1.36 kcal/mol in the free energies of products A and B results in a factor of 10 in selectivity at room temperature (298 K), a principle known as the "1.36 rule":
().
Analogously, every 1.36 kcal/m... | Transition state theory | Wikipedia | 391 | 9217017 | https://en.wikipedia.org/wiki/Transition%20state%20theory | Physical sciences | Kinetics | Chemistry |
Limitations
In general, TST has provided researchers with a conceptual foundation for understanding how chemical reactions take place. Even though the theory is widely applicable, it does have limitations. For example, when applied to each elementary step of a multi-step reaction, the theory assumes that each intermed... | Transition state theory | Wikipedia | 496 | 9217017 | https://en.wikipedia.org/wiki/Transition%20state%20theory | Physical sciences | Kinetics | Chemistry |
Microcanonical variational TST
A fundamental flaw of transition state theory is that it counts any crossing of the transition state as a reaction from reactants to products or vice versa. In reality, a molecule may cross this "dividing surface" and turn around, or cross multiple times and only truly react once. As suc... | Transition state theory | Wikipedia | 348 | 9217017 | https://en.wikipedia.org/wiki/Transition%20state%20theory | Physical sciences | Kinetics | Chemistry |
Enzymatic reactions
Enzymes catalyze chemical reactions at rates that are astounding relative to uncatalyzed chemistry at the same reaction conditions. Each catalytic event requires a minimum of three or often more steps, all of which occur within the few milliseconds that characterize typical enzymatic reactions. A... | Transition state theory | Wikipedia | 485 | 9217017 | https://en.wikipedia.org/wiki/Transition%20state%20theory | Physical sciences | Kinetics | Chemistry |
It is now accepted that enzymes function to stabilize transition states lying between reactants and products, and that they would therefore be expected to bind strongly any inhibitor that closely resembles such a transition state. Substrates and products often participate in several enzyme catalyzed reactions, whereas... | Transition state theory | Wikipedia | 273 | 9217017 | https://en.wikipedia.org/wiki/Transition%20state%20theory | Physical sciences | Kinetics | Chemistry |
A ceramic capacitor is a fixed-value capacitor where the ceramic material acts as the dielectric. It is constructed of two or more alternating layers of ceramic and a metal layer acting as the electrodes. The composition of the ceramic material defines the electrical behavior and therefore applications. Ceramic capacit... | Ceramic capacitor | Wikipedia | 345 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Mica is a natural material and not available in unlimited quantities. So in the mid-1920s the deficiency of mica in Germany and the experience in porcelain—a special class of ceramic—led in Germany to the first capacitors using ceramic as dielectric, founding a new family of ceramic capacitors. Paraelectric titanium di... | Ceramic capacitor | Wikipedia | 512 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
The typical style for ceramic capacitors beneath the disc (at that time called condensers) in radio applications at the time after the War from the 1950s through the 1970s was a ceramic tube covered with tin or silver on both the inside and outside surface. It included relatively long terminals forming, together with r... | Ceramic capacitor | Wikipedia | 473 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
New developments in ceramic materials have been made with anti-ferroelectric ceramics. This material has a nonlinear antiferroelectric/ferroelectric phase change that allows increased energy storage with higher volumetric efficiency. They are used for energy storage (for example, in detonators).
Application classes, d... | Ceramic capacitor | Wikipedia | 460 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Class 1 ceramic capacitors
Class 1 ceramic capacitors are accurate, temperature-compensating capacitors. They offer the most stable voltage, temperature, and to some extent, frequency. They have the lowest losses and therefore are especially suited for resonant circuit applications where stability is essential or where... | Ceramic capacitor | Wikipedia | 441 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
In addition to the EIA code, the temperature coefficient of the capacitance dependence of class 1 ceramic capacitors is commonly expressed in ceramic names like "NP0", "N220" etc. These names include the temperature coefficient (α). In the IEC/EN 60384-8/21 standard, the temperature coefficient and tolerance are replac... | Ceramic capacitor | Wikipedia | 471 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Class 2 capacitors are made of ferroelectric materials such as barium titanate () and suitable additives such as aluminium silicate, magnesium silicate and aluminium oxide. These ceramics have very high permittivity (200 to 14,000), allowing an extreme electric field and therefore capacitance within relatively small pa... | Ceramic capacitor | Wikipedia | 360 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Some commonly used class 2 ceramic capacitor materials are listed below:
X8R (−55/+150, ΔC/C0 = ±15%),
X7R (−55/+125 °C, ΔC/C0 = ±15%),
X6R (−55/+105 °C, ΔC/C0 = ±15%),
X5R (−55/+85 °C, ΔC/C0 = ±15%),
X7S (−55/+125, ΔC/C0 = ±22%),
Z5U (+10/+85 °C, ΔC/C0 = +22/−56%),
Y5V (−30/+85 °C, ΔC/C0 = +22/−82%),
The IEC/E... | Ceramic capacitor | Wikipedia | 417 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Class 3 ceramic capacitors
Class 3 barrier layer or semiconductive ceramic capacitors have very high permittivity, up to 50,000 and therefore a better volumetric efficiency than class 2 capacitors. However, these capacitors have worse electrical characteristics, including lower accuracy and stability. The dielectric is... | Ceramic capacitor | Wikipedia | 468 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Ceramic capacitors come in various shapes and styles. Some of the most common are:
Multilayer ceramic chip capacitor (MLCC), rectangular block, for surface mounting
Ceramic disc capacitor, single layer disc, resin coated, with through-hole leads
Feedthrough ceramic capacitor, used for bypass purposes in high-frequen... | Ceramic capacitor | Wikipedia | 478 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Miniaturizing
The capacitance formula (C) of a MLCC capacitor is based on the formula for a plate capacitor enhanced with the number of layers:
where ε stands for dielectric permittivity; A for electrode surface area; n for the number of layers; and d for the distance between the electrodes.
A thinner dielectric or... | Ceramic capacitor | Wikipedia | 418 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
MLCCs are manufactured in standardized shapes and sizes for comparable handling. Because the early standardization was dominated by American EIA standards the dimensions of the MLCC chips were standardized by EIA in units of inches. A rectangular chip with the dimensions of 0.06-inch length and 0.03-inch width is coded... | Ceramic capacitor | Wikipedia | 448 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
The picture right shows the maximum capacitance for class 1 and class 2 multilayer ceramic chip capacitors. The following two tables, for ceramics NP0/C0G and X7R each, list for each common case size the maximum available capacitance value and rated voltage of the leading manufacturers Murata, TDK, KEMET, AVX. (Status ... | Ceramic capacitor | Wikipedia | 383 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
A standard multi-layer ceramic capacitor has many opposing electrode layers stacked inside connected with two outer terminations. The X2Y ceramic chip capacitor however is a 4 terminal chip device. It is constructed like a standard two-terminal MLCC out of the stacked ceramic layers with an additional third set of shie... | Ceramic capacitor | Wikipedia | 362 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Mechanical susceptibility
Ceramics are brittle, and MLCC chips surface-mount soldered to a circuit board are often vulnerable to cracking from thermal expansion or mechanical stresses like depanelization, more so than leaded through-hole components.
The cracks can come from automated machine assembly line, or from hig... | Ceramic capacitor | Wikipedia | 422 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
With a similar construction called "Floating Electrode Design" (FED) or "Multi-layer Serial Capacitors" (MLSC), also, only capacitance reduction results if parts of the capacitor body break. This construction works with floating electrodes without any conductive connection to the termination. A break doesn't lead to a ... | Ceramic capacitor | Wikipedia | 402 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
EMI/RFI suppression capacitors are designed so that any remaining interference or electrical noise does not exceed the limits of EMC directive EN 50081. Suppression components are connected directly to mains voltage for 10 to 20 years or more and are therefore exposed to potentially damaging overvoltages and transients... | Ceramic capacitor | Wikipedia | 454 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
As modern electronic equipment gained the ability to handle power levels that were previously the exclusive domain of "electrical power" components, the distinction between the "electronic" and "electrical" power ratings has become less distinct. In the past, the boundary between these two families was approximately at... | Ceramic capacitor | Wikipedia | 489 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
The use of a series equivalent circuit instead of a parallel equivalent circuit is defined in IEC/EN 60384-1.
Capacitance standard values and tolerances
The "rated capacitance" CR or "nominal capacitance" CN is the value for which the capacitor has been designed. The actual capacitance depends on the measuring frequen... | Ceramic capacitor | Wikipedia | 440 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Temperature dependence of capacitance
Capacitance of ceramic capacitors varies with temperature. The different dielectrics of the many capacitor types show great differences in temperature dependence. The temperature coefficient is expressed in parts per million (ppm) per degree Celsius for class 1 ceramic capacitors o... | Ceramic capacitor | Wikipedia | 475 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
The voltage proof of ceramic capacitors is specified as rated voltage (UR). This is the maximum DC voltage that may be continuously applied to the capacitor up to the upper temperature limit. This guaranteed voltage proof is tested according to the voltages shown in the adjacent table.
Furthermore, in periodic life ti... | Ceramic capacitor | Wikipedia | 431 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
ESR, dissipation factor, and quality factor
The summarized losses in ceramic capacitors are ohmic AC losses. DC losses are specified as "leakage current" or "insulating resistance" and are negligible for an AC specification. These AC losses are nonlinear and may depend on frequency, temperature, age, and for some speci... | Ceramic capacitor | Wikipedia | 509 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
The ohmic losses of ceramic capacitors are frequency, temperature and voltage dependent. Additionally, class 2 capacitor measurements change because of aging. Different ceramic materials have differing losses over the temperature range and the operating frequency. The changes in class 1 capacitors are in the single-dig... | Ceramic capacitor | Wikipedia | 486 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Sample self-resonant frequencies for one set of NP0/C0G and one set of X7R ceramic capacitors are:
Note that X7Rs have better frequency response than C0Gs. It makes sense, however, since class 2 capacitors are much smaller than class 1, so they ought to have lower parasitic inductance.
Aging
In ferroelectric class 2... | Ceramic capacitor | Wikipedia | 483 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Insulation resistance and self-discharge constant
The resistance of the dielectric is never infinite, leading to some level of DC "leakage current", which contributes to self-discharge. For ceramic capacitors this resistance, placed in parallel with the capacitor in the series-equivalent circuit of capacitors, is calle... | Ceramic capacitor | Wikipedia | 428 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
In many applications of capacitors dielectric absorption is not a problem but in some applications, such as long-time-constant integrators, sample-and-hold circuits, switched-capacitor analog-to-digital converters and very low-distortion filters, it is important that the capacitor does not recover a residual charge aft... | Ceramic capacitor | Wikipedia | 498 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
The definition of the characteristics and the procedure of the test methods for capacitors for use in electronic equipment are set out in the generic specification:
IEC 60384-1, Fixed capacitors for use in electronic equipment – Part 1: Generic specification
The tests and requirements to be met by ceramic capacitors ... | Ceramic capacitor | Wikipedia | 500 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Examples
A capacitor with the following text on its body: 105K 330V has a capacitance of 10 × 105 pF = 1 μF (K = ±10%) with a working voltage of 330 V.
A capacitor with the following text: 473M 100V has a capacitance of 47 × 103 pF = 47 nF (M = ±20%) with a working voltage of 100 V.
Capacitance, tolerance and date o... | Ceramic capacitor | Wikipedia | 370 | 9221221 | https://en.wikipedia.org/wiki/Ceramic%20capacitor | Technology | Components | null |
Cuvier's dwarf caiman (Paleosuchus palpebrosus) is a small crocodilian in the alligator family from northern and central South America. It is found in Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, Trinidad and Venezuela. It lives in riverine forests, flooded forests near lakes, an... | Cuvier's dwarf caiman | Wikipedia | 473 | 6935153 | https://en.wikipedia.org/wiki/Cuvier%27s%20dwarf%20caiman | Biology and health sciences | Crocodilia | Animals |
Etymology
The genus name Paleosuchus is derived from the Greek palaios meaning "ancient" and soukhos meaning "crocodile". This refers to the belief that this crocodile comes from an ancient lineage that diverged from other species of caimans some 30 million years ago. The specific name palpebrosus is derived from the L... | Cuvier's dwarf caiman | Wikipedia | 512 | 6935153 | https://en.wikipedia.org/wiki/Cuvier%27s%20dwarf%20caiman | Biology and health sciences | Crocodilia | Animals |
A genetic study in 2012 found clear differences between various populations of Cuvier's dwarf caiman (Pantanal; Madeira River basin; Rio Negro basin), and these are apparently isolated from each other, leading to the suggestion that it may be a cryptic species complex.
Description
Cuvier's dwarf caiman is the smallest... | Cuvier's dwarf caiman | Wikipedia | 459 | 6935153 | https://en.wikipedia.org/wiki/Cuvier%27s%20dwarf%20caiman | Biology and health sciences | Crocodilia | Animals |
Distribution and habitat
Cuvier's dwarf caiman is native to tropical northern and central South America. It is present in the drainages of the Orinoco River, the São Francisco River, and the Amazon River, and the upper reaches of the Paraná River and the Paraguay River. The countries in which it is found include Peru, ... | Cuvier's dwarf caiman | Wikipedia | 493 | 6935153 | https://en.wikipedia.org/wiki/Cuvier%27s%20dwarf%20caiman | Biology and health sciences | Crocodilia | Animals |
Adult Cuvier's dwarf caimans are usually found singly or in pairs. The breeding of this species has been little studied, but it does not appear to be seasonal in nature. The female builds a mound nest out of vegetation and mud somewhere in a concealed location and lays a clutch of 10 to 25 eggs, hiding them under furth... | Cuvier's dwarf caiman | Wikipedia | 424 | 6935153 | https://en.wikipedia.org/wiki/Cuvier%27s%20dwarf%20caiman | Biology and health sciences | Crocodilia | Animals |
Status and conservation
Many crocodilians are hunted for their skins, but this is not the case with the Cuvier's dwarf caiman. This may be because the ventral skin in this species is too heavily armored to make it easy to tan. Some individuals are killed by indigenous peoples for food and some traditional South America... | Cuvier's dwarf caiman | Wikipedia | 266 | 6935153 | https://en.wikipedia.org/wiki/Cuvier%27s%20dwarf%20caiman | Biology and health sciences | Crocodilia | Animals |
A gunshot wound (GSW) is a penetrating injury caused by a projectile (e.g. a bullet) shot from a gun (typically a firearm). Damage may include bleeding, bone fractures, organ damage, wound infection, and loss of the ability to move part of the body. Damage depends on the part of the body hit, the path the bullet follow... | Gunshot wound | Wikipedia | 458 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
Signs and symptoms
Trauma from a gunshot wound varies widely based on the bullet, velocity, mass, entry point, trajectory, affected anatomy, and exit point. Gunshot wounds can be particularly devastating compared to other penetrating injuries because the trajectory and fragmentation of bullets can be unpredictable afte... | Gunshot wound | Wikipedia | 336 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
The degree of tissue disruption caused by a projectile is related to the cavitation the projectile creates as it passes through tissue. A bullet with sufficient energy will have a cavitation effect in addition to the penetrating track injury. As the bullet passes through the tissue, initially crushing then lacerating, ... | Gunshot wound | Wikipedia | 498 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
Fragmentation: Most commonly, bullets do not fragment, and secondary damage from fragments of shattered bone is a more common complication than bullet fragments. | Gunshot wound | Wikipedia | 28 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
Diagnosis
Classification
Gunshot wounds are classified according to the speed of the projectile using the Gustilo open fracture classification:
Low-velocity: Less than 335 m/s (1,100 ft/s)
Low velocity wounds are typical of small caliber handguns. They do not usually cause extensive soft tissue damage, and in the Gu... | Gunshot wound | Wikipedia | 414 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
Kronlein shot
The "Kronlein shot" (German: Krönleinschuss) is a distinctive type of headshot wound that can only be created by a high velocity rifle bullet or shotgun slug. In a Kronlein shot, the intact brain is ejected from the skull and deposited some distance from the victim's body. This type of wound is believed t... | Gunshot wound | Wikipedia | 349 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
Management
Initial assessment for a gunshot wound is approached in the same way as other acute trauma using the advanced trauma life support (ATLS) protocol. These include:
A) Airway - Assess and protect airway and potentially the cervical spine
B) Breathing - Maintain adequate ventilation and oxygenation
C) Circula... | Gunshot wound | Wikipedia | 460 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
Due to the advances in diagnostic imaging, management of PNI has been shifting from a "zone-based" approach, which uses anatomical site of injury to guide decisions, to a "no-zone" approach which uses a symptom-based algorithm. The no-zone approach uses a hard signs and imaging system to guide next steps. Hard signs in... | Gunshot wound | Wikipedia | 338 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
Initial workup as outlined in the Workup section is particularly important with gunshot wounds to the chest because of the high risk for direct injury to the lungs, heart, and major vessels. Important notes for the initial workup specific for chest injuries are as follows. In people with pericardial tamponade or tensio... | Gunshot wound | Wikipedia | 483 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
Important anatomy in the abdomen includes the stomach, small bowel, colon, liver, spleen, pancreas, kidneys, spine, diaphragm, descending aorta, and other abdominal vessels and nerves. Gunshots to the abdomen can thus cause severe bleeding, release of bowel contents, peritonitis, organ rupture, respiratory compromise, ... | Gunshot wound | Wikipedia | 479 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
Vital sign stability and vascular assessment are the most important determinants of management in extremity injuries. As with other traumatic cases, those with uncontrolled bleeding require immediate surgical intervention. If surgical intervention is not readily available and direct pressure is insufficient to control ... | Gunshot wound | Wikipedia | 432 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
As of 2016, the countries with the highest rates of gun violence per capita were El Salvador, Venezuela, and Guatemala with 40.3, 34.8, and 26.8 violent gun deaths per 100,000 people respectively. The countries with the lowest rates of were Singapore, Japan, and South Korea with 0.03, 0.04, and 0.05 violent gun deaths ... | Gunshot wound | Wikipedia | 476 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
At almost the same time, in Tombstone, Arizona Territory, on 13 July 1881, George E. Goodfellow performed the first laparotomy to treat an abdominal gunshot wound. Goodfellow pioneered the use of sterile techniques in treating gunshot wounds, washing the person's wound and his hands with lye soap or whisky, and his pat... | Gunshot wound | Wikipedia | 341 | 10725984 | https://en.wikipedia.org/wiki/Gunshot%20wound | Biology and health sciences | Types | Health |
The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked like mammals. The lineage leading to today's mammals split up in the Jurassic... | Evolution of mammals | Wikipedia | 415 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Throughout the Permian period, the synapsids included the dominant carnivores and several important herbivores. In the subsequent Triassic period, however, a previously obscure group of sauropsids, the archosaurs, became the dominant vertebrates. The mammaliaforms appeared during this period; their superior sense of sm... | Evolution of mammals | Wikipedia | 441 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
One such feature available for paleontology, shared by all living mammals (including monotremes), but not present in any of the early Triassic therapsids, is shown in Figure 1 (on the right), namely: mammals use two bones for hearing that all other amniotes use for eating. The earliest amniotes had a jaw joint composed... | Evolution of mammals | Wikipedia | 499 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Within a few million years, two important amniote lineages became distinct: synapsids, from which mammals are descended, and sauropsids, from which lizards, snakes, turtles/tortoises, crocodilians, dinosaurs, and birds are descended. The earliest known fossils of synapsids and sauropsids (such as Archaeothyris and Hylo... | Evolution of mammals | Wikipedia | 319 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Pelycosaurs — all synapsids, and all of their descendants, except for therapsids – the eventual ancestor of mammals. The pelycosaurs included the largest land vertebrates of the Early Permian, such as the 6 metre (20 foot)-long Cotylorhynchus hancocki. Among the other large pelycosaurs were Dimetrodon grandis and Edaph... | Evolution of mammals | Wikipedia | 501 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Therapsid family tree
A simplified phylogenetic tree showing only what is most relevant to the evolution of mammals is shown below:
Only the dicynodonts, therocephalians, and cynodonts survived into the Triassic.
Biarmosuchia
The Biarmosuchia were the most primitive and pelycosaur-like of the therapsids.
Dinocephali... | Evolution of mammals | Wikipedia | 413 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
The gorgonopsians still had some primitive features: no bony secondary palate (other bones in the right places perform the same functions); sprawling forelimbs; hindlimbs that could operate in both sprawling and erect postures. The therocephalians ("beast heads"), which appear to have arisen at about the same time as t... | Evolution of mammals | Wikipedia | 328 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Their primitive synapsid and therapsid ancestors were very large (between ) but cynodonts gradually decreased in size (to ) even before the Permian-Triassic extinction event, probably due to competition with other therapsids. After the extinction event, the probainognathian cynodont group rapidly decreased in size (to ... | Evolution of mammals | Wikipedia | 471 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
The archosaurs quickly became the dominant carnivores, a development often called the "Triassic takeover". Their success may have been due to the fact that the early Triassic was predominantly arid and therefore archosaurs' superior water conservation gave them a decisive advantage. All known archosaurs have glandless ... | Evolution of mammals | Wikipedia | 306 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
The therapsid trend towards differentiated teeth with precise occlusion accelerated, because of the need to hold captured arthropods and crush their exoskeletons.
As the body length of the mammals' ancestors fell below , advances in thermal insulation and temperature regulation would have become necessary for nocturnal... | Evolution of mammals | Wikipedia | 483 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Mammals or mammaliaforms
Some writers restrict the term "mammal" to the crown group mammals, the group consisting of the most recent common ancestor of the monotremes, marsupials, and placentals, together with all the descendants of that ancestor. In an influential 1988 paper, Timothy Rowe advocated this restriction, a... | Evolution of mammals | Wikipedia | 443 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Docodonts, among the most common Jurassic mammaliaforms, are noted for the sophistication of their molars. They are thought to have had general semi-aquatic tendencies, with the fish-eating Castorocauda ("beaver tail"), which lived in the mid-Jurassic about 164M years ago and was first discovered in 2004 and described ... | Evolution of mammals | Wikipedia | 390 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
The jaw joint consists only of the squamosal and dentary bones, and the jaw contains no smaller bones to the rear of the dentary, unlike the therapsid design.
In therapsids and early mammaliaforms, the eardrum may have stretched over a trough at the rear of the lower jaw. But Hadrocodium had no such trough, which sugge... | Evolution of mammals | Wikipedia | 485 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Earliest crown mammals
The crown group mammals, sometimes called 'true mammals', are the extant mammals and their close relatives back to their last common ancestor. Since this group has living members, DNA analysis can be applied in an attempt to explain the evolution of features that do not appear in fossils. This en... | Evolution of mammals | Wikipedia | 285 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Australosphenida and Ausktribosphenidae
Ausktribosphenidae is a group name that has been given to some rather puzzling finds that:
appear to have tribosphenic molars, a type of tooth that is otherwise known only in placentals and marsupials.
come from mid-Cretaceous deposits in Australia — but Australia was connected o... | Evolution of mammals | Wikipedia | 447 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
MonotremesTeinolophos, from Australia, is the earliest known monotreme. A 2007 study (published 2008) suggests that it was not a basal (primitive, ancestral) monotreme but a full-fledged platypus, and therefore that the platypus and echidna lineages diverged considerably earlier. A more recent study (2009), however, ha... | Evolution of mammals | Wikipedia | 473 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Multituberculates (named for the multiple tubercles on their "molars") are often called the "rodents of the Mesozoic", but this is an example of convergent evolution rather than meaning that they are closely related to the Rodentia. They existed for approximately 120 million years—the longest fossil history of any mamm... | Evolution of mammals | Wikipedia | 509 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Theria ("beasts") is the clade originating with the last common ancestor of the Eutheria (including placentals) and Metatheria (including marsupials). Common features include:
no interclavicle.
coracoid bones non-existent or fused with the shoulder blades to form coracoid processes.
a type of crurotarsal ankle joint in... | Evolution of mammals | Wikipedia | 339 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
The best-known feature of marsupials is their method of reproduction:
The mother develops a kind of yolk sack in her womb that delivers nutrients to the embryo. Embryos of bandicoots, koalas and wombats additionally form placenta-like organs that connect them to the uterine wall, although the placenta-like organs are s... | Evolution of mammals | Wikipedia | 411 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Marsupials also have a pair of marsupial bones (sometimes called "epipubic bones"), which support the pouch in females. But these are not unique to marsupials, since they have been found in fossils of multituberculates, monotremes, and even eutherians — so they are probably a common ancestral feature that disappeared a... | Evolution of mammals | Wikipedia | 295 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Epipubic bones extending forwards from the pelvis, which are not found in any modern placental, but are found in all other mammals — early mammaliaforms, non-placental eutherians, marsupials, and monotremes — as well as in the cynodont therapsids that are closest to mammals. Their function is to stiffen the body during... | Evolution of mammals | Wikipedia | 452 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
make the interface between the placenta and uterus into a syncytium, i.e. a thin layer of cells with a shared external membrane. This allows the passage of oxygen, nutrients and waste products, but prevents the passage of blood and other cells that would cause the mother's immune system to attack the fetus.
reduce the... | Evolution of mammals | Wikipedia | 217 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
The therian Patagomaia, found in the Late Cretaceous Chorrillo Formation (Argentina) is the largest known Mesozoic mammal, weighing an estimated .
Adalatherium hui is a large sized, erect limbed herbivore from the Cretaceous of Madagascar.Castorocauda, a member of Docodonta which lived in the middle Jurassic about 164... | Evolution of mammals | Wikipedia | 499 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Repenomamus, a eutriconodont from the early Cretaceous 130 million years ago, was a stocky, badger-like predator that sometimes preyed on young dinosaurs. Two species have been recognized, one more than long and weighing about , the other less than long and weighing .
Schowalteria is a Late Cretaceous species almost... | Evolution of mammals | Wikipedia | 476 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
A study on Mesozoic mammaliaforms suggests that they were a primary factor in constraining mammalian body size, rather than solely competition from dinosaurs. In general, it appears mammal faunas on southern continents had attained larger body sizes than those of northern continents.
Evolution of major groups of livin... | Evolution of mammals | Wikipedia | 345 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Here are the most significant of the differences between this family tree and the one familiar to paleontologists:
The top-level division is between Atlantogenata and Boreoeutheria, instead of between Xenarthra and the rest. However, analysis of transposable element insertions supports a three-way top-level split betw... | Evolution of mammals | Wikipedia | 471 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Nevertheless, these proposals have been controversial. Paleontologists naturally insist that fossil evidence must take priority over deductions from samples of the DNA of modern animals. More surprisingly, these new family trees have been criticised by other molecular phylogeneticists, sometimes quite harshly:
Mitocho... | Evolution of mammals | Wikipedia | 501 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
One analysis of the monotreme Teinolophos suggested that this animal had a pre-mammalian jaw joint formed by the angular and quadrate bones and that the definitive mammalian middle ear evolved twice independently, in monotremes and in therian mammals, but this idea has been disputed. In fact, two of the suggestion's au... | Evolution of mammals | Wikipedia | 475 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Digestive system
The evolution of the digestive system has formed a significant influence in mammal evolution. With the emergence of mammals, the digestive system was modified in a variety of ways depending on the animal's diet. For example, cats and most carnivores have simple large intestines, while the horse as a he... | Evolution of mammals | Wikipedia | 442 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
In the mid-1950s, some scientists interpreted the foramina (passages) in the maxillae (upper jaws) and premaxillae (small bones in front of the maxillae) of cynodonts as channels that supplied blood vessels and nerves to vibrissae (whiskers) and suggested that this was evidence of hair or fur. It was soon pointed out, ... | Evolution of mammals | Wikipedia | 441 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Erect limbs
Understanding of the evolution of erect limbs in mammals is incomplete — living and fossil monotremes have sprawling limbs. Some scientists think that the parasagittal (non-sprawling) limb posture is limited to the Boreosphenida, a group that contains the therians but not, for example, the multituberculates... | Evolution of mammals | Wikipedia | 480 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Respiratory turbinates
Modern mammals have respiratory turbinates, convoluted structures of thin bone in the nasal cavity. These are lined with mucous membranes that warm and moisten inhaled air and extract heat and moisture from exhaled air. An animal with respiratory turbinates can maintain a high rate of breathing w... | Evolution of mammals | Wikipedia | 499 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Limb posture
The therapsids had sprawling forelimbs and semi-erect hindlimbs. This suggests that Carrier's constraint would have made it rather difficult for them to move and breathe at the same time, but not as difficult as it is for animals such as lizards, which have completely sprawling limbs. Advanced therapsids m... | Evolution of mammals | Wikipedia | 305 | 10727548 | https://en.wikipedia.org/wiki/Evolution%20of%20mammals | Biology and health sciences | Basics_4 | Biology |
Construction aggregate, or simply aggregate, is a broad category of coarse- to medium-grained particulate material used in construction. Traditionally, it includes natural materials such as sand, gravel, crushed stone. As with other types of aggregates, it is a component of composite materials, particularly concrete an... | Construction aggregate | Wikipedia | 442 | 7096085 | https://en.wikipedia.org/wiki/Construction%20aggregate | Technology | Building materials | null |
The American Society for Testing and Materials publishes an exhaustive listing of specifications including ASTM D 692 and ASTM D 1073 for various construction aggregate products, which, by their individual design, are suitable for specific construction purposes. These products include specific types of coarse and fine ... | Construction aggregate | Wikipedia | 443 | 7096085 | https://en.wikipedia.org/wiki/Construction%20aggregate | Technology | Building materials | null |
Large stone quarry and sand and gravel operations exist near virtually all population centers due to the high cost of transportation relative to the low value of the product. Trucking aggregate more than 40 kilometers is typically uneconomical. These are capital-intensive operations, utilizing large earth-moving equipm... | Construction aggregate | Wikipedia | 463 | 7096085 | https://en.wikipedia.org/wiki/Construction%20aggregate | Technology | Building materials | null |
In 2006, according to the USGS, air-cooled blast furnace slag sold or used in the U.S. was 7.3 million tonnes valued at $49 million, granulated blast furnace slag sold or used in the U.S. was 4.2 million tonnes valued at $318 million, and steel furnace slag sold or used in the U.S. was 8.7 million tonnes valued at $40 ... | Construction aggregate | Wikipedia | 456 | 7096085 | https://en.wikipedia.org/wiki/Construction%20aggregate | Technology | Building materials | null |
According to the USGS in 2006, 2.9 million tonnes of Portland cement concrete (including aggregate) worth $21.9 million was recycled, and 1.6 million tonnes of asphalt concrete (including aggregate) worth $11.8 million was recycled, both by crushed stone operations. Much more of both materials are recycled by construct... | Construction aggregate | Wikipedia | 491 | 7096085 | https://en.wikipedia.org/wiki/Construction%20aggregate | Technology | Building materials | null |
Archaeopteris is an extinct genus of progymnosperm tree with fern-like leaves. A useful index fossil, this tree is found in strata dating from the Upper Devonian to Lower Carboniferous (), the oldest fossils being 385 million years old, and had global distribution.
Until the 2007 discovery of Wattieza, many scientist... | Archaeopteris | Wikipedia | 455 | 1495085 | https://en.wikipedia.org/wiki/Archaeopteris | Biology and health sciences | Pteridophytes | Plants |
Relationship to spermatophytes
Archaeopteris is a member of a group of free-sporing woody plants called the progymnosperms that are interpreted as distant ancestors of the gymnosperms. Archaeopteris reproduced by releasing spores rather than by producing seeds, but some of the species, such as Archaeopteris halliana w... | Archaeopteris | Wikipedia | 469 | 1495085 | https://en.wikipedia.org/wiki/Archaeopteris | Biology and health sciences | Pteridophytes | Plants |
Habitat
Evidence indicates that Archaeopteris preferred wet soils, growing close to river systems and in floodplain woodlands. It would have formed a significant part of the canopy vegetation of early forests. Speaking of the first appearance of Archaeopteris on the world-scene, Stephen Scheckler, a professor of biolo... | Archaeopteris | Wikipedia | 314 | 1495085 | https://en.wikipedia.org/wiki/Archaeopteris | Biology and health sciences | Pteridophytes | Plants |
Li or ri (, lǐ, or , shìlǐ), also known as the Chinese mile, is a traditional Chinese unit of distance. The li has varied considerably over time but was usually about one third of an English mile and now has a standardized length of a half-kilometer (). This is then divided into 1,500 chi or "Chinese feet".
The charac... | Li (unit) | Wikipedia | 500 | 1495421 | https://en.wikipedia.org/wiki/Li%20%28unit%29 | Physical sciences | East Asian | Basics and measurement |
The basic units of measurement remained stable over the Qin and Han periods. A bronze imperial standard measure, dated AD 9, had been preserved at the Imperial Palace in Beijing and came to light in 1924. This has allowed very accurate conversions to modern measurements, which has provided a new and extremely useful ad... | Li (unit) | Wikipedia | 436 | 1495421 | https://en.wikipedia.org/wiki/Li%20%28unit%29 | Physical sciences | East Asian | Basics and measurement |
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